Effectiveness of oral semaglutide on glucose control and body weight up to 18 months: a multicenter retrospective real-world study.

AIM: Oral semaglutide, an innovative orally administered GLP-1 receptor agonist for type 2 diabetes (T2D) management was herein evaluated for its effectiveness in a multi-center retrospective real-world study. METHODS: We included new-users of oral semaglutide from 18 specialist care centres and collected retrospective data on baseline clinical characteristics. Updated values of HbA1c and body weight were analyzed using the mixed model for repeated measures. RESULTS: The study included 166 individuals with T2D, predominantly men (64.5%), with a mean age of 64.4 years and a mean diabetes duration of 10.1 years. In the majority of patients (68.3%) oral semaglutide was used as a second-line drug, mostly with metformin. At baseline, mean BMI was 28.9 kg/m2 and HbA1c was 7.5%. During the 18-month observation period, oral semaglutide demonstrated significant reductions in HbA1c, with a maximum change of - 0.9%, and 42.1% of patients achieved HbA1c values below 7.0%. Additionally, there was a substantial reduction in body weight, with an estimated change of - 3.4 kg at 18 months, and 30.3% of patients experienced a 5% or greater reduction in baseline body weight. Only 24.2% of patients reached the 14 mg dose. Subgroup analysis revealed that baseline HbA1c > 7%, persistence on drug, not being on a prior therapy with DPP-4 inhibitors, and loosing 5% or more the initial body weight were associated with greater HbA1c reductions. CONCLUSION: This study supports oral semaglutide as an effective option for T2D treatment, offering improved glucose control and weight management in a real-world setting.

Noradrenergic fibers are associated with beta-cell dedifferentiation and impaired beta-cell function in humans.

AIMS/HYPOTHESIS: Type 2 diabetes (T2D) is characterized by a progressive loss of beta-cell function, and the "disappearance" of beta-cells in T2D may also be caused by the process of beta -cell dedifferentiation. Since noradrenergic innervation inhibits insulin secretion and density of noradrenergic fibers is increased in type 2 diabetes mouse models, we aimed to study the relation between islet innervation, dedifferentiation and beta-cell function in humans. METHODS: Using immunohistochemistry and electron microscopy, we analyzed pancreata from organ donors and from patients undergoing pancreatic surgery. In the latter, a pre-surgical detailed metabolic characterization by oral glucose tolerance test (OGTT) and hyperglycemic clamp was performed before surgery, thus obtaining in vivo functional parameters of beta-cell function and insulin secretion. RESULTS: The islets of diabetic subjects were 3 times more innervated than controls (0.91 ±â€¯0.21 vs 0.32 ±â€¯0.10, n.fibers/islet; p = 0.01), and directly correlated with the dedifferentiation score (r = 0.39; p = 0.03). In vivo functional parameters of insulin secretion, assessed by hyperglycemic clamp, negatively correlated with the increase in fibers [beta-cell Glucose Sensitivity (r = -0.84; p = 0.01), incremental second-phase insulin secretion (r = -0.84, p = 0.03) and arginine-stimulated insulin secretion (r = -0.76, p = 0.04)]. Moreover, we observed a progressive increase in fibers, paralleling worsening glucose tolerance (from NGT through IGT to T2D). CONCLUSIONS/INTERPRETATION: Noradrenergic fibers are significantly increased in the islets of diabetic subjects and this positively correlates with beta-cell dedifferentiation score. The correlation between in vivo insulin secretion parameters and the density of pancreatic noradrenergic fibers suggests a significant involvement of these fibers in the pathogenesis of the disease, and indirectly, in the islet dedifferentiation process.

Italian Titration Approach Study (ITAS) with insulin glargine 300 U/mL in insulin-naïve type 2 diabetes: Design and population.

BACKGROUND AND AIMS: Fostering patient's self-managing of basal insulin therapy could improve glucose control, by removing patient's and physician's barriers to basal insulin initiation, titration and glucose monitoring. The Italian Titration Approaches Study (ITAS) aims at demonstrating non-inferiority (<0.3% margin) in efficacy of glucose control (change in glycated hemoglobin [HbA1c] after 24 weeks) by the same titration algorithm of insulin glargine 300 U/mL (Gla-300), managed by the (nurse assisted) patient versus the physician, in insulin naïve patients with Type 2 Diabetes Mellitus (T2DM), uncontrolled with previous treatments. METHODS AND RESULTS: ITAS is a phase IV, 24-week, national, multicenter, open label, randomized (1:1) parallel group study. 458 patients were enrolled, 359 randomized, and 339 completed the study, in 46 Italian centers. Baseline characteristics and previous medications of the ITT population (N = 355) are reported. Mean ± SD age, T2DM duration, HbA1c, FPG and BMI were 64.0 ± 9.8 years, 11.6 ± 7.6 years, 8.79 ± 0.65%, 170.9 ± 42.3 mg/dL, and 30.3 ± 5.6 kg/m2, respectively. Vascular and metabolic disorders were most frequent (73.8% and 58.3%, respectively). More than 90% of patients were on metformin. CONCLUSION: ITAS is the first study to compare two different managers (nurse-assisted patient vs physician) of the same titration algorithm of Gla-300 in insulin naïve patients with T2DM in unsatisfactory glucose control. This study might provide novel evidence on the efficacy/effectiveness of patient-managed titration algorithm of Gla-300 in a pragmatic setting and may reduce barriers to basal insulin initiation and its titration.

Management of diabetes in older adults.

Type 2 diabetes prevalence is high in older adults and is expected to rise in the next decades. Diabetes in the population of frail older adults is accompanied by functional disability, several comorbidities, and premature mortality. A comprehensive geriatric assessment, including functional, cognitive, mental and social status, is advisable for identifying the glycemic targets and glucose-lowering therapies, focused on patient preferences, needs, and risks. The therapeutic options for older adults with diabetes are like those for the adult population. However, the pharmacological treatments must be carefully prescribed and monitored, taking into consideration the patient cognitive capacities, the potentially life-threatening drug-drug interactions, the cardiovascular risk, and with the main goal of avoiding hypoglycemia. Also, a careful nutritional evaluation with appropriate tools, as well as a balanced and periodically monitored physical activity, contribute to an effective tailored care plan, as needed by older adults with diabetes. This review evaluates the currently available hypoglycemic drugs and the current indications to the Italian diabetology community, specifically with regard to the treatment of adults aged 75 years or older with diabetes, including the unmet needs by the guidelines.

A consensus statement for the clinical use of the renal sodium-glucose co-transporter-2 inhibitor dapagliflozin in patients with type 2 diabetes mellitus.

INTRODUCTION: The present review developed a clinical consensus based on a Delphi method on Dapagliflozin, a selective inhibitor of the renal sodium-glucose co-transporter-2 (SGLT2-I) in the treatment of patients with Type 2 diabetes mellitus. Areas covered: Panel members, using a 5-point scale, were asked to rate 9 statements on pharmakodinamic, mode of action on glycaemic and extra-glycaemic effects, and safety of dapaglifozin, Members also aimed to identify the patient most susceptible to the treatment with dapagliflozin . Expert commentary: Dapagliflozin is effective in lowering the plasma glucose concentration with a good safety profile. Dapagliflozin can be utilized in combination with all other antihyperglycaemic agents at all stages of the disease: however, a reduced GFR limits its efficacy. As for the other drugs of the class, Dapagliflozin positively modifies other risk factors for CV disease: these effects will be tested in the so far largest cardiovascular outcome trial for the SGLT2 inhibitors so far, the DECLARE trial, which will communicate whether this class of drugs will be disease-modifier in patients with type 2 diabetes also in primary prevention.

Vitamin D deficiency: a new risk factor for type 2 diabetes?.

Recent compelling evidence suggests a role of vitamin D deficiency in the pathogenesis of insulin resistance and insulin secretion derangements, with a consequent possible interference with type 2 diabetes mellitus. The mechanism of this link is incompletely understood. In fact, vitamin D deficiency is usually detected in obesity in which insulin resistance is also a common finding. The coexistence of insulin resistance and vitamin D deficiency has generated several hypotheses. Some cross-sectional and prospective studies have suggested that vitamin D deficiency may play a role in worsening insulin resistance; others have identified obesity as a risk factor predisposing individuals to exhibit both vitamin D deficiency and insulin resistance. The available data from intervention studies are largely confounded, and inadequate considerations of seasonal effects on 25(OH)D concentrations are also a common design flaw in many studies. On the contrary, there is strong evidence that obesity might cause both vitamin D deficiency and insulin resistance, leaving open the possibility that vitamin D and diabetes are not related at all. Although it might seem premature to draw firm conclusions on the role of vitamin D supplementation in reducing insulin resistance and preventing type 2 diabetes, this manuscript will review the circumstances leading to vitamin D deficiency and how such a deficiency can eventually independently affect insulin sensitivity.

Early insulin treatment in type 2 diabetes: ORIGINal sin or valuable choice as ORIGINal treatment? An open debate on the ORIGIN study results.

Diabetes is ultimately the result of relative or absolute insulin deficiency; insulin should therefore represent its "natural" treatment, from the very moment of diagnosis, or even earlier, such as any other hormonal deficiency. Insulin treatment, however, has been accused of the worst crimes, including that of fostering obesity, insulin resistance, atherosclerosis, and, lately, cancer. Are these charges real? Does insulin treatment truly carry in its nature the original sin of causing such terrible consequences? This unresolvable, past and present dispute has had important effects on our clinical behavior in insulin initiation in the management of Type 2 diabetes, and we all hoped that a specifically designed trial could help us on this controversy. The ORIGIN (Outcome Reduction with an Initial Glargine Intervention) trial aimed to establish whether an initial insulin treatment with glargine, as compared with standard treatments, was able to delay the onset of cardiovascular disease. Although the trial appeared negative, several viewpoints came out, alimenting the debate on how to analyze results from the ORIGIN trial and, ultimately, on the role of early insulin treatment in type 2 diabetes. In these pages we invited two experienced scientists to freely argument their interpretation of the trial, aiming to help our understanding of the consequences of the ORIGIN trial on insulin therapy.

Metabolic syndrome in transplant patients: an updating point of view.

Metabolic syndrome (MS) is a cluster of risk factors that predispose to major cardiovascular diseases and its complications, determining liver and kidney impairment. In the last decade, the indications to transplantation are increasing, with a linear incidence of the complications of the procedure. MS represents one of the commonest, being in turn may the consequence of the underlying disease that required the transplantation, or the result of the medical treatment, as well as one of the most important factor influencing the morbidity and mortality of the transplanted patients. Due to the growing incidence of the MS in these patients, it is crucial to focus and clarify the leading causes determining the onset of the metabolic disarrangement, its outcome and the hypothetical mechanism through which the clinicians could reduce the impact of the disease. In fact, prevention, early recognition, and treatment of the factor that could predict the onset or progression of the MS after the transplantation may impact long term survival of patients, that is again the scope of the same transplant. This review will update the different mechanisMS of the pathogenesis of MS in this population, the clinical effects of the presence of the MS, observing the risk factors to be treated before and after the transplantation and suggesting the management of the follow-up.

Can vitamin D deficiency cause diabetes and cardiovascular diseases? Present evidence and future perspectives.

Several studies have shown that vitamin D may play a role in many biochemical mechanisms in addition to bone and calcium metabolism. Recently, vitamin D has sparked widespread interest because of its involvement in the homeostasis of the cardiovascular system. Hypovitaminosis D has been associated with obesity, related to trapping in adipose tissue due to its lipophilic structure. In addition, vitamin D deficiency is associated with increased risk of cardiovascular disease (CVD) and this may be due to the relationship between low vitamin D levels and obesity, diabetes mellitus, dyslipidaemia, endothelial dysfunction and hypertension. However, although vitamin D has been identified as a potentially important marker of CVD, the mechanisms through which it might modulate cardiovascular risk are not fully understood. Given this background, in this work we summarise clinical retrospective and prospective observational studies linking vitamin D levels with cardio-metabolic risk factors and vascular outcome. Moreover, we review various randomised controlled trials (RCTs) investigating the effects of vitamin D supplementation on surrogate markers of cardiovascular risk. Considering the high prevalence of hypovitaminosis D among patients with high cardiovascular risk, vitamin D replacement therapy in this population may be warranted; however, further RCTs are urgently needed to establish when to begin vitamin D therapy, as well as to determine the dose and route and duration of administration.

In anorexia nervosa, even a small increase in abdominal fat is responsible for the appearance of insulin resistance.

CONTEXT: The aim of treatment in patients affected by anorexia nervosa (AN) is weight recovery. However, during weight gain, anorectic patients' body composition is changed, with an increase in abdominal fat, particularly in the visceral compartment. OBJECTIVE: We hypothesized that changes in body composition, particularly in abdominal fat, are responsible for the variability in insulin sensitivity (IS) in different stages of AN. DESIGN AND MEASUREMENTS: We compared 20 anorectic patients in the acute stage, 19 in the weight-recovery stage and 21 controls. All subjects underwent an oral glucose tolerance test, hyperinsulinaemic euglycaemic clamp and dual energy X-ray absorptiometry to measure body composition. RESULTS: The percentage of trunk fat was higher in weight recovery than in the acute phase (47·7 ± 8·4%vs 34·6 ± 7·6%; P ≤ 0·01) and in the control group (33·4 ± 7·6; P < 0·01 vs weight recovery). Although the recovery group gained weight, their body mass index (BMI) was not statistically different from that of the acute group (14·4 ± 1·1 vs 13·6 ± 1·8 kg/m(2) ). Insulin sensitivity was lower in the weight-recovery group than the acute group (4·7 ± 1·5 vs 7·8 ± 1·6 mg/kg/min; P < 0·01) and controls (7·7 ± 1·4 mg/kg/min; P < 0·01). A linear negative correlation was found between IS and the percentage of abdominal fat in the weight-recovery and acute groups (r = -0·51; P = 0·04 and r = -0·53; P = 0·04 respectively), while IS did not correlate with BMI. CONCLUSION: Although weight-recovery represents the main aim of treatment in AN, refeeding is associated with an increase in abdominal fat which might be responsible of the onset of insulin resistance. As BMI and weight-recovery were associated with impaired IS, they cannot be considered the only aim of treatment of AN.

Metabolic syndrome in transplant patients: an academic or a health burden?

Metabolic syndrome is a cluster of risk factors that predispose to major cardiovascular diseases, liver steatosis and fibrosis, as well as reduced renal function. Metabolic syndrome and its early hepatic manifestation, non-alcoholic fatty liver disease, are prevalent both among the general population and in pre- and posttransplantation settings. Because indications for solid-organ transplantation are gradually increasing, attention should focus on the incidence of metabolic syndrome among transplanted patients, defined as posttransplant metabolic syndrome (PTMS). Subjects with worse metabolic profiles with two or more criteria of the syndrome show lower survival rates and greater co-morbidities. However, it is still unclear whether the pathophysiology of posttransplantation metabolic syndrome differ from that of the general population and may be determined by the primary disease affecting the liver or kidney, or amplified or altered by the immunosuppressive treatment, as it has already been established that corticosteroids and calcineurin inhibitors cause metabolic disarrangements. Although there is controversy regarding the definition and the impact of PTMS on overall survival rates following transplantation, these patients are at increased risk for cardiovascular morbidity and mortality. Early recognition, prevention, and treatment of these conditions may impact long-term survival after transplantation. Thus, even if metabolic syndrome in transplant patients remains an unclear definition, an insulin resistance is present in these patients. The treatment of this condition represents a health problem that requires intervention by clinicians before and after transplantation.

Metabolic syndrome in subjects at high risk for type 2 diabetes: the genetic, physiopathology and evolution of type 2 diabetes (GENFIEV) study.

BACKGROUND AND AIM: We evaluated the relationship between insulin resistance (IR) and insulin secretion with the metabolic syndrome (MS) in 885 subjects (377 men/508 women, age 49±11 years, BMI 29±5.2kgm(-2)) at risk of diabetes enrolled in the genetics, pathophysiology and evolution of type 2 diabetes (GENFIEV) study. METHODS AND RESULTS: All subjects underwent a 75-g oral glucose tolerance test (OGTT) for the estimation of plasma levels of glucose and C-peptide, as well as fasting insulin and lipid profile. IR was arbitrarily defined as HOMA-IR value above the 75th centile of normal glucose tolerance (NGT) subjects. Overall MS prevalence (National Cholesterol Treatment Panel-Adult Treatment Panel (NCEP-ATPIII) criteria) was 33%, 19% in subjects with NGT, 42% in impaired fasting glucose (IFG), 34% in impaired glucose tolerance (IGT), 74% in IFG+IGT subjects, and 56% in newly diagnosed diabetic patients. Prevalence was slightly higher with IDF criteria. MS prevalence was >50% in subjects with 2h glucose >7.8mmoll(-1), independently of fasting plasma glucose. IR prevalence was higher in subjects with MS than in those without (63% vs. 23%; p<0.0001) and increased from 54% to 73% and 88% in the presence of three, four or five traits, respectively. IR occurred in 42% of subjects with non-diabetic alterations of glucose homeostasis, being the highest in those with IFG+IGT (IFG+IGT 53%, IFG 45%, IGT 38%; p<0.0001). Individuals with MS were more IR irrespective of glucose tolerance (p<0.0001) with no difference in insulinogenic index. Hypertriglyceridaemia (OR: 3.38; Confidence Interval, CI: 2.294.99), abdominal obesity (3.26; CI: 2.18-4.89), hyperglycaemia (3.02; CI: 1.80-5.07) and hypertension (1.69; CI: 1.12-2.55) were all associated with IR. CONCLUSIONS: These results show that in subjects with altered glucose tolerance (in particular IFG+IGT) MS prevalence is high and is generally associated to IR. Some combinations of traits of MS may significantly contribute to identify subjects with IR.

Glucose toxicity: the leading actor in the pathogenesis and clinical history of type 2 diabetes - mechanisms and potentials for treatment.

AIM: Although it is now well established that the deleterious effects of chronic hyperglycaemia (i.e., glucose toxicity) play an important role in the progressive impairment of insulin secretion and sensitivity, the two major actors of the pathogenesis of type 2 diabetes mellitus, the precise biochemical and molecular mechanisms responsible for the defects induced by glucose toxicity still remain to be defined. DATA SYNTHESIS: here we will briefly report on convincing evidence that glucose toxicity acts through oxidative stress, modifications in the exosamine pathway, protein kinase C and others. After inducing or contributing to the genesis of type 2 diabetes, these same mechanisms are considered responsible for the appearance and worsening of diabetic specific microvascular complications, while its role in increasing the risk of cardiovascular diseases is less clear. Recent intervention studies (ADVANCE, ACCORD, VADT), conducted to evaluate the effects of strict glycaemic control, apparently failed to demonstrate an effect of glucose toxicity on cardiovascular diseases, at least in secondary prevention or when diabetes is present for a prolonged time. The re-examination, 20 years later, of the population studied in the UKPDS study, however, clearly demonstrated that the earliest is the strict glycaemic control reached, the lowest is the incidence of cardiovascular diseases observed, including myocardial infarction. CONCLUSION: The acquaintance of the role of glucose toxicity should strongly influence the usual therapeutic choices and glycaemic targets where the reduced or absent risk of hypoglycaemia, durability of action, and data on prolonged safety should be the preferred characteristics of the drug of choice in the treatment of type 2 diabetes mellitus.

Rats that are made insulin resistant by glucosamine treatment have impaired skeletal muscle insulin receptor phosphorylation.

The current study sought to verify whether glucosamine (GlcN)-induced insulin resistance is associated with impaired insulin receptor (IR) autophosphorylation. Rats were given either saline or primed continuous GlcN infusion (5 micromol x kg(-1) x min(-1)) 10 minutes prior to and during euglycemic hyperinsulinemic clamp (primed continuous infusion of 20 mU x kg(-1) x min(-1) insulin for 2 hours). IR autophosphorylation was measured in skeletal muscle after in vivo insulin stimulation (ie, during clamp) by Western blot and then retested after subsequent in vitro 0.1 to 100 nmol/L insulin stimulation (by enzyme-linked immunosorbent assay [ELISA]). Tissue PC-1 enzymatic activity was also measured. In vivo, insulin/GlcN rats had decreased (P <.01) whole body glucose uptake (37.7 +/- 2.1 v 49.7 +/- 2.7 mg x kg(-1) x min(-1) in respect to insulin/saline), receptor autophosphorylation (37 +/- 5 v 82 +/-.0 arbitrary units/mg protein), and insulin receptor substrate-1 (IRS-1) phosphorylation (112% +/- 15% v 198% +/- 23% of saline infusion rats). Receptor autophosphorylation was correlated with whole body glucose uptake (r = 0.62, P <.05). Skeletal muscle PC-1 activity (58.8 +/- 10.7 v 55.7 +/- 5.8 nmol x mg(-1) x min(-1)) was not different in the 2 groups. Our data show that GlcN-induced insulin resistance is mediated, at least in part, by impaired skeletal muscle IR autophosphorylation.

Transgenic mice with dominant negative PKC-theta in skeletal muscle: a new model of insulin resistance and obesity.

Protein kinase C theta (PKC-theta) is the PKC isoform predominantly expressed in skeletal muscle, and it is supposed to mediate many signals necessary for muscle histogenesis and homeostasis, such as TGFbeta, nerve-dependent signals and insulin. To study the role of PKC-theta in these mechanisms we generated transgenic mice expressing a "kinase dead" mutant form of PKC-theta (PKC-thetaK/R), working as "dominant negative," specifically in skeletal muscle. These mice are viable and fertile, however, by the 6-7 months of age, they gain weight, mainly due to visceral fat deposition. Before the onset of obesity (4 months of age), they already show increased fasting and fed insulin levels and reduced insulin-sensitivity, as measured by ipITT, but normal glucose tolerance, as measured by ipGTT. After the 6-7 months of age, transgenic mice develop hyperinsulinemia in the fasting and fed state. The ipGTT revealed in the transgenic mice both hyperglycemia and hyperinsulinemia. At the molecular level, impaired activation of the IR/IRS/PI3K pathway and a significant decrease both in the levels and in insulin-stimulated activation of the serine/threonine kinase Akt were observed. Taken together these data demonstrate that over-expression of dominant negative PKC-theta in skeletal muscle causes obesity associated to insulin resistance, as demonstrated by defective receptor and post-receptorial activation of signaling cascade.

Acute hyperglycemia and acute hyperinsulinemia decrease plasma fibrinolytic activity and increase plasminogen activator inhibitor type 1 in the rat.

Decreased plasma fibrinolysis may contribute to accelerated atherothrombosis in diabetes. To observe whether hyperglycemia and hyperinsulinemia, common findings in type 2 diabetes, acutely affect plasma fibrinolysis in vivo, we evaluated plasma fibrinolysis (lysis of fibrin plates, free PAI-1 activity and t-PA activity) in the rat after a hyperglycemic euinsulinemic clamp (n=8), an euglycemic hyperinsulinemic clamp (n=7) or a saline infusion (n=15). Plasma fibrinolytic activity was sharply reduced after both the hyperglycemic and hyperinsulinemic clamps as compared to the respective controls (mean lysis areas on the fibrin plate, 139+/-21 vs. 323+/-30 mm2, p<0.001; 78+/-27 vs. 312+/-27 mm2 p<0.001, respectively). Plasma PAI-1 activity was greater after both hyperglycemic and hyperinsulinemic clamps as compared to saline infusion (6.6+/-2.6 vs. 1.6+/-0.6 IU/ml, p<0.001; 26+/-4 vs. 1.3+/-0.7 IU/ml, p<0.0001, respectively). Plasma t-PA activity was significantly reduced both after the hyperglycemic (0.36+/-0.15 vs. 2.17+/-0.18 IU/ml in controls, p<0.001) and the hyperinsulinemic (0.3+/-0.1 vs. 2.3+/-0.3 IU/ml in control, p<0.001) clamps. These data show that in vivo both acute hyperglycemia and acute hyperinsulinemia can decrease plasma fibrinolytic potential and that this is due to increased plasma PAI-1 and decreased free t-PA activities.

Effects of glucosamine infusion on insulin secretion and insulin action in humans.

Glucose toxicity (i.e., glucose-induced reduction in insulin secretion and action) may be mediated by an increased flux through the hexosamine-phosphate pathway. Glucosamine (GlcN) is widely used to accelerate the hexosamine pathway flux, independently of glucose. We tested the hypothesis that GlcN can affect insulin secretion and/or action in humans. In 10 healthy subjects, we sequentially performed an intravenous glucose (plus [2-3H]glucose) tolerance test (IVGTT) and a euglycemic insulin clamp during either a saline infusion or a low (1.6 micromol x min(-1) x kg(-1)) or high (5 micromol x min(-1) x kg(-1) [n = 5]) GlcN infusion. Beta-cell secretion, insulin (SI*-IVGTT), and glucose (SG*) action on glucose utilization during the IVGTT were measured according to minimal models of insulin secretion and action. Infusion of GlcN did not affect readily releasable insulin levels, glucose-stimulated insulin secretion (GSIS), or the time constant of secretion, but it increased both the glucose threshold of GSIS (delta approximately 0.5-0.8 mmol/l, P < 0.03-0.01) and plasma fasting glucose levels (delta approximately 0.3-0.5 mmol/l, P < 0.05-0.02). GlcN did not change glucose utilization or intracellular metabolism (glucose oxidation and glucose storage were measured by indirect calorimetry) during the clamp. However, high levels of GlcN caused a decrease in SI*-IVGTT (delta approximately 30%, P < 0.02) and in SG* (delta approximately 40%, P < 0.05). Thus, in humans, acute GlcN infusion recapitulates some metabolic features of human diabetes. It remains to be determined whether acceleration of the hexosamine pathway can cause insulin resistance at euglycemia in humans.

Evidence for glucose/hexosamine in vivo regulation of insulin/IGF-I hybrid receptor assembly.

Hybrid receptors composed of an insulin alphabeta-hemireceptor and a type 1 IGF alphabeta-hemireceptor are formed in tissues expressing both molecules. We recently reported an increased hybrid receptor expression in skeletal muscle of type 2 diabetic patients that is inversely correlated with in vivo insulin sensitivity. It is unclear whether these changes were due to primary abnormalities or to secondary derangements acting in vivo, such as hyperglycemia. To address this, we determined abundance of hybrids in skeletal muscle from three groups of rats: controls, diabetic (90% pancreatectomy), and diabetic treated with phlorizin to normalize plasma glucose levels. We found that the abundance of hybrid receptors was higher in diabetic rats compared with control and phlorizin-treated diabetic rats (percentage of 125I-insulin bound versus total added radioactivity [B/T] = 1.8+/-0.11, 0.4+/-0.01, and 0.32+/-0.04, respectively; P < 0.0001). Fasting plasma glucose levels were positively correlated with hybrids abundance (r = 0.77, P < 0.002). Hybrid receptor protein content, assessed by immunoblotting, was 2.4-fold higher in diabetic rats as compared with control and phlorizin-treated diabetic rats. Because it has been shown that some of the regulatory effects of glucose may be mediated by the glucosamine pathway, we subsequently determined the effect of an in vivo glucosamine infusion on hybrid receptor formation. We found that abundance of hybrids was significantly higher in muscle from glucosamine-treated rats compared with control rats (B/T = 0.17+/-0.02 and 0.11+/-0.01, respectively; P < 0.009). Quantitation of hybrid content by immunoblotting revealed that their abundance was 1.9-fold higher in glucosamine-treated rats. The results demonstrate that 1) elevated glucose levels in diabetic rats are associated with increased expression of hybrid receptors in muscle, 2) correction of hyperglycemia with phlorizin completely reverses increased expression of hybrids, and 3) glucosamine infused into control rats mimics the effects of hyperglycemia on hybrid receptor formation. Thus, the results support the hypothesis that glucose acting, at least in part, through the glucosamine pathway may play an important role in regulating hybrid receptor assembly in vivo.

Increased OB gene expression leads to elevated plasma leptin concentrations in patients with chronic primary hyperinsulinemia.

Leptin, a hormone secreted by adipocytes, decreases food intake and increases energy expenditure. The role of insulin in the regulation of leptin secretion is poorly understood and is still a topic of debate. Insulin increases leptin mRNA synthesis in rodents, but in humans, the available data are discordant. To investigate the role of chronic hyperinsulinemia in the regulation of plasma leptin concentrations, we studied 13 patients with surgically confirmed insulinoma before and after tumor removal, along with 15 healthy control subjects matched for sex, age, and BMI. Immunoreactive plasma leptin levels were measured by radioimmunoassay; leptin mRNA levels were also determined by reverse transcription-competitive polymerase chain reaction in a subgroup of six patients with insulinoma and six control subjects. All determinations were made with subjects in the fasting state. Plasma leptin concentrations correlated positively with leptin mRNA levels (r = 0.880, P < 0.001). Leptin levels, both plasma protein and mRNA, were significantly higher in the insulinoma patients than in the control subjects (plasma protein: 17.5 +/- 3.6 vs. 2.9 +/- 0.4 ng/ml, respectively, P < 0.001; mRNA: 0.98 +/- 0.33 vs. 0.19 +/- 0.064 amol/microg RNA, respectively, P < 0.05), and they correlated positively with fasting plasma insulin levels in the patients with insulinoma (plasma protein: r = 0.686, P < 0.01; mRNA: 0.796, P < 0.05). Finally, removal of the insulin-secreting tumor was followed by the normalization of plasma leptin levels. In summary, in patients with insulinoma, 1) plasma leptin levels and leptin mRNA are elevated; 2) a direct relationship exists between leptin, both circulating protein and mRNA, and insulin concentrations; and 3) plasma leptin returns to normal levels after tumor removal. These data, therefore, support a role for insulin in the chronic regulation of leptin gene expression.