Fig. 4.

Biological targets of o-quinones.

The various targets of o-quinones lead to biological activities, including detoxification, chemoprevention, and toxicity. o-Quinones can deplete GSH causing oxidative stress or directly alkylate proteins (PSH) to elicit chemopreventive activity (e.g. Keap1 and IKK) or stress response (e.g. HSP, PDI, BiP, GST-P1). The toxic effects from o-quinones arise from DNA adducts/oxidation which leads to mutagenesis and P450 oxidative enzyme inhibition or from alkylation of key proteins that can lead to toxicity, such as liver toxicity in the case of kava lactones.