We assessed the inhibitory effects of curcumin and its chemically modified homologues against H202-induced cytotoxicity toward Chinese hamster lung fibroblasts V79 cells with a colony formation assay. Among 4 curcuminoids, dihydroxycurcumin and dihydroxytetrahydrocurcumin suppressed H202-induced cytotoxicity. On the contrary, neither curcumin nor tetrahydrocurcumin showed any suppressive effects. These results support our empirical rule that the o-dihydroxy (catechol) moiety is essential for the inhibitory effects.Keywords: curcumin, turmeric, hydrogen peroxide, V79, cytotoxicity, polyphenol, cultured cell Curcumin is the major component of turmeric. Despite its anticarcinogenic effect in vivo experiments (LU et al, 1994; Tanaka et al., 1994) and antioxldant effects in vitro experiments (Joe & Lokesh, 1994; Lin & Shih, 1994;Osawa et al., 1995;Sugiyama et al, 1996), its inhibitory effect against hydroperoxide-induced cytotoxicity in mammalian cells has not been reported. Tetrahydrocurcumin suggested as a metabolite of curcumin shows more potent antioxidative activity than curcumin (Osawa et al, 1995;Sugiyama et al., 1996). We have reported that plant polyphenols bearing the o-dihydroxy structure were effective for protection against H202-induced cytotoxicity and H202-induced DNA singlestrand breaks in mammalian cells (Nakayama, 1994;Nakayama et al, 1996). On the other hand, plant polyphenols bearing an o-methoxy structure showed no effect. Because curcumin and tetrahydrocurcumin bear an o-methoxyphenol structure, we tried to prepare the respective o-dihydroxy compounds, expecting that the chemically modified curcuminoids would show protective effects against H202-induced cytotoxicity.H202 was obtained from Mitsubishi Gas Chemical Co., Ltd. (Tokyo). Highly purlfied curcumin and tetrahydrocurcumin (THC), which was prepared by hydrogenation of curcumin, were gifts of Nikken Fine Chemicals Co., Ltd. (Chlta). Dihydroxycurcumin (DHC) and dihydroxytetrahydrocurcumin (DHTHC) were prepared by demethylation of curcumin and THC respectively, according to the method of Naito et al ( 1991). The structures of both compounds as shown in Fig, I were identified by FABMS with a JEOL DX-303HF mass spectrometer: DHC, m/z 340; DHTHC, ml z 344. All other chemicals were reagent grade and were used without further purification. The cytotoxic effects of H202 and the protective effects of chemlcally modified curcumins against H202-induced cytotoxicity were assessed by a colonyformation assay (Nakayarna et al., 1996). Chinese hamster lung fibroblast V79 cells were seeded in 60-mm petri dishes pM. These results suggest that curcumin and DHC were incorporated into the cells more efficiently than THC and DHTHC, and the former compounds exerted their biological effects at lower concentrations in the medium than the latter compounds. We next investigated the protective effects of these compounds against H202-induced cytotoxicity at concentrations at which each compound was itself not toxic.Although it was difficult to maintain a constant dos...
