Physiological aspects of low-density lipoprotein oxidation

The effect of a sol–gel derived silica coating doped with vitamin E on oxidative stress and senescence of human adipose-derived mesenchymal stem cells (AMSCs)

A sol–gel-derived silica coating functionalized with vitamin E reduces ROS and senescence in AMSCs isolated from elderly patients.

Role of free radical in atherosclerosis, diabetes and dyslipidaemia: larger-than-life

During the past few decades, there have been numerous studies related to free radical chemistry. Free radicals including reactive oxygen species (ROS) and reactive nitrogen species are generated by the human body by various endogenous systems, exposure to different physiochemical conditions, or pathological states, and have been implicated in the pathogenesis of many diseases. These free radicals are also the common by-products of many oxidative biochemical reactions in cells. When free radicals overwhelm the body's ability to regulate them, a condition known as oxidative stress ensues. They adversely alter lipids, proteins, and DNA, which trigger a number of human diseases. In a number of pathophysiological conditions, the delicate equilibrium between free radical production and antioxidant capability is distorted, leading to oxidative stress and increased tissue injury. ROS which are mainly produced by vascular cells are implicated as possible underlying pathogenic mechanisms in a progression of cardiovascular diseases including ischemic heart disease, atherosclerosis, cardiac arrhythmia, hypertension, and diabetes. This review summarizes the key roles played by free radicals in the pathogenesis of atherosclerosis, diabetes, and dyslipidaemia. Although not comprehensive, this review also provides a brief perspective on some of the current research being conducted in this area for a better understanding of the role free radicals play in the pathogenesis of atherosclerosis, diabetes, and dyslipidaemia.

Lipid metabolism, apoptosis and cancer therapy

Lipid metabolism is regulated by multiple signaling pathways, and generates a variety of bioactive lipid molecules. These bioactive lipid molecules known as signaling molecules, such as fatty acid, eicosanoids, diacylglycerol, phosphatidic acid, lysophophatidic acid, ceramide, sphingosine, sphingosine-1-phosphate, phosphatidylinositol-3 phosphate, and cholesterol, are involved in the activation or regulation of different signaling pathways. Lipid metabolism participates in the regulation of many cellular processes such as cell growth, proliferation, differentiation, survival, apoptosis, inflammation, motility, membrane homeostasis, chemotherapy response, and drug resistance. Bioactive lipid molecules promote apoptosis via the intrinsic pathway by modulating mitochondrial membrane permeability and activating different enzymes including caspases. In this review, we discuss recent data in the fields of lipid metabolism, lipid-mediated apoptosis, and cancer therapy. In conclusion, understanding the underlying molecular mechanism of lipid metabolism and the function of different lipid molecules could provide the basis for cancer cell death rationale, discover novel and potential targets, and develop new anticancer drugs for cancer therapy.

Antihypercholesterolemic and Antioxidative Potential of an Extract of the Plant, Piper betle, and Its Active Constituent, Eugenol, in Triton WR-1339-Induced Hypercholesterolemia in Experimental Rats

Hypercholesterolemia is a dominant risk factor for atherosclerosis and cardiovascular diseases. In the present study, the putative antihypercholesterolemic and antioxidative properties of an ethanolic extract of Piper betle and of its active constituent, eugenol, were evaluated in experimental hypercholesterolemia induced by a single intraperitoneal injection of Triton WR-1339 (300 mg/kg b.wt) in Wistar rats. Saline-treated hypercholesterolemic rats revealed significantly higher mean blood/serum levels of glucose, total cholesterol, triglycerides, low density and very low density lipoprotein cholesterol, and of serum hepatic marker enzymes; in addition, significantly lower mean serum levels of high density lipoprotein cholesterol and significantly lower mean activities of enzymatic antioxidants and nonenzymatic antioxidants were noted in hepatic tissue samples from saline-treated hypercholesterolemic rats, compared to controls. However, in hypercholesterolemic rats receiving the Piper betle extract (500 mg/kg b.wt) or eugenol (5 mg/kg b.wt) for seven days orally, all these parameters were significantly better than those in saline-treated hypercholesterolemic rats. The hypercholesterolemia-ameliorating effect was better defined in eugenol-treated than in Piper betle extract-treated rats, being as effective as that of the standard lipid-lowering drug, lovastatin (10 mg/kg b.wt). These results suggest that eugenol, an active constituent of the Piper betle extract, possesses antihypercholesterolemic and other activities in experimental hypercholesterolemic Wistar rats.

Vitamin E-stabilized UHMWPE for total joint implants: a review

BACKGROUND

Osteolysis due to wear of UHMWPE limits the longevity of joint arthroplasty. Oxidative degradation of UHMWPE gamma-sterilized in air increases its wear while decreasing mechanical strength. Vitamin E stabilization of UHMWPE was proposed to improve oxidation resistance while maintaining wear resistance and fatigue strength.

QUESTIONS/PURPOSES

We reviewed the preclinical research on the development and testing of vitamin E-stabilized UHMWPE with the following questions in mind: (1) What is the rationale behind protecting irradiated UHMWPE against oxidation by vitamin E? (2) What are the effects of vitamin E on the microstructure, tribologic, and mechanical properties of irradiated UHMWPE? (3) Is vitamin E expected to affect the periprosthetic tissue negatively?

METHODS

We performed searches in PubMed, Scopus, and Science Citation Index to review the development of vitamin E-stabilized UHMWPEs and their feasibility as clinical implants.

RESULTS

The rationale for using vitamin E in UHMWPE was twofold: improving oxidation resistance of irradiated UHMWPEs and fatigue strength of irradiated UHMWPEs with an alternative to postirradiation melting. Vitamin E-stabilized UHMWPE showed oxidation resistance superior to that of irradiated UHMWPEs with detectable residual free radicals. It showed equivalent wear and improved mechanical strength compared to irradiated and melted UHMWPE. The biocompatibility was confirmed by simulating elution, if any, of the antioxidant from implants.

CONCLUSIONS

Vitamin E-stabilized UHMWPE offers a joint arthroplasty technology with good mechanical, wear, and oxidation properties.

CLINICAL RELEVANCE

Vitamin E-stabilized, irradiated UHMWPEs were recently introduced clinically. The rationale behind using vitamin E and in vitro tests comparing its performance to older materials are of great interest for improving longevity of joint arthroplasties.

Serum vitamin E concentration and osmotic fragility in female long-distance runners

The objective of this study was to assess the nutritional adequacy of sub-elite runners with irregular menstrual function (n=10) and that of a comparable group of runners with regular menstrual function (n=10), with a special focus on vitamin E. Based on 3 days' records of weighed dietary intake, the mean energy intakes of micro- and macronutrients were estimated. Both estimated daily energy intake (irregular: 9.9+/-0.4 MJ; regular: 12.2+/-0.7 MJ; mean+/-sx) and intake of dietary fat (irregular: 61+/-6 g; regular: 98+/-12 g) were lower in athletes with irregular menstrual function than in athletes with regular menstrual function (P=0.01). Estimated intake of vitamin E was below recommended values in both groups. Serum concentrations of alpha-tocopherol were used to evaluate vitamin E status, which were normal in athletes with regular menstrual function (27.3+/-3.6 micromol.l(-1)) but below normal values in athletes with irregular menstrual function (15.7+/-0.8 micromol.l(-1); P=0.01). Furthermore, post-exercise osmotic fragility in red blood cells was inversely related to resting alpha-tocopherol concentrations. Our results indicate that irregular menstrual function in athletes on a low-fat diet is associated with low concentrations of circulating alpha-tocopherol, rendering the red blood cells more susceptible to haemolysis in connection with physical activity.

Increasing Oxidative Stress with Progressive Hyperlipidemia in Human: Relation between Malondialdehyde and Atherogenic Index

The aim of this study was to examine whether malondialdehyde (MDA) formation, a marker of oxidant stress, is altered in different stages of development of hyperlipidemia and whether it correlates with atherogenic index (AI), an important risk factor of atherosclerosis. Commercial kits were used to measure the levels of lipid profile and antioxidant status in the serum of 15 hyperlipidemic patients and 30 age and sex-matched normolipidemic subjects. The normolipidemic subjects were divided into lower and higher lipid groups according to their blood lipid level. The activities of superoxide dismutase and glutathione peroxidase decreased in higher lipid group compared with lower lipid group, and were even lower in hyperlipidemic subjects. An increase in the levels of MDA, triglycerides, total cholesterol and LDL-C concentration were observed in higher lipid group, and even significantly increased in hyperlipidemic patients. A significant progressive decline in HDL-C concentration was found during hyperlipidemia evolution. There was a positive correlation between MDA and AI (r = 0.61, p<0.05). These data indicate that oxidative stress is an early event in the evolution of hyperlipidemia, and appropriate support for enhancing antioxidant supply in higher lipid subjects may help prevent the course of the disease.

Lectin-like oxidized low-density lipoprotein receptor-1, a new promising target for the therapy of atherosclerosis?

Endothelial activation and dysfunction induced by oxidized modified low-density lipoprotein (ox-LDL) is one of the key steps in the initiation of atherosclerosis. Recent studies have shown that a new lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) mediates the recognition and internalization of ox-LDL. LOX-1 is the main receptor for ox-LDL and may play an important role in the pathogenesis of hypertension, diabetes, and, especially, of atherosclerosis. The potential role of LOX-1 in the pathogenesis of atherosclerosis includes: endocytosis of ox-LDL, expression co-location with atherosclerosis enhanced by atherosclerosis-related risk factors, elevated LOX-1 protein in cardiovascular disease, effects related to atherosclerosis and eliminated by antiatherosclerotic drugs. Identification and regulation of LOX-1 and understanding its signal transduction pathways might improve our insight toward the pathogenesis of atherosclerosis and provide a selective treatment approach. LOX-1 might be a potential and promising target for the development of novel antiatherosclerotic drugs. However, due to limited knowledge about LOX-1, there are still many questions to be answered.

Effect of bicarbonate on iron-mediated oxidation of low-density lipoprotein

Oxidation of low-density lipoprotein (LDL) may play an important role in atherosclerosis. We studied the effects of bicarbonate/CO2 and phosphate buffer systems on metal ion-catalyzed oxidation of LDL to malondialdehyde (MDA) and to protein carbonyl and MetO derivatives. Our results revealed that LDL oxidation in mixtures containing free iron or heme derivatives was much greater in bicarbonate/CO2 compared with phosphate buffer. However, when copper was substituted for iron in these mixtures, the rate of LDL oxidation in both buffers was similar. Iron-catalyzed oxidation of LDL was highly sensitive to inhibition by phosphate. Presence of 0.3-0.5 mM phosphate, characteristic of human serum, led to 30-40% inhibition of LDL oxidation in bicarbonate/CO2 buffer. Iron-catalyzed oxidation of LDL to MDA in phosphate buffer was inhibited by increasing concentrations of albumin (10-200 microM), whereas MDA formation in bicarbonate/CO2 buffer was stimulated by 10-50 microM albumin but inhibited by higher concentrations. However, albumin stimulated the oxidation of LDL proteins to carbonyl derivatives at all concentrations examined in both buffers. Conversion of LDL to MDA in bicarbonate/CO2 buffer was greatly stimulated by ADP, ATP, and EDTA but only when EDTA was added at a concentration equal to that of iron. At higher than stoichiometric concentrations, EDTA prevented oxidation of LDL. Results of these studies suggest that interactions between bicarbonate and iron or heme derivatives leads to complexes with redox potentials that favor the generation of reactive oxygen species and/or to the generation of highly reactive CO2 anion or bicarbonate radical that facilitates LDL oxidation.

Effects of atorvastatin on serum lipids, lipoproteins, and hemostasis

Serum levels of lipids and lipoproteins were examined in individuals with hyperlipidemia treated with atorvastatin or colestimide and in healthy volunteers. Modified low-density lipoprotein (LDL) was measured by its faster electrophoretic mobility and expressed as charge modification frequency (CMF). Serum levels of total cholesterol (t-chol), triglyceride (TG), very low-density lipoprotein (VLDL)-chol, low-density lipoprotein (LDL)-chol, and CMF were significantly higher in hyperlipidemia, but there was no significant difference in serum high-density lipoprotein (HDL)-chol levels between hyperlipidemic and healthy subjects. Treatment with atorvastatin resulted in significant decreases of serum t-chol, TG, and LDL-chol levels but not serum HDL-chol and VLDL-chol. Treatment with colestimide significantly reduced serum t-chol, HDL-chol, and LDL-chol levels but not those of TG and VLDL-chol. CMF was significantly reduced by treatment with atorvastatin but not by colestimide. Atorvastatin significantly reduced plasma levels of thrombomodulin, thrombin antithrombin complex (TAT) and tissue type plasminogen activator-plasminogen activator inhibitor-I complex. Colestimide moderately prolonged activated partial thromboplastin time and reduction of TAT. Based on its actions of lowering modified LDL and improving hemostatic abnormalities, we postulate that atorvastatin might inhibit the onset of ischemic diseases.

Evaluation of the atherogenic tendency of lipids and lipoprotein content and their relationships with oxidant-antioxidant system in patients with psoriasis

BACKGROUND

Psoriasis is a common chronic and recurrent inflammatory skin disease that can occur due to abnormalities in essential fatty acid metabolism, lymphokine secretion, free radical generation, lipid peroxidation and eicosanoid metabolism, and has been associated with increased frequency of cardiovascular events. The current study was designed to evaluate plasma lipids, susceptibility of LDL to oxidation and oxidant-antioxidant status and their relationships in patients with psoriasis.

METHODS

The study group included 35 patients with psoriasis (18 females and 17 males), and 35 sex- and age-matched healthy volunteers (16 females and 19 males). From blood samples, their lipids, lipoproteins, acute phase reactants, lipid peroxidation products [lipid hydroperoxide (LHP) and malondialdehyde (MDA)], antioxidant enzymes [glutathione peroxidase (GSH-Px), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT)], total antioxidant status (TAS) and autoantibodies against oxidized low-density lipoprotein (AuAb-oxLDL) levels were determined. Moreover, the susceptibility of copper-induced in vitro oxidation of LDL was examined.

RESULTS

The mean levels of atherogenic lipids (total cholesterol [TC], triacylglycerol [TG] and LDL cholesterol [LDL-C]), acute-phase reactants (CRP, ESR, PMNLs, ceruloplasmin and fibrinogen) and lipid peroxidation products, AuAb-oxLDL levels in patients with psoriasis were found to be significantly higher than those of healthy subjects. On the other hand, TAS and antioxidant enzyme activities (CAT, SOD and GSH-Px in erythrocyte and SOD in plasma) were significantly lower when compared to healthy subjects. The lag times [t(lag)], a measure of resistance to oxidation of LDL, were also lower. The levels of AuAb-oxLDL in patients were correlated with TC, LDL-C, plasma LHP, erythrocyte MDA, oxidized LDL-MDA (oxLDL-MDA), fibrinogen, CRP, PMNL levels and plasma SOD activities (r = 0.69, P < 0.01; r = 0.64, P < 0.01; r = 0.38, P < 0.05; r = 0.65, P < 0.01; r = 0.34, P < 0.05; r = 0.34, P < 0.05; r = 0.53, P < 0.01, r = 0.34, P < 0.05; r = -0.67, P < 0.01, respectively). On the other hand, t(lag) was correlated negatively with the levels of VLDL-TG, VLDL-TC and LDL-TG but positively correlated with the levels of TAS in psoriatics (r = -0.49, P < 0.01; r = -0.49, P < 0.01, r = -0.65, P < 0.05; r = 0.37, P < 0.05).

CONCLUSIONS

It was concluded that the psoriatic patients could be considered as a group with an increased atherosclerotic risk because of increased oxidant stress, decreased antioxidant capacity and susceptibility in lipid profile and lipoprotein content to atherogenicity.

An overview on peripheral vascular disease in blackfoot disease-hyperendemic villages in Taiwan

The arsenic-related peripheral vascular disease found to be endemic along the southwestern coast of Taiwan is reviewed. In the early 20th century a strange disease involving the lower extremities characterized by typical clinical symptoms and signs of progressive arterial occlusion was reported in a confined area located along the southwestern coast of Taiwan. The disease was locally called "blackfoot disease" because of its gangrenous appearance involving the feet of the patients. The prevalence of this disease ranged from 6.51 to 18.85 per 1,000 population in different villages. Epidemiologic studies revealed that blackfoot disease was associated with the consumption of artesian well water containing high levels of arsenic. High co-occurrence of blackfoot disease and arsenic-related skin lesions such as hyperpigmentation, hyperkeratosis, and skin cancer was also observed. Recent studies also confirmed the association of preclinical peripheral vascular disease with arsenic exposure in a dose-response pattern. Subclinical arterial insufficiency and defects in cutaneous microcirculation can also be demonstrated in seemingly normal subjects living in the endemic villages. The incidence of clinical manifestation of blackfoot disease decreased dramatically after the implementation of tap water in these villages over the past 2-3 decades. The atherogenicity of arsenic could be associated with its effects on hypercoagulability, endothelial injury, smooth muscle cell proliferation, somatic mutation, oxidative stress, and apoptosis. However, its interaction with some trace elements and its association with hypertension and diabetes mellitus could also explain part of its higher risk of developing atherosclerosis.

Heme oxygenase as an intrinsic defense system in vascular wall: implication against atherogenesis

Recent developments in our understanding of the atherosclerotic process and factors that trigger ischemic cardiovascular disease have led to the consideration of antioxidative responses or exogenous antioxidants, which are proposed to inhibit multiple proatherogenic and prothrombotic events in arterial wall. Heme oxygenases (HO), an enzyme essential for heme degradation, have been shown to have such antioxidative properties via the production of bile pigments, carbon monoxide and ferritin induction. We have demonstrated that mildly oxidized LDL markedly induces HO-1, an inducible form of HO, in human aortic endothelial and smooth muscle cell cocultures and that its induction results in the attenuation of monocyte chemotaxis induced by mildly oxidized LDL. We also confirmed abundant expression of HO-1 in human, murine and rabbit atherosclerotic lesions. By modulating HO activities in LDL-receptor knockout mice and Watanabe heritable hyperlipidemic rabbits during their atherosclerotic lesion developments, anti-atherogenic properties of HO have demonstrated as judged by the quantitative analyses of atherosclerotic lesion formation. HO expression was inversely correlated with the levels of plasma and tissue lipid peroxides. HO also influenced on nitric oxide pathway. These observations may suggest that HO, induced during atherosclerotic process, functions as an intrinsic protective pathway in vascular wall.

Resveratrol and vitamin C as antioxidants in blood platelets

We investigated the effects of two different compounds with potential antioxidative action (found in many fruits, which can be used in therapy of cardiovascular disorders): trans-resveratrol (3,4',5-trihydroxystilbene) and vitamin C on oxidative stress in blood platelets. Oxidative stress in blood platelets was estimated by the measurement of: (1) the generation of superoxide radicals (O(2)(-*)) (reduction of cytochrome c) and other reactive oxygen species--ROS: H(2)O(2), singlet oxygen and organic radicals (chemiluminescence), (2) the production of thiobarbituric acid reactive substances (TBARS) and the level of conjugate dienes as markers of lipid peroxidation. We have shown that vitamin C at the concentrations of 750-3000 microM, but not at the concentration of 100 microM (prooxidative action) significantly inhibited peroxidation of lipids (measured by TBARS and conjugate dienes) and the production of ROS in blood platelets. After the incubation of blood platelets for 30 min at 37 degrees C with vitamin C at the concentration of 3000 microM, inhibition of ROS generation (above 90%) was achieved. The inhibition of ROS production caused by resveratrol at physiological plasma concentrations 0.05-2 microM was lower than by vitamin C. At the highest concentration of vitamin C used (3000 microM), the inhibition of O(2)(-*) generation was about 40%. Moreover, we did not observe any synergistic action of resveratrol and vitamin C at antioxidative dose (3000 microM) on the inhibition of lipid peroxidation and the production of O(2)(-*) or ROS in blood platelets. Resveratrol as an antioxidant reduced oxidative stress in blood platelets caused by vitamin C at prooxidative dose (100 microM).

Effects of differently oxidized LDL on the expression of pro-inflammatory molecules in human monocytes in vitro

The oxidation of low-density lipoprotein (LDL) is thought to be a major contributor to the development of atherosclerosis and considerable evidence has accumulated showing that oxidized LDL (ox LDL) induces cell damage and pro-atherogenic events. However, evidence that oxidized LDL directly causes atherosclerosis is lacking. We studied whether native and enzymatically or chemically ox LDL at concentrations of 5 and 100 microg/mL is cytotoxic to or promotes pro-atherogenic activation of human primary monocytes in culture. Both types of ox LDL (100 microg/mL), but not native LDL added to monocytes for 24 h significantly diminish DNA synthesis and increase cell death. In addition, both preparations of ox LDL inhibit cytokine and metalloproteinase production, diminish cellular oxygen consumption and induce PPAR gamma expression. Enzymatically ox LDL, but not LDL oxidized by copper sulfate, also increases the monocyte metabolic rate and induces intracellular lipid accumulation. Low concentrations of either preparation of oxidized and native LDL did not show significant effects on all parameters measured. These data establish a direct link between ox LDL concentration and cytotoxicity and suggest that oxidation by copper of the lipid moiety in LDL and of the protein moiety by enzyme creates ox LDL, which can damage monocytes without release of pro-inflammatory molecular species. In contrast to native and enzymatically ox LDL, copper ox LDL does not induce intracellular lipid accumulation. Differently oxidized LDL molecules may exert distinct effects in lesion development in atherosclerosis.

Protection against oxidized low-density lipoprotein-induced vascular endothelial cell death by integrin-linked kinase

BACKGROUND

Integrin-linked kinase (ILK) is a protein that plays important roles in extracellular matrix-mediated signaling. It has been shown that ILK is expressed preferentially in cardiac and skeletal muscles. Evidence points to its role as an upstream regulator of protein kinase B, a critical player in apoptosis. Because oxidized LDL (oxLDL) is thought to promote atherogenesis by causing the apoptosis of endothelial cells, we investigated the potential roles that ILK may play in oxLDL-induced apoptosis in vascular endothelial cells.

METHODS AND RESULTS

Transcriptional and translational levels of ILK were investigated with reverse-transcriptase polymerase chain reaction and Western analysis. oxLDL treatment induced both the transcription and the translation of the ILK gene in endothelial cells. A recombinant adenovirus vector encoding the ILK gene was constructed to investigate its potential role in oxLDL-induced apoptosis in human umbilical vein endothelial cells and mouse lymphoid vein endothelial cells transformed by simian virus 40. In both types of cells, overexpression of the ILK gene significantly prevented oxLDL-induced apoptosis or cell death, as evaluated by 2 independent assay methods. Furthermore, we showed that ILK could inhibit oxLDL-induced upregulation of the kinase activity of p38 mitogen-activated protein kinase, which is often associated with stress-induced pro-apoptotic signal transduction. Finally, examination of other factors, such as bcl-2, bcl-xl, caspase 3, and caspase 9, demonstrated significant changes that were correlated with oxLDL treatment and ILK overexpression.

CONCLUSIONS

ILK may be an important factor involved in the regulation of oxLDL-induced apoptosis in vascular endothelial cells. Modifying its activity may be a useful approach for prevention of endothelial cell injury in oxLDL-induced atherosclerosis.

Different susceptibility to oxidation of proline and arginine residues of apolipoprotein B-100 among subspecies of low density lipoproteins

gamma-Glutamyl semialdehyde is a primary oxidation product of apolipoprotein (apo) B-100 proline (Pro) and arginine (Arg) side chain residues. By reduction gamma-glutamyl semialdehyde forms 5-hydroxy-2-aminovaleric acid (HAVA). Here we describe the application of sensitive and specific HAVA measurement to characterize the formation of gamma-glutamyl semialdehyde in several domains of apoB-100 in LDL(1) (S(f) 7-12) and LDL(2) (S(f) 0-7) subfractions subjected to oxidative damage in the presence of iron in vitro. Results suggest that susceptibility of apoB-100 Pro and Arg residues toward oxygen radicals drastically changes along the lipoprotein metabolic cascade.

Metabolism of oxidized LDL by macrophages

Oxidation products of lipids and proteins are found in atherosclerotic plaque and in macrophage foam cells. Macrophages avidly endocytose in-vitro oxidized LDL and accumulate sterols. What is the evidence that such a process is involved in in-vivo foam cell formation? The present review surveys current knowledge on the metabolism of oxidized LDL by macrophages, and the types, amounts and location of oxidation products that accumulate in these cells. Comparable studies of lesion lipoproteins and foam cells indicate that limited extracellular lipoprotein oxidation, perhaps followed by more extensive intracellular oxidation subsequent to uptake by macrophages, is a more likely scenario in vivo.