Mitochondrial impairment and cytotoxicity effects induced by the marine epibenthic dinoflagellate Coolia malayensis

•The toxicity of the dinoflagellate Coolia malayensis crude extract was studied.•Mitochondrial toxicity assessment and cell-based assays were performed.•Coolia malayensis crude extract was found to be toxic to mitochondrial bioenergetics.•Toxicity in mitochondria also elicited HepG2 and H9c2(2−1) cell mass decrease.•Coolia malayensis toxicity at sub-cellular and cellular levels were demonstrated. Mitochondria was used to clarify the effects of Coolia malayensis strain UNR-02 crude extract by studying mitochondrial membrane potential (ΔΨm) generation and the fluctuations of ΔΨm associated with the induction of mitochondrial permeability transition (MPT). The cytoxicity of C. malayensis was also determined using both HepG2 and H9c2(2−1) cells. C. malayensis extract significantly depressed the oxidative phosphorylation efficiency, as was inferred from the perturbations in ΔΨm and in the phosphorylative cycle induced by ADP. Increased susceptibility to Ca2+-induced MPT was also observed. At the cellular level, the extract significantly decreased cell mass of both cell lines.