Increased monocyte adhesion to aortic endothelium in rats with hyperhomocysteinemia: role of chemokine and adhesion molecules

The up-regulation of monocyte chemoattractant protein-1 (MCP-1) in Ea.hy 926 endothelial cells under long-term low folate stress is mediated by the p38 MAPK pathway

OBJECTIVE

Monocyte chemoattractant protein-1 (MCP-1), encoded by the CCL2 gene, plays an important role in the initiation and progression of atherosclerosis. Ea.hy 926 endothelial cells grown under low folate conditions (LO cells) synthesize more MCP-1 mRNA and secrete more MCP-1 protein than folate-replete control cells (HI cells). We investigated the mechanisms underlying the modulation of MCP-1 expression by long-term "folate stress".

METHODS AND RESULTS

CCL2 transcription, assessed using promoter-reporter assays, is up-regulated in LO cells relative to HI cells, whereas MCP-1 mRNA stability is unchanged. This quantitative transcriptional bias under chronic low folate conditions is not attributable to differences in active NF-kappaB, but is associated with elevated levels of both total p38 and phospho-p38 that are detectable by Western immunoblotting. Transient, acute methotrexate-mediated folate depletion or exposure to high concentrations of homocysteine (Hcy) had no effect on MCP-1 synthesis by Ea.hy 926 cells. The p38 inhibitor SB-203580 abolished the excess MCP-1 production by LO cells. The quantitative transcriptional bias of CCL2 in LO cells was retained following massive induction by TNF-alpha.

CONCLUSION

During long-term folate stress, p38 is the primary determinant of CCL2 transcription. Long-term folate insufficiency "primes" Ea.hy 926 endothelial cells to have a quantitatively more vigorous response to cytokine-mediated inflammatory stress.

Vascular oxidative stress increases dendritic cell adhesion and transmigration induced by homocysteine

Atherosclerosis is a long-term chronic inflammatory and immunological disease. Endothelial dysfunction and the dendritic cell (DC) immune response are pivotal early events in atherogenesis. This study investigated the effects and possible mechanisms of action of homocysteine (Hcy) on DC adhesion to and transmigration between endothelial cells (ECs), and indicated a novel immunoregulatory mechanism by which Hcy induces atherogenesis. When ECs were stimulated with increasing concentrations of Hcy, immunofluorescence showed that endothelial reactive oxygen species (ROS) generation strikingly increased, while nitrite assay showed that nitric oxide (NO) release markedly decreased. Furthermore, DC adhesion and transmigration were significantly increased when ECs were activated by Hcy. However, pretreatment of ECs with antioxidant before Hcy markedly attenuated the induction of DC adhesion and transmigration, dependent on the intracellular ROS decrease and endothelial NO increase. In conclusion, DC adhesion and transmigration are significantly increased by vascular oxidative stress under conditions of elevated Hcy levels. These findings provide insight into the inflammatory processes and immune responses occurring in atherosclerosis induced by Hcy.

Effects of red wine polyphenolic compounds on paraoxonase-1 and lectin-like oxidized low-density lipoprotein receptor-1 in hyperhomocysteinemic mice

Hyperhomocysteinemia, or abnormally high plasma homocysteine (Hcy) concentration, has often been associated with vascular thrombosis and the development of premature atherosclerosis. Many studies have shown that moderate wine consumption has potential beneficial effects related to the prevention of atherosclerosis, in part attributed to the biological properties of polyphenolic components, mainly flavonoids. The aim of the present study is to determine the effects of a red wine polyphenolic extract (PE) administration on hyperhomocysteinemia due to cystathionine beta-synthase (CBS) deficiency and on the associated biochemical markers of hepatic and endothelial dysfunctions in mice. Red wine PE was added for 4 weeks to the drinking water of heterozygous CBS-deficient mice fed a high-methionine diet, a murine model of hyperhomocysteinemia. Red wine PE supplementation at low dose significantly reduced plasma Hcy levels and restored the hepatic and plasma-decreased paraoxonase-1 activity induced by chronic hyperhomocysteinemia. Moreover, aortic expression of proinflammatory cytokines and adhesion molecules and levels of soluble lectin-like oxidized low-density lipoprotein receptor-1 were reduced in hyperhomocysteinemic mice fed the red wine PE supplementation. These findings suggest that red wine PE administration in low quantities has beneficial effects on biochemical markers of endothelial dysfunction due to hyperhomocysteinemia.

Homocysteine stimulates monocyte chemoattractant protein-1 expression in mesangial cells via NF-kappaB activation

Hyperhomocysteinemia is regarded as an independent risk factor for cardiovascular disorders. Although renal dysfunction or failure is one of the important factors causing hyperhomocysteinemia, the role of homocysteine (Hcy) in the development of glomerulosclerosis is largely unknown. One of the key events in the pathogenesis of glomerulosclerosis is the infiltration of circulating monocytes into affected glomeruli. The objective of the present study was to investigate the effect of Hcy on the expression of monocyte chemoattractant protein-1 (MCP-1) in kidney mesangial cells and the mechanisms involved. Levels of MCP-1 and mRNA were significantly elevated in Hcy-treated rat mesangial cells. This increase was associated with activation of NF-kappaB as a result of increased phosphorylation of the inhibitor protein IkappaBalpha. Monocyte chemotactic activity in these cells was also enhanced. In addition, there was a significant elevation of superoxide anion produced by Hcy-treated cells, which preceded the increased phosphorylation of IkappaBalpha. Addition of superoxide dismutase or NF-kappaB inhibitors to the culture medium abolished Hcy-induced NF-kappaB activation and MCP-1 expression. Taken together, these results indicate that Hcy induced MCP-1 expression in mesangial cells. Such a process was mediated by oxidative stress and NF-kappaB activation. This may further aggravate renal function in patients with hyperhomocysteinemia.

Elevated concentrations of retinol-binding protein-4 (RBP-4) in gestational diabetes mellitus: negative correlation with soluble vascular cell adhesion molecule-1 (sVCAM-1)

BACKGROUND

Retinol-binding protein-4 (RBP-4) may increase insulin resistance (IR) in animals, with elevated levels reported in humans with obesity and type 2 diabetes. There are, however, few data on concentrations of RBP-4 in gestational diabetes mellitus (GDM).

METHODS

We measured fasting serum levels of RBP-4, soluble intercellular adhesion molecule-1 (sICAM-1) and soluble vascular cell adhesion molecule-1 (sVCAM-1) in 50 women at 28 weeks of gestation, divided according to the results of a 50 g glucose challenge test (GCT) and a 75 g oral glucose tolerance test (OGTT): (1) controls (n = 20), normal responses to both GCT and OGTT; (2) intermediate group (IG) (n = 15): false positive GCT, but normal OGTT; and (3) GDM group (n = 15), both GCT and OGTT abnormal. IR was assessed by homeostasis model assessment (HOMA-IR) and by insulin resistance index (IRI) based on glycemia and insulinemia during OGTT.

RESULTS

All groups were matched for age and body mass index (BMI). RBP-4 levels (microg/ml, mean+/-standard deviation) were higher in women with GDM vs. controls (53.9 +/- 17.9 vs. 29.7 +/- 13.9, p < or = 0.001), with a trend towards higher RBP-4 in GDM compared with IG (38.0 +/- 19.3, p = 0.07). There was no significant correlation between RBP-4 and age, BMI, insulin, IRI or HOMA-IR, but there was a moderate, significant negative correlation between RBP-4 and sVCAM-1 (r(2) = 0.20, p = 0.001).

CONCLUSIONS

RBP-4 levels are elevated in women with GDM, but do not correlate with IR indices and correlate negatively with sVCAM-1. The physiological significance of RBP-4 rise in women with GDM remains to be elucidated.

Homocysteine upregulates resistin production from adipocytes in vivo and in vitro

OBJECTIVE

Homocysteine (Hcy) is epidemiologically related to insulin resistance, which has been speculated to be a low-grade systemic inflammatory condition. Resistin acts as a critical mediator of insulin resistance associated with inflammatory conditions. We aimed to determine whether Hcy can induce insulin resistance by directly regulating the expression and secretion of resistin from adipose tissue.

RESEARCH DESIGN AND METHODS

The effect of Hcy on the expression and secretion of resistin and insulin resistance was investigated using primary rat adipocytes and mice with hyperhomocysteinemia (HHcy).

RESULTS

Hcy impaired glucose transport and, particularly, the insulin signaling pathway as shown by decreased insulin-stimulated tyrosine phosphorylation of insulin receptor and insulin receptor substrate (IRS)-1, increased serine phosphorylation of IRS-1, and inhibited Akt phosphorylation both in vitro and in vivo, and these impairments were accompanied by an increase in resistin expression. Compared with normal mice, HHcy mice with a clinically relevant level of plasma Hcy (19 micromol/l) showed significantly increased resistin production from adipose tissue (33.38 +/- 3.08 vs. 19.27 +/- 1.71 ng/ml, P < 0.01). Hcy (300-1000 micromol/l) also increased mRNA expression of resistin in primary rat adipocytes in a time- and concentration-dependent manner, with maximal induction at 24 h of approximately fourfold with 1,000 micromol/l. In addition, Hcy-induced resistin expression attenuated by treatment with reactive oxygen species (ROS) scavengers, protein kinase C (PKC), and nuclear factor (NF)-kappaB inhibitors implies a role in the process for ROS, PKC, and NF-kappaB.

CONCLUSIONS

HHcy may promote insulin resistance through the induction of resistin expression and secretion from adipocytes via the activation of the ROS-PKC-NF-kappaB pathway.

Priming effect of homocysteine on inducible vascular cell adhesion molecule-1 expression in endothelial cells

Hyperhomocysteinemia is an independent risk factor for the development of atherosclerosis, as well as for arterial and venous thrombosis. However, the mechanisms through which elevated circulating levels of homocysteine cause vascular injury and promote thrombosis remain unclear. Here, we tested the hypothesis that homocysteine (Hcy) sensitizes endothelial cells to the effect of inflammatory mediators. Human umbilical vein endothelial cells (HUVEC) were incubated with Hcy 1.0 mM for varying time points, and then treated in the absence or presence of 1.5 U/ml thrombin or 10 mg/ml lipopolysaccharide (LPS). Hcy alone had no effect on the expression of vascular cell adhesion molecule (VCAM)-1. However, Hcy enhanced thrombin- and LPS-mediated induction of VCAM-1 mRNA and protein levels. Consistent with these results, pretreatment of HUVEC with Hcy resulted in a two-fold increase in LSP-mediated induction of leukocyte adhesion. The latter effect was significantly inhibited by anti-VCAM-1 antibodies. Together, these findings suggest that Hcy sensitizes HUVEC to the effect of inflammatory mediators thrombin and LPS, at least in part through VCAM-1 expression and function.

Homocysteine inhibits arterial endothelial cell growth through transcriptional downregulation of fibroblast growth factor-2 involving G protein and DNA methylation

Homocysteine (Hcy) contributes to atherogenesis and angiostasis by altering the phenotype of arterial endothelial cells (ECs). The present study was aimed at elucidating potential mechanisms by which Hcy can slow EC proliferation and induce EC apoptosis, thereby disrupting endothelial integrity. Given the strong mitogenic and antiapoptotic properties of fibroblast growth factor (FGF)2, we examined whether Hcy can modulate its expression. In cultured human coronary and bovine aortic ECs, Hcy exerted time- and concentration-dependent (0 to 500 micromol/L) reduction of the mRNA and protein levels of FGF2, whereas vascular endothelial growth factor expression was not affected until Hcy reached a proapoptotic 500 micromol/L. By testing a panel of signal transduction inhibitors, we found that the Hcy-induced downregulation of FGF2 was specifically attenuated by pertussis toxin, an inhibitor of Gi protein signaling. Hcy induced cell cycle arrest at the G(1)/S transition and increased TUNEL-positive apoptotic cells in a graded manner. These effects were effectively counteracted by exogenous FGF2. Reporter gene assays showed that Hcy downregulated FGF2 by transcriptional repression of the gene promoter encompassed in a CpG dinucleotide-rich island. This region was heavily methylated at the cytosine residues by Hcy despite decreased methylation potential (S-adenosylmethionine to S-adenosylhomocysteine ratio). Normal levels of FGF2 transcription were restored to ECs simultaneously exposed to Hcy and 5-aza-deoxycytidine. We conclude that homocysteine disrupts the growth and survival of ECs through a G protein-mediated pathway associated with altered promoter DNA methylation and the transcriptional repression of FGF2.

Direct effect of statins on homocysteine-induced endothelial adhesiveness: potential impact to human atherosclerosis

BACKGROUND

Although homocysteine (HCY) is a risk factor for cardiovascular diseases, recent clinical trials failed to show the benefits by reducing plasma HCY. Alternative strategy with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, statins, might be feasible. This study investigated HCY-induced endothelial adhesiveness with mononuclear cells (MNCs) from patients with coronary artery disease (CAD). The direct endothelial protective effects of statins were also examined.

MATERIALS AND METHODS

Circulating MNCs were isolated from 14 stable CAD patients and 7 age- and gender-matched healthy subjects. Superoxide production of MNCs was determined by Ultra-weak and luminol-enhanced chemiluminescence. Human aortic endothelial cells (HAECs) were used for endothelial adhesiveness to MNCs or U937 human monocytic cells. Endothelial expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) were examined by Western blot.

RESULTS

Superoxide production of MNCs and plasma HCY and high-sensitive CRP levels were significantly increased in CAD patients than in healthy subjects. Stimulation with HCY enhanced the endothelial adhesiveness to MNCs from CAD patients or to U937 cells in a dose-dependent manner, whereas it was obscure with MNCs from healthy subjects. HCY stimulated endothelial VCAM-1 but not ICAM-1 expression in a dose-dependent manner. Monoclonal antibodies to VCAM-1 attenuated HCY-induced endothelial adhesiveness. Simvastatin or pravastatin significantly reduced HCY-induced VCAM-1 expression and endothelial adhesiveness to MNCs from CAD patients.

CONCLUSION

Circulating MNCs were activated in CAD patients, which was critical to HCY-induced endothelial adhesiveness. Statins could directly reduce HCY-induced endothelial-MNC adhesion via VCAM-1 inhibition, suggesting its potential implication in HCY-related atherosclerosis disease.

Visfatin enhances ICAM-1 and VCAM-1 expression through ROS-dependent NF-kappaB activation in endothelial cells

Visfatin has recently been identified as a novel visceral adipokine which may be involved in obesity-related vascular disorders. However, it is not known whether visfatin directly contributes to endothelial dysfunction. Here, we investigated the effect of visfatin on vascular inflammation, a key step in a variety of vascular diseases. Visfatin induced leukocyte adhesion to endothelial cells and the aortic endothelium by induction of the cell adhesion molecules, ICAM-1 and VCAM-1. Promoter analysis revealed that visfatin-mediated induction of CAMs is mainly regulated by nuclear factor-kappaB (NF-kappaB). Visfatin stimulated IkappaBalpha phosphorylation, nuclear translocation of the p65 subunit of NF-kappaB, and NF-kappaB DNA binding activity in HMECs. Furthermore, visfatin increased ROS generation, and visfatin-induced CAMs expression and NF-kappaB activation were abrogated in the presence of the direct scavenger of ROS. Taken together, our results demonstrate that visfatin is a vascular inflammatory molecule that increases expression of the inflammatory CAMs, ICAM-1 and VCAM-1, through ROS-dependent NF-kappaB activation in endothelial cells.

Homocysteine up-regulates vascular transmembrane chemokine CXCL16 and induces CXCR6+ lymphocyte recruitment in vitro and in vivo

Objective: Hyperhomocysteinemia induces endothelial dysfunction and promotes atherosclerotic vascular disease. Infiltrates of activated macrophages and lymphocytes are observed in human and experimental atherosclerotic lesions, their emigration being guided by endothelial-leukocyte adhesion molecules and chemoattractants. The CXC-chemokine CXCL16 functions as an adhesion molecule by interacting with its receptor (CXCR6) and also as a scavenger for oxidized low density lipoprotein (oxLDL). We investigated the modulation of CXCL16 on cultured endothelial cells (EC) and the recruitment of CXCR6⁺ lymphocytes in response to homocysteine (Hcy), in vitro and in vivo. Methods and Results: Hcy-stimulated EC show a significant increase in CXCL16 mRNA and protein expression. Incubation of EC with d,l-Hcy and l-Hcy significantly increased CXCR6⁺ lymphocyte adhesion to EC while l-Cysteine (l-Cys) had no effect. Furthermore, EC stimulation with Hcy increased uptake of DiI-oxLDL. An anti-CXCL16 monoclonal antibody, antioxidants (Tiron) and PPAR-γ agonists (Pioglitazone) considerably reduced CXCR6⁺ lymphocyte adhesion and uptake of DiI-oxLDL. Upon injection in the peritoneal cavities of mice, l-Hcy and not l-Cys, increased the number of CXCR6⁺ lymphocytes, which was reduced by coinjection with Pioglitazone or anti-human CXCL16 antibody. Conclusions: Hyperhomocysteinemia up-regulates CXCL16 leading to increased recruitment of CXCR6⁺ lymphocytes and scavenging of modified lipids via a potential involvement of a PPAR-γ-dependent mechanism. CXCL16 may therefore contribute to the formation and progression of atherosclerotic lesions under conditions of hyperhomocysteinemia.

Homocysteine induces connective tissue growth factor expression in vascular smooth muscle cells

BACKGROUND

Increased homocysteine levels in blood might be an important risk factor for the development of cardiovascular diseases. Connective tissue growth factor (CTGF) was found to be involved in atherosclerotic plaque progression. So far, the possible connection between homocysteine and CTGF has not been studied.

OBJECTIVE

This study was designed to test whether homocysteine could induce CTGF expression in vascular smooth muscle cells (VSMC).

METHODS AND RESULTS

Hyperhomocysteinemia was induced in Sprague-Dawley rats after 4 weeks of a high-methionine diet. CTGF mRNA and protein expression was detected in the aortas isolated from hyperhomocysteinemic rats, but not in the controls. The underlying mechanism of homocysteine-induced CTGF expression was investigated in cultured human umbilical vein smooth muscle cells (HUVSMC). CTGF mRNA expression was induced after treatment with dl-homocysteine (50 micromol L(-1)) for 1 h, which remained at the elevated level for up to 8 h. CTGF protein level increased after homocysteine treatment for 8 h, and the elevated status was maintained for up to 48 h. Several intracellular signals elicited by homocysteine are involved in CTGF synthesis, including protein kinase C (PKC) activation and reactive oxygen species (ROS). Transfection HUVSMCs with a CTGF small interference RNA (siRNA) plasmid, which specifically inhibited the expression of CTGF, decreased extracellular matrix (ECM) accumulation caused by homocysteine.

CONCLUSION

Our results demonstrate that homocysteine could increase the expression of CTGF in VSMC both in vivo and in vitro. The novel findings suggest that homocysteine might contribute to accelerated progression of atherosclerotic lesions by inducing CTGF expression.

Homocysteine stimulates monocyte chemoattractant protein-1 expression in the kidney via nuclear factor-κB activation

Hyperhomocysteinemia, or an elevation of blood homocysteine (Hcy) levels, is associated with cardiovascular disorders. Although kidney dysfunction is an important risk factor causing hyperhomocysteinemia, the direct effect of Hcy on the kidney is not well documented. There is a positive association between an elevation of blood Hcy levels and the development of chronic kidney disease. Inflammatory response such as increased chemokine expression has been implicated as one of the mechanisms for renal disease. Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that is involved in the inflammatory response in renal disease. Nuclear factor-κB (NF-κB) plays an important role in upregulation of MCP-1 expression. We investigated the effect of hyperhomocysteinemia on MCP-1 expression and the molecular mechanism underling such an effect in rat kidneys as well as in proximal tubular cells. Hyperhomocysteinemia was induced in rats fed a high-methionine diet for 12 wk. The MCP-1 mRNA expression and MCP-1 protein levels were significantly increased in kidneys isolated from hyperhomocysteinemic rats. The NF-κB activity was significantly increased in the same kidneys. Pretreatment of hyperhomocysteinemic rats with a NF-κB inhibitor abolished hyperhomocysteinemia-induced MCP-1 expression in the kidney. To confirm the causative role of NF-κB activation in MCP-1 expression, human kidney proximal tubular cells were transfected with decoy NF-κB oligodeoxynucleotide to inhibit NF-κB activation. Such a treatment prevented Hcy-induced MCP-1 mRNA expression in tubular cells. Our results suggest that hyperhomocysteinemia stimulates MCP-1 expression in the kidney via NF-κB activation. Such an inflammatory response may contribute to renal injury associated with hyperhomocysteinemia.

Homocysteine stimulates NADPH oxidase-mediated superoxide production leading to endothelial dysfunction in rats

Elevation of blood homocysteine (Hcy) levels (hyperhomocysteinemia) is a risk factor for cardiovascular disorders. We previously reported that oxidative stress contributed to Hcy-induced inflammatory response in vascular cells. In this study, we investigated whether NADPH oxidase was involved in Hcy-induced superoxide anion accumulation in the aorta, which leads to endothelial dysfunction during hyperhomocysteinemia. Hyperhomocysteinemia was induced in rats fed a high-methionine diet. NADPH oxidase activity and the levels of superoxide and peroxynitrite were markedly increased in aortas isolated from hyperhomocysteinemic rats. Expression of the NADPH oxidase subunit p22phox increased significantly in these aortas. Administration of an NADPH oxidase inhibitor (apocynin) not only attenuated aortic superoxide and peroxynitrite to control levels but also restored endothelium-dependent relaxation in the aortas of hyperhomocysteinemic rats. Transfection of human endothelial cells or vascular smooth muscle cells with p22phox siRNA to inhibit NADPH oxidase activation effectively abolished Hcy-induced superoxide anion production, thus indicating the direct involvement of NADPH oxidase in elevated superoxide generation in vascular cells. Taken together, these results suggest that Hcy-stimulated superoxide anion production in the vascular wall is mediated through the activation of NADPH oxidase, which leads to endothelial dysfunction during hyperhomocysteinemia.

Homocysteine induces monocyte chemoattractant protein-1 expression in hepatocytes mediated via activator protein-1 activation

Hyperhomocysteinemia is characterized by abnormally high concentrations of homocysteine (Hcy) in the plasma. It is a metabolic disorder associated with dysfunction of several organs such as atherosclerosis, altered lipid metabolism, and liver injury. In this study we investigated the effect of Hcy on transcriptional regulation of monocyte chemoattractant protein-1 (MCP-1), a potent chemokine, expression in hepatocytes. Hyperhomocysteinemia was induced in rats by a high-methionine diet for 4 weeks. MCP-1 mRNA and protein levels were significantly elevated in the liver tissue homogenate and in hepatocytes of hyperhomocysteinemic rats. The role of transcription factors in MCP-1 expression was examined by electrophoretic mobility shift assay. Activation of activator protein (AP)-1 but not nuclear factor kappaB was detected in the liver tissue of those rats. Incubation of rat hepatocytes with Hcy (50-200 microm) caused a significant increase in AP-1 activation followed by an increase in intracellular MCP-1 mRNA expression and an elevation of MCP-1 protein secreted into the culture medium. Hcy markedly increased the DNA binding activity of human recombinant AP-1 (c-Fos and c-Jun proteins). The presence of a sulfhydryl group in Hcy was essential for Hcy-induced AP-1 activation. When hepatocytes were transfected with decoy AP-1 oligodeoxynucleotide to inhibit AP-1 activation, Hcy-induced MCP-1 mRNA expression was abolished. Further analysis revealed that increased hepatic MCP-1 expression was positively correlated with the serum MCP-1 level. These results suggest that Hcy-induced MCP-1 expression in the liver is mediated via AP-1 activation, which may contribute to chronic inflammation associated with hyperhomocysteinemia.

Vascular oxidant stress and inflammation in hyperhomocysteinemia

Elevated plasma levels of homocysteine are a metabolic risk factor for atherosclerotic vascular disease, as shown in numerous clinical studies that linked elevated homocysteine levels to de novo and recurrent cardiovascular events. High levels of homocysteine promote oxidant stress in vascular cells and tissue because of the formation of reactive oxygen species (ROS), which have been strongly implicated in the development of atherosclerosis. In particular, ROS have been shown to cause endothelial injury, dysfunction, and activation. Elevated homocysteine stimulates proinflammatory pathways in vascular cells, resulting in leukocyte recruitment to the vessel wall, mediated by the expression of adhesion molecules on endothelial cells and circulating monocytes and neutrophils, in the infiltration of leukocytes into the arterial wall mediated by increased secretion of chemokines, and in the differentiation of monocytes into cholesterol-scavenging macrophages. Furthermore, it stimulates the proliferation of vascular smooth muscle cells followed by the production of extracellular matrix. Many of these events involve redox-sensitive signaling events, which are promoted by elevated homocysteine, and result in the formation of atherosclerotic lesions. In this article, we review current knowledge about the role of homocysteine on oxidant stress-mediated vascular inflammation during the development of atherosclerosis.

Cholestin (Monascus purpureus rice) inhibits homocysteine-induced reactive oxygen species generation, nuclear factor-κB activation, and vascular cell adhesion molecule-1 expression in human aortic endothelial cells

Hyperhomocysteinemia is associated with dysfunction and an independent risk factor of cardiovascular diseases. Cholestin (Monascus purpureus-fermented rice), contains a naturally-occurring statin, which has lipid-modulating and anti-inflammatory effects. We investigated the effects of Cholestin extract on the expression of vascular cell adhesion molecule-1 (VCAM-1) by homocysteine (HCY)-treated human aortic endothelial cells (HAECs). Supplement of HAECs with Cholestin extract significantly suppressed cellular binding between the human monocytic cells U937 and HCY-stimulated HAECs. Quantitative PCR and immunoblot analysis showed that Cholestin extract significantly attenuated HCY-induced expression of VCAM-1 mRNA and protein, respectively. Gel shift assays showed that Cholestin treatment reduced HCY-activated transcription factor nuclear factor-kappaB (NF-kappaB). Furthermore, Cholestin also attenuated reactive oxygen species (ROS) generation in vitro and in HCY-treated HAECs. Supplement with statins including simvastatin and parastatin gave similar results as compared with Cholestin. In conclusion, Cholestin reduces HCY-stimulated endothelial adhesiveness as well as downregulating intracellular ROS formation, NF-kappaB activation, and VCAM-1 expression in HAECs, supporting the notion that the natural compound Cholestin may have potential implications in clinical atherosclerosis disease.

Folic acid reduces chemokine MCP-1 release and expression in rats with hyperhomocystinemia

OBJECTIVE

This study aimed to investigate the effects of folate on the monocyte chemoattractant protein-1 (MCP-1) expression and release in rats with hyperhomocystinemia induced by ingestion of excess methionine.

METHODS AND RESULTS

Thirty male Sprague-Dawley rats (200+/-20 g) were randomly divided into three groups (n=10 for each group): control group (Control), high-homocystinemia (Hhcy) group, and folate treatment (FA) group. They were fed with a normal regular diet, enriched by 1.7% methionine plus 1.7% methionine and 0.006% folate for 45 days. Our study showed the following: (a) A high methionine diet for 45 days is sufficient to induce hyperhomocystinemia; folate supplementation to the rats fed the high-methionine diet prevented an elevation homocysteine (Hcy) levels in the blood (P<.01). (b) Compared with the Control group, the Hhcy group had elevated plasma levels of MCP-1, and Hcy was significantly correlated with MCP-1 (P<.05). (c) The protein and mRNA expression of MCP-1 in the aorta was higher in rats from the Hhcy group than in rats from the Control group. (d) Most important, after folic acid supplementation, the lowering of Hcy levels was accompanied by a marked reduction of MCP-1 expressed in aortae and released from plasma and peripheral blood mononuclear cells (PBMCs) stimulated by oxidized low-density lipoprotein (P<.05, P<.01).

CONCLUSION

Folic acid supplementation not only can blunt the rise in Hcy and reduce MCP-1 released from both plasma and PBMCs of rats with hyperhomocystinemia but also can downgrade MCP-1 expression in the aorta of rats with hyperhomocystinemia.

Homocysteine-lowering therapy: a role in stroke prevention?

On the basis of the results of several recent clinical trials, many researchers have concluded that vitamin therapy designed to lower total homocysteine concentrations is not effective in reducing the risk of cardiovascular events. However, whereas almost all myocardial infarctions are due to plaque rupture, stroke has many more pathophysiological mechanisms, and thrombosis-which is increased by raised total homocysteine concentrations-has an important role in many of these processes. Thus, stroke and myocardial infarction could respond differently to vitamin therapy. A detailed assessment of the results of the recent HOPE-2 trial and a reanalysis of the VISP trial restricted to patients capable of responding to vitamin therapy suggest that higher doses of vitamin B12 and perhaps new approaches to lowering total homocysteine besides routine vitamin therapy with folate, vitamin B6, and vitamin B12 could reduce the risk of stroke. Thus, therapy to lower homocysteine could still help to prevent stroke, if not other vascular outcomes.

The MTHFR 677 C/T polymorphism influences plasma levels of adhesion molecules and nitric oxide

BACKGROUND

Hyperhomocysteinemia is an independent risk factor for cardiovascular events. The T allele of 677 C/T polymorphism at the methylenetetrahydrofolate reductase (MTHFR) gene has been reported to induce mild hyperhomocysteinemia. In the present study, we investigated the relationship between this polymorphism and adhesion molecules and total nitric oxide (NOx).

METHODS

The adhesion molecules tested in the present study were soluble E-selectin (sE-selectin), vascular adhesion molecule (sVCAM), and intercellular adhesion molecule (sICAM). A total of 297 subjects had data on these atherosclerotic biomarkers and the MTHFR genotypes. The genetic effect was estimated in the multivariate regression models with adjustment of covariates. Homocysteine, folate, vitamin B6 and vitamin B12 levels were measured in 181 subjects for the test of association between the biomarkers and homocysteine levels.

RESULTS

The genotype distribution was in Hardy-Weinberg equilibrium. The sVCAM levels increased with the number of the T allele, while the NOx levels decreased with the number of the T allele. We found that the T allele was significantly associated with high sVCAM levels (p=0.002) and low NOx levels (p=0.011) in the regression models. The MTHFR genotypes were associated with homocysteine levels (p=0.031). Mild hyperhomocysteinemia (>12 micromol/L) was significantly associated with sVCAM levels (p=0.036). The NOx levels were lower in the hyperhomocysteinemia group than in the normal homocysteine group, but the difference was not significant. The genotypes were not significantly associated with either sE-selectin or sICAM.

CONCLUSIONS

The detrimental T allele exerted an additive effect to increase sVCAM and decrease NOx concentrations, which may contribute to atherosclerosis.

No evidence for prooxidative effects of homocysteine in vascular endothelial cells

Many epidemiological studies predict a role for homocysteine (HCys) in cardiovascular disease occurrence, progression, and risk factors. In vitro studies demonstrated that HCys is an atherogenic determinant that promotes oxidant stress, inflammation, endothelial dysfunction and cell proliferation. This study originally attempted to examine the mechanism by which exposure of endothelial cells to HCys (0-250 microM) initiates inflammatory reaction and oxidative stress, by (i) investigating whether physiological and pathophysiological concentrations of HCys exhibit a prooxidative activity in vitro, (ii) examining the interaction of monocyte adhesion (Mono Mac 6) to monolayers of human microvascular endothelial cells (HMEC-1) exposed to different HCys concentrations, and (iii) examining if adherent monocytes increase reactive oxygen species either in endothelial cells or in monocytes themselves. However, our results demonstrate that HCys had neither prooxidative nor cytotoxic effects on endothelial cells. Only a moderate time- and concentration-dependent increase in monocyte adhesion up to 28.3 +/- 5.5% was achieved relative to control after 4 h of HCys stimulation. This effect was accompanied by an increased VCAM and ICAM-1 mRNA expression. This "proinflammatory" effect appeared also when HMEC-1 cells were incubated with cysteine or glutathione at the concentration range 0-250 microM, demonstrating a non-specific rather than a specific HCys effect. In addition, adherent monocytes did not increase ROS formation neither in endothelial cells nor in monocytes themselves, indicating no direct or indirect cytotoxic or prooxidative effects of HCys.

Homocysteine induces VCAM-1 gene expression through NF-kappaB and NAD(P)H oxidase activation: protective role of Mediterranean diet polyphenolic antioxidants

Hyperhomocysteinemia is a recognized risk factor for vascular disease, but pathogenetic mechanisms involved in its vascular actions are largely unknown. Because VCAM-1 expression is crucial in monocyte adhesion and early atherogenesis, we evaluated the NF-kappaB-related induction of VCAM-1 by homocysteine (Hcy) and the possible inhibitory effect of dietary polyphenolic antioxidants, such as trans-resveratrol (RSV) and hydroxytyrosol (HT), which are known inhibitors of NF-kappaB-mediated VCAM-1 induction. In human umbilical vein endothelial cells (HUVEC), Hcy, at 100 micromol/l, but not cysteine, induced VCAM-1 expression at the protein and mRNA levels, as shown by enzyme immunoassay and Northern analysis, respectively. Transfection studies with deletional VCAM-1 promoter constructs demonstrated that the two tandem NF-kappaB motifs in the VCAM-1 promoter are necessary for Hcy-induced VCAM-1 gene expression. Hcy-induced NF-kappaB activation was confirmed by EMSA, as shown by the nuclear translocation of its p65 (RelA) subunit and the degradation of the inhibitors IkappaB-alpha and IkappaB-beta by Western analysis. Hcy also increased intracellular reactive oxygen species by NAD(P)H oxidase activation, as shown by the membrane translocation of its p47(phox) subunit. NF-kappaB inhibitors decreased Hcy-induced intracellular reactive oxygen species and VCAM-1 expression. Finally, we found that nutritionally relevant concentrations of RSV and HT, but not folate and vitamin B6, reduce (by >60% at 10(-6) mol/l) Hcy-induced VCAM-1 expression and monocytoid cell adhesion to the endothelium. These data indicate that pathophysiologically relevant Hcy concentrations induce VCAM-1 expression through a prooxidant mechanism involving NF-kappaB. Natural Mediterranean diet antioxidants can inhibit such activation, suggesting their possible therapeutic role in Hcy-induced vascular damage.

Triglyceride-Rich Lipoproteins Prime Aortic Endothelium for an Enhanced Inflammatory Response to Tumor Necrosis Factor-α

High levels of triglyceride-rich lipoproteins (TGRLs) in blood are linked to development of atherosclerosis, yet the mechanisms by which these particles initiate inflammation of endothelium are unknown. TGRL isolated from human plasma during the postprandial state was examined for its capacity to bind to cultured human aortic endothelial cells (HAECs) and alter the acute inflammatory response to tumor necrosis factor-α. HAECs were repetitively incubated with dietary levels of freshly isolated TGRL for 2 hours per day for 1 to 3 days to mimic postprandial lipidemia. TGRL induced membrane upregulation of the low-density lipoprotein family receptors LRP and LR11, which was inhibited by the low-density lipoprotein receptor-associated protein-1. TGRLs alone did not elicit inflammation in HAECs but enhanced the inflammatory response via a 10-fold increase in sensitivity to cytokine stimulation. This was reflected by increased mitogen-activated protein kinase activation, nuclear translocation of NF-κB, amplified expression of endothelial selectin and VCAM-1, and a subsequent increase in monocyte-specific recruitment under shear flow as quantified in a microfabricated vascular mimetic device.

Detrimental role of homocysteine in renal ischemia-reperfusion injury

Ischemia followed by reperfusion is a major cause for renal injury in both native kidney and renal allografts. Hyperhomocysteinemia, a condition of elevated plasma homocysteine (Hcy) level, is associated with cardiovascular diseases. Recent evidence suggests that Hcy, at higher levels, may be harmful to other organs such as the kidney. In this study, we investigated the role of Hcy in ischemia-reperfusion-induced renal injury. The left kidney of a Sprague-Dawley rat was subjected to either 30-min or 1-h ischemia followed by 1- or 24-h reperfusion. Ischemia-reperfusion caused a significant increase in peroxynitrite formation and lipid peroxidation in kidneys, which reflected oxidative stress. The number of apoptotic cells in those kidneys was also markedly increased. Hcy levels were elevated 2.9- and 1.5-fold in kidneys subjected to ischemia alone or ischemia-reperfusion, respectively. Further investigation revealed that elevation of Hcy level in the kidney upon ischemia-reperfusion was due to reduced activity of cystathionine-beta-synthase, a key enzyme in Hcy metabolism. Administration of anti-Hcy antibodies into the kidney not only abolished ischemia-reperfusion-induced oxidative stress and cell death in the kidneys but also restored renal function after 1 h of reperfusion. However, such a protective effect was not sustained after 24 h of reperfusion. In conclusion, ischemia-reperfusion impairs Hcy metabolism in the kidney. Hcy, at elevated levels, is capable of inducing oxidative stress and renal injury. Neutralization of Hcy with antibodies offers transient functional benefit against ischemia-reperfusion-induced oxidative stress and renal injury. These results suggest that Hcy may play a detrimental role in the kidney during ischemia-reperfusion.

Association between homocysteine, vitamin B6 concentrations and inflammation

During the last years, a growing body of evidence has been accumulated on the role of hyperhomocysteinemia in the occurrence of coronary artery disease and other arterial occlusive diseases. The mechanism by which high circulating homocysteine concentrations are a risk factor for atherothrombosis is incompletely understood. The present review is aimed to evaluate the role of inflammation in influencing homocysteine (Hcy) and vitamin B

Clin Chem Lab Med 2007;45:1728–36.

Lysophospholipids increase IL-8 and MCP-1 expressions in human umbilical cord vein endothelial cells through an IL-1-dependent mechanism

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) are both low-molecular-weight lysophospholipid (LPL) ligands which are recognized by the Edg family of G protein-coupled receptors (GPCRs). In endothelial cells, these two ligands activate Edg receptors resulting in cell proliferation and cell migration. Interleukin-8 (IL-8) is a C-X-C chemokine and acts as a chemoattractant of neutrophils, whereas monocyte chemoattractant protein-1 (MCP-1) is a C-C chemokine and functions mainly as a chemoattractant of monocytes/macrophages. Both factors are secreted from endothelial cells and have been implicated in the processes leading to atherosclerosis. We examined the effects of LPLs on the expression of IL-8 and MCP-1, key regulators of leukocyte recruitment in human umbilical cord vein endothelial cells (HUVECs). Work illustrated in this article showed that LPA and S1P enhanced IL-8 and MCP-1 mRNA expressions, and protein secretions in dose- and time-dependent fashions. Maximal mRNA expression appeared at 16 hr post-ligand treatment. Using prior treatments with chemical inhibitors, LPLs enhanced IL-8 and MCP-1 expressions through a Gi-, Rho-, and NFkappaB-dependent mechanism. In a chemotaxis assay system, LPL treatments of endothelial cells enhanced monocyte recruitment through upregulating IL-8 and MCP-1 protein secretions. Pre-incubation with AF12198, an IL-1 receptor antagonist or IL-1 functional blocking antibody both suppressed the enhanced effects elicited by LPLs of IL-8 and MCP-1 mRNA expressions in HUVECs. These results suggest that LPLs released by activated platelets might enhance the IL-8- and MCP-1-dependent chemoattraction of monocytes toward the endothelium through an IL-1-dependent mechanism, which may play an important role in facilitating wound-healing and inflammation processes.

Role of redox factor-1 in hyperhomocysteinemia-accelerated atherosclerosis

Hyperhomocysteinemia (HHcy) is an independent risk factor for atherosclerosis. We have previously shown that homocysteine can induce monocyte chemoattractant protein-1 (MCP-1) secretion via reactive oxygen species (ROS) in human monocytes in vitro. In the present study, we investigated whether redox factor-1 (Ref-1) is involved in HHcy-accelerated atherosclerosis. We used a mild HHcy animal model, aortic roots and peritoneal macrophages were isolated for immunohistochemistry and Western blotting, from apoE-/- and C57BL/6J mice fed a high Hcy diet (1.8 g/L) for 4 or 12 weeks. Four-week HHcy apoE-/- mice showed more plaques and significantly increased immunostaining of Ref-1 and MCP-1 in foam cells, and HHcy mice showed enhanced Ref-1 expression in peritoneal macrophages. To explore the mediating mechanism, incubation with Hcy (100 microM) increased Ref-1 protein level and translocation in human monocytes in vitro. In addition, Hcy-induced NADPH oxidase activity mediated the upregulation of Ref-1. Furthermore, overexpressed Ref-1 upregulated NF-kappaB and MCP-1 promoter activity, and antisense Ref-1 reduced Hcy-induced NF-kappaB DNA-binding activity and MCP-1 secretion. These data indicate that Hcy-induced ROS upregulate the expression and translocation of Ref-1 via NADPH oxidase, and then Ref-1 increases NF-kappaB activity and MCP-1 secretion in human monocytes/macrophages, which may accelerate the development of atherosclerosis.

Asymmetrical dimethylarginine regulates endothelial function in methionine-induced but not in chronic homocystinemia in humans: effect of oxidative stress and proinflammatory cytokines

BACKGROUND

Homocystinemia is a metabolic abnormality associated with endothelial dysfunction and increased cardiovascular disease risk. The underlying mechanisms of these effects, however, are obscure.

OBJECTIVE

We examined the effect of asymmetrical dimethylarginine (ADMA) on endothelial dysfunction in methionine-induced and chronic homocystinemia and evaluated the regulatory role of oxidative stress and proinflammatory cytokines on the release of ADMA.

DESIGN

In this double-blind, placebo-controlled parallel group study, 30 subjects of both sexes (15 with homocystinemia and 15 healthy controls) underwent methionine loading, with simultaneous administration of a combination of vitamin C (2 g) plus alpha-tocopherol (800 IU) or placebo. Endothelial function in forearm resistance vessels and concentrations of ADMA, oxidized LDL, and proinflammatory cytokines were determined at baseline and 4 h after methionine loading.

RESULTS

Both chronic and methionine-induced homocystinemia were associated with increased oxidized LDL (P < 0.01), higher expression of the proinflammatory cytokine interleukin 6 (P < 0.05), and endothelial dysfunction (P < 0.01). Although ADMA rapidly increased in acute homocystinemia (P < 0.01) and was correlated with forearm hyperemic response at 4 h after methionine loading (r = -0.722, P = 0.0001), it was not higher in subjects with high versus low fasting homocysteine. High-dose antioxidant treatment prevented methionine-induced elevation of oxidized LDL and interleukin 6 but failed to prevent the increase in ADMA or endothelial dysfunction.

CONCLUSIONS

Both chronic and methionine-induced homocystinemia are characterized by increased oxidative stress and proinflammatory cytokines, which may contribute to the development of endothelial dysfunction. However, the ADMA pathway is activated only in acute homocystinemia by mechanisms not mediated by oxidized LDL or proinflammatory stimuli.

Folic acid inhibits homocysteine-induced superoxide anion production and nuclear factor kappa B activation in macrophages

Folic acid supplementation is a promising approach for patients with cardiovascular diseases associated with hyperhomocysteinemia. We have demonstrated that homocysteine (Hcy) activates nuclear factor-kappaB (NF-kappaB), a transcription factor that plays an important role in inflammatory responses. The aim of the present study was to investigate the effect of folic acid on Hcy-induced NF-kappaB activation in macrophages. Hcy treatment (100 micromol/L) resulted in NF-kappaB activation and increased monocyte chemoattractant protein-1 (MCP-1) expression in THP-1 derived macrophages. Hcy-induced NF-kappaB activation was associated with a significant increase in the intracellular superoxide anion levels. There was a significant increase in phosphorylation and membrane translocation of NADPH oxidase p47phox subunit in Hcy-treated cells. Addition of folic acid (200 ng/mL) to the culture medium abolished NADPH oxidase-dependent superoxide anion generation in macrophages by preventing phosphorylation of p47phox subunit. Consequently, Hcy-induced NF-kappaB activation and MCP-1 expression was inhibited. Such an inhibitory effect of folic acid was independent of its Hcy-lowering ability. Taken together, these results suggest that folic acid treatment can effectively inhibit Hcy-induced oxidative stress and inflammatory responses in macrophages. This may represent one of the mechanisms by which folic acid supplementation exerts a protective effect in cardiovascular disorders.

Hyperhomocysteinemia induces liver injury in rat: Protective effect of folic acid supplementation

Hyperhomocysteinemia, a condition of elevated blood homocysteine level, is an independent risk factor for cardiovascular diseases. Hyperhomocysteinemia is also found in patients with liver diseases. However, the direct effect of homocysteine on liver injury is not well known. Folic acid supplementation is a promising approach for improving endothelial function in patients with hyperhomocysteinemia. The aim of this study was to investigate the direct effect of hyperhomocysteinemia on liver injury and whether folic acid could offer any protective effect to the liver. Hyperhomocysteinemia was induced in rats fed a high-methionine diet for 4 weeks. There was a significant increase in the serum aspartate aminotransferase and alanine aminotransferase activities reflecting liver injury in hyperhomocysteinemic rats. Hepatic NAD(P)H oxidase was activated during hyperhomocysteinemia leading to increased superoxide anion production and peroxynitrite formation in the liver. As a consequence, the level of lipid peroxides was significantly elevated in livers of hyperhomocysteinemic rats. Folic acid supplementation effectively inhibited NAD(P)H oxidase-mediated superoxide anion production leading to reduced lipid peroxidation in the liver. Folic acid supplementation also alleviated hyperhomocysteinemia-induced liver injury. These results suggest that hyperhomocysteinemia can cause liver injury and supplementation of folic acid offers a hepatoprotective effect.

Tissue factor upregulation drives a thrombosis-inflammation circuit in relation to cardiovascular complications

The extrinsic coagulation is recognized as an 'inducible' signalling cascade resulting from tissue factor (TF) upregulation by exposure to clotting zymogen FVII upon inflammation or tissue injury. Following the substantial initiation, an array of proteolytic activation generates mediating signals (active serine proteases: FVIIa, FXa and FIIa) that lead to hypercoagulation with fibrin overproduction manifesting thrombosis. In addition, TF upregulation plays a central role in driving a thrombosis-inflammation circuit. Coagulant mediators (FVIIa, FXa and FIIa) and endproduct (fibrin) are proinflammatory, eliciting tissue necrosis factor, interleukins, adhesion molecules and many other intracellular signals in different cell types. Such resulting inflammation could ensure 'fibrin' thrombosis via feedback upregulation of TF. Alternatively, the resulting inflammation triggers platelet/leukocyte/polymononuclear cell activation thus contributing to 'cellular' thrombosis. TF is very vulnerable to upregulation resulting in hypercoagulability and subsequent thrombosis and inflammation, either of which presents cardiovascular risks. The prevention and intervention of TF hypercoagulability are of importance in cardioprotection. Blockade of inflammation reception and its intracellular signalling prevents TF expression from upregulation. Natural (activated protein C, tissue factor pathway inhibitor, or antithrombin III) or pharmacological anticoagulants readily offset the extrinsic hypercoagulation mainly through FVIIa, FXa or FIIa inhibition. Therefore, anticoagulants turn off the thrombosis-inflammation circuit, offering not only antithrombotic but anti-inflammatory significance in the prevention of cardiovascular complications.

Stereospecific and Redox-Sensitive Increase in Monocyte Adhesion to Endothelial Cells by Homocysteine

Objective— Previous studies have shown that elevated homocysteine (Hcy) levels promote the development of atherosclerotic lesions in atherosclerosis-prone animal models. There is evidence that oxidant stress contributes to Hcy’s deleterious effects on the vasculature. The accumulation and adhesion of monocytes to the vascular endothelium is a critical event in the development of atherosclerosis. We investigated the effects of Hcy on the interaction between human endothelial cells (EC) (EC line EA.hy 926 and primary human umbilical vein EC [HUVEC]) and the monocytic cell line THP-1, and the impact of vascular oxidant stress and redox-sensitive signaling pathways on these events.

Methods and Results— L-Hcy, but not D-Hcy, increases the production of reactive oxygen species inside EC, enhances nuclear factor(NF)-κB activation, and stimulates intercellular adhesion molecule-1 (ICAM-1) RNA transcription and cell surface expression. This leads to a time- and dose-dependent increase in monocyte adhesion to ECs. Pretreatment of ECs with superoxide scavengers (MnTBAP and Tiron) or with an inhibitor of NF-κB activation abolished Hcy-induced monocyte adhesion, ICAM-1 expression, and nuclear translocation of NF-κB.

Conclusions— These findings suggest that reactive oxygen species produced under hyperhomocysteinemic conditions may induce a proinflammatory situation in the vessel wall that initiates and promotes atherosclerotic lesion development.

Homocysteine activates cAMP-response element binding protein in HepG2 through cAMP/PKA signaling pathway

OBJECTIVE

Hyperhomocysteinemia is an independent risk factor for cardiovascular disorders. Our previous studies demonstrated that hyperhomocysteinemia not only elicited inflammatory responses in the vascular endothelium but also induced fatty liver and hypercholesterolemia via transcriptional regulation. One of the transcription factors activated in the liver during hyperhomocysteinemia was cAMP-response element binding protein (CREB). CREB regulates the expression of many genes including those involved in lipid and glucose metabolism. In this study, we investigated the molecular mechanism by which Hcy activated CREB in rat liver and in hepatocytes (HepG2).

METHOD AND RESULTS

Hyperhomocysteinemia was induced in rats by feeding high-methionine diet for 4 weeks. There was a significant increase in hepatic cAMP levels, protein kinase A (PKA) activity and an activation of CREB. Incubation of HepG2 cells with Hcy (50 to 100 micromol/L) significantly enhanced CREB phosphorylation and subsequently increased CREB/DNA binding activity. PKA was activated in Hcy-treated cells as a result of increased cellular cAMP level. Inhibition of adenylyl cyclase not only reduced the intracellular cAMP levels elevated by Hcy treatment but also inhibited PKA activation and prevented Hcy-induced CREB phosphorylation.

CONCLUSIONS

These results suggest that the cAMP/PKA signaling pathway plays an important role in mediating Hcy-induced CREB activation in hepatocyte.

Hyperhomocystinemia impairs endothelial function and eNOS activity via PKC activation

OBJECTIVE

A risk factor for cardiovascular disease, hyperhomocystinemia (HHcy), is associated with endothelial dysfunction. In this study, we examined the mechanistic role of HHcy in endothelial dysfunction.

METHODS AND RESULTS

Through the use of 2 functional models, aortic rings and intravital video microscopy of the cremaster, we found that arterial relaxation in response to the endothelium-dependent vessel relaxant, acetylcholine or the nitric oxide synthase (NOS) activator (A23187), was significantly impaired in cystathionine beta-synthase null (CBS(-/-)) mice. However, the vascular smooth muscle cell (VSMC) response to the nitric oxide (NO) donor (SNAP) was preserved in CBS(-/-) mice. In addition, superoxide dismutase and catalase failed to restore endothelium-dependent vasodilatation. Endothelial nitric oxide synthase (eNOS) activity was significantly reduced in mouse aortic endothelial cells (MAECs) of CBS(-/-) mice, as well as in Hcy-treated mouse and human aortic endothelial cells (HAECs). Hcy-mediated eNOS inhibition--which was not rescued by adenoviral transduction of superoxide dismutase and glutathione peroxidase, or by tetrahydrobiopterin, sepiapterin, and arginine supplementations in MAEC--was associated with decreased protein expression and increased threonine 495 phosphorylation of eNOS in HAECs. Ultimately, a protein kinase C (PKC) inhibitor, GF109203X (GFX), reversed Hcy-mediated eNOS inactivation and threonine 495 phosphorylation in HAECs.

CONCLUSIONS

These data suggest that HHcy impairs endothelial function and eNOS activity, primarily through PKC activation.

Associations between inherited thrombophilias, gestational age, and cerebral palsy

OBJECTIVE

This study was undertaken to investigate associations between inherited thrombophilic polymorphisms and cerebral palsy (CP) in a large case-control study.

STUDY DESIGN

This is a population-based case-control study. Genomic DNA from newborn screening cards of 443 white CP cases and 883 white controls was tested for factor V Leiden (FVL, G1691A), prothrombin gene mutation (PGM, G20210A), and methylenetetrahydrofolate reductase (MTHFR) C677T and MTHFR A1298C.

RESULTS

MTHFR C677T was associated with an increased risk of developing any CP (32-36 weeks' gestation, homozygous odds ratio [OR] 2.55, 95% CI 1.12-5.74; heterozygous OR 1.91, 95% CI 1.01-3.66). MTHFR C677T was also associated with diplegia at both less than 32 weeks' gestation (homozygous OR 2.76, 95% CI 1.21-6.12) and all gestations (heterozygous OR 1.58 95%, CI 1.02-2.45). For children less than 32 weeks, FVL homozygosity may be associated with an increase in the risk of developing quadriplegia (OR 9.12, 95% CI 0.86-53.71). MTHFR A1298C (heterozygous) was associated with a reduced risk of diplegia developing at 32 to 36 weeks' gestation (OR 0.16, 95% CI 0.02-0.70). There were no associations between any type of CP and thrombophilia for children born 37 weeks or greater. Heterozygous PGM and homozygous MTHFR C677T combined were associated with quadriplegia at all gestational ages (OR 5.33, 95% CI 1.06-23.25).

CONCLUSION

MTHFR C677T approximately doubles the risk of CP in preterm infants. A combination of homozygous MTHFR C677T and heterozygous PGM increases the risk of quadriplegia 5-fold at all gestational ages.

Elevated levels of homocysteine compromise blood-brain barrier integrity in mice

Elevated levels of plasma homocysteine (Hcy) correlate with increased risk of cardiovascular and Alzheimer diseases. We studied the effect of elevated Hcy on the blood-brain barrier (BBB) to explore the possibility of a vascular link between the 2 diseases. On a hyperhomocysteinemic diet, cystathionine beta-synthase (Cbs)-heterozygous mice develop hyperhomocysteinemia. Intravital microscopy analysis of the mesenteric venules showed that leukocyte rolling velocity was markedly decreased and numbers of adherent cells were increased in the mutant mice. This was due at least in part to increased expression of P-selectin. BBB permeability was measured by Evans blue dye permeation and was found to be 25% greater in the Cbs(+/-) cortex compared with wild-type controls. Our study suggests an important toxic effect of elevated Hcy on brain microvessels and implicates Hcy in the disruption of the BBB.

Endothelial function markers in parkinsonian patients with hyperhomocysteinemia

Hyperhomocysteinemia is considered a risk factor for vascular disease causing endothelial damage and consequently atherogenesis. The purpose of this study was to investigate the effect of elevated homocysteine on certain biochemical markers of endothelial function in patients with idiopathic Parkinson's disease (PD). Blood homocysteine levels were assessed in 57 PD patients and 40 matched normal controls. Investigation of the C677T 5,10 methylenetetrahydrofolate reductase (MTHFR) genotype was also performed in 43 PD patients. The following markers of endothelial function were assessed: superoxide dismutase (SOD), nitric oxide (NO), sICAM-1 and sE-selectin. Homocysteine levels were found mildly elevated in PD patients particularly in those treated with L-Dopa. MTHFR genotype did not influence significantly this finding. SOD activity was found reduced but it was not correlated to homocysteine levels. All other parameters measured were normal and were not related to hyperhomocysteinemia. Our findings indicate that mild hyperhomocysteinemia in PD patients was not associated with endothelial dysfunction.

Rosiglitazone reduces serum homocysteine levels, smooth muscle proliferation, and intimal hyperplasia in Sprague-Dawley rats fed a high methionine diet

Homocysteine (Hcy) is a metabolite of the essential amino acid methionine. Hyperhomocysteinemia is associated with vascular disease, particularly carotid stenosis. Rosiglitazone, a ligand of the peroxisome proliferator-activated receptor gamma , attenuates balloon catheter-induced carotid intimal hyperplasia in type 2 diabetic rats. We studied 4 groups (n = 7 per group) of adult female Sprague-Dawley rats fed (a) powdered laboratory chow (control), (b) control diet with rosiglitazone (3.0 mg/kg/d), (c) diet containing 1.0% l -methionine, and (d) diet containing methionine and rosiglitazone. After 1 week on high methionine diet, the rats were administered an aqueous preparation of rosiglitazone by oral gavage. One week after initiation of rosiglitazone, balloon catheter injury of the carotid artery was carried out using established methods, and the animals continued on their respective dietary and drug regimens for another 21 days. At the end of the experimental period, blood samples were collected, and carotid arteries and liver were harvested. Serum Hcy increased significantly on methionine diet compared with controls (28.9 +/- 3.2 vs 6.3 +/- 0.04 micromol/L). Development of intimal hyperplasia was 4-fold higher in methionine-fed rats; this augmentation was significantly reduced ( P < .018) in rosiglitazone-treated animals. Rosiglitazone treatment significantly ( P < .001) suppressed Hcy levels and increased the activity of the Hcy metabolizing enzyme, cystathionine-beta-synthase in the liver samples. Hcy (100 micromol/L) produced a 3-fold increase in proliferation of rat aortic vascular smooth muscle cells; this augmentation was inhibited by incorporating rosiglitazone (10 micromol/L). After balloon catheter injury to the carotid artery of animals on a high methionine diet, there was an increase in the rate of development of intimal hyperplasia consistent with the known effects of Hcy. It is demonstrated for the first time that the peroxisome proliferator-activated receptor gamma agonist rosiglitazone can attenuate the Hcy-stimulated increase in the rate of development of intimal hyperplasia indirectly by increasing the rate of catabolism of Hcy by cystathionine-beta-synthase and directly by inhibiting vascular smooth muscle cell proliferation. These findings may have important implications for the prevention of cardiovascular disease and events in patients with hyperhomocysteinemia (HHcy).

Role of hyperhomocysteinemia in endothelial dysfunction and atherothrombotic disease

Hyperhomocysteinemia (HHcy) is an independent risk factor for cardiovascular disease, including ischemic heart disease, stroke, and peripheral vascular disease. Mutations in the enzymes responsible for homocysteine metabolism, particularly cystathionine beta-synthase (CBS) or 5,10-methylenetetrahydrofolate reductase (MTHFR), result in severe forms of HHcy. Additionally, nutritional deficiencies in B vitamin cofactors required for homocysteine metabolism, including folic acid, vitamin B6 (pyridoxal phosphate), and/or B12 (methylcobalamin), can induce HHcy. Studies using animal models of genetic- and diet-induced HHcy have recently demonstrated a causal relationship between HHcy, endothelial dysfunction, and accelerated atherosclerosis. Dietary enrichment in B vitamins attenuates these adverse effects of HHcy. Although oxidative stress and activation of proinflammatory factors have been proposed to explain the atherogenic effects of HHcy, recent in vitro and in vivo studies demonstrate that HHcy induces endoplasmic reticulum (ER) stress, leading to activation of the unfolded protein response (UPR). This review summarizes the current role of HHcy in endothelial dysfunction and explores the cellular mechanisms, including ER stress, that contribute to atherothrombosis.

Is homocysteine important as risk factor for coronary heart disease?

AIM

Homocysteine (Hcy), a sulfur-containing amino acid product of methionine metabolism, may play an important role in the development of cardiovascular disease. In this paper we review available knowledge on the pathways leading to synthesis and degradation of Hcy, as well as on the genetic and environmental factors affecting its plasma levels, focussing on its potential role in the development of coronary heart disease.

DATA SYNTHESIS

Hyperhomocysteinemia (HHcy) is determined by genetic and environmental factors and represents a modifiable cardiovascular risk factor since vitamin supplementation has been shown to effectively lower plasma homocysteine levels. While case-control and cross-sectional studies consistently showed an association of HHcy with cardiovascular disease, prospective studies have given conflicting results. Thus, the role of HHcy in the development of coronary heart disease is still under debate. Furthermore, it remains unclear which patients should be screened for HHcy and treated to correct HHcy.

CONCLUSIONS

Available information collectively suggests that although HHcy can be regarded as a minor risk factor for coronary heart disease, it interacts with other risk factors in triggering new events in patients with known CAD. Thus, the treatment of mild HHcy with folate supplementation is appropriate in particular in high risk patients or patients with established CAD who do not present with the "traditional" risk factors.

Atherosclerosis: humoral and cellular factors of inflammation

In the past decade, atherosclerosis has come to be recognized as active and inflammatory rather than simply a passive process of lipid infiltration or a reparative process after endothelial injury. In general, atherosclerosis can be considered as an intramural chronic inflammation resulting from interactions between modified lipoproteins, monocyte-derived macrophages, lymphocytes, and the normal cellular elements of the arterial wall. The process of inflammation occurs in response to functional and structural injury through a variety of known and unknown stimuli and is active over years and decades. Here, we review recent experimental and human studies of inflammatory mechanisms underlying the pathogenesis of atherosclerosis.

Negative association between circulating total homocysteine and proinflammatory chemokines MCP-1 and RANTES in prepubertal lean, but not in obese, children

This study investigated in prepubertal obese children (POC), compared with prepubertal lean children (PLC), a possible relation among plasma total homocysteine (tHcy)-an independent risk factor for future atherosclerosis-and MCP-1 and RANTES, two circulating chemokines inducing leukocyte transendothelial migration (TEM), implicated in the initial stages of the inflammatory part of the atherosclerotic process. Seventy-two POC were evaluated for circulating tHcy, MCP-1, and RANTES, and compared with 42 healthy PLC. The mean adjusted (for age, sex as well as log10total insulin, vitB12, folate, total cholesterol, HDL cholesterol, log10triglycerides, and log10glucose levels) differences in tHcy, MCP-1, and RANTES levels between PLC and POC were all significant [1.16 nmol/mL (P = 0.03), 26.6 pg/mL (P = 0.02), and 52.9 pg/mL (P = 0.03), respectively]. In PLC, but not in POC, tHcy levels were negatively associated with both circulating MCP-1 (B = -1.68, P = 0.007) and RANTES (B = -1.16, P = 0.01) after adjusting for age, sex, BMI, as well as log10total insulin, vitB12, folate, total cholesterol, HDL cholesterol, log10triglycerides, and log10glucose levels. In conclusion, in POC there is a lack, in contrast to PLC, of a possibly autoregulatory, negative association of elevated tHcy levels to increased MCP-1 and RANTES levels. This could contribute to future, homocysteine-induced atherosclerosis.

Endothelial Lipase Modulates Monocyte Adhesion to the Vessel Wall

Endothelial lipase (EL), a new member of the lipoprotein lipase gene family, plays a central role in high density lipoprotein metabolism. Previous studies indicated that EL is expressed in endothelial cells, macrophages, and smooth muscle cells in atherosclerotic lesions in human coronary arteries. However, the functional role of EL in the local vessel wall remains obscure. In this study, we evaluated the ability of EL to modulate monocyte adhesion to the endothelial cell surface. EL mRNA and protein levels were markedly increased in tissues of the mouse model of inflammation induced by lipopolysaccharide injection. Adhesion assays in vitro revealed that overexpression of EL in COS7 or Pro5 cells enhanced monocyte bindings to the EL-expression cells. Heparin or heparinase treatment inhibited EL-mediated increases of monocyte adhesion in a dose-dependent manner. Moreover, ex vivo adhesion assays revealed that the number of adherent monocytes on aortic strips was significantly increased in EL transgenic mice and decreased in EL knock-out mice as compared with wild-type mice. These results suggest that EL on the endothelial cell surface can promote monocyte adhesion to the vascular endothelium through the interaction with heparan sulfate proteoglycans. Thus, the up-regulation of EL by inflammatory stimuli may be involved in the progression of inflammation.

Hyperhomocysteinemia activates NF-kappaB and inducible nitric oxide synthase in the kidney

BACKGROUND

Hyperhomocysteinemia is an independent risk factor for cardiovascular disorders. Injury of multiple organs, including the kidney, was observed in hyperhomocysteinemic individuals. Activation of a transcription factor, namely, nuclear factor kappa B (NF-kappaB), plays an important role in inflammatory response and can exacerbate organ injury. The objective of the present study was to investigate the effect of hyperhomocysteinemia on renal NF-kappaB activation and the consequence of such activation.

METHODS

Hyperhomocysteinemia was induced in Sprague-Dawley rats after 4 weeks of a high-methionine diet. Activation of NF-kappaB was determined by electrophoretic mobility shift assay. Role of inhibitor protein IkappaBalpha was examined by Western immunoblotting analysis.

RESULTS

There was a significant increase in the level of phosphorylated IkappaBalpha protein in kidneys of hyperhomocysteinemic rats. This resulted in a decrease in the IkappaBalpha protein level leading to NF-kappaB activation. As a consequence, the expression of inducible nitric oxide synthase (iNOS) mRNA and protein was significantly elevated in kidneys of hyperhomocysteinemic rats. Increased nitric oxide production (150% of the control) resulted in peroxynitrite formation in these kidneys. Pretreatment of rats with a NF-kappaB inhibitor not only abolished NF-kappaB activation, but also reversed hyperhomocysteinemia-induced iNOS expression in the kidney.

CONCLUSION

Hyperhomocysteinemia alone can activate NF-kappaB and hence induce iNOS-mediated nitric oxide production in the kidney leading to increased peroxynitrite formation. This may represent one of the mechanisms for renal dysfunction in hyperhomocysteinemia.

Effects of heparin-mediated extracorporeal low-density lipoprotein precipitation beyond lowering proatherogenic lipoproteins—reduction of circulating proinflammatory and procoagulatory markers

In addition to hypercholesterolemia, proinflammatory and prothrombotic markers have been suggested to play an important role in atherogenesis. We examined whether heparin-mediated extracorporeal low-density lipoprotein precipitation (HELP) therapy modulates the circulating levels of proinflammatory and prothrombotic markers. Twenty-two coronary heart disease (CHD) patients undergoing regular HELP-apheresis (18 males, 4 females, mean age 57.3 +/- 10.9 years) were enrolled in this study. A single HELP therapy treatment significantly decreased the circulating levels of high sensitivity C-reactive protein (hs-CRP), soluble vascular adhesion molecule-1 (sVCAM-1), soluble E-selectin, lipopolysaccharide binding protein (LBP), endothelin-1 (ET-1), and monocyte chemoattractant protein-1 (MCP-1) on average by 67, 37, 24, 27, 24, and 15%, respectively. Prothrombotic factors including fibrinogen, tissue factor (TF), soluble CD40 ligand (sCD40L), and homocysteine were decreased by 66, 27, 16, and 22%, respectively. In accordance with previous studies HELP therapy reduced total cholesterol, low density lipoprotein (LDL) cholesterol, and Lp(a) mass by 50, 61, and 62%, respectively. Our data suggest that simultaneous reduction of proinflammatory and prothrombotic factors together with atherogenic lipoproteins by HELP-apheresis may contribute to improvement of endothelial dysfunction and thereby inhibit progression of atherosclerotic lesions and stabilize the existing plaque.

Association of multiple cellular stress pathways with accelerated atherosclerosis in hyperhomocysteinemic apolipoprotein E-deficient mice

BACKGROUND

A causal relation between hyperhomocysteinemia (HHcy) and accelerated atherosclerosis has been established in apolipoprotein E-deficient (apoE-/-) mice. Although several cellular stress mechanisms have been proposed to explain the atherogenic effects of HHcy, including oxidative stress, endoplasmic reticulum (ER) stress, and inflammation, their association with atherogenesis has not been completely elucidated.

METHODS AND RESULTS

ApoE-/- mice were fed a control or a high-methionine (HM) diet for 4 (early lesion group) or 18 (advanced lesion group) weeks to induce HHcy. Total plasma homocysteine levels and atherosclerotic lesion size were significantly increased in early and advanced lesion groups fed the HM diet compared with control groups. Markers of ER stress (GRP78/94, phospho-PERK), oxidative stress (HSP70), and inflammation (phospho-IkappaB-alpha) were assessed by immunohistochemical staining of these atherosclerotic lesions. GRP78/94, HSP70, and phospho-IkappaB-alpha immunostaining were significantly increased in the advanced lesion group fed the HM diet compared with the control group. HSP47, an ER-resident molecular chaperone involved in collagen folding and secretion, was also increased in advanced lesions of mice fed the HM diet. GRP78/94 and HSP47 were predominantly localized to the smooth muscle cell-rich fibrous cap, whereas HSP70 and phospho-IkappaB-alpha were observed in the lipid-rich necrotic core. Increased HSP70 and phospho-IkappaB-alpha immunostaining in advanced lesions of mice fed the HM diet are consistent with enhanced carotid artery dihydroethidium staining. Interestingly, GRP78/94 and phospho-PERK were markedly increased in macrophage foam cells from early lesions of mice fed the control or the HM diet.

CONCLUSIONS

Multiple cellular stress pathways, including ER stress, are associated with atherosclerotic lesion development in apoE-/- mice.

Hyperhomocyst(e)inemia and elevated soluble vascular cell adhesion molecule-1 concentrations are associated with an increased risk of preeclampsia

Hyperhomocyst(e)inemia (HHcy) is a risk factor of endothelial dysfunction and preeclampsia. Soluble vascular cell adhesion molecule-1 (sVCAM-1), a specific marker of endothelial dysfunction, is elevated in preeclampsia. Few have assessed the joint contribution of these biomarkers in predicting preeclampsia. We assessed the extent to which HHcy and elevated sVCAM-1 are independently and jointly associated with preeclampsia. We conducted a case-control analysis of 100 preeclampsia cases and 100 controls to test our study hypothesis. Maternal plasma was collected before labor onset. Total plasma homocysteine (tHcy) was measured using high-performance liquid chromatography with electrochemical detection procedures. Plasma sVCAM-1 was determined using ELISA. Using the distribution of each analyte among controls, elevated tHcy was defined as plasma tHcy >6.6 micromol/l and elevated sVCAM-1 was defined as plasma concentrations >845 ng/ml (i.e., values above the median). Odds ratios (OR) and 95% confidence intervals (CIs) were calculated. Compared with women without elevated tHcy and without elevated sVCAM-1 (the referent group), those with elevated sVCAM-1 alone had a 4.1-fold increased risk of preeclampsia (95% CI 1.2-13.8). The OR for women with elevated tHcy alone was 2.2 (95% CI 0.6-7.9). The OR for women with elevated tHcy and sVCAM-1 was 13.2 (95% CI 4.1-42.2). Elevated tHcy and sVCAM-1 together were strongly associated with an increased risk of preeclampsia. Larger, prospective studies are needed to confirm these findings and to determine the extent to which elevated tHcy and sVCAM-1 together in early pregnancy are predictive of preeclampsia risk.

Lysosomal cysteine proteases in atherosclerosis

Atherosclerosis is an inflammatory disease characterized by extensive remodeling of the extracellular matrix architecture of the arterial wall. Although matrix metalloproteinases and serine proteases participate in these pathologic events, recent data from atherosclerotic patients and animals suggest the participation of lysosomal cysteine proteases in atherogenesis. Atherosclerotic lesions in humans overexpress the elastolytic and collagenolytic cathepsins S, K, and L but show relatively reduced expression of cystatin C, their endogenous inhibitor, suggesting a shift in the balance between cysteine proteases and their inhibitor that favors remodeling of the vascular wall. Extracts of human atheromatous tissue show greater elastolytic activity in vitro than do those from healthy donors. The cysteinyl protease inhibitor E64d limits this increased elastolysis, indicating involvement of cysteine proteases in elastin degradation during atherogenesis. Furthermore, inflammatory cytokines augment expression and secretion of active cysteine proteases from cultured monocyte-derived macrophages, vascular smooth muscle cells, and endothelial cells and increase degradation of extracellular elastin and collagen. Cathepsin S-deficient cells or those treated with E64d show significantly impaired elastolytic or collagenolytic activity. Additionally, recent in vivo studies of atherosclerosis-prone, LDL receptor-null mice lacking cathepsin S show participation of this enzyme in the initial infiltration of leukocytes, medial elastic lamina degradation, endothelial cell invasion, and neovascularization, illustrating an important role for cysteine proteases in arterial remodeling and atherogenesis.