Analysis of angiogenesis biomarkers for ramucirumab efficacy in patients with metastatic colorectal cancer from RAISE, a global, randomized, double-blind, phase III study

Background

The phase III RAISE trial (NCT01183780) demonstrated that the vascular endothelial growth factor (VEGF) receptor (VEGFR)-2 binding monoclonal antibody ramucirumab plus 5-fluororuracil, leucovorin, and irinotecan (FOLFIRI) significantly improved overall survival (OS) and progression-free survival (PFS) compared with placebo + FOLFIRI as second-line metastatic colorectal cancer (mCRC) treatment. To identify patients who benefit the most from VEGFR-2 blockade, the RAISE trial design included a prospective and comprehensive biomarker program that assessed the association of biomarkers with ramucirumab efficacy outcomes.

Patients and methods

Plasma and tumor tissue collection was mandatory. Overall, 1072 patients were randomized 1 : 1 to the addition of ramucirumab or placebo to FOLFIRI chemotherapy. Patients were then randomized 1 : 2, for the biomarker program, to marker exploratory (ME) and marker confirmatory (MC) groups. Analyses were carried out using exploratory assays to assess the correlations of baseline marker levels [VEGF-C, VEGF-D, sVEGFR-1, sVEGFR-2, sVEGFR-3 (plasma), and VEGFR-2 (tumor tissue)] with clinical outcomes. Cox regression analyses were carried out for each candidate biomarker with stratification factor adjustment.

Results

Biomarker results were available from >80% (n = 894) of patients. Analysis of the ME subset determined a VEGF-D level of 115 pg/ml was appropriate for high/low subgroup analyses. Evaluation of the combined ME + MC populations found that the median OS in the ramucirumab + FOLFIRI arm compared with placebo + FOLFIRI showed an improvement of 2.4 months in the high VEGF-D subgroup [13.9 months (95% CI 12.5-15.6) versus 11.5 months (95% CI 10.1-12.4), respectively], and a decrease of 0.5 month in the low VEGF-D subgroup [12.6 months (95% CI 10.7-14.0) versus 13.1 months (95% CI 11.8-17.0), respectively]. PFS results were consistent with OS. No trends were evident with the other antiangiogenic candidate biomarkers.

Conclusions

The RAISE biomarker program identified VEGF-D as a potential predictive biomarker for ramucirumab efficacy in second-line mCRC. Development of an assay appropriate for testing in clinical practice is currently ongoing.

Clinical trials registration

NCT01183780.

Low incidence of anti-drug antibodies in patients with type 2 diabetes treated with once-weekly glucagon-like peptide-1 receptor agonist dulaglutide

Therapeutic administration of peptides may result in anti-drug antibody (ADA) formation, hypersensitivity adverse events (AEs) and reduced efficacy. As a large peptide, the immunogenicity of once-weekly glucagon-like peptide-1 (GLP-1) receptor agonist dulaglutide is of considerable interest. The present study assessed the incidence of treatment-emergent dulaglutide ADAs, hypersensitivity AEs, injection site reactions (ISRs), and glycaemic control in ADA-positive patients in nine phase II and phase III trials (dulaglutide, N = 4006; exenatide, N = 276; non-GLP-1 comparators, N = 1141). Treatment-emergent dulaglutide ADAs were detected using a solid-phase extraction acid dissociation binding assay. Neutralizing ADAs were detected using a cell-based assay derived from human endothelial kidney cells (HEK293). A total of 64 dulaglutide-treated patients (1.6% of the population) tested ADA-positive versus eight (0.7%) from the non-GLP-1 comparator group. Of these 64 patients, 34 (0.9%) had dulaglutide-neutralizing ADAs, 36 (0.9%) had native-sequence GLP-1 (nsGLP-1) cross-reactive ADAs and four (0.1%) had nsGLP-1 neutralization ADAs. The incidence of hypersensitivity AEs and ISRs was similar in the dulaglutide versus placebo groups. No dulaglutide ADA-positive patient reported hypersensitivity AEs. Because of the low incidence of ADAs, it was not possible to establish their effect on glycaemic control.

Evaluation of immunogenicity of LY2963016 insulin glargine compared with Lantus® insulin glargine in patients with type 1 or type 2 diabetes mellitus

AIMS

To compare the immunogenicity profiles and the potential effects on clinical outcomes of LY2963016 insulin glargine (LY IGlar) and Lantus® insulin glargine (IGlar), products with identical primary amino acid sequences, in patients with type 1 or type 2 diabetes mellitus (T1DM or T2DM).

METHODS

To assess immunogenicity, anti-insulin glargine antibodies (measured as percent binding) were compared between treatments in 52-week (open-label) and 24-week (double-blind) randomized studies in total study populations of patients with T1DM (N = 535) and T2DM (N = 756), respectively, and two subgroups of patients with T2DM: insulin-naïve patients and those reporting prestudy IGlar treatment (prior IGlar). Relationships between insulin antibody levels and clinical outcomes were assessed using analysis of covariance and partial correlations. Insulin antibody levels were assessed using Wilcoxon rank sum. Treatment comparisons for treatment-emergent antibody response (TEAR) and incidence of detectable antibodies were analysed using Fisher's exact test.

RESULTS

No significant treatment differences were observed for insulin antibody levels, incidence of detectable anti-insulin glargine antibodies, or incidence of TEAR [overall and endpoint, by last-observation-carried-forward (LOCF)] in patients with T1DM or patients with T2DM, including the insulin-naïve subgroup. A statistically significant difference was noted in the overall incidence of detectable antibodies but not at endpoint (LOCF) nor in TEAR for the prior IGlar subgroup of patients with T2DM. Insulin antibody levels were low (<5%) in both treatment groups. Insulin antibody levels or developing TEAR was not associated with clinical outcomes.

CONCLUSIONS

LY IGlar and IGlar have similar immunogenicity profiles; anti-insulin glargine antibody levels were low for both treatments, with no observed effect on efficacy and safety outcomes.

Plasma proprotein convertase subtilisin kexin type 9 levels are related to markers of cholesterol synthesis in familial combined hyperlipidemia

BACKGROUND AND AIMS

Two recent independent studies showed that patients with familial combined hyperlipidemia (FCHL) have elevated plasma levels of proprotein convertase subtilisin kexin type 9 (PCSK9) and markers of cholesterol synthesis. Both PCSK9 expression and cholesterol synthesis are downstream effects of hepatic activation of sterol regulatory element binding protein 2 (SREBP2). The present study was conducted to study the relationship between plasma PCSK9 and markers of cholesterol synthesis in FCHL.

METHODS AND RESULTS

Markers of cholesterol synthesis (squalene, desmosterol, lathosterol), cholesterol absorption (campesterol, sitosterol, cholestanol) and PCSK9 were measured in plasma of FCHL patients (n = 103) and their normolipidemic relatives (NLR; n = 240). Plasma PCSK9, lathosterol and desmosterol levels were higher in FCHL patients than their NLR (p < 0.001, age and sex adjusted). Heritability calculations demonstrated that 35% of the variance in PCSK9 levels could be explained by additive genetic effects (p < 0.001). Significant age- and sex-adjusted correlations were observed for the relationship between PCSK9 and lathosterol, both unadjusted and adjusted for cholesterol, in the overall FCHL population (both p < 0.001). Multivariate regression analyses, with PCSK9 as the dependent variable, showed that the regression coefficient for FCHL status decreased by 25% (from 0.8 to 0.6) when lathosterol was included. Nevertheless, FCHL status remained an independent contributor to plasma PCSK9 (p < 0.001).

CONCLUSIONS

The present study confirms the previously reported high and heritable PCSK9 levels in FCHL patients. Furthermore, we now show that high PCSK9 levels are, in part, explained by plasma lathosterol, suggesting that SREBP2 activation partly accounts for elevated PCSK9 levels in FCHL.

The role of apolipoprotein A5 in non-alcoholic fatty liver disease

BACKGROUND

Apolipoprotein A5 (apoA5) is a recently described liver-specific protein that has been shown to influence triglyceride (TG) metabolism. ApoA5 transgenic mice display dramatically reduced TG levels, while in contrast apoA5 deficiency in humans was reported to result in marked hypertriglyceridemia. ApoA5 exerts its extracellular effects by increasing lipolysis of TG-rich lipoproteins, while in vitro data suggest additional intrahepatic effects.

METHODS

In this study the authors set out to investigate a possible role of apoA5 in non-alcoholic fatty liver disease (NAFLD). We thus determined hepatic apoA5 expression in 15 obese subjects with histologically proven NAFLD undergoing bariatric surgery. In addition, the authors established a hepatic cell culture model of apoA5 knockdown by transfecting human hepatoma cells (HepG2) with apoA5 small interfering (si) RNA, and determined intracellular TG content and expression levels of key enzymes and transcription factors of intrahepatic lipid metabolism in these cells.

RESULTS

Pronounced weight loss and associated histologically verified improvement of hepatic steatosis were accompanied by significant reductions of hepatic apoA5 mRNA expression levels. Significant apoA5 knockdown in HepG2 cells resulted in a marked decrease of intracellular TG content. When HepG2 cells were co-transfected with apoA5 and peroxisome proliferator-activated receptor gamma (PPARγ), reductions in hepatic TG accumulation were significantly less pronounced when compared to apoA5 siRNA transfected HepG2 cells.

CONCLUSIONS

In obese subjects, hepatic apoA5 mRNA expression decreases after weight loss and improvements in hepatic steatosis. The authors' in vitro data demonstrate that apoA5 influences intrahepatic TG metabolism and that these intracellular effects of apoA5 are accompanied by changes in PPARγ mRNA expression. In summary, the data suggest that as well as several other factors, apoA5 might be involved in the pathogenesis of hepatic steatosis.

The influence of matrix type, diurnal rhythm and sample collection and processing on the measurement of plasma beta-amyloid isoforms using the INNO-BIA plasma Abeta forms multiplex assay

OBJECTIVE

The aim of the study was to determine the extent to which plasma matrix types, diurnal rhythm and sample collection and processing procedures contribute to overall variability of measurements with the INNO-BIA plasma Abeta forms assay.

METHODS

Plasma samples from healthy volunteers were collected at BARC-CRI. Analyte concentrations from various plasma matrix types (EDTA, heparin, fluoride) were compared to serum after collection of blood in commercial plastic and glass tubes. Sample processing variables including time and temperature before and after centrifugation, centrifugal force and plasma dilution factor were also investigated. Diurnal variability in plasma Abeta isoforms was determined in 29 healthy volunteers by analysis of EDTA plasma specimens serially collected over 24 hours and stored frozen following oral administration of a placebo treatment. All plasma samples from a given individual and experiment were analyzed in a single analytical run.

RESULTS

Highest Abeta levels were obtained using EDTA-plasma samples (in contrast to serum, heparin, citrate, or fluoride). Addition of aprotinin to EDTA plasma had no effect on Abeta peptide recovery. The elapsed time and temperature exposure, before and after sample processing affects the recovery of Abeta isoforms. Analyte recovery was not significantly affected by the presence of platelets in plasma samples. At the subject level, analysis of serially collected EDTA plasma specimens from healthy volunteers revealed no evidence of diurnal variation in any of the Abeta isoforms investigated and results from samples collected on a monthly basis showed only very limited intra-individual variation.

CONCLUSIONS

Optimal recovery of Abeta peptides was obtained from blood drawn into EDTA tubes and processed within 4 h. Plasma that was refrigerated after separation and analysed within 4 h gave comparable results to samples immediately processed and frozen at -70 degrees C.

Development and validation of a phosphorylated SMAD ex vivo stimulation assay

Assessing the pharmacodynamics (PD) of a potential therapeutic through the use of a downstream biomarker is essential. This is traditionally performed in the target tissue but limited volume and invasiveness of sampling pose challenges with solid tumours. Currently, there are several small molecule receptor kinase inhibitors and large molecule therapeutic antibodies in clinical trials that interfere with TGFbeta signalling to treat various forms of cancer. With the advent of these new therapies, there is a need for a surrogate tissue that is easily accessible and indicative of tumour response. We propose the use of an ex vivo TGFbeta1 stimulation of peripheral blood mononuclear cells (PBMCs) coupled with the measurement of phosphorylated SMAD2 (Sma/Mothers Against dpp, a downstream transcriptional activator) using a sandwich ELISA. TGFbeta is involved in many different cellular responses, such as proliferation, angiogenesis, migration, invasion and immunomodulation. SMAD2 and SMAD3 are phosphorylated as a result of the canonical cascade through ligand binding and receptor kinase activation. These phosphorylated SMADs (pSMAD) associate with SMAD4, a co-SMAD, and transcriptionally activate TGFbeta-mediated genes. This paper describes the novel method for measuring the downstream effects of inhibiting canonical TGFbeta signalling using ex vivo stimulation of surrogate tissue to predict tumour response. In addition, we present the assay validation rationale and data. This novel, validated assay can be used to gain insight into clinical trials regarding TGFbeta signal modulation by multiple inhibitor platforms for both large and small molecules.

Purification of the O-glycosylated protein p135 and identification as O-GlcNAc transferase

We have previously shown that rat pancreatic islets contain a predominant 135 kDa O-glycosylated protein (p135) that is recognized by immunoprecipitation and Western blotting with anti-O-GlcNAc antibody. In this paper, we show that p135 is also detectable in other rat tissues including brain, heart, liver, spleen, and lung, but not kidney. To identify p135, the protein was purified from rat brain using a multistep procedure including selective absorption with anti-O-GlcNAc antibody. After electrophoresis, and Coomassie staining, the protein was excised from the gel for tryptic digestion. Next, O-methylisourea was used to convert lysine residues to homoarginine to increase the sequence coverage, and MALDI-TOF mass spectrometry detection was performed. MALDI-TOF identified p135 as rat O-GlcNAc transferase (OGT), an identity confirmed by LC/MS of individual peptides. The identification of p135 as OGT is consistent with previous reports of the tissue distribution of OGT, as well as reports that OGT is itself O-glycosylated.

The potential mechanism of the diabetogenic action of streptozotocin: inhibition of pancreatic beta-cell O-GlcNAc-selective N-acetyl-beta-D-glucosaminidase

Streptozotocin (STZ), an analogue of GlcNAc, inhibits purified rat spleen O-GlcNAc-selective N-acetyl-beta-D-glucosaminidase (O-GlcNAcase), the enzyme that removes O-GlcNAc from protein. We have shown previously that STZ increases pancreatic islet O-linked protein glycosylation. In light of these data, we investigated the possibility further that STZ causes beta-cell death by inhibiting O-GlcNAcase. In isolated islets, the time course and dose curve of STZ-induced O-glycosylation correlated with beta-cell toxicity. STZ inhibition of rat islet O-GlcNAcase activity also paralleled that of its beta-cell toxicity, with significant inhibition occurring at a concentration of 1 mM. In contrast, STZ inhibition of rat brain O-GlcNAcase and beta-TC3 insulinoma cell O-GlcNAcase was significantly right-shifted compared with islets, with STZ only significantly inhibiting activity at a concentration of 5 mM, the same concentration required for beta-TC3 cell toxicity. In comparison, N-methyl-N-nitrosourea, the nitric oxide-donating portion of STZ, did not cause increased islet O-glycosylation, beta-cell toxicity or inhibition of beta-cell O-GlcNAcase. Enhanced STZ sensitivity of islet O-GlcNAcase compared with O-GlcNAcase from other tissues or an insulinoma cell line suggests why actual islet beta-cells are particularly sensitive to STZ. Confirming this idea, STZ-induced islet beta-cell toxicity was completely blocked by GlcNAc, which also prevented STZ-induced O-GlcNAcase inhibition, but was not even partially blocked by glucose, glucosamine or GalNAc. Together, these data demonstrate that STZ's inhibition of beta-cell O-GlcNAcase is the mechanism that accounts for its diabetogenic toxicity.

An unusual multiple drug intoxication case involving citalopram

A 47-year-old male with a history of drug abuse and suicide attempts was found dead at home. The death scene investigation showed evidence of cocaine abuse and multiple drug ingestion. Citralopram, a new selective serotonin reuptake inhibitor, cocaine, oxycodone, promethazine, propoxyphene, and norpropoxyphene were identified and quantitated in the postmortem samples by gas chromatography-mass spectrometry. The concentration of citalopram in the femoral blood was 0.88 mg/L. The heart blood concentration was 1.16 mg/L. Femoral blood concentrations of the other drugs were as follows: cocaine, 0.03 mg/L; oxycodone, 0.06 mg/L; promethazine, 0.02 mg/L; propoxyphene, 0.02 mg/L; and norpropoxyphene, 0.07 mg/L. Other tissue samples were also analyzed. The concentrations of cocaine, oxycodone, promethazine, and propoxyphene in the blood, liver, brain, and gastric contents did not suggest an intentional overdose. However, the possibility of multiple drug interactions including citalopram was evident. In this case, the citalopram concentrations were consistent with those reported in fatal cases involving multiple drug use. Citalopram was present in urine at a concentration of 0.9 mg/L.

A modified method of islet isolation preserves the ability of pancreatic islets to increase protein O-glycosylation in response to glucose and streptozotocin

An important link has recently been shown in vivo between beta-cell O-linked protein glycosylation and beta-cell apoptosis, with hyperglycemia having been demonstrated to reversibly increase beta-cell O-linked protein glycosylation by providing substrate for the glucosamine pathway. In contrast, the same study showed that the administration of streptozotocin to rats prior to the induction of hyperglycemia results in irreversible increases in O-glycosylation and subsequent beta-cell apoptosis. In light of these data, we investigated beta-cell O-glycosylation in vitro by exposing isolated rat islets to high glucose, glucosamine, or streptozotocin and analyzing the pattern of O-glycosylated proteins present. All three compounds acutely increased O-glycosylation of a predominate 135-kDa protein (p135); however, their ability to stimulate p135 O-glycosylation was only consistently observed when islets were isolated in the presence of high glucose and 1 mM L-glutamine. Islets isolated in low glucose and no added L-glutamine demonstrated no consistent increase in p135 O-glycosylation in response to glucose, glucosamine, or streptozotocin. These data suggest that during islet isolation, beta-cell enzymes responsible for regulating p135 O-glycosylation may be adversely affected by the absence of high glucose and glutamine, which together are necessary for O-linked N-acetylglucosamine synthesis. We propose that the combination of high glucose and glutamine during islet isolation generates UDP-N-acetylglucosamine and O-linked N-acetylglucosamine, thus providing substrate protection for these enzymes and preserving the ability of isolated islets to O-glycosylate p135.

Glucose and streptozotocin stimulate p135 O-glycosylation in pancreatic islets

Streptozotocin has been widely used to create animal models of diabetes. Structurally, streptozotocin resembles N-acetylglucosamine, with a nitrosourea group corresponding to the acetate present in N-acetylglucosamine. Streptozotocin has recently been shown to inhibit O-GlcNAc-selective N-acetyl-beta-d-glucosaminidase, which removes O-linked N-acetylglucosamine from proteins. Compared to other cells, beta-cells express much more of the enzyme O-GlcNAc transferase, which catalyzes addition of O-linked N-acetylglucosamine to proteins. This suggests why beta-cells might be particularly sensitive to streptozotocin. In this report, we demonstrate that both streptozotocin and glucose stimulate O-glycosylation of a 135 kD beta-cell protein. Only the effect of glucose, however, was blocked by inhibition of fructose-6-phosphate amidotransferase, suggesting that glucose acts through the glucosamine pathway to provide UDP-N-acetylglucosamine for p135 O-glycosylation. The fact that both glucose and streptozotocin stimulate p135 O-glycosylation provides a possible mechanism by which hyperglycemia may cause streptozotocin-like effects in beta-cells and thus contribute to the development of type 2 diabetes.

Evaluation of a fully automated high-performance liquid chromatography assay for hemoglobin A1c

INTRODUCTION

Measurement of hemoglobin A1c (HbA1c) is used as an objective measure of long-term blood glucose control in diabetic patients. Recent improvements in automation combined with new recommendations for precision and accuracy have caused us to reevaluate our methods for measuring HbA1c.

OBJECTIVE

We evaluated a newly automated high-performance liquid chromatography (HPLC) instrument for measurement of HbA1c (Tosoh A1c 2.2 Plus Glycohemoglobin Analyzer, Tosoh Medics, Foster City, Calif) and compared the results obtained by HPLC to those obtained with an immunoassay (Hitachi 911, Boehringer Mannheim Corporation, Indianapolis, Ind).

RESULTS

The Tosoh analyzer was found to be linear in a range of 5.3% to 17% and had a throughput of 20 samples per hour. HbA1c results for 102 patient samples by the 2 techniques showed good correlation, with a slope of 0.87 and an intercept at 1.27% +/- 0.15%. Both the total and within-run coefficients of variation were consistently lower for the HPLC method compared with the immunoassay method. The HPLC method produces a chromatogram that shows the different hemoglobin fractions, allowing identification of abnormal hemoglobin variants. In heterozygous individuals, HbA1c measurements are made with no interference from the hemoglobin variant. In the case of homozygous or doubly heterozygous hemoglobin variants, the Tosoh HPLC identifies the hemoglobin variants as such and correctly does not report a HbA1c value in the presence of a markedly decreased amount of hemoglobin A.

CONCLUSIONS

The Tosoh HPLC provides adequate throughput and improved precision, and the method is traceable to the Diabetes Control and Complications Trial.

Postmortem diagnosis of unsuspected diabetes mellitus established by determination of decedent's hemoglobin A1c level

Although approximately 15.7 million Americans have diabetes mellitus, with the vast majority having type 2 diabetes, it is estimated that as many as 5.4 million are undiagnosed. The present case illustrates that undiagnosed diabetes can be a factor in otherwise unexplained deaths. A 39-year-old white male with no significant past medical history other than alcohol abuse was found deceased at his residence. The manner of death appeared to be natural, but no anatomic cause was found. Toxicological analysis revealed a blood ethanol level of 0.02 g/dL and was negative for drugs of abuse. Analysis of the vitreous fluid revealed a glucose level of 502 mg/dL. The blood glucose level was 499 mg/dL, and the hemoglobin A1c (HbA1c) level was 10.6%. Only trace urine ketones were detected, suggesting that the death was the result of hyperglycemic hyperosmolar non-ketosis (HHNK) from unsuspected diabetes. The postmortem HbA1c value serves as a definitive indicator of prolonged hyperglycemia. In order to aid the interpretation of the clinical data, this case is discussed in conjunction with a similar case of a known diabetic patient.

Glucose-induced tyrosine phosphorylation of p125 in beta cells and pancreatic islets. A novel proximal signal in insulin secretion

In this study, we demonstrate that stimulation of beta cells with carbachol and glucose causes increased tyrosine phosphorylation of a 125-kDa protein concurrently with increased insulin secretion. The effect was observed in two different insulin-secreting cell lines and in rat pancreatic islets. Tyrosine phosphorylation was largely calcium independent and occurred within 2 min after stimulation of beta cells with glucose and the muscarinic agonist carbachol. In islets, the effect of glucose was greatly diminished by the addition of mannoheptulose, a seven-carbon sugar that inhibits glucokinase, suggesting that glucose metabolism is required for tyrosine phosphorylation of the protein to occur. Neither insulin nor insulin-like growth factor I significantly increased tyrosine phosphorylation of the 125-kDa protein, suggesting that it was not an autocrine effect. Depolarization of beta cells with glyburide or 50 m potassium dramatically increased insulin secretion but had no significant effect on tyrosine phosphorylation. Addition of phorbol ester caused a less than 2-fold increase in tyrosine phosphorylation, whereas the calcium ionophore A23187 had no effect. Among the various fuel secretagogues tested, only -glucose stimulated tyrosine phosphorylation, both alone and in combination with carbachol. Finally, the tyrosine kinase inhibitor AG879 inhibited both tyrosine phosphorylation and insulin secretion in a dose-dependent manner. Taken together, these data demonstrate the presence of a novel signaling pathway in glucose-induced insulin secretion: tyrosine phosphorylation of beta cell p125, which is a proximal step in insulin secretion. Our current working hypothesis is that glucose stimulation of beta cell p125 tyrosine phosphorylation is an essential step for insulin secretion.

Wortmannin inhibits insulin secretion in pancreatic islets and beta-TC3 cells independent of its inhibition of phosphatidylinositol 3-kinase

Glucose is the primary stimulus for insulin secretion by pancreatic beta-cells, and it triggers membrane depolarization and influx of extracellular Ca2+. Cholinergic agonists amplify insulin release by several pathways, including activation of phospholipase C, which hydrolyzes membrane polyphosphoinositides. A novel phospholipid, phosphatidylinositol 3,4,5- trisphosphate [PtdIns(3,4,5)P3], a product of phosphatidylinositol 3-kinase (PI 3-kinase), has recently been found in various cell types. We demonstrate by immunoblotting that PI 3-kinase is present in both cytosolic and membrane fractions of insulin-secreting beta-TC3 cells and in rat islets. The catalytic activity of PI 3-kinase in immunoprecipitates of islets and beta-TC3 cells was measured by the production of radioactive phosphatidylinositol 3-monophosphate from phosphatidylinositol (PtdIns) in the presence of [gamma-32P]ATP. Wortmannin, a fungal metabolite, dose dependently inhibited PI 3-kinase activity of both islets and beta-TC3 cells, with an IC50 of 1 nmol/l and a maximally effective concentration of 100 nmol/l, when it was added directly to the kinase assay. However, if intact islets were incubated with wortmannin and PI 3-kinase subsequently was determined in islet immunoprecipitates, approximately 50% inhibition of PI 3-kinase activity (but no inhibition of glucose- and carbachol-stimulated insulin secretion) from intact islets was obtained at wortmannin concentrations of 100 nmol/l. Wortmannin, at higher concentrations (1 and 10 micromol/l), inhibited glucose- and carbachol-induced insulin secretion of Intact rat islets by 58 and 92%, respectively. Wortmannin had no effect on the basal insulin release from rat islets. A similar dose curve of inhibition of glucose- and carbachol-induced insulin secretion by wortmannin was obtained when beta-TC3 cells were used. Cellular metabolism was, not changed by any wortmannin concentrations tested (0.01-10 micromol/l). Both basal cytosolic [Ca2+]i and carbamyl choline-induced increases of [Ca2]i were unaffected by wortmannin in the presence of 2.5 mmol/l Ca2+, while Ca2+ mobilization from intracellular stores was partially decreased by wortmannin. Together, these data suggest that wortmannin at concentrations that inhibit PI 3-kinase does not affect insulin secretion. PI 3-kinase is unlikely to have a major role in insulin secretion induced by glucose and carbachol.

The heterotrimeric G-protein Gi is localized to the insulin secretory granules of beta-cells and is involved in insulin exocytosis

Mastoparan, a tetradecapeptide found in wasp venom that stimulates G-proteins, increases insulin secretion from beta-cells. In this study, we have examined the role of heterotrimeric G-proteins in mastoparan-induced insulin secretion from the insulin-secreting beta-cell line beta-TC3. Mastoparan stimulated insulin secretion in a dose-dependent manner from digitonin-permeabilized beta-TC3 cells. Active mastoparan analogues mastoparan 7, mastoparan 8, and mastoparan X also stimulated secretion. Mastoparan 17, an inactive analogue of mastoparan, did not increase insulin secretion from permeabilized beta-TC3 cells. Mastoparan-induced insulin secretion from permeabilized beta-TC3 cells was inhibited by pretreatment of the cells with pertussis toxin, suggesting that mastoparan-induced insulin secretion is mediated through a pertussis toxin-sensitive G-protein present distally in exocytosis. Enriched insulin secretory granules (ISG) were prepared by sucrose/nycodenz ultracentrifugation. Western immunoblotting performed on beta-TC3 homogenate and ISG demonstrated that G alpha i was dramatically enriched in ISG. Levels of G alpha o and G alpha q were comparable in homogenate and ISG. Mastoparan stimulated ISG GTPase activity in a pertussis toxin-sensitive manner. Mastoparan 7 and mastoparan 8 also stimulated GTPase activity in the ISG, while the inactive analogue mastoparan 17 had no effect. Selective localization of G alpha i to ISG was confirmed with electron microscopic immunocytochemistry in beta-TC3 cells and beta-cells from rat pancreas. In contrast to G alpha o and G alpha q, G alpha was clearly localized to the ISG. Together, these data suggest that mastoparan may act through the heterotrimeric G-protein G alpha i located in the ISG of beta-cells to stimulate insulin secretion.

Muscarinic regulation of Alzheimer's disease amyloid precursor protein secretion and amyloid beta-protein production in human neuronal NT2N cells

The Alzheimer amyloid precursor protein (APP) undergoes complex processing resulting in the production of a 4-kDa amyloid peptide (A beta) which has been implicated in the pathogenesis of Alzheimer's disease. Recent studies have shown that cells can secrete carboxyl terminus truncated APP derivatives (APP-S) in response to physiological stimulus. We have used human central nervous system neurons (NT2N) derived from a teratocarcinoma cell line (NT2) to study the signal transduction pathways involved in APP-S secretion and A beta production. Muscarinic receptors (m2 and m3) as well as the heterotrimeric GTP-binding protein Gq and the beta 1 isoform of phospholipase C were present in NT2N neurons. Stimulation of the muscarinic receptor with carbachol resulted in phospholipase C activation as shown by a transient increase in the second messengers 1,2-diacyl-sn-glycerol and inositol 1,4,5-trisphosphate. Carbachol also caused an increase in intracellular Ca2+ levels measured in single NT2N neurons. Under these conditions, carbachol caused a time-dependent 2-fold increase in APP-S secretion into the medium. In contrast, prolonged treatment with carbachol caused a decrease in A beta production into the medium. These results suggest that APP-S secretion and A beta production in NT2N neurons are regulated by the muscarinic/phospholipase C signal transduction pathway. Furthermore, activation of this pathway results in dissociation of APP-S secretion and A beta production.

Diacylglycerol hydrolysis to arachidonic acid is necessary for insulin secretion from isolated pancreatic islets: sequential actions of diacylglycerol and monoacylglycerol lipases

Arachidonic acid has been implicated as a second messenger in insulin secretion on the basis of (1) mobilization of intracellular Ca2+ from the endoplasmic reticulum of islets and (2) amplification of voltage-dependent Ca2+ entry. The insulin secretagogues D-glucose and the muscarinic agonist carbachol both increase unesterified arachidonic acid accumulation in isolated islets. We now show that diacylglycerol, a product of phospholipase C action, is a major source of free arachidonic acid in islets. Diacylglycerol hydrolysis in islets occurs through a two-step process. In the first step, the sn-1 bond of 1-stearoyl-2-arachidonyl-sn-glycerol is hydrolyzed by a diacylglycerol lipase, giving rise to 2-arachidonyl-sn-glycerol. Next, the sn-2 bond of 2-arachidonyl-sn-glycerol is hydrolyzed by a monoacylglycerol lipase, which is the rate-limiting step, releasing unesterified arachidonic acid. Both diacylglycerol lipase and monoacylglycerol lipase are highly enriched in the plasma membrane of beta-cells. Diacylglycerol lipase activity in islet homogenates is selectively inhibited in a dose-dependent manner by the compound RHC-80267, a specific diacylglycerol lipase inhibitor. RHC-80267 inhibits glucose- and carbachol-induced insulin release from intact islets in a dose-dependent manner that parallels its inhibition of diacylglycerol lipase activity. Importantly, RHC-80267, at concentrations that almost completely inhibit diacylglycerol lipase activity and glucose- and carbachol-induced insulin secretion by islets, markedly inhibits glucose- and carbachol-induced increases in islet arachidonic acid levels, as measured by gas chromatography with electron-capture detection of its pentafluorobenzyl esters. RHC-80267 did not significantly affect islet glucose oxidation, phospholipase C, monoacylglycerol lipase, or phospholipase A2. Since glucose and carbachol are known to stimulate phospholipase C, our observations indicate that diacylglycerol is an important source of arachidonic acid and other free fatty acids in islets. Furthermore, production of arachidonic acid from the hydrolysis of diacylglycerol is essential for glucose- and carbachol-induced insulin secretion.

Linkage disequilibrium between TAP2 variants and HLA class II alleles; no primary association between TAP2 variants and insulin-dependent diabetes mellitus

The TAP1 and TAP2 genes, located in the HLA class II region, encode subunits of a peptide transporter. Both genes display limited genetic variability; four different nucleotide substitutions have been found in the TAP2 gene. Here studies on linkage disequilibrium between TAP2 variants and HLA class II alleles are reported, in an attempt to evaluate whether TAP2 variants are associated with insulin-dependent diabetes mellitus (IDDM). As reported previously, a significant decrease of homozygosity for TAP2 alleles encoding alanine at residue 665 (665 Ala) and glutamine at 687 (687 Gln) paralleled by an increase in homozygosity for TAP2 alleles encoding threonine at residue 665 (665 Thr) and a stop codon at 687 (687 Stop), was found in both Finnish and Norwegian IDDM patients compared to random controls. However, a strong linkage disequilibrium between these TAP2 polymorphisms and given HLA-DR and -DQ genes was observed among healthy controls. The frequent 665 Thr and 687 Stop variants were in linkage disequilibrium both with the DR4-DQ8 and the DR3-DQ2 haplotypes, haplotypes which are strongly associated with IDDM. In contrast, the DR1-DQ5 and DR13-DQ6 (e.g. DQB1*0603) haplotypes, which are decreased among IDDM patients, were associated with the 665 Ala and 687 Gln variants. Thus, when DR- and DQ-matched patients and controls were compared, associations of the investigated TAP2 variants and IDDM were no longer detectable. These data, therefore, indicate that the associations previously found between certain TAP2 variants and IDDM are secondary to a primary association between this disease and particular DQ alpha beta heterodimers.

Fuel secretagogue stimulation of arachidonic acid accumulation in fresh and cultured pancreatic islets

It has been previously demonstrated that glucose stimulation of islets of Langerhans causes an accumulation of unesterified arachidonic acid that correlates with insulin secretion. In addition, it is well established that glucose metabolism is essential for insulin secretion. We show that non-metabolizable analogs of glucose which do not stimulate insulin secretion fail to cause significant accumulation of unesterified arachidonic acid. In addition, mannoheptulose, an inhibitor of glucose metabolism, completely blocks the glucose-induced increase in arachidonic acid accumulation. Among the nutrient secretagogues tested, only alpha-ketoisocaproic acid causes a significant increase in unesterified arachidonic acid accumulation. Mannose, fructose, and glyceraldehyde, in particular, failed to elicit a significant increase in unesterified arachidonic acid accumulation. Our data, taken together with previous studies, suggests that glucose must be metabolized to induce accumulation of unesterified arachidonic acid in pancreatic islets.

Carbachol stimulation of phospholipase A2 and insulin secretion in pancreatic islets

Arachidonic acid has been implicated as a second messenger in insulin secretion by islets of Langerhans. D-Glucose, the major physiological stimulus, increases unesterified arachidonate accumulation in islets. We now show, for the first time, that the muscarinic agonist carbachol, at concentrations which stimulate insulin secretion, causes a rapid and nearly 3-fold increase in arachidonic acid accumulation in islets. The combination of glucose and carbachol has an additive effect on unesterified arachidonate release. There is a large component of secretagogue-induced arachidonate accumulation that is independent of extracellular Ca2+. Carbachol stimulation of arachidonic acid release is mediated by activation of phospholipase A2, as demonstrated by early increases in endogenous lysophosphatidylcholine. In addition to phospholipase A2 activation, carbachol-induced arachidonic acid accumulation also appears to involve diacylglycerol hydrolysis, since the diacylglycerol lipase inhibitor RG80267 partly inhibited arachidonic acid accumulation. In contrast, glucose-induced arachidonic acid accumulation appears to reflect diacylglycerol hydrolysis entirely. Our observations indicate that phospholipase A2 has an important role in muscarinic-induced insulin secretion.

Inhibition of phospholipase A2 and insulin secretion in pancreatic islets

Arachidonic acid may be an important mediator of insulin secretion since (1) glucose activates phospholipase A2 thus increasing endogenous unesterified levels of arachidonic acid, (2) arachidonic acid mobilizes Ca2+ from the islet endoplasmic reticulum and (3) arachidonic acid has been proposed to regulate voltage-dependent Ca2+ channels in the beta-cell. We have used the phospholipase A2 inhibitor, (p-amylcinnamoyl)anthranilic acid (ACA), to determine whether phospholipase A2 activation is required for glucose-induced insulin secretion. ACA inhibited in a dose-dependent manner glucose-induced insulin secretion, as well as glyceraldehyde and alpha-ketoisocaproic acid-induced insulin secretion. ACA also totally abolished glucose-induced arachidonate accumulation but did not affect phospholipase C suggesting that it was specific for phospholipase A2. Furthermore, ACA did not inhibit glucose oxidation. These observations suggest that glucose-induced arachidonate increase is essential for insulin secretion.

Glucose and carbachol synergistically stimulate phosphatidic acid accumulation in pancreatic islets

Phosphatidic acid has been previously implicated as an intracellular mediator of insulin secretion. Very little is known, however, about endogenous phosphatidic acid levels in islets. We now show, for the first time, that glucose and carbachol, at concentrations which stimulate insulin secretion, significantly increase endogenous phosphatidic acid levels in pancreatic islets by 2-fold at 1 min, nearly 3-fold at 2 min, and over 3-fold at 30 min compared to control. Possible mechanisms include de novo synthesis from glucose and/or activation of phospholipase D. Our data, taken together with previous studies, suggest that phosphatidic acid may have a central role in insulin secretion as an intracellular mediator.