Development and Clinical Application of a Method to Determine Cholesterol Synthesis and Absorption Markers and Metabolites in Vivo

Abstract

Cholesterol is an important component of cell membranes and a precursor of steroid hormones. However, it causes hyper-LDL-cholesterolaemia in dyslipidaemia, a lifestyle-related disease. Therefore, the quantification of plasma cholesterol is important for determining the pathological conditions and efficacy of therapeutic agents. However, lipids, such as cholesterol, which are highly fat-soluble in the blood, are incorporated into lipoproteins; making their extraction difficult. Measurement of cholesterol, its precursors, plant sterols, cholestanol, and oxysterols in plasma are useful for diagnosis of inherited disorders of cholesterol biosynthesis, malformation syndromes, familial hypercholesterolemia, cerebrotendinous xanthomatosis, and sitosterolemia, as well as for evaluating the effects of drug administration. In this study, a highly accurate and sensitive method was developed for determining cholesterol biosynthesis, absorption, and metabolites (oxysterols). The developed method was applied to patient blood samples to discover new activities of the dyslipidemic drug ezetimibe (enhancement of cholesterol biosynthesis as a compensatory effect on cholesterol absorption and inhibition of 7β-hydroxycholesterol absorption). Additionally, cerebrotendinous xanthomatosis and sitosterolemia were identified as biomarkers of the disease. Moreover, 24S-hydroxycholesterol (24OHC) was identified as a potential marker of central nervous system disorders in phenylketonuria, and the increase in 24OHC levels in the brain due to growth hormone administration in small-for-gestational-age patients was measured. Additionally, an association between cardiovascular risk factors and oxysterol concentrations in patients with type 2 diabetes mellitus was observed. On further application to cell culture and animal experimental systems, it was found that ergosterol in mushrooms, daidzein in soya and lactic acid bacteria have an inhibitory effect on cholesterol biosynthesis by inhibiting the downstream of cholesterol biosynthesis pathway.