Plasma Protein Carbonylation in Haemodialysed Patients: Focus on Diabetes and Gender

Supplemental ferulic acid does not affect metabolic markers and improves some oxidative damage parameters in diabetic rats

This study investigated the differences in health outcomes associated with ferulic acid (FA) supplementation in animals before the induction of diabetes with streptozotocin (STZ) treatment and post-STZ treatment. 18 male Wistar rats were equally distributed into three groups: groups 1 and 2 received FA (50 mg/kg body weight) supplementation one week before STZ treatment (60 mg/kg body weight, intraperitoneal) and one week after STZ treatment, respectively; group 3 received STZ without FA supplementation. FA supplementation was continued for 12 weeks after STZ treatment. The results indicated no difference in glucose and lipid profile with FA supplementation. However, FA supplementation reduced lipid and protein oxidative damage in the heart, liver and pancreas and increased glutathione in the pancreas. The results indicate that while oxidative damages were positively affected by FA, it was not sufficient to improve metabolic markers of diabetes.

A cross-sectional study to correlate antioxidant enzymes, oxidative stress and inflammation with prevalence of hypertension

AIMS

Hypertension a multifactorial consequence of environmental factors, life style and genetics is the well-recognized risk factor contributing to coronary heart diseases. The antioxidant imbalance, excessive reactive oxygen species (ROS) leads to oxidative stress which is pivotal in progression of hypertension. The present study aims to understand the complex interaction between oxidative stress, inflammation and antioxidant system which is crucial to maintain cellular homeostasis which further can exaggerate hypertension pathophysiology.

MATERIALS AND METHODS

The metabolic profile of hypertensive and normotensive subjects from Malwa region, Punjab was compared by estimating lipid profile, cardiac, hepatic and renal markers. The oxidative stress markers (protein carbonyls and lipid peroxidation), inflammatory markers (Nitric oxide, Myeloperoxidase and advanced oxygen protein products), and antioxidant enzymes (Superoxide Dismutase, Catalase, and Total Antioxidant Capacity) were analyzed.

KEY FINDINGS

It is observed that the metabolic markers are altered in hypertensive subjects which further these subjects showed increased oxidative, inflammatory profile and compromised antioxidant status when compared with normotensive subjects. Co-relation analysis validated the involvement of inflammation and oxidative stress in impaired endothelial function and vital organ damage.

SIGNIFICANCE OF STUDY

These markers may act as early indicators of hypertension which usually do not show any physical symptoms, thus can be diagnosed and treated at the earliest. The current study suggests that disturbed homeostasis, a consequence of altered interaction between antioxidant system and inflammatory events raises the oxidative stress levels which eventually leads to hypertension and associated complications. These indicators can serve as early indicators of future chronic complications of hypertension.

Head-to-Head Comparison of Oxidative Stress Biomarkers for All-Cause Mortality in Hemodialysis Patients

Oxidative stress (OS) presents even in the early chronic kidney disease (CKD) stage and is exacerbated in patients with end-stage renal disease (ESRD) undergoing maintenance hemodialysis (MHD). There is still a debate over the association between oxidative stress and mortality. Our study aims to compare head-to-head the prognostic value of different oxidative markers for all-cause mortality in hemodialysis (HD) patients. We thus enrolled 347 patients on HD in this prospective study. Four OS biomarkers were measured (carbonyl proteins, myeloperoxidase (MPO), advanced oxidation protein products (AOPPs), and oxidized low-density lipoprotein (ox-LDL)). During the 60-month follow-up period, 9 patients have been lost to follow-up and 168 (48.4%) patients died. Concerning the oxidative stress (ox-stress) byproducts, carbonyl proteins were lower in survivors (105.40 ng/mL (IQR 81.30−147.85) versus 129.65 ng/mL (IQR 93.20−180.33); p < 0.001), with similar results for male patients (103.70 ng/mL (IQR 76.90−153.33) versus 134.55 ng/mL (IQR 93.95−178.68); p = 0.0014). However, there are no significant differences in MPO, AOPP, and ox-LDL between the two groups. Kaplan−Meier survival analysis indicated that patients in the higher carbonyl proteins concentration (>117.85 ng/mL group) had a significantly lower survival rate (log-rank test, p < 0.001). Univariate Cox regression analysis showed a positive correlation between carbonyl proteins and all-cause mortality in the higher and lower halves. Even after adjustment for conventional risk factors, it remained a statistically significant predictor of an increased risk of death in MHD. Univariate Cox regression analysis of MPO showed that continuous MPO and Log MPO were significantly associated with all-cause mortality, except for binary MPO (divided according to the median of MPO). Multivariate Cox analysis for MPO showed that the mortality prediction remains significant after adjusting for multiple factors. In conclusion, not all ox-stress biomarkers predict all-cause mortality in HD patients to a similar extent. In the present study, carbonyl proteins and MPO are independent predictors of all-cause mortality in HD patients, whereas AOPPs and oxLDL are clearly not associated with all-cause mortality in HD patients.

Blood Thiol Redox State in Chronic Kidney Disease

Thiols (sulfhydryl groups) are effective antioxidants that can preserve the correct structure of proteins, and can protect cells and tissues from damage induced by oxidative stress. Abnormal levels of thiols have been measured in the blood of patients with moderate-to-severe chronic kidney disease (CKD) compared to healthy subjects, as well as in end-stage renal disease (ESRD) patients on haemodialysis or peritoneal dialysis. The levels of protein thiols (a measure of the endogenous antioxidant capacity inversely related to protein oxidation) and S-thiolated proteins (mixed disulphides of protein thiols and low molecular mass thiols), and the protein thiolation index (the molar ratio of the S-thiolated proteins to free protein thiols in plasma) have been investigated in the plasma or red blood cells of CKD and ESRD patients as possible biomarkers of oxidative stress. This type of minimally invasive analysis provides valuable information on the redox status of the less-easily accessible tissues and organs, and of the whole organism. This review provides an overview of reversible modifications in protein thiols in the setting of CKD and renal replacement therapy. The evidence suggests that protein thiols, S-thiolated proteins, and the protein thiolation index are promising biomarkers of reversible oxidative stress that could be included in the routine monitoring of CKD and ESRD patients.

Effect of Normobaric Hypoxia on Alterations in Redox Homeostasis, Nitrosative Stress, Inflammation, and Lysosomal Function following Acute Physical Exercise

Hypoxia is a recognized inducer of oxidative stress during prolonged physical activity. Nevertheless, previous studies have not systematically examined the effects of normoxia and hypoxia during acute physical exercise. The study is aimed at evaluating the relationship between enzymatic and nonenzymatic antioxidant barrier, total antioxidant/oxidant status, oxidative and nitrosative damage, inflammation, and lysosomal function in different acute exercise protocols under normoxia and hypoxia. Fifteen competitive athletes were recruited for the study. They were subjected to two types of acute cycling exercise with different intensities and durations: graded exercise until exhaustion (GE) and simulated 30 km individual time trial (TT). Both exercise protocols were performed under normoxic and hypoxic ( $\text{Fi}{\text{O}}_2=16.5\%$ ) conditions. The number of subjects was determined based on our previous experiment, assuming the test $\text{power}=0.8$ and $\alpha =0.05$ . We demonstrated enhanced enzymatic antioxidant systems during hypoxic exercise (GE: ↑ catalase (CAT), ↑ superoxide dismutase; TT: ↑ CAT) with a concomitant decrease in plasma reduced glutathione. In athletes exercising in hypoxia, redox status was shifted in favor of oxidation reactions (GE: ↑ total oxidant status, ↓ redox ratio), leading to increased oxidation/nitration of proteins (GE: ↑ advanced oxidation protein products (AOPP), ↑ ischemia-modified albumin, ↑ 3-nitrotyrosine, ↑ S-nitrosothiols; TT: ↑ AOPP) and lipids (GE: ↑ malondialdehyde). Concentrations of nitric oxide and its metabolites (peroxynitrite) were significantly higher in the plasma of hypoxic exercisers with an associated increase in inflammatory mediators (GE: ↑ myeloperoxidase, ↑ tumor necrosis factor-alpha) and lysosomal exoglycosidase activity (GE: ↑ N-acetyl-β-hexosaminidase, ↑ β-glucuronidase). Our study indicates that even a single intensive exercise session disrupts the antioxidant barrier and leads to increased oxidative and nitrosative damage at the systemic level. High-intensity exercise until exhaustion (GE) alters redox homeostasis more than the less intense exercise (TT, near the anaerobic threshold) of longer duration ( $20.2\pm 1.9$  min vs. $61.1\pm 5.4$  min—normoxia; $18.0\pm 1.9$  min vs. $63.7\pm 3.0$  min—hypoxia), while hypoxia significantly exacerbates oxidative stress, inflammation, and lysosomal dysfunction in athletic subjects.

Plasma Protein Carbonyls as Biomarkers of Oxidative Stress in Chronic Kidney Disease, Dialysis, and Transplantation

Accumulating evidence indicates that oxidative stress plays a role in the pathophysiology of chronic kidney disease (CKD) and its progression; during renal replacement therapy, oxidative stress-derived oxidative damage also contributes to the development of CKD systemic complications, such as cardiovascular disease, hypertension, atherosclerosis, inflammation, anaemia, and impaired host defence. The main mechanism underlying these events is the retention of uremic toxins, which act as a substrate for oxidative processes and elicit the activation of inflammatory pathways targeting endothelial and immune cells. Due to the growing worldwide spread of CKD, there is an overwhelming need to find oxidative damage biomarkers that are easy to measure in biological fluids of subjects with CKD and patients undergoing renal replacement therapy (haemodialysis, peritoneal dialysis, and kidney transplantation), in order to overcome limitations of invasive monitoring of CKD progression. Several studies investigated biomarkers of protein oxidative damage in CKD, including plasma protein carbonyls (PCO), the most frequently used biomarker of protein damage. This review provides an up-to-date overview on advances concerning the correlation between plasma protein carbonylation in CKD progression (from stage 1 to stage 5) and the possibility that haemodialysis, peritoneal dialysis, and kidney transplantation improve plasma PCO levels. Despite the fact that the role of plasma PCO in CKD is often underestimated in clinical practice, emerging evidence highlights that plasma PCO can serve as good biomarkers of oxidative stress in CKD and substitutive therapies. Whether plasma PCO levels merely serve as biomarkers of CKD-related oxidative stress or whether they are associated with the pathogenesis of CKD complications deserves further evaluation.

Serum levels of protein carbonyl, a marker of oxidative stress, are associated with overhydration, sarcopenia and mortality in hemodialysis patients

Background

Increased oxidative stress in end-stage renal disease is regarded as one of the important mechanisms in the atherosclerosis and muscle wasting. However, studies examining the clinical significance of oxidative stress by direct measurement of these markers and its association with volume status and sarcopenia are limited.

Methods

A follow-up cross-sectional study was performed in stable hemodialysis (HD) patients and serum protein carbonyl levels were measured as a biomarker of oxidative stress. Additionally, multi-frequency body composition analysis, handgrip strength (HGS) and nutritional assessments were performed at baseline.

Results

Eighty-eight patients undergoing HD were included and 30 (34.1%) patients died during a mean follow-up of 5.2 years. The mean patient age was 60.6 ± 13.5 years, and the mean HD duration was 50.8 ± 41.3 months. In total, 16 patients (18.2%) were overhydrated, 49 (55.7%) had low HGS and 36 (40.9%) had low muscle mass. Serum protein carbonyl levels were associated with serum levels of albumin, prealbumin and transferrin, hydration status and low HGS. Overhydration (odds ratio [OR] 7.01, 95% CI 1.77–27.79, p = 0.006), prealbumin (OR 0.91, 95% CI 0.83–0.99, p = 0.030), subjective global assessment (OR 3.52, 95% CI 1.08–11.46, p = 0.037) and sarcopenia (OR 3.41, 95% CI 1.02–11.32, p = 0.046) were significantly related to increased serum protein carbonyl levels. Multivariate analysis showed that the serum levels of protein carbonyl (Hazard ratio [HR] 2.37, 95% CI 1.02–5.55, p = 0.036), albumin (HR 0.17, 95% CI 0.06–0.46, p = 0.003), prealbumin (HR 0.86, 95% CI 0.80–0.92, p = 0.001), overhydration (HR 2.31, 95% CI 1.26–8.71, p = 0.015) and sarcopenia (HR 2.72, 95% CI 1.11–6.63, p = 0.028) were independent determinants of all-cause mortality.

Conclusions

Serum protein carbonyl was significantly associated with overhydration, nutritional status and sarcopenia, and could be a new predictor of mortality in patients undergoing HD.

Visualization of oxidative stress-induced carbonylation in live mammalian cells

Oxidative stress (OS) is associated with a wide variety of diseases and disorders. Detection of oxidative stress in living systems typically relies on fluorescent probes for reactive oxygen species (ROS), which is challenging because of their short life span and high reactivity. Oxidative damage caused by OS produces a more stable signal, but these biomarkers are usually detected using techniques that are not compatible with live cells. OS-induced biomolecule carbonylation is a stable modification that also possesses a chemically reactive functional group, and its detection typically employs a chemical reaction with a hydrazine-containing probe within the process. These hydrazone-forming reactions require strong acid catalysis or nucleophilic catalysis with an aromatic amine when performed on isolated biomaterial or on fixed cells. In live cells, however, hydrazone-forming reactions are surprisingly facile. Fluorophores possessing hydrazine or hydrazide functional groups can undergo reaction with carbonylated biomolecules in live cells, and these products can be observed using fluorescence microscopy. In this chapter, standard methods for detection of biomolecule carbonylation in cell lysate and in intact cells are enumerated. Protocols for fluorescently labeling biomolecule carbonylation in live cells are provided for commercially available fluorophores. Also described is a one-step protocol that employs one of the hydrazine-modified fluorophores developed in our lab, which are designed to be live-cell compatible and to undergo a spectral change upon hydrazone formation. Finally, a procedure for observing both biomolecule carbonylation and ROS production simultaneously is provided.

Proatherogenic Importance of Carbamylation-induced Protein Damage and Type 2 Diabetes Mellitus: A Systematic Review

INTRODUCTION & BACKGROUND

Protein carbamylation is a non-enzymatic and irreversible posttranslational process. It affects functions of numerous enzymes, hormones and receptors playing several roles in diabetes pathogenesis by changing their native structures. Detrimental consequences of oxidative protein damage comprise, but are not limited to glyoxidation, lipoxidation and carbonylation reactions. Since the carbamylated plasma proteins are strongly related to the glycemic control parameters of diabetes, they may have an additive value and emerge as potential biomarkers for the follow up, prognosis and treatment of diabetes mellitus.

METHODS & RESULTS

To conduct our systematic review, we used PubMed and Semantic Scholar, and used 'Protein carbamylation and diabetes' and 'Protein carbamylation and atherosclerosis' as keywords and looked into about five hundred manuscripts. Manuscripts that are not in English were excluded as well as manuscripts that did not mention carbamylation to maintain the focus of the present article. Similar to glycation, carbamylation is able to alter functions of plasma proteins and their interactions with endothelial cells and has been shown to be involved in the development of atherosclerosis.

CONCLUSION

At this stage, it seems clear that protein carbamylation leads to worse clinical outcomes. To improve patient care, but maybe more importantly to improve healthcare-prevention, we believe the next stage involves understanding how exactly protein carbamylation leads to worse outcomes and when and in what group of people anti-carbamylation therapies must be employed.

Protein Carbonyl Content Is a Predictive Biomarker of Eccentric Left Ventricular Hypertrophy in Hemodialysis Patients

High prevalence of left ventricular hypertrophy (LVH) and elevated oxidative stress are associated with poor outcomes in chronic hemodialysis patients. Abnormal left ventriculаr geomеtry and different geometric patterns play an important role as well. Our study analyzed the role of oxidative stress on myocardial remodeling in these patients. Plasma malondialdehyde (MDA), protein carbonyl (PC) content, and total antioxidative capacity (TAC) were investigated in 104 hemodialysis patients together with transthoracic echocardiography. Compared to patients with normal ventricular geometry, patients with LVH had increased MDA and PC plasma concentration. Multivariate analysis demonstrated that protein carbonyls, as biomarkers of oxidative protein modification, were an independent predictor of eccentric hypertrophy (eLVH), including higher LV end-diastolic diameter and LV end-diastolic volume, (β = 0.32 and β = 0.28, p < 0.001 for both). The incidence of eLVH increased progressively from the lowest to the highest baseline PC tertile (p < 0.001 for the trend) and the subjects in the former group showed a 76% greater risk of developing eLVH compared to their counterparts. After further adjustment for the potential mediators, PCs carried eLVH odds (95% confidence interval (CI)) of 1.256 (0.998-1.514), per standard deviation increase. High plasma protein carbonyls levels are a significant independent predictor of eccentric LVH in chronic hemodialysis patients.

Advanced oxidation protein products in nondiabetic end stage renal disease patients on maintenance haemodialysis

In chronic kidney disease (CKD), the impairment of the excretory function leads to elevation in the blood concentrations of urea, creatinine, and various protein metabolic products. Advanced oxidation protein products (AOPP), along with protein carbonyls, protein-bound di-tyrosines and S-thiolated proteins, are considered biomarkers of oxidative stress in end-stage renal disease (ESRD) patients on maintenance haemodialysis (HD). In this study, we evaluated the correlations between plasma levels of AOPP (measured by size exclusion/gel filtration high performance liquid chromatography) and those of protein-bound di-tyrosines, protein carbonyls, albumin and fibrinogen in 50 nondiabetic ESRD patients on maintenance HD. Considering that AOPP could represent the bridge between oxidative stress and inflammation, having been identified as proinflammatory mediators, we also evaluated the association between AOPP levels, C-reactive protein concentration and white blood cells count. Finally, we assessed the associations between plasma level of AOPP and serum concentrations of creatinine and urea, both of which showed a strong dependence on the chronological age of haemodialysed patients. Taken together, our results confirm the robust relationship between uraemia and oxidative stress, especially when measured as biomarkers of severe protein oxidative damage (e.g. plasma AOPP).

Oxidative Status before and after Renal Replacement Therapy: Differences between Conventional High Flux Hemodialysis and on-Line Hemodiafiltration

Hemodialysis patients experience high oxidative stress because of systemic inflammation and depletion of antioxidants. Little is known about the global oxidative status during dialysis or whether it is linked to the type of dialysis. We investigated the oxidative status before (pre-) and after (post-) one dialysis session in patients subjected to high-flux dialysis (HFD) or on-line hemodiafiltration (OL-HDF). We analyzed carbonyls, oxidized LDL (oxLDL), 8-hydroxy-2′-deoxyguanosine, and xanthine oxidase (XOD) activity as oxidative markers, and total antioxidant capacity (TAC), catalase, and superoxide dismutase activities as measures of antioxidant defense. Indices of oxidative damage (OxyScore) and antioxidant defense (AntioxyScore) were computed and combined into a global DialysisOxyScore. Both dialysis modalities cleared all markers (p < 0.01) except carbonyls, which were unchanged, and oxLDL, which increased post-dialysis (p < 0.01). OxyScore increased post-dialysis (p < 0.001), whereas AntioxyScore decreased (p < 0.001). XOD and catalase activities decreased post-dialysis after OL-HDF (p < 0.01), and catalase activity was higher after OL-HDF than after HFD (p < 0.05). TAC decreased in both dialysis modalities (p < 0.01), but remained higher in OL-HDF than in HFD post-dialysis (p < 0.05), resulting in a lower overall DialysisOxyScore (p < 0.05). Thus, patients on OL-HDF maintain higher levels of antioxidant defense, which might balance the elevated oxidative stress during dialysis, although further longitudinal studies are needed.