Effects of probucol on cholesterol metabolism in mouse peritoneal macrophages: inhibition of HDL-mediated cholesterol efflux

Effects of lycopene on the induction of foam cell formation by modified LDL

The effect of lycopene on macrophage foam cell formation induced by modified low-density lipoprotein (LDL) was studied. Human monocyte-derived macrophages (HMDM) were incubated with lycopene in the presence or absence of native LDL (nLDL) or LDL modified by oxidation (oxLDL), aggregation (aggLDL), or acetylation (acLDL). The cholesterol content, lipid synthesis, scavenger receptor activity, and the secretion of inflammatory [interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha] and anti-inflammatory (IL-10) cytokines was determined. Lycopene was found to decrease the synthesis of cholesterol ester in incubations without LDL or with oxLDL while triacylglycerol synthesis was reduced in the presence of oxLDL and aggLDL. Scavenger receptor activity as assessed by the uptake of acLDL was decreased by approximately 30% by lycopene. In addition, lycopene inhibited IL-10 secretion by up to 74% regardless of the presence of nLDL or aggLDL but did not affect IL-1beta or TNF-alpha release. Lycopene also reduced the relative abundance of mRNA transcripts for scavenger receptor A (SR-A) in THP-1 macrophages treated with aggLDL. These findings suggest that lycopene may reduce macrophage foam cell formation induced by modified LDL by decreasing lipid synthesis and downregulating the activity and expression of SR-A. However, these effects are accompanied by impaired secretion of the anti-inflammatory cytokine IL-10, suggesting that lycopene may also exert a concomitant proinflammatory effect.

Reduction of oxidative stress and apoptosis in hyperlipidemic rabbits by ellagic acid

Oxidative stress is one of the major risk factors for coronary artery disease. Ellagic acid is a phenolic compound present in fruits and nuts, and has been found to have antioxidative property. Twenty-four New Zealand white (NZW) rabbits were assigned randomly into four dietary groups. The normal group was fed regular rabbit chow, and the cholesterol group was fed a high fat and cholesterol diet. The ellagic acid (E) group and probucol group were fed the same diet as the cholesterol group plus the addition of 1% (w/w diet) ellagic acid and probucol, respectively. Oxidative stress [as measured by plasma lipids, oxygen free radicals and thiobarbituric acid reactive substances (TBARS)] increased in the cholesterol group compared with the normal group; however, it decreased in the probucol and E groups compared with the cholesterol group. Forty-five percent of the intimal surface of the thoracic aorta was covered with atherosclerotic lesions in the cholesterol group, but only 2-3% was covered in the E and probucol groups. The aortic level of 8-(OH)dG and the expression of caspase-8, caspase-9 and Fas ligand were also suppressed after ellagic acid supplement. These results indicated that ellagic acid could prevent atherosclerosis via suppression of oxidative stress and apoptosis in hyperlipidemic rabbits.

Probucol inhibits ABCA1-mediated cellular lipid efflux

OBJECTIVE

ATP-binding cassette transporter A1 (ABCA1) mediates the efflux of lipids from cells to lipid-poor apolipoproteins. In this article, we characterize the effect of probucol on cellular ABCA1-mediated lipid efflux.

METHODS AND RESULTS

Probucol inhibited cholesterol efflux up to 80% in J774 macrophages expressing ABCA1. In Fu5AH hepatoma cells that contain scavenger receptor class B, type I, but not functional ABCA1, we observed no effect of probucol on cholesterol efflux. Probucol inhibited cholesterol efflux from normal human skin fibroblasts but not from fibroblasts from a Tangier patient. Fluorescent confocal microscopy and biotinylation assay demonstrated that in J774 cells probucol impaired the translocation of ABCA1 from intracellular compartments to the plasma membrane. Probucol also inhibited the formation of an ABCA1-linked cholesterol oxidase sensitive plasma membrane domain. Consistent with the inhibitory effect on ABCA1 translocation to the plasma membrane, probucol reduced cell surface-specific [125I]-labeled apolipoprotein-AI binding.

CONCLUSIONS

We conclude that probucol is an effective inhibitor of ABCA1-mediated cholesterol efflux without influencing scavenger receptor class B type I-mediated efflux. The inhibition of ABCA1 translocation to the plasma membrane may in part explain the reported in vivo high-density lipoprotein-lowering action of probucol.

Protection of chylomicron remnants from oxidation by incorporation of probucol into the particles enhances their uptake by human macrophages and increases lipid accumulation in the cells

The effects of protection of chylomicron remnants from oxidation on their uptake and induction of lipid accumulation in macrophages were investigated using chylomicron remnant-like particles (CRLPs) containing the lipophilic antioxidant drug, probucol, and macrophages derived from the human monocyte cell line, THP-1. The total lipid content of THP-1 macrophages was markedly higher (x2.2) after 48 h of incubation of THP-1 macrophages with CRLPs containing probucol (pCRLPs) when compared to CRLPs without probucol, and this was because of increases in triacylglycerol (x2.3) and cholesterol (x1.8) levels, while cholesteryl ester concentrations were not significantly changed. Determination of the uptake of CRLPs and pCRLPs by the cells using particles labelled with the fluorescent probe 1,1'-dioctadecyl-3,3,3'3'-tetramethylindo-carbocyanine perchlorate showed that pCRLPs are taken up at a faster rate than CRLPs. The synthesis of triacylglycerol, as measured by the incorporation of [(3)H]oleate and [(3)H]glycerol, was also increased in macrophages incubated with pCRLPs as compared to CRLPs without probucol, but phospholipid and cholesteryl ester formation from [(3)H]oleate was unaffected. In addition, no differences between the effects of CRLPs and pCRLPs on the expression of mRNA for a range of genes believed to be involved in lipoprotein uptake, intracellular lipid metabolism and the efflux of cholesterol from macrophages was detected. These results suggest that antioxidants carried in chylomicron remnants enhance lipid accumulation in macrophages by increasing the rate of uptake of the particles and raising the intracellular synthesis of triacylglycerol, but not cholesteryl ester, and that these effects are brought about by changes at the post-transcriptional level. Antioxidants carried in chylomicron remnants therefore may promote the development of atherosclerosis, and this is likely to be particularly important in conditions where clearance of remnants from the circulation is delayed.

The effect of probucol on atherosclerosis in streptozotocin-induced diabetic-hyperlipidemic APA hamsters in different stages of atherosclerosis

We investigated the effect of probucol (PB) on atherosclerosis in streptozotocin (SZ)-induced diabetic-hyperlipidemic APA hamsters in three different stages, the early, middle and late stages of atherosclerosis. Male APA hamsters were injected intraperitoneally with SZ or vehicle alone (citrate buffer; CB) as a control at the age of 8 weeks. At 6 weeks after injection (WAI) of SZ or CB (the early stage), 14 WAI (the middle stage) and 26 WAI (the late stage), animals were assigned to PB treated- or non-treated groups (CBPB, SZPB, CB, SZ). After 8 weeks of PB administration with diet, the aorta was taken from each animal for assessment of atheromatous lesions and blood samples were subjected to serum biochemical analysis and the measurement of blood lipid peroxide (LPO). In the middle stage, PB treatment significantly decreased serum total cholesterol level, slightly decreased LPO, and also tended to reduce the lesion area, although no statistical difference was seen. There was no marked effect of PB treatment in the early and late stages. These findings suggest that single use of PB has little effect on atherosclerosis of a hyperglycemia-hyperlipidemia animal model.

Antioxidative and hypolipidemic effects of barley leaf essence in a rabbit model of atherosclerosis

The antioxidative and hypolipidemic effects of barley leaf essence (BL) were investigated in a rabbit model of atherosclerosis. Twenty-four New Zealand White male rabbits were assigned randomly into four dietary groups. The normal group was fed regular rabbit chow and the control group was fed a chow containing 0.5% cholesterol and 10% corn oil. The BL group and the probucol group were fed the same diet as the control group plus 1% (w/w) BL or 1% (w/w) probucol, respectively. The plasma levels of total cholesterol, triacylglycerol, lucigenin-chemiluminescence (CL) and luminol-CL were increased in the control group compared to the normal group; and they were decreased in the BL group and the probucol group compared to the control group. The value of T50 of red blood cell hemolysis and the lag phase of low-density lipoprotein oxidation increased in the BL group and in the probucol group compared to the controls. Ninety percent of the intimal surface of the thoracic aorta was covered with atherosclerotic lesions in the control group, but only 60% of the surface was covered in the BL group. This 30% inhibition of hyperlipidemic atherosclerosis by BL was associated with a decrease in plasma lipids and an increase in antioxidative abilities (as measured by T50, lag phase and CL). These results suggest that the antioxidant and hypolipidemic effects of BL could be useful in the prevention of cardiovascular disease in which atherosclerosis is important.