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Combination of Sitagliptin and Insulin against Type 2 Diabetes Mellitus with Neuropathy in Rats: Neuroprotection and Role of Oxidative and Inflammation Stress

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      Aims: The present study evaluated the effects of sitagliptin-insulin against type 2 diabetes mellitus with neuropathy in rats and possible neuroprotective mechanisms. Methods: Diabetes was induced in 32 adult male albino rats by 6-week high-fat high-sugar diet followed by streptozotocin 30 mg/kg intraperitoneal injection. For 4 weeks thereafter, diabetic rats were divided into 4 groups, each group receiving one of the following daily: vehicle (untreated diabetic), insulin 10 IU/kg SC, sitagliptin 30 mg/kg PO or sitagliptin-insulin. We assessed systolic blood pressure (SBP), blood glucose, serum insulin and advanced glycation end-products (AGEs), thermal hyperalgesia and sciatic nerve tumor necrosis factor-alpha (TNF-α), superoxide dismutase (SOD) and malondialdehyde (MDA) and sciatic histopathology. Results: Compared to untreated and insulin-treated groups, sitagliptin decreased SBP, serum AGEs and sciatic MDA and TNF-α, and increased serum insulin and sciatic SOD, but insulin decreased blood glucose more. Sitagliptin-insulin (greater than sitagliptin or insulin alone) superiorly decreased and increased the above respective parameters, and ameliorated hyperalgesia and sciatic histopathological changes, but was similar to insulin in decreasing blood glucose, and similar to sitagliptin in rising serum insulin. Conclusions: Sitagliptin-insulin combination produced hypoglycemic and neuroprotective effect and ameliorated hyperalgesia, oxidative stress and inflammation more than either drug alone. This combination might have clinical efficacy in uncontrolled type 2 diabetes with neuropathy.

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      Most cited references 29

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      Assay for lipid peroxidation in animal tissues by thiobarbituric acid reaction

       H. OHKAWA,  N Ohishi,  K. YAGI (1979)
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        A new rat model of type 2 diabetes: the fat-fed, streptozotocin-treated rat.

        This study was initiated to develop an animal model of type 2 diabetes in a non-obese, outbred rat strain that replicates the natural history and metabolic characteristics of the human syndrome and is suitable for pharmaceutical research. Male Sprague-Dawley rats (n = 31), 7 weeks old, were fed normal chow (12% of calories as fat), or high-fat diet (40% of calories as fat) for 2 weeks and then injected with streptozotocin (STZ, 50 mg/kg intravenously). Before STZ injection, fat-fed rats had similar glucose concentrations to chow-fed rats, but significantly higher insulin, free fatty acid (FFA), and triglyceride (TG) concentrations (P < .01 to .0001). Plasma insulin concentrations in response to oral glucose (2 g/kg) were increased 2-fold by fat feeding (P < .01), and adipocyte glucose clearance under maximal insulin stimulation was significantly reduced (P < .001), suggesting that fat feeding induced insulin resistance. STZ injection increased glucose (P < .05), insulin (P < .05), FFA (P < .05), and TG (P < .0001) concentrations in fat-fed rats (Fat-fed/STZ rats) compared with chow-fed, STZ-injected rats (Chow-fed/STZ rats). Fat-fed/STZ rats were not insulin deficient compared with normal chow-fed rats, but had hyperglycemia and a somewhat higher insulin response to an oral glucose challenge (both P < .05). In addition, insulin-stimulated adipocyte glucose clearance was reduced in Fat-fed/STZ rats compared with both chow-fed and Chow-fed/STZ rats (P < .001). Finally, Fat-fed/STZ rats were sensitive to the glucose lowering effects of metformin and troglitazone. In conclusion, Fat-fed/STZ rats provide a novel animal model for type 2 diabetes, simulates the human syndrome, and is suitable for the testing of antidiabetic compounds.
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          Glucagon-like peptide-1 receptor is involved in learning and neuroprotection.

          Glucagon-like peptide-1 (GLP-1) is a gut peptide that, together with its receptor, GLP-1R, is expressed in the brain. Here we show that intracerebroventricular (i.c.v.) GLP-1 and [Ser(2)]exendin(1-9) (HSEGTFTSD; homologous to a conserved domain in the glucagon/GLP-1 family) enhance associative and spatial learning through GLP-1R. [Ser(2)]exendin(1-9), but not GLP-1, is also active when administered peripherally. GLP-1R-deficient mice have a phenotype characterized by a learning deficit that is restored after hippocampal Glp1r gene transfer. In addition, rats overexpressing GLP-1R in the hippocampus show improved learning and memory. GLP-1R-deficient mice also have enhanced seizure severity and neuronal injury after kainate administration, with an intermediate phenotype in heterozygotes and phenotypic correction after Glp1r gene transfer in hippocampal somatic cells. Systemic administration of [Ser(2)]exendin(1-9) in wild-type animals prevents kainate-induced apoptosis of hippocampal neurons. Brain GLP-1R represents a promising new target for both cognitive-enhancing and neuroprotective agents.

            Author and article information

            aDepartment of Clinical Pharmacology, Faculty of Medicine, Jazan University, Jazan, Saudi Arabia; bDepartment of Clinical Pharmacology, Faculty of Medicine, Zagazig University, Zagazig, Egypt; cDepartment of Clinical Pharmacology and dDepartment of Physiology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
            S. Karger AG (Basel, Switzerland karger@ )
            December 2016
            23 July 2016
            : 98
            : 5-6
            : 242-250
            Pharmacology 2016;98:242-250
            © 2016 S. Karger AG, Basel

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            Figures: 1, Tables: 2, References: 49, Pages: 9
            Original Paper

            Medicine, General social science

            Rats, Neuropathy, Diabetes mellitus, Insulin, Sitagliptin


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