Physical activity patterns in type 1 diabetes in Spain: The SED1 study.

AIMS: To describe the physical activity (PA) frequency and intensity in the Spanish type 1 diabetes mellitus (T1D) population and its association with their glycemic control. METHODS: A cross-sectional observational study was carried out in 75 Spanish public hospitals (the SED1 study). T1D patients over 14years of age self-completed the International Physical Activity Questionnaire (IPAQ) to determine their level of exercise. The relationship between PA frequency and intensity in T1D patients and glycemic control and the diabetes therapeutic education received were analyzed. RESULTS: A total of 592 patients were evaluable. A 6.8% of the sample performed light PA, 20.9% moderate and 72.3% vigorous. Estimated PA presented a high inter-individual variability. Men consumed more energy (METS) than women, these differences being more noticeable in vigorous METS (2865.80 in men vs 1352.12 in women). Women invested more min/week in the domestic and garden area (639.03 vs 344.39, p = 0,022). A correlation between glycemic control and the METs was not observed. CONCLUSIONS: The Spanish T1D population performed PA in a higher frequency and intensity than the general population. A relationship between PA and glycemic control couldn´t be shown. However, limitations of the study should be kept in mind to discard a long-term positive influence.

miR-10b and miR-223-3p in serum microvesicles signal progression from prediabetes to type 2 diabetes.

PURPOSE: Type 2 diabetes frequently remains undiagnosed for years, whereas early detection of affected individuals would facilitate the implementation of timely and cost-effective therapies, hence decreasing morbidity. With the intention of identifying novel diagnostic biomarkers, we characterized the miRNA profile of microvesicles isolated from retroactive serum samples of normoglycemic individuals and two groups of subjects with prediabetes that in the following 4 years either progressed to overt diabetes or remained stable. METHODS: We profiled miRNAs in serum microvesicles of a selected group of control and prediabetic individuals participating in the PREDAPS cohort study. Half of the subjects with prediabetes were diagnosed with diabetes during the 4 years of follow-up, while the glycemic status of the other half remained unchanged. RESULTS: We identified two miRNAs, miR-10b and miR-223-3p, which target components of the insulin signaling pathway and whose ratio discriminates between these two subgroups of prediabetic individuals at a stage at which other features, including glycemia, are less proficient at separating them. In global, the profile of miRNAs in microvesicles of prediabetic subjects primed to progress to overt diabetes was more similar to that of diabetic patients than the profile of prediabetic subjects who did not progress. CONCLUSION: We have identified a miRNA signature in serum microvesicles that can be used as a new screening biomarker to identify subjects with prediabetes at high risk of developing diabetes, hence allowing the implementation of earlier, and probably more effective, therapeutic interventions.

Carbohydrate Management in Athletes with Type 1 Diabetes in a 10 km Run Competition.

The aim of this study was to identify the real consumption of CHO during a 10 km competitive run, to compare data with the recommended quantities according to current guidelines, and to analyse the clinical events associated with these different amounts. Protocol 1: observational study including 31 athletes with T1D and 127 athletes without diabetes, comparing data taken from dietary records of CHO intake on the competition day. Protocol 2: single-blind randomized trial in 18 athletes with T1D, testing a pre-exercise CHO supplement of 0.7 g CHO·kg(- 1) (n=10) or 0.35 g CHO·kg(- 1) (n=8). The results showed that T1D athletes consumed a lower quantity of CHO than athletes without diabetes at their usual breakfast and during the meal taken<1 h after the competition, but no differences were found in the supplement taken before the competition. In the randomized study, athletes consuming the higher dose of CHO (0.7 g CHO·kg(- 1)) showed increased glycemic levels, comparing with the lower dose (0.35 g CHO·kg(- 1)). In conclusion, athletes with T1D seem to increase CHO intake prior to the competition consuming similar amounts to those athletes without diabetes, but consuming smaller quantities of CHO than the recommended amounts. This appears to induce a more stable glycemic response, in comparison with supplements with high-CHO content.

Pancreatic polypeptide regulates glucagon release through PPYR1 receptors expressed in mouse and human alpha-cells.

BACKGROUND: Plasma levels of pancreatic polypeptide (PP) rise upon food intake. Although other pancreatic islet hormones, such as insulin and glucagon, have been extensively investigated, PP secretion and actions are still poorly understood. METHODS: The release of PP upon glucose stimulation and the effects of PP on glucagon and insulin secretion were analyzed in isolated pancreatic islets. Expression of PP receptor (PPYR1) was investigated by immunoblotting, quantitative RT-PCR on sorted pancreatic islet cells, and immunohistochemistry. RESULTS: In isolated mouse pancreatic islets, glucose stimulation increased PP release, while insulin secretion was up and glucagon release was down. Direct exposure of islets to PP inhibited glucagon release. In mouse islets, PPYR1 protein was observed by immunoblotting and quantitative RT-PCR revealed PPYR1 expression in the FACS-enriched glucagon alpha-cell fraction. Immunohistochemistry on pancreatic sections showed the presence of PPYR1 in alpha-cells of both mouse and human islets, while the receptor was absent in other islet cell types and exocrine pancreas. CONCLUSIONS: Glucose stimulates PP secretion and PP inhibits glucagon release in mouse pancreatic islets. PP receptors are present in alpha-cells of mouse and human pancreatic islets. GENERAL SIGNIFICANCE: These data demonstrate glucose-regulated secretion of PP and its effects on glucagon release through PPYR1 receptors expressed by alpha-cells.

Hyperglycemia following recovery from hypoglycemia worsens endothelial damage and thrombosis activation in type 1 diabetes and in healthy controls.

BACKGROUND AND AIMS: Hypoglycemia produces thrombosis activation, but little attention has been paid to the effects of hyperglycemia following recovery from hypoglycemia on thrombosis activation. METHODS AND RESULTS: In both twenty-two healthy subjects and twenty-one matched persons with type 1 diabetes, recovery from a 2-h induced hypoglycemia was obtained by reaching normo-glycemia or hyperglycemia for another 2 h. After this, normal glycemia was maintained for the following 6 h. Hyperglycemia after hypoglycemia was also repeated with the concomitant infusion of vitamin C. In both controls and people with diabetes, the recovery with normo-glycemia was accompanied by a significant improvement of Von Willebrand factor (vWF), prothrombin fragment 1 + 2 (F1 + 2), thrombin-antithrombin III-complexes (TAT), P-selectin, plasminogen activator inhibitor-1 (PAI-1), nitrotyrosine and 8-iso-prostaglandin F2α (8-iso-PGF2α) (p < 0.01 vs hypoglycemia for all the parameters), all directly affected by hypoglycemia itself (p < 0.01 vs baseline for all the parameters). On the contrary, the recovery with hyperglycemia after hypoglycemia worsens all these parameters (p < 0.01 vs normoglycemia for all the parameters), an effect persisting even after the additional 6 h of normo-glycemia. The effect of hyperglycemia following hypoglycemia was partially counterbalanced when vitamin C was infused (p < 0.01 vs hyperglycemia alone for all the parameters), suggesting that hyperglycemia following hypoglycemia may activate thrombosis through the oxidative stress production. CONCLUSION: This study shows that, in type 1 diabetes as well as in controls, the way in which recovery from hypoglycemia takes place could play an important role in favoring the activation of thrombosis and oxidative stress, widely recognized cardiovascular risk factors.

Glucose regulation of a cell cycle gene module is selectively lost in mouse pancreatic islets during ageing.

AIMS/HYPOTHESIS: Transcriptional networks in beta cells are modulated by extracellular signals such as glucose, thereby ensuring beta cell adaptation to systemic insulin demands. Ageing is a main risk factor for type 2 diabetes and has been associated with perturbed expression of genes essential for beta cell function. We aimed to uncover glucose-dependent gene modules in mouse pancreatic islets and investigate how this regulation is affected by ageing. METHODS: Global gene expression was assessed in pancreatic islets from young and aged wild-type and Cdkn2a (Ink4a/Arf)-deficient mice exposed to different glucose concentrations. Gene modules were identified by gene ontology and gene set enrichment analysis. RESULTS: Gene expression profiling revealed that variations in glucose levels have a widespread and highly dynamic impact on the islet transcriptome. Stimulatory glucose levels induced the expression of highly beta cell-selective genes and repressed the expression of ubiquitous genes involved in stress and antiproliferative responses, and in organelle biogenesis. Interestingly, a module comprising cell cycle genes was significantly induced between non-stimulatory and stimulatory glucose concentrations. Unexpectedly, glucose regulation of gene expression was broadly maintained in islets from old mice. However, glucose induction of mitotic genes was selectively lost in aged islets and was not even restored in the absence of the cell cycle inhibitors p16(INK4a) and p19(ARF), which have been implicated in the restricted proliferative capacity of beta cells with advanced age. CONCLUSIONS/INTERPRETATION: Glucose-dependent transcriptional networks in islets are globally conserved during ageing, with the exception of the ability of stimulatory glucose levels to induce a cell cycle gene module.

Amylin exerts osteogenic actions with different efficacy depending on the diabetic status.

Amylin displays osteogenic features, but its role in diabetic osteopenia is unclear. We examined the possible osteogenic action of amylin infusion for 3days into fructose-induced insulin-resistant (IR) and streptozotocin-induced type 2 diabetic (T2D) and normal (N) rats. Amylin failed to affect glycaemia or parathyroid hormone levels in any group, but reduced hyperinsulinemia in IR rats. In N rats, amylin increased bone formation rate and reduced osteoclast surface and erosive surface in the femoral metaphysis, and increased osteoprotegerin (OPG)/receptor activator of NFκB ligand (RANKL) mRNA ratio in the tibia. In T2D rats, amylin normalized trabecular structure parameters and increased osteoblast number and osteocalcin (OC) expression in long bones. In contrast, in IR rats, no apparent osteogenic effect of amylin in the femur was observed, although both OC and OPG/RANKL ratio were increased in the tibia. Our findings demonstrate a different osteogenic efficacy of amylin in two diabetic settings.

Amylin effect in extrapancreatic tissues participating in glucose homeostasis, in normal, insulin-resistant and type 2 diabetic state.

Amylin is co-secreted with insulin, responds to the same stimuli, is anorectic, lowers body weight by reducing fat mass, and is proposed for diabetes treatment. We examined the effect of a 3-day constant infusion of close to physiological doses of amylin in Wistar rats, on glucotransporter expression, glycogen content (G), glycogen synthase a activity (GSa) and glucose transport (GT), in liver, muscle and fat from insulin resistant (IR) and type 2 diabetic (T2D) models, compared to normal (N) animals; plasma glucose and insulin were measured. Plasma insulin in IR was higher than in N or T2D, and amylin normalized the value. In both, IR and T2D, liver G was lower than normal, accompanied by GLUT-2, mRNA and protein, higher and lower, respectively, than in N; amylin normalized G in both groups, without changes in GLUT-2, except for an mRNA increase in T2D. In IR and T2D, muscle GSa was reduced, together with respective over- and under-GLUT-4 expression; amylin induced only a trend toward GSa normalization in both groups. In isolated adipocytes, GT and GLUT-4 in IR and T2D were lower and higher, respectively, than in N; after amylin, not only GT was normalized in both groups but also the response to insulin was much more pronounced, including that in N, without major changes in GLUT-4. This suggests that the beneficial effect of amylin in states running with altered glucose homeostasis could occur by partially acting on the hexose metabolism of the liver and mainly on that of the adipose tissue.

One year follow-up in a group of half-marathon runners with type-1 diabetes treated with insulin analogues.

AIM: The objective was to describe the strategies that type-1 diabetic runners treated with insulin analogues apply in a half-marathon race and the changes after a year of experience participating in long-distance athletic competitions. METHODS: Fourteen male amateur athletes with type-1 diabetes treated with insulin analogues, participating in two consecutive editions of the same half-marathon were assessed. Data about insulin dosage and carbohydrate intake from their regular daily training and from the two half-marathons were compared. Capillary glycemic values from throughout the competition and in the following 24 h period were monitored and the frequency of hypoglycemia and glucose fluctuations was compared, using MAGE method. RESULTS: During the half-marathon day, athletes reduced total insulin doses a 18.3% in 2006 and 14.2% in 2007, with a reduction of basal insulin (23.3% in 2006 vs 20.4% in 2007, P<0.05) and of short-insulin at breakfast prior to the competition (31.7% in 2006 vs 15.3% in 2007, P<0.001). Carbohydrate consumption during competition was higher in second edition (49.0±16.4 g vs 59.1±11.2 g, P<0.05). Glycaemic excursions, assessed by MAGE, were higher in the first edition (108.1±47.3 mg/dL vs 62.2±45.6 mg/dL, P<0.05). CONCLUSION: Type-1 diabetes athletes, treated with insulin analogues, participating in half-marathon competitions exhibited less insulin reduction in comparison with traditional guidelines and they needed to take an important quantity of carbohydrate supplements to avoid hypoglycemia during and after the competition. We suggest reconsidering traditional recommendations of insulin therapy and carbohydrate supplementation (amount and timing) to athletes treated with current insulin analogues participating in long-distance competitions.

Role of iduronate-2-sulfatase in glucose-stimulated insulin secretion by activation of exocytosis.

Iduronate-2-sulfatase (IDS) is a lysosomal enzyme expressed in pancreatic islets responsible for the degradation of proteoglycans such as perlecan and dermatan sulfate. Previous findings of our group demonstrated the involvement of IDS in the normal pathway of lysosomal degradation of secretory peptides, suggesting a role of this enzyme in beta-cell secretory functionality. The present study was undertaken to characterize the effect of IDS overexpression on insulin release. INS1E cells were transiently transfected with a construct encoding human IDS (hIDS). hIDS overexpression was associated with a gain of function detected by a reduction in heparan sulfate content. hIDS potentiated the glucose-stimulated insulin secretory response compared with controls (61%) with no changes in insulin mRNA levels or insulin peptide content. Results on quantification of the exocytotic process showed a significant increase in hIDS-transfected cells compared with controls. Furthermore, ultramorphological analysis demonstrated an increase in the number of granules in the immediate vicinity of the plasma membrane in hIDS-transfected cells and a decrease in total vesicles per square micrometer. hIDS overexpression induced phosphorylation of protein kinase C (PKC) alpha and its newly myristoylated alanine-rich C kinase substrate, MARCKS. We conclude that IDS has a role in glucose-stimulated insulin secretion via a mechanism that involves the activation of exocytosis through phosphorylation of PKCalpha and MARCKS.

Calcium elevation in mouse pancreatic beta cells evoked by extracellular human islet amyloid polypeptide involves activation of the mechanosensitive ion channel TRPV4.

AIMS/HYPOTHESIS: To investigate the mechanism by which human islet amyloid polypeptide (hIAPP) fibril formation results in calcium influx across the plasma membrane of pancreatic beta cells, and its association with apoptosis. METHODS: Cytoplasmic intracellular calcium concentrations ([Ca(2+)](i)) were monitored for 2 h as the 340/380 nm fluorescence ratio in fura-2 loaded cells of the MIN6 mouse pancreatic beta cell line. Cell morphology was evaluated by transmission electron microscopy, and viability by FACS. RESULTS: hIAPP (10 micromol/l) increased [Ca(2+)](i) in 21% of MIN6 cells in standard buffer, and in 8% of cells in Na(+)-free buffer. Transient receptor potential (TRP) channel inhibitors (gadolinium and ruthenium red) prevented the [Ca(2+)](i) rise under both conditions, whilst nifedipine was only effective in the presence of Na(+). hIAPP increased apoptosis in both insulinoma cells and islets in primary culture, and cell viability was partially rescued by ruthenium red (p < 0.001). By RT-PCR, we detected expression of the mechanosensitive TRP cation channel subfamily V member 4 (Trpv4) in MIN6 cells and mouse pancreas. Small interference RNA against Trpv4 prevented hIAPP-induced [Ca(2+)](i) rises, decreased hIAPP-triggered expression of the endoplasmic reticulum (ER) stress response, and reduced hIAPP-triggered cell death by 50% (p < 0.05). CONCLUSIONS/INTERPRETATION: Alterations in [Ca(2+)](i) play a key role in hIAPP-induced beta cell cytotoxicity. By electron microscopy, we detected extracellular hIAPP aggregates adjacent to irregular invaginated regions of the plasma membrane. We propose that TRPV4 channels may sense physical changes in the plasma membrane induced by hIAPP aggregation, enabling Ca(2+) entry, membrane depolarisation and activation of L-type Ca(2+) channels. Decreasing the activity of TRPV4 prevented hIAPP-induced [Ca(2+)](i) changes, reduced hIAPP-triggered ER stress and improved cell viability.

GUIDE study: double-blind comparison of once-daily gliclazide MR and glimepiride in type 2 diabetic patients.

BACKGROUND: Progressive beta-cell failure is a characteristic feature of type 2 diabetes; consequently, beta-cell secretagogues are useful for achieving sufficient glycaemic control. The European GUIDE study is the first large-scale head-to-head comparison of two sulphonylureas designed for once-daily administration used under conditions of everyday clinical practice. DESIGN: Eight hundred and forty-five type 2 diabetic patients were randomized to either gliclazide modified release (MR) 30-120 mg daily or glimepiride 1-6 mg daily as monotherapy or in combination with their current treatment (metformin or an alpha-glucosidase inhibitor) according to a double-blind, 27-week, parallel-group design. Efficacy was evaluated by HbA1c and safety by hypoglycaemic episodes using the European Agency definition. RESULTS: HbA1c decreased similarly in both groups from 8.4% to 7.2% on gliclazide MR and from 8.2% to 7.2% on glimepiride. Approximately 50% of the patients achieved HbA1c levels less than 7%, and 25% less than 6.5%. The mean difference between groups of the final HbA1c was -0.06% (noninferiority test P < 0.0001). No hypoglycaemia requiring external assistance occurred. Hypoglycaemia with blood glucose level < 3 mmol L(-1) occurred significantly less frequently (P = 0.003) with gliclazide MR (3.7% of patients) compared with glimepiride (8.9% of patients). The distribution of the sulphonylurea doses was similar in both groups. CONCLUSIONS: This study provides new insights into therapeutic strategies using sulphonylureas. It shows that gliclazide MR is at least as effective as glimepiride, either as monotherapy or in combination. The safety of gliclazide MR was significantly better, demonstrating approximately 50% fewer confirmed hypoglycaemic episodes in comparison with glimepiride.

Mutation at position -132 in the islet amyloid polypeptide ( IAPP) gene promoter enhances basal transcriptional activity through a new CRE-like binding site.

AIMS/HYPOTHESIS: Mutations in the islet amyloid polypeptide ( IAPP) gene may play a potential role in the abnormal regulation or expression of the peptide. The aim of this study was to determine the functional role of the -132 G/A mutation reported in the promoter region of the IAPP gene in a population of Spanish Type 2 diabetic patients. METHODS: We investigated the transcriptional activity using MIN6 cells and luciferase reporter plasmids in several culture conditions. Key regulatory elements of the IAPP promoter region were also analysed by electrophoretic mobility shift assays (EMSA). RESULTS: The mutant construct doubled IAPP transcriptional activity ( p<0.001). Both constructs showed severely reduced promoter activity (four-fold decrease) in the presence of verapamil and diazoxide. In contrast, IAPP promoter activity was doubled after incubation with forskolin or dexamethasone, regardless of the glucose concentrations in the culture media. EMSA revealed that the -132 G/A mutation increased the binding affinity through two DNA-protein complexes. In addition, a cAMP-responsive element binding protein (CREB) was identified by super-shift EMSA. CONCLUSIONS/INTERPRETATION: Our studies show that the wild-type and the mutant constructs are regulated in a similar pattern under all conditions, strongly indicating that the -132 G/A mutation increases basal but not inducible transcription. These results may be explained by new binding to the mutant region through CREB and other transcription factors not yet identified.

Identification of iduronate-2-sulfatase in mouse pancreatic islets.

The lysosomal enzyme iduronate-2-sulfatase (IDS) is expressed in pancreatic islets and is responsible for degradation of proteoglycans, such as perlecan and dermatan sulfate. To determine the role of IDS in islets, expression and regulation of the gene and localization of the enzyme were investigated in mouse pancreatic islets and clonal cells. The Ids gene was expressed in mouse islets and beta- and alpha-clonal cells, in which it was localized intracellularly in lysosomes. The transcriptional expression of Ids in mouse islets increased with glucose in a dose-dependent manner (11.5, 40.2, 88, and 179% at 5.5, 11.1, 16.7, and 24.4 mM, respectively, P < 0.01 for 16.7 and 24.4 mM glucose vs. 3 mM glucose). This increase was not produced by glyceraldehyde (1 mM) or 6-deoxyglucose (21.4 mM) and was blocked by the addition of mannoheptulose (21.4 mM). Neither insulin content nor secretory response to glucose (16.7 mM) was altered in mouse islets infected with lentiviral constructs carrying the IDS gene in sense orientation. Furthermore, no decrease in islet cell viability was observed in mouse islets carrying lentiviral contracts compared with controls. However, insulin content was reduced (35% vs. controls, P < 0.001) in islets infected with IDS antisense construct, while the secretory response of those islets to glucose was maintained. Inhibition of IDS by antisense infection led to an increase in lysosomal size and a high rate of insulin granule degradation via the crinophagic route in pancreatic beta-cells. We conclude that IDS is localized in lysosomes in pancreatic islet cells and expression is regulated by glucose. IDS has a potential role in the normal pathway of lysosomal degradation of secretory peptides and is likely to be essential to maintain pancreatic beta-cell function.

Polymorphism in intron 2 of islet amyloid polypeptide gene is associated with lower low-density lipoprotein cholesterol in nondiabetic subjects and in type 2 diabetic patients.

The aim of this study was to investigate the presence of mutations in the islet amyloid polypeptide (IAPP) gene in a Spanish population with type 2 diabetes and gestational diabetes mellitus (GDM). Using polymerase chain reaction single-stranded conformation polymorphism, we examined the coding region and the 5'-untranslated region (UTR) of the IAPP gene in 177 unrelated type 2 diabetic patients, 110 healthy control subjects, 38 women with GDM, and 38 gestational control subjects. Mutations were confirmed by DNA sequencing. A heterozygous C-to-A nucleotide substitution at +79 bp in intron 2 of the IAPP gene was detected. The frequencies of the +79-bp polymorphism (A allele) were 6.8% in type 2 diabetic patients, 7.7% in nondiabetic control subjects, 11.8% in women with GDM, and 9.2% in gestational control subjects. No AA genotypes were detected. Nondiabetic subjects and patients with type 2 diabetes bearing the CA genotype had lower low-density lipoprotein (LDL) cholesterol levels than subjects bearing wild genotype. Multivariate logistic regression analysis showed an independent association (p < 0.001; odds ratio: 0.33; 95% confidence interval: 0.17-0.63). We did not detect any sequence variant within exons 1 or 2. One diabetic patient was heterozygous for a silent mutation at codon 31 of exon 3 (Asn31 AAC --> AAT). Our findings indicate that the presence of the +79-bp polymorphism of the IAPP gene in nondiabetic subjects and in patients with type 2 diabetes is associated with lower levels of LDL cholesterol. Furthermore, abnormalities of the coding regions or the 5'-UTR of the IAPP gene are not associated with type 2 diabetes or GDM in the Spanish population.

What is the relevance of the HOPE study in general practice?

The unique findings from the HOPE (Heart Outcomes Prevention Evaluation) study strongly support extending the use of the angiotensin-converting enzyme (ACE) inhibitor ramipril as a preventive agent for patients at high risk of cardiovascular events with normal left ventricular function. In addition, ramipril provides significant benefit in diabetic patients. These findings will impact on how ramipril is used in primary care, where ACE inhibitors are currently underprescribed. Patients reflecting the inclusion criteria of the HOPE study should be considered as suitable candidates for long-term ramipril therapy as an addition to their existing drug regimen. Screening should include control of kidney function (by serum creatinine), particularly within the first two weeks of treatment, in addition to regular monitoring of serum potassium. However, the HOPE study shows that ramipril is well tolerated at high doses and over a long treatment period. The effectiveness of therapy should also be regularly reviewed and dose adjustments made where necessary. If concern remains, referral to a specialist--a cardiologist or a diabetologist--may ultimately be necessary.

High glucose concentration favors the selective secretion of islet amyloid polypeptide through a constitutive secretory pathway in human pancreatic islets.

We studied the contribution of the constitutive and the regulated pathways to the total secretion of islet amyloid polypeptide (IAPP) in human pancreatic islets after prolonged culture at either 5.5 or 24.4 mM glucose. In islets cultured in low concentrations of glucose, the secretion of IAPP in response to glucose was unaffected by brefeldin A (BFA) and completely blocked by ethyleneglycoltetraacetic acid. In islets cultured in high glucose concentrations, it was strongly inhibited by both agents. BFA had no effect on the glucose-induced insulin secretion. The determination of the islet peptide contents and the mRNA levels revealed a several-fold increase in the IAPP/insulin molar ratio of islets cultured in high glucose concentrations. Thus, prolonged exposure of human islets to high concentrations of glucose results in an increase in the synthesis of IAPP with respect to insulin. As a result, the release of IAPP through a mechanism sensitive to BFA is favored. These data support the hypothesis that IAPP and insulin are regulated in a noncoordinated way in human pancreatic islets.

Identification and functional analysis of mutations in FAD-binding domain of mitochondrial glycerophosphate dehydrogenase in caucasian patients with type 2 diabetes mellitus.

Ca2+-responsive mitochondrial FAD-linked glycerophosphate dehydrogenase (mGPDH) is a key component of the pancreatic beta-cell glucose-sensing device. The purpose of this study was to examine the association of mutations in the cDNA coding for the FAD-binding domain of mGPDH and to explore the functional consequences of these mutations in vitro. To investigate this association in type 2 diabetes mellitus, we studied a cohort of 168 patients with type 2 diabetes and 179 glucose-tolerant control subjects of Spanish Caucasian origin by single-stranded conformational polymorphism analysis. In vitro site-directed mutagenesis was performed in the mGPDH cDNA sequence to reproduce those mutations that produce amino acid changes in a patient with type 2 diabetes. We detected mutations in the mGPDH FAD-binding domain in a single patient, resulting in a Gly to Arg amino acid change at positions 77, 78, and 81 and a Thr to Pro at position 90. In vitro expression of the mutated constructs in Xenopus oocytes resulted in a significantly lower enzymatic activity than in cells expressing the wild-type form of the enzyme. Our results indicate that although mutations in the mGPDH gene do not appear to have a major role in type 2 diabetes mellitus, the reduction in mGPDH enzymatic activity associated with the newly described mGPDH mutations suggests that they may contribute to the disease in some patients.