Biol. Pharm. Bull. 28(2) 299—304 (2005)

stream and exists in all the cells of the body. While cholesterol is an essential part of a healthy body, high levels of cholesterol in the blood (known as hypercholesterolemia) increase a person’s risk for cardiovascular disease, which can lead to stroke or heart attack. Properly controlling of cholesterol level in the body is considered to be important both in treatment and prevention of hypercholesterolemia. Total amount of cholesterol in the body depends on the sum of an intake from diet and de novo cholesterol biosynthesis in the body. For patients of hypercholesterolemia, diet therapy and/or the administration of inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (Fig. 1) are effective in treatment. Although administration of drug is quite effective for the patients, it’s use for healthy people to prevent from hypercholesterolemia is undesirable due to the potential side effects. Therefore, diet therapy is a good choice for disease prevention as well as taking a sufficient exercise. Restraint of ingesting of cholesterol-rich foods such as beef, egg, etc. is recommended, and vegetables are generally encouraged to take. Many attentions have been paid to cholesterol-rich foods to avoid excess intake of cholesterol, but no attention has been paid to the food that reduces de novo cholesterol biosynthesis in the body. In these days, foods and foodstuffs have become recognized to have not only nutritional but also biomodulatory effects. Researches to clarify the biochemical properties of functional foods or foodstuffs, have been proceeding. In this study, inhibition of cholesterol biosynthesis was investigated to find foods useful for hypercholesterolemia prevention. As mentioned above, clinically used drugs for hypercholesterolemia are HMG-CoA reductase inhibitors. The longterm administration of these drugs is apprehended for unexpected side effects since inhibition of HMG-CoA reductase results in decrease of the physiologically essential nonsteroidal isoprenoid metabolites such as dolichol, geranyl diphosphate (GPP) and farnesyl diphosphate (FPP). The three enzymes, squalene synthase, squalene epoxidase and lanosterol synthase, that locate at more downstream than HMG-CoA reductase in the pathway (Fig. 1), are considered as more selective target of suppression of cholesterol biosynthesis. Extensive screening works to find inhibitors of these enzyme from natural origin resulted in isolation of squalestatins, zaragozic acids (squalene synthase inhibitors), gallotannins, ellagitannins (squalene epoxidase inhibitors), lanopylins, and epohelmins (lanosterol synthase inhibitors), respectively. In this study, ethanol extracts of lyophilized vegetables were tested for inhibition using recombinant human lanosterol synthase (hOSC) as reported. Of 130 samples tested, twelve samples showed significant inhibition. Among them, Colocasia esculenta (taro) showed the highest inhibition (55 % inhibition at 300 mg/ml). Monogalactosyldiacylglycerols (MGDGs) and digalactosyldiacylglycerols (DGDGs) (Fig. 2), were identified as the active constituents in C. esculenta. February 2005 Biol. Pharm. Bull. 28(2) 299—304 (2005) 299