The ability to synthesize ascorbic acid is absent in the insects, invertebrates, and fishes. The biosynthetic capacity started in the kidney of amphibians, resided in the kidney of reptiles, became transferred to the liver of mammals, and finally disappeared from the guinea pig, the flying mammals, monkey, and man. A similar transition in the biosynthetic ability was observed in the branched evolution of the birds.

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Introduction: Arsenic, an established poisonous metalloid has widespread occurrence in the environment which is posing a constant threat to health and survival of all living organisms. In view of arsenic induced oxidative stress and toxicity, this study focuses on the mitigatory role of thymoquinone, a major active component in the volatile oil of Nigella sativa (commonly known as black cumin); as its nutraceutical value can fulfil the demand of such dietary supplements in high risk population areas. Methods: In the current study, brain preparations of male wistar rats were used to assess different biochemical markers of oxidative stress and genotoxicity. Results: Significant and dose-dependent alterations in the level of enzymatic and biochemical biomarkers of oxidative stress were observed in the As-treated system. However, pre-treatment with thymoquinone brought about significant reduction in the As-induced neurotoxicity. Also, a significant decline in arsenic-induced DNA damage was recorded on pre-treatment with thymoquinone in comet assay. Conclusion: This study proves usefulness of antioxidant potential of thymoquione in mitigating the arsenic induced neurotoxicity.

The ability of several species of birds to synthesize L-ascorbic acid is correlated with their phylogeny. In the more primitive species, synthesis of L-ascorbic acid occurs in the kidney. Among the highly evolved passeriform species, kidney and liver can synthesize L-ascorbic acid in some, whereas in others synthesis occurs in the liver. In still others, the capacity for the synthesis of L-ascorbic acid is apparently lost. The pattern of evolution of the ascorbic acid pathway among birds is thus similar to that among mammals.

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