Oxidation of albumin is enhanced in the presence of uremic toxins

In vitro Removal of Protein-Bound Retention Solutes by Extracorporeal Blood Purification Procedures

INTRODUCTION

When the kidneys or liver fail, toxic metabolites accumulate in the patient's blood, causing cardiovascular and neurotoxic complications and increased mortality. Conventional membrane-based extracorporeal blood purification procedures cannot remove these toxins efficiently. The aim of this in vitro study was to determine whether commercial hemoperfusion adsorbers are suitable for removing protein-bound retention solutes from human plasma and whole blood as well as to compare the removal to conventional hemodialysis.

METHODS

For in vitro testing of the removal of protein-bound substances, whole blood and plasma were spiked with uremic retention solutes (homocysteine, hippuric acid, indoxyl sulfate, 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid) and the toxins of liver failure (bilirubin, cholic acid, tryptophan, phenol). Subsequently, the protein binding of each retention solute was determined. The adsorption characteristics of the hemoperfusion adsorbers, Jafron HA and Biosky MG, both approved for the adsorption of protein-bound uremic retention solutes and Cytosorb, an adsorber recommended for adsorption of cytokines, were tested by incubating them in spiked whole blood or plasma for 1 h. Subsequently, the adsorption characteristics of the adsorbers were tested in a dynamic system. For this purpose, a 6-h in vitro hemoperfusion treatment was compared with an equally long in vitro hemodialysis treatment.

RESULTS

Hippuric acid, homocysteine, indoxyl sulfate, and tryptophan were most effectively removed by hemodialysis. Bilirubin and cholic acid were removed best by hemoperfusion with Cytosorb. A treatment with Jafron HA and Biosky MG showed similar results for the adsorption of the tested retention solutes and were best for removing phenol. 3-Carboxy-4-methyl-5-propyl-2-furanpropionic acid could not be removed with any treatment method.

DISCUSSION/CONCLUSION

A combination of hemodialysis with hemoperfusion seems promising to improve the removal of some toxic metabolites in extracorporeal therapies. However, some very strongly protein-bound metabolites cannot be removed adequately with the adsorbers tested.

Cumulative postoperative change in serum albumin levels and organ failure after living-donor liver transplantation: A retrospective cohort analysis

Many studies have reported that hypoalbuminemia could be associated with organ failure after liver transplantation. However, most of them focused on serum albumin levels measured at specific time points and not on the trend of serum albumin change. We investigated whether a cumulative postoperative change in serum albumin level up to postoperative day (POD) 5 is related to organ failure in patients who underwent living-donor liver transplantation (LDLT). Data of adult recipients who underwent LDLT between January 2016 and December 2020 at a single tertiary hospital were reviewed (n = 399). After screening, three patients were excluded because of insufficient data. A cumulative change in serum albumin level was demonstrated using the area under the threshold (AUT, threshold = 3.0 g/dL) of the serum albumin curve up to POD 5. Based on the AUT, the patients were divided into a high-decrease group (n = 156) and a low-decrease group (n = 240). All analyses were conducted using 1:1 propensity score matching. The primary endpoint was the Sequential Organ Failure Assessment (SOFA) score on POD 5. The secondary endpoints were postoperative hospital stay and postoperative 90-day mortality. A total of 162 patients were included. The SOFA score on POD 5 was significantly higher in the High-decrease group compared with the Low-decrease group (5.2 ± 2.6 vs. 4.1 ± 2.3; mean difference: 1.1, 95% CI: 0.3 to 1.8; P = 0.005). However, the length of postoperative hospital stay (P = 0.661) and 90-day mortality (P = 0.497) did not differ between the groups. In conclusion, a cumulative postoperative change in serum albumin level up to POD 5 could help predict postoperative organ failure on POD 5 in patients who underwent LDLT.

The Interplay between Uremic Toxins and Albumin, Membrane Transporters and Drug Interaction

Uremic toxins are a heterogeneous group of molecules that accumulate in the body due to the progression of chronic kidney disease (CKD). These toxins are associated with kidney dysfunction and the development of comorbidities in patients with CKD, being only partially eliminated by dialysis therapies. Importantly, drugs used in clinical treatments may affect the levels of uremic toxins, their tissue disposition, and even their elimination through the interaction of both with proteins such as albumin and cell membrane transporters. In this context, protein-bound uremic toxins (PBUTs) are highlighted for their high affinity for albumin, the most abundant serum protein with multiple binding sites and an ability to interact with drugs. Membrane transporters mediate the cellular influx and efflux of various uremic toxins, which may also compete with drugs as substrates, and both may alter transporter activity or expression. Therefore, this review explores the interaction mechanisms between uremic toxins and albumin, as well as membrane transporters, considering their potential relationship with drugs used in clinical practice.

Preoperative hypoalbuminemia was associated with acute kidney injury in high-risk patients following non-cardiac surgery: a retrospective cohort study

Background

Acute kidney injury (AKI) is a common complication following non-cardiac surgery with adverse short- and long- term morbidity and mortality. Evidence shows that hypoalbuminemia is associated with increased AKI risk in patients with infectious diseases and cancer and following cardiac surgery and transplant surgery. However, little evidence is available on non-cardiac surgery population. Thus, we investigated the association between preoperative hypoalbuminemia and AKI following non-cardiac surgery.

Methods

We retrospectively assessed perioperative risk factors and preoperative serum albumin concentration in 729 consecutive adult patients who underwent non-cardiac surgery from July 1, 2017, to June 30, 2018. Each patient was categorized according to maximal Kidney Disease Improving Global Outcomes criteria based on creatinine changes and urine output within the first week after surgery. Multivariate Logistic regression models were used to analyze the association between preoperative hypoalbuminemia and postoperative AKI.

Results

Of 729 patients, 188 (25.8%) developed AKI. AKI incidence was higher in patients with preoperative serum albumin < 37.5 g/L than in those with preoperative serum albumin ≥37.5 g/L [35.9% (98/273) vs. 19.7% (90/456), P < 0.001]. Multivariate logistic regression analysis showed that preoperative serum albumin < 37.5 g/L (odds ratio 1.892; 95% confidence interval 1.238–2.891; P = 0.003) was independently associated with postoperative AKI. Patients with preoperative serum albumin < 37.5 g/L tended to have a higher but not significant ratio in AKI stage 2 (2.6% vs 1.1%, P = 0.144) and much higher ratio in AKI stage 3 (4.8% vs 0.7%, P < 0.001) than those with preoperative serum albumin ≥37.5 g/L. AKI patients had a higher in-hospital mortality rate [6.9% (13/188) vs. 0.2% (1/541), P < 0.001]. Kaplan-Meier analysis revealed that the cumulative survival rate decreased with increasing AKI severity (P < 0.001). Postoperative AKI was also associated with other worse outcomes, such as prolonged mechanical ventilation [53.4 (33.0, 73.8) vs 14.7 (11.1, 18.3) hours, P < 0.001], intensive care unit stay [4.0 (3.1, 4.9) vs 2.0 (1.8, 2.3) days, P < 0.001], postoperative hospital stay [17.8 (14.8, 20.9) vs 12.3 (11.3, 13.3) days, P < 0.001], and higher total cost [13,453 (8538, 20,228) vs 11,306 (6277, 16,400) dollars, P < 0.001].

Conclusions

Preoperative hypoalbuminemia was independently associated with AKI after non-cardiac surgery, and postoperative AKI was associated with poor outcomes.

Electronic supplementary material

The online version of this article (10.1186/s12871-019-0842-3) contains supplementary material, which is available to authorized users.

Early postoperative hypoalbuminemia is a risk factor for postoperative acute kidney injury following hip fracture surgery

INTRODUCTION

Acute kidney injury (AKI) is a common and serious complication after hip fracture surgery in older adults. Hypoalbuminemia is a known independent risk factor for AKI. However, few studies have investigated the relationship between early postoperative hypoalbuminemia and AKI after hip fracture surgery. Therefore, we sought to determine the incidence of and risk factors for AKI and the effects of early postoperative hypoalbuminemia on AKI incidence after surgery for hip fractures, especially intertrochanteric fractures of the proximal femur.

PATIENTS AND METHODS

In this retrospective cohort study from a single center, we reviewed the medical records of 481 consecutive patients (>60 years) who underwent surgery for intertrochanteric fracture of the proximal femur. Multiple logistic regression was performed to identify independent risk factors for AKI. After determining the cut-off value of the minimal level of postoperative serum albumin during the first two postoperative days, we divided the patients into two groups: group 1 included 251 patients whose minimal early postoperative serum albumin level was <2.9 g/dL during the first two postoperative days; and group 2 included 230 patients whose minimal early postoperative serum albumin level was ≥2.9 g/dL. The incidence of AKI was analyzed using inverse probability of treatment weighting (IPTW), propensity score matching (PSM), and propensity score matching weighting (PSMW) analyses.

RESULTS

The incidence of AKI, defined based on the Kidney Disease Improving Global Outcomes criteria, was 11.8% (n = 57). Chronic kidney disease and the minimal early postoperative serum albumin level <2.9 g/dL at any point during the first two postoperative days were independent risk factors for AKI. The IPTW, PSM, and PSMW analyses comparing the incidence of AKI between the two groups revealed that the minimal early postoperative serum albumin level <2.9 g/dL was significantly associated with AKI development (P < 0.001, P = 0.025, and P = 0.011, respectively).

CONCLUSION

The incidence of postoperative AKI was 11.8%. Our findings demonstrate that early postoperative hypoalbuminemia is an independent risk factor for AKI in patients undergoing surgery for intertrochanteric fracture of the proximal femur.

Association of preoperative hypoalbuminemia with postoperative acute kidney injury in patients undergoing brain tumor surgery: a retrospective study

OBJECTIVE Hypoalbuminemia is known to be independently associated with postoperative acute kidney injury (AKI). However, little is known about the association between the preoperative serum albumin level and postoperative AKI in patients undergoing brain tumor surgery. The authors investigated the incidence of AKI, impact of preoperative serum albumin level on postoperative AKI, and death in patients undergoing brain tumor surgery. METHODS The authors retrospectively reviewed the electronic medical records and laboratory results of 2363 patients who underwent brain tumor surgery between January 2008 and December 2014. Postoperative AKI was defined according to Kidney Disease: Improving Global Outcomes Definition and Staging (KDIGO). Multivariate logistic regression analysis was used to identify demographic, preoperative laboratory, and intraoperative factors associated with AKI development. Cox proportional hazards models were used to investigate the adjusted odds ratio and hazard ratio for the association between preoperative serum albumin level and outcome variables. RESULTS The incidence of AKI was 1.8% (n = 43) using KDIGO criteria. The incidence of AKI was higher in patients with a preoperative serum albumin level < 3.8 g/dl (3.5%) than in those with a preoperative serum albumin level ≥ 3.8 g/dl (1.2%, p < 0.001). The overall mortality was also higher in the former than in the latter group (5.0% vs 1.8%, p < 0.001). After inverse probability of treatment-weighting adjustment, a preoperative serum albumin level < 3.8 g/dl was also found to be associated with postoperative AKI (OR 1.981, 95% CI 1.022-3.841; p = 0.043) and death (HR 2.726, 95% CI 1.522-4.880; p = 0.001). CONCLUSIONS The authors' results demonstrated that a preoperative serum albumin level of < 3.8 g/dl was independently associated with AKI and mortality in patients undergoing brain tumor surgery.

Role of mitochondrial dysfunction in renal fibrosis promoted by hypochlorite-modified albumin in a remnant kidney model and protective effects of antioxidant peptide SS-31

Oxidative stress aggravates renal fibrosis, a pathway involved in almost all forms of chronic kidney disease (CKD). However, the underlying mechanism involved in the pathogenesis of renal oxidative stress has not been completely elucidated. In this study, we explored the role and mechanism of hypochlorite-modified albumin (HOCl-alb) in mediating oxidative stress and fibrotic response in a remnant-kidney rat model. Five-sixths nephrectomy (5/6 NX) was performed on the rats and then the animals were randomly assigned to intravenous treatment with either vehicle alone, or HOCl-rat serum albumin (RSA) in the presence or absence of SS-31 (administered intraperitoneally). A sham-operation control group was set up concurrently. Compared with the control group, 5/6 NX animals displayed marked mitochondrial (mt) dysfunction, as evidenced by decrease of mitochondrial membrane potential (MMP), ATP production, mtDNA copy number alterations and manganese superoxide dismutase (MnSOD) activity, release of cytochrome C (Cyto C) from mitochondria to the cytoplasm, and increase of mitochondrial reactive oxygen species in renal tissues. They also displayed increased levels of HOCl-alb in both plasma and renal tissues. These changes were accompanied by accumulation of extracellular matrix, worsened proteinuria, deteriorated renal function, and a marked increase of macrophage infiltration along with up-regulation of monocyte chemoattractant protein (MCP)-1 and transforming growth factor (TGF)-β1 expression. HOCl-alb challenge further exacerbated the above biological effects in 5/6 NX animals, but these adverse effects were prevented by administration of SS-31, a mitochondrial targeted antioxidant peptide. These data suggest that accumulation of HOCl-alb may promote renal inflammation and fibrosis, probably related to mitochondrial oxidative stress and dysfunction and that the mitochondrial targeted peptide SS-31 might be a novel therapy for renal fibrosis and chronic renal failure (CRF).

Overview of Albumin and Its Purification Methods

As the most frequent plasma protein, albumin constitutes more than 50% of the serum proteins in healthy individuals. It has a key role in oncotic pressure maintenance and it is known as a versatile protein carrier for transportation of various endogenous and exogenous ligands. Reduced amounts of albumin in the body will lead to different kinds of diseases such as hypovolemia and hypoproteinemia. It also has various indications in shocks, burns, cardiopulmonary bypass, acute liver failure and etc. Further applications in research consist of cell culture supplement, drug delivery carrier and protein/drug stabilizer. So, the demand for albumin increased annually worldwide. Due to different applications of albumin, many efforts have been accomplished to achieve albumin during a long period of time. In this review, an overview of serum albumin and different purification methods are summarized.

Hypoalbuminemia Within Two Postoperative Days Is an Independent Risk Factor for Acute Kidney Injury Following Living Donor Liver Transplantation: A Propensity Score Analysis of 998 Consecutive Patients

OBJECTIVE

Acute kidney injury is a known major complication of liver transplantation. Previous reports have shown that hypoalbuminemia is associated with an increased risk of acute kidney injury. However, little is known about the relationship between the early postoperative albumin level and acute kidney injury after living donor liver transplantation. The aim of this study was to identify the influence of the postoperative albumin level on acute kidney injury prevalence after living donor liver transplantation.

DESIGN

A retrospective analysis.

SETTING

A tertiary care university hospital.

PATIENTS

Nine hundred and ninety-eighty patients underwent living donor liver transplantation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We divided the enrolled patients into two groups: group 1 included patients whose postoperative albumin level was less than 3.0 g/dL (n = 522), and group 2 included patients with an albumin level greater than or equal to 3.0 g/dL (n = 476). The prevalence of acute kidney injury, major adverse cardiac events, hospital stay, ICU stay, 30-day mortality, and overall mortality was analyzed using inverse probability of treatment weighting and propensity-score matching (n = 249 pairs) analysis. The prevalence of acute kidney injury was higher in group 1 defined by both Acute Kidney Injury Network (after adjusting for inverse probability of treatment weighting [n = 364; 69.7%] and propensity-score matching [n = 152; 61.0%]) and Risk, Injury, Failure, Loss, and End-stage kidney disease criteria (after adjusting for inverse probability of treatment weighting [n = 419; 80.3%] and propensity-score matching [n = 190; 76.3%]). The overall mortality was higher in group 1 after adjusting for inverse probability of treatment weighting (n = 61; 11.7%) and propensity-score matching (n = 23; 9.2%). The hospital (p < 0.001) and ICU (p = 0.006) stays were significantly prolonged in group 1. Acute kidney injury was associated with ICU stay by the Acute Kidney Injury Network criteria (p = 0.034), and overall mortality was correlated with acute kidney injury by the Risk, Injury, Failure, Loss, and End-stage kidney disease criteria (p = 0.014).

CONCLUSIONS

Early postoperative hypoalbuminemia is an independent risk factor for acute kidney injury, and postoperative acute kidney injury is related to postoperative ICU stay and overall mortality after living donor liver transplantation.

Homocysteine in Chronic Kidney Disease

Hyperhomocysteinemia occurs in chronic- and end-stage kidney disease at the time when dialysis or transplant becomes indispensable for survival. Excessive accumulation of homocysteine (Hcy) aggravates conditions associated with imbalanced homeostasis and cellular redox thereby resulting in severe oxidative stress leading to oxidation of reduced free and protein-bound thiols. Thiol modifications such as N-homocysteinylation, sulfination, cysteinylation, glutathionylation, and sulfhydration control cellular responses that direct complex metabolic pathways. Although cysteinyl modifications are kept low, under Hcy-induced stress, thiol modifications persist thus surpassing cellular proteostasis. Here, we review mechanisms of redox regulation and show how cysteinyl modifications triggered by excess Hcy contribute development and progression of chronic kidney disease. We discuss different signaling events resulting from aberrant cysteinyl modification with a focus on transsulfuration.

Simultaneous determination of albumin and low-molecular-mass thiols in plasma by HPLC with UV detection

In this paper, we describe a simple and robust HPLC based method for determination of total low- and high-molecular-mass thiols, protein S-linked thiols and reduced albumin in plasma. The method is based on derivatization of analytes with 2-chloro-1-methylquinolinium tetrafluoroborate, separation and quantification by reversed-phase liquid chromatography followed by UV detection. Disulfides were converted to their thiol counterparts by reductive cleavage with tris(2-carboxyethyl)phosphine. Linearity in detector response for total thiols was observed over the range of 1-40 μmol L(-1) for Hcy and glutathione (GSH), 5-100 μmol L(-1) for Cys-Gly, 20-300 μmol L(-1) for Cys and 3.1-37.5 μmol L(-1) (0.2-2.4gL(-1)) for human serum albumin (HSA). For the protein S-bound forms these values were as follows: 0.5-30 μmol L(-1) for Hcy and GSH, 2.5-60 μmol L(-1) for Cys-Gly and 5-200 μmol L(-1) for Cys. The LOQs for total HSA, Cys, Hcy, Cys-Gly and GSH were 0.5, 0.2, 0.4, 0.3 and 0.4 μmol L(-1), respectively. The estimated validation parameters for all analytes are more than sufficient to allow the analytical method to be used for monitoring of the total and protein bound thiols as well as redox status of HSA in plasma.

HSA carbonylation with methylglyoxal and the binding/release of copper(ii) ions

HSA carbonylation in vitro (with MG) and in vivo (diabetes) leads to copper(ii) binding affinity decrease and copper(ii) release from copper–HSA complexes depending mainly on the redox state of the Cys34-SH group.

Clinical indications for the albumin use: still a controversial issue

Human serum albumin (HSA) is the most abundant circulating protein and accounts for about 70% of the plasma colloid osmotic pressure. Beside the well known capacity to act as plasma-expander, HSA is provided of many other properties which are unrelated to the regulation of fluid compartmentalization, including binding and transport of many endogenous and exogenous substances, antioxidant function, immuno-modulation, anti-inflammatory activity, and endothelial stabilization. Treatment (hepatorenal syndrome) or prevention (renal failure after spontaneous bacterial peritonitis and post-paracentesis circulatory dysfunction after large volume paracentesis) of severe clinical complications in patients with cirrhosis and fluid resuscitation in critically ill patients, when crystalloids and non-proteic colloids are not effective or contra-indicated, represents the major evidence-based clinical indications for HSA administration. However, a large proportion of HSA prescription is inappropriate. Despite the existence of solid data against a real benefit, HSA is still given for nutritional interventions or for correcting hypoalbuminemia per se (without hypovolemia). Other clinical uses for HSA administration not supported by definitive scientific evidence are long-term treatment of ascites, nephrotic syndrome, pancreatitis, abdominal surgery, acute distress respiratory syndrome, cerebral ischemia, and enteric diseases. HSA prescription should be not uncritically restricted. Enforcement of clinical practice recommendations has been shown to allow a more liberal use for indications supported by strong scientific data and to avoid the futile administration in settings where there is a lack of clinical evidence of efficacy. As a result, a more appropriate HSA use can be achieved maintaining the health care expenditure under control.

Human serum albumin: from bench to bedside

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.

Matrix-embedded endothelial cells are protected from the uremic milieu

BACKGROUND

Endothelial cells (ECs) embedded in 3D matrices [matrix-embedded endothelial cells (MEECs)] of denatured collagen implanted around vascular access anastomoses preserve luminal patency. MEEC implant efficacy depends on embedded EC health. As the uremic milieu inhibits proliferation and induces apoptosis of ECs, we examined whether uremia might impact MEECs.

METHODS

ECs grown on 2D gelatin-coated polystyrene tissue culture plates (gTCPS) or in MEEC were treated with sera pooled from 20 healthy control or uremic patients with end-stage renal disease. EC viability was examined using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide assay, cell counting and Trypan blue exclusion. Media conditioned (CM) with 2 and 3D-supported ECs were examined for its potential to inhibit vascular smooth muscle cell (vSMC) proliferation using (3)[H] thymidine incorporation and cyclin D1 expression. ECs grown on gTCPS were treated with uremic serum filtered through matrices to examine if matrices retain uremic toxins or whether EC effects were cell mediated.

RESULTS

Uremic serum significantly reduced viability and number of live, and increased dead ECs when grown on gTCPS, but not in MEECs. EC survival correlated with vSMC inhibition. While CM from ECs grown in gTCPS with uremic serum inhibited vSMC proliferation no better than uremic serum alone (22 versus 27%), MEEC CM inhibited vSMC proliferation by 47% (P = 0.0004). Cyclin D1 expression tracked with indices of vSMC proliferation. There was no significant difference in EC viability between EC treated with matrix-filtered or unfiltered uremic serum.

CONCLUSION

The viability, number and efficacy of MEECs were preserved in uremic serum compared to those of ECs on gTCPS. MEECs are protected from uremic toxicity, not from retention of uremic toxins by matrices, but likely from intrinsic changes in EC sensitivity to uremia. MEECs implanted at vascular access sites should inhibit neointimal hyperplasia in uremia. This study underscores the robustness of matrix embedding as a cell protectant, especially in hostile environments like uremia.

Hyperoncotic colloids and acute kidney injury: a meta-analysis of randomized trials

Introduction

It has been hypothesized that hyperoncotic colloids might contribute to acute kidney injury (AKI). However, the validity of this hypothesis remains unclear.

Methods

A meta-analysis was conducted of randomized controlled trials evaluating AKI after infusion of hyperoncotic albumin and hydroxyethyl starch (HES) solutions. Mortality was a secondary endpoint. Eligible trials were sought by multiple methods, and the pooled odds ratios (OR) for AKI and death and 95% confidence intervals (CI) were computed under a random effects model.

Results

Eleven randomized trials with a total of 1220 patients were included: 7 evaluating hyperoncotic albumin and 4 hyperoncotic HES. Clinical indications were ascites, surgery, sepsis and spontaneous bacterial peritonitis. Hyperoncotic albumin decreased the odds of AKI by 76% (OR, 0.24; CI, 0.12-0.48; P < 0.0001), while hyperoncotic HES increased those odds by 92% (OR, 1.92; CI, 1.31-2.81; P = 0.0008). Parallel effects on mortality were observed, with hyperoncotic albumin reducing the odds of death by 48% (OR, 0.52; CI, 0.28-0.95; P = 0.035) and hyperoncotic HES raising those odds by 41% (OR, 1.41; CI, 1.01-1.96; P = 0.043).

Conclusions

This meta-analysis does not support the hypothesis that hyperoncotic colloid solutions per se injure the kidney. Renal effects appear instead to be colloid-specific, with albumin displaying renoprotection and HES showing nephrotoxicity.

Oxidation of bovine serum albumin: identification of oxidation products and structural modifications

Albumin is an important plasma antioxidant protein, contributing to protecting mechanisms of cellular and regulatory long-lived proteins. The metal-catalyzed oxidation (MCO) of proteins plays an important role during oxidative stress. In this study, we examine the oxidative modification of albumin using an MCO in vitro system. Mass spectrometry, combined with off-line nano-liquid chromatography, was used to identify modifications in amino acid residues. We have found 106 different residues oxidatively damaged, being the main oxidized residues lysines, cysteines, arginines, prolines, histidines and tyrosines. Besides protein hydroxyl derivatives and oxygen additions, we detected other modifications such as deamidations, carbamylations and specific amino acid oxidative modifications. The oxidative damage preferentially affects particular subdomains of the protein at different time-points. Results suggest the oxidative damage occurs first in exposed regions near cysteine disulfide bridges with residues like methionine, tryptophan, lysine, arginine, tyrosine and proline appearing as oxidatively modified. The damage extended afterwards with further oxidation of cysteine residues involved in disulfide bridges and other residues like histidine, phenylalanine and aspartic acid. The time-course evaluation also shows the number of oxidized residues does not increase linearly, suggesting that oxidative unfolding of albumin occurs through a step-ladder mechanism.

Pharmaceutically important pre- and posttranslational modifications on human serum albumin

Recombinant technology allows engineering and production of proteins with desirable properties. Human serum albumin has been developed with recombinant technology, and thus plays an increasing role as a drug carrier in the clinical setting. Genetic variations usually occur on the surface of the protein, and do not impose significant effects on the conformation of albumin. However, binding of fatty acids by genetic variants is affected according to the location of the mutation. Albumin undergoes three major posttranslational modifications, namely, oxidation, glycation, and S-nitrosylation. This review gives an account of the different posttranslational modifications that should be taken into consideration when designing albumin mutant analogues with desirable pharmaceutical properties.

Diversity of protein carbonylation in allergic airway inflammation

Oxidative stress is involved in asthma. This study assessed the carbonylation of sputum proteins in 23 uncontrolled adult asthmatic patients and 23 healthy controls. Carbonylated proteins (68 kDa and 53 kDa) were elevated in asthmatics when compared to controls and the 68-kDa carbonylated protein was significantly correlated with sputum eosinophilia. The kinetics of protein carbonylation in bronchoalveolar lavage fluid (BALF) were then examined in a mouse ovalbumin-induced allergic inflammation model. It was found that the carbonylation of various BALF proteins did not uniformly occur after challenge. The appearance of the 53-kDa carbonylated protein was limited within 24 h, while carbonylation of 68-kDa protein peaked at 48 h and was associated with BALF eosinophilia. Thus, it was demonstrated that the 68-kDa and 53-kDa proteins, corresponding to albumin and alpha1-antitrypsin, respectively, were specifically carbonylated in allergic inflammation in humans and in mice and that eosinophils may play a role in mediating carbonylation of albumin.

The preparation of sustained release erythropoietin microparticle

PURPOSE

Protein microencapsulation in biodegradable polymers is a promising route to provide for sustained release. The erythropoietin (EPO) microparticles are using human serum albumin (HSA) and poly-L-lysine (PK) as the protection complex to increased EPO integrity, entrapped efficiency and active EPO release by w/o/w solvent evaporation techniques. The optimum formulation development process was also reported by using FITC-OVA as a model protein.

METHODS

The model protein FITC-ovalbumin and EPO are protected by human serum albumin and poly-L-lysine complex and encapsulated in 50:50 poly(DL-lactide-co-glycolide) by a w/o/w solvent evaporation method. Protein active integrity and degradation compound is measured by size-exclusion chromatography. Protein-loaded microparticle physical properties and in vitro active and degradation compounds release profile are characterized.

RESULTS

High active integrity protein loading efficiency and particle yield of EPO or OVA-HSA/PK-loaded PLG microparticles are successfully produced by a w/o/w solvent evaporation method. Varied protection protein complex formulations and encapsulation processes are investigated. The high OVA model protein loading efficiency (80.2%), FITC-OVA content (0.24 microg mg(-1)) and yield (72.4%) are obtained by adding 100 microg mL(-1) FITC-OVA complex with 10% HSA/0.05% PK (Mw 1.5-3 kD) in the initial solution to protect the model protein. In vitro release profiles show more active OVA release from HSA/PK OVA-loaded than OVA-loaded only microparticles and also the amount of degraded protein that comes out after 3 weeks incubated in the PBS medium for OVA-loaded only microparticles is observed. The same formulation and preparation process resulted in EPO loading efficiency (68.4%), EPO content (0.23 microg mg(-1)) and yield (76.1%) for HSA/PK EPO-loaded microparticles. In vitro release profiles show active EPO sustained release over 7 days. Using HSA/PK as carried in the primary emulsion of EPO-loaded microparticles resulted in less burst release% than EPO-loaded only microparticles.

Dialyzable uremic solutes contribute to enhanced oxidation of serum albumin in regular hemodialysis patients

BACKGROUND

Oxidative stress (OS) is reportedly enhanced in patients receiving regular hemodialysis (HD). However, the in vivo redox state of HD patients, particularly after HD sessions, remains unclear. This study aimed to clarify the influence of HD on OS using the albumin redox state as a marker.

METHOD

Blood samples of 8 regular HD patients were obtained during the course of study. The redox state of albumin was determined using high-performance liquid chromatography.

RESULTS

The mean fraction of reversibly oxidized albumin [f(HNA-1)] declined significantly over the course of the session and reached a minimum 4 h after the session had ended (pre-HD, 36.16 +/- 7.50%; 4 h after HD, 25.71 +/- 6.41%), then gradually rose to predialytic levels. The proportion of irreversibly oxidized albumin did not change significantly over time. Positive correlations were demonstrated between f(HNA-1) and uremic small solutes in each case.

CONCLUSION

Accumulation of dialyzable uremic solutes may contribute to OS in HD patients.

Oxidatively-modified and glycated proteins as candidate pro-inflammatory toxins in uremia and dialysis patients

End stage renal disease (ESRD) patients accumulate blood hallmarks of protein glycation and oxidation. It is now well established that these protein damage products may represent a heterogeneous class of uremic toxins with pro-inflammatory and pro-oxidant properties. These toxins could be directly involved in the pathogenesis of the inflammatory syndrome and vascular complications, which are mainly sustained by the uremic state and bioincompatibility of dialysis therapy. A key underlying event in the toxicity of these proteinaceous solutes has been identified in scavenger receptor-dependent recognition and elimination by inflammatory and endothelial cells, which once activated generate further and even more pronounced protein injuries by a self-feeding mechanism based on inflammation and oxidative stress-derived events. This review examines the literature and provides original information on the techniques for investigating proteinaceous pro-inflammatory toxins. We have also evaluated therapeutic - either pharmacological or dialytic - strategies proposed to alleviate the accumulation of these toxins and to constrain the inflammatory and oxidative burden of ESRD.

Carbonylated proteins in bronchoalveolar lavage of patients with sarcoidosis, pulmonary fibrosis associated with systemic sclerosis and idiopathic pulmonary fibrosis

Oxygen-derived free radicals produced by phagocytes have been postulated to contribute to lung tissue damage occurring during diffuse lung diseases (DLD). The two-dimensional electrophoretic (2-DE) analysis of bronchoalveolar lavage (BAL) protein composition revealed different protein profiles in sarcoidosis (S), idiopathic pulmonary fibrosis (IPF) and systemic sclerosis (SSc) with a significant increase of low molecular weight proteins in IPF. Some of these proteins are involved in antioxidant processes. The aims of this report were to analyse the oxidative stress occurring in patients with DLD through determination of BAL protein carbonyl content and to identify target proteins of oxidation by a proteomic approach (2-DE combined with immunoblotting with specific antibodies for carbonyl groups). Carbonylated proteins detected by enzyme-linked immunosorbent assay (ELISA) were increased in BAL of patients with S, IPF and SSc compared to healthy controls with a significant difference for S and IPF. The proteomic approach to the analysis of BAL revealed that protein carbonylation was a process involving specific carbonylation-sensitive proteins and that in IPF a greater number of proteins target of oxidation were present. In conclusion, to our knowledge, this is the first report providing a database of proteins target of oxidation in BAL of patients with sarcoidosis, idiopathic pulmonary fibrosis and systemic sclerosis.

Evaluation of oxidative stress measurements in obstructive sleep apnea syndrome

Assessment of reactive oxygen species (ROS) is highly important in neurodegenerative disorders and neuroleptic treatment. However, conflicting results have been reported, which may arise from methodological difficulties. Obstructive sleep apnea (OSA) syndrome with episodic hypoxia-reoxygenation is proposed as a human model for the investigation of ROS measurements. Despite a broad analytical approach comprising lipid peroxidation and amino acid oxidation products, oxidative DNA damage, and activity of the antioxidant defense, only plasma malondialdehyde (MDA) and urinary o,o'-dityrosine seemed to be appropriate, robust biomarkers of oxidative stress, which are also simple enough for routine clinical use. MDA concentrations correlated with a duration of nocturnal desaturation below 85% (r = 0.77, p<0.0005), and o,o'-dityrosine levels decreased after therapy (p<0.05) as a function of baseline concentrations (r = -0.61, p<0.05). Gender effects in ROS generation also have to be considered. At present, we recommend the application of several oxidative stress measurements at different time points, preferably involving plasma MDA and urinary o,o'-dityrosine.

Oxidative stress is enhanced in correlation with renal dysfunction: examination with the redox state of albumin

BACKGROUND

Cardiovascular disease is known to be the most important complication among patients with renal failure, and oxidative stress has been proposed to play a major role as the source of such complications. Human serum albumin (HSA) is composed of human mercaptoalbumin (HMA) with cysteine residues having reducing powers, of reversibly oxidized human non-mercaptoalbumin-1 (HNA-1), and strongly oxidized human non-mercaptoalbumin-2 (HNA-2).

METHODS

We used the "redox state of HSA" as a marker to investigate the current status of oxidative stress in predialysis patients with renal failure. The subjects were 55 nondialysis patients (31 males and 24 females) with chronic renal diseases, and having various degrees of renal function. The subjects' redox state of HSA was determined by a high-performance liquid chromatographic (HPLC) procedure, and the results presented in terms of the ratios between HNA-total(HNA-1 + HNA-2) and HNA-2.

RESULTS

The values for each fraction of HNA-total (f(HNA-total)) and f(HNA-2) were increased with a decrease of renal functions, and a significant positive correlation with serum creatinine (R= 0.529, P < 0.0001 and R= 0.618, P < 0.0001) was detected. Multiple (forward stepwise) regression analysis using f(HNA-total) and f(HNA-2) as the criterion variables was performed, and creatinine was adopted as significant explanatory variable in both equations.

CONCLUSION

We found that even before dialysis, oxidative stress was enhanced in correlation with the level of renal dysfunction among patients with chronic renal failure. In the future, antioxidant strategies should become part of treatment for predialysis renal failure.

Effect of Hemodiafiltration against Radical Stress in the Course of Blood Purification

The involvement of radical stress has been suggested as a cause for complications in patients on dialysis, such as arteriosclerosis, dialysis-related amyloidosis, etc. It has been reported that the increase in radical stress is not only seen in renal failure, but that its amplified effect is also seen in the process of blood purification. Our group has reported on the radical stress-reducing effect of HDF. We performed four types of blood purification (HD; on-line HDF; pre, on-line HDF; post, P/P HDF) in patients on maintenance dialysis using the polysulfone (APS) dialyzer. The change in radical related markers such as pentosidine (total, free) and CML (total, free), and the CTL/Cr ratio, and the hydroperoxide radicals were studied. In HDF (post, pre), the amplification rate of hydroperoxide radicals was significantly low, whereas the reduction rate of CTL/Cr ratio as index for hydroxy radicals was significantly higher in on-line HDF than in HD. Both the total CML and T-pentosidine increased in HD but showed a decrease in HDF. As HDF uses large amounts of replacement solution, the following effects can be expected: (a) suppression of the amplification of hydroperoxide radicals and suppression of the amplification of hydroxy radicals, and (b) suppression of fat oxidation by AGEs themselves. These antiradical stress effects are presumed to be exerted by effective removal of radical carrier protein, denatured protein, and complement protein in HDF, by dilution of radicals by massive use of replacement solution, and by the sequential reduction of the excitation and amplification effects.

No acute impact of haemodialysis treatment on free radical scavenging enzyme gene expression in white blood cells

OBJECTIVE

Oxidative stress has been implicated in the side-effects caused by haemodialysis (HD) treatment.

DESIGN

In the present study we have investigated whether gene expression of the enzymatic defence system provided by cellular glutathione peroxidase (GPx-1), phospholipid glutathione peroxidase (GPx-4), glutathione reductase (GSSG-R), glutathione synthethase (GSH-S), Cu/Zn-superoxide dismutase (SOD-1) and catalase (CAT) is affected by HD. The GPx-1, GPx-4, GSSG-R, GSH-S, SOD-1 and CAT mRNA were determined in white blood cells by quantitative reverse transcriptase-polymerase chain reaction with the LightCycler instrument and transcription elongation factor-2 as reference gene at the start (SD) and immediately after (ED) dialysis treatment (n = 36). In a subgroup (n = 10), messenger RNA (mRNA) expression was determined hourly during a 5 h HD.

RESULTS

The expression of GPx-1, GPx-4, GSSG-R, GSH-S, SOD-1 and CAT mRNA was not affected by a single HD treatment. All mRNAs were significantly (P < 0.05) increased in HD patients [median (16. percentiles (perc.); 84. perc.)]: GPx-1: 2.18 (0.89; 3.23); GPx-4: 0.41 (0.26; 0.74); GSSG-R: 0.04 (0.02; 0.10); GSH-S: 0.04 (0.02; 0.08); SOD-1: 0.32 (0.20; 0.62); CAT: 0.12 (0.06; 0.18) when compared with healthy blood donors (GPx-1: 0.91 (0.60; 1.44); GPx-4: 0.27 (0.16; 0.43); GSSG-R: 0.02 (0.01; 0.02); GSH-S: 0.02 (0.02; 0.04); SOD-1: 0.15 (0.10; 0.18); CAT: 0.07 (0.04; 0.16).

CONCLUSIONS

These results show that the HD procedure does not acutely affect the antioxidant defence system on the gene level but suggest that the chronic stress caused by uraemia and/or HD may cause gene induction of the enzymatic defence system.

Evolution of oxidative stress and inflammation during hemodialysis and their contribution to cardiovascular disease

End-stage renal disease patients have increased cardiovascular morbidity and mortality. These patients have many unique risk factors, such as an accumulation of uremic toxins, electrolyte imbalances, metabolic disturbances, anemia, chronic inflammation, and thrombogenic disturbances. Oxidative stress has been implicated in many of these disturbances. This review will focus on some of the factors that may accelerate cardiovascular disease in uremic patients, with an emphasis on mechanisms and interactions of various components of oxidative stress and inflammation. Understanding the mechanisms of these pathways may be useful in developing effective prevention and treatment strategies.

Scavenging property of three cresol isomers against H2O2, hypochlorite, superoxide and hydroxyl radicals

Formocresol has long been used for pulpotomy of primary teeth and as an intracanal medicament. Little is known, however, about the pharmacological effect of tricresols. This study showed that three cresol isomers, o-cresol, m-cresol and p-cresol, are H2O2 scavengers with a 50% inhibitory concentration (IC50) of 502, 6.7 and 10.16 microM, respectively. o-, m- and p-cresol were also shown to be effective scavengers of superoxide radicals generated by xanthine/xanthine oxidase with an IC50 of 282, 153 and > 4000 microM, respectively, as analyzed by luminometer. o-, m- and p-cresol showed protective effects on the DNA breaks generated by H2O2/FeCl2 and FeCl3/ascorbate/H2O2 systems at concentrations ranging from 70 microM to 1.43 mM, o-, m- and p-cresol also showed differential protective effects against DNA breaks induced by 0.17% NaOCl with 100% inhibitory concentration (IC100) of about 10, 1 and 10 mM, respectively. In addition, reaction with 3% H2O2 and 0.17% NaOCl completely prevented NaOCl-induced DNA breaks. The results indicate that the three cresol isomers are effective ROS scavengers and may prevent ROS induced damage when used as pulpotomy agents or as intracanal medicaments. Owing to the difference in the position of the functional hydroxyl group in the three cresol isomers, m-cresol is the most effective ROS scavenger. Concomitant use of H2O2 for root canal irrigation may diminish both the tissue dissolving capacity of NaOCl and NaOCl-induced DNA damage.

Pharmaceutical strategies utilizing recombinant human serum albumin

Gene manipulation techniques open up the possibility of making recombinant human serum albumin (rHSA) or mutants with desirable therapeutic properties and for protein fusion products. rHSA can serve as a carrier in synthetic heme protein, thus reversibly carrying oxygen. Myristoylation of insulin results in a prolonged half-life because of self aggregation and increased albumin binding. Preferential albumin uptake by tumor cells serves as the basis for albumin-anticancer drug conjugate formulation. Furthermore, drug targeting can be achieved by incorporating drugs into albumin microspheres whereas liver targeting can be achieved by conjugating drug with galactosylated or mannosylated albumin. Microspheres and nanoparticles of different sizes can, with or without drugs and/or radioisotopes, be used for drug delivery or diagnostic purposes. In vivo implantation of albumin fusion protein expressing cells encapsulated in HSA-alginate coated beads showed promising results compared to organoids in rats. Chimeric peptide strategy with cationized albumin as the transport can deliver drugs via receptor mediated transcytosis through the blood brain barrier. Gene bearing, albumin microbubbles containing ultrasound contrast agents can non-invasively deliver gene after destruction by ultrasound. Various site-directed mutants of HSA can be tailor made depending on the application required.

Albumin loss in on-line hemodiafiltration

BACKGROUND

Based on the increased hydraulic permeability of the new high permeability polyethersulfone membrane, DIAPES HF-800, we investigated the kinetics and handling of albumin in high volume on-line hemodiafiltration (HDF).

METHODS

Seven patients on predilutional HDF were studied in two consecutive sessions. Blood flow rate and transmembrane pressure were continuously monitored. Spent dialysate was spilled at 20 ml/h every hour. Albumin was measured in blood and dialysate by immunonephelometry. Albumin and proteins adsorbed onto the dialyzer membrane were eluted after treatment with Triton X. Ultrafiltrates collected at 1 and 2 hours of treatment were pooled from different patients and incubated for 24 hours at 37 degrees C with bovine serum albumin (BSA). Total sulphydryl groups were evaluated using Ellmann's reagent [5, 5'-dithio-bis(2-nitrobenzoic acid)].

RESULTS

In all 7 patients, the total loss of albumin was 3.99 +/- 1.81 g, ranging between 1.09 and 6.82 g/session. Most albumin loss occurred in the first 60 min of pre-dilutional hemodiafiltration (1.92+0.83 g). There was no correlation between transmembrane pressure, urea clearance and the loss of albumin. Plasma water urea clearance values were stable over the treatment (234 +/- 14.3 ml/min). Plasma albumin concentration did not decrease during HDF sessions. Albumin adsorbed onto the dialyzers was 0.7 +/- 1.6 mg but the total amount of adsorbed proteins was much higher (130 + 90 mg). In addition, the ultrafiltrate collected during HDF sessions was able to induce oxidation of bovine serum albumin as measured by total protein sulfhydryl groups: bovine serum albumin incubated in the presence of ultrafiltrate collected at 1 hour had a sulfhydryl loss of 56.3 +/- 5.7% (p < 0.0001 vs control), and bovine serum albumin incubated with ultrafiltrate collected at 2 hours had a loss of 67.5 +/- 3.8% (p < 0.003 vs control).

CONCLUSION

The present study shows the high inter- and intra-patient variability of transmembrane passage of albumin in chronically uremic patients undergoing pre-dilutional HDF. Factors involved do not seem to be correlated to transmembrane pressure but rather to an interaction with the polymer surface. Albumin adsorption was minimal and was significantly lower than that of other plasma proteins. Albumin loss during HDF seemed to have no acute impact on plasma albumin. In addition, we demonstrated the presence of prooxidative compounds able to oxidize albumin, of which extracorporeal removal by HDF procedure could be beneficial for HD patients.