Plantago asiatica is a commonly used folk medicine in Eastern Asia and its essential oils have various bioactive compounds. Previously, we have showed that Plantago asiatica essential oils (PAEO) have hypolipidemic effects. Since compound A(82.6%) was a major component in the PAEO, we further examined hypolipidemic effects of compound A as well as the PAEO in diet‐induced obese mice. Mice (C57BL/6CrSlc) were fed a high fat diet for 5 weeks and then compound A and the PAEO were orally administered for 6 weeks under high fat diet. The PAEO and the compound A feeding significantly reduced plasma total cholesterol and triglyceride levels after 3 and 6 weeks, respectively, compared with the controls. Compound A reduced plasma cholesterol concentrations by approximately 20%. We investigated the effects of the PAEO and compound A on the expression of cholesterol metabolism genes. The expression of the HMG‐CoA reductase, assessed by RT‐PCR, was significantly reduced by 50% in the livers of compound A‐fed mice compared with the control livers after 6 weeks. Our data suggest that compound A, a major compound in the PAEO, may exert hypocholesterolaemic effects by downregulation of the HMG‐CoA reductase expression in diet‐induced obese mouse.

Agostach rugosa is a medicinal and ornamental plant in Korea and its essential oils have several bioactive compounds. The HepG2 cells were incubated with 0.1, 0.2, 0.4 and 1 mg/mL of Agostach rugosa essential oils (AREO) for 24 hrs. The mRNA and protein expressions were assessed by RT‐PCR and western blot analysis, respectively. At 1 mg/ml AREO treatment, the levels of the HMG‐CoA reductase mRNA and protein were significantly reduced, whereas the LDL receptor mRNA and protein levels were induced. Next, mice (C57BL/6CrSLC), either on chow or high fat diet, were orally administered with AREO for 6 weeks. In chow fed mice, plasma triglyceride and cholesterol levels were significantly decreased in AREO fed group. The plasma triglyceride levels were also significantly lowered in the AREO fed group compared with controls under high fat diet. The hepatic HMG‐CoA reductase mRNA and protein levels were significantly lowered in the AREO group after 6‐week feeding. These suggest that the AREO may be hypolipidemic by reducing the expression of HMG‐CoA reductase.