Proinsulin Levels Research Articles

Intact proinsulin level is associated with insulin resistance but not insulin secretory capacity in subjects with abnormal glucose tolerance

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Obesity and Cardiovascular Risk: Variations in Visfatin Gene Can Modify the Obesity Associated Cardiovascular Risk. Results from the Segovia Population Based-Study. Spain.

ObjectivesOur aim was to investigate if genetic variations in the visfatin gene (SNPs rs7789066/ rs11977021/rs4730153) could modify the cardiovascular-risk (CV-risk) despite the metabolic phenotype (obesity and glucose tolerance). In addition, we investigated the relationship between insulin sensitivity and variations in visfatin gene.Material and MethodsA population-based study in rural and urban areas of the Province of Segovia, Spain, was carried out in the period of 2001–2003 years. A total of 587 individuals were included, 25.4% subjects were defined as obese (BMI ≥30 Kg/m2).ResultsPlasma visfatin levels were significantly higher in obese subjects with DM2 than in other categories of glucose tolerance. The genotype AA of the rs4730153 SNP was significantly associated with fasting glucose, fasting insulin and HOMA-IR (Homeostasis model assessment-insulin resistance) after adjustment for gender, age, BMI and waist circumference.The obese individuals carrying the CC genotype of the rs11977021 SNP showed higher circulating levels of fasting proinsulin after adjustment for the same variables.The genotype AA of the rs4730153 SNP seems to be protective from CV-risk either estimated by Framingham or SCORE charts in general population; and in obese and non-obese individuals. No associations with CV-risk were observed for other studied SNPs (rs11977021/rs7789066).ConclusionsIn summary, this is the first study which concludes that the genotype AA of the rs4730153 SNP appear to protect against CV-risk in obese and non–obese individuals, estimated by Framingham and SCORE charts. Our results confirm that the different polymorphisms in the visfatin gene might be influencing the glucose homeostasis in obese individuals.

RNA-sequencing of WFS1-deficient pancreatic islets.

Wolfram syndrome, an autosomal recessive disorder characterized by juvenile‐onset diabetes mellitus and optic atrophy, is caused by mutations in the WFS1 gene. WFS1 encodes an endoplasmic reticulum resident transmembrane protein. The Wfs1‐null mice exhibit progressive insulin deficiency and diabetes. The aim of this study was to describe the insulin secretion and transcriptome of pancreatic islets in WFS1‐deficient mice. WFS1‐deficient (Wfs1KO) mice had considerably less pancreatic islets than heterozygous (Wfs1HZ) or wild‐type (WT) mice. Wfs1KO pancreatic islets secreted less insulin after incubation in 2 and 10 mmol/L glucose and with tolbutamide solution compared to WT and Wfs1HZ islets, but not after stimulation with 20 mmol/L glucose. Differences in proinsulin amount were not statistically significant although there was a trend that Wfs1KO had an increased level of proinsulin. After incubation in 2 mmol/L glucose solution the proinsulin/insulin ratio in Wfs1KO was significantly higher than that of WT and Wfs1HZ. RNA‐seq from pancreatic islets found melastatin‐related transient receptor potential subfamily member 5 protein gene (Trpm5) to be downregulated in WFS1‐deficient mice. Functional annotation of RNA sequencing results showed that WFS1 deficiency influenced significantly the pathways related to tissue morphology, endocrine system development and function, molecular transport network.

Spontaneous hypoglycemia: diagnostic evaluation and management

Spontaneous hypoglycemia is a puzzling clinical problem and an important reason for referral to endocrinologists. Several clinical conditions such as insulinomas, non-insulinoma pancreatogenous hypoglycemia syndrome, insulin autoimmune syndrome, postprandial hypoglycemia (reactive hypoglycemia), non-islet cell tumor hypoglycemia, primary adrenal insufficiency, hypopituitarism, and critical illness can be associated with spontaneous hypoglycemia. Rarely, in patients with mental health issues, factious hypoglycemia from extrinsic insulin use or ingestion of oral hypoglycemic agents can obfuscate the clinical picture for clinicians trying to identify an organic cause. In those presenting with Whipple's triad (symptoms±signs of hypoglycemia, low plasma glucose, and resolution symptoms±signs after hypoglycemia correction), a 72-h supervised fast test with measurement of plasma insulin, c-peptide, pro-insulin, and beta-hydroxybutyrate levels, coupled with plasma/urine sulphonylurea screen, forms the first step in diagnostic evaluation. A mixed meal test is preferable for those with predominantly postprandial symptoms. Additional non-invasive and/or invasive diagnostic evaluation is necessary if an organic hypoglycemic disorder is suspected. With the aid of a few brief clinical case scenarios, we discuss the diagnostic evaluation and management of spontaneous hypoglycemia through this comprehensive article.

Effect of Different Insulin Response Patterns During Oral Glucose Tolerance Test on Glycemia in Individuals with Normal Glucose Tolerance.

Research is still going on for detecting the earliest glucose homeostasis derangements in individuals, which is crucial for the prevention of glucose intolerance. This cross-sectional study analyzes different insulin response patterns during the oral glucose tolerance test (OGTT) and their implications on glycemia in normoglycemic individuals. The sample frame was the "Offspring of Individuals with Diabetes Study" database. All participants underwent OGTT. Blood samples were collected at 0, 30, 60, and 120 min for measurement of insulin, C-peptide, and proinsulin levels. Normal glucose tolerant individuals were selected for analysis. Four hundred fifty subjects (mean age, 25 years) were included and divided into two groups according to timing of plasma insulin peaking during OGTT: Group 1, peaking at 30 min; and Group 2, peaking at 60 or 120 min. Body mass index (BMI) and insulin resistance were comparable between the groups; however, Group 2 showed a significantly higher 60- and 120-min glucose level and lower disposition index. Based on the magnitude of the insulin levels, Group 1 was subdivided into Group N (normal pattern) and Group E (exaggerated pattern) with a 30-min insulin cutoff of 74 μU/mL (Group E, ≥74 μU/mL). Group 2 was subdivided into Group DL (delayed and limited pattern; 60-min insulin <73.0 μU/mL and 120-min insulin <80.0 μU/mL) and Group DE (delayed and exaggerated pattern; 60-min insulin ≥73.0 μU/mL or 120-min insulin ≥80.0 μU/mL). Group DE showed a significantly higher area under the curve (AUC) of glucose compared with the other groups and had a lower disposition index and high-density lipoprotein levels. Group DL had significantly lower insulin resistance and BMI compared with Group E but showed a similar AUC of glucose. A delayed insulin pattern was associated with higher postprandial glucose levels. Individuals with delayed and exaggerated insulin secretion may have a higher risk for glucose intolerance.

Jagn1 Is Induced in Response to ER Stress and Regulates Proinsulin Biosynthesis.

The Jagn1 protein was indentified in a SILAC proteomic screen of proteins that are increased in insulinoma cells expressing a folding-deficient proinsulin. Jagn1 mRNA was detected in primary rodent islets and in insulinoma cell lines and the levels were increased in response to ER stress. The function of Jagn1 was assessed in insulinoma cells by both knock-down and overexpression approaches. Knock-down of Jagn1 caused an increase in glucose-stimulated insulin secretion resulting from an increase in proinsulin biosynthesis. In contrast, overexpression of Jagn1 in insulinoma cells resulted in reduced cellular proinsulin and insulin levels. Our results identify a novel role for Jagn1 in regulating proinsulin biosynthesis in pancreatic β-cells. Under ER stress conditions Jagn1 is induced which might contribute to reducing proinsulin biosynthesis, in part by helping to relieve the protein folding load in the ER in an effort to restore ER homeostasis.

Hypoglycemic Syndrome without Hyperinsulinemia. A Diagnostic Challenge.

The most common cause of organic fasting hypoglycemia in adults is the presence of an insulin-producing pancreatic adenoma, but when high insulin levels are not found, the differential diagnosis is challenging. Misdiagnosis can lead to an unnecessary pancreatectomy. Insulin concentrations may be low in some cases despite a clinical history suggestive of insulinoma. In these cases, a proinsulinoma should be suspected, although the rarity of this condition requires an extensive workup before reaching a final diagnosis. We describe an unusual case of a 38-year-old man with a severe hypoglycemic syndrome due to a proinsulin-secreting pancreatic adenoma. Insulin was measured by the specific assay and suppressed under the lower detection limit during fasting hypoglycemia. Serum proinsulin and C-peptide levels were abnormally elevated, and further tests revealed an islet cell tumor. The tumor was surgically removed, relieving the fasting hypoglycemia. Histopathological study showed a conventional well-differentiated neuroendocrine tumor with high immunoreactivity against proinsulin and with lesser intensity against insulin. Interestingly, GS-9A8 antibody clone used for immunostaining proinsulin did not cross-react with human insulin or C-peptide, providing an unbiased picture of proinsulin secretion. The resolution of symptoms, the fall of proinsulin concentrations after tumor removal and the histopathology study confirmed the diagnosis of proinsulinoma.

Disproportionately Elevated Proinsulin Levels as an Early Indicator of β-Cell Dysfunction in Nondiabetic Offspring of Chinese Diabetic Patients.

Objective. To study the characteristics of β-cell dysfunction and insulin resistance (IR) in the first-degree relatives (FDRs) of T2DM in Chinese population and to examine the usefulness of proinsulin (PI) for evaluating β-cell dysfunction. Methods. 229 subjects of nondiabetic FDRs, 71 newly diagnosed T2DM, and 114 with normal glucose tolerance (NGT) but not FDRs (NGT-non-FDRs) were verified by a 2-hour oral glucose tolerance test. Specific insulin (SI) and PI were measured by highly sensitive ELISA. Results. Compared to NGT-non-FDRs, NGT-FDRs showed higher levels of fasting and 2-hour PI, fasting PI-to-SI ratio (FPI/SI), and HOMA-IR (p < 0.01). Meanwhile, fasting PI, FPI/SI, and HOMA-IR were increased steadily from NGT-FDRs to prediabetes-FDRs and were highest in T2DM group (p < 0.001), whereas a significant decrease in HOMA-B could be observed only in T2DM group. Moreover, a progressive deterioration of β-cell function in NGT-FDRs, prediabetes-FDRs, and T2DM could be identified by FPI/SI even after adjusting for HOMA-IR: relative to non-FDRs controls, mean FPI/SI levels were increased 1.5, 2.0, and 4.7-fold, respectively (all p < 0.01). Conclusions. β-cell dysfunction as assessed by disproportionate secretion of proinsulin and IR by HOMA (using specific insulin assay) already exist in FDRs of T2DM even with normal glucose status. Compared with HOMA-B, FPI/SI could detect β-cell failure in earlier stage of diabetes development.

An Okinawan-based Nordic diet improves anthropometry, metabolic control, and health-related quality of life in Scandinavian patients with type 2 diabetes: a pilot trial

BackgroundOur hypothesis was that a modified diet would improve blood glucose control with beneficial impact on weight management and overall health in established diabetes.ObjectiveThis prospective interventional study investigated the clinical effect of an Okinawan-based Nordic diet on anthropometry, metabolic control, and health-related quality of life (HRQoL) in Scandinavian type 2 diabetes patients.DesignFood was prepared and delivered to 30 type 2 diabetes patients. Clinical information along with data on HRQoL, blood samples, and urine samples were collected during 12 weeks of diet interventions, with follow-up 16 weeks after diet completion.ResultsAfter 12 weeks of dietary intervention, a reduction in body weight (7%) (p<0.001), body mass index (p<0.001), and waist circumference (7.0 cm) (p<0.001) was seen. Improved levels of proinsulin (p=0.005), insulin (p=0.011), and fasting plasma glucose (p<0.001) were found already after 2 weeks; these improved levels remained after 12 weeks when lowered levels of C-peptide (p=0.015), triglycerides (p=0.009), total cholesterol (p=0.001), and low-density lipoprotein-cholesterol (p=0.041) were also observed. Insulin resistance homeostasis model assessment for insulin resistance was lowered throughout the study, with a 20% reduction in hemoglobin A1c levels (p<0.001) at week 12, despite reduced anti-diabetes treatment. Lowered systolic blood pressure (9.6 mmHg) (p<0.001), diastolic blood pressure (2.7 mmHg) (p<0.001), and heart and respiratory rates (p<0.001) were accompanied by decreased cortisol levels (p=0.015) and improvement in HRQoL. At follow-up, increased levels of high-density lipoprotein-cholesterol were found (p=0.003).ConclusionThis interventional study demonstrates a considerable improvement of anthropometric and metabolic parameters and HRQoL in Scandinavian type 2 diabetes patients when introducing a modified Okinawan-based Nordic diet, independently of exercise or other interventions. Through these dietary changes, anti-diabetes treatment could be decreased or cancelled.

In Vitro Assessment of Human Islet Vulnerability to Instant Blood-Mediated Inflammatory Reaction (IBMIR) and Its Use to Demonstrate a Beneficial Effect of Tissue Culture.

Culture of human pancreatic islets is now routinely carried out prior to clinical islet allotransplantation, using conditions that have been developed empirically. One of the major causes of early islet destruction after transplantation is the process termed instant blood-mediated inflammatory reaction (IBMIR). The aim of this study was to develop in vitro methods to investigate IBMIR and apply them to the culture conditions used routinely in our human islet isolation laboratory. Freshly isolated or precultured (24 h, 48 h) human islets were incubated in either ABO-compatible allogeneic human blood or Hank's buffered salt solution (HBSS) for 1 h at 37°C. Tissue factor (TF) expression and leukocyte migration were assessed by light microscopy. TF was also quantified by ELISA. To assess β-cell function, glucose-stimulated insulin secretion (GSIS) assay was carried out. The extent of islet β-cell damage was quantified using a proinsulin assay. Islets cultured for 24 h had higher GSIS when compared to freshly isolated or 48-h precultured islets. Freshly isolated islets had significantly higher TF content than 24-h and 48-h precultured islets. Incubation of freshly isolated human islets in allogeneic human blood released 6.5-fold higher level of proinsulin in comparison to freshly isolated human islets in HBSS. The high level of proinsulin released was significantly attenuated when precultured islets (24 h or 48 h) were exposed to fresh blood. Histological examination of fresh islets in blood clot showed that some islets were fragmented, showing signs of extraislet insulin leakage and extensive neutrophil infiltration and necrosis. These features were markedly reduced when the islets were cultured for 24 h. These results suggest that our standard 24-h islet culture is markedly beneficial in attenuating IBMIR, as evidenced by increased GSIS, lower content of TF, decrease islet fragmentation, and proinsulin release.

Nesidioblastosis: A Rare Case of Post Prandial Hypoglycemia in a Patient With Gastric Bypass Surgery

A 46-year-old man with recurrent episodes of hypoglycemia for two-years admitted with recent worsening of symptoms that ranged from dizziness, diaphoresis and disorientation to seizures and loss of consciousness. His symptoms were mostly postprandial with low random home sugars (50-80 mg/dL) despite consuming sugary drinks and candies. History remarkable for Roux-en-Y gastric bypass (RYGB) surgery 5 years ago for obesity, anxiety disorder and daily alcohol use (40 g/day). Denied diabetes, use of diabetic medications or weight loss supplements. Unremarkable physical exam with normal mental status. Labs [Table 1] demonstrated elevated proinsulin and C-peptide levels with negative urine toxicology screen and sulfonylurea assay. CT scan of the head and abdomen were unremarkable. Gastroenterology (GI) was consulted for an evaluation with endoscopic ultrasound (EUS) to rule out insulinoma. Although insulinoma was the working diagnosis in-addition to other differential diagnoses as listed [Table 2], a negative monitored 72-hour fasting test [Fig. 1] without any symptomatic hypoglycemic episodes essentially ruled out insulinoma. Recurrent post-prandial hypoglycemia with neuroglycopenic symptoms in the setting of RYGB and endogenous hyperinsulinism with negative 72-hour fasting test suggested nesidioblastosis as the likely diagnosis. Our patient was managed with Diazoxide (3-8mg/kg/day divided into 3 doses) and, complex carbohydrates were added to his diet. His hypoglycemic symptoms improved at subsequent follow-ups. Nesidioblastosis is rare in adults and, seen in patients who had undergone gastric bypass surgery with etiology linked to persistent hyper-secretion of glucagon-likepeptide-1 causing beta cells hypertrophy. Post-prandial neuroglycopenia is a classic manifestation but can be challenging to diagnose due to its rarity and the difficulty to localize on imaging. Selective arterial calcium stimulation and venous sampling can confirm the diagnosis, invasively [1-3]. Often patients are referred to GI for evaluation with EUS, but with RYGB, EUS is technically not feasible to evaluate pancreas due to the altered anatomy. However, a certain diagnosis can be made based on the history, labs [Table 1] and a negative 72-hour fasting test without the need for invasive tests. With increasing prevalence of obesity and gastric bypass surgeries, we as gastroenterologists shall expect to see more of this rare, but interesting metabolic complication of gastric bypass surgery.Figure 1Reference: [1] Service, G.J., et al. N Engl J Med, 2005. 353(3): p. 249-54. [2]. Kellogg, T.A., et al. Surg Obes Relat Dis, 2008. 4(4): p. 492-9. [3] Ritz, P. and H. Hanaire. Diabetes Metab, 2011. 37(4): p. 274-81.Figure 2Figure 3

Elevated Intact Proinsulin Levels During an Oral Glucose Challenge Indicate Progressive ß-Cell Dysfunction and May Be Predictive for Development of Type 2 Diabetes.

Elevated fasting intact proinsulin is a biomarker of late-stage ß-cell-dysfunction associated with clinically relevant insulin resistance. In this pilot investigation, we explored the potential value of measuring intact proinsulin as a functional predictor of ß-cell exhaustion during an oral glucose tolerance test (OGTT). The study was performed with 31 participants, 11 of whom were healthy subjects (7 female, age: 59 ± 20 years), 10 had impaired glucose tolerance (IGT, 6 female, 62 ± 10 years), and 10 had known type 2 diabetes (T2DM, 5 female, 53 ± 11 years, HbA1c: 7.0 ± 0.6%, disease duration: 8 ± 5 years). During OGTT, blood was drawn after 0 hours, 1 hour, and 2 hours for determination of glucose and intact proinsulin. Five years later, patients were again contacted to assess their diabetes status and the association to the previous OGTT results was analyzed. The OGTT (0 hours/1 hour/2 hours) results were as follows: healthy subjects: glucose: 94 ± 8 mg/dL/140 ± 29 mg/dL/90 ± 24 mg/dL, intact proinsulin: 3 ± 2 pmol/L/10 ± 7 pmol/L/10 ± 5 pmol/L); IGT: glucose: 102 ± 9 mg/dL/158 ± 57 mg/dL/149 ± 34 mg/dL, intact proinsulin: 7 ± 4 pmol/L/23 ± 8 pmol/L/28 ± 6 pmol/L; T2DM: glucose: 121 ± 20 mg/dL/230 ± 51 mg/dL/213 ± 34 mg/dL; intact proinsulin: 7 ± 7 pmol/L/26 ± 9 pmol/L/27 ± 10 pmol/L). Five years later, all of the IGT and 2 of the healthy subjects had developed T2DM and one had devloped IGT. All of them had elevated 2-hour proinsulin values in the initial OGTT, while patients with normal intact proinsulin results did not develop diabetes. Elevated 2-hour intact proinsulin levels during OGTT were predictive for later type 2 diabetes development. Further studies need to confirm our findings in larger populations.

Differences in insulin biosynthesis pathway between small and large islets do not correspond to insulin secretion

In a variety of mammalian species, small islets secrete more insulin per volume than large islets. This difference may be due to diffusional limitations of large islets, or inherent differences in the insulin production pathways. The purpose of this study was to identify possible differences in the early phase of glucose-stimulated insulin biosynthesis between large and small islets. Isolated small and large rat islets were challenged with 30 minutes of high glucose. The expression of insulin gene transcription factors (MafA, NeuroD/ Beta2, and PDX-1), preproinsulin mRNA, proinsulin and insulin were compared between large and small islets. Under basal (low glucose) conditions, MafA and NeuroD had higher mRNA levels and greater protein amounts in large islets compared to small when normalized to GAPDH levels. 30 minutes of high glucose stimulation failed to alter the mRNA or subsequent protein levels of either gene. However, 30 minutes of high glucose suppressed activated PDX-1 protein levels in both small and large islets. High glucose stimulation did not statistically alter the preproinsulin mRNA (insulin 1 and insulin 2) levels. At the translational level, high glucose increased the proinsulin levels, and large islets showed a higher proinsulin content per cell than small islets. Insulin content per cell was not significantly different between small and large islets under basal or high glucose levels. The results fail to explain the higher level of insulin secretion noted in small versus large islets and may suggest that possible differences lie downstream in the secretory pathway rather than insulin biosynthesis.

Autophagy: Starved β-cells seem different from starved body.

Autophagy: Starved β-cells seem different from starved body.

Recent advances in understanding the genetic architecture of type 2 diabetes.

Genome-wide association (GWAS) and sequencing studies are providing new insights into the genetic basis of type 2 diabetes (T2D) and the inter-individual variation in glycemic traits, including levels of glucose, insulin, proinsulin and hemoglobin A1c (HbA1c). At the end of 2011, established loci (P < 5 × 10(-8)) totaled 55 for T2D and 32 for glycemic traits. Since then, most new loci have been detected by analyzing common [minor allele frequency (MAF)>0.05] variants in increasingly large sample sizes from populations around the world, and in trans-ancestry studies that successfully combine data from diverse populations. Most recently, advances in sequencing have led to the discovery of four loci for T2D or glycemic traits based on low-frequency (0.005 < MAF ≤ 0.05) variants, and additional low-frequency, potentially functional variants have been identified at GWAS loci. Established published loci now total ∼88 for T2D and 83 for one or more glycemic traits, and many additional loci likely remain to be discovered. Future studies will build on these successes by identifying additional loci and by determining the pathogenic effects of the underlying variants and genes.

The role of dipeptidyl peptidase 4 inhibitors in fat metabolism in patients with type 2 diabetes and obesity

Objective. To evaluate the influence of combined therapy of sitagliptin and metformin on fat metabolism in patients with type 2 diabetes mellitus.Methods. The study included 82 patients (age, 55.3±9.1 years) with obesity and lipid metabolism disorders. None of the patients had reached their target glycated haemoglobin levels after metformin and diet therapy. Patients in group 1 (n=42) received 1.5–2-g metformin daily before the study and were switched to a formulation of 100-mg sitagliptin and 2-g metformin once a day. Patients in group 2 (n=40) were on a diet therapy before inclusion and were started on 2-g metformin/day. The following were evaluated at baseline and after 6 months of therapy: fasting glucose levels, postprandial glucose levels, glycated haemoglobin, weight, body mass index, waist circumference and lipid profile; insulin, proinsulin, leptin and adiponectin levels; insulin resistance using the homeostatic model assessment (HOMA) of β-cell function (HOMA-β) and insulin resistance (HOMA-IR). In addition, magnetic resonance imaging was performed to assess the amount of visceral fat for the total cohort.Results. After 6 months, glycated haemoglobin decreased by 18.52% (p 0.001) in group 1 and by 8.17% (p 0.001) in group 2. Fasting plasma glucose and postprandial glucose levels in group 1 were reduced by 21% (p 0.001) and 26.35% (p 0.001), respectively; the corresponding reductions in group 2 were 1.45% (p 0.05) and 5.31% (p 0.05), respectively. HOMA-β increased by 33% in group 1 (p 0.001) and by 11% in group 2 (p 0.05). Adiponectin levels increased by 27.06% (p 0.001) in group 1 and by 7.16% in group 2 (p 0.001). Leptin levels were reduced by 30.47% (p 0.001) in group 1 and by 5.41% in group 2 (p 0.001). Magnetic resonance imaging showed a 7.52% reduction in visceral fat for group 1 (p 0.001) and a 1.76% reduction for group 2 (p 0.01). The comparison of subcutaneous fat dynamics did not show statistically significant differences between the groups.Conclusion. Compared with metformin monotherapy, sitagliptin and metformin combination therapy had a prominent effect on non-glycaemic parameters, with more marked decreases in visceral fat and leptin and increases in adiponectin levels.

Proteasomal Degradation of Proinsulin Requires Derlin-2, HRD1 and p97.

Patients with type 1 diabetes (T1D) suffer from beta-cell destruction by CD8+ T-cells that have preproinsulin as an important target autoantigen. It is of great importance to understand the molecular mechanism underlying the processing of preproinsulin into these CD8+ T-cell epitopes. We therefore studied a pathway that may contribute to the production of these antigenic peptides: degradation of proinsulin via ER associated protein degradation (ERAD). Analysis of the MHC class I peptide ligandome confirmed the presentation of the most relevant MHC class I-restricted diabetogenic epitopes in our cells: the signal peptide-derived sequence A15-A25 and the insulin B-chain epitopes H29-A38 and H34-V42. We demonstrate that specific silencing of Derlin-2, p97 and HRD1 by shRNAs increases steady state levels of proinsulin. This indicates that these ERAD constituents are critically involved in proinsulin degradation and may therefore also play a role in subsequent antigen generation. These ERAD proteins therefore represent interesting targets for novel therapies aiming at the reduction and possibly also prevention of beta-cell directed auto-immune reactions in T1D.

Development of a novel immunoassay specific for mouse intact proinsulin

The blood concentration of intact proinsulin, but not total proinsulin, has been suggested to be a diagnostic marker for type 2 diabetes mellitus (T2DM), but a sensitive assay specific for rodent intact proinsulin is lacking. Here, a novel enzyme-linked immunosorbent assay (ELISA) for mouse intact proinsulin was developed. The developed ELISA detected mouse intact proinsulin with the working range of 8.3 to 2700pg/ml. Cross-reactivity with mouse split-32,33 proinsulin was approximately 100times lower than the reactivity with mouse intact proinsulin, and no cross-reactivity with mouse insulin was detected. The developed ELISA was sufficiently sensitive to detect low levels of intact proinsulin in normal mouse plasma. The measurement by the developed ELISA revealed that intact proinsulin was elevated in the plasma of type 2 diabetic db/db mice as mice aged, and the ratio of intact proinsulin/insulin in plasma was correlated with levels of glycated hemoglobin A1c as seen in T2DM patients. These results suggest that the plasma level of intact proinsulin, but not total proinsulin, is a sensitive marker for pancreatic dysfunction and the ensuring diabetic disease progression of db/db mice. This ELISA could aid nonclinical evaluation of therapeutic interventions in T2DM.

Both fasting and glucose-stimulated proinsulin levels predict hyperglycemia and incident type 2 diabetes: a population-based study of 9,396 Finnish men.

BackgroundHyperproinsulinemia is an indicator of β-cell dysfunction, and fasting proinsulin levels are elevated in patients with hyperglycemia. It is not known whether proinsulin levels after a glucose load are better predictors of hyperglycemia and type 2 diabetes than fasting proinsulin.MethodsParticipants were 9,396 Finnish men (mean±SD, age 57.3±7.1 years, BMI 27.0±4.0 kg/m2) of the population-based METabolic Syndrome In Men Study who were non-diabetic at the recruitment, and who participated in a 6-year follow-up study. Proinsulin and insulin levels were measured in the fasting state and 30 and 120 min after an oral glucose load. Area under the curve (AUC) and proinsulin to insulin ratios were calculated.ResultsFasting proinsulin, proinsulin at 30 min and proinsulin AUC during the first 30 min of an oral glucose tolerance test significantly predicted both the worsening of hyperglycemia and type 2 diabetes after adjustment for confounding factors. Further adjustment for insulin sensitivity (Matsuda index) or insulin secretion (Disposition index) weakened these associations. Insulin sensitivity had a major impact on these associations.ConclusionOur results suggest that proinsulin in the fasting state and after an oral glucose load similarly predict the worsening of hyperglycemia and conversion to type 2 diabetes.

Insulin autoimmune syndrome (IAS)

We report the case of a 54 year old man with a symptomatic hypoglycemia (tremor; sweating) since six weeks. Habitus and medical history conformed the criteria for metabolic syndrome (arterial hypertension, obesity, BMI 40.1 kg/m2, hyperlipidemia). Neither diabetes nor neuroendocrine tumors in the family history. The laboratory analysis revealed after an abrosia period of 72 hours the lowest plasma glucose at 68 mg/dl. The insulin secretion showed a decreasing tendency starting at 891 mU/l and falling down to 391 mU/l within a 72 hours fasting period. Glucose tolerance test detected extreme high insulin levels over 1000 mg/dl before glucose intake and throughout the whole testing. 180 Minutes after the glucose intake broke the patient into a sweat and reported nausea and indisposition. We detected a hypoglycemia (22 mg/dl). Non corresponding proinsulin and C-peptide levels were measured. Anti-insulin antibodies showed a non mensurable high titer (> 100 U/ml). Endoscopic ultrasound substantiated a small lesion (6 mm) without any reasonable suspicion of being an insulinoma. Insulin autoimmune syndrome (IAS) is an extremely rare cause of hypoglycemia, particularly in non-Asian populations. In patients presenting with hypoglycemia and excessively high insulin levels, consideration should be given to autoimmune hypoglycemia due to anti-insulin antibodies as a cause.