Cytotoxicity of Extract of Malaysian Kratom and its Dominant Alkaloid Mitragynine, on Human Cell Lines

Kratom (Mitragyna speciosa Korth), an herb of the Rubiaceae family is indigenous in Southeast Asia mainly in Malaysia and Thailand. It's used as an opium substitute and has been increasingly abused by drug addicts in Malaysia. Recently, the potent analgesic effect of extract (MSE) and its major alkaloid mitragynine was confirmed in vivo and in vitro (1). It acted primarily on µ-and δ-opioid receptors, (2) suggesting promising alternatives for future pain management treatment. However, its potential cytotoxicity has not been elucidated. An attempt was made to characterize the cytotoxicity effects of MSE and mitragynine on human cell lines (HepG2, HEK 293, MCL-5, cHol and SH-SY5Y cells). MSE appeared to exhibit dose-dependent inhibition of cell proliferation in all cell lines examined, at concentration > 100 µg/ml with substantial cell death at 1000 µg/ml. SH-SY5Y was the most sensitive cell line tested. Mitragynine also showed the same response but appeared to be less toxic. Clonogenicity assay was performed to assess the longer-term effects of MSE. The colony forming ability of HEK 293 cells and SH-SY5Y cells was inhibited in a dose-dependent manner. Involvement of metabolism in cytotoxicity was further assessed by clonogenicity assay using rat S9 (induced by Arochlor 1254); toxicity increased 10-fold in both cell lines. Whether cytotoxicity was accompanied by DNA damage, was investigated using Mouse Lymphoma tk gene mutation assay. The results were negative for both compounds. These data suggest that MSE and the major alkaloid mitragynine are toxic at high dose with little evidence of genotoxicity. Acknowledgements: Thanks go to Ministry of Higher Education of Malaysia and International Islamic University Malaysia for funding this project. References: [1] Takayama H (2004) Chem. Pharm. Bull. 52(8): 916–928. [2] Matsumoto K, et al. (2006) Life Sci. 78: 2265.