Abstract: Objective To study the protective mechanism of dendrobium candidum polysaccharides on liver injury in rats with non-acute toxic dose of arsenic poisoning. Methods Totally 60 healthy adult SD rats（half male and half female） were randomly divided into five groups,12 in each group,namely,normal control group,arsenic exposure group and dendrobium candidum polysaccharides treatment group 1[15 mg/（kg·d）],dendrobium candidum polysaccharides treatment group 2[30 mg/（kg·d）] and dendrobium candidum polysaccharides treatment group 3[45 mg/（kg·d）]. The last four groups were treated with 30 mg/L aqueous solution containing sodium arsenite（NaAsO₂） by gavage to build arsenism rat model,and the dendrobium candidum polysaccharides treatment groups were treated with dendrobium candidum polysaccharides by gavage after successful modeling,and the control group and arsenic exposure group were given the same dose of distilled water by gavage. The HE staining was used to observe the pathological changes of rat liver tissue,biochemical instrument was used to measure the liver function index of rats,and ELISA was used to measure the oxidative stress index of rats. The experimental period was four months. Results The liver function indicators of arsenic exposure group,total bile acid（TBA）[（21.59±7.39）μmol/L],alanine transaminase（ALT）[（46.57±22.91）U/L],and aspartate transaminase（AST）[（49.95±15.74）U/L],were higher than those of the control group[（6.19±1.17）μmol/L,（19.05±7.60）U/L,（29.98±6.11）U/L]（all P<0.01）,with significant damage of liver function. The oxidation indicators of arsenic exposure group,malondialdehyde（MDA）[（13.50±5.83）nmol/mL] and sulfhydryl（-SH）[（0.34±0.06）U/L],were higher than those of the control group[（6.25±2.15）nmol/L,（0.19±0.03）U/L]（both P<0.05）. The antioxidant indicators of superoxide dismutase（SOD）[（42.38±2.97）U/mL],glutathione peroxidase（GPx）[（546.56±40.08）U/L] and thioredoxin reductase（TrxR）[（17.55±2.24）U/L] activities were lower than those of the control group[（68.38±3.44）U/mL,（726.77±56.51）U/L,（31.94±3.22）U/L]（all P<0.05）. Compared with the arsenic exposure group,the contents of ALT,AST,TBA,MDA and-SH in dendrobium candidum polysaccharides treatment groups decreased,while the activities of SOD,GPx and TrxR increased,and the differences were statistically significant（all P<0.05）. Conclusion The chronic arsenic exposure can weaken the activity of antioxidant enzymes in the liver and increase the oxidative stress response,leading to liver injury,and the dendrobium candidum polysaccharides has a good protective effect on liver injury caused by chronic arsenic exposure.

Key words: Dendrobium candidum polysaccharides, Arsenic poisoning, Oxidative stress, Liver injury