Evidence for an additional intracellular site of action of probucol in the prevention of oxidative modification of low density lipoprotein. Use of a new water-soluble probucol derivative.

Oxidative modification of low density lipoprotein (LDL) renders it more atherogenic. Probucol, a highly nonpolar antioxidant, is transported in lipoproteins, including LDL, and inhibits oxidative modification of LDL in vitro. The ability of probucol to inhibit atherogenesis in the LDL receptor-deficient rabbit has been attributed to its antioxidant effect. We report synthesis of a new water-soluble analogue of probucol that is very effective in preventing cell-induced LDL oxidation. The polar probucol derivative, diglutaryl probucol, is efficiently taken up by endothelial cells and macrophages in culture and is hydrolyzed to release the active antioxidant, probucol. The treated cells, after thorough washing, show a marked decrease in their capacity to oxidize LDL during a subsequent incubation. At high concentrations of the derivative, the cells also released free probucol into the medium. Thus, the effectiveness of probucol in vivo may be related both to its presence in LDL, acting as a nonspecific antioxidant, and to an additional ability to inhibit cell-mediated oxidation of LDL by virtue of its uptake into cells.     

Preservation of the endogenous antioxidants in low density lipoprotein by ascorbate but not probucol during oxidative modification.

Several lines of evidence indicate that the oxidative modification of low density lipoproteins (LDL) may provide an important link between plasma LDL and the genesis of the atherosclerotic lesion. Ascorbate is an important water-soluble, chain-breaking antioxidant in humans. Probucol, a lipid-soluble antioxidant drug has been shown to retard the progression of atherosclerosis. The aim of the present study was to compare the effects of probucol and physiologic levels of ascorbate on the oxidative modification of LDL in both a cell-free (2.5 microM Cu++ in phosphate-buffered saline) and cellular system (human monocyte macrophages in Ham's F-10 medium). Both ascorbate and probucol inhibited the oxidative modification of LDL in both systems to a similar degree as evidenced by the thiobarbituric acid-reacting substance activity, electrophoretic mobility, and degradation by macrophages. However, whereas co-incubation with physiologic levels of ascorbate resulted in a substantial preservation of the alpha-tocopherol, gamma-tocopherol, and beta-carotene of the LDL, probucol in concentrations ranging from 10 to 80 microM failed to protect these antioxidants. Thus, in addition to being as potent as probucol in inhibiting the oxidation of LDL, ascorbate in contrast preserves the endogenous antioxidants in the LDL.     

Dissociation of atherogenesis from aortic accumulation of lipid hydro(pero)xides in Watanabe heritable hyperlipidemic rabbits

Antioxidants can inhibit atherosclerosis, but it is unclear how inhibition of intimal lipid oxidation relates to atherogenesis. Here we tested the effect of probucol and its metabolite bisphenol on aortic lipid (per)oxidation and atherogenesis in Watanabe heritable hyperlipidemic (WHHL) rabbits. LDL and aortas from rabbits fed probucol contained bisphenol at concentrations comparable to those in bisphenol-treated animals. Bisphenol treatment increased plasma cholesterol slightly, and plasma and aortic alpha-tocopherol more substantially; these parameters were unaffected by probucol. Bisphenol and probucol treatment both enhanced the resistance of circulating LDL to peroxyl radical-induced lipid peroxidation; this was due to bisphenol, not probucol. Only probucol enhanced LDL's resistance to Cu(2+)-induced oxidation. Both bisphenol and probucol treatment strongly inhibited aortic accumulation of hydroperoxides and hydroxides of cholesteryl esters and triglycerides [LO(O)H]. Despite this, however, probucol had a modestly significant effect on the extent of lesion formation; bisphenol had no inhibitory effect. In addition, the extent of atherosclerosis did not correlate with amounts of aortic LO(O)H present, but, as expected, it did correlate with aortic alpha-tocopherol and cholesterol. Together, these results suggest that aortic accumulation of LO(O)H is not required for, nor is alpha-tocopherol depleted during, the initiation and progression of atherogenesis in WHHL rabbits.     

On the mechanism of plasma cholesterol reduction in the rat given probucol

1. The effects of the cholesterol-lowering drug probucol on lipoprotein metabolism and on the key enzymes that regulate hepatic cholesterol metabolism in the rat were studied. 2. Probucol given for 2 weeks was accompanied by a significant reduction in plasma concentrations of low-density and high-density lipoproteins (LDL,HDL). The fractional catabolic rates of the apolipoproteins of HDL and LDL (apoHDL, apoLDL) were not affected by probucol, although the absolute rates of catabolism of both the apolipoproteins were significantly reduced. 3. The activities of 3-hydroxy-3-methylglutaryl-coenzyme A (CoA) reductase and cholesterol 7 alpha-mono-oxygenase, as well as the rate of hepatic sterol synthesis, were unchanged during the first 2 weeks of probucol. More prolonged probucol led to inhibition of the activity of these enzymes and reduction in sterol synthesis, although the liver cellular content of cholesterol significantly increased. 4. It is postulated that a principal mode of action of the drug is to reduce the rate of lipoprotein synthesis.     

The effect of probucol and vitamin E treatment on the oxidation of low-density lipoprotein and forearm vascular responses in humans

Abstract This study investigates the hypothesis that lipid soluble antioxidants may increase the resistance of low-density lipoprotein (LDL) to oxidation and also enhance vascular endothelial responses in humans. In a double-blind parallel group study, 24 hypercholesterolaemic patients, already on treatment with simvastatin (20mg day^-1), were randomized to supplementary treatment with probucol (500 mg bd), vitamin E (400 IU daily) or placebo for 8 weeks. Mean serum cholesterol before antioxidant treatment was 7·00 mmol l^-1. Resistance of LDL to oxidation by copper was increased by 830% in the probucol group and by 30% in the vitamin E group. However, thiobarbituric acid reacting substances in whole serum were not altered by either antioxidant. Probucol lowered HDL-and LDL-cholesterol levels and increased the QT interval. Forearm vascular responses, as measured by venous occlusion plethysmography, to acetylcholine, glyceryl trinitrate and N^G-monomethyl-L-arginine, were not significantly changed by antioxidant treatment. Probucol has a major, and vitamin E a minor, effect on LDL resistance to oxidation but neither compound appears to alter forearm vascular responses in vivo.     

Paradoxical enhancement of atherosclerosis by probucol treatment in apolipoprotein E-deficient mice.

Dietary administration of probucol (0.5%, wt/wt) efficiently reduced total plasma cholesterol levels in apolipoprotein E-deficient mice (apoE-/-) by 40%, with decreases in high density lipoprotein (HDL) and apoAI by 70 and 50%, respectively. Paradoxically, however, aortic atherosclerotic plaques in the probucol-treated apoE-/- mice formed more rapidly than in the untreated apoE-/- mice, and the lesions were two to four times larger and more mature regardless of sex, age, and genetic background (P < 10(-)6). Histologically, lesions in probucol-treated mice contained increased fibrous materials and cells other than foam cells, and were commonly associated with focal inflammation and aneurysmal dilatation. Probucol treatment also accelerated lesion development in apoE+/- mice fed an atherogenic diet, indicating that the adverse effect is not dependent on the complete absence of apoE. Furthermore, mice lacking apoE and apoAI have plasma lipoprotein profiles very similar to the probucol-treated apoE-/- mice, but do not have accelerated plaque development. Thus, the enhanced atherosclerosis in the probucol-treated animals is unlikely to be caused by the reduction of HDL and apoAI levels. Our data indicate that a reduction in plasma cholesterol caused by probucol does not necessarily lead to an antiatherogenic effect.     

Acute and long-term effects of low-density lipoprotein (LDL)-apheresis on oxidative damage to LDL and reducing capacity of erythrocytes in patients with severe familial hypercholesterolaemia

Several studies have suggested that the oxidative modification of low-density lipoprotein (LDL) could play a key role in the early stages of atherosclerosis. The susceptibility of LDL to oxidation has been found to be greater in patients with coronary heart disease. Familial hypercholesterolaemia (FH) is a powerful clinical model in which to study the predictive role of LDL in atherogenesis. LDL-apheresis is a treatment that is able to decrease lipid levels in plasma. This study was aimed at investigating the reducing capacity of erythrocytes and the in vitro susceptibility to oxidation of LDL isolated from patients with homozygous, heterozygous and double-heterozygous FH, who were treated fortnightly with LDL-apheresis or left untreated. In 14 FH patients, at baseline and after a cycle of treatment, the susceptibility of LDL to oxidative modification was analysed by studying the kinetics of conjugate diene formation. Plasma hydroperoxides, polyunsaturated fatty acid content, LDL electrophoretic mobility on agarose, the titre of auto-antibodies against oxidized LDL and serum paraoxonase activity were also measured. Furthermore, in order to evaluate a potential relationship between LDL oxidation and redox status, erythrocyte GSH and ATP levels were determined in FH patients treated regularly or never treated previously by LDL-apheresis. Unlike in the control group, the oxidative status of LDL in all FH patients was modified by LDL-apheresis, as revealed by the higher negative charge and the increase in levels of hydroperoxides and antibodies against oxidized LDL in the plasma. Our findings suggest both an acute effect and a long-term effect of LDL-apheresis in FH patients treated with dextran sulphate cellulose apheresis. The acute effect of LDL-apheresis on the susceptibility to oxidation of plasma and LDL was demonstrated by significant decreases in plasma hydroperoxide content, total LDL concentration and polyunsaturated fatty acid content. The increased resistance of LDL to oxidation was shown by prolongation of the lag time (P<0.05) in samples after a single cycle of treatment. The long-term effect of LDL-apheresis was demonstrated by the comparable values for lag phases (obtained from the kinetics of conjugate diene formation) in patients under active treatment and controls. Compared with healthy controls and untreated patients, the erythrocyte GSH content was significantly higher (P相似文献   

Probucol inhibits oxidative modification of low density lipoprotein.

Previous studies have established that low density lipoprotein (LDL) incubated with endothelial cells (EC) undergoes extensive oxidative modification in structure and that the modified LDL is specifically recognized by the acetyl LDL receptor of the macrophage. Thus, in principle, EC-modified LDL could contribute to foam cell formation during atherogenesis. Oxidatively modified LDL is also potentially toxic to EC. The present studies show that addition of probucol during the incubation of LDL with EC prevents the increase in the electrophoretic mobility, the increase in peroxides, and the increase in subsequent susceptibility to macrophage degradation. It has also been shown that oxidation of LDL catalyzed by cupric ion induces many of the same changes occurring during EC modification. Addition of probucol (5 microM) also prevented this copper-catalyzed modification of LDL. Most importantly, samples of LDL isolated from plasma of hypercholesterolemic patients under treatment with conventional dosages of probucol were shown to be highly resistant to oxidative modification either by incubation with endothelial cells or by cupric ion in the absence of cells. The findings suggest the hypothetical but intriguing possibility that probucol, in addition to its recognized effects on plasma LDL levels, may inhibit atherogenesis by limiting oxidative LDL modification and thus foam cell formation and/or EC injury. Other compounds with antioxidant properties might behave similarly.     

Beta-carotene inhibits atherosclerosis in hypercholesterolemic rabbits.

Oxidatively damaged LDL may be of central importance in atherogenesis. Epidemiological evidence suggests that high dietary intakes of beta-carotene and vitamin E decreases the risk for atherosclerotic vascular disease, raising the possibility that lipid-soluble antioxidants slow vascular disease by protecting LDL from oxidation. To test this hypothesis, we fed male New Zealand White rabbits a high-cholesterol diet or the same diet supplemented with either 1% probucol, 0.01% vitamin E, 0.01% all-trans beta-carotene, or 0.01% 9-cis beta-carotene; then we assessed both the susceptibility of LDL to oxidation ex vivo and the extent of aortic atherosclerosis. As in earlier studies, probucol protected LDL from oxidation and inhibited lesion formation. In contrast, vitamin E modestly inhibited LDL oxidation but did not prevent atherosclerosis. While beta-carotene had no effect on LDL oxidation ex vivo, the all-trans isomer inhibited lesion formation to the same degree as probucol. Moreover, all-trans beta-carotene was undetectable in LDL isolated from rabbits fed the compound, although tissue levels of retinyl palmitate were increased. The effect of all-trans beta-carotene on atherogenesis can thus be separated from the resistance of LDL to oxidation, indicating that other mechanisms may account for the ability of this compound to prevent vascular disease. Our results suggest that metabolites derived from all-trans beta-carotene inhibit atherosclerosis in hypercholesterolemic rabbits, possibly via stereospecific interactions with retinoic acid receptors in the artery wall.     

Dietary probucol preserves endothelial function in cholesterol-fed rabbits by limiting vascular oxidative stress and superoxide generation.

Excess vascular oxidative stress and the local formation of oxidized LDL (ox-LDL) have been implicated in the development of impaired endothelium-dependent arterial relaxation in hypercholesterolemia and atherosclerosis. Dietary antioxidants limit LDL oxidation in vitro and treatment of cholesterol-fed rabbits with dietary antioxidants preserves endothelium-derived relaxing factor (EDRF) action. To investigate the mechanism(s) responsible for these observations, we examined EDRF action, vascular oxidative stress, and antioxidant protection in male New Zealand White rabbits using four dietary treatments. Animals consumed standard chow (chow group) or chow supplemented with: (a) 0.5% cholesterol (0.5% cholesterol group); (b) 1% cholesterol (1% cholesterol group); or (c) 1% cholesterol and 1% probucol (probucol group). After 28 d of dietary treatment, segments of thoracic aorta from the 0.5 and 1% cholesterol groups demonstrated impairment of acetylcholine-mediated endothelium-dependent arterial relaxation compared to chow-fed animals (57 +/- 11% and 45 +/- 9% vs 78 +/- 3%, respectively; P < 0.05). In contrast, vessels from the probucol group demonstrated normal relaxation to acetylcholine (83 +/- 5%). Plasma cholesterol levels and the extent of atherosclerosis were similar among all cholesterol-fed groups. Probucol treatment was associated a threefold increase in LDL resistance to copper-induced oxidative modification (P < 0.05) and a reduction in tissue lipid peroxidation (as assessed by thiobarbituric acid-reactive substances; P < 0.05) compared to animals fed cholesterol alone. Most importantly, both of these changes were strongly correlated with preserved EDRF action. Moreover, cholesterol feeding was associated with a dose-dependent increase in vascular superoxide generation and lysophosphatidylcholine content, both of which were prevented by probucol treatment. From these findings, we conclude that probucol, a lipid-soluble antioxidant, preserves EDRF action in cholesterol-fed rabbits in association with limiting vascular oxidative stress and superoxide generation.     

Antioxidants protect from atherosclerosis by a heme oxygenase-1 pathway that is independent of free radical scavenging

Oxidative stress is implicated in atherogenesis, yet most clinical trials with antioxidants, particularly vitamin E, have failed to protect against atherosclerotic diseases. A striking exception is probucol, which retards atherosclerosis in carotid arteries and restenosis of coronary arteries after angioplasty. Because probucol has in vitro cellular-protective effects independent of inhibiting lipid oxidation, we investigated the mode of action of probucol in vivo. We used three models of vascular disease: apolipoprotein E-deficient mice, a model of atherosclerosis; rabbit aortic balloon injury, a model of restenosis; and carotid injury in obese Zucker rats, a model of type 2 diabetes. Unexpectedly, we observed that the phenol moieties of probucol were insufficient, whereas its sulphur atoms were required for protection. Probucol and its sulphur-containing metabolite, but not a sulphur-free phenolic analogue, protected via cell-specific effects on inhibiting macrophage accumulation, stimulating reendothelialization, and inhibiting vascular smooth muscle cell proliferation. These processes were mediated via induction of heme oxygenase-1 (HO-1), an activity not shared by vitamin E. Our findings identify HO-1 as the molecular target of probucol. They indicate 2-electron rather than radical (1-electron) oxidants as important contributors to atherogenesis, and point to novel lead compounds for therapeutic intervention against atherosclerotic diseases.     

Lipid peroxidation and susceptibility of low-density lipoprotein to in vitro oxidation in hyperhomocysteinaemia

Abstract. The pathobiochemical mechanism of arteriosclerosis in hyperhomocysteinaemia has not yet been elucidated. In vitro studies have shown that the cytotoxic properties of homocysteine can be ascribed to its generation of reactive oxygen species. We studied lipid peroxidation, both in vivo and in vitro , in 10 homozygous cystathionine synthase-deficient (CSD) patients and in a control group of 10 healthy subjects of comparable age and sex. The susceptibility of low-density lipoprotein (LDL) from hyperhomo-cysteinaemic patients to oxidation was determined in vitro by continuously measuring the conjugated diene production induced by incubation with copper ions. Oxidation resistance (expressed as lag time), maximal oxidation rate, and extent of oxidation (expressed as total diene production) of LDL from CSD patients were not significantly different from those of LDL from controls. Furthermore, the time needed to reach maximal diene production, i.e. t(max), was similar for LDL from patients and controls. In addition, the vitamin E concentrations in LDL of CSD patients and controls were similar. The mean concentration (± SD) of plasma thiobarbituric acid reactive substances (TBARS), an indicator of in vivo lipid peroxidation, was 2.2 ± 0.7 μmol L^-1 in CSD patients, a lower value than that measured in the matched controls (50± 2.0 μmol L^-1). Investigation of in vivo and in vitro parameters of lipid peroxidation shows that the increased risk of arteriosclerosis in hyperhomocysteinaemia is unlikely to be due to increased lipid peroxidation.     

Comparison of antioxidant effects of naringin and probucol in cholesterol-fed rabbits

BACKGROUND: Due to the strong evidence on the involvement of active oxygen species in a variety of disorders, the role of antioxidants against oxidative stress has recently received increased attention. METHODS: Twenty male rabbits were served a high-cholesterol (HC, 5 g/kg diet) diet or high-cholesterol diet supplemented with naringin (0.5 g/kg diet) or probucol (0.5 g/kg diet) for 8 weeks to compare the antioxidative effects of the citrus bioflavonoid (naringin) and antioxidative cholesterol-lowering drug (probucol). RESULTS: The plasma thiobarbituric acid-reactive substances (TBARS) concentration was not significantly different between the groups, whereas the hepatic TBARS concentration was significantly lower in the probucol group than in both normal and HC control or naringin group. Probucol and naringin supplementation led to an increase in the hepatic superoxide dismutase (SOD) and catalase (CAT) activities, and a decrease in the hepatic mitochondrial hydrogen peroxide (H(2)O(2)) content compared to the HC-control group. However, there was no difference in the cytosolic H(2)O(2) content or cytosolic glutathion peroxidase (GSH-Px) activity in the liver between the groups. Both naringin and probucol supplements significantly increased the plasma vitamin E concentration compared to the HC-control group. As regards the antioxidant enzyme gene expressions, naringin significantly increased the expression of three antioxidant enzyme mRNAs compared to the HC-control group, whereas probucol significantly increased the only SOD mRNA expression. CONCLUSIONS: The probucol supplement was very potent in the antioxidative defense system, whereas naringin exhibited a comparable antioxidant capacity based on increasing the gene expressions in the antioxidant enzymes, while also increasing the hepatic SOD and CAT activities, sparing plasma vitamin E, and decreasing the hepatic mitochondrial H(2)O(2) content.     

Susceptibility of LDL to oxidation in vitro and antioxidant capacity in familial combined hyperlipidemia: comparison of patients with different lipid phenotypes

BACKGROUND: There is increasing evidence that oxidation of low-density lipoprotein (LDL) plays an important role in atherogenesis. AIM: To explore the LDL oxidizability and its determinants in familial combined hyperlipidemia (FCHL) patients with different phenotypes. METHOD: The study included 59 FCHL family members with different lipid phenotypes, 39 non-affected relatives, and 30 spouses as healthy controls. RESULTS: The lag time for LDL oxidation was significantly shorter in FCHL patients with different lipid phenotypes as compared to healthy controls. There were no significant differences in the propagation rate and conjugated diene formation and alpha-tocopherol content in LDL between the FCHL groups and healthy controls. Plasma concentrations of alpha-tocopherol in all FCHL patients and uric acid in FCHL patients with IIB and IV phenotypes were significantly higher than in healthy controls. Plasma total peroxyl radical trapping capacity measured (TRAPmea) and TRAPcalc tended to be higher in affected FCHL groups, but the difference was significant only for IIB phenotype. The peak LDL particle size in the combined group of FCHL patients was significantly smaller than in healthy controls. The lag time for LDL oxidation correlated significantly with LDL size both in the group of FCHL family members (r = 0.477, P<0.001) and in the healthy controls (r = 0.482, P<0.01). CONCLUSIONS: LDL from FCHL patients irrespectively of lipid phenotypes is more susceptible to oxidation in vitro than LDL from healthy controls. This increased susceptibility of LDL to oxidation in vitro seems to be attributed to the abundance of small dense LDL particles and not to the defect of antioxidant capacity in FCHL     

普罗布考对缺血再灌注心肌细胞凋亡的作用

背景已发现细胞凋亡在缺血再灌注损伤中起重要作用.普罗布考除可降低血清低和高密度脂蛋白胆固醇浓度,有效治疗高胆固醇血症外,还有抗氧化活性,抑制低密度脂蛋白胆固醇的氧化修饰,减少其在血管壁沉积的作用.还有研究证明普罗布考可改善左心室功能、防止左心室扩张和减少心肌纤维化.但普罗布考保护心肌作用的确切机制尚未清楚.目的探讨普罗布考对新西兰白兔缺血再灌注心肌细胞凋亡的作用及其可能机制;并探讨其对血清超氧化物歧化酶(serum superoxide dismuase,SOD)和丙二醛水平的影响.设计随机对照的实验研究.地点、材料和干预本实验在广西医科大学医学科学实验中心完成.实验选用30只雄性新西兰白兔,白兔被随机分成3组假手术组、对照组和预治疗组,每组各10只.对照组(标准兔饲料饲养)和预治疗组(标准兔饲料饲养+普罗布考每日每只1 000 mg灌胃)各4周后建立缺血再灌注模型;假手术组(标准兔饲料饲养)4周后开胸用4-0号线穿过冠状动脉左前降支近端,但不予结扎.测定3组白兔心肌细胞凋亡指数、血清丙二醛、SOD水平.主要观察指标①普罗布考对心肌细胞凋亡的影响.②普罗布考对血清SOD和丙二醛水平的影响.结果对照组凋亡指数[(34.75±3.20)%]、血清丙二醛水平[(2.70±0.64)μmol/L]显著高于假手术组[(0.48±0.20)%,(1.06±0.46)μmol/L,q=18.42,6.29,P＜0.01].对照组血清SOD水平显著低于假手术组(q=8.78,P＜0.01).预治疗组凋亡指数和血清丙二醛水平明显低于对照组(q=9.17,4.68,P＜0.01),血清SOD水平高于与对照组(q=3.02,P＜0.05).结论普罗布考降低缺血再灌注心肌细胞凋亡,这一保护作用可能部分是通过减少血清丙二醛水平和提高血清SOD水平来实现的.     

Lipoprotein composition and HDL particle size distribution in women with non-insulin-dependent diabetes mellitus and the effects of probucol treatment

To further characterize the spectrum of potentially atherogenic disturbances in lipoprotein composition in non-insulin-dependent diabetes mellitus (NIDDM), we have studied a subset of women with NIDDM before and after treatment with the lipophilic lipid-lowering drug probucol (1 gm day), which we have shown corrects certain compositional abnormalities these women share with subjects who have hypercholesterolemia. Before treatment, the NIDDM group had a somewhat higher plasma triglyceride level (154 +/- 58.3 mg/dl, vs control, 80.0 +/- 21 mg/dl [mean +/- SD]; p less than 0.025) than controls but their cholesterol and high-density lipoprotein cholesterol (HDL-C) levels did not differ from control levels. A number of significant disturbances, however, were present in the surface and core lipid composition of their lipoproteins. Although the cholesterol content of NIDDM low-density lipoprotein (LDL) was similar to that of controls, its content of sphingomyelin and phosphatidylinositol plus phosphatidylserine and sphingomyelin-to-lecithin ratio all were significantly reduced. Moreover, their very-low-density lipoprotein (VLDL) and HDL2 tended to have reduced amounts of free (unesterified) cholesterol (FC) relative to lecithin, and their HDL2 and HDL3 tended to be triglyceride enriched. Probucol therapy resulted in significant decreases in total plasma cholesterol (-15%), FC (-28%), HDL-C (-22%), and triglyceride (-16%) and in apoproteins A-I, B, and E (apo A-I, B, and E), without changing diabetic control (before probucol: hemoglobin A1, cholesterol, 10.7% +/- 2.7%; after probucol: 10.9% +/- 3.0%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of Soybean Hypocotyl Extract on Lipid Peroxidation in GK Rats

Vascular complications, as a consequence of atherosclerosis, are main causes of morbidity and mortality in patients with diabetes mellitus. There is increasing evidence that lipid peroxidation and oxidative modification of low density lipoprotein (LDL) is important in atherogenesis. In this study we investigated the effect of soybean hypocotyl extract (SHE), rich in isoflavones and saponins, on lipid peroxide (LPO) levels in liver, plasma and lipoproteins in GK diabetic rats, and its efficacy on the reduction of susceptibility of LDL and high density lipoprotein (HDL) to oxidation. The oxidative modification of LDL and HDL was determined with the lag time of copper ion-induced oxidation curve identified by the conjugated dienes. In SHE group which were fed diet containing 40 g/kg of SHE for 16 weeks, LPO levels in liver, plasma and HDL fraction were significantly decreased compared with the control group. The lag phage of LDL oxidation curve was prolonged noticeably by a mean of 27 min in SHE group as compared to the control group, indicating a reduced susceptibility to oxidation. The results suggest that intake of soybean hypocotyl extract might be useful for the prevention and treatment of diabetes mellitus and diabetes-associated diseases.     

Probucol, incorporated into LDL particles in vivo, inhibits generation of lipid peroxides more effectively than endogenous antioxidants alone.

One of the first steps in lipid autoxidation leads to the generation of lipid peroxides (LPO). The time course of LPO generation during Cu++ catalyzed oxidation of LDL before and after treatment with probucol was determined in this study. Before analysis the samples had been stored for about 3 years at -20 degrees C. The results show that in LDL samples without probucol the total antioxidative potential had been depleted during the long-term storage. In contrast, LDL containing probucol showed almost no signs of lipid autoxidation. In addition, the ratio of vitamin E to cholesterol was significantly higher in serum samples containing probucol. We conclude that, in vivo, probucol is incorporated into LDL particles in concentrations high enough to inhibit even early steps of lipid autoxidation.     

Mechanisms of anti-atherogenic action of probucol

Probucol has been recognized to have antioxidant properties as well as lipid-lowering effects, and contribute to prevention of atherosclerosis. Pharmacologically, this agent has shown several unique actions, and a lot of investigations have been reported regarding the mechanisms. Recently, it has been reported that probucol increases selective uptake of high density lipoprotein cholesterol esters by the medium of the class B, type I scavenger receptor (SR-BI), and that antioxidant potent may inhibit the restenosis of post coronary angioplasty. This review attempts to focus on the mechanism of antioxidant and HDL-lowering effects of probucol.     

Probucol increases cholesteryl ester transfer protein activity in hypercholesterolaemic patients

Probucol, a widely used lipid lowering drug, reduces both low- and high-density (LDL and HDL) lipoprotein levels and can induce a regression of tissue lipid deposits in both animals and man. The suggested mechanism(s) involve the prevention of LDL oxidative modifications and, possibly, an improvement in the reverse cholesteryl ester transport system. Probucol administration to 10 hypercholesterolaemic patients increased the activity of the cholesteryl ester transfer protein (CETP) by 50%. The rise of CETP activity was significantly related with the plasma steady-state drug levels (r = 0.51, P less than 0.005), thus suggesting that probucol may directly stimulate CEPT synthesis and/or release. Furthermore, CETP activity was inversely related with HDL-cholesterol levels, both in the whole series of 10 patients (r = -0.56, P less than 0.001) and, more so, in the single individuals (r between -0.77 and -0.97), thus suggesting that the reduction of plasma HDL-cholesterol levels is a direct consequence of CETP stimulation. These findings support the hypothesis that an improvement in the reverse cholesteryl ester transport is a major mechanism of probucol and that this may explain the drug induced plasma lipoprotein changes.