Lipid peroxidation in hemodialysis patients: effect of vitamin C supplementation

Paraoxonase 1 Activity and Renal Replacement Therapy for Chronic Renal Failure: A Meta-Analysis

Chronic renal failure (CRF) is associated with the development of cardiovascular disease (CVD). Paraoxonase 1 (PON1), an antioxidant enzyme, shows cardioprotective properties and has been proposed as a therapeutic marker for CRF. A systematic analysis of the literature assessing the association between PON1 activity and renal replacement therapy (RRT) of CRF is currently lacking. Therefore, we set out to perform a meta-analysis of the available data on PON1 in RRT of CRF. We searched three electronic databases for studies on PON1 activity in CRF patients with RRT such as hemodialysis (HD), peritoneal dialysis (PD), or renal transplantation (RTx), published before June 2023. A random-effects and network meta-analysis were performed. A total of 53 studies were eligibly identified. Compared to CRF patients without RRT, RTx patients had higher paraoxonase activity (standard mean difference (SMD), 1.76, 95% confidence interval (CI), 0.76-2.75), followed by HD (SMD, 0.73; 95% CI, 0.02-1.45) and PD patients. Likewise, RTx patients had higher arylesterase activity (SMD, 1.84, 95% CI, 0.18-3.50), followed by HD and PD patients. Also, paraoxonase activity was increased after HD (SMD, 0.59, 95% CI, 0.16-1.03). In conclusion, the overall data demonstrated that PON1 activity is higher in CRF patients with RRT, particularly RTx, followed by that of HD and PD. Measuring PON1 activity can also be included to the paraclinical toolbox for the management of RRT, in addition to the understanding of CRF-related pathophysiology. Regarding the selection of RRT types and their potential to prevent CVD, more research is required.

Effects of vitamin C supplementation on oxidative stress and serum paraoxonase/arylesterase activities in patients on long-term hemodialysis

BACKGROUND

Oxidative stress increases oxidizability of apolipoprotein-B containing lipoproteins and decreases paraoxonase (PON) activity in hemodialysis (HD) patients and plays an important part in the development of atherosclerotic cardiovascular diseases. In HD patients, plasma ascorbic acid (AA) levels are decreased either due to the loss by hemodialysis membranes or due to malnutrition and contribute to the imbalance of antioxidant defense mechanisms. We hypothesized that long-term ascorbic acid (AA) supplementation recovers oxidizability of lipoproteins in HD patients by reinforcing PON activity.

METHODS

Twenty-nine adult patients were treated with 100mg and 500mg AA at the end of each HD session thrice a week for two consecutive 16 weeks-periods, respectively. Blood samples were obtained before the first HD session and prior to the first HD sessions following the 100mg AA-supplemented and the 500mg AA-supplemented periods.

RESULTS

PON activities were significantly increased after 100mg (p<0.05) and 500mg AA (p<0.001) supplementation periods compared to the basal level. Apo-B lipoprotein oxidizability (Δ-MDA) was significantly decreased after 500mg AA supplementation compared to both basal (p<0.05) and 100mg AA supplementation periods (p<0.05). Plasma AA concentrations were negatively correlated with Δ-MDA levels (R=-0.327; p<0.01).

CONCLUSION

Our results suggest that long-term parenteral 500mg AA supplementation improves PON activity alleviating apo B-containing lipoproteins oxidizability in HD patients.

Could Antioxidant Supplementation Delay Progression of Cardiovascular Disease in End-Stage Renal Disease Patients?

In end-stage renal disease patients, the leading causes of mortality are of cardiovascular (CV) origin. The underlying mechanisms are complex, given that sudden heart failure is more common than acute myocardial infarction. A contributing role of oxidative stress is postulated, which is increased even at early stages of chronic kidney disease, is gradually augmented in parallel to progression to endstage renal disease and is further accelerated by renal replacement therapy. Oxidative stress ensues when there is an imbalance between reactive pro-oxidants and physiologically occurring electron donating antioxidant defence systems. During the last decade, a close association of oxidative stress with accelerated atherosclerosis and increased risk for CV and all-cause mortality has been established. Lipid peroxidation has been identified as a trigger for endothelial dysfunction, the first step towards atherogenesis. In order to counteract the deleterious effects of free radicals and thereby ameliorate, or delay, CV disease, exogenous administration of antioxidants has been proposed. Here, we attempt to summarize existing data from studies that test antioxidants for CV protection, such as vitamins E and C, statins, omega-3 fatty acids and N-acetylcysteine.

Paraoxonase 1 concerning dyslipidaemia, cardiovascular diseases, and mortality in haemodialysis patients

Paraoxonase 1 (PON1) is known for preventing atherosclerosis through lipid-modifying features, antioxidant activity, anti-inflammatory, anti-apoptosis, anti-thrombosis, and anti-adhesion properties. Uremic patients requiring haemodialysis (HD) are especially prone to atherosclerosis and its complications. We analysed the PON1 gene (PON1) polymorphisms and serum PON1 (paraoxonase) activity concerning dyslipidaemia and related cardiovascular diseases and mortality to show how they associate under uremic conditions modified by maintenance HD treatment. The rs662 AA + AG (OR 1.76, 95%CI 1.10-2.80, P = 0.018), rs854560 TT (OR 1.48, 95%CI 1.04-2.11, P = 0.031), and rs854560 AT + TT (OR 1.28, 95%CI 1.01-1.63, P = 0.040) contributed to the prevalence of atherogenic dyslipidaemia diagnosed by the triglyceride (TG)/HDL-cholesterol ratio ≥ 3.8. The normalized serum PON1 activity positively correlated with atherogenic dyslipidaemia (ẞ 0.67 ± 0.25, P = 0.008). The PON1 rs854560 allele T was involved in the higher prevalence of ischemic cerebral stroke (OR 1.38, 1.02-1.85, P = 0.034). The PON1 rs705379 TT genotype contributed to cardiovascular (HR 1.27, 95% CI 1.03-1.57, P = 0.025) and cardiac (HR 1.34, 95% CI 1.05-1.71, P = 0.018) mortality. All P-values were obtained in multiple regression analyses, including clinical variables. Multifaceted associations of PON1 with dyslipidaemia, ischemic cerebral stroke, and cardiovascular mortality in HD patients provide arguments for the consideration of PON1 and its protein product as therapeutic targets in the prevention of atherosclerosis and its complications in uremic patients.

Two Faces of Vitamin C in Hemodialysis Patients: Relation to Oxidative Stress and Inflammation

Hemodialysis (HD) is the most common method of renal replacement therapy. Besides toxins, it eliminates nutrients from the circulation, such as ascorbic acid (AA). HD-patients present AA deficiency more often than representatives of the general population, also due to dietary restrictions. This condition aggravates oxidative stress and inflammation related to uremia and extracorporeal circulation and increases cardiovascular risk followed by mortality. Supplementation of AA seems to be a promising approach in the treatment of hemodialysis patients. Many successful interventions restored plasma AA concentration in HD patients by enteral or intravenous supplementation, concomitantly inhibiting oxidative stress and inflammation. A significant number of studies reported opposite, serious pro-oxidant effects of AA. In this narrative review, we present studies, commenting on their limitations; on AA plasma or serum concentration and the influence of its supplementation on protein and lipid peroxidation, DNA damage, reactive oxygen species generation, paraoxonase activity, advanced glycation endproducts, and C-reactive protein (CRP) concentration. Moreover, in terms of safety, the possible development of oxalosis in HD patients regarding the intravenous or enteral route of AA administration is discussed. Unequivocal clinical results of recent studies on hemodialysis patients are displayed.

Arylesterase activity but not PCSK9 levels is associated with chronic kidney disease in type 2 diabetes

PURPOSE

Oxidative stress and dyslipidemia have been found to be associated with the progression of chronic kidney disease (CKD) in type 2 diabetes mellitus (T2DM) patients. Paraoxonase 1 (PON-1) activity, and proprotein convertase subtilisin kexin type 9 (PCSK9) levels play an important role regarding anti-oxidants, and lipid metabolism, respectively. The aim of this study was to investigate the association of PON-1 activity, and PCSK9 levels with CKD in T2DM.

METHODS

A total of 180 T2DM (87 CKD, and 93 non-CKD) with age-, and gender-matched subjects were recruited in this study. PON-1 activity was measured with two kinds of substrate: paraoxon for paraoxonase (PONase) activity and phenylacetate for arylesterase (AREase) activity. PCSK9 levels were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

AREase activity was significantly lower in CKD compared with non-CKD (225.53 ± 108.73 vs. 257.45 ± 106.12 kU/L, p = 0.044) in T2DM, whereas there was no significant difference in PONase activity and PCSK9 levels between CKD and non-CKD groups. In addition, multivariate logistic regression analysis showed that the lowest tertile of AREase increased the risk for CKD in T2DM (OR 3.251; 95% CI 1.333-7.926, p = 0.010), whereas PONase activity and PCSK9 levels were not associated with CKD in T2DM.

CONCLUSION

Reduced AREase activity can increase the risk for CKD in T2DM patients. AREase activity, but not PONase activity and PCSK9 levels, may be used as the biomarker for predicting the progression of CKD in T2DM.

Phenotypes and concentration of PON1 in cardiovascular disease: The role of nutrient intake

BACKGROUND AND AIMS

Paraoxonase 1 (PON1) is considered to play a crucial role as an anti-atherosclerotic factor. The PON1 activity is affected by genetic polymorphisms, environmental factors, age, sex, lifestyle, pharmaceutical drugs, and dietary factors. The aim of this study was to evaluate the association between macro- and micronutrients as well as PON1 concentration and activities in patients with cardiovascular diseases (CVD), cardiovascular risk factors but no CVD (CRF), and in healthy controls (control group).

METHODS AND RESULTS

A case-control study was carried out with 356 volunteers from the Mexican Institute of Social Security, Mexico. Clinical parameters, lipid profile, PON1 activities (AREase, LACase, CMPAase and PONase), and PON1 concentration were evaluated. There was a differential intake of macro- and micronutrients among the study groups. The intake of proteins and carbohydrates was higher in the CVD group than in the CFR and control groups (p < 0.05). AREase, LACase, and CMPAase activities and PON1 concentration were lowest in the CVD group.

CONCLUSION

LACase and CMPAase activities, as well as PON1 concentration, could be included in the battery of CVD predictive biomarkers in the Mexican population.

Antioxidant Supplementation in Renal Replacement Therapy Patients: Is There Evidence?

The disruption of balance between production of reactive oxygen species and antioxidant systems in favor of the oxidants is termed oxidative stress (OS). To counteract the damaging effects of prooxidant free radicals, all aerobic organisms have antioxidant defense mechanisms that are aimed at neutralizing the circulating oxidants and repair the resulting injuries. Antioxidants are either endogenous (the natural defense mechanisms produced by the human body) or exogenous, found in supplements and foods. OS is present at the early stages of chronic kidney disease, augments progressively with renal function deterioration, and is further exacerbated by renal replacement therapy. End-stage renal disease patients, on hemodialysis (HD) or peritoneal dialysis (PD), suffer from accelerated OS, which has been associated with increased risk for mortality and cardiovascular disease. During HD sessions, the bioincompatibility of dialyzers and dialysate trigger activation of white blood cells and formation of free radicals, while a significant loss of antioxidants is also present. In PD, the bioincompatibility of solutions, including high osmolality, elevated lactate levels, low pH, and accumulation of advanced glycation end-products trigger formation of prooxidants, while there is significant loss of vitamins in the ultrafiltrate. A number of exogenous antioxidants have been suggested to ameliorate OS in dialysis patients. Vitamins B, C, D, and E, coenzyme Q10, L-carnitine, a-lipoic acid, curcumin, green tea, flavonoids, polyphenols, omega-3 polyunsaturated fatty acids, statins, trace elements, and N-acetylcysteine have been studied as exogenous antioxidant supplements in both PD and HD patients.

The Search for Dietary Supplements to Elevate or Activate Circulating Paraoxonases

Low levels of paraoxonase 1 (PON1) have been associated with the development of several pathological conditions, whereas high levels have been shown to be anti-atherosclerotic in mouse models. These findings suggest that PON1 could be a good surrogate biomarker. The other members of the family, namely PON2 and PON3, the role of which has been much less studied, deserve more attention. This paper provides a systematic review of current evidence concerning dietary supplements in that regard. Preliminary studies indicate that the response to dietary supplements may have a nutrigenetic aspect that will need to be considered in large population studies or in clinical trials. A wide range of plant preparations have been found to have a positive action, with pomegranate and some of its components being the best characterized and Aronia melanocarpa one of the most active. Flavonoids are found in the composition of all active extracts, with catechins and genistein being the most promising agents for increasing PON1 activity. However, some caveats regarding the dose, length of treatment, bioavailability, and stability of these compounds in formulations still need to be addressed. Once these issues have been resolved, these compounds could be included as nutraceuticals and functional foods capable of increasing PON1 activity, thereby helping with the long-term prevention of atherosclerosis and other chronic ailments.

Plasma protein-bound di-tyrosines as biomarkers of oxidative stress in end stage renal disease patients on maintenance haemodialysis

Background

Patients with end-stage renal disease (ESRD) undergoing haemodialysis (HD) experience enhanced oxidative stress and systemic inflammation, which are risk factors for cardiovascular disease, the most common cause of excess morbidity and mortality for these patients. Different pathways producing different types of oxidative stress occur in ESRD. The purpose of our study was to determine the effect of HD on plasma levels of protein-bound dityrosine (di-Tyr), a biomarker of protein oxidation.

Methods

Protein-bound di-Tyr formation was measured by size exclusion HPLC coupled to fluorescence detector. Clinical laboratory parameters were measured by standardized methods.

Results

In most ESRD patients, a single HD session decreased significantly the plasma protein-bound di-Tyr level, although the mean post-HD level remained significantly greater than the one in healthy people. Furthermore, pre-HD plasma protein-bound di-Tyr level was positively correlated with pre-HD serum creatinine and albumin concentrations. No significant correlation was found between plasma protein-bound di-Tyr level and serum concentration of C-reactive protein, a biomarker of systemic inflammation.

Conclusions

This study demonstrates that a single HD session does not increase, rather partially decreases, oxidative pathways producing di-Tyr in the haemodialyzed patient.

General significance

The choice of the most pertinent biomarkers of oxidative stress is critical for the development of novel treatments for ESRD. However, the relative importance of oxidative stress and inflammation in ESRD remains largely undetermined, and several questions concerning oxidative stress and inflammation remain poorly defined. These results could stimulate further studies on the use of plasma protein-bound di-Tyr as a long-lasting oxidative stress biomarker in ESRD.

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Haemodialyzed patients experience oxidative stress and systemic inflammation.

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We assessed haemodialysis (HD) effect on plasma protein-bound dityrosine (di-Tyr).

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In most patients, a single HD session decreased significantly the di-Tyr level.

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Pre-HD di-Tyr level was positively correlated with those of creatinine and albumin.

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No correlation was found between di-Tyr level and C-reactive protein concentration.

Decreased paraoxonase1 activity and increased malondialdehyde and oxidative DNA damage levels in primary open angle glaucoma

To investigate the malondialdehyde (MDA) levels, paraoxonase1 (PON1) activity and 8-hydroxy 2-deoxyguanosine (8-OHdG) levels in the primary open angle glaucoma (POAG) patient. Blood samples from 52 healthy individuals and 53 patients with POAG were analyzed for MDA and 8-OHdG by HPLC (high-performance liquid chromatography) and PON1 by spectrophotometry. The data obtained were analyzed statistically. MDA levels were 10.46±8.4 and 4.70±1.79 µmol; PON1 levels were 121±39.55 and 161.62±60.22 U/mL; and 8-OHdG values were 1.32±0.53/10⁶ dG and 0.47±0.27/10⁶ dG in the POAG patients and the control group, respectively. The difference was significant in MDA levels, 8-OHdG levels and PON1 activity in POAG patients in comparison with controls (P<0.001). We concluded that the observed increase in MDA and 8-OHdG levels may be correlated with decreased PON1 activity. Oxidative stress plays an important role in glaucoma development.

PON1 and Mediterranean Diet

The Mediterranean diet has been proven to be highly effective in the prevention of cardiovascular diseases. Paraoxonase 1 (PON1) has been implicated in the development of those conditions, especially atherosclerosis. The present work describes a systematic review of current evidence supporting the influence of Mediterranean diet and its constituents on this enzyme. Despite the differential response of some genetic polymorphisms, the Mediterranean diet has been shown to exert a protective action on this enzyme. Extra virgin olive oil, the main source of fat, has been particularly effective in increasing PON1 activity, an action that could be due to low saturated fatty acid intake, oleic acid enrichment of phospholipids present in high-density lipoproteins that favor the activity, and increasing hepatic PON1 mRNA and protein expressions induced by minor components present in this oil. Other Mediterranean diet constituents, such as nuts, fruits and vegetables, have been effective in modulating the activity of the enzyme, pomegranate and its compounds being the best characterized items. Ongoing research on compounds isolated from all these natural products, mainly phenolic compounds and carotenoids, indicates that some of them are particularly effective, and this may enhance the use of nutraceuticals and functional foods capable of potentiating PON1 activity.

Vitamin C supplementation in patients on maintenance dialysis

As one of the most important water-soluble non-enzymatic antioxidants, vitamin C consists of ascorbic acid and its oxidized form, dehydroascorbic acid. Maintenance hemodialysis (MHD) patients have a generally lower plasma vitamin C level compared with general population. Moreover, dialysis patients also exhibit a low plasma vitamin C level, which is largely related with increased inflammation, refractory anemia and oxidative stress. In this review, we described, in great detail, the vitamin C deficiency in MHD patients and its effects on anti-oxidation, anti-inflammation, pro-oxidation and secondary hyperparathyroidism. In addition, we described the possible potential value of vitamin C in anemia, and the side effects of over-doses of vitamin C supplementation in this particular population. In summary, MHD patients may benefit from vitamin C administration. However, further research should be carried out to confirm its potential beneficial effects, optimal dosage and side effects from vitamin C supplementation.

Modulation of NADPH oxidase activity by known uraemic retention solutes

BACKGROUND

Uraemia and cardiovascular disease appear to be associated with an increased oxidative burden. One of the key players in the genesis of reactive oxygen species (ROS) is nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Based on initial experiments demonstrating a decreased inhibitory effect on NADPH oxidase activity in the presence of plasma from patients with CKD-5D after dialysis compared with before dialysis, we investigated the effect of 48 known and commercially available uraemic retention solutes on the enzymatic activity of NADPH oxidase.

METHODS

Mononuclear leucocytes isolated from buffy coats of healthy volunteers were isolated, lysed and incubated with NADH in the presence of plasma from healthy controls and patients with CKD-5D. Furthermore, the leucocytes were lysed and incubated in the presence of uraemic retention solute of interest and diphenyleneiodonium chloride (DPI), an inhibitor of NADPH oxidase. The effect on enzymatic activity of NADPH oxidase was quantified within an incubation time of 120 min.

RESULTS

Thirty-nine of the 48 uraemic retention solutes tested had a significant decreasing effect on NADPH oxidase activity. Oxalate has been characterized as the strongest inhibitor of NADPH oxidase (90% of DPI inhibition). Surprisingly, none of the uraemic retention solutes we investigated was found to increase NADPH oxidase activity. Furthermore, plasma from patients with CKD-5D before dialysis caused significantly higher inhibitory effect on NADPH oxidase activity compared with plasma from healthy subjects. However, this effect was significantly decreased in plasma from patients with CKD-5D after dialysis.

CONCLUSIONS

The results of this study show that uraemic retention solutes modulated the activity of the NADPH oxidase. The results of this study might be the basis for the development of inhibitors applicable as drug in the situation of increased oxidative stress.

The assessment of oxidative stress on patients with chronic renal failure at different stages and on dialysis patients receiving different hypertensive treatment

The aim of this study is to evaluate the oxidative stress in predialysis, hemodialysis (HD) and peritoneal dialysis patients and to test the effects of antihypertensive drugs and volume control on oxidative stress parameters. The study was composed of five groups as follows: control group (n = 30), predialysis group (n = 30), peritoneal dialysis group (n = 30), hemodialysis group, (normotensive with strict volume control, n = 30), hemodialysis group (normotensive with medication, n = 30). Plasma malondialdehyde (MDA), erythrocyte superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSHPx) and routine biochemical parameters were studied in all patients. Hemodialysis patients with strict volume control (HDvc) had lower levels of MDA than other patient groups (p < 0.001), and CAT, SOD values had highest level other patient groups (p < 0.001). The treatment of hypertension with strict volume control in chronic renal failure patients causes less damage to the antioxidant capacity.

Paraoxonase 1 in chronic kidney failure

In this review we summarize the findings from the literature and our own laboratory on the decreased PON1 activity in renal failure, the mechanisms proposed and the effect of interventions. In addition to profound alterations in lipoproteins, reduced serum PON1 activity has been clearly established in the past decade and could contribute to accelerated development of atherosclerosis in ESRD and in HD. PON1 lactonase activity is lower in ESRD patients. Hemodialysis partially restores PON1 lactonase and the other activities. PON1 activity recovery after dialysis suggests that uremic toxins may play a mechanistic role in PON1 inactivation. Lower PON1 activity in CRF patients is associated with low thiol concentration, high CRP, and is beneficially enhanced with vitamin C and flavonoids. Changes in HDL subclasses, namely lower HDL₃ in these patients may also play a role in PON1 lower activity. Future research should focus on: (1) mechanistic studies on causes for low PON1 activity and mass; (2) prospective studies focusing on whether there is an added predictive value in measuring PON1 activity (and PON1 activity in HDL₃) in this patient population; (3) intervention studies attempting to increase PON1 activity.

Paraoxonase-1 and ischemia-modified albumin in patients with end-stage renal disease

End-stage renal disease (ESRD) with and/or without treatment by hemodialysis (HD) is associated with accelerated atherosclerosis, leading to cardiovascular disease (CVD) including acute coronary syndromes. Therefore, the regulation of CVD is a crucial issue for ESRD patients. Given the recent reports that paraoxonase-1 (PON-1) and ischemia-modified albumin (IMA) could predict CVD-related mortality in ESRD, the two recent biomarkers may be useful for preventive strategies for CVD. This review paper presents current data on the relationships between PON-1, IMA, and ESRD. Many studies have shown that circulating PON-1 activity is lower in ESRD patients, and we have shown that its levels increase after HD. Although circulating IMA levels can increase before HD in ESRD patients, there remains to be little data. Our pilot study has shown a significant inverse correlation between PON-1 and IMA in ESRD patients. Although the pathogenic link between PON-1 and IMA remains speculative, considering both biomarkers may provide new insights into the prevention of CVD in ESRD patients.

Hemodialysis alters lipid profiles, total antioxidant capacity, and vitamins A, E, and C concentrations in humans

Although hemodialysis (HD) is essential for end-stage renal disease patients, at the same time it causes oxidative stress and long-term pro-atherosclerotic effects. This study aimed to determine lipid profile as well as the total antioxidant capacity (TAC) and vitamins A, E, and C in HD patients. The study enrolled 31 patients (50.3 ± 14.9 years old) undergoing maintenance 4-hour HD three times per week with a polysulfone membrane dialyzer for a mean of 76.1 months (range, 7-120 months) and 31 healthy individuals (47.8 ± 13.9 years old). Lipid profiles were determined spectrophotometrically using commercially available kits. Total antioxidant capacity was determined by ferric reducing/antioxidant power assay, levels of vitamins A and E were assayed using high-pressure liquid chromatography, and the level of vitamin C was measured by a photometric method. Our results showed that before HD, the levels of TAC and vitamin A were significantly higher than in normal subjects, whereas the levels of high-density lipoprotein (HDL) and vitamin C were lower than in control subjects (P < .001). There was no significant difference between normal subjects and patients before dialysis regarding low-density lipoprotein (LDL) and vitamin E levels (P > .05). After HD, the levels of HDL-cholesterol, vitamins E and C, and TAC decreased significantly (P < .001), but the decreased level of vitamin A still remained higher than controls (P < .05), whereas the levels of LDL were significantly higher than controls (P < .001). In conclusion, alterations in the lipoprotein profiles and antioxidant markers following HD suggest an increased risk of atherosclerosis in these patients.

Mechanism of endothelial dysfunction in chronic kidney disease

Endothelium is the largest organ in the body strategically located between the wall of blood vessels and the blood stream. The human body contains approximately 10(13) endothelial cells weighing approximately 1kg, and covering a surface area of 4000 to 7000m(2) equivalent to the soccer playground. Hypertension and shear stress, inflammation, diabetes-associated factors such as advanced glycated end products, and uremic toxins are some of the prevalent risk factors of endothelial dysfunction in chronic kidney disease. In renal failure endothelial dysfunction and atherosclerosis are almost universal, as well as cardiovascular complications. Endothelial cell damage or injury is invariably associated with such clinical conditions as thrombosis, hypertension, renal failure and atherosclerosis and may be also responsible for accelerated atherosclerosis in patients with chronic renal failure. Traditional risk factor cannot explain the high prevalence and incidence of cardiovascular disease in chronic kidney disease, therefore other non-traditional risk factors such as endothelial dysfunction, oxidative stress or insulin resistance have increasingly been studied. In this review paper mechanism of endothelial dysfunction, including the role of nitric oxide pathway, adipocytokines and hemodialysis-induced endothelial dysfunction is discussed.

Disorders of lipid metabolism and chronic kidney disease in the elderly

The growing population of elderly with chronic kidney disease (CKD) is at greater risk for cardiovascular disease given an independent risk of CKD, as well as from added dyslipidemia of aging and renal dysfunction. Changes in lipid metabolism with more isodense and high-dense, triglyceride-rich particles, low high-density lipoprotein cholesterol, and increased triglyceride levels occur with CKD and aging, which are noted to have significant atherogenic potential. In addition, lipid abnormalities may lead to the progression of CKD. Cardiovascular mortality in the end-stage renal disease population is more than 10 times higher than the general population. Treatment of dyslipidemia in the general population suggests important benefits both in reducing cardiovascular risk and in the prevention of cardiovascular disease. Secondary analyses of elderly subgroups of various large prospective studies with statins suggest treatment benefit with statin use in the elderly. Similarly limited data from secondary analyses of CKD subgroups of larger prospective trials using statins also suggest a possible benefit in cardiovascular outcomes and the progression of kidney disease. However, randomized trials have yet to confirm similar benefits and targets of treatment for dyslipidemia in the elderly with CKD and end-stage renal disease. Treatment in the elderly with CKD should be individualized and outweigh risks of side effects and drug-drug interactions. There is a need for further specific investigation of dyslipidemia of CKD in the aging population in relation to renal disease progression and cardiovascular outcome.

Vitamin C attenuates hypochlorite-mediated loss of paraoxonase-1 activity from human plasma

Paraoxonase 1 (PON1) is a cardioprotective enzyme associated with high-density lipoprotein (HDL). We tested the hypothesis that vitamin C protects HDL and PON1 from deleterious effects of hypochlorous acid, a proinflammatory oxidant. In our experiments, HDL (from human plasma) or diluted human plasma was incubated with hypochlorite in either the absence (control) or presence of vitamin C before measuring chemical modification and PON1 activities. Vitamin C minimized chemical modification of HDL, as assessed by lysine modification and accumulation of chloramines. In the absence of vitamin C, chloramines accumulated to 114 +/- 4 micromol/L in HDL incubated with a 200-fold molar excess of hypochlorite; but addition of vitamin C (200 micromol/L) limited formation to 36 +/- 6 micromol/L (P < .001). In plasma exposed to hypochlorite, IC(50) values of 1.2 +/- 0.1, 9.5 +/- 1.0, and 5.0 +/- 0.6 mmol/L were determined for PON1's phosphotriesterase, arylesterase, and (physiologic) lactonase activities, respectively. Vitamin C lessened this inhibitory effect of hypochlorite on PON1 activities. In plasma supplemented with vitamin C (400 micromol/L), PON1 phosphotriesterase activity was 72% +/- 17% of normal after incubation with hypochlorite (2 mmol/L), compared with 42% +/- 6% for unsupplemented plasma (P < .05). Similar effects were seen for other PON1 activities. In some experiments, vitamin C also appeared to reverse hypochlorite-mediated loss of PON1 phosphotriesterase activity; but this effect was not observed for the other PON1 activities. In conclusion, vitamin C attenuated hypochlorite-mediated loss of PON1 activity in vitro and may, therefore, preserve cardioprotective properties of HDL during inflammation.

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.

Parenteral ascorbic acid in haemodialysis patients

PURPOSE OF REVIEW

Parenteral ascorbic acid has been frequently used to overcome problems of vitamin C deficiency in haemodialysis patients. The benefits of vitamin C supplementation in clinical studies have been controversial and did not consider toxicological aspects. The review summarizes recent findings of the effects of parenteral ascorbic acid and discusses toxicological effects.

RECENT FINDINGS

Vitamin C deficiency in haemodialysis patients, which has been frequently described, cannot be improved with oral supplementation due to limited absorption of high dosages. To avoid consequences of vitamin C deficiency, parenteral vitamin C solutions should be administered because this intervention is the only way to guarantee a sufficient supply to the cells. A beneficial consequence of parenteral vitamin C on the recombinant human erythropoietin resistance is an additional therapeutic effect, which contributes to the prevention of iron deficiency anaemia in haemodialysis patients. Thus, large amount of supplemental vitamin C are required for extended periods of time (up to 500 mg 3 times a week). To avoid hyperoxaluria, plasma oxalate levels should be monitored on a regular basis, for example, once a week.

SUMMARY

Parenteral administration of ascorbic acid may be an approach that can overcome problems of vitamin C deficiency in haemodialysis patients - in particular problems of iron overload, erythropoetin resistance, and chronic inflammation.