Immunosuppressive activity on the murine immune responses of glycyrol from Glycyrrhiza uralensis via inhibition of calcineurin activity

Abstract

Context: Calcineurin (CN), a unique protein phosphatase, plays an important role in immune regulation. Our laboratory has established an effective molecular drug-screening model based on CN activity.

Objective: Our aim is to search for an effective immunosuppressant from Glycyrrhiza uralensis (Leguminosae).

Materials and methods: As guided by CN inhibitory test, an active compound was purified and identified as glycyrol. Immunosuppressive activity of glycyrol in vitro was assayed by T lymphocytes proliferation and mixed lymphocyte reaction (MLR). In addition, delayed-type hypersensitivity reaction (DTH) and skin allograft test in vivo were also carried out. Further, we have investigated the effect of glycyrol on phorbol 12-myristate 13-acetate (PMA)/ionomycin (Io)-stimulated IL-2 expression in Jurkat cells.

Results: The enzymatic assay showed glycyrol (IC₅₀ = 84.6 μM) inhibited calcineurin activity in a dose-dependent manner. Glycyrol, at the non-cytotoxic concentration, significantly inhibited proliferation of murine spleen T lymphocytes induced by Concanavalin A (Con A) and mixed lymphocyte reaction (MLR) in vitro. In addition, mice treated with glycyrol had shown the dose-dependent decrease in delayed type hypersensitivity (DTH) and prolonged the graft survival by 59% compared to the control group (*p < 0.05). RT-PCR showed glycyrol suppressed IL-2 production in a concentration-dependent manner.

Discussion and conclusion: Our results show the immunosuppressive activity of glycyrol and this activity should be due to its inhibitory effect on CN activity, thereby suppressing IL-2 production and regulating T lymphocytes. Thus, glycyrol could be a candidate for development as a novel immunomodulatory drug.

Keywords::

• Glycyrol
• calcineurin
• immunosuppressive
• inhibit
• T lymphocytes

Acknowledgments

We acknowledge Dr. Hu Wang and Professor Jing Luo for their helpful suggestions.

Declaration of interest

This work was partly supported by the National Natural Science Foundation of China, the research Fund for Doctoral Program of Higher Education and the National Important Basic Research Project.