Biologic effect and molecular regulation of vascular apoptosis in atherosclerosis

The effect of dual antioxidant modification on oxidative stress resistance and anti-dysfunction of non-split HDL and recombinant HDL

Recombinant high-density lipoprotein (rHDL) as anti-atherosclerosis (AS) vehicle has unique advantages including multiple anti-atherogenic functions and homing features to plaques. However, rHDL may be converted into dysfunctional forms due to complex treatment during preparation. Herein, oxidation-induced dysfunction of non-split HDL and rHDL was initially investigated. It was found that although both non-split HDL and rHDL showed oxidative dysfunction behavior, non-split HDL demonstrated superior oxidation defense compared to rHDL due to its intact composition and avoidance of overprocessing such as split and recombination. Unfortunately, in vivo oxidative stress could compromise the functionality of HDL. Therefore, surface engineering of non-split HDL and rHDL with cascade antioxidant enzyme analogues Ebselen and mitochondrial-targeted TPGS-Tempo was conducted to construct a dual-line defense HDL nano system (i.e., T@E-HDLs/rHDL), aiming to restore plaque redox balance and preserving the physiological function of HDL. Results indicated that both T@E-HDLs and rHDLs performed without distinction and exhibited greater resistance to oxidative stress damage as well as better functions than unmodified HDLs in macrophage foam cells. Overall, the modification of dual antioxidants strategy bridges the gap between non-split HDL and rHDL, and provides a promising resolution for the dilemmas of oxidative stress in plaques and HDL self dysfunction.

Knockdown of ADAMDEC1 ameliorates ox-LDL-induced endothelial cell injury and atherosclerosis progression

This study was designed to investigate the role of a disintegrin and metalloproteinase domain-like protein decysin 1 (ADAMDEC-1) in atherosclerosis (AS). The Gene Expression Omnibus (GEO) database was utilized to identify differentially expressed genes (DEGs) between carotid atheroma plaque and carotid tissue adjacent atheroma plaque obtained from AS patients. Gene functional enrichment analysis was conducted on DEGs using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG). QRT-PCR was employed to quantify mRNAs expression. AS animal model was established using ApoE-/- mice; serum triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) levels were detected. Aortic sinus atherosclerotic lesions were observed using H&E staining and Oil Red O staining. ADAMDEC-1 was silenced using small interfering RNAs (siRNAs) in human vascular smooth muscle cells (HVSMCs). Cell proliferation, migration, and cell cycle progression were detected by cell count kit-8 (CCK8), 5-ethynyl-2'-deoxyuridine (EDU), wound scratch healing assay, transwell assay, and flow cytometry, respectively. Western blot was used to evaluate various protein expression levels. Our results showed that ADAMDEC-1 was highly expressed in the serum of AS patients, consistent with the in silico results. The elevated TG, LDL-C, and HDL-C levels along with H&E and Oil Red O staining confirmed the successful establishment of the AS mouse model. ADAMDEC-1 expression was also elevated in AS mice. ADAMDEC-1 knockdown in HVSMCs suppressed cell proliferation, inhibited the expression of proliferating cell nuclear antigen (PCNA), and reduced the levels of matrix metalloproteinases (MMP2 and MMP9) proteins. Protein-protein interaction (PPI) analysis indicated that ADAMDEC-1 was associated with CXCL9, CCR5, TNF-α, TNFR1, and NF-κB-p50. The expression levels of CXCL9, CCR5, TNF-α, TNFR1, and NF-κB-p50 increased, while ADAMDEC-1 knockdown attenuated the expression of these proteins. Our study findings substantiate that ADAMDEC-1 may represent a novel target for AS.

Investigation of highly expressed PCSK9 in atherosclerotic plaques and ox-LDL-induced endothelial cell apoptosis

The present study aimed to explore the direct toxicity of proprotein convertase subtilisin/kexin type 9 (PCSK9) to atherosclerosis (AS) and its association with apoptotic endothelial cells. Apolipoprotein E−/− mice were randomly divided into two groups, control and experimental. The control group was administered a normal diet and the experimental group was administered a high-fat diet. After 20 weeks, the aorta was isolated and dissected. Hematoxylin and eosin staining, and immunohistochemical analysis were performed. Human umbilical vein endothelial cells were incubated with varied concentrations of oxidized low-density lipoprotein (ox-LDL) for different times. The apoptotic rate was detected by flow cytometry. Western blotting and reverse transcription-quantitative polymerase chain reaction analysis were conducted to detect the expression of PCSK9, B-cell lymphoma 2 (Bcl-2), bcl-2-like protein 4 (Bax) and caspase-3. Short hairpin (sh) RNA-PCSK9 was transfected into endothelial cells using lentiviral transfection. The expression levels of PCSK9, Bax, Bcl-2, caspase-3 and the mitogen-activated protein kinase (MAPK) pathway proteins were detected. The high-fat group was successfully established as an AS model and PCSK9 was highly expressed in the AS plaque. Treatment with ox-LDL induced apoptosis and increased mRNA and protein levels of PCSK9. PCSK9 mRNA and proteins levels were downregulated by shRNA-PCSK9. The deficiency of PCSK9 markedly inhibited the expression of pro-apoptotic proteins and promoted anti-apoptotic proteins. In addition, phosphorylation of p38 and c-Jun N-terminal kinases was altered by shRNA-PCSK9. Targeting of PCSK9 by shRNA-PCSK9 may repress endothelial cell apoptosis through MAPK signaling in AS, providing a novel direction for understanding the mechanism and treatment of AS.

CD1d serves as a surface receptor for oxidized cholesterol induction of peroxisome proliferator-activated receptor-γ

OBJECTIVE

The cluster of differentiation-1d (CD1d) recognizes and presents the lipid antigens to NK-T lymphocytes. Atherosclerotic lesions contain atherogenic lipids, mainly cholesterol and its oxides. Peroxisome proliferator-activated receptor-γ (PPARγ) is also known to exist in atherosclerotic lesions, participating in regulation of lipid metabolism. The current study tested whether CD1d acts as a surface receptor that mediates induction and activation of PPARγ by oxysterols commonly found in atherosclerotic lesions.

METHODS AND RESULTS

CD1d overexpression in HEK 293 cells transfected with CD1d cDNA was confirmed by fluorescence, flow cytometry, Western blotting and mRNA expression. Tritiated ((3)H) 7-ketocholesterol (7K) was used for lipid binding assays. Radioactive assessment demonstrated an increased 7K-binding activity HEK 293 cells with CD1d overexpression. The 7K binding could be blocked by another oxysterol, 25-hydroxycholesterol, but not by native free cholesterol. Addition of CD1d:IgG dimer protein or an anti-CD1d antibody, but not control IgG, significantly diminished 7K binding to CD1d-expressing HEK 293 cells. CD1d deficiency markedly diminished the 7K-binding in macrophages and smooth muscle cells. Western blot and gel shift assays demonstrated that CD1d-mediated 7K binding induced expression and activation of PPARγ. The PPARγ agonist PGJ2 enhances the 7K stimulatory effect on PPARγ expression and activity but the antagonist GW9662 inhibits the 7K effect on the CD1d-expressing cells.

CONCLUSIONS

CD1d acts as a cell surface receptor that recognizes and binds oxysterols and initializes a pathway connecting oxysterol binding to PPARγ activation.

Essential Oils from Fructus A. zerumbet Protect Human Aortic Endothelial Cells from Apoptosis Induced by Ox-LDL In Vitro

Alpinia zerumbet is a miao folk medicinal plant widely used in the Guizhou Province of southwest China that contains several bioactive constituents and possesses protective effects against cardiovascular diseases. In the present study, we evaluated the protective effect of essential oils derived from Fructus Alpiniae zerumbet (EOFAZ) on oxidized lowdensity-lipoprotein- (ox-LDL-) induced apoptosis in human aortic endothelial cells (HAECs). Following exposure to ox-LDL, HAECs presented with classical characteristics of apoptosis. However, EOFAZ ameliorated these morphological alterations and also inhibited the decrease in cell viability. In addition, EOFAZ abrogated the number of TUNEL or Hoechst 33258 stained positive cells observed after ox-LDL challenge. Investigation into the mechanisms of this inhibition revealed that EOFAZ treatment resulted in a downregulation of Bax and Caspase-3 at both the protein and mRNA expression levels. Moreover, EOFAZ was found to upregulate Bcl-2 protein and mRNA levels and to attenuate ox-LDL-induced HAECs injury caused by apoptosis, revealing both its therapeutic potential for endothelial cell injury protection and its clinical application for atherosclerosis.

DaoTan decoction (DTD) inhibits tumor necrosis factor-α (TNF-α)-induced expression of intercellular adhesion molecule-1 (ICAM-1), p53 and p21, in human umbilical vein endothelia cells (HUVECs)

CONTEXT

DTD is a Chinese herb prescription used for centuries to treat atherosclerosis or dizziness. Previous studies show that DTD could inhibit ICAM-1 expression induced by TNF-α. However, its mechanism has never been clearly described.

OBJECTIVE

To examine the hypothesis that DTD might inhibit TNF-α-induced ICAM-1 expression through regulating the expression of p53 and p21.

MATERIALS AND METHODS

The rats were orally treated with DTD for 3 d (2.3 g/kg per day), and then the serum was collected. HUVECs were cultured and stimulated by TNF-α with or without DTD serum (5, 10, and 20%). The expression of ICAM-1 mRNA was examined by RT-PCR and the expression of p53 and p21 was examined by western blot analysis.

RESULTS

The ICAM-1 mRNA levels induced by TNF-α were significantly reduced from 23 to 47%, and the expression of p53 and p21 mRNA levels were significantly reduced from 13 to 43% and 14 to 42%, as the concentration of DTD serum increased. In western blot, TNF-α-induced the expression of p53 and was inhibited from 15 to 53%, by DTD serum in a concentration-dependent manner. TNF-α-induced expression of p21 was inhibited from 2 to 37%, by DTD serum in a concentration-dependent manner.

DISCUSSION AND CONCLUSION

DTD has a function of "dissolving phlegm", thus it is chosen for the treatment of atherosclerosis. This study demonstrated that DTD could significantly inhibit the expression of ICAM-1, p53 and p21, which are important factors of atherosclerosis. Therefore, the present study indicates the pharmacological basis for treatment of atherosclerosis with DTD.

Proteases in cardiometabolic diseases: Pathophysiology, molecular mechanisms and clinical applications

Cardiovascular disease is the leading cause of death in the U.S. and other developed countries. Metabolic syndrome, including obesity, diabetes/insulin resistance, hypertension and dyslipidemia is a major threat for public health in the modern society. It is well established that metabolic syndrome contributes to the development of cardiovascular disease collective called as cardiometabolic disease. Despite documented studies in the research field of cardiometabolic disease, the underlying mechanisms are far from clear. Proteases are enzymes that break down proteins, many of which have been implicated in various diseases including cardiac disease. Matrix metalloproteinase (MMP), calpain, cathepsin and caspase are among the major proteases involved in cardiac remodeling. Recent studies have also implicated proteases in the pathogenesis of cardiometabolic disease. Elevated expression and activities of proteases in atherosclerosis, coronary heart disease, obesity/insulin-associated heart disease as well as hypertensive heart disease have been documented. Furthermore, transgenic animals that are deficient in or over-express proteases allow scientists to understand the causal relationship between proteases and cardiometabolic disease. Mechanistically, MMPs and cathepsins exert their effect on cardiometabolic diseases mainly through modifying the extracellular matrix. However, MMP and cathepsin are also reported to affect intracellular proteins, by which they contribute to the development of cardiometabolic diseases. On the other hand, activation of calpain and caspases has been shown to influence intracellular signaling cascade including the NF-κB and apoptosis pathways. Clinically, proteases are reported to function as biomarkers of cardiometabolic diseases. More importantly, the inhibitors of proteases are credited with beneficial cardiometabolic profile, although the exact molecular mechanisms underlying these salutary effects are still under investigation. A better understanding of the role of MMPs, cathepsins, calpains and caspases in cardiometabolic diseases process may yield novel therapeutic targets for treating or controlling these diseases. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Lipoprotein-associated phospholipase A2 regulates macrophage apoptosis via the Akt and caspase-7 pathways

AIM

Mutations in lipoprotein-associated phospholipase A2 (Lp-PLA2) are related to atherosclerosis. However, the molecular effects of Lp-PLA2 on atherosclerosis have not been fully investigated. Therefore, this study attempted to elucidate this issue.

METHODS

Monocytes were isolated from randomly selected healthy male volunteers according to each Lp-PLA2 genotype (wild-type Lp-PLA2 [Lp-PLA2 (V/V)], the heterozygous V279F mutation [LpPLA2 (V/F)] and the homozygous V279F mutation [Lp-PLA2 (F/F)]) and differentiated into macrophages. The level of apoptosis in the macrophages following incubation without serum was measured using the annexin V/propidium iodide double staining method, and the underlying mechanisms were further examined using a culture cell line.

RESULTS

The average plasma Lp-PLA2 concentration [Lp-PLA2 (V/V): 129.4 ng/mL, Lp-PLA2 (V/F): 70.7 ng/mL, Lp-PLA2 (F/F): 0.4 ng/mL] and activity [Lp-PLA2 (V/V): 164.3 nmol/min/mL, LpPLA2 (V/F): 100.9 nmol/min/mL, Lp-PLA2 (F/F): 11.6 nmol/min/mL] were significantly different between each genotype, although the basic clinical characteristics were similar. The percentage of apoptotic cells was significantly higher among the Lp-PLA2 (F/F) macrophages compared with that observed in the Lp-PLA2 (V/V) macrophages. This induction of apoptosis was independent of the actions of acetylated low-density lipoproteins. In addition, the transfection of the expression plasmid of V279F mutant Lp-PLA2 into Cos-7 cells or monocyte/macrophage-like U937 cells promoted apoptosis. The knockdown of Lp-PLA2 also increased the number of apoptotic cells. Among the cells expressing mutant Lp-PLA2, the caspase-7 activity was increased, while the activated Akt level was decreased.

CONCLUSIONS

The V279F mutation of Lp-PLA2 positively regulates the induction of apoptosis in macrophages and Cos-7 cells. An increase in the caspase-7 activity and a reduction in the activated Akt level are likely to be involved in this phenomenon.

MicroRNA-133a regulates insulin-like growth factor-1 receptor expression and vascular smooth muscle cell proliferation in murine atherosclerosis

OBJECTIVE

MicroRNA-133a (miR-133a) and insulin-like growth factor-1 (IGF-1) are two different molecules known to regulate cardiovascular cell proliferation. This study tested whether miR-133a affects expression of IGF-1 receptor (IGF-1R) and proliferation of IGF-1-stimulated vascular smooth muscle cells (VSMC) in a murine model of atherosclerosis.

METHODS AND RESULTS

Expression of IGF-1R was analyzed by immuno-fluorescence and immuno-blotting, and miR-133a by qRT-PCR in the aortas of wild-type C57BL/6J (WT) and apolipoprotein-E deficient (ApoE(-/-)) mice. Compared to those in WT aortas, the IGF-1R and miR-133a levels were lower in ApoE(-/-) aortas. ApoE(-/-) VSMC grew slower than WT cells in the cultures with IGF-1-containing medium. MiR-133a-specific inhibitor decreased miR-133a, IGF-1R expression, IGF-1-stimulated VSMC growth in lipoprotein deficient media. By contrast, miR-133a precursor increased IGF-1R levels and promoted IGF-1-induced VSMC proliferation. In the luciferase-IGF-1R 3'UTR reporter system, the reporter luciferase activity was not inhibited in VSMC with miR-133a overexpression. IGF-1R mRNA half-life in ApoE(-/-) VSMC was shorter than that in WT VSMC. MiR-133a inhibitor reduced but precursor increased the mRNA half-life, although the effects appeared less striking in ApoE(-/-) VSMC than in WT cells.

CONCLUSION

MiR-133a serves as a stimulatory factor for IGF-1R expression through prolonging IGF-1R mRNA half-life. In atherosclerosis induced by ApoE deficiency, reduced miR-133a expression is associated with lower IGF-1R levels and suppressive VSMC growth. Administration of miR-133a precursor may potentiate IGF-1-stimulated VSMC survival and growth.

Serum levels of γ-glutamyltransferase and progression of coronary atherosclerosis

BACKGROUND

Progression of coronary atherosclerosis (ATS) has clinical implications. Serum levels of γ-glutamyltransferase (GGT), a marker of oxidative stress, predict the risk of cardiovascular events. However, the role of GGT levels in the progression of coronary ATS has never been established.

MATERIALS AND METHODS

Consecutive patients undergoing two coronary angiographies (CAs) separated by at least 6 months were prospectively enrolled between May 2008 and June 2010. All patients were discharged on statins after the first CA. The severity and extent of coronary ATS were graded according to Bogaty's score, and the variation (Δ) in stenosis score and extent index between follow-up (S2 and E2) and basal values (S1 and E1) were calculated. Predictors of ΔS2-1 and ΔE2-1 were assessed among clinical and laboratory data, including GGT levels, analyzed as Δ between follow-up and basal values (ΔGGT2-1).

RESULTS

We enrolled 100 consecutive patients (age 64±11 years, 68% men). Compliance with statin therapy was 100%. At multiple regression analysis, ΔGGT2-1 was the only independent predictor of ΔS2-1 (B=0.18, SE=0.07, P=0.05), with Δlow-density lipoprotein-cholesterol2-1 levels being of borderline statistical significance (P=0.07). On multiple regression analysis, ΔGGT2-1 was the only independent predictor of ΔE2-1 (B=0.32; SE=0.11; P=0.04), with active smoking habit and Δfibrinogen2-1 levels being of borderline statistical significance (P=0.08 and 0.06, respectively).

CONCLUSION

ΔGGT2-1 is associated with angiographic coronary ATS progression in patients with ischemic heart disease on statin treatment, suggesting that oxidative stress may be another therapeutic target for preventing ATS progression beyond that of lipid-lowering therapies.

p53 Levels positively correlate with carotid intima-media thickness in patients with subclinical atherosclerosis

BACKGROUND

The level of circulating p53 is related to inflammation in asymptomatic subjects with cardiovascular risk factors. Whether p53 is associated with the severity of atherosclerosis remains to be determined.

HYPOTHESIS

This study examines the relationship of systemic p53 levels with atherosclerotic risk factors and subclinical atherosclerosis.

METHODS

Circulating levels of p53 and markers of inflammation were measured in 356 subjects with cardiovascular risk factors but who were free from clinical cardiovascular disease. Subclinical atherosclerosis was evaluated by both the mean carotid intima-media thickness (IMT) and the presence of atherosclerotic plaques with the use of B-mode ultrasound in all subjects.

RESULTS

p53 levels were positively correlated with age (r = 0.382, P < 0.001), intercellular adhesion molecular-1 (ICAM-1; r = 0.510, P < 0.01), vascular cell adhesion molecular-1 (VCAM-1; r = 0.497, P < 0.01), E-selectin (r = 0.337, P < 0.01), and carotid IMT (r = 0.594, P < 0.01). The association between p53 and IMT remained significant in multiple regression analysis (P < 0.01) when controlling for traditional atherosclerotic risk factors and inflammatory markers.

CONCLUSION

Higher plasma p53 levels were associated with an increase in inflammatory markers, as well as increased carotid IMT. Circulating p53 may be useful in identifying subclinical atherosclerosis in subjects symptomatically free from cardiovascular disease.

Effects of arsenic exposure and genetic polymorphisms of p53, glutathione S-transferase M1, T1, and P1 on the risk of carotid atherosclerosis in Taiwan

To evaluate the joint effects between genetic polymorphisms of glutathione S-transferase M1, T1, P1, and p53, and arsenic exposure through drinking well water on the risk of carotid atherosclerosis, 605 residents including 289 men and 316 women were recruited from a northeastern area of Taiwan. Carotid atherosclerosis was diagnosed by either a carotid artery intima-media thickness (IMT) of >1.0 mm, a plaque score of > or =1, or stenosis of >50%. A significant age- and gender-adjusted odds ratio of 3.3 for the development of carotid atherosclerosis was observed among the high-arsenic exposure group who drank well water containing arsenic at levels >50 microg/L. The high-arsenic exposure group with GSTP1 variant genotypes of Ile/Val and Val/Val, and with the p53 variant genotypes of Arg/Pro and Pro/Pro had 6.0- and 3.1-fold higher risks of carotid atherosclerosis, respectively. In addition, the high-arsenic exposure group with one or two variant genotypes of GSTP1 and p53 had 2.8- and 6.1-fold higher risks of carotid atherosclerosis, respectively, and showed a dose-dependent relationship. A multivariate-adjusted odds ratio of 3.4 for the risk of carotid atherosclerosis among study subjects with the two variant genotypes of GSTP1 and p53 was also found. Our study showed the joint effects on the risk of carotid atherosclerosis between the genetic polymorphisms of GSTP1 and p53, and arsenic exposure.

Identifying novel genes for atherosclerosis through mouse-human comparative genetics

Susceptibility to atherosclerosis is determined by both environmental and genetic factors. Its genetic determinants have been studied by use of quantitative-trait-locus (QTL) analysis. So far, 21 atherosclerosis QTLs have been identified in the mouse: 7 in a high-fat-diet model only, 9 in a sensitized model (apolipoprotein E- or LDL [low-density lipoprotein] receptor-deficient mice) only, and 5 in both models, suggesting that different gene sets operate in each model and that a subset operates in both. Among the 27 human atherosclerosis QTLs reported, 17 (63%) are located in regions homologous (concordant) to mouse QTLs, suggesting that these mouse and human atherosclerosis QTLs have the same underlying genes. Therefore, genes regulating human atherosclerosis will be found most efficiently by first finding their orthologs in concordant mouse QTLs. Novel mouse QTL genes will be found most efficiently by using a combination of the following strategies: identifying QTLs in new crosses performed with previously unused parental strains; inducing mutations in large-scale, high-throughput mutagenesis screens; and using new genomic and bioinformatics tools. Once QTL genes are identified in mice, they can be tested in human association studies for their relevance in human atherosclerotic disease.

Positional identification of TNFSF4, encoding OX40 ligand, as a gene that influences atherosclerosis susceptibility

Ath1 is a quantitative trait locus on mouse chromosome 1 that renders C57BL/6 mice susceptible and C3H/He mice resistant to diet-induced atherosclerosis. The quantitative trait locus region encompasses 11 known genes, including Tnfsf4 (also called Ox40l or Cd134l), which encodes OX40 ligand. Here we report that mice with targeted mutations of Tnfsf4 had significantly (P <or= 0.05) smaller atherosclerotic lesions than did control mice. In addition, mice overexpressing Tnfsf4 had significantly (P <or= 0.05) larger atherosclerotic lesions than did control mice. In two independent human populations, the less common allele of SNP rs3850641 in TNFSF4 was significantly more frequent (P <or= 0.05) in individuals with myocardial infarction than in controls. We therefore conclude that Tnfsf4 underlies Ath1 in mice and that polymorphisms in its human homolog TNFSF4 increase the risk of myocardial infarction in humans.

Tumor necrosis factor-alpha-induced apoptosis of human coronary artery endothelial cells: modulation by the peroxisome proliferator-activated receptor-gamma ligand pioglitazone

The cytokine tumor necrosis factor-alpha (TNF-alpha) plays an important role in endothelial injury, which is associated with the release of reactive oxygen species and the induction of apoptosis. We report on our study of TNF-alpha-induced apoptosis in human coronary artery endothelial cells and its modulation by the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligand pioglitazone. Treatment of cells with TNF-alpha (40 ng/mL) resulted in apoptosis as measured by DNA laddering and caspase-3 activation. TNF-alpha treatment decreased the expression of antiapoptotic protein Bcl-2 (P <.05 vs control), but not the expression of Fas or FLIP, in human coronary artery endothelial cells. Treatment of cells with TNF-alpha also enhanced lipid peroxidation (P <.01 vs control). Pretreatment of cells with the PPAR-gamma ligand pioglitazone blocked TNF-alpha-mediated apoptosis, caspase-3 activation, expression of Bcl-2, and lipid peroxidation (P <.01 vs TNF-alpha alone). These results indicate that TNF-alpha induces oxidative stress in human coronary artery endothelial cells, resulting in apoptosis through a reduction in Bcl-2 expression and the subsequent activation of caspase-3. The PPAR-gamma ligand pioglitazone modulates lipid peroxidation, alters Bcl-2 expression and caspase-3 activation, and finally reduces apoptosis. The antioxidant and antiapoptotic effects of pioglitazone may be the mechanism by which this agent reduces endothelial injury.

Oxidation of LDL, atherogenesis, and apoptosis

A plethora of studies in cultured cells have established that oxidized low-density lipoprotein (oxLDL) may enhance arterial apoptosis that involves both mitochondrial and death receptor pathways (Fas/FasL, TNF receptors I and II), thereby activating caspase cascade and other proteases. When apoptosis is inhibited by Bcl-2 overexpression, oxLDL may trigger necrosis through a calcium-dependent pathway. Despite this effort, the pathophysiological relevance of apoptosis in vivo remains to be elucidated. In principle, apoptosis occurring in atherosclerotic areas could be involved in endothelial cell lining defects, necrotic core formation, and plaque rupture or fissuring. This complex pathogenic framework may favor coronary atherothrombotic events. To date, the pathogenic role of apoptosis in thrombosis is attractive, but a solid evidence is still needed. When the precise role of oxLDL in vascular programmed cell death occurring in vivo is clarified, this may aid in the development of novel therapeutic approaches to adverse atherogenesis and its clinical sequelae.

Molecular mechanisms for cardiovascular stem cell apoptosis and growth in the hearts with atherosclerotic coronary disease and ischemic heart failure

In the heart with atherosclerotic coronary disease, chronic ischemia causes progressive loss of cardiovascular cells and ultimately triggers myocardial dysfunctions or heart failure. Various types of stem cells from embryonic and adult tissues have potentials for regenerating functional cardiovascular cells in the heart undergoing ischemic injury. However, native or exogenous stem cells in the ischemic hearts are exposed to various proapoptotic or cytotoxic factors. Furthermore, during repopulation and differentiation, certain numbers of newly produced cells may die by apoptosis during neocardiovascular tissue remodeling and morphogenesis. Embryonic and adult stem cells may have different life spans, as being programmed genetically to apoptosis. The endogenous and environmental factors play important roles in regulation of stem cells, including inflammatory cytokines, growth factors, surface receptors, proteolytic enzymes, mitochondrial respiration, nuclear proteins, telomerase activities, hypoxia-responding proteins, and stem cell-host cell interaction. Clarification of the molecular mechanisms may help us understand and design stem cell therapies.

Oxidation-sensitive mechanisms, vascular apoptosis and atherosclerosis

Increased generation of oxidants, resulting from disruption of aerobic metabolism and from respiratory burst, is an essential defense mechanism against pathogens and aberrant cells. However, oxidative stress can also trigger and enhance deregulated apoptosis or programmed cell death, characteristic of atherosclerotic lesions. Oxidation-sensitive mechanisms also modulate cellular signaling pathways that regulate vascular expression of cytokines and growth factors, and influence atherogenesis, in particular when increased levels of plasma lipoproteins provide ample substrate for lipid peroxidation and lead to increased formation of adducts with lipoprotein amino acids. In some cases, increased oxidation and apoptosis in a group of cells might be beneficial for survival and function of other groups of arterial cells. However, overall, oxidation and apoptosis appear to promote the progression of diseased arteries towards a lesion that is vulnerable to rupture, and to give rise to myocardial infarction and ischemic stroke. Recent rapid advances in our understanding of the interactions between oxidative stress, apoptosis and arterial gene regulation suggest that selective interventions targeting these biological functions have great therapeutic potential.

Soluble Fas: a novel predictor of atherosclerosis in dialysis patients

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of death in patients with end-stage renal disease (ESRD). Disregulation of apoptosis within the vessel wall and upregulation of the Fas/Fas-ligand (Fas-L) system contribute to the development of atherosclerosis. Cross-sectional studies have suggested that elevated plasma levels of the soluble form of Fas (sFas) are associated with CVD. However, the role of sFas and sFas-L in predicting future cardiovascular events has yet to be defined.

METHODS

We evaluated the role of plasma sFas and sFas-L levels as predictors of CVD in a prospective cohort of 107 chronic hemodialysis patients.

RESULTS

During the study period (27 months), 53 patients (49.5%) presented with at least one cardiovascular end point. On univariate analysis, baseline sFas levels were significantly associated with the occurrence of cardiovascular end points, whereas sFas-L levels were not. Using Cox proportional hazards, increased sFas levels were associated with a significantly greater risk for cardiovascular end points (P = 0.03). This effect was independent of baseline CVD history, classic risk factors for atherosclerosis (diabetes, hypercholesterolemia, hypertension, and smoking), and markers of inflammation (C-reactive protein [CRP], soluble intercellular adhesion molecule-1). Increased CRP levels also were associated with cardiovascular end points (P = 0.04). In addition, increased cardiovascular mortality was found in patients in the highest sFas tertile compared with those in the lowest tertile (27.8% versus 8.6%; P = 0.04).

CONCLUSION

Increased plasma sFas levels are predictive of future CVD. These results suggest that sFas is a novel and independent predictor of active atherosclerotic disease in patients with ESRD.

New understanding, diagnosis, and prognosis of atherothrombosis and the role of imaging

Despite crucial advances in our knowledge of the pathologic mechanisms and the availability of effective diagnostic and treatment modalities, coronary atherothrombosis remains the most frequent cause of ischemic heart disease. Plaque disruption with superimposed thrombosis is the main cause of unstable angina, myocardial infarction, and sudden death. New findings have recently introduced exciting concepts that could have major impact on the treatment of the atherothrombotic disease. We will discuss the mechanisms that lead to the development of atherothrombosis and those responsible for the acute coronary syndromes, as well as some of the concepts derived from in vivo observations using new imaging technologies (eg, high-resolution magnetic resonance imaging).

Biologic aspects of vulnerable plaque

Atherosclerosis and its thrombotic complications are the major cause of morbidity and mortality in the industrialized world. The progression of atherosclerotic plaques in coronary circulation is modulated by several risk factors. It is now clear that plaque composition is a major determinant of plaque disruption and superimposed thrombosis. Plaque vulnerability, defined as the propensity of plaques to disrupt, is further determined by intrinsic and extrinsic triggering factors. After disruption, the fatty core of the plaque and its high content of tissue factor provide a powerful substrate for the activation of the coagulation cascade. Plaque disruption can be clinically silent or cause symptoms of ischemia depending on thrombus burden and the degree of vessel occlusion. In addition, plaque disruption and subsequent healing are recognized to play key roles in the rapid plaque progression. This review looks at the mechanisms underlying the development and progression of atherosclerotic plaques, factors leading to plaque rupture and subsequent thrombosis, and their clinical consequences as potential targets for future research.

Preparation of monoclonal antibody against apoptosis-associated antigens of hepatoma cells by subtractive immunization

AIM: To elucidate the expression of the apoptosis-associated molecules in human primary hepatocellular carcinoma (HCC) cells, and prepare the monoclonal antibodies (mAb) against the apoptosis-associated antigens of HCC cells.

METHODS: Human HCC cell line HCC-9204 cells were induced apoptosis with 60 mL•L^-1 ethanol for 6 h and their morphological changes were observed by transmission electron microscope. The cell DNA fragmentations were detected by Terminal Deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, and the cell DNA contents by flow cytometry. Ten mice were immunized with ethanol-induced apoptotic HCC-9204 cells with the method of subtractive immunization, while the other 10 mice used as the control were immunized by the routine procedures. The tail blood of all the mice were prepared after the last immunization, and the produced antibodies were determined by the immunocytochemical ABC staining. The splenic cells of the mice whose tail blood sera-HCC-9204 cells serum reactions were most different between the apoptotic and the non-apoptotic were prepared and fused with the mouse myeloma cell line SP2/0 cells. The positive antibodies were selected by ELISA assay. The fusion rates of hybridoma cells and the producing rates of antibodies were calculated. The fused cells that secreted candidate objective antibody were cloned continually with the of limited dilution method, and then selected and analyzed further by the immunocytochemical ABC staining. The chromosomes of the cloned hybridoma cells that secreted objective mAb and the mAb immunoglobulin (Ig) subtype of the prepared mAb were also determined. The molecular mass of the mAb associated antigen was analyzed by Western blot assay.

RESULTS: HCC-9204 cells treated with 60 mL•L^-1 ethanol for 6 h, manifested obvious apoptotic morphological changes, the majority of the cells were TUNEL-positive, and the sub-G1 apoptotic peak was evident. There were 2 mice in the experimental group whose tail blood serum reacted strongly with the apoptotic HCC-9204 cells, but weakly with their non-apoptotic counterparts. In the fusion rates of hybridoma cells as well as the producing rates of the antibody deseribed above, there did not show significant difference between the experimental and the control group, but weakly with non-apoptotic HCC-9204. However, the total producing rate of antibodies in the experimental group was significantly lower compared with the control (P < 0.01), and so was the producing rate of the antibodies which reacted strongly with both apoptotic and non-apoptotic HCC-9204 cells (P < 0.01). After cloned continually for several times the cell that produce mAb which reacted strongly with the nuclei of ethanol-induced apoptotic HCC-9204 cells, but very weakly with that of non-apoptotic cells was selected out. Chromosome analysis revealed that the selected cell was with the universal characteristics of the monoclonal hybridoma cells which secreted mAb, and the Ig subtype of the prepared mAb was IgG1. The molecular mass of this mAb associated antigen of was about 75 ku.

CONCLUSION: Subtractive immunization is a useful method to prepare the mAb against the apoptosis-associated antigens of cells. The expression of some molecules increases to some extent in HCC-9204 cells in the process of apoptosis induced by low-concentration ethanol. The mAb that may be against ethanol-induced apoptosis-associated antigens of HCC cells was successfully prepared and primarily identified.

Progression of atheroma: a struggle between death and procreation

Traditional thinking accorded a major role to deranged cell proliferation as a determinant of the abnormal cellularity of atheroma. However, studies conducted in several laboratories have documented the occurrence of disordered apoptosis during atherogenesis, leading to the death of lipid-rich foam cells (promoting lipid-core formation) and depletion of vascular smooth muscle cells (fostering fragility of the fibrous cap). A complex interplay of environmental factors and endogenous proteins regulates apoptosis and contributes to the struggle between cell death and procreation in atherosclerosis. In addition to a variety of growth factors, chemically modified lipids, reactive oxygen species, proinflammatory cytokines, and Fas ligand produced by activated immune cells may influence cell viability through a diversity of pathways, including the caspase cascade, the Bcl-2 protein family, and the oncogene/antioncogene system. A clarification of the molecular mechanisms responsible for vascular cell death may aid in the development of novel therapeutic strategies to treat atherosclerosis and its complications, including the acute coronary syndromes.

c-Myc oncoprotein: a dual pathogenic role in neoplasia and cardiovascular diseases?

A growing body of evidence indicates that c-Myc can play a pivotal role both in neoplasia and cardiovascular diseases. Indeed, alterations of the basal machinery of the cell and perturbations of c-Myc-dependent signaling network are involved in the pathogenesis of certain cardiovascular disorders. Down-regulation of c-Myc induced by intervention with antioxidants or by antisense technology may protect the integrity of the arterial wall as well as neoplastic tissues. Further intervention studies are necessary to investigate the effects of tissue-specific block of c-Myc overexpression in the development of cardiovascular diseases.

Pathophysiology of plaque instability: insights at the genomic level

Atherosclerosis and plaque rupture represent complex "traits" of unknown cause that involve multiple genes and their variants. Novel genomic technologies provide us with the tools that will allow for the identification of groupings of genes that determine either susceptibility or resistance relative to the development of atherosclerosis and its thromboembolic complications. This information may, in turn, lead to a clearer understanding of the cause and risk for atherosclerosis. Diagnostic tools, as well as preventive and therapeutic strategies, will be derived from such heightened understanding of the disease process. With this chapter, we have presented the current state of knowledge of atherosclerosis genomics.