Context: Leaf extracts of plants of the genus Betula have traditionally been used as diuretic, anti-rheumatic and diaphoretic preparations. One of the main active ingredients of Betula bark is betulin, lupane-type triterpene alcohol, with multiple biological activities. Objectives: The aim of this study was to investigate in vitro and in vivo immunomodulatory effects of a newly synthesized ester of betulin: 28-O-phosphatidylbetulin [28-O-(1,2-diacyl-sn-glycero-3-phospho)-betulin, DAPB] in comparison with betulin in mice. Materials and methods: Cytotoxic activity of DAPB or betulin was tested against non-cancer (D10.G4.1 and J774E.1) and cancer (GL-1; CL-1 and Jurkat) cell lines. The in vivo part assessed total lymphocyte count, weight ratio and subsets of lymphocytes in the lymphatic organs, and humoral immune response to sheep erythrocytes (SRBC). Results: In vitro assay showed that DAPB, contrary to betulin, had no antiproliferative activity. Exposure to four doses of DAPB increased the absolute count of immature CD4+CD8+ thymic cells as well as the percentage and absolute count of mature CD4+ and CD8+ thymocytes. DAPB enhanced the percentage or absolute count of CD3+ cells in spleen and lymph nodes with corresponding decrease in the percentage and/or absolute count of CD19+ cells. Both DAPB and betulin enhanced the percentage and absolute count of CD8+ lymphocytes in lymph nodes. In SRBC-immunized mice, betulin contrary to DAPB enhanced the number of splenocytes producing anti-SRBC antibodies (PFC). Both DAPB and betulin increased the level of total (IgM + IgG) and IgG titers. Conclusion: Despite the lack of cytotoxic activity, DAPB shows valuable immunomodulatory properties.
Keywords: 28--phosphatidylbetulin; betulin; cell lines; cytotoxic activity; humoral immune response; lymphocyte subsets; mice.