Increased urinary glucocorticoid metabolites are associated with metabolic syndrome, hypoadiponectinemia, insulin resistance and β cell dysfunction

Metabolic syndrome (MetS) may have increased cortisol (F) production caused by 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) in liver and adipose tissue and/or by HPA axis dysregulation. F is then mainly metabolized by liver reductases into inactive tetrahydrometabolites (THMs). We measured THM levels in patients with or without MetS and evaluate the correlation between THMs and anthropometric and biochemical parameters. We recruited 221 subjects, of whom 130 had MetS by ATP III. We evaluated F, cortisone (E), adipokines, glucose, insulin and lipid profiles as well as urinary (24 h) F, E and THM levels. β Cell function was estimated by the HOMA Calculator. We observed that patients with MetS showed higher levels of THMs, HOMA-IR and leptin and lower levels of adiponectin and HOMA-β but no differences in F and E in plasma or urine. THM was associated with weight (r = +0.44, p < 0.001), waist circumference (r = +0.38, p < 0.01), glycemia (r = +0.37, p < 0.01), and triglycerides (r = +0.18, p = 0.06) and negatively correlated with adiponectin (r = −0.36, p < 0.001), HOMA-β (r = −0.21, p < 0.001) and HDL (r = −0.29, p < 0.01). In a logistic regression model, THM levels were associated with hypertension, hyperglycemia and dyslipidemia. We conclude that MetS is associated with increased urinary THMs but not with F and E levels in plasma or urine. Increased levels of THM, reflecting the daily cortisol production subsequently metabolized, are correlated with hypoadiponectinemia, hypertension, dyslipidemia, insulin resistance and β cell dysfunction. A subtle increased in glucocorticoid production may further account for the phenotypic and biochemical similarities observed in central obesity and Cushing’s syndrome.     

Two incretin hormones GLP-1 and GIP: comparison of their actions in insulin secretion and β cell preservation

Gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the two primary incretin hormones secreted from the intestine upon ingestion of glucose or nutrients to stimulate insulin secretion from pancreatic β cells. GIP and GLP-1 exert their effects by binding to their specific receptors, the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R), which belong to the G-protein coupled receptor family. Receptor binding activates and increases the level of intracellular cAMP in pancreatic β cells, thereby stimulating insulin secretion glucose-dependently. In addition to their insulinotropic effects, GIP and GLP-1 have been shown to preserve pancreatic β cell mass by inhibiting apoptosis of β cells and enhancing their proliferation. Due to such characteristics, incretin hormones have been gaining mush attention as attractive targets for treatment of type 2 diabetes, and indeed incretin-based therapeutics have been rapidly disseminated worldwide. However, despites of plethora of rigorous studies, molecular mechanisms underlying how GIPR and GLP-1R activation leads to enhancement of glucose-dependent insulin secretion are still largely unknown. Here, we summarize the similarities and differences of these two incretin hormones in secretion and metabolism, their insulinotropic actions and their effects on pancreatic β cell preservation. We then try to discuss potential of GLP-1 and GIP in treatment of type 2 diabetes.     

Ghrelin inhibits insulin secretion through the AMPK-UCP2 pathway in β cells

Ghrelin inhibits insulin secretion partly via induction of IA-2β. However, the orexigenic effect of ghrelin is mediated by the AMP-activated protein kinase (AMPK)-uncoupling protein 2 (UCP2) pathway. Here, we demonstrate that ghrelin’s inhibitory effect on insulin secretion also occurs through the AMPK-UCP2 pathway. Ghrelin increased AMPK phosphorylation and UCP2 mRNA expression in MIN6 insulinoma cells. Overexpression or downregulation of UCP2 attenuated or enhanced insulin secretion, respectively. Furthermore, AMPK activator had a similar effect to ghrelin on UCP2 and insulin secretion in MIN6 cells. In conclusion, ghrelin’s inhibitory effect on insulin secretion is partly mediated by the AMPK-UCP2 pathway, which is independent of the IA-2β pathway.     

Transcellular neuroligin-2 interactions enhance insulin secretion and are integral to pancreatic β cell function

Normal glucose-stimulated insulin secretion is dependent on interactions between neighboring β cells. Elucidation of the reasons why this cell-to-cell contact is essential will probably yield critical insights into β cell maturation and function. In the central nervous system, transcellular protein interactions (i.e. interactions between proteins on the surfaces of different cells) involving neuroligins are key mediators of synaptic functional development. We previously demonstrated that β cells express neuroligin-2 and that insulin secretion is affected by changes in neuroligin-2 expression. Here we show that the effect of neuroligin-2 on insulin secretion is mediated by transcellular interactions. Neuroligin-2 binds with nanomolar affinity to a partner on the β cell surface and contributes to the increased insulin secretion brought about by β cell-to-β cell contact. It does so in a manner seemingly independent of interactions with neurexin, a known binding partner. As in the synapse, transcellular neuroligin-2 interactions enhance the functioning of the submembrane exocytic machinery. Also, as in the synapse, neuroligin-2 clustering is important. Neuroligin-2 in soluble form, rather than presented on a cell surface, decreases insulin secretion by rat islets and MIN-6 cells, most likely by interfering with endogenous neuroligin interactions. Prolonged contact with neuroligin-2-expressing cells increases INS-1 β cell proliferation and insulin content. These results extend the known parallels between the synaptic and β cell secretory machineries to extracellular interactions. Neuroligin-2 interactions are one of the few transcellular protein interactions thus far identified that directly enhance insulin secretion. Together, these results indicate a significant role for transcellular neuroligin-2 interactions in the establishment of β cell function.     

Role of exopolysaccharide in salt stress resistance and cell motility of Mesorhizobium alhagi CCNWXJ12–2T

Applied Microbiology and Biotechnology - Mesorhizobium alhagi, a legume-symbiont soil bacterium that forms nodules with the desert plant Alhagi sparsifolia, can produce large amounts of...     

Successful treatment of prediabetes in clinical practice: targeting insulin resistance and β-cell dysfunction

ObjectiveTo determine the effectiveness of targeted pharmacologic interventions to reverse documented pathophysiologic abnormalities in prediabetes.MethodsPatients with impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG) were treated with insulin sensitizers (pioglitazone + metformin) or insulin sensitizers + exenatide on the basis of oral glucose tolerance testing-derived indices of insulin resistance and impaired b-cell function. Patients who declined pharmacologic therapy received lifestyle modification only.ResultsOne hundred five patients with IGT and/or IFG were treated with insulin sensitizers (pioglitazone + metformin) (n = 40), insulin sensitizers + exenatide (n = 47), or lifestyle modification only (n = 18). After a mean follow-up period of 8.9 months, the lifestyle modification group demonstrated no significant changes in fasting plasma glucose, plasma glucose area under the curve during oral glucose tolerance testing, insulin sensitivity, or b-cell function. In the pioglitazone + metformin group (24 hours off medication), fasting plasma glucose fell from 109 to 102 mg/dL; plasma glucose area under the curve decreased by 12.0%; insulin sensitivity and b-cell function improved by 42% and 50%, respectively (all P < .001); 14.3% converted to normal glucose tolerance; and no patient developed diabetes. In the pioglitazone + metformin + exenatide group (24 hours off medication), fasting plasma glucose fell from 109 to 98 mg/dL; plasma glucose area under the curve decreased by 21.2%; insulin sensitivity and b-cell function improved by 52% and 109%, respectively (all P < .001); 59.1% of patients with IGT reverted to normal glucose tolerance; and no patient developed diabetes.ConclusionsTargeted pathophysiologic therapy based on oral glucose tolerance test-derived measures of insulin sensitivity and b-cell function can be implemented in general internal medicine and endocrine practice and is associated with marked improvement in glucose tolerance and reversion of prediabetes to normal glucose tolerance in more than 50% of patients. (Endocr Pract. 2012;18: 342-350)     

Role of mitochondrial dysfunction and oxidative stress in the pathogenesis of selective neuronal loss in Wernicke’s encephalopathy

Thiamine deficiency results in Wernicke’s encephalopathy and is commonly encountered in chronic alcoholism, gastrointestinal diseases, and HIV AIDS. The earliest metabolic consequence of thiamine deficiency is a selective loss in activity of the thiamine diphosphate-dependent enzyme α-ketoglutarate dehydrogenase (α-KGDH), a rate-limiting tricarboxylic acid cycle enzyme. Thiamine deficiency is characterized neuropathologically by selective neuronal cell death in the thalamus, pons, and cerebellum. The cause of this region-selective neuronal loss is unknown, but mechanisms involving cellular energy failure, focal lactic acidosis, and NMDA receptor-mediated excitotoxicity have classically been implicated. More recently, evidence supports a role for oxidative stress. Evidence includes increased endothelial nitric oxide synthase, nitrotyrosine deposition, microglial activation, and lipid peroxidation. Reactive oxygen species production results in decreased expression of astrocytic glutamate transporters and decreased activities of α-KGDH, resulting in an amplification of cell death mechanisms in thiamine deficiency.     

From insulin synthesis to secretion: Alternative splicing of type 2 ryanodine receptor gene is essential for insulin secretion in pancreatic β cells

Increases in the intracellular Ca²⁺ concentration in pancreatic islets, resulting from the Ca²⁺ mobilization from the intracellular source through the ryanodine receptor, are essential for insulin secretion by glucose. Cyclic ADP-ribose, a potent Ca²⁺ mobilizing second messenger synthesized from NAD⁺ by CD38, regulates the opening of ryanodine receptor. A novel ryanodine receptor mRNA (the islet-type ryanodine receptor) was found to be generated from the type 2 ryanodine receptor gene by the alternative splicing of exons 4 and 75. The islet-type ryanodine receptor mRNA is expressed in a variety of tissues such as pancreatic islets, cerebrum, cerebellum, and other neuro-endocrine cells, whereas the authentic type 2 ryanodine receptor mRNA (the heart-type ryanodine receptor) was found to be generated using GG/AG splicing of intron 75 and is expressed in the heart and the blood vessel. The islet-type ryanodine receptor caused a greater increase in the Ca²⁺ release by caffeine when expressed in HEK293 cells pre-treated with cyclic ADP-ribose, suggesting that the novel ryanodine receptor is an intracellular target for the CD38-cyclic ADP-ribose signal system in mammalian cells and that the tissue-specific alternative splicing of type 2 ryanodine receptor mRNA plays an important role in the functioning of the cyclic ADP-ribose-sensitive Ca²⁺ release.     

Role of inhibitory κB kinase and c-Jun NH2-terminal kinase in the development of hepatic insulin resistance in critical illness diabetes

Hyperglycemia and insulin resistance induced by acute injuries or critical illness are associated with increased mortality and morbidity, as well as later development of type 2 diabetes. The molecular mechanisms underlying the acute onset of insulin resistance following critical illness remain poorly understood. In the present studies, the roles of serine kinases, inhibitory κB kinase (IKK) and c-Jun NH(2)-terminal kinase (JNK), in the acute development of hepatic insulin resistance were investigated. In our animal model of critical illness diabetes, activation of hepatic IKK and JNK was observed as early as 15 min, concomitant with the rapid impairment of hepatic insulin signaling and increased serine phosphorylation of insulin receptor substrate 1. Inhibition of IKKα or IKKβ, or both, by adenovirus vector-mediated expression of dominant-negative IKKα or IKKβ in liver partially restored insulin signaling. Similarly, inhibition of JNK1 kinase by expression of dominant-negative JNK1 also resulted in improved hepatic insulin signaling, indicating that IKK and JNK1 kinases contribute to critical illness-induced insulin resistance in liver.     

Oestradiol and insulin secretion in the rat: when does oestradiol start stimulating the insulin release?

Long-term oestradiol treatments induce hyperinsulinism and low glycaemia. Time-related experiments were performed to determine when this effect appears in islets from treated rats. Oestradiol first inhibited the insulin secretion for 2 days and later stimulated the B cells functioning from the 3rd day of treatment onward. This effect of oestradiol was dose-dependent. The beginning of this stimulating action of oestradiol was characterized by a normal tolerance to glucose and normoglycaemia, still maintained in spite of hyperinsulinaemia, hypoglucagonaemia and lowered food intake. This suggested that the long-term oestradiol-induced low glycaemia was a consequence of the hyperinsulinism.     

Mitochondrial dysfunction in non-alcoholic fatty liver disease and insulin resistance: Cause or consequence?

Abstract

Non-alcoholic fatty liver disease (NAFLD) is considered the hepatic manifestation of the metabolic syndrome and refers to a spectrum of disorders ranging from steatosis to steatohepatitis, a disease stage characterized by inflammation, fibrosis, cell death and insulin resistance (IR). Due to its association with obesity and IR the impact of NAFLD is growing worldwide. Consistent with the role of mitochondria in fatty acid (FA) metabolism, impaired mitochondrial function is thought to contribute to NAFLD and IR. Indeed, mitochondrial dysfunction and impaired mitochondrial respiratory chain have been described in patients with non-alcoholic steatohepatitis and skeletal muscle of obese patients. However, recent data have provided evidence that pharmacological and genetic models of mitochondrial impairment with reduced electron transport stimulate insulin sensitivity and protect against diet-induced obesity, hepatosteatosis and IR. These beneficial metabolic effects of impaired mitochondrial oxidative phosphorylation may be related not only to the reduction of reactive oxygen species production that regulate insulin signaling but also to decreased mitochondrial FA overload that generate specific metabolites derived from incomplete FA oxidation (FAO) in the TCA cycle. In line with the Randle cycle, reduced mitochondrial FAO rates may alleviate the repression on glucose metabolism in obesity. In addition, the redox paradox in insulin signaling and the delicate mitochondrial antioxidant balance in steatohepatitis add another level of complexity to the role of mitochondria in NAFLD and IR. Thus, better understanding the role of mitochondria in FA metabolism and glucose homeostasis may provide novel strategies for the treatment of NAFLD and IR.     

Role of peroxisomes in the biosynthesis and secretion of β-lactams and other secondary metabolites

Peroxisomes are eukaryotic organelles surrounded by a single bilayer membrane, containing a variety of proteins depending on the organism; they mainly perform degradation reactions of toxic metabolites (detoxification), catabolism of linear and branched-chain fatty acids, and removal of H₂O₂ (formed in some oxidative processes) by catalase. Proteins named peroxins are involved in recruiting, transporting, and introducing the peroxisomal matrix proteins into the peroxisomes. The matrix proteins contain the peroxisomal targeting signals PTS1 and/or PTS2 that are recognized by the peroxins Pex5 and Pex7, respectively. Initial evidence indicated that the penicillin biosynthetic enzyme isopenicillin N acyltransferase (IAT) of Penicillium chrysogenum is located inside peroxisomes. There is now solid evidence (based on electron microscopy and/or biochemical data) confirming that IAT and the phenylacetic acid- and fatty acid-activating enzymes are also located in peroxisomes. Similarly, the Acremonium chrysogenum CefD1 and CefD2 proteins that perform the central reactions (activation and epimerization of isopenicillin N) of the cephalosporin pathway are targeted to peroxisomes. Growing evidence supports the conclusion that some enzymes involved in the biosynthesis of mycotoxins (e.g., AK-toxin), and the biosynthesis of signaling molecules in plants (e.g., jasmonic acid or auxins) occur in peroxisomes. The high concentration of substrates (in many cases toxic to the cytoplasm) and enzymes inside the peroxisomes allows efficient synthesis of metabolites with interesting biological or pharmacological activities. This compartmentalization poses additional challenges to the cell due to the need to import the substrates into the peroxisomes and to export the final products; the transporters involved in these processes are still very poorly known. This article focuses on new aspects of the metabolic processes occurring in peroxisomes, namely the degradation and detoxification processes that lead to the biosynthesis and secretion of secondary metabolites.     

Role of the adipocyte-specific NF-κB activity in the regulation of IP-10 and T cell migration

Infiltration of immune cells into adipose tissue plays a central role in the pathophysiology of obesity-associated low-grade inflammation. The aim of this study was to analyze the role of adipocyte NF-κB signaling in the regulation of the chemokine/adipokine interferon-γ-induced protein 10 kDa (IP-10) and adipocyte-mediated T cell migration. Therefore, the regulation of IP-10 was investigated in adipose tissue of male C57BL/6J mice, primary human and 3T3-L1 preadipocytes/adipocytes. To specifically block the NF-κB pathway, 3T3-L1 cells stably overexpressing a transdominant mutant of IκBα were generated, and the chemical NF-κB inhibitor Bay117082 was used. Adipocyte-mediated T cell migration was assessed by a migration assay. It could be shown that IP-10 expression was higher in mature adipocytes compared with preadipocytes. Induced IP-10 expression and secretion were completely blocked by an NF-κB inhibitor in 3T3-L1 and primary human adipocytes. Stable overexpression of a transdominant mutant of IκBα in 3T3-L1 adipocytes led to an inhibition of basal and stimulated IP-10 expression and secretion. T cell migration was induced by 3T3-L1 adipocyte-conditioned medium, and both basal and induced T cell migration was strongly inhibited by stable overexpression of a transdominant IκBα mutant. In addition, with the use of an anti-IP-10 antibody, a significant decrease of adipocyte-induced T cell migration was shown. In conclusion, in this study, we could demonstrate that the NF-κB pathway is essential for the regulation of IP-10 in 3T3-L1 and primary human adipocytes. Adipocytes rather than preadipocytes contribute to NF-κB-dependent IP-10 expression and secretion. Furthermore, NF-κB-dependent factors and especially IP-10 represent novel signals from adipocytes to induce T cell migration.     

Does obesity play a major role in the pathogenesis of sleep apnoea and its associated manifestations via inflammation, visceral adiposity, and insulin resistance?

Despite the early recognition of the strong association between obstructive sleep apnoea (OSA) and obesity, and OSA and cardiovascular problems, sleep apnoea has been treated as a \"local abnormality\" of the respiratory track rather than as a \"systemic illness\". In 1997, we first reported that the pro-inflammatory cytokines interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNFalpha) were elevated in patients with disorders of excessive daytime sleepiness (EDS) and proposed that these cytokines were mediators of daytime sleepiness. In subsequent studies, it was shown that IL-6, TNFalpha, and insulin levels were elevated in sleep apnoea independently of obesity and that visceral fat was the primary parameter linked with sleep apnoea. Further studies showed that women with the polycystic ovary syndrome (PCOS) were much more likely than controls to have sleep-disordered breathing (SDB) and daytime sleepiness, suggesting a pathogenetic role of insulin resistance in OSA. Additional accumulated evidence that supports the role of obesity and the associated metabolic aberrations in the pathogenesis of sleep apnoea and related symptoms include: obesity without sleep apnoea is associated with daytime sleepiness; the protective role of gonadal hormones as suggested by the increased prevalence of sleep apnoea in post-menopausal women and the significantly reduced risk for OSA in women on hormonal therapy; partial effects of continuous positive airway pressure (CPAP) in obese patients with apnoea on hypercytokinemia, insulin resistance indices, and visceral fat; and that the prevalence of the metabolic syndrome in the U.S. population from the Third National Health and Nutrition Examination Survey (1988-1994) parallels the prevalence of symptomatic sleep apnoea in general random samples. Furthermore, the beneficial effect of a cytokine antagonist on EDS and apnoea in obese, male apnoeics and that of exercise and weight loss on SDB and EDS in general random or clinical samples, supports the hypothesis that cytokines and insulin resistance are mediators of EDS and sleep apnoea in humans. Finally, our recent finding that in obese, hypothalamic CRH neuron is hypoactive, provides additional evidence on the potential central neural mechanisms for depressed ventilation and consequent development of sleep apnoea in obese individuals. In conclusion, accumulating evidence provides support to our thesis that obesity via inflammation, insulin resistance, visceral adiposity, and central neural mechanisms, e.g. hypofunctioning hypothalamic CRH, play a major role in the pathogenesis of sleep apnoea, sleepiness, and the associated cardiovascular co-morbidities.     

Insulin resistance in the liver: Deficiency or excess of insulin?

In insulin-resistant states (obesity, pre-diabetes, and type 2 diabetes), hepatic production of glucose and lipid synthesis are heightened in concert, implying that insulin deficiency and insulin excess coexists in this setting. The fact that insulin may be inadequate or excessive at any one point in differing organs and tissues has many biologic ramifications. In this context the concept of metabolic compartmentalization in the liver is offered herein as one perspective of this paradox. In particular, we focus on the hypothesis that insulin resistance accentuates differences in periportal and perivenous hepatocytes, namely periportal glucose production and perivenous lipid synthesis. Subsequently, excessive production of glucose and accumulation of lipids could be expected in the livers of patients with obesity and insulin resistance. Overall, in this review, we provide our integrative perspective regarding how excessive production of glucose in periportal hepatocytes and accumulation of lipids in perivenous hepatocytes interact in insulin resistant states.     

Role of the mitochondria in immune-mediated apoptotic death of the human pancreatic β cell line βLox5

Mitochondria are indispensable in the life and death of many types of eukaryotic cells. In pancreatic beta cells, mitochondria play an essential role in the secretion of insulin, a hormone that regulates blood glucose levels. Unregulated blood glucose is a hallmark symptom of diabetes. The onset of Type 1 diabetes is preceded by autoimmune-mediated destruction of beta cells. However, the exact role of mitochondria has not been assessed in beta cell death. In this study, we examine the role of mitochondria in both Fas- and proinflammatory cytokine-mediated destruction of the human beta cell line, βLox5. IFNγ primed βLox5 cells for apoptosis by elevating cell surface Fas. Consequently, βLox5 cells were killed by caspase-dependent apoptosis by agonistic activation of Fas, but only after priming with IFNγ. This beta cell line undergoes both apoptotic and necrotic cell death after incubation with the combination of the proinflammatory cytokines IFNγ and TNFα. Additionally, both caspase-dependent and -independent mechanisms that require proper mitochondrial function are involved. Mitochondrial contributions to βLox5 cell death were analyzed using mitochondrial DNA (mtDNA) depleted βLox5 cells, or βLox5 ρ(0) cells. βLox5 ρ(0) cells are not sensitive to IFNγ and TNFα killing, indicating a direct role for the mitochondria in cytokine-induced cell death of the parental cell line. However, βLox5 ρ(0) cells are susceptible to Fas killing, implicating caspase-dependent extrinsic apoptotic death is the mechanism by which these human beta cells die after Fas ligation. These data support the hypothesis that immune mediators kill βLox5 cells by both mitochondrial-dependent intrinsic and caspase-dependent extrinsic pathways.     

Role of fatty acid uptake and fatty acid β-oxidation in mediating insulin resistance in heart and skeletal muscle

Fatty acids are a major fuel source used to sustain contractile function in heart and oxidative skeletal muscle. To meet the energy demands of these muscles, the uptake and β-oxidation of fatty acids must be coordinately regulated in order to ensure an adequate, but not excessive, supply for mitochondrial β-oxidation. However, imbalance between fatty acid uptake and β-oxidation has the potential to contribute to muscle insulin resistance. The action of insulin is initiated by binding to its receptor and activation of the intrinsic protein tyrosine kinase activity of the receptor, resulting in the initiation of an intracellular signaling cascade that eventually leads to insulin-mediated alterations in a number of cellular processes, including an increase in glucose transport. Accumulation of fatty acids and lipid metabolites (such as long chain acyl CoA, diacylglycerol, triacylglycerol, and/or ceramide) can lead to alterations in this insulin signaling pathway. An imbalance between fatty acid uptake and oxidation is believed to be responsible for this lipid accumulation, and is thought to be a major cause of insulin resistance in obesity and diabetes, due to lipid accumulation and inhibition of one or more steps in the insulin-signaling cascade. As a result, decreasing muscle fatty acid uptake can improve insulin sensitivity. However, the potential role of increasing fatty acid β-oxidation in the heart or skeletal muscle in order to prevent cytoplasmic lipid accumulation and decrease insulin resistance is controversial. While increased fatty acid β-oxidation may lower cytoplasmic lipid accumulation, increasing fatty acid β-oxidation can decrease muscle glucose metabolism, and incomplete fatty acid oxidation has the potential to also contribute to insulin resistance. In this review, we discuss the proposed mechanisms by which alterations in fatty acid uptake and oxidation contribute to insulin resistance, and how targeting fatty acid uptake and oxidation is a potential therapeutic approach to treat insulin resistance.