Marked neointimal lipoprotein lipase increase in distinct models of proclivity to atherosclerosis: a feature independent of endothelial layer integrity

Lipoprotein lipase: Biosynthesis, regulatory factors, and its role in atherosclerosis and other diseases

Lipoprotein lipase (LPL) is a rate-limiting enzyme that catalyzes hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins including chylomicrons (CM), low-density lipoproteins (LDL) and very low-density lipoproteins (VLDL). A variety of parenchymal cells can synthesize and secrete LPL. Recent studies have demonstrated that complicated processes are involved in LPL biosynthesis, secretion and transport. The enzyme activity of LPL is regulated by many factors, such as apolipoproteins, angiopoietins, hormones and miRNAs. In this article, we also reviewed the roles of LPL in atherosclerosis, coronary heart disease, cerebrovascular accident, Alzheimer disease and chronic lymphocytic leukemia. LPL in different tissues exerts differential physiological functions. The role of LPL in atherosclerosis is still controversial as reported in the literature. Here, we focused on the properties of LPL derived from macrophages, endothelial cells and smooth muscle cells in the vascular wall. We also explore the existence of crosstalk between LPL and those cells when the molecule mainly plays a proatherogenic role. This review will provide insightful knowledge of LPL and open new therapeutic perspectives.

Lipid lowering effect of antioxidant alpha-lipoic Acid in experimental atherosclerosis

Accumulating data demonstrated that hypercholesterolemia and oxidative stress play an important role in the development of atherosclerosis. In the present study, a protective activity of alpha-lipoic acid; a metabolic antioxidant in hypercholesterolemic-induced animals was investigated. Eighteen adult male New Zealand White (NZW) rabbit were segregated into three groups labelled as group N, HCD and ALA (n = 6). Group N (normal control) was fed with normal chow, the rest (HCD and ALA) were fed with 100 g/head/day of 1% cholesterol rich diet to induce hypercholesterolemia. Four point two mg/body weight of alpha lipoic acid was concomintantly supplemented to the ALA group. Drinking water was given ad-libitum. The study was designed for 10 weeks. Blood sampling was taken from the ear lobe vein at the beginning, week 5 and week 10. Plasma was prepared for lipid profile estimation and microsomal lipid peroxidation index indicated with malondialdehyde (MDA) formation. At the end of the experiment, the animals were sacrificed and the aorta were excised for intimal lesion analysis. The plasma total cholesterol (TC) and low density lipoprotein (LDL) levels were found to be significantly low in ALA group compared to that of the HCD group (p<0.05). Similarly, low level of MDA (p<0.05) in ALA group was observed compared to that of the HCD group showing a significant reduction of lipid peroxidation activity. Histomorphometric intimal lesion analysis of the aorta showing less of atheromatous plaque formation in alpha lipoic acid supplemented group (p<0.05) compared to HCD group. These findings suggested that alpha lipoic acid posses a dual lipid lowering and anti-atherosclerotic properties indicated with low plasma TC and LDL levels and reduction of athero-lesion formation in hypercholesterolemic-induced rabbits.

Alpha lipoic acid possess dual antioxidant and lipid lowering properties in atherosclerotic-induced New Zealand White rabbit

There is accumulating data demonstrated hypercholesterolemia and oxidative stress play an important role in the development of atherosclerosis. In the present study, a protective activity of alpha-lipoic acid; a metabolic antioxidant in hypercholesterolemic-induced animals was investigated. Eighteen adult male New Zealand White (NZW) rabbit were segregated into three groups labelled as group K, AT and ALA (n=6). While group K was fed with normal chow and acted as a control, the rest fed with 100 g/head/day with 1% high cholesterol diet to induce hypercholesterolemia. 4.2 mg/body weight of alpha lipoic acid was supplemented daily to the ALA group. Drinking water was given ad-libitum. The study was designed for 10 weeks. Blood sampling was taken from the ear lobe vein at the beginning of the study, week 5 and week 10 and plasma was prepared for lipid profile estimation and microsomal lipid peroxidation index indicated with malondialdehyde (MDA) formation. Animals were sacrificed at the end of the study and the aortas were excised for intimal lesion analysis. The results showed a significant reduction of lipid peroxidation index indicated with low MDA level (p<0.05) in ALA group compared to that of the AT group. The blood total cholesterol (TCHOL) and low density lipoprotein (LDL) levels were found to be significantly low in ALA group compared to that of the AT group (p<0.05). Histomorphometric intimal lesion analysis of the aorta showing less of atheromatous plaque formation in alpha lipoic acid supplemented group (p<0.05) compared to that of AT group. These findings suggested that apart from its antioxidant activity, alpha lipoic acid may also posses a lipid lowering effect indicated with low plasma TCHOL and LDL levels and reduced the athero-lesion formation in rabbits fed a high cholesterol diet.

Localized vessel expression of lipoprotein lipase in rabbits leads to rapid lipid deposition in the balloon-injured arterial wall

Recent studies on mice demonstrated that lipoprotein lipase (LPL) located in the arterial wall might play a pro-atherogenic role. There are major differences between humans and mice in lipoprotein metabolism and in susceptibility to atherosclerosis. We have therefore used rabbits fed normal chow diet as a model to assess such localized effects by adenovirus-mediated gene transfer of human catalytically active wild type LPL (hLPLwt) and an inactive mutant (hLPL194) to balloon-injured carotid arteries. By morphometric analysis on cryosections stained with Oil Red O (ORO) we found 7- and 4-fold increases, respectively, of lipid deposition in the arterial walls 7 days after infection with adenovirus expressing hLPLwt or hLPL194, when compared with a virus expressing human alkaline phosphatase (hAP) as control. Macrophages were detected in the arteries expressing both forms of LPL, but apoB was only found in arteries expressing hLPLwt. Expression of the LPL gene products was transient and was gone after 2 weeks, but the accumulated lipid deposits remained between the neointimal and the media layers even after 8 weeks. Our data demonstrate that expression of LPL in the arterial wall (with or without lipase activity) leads to lipid accumulation in balloon-injured rabbit arteries, and could result in enhanced formation of atherosclerotic lesions.

Involvement of endothelium and endothelin-1 in lead-induced smooth muscle cell dysfunction in rats

Lead exposure induces dysfunction of the cyclic guanosine monophosphate-dependent vasodilator system through downregulation of soluble guanylate cyclase (sGC) expression. The endothelium not only releases vasodilators but also vasoconstrictors such as endothelin-1 (ET-1). Our aim was to explore the role of the vascular endothelium and ET-1 as possible mediators of lead-induced downregulation of sGC. Isolated aortic segments from Wistar Kyoto rats were incubated in the presence or absence of lead (1 parts per million) for 24 h. Endothelium was mechanically removed in some of the aorta segments. As reported previously, lead exposure induced downregulation of sGC protein expression in the intact aortic segments. However, lead exposure failed to significantly modify sGC-beta1 subunit expression in the endothelium-denuded aortic segments. Incubation with a selective ETA-type receptor inhibitor, BQ-123 (10(-6) mol/l), restored sGC protein expression in lead-exposed intact aortic segments. As it has also been previously observed, incubation in lead-containing medium resulted in the upregulation of cyclooxygenase-2 (COX-2) in the intact aortic segments. Denudation of endothelium partially abrogated this effect of lead. Incubation with BQ-123 prevented the lead-induced upregulation COX-2 in the intact aortic segments. However, neither ET-1 content nor ETA-type receptor expression were modified by lead exposure of the aortic segments. As conclusion, the endothelium through the activation of ETA-type receptors mediates the downregulation of sGC expression by lead in the vascular wall.

Sialic acid as a protective barrier against neointima development

Arterial sialic acid (SA) has been shown to attenuate the binding of fibrinogen and low-density lipoproteins (LDL) to the vessel wall, presumably protecting against atherosclerosis. This study was aimed to assess the effect of changes in SA content in intimal thickening, an early step in the development of atherosclerosis. New Zealand white rabbits were subjected to bilateral carotid periarterial collaring, followed by in situ-perfusion with neuroaminidase (random artery) and with vehicle (contralateral control artery). The efficiency of SA removal was evaluated in perfusates and arterial homogenates, and arterial tissue samples were obtained 7 and 14 days after the intervention to assess morphological changes. Neuraminidase significantly reduced SA by 16.7%. Arterial desialylation was associated with a significantly increased neointimal formation. Proliferation of smooth muscle cells (SMCs), assessed by incorporation of bromo-2'-deoxyuridine into replicating DNA was also significantly increased in desialylated arteries. In addition, immunohistochemical studies showed a slightly stronger oxidized-LDL (ox-LDL) immunostaining in neointima of desialylated arteries than in control vessels. A mild reduction of SA increases intimal thickening, at least partly due to an enhanced proliferation of SMCs, and may facilitate the accretion of atherogenic lipoproteins, providing evidence for the potential role of SA in the protection against neointimal development.