[Effects of AdipoRon orally on the functions of spleen and pancreas in type 2 diabetic mice]

OBJECTIVE

To observe the effects of AdipoRon orally on the functions of spleen and pancreas in type 2 diabetic mice, in order to present data for clinical application.

METHODS

Forty C57/BL6 male mice were randomly divided into 2 groups: normal control group (n=10) and model group (n=30), the former group was fed normally, while the later group was fed with high fat and sugar for 4 weeks.After that, type 2 diabetes model was established in DM group induced by intraperitoneal injection of streptozotocin (STZ, 40 mg/kg).As type 2 diabetes model established successfully, the model mice were randomly divided into three groups (n=10): diabetes mellitus (DM) group, high dose of AdipoRon group (DM + H) and low dose of adiponRon group (DM + L).All the four groups were treated with saline, saline, AdipoRon at the doses of 20 mg/kg and 50 mg/kg by gavages respectively, once a day for 10 days.And then put them to death for collecting blood, pancreas and spleen.Pathological changes of pancreas were observed with a light microscope after HE staining.Protein contents of insulin receptor (INSR), insulin receptor substrate 1( IRS-1) and tumor necrosis factor-α(TNF-α) in pancreatic and spleen tissues were detected by ELISA.The protein level of phosphorylation insulin receptor substrate 1(p-IRS-1) in pancreas was determined by Western blot, and the expression of insulin mRNA in pancreas was tested by RT-PCR.

RESULTS

Under the light microscope, it was visible that the pancreatic tissue in NC group was full and closely packed, and the islet was big.Pancreatic tissue of DM mice was incompact and the islet of DM mice was smaller than that of normal mice.As for the mice treated with AdipoRon orally, the pancreatic tissue was full and closely arranged, and the islet was slightly smaller.Compared with NC group, the levels of TNF-α in pancreas and spleen of DM group were increased markedly, the levels of INSR and IRS-1 were decreased, the spleen coefficient, p-IR-1 protein level and insulin mRNA expression in pancreas were decreased, all were significant statistically (P＜0.05).Compared with DM group, the levels of TNF-α in pancreas and spleen of AdipoRon groups were decreased, the levels of INSR and IRS-1 in pancreas and spleen of AdipoRon groups were increased, while the spleen coefficient was increased (P＜0.05).The p-IRS-1 protein level and insulin mRNA expression in pancreas in DM+H group were increased (P＜0.05).Compared with DM + L group, the level of TNF-α was decreased, and the levels of INSR and IRS-1 were significantly increased (P＜0.05) in DM + H group (P＜0.05).

CONCLUSION

Oral administration of AdipoRon can protect the spleen and pancreas of diabetic mice by decreasing the inflammatory response, up-regulating the expression of INSR, and increasing p-IRS-1 level in diabetic mice.

Effect of Alkaloids from Nelumbinis Plumula against Insulin Resistance of High-Fat Diet-Induced Nonalcoholic Fatty Liver Disease in Mice

This study aimed to investigate the effects of total alkaloids from Nelumbinis Plumula (NPA) on insulin resistance (IR) of high-fat diet- (HFD-) induced nonalcoholic fatty liver disease (NAFLD). Rats were fed with HFD for 8 weeks to induce NAFLD. Then, the effect of NPA on ameliorating IR in HFD-induced NAFLD was evaluated. Fasting serum insulin was determined using an enzyme-linked immunosorbent assay (ELISA) kit for insulin following the manufacturer's protocol. Some inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) were determined using ELISA kits to assess the inflammatory burden in rats. The results showed that HFD could induce a significant increase in blood glucose and IR in rats. However, rats treated with NPA (400 or 600 mg/kg) showed improved IR and reduction in serum inflammatory cytokines TNF-α and IL-6. Further investigation indicated that NPA could inhibit IR by restoring the insulin receptor substrate-1 (IRS-1) and suppressing the expression of c-Jun N-terminal kinase (JNK) phosphorylation. The present results supported the view that the pathogenesis of NAFLD was complex with inflammation, together with increasing serum glucose and IR. Also, JNK and IRS phosphorylation were suggested for their involvement in the modulating of IR during NAFLD progression. Therefore, NPA may serve as a potential natural remedy against IR in NAFLD.

Urotensin II-induced insulin resistance is mediated by NADPH oxidase-derived reactive oxygen species in HepG2 cells

AIM: To investigated the effects of urotensin II (UII) on hepatic insulin resistance in HepG2 cells and the potential mechanisms involved.

METHODS: Human hepatoma HepG2 cells were cultured with or without exogenous UII for 24 h, in the presence or absence of 100 nmol/L insulin for the last 30 min. Glucose levels were detected by the glucose-oxidase method and glycogen synthesis was analyzed by glycogen colorimetric/fluorometric assay. Reactive oxygen species (ROS) levels were detected with a multimode reader using a 2′,7′-dichlorofluorescein diacetate probe. The protein expression and phosphorylation levels of c-Jun N-terminal kinase (JNK), insulin signal essential molecules such as insulin receptor substrate -1 (IRS-1), protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β), and glucose transporter-2 (Glut 2), and NADPH oxidase subunits such as gp91^phox, p67^phox, p47^phox, p40^phox, and p22^phox were evaluated by Western blot.

RESULTS: Exposure to 100 nmol/L UII reduced the insulin-induced glucose consumption (P < 0.05) and glycogen content (P < 0.01) in HepG2 cells compared with cells without UII. UII also abolished insulin-stimulated protein expression (P < 0.01) and phosphorylation of IRS-1 (P < 0.05), associated with down-regulation of Akt (P < 0.05) and GSK-3β (P < 0.05) phosphorylation levels, and the expression of Glut 2 (P < 0.001), indicating an insulin-resistance state in HepG2 cells. Furthermore, UII enhanced the phosphorylation of JNK (P < 0.05), while the activity of JNK, insulin signaling, such as total protein of IRS-1 (P < 0.001), phosphorylation of IRS-1 (P < 0.001) and GSK-3β (P < 0.05), and glycogen synthesis (P < 0.001) could be reversed by pretreatment with the JNK inhibitor SP600125. Besides, UII markedly improved ROS generation (P < 0.05) and NADPH oxidase subunit expression (P < 0.05). However, the antioxidant/NADPH oxidase inhibitor apocynin could decrease UII-induced ROS production (P < 0.05), JNK phosphorylation (P < 0.05), and insulin resistance (P < 0.05) in HepG2 cells.

CONCLUSION: UII induces insulin resistance, and this can be reversed by JNK inhibitor SP600125 and antioxidant/NADPH oxidase inhibitor apocynin targeting the insulin signaling pathway in HepG2 cells.

Neuregulin improves response to glucose tolerance test in control and diabetic rats

Neuregulin (NRG) is an EGF-related growth factor that binds to the tyrosine kinase receptors ErbB3 and ErbB4, thus inducing tissue development and muscle glucose utilization during contraction. Here, we analyzed whether NRG has systemic effects regulating glycemia in control and type 2 diabetic rats. To this end, recombinant NRG (rNRG) was injected into Zucker diabetic fatty (ZDF) rats and their respective lean littermates 15 min before a glucose tolerance test (GTT) was performed. rNRG enhanced glucose tolerance without promoting the activation of the insulin receptor (IR) or insulin receptor substrates (IRS) in muscle and liver. However, in control rats, rNRG induced the phosphorylation of protein kinase B (PKB) and glycogen synthase kinase-3 (GSK-3) in liver but not in muscle. In liver, rNRG increased ErbB3 tyrosine phosphorylation and its binding to phosphatidylinositol 3-kinase (PI3K), thus indicating that rNRG activates the ErbB3/PI3K/PKB signaling pathway. rNRG increased glycogen content in liver but not in muscle. rNRG also increased the content of fructose-2,6-bisphosphate (Fru-2,6-P2), an activator of hepatic glycolysis, and lactate in liver but not in muscle. Increases in lactate were abrogated by wortmannin, a PI3K inhibitor, in incubated hepatocytes. The liver of ZDF rats showed a reduced content of ErbB3 receptors, entailing a minor stimulation of the rNRG-induced PKB/GSK-3 cascade and resulting in unaltered hepatic glycogen content. Nonetheless, rNRG increased hepatic Fru-2,6-P2 and augmented lactate both in liver and in plasma of diabetic rats. As a whole, rNRG improved response to the GTT in both control and diabetic rats by enhancing hepatic glucose utilization.

Hypoglycemic Activity through a Novel Combination of Fruiting Body and Mycelia of Cordyceps militaris in High-Fat Diet-Induced Type 2 Diabetes Mellitus Mice

Diabetes mellitus (DM) is currently ranked among leading causes of death worldwide in which type 2 DM is reaching an epidemic proportion. Hypoglycemic medications for type 2 DM have either proven inadequate or posed adverse effects; therefore, the Chinese herbal products are under investigation as an alternative treatment. In this study, a novel combination of fruiting body and mycelia powder of herbal Cordyceps militaris number 1 (CmNo1) was administered to evaluate their potential hypoglycemic effects in high-fat diet- (HFD-) induced type 2 DM in C57BL/6J mice. Body weight, fasting blood glucose (FBG), oral glucose tolerance test (OGTT), and blood biochemistry indexes were measured. Results indicated that CmNo1 lowered the blood glucose level by increasing insulin sensitivity, while no change in body weight was observed. Increased protein expression of IRS-1, pIRS-1, AKT, pAKT, and GLUT-4 in skeletal muscle and adipose tissue was found indicating restoration of insulin signaling. Additionally, PPAR-γ expression in adipose tissue restored the triglyceride and cholesterol levels. Finally, our results suggest that CmNo1 possesses strong hypoglycemic, anticholesterolemic, and antihypertriglyceridemic actions and is more economical alternate for DM treatment.

Effect of insulin in combination with selenium on Irs/PI3K-mediated GLUT4 expression in cardiac muscle of diabetic rats

BACKGROUND

Oral administration of selenium is an effective treatment for diabetes in animal models. However, selenium exerts these effects at high doses and several toxic effects are produced. Low doses of selenium are relatively safe but are unable to elicit any antidiabetic effect.

OBJECTIVES

The present study explored the prospect of using low doses of insulin in combination with selenium to evaluate their antidiabetic effect, and to evaluate their effect on IRS-1, PI3K and GLUT4 levels in cardiac muscle of diabetic rats.

MATERIALS AND METHODS

Diabetic rats were treated with insulin, selenium, and insulin and selenium in combination for four weeks. The effect of these antidiabetic compounds was examined on general physiological parameters and distribution of IRS-1, PI3K and GLUT4 in cardiac muscle by immunoblotting and immunohistochemistry.

RESULTS

Insulin in combination with selenium could significantly revive normoglycemia, and restore the disturbances in IRS-1, PI3K and GLUT4 levels in cardiac muscle. Treatment with insulin was only partially effective in the restoration of diabetic alterations.

CONCLUSION

The treatment of diabetic rats with combined doses of insulin and selenium was most effective in controlling glycaemia, and remarkably restored GLUT4 distribution by IRS-1/PI3K-dependent pathway in cardiac muscle of diabetic rat.

Genetic variants of the insulin receptor substrate-1 are influencing the therapeutic efficacy of oral antidiabetics

AIM

The therapeutic efficacy of oral hypoglycaemic drugs varies between individuals, and pharmacogenetic factors contribute to this variability. The Gly972Arg polymorphism in the insulin receptor substrate-1 (IRS-1) has been shown to play a role in insulin signal transduction and therapeutic failure to sulphonylurea drugs.

METHODS

We studied the association between the IRS-1 polymorphism and the haemoglobin A1c (HbA1c) level in diabetic patients treated with insulinotropic versus non-insulinotropic hypoglycaemic drugs as a marker for the efficacy of an antidiabetic treatment. Genotyping of the IRS-1 Arg(972) variant was performed in type 2 diabetes patients treated with either sulphonylurea drugs, glinides or insulin or with metformin, acarbose or glitazones using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

Significantly higher HbA1c levels were observed in carriers of the Arg(972) variant after treatment with insulinotropic drugs compared to wild-type carriers (8.3 vs. 7.6%, p = 0.005, independent t-test). Furthermore, patients with secondary failure to insulinotropic hypoglycaemic drugs switching finally to insulin showed even higher HbA1c levels in carriers of Arg(972) compared to wild-type (8.7 vs. 7.6%, p = 0.005, independent t-test).

CONCLUSIONS

Thus, we were able to replicate the earlier findings of an association between the IRS-1 Arg(972) variant and secondary failure to sulphonylurea drugs, and further observed a general association between HbA1c and this polymorphism in type 2 diabetes patients treated with insulinotropic hypoglycaemic drugs but not with metformin.

SOCS3 inhibits insulin signaling in porcine primary adipocytes

Insulin resistance is a major player in the pathogenesis of type II diabetes, the metabolic syndrome, and obesity. SOCS3 plays an important role in the development of insulin resistance. To investigate the role of SOCS3 in porcine adipocyte insulin signaling, we first detected the effect of insulin on SOCS3 mRNA and protein expression in porcine primary adipocytes by real-time RT-PCR and Western blotting. Then, we constructed a recombinant adenovirus encoding SOCS3 gene (Ad-SOCS3) which was used to infect differentiated porcine primary adipocytes for 3 days. The expression and phosphorylation of main insulin signaling components were detected by Western blotting. The results showed that 100 nM insulin could induce SOCS3 mRNA expression but not protein expression, and overexpression of SOCS3 decreased IRS1 protein level, insulin-stimulated IRS1 tyrosine phosphorylation, PI3K activation, and Akt phosphorylation, but increased IRS1 serine phosphorylation in porcine primary adipocytes. These results indicate that SOCS3 is an important negative regulator of insulin signaling in porcine adipocytes. Thus, SOCS3 may be a novel therapeutic target for the prevention or treatment of insulin resistance and type II diabetes.

EGFR tyrosine kinase inhibitor (PD153035) improves glucose tolerance and insulin action in high-fat diet-fed mice

OBJECTIVE

In obesity, an increased macrophage infiltration in adipose tissue occurs, contributing to low-grade inflammation and insulin resistance. Epidermal growth factor receptor (EGFR) mediates both chemotaxis and proliferation in monocytes and macrophages. However, the role of EGFR inhibitors in this subclinical inflammation has not yet been investigated. We investigated, herein, in vivo efficacy and associated molecular mechanisms by which PD153035, an EGFR tyrosine kinase inhibitor, improved diabetes control and insulin action.

RESEARCH DESIGN AND METHODS

The effect of PD153035 was investigated on insulin sensitivity, insulin signaling, and c-Jun NH(2)-terminal kinase (JNK) and nuclear factor (NF)-kappaB activity in tissues of high-fat diet (HFD)-fed mice and also on infiltration and the activation state of adipose tissue macrophages (ATMs) in these mice.

RESULTS

PD153035 treatment for 1 day decreased the protein expression of inducible nitric oxide synthase, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-6 in the stroma vascular fraction, suggesting that this drug reduces the M1 proinflammatory state in ATMs, as an initial effect, in turn reducing the circulating levels of TNF-alpha and IL-6, and initiating an improvement in insulin signaling and sensitivity. After 14 days of drug administration, there was a marked improvement in glucose tolerance; a reduction in insulin resistance; a reduction in macrophage infiltration in adipose tissue and in TNF-alpha, IL-6, and free fatty acids; accompanied by an improvement in insulin signaling in liver, muscle, and adipose tissue; and also a decrease in insulin receptor substrate-1 Ser(307) phosphorylation in JNK and inhibitor of NF-kappaB kinase (IKKbeta) activation in these tissues.

CONCLUSIONS

Treatment with PD153035 improves glucose tolerance, insulin sensitivity, and signaling and reduces subclinical inflammation in HFD-fed mice.

Tolerability and safety of GS-101 eye drops, an antisense oligonucleotide to insulin receptor substrate-1: a 'first in man' phase I investigation

AIMS

GS-101 (GeneSignal, Epalinges, Switzerland) is an antisense oligonucleotide that inhibits the expression of the scaffold protein insulin receptor substrate-1 (IRS-1). Inhibition of IRS-1 results in the prevention of neovascular growth and was shown to prevent the angiogenic process in preclinical in vitro and in vivo experiments. There is therefore a strong therapeutic rational for targeting angiogenesis in pathological neovascularization. We aimed to investigate the safety, tolerability and bioavailability of GS-101 eye drops.

METHODS

This was a Phase I open-label study. The investigation was performed in two steps. Local ocular tolerability was first assessed with the application of one single low dose in one eye. After no signs of intolerance were observed in the subjects, the dose escalation phase of the study was initiated, and the remaining subjects received three times daily escalating doses of GS-101 in one eye for 14 days.

RESULTS

The 14 healthy volunteers tolerated well 14 days' continued use of escalating doses of GS-101 from 43 to 430 microg per day. Other than itching, experienced also in the control eye by one subject and determined to be unrelated to the study treatment, no signs of intolerance were observed.

CONCLUSIONS

The tolerability profile obtained from this study suggests that GS-101 is safe for human use. Further clinical evaluations in diseases related to abnormal angiogenesis are being targeted. In particular, the neovascularization-related orphan indications of corneal graft rejection, retinopathy of pre-maturity and neovascular glaucoma are currently under Phase II clinical investigation and are showing promising results.

Combined thiazolidinedione-metformin treatment synergistically improves insulin signalling to insulin receptor substrate-1-dependent phosphatidylinositol 3-kinase, atypical protein kinase C and protein kinase B/Akt in human diabetic muscle

AIMS/HYPOTHESES

Insulin-stimulated glucose transport in muscle is impaired in type 2 diabetes, presumably reflecting reduced activation of atypical protein kinase C (aPKC) and protein kinase B (PKB/Akt). As previously shown, reductions in aPKC activation are seen at sub-maximal and maximal insulin stimulation, reductions in PKB activation are best seen at sub-maximal insulin stimulation and aPKC reductions at maximal insulin are partly improved by thiazolidinedione or metformin treatment. However, effects of combined thiazolidinedione-metformin treatment on aPKC or PKB activation by sub-maximal and maximal insulin are unknown.

METHODS

Type 2 diabetic patients were examined before and 5 to 6 weeks after combined thiazolidinedione-metformin therapy for activation of muscle aPKC and PKBbeta and their upstream activators, the insulin receptor (IR) and IRS-1-associated phosphatidylinositol 3-kinase (PI3K), during euglycaemic-hyperinsulinaemic clamp studies conducted with sub-maximal (400-500 pmol/l) and maximal (1400 pmol/l) insulin concentrations.

RESULTS

Following combined thiazolidinedione-metformin therapy, increases in glucose disposal and increases in sub-maximal and maximal insulin-induced activities of all four muscle signalling factors, IR, IRS-1-dependent PI3K (IRS-1/PI3K), aPKC and PKBbeta, were observed. Increases in PKBbeta enzyme activity were accompanied by increases in phosphorylation of PKB and its substrate, AS160, which is needed for glucose transport. Despite improved aPKC activity, muscle aPKC levels, which are diminished in type 2 diabetes, were not altered.

CONCLUSIONS/INTERPRETATION

Combined thiazolidinedione-metformin treatment markedly improves sub-maximal and maximal insulin signalling to IR, IRS-1/PI3K, aPKC and PKBbeta in type 2 diabetic muscle. These improvements exceed those previously reported after treatment with either agent alone.