Alteration in the glutathione, glutathione peroxidase, superoxide dismutase and lipid peroxidation by ascorbic acid in the skin of mice exposed to fractionated γ radiation

Abstract

Background: In spite of the immense therapeutic gains produced by the fractionated irradiation (IR) regimen, radiation burden on the skin increases significantly. Protection of skin might enable use of higher radiation doses for better therapeutic gains. Ascorbic acid (AA), an essential ingredient of the human diet, is known to be a free radical scavenger and radioprotective agent. This study was undertaken to evaluate the effect of ascorbic acid on the radiation-induced changes in the status of glutathione (GSH), glutathione peroxidase (GPx), superoxide dismutase (SOD) and lipid peroxidation (LPx) in the skin of mice exposed to 10, 16 and 20 Gy of fractionated γ radiation. Methods: One group of the animals was administered daily with double distilled water (DDW), while the other group received 250 mg/kg b. wt. of ascorbic acid once daily, consecutively for 5, 8 or 10 days, before hemibody (below rib cage) exposure to 2 Gy/day of γ-rays. Skin biopsies from both the groups were collected for the biochemical estimations. Results: The irradiation of animals resulted in a dose-dependent decline in the activities of superoxide dismutase, glutathione peroxidase and glutathione contents. Ascorbic acid pretreatment resulted in a significant increase in the activities of both the enzymes and glutathione in the irradiated mouse skin. Normal concentrations of glutathione could not be restored even by day 6 post-irradiation. Conversely, lipid peroxidation increased in a dose-dependent manner in both the groups reaching a peak concentration by 3 h post-irradiation, while the ascorbic acid pretreatment inhibited the radiation-induced increase in lipid peroxidation. Conclusions: The ascorbic acid treatment arrested the decline in the activities of superoxide dismutase and glutathione peroxidase, glutathione contents and inhibited the radiation-induced lipid peroxidation in the skin of mice exposed to different doses of fractionated γ radiation.

Introduction

Ionizing radiations have been found to produce deleterious effect on the biological system and this property of ionizing radiation has been ingeniously exploited to the advantage of human, especially in the treatment of various neoplastic disorders. A fundamental concept of radiotherapy is to achieve maximum tumor control with minimum complications to the normal tissues. During cancer treatment, the therapeutic efficacy of radiation is increased by delivering 20–30 fractions of 2–3 Gy each spread over a period of 5–6 weeks. Though the therapeutic gains are immense, normal skin invariably suffers from the cytotoxic effect of radiation. According to the classification of the detrimental somatic effects of ionizing radiation by ICRP, radiation-induced damage to the skin can be both stochastic and non-stochastic [1], [2].

Most cell damage caused by ionizing radiation is mediated by the reactive oxygen species (ROS) generated from the interaction between radiation and water molecules in cells [3]. Although skin possesses an extensive and most effective network of antioxidant system, many of the free radicals produced by various agents can escape this surveillance, inducing substantial damage to cutaneous constituents, especially when skin defense mechanisms are overwhelmed. ROS may cause cellular damage by inducing oxidative stress in the skin [4]. Some of the general events associated with the early phase of oxidative stress response in the skin are depletion of endogenous intra- and intercellular antioxidants [5], enhancement of intracellular lipid peroxidation (LPx) concentrations [6] and the induction of specific signal transduction pathways that can modulate inflammatory, immune suppressive or apoptotic processes in the skin [7]. To modulate the redox (antioxidant/pro-oxidant) balance in vivo, there is a general need for safe and effective antioxidant/skin protectant. Consequently, exogenous antioxidants that scavenge ROS and restore normal redox state may be beneficial in such a case [8], [9]. Use of such antioxidants has aroused increasing interest, since it was noticed that the protection of normal tissues like skin might allow one to increase the radiation dose to the tumor thus increasing the probability of tumor control.

Ordinary metabolites are part of the normal human diet. They are relatively non-toxic to the biological system. Therefore, it is likely that an effect of such agents may be beneficial to the patients undergoing radiotherapy, simply because, their concentrations may be easily manipulated and can be safely administered in fractionated doses without untoward side effects, than those of other non-dietary metabolites. The patients may also tolerate them better than the other more promising exotic drugs. Ascorbic acid (AA) forms an essential ingredient of the human diet and it is relatively non-toxic. Ascorbic acid is known to act as a good antioxidant [10], free radical scavenger [11] and is involved in the recycling of vitamin E and glutathione (GSH) [12], [13]. Ascorbic acid treatment has also been reported to increase the survival of irradiated cells in vitro and in vivo [14], [15], [16], [17]. Earlier investigations in mice demonstrated the inhibitory effect of ascorbic acid on UV-induced skin damage [18], [19]. Our earlier study has shown that treatment of mice with 250 mg/kg b. wt. of ascorbic acid once daily before fractionated irradiation (IR) enhanced healing of excision wound [20]. We studied the effect of ascorbic acid on the antioxidant status and lipid peroxidation during the healing of excision skin wound of mice exposed to 10, 16 and 20 Gy of fractionated gamma radiation.