Abstract:

OBJECTIVE: To observe the effect of ursolic acid (UA) on tumor growth in H22 mice and explore its mechanism. METHODS：H22 cells were inoculated subcutaneously into left anteromedial axilla of KM mice. 24 h later，mice were randomly divided into five groups：the model group，the cyclophosphamide(CP) control group [(25 mg/(kg·d)] and the UA low，mid，high dose groups [50，100，150 mg/(kg·d)]. Animals of the UA groups and the CP control group were treated with ig UA of different dosage and CP for 2 weeks. The model group were treated with equal volume of peanut oil intragastrically. 24 h after the last administration，the mice were weighed，and sacrificed after taking blood sample from eyeball extraction. Tumor， liver， kidney and spleen were removed under aseptic condition.  Tumor inhibition rate and liver，kidney，spleen indexes were calculated. Tumor histopathological change were examined by HE staining. Cell counting kit8 (CCK8) was used to determine proliferation activity of spleen lymphocyte.  The CD4+ and CD8+ T cell subsets in tumor tissue were assessed by immunohistochemistry. The number of CD4+T，CD8+ T cells in five random microscopic fields (×400) of each section were counted and the average number of every microscopic field calculated. The cells with cytoplasm containing claybank granules were positive cells. Serum IL-12 concentration was measured by enzyme linked immunosorbent assay. RESULTS：The H22 tumors in UA groups grew slowly. Compared with model group，the tumor weights of mid-dose and high-dose UA groups were reduced significantly (P<0.05). The tumor inhibition rate of mid-dose and high-dose UA groups were 30.15% and 39.80%，respectively. The liver and kidney indexes of UA groups and model group showed no significant change，but the spleen index gradually increased with dose of UA.  The spleen index of mid-dose and high-dose UA groups was significant different with model group (P<0.05). Tumor cells in model group grew well and had less necrotic area，while the growth of tumor cells in UA groups were significantly inhibited. Karyopyknosis，karyolysis，intercellular substance and necrotic area were increased，whilst the karyoplasmic ratio was reduced.  Proliferation activity of spleen lymphocyte increased with the dose of UA.  Proliferation activities of mid-dose and high-dose UA groups were higher than model group (P<0.05). The number of CD4+ T，CD8+ T cells in tumor per high power field (×400) of mid-dose and high-dose UA groups were significantly more than model group (P<0.05). Serum IL-12 concentrations of low-dose，mid-dose and high-dose UA groups were significantly higher than model group (P<0.05). Serum IL-12 concentration of high-dose UA group was significantly higher than CP group (P<0.05).  CONCLUSION： UA could inhibit the growth of H22 tumor in mice. The possible mechanism is growth promotion of immune organs and lymphocyte proliferation，inducing CD4+，CD8+ T cell infiltration in tumor tissue and enhancing serum IL-12 concentration to induce cellular immunity.

Key words: ursolic acid , mice , neoplasms