Interactions between myoblasts and macrophages under high glucose milieus result in inflammatory response and impaired insulin sensitivity

BACKGROUND Skeletal muscle handles about 80% of insulin-stimulated glucose uptake and become the major organ occurring insulin resistance(IR).Many studies have confirmed the interactions between macrophages and skeletal muscle regulated the inflammation and regeneration of skeletal muscle.However,despite of the decades of research,whether macrophages infiltration and polarization in skeletal muscle under high glucose(HG)milieus results in the development of IR is yet to be elucidated.C2C12 myoblasts are well-established and excellent model to study myogenic regulation and its responses to stimulation.Further exploration of macrophages'role in myoblasts IR and the dynamics of their infiltration and polarization is warranted.AIM To evaluate interactions between myoblasts and macrophages under HG,and its effects on inflammation and IR in skeletal muscle.METHODS We detected the polarization status of macrophages infiltrated to skeletal muscles of IR mice by hematoxylin and eosin and immunohistochemical staining.Then,we developed an in vitro co-culture system to study the interactions between myoblasts and macrophages under HG milieus.The effects of myoblasts on macrophages were explored through morphological observation,CCK-8 assay,Flow Cytometry,and enzyme-linked immunosorbent assay.The mediation of macrophages to myogenesis and insulin sensitivity were detected by morphological observation,CCK-8 assay,Immunofluorescence,and 2-NBDG assay.RESULTS The F4/80 and co-localization of F4/80 and CD86 increased,and the myofiber size decreased in IR group(P<0.01,g=6.26).Compared to Mc group,F4/80+CD86+CD206-cells,tumor necrosis factor-α(TNFα),inerleukin-1β(IL-1β)and IL-6 decreased,and IL-10 increased in McM group(P<0.01,g>0.8).In McM+HG group,F4/80+CD86+CD206-cells,monocyte chemoattractant protein 1,TNFα,IL-1βand IL-6 were increased,and F4/80+CD206+CD86-cells and IL-10 were decreased compared with Mc+HG group and McM group(P<0.01,g>0.8).Compered to M group,myotube area,myotube number and E-MHC were increased in MMc group(P<0.01,g>0.8).In MMc+HG group,myotube area,myotube number,E-MHC,GLUT4 and glucose uptake were decreased compared with M+HG group and MMc group(P<0.01,g>0.8).CONCLUSION Interactions between myoblasts and macrophages under HG milieus results in inflammation and IR,which support that the macrophage may serve as a promising therapeutic target for skeletal muscle atrophy and IR.

Anti-diabetic effects of Caulerpa lentillifera:stimulation of insulin secretion in pancreatic β-cells and enhancement of glucose uptake in adipocytes

Objective:To evaluate anti-diabetic effect of Caulrpa kntillifera(C.lentillifera).Methods:The inhibitory effect of C.lentillifera extract on dipeptidyl peptidase-IV and a-glucosidase enzyme was measured in a cell free system.Then,interleukin-1βand interferon-γinduced cell death and insulin secretion were measured in rat insulinoma(RIN)cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and ELISA kit,respectively.Glucose uptake and glucose transporter expression were measured by fluorometry and western blotting,using 3T3-Ll adipocytes.Results:C.lentillifera extract significantly decreased dipeptidyl peptidase-IV and a-glucosidase enzyme activities,and effectively inhibited cell death and iNOS expression in interleukin-1βand interfcron-γinduced RIK cells.Furthermore,C.lntillifera extract significantly enhanced insulin secretion in RTN cells and glucose transporter expression and glucose uptake in 3T3-L1adipocytes.Conclusions:Thus,our results suggest that C.lentillifera could be used as a potential antidiabetic agenl.

Natural products:Regulating glucose metabolism and improving insulin resistance

Compounds with regulating glucose metabolism and improving insulin resistance(IR)activity are abundant in nature and can be obtained from several sources.They have high potential to be used to treat diabetes mellitus.These compounds isolated from natural plants can be classified seven categories:terpenoids,alkaloids,quinones,flavonoids,phenols,phenyl propanoids,steroids,and other types of compounds.They exert biological effects by different ways and mechanisms.This review illustrated the potential natural products as a rich resource in regulation of glucose metabolism and IR,as well as their mechanisms.

Decabromodiphenyl ether causes insulin resistance and glucose and lipid metabolism disorders in mice

BACKGROUND Decabromodiphenyl ether(BDE-209)is the most commonly used brominated flame retardant.Recently,BDE-209 has been suspected of being an environmental risk factor for metabolic diseases such as obesity,insulin resistance(IR),type 2 diabetes mellitus,and hypertension.AIM To investigate the effects of BDE-209 on IR and glucose and lipid metabolism in C57BL/6 mice.METHODS Adult male C57BL/6 mice were randomly divided into high,medium-high,medium,medium-low,and low dose BDE-209 groups,and a control group(n=6 per group),which received 1000,800,600,450,300,and 0 mg/kg BDE-209,respectively.After BDE-209 exposure for 60 d,the mice were fasted overnight,and then sacrificed to obtain tissues.An automatic biochemical analyzer was used to detect serum triglyceride(TG),total cholesterol(TC),low-density lipoprotein cholesterol(LDL-C),and high density lipoprotein cholesterol(HDL-C);enzymelinked immunosorbent assay kits were used to detect fasting serum insulin(FINS),leptin(LEP),and adiponectin(Adp)levels;a blood glucose meter was used to detect fasting blood glucose(FBG).Morphological changes of the liver were observed by hematoxylin and eosin staining.Real-time quantitative polymerase chain reaction and Western blot were used to determine the messenger ribonucleic acid(mRNA)and protein levels,respectively,of LEP,Adp,and peroxisome proliferators activated receptor-γ(PPARγ)in mouse liver and adipose tissues.RESULTS There was a statistically significant difference in the weight of mice in each group after 45 and 60 d of exposure(P<0.05).After 60 d of exposure,the weight of liver and adipose tissues in the exposure groups were greater than that of the control group(P<0.05).The liver tissue structure was disordered and the liver tissues were accompanied by local inflammatory cell infiltration in the high,mediumhigh,and medium dose BDE-209 groups.The levels of FINS,insulin sensitivity index,Adp,and HDL-C were decreased in the BDE-209 group compared with the control group,as were the mRNA and protein levels of Adp in liver and adipose tissues(P<0.05).Serum level of FBG and LEP were higher in the BDE-209 group than in controls.TC,TG,and LDL-C levels as well as the mRNA and protein expression of LEP and PPARγin liver and adipose tissues were higher than those in the control group(P<0.05).Homeostatic assessment model of IR was higher in the medium and medium-low dose BDE-209 groups(P<0.05).CONCLUSION BDE-209 increases the body weight,fat and liver tissue weight,TC,TG,and LDLC,reduces HDL-C,and causes IR in mice,which may be related to activating the PPARγreceptor.

Roles of sulfonylurea receptor 1 and multidrug resistance protein 1 in modulating insulin secretion in human insulinoma

BACKGROUND:Sulfonylurea receptor 1(SUR1)and multidrug resistance protein 1(MRP1)are two prominent members of multidrug resistance proteins associated with insulin secretion. The aims of this study were to investigate their expression in insulinomas and their sole and synergistic effects in modulating abnormal insulin secretion. METHODS:Fasting glucose,insulin and C-peptide were measured in 11 insulinoma patients and 11 healthy controls. Prolonged oral glucose tolerance tests were performed in 6 insulinoma patients.Insulin content,SUR1 and MRP1 were detected in 11 insulinoma patients by immunohistochemistry. SUR1 and MRP1 were also detected in 6 insulinoma patients by immunofluorescence. RESULTS:Insulinoma patients presented the typical demons-trations of Whipple’s triad.Fasting glucose of each insulinoma patient was lower than 2.8 mmol/L,and simultaneous insulin and C-peptide were increased in insulinoma patients. Prolonged oral glucose tolerance tests showed that insulin secretion in insulinoma patients were also stimulated by high glucose.Immunohistochemistry and immunofluorescence staining showed that SUR1 increased,but MRP1 decreased in insulinoma compared with the adjacent islets. CONCLUSIONS:The hypersecretion of insulin in insulinomas might be,at least partially,due to the enrichment of SUR1. In contrast,MRP1,which is down-regulated in insulinomas, might reflect a negative feedback in insulin secretion.

Effects of vitamin D supplementation on glucose and lipid metabolism in patients with type 2 diabetes mellitus and risk factors for insulin resistance

BACKGROUND Type 2 diabetes mellitus(T2DM)is a chronic metabolic disease featured by insulin resistance(IR)and decreased insulin secretion.Currently,vitamin D deficiency is found in most patients with T2DM,but the relationship between vitamin D and IR in T2DM patients requires further investigation.AIM To explore the risk factors of IR and the effects of vitamin D supplementation on glucose and lipid metabolism in patients with T2DM.METHODS Clinical data of 162 T2DM patients treated in First Affiliated Hospital of Harbin Medical University between January 2019 and February 2022 were retrospectively analyzed.Based on the diagnostic criteria of IR,the patients were divided into a resistance group(n=100)and a non-resistance group(n=62).Subsequently,patients in the resistance group were subdivided to a conventional group(n=44)or a joint group(n=56)according to the treatment regimens.Logistic regression was carried out to analyze the risk factors of IR in T2DM patients.The changes in glucose and lipid metabolism indexes in T2DM patients with vitamin D deficiency were evaluated after the treatment.RESULTS Notable differences were observed in age and body mass index(BMI)between the resistance group and the non-resistance group(both P<0.05).The resistance group exhibited a lower 25-hydroxyvitamin D_(3)(25(OH)D_(3))level,as well as notably higher levels of 2-h postprandial blood glucose(2hPG),fasting blood glucose(FBG),and glycosylated hemoglobin(HbA1c)than the non-resistance group(all P<0.0001).Additionally,the resistance group demonstrated a higher triglyceride(TG)level but a lower high-density lipoprotein-cholesterol(HDL-C)level than the non-resistance group(all P<0.0001).The BMI,TG,HDL-C,25(OH)D_(3),2hPG,and HbA1c were found to be risk factors of IR.Moreover,the posttreatment changes in levels of 25(OH)D_(3),2hPG,FBG and HbA1c,as well as TG,total cholesterol,and HDL-C in the joint group were more significant than those in the conventional group(all P<0.05).CONCLUSION Patients with IR exhibit significant abnormalities in glucose and lipid metabolism parameters compared to the noninsulin resistant group.Logistic regression analysis revealed that 25(OH)D_(3)is an independent risk factor influencing IR.Supplementation of vitamin D has been shown to improve glucose and lipid metabolism in patients with IR and T2DM.

A review on mechanisms of action of bioactive peptides against glucose intolerance and insulin resistance

Insulin resistance leads to impaired glucose metabolism by disrupting both insulin secretion and sensitivity.Insulin resistance plays a key role in the pathophysiology of type 2 diabetes and metabolic syndrome.Reviews on the mechanisms of action of bioactive peptides on glucose homeostasis and insulin resistance are scarce.The recent discoveries of pathways and target cells in the management of glucose and energy metabolism have opened up new opportunities for identification of novel bioactive peptides on enhancing adipocyte differentiation and insulin signaling,glucose uptake,cholecystokinin receptor expression and activation,as well as insulin mimetics and incretin stimulants.Examples of food-derived bioactive peptides with glucoregulatory properties include Trp-Glu-Lys-Ala-Phe-Lys-Asp-Glu-Asp(WEKAFKDED),Gln-Ala-MetPro-Phe-Arg-Val-Thr-Glu-Gln-Glu(QAMPFRVTEQE),Glu-Arg-Tyr-Pro-Ile-Leu(ERKPIL),Val-Phe-LysGly-Leu(VFKGL),Phe-Leu-Val(FLV),Val-Pro-Pro(VPP),Ile-Arg-Trp(IRW),Ala-Lys-Ser-Pro-Leu-Phe(AKSPLF),Ala-Thr-Gln-Pro-Leu-Phe(ATNPLF),Phe-Glu-Glu-Leu-Gln(FEELN),Leu-Ser-Val-Ser-Val-Leu(LSVSVL),Val-Arg-Ileu-Arg-Leu-Leu-Gln-Arg-Phe-Asn-Lys-Arg-Ser(VRIRLLQRFNKRS),and Ala-GlyPhe-Ala-Gly-Asp-Asp-Ala-Pro-Arg(AGFAGDDAPR).However,as yet,clinical evidence on the effi cacy of such bioactive peptides is rare but is inevitable to establish their applications against glucose intolerance and insulin resistance.

A Triterpene Glycoside Fraction, TG from <i>Gymnema sylvestre</i>Ameliorates Insulin Resistance by Stimulating Glucose Uptake in 3T3L1 Adipocytes and C2C12 Skeletal Muscle Cells

Type 2 diabetes mellitus (T2DM) which is characterized by insulin resistance in muscle and adipose tissues is a major problem worldwide. Plant based medications are well known from ancient times for possessing antidiabetic properties. Amongst them, Gymnema sylvestre (GS) is one such antidiabetic medicinal plant which has been used traditionally over the years for the treatment of T2DM. The aim of the present study was to investigate the effect of triterpene glycoside (TG), an active fraction isolated from ethanolic extract of Gymnema sylvestre (EEGS) on a battery of targets;glucose transporter (GLUT- 4), peroxisome proliferator activator receptor gamma (PPAR-γ), adiponectin and leptin involved in glucose transport and metabolism. No cytotoxic effects were observed in treated cells up to 600 μg/ml of TG as measured by MTT and ROS assays. Elevation of GLUT-4 and PPAR-γ by TG in association with glucose transport supported the upregulation of glucose uptake at concentrations of 50 and 100 μg/ml respectively. Additionally, TG showed higher expression of adiponectin and leptin, confirming the favorable pharmacological effect of TG on insulin resistance. The results were comparable to the known antidiabetic drug pioglitazone and commercial standard DAG. Thus TG could be considered as a safe nutraceutical candidate/functional phytoingredient in amelioration of insulin resistance.

Measurement of lumbar muscle glucose utilization rate can be as useful in estimating skeletal muscle insulin resistance as that of thigh muscle

Background: Skeletal muscle glucose utilization (SMGU) can be accessed by positron emission tomography (PET) and18F-FDG to characterize insulin resistance. The quantity of skeletal muscle in the lumbar is sufficient to indicate that SMGU in the lumbar (SMGU- lumbar) can be measured with18F-FDG PET of the chest instead of obtaining thigh muscle SMGU (SMGU-thigh). This would reduce PET scan time to avoid thigh muscle PET scan. This study was aimed to compare SMGU-lumbar and thigh muscle SMGU under insulin clamping to identify the validity of measurements of SMGU in the lumbar for studies of insulin resistance. Methods: Thirty-three patients underwent sequential dynamic18F-FDG PET of both the thoracic (37 min) and thigh region (22 min) during hyperinsulinemic euglycemic insulin clamping. Both SMGU-lumbar and SMGU-thigh were calculated by Patlak graphical analysis. Whole body insulin resistance was assessed by a whole body glucose disposal rate during hyperinsulinemic euglycemic insulin clamping. Input function was obtained from the time activity curve of the descending aorta and venous blood sampling as previously validated. Results: SMGU-thigh (0.0506 ± 0.0334 μmol/min/g) was comparable to SMGU-lumbar (0.0497 ± 0.0255 μmol/min/g). The Bland-Altman method of difference plot analysis showed a significant correlationship between SMGU- thigh and SMGU-lumbar (r = 0.506, p = 0.0028). There were seen very good significant correlationship between whole body glucose utilization rate in both thigh (r = 0.737, p = 0.0001) and lumbar (r = 0.772, p = 0.0001). Conclusion: These results support the validity of measuring SMGU-lumbar to estimate insulin resistance during PET imaging of the chest.

Functional imaging of skeletal muscle glucose metabolism by ¹⁸FDG PET to characterize insulin resistance in patients at high risk for coronary artery disease

Insulin resistance is associated with several coronary risk factors and is thought to play a critical role for the development of coronary artery disease. Insulin resistance has several causes, including an impaired skeletal muscle glucose utilization rate (SMGU), reduced peripheral blood flow, and altered fatty tissue metabolism, with SMGU being considered the most important. Nonetheless, insulin resistance has only been estimated by the glucose disposal rate (GDR) in previous studies. Methods: Skeletal muscle metabolic imaging with 18FDG and positron emission tomography (PET) was undertaken to measure SMGU during hyperinsulinemiceuglycemic clamping in 22 normotensive type-2 diabetics under no medications (T2- DM), 17 normotensive non-diabetic hypertriglyceridemics, 22 patients with hypertension, and 12 agematched controls. Whole body insulin resistance was assessed by the GDR during hyperinsulinemiceuglycemic insulin clamping. Results: The SMGU and GDR were significantly reduced in T2DM (32.1 ± 16.6 μmol/min/kg and 24.3 ± 13.0 μmol/min/kg, respectively), hypertriglyceridemics (36.5 ± 13.5 μmol/min/ kg and 22.7 ± 8.07 μmol/min/kg respectively) and patients with hypertension (35.4 ± 26.6 μmol/min/kg and 29.0 ± 9.90 μmol/min/kg, respectively) compared with controls (72.2 ± 44.1 μmol/min/kg and 43.0 ± 22.9 μmol/min/kg, p < 0.01, respectively). In all groups studied, SMGU was significantly correlated with GDR (r = 0.76, p < 0.01) and GDR (F = 13.9) was independently related to SMGU (r = 0.81, p < 0.01). Conclusion: Insulin resistance is significantly associated with SMGU to a similar degree among patients with T2DM, essential hypertension and hypertriglyceridemia. 18FDG PET functional imaging allows insulin resistance to be assessed.

Anti-Hyperglycemic Effect of Single Administered Gardeniae Fructus in Streptozotocin-Induced Diabetic Mice by Improving Insulin Resistance and Enhancing Glucose Uptake in Skeletal Muscle

The mechanisms of Gardeniae Fructus (GF) for anti-hyperglycemic action were demonstrated in streptozotocin (STZ)-diabetic mice. Six hours after single intraperitoneal administration of GF (300 mg/kg) or H2O into 3 hour-fasted STZ-diabetic mice, glucose and insulin tolerances were assessed by intraperitoneal glucose (1.5 g/kg) tolerance test (IPGTT) and intraperitoneal insulin (0.65 U/kg) tolerance test (IPITT), respectively. Effects of GF on insulin signaling pathways in soleus muscle such as glucose uptake, expression of glucose transporter 4 (GLUT4) in the plasma membrane and phosphorylation of Akt (P-Akt) in cytosolic fraction were examined in STZ-diabetic mice. In IPGTT test, GF significantly accelerated clearance of exogenous glucose and its glucose-lowering action was greater than H2O-treated controlin STZ-diabetic mice. GF also promoted an exogenous glucose-increased insulin level in STZ-diabetic mice. In IPITT test, GF decreased glucose level to the greater extent than H2O-treated control in STZ-diabetic mice. Furthermore, GF significantly decreased high HOMA-IR in STZ-diabetic mice from 21.6 ± 2.4 to 12.4 ± 1.9 (mg/dl × μU/ml). These results implied that GF improved insulin resistance in STZ-diabetic mice. GF increased glucose uptake of soleus muscle 1.5 times greater than H2O-treated control in STZ-diabetic mice. GF enlarged insulin (10 nmol/ml)-increased glucose uptake to 1.8 time-greater. Correspondingly, GF increased expression of GLUT4 in the plasma membrane of soleus muscle to 1.4 time-greater, and P-Akt in the cytosolic fraction of soleus muscle to 1.9 time-greater than those in H2O-treated control. In conclusion, the improvement of GF on insulin resistance is associated with the repair of insulin signaling via P-Akt, GLUT4 and glucose uptake pathway in soleus muscle of STZ-diabetic mice.

NLRP3 Inflammasome in Relation to Glucose and Lipid Metabolism, and Insulin Resistance in Diabetes and Pre-Diabetes

Aims: To investigate the relationship among NLRP3 inflammasome, glucose and lipid metabolism, and insulin resistance (IR) in the serum of patients with diabetes and pre-diabetes. Methods: A total of 100 patients with abnormal blood glucose divided into the pre-diabetes mellitus (PDM) group (N = 46) and the type 2 diabetes mellitus (T2DM) group (N = 54). 20 normoglycemic subjects (NG, N = 20) were selected as a control group. The serum levels of glucose and lipid metabolism, IR, and the expression of NLRP3, ASC and Caspase-1 were measured. Besides, the correlations of NLRP3 inflammasome with glucose and lipid metabolism, and IR were analyzed. Results: Compared with the NG group, the levels of NLRP3, ASC, Caspase-1, FBG, HbA1C, TG, LDL-C, FINs, and HOMA-IR were higher (P β were lower (P P β were seen (P P β. Regression analysis further showed that blood glucose related indexes, FINs, and NLRP3 have made a decisive contribution to IR. Conclusions: Collectively, this evidence suggested that NLRP3 is closely related to glucose and lipid metabolism, and IR, and activated in PDM and T2DM.

Relationship Between Serum microRNA-372-3p and Glucose Transporter 4 Levels and Insulin Resistance in Gestational Diabetes Mellitus

Objective:To observe the changes in insulin resistance in patients with gestational diabetes mellitus(GDM)based on the detection of serum microRNA-372-3p and glucose transporter protein 4(GLUT4)levels.Methods:We conducted a retrospective cohort study of 42 patients who were diagnosed with GDM and hospitalized in our hospital during the period from January 2017 to December 2021 and another 42 patients who had normal pregnancy during the same period by collecting their clinical data.We analyzed their serum microRNA expression profiles and miR-372-3p levels to study the relationship between GDM and insulin resistance.Results:The relative expression of miR-372-3p in the serum of patients in the GDM group was significantly higher than that of patients in the control group,but the GLUT 4 level of the GDM group was significantly lower than that of the control group(P<0.05).Compared with the control group,the GDM group had significantly higher levels of fasting blood glucose(FBG),fasting insulin(FINS),2-hour postprandial blood glucose(2h-BG),total cholesterol(TC),triglyceride(TG),and homeostatic model assessment for insulin resistance(HOMA-IR)index but significantly lower homeostasis model assessment ofβ-cell function(HOMA-β)index(P<0.05).The relative expression of miR-372-3p in serum was independently and positively correlated with HOMA-IR,while the level of GLUT4 was independently and negatively correlated with HOMA-IR(P<0.05).Conclusion:Glycosylated hemoglobin test in the early stages of pregnancy(12–13 weeks of gestation)is important to ensure the health of pregnant women and fetuses.The screening and intervention for elevated glucose in pregnant women act as a guideline for the treatment of GDM.Patients with insulin resistance and related complications such as hyperinsulinemia and hypoglycemia should be given priority.

Hepatitis C virus infection and insulin resistance

Approximately 170 million people worldwide are chronically infected with hepatitis C virus(HCV).Chronic HCV infection is the leading cause for the development of liver fibrosis,cirrhosis,hepatocellular carcinoma(HCC)and is the primary cause for liver transplantation in the western world.Insulin resistance is one of the pathological features in patients with HCV infection and often leads to development of typeⅡdiabetes.Insulin resistance plays an important role in the development of various complications associated with HCV infection.Recent evidence indicates that HCV associated insulin resistance may result in hepatic fibrosis,steatosis,HCC and resistance to anti-viral treatment.Thus,HCV associated insulin resistance is a therapeutic target at any stage of HCV infection.HCV modulates normal cellular gene expression and interferes with the insulin signaling pathway.Various mechanisms have been proposed in regard to HCV mediated insulin resistance,involving up regulation of inflammatory cytokines,like tumor necrosis factor-α,phosphorylation of insulin-receptor substrate-1,Akt,up-regulation of gluconeogenic genes like glucose 6 phosphatase,phosphoenolpyruvate carboxykinase 2,and accumulation of lipid droplets.In this review,we summarize the available information on how HCV infection interferes with insulin signaling pathways resulting in insulin resistance.

Effect of sodium salicylate on oxidative stress and insulin resistance induced by free fatty acids

BACKGROUND: It has been reported that high-dose salicylates improve free fatty acids (FFAs)-induced insulin resistance and beta-cell dysfunction in vitro, but the mechanism remains uncertain. In insulin-resistant rats, we found that the supplementation of sodium salicylate is associated with a reduction of plasma malondialdehyde (MDA), a marker of oxidative stress. Few studies have investigated the effects of salicylates on oxidative stress levels in insulin-resistant animal models. This study aimed to assess the effect of sodium salicylate on insulin sensitivity and to explore the potential mechanism by which it improves hepatic and peripheral insulin resistance. METHODS: Intralipid+heparin (IH), saline (SAL), or intralipid+heparin+sodium salicylate (IHS) were separately infused for 7 hours in normal Wistar rats. During the last 2 hours of the infusion, hyperinsulinemic-euglycemic clamping was 3 performed with [6-(3)H] glucose tracer. Plasma glucose was measured using the glucose oxygenase method. Plasma insulin and C-peptide were determined by radioimmunoassay. MDA levels and glutathione peroxidase (GSH-PX) activity in the liver and skeletal muscle were measured with colorimetric kits. RESULTS: Compared with infusion of SAL, IH infusion increased hepatic glucose production (HGP), and decreased glucose utilization (GU) (P<0.05). The elevation of plasma free fatty acids increased the MDA levels and decreased the GSH-PX activity in the liver and muscle (P<0.01). Sodium salicylate treatment decreased HGP, elevated GU (P<0.05), reduced MDA content by 60% (P<0.01), and increased the GSH-PX activity by 35% (P<0.05). CONCLUSIONS: Short-term elevation of fatty acids induces insulin resistance by enhancing oxidative stress levels in the liver and muscle. The administration of the anti-inflammatory drug sodium salicylate reduces the degree of oxidative stress, therefore improving hepatic and peripheral insulin resistance. IKK-beta and NF-kappa B provide potential pathogenic links to oxidative stress.

Effects of different free fatty acids on insulin resistance in rats

BACKGROUND: Much evidence demonstrates that elevated free fatty acids (FFAs) are associated with insulin resistance. However, it is not clear whether different FFAs can cause different degrees of peripheral insulin resistance. This study aimed to investigate the effects of short-term elevation of FFAs on hepatic and peripheral insulin action, and determine whether FFAs with different degrees of saturation have differential effects on hepatic insulin resistance. METHODS: Intralipid+heparin (IH, polyunsaturated fatty acids), oleate (OLE), lard oil+heparin (LOH), and saline (SAL) were separately infused intravenously for 7 hours in normal Wistar rats. During the last 2 hours of the fat/saline infusion, a hyperinsulinemic-euglycemic clamping was performed with [6-H-3] glucose tracer. Plasma glucose was measured using the glucose oxygenase method. Plasma insulin and C-peptide were determined by radioimmunoassays. Plasma FFAs were measured using a colorimetric method. RESULTS: Compared with infusion of SAL, plasma FFA levels were significantly elevated by infusions of IH, OLE, and LOH (P<0.001). All three fat infusions caused remarkably higher hepatic glucose production (HGP) than SAL (P<0.001). OLE and LOH infusions induced much higher HGP than IH (P<0.01). Glucose utilization (GU) was decreased with all three fat infusions relative to SAL (P<0.001), but GU did not differ among the three types of fat infusions. CONCLUSIONS: Short-term elevation of FFAs can induce hepatic and peripheral insulin resistance. Polyunsaturated fatty acids induced less hepatic insulin resistance than monounsaturated or saturated fatty acids. However, IH, OLE, and LOH infusions induced similar peripheral insulin resistance.

Elevated alanine aminotransferase activity is not associated with dyslipidemias,but related to insulin resistance and higher disease grades in non-diabetic non-alcoholic fatty liver disease

Objective:To explore demographic and metabolic factors associated with increased alanine aminotransferase(ALT)activity in non-diabetic non-alcoholic fatty liver disease(NAFLD)patients.Methods:Overall 372 patients who consecutively attended to Gastroenterology Clinic of Baqiyatallah University of Medical Sciences,Tehran,Iran awere diagnosed as NAFLD entered into analysis.Exclusion criteria were having diabetes mellitus and fasting blood glucose over126 mg/dL,active hepatitis B virus infection,having hepatitis C virus positive serology,and to be under corticosteroid therapy.ALT levels were considered pathologically high when it was over30 IU/L for men and over 19 IU/L for women.Results:Bivariate analyses using t test and chisquare test showed that patients with pathologically augmented ALT levels had significantly higher NAFLD grades in their ultrasonographic evaluations(P=0.003).Moreover,these patients represented significantly higher homeostatic model assessment levels(P=0.003),levels of serum insulin(P=0.002),fasting blood glucose(P<0.001),and uric acid(P=0.02).The prevalence of insulin resistance was also higher in patients with increased serum ALT concentrations.Multifactorial logistic regression models showed that ultrasonographic grading of NAFLD(P=0.027)and insulin resistance(P=0.013)were the only variables significantly associated with abnormal ALT levels.Conclusions:This study shows that the associations of increased ALT serum levels in NAFLD patients are different from what are supposed before.By excluding diabetic patients from our population,we find that increased ALT levels are not associated with dyslipidemias but are independently associated with insulin resistance and NAFLD grading on ultrasonographic evaluations.Further studies are needed to confirm our results.

interrelationships between ghrelin, insulin and glucose homeostasis: physiological relevance

Ghrelin is a 28 amino acid peptide mainly derived from the oxyntic gland of the stomach. Both acylated(AG) and unacylated(UAG) forms of ghrelin are found in the circulation. Initially, AG was considered as the only bioactive form of ghrelin. However, recent advances indicate that both AG and UAG exert distinct and common effects in organisms. Soon after its discovery, ghrelin was shown to promote appetite and adiposity in animal and human models. In response to these anabolic effects, an impressive number of elements have suggested the influence of ghrelin on the regulation of metabolic functions and the development of obesityrelated disorders. However, due to the complexity ofits biochemical nature and the physiological processes it governs, some of the effects of ghrelin are still debated in the literature. Evidence suggests that ghrelin influences glucose homeostasis through the modulation of insulin secretion and insulin receptor signaling. On the other hand, insulin was also shown to influence circulating levels of ghrelin. Here, we review the relationship between ghrelin and insulin and we describe the impact of this interaction on the modulation of glucose homeostasis.

The Expression of Resistin in Adipose Tissues of Patients with Polycystic Ovary Syndrome and Insulin Resistance

The relationship between the expression of resistin in polycystic ovary syndrome （PCOS） and insulin resistance was investigated. The plasma resistin concentrations in 35 patients with PCOS and 40 controls were measured by ELISA. Luteinizing hormone （LH）, follicle-stimulating hormone （FSH）, and fasting insulin （FIN） were tested by radioimmunoassay. Insulin resistance index （HOMA-IR） was calculated. Fasting plasma glucose （FPG） was determined by oxidase test. Western blot and reverse transcriptase PCR （RT-PCR） methods were used to detect the expression of resistin in adipose tissues. The levels of plasma resistin, LH, LH/FSH and FIN and HOMA-IR in patients with PCOS were significantly higher than those in control group （all P〈0.05）. Plasma resistin was correlated positively with FPG, FIN, HOMA-IR, LH and LH/FSH （r=0.56, 0.60, 0.65, 0.48, and 0.42 respectively）. Resistin protein and mRNA expression levels in patients with PCOS were significantly higher than those in normal tissues （all P〈0.01）. It was concluded that resistin might be involved in the pathogenesis of insulin resistance of PCOS.

Assessing and treating insulin resistance in women with polycystic ovarian syndrome

Polycystic ovarian syndrome(PCOS) is a highly prevalent hormonal and metabolic disorder among reproductive aged women worldwide.Women with PCOS have widely varying phenotypes and seek medical care for differing reasons.In addition to concern for menstrual cycle function,ovulation,hirsutism and acne,many PCOS women have abnormal glucose metabolism.While diabetes mellitus and impaired glucose tolerance are easily diagnosed,the diagnosis of and concern for insulin resistance as a precursor disorder is underappreciated.Insulin resistance may be the first important marker of metabolic disease in PCOS women at risk for metabolic syndrome and coronary artery disease.