Probucol inhibits mononuclear cell adhesion to vascular endothelium in the cholesterol-fed rabbit

Red algae (Gelidium amansii) hot-water extract ameliorates lipid metabolism in hamsters fed a high-fat diet

The purpose of this study was to investigate the effects of Gelidium amansii (GA) hot-water extracts (GHE) on lipid metabolism in hamsters. Six-week-old male Syrian hamsters were used as the experimental animals. Hamsters were divided into four groups: (1) control diet group (CON); (2) high-fat diet group (HF); (3) HF with GHE diet group (HF + GHE); (4) HF with probucol diet group (HF + PO). All groups were fed the experimental diets and drinking water ad libitum for 6 weeks. The results showed that GHE significantly decreased body weight, liver weight, and adipose tissue (perirenal and paraepididymal) weight. The HF diet induced an increase in plasma triacylglycerol (TG), total cholesterol (TC), low-density lipoprotein cholesterol and very-low-density lipoprotein cholesterol levels. However, GHE supplementation reversed the increase of plasma lipids caused by the HF diet. In addition, GHE increased fecal cholesterol, TG and bile acid excretion. Lower hepatic TC and TG levels were found with GHE treatment. GHE reduced hepatic sterol regulatory element-binding proteins (SREBP) including SREBP 1 and SREBP 2 protein expressions. The phosphorylation of adenosine monophosphate (AMP)-activated protein kinase (AMPK) protein expression in hamsters was decreased by the HF diet; however, GHE supplementation increased the phosphorylation of AMPK protein expression. Our results suggest that GHE may ameliorate lipid metabolism in hamsters fed a HF diet.

Synergistic Effects of Cilostazol and Probucol on ER Stress-Induced Hepatic Steatosis via Heme Oxygenase-1-Dependent Activation of Mitochondrial Biogenesis

The selective type-3 phosphodiesterase inhibitor cilostazol and the antihyperlipidemic agent probucol have antioxidative, anti-inflammatory, and antiatherogenic properties. Moreover, cilostazol and probucol can regulate mitochondrial biogenesis. However, the combinatorial effect of cilostazol and probucol on mitochondrial biogenesis remains unknown. Endoplasmic reticulum (ER) stress is a well-known causative factor of nonalcoholic fatty liver disease (NAFLD) which can impair mitochondrial function in hepatocytes. Here, we investigated the synergistic effects of cilostazol and probucol on mitochondrial biogenesis and ER stress-induced hepatic steatosis. A synergistic effect of cilostazol and probucol on HO-1 and mitochondrial biogenesis gene expression was found in human hepatocellular carcinoma cells (HepG2) and murine primary hepatocytes. Furthermore, in an animal model of ER stress involving tunicamycin, combinatorial treatment with cilostazol and probucol significantly increased the expression of HO-1 and mitochondrial biogenesis-related genes and proteins, whereas it downregulated serum ALT, eIF2 phosphorylation, and CHOP expression, as well as the lipogenesis-related genes SREBP-1c and FAS. Based on these results, we conclude that cilostazol and probucol exhibit a synergistic effect on the activation of mitochondrial biogenesis via upregulation of HO-1, which confers protection against ER stress-induced hepatic steatosis.

Effects of probucol on restenosis after percutaneous coronary intervention: a systematic review and meta-analysis

BACKGROUND

Restenosis after percutaneous coronary intervention (PCI) is a remained clinical problem which limits long-term success of PCI. Although there was recognition that probucol in treating restenosis after percutaneous transluminal coronary angioplasty, the efficacy of probucol on restenosis after stent-implantation is controversial. So this meta-analysis was conducted to investigate the association between probucol and late restenosis.

METHODS

Articles were assessed by four trained investigators, with divergences resolved by consensus. PubMed, EMBASE, ScienceDirect and the Cochrane Central Register of clinical trials were searched for pertinent studies. Inclusion criteria were random allocated to treatment and a comparison of probucol-treated patients and control patients (not treated with lipid-lowering drug) undergoing PCI.

RESULTS

Fifteen studies with 859 subjects were analyzed. Major outcome, binary angiographic restenosis defined as >50% stenosis upon follow-up angiography, was significantly decreased with probucol treatment (RR = 0.59 [0.43, 0.80] among vessels, P = 0.0007; and RR = 0.52 [0.40, 0.68] among patients, P<0.00001). Probucol also increased the minimal luminal diameter (SMD = 0.45 [0.30, 0.61], P<0.00001) and decreased late loss upon follow-up after 6 months (SMD = -0.41 [-0.60, -0.22], P<0.0001). Moreover, there was a significantly lower incidence of major adverse cardiac events (MACE) in the probucol group than control group (RR = 0.69 [0.51, 0.93], P = 0.01).

CONCLUSION

Probucol is more than a lipid-lowering drug. It is also effective in reducing the risk of restenosis and incidence of MACE after PCI.

Polymer-free sirolimus- and probucol-eluting versus new generation zotarolimus-eluting stents in coronary artery disease: the Intracoronary Stenting and Angiographic Results: Test Efficacy of Sirolimus- and Probucol-Eluting versus Zotarolimus-eluting Stents (ISAR-TEST 5) trial

BACKGROUND

Durable polymer coatings have been implicated in mid- and long-term adverse events after drug-eluting stent implantation. A polymer-free dual-drug sirolimus- and probucol-eluting stent and a new generation permanent polymer zotarolimus-eluting stent are recently developed technologies demonstrating encouraging results.

METHODS AND RESULTS

In a clinical trial with minimal exclusion criteria, we randomly assigned 3002 patients to treatment with sirolimus- and probucol-eluting stents versus zotarolimus-eluting stents. The trial was designed to demonstrate noninferiority of the sirolimus- and probucol-eluting stents. The primary end point was the combined incidence of cardiac death, target-vessel-related myocardial infarction, or target-lesion revascularization at 1-year follow-up. Follow-up angiography was scheduled at 6 to 8 months. The sirolimus- and probucol-eluting stent was noninferior to the zotarolimus-eluting stent in terms of occurrence of the primary end point (13.1% versus 13.5%, respectively, P(noninferiority)=0.006; hazard ratio=0.97, 95% confidence interval, 0.78 to 1.19; P(superiority)=0.74). The incidence of definite/probable stent thrombosis was low in both groups (1.1% versus 1.2%, respectively; hazard ratio=0.91 [95% confidence interval, 0.45 to 1.84], P=0.80). With regard to angiographic efficacy, there were no differences between the sirolimus- and probucol-eluting stent and the zotarolimus-eluting stent in terms of either in-segment binary angiographic restenosis (13.3% versus 13.4% respectively; P=0.95) or in-stent late luminal loss (0.31±0.58 mm versus 0.29±0.56 mm, respectively; P=0.46).

CONCLUSION

In this large-scale study powered for clinical end points, a polymer-free sirolimus- and probucol-eluting stent was noninferior to a new generation durable polymer-based zotarolimus-eluting stent out to 12 months.

CLINICAL TRIAL REGISTRATION

http://www.clinicaltrials.gov. Unique identifier NCT 00598533.

Molecular mechanisms underlying the antiatherosclerotic and antidiabetic effects of probucol, succinobucol, and other probucol analogues

PURPOSE OF REVIEW

New therapies for the management of cardiovascular disease remain highly desirable, yet the recently developed agents, such as the cholesterylester transfer protein inhibitor torcetrapib, the antidiabetic agent rosiglitazone, and anti-inflammatory inhibitors of cyclooxygenase-2, have failed. In this review, the more recent developments in the molecular mechanisms underlying the beneficial activities of probucol and related compounds are described.

RECENT FINDINGS

In-vivo and in-vitro studies have revealed that several of the protective activities of probucol can be explained by the ability of this drug to induce the enzyme heme oxygenase-1. It is now apparent that the sulfur atoms, rather than the phenol moieties of probucol, are required for its antiatherogenic and antirestenotic activities. Compounds related to probucol that have improved efficacy without the adverse effects offer promise as novel therapies of cardiovascular disease. Recent results suggest these compounds may also be used for the prevention of type-2 diabetes, a disease that is increasing in prevalence and importance worldwide.

SUMMARY

The development of derivatives of probucol targeting anti-inflammatory and antioxidant processes, perhaps via induction of heme oxygenase-1, may add to the armamentarium of current agents used in treatment of atherosclerotic disease and diabetes.

Synergistic efficacy of concurrent treatment with cilostazol and probucol on the suppression of reactive oxygen species and inflammatory markers in cultured human coronary artery endothelial cells

In the present study, we aimed to identify the synergistic effects of concurrent treatment of low concentrations of cilostazol and probucol to inhibit the oxidative stress with suppression of inflammatory markers in the cultured human coronary artery endothelial cells (HCAECs). Combination of cilostazol (0.3~3 microM) with probucol (0.03~0.3 microM) significantly suppressed TNF-alpha-stimulated NAD(P)H-dependent superoxide, lipopolysaccharide (LPS)-induced intracellular reactive oxygen species (ROS) production and TNF-alpha release in comparison with probucol or cilostazol alone. The combination of cilostazol (0.3~3 microM) with probucol (0.1~0.3 microM) inhibited the expression of vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1) more significantly than did the monotherapy with either probucol or cilostazol. In line with these results, combination therapy significantly suppressed monocyte adhesion to endothelial cells. Taken together, it is suggested that the synergistic effectiveness of the combination therapy with cilostazol and probucol may provide a beneficial therapeutic window in preventing atherosclerosis and protecting from cerebral ischemic injury.

Beneficial synergistic effects of concurrent treatment with cilostazol and probucol against focal cerebral ischemic injury in rats

In the present study, we assessed the beneficial synergistic effects of concurrent treatment with low doses of cilostazol and probucol against focal cerebral ischemic infarct in rats. The ischemic infarct induced by 2-h occlusion of middle cerebral artery (MCA) and 22-h reperfusion was significantly reduced in rat brain that received cilostazol (20 mg/kg) and probucol (30 mg/kg) twice together with prominent improvement of neurological function compared to the effect of cilostazol or probucol monotherapy. Increased myeloperoxidase activity, a marker of neutrophil infiltration, observed in the penumbral zone of vehicle-treated brain was more significantly reduced by cilostazol plus probucol in combination. Increased superoxide-, nitrotyrosine (a marker of peroxynitrite)-, poly(ADP-ribose) [a marker for poly(ADP-ribose) polymerase activity]-, and cleaved caspase-3-positive cells (a proapoptotic marker) in the vehicle sample were significantly attenuated by the combination therapy, while individual treatment with low dose of cilostazol or probucol showed a marginal effect. Taken together, it is suggested that the neuroprotective potentials of combination therapy with low doses of cilostazol plus probucol may provide beneficial therapeutic intervention in reducing the focal cerebral ischemic infarct in rats.

Role of probucol in inhibiting intimal hyperplasia after coronary stent implantation: a randomized study

BACKGROUND

Oxygen-free radicals can stimulate smooth muscle cell proliferation and may therefore be involved in the genesis of in-stent restenosis. Thus, treatment with probucol, a potent antioxidant agent that has been shown to reduce restenosis after balloon angioplasty, may be an effective strategy to prevent intimal hyperplasia after stenting.

METHODS

In a prospective double-blind study, 59 patients submitted to coronary stent implantation were randomly assigned to treatment with either probucol (1 g/d) or placebo, starting two weeks before the procedure and continued for 6 months. The primary end point was the intimal hyperplasia volume at 6 months measured by intravascular ultrasound (IVUS) imaging.

RESULTS

Of the 59 randomized patients, 54 underwent successful stent implantation, completed the follow-up period, and underwent repeat angiography, 6.1 +/- 1.1 months after the procedure. Volumetric IVUS analysis revealed similar intimal hyperplasia volumes (403 +/- 26.7 mm3 for probucol vs 44.8 +/- 28.3 mm3 for placebo) and percent volume obstruction of the lumen (30.4% +/- 14.5% for probucol versus 30.7% +/- 17.2% for placebo) in both groups. In addition, quantitative coronary angiography showed no differences in late loss (1.0 +/- 0.8 mm vs 1.1 +/- 0.8 mm), loss index (0.5 +/- 0.4 for both groups), or angiographic restenosis rates (19.4% vs 18.5%) between the probucol and placebo groups, despite the observation of significant changes in the lipid profile and in the plasma antioxidant defenses in patients receiving probucol.

CONCLUSIONS

Treatment with the antioxidant probucol failed to reduce neointimal formation after coronary stent implantation as assessed by IVUS volumetric analysis.

Characterization of the in vitro anti-inflammatory activity of AL-5898 and related benzopyranyl esters and amides

Selected ester- (AL-5898 and AL-8417) and amide-linked benzopyran analogues (AL-7538 and AL-12615) were evaluated in vitro for their ability to inhibit key enzymes/processes of the inflammatory response. AL-7538 and AL-12615 exhibited weak intrinsic cyclooxygenase inhibitory activity (IC50 = 13 microM, 37 microM). In contrast, 5-HETE and LTB4 synthesis in A(23187)-stimulated neutrophils was effectively inhibited by both ester and amide analogs (IC50 = 2-3 microM). While there was some indication for differing sensitivities among benzopyran esters and amides in the suppression of cytokine synthesis in stimulated U-937 cells, there appeared to be no great discrimination when assessing their effect on U-937 cell adhesion to IL-1beta activated HMVEC-L cells. Inhibition of cell adhesion was concentration-dependent, with IC50 values ranging between 18 microM and 30 microM for AL-5898. Concentration-dependent inhibition of inflammatory cytokine production (i.e., IL-1beta, TNF-alpha, GM-CSF and IL-6) was also apparent in LPS-stimulated, cultured PBMC as well as in PMA/A(23187) activated U-937 cells monitoring the synthesis of IL-1beta, IL-8, TNF-alpha, and MCP-1. Notably, the hydrolysis products of the benzopyranyl ester, AL-5692 and (S)-6-methoxy-alpha-methyl-2-naphthaleneacetic acid, were devoid of pharmacological activity when assessed for inhibition of monocyte adhesion or IL-1beta synthesis. Collectively, our data demonstrate the unique in vitro polypharmacology of a novel series of benzopyran analogs that suppress pivotal enzymes and processes in the inflammatory response.

Selective inhibition by probucol of vascular cell adhesion molecule-1 (VCAM-1) expression in human vascular endothelial cells

An early event in atherogenesis is the adhesion of monocytes to endothelium via adhesion molecules, such as VCAM-1 and intracellular adhesion molecule-1 (ICAM-1). It has been suggested that VCAM-1 plays a very important role in the recruitment of monocytes in atherosclerosis. Probucol is a potent inhibitor of atherosclerosis in animal models. However, the mechanism of its antiatherogenic effect is poorly understood. The aim of our study was to evaluate whether probucol can influence the expression of endothelial cell adhesion molecules and endothelial adhesiveness. The study was performed on cultured human umbilical vein endothelial cells (HUVEC). HUVEC were pretreated with probucol (50 microM) at different time periods before stimulation with TNFalpha (100 U ml(-1)) or IL-1beta (100 U ml(-1)). The protein expression of VCAM-1 and ICAM-1 was measured by flow cytometry. VCAM-1 mRNA expression was measured by reverse transcription polymerase chain reaction (RT PCR). Probucol time dependently reduced agonist-induced VCAM-1 ( approximately 45%, 48 h) surface protein and mRNA expression ( approximately 40%, 48 h) in HUVEC, but not ICAM-1 surface protein expression. Decreased VCAM-1 expression was associated with reduction ( approximately 40%) of adherence between cytokine-stimulated HUVEC and peripheral blood mononuclear leukocytes (PBMC). Our results suggest that the antiatherogenic effect of probucol may, in part, be due to a downregulation of VCAM-1 expression.

Site-specific antiatherogenic effect of probucol in apolipoprotein E-deficient mice

-The lipid-lowering antioxidant probucol can inhibit atherosclerosis in animals and restenosis in humans. However, probucol has been shown to promote atherosclerosis in the aortic root of apolipoprotein E-deficient (apoE-/-) mice. In the current study, we examined the effects of probucol on both lesion formation at 4 sites along the aorta and lipoprotein oxidation in the plasma and aortas of apoE-/- mice receiving a diet containing 21.2% (wt/wt) fat and 0. 15% (wt/wt) cholesterol without or with 1% (wt/wt) probucol. After 6 months, controls had developed lesions at all sites investigated. Lesion development was strongly (P=0.0001) affected by probucol, but this effect was not uniform: lesion size was increased in the aortic root but significantly decreased in the arch, the descending thoracic aorta, and proximal abdominal aorta. Plasma and aortas of probucol-treated mice contained high concentrations of probucol and its metabolites (bisphenol and diphenoquinone); increased vitamin C; markedly decreased very low density lipoprotein (but not low density lipoprotein and high density lipoprotein); and decreased cholesterol, cholesteryl esters, triglycerides, vitamin E, and oxidized lipids compared with controls. Interestingly, probucol treatment did not decrease the proportion of aortic lipids that were oxidized. Plasma vitamin C and bisphenol, but not probucol, protected plasma lipids from ex vivo oxidation by peroxyl radicals. These results show that as in other species, probucol can inhibit lesion formation in most parts of the aorta of apoE-/- mice. This effect may involve lipid oxidation-independent mechanisms localized within the vessel wall as well as lipid lowering.

The mechanisms of coronary restenosis: insights from experimental models

Since its introduction into clinical practice, more than 20 years ago, percutaneous transluminal coronary angioplasty (PTCA) has proven to be an effective, minimally invasive alternative to coronary artery bypass grafting (CABG). During this time there have been great improvements in the design of balloon catheters, operative procedures and adjuvant drug therapy, and this has resulted in low rates of primary failure and short-term complications. However, the potential benefits of angioplasty are diminished by the high rate of recurrent disease. Up to 40% of patients undergoing angioplasty develop clinically significant restenosis within a year of the procedure. Although the deployment of endovascular stents at the time of angioplasty improves the short-term outcome, 'in-stent' stenosis remains an enduring problem. In order to gain an insight into the mechanisms of restenosis, several experimental models of angioplasty have been developed. These have been used together with the tools provided by recent advances in molecular biology and catheter design to investigate restenosis in detail. It is now possible to deliver highly specific molecular antagonists, such as antisense gene sequences, to the site of injury. The knowledge provided by these studies may ultimately lead to novel forms of intervention. The present review is a synopsis of our current understanding of the pathological mechanisms of restenosis.

Dietary copper supplementation reduces atherosclerosis in the cholesterol-fed rabbit

There has been considerable debate about how copper status may affect the biochemical and cellular processes associated with atherogenesis. In the present study we have attempted to address this issue directly by investigating the effects of dietary copper supplementation on processes likely to contribute to atherogenesis, using the cholesterol-fed New Zealand White rabbit model. Age matched rabbits (n = 16) were fed a 0.25-1% cholesterol diet to maintain plasma cholesterol concentrations at approximately 30 mmol/l. Eight of these animals also received 0.2% copper acetate. Control animals (n = 8) received rabbit chow without supplements. After 13 weeks on the experimental diets the animals were killed. Integrated cholesterol levels were similar for the cholesterol-fed animals (31.1+/-2.5 vs. 29.9+/-1.9 mmol/l weeks; P>0.05). Although integrated plasma copper levels were higher in the animals receiving the copper supplements, these did not differ significantly (19.0+/-4.8 vs. 15.1+/-2.9 micromol/l weeks; P>0.05). Tissue concentrations of copper were higher in the copper fed animals compared to those on cholesterol alone in aortic 14.0+/-0.75 vs. 1.8+/-0.2 microg/g wet tissue; P<0.05), carotid artery (11.4+/-3.5 vs. 4.9+/-0.9 microg/g wet tissue; P<0.05), and hepatic (332.5+/-28.6 vs. 3.3+/-1.1 microg/g wet tissue; P<0.0001) samples. The concentration of copper within the carotid artery was also significantly higher than that within the aorta (7.5+/-1.8 vs. 2.4+/-0.4 microg/g wet tissue; P<0.05). In animals fed a normal rabbit chow aortic, carotid and hepatic copper concentrations were 3.7+/-0.8, 9.4+/-3.4, and 5.0+/-1.6 microg/g, respectively. These values did not differ significantly from the cholesterol-fed animals (P>0.05). Plasma concentrations of caeruloplasmin, the major copper carrying protein, were estimated as plasma ferroxidase activity and were similar for the groups (P>0.05), as were aortic superoxide dismutase activity levels (P>0.05). Copper supplementation was associated with increased mononuclear cell adhesion to the endothelium of the carotid endothelium, with 2.6+/-0.3 adherent monocytes/1000 endothelial cells in the cholesterol plus copper-fed animals compared to 1.3+/-0.3 in the cholesterol-fed group (P = 0.0006), and 0.1+/-0.1 in the control animals (P<0.002). This may reflect the higher concentrations of copper found within the carotid artery. Histology of the thoracic aorta at the level of the third and sixth intercostal arteries, showed that copper supplementation was associated with significantly smaller intimal lesions (P<0.05 and P<0.01, respectively). These data suggest that copper supplements possibly inhibit the progression of atherogenesis.

Effects of vitamin E on human platelet and mononuclear cell responses in vitro

Recent epidemiological studies have provided evidence supporting the potential benefits of antioxidants in coronary prevention. We have investigated the effects of vitamin E on platelets, monocytes and endothelial cells in vitro. Pre-incubation of platelets with vitamin E inhibited subsequent thrombin- (P < 0.05, n = 5), collagen- (P < 0. 0001, n = 5) and ADP-(P < 0.05, n = 4) induced platelet aggregation measured using a microtitre plate method, or conventional aggregometry. The adhesion of thrombin-activated platelets to collagen was also inhibited by vitamin E (P < 0.05, n = 8), but not by vitamin C (P > 0.05, n = 8); nor was the adhesion of unstimulated platelets significantly affected (P > 0.05, n = 8). Pre-incubation of monocytes with vitamin E inhibited their subsequent adhesion to plastic (P < 0.05, n = 9), and was also associated with an 18% reduction in adhesion to EA.hy 926 endothelial cells (n = 8), although this failed to reach statistical significance. Pre-incubation of the endothelial cells with vitamin E also significantly reduced subsequent mononuclear cell adhesion by 56% (P < 0.05, n = 3).

Probucol inhibits oxidized-low density lipoprotein-induced adhesion of monocytes to endothelial cells by reducing P-selectin synthesis in vitro

Probucol (PBC) is an unique antiatherogenic drug producing its effect by antioxidant action rather than hypolipidaemic effect. However, the exact mechanism of its antiatherogenic effect is unclear. Therefore we investigated the PBC effects on the adhesion of monocytes to endothelial cells, an early event in atherogenesis. Monocyte adhesion to cultured pig aortic endothelial cells (EC) was induced by oxidized low density lipoprotein (Ox-LDL). To elucidate the mechanisms of the inhibition on adhesion, PBC effects on the Ox-LDL-induced expression of P-selectin, on the synthesis of von Willebrand factor (vWF) and prostacyclin (PGI2) were examined. The results showed that Ox-LDL enhanced the adhesion of monocytes to EC in a concentration-dependent and time-related manner. PBC 25, 50 and 75 micromol/L inhibited the Ox-LDL-induced adhesion index from 37.3% to 19.7, 16.6 and 14.6% respectively (p all < 0.05), and inhibited the Ox-LDL-induced expression of P-selectin from 293.0 ng/ml to 180.0, 132.9 and 132.6 ng/ml respectively. Furthermore, PBC significantly attenuated the Ox-LDL-impaired synthesis of PGI2 and vWF. These results indicate that PBC may provide a new approach in the prevention of atherosclerosis (AS) by intervention of monocyte adhesion to EC. In conclusion, PBC inhibits the Ox-LDL-induced adhesion of monocytes to EC. This effect is associated with the inhibition of the Ox-LDL-induced expression of P-selectin and the protection on the synthesis of PGI2.

Vitamin E inhibits low-density lipoprotein-induced adhesion of monocytes to human aortic endothelial cells in vitro

Monocyte adhesion to human aortic endothelial cells (ECs) is one of the early events in the development of atherogenesis. ECs were used to investigate the role of vitamin E in human monocyte adhesion to ECs in vitro. ECs incubated with 40 to 193 mg/dL of low-density lipoprotein cholesterol (LDL) for 22 hours exhibited increasing dose-dependent adherence for untreated, isolated human monocytes (P < .05). ECs exposed to the highest dose of LDL (193 mg/dL) but pretreated with 19 mumol/L alpha-tocopherol for 24 hours showed a trend to lower adherence for monocytes compared with non-treated ECs (4.4 +/- 1.2% versus 7.6 +/- 1.9%; P = .09). This effect of vitamin E became more significant (P < .05) when ECs were exposed to a lower level of LDL (40 mg/dL) or were pretreated with a higher level of alpha-tocopherol (42 mumol/L) and then exposed to 80 mg/dL LDL. Presupplementation of ECs with 15, 19, and 37 mumol/L alpha-tocopherol significantly (P < .05) reduced monocyte adhesion by 6 +/- 1%, 37 +/- 6%, and 69 +/- 17%, respectively. Levels of soluble intercellular adhesion molecule-1 (sICAM-1), one of the adhesion molecules for monocytes, increased after incubation of ECs with LDL 80 mg/dL (4.7 +/- 0.7 versus 6.4 +/- 1.2 ng/mL, respectively; P < .05). Treatment of ECs with alpha-tocopherol (42 mumol/L) significantly reduced induction of sICAM-1 by LDL to 2.2 +/- 2.3 ng/mL. After exposure to LDL, prostaglandin I2 production by ECs was diminished, whereas presupplementation of ECs with alpha-tocopherol partially reversed the LDL effect. Production of interleukin-1 beta was not detectable when ECs were treated with alpha-tocopherol, LDL, or alpha-tocopherol followed by LDL. Our findings indicate that vitamin E has an inhibitory effect on LDL-induced production of adhesion molecules and adhesion of monocytes to ECs via its antioxidant function and/or its direct regulatory effect on sICAM-1 expression.

Probucol downregulates E-selectin expression on cultured human vascular endothelial cells

Probucol, which inhibits monocyte adhesion, is a potent antioxidant to vascular endothelium in the cholesterol-fed rabbit. The accumulation of macrophages in the lesion is influenced by increased expression of specific adhesion molecules on vascular endothelial cells. We investigated the effect of probucol on the expression of cell adhesion molecules in cultured human umbilical vein endothelial cells (HUVECs). HUVECs were treated with lipopolysaccharide in the presence or absence of probucol (0 to 5 mumol/L) and assayed for the expression of adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) and E-selectin by cell-enzyme-linked immunosorbent assay. Probucol significantly downregulated the expression of E-selectin on HUVECs in a dose-dependent manner. In contrast, the expression of ICAM-1 was not affected. E-selectin but not ICAM-1 mRNA expression on HUVECs was also significantly inhibited by probucol in a dose-dependent manner. We also examined whether probucol affects cellular binding between the human monocytic cell line U937 and lipopolysaccharide-stimulated HUVECs by using an in vitro binding assay and found that probucol significantly suppressed their mutual binding in a dose-dependent manner. These data indicate a novel mechanism of action for probucol to reduce the development of atherosclerotic lesions in hyperlipidemic states.

Lack of effect of high dose vitamin E on xanthoma regression in homozygous familial hypercholesterolaemia

There is increasing evidence that oxidative modification of low-density lipoprotein (LDL) plays an important role in the pathogenesis of atherosclerosis. Homozygous familial hypercholesterolaemia (HFH) is characterized by premature, severe atherosclerosis. Drugs available at present are ineffective in lowering the markedly elevated LDL levels in this condition; antioxidant therapy to protect the LDL against oxidation may be of benefit. Probucol, the only drug shown to induce xanthoma regression in HFH, is a potent antioxidant, but it also lowers high-density lipoprotein cholesterol (HDL-C) levels, causing some concern. Vitamin E is a naturally occurring antioxidant that does not affect HDL-C levels. We have therefore evaluated the effect of long-term high dose vitamin E on xanthoma regression in HFH. Ten subjects with HFH, mean age 17 years (range 4-34), received vitamin E (400-1000 mg/dl alpha-tocopherol acetate/day) for a period of 23 months (range 12-27). There was a 4.2-fold increase in the mean serum vitamin E level (mean (S.D.) 49.7 (19.9) to 177.9 (45.6) mumol/l; P < 0.005), but no change in serum lipid or lipoprotein concentrations. Although there was an increase in the in vitro resistance of LDL to oxidation as determined by the duration of the lag phase during copper-mediated oxidation (116 (8.34) vs. 141.5 (9.23) min; P < 0.005) there was no xanthoma regression; in fact they progressed in 4 subjects. Unlike probucol, high dose long-term vitamin E has no demonstrable effect on xanthoma regression in HFH.