Influence of Antioxidant Vitamin (L –ascorbic Acid) on Hypoxia Induced Oxidative and Nitrosative Stress in Physiological System of Male Albino Rats Exposed to Sodium Fluoride (NaF)

Abstract

Objective : To evaluate the supplementation of L-ascorbic acid as an antioxidant on chronic hypoxia induced alterations of cardiac autonomic functions, biochemical, histopathological and oxygen sensing transcriptional pathways in male albino rats exposed to sodium fluoride toxicity. Methods : Male albino rats were randomly divided into 8 groups (n= 6/group), and groups were named accordingly .Group I(control) , group II (L-ascorbic acid ,50 mg / 100g. b.wt, orally), group III (Chronic hypoxia, 10%O2), group IV (NaF ;20 mg/kg b.wt /day ; ip), group V (NaF + Chronic hypoxia, 10% O2), group VI (L–ascorbic acid + Chronic hypoxia, 10% O2), group VII (L-ascorbic acid + NaF) and group VIII (L-ascorbic acid + NaF + Chronic hypoxia, 10% O2). The treatments were carried for 21 days. Animals of all the groups were weighed on the starting day of protocol and immediately after the end of 21st day. Percentage change of body weight gain and OSI was determined. Electrophysiological parameters like pneumogram, noninvasive blood pressure (NIBP) and ECG were recorded. HRV analysis was done to assess cardiac autonomic functions. Oxidant status were assessed by evaluating serum MDA and NO levels . Antioxidant status were assessed by evaluating serum SOD, vitamin E, vitamin C and hepatic Vitamin C. Oxygen sensing molecular markers like vascular endothelial growth factor (VEGF ) and nitric oxide synthase 3 (NOS3) were also assessed. Histopathological evaluations were done to identify changes in myocardial tissue (ventricle), lungs, hepatic tissue and kidney Results : Our results on gravimetry are indicative of decrease in % of body weight gain and OSI of heart, lungs, liver and kidneys in CH, NaF and CH + NaF treated groups. Electrophysiological studies in CH group are indicative of altered sympathovagal balance and sympathetic dominance. Increase in heart rate and MAP in CH group are also indicative of sympathetic stimulation. Whereas NaF treated rats showed parasympathetic dominance along with the decrease in heart rate and MAP, which also indicates altered autonomic functions. Imbalance in oxidants and antioxidant status in CH, NaF and CH + NaF groups are indicative of oxidative and nitrosative stress with upregulation of oxygen sensing molecular markers like NOS3 and VEGF. Histopathological evaluation was also done to identify changes in myocardial tissue (ventricle), lungs, hepatic tissue and kidney. It is evident from the above results that fluoride toxicity and chronic hypoxia induce oxidative and nitrosative stress leading to cardiac autonomic dysfunctions by the molecular mechanisms mediated by HIF through VEGF and NOS3 pathways and also impacting the development of cardiopulmonary and hepatorenal pathophysiology. In the groups treated with L-ascorbic acid showed improvements in gravimetry , sympathovagal balance, heart rate, MAP, it has also led to decrease in oxidative stress and nitrosative stress in chronic hypoxia and NaF treated groups. This could be due to potential antioxidant property of L- ascorbic acid. CONCLUSION : Results from our study shows that chronic hypoxia (CH) exposure and sodium fluoride( NaF) toxicity leads to cardiac autonomic dysfunctions, causes oxidative and nitrosative stress in cardiopulmonary and hepatorenal systems, enhances nitric oxide production by up regulation of VEGF & NOS3 genes leading to activation of apoptotic pathways. The supplementation of L-ascorbic acid has ameliorating effects on cardiac autonomic functions in chronic hypoxia (CH) induced male albino rats exposed to sodium fluoride (NaF). L-ascorbic acid supplementation is also salubrious to combat both chronic hypoxia (CH) and sodium fluoride (NaF) induced apoptotic cell signalling pathways leading to cellular adaptability