PPARδ agonists have opposing effects on insulin resistance in high fat-fed rats and mice due to different metabolic responses in muscle

BACKGROUND AND PURPOSE

The peroxisome proliferator-activated receptor (PPAR)δ has been considered a therapeutic target for diabetes and obesity through enhancement of fatty acid oxidation. The present study aimed to characterize the effects of PPARδ agonists during insulin resistance of the whole body, muscle and liver.

EXPERIMENTAL APPROACH

Wistar rats and C57BL/J6 mice were fed a high fat diet (HF) and then treated with PPARδ agonists NNC61-5920 and GW501516. The effects on insulin resistance were evaluated by hyperinsulinaemic clamp or glucose tolerance tests combined with glucose tracers.

KEY RESULTS

In HF rats, 3 weeks of treatment with NNC61-5920 reduced the glucose infusion rate (by 14%, P < 0.05) and glucose disposal into muscle (by 20–30%, P < 0.01) during hyperinsulinaemic clamp. Despite increased mRNA expression of carnitine palmitoyltransferase-1, pyruvate dehydrogenase kinase 4 and uncoupling protein 3 in muscle, plasma and muscle triglyceride levels were raised (P < 0.01). Similar metabolic effects were observed after extended treatment with NNC61-5920 and GW501516 to 6 weeks. However, HF mice treated with NNC61-5920 improved their plasma lipid profile, glucose tolerance and insulin action in muscle. In both HF rats and mice, NNC61-5920 treatment attenuated hepatic insulin resistance and decreased expression of stearoyl-CoA desaturase 1, fatty acid translocase protein CD36 and lipoprotein lipase in liver.

CONCLUSIONS AND IMPLICATIONS

PPARδ agonists exacerbated insulin resistance in HF rats in contrast to their beneficial effects on metabolic syndrome in HF mice. These opposing metabolic consequences result from their different effects on lipid metabolism and insulin sensitivity in skeletal muscle of these two species.     

Rutaecarpine ameliorates hyperlipidemia and hyperglycemia in fat-fed,streptozotocin-treated rats via regulating the IRS-1/PI3K/Akt and AMPK/ACC2 signaling pathways

Aim:

We have shown that rutaecarpine extracted from the dried fruit of Chinese herb Evodia rutaecarpa (Juss) Benth (Wu Zhu Yu) promotes glucose consumption and anti-inflammatory cytokine expression in insulin-resistant primary skeletal muscle cells. In this study we investigated whether rutaecarpine ameliorated the obesity profiles, lipid abnormality, glucose metabolism and insulin resistance in rat model of hyperlipidemia and hyperglycemia.

Methods:

Rats fed on a high-fat diet for 8 weeks, followed by injection of streptozotocin (30 mg/kg, ip) to induce hyperlipidemia and hyperglycemia. One week after streptozotocin injection, the fat-fed, streptozotocin-treated rats were orally treated with rutaecarpine (25 mg·kg⁻¹·d⁻¹) or a positive control drug metformin (250 mg·kg⁻¹·d⁻¹) for 7 weeks. The body weight, visceral fat, blood lipid profiles and glucose levels, insulin sensitivity were measured. Serum levels of inflammatory cytokines were analyzed. IRS-1 and Akt/PKB phosphorylation, PI3K and NF-κB protein levels in liver tissues were assessed; pathological changes of livers and pancreases were examined. Glucose uptake and AMPK/ACC2 phosphorylation were studied in cultured rat skeletal muscle cells in vitro.

Results:

Administration of rutaecarpine or metformin significantly decreased obesity, visceral fat accumulation, water consumption, and serum TC, TG and LDL-cholesterol levels in fat-fed, streptozotocin-treated rats. The two drugs also attenuated hyperglycemia and enhanced insulin sensitivity. Moreover, the two drugs significantly decreased NF-κB protein levels in liver tissues and plasma TNF-α, IL-6, CRP and MCP-1 levels, and ameliorated the pathological changes in livers and pancreases. In addition, the two drugs increased PI3K p85 subunit levels and Akt/PKB phosphorylation, but decreased IRS-1 phosphorylation in liver tissues. Treatment of cultured skeletal muscle cells with rutaecarpine (20–180 μmol/L) or metformin (20 μmol/L) promoted the phosphorylation of AMPK and ACC2, and increased glucose uptake.

Conclusion:

Rutaecarpine ameliorates hyperlipidemia and hyperglycemia in fat-fed, streptozotocin-treated rats via regulating IRS-1/PI3K/Akt signaling pathway in liver and AMPK/ACC2 signaling pathway in skeletal muscles.     

The phospholipase A2 inhibitor methyl indoxam suppresses diet-induced obesity and glucose intolerance in mice

Background and purpose:

Previous results have shown that mice lacking in the group 1B phospholipase A₂ (Pla2g1b) are resistant to obesity and diabetes induced by feeding a diabetogenic high-fat/high-carbohydrate diet. This study examined the potential of using the Pla2g1b inhibitor methyl indoxam as therapy to suppress diet-induced obesity and diabetes.

Experimental approach:

Male C57BL/6 mice were fed the diabetogenic diet with or without methyl indoxam supplementation. Body weight gain, fasting plasma glucose levels, glucose tolerance and postprandial lysophospholipid absorption were compared.

Key results:

Wild-type C57BL/6 mice fed the diabetogenic diet without Pla2g1b inhibitor showed 31 and 69% body weight gain after 4 and 10 weeks respectively. These animals also showed elevated plasma glucose levels and were glucose intolerant. In contrast, C57BL/6 mice fed the diabetogenic diet with 90 mg·kg⁻¹ of methyl indoxam gained only 5% body weight after 10 weeks. These animals were also euglycaemic and displayed normal glucose excursion rates in glucose tolerance test. Methyl indoxam suppression of diet-induced body weight gain and glucose intolerance was correlated with the inhibition of Pla2g1b-mediated postprandial lysophospholipid absorption.

Conclusions and implications:

These results show that oral supplementation of a diabetogenic diet with the Pla2g1b inhibitor methyl indoxam effectively suppresses diet-induced obesity and diabetes in mice. This suggests that Pla2g1b inhibition may be a potentially effective oral therapeutic option for treatment of obesity and diabetes.     

Implementation of the glucommander method of adjusting insulin infusions in critically ill patients

Background:

Intensive glycemic control has been associated with reduced morbidity and mortality in critically ill patients. Web-based, patient-specific insulin nomograms may facilitate improved glucose control.

Objective:

To compare 2 algorithms for individualizing insulin infusion therapy (a web-based system [Glucommander method] and a standard paper-based nomogram) in a cardiovascular surgery intensive care unit (ICU).

Methods:

In this prospective, before–after cohort study, measures of glycemic control for 50 patients receiving insulin according to the Glucommander system were compared with a control group (n = 50) who received insulin according to the standard paper-based nomogram used in the cardiovascular surgery ICU.

Results:

There was no significant difference between the 2 groups with respect to time to target blood glucose (5.1–8.0 mmol/L), percentage of time within the target range, or mean amplitude of glucose excursion. Patients in the intervention group spent less time above the target range (p = 0.007) and more time below the target range (p < 0.001), and the mean glucose was lower in this group compared with the control group (7.9 versus 8.6 mmol/L, p = 0.002). The percentage of blood glucose measurements below 4 mmol/L was higher in the intervention group than in the control group (3.7% versus 1.4%, p = 0.003). Satisfaction surveys revealed that the program was well accepted by the nursing staff in the cardiovascular surgery ICU.

Conclusions:

A web-based insulin nomogram was an easy-to-use instrument for achieving tighter glucose control for patients in the cardiovascular surgery ICU. Use of the Glucommander system led to lower mean blood glucose but an increase in episodes of hypoglycemia.     

Effects of smoking cessation, acute re-exposure and nicotine replacement in smokers on AIR inhaled insulin pharmacokinetics and glucodynamics

Aims

To explore the effects of smoking cessation and acute smoking re-exposure on the pharmacokinetic (PK) and glucodynamic (GD) profiles of AIR® inhaled insulin (AIR Insulin) with or without nicotine replacement therapy (NRT).

Methods

Nondiabetic smokers (n = 24) with normal pulmonary function completed a two-phase (four-period), open-label, randomized euglycaemic clamp study. During the initial study phase, subjects underwent glucose clamps following AIR Insulin dosing, shortly after smoking, 8–12 h after smoking, or following subcutaneous insulin lispro shortly after smoking. AIR Insulin PK and GD were again assessed during and after a 4-week smoking-cessation period with or without NRT. In the last study period, subjects smoked one cigarette shortly before final AIR Insulin dosing and glucose clamp, to study the effect of acute smoking re-exposure on inhaled insulin PK and GD.

Results

Compared with the preceding active smoking phase, the administration of AIR Insulin in nondiabetic subjects undergoing a 4-week period of smoking abstinence resulted in a decrease in PK and GD of approximately 25% (P = 0.008 for both), an effect which was greater in subjects using NRT. Following rechallenge with a single cigarette (without NRT), GD response to AIR Insulin increased significantly (P = 0.006) towards precessation levels, relative to smoking abstinence. In subjects using NRT, however, the increase in GD was less pronounced.

Conclusion

Smoking, smoking cessation and acute re-exposure with a single cigarette are associated with clinically significant alterations in AIR Insulin pharmacokinetics and glucodynamics. AIR Insulin should not be used by smokers or those at risk for recidivism.

What is already known about this subject

• Only one other study (Becker et al.) has reported on the influence of smoking cessation and smoking resumption on inhaled insulin pharmacokinetics and glucodynamics, concluding that the rapid changes associated with smoking resumption carry the risk for hypoglycaemia and thus should not be used by active smokers.

What this study adds

• This is the first euglycaemic clamp study on the impact of smoking cessation, acute smoking re-exposure and nicotine replacement on AIR® inhaled insulin pharmacokinetics and glucodynamics.
• We demonstrate clinically and statistically significant shifts in glucodynamic response to acute re-exposure to a single cigarette, leading us to conclude that active smokers should be advised against inhaled insulin therapy until smoking abstinence is stable.
• Additionally, these results are also the first to demonstrate an apparent independent effect of nicotine replacement therapy on insulin exposure and glucodynamic response.

     

Astragalus polysaccharides alleviates glucose toxicity and restores glucose homeostasis in diabetic states via activation of AM PK

Aim:

To establish the mechanism underlying the improvement of glucose toxicity by Astragalus polysaccharide (APS), which occurred via an AMP activated protein kinase (AMPK)-dependent pathway.

Methods:

In vivo and in vitro effects of APS on glucose homeostasis were examined in a type 2 diabetes mellitus (T2DM) rat model. The T2DM rat model was duplicated by a high-fat diet (58% fat, 25.6% carbohydrate, and 16.4% protein) and a small dose of streptozotocin (STZ, 25 mg/kg, ip). After APS therapy (700 mg·kg⁻¹·d⁻¹, ig) for 8 weeks, blood glucose, glycosylated hemoglobin, and serum insulin were measured. Insulin sensitivity was evaluated by the comprehensive analysis of oral glucose tolerance tests (OGTT) and HOMA IR index. Hepatic glycogen was observed by the PAS staining method. The expression and activity of skeletal muscle AMPKα and acetyl-CoA carboxylase (ACC), and the phosphorylation of hepatic glycogen synthase (GS), the glycogen synthase (GS),were measured by Western blotting. Glucose uptake was measured with the 2-deoxy-[³H]-D-glucose method in C2C12 cells.

Results:

The hyperglycemia status, insulin sensitivity, glucose uptake, and activation level of AMPK in diabetic rats were improved in response to APS administration. APS could also alleviate glucose toxicity in cultured mouse cells by the activation of AMPK.

Conclusion:

APS can alleviate glucose toxicity by increasing liver glycogen synthesis and skeletal muscle glucose translocation in the T2DM rat model, via activation of AMPK.     

Co-administration of paroxetine and pravastatin causes deregulation of glucose homeostasis in diabetic rats via enhanced paroxetine exposure

Aim： Clinical evidence shows that co-administration of pravastatin and paroxetine deregulates glucose homeostasis in diabetic patients. The aim of this study was to verify this phenomenon in diabetic rats and to elucidate the underlying mechanisms.
Methods： Diabetes mellitus was induced in male SD rats by a high-fat diet combined with a low-dose streptozotocin injection. The rats were orally administered paroxetine （10 mg/kg） and pravastatin （10 mg/d） or both the drugs daily for 28 d. The pharmacokinetics of paroxetine and pravastatin were examined on d 1 and d 28. Biochemical parameters including serum insulin, glucose and lipids were monitored during the treatments. An insulin-secreting cell line （INS-1） was used for measuring insulin secretion.
Results： In diabetic rats, co-administration of paroxetine and pravastatin markedly increased the concentrations of both the drugs compared with administration of each drug alone. Furthermore, co-administration severely impaired glucose homeostasis in diabetic rats, as demonstrated by significantly increased serum glucose level, decreased serum and pancreatic insulin levels, and decreased pancreatic Insulin-2 mRNA and tryptophan hydroxylase-1 （Tph-1） mRNA levels. Treatment of INS-1 cells with paroxetine （5 and 10 μmol/L） significantly inhibited insulin secretion, decreased the intracellular insulin, 5-HT, Insulin-2 mRNA and Tph-1 mRNA levels. Treatment of the cells with pravastatin （10 μmol/L） significantly stimulated insulin secretion, which was weakened by co-treatment with paroxetine.
Conclusion： Paroxetine inhibits insulin secretion at least via decreasing intracellular 5-HT and insulin biosynthesis. The deregulation of glucose homeostasis by co-administration of paroxetine and pravastatin in diabetic rats can be attributed to enhanced paroxetine exposure.     

Glucagon and a glucagon-GLP-1 dual-agonist increases cardiac performance with different metabolic effects in insulin-resistant hearts

BACKGROUND AND PURPOSE

The prevalence of heart disease continues to rise, particularly in subjects with insulin resistance (IR), and improved therapies for these patients is an important challenge. In this study we evaluated cardiac function and energy metabolism in IR JCR:LA-cp rat hearts before and after treatment with an inotropic compound (glucagon), a glucagon-like peptide-1 (GLP-1) receptor agonist (ZP131) or a glucagon-GLP-1 dual-agonist (ZP2495).

EXPERIMENTAL APPROACH

Hearts from IR and lean JCR:LA rats were isolated and perfused in the working heart mode for measurement of cardiac function and metabolism before and after addition of vehicle, glucagon, ZP131 or ZP2495. Subsequently, cardiac levels of nucleotides and short-chain CoA esters were measured by HPLC.

KEY RESULTS

Hearts from IR rats showed decreased rates of glycolysis and glucose oxidation, plus increased palmitate oxidation rates, although cardiac function and energy state (measured by ATP/AMP ratios) was normal compared with control rats. Glucagon increased glucose oxidation and glycolytic rates in control and IR hearts, but the increase was not enough to avoid AMP and ADP accumulation in IR hearts. ZP131 had no significant metabolic or functional effects in either IR or control hearts. In contrast, ZP2495 increased glucose oxidation and glycolytic rates in IR hearts to a similar extent to that of glucagon but with no concomitant accumulation of AMP or ADP.

CONCLUSION AND IMPLICATIONS

Whereas glucagon compromised the energetic state of IR hearts, glucagon-GLP-1 dual-agonist ZP2495 appeared to preserve it. Therefore, a glucagon-GLP-1 dual-agonist may be beneficial compared with glucagon alone in the treatment of severe heart failure or cardiogenic shock in subjects with IR.     

Insulin therapy stimulates lipid synthesis and improves endocrine functions of adipocytes in dietary obese C57BL/6 mice

Aim:

To evaluate whether insulin intervention could affect the metabolic and endocrine functions of adipose tissue.

Methods:

C57BL/6 mice were fed on a high-fat-diet for 12−16 weeks to induce insulin resistance. Insulin intervention was administered in the high-fat-diet mice for 4 weeks at 12 weeks (early insulin treatment) or 16 weeks (late insulin treatment). Intraperitoneal glucose tolerance tests were performed before and after insulin treatment. Expression levels of factors involved in the triglyceride synthesis and endocrine functions of adipose tissue including phosphoenolpyruvate carboxykinase (PEPCK-C), fatty acid synthase (FAS), aquaporin 7 (AQP7), adiponectin, visfatin, and interleukin-6 (IL-6) were determined by Western blot.

Results:

In the obese mice, glucose tolerance was impaired; triglyceride content was increased in the liver tissue; protein expression of FAS and adiponectin was decreased; expression of visfatin was increased in adipose tissue. After 4-week insulin treatment, glucose tolerance was improved; triglyceride content was decreased in the liver and skeletal muscle; expression of PEPCK-C, FAS, and adiponectin was increased in the adipose tissue; IL-6 and AQP7 expression was reduced in the fat. Early insulin treatment had better effect in increasing the expression of FAS and PEPCK-C and decreasing the expression of IL-6.

Conclusion:

These results indicate that insulin can target adipocytes for improvement of insulin sensitivity through stimulating triglyceride synthesis and partly improving endocrine functions.     

Pharmacokinetic/pharmacodynamic studies on exenatide in diabetic rats

Aim:

To quantitatively evaluate the blood glucose-lowering effect of exenatide in diabetic rats.

Methods:

Male Harlan-Sprague-Dawley rats were treated with high-fat diet/streptozotocin to induce type 2 diabetes. After subcutaneous administration of a single dose of exenatide (4.2, 42, or 210 μg/kg), serum exenatide, insulin concentration and blood glucose were measured. The pharmacokinetics of exenatide was characterized by a two-compartment model with first-order absorption. Insulin turnover was characterized by an effect compartment and indirect response combined model. Glucose turnover was described using an indirect response model with insulin (in effect compartment) stimulating glucose disposition and insulin (in insulin compartment) inhibiting glucose production simultaneously. The model parameters were estimated using nonlinear mixed-effects model program. Visual predictive check and model evaluation were used to make assessments.

Results:

Exenatide exhibited rapid absorption with k_a=4.45 h^-1, and the two-compartment model well described its pharmacokinetic profile. For the pharmacodynamic model, exenatide increased insulin release with the estimated S_m1 of 0.822 and SC₅₀ of 4.02 μg/L. It was demonstrated that insulin stimulated glucose dissipation (S_m2=0.0513) and inhibited the production of glucose (I_m=0.0381). Visual predictive check and model evaluation study indicated that a credible model was developed.

Conclusion:

The glucose-lowering effect of exenatide in diabetic rats is reliably described and predicted by the combined effect compartment/indirect response model.     

SHR3824, a novel selective inhibitor of renal sodium glucose cotransporter 2, exhibits antidiabetic efficacy in rodent models

Aim： The sodium glucose cotransporter 2 （SGLT2） plays an Jmportant role in renal glucose reabsorption, thus serves as a new target for the treatment of diabetes. The purpose of this study was to evaluate SHR3824 as a novel selective SGLT2 inhibitor and to characterize its in vivo effects on glucose homeostasis. The effects of chronic administration of SHR3824 on peripheral insulin sensitivity and pancreatic !5-cell function were also investigated. Methods： The in vitro potency and selectivity of SHR3824 were assessed in HEK293 cells transfected with human SGLT2 or SGLTI. Acute and multi-dose studies were performed on ICR mice, GK rats and db/db mice to assess the ability of SHR3824 to enhance urinary glucose excretion and improve blood glucose levels. 2-Deoxyglucose uptake and insulin immunohistochemical staining were performed in the soleus muscle and pancreas, respectively, of db/db mice. A selective SGLT2 inhibitor BMS512148 （dapagliflozin） was taken as positive control. Results： SHR3824 potently inhibited human SGLT2 in vitro, but exerted much weak inhibition on human SGLT1 （the IC50 values of SHR3824 against human SGLT2 and SGLT1 were 2.38 and 4324 nmol/L, respectively）. Acute oral administration of SHR3824 （0.3, 1.0, 3.0 mg/kg） dose-dependently improved glucose tolerance in ICR mice, and reduced hyperglycemia by increasing urinary glucose excretion in GK rats and db/db mice. Chronic oral administration of SHR3824 （0.3, 1.0, 3.0 mg·kg·d-1） dose-dependently reduced blood glucose and HbAlc levels in GK rats and db/db mice, and significantly increased insulin-stimulated glucose uptake in the soleus muscles and enhanced insulin staining in the islet cells of db/db mice. Conclusion： SHR3824 is a potent and selective SGLT2 inhibitor and exhibits antidiabetic efficacy in several rodent models, suggesting its potential as a new therapeutic agent for the treatment of type 2 diabetes.     

Pharmacological inhibition of diacylglycerol acyltransferase 1 reduces body weight gain, hyperlipidemia, and hepatic steatosis in db/db mice

Aim:

To test whether pharmacological inhibition of Diacylglycerol acyltransferase 1 (DGAT1) by a small-molecule inhibitor H128 can improve metabolism disorders in leptin receptor-deficient db/db mice.

Methods:

To investigate the effect of H128 on intestinal fat absorption,db/db mice were acutely given a bolus of corn oil by gavage. The mice were further orally administered H128 (3 and 10 mg/kg) for 5 weeks. Blood glucose, lipids, insulin, ALT, and AST as well as hepatic triglycerides were measured. The insulin tolerance test was performed to evaluate insulin sensitivity. The expression of genes involved in fatty acid oxidation was detected by RT-PCR.

Results:

Oral administration of H128 (10 mg/kg) acutely inhibited intestinal fat absorption following a lipid challenge in db/db mice. Chronic treatment with H128 significantly inhibited body weight gain, decreased food intake, and induced a pronounced reduction of serum triglycerides. In addition, H128 treatment markedly ameliorated hepatic steatosis, characterized by decreased liver weight, lipid droplets, and triglyceride content as well as serum ALT and AST levels. Furthermore, H128 treatment increased the expression of the CPT1 and PPARα genes in liver, suggesting that H128 enhanced fatty acid oxidation in db/db mice. However, neither blood glucose nor insulin tolerance was affected by H128 treatment throughout the 5-week experimental period.

Conclusion:

DGAT1 may be an effective therapeutic target for the treatment of obesity, hyperlipidemia and hepatic steatosis.     

The insulin sensitizing effect of topiramate involves KATP channel activation in the central nervous system

BACKGROUND AND PURPOSE

Topiramate improves insulin sensitivity, in addition to its antiepileptic action. However, the underlying mechanism is unknown. Therefore, the present study was aimed at investigating the mechanism of the insulin-sensitizing effect of topiramate both in vivo and in vitro.

EXPERIMENTAL APPROACH

Male C57Bl/6J mice were fed a run-in high-fat diet for 6 weeks, before receiving topiramate or vehicle mixed in high-fat diet for an additional 6 weeks. Insulin sensitivity was assessed by hyperinsulinaemic-euglycaemic clamp. The extent to which the insulin sensitizing effects of topiramate were mediated through the CNS were determined by concomitant i.c.v. infusion of vehicle or tolbutamide, an inhibitor of ATP-sensitive potassium channels in neurons. The direct effects of topiramate on insulin signalling and glucose uptake were assessed in vivo and in cultured muscle cells.

KEY RESULTS

In hyperinsulinaemic-euglycaemic clamp conditions, therapeutic plasma concentrations of topiramate (∼4 μg·mL⁻¹) improved insulin sensitivity (glucose infusion rate + 58%). Using 2-deoxy-D-[³H]glucose, we established that topiramate improved the insulin-mediated glucose uptake by heart (+92%), muscle (+116%) and adipose tissue (+586%). Upon i.c.v. tolbutamide, the insulin-sensitizing effect of topiramate was completely abrogated. Topiramate did not directly affect glucose uptake or insulin signalling neither in vivo nor in cultured muscle cells.

CONCLUSION AND IMPLICATIONS

In conclusion, topiramate stimulates insulin-mediated glucose uptake in vivo through the CNS. These observations illustrate the possibility of pharmacological modulation of peripheral insulin resistance through a target in the CNS.     

Implantation of bFGF-treated islet progenitor cells ameliorates streptozotocin-induced diabetes in rats

Aim:

To examine whether implantation of islet preparation-derived proliferating islet cells (PIC) could ameliorate diabetes in rats.

Methods:

PIC were expanded from rat islet preparation by supplementation of basic fibroblast growth factor (bFGF) and implanted into rats with streptozotocin (STZ)-induced diabetes through the portal vein. Body weight and blood glucose levels were measured. Serum insulin levels were measured by radioimmunoassay. The presence of insulin-positive cells was determined by hematoxylin and immunohistochemical staining.

Results:

Cultured islet cells (CIC) were demonstrated to dedifferentiate in vitro, and the apoptosis ratios reached more than 50% by the 15th day post-isolation. PIC cells treated with bFGF (20 ng/mL) continued growing within 30 days after isolation, and no apoptotic cells were detected. Implantation of PIC into diabetic rats was capable of ameliorating diabetes, in terms of the restoration of euglycemia, weight gain, improved glucose response and elevated serum insulin levels for up to 130 days. Livers derived from PIC-implanted rats were examined for insulin expression and single insulin-positive cells. In addition, most islets of PIC-implanted STZ-induced diabetic rats were intact at 130 days post-transplantation and comparable to those of normal rats.

Conclusion:

Implantation of bFGF-treated proliferating islet cells is a promising cellular therapeutic approach for diabetes.     

PPARβ activation restores the high glucose-induced impairment of insulin signalling in endothelial cells

BACKGROUND AND PURPOSE

PPARβ enhances insulin sensitivity in adipocytes and skeletal muscle cells, but its effects on insulin signalling in endothelial cells are not known. We analysed the effects of the PPARβ/δ (PPARβ) agonists, GW0742 and L165041, on impaired insulin signalling induced by high glucose in HUVECs and aortic and mesenteric arteries from diabetic rats.

EXPERIMENTAL APPROACH

Insulin-stimulated NO production, Akt-Ser⁴⁷³ and eNOS-Ser¹¹⁷⁷ phosphorylation, and reactive oxygen species (ROS) production were studied in HUVECs incubated in low- or high-glucose medium. Insulin-stimulated relaxations and protein phosphorylation in vessels from streptozotocin (STZ)-induced diabetic rats were also analysed.

KEY RESULTS

HUVECs incubated in high-glucose medium showed a significant reduction in insulin-stimulated production of NO. High glucose also reduced insulin-induced Akt-Ser⁴⁷³ and eNOS-Ser¹¹⁷⁷ phosphorylation, increased IRS-1-Ser⁶³⁶ and ERK1/2-Thr¹⁸³-Tyr¹⁸⁵ phosphorylation and increased ROS production. The co-incubation with the PPARβ agonists GW0742 or L165041 prevented all these effects induced by high glucose. In turn, the effects induced by the agonists were suppressed when HUVEC were also incubated with the PPARβ antagonist GSK0660, the pyruvate dehydrogenase kinase (PDK)4 inhibitor dichloroacetate or after knockdown of both PPARβ and PDK4 with siRNA. The ERK1/2 inhibitor PD98059, ROS scavenger catalase, inhibitor of complex II thenoyltrifluoroacetone or uncoupler of oxidative phosphorylation, carbonyl cyanide m-chlorophenylhydrazone, also prevented glucose-induced insulin resistance. In STZ diabetic rats, oral GW0742 also improved insulin signalling and the impaired NO-mediated vascular relaxation.

CONCLUSION AND IMPLICATIONS

PPARβ activation in vitro and in vivo restores the endothelial function, preserving the insulin-Akt-eNOS pathway impaired by high glucose, at least in part, through PDK4 activation.     

Association of serum 25-hydroxyvitamin D with insulin resistance and β-cell function in a healthy Chinese female population

Aim:

To assess associations of the serum level of 25-hydroxyvitamin D with insulin resistance and β-cell function in a healthy Chinese female population.

Methods:

This cross-sectional study included 1382 female participants free of type 2 diabetes who were recruited in Shanghai. Blood samples were collected within a winter season and the serum levels of 25-hydroxyvitamin D, fasting plasma glucose and insulin, and other biochemical parameters were determined. Insulin resistance and β-cell function were assessed using the homeostasis model assessments of insulin resistance (HOMA-IR) and β-cell function (HOMA-B), respectively.

Results:

Multiple linear regression analyses adjusted for age, parathyroid hormone, Ca²⁺ and BMI revealed that independent inverse associations existed between the serum level of 25-hydroxyvitamin D and HOMA-IR (P<0.001) and between the serum level of 25-hydroxyvitamin D and HOMA-B (P=0.001).

Conclusion:

Serum vitamin D level is significantly and independently associated with insulin resistance and β-cell function in a healthy Chinese female population.     

TS-071 is a novel, potent and selective renal sodium-glucose cotransporter 2 (SGLT2) inhibitor with anti-hyperglycaemic activity

BACKGROUND AND PURPOSE

The renal sodium-glucose cotransporter 2 (SGLT2) plays an important role in the reuptake of filtered glucose in the proximal tubule and therefore may be an attractive target for the treatment of diabetes mellitus. This study characterizes the pharmacological profile of TS-071 ((1S)-1,5-anhydro-1-[5-(4-ethoxybenzyl)-2-methoxy-4-methylphenyl]-1-thio-d-glucitol hydrate), a novel SGLT2 inhibitor in vitro and in vivo.

EXPERIMENTAL APPROACH

Inhibition of glucose uptake by TS-071 was studied in CHO-K1 cells stably expressing either human SGLT1 or SGLT2. Single oral dosing studies were performed in rats, mice and dogs to assess the abilities of TS-071 to increase urinary glucose excretion and to lower plasma glucose levels.

KEY RESULTS

TS-071 inhibited SGLT2 activity in a concentration-dependent manner and was a potent and highly selective inhibitor of SGLT2. Orally administered TS-071 increased urinary glucose excretion in Zucker fatty rats and beagle dogs at doses of 0.3 and 0.03 mg·kg⁻¹ respectively. TS-071 improved glucose tolerance in Zucker fatty rats without stimulating insulin secretion and reduced hyperglycaemia in streptozotocin (STZ)-induced diabetic rats and db/db mice at a dose of 0.3 mg·kg⁻¹.

CONCLUSION AND IMPLICATIONS

These data indicate that TS-071 is a potent and selective SGLT2 inhibitor that improves glucose levels in rodent models of type 1 and 2 diabetes and may be useful for the treatment for diabetes mellitus.     

LKB1 gene inactivation does not sensitize non-small cell lung cancer cells to mTOR inhibitors in vitro

Aim:

Previous study has shown that endometrial cancers with LKB1 inactivation are highly responsive to mTOR inhibitors. In this study we examined the effect of LKB1 gene status on mTOR inhibitor responses in non-small cell lung cancer (NSCLC) cells.

Methods:

Lung cancer cell lines Calu-1, H460, H1299, H1792, and A549 were treated with the mTOR inhibitors rapamycin or everolimus (RAD001). The mTOR activity was evaluated by measuring the phosphorylation of 4EBP1 and S6K, the two primary mTOR substrates. Cells proliferation was measured by MTS or sulforhodamine B assays.

Results:

The basal level of mTOR activity in LKB1 mutant A549 and H460 cells was significantly higher than that in LKB1 wild-type Calu-1 and H1792 cells. However, the LKB1 mutant A549 and H460 cells were not more sensitive to the mTOR inhibitors than the LKB1 wild-type Calu-1 and H1792 cells. Moreover, knockdown of LKB1 gene in H1299 cells did not increase the sensitivity to the mTOR inhibitors. Treatment with rapamycin or RAD001 significantly increased the phosphorylation of AKT in both LKB1 wild-type and LKB1 mutant NSCLC cells, which was attenuated by the PI3K inhibitor {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002. Furthermore, RAD001 combined with {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 markedly enhanced the growth inhibition on LKB1 wild-type H1792 cells and LKB1 mutant A549 cells.

Conclusion:

LKB1 gene inactivation in NSCLC cells does not increase the sensitivity to the mTOR inhibitors. The negative feedback activation of AKT by mTOR inhibition may contribute to the resistance of NSCLC cells to mTOR inhibitors.     

A sesquiterpene quinone,dysidine, from the sponge Dysidea villosa,activates the insulin pathway through inhibition of PTPases

Aim:

The sesquiterpene hydroquinones/quinones belong to one class of marine sponge metabolites, and they have received considerable attention due to their varied biological activities, including anti-tumor, anti-HIV, and anti-inflammatory action. In order to probe the potential anti-diabetic effect of the sesquiterpene hydroquinones/quinones, the effect of dysidine on the insulin pathway was studied.

Methods:

The promotion of glucose uptake by dysidine was studied in differentiated 3T3-L1 cells. The increase in membrane-located GLUT4 by dysidine was studied in CHO-K1/GLUT4 and 3T3-L1 cells by immuno-staining. The activation of the insulin signaling pathway by dysidine was probed by Western blotting. The inhibition of PTPases by dysidine was detected in vitro.

Results:

Dysidine, found in the Hainan sponge Dysidea villosa in the Chinese South Sea, effectively activated the insulin signaling pathway, greatly promoted glucose uptake in 3T3-L1 cells, and showed strong insulin-sensitizing activities. The potential targets of action for dysidine were probed, and the results indicated that dysidine exhibited its cellular effects through activation of the insulin pathway, possibly through the inhibition of protein tyrosine phosphatases, with more specific inhibition against protein tyrosine phosphatase 1B (PTP1B).

Conclusion:

Our findings are expected to expand understanding of the biological activities of sesquiterpene hydroquinones/quinones, and they show that dysidine could be a potential lead compound in the development of an alternative adjuvant in insulin therapy.     

The effect of exercise on the absorption of inhaled human insulin in healthy volunteers

Aims

To investigate the effect of moderate exercise on the absorption of inhaled insulin.

Methods

A single-centre, randomized, open-label, three-period cross-over trial was carried out in 12 nonsmoking healthy subjects. A dose of 3.5 mg inhaled human insulin was administered via a nebulizer and followed in random order by either 1) no exercise (NOEX), 2) 30 min exercise starting immediately after dosing (EX0), or 3) 30 min exercise starting 30 min after dosing (EX30). The study was carried out as a 10 h euglycaemic glucose clamp (90 mg dl⁻¹ (5.0 mmol l⁻¹)).

Results

The absorption of insulin over the first 2 h after start of exercise was 16% increased for EX0 (ratio (95%CI) 1.16 (1.04, 1.30), P = 0.01) and 20% increased for EX30 (1.20 (1.05, 1.36), P < 0.01), both compared with NOEX; the overall insulin absorption during 6 h and 10 h after dosing was not influenced by exercise. The maximum insulin concentration (C_max) increased by 32% for EX0 and 35% for EX30 (both P < 0.01) compared with NOEX, while the time to C_max was 31 min faster for EX0 (P < 0.01), but not significantly different after EX30, compared with NOEX.

Conclusions

A significant and clinically relevant increase of insulin absorption over the first 2 h after the beginning of exercise was observed. Until data from studies using the specific insulin inhalers exists, patients using inhaled insulin should be made aware of a potential increased absorption and higher concentration of insulin in connection with exercise.

What is already known about this subject

• Exercise is known to affect absorption of other inhaled substances, but so far there are no reports on the effect of exercise on the absorption of inhaled insulin in humans.

What this paper adds

• This report is the first to investigate the effect of exercise on the absorption of inhaled insulin.
• In this study in healthy volunteers we found that exercise early after dosing increased absorption (15–20%) of inhaled insulin over the first 2 h after start of exercise, with an approximately 30% increase in maximal insulin concentration, and unchanged overall absorption.