Cytostatic and cytotoxic effects of a hot water and methanol extract of Acokanthera oppositifolia in HepG2 hepatocarcinoma cells

Abstract

ETHNOPHARMACOLOGICAL RELEVANCE : Herb-induced liver injury is poorly described for African herbal remedies, such as Acokanthera oppositifolia. Although a commonly used treatment for pain, snake bites and anthrax, it is also a wellknown arrow poison, thus toxicity is to be expected. AIM OF THE STUDY : The cytotoxicity and preliminary mechanisms of toxicity in HepG2 hepatocarcinoma cells were assessed. MATERIALS AND METHODS : The effect of hot water and methanol extracts were on cell density, oxidative status, mitochondrial membrane potential, fatty acids, caspase-3/7 activity, adenosine triphosphate levels, cell cycling and viability was assessed. Phytochemicals were tentatively identified using ultra-performance liquid chromatography. RESULTS : The hot water extract displayed an IC50 of 24.26 μg/mL, and reduced proliferation (S- and G2/M-phase arrest) and viability (by 30.71%) as early as 24 h after incubation. The methanol extract had a comparable IC50 of 26.16 μg/mL, and arrested cells in the G2/M-phase (by 18.87%) and induced necrosis (by 13.21%). The hot water and methanol extracts depolarised the mitochondrial membrane (up to 0.84- and 0.74-fold), though did not generate reactive oxygen species. The hot water and methanol extracts decreased glutathione (0.42- and 0.62-fold) and adenosine triphosphate (0.08- and 0.26-fold) levels, while fatty acids (2.00- and 4.61-fold) and caspase-3/7 activity (1.98- and 5.82-fold) were increased. CONCLUSION : Extracts were both cytostatic and cytotoxic in HepG2 cells. Mitochondrial toxicity was evident and contributed to reducing adenosine triphosphate production and fatty acid accumulation. Altered redox status perturbed proliferation and promoted necrosis. Extracts of A. oppositifolia may thus promote necrotic cell death, which poses a risk for inflammatory hepatotoxicity with associated steatosis.