ABSTRACT
Accumulating evidence indicates that a number of tissues are damaged due to build-up of abnormal amount of Advanced Glycation End products (AGEs) in several diseases including diabetes. Currently AGE inhibitors are scarce in clinical use indicating a need for development of new anti-AGE agents. The aim of the current study is to identify the new AGE inhibitors and to decipher their mechanism of action for alleviating symptoms of diabetes in mice. Among several derivatives, one of the derivatives of indanedione, IDD-24 demonstrated highest inhibition of AGE formation and AGE mediated reactive oxygen species production in HepG-2 and mature 3T3-L1 adipocytes. In mice treated with IDD-24, reduction in serum AGE formation and expression of Receptor for AGEs (RAGE) was seen in IDD-24 treated db/db mice. In vivo, glycogen synthesis was also increased in muscle tissue. In adipocytes, anti-AGE agent restored AGEs' induced diminished glucose uptake in fat cells. Mice treated with IDD-24 exhibited increased glucose tolerance, increaed serum adiponectin levels and decreased insulin resistance. Deciphering mechanism of IDD-24 in diabetic mice, it was observed that nuclear factor-κB (NF-κB) and serine phosphorylation of Insulin receptor substrate-1 (IRS-1) declined, while diminished activation of c-Jun NH2-terminal kinase (JNK) appears to be partly responsible for restoration of insulin signaling. We conclude that IDD-24 can be a possible treatment target to address symptoms of diabetes.
Subject(s)
Diabetes Mellitus, Experimental/drug therapy , Diabetes Mellitus, Experimental/metabolism , Indans/therapeutic use , NF-kappa B/metabolism , Receptor for Advanced Glycation End Products/metabolism , Signal Transduction , 3T3-L1 Cells , Adipocytes/drug effects , Adipocytes/metabolism , Adiponectin/metabolism , Animals , Cell Survival/drug effects , Diabetes Mellitus, Experimental/genetics , Disease Models, Animal , Gene Expression Regulation/drug effects , Glucose/metabolism , Glycation End Products, Advanced/metabolism , Hep G2 Cells , Hepatocytes/drug effects , Hepatocytes/metabolism , Humans , Indans/chemistry , Indans/pharmacology , Insulin Resistance/genetics , Mice , Mice, Inbred C57BL , Reactive Oxygen Species/metabolism , Signal Transduction/drug effectsABSTRACT
Several members of cucurbitaceae family have been reported to regulate growth of cancer by interfering with STAT3 signaling. In the present study, we investigated the unique role and molecular mechanism of cucurbitacins (Cucs) in reducing symptoms of metabolic syndrome in mice. Cucurbitacin E (CuE) was found to reduce adipogenesis in murine adipocytes. CuE treatment diminished hypertrophy of adipocytes, visceral obesity and lipogenesis gene expression in diet induced mice model of metabolic syndrome (MetS). CuE also ameliorated adipose tissue dysfunction by reducing hyperleptinemia and TNF-alpha levels and enhancing hypoadiponectinemia. Results show that CuE mediated these effects by attenuating Jenus kinase- Signal transducer and activator of transcription 5 (JAK- STAT5) signaling in visceral fat tissue. As a result, CuE treatment also reduced PPAR gamma expression. Glucose uptake enhanced in adipocytes after stimulation with CuE and insulin resistance diminished in mice treated with CuE, as reflected by reduced glucose intolerance and glucose stimulated insulin secretion. CuE restored insulin sensitivity indirectly by inhibiting JAK phosphorylation and improving AMPK activity. Consequently, insulin signaling was up-regulated in mice muscle. As CuE positively regulated adipose tissue function and suppressed visceral obesity, dyslipedemia, hyperglycemia and insulin resistance in mice model of MetS, we suggest that CuE can be used as novel approach to treat metabolic diseases.
Subject(s)
Energy Metabolism/drug effects , Janus Kinases/metabolism , Obesity/metabolism , STAT5 Transcription Factor/metabolism , Signal Transduction/drug effects , Triterpenes/pharmacology , Adipocytes/metabolism , Adipogenesis/drug effects , Adipose Tissue/metabolism , Animals , Body Weight/drug effects , Cell Line , Disease Models, Animal , Glucose/metabolism , Insulin/metabolism , Insulin Resistance , Lipids/blood , Male , Metabolic Syndrome/etiology , Metabolic Syndrome/metabolism , Mice , Muscle, Skeletal/drug effects , Muscle, Skeletal/metabolism , Triterpenes/chemistryABSTRACT
Several reports indicate anti-hyperglycemic effects of Syzygium aromaticum. In the present study, we report for the first time that clove extract (SAM) and its compound nigricin (NGC) decreases free fatty acid-mediated insulin resistance in mouse myoblasts. In addition, NGC was able to diminish insulin resistance in a diabetic mouse model. We observed that SAM and its compound NGC exhibited significant antioxidant activity in murine skeletal muscle cells. They also modulated stress signaling by reducing p38 MAP kinase phosphorylation. NGC and SAM treatments enhanced proximal insulin signaling by decreasing serine phosphorylation of insulin receptor substrate-1 (IRS-1) and increasing its tyrosine phosphorylation. SAM and NGC treatments also modified distal insulin signaling by enhancing protein kinase B (PKB) and glycogen synthase kinase-3-beta (GSK-3 beta) phosphorylation in muscle cells. Glucose uptake was enhanced in muscle cells after treatment with SAM and NGC. We observed increased glucose tolerance, glucose-stimulated insulin secretion, decreased insulin resistance, and increased beta cell function in diabetic mice treated with NGC. The results of our study demonstrate that clove extract and its active agent NGC can be potential therapeutic agents for alleviating insulin resistance.
Subject(s)
Fatty Acids, Nonesterified/pharmacology , Insulin Resistance , Muscle Fibers, Skeletal/drug effects , Syzygium/chemistry , Animals , Benzodioxoles/pharmacology , Chromatography, Liquid , Diabetes Mellitus, Experimental/drug therapy , Female , Flowers/chemistry , Glucose/metabolism , Glucose Tolerance Test , Glycogen Synthase Kinase 3/metabolism , Insulin Receptor Substrate Proteins/metabolism , Insulin-Secreting Cells/drug effects , Mice , Mice, Inbred BALB C , Muscle Fibers, Skeletal/metabolism , Myoblasts, Skeletal/drug effects , Myoblasts, Skeletal/metabolism , Phosphorylation , Plant Extracts/pharmacology , Proto-Oncogene Proteins c-akt/metabolism , Reactive Oxygen Species/metabolism , Signal Transduction , Tyrosine/chemistryABSTRACT
Glycotoxins/Advanced glycation end products (AGEs) have implications in development of diabetes and related diseases. In the present study we deciphered the mechanisms of action of URM-II-81, a new derivative of isatin, in alleviation of insulin resistance in human hepatocytes and murine adipocytes. URM-II-81 reduced AGEs formation and receptor for advanced glycation end products (RAGE) expression in both cell types. We also observed suppression of methylglyoxal (MGO) mediated ROS production and deactivation of PKC-α. URM-II-81 restored proximal insulin signaling by modulating IRS-1 phosphorylation. URM-II-81 also alleviated MGO mediated diminished distal insulin signaling by increasing protein kinase B (PKB) and glycogen synthase kinase 3-beta (GSK-3-beta) phosphorylation. Glycogen synthesis was also increased in hepatocytes after treatment with URM-II-81. In adipocytes URM-II-81 prevented MGO induced reduced glucose uptake. We conclude that URM-II-81 can be a possible treatment target to address glycotoxins induced insulin resistance.
Subject(s)
Adipocytes/drug effects , Glycation End Products, Advanced/antagonists & inhibitors , Insulin Resistance , Insulin/metabolism , Isatin/analogs & derivatives , Isatin/pharmacology , Liver/drug effects , 3T3-L1 Cells , Adipocytes/cytology , Adipocytes/metabolism , Animals , Cell Proliferation/drug effects , Enzyme Activation/drug effects , Glucose/metabolism , Glycogen Synthase Kinase 3/metabolism , Hep G2 Cells , Hepatocytes/cytology , Hepatocytes/drug effects , Hepatocytes/metabolism , Humans , Insulin Receptor Substrate Proteins/metabolism , Liver/metabolism , Mice , Phosphorylation/drug effects , Protein Kinase C-alpha/metabolism , Reactive Oxygen Species/metabolismABSTRACT
The present study aimed to decipher the mechanism of action of selected anti-diabetic plants extracts on palmitic acid mediated insulin resistance in muscle cells. Our results showed that extract from Peganum harmala seeds, Eucalyptus camaldulensis and Syzygium aromaticum leaves, showed significant antioxidant activity. We found that these extracts were able to affect stress signalling by reducing p-38 MAP kinase phosphorylation. They also reduced phosphorylation of substrate for insulin receptor (IRS) at serine residues and increased its phosphorylation at tyrosine residues and also enhanced PKB phosphorylation. Glucose uptake was also enhanced in muscle cells after treatment with these extracts. Extracts from Lantana camara, Psidium gujava fruit and different parts of Cassia alata did not affect FFA mediated down-regulation of insulin signalling. The study conclude that seeds of Peganum harmala and leaves of Eucalyptus camaldulensis and Syzygium aromaticum enhanced insulin signal transduction and glucose uptake in muscle cells via reducing oxidative stress. As a result, these herbal extracts may be considered useful to protect from insulin resistance.
Subject(s)
Hypoglycemic Agents/administration & dosage , Insulin Resistance , Palmitic Acid/administration & dosage , Peganum/chemistry , Plant Extracts/administration & dosage , Syzygium/chemistry , Animals , Cell Line , Glucose/metabolism , Insulin/metabolism , Insulin Receptor Substrate Proteins/chemistry , Insulin Receptor Substrate Proteins/metabolism , Mice , Phosphorylation , Reactive Oxygen Species/metabolism , Signal TransductionABSTRACT
Methylglyoxal (MGO) is a highly reactive advanced glycation end products (AGEs) precursor and its abnormal accumulation causes damage to various tissues and organs. In our previous study, we synthesized a novel MGO inhibitor, MK-I-81, a bis-Schiff base derivative of isatin. In this study we demonstrate the mechanism of action of MK-I-81, on insulin resistance in skeletal muscle cells. MK-I-81 reduced AGEs formation and restored proximal insulin signaling by modulating IRS-1 phosphorylation. MK-I-81 also alleviated MGO mediated diminished distal insulin signaling by increasing protein kinase B and glycogen synthase kinase 3-beta phosphorylation. We also observed that MK-I-81 prevented reduced glucose uptake and glycogen synthesis induced by MGO in muscle cells. We found that the mechanism of action by which MK-I-81 reduced insulin resistance was suppression of production of MGO mediated ROS production in C2C12 cells. We evaluated deactivation of PKC-α and receptor for advanced glycation end products (RAGE) after treatment of cells with MK-I-81. MK-I-81 also reduced MGO mediated IRS-1, PKC-α and RAGE interaction in muscle cells. MK-I-81 also promoted nuclear factor erythroid 2-related factor-2 phosphorylation, heme oxygenase-1 and glyoxalase expression levels. We conclude that MK-I-81 can be a potential therapeutic target to address AGEs mediated insulin resistance. A novel Advanced Glycation End products (AGEs) inhibitor, MK-I-81 (a bis Schiff base of isatin), restored AGEs mediated down regulation of insulin signaling via modulating key molecules of proximal and distal insulin signaling. MK-I-81 also increased glucose uptake and glycogen synthesis in muscle cells. Novel bis-Schiff base of isatin showed significant antioxidant activity and also reduced receptor for AGEs (RAGE) expression and PKC-alpha activation therefore; MK-I-81 reduces AGEs induced insulin resistance.
