Oxidation of low density lipoprotein in hemodialysis patients: effect of dialysis and comparison with matched controls

Effects of Lipid Abnormalities on Arteriosclerosis and Hemostatic Markers in Patients under Hemodialysis

Vascular events caused by arteriosclerosis are the major cause of death in patients under hemodialysis (HD). Arteriosclerosis is associated with lipoprotein abnormalities such as increased serum levels of low-density lipoprotein (LDL), especially of modified LDL (M-LDL) and oxidized LDL (Ox-LDL). We examined the relationship between markers of arteriosclerosis, hemostasis, and lipid metabolism in patients with chronic renal failure, hyperlipidemia, and healthy volunteers. In patients under HD, the serum levels of total cholesterol, LDL, and triglyceride (TG) were decreased, but the serum levels of M-LDL were increased compared to HL and healthy volunteers. In patients with CRF, the serum levels of OxLDL in patients under HD were lower than in those under continuous ambulatory peritoneal dialysis or conservative therapy. The plasma levels of antithrombin and protein C were significantly lower and the plasma levels of thrombomodulin were significantly higher in patients under HD compared to those under conservative therapy. These data show that patients under HD were more in hypercoagulable state than those under conservative therapy. Among patients under HD, only the plasma levels of von Willebrand factor were significantly increased in patients with more than 30 U/L of Ox-LDL compared to those with less than 30 U/L of Ox-LDL. There was no significant difference in the tests of arteriosclerosis among M-LDL values and OxLDL values. These findings suggest that abnormalities of lipid are not the main risk factor for arteriosclerosis disease in patients under HD.

Unfermented grape juice reduce genomic damage on patients undergoing hemodialysis

Chronic kidney disease (CKD) patients in dialysis (HD) are considered to be submitted to a continuous oxidative stress. This stress can cause damage on DNA and, consequently, contribute to the high levels of DNA damage observed in these patients. Due to the well-known role of polyphenols as antioxidant agents we proposed its use to reduce the levels of genotoxicity present in HD-CKD patients. The objective of this study was to evaluate the antigenotoxic effects of unfermented grape juice (UGJ) on HD-CKD patients. The levels of DNA damage were analyzed using different biomarkers, such as breaks and oxidized DNA bases by the comet assay, chromosome damage by the micronucleus test. In addition, TEAC (Trolox equivalent antioxidant capacity) was also evaluated. Thirty-nine patients were followed for six months, of whom 25 were supplemented by UGJ and 14 were not supplemented. The obtained results showed a significant decrease in the underlying levels of oxidative DNA damage, in the supplemented group. Regarding the clinical parameters, LDL and cholesterol, were significantly reduced in the patients studied after the supplementation period, although cholesterol was also decreased in the non-supplemented patients. In conclusion, in our studied group the supplementation with UGJ reduced the levels of oxidative DNA damage of HD-CKD patients.

Oxidative stress and inflammation, a link between chronic kidney disease and cardiovascular disease

Patients with chronic kidney disease (CKD) show a high cardiovascular morbidity and mortality. This seems to be consequence of the cardiovascular risk factor clustering in CKD patients. Non traditional risk factors such as oxidative stress and inflammation are also far more prevalent in this population than in normal subjects. Renal disease is associated with a graded increase in oxidative stress markers even in early CKD. This could be consequence of an increase in reactive oxygen species as well as a decrease in antioxidant defence. This oxidative stress can accelerate renal injury progression. Inflammatory markers such as C reactive protein and cytokines increase with renal function deterioration suggesting that CKD is a low-grade inflammatory process. In fact, inflammation facilitates renal function deterioration. Several factors can be involved in triggering the inflammatory process including oxidative stress. Statin administration is accompanied by risk reduction in all major vascular events in patients with CKD that are considered high-risk patients. These beneficial effects seem to be consequence of not only their hypolipidemic effect but especially their pleitropic actions that involve modulation of oxidative stress and inflammation.

Oxidized Low-Density Lipoproteins Activate CD4+T Cell Apoptosis in Patients with End-Stage Renal Disease through Fas Engagement

Oxidized LDL (oxLDL) are cytotoxic to vascular cells, but their possible toxic action on T cells from patients with ESRD has not been evaluated. oxLDL concentrations were measured and compared in patients who were on long-term hemodialysis (HD), in patients who had ESRD and were on continuous ambulatory peritoneal dialysis, in nondialyzed patients with chronic kidney disease, and in age- and gender-matched control subjects. In parallel, the proliferative capacity of CD69+/CD4+ T cells and their rate of apoptosis, IL-2 expression, and intracellular expression of Bcl-2 and Bax were determined in vitro. The oxLDL concentrations were significantly higher in HD patients (all P = 0.001). Upon phytohemagglutinin stimulation, CD69+/CD4+ T cells from HD patients proliferated significantly less than those from the other patients' group (both P < 0.001). oxLDL but not the native LDL were led to CD69+/CD4+ T cells' program cell death in a dosage- and time-dependent manner through Fas pathway (P = 0.001). Cell surface Fas expression was followed by DNA fragmentation when CD69+/CD4+ T cells from HD patients or control subjects were cultured with oxLDL (200 microg/ml; 31 +/- 3 versus 25 +/- 3%; P = 0.001). In the presence of oxLDL, CD69+/CD4+ T cells from HD patients expressed significantly lower IL-2 levels, which strongly correlated with a decrease in the antiapoptotic Bcl-2 and conversely with an increase in the proapoptotic Bax expression. In conclusion, these data suggest that, in HD patients, exposure of activated CD4+ T cells to oxLDL leads to Fas-mediated apoptosis in association with inhibition of IL-2 expression. Subsequently, this may favor activation of mitochondria-dependent apoptotic pathways, leading to activated CD4+ T cell dysfunction.

Hemodialysis reduces inhibitory effect of plasma ultrafiltrate on LDL oxidation and subsequent endothelial reactions

Oxidative modification of low-density lipoprotein (LDL) and its deleterious effect on endothelium is implicated in the pathogenesis of atherosclerosis. Endothelium responds to such an insult by upregulating the synthesis of heme oxygenase-1 (HO-1) and ferritin. Endothelial cell damage and dysfunction have been observed in patients with chronic kidney disease (CKD) on maintenance hemodialysis (HD). We studied the effect of low-molecular-weight components of uremic plasma on LDL oxidation and LDL-oxidation-provoked endothelial cell reactions, such as the induction of cytotoxicity and the upregulation of cell-protective HO-1 and ferritin. Plasma ultrafiltrate (molecular weight<5000 Da) from CKD patients on HD or when treated conservatively exhibited a pronounced inhibition on heme-mediated oxidative modification of LDL. Endothelial cell cytotoxicity provoked by LDL oxidation was also attenuated by plasma ultrafiltrate from CKD patients. During HD treatment, a dramatic drop occurred in the retardation of oxidative reactions, and a loss of endothelial cytoprotection exerted by plasma ultrafiltrate was noted. The upregulation of HO-1 and ferritin in response to oxidative stress of LDL was blunted by uremic plasma ultrafiltrate that was released by the end of HD. The decreased antioxidant capacity of ultrafiltrate after HD occurred as a consequence of the intradialytic removal of L-ascorbic acid, uric acid, bilirubin, 3-indoxyl sulfate, indoxyl-beta-D-glucuronide, p-cresol, and phenol. Intradialytic removal of L-ascorbic acid, uric acid, bilirubin, 3-indoxyl sulfate, indoxyl-beta-D-glucuronide, p-cresol, and phenol increases the risk of LDL oxidation and subsequent endothelial cell damage, which underlines the importance of activation of cytoprotective HO-1 and ferritin in endothelium.

The effect of the initiation of renal replacement therapy on lipid profile and oxidative stress during the first 6 months of treatment

BACKGROUND

Disturbed lipoproteins and increased oxidative stress are two of the "non-traditional" cardiovascular risk factors in chronic renal failure. There are very few prospective data of the influence of dialysis on these two factors. In the present study we investigated the effects of the initiation of both hemo- and peritoneal dialysis therapy on lipoproteins and parameters of LDL oxidation.

METHODS

In this prospective cohort study, we assessed lipoproteins, plasma lipid peroxides and in vitro copper-induced LDL oxidation in 46 patients with end-stage renal disease prior to the start of dialysis and after 6 months of treatment with either hemodialysis (n=33) or peritoneal dialysis (n=13).

RESULTS

After 6 months of treatment with hemodialysis there was an increase in total cholesterol (4.6+/-1.1 vs. 5.0+/-1.3 mmol/l; p<0.05) and triglycerides (2.0+/-0.9 vs. 2.8+/-1.6 mmol/l; p<0.03). In the peritoneal dialysis group the lipoproteins did not change. Regarding lipid peroxides and in vitro copper-induced LDL oxidation, also no changes were observed after 6 months of treatment in both groups.

CONCLUSION

Dyslipidemia aggravates after 6 months of hemodialysis but not after 6 months of peritoneal dialysis. During this period, no net effects on oxidative stress were demonstrated.

LDL susceptibility to oxidation and HDL antioxidant capacity in patients with renal failure

OBJECTIVES

This study examines the susceptibility to oxidation and the ability to stimulate reactive oxygen species of LDL from hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD) patients. It was also designed to evaluate the antioxidant activity of HDL from uremic patients.

DESIGN AND METHODS

Lipoprotein properties were determined in 28 HD patients, 30 CAPD patients and 30 control subjects by spectrophotometric, chemiluminescence and electrophoresis methods.

RESULTS

CAPD LDL were more resistant to oxidation than control LDL. HD and control LDL, in contrast to CAPD LDL, stimulated reactive oxygen species generation in granulocytes. The HDL ability to protect LDL against oxidation was impaired in renal patients.

CONCLUSIONS

The risk of atherosclerosis development in patients with renal failure does not appear to be related to less resistance of LDL to oxidation, but rather to the decreased HDL antioxidant capacity.

Pro-oxidative effect of α-tocopherol in the oxidation of LDL isolated from co-antioxidant-depleted non-diabetic hemodialysis patients

The association between the antioxidants in LDL and the oxidizability of LDL assessed by the oxidation lag time during copper ion-catalyzed oxidation was investigated in 69 non-diabetic hemodialysis patients and 23 healthy volunteers. The concentrations of co-antioxidants, including ubiquinol-10, lycopene and beta-carotene, in LDL were significantly lower in the hemodialysis patients than in the healthy volunteers, while there was no difference in the alpha-tocopherol concentration between the groups. The lag time showed a significantly positive correlation with the alpha-tocopherol level (r = 0.62, P < 0.01) in the healthy subjects, but a significantly negative correlation (r = -0.38, P < 0.05) in the hemodialysis patients. Furthermore, in vitro incubation of LDL with alpha-tocopherol prolonged the lag time in the healthy subjects, but shortened it in the hemodialysis patients. These results suggested that the alpha-tocopherol might exert the pro-oxidative effect in co-antioxidant-depleted LDL that was isolated from the hemodialysis patients. Despite such co-antioxidant depletion and the pro-oxidative effect of alpha-tocopherol, the lag time in the hemodialysis patients was not statistically different from that in the healthy volunteers. This might have been because the polyunsaturated fatty acids concentration, another determinant of the lag time, in LDL was less in the hemodialysis patients than in the healthy controls.

Lipoproteins in the DCCT/EDIC cohort: associations with diabetic nephropathy

BACKGROUND

Lipoproteins may contribute to diabetic nephropathy. Nuclear magnetic resonance (NMR) can quantify subclasses and mean particle size of very low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL), and LDL particle concentration. The relationship between detailed lipoprotein analyses and diabetic nephropathy is of interest.

METHODS

In a cross-sectional study, lipoproteins from 428 women and 540 men from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) cohort were characterized by conventional lipid enzymology, NMR, apolipoprotein levels, and LDL oxidizibility. Linear regression was performed for each lipoprotein parameter versus log albumin excretion rate (AER), with and without covariates for age, diabetes duration, HbA1c, hypertension, body mass index, waist-hip ratio, and DCCT treatment group. Significance was taken at P < 0.05.

RESULTS

By multivariate analysis, conventional profile, total triglycerides, total- and LDL cholesterol, but not HDL cholesterol, were associated with AER. NMR-determined large, medium, and small VLDL were associated with AER in both genders (except large VLDL in women), and intermediate density lipoprotein (IDL) was associated with AER (men only). LDL particle concentration and ApoB were positively associated with AER (in men and in the total cohort), and there was a borderline inverse association between LDL diameter and AER in men. Small HDL was positively associated with AER and a borderline negative association was found for large HDL. No associations were found with ApoA1, Lp(a), or LDL oxidizibility.

CONCLUSION

Potentially atherogenic lipoprotein profiles are associated with renal dysfunction in type 1 diabetes and further details are gained from NMR analysis. Longitudinal studies are needed to determine if dyslipoproteinemia can predict patients at risk of nephropathy, or if lipoprotein-related interventions retard nephropathy.

Accelerated atherosclerosis, dyslipidemia, and oxidative stress in end-stage renal disease

Premature atherosclerosis is a major cause of morbidity and mortality in end-stage renal disease patients. Dyslipidemia and increased oxidative stress contribute to premature atherogenesis in these patients. The dyslipidemia of end-stage renal disease consists of both quantitative and qualitative abnormalities in serum lipoproteins. Qualitative changes include hypertriglyceridemia (increased remnant lipoproteins), low high-density lipoprotein-cholesterol, and increased lipoprotein (a). In addition to quantitative changes, lipoproteins in end-stage renal disease undergo compositional and qualitative changes that make them pro-atherogenic, such as various modifications of apolipoprotein B, including oxidation, and modification by advanced glycation end-products. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors and low-dose fibrates could be effective therapies for lipid disorders. The best evidence for increased oxidative stress in end-stage renal disease is the demonstration of increased plasma F2-isoprostanes. Confirmation of the positive findings with high-dose alpha-tocopherol in the Secondary Prevention with Antioxidants of Cardiovascular Disease in End-stage Renal Disease Study is urgently needed. Clinical trials with statins and other drugs that improve dyslipidemia also need to be undertaken. These therapies could clearly lead to a reduction in cardiovascular morbidity and mortality in these patients.

Serum lipid metabolism abnormalities and change in lipoprotein contents in patients with advanced-stage renal disease

BACKGROUND

Arteriosclerosis is the major cause of death in patients with chronic renal failure. There is much interest in the lipid metabolism of patients treated with hemodialysis.

METHODS

We analyzed low-density lipoproteins (LDL) and high-density lipoproteins (HDL) in chronic renal failure (CRF) patients according to patients on hemodialysis (HD), patients with diabetic nephropathy before initiation of dialysis (DN), and patients with chronic glomerulonephritis in the conservative stage (CGN); and compared the lipid metabolic abnormalities in patients on hemodialysis and those not yet on hemodialysis. We also analyzed the qualitative abnormalities of LDL and HDL and their relationship with the pathological stages.

RESULTS

Electrophoretic patterns identified small LDL particles and small HDL particles in the three groups, and the degree of denaturation was more enhanced in CRF patients in the conservative stage than in HD patients. For LDL susceptibility to oxidation LDL (oxLDL) by addition of Cu(2+), the lag time was approximately 57 min in healthy controls and CGN patients, but was prolonged to approximately 75 min in HD and DN patients. For HDL susceptibility to oxidation HDL (oxHDL), HD, DN and CGN patients showed lag times shorter than those found in healthy control subjects. These results showed that LDL and HDL in the serum of CRF patients were in a state of enhanced susceptibility to oxidative modification. In Western blot analysis using anti-human-denatured LDL and anti-human-oxidized HDL monoclonal antibodies, bands of low molecular oxLDL at 150-197 kDa were detected in all CRF patients, with marked tailing in CGN patients. Similarly, bands of small oxHDL particles at 110 and 120 kDa were found in HD, DN and CGN patients.

CONCLUSIONS

Oxidative modification of both LDL and HDL occurs in patients with advanced CRF resulting in small lipoproteins. Increased production of oxLDL and oxHDL is the main cause of lipid metabolic abnormality in CRF patients.

Elevated plasma F2-isoprostanes in patients on long-term hemodialysis

BACKGROUND

End-stage renal disease (ESRD) patients on long-term hemodialysis (HD) may be under increased oxidative stress, caused by either HD or renal failure. Plasma F2-isoprostanes have been established as an important indicator of in vivo oxidative stress.

METHODS

Plasma esterified F2-isoprostanes were measured in 25 HD patients and 23 controls with normal renal function, employing gas chromatography-mass spectrometry with negative chemical ionization (GC-MS-NCI). C-reactive protein (CRP) was determined concurrently in patients and controls by enzyme-linked immunosorbent assay (ELISA). alpha-Tocopherol, retinol, albumin and creatinine were also determined.

RESULTS

The average total esterified F2-isoprostanes in the ESRD patients was 1.62 +/- 0.73 vs. 0.27 +/- 0.10 ng/mL in controls (P < 0.001), with no overlap between patients and controls. Plasma F2-isoprostanes in diabetic ESRD patients were similar to F2-isoprostanes in patients with other causes for renal failure. In a subset of 10 of these ESRD patients evaluated eight months after the initial measurement, plasma-esterified F2-isoprostanes were not altered by an individual dialysis session. Average plasma CRP values were also higher in HD patients (P < 0.02), but some patients had CRP values that were similar to controls. In the HD patients, total plasma F2-isoprostanes and plasma CRP were correlated (r = 0.48, P = 0.015). Plasma alpha-tocopherol did not differ between patients and controls, but plasma retinol was higher in patients (3.15 +/- 1.71 micromol/L) than in controls (1.97 +/- 0.51 micromol/L, P < 0.05).

CONCLUSIONS

These results are consistent with the hypothesis that oxidative stress in ESRD patients contributes to increased values of esterified plasma F2-isoprostanes, with concurrent increases in plasma CRP levels in some patients. Impaired clearance of esterified F2-isoprostanes may contribute to the elevated levels in renal failure. Plasma esterified F2-isoprostanes may be a useful indicator to evaluate effectiveness of interventions to decrease oxidative stress and associated inflammation.

Blood oxidative stress and lipoprotein oxidizability in haemodialysis patients: effect of the use of a vitamin E-coated dialysis membrane

BACKGROUND

Oxidative stress has been shown in haemodialysis patients in relation with an increased production of free radicals due to membrane-induced complement and leukocyte activation. In order to minimize membrane bioincompatibility and thereby oxidative stress, more compatible filters have been perfected. Among them, a high-flux vitamin E-coated membrane (CL-EE) has been proposed recently. In vivo, little data is available on the consequences of the use of vitamin E-coated membranes. In the present study, the effects of a 3-month use of CL-EE dialysis membranes compared to conventional membranes have been evaluated in 12 haemodialysis patients on the blood oxidative stress status before and after the dialysis session.

METHODS

We determined the lipid peroxidation status (plasma thiobarbituric acid-reactive substances) and antioxidant defence (erythrocyte Cu,Zn-superoxide dismutase and plasma and erythrocyte glutathione peroxidase activities, plasma vitamin E, beta-carotene, vitamin A and total antioxidant status). Also, we simultaneously determined the antioxidant content and the copper oxidizability of isolated low density- and high density-lipoproteins (LDLs and HDLs).

RESULTS

The main consequence observed under these conditions was a marked enrichment of plasma with vitamin E, which was also significantly and selectively noted in HDLs (no changes in LDL vitamin E content), perhaps related to a specific storage capacity for vitamin E in HDLs of haemodialysis patients. The beta-carotene content of plasma, LDLs and HDLs was also higher after use of vitamin E-coated membranes than after use of high-flux biocompatible membranes. HDL copper oxidizability was reduced (as shown by an increased lag time) before dialysis after use of CL-EE membranes compared to conventional membranes, whereas LDL oxidizability remained unchanged.

CONCLUSION

A 3-month use of vitamin E-coated membranes resulted in a significant increase in plasma and HDL vitamin E content, associated with a lower oxidizability of HDLs, which could be beneficial for haemodialysis patients.

Non-traditional cardiovascular disease risk factors in end-stage renal disease: oxidate stress and hyperhomocysteinemia

Studies in experimental animals have shown that oxidative stress and hyperhomocyst(e)inemia culminate in abnormal vascular and endothelial regulation, functional nitric oxide deficiency, vascular hypertrophy, and atherosclerosis. Oxidative stress is accompanied by increased advanced glycation endproducts and oxidized low density lipoproteins. Studies of patients with end-stage renal disease provide extensive indirect, evidence of increased oxidative stress and more than ninety percent are hyperhomocyt(e)inemic. Presently, only uncontrolled or observational studies are available to assess the effects of anti-oxidant therapy for oxidative stress or folate therapy for hyperhomocyst(e)inemia in these patients. Promising developments include the reports of beneficial effects of a vitamin E coated dialyzer, and the reduction in homocyst(e)ine levels in patients with end-stage renal disease given an intravenous folate metabolite. However, there is presently no therapy available to reverse fully oxidative stress or hyperhomocyst(e)inemia. Therefore, the causative role of these nontraditional risk factors of cardiovascular disease remains untested.

Alpha-tocopherol supplementation decreases the oxidative susceptibility of LDL in renal failure patients on dialysis therapy

Atherosclerotic cardiovascular disease is the leading cause of death in patients with end stage renal disease (ESRD) who have undergone dialysis treatment. The oxidation of low density lipoprotein (LDL) appears to be a crucial step in the pathogenesis of atherosclerosis. The increased oxidative stress and attendant increased oxidizability of lipoproteins, such as LDL could contribute to the accelerated atherosclerosis in dialysis patients. Since alpha-tocopherol (AT) is the major antioxidant in LDL, the aim of the present study was to test the effectiveness of RRR-AT supplementation (800 I.U. per day) for 12 weeks on the susceptibility of LDL to oxidation. The study subjects comprised patients with chronic renal failure on hemodialysis (HD), peritoneal dialysis (PD), and age and sex matched controls (C). Plasma fatty acids, lipoproteins and AT levels were measured in these subjects before and after supplementation. Also, LDL AT and oxidizability was studied. LDL was isolated by ultracentrifugation at baseline and after 12 weeks of supplementation, and subjected to a 5-h time course of copper catalyzed oxidation. Oxidation was measured by the formation of conjugated dienes (CD) and lipid peroxides (LP). Supplementation with AT did not alter the plasma lipid or lipoprotein profile of these subjects. Plasma lipid-standardized AT and LDL AT concentrations were not different among the groups at baseline. AT supplementation significantly increased plasma lipid-standardized AT (C=150%, HD=149%, PD=217%, P<0.001) and LDL AT concentrations (C=94%, HD=94%, PD=135%, P<0.003). AT enrichment of LDL resulted in a significant prolongation in conjugated diene lag phase in all groups (C=34%, HD=21%, PD=54%, P<0.02). Lipid peroxide lag phase was also increased significantly in C (27%,) and PD (40%) groups after AT supplementation (P<0.01). There was a significant positive correlation between plasma lipid standardized AT and lag phase (r=0. 54, P=0.0003). Overall, AT decreased the susceptibility of LDL to oxidation in patients with chronic renal failure but the benefit appears to be greater in patients on PD. Therefore, AT supplementation may also provide a measure of protection against CAD in patients with chronic renal failure on dialysis therapy.

Protective effects of high-density lipoprotein against oxidative stress are impaired in haemodialysis patients

INTRODUCTION

Cardiovascular diseases represent the major cause of mortality in haemodialysis (HD) patients. Oxidized low-density lipoprotein (Ox-LDL) is a major cardiovascular risk factor, implicated in atherosclerotic plaque formation. It has been suggested that high-density lipoprotein (HD) has the capacity to reduce the oxidative modifications of LDL. The aim of this study is to analyse the protective effects of HDL in HD patients.

METHODS

In vitro copper-induced LDL oxidation was evaluated in 12 patients with chronic renal failure (mean age 61.0+/-12.8 years) and compared to 25 healthy subjects (mean age 57.3+/-19.2 years). LDL were incubated in oxygen-saturated PBS, LDL oxidation was initiated by Cu (II) in the presence and absence of HDL and assessed by measuring the absorbance (abs) increase at 234 nm due to conjugated diene formation. Duration of lag time, maximum velocity (V(max.)) of lipid peroxidation, oxidation slope and half-time of maximum diene formation (T (1/2)) were obtained by kinetic modelling analysis.

RESULTS

HDL (1.06+/-0.31 vs 1.23+/-0.39 mmol/l) and Apo AI (1. 17+/-0.39 vs 1.49+/-0.20 g/l) levels were decreased in HD patients. In the absence of HDL, LDL obtained from HD patients showed an enhanced susceptibility to oxidation in vitro as demonstrated by the significant decrease in lag time (54.5+/-22.2 vs 79.4+/-37.8 min) and a significant increase in V(max.) (0.026+/-0.006 vs 0.017+/-0. 005 abs/min). In all cases, HDL (from 0.1 to 2 microM) prevented LDL oxidation in vitro; however, this effect was significantly reduced in HD patients: increase in lag time 54.2% vs 150.4% in HD vs controls; increase in T (1/2) 52.2% vs 124.6% in HD vs controls; decrease in V(max). 13.5% vs 38.5% in HD vs controls.

CONCLUSIONS

These results suggest that qualitative abnormalities such as an impairment of HDL-associated enzymes are associated with a decrease of HDL levels during HD. Hence, in addition to the known impairment of reverse cholesterol transport, the reduction of HDL protective capacity against oxidative stress could be involved in the development of HD-induced atherosclerosis.

Activation of 5-lipoxygenase and related cell membrane lipoperoxidation in hemodialysis patients

Lipid peroxidation was shown at the membrane level in peripheral blood cells of patients hemodialyzed on cuprophan dialyzers, and was mainly attributable to the generation of conjugated hydroperoxides in the lipid bilayer. The oxidative index (i.e., the A234/205 ratio) of membrane lipids was 3.2-fold higher in hemodialysis patients than in healthy control subjects, and also the level of leukotriene B4 was significantly increased (up to 1.7-fold over control). Both membrane peroxidation and release of leukotriene B4 were linked to upregulation of 5-lipoxygenase activity (up to 2.4-fold over control) and expression at the protein level (up to 1.9-fold). Vitamin E, the most important lipophilic antioxidant, prevented both membrane peroxidation and release of leukotriene B4 by inhibiting 5-lipoxygenase activity without affecting enzyme expression. Similar results were observed in patients hemodialyzed on polymethylmetacrylate membranes, but in this case the activation of 5-lipoxygenase was less pronounced. The use of a purified 5-lipoxygenase demonstrated that vitamin E was a reversible inhibitor of enzyme activity (IC50 = 35 +/- 4 microM), further characterized as noncompetitive (Ki = 30 +/- 3 microM). Taken together, the results reported here shed some light on the mechanism responsible for the oxidative damage in hemodialysis. Moreover, the beneficial effect of vitamin E described here may have relevance for the therapy of patients with kidney disease.

Critical evaluation of plasma and LDL oxidant-trapping potential in hemodialysis patients

BACKGROUND

We investigated whether the total peroxyl radical-trapping antioxidant potential (TRAP) assay, which has recently been proposed as a gauge of oxidative stress, could serve to evaluate plasma and low density lipoprotein (LDL) antioxidant state in hemodialysis (HD) patients.

METHODS

TRAP was determined by the lag time of the chemiluminescence reaction induced by azo-initiator-catalyzed linoleic acid peroxidation in the plasma and corresponding LDL preparations of 23 HD patients and 22 healthy subjects. Antioxidant systems, including glutathione peroxidase (GSH-Px), ascorbate, vitamin E, and uric acid, oxidative stress markers including malondialdehyde (MDA), carbonyls, and advanced oxidation protein products (AOPP), and lipids, including cholesterol and triglycerides, were also determined in the plasma.

RESULTS

Both plasma and LDL-TRAP were significantly increased in HD patients despite decreased GSH-Px and ascorbate and increased MDA, carbonyl, and AOPP plasma levels. Plasma TRAP values were closely related to both uric acid and AOPP levels, and LDL-TRAP values were related to triglycerides and AOPP levels. In vitro studies showed that: (a) plasma TRAP of control plasma increased regularly with supplementation of uric acid, although not reaching that of HD plasma with similar uric acid levels; (b) the addition of human serum albumin-AOPP also regularly increased control plasma TRAP, but was close to that of HD plasma with similar AOPP levels; and (c) LDL-TRAP was increased following LDL enrichment with triglycerides.

CONCLUSION

Our study demonstrates that TRAP is not a relevant parameter for evaluating plasma or LDL antioxidant capacity in HD patients, due to the high plasma levels of uric acid, triglycerides and AOPP, which by themselves do not exert efficient antioxidant activity in vivo, but in vitro are able to scavenge the peroxyl radicals involved in the TRAP assay.

Regulation of platelet-activating factor (PAF) activity in human diseases by phospholipase A2 inhibitors, PAF acetylhydrolases, PAF receptor antagonists and free radical scavengers

The aim of this review is to present recent findings indicating the likely involvement of platelet-activating factor (PAF) in human diseases, and possible ways of alleviating its harmful effects. PAF is a potent proinflammatory mediator and promotes adhesive interactions between leukocytes and endothelial cells, leading to transendothelial migration of leukocytes, by a process of juxtacrine intercellular signalling. This process leads to activation of leukocytes and the release of reactive oxygen radicals, lipid mediators, cytokines and enzymes. These reaction products subsequently contribute to the pathological features of various inflammatory diseases. The reactive oxygen radicals cause low density lipoprotein (LDL) oxidation which mediates the development of atherosclerosis. Oxidized LDL may damage cellular and subcellular membranes, leading to tissue injury and cell death. Among the therapeutic approaches considered are agents that inhibit/degrade proinflammatory mediators and thereby have anti-inflammatory and/or anti-atherogenic potential. These include inhibitors of phospholipase A2 activity, PAF-acetylhydrolases, PAF antagonists and free radical scavengers/antioxidants, the latter protecting against oxidized LDL-induced cytotoxicity.

Review: the oxidant/antioxidant balance during regular low density lipoprotein apheresis

Low density lipoprotein (LDL) apheresis is a safe procedure to treat severe hypercholesterolemia in patients with chronic heart disease (CHD). However, both hypercholesterolemia and extracorporeal treatment have been associated with oxidative stress. Even though LDL lowering has been proven to reduce CHD, the oxidative modification of LDL has been suggested to render these lipoproteins more atherogenic. It is therefore important to know whether LDL apheresis is safe with respect to oxidative stress including LDL oxidation. The contact of living cells such as leukocytes with artificial surfaces during extracorporeal treatment induces the liberation of various chemokines and cytokines as well as oxygen-derived radicals also known as respiratory burst. These effects justify the consideration of leukocyte activation resulting from extracorporeal treatment as an inflammatory reaction. In extracorporeal circuits such as those used for hemodialysis, the release of oxygen radicals has been shown and depends on the fiber material used in the dialyzer membranes. Reactive oxygen radicals can interact with different cell components such as carbohydrates, DNA, proteins, and lipids. Antioxidants in the form of low molecular weight molecules such as glutathione or radical scavenging enzymes such as superoxide dismutase offer protection against the damaging effects of prooxidants. The disturbed balance between prooxidants and antioxidants is considered as oxidative stress. Therefore, either an increase in oxygen radical formation or a decrease of antioxidants will lead to oxidative stress. During LDL apheresis, a decrease of low molecular weight antioxidants has been reported. In contrast, we have observed an increase in plasma glutathione concentrations but no severe reduction in the activity of antioxidant enzymes in plasma, red cells, or granulocytes, which may explain the lack of plasma lipid peroxidation shown during this kind of extracorporeal treatment. In addition, LDL isolated at the end of apheresis procedures are more resistant to oxidation. These findings suggest that LDL apheresis is safe with respect to radical mediated injury.

HDL composition and HDL antioxidant capacity in patients on regular haemodialysis

Recent evidence suggests that HDL can directly inhibit LDL oxidation, a key early stage in atherogenesis. Patients with chronic renal failure are at increased cardiovascular risk, have reduced HDL levels and altered HDL composition. We have therefore investigated whether compositional changes in HDL lead to decreased HDL antioxidant capacity in these patients. In comparison to control subject HDL, patient HDL contained less total cholesterol, cholesterol esters, phospholipids and alpha-tocopherol. LDL, HDL and LDL + HDL were standardised for protein and oxidised in the presence of Cu2+. The rate of propagation during HDL oxidation was reduced in the patient group (3.28+/-0.65 x 10(-5) vs. 4.60+/-0.97 x 10(-5) abs. U/min, P < 0.01). Lipid peroxide generation in patient HDL was decreased: 6.56+4.4 versus 13.42+/-7.0 nmol malondialdehyde (MDA)/mg HDL protein after 90 min and 14.45+/-3.8 versus 20.11+/-7.8 nmol MDA/mg HDL protein after 180 min. This is attributable to reduced HDL polyunsaturated fatty acid content in patients (0.53+/-0.12 vs. 0.72+/-0.16 mmol/g HDL, P < 0.01). The inhibitory effect of HDL on LDL oxidation was similar: 71 and 33% for patient HDL compared to 68 and 31% for control HDL, after 90 and 180 min, respectively. Compositional changes of HDL in patients on haemodialysis did not affect the antioxidant capacity of HDL after standardisation for HDL protein. However, reduced HDL levels in vivo may result in reduced HDL antioxidant capacity in these patients.

Measurement of oxidation in plasma Lp(a) in CAPD patients using a novel ELISA

BACKGROUND

LGE2 is produced by the cyclooxygenase- or free radical-mediated modification of arachidonate and is formed during the oxidation of low density lipoprotein (LDL) with subsequent adduction to lysine residues in apo B. We have developed a sensitive enzyme-linked sandwich immunosorbent assay (ELISA) for detection and measurement of LGE2-protein adducts as an estimate of oxidation of plasma LDL and Lp(a).

METHODS

The assay employs rabbit polyclonal antibodies directed against LGE2-protein adducts that form pyrroles, and alkaline phosphatase-conjugated polyclonal antibodies specific for apo B or apo (a). It demonstrates a high degree of specificity, sensitivity and validity.

RESULTS

Epitopes characteristic for LGE2-pyrroles were quantified in patients with end-stage renal disease (ESRD) that had undergone continuous ambulatory peritoneal dialysis (CAPD) and in a gender- and age-matched control population. In addition to finding that both LDL and Lp(a) levels were elevated in CAPD patients, we also found that plasma Lp(a) but not LDL was more oxidized in CAPD patients when compared to corresponding lipoproteins from healthy subjects. Using density gradient ultra-centrifugation of plasma samples, we found that modified Lp(a) floats at the same density as total Lp(a).

CONCLUSIONS

The results of this study demonstrate that oxidation of plasma Lp(a) is a characteristic of ESRD patients undergoing CAPD. This ELISA may be useful for further investigations on oxidation of lipoproteins in the circulation of specific patient populations.

Oxidative stress in chronic renal failure

Cardiovascular disease is the major cause of morbidity and mortality in chronic renal failure. The aim of this review is to summarise current evidence suggesting that there is increased free radical production, antioxidant depletion and changes in lipoprotein composition in renal failure which will lead to oxidation of LDL and hence to accelerated development of atherosclerosis.