Genetic toxicity of a standardized mixture of citrus polymethoxylated flavones

Flavonoids are a ubiquitous family of phytochemicals that display a variety of biological effects, both beneficial and adverse depending on the individual compound. Certain flavonoids are genotoxic while others inhibit the genotoxicity of other mutagens. In the present studies, the mutagenicity of a mixture of polymethoxylated flavones (PMFs) purified from citrus peel oil was evaluated. The mixture consisted of nobiletin (32.5%), 3,3′,4′,5,6,7,8-heptamethoxyflavone (25.0%), tangeretin (14.0%), trimethylscutellarein (9.1%), sinensetin (3.9%), 5-demethyl-nobiletin (2.8%), hexa-O-methylquercetagetin (3.3%), 5-demethyl-tetramethylscutellarein (0.7%), 5-hydroxy-3,3′,4′,6,7,8-hexamethoxyflavone (0.7%), and a small quantity of unidentified flavonoid compounds (3.9%). In vitro addition of the PMF mixture over a concentration range that spanned four log doses (0.0005–5.0 mg/plate) did not reveal any evidence of mutagenicity in five bacterial tester strains (Salmonella typhimurium TA98, TA100, TA102, TA1535 and TA1537) either in the absence or presence of S9 activation. The PMF mixture exhibited a statistically significant increase in mutagenicity of L5178Y tk+/− mouse lymphoma cells at 0.05 (38.5×10−6; P<0.05) and 0.1 mg/ml (61×10−6; P<0.01) compared with vehicle-treated controls (mutation frequency=19.7×10−6). However, these responses were within historical values observed in negative control cultures and extremely small compared to the positive control (EMS 0.5 μl/ml; 1685.3×10−6). Furthermore, in the presence of S9 there was no indication of genetic toxicity in L5178Y tk+/− cells. These results demonstrate that the PMF mixture is not genotoxic in in vitro assay systems.