Radiotherapy is one of the key factors in gastric ulcer; therefore, the necessity of an efficient radio protective agent is apparent. The aim study is divided into two parts, the first part was to isolate and purify exopolysaccharide (PSEPS) from marine Pseudomonas sp. RD2SR3 and the chemical analysis and functional groups were detected by HPLC and IR spectrophotometry. After that the antioxidant activity was investigated by using DPPH radical scavenging hydroxyl radical in vitro. The results revealed that PSEPS consisted of glucose, mannose, galactose and glucouronic acid with molar ratio 2.1:0.1:0.1: 3.2 and had MW of 3.75´104 g/mole and it had scavenging activities on DPPH and increased antioxidant activity with an increase in its concentration. The second part investigated the mechanism of the potential of polysaccharides in the remedy and protection of gastric ulcer produced by gamma radiation. Its workings in the treatment and obstructive of gastric ulcer remain unclear. Methods: In this study, thirty two male rats were separated into four equal groups. The First group (Control) and 2nd group was exposed to whole-body gamma- radiation (γ-rays) (3Gy). The Third group (PSEPS) and 4th group (γ-rays + PSEPS) were administered 100 mg/kg of PSEPS 24 h after irradiation. Rats were exposed to gamma-radiation (3 Gy) treated with PSEPS (100 mg/kg) once daily for 30 days post irradiation. Prospect ulceration impediment of PSEPS was assessed quantitative of gastric injures, gastric juice acidity, mucus production, which generated by gamma rays. Oral administration of PSEPS 24 h after irradiation produced a significant protection which was demonstrated by a significant reduction in the activity of the myeloperoxidase (MPO), anti- inflammatory interleukin-10 (IL-10), pro-inflammatory cytokine interleukin-12 (IL-12), and thiobarbituric acid reactive substances (TBARS) assay accompanied with a significant increase in the antioxidant enzymes in stomach such as superoxide dismutase (SOD), glutathione reductase (GR), and glutathione-s-transferase (GST). Moreover, PSEPS significantly increased vascular endothelial growth factor (VEGF) and prostaglandin (PGE2) connected with a significant depletion in the gastric index compared to the irradiated group. Membrane damage is quite apparent in histological studies undertaken in the stomach tissue, which is susceptible to radiation damage. Medication of PSEPS prevented the radiation-induced exploit to an appreciable extent. This study suggests that PSEPS may serve as a prospect protective agent against gamma-irradiation-induced gastric damage in the experimental model via enhancing the antioxidant activity and inhibition of endothelial dysfunction. _____________________________________________________________________________________________
