Abstract:
The use of Jatropha curcas in biodiesel production is one of the emerging alternative sources of renewable energy. However, the extraction process leaves a seed cake waste and the lack of disposal protocols poses serious threat to ecosystems. This study aims to determine the toxicity of the seed cake extract to zebrafish through the analysis of heat shock protein 70 expression. The median lethal concentration (LC) was first determined through an acute toxicity test coupled with probit analysis. For the HSP70 induction test, fishes were subjected to a nonexposed setup and sub-lethal concentration setups of detoxified, washed, and untreated seed cake. RNA was isolated and reverse transcribed followed by polymerase chain reaction and gel profiling. Results indicate an LC50 of 0.172% (w/v) or 1.72 g/L. The heat shock induction test showed a significant downregulation of HSP70 expression in fishes exposed to washed and untreated setups. This under-expression may be attributed to phytochemicals such as lectins which have been noted to interact with HSP70. Furthermore, mRNA levels in the detoxified setup have no significant difference with the non-exposed setup, possibly indicating a successful inactivation of toxic phytochemicals in the seed cake. Moreover, the present study shows that downregulation of HSP70 is also an indicator of stress, and low HSP70 levels may lead to decreased resistance to stress-inducing agents.
