Enhanced susceptibility of LDL to oxidative modification in a CTX patient:- role of chenodeoxycholic acid in xanthoma formation.

Cerebrotendinous xanthomatosis (CTX) is a rare familial sterol storage disease, causing multiple xanthomas in tendons and the brain. The underlying biochemical defect is a lack of the hepatic mitochondrial cholesterol 27-hydroxylase involved in the normal biosynthesis of bile acid, resulting in reduced biosynthesis of chenodeoxycholic acid (CDCA). It has been reported that administration of CDCA to CTX patients improves neurological disorders and xanthomas of the Achilles tendon. The present study investigated the effect of CDCA on the mechanism of cholesterol accumulation in macrophages, the major cells in xanthoma. The LDL from the patients in this study was significantly more susceptible to oxidative modification than normal LDL, and supplement therapy with CDCA resulted in an improvement in the susceptibility to oxidative modification. In the incubation of CDCA with plasma, 13% of the CDCA added to serum was recovered in the LDL fraction. In addition, supplementation with CDCA enhanced cholesteryl ester transfer protein (CETP) activity and reduced high-density-lipoprotein cholesterol levels in the plasma. This evidence suggests that the multiple xanthomas observed in CTX may be induced by increased oxidized LDL and the low activity of CETP, both of which are caused by a lack of CDCA.

Scavenger receptor type BI potentiates reverse cholesterol transport system by removing cholesterol ester from HDL.

High-density lipoprotein (HDL) plays an important role in reverse cholesterol transport by removing accumulated cholesterol from extrahepatic tissues. Subsequently, cholesterol ester (CE) on HDL in humans is transported to apolipoprotein B-containing lipoproteins by cholesteryl ester transfer protein (CETP). CETP deficiency, which is common in the Japanese population, leads to a marked increase in HDL-cholesterol levels due to impaired CE transport from HDL to LDL. It has been reported that the HDL observed in CETP deficiency is an atherogenic lipoprotein, as it contains a large amount of CE. Scavenger receptor class B type I (SR-BI) has been found to be an authentic HDL receptor that mediates the selective uptake of HDL CE and the bi-directional transfer of free cholesterol between HDL and cells. In the present study, the interaction between SR-BI and CE-rich HDL from CETP-deficient patient was studied in order to evaluate the anti-atherosclerotic role of SR-BI in relation to CE uptake and reverse cholesterol transport. When CE-rich HDL was added to the medium of SR-BI-transfected CHO (SR-BI CHO) cells, more CE accumulated in SR-BI CHO cells compared to control HDL. In contrast, the amount of cholesterol efflux from SR-BI CHO cells into HDL was almost the same between the two HDLs. Therefore, when CE-rich HDL was added to the medium of SR-BI CHO cells, the intracellular CE content increased significantly. Moreover, the particle size of HDL in CETP-deficient patient decreased significantly when the HDL was added to the medium of SR-BI CHO cells, and this HDL showed an increment of CE efflux from foam cells. These results indicate that SR-BI reduces the cholesterol content and size of the CE-rich HDL from CETP deficiency, which ultimately activate reverse cholesterol transport system.