Showing papers in "Diabetes in 1997"
TL;DR: Continuously elevated levels of plasma FFAs may play a key role in the pathogenesis of NIDDM in predisposed individuals by impairing peripheral glucose utilization and by promoting hepatic glucose overproduction.
Abstract: Evidence is reviewed that free fatty acids (FFAs) are one important link between obesity and insulin resistance and NIDDM. First, plasma FFA levels are elevated in most obese subjects. Second, physiological elevations in plasma FFA concentrations inhibit insulin stimulated peripheral glucose uptake in a dose-dependent manner in normal controls and in patients with NIDDM. Two possible mechanisms are identified: 1) a fat-related inhibition of glucose transport or phosphorylation, which appears after 3-4 h of fat infusion, and 2) a decrease in muscle glycogen synthase activity, which appears after 4-6 h of fat infusion. Third, FFAs stimulate insulin secretion in nondiabetic individuals. Some of this insulin is transmitted in the peripheral circulation and is able to compensate for FFA-mediated peripheral insulin resistance. FFA-mediated portal hyperinsulinemia counteracts the stimulation of FFAs on hepatic glucose production (HGP) and thus prevents hepatic glucose overproduction. We speculate that, in obese individuals who are genetically predisposed to develop NIDDM, FFAs will eventually fail to promote insulin secretion. The stimulatory effect of FFAs on HGP would then become unchecked, resulting in hyperglycemia. Hence, continuously elevated levels of plasma FFAs may play a key role in the pathogenesis of NIDDM in predisposed individuals by impairing peripheral glucose utilization and by promoting hepatic glucose overproduction.
1,726 citations
TL;DR: The results suggest that in this human population, as in animal models, skeletal muscle insulin sensitivity is strongly influenced by local supplies of triglycerides, as well as by remote depots and circulating lipids.
Abstract: In animal studies, increased amounts of triglyceride associated with skeletal muscle (mTG) correlate with reduced skeletal muscle and whole body insulin action. The aim of this study was to test this relationship in humans. Subjects were 38 nondiabetic male Pima Indians (mean age 28 ± 1 years). Insulin sensitivity at physiological ( M ) and supraphysiological ( MZ ) insulin levels was assessed by the euglycemic clamp. Lipid and carbohydrate oxidation were determined by indirect calorimetry before and during insulin administration. mTG was determined in vastus lateralis muscles obtained by percutaneous biopsy. Percentage of body fat (mean 29 ± 1%, range 14–44%) was measured by underwater weighing. In simple regressions, negative relationships were found between mTG (mean 5.4 ± 0.3 μmol/g, range 1.3–1.9 μmol/g) and log10 M ( r = −0.53, P ≤ 0.001), MZ ( r = −0.44, P = 0.006), and nonoxidative glucose disposal ( r = −0.48 and −0.47 at physiological and supraphysiological insulin levels, respectively, both P = 0.005) but not glucose or lipid oxidation. mTG was not related to any measure of adiposity. In multiple regressions, measures of insulin resistance (log10 M , MZ , log10[fasting insulin]) were significantly related to mTG independent of all measures of obesity (percentage of body fat, BMI, waist-to-thigh ratio). In turn, all measures of obesity were related to the insulin resistance measures independent of mTG. The obesity measures and mTG accounted for similar proportions of the variance in insulin resistance in these relationships. The results suggest that in this human population, as in animal models, skeletal muscle insulin sensitivity is strongly influenced by local supplies of triglycerides, as well as by remote depots and circulating lipids. The mechanism(s) underlying the relationship between mTG and insulin action on skeletal muscle glycogen synthesis may be central to an understanding of insulin resistance.
1,180 citations
TL;DR: Insulin-producing cells cannot adapt the low antioxidant enzyme activity levels to typical situations of cellular stress by an upregulation of gene expression, and inactiva-tion of hydrogen peroxide through catalase seems to be a step of critical importance for the removal of reactive oxygen species in insulin- producing cells.
Abstract: Antioxidant enzyme expression was determined in rat pancreatic islets and RINm5F insulin-producing cells on the level of mRNA, protein, and enzyme activity in comparison with 11 other rat tissues. Although superoxide dismutase expression was in the range of 30% of the liver values, the expression of the hydrogen peroxide-inactivating enzymes catalase and glutathione peroxidase was extremely low, in the range of 5% of the liver. Pancreatic islets but not RINm5F cells expressed an additional phospholipid hydroperoxide glutathione peroxidase that exerted protective effects against lipid peroxidation of the plasma membrane. Regression analysis for mRNA and protein expression and enzyme activities from 12 rat tissues revealed that the mRNA levels determine the enzyme activities of the tissues. The induction of cellular stress by high glucose, high oxygen, and heat shock treatment did not affect antioxidant enzyme expression in rat pancreatic islets or in RINm5F cells. Thus insulin-producing cells cannot adapt the low antioxidant enzyme activity levels to typical situations of cellular stress by an upregulation of gene expression. Through stable transfection, however, we were able to increase catalase and glutathione peroxidase gene expression in RINm5F cells, resulting in enzyme activities more than 100-fold higher than in nontransfected controls. Catalase-transfected RINm5F cells showed a 10-fold greater resistance toward hydrogen peroxide toxicity, whereas glutathione peroxidase overexpression was much less effective. Thus inactivation of hydrogen peroxide through catalase seems to be a step of critical importance for the removal of reactive oxygen species in insulin-producing cells. Overexpression of catalase may therefore be an effective means of preventing the toxic action of reactive oxygen species.
1,170 citations
TL;DR: As a component of central adiposity, subcutaneous abdominal fat has as strong an association with insulin resistance as visceral fat, and altered muscle composition, suggestive of increased fat content, is an important independent marker of insulin resistance in obesity.
Abstract: Whether visceral adipose tissue has a uniquely powerful association with insulin resistance or whether subcutaneous abdominal fat shares this link has generated controversy in the area of body composition and insulin sensitivity. An additional issue is the potential role of fat deposition within skeletal muscle and the relationship with insulin resistance. To address these matters, the current study was undertaken to measure body composition, aerobic fitness, and insulin sensitivity within a cohort of sedentary healthy men ( n = 26) and women ( n = 28). The subjects, who ranged from lean to obese (BMI 19.6-41.0 kg/m2), underwent dual energy X-ray absorptiometry (DEXA) to measure fat-free mass (FFM) and fat mass (FM), computed tomography to measure cross-sectional abdominal subcutaneous and visceral adipose tissue, and computed tomography (CT) of mid-thigh to measure muscle cross-sectional area, muscle attenuation, and subcutaneous fat. Insulin sensitivity was measured using the glucose clamp technique (40 mU · m∼2 · min−1), in conjunction with [3-3H]glucose isotope dilution. Maximal aerobic power (Vo2max) was determined using an incremental cycling test. Insulin-stimulated glucose disposal ( R d) ranged from 3.03 to 16.83 mg · min−1· kg−1 FFM. R d was negatively correlated with FM ( r = -0.58), visceral fat ( r = -0.52), subcutaneous abdominal fat ( r = -0.61), and thigh fat ( r = -0.38) and positively correlated with muscle attenuation ( r = 0.48) and Vo2max ( r = 0.26, P < 0.05). In addition to manifesting the strongest simple correlation with insulin sensitivity, in stepwise multiple regression, subcutaneous abdominal fat retained significance after adjusting for visceral fat, while the converse was not found. Muscle attenuation contributed independent significance to multiple regression models of body composition and insulin sensitivity, and in analysis of obese subjects, muscle attenuation was the strongest single correlate of insulin resistance. In summary, as a component of central adiposity, subcutaneous abdominal fat has as strong an association with insulin resistance as visceral fat, and altered muscle composition, suggestive of increased fat content, is an important independent marker of insulin resistance in obesity.
972 citations
TL;DR: The finding that leptin reverses this effect in ob/ob, but not db/db, mice suggests that leptin stimulates arcuate nucleus POMC gene expression via a pathway involving leptin receptors, and supports the hypothesis that leptin signaling in the brain involves activation of the hypothalamic melanocortin system.
Abstract: Melanocortins are peptides, cleaved from the pro-opiomelanocortin (POMC) precursor, that act in the brain to reduce food intake and are potential mediators of leptin action. In the forebrain, melanocortins are derived from POMC-containing neurons of the hypothalamic arcuate nucleus. To test the hypothesis that these POMC neurons are regulated by leptin, we used in situ hybridization to determine whether reduced leptin signaling (as occurs in fasting), genetic leptin deficiency (in obese ob/ob mice), or genetic leptin resistance (in obese db/db mice) lower expression of POMC mRNA. We further hypothesized that leptin administration would raise hypothalamic POMC mRNA levels in leptin-deficient animals, but not in mice with defective leptin receptors. In wild-type mice (n = 12), fasting for 48 h lowered POMC mRNA levels in the rostral arcuate nucleus by 53%, relative to values in fed controls (n = 8; P < 0.001). Similarly, arcuate nucleus POMC mRNA levels were reduced by 46 and 70% in genetically obese ob/ob (n = 6) and db/db mice (n = 6), respectively, as compared with wild-type mice (n = 5) (P < 0.01 for both comparisons). Five daily intraperitoneal injections of recombinant murine leptin (150 microg) raised levels of POMC mRNA in the rostral arcuate nucleus of ob/ob mice (n = 8) by 73% over saline-treated ob/ob control values (n = 8; P < 0.01), but was without effect in db/db mice (n = 6). In normal rats, two injections of a low dose of leptin (3.5 microg) into the third cerebral ventricle (n = 15) during a 40-h period of fasting also increased POMC mRNA levels in the rostral arcuate nucleus to values 39% greater than those in vehicle-treated controls (n = 14; P = 0.02). We conclude that reduced central nervous system leptin signaling owing to fasting or to genetic defects in leptin or its receptor lower POMC mRNA levels in the rostral arcuate nucleus. The finding that leptin reverses this effect in ob/ob, but not db/db, mice suggests that leptin stimulates arcuate nucleus POMC gene expression via a pathway involving leptin receptors. These findings support the hypothesis that leptin signaling in the brain involves activation of the hypothalamic melanocortin system.
887 citations
TL;DR: Obesity is not associated with alteration in PPAR gene expression in abdominal subcutaneous adipose tissue in humans, indicating that improvement of insulin resistance with thiazolidinediones may not result from a direct effect of these agents on PPARγ in muscle.
Abstract: Members of the peroxisome proliferator-activated receptor (PPAR) family might be involved in pathologies with altered lipid metabolism. They participate in the control of the expression of genes involved in lipid metabolism and adipocyte differentiation. In addition, thiazolidinediones improve insulin resistance in vivo by activating PPAR gamma. However, little is known regarding their tissue distribution and relative expression in humans. Using a quantitative and sensitive reverse transcription (RT)-competitive polymerase chain reaction (PCR) assay, we determined the distribution and relative mRNA expression of the four PPARs (alpha,beta, gamma1, and gamma2) and liver X receptor-alpha (LXR alpha) in the main tissues implicated in lipid metabolism. PPAR alpha and LXR alpha were mainly expressed in liver, while PPAR gamma1 predominated in adipose tissue and large intestine. We found that PPAR gamma2 mRNA was a minor isoform, even in adipose tissue, thus causing question of its role in humans. PPAR beta mRNA was present in all the tissues tested at low levels. In addition, PPAR gamma mRNA was barely detectable in skeletal muscle, suggesting that improvement of insulin resistance with thiazolidinediones may not result from a direct effect of these agents on PPAR gamma in muscle. Obesity and NIDDM were not associated with change in PPARs and LXR alpha expression in adipose tissue. The mRNA levels of PPAR gamma1, the predominant form in adipocytes, did not correlate with BMI, leptin mRNA levels, or fasting insulinemia in 29 subjects with various degrees of obesity. These results indicated that obesity is not associated with alteration in PPAR gene expression in abdominal subcutaneous adipose tissue in humans.
749 citations
TL;DR: It is demonstrated that intravitreal injection of VEGF rapidly activates protein kinase C in the retina at concentrations observed clinically, inducing membrane translocation of PKC isoforms α, βII, and δ and > threefold increases in retinal vasopermeability in vivo.
Abstract: Increased vascular permeability and excessive neovascularization are the hallmarks of endothelial dysfunction, which can lead to diabetic macular edema and proliferative diabetic retinopathy in the eye. Vascular endothelial growth factor (VEGF) is an important mediator of ocular neovascularization and a known vasopermeability factor in nonocular tissues. In these studies, we demonstrate that intravitreal injection of VEGF rapidly activates protein kinase C (PKC) in the retina at concentrations observed clinically, inducing membrane translocation of PKC isoforms alpha, betaII, and delta and >threefold increases in retinal vasopermeability in vivo. The effect of VEGF on retinal vascular permeability appears to be mediated predominantly by the beta-isoform of PKC with >95% inhibition of VEGF-induced permeability by intravitreal or oral administration of a PKC beta-isoform-selective inhibitor that did not inhibit histamine-mediated effects. These studies represent the first direct demonstration that VEGF can increase intraocular vascular permeability through activation of PKC in vivo and suggest that oral pharmacological therapies involving PKC beta-isoform-selective inhibitors may prove efficacious for the treatment of VEGF-associated ocular disorders such as diabetic retinopathy.
655 citations
TL;DR: Analysis of data from six prospective studies indicates that persons with IGT are at high risk of NIDDM and that further refinement of risk can be made by other simple measurements, and the ability to identify persons at high Risk should facilitate clinical trials in diabetes prevention.
Abstract: Risk factors associated with the progression from impaired glucose tolerance (IGT) to NIDDM were examined in data from six prospective studies. IGT and NIDDM were defined in all studies by World Health Organization (WHO) criteria, and baseline risk factors were measured at the time of first recognition of IGT. The studies varied in size from 177 to 693 participants with IGT, and included men and women followed from 2 to 27 years after the recognition of IGT. Across the six studies, the incidence rate of NIDDM was 57.2/1,000 person-years and ranged from 35.8/1,000 to 87.3/1,000 person-years. Although baseline measures of fasting and 2-h postchallenge glucose levels were both positively associated with NIDDM incidence, incidence rates were sharply higher for those in the top quartile of fasting plasma glucose levels, but increased linearly with increasing 2-h postchallenge glucose quartiles. Incidence rates were higher among the Hispanic, Mexican-American, Pima, and Nauruan populations than among Caucasians. The effect of baseline age on NIDDM incidence rates differed among the studies; the rates did not increase or rose only slightly with increasing baseline age in three of the studies and formed an inverted U in three studies. In all studies, estimates of obesity (including BMI, waist-to-hip ratio, and waist circumference) were positively associated with NIDDM incidence. BMI was associated with NIDDM incidence independently of fasting and 2-h post challenge glucose levels in the combined analysis of all six studies and in three cohorts separately, but not in the three studies with the highest NIDDM incidence rates. Sex and family history of diabetes were generally not related to NIDDM progression. This analysis indicates that persons with IGT are at high risk and that further refinement of risk can be made by other simple measurements. The ability to identify persons at high risk of NIDDM should facilitate clinical trials in diabetes prevention.
644 citations
TL;DR: The results strongly suggest that human adipose tissue, in particular visceral tissue, can be an important contributor to the elevated plasma PAI-1 levels observed in central obesity.
Abstract: Plasminogen activator inhibitor type 1 (PAI-1) contributes to the pathogenesis of atherothrombosis. Its plasma level is strongly correlated with parameters that define the insulin resistance syndrome, in particular with BMI and visceral accumulation of body fat, suggesting that PAI-1 may be an adipose tissue-derived circulating peptide. The present study was designed to investigate PAI-1 expression by human adipose tissue and its different cellular fractions. Special interest has been paid to the amount of PAI-1 antigen produced by omental versus subcutaneous fat. PAI-1 protein detected by immunolocalization was present at the stromal and adipocyte levels. PAI-1 mRNA was detected in stromal vascular cells freshly isolated and under culture conditions. It was also detected in whole adipose tissue and adipocyte fraction under culture conditions. The mRNA signal from the adipocyte fraction was detected as early as 2 h of incubation. The increase in PAI-1 mRNA was followed by an increase in PAI-1 antigen in the conditioned medium that was suppressed by treatment with cycloheximide. Transforming growth factor-beta1 significantly increased PAI-1 antigen production by the adipocyte fraction, whereas tumor necrosis factor-alpha did not have any effect. Interestingly, after 5 h of incubation, omental tissue explants produced significantly more PAI-1 antigen than did subcutaneous tissue from the same individual, whereas similar production of leptin by the two territories was observed. These results strongly suggest that human adipose tissue, in particular visceral tissue, can be an important contributor to the elevated plasma PAI-1 levels observed in central obesity.
637 citations
TL;DR: It is demonstrated that supplemental chromium had significant beneficial effects on HbA1c, glucose, insulin, and cholesterol variables in subjects with type 2 diabetes and was observed at levels higher than the upper limit of the Estimated Safe and Adequate Daily Dietary Intake.
Abstract: Chromium is an essential nutrient involved in normal carbohydrate and lipid metabolism. The chromium requirement is postulated to increase with increased glucose intolerance and diabetes. The objective of this study was to test the hypothesis that the elevated intake of supplemental chromium is involved in the control of type 2 diabetes. Individuals being treated for type 2 diabetes (180 men and women) were divided randomly into three groups and supplemented with: 1) placebo, 2) 1.92 micromol (100 microg) Cr as chromium picolinate two times per day, or 3) 9.6 micromol (500 microg) Cr two times per day. Subjects continued to take their normal medications and were instructed not to change their normal eating and living habits. HbA1c values improved significantly after 2 months in the group receiving 19.2 pmol (1,000 microg) Cr per day and was lower in both chromium groups after 4 months (placebo, 8.5 +/- 0.2%; 3.85 micromol Cr, 7.5 +/- 0.2%; 19.2 micromol Cr, 6.6 +/- 0.1%). Fasting glucose was lower in the 19.2-micromol group after 2 and 4 months (4-month values: placebo, 8.8 +/- 0.3 mmol/l; 19.2 micromol Cr, 7.1 +/- 0.2 mmol/l). Two-hour glucose values were also significantly lower for the subjects consuming 19.2 micromol supplemental Cr after both 2 and 4 months (4-month values: placebo, 12.3 +/- 0.4 mmo/l; 19.2 micromol Cr, 10.5 +/- 0.2 mmol/l). Fasting and 2-h insulin values decreased significantly in both groups receiving supplemental chromium after 2 and 4 months. Plasma total cholesterol also decreased after 4 months in the subjects receiving 19.2 micromol/day Cr. These data demonstrate that supplemental chromium had significant beneficial effects on HbA1c, glucose, insulin, and cholesterol variables in subjects with type 2 diabetes. The beneficial effects of chromium in individuals with diabetes were observed at levels higher than the upper limit of the Estimated Safe and Adequate Daily Dietary Intake.
599 citations
TL;DR: Leptin mRNA appears to be expressed predominantly by subcutaneous adipocytes, particularly in women, suggesting a possible role for leptin in the control of adipose tissue distribution and mass.
Abstract: Obese subjects with excess intra-abdominal fat deposition suffer greater adverse metabolic consequences than do similarly overweight subjects with a predominantly subcutaneous distribution of adiposity. Little is known about the factors regulating the regional distribution of body fat. Leptin is a recently characterized protein secreted by adipocytes that appears to provide a long-term hormonal feedback signal regulating fat mass. No systematic evaluation of site-related differences in human adipocyte leptin expression has been reported to date. Levels of leptin mRNA were examined by quantitative reverse transcription-polymerase chain reaction in adipocytes isolated from omental and subcutaneous adipose depots of nonobese and mildly obese individuals undergoing elective surgery. In all individuals studied (n = 24), leptin mRNA levels were higher in subcutaneous than in omental adipocytes (P < 0.0001). In contrast, there were no consistent site-specific differences in the expression of glycerol-3-phosphate dehydrogenase mRNA. The subcutaneous-to-omental ratio of leptin mRNA expression was markedly higher in women (5.5 +/- 1.1-fold) than in men (1.9 +/- 0.2-fold) (P < 0.02). A significant relationship between BMI and leptin mRNA expression was demonstrable in the subcutaneous adipocytes of women (P < 0.006). Thus, leptin mRNA appears to be expressed predominantly by subcutaneous adipocytes, particularly in women. These findings suggest a possible role for leptin in the control of adipose tissue distribution and mass.
TL;DR: Results provide evidence that a functional leptin receptor is present in pancreatic islets and suggest that leptin overproduction, particularly from abdominal adipose tissue, may modify directly both basal and glucose-stimulated insulin secretion.
Abstract: Leptin, encoded for by the mouse ob gene, regulates feeding behavior and energy metabolism. Its receptor (Ob-R) is encoded by the mouse diabetic (db) gene and is mutated in the db/db mouse so that it lacks the cytoplasmic domain. We show that the full-length leptin receptor (Ob-Rb), which is believed to transmit the leptin signal, is expressed in pancreatic islets of ob/ob and wild-type mice, as well as in hypothalamus, liver, kidney, spleen, and heart. Recombinant leptin inhibited basal insulin release in the perfused pancreas preparation from ob/ob mice but not in that from Zucker fa/fa rats. Leptin (1-100 nmol/l) also produced a dose-dependent inhibition of glucose-stimulated insulin secretion by isolated islets from ob/ob mice. In contrast, leptin at maximum effective concentration (100 nmol/l) did not inhibit glucose-stimulated insulin secretion by islets from db/db mice. These results provide evidence that a functional leptin receptor is present in pancreatic islets and suggest that leptin overproduction, particularly from abdominal adipose tissue, may modify directly both basal and glucose-stimulated insulin secretion.
TL;DR: These results were consistent with more than one independent physiological process underlying risk variable clustering: a central metabolic syndrome (characterized by hyperinsulinemia, dyslipidemia, and obesity), glucose intolerance, and hypertension.
Abstract: Insulin resistance has been hypothesized to unify the clustering of hypertension, glucose intolerance, hyperinsulinemia, increased levels of triglyceride and decreased HDL cholesterol, and central and overall obesity. We tested this hypothesis with factor analysis, a statistical technique that should identify one factor if a single process underlies the clustering of these risk variables. From 2,458 nondiabetic subjects of the Framingham Offspring Study, we collected clinical data, fasting and 2-h postchallenge glucose and insulin levels, and fasting lipid levels. We performed factor analyses separately for men and women in the entire population and among subgroups with features of the insulin resistance syndrome. Subjects ranged in age from 26 to 82 years (mean age 54); 53% were women, 13.4% had impaired glucose tolerance, 27.6% had hypertension, 40% were obese, and 11.6% were hyperinsulinemic, defined by elevated fasting insulin levels. Underlying the clustering of these risk variables were three factors. Fasting and 2-h postchallenge insulin levels, fasting triglyceride and HDL cholesterol levels, BMI, and waist-to-hip ratio were associated with one factor. Fasting and 2-h levels of glucose and insulin were associated with a second factor. Systolic blood pressure, diastolic blood pressure, and BMI were associated with a third factor. Results were similar for men and women and for all subgroups. These results were consistent with more than one independent physiological process underlying risk variable clustering: a central metabolic syndrome (characterized by hyperinsulinemia, dyslipidemia, and obesity), glucose intolerance, and hypertension. Glucose intolerance and hypertension were linked to the central syndrome through shared correlations with insulin levels and obesity. Insulin resistance (reflected by hyperinsulinemia) alone did not appear to underlie all features of the insulin resistance syndrome.
TL;DR: Observations suggest that UCPH, like UCP, uncouples oxidative phosphorylation and the possibility that the U CPH protein is an important mediator of human thermogenesis is discussed.
Abstract: We have identified a novel cDNA encoding a protein highly homologous to the mammalian brown fat uncoupling protein (UCP). Unlike the known UCP, which is expressed specifically in brown adipose tissue, the UCP homolog (UCPH) mRNA is expressed in a variety of tissues, with predominant expression in human white adipose tissue and skeletal muscle. In the white adipose tissue of ob/ob and db/db mice, the UCPH transcript is induced approximately fivefold relative to lean littermate controls. Expression of murine UCPH in yeast results in growth inhibition under conditions that require aerobic respiration, but does not affect growth under anaerobic conditions. Furthermore, UCPH expression in yeast causes a decrease in the mitochondrial membrane potential, as judged by staining with the potential-sensitive dye DiOC6. These observations suggest that UCPH, like UCP, uncouples oxidative phosphorylation. The possibility that the UCPH protein is an important mediator of human thermogenesis is discussed.
TL;DR: Histological examinations of the pancreas in diabetic mice, from 4 to 35 weeks of age, revealed decreases in the numbers of active β-cells without insulitis, and Morphometry demonstrated specific decreases in immunologically detectable insulin density in islets in diabetic dogs, even at 4 weeks of year, without changes of relative islet areas.
Abstract: In this article, we report on a nonobese C57BL/6 (B6) mouse model of NIDDM named Akita mouse, characterized by early age onset and autosomal dominant mode of inheritance. At 7 weeks of age, the mean morning blood glucose levels (mmol/l) under ad libitum feeding conditions were significantly higher (P < 0.01, analysis of variance [ANOVA]) in diabetic mice than in unaffected mice: 27.3 +/- 5.3 for diabetic males (n = 50) and 9.3 +/- 1.2 for unaffected males (n = 50); 13.6 +/- 3.8 for diabetic females (n = 50) and 8.7 +/- 1.1 for unaffected females (n = 50), while corresponding immunoreactive insulin levels in plasma were significantly lower in diabetic mice than in unaffected mice. In vitro insulin secretion was also impaired, even at 4 weeks of age. The 50% survival time for male diabetic mice (305 days) was significantly shorter than that of unaffected counterpart mice but not for diabetic females. Obesity did not occur in diabetic mice. Histological examinations of the pancreas in diabetic mice, from 4 to 35 weeks of age, revealed decreases in the numbers of active beta-cells without insulitis. Morphometry demonstrated specific decreases in immunologically detectable insulin density in islets in diabetic mice, even at 4 weeks of age, without changes of relative islet areas. By linkage analysis, a single locus was identified on the basis of 178 N2 mice [(B6 x C3H/He)F1 x B6 and (B6 x C3H/He)F1 x C3H/He]. This locus, which we named Mody4, was mapped to chromosome 7 in a region 2-8 cM distal to D7Mit189 (logarithm of odds [LOD] score = 15.6 and 10.3).
TL;DR: It is demonstrated that leptin has direct and acute effects on skeletal muscle, and that when both hormones were present, leptin attenuated both the antioxidative and the lipogenic effects of insulin by 50%.
Abstract: Leptin, an adipocyte-derived hormone that directly regulates both adiposity and energy homeostasis, decreases food intake and appears to partition metabolic fuels toward utilization and away from storage. Because skeletal muscle expresses the leptin receptor and plays a major role in determining energy metabolism, we studied leptin's effects on glucose and fatty acid (FA) metabolism in isolated mouse soleus and extensor digitorum longus (EDL) muscles. One muscle from each animal served as a basal control. The contralateral muscle was treated with insulin (10 mU/ml), leptin (0.01-10 microg/ml), or insulin plus leptin, and incorporation of [14C]glucose or [14C]oleate into CO2 and into either glycogen or triacylglycerol (TAG) was determined. Leptin increased soleus muscle FA oxidation by 42% (P < 0.001) and decreased incorporation of FA into TAG by 35% (P < 0.01) in a dose-dependent manner. In contrast, insulin decreased soleus muscle FA oxidation by 40% (P < 0.001) and increased incorporation into TAG by 70% (P < 0.001). When both hormones were present, leptin attenuated both the antioxidative and the lipogenic effects of insulin by 50%. Less pronounced hormone effects were observed in EDL muscle. Leptin did not alter insulin-stimulated muscle glucose metabolism. These data demonstrate that leptin has direct and acute effects on skeletal muscle.
TL;DR: Analysis of strategies based on detection of ≥2 antibodies with primary testing for GAD and IA-2 antibodies and second line testing for ICAs and/or IAAs suggests that antibody combinations can predict diabetes in the general population.
Abstract: Strategies for assessing risk of progression to IDDM, based on single and combined autoantibody measurement, were evaluated in 2,855 schoolchildren (median age 11.4 years) and 256 children with newly diagnosed IDDM (median age 10.2 years), recruited to a population-based study in the Oxford region. In 256 children with IDDM, levels of antibodies > or =97.5th centile of the schoolchild population were found in 225 (88%) for islet cell antibodies (ICAs), in 190 (74%) for antibodies to GAD, in 193 (75%) for antibodies to protein tyrosine phosphatase IA-2 (IA-2), and in 177 (69%) for autoantibodies to insulin (IAAs). Estimates of risk of progression to IDDM within 10 years, derived by comparing the distribution of antibody markers in the two populations (schoolchildren and children with IDDM), were 6.7% (ICAs), 6.6% (GAD antibodies), 5.6% (IA-2 antibodies), and 4.8% (IAAs) for schoolchildren with levels above the 97.5th centile, increasing to 20, 23, 24, and 11%, respectively, for antibody levels >99.5th centile. Most children with IDDM had multiple antibody markers, and 89% of those diagnosed over age 10 years had > or =2 antibodies above the 97.5th centile, as compared against 0.7% of schoolchildren, in whom this combination gave a 27% 10-year estimated risk of IDDM. Risk increased but sensitivity fell as combined antibody thresholds were raised, or the number of antibodies above the threshold was increased. Strategies based on detection of > or =2 antibodies with primary testing for GAD and IA-2 antibodies and second line testing for ICAs and/or IAAs were evaluated. Detection of at least two markers selected from GAD antibodies > or =97.5th centile and/or IA-2 antibodies > or =99.5th centile and/or ICAs > or =97.5th centile identified 0.25% of schoolchildren and 83% of children with newly diagnosed IDDM, with an estimated risk of 71% (95% CI 57-91). Although confirmation from prospective studies is still needed, this analysis suggests that antibody combinations can predict diabetes in the general population.
TL;DR: It is concluded that ICV leptin increases MAP by decreasing arterial blood flow to the skeletal muscle and the splanchnic vascular bed and may serve as a link in the triad of obesity and hyperinsulinism and hypertension.
Abstract: Obesity and hyperinsulinism are known to be major stimuli of leptin production by adipose tissue, leading to increased leptin levels in the circulation. It has also been demonstrated that increased leptin production leads to satiety, possibly by decreasing the levels of neuropeptide Y (NPY) in the central nervous system (CNS). Because obesity and hyperinsulinism are also frequently associated with hypertension, we studied the effect of the intracerebroventricular (ICV) administration of leptin on mean arterial pressure (MAP), heart rate, vascular flows, and lumbar and renal sympathetic nerve activity (SNA). Normal Wistar rats were implanted with an ICV cannula and allowed to recover. On the day of the study, the animals were fasted and anesthetized with chloralose/urethane. Catheters were placed in a femoral artery and vein, and Doppler flow probes were placed around the iliac, renal, and superior mesenteric arteries for measurement of MAP, heart rate, and blood flows. In other experiments, lumbar SNA and renal SNA were recorded. ICV leptin administration resulted in an MAP that was slowly but progressively increasing. Blood flows decreased in the iliac and superior mesenteric arteries, but not in the renal artery. Leptin injection increased the lumbar SNA and renal SNA. The plasma glucose and insulin levels were not changed. We concluded that ICV leptin increases MAP by decreasing arterial blood flow to the skeletal muscle and the splanchnic vascular bed. This increased peripheral resistance is the result of an increased activity of the sympathetic nerves. We suggest that increased leptin may serve as a link in the triad of obesity and hyperinsulinism and hypertension.
TL;DR: In the insulin-resistant HFF rat, acute hyperinsulinemia fails to quench elevated muscle and liver lipid availability, and evidence is provided for pivotal involvement of G-6-Pase and GK in the regulation of HGP by insulin, independent of the glucose source.
Abstract: To elucidate cellular mechanisms of insulin resistance induced by excess dietary fat, we studied conscious chronically high-fat-fed (HFF) and control chow diet-fed rats during euglycemic-hyperinsulinemic (560 pmol/l plasma insulin) clamps. Compared with chow diet feeding, fat feeding significantly impaired insulin action (reduced whole body glucose disposal rate, reduced skeletal muscle glucose metabolism, and decreased insulin suppressibility of hepatic glucose production [HGP]). In HFF rats, hyperinsulinemia significantly suppressed circulating free fatty acids but not the intracellular availability of fatty acid in skeletal muscle (long chain fatty acyl-CoA esters remained at 230% above control levels). In HFF animals, acute blockade of beta-oxidation using etomoxir increased insulin-stimulated muscle glucose uptake, via a selective increase in the component directed to glycolysis, but did not reverse the defect in net glycogen synthesis or glycogen synthase. In clamp HFF animals, etomoxir did not significantly alter the reduced ability of insulin to suppress HGP, but induced substantial depletion of hepatic glycogen content. This implied that gluconeogenesis was reduced by inhibition of hepatic fatty acid oxidation and that an alternative mechanism was involved in the elevated HGP in HFF rats. Evidence was then obtained suggesting that this involves a reduction in hepatic glucokinase (GK) activity and an inability of insulin to acutely lower glucose-6-phosphatase (G-6-Pase) activity. Overall, a 76% increase in the activity ratio G-6-Pase/GK was observed, which would favor net hepatic glucose release and elevated HGP in HFF rats. Thus in the insulin-resistant HFF rat 1) acute hyperinsulinemia fails to quench elevated muscle and liver lipid availability, 2) elevated lipid oxidation opposes insulin stimulation of muscle glucose oxidation (perhaps via the glucose-fatty acid cycle) and suppression of hepatic gluconeogenesis, and 3) mechanisms of impaired insulin-stimulated glucose storage and HGP suppressibility are not dependent on concomitant lipid oxidation; in the case of HGP we provide evidence for pivotal involvement of G-6-Pase and GK in the regulation of HGP by insulin, independent of the glucose source.
TL;DR: For example, Alpha-lipoic acid is a potent antioxidant that prevents lipid peroxidation in vitro and in vivo as mentioned in this paper, and it has been shown to prevent myelinopathy of dorsal roots and a vacuolar neuropathy of dorsal root ganglion.
Abstract: Oxidative stress is present in the diabetic state Our work has focused on its presence in peripheral nerves Antioxidant enzymes are reduced in peripheral nerves and are further reduced in diabetic nerves That lipid peroxidation will cause neuropathy is supported by evidence of the development of neuropathy de novo when normal nerves are rendered alpha-tocopherol deficient and by the augmentation of the conduction deficit in diabetic nerves subjected to this insult Oxidative stress appears to be primarily due to the processes of nerve ischemia and hyperglycemia auto-oxidation The indexes of oxidative stress include an increase in nerve, dorsal root, and sympathetic ganglia lipid hydroperoxides and conjugated dienes The most reliable and sensitive index, however, is a reduction in reduced glutathione Experimental diabetic neuropathy results in myelinopathy of dorsal roots and a vacuolar neuropathy of dorsal root ganglion The vacuoles are mitochondrial; we posit that lipid peroxidation causes mitochondrial DNA mutations that increase reduced oxygen species, causing further damage to mitochondrial respiratory chain and function and resulting in a sensory neuropathy Alpha-lipoic acid is a potent antioxidant that prevents lipid peroxidation in vitro and in vivo We evaluated the efficacy of the drug in doses of 20, 50, and 100 mg/kg administered intraperitoneally in preventing the biochemical, electrophysiological, and nerve blood flow deficits in the peripheral nerves of experimental diabetic neuropathy Alpha-lipoic acid dose- and time-dependently prevented the deficits in nerve conduction and nerve blood flow and biochemical abnormalities (reductions in reduced glutathione and lipid peroxidation) The nerve blood flow deficit was 50% (P < 0001) Supplementation dose-dependently prevented the deficit; at the highest concentration, nerve blood flow was not different from that of control nerves Digital nerve conduction underwent a dose-dependent improvement at 1 month (P < 005) By 3 months, all treated groups had lost their deficit The antioxidant drug is potentially efficacious for human diabetic sensory neuropathy
TL;DR: An important physiological role for leptin as an inhibitor of insulin secretion is indicated and the failure of leptin to inhibit insulin secretion from the β-Cells of ob/ob and db/db mice may explain, in part, the development of hyperinsulinemia, insulin resistance, and the progression to NIDDM.
Abstract: In the genetic mutant mouse models ob/ob or db/db , leptin deficiency or resistance, respectively, results in severe obesity and the development of a syndrome resembling NIDDM. One of the earliest manifestations in these mutant mice is hyperinsulinemia, suggesting that leptin may normally directly suppress the secretion of insulin. Here, we show that pancreatic islets express a long (signal-transducing) form of leptin-receptor mRNA and that β-cells bind a fluorescent derivative of leptin (Cy3-leptin). The expression of leptin receptors on insulin-secreting β-cells was also visualized utilizing antisera generated against an extracellular epitope of the receptor. A functional role for the β-cell leptin receptor is indicated by our observation that leptin (100 ng/ml) suppressed the secretion of insulin from islets isolated from ob/ob mice. Furthermore, leptin produced a marked lowering of ]Ca 2+ ] i in ob/ob β-cells, which was accompanied by cellular hyperpolarization and increased membrane conductance. Cell-attached patch measurements of ob/ob β-Cells demonstrated that leptin activated ATP-sensitive potassium channels (K ATP ) by increasing the open channel probability, while exerting no effect on mean open time. These effects were reversed by the sulfonylurea tolbutamide, a specific inhibitor of K ATP . Taken together, these observations indicate an important physiological role for leptin as an inhibitor of insulin secretion and lead us to propose that the failure of leptin to inhibit insulin secretion from the β-Cells of ob/ob and db/db mice may explain, in part, the development of hyperinsulinemia, insulin resistance, and the progression to NIDDM.
TL;DR: Evidence is provided that dyslipidemia and poor glycemic control predict CHD mortality and morbidity in patients with NIDDM, and a 7-year follow-up study on risk factors for CHD provides evidence.
Abstract: Patients with NIDDM are at increased risk for coronary heart disease (CHD). However, information on the predictive value of cardiovascular risk factors and the degree of hyperglycemia with respect to the risk for CHD in diabetic patients is still limited. Therefore, we carried out a prospective study on risk factors for CHD, including a large number of NIDDM patients. At baseline, risk factor levels of CHD were determined in 1,059 NIDDM patients (581 men and 478 women), aged from 45 to 64 years. These patients were followed up to 7 years with respect to CHD events. Altogether, 158 NIDDM patients (97 men [16.7%] and 61 women [12.8%]) died of CHD and 256 NIDDM patients (156 men [26.8%] and 100 women [20.9%]) had a serious CHD event (death from CHD or nonfatal myocardial infarction). A previous history of myocardial infarction, low HDL cholesterol level ( 5.2 mmol/l), high total triglyceride level (>2.3 mmol/l), and high fasting plasma glucose (>13.4 mmol/l) were associated with a twofold increase in the risk of CHD mortality or morbidity, independently of other cardiovascular risk factors. High calculated LDL cholesterol level (≥4.1 mmol/l) was significantly associated with all CHD events. The simultaneous presence of high fasting glucose (>13.4 mmol/l) with low HDL cholesterol, low HDL–to–total cholesterol ratio, or high total triglycerides further increased the risk for CHD events up to threefold. Our 7-year follow-up study provides evidence that dyslipidemia and poor glycemic control predict CHD mortality and morbidity in patients with NIDDM.
TL;DR: Treatment with troglitazone appears to have a favorable impact on known cardiovascular risk factors and could potentially lower cardiovascular morbidity in NIDDM patients.
Abstract: Troglitazone is a thiazolidinedione under development for the treatment of NIDDM and potentially other insulin-resistant disease states. Treatment with troglitazone is associated with an improvement in hyperglycemia, hyperinsulinemia, and insulin-mediated glucose disposal. No significant side effects have been observed in humans. Because of reported cardiac changes in animals treated with drugs of this class, this multicenter 48-week study was conducted to evaluate whether NIDDM patients treated with troglitazone develop any cardiac mass increase or functional impairment. A total of 154 NIDDM patients were randomized to receive troglitazone 800 mg q.d. or glyburide titrated to achieve glycemic control (< or =20 mg b.i.d. or q.d.). Two-dimensional echocardiography and pulsed Doppler were used to measure left ventricular mass index (LVMI), cardiac index (CI), and stroke volume index (SVI). All echocardiograms were performed at each center (baseline, 12, 24, 36, and 48 weeks), recorded on videotape, and forwarded to a blinded central echocardiographic interpreter for analysis. The results showed that LVMI of patients treated with troglitazone was not statistically or clinically different from baseline after 24 or 48 weeks. Statistically significant increases in SVI and CI and a statistically significant decrease in diastolic pressure and estimated peripheral resistance were observed in troglitazone-treated patients. These results were not sex-specific. Glycemic benefits of troglitazone treatment were observed as evidenced by long-term improvement of HbA1c and C-peptide levels. Furthermore, triglycerides were significantly lower, and HDL was significantly higher at weeks 24 and 48. In conclusion, NIDDM patients treated with troglitazone do not show any cardiac mass increase or cardiac function impairment. Conversely, patients on troglitazone benefited from enhanced cardiac output and stroke volume, possibly as a result of decreased peripheral resistance. Treatment with troglitazone appears to have a favorable impact on known cardiovascular risk factors and could potentially lower cardiovascular morbidity in NIDDM patients.
TL;DR: The present findings couple both reduced insulin- Stimulated IRS-1 tyrosine phosphorylation and PI 3-kinase activity to the impaired insulin-stimulated glucose transport in skeletal muscle from lean–to–moderately obese NIDDM subjects.
Abstract: We examined the effect of physiological hyperinsulinemia on insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation and phosphatidylinositol (PI) 3-kinase activity in skeletal muscle from six lean-to-moderately obese NIDDM patients and six healthy subjects. A rise in serum insulin levels from approximately 60 to approximately 650 pmol/l increased IRS-1 tyrosine phosphorylation sixfold over basal levels in control muscle (P < 0.01), whereas no significant increase was noted in NIDDM muscle. The reduced IRS-1 phosphorylation in the NIDDM muscle was not related to changes in IRS-1 protein content, since IRS-1 protein expression was similar between control and NIDDM subjects (16.0 +/- 1.7 vs. 22.9 +/- 4.0 arbitrary units/mg protein for control and NIDDM, respectively; NS). Physiological hyperinsulinemia increased PI 3-kinase activity in control muscle twofold (P < 0.01), whereas no increase in insulin-stimulated PI 3-kinase activity was noted in the NIDDM muscle. Furthermore, in vitro insulin-stimulated (600 pmol/l) 3-O-methylglucose transport was 40% lower in isolated muscle from NIDDM subjects (P < 0.05). The present findings couple both reduced insulin-stimulated IRS-1 tyrosine phosphorylation and PI 3-kinase activity to the impaired insulin-stimulated glucose transport in skeletal muscle from lean-to-moderately obese NIDDM subjects.
TL;DR: It is demonstrated that incubation of cultured bovine aortic endothelial cells with AGE albumin resulted in the impairment of reduced glutathione and ascorbic acid levels, and supplementation of cellular antioxidative defense mechanisms by extracellularly administered α-lipoic acid reduces AGEalbumin-induced endothelial dysfunction in vitro.
Abstract: Depletion of cellular antioxidant defense mechanisms and the generation of oxygen free radicals by advanced glycation end products (AGEs) have been proposed to play a major role in the pathogenesis of diabetic vascular complications. Here we demonstrate that incubation of cultured bovine aortic endothelial cells (BAECs) with AGE albumin (500 nmol/l) resulted in the impairment of reduced glutathione (GSH) and ascorbic acid levels. As a consequence, increased cellular oxidative stress led to the activation of the transcription factor NF-kappaB and thus promoted the upregulation of various NF-kappaB-controlled genes, including endothelial tissue factor. Supplementation of the cellular antioxidative defense with the natural occurring antioxidant alpha-lipoic acid before AGE albumin induction completely prevented the AGE albumin-dependent depletion of reduced glutathione and ascorbic acid. Electrophoretic mobility shift assays (EMSAs) revealed that AGE albumin-mediated NF-kappaB activation was also reduced in a time- and dose-dependent manner as long as alpha-lipoic acid was added at least 30 min before AGE albumin stimulation. Inhibition was not due to physical interactions with protein DNA binding, since alpha-lipoic acid, directly included into the binding reaction, did not prevent binding activity of recombinant NF-kappaB. Western blots further demonstrated that alpha-lipoic acid inhibited the release and translocation of NF-kappaB from the cytoplasm into the nucleus. As a consequence, alpha-lipoic acid reduced AGE albumin-induced NF-kappaB mediated transcription and expression of endothelial genes relevant in diabetes, such as tissue factor and endothelin-1. Thus, supplementation of cellular antioxidative defense mechanisms by extracellularly administered alpha-lipoic acid reduces AGE albumin-induced endothelial dysfunction in vitro.
TL;DR: It is argued that dysfunction of peripheral vascular endothelium, at arteriolar and capillary level, plays the primary role in the pathogenesis of both insulin resistance and the associated features of the insulin resistance syndrome.
Abstract: Insulin resistance has been proposed as the metabolic basis of atherogenesis. This hypothesis is based on the concept of the "insulin resistance syndrome," according to which insulin resistance is viewed as the primary abnormality that gives rise to dyslipidemia, essential hypertension, impaired glucose tolerance, and NIDDM. However, this hypothesis takes no account of the well-established and central role of vascular endothelium in the atherogenic process. Although endothelial injury is an early and prominent feature of atherogenesis, relatively little attention has been given to its metabolic consequences. In subjects with NIDDM, we have shown that endothelial dysfunction is associated with insulin resistance, raising the question of whether this relationship could be causal. In this article, we review the factors that are considered to be responsible for the development of endothelial dysfunction during atherogenesis, together with the metabolic consequences of endothelial dysfunction. While dysfunction of the endothelium in large and medium-sized arteries plays a central role in atherogenesis, we argue that dysfunction of peripheral vascular endothelium, at arteriolar and capillary level, plays the primary role in the pathogenesis of both insulin resistance and the associated features of the insulin resistance syndrome. We propose that the insulin resistance syndrome, together with many aspects of atherogenesis, can be viewed as the diverse consequences of endothelial dysfunction in different vascular beds. This new and testable hypothesis accounts for both the endothelial and metabolic abnormalities associated with atherogenesis.
TL;DR: It is demonstrated that leptin inhibits cortisol production in adrenocortical cells and therefore appears to be a metabolic signal that directly acts on the adrenal gland.
Abstract: The crucial role of glucocorticoids in obesity and insulin resistance and the actions of the OB protein leptin on the hypothalamic-pituitary-adrenal (HPA) axis suggest that there is an important interaction of leptin with the glucocorticoid system. Therefore, we designed a study to test the effect of leptin directly on adrenocortical steroidogenesis. Primary cultures of bovine adrenocortical cells were incubated with increasing concentrations (10–1,000 ng/ml) of recombinant mouse leptin for 24 h, and the effects of leptin on basal and ACTH-stimulated cortisol secretion were determined. The accumulation of P450 17α mRNA following incubation with ACTH (10 nmol/1) and leptin (10–1,000 ng/ml) was analyzed by Northern blot. Adrenocortical cells were characterized by immunohistochemical staining for 17α-hydroxyprogesterone. Leptin (10–1,000 ng/ml) inhibited basal and ACTHstimulated cortisol release. At a concentration that occurs in obese individuals in vivo (100 ng/ml), it reduced basal cortisol secretion to 52.7 ± 37% (mean ± SE). The rise in cortisol secretion following maximal ACTH stimulation (10 nmol/1) was blunted to 55.2 ± 27%. At more physiological concentrations of ACTH (0.1 nmol/1), the inhibition of cortisol release by coincubation with low doses of leptin (10 ng/ml) was even more pronounced, leading to a reduction to 32.8% (1,248 ± 134 vs. 410 ± 157 nmol/1). Addition of OB protein (10–1,000 ng/ml) led to a dose-dependent reduction of ACTH-stimulated cytochrome P450 17α mRNA accumulation (from 80 to 45%), suggesting that leptin regulates adrenal steroidogenesis at the transcriptional level. These data clearly demonstrate that leptin inhibits cortisol production in adrenocortical cells and therefore appears to be a metabolic signal that directly acts on the adrenal gland.
TL;DR: In conclusion, insulin lispro improves postprandial control, reduces hypoglycemic episodes, and improves patient convenience, compared with regular human insulin, in IDDM patients.
Abstract: Insulin lispro, an insulin analog recently developed particularly for mealtime therapy, has a fast absorption rate and a short duration of action. We compared insulin lispro and regular human insulin in the mealtime treatment of 1,008 patients with IDDM. The study was a 6-month randomized multinational (17 countries) and multicenter (102 investigators) clinical trial performed with an open-label crossover design. Insulin lispro was injected immediately before the meal, and regular human insulin was injected 30-45 min before the meal. Throughout the study, the postprandial rise in serum glucose was significantly lower during insulin lispro therapy. At the endpoint, the postprandial rise in serum glucose was reduced at 1 h by 1.3 mmol/l and at 2 h by 2.0 mmol/l in patients treated with insulin lispro (P < 0.001). The rate of hypoglycemia was 12% less with insulin lispro (6.4 +/- 0.2 vs. 7.2 +/- 0.3 episodes/30 days, P < 0.001), independent of basal insulin regimen or HbA1c level. The reduction was observed equally in episodes with and without symptoms. When the total number of episodes for each patient was analyzed according to the time of occurrence, the number of hypoglycemic episodes was less with insulin lispro than with regular human insulin therapy during three of four quarters of the day (P < 0.001). The largest relative improvement was observed at night. In conclusion, insulin lispro improves postprandial control, reduces hypoglycemic episodes, and improves patient convenience, compared with regular human insulin, in IDDM patients.
TL;DR: Under normal conditions, this inhibitory influence of glucocorticoids may prevent lasting hypophagia in obesity with degrees of hypercorticism, and may contribute to “leptin resistance,” whose etiology is still little understood.
Abstract: The product of the ob gene, leptin, is a hormone secreted by adipose tissue that acts in the hypothalamus to regulate the size of the body fat depot. Its central administration has been shown to decrease food intake and body weight, while favoring energy dissipation. As glucocorticoids are known to play a permissive role in the establishment and maintenance of obesity syndromes in rodents, it was hypothesized that they do so by restraining the effect of leptin. Leptin injected intracerebroventricularly as a bolus of 3 μg in normal rats induced modest reductions in body weight and food intake. In marked contrast, the same dose of leptin had very potent and long-lasting effects in decreasing both body weight and food intake when administered to adrenalectomized rats. Further, glucocorticoid supplementation of adrenalectomized rats dose-dependently inhibited these potent effects of leptin. These data suggest that glucocorticoids play a key inhibitory role in the action of leptin. Under normal conditions, this inhibitory influence of glucocorticoids may prevent lasting hypophagia. In obesity with degrees of hypercorticism, it may contribute to “leptin resistance,” whose etiology is still little understood.
TL;DR: Islets isolated with Liberase enzyme, assessed both in vitro and in vivo, revealed a functional profile similar to that of islets separated with collagenase, suggesting a gentler enzymatic action and better preservation of anatomical integrity.
Abstract: Enzymatic digestion of donor pancreases is a vital step in human and large mammalian islet isolation. The variable enzymatic activities of different batches of commercially available collagenase is a major obstacle in achieving reproducibility in islet isolation procedures. In the present work, the effectiveness of Liberase, a standardized mixture of highly purified enzymes recently developed for the separation of human islets, was compared with that of a traditional collagenase preparation (type P). The results of 50 islet isolations using Liberase enzyme were compared with those of 36 isolations with collagenase, type P. No significant differences in donor age, cold ischemia time, digestion time, or weight of the pancreases were observed between the two groups. Islet yield was significantly higher in the group where the Liberase enzyme was used. All parameters examined (islet number, islet number per gram of tissue, islet equivalent number, and islet equivalent number per gram of tissue) were significantly improved when Liberase enzyme was used. Different lots of Liberase enzyme were tested, and no difference was observed. Islets isolated with Liberase enzyme were also of larger size and were much less fragmented, suggesting a gentler enzymatic action and better preservation of anatomical integrity. Islets isolated with Liberase enzyme, assessed both in vitro and in vivo, revealed a functional profile similar to that of islets separated with collagenase. Liberase enzyme appears, therefore, to represent a new powerful tool for improving the quality of human islet isolation.