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Department of Biochemistry, Jawaharlal Institute of Postgraduate Medical Education and Research, Pondicherry 605 006, India
(Correspondence should be addressed to Z Bobby; Email: zacbobby{at}yahoo.com)
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Abstract |
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-lipoic acid; high-fat group – received high-fat diet; and high fat+antioxidant group – fed with high-fat diet supplemented with above antioxidants. Fat feeding to rats for 9 weeks significantly increased IRS-1 serine phoshorylation, reduced insulin-stimulated IRS-1 tyrosine phosphorylation and insulin sensitivity. High-fat diet also impaired redox balance and activated the redox-sensitive serine kinase – JNK pathway. Antioxidant supplementation along with high-fat diet preserved the free radical defense system, inhibited the activation of JNK pathway, and improved insulin signaling and insulin sensitivity. The present study shows for the first time that antioxidants inhibit JNK pathway and IRS-1 serine phosphorylation while improving insulin sensitivity in fat-fed rats. These findings implicate the beneficial effect of antioxidants in obesity-/dyslipidemia-induced insulin resistance in humans. |
Introduction |
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Recently, we (Vinayagamoorthi et al. 2006) along with others (Rudich et al. 1997, 1999, Maddux et al. 2001) reported the role of oxidative stress in the pathogenesis of insulin resistance. A decline in reduced glutathione, vitamin C, vitamin E, and lipoic acid is noted in patients with diabetes (Shigeta et al. 1961, Maxwell et al. 1997, Opara et al. 1999). In vitro studies and studies in animal insulin resistance models have shown that antioxidants, especially -lipoic acid, vitamin E, and vitamin C improve insulin sensitivity (Evans & Goldfine 2000, Jacob et al. 2000). When rat L6 muscle cells and mouse 3T3L1 adipocytes were exposed to oxidative stress, insulin-stimulated glucose uptake was inhibited (Rudich et al. 1999, Maddux et al. 2001). Antioxidant treatment to these cell lines protects against the oxidative stress-induced insulin resistance (Maddux et al. 2001, Evans et al. 2002). However, the outcomes of several clinical studies have yielded disappointing results when these antioxidants were used independently (Yusuf et al. 2000). Studies have shown that when these antioxidants were used in combination their insulin-sensitizing/antidiabetic action was enhanced through their interaction and effective regeneration of endogenous antioxidants (Evans et al. 2002). Although the insulin-sensitizing property of antioxidants is identified, the potential mechanism(s) by which antioxidants improve insulin sensitivity in insulin resistance is not clearly known.
Elevated levels of fatty acids are known to cause the production of reactive oxygen species (ROS) and oxidative stress (Carisson et al. 1999, Rao & Reddy 2001). Many studies have shown that the ROS induces activation of multiple stress-sensitive serine kinase cascades and their role in the pathogenesis of insulin resistance (Adler et al. 1999, Qiao et al. 1999). One such major intracellular serine kinase target for oxidative stress is C-Jun-N-terminal kinase (JNK). The JNK pathway is the member of serine/threonine protein kinase superfamily of mitogen-activated protein kinase pathway. The JNK pathway is activated by variety of exogenous and endogenous stress signals including oxidative stress, osmotic stress, proinflammatory cytokines, heat shock, and u.v. irradiation (Tibbles & Woodgett 1999). The activation of JNK pathway is known to interfere with insulin action (Agirre et al. 2000). It has been reported that JNK pathway is activated in various tissues under diabetic condition (Purves et al. 2001, Hirosumi et al. 2002, Qiao et al. 1999). Thus, it is likely that the oxidative stress-induced activation of JNK pathway is a crucial mediator of the progression in insulin resistance. Even though oxidative stress, the activation of JNK pathway and impaired insulin signaling is reported in high-fat feeding, their associated role in the pathogenesis of insulin resistance and effect of antioxidants are not studied in detail. It is worth investigating the interrelationship between the above-mentioned biochemical events because these studies could yield new insights into the molecular basis of obesity-/dyslipidemia-induced insulin resistance as well as help to identify new pharmaceutical targets for the treatment of type 2 diabetes. In view of the above, the present study was designed to investigate the effect of antioxidants on redox balance, insulin action, and JNK pathway in high-fat-fed rats which closely mimic the obesity-/dyslipidemia-induced insulin resistance in humans (Buettner et al. 2007).
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Materials and Methods |
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Dulbecco's modified Eagle's medium (DMEM), fetal calf serum (FCS), penicillin, streptomycin, glucose oxidase, 1,1-diphenyl-2-picryl hydrazyl (DPPH), insulin (human recombinant), sodium vandate, phenyl methyl sulfonyl fluoride, aprotinin, leupeptin, okadaic acid, and all other chemicals were purchased from Sigma Chemicals. 2-Deoxy-14C-D-glucose was purchased from Amersham Life Sciences. Insulin receptor, IRS-1, JNK1, phosphor-JNK1, and phosphor-tyrosine antibodies were purchased from Upstate Biotechnology (Lake Placid, NY, USA). Phosphor-serine antibody was obtained from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Protein A-agarose slurry was purchased from Bangalore Genei (Bangalore, India).
Treatment of animals
Male Wistar rats weighing 150–200 g were maintained in the standard laboratory conditions at 22±2 °C with 12-h darkness:12-h light cycle. All experimental procedures were approved by the Institute Animal Experimentation Ethics Committee. The rats were randomly assigned to the following groups.
-lipoic acid. -lipoic acid. The semi-purified high-fat diet was prepared as described previously (Storlien et al. 1986), with 59% of total calories derived from fat, 21% from protein, and 20% from carbohydrate. The energy of the high-fat diet was 5.2 kcal/g whereas that of the chow diet was 3.3 kcal/g. The rats were provided with specific diets and water ad libitum for 9 weeks.
i.p. Glucose and insulin tolerance tests in male Wistar rats
At the end of the 9-week experimental period, i.p. glucose and insulin tolerance tests were performed as described by Yuan et al. (2001). i.p. Glucose tolerance test was performed in overnight fasted rats after i.p. injection of glucose (2.0 g/kg body weight). For insulin tolerance test, insulin was injected i.p. (2.0 U/kg body weight) after 6-h fasting. Blood samples were taken at different time intervals to estimate plasma glucose. Area under curve was calculated from the graph using NCSS software (NCCS2007 for Windows, Statistical solutions, CA, USA).
Analysis of plasma parameters
After 9 weeks of fat feeding, plasma glucose, triglycerides, and total cholesterol were estimated in overnight fasting samples using standard reagent kits in 550 Express plus autoanalyzer (Ciba Corning Diagnostics, MA, USA). Fasting plasma insulin was estimated using rat insulin ELISA kit purchased from Boehringer Mannheim. Homeostatic model assessment-insulin resistance (HOMA-IR) was calculated using the following formula: HOMA-IR=fasting insulin (µU/ml)xfasting glucose (mM)/22.5 (Pickavance & Wilding 2007).
Cell culture
Rat L6 myoblasts (American Type Culture Collection, Manassas, VA, USA) were cultured (37 °C, 5% CO2) in growth medium (DMEM, 10% FCS, 100 units/ml penicillin, and 100 µg/ml streptomycin). L6 myoblasts were allowed to differentiate into myotubes in differentiation medium (DMEM, 2% FCS, 100 units/ml penicillin, and 100 µg/ml streptomycin) as described previously (Vinayagamoorthi et al. 2006).
Hydrogen peroxide treatment to rat L6 myotubes
Rat L6 myotubes were incubated with antioxidant mixture (5 µM vitamin E, 300 µM lipoic acid, and 500 µM vitamin C) in DMEM supplemented with 0.5% BSA for 18 h. After antioxidant treatment, myotubes were washed with DMEM supplemented with 0.5% BSA and incubated in DMEM (phenol red free) supplemented with 0.5% BSA, 25 mU/ml glucose oxidase, and 5 mM glucose for 12 h. H2O2 generated by this system was estimated from the media collected at different time intervals using Amplex red – hydrogen peroxide/peroxidase assay kit (Molecular Probes, NJ, USA). Creatine kinase (CK) activity was measured in the culture medium using colorimetric kit (Teco Diagnostics, USA) in 550 Express plus autoanalyzer (Ciba Corning Diagnostics). H2O2-induced cytotoxicity was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) as described previously (Ferrai et al. 1999).
Determination of glucose transport into rat L6 myotubes
Rat L6 myotubes were treated with antioxidants (18 h) followed by H2O2 (12 h) as described above. After glucose/glucose oxidase treatment, L6 myotubes were washed with DMEM supplemented with 0.5% BSA and then incubated with serum-free DMEM for 3 h. After serum starvation, insulin (100 nM) was added to the serum-free medium and further incubated for 30 min. Myotubes were washed with HBS (140 nM NaCl, 20 mM HEPES pH 7.4, 5.0 mM KCl, 2.5 nM MgSO4, and 1.0 mM CaCl2) and glucose uptake was measured as described previously (Blair et al. 1999). Briefly, after insulin stimulation, myotubes were incubated with 2-deoxy-14C-D-glucose (0.5 µCi/ml) in HBS for 10 min. Radioactive medium was aspirated rapidly and the cells were washed with ice-cold isotonic saline (0.9% NaCl). The cells were lysed in 0.05 M NaOH, and radioactivity was determined by liquid scintillation counting (Packyard Top Count LSC, GMI Inc., MN, USA). Protein content of lysates was estimated by the method of Bradford (1976). Non-specific glucose uptake was determined in the presence of cytochalasin B (50 µM) an inhibitor of facilitative glucose transport and was subtracted from total uptake.
Analysis of oxidative stress parameters and antioxidant status in fat-fed rats and rat L6 myotubes
At the end of 9-week experimental period, plasma and skeletal muscle malondialdehyde (MDA) were estimated by TBARS method (Yagi 1984), and erythrocyte-reduced glutathione content was determined using Ellman's reagent (5,5'-dithio-bis-2-nitrobenzoic acid) as described by Beutle et al. (1963). Hemoglobin content of blood was estimated by cyanmethemoglobin method of Drabkin & Austin (1932) and the catalase activity in erythrocytes was estimated by the method of Aebi (1984).
Rat L6 myotubes were treated with LA (18 h) followed by H2O2 (12 h) as described previously and lysed in 0.5 ml PBS by repeated freezing and thawing. Total antioxidant status of cell lysates was quantified by trolox equivalent antioxidant capacity assay using DPPH as described previously (Vinayagamoorthi et al. 2006). Reduced glutathione concentration in cell lysates was estimated as described by Beutle et al. (1963).
Insulin stimulation
At the end of 9-week experimental period, the animals were killed with and without insulin stimulation. Insulin stimulation was performed as described earlier by i.p. injection of 15 units of insulin/kg body weight (Youngren et al. 2001). After an interval of 30 min for the maximum effect of insulin to occur, the animals were killed and the hind limb muscle was removed. Muscle homogenates were prepared in homogenization buffer (50 mM Tris–HCl (pH 7.4), 1% Nonidet P-40, 0.25% sodium deoxycholate, 150 mM NaCl, 1 mM sodium vandate, 1 mM phenyl methyl sulfonyl fluoride, 1 mM aprotinin, 1 mM leupeptin, and 0.5 µg/ml okadaic acid) as described previously (Saad et al. 1992).
Rat L6 myotubes were treated with antioxidants (18 h) followed by H2O2 (12 h) as described previously and incubated with serum-free DMEM for 30 min. After serum starvation, insulin (100 nM) was added to the serum-free medium and incubated for 15 min. Myotubes were washed with ice-cold PBS and scraped into ice-cold homogenization buffer. Muscle homogenates and cell lysates were centrifuged at 12 000 g for 15 min at 4 °C. Protein content of the supernatant collected was estimated by the method of Bradford (1976).
Western blotting analysis of JNK pathway
Muscle homogenates and rat L6 cell lysates (100 µg protein) were resolved by 12% SDS-PAGE, electrotransferred onto nitrocellulose membrane, and immunoblotted with antibody specific to phosphorylated JNK1. Furthermore, the membrane was stripped of bound antibodies and then reprobed with antibody specific to JNK1. Protein bands were visualized by enhanced chemiluminescence method using Amersham ECL kit (Amersham Life Sciences). Bands were scanned using a densitometer (Bio-Rad, Model GS-710) and quantified by Quantity 1 software (Bio-Rad). The band density of phosphorylated JNK1 was normalized with the total JNK1.
Insulin signaling analysis
Muscle homogenates (250 µg protein) and rat L6 cell lysates (500 µg protein) were incubated overnight at 4 °C with insulin receptor and IRS-1 antibodies. The immune complex was captured by adding 50 µl protein A-agarose beads for 2 h at 4 °C. The immune complex was pelleted at 12 000 g for 15 min at 4 °C and washed thrice with homogenization buffer. The immune complex was suspended in Laemmli (1970) sample buffer and boiled for 5 min. Protein A agarose was removed from the denatured proteins by centrifugation at 12 000 g for 15 min at 4 °C. The supernatant was resolved by 8.0% SDS-PAGE and further electrotransferred to nitrocellulose membrane. Proteins were immunoblotted with the antibody specific for phosphorylated tyrosine, and the immunoblot was stripped of bound antibodies and then reprobed with an antibody specific to phosphorylated serine. Protein band detection and quantification were performed as mentioned previously. The band densities of tyrosine and serine phosphorylation were normalized with the band densities of immunoprecipitated insulin receptor and IRS-1 respectively.
RT-PCR analysis of antioxidant enzymes in male Wistar rats
At the end of 9-week experimental period, RT-PCR analysis was performed in skeletal muscle of male Wistar rats as described previously (Piro et al. 2002, Bhor et al. 2004). Briefly, total RNA was extracted from rat skeletal muscle using Trizol reagent (Invitrogen). The cDNA was synthesized from total RNA (2 µg) using cDNA synthesis kit (Roche Molecular Biochemicals) following the manufacturer's protocol. The PCR was performed using 2 µl cDNA in a total volume of 20 µl reaction. Amplification of all the genes of interest was done with the forward and reverse gene-specific primers (Bhor et al. 2004) at a concentration of 0.6 µM in PCR mixture (50 mM KCl, 1.5 mM MgCl2, 10 mM Tris–HCl (pH 9.0), 200 µM each dNTP, 2.5U Taq polymerase). Reverse transcription and gene amplification reactions were carried out in a gradient thermal cycler (Eppendorff, Gradient Mastercycler, Germany). The electrophoresis analysis of PCR products was performed in 1.5% agarose gel containing 0.5 µg/ml ethidium bromide. The gels were photographed using a gel-documentation system (Bio-Rad, Gel Doc EQ) and were analyzed in Quantity 1 software (Bio-Rad).
Statistical analysis
Data are expressed as mean±S.E.M. Analysis of difference between the means of groups was done by one-way ANOVA followed by Tukey's post-test. A P value <0.05 was considered statistically significant.
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Results |
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Glucose and insulin tolerance tests (Fig. 1(a) and (b)) in male Wistar rats showed that fat feeding for 9 weeks increases the area under curve significantly (P<0.01) compared with control and antioxidant-supplemented groups. The fasting insulin and HOMA-IR (Table 1) were significantly (P<0.001) increased in fat-fed group compared with other groups. Increased area under curve and HOMA-IR in fat-fed group show impaired glucose tolerance and insulin resistance. Antioxidant supplementation along with high-fat diet improves the glucose tolerance and insulin sensitivity in fat-fed rats.
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Effect of high-fat diet and antioxidants on plasma lipids, body weight, and epididymal fat weight
As shown in Table 1, fat feeding for 9 weeks in male Wistar rats significantly increases the fasting plasma triglycerides (P<0.001), total cholesterol (P<0.01), body weight, and epididymal fat weight (P<0.001) compared with control group. This reveals induction of insulin resistance by high-fat feeding in rats closely mimics the obesity-/dyslipidemia-induced insulin resistance in humans. Antioxidant supplementation along with high fat did not have any significant effect on the above parameters.
Antioxidants inhibit IRS-1 serine phosphorylation and improve insulin-stimulated IRS-1 tyrosine phosphorylation in fat-fed rats and H2O2-treated rat L6 myotubes
Fat feeding to rats and H2O2 treatment to L6 myotubes did not have significant effect on insulin receptor tyrosine and serine phosphorylation (data not shown). However, feeding rats with high-fat diet and H2O2 treatment to L6 myotubes significantly (P<0.01) reduced the insulin-stimulated tyrosine phosphorylation of IRS-1 compared with control and antioxidant-treated groups (Fig. 2(a) and (c)). In addition, above treatments significantly (P<0.01) increased the basal serine phosphorylation of IRS-1 compared with other groups (Fig. 2(b) and (d)). Antioxidant treatment inhibited the high-fat diet and H2O2-induced IRS-1 serine phosphorylation and improved the insulin-stimulated IRS-1 tyrosine phosphorylation.
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Fat feeding to rats for 9 weeks significantly (P<0.001) increased the plasma and skeletal muscle TBARS (Table 1) and expression of skeletal muscle antioxidant enzymes (Fig. 4(a)) compared with control and antioxidant groups. High-fat feeding significantly (P<0.001) increased the erythrocyte catalase activity and decreased the reduced glutathione concentration (Table 1) compared with control and antioxidant groups. High-fat diet also activated the redox-sensitive JNK pathway in skeletal muscle (Fig. 3(a)). Antioxidant supplementation preserved the redox balance in fat-fed rats and inhibited the activation of JNK pathway.
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Discussion |
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Previous studies in high-fat-fed rats demonstrated severe insulin resistance and defects in proximal insulin signaling pathway (Saad et al. 1992). Hansen et al. (1998) reported a decreased insulin-stimulated IRS-1 tyrosine phosphorylation in fat-fed rats. In the present study, fat feeding for 9 weeks significantly increased the IRS-1 serine phosphorylation and decreased the insulin-stimulated IRS-1 tyrosine phosphorylation. Numerous studies have documented increased IRS-1 serine phosphorylation as a potential molecular mechanism for insulin resistance (Le Roith & Zick 2001, Sykiotis & Papavassiou 2001, Anna et al. 2005). In patients with type 2 diabetes and animal models of insulin resistance, IRS-1 serine phosphorylation was found to be increased (Qiao et al. 1999). IRS-1 contains a total of 232 serine/threonine amino acid residues that provide a potential site for phosphorylation by Ser/Thr kinases (Werner et al. 2004). Serine phosphorylation of IRS-1 impairs its interaction with the juxtamembrane domain of insulin receptor and thus renders IRS-1 as a poorer substrate for insulin receptor kinase (Paz et al. 1997). Numerous agents that induce insulin resistance, such as TNF-, okadaic acid, platelet-derived growth factor, and angiotensin II, increase IRS-1 phospho-serine content (Sykiotis & Papavassiou 2001). Basal levels of IRS-1 serine phosphorylation are increased in cells under various conditions, leading to observable shifts in electrophoretic mobility (Tanti et al. 1994, Mothe & Obberghen 1996). The magnitudes of the shifts demonstrate that multiple sites are phosphorylated. Numerous studies have shown that serine phosphorylation of IRS-1 (in mouse) at ser302, ser307, ser612, ser636, ser731, and ser789 inhibits its interaction with insulin receptor (Mothe & Obberghen 1996). Out of all this, the inhibitory effect of IRS-1 ser307 phosphorylation on insulin action is extensively studied (Tanti et al. 1994, Mothe & Obberghen 1996, Paz et al. 1997, Sykiotis & Papavassiou 2001). However, there are reports for the requirement of clusters of serine phosphorylation to disturb IRS-1 function (Werner et al. 2004). To this end, it is evident that different stimuli may phosphorylate different serine residues of IRS-1 and inhibit insulin action. Thus, the specific signals and the phosphorylated serine residues, which inhibit IRS-1 function, need to be identified. In the present study, we identified the oxidative stress-induced increased global serine phosphorylation of IRS-1 and impaired insulin action in fat-fed rats and cultured rat L6 myotubes. However, additional studies are clearly required to identify the oxidative stress induced specific phosphorylated serine residues and their role in insulin action.
Increased intake of fat and its derivatives are reported to cause oxidative stress (Bakker et al. 2000). Elevated fats can cause oxidative stress due to increased β-oxidation (Otczalk & Schonfeld 1993, Carisson et al. 1999) and mitochondrial respiration (Rao & Reddy 2001). In the process of mitochondrial respiration, molecular oxygen is essential for the production of ATP. During the course of normal oxidative phosphorylation between 0.4 and 4.0% of the total oxygen consumed is converted into the free radical superoxide anion 
(Chance et al. 1979, Boveris 1984). Subsequently, 
can be converted into other ROS. However, the endogenous antioxidant system that exists within the cells neutralize these ROS and maintains redox balance. Oxidative stress sets in when endogenous antioxidant network fails to provide a compensatory response to restore cellular redox balance. In agreement with previous studies (Rudich et al. 1997,1999, Maddux et al. 2001), our results from cultured rat L6 myotubes demonstrate oxidative stress can cause insulin resistance. Recently we reported the reduction in insulin-stimulated glucose uptake in rat L6 muscle cell lines when exposed to oxidative stress and its reversal on vitamin E treatment (Vinayagamoorthi et al. 2006). ROS can function as signaling molecules and activate a number of redox-sensitive Ser/Thr kinase cascades linked to insulin resistance (Evans et al. 2002). Our results show that fat feeding to rats impairs redox balance and activates the redox-sensitive serine kinase – JNK pathway. Evidence from cellular models and transgenic animals demonstrated the role of JNK in the pathogenesis of insulin resistance. Support for the importance of JNK pathway in insulin resistance is provided by the results of gene knockout experiments in mice. Suppression of JNK pathway improves insulin sensitivity in db/db mice and sucrose-fed rats (Nakatani et al. 2004). Several studies have shown inhibitors of JNK pathway improve insulin signaling and insulin sensitivity (Kaneto 2005, Liu & Rondinone 2005). Agirre et al. (2000) showed in CHO cells, that anisomycin a strong activator of JNK, stimulated the binding activity of JNK to IRS-1, and inhibited the insulin-stimulated tyrosine phosphorylation of IRS-1.
Our results from rat L6 myotubes demonstrate that oxidative stress-induced insulin resistance is associated with the activation of JNK pathway and increased IRS-1 serine phosphorylation. Antioxidant pre-treatment to rat L6 myotubes preserved redox balance, inhibited JNK pathway and IRS-1 serine phosphorylation, retained insulin-stimulated IRS-1 tyrosine phosphorylation, and restored insulin sensitivity. In this regard, here we propose (Fig. 5) that fat feeding to rats increases ROS formation and causes redox imbalance. This results in the activation of redox-sensitive JNK cascade. Oxidative stress-induced activation of JNK in turn phosphorylates IRS-1 and increases phosphor-serine content of IRS-1. Increased IRS-1 serine phosphorylation inhibits its interaction with insulin receptor and decreases insulin-stimulated IRS-1 tyrosine phosphorylation. This results in insulin resistance in fat-fed rats. The insulin-sensitizing property of antioxidants in high-fat-induced insulin resistance could be related to their ability to preserve the intracellular redox balance and thereby preventing the activation of redox-sensitive JNK pathway and IRS-1 serine phosphorylation. In conclusion, the present study helps us to understand the molecular basis of high-fat-induced insulin resistance and insulin-sensitizing property of antioxidants. More detailed understanding of the role of oxidative stress and antioxidants on redox-sensitive Ser/Thr kinase cascades in humans and animal models of insulin resistance might open novel therapeutic targets for the treatment of type 2 diabetes and its complications.
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Acknowledgements |
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Aebi H 1984 Catalase in vitro. Methods in Enzymology 105 121–126.[Web of Science][Medline]
Agirre V, Uchiuda T, Yenush L, Davis R & White MF 2000 The c-Jun NH(2) terminal kinase promotes insulin resistance during association with insulin receptor substrate-1 and phosphorylation of Ser (307). Journal of Biological Chemistry 277 30010–30018.[CrossRef]
Anna D, Anita O, Fredrik HN & Peter S 2005 Attenuation of insulin – stimulated insulin receptor substrate-1 serine 307 phosphorylation in insulin resistance of type 2 diabetes. Journal of Biological Chemistry 280 34389–34392.
Bakker SJ, Ijzermen RG, Teerlink T, Westerhoff HV, Gans RO & Heine RJ 2000 Cytosolic triglycerides and oxidative stress in central obesity: the missing link between excessive atherosclerosis, endothelial dysfunction, and β-cell failure? Atherosclerosis 148 17–21.[CrossRef][Web of Science][Medline]
Beutle E, Duron O & Kelly BM 1963 Improved method for the determination of blood glutathione. Journal of Laboratory and Clinical Medicine 61 882–888.[Web of Science][Medline]
Bhor VM, Raghuram N & Sivakami S 2004 Oxidative damage and altered antioxidant enzyme activities in the small intestine of streptozotocin-induced diabetic rats. International Journal of Biochemistry and Cell Biology 36 89–97.[CrossRef][Web of Science][Medline]
Blair AS, Hajduch E, Litherland GJ & Hundal SH 1999 Regulation of glucose transport and glycogen synthesis in L6 muscle cells during oxidative stress. Journal of Biological Chemistry 274 36293–36299.
Boveris A 1984 Determination of the production of superoxide radicals and hydrogen peroxide in mitochodria. Methods in Enzymology 105 429–435.[Web of Science][Medline]
Bradford M 1976 A rapid and sensitive method for the quantification of microgram quantity of protein utilizing the principle of protein dye binding. Analytical Biochemistry 72 248–254.[CrossRef][Web of Science][Medline]
Buettner R, Scholmerich B & Bollheimer C 2007 High-fat diets: modeling the metabolic disorders of human obesity in rodents. Obesity 15 798–808.[Web of Science][Medline]
Carisson G, Borg LA & Welsh N 1999 Sodium palmitate induces partial mitochondrial uncoupling and reactive oxygen species in rats pancreatic islets in vitro. Endocrinology 140 3422–3428.
Chance B, Sies H & Boveris A 1979 Hydrogen peroxide metabolism in mammalian organs. Physiological Reviews 59 527–605.
Drabkin DL & Austin JN 1932 Spectrophotometric constants for common hemoglobin derivatives in human, dog and rabbit. Journal of Biological Chemistry 98 719–733.
Evans JL & Goldfine ID 2000 -Lipoic acid: a multi-functional antioxidant that improves insulin sensitivity in patients with type 2 diabetes. Diabetes Technology and Therapeutics 2 401–413.[CrossRef]
Evans JL, Goldfine ID, Maddux BA & Grodsky GM 2002 Oxidative stress and stress-activated signaling pathways: a unifying hypothesis of type 2 diabetes. Endocrine Reviews 23 599–622.
Ferrai M, Fornasiero MC & Isetta AM 1999 MTT colorimetric assay for testing macrophage cytotoxic activity in vitro. Journal of Immunological Methods 131 165–172.
Hansen PA, Han HD, Marshall BA, Nolte LA, Chen MM, Mueckler M & Holloszy OJ 1998 A high fat diet impairs stimulation of glucose transport in muscle. Functional evaluation of potential mechanisms. Journal of Biological Chemistry 273 26157–26163.
Hirosumi J, Tuneman G, Chang L, Gorgun CZ, Uysal KT, Maeda K, Karin M & Hotamisligil GS 2002 A central role for JNK in obesity and insulin resistance. Nature 420 333–336.[CrossRef][Medline]
Jacob S, Lehmann R, Rett K & Haring HU 2000 Oxidative stress and insulin action: a role for antioxidant. In Antioxidant in Diabetes Management , pp 319–338. Eds L Packer, P Rosen, H Tritschler & GL King. New York: Marcel dekker.
Kaneto H 2005 The JNK pathway as a therapeutic target for diabetes. Expert Opinion on Therapeutic Targets 9 581–592.[CrossRef][Web of Science][Medline]
Krssak M, Petersen KF & Dresner A 1999 Intramyocellular lipid concentrations are correlated with insulin sensitivity in humans: H-1 NMR spectroscopy study. Diabetes 42 113–116.[CrossRef]
Laemmli UK 1970 Cleavage of structural proteins during the assembly of head of bacteriophage T4. Nature 227 680–685.[CrossRef][Medline]
Leng Y, Karlsson HK & Zierath JR 2004 Insulin signaling defects in type 2 diabetes. Reviews in Endocrine and Metabolic Disorders 5 111–117.[CrossRef]
Liu G & Rondinone CM 2005 JNK bridging the insulin signaling and inflammatory pathway. Current Opinion in Investigational Drugs 6 979–987.[Medline]
Maddux BA, See W, Lawrence JC Jr, Goldfine AL, Goldfine ID & Evans JL 2001 Production against oxidative stress induced insulin resistance in rat L6 muscle cells by micromolar concentrations of -lipoic acid. Diabetes 50 404–410.
Maxwell SRJ, Thomanson H, Sandler D, Leguen C, Baxter MA, Thorpe GH, Jones AF & Barnett AH 1997 Antioxidant status in patients with uncomplicated insulin-dependent and non -insulin dependent diabetes mellitus. European Jouranl of Clinical Investigation 27 487–490.
Mothe I & Obberghen VE 1996 Phosphorylation of insulin receptor substrate-1 on multiple serine residues, 612, 632, 662, and 731, modulates insulin action. Journal of Biological Chemistry 271 11222–11227.
Nakatani Y, Kaneto H, Kawamori D, Hatazaki M, Miyatsuka T, Matsuoka TA, Kajimoto Y, Matsuhisa M, Yamasaki Y & Hori M 2004 Modulation of the JNK pathway in liver affects insulin resistance status. Journal of Biological Chemistry 279 45803–45809.
Opara EC, Abdel Rahman E, Soliman E, Kamel WA, Souka S, Lowe JE & Abdel-Aleem S 1999 Depletion of total antioxidant capacity in type 2 diabetes. Metabolism 48 1414–1417.[CrossRef][Web of Science][Medline]
Otczalk L & Schonfeld P 1993 Effect of fatty acids on energy coupling processes in mitochondria. Biochemica et Biophysica Acta 1183 41–57.[Medline]
Pan DA, Lillioja S, Kriketos AD, Milner MR, Baur LR, Bogardus C, Jenkins AB & Storlien LH 1997 Skeletal muscle triglyceride levels are inversely related to insulin action. Diabetes 46 983–988.[Abstract]
Paz K, Hemi R, LeRoith D, Karasik A, Elhanany E, Kanety H & Ziok Y 1997 A molecular basis of insulin resistance: elevated serine/threonine phosphorylation of IRS-1 and IRS-2 inhibits their binding to the jextamembrane region of the insulin receptor and impairs their ability to undergo insulin induced tyrosine phosphorylation. Journal of Biological Chemistry 272 29911–29918.
Perseghin G, Ghosh S, Gerow K & Shulman GI 1997 Metabolic defects in lean nondiabetic offspring of NIDDM parents: a cross-sectional study. Diabetes 46 1001–1009.[Abstract]
Phillips DI, Caddy S, IIic V, Fielding BA, Frayn KN, Borthwick AC & Taylor R 1996 Intramuscular triglycerides and muscle insulin sensitivity: evidence for a relationship in nondiabetic subjects. Metabolism 45 947–950.[CrossRef][Web of Science][Medline]
Pickavance LC & Wilding JP 2007 Effects of S 15511, a therapeutic metabolite of insulin sensitizing agent S15261, in Zucker Diabetic Fatty rat. Diabetes, Obesity and Metabolism 9 114–120.[CrossRef][Web of Science][Medline]
Piro S, Anello M, Di Pietro C, Lizzio MN, Patane` G, Rabuazzo AM, Vigneri R, Purello M & Purello F 2002 Chronic exposure to fatty acids or high glucose induces apoptosis in rat pancreatic islets: possible role of oxidative stress. Metabolism 51 1340–1347.[CrossRef][Web of Science][Medline]
Purves T, Middlemas A, Agthong S, Jude EB, Boulron AJ, Feroyhough P & Tomlinson DR 2001 A role for mitogen-activated protein kinases in the etiology of diabetic neuropathy. FASEB Journal 15 2508–2514.
Qiao LY, Goldberg JL, Russell JC & Sun XJ 1999 Identification of enhanced serine kinase activity in insulin resistance. Journal of Biological Chemistry 274 10625–10632.
Rao MS & Reddy JK 2001 Peroxisomal β-oxidation and steatohepatitis. Seminars in Liver Disease 21 43–55.[CrossRef][Web of Science][Medline]
LeRoith D & Zick Y 2001 Recent advances in our understanding of insulin action and insulin resistance. Diabetes Care 24 588–597.
Rudich A, Kozlovsky N, Potashnik R & Bashan N 1997 Oxidant stress reduces insulin responsiveness in 3T3LI adipocytes. American Journal of Physiology 35 E935–E940.
Rudich A, Tirosh A, Potashnik R, Khamaisi M & Bashan N 1999 Lipoic acid protects against oxidative stress induced insulin resistance impairment in insulin stimulation of proteinkinase B and glucose transport in 3T3L1 adipocytes. Diabetologia 42 949–957.[CrossRef][Web of Science][Medline]
Saad MJA, Araki E, Miralpeix M, Rothenberg PL, White MF & Kohn CR 1992 Regulation of insulin receptor substrate-1 in liver and muscle of animal models of insulin resistance. Journal of Clinical Investigation 90 1839–1849.[Web of Science][Medline]
Saltiel AR & Kahn CR 2001 Insulin signaling and the regulation of glucose and lipid metabolism. Nature 414 799–806.[CrossRef][Medline]
Shigeta Y, Hiraizumi G, Wada M, Oji K & Yoshida T 1961 Study on the serum levels of thioctic acid in patients with various diseases. Journal of Vitaminology 7 48–52.[Web of Science]
Spiegelman BM & Flier JS 2001 Obesity and the regulation of energy balance. Cell 104 531–543.[CrossRef][Web of Science][Medline]
Storlien LH, James DE, Burleigh KM, Chisholm DJ & Kraegen EW 1986 Fat feeding causes widespread in vivo insulin resistance, decreased energy expenditure, and obesity in rats. American Journal of Physiology. Endocrinology and Metabolism 251 E576–E583.
Sykiotis GP & Papavassiou AG 2001 Serine phosphorylation of insulin receptor substrate -1: a novel target for the reversal of insulin resistance. Molecular Endocrinology 15 1864–1869.
Tanti JF, Gremeaux T, Obberghen E & Marchand-Brustel Y 1994 Serine/threonine phosphorylation of insulin receptor substrate 1 modulates insulin receptor signaling. Journal of Biological Chemistry 269 6051–6057.
Tibbles LA & Woodgett JR 1999 The stress activated protein kinase pathways. Cellular and Molecular Life Sciences 55 1230–1254.[CrossRef][Web of Science][Medline]
Vinayagamoorthi R, Bobby Z, Selvaraj N & Sridhar MG 2006 Vitamin E protects the insulin sensitivity and redox balance in rat L6 muscle cells exposed to oxidative stress. Clinica Chimica Acta 367 132–136.[CrossRef][Web of Science][Medline]
Werner ED, Lee J, Hansen L, Yuan M & Shoelson SE 2004 Insulin resistance due to phosphorylation of insulin receptor substrate-1 at serine 302. Journal of Biological Chemistry 279 35298–35305.
Yagi K 1984 Assay for blood plasma or serum lipid peroxides. Methods in Enzymology 105 28–31.
Youngren JF, John P & Bernard JR 2001 Impaired insulin- receptor autophosphorylation is an early defect in fat-fed insulin resistant rats. American Journal of Physiology 91 2240–2247.
Yuan M, Konstantopoulos N, Lee J, Hansen L, Li ZW, Karin M & Shoelson SM 2001 Reversal of obesity – and diet – induced insulin resistance with salicylates or targeted disruption of IKKβ. Science 293 1673–1677.
Yusuf S, Dagenais G, Pogue J, Bosch J & Sleight P 2000 Vitamin E supplementation and cardiovascular events in high-risk patients: the Heart Outcomes Prevention Evaluation Study Investigators. New England Journal of Medicine 342 154–160.
Received in final form 3 February 2008
Accepted 20 February 2008
Made available online as an Accepted Preprint 20 February 2008
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P<0.001 compared with insulin-stimulated control and insulin-stimulated antioxidant groups. $P<0.01 compared with control and antioxidant groups.
