The investigation of protective effects of glukagon-like peptide-1 (glp-1) analogue-exenatide- on glucose and fructose induced neurotoxicity

Aim: Diabetes mellitus is one of the most common metabolic disorders characterized by hyperglycemia due to insufficiency of insulin and/ or insulin resistance. Clinical studies have revealed a higher risk of neurodegenerative disorders such as Alzheimer or Parkinson's disease in diabetic patients. Recently, glucagon-like peptide (GLP-1) is an attractive potential treatment modality for various neurodegenerative diseases. In our study, we aimed to investigate the toxic effects of both high glucose and fructose on neuronal cells. Also, we aimed to assess whether exenatide, a GLP-1 analogue, has neuroprotective effects against glucose and fructose-induced toxicity. Materials and Methods: Human SH-SY5Y neuroblastoma cell lines were used to evaluate the toxic effects of glucose and fructose. Neurotoxicity was induced by incubating SH-SY5Y cells with different doses (0-100 mM) of glucose and fructose for 24, 48 and 72 hours. Following determination of the significant toxic doses of glucose and fructose, various doses of exenatide (0-500 nM) were added in the culture medium to assess its protective effect. MTT assay was used to measure cell viability in the cultures. In order to clarify the underlying mechanism of glucose and fructose induced-neurotoxicity, we evaluated apoptotic cell death by Hoechst 33258 staining and caspase-3 activity. Also, we measured AGE levels in cytosolic fractions of treated cells. Data were evaluated by one way analysis of variance (ANOVA) and post-hoc test. Data were expressed as mean ± standart error of mean. Results: Both glucose and fructose treatments decreased cell viability in neuronal cells dose and time-dependently. The cell viability was measured 88.47 ± 2.23 % and 89.9 ± 1.08 % for 50 mM glucose and 50 mM fructose-treated medium for 24 hour, respectively. Glucose and fructose- treated groups showed increased numbers of apoptotic cells, caspase-3 activity and AGE levels in cytosolic fractions. However, addition of exenadite in growth medium significantly prevented cell death in a dose-dependent manner. The most prominent effect was observed in 100 nM exenatide-treated cultures. Treatment of the cells with exenatide decreased apoptotic cell death and caspase-3 activity. However, no significant change was observed in cytosolic AGE contents in exenatide treated groups. Conclusion: Our results suggest that high doses of glucose and fructose may lead to neurotoxicity and GLP-1 may have neuroprotective effects against neuronal damage by suppressing anti-apoptotic pathways.