Developmental neurotoxic effects of graphene oxide exposure in zebrafish larvae (Danio rerio)

Although graphene oxide (GO), a nanomaterial with hexagonal planar layer, has been widely studied due to its applications in neurobiology that include drug delivery and tissue engineering, additional studies to assess its potential toxic effects are still needed. Thus, this study evaluated the effects of GO exposure (at 5, 10, 50 or 100mg/L) during six consecutive days on mortality, hatching, spontaneous movement, heart rate, morphology, locomotion behavior, acetylcholinesterase (AChE) activity, dopamine levels and relative gene expression of developmental neurology-related genes using zebrafish larvae. In the 5mg/L dose, synapsin IIa expression up-regulation was seen concomitantly with down-regulation of dat expression, showing a potential compensatory mechanism. Moreover, the 10mg/L exposure caused an increase in heart rate, in absolute turn angle, brain cell damage and a decrease in dopamine levels. These alterations may be associated with autophagosome formation found in GO-exposed larval brain. No changes were observed on higher doses of GO exposure, probably due to nanomaterial agglomeration. Taken together, these results show that toxic effects of GO exposure are not dose-dependent, and are preeminent in lower concentrations. Additional studies are needed to deepen the specific mechanisms of GO neurotoxicity and are required to elucidate its potential biomedical use.