Screening of antimutagenicity via antioxidant activity in Cuban medicinal plants

The reducing activity on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, z.rad;OH radical scavenging potential, in vitro inhibition of lipid peroxidation and modulation of mutagenicity induced by ter-butyl hydroperoxide (TBH) in Escherichia coli were sequentially screened in 45 species of plants used with medicinal purposes in Cuba, in a search for antioxidant agents which protect DNA against oxidative stress.Five species, e.g. Tamarindus indica L., Lippia alba L., Pimenta dioica (L.) Merr, Rheedia aristata Griseb. and Curcuma longa L. displayed IC(50)<30 micro g/ml in the DPPH radical reduction assay and IC(50)<32 micro g/ml in lipid peroxidation inhibition testing. Pimenta dioica and Curcuma longa L. showed also a 20% inhibition of the in vitro induced z.rad;OH attack to deoxyglucose. Further antimutagenesis assay in Escherichia coli IC 188 evidenced that only Pimenta dioica prevents DNA damage by TBH to the test bacteria. A role of antioxidant enzymes is presumed in this case, as judged by a different response in the isogenic Escherichia coli IC 203 deficient in catalase and alkyl hydroperoxide reductase and the discrete inhibition of oxidative mutagenesis also observed when pre-treatment of the extract was assayed. Eugenol, the main constituent of the essential oil of Pimenta dioica, also inhibited oxidative mutagenesis by TBH in Escherichia coli, at concentrations ranging from 150 to 400 micro g/plate.

Assessment of mutagenicity in Parthenium hysterophorus L

The mutagenic potential of a crude extract of Parthenium hysterophorus L. was assessed in the Salmonella/microsome (Ames) assay and the mouse bone marrow micronucleus test. Results in the bacterial mutagenicity assay were negative for the five strains employed, e.g. TA 1535, TA1537, TA 98, TA 100 and TA 102, while cytotoxicity was evident in all cases at 5000 microg per plate, the highest concentration assayed. A decrease in toxicity was observed with exogenous mammalian metabolic activation (S9) or glutathione (5 micromol per plate). When mutagenicity was monitored after column chromatography fractionation of the crude, fraction 1 was mutagenic in strain TA 98 (+S9). Besides, cytotoxicity was found in fraction 5, where parthenin was eluted. The micronucleus test was negative in mice upon oral administration, at doses up to 96 mg of crude per kg. Bone marrow toxicity was not observed. The crude extract exhibited some in vitro pro-oxidant activity. It also inhibited lipid peroxidation (IC(50)=4.1 microg/ml) but failed to act as .OH scavenger.

Mutagenicity and antioxidant assessment of Stachitarpheta jamaicensis (L.) Vahl

Stachitarpheta jamaicensis (L.) Vahl. is a member of the Verbenaceae commonly used in Cuba, mainly as vermifugue and against diarrhoea. The mutagenic potential of a hydroalcohol extract of its aerial parts was assessed in vitro using the Salmonella/microsome assay and in vivo in the mouse bone marrow micronucleus test. No positive response was observed in a battery of four Salmonella typhimurium strains employed: TA 1535, TA 1537, TA 98 and TA 100, when exposed to concentrations up to 5 mg/plate, with and without mammalian metabolic activation. In the same way, no increase in the micronucleus frequency in mitotic erythropoietic tissue was observed when animals were administered the extract orally in doses of 500, 1000 and 2000 mg/kg. The extract inhibited lipid peroxidation in the rat liver microsomal fraction (IC(50) = 3.6 microg/mL) but it does not seem to be an effective.OH radical scavenger (IC(50) = 76.7 microg/mL). Noteworthy, it increased in a dose dependent way the level of revertant colonies in E. coli IC 203, a strain sensitive to oxidative mutagenesis, when assayed together with hydrogen peroxide and ferrous sulphate, which suggests a pro-oxidant action.