الفهرس 
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Abstract
Oxidative stress plays a pivotal role in the pathogenesis and progression of γ-irradiation-induced cellular damage and the administration of dietary antioxidants has been suggested to play an appreciable role in protection against the subsequent tissue damage.
In spite of more than six decades of research on the development of radioprotectors, there is no safe and effective nontoxic radioprotector available for human use. This has enthused extensive search to find effective and nontoxic radioprotectors. Hence the interest has shifted towards the use of natural products in radioprotection.
Hesperidin belongs to the class of flavonoids called flavonones, which are abundant in citrus fruits and it is significantly contributed to the intracellular antioxidant defense system and has been reported to act as a powerful agent against superoxide, singlet oxygen and hydroxyl radicals. Hesperidin has also been reported to have membrane stabilizing properties as well as anti-inflammatory and anti-cancer properties. Administration of hesperidin maintained the level of liver enzymes to near normalcy thereby restoring the membrane function. Previous documentations reported that hesperidin, due to its surefootedness in providing protective effect, is efficient in combating free radicals causing oxidative stress. The aim of the present study was to investigate the radioprotective role of hesperidin against γ-irradiation-induced hepatocellular and DNA damage in rat model.
Albino rats were divided into 6 groups. The experimental design and treatment protocol was as follows:
group 1: control rats were orally administered 0.5 ml of the vehicle (DMSO+ H2O, 1: 9; v/v) every other day for 30 days.
group 2: Rats were orally administered HES (100 mg/kg body wt. dissolved in the vehicle) every other day for 30 days.
group 3: Rats were orally administered the vehicle every other day for 30 days followed by the exposure to fractionated doses (F.D.) 10 Gy (2 Gy x 5 times) given as 2 Gy every other day.
group 4: Rats were orally administered the vehicle every other day for 30 days followed by the exposure to a single dose (S.D.) of 8 Gy.
Group5: Rats were administered HES (100 mg/kg) orally every other day for 30 days followed by 10 Gy of radiation given fractionated (F.D.) as 5 doses each of 2 Gy every other day.
group 6: Rats were administered HES (100 mg/kg) orally every other day for 30 days followed by 8 Gy of radiation given as a single dose (S.D.).
The investigated parameters comprised the liver thiobarbuturic acid reactive substance as an index for lipid peroxidation (MDA), the activity of the enzymatic antioxidants superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and the level of the non-enzymatic (GSH) antioxidant as indices afor oxidative stress. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and γ-glutamyl transpeptidase (γ-GT) levels were determined. The liver tissue DNA fragmentation (Comet assay), SOD & GPx gene expression in hepatocyte (qRT-PCR), hepatocytes apoptosis, via assessment of the immunohistochemistry of caspase-3, and Feulgen’s stain were also performed. Finally, liver sections were examined to assess the histopathological alterations.
The results showed that the ionizing radiation-induced oxidative stress was evidenced by elevated levels of lipid peroxidation (MDA) and decreased level GSH. The antioxidant enzymes SOD, CAT and GPx activities in the liver tissue were significantly inhibited. The data also revealed elevation in the serum levels of AST, ALT, ALP and GGT, increase in comet parameters (tailed %, tail length, % DNA in the tail and tail moment) as indication of DNA fragmentation of liver tissue. Moreover, there was a prominent decrease in GPx and SOD gene expression. The immunohistochemistry of caspase-3 and Feulgent stain of liver tissue revealed increased level of apoptosis. The histopathological examination of liver tissues revealed noticeable structural changes indicative of tissue damage following the radiation exposure.
The gamma irradiation-induced toxic effects were noticeably diminished by hesperidin administration prior to exposure to irradiation as indicated by the restoration of most of the studied parameters to near normal status. The pre-treatment with hesperidin reduced lipid peroxidation and increased the activities of SOD, CAT and GPx as well as GSH level. Pre-treatment with hesperidin brought the serum level of the liver enzymes AST, ALT, ALP and GGT back to normal and increased GPx and SOD gene expression in the liver tissue. Further more, hesperidin decreased DNA fragmentation in liver tissue, which was reflected on the reduction of the the liver tissue apoptosis. Similarly, there was an obvious amelioration in the liver histopathological alterations induced by γ-radiation when hesperidin was administered prior to the radiation exposure.
To conclude, hesperidin, a flavonoid glycoside, affords radioprotection against γ-irradiation by three different, but coherent mechanisms. Firstly, it maintains cellular antioxidant status, thus preserving the cellular biochemistry and physiology and consequently prevents tissue degeneration. Secondly, it protects the genomic integrity, thereby prevents DNA damage and apoptosis in a highly proliferative organ such as the liver. Thirdly, it regulates gene expression of the antioxidant enzymes GPx and SOD, which contributes to strengthening the antioxidant enzymatic component. So, the radio-protective potential of hesperidin could be the outcome of combined effects pertaining to conservation of the genomic integrity, modulation of cytoplasmic antioxidant status, and promoting gene expression.