Native and oxidized LDL enhances production of PDGF AA and the surface expression of PDGF receptors in cultured human smooth muscle cells

Hyperlipidaemia in renal transplantation--risk factor for long-term graft outcome

The role of hyperlipidaemia for the outcome of renal transplantation was evaluated in a prospective study involving 151 patients. Graft losses were associated with more pronounced pre-transplant lipid abnormalities. An increased risk of graft loss during the first two post-transplant years was found in patients with marked pre-transplant hypercholesterolaemia (> or = 6.9 mmol L-1, P = 0.014; relative risk 2.2). Hypercholesterolaemia > or = 6.9 mmol L-1 at 6 months after transplantation, present in 41/115 patients, was associated with a lower GFR (P = 0.007) and more pronounced albuminuria (P = 0.009) at 2 years. In patients with graft dysfunction (serum creatinine > 160 mumol L-1) at 2 years, more pronounced lipid abnormalities before and at 6 months after transplantation were found. Between 6 months and 2 years, total and LDL cholesterol did not change significantly, but HDL cholesterol decreased (P = 0.03). In conclusion, hyperlipidaemia is also a risk factor for the long-term outcome in renal transplantation. Further investigations are needed to determine whether graft losses and late graft failure can be prevented or ameliorated by treating hyperlipidaemia in renal transplantation.

Oxidized low density lipoprotein stimulates collagen production in cultured arterial smooth muscle cells

We examined the interactive effect of oxidized low density lipoprotein (LDL) and ascorbic acid on collagen production in cultured smooth muscle cells (SMCs). Porcine aortic SMCs were incubated with 50-200 micrograms/ml of human LDL with/without 5 microM Cu2+ for 24 h. Collagen production was assayed by successive salt precipitation at acidic and neutral pH after pepsin digestion of 3H-proline-labeled collagenous protein. Oxidation of LDL was evaluated by electrophoresis and by the level of thiobarbituric acid reactive substances (TBARS). Ascorbic acid reduced the oxidation of LDL + Cu2+ (53% reduction). In the presence of ascorbic acid, no differences were noted in collagen production between LDL and LDL + Cu2+. Without ascorbic acid, collagen production with LDL + Cu2+ was increased dose-dependently up to 6-fold with 150 micrograms/ml LDL, while no such effects were observed at any doses of native LDL. The addition of butylated hydroxytoluene to LDL + Cu2+ strongly suppressed oxidation (88% reduction), and significantly reduced collagen production close to that seen with native LDL. These results indicate that oxidized LDL stimulates collagen production in SMCs, while native LDL does not. Therefore, oxidized LDL may play a direct role in stimulating collagen production in SMCs, which could lead to collagenosis in atherosclerosis.

Allele-specific increase in basal transcription of the plasminogen-activator inhibitor 1 gene is associated with myocardial infarction

Increased plasminogen-activator inhibitor 1 (PAI-1) activity is a common finding in patients with coronary heart disease. Here we provide evidence for an independent, etiological role of PAI-1 in myocardial infarction. The 4G allele of a recently described common 4/5-guanine-tract (4G/5G) polymorphism in the PAI-1 promoter is associated with higher plasma PAI-1 activity. The prevalence of the 4G allele is significantly higher in patients with myocardial infarction before the age of 45 than in population-based controls (allele frequencies of 0.63 vs. 0.53). Both alleles bind a transcriptional activator, whereas the 5G allele also binds a repressor protein to an overlapping binding site. In the absence of bound repressor, the basal level of PAI-1 transcription is increased.

Effect of alpha-tocopherol on restenosis after angioplasty in a model of experimental atherosclerosis

The ability of alpha-tocopherol to reduce restenosis after angioplasty was tested in a rabbit model in which angioplasty was performed on established atherosclerotic lesions. Lesions induced by 4 wk of cholesterol feeding after focal desiccation of femoral arteries were balloon dilated. 3 wk after angioplasty, angiographically determined minimum luminal diameters were less in the untreated group (0.80 +/- 0.51 mm) than in the group treated with oral alpha-tocopherol beginning 19 d before angioplasty (1.38 +/- 0.29 mm; P < 0.01). The cross-sectional area of the intima-media was greater in the untreated group (1.18 +/- 0.48 mm2) than in the alpha-tocopherol group (0.62 +/- 0.25 mm2, P < 0.0001). These differences were not due to vasoconstriction or altered plasma cholesterol. Alpha-tocopherol thus reduced restenosis after angioplasty in this model. In rabbit vascular smooth muscle cells, oxidized low density lipoprotein stimulated DNA synthesis. Alpha-tocopherol treatment inhibited DNA synthesis stimulated by oxidized low density lipoprotein, but not by serum. The findings are consistent with the hypothesis that oxidized lipids can stimulate hyperplasia and that antioxidants may limit hyperplasia by inhibiting either the oxidation or the proliferative effects of oxidants on cells.

Effects of angiopeptin on transplant arteriosclerosis in the rat

The influence of the somatostatin analogue angiopeptin on transplant arteriosclerosis was investigated using two aortic transplantation rat models. One was characterized by ischemia/reperfusion-induced changes in syngeneic transplants while immunologically induced changes dominated in the other allogeneic model. Angiopeptin, 100 micrograms/kg per day, was administered continuously until the sacrifice of the rats after 8 weeks. No additional immunosuppression was used in either model. An image analysis system was used to quantify the intimal and medial thicknesses of the grafts. In the syngeneic grafts, the intimal thickness was less than 50% of that of control grafts (P < 0.05), but no difference was seen in the allogeneic model. The expression of selected cells, TGF-beta s, and PDGF and PDGF alpha-receptors was detected immunohistochemically and displayed a similar picture in control and angiopeptin-treated grafts in both models. We conclude that angiopeptin has no clear immunosuppressive properties but may counteract ischemia-induced transplant arteriosclerosis.

Different functions of the platelet-derived growth factor-alpha and -beta receptors for the migration and proliferation of cultured baboon smooth muscle cells

Migration of medial smooth muscle cells (SMCs) and their proliferation in the intima contribute to thickening of injured and atherosclerotic vessels. These events have been proposed to be regulated in part by platelet-derived growth factor (PDGF). Two separate PDGF receptors have been identified, PDGF-R alpha and PDGF-R beta. To study the functions of PDGF-R alpha and PDGF-R beta in vascular SMCs, neutralizing monoclonal antibodies (mAbs) specific for each of the two receptors were used. These antibodies allowed us to evaluate the role of each receptor for PDGF-induced proliferation and migration of cultured baboon SMCs. Both PDGF-AA and PDGF-BB stimulated SMC growth, with PDGF-BB being more potent than PDGF-AA. Studies with anti-PDGF-R alpha and anti-PDGF-R beta mAbs revealed that both PDGF receptors promoted the stimulatory signals for proliferation. In contrast, PDGF-BB stimulated SMC migration, whereas PDGF-AA had no stimulatory activity on its own. Additionally, PDGF-AA was able to suppress migration induced by PDGF-BB or fibronectin in modified Boyden's chamber assay. When PDGF-BB-induced migration was separated into chemotactic and chemokinetic activities, only the chemotactic component was inhibited by PDGF-AA. The suppression of SMC migration by PDGF-AA was eliminated by anti-PDGF-R alpha mAb. In addition, PDGF-BB, in the presence of anti-PDGF-R beta, bound only to PDGF-R alpha and caused suppression of SMC migration induced by fibronectin. These results suggest that when activated by ligand binding, both PDGF-R alpha and PDGF-R beta stimulate proliferation. In contrast, only activation of PDGF-R beta stimulates migration, whereas ligand binding to PDGF-R alpha leads to inhibition of cell migration. These observations provide support for the conclusion that PDGF-R alpha and PDGF-R beta may play different roles in SMC function and may be involved in different regulatory mechanisms during vascular remodeling.

Lipoproteins and the haemostatic system in atherothrombotic disorders

The early belief that the haemostatic system has no active role in the formation of the atheromatous plaque is no longer tenable. Rather, the association between hypercholesterolaemia and atherosclerosis appears to arise in part because of various effects of high concentrations of LDL and VLDL particles on the cellular and humoral components of the system, thereby promoting plaque growth and thrombosis. These may be summarized as follows: 1. High concentrations of native LDL have been reported to promote the adhesion of monocytes to the endothelial cell, suggesting that the latter undergoes a form of activation upon such exposure. Oxidized LDL is more potent in this respect, and persistent exposure of endothelium to such particles can eventually lead to cell injury. 2. Activated endothelial cells acquire characteristics on their luminal surface conducive to thrombin generation and fibrin production. Thrombin has several actions on the endothelial cell, monocyte, smooth muscle cell and platelet which in the presence of hypercholesterolaemia will promote the formation of atheroma. 3. Oxidatively modified LDL can activate circulating monocytes, when they also acquire procoagulant properties which favour thrombin production. 4. Platelets show an increased tendency to aggregate when exposed to hypercholesterolaemic plasma. This effect may arise in part because the platelet of the hypercholesterolaemic patient expresses an increased number of fibrinogen binding sites on its surface following activation by agonists such as ADP. These hyperaggregable platelets adhere to activated endothelial cells which express von Willebrand factor on their surface, and to subendothelial proteins exposed in the gaps that open between injured endothelial cells. Platelets exposed to raised LDL levels also show a reduced sensitivity to prostacyclin, an antiaggregatory agent. Oxidatively modified LDL has been reported to stimulate aggregation of platelets in the absence of other agonists such as ADP or thrombin (spontaneous aggregation). 5. Platelet aggregation and fibrin deposition at sites of endothelial injury will create microthrombi which become incorporated into the lesion by organization, thereby increasing the fibrous and cellular content of the atheromatous plaque. 6. Lipolysis of triglyceride-rich lipoproteins at the endothelial cell surface leads to transient activation of the coagulation mechanism with activation of factor VII. Activated factor VII is a potent procoagulant when it forms a complex with tissue factor in the atheromatous lesion. Persistent hypertriglyceridaemia is accompanied by raised concentrations of factor X, factor IX, factor VII and prothrombin. 7. Hypertriglyceridaemia is associated with an increased plasma concentration of PAI-1 and a reduction in plasma fibrinolytic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Oxidized lipoproteins, altered cell function and atherosclerosis

A correlation between atherogenesis and lipoprotein oxidation was first suggested by experiments showing increased uptake by macrophages of oxidized LDL and oxidized LDL injury to cultured cells. Recent data which demonstrate the existence of oxidized lipoproteins in vivo, combined with studies showing a 'protective' effect of antioxidants against atherosclerosis progression, have greatly increased the interest in theories posing that lipoprotein oxidation is causally related to arterial disease. The fact that dozens of new compounds are produced upon the oxidation of low density lipoprotein has led, perhaps not surprisingly, to numerous discoveries in vitro of altered cell function induced by exposure of cells to oxidized LDL that are distinct from those resulting from exposure to native LDL. This brief overview will describe selected altered cell functions of oxidized lipoproteins and how they may impact on atherosclerosis.

Oxidation, lipoxygenase, and atherogenesis

Mounting evidence suggests that oxidative processes contribute to the pathogenesis of atherosclerosis and that antioxidants may represent a strategy to complement the lowering of lipids in the therapy of this disease. Although multiple molecular events have been identified in vitro and although it is tempting to ascribe multiple atherogenic properties to oxidized LDL, our understanding of this process remains incomplete. Further research is warranted in several areas. First, it will be important to selectively inhibit different aspects of the process to determine the relative contribution of various biological targets. In this regard pharmacological inhibition of 15-lipoxygenase in vivo in relevant animal models is required to address the question of the contribution of this enzyme to significant oxidative events. The lack of specific inhibitors has made this task more difficult. It will also be important to define the biologically active moiety of oxidized LDL to begin to determine the mechanisms through which it exerts its atherogenic effects. It is likely that alternate protein targets can be identified both downstream and upstream of the oxidative process. Research is only now beginning to elucidate the inflammatory mechanisms that account for the cellular response. Further research into adhesion events, cytokine profiles, and downstream effector molecules of the oxidative process are likely to identify alternate targets for therapeutic intervention.

Isolation of lipoprotein-proteoglycan complexes from balloon catheter deendothelialized aortas and the uptake of these complexes by blood monocyte-derived macrophages

Lipoprotein-Proteoglycan (LP-PG) complexes from the neointima, developed in response to injury, were studied to examine their ability to stimulate lipid accumulation in blood monocyte-derived macrophages (BMDM). LP-PG complexes were extracted from intimal-medial tissues from normal and balloon catheter deendothelialized aortas of normocholesterolemic rabbits, in 0.16 M NaCl for 24 h at 4 degrees C. The extract was purified through an anti-apo-B affinity column. Adsorbed material dissociated with 4 M Gu-HCI buffer was analyzed for lipoproteins (LP) and glycosaminoglycans (GAG). Results demonstrated that LP-PG complexes consisted of apo-B associated with chondroitin sulfate and hyaluronic acid. BMDM were incubated with 125I-LP, 125I-LP-NPG (from normal aortas) or 125I-LP-IPG (from injured aortas) for 20 h at 37 degrees C. LP binding, internalization and degradation was markedly increased for LP-NPG and LP-IPG over native LP. Phagocytosis appeared to be the primary route of uptake of LP-PG complexes. Competition experiments indicated that about 40% of the uptake of LP-PG complexes is mediated by the apo-B/E receptor pathway. The scavenger receptor played a minor part in the uptake of LP-PG complexes. Data from this study indicate that LP-PG complexes are present in normal and injured aortas of normocholesterolemic rabbits and these complexes accelerate LP uptake by BMDM more than native LP. Therefore, LP-PG complexes may contribute to lipid accumulation by BMDM, thus generating foam cells. Furthermore, LP-PG complexes prepared from PG of injured aortas are more effective in lipid accumulation than LP-PG complexes from PG of normal aortas.

Lipoprotein-proteoglycan complexes from injured rabbit aortas accelerate lipoprotein uptake by arterial smooth muscle cells

Lipoprotein-proteoglycan (LP-PG) complexes are taken up more avidly by macrophages and smooth muscle cells (SMCs) than native lipoproteins (LPs). The enhanced uptake may contribute to lipid accumulation and foam cell formation during atherogenesis. Endothelial injury is known to alter proteoglycan (PG) synthesis and distribution in the neointima developed in response to injury. The present study examines the uptake and degradation of LP-PG complexes, derived from PG of injured aortas by arterial SMCs. Rabbit apo-B lipoprotein (LP), including VLDL, IDL and LDL was isolated by ultracentrifugation and coupled with PG extracted from normal aortas (NPG) or with PG from injured aortas (IPG). Rabbit aortic SMCs were cultured from intima-media explants, incubated with 125I-LP, 125I-LP-NPG or 125I-LP-IPG for 20 h at 37 degrees C. LP binding, internalization and degradation were markedly increased (P < 0.001) for LP-NPG and LP-IPG over native LP. Competition experiments indicated that more than 50% of the LP-PG complexes were taken up by the apo-B/E receptor pathway. Phagocytosis was the second important route of uptake of these complexes, whereas the scavenger receptor played a minor part in the uptake and degradation of LP-PG complexes. Data from this study indicate that LP-PG complexes accelerate LP uptake and degradation by SMC more than native LP. Therefore, these complexes may contribute to lipid accumulation by SMC, thus generating foam cells. Furthermore, LP-PG complexes prepared from PG of injured aortas are more effective in lipid accumulation than LP-PG complexes from PG of normal aortas.

The biology of the artery wall in atherogenesis

A great deal of progress has been made in the past few years in our understanding of the processes involved in atherogenesis and in mechanisms by which commonly accepted risk factors may affect these processes. These insights have allowed us to understand how various interventions may retard atherogenesis and decrease clinical events by improving plaque stability. The identification of new risk factors, such as lipoprotein(a), and of particular molecules that can be identified in atherosclerotic tissue, such as adhesion molecules, growth factors, cytokines, and proteins that regulate cholesterol uptake and removal, have identified several potential new targets for therapeutic intervention. Advances in molecular biologic techniques, including transgenic techniques, have markedly increased the types of potential interventions available. A major challenge for the future will be to determine which among this plethora of therapeutic possibilities holds the most promise for decreasing the morbidity and mortality associated with this disease.

Pathogenesis and treatment perspectives of chronic graft rejection (CVR)

Chronic rejection is a major threat towards the long-term function and survival of transplanted hearts and kidneys. It is characterized by a proliferative remodelling of the graft vessels along with structural changes of the parenchyma and gradual deterioration of graft function. The pathogenesis is complex and multifactorial. Since grafts with chronic rejection are also subjected to a more or less intense invasion of immunoreactive cells, an important primary objective is to optimize the immunosuppressive treatment. There is no established means of prevention or treatment of chronic rejection. Pharmacological agents interfering with prostaglandin metabolism have been tried most frequently and preliminary results are also available from the use of polyunsaturated fatty acids of the omega-3 series and of heparin derivatives. Based on experimental studies the somatostatin analogue angiopeptin seems very promising today. There will certainly be an increased interest in the use of lipid-reducing agents in the future as well as antioxidant agents acting against the effects of reactive oxygen radicals and oxidative modification of LDL fractions. A strong novel candidate is carvedilol, exerting both antihypertensive, antioxidant and antiproliferative properties.

d-alpha-Tocopherol inhibits low density lipoprotein induced proliferation and protein kinase C activity in vascular smooth muscle cells

Native and malondialdehyde modified low density lipoproteins have been shown to stimulate smooth muscle cell proliferation (A7r5) in vitro. The stimulation is associated with an increase of protein kinase C activity. d-alpha-Tocopherol, at physiological concentrations, has been found to inhibit both protein kinase C activity and cell proliferation.

Antioxidant treatment inhibits the development of intimal thickening after balloon injury of the aorta in hypercholesterolemic rabbits

The effect of the antioxidant butylated hydroxytoluene (BHT) on the accumulation of intimal smooth muscle cells (SMC) and development of intimal thickening after balloon catheter injury of the aorta were studied in rabbits with dietary-induced hyperlipidemia. Two sets of New Zealand White rabbits (eight rabbits in each group) were fed either 0.25% cholesterol or 0.25% cholesterol/1% BHT for a total of 6 wk. Serum lipid levels did not differ between the two groups. 3 wk after the start of the study, a balloon injury of the aorta was performed, after which the rabbits were kept on their respective diets for another 3 wk. After this period of time, the rabbits were killed and their aortas were investigated. The BHT-treated rabbits had only one fourth of the intimal thickness (P < 0.0001) and half the number of SMC/mm intima (P < 0.001), as compared to the rabbits fed only cholesterol. There was also a lower number of macrophages in the BHT-treated group. T lymphocytes were present in the intima of cholesterol-fed rabbits, whereas no such cells could be identified in the BHT-fed animals. There were significantly lower levels of autooxidation products of cholesterol (7-oxocholesterol, cholesterol-5,6-epoxide, and 7 beta-hydroxycholesterol) in the aortas of BHT-treated rabbits, P < 0.001. In conclusion, the antioxidant BHT effectively inhibited the accumulation of intimal SMC and the development of intimal thickening of the aorta in hypercholesterolemic rabbits after a balloon catheter-induced injury. These results indicate that antioxidants may modify intimal response to injury.