Obesity effect on newly diagnosed and recurrent post-ablation atrial fibrillation: a systematic review and meta-analysis.

BACKGROUND AND AIMS: The role of overweight and obesity in the development of atrial fibrillation (AF) is well established; however, the differential effect on the occurrence and recurrence of AF remains uncertain. The aim of this review is to compare the effect of underweight and varying degrees of obesity on onset of AF and in recurrent post-ablation AF, and, when possible, in relation to sex. METHODS: A systematic literature search was conducted in PubMed, Embase, and Cochrane Library from inception to January 31, 2023. Studies reporting frequency of newly-diagnosed AF and of recurrent post-ablation AF in different BMI categories, were included. 3400 records were screened and 50 met the inclusion criteria. Standardized data search and abstraction were performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) Statement. Data were extracted from the manuscripts and were analyzed using a random effect model. The outcome was the occurrence of AF in population studies and in patients undergoing ablation. RESULTS: Data from 50 studies were collected, of which 27 for newly-diagnosed AF and 23 for recurrent post-ablation AF, for a total of 15,134,939 patients, of which 15,115,181 in studies on newly-diagnosed AF and 19,758 in studies on recurrent post-ablation AF. Compared to normal weight, the increase in AF was significant (p < 0.01) for overweight, obese, and morbidly obese patients for newly-diagnosed AF, and for obese and morbidly obese patients for recurrent post-ablation AF. Newly-diagnosed AF was more frequent in obese female than obese male patients. CONCLUSION: The effect of increased BMI was greater on the onset of AF, and obese women were more affected than men.

Multiple beneficial effects of 1-year nutritional-behavioral intervention on anthropometric and metabolic parameters in overweight and obese boys.

PURPOSE: Childhood obesity is on the rise worldwide increasing the risk for metabolic, cardiovascular and liver diseases in children. Eating habits and lifestyle changes are currently the standard of care for treating pediatric obesity. Our study aimed to determine the impact of a dietary intervention based on the Mediterranean Diet (MD) and the Health Eating Plate, on anthropometric and metabolic parameters in obese and overweight boys. METHODS: We studied 126 overweight/obese boys with anthropometric measurements, blood biochemistry and nutrient intakes evaluation by means of Food Frequency Questionnaire (FFQ) at baseline, at 6 and 12 months after a nutritional-behavioral intervention. RESULTS: We observed a significant reduction in energy, macronutrients and micronutrients intakes. BMI-SDS significantly decreased after 1 year with the proportion of obese boys decreasing by 33% and of overweight boys by 41%, while also all fat mass measures decreased both in obese and overweight individuals. In obese boys, ALT decreased significantly after 1-year nutritional intervention and these changes correlated with BMI-SDS reduction. Insulin-resistance and secretion indexes correlated with fat mass and BMI-SDS. In obese boys, significant changes were observed at 6 months for insulin concentrations, 1/HOMA-IR and QUICKI. With regard to the lipid profile, significant decreases were observed for total and LDL cholesterol in obese boys. CONCLUSION: Metabolic and anthropometric risk factors in overweight and obese boys can be improved by a nutritional-behavioral intervention of 1-year duration.

Blood pressure control in type 2 diabetes mellitus with arterial hypertension. The important ancillary role of SGLT2-inhibitors and GLP1-receptor agonists.

Type 2 diabetes mellitus and arterial hypertension are major cardiovascular risks factors which shares metabolic and haemodynamic abnormalities as well as pathophysiological mechanisms. The simultaneous presence of diabetes and arterial hypertension increases the risk of left ventricular hypertrophy, congestive heart failure, and stroke, as compared to either condition alone. A number of guidelines recommend lifestyle measures such as salt restriction, weight reduction and ideal body weight mainteinance, regular physical activity and smoking cessation, together with moderation of alcohol consumption and high intake of vegetables and fruits, as the basis for reduction of blood pressure and prevention of CV diseases. Despite the availability of multiple drugs effective for hypertension, BP targets are reached in only 50 % of patients, with even fewer individuals with T2DM-achieving goals. It is established that new emerging classes of type 2 diabetes mellitus treatment, SGLT2 inhibitors and GLP1-receptor agonists, are efficacious on glucose control, and safe in reducing HbA1c significantly, without increasing hypoglycemic episodes. Furthermore, in recent years, many CVOT trials have demonstrated, using GLP1-RA or SGLT2-inihibitors compared to placebo (in combination with the usual diabetes medications) important benefits on reducing MACE (cardio-cerebral vascular events) in the diabetic population. In this hypothesis-driven review, we have examined the anti-hypertensive effects of these novel molecules of the two different classes, in the diabetic population, and suggest that they could have an interesting ancillary role in controlling blood pressure in type 2 diabetic patients.

Pilot survey of norovirus in Northern Italy: an example of surveillance of norovirus gastroenteritis.

In this study, we describe the results of virological investigations carried out on cases of gastroenteritis reported in different communities within a 2-year pilot surveillance programme (January 2012 to December 2013) in the autonomous province of Bolzano (Northern Italy). Among the 162 norovirus (NoV)-positive cases out of 702 cases investigated, 76 were grouped in nine suspected outbreaks, 37 were hospital-acquired and 49 were community-acquired sporadic cases. NoV infections were found in all age groups in outbreak and community-acquired cases, while the highest peak of hospital-acquired infections occurred in the elderly. Sequence analyses helped to identify suspected outbreaks both in the community and in hospital wards. Although GII.4 is the predominant genotype, sequence data confirmed that at least seven genotypes circulate causing sporadic cases. Findings in this study confirmed the relevance of NoV infections as a cause of outbreaks, and impact of NoV infections in community-acquired sporadic cases in adults that are rarely described because of a lack of reporting.

Impairment of body mass reduction-associated activation of brown/beige adipose tissue in patients with type 2 diabetes mellitus.

Backgrounds/Objectives:The activity of brown/beige adipose tissue (B/BAT) is inversely proportional to body adiposity. Studies have shown that obese subjects submitted to distinct approaches aimed at reducing body mass present an increase of B/BAT activation. However, it is unknown if this beneficial effect of body mass reduction applies to patients with type 2 diabetes mellitus. In this study, we evaluated the impact of massive body mass reduction obtained as a consequence of bariatric surgery in the cold-induced activation of B/BAT in obese non-diabetic (OND) and obese diabetic (OD) subjects. SUBJECTS/METHODS: This is an observational study. Fourteen OND, 14 OD and 11 subjects were included in the study. All obese subjects were submitted to Roux-in-Y gastric bypass and measurements were performed before and 8 months after surgery. B/BAT was evaluated by (18F)-FDG-PET/CT scan and determination of signature transcript expression in specimens obtained in biopsies. RESULTS: Before surgery, mean B/BAT activity and the expression of signature transcripts were similar between OND and OD groups. Eight months after surgery, body mass reduction was similar between the obese groups. Nevertheless, the activity of B/BAT was increased in OND and unchanged in OD subjects. This effect was correlated with a more pronounced improvement of insulin resistance, as evaluated by the hyperinsulinemic, euglycemic clamp, in OND subjects as compared with OD subjects. CONCLUSIONS: Body mass reduction has a more efficient effect to induce the activation of B/BAT in non-diabetic than in diabetic subjects. This effect is accompanied by more pronounced insulin sensitivity and serine 473 phosphorylation of Akt in B/BAT of non-diabetic than in diabetic subjects.

Pioglitazone treatment increases food intake and decreases energy expenditure partially via hypothalamic adiponectin/adipoR1/AMPK pathway.

INTRODUCTION: Thiazolidinediones (TZDs) enhanced body weight (BW) partially by increased adipogenesis and hyperphagia. Neuronal PPARγ knockout mice on high-fat diet (HFD) are leaner because of enhanced leptin response, although it could be secondary to their leanness. Thus, it still is an open question how TZDs may alter energy balance. Multiple factors regulate food intake (FI) and energy expenditure (EE), including anorexigenic hormones as insulin and leptin. Nonetheless, elevated hypothalamic AMPK activity increases FI and TZDs increase AMPK activity in muscle cells. Thus, the aim of the present study was to investigate whether Pioglitazone (PIO) treatment alters hypothalamic insulin and leptin action/signaling, AMPK phosphorylation, and whether these alterations may be implicated in the regulation of FI and EE. METHODS: Swiss mice on HFD (2 months) received PIO (25 mg kg(-1) per day-gavage) or vehicle for 14 days. AMPK and AdipoR1 were inhibited via Intracerebroventricular injections using Compound C (CompC) and small interference RNA (siRNA), respectively. Western blot, real-time PCR and CLAMS were done. RESULTS: PIO treatment increased BW, adiposity, FI, NPY mRNA and decreased POMC mRNA expression and EE in HFD mice. Despite higher adiposity, PIO treatment improved insulin sensitivity, glucose tolerance, decreased insulin and increased adiponectin serum levels. This result was associated with, improved insulin and leptin action/signaling, decreased α2AMPK(Ser491) phosphorylation and elevated Acetyl-CoA carboxylase and AMPK(Thr172) phosphorylation in hypothalamus. The inhibition of hypothalamic AMPK with CompC was associated with decreased adiposity, FI, NPY mRNA and EE in PIO-treated mice. The reduced expression of hypothalamic AdipoR1 with siRNA concomitantly with PIO treatment reverted PIO induced obesity development, suggesting that adiponectin may be involved in this effect. CONCLUSIONS: These results demonstrated that PIO, despite improving insulin/leptin action in hypothalamus, increases FI and decreases EE, partially, by activating hypothalamic adiponectin/AdipoR1/AMPK axis. Suggesting a novel mechanism in the hypothalamus by which TZDs increase BW.

Distinct regulation of hypothalamic and brown/beige adipose tissue activities in human obesity.

BACKGROUND/OBJECTIVES: The identification of brown/beige adipose tissue in adult humans has motivated the search for methods aimed at increasing its thermogenic activity as an approach to treat obesity. In rodents, the brown adipose tissue is under the control of sympathetic signals originating in the hypothalamus. However, the putative connection between the depots of brown/beige adipocytes and the hypothalamus in humans has never been explored. The objective of this study was to evaluate the response of the hypothalamus and brown/beige adipose tissue to cold stimulus in obese subjects undergoing body mass reduction following gastric bypass. SUBJECTS/METHODS: We evaluated twelve obese, non-diabetic subjects undergoing Roux-in-Y gastric bypass and 12 lean controls. Obese subjects were evaluated before and approximately 8 months after gastric bypass. Lean subjects were evaluated only at admission. Subjects were evaluated for hypothalamic activity in response to cold by functional magnetic resonance, whereas brown/beige adipose tissue activity was evaluated using a (F 18) fluorodeoxyglucose positron emisson tomography/computed tomography scan and real-time PCR measurement of signature genes. RESULTS: Body mass reduction resulted in a significant increase in brown/beige adipose tissue activity in response to cold; however, no change in cold-induced hypothalamic activity was observed after body mass reduction. No correlation was found between brown/beige adipose tissue activation and hypothalamus activity in obese subjects or in lean controls. CONCLUSIONS: In humans, the increase in brown/beige adipose tissue activity related to body mass reduction occurs independently of changes in hypothalamic activity as determined by functional magnetic resonance.

Impact of obesity severity and duration on pancreatic ß- and α-cell dynamics in normoglycemic non-human primates.

OBJECTIVE: Obesity is associated with high insulin and glucagon plasma levels. Enhanced ß-cell function and ß-cell expansion are responsible for insulin hypersecretion. It is unknown whether hyperglucagonemia is due to α-cell hypersecretion or to an increase in α-cell mass. In this study, we investigated the dynamics of the ß-cell and α-cell function and mass in pancreas of obese normoglycemic baboons. METHODS: Pancreatic ß- and α-cell volumes were measured in 51 normoglycemic baboons divided into six groups according to overweight severity or duration. Islets morphometric parameters were correlated to overweight and to diverse metabolic and laboratory parameters. RESULTS: Relative α-cell volume (RαV) and relative islet α-cell volume (RIαV) increased significantly with both overweight duration and severity. Conversely, in spite of the induction of insulin resistance, overweight produced only modest effects on relative ß-cell volume (RßV) and relative islet ß-cell volume (RIßV). Of note, RIßV did not increase neither with overweight duration nor with overweight severity, supposedly because of the concomitant, greater increase in RIαV. Baboons' body weights correlated with serum levels of interleukin-6 and tumor necrosis factor-α soluble receptors, demonstrating that overweight induces abnormal activation of the signaling of two cytokines known to impact differently ß- and α-cell viability and replication. CONCLUSION: In conclusion, overweight and insulin resistance induce in baboons a significant increase in α-cell volumes (RαV, RIαV), whereas have minimal effects on the ß cells. This study suggests that an increase in the α-cell mass may precede the loss of ß cells and the transition to overt hyperglycemia and diabetes.

Bariatric surgery and bone disease: from clinical perspective to molecular insights.

The use of bariatric surgery for the treatment of morbid obesity has increased annually for the last decade. Although many studies have demonstrated the efficacy and durability of bariatric surgery for weight loss, there are limited data regarding long-term side effects of these procedures. Recently, there has been an increased focus on the impact of bariatric surgery on bone metabolism. Bariatric surgery utilizes one or more of three mechanisms of action resulting in sustained weight loss. These include restriction (gastric banding, vertical banded gastroplasty and sleeve gastrectomy), malabsorption surgery with or without associated restriction (Roux en Y gastric bypass, duodenal switch, biliopancreatic diversion and jejunoileal bypass) and changes in gut-derived hormones that control energy metabolism also referred to as neuro-hormonal control of energy metabolism (Roux en Y gastric bypass, duodenal switch, biliopancreatic diversion, jejunoileal bypass, surgical procedures as above and gastric sleeve). Weight reduction has been associated with increased bone resorption but the mechanisms behind this have not yet been fully elucidated. Each of the mechanisms of action of bariatric surgery (restriction, malabsorption, neuro-hormonal control of energy metabolism) may uniquely affect bone resorption. In this paper we will review the current state of knowledge regarding the relationship between bariatric surgery and bone metabolism with emphasis on possible mechanisms of action such as malnutrition, hormonal interactions and mechanical unloading of the skeleton. Further, we suggest a future research agenda.

Increased levels of the Akt-specific phosphatase PH domain leucine-rich repeat protein phosphatase (PHLPP)-1 in obese participants are associated with insulin resistance.

AIMS/HYPOTHESIS: We determined the contribution to insulin resistance of the PH domain leucine-rich repeat protein phosphatase (PHLPP), which dephosphorylates Akt at Ser473, inhibiting its activity. We measured the abundance of PHLPP in fat and skeletal muscle from obese participants. To study the effect of PHLPP on insulin signalling, PHLPP (also known as PHLPP1) was overexpressed in HepG2 and L6 cells. METHODS: Subcutaneous fat samples were obtained from 82 morbidly obese and ten non-obese participants. Skeletal muscle samples were obtained from 12 obese and eight non-obese participants. Quantification of PHLPP-1 in human tissues was performed by immunoblotting. The functional consequences of recombinant PHLPP1 overexpression in hepatoma HepG2 cells and L6 myoblasts were investigated. RESULTS: Of the 82 obese participants, 31 had normal fasting glucose, 33 impaired fasting glucose and 18 type 2 diabetes. PHLPP-1 abundance was twofold higher in the three obese groups than in non-obese participants (p = 0.004). No differences were observed between obese participants with normal fasting glucose, impaired fasting glucose or type 2 diabetes. PHLPP-1 abundance was correlated with basal Akt Ser473 phosphorylation (r = -0.48; p = 0.001), BMI (r = 0.44; p < 0.0001), insulin (r = 0.35; p < 0.0001) and HOMA (r = 0.38; p < 0.0001). PHLPP-1 abundance was twofold higher in the skeletal muscle of 12 obese participants than in that of eight non-obese participants (p < 0.0001). Insulin treatment of HepG2 cells resulted in a dose- and time-dependent upregulation of PHLPP-1. Overexpression of PHLPP1 in HepG2 cells and L6 myoblasts resulted in impaired insulin signalling involving Akt/glycogen synthase kinase 3, glycogen synthesis and glucose transport. CONCLUSIONS/INTERPRETATION: Increased abundance of PHLPP-1, production of which is regulated by insulin, may represent a new molecular defect in insulin-resistant states such as obesity.

The synaptic vesicle-associated protein amphiphysin is the 128-kD autoantigen of Stiff-Man syndrome with breast cancer.

Stiff-Man syndrome (SMS) is a rare disease of the central nervous system (CNS) characterized by progressive rigidity of the body musculature with superimposed painful spasms. An autoimmune origin of the disease has been proposed. In a caseload of more than 100 SMS patients, 60% were found positive for autoantibodies directed against the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD). Few patients, all women affected by breast cancer, were negative for GAD autoantibodies but positive for autoantibodies directed against a 128-kD synaptic protein. We report here that this antigen is amphiphysin. GAD and amphiphysin are nonintrinsic membrane proteins that are concentrated in nerve terminals, where a pool of both proteins is associated with the cytoplasmic surface of synaptic vesicles. GAD and amphiphysin are the only two known targets of CNS autoimmunity with this distribution. This finding suggests a possible link between autoimmunity directed against cytoplasmic proteins associated with synaptic vesicles and SMS.

Impaired regulation of the TNF-alpha converting enzyme/tissue inhibitor of metalloproteinase 3 proteolytic system in skeletal muscle of obese type 2 diabetic patients: a new mechanism of insulin resistance in humans.

AIMS/HYPOTHESIS: TNF-alpha levels are increased in obesity and type 2 diabetes. The regulation of TNF-alpha converting enzyme (TACE) and its inhibitor, tissue inhibitor of metalloproteinase 3 (TIMP3), in human type 2 diabetes is unknown. METHODS: We examined TACE/TIMP3 regulation: (1) in lean and obese normal glucose tolerant (NGT) individuals and in type 2 diabetes patients; (2) following 6 h of lipid/saline infusion in NGT individuals; and (3) in cultured human myotubes from lean NGT individuals incubated with palmitate. Insulin sensitivity was assessed by a euglycaemic clamp and TACE/TIMP3 was evaluated by confocal microscopy, RT-PCR, western blotting and an in vitro activity assay. Circulating TNF-alpha, TNF-alpha-receptor 1 (TNFR1), TNF-alpha-receptor 2 (TNFR2), IL-6 receptor (IL-6R), vascular cell adhesion molecule (VCAM) and intercellular adhesion molecule (ICAM) levels were evaluated. RESULTS: TIMP3 levels were reduced and TACE enzymatic activity was increased in type 2 diabetes skeletal muscle. TACE expression, and TACE, TNF-alpha, TNFR1 and IL-6R levels were increased in type 2 diabetes, and positively correlated with insulin resistance. A 6 h lipid infusion into NGT individuals decreased insulin-stimulated glucose metabolism by 25% with increased TACE, decreased expression of the gene encoding TIMP3 and increased IL-6R release. Palmitate induced a dramatic reduction of TIMP3 and increased the TACE/TIMP3 ratio in cultured myotubes. CONCLUSIONS/INTERPRETATION: TACE activity was increased in skeletal muscle of obese type 2 diabetes patients and in lipid-induced insulin resistance. We propose that dysregulation of membrane proteolysis by TACE/TIMP3 of TNF-alpha and IL-6R is an important factor for the development of skeletal muscle insulin resistance in obese type 2 diabetes patients by a novel autocrine/paracrine mechanism.

Spontaneous pathology of the baboon endocrine system.

BACKGROUND: Study of endocrine pathology in animal models is critical to understanding endocrine pathology in humans. METHODS: We evaluated 434 endocrine-related diagnoses from 4619 baboon necropsies, established the incidence of spontaneous endocrine pathology, and analyzed the clinical and biochemical data associated with the individual cases. RESULTS: The most common diagnoses in descending order, were pancreatic islet cell amyloidosis (n = 259), ovarian cysts (n = 50), pituitary adenoma (n = 37), pancreatic islet cell adenoma (n = 20), granulosa cell tumor (n = 15), thyroid adenoma (n = 11), adrenal hyperplasia (n = 10), thyroid carcinoma (n = 8), and pheochromocytoma (n = 6). The incidence of pancreatic islet cell amyloidosis progressively increased with age. Pheochromocytomas were associated with renal and heart failure. The incidence of pancreatic islet cell amyloidosis and adrenal pathology was similar to humans; the incidence of pituitary adenoma and thyroid pathology was lower than in humans. CONCLUSIONS: Endocrine disease in baboons is common and shares clinical and biochemical characteristics with endocrine disease in humans.

Effect of weight loss through laparoscopic gastric banding on blood pressure, plasma renin activity and aldosterone levels in morbid obesity.

BACKGROUND AND AIMS: Several mechanisms are probably involved in obesity-related hypertension. This study was aimed to investigate the effect of significant weight loss on blood pressure and plasma renin activity (PRA) and aldosterone levels, other then on metabolic profile, in normotensive and hypertensive obese subjects. METHODS AND RESULTS: Forty hypertensive and 55 normotensive obese subjects were studied under basal conditions and again 1 year after significant weight loss obtained through laparoscopic adjustable gastric banding (LAGB). Weight, waist circumference, blood glucose, insulin, electrolytes (Na and K), lipids and supine and upright PRA and aldosterone were evaluated. All parameters evaluated improved, except for total cholesterol, and electrolytes that did not change. Blood pressure decreased in hypertensive subjects, with a concordant decrease in PRA and supine aldosterone levels, not observed in normotensive patients. CONCLUSION: Weight loss is associated with reduction of blood pressure and of PRA and aldosterone levels in obese hypertensive subjects.

Bariatric surgery in obesity: changes of glucose and lipid metabolism correlate with changes of fat mass.

BACKGROUND AND AIM: Bariatric surgery induces significant weight loss and improves glucose metabolism in obese patients (BMI>35 kg/m(2)). Our aim was to compare restrictive (LAGB, laparoscopic gastric banding) and malabsorptive approaches (BIBP, biliary-intestinal bypass) on the loss of fat-free mass (FFM), fat mass (FM), and on changes of glucose and lipid metabolism. METHODS AND RESULTS: Body composition (bio-impedance analysis, BIA), blood glucose (BG), insulin, triglycerides, total- and HDL-cholesterol, liver enzymes (AST and ALT) were measured at baseline and 1 year after surgery in patients undergoing LAGB, BIBP, and in diet-treated control patients. In the main study, with patients matched for initial BMI (43-55 kg/m(2), LAGB=24, BIBP=12, controls=6), decreases of BMI, FM, BG and cholesterol were greater in patients with BIBP than with LAGB (p<0.01), while decreases of FFM, insulin, HOMA-IR and triglycerides were similar. No effects on BMI, FM, FFM, BG, insulin, HOMA-IR or cholesterol were observed in the control patients. Decreases of BG, insulin, HOMA-IR, cholesterol and triglycerides correlated with FM but not with FFM decrease. Similar results were obtained in an additional study in patients with a different initial BMI (LAGB=25, BIBP=6, controls=24) and when considering all subjects together. A decrease of liver enzymes (ALT) was greater with LAGB than with BIBP, and HDL-cholesterol increased with LAGB and decreased with BIBP. CONCLUSION: BMI, FM, BG and cholesterol decrease more with malabsorptive than with restrictive surgery, while FFM, insulin, HOMA-IR and triglycerides decrease in a similar way. FFM loss is of low entity. Changes of glucose and lipid metabolism are proportional to a decrease of fat mass but not of fat-free mass.

Regulation of phosphatidylinositol 3-kinase activity in liver and muscle of animal models of insulin-resistant and insulin-deficient diabetes mellitus.

Insulin stimulates tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1), which in turn binds to and activates phosphatidylinositol 3-kinase (PI 3-kinase). In the present study, we have examined these processes in animal models of insulin-resistant and insulin-deficient diabetes mellitus. After in vivo insulin stimulation, there was a 60-80% decrease in IRS-1 phosphorylation in liver and muscle of the ob/ob mouse. There was no insulin stimulation of PI 3-kinase (85 kD subunit) association with IRS-1, and IRS-1-associated PI 3-kinase activity was reduced 90%. Insulin-stimulated total PI 3-kinase activity was also absent in both tissues of the ob/ob mouse. By contrast, in the streptozotocin diabetic rat, IRS-1 phosphorylation increased 50% in muscle, IRS-1-associated PI 3-kinase activity was increased two- to threefold in liver and muscle, and there was a 50% increase in the p85 associated with IRS-1 after insulin stimulation in muscle. In conclusion, (a) IRS-1-associated PI 3-kinase activity is differentially regulated in hyperinsulinemic and hypoinsulinemic diabetic states; (b) PI 3-kinase activation closely correlates with IRS-1 phosphorylation; and (c) reduced PI 3-kinase activity may play a role in the pathophysiology of insulin resistant diabetic states, such as that seen in the ob/ob mouse.

Modulation of insulin receptor, insulin receptor substrate-1, and phosphatidylinositol 3-kinase in liver and muscle of dexamethasone-treated rats.

Insulin rapidly stimulates tyrosine kinase activity of its receptor resulting in phosphorylation of its cytosolic substrate, insulin receptor substrate-1 (IRS-1), which in turn associates with phosphatidylinositol 3-kinase (PI 3-kinase), thus activating the enzyme. Glucocorticoid treatment is known to produce insulin resistance, but the exact molecular mechanism is unknown. In the present study we have examined the levels and phosphorylation state of the insulin receptor and IRS-1, as well as the association/activation between IRS-1 and PI 3-kinase in the liver and muscle of rats treated with dexamethasone. After dexamethasone treatment (1 mg/kg per d for 5 d), there was no change in insulin receptor concentration in liver of rats as determined by immunoblotting with antibody to the COOH-terminus of the receptor. However, insulin stimulation of receptor autophosphorylation determined by immunoblotting with antiphosphotyrosine antibody was reduced by 46.7 +/- 9.1%. IRS-1 and PI 3-kinase protein levels increased in liver of dexamethasone-treated animals by 73 and 25%, respectively (P < 0.05). By contrast, IRS-1 phosphorylation was decreased by 31.3 +/- 10.9% (P < 0.05), and insulin stimulated PI 3-kinase activity in anti-IRS-1 immunoprecipitates was decreased by 79.5 +/- 11.2% (P < 0.02). In muscle, the changes were less dramatic, and often in opposite direction of those observed in liver. Thus, there was no significant change in insulin receptor level or phosphorylation after dexamethasone treatment. IRS-1 and PI 3-kinase levels were decreased to 38.6 and 65.6%, respectively (P < 0.01 and P < 0.05). IRS-1 phosphorylation showed no significant change in muscle, but insulin-stimulated IRS-1 associated PI 3-kinase was decreased by 41%. Thus, dexamethasone has differential effects on the proteins involved in the early steps in insulin action in liver and muscle. In both tissues, dexamethasone treatment results in a reduction in insulin-stimulated IRS-1-associated P I3-kinase, which may play a role in the pathogenesis of insulin resistance at the cellular level in these animals.

Angiotensin II inhibits insulin signaling in aortic smooth muscle cells at multiple levels. A potential role for serine phosphorylation in insulin/angiotensin II crosstalk.

To investigate potential interactions between angiotensin II (AII) and the insulin signaling system in the vasculature, insulin and AII regulation of insulin receptor substrate-1 (IRS-1) phosphorylation and phosphatidylinositol (PI) 3-kinase activation were examined in rat aortic smooth muscle cells. Pretreatment of cells with AII inhibited insulin-stimulated PI 3-kinase activity associated with IRS-1 by 60%. While AII did not impair insulin-stimulated tyrosine phosphorylation of the insulin receptor (IR) beta-subunit, it decreased insulin-stimulated tyrosine phosphorylation of IRS-1 by 50%. AII inhibited the insulin-stimulated association between IRS-1 and the p85 subunit of PI 3-kinase by 30-50% in a dose-dependent manner. This inhibitory effect of AII on IRS-1/PI 3-kinase association was blocked by the AII receptor antagonist saralasin, but not by AT1 antagonist losartan or AT2 antagonist PD123319. AII increased the serine phosphorylation of both the IR beta-subunit and IRS-1. In vitro binding experiments showed that autophosphorylation increased IR binding to IRS-1 from control cells by 2.5-fold versus 1.2-fold for IRS-1 from AII-stimulated cells, suggesting that AII stimulation reduces IRS-1's ability to associate with activated IR. In addition, AII increased p85 serine phosphorylation, inhibited the total pool of p85 associated PI 3-kinase activity, and decreased levels of the p50/p55 regulatory subunit of PI 3-kinase. These results suggest that activation of the renin-angiotensin system may lead to insulin resistance in the vasculature.

High glucose causes apoptosis in cultured human pancreatic islets of Langerhans: a potential role for regulation of specific Bcl family genes toward an apoptotic cell death program.

Type 2 diabetes is characterized by insulin resistance and inadequate insulin secretion. In the advanced stages of the disease, beta-cell dysfunction worsens and insulin therapy may be necessary to achieve satisfactory metabolic control. Studies in autopsies found decreased beta-cell mass in pancreas of people with type 2 diabetes. Apoptosis, a constitutive program of cell death modulated by the Bcl family genes, has been implicated in loss of beta-cells in animal models of type 2 diabetes. In this study, we compared the effect of 5 days' culture in high glucose concentration (16.7 mmol/l) versus normal glucose levels (5.5 mmol/l) or hyperosmolar control (mannitol 11 mmol/l plus glucose 5 mmol/l) on the survival of human pancreatic islets. Apoptosis, analyzed by flow cytometry and electron and immunofluorescence microscopy, was increased in islets cultured in high glucose (HG5) as compared with normal glucose (NG5) or hyperosmolar control (NG5+MAN5). We also analyzed by reverse transcriptase-polymerase chain reaction and Western blotting the expression of the Bcl family genes in human islets cultured in normal glucose or high glucose. The antiapoptotic gene Bcl-2 was unaffected by glucose change, whereas Bcl-xl was reduced upon treatment with HG5. On the other hand, proapoptotic genes Bad, Bid, and Bik were overexpressed in the islets maintained in HG5. To define the pancreatic localization of Bcl proteins, we performed confocal immunofluorescence analysis on human pancreas. Bad and Bid were specifically expressed in beta-cells, and Bid was also expressed, although at low levels, in the exocrine pancreas. Bik and Bcl-xl were expressed in other endocrine islet cells as well as in the exocrine pancreas. These data suggest that in human islets, high glucose may modulate the balance of proapoptotic and antiapoptotic Bcl proteins toward apoptosis, thus favoring beta-cell death.

Regulation of insulin receptor, insulin receptor substrate-1 and phosphatidylinositol 3-kinase in 3T3-F442A adipocytes. Effects of differentiation, insulin, and dexamethasone.

Insulin rapidly stimulates tyrosine kinase activity of its receptor resulting in phosphorylation of its cytosolic substrate insulin receptor substrate 1 (IRS-1), which in turn associates with and activates the enzyme phosphatidylinositol 3-kinase (PI 3-kinase). In the present study we have examined these three initial steps in insulin action during the differentiation of 3T3-F442A adipocytes and after treatment with dexamethasone or insulin. The differentiation of 3T3-F442A cells was characterized by a 13-fold increase in insulin receptor protein, a 9-fold increase in IRS-1, and a 10- and 4.5-fold increase in their insulin-stimulated phosphorylation, respectively. The mRNA expression of these two proteins showed a similar 8-fold increase during differentiation. In addition there was a 3.5-fold increase in PI 3-kinase protein [85 kilodalton (kDa) subunit] and a 16-fold increase in IRS-1-associated PI 3-kinase activity between day 0 and day 8 of differentiation. Dexamethasone (1 microM) treatment of differentiated cells induced a further 48% (P < 0.05) increase in insulin receptor level, but the autophosphorylation of the receptor was decreased by 31 +/- 1% (P < 0.02). At the same time there was a decrease by 56 +/- 4% (P < 0.005) in IRS-1 protein and by 31 +/- 1% (P < 0.001) in IRS-1 phosphorylation. The expression of insulin receptor mRNA was unchanged, but the expression of IRS-1 mRNA was decreased by approximately 75% after dexamethasone. By contrast, dexamethasone induced a 69% increase in the level of PI 3-kinase as determined by immunoblotting. The combined effect of decreased IRS-1 phosphorylation and increased PI 3-kinase protein was a minimal change (15% decrease) in the association/activation between IRS-1 and PI 3-kinase. Chronic treatment with 100 nM insulin induced a time- and dose-dependent decrease in insulin receptor and IRS-1 protein levels reaching a nadir of 34 +/- 5% (P < 0.005) and 39 +/- 5% (P < 0.01) of control levels after 24 h, respectively. There was an even more marked decrease in the phosphorylation level of these proteins. Chronic insulin treatment also produced a 30% decrease in PI 3-kinase protein levels and a approximately 50% decrease in the association/activation between IRS-1/PI 3-kinase. The expression of insulin receptor and IRS-1 mRNA was unchanged during chronic insulin treatment.(ABSTRACT TRUNCATED AT 400 WORDS)