Serum Concentrations of F2-Isoprostanes and 4-Hydroxynonenal in Hemodialysis Patients in Relation to Inflammation and Renal Anemia

Recent Approaches to Determine Static and Dynamic Redox State-Related Parameters

Oxidative stress refers to an imbalance between oxidant and antioxidant molecules, which is usually associated with oxidative damage to biomolecules and mitochondrial malfunction. Redox state-related parameters include (1) the direct measurement of ROS, (2) the assessment of the antioxidant defense status, and (3) the analysis of the resulting oxidative damage to molecules. Directly measuring ROS appears to be the preferred method among scientists, but most ROS are extremely unstable and difficult to measure. The processes of determining both the oxidative damage to biomolecules and the antioxidant system status, although both are indirect approaches, provide a reliable method to measure oxidative stress on a given sample. Recently, the Seahorse XF and the Oroboros O2k systems have provided new insights into the redox state from a more dynamic point of view. These techniques assess mitochondrial oxidative phosphorylation function and bioenergetics on isolated mitochondria, cultured cells, or specific tissues such as permeabilized fibers. This review describes a range of methodologies to measure redox state-related parameters, their strengths, and their limitations. In conclusion, all these techniques are valid and none of them can be replaced by another. Indeed, they have the potential to complement each other for a complete evaluation of the redox state of a given sample.

Rotating-disc micro-solid phase extraction of F2-isoprostanes from maternal and cord plasma by using oxidized buckypaper as sorbent membrane

This paper describes the development of an original micro-solid phase extraction device and its evaluation for the isolation of F2-isoprostanes (F2-IsoPs) from cord and maternal plasma samples. The unit is very simple and consists in a rotating disc (1.8 cm diameter) of oxidized buckypaper (BP), enwrapped in a polypropylene mesh pouch. Even if the selected F2-IsoPs have logP and pKa values that make them suitable candidates for their sorption on BP, several parameters were optimized to maximize recoveries: time of adsorption and desorption; stirring speed; volume, pH and ionic strength of the sample; type, volume, and fractions of the elution solvent; oxidation grade of BP. Among all, the last one was crucial in affecting extraction yields because of the analyte interactions with polar functionalities, introduced by a preliminary oxidative acid treatment. The investigation established the optimal oxidation time and highlighted the pros and cons of the acid activation step. All extracts were analyzed by means of liquid chromatography-tandem mass spectrometry (LC-MS/MS). Validation was performed according to the main FDA guidelines for bioanalytical methods. Depending on the spike level and analyte, recoveries ranged between 30 and 120% with precision and accuracy values lower than 20%. Quantitative analysis was accomplished by matrix-matched calibration curves whose determination coefficients were higher than 0.95. Lower limit of quantitation (LLOQ) spanned the range 2.45-6.77 μg L^-1. The validated method was applied to the analysis of eight pairs of mother/child plasma samples, revealing the presence of 8-iso-15-keto-PGF_2α and 8-iso-PGE₂ at a concentration of about 10 μg L^-1 in most cord plasma samples of preterm newborns.

Oxidative stress in hemodialysis: Causative mechanisms, clinical implications, and possible therapeutic interventions

Oxidative stress (OS) is the result of prooxidant molecules overwhelming the antioxidant defense mechanisms. Hemodialysis (HD) constitutes a state of elevated inflammation and OS, due to loss of antioxidants during dialysis and activation of white blood cells triggering production of reactive oxygen species. Dialysis vintage, dialysis methods, and type and condition of vascular access, biocompatibility of dialyzer membrane and dialysate, iron administration, and anemia all can play a role in aggravating OS, which in turn has been associated with increased morbidity and mortality. Oral or intravenous administration of antioxidants may detoxify the oxidative molecules and at least in part repair OS-mediated tissue damage. Lifestyle interventions and optimization of a highly biocompatible HD procedure might ameliorate OS development in dialysis.

Glutathione Peroxidase Activity, Plasma Total Antioxidant Capacity, and Urinary F2- Isoprostanes as Markers of Oxidative Stress in Anemic Dogs

Background

Oxidative stress plays a role in the pathophysiology of several diseases and has been documented as a contributor to disease in both the human and veterinary literature. One at‐risk cell is the erythrocyte, however, the role of oxidative stress in anemia in dogs has not been widely investigated.

Hypothesis/Objective

Anemic dogs will have an alteration in the activity of glutathione peroxidase (GPx), a decrease in of total antioxidant capacity (TAC), and an increased concentration of urinary 15‐F₂‐isoprostanes (F₂‐IsoP) when compared to healthy dogs.

Animals

40 client‐owned dogs with anemia (PCV <30%) age‐matched to 40 client‐owned healthy control dogs.

Methods

Prospective, cross‐sectional study. Whole blood GPx activity, plasma TAC, and urinary F₂‐isoprostane concentrations were evaluated in each dog and compared between groups.

Results

Anemic dogs had significantly lower GPx activity (43.1 × 10³ +/‐ 1.6 × 10³ U/L) than did dogs in the control group (75.8 × 10³ +/‐ 2.0 × 10³ U/L; P < 0.0001). The GPx activity in dogs with hemolysis (10³ +/‐ 0.8 × 10³ U/L) was not significantly different (P = 0.57) than in dogs with nonhemolytic anemia (43.5 × 10³ +/‐ 1.1 × 10³ U/L). The TAC concentrations (P = 0.15) and urinary F₂‐isoprostanes (P = 0.73) did not significantly differ between groups.

Conclusions and Clinical Importance

Glutathione peroxidase activity was significantly decreased in anemic dogs indicating oxidative stress. Additional studies are warranted to determine if antioxidant supplementation would improve survival and overall outcome as part of a therapeutic regimen for anemic dogs.

Oxidative Stress in Hemodialysis Patients: A Review of the Literature

Hemodialysis (HD) patients are at high risk for all-cause mortality and cardiovascular events. In addition to traditional risk factors, excessive oxidative stress (OS) and chronic inflammation emerge as novel and major contributors to accelerated atherosclerosis and elevated mortality. OS is defined as the imbalance between antioxidant defense mechanisms and oxidant products, the latter overwhelming the former. OS appears in early stages of chronic kidney disease (CKD), advances along with worsening of renal failure, and is further exacerbated by the HD process per se. HD patients manifest excessive OS status due to retention of a plethora of toxins, subsidized under uremia, nutrition lacking antioxidants and turn-over of antioxidants, loss of antioxidants during renal replacement therapy, and leukocyte activation that leads to accumulation of oxidative products. Duration of dialysis therapy, iron infusion, anemia, presence of central venous catheter, and bioincompatible dialyzers are several factors triggering the development of OS. Antioxidant supplementation may take an overall protective role, even at early stages of CKD, to halt the deterioration of kidney function and antagonize systemic inflammation. Unfortunately, clinical studies have not yielded unequivocal positive outcomes when antioxidants have been administered to hemodialysis patients, likely due to their heterogeneous clinical conditions and underlying risk profile.

Associations among apolipoproteins, oxidized high-density lipoprotein and cardiovascular events in patients on hemodialysis

Apolipoproteins are associated with survival among patients on hemodialysis (HD), but these associations might be influenced by dysfunctional (oxidized) high-density lipoprotein (HDL). We assessed associations among apolipoproteins and oxidized HDL, mortality and cardiovascular disease (CVD) events in patients on HD. This prospective observational study examined 412 patients on prevalent HD. Blood samples were obtained before dialysis at baseline to measure lipids, apolipoproteins, oxidized LDL, oxidized HDL, high-sensitivity C-reactive protein (hs-CRP) and interleukin (IL)-6 at baseline, and HDL-C and hs-CRP were measured 12 months later. Patients were then prospectively followed-up (mean, 40 months) and all-cause mortality and composite CVD events were analyzed. Associations between variables at baseline and clinical outcome were assessed by Cox proportional hazards modeling (n = 412) and Cox hazards modeling with a time-varying covariate with HDL-C and hs-CRP (n = 369). Quartiles of apolipoproteins and oxidized HDL were not associated with all-cause mortality. However, Cox proportional hazards models with quartiles of each variable adjusted for confounders and hs-CRP or IL-6 identified apolipoprotein (apo)B-to-apoA-I ratio (apoB/apoA-I) and oxidized HDL, but not apoA-I or apoA-II, as independent risk factors for composite CVD events. These associations were confirmed by Cox proportional hazards modeling with time-varying covariates for hs-CRP. ApoB/apoA-I was independently associated with composite CVD events in 1-standard deviation (SD) increase-of-variables models adjusted for the confounders, oxidized HDL and hs-CRP. However, these associations disappeared from the model adjusted with IL-6 instead of hs-CRP, and oxidized HDL and IL-6 were independently associated with composite CVD events. Findings resembled those from Cox proportional hazards modeling using time-varying covariates with HDL-C adjusted with IL-6. In conclusion, both oxidized HDL and apoB/apoA-I might be associated with CVD events in patients on prevalent HD, while associations of apoB/apoA-I with CVD events differed between models of apoB/apoA-I quartiles and 1-SD increases, and were influenced by IL-6.

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.

•

Haemodialyzed patients experience oxidative stress and systemic inflammation.

•

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

•

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

•

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

•

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

Modified Lipids and Lipoproteins in Chronic Kidney Disease: A New Class of Uremic Toxins

Chronic kidney disease (CKD) is associated with an enhanced oxidative stress and deep modifications in lipid and lipoprotein metabolism. First, many oxidized lipids accumulate in CKD and were shown to exert toxic effects on cells and tissues. These lipids are known to interfere with many cell functions and to be pro-apoptotic and pro-inflammatory, especially in the cardiovascular system. Some, like F2-isoprostanes, are directly correlated with CKD progression. Their accumulation, added to their noxious effects, rendered their nomination as uremic toxins credible. Similarly, lipoproteins are deeply altered by CKD modifications, either in their metabolism or composition. These impairments lead to impaired effects of HDL on their normal effectors and may strongly participate in accelerated atherosclerosis and failure of statins in end-stage renal disease patients. This review describes the impact of oxidized lipids and other modifications in the natural history of CKD and its complications. Moreover, this review focuses on the modifications of lipoproteins and their impact on the emergence of cardiovascular diseases in CKD as well as the appropriateness of considering them as actual mediators of uremic toxicity.

Asymmetric Dimethylarginine and Its Relation As a Biomarker in Nephrologic Diseases

It is encouraging to observe that a search for publications on "asymmetric dimethylarginine (ADMA)" in PubMed, as updated on June 2016, yielded >2500 items, 24 years after a splendid paper published by Vallance et al in which the authors proposed that ADMA accumulation could be a cardiovascular risk factor in chronic kidney diseases. ADMA is the endogenous inhibitor of nitric oxide synthase and is related to endothelial dysfunction, which plays an important role in vascular damage elicited by various cardiometabolic risk factors. Although current knowledge suggests that ADMA has critical central roles in renal diseases, there are still unexplained details. The present article aims to provide a review on ADMA and its relation as a biomarker in nephrologic diseases. We aimed to systematize articles in which ADMA levels were assessed in order to clarify its role in many diseases and establish its reference values in different populations.

The effect of pentoxifylline on oxidative stress in chronic kidney disease patients with erythropoiesis-stimulating agent hyporesponsiveness: Sub-study of the HERO trial

OBJECTIVE

Pentoxifylline has previously been shown to increase haemoglobin levels in patients with chronic kidney disease (CKD) and erythropoietin-stimulating agent (ESA)-hyporesponsive anaemia in the HERO multi-centre double-blind, randomized controlled trial. The present study evaluated the effects of pentoxifylline on oxidative stress in ESA-hyporesponsive CKD patients.

METHODS

This sub-study of the HERO trial compared 15 patients in the pentoxifylline arm (400 mg daily) and 17 in the matched placebo arm on oxidative stress markers: plasma total F2-isoprostanes, protein carbonyls, glutathione peroxidase (GPX), and superoxide dismutase (SOD) activities.

RESULTS

Pentoxifylline did not significantly alter total F2-isoprostanes (adjusted mean difference (MD) 35.01 pg/ml, P = 0.11), SOD activity (MD 0.82 U/ml, P = 0.07), GPX activity (MD -6.06 U/l, P = 0.09), or protein carbonyls (MD -0.04 nmol/mg, P = 0.52). Replicating results from the main study, pentoxifylline significantly increased haemoglobin concentration compared with controls (MD 7.2 g/l, P = 0.04).

CONCLUSIONS

Pentoxifylline did not alter oxidative stress biomarkers, suggesting that alternative mechanisms may be responsible for the agent's ability to augment haemoglobin levels in CKD patients with ESA-hyporesponsive anaemia.

Evaluation of oxidative stress in the anemia of dogs with chronic kidney disease

BACKGROUND

Anemia and systemic oxidative stress may occur in dogs with chronic kidney disease (CKD). Only scarce information regarding the intraerythrocytic redox status under these conditions is available at this time.

OBJECTIVE

The aim of this study was to evaluate the indicators of oxidative stress and intraerythrocytic antioxidant defense in dogs with anemia of CKD.

METHODS

Thirty dogs with CKD in stages 3 or 4 with nonregenerative anemia (HCT ≤ 37%) were compared to 20 healthy dogs. Complete blood count, reticulocyte %, blood smear evaluation, intraerythrocytic concentrations of total (GSHt), reduced (GSH), and oxidized glutathione (GSSH), and activities of glutathione peroxidase, glutathione reductase and superoxide dismutase (SOD), as well as plasma concentrations of thiobarbituric acid-reactive substances (TBAR) were determined.

RESULTS

Anemia of CKD dogs was nonregenerative (reticulocytes ≤ 0.2% with scarce anisocytosis and poikilocytosis). Intraerythrocytic GSSH and SOD, and plasma TBAR were higher in dogs with CKD. There was a positive correlation between the creatinine concentration and TBAR, and negative correlations between creatinine concentration and HCT, as well as between HCT and TBAR. In CKD dogs with a higher degree of anemia, SOD levels were higher and GSSH concentrations were lower. Despite the evidence of increased systemic oxidative stress, the compensatory response of SOD and the sustained intraerythrocytic concentrations of GSSH in CKD dogs with anemia indicated that the erythrocytes maintained the antioxidant defense.

CONCLUSIONS

There was no strong evidence that oxidative stress was associated with higher degrees of anemia in dogs with CKD.

Higher serum iron is associated with increased oxidant stress in HIV-infected men

BACKGROUND

F₂-isoprostanes (F₂-IsoP) are oxidant stress biomarkers that are higher in HIV-infected women than men. We explored whether the effect of hemoglobin (Hgb), serum iron, or anemia on F₂-IsoP is different between HIV-infected women and men.

METHODS

Plasma F₂-IsoP were quantified by gas chromatography/mass spectrometry; clinical and laboratory data were collected at enrollment or from the medical record. Multivariable linear regression was used to assess associations between F₂-IsoP and Hgb, anemia as a dichotomous variable, and serum iron with adjustment for age, sex, race, body mass index, CD4 lymphocyte count, self-reported current smoking status, and antiretroviral therapy.

RESULTS

Compared with men, women had lower Hgb [median: 12.7 (interquartile range: 11.8-13.9) vs. 14.9 (13.7-15.8) g/dL, P < 0.001], lower iron levels [75 (47-97) vs. 90 (69-121) µg/dL, P = 0.004], more anemia (29% vs. 10%, P < 0.001), and higher levels of F₂-IsoP [42 (32-62) vs. 36 (25-46) pg/mL, P < 0.001]. The relationship between iron and F₂-IsoP differed significantly between men and women (interaction P = 0.02). Men had a 21% (95% confidence interval: 8 to 36) increase in F₂-IsoP per interquartile increase in iron (P = 0.001), whereas no relationship was seen among women [-4% (-17 to 13, P = 0.65].

CONCLUSIONS

Although women have overall higher F₂-IsoP than men, a relationship between circulating F₂-IsoP and iron levels was observed in men but not in women with HIV infection. The association between female sex and higher F₂-IsoP is not explained by iron or Hgb levels because the association persists when controlling for these factors. The role of iron in oxidant stress and sex-specific differences among HIV-infected individuals require further study.

A randomized controlled trial evaluating the erythropoiesis stimulating agent sparing potential of a vitamin E-bonded polysulfone dialysis membrane

Background

Vitamin E (VE) bonded polysulfone dialysis membranes have putative erythropoiesis stimulating agent (ESA)-sparing and anti-inflammatory properties based on data from a small number of studies. We sought to investigate this in a large, prospective 12-month randomized controlled trial.

Methods

Two-hundred and sixty prevalent haemodialysis (HD) patients were randomized to dialysis with VE-bonded polysulfone membranes or non-VE-bonded equivalents. All ESA-dosing was performed by means of a computer-based anaemia management decision support system. Monthly data were used to calculate the ESA resistance index (ERI) and blood tests were performed at baseline, 6 and 12 months for measurement of C-reactive protein (CRP) levels.

Results

Of the 260 patients, 123 were randomized to dialysis with the VE-membrane and 12-month data was available for 220 patients. At the study population level, no beneficial effect of the VE membranes on the ERI or CRP levels was observed. Post hoc analyses indicated that there was a significant fall in ERI for patients with the highest baseline ESA resistance dialysed with the VE (9.28 [7.70–12.5] versus 7.70 [5.34–12.7] IU/week/kg/g/dL Hb, P = 0.01) but not the control membranes (9.45 [7.62–12.3] versus 8.14 [4.44–15.6] IU/week/kg/g/dL Hb, P = 0.41); this was not attributable to changes in CRP levels.

Conclusions

Wholesale switching of all chronic HD patients to dialysis with VE-bonded polysulfone membranes appears not to be associated with improvements in ESA-responsiveness or CRP. These membranes may have utility in patients with heightened ESA resistance.

The relationship between the antioxidant system and anaemia in haemodialysis patients

Anaemia and oxidative stress are common features of chronic kidney disease, and both are associated with an increase in morbidity and mortality. There is growing evidence, from experimental and clinical studies, that oxidative stress may be implicated in the pathogenesis of anaemia. This study investigated the relationship between total antioxidant capacity, anaemia and serum albumin levels in 127 non-diabetic patients requiring haemodialysis. Total serum antioxidant capacity levels were determined and were found to be significantly correlated with levels of haemoglobin, haematocrit, serum albumin, serum total protein, malondialdehyde (a product of lipid peroxidation), potassium, phosphorus and alanine transaminase. There was also a significant correlation between serum albumin levels and haemoglobin and haematocrit levels. In conclusion, total antioxidant capacity was found to be inversely correlated with malondialdehyde levels and positively correlated with haemoglobin and haematocrit levels in non-diabetic patients requiring haemodialysis. Patients with high serum albumin concentrations and high total antioxidant capacity may also have high (i.e. normal) levels of haemoglobin.

Oxidative stress, renal anemia, and its therapies: is there a link?

In chronic kidney disease, anemia and oxidative stress are common features and both are involved in increasing morbidity and mortality. However, their relationship is still a matter of debate. This article is a review of published data and our experience and is intended to debate the pro and contra arguments concerning renal anemia and its 2 main therapeutic approaches, that are, erythropoietin and intravenous iron supplementation, as additional causes of oxidative stress in end-stage renal disease patients. To date, it seems more likely that renal anemia itself is the main contributor, and intravenous iron further enhances oxidative stress associated with chronic kidney disease. Future randomized prospective trials, with "hard" clinical end-points, are needed to establish the real effect of biochemical pro-oxidative changes on patient's outcome.

Time course and dose response of alpha tocopherol on oxidative stress in haemodialysis patients

Background

Oxidative stress is associated with increased cardiovascular morbidity and mortality particularly in patients with end stage kidney disease. Although observational data from the general population has shown dietary antioxidant intake is associated with reduced cardiovascular morbidity and mortality, most clinical intervention trials have failed to support this relationship. This may be a consequence of not using an effective antioxidant dose and/or not investigating patients with elevated oxidative stress. The SPACE study, conducted in haemodialysis patients, reported that 800 IU/day of alpha tocopherol significantly reduced cardiovascular disease endpoints. A recent time course and dose response study conducted in hypercholesterolaemic patients that found 1600 IU/day of alpha tocopherol was an optimal dose. There is no such dose response data available for haemodialysis patients. Therefore the aim of this study is to investigate the effect of different doses of oral alpha tocopherol on oxidative stress in haemodialysis patients with elevated oxidative stress and the time taken to achieve this effect.

Methods

The study will consist of a time-course followed by a dose response study. In the time course study 20 haemodialysis patients with elevated oxidative stress will take either 1600 IU/day natural (RRR) alpha tocopherol for 20 weeks or placebo. Blood will be collected every two weeks and analysed for a marker of oxidative stress (plasma F₂-isoprostanes) and alpha tocopherol. The optimum time period to significantly decrease plasma F₂-isoprostanes will be determined from this study. In the dose response study 60 patients will be randomised to receive either placebo, 100, 200, 400, 800 or 1600 IU/day of natural (RRR) alpha tocopherol for a time period determined from the time course study. Blood will be collected at baseline and every two weeks and analysed for plasma F₂-isoprostanes and alpha tocopherol. It is hypothesised that doses ≥ 800 IU of vitamin E will be required to significantly decrease plasma F₂-isoprostanes.

Discussion

This study will determine the time and dose required for alpha tocopherol to significantly decrease oxidative stress in haemodialysis patients. Data will be used to plan a large randomised controlled trial to assess the effects of alpha tocopherol on cardiovascular outcomes in haemodialysis patients.

Trial Registration

ACTRN12609000608268