HDL composition and HDL antioxidant capacity in patients on regular haemodialysis

Factors associated to serum paraoxonase 1 activity in patients with cardiovascular disease

OBJECTIVE

Paraoxonase 1 (PON1) is an enzyme that has antioxidant potential, which confers a protective effect against the atherosclerotic process. However, studies associating genetics, dietary patterns and PON1 activity in individuals with cardiovascular disease (CVD) are scarce. Thus, the aim of the current study was to evaluate the influence of dietary factors on serum PON1 in CVD patients.

METHODS

Cross-sectional, sub-study of the BALANCE Program Trial. All patients aged 45 years or older and had evidence of established atherosclerotic disease in the preceding 10 years. Body weight, height, waist circumference, blood pressure, lipid profile and fasting glucose were collected. Food intake was assessed with 24-h dietary recall. Data was analyzed using SAS University Edition and a P value ≤ 0.05 was considered statistically significant. Sample was divided into three groups, according to the PON1 T(-107)C genotype (CC, CT and TT) and serum PON1 activity (Low, Medium, High).

RESULTS

There were no genotype differences for major factors. However, the systolic blood pressure was lower for CT individuals (p<0.05). Intake of cholesterol, saturated fatty acids (SFA) and monounsaturated fatty acids (MUFAS) was higher in patients with lower PON1 activity. Lipid ingestion tended to be higher in patients with lower PON1 activity (p=0.08). In the multivariate logistic regression model, SFA intake (P=0.03), genotype (P=0.09), gender (P=0.04), age (P=0.07) and carbohydrate intake (P=0.16) contributed the most to the serum PON1 activity.

CONCLUSION

Based on these findings, nutritional guidance for these patients becomes essential, since dietary components interact with serum PON1 activity more than genotype.

Paraoxonase 1 serum activity in women: the effects of menopause, the C(-107)T polymorphism and food intake

OBJECTIVE

The aims of this study were to investigate changes in serum paraoxonase 1 (PON1) activity in women at the pre and postmenopausal stages and its association with the PON1 C(-107)T polymorphism and food intake profile.

SUBJECTS AND METHODS

A cross-sectional study with female patients aged between 35 and 59 years old was conducted. Women were divided into two groups: premenopausal (n = 40) and postmenopausal (n = 36). Women enrolled in the study had serum PON1, total cholesterol, HDL, LDL, glucose and HbA1c, as well as the BMI measured. Additionally, women were genotyped for the PON1 T(-107)C polymorphism and the food intake profile was obtained through interview.

RESULTS

Glucose (p = 0.03), HbA1c (p = 0.002) and total cholesterol (p = 0.002)concentrations were higher in post than premenopausal women, however PON1 activity was not different (p > 0.05). Carriers of the C allele had higher PON1 activity (CC: 88.9 ± 6.5 U/mL and CT: 79.9 ± 4.7 U/mL) than women of the TT genotype (66.6 ± 5.9 U/mL) (p < 0.05). However, the model predicting PON1 activity was slightly better when genotype, total fat and cholesterol content in the diet were all included.

CONCLUSION

In sum, we observed that the PON1 C(-107)T genotype was the major regulator of PON1 activity, and menopause had no effect on PON1 activity. The lipid and glycemic profile were altered in postmenopausal women.

Oxidative stress in lung cancer patients is associated with altered serum markers of lipid metabolism

In lung cancer (LC), alterations in redox balance are extensively observed and are a consequence of disease as well as co-occurrent with smoking. We previously demonstrated that metabolic disturbances such as trace element status and carbohydrate metabolism alterations are linked with redox status. The aim of this study was to evaluate relationships between the serum parameters of lipid metabolism and redox balance in LC patients. Serum parameters of lipid metabolism, i.e. total cholesterol (T-C), HDL cholesterol (HDL-C), LDL cholesterol (LDL-C), triglycerides (TG), T-C:HDL-C ratio, non-HDL-C, apolipoprotein A1 (Apo-A1), apolipoprotein B (Apo-B) and Apo-B:Apo-A1 ratio, as well as systemic redox status, i.e. total antioxidant status (TAS), total oxidant status (TOS), oxidative stress index (OSI), vitamin E (VE), vitamin C (VC), malonyldialdehyde (MDA), conjugated dienes (CD), and 4-hydroxynonenal (4-HNE) were determined in 92 LC patients and 82 control subjects (CS). LC women had significantly lower T-C and LDL-C, and higher TG, while HDL-C, Apo-A1 and Apo-B were significantly decreased in LC patients regardless of sex, when compared to CS. LC men had alterations in the systemic total redox balance such as lower TAS and higher OSI than CS men. LC women had lower VC, but VE was decreased in LC patients, regardless of sex. We observed higher lipid peroxidation in LC patients expressed via higher 4-HNE and CD. Systemic redox disturbances were associated with serum lipid alterations: TOS and OSI were positively correlated with T-C:HDL-C ratio and Apo-B:Apo-A1 ratio and negatively with HDL-C. The parameters of lipid peroxidation CD and MDA were significantly associated with variables reflecting lipid disturbances. The observed correlations were strengthened by general overweight/obesity, abdominal obesity, hypertriglyceridemia and non-smoking status. In conclusion, parameters related to lipid alterations are associated with oxidative stress in LC patients. The largest contribution from lipid parameters was revealed for T-C:HDL-C ratio, HDL-C and Apo-B:Apo-A1 ratio, while the largest contribution from redox status was revealed for OSI and VE. Overweight, obesity, hypertriglyceridemia and non-smoking status intensified these relationships.

Type 2 Diabetes in Young Females Results in Increased Serum Amyloid A and Changes to Features of High Density Lipoproteins in Both HDL2 and HDL3

Persons with type 2 diabetes mellitus (T2DM) have an elevated risk of atherosclerosis. High-density lipoproteins (HDL) normally protect against cardiovascular disease (CVD), but this may be attenuated by serum amyloid A (SAA). In a case-control study of young females, blood samples were compared between subjects with T2DM (n = 42) and individuals without T2DM (n = 42). SAA and apolipoprotein AI (apoAI) concentrations, paraoxonase-1 (PON-1), cholesteryl ester transfer protein (CETP), and lecithin-cholesterol acyltransferase (LCAT) activities were measured in the serum and/or HDL₂ and HDL₃ subfractions. SAA concentrations were higher in T2DM compared to controls: serum (30 mg/L (17, 68) versus 15 mg/L (7, 36); p = 0.002), HDL₂ (1.0 mg/L (0.6, 2.2) versus 0.4 mg/L (0.2, 0.7); p < 0.001), and HDL₃, (13 mg/L (8, 29) versus 6 mg/L (3, 13); p < 0.001). Serum-PON-1 activity was lower in T2DM compared to that in controls (38,245 U/L (7025) versus 41,109 U/L (5690); p = 0.043). CETP activity was higher in T2DM versus controls in HDL₂ (232.6 μmol/L (14.1) versus 217.1 μmol/L (25.1); p = 0.001) and HDL₃ (279.5 μmol/L (17.7) versus 245.2 μmol/L (41.2); p < 0.001). These results suggest that individuals with T2DM have increased SAA-related inflammation and dysfunctional HDL features. SAA may prove to be a useful biomarker in T2DM given its association with elevated CVD risk.

Plasma Nitration of High-Density and Low-Density Lipoproteins in Chronic Kidney Disease Patients Receiving Kidney Transplants

BACKGROUND

Functional abnormalities of high-density lipoprotein (HDL) could contribute to cardiovascular disease in chronic kidney disease patients. We measured a validated marker of HDL dysfunction, nitrated apolipoprotein A-I, in kidney transplant recipients to test the hypothesis that a functioning kidney transplant reduces serum nitrated apoA-I concentrations.

METHODS

Concentrations of nitrated apoA-I and apoB were measured using indirect sandwich ELISA assays on sera collected from each transplant subject before transplantation and at 1, 3, and 12 months after transplantation. Patients were excluded if they have history of diabetes, treatment with lipid-lowering medications or HIV protease inhibitors, prednisone dose > 15 mg/day, nephrotic range proteinuria, serum creatinine > 1.5 mg/dL, or active inflammatory disease. Sera from 18 transplanted patients were analyzed. Four subjects were excluded due to insufficient data. Twelve and eight patients had creatinine < 1.5 mg/dL at 3 and 12 months after transplantation, respectively. RESULTS. Nitrated apoA-I was significantly reduced at 12 months after transplantation (p = 0.039). The decrease in apoA-I nitration was associated with significant reduction in myeloperoxidase (MPO) activity (p = 0.047). In contrast to apoA-I, nitrated apoB was not affected after kidney transplantation.

CONCLUSIONS

Patients with well-functioning grafts had significant reduction in nitrated apoA-I 12 months after kidney transplantation. Further studies are needed in a large cohort to determine if nitrated apoA-I can be used as a valuable marker for cardiovascular risk stratification in chronic kidney disease.

A randomised controlled trial of increasing fruit and vegetable intake and how this influences the carotenoid concentration and activities of PON-1 and LCAT in HDL from subjects with type 2 diabetes

Background

High density lipoproteins (HDL) have many cardioprotective roles; however, in subjects with type 2 diabetes (T2D) these cardioprotective properties are diminished. Conversely, increased fruit and vegetable (F&V) intake may reduce cardiovascular disease risk, although direct trial evidence of a mechanism by which this occurs in subjects with T2D is lacking. Therefore, the aim of this study was to examine if increased F&V consumption influenced the carotenoid content and enzymes associated with the antioxidant properties of HDL in subjects with T2D.

Methods

Eighty obese subjects with T2D were randomised to a 1- or ≥6-portion/day F&V diet for 8-weeks. Fasting serum was collected pre- and post-intervention. HDL was subfractionated into HDL₂ and HDL₃ by rapid ultracentrifugation. Carotenoids were measured in serum, HDL₂ and HDL₃ by high performance liquid chromatography. The activity of paraoxonase-1 (PON-1) was measured in serum, HDL₂ and HDL₃ by a spectrophotometric assay, while the activity of lecithin cholesterol acyltransferase (LCAT) was measured in serum, HDL₂ and HDL₃ by a fluorometric assay.

Results

In the ≥6- vs. 1-portion post-intervention comparisons, carotenoids increased in serum, HDL₂ and particularly HDL₃, (α-carotene, p = 0.008; β-cryptoxanthin, p = 0.042; lutein, p = 0.012; lycopene, p = 0.016), as did the activities of PON-1 and LCAT in HDL₃ (p = 0.006 and 0.044, respectively).

Conclusion

To our knowledge, this is the first study in subjects with T2D to demonstrate that increased F&V intake augmented the carotenoid content and influenced enzymes associated with the antioxidant properties of HDL. We suggest that these changes would enhance the cardioprotective properties of this lipoprotein.

Clinical trial registration

ISRCTN21676269

The two faces of α- and γ-tocopherols: an in vitro and ex vivo investigation into VLDL, LDL and HDL oxidation

BACKGROUND

Vitamin E and its derivatives, namely, the tocopherols, are known antioxidants, and numerous clinical trials have investigated their role in preventing cardiovascular disease; however, evidence to date remains inconclusive. Much of the in vitro research has focused on tocopherol's effects during low-density lipoprotein (LDL) oxidation, with little attention being paid to very LDL (VLDL) and high-density lipoprotein (HDL). Also, it is now becoming apparent that γ-tocopherol may potentially be more beneficial in relation to cardiovascular health.

OBJECTIVES

Do α- and γ-tocopherols become incorporated into VLDL, LDL and HDL and influence their oxidation potential in an in vitro and ex vivo situation?

DESIGN

Following (i) an in vitro investigation, where plasma was preincubated with increasing concentrations of either α- or γ-tocopherol and (ii) an in vivo 4-week placebo-controlled intervention with α- or γ-tocopherol. Tocopherol incorporation into VLDL, LDL and HDL was measured via high-pressure liquid chromatography, followed by an assessment of their oxidation potential by monitoring conjugated diene formation.

RESULTS

In vitro: Both tocopherols became incorporated into VLDL, LDL and HDL, which protected VLDL and LDL against oxidation. However and surprisingly, the incorporation into HDL demonstrated pro-oxidant properties. Ex vivo: Both tocopherols were incorporated into all three lipoproteins, protecting VLDL and LDL against oxidation; however, they enhanced the oxidation of HDL.

CONCLUSIONS

These results suggest that α- and γ-tocopherols display conflicting oxidant activities dependent on the lipoprotein being oxidized. Their pro-oxidant activity toward HDL may go some way to explain why supplementation studies with vitamin E have not been able to display cardioprotective effects.

Multiple antioxidants and L-arginine modulate inflammation and dyslipidemia in chronic renal failure rats

The kidney is an important source of L-arginine, the endogenous precursor of nitric oxide (NO). Surgical problems requiring extensive renal mass reduction (RMR) decrease renal NO production, leading to multiple hemodynamic and homeostatic disorders manifested by hypertension, oxidative stress, and increased inflammatory cytokines. Using the RMR model of chronic renal failure (CRF), we assessed the effects of twelve weeks' administration of L-arginine and/or a mixture of antioxidants (L-carnitine, catechin, vitamins E and C) on plasma cytokines, soluble intercellular adhesion molecule-1 (sICAM-1), nitrate and nitrites (NO(2)/NO(3)), lipid profile, blood pressure, and renal function. CRF rats showed increased plasma IL-1 alpha, IL1-beta, IL-6, TNF-alpha, and sICAM-1 levels and decreased anti-inflammatory cytokines IL-4 and 10 levels, hypertension, and dyslipidemia. L-arginine treatment improved kidney functions, decreased systolic blood pressure, and decreased inflammatory cytokines levels. Antioxidants administration decreased inflammatory cytokines and sICAM-1 levels and increased IL-4 levels. Combined use of both L-arginine and the antioxidant mixture were very effective in their tendency to recover normal values of kidney functions, plasma cytokines, sICAM-1, blood pressure, NO(2)/NO(3), cholesterol, and triglycerides concentrations. Indeed, the effects of L-arginine and the antioxidants on the reduction of proinflammatory cytokines may open new perspectives in the treatment of uremia.

Impaired antioxidant activity of high-density lipoprotein in chronic kidney disease

Chronic kidney disease (CKD) is associated with accelerated atherosclerosis and increased mortality from cardiovascular disease. CKD results in oxidative stress, inflammation, and high-density lipoprotein (HDL) deficiency, which work in concert to promote atherosclerosis. Normal HDL confers protection against atherosclerosis by inhibiting the oxidation of lipids and lipoproteins and by retrieving surplus cholesterol and phospholipids from lipid-laden cells in the artery wall for disposal in the liver (reverse cholesterol transport). The plasma level of oxidized low-density lipoprotein (LDL) is increased, plasma HDL-cholesterol is reduced, and HDL maturation is impaired in CKD. This study was designed to examine the antioxidant properties of HDL in patients with CKD. In all, 32 stable hemodialysis-dependent patients and 13 age-matched controls were studied. HDL was isolated and used for determination of in vitro antioxidant activity. In addition, the plasma level of key components of HDL, namely paraoxonase (PON), glutathione peroxidase (GPX), platelet activating factor acetylhydrolase (PAF-AH), lecithin cholesterol acyltransferase (LCAT), and apolipoprotein A-I (ApoA-I), were measured. The end-stage renal disease (ESRD) patients exhibited significant reductions of HDL-cholesterol, ApoA-I (-41%), GPX (-50%), and LCAT (-60%) concentrations, and a decrease in PON (-30%) and GPX (-50%) activities. These results were accompanied by a marked reduction of antioxidant activity of HDL (-127%), which was unaffected by the hemodialysis procedure. Thus, in addition to diminished plasma HDL concentration, the composition and antioxidant activity of HDL are altered in CKD; these events can contribute to a heightened risk of atherosclerosis.

Acrolein inactivates paraoxonase 1: changes in free acrolein levels after hemodialysis correlate with increases in paraoxonase 1 activity in chronic renal failure patients

BACKGROUND

Acrolein is a very reactive aldehyde present in cigarette smoke and endogenously generated by pathways such as lipid peroxidation and threonine metabolism by phagocytes. Acrolein has been shown to affect uptake of cholesterol by HDL. We hypothesized that acrolein could also have deleterious effects on paraoxonase 1 (PON-1) activity. We also determined whether free serum acrolein levels are higher in renal failure, and assessed whether they decrease after hemodialysis (HD) and whether this change correlates with increases in PON-1 activity.

METHODS

We incubated human HDL with 0-10 mmol/l acrolein for 2 h and measured PON-1 activity and structural changes. Acrolein was also measured in 40 end stage renal disease (ESRD) patients (before and after a hemodialysis session), and 40 control subjects.

RESULTS

We found that acrolein inhibits PON-1 activity in HDL in a time and concentration dependent fashion. Inhibition occurred at 40% at 0.5 mmol/l and was cancelled by cysteine but not by aminoguanidine or carnosine. We confirm that free serum acrolein levels are higher in chronic renal failure patients and demonstrate that they are partially removed by HD. Decrease in acrolein levels after dialysis correlate with increases in PON-1 activity (r=0.32, p 0.01).

CONCLUSION

Acrolein inactivates paraoxonase 1 in HDL, a process that is inhibited by N-acetylcysteine. We confirm that acrolein levels are higher in ESRD and show for the first time, data supporting that acrolein is partially removed by hemodialysis. Decrease in acrolein levels after dialysis correlates with increase in PON-1 activity. This could offer new insights to explain low PON-1 activities in smokers and renal failure subjects as well as pointing at thiol-conserving reducing compounds such as N-acetylcysteine, as putative therapeutic palliatives.

Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis

High-density lipoproteins (HDL) possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, and anti-oxidative and anti-inflammatory activities. Plasma HDL particles are highly heterogeneous in physicochemical properties, metabolism, and biological activity. Within the circulating HDL particle population, small, dense HDL particles display elevated cellular cholesterol efflux capacity, afford potent protection of atherogenic low-density lipoprotein against oxidative stress and attenuate inflammation. The antiatherogenic properties of HDL can, however be compromised in metabolic diseases associated with accelerated atherosclerosis. Indeed, metabolic syndrome and type 2 diabetes are characterized not only by elevated cardiovascular risk and by low HDL-cholesterol (HDL-C) levels but also by defective HDL function. Functional HDL deficiency is intimately associated with alterations in intravascular HDL metabolism and structure. Indeed, formation of HDL particles with attenuated antiatherogenic activity is mechanistically related to core lipid enrichment in triglycerides and cholesteryl ester depletion, altered apolipoprotein A-I (apoA-I) conformation, replacement of apoA-I by serum amyloid A, and covalent modification of HDL protein components by oxidation and glycation. Deficient HDL function and subnormal HDL-C levels may act synergistically to accelerate atherosclerosis in metabolic disease. Therapeutic normalization of attenuated antiatherogenic HDL function in terms of both particle number and quality of HDL particles is the target of innovative pharmacological approaches to HDL raising, including inhibition of cholesteryl ester transfer protein, enhanced lipidation of apoA-I with nicotinic acid and infusion of reconstituted HDL or apoA-I mimetics. A preferential increase in circulating concentrations of HDL particles possessing normalized antiatherogenic activity is therefore a promising therapeutic strategy for the treatment of common metabolic diseases featuring dyslipidemia, inflammation, and premature atherosclerosis.

Paraoxonase-1 concentrations in end-stage renal disease patients increase after hemodialysis: correlation with low molecular AGE adduct clearance

BACKGROUND

Hemorrhagic stroke and ischemic heart disease continue to be key problems in patients with end stage renal failure. Reduced serum paraoxonase (PON-1) activity has been described in these patients, which could contribute to the accelerated development of atherosclerosis. We hypothesized that retention of uremic toxins and or "middle molecules" including advanced glycation (AGE) free adducts and peptides could play a mechanistic role in decreasing PON-1 activity.

METHODS

We enrolled 22 ESRD patients undergoing hemodialysis in whom paired pre- and post-dialysis samples were studied along with 30 age-matched control subjects.

RESULTS

ESRD patients showed a 76% decrease in PON-1 activity. As expected, ESRD patients had an increase in lipoperoxides and advanced oxidation protein products (AOPP). Our patients had a 3-fold increase in serum AGEs and a striking 10-fold increase in low molecular weight (<10 kDa) AGEs. Post-dialysis samples in all patients displayed an increase in PON-1 activity, which ranged from 4 to 40% of the predialysis value. HDL-cholesterol, apoAI, free cholesterol (as a LCAT surrogate), HDL-subclasses and TG did not change significantly after dialysis. Changes in PON-1 activity display a good correlation (r=0.66, p<0.001) with rates in which creatinine and urea are cleared. Clearance of low molecular weight AGEs after hemodialysis explains 79% of the changes in PON-1 activity and are hence a much better predictor than creatinine changes (r=0.89, p<0.00). In vitro incubation of paraoxonase with serum ultrafiltrates show a time and concentration dependent inhibition of PON-1 by the ultrafiltrates, an inhibition that is up to 3 times higher (from 8 to 24%) when chronic renal failure patients are the source of the ultrafiltrate.

CONCLUSION

We showed that HD results in a significant, consistent increase in the activity of the antioxidant enzyme PON-1. The effect, correlates with the effectiveness of dialysis to clear creatinine and urea, and with the clearance of AGE adducts of low molecular weight. This effect was replicated in vitro, showing time and dose dependency. Our results suggest that another cause for the observed lower PON-1 concentrations in CRF are the retention of low-middle molecules and demonstrate a positive effect of hemodialysis in the delicate oxidant-antioxidant state of these patients, that should be weighted against other pro-oxidant effects that have also been shown to occur previously. If the hypothesis that AGEs are the main culprits is proved in further research, this opens a putative therapeutic avenue for AGE blockers in ESRD.

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.

Oxidative stress and high-density lipoprotein function in Type I diabetes and end-stage renal disease

In a cross-sectional study, oxidative stress in high vascular disease risk groups, ESRD (end-stage renal disease) and Type I diabetes, was assessed by measuring plasma protein carbonyls and comparing antioxidant capacity of HDL (high-density lipoprotein) as pertaining to PON1 (paraoxonase 1) activity and in vitro removal of LPO (lipid peroxides). ESRD subjects on haemodialysis (n=22), Type I diabetes subjects (n=20) without vascular complications and healthy subjects (n=23) were compared. Plasma protein carbonyls were higher in ESRD patients [0.16 (0.050) nmol/mg of protein; P=0.001; value is mean (SD)] relative to subjects with Type I diabetes [0.099 (0.014) nmol/mg of protein] and healthy subjects [0.093 (0.014) nmol/mg of protein]. Plasma PON1 activity, with and without correction for HDL-cholesterol, was lower in diabetes but did not differ in ESRD compared with healthy subjects. Plasma PON1 activity, without correction for HDL, did not differ between the three groups. In ESRD, plasma PON1 activity and plasma protein carbonyl concentrations were inversely related (r=−0.50, P<0.05). In an in vitro assay, LPO removal by HDL in ESRD subjects was greater than HDL from healthy subjects (P<0.01), whereas HDL from patients with Type I diabetes was less effective (P<0.01). Efficacy of LPO removal was unrelated to plasma PON1 activity, in vitro glycation or mild oxidation, but was impaired by marked oxidation and glycoxidation. Protein carbonyl levels are increased in ESRD but not in complication-free Type I diabetes. HDL antioxidant function is increased in ESRD, perhaps a compensatory response to increased oxidative stress, but is lower in Type I diabetes. HDL dysfunction is related to glycoxidation rather than glycation or PON1 activity.

Defective antioxidative activity of small dense HDL3 particles in type 2 diabetes: relationship to elevated oxidative stress and hyperglycaemia

AIMS/HYPOTHESIS

Elevated oxidative stress, hyperglycaemia, and dyslipidaemia involving low levels of HDL particles are key proatherogenic factors in type 2 diabetes mellitus. We examined the relationship of oxidative stress, and the degree of glycaemia and triglyceridaemia, to antioxidative function of HDL particle subspecies in type 2 diabetes.

SUBJECTS AND METHODS

Five HDL subfractions (2b, 2a, 3a, 3b, 3c) were isolated by density gradient ultracentrifugation from well-controlled type 2 diabetic subjects (n=20) and normolipidaemic, non-diabetic controls (n=10). Specific antioxidative activity (capacity to protect LDL from oxidation on a unit particle mass or on a particle number basis), chemical composition and enzymatic activities were measured in each subfraction. Systemic oxidative stress was assessed as plasma levels of 8-isoprostanes.

RESULTS

Specific antioxidative activity of small dense HDL3b and 3c particles in diabetic patients was significantly diminished (up to -47%, on a particle mass or particle number basis) as compared with controls. Plasma 8-isoprostanes were markedly elevated (2.9-fold) in diabetic patients, were negatively correlated with both specific antioxidative activity of HDL3 subfractions and plasma HDL cholesterol (HDL-C) levels, and were positively correlated with glycaemia and triglyceridaemia. Paraoxonase 1 activity was consistently lower in diabetic HDL subfractions and was positively correlated with HDL3 antioxidative activity. The altered chemical composition of diabetic HDL3 subfractions (core cholesteryl ester depletion, triglyceride enrichment) was equally correlated with diminished antioxidative activity.

CONCLUSIONS/INTERPRETATION

Antioxidative activity of small dense HDL is deficient in type 2 diabetes, is intimately linked to oxidative stress, glycaemia and hypertriglyceridaemia and primarily reflects abnormal intrinsic physicochemical properties of HDL particles.

Characteristics and effects of inflammation in end-stage renal disease

Malnutrition and cardiovascular disease are associated with end-stage renal disease (ESRD) and both are closely associated with one another, both in cross-sectional analysis and when the courses of individual patients are followed over time. Inflammation, by suppressing synthesis of albumin, transferrin, and other negative acute-phase proteins and increasing their catabolic rates, either combines with modest malnutrition or mimics malnutrition, resulting in decreased levels of these proteins in dialysis patients. Inflammation also leads to reduced muscle mass by increasing muscle protein catabolism and blocking synthesis of muscle protein. More importantly, inflammation alters plasma protein composition and endothelial structure and function so as to promote vascular disease. Markers of inflammation, C-reactive protein (CRP), and interleukin (IL)-6 powerfully predict death from all causes and from cardiovascular disease in dialysis patients as well as progression of vascular injury. The causes of inflammation are likely multifactorial, including oxidative modification of plasma proteins, interaction of blood with nonbiocompatible membranes and lipopolysaccharides in dialysate, subclinical infection of vascular access materials, oxidative catabolism of endothelium-derived nitric oxide, and other infectious processes. Treatment should be focused on identifying potential causes of inflammation, if obvious, and reduction of other risk factor for cardiovascular disease.

Hypochlorous acid and low serum paraoxonase activity in haemodialysis patients: an in vitro study

BACKGROUND

Serum paraoxonase 1 (PON1) is an oxidant-sensitive enzyme associated with high-density lipoprotein (HDL) that inhibits the atherogenic oxidation of low-density lipoprotein (LDL). In haemodialysis patients, production of reactive oxygen species, such as hypochlorous acid (HOCl) and hydrogen peroxide, is increased and serum PON1 arylesterase is abnormally low. We have examined the effect of HOCl and the uraemic milieu on serum PON1 arylesterase activity and the ability of HDL to inhibit LDL oxidation in vitro.

METHODS

Serum was incubated with HOCl, hydrogen peroxide and products of HOCl reaction with excess cysteine, lysine and taurine and then serum PON1 arylesterase and serum protein tryptophan fluorescence were measured. The ability of plasma HDL fractions isolated by a dextran-sulphate method, to protect LDL from mild oxidation in air, was determined by a fluorimetric method using oxidation of 2,7-dichlorofluorescein (DCFH).

RESULTS

Incubation of healthy serum with HOCl in the range 6.5-32.9 mmol/l resulted in a linear decrease in serum PON1 arylesterase activity to 40% of that without HOCl and a parallel decrease in protein tryptophan fluorescence. The HOCl-induced decrease in serum PON1 activity was completely removed by reaction of HOCl with a 2.7-fold excess of alpha-amino acids but not taurine. In serum incubated for 1 week, the decrease in serum PON1 activity was significantly (P = 0.04) less while the increase in protein fluorescent advanced glycation end-products was significantly larger (P = 0.01) in haemodialysis patients compared with healthy subjects. The mean decrease in mild oxidation of LDL was not significantly different on addition of HDL-rich fractions from haemodialysis patients (100 +/- 6%, n = 7) and healthy subjects (95 +/- 6%, n = 7) or on addition of the HDL-rich fraction from plasma treated with 0.95 mmol/l HOCl (95%) and control HDL (96%). The fraction rich in HDL and other high molecular weight compounds from plasma that had been incubated with increasing HOCl concentrations up to 1.9 mmol/l significantly (P = 0.001) increased (471%) the oxidation of DCFH.

CONCLUSIONS

These results suggest that high concentrations of HOCl that severely oxidize serum proteins and tryptophan residues in the active site of PON1 are required to decrease PON1 arylesterase activity in serum. In haemodialysis patients, overproduction of HOCl that leads to high concentrations of severely oxidized proteins and increased oxidants in plasma might also contribute to low serum PON1 arylesterase activity, but does not appear to impair the ability of an HDL molecule to protect LDL from mild oxidation.

The microinflammatory state in uremia: causes and potential consequences

Mortality is markedly elevated in patients with end-stage renal disease. The leading cause of death is cardiovascular disease. Lipoprotein levels are only slightly elevated in dialysis patients, and cardiovascular risk is inversely correlated with serum cholesterol, suggesting that a process other than hyperlipidemia plays a role in the incidence of cardiovascular disease. Hypoalbuminemia, ascribed to malnutrition, has been one of the most powerful risk factors that predict all-cause and cardiovascular mortality in dialysis patients. The presence of inflammation, as evidenced by increased levels of specific cytokines (interleukin-6 and tumor necrosis factor alpha) or acute-phase proteins (C-reactive protein and serum amyloid A), however, has been found to be associated with vascular disease in the general population as well as in dialysis patients. The process of inflammation, also called the acute-phase response, additionally causes loss of muscle mass and changes in plasma composition-decreases in serum albumin, prealbumin, and transferrin levels, also associated with malnutrition. Inflammation alters lipoprotein structure and function as well as endothelial structure and function to favor atherogenesis and increases the concentration of atherogenic proteins in serum, such as fibrinogen and lipoprotein (a). Inflammation in dialysis patients is episodic. The causes are likely to be multifactorial and include vascular access infection, less-than-sterile dialysate, dialysate back leak, and nonbiocompatible membranes in addition to clinically apparent infection. In addition, proinflammatory compounds, such as advanced glycation end products, accumulate in renal failure, and defense mechanisms against oxidative injury are reduced, contributing to inflammation and to its effect on the vascular endothelium.

Smoking or its cessation does not alter the susceptibility to in vitro LDL oxidation

BACKGROUND

Enhanced induction of low density lipoprotein (LDL) oxidation may play a role in the increased cardiovascular risk in smokers. We determined LDL oxidisability in vitro in non-smokers, smokers and in subjects after smoking cessation.

PATIENTS AND METHODS

Plasma lipids and copper induced LDL oxidation in vitro were measured in 31 persistent smokers, 47 smokers who tried to stop smoking and 25 non-smokers. In the smoking cessation group, blood was collected before then 1, 3, 6 and 12 months after smoking cessation, and in the persistent smoking and non-smoking groups at baseline and after 12 months. Plasma thiobarbituric acid reactive substances (TBARS) were measured 3 times (at baseline then after 1 and 3 months) in all subjects who refrained from smoking (controlled by urinary cotinine concentrations) for at least 3 months.

RESULTS

At baseline, no differences in mean age, body mass index and lipid profiles between groups were present. Seventeen subjects of the smoking cessation group (36%) managed to quit during 12 months. Smoking cessation was associated with an increase in mean weight (P </= 0.001) and waist-hip ratio (P </= 0.001). No major differences in LDL oxidisability were found between groups. A significant transient increase in high density lipoprotein (HDL) cholesterol was seen (from 1.20 +/- 0.39 to 1.34 +/- 0.42 mmol L-1) after 1 month of smoking cessation that disappeared after 3 months. However, after 1 month of smoking cessation, plasma TBARS decreased significantly (P < 0.05).

CONCLUSIONS

Neither the previously observed increased cardiovascular risk in smokers nor the decreased risk in those who stopped smoking seem to be mediated by permanent changes in lipid profiles or by alterations in the susceptibility to in vitro oxidation of LDL.

Smoking is associated with reduced serum paraoxonase activity and concentration in patients with coronary artery disease

BACKGROUND

Paraoxonase is an HDL-associated enzyme that protects lipoproteins from oxidative modifications. Smoking is a major cardiovascular risk factor that promotes lipid peroxidation. Cigarette smoke has been shown in vitro to inhibit paraoxonase. The present study examined the hypothesis that smoking is associated with modulated serum activities and concentrations of paraoxonase.

METHODS AND RESULTS

Coronary artery disease was assessed with the use of coronary arteriography in participants recruited from a hospital cardiology division. Medical and lifestyle data were obtained, and a fasting blood sample was provided. Three smoking categories were established (never, ex-smokers, and current smokers), and serum paraoxonase variables were compared among them. The activities and concentrations of paraoxonase were significantly lower in current than in never smokers. Ex-smokers had values comparable to those of never smokers. Ex-smokers who had recently stopped (<3 months) had activities and concentrations comparable to those of current smokers; values returned to the levels of never smokers within 2 years of cessation of smoking. Smoking status was an independent determinant of paraoxonase activity and concentration in multivariate analysis. Finally, lower paraoxonase was associated with more severe coronary disease and a reduced capacity to protect LDL from oxidation.

CONCLUSIONS

Smoking is independently associated with significant decreases in serum paraoxonase activities and concentrations, which normalize within a relatively short time of cessation. Lower serum paraoxonase is linked to more severe coronary artery disease and a lower antioxidant capacity. The data are consistent with the hypothesis that smoking modifies serum paraoxonase such that there is an increased risk of coronary artery disease due to a diminished capacity to protect lipoproteins from oxidative stress.