Voluntary running exercise prevents ß-cell failure in susceptible islets of the Zucker diabetic fatty rat.

Physical activity improves glycemic control in type 2 diabetes (T2D), but its contribution to preserving ß-cell function is uncertain. We evaluated the role of physical activity on ß-cell secretory function and glycerolipid/fatty acid (GL/FA) cycling in male Zucker diabetic fatty (ZDF) rats. Six-week-old ZDF rats engaged in voluntary running for 6 wk (ZDF-A). Inactive Zucker lean and ZDF (ZDF-I) rats served as controls. ZDF-I rats displayed progressive hyperglycemia with ß-cell failure evidenced by falling insulinemia and reduced insulin secretion to oral glucose. Isolated ZDF-I rat islets showed reduced glucose-stimulated insulin secretion expressed per islet and per islet protein. They were also characterized by loss of the glucose regulation of fatty acid oxidation and GL/FA cycling, reduced mRNA expression of key ß-cell genes, and severe reduction of insulin stores. Physical activity prevented diabetes in ZDF rats through sustaining ß-cell compensation to insulin resistance shown in vivo and in vitro. Surprisingly, ZDF-A islets had persistent defects in fatty acid oxidation, GL/FA cycling, and ß-cell gene expression. ZDF-A islets, however, had preserved islet insulin mRNA and insulin stores compared with ZDF-I rats. Physical activity did not prevent hyperphagia, dyslipidemia, or obesity in ZDF rats. In conclusion, islets of ZDF rats have a susceptibility to failure that is possibly due to altered ß-cell fatty acid metabolism. Depletion of pancreatic islet insulin stores is a major contributor to islet failure in this T2D model, preventable by physical activity.

Adipose triglyceride lipase is implicated in fuel- and non-fuel-stimulated insulin secretion.

Reduced lipolysis in hormone-sensitive lipase-deficient mice is associated with impaired glucose-stimulated insulin secretion (GSIS), suggesting that endogenous beta-cell lipid stores provide signaling molecules for insulin release. Measurements of lipolysis and triglyceride (TG) lipase activity in islets from HSL(-/-) mice indicated the presence of other TG lipase(s) in the beta-cell. Using real time-quantitative PCR, adipose triglyceride lipase (ATGL) was found to be the most abundant TG lipase in rat islets and INS832/13 cells. To assess its role in insulin secretion, ATGL expression was decreased in INS832/13 cells (ATGL-knockdown (KD)) by small hairpin RNA. ATGL-KD increased the esterification of free fatty acid (FFA) into TG. ATGL-KD cells showed decreased glucose- or Gln + Leu-induced insulin release, as well as reduced response to KCl or palmitate at high, but not low, glucose. The K(ATP)-independent/amplification pathway of GSIS was considerably reduced in ATGL-KD cells. ATGL(-/-) mice were hypoinsulinemic and hypoglycemic and showed decreased plasma TG and FFAs. A hyperglycemic clamp revealed increased insulin sensitivity and decreased GSIS and arginine-induced insulin secretion in ATGL(-/-) mice. Accordingly, isolated islets from ATGL(-/-) mice showed reduced insulin secretion in response to glucose, glucose + palmitate, and KCl. Islet TG content and FFA esterification into TG were increased by 2-fold in ATGL(-/-) islets, but glucose usage and oxidation were unaltered. The results demonstrate the importance of ATGL and intracellular lipid signaling for fuel- and non-fuel-induced insulin secretion.

Vagal control of pancreatic ß-cell proliferation.

The physiological mechanisms that preserve pancreatic ß-cell mass (BCM) are not fully understood. Although the regulation of islet function by the autonomic nervous system (ANS) is well established, its potential roles in BCM homeostasis and compensatory growth have not been adequately explored. The parasympathetic vagal branch of the ANS serves to facilitate gastrointestinal function, metabolism, and pancreatic islet regulation of glucose homeostasis, including insulin secretion. Given the functional importance of the vagus nerve and its branches to the liver, gut, and pancreas in control of digestion, motility, feeding behavior, and glucose metabolism, it may also play a role in BCM regulation. We have begun to examine the potential roles of the parasympathetic nervous system in short-term BCM maintenance by performing a selective bilateral celiac branch-vagus nerve transection (CVX) in normal Sprague-Dawley rats. CVX resulted in no detectable effects on basic metabolic parameters or food intake through 1 wk postsurgery. Although there were no differences in BCM or apoptosis in this 1-wk time frame, ß-cell proliferation was reduced 50% in the CVX rats, correlating with a marked reduction in activated protein kinase B/Akt. Unexpectedly, acinar proliferation was increased 50% in these rats. These data suggest that the ANS, via the vagus nerve, contributes to the regulation of BCM maintenance at the level of cell proliferation and may also mediate the drive for enhanced growth under physiological conditions when insulin requirements have increased. Furthermore, the disparate effects of CVX on ß-cell and acinar cells suggest that the endocrine and exocrine pancreas respond to different neural signals in regard to mass homeostasis.

GPR40 is necessary but not sufficient for fatty acid stimulation of insulin secretion in vivo.

Long-chain fatty acids amplify insulin secretion from the pancreatic beta-cell. The G-protein-coupled receptor GPR40 is specifically expressed in beta-cells and is activated by fatty acids; however, its role in acute regulation of insulin secretion in vivo remains unclear. To this aim, we generated GPR40 knockout (KO) mice and examined glucose homeostasis, insulin secretion in response to glucose and Intralipid in vivo, and insulin secretion in vitro after short- and long-term exposure to fatty acids. Our results show that GPR40 KO mice have essentially normal glucose tolerance and insulin secretion in response to glucose. Insulin secretion in response to Intralipid was reduced by approximately 50%. In isolated islets, insulin secretion in response to glucose and other secretagogues was unaltered, but fatty acid potentiation of insulin release was markedly reduced. The Galpha(q/11) inhibitor YM-254890 dose-dependently reduced palmitate potentiation of glucose-induced insulin secretion. Islets from GPR40 KO mice were as sensitive to fatty acid inhibition of insulin secretion upon prolonged exposure as islets from wild-type animals. We conclude that GPR40 contributes approximately half of the full acute insulin secretory response to fatty acids in mice but does not play a role in the mechanisms by which fatty acids chronically impair insulin secretion.

Impact of Adalimumab Patient Support Program's Care Coach Calls on Clinical Outcomes in Patients with Crohn's Disease in Canada: An Observational Retrospective Cohort Study.

BACKGROUND: Adalimumab is an antitumour necrosis factor (TNFα) biologic therapy indicated for the treatment of Crohn's disease (CD). Patients receiving adalimumab in Canada are eligible to enroll in the AbbVie Care™ patient support program (AC-PSP), which provides personalized services, including care coach calls (CCCs). The objective of this study was to compare the likelihood of achieving clinical remission in a cohort of CD patients treated with adalimumab who did and did not receive CCCs. METHODS: A longitudinal analysis was performed using de-identified aggregate-level data collected through the AC-PSP. Patients were indexed on the date of their first injection of adalimumab between July 2010 and October 2014. The AC-PSP database included measurements of the Harvey-Bradshaw Index (HBI), a symptom-based measure of disease severity. Eligible patients had an initial HBI measurement performed between 90 days before and up to 30 days after the index date and a follow-up HBI measurement six to 18 months later. Adjusted relative risk (RR) of achieving remission (HBI ≤ 4) at the time of the follow-up was estimated comparing patients who received and did not receive CCCs. RESULTS: There were 381 CD patients who met eligibility criteria; 224 (59%) received CCCs, and 157 (41%) did not receive CCCs. Multivariate regression analysis demonstrated that CD patients receiving CCCs had a 17% increased likelihood of achieving HBI remission when compared with patients who did not receive CCCs (RR = 1.17; 95% CI, 1.03-1.34; P = 0.0192). CONCLUSIONS: This study provides preliminary evidence that a phone call intervention, aiming to improve the overall patient experience with adalimumab treatment, may increase the likelihood of HBI remission in patients taking adalimumab to manage CD.

Impact of the Adalimumab Patient Support Program on Clinical Outcomes in Ankylosing Spondylitis: Results from the COMPANION Study.

INTRODUCTION: Adalimumab (ADA) is a tumor necrosis factor (TNF)-alpha inhibitor indicated for the treatment of inflammatory autoimmune diseases, including ankylosing spondylitis (AS). Patients receiving ADA in Canada are eligible to enroll in the AbbVie Care™ patient support program (AC-PSP), which provides personalized services, including care coach calls (CCCs). We estimated the likelihood of controlled disease in a cohort of AS patients treated with ADA enrolled in the AC-PSP and who received CCCs versus those who did not. METHODS: A longitudinal analysis using de-identified aggregate-level data collected through the AC-PSP was performed. A probabilistic matching algorithm was used to link patient-level records from the AC-PSP database to records from the QuintilesIMS longitudinal prescription transactions database. Patients were indexed on the date of their first prescription of ADA between January 2010 and October 2015. The AC-PSP database included patient assessments of the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), a measure of disease activity. Eligible patients had a baseline BASDAI assessment performed between 90 days before and 30 days after the index date, and a follow-up BASDAI assessment 6-18 months later. Poisson regression was used to estimate the adjusted relative risk (RR) of controlled disease (BASDAI < 4) at the time of follow-up, comparing patients who received CCCs with those who did not. RESULTS: In total 249 AS patients met eligibility criteria, and 123 (49%) received CCCs. Of the 249 patients, 184 (74%) had controlled disease (BASDAI < 4) at follow-up assessment, 98 (80%) in the CCC group and 86 (68%) in the no CCC group. Multivariable regression analysis demonstrated a 23% increased likelihood of controlled disease in patients who received CCCs relative to those who did not (RR = 1.23; 95% confidence interval, 1.06-1.42; p = 0.0055). CONCLUSION: AS patients receiving tailored services through the AC-PSP in the form of CCCs have an increased likelihood of controlled disease within 6-18 months. FUNDING: AbbVie.

Canada's Study of Adherence Outcomes in Patients Receiving Adalimumab: 3-year Results From the COMPANION Study.

PURPOSE: The aim of this study was to quantify the association between receiving care-coach calls (CCCs), a service provided by a patient-support program (PSP) in Canada, and persistence with and adherence to adalimumab therapy over a 3-year period in patients with immune-related inflammatory diseases (IMID). METHODS: COMPANION, a longitudinal, retrospective cohort study, was conducted using patient-level data from the PSP combined with those from a longitudinal pharmacy-transaction database in patients initiating adalimumab therapy between 2010 and 2012. Patients aged ≥18 years who were naive to adalimumab therapy were selected, and data from their prescriptions from 36 months or until drug discontinuation, defined as >90 days without drug supply, were evaluated. Cox proportional hazards modeling was used to estimate hazard ratios for the association between persistence, and patient characteristics and PSP services. Adherence was measured using the medication possession ratio. Multivariate logistic regression was used to estimate adjusted odds ratios to determine the relationship between adherence (medication possession ratio ≥80%), and patient characteristics and PSP services. FINDINGS: A total 4772 patients were included (55% women; 24% aged 50-59 years). Of these, 2866 qualified for the persistence analysis, and 51% received CCCs (n = 1452). Of the 4772 patients, 4630 qualified for the adherence analysis, and 33% received CCCs (n = 1511). Baseline characteristics were similar between the group that received CCCs versus the group that did not. During the follow-up period, patients who received CCCs had a significantly reduced risk for treatment discontinuation (hazard ratio = 0.350; 95% CI, 0.298-0.413; P < 0.0001) and a greater likelihood of being adherent (odds ratio, 2.248; 95% CI, 1.927-2.624; P < 0.0001). IMPLICATIONS: CCCs were associated with greater adherence and improved persistence in these patients receiving adalimumab therapy over a 3-year period for IMID.

Impact of the Adalimumab Patient Support Program's Care Coach Calls on Persistence and Adherence in Canada: An Observational Retrospective Cohort Study.

PURPOSE: Adalimumab (ADA) is a tumor necrosis factor-α inhibitor indicated for use in various immune-mediated inflammatory diseases. Patients receiving ADA in Canada are eligible to enroll in the AbbVie Care's Patient Support Program (PSP), which provides personalized services, including tailored interventions in the form of nurse-provided care coach calls (CCCs), with the goal of improving patients' experiences and outcomes. The primary objective of this study was to evaluate the impact of PSP services, including CCCs and patient characteristics, on persistence with and adherence to ADA for those patients enrolled in the PSP. A secondary objective was to estimate the effect of initial CCCs on treatment-initiation abandonment (ie, failure to initiate therapy after enrollment in the PSP). METHODS: An observational retrospective cohort study was conducted. A patient linkage algorithm based on probabilistic matching was developed to link the AbbVie Care PSP database to the QuintilesIMS longitudinal pharmacy transaction database. Patients who started ADA therapy between July 2010 and August 2014 were selected, and their prescriptions were evaluated for 12 months after the date of ADA start to calculate days until drug discontinuation, that is, the end of persistence, defined as >90 days without therapy. Cox proportional hazards modeling was used for estimating hazard ratios for the association between persistence and patient characteristics and each PSP service. Adherence, measured by medication possession ratio, was calculated, and multivariate logistic regression provided adjusted odds ratios for the relationship between being adherent (medication possession ratio ≥80%) and patient characteristics and each PSP service. Treatment-initiation abandonment among patients who received an initial CCC compared with those who did not was analyzed using the χ2 test. FINDINGS: Analysis of 10,857 linked patients yielded statistically significant differences in the hazard ratio of discontinuation and the likelihood of being adherent across multiple variables between patients who received CCCs in comparison to patients who did not. Patients receiving CCCs were found to have a 72% decreased risk for therapy discontinuation (hazard ratio = 0.282; P < 0.0001), and a greater likelihood of being adherent (odds ratio = 1.483; P < 0.0001), when compared with those patients who did not receive CCCs. The rate of treatment-initiation abandonment was significantly higher in patients who did not receive initial CCCs (P < 0.0001). IMPLICATIONS: Ongoing CCCs, provided by AbbVie Care PSP, were associated with greater patient persistence and adherence over the first 12 months of treatment, while initial CCCs were associated with a lower rate of treatment-initiation abandonment. Results may inform the planning of interventions aimed at improving treatment adherence and patient outcomes.

Influence of prior exercise and liver glycogen content on the sensitivity of the liver to glucagon.

The purpose of the present study was to test the hypothesis that a prior period of exercise is associated with an increase in hepatic glucagon sensitivity. Hepatic glucose production (HGP) was measured in four groups of anesthetized rats infused with glucagon (2 microg. kg(-1). min(-1) iv) over a period of 60 min. Among these groups, two were normally fed and, therefore, had a normal level of liver glycogen (NG). One of these two groups was killed at rest (NG-Re) and the other after a period of exercise (NG-Ex; 60 min of running, 15-26 m/min, 0% grade). The two other groups of rats had a high hepatic glycogen level (HG), which had been increased by a fast-refed diet, and were also killed either at rest (HG-Re) or after exercise (HG-Ex). Plasma glucagon and insulin levels were increased similarly in all four conditions. Glucagon-induced hyperglycemia was higher (P < 0.01) in the HG-Re group than in all other groups. HGP in the HG-Re group was not, however, on the whole more elevated than in the NG-Re group. Exercised rats (NG-Ex and HG-Ex) had higher hyperglycemia, HGP, and glucose utilization than rested rats in the first 10 min of the glucagon infusion. HG-Ex group had the highest HGP throughout the 60-min experiment. It is concluded that hyperglucagonemia-induced HGP is stimulated by a prior period of exercise, suggesting an increased sensitivity of the liver to glucagon during exercise.

The hepatic vagus nerve in the control of insulin sensitivity in the rat.

The objective was to determine if the cervical vagus or hepatic branch of the vagus nerve is a suitable site to produce functional parasympathetic denervation of the liver in the rat as assessed from the ability to produce insulin resistance. Anterior plexus denervation in both anesthetized rats and cats results in insulin resistance as assessed by the rapid insulin sensitivity test (RIST). This diagnostic test is a modified euglycemic clamp using the amount of glucose required to be infused to maintain euglycemia following a bolus administration of insulin (50 mU kg(-1) over 5 min, 0.1 ml min(-1) infusion) as the index of insulin sensitivity. Blood sampling was achieved through an arteriovenous silicone vascular shunt connecting the left carotid artery and the right jugular vein and allowed the close monitoring of blood glycemia throughout the test (every 2 min). The control RIST index (249.2 +/- 10.2 mg kg(-1)) was significantly decreased (P<0.001) following hepatic vagotomy (134.0 +/- 13.9). The intraportal infusion of 2.5 microg kg(-1) min(-1) of acetylcholine partially reversed (202.1 +/- 12.3) the insulin resistance. Intravenous atropine (1 mg kg(-1)) or hepatic anterior plexus denervation did not produce significant further insulin resistance. A similar degree of insulin resistance was produced by bilateral cervical vagotomy which was also partially reversed by acetylcholine. Complete hepatic parasympathetic denervation was achieved by selective hepatic vagal branch section. The data suggest that all of the parasympathetic nerves that regulate hormonal control of insulin resistance pass through the cervical vagus and the hepatic branch, and finally, through the anterior hepatic plexus along the common hepatic artery and that denervation at any of these sites leads to functional elimination of all hepatic parasympathetic input regulating insulin sensitivity. This approach provides an additional research tool to study the hepatic parasympathetic reflex control of peripheral insulin action.

Estrogen receptor activation reduces lipid synthesis in pancreatic islets and prevents ß cell failure in rodent models of type 2 diabetes.

The failure of pancreatic ß cells to adapt to an increasing demand for insulin is the major mechanism by which patients progress from insulin resistance to type 2 diabetes (T2D) and is thought to be related to dysfunctional lipid homeostasis within those cells. In multiple animal models of diabetes, females demonstrate relative protection from ß cell failure. We previously found that the hormone 17ß-estradiol (E2) in part mediates this benefit. Here, we show that treating male Zucker diabetic fatty (ZDF) rats with E2 suppressed synthesis and accumulation of fatty acids and glycerolipids in islets and protected against ß cell failure. The antilipogenic actions of E2 were recapitulated by pharmacological activation of estrogen receptor α (ERα) or ERß in a rat ß cell line and in cultured ZDF rat, mouse, and human islets. Pancreas-specific null deletion of ERα in mice (PERα-/-) prevented reduction of lipid synthesis by E2 via a direct action in islets, and PERα-/- mice were predisposed to islet lipid accumulation and ß cell dysfunction in response to feeding with a high-fat diet. ER activation inhibited ß cell lipid synthesis by suppressing the expression (and activity) of fatty acid synthase via a nonclassical pathway dependent on activated Stat3. Accordingly, pancreas-specific deletion of Stat3 in mice curtailed ER-mediated suppression of lipid synthesis. These data suggest that extranuclear ERs may be promising therapeutic targets to prevent ß cell failure in T2D.

Lack of preservation of insulin gene expression by a glucagon-like peptide 1 agonist or a dipeptidyl peptidase 4 inhibitor in an in vivo model of glucolipotoxicity.

UNLABELLED: Prolonged exposure of pancreatic beta-cells to elevated levels of glucose and fatty acids adversely affects insulin secretion and gene expression. AIM: To examine whether the GLP-1 agonist exenatide or the inhibitor of the GLP-1-degrading enzyme dipeptidyl peptidase 4 (DPP-4) sitagliptin rescue insulin gene expression in rats infused for 72h with glucose+Intralipid, independently from their glucose-lowering action. METHODS: Wistar rats were infused alternatively with glucose or Intralipid for cycles of 4h each for a total of 72h. The animals received exenatide (5microg/kg/day IV) or sitagliptin (5mg/kg/day IV) continuously starting 4 days prior to and continuing throughout the 3-day infusion period. RESULTS: Plasma glucose, fatty acids, insulin and C-peptide levels were unaffected by exenatide or sitagliptin treatment during the infusion period. Insulin mRNA levels increased in response to the glucose infusion, but this increase was abolished in islets from rats receiving glucose+Intralipid. Neither exenatide nor sitagliptin administration rescued insulin mRNA in glucose+Intralipid infused rats. CONCLUSIONS: Neither a GLP-1 agonist nor a DPP-4 inhibitor, at doses that do not alter blood glucose levels, prevented the inhibition of insulin gene expression in this in vivo model of glucolipotoxicity.

Beta-cell failure in diet-induced obese mice stratified according to body weight gain: secretory dysfunction and altered islet lipid metabolism without steatosis or reduced beta-cell mass.

OBJECTIVE: C57Bl/6 mice develop obesity and mild hyperglycemia when fed a high-fat diet (HFD). Although diet-induced obesity (DIO) is a widely studied model of type 2 diabetes, little is known about beta-cell failure in these mice. RESEARCH DESIGN AND METHODS: DIO mice were separated in two groups according to body weight gain: low- and high-HFD responders (LDR and HDR). We examined whether mild hyperglycemia in HDR mice is due to reduced beta-cell mass or function and studied islet metabolism and signaling. RESULTS: HDR mice were more obese, hyperinsulinemic, insulin resistant, and hyperglycemic and showed a more altered plasma lipid profile than LDR. LDR mice largely compensated insulin resistance, whereas HDR showed perturbed glucose homeostasis. Neither LDR nor HDR mice showed reduced beta-cell mass, altered islet glucose metabolism, and triglyceride deposition. Insulin secretion in response to glucose, KCl, and arginine was impaired in LDR and almost abolished in HDR islets. Palmitate partially restored glucose- and KCl-stimulated secretion. The glucose-induced rise in ATP was reduced in both DIO groups, and the glucose-induced rise in Ca(2+) was reduced in HDR islets relatively to LDR. Glucose-stimulated lipolysis was decreased in LDR and HDR islets, whereas fat oxidation was increased in HDR islets only. Fatty acid esterification processes were markedly diminished, and free cholesterol accumulated in HDR islets. CONCLUSIONS: beta-Cell failure in HDR mice is not due to reduced beta-cell mass and glucose metabolism or steatosis but to a secretory dysfunction that is possibly due to altered ATP/Ca(2+) and lipid signaling, as well as free cholesterol deposition.

Deletion of GPR40 impairs glucose-induced insulin secretion in vivo in mice without affecting intracellular fuel metabolism in islets.

OBJECTIVE: The G-protein-coupled receptor GPR40 mediates fatty acid potentiation of glucose-stimulated insulin secretion, but its contribution to insulin secretion in vivo and mechanisms of action remain uncertain. This study was aimed to ascertain whether GPR40 controls insulin secretion in vivo and modulates intracellular fuel metabolism in islets. RESEARCH DESIGN AND METHODS: Insulin secretion and sensitivity were assessed in GPR40 knockout mice and their wild-type littermates by hyperglycemic clamps and hyperinsulinemic euglycemic clamps, respectively. Transcriptomic analysis, metabolic studies, and lipid profiling were used to ascertain whether GPR40 modulates intracellular fuel metabolism in islets. RESULTS: Both glucose- and arginine-stimulated insulin secretion in vivo were decreased by approximately 60% in GPR40 knockout fasted and fed mice, without changes in insulin sensitivity. Neither gene expression profiles nor intracellular metabolism of glucose and palmitate in isolated islets were affected by GPR40 deletion. Lipid profiling of isolated islets revealed that the increase in triglyceride and decrease in lyso-phosphatidylethanolamine species in response to palmitate in vitro was similar in wild-type and knockout islets. In contrast, the increase in intracellular inositol phosphate levels observed in wild-type islets in response to fatty acids in vitro was absent in knockout islets. CONCLUSIONS: These results indicate that deletion of GPR40 impairs insulin secretion in vivo not only in response to fatty acids but also to glucose and arginine, without altering intracellular fuel metabolism in islets, via a mechanism that may involve the generation of inositol phosphates downstream of GPR40 activation.

The fatty acid receptor GPR40 plays a role in insulin secretion in vivo after high-fat feeding.

OBJECTIVE: The G-protein-coupled receptor GPR40 is expressed in pancreatic beta-cells and is activated by long-chain fatty acids. Gene deletion studies have shown that GPR40 mediates, at least in part, fatty acid-amplification of glucose-induced insulin secretion (GSIS) but is not implicated in GSIS itself. However, the role of GPR40 in the long-term effects of fatty acids on insulin secretion remains controversial. This study aimed to test the hypothesis that GPR40 plays a role in insulin secretion after high-fat feeding. RESEARCH DESIGN AND METHOD GPR40 knockout (KO) mice on a C57BL/6 background and their wild-type (WT) littermates were fed a high-fat diet (HFD) for 11 weeks. Glucose tolerance, insulin tolerance, and insulin secretion in response to glucose and Intralipid were assessed during the course of the diet period. RESULTS: GPR40 KO mice had fasting hyperglycemia. They became as obese, glucose intolerant, and insulin resistant as their WT littermates given HFD and developed a similar degree of liver steatosis. Their fasting blood glucose levels increased earlier than those of control mice during the course of the HFD. The remarkable increase in insulin secretory responses to intravenous glucose and Intralipid seen in WT mice after HFD was of much lower magnitude in GPR40 KO mice. CONCLUSIONS: GPR40 plays a role not only in fatty acid modulation of insulin secretion, but also in GSIS after high-fat feeding. These observations raise doubts on the validity of a therapeutic approach based on GPR40 antagonism for the treatment of type 2 diabetes.

Cyclical and alternating infusions of glucose and intralipid in rats inhibit insulin gene expression and Pdx-1 binding in islets.

OBJECTIVE: Prolonged exposure of isolated islets of Langerhans to elevated levels of fatty acids, in the presence of high glucose, impairs insulin gene expression via a transcriptional mechanism involving nuclear exclusion of pancreas-duodenum homeobox-1 (Pdx-1) and loss of MafA expression. Whether such a phenomenon also occurs in vivo is unknown. Our objective was therefore to ascertain whether chronic nutrient oversupply inhibits insulin gene expression in vivo. RESEARCH DESIGN AND METHODS: Wistar rats received alternating 4-h infusions of glucose and Intralipid for a total of 72 h. Control groups received alternating infusions of glucose and saline, saline and Intralipid, or saline only. Insulin and C-peptide secretion were measured under hyperglycemic clamps. Insulin secretion and gene expression were assessed in isolated islets, and beta-cell mass was quantified by morphometric analysis. RESULTS: Neither C-peptide secretion nor insulin sensitivity was different among infusion regimens. Insulin content and insulin mRNA levels were lower in islets isolated from rats infused with glucose plus Intralipid. This was associated with reduced Pdx-1 binding to the endogenous insulin promoter, and an increased proportion of Pdx-1 localized in the cytoplasm versus the nucleus. In contrast, MafA mRNA and protein levels and beta-cell mass and proliferation were unchanged. CONCLUSIONS: Cyclical and alternating infusions of glucose and Intralipid in normal rats inhibit insulin gene expression without affecting insulin secretion or beta-cell mass. We conclude that fatty acid inhibition of insulin gene expression, in the presence of high glucose, is an early functional defect that may contribute to beta-cell failure in type 2 diabetes.

Obese mice lacking inducible nitric oxide synthase are sensitized to the metabolic actions of peroxisome proliferator-activated receptor-gamma agonism.

OBJECTIVE: Synthetic ligands for peroxisome proliferator-activated receptor-gamma (PPAR-gamma) improve insulin sensitivity in obesity, but it is still unclear whether inflammatory signals modulate their metabolic actions. In this study, we tested whether targeted disruption of inducible nitric oxide (NO) synthase (iNOS), a key inflammatory mediator in obesity, modulates the metabolic effects of rosiglitazone in obese mice. RESEARCH DESIGN AND METHODS: iNOS(-/-) and iNOS(+/+) were subjected to a high-fat diet or standard diet for 18 weeks and were then treated with rosiglitazone for 2 weeks. Whole-body insulin sensitivity and glucose tolerance were determined and metabolic tissues harvested to assess activation of insulin and AMP-activated protein kinase (AMPK) signaling pathways and the levels of inflammatory mediators. RESULTS: Rosiglitazone was found to similarly improve whole-body insulin sensitivity and insulin signaling to Akt/PKB in skeletal muscle of obese iNOS(-/-) and obese iNOS(+/+) mice. However, rosiglitazone further improved glucose tolerance and liver insulin signaling only in obese mice lacking iNOS. This genotype-specific effect of rosiglitazone on glucose tolerance was linked to a markedly increased ability of the drug to raise plasma adiponectin levels. Accordingly, rosiglitazone increased AMPK activation in muscle and liver only in obese iNOS(-/-) mice. PPAR-gamma transcriptional activity was increased in adipose tissue of iNOS(-/-) mice. Conversely, treatment of 3T3-L1 adipocytes with a NO donor blunted PPAR-gamma activity. CONCLUSIONS: Our results identify the iNOS/NO pathway as a critical modulator of PPAR-gamma activation and circulating adiponectin levels and show that invalidation of this key inflammatory mediator improves the efficacy of PPAR-gamma agonism in an animal model of obesity and insulin resistance.

Regulatory impact of intra-hepatic carbohydrate and lipid metabolism.

The first evidence that the liver can afferently contribute to regulatory activities comes from studies on regulation of food intake. The hepatic afferent pathway has been shown to be responsive to glucoprivic as well as lipoprivic stimuli. Similarly to regulation of food intake, it has been reported that the liver may afferently contribute to the metabolic regulation of exercise. The best reported evidence of this view is the observation that the decrease in insulin and the increase in glucagon and noradrenaline levels during exercise are diminished in hepatic vagotomized rats (Lavoie et al., 1989). The concept behind these observations is that the liver, through the existence of hepatic glucoreceptors, is responsive to a decrease in glycogen content or to some metabolites of the glycolytic chain related to liver glycogen content. There is also some evidence that lipids in the liver may have some regulatory impact inside and outside the liver. Recent interest in looking at lipid metabolism in liver has been spurred by the observation that the increased flux of lipids through the hepatic portal vein has been associated with increased risks of metabolic and cardiovascular abnormalities. To explore this avenue, a 10% triglyceride emulsion was infused into either the portal or a peripheral vein of rats for 48 hrs while another group of rats was acutely infused for 2 hrs into the portal vein. The results indicate that all of these lipid infusions resulted in an increase in liver lipid infiltration, which may be associated with the development of a state of hepatic and peripheral insulin resistance.

Insulin sensitivity regulated by feeding in the conscious unrestrained rat.

Hepatic insulin sensitizing substance (HISS), a putative hormone released from the liver in response to insulin in fed animals, accounts for 50-60% of insulin action. HISS release is regulated by permissive control of the hepatic parasympathetic nerves. The objectives were to develop the rapid insulin sensitivity test (RIST) in conscious rats, and to assess the effects of anesthesia, atropine, feeding, and fasting on insulin action. The RIST index, expressed as milligrams glucose per kilogram body weight required to maintain euglycemia after a 50 mU/kg bolus of insulin, was similar in conscious and anesthetized rats (238.6+/-42.5 vs. 225.3+/-30.4 mg/kg). Atropine produced a 56% inhibition of insulin action in fed rats. After a 24 h fast, full HISS-dependent insulin resistance had developed as shown by a low RIST index that was not reduced further by atropine. Fasting caused a 10.5% decrease in insulin action per hour over six hours. HISS-dependent insulin resistance in 24-h fasted rats was reversed 4 h after re-feeding (90.9+/-12.3 vs. 204.5+/-30.5 mg/kg). We conclude that HISS-dependent and HISS-independent insulin action, as assessed by the RIST, is similar in conscious and pentobarbital-anesthetized rats. Pharmacological blockade of HISS-dependent insulin action and physiological regulation of HISS action by feeding-fasting is confirmed. Re-feeding fasted rats reversed HISS-dependent insulin resistance. Merits of use of the RIST in conscious versus anesthetized rats are discussed.

Comparison of the rapid insulin sensitivity test (RIST), the insulin tolerance test (ITT), and the hyperinsulinemic euglycemic clamp (HIEC) to measure insulin action in rats.

The objective was to compare the ability of the rapid insulin sensitivity test (RIST), the hyperinsulinemic euglycemic clamp (HIEC), and the insulin tolerance test (ITT) to detect hepatic insulin sensitizing substance (HISS) dependent insulin action. HISS action was augmented by feeding and inhibited by fasting, blockade of hepatic nitric oxide synthase, or blockade of hepatic muscarinic cholinergic receptors. A significant correlation was found between the RIST index and ITT nadir (r2 = 0.84) but not between the glucose infusion rate of the HIEC and RIST index. There was, however, a relationship between the RIST index and the initial response during the HIEC. Use of the HIEC resulted in HISS-dependent insulin resistance in both conscious and anesthetized animals. We concluded that since the RIST and ITT were comparable in quantifying both HISS-dependent and HISS-independent insulin action, the RIST was validated against this standard. The observation that the HIEC is capable of detecting HISS action in the first rising slope of the test but not at the end of the test and that HISS release is fully blocked after the conclusion of the HIEC raises concerns about the use of the commonly used HIEC.