Visceral abdominal fat accumulation predicts the conversion of metabolically healthy obese subjects to an unhealthy phenotype.

BACKGROUND: A proportion of obese subjects appear metabolically healthy (MHO) but little is known about the natural history of MHO and factors predicting its future conversion to metabolically unhealthy obese (MUO). OBJECTIVES: The aim was to determine prospectively the frequency of conversion of MHO to MUO and the clinical variables that independently predicted this conversion, with a particular focus on the role of body composition. METHODS: We identified 85 Japanese Americans with MHO (56 men, 29 women), aged 34-73 years (mean age 49.8 years) who were followed at 2.5, 5 and 10 years after enrollment with measurements of metabolic characteristics, lifestyle and abdominal and thigh fat areas measured by computed tomography. Obesity was defined using the Asian body mass index criterion of ⩾25 kg m(-2). Metabolically healthy was defined as the presence of ⩽2 of 5 metabolic syndrome components proposed by the National Cholesterol Education Program Adult Treatment Panel III, while metabolically unhealthy was defined as ⩾3 components. RESULTS: Over 10 years of follow-up, 55 MHO individuals (64.7%) converted to MUO. Statistically significant univariate predictors of conversion included dyslipidemia, greater insulin resistance and greater visceral abdominal (VAT) and subcutaneous abdominal fat area (SAT). In multivariate analysis, VAT (odds ratio per 1-s.d. increment (95% confidence interval) 2.04 (1.11-3.72), P=0.021), high-density lipoprotein (HDL) cholesterol (0.24 (0.11-0.53), P<0.001), fasting plasma insulin (2.45 (1.07-5.62), P=0.034) and female sex (5.37 (1.14-25.27), P=0.033) were significantly associated with future conversion to MUO. However, SAT was not an independent predictor for future conversion to MUO. CONCLUSIONS: In this population, MHO was a transient state, with nearly two-thirds developing MUO over 10 years, with higher conversion to MUO independently associated with VAT, female sex, higher fasting insulin level and lower baseline HDL cholesterol level.

Clinical and immunological profiles in 17 Japanese patients with drug-induced pemphigus studied at Kurume University.

BACKGROUND: Drug-induced pemphigus (DIP) shows clinical, histopathological and immunological features of pemphigus. However, little is known about immunological profiles in DIP. OBJECTIVES: To characterize clinical and immunological profiles in patients with DIP. METHODS: We studied 17 Japanese patients with DIP who were treated at Kurume University Hospital or who consulted from other hospitals between 1997 and 2012. Complicated diseases, clinical and histopathological manifestations, responsible drugs and findings in immunofluorescence, enzyme-linked immunosorbent assays (ELISAs), immunoblotting (IB) and prognosis were analysed. RESULTS: Eight of the 17 patients with DIP showed pemphigus foliaceus-like appearance, three showed pemphigus herpetiformis-like appearance, and six showed atypical bullous lesions. Responsible drugs were thiol-containing drugs in 16 patients (bucillamine in nine cases, d-penicillamine in four cases, and cetapril, thiopronine and captopril in one patient each), and a nonthiol drug, sulfasalazine, in one patient. By ELISAs and/or IB analyses, nine patients reacted only with desmoglein 1 (Dsg1), four reacted with Dsg1 and Dsg3, and four showed no specific reactivity. By IB of normal human epidermal extracts, in addition to positive reactivity with Dsg1, four patients with no detectable malignancy showed paraneoplastic pemphigus-like reactivity with the 210-kDa envoplakin and the 190-kDa periplakin. Four cases showed anti-Dsg3 antibodies without mucosal lesions. While 11 cases recovered after discontinuation of the causative drugs, six patients had a very protracted or intractable disease course, and might develop true pemphigus. CONCLUSIONS: The present study indicated that the majority of the patients with DIP studied showed a pemphigus foliaceus-type phenotype with anti-Dsg1 autoantibodies, caused by thiol-containing drugs.

Ras-related C3 botulinum toxin substrate 1 (RAC1) regulates glucose-stimulated insulin secretion via modulation of F-actin.

AIMS/HYPOTHESIS: The small G-protein ras-related C3 botulinum toxin substrate 1 (RAC1) plays various roles in mammalian cells, such as in the regulation of cytoskeletal organisation, cell adhesion, migration and morphological changes. The present study examines the effects of RAC1 ablation on pancreatic beta cell function. METHODS: Isolated islets from pancreatic beta cell-specific Rac1-knockout (betaRac1(-/-)) mice and RAC1 knockdown INS-1 insulinoma cells treated with small interfering RNA were used to investigate insulin secretion and cytoskeletal organisation in pancreatic beta cells. RESULTS: BetaRac1(-/-) mice showed decreased glucose-stimulated insulin secretion, while there were no apparent differences in islet morphology. Isolated islets from the mice had blunted insulin secretion in response to high glucose levels. In RAC1 knockdown INS-1 cells, insulin secretion was also decreased in response to high glucose levels, consistent with the phenotype of betaRac1(-/-) mice. Even under high glucose levels, RAC1 knockdown INS-1 cells remained intact with F-actin, which inhibits the recruitment of the insulin granules, resulting in an inhibition of insulin secretion. CONCLUSIONS/INTERPRETATION: In RAC1-deficient pancreatic beta cells, F-actin acts as a barrier for insulin granules and reduces glucose-stimulated insulin secretion.

A Pro12Ala substitution in PPARgamma2 associated with decreased receptor activity, lower body mass index and improved insulin sensitivity.

The peroxisome proliferator-activated receptor-gamma (PPARgamma) is a transcription factor that has a pivotal role in adipocyte differentiation and expression of adipocyte-specific genes. The PPARgamma1 and gamma2 isoforms result from alternative splicing and have ligand-dependent and -independent activation domains. PPARgamma2 has an additional 28 amino acids at its amino terminus that renders its ligand-independent activation domain 5-10-fold more effective than that of PPARgamma1. Insulin stimulates the ligand-independent activation of PPARgamma1 and gamma2 (ref. 5), however, obesity and nutritional factors only influence the expression of PPARgamma2 in human adipocytes. Here, we report that a relatively common Pro12Ala substitution in PPARgamma2 is associated with lower body mass index (BMI; P=0.027; 0.015) and improved insulin sensitivity among middle-aged and elderly Finns. A significant odds ratio (4.35, P=0.028) for the association of the Pro/Pro genotype with type 2 diabetes was observed among Japanese Americans. The PPARgamma2 Ala allele showed decreased binding affinity to the cognate promoter element and reduced ability to transactivate responsive promoters. These findings suggest that the PPARgamma2 Pro12Ala variant may contribute to the observed variability in BMI and insulin sensitivity in the general population.

Clinical evolution of beta cell function in youth with diabetes: the SEARCH for Diabetes in Youth study.

AIMS/HYPOTHESIS: Few studies have explored the epidemiology of beta cell loss in youth with diabetes. This report describes the evolution and major determinants of beta cell function, assessed by fasting C-peptide (FCP), in the SEARCH for Diabetes in Youth study. METHODS: Participants were 1,277 youth with diabetes (948 positive for diabetes autoantibodies [DAs] and 329 negative for DAs), diagnosed when aged <20 years, who were followed from a median of 8 months post diagnosis, for approximately 30 months. We modelled the relationship between rate of change in log FCP and determinants of interest using repeated measures general linear models. RESULTS: Among DA-positive youth, there was a progressive decline in beta cell function of 4% per month, independent of demographics (age, sex, race/ethnicity), genetic susceptibility to autoimmunity (HLA risk), HbA(1c) and BMI z score, or presence of insulin resistance. Among DA-negative youth, there was marked heterogeneity in beta cell loss, reflecting an aetiologically mixed group. This group likely includes youths with undetected autoimmunity (whose decline is similar to that of DA-positive youth) and youth with non-autoimmune, insulin-resistant diabetes, with limited decline (~0.7% per month). CONCLUSIONS/INTERPRETATION: SEARCH provides unique estimates of beta cell function decline in a large sample of youth with diabetes, indicating that autoimmunity is the major contributor. These data contribute to a better understanding of clinical evolution of beta cell function in youth with diabetes, provide strong support for the aetiological classification of diabetes type and may inform tertiary prevention efforts targeted at high-risk groups.

Arm length is associated with type 2 diabetes mellitus in Japanese-Americans.

AIMS/HYPOTHESIS: The aim of the study was to examine the association of type 2 diabetes mellitus with arm length as a marker for early life environment and development. METHODS: This was a cross-sectional analysis of 658 second- and third-generation Japanese-Americans (349 men and 309 women). Different arm length (total, upper and forearm length) and leg length (total and lower leg length) measurements were performed. Type 2 diabetes was defined by the use of hypoglycaemic medication, fasting plasma glucose (FPG) ≥ 7 mmol/l or glucose at 2 h ≥ 11.1 mmol/l during an OGTT. Persons meeting the criteria for impaired glucose tolerance were excluded from these analyses (FPG <7 mmol/l and 2 h glucose during an OGGT <11.1 but ≥ 7.8 mmol/l). Multivariable logistic regression was used to estimate associations between prevalence of diabetes and limb length while adjusting for possible confounders. RESULTS: A total of 145 individuals had diabetes. On univariate analysis, arm and leg length were not associated with diabetes. After adjustment for age, sex, computed tomography-measured intra-abdominal fat area, height, weight, smoking status and family history of diabetes, total arm length and upper arm length were inversely related to diabetes (OR for a 1 SD increase 0.49, 95% CI 0.29, 0.84 for total arm length, and OR 0.56, 95% CI 0.36, 0.87 for upper arm length). Forearm length, height and leg length were not associated with diabetes after adjustment for confounding variables. CONCLUSIONS/INTERPRETATION: Our findings of associations between arm lengths and prevalence of type 2 diabetes supports a role for factors that determine bone growth or their correlates in the development of this condition.

Subcutaneous thigh fat area is unrelated to risk of type 2 diabetes in a prospective study of Japanese Americans.

AIMS/HYPOTHESIS: Cross-sectional research has reported a negative association between subcutaneous thigh fat (STF) and type 2 diabetes prevalence but no prospective research on this association exists using direct measurements of STF obtained from imaging studies while adjusting for other fat depots. We studied the independent associations of intra-abdominal fat (IAF), subcutaneous abdominal fat (SAF) and STF with future risk of diabetes. METHODS: We prospectively followed 489 non-diabetic Japanese Americans (BMI 25.0-29.9 kg/m(2) 32.7%, ≥30.0 kg/m(2) 5.4%) over 10 years for the development of diabetes defined by use of hypoglycaemic medication or a fasting plasma glucose ≥7.0 mmol/l or 2 h ≥11.1 mmol/l during an OGTT. STF, SAF and IAF area were measured by computed tomography scan and mid-thigh circumference (TC) by tape measure at baseline. RESULTS: Over 10 years, 103 people developed diabetes. STF area was not independently associated with the odds of developing diabetes in a univariate or multiple logistic regression model (OR for a 1 SD increase 0.8 [95% CI 0.5, 1.2]) adjusted for age, sex, BMI, IAF and SAF. The only fat depot associated with diabetes odds in this model was IAF. TC was borderline significantly associated with a lower odds of developing diabetes (0.7 [95% CI 0.5, 1.0], p = 0.052). CONCLUSIONS/INTERPRETATION: Similar to other research, TC was negatively associated with diabetes risk, whereas STF was not, arguing that the negative association between TC and diabetes observed in other research is not due to STF mass. IAF area emerged as the only measured fat depot that was independently associated with type 2 diabetes risk.

Does abnormal insulin action or insulin secretion explain the increase in prevalence of impaired glucose metabolism with age in populations of different ethnicities?

BACKGROUND: Age is associated with both impaired glucose and insulin metabolism. To what extent the age-related changes in insulin resistance (IR) and beta-cell function contribute to the increase in prevalence of impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) is less known, and this is investigated in this study. METHODS: This study included 6610 men and 7664 women of different ethnic groups aged 30-69 years. IR and beta-cell function were examined by the homeostasis model assessment of insulin resistance (HOMA-IR) and homeostasis model assessment of beta-cell function (HOMA-B). Odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated using logistic regression analysis adjusting for body mass index and study. RESULTS: In Chinese men, the ORs (95% CIs) for IFG were 2.69 (1.70, 4.26), 2.51 (1.49, 4.21) and 2.89 (1.68, 4.97), respectively, in age groups of 40-49, 50-59 and 60-69 years compared with 30-39 years (p < 0.001 for trend); the corresponding figures for IGT were 1.73 (1.25, 2.38), 2.54 (1.78, 3.63) and 3.57 (2.46, 5.19) (p < 0.001 for trend). Similar trends for IGT were observed also in Chinese women and other ethnic groups, but not for IFG in Mauritius Indian and Creole men. Adjustment for HOMA-IR and HOMA-B reduced the ORs in all age groups of all ethnicities for both IFG and IGT, but the risk gradient between age groups remained particularly for the IGT. CONCLUSIONS: The age-related increase in glucose intolerance may not be fully explained by the defect in HOMA-IR and HOMA-B. As HOMA-IR and HOMA-B are only surrogate measures of insulin sensitivity and insulin secretion, the results need to be further investigated.

Reductive alteration of the regulatory function of the CD4(+)CD25(+) T cell fraction in silicosis patients.

Causal links have been documented between silica and rheumatoid arthritis, lupus erythematosus, systemic sclerosis and glomerulonephritis. Two different effects of silica have been suggested, an enhanced inflammatory response in the pulmonary region (e.g. activation of alveolar macrophages) and dysregulation of autoimmunity. Based on our previous reports showing in vitro activation of peripheral T cells by silica and reduced regulatory function of the peripheral CD4(+)CD25(+) fraction in which FoxP(3)+ regulatory T cells (Treg) are located, reconstitution of the CD4(+)CD25(+) fraction in silicosis patients (SILs) was investigated. Since T cells in peripheral CD4(+)CD25(+) and CD4(+)CD25(-) (effector T cells; Teff) fractions from SILs showed higher expression of pd-1 (a marker gene for T cell activation) in comparison to that of healthy donors (HDs), chronic T cell activation was considered to have occurred in SILs. In this study, a higher expression of the CD95/Fas molecule in Treg was recorded from silicosis patients (SILs) compared to healthy donors (HDs), and excess loss of FoxP3(+) Treg in freshly isolated peripheral blood mononuclear cells (PBMCs) from SILs relative to HDs was demonstrated when these cells were cultured with silica ex vivo, whereas CD25(+) cells were not reduced due to contamination of activated Teff in the CD4(+)CD25(+) fraction. The activation of both Teff and Treg results in reconstitution of the peripheral CD4(+)CD25(+) fraction, loss of Treg and contamination of activated Teff, resulting in reduction of the number and function of Treg. These results contribute to our understanding of the development of autoimmune diseases found in SILs.

Niflumic acid-sensitive ion channels play an important role in the induction of glucose-stimulated insulin secretion by cyclic AMP in mice.

AIMS/HYPOTHESIS: We have previously reported that glucose-stimulated insulin secretion (GSIS) is induced by glucagon-like peptide-1 (GLP-1) in mice lacking ATP-sensitive K(+) (K(ATP)) channels (Kir6.2(-/-) mice [up-to-date symbol for Kir6.2 gene is Kcnj11]), in which glucose alone does not trigger insulin secretion. This study aimed to clarify the mechanism involved in the induction of GSIS by GLP-1. METHODS: Pancreas perfusion experiments were performed using wild-type (Kir6.2(+/+)) or Kir6.2(-/-) mice. Glucose concentrations were either changed abruptly from 2.8 to 16.7 mmol/l or increased stepwise (1.4 mmol/l per step) from 2.8 to 12.5 mmol/l. Electrophysiological experiments were performed using pancreatic beta cells isolated from Kir6.2(-/-) mice or clonal pancreatic beta cells (MIN6 cells) after pharmacologically inhibiting their K(ATP) channels with glibenclamide. RESULTS: The combination of cyclic AMP plus 16.7 mmol/l glucose evoked insulin secretion in Kir6.2(-/-) pancreases where glucose alone was ineffective as a secretagogue. The secretion was blocked by the application of niflumic acid. In K(ATP) channel-inactivated MIN6 cells, niflumic acid similarly inhibited the membrane depolarisation caused by cAMP plus glucose. Surprisingly, stepwise increases of glucose concentration triggered insulin secretion only in the presence of cAMP or GLP-1 in Kir6.2(+/+), as in Kir6.2(-/-) pancreases. CONCLUSIONS/INTERPRETATION: Niflumic acid-sensitive ion channels participate in the induction of GSIS by cyclic AMP in Kir6.2(-/-) beta cells. Cyclic AMP thus not only acts as a potentiator of insulin secretion, but appears to be permissive for GSIS via novel, niflumic acid-sensitive ion channels. This mechanism may be physiologically important for triggering insulin secretion when the plasma glucose concentration increases gradually rather than abruptly.

Roles of cAMP signalling in insulin granule exocytosis.

Insulin secretion is regulated by a series of complex events generated by various intracellular signals including Ca(2+), ATP, cAMP and phospholipid-derived signals. Glucose-stimulated insulin secretion is the principal mode of insulin secretion, and the mechanism potentiating the secretion is critical for physiological responses. Among the various intracellular signals involved, cAMP is particularly important for amplifying insulin secretion. Recently, glucagon-like peptide-1 (GLP-1) analogues and dipeptidyl peptidase-IV (DPP-IV) inhibitors have been developed as new antidiabetic drugs. These drugs all act through cAMP signalling in pancreatic beta-cells. Until recently, cAMP was generally thought to potentiate insulin secretion through protein kinase A (PKA) phosphorylation of proteins associated with the secretory process. However, it is now known that in addition to PKA, cAMP has other targets such as Epac (also referred to as cAMP-GEF). The variety of the effects mediated by cAMP signalling may be linked to cAMP compartmentation in the pancreatic beta-cells.

Soluble interleukin-2 receptor as an indicator of immunological disturbance found in silicosis patients.

Silicosis patients (SILs) possess not only respiratory disorders but also alterations in autoimmunity. To determine an early indicator of immunological disturbance in SILs, the role of serum-soluble interleukin (IL)-2 receptor (sIL-2R) was analyzed. Of ten SILs, immunological clinical parameters such as immunoglobulin (Ig) G, complements, the titer of autoantibodies including anti-nuclear antibodies (ANA), anti-Scl-70 antibody (Ab) and anti-centromere (CM) Ab, and experimental indicators such as serum-soluble Fas, serum IL-2, CD25+ cells in CD4+ or CD8+ fractions, and sIL-2R were divided from respiratory parameters such as percent vital capacity (%VC), percentage of forced expiratory volume in 1 second (FEV1.0%) and v25/Ht (liter/second/m(body height) by a correlation assay. Additionally, a stepwise regression test showed that sIL-2R was correlated with Ig G, ANA and anti-CM Ab. Furthermore, factor analysis revealed that sIL-2R contributed to the subpopulation of SILs with poorer immunological status in the absence of alterations in respiratory status. By defining healthy donors as 1, SILs as 2 and patients with systemic sclerosis as 3 for immunopathological progression status as metric variables, sIL2R and ANA showed a strong positive correlation. This suggests that sIL-2R is a good clinical indicator of immunological disturbance found in SILs without clinical manifestations of any disturbance in autoimmunity. Further analysis using a large-scale number of patients should be performed to confirm these findings.

Lipoxygenase pathway in islet endocrine cells. Oxidative metabolism of arachidonic acid promotes insulin release.

Metabolism of arachidonic acid (AA) via the cyclooxygenase pathway reduces glucose-stimulated insulin release. However, metabolism of AA by the lipoxygenase pathway and the consequent effects on insulin secretion have not been simultaneously assessed in the endocrine islet. Both dispersed endocrine cell-enriched pancreatic cells of the neonatal rat, as well as intact islets of the adult rat, metabolized [(3)H]AA not only to cyclooxygenase products (prostaglandins E(2), F(2alpha), and prostacyclin) but also to the lipoxygenase product 12-hydroxyeicosatetraenoic acid (12-HETE). 12-HETE was identified by coelution with authentic tritiated or unlabeled 12-HETE using four high performance liquid chromatographic systems under eight mobile-phase conditions and its identity was confirmed by gas chromatography/mass spectrometry using selected ion monitoring. The predominant effect of exogenous AA (5 mug/ml) was to stimulate insulin release from pancreatic cells grown in monolayer. This effect was concentration- and time-dependent, and reversible. The effect of AA upon insulin release was potentiated by a cyclooxygenase inhibitor (indomethacin) and was prevented by either of two lipoxygenase inhibitors (5,8,11,14-eicosatetraynoic acid [ETYA] and BW755c). In addition, glucose, as well as two structurally dissimilar agents (the calcium ionophore A23187 and bradykinin), which activate phospholipase(s) and thereby release endogenous AA in several cell systems, also stimulated insulin secretion. The effects of glucose, glucagon, bradykinin and high concentrations of A23187 (5 mug/ml) to augment insulin release were blocked or considerably reduced by lipoxygenase inhibitors. However, a lower concentration of the ionophore (0.25 mug/ml), which did not appear to activate phospholipase, was resistant to blockade. Exogenous 12-HETE (up to 2,000 ng/ml) did not alter glucose-induced insulin release. However, the labile intermediate 12-hydroperoxy-ETE increased insulin release. Furthermore, diethylmaleate (which binds intracellular glutathione and thereby impedes conversion of the lipoxygenase intermediates hydroperoxy-ETE and leukotriene A(4) to HETE and leukotriene C(4), respectively) potentiated the effect of glucose and of exogenous AA. Finally, 5,6-epoxy, 8,11,14-eicosatrienoic acid (a relatively stable epoxide analogue of leukotriene A(4)) as well as two other epoxy-analogues, potentiated glucose-induced insulin release. We conclude that dual pathways of AA metabolism exist in islet endocrine cells and have opposing regulatory effects on the beta cell-an inhibitory cyclooxygenase cascade and a stimulatory lipoxygenase cascade. Labile products of the latter pathway may play a pivotal role in stimulus-secretion coupling in the islet.

Two cholesterol ester hydrolases. Distribution in rat tissues and in cultured human fibroblasts and monkey arterial smooth muscle cells.

Hydrolytic activity against acetone-dispersed [4-14C]cholesterol oleate has been assayed as a function of pH in seven parenchymal tissues, blood cells, and plasma of the rat, as well as in cultured human fibroblasts and monkey (Macaca nemestrina) arterial smooth muscle cells. Both acid and neutral hydrolytic activities were present in all of these except rat plasma. The pH optima were in all cases close to pH 4.5 and pH 6.8. Acid activity was quite constant from tissue to tissue, while neutral activity varied greatly, being greatest in adrenal, testis, and adipose tissue. Subcellular fractionation of human fibroblasts allowed demonstration that activities at pH 4.5 and pH 6.8 were concentrated in different fractions, apparently lysosomal and polysomal, respectively. It appears most cell types, including fibroblasts and smooth muscle cells, contain two separate enzymes capable of hydrolyzing cholesterol esters. The neutral pH polysomal enzyme, which is especially prominent in certain tissues, may have a function related to the specialized roles of these tissues.

Inhibitory effects of glucocorticoids on collagen synthesis by mouse sponge granulomas and granuloma fibroblasts in culture.

The basis for the glucocorticoid-mediated decrease in tissue collagen was studied in mouse granulomas and in primary granuloma fibroblast cultures. Injection of mice for 12 days with dexamethasone (0.35 mg/kg body weight) resulted in a 50--70% inhibition of collagen synthesis and accumulation in polyvinyl sponge-induced granulomas whereas total protein synthesis was inhibited by only about 25%. The decreased collagen content of the granuloma was accounted for by both a reduced fibroblast number and diminished synthesis per cell. Growth rates, total protein synthesis and collagen synthesis were the same in granuloma fibroblast cultures derived from control or steroid-treated mice. However, addition of 3.10(-7) M hydrocortisone to the culture medium caused a 30--50% inhibition of both collagen and non-collagen protein synthesis in firbroblasts from either source. These inhibitory effects were dose- and time-dependent with a lag time of 12--24 h. Prolyl hydroxylase activity was reduced both in sponge granulomas from glucocorticoid-treated mice and in hydrocortisone-treated fibroblast cultures. However, protein synthesis was inhibited to the same extent as the inhibition of prolyl hydroxylase activity and there was no effect on peptidyl prolyl hydroxylation. These results indicate that the glucocorticoid-induced reduction of collagen synthesis and accumulation observed in mouse granulomas and primary granuloma fibroblast cultures is not specific for this protein. Furthermore, glucocorticoid-induced inhibition of collagen synthesis cannot be attributed to underhydroxylation of collagen prolyl residues.

Phasic effects of glucose, p-hydroxymercuribenzoate, and lysophosphatidylcholine on insulin secretion from HIT cells.

Monolayer cultures of HIT cells were superfused to examine phasic insulin secretion. A biphasic pattern of insulin secretion was observed when cells were stimulated with a constant glucose concentration as low as 0.28 mM, with increasing stimulation at 0.56, 1.7, and 5.6 mM glucose. Higher glucose concentrations did not increase insulin secretion. In the absence of glucose, p-hydroxymercuribenzoate (15, 30, and 50 microM), which blocks the reacylation of lysophospholipids with arachidonic acid, also evoked a concentration-dependent biphasic release of insulin. Lysophosphatidylcholine (50, 75, and 100 micrograms/ml) also caused a concentration-dependent biphasic release of insulin in the absence of glucose. These observations were similar to those previously reported for superfused monolayer culture of rat islet cells and suggest that the HIT cell is a beta-cell line that may be valuable in the further examination of the relationships among glucose, phospholipid metabolism, and insulin secretion. The data are consistent with the hypothesis that glucose-stimulated release of lysophospholipids may be important in initiation of the biphasic pattern of glucose-stimulated insulin release.

Phasic glucose-stimulated insulin secretion by neonatal rat pancreatic islet cells. Enhancement by sodium salicylate.

UNLABELLED: Monolayer cultures of neonatal rat pancreatic islets were superfused to examine phasic insulin secretion. When stimulated with a constant glucose concentration of 300 mg/dl, insulin secretion promptly rose to a peak more than eightfold higher than the basal levels observed with glucose 30 mg/dl. This first-phase peak was followed by a quick decline in insulin to a level about four- to fivefold higher than basal, representing second-phase insulin secretion. Addition of sodium salicylate 20 mg/dl enhanced glucose-stimulated insulin secretion. Addition of salicylate concurrently with glucose greatly enhanced second-phase insulin secretion, but did not affect the first-phase peak, thereby converting the biphasic pattern to one that appeared to be monophasic. However, when cultures were superfused with salicylate both before and concurrent with stimulation by glucose, both the first-phase peak and the second phase of insulin secretion were increased, resulting in not only preservation but enhancement of the biphasic pattern. Salicylate had no effect on basal insulin secretion at glucose 30 mg/dl. During the transition from glucose 300 mg/dl to 30 mg/dl, immediately as glucose concentration began to fall in the superfusate, insulin secretion showed a transient increase ("off response"). CONCLUSIONS: (1) Cultures of neonatal rat pancreatic islet cells respond with a biphasic pattern of insulin secretion when exposed to a continuous and constant glucose stimulus. (2) When endogenous prostaglandin synthesis is inhibited by sodium salicylate, the biphasic pattern not only remains but is enhanced, indicating that endogenous prostaglandin synthesis exerts a tonic restraint throughout the entire period of glucose-stimulated phasic insulin release.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects on glucose-induced insulin secretion of lipoxygenase-derived metabolites of arachidonic acid.

Our previous data suggested that lipoxygenation of endogenously released arachidonic acid (AA) is a critical step in stimulus-secretion coupling in the pancreatic beta cell. In the current study using monolayer cultures of neonatal rat islet cells, exogenous arachidonic acid (AA) (5 micrograms/ml) potently stimulated insulin release in the presence of a substimulatory glucose concentration, and potentiated release induced by glucose. Since the latter stimulatory effect of AA is prevented by inhibitors of the lipoxygenase pathway, we examined the effects of various lipoxygenase pathway products on glucose-induced insulin secretion. The mediator was not one of the stable end-products of either limb of the lipoxygenase pathway: 12- or 5-hydroxyeicosatetraenoic acid (HETE) (0.5-2000 ng/ml) did not alter insulin release, whereas 11-HETE, 15-HETE, leukotriene (LT)B4 and the delta 6 trans isomers of LTB4, LTC4 and 11-trans LTC4 all inhibited insulin release. Furthermore, diethylcarbamazine, a selective leukotriene synthesis inhibitor, did not prevent AA- or glucose-induced insulin release, arguing against a role for LTs as the mediator of AA's stimulatory effect. However, the unstable intermediate 12-hydroperoxyeicosatetraenoic acid (12-HPETE), and positional isomers of 12-HPETE, potentiated glucose-induced insulin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Disparate effects of enkephalin and morphine upon insulin and glucagon secretion by islet cell cultures.

Insulin and glucagon release from monolayer pancreatic islet cell cultures were inhibited in a dose-response fashion by various enkephalins. Morphine, however, stimulated insulin and glucagon release. Both effects were blocked by naloxone, while naloxone alone had no effect. In isolated and denervated islet cells, opiates directly influence secretion from islet cells.

Effects of glucagonlike peptide I-(7-36) on release of insulin, glucagon, and somatostatin by rat pancreatic islet cell monolayer cultures.

Glucagonlike peptide I (GLP-I-(7-36] is cleaved from proglucagon in ileal epithelial cells and increases in human plasma after nutrient ingestion. This peptide has been shown to stimulate insulin secretion in vitro and in vivo and thus potentially acts as an incretin. To characterize its action on islet cells, the release of insulin, glucagon, and somatostatin by rat pancreatic islet monolayer cultures at varying concentrations of GLP-I-(7-36) was measured. The interaction of GLP-I-(7-36) with nutrient substrates was assessed by adding amino acids and differing glucose concentrations to the cultures. Islet cell cultures (n = 5) were incubated for 1 h in medium containing 1.67 or 16.7 mM glucose or 1.67 mM glucose supplemented with amino acids and GLP-I-(7-36) at 10(-13)-10(-7) M. Hormone release was compared with control cultures containing no GLP-I-(7-36); 1.67-16.7 mM glucose with and without GLP-I-(7-36) at 10(-11) M; and 1.67, 3.3, 8.3, or 11.1 mM glucose alone or supplemented with amino acids, GLP-I-(7-36) 10(-11) M, or both amino acids and GLP-I-(7-36). In medium with 1.67 or 16.7 mM glucose or 1.67 mM glucose and amino acids, GLP-I-(7-36) increased insulin secretion two- to threefold over control at concentrations of 10(-9), 10(-11), and 10(-12) M, respectively. In medium with increasing concentrations of glucose, GLP-I-(7-36) at 10(-11) M significantly increased insulin secretion at glucose concentrations greater than or equal to 3.34 mM.(ABSTRACT TRUNCATED AT 250 WORDS)