Adipokines, the bioactive factors derived mainly from adipocytes, regulate pancreatic beta-cell function including insulin secretion, gene expression and apoptosis. In this review, we propose that adipokines influence beta-cell function through three interdependent pathways. The first is through regulating lipid and glucose metabolism in beta-cells. The second implicates the change of ion channel opening and closing in beta-cells. The third pathway is via the modification of insulin sensitivity of beta-cells. The endocrine function of adipocytes is dynamic, and the secretion of various adipokines changes under different metabolic conditions. During the progression from the normal state to obesity and to type 2 diabetes, adipokines contribute to the occurrence and development of beta-cell dysfunction in type 2 diabetes.
Adipocytes ; physiology ; Adiponectin ; physiology ; Animals ; Diabetes Mellitus, Type 2 ; physiopathology ; Glucose ; metabolism ; Humans ; Insulin ; pharmacology ; Insulin-Secreting Cells ; physiology ; Leptin ; physiology ; Lipid Metabolism

Branched chain amino acids, as essential amino acids, can be used to synthesize nitrogen-containing compounds and also act as signal molecules to regulate substance metabolism. Studies have shown that the elevated level of branched chain amino acids is closely related to insulin resistance and type 2 diabetes. It can affect insulin signal transduction by activating mammalian target of rapamycin (mTOR) signal pathway, and regulate insulin resistance by damaging lipid metabolism and affecting mitochondrial function. In addition, abnormal catabolism of branched amino acids can lead to the accumulation of metabolic intermediates, such as branched chain α-keto acids, 3-hydroxyisobutyrate and β-aminoisobutyric acid. Branched chain α-keto acids and 3-hydroxyisobutyrate can induce insulin resistance by affecting insulin signaling pathway and damaging lipid metabolism. β-aminoisobutyric acid can improve insulin resistance by reducing lipid accumulation and inflammatory reaction and enhancing fatty acid oxidation. This paper systematically reviewed the regulatory effects and mechanisms of branched chain amino acids and their metabolic intermediates on insulin resistance, which will provide a new direction for the prevention and treatment of insulin resistance and type 2 diabetes.
Humans ; Amino Acids, Branched-Chain/metabolism* ; Insulin Resistance/physiology* ; Diabetes Mellitus, Type 2 ; Insulin/pharmacology* ; Keto Acids/metabolism*

OBJECTIVETo investigate the effect of high glucose on mitochondrial respiratory chain function in INS-1 cells.

METHODSThe pancreatic beta cell line INS-1 was divided into the normal control (NC), high glucose (HG), and N-acetyl-L-cysteine (NAC) pretreatment groups, which were cultured for 72 h in the presence of 5.5 mmol/L glucose, 16.7 mmol/L glucose, and 16.7 mmol/L glucose with 1.0 mmol/L NAC, respectively. The activities of the enzyme complexes I and III of the respiratory chain in the cells were assessed with spectrophotometry, the ATP levels were examined using a luciferinluciferase kit, and insulin levels detected by radioimmunoassay.

RESULTSThe activities of the respiratory chain enzyme complexes I and III were 1.53-/+0.24 and 1.08-/+0.22 micromol.mg(-1).min(-1) in high glucose group, respectively, significantly lower than those in the normal control group (2.31-/+0.33 and 1.92-/+0.39 micromol.mg(-1).min(-1), P<0.01). ATP and insulin levels also decreased significantly in high glucose group as compared with those in the normal control group (P<0.01). The addition of NAC partially inhibited high glucose-induced decreases in the enzyme complex activities, ATP levels and insulin secretion (P<0.05).

CONCLUSIONThe respiratory chain function is positively correlated to insulin secretion in INS-1 cells, and exposure to high glucose causes impairment of the two enzyme complexes activities through oxidative stress, resulting in the mitochondrial respiratory chain dysfunction. High glucose-induced damages of the mitochondrial respiratory chain function can be partially inhibited by NAC.

Cell Respiration ; drug effects ; Cells, Cultured ; Glucose ; pharmacology ; Humans ; Insulin-Secreting Cells ; cytology ; physiology ; Mitochondria ; physiology ; Oxidative Stress ; drug effects

The testicular gubernaculum plays an important role in testicular descent and development. Its differentiation and development are affected by many factors. Androgens, calcitonin gene-related peptide (CGRP), insulin-like factor 3 (INSL3), Müllerian inhibiting substance (MIS), epidermal growth factor (EGF) and environmental estrogens (EEs) are involved in gubernacular development. The effect of CGRP, INSL3 and especially EEs on genital system has been attracted more attention.
Animals ; Calcitonin Gene-Related Peptide ; physiology ; Estrogens ; pharmacology ; Humans ; Insulin ; physiology ; Male ; Mice ; Proteins ; physiology ; Rats ; Testis ; drug effects ; embryology ; physiology

OBJECTIVETo investigate the central mechanism of hypoglycemic effect induced by ear acupuncture.

METHODSExtracellular single-unit recordings were carried out in nucleus tractus solitarius (NTS) of rats after infusion of glucose, insulin via jugular venous and electroacupuncture at auricular concha, observing responses of glucose-sensitive neurons and insulin-sensitive neurons in NTS to electroacupuncture stimulation at auricular concha.

RESULTSThere existed glucose-sensitive neurons and insulin-sensitive neurons in NTS. Among glucose-sensitive neurons, inhibitory ones accounted for 37.3%, and excitable ones accounted for 10.9%. Among the insulin-sensitive neurons, excitable ones accounted for 33.3%, and inhibitory ones accounted for 4.9%. When electroacupuncture was given at auricular concha, 49.3% (34/69) of total neurons recorded in NTS showed increase in firing rate, while 4.3% (3/69) showed decrease in firing rate. Among the 34 exciting-responsive neurons, there were 18 neurons responding to glucose infusion with a discharge decreased in frequency, and there were 8 neurons responding to insulin infusion with a discharge increased in firing rate.

CONCLUSIONAcupuncture stimulation at auricular concha can irritate the neurons in NTS, which show largely inhibitory and excitable response to glucose and insulin infusion, respectively. The hypoglycemic effect induced by auricular acupuncture possibly results from regulating these neurons' firing activities.

Acupuncture, Ear ; Animals ; Electroacupuncture ; Glucose ; pharmacology ; Insulin ; pharmacology ; Male ; Rats ; Rats, Sprague-Dawley ; Solitary Nucleus ; drug effects ; physiology

BACKGROUNDIslet transplantation represents an ideal therapeutic approach for treatment of type 1 diabetes but islet function and regeneration may be influenced by necrosis or apoptosis induced by oxidative stress and other insults. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in the catabolism of heme into biliverdin, releasing free iron and carbon monoxide. It has also been reported to be an antioxidant enzyme which can improve the function of grafted islets by cytoprotection via free radical scavenging and apoptosis prevention. In the present study, we investigated whether transduction of HO-1 genes into human islets with an adenovirus vector has cytoprotective action on islets cultured in vitro and discuss this method of gene therapy for clinical islet transplantation.

METHODSCadaveric pancreatic islets were isolated and purified in vitro. Transduction efficiency of islets was determined by infecting islets with adenovirus vector containing the enhanced green fluorescent protein gene (Ad-EGFP) at multiplicities of infection (MOI) of 2, 5, 10, or 20. Newly isolated islets were divided into three groups: EGFP group, islets transduced with Ad-EGFP using MOI = 20; HO-1 group, transduced with adenovirus vectors containing the human HO-1 gene using MOI = 20; and control group, mock transduced islets. Insulin release after glucose stimulation of the cell lines was determined by a radioimmunoassay kit and the stimulation index was calculated. Flow cytometry was used to detect apoptotic cells in the HO-1 group and in the control group after induction by recombinant human tumor necrosis factor-alpha (rTNFalpha) and cycloheximide (CHX) for 48 hours.

RESULTSAdenovirus vectors have a high efficiency of gene transduction into adult islet cells. Transduction of islets with the Ad-EGFP was most successful at MOI 20, at which MOI fluorescence was very intense on day 7 after transduction and EGFP was expressed in cultured islet cells for more than four weeks in vitro. The insulin release in the control group was (182.36 +/- 58.96) mIU/L after stimulation by high glucose media (16.7 mmol/L), while insulin release from the HO-1 group and the EGFP group were (270.09 +/- 89.37) mIU/L and (175.95 +/- 75.05) mIU/L respectively. Compared to the control group and the EGFP group, insulin release in the HO-1 group increased significantly (P < 0.05). After treatment with rTNFalpha and CHX the apoptotic ratio of islet cells was (63.09 +/- 10.86)% in the HO-1 group, significantly lower than (90.86 +/- 11.25)% in the control group (P < 0.05).

CONCLUSIONSTransduction of human islets with Ad-HO-1 can protect against TNF-alpha and CHX mediated cytotoxicity. The HO-1 gene also appears to facilitate insulin release from human islets. Transduction of donor islets with the adenovirus vector containing an HO-1 gene might have potential value in clinical islet transplantation.

Adenoviridae ; genetics ; Apoptosis ; drug effects ; Cycloheximide ; pharmacology ; Cytoprotection ; Genetic Therapy ; Heme Oxygenase-1 ; genetics ; physiology ; Humans ; Insulin ; secretion ; Islets of Langerhans ; physiology ; Transduction, Genetic ; Tumor Necrosis Factor-alpha ; pharmacology

To investigate the influence of vasoactive intestinal peptide (VIP) on chemotaxis of bronchial epithelial cells (BECs). Rabbit chemotactic migration of primary BEC was assessed in a blind-well Boyden chamber. Radioimmunoassay and radio-ligand affinity analysis were used for determining VIP secretion and vasoactive intestinal peptide receptor (VIPR) expression. The results showed: (1) the method for determining chemotaxis of BECs by using insulin as chemotactic factor was stable and reproducible (r=0.9703, P<0.01). (2) VIP (0.001-1 micromol/L) elicited chemotaxis of BECs which was substantial and concentration-dependent. The effects of VIP were inhibited by W-7 and H-7 (P<0.01). (3) Heat stress enhanced the secretion of VIP (P<0.01) and upregulated the expression of VIPR on BECs (P<0.05). These results indicate that VIP in the lungs may play an important role in the repair of damaged epithelium, accelerating restoration of the airway to its normal state. Calmodulin and protein kinase C may be involved in the signal transduction of VIP effects.
Animals ; Bronchi ; cytology ; Cells, Cultured ; Chemotaxis ; drug effects ; physiology ; Epithelial Cells ; drug effects ; physiology ; Female ; Insulin ; pharmacology ; Male ; Rabbits ; Receptors, Vasoactive Intestinal Peptide ; biosynthesis ; Vasoactive Intestinal Peptide ; pharmacology

OBJECTIVETo investigate the effect of Bushen Tongmai recipe (BSTMR) on the tyrosine phosphorylation of insulin receptor (InsR) and insulin receptor substrate-1 (IRS-1) after insulin stimulation in muscle and fat tissues of insulin resistant (IR) rats induced by high-fat forage.

METHODSMale Wistar rats were randomly divided into normal group (normal forage), model group (high fat forage, in which 61% calories were supplied by fat) and treated group (same forage as model group and treated with BSTMR). All animals were fed for 8 weeks, fasting blood glucose (FBG), blood glucose (BG) levels 1- and 2-hrs after glucose loading were determined routinely, serum fasting insulin (Ins) was determined with radioimmunoassay (RIA) and tyrosine phosphorylation level of InsR and IRS-1 in fatty and muscular tissues was measured by immunoprecipitation and Western blot.

RESULTSCompared with the model group, FBG in the treated group changed insignificantly, but level of Fins decreased markedly (P < 0.01), so the insulin sensitivity index was significantly elevated in the treated group (P < 0.01), levels of BG 1- and 2-hrs after glucose loading in the treated group were greatly improved in comparison with those in the model group (P < 0.05 and P < 0.01 respectively). Meanwhile, the density of electrophoresis bands of tyrosine phosphorylated InsR and IRS-1 proteins in muscular and fatty tissues in the treated group increased obviously.

CONCLUSIONBSTMR could attenuate the insulin resistance in rats, its pharmaceutical mechanisms might be closely related with the elevation of the tyrosine phosphorylation levels of InsR and IRS-1 in muscular and fatty tissues after insulin stimulation, and improvement of insulin signal transduction in target tissues.

Animals ; Blood Glucose ; metabolism ; Drugs, Chinese Herbal ; pharmacology ; Insulin ; metabolism ; Insulin Receptor Substrate Proteins ; Insulin Resistance ; physiology ; Male ; Phosphoproteins ; drug effects ; Phosphorylation ; Random Allocation ; Rats ; Rats, Wistar ; Receptor, Insulin ; metabolism ; Signal Transduction ; drug effects ; Tyrosine ; metabolism

AIMTo build a easy and reliable rat model of insulin resistance.

METHODSChanges concerning sugar metabolism were observed in experimental rats injected intraperitoneally by different doses of dexamethasone.

RESULTSThe changes by dexamethasone in fasting blood insulin and insulin resistance prior to that of fasting blood glucose were dose and time dependent.

CONCLUSIONIt was convenience to set up a insulin resistance model induced by dexamethasone in rats which would favor other related research.

Animals ; Blood Glucose ; analysis ; Dexamethasone ; pharmacology ; Disease Models, Animal ; Dose-Response Relationship, Drug ; Insulin ; blood ; Insulin Resistance ; physiology ; Male ; Rats ; Rats, Sprague-Dawley ; Time Factors

Dysfunction of the pancreatic beta-cell is an important defect in the pathophysiological changes of type 2 diabetes, and type 2 diabetes is evidently associated with obesity. But the role of the adipocyte in the dysfunction of the pancreatic beta-cell remains unknown. In the present study, we examined the direct effects of 3T3-L1 adipocytes on the expression of ATP-sensitive potassium channels (K(ATP) channels) in MIN6 insulin-secreting cells. MIN6 cells were divided into two groups as control group, where MIN6 cells were cultured in normal culture medium, and coculture group, where MIN6 cells were cocultured with differentiated 3T3-L1 adipocytes for 1 week. Semi-quantitative RT-PCR was employed to measure the expression of K(ATP) channel subunit Kir6.2 in MIN6 cells. Fura-2 was used to reflect changes in intracellular calcium concentration ([Ca(2+)](i)) in MIN6 cells. The secretary function of MIN6 cells from both groups was estimated by radioimmunoassay method. The results showed that the Kir6.2 cDNA levels corrected by GAPDH cDNA levels after densitometric analysis were 0.989+/-0.035 in control group and 0.726+/-0.087 in coculture group. The expression of Kir6.2 was significantly decreased in MIN6 cells in the coculture group as compared with that in control. MIN6 cells cocultured with 3T3-L1 adipocytes lost the ability to increase [Ca(2+)](i) when stimulated by tolbutamide (0.1 mmol/L), a highly selective KATP channel closer. In contrast, MIN6 cells in control group had typical responses to tolbutamide with a significant increase in [Ca(2+)](i). The magnitudes to basal levels of [Ca(2+)](i) after tolbutamide stimulation were 1.520+/-0.203 in control and 1.114+/-0.097 in coculture group (P<0.05, n=6). MIN6 cells in control showed a significant increase in insulin secretion from 0.38+/-0.099 mU/min to 2.87+/-0.248 mU/min after being stimulated by tolbutamide, whereas MIN6 cells in coculture group did not increase insulin secretion when stimulated by tolbutamide (0.21+/-0.055 mU/min to 0.22+/-0.082 mU/min). It is demonstrated that 3T3-L1 adipocytes decrease the expression of K(ATP) channels in MIN6 cells through secreting certain factors, which impair the secretary function of MIN6 cells. The present results indicate that adipocytes are directly involved in pancreatic beta-cell dysfunction, which may facilitate the development of type 2 diabetes.
3T3 Cells ; Adipocytes ; cytology ; Animals ; Cell Differentiation ; physiology ; Cells, Cultured ; Coculture Techniques ; Gene Expression ; Hypoglycemic Agents ; pharmacology ; Insulin ; biosynthesis ; Insulin Resistance ; Islets of Langerhans ; cytology ; metabolism ; Mice ; Potassium Channels, Inwardly Rectifying ; biosynthesis ; genetics ; physiology ; Tolbutamide ; pharmacology ; Transcription, Genetic ; drug effects