bluuebunny/crossref_metadata_2025 huggingface dataset:
Elevated PC-1 content in cultured skin fibroblasts correlates with decreased in vivo and in vitro insulin action in nondiabetic subjects: evidence that PC-1 may be an intrinsic factor in impaired insulin receptor signaling.
Authors: Frittitta L , Spampinato D , Solini A , Nosadini R , Goldfine I D , Vigneri R , Trischitta V
Published: March 2007

Membrane glycoprotein PC-1 inhibits insulin receptor (IR) tyrosine kinase activity and subsequent cellular signaling. PC-1 content is elevated in muscle and adipose tissue from insulin-resistant subjects, and its elevation correlates with in vivo insulin resistance. To determine whether elevated PC-1 content is a primary cause of insulin resistance, we have now measured PC-1 content in cultured skin fibroblasts from nonobese nondiabetic insulin-resistant subjects and found that 1) PC-1 content was significantly higher in these cells when compared with cells from insulin-sensitive subjects (6.7 +/- 0.9 vs. 3.1 +/- 0.6 ng/0.1 mg protein, mean +/- SE, P < 0.01); 2) PC-1 content in fibroblasts was highly correlated with PC-1 content in muscle tissue (r = 0.95, P = 0.01); 3) PC-1 content in fibroblasts negatively correlated with both decreased in vivo insulin sensitivity and decreased in vitro IR autophosphorylation; and 4) in cells from insulin-resistant subjects, insulin stimulation of glycogen synthetase was decreased. These studies indicate, therefore, that the elevation of PC-1 content may be a primary factor in the cause of insulin resistance.
Familial and perinatal risk factors for micro- and macroalbuminuria in young IDDM patients.
Authors: Rudberg S , Stattin E L , Dahlquist G
Published: March 2007

It has been suggested that hereditary risk for hypertension and cardiovascular disease (CVD) as well as intrauterine growth may be involved in the pathogenesis of diabetic nephropathy. In the present study, we investigated the influence of familial and perinatal risk factors on the occurrence of micro- and macroalbuminuria in young IDDM patients. A cohort of 1,150 young patients with > or =5 years' duration of IDDM was screened for microalbuminuria. Data on family history of hypertension, CVD, IDDM, and NIDDM; perinatal factors such as birth weight, gestational age, and duration of breastfeeding; and maternal education, smoking, hypertension, and proteinuria during pregnancy were collected. We identified 75 patients with an albumin excretion rate > or =15 microg/min in more than two overnight urinary samples and compared them in a nested case-control study with three normoalbuminuric control subjects per patient from the same cohort, matched for diabetes duration. Perinatal factors were analyzed in all patients born at term (+/- 2 weeks), 59 of the 75 patients and 155 of the 225 control subjects. In univariate analysis, hypertension in parents (odds ratio [OR] 4.21), CVD in parents and grandparents (OR 1.26), maternal smoking during pregnancy (OR 3.21), and a low level of maternal education (OR 2.33) were significantly associated with the development of micro- and macroalbuminuria. When adjusted for other familial and perinatal factors, current mean blood pressure, HbA1c, smoking, BMI, sex, age, and postpubertal diabetes duration, using logistic regression analyses, only parental hypertension in all patients and maternal smoking during pregnancy and low level of maternal education in full-term patients were independent risk factors. When patients with poor glycemic control were analyzed separately, familial CVD, poor metabolic control, parental hypertension, maternal smoking during pregnancy, and level of maternal education were independent risk factors, with the adjusted OR markedly increased, compared with the matched subgroup with better HbA1c. In conclusion, familial hypertension and CVD, maternal smoking during pregnancy, and low level of maternal education may independently increase the risk for incipient nephropathy in full-term offspring who later develop IDDM. Current poor glycemic control seemed to increase the effect of these risk factors.
Contribution of the endothelium to transcapillary insulin transport in rat isolated perfused hearts.
Authors: Brunner F , Wascher T C
Published: March 2007

Capillary endothelial cells are thought to limit the transport of insulin from the vascular to the interstitial space, resulting in attenuated hormonal action at target sites. This study examined the contribution of endothelial cells to the regulation of transcapillary insulin transport in rat hearts in vitro. Hearts were perfused with a protein-free buffer that resulted in the generation of a substantial amount of interstitial fluid (transudate) that was collected at the surface of ventricles. Insulin (0.05-1 U/l) was added to the perfusate, and its transfer kinetics to and clearance from the interstitium were analyzed from insulin measurements in transudate of hearts with intact or collagenase-disrupted endothelium. In endothelium-intact hearts (n = 5-8), the steady-state insulin concentration in transudate was 29 +/- 4, 30 +/- 2, 53 +/- 1, 103 +/- 6, and 97 +/- 4% of perfusate concentrations at 0.05, 0.1, 0.2, 0.5, and 1 U/l insulin, respectively. The corresponding apparent rate constants for transport (k(in)) increased from 0.03/min to -0.27/min, indicating a nonsaturable transport process. The transport rate for [3H]insulin (1.2 nmol/l; n = 5) was identical to an equimolar concentration of insulin (0.2 U/l), strongly indicating the same mode of transport. In endothelium-disrupted hearts (n = 3-5), the same perfusate/transudate concentration ratios were observed--that is, a gradient at low insulin concentrations (0.05-0.2 U/l) and complete equilibration at higher insulin concentrations, suggesting a contribution of reabsorption processes back into the vascular space in the generation of the gradient. Finally, inhibition of endothelial nitric oxide (NO) formation by NG-nitro-L-arginine (200 micromol/l) affected neither k(in) nor the extent of transendothelial insulin transport in the presence of an intact endothelium. We concluded that 1) capillary endothelial cells affect the transcapillary transport of insulin by slowing the transfer to the interstitium, 2) insulin is transported by a bidirectional convective transport rather than by a saturable receptor-mediated mechanism, and 3) endothelium-derived NO is without effect on transcapillary insulin transport in this model.
Functional analyses of novel mutations in the sulfonylurea receptor 1 associated with persistent hyperinsulinemic hypoglycemia of infancy.
Authors: Shyng S L , Ferrigni T , Shepard J B , Nestorowicz A , Glaser B , Permutt M A , Nichols C G
Published: March 2007

The ATP-sensitive potassium channel, K(ATP) channel, a functional complex of the sulfonylurea receptor 1, SUR1, and an inward rectifier potassium channel subunit, Kir6.2, regulates insulin secretion in the pancreas. Mutations in both the Kir6.2 and SUR1 genes are associated with persistent hyperinsulinemic hypoglycemia of infancy (PHHI), a disorder of pancreatic beta-cell function characterized by excess insulin secretion and hypoglycemia. We have studied the functional properties of novel SUR1 mutations identified in PHHI patients, including H125Q, N188S, F591L, T1139M, R1215Q, G1382S, and R1394H. R1394H and deltaF1388 SUR1, a previously identified PHHI mutation, resulted in no functional channels when coexpressed with Kir6.2 in COS cells, while H125Q, N188S, F591L, T1139M, R1215Q, and G1382S SUR1 generated functional channels in the absence of ATP. With the exception of N188S and H125Q, all mutants had reduced response to stimulation by MgADP. These results indicate that lack of, or reduction of, K(ATP) channel sensitivity to MgADP is a common molecular defect associated with the disease. The mutant channels also showed varied response to activation by the potassium channel opener diazoxide. Because these mutations are distributed throughout the molecule, our data have new implications for structure-function relationships of the K(ATP) channel, suggesting that structural elements in SUR1 outside of the two nucleotide-binding folds are also important in regulating channel activity.
Glucose utilization and production in patients with maturity-onset diabetes of the young caused by a mutation of the hepatocyte nuclear factor-1alpha gene.
Authors: Surmely J F , Guenat E , Philippe J , Dussoix P , Schneiter P , Temler E , Vaxillaire M , Froguel P , Jéquier E , Tappy L
Published: March 2007

Mutations of the hepatocyte nuclear factor (HNF)-1alpha gene cause impaired insulin secretion and hyperglycemia in patients with maturity-onset diabetes of the young (MODY)3. Whether these mutations also affect glucose metabolism in tissues other than the beta-cell has not yet been documented. We therefore assessed, in five MODY3 patients and a dozen healthy control subjects, insulin secretion, oxidative and nonoxidative glucose disposal, and glucose production during a two-step hyperglycemic clamp and a euglycemic hyperinsulinemic (0.4 mU x kg(-1) x min(-1)) clamp. Compared with healthy control subjects, MODY3 patients had higher fasting plasma glucose (+100%) but similar rates of fasting glucose production and oxidation. Both the early and late phases of insulin secretion were virtually abolished during the hyperglycemic clamp, and glucose production was suppressed by only 43% in MODY3 patients vs. 100% in healthy control subjects. The rate of glucose infusion required to produce a 5 mmol/l increase above basal glycemia was reduced by 30%, net nonoxidative glucose disposal (which is equal to net glycogen deposition) was inhibited by 39%, and net carbohydrate oxidation during hyperglycemia was 25% lower in MODY3 patients compared with control subjects. Insulin-stimulated glucose utilization and oxidation measured during the hyperinsulinemic clamp (at approximately 200 pmol/l insulin) were identical in MODY3 patients and in healthy control subjects, indicating that peripheral insulin sensitivity was not altered. Suppression of endogenous glucose production was, however, mildly impaired. It is concluded that MODY3 patients have severely depressed glucose-induced insulin secretion. The development of hyperglycemia in these patients appears to be caused by a decreased stimulation of glucose utilization, oxidation, and nonoxidative glucose disposal as well as by a blunted suppression of endogenous glucose output. These phenomena are essentially secondary to insulinopenia, whereas insulin sensitivity remains intact.
Hypoxia upregulates glucose transport activity through an adenosine-mediated increase of GLUT1 expression in retinal capillary endothelial cells.
Authors: Takagi H , King G L , Aiello L P
Published: March 2007

Elevation of intracellular glucose within retinal vascular cells is believed to be an important causal factor in the development of diabetic retinopathy. The intracellular glucose concentration is regulated by both the rate of glucose metabolism and glucose transport. Because retinal hypoxia often precedes proliferative diabetic retinopathy, we have studied the regulation of the glucose transport system by hypoxia in cultured bovine retinal endothelial cells (BRECs). Because retinal ischemia is known to increase intracellular adenosine levels, which subsequently regulate hypoxia-inducible genes, such as vascular endothelial growth factor and erythropoietin, the role of adenosine and its receptor-mediated pathways has also been evaluated. Hypoxia (0.5% O2, 5% CO2, and 94.5% N2) stimulated GLUT1 mRNA expression in BRECs in a time-dependent manner with an 8.9 +/- 1.5-fold (P < 0.01) increase observed after 12 h. GLUT1 mRNA expression returned to baseline (1.4 +/- 0.3-fold of control) within 12 h after reinstitution of normoxia. N6-Cyclopentyl adenosine (adenosine A1 receptor agonist, Kd = 1 nmol/l) did not affect GLUT1 mRNA expression at concentrations up to 1 micromol/l, while 2-p-(2-carboxyethyl)-phenethyl-amino-5'-N-ethylcarboxamidoadenosine and 5'-(N-ethylcalboxamido)-adenosine (adenosine A2 receptor [A2R] agonists, Kd = 15 and 16 nmol/l, respectively) increased mRNA levels at concentrations as low as 10 nmol/l. Maximal stimulation was 2.3 +/- 0.2- and 2.1 +/- 0.2-fold, respectively (P < 0.01). The adenosine A2a receptor antagonist 8-(3-chlorostyryl)caffeine (CSC) (Kd = 100 nmol/l for A2R) inhibited hypoxia-stimulated GLUT1 mRNA expression by 40 +/- 8% at 100 nmo/l. Hypoxia upregulated GLUT1 protein expression by 3.0 +/- 0.3-fold after 12 h (P < 0.01), but this response was attenuated by CSC (P < 0.05). Hypoxia increased glucose transport activity by 2.1 +/- 0.3-fold (P < 0.001) after 12 h, a response inhibited 65% by CSC (P < 0.01). A protein kinase A (PKA) inhibitor (H89, 20 micromol/l) suppressed hypoxia-induced GLUT1 mRNA expression by 42 +/- 9% (P < 0.01). These data suggest that hypoxia in BRECs upregulates glucose transport activity through an increase of GLUT1 expression that is partially mediated by adenosine, A2R, and the cAMP-PKA pathway.
Intrauterine diabetes exposure and the risk of renal disease in diabetic Pima Indians.
Authors: Nelson R G , Morgenstern H , Bennett P H
Published: March 2007

The association between the diabetic intrauterine environment and renal disease was examined cross-sectionally in 503 Pima Indians with type 2 diabetes. Subjects were selected from participants in an ongoing study of diabetes and its complications in the Gila River Indian Community of Arizona. Subjects' exposure to diabetes in utero was established from periodic examinations conducted as part of the study. The prevalence of elevated urinary albumin excretion (UAE) (albumin-to-creatinine ratio > or = 30 mg/g) was 40% (83 of 207) in the offspring of nondiabetic mothers, 43% (105 of 246) in the offspring of prediabetic mothers (i.e., women who were not diabetic at the time of the pregnancy but who developed diabetes after the pregnancy), and 58% (29 of 50) in the offspring of mothers who had diabetes during pregnancy. After controlling for age, sex, duration of diabetes, HbA1c, and mean arterial pressure in the offspring in a logistic regression analysis using generalized estimating equations, maternal diabetes during pregnancy was strongly associated with elevated UAE. The odds of elevated UAE in the offspring of mothers who had diabetes during pregnancy was 3.8 times (95% CI 1.7-8.4) that of the offspring of prediabetic mothers; the odds of elevated UAE in the offspring of nondiabetic and prediabetic mothers were similar (odds ratio of 0.94; 95% CI 0.59-1.5). We concluded that exposure to a diabetic intrauterine environment increases the risk of elevated UAE in diabetic Pima Indians. The effect of this exposure appears to be independent of other susceptibility factors that lead to nephropathy in diabetes.
Uncoupling protein 3 is reduced in skeletal muscle of NIDDM patients.
Authors: Krook A , Digby J , O'Rahilly S , Zierath J R , Wallberg-Henriksson H
Published: March 2007

Two recently described proteins in the mitochondrial uncoupling protein (UCP) family, UCP-2 and UCP-3, have been linked to phenotypes of obesity and NIDDM. We determined the mRNA levels of UCP-2 and UCP-3 in skeletal muscle of NIDDM patients and of healthy control subjects. No difference in the mRNA levels or in the protein expression of UCP-2 was observed between the two groups. In contrast, mRNA levels of UCP-3 were significantly reduced in skeletal muscle of NIDDM patients compared with control subjects. In the NIDDM patients, a positive correlation between UCP-3 expression and whole-body insulin-mediated glucose utilization rate was also noted. These results suggest that UCP-3 regulation may be altered in states of insulin resistance.
Insulin regulation of regional free fatty acid metabolism.
Authors: Meek S E , Nair K S , Jensen M D
Published: March 2007

Studies were conducted to determine whether regional free fatty acid (FFA) release is differentially regulated by insulin. Systemic, leg, and splanchnic palmitate rate of appearance ([9,10-(3)H]palmitate) was measured in 26 healthy adults using the euglycemic-hyperinsulinemic clamp technique to achieve a physiological range of plasma insulin concentrations. We found that insulin inhibited systemic, leg, and splanchnic palmitate release in a dose-dependent fashion over the range of insulin infused (0-1.0 mU x kg(-1) x min(-1)). Progressive hyperinsulinemia changed the leg from a net producer to a net FFA consumer, whereas the splanchnic bed converted from a net FFA consumer to a net producer. At the 0.5 mU x kg(-1) x min(-1) insulin infusion rate, leg FFA release was almost completely suppressed, whereas even with the 1.0 mU x kg(-1) x min(-1) insulin infusion rate, splanchnic FFA release decreased by only approximately 65% (P < 0.05 leg vs. splanchnic). These results demonstrate the regional heterogeneity of insulin-regulated FFA release in vivo, and indicate that visceral adipose tissue lipolysis is more resistant to insulin suppression than is leg lipolysis in humans.
Relationships between maternal risk of insulin resistance and the child's muscle membrane fatty acid composition.
Authors: Baur L A , O'Connor J , Pan D A , Storlien L H
Published: March 2007

In adult humans, insulin resistance is associated with relatively low proportions of polyunsaturated fatty acids (PUFAs) in muscle membrane structural lipid. The aim of the present study was to determine the relationship between young children's muscle membrane fatty acid (FA) composition and indices of insulin resistance in their mothers. Muscle biopsy specimens obtained at the time of elective surgery from 83 children (54 boys), aged 0.78 +/- 0.05 year (mean +/- SE), were analyzed for phospholipid FA composition. Fasting blood samples were collected from the mothers of the children, and maternal BMIs were calculated. Stepwise multiple regression analysis showed that after accounting for the effect of breast-feeding, log maternal insulin levels were inversely associated with the child's muscle membrane docosahexaenoic acid (22:6 n-3; R2 = 0.29, P = 0.0006) and the sum of the n-3 PUFAs (R2 = 0.23, P = 0.0016) but positively associated with the sum of the n-6 PUFAs (R2 = 0.05, P = 0.03) and the n-6/n-3 PUFA ratio (R2 = 0.20, P = 0.007). Independent of breast-feeding, log maternal triglyceride levels were inversely associated with the child's muscle membrane unsaturation index (a measure of unsaturation) (R2 = 0.08, P = 0.005). Maternal BMI; total, LDL, and HDL cholesterol; and the child's age, sex, and birth weight were not significant predictors of the child's muscle membrane FA composition. Thus, maternal fasting insulin and triglyceride levels are significant predictors of the FA composition of the child's muscle membrane. The less unsaturated muscle membranes in children whose mothers have higher fasting insulin and triglyceride levels may reflect a genetic reluctance to incorporate PUFAs into membranes, thus predisposing them to insulin resistance syndromes.
Skeletal muscle uncoupling protein 3 expression is a determinant of energy expenditure in Pima Indians.
Authors: Schrauwen P , Xia J , Bogardus C , Pratley R E , Ravussin E
Published: March 2007

The recent discovery of uncoupling protein (UCP)-2 and UCP-3, and their high expression in skeletal muscle, has renewed interest in a possible role for these proteins in underlying the variability in energy expenditure and therefore metabolic efficiency. Using reverse transcription-polymerase chain reaction, levels of expression of UCP-2 and long and short forms of UCP-3 were measured in skeletal muscle of 19 nondiabetic, male Pima Indians covering a wide range of body weight. Twenty-four-hour energy expenditure was measured in a respiratory chamber in 16 of these individuals. BMI was negatively correlated with the expression levels of the long (r = -0.53, P = 0.025) and short (r = -0.46, P = 0.047) forms of UCP-3. BMI was not correlated with UCP-2 expression. Metabolic rate during sleep, adjusted for fat-free mass and fat mass, was positively correlated with the long form of UCP-3 (r = 0.69, P = 0.006). These results indicate that UCP-3 may be a determinant of energy expenditure and metabolic efficiency in Pima Indians.
Leptin enhances glycogen storage in hepatocytes by inhibition of phosphorylase and exerts an additive effect with insulin.
Authors: Aiston S , Agius L
Published: March 2007

The effects of the adipocyte-derived hormone leptin on glucose metabolism in hepatocytes were investigated. Incubation of hepatocytes from Wistar rats with leptin for 16 h caused a dose-dependent increase in incorporation of [14C]glucose into glycogen, with a maximal effect at 30 nmol/l leptin. This effect of leptin was observed over a range of glucose concentrations (10-25 mmol/l) and was associated with stimulation of net glycogen deposition. It was not counteracted by mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase, indicating that it is not due to increased gluconeogenic flux. Leptin also enhanced the short-term stimulation of glycogen synthesis by insulin. These effects of leptin were associated with inhibition of phosphorylase a, which occurred after 4 h of exposure to leptin. Culture with leptin for 16 h did not affect the activities of glucose-6-phosphatase or glucokinase or the activation state of glycogen synthase. Leptin did not affect glycolysis determined from the detritiation of [3-(3)H]glucose. The inhibitory effects of leptin on phosphorylase a were counteracted by short-term incubation with glucagon but were additive with the inhibitory effects of insulin and also with the inhibition caused by resorcinol (25 pmol/l), which inhibits phosphorylase kinase by a mechanism analogous to the antidiabetic drug proglycosyn. These results show that leptin has additive effects with insulin in inhibiting phosphorylase and stimulating glycogen storage in hepatocytes, indicating that these hormones act by separate but convergent mechanisms. It is concluded that the primary action of leptin in hepatocytes is to enhance glycogen storage. This may be an important compensatory mechanism for the inhibition of insulin secretion.
Clinical and genetic characteristics of type 2 diabetes with and without GAD antibodies.
Authors: Tuomi T , Carlsson A , Li H , Isomaa B , Miettinen A , Nilsson A , Nissén M , Ehrnström B O , Forsén B , Snickars B , Lahti K , Forsblom C , Saloranta C , Taskinen M R , Groop L C
Published: March 2007

The aim of the study was 1) to establish the prevalence of GAD antibodies (GADab) in a population-based study of type 2 diabetes in western Finland, 2) to genetically and phenotypically characterize this subgroup, and 3) to provide a definition for latent autoimmune diabetes in adults (LADA). The prevalence of GADab was 9.3% among 1,122 type 2 diabetic patients, 3.6% among 558 impaired glucose tolerance (IGT) subjects, and 4.4% among 383 nondiabetic control subjects. Islet antigen 2 antibodies (IA2ab) or islet cell antibodies were detected in only 0.5% of the GADab- patients. The GADab+ patients had lower fasting C-peptide concentrations (median [interquartile range]: 0.46 [0.45] vs. 0.62 [0.44] nmol/l, P = 0.0002) and lower insulin response to oral glucose compared with GADab- patients. With respect to features of the metabolic syndrome, the GADab+ patients had lower systolic (140 [29.1] vs. 148 [26.0] mmHg, P = 0.009) and diastolic (79.2 [17.6] vs. 81.0 [13.1] mmHg, P = 0.030) blood pressure values, as well as lower triglyceride concentrations (1.40 [1.18] vs. 1.75 [1.25] mmol/l, P = 0.003). GADab+ men had a lower waist-to-hip ratio compared with GADab- patients. Compared with GADab- patients and control subjects, the GADab+ patients had an increased frequency HLA-DQB1*0201/0302 (13 vs. 4%; P = 0.002) and other genotypes containing the *0302 allele (22 vs. 12%; P = 0.010). However, the frequency of these high-risk genotypes was significantly lower in GADab+ type 2 patients than in type 1 diabetes of young or adult onset (0201/0302 or 0302/X: 36 vs. 66 vs. 64%, P < 0.001). The GADab+ type 2 group did not differ from control subjects with respect to genotypes containing the protective DQB1-alleles *0602 or *0603, nor with respect to the type 1 high-risk genotype in the IDDM1 (Hph1 +/+). We conclude that GADab+ patients differ from both GADab- type 2 diabetic patients and type 1 diabetic patients with respect to beta-cell function, features of the metabolic syndrome, and type 1 diabetes susceptibility genes. Further, we propose that LADA be defined as GADab positivity (>5 relative units) in patients older than 35 years at onset of type 2 diabetes.
Relationship of beta-cell function and autoantibodies to progression and nonprogression of subclinical type 1 diabetes: follow-up of the Seattle Family Study.
Authors: Greenbaum C J , Sears K L , Kahn S E , Palmer J P
Published: March 2007

A total of 85 islet cell antibody (ICA)+ or insulin autoantibody (IAA)+ relatives of patients with type 1 diabetes have been followed as part of the Seattle Family Study for a mean of 2.8 years. Of the subjects followed, 10 developed diabetes during this time period. The presence of GAD antibodies was strongly associated with the development of diabetes. In contrast, the presence of IAAs did not influence the risk of diabetes among ICA+ GAD+ subjects. When either the initial absolute acute insulin response to glucose (AIRg) or the AIR percentile, which accounts for the individual's insulin sensitivity, was below the 10th percentile of normal subjects, the risk of diabetes approached 50% at 5 years. However, impaired beta-cell function did not influence the risk of diabetes among those who were GAD+. There were 13 subjects with low AIRg and 13 subjects with two or more antibodies who had not progressed to diabetes during the course of the study. Other measurements of beta-cell function or demographic characteristics were not different in this group of nonprogressors compared with those with low AIRg who did not progress to diabetes. We conclude that ICA+ relatives with GAD antibodies or low AIRg have a high risk for development of diabetes, but among ICA+ GAD+ relatives, the addition of IAA or a single determination of AIRg does not enhance the prediction of diabetes. We suggest that prediction of diabetes risk depends on both the type and the number of antibodies present. In addition, there are a group of ICA+ relatives with low AIRg and/or multiple antibodies who have not progressed to diabetes over the course of the study.
IDDM patients neither show humoral reactivities against endogenous retroviral envelope protein nor do they differ in retroviral mRNA expression from healthy relatives or normal individuals.
Authors: Badenhoop K , Donner H , Neumann J , Herwig J , Kurth R , Usadel K H , Tönjes R R
Published: March 2007

Recently, human endogenous retrovirus type K (HERV-K [IDDMK(1,2)22]) was isolated from an IDDM patient's beta-cell supernatant and shown to be implicated in expression as a superantigen. Furthermore, HERV-K RNA was found in plasma samples from newly diagnosed patients but not in those from healthy control subjects. We had earlier identified the presence of a HERV-K long terminal repeat element of the HLA DQ gene (DQ-LTR) to be positively associated with IDDM, which led us to investigate whether DQ-LTR is related to transcription of the putative retroviral superantigen. Additionally, we sought immunological evidence to determine whether those retroviral antigens could evoke an antibody response. Patients with IDDM (n = 14), Hashimoto's thyroiditits (n = 5), and Graves' disease (n = 12), as well as healthy control subjects (n = 12), were investigated, as were four nuclear families of Graves' disease patients and two of IDDM patients. RNA was isolated from plasma and peripheral blood lymphocytes and subjected to reverse transcription-polymerase chain reaction for transcripts of the env region of the HERV-K (IDDMK(1,2)22) sequence. We identified env transcripts in both plasma and peripheral blood lymphocytes in all individuals studied: patients with recent-onset or long-standing IDDM, their relatives, and healthy control subjects, as well as patients with thyroid autoimmune disorders. Furthermore, we screened the sera of patients (n = 62) and control subjects (n = 35) for evidence of humoral immunity against HERV-K by Western blot specific for the ENV protein. Similar frequencies of antibody-positives were observed both in patients with IDDM (29%) and in healthy control subjects (26%). We conclude that neither the ubiquitous HERV-K transcripts nor the comparable percentage of ENV protein antibodies are associated with IDDM. An earlier, presymptomatic antibody response against HERV-K (IDDMK(1,22)22) ENV cannot be ruled out. However, the superantigen hypothesis of an endogenous retrovirus in beta-cell autoimmunity awaits confirmation.
The IDDMK(1,2)22 retrovirus is not detectable in either mRNA or genomic DNA from patients with type 1 diabetes.
Authors: Muir A , Ruan Q G , Marron M P , She J X
Published: March 2007

A new viral sequence (IDDMK(1,2)22) similar to the human endogenous retrovirus (HERV)-K10/K18 subfamilies has recently been isolated from the culture supernatants of leukocyte-infiltrated islets from two patients who died at the onset of type 1 diabetes. It was claimed that this endogenous retrovirus is expressed in patients with type 1 diabetes but not in healthy control subjects, suggesting an important role of the retrovirus in beta-cell-specific autoimmunity that results in type 1 diabetes. However, despite exhaustive attempts involving identical and expanded methods of detection, we did not observe the IDDMK(1,2)22 viral sequence in genomic DNA, lymphocyte, or plasma RNA in any subject. Therefore, we believe that the viral sequence is not derived from an endogenous retrovirus and that a role for the retrovirus in the pathogenesis of type 1 diabetes must be reconsidered.
Heme oxygenase and carbon monoxide: regulatory roles in islet hormone release: a biochemical, immunohistochemical, and confocal microscopic study.
Authors: Henningsson R , Alm P , Ekström P , Lundquist I
Published: March 2007

Carbon monoxide (CO) has been suggested as a novel messenger molecule in the brain. We now report on the cellular localization and hormone secretory function of a CO-producing constitutive heme oxygenase (HO-2) in mouse islets. Islet homogenates produced large amounts of CO which were suppressed dose-dependently by the HO inhibitor zincprotoporphyrin-IX (ZnPP-IX). We also show, for the first time, that glucose markedly stimulates the HO activity (CO production) in intact islets. A further potentiation was induced by the HO substrate hemin. Western blot showed that islet tissue expressed HO-2, and confocal microscopy revealed that HO-2 resided in insulin, glucagon, somatostatin, and pancreatic polypeptide cells. ZnPP-IX dose-dependently inhibited, whereas hemin enhanced, both insulin and glucagon secretion from glucose-stimulated islets. Stimulation or inhibition of CO production was accompanied by corresponding changes in islet cGMP levels. Exogenously applied CO stimulated insulin and glucagon release from isolated islets, whereas exogenous nitric oxide (NO) inhibited insulin and stimulated glucagon release. Islets stimulated by glucose or L-arginine displayed a marked increase in their NO-synthase (NOS) activity. Such an increase was suppressed by hemin, conceivably because NOS activity was inhibited by hemin-derived CO. Consequently, hemin enhanced L-arginine-induced insulin secretion. Insulin release stimulated by either hemin-derived CO or exogenous CO was strongly inhibited by the guanylate cyclase inhibitor ODQ, but it was unaffected by ZnPP-IX. Glucagon release induced by CO (but not by hemin) was inhibited by ODQ and partly inhibited by ZnPP-IX. We propose that the islets of Langerhans are equipped with a heme oxygenase-carbon monoxide pathway, which constitutes a novel regulatory system of physiological importance for the stimulation of insulin and glucagon release. This pathway is stimulated by glucose, is at least partly dependent on the cGMP system, and displays interaction with islet NOS activity.
Glucagon-like peptide 1 has a physiological role in the control of postprandial glucose in humans: studies with the antagonist exendin 9-39.
Authors: Edwards C M , Todd J F , Mahmoudi M , Wang Z , Wang R M , Ghatei M A , Bloom S R
Published: March 2007

Glucagon-like peptide 1(7-36) amide (GLP-1) is postulated to be the major physiological incretin in humans, but evidence is indirect. We report the first studies examining the physiological role of GLP-1 in the postprandial state in humans using the GLP-1 antagonist exendin 9-39. Exendin 9-39 completely blocked GLP-1-induced glucose-stimulated insulin release from perifused human islets of Langerhans. In healthy fasted volunteers, intravenous infusion of exendin 9-39 at 500 pmol x kg(-1) x min(-1) in the hyperglycemic state abolished the insulinotropic effect of a physiological dose of GLP-1 and fully reversed the glucose-lowering effect of GLP-1. Nine healthy subjects consumed a 150-g oral glucose tolerance test and were infused with 500 pmol x kg(-1) x min(-1) exendin 9-39 or saline. Exendin 9-39 increased the peak postprandial glucose level (exendin 9-39, 8.67 +/- 0.35 vs. saline, 7.67 +/- 0.35 mmol/l, P < or = 0.005) and increased postprandial plasma glucose incremental area under the curve by 35% (exendin 9-39, 152 +/- 19 vs. saline, 113 +/- 16 mmol x min x l(-1), P < or = 0.05). This could be explained as partly secondary to the blockade of glucose-induced suppression of glucagon and maybe also to an increased rate of gastric emptying. Thus, in humans exendin 9-39 acts as an antagonist of GLP-1 both in vitro and in vivo. When infused alone, exendin 9-39 causes a deterioration in postprandial glycemic control, suggesting that GLP-1 may be important for maintenance of normal postprandial glucose homeostasis in humans.
Vascular endothelial growth factor and diabetes: the agonist versus antagonist paradox.
Authors: Duh E , Aiello L P
Published: March 2007

Much of the morbidity and mortality associated with diabetes is primarily attributable to sequelae of microvascular and macrovascular disease. Over the past decade, dramatic progress has been achieved in elucidating the fundamental processes underlying the pathogenesis of these complications. Angiogenic factors in particular now appear to play a pivotal role in the development of microvascular complications as well as the response to macrovascular disease. Hyperglycemia, other growth factors, advanced glycation end products, oxidative stress, and ischemia can increase growth factor expression. In some microvascular tissues, the result is pathologic neovascularization and increased vascular permeability. These responses account for much of the visual loss associated with diabetic retinopathy and may, in addition, serve a significant role in nephropathy and neuropathy. In contrast, recent data suggest that vascular collateralization resulting from ischemia-induced growth factor release in tissues compromised by macrovascular disease may be important in reducing clinical symptoms and tissue damage. This angiogenic response, which may be beneficial in coronary artery and peripheral limb disease, appears to be reduced in patients with diabetes. Thus, two apparently diametrically opposed therapeutic paradigms are arising for the treatment of vascular complications in diabetes. Indeed, growth factor antagonists have been used successfully in diabetes-related animal models to block angiogenic and permeability complications in the retina and kidney. Conversely, growth factor agonists have been successfully used to stimulate collateral vessel formation and reduce ischemic symptoms from macrovascular disease in the coronary arteries and peripheral limbs. Both of these approaches are currently being evaluated in clinical trials for their respective indications. Thus, as these divergent therapeutic modalities begin to enter the clinical arena, this apparent paradox necessitates careful consideration of the potential risks, benefits, and interactions of the opposing regimens. Using vascular endothelial growth factor as a classic example of growth factor involvement, we discuss the current preclinical and clinical data supporting these approaches and the implications arising from the probable coexistence of these two therapeutic modalities.
No effect of insulin on glucose blood-brain barrier transport and cerebral metabolism in humans.
Authors: Hasselbalch S G , Knudsen G M , Videbaek C , Pinborg L H , Schmidt J F , Holm S , Paulson O B
Published: March 2007

The effect of hyperinsulinemia on glucose blood-brain barrier (BBB) transport and cerebral metabolism (CMRglc) was studied using the intravenous double-indicator method and positron emission tomography using [18F]fluorodeoxyglucose as tracer (PET-FDG). Sixteen normal healthy control subjects (25 +/- 4 years old) were studied twice during a euglycemic and a euglycemic-hyperinsulinemic condition. Our hypothesis was that high physiologic levels of insulin did not affect the BBB transport or net metabolism of glucose. During insulin infusion, arterial plasma insulin levels increased from 48.5 to 499.4 pmol/l. The permeability-surface area products for glucose and FDG BBB transport obtained with the double-indicator method remained constant during hyperinsulinemia. Similarly using PET-FDG, no changes were observed in the unidirectional clearance of FDG from blood to brain. k2* (FDG transport from brain to blood) increased significantly by 15 and 18% (gray and white matter, respectively), and k4* (dephosphorylation of FDG) increased by 18%. The increase in k2* may be caused by insulin inducing a decrease in the available FDG brain pool. The increase in k4* may be related to an increased loss of labeled products during insulin fusion. Irrespective of these changes, CMRglc remained unchanged in all brain regions. We conclude that hyperinsulinemia within the normal physiologic range does not affect BBB glucose transport or net cerebral glucose metabolism.
Identification of peptides from autoantigens GAD65 and IA-2 that bind to HLA class II molecules predisposing to or protecting from type 1 diabetes.
Authors: Harfouch-Hammoud E , Walk T , Otto H , Jung G , Bach J F , van Endert P M , Caillat-Zucman S
Published: March 2007

Type 1 diabetes is a T-cell-mediated disease in which presentation of autoantigens to CD4+ T-cells is thought to play a crucial role. Polymorphism of HLA class II genes accounts for 50% of the genetic risk of contracting type 1 diabetes. HLA-DQ and -DR molecules predisposing to or protecting from type 1 diabetes have been identified, but the molecular basis controlling these associations is as yet undefined. Apart from distinct thymic selection of autoreactive T-cells by susceptible and protective HLA molecules, exclusive presentation of autoantigenic peptides by type 1 diabetes-predisposing HLA molecules or, alternatively, induction of regulatory T-cells by protective alleles are potential mechanisms for modification of type 1 diabetes risk by HLA polymorphism. As a first step in exploring the role of HLA molecules in autoantigen-specific cellular responses in type 1 diabetes, we have screened peptides covering the sequence of two major autoantigens targeted by humoral and cellular immune responses, GAD65 and islet associated-2 (IA-2), for binding to class II molecules. We developed a sensitive novel competition binding assay allowing us to measure peptide binding on intact cells to 10 HLA-DR and 4 HLA-DQ molecules. For all tested alleles, multiple peptides binding with high affinity were identified. We report clustering of binding peptides in the COOH-terminal regions of GAD65 and IA-2, as well as highly promiscuous binding patterns of some peptides. Our results demonstrate that most peptides derived from the GAD and IA-2 autoantigens can bind to both type 1 diabetes-predisposing and type 1 diabetes-protective HLA molecules, although some exceptions were observed. The binding inventory presented here for GAD and IA-2 peptides can be useful for mapping natural epitopes and predicting peptide-specific responses induced by preventive immunization.
Altered cAMP and Ca2+ signaling in mouse pancreatic islets with glucagon-like peptide-1 receptor null phenotype.
Authors: Flamez D , Gilon P , Moens K , Van Breusegem A , Delmeire D , Scrocchi L A , Henquin J C , Drucker D J , Schuit F
Published: March 2007

1-Cells from rodents and humans express different receptors recognizing hormones of the secretin-glucagon family, which--when activated--synergize with glucose in the control of insulin release. We have recently reported that isolated islets from mice homozygous for a GLP-1 receptor null mutation (GLP-1R(-/-)) exhibit a well-preserved insulin-secretory response to glucose. This observation can be interpreted in two different ways: 1) the presence of GLP-1R is not essential for the secretory response of isolated islets to glucose alone; 2) beta-cells in GLP-1R(-/-) pancreases underwent compensatory changes in response to the null mutation. To explore these possibilities, we studied islets from control GLP-IR(+/+) mice in the absence or presence of 1 pmol/l exendin (9-39)amide, a specific and potent GLP-1R antagonist. Exendin (9-39)amide (15-min exposure) reduced glucose-induced insulin secretion from both perifused and statically incubated GLP-1R(+/+) islets by 50% (P < 0.05), and reduced islet cAMP production in parallel (P < 0.001). Furthermore, GLP-1R(-/-) islets exhibited: 1) reduced cAMP accumulation in the presence of 20 mmol/l glucose (knockout islets versus control islets, 12 +/- 1 vs. 27 +/- 3 fmol x islet(-1) x 15 min(-1); P < 0.001) and exaggerated acceleration of cAMP production by 10 nmol/l glucose-dependent insulinotropic peptide (GIP) (increase over 20 mmol/l glucose by GIP in knockout islets versus control islets: 66 +/- 5 vs. 14 +/- 3 fmol x islet(-1) x 15 min(-1); P < 0.001); 2) increased mean cytosolic [Ca2+] ([Ca2+]c) at 7, 10, and 15 mmol/l glucose in knockout islets versus control islets; and 3) signs of asynchrony of [Ca2+]c oscillations between different islet subregions. In conclusion, disruption of GLP-1R signaling is associated with reduced basal but enhanced GIP-stimulated cAMP production and abnormalities in basal and glucose-stimulated [Ca2+]c. These abnormalities suggest that GLP-1R signaling is an essential upstream component of multiple beta-cell signaling pathways.
Role of angiotensin II in glucose-induced inhibition of mesangial matrix degradation.
Authors: Singh R , Alavi N , Singh A K , Leehey D J
Published: March 2007

Accumulation of mesangial matrix in diabetic nephropathy is caused by increased synthesis and decreased degradation. We have previously demonstrated that incubation in high-glucose medium decreases mesangial cell collagenase activity (Diabetes 44:929-935, 1995). Because angiotensin II (AII) is involved in the pathogenesis of diabetic nephropathy, the present studies were performed to determine if AII mediates glucose-induced 1) inhibition of mesangial collagenase activity, 2) mesangial matrix accumulation, and 3) in-crease in transforming growth factor (TGF)-beta1 secretion in mesangial cells. The direct effect of high glucose on AII generation in mesangial cells was also determined. Primary mesangial cells from normal Sprague-Dawley rats were used in all studies. Collagenase activity in cell medium was determined using three methods: 1) zymography; 2) quantitative assay using fluoresceinated gelatin as substrate; and 3) a new enzyme-linked immunosorbent assay (ELISA) that specifically measures 72-kDa collagenase (MMP-2), the principal collagenase synthesized by mesangial cells. Matrix accumulation was estimated by immunoperoxidase assay on cell layers using anti-glomerular basement membrane (GBM) antibodies. TGF-beta1 and AII levels were determined by ELISA. Exposure of mesangial cells to 30 mmol/l glucose (high glucose) vs. 5 mmol/glucose (normal glucose) for 5 days resulted in a significant decrease in collagenase activity (25%) that was normalized by 10(-4) mol/l losartan, a type 1 angiotensin II (AT1) receptor antagonist. High glucose increased anti-GBM binding compared with normal glucose; this effect of glucose was reversed by losartan. Incubation of cells with 30 mmol/l glucose increased total TGF-beta1 secretion, which was also normalized by losartan. Addition of AII (10(-6) mol/l) for 24 h to the culture medium inhibited collagenase activity by 33%; losartan (10(-4) mol/l) blocked this inhibition of enzyme activity. Also, AII decreased collagenase (MMP-2) levels but stimulated TGF-beta1 secretion in mesangial cells. Finally, glucose increased mesangial AII generation in a concentration-dependent manner, with incubation in 30 mmol/l glucose increasing AII by 25% compared with 5 mmol/l glucose. We conclude that glucose increases AII production by mesangial cells, which results in stimulation of TGF-beta1 secretion, decreased matrix degradation, and increased matrix accumulation. These effects of AII are mediated by the AT1 receptor.
Low phagocytic activity of resident peritoneal macrophages in diabetic mice: relevance to the formation of advanced glycation end products.
Authors: Liu B F , Miyata S , Kojima H , Uriuhara A , Kusunoki H , Suzuki K , Kasuga M
Published: March 2007

Formation of advanced glycation end products (AGEs) is accelerated in diabetic subjects along with hyperglycemia. Although several lines of evidence indicate that AGEs stimulate macrophages to secrete several cytokines and growth factors, little is known about the effect of AGEs on the primary function of macrophages, such as phagocytosis. On the other hand, impairment of the phagocytic function of monocytes/macrophages is suggested to contribute to the low resistance to infection in diabetic subjects. In the present study, we examined the effect of AGEs on the phagocytic function of macrophages. Using flow cytometric analysis of mouse resident peritoneal macrophages, we showed that AGEs suppress phagocytosis of fluorescent microspheres by cultured macrophages. In addition, experiments using streptozotocin-induced diabetic mice demonstrated a significant decrease in the phagocytic activity of resident peritoneal macrophages 12 weeks after induction of diabetes compared with age-matched control mice. The phagocytic activity of peritoneal macrophages correlated inversely with AGE content in the adjacent peritoneal tissue. Furthermore, reduced phagocytic activity of macrophages was associated with a reduction in intracellular ATP content. Because phagocytosis is an important component of the defense system, suppression of such activity by AGEs may explain, at least in part, the increased susceptibility of diabetic patients to infection.
Hypothalamic orexin expression: modulation by blood glucose and feeding.
Authors: Cai X J , Widdowson P S , Harrold J , Wilson S , Buckingham R E , Arch J R , Tadayyon M , Clapham J C , Wilding J , Williams G
Published: March 2007

Orexins (hypocretins), novel peptides expressed in specific neurons of the lateral hypothalamic area (LHA), stimulate feeding when injected intracerebroventricularly. We investigated their role in feeding in the rat by measuring hypothalamic prepro-orexin mRNA levels under contrasting conditions of increased hunger. Prepro-orexin mRNA levels increased significantly after 48 h of fasting (by 90-170%; P < 0.05) and after acute (6 h) hypoglycemia when food was withheld (by 90%; P < 0.02). By contrast, levels were unchanged during chronic food restriction, streptozotocin-induced diabetes, hypoglycemia when food was available, voluntary overconsumption of palatable food, or glucoprivation induced by systemic 2-deoxy-D-glucose. Orexin expression was not obviously related to changes in body weight, insulin, or leptin, but was stimulated under conditions of low plasma glucose in the absence of food. Orexins may participate in the short-term regulation of energy homeostasis by initiating feeding in response to falls in glucose and terminating it after food ingestion. The LHA is known to contain neurons that are stimulated by falls in circulating glucose but inhibited by feeding-related signals from the viscera; orexin neurons may correspond to this neuronal population.