Key Spec Table
|Analytes Available||Species Reactivity||Key Applications||Detection Methods|
|Description||Sensitive Rat Insulin RIA|
|Background Information||Insulin, a 5.8 kDa hormone is secreted by the islet beta cells in the pancreas. This kit offers sensitive assay for rat/mouse insulin|
|Detection method||Radioactive 125I|
|Linearity of Dilution||84–119%|
|Standard Curve Range||
|Safety Information according to GHS|
|Storage and Shipping Information|
|Material Size||250 tubes|
|Protocol: Sensitive Rat Insulin|
References | 35 Available | See All References
|Reference overview||Pub Med ID|
|Hypoxic Exercise Training Causes Erythrocyte Senescence and Rheological Dysfunction by Depressed Gardos Channel Activity. |
Mao TY, Fu LL, Wang JS
J Appl Physiol 2011
Despite enhancing cardiopulmonary and muscular fitness, the effect of hypoxic exercise training (HE) on hemorheological regulation remains unclear. This study investigates how HE modulates erythrocyte rheological properties, and further explores the underlying mechanisms in the hemorheological alterations. Twenty four sedentary males were randomly divided into hypoxic (HE, n=12) and normoxic (NE, n=12) exercise training groups. The subjects were trained on 60% of maximum work-rate under 15% (HE) or 21% (NE) O(2) condition for 30 minutes daily, 5 days weekly for 5 weeks. The results demonstrated that HE (i) down-regulated CD47 and CD147expressions on erythrocyte, (ii) decreased actin and spectrin contents in erythrocyte, (iii) reduced erythrocyte deformability under shear flow, and (iv) diminished erythrocyte volume changed by hypotonic stress. Treatment of erythrocytes with H(2)O(2) that mimicked in vivo pro-oxidative status resulted in the cell shrinkage, rigidity, and phosphatidylserine exposure, whereas HE enhanced the eryptotic responses to H(2)O(2). However, HE decreased the degrees of clotrimazole to blunt ionomycin-induced shrinkage, rigidity, and cytoskeleton breakdown of erythrocytes, referred to as Gardos effects. Reduced erythrocyte deformability by H(2)O(2) was inversely related to the erythrocyte Gardos effect on the rheological function. Conversely, NE intervention did not significantly change resting and exercise erythrocyte rheological properties. Therefore, we conclude that HE rather than NE reduces erythrocyte deformability and volume regulation, accompanied by an increase in the eryptotic response to oxidative stress. Simultaneously, this intervention depresses Gardos channel-modulated erythrocyte rheological functions. Results of this study provide further insight into erythrocyte senescence induced by HE.
|Telmisartan reduces neointima volume and pulse wave velocity 8 months after zotarolimus-eluting stent implantation in hypertensive h |
Hong SJ, Choi SC, Ahn CM, Park JH, Kim JS, Lim DS
Heart (British Cardiac Society) 97 1425-32. Epub 2011 Jun 23. 2011
|Differential roles of hyperglycemia and hypoinsulinemia in diabetes induced retinal cell death: evidence for retinal insulin resistance. |
Patrice E Fort,Mandy K Losiewicz,Chad E N Reiter,Ravi S J Singh,Makoto Nakamura,Steven F Abcouwer,Alistair J Barber,Thomas W Gardner
PloS one 6 2011
Diabetes pathology derives from the combination of hyperglycemia and hypoinsulinemia or insulin resistance leading to diabetic complications including diabetic neuropathy, nephropathy and retinopathy. Diabetic retinopathy is characterized by numerous retinal defects affecting the vasculature and the neuro-retina, but the relative contributions of the loss of retinal insulin signaling and hyperglycemia have never been directly compared. In this study we tested the hypothesis that increased retinal insulin signaling and glycemic normalization would exert differential effects on retinal cell survival and retinal physiology during diabetes. We have demonstrated in this study that both subconjunctival insulin administration and systemic glycemic reduction using the sodium-glucose linked transporter inhibitor phloridzin affected the regulation of retinal cell survival in diabetic rats. Both treatments partially restored the retinal insulin signaling without increasing plasma insulin levels. Retinal transcriptomic and histological analysis also clearly demonstrated that local administration of insulin and systemic glycemia normalization use different pathways to counteract the effects of diabetes on the retina. While local insulin primarily affected inflammation-associated pathways, systemic glycemic control affected pathways involved in the regulation of cell signaling and metabolism. These results suggest that hyperglycemia induces resistance to growth factor action in the retina and clearly demonstrate that both restoration of glycemic control and retinal insulin signaling can act through different pathways to both normalize diabetes-induced retinal abnormality and prevent vision loss.Full Text Article
|Prenatal androgen exposure programs metabolic dysfunction in female mice. |
Roland AV, Nunemaker CS, Keller SR, Moenter SM
J Endocrinol 2010
Polycystic ovary syndrome (PCOS) is a common fertility disorder with metabolic sequelae. Our lab previously characterized reproductive phenotypes in a prenatally androgenized (PNA) mouse model for PCOS. PNA mice exhibited elevated testosterone and luteinizing hormone (LH) levels, irregular estrous cycles, and neuroendocrine abnormalities suggesting increased central drive to the reproductive system. In this study we examined metabolic characteristics of female PNA mice. PNA mice exhibited increased fasting glucose and impaired glucose tolerance (IGT) that were independent of age and were not associated with changes in body composition or peripheral insulin sensitivity. IGT was associated with defects in pancreatic islet function leading to an impaired response to high glucose, consistent with impaired insulin secretion. Exposure of isolated pancreatic islets to androgen in vitro demonstrated an impaired response to glucose stimulation similar to that in PNA mice, suggesting androgens may have activational in addition to organizational effects on pancreatic islet function. PNA mice also exhibited increased size of visceral adipocytes, suggesting androgens programmed differences in adipocyte differentiation and/or function. These studies demonstrate that in addition to causing reproductive axis abnormalities, in utero androgen exposure can induce long-term metabolic alterations in female mice.
|Activity of the histone deacetylase inhibitor FR235222 on Toxoplasma gondii: inhibition of stage conversion of the parasite cyst form and study of new derivative compounds. |
Maubon D, Bougdour A, Wong YS, Brenier-Pinchart MP, Curt A, Hakimi MA, Pelloux H
Antimicrob Agents Chemother 54 4843-50. Epub 2010 Aug 16. 2010
Bradyzoite-to-tachyzoite conversion plays a role in the pathogenesis of recrudescence of ocular toxoplasmosis and disease in immunocompromised persons. The currently available medicines are ineffective on cysts and fail to prevent reactivation of latent toxoplasmosis. A previous study showed that the histone deacetylase inhibitor FR235222 has a dramatic effect on tachyzoite growth and induces tachyzoite-to-bradyzoite conversion in vitro. The present study shows that FR235222 can target in vitro-converted cysts and bradyzoites. Moreover, the compound is active on ex vivo T. gondii cysts. Free bradyzoites isolated after lysis of the cell wall did not proliferate in vitro when the cyst was treated with FR235222. The results imply that this compound is able to cross the T. gondii cystic cell wall. Fluorescent labeling shows that the compound impairs the capacity of the bradyzoites to convert without damaging the cyst wall integrity. In vivo inoculation of formerly treated cysts fails to infect mice when these cysts were treated with FR235222. We used our structural knowledge of FR235222 and its target, T. gondii HDAC3, to synthesize new FR235222 derivative compounds. We identified two new molecules that are highly active against tachyzoites. They harbor a better selectivity index that is more suitable for a future in vivo approach. These results identify FR235222 and its derivatives as new lead compounds in the range of therapeutics available for acute and chronic toxoplasmosis.
|PKA-dependent potentiation of glucose-stimulated insulin secretion by Epac activator 8-pCPT-2'-O-Me-cAMP-AM in human islets of Langerhans. |
Chepurny OG, Kelley GG, Dzhura I, Leech CA, Roe MW, Dzhura E, Li X, Schwede F, Genieser HG, Holz GG
American journal of physiology. Endocrinology and metabolism 298 E622-33. Epub 2009 Dec 15. 2010
Potential insulin secretagogue properties of an acetoxymethyl ester of a cAMP analog (8-pCPT-2'-O-Me-cAMP-AM) that activates the guanine nucleotide exchange factors Epac1 and Epac2 were assessed using isolated human islets of Langerhans. RT-QPCR demonstrated that the predominant variant of Epac expressed in human islets was Epac2, although Epac1 was detectable. Under conditions of islet perifusion, 8-pCPT-2'-O-Me-cAMP-AM (10 microM) potentiated first- and second-phase 10 mM glucose-stimulated insulin secretion (GSIS) while failing to influence insulin secretion measured in the presence of 3 mM glucose. The insulin secretagogue action of 8-pCPT-2'-O-Me-cAMP-AM was associated with depolarization and an increase of [Ca(2+)](i) that reflected both Ca(2+) influx and intracellular Ca(2+) mobilization in islet beta-cells. As expected for an Epac-selective cAMP analog, 8-pCPT-2'-O-Me-cAMP-AM (10 microM) failed to stimulate phosphorylation of PKA substrates CREB and Kemptide in human islets. Furthermore, 8-pCPT-2'-O-Me-cAMP-AM (10 microM) had no significant ability to activate AKAR3, a PKA-regulated biosensor expressed in human islet cells by viral transduction. Unexpectedly, treatment of human islets with an inhibitor of PKA activity (H-89) or treatment with a cAMP antagonist that blocks PKA activation (Rp-8-CPT-cAMPS) nearly abolished the action of 8-pCPT-2'-O-Me-cAMP-AM to potentiate GSIS. It is concluded that there exists a permissive role for PKA activity in support of human islet insulin secretion that is both glucose dependent and Epac regulated. This permissive action of PKA may be operative at the insulin secretory granule recruitment, priming, and/or postpriming steps of Ca(2+)-dependent exocytosis.Full Text Article
|Persistent diet-induced obesity in male C57BL/6 mice resulting from temporary obesigenic diets. |
Juen Guo, William Jou, Oksana Gavrilova, Kevin D Hall
PloS one 4 e5370 2009
BACKGROUND: Does diet-induced obesity persist after an obesigenic diet is removed? We investigated this question by providing male C57BL/6 mice with free access to two different obesigenic diets followed by a switch to chow to determine if obesity was reversible. METHODOLOGY/PRINCIPAL FINDINGS: Male C57BL/6 mice were randomly assigned to five weight-matched groups: 1) C group that continuously received a chow diet; 2) HF group on a 60% high fat diet; 3) EN group on the high fat diet plus liquid Ensure; 4) HF-C group switched from high fat to chow after 7 weeks; 5) EN-C group switched from high fat plus Ensure to chow after 7 weeks. All food intake was ad libitum. Body weight was increased after 7 weeks on both obesigenic diets (44.6+/-0.65, 39.8+/-0.63, and 28.6+/-0.63 g for EN, HF, and C groups, respectively) and resulted in elevated concentrations of serum insulin, glucose, and leptin and lower serum triglycerides. Development of obesity in HF and EN mice was caused by increased energy intake and a relative decrease of average energy output along with decreased ambulatory activity. After the switch to chow, the HF-C and EN-C groups lost weight but subsequently maintained a state of persistent obesity in comparison to the C group (34.8+/-1.2, 34.1+/-1.2 vs. 30.8+/-0.8 g respectively; P0.05) with a 40-50% increase of body fat. All serum hormones and metabolites returned to control levels with the exception of a trend for increased leptin. The HF-C and EN-C groups had an average energy output in line with the C group and the persistent obesity was maintained despite a non-significant increase of energy intake of less than 1 kcal/d at the end of the study. CONCLUSION: Our results illustrate the importance of considering the history of energy imbalance in determining body weight and that a persistent elevation of body weight after removal of obesigenic diets can result from very small increases of energy intake.Full Text Article
|Assembly of multilayer PSS/PAH membrane on coherent alginate/PLO microcapsule for long-term graft transplantation. |
Andy Leung, Matt Trau, Lars Keld Nielsen
Journal of biomedical materials research. Part A 88 226-37 2009
Conventional alginate/poly-L-ornithine (AP) membranes used to immunoisolate foreign tissue transplants fail in long-term transplantations of immortal cell lines. We have developed a novel layer-by-layer (LbL) membrane using polystyrene sulfonate and polyallylamine hydrochloride (PSS/PAH) on top of the coherent AP membrane. Assembly of the LbL membrane was followed by electrophoresis, and the surface morphologies and structure were characterized and examined by cryo-scanning electron microscope and transmission electron microscopy. Unlike the standard AP membrane, the LbL membrane withstood the internal pressure generated by continuous cell proliferation of microencapsulated HEK-293 and Min-6 cells. The new membrane did not affect insulin secretion or diffusion by Min-6 cells.
|Development of a compartmental model of zinc kinetics in mice. |
Meryl E Wastney, William A House
The Journal of nutrition 138 2148-55 2008
To investigate zinc (Zn) kinetics in mice, tracer ((65)Zn) was administered orally to 9-wk-old female mice in the fed state and tracer and Zn concentration were measured in 21 tissues over the following 8 d. Data were analyzed by compartmental modeling using WinSAAM. A published model for Zn kinetics in rats was modified to fit the data from mice and to calculate transfer rates and pool sizes of Zn. Parallel studies were performed in mice lacking genes for metallothionein (MT), MT-I and MT-II (MT-/-), to quantify differences in Zn kinetics in the absence of these proteins in vivo. We confirmed that tracer time course in most tissues was similar in wild-type mice and those lacking MT, except for the pancreas of MT-/-, which retained less tracer. By fitting tissue and intestinal data simultaneously, we found that intestinal tracer could be explained by unabsorbed isotope and loss of Zn from pancreas went through plasma. Differences in pancreatic data in MT-/- were explained by Zn turning over twice as fast in this tissue (4 h) compared with wild type (9 h). These kinetic studies provide parameter values for normal, fed mice that can be used to assess Zn kinetics in abnormal conditions, as demonstrated by the higher turnover of Zn in the pancreas of MT knockout mice.Full Text Article
|Alleviative effects of s-allyl cysteine and s-ethyl cysteine on MCD diet-induced hepatotoxicity in mice. |
Chun-che Lin, Mei-chin Yin, Wen-hu Liu
Food and chemical toxicology : an international journal published for the British Industrial Biological Research Association 46 3401-6 2008
Alleviative effects of s-allyl cysteine (SAC) and s-ethyl cysteine (SEC) upon methionine and choline deficient (MCD) diet-induced hepatotoxicity in mice were examined. SAC or SEC at 1g/L was added into drinking water for 7 weeks with MCD diet. MCD feeding significantly increased hepatic triglyceride and cholesterol levels, and elevated the activity of glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme, fatty acid synthase (FAS) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (P 0.05). However, the intake of SAC or SEC significantly decreased hepatic triglyceride accumulation, and reduced G6PDH and FAS activities (P 0.05). MCD feeding significantly lowered serum and hepatic glutathione (GSH) levels, increased malondialdehyde (MDA) and oxidized glutathione (GSSG) formation, and suppressed the activity and mRNA expression of glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase (P 0.05). The intake of SAC or SEC significantly increased serum and hepatic GSH levels, decreased MDA and GSSG formation, restored the activity and mRNA expression of GPX, SOD and catalase (P 0.05). MCD feeding significantly enhanced the mRNA expression of interleukin (IL)-1beta, IL-6, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta1, matrix metalloproteinases-9 (MMP-9) and collagen-alpha1 (P 0.05). The intake of SAC and SEC significantly blunted the mRNA expression of IL-1beta, IL-6, TNF-alpha, TGF-beta1 and collagen-alpha1 (P 0.05). SEC was greater than SAC in suppressing IL-6 and TNF-alpha expression (P 0.05), but SAC was greater than SEC in suppressing collagen-alpha1 and TGF-beta1 expression (P 0.05). These data suggest that SAC and SEC are potent agents against MCD-induced hepatotoxicity.
|Impaired adipogenesis caused by a mutated thyroid hormone alpha1 receptor. |
Hao Ying, Osamu Araki, Fumihiko Furuya, Yasuhito Kato, Sheue-Yann Cheng
Molecular and cellular biology 27 2359-71 2007
Thyroid hormone (T3) is critical for growth, differentiation, and maintenance of metabolic homeostasis. Mice with a knock-in mutation in the thyroid hormone receptor alpha gene (TRalpha1PV) were created previously to explore the roles of mutated TRalpha1 in vivo. TRalpha1PV is a dominant negative mutant with a frameshift mutation in the carboxyl-terminal 14 amino acids that results in the loss of T3 binding and transcription capacity. Homozygous knock-in TRalpha1(PV/PV) mice are embryonic lethal, and heterozygous TRalpha1(PV/+) mice display the striking phenotype of dwarfism. These mutant mice provide a valuable tool for identifying the defects that contribute to dwarfism. Here we show that white adipose tissue (WAT) mass was markedly reduced in TRalpha1(PV/+) mice. The expression of peroxisome proliferator-activated receptor gamma (PPARgamma), the key regulator of adipogenesis, was repressed at both mRNA and protein levels in WAT of TRalpha1(PV/+) mice. Moreover, TRalpha1PV acted to inhibit the transcription activity of PPARgamma by competition with PPARgamma for binding to PPARgamma response elements and for heterodimerization with the retinoid X receptors. The expression of TRalpha1PV blocked the T3-dependent adipogenesis of 3T3-L1 cells and repressed the expression of PPARgamma. Thus, mutations of TRalpha1 severely affect adipogenesis via cross talk with PPARgamma signaling. The present study suggests that defects in adipogenesis could contribute to the phenotypic manifestation of reduced body weight in TRalpha1(PV/+) mice.Full Text Article
|Muscle-specific knockout of PKC-lambda impairs glucose transport and induces metabolic and diabetic syndromes. |
Robert V Farese, Mini P Sajan, Hong Yang, Pengfei Li, Steven Mastorides, William R Gower, Sonali Nimal, Cheol Soo Choi, Sheene Kim, Gerald I Shulman, C Ronald Kahn, Ursula Braun, Michael Leitges
The Journal of clinical investigation 117 2289-301 2007
Obesity, the metabolic syndrome, and type 2 diabetes mellitus (T2DM) are major global health problems. Insulin resistance is frequently present in these disorders, but the causes and effects of such resistance are unknown. Here, we generated mice with muscle-specific knockout of the major murine atypical PKC (aPKC), PKC-lambda, a postulated mediator for insulin-stimulated glucose transport. Glucose transport and translocation of glucose transporter 4 (GLUT4) to the plasma membrane were diminished in muscles of both homozygous and heterozygous PKC-lambda knockout mice and were accompanied by systemic insulin resistance; impaired glucose tolerance or diabetes; islet beta cell hyperplasia; abdominal adiposity; hepatosteatosis; elevated serum triglycerides, FFAs, and LDL-cholesterol; and diminished HDL-cholesterol. In contrast to the defective activation of muscle aPKC, insulin signaling and actions were intact in muscle, liver, and adipocytes. These findings demonstrate the importance of aPKC in insulin-stimulated glucose transport in muscles of intact mice and show that insulin resistance and resultant hyperinsulinemia owing to a specific defect in muscle aPKC is sufficient to induce abdominal obesity and other lipid abnormalities of the metabolic syndrome and T2DM. These findings are particularly relevant because humans who have obesity, impaired glucose tolerance, and T2DM reportedly have defective activation and/or diminished levels of muscle aPKC.Full Text Article
|Adult rat liver cells transdifferentiated with lentiviral IPF1 vectors reverse diabetes in mice: an ex vivo gene therapy approach. |
A Fodor, C Harel, L Fodor, M Armoni, P Salmon, D Trono, E Karnieli
Diabetologia 50 121-30 2007
AIMS/HYPOTHESIS: We examined a clinical model of ex vivo transdifferentiation of primary adult hepatocytes to insulin-secreting cells for the treatment of type 1 diabetes. MATERIALS AND METHODS: Isolated rat hepatocytes were transduced in primary culture with a human lentivirus containing pancreatic duodenal homeobox 1 (PDX1, now known as insulin promoter factor 1, homeodomain transcription factor [IPF1]). Insulin expression and secretion of the newly engineered cells were assessed in vitro by RT-PCR, in situ hybridisation, immunostaining and radioimmunoassay. PDX1-transduced hepatocytes were further studied in vivo by injecting them under the renal capsule of diabetic SCID mice. RESULTS: Isolated rat hepatocytes were efficiently transduced with the lentiviral vector, as assessed by green fluorescent reporter gene expression. The transduced cells exhibited insulin at both mRNA (RT-PCR, in situ hybridisation) and protein levels (immunostaining and radioimmunoassay). Moreover, insulin secretion by the engineered cells was dependent on glucose and sulfonylurea. Other beta cell genes, including those encoding solute carrier family 2 (facilitated glucose transporter), member 2 (Slc2a2), glucokinase (Gck), ATP-binding cassette, sub-family C (CFTR/MRP), member 8 (Abcc8), the potassium inwardly-rectifying channel, subfamily J, member 11 (Kcnj11) and proprotein convertase subtilisin/kexin type 1 (Pcsk1) were also expressed. The PDX1-transduced hepatocytes expressed several pancreatic transcription factors related to early pancreatic endocrine development (endogenous Pdx1, neurogenic differentiation factor 1 [Neurod1], and NK6 transcription factor related, locus 1 [Nkx6-1]) as well as the late-stage pancreatic transcription factors (paired box gene 4 [Pax4], paired box gene 6 [Pax6], and v-maf musculoaponeurotic fibrosarcoma oncogene homolog A [Mafa]). Transplantation of 3 x 10(6) transdifferentiated liver cells under the renal capsule of seven streptozotocin-induced diabetic SCID mice resulted in significant reduction of non-fasting blood glucose levels from 30.7 +/- 1.3 to 8.7 +/- 3.7 mmol/l (mean +/- SEM, p = 0.01), in 6 to 8 weeks. Removal of the graft resulted in severe hyperglycaemia. CONCLUSIONS/INTERPRETATION: Ex vivo lentiviral-mediated PDX1 expression in isolated adult liver cells represents a potential model for type 1 diabetes mellitus therapy.
|Improvement of insulin sensitivity after peroxisome proliferator-activated receptor-alpha agonist treatment is accompanied by paradoxical increase of circulating resistin levels. |
M M Haluzik, Z Lacinova, M Dolinkova, D Haluzikova, D Housa, A Horinek, Z Vernerova, T Kumstyrova, M Haluzik
Endocrinology 147 4517-24 2006
We studied the effect of peroxisome proliferator-activated receptor-alpha (PPAR-alpha) activation on serum concentrations and tissue expression of resistin, adiponectin, and adiponectin receptor-1 and -2 (AdipoR1 and AdipoR2) mRNA in normal mice and mice with insulin resistance induced by lipogenic, simple-carbohydrate diet (LD). Sixteen weeks of LD feeding induced obesity with liver steatosis and increased insulin levels but did not significantly affect circulating adiponectin or resistin. Treatment with PPAR-alpha agonist fenofibrate decreased body weight and fat pad weight and ameliorated liver steatosis in LD-fed mice with concomitant reduction in blood glucose, free fatty acid, triglyceride, serum insulin levels, and homeostasis model assessment index values. Euglycemic-hyperinsulinemic clamp demonstrated the development of whole-body and liver insulin resistance in LD-fed mice, which were both normalized by fenofibrate. Fenofibrate treatment markedly increased circulating resistin levels on both diets and adiponectin levels in chow-fed mice only. Fat adiponectin mRNA expression was not affected by fenofibrate treatment. Resistin mRNA expression increased in subcutaneous but not gonadal fat after fenofibrate treatment. In addition to fat, a significant amount of adiponectin mRNA was also expressed in the muscle. This expression markedly increased after fenofibrate treatment in chow- but not in LD-fed mice. Adipose tissue expression of AdipoR1 mRNA was significantly reduced in LD-fed mice and increased after fenofibrate treatment. In conclusion, PPAR-alpha activation ameliorated the development of insulin resistance in LD-fed mice despite a major increase in serum resistin levels. This effect could be partially explained by increased AdipoR1 expression in adipose tissue after fenofibrate treatment.
|Obese state leads to elevated levels of TGF-beta and COX isoforms in platelets of Zucker rats. |
Jayadev Raju, Gagan Bajaj, Jennifer Chrusch, Ranjana P Bird
Molecular and cellular biochemistry 284 19-24 2006
Platelets are rich sources of growth factors and enzymes that are implicated in a number of diseases including obesity, atherosclerosis, heart disease, syndrome X, liver and kidney diseases and certain types of cancers. In this research we investigated, if platelets in Zucker obese rats differ from their lean counterparts with respect to the levels of TGF-beta and COX isoforms, implicated in the pathogenesis of chronic diseases. In addition, we investigated if energy intake of the animals affects the platelet physiology. Platelets were isolated from obese and lean rats bearing preneoplastic lesions in their colon. Prior to platelet isolation these rats were fed either ad libitum (Ob or Ln) or energy restricted (Ob-ER or Ln-ER) diets for 8 weeks (n = 8/group). The levels of TGF-beta1/-beta2 and COX-1/-2 proteins in platelets were analyzed by Western blot. The platelets of the Ob rats had significantly higher levels of TGF-beta1, COX-1/-2 (p 0.001) than did the platelets of the Ln rats and were not affected by moderate energy restriction. There were no significant differences in the protein expression of platelet TGF-beta2 among any of the groups. These results demonstrate that cytokines and candidates playing a role in the pathogenesis of chronic diseases, such as TGF-beta1 and COX-1/-2, are over-expressed in platelets of Zucker obese rats by comparison to their lean counterparts. These findings also demonstrate that the genotype of the animals exerts a significant effect on the biochemical composition of the platelets and could contribute to the pathogenesis of colon cancer and other metabolic abnormalities associated with obesity.
|The role of hyperglycemia in FAT/CD36 expression and function. |
Min Chen, Ying-Kui Yang, Tara J Loux, Keith E Georgeson, Carroll M Harmon
Pediatric surgery international 22 647-54 2006
FAT/CD36 is a long-chain fatty acid transporter and scavenger receptor for oxidized LDL. Defects in FAT/CD36 have been linked to the hypertriglyceridemia and insulin resistance. Expression of FAT/CD36 was reported increase in type 1 diabetes; however, it remains unclear whether serum glucose or insulin plays an important role in this regulation. To elucidate the individual contribution of plasma glucose and insulin in the regulation of FAT/CD36 mRNA expression, we induced type 1 diabetes in male Sprague-Dawley rats using streptozotocin (STZ) and compared traditional insulin treatment with administration of the orally absorbed chemical agent vanadate, which reduces blood glucose levels via mechanisms that bypass insulin receptor action. STZ-exposed animals showed significant decreases in body weight (285.5 +/- 2.8 vs. 233.1 +/- 3.5 g, P 0.001) and serum insulin levels (9.7 +/- 0.7 vs. 2.8 +/- 0.6 microU/ml, P 0.05), accompanied by significant increases in blood glucose (71 +/- 3 vs. 433 +/- 11 mg/dl, P 0.001), water intake (38.9 +/- 0.9 vs. 205.9 +/- 3.3 ml/day, P 0.001) and food intake (22.0 +/- 0.4 vs. 36.9 +/- 1.0 g/day, P 0.001). Diabetic animals demonstrated significant increases in FAT/CD36 mRNA levels in duodenum (2.2-fold), jejunum (1.8-fold), ileum (1.5-fold), adipose tissue (1.7-fold), and heart (2.5-fold) (P 0.05). Insulin treatment reversed body weight loss and corrected hyperglycemia at diabetic rats as expected. Insulin treatment also corrected increased FAT/CD36 mRNA expression at diabetic rats. Vanadate significantly reduced serum glucose levels without increasing serum insulin or affecting body weight but reversed increased FAT/CD36 mRNA expression in diabetic rats. These data suggest that plasma glucose levels play more important role in the regulation of FAT/CD36 expression than concurrent changes in plasma insulin.
|Glucose production and substrate cycle activity in a fasting adapted animal, the northern elephant seal. |
Cory D Champagne, Dorian S Houser, Daniel E Crocker
The Journal of experimental biology 208 859-68 2005
During prolonged fasting physiological mechanisms defend lean tissue from catabolism. In the fasting state, glucose is derived solely from gluconeogenesis, requiring some catabolism of amino acids for gluconeogenic substrates. This creates a conflict in animals undergoing fasts concurrently with metabolically challenging activities. This study investigated glucose metabolism in fasting and developing neonatal elephant seals. Glucose production and glucose cycle activity were measured early (2 weeks) and late (6 weeks) in the postweaning fasting period. Additionally the role of regulatory hormones on glucose production and glucose cycle activity were investigated. Glucose cycle activity was highly variable throughout the study period, did not change over the fasting period, and was not correlated with insulin or glucagon level. Endogenous glucose production (EGP) was 2.80+/-0.65 mg kg(-1) min(-1) early and 2.21+/-0.12 during late fasting. Insulin to glucagon molar ratio decreased while cortisol levels increased over the fast (t=5.27, 2.84; P=0.003, 0.04; respectively). There was no relationship between EGP and hormone levels. The glucose production values measured in this study were high and exceeded the estimated gluconeogenic substrate available. These data suggest extensive glucose recycling via Cori cycle activity occurring in northern elephant seals, and we propose a possible justification for this recycling.
|Thioredoxin-interacting protein deficiency disrupts the fasting-feeding metabolic transition. |
Sonal S Sheth, Lawrence W Castellani, Soumya Chari, Cory Wagg, Christopher K Thipphavong, Jackie S Bodnar, Peter Tontonoz, Alan D Attie, Gary D Lopaschuk, Aldons J Lusis
Journal of lipid research 46 123-34 2005
Through a positional cloning approach, the thioredoxin-interacting protein gene (Txnip) was recently identified as causal for a form of combined hyperlipidemia in mice (Bodnar, J. S., A. Chatterjee, L. W. Castellani, D. A. Ross, J. Ohmen, J. Cavalcoli, C. Wu, K. M. Dains, J. Catanese, M. Chu, S. S. Sheth, K. Charugundla, P. Demant, D. B. West, P. de Jong, and A. J. Lusis. 2002. Positional cloning of the combined hyperlipidemia gene Hyplip1. Nat. Genet. 30: 110-116). We now show that Txnip-deficient mice in the fed state exhibit a metabolic profile similar to fasted mice, including increased levels of plasma ketone bodies and free fatty acids, decreased glucose, and increased hepatic expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha, phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, and acyl-CoA oxidase. Dramatic differences in the expression of key metabolic enzymes were also observed in other tissues, and the fat-to-muscle ratio of Txnip-deficient mice was increased by approximately 40%. We demonstrate an effect of Txnip on the redox status, as the Txnip-deficient mice in the fed state had a significant increase in the ratio of NADH to NAD(+). Surprisingly, we observed that Txnip-deficient mice and wild-type mice had similar levels of thioredoxin activity, suggesting that the effects of Txnip deficiency may be mediated in part by other interactions. These results indicate a role for Txnip in the metabolic response to feeding and the maintenance of the redox status.
|Role of the duodenum and macronutrient type in ghrelin regulation. |
Joost Overduin, R Scott Frayo, Harvey J Grill, Joel M Kaplan, David E Cummings
Endocrinology 146 845-50 2005
The orexigenic hormone ghrelin is implicated in preprandial hunger and meal initiation in part because circulating levels increase before meals and decrease after food intake. The mechanisms underlying postprandial ghrelin suppression are unknown. Although most ghrelin is produced by the stomach, we have shown that neither gastric nutrients nor gastric distension affect ghrelin levels. We hypothesized that the nutrient-sensing mechanism regulating ghrelin is in the duodenum, the second richest source of ghrelin. To test whether duodenal nutrient exposure is required for ghrelin suppression, we infused nutrients into either the proximal duodenum or proximal jejunum in rats bearing chronic intestinal cannulas. At 0, 30, 60, 90, 120, 180, 240, and 300 min after infusions, blood was sampled via jugular-vein catheters for ghrelin, insulin, and glucose measurements. To elucidate further the mechanisms governing nutrient-related ghrelin suppression, we also assessed the ghrelin responses to isocaloric (3 kcal) infusions of glucose, amino acids, or lipids delivered into the stomach or small intestine of chronically catheterized rats. Regardless of macronutrient type, the depth and duration of ghrelin suppression were equivalent after gastric, duodenal, and jejunal infusions. Glucose and amino acids suppressed ghrelin more rapidly and strongly (by approximately 70%) than did lipids (by approximately 50%). Because jejunal nutrient infusions suppressed ghrelin levels as well as either gastric or duodenal infusions, we conclude that the inhibitory signals mediating postprandial ghrelin suppression are not derived discretely from either the stomach or duodenum. The relatively weak suppression of ghrelin by lipids compared with glucose or amino acids could represent one mechanism promoting high-fat dietary weight gain.
|Histidine and carnosine delay diabetic deterioration in mice and protect human low density lipoprotein against oxidation and glycation. |
Yuan-ti Lee, Cheng-chin Hsu, Meng-hsiao Lin, Keh-sen Liu, Mei-chin Yin
European journal of pharmacology 513 145-50 2005
In vivo effects of histidine and carnosine against diabetic deterioration in diabetic Balb/cA mice were studied. Histidine and carnosine at 0.5, 1 g/l were added into drinking water. After 4 weeks intake of these agents, the content of histidine and carnosine in plasma, heart and liver significantly elevated (P 0.05). The intake of these agents significantly decreased plasma glucose and fibronectin levels (P 0.05); however, only 1 g/l histidine and carnosine treatments significantly increased insulin level (P 0.05) in diabetic mice. Triglyceride level in heart and liver was dose-dependently reduced by histidine or carnosine treatments (P 0.05); however, only 1 g/l histidine and carnosine treatments significantly reduced cholesterol level in heart and liver (P 0.05). The administration of histidine or carnosine significantly enhanced catalase activity and decreased lipid oxidation levels in kidney and liver (P 0.05); however, only 1 g/l histidine and carnosine treatments significantly increased glutathione peroxidase activity (P 0.05). The increased interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha in diabetic mice were significantly suppressed by the intake of histidine or carnosine (P 0.05). In human low density lipoprotein, histidine or carnosine showed dose-dependently suppressive effect in glucose-induced oxidation and glycation (P 0.05). These data suggest that histidine and carnosine are potential multiple-protective agents for diabetic complications prevention or therapy.
|Leptin improves insulin resistance and hyperglycemia in a mouse model of type 2 diabetes. |
Yuka Toyoshima, Oksana Gavrilova, Shoshana Yakar, William Jou, Stephanie Pack, Zeenat Asghar, Michael B Wheeler, Derek LeRoith
Endocrinology 146 4024-35 2005
Leptin has metabolic effects on peripheral tissues including muscle, liver, and pancreas, and it has been successfully used to treat lipodystrophic diabetes, a leptin-deficient state. To study whether leptin therapy can be used for treatment of more common cases of type 2 diabetes, we used a mouse model of type 2 diabetes (MKR mice) that show normal leptin levels and are diabetic due to a primary defect in both IGF-I and insulin receptors signaling in skeletal muscle. Here we show that leptin administration to the MKR mice resulted in improvement of diabetes, an effect that was independent of the reduced food intake. The main effect of leptin therapy was enhanced hepatic insulin responsiveness possibly through decreasing gluconeogenesis. In addition, the reduction of lipid stores in liver and muscle induced by enhancing fatty acid oxidation and inhibiting lipogenesis led to an improvement of the lipotoxic condition. Our data suggest that leptin could be a potent antidiabetic drug in cases of type 2 diabetes that are not leptin resistant.
|Genetic background (C57BL/6J versus FVB/N) strongly influences the severity of diabetes and insulin resistance in ob/ob mice. |
Martin Haluzik, Carlo Colombo, Oksana Gavrilova, Streamson Chua, Nicole Wolf, Min Chen, Bethel Stannard, Kelly R Dietz, Derek Le Roith, Marc L Reitman
Endocrinology 145 3258-64 2004
We studied the effects of genetic background on the phenotype of ob/ob mice, a model of severe obesity, insulin resistance, and diabetes caused by leptin deficiency. Despite a comparable degree of obesity and hyperinsulinemia, C57BL/6J ob/ob mice had much milder hyperglycemia and, surprisingly, normal circulating adiponectin levels despite still-prominent signs of insulin resistance. Hyperinsulinemic-euglycemic clamp revealed relatively less whole-body and muscle insulin resistance in C57BL/6J ob/ob mice, whereas liver insulin resistance tended to be more severe than in FVB/N ob/ob mice. C57BL/6J ob/ob mice had also more rapid clearance of circulating triglycerides and more severe hepatic steatosis. We suggest that strain-related distinction in lipid handling is the most important player in the differences in diabetic phenotype and insulin sensitivity, whereas the impact of circulating adiponectin levels on the overall phenotype of ob/ob mice is less important.
|Increased insulin sensitivity in paternal Gnas knockout mice is associated with increased lipid clearance. |
Min Chen, Martin Haluzik, Nicole J Wolf, Javier Lorenzo, Kelly R Dietz, Marc L Reitman, Lee S Weinstein
Endocrinology 145 4094-102 2004
The G protein alpha-subunit Gsalpha is required for hormone-stimulated cAMP generation. The Gsalpha gene Gnas is a complex gene with multiple imprinted gene products. Mice with heterozygous disruption of the Gnas paternal allele (+/p-) are partially Gsalpha deficient and totally deficient in XLalphas, a neuroendocrine-specific Gsalpha isoform that is expressed only from the paternal Gnas allele. We previously showed that these mice are hypermetabolic and lean and have increased insulin sensitivity. We now performed hyperinsulinemic-euglycemic clamp studies, which confirmed the markedly increased whole body insulin sensitivity in +/p- mice. +/p- mice had 1.4-, 7- and 3.8-fold increases in insulin-stimulated glucose uptake in muscle and white and brown adipose tissue, respectively, and markedly suppressed endogenous glucose production from the liver. This was associated with increased phosphorylation of insulin receptor and a downstream effector (Akt kinase) in both liver and muscle in response to insulin. Triglycerides cleared more rapidly in +/p- mice after a bolus administered by gavage. This was associated with decreased liver and muscle triglyceride content and increased muscle acyl-CoA oxidase mRNA expression. Resistin and adiponectin were overexpressed in white adipose tissue of +/p- mice, although there was no difference in serum adiponectin levels. The lean phenotype and increased insulin sensitivity observed in +/p- mice is likely a consequence of increased lipid oxidation in muscle and possibly other tissues. Further studies will clarify whether XLalphas deficiency is responsible for these effects and if so, the mechanism by which XLalphas deficiency leads to this metabolic phenotype.
|Peroxisome proliferator-activated receptor-alpha deficiency does not alter insulin sensitivity in mice maintained on regular or high-fat diet: hyperinsulinemic-euglycemic clamp studies. |
Martin Haluzik, Oksana Gavrilova, Derek LeRoith
Endocrinology 145 1662-7 2004
Chronic peroxisome proliferator-activated receptor (PPAR)-alpha activation improves glucose metabolism in rodent models of insulin resistance and diabetes; however, PPAR-alpha deficiency was also reported to protect against high-fat diet (HFD)-induced insulin resistance. The aim of this study was to clarify the role of PPAR-alpha in the development of insulin resistance using PPAR-alpha knockout (KO) mice and wild-type controls (WT). Both WT and PPAR-alpha KO mice on HFD gained significantly more weight relative to chow-fed groups and displayed an increase in insulin levels and a decrease in adiponectin levels. Hyperinsulinemic-euglycemic clamp performed in the nonfasting state demonstrated that HFD caused a marked reduction in whole body, muscle, and white and brown adipose tissue glucose uptake in both WT and PPAR-alpha KO mice relative to chow-fed groups. Suppression of endogenous glucose production during the clamp was markedly blunted in both WT and PPAR-alpha KO HFD-fed mice, indicating liver insulin resistance. The magnitude of HFD-induced changes in the clamp parameters of insulin sensitivity was comparable in PPAR-alpha KO and WT mice. In conclusion, these data show that PPAR-alpha deficiency does not alter insulin sensitivity in mice fed normal chow diet and does not protect against HFD-induced insulin resistance as measured by hyperinsulinemic-euglycemic clamp in nonfasted state.
|Opposite effects of background genotype on muscle and liver insulin sensitivity of lipoatrophic mice. Role of triglyceride clearance. |
Carlo Colombo, Martin Haluzik, Jaime J Cutson, Kelly R Dietz, Bernice Marcus-Samuels, Charles Vinson, Oksana Gavrilova, Marc L Reitman
The Journal of biological chemistry 278 3992-9 2003
The metabolic phenotype of the A-ZIP/F-1 (AZIP) lipoatrophic mouse is different depending on its genetic background. On both the FVB/N (FVB) and C57BL/6J (B6) backgrounds, AZIP mice have a similarly severe lack of white adipose tissue and comparably increased insulin levels and triglyceride secretion rates. However, on the B6 background, the AZIP mice have less hyperglycemia, lower circulating triglyceride and fatty acid levels, and lower mortality. AZIP characteristics that are more severe on the B6 background include increased liver size and liver triglyceride content. A unifying hypothesis is that the B6 strain has higher triglyceride clearance into the liver, with lower triglyceride levels elsewhere. This may account for the observation that the B6 AZIP mice have less insulin-resistant muscles and more insulin-resistant livers, than do the FVB AZIP mice. B6 wild type, as well as B6 AZIP, mice have increased triglyceride clearance relative to FVB, which may be explained in part by higher serum lipase levels and liver CD36/fatty acid translocase mRNA levels. Thus, it is likely that increased triglyceride clearance in B6, as compared with FVB, mice contributes to the strain differences in insulin resistance and lipid metabolism.
|Severe diabetes, age-dependent loss of adipose tissue, and mild growth deficiency in mice lacking Akt2/PKB beta. |
Robert S Garofalo, Stephen J Orena, Kristina Rafidi, Anthony J Torchia, Jeffrey L Stock, Audrey L Hildebrandt, Timothy Coskran, Shawn C Black, Dominique J Brees, Joan R Wicks, John D McNeish, Kevin G Coleman
The Journal of clinical investigation 112 197-208 2003
The serine/threonine kinase Akt/PKB plays key roles in the regulation of cell growth, survival, and metabolism. It remains unclear, however, whether the functions of individual Akt/PKB isoforms are distinct. To investigate the function of Akt2/PKBbeta, mice lacking this isoform were generated. Both male and female Akt2/PKBbeta-null mice exhibit mild growth deficiency and an age-dependent loss of adipose tissue or lipoatrophy, with all observed adipose depots dramatically reduced by 22 weeks of age. Akt2/PKBbeta-deficient mice are insulin resistant with elevated plasma triglycerides. In addition, Akt2/PKBbeta-deficient mice exhibit fed and fasting hyperglycemia, hyperinsulinemia, glucose intolerance, and impaired muscle glucose uptake. In males, insulin resistance progresses to a severe form of diabetes accompanied by pancreatic beta cell failure. In contrast, female Akt2/PKBbeta-deficient mice remain mildly hyperglycemic and hyperinsulinemic until at least one year of age. Thus, Akt2/PKBbeta-deficient mice exhibit growth deficiency similar to that reported previously for mice lacking Akt1/PKBalpha, indicating that both Akt2/PKBbeta and Akt1/PKBalpha participate in the regulation of growth. The marked hyperglycemia and loss of pancreatic beta cells and adipose tissue in Akt2/PKBbeta-deficient mice suggest that Akt2/PKBbeta plays critical roles in glucose metabolism and the development or maintenance of proper adipose tissue and islet mass for which other Akt/PKB isoforms are unable to fully compensate.Full Text Article
|Insulin resistance in the liver-specific IGF-1 gene-deleted mouse is abrogated by deletion of the acid-labile subunit of the IGF-binding protein-3 complex: relative roles of growth hormone and IGF-1 in insulin resistance. |
Martin Haluzik, Shoshana Yakar, Oksana Gavrilova, Jennifer Setser, Yves Boisclair, Derek LeRoith
Diabetes 52 2483-9 2003
Liver IGF-1 deficient (LID) mice demonstrate a 75% reduction in circulating IGF-1 levels and a corresponding fourfold increase in growth hormone (GH) levels. At 16 weeks of age, LID mice demonstrate, using the hyperinsulinemic-euglycemic clamp, insulin insensitivity in muscle, liver, and fat tissues. In contrast, mice with a gene deletion of the acid-labile subunit (ALSKO) demonstrate a 65% reduction in circulating IGF-1 levels, with normal GH levels and no signs of insulin resistance. To further clarify the relative roles of increased GH and decreased IGF-1 levels in the development of insulin resistance, we crossed the two mouse lines and created a double knockout mouse (LID+ALSKO). LID+ALSKO mice demonstrate a further reduction in circulating IGF-1 levels (85%) and a concomitant 10-fold increase in GH levels. Insulin tolerance tests showed an improvement in insulin responsiveness in the LID+ALSKO mice compared with controls; LID mice were very insulin insensitive. Surprisingly, insulin sensitivity, while improved in white adipose tissue and in muscle, was unchanged in the liver. The lack of improvement in liver insulin sensitivity may reflect the absence of IGF-1 receptors or increased triglyceride levels in the liver. The present study suggests that whereas GH plays a major role in inducing insulin resistance, IGF-1 may have a direct modulatory role.
|Functional, persistent, and extended liver to pancreas transdifferentiation. |
Idit Ber, Keren Shternhall, Shira Perl, Zohar Ohanuna, Iris Goldberg, Iris Barshack, Luna Benvenisti-Zarum, Irit Meivar-Levy, Sarah Ferber
The Journal of biological chemistry 278 31950-7 2003
Pancreatic and duodenal homeobox gene-1 (PDX-1) regulates pancreas development during embryogenesis, whereas in the adult it controls beta-cell function. Here we analyze whether PDX-1 functions as a pancreatic differentiation factor and a bona fide master regulator when ectopically expressed in mature fully differentiated liver in vivo. By ectopic and transient PDX-1 expression in liver in vivo, using the first generation recombinant adenoviruses, we demonstrate that PDX-1 induces in liver a wide repertoire of both exocrine and endocrine pancreatic gene expression. Moreover, PDX-1 induces its own expression (auto-induction), which in turn may explain the long lasting nature of the liver to pancreas transdifferentiation. Insulin as well glucagon-producing cells are mainly located in the proximity of hepatic central veins, possibly allowing direct hormone release into the bloodstream, without affecting normal hepatic function. Importantly, we demonstrate that hepatic insulin production triggered by Ad-CMV-PDX-1 recombinant adenovirus administration is functional and prevents streptozotocin-induced hyperglycemia in Balb/c mice even 8 months after the initial treatment. We conclude that PDX-1 plays an important instructive role in pancreas differentiation, not only from primitive gut endoderm but also from mature liver. Transconversion of liver to pancreas may serve as a novel approach for generating endocrine-pancreatic tissue that can replace malfunctioning beta-cells in diabetics.
|Adrenalectomy improves diabetes in A-ZIP/F-1 lipoatrophic mice by increasing both liver and muscle insulin sensitivity. |
Martin Haluzik, Kelly R Dietz, Jason K Kim, Bernice Marcus-Samuels, Gerald I Shulman, Oksana Gavrilova, Marc L Reitman
Diabetes 51 2113-8 2002
The virtually fatless A-ZIP/F-1 mouse is profoundly insulin resistant, diabetic, and a good model for humans with severe generalized lipoatrophy. Like a number of other mouse models of diabetes, the A-ZIP/F-1 mouse has elevated serum corticosterone levels. Leptin infusion lowers the corticosterone levels, suggesting that leptin deficiency contributes to the hypercorticosteronemic state. To test the hypothesis that the increased glucocorticoids contribute to the diabetes and insulin resistance, we examined the effect of adrenalectomy on A-ZIP/F-1 mice. Adrenalectomy significantly decreased the blood glucose, serum insulin, and glycated hemoglobin levels. Hyperinsulinemic-euglycemic clamps were performed to characterize the changes in whole-body and tissue insulin sensitivity. The adrenalectomized A-ZIP/F-1 mice displayed a marked improvement in insulin-induced suppression of endogenous glucose production, indicating increased hepatic insulin sensitivity. Adrenalectomy also increased muscle glucose uptake and glycogen synthesis. These results suggest that the chronically increased serum corticosterone levels contribute to the diabetes of the A-ZIP/F-1 mice and that removal of the glucocorticoid excess improves the insulin sensitivity in both muscle and liver.
|IGF-I and insulin regulate eIF4F formation by different mechanisms in muscle and liver in the ovine fetus. |
Weihua Shen, Daniel Mallon, David W Boyle, Edward A Liechty
American journal of physiology. Endocrinology and metabolism 283 E593-603 2002
The mechanisms by which insulin-like growth factor I (IGF-I) and insulin regulate eukaryotic initiation factor (eIF)4F formation were examined in the ovine fetus. Insulin infusion increased phosphorylation of eIF4E-binding protein (4E-BP1) in muscle and liver. IGF-I infusion did not alter 4E-BP1 phosphorylation in liver. In muscle, IGF-I increased 4E-BP1 phosphorylation by 27%; the percentage in the gamma-form in the IGF-I group was significantly lower than that in the insulin group. In liver, only IGF-I increased eIF4G. Both IGF-I and insulin increased eIF4E. eIF4G binding in muscle, but only insulin decreased the amount of 4E-BP1 associated with eIF4E. In liver, only IGF-I increased eIF4E. eIF4G binding. Insulin increased the phosphorylation of p70 S6 kinase (p70(S6k)) in both muscle and liver and protein kinase B (PKB/Akt) in muscle, two indicative signal proteins in the phosphatidylinositol (PI) 3-kinase pathway. IGF-I increased PKB/Akt phosphorylation in muscle but had no effect on p70(S6k) phosphorylation in muscle or liver. We conclude that insulin and IGF-I modulate eIF4F formation; however, the two hormones have different regulatory mechanisms. Insulin increases phosphorylation of 4E-BP1 and eIF4E. eIF4G binding in muscle, whereas IGF-I regulates eIF4F formation by increasing total eIF4G. Insulin, but not IGF-I, decreased 4E-BP1 content associated with eIF4E. Insulin regulates translation initiation via the PI 3-kinase-p70(S6k) pathway, whereas IGF-I does so mainly via mechanisms independent of the PI 3-kinase-p70(S6k) pathway.
|Transplantation of adipose tissue lacking leptin is unable to reverse the metabolic abnormalities associated with lipoatrophy. |
Carlo Colombo, Jaime J Cutson, Toshimasa Yamauchi, Charles Vinson, Takashi Kadowaki, Oksana Gavrilova, Marc L Reitman
Diabetes 51 2727-33 2002
Severe adipose tissue deficiency (lipoatrophy) causes insulin-resistant diabetes, elevated serum triglyceride and fatty acid levels, and massive triglyceride deposition in the liver. In lipoatrophic A-ZIP/F-1 mice, transplantation of normal adipose tissue greatly improved these parameters, whereas 1 week of leptin infusion had more modest effects. In contrast, leptin infusion was strikingly more effective in the aP2-n sterol response element binding protein 1 lipoatrophic mouse. Here we show that a longer duration of leptin infusion further improves the metabolic status of the A-ZIP/F-1 mice and that genetic background does not make a major contribution to the effect of leptin on glucose and insulin levels. Adipose transplantation using leptin-deficient ob/ob fat had no effect on the phenotype of the A-ZIP/F-1 mice. Moreover, the presence of ob/ob adipose tissue did not enhance the effects of leptin infusion. Serum adiponectin levels were 2% of control levels in the A-ZIP/F-1 mouse and increased only twofold with adipose transplantation and not at all after leptin infusion, suggesting that adiponectin deficiency is not a major contributor to the diabetic phenotype. Taken together, these results suggest that sequestration of triglycerides into fat may not be enough to restore a nondiabetic phenotype and that leptin deficiency plays a major role in causing the metabolic complications of lipoatrophy.
|Effects of the imidazoline ligands efaroxan and KU14R on blood glucose homeostasis in the mouse. |
Gaëll Mayer, Peter V Taberner
European journal of pharmacology 454 95-102 2002
The putative imidazoline I(3) receptor antagonist 2-(2-ethyl-2,3-dihydrobenzo[b]furan-2-yl)-1H-imidazole (KU14R) has been shown to block the effects of the atypical I(3) agonist efaroxan at the level of the ATP-sensitive K(+) (K(ATP)) channel in isolated pancreatic islet beta cells, but its effects in vivo are not known. We have therefore investigated the effects of KU14R on blood glucose and insulin level in vivo. When KU14R was administered before or after a hypoglycaemic dose of efaroxan, the fall in blood glucose was at least additive. When the antihyperglycaemic imidazoline ligand S22068 was administered after a dose of KU14R, it did not alter the hypoglycaemic response. In the mouse isolated vas deferens preparation, neither rauwolscine (at concentrations which competitively antagonised the inhibitory response to 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK14304)) nor KU14R affected inhibition produced by S22068. At 10(-4) M, KU14R had weak alpha(2)-adrenoceptor antagonist activity. We conclude that KU14R does not act as an antagonist of either efaroxan or S22068 at an imidazoline site in vivo.
|Targeted disruption of the pituitary adenylate cyclase-activating polypeptide gene results in early postnatal death associated with dysfunction of lipid and carbohydrate metabolism. |
S L Gray, K J Cummings, F R Jirik, N M Sherwood
Molecular endocrinology (Baltimore, Md.) 15 1739-47 2001
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a hormone belonging to the glucagon superfamily of hormones. These hormones are known to play important roles in metabolism and growth. PACAP is a neuropeptide that causes accumulation of cAMP in a number of tissues and affects the secretion of other hormones, vasodilation, neural and immune functions, as well as the cell cycle. To determine whether PACAP is essential for survival and to evaluate its function(s), we have generated mice lacking the PACAP gene via homologous recombination. We found that most PACAP null mice died in the second postnatal week in a wasted state with microvesicular fat accumulation in liver, skeletal muscle, and heart. Gas chromatography-mass spectrometry showed that fatty acid beta-oxidation in liver mitochondria of PACAP(-/-) mice was not blocked based on the distribution of 3-hydroxy-fatty acids (C6-16) in the plasma. Instead, increased metabolic flux through the beta-oxidation pathway was suggested by the presence of ketosis. Also, serum triglycerides and cholesterol were significantly higher (2- to 3-fold) in PACAP null mice than littermates. In the fed state, both serum insulin and blood glucose were normal in 5-d-old null mice compared with their littermates. In contrast, fasted PACAP null pups had a significant increase in insulin, but a decrease in blood glucose compared with littermates. Glycogen in the liver was reduced. These results suggest PACAP is a critical hormonal regulator of lipid and carbohydrate metabolism.
|Post-transcriptional stimulation of the assembly and secretion of triglyceride-rich apolipoprotein B lipoproteins in a mouse with selective deficiency of brown adipose tissue, obesity, and insulin resistance. |
P Siri, N Candela, Y L Zhang, C Ko, S Eusufzai, H N Ginsberg, L S Huang
The Journal of biological chemistry 276 46064-72 2001
A mouse model of insulin resistance and its associated dyslipidemia was generated by crossing mice expressing human apolipoprotein B (apoB) with mice lacking only brown adipose tissue (BATless). On a high fat diet, male apoB/BATless mice became obese, hypercholesterolemic, hypertriglyceridemic, and hyperinsulinemic compared with control apoB mice. Fast performance liquid chromatography revealed increased triglyceride concentrations in intermediate density lipoprotein/low density lipoprotein (LDL) and reduced high density lipoprotein cholesterol concentrations. Inhibition of lipolysis by the drug, tetrahydrolipostatin, demonstrated that very low density lipoprotein-sized particles were initially secreted. Metabolic studies employing Triton WR-1339 and either [(3)H]glycerol or [(3)H]palmitate showed that the hypertriglyceridemia in apoB/BATless mice was due to the increased synthesis and secretion of triglyceride. Furthermore, lipoprotein lipase and hepatic lipase activities were not defective. ApoB was also secreted at increased rates in the apoB/BATless mice. Similar levels of apoB mRNA in apoB and apoB/BATless mice indicated that apoB secretion was regulated post-transcriptionally. LDL receptor mRNA was increased in the apoB/BATless mice, indicating that the observed increase in apoB-lipoprotein secretion was not due to their decreased reuptake. Finally, mRNA levels of the large subunit of microsomal triglyceride transfer protein, a required component for very low density protein assembly, were not different between apoB and apoB/BATless mice. This rodent model should prove useful in exploring mechanisms underlying the regulation of apoB secretion in the context of insulin resistance.
|Ectopic PDX-1 expression in liver ameliorates type 1 diabetes. |
Keren Shternhall-Ron,Francisco J Quintana,Shira Perl,Irit Meivar-Levy,Iris Barshack,Irun R Cohen,Sarah Ferber
Journal of autoimmunity 28 2001
Type 1 diabetes mellitus (T1DM) results from a specific autoimmune mediated destruction of the pancreatic beta-cells. PDX-1 induced developmentally redirected liver cells were suggested to restore the ablated pancreatic function in chemically induced diabetes. However, developmentally redirected liver cells, may have acquired along with the desired beta-cell characteristics and functions, also undesired sensitivity to autoimmune attack and therefore may be inefficient in ameliorating T1DM. This study analyzes whether subjects with beta-cell autoimmunity could benefit from Ad-CMV-PDX-1 gene therapy. Using the model of cyclophosphamide-accelerated diabetes in non-obese diabetic (CAD-NOD) mice, we report that recombinant adenovirus mediated PDX-1 gene therapy, ameliorates hyperglycemia in CAD-NOD mice. Our data demonstrate that 43% of the overtly diabetic CAD-NOD mice treated with Ad-CMV-PDX-1 became normoglycemic and maintained a stable body weight. Ectopic PDX-1 expression induced pancreatic gene expression and insulin production in the mice livers. The amelioration of hyperglycemia, in PDX-1 treated diabetic mice was associated with an immune modulation manifested by Th1 to Th2 shift in the autoimmune T-cell response to antigens associated with NOD diabetes. Thus, liver-to-pancreas transdifferentiation ameliorates T1DM in a process which is associated with a concomitant modulation of the autoimmune attack. Our findings suggest a beneficial therapeutic effect of the PDX-1 gene therapy for treating autoimmune type 1 diabetes mellitus (T1DM).
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