Effects of 26-aminocholesterol, 27-hydroxycholesterol, and 25-hydroxycholesterol on proliferation and cholesterol homeostasis in arterial myocytes

Cholesterol Metabolites 25-Hydroxycholesterol and 25-Hydroxycholesterol 3-Sulfate Are Potent Paired Regulators: From Discovery to Clinical Usage

Oxysterols have long been believed to be ligands of nuclear receptors such as liver × receptor (LXR), and they play an important role in lipid homeostasis and in the immune system, where they are involved in both transcriptional and posttranscriptional mechanisms. However, they are increasingly associated with a wide variety of other, sometimes surprising, cell functions. Oxysterols have also been implicated in several diseases such as metabolic syndrome. Oxysterols can be sulfated, and the sulfated oxysterols act in different directions: they decrease lipid biosynthesis, suppress inflammatory responses, and promote cell survival. Our recent reports have shown that oxysterol and oxysterol sulfates are paired epigenetic regulators, agonists, and antagonists of DNA methyltransferases, indicating that their function of global regulation is through epigenetic modification. In this review, we explore our latest research of 25-hydroxycholesterol and 25-hydroxycholesterol 3-sulfate in a novel regulatory mechanism and evaluate the current evidence for these roles.

Inflammation and the pathogenesis of atherosclerosis in systemic lupus erythematosus

Atherosclerosis is a complicated inflammatory process characterized by the interactions of numerous different moieties including lipids, enzymes, endothelial cells, cytokines, chemokines, leukocytes, adhesion molecules, complement and antibodies. As in the pathogenesis of many lupus disease processes, the increased risk of atherosclerosis seen in systemic lupus erythematosus (SLE) is likely due to the complex interplay of many of these inflammatory mediators. Expanding our understanding of the pathogenesis of atherosclerosis in SLE is critical if we are to improve the quality of care and reduce mortality in this vulnerable population.

Suppressor of Cytokine Signaling-3 (SOCS-3) Induces Proprotein Convertase Subtilisin Kexin Type 9 (PCSK9) Expression in Hepatic HepG2 Cell Line

The suppressor of cytokine signaling (SOCS) proteins are negative regulators of the JAK/STAT pathway activated by proinflammatory cytokines, including the tumor necrosis factor-α (TNF-α). SOCS3 is also implicated in hypertriglyceridemia associated to insulin resistance. Proprotein convertase subtilisin kexin type 9 (PCSK9) levels are frequently found to be positively correlated to insulin resistance and plasma very low density lipoprotein (VLDL) triglycerides concentrations. The present study aimed to investigate the possible role of TNF-α and JAK/STAT pathway on de novo lipogenesis and PCSK9 expression in HepG2 cells. TNF-α induced both SOCS3 and PCSK9 in a concentration-dependent manner. This effect was inhibited by transfection with siRNA anti-STAT3, suggesting the involvement of the JAK/STAT pathway. Retroviral overexpression of SOCS3 in HepG2 cells (HepG2(SOCS3)) strongly inhibited STAT3 phosphorylation and induced PCSK9 mRNA and protein, with no effect on its promoter activity and mRNA stability. Consistently, siRNA anti-SOCS3 reduced PCSK9 mRNA levels, whereas an opposite effect was observed with siRNA anti-STAT3. In addition, HepG2(SOCS3) express higher mRNA levels of key enzymes involved in the de novo lipogenesis, such as fatty-acid synthase, stearoyl-CoA desaturase (SCD)-1, and apoB. These responses were associated with a significant increase of SCD-1 protein, activation of sterol regulatory element-binding protein-1c (SREBP-1), accumulation of cellular triglycerides, and secretion of apoB. HepG2(SOCS3) show lower phosphorylation levels of insulin receptor substrate 1 (IRS-1) Tyr(896) and Akt Ser(473) in response to insulin. Finally, insulin stimulation produced an additive effect with SOCS3 overexpression, further inducing PCSK9, SREBP-1, fatty acid synthase, and apoB mRNA. In conclusion, our data candidate PCSK9 as a gene involved in lipid metabolism regulated by proinflammatory cytokine TNF-α in a SOCS3-dependent manner.

Sulfation of 25-hydroxycholesterol regulates lipid metabolism, inflammatory responses, and cell proliferation

Intracellular lipid accumulation, inflammatory responses, and subsequent apoptosis are the major pathogenic events of metabolic disorders, including atherosclerosis and nonalcoholic fatty liver diseases. Recently, a novel regulatory oxysterol, 5-cholesten-3b, 25-diol 3-sulfate (25HC3S), has been identified, and hydroxysterol sulfotransferase 2B1b (SULT2B1b) has been elucidated as the key enzyme for its biosynthesis from 25-hydroxycholesterol (25HC) via oxysterol sulfation. The product 25HC3S and the substrate 25HC have been shown to coordinately regulate lipid metabolism, inflammatory responses, and cell proliferation in vitro and in vivo. 25HC3S decreases levels of the nuclear liver oxysterol receptor (LXR) and sterol regulatory element-binding proteins (SREBPs), inhibits SREBP processing, subsequently downregulates key enzymes in lipid biosynthesis, decreases intracellular lipid levels in hepatocytes and THP-1-derived macrophages, prevents apoptosis, and promotes cell proliferation in liver tissues. Furthermore, 25HC3S increases nuclear PPARγ and cytosolic IκBα and decreases nuclear NF-κB levels and proinflammatory cytokine expression and secretion when cells are challenged with LPS and TNFα. In contrast to 25HC3S, 25HC, a known LXR ligand, increases nuclear LXR and decreases nuclear PPARs and cytosol IκBα levels. In this review, we summarize our recent findings, including the discovery of the regulatory oxysterol sulfate, its biosynthetic pathway, and its functional mechanism. We also propose that oxysterol sulfation functions as a regulatory signaling pathway.

Cholesterol metabolite, 5-cholesten-3β-25-diol-3-sulfate, promotes hepatic proliferation in mice

Oxysterols are well known as physiological ligands of liver X receptors (LXRs). Oxysterols, 25-hydroxycholesterol (25HC) and 27-hydroxycholesterol as endogenous ligands of LXRs, suppress cell proliferation via LXRs signaling pathway. Recent reports have shown that sulfated oxysterol, 5-cholesten-3β-25-diol-3-sulfate (25HC3S) as LXRs antagonist, plays an opposite direction to oxysterols in lipid biosynthesis. The present report was to explore the effect and mechanism of 25HC3S on hepatic proliferation in vivo. Following administration, 25HC3S had a 48 h half life in the circulation and widely distributed in mouse tissues. Profiler™ PCR array and RTqPCR analysis showed that either exogenous or endogenous 25HC3S generated by overexpression of oxysterol sulfotransferase (SULT2B1b) plus administration of 25HC significantly up-regulated the proliferation gene expression of Wt1, Pcna, cMyc, cyclin A, FoxM1b, and CDC25b in a dose-dependent manner in liver while substantially down-regulating the expression of cell cycle arrest gene Chek2 and apoptotic gene Apaf1. Either exogenous or endogenous administration of 25HC3S significantly induced hepatic DNA replication as measured by immunostaining of the PCNA labeling index and was associated with reduction in expression of LXR response genes, such as ABCA1 and SREBP-1c. Synthetic LXR agonist T0901317 effectively blocked 25HC3S-induced hepatic proliferation.

CONCLUSIONS

25HC3S may be a potent regulator of hepatocyte proliferation and oxysterol sulfation may represent a novel regulatory pathway in liver proliferation via inactivating LXR signaling.

Matrine inhibits vascular smooth muscle cell proliferation by modulating the expression of cell cycle regulatory genes

AIM

To investigate the effect of matrine on proliferation of vascular smooth muscle cells (VSMCs) and elucidate the underlying mechanisms.

METHODS

Rat aortic VSMCs were cultured in medium supplemented with 10% fetal bovine serum and treated with various concentrations (0, 5, 10, 15, and 20 mg/L) of matrine for 72 h. VSMCs proliferation and cell cycle profiling were assessed using a methylene blue incorporation assay and flow cytometry, respectively. The underlying protein signaling mechanisms were determined using Western blot analysis of the expression levels of cell cycle regulatory genes, including p53, p21, p27, cyclin D1, cyclin E, cyclin-dependent kinase 2 and 4 (cdk2, cdk4), and phosphorylated Rb. The involvement of p21 and p27 pathways was further determined using small interfering RNA (siRNA) knockdown.

RESULTS

Matrine inhibited VSMC proliferation in a dose-dependent manner by promoting G(1) arrest. The G(1) arrest was accompanied by up-regulation of p53 and p21 protein levels, and down-regulation of cyclin D1/cdk4, cyclin E/cdk2 and phosphorylated Rb protein levels. Matrine did not affect p27 expression. Furthermore, the anti-proliferative effect of matrine was abolished by silencing of p21, but not by silencing of p27.

CONCLUSION

Our data indicate that matrine has an inhibitory effect on VSMC proliferation via up-regulation of the p53/p21 signaling pathway and modulation of other cell cycle regulatory genes.

Metabolism and actions of conjugated linoleic acids on atherosclerosis-related events in vascular endothelial cells and smooth muscle cells

Conjugated linoleic acids (CLAs) are biologically highly active lipid compounds that have attracted great scientific interest due to their ability to cause either inhibition of atherosclerotic plaque development or even regression of pre-established atherosclerotic plaques in mice, hamsters and rabbits. The underlying mechanisms of action, however, are only poorly understood. Since cell culture experiments are appropriate to gain insight into the mechanisms of action of a compound, the present review summarizes data from cell culture studies about the metabolism and the actions of CLAs on atherosclerosis-related events in endothelial cells (ECs) and smooth muscle cells (SMCs), which are important cells contributing to atherosclerotic lesion development. Based on these studies, it can be concluded that CLAs exert several beneficial actions including inhibition of inflammatory and vasoactive mediator release from ECs and SMCs, which may help explain the anti-atherogenic effect of CLAs observed in vivo. The observation that significant levels of CLA metabolites, which have been reported to have significant biological activities, are well detectable in ECs and SMCs indicates that the anti-atherogenic effects observed with CLAs are presumably mediated not only by CLAs themselves but also by their metabolites.

Influence of conjugated linoleic acids on functional properties of vascular cells

Conjugated linoleic acids (CLA) are biologically highly active lipid compounds that inhibit the development of atherosclerotic plaques in experimental animals. The underlying mechanisms of action, however, are only poorly understood. Since cell-culture experiments are appropriate to provide a detailed view into the mechanisms of action of a compound, the present review summarises results fromin vitrostudies dealing with the effects of CLA isomers and CLA mixtures on functional properties of cells of the vascular wall, such as endothelial cells, smooth muscle cells and monocyte-derived macrophages, which are amongst the major cells contributing to atherosclerotic lesion development. Based on these studies, it can be concluded that CLA exert several beneficial actions in cells of the vascular wall through the activation of nuclear PPAR. These actions of CLA, which may, at least partially, explain the inhibition of atherogenesis by dietary CLA, include modulation of vasoactive mediator release from endothelial cells, inhibition of inflammatory and fibrotic processes in activated smooth muscle cells, abrogation of inflammatory responses in activated macrophages, and reduction of cholesterol accumulation in macrophage-derived foam cells.

25-Hydroxycholesterol-3-sulfate regulates macrophage lipid metabolism via the LXR/SREBP-1 signaling pathway

The oxysterol receptor LXR is a key transcriptional regulator of lipid metabolism. LXR increases expression of SREBP-1, which in turn regulates at least 32 genes involved in lipid synthesis and transport. We recently identified 25-hydroxycholesterol-3-sulfate (25HC3S) as an important regulatory molecule in the liver. We have now studied the effects of 25HC3S and its precursor, 25-hydroxycholesterol (25HC), on lipid metabolism as mediated by the LXR/SREBP-1 signaling in macrophages. Addition of 25HC3S to human THP-1-derived macrophages markedly decreased nuclear LXR protein levels. 25HC3S administration was followed by dose- and time-dependent decreases in SREBP-1 mature protein and mRNA levels. 25HC3S decreased the expression of SREBP-1-responsive genes, acetyl-CoA carboxylase-1, and fatty acid synthase (FAS) as well as HMGR and LDLR, which are key proteins involved in lipid metabolism. Subsequently, 25HC3S decreased intracellular lipids and increased cell proliferation. In contrast to 25HC3S, 25HC acted as an LXR ligand, increasing ABCA1, ABCG1, SREBP-1, and FAS mRNA levels. In the presence of 25HC3S, 25HC, and LXR agonist T0901317, stimulation of LXR targeting gene expression was repressed. We conclude that 25HC3S acts in macrophages as a cholesterol satiety signal, downregulating cholesterol and fatty acid synthetic pathways via inhibition of LXR/SREBP signaling. A possible role of oxysterol sulfation is proposed.

Biosynthesis of the regulatory oxysterol, 5-cholesten-3beta,25-diol 3-sulfate, in hepatocytes

Cellular cholesterol homeostasis is maintained through coordinated regulation of cholesterol synthesis, degradation, and secretion. Nuclear receptors for oxygenated cholesterol derivatives (oxysterols) are known to play key roles in the regulation of cholesterol homeostasis. We recently identified a sulfated oxysterol, 5-cholesten-3beta,25-diol 3-sulfate (25HC3S), that is localized to liver nuclei. The present study reports a biosynthetic pathway for 25HC3S in hepatocytes. Assays using mitochondria isolated from rats and sterol 27-hydroxylase (Cyp27A1) gene knockout mice indicated that 25-hydroxycholesterol (25HC) is synthesized by CYP27A1. Incubation of cholesterol or 25HC with mitochondrial and cytosolic fractions in the presence of 3'-phosphoadenosyl 5'-phosphosulfate resulted in the synthesis of 25HC3S. Real-time RT-PCR and Western blot analysis showed the presence of insulin-regulated hydroxycholesterol sulfotransferase 2B1b (SULT2B1b) in hepatocytes. 25HC3S, but not 25HC, decreased SULT2B1b mRNA and protein levels. Specific small interfering RNA decreased SULT2B1b mRNA, protein, and activity levels. These findings demonstrate that mitochondria synthesize 25HC, which is subsequently 3beta-sulfated to form 25HC3S.

Sulfated oxysterol, 25HC3S, is a potent regulator of lipid metabolism in human hepatocytes

Recently, a novel oxysterol, 5-cholesten-3beta, 25-diol 3-sulfate (25HC3S) was identified in primary rat hepatocytes following overexpression of the cholesterol transport protein, StarD1. This oxysterol was also detected in human liver nuclei. In the present study, 25HC3S was chemically synthesized. Addition of 25HC3S (6 microM) to human hepatocytes markedly inhibited cholesterol biosynthesis. Quantitative RT-PCR and Western blot analysis showed that 25HC3S markedly decreased HMG-CoA reductase mRNA and protein levels. Coincidently, 25HC3S inhibited the activation of sterol regulatory element binding proteins (SREBPs), suggesting that inhibition of cholesterol biosynthesis occurred via blocking SREBP-1 activation, and subsequently by inhibiting the expression of HMG CoA reductase. 25HC3S also decreased SREBP-1 mRNA levels and inhibited the expression of target genes encoding acetyl CoA carboxylase-1 (ACC-1) and fatty acid synthase (FAS). In contrast, 25-hydroxycholesterol increased SREBP1 and FAS mRNA levels in primary human hepatocytes. The results imply that 25HC3S is a potent regulator of SREBP mediated lipid metabolism.

Atherosclerosis: immune and inflammatory aspects

This review article discusses the historical origin of our continuously evolving model of the etiology of atherosclerotic cardiovascular disease. The basic molecular biologic concepts underlying the development of coronary artery disease and the dynamic connection between the immune system and arterial integrity are explored. Emphasis is placed on the role of inflammation as a driving force in the process of atherosclerosis and vascular endothelium as a modulating factor in the pathogenesis of coronary artery disease.

Identification of a novel sulfonated oxysterol, 5-cholesten-3beta,25-diol 3-sulfonate, in hepatocyte nuclei and mitochondria

This study reports the discovery of a novel sulfonated oxysterol found at high levels in the mitochondria and nuclei of primary rat hepatocytes after overexpression of the gene encoding steroidogenic acute regulatory protein (StarD1). Forty-eight hours after infection of primary rat hepatocytes with recombinant adenovirus encoding StarD1, rates of bile acid synthesis increased by 4-fold. Concurrently, [(14)C]cholesterol metabolites (oxysterols) were increased dramatically in both the mitochondria and nuclei of StarD1-overexpressing cells, but not in culture medium. A water-soluble [(14)C]oxysterol product was isolated and purified by chemical extraction and reverse-phase HPLC. Enzymatic digestion, HPLC, and tandem mass spectrometry analysis identified the water-soluble oxysterol as 5-cholesten-3beta,25-diol 3-sulfonate. Further experiments detected this cholesterol metabolite in the nuclei of normal human liver tissues. Based upon these observations, we hypothesized a new pathway by which cholesterol is metabolized in the mitochondrion.

CLA isomers inhibit TNFalpha-induced eicosanoid release from human vascular smooth muscle cells via a PPARgamma ligand-like action

Conjugated linoleic acids (CLAs) were reported to have anti-atherogenic properties in animal feeding experiments. In an attempt to elucidate the molecular mechanisms of these anti-atherogenic effects, the modulatory potential of CLA on cytokine-induced eicosanoid production from smooth muscle cells (SMCs), which contributes to the chronic inflammatory response associated with atherosclerosis, has been investigated in the present study. cis-9, trans-11 CLA and trans-10, cis-12 CLA were shown to reduce proportions of the eicosanoid precursor arachidonic acid in SMC total lipids and to inhibit cytokine-induced NF-kappaB DNA-binding activity, mRNA levels of inducible enzymes involved in eicosanoid formation (cPLA2, COX-2, mPGES), and the production of the prostaglandins PGE2 and PGI2 by TNFalpha-stimulated SMCs in a dose-dependent manner. The effect of 50 micromol/L of either CLA isomer was as effective as 10 micromol/L of the PPARgamma agonist troglitazone in terms of inhibiting the TNFalpha-stimulated eicosanoid production by SMCs. PPARgamma DNA-binding activity was increased by both CLA isomers compared to control cells. Moreover, it was shown that the PPARgamma antagonist T0070907 partially abrogated the inhibitory action of CLA isomers on cytokine-induced eicosanoid production and NF-kappaB DNA-binding activity by vascular SMCs suggesting that PPARgamma signalling is at least partially involved in the action of CLA in human vascular SMCs. With respect to the effects of CLA on experimental atherosclerosis, our findings suggest that the anti-inflammatory effect of CLA is at least partially responsible for the anti-atherogenic effects of CLA observed in vivo.

Isothiazole dioxide derivative 6n inhibits vascular smooth muscle cell proliferation and protein farnesylation

Isothiazole dioxides have been shown to inhibit Trypanosoma brucei protein farnesyltransferase (PFTase) in isolated enzyme, but elicited only a minor effect on mammalian PFTase. In the present study we have evaluated the effect of 3-diethylamino-4-(4-methoxyphenyl)-isothiazole 1,1-dioxides with different substituents at C5, on rat PFTase and protein geranylgeranyltransferase-I (PGGTase-I) with the final aims to improve the potency against mammalian PFTase and to identify new compounds with antiproliferative properties. For these purposes, in vitro and cell culture models have been utilized. The results showed that isothiazole dioxides with C4-C5 double bond and sulfaryl substituted at the C5 position but none of the dihydro-derivatives, were able to inhibit in vitro PFTase in a concentration dependent manner (IC50 ranging from 8.56 to 1015 microM). Among those, compound 6n (C5; methyl-S) displayed 500-fold higher inhibitory potency on PFTase than PGGTase-I. Compound 6n was shown to affect rat smooth muscle cell (SMC) proliferation at concentrations similar (IC50 = 61.4 microM) to those required to inhibit [3H]-farnesol incorporation into cellular proteins (-44.1% at 100 microM). Finally, compound 6n interferes with rat SMC proliferation by blocking the progression of G0/G1 phase without inducing apoptosis, as assessed by [3H]-thymidine incorporation assay and flow cytometry analysis. Taken together, we described a new PFTase inhibitor containing the isothiazole dioxide moiety that affects mammalian protein farnesylation and SMC proliferation by inhibiting G0/G1 phase of the cell cycle.

Update on vascular disease in systemic lupus erythematosus

PURPOSE OF REVIEW

Young women with systemic lupus erythematosus have strikingly high rates of coronary heart disease. Current knowledge indicates that atherosclerosis is an active inflammatory and immune-mediated process. Therefore, the chronic inflammation and immune dysregulation characteristic of systemic lupus erythematosus undoubtedly contribute to the accelerated vascular disease seen in these patients. Carefully considering what is known about atherogenesis in the general population will provide clues to unraveling the complexity of why systemic lupus erythematosus and atherosclerosis are linked so frequently.

RECENT FINDINGS

Inflammation is involved in all aspects of atherogenesis from the initial endothelial "response to injury," to foam cell formation leading to the atherosclerotic lesion, to the rupture of the "vulnerable" fibrous cap, resulting in the acute coronary syndrome and potentially in death. The authors review how factors commonly seen in systemic lupus erythematosus or inherent to the underlying disease mechanism may contribute to each of the stages of atherogenesis.

SUMMARY

Our focus on the causes of vascular disease in systemic lupus erythematosus must now include nontraditional risk factors such as immune and inflammatory mediators. With the advent of noninvasive screening tools for atherosclerosis, we are better equipped to measure subclinical vascular disease and associated risk factors, including immune and inflammatory mediators. When considering strategies for preventing premature cardiovascular disease in systemic lupus erythematosus, modifying immune and inflammatory risk factors will likely become a major component of the program in addition to modifying the current traditional risk factors.

Ajoene, a garlic compound, inhibits protein prenylation and arterial smooth muscle cell proliferation

(1) Ajoene is a garlic compound with anti-platelet properties and, in addition, was shown to inhibit cholesterol biosynthesis by affecting 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase and late enzymatic steps of the mevalonate (MVA) pathway. (2) MVA constitutes the precursor not only of cholesterol, but also of a number of non-sterol isoprenoids, such as farnesyl and geranylgeranyl groups. Covalent attachment of these MVA-derived isoprenoid groups (prenylation) is a required function of several proteins that regulate cell proliferation. We investigated the effect of ajoene on rat aortic smooth muscle cell proliferation as related to protein prenylation. (3) Cell counting, DNA synthesis, and cell cycle analysis showed that ajoene (1-50 micro M) interfered with the progression of the G1 phase of the cell cycle, and inhibited rat SMC proliferation. (4) Similar to the HMG-CoA reductase inhibitor simvastatin, ajoene inhibited cholesterol biosynthesis. However, in contrast to simvastatin, the antiproliferative effect of ajoene was not prevented by the addition of MVA, farnesol (FOH), and geranylgeraniol (GGOH). Labelling of smooth muscle cell cellular proteins with [3H]-FOH and [3H]-GGOH was significantly inhibited by ajoene. (5) In vitro assays for protein farnesyltransferase (PFTase) and protein geranylgeranyltransferase type I (PGGTase-I) confirmed that ajoene inhibits protein prenylation. High performance liquid chromatography (HPLC) and mass spectrometry analyses also demonstrated that ajoene causes a covalent modification of the cysteine SH group of a peptide substrate for protein PGGTase-I. (6) Altogether, our results provide evidence that ajoene interferes with the protein prenylation reaction, an effect that may contribute to its inhibition of SMC proliferation.

Effect of S(-) perillic acid on protein prenylation and arterial smooth muscle cell proliferation

A number of proteins post-translationally modified by the covalent attachment of mevalonate-derived isoprene groups farnesol (FOH) or geranylgeraniol (GGOH), play a role in cell proliferation. For this reason, protein farnesyltransferase (PFTase) and protein geranylgeranyltransferases (PGGTases) I and II have gained attention as novel targets for the development of antiproliferative agents. Monoterpenes [limonene, perillic acid (PA) and its derivatives] have been shown to inhibit cell growth and protein prenylation in cancer cells. In the present study, we evaluated the effect of S(-) PA on diploid rat aorta smooth muscle cell (SMC) proliferation as related to protein prenylation. S(-) PA (1-3.5 mM) decreased, in a concentration-dependent manner, rat SMC proliferation as evaluated by cell counting and DNA synthesis. Morphological criteria and flow cytometry analysis excluded the induction of apoptosis as a potential antiproliferative mechanism of S(-) PA on SMC and confirmed a block of the cell cycle progression in G(0)/G(1) phase. The antiproliferative effect of S(-) PA could not be prevented by the addition of mevalonate, FOH, and GGOH to the culture medium and was independent of cholesterol biosynthesis. Densitometric analysis of fluorographed gels, after sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the cell lysates, further supported that S(-) PA (1-3.5 mM), under the same experimental conditions, concentration-dependently inhibited FOH (up to 70%) and GGOH (up to 70%) incorporation into cellular proteins. We provide evidence that S(-) PA affects protein prenylation, an effect that may contribute to its inhibition of SMC proliferation.

Plant sterols regulate rat vascular smooth muscle cell growth and prostacyclin release in culture

Cardiovascular disease (CVD) is the leading cause of death in the USA and other industrialized countries. A large number of epidemiological studies have established a direct correlation between diet and the development and progression of atherosclerosis. Several studies have shown the incidence of CVD to be lower in populations consuming a predominantly plant-based diet, as compared to meat-based diets. Besides being low in fat and cholesterol, vegetarian and Asian diets contain a large variety of phytochemicals, which may function in the body. For example, phytosterols (PS) are plant sterols that interfere with the absorption of cholesterol from the intestine when present in adequate amounts. Although PS may also function at a cellular level in the body, there are few studies examining the action of PS on cells involved in atherosclerosis. The purpose of this study was to examine the effect of dietary PS on vascular smooth muscle cell (VSMC) growth and function, since VSMC play a central role in the development of atherosclerosis. VSMC were treated with 16 microM cholesterol, 25-hydroxycholesterol, campesterol and beta-sitosterol (SIT) using an ethanol as a vehicle. Cell growth was determined by cell counting and cell proliferation by DNA synthesis, which was measured by [(3)H]-thymidine incorporation. Cholesterol supplementation had no effect on cell growth and proliferation. 25-Hydroxycholesterol decreased cell growth by 68% and DNA synthesis by 99%. SIT was found to inhibit VSMC growth more effectively than campesterol. Of the two PS, campesterol decreased cell growth by 16% and SIT decreased cell growth by 30%. DNA synthesis was decreased 25% by SIT supplementation but was not influenced by campesterol or cholesterol supplementation. Cholesterol, campesterol and SIT were not cytotoxic to VSMC and did not significantly alter cell viability. 25-Hydroxycholesterol, however, was cytotoxic and decreased cell viability by 45% as determined by lactate dehydrogenase release and a trypan blue dye exclusion test. De novo cholesterol synthesis was decreased 28% by campesterol, 49% by SIT and 23% by cholesterol. Beta-sitosterol exhibited a greater effect on cholesterol synthesis than campesterol or cholesterol supplementation. Measurement of cell sterol content demonstrated incorporation of PS into VSMC at the expense of cholesterol. Campesterol decreased VSMC cholesterol content by 36%, representing 40% of the total sterol content following treatment. Beta-sitosterol decreased VSMC cholesterol by 41% following supplementation and represented 49% of the total sterol amount. Cholesterol treatment did not alter the cholesterol content of the cells. Prostacyclin production was significantly altered by PS treatment. Basal prostacyclin release was increased 43% by campesterol and 81% by SIT. A23187 stimulated prostacyclin release was increased 25% by campesterol and 54% by SIT. SIT supplementation induced a greater effect on prostacyclin release from VSMC than cholesterol or campesterol supplementation. The in vitro results presented here suggest that dietary PS, especially SIT, may offer protection from the VSMC hyperproliferation found in atherosclerosis. Further in vivo research is needed to support these observations.

Comparative effects of phytosterol oxides and cholesterol oxides in cultured macrophage-derived cell lines

The cytotoxicity of cholesterol and a mixture of beta-sitosterol/campesterol (50%/40%) and their oxides was examined in a cultured-derived macrophage cell line, C57BL/6. Cell numbers, lactate dehydrogenase (LDH) leakage, protein content, lipid uptake, and mitochondria dehydrogenase activity were determined after exposure of cell mononlayers to sterols and sterol oxides at a concentration of 200 microg/mL for up to 120 h. Results indicate that the oxides of cholesterol, beta-sitosterol, and campesterol exhibited similar patterns of toxicity as indicated by LDH leakage, cell viability, and mitochondria dehydrogenase activity. Greatest cell damage was associated with treatments containing 5 alpha,6 alpha-epoxide or cholesterol oxides, followed by beta-sitosterol/campesterol oxides, cholesterol, and beta-sitosterol. The oxides of beta-sitosterol/campesterol caused less LDH leakage and less of an effect on protein content. Results of this study demonstrate that phytosterols contained in vegetable oils, when subjected to frying conditions, do oxidize and may cause cellular damage in an in vitro cell line similar to cholesterol oxides, although less severe.

Kinetics and plasma concentrations of 26-hydroxycholesterol in baboons

26-Hydroxycholesterol (26OHC), a major oxysterol in human blood, is believed to play an important role in reverse cholesterol transport, bile acid formation, and regulation of various cellular processes. Using isotope dilution mass spectrometry, we measured plasma 26OHC concentrations in baboons fed either a high cholesterol/saturated fat (HC-SF) or normal chow diet. Plasma 26OHC levels in baboons were comparable to those reported for humans and were positively correlated with plasma cholesterol concentrations. Animals on the HC-SF diet had significantly higher 26OHC levels (0.274+/-0.058 microM, mean+/-S.D.) than those on the chow diet (0.156+/-0.046 microM). In separate experiments, [(3)H]26OHC was injected into four tethered baboons, and multiple blood samples drawn over a 1-h period were analyzed for [(3)H]26OHC and 26OHC. Fitting the specific radioactivity data to a two-pool compartmental model indicated a rapidly turning over plasma compartment (t(1/2) 2.9-6.0 min) and a second compartment with slow turnover (t(1/2) 76-333 min). The calculated 26OHC production rate was 2.5 micromol/kg body weight/day. Assuming all 26OHC is converted to bile acids, the 26OHC production rate corresponds to about 10% of total bile acid production in adult baboons. These results indicate that rapid turnover of plasma 26OHC at submicromolar concentrations could significantly contribute to bile acid synthesis.

Oxysterols: modulators of cholesterol metabolism and other processes

Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.

The new calcium antagonist lercanidipine and its enantiomers affect major processes of atherogenesis in vitro: is calcium entry involved?

Atherosclerosis results from multiple factors and involves several mechanisms, including endothelial monocyte and smooth muscle cell (SMC) changes, cholesterol accumulation, plaque rupture and thromboembolism. Calcium ions play a role in the initial and chronic development of atherosclerotic lesions. Several studies in experimental animal models have demonstrated the potential direct antiatherosclerotic effects of calcium antagonists. In this study the antiatherogenic activity of lercanidipine, a new lipophilic, second-generation calcium antagonist, was investigated. Lercanidipine and its enantiomers inhibited the replication and migration of arterial myocytes in concentrations ranging from 10 to 50 microM. The antiproliferative effect of lercanidipine was dose dependent, with a potency similar to that of lacidipine and nifedipine, and was unrelated to the stereoselectivity of enantiomers to bind L-type calcium channels. Lercanidipine and its enantiomers (25 microM) decreased the serum-induced elevation of [Ca2+]i in SMC, with the (S)-enantiomer (69% inhibition) being 2.4-fold more active than the (R)-counterpart (29% inhibition). The studies performed with enantiomers of lercanidipine suggest that the observed effects are not related to the blockade of voltage-dependent Ca2+ channels and confirm, at least in vitro, the pharmacological potential of the compound to influence negatively the process of atherogenesis.

Picotamide, an antithromboxane agent, inhibits the migration and proliferation of arterial myocytes

Picotamide is an antiplatelet drug with a peculiar dual mechanism of action: it inhibits thromboxane A2 synthase and antagonizes the pharmacological responses mediated by thromboxane A2 receptor. We investigated the in vitro effect of picotamide on smooth muscle cell migration and proliferation. Picotamide (1-500 microM) decreased human and rat smooth muscle cell proliferation, evaluated as cell number, in a concentration-dependent and reversible manner. Picotamide inhibited DNA synthesis induced by fetal calf serum (10%), platelet-derived growth factor (PDGF-BB (20 ng/ml)), epidermal growth factor (EGF (1 nM)) and (15S)-hydroxy-11,9-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619 (10 microM, thromboxane A2 receptor agonist)). Co-incubation of U46619 together with EGF or PDGF-BB resulted in a marked amplification of [3H]thymidine incorporation that was completely reversed by picotamide. The drug also inhibited smooth muscle cell migration induced by fibrinogen (600 microg/ml) or PDGF-BB (20 ng/ml) in a concentration-dependent manner. The ability of picotamide to interfere with myocyte migration and proliferation confers, at least in vitro, a pharmacological interest on the compound in atherogenesis.

Effect of the new calcium antagonist lercanidipine and its enantiomers on the migration and proliferation of arterial myocytes

The in vitro effects were investigated of the new dihydropyridine calcium antagonist (CA) lercanidipine and its enantiomers on arterial myocyte (smooth muscle cell; SMC) migration and proliferation as related to L-type calcium channel inhibition. Lercanidipine and its enantiomers inhibited the replication and migration of arterial myocytes in concentration ranging from 10 to 50 microM. The antiproliferative effect of lercanidipine, evaluated as cell number, was dose dependent, with a potency similar to that of lacidipine and nifedipine, and was unrelated to the stereoselectivity of enantiomers to bind L-type calcium channels. The cell doubling time increased with drug concentration < or = 122 versus 38 h for controls. The cell growth inhibition induced by lercanidipine and its enantiomers was reversible. Lercanidipine dose dependently decreased [3H]thymidine incorporation into DNA; the (R)-enantiomer, displaying the lowest CA activity, was the most potent in this respect. The tested compounds were able to inhibit fibrinogen-induced myocyte migration in a dose-dependent manner, with the (R)-enantiomer showing the more pronounced effect. To directly rule out the role of calcium channels in the antiatherosclerotic properties of lercanidipine, we examined the effect of the compounds on serum-stimulated calcium influx in SMC. Fluorimetry of Fluo 3 was used to measure changes in free cytosolic Ca2+ concentration ([Ca2+]i) in SMC after long-term preincubation (24 h) with the tested CA. Lercanidipine and its enantiomers (25 microM) decreased the serum-induced elevation of [Ca2+]i in SMC with the (S)-enantiomer (69% inhibition) 2.4-fold more active than the counterpart and the racemate (29% inhibition). In conclusion, our in vitro results suggest that lercanidipine may directly interfere with events involved in atherogenesis. The studies performed with enantiomers of lercanidipine suggest that the observed effects are not related to the blockade of voltage-dependent Ca2+ channels and confirm at least in vitro a pharmacologic potential of the compound to negatively influence the process of atherogenesis.

Review of progress in sterol oxidations: 1987-1995

Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.