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

Niacin ameliorates oxidative stress, inflammation, proteinuria, and hypertension in rats with chronic renal failure

Significant reduction of renal mass causes progressive deterioration of renal function and structure which is mediated by systemic and glomerular hypertension, hyperfiltration, oxidative stress, inflammation, and dyslipidemia. Niacin is known to improve lipid metabolism and exert antioxidant/anti-inflammatory actions. Therefore, we considered that niacin supplementation may attenuate oxidative stress, inflammation, and tissue injury in the remnant kidney. To this end, 56 nephrectomized [chronic kidney disease (CKD)] rats were randomly assigned to niacin-treated (50 mg x kg(-1) x day(-1) in the drinking water for 12 wk) and untreated groups. Sham-operated rats served as controls. The untreated CKD rats exhibited azotemia, hypertension, hypertriglyceridemia, proteinuria, glomerulosclerosis, tubulointerstitial damage, upregulation of MCP-1, plasminogen activator inhibitor-1 (PAI-1), transforming growth factor (TGF)-beta, cyclooxygenase (COX)-1, COX-2, and NAD(P)H oxidase (NOX-4, gp91(phox), p47(phox) and p22(phox) subunits) and activation of NF-kappaB (IkappaB phosphorylation). Niacin administration reduced MCP-1, PAI-1, TGF-beta, p47(phox), p22(phox), COX-1, and NF-kappaB activation, ameliorated hypertension, proteinuria, glomerulosclerosis, and tubulointerstitial injury. Although niacin lowered serum creatinine and raised creatinine clearance, the differences did not reach statistical significance. Thus niacin supplementation helps to attenuate histological injury and mitigate upregulation of oxidative and inflammatory systems in the remnant kidney.

Melatonin ameliorates oxidative stress, inflammation, proteinuria, and progression of renal damage in rats with renal mass reduction

The progressive deterioration of renal function and structure resulting from renal mass reduction are mediated by a variety of mechanisms, including oxidative stress and inflammation. Melatonin, the major product of the pineal gland, has potent_antioxidant and anti-inflammatory properties, and its production is impaired in chronic renal failure. We therefore investigated if melatonin treatment would modify the course of chronic renal failure in the remnant kidney model. We studied rats followed 12 wk after renal ablation untreated (Nx group, n = 7) and treated with melatonin administered in the drinking water (10 mg/100 ml) (Nx + MEL group, n = 8). Sham-operated rats (n = 10) were used as controls. Melatonin administration increased 13-15 times the endogenous hormone levels. Rats in the Nx + MEL group had reduced oxidative stress (malondialdehyde levels in plasma and in the remnant kidney as well as nitrotyrosine renal abundance) and renal inflammation (p65 nuclear factor-kappaB-positive renal interstitial cells and infiltration of lymphocytes and macrophages). Collagen, alpha-smooth muscle actin, and transforming growth factor-beta renal abundance were all increased in the remnant kidney of the untreated rats and were reduced significantly by melatonin treatment. Deterioration of renal function (plasma creatinine and proteinuria) and structure (glomerulosclerosis and tubulointerstitial damage) resulting from renal ablation were ameliorated significantly with melatonin treatment. In conclusion, melatonin administration improves the course of chronic renal failure in rats with renal mass reduction. Further studies are necessary to define the potential usefulness of this treatment in other animal models and in patients with chronic renal disease.

The Impact of Standard High-Flux Polysulfone Versus Novel High-Flux Polysulfone Dialysis Membranes on Inflammatory Markers: A Randomized, Single-Blinded, Controlled Clinical Trial

BACKGROUND

This study is a prospective, randomized, single-blind, clinical trial over 12 months involving 60 stable hemodialysis patients comparing standard high-flux polysulfone dialyzer membranes with a novel high-flux polysulfone dialyzer membrane (Helixone; Fresenius Medical Care, St Wendel, Germany) modified in the fiber-spinning process to enhance middle-molecule clearance through changing the distribution of pore size and increased filtration.

METHODS

Markers of protein and lipid oxidation and inflammatory markers, including proinflammatory cytokines and cell adhesion molecules, were compared. The hypothesis tested was that improved clearances of middle molecules with the FX80 membrane would lead to less oxidative stress and inflammation compared with the high-flux polysulfone (HF80) membrane.

RESULTS

Type of dialysis membrane used did not significantly affect lipid and protein peroxidation, C-reactive protein level, interleukin 6 level, or sgp130 level during 12 months. beta(2)-Microglobulin concentrations decreased significantly in the Helixone membrane group compared with those dialyzed using conventional polysulfone membranes during the study (-15%; 95% confidence interval, -20 to -10).

CONCLUSION

Long-term dialysis with a Helixone membrane did not modify any parameters of oxidative stress or inflammation in this stable hemodialysis population compared with a high-flux polysulfone dialysis membrane.

Hemodialysis and Protein Oxidation Products

The presence of a chronic inflammatory state has also been widely documented in end-stage renal disease patients receiving maintenance hemodialysis (HD). It is commonly attributed to the constantly renewed activation of circulating neutrophils and monocytes following blood passage through dialysis circuits and subsequent generation of activated complement components due to contact of plasma with bioincompatible membranes and/or transfer of endotoxins from the dialyzate to the blood compartment. This conjunction leads to a massive generation of reactive oxygen species (ROS), for example, superoxide anion, hydrogen peroxide, hydroxyl radical, and chlorinated oxidants, such as hypochlorous acid by activated neutrophils. The exquisite vulnerability of proteins to ROS is now well documented. Oxidation of amino acid residues, such as tyrosine, leads to the formation of dityrosine, protein aggregation, cross-linking, and fragmentation. Dityrosine-containing protein cross-linking products in the plasma of dialysis patients are named as advanced oxidation protein products (AOPP). In addition, advanced glycation end-products (AGE) is a protein carbonyl compound and produced by protein-ROS interaction. We investigated both the effect of the renewed activation of the immune cells, due to blood-dialyzer interaction over protein oxidation products like AOPP and AGE, among chronic renal failure (CRF) patients receiving maintenance HD, and choice of dialyzers like high flux or the other group on protein oxidation product levels.

Anemia and Cardiovascular Disease, Hospitalization, End Stage Renal Disease, and Death in Older Patients with Chronic Kidney Disease

BACKGROUND

Large observational studies examining the association between anemia and "hard" clinical outcomes are rare in patients with chronic kidney disease (CKD).

METHODS

We used the General Medicare 5% Denominator Files to identify patients aged 67 years or more with CKD on December 31, 1999. Outcomes in the ensuing 2 years were compared in patients with and those without anemia (entry period, 1998-1999; follow-up period, 2000-2001).

RESULTS

Of 41,522 CKD patients identified, 49.0% had claims of anemia diagnosis. The factors associated (p< 0.0001) with anemia included older age, female gender, black race, and all 10 comorbid conditions studied; adjusted odds ratios (ORs) exceeded 1.5 for age 80 years old or older (OR, 1.54 compared to <70 years), for black race (OR, 1.52), and for co-existing diagnoses of congestive heart failure (OR, 1.64), gastrointestinal bleeding (OR, 3.65), and liver disease (OR, 2.16). During the follow-up period, outcome event rates (expressed per 1000 patient-years) were as follows: renal replacement therapy, 23.5; death, 186.4; congestive heart failure, 390.0; atherosclerotic vascular disease, 410.5; and first hospitalization, 552.6. Using proportional hazards modeling, the presence of anemia was associated (p < 0.0001) with the following adjusted hazards ratios: atherosclerotic vascular disease, 1.09; congestive heart failure, 1.14; renal replacement therapy, 2.61 and death, 1.40.

CONCLUSION

A diagnosis of anemia is present in nearly half of all patients with CKD, aged 67 years or more, a group at very high risk of cardiovascular disease, hospitalization, end-stage renal disease, and death. Anemia is associated with each of these events.

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.

Folic acid supplementation to prevent adverse events in individuals with chronic kidney disease and end stage renal disease

PURPOSE OF REVIEW

This review summarizes our current understanding of the role of folate in the treatment of hyperhomocysteindemia and the prevention of cardiovascular disease in patients with chronic kidney disease and end stage renal disease. Relevant papers published between 2003 and 2004 are referenced.

RECENT FINDINGS

With the exception of one paper, recent therapeutic studies supported previous findings that folate therapy achieves only a modest reduction in plasma homocysteine and seldom normalizes homocysteine. Large prospective studies are under way to evaluate the causal relationship between homocysteine and cardiovascular risk. Recent work supports earlier data that suggested that homocysteine inflicts its damage by oxidative stress. A newly described consequence of hyperhomocysteindemia is DNA hypomethylation and alteration of gene expression. A recent study in the general population suggested that while folate may lower homocysteine it does not improve endothelial function in individuals without cardiovascular disease.

SUMMARY

The causes of hyperhomocysteindemia in renal failure remain obscure. The possibilities include impairment of both renal and extrarenal metabolic pathways by uraemia. Hyperhomocysteindemia is associated in some but not all studies with an increased risk for cardiovascular disease. A low homocysteine may reflect malnutrition and predict a poor outcome. Folate achieves modest reductions of homocysteine in some but not all studies. There are no data to support therapy with very high-dose folic acid. Hyperhomocysteindemia impairs endothelial function which is not adequately reversed by folate.

Nitric oxide, oxidative stress, and progression of chronic renal failure

Cellular injury or organ dysfunction from oxidative stress occurs when reactive oxygen species (ROS) accumulate in excess of the host defense mechanisms. The deleterious effect of ROS occurs from 2 principal actions. First, ROS can inactivate mitochondrial enzymes, damage DNA, or lead to apoptosis or cellular hypertrophy. Second, nitric oxide (NO), which is a principal endothelial-derived relaxing factor, reacts with superoxide anion (O2-) to yield peroxynitrite (ONOO-), which is a powerful oxidant and nitrosating agent. The inactivation of NO by O2- creates NO deficiency. Oxidative stress can promote the production of vasoconstrictor molecules and primary salt retention by the kidney. Several hypertensive animal models showed increased activity of nicotine adenine dinucleotide phosphate (NADPH) oxidase, which is the chief source of O2- in the vessel wall and kidneys. NO regulates renal blood flow, tubuloglomerular feedback (TGF), and pressure natriuresis. Animal models of NO deficiency develop hypertension, proteinuria, and glomerulosclerosis. Evidence is presented that chronic renal failure (CRF) is a state of NO deficiency secondary to decreased kidney NO production and/or increased bioinactivation of NO by O2-. Patients with CRF show decreased endothelium-dependent vasodilatation to acetylcholine, have increased markers of oxidative stress, and diminished antioxidant activity. Therapy for oxidative stress has focused on antioxidants and agents that modify the renin-angiotensin system. The effects of such treatments are more compelling in animal models than in human studies.

Cardiac calcification in renal patients: what we do and don't know

Cardiovascular (CV) disease is one of the major causes of mortality in patients with renal diseases, with an increased odds ratio of mortality with risk factors as diverse as blood pressure (high or low), cholesterol level (high or low), left ventricular hypertrophy, vascular stiffness, chronic inflammation, and hyperhomocysteinemia. Mainly cross-sectional studies of renal patients showed excess CV calcification (CVC) compared with the general population, but a clear link between calcification and subsequent mortality is tenuous to date. Several factors have been incriminated to explain the increase in CVC in this particular population. Increased duration of dialysis therapy, dyslipidemia, altered calcium-phosphorus metabolism, and chronic inflammation have all been associated with increased CVC. However, with the shortage of large, observational, population-based, prospective studies tracking these potential risk factors and the pathogenesis of CVC in renal patients not yet sufficiently understood, it is difficult with the present state of knowledge to make robust recommendations about care strategies. The purpose of this review is to examine the 10 available studies of renal patients that have used modern CVC imaging and quantification techniques for clues to likely targets for future interventional studies.

Oxidative stress and hemodynamic maladjustment in chronic renal disease: a therapeutic implication

Hemodynamic maladjustment with predominant constriction at the efferent arteriole has been encountered in a variety of clinical settings of glomerulonephropathy. In essence, it induces not only intraglomerular hypertension but also exaggeratedly reduces the peritubular capillary flow, which supplies the tubulointerstitial compartment. The hemodynamic maladjustment is believed to reflect a glomerular endothelial cell dysfunction. In this regard, oxidative stress and antioxidant defect are likely responsible for the glomerular endothelial dysfunction. Improvement in renal function was accomplished following the correction of oxidant and antioxidant imbalance with antioxidant therapy and vasodilators. Following such therapy, there was a correction in hemodynamic maladjustment with a decline in intraglomerular hydrostatic pressure and an increase in renal perfusion with a subsequent increase in renal functions namely creatinine clearance, glomerular filtration rate and a decline in FEMg.

Homocysteine and lipid peroxidation in haemodialysis: role of folinic acid and vitamin E

BACKGROUND

Cardiovascular diseases are the leading cause of death in haemodialysis patients. Hyperhomocysteinaemia is an independent risk factor. Basic research has provided strong evidence that oxidation of low-density lipoprotein (LDL) plays an important role in the pathogenesis of atherosclerosis. Oxidative stress, lipid metabolism alterations, and hyperhomocysteinaemia observed in haemodialysis patients could induce increases in LDL oxidation. This study was designed to determine the effect of folinic acid on hyperhomocysteinaemia and to assess the antioxidant efficacy of folinic acid. The antioxidant effect of folinic acid was compared with that of vitamin E.

METHODS

Sixteen stable patients (11 men, five women; mean age 54.3+/-6.32 years) on standard haemodialysis received 400 mg of vitamin E, orally, at the end of each haemodialysis session for 3 months. After a 1-month wash-out, they received 10 mg of folinic acid, intravenously, at the end of each haemodialysis session for an additional 3 months. Blood samples were drawn in the morning after an overnight fast and before dialysis. Plasma vitamin E was analysed by high-pressure liquid chromatography. Malondialdehyde (MDA) was determined using a fluorimetric method and plasma copper oxidized anti-LDL antibodies (Ab-LDLox) were measured with an ELISA method using native LDL and oxLDL as antigens. Plasma homocysteine was determined by an FPIA method.

RESULTS

Folinic acid supplements significantly reduced hyperhomocysteinaemia (-44%), MDA concentrations (-40%), and IgG-LDLox titres (-13%).

CONCLUSIONS

Treatment with folinic acid lowers plasma homocysteine levels and, like vitamin E, affords antioxidant protection, which prevents lipid peroxidation. This lowering of lipid peroxidation may reduce the risk of atherosclerosis and prevent or delay cardiovascular complications in HD patients.

Abnormalities in uremic lipoprotein metabolism and its impact on cardiovascular disease

Patients with end-stage renal disease (ESRD) suffer from a secondary form of complex dyslipidemia consisting of both quantitative and qualitative abnormalities in serum lipoproteins resulting from alterations in lipoprotein metabolism and composition. The prominant features of uremic dyslipidemia are an increase in serum triglyceride levels (due to elevated very low density lipoprotein [VLDL]-remnants and intermediate-density lipoprotein [IDL]) and low high-density lipoprotein (HDL) cholesterol. Low-density lipoprotein (LDL) cholesterol often is normal, but the cholesterol may originate from the atherogenic small and dense LDL subclass (sdLDL). The apolipoprotein B (apoB)-containing part of the lipoprotein may undergo modifications (enzymatic- and advanced glycation end-product [AGE]-peptide modification, oxidation, or glycosilation). Modifications contribute to impaired LDL receptor-mediated clearance from plasma and promote prolonged circulation. While LDL particles undergo a vicious cycle of accumulation and modification, reverse cholesterol transport is also impaired due to low lecithin:cholesterol acyltransferase (LCAT) and paraoxonase activity. Therefore, discoid HDL particles are structurally altered and hepatic cholesterol clearance is limited. The composition of HDL may also be altered during states of inflammation. The contribution of this complex and atherogenic form of dyslipidemia to cardiovascular disease in patients with renal disease is unclear at present. Most studies are negative in demonstrating the predictive power of serum lipids for the development of cardiovascular disease. This is most likely due to interference with deteriorating aspects of the activated acute-phase response. Nevertheless, patients with renal disease belong to a very high cardiovascular risk group and dyslipidemia should most likely be subjected to sufficient lipid-lowering therapy in most patients. Because it is also still unclear whether we have available therapies with sufficient impact on LDL size, remnant lipoprotein-lowering, and restoration of HDL function, we urgently need the results from large scale intervention trials such as the 4D-trial and the CHORUS study.

Homocysteine stimulates the expression of monocyte chemoattractant protein-1 receptor (CCR2) in human monocytes: possible involvement of oxygen free radicals

Homocysteinaemia is an independent risk factor for atherosclerosis. The development of atherosclerosis involves monocyte chemoattractant protein 1 (MCP-1)-mediated monocyte recruitment to the lesion site. The action of MCP-1 is mostly via its interaction with MCP-1 receptor (CCR2), which is the major receptor for MCP-1 on the surface of monocytes. The objective of the present study was to investigate the effect of homocysteine on CCR2 expression in human THP-1 monocytes. Cells were incubated with various concentrations of homocysteine for 6, 12, 24 and 48 h. The expression of CCR2 mRNA was determined by nuclease protection assay and the CCR2 protein was measured by Western immunoblotting analysis. The binding of MCP-1 to CCR2 as a functional receptor on the monocyte surface was determined by flow cytometry. Homocysteine (0.05-0.2 mM) significantly enhanced the expression of CCR2 mRNA (129-209% of the control) and CCR2 protein (up to 183% of control) in these cells after 24 h of incubation. Stimulation of CCR2 expression was associated with a parallel increase in the binding activity of CCR2 (129-191% of control) as well as an enhanced chemotactic response of homocysteine-treated monocytes. Further investigation revealed that the levels of superoxide were significantly elevated in cells incubated with homocysteine for 12-48 h. The addition of superoxide dismutase, a scavenger of superoxide, to the culture medium abolished the stimulatory effect of homocysteine on CCR2 expression as well as the binding activity of the receptor. The stimulatory effect of homocysteine on the expression of CCR2 mRNA and the levels of CCR2 protein was also observed in human peripheral blood monocytes. In conclusion, the present study has clearly demonstrated that homocysteine stimulates CCR2 expression in monocytes, leading to an enhanced binding activity and chemotatic response. Homocysteine-induced superoxide formation might serve as one of the underlying mechanisms for this effect.