Asian plantain (Plantago asiatica) essential oils suppress 3-hydroxy-3-methylglutaryl-co-enzyme A reductase expression in vitro and in vivo and show hypocholesterolaemic properties in mice

Asian plantain (Plantago asiatica) essential oil (PAEO) contains multiple bioactive compounds, but its potential effects on lipid metabolism have not been examined. PAEO was found to be mostly composed of oxygenated monoterpenes, with linalool as the major component (82.5%, w/w), measured using GC-MS. Incubation of 0-200 μg PAEO/ml with HepG2 cells for 24 h resulted in no significant toxicity. Incubation with 0.2 mg PAEO/ml altered the expression of LDL receptor (+83%; P<0.05) and 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase (-37%; P<0.05), as assessed using RT-PCR. LDL oxidation was markedly inhibited by PAEO treatment due to the prevalence of linalool compounds in PAEO. Oral administration of PAEO for 3 weeks in C57BL/6 mice significantly reduced plasma total cholesterol and TAG concentrations by 29 and 46%, respectively. The mRNA (+58%; P<0.05), but not protein, levels of the LDL receptor were significantly higher, whereas both mRNA and protein levels of HMG-CoA reductase were significantly lower (-46 and -11%, respectively; P<0.05) in the liver of PAEO-fed than of control mice. The mRNA levels of CYP7A1 were marginally reduced in HepG2 cells, but not in mouse liver after PAEO treatment. Thus, PAEO may have hypocholesterolaemic effects by altering the expression of HMG-CoA reductase. Reduced TAG and oxidised LDL may provide additional cardiovascular protective benefits.