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.

Membrane damaging potential of photosensitized riboflavin.

Riboflavin upon exposure to UV and visible radiations has been shown to produce active oxygen species. The present work deals with erythrocyte membrane as model system to study the damaging potential of photosensitized riboflavin. Membrane preparations (2.5 mg protein/ml) following exposure to sunlight in presence of riboflavin for different time intervals revealed significant inhibition of ATPases, p-nitrophenyl phosphatase and acetylcholinesterase. Considerable increase in lipid peroxidation was caused by the photosensitized riboflavin. Quenching studies using specific scavengers indicated remarkable inhibition. The production and identification of reactive oxygen species by photosensitized riboflavin and their possible involvement in membrane damaging effect has been discussed.

Toxicological evaluation of karaya gum; acute and subacute oral toxicity in rats.

Male and female albino rats (Wistar strain) were given single and multiple doses of karaya gum suspended either in peanut oil or mixed with basal diet at different concentrations ranging from 0·5 to 8 g gum/kg body weight. The plant gum did not elicit any overt signs of toxicity or death in both sexes of rats. Daily administration of karaya gum mixed with basal diet at different dose levels (0, 5, 20 and 40 g gum/kg diet) for a period of 90 days showed no adverse effects in male and female rats. The body weight, growth pattern, food and water intake were comparable with those of the normal rats. There were no significant biochemical, or morphological alterations in the vital organs of experimental animals.