Lipoprotein oxidation and gene expression in the artery wall. New opportunities for pharmacologic intervention in atherosclerosis

Association between a urinary biomarker for exposure to PAH and blood level of the acute phase protein serum amyloid A in coke oven workers

BACKGROUND

Coke oven workers are exposed to both free and particle bound PAH. Through this exposure, the workers may be at increased risk of cardiovascular diseases. Systemic levels of acute phase response proteins have been linked to cardiovascular disease in epidemiological studies, suggesting it as a marker of these conditions. The aim of this study was to assess whether there was association between PAH exposure and the blood level of the acute phase inflammatory response marker serum amyloid A (SAA) in coke oven workers.

METHODS

A total of 87 male Polish coke oven workers from two different plants comprised the study population. Exposure was assessed by means of the individual post-shift urinary excretion of 1-hydroxypyrene, as internal dose of short-term PAH exposure, and by anti-benzo[a]pyrene diolepoxide (anti-B[a]PDE)-DNA), as a biomarker of long-term PAH exposure. Blood levels of acute phase proteins SAA and CRP were measured by immunoassay. C-reactive protein (CRP) levels were included to adjust for baseline levels of SAA.

RESULTS

Multiple linear regression showed that the major determinants of increased SAA levels were urinary 1-hydroxypyrene (beta = 0.56, p = 0.030) and serum CRP levels (beta = 7.08; p < 0.0001) whereas anti-B[a]PDE-DNA, the GSTM1 detoxifying genotype, diet, and smoking were not associated with SAA levels.

CONCLUSIONS

Urinary 1-hydroxypyrene as biomarker of short-term PAH exposure and serum levels of CRP were predictive of serum levels of SAA in coke oven workers. Our data suggest that exposure of coke oven workers to PAH can lead to increased systemic acute response and therefore potentially increased risk of cardiovascular disease.

Varying dietary protein and fat elicits differential transcriptomic expression within stress response pathways in preweaned Holstein heifers

Increases in milk replacer dietary energy subsequently increase growth and weight in preweaned dairy heifers. However, the underlying effects of dietary component increases on key functional pathways have yet to be fully investigated. Elucidating these relationships may provide insights into the mechanisms through which protein and fat are partitioned for tissue growth and metabolism. We hypothesized that genes within key growth and metabolic pathways would be differentially expressed between calves fed a protein- and fat-restricted diet and calves fed a protein- and fat-enhanced diet. The objectives of this study were to (1) identify genes differentially expressed between dietary restricted calves and enhanced calves and (2) determine the key regulatory pathways influenced by these genes. Preweaned Holstein heifers (n = 12; 6 ± 0.02 d of age) were randomly assigned to 1 of 2 milk replacer diets: enhanced (28.9% crude protein, 26.2% fat; n = 6) or restricted (20.9% crude protein, 19.8% fat; n = 6). Growth measures included average daily gain and gain-to-feed ratio. After 56 d, calves were killed for tissue collection. Samples from longissimus dorsi, adipose, and liver tissues were collected and RNA was isolated for RNA sequencing analysis. The MIXED procedure of SAS (SAS Institute Inc., Cary, NC) was used to evaluate relationships of growth with dietary energy. Fixed effects included date of collection and time (day). Random effects included sire and birth weight. The RNA sequencing analysis was performed using CLC Genomics Workbench (Qiagen, Germantown, MD), and the Robinson and Smith exact test was used to identify differentially expressed genes between diets. The Protein Analysis Through Evolutionary Relationships (PANTHER) database was then used to identify functional categories of differentially expressed genes. Enhanced calves had increased growth rates and feed efficiency compared with restricted calves (average daily gain = 0.76 and 0.22, respectively; gain-to-feed ratio = 0.10 and 0.06, respectively). There were 238 differentially expressed genes in adipose, 227 in longissimus dorsi, and 40 in liver. We identified 10 genes concordant among tissues. As expected, functional analyses suggested that the majority of genes were associated with metabolic or cellular processes, predominantly cell communication and cell cycle. Overall, it appears that varying levels of dietary protein and fat influence calf growth and development through metabolic processes, including oxidative phosphorylation and glyceroneogenesis. However, protein- and fat-restricted calves appeared to experience metabolic stress at a cellular level, as evidenced by an upregulation in stress response pathways, including genes in the p53 pathway. Calves could be fed at a higher level of protein and fat to decrease the prevalence of metabolic stress at the cellular level, but evidence indicating the presence of inflammatory stress and adipose fibrosis in enhanced calves prompts further investigation of the effects of milk replacer component levels.

Effects of electromagnetic fields exposure on the antioxidant defense system

Technological devices have become essential components of daily life. However, their deleterious effects on the body, particularly on the nervous system, are well known. Electromagnetic fields (EMF) have various chemical effects, including causing deterioration in large molecules in cells and imbalance in ionic equilibrium. Despite being essential for life, oxygen molecules can lead to the generation of hazardous by-products, known as reactive oxygen species (ROS), during biological reactions. These reactive oxygen species can damage cellular components such as proteins, lipids and DNA. Antioxidant defense systems exist in order to keep free radical formation under control and to prevent their harmful effects on the biological system. Free radical formation can take place in various ways, including ultraviolet light, drugs, lipid oxidation, immunological reactions, radiation, stress, smoking, alcohol and biochemical redox reactions. Oxidative stress occurs if the antioxidant defense system is unable to prevent the harmful effects of free radicals. Several studies have reported that exposure to EMF results in oxidative stress in many tissues of the body. Exposure to EMF is known to increase free radical concentrations and traceability and can affect the radical couple recombination. The purpose of this review was to highlight the impact of oxidative stress on antioxidant systems. Abbreviations: EMF, electromagnetic fields; RF, radiofrequency; ROS, reactive oxygen species; GSH, glutathione; GPx, glutathione peroxidase; GR, glutathione reductase; GST, glutathione S-transferase; CAT, catalase; SOD, superoxide dismutase; HSP, heat shock protein; EMF/RFR, electromagnetic frequency and radiofrequency exposures; ELF-EMFs, exposure to extremely low frequency; MEL, melatonin; FA, folic acid; MDA, malondialdehyde.

Chemical constituents and free radical scavenging activity of corn pollen collected from Apis mellifera hives compared to floral corn pollen at Nan, Thailand

BACKGROUND

Bee pollen is composed of floral pollen mixed with nectar and bee secretion that is collected by foraging honey (Apis sp.) and stingless bees. It is rich in nutrients, such as sugars, proteins, lipids, vitamins and flavonoids, and has been ascribed antiproliferative, anti-allergenic, anti-angiogenic and free radical scavenging activities. This research aimed at a preliminary investigation of the chemical constituents and free radical scavenging activity in A. mellifera bee pollen.

METHODS

Bee pollen was directly collected from A. mellifera colonies in Nan province, Thailand, in June, 2010, whilst floral corn (Zea mays L.) pollen was collected from the nearby corn fields. The pollen was then sequentially extracted with methanol, dichloromethane (DCM) and hexane, and each crude extract was tested for free radical scavenging activity using the DPPH assay, evaluating the percentage scavenging activity and the effective concentration at 50% (EC50). The most active crude fraction from the bee pollen was then further enriched for bioactive components by silica gel 60 quick and adsorption or Sephadex LH-20 size exclusion chromatography. The purity of all fractions in each step was observed by thin layer chromatography and the bioactivity assessed by the DPPH assay. The chemical structures of the most active fractions were analyzed by nuclear magnetic resonance.

RESULTS

The crude DCM extract of both the bee corn pollen and floral corn pollen provided the highest active free radical scavenging activity of the three solvent extracts, but it was significantly (over 28-fold) higher in the bee corn pollen (EC(50) = 7.42 ± 0.12 μg/ml), than the floral corn pollen (EC(50) = 212 ± 13.6% μg/ml). After fractionation to homogeneity, the phenolic hydroquinone and the flavone 7-O-R-apigenin were found as the minor and major bioactive compounds, respectively. Bee corn pollen contained a reasonably diverse array of nutritional components, including biotin (56.7 μg/100 g), invert sugar (19.9 g/100 g), vitamin A and β carotene (1.53 mg/100 g).

CONCLUSIONS

Bee pollen derived from corn (Z. mays), a non-toxic or edible plant, provided a better free radical scavenging activity than floral corn pollen.

Anti-oxidized LDL antibody levels are reduced in women with hypertension

BACKGROUND

Previous studies have suggested that hypertension may be associated with increased oxidized low-density lipoprotein (LDL). Increased in vitro oxidizability of LDL or elevated titers of anti-oxidized LDL antibodies have been shown in subjects with essential hypertension. However, the relationship between oxidized LDL and hypertension is equivocal. We examined the association between hypertension and levels of IgG anti-oxidized LDL antibodies in a group of women from the general population.

MATERIALS AND METHODS

The study included 619 women classified according to their blood pressure values. IgG anti-oxidized LDL antibodies were measured by enzyme-linked immunosorbent assay and the women were classified as being above or below the 50th percentile.

RESULTS

Hypertension was present in 54.3% of the women. These women had significantly lower levels of IgG anti-oxidized LDL antibodies than the normotensive women (0.280 +/- 0.117 vs. 0.336 +/- 0.125, P < 0.001). Both systolic and the diastolic blood pressures showed a significant negative correlation with the levels of IgG anti-oxidized LDL antibodies (r = -0.204, P < 0.001; r = -0.225, P < 0.001, respectively). Women with IgG anti-oxidized LDL antibody levels above the 50th percentile had a lower prevalence of hypertension than those with IgG anti-oxidized LDL antibody levels below the 50th percentile (40.2% vs. 59.8%) (P < 0.001).

CONCLUSIONS

Women with hypertension had lower levels of IgG anti-oxidized LDL antibodies than normotensive women.

Simultaneous total antioxidant capacity assay of lipophilic and hydrophilic antioxidants in the same acetone-water solution containing 2% methyl-beta-cyclodextrin using the cupric reducing antioxidant capacity (CUPRAC) method

Antioxidants are health beneficial compounds that can protect cells from the damage caused by unstable molecules known as reactive oxygen species (ROS). This work reports the capacity assay of both lipophilic and hydrophilic antioxidants simultaneously, by making use of their 'host-guest' complexes with methyl-beta-cyclodextrin (M-beta-CD), a cyclic oligosaccharide, in acetonated aqueous medium using the cupric reducing antioxidant capacity (CUPRAC) method. Thus the order of antioxidant potency of various compounds irrespective of their lipophilicity could be established in the same solvent medium. M-beta-CD was introduced as the water solubility enhancer for lipophilic antioxidants. Two percent M-beta-CD (w/v) in an acetone-H(2)O (9:1, v/v) mixture was found to sufficiently solubilize beta-carotene, lycopene, vitamin E, vitamin C, synthetic antioxidants and other phenolic antioxidants. This assay was validated through linearity, additivity, precision, and recovery. The validation results demonstrate that the CUPRAC assay is reliable and robust. In acetonated aqueous solution of M-beta-CD, only CUPRAC and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays were capable of measuring carotenoids together with hydrophilic antioxidants. The CUPRAC antioxidant capacities of a wide range of polyphenolics and flavonoids were experimentally reported in this work as trolox equivalent antioxidant capacity (TEAC) in the CUPRAC assay, and compared to those found by reference methods, ABTS/horseradish peroxidase (HRP)-H(2)O(2) and ferric reducing antioxidant power (FRAP) assays.

Influence of Crocetin on experimental atherosclerosis in hyperlipidamic-diet quails

Antioxidants have been expected to have potential as antiatherogenic agents. Crocetin is a natural carotenoid antioxidant isolated from Gardenia jasminoids Ellis. Therefore, in the present study, we investigated the inhibitory effect of Crocetin on experimental atherosclerosis in quails. The atherosclerosis model was established by feeding hyperlipidamic diet to quail and Crocetin (25, 50, 100 mg/kg/day) was administered by oral gavage. At the 9th week, serum lipids, malondialdehyde and nitric oxide were measured, and Hematoxylin-Eosin (H&E) stains was used to investigate the histopathological changes of aorta. Results showed that Crocetin could reduce the levels of serum total cholesterol, triglyceride, low density lipoprotein cholesterol and inhibit the formation of aortic plaque. Crocetin could also reduce malondialdehyde and inhibit the descending of nitric oxide in serum. The results suggested that Crocetin could inhibit the formation of atherosclerosis in quails, which might be related to the hypolipidemic effects along with the antioxidative properties of Crocetin.

Differential effects of oxidized LDL on apolipoprotein AI and B synthesis in HepG2 cells

Oxidized low-density lipoproteins (Ox-LDL) are key elements in atherogenesis. Apolipoprotein AI (apoAI) is an active component of the antiatherogenic high-density lipoproteins (HDL). In contrast, plasma apolipoprotein B (apoB), the main component of LDL, is highly correlated with coronary risk. Our results, obtained in HepG2 cells, show that Ox-LDL, unlike native LDL, leads to opposite effects on apoB and apoAI, namely a decrease in apoAI and an increase in apoB secretion as evaluated by [(3)H]leucine incorporation and specific immunoprecipitation. Parallel pulse-chase studies show that Ox-LDL impaired apoB degradation, whereas apoAI degradation was increased and mRNA levels were decreased. We also found that enhanced lipid biosynthesis of both triglycerides and cholesterol esters was involved in the Ox-LDL-induced increase in apoB secretion. Our data suggest that the increase in apoB and decrease in apoAI secretion may in part contribute to the known atherogenicity of Ox-LDL through an elevated LDL/HDL ratio, a strong predictor of coronary risk in patients.

Effect of crocin on experimental atherosclerosis in quails and its mechanisms

In the present study, we examined the prophylaxis effect of crocin on experimental atherosclerosis and its possible mechanisms. The atherosclerosis formation was induced by hyperlipidamic diet in quails. At the 9th week, serum lipid, MDA and NO were measured, and HE staining was used to investigate the histopathological changes of aorta. Bovine aortic endothelial cells (EC) were obtained from the thoracic aorta of newborn calves. After incubation of the cells with Ox-LDL (50 mg x L(-1)) for 24 h, the activities of LDH, NO in culture media and activity of NOS in endothelial cells were measured, flow cytometer was used to determine the rate of endothelial cells apoptosis. Peritoneal macrophages were obtained from thioglycolate-injected mice. Cholesterol and free cholesterol in cells were assayed after incubation of the cells with Ox-LDL. Bovine aortic smooth muscle cells (SMC) were obtained from the thoracic aorta of newborn calf. Proliferation was induced by 100 microg x L(-1) Ox-LDL and antiproliferative effect of crocin on SMCs were observed. SMCs cycle phases were measured by flow cytometry. SMCs were loaded with Fluo-3/AM and [Ca2+]i was measured by Laser Scanning Confocal Microscope (LSCM). Crocin could reduce the level of serum TC, TG, LDL-C and inhibit the formation of aortic plaque. Crocin could reduce MDA and inhibit the descending of NO in serum. Compared with control, Ox-LDL group could increase the activity of LDH and decrease activity of NO in culture media and activity of NOS in endothelial cells, preincubated with crocin, the effects of Ox-LDL were inhibited. Crocin could decrease the EC apoptosis induced by Ox-LDL. Crocin concentration-dependently inhibited the TC and CE elevation induced by Ox-LDL in macrophages. Crocin could inhibit the proliferation of SMCs induced by Ox-LDL. In the presence or absence of extracellular Ca2+, crocin concentration-dependently inhibited the [Ca2+]i elevation induced by 120 mg x L(-1)Ox-LDL, In the absence of extracellular Ca2+, crocin could inhibit the [Ca2+]i elevation induced by CHCl3 in a concentration-dependent manner. The results indicated that crocin could inhibit the formation of atherosclerosis in quails. Crocin had protective effects on endothelial cells. Crocin could decrease CE in macrophages and uptake of Ox-LDL, inhibiting the formation of foam cell, which would promote the initiation and progression of atherosclerosis. Crocin could inhibit the [Ca2+]i elevation in smooth muscle cell, Ca2+ is an important second messenger that regulates a variety of cellular processes, including smooth muscle cell proliferation and gene expression . Crocin exerted antiatherosclerotic effects through decreasing the level of Ox-LDL that plays an important role in the initiation and progression of atherosclerosis.

Cholesterol-receptor-mediated genomics in health and disease

Cross-talk between cell-surface receptor C(k) and intracellular receptors (liver X receptor-alpha and peroxisome-proliferator-activated receptors) controls a set of crucial genes that maintain a finely orchestrated balance between various cellular processes involved in cell growth, differentiation, apoptosis, cholesterol homeostasis and inflammation. Abnormal cross-talk of these receptors can lead to several human diseases, particularly atherosclerosis, cancer and autoimmune diseases. As our understanding of the complex signaling events that link these receptors to human health improves, we are beginning to appreciate the enormous potential of the proposed cross-talk model of cholesterol receptors in the prevention and/or treatment of diseases.

A water-extract of the Korean traditional formulation Geiji-Bokryung-Hwan reduces atherosclerosis and hypercholesteremia in cholesterol-fed rabbits

Geiji-Bokryung-Hwan (GBH), a drug preparation consisting of five herbs of Cinnamomi Ramulus (Geiji), Poria Cocos (Bokryun), Mountan Cortex Radicis (Mokdanpi), Paeoniae Radix (Jakyak) and Persicae Semen (Doin), is a traditional Korean herbal medicine that is widely used in the treatment of atherosclerosis-related disorders. A water extract of GBH was found to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and inhibit low-density lipoprotein (LDL) oxidation more effectively than probucol, a well-known commercially available antioxidant. In order to evaluate the anti-atherogenic potential of this medication, New Zealand White (NZW) rabbits were fed a normal diet for 12 weeks, a high cholesterol diet, a high cholesterol diet containing 1% probucol or a high cholesterol diet containing 5% water-soluble extract of GBH. Both GBH and probucol reduced plasma cholesterol levels. LDLs from the GBH-treated group were more resistant to Cu(2+)-induced oxidation and contained more vitamin E than LDLs from the high cholesterol diet group. Endothelial damage, determined at week 6, was reduced by 55% in the GBH group (P<0.01). GBH treatment reduced an atherosclerotic area in the abdominal aorta by 58% (P<0.05) and cholesterol deposition in the thoracic aorta by 55% (P<0.05). The severity of atherosclerosis in the GBH group was significantly reduced after an adjustment using cholesterol exposure as an index of the cholesterol-lowering effect. On the other hand, diet-induced hyperlipidemic rabbits were given water extract of GBH in doses of 50 (Group B) and 200 mg/kg (Group C) and compared with controls (Group A). At 40 days after intervention in groups A, B and C, total and LDL cholesterol levels were significantly lowered (P<0.01). LDL/high density lipoprotein (HDL) ratio was also significantly decreased (P<0.01). This study concludes that the reduction in atherosclerosis by GBH relies not only on its cholesterol-lowering effect but also more heavily on its antioxidant potential, which prevents endothelial damage and inhibits LDL oxidative modification in hypercholesterolemic animals.

Molecular link between cholesterol, cytokines and atherosclerosis

Current investigation on the origin of atherosclerosis has initiated an intense debate over whether atherosclerosis results from hypercholesterolemia or an inappropriate immune response to vascular injury. Although the role of the immune system has been questioned, the overwhelming body of evidence clearly indicates that atherogenesis is initiated by the interplay between cholesterol and cellular secretion of cytokines (especially IL-6) and apolipoprotein 'E' within the arterial wall. Recent studies have revealed that cells possess two cholesterol-sensors: (a) Receptor-Ck which senses the extracellular cholesterol and initiates signalling pathway responsible for the regulation of genes involved in the cell cycle, cell death, cellular cholesterol homeostasis and cytokines including IL-6; (b) LxR alpha which senses intracellular oxysterols and controls genes involved in cell death, cellular cholesterol homeostasis and cytokine IL-8. These cholesterol sensors define the molecular mechanism responsible for cholesterol-depended regulation of cellular synthesis and secretion of cytokines (IL-6, IL-8) within arterial wall. On the basis of this mechanism, presence of cholesterol and its oxy-derivative in the modified LDL will result in transient activation/deactivation of Receptor-Ck-dependent genes which will give rise to repeated cycles of growth coupled with apoptosis leading to a situation where apoptotic-deficient cells in the arterial wall, would be selected resulting in their accumulation and formation of oligoclonal atherosclerotic plaque.

Salvia miltiorrhiza inhibits intimal hyperplasia and monocyte chemotactic protein-1 expression after balloon injury in cholesterol-fed rabbits

Antioxidants that prevent low density lipoproteins (LDL) from oxidation may inhibit atherosclerosis and post-angioplasty restenosis. Salvia miltiorrhiza (SM) has been shown to inhibit LDL oxidation and reduce atherosclerosis in cholesterol-fed rabbits. The effects of SM on neointimal hyperplasia and monocyte chemotactic protein-1 (MCP-1) expression after balloon injury were studied. Male New Zealand white rabbits were fed a 2% cholesterol diet together with daily SM (4.8 gm/kg body wt.) treatment (SM; n=10) or without SM as a control (C; n=9) for 6 weeks. Probucol-treated (0.6 gm/kg body wt.) rabbits (P; n=9) were used as a positive control group. A balloon injury of the abdominal aorta was performed at the end of the third week. Aortas were harvested at the end of 6 weeks. The plasma cholesterol levels were lowered in SM group. The neointimal hyperplasia in abdominal aortas was significantly inhibited in SM group [neointima/media area ratio: 0.63+/-0.05 (SM) versus 0.78+/-0.05 (C); P < 0.05] and in P group [0.45+/-0.02 (P) versus 0.78+/-0.05 (C); P < 0.05] when compared with C group. SM treatment significantly reduced MCP-1 mRNA and protein expression in balloon-injured abdominal aorta. These inhibitory effects on intimal response after balloon injury might be attributed to antioxidant capacity and cholesterol lowering effect of SM. SM treatment may offer some protection against post-angioplasty restenosis.

Antioxidant principles from Ephemerantha lonchophylla

One dihydrostilbene and three phenanthrene antioxidants were isolated from an ethanolic extract of the Chinese herbal Ephemerantha lonchophylla. One of these compounds, ephemeranthone (4) is a new natural product. Denbinobin (1) and 3-methylgigantol (3) have been previously isolated from this plant, and 3-ethoxy-5-hydroxy-7-methoxy-1,4-phenanthraquinone (2) is an artifact. The structures of these compounds were determined by spectroscopic analysis. The antioxidative activities for inhibiting human low density lipoprotein oxidation in vitro of compounds 1-4 were determined, and only 4 was active (5.3 times that of probucol).

Reactive oxygen metabolites, antioxidants and head and neck cancer

This manuscript will review the probable role of reactive oxygen metabolites (ROM) in the etiopathogenesis of head and neck cancer (HNC). Cancer is a heterogeneous disorder with multiple etiologies including somatic and germ-line mutations, cellular homeostatic disturbances, and environmental triggers. Certain etiologies are characteristic of HNC and include infectious agents such as the Epstein-Barr virus, the use of tobacco, and consumption of alcohol. A large body of evidence implicates ROM in tumor formation and promotion. ROM species are formed in the process of cellular respiration, specifically during oxidative phosphorylation. These ubiquitous molecules are highly toxic in the cellular environment. Of the many effects of ROM, especially important are their effect on DNA. Specifically, ROM cause a variety of DNA damage, including insertions, point mutations, and deletions. Thus, it is hypothesized that ROM may be critically involved in the etiology of malignant disease through their possible impact on protooncogenes and tumor suppressor genes. Additionally, empirical evidence suggests that ROM may also affect the balance between apoptosis and cellular proliferation. If apoptotic mechanisms are overwhelmed, uncontrolled cellular proliferation may follow, potentially leading to tumor formation. Thus, this manuscript will critically review the evidence that supports the role of ROM in tumorigenesis. ROM scavengers and blockers have shown both in vivo and in vitro effects of attenuating the toxicity of ROM. Such compounds include the antioxidant vitamins (A, C, and E), nutrient trace elements (selenium), enzymes (superoxide dismutase, glutathione peroxidase, and catalase), hormones (melatonin), and a host of natural and synthetic compounds (lazaroids, allopurinol, gingko extract). Thus, this paper will also review the possible benefit derived from the use of such scavengers/blockers in the prevention of HNC.

Mechanism of minimally modified LDL-mediated induction of serum amyloid A gene in monocyte/macrophage cells

Minimally modified low-density lipoprotein (MM-LDL) is regarded as a major risk factor for the development of atherosclerosis. In this report, we show that this lipoprotein complex can induce expression of an inflammatory protein, serum amyloid A (SAA), in monocyte/macrophage cells, a key cell type implicated in the pathogenesis of atherosclerosis. By promoter function analysis and site-directed mutagenesis, we have located promoter regions responsive to MM-LDL action. Using electrophoretic mobility shift, antibody ablation/supershift, and Western blot assays, we showed that induction of SAA by MM-LDL is mediated via activation of SAS binding factor (SAF) and C/EBP transcription factors. We further show that tamoxifen, a downregulator of CD36, one of the major scavenger receptors which binds MM-LDL, can inhibit MM-LDL-mediated SAA induction in THP-1 cells. This finding suggests that CD36 participates in the manifestation of the inflammatory effects of MM-LDL. Our experiments provide the first evidence for transcription factor activation by MM-LDL.

Transcriptional activation of scavenger receptor expression in human smooth muscle cells requires AP-1/c-Jun and C/EBPbeta: both AP-1 binding and JNK activation are induced by phorbol esters and oxidative stress

Reactive oxygen species generated by treatment of smooth muscle cells (SMCs) with either phorbol 12-myristate 13-acetate or with the combination of H2O2 and vanadate strongly induce expression of the class A scavenger receptor (SR-A) gene. In the current studies, cis-acting elements in the proximal 245 bp of the SR-A promoter were shown to direct luciferase reporter expression in response to oxidative stress in both SMCs and macrophages. A composite activating protein-1 (AP-1)/ets binding element located between -67 and -50 bp relative to the transcriptional start site is critical for macrophage SR-A activity. Mutation of either the AP-1 or the ets component of this site also prevented promoter activity in SMCs. Mutation of a second site located between -44 and -21 bp, which we have identified as a CCAAT/enhancer binding protein (C/EBP) element, reduced the inducible activity of the promoter in SMCs by 50%, suggesting that combinatorial interactions between these sites are necessary for optimal gene induction. Interactions between SMC nuclear extracts and the SR-A promoter were analyzed by electrophoretic mobility shift assay. c-Jun/AP-1 binding activity, specific for the -67- to -50-bp site, was induced in SMCs by the same conditions that increased SR-A expression. Moreover, phorbol 12-myristate 13-acetate, H2O2, or the combination of H2O2 and sodium orthovanadate (vanadate) activated c-Jun-activating kinase. The binding activity within SMC extracts specific for the C/EBP site was shown to be C/EBPbeta in SMCs. Taken together, these findings demonstrate that reactive oxygen species regulate the interactions between c-Jun/AP-1 and C/EBPbeta in the SR-A promoter. Furthermore, induction of oxidative stress in THP-1 cells, with a combination of 10 micromol/L vanadate and 100 micromol/L H2O2, induced macrophage differentiation, adhesion, and SR activity. These data suggest that vascular oxidative stress may contribute to the induction of SR-A expression and thereby promote the uptake of oxidatively modified low density lipoprotein by both macrophage and SMCs to produce foam cells in atherosclerotic lesions.

Functional food science and defence against reactive oxidative species

This paper assesses critically the science base that underpins the argument that oxidative damage is a significant causative factor in the development of human diseases and that antioxidants are capable of preventing or ameliorating these disease processes. The assessment has been carried out under a number of headings, and some recommendations for future research are made based on the present day knowledge base. The knowledge database (1) Consideration of the basic science that underlies understanding of the role of free radicals in causing cellular pathologies, and the role of antioxidants in preventing this, shows that an imbalance of reactive oxygen species and antioxidant defence systems may lead to chemical modifications of biologically relevant macromolecules. This imbalance provides a logical pathobiochemical mechanism for the initiation and development of several disease states. Experimental data obtained in vivo provide evidence that antioxidants function in systems that scavenge reactive oxygen species and that these are relevant to what occurs in vivo. The relevance in vivo of these observations depends inter alia on knowledge of the uptake and distribution of the antioxidant within the human body, and on what tissue levels of the antioxidant may be expected in relation to dietary levels. (2) There is some way to go until validated precise methods are available for measuring biomarkers of oxidative damage in human subjects in vivo under minimally invasive conditions. With respect to oxidative damage in DNa, HPLC and GC-mass spectrophotometry methods have both merits and limitations. Lipid oxidation products in plasma are best measured as isoprostanes or as lipid hydroperoxides using specific HPLC techniques. Development of isoprostane measurement will advance specificity and precision. The measurement of oxidative damage to proteins has some potential but such methods have not been effectively exploited. (3) Epidemiological studies support the hypothesis that the major antioxidant nutrients vitamin E and vitamin C, and beta-carotene (which may or may not be acting as an antioxidant in vivo), may play a beneficial role in prevention of several chronic disorders. More research is needed on the impact of other non-nutrient compounds, such as other carotenoids and flavonoids, on human health. In general, human intervention studies using hard end-points are the gold standard. Trials are restricted mainly to the major antioxidants and do not allow firm conclusions because of inconsistent findings, an insufficient number of studies and the use of varying doses. There is evidence that large doses of beta-carotene may be deleterious to the health of certain subgroups of the population such as heavy habitual smokers. (4) With respect to the safety of administration of supplementary vitamins, vitamin C is safe at levels of supplementation up to 600 mg/d, and higher levels, up to 2000 mg/d, are without risk. Vitamin E has a very low human toxicity and an intake of 1000 mg/d is without risk; 3200 mg/d has been shown to be without any consistent risk. Large intakes of beta-carotene must be viewed with caution because they have been shown to confer detriment to a population at high risk of lung cancer when administered after many years of high risk (smoking) behaviour. Until further work clarifies the situation in heavy smokers with respect to taking supplements, larger doses should be avoided by such individuals. There is little reliable information about the human toxicology of flavonoids and related non-nutrient antioxidant constituents of the diet. (5) The food industry has long experience in the control of oxidative damage in foods and this experience can be used to advantage for the protection of food antioxidants which are beneficial. Some of these, such as vitamins C and E and beta-carotene, are well known, and strategies for their protection in foods are already exploited by food technologies. (ABSTRACT TRUNCATED)

Increase of vitamin E content in LDL and reduction of atherosclerosis in cholesterol-fed rabbits by a water-soluble antioxidant-rich fraction of Salvia miltiorrhiza

Antioxidants that prevent LDL from oxidation may reduce atherosclerosis. Salvia miltiorrhiza Bunge is a Chinese herb widely used for the treatment of atherosclerosis-related disorders. Salvianolic acid B (Sal B), a water-soluble polyphenolic antioxidant isolated from the roots of this plant, was found to scavenge 1,1-diphenyl-2-picrylhydrazyl radicals and inhibit LDL oxidation more effectively than probucol. In order to evaluate the antiatherogenic potential, New Zealand White rabbits were fed for 12 weeks a normal diet, a high cholesterol diet, a high cholesterol diet containing 1% probucol, or a high cholesterol diet containing a 5% water-soluble extract of S miltiorrhiza (SM). Both SM and probucol feeding reduced plasma cholesterol. LDLs from the SM-treated group were more resistant to Cu2+-induced oxidation and contained more vitamin E (21.7+/-2.1 mmol/micromol LDL cholesterol) than did LDLs from the high cholesterol diet group (9.6+/-1.8 nmnol/micromol LDL cholesterol) (P<.005). Endothelial damage, determined at week 6, was reduced by 53% in the SM group (P<.01). SM treatment reduced the atherosclerotic area in the abdominal aorta by 56% (P<.005) and cholesterol deposition in the thoracic aorta by 50% (P<.005). The severity of atherosclerosis in the SM group was significantly reduced after adjustment by using cholesterol exposure as an index of the cholesterol-lowering effect. This study concludes that the reduction of atherosclerosis by SM relies not only on its cholesterol-lowering effect but more heavily on its antioxidant potential to prevent endothelial damage and inhibit LDL oxidative modification in hypercholesterolemic animals.

Sustained increase in intracellular free calcium and activation of cyclooxygenase-2 expression in mouse hepatoma cells treated with dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a non-genotoxic environmental pollutant that causes multiple adverse effects in experimental animals and in humans. We show here that TCDD treatment of mouse hepatoma cells causes a rapid mobilization of intracellular calcium both in wild type Hepa-1 cells and in its c2 variant, a cell line that has highly reduced levels of functional aromatic hydrocarbon (Ah) receptor (AHR). In wild type cells, but not in the c2 variant, TCDD treatment leads to a sustained elevation of cytosolic free calcium. TCDD also induces elevated levels of cyclooxygenase-2 (COX-2) mRNA in wild type and in c37, a CYP1A1-deficient cell line, but not in c2 cells. Induction of Cox-2 is in fact dependent on the presence of a functional Ah receptor, since it can be blocked by antisense oligonucleotides to Ah receptor mRNA. Most likely as a consequence of Cox-2 induction, we find a significant increase in the level of 12-hydroxyheptadecatrienoic acid (12-HHT) secreted from TCDD-treated Hepa-1 cells. In addition, we observe elevated levels of 6-keto prostaglandin F1alpha in c2 cells and high levels of secreted prostaglandin F2alpha in c2, c37 and c4, the variant cell line lacking aromatic hydrocarbon nuclear translocator protein. These data suggest that Cox-2 activation by TCDD leads to the release of prostaglandins, eicosanoids and other mediators which may have an important role in the biological and toxic effects of TCDD.

Induction of serum amyloid A (SAA) gene by SAA-activating sequence-binding factor (SAF) in monocyte/macrophage cells. Evidence for a functional synergy between SAF and Sp1

Serum amyloid A (SAA) is a plasma protein that is associated with many inflammatory diseases including amyloidosis, arthritis, and atherosclerosis. SAA level is significantly increased during inflammatory condition, and such abnormal expression of this protein is linked to the pathogenesis of the above-mentioned diseases. A promoter element, designated as SAA-activating sequence (SAS), located between -280 and -226 has been implicated in the induction mechanism and a nuclear factor, SAS-binding factor (SAF), has been shown to bind to this region. In this report, using a cloned SAF gene in transient transfection assay, we provide evidence that SAF potentiates SAA gene expression through SAS element. Furthermore, we show that during lipopolysaccharide-mediated induction of SAF, heteromeric complex with transcription factor Sp1 is formed. Transfection assays using both transcription factor genes have demonstrated that SAF-Sp1 heteromer is a highly potent transactivator of SAA expression.

Oxidized low density lipoprotein stimulates protein kinase C (PKC) activity and expression of PKC-isotypes via prostaglandin-H-synthase in P388D1 cells

Treatment of P388D1 macrophage-like cells with oxLDL enhanced protein kinase C (PKC) activity in cell extracts. Similar effects were induced by acetylated LDL (acLDL) and maleylated albumin (malBSA). Treatment with oxLDL, acLDL and malBSA was also accompanied by increased production of prostaglandins as well as by an enhanced level of prostaglandin H synthase 2 (cyclooxygenase 2, COX 2). Modified (lipo)proteins differentially affected the levels of individual cytosolic PKC-isoenzymes. Effects of oxLDL on PKC activity/expression were abrogated by indometacin, by pre-exposure to the dual lipoxygenase/cyclooxygenase inhibitor ML 3000 and by treatment with N-(2-cyclohexyloxy-4-nitrophenyl)methane sulfonamide (NS-398). These results suggest a predominantly COX 2-dependent and isotype-specific effect of modified (lipo)proteins on PKC.

Lipoprotein trafficking in vascular cells. Molecular Trojan horses and cellular saboteurs

During the pathogenesis of atherosclerosis, inflammatory cells such as the monocyte-derived macrophage accumulate in the vessel wall where they release cytokines. Initially, cytokines may assist in CE removal of lipoprotein-derived cholesterol/CE hydrolysis to clear intracellular lipid. When plasma levels of LDL become elevated, the vessel wall becomes lipid-engorged over time because it is unable to traffick the large amounts of endocytosed LDL-CE from the cell. In addition, lipoprotein entrapment by the extracellular matrix can lead to the progressive oxidation of LDL because of the action of lipoxygenases, reactive oxygen species, peroxynitrite, and/or myeloperoxidase. A range of oxidized LDL species is thus generated, ultimately resulting in their delivery to vascular cells through several families of scavenger receptors (Fig 1). These molecular Trojan horses and cellular saboteurs once formed or deposited in the cell can contribute to, and participate in, formation of macrophage- and smooth muscle-derived foam cells. A lipid-enriched fatty streak along the vessel wall can ensue. In addition to foam cell development, products of LDL peroxidation may activate endothelial cells, increase smooth muscle mitogenesis, or induce apoptosis because of the effects of oxysterols and products of lipid peroxidation (Fig 1). Because antioxidant defenses may be limited in the microenvironment of the cell or within LDL, the oxidation process continues to progress. Enzymes associated with HDL such as PAF acetylhydrolase and paraoxonase can participate in the elimination of biologically active lipids, but diminished cellular antioxidant activity coupled with low levels of HDL may allow acceleration of the clinical course of vascular disease. There is still much to be learned about how modified LDL initiate cellular signals that lead to inflammation, mitosis, or cholesterol accumulation. The present challenges include elucidation of the key signaling events that regulate lipoprotein-derived cholesterol trafficking in the vessel wall, which can impact on the pathogenesis of vascular disease.

Native and modified low density lipoproteins increase the functional expression of the macrophage class B scavenger receptor, CD36

The uptake of oxidized low density lipoprotein (OxLDL) by macrophages is a key event implicated in the initiation and development of atherosclerotic lesions. Two macrophage surface receptors, CD36 (a class B scavenger receptor) and the macrophage scavenger receptor (a class A scavenger receptor), have been identified as the major receptors that bind and internalize OxLDL. Expression of CD36 in monocyte/macrophages in tissue culture is dependent both on the differentiation state as well as exposure to soluble mediators (cytokines and growth factors). The regulatory mechanisms of this receptor in vivo are undetermined as is the role of lipoproteins themselves in modulating CD36 expression. We studied the effect of lipoproteins, native LDL and modified LDL (acetylated LDL (AcLDL) and OxLDL) on the expression of CD36 in J774 cells, a murine macrophage cell line. Exposure to lipoproteins resulted in a marked induction of CD36 mRNA expression (4-8-fold). Time course studies showed that maximum induction was observed 2 h after treatment with AcLDL and at 4 h with LDL and OxLDL. Increased expression of CD36 mRNA persisted for 24 h with each treatment group. Induction of CD36 mRNA expression was paralleled by an increase in CD36 protein as determined by Western blot with the greatest induction by OxLDL (4-fold). In the presence of actinomycin D, treatment of macrophages with LDL, AcLDL, or OxLDL did not affect CD36 mRNA stability, implying that CD36 mRNA was transcriptionally regulated by lipoproteins. To determine the mechanism(s) by which lipoproteins increased expression of CD36 we evaluated the effects of lipoprotein components on CD36 mRNA expression. ApoB 100 increased CD36 mRNA expression significantly, whereas phospholipid/cholesterol liposomes had less effect. Incubation of macrophages with bovine serum albumin or HDL reduced expression of CD36 mRNA in a dose-dependent manner. Finally, to evaluate the in vivo relevance of the induction of CD36 mRNA expression by lipoproteins, peritoneal macrophages were isolated from mice following intraperitoneal injection of lipoproteins. Macrophage expression of CD36 mRNA was significantly increased by LDL, AcLDL, or OxLDL in relation to mice infused with phosphate-buffered saline, with OxLDL causing the greatest induction (8-fold). This is the first demonstration that exposure to free and esterified lipids augments functional expression of the class B scavenger receptor, CD36. These data imply that lipoproteins can further contribute to foam cell development in atherosclerosis by up-regulating a major OxLDL receptor.

Efficacy of simvastatin and pumpkin-seed oil in the management of dietary-induced hypercholesterolemia

Pumpkin-seed oil (PSO), a natural supplement rich with antioxidants and polyunsaturated fatty acids (PUFAs), was given in combination with simvastatin, as antihypercholesterolemic drug, to high cholesterol-fed rabbits, for three weeks. In comparison with normal rabbits, a significant increase of the aortic contractile response to norepinephrine was observed which could be attributed to endothelium dysfunction. In addition, serum levels of total lipids, triacylglycerols, total cholesterol and low density lipoprotein-cholesterol (LDL-C) were increased while phospholipids and high density lipoprotein-cholesterol (HDL-C) were decreased in hypercholesterolemic rabbits. These changes could be related to the predominance of LDL and oxidized-LDL particles caused by high levels of reactive oxygen species during hypercholesterolemia (HC). Treatment with simvastatin modulated most of the altered parameters affected during HC that might be, in part, due to inhibition of cholesterol biosynthesis. While concomitant administration of simvastatin and PSO succeeded to cause marked reduction of the aortic contractile response to norepinephrine and to normalize the most adverse effects observed during HC. These effects were explained by the potentiating effects of simvastatin with antioxidants and essential fatty acids in PSO. On the contrary, serum activities of aminotransferases and creatine phosphokinase were increased with simvastatin treatment but not with the combination therapy in hypercholesterolemic rabbits.

Mildly oxidized LDL induces an increased apolipoprotein J/paraoxonase ratio

We have examined the effects of mildly oxidized LDL and atherosclerosis on the levels of two proteins associated with HDL; apolipoprotein J (apoJ), and paraoxonase (PON). On an atherogenic diet, PON activity decreased by 52%, and apoJ levels increased 2.8-fold in fatty streak susceptible mice, C57BL/6J (BL/6), but not in fatty streak resistant mice, C3H/HeJ (C3H). Plasma PON activity was also significantly decreased, and apoJ levels were markedly increased in apolipoprotein E knockout mice on the chow diet, resulting in a 9.2-fold increase in the apoJ/PON ratio as compared to controls. Furthermore, a dramatic increase in the apoJ/PON ratio (over 100-fold) was observed in LDL receptor knockout mice when they were fed a 0.15%-cholesterol-enriched diet. Injection of mildly oxidized LDL (but not native LDL) into BL/6 mice (but not in C3H mice) on a chow diet resulted in a 59% decrease in PON activity (P < 0.01) and a 3.6-fold increase in apoJ levels (P < 0.01). When an acute phase reaction was induced in rabbits, or the rabbits were placed on an atherogenic diet, hepatic mRNA for apoJ was increased by 2.7-fold and 2.8-fold, respectively. Treatment of HepG2 cells in culture with mildly oxidized LDL (but not native LDL) resulted in reduced mRNA levels for PON (3.0-fold decrease) and increased mRNA levels for apoJ (2.0-fold increase). In normolipidemic patients with angiographically documented coronary artery disease who did not have diabetes and were not on lipid-lowering medication (n = 14), the total cholesterol/HDL cholesterol ratio was 3.1+/-0.9 as compared to 2.9+/-0.4 in the controls (n = 19). This difference was not statistically significant. In contrast, the apoJ/PON ratio was 3.0+/-0.4 in the patients compared to 0.72+/-0.2 in the controls (P < 0.009). In a subset of these normolipidemic patients (n = 5), the PON activity was low (48+/-6.6 versus 98+/-17 U/ml for controls; P < 0.009), despite similar normal HDL levels, and the HDL from these patients failed to protect against LDL oxidation in co-cultures of human artery wall cells. We conclude that: (a) mildly oxidized LDL can induce an increased apoJ/PON ratio, and (b) the apoJ/PON ratio may prove to be a better predictor of atherosclerosis than the total cholesterol/HDL cholesterol ratio.

Human phagocytes employ the myeloperoxidase-hydrogen peroxide system to synthesize dityrosine, trityrosine, pulcherosine, and isodityrosine by a tyrosyl radical-dependent pathway

Myeloperoxidase, a heme protein secreted by activated phagocytes, may be a catalyst for lipoprotein oxidation in vivo. Active myeloperoxidase is a component of human atherosclerotic lesions, and atherosclerotic tissue exhibits selective enrichment of protein dityrosine cross-links, a well characterized product of myeloperoxidase. Tyrosylation of lipoproteins with peroxidase-generated tyrosyl radical generates multiple protein-bound tyrosine oxidation products in addition to dityrosine. The structural characterization of these products would thus serve as an important step in determining the role of myeloperoxidase in lipoprotein oxidation in the artery wall. We now report the identification and characterization of four distinct tyrosyl radical addition products generated by human phagocytes. Activated neutrophils synthesized three major fluorescent products from -tyrosine; on reverse phase HPLC, each compound coeluted with fluorescent oxidation products formed by myeloperoxidase. We purified the oxidation products to apparent homogeneity by cation and anion exchange chromatographies and identified the compounds as dityrosine (3,3'-dityrosine), trityrosine (3,3',5',3"-trityrosine) and pulcherosine (5-[4"-(2-carboxy-2-aminoethyl)phenoxy]3, 3'-dityrosine) by high resolution NMR spectroscopy and mass spectrometry. Additionally, we have found that dityrosine is a precursor to trityrosine, but not pulcherosine. In a search for a precursor to pulcherosine, we identified isodityrosine (3-[4'-(2-carboxy-2-aminoethyl)phenoxy]tyrosine), a non-fluorescent product of L-tyrosine oxidation by human phagocytes. Our results represent the first identification of this family of tyrosyl radical addition products in a mammalian system. Moreover, these compounds may serve as markers specific for tyrosyl radical-mediated oxidative damage in atherosclerosis and other inflammatory conditions.

Blood radicals: reactive nitrogen species, reactive oxygen species, transition metal ions, and the vascular system

Free radicals, such as superoxide, hydroxyl and nitric oxide, and other "reactive species", such as hydrogen peroxide, hypochlorous acid and peroxynitrite, are formed in vivo. Some of these molecules, e.g. superoxide and nitric oxide, can be physiologically useful, but they can also cause damage under certain circumstances. Excess production of reactive oxygen or nitrogen species (ROS, RNS), their production in inappropriate relative amounts (especially superoxide and NO) or deficiencies in antioxidant defences may result in pathological stress to cells and tissues. This oxidative stress can have multiple effects. It can induce defence systems, and render tissues more resistant to subsequent insult. If oxidative stress is excessive or if defence and repair responses are inadequate, cell injury can be caused by such mechanisms as oxidative damage to essential proteins, lipid peroxidation, DNA strand breakage and base modification, and rises in the concentration of intracellular "free" Ca(2+). Considerable evidence supports the view that oxidative damage involving both ROS and RNS is an important contributor to the development of atherosclerosis. Peroxynitrite (derived by reaction of superoxide with nitric oxide) and transition metal ions (perhaps released by injury to the vessel wall) may contribute to lipid peroxidation in atherosclerotic lesions.

Oxidation of low density lipoproteins greatly enhances their association with lipoprotein lipase anchored to endothelial cell matrix

Native and oxidized low density lipoprotein retention within arterial wall endothelial cell matrix (ECM) is an early event in the pathogenesis of atherosclerosis. Previously we showed lipoprotein lipase (LPL) addition to ECM enhanced the retention of apoB-containing lipoproteins. In the present studies we examined whether the oxidation of low density lipoprotein (LDL) increases its retention by LPL-containing ECM. Except where noted, 125I-labeled moderately oxidized LDL (ModOxLDL) was prepared by long term storage of 125I-LDL. Without LPL, 125I-ModOxLDL matrix binding was low and nonsaturable. LPL preanchored to ECM resulted in 125I-ModOxLDL binding that was saturable and 20-fold greater than in the absence of LPL, with an association constant equal to 2.6 nM. Copper-oxidized LDL (Cu-OxLDL) was able to compete with 125I-ModOxLDL, whereas a 60-fold native LDL excess had no effect. Reconstituted apolipoprotein B from Cu-OxLDL also reduced 125I-ModOxLDL to LPL, whereas liposomes derived from the lipid extract of Cu-OxLDL had no effect on binding. These data suggest that the increased binding of oxidized LDL to LPL-ECM may be due to the exposure of novel apoB binding sites and not an oxidized lipid moiety. 125I-ModOxLDL binding was also not affected by either preincubation with a 300-fold molar excess of apoE-poor HDL or an 340-fold molar excess of Cu-Ox-HDL. In contrast, a 4-fold apoE-rich HDL excess (based on protein) totally inhibited 125I-ModOxLDL matrix retention. Positively charged peptides of polyarginine mimicked the effect of apoE-rich HDL in reducing the 125I-ModOxLDL retention; however, polylysine had no effect. We postulate that the oxidation of LDL may be a mechanism that enhances LDL retention by the ECM-bound LPL and that the protective effects of apoE-containing HDL may in part be due to its ability to block the retention of oxidized LDL in vivo.

Atherosclerosis: basic mechanisms. Oxidation, inflammation, and genetics

The clinical events resulting from atherosclerosis are directly related to the oxidation of lipids in LDLs that become trapped in the extracellular matrix of the subendothelial space. These oxidized lipids activate an NF kappa B-like transcription factor and induce the expression of genes containing NF kappa B binding sites. The protein products of these genes initiate an inflammatory response that initially leads to the development of the fatty streak. The progression of the lesion is associated with the activation of genes that induce arterial calcification, which changes the mechanical characteristics of the artery wall and predisposes to plaque rupture at sites of monocytic infiltration. Plaque rupture exposes the flowing blood to tissue factor in the lesion, and this induces thrombosis, which is the proximate cause of the clinical event. There appear to be potent genetically determined systems for preventing lipid oxidation, inactivating biologically important oxidized lipids, and/or modulating the inflammatory response to oxidized lipids that may explain the differing susceptibility of individuals and populations to the development of atherosclerosis. Enzymes associated with HDL may play an important role in protecting against lipid oxidation in the artery wall and may account in part for the inverse relation between HDL and risk for atherosclerotic clinical events.

Free radicals and antioxidants: a personal view

Free radicals and other oxygen-derived species are constantly generated in vivo, both by "accidents of chemistry" and for specific metabolic purposes. The reactivity of different free radicals varies, but some can cause severe damage to biological molecules, especially to DNA, lipids, and proteins. Antioxidant defense systems scavenge and minimize the formation of oxygen-derived species, but they are not 100% effective. Hence, diet-derived antioxidants may be particularly important in diminishing cumulative oxidative damage and helping us to stay healthier for longer. Repair systems exist to deal with molecules that have been oxidatively damaged. Damage to DNA by hydroxyl radicals appears to occur in all aerobic cells, and might be a significant contributor to the age-dependent development of cancer. Lipid peroxidation probably contributes significantly to the development of atherosclerosis.