Inhibitory Effects Of Rhizopus Nigricans Exopolysaceharide On The Chronic Atrophic Gastritis Caused By N-methyl-N’-nitro-N-nitrosoguanidine In Mice

Chronic atrophic gastritis (CAG) is a common disease in the digestive system, which seriously affects the digestion of patients. CAG may cause intestinal metaplasia and atypical hyperplasia which are considered as precancerous lesions of gastric cancer in clinical diagnosis. At present, drugs for CAG show questionable effectiveness, only reducing the swell and pain of inflammation regions, and may cause adverse effects including chemical dependency and organ injury. Therefore, to find novel drugs with better efficacy and enhancing immunological activities is going to be important.Fungi polysaccharides possess medicinal properties, such as antioxidant, anti-inflammatory and immunomodulatory. Rhizopus nigricans is a filamentous fungus which is assigned to the class of Zygomycetes. In the previous study, Rhizopus nigricans exopolysaccharides (EPS) was isolated from its fermentation liquid. EPS can significantly inhibit the proliferation of HCT-116 and K562 tumor cells. EPS induced apoptosis mainly through mitochondria-dependent pathway in HCT-116 cells. The tests in vivo confirmed directly anti-tumor effects of EPS in S180-bearing mice. EPS was improved the immune ability in S180-beaing mice and improved the survival time of S180-bearing mice.In this study, we established the CAG mice model and studied the inhibitory effects of EPS on the CAG formation in N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) induced CAG.1. The effect of EPS on MNNG bearing mice. The BALB/c mice of 5-week-old were randomly divided into 3 groups (n=5), these are normal group MNNG group (MNNG 66.7 mg/kg/d) and MNNG+EPS group (MNNG 66.7 mg/kg/d EPS 75 mg/kg/d). The mice were administrated with different dosages of EPS and MNNG for 20 weeks. The results showed that body weight (28.3±0.9 g) and food-intake (168.5 g) of MNNG group is lower than the body weight (34.4±1.1 g) and food-intake (189 g) of normal group, the body weight (30.0±0.8 g) and food-intake (174 g) of MNNG+EPS group is higher than MNNG group. Pathologic analysis showed that the gastric cells and liver cells are intact in normal group. But in the MNNG group, the area of gastric mucosa atrophy is expansion and hyperplasia of the gastric mucosa is observed, the gastric mucosa with large areas of haemorrhage, accompanied with morphology irregularity of liver cells and intercellular spaces dilatation. The area of gastric mucosa atrophy is reduced and inflammation relieved and only with mucosal hyperemia in MNNG+EPS group, the morphology of liver cells is completed and the cell spaces are small. The thymus index (0.68±0.002 mg/g) (P<0.05) and spleen index (3.55±0.02 mg/g) in MNNG+EPS group is higher than MNNG group but less than normal group. The content of Aspartate aminotransferase (AST) (183.0±40.0 U/l) in MNNG+EPS group is greater than MNNG group but less than normal group. The content of Serum creatinine (Cr) (24.8±7.85 mg/dl) and Blood urea nitrogen (BUN) (7.8+-0.98 mg/dl) in normal group are less than MNNG group. The content of Cr (28.8+-8.41 mg/dl) and BUN (9.5±1.17 mg/dl) in MNNG+EPS group are less than MNNG group. So, the administration of EPS inhibited the progression of CAG induced by MNNG.2. The prophylactic effect of EPS on MNNG bearing mice. The BALB/c mice of 5-week-old were randomly divided into 3 groups (n=8), these are normal group MNNG group (MNNG 133 mg/kg/d) and MNNG+EPS group (MNNG 133 mg/kg/d EPS 200 mg/kg/d). At the first 2 weeks, the mice in MNNG+EPS group were only treated with EPS aqueous solution, and the mice of other group were taken water. After two weeks, according to the above method, the mice were treated for after 18 weeks. The appearance of each mice showed, in normal group, the mice were fleshy and had luxuriant and shiny coat with powerful grip strength. The mice in MNNG group were thin and weak with sparse coat and vulnerale grasp. The mice of MNNG+EPS group have moderate size, the fur were dense and have less of powerful of grasp. The ratio of moderate and severe in CAG of mice in normal group was 0/8, the ratio in MNNG group and EPS group was 5/8 and 2/8, respectively. The mRNA expression levels of COX-2 and EGF were up-regulation in MNNG group compared with normal group. The EPS treatment decreased the COX-2 and EGF mRNA expression levels induced by MNNG. So, in the prophylactic study, the administration of EPS inhibited the progression of CAG induced by MNNG.3. In vitro experiments, the effect of EPS in MNNG treated with liver cells was researched by SRB method. Liver cells were treated with EPS (0.10.3 and 0.5 mg/mL) and MNNG (0.05 mg/mL) for 20 h. The results showed that EPS can increase the liver cells viability in a dose-dependent manner; different doses EPS treated with liver cells would not inhibit the liver cells viability and proliferation.In summary, EPS can improve the cells viability and inhibited MNNG-induced CAG formation in BALB/c mice. EPS improved the immune ability and enhance hepatic and renal function of the mice.