Exaggerated Insulin Secretion Research Articles

SAT163 Title: Adult-onset Hyperinsulinemic Hypoglycemia Due To An Activating Mutation In Glucokinase

Abstract Disclosure: S. Vaid: None. R. Ghosh: None. H. Elenius: None. C. Cochran: None. R. Chang: None. N. Nilubol: None. R. Muniyappa: None. Introduction: Glucokinase (GK), the key β-cell glucose sensor, determines the threshold for glucose-stimulated insulin secretion. Activating mutations of GK are infrequent causes (prevalence of 1.2%) of congenital hyperinsulinemic hypoglycemia (HH). Adult-onset of severe hypoglycemia due to GK-HH is extremely rare. Clinical Case: A 26-year-old well-nourished female (BMI, 27 kg/m2) with a recent history of dizziness, tremulousness, fatigue, sweating, and hunger, associated with weight gain presented for further workup. Hypoglycemia was noted, and Whipple's triad was confirmed. She had no family history of endocrine disease or hypoglycemia. Supervised fasting promptly produced symptomatic hypoglycemia with hyperinsulinemia. Laboratory studies revealed a low glucose level at 44 mg/dL; a plasma insulin level at 93 μIU/mL (<3 μIU/ml); a C-peptide level at 8.1 ng/mL (<0.6 ng/mL); pro-insulin at 266 pmol/L (<5 pmol/L); and beta-hydroxybutyrate <2.7 mmol/L. IGF2/IGF-1 ratio was 3.1 (<10) and renal and liver function was normal. Interestingly, a mixed meal also provoked significant hypoglycemia within an hour of consumption of a meal. Urine for sulfonylurea screen was negative, and so were anti-insulin antibodies. Imaging of the pancreas with computed tomography (CT), magnetic resonance imaging (MRI), and endoscopic ultrasound revealed a 1.2x0.8cm nodule on the superior margin of the body of the pancreas. 68Ga-DOTATATE​​ PET/CT (targeting somatostatin receptors) showed mild uptake coinciding with the nodule on the CT scan. Arteriography with calcium stimulation and venous sampling (ASVS) was non-localizing. The patient subsequently underwent laparoscopic exploration with intraoperative ultrasound (IOUS) of the pancreas followed by the enucleation of the pancreatic nodule. Histopathology of the nodule revealed a normal pancreatic tissue with no evidence of a neuroendocrine tumor. Change to multiple small meals, addition of cornstarch to diet, continuous blood glucose monitoring (CGM), diazoxide (70 mg oral, three times a day), and monthly octreotide LAR (30 mg) has allowed the patient to avoid hypoglycemia. Genetic testing by analysis of the genes known to cause hypoglycemia revealed a heterozygous GCK variant [c.1367C>T (p.Ala456Val), which was predicted to be a pathological mutation. This mutation is known to increase affinity for glucose, which leads to exaggerated insulin secretion. Conclusion: Our study highlights that in adults with non-insulinoma pancreatogenous hypoglycemia, genetic causes of HH should be considered in the differential diagnosis. Presentation: Saturday, June 17, 2023

295-LB: Pancreatic Peroxisomes Are Required for Physiological Regulation of Insulin Secretion and Maintenance of Normal Glucose Tolerance in Male Mice

The regulation of glucose-stimulated insulin secretion (GSIS) is central to maintenance of glucose disposal. The role of lipid storage and lipid oxidation to regulate pancreatic islet β-cell insulin secretion is not completely understood. Peroxisomes are enriched in insulin-producing β-cells, but their contribution to β-cell function and maturity is lacking. Therefore, we generated a novel model of peroxisomal dysfunction to test the hypothesis that peroxisomal lipid metabolism is required to prevent a hyperlipidemic environment that interferes with β-cell function and maturity. Pex5 plays a critical role in importing the majority of peroxisomal proteins into the peroxisomal matrix; thus, deletion of the Pex5 gene creates a cellular environment with reductions in function of this organelle. In this study, we bred Pex5 mice on a C57BL/6J background containing ‘floxed’ alleles to Pdx1-cre mice to generate offspring with a pancreas-wide deficiency in Pex5 expression and abundance. Glucose tolerance was impaired by 12 weeks in male mice (n=20; AUC p<0.05). Surprisingly, GSIS was elevated in Pex5Pdx1-/- mice compared to littermate controls both in vivo (n=15; AUC p<0.05) and ex vivo in isolated islets as measured by perifusion analysis (n=12; AUC p<0.01). We further found that a subset of β-cells from Pex5Pdx1-/- mice expressed the de-differentiation marker Aldh1a3, while a subset of β-cells showed reductions in MafA and Nkx6.1 staining compared to controls. Perilipin-1 staining showed increased presence of lipid droplets in pancreatic tissue of Pex5Pdx1-/- mice versus controls. Thus, pancreatic deletion of peroxisomal function results in increased lipid storage in pancreatic tissue that is correlated with exaggerated insulin secretion. Collectively, these data are in support of a model whereby peroxisomal function supports β-cell insulin secretion and maintenance of the fully differentiated state. Disclosure S. Burke: None. S. Ghosh: None. D. Burk: None. R. Noland: None. J. Collier: None.

Targeted Derivation of Organotypic Glucose- and GLP-1-Responsive β Cells Prior to Transplantation into Diabetic Recipients.

SummaryGeneration of functional β cells from pluripotent sources would accelerate diagnostic and therapeutic applications for diabetes research and therapy. However, it has been challenging to generate competent β cells with dynamic insulin-secretory capacity to glucose and incretin stimulations. We introduced transcription factors, critical for β-cell development and function, in differentiating human induced pluripotent stem cells (PSCs) and assessed the impact on the functionality of derived β-cell (psBC) progeny. A perifusion system revealed stepwise transduction of the PDX1, NEUROG3, and MAFA triad (PNM) enabled in vitro generation of psBCs with glucose and GLP-1 responsiveness within 3 weeks. PNM transduction upregulated genes associated with glucose sensing, insulin secretion, and β-cell maturation. In recipient diabetic mice, PNM-transduced psBCs showed glucose-responsive insulin secretion as early as 1 week post transplantation. Thus, enhanced pre-emptive β-cell specification of PSCs by PNM drives generation of glucose- and incretin-responsive psBCs in vitro, offering a competent tissue-primed biotherapy.

The incretin effect in obese adolescents with and without type 2 diabetes: impaired or intact?

The incretin effect reflects the actions of enteral stimuli to promote prandial insulin secretion. Impairment of this measure has been proposed as an early marker of β-cell dysfunction and described in T2D, IGT, and even obesity without IGT. We sought to determine the effects of obesity and diabetes on the incretin effect in young subjects with short exposures to metabolic abnormalities and a few other confounding medical conditions. Subjects with T2D (n = 10; 18.0 ± 0.4 yr) or NGT, either obese (n = 11; 17.7 ± 0.4 yr) or lean (n = 8; 26.5 ± 2.3 yr), had OGTT and iso-iv. The incretin effect was calculated as the difference in insulin secretion during these tests and was decreased ∼50% in both the NGT-Ob and T2D subjects relative to the NGT-Ln group. The T2D group had impaired glucose tolerance and insulin secretion during the OGTT, whereas the lean and obese NGT subjects had comparable glucose excursions and β-cell function. During the iso-iv test, the NGT-Ob subjects had significantly greater insulin secretion than the NGT-Ln and T2D groups. These findings demonstrate that in young subjects with early, well-controlled T2D the incretin effect is reduced, similar to what has been described in diabetic adults. The lower incretin effect calculated for the obese subjects with NGT is driven by a disproportionately greater insulin response to iv glucose and does not affect postprandial glucose regulation. These findings confirm that the incretin effect is an early marker of impaired insulin secretion in persons with abnormal glucose tolerance but suggest that in obese subjects with NGT the incretin effect calculation can be confounded by exaggerated insulin secretion to iv glucose.

Effect of Different Insulin Response Patterns During Oral Glucose Tolerance Test on Glycemia in Individuals with Normal Glucose Tolerance.

Research is still going on for detecting the earliest glucose homeostasis derangements in individuals, which is crucial for the prevention of glucose intolerance. This cross-sectional study analyzes different insulin response patterns during the oral glucose tolerance test (OGTT) and their implications on glycemia in normoglycemic individuals. The sample frame was the "Offspring of Individuals with Diabetes Study" database. All participants underwent OGTT. Blood samples were collected at 0, 30, 60, and 120 min for measurement of insulin, C-peptide, and proinsulin levels. Normal glucose tolerant individuals were selected for analysis. Four hundred fifty subjects (mean age, 25 years) were included and divided into two groups according to timing of plasma insulin peaking during OGTT: Group 1, peaking at 30 min; and Group 2, peaking at 60 or 120 min. Body mass index (BMI) and insulin resistance were comparable between the groups; however, Group 2 showed a significantly higher 60- and 120-min glucose level and lower disposition index. Based on the magnitude of the insulin levels, Group 1 was subdivided into Group N (normal pattern) and Group E (exaggerated pattern) with a 30-min insulin cutoff of 74 μU/mL (Group E, ≥74 μU/mL). Group 2 was subdivided into Group DL (delayed and limited pattern; 60-min insulin <73.0 μU/mL and 120-min insulin <80.0 μU/mL) and Group DE (delayed and exaggerated pattern; 60-min insulin ≥73.0 μU/mL or 120-min insulin ≥80.0 μU/mL). Group DE showed a significantly higher area under the curve (AUC) of glucose compared with the other groups and had a lower disposition index and high-density lipoprotein levels. Group DL had significantly lower insulin resistance and BMI compared with Group E but showed a similar AUC of glucose. A delayed insulin pattern was associated with higher postprandial glucose levels. Individuals with delayed and exaggerated insulin secretion may have a higher risk for glucose intolerance.

Thrombin stimulates insulin secretion via protease-activated receptor-3

The disease mechanisms underlying type 2 diabetes (T2D) remain poorly defined. Here we aimed to explore the pathophysiology of T2D by analyzing gene co-expression networks in human islets. Using partial correlation networks we identified a group of co-expressed genes (‘module’) including F2RL2 that was associated with glycated hemoglobin. F2Rl2 is a G-protein-coupled receptor (GPCR) that encodes protease-activated receptor-3 (PAR3). PAR3 is cleaved by thrombin, which exposes a 6-amino acid sequence that acts as a ‘tethered ligand’ to regulate cellular signaling. We have characterized the effect of PAR3 activation on insulin secretion by static insulin secretion measurements, capacitance measurements, studies of diabetic animal models and patient samples. We demonstrate that thrombin stimulates insulin secretion, an effect that was prevented by an antibody that blocks the thrombin cleavage site of PAR3. Treatment with a peptide corresponding to the PAR3 tethered ligand stimulated islet insulin secretion and single β-cell exocytosis by a mechanism that involves activation of phospholipase C and Ca2+ release from intracellular stores. Moreover, we observed that the expression of tissue factor, which regulates thrombin generation, was increased in human islets from T2D donors and associated with enhanced β-cell exocytosis. Finally, we demonstrate that thrombin generation potential in patients with T2D was associated with increased fasting insulin and insulinogenic index. The findings provide a previously unrecognized link between hypercoagulability and hyperinsulinemia and suggest that reducing thrombin activity or blocking PAR3 cleavage could potentially counteract the exaggerated insulin secretion that drives insulin resistance and β-cell exhaustion in T2D.

Hydroxypropyl methylcellulose, a viscous soluble fiber, reduces insulin resistance and decreases fatty liver in Zucker Diabetic Fatty rats

BackgroundDiets producing a high glycemic response result in exaggerated insulin secretion which induces hepatic lipogenesis, contributing to development of insulin resistance and fatty liver. Viscous dietary fibers blunt the postprandial rise in blood glucose, however their effect on type 2 diabetes and obesity are not entirely known. This study examined the effect of chronic consumption of the viscous, non-fermentable dietary fiber, hydroxypropyl methylcellulose (HPMC), on glucose control, insulin resistance and liver lipids in an obese diabetic rat model.MethodsThree groups of Zucker Diabetic Fatty (ZDF) rats were fed diets containing either 5% non-viscous cellulose (control), low viscosity HPMC (LV-HPMC) or high viscosity HPMC (HV- HPMC) for six weeks. Zucker lean littermates consuming cellulose served as a negative control. Markers of glucose control, including oral glucose tolerance test, glycated hemoglobin and urinary glucose, were measured as well as adiposity and the accumulation of liver lipids.ResultsThe HPMC diets increased the viscosity of the small intestinal contents and reduced the postprandial rise in blood glucose. The food efficiency ratio was greater with HPMC feeding compared to the obese control and urinary excretion of glucose and ketone bodies was reduced. The two HPMC groups had lower glycated hemoglobin and kidney weights and a reduced area under the curve during a glucose tolerance test, indicating improved glucose control. Epididymal fat pad weight as percent of body weight was reduced in the HV-HPMC group compared to the obese control group. The HV-HPMC group also had lower concentrations of liver lipid and cholesterol and reduced liver weight. However, HV-HPMC feeding did not affect hepatic gene expression of SREBP-1c or FAS. Muscle concentration of acylcarnitines, a lipid intermediate in fatty acid β-oxidation, was not different between the HPMC groups and obese control, suggesting no change in muscle fatty acid oxidation by HPMC.ConclusionsConsumption of the viscous non-fermentable fiber HPMC decreased diabetic wasting, improved glucose control and reduced insulin resistance and fatty liver in a model of obesity with diabetes.

Sitagliptin lowers glucagon and improves glucose tolerance in prediabetic obese SHROB rats

The SHROB (spontaneously hypertensive rat - obese strain) is a model of prediabetes and metabolic syndrome with insulin resistance, glucose intolerance and hypertension. Inhibitors of dipeptidyl dipeptidase IV (DPP-IV) are effective hypoglycemic agents in type 2 diabetes through potentiation of incretin hormones that act in the pancreas to increase insulin and decrease glucagon release. We sought to determine whether the DPP-IV inhibitor sitagliptin might be effective in prediabetes relative to standard therapy with the sulfonylurea glyburide, by using the SHROB model. SHROB show normal fasting glucose but are insulin resistant and hyperglucagonemic. SHROB were treated for six weeks with vehicle, sitagliptin (30 mg/kg/d) or glyburide (1 mg/kg/d) and compared with untreated lean spontaneously hypertensive rats. Body weight, food intake and fasting glucose were all unchanged in all three SHROB groups, but glucagon was reduced by 33% by sitagliptin while remaining unchanged following glyburide or vehicle. In oral glucose (6 g/kg) tolerance testing, both sitagliptin and glyburide lowered plasma glucose. Both sitagliptin and glyburide shifted peak insulin secretion earlier (30 min for glyburide and 60 min for sitagliptin but 240 min for vehicle). Only sitagliptin significantly enhanced insulin secretion. Sitagliptin is effective in normalizing excess glucagon levels and delaying exaggerated insulin secretion in response to a glucose challenge in a prediabetic model.

Sitagliptin lowers glucagon and improves glucose tolerance in prediabetic obese SHROB rats

Inhibitors of dipeptidyl dipeptidase IV (DPP‐IV) are effective hypoglycemic agents in type 2 diabetes through potentiation of incretin hormones that act in the pancreas to increase insulin and decrease glucagon release. We sought to determine whether the DPP‐IV inhibitor sitagliptin might be effective in prediabetes relative to standard therapy with the sulfonylurea glyburide, by using the spontaneously hypertensive obese (SHROB) rat model. SHROB show normal fasting glucose but are insulin resistant and hyperglucagonemic. SHROB were treated for 6 wk with vehicle, sitagliptin (30 mg/kg/d) or glyburide (1 mg/kg/d). Body weight, food intake and fasting glucose were all unchanged in all 3 groups, but glucagon was reduced 33% by sitagliptin while unchanged following glyburide or vehicle. In oral glucose (6g/kg) tolerance testing, both sitagliptin and glyburide lowered plasma glucose. Both sitagliptin and glyburide shifted peak insulin secretion earlier (30 min for glyburide and 60 min for sitagliptin but 240 min for vehicle). Only sitagliptin significantly enhanced insulin secretion. Sitagliptin is effective in normalizing excess glucagon levels and delayed exaggerated insulin secretion in response to a glucose challenge in a prediabetic model.

Effects of High-monounsaturated Fatty Acid Enteral Formula versus High-carbohydrate Enteral Formula on Plasma Glucose Concentration and Insulin Secretion in Healthy Individuals and Diabetic Patients

We investigated the effects of high-monounsaturated fatty acid (MUFA) versus high-carbohydrate enteral formula on post-prandial plasma glucose concentration and insulin response in Japanese patients with type 2 diabetes mellitus and healthy Japanese volunteers. Ten healthy volunteers aged 20.8 +/- 1.2 years and 12 diabetic patients with good glycaemic control (glycosylated haemoglobulin < 7%) aged 58.6 +/- 7.7 years were randomly assigned to take high-MUFA or high-carbohydrate formula after a 12-h overnight fast. The patients switched to the other formula after 7 days. Post-prandial plasma glucose and insulin response were significantly lower in all subjects after taking high-MUFA formula compared with high-carbohydrate formula. No differences were observed in free fatty acids, triglycerides and plasma glucagon between the two diet groups. In conclusion, a high-MUFA enteral formula suppresses post-prandial hyperglycaemia without exaggerated insulin secretion compared with a high-carbohydrate enteral diet in patients with type 2 diabetes and healthy subjects.

Olanzapine-Induced Hyperglycemia in Anorexia Nervosa

Back to table of contents Previous article Next article Letters to the EditorFull AccessOlanzapine-Induced Hyperglycemia in Anorexia NervosaDAISUKE YASUHARA M.D.TOSHIHIRO NAKAHARA M.D., Ph.D.TOSHIRO HARADA M.D.AKIO INUI M.D., Ph.D.,DAISUKE YASUHARA M.D.Search for more papers by this authorTOSHIHIRO NAKAHARA M.D., Ph.D.Search for more papers by this authorTOSHIRO HARADA M.D.Search for more papers by this authorAKIO INUI M.D., Ph.D.Search for more papers by this author,Published Online:1 Mar 2007AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To The Editor: Recent studies on anorexia nervosa have suggested that the atypical antipsychotic agent olanzapine has favorable effects on agitation, repetitive thinking about becoming obese, and subsequent weight gain (1 , 2) . Although hyperglycemia is a serious adverse effect of olanzapine (3) , the incidence varies from less than 1% to 10%, and to the best of our knowledge, there have been no previous reports of this effect in patients with anorexia nervosa. We present a case report of a patient with anorexia nervosa with olanzapine-induced hyperglycemia. A 27-year-old Japanese woman with a 2-year history of anorexia nervosa (restricting type) and no personal or family history of diabetes mellitus or other metabolic or mental disorders was admitted to our hospital with agitation, general fatigue, and fear of obesity. Laboratory results revealed aspartate aminotransferase of 39 IU/l and alanine aminotransferase of 61 IU/l; results of other laboratory examinations (e.g., antiglutamic acid decarboxylase antibodies) were normal. During the first week of hospitalization (body mass index: 14.1 kg/m 2 , mean value of daily energy intake: 1,043 kcal/day), we performed a corrected (1.75g-glucose/kg) oral glucose tolerance test, which showed impaired glucose tolerance (4.3 mmol/l at baseline, peak value of 9.2 mmol/l at 60 minutes, 8.6 mmol/l at 120 minutes) by World Health Organization criteria (4), with delayed insulin secretion (34.6 pmol/l at baseline, peak value of 198 pmol/l at 120 minutes). Thereafter, we prescribed olanzapine 5 mg/day to reduce agitation and fear of obesity; we also started a multidisciplinary treatment program (4). The patient’s agitation improved, and we performed another oral glucose tolerance test during the third week (body mass index: 14.2 kg/m 2 , energy intake: 1,157 kcal/day). Results showed diabetes mellitus (4.2 mmol/l at baseline, peak value of 12.2 mmol/l at 120 minutes) with exaggerated insulin secretion (30.8 pmol/L at baseline, peak value of 1,210 pmol/L at 60 minutes). However, symptoms of diabetes (e.g., excessive thirst or urination) were absent. The patient’s fear of obesity gradually decreased, and olanzapine therapy at 5 mg/day was carefully continued with monitoring of diabetic symptoms, weekly fasting blood glucose levels, and monthly oral glucose tolerance test examinations (3). The lack of symptoms of diabetes and weekly fasting blood glucose levels (range 4.2 to 4.8 mmol/l) remained stable over 10 weeks. Although the patient showed impaired glucose tolerance during the seventh week (body mass index: 15.2 kg/m 2 , energy intake: 1,600 kcal/day), the oral glucose tolerance test results returned to normal at the time of her discharge (body mass index: 18.3 kg/m 2 , energy intake: 1,800 kcal/day). The underlying mechanism of olanzapine-induced hyperglycemia remains unclear (3 , 5 , 6) . Theories regarding this mechanism include the induction of insulin resistance via 5-HT 1A antagonism or impaired insulin-signaling cascade, increased food intake via H 1 antagonism, impaired pancreatic beta cell function, induction of glucogenesis via a decrease in glycogen synthase (5) , increase in glycogen phosphorylase, and upregulation of cocaine and amphetamine regulated transcripts (6) . Exacerbating glucose tolerance with exaggerated insulin secretion was evident on the second oral glucose tolerance test despite no marked differences in fasting plasma glucose levels, body mass index, and energy intake compared with the first oral glucose tolerance test. These findings suggest that glucose intolerance might have been induced by olanzapine via insulin resistance (3 , 5 , 6) . Moreover, hyperglycemia improved after weight restoration despite continuous use of olanzapine, which indicates that undernutrition itself might be a risk factor for olanzapine-induced hyperglycemia, particularly in patients with anorexia nervosa. Clinicians treating acute patients with anorexia nervosa should carefully monitor glucose metabolism, especially in patients being treated with olanzapine. Sakuragaoka, Kagoshima City, JapanSupported by a research grant from the Japanese Ministry of Health, Labor, and Welfare. The authors report no competing interests.Reprints are not available; however, Letters to the Editor can be downloaded at http://ajp.psychiatryonline.org.

Olanzapine-Induced Hyperglycemia in Anorexia Nervosa

Back to table of contents Previous article Next article Letters to the EditorFull AccessOlanzapine-Induced Hyperglycemia in Anorexia NervosaDAISUKE YASUHARA M.D.TOSHIHIRO NAKAHARA M.D., Ph.D.TOSHIRO HARADA M.D.AKIO INUI M.D., Ph.D.,DAISUKE YASUHARA M.D.Search for more papers by this authorTOSHIHIRO NAKAHARA M.D., Ph.D.Search for more papers by this authorTOSHIRO HARADA M.D.Search for more papers by this authorAKIO INUI M.D., Ph.D.Search for more papers by this author,Published Online:1 Mar 2007AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To The Editor: Recent studies on anorexia nervosa have suggested that the atypical antipsychotic agent olanzapine has favorable effects on agitation, repetitive thinking about becoming obese, and subsequent weight gain (1 , 2) . Although hyperglycemia is a serious adverse effect of olanzapine (3) , the incidence varies from less than 1% to 10%, and to the best of our knowledge, there have been no previous reports of this effect in patients with anorexia nervosa. We present a case report of a patient with anorexia nervosa with olanzapine-induced hyperglycemia. A 27-year-old Japanese woman with a 2-year history of anorexia nervosa (restricting type) and no personal or family history of diabetes mellitus or other metabolic or mental disorders was admitted to our hospital with agitation, general fatigue, and fear of obesity. Laboratory results revealed aspartate aminotransferase of 39 IU/l and alanine aminotransferase of 61 IU/l; results of other laboratory examinations (e.g., antiglutamic acid decarboxylase antibodies) were normal. During the first week of hospitalization (body mass index: 14.1 kg/m 2 , mean value of daily energy intake: 1,043 kcal/day), we performed a corrected (1.75g-glucose/kg) oral glucose tolerance test, which showed impaired glucose tolerance (4.3 mmol/l at baseline, peak value of 9.2 mmol/l at 60 minutes, 8.6 mmol/l at 120 minutes) by World Health Organization criteria (4), with delayed insulin secretion (34.6 pmol/l at baseline, peak value of 198 pmol/l at 120 minutes). Thereafter, we prescribed olanzapine 5 mg/day to reduce agitation and fear of obesity; we also started a multidisciplinary treatment program (4). The patient’s agitation improved, and we performed another oral glucose tolerance test during the third week (body mass index: 14.2 kg/m 2 , energy intake: 1,157 kcal/day). Results showed diabetes mellitus (4.2 mmol/l at baseline, peak value of 12.2 mmol/l at 120 minutes) with exaggerated insulin secretion (30.8 pmol/L at baseline, peak value of 1,210 pmol/L at 60 minutes). However, symptoms of diabetes (e.g., excessive thirst or urination) were absent. The patient’s fear of obesity gradually decreased, and olanzapine therapy at 5 mg/day was carefully continued with monitoring of diabetic symptoms, weekly fasting blood glucose levels, and monthly oral glucose tolerance test examinations (3). The lack of symptoms of diabetes and weekly fasting blood glucose levels (range 4.2 to 4.8 mmol/l) remained stable over 10 weeks. Although the patient showed impaired glucose tolerance during the seventh week (body mass index: 15.2 kg/m 2 , energy intake: 1,600 kcal/day), the oral glucose tolerance test results returned to normal at the time of her discharge (body mass index: 18.3 kg/m 2 , energy intake: 1,800 kcal/day). The underlying mechanism of olanzapine-induced hyperglycemia remains unclear (3 , 5 , 6) . Theories regarding this mechanism include the induction of insulin resistance via 5-HT 1A antagonism or impaired insulin-signaling cascade, increased food intake via H 1 antagonism, impaired pancreatic beta cell function, induction of glucogenesis via a decrease in glycogen synthase (5) , increase in glycogen phosphorylase, and upregulation of cocaine and amphetamine regulated transcripts (6) . Exacerbating glucose tolerance with exaggerated insulin secretion was evident on the second oral glucose tolerance test despite no marked differences in fasting plasma glucose levels, body mass index, and energy intake compared with the first oral glucose tolerance test. These findings suggest that glucose intolerance might have been induced by olanzapine via insulin resistance (3 , 5 , 6) . Moreover, hyperglycemia improved after weight restoration despite continuous use of olanzapine, which indicates that undernutrition itself might be a risk factor for olanzapine-induced hyperglycemia, particularly in patients with anorexia nervosa. Clinicians treating acute patients with anorexia nervosa should carefully monitor glucose metabolism, especially in patients being treated with olanzapine. Sakuragaoka, Kagoshima City, JapanSupported by a research grant from the Japanese Ministry of Health, Labor, and Welfare. The authors report no competing interests.Reprints are not available; however, Letters to the Editor can be downloaded at http://ajp.psychiatryonline.org.

Impact of Steatosis on Insulin Secretion in Chronic Hepatitis C Patients

Liver steatosis is frequently observed in patients with chronic hepatitis C (CHC) and is an identified risk factor for progression of liver fibrosis. This study aimed to evaluate the relationship between steatosis and host/viral factors, and the correlation between steatosis and insulin secretion in CHC patients with normal glucose tolerance (NGT). A total of 212 CHC patients were enrolled in this study. Insulin resistance and insulin secretion were determined in response to oral loading of 75 g glucose. Liver fibrosis and steatosis were quantified by the image analysis. Of the 212 CHC patients, 165 (78%) had steatosis, mostly of a mild degree. Multiple ordinal regression analysis revealed body mass index (BMI) (P= 0.011) as the main factor associated with severe steatosis. Of the 212 CHC patients, 148 (61%) showed NGT, and the serum insulin response to oral glucose loading in these NGT patients with steatosis was significantly different from that in patients with NGT but no steatosis. The peak insulin response occurred at 60 min in cases of mild steatosis, and at 90 min in patients with moderate or severe steatosis. The insulin level at 120 min in patients with severe steatosis was higher than that in those without steatosis. The total area under the response curve of insulin during OGTT in the patients with steatosis is higher than that in those without steatosis. Exaggerated insulin secretion was observed even in CHC patients with mild steatosis and NGT, suggesting the presence of insulin resistance. Exaggerated insulin secretion may accelerate the progression of liver fibrosis in CHC patients.

Exaggerated insulin secretion in Pima Indians and African-Americans but higher insulin resistance in Pima Indians compared to African-Americans and Caucasians.

African-Americans have a higher prevalence of Type 2 diabetes than Caucasians, but a lower prevalence than Pima Indians. Studies suggest that both African-Americans and Pima Indians are more insulin resistant and have higher acute insulin secretory responses to glucose than Caucasians; however, a direct comparison between these three populations is lacking. We measured insulin secretory responses to intravenous glucose (acute insulin response, AIR, 25 g ivGTT); insulin action at physiological (M-low) and supra-physiological (M-high) levels of hyperinsulinaemia (2-step hyperinsulinaemic clamp); basal and insulin-suppressed endogenous glucose production in 30 African-Americans, 30 Pima Indians and 30 Caucasians with normal glucose tolerance who were carefully matched for age, sex, and body fat (hydrodensitometry or DEXA). A subgroup of 24 subjects from each group additionally underwent a standardized mixed meal test. M-low was lower in Pima Indians (0.50 +/- 0.03) compared to Caucasians (0.59 +/- 0.02, P = 0.02) and African-Americans [0.58 +/- 0.03 mg/kgEMBS/min, log10 (means +/- SE), P = 0.03] but was not different between African-Americans and Caucasians. Basal endogenous glucose production was lower in Pima Indians (2.43 +/- 0.06) compared to African-Americans (2.70 +/- 0.06, P = 0.02) and was not different between Pima Indians and Caucasians (2.59 +/- 0.09 mg/kgEMBS/min) or African-Americans and Caucasians (all P > 0.18). Insulin-suppressed endogenous glucose production during the clamp was not different among the groups (all P > 0.40). AIR was higher in both African-Americans (13.51 +/- 0.26) and Pima Indians (13.72 +/- 0.27) compared to Caucasians (12.33 +/- 0.25 pM, log10, both P < 0.01). The areas under the curve for glucose in response to the oral glucose tolerance test and mixed meal test were higher in Pima Indians compared to African-Americans (P = 0.03 and P = 0.03, respectively) and Caucasians (P = 0.01, mixed meal test), but not different between African-Americans and Caucasians. Exaggerated glucose-stimulated insulin secretion, manifested initially as an increased response to an intravenous glucose challenge, appears to be a characteristic in people with normal glucose tolerance at higher risk for diabetes. Lower whole-body insulin sensitivity in Pima Indians compared to African-Americans, however, may contribute to the higher risk for Type 2 diabetes in Pima Indians compared to African-Americans.

Use of naltrexone in postmenopausal women with exaggerated insulin secretion: a pilot study

Objective To determine the effect of naltrexone (an opiate receptor blocker) on insulin metabolism in postmenopausal women with different insulinemic patterns. Design Randomized placebo-controlled study. Setting Academic research environment. Patient(s) Forty-one healthy normoinsulinemic or hyperinsulinemic postmenopausal women. Intervention(s) Oral glucose tolerance test (OGTT) before and after 5 weeks of the opioid antagonist (naltrexone, 50 mg/d orally) or the placebo administration; euglycemic–hyperinsulinemic glucose clamp. Main outcome measure(s) Glucose, insulin, and C-peptide plasma levels assessed in fasting condition and during the OGTT. Insulin sensitivity was calculated as total body glucose utilization. Result(s) Naltrexone reduced fasting and stimulated insulin response to the glucose load while inducing a significant improvement of the hepatic extraction, only in the hyperinsulinemic patients. No differences were found in the C-peptide pancreatic secretion and in the peripheral insulin sensitivity. No net change in the glycoinsulinemic metabolism was observed in normoinsulinemic patients or in placebo-controlled normoinsulinemic and hyperinsulinemic subjects. Conclusion(s) Similar to that reported in premenopausal women, endogenous opioid peptides are involved in the modulation of glycoinsulinemic metabolism in postmenopause. Through a prevalent action on liver insulin metabolism, without any clear improvement of insulin resistance and pancreatic β-cell function, the chronic administration of naltrexone appears to reduce the hyperinsulinemia in those women with an exaggerated insulin response to the OGTT.

Overexpression of constitutively activated glutamate dehydrogenase induces insulin secretion through enhanced glutamate oxidation.

Glutamate dehydrogenase (GDH) catalyzes reversible oxidative deamination of l-glutamate to alpha-ketoglutarate. Enzyme activity is regulated by several allosteric effectors. Recognition of a new form of hyperinsulinemic hypoglycemia, hyperinsulinism/hyperammonemia (HI/HA) syndrome, which is caused by gain-of-function mutations in GDH, highlighted the importance of GDH in glucose homeostasis. GDH266C is a constitutively activated mutant enzyme we identified in a patient with HI/HA syndrome. By overexpressing GDH266C in MIN6 mouse insulinoma cells, we previously demonstrated unregulated elevation of GDH activity to render the cells responsive to glutamine in insulin secretion. Interestingly, at low glucose concentrations, basal insulin secretion was exaggerated in such cells. Herein, to clarify the role of GDH in the regulation of insulin secretion, we studied cellular glutamate metabolism using MIN6 cells overexpressing GDH266C (MIN6-GDH266C). Glutamine-stimulated insulin secretion was associated with increased glutamine oxidation and decreased intracellular glutamate content. Similarly, at 5 mmol/l glucose without glutamine, glutamine oxidation also increased, and glutamate content decreased with exaggerated insulin secretion. Glucose oxidation was not altered. Insulin secretion profiles from GDH266C-overexpressing isolated rat pancreatic islets were similar to those from MIN6-GDH266C, suggesting observation in MIN6 cells to be relevant in native beta-cells. These results demonstrate that, upon activation, GDH oxidizes glutamate to alpha-ketoglutarate, thereby stimulating insulin secretion by providing the TCA cycle with a substrate. No evidence was obtained supporting the hypothesis that activated GDH produced glutamate, a recently proposed second messenger of insulin secretion, by the reverse reaction, to stimulate insulin secretion.

Glucose-Induced Insulin Hypersecretion in Lipid-Infused Healthy Subjects Is Associated with a Decrease in Plasma Norepinephrine Concentration and Urinary Excretion

We investigated the effect of a 48 h triglyceride infusion on the subsequent insulin secretion in response to glucose in healthy men. We measured the variations in plasma concentration and urinary excretion of catecholamines as an indirect estimation of sympathetic tone. For 48 h, 20 volunteers received a triglyceride/heparin or a saline solution, separated by a 1-month interval. At time 48 h, insulin secretion in response to glucose was investigated by a single iv glucose injection (0.5 g/kg−1) followed by an hyperglycemic clamp (10 mg·kg−1·min−1, during 50 min). The triglyceride infusion resulted in a 3-fold elevation in plasma free fatty acids and an increase in insulin and C-peptide plasma concentrations (1.5- and 2.5-fold, respectively, P < 0.05), compared with saline. At time 48 h of lipid infusion, plasma norepinephrine (NE) concentration and urinary excretion levels were lowered compared with saline (plasma NE: 0.65 ± 0.08 vs. 0.42 ± 0.06 ng/ml, P < 0.05; urinary excretion: 800 ± 70 vs. 620 ± 25 nmol/24 h, P < 0.05). In response to glucose loading, insulin and C-peptide plasma concentrations were higher in lipid compared with saline infusion (plasma insulin: 600 ± 98 vs. 310 ± 45 pm, P < 0.05; plasma C-peptide 3.5 ± 0.2 vs. 1.7 ± 0.2 nm, P < 0.05). In conclusion, in healthy subjects, a 48-h lipid infusion induces basal hyperinsulinemia and exaggerated insulin secretion in response to glucose which may be partly related to a decrease in sympathetic tone.

Impact of insulin and body mass index on metabolic and endocrine variables in polycystic ovary syndrome

To assess the differential impact of the insulin secretory pattern and obesity on the endocrinometabolic features of the polycystic ovary syndrome (PCOS), we studied 110 PCOS women. Patients underwent a gonadotropin-releasing hormone (GnRH) test, an oral glucose tolerance test (OGTT), and basal evaluation of hormonal and biochemical parameters. Basal androgens and lipids, basal and stimulated gonadotropins, insulin, and glucose levels were measured. Patients were classified into four groups according to the body mass index (BMI) and insulin secretion: normoinsulinemic-lean ([NL] n = 24), normoinsulinemic obese ([NO] n = 24), hyperinsulinemic lean ([HL] n = 17), hyperinsulinemic obese ([HO] n = 45). HL patients showed a higher luteinizing hormone (LH) area under curve (AUC) after GnRH stimulus compared with NL patients (HL v NL, 4,285 +/- 348 v 3,377 +/- 314 IU/L x 120 min, P < .05), whereas we failed to find a statistically significant difference in a similar comparison among obese subjects (HO v NO, 3,606 +/- 302 v 3,129 +/- 602 IU/L x 120 min). A trend toward increased plasma testosterone and decreased sex hormone-binding globulin (SHBG) was found in relation to hyperinsulinemia and obesity, thus resulting in a higher free androgen index (FAI) in groups HL and NO versus NL (HL, 5.54 +/- 0.51; NO, 5.64 +/- 0.49; NL, 4.13 +/- 0.33; P < .05 and P < .01, respectively). The presence of both exaggerated insulin secretion and obesity resulted in a synergistic additive effect on the FAI in the HO group (6.81 +/- 0.34). Concerning the lipoprotein lipid profile, the NL group showed lower plasma triglyceride levels compared with the other three groups, whereas no significant differences were found for nonesterified fatty acid (NEFA) concentrations. Higher low-density lipoprotein cholesterol (LDL-C) and very-low-density lipoprotein cholesterol (VLDL-C) and lower high-density lipoprotein cholesterol (HDL-C) levels were found in the obese groups compared with the lean counterparts, whereas the same parameters did not significantly differ in a comparison between normoinsulinemic and hyperinsulinemic groups. In conclusion, our data suggest an important role of hyperinsulinemia in the LH response to a GnRH stimulus and an independent and synergistic additive effect of obesity and hyperinsulinemia on the FAI in PCOS.

Opioid Blockade Effect on Insulin β-Cells Secretory Patterns in Polycystic Ovary Syndrome

In order to evaluate the involvement of endogenous opiates in the insulin disorders of polycystic ovary syndrome (PCOs) a total of 25 PCOs women and 11 normo-ovulatory controls were studied by comparing the effect of a chronic opioid blockade on β-cells responsiveness to oral glucose load and to intravenous glucagon bolus. Each patient, studied on follicular phase, underwent to oral glucose tolerance test (OGTT), and, 2 days later, to a glucagon intravenous bolus (1 mg); these tests were then repeated after 6 weeks of naltrexone treatment (50 mg orally). Naltrexone treatment did not modify the insulin secretory patterns of control subjects, whereas the same therapy significantly reduced, in hyperinsulinemic PCOs women, the β-cell hyperresponsiveness both to oral glucose load and to intravenous glucagon (p < 0.05 and p < 0.01, respectively), even if with different mean percent decrease (32% OGTT vs. 45% glucagon, p < 0.05). Moreover, normoinsulinemic PCOs patients showed a slight, but not significantly increase in the β-cells response to OGTT after opioid blockade, whereas, in the same situation, the insulin release after glucagon bolus was significantly reduced (p < 0.01). Chronic opioid blockade did not modify gonadotropins, steroids and SHBG levels in either group. Our data show that naltrexone treatment is able to reduce the β-cell response to a direct intravenous secretagogue stimulus in all PCOs patients, while only in hyperinsulinemic PCOs subjects the same treatment is effective in reducing the exaggerated insulin secretion after oral glucose load. The reason for such a discrepancy could be ascribed to a different effect of opioids on first- and second-phase insulin secretion, or, alternatively, to an involvement of other secretagogue factors, such as glucoincretins.

Effects of 3-month nifedipine treatment on endocrine-metabolic parameters in patients with abdominal obesity and mild hypertension.

It is widely accepted that abdominal obesity presents with exaggerated insulin secretion, insulin resistance and a trend toward glucose intolerance. Hypertension is frequently associated to abdominal obesity, and hyperinsulinism could play a role in its pathogenesis. Some studies reported that Ca-antagonists positively influence insulin sensitivity and glucose tolerance in obese patients with normal or elevated blood pressure. However, other studies reported worsening of metabolic balance during treatment with Ca-antagonists in hypertensive non-insulin-dependent diabetes mellitus (NIDDM) patients and in normal subjects. We studied 19 patients with abdominal obesity, mild hypertension and insulin resistance on balanced, mild hypocaloric diet (1400 Kcal), to verify the effects of the Ca-antagonist nifedipine on both basal and oral glucose tolerance test (OGTT)-induced glucose and insulin levels as well as on IGF-I basal and DHEA-S levels and fat mass (FM). To achieve this goal, 10 hypertensive obese subjects (HOB-NIFE, 3 males, 7 females, mean age +/- SD 44.6 +/- 1.7 yr; body mass index (BMI) 37.1 +/- 2.5 Kg/m2, WHR 0.95 +/- 0.02) received 3-month treatment with nifedipine (Adalat Crono 30 Bayer, 1 tab daily) while other 9 hypertensive obese (HOB, 3 males, 6 females, 42 +/- 2.4 yr, BMI 35.8 +/- 1.8 Kg/m2, WHR 0.91 +/- 0.03) were studied during diet only. The same parameters were studied also in 8 normotensive obese patients (OB: 3 males, 5 females, 48.1 +/- 2.1 yr, BMI 35.8 +/- 2.4 Kg/m2, WHR 0.90 +/- 0.03) on the same balanced hypocaloric diet. Basal systolic (SBP) and diastolic (DBP) blood pressure levels in HOB-NIFE and HOB were similar. At baseline, all groups had similar basal and OGTT-induced glucose, insulin and glucose insulin ratio (GIR) levels as well as IGF-I and DHEA-S levels. After 3 months BMI fell to the same extent in all groups (p < 0.05 vs baseline) while WHR and FFM/FM ratio did not change. SBP and DBP decreased HOB-NIFE (p < 0.02) but also during diet alone in both HOB and OB, though to a lesser extent (p < 0.05). Both basal and OGTT-stimulated glucose and insulin levels as well as IGF-I and DHEA-S levels were not modified in HOB-NIFE as well as in HOB and OB. In conclusion, our data indicate that nifedipine treatment does not modify glucose tolerance as well as insulin secretion and sensitivity, IGF-I and DHEA-S levels in hypertensive abdominal obese patients. Thus, nifedipine treatment has no detrimental effects on endocrine-metabolic balance in hypertensive obese patients.