RP-HPLC estimation of thermal oxidation of thymoquinone in Nigella sativa with reference to its antioxidant potential and vis-a-vis in-vitro DNA damage inhibition

Nigella sativa (NS), a popular herbal plant is known for its imperative therapeutic potentials. NS possesses active phytochemicals with unique antioxidant properties. Thymoquinone (TQ) is one of the active phytochemical of NS. Our investigation aimed to elucidate the effect of thermal oxidation of NS and TQ for antioxidant property and its effect on DNA damage inhibition (DDI). In the present study methanolic NS extract (NSE) and standard TQ were treated at different temperatures, at a range of 0 to 100 °C. The antioxidant potential was correlated to in-vitro DDI activity. The results elucidated that maximum TQ content was observed at 0 °C for NSE (18.545 ± 2.063%), while nil (0.000 ± 0.000%) was found at 100 °C for NSE. However, for standard TQ maximum content (99.086 ± 0.470%) was observed at 0 °C and minimum content (42.783 ± 3.233%) was observed at 100 °C. When the antioxidant activity was estimated, again a linear decline was observed. NSE kept at 0 °C showed maximum activity (4.252 ± 0.406%), while, at 100 °C showed minimum activity (0.621 ± 0.158%). For standard TQ maximum activity was observed at 0 °C (3.295 ± 0.265%), while the minimum was recorded at 100 °C (0.337 ± 0.087%). With consideration to positive antioxidant activity, in-vitro DDI was targeted. NSE kept at 0 °C demonstrated maximum DDI activity (24.145 ± 2.508%), while the minimum was observed at 100 °C (11.964 ± 1.768%). Standard TQ showed abridged results when compared to NSE. It showed only 17.991 ± 2.077% DDI activity with the sample kept at 0 °C, while with the sample at 100 °C was least effective for DDI (3.442 ± 0.608%). Electrophoresis study clearly reveals the degradation of calf thymus DNA upon oxidative stress. However, the antioxidant potential of NSE and standard TQ inhibited the calf thymus DNA damage. Statistically, a significant variation with p-value ≤ 0.05 was observed when two-way ANOVA was applied between the various parameters studied. When correlation was established between the various parameters, a strong positive correlation of approximately 0.9 was observed. Thus, it can be concluded that variation in temperature causes an effect on TQ content, thereby, affecting its antioxidant property due to thermal oxidation. It was observed that within the temperature range of 60 to 100 °C, TQ was quite stable but antioxidant potential was deprived as the temperature increased, thereby affecting DDI activity. Overall, our study is an open-end finding for future investigation in the development of drug formulation using NSE or its active phytochemical TQ.