Phototoxicity evaluation--Tetrahymena thermophila as an alternative model

Interest in utilizing an alternative to animal method for toxicological evaluation has received considerable attention due to cost effectiveness and the ethical issues involving animal experimentation. Alternative methods for phototoxicity evaluation are significant because of growing concern over increasing health effects due to stratospheric ozone depletion resulting in an increasing penetration of ultraviolet light-B radiation (UVB, 290-320 nm) which contributes to activation of chemical and biological molecules to potential phototoxic agents. The classic rabbit eye-irritancy test referred to as Draize test has been the subject of severe criticism by animal welfare groups. Dermal toxicity test using guinea pigs and mouse tail phototoxicity test is time consuming and requires a large number of laboratory animals. In photohaemolysis assay some of the phototoxic agents (such as riboflavin) react with the membrane proteins of the erythrocyte. However, in vitro test system using protozoa offers a promising alternative means of phototoxicity evaluation. Our previous studies have demonstrated that synergistic action of photochemically reactive agents and sunlight produces lethal effects to Paramecium but the protozoan has not received serious consideration for use as an alternative model for phototoxicity evaluation. In the present communication we have described the potential application of Tetrahymena as an alternative model to study the radiation-induced changes both in the presence or absence of photoreactive chemical agents. This model is likely to provide scope for studying the biological effects of environmental UVB radiation, DNA damage and defence against oxidative stress.