Growth factors are believed to play significant roles on the progression of atherosclerosis. In this article, I will focus on two growth factors, bFGF and TGF-β, and will describe the effects of those growth factors on endothelial cells.
bFGF is synthesized by various cell types including endothelial cells and smooth muscle cells. In case of endothelial denudation, bFGF acts as an autocrine factor and accerelates the reendothelialization of luminal surface, preventing from intimal thickening. However bFGF induces angiogenesis from vasa vasara into intimal lesion and stimulates the migration and proliferation of smooth muscle cells.
Although TGF-β is alway secreted in a latent form, the contact of endothelial cells and intimal smooth muscle cells at atherosclerotic lesion will generate active form. Active TGF-β has versatile effects on endothelial cells, smooth muscle cells and macrophages and may affect the course of atherosclerosis. However, the precise role of TGF-β on the development of atherosclerosis is remain to be elucidated.

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It has been demonstrated by several lines of studies that oxidized LDL plays an important role in early stage of atherogenesis. The antioxidant, probucol, inhibits oxidative modification of LDL and prevents progression of atherosclerosis in WHHL rabbits. Probucol also has been reported to stimulate regression of atheromatous lesions. In this study, we tried to elucidate the mechanism which probucol stimulates regression of atherosclerosis.
HDL has been reported to stimulate efflux of cholesterol from foam cells by making direct contact with them in subendothelial space, and this is the very place where oxidative modification of LDL is considered to occur. Therefore, it can be strongly speculated that oxidative modification of HDL occurs in vivo. When HDL was incubated with 5 μM cupric ion, the amount of lipid peroxide increased significantly, and he band of apolipoprotein Al on SDS-PAGE disappeared (Fig. 2). Next, we compared native HDL and oxidized HDL concerning their effect to stimulate efflux of cholesterol from foam cells. The results revealed that oxidized HDL stimulated significantly less amount of cholesterol efflux (Fig. 3). These data suggest that oxidative modification of HDL reduces its antiatherogenic property, and probucol might possibly inhibit oxidative modification of HDL in vivo. Thus, the antioxidative effect of probucol on HDL could be an explanation for stimulating regression of atheromatous plaque.
When atheromatous plaques of probucol-treated and non-treated rabbits were compared, the former contained much less number of macrophages. In order to clarify the mechanism of this phenomenon, we prepared mouse peritoneal macrophages pretreated with or without probucol and compared their chemotactic activity using modified Boyden chamber system. As shown in Fig. 4, probucol-treated macrophages showed increased chamotaxis towards LDL compared with control macrophages, and this couldbe an explanation for macrophage-poor-lesions in probucol-treated rabbits. Our current study demonstrated that an antioxidant, probucol, contributed to the regression of atheromatous plaques by at least two different mechanisms.

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To investigat the mechanism of acceleration of atherogenesis in diabetes mellitus, oxidative modification of glycated LDL (low-density lipoproteins) induced by vascular endothelial cells were examined with or without the addition of an glycation inhibitor, aminoguanidine. Negative charge of glycated LDL was significantly increased by endothelial cell-modification (200.5±11.9% of control, n=8, p<0.01) as compared with the endotheliummodified native LDL. Similar results were obtained on the change in fluorescence, but there was no significant difference on the change in lipid peroxide contents between native and glycated lipoproteins. Dose-dependent inhibition was demonstrated by the addition of aminoguanidine on these parameters of modified LDLs. Further studies were performed to examine the effects of these modified lipoproteins on the cholesteryl ester accumulation in rat peritoneal macrophages and the effects of aminoguanidine on the binding between LDL and/or collagen and malondialdehydes. These results suggest that glycated LDL may be more atherogeric than native LDL in view of oxidative modification induced by vascular endothelial cells, and that aminoguanidine may be able to inhibit such complicated modifications of LDLs.

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It has been reported that endothelial cells are extremely sensitive to cytotoxic effect of active oxygen radicals (O₂^-, H₂O, OH·). Oxygen radicals can be scavenged by superoxide dismutase, catalase or glutathione redox (GR) cycle. Interestingly, a previous paper suggest a significant role of GR cycle for maintaining endothelial cell integrity by scavenging hydrogen peroxide. It is clear that GR cycle activity is dependent on NADPH supply as a result of activation of hexose monophosphate shunt (HMS) pathway. Therefore, high medium glucose concentration can modulate intracellular GR cycke activity. In the present study, we studied a possible impairment of GR cycle in the cells cultured in the presence of high glucose media due to an insufficient NADPH supply as a result of impaired HMS activation in the presence of hydrogen peroxide in cultured human umbilical vein endothelial cells.
Glutathione redox cycle-dependent H₂O₂ degradation in endothelial cells cultured in the presence of 5.5 mM (NG), 11 mM, 22 mM, 33 mM (HG) or 66 mM D-glucose for 4-5 days decreased as a dosedependent manner. In contrast, neither 27.5 mM D-raffinose (HR) or L-glucose (HLG) in the media had no effect on the degradation. In contrast, there was no impairment of catalase-dependent H₂0₂-degradation in the cells cultured in both glucose concentrations.
There was no difference in basal NADPH level between HG and NG groups. However, after an exposure of 500 μM H₂O₂, NADPH level in HG group was 41% (P<0.01) and 36% (P<0.05) less than that in NG and HR groups, respectively. The glucose effect on NADPH concentration in the cells exposed by H₂O₂ was D-glucose concentrationdependent. Similarly, there was no difference in basal HMS activity which was calculated by [1-14C] Glut+[2-14C] Glu-2×[6-14C] Glu between HG and NG groups. However, after an exposure of H₂O₂, HMS activity in HG group was significantly (P<0.01) less than the values of NG group and HR group, respectively.
⁵¹Cr-release from cells in HG group utilized as a marker of cell injury which was measured in the presence of 20-500 μM H₂O₂ was significantly (P<0.01) greater than that of NG group. The high glucose-induced enhancement of H₂O₂-induced ⁵¹Cr-release was completely normalized by preincubating the cells in the presence of eigher 100 μM deferoxamine or 10 mM dimethylthiourea. Lipid peroxide content in plasma membrane fraction obtained from cells cultured in HG condition was 36% higher (P<0.05) than that of NG group.
These results indicate that glutathione redox cycle in cells cultured in high glucose media is impaired as D-glucose specific and medium glucose concentration-dependent manner. These abnormal radical scavenger functions in the cells cultured in high glucose media are impaired via an insufficient NADPH supply as a result of an impairment of HMS activity. The impairment of H₂O₂-degrading activity in high glucose condition may associate with a potentiation of oxygen radicals-induced endothelial cell injury.

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The mechanism of diabetic macroangiopathy was studied from the view point of phenotypic change of aortic smooth muscle cells (SMC). The growth rates of cultured SMC of diabetic rats or rabbits were higher than those of non-diabetic animals (controls). This difference of the growth responses was observed specifically with platelet-derived growth factor (PDGF). Of the three PDGF dimers, PDGF-AB heterodimer (PDGF-AB) and PDGF-BB homodimer (PDGF-BB) stimulated growth of diabetic SMC more than that of control SMC but PDGF-AA homodimer (PDGF-AA) did not. The binding of ¹²⁵I-PDGF to the diabetic SMC was greater than that to control SMC. This was due to increase in the number of cell surface receptors for PDGF. On in vitro culture, SMC from diabetic rats expressed more PDGF β-receptor mRNA and protein than SMC from non-diabetic rats. Moreover, in vivo, the aortic media of diabetic rabbits expressed PDGF β-receptor mRNA, but that from non-diabetic rabbits did not. And stronger arterial intimal thickening was observed in diabetic rabbits treated with balloon catheter injury compared with control rabbits treated with balloon catheter. The significance of these facts in development of diabetic macroangiopathy is discussed.

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