Psoralen induces hepatotoxicity by covalently binding to glutathione-S-transferases and the hepatic cytochrome P450

Background: Psoraleae Fructus has been widely used in China and its surroundings; however, Psoraleae Fructus and its compound preparation have been reported recently to cause liver injury in clinics. Thus, its safe use has attracted increasing attention. The possible mechanism is related to the metabolism of psoralen, but it still needs further clarification.

Purpose: The present study was designed to evaluate the toxicity of psoralen and investigate the potentially related molecular mechanisms using chemical biology methods combined with animal experiments to provide evidence for the rational clinical use of psoralen.

Methods: An in vivo experiment was conducted with a time series of 20-80 mg/kg psoralen to verify its toxic performance. Target capture and click reactions were used to investigate direct targets of psoralen. Selectivity for different glutathione-S-transferase (GST) subtypes in the liver and inhibition of cytochrome P450 (CYP450) were also detected.

Results: Psoralen build-up in the liver is the primary cause of liver damage. Our study revealed the mechanism by which psoralen induces liver injury. Psoralen can bind directly to CYP2D6, CYP3A4, GST-α, and GST-μ and inhibit their activities, causing the depletion of glutathione (GSH) in vivo, which in turn induces hepatic damage. The special structure of α,β-unsaturated lactones in psoralen facilitates its attachment to its target; therefore, complementing psoralen with GSH can efficiently protect the liver from damage.

Conclusions: Psoralen causes a disorder in drug metabolism by inhibiting the activity of CYPs and GSTs, causing exhaustion of GSH, and subsequently leading to liver damage. The co-administration of GSH and psoralen is an effective way to avoid liver injury in clinical settings.