Correlation of fasting serum apolipoprotein B-48 with coronary artery disease prevalence.

BACKGROUND: Postprandial hyperlipidemia partially refers to the postprandial accumulation of chylomicrons and chylomicron remnants (CM-R). Many in vitro studies have shown that CM-R has highly atherogenic properties, but consensus is lacking on whether CM-R accumulation correlates with the development of atherosclerotic cardiovascular diseases. We investigated the correlation between CM-R accumulation and the prevalence of coronary artery disease (CAD). DESIGN: Subjects who received a coronary angiography and did not take any lipid-lowering drugs (n = 189) were enrolled. Subjects with coronary artery stenosis (≥ 75%) were diagnosed as CAD. Biochemical markers for glucose and lipid metabolism including fasting apolipoprotein (apo) B-48 concentration were compared between CAD patients (n = 96) and age-, sex-, and body mass index (BMI)-matched non-CAD subjects without overt coronary stenosis (< 75%) (n = 67). We tried to determine which metabolic parameters were correlated with the prevalence of CAD by multiple logistic regression analysis, and whether or not the combination of high apo B-48 and other coronary risk factors (high triglyceride, low HDL-C, high HbA1c or low adiponectin levels) increased the prevalence of CAD. RESULTS: Fasting serum apo B-48 levels were significantly higher in CAD patients than in non-CAD subjects (3·9 ± 2·4 vs. 6·9 ± 2·6 µg/mL, P < 0·0001) and had the most significant correlation with the existence of CAD. The clustering of high fasting apo B-48 levels (> 4·34 µg/mL, the cut-off value) and other coronary risk factors were found to be associated with a stronger risk of CAD compared with single high fasting apo B-48 levels. CONCLUSION: Fasting serum apo B-48 levels significantly correlated with the prevalence of CAD.

Adiponectin accelerates reverse cholesterol transport by increasing high density lipoprotein assembly in the liver.

Plasma high density lipoprotein (HDL)-cholesterol levels are negatively correlated with the incidence of coronary artery disease. HDL plays an important role in protecting against atherosclerosis by removing cholesterol from atheroma and transporting it back to the liver. The ATP-binding cassette transporters (ABCA1 and ABCG1) and scavenger receptor BI (SR-BI) are thought to be one of the rate-limiting factors to generate HDL in the liver. Adiponectin (APN) secreted from adipocytes is also one of the important molecules to inhibit the development of atherosclerosis. Recently, it has been reported that plasma HDL-cholesterol levels are positively correlated with plasma APN concentrations in humans. Therefore, we investigated the association of APN with HDL assembly in the liver. Human hepatoma cell line, HepG2 cells, were incubated for 24h in the culture medium with the indicated concentrations of recombinant APN. APN enhanced the mRNA level of apolipoprotein A-I (apoA-I) in HepG2 cells and increased the secretion of apoA-I from the cells to the medium. Furthermore, APN increased both mRNA and protein levels of ABCA1, but not ABCG1 and SR-BI, in HepG2 cells. Taken together, the current study demonstrates that APN might protect against atherosclerosis by increasing HDL assembly through enhancing ABCA1 pathway and apoA-1 synthesis in the liver.

Senescent phenotypes of skin fibroblasts from patients with Tangier disease.

Tangier disease (TD) is characterized by a deficiency of high density lipoprotein (HDL) in plasma and patients with TD have an increased risk for coronary artery disease (CAD). Recently, we reported that fibroblasts from TD exhibited large and flattened morphology, which is often observed in senescent cells. On the other hand, data have accumulated to show the relationship between cellular senescence and development of atherosclerotic CAD. The aim of the present study was to investigate whether TD fibroblasts exhibited cellular senescence. The proliferation of TD fibroblasts was gradually decreased at population doubling level (PDL) approximately 10 compared with control cells. TD cells practically ceased proliferation at PDL approximately 30. DNA synthesis was markedly decreased in TD fibroblasts. TD cells exhibited a higher positive rate for senescence-associated beta-galactosidase (SA-beta-gal), which is one of the biomarkers of cellular senescence in vitro. These data showed that TD cells reached cellular senescence at an earlier PDL compared with controls. Although, there was no difference in the telomere length of fibroblasts between TD and controls at the earlier passage (PDL 6), the telomere length of TD cells was shorter than that of controls at the late passage (PDL 25). Taken together, the current study demonstrates that the late-passaged TD fibroblasts showed senescent phenotype in vitro, which might be related to the increased cardiovascular manifestations in TD patients.

Probucol enhances the expression of human hepatic scavenger receptor class B type I, possibly through a species-specific mechanism.

OBJECTIVE: Scavenger receptor class B type I (SR-BI) is a major receptor for high-density lipoproteins (HDL) in the liver, which is the terminus of reverse cholesterol transport. Overexpression of SR-BI attenuated experimental atherosclerosis in murine models, concomitant with a reduction in plasma HDL-cholesterol levels. Probucol is known to be a potent hypolipidemic drug to regress xanthoma formation and carotid atherosclerosis in conjunction with a marked reduction in HDL-cholesterol levels. The aim of the present study was to know the effect of probucol on the expression of SR-BI and the underlying mechanism. METHODS AND RESULTS: We found that probucol increased the expression of SR-BI proteins in in vitro human liver cells and an in vivo rabbit model, but not in wild-type C57Bl6 mice. The decay curve of SR-BI protein was markedly retarded in probucol-treated HepG2 cells in the presence of cycloheximide, indicating that probucol may stabilize human SR-BI protein. To determine the underlying mechanism for the observed species-specific effect, we conducted the following host-swap experiments, in which SR-BI was transfected or expressed in heterologous cells or hosts. Probucol did not increase human SR-BI protein in the liver of transgenic mice carrying the entire human SR-BI genome. Although probucol could stabilize even murine SR-BI, when transfected into a human cell line, HepG2, human SR-BI was not stabilized in a mouse hepatoma cell line, Hepa 1-6, treated with probucol. CONCLUSIONS: Probucol enhances hepatic SR-BI protein expression, possibly through species-specific stabilization of the protein.

Familial massive tendon xanthomatosis with decreased high-density lipoprotein-mediated cholesterol efflux.

We experienced a family with novel massive tendon xanthomatosis which can be excluded from known disease causing xanthomatosis. The proband was a 58-year-old man who had necrosis in his massive Achilles tendon xanthoma. Three of 5 brothers including him and his nephew had the same clinical phenotype. The systemic tendon xanthomatosis became apparent around 30 years of their age. The proband and his elder brother had mild elevations of serum total cholesterol level (251 and 228 mg/dL, respectively). The low-density lipoprotein receptor activity of the proband's lymphocytes was normal. Neither plant sterol nor cholestanol level was increased in the proband's plasma. Magnetic resonance image of the proband's Achilles tendon demonstrated a massive expansion of the soft tissue with salami sausage-like appearance in his heels (50 mm in thickness). The physiological function of macrophages (MPhi) from the patients was investigated to clarify the mechanism for the formation of xanthomatosis. There was no significant difference in the uptake of oxidized low-density lipoprotein between the proband's MPhi and the control. High-density lipoprotein 3-mediated cholesterol efflux from the patients' MPhi (n = 2) was significantly reduced compared with the controls (n = 3), whereas there was no difference in apolipoprotein (apo) A-I-mediated cholesterol efflux between the patients' MPhi and the controls. Furthermore, there was no reduction of the messenger RNA levels of ATP-binding cassette transporter 1 (ABCA1), which is involved in apo A-I-mediated cholesterol efflux, in the proband's MPhi compared with the control. The present study demonstrates that the mechanism for the formation of novel familial massive tendon xanthomatosis may be, at least in part, associated with decreased high-density lipoprotein 3, but not free apo A-I-mediated cholesterol efflux from MPhi in vivo.

Human scavenger receptor class B type I is expressed with cell-specific fashion in both initial and terminal site of reverse cholesterol transport.

The reverse cholesterol transport (RCT) is one of the major protective systems against atherosclerosis, in which high-density lipoprotein (HDL) removes cholesterol from lipid-laden cells and delivers it to the liver. Scavenger receptor class B type I (SR-BI) is a HDL receptor in the liver and adrenal glands and is involved in the selective uptake of cholesteryl ester from HDL, which has been extensively, analyzed using rodent models. However, the expression and regulation of the human homologue of this receptor are not known yet. We previously reported that this receptor is expressed in in vitro differentiated macrophages and its expression is up-regulated by the addition of modified lipoproteins into the medium [Hirano K, Yamashita S, Nakagawa Y, et al. Expression of human scavenger receptor class B type I in cultured human monocyte-derived macrophages and atherosclerotic lesions. Circ Res 1999;85:108-16]. In order to further investigate the physiological significance of this receptor in humans, we have performed extensive immunohistochemical analyses with specimens of the liver and adrenal glands as well as arteries with different stages of atherosclerotic lesions. In human liver and adrenal glands, a positive SR-BI immunoreactivity was detected in both hepatic and adrenal parenchymal cells as well as Kupffer cells. These parenchymal cells had a strong signal on the cell surface, whereas Kupffer cells showed a heterogeneous and punctate pattern. In human aorta and coronary arteries, SR-BI was highly expressed in atherosclerotic plaques, but not in non-atherosclerotic lesions. Double immunostaining revealed that SR-BI was expressed in a subpopulation of macrophages, of which staining pattern was similar to that observed in Kupffer cells. These data clearly demonstrated that SR-BI was expressed with cell-specific fashions in both the initial and terminal step of RCT in humans. Thus, SR-BI might be physiologically relevant and have distinct tissue-specific functions.

Dominant expression of ATP-binding cassette transporter-1 on basolateral surface of Caco-2 cells stimulated by LXR/RXR ligands.

ATP-binding cassette transporter-1 (ABCA1) is a cause of Tangier disease, which is a familial deficiency of plasma high density lipoproteins (HDL). This molecule is known to be expressed in the multiple tissues and organs including small intestines, liver, and macrophages in the blood vessels. Recent in vivo studies suggested that ABCA1 plays some roles in the flux of cholesterol in the intestines. One of the major questions to understand the roles of ABCA1 in the intestines is the expression pattern in the intestinal epithelial cells. To address this issue, we have investigated the expression and regulation of ABCA1 in Caco-2 cells cultured on Transwell as a model, especially focusing on possible polarized expression of ABCA1. The expression of ABCA1 was up-regulated during the differentiation and under the stimulation of LXR/RXR by the addition of 9-cis-retinoic acid (9-cis-RA) and 22-R-hydroxycholesterol (22-OH). Apolipoprotein-AI-mediated cholesterol efflux was dominant toward the basolateral side of polarized cells when stimulated by 9-cis-RA and 22-OH. The cell surface biotinylation experiment followed by Western blot analyses demonstrated a markedly dominant expression of ABCA1 on the basolateral surface, which was clearly confirmed by the confocal laser scanning microscopy. In conclusion, the present study demonstrates that ABCA1 is dominantly expressed on the basolateral surface of Caco-2 cells tested, suggesting that this molecule may play a role in the basolateral movement of cholesterol at least when stimulated by LXR/RXR ligands.