Investigation of the effects of peppermint oil and valerian on rat liver and cultured human liver cells

1. The aim of the present study was to investigate the effects of peppermint oil and valerian on rat liver and cultured human hepatoma cells. 2. Rats received a single oral dose of peppermint oil (8.3 - 830 muL/kg) or valerian (0.31 - 18.6 g/kg), or daily oral doses of 83 muL/kg peppermint oil or 3.1 g/kg valerian for 28 days. After 24 h, rats were anaesthetized and measurements made of bile flow, liver function and in vivo sinusoidal area. Livers were then removed for histology. 3. Bile flow was unaffected by any treatment, except acute high-dose peppermint oil (830 muL/kg; 70% increase in flow). No change in liver enzyme activity was found, except for a 45% increase in alkaline phosphatase after chronic peppermint oil. No change in sinusoidal area in vivo or in histology was found following any treatment, although pretreatment with carbon tetrachloride reduced sinusoidal bed area and produced histological damage. Incubation of human hepatoma cells with 0.5 muL/mL (but not 0.05 muL/mL) peppermint oil or 20 mg/mL ( but not 2 mg/mL) valerian resulted in increased cell death. 4. In conclusion, the present study demonstrated in vitro toxicity of high doses of valerian and peppermint oil in cultured human hepatoma cells and, at doses 2 - 3 orders of magnitude greater than those recommended for human use, an increase in rat bile flow after acute peppermint oil and an increase in alkaline phosphatase after chronic peppermint oil.