Effects of injury on apoB kinetics and concentration in rabbit aorta

Role of reactive oxygen species in inhibition of endothelial cell migration by oxidized low-density lipoprotein

OBJECTIVE

Endothelial cell migration is inhibited by oxidized low-density lipoprotein (oxLDL) and lysophosphatidylcholine (lysoPC). The purpose of this study was to explore the mechanism of this inhibition, specifically the role of reactive oxygen species.

METHODS

The ability of oxLDL, lysoPC, and known superoxide generators to stimulate endothelial cell production of reactive oxygen species and inhibit endothelial cell migration under the same conditions was assessed. Reactive oxygen species production was assessed with dichlorofluorescein. Migration was studied with a razor scrape assay and measured after 24 hours. In addition, the ability of various antioxidants, added before initiation of the scrape assay, to restore endothelial cell migration in oxLDL was determined.

RESULTS

OxLDL and lysoPC, at concentrations that stimulated reactive oxygen species production, also inhibited endothelial cell migration. Other agents that generated superoxide also inhibited endothelial cell migration, but hydrogen peroxide did not. Of a variety of antioxidants assessed for their ability to preserve endothelial cell migration in the presence of oxLDL, only superoxide dismutase and reduced nicotinamide adenine dinucleotide (phosphate) oxidase inhibitors (diphenyleneiodonium, quinacrine, hydralazine) preserved endothelial cell migration.

CONCLUSIONS

These data suggest that oxLDL inhibits endothelial cell migration through a superoxide-dependent mechanism and that reduced nicotinamide adenine dinucleotide (phosphate) oxidase is the cellular source of the superoxide.

CLINICAL RELEVANCE

OxLDL inhibits endothelial cell migration, and may impair healing of arterial injuries. The mechanism of oxidized LDL inhibition is not known. Our in vitro studies show that the inhibitory properties are related to production of reactive oxygen species. Superoxide dismutase or inhibitors of reduced nicotinamide adenine dinucleotide phosphate oxidase can preserve endothelial migration in the presence of oxLDL. This might improve the healing of endothelial injuries at sites of arterial repair or angioplasty, especially in lipid-laden arterial walls.

Metabolic evidence for sequestration of low-density lipoprotein in abdominal aorta of normal rabbits

In rabbits, atherosclerosis develops preferentially at branch sites compared with the adjacent uniform aorta. This study investigated the hypothesis that low-density lipoprotein (LDL) is "sequestered" (present in a form that exchanges slowly with plasma LDL) in the aortas of normal rabbits and that more LDL is sequestered at branch sites. Thus 33 normal rabbits were injected with LDL labeled with (125)I-labeled tyramine cellobiose ((125)I-TC) to trace both undegraded LDL and aortic LDL degradation products. For 25 rabbits, LDL was also labeled with (131)I to trace undegraded LDL alone. The time-dependent aortic (125)I-TC and (131)I accumulation was determined from 0.6 to 120 h after injection. Compartmental modeling provided metabolic evidence for sequestration of LDL at the branch (P < 0.01) and uniform (P < 0.005) abdominal aorta. Concentrations of sequestered LDL were 109 +/- 28% higher (P < 0.0005) for branch sites. LDL mean residence time was 23.5 +/- 3.1 h for branch sites, 7.6 +/- 3.5 h longer (P < 0.05) than for the uniform abdominal aorta. Enhanced retention of higher concentrations of sequestered LDL at branch sites could account for the increased susceptibility of these aortic sites to atherosclerosis.

Isradipine lowers human arterial low density lipoprotein retention in vivo

During the recent past it has been discussed that calcium antagonists may exert antiatherosclerotic actions at the vessel wall. Apolipoprotein B containing lipoproteins were isolated by immunoaffinity chromatography and radiolabeled with 123-iodine. The effect of 2 x 2.5 mg isradipine on the low density lipoproteins (LDL) entry into the carotid and femoral arteries of 12 hypertensive patients with primary hyperlipoproteinemia (total cholesterol >6.5 mmol/l [250 mg/dL) was examined. Cholesterol -1.7% (P< 0.05 664), high density lipoprotein (HDL) cholesterol +4.5% (P< 0.01 123), and LDL cholesterol -1% (P< 0.01 563) did not change, nor did any of the safety parameters. The types of entry kinetics reflecting vascular surface lining did not change while the LDL retention 20 h after tracer application was depressed by up to 23.5%. The data were comparable in the carotid and femoral artery segments, the significance level ranging up to 0.0009. These results indicate a decreased LDL retention in the arterial wall of hypertensive patients induced by isradipine. The clinical implications of the findings ought to be pursued in properly designed clinical trials.

Delivery of benzoporphyrin derivative, a photosensitizer, into atherosclerotic plaque of Watanabe heritable hyperlipidemic rabbits and balloon-injured New Zealand rabbits

In this study we compared the plasma distribution and arterial accumulation of a photosensitizer, benzoporphyrin derivative (BPD), in two models of atherosclerosis: the spontaneous lesions of the Watanabe heritable hyperlipidemic (WHHL) rabbit and induced lesions of the balloon-injured, cholesterol-fed New Zealand white (NZW) rabbit. Selective uptake and retention of a photosensitizer by the abnormal portion of a vessel is a necessity in order for photodynamic therapy to become a successful modality for inhibition of intimal hyperplasia, selective removal of atherosclerotic tissue or imaging of diseased arteries. Liposome-based formulations were compared to freshly isolated native low density lipoprotein (LDL) and acetylated-LDL (Ac-LDL) as delivery vehicles for BPD. Plasma distribution of the photosensitizer was analyzed by KBr density gradient ultracentrifugation. Although the delivery vehicle influenced plasma distribution immediately postinjection, BPD subsequently partitioned according to the plasma concentration of the lipoproteins. Photosensitizer level in plaque and normal artery specimens was determined by ethyl acetate extraction and spectrofluorometric measurement. The measurement of BPD in normal and atherosclerotic arterial tissue demonstrated a selective accumulation in atherosclerotic tissue. Preassociation with LDL and Ac-LDL enhanced accumulation of BPD in atherosclerotic tissue when compared with normal artery (mean ratios of 2.8 and 4.1 were achieved, respectively). These results indicate that the preferential uptake of BPD by atherosclerotic plaque can be enhanced by preassociation with plasma lipoproteins, suggesting that light activation could lead to a highly selective destruction of diseased vascular tissue.