Hepatocellular toxicity of kava leaf and root extracts

Kava extracts are used widely for different purposes and were thought to be safe. Recently, several cases of hepatotoxicity have been published. To explore possible mechanisms of kava hepatotoxicity, we prepared and analyzed three different kava extracts (a methanolic and an acetonic root and a methanolic leaf extract), and investigated their toxicity on HepG2 cells and isolated rat liver mitochondria. All three extracts showed cytotoxicity starting at a concentration of 50 μg/ml (lactate dehydrogenase leakage) or 1 μg/ml (MTT test). The mitochondrial membrane potential was decreased (root extracts starting at 50 μg/ml) and the respiratory chain inhibited and uncoupled (root extracts) or only uncoupled (leaf extract) at 150 μg/ml, and mitochondrial β-oxidation was inhibited by all extracts starting at 100 μg/ml. The ratio oxidized to reduced glutathione was increased in HepG2 cells, whereas the cellular ATP content was maintained. Induction of apoptosis was demonstrated by all extracts at a concentration of 150 μg/ml. These results indicate that the kava extracts are toxic to mitochondria, leading to inhibition of the respiratory chain, increased ROS production, a decrease in the mitochondrial membrane potential and eventually to apoptosis of exposed cells. In predisposed patients, mitochondrial toxicity of kava extract may explain hepatic adverse reactions of this drug.