Identification and characterization of oxidized human serum albumin

Quantitation of oxidized and reduced albumin in mammals. An intriguing analytical question

Oxidized albumin is considered a short-term biomarker of oxidative stress and its measurement in blood contributes to evaluate the impact of diseases, drugs, dialytic treatments, physical activity, environmental contaminants etc. on the red-ox balance of humans as well as of other mammalians. Nevertheless, the most common methods for quantifying the oxidized and reduced albumins are costly and time-consuming. Furthermore, there is a dearth of information regarding the proper ways to store human serum or plasma samples in order to prevent inaccurate quantification of these various albumin forms. This paper explores these aspects and proposes a few spectrophotometric assay procedures which make the quantitation of oxidized and reduced albumin very fast, precise and un-expensive in various mammals.

Exogenous and endogenous antioxidants in osteoporosis risk: causal associations unveiled by Mendelian Randomization analysis

Background

Recent epidemiological studies and animal experiments have highlighted the significant role of oxidative stress in the development of osteoporosis (OP). The provision of antioxidants is widely considered a fundamental strategy to combat free radical-induced stress, inhibit oxidative damage, and potentially reverse the adverse effects of oxidative stress on bone health. However, there is no consensus in the scientific literature regarding the practical effectiveness of antioxidants in OP prevention and treatment. Some studies have not shown a clear connection between antioxidant supplementation and decreased OP risk. Therefore, it is essential to clarify the potential causal relationship between antioxidants and the development of OP.

Methods

The study utilized the inverse variance weighted (IVW) approach as the primary analytical method in the Mendelian Randomization (MR) framework to investigate the causal effects of five exogenous and six endogenous antioxidants on the risk of OP. To thoroughly assess potential pleiotropic effects and heterogeneity among the data analyzed, the MR-Egger intercept test was employed, and Cochran's Q statistic was calculated.

Results

In the evaluation of exogenous antioxidants, single-directional two-sample MR analyses did not reveal any statistically significant relationship between these agents and the risk of OP. Regarding endogenous antioxidants, bidirectional two-sample MR analyses were conducted, which generally indicated that most genetically regulated endogenous antioxidants had no significant association with the onset risk of OP. A significant causal relationship was found between OP and serum albumin levels (β: -0.0552, 95%CI: -0.0879 to -0.0225, p < 0.0011 after Bonferroni adjustment, power = 100%).

Conclusion

The research uncovers OP as a possible determinant contributing to a decrement in serum albumin levels, and further suggests a potentially intimate relationship between the downward trajectory of serum albumin concentrations and the advancement of the OP disease process.

Early detection of liver injuries by the Serum enhanced binding test sensitive to albumin post-transcriptional modifications

Early and sensitive biomarkers of liver dysfunction and drug-induced liver injury (DILI) are still needed, both for patient care and drug development. We developed the Serum Enhanced Binding (SEB) test to reveal post-transcriptional modifications (PTMs) of human serum albumin resulting from hepatocyte dysfunctions and further evaluated its performance in an animal model. The SEB test consists in spiking serum ex-vivo with ligands having specific binding sites related to the most relevant albumin PTMs and measuring their unbound fraction. To explore the hypothesis that albumin PTMs occur early during liver injury and can also be detected by the SEB test, we induced hepatotoxicity in male albino Wistar rats by administering high daily doses of ethanol and CCl4 over several days. Blood was collected for characterization and quantification of albumin isoforms by high-resolution mass spectrometry, for classical biochemical analyses as well as to apply the SEB test. In the exposed rats, the appearance of albumin isoforms paralleled the positivity of the SEB test ligands and histological injuries. These were observed as early as D3 in the Ethanol and CCl4 groups, whereas the classical liver tests (ALT, AST, PAL) significantly increased only at D7. The behavior of several ligands was supported by structural and molecular simulation analysis. The SEB test and albumin isoforms revealed hepatocyte damage early, before the current biochemical biomarkers. The SEB test should be easier to implement in the clinics than albumin isoform profiling.

Albumin Redox Modifications Promote Cell Calcification Reflecting the Impact of Oxidative Status on Aortic Valve Disease and Atherosclerosis

Calcific aortic valve disease (CAVD) and coronary artery disease (CAD) are related cardiovascular diseases in which common mechanisms lead to tissue calcification. Oxidative stress plays a key role in these diseases and there is also evidence that the redox state of serum albumin exerts a significant influence on these conditions. To further explore this issue, we used multimarker scores (OxyScore and AntioxyScore) to assess the global oxidative status in patients with CAVD, with and without CAD, also evaluating their plasma thiol levels. In addition, valvular interstitial cells were treated with reduced, oxidized, and native albumin to study how this protein and its modifications affect cell calcification. The differences we found suggest that oxidative status is distinct in CAVD and CAD, with differences in redox markers and thiol levels. Importantly, the in vitro interstitial cell model revealed that modified albumin affects cell calcification, accelerating this process. Hence, we show here the importance of the redox system in the development of CAVD, emphasizing the relevance of multimarker scores, while also offering evidence of how the redox state of albumin influences vascular calcification. These data highlight the relevance of understanding the overall redox processes involved in these diseases, opening the door to new studies on antioxidants as potential therapies for these patients.

Unraveling the versatility of human serum albumin - A comprehensive review of its biological significance and therapeutic potential

Human serum albumin (HSA) is a multi-domain macromolecule with diverse ligand binding capability because of its ability to allow allosteric modulation despite being a monomeric protein. Physiologically, HSA act as the primary carrier for various exogenous and endogenous compounds and fatty acids, and alter the pharmacokinetic properties of several drugs. It has antioxidant properties and is utilized therapeutically to improve the drug delivery of pharmacological agents for the treatment of several disorders. The flexibility of albumin in holding various types of drugs coupled with a variety of modifications makes this protein a versatile drug carrier with incalculable potential in therapeutics. This review provides a brief outline of the different structural properties of HSA, and its various binding sites, moreover, an overview of the genetic, biomedical, and allosteric modulation of drugs and drug delivery aspects of HSA is also included, which may be helpful in guiding advanced clinical applications and further research on the therapeutic potential of this extraordinary protein.

Semi-synthetic human albumin isoforms: Production, structure, binding capacities and influence on a routine laboratory test

Human Serum Albumin (HSA) undergoes Post-Translational-Modifications (PTMs) leading to isoforms affecting its oncotic and non-oncotic properties. HSA is comprised of several isoforms whose abundance may vary with pathologies such as diabetes, kidney and liver diseases. Studying their impact separately may help to understand their sources and potential pathogenicity and further their evaluation as biomarkers. The present study examined semi-synthetic HSA isoforms to investigate independently their structure by means of advanced mass spectrometry techniques (LC-TOF-MS and ICP-MS), influence on the HSA binding/antioxidant activities using a binding capacity test, and potential impact on albumin quantification by a routine immunoturbidimetric assay. Applying different chemical reactions to a commercial HSA solution, we obtained different solutions enriched up to 53 % of native HSA, 78 % of acetylated HSA, 71 % of cysteinylated HSA, 94 % of oxidized HSA, 58 % of nitrosylated HSA and 96 % of glycated HSA, respectively. Moreover, the semi-synthetic isoforms showed differently altered binding capacities for a panel of ligands (Cu, Cd, Au, Ds and L-T4). Furthermore, immunoturbidimetry was found to be insensitive to the presence and abundance of the different isoforms. The fully characterized semi synthetic HSA isoforms obtained should be useful to further investigate their pathogenicity and potential roles as biomarkers.

Effects of amino acids and albumin administration on albumin metabolism in surgically stressed rats: A basic nutritional study

BACKGROUND

Nutrition therapy and administration of albumin preparations are common in postsurgical patients. However, the effects of these interventions on albumin metabolism are unclear. We elucidated the effect of postoperative albumin and/or parenteral nutrition administration on it.

METHODS

Sprague-Dawley rats underwent surgery involving intestinal rubbing followed by intestinal exposure. Subsequently, they were administered experimental solutions for 48 h, their blood samples were collected at 24 and 48 h, and livers were excised at 48 h. Based on experimental solutions, rats were divided into five groups: non-surgical (Non-surg); glucose and electrolyte solution (GE); amino acid, glucose, and electrolyte solution (AGE); GE + rat serum albumin (Alb) (GE + Alb); and AGE + Alb. Their plasma albumin concentrations; albumin fractional synthesis rate (ALB FSR); mercaptoalbumin/total albumin ratio (MA ratio); and messenger RNA (mRNA) expressions of albumin and hepatocyte nuclear factor-1 (HNF-1) in the liver were measured.

RESULTS

The GE and AGE groups showed significant decline in albumin concentrations. ALB FSR was significantly enhanced in the AGE group compared with the GE group. The mRNA expression of albumin was similar to ALB FSR in all groups and that of HNF-1 was significantly decreased in the GE + Alb and AGE + Alb groups compared with the Non-surg group. The MA ratio in the AGE group was similar to the Non-surg group.

CONCLUSION

The administration of amino acids comprising parenteral nutrition after surgery augmented ALB FSR and maintained the MA ratio only without simultaneous albumin administration.

Delivery of Drugs into Cancer Cells Using Antibody-Drug Conjugates Based on Receptor-Mediated Endocytosis and the Enhanced Permeability and Retention Effect

Innumerable people worldwide die of cancer every year, although pharmaceutical therapy has actualized many benefits in human health. For background, anti-cancer drug development is difficult due to the multifactorial pathogenesis and complicated pathology of cancers. Cancer cells excrete hydrophobic low-molecular anti-cancer drugs by overexpressed efflux transporters such as multiple drug resistance 1 (MDR1) at the apical membrane. Mutation-driven drug resistance is also developed in cancer. Moreover, the poor distribution of drug to cancer cells is a serious problem, because patients suffer from off-target side effects. Thus, highly selective and effective drug delivery into solid cancer cells across the membrane should be established. It is known that substances (10-100 nm in diameter) such as monoclonal antibodies (mAbs) (approximately 14.2 nm in diameter) or nanoparticles spontaneously gather in solid tumor stroma or parenchyma through the capillary endothelial fenestration, ranging from 200-2000 nm, in neovasculatures due to the enhanced permeability and retention (EPR) effect. Furthermore, cancer antigens, such as HER2, Nectin-4, or TROP2, highly selectively expressed on the surface of cancer cells act as a receptor for receptor-mediated endocytosis (RME) using mAbs against such antigens. Thus, antibody-drug conjugates (ADCs) are promising anti-cancer pharmaceutical agents that fulfill accurate distribution due to the EPR effect and due to antibody-antigen binding and membrane permeability owing to RME. In this review, I introduce the implementation and possibility of highly selective anti-cancer drug delivery into solid cancer cells based on the EPR effect and RME using anti-cancer antigens ADCs with payloads through suitable linkers.

Oxidative Modification Status of Human Serum Albumin Caused by Chronic Low-Dose Radiation Exposure in Mamuju, Sulawesi, Indonesia

The recently discovered high-level natural background radiation area (HBRA) of Mamuju in Indonesia provides a unique opportunity to study the biological effects of chronic low-dose radiation exposure on a human population. The mean total effective dose in the HBRA was approximately 69.6 mSv y^-1 (range: 47.1 to 115.2 mSv y^-1), based on a re-evaluation of the individual radiation exposure dose; therefore, proteomic analyses of serum components and oxidative modification profiling of residents living in the HBRA were reconducted using liquid chromatography-tandem mass spectrometry. The analysis of the oxidative modification sequences of human serum albumin revealed significant moderate correlations between the radiation dose and the modification of 12 sequences, especially the 111th methionine, 162nd tyrosine, 356th tyrosine, and 470th methionine residues. In addition, a dose-dependent variation in 15 proteins of the serum components was detected in the serum of residents exposed to chronic low-dose radiation. These findings suggest that the alterations in the expression of specific proteins and the oxidative modification responses of serum albumin found in exposed humans may be important indicators for considering the effects of chronic low-dose radiation exposure on living organisms, implying their potential utility as biomarkers of radiation dose estimation.

Use of human albumin infusion in cirrhotic patients: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Human albumin infusion is effective for controlling systemic inflammation, thereby probably managing some liver cirrhosis-related complications, such as spontaneous bacterial peritonitis (SBP), hepatic encephalopathy (HE), and hepatorenal syndrome. However, its clinical benefits remain controversial.

METHODS

EMBASE, PubMed, and Cochrane Library databases were searched. Randomized controlled trials (RCTs) regarding use of human albumin infusion in cirrhotic patients were eligible. Mortality and incidence of liver cirrhosis-related complications were pooled. Effect of human albumin infusion on mortality was also evaluated by subgroup analyses primarily according to target population and duration of human albumin infusion treatment. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated.

RESULTS

Forty-two RCTs were finally included. Meta-analysis showed that human albumin infusion could significantly decrease the mortality of cirrhotic patients (OR = 0.81, 95% CI = 0.67-0.98, p = 0.03). Subgroup analyses showed that human albumin infusion could significantly decrease the mortality of cirrhotic patients with SBP (OR = 0.36, 95% CI = 0.20-0.64, p = 0.0005) and HE (OR = 0.43, 95% CI = 0.22-0.85, p = 0.02), but not those with ascites or non-SBP infections or undergoing large-volume paracentesis. Short-term human albumin infusion treatment could significantly decrease short-term mortality (OR = 0.67, 95% CI = 0.50-0.89, p = 0.005), but not long-term mortality. Long-term human albumin infusion treatment could not significantly decrease long-term mortality (OR = 0.72, 95% CI = 0.48-1.08, p = 0.11). In addition, human albumin infusion could significantly decrease the incidence of renal impairment (OR = 0.63, 95% CI = 0.45-0.88, p = 0.007) and ascites (OR = 0.45, 95% CI = 0.25-0.81, p = 0.007), but not infections or gastrointestinal bleeding.

CONCLUSIONS

Human albumin infusion may improve the outcomes of cirrhotic patients. However, its indications for different complications and infusion strategy in liver cirrhosis should be further explored.

Changing Perspectives from Oxidative Stress to Redox Signaling-Extracellular Redox Control in Translational Medicine

Extensive research has changed the understanding of oxidative stress that has been linked to every major disease. Today we distinguish oxidative eu- and distress, acknowledging that redox modifications are crucial for signal transduction in the form of specific thiol switches. Long underestimated, reactive species and redox proteins of the Thioredoxin (Trx) family are indeed essential for physiological processes. Moreover, extracellular redox proteins, low molecular weight thiols and thiol switches affect signal transduction and cell–cell communication. Here, we highlight the impact of extracellular redox regulation for health, intermediate pathophenotypes and disease. Of note, recent advances allow the analysis of redox changes in body fluids without using invasive and expensive techniques. With this new knowledge in redox biochemistry, translational strategies can lead to innovative new preventive and diagnostic tools and treatments in life sciences and medicine.

Albumin Lipidomics Reveals Meaningful Compositional Changes in Advanced Cirrhosis and Its Potential to Promote Inflammation Resolution

Albumin infusions are therapeutically used to revert hypoalbuminemia and to replace the extensively oxidized albumin molecule circulating in patients with acutely decompensated (AD) cirrhosis. Because albumin has high affinity for lipids, here we characterized the albumin lipidome in patients with AD and explored the albumin effects on the release of fatty acid (FA)-derived lipid mediators by peripheral leukocytes. Lipids and lipid mediators were measured by liquid chromatography-tandem mass spectrometry in albumin-enriched and albumin-depleted plasma fractions separated by affinity chromatography and in leukocyte incubations from 18 patients with AD and 10 healthy subjects (HS). Lipid mediators were also measured in 41 patients with AD included in an albumin therapy trial. The plasma lipidome associated with AD cirrhosis was characterized by generalized suppression of all lipid classes except FAs. In contrast to HS, albumin from patients with AD had lower content of polyunsaturated FAs (PUFAs), especially of the omega-3-PUFA docosahexaenoic acid. Consistent with this, the PUFA-derived lipid mediator landscape of albumin from patients with AD was dominated by lower content of monohydroxy FA precursors of anti-inflammatory/pro-resolving lipid mediators (i.e., 15-hydroxyeicosatetraenoic acid [15-HETE]). In addition, albumin from patients with AD was depleted in prostaglandin (PG) E₂ , suggesting that this proinflammatory PG primarily travels disassociated to albumin in these patients. Incubation of leukocytes with exogenous albumin reduced PG production while inducing 15-lipoxygenase expression and 15-HETE release. Similar effects were seen under lipopolysaccharide plus N-formylmethionyl-leucyl-phenylalanine-stimulated conditions. Finally, PG levels were lower in patients with AD receiving albumin therapy, whereas 15-HETE was increased after albumin treatment compared with baseline. Conclusion: Our findings indicate that the albumin lipid composition is severely disorganized in AD cirrhosis and that administration of exogenous albumin has the potential to redirect leukocyte biosynthesis from pro-inflammatory to pro-resolving lipid mediators.

Targeted Albumin Infusions Do Not Improve Systemic Inflammation or Cardiovascular Function in Decompensated Cirrhosis

INTRODUCTION

Albumin is recommended in decompensated cirrhosis, and studies have shown potential immunomodulatory effects. However, 2 large trials of repeated albumin infusions demonstrated contrasting results between outpatients and hospitalized patients. We investigated markers of systemic inflammation, immune function, albumin binding, and cardiovascular function using samples from Albumin To prevenT Infection in chronic liveR failurE (ATTIRE) taken at baseline, day 5, and day 10 of the trial to identify why targeted albumin infusions had no effect in hospitalized patients.

METHODS

Plasma samples were analyzed from 143 patients (n = 71 targeted albumin; n = 72 standard care at baseline) for cytokines, cardiovascular markers, prostaglandin E2, the effect of plasma on macrophage function, and albumin radioligand binding and oxidation status. The sample size was based on our feasibility study, and samples were selected by a trial statistician stratified by the serum albumin level and the presence of infection at randomization and analyses performed blinded to the study arm. Data were linked to 3-month mortality and treatment groups compared.

RESULTS

Increased baseline model for end-stage liver disease score, white cell count, calprotectin, CD163, tumor necrosis factor, renin, atrial natriuretic peptide, and syndecan-1 were associated with 3-month mortality. Despite infusing substantially differing volumes of albumin, there were no significant differences in inflammatory markers, albumin-prostaglandin E2 binding, or cardiovascular markers between treatment arms.

DISCUSSION

Contrary to many preclinical studies, targeted intravenous albumin therapy in hospitalized decompensated cirrhosis had no effect across a broad range of systemic inflammation, albumin function, and cardiovascular mediators and biomarkers compared with standard care, consistent with the null clinical findings.

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.

Redox index of Cys-thiol residues of serum apolipoprotein E and its diagnostic potential

Background: The redox modulation of Cys-thiol participates in various pathophysiological processes. We explored the proper index for estimating the redox status of Cys-thiol of serum apolipoprotein E (apoE), named “redox-IDX-apoE,” which is necessary to understand the redox biology of age-related diseases.

Methods: The fractions of the reduced form (red-), reversible oxidized form (roxi-), and irreversibly oxidized form (oxi-) apoE in serum, obtained from the patients with no apparent disease (controls, n=192) and with atherosclerosis and type 2 diabetes (patients, n=16), were measured by a band-shift assay using a maleimide compound. Redox-IDX-apoE candidates were determined by calculating the values of these fractions and the total apoE concentration.

Results: Cys number of apoE significantly increased for the ratio of roxi-apoE to total-apoE (roxi/total) (E2/E3>E3/E3>E3/E4) but decreased for the ratios of red-apoE to roxi-apoE (red/roxi) and [red-apoE + oxi-apoE] to roxi-apoE ([red + oxi]/roxi) (E2/E3<E3/E3<E3/E4). Considering the subjects with apoE3/E3, these ratios were independent of age and sex. Roxi/total showed negative correlations with serum triglyceride (TG) and HbA1c levels, while both red/roxi and [red + oxi]/roxi showed significant positive correlations with them. However, red/roxi and [red + oxi]/roxi in patients were significantly lower than those in controls, although serum TG and HbA1c levels in the patients were significantly higher than those in controls.

Conclusion: The redox status of serum apoE-Cys-thiol is closely involved in the metabolism of TG-rich lipoproteins and glucose. The appropriate use of redox-IDX-apoE could be helpful in the diagnosis and prognosis of age-related diseases and in understanding the underlying mechanisms.

Albumin in patients with liver disease shows an altered conformation

Human serum albumin (HSA) constitutes the primary transporter of fatty acids, bilirubin, and other plasma compounds. The binding, transport, and release of its cargos strongly depend on albumin conformation, which is affected by bound ligands induced by physiological and pathological conditions. HSA is both highly oxidized and heavily loaded with fatty acids and bilirubin in chronic liver disease. By employing small-angle X-ray scattering we show that HSA from the plasma of chronic liver disease patients undergoes a distinct opening compared to healthy donors. The extent of HSA opening correlates with clinically relevant variables, such as the model of end-stage liver disease score, bilirubin, and fatty acid levels. Although the mild oxidation of HSA in vitro does not alter overall structure, the alteration of patients’ HSA correlates with its redox state. This study connects clinical data with structural visualization of albumin dynamicity in solution and underlines the functional importance of albumin’s inherent flexibility.

Paar et al. propose a SAXS-based approach to study conformations of human serum albumin (HSA) from patients with liver disease and a structural understanding of HSA dynamicity and its correlation with clinical variables are provided. Using it on real clinical samples, this study has concrete practical implications too.

Protein-aggregating ability of different protoporphyrin-IX nanostructures is dependent on their oxidation and protein-binding capacity

Porphyrias are rare blood disorders caused by genetic defects in the heme biosynthetic pathway and are associated with the accumulation of high levels of porphyrins that become cytotoxic. Porphyrins, due to their amphipathic nature, spontaneously associate into different nanostructures, but very little is known about the cytotoxic effects of these porphyrin nanostructures. Previously, we demonstrated the unique ability of fluorescent biological porphyrins, including protoporphyrin-IX (PP-IX), to cause organelle-selective protein aggregation, which we posited to be a major mechanism by which fluorescent porphyrins exerts their cytotoxic effect. Herein, we tested the hypothesis that PP-IX-mediated protein aggregation is modulated by different PP-IX nanostructures via a mechanism that depends on their oxidizing potential and protein-binding ability. UV–visible spectrophotometry showed pH-mediated reversible transformations of PP-IX nanostructures. Biochemical analysis showed that PP-IX nanostructure size modulated PP-IX-induced protein oxidation and protein aggregation. Furthermore, albumin, the most abundant serum protein, preferentially binds PP-IX dimers and enhances their oxidizing ability. PP-IX binding quenched albumin intrinsic fluorescence and oxidized His-91 residue to Asn/Asp, likely via a previously described photo-oxidation mechanism for other proteins. Extracellular albumin protected from intracellular porphyrinogenic stress and protein aggregation by acting as a PP-IX sponge. This work highlights the importance of PP-IX nanostructures in the context of porphyrias and offers insights into potential novel therapeutic approaches.

The redox status of cysteine thiol residues of apolipoprotein E impacts on its lipid interactions

Redox-mediated modulation of cysteine (Cys) thiols has roles in various pathophysiological functions. We recently found that formation of disulfide-linked complexes of apolipoprotein (apo) E3 prevented apoE3 from irreversible oxidation. In this report, the influence of modification of Cys thiols in apoE2 and apoE3 on interactions with lipids was investigated. The apoE redox status was examined by a band-shift assay using a maleimide compound, and interactions with lipids were evaluated by a kinetic assay using dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and non-denaturing polyacrylamide gel electrophoresis. A reduction in DMPC clearance activity of apoE2 and apoE3 but not apoE4 was observed. Although hydrogen peroxide-induced oxidation decreased the clearance activity of the isoforms, apoE2 showed the greatest residual activity. Both Cys thiol masking and dimerization decreased the activity of apoE2 and apoE3 but not apoE4. In contrast, apoAII preincubation markedly increased the activity (apoE2 > apoE3 > apoE4), in accordance with the formation of apoE-AII and apoAII-E2-AII complexes. ApoAII preincubation also reduced the particle size of apoE-DMPC liposome complexes, especially for apoE2. Redox-mediated modification of Cys thiols of apoE2 or apoE3, especially disulfide bond formation with apoAII, affects lipid metabolism and consequently may be responsible for the diverse isoform specificity of apoE.

Post-translational modifications and antioxidant properties of different therapeutic human serum albumins

Human serum albumin (HSA) is widely used for the treatment of diverse clinical conditions to restore plasma volume, manage burns and treat hypoproteinemia.Although the HSA preparations should ideally preserve its functionality, the structural integrity and antioxidant properties of HSA may be compromised as a result of the manufacturing process. The present study examined seven commercially available HSA preparations for clinical use to investigate their post-translational modifications (PTMs) and antioxidant activity, including DPPH radical-scavenging, peroxyl radical antioxidant and metal binding activities, by means of mass spectrometry and Ellman's assay. The results confirmed that most of the PTMs of HSA and especially the oxidation of the free thiol residue varied between the different commercial albumins and the percentage of these PTMs were higher than those of physiological HSA. Moreover, HSA-DA isoform was increased at the end of the stability time and new oxidative modifications occurred in these samples. In conclusion, the bioprocesses for production of commercial albumins are responsible of their wide heterogeneity, being the ethanol fractionation and their storage conditions the more critical phases. Nonetheless, the Kedrion albumin shows a high content of free thiol and a lower concentration of PTMs than other commercial albumins.

Serum Albumin Redox States: More Than Oxidative Stress Biomarker

Serum albumin is the most abundant circulating protein in mammals including humans. It has three isoforms according to the redox state of the free cysteine residue at position 34, named as mercaptalbumin (reduced albumin), non-mercaptalbumin-1 and -2 (oxidized albumin), respectively. The serum albumin redox state has long been viewed as a biomarker of systemic oxidative stress, as the redox state shifts to a more oxidized state in response to the severity of the pathological condition in various diseases such as liver diseases and renal failures. However, recent ex vivo studies revealed oxidized albumin per se could aggravate the pathological conditions. Furthermore, the possibility of the serum albumin redox state as a sensitive protein nutrition biomarker has also been demonstrated in a series of animal studies. A paradigm shift is thus ongoing in the research field of the serum albumin. This article provides an updated overview of analytical techniques for serum albumin redox state and its association with human health, focusing on recent findings.

Crosslinking of human plasma C-reactive protein to human serum albumin via disulfide bond oxidation

Inter- and intra-molecular crosslinks can generate protein dysfunction, and are associated with protein aggregate accumulation in aged and diseased tissues. Crosslinks formed between multiple amino acid side chains can be reversible or irreversible. Disulfides formed either enzymatically, or as a result of oxidant-mediated reactions, are a major class of reversible crosslinks. Whilst these are commonly generated via oxidation of Cys thiol groups, they are also formed by ‘oxidant-mediated thiol-disulfide reactions’ via initial disulfide oxidation to a thiosulfinate or zwitterionic peroxide, and subsequent reaction with another thiol including those on other proteins. This generates new intermolecular protein-protein crosslinks. Here we demonstrate that photooxidation, or reaction with the biological oxidants HOCl and ONOOH, of the single disulfide present in the major human plasma inflammatory protein, C-reactive protein (CRP) can give rise to reversible disulfide bond formation with human serum albumin (HSA). This occurs in an oxidant dose-, or illumination-time-, dependent manner. These CRP-HSA crosslinks are formed both in isolated protein systems, and in fresh human plasma samples containing high, but not low, levels of CRP. The inter-protein crosslinks which involve Cys36 of CRP and Cys34 of HSA, have been detected by both immunoblotting and mass spectrometry (MS). The yield of protein-protein crosslinks depends on the nature and extent of oxidant exposure, and can be reversed by dithiothreitol and tris(2-carboxyethyl)phosphine hydrochloride. These data indicate that oxidation of disulfide bonds in proteins can be a source of novel inter-protein crosslinks, which may help rationalize the accumulation of crosslinked proteins in aged and diseased tissues.

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C-reactive protein (CRP) is a major acute phase inflammatory protein in human plasma.

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Oxidation of the single Cys36-Cys97 disulfide in CRP generates reactive intermediates.

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The oxidized disulfide reacts with Cys34 of human serum albumin to forms a new crosslink.

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The inter-protein CRP-HSA crosslink has been characterized by immunoblotting and LS-MS/MS.

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This novel crosslink may be a long-lived plasma marker of inflammation-induced damage.

Crystal structure of pharmaceutical-grade human serum albumin

Human serum albumin (HSA) is the most abundant protein in human plasma and plays versatile biological role. HSA has been widely used to treat several diseases and develop biocompatible biomaterials for biomedical applications. However, pharmaceutical-grade HSA (p-HSA) showed the altered oxidative and ligand-binding properties compare to native HSA. To investigate the influences of the manufacturing process on the molecular state of HSA, we determined the first crystal structure of p-HSA using the commercial HSA solution without any defatting step and further purification and carried out mass spectrometry to identify bound ligands. The crystal structure of p-HSA revealed that medium- and long-chain fatty acids and tryptophan are bound to p-HSA and one free cysteine is oxidized to cysteine-sulfenic acid. The mass spectra of p-HSA also confirmed the existence of fatty acids and tryptophan in p-HSA. Our results enhance understanding of the molecular state of p-HSA and can be utilized to produce p-HSA solutions and HSA-based biomaterials that has a higher biorelevance.

S-Thiolation Targets Albumin in Heart Failure

Human serum albumin (HSA) is associated with several physiological functions, such as maintaining oncotic pressure and microvascular integrity, among others. It also represents the major and predominant antioxidant in plasma due to the presence of the Cys34 sulfhydryl group. In this study, we assessed qualitative and quantitative changes in HSA in patients with heart failure (HF) and their relationship with the severity of the disease. We detected by means of mass spectrometry a global decrease of the HSA content in the plasma of HF patients in respect to control subjects, a significant increase of thio-HSA with a concomitant decrease in the reduced form of albumin. Cysteine and, at a lesser extent, homocysteine represent the most abundant thiol bound to HSA. A strong inverse correlation was also observed between cysteine-HSA and peak VO₂/kg, an index of oxygen consumption associated with HF severity. Moreover, in HL-1 cardiomyocytes incubated with H₂O₂, we showed a significant decrease of cell viability in cells treated with thio-HSA in respect to restored native-HSA. In conclusion, we found for the first time that S-thiolation of albumin is increased in the plasma of HF patients and induced changes in the structure and antioxidant function of HSA, likely contributing to HF progression.

Albumin Protects Lung Cells against Acrolein Cytotoxicity and Acrolein-Adducted Albumin Increases Heme Oxygenase 1 Transcripts

Albumin is an abundant protein in the lung lining fluid that forms an interface between lung epithelial cells and the external environment. In the lung, albumin can be targeted for adduction by inhaled acrolein. Acrolein, an α,β-unsaturated aldehyde, reacts with biomolecules via Michael addition at the β-carbon or Schiff base formation at the carbonyl carbon. To gain insight into acrolein's mode of action, we investigated in vitro albumin-acrolein reactivity and the consequence of albumin adduction by acrolein on cytotoxicity and transcript changes in NCI-H441 and human airway epithelial cells (HAEC). Albumin protected NCI-H441 cells from acrolein toxicity. In addition, albumin inhibited acrolein-induced increase of transcripts associated with cellular stress response, activating transcription factor 3 (ATF3), and antioxidant response, heme oxygenase 1 (HMOX1) in HAEC cells. Acrolein-adducted albumin itself increased HMOX1 transcripts but not ATF3 transcripts. The HMOX1 transcript increase was inhibited by hydralazine, a carbonyl scavenger, suggesting that the carbonyl group of acrolein-adducted albumin mediated HMOX1 transcript increase. In acutely exposed C57BL/6J mice, bronchoalveolar lavage protein carbonylation increased. Acrolein-adducted albumin Cys34 was identified by nLC-MS/MS. These findings indicate that adduction of albumin by acrolein confers a cytoprotective function by scavenging free acrolein, decreasing a cellular stress response, and inducing an antioxidant gene response. Further, these results suggest that β-carbon reactivity may be required for acrolein's cytotoxicity and ATF3 transcript increase, and the carbonyl group of acrolein-adducted albumin can induce HMOX1 transcript increase.

Controlling Nutritional Status (CONUT) Score is Associated with Overall Survival in Patients with Unresectable Hepatocellular Carcinoma Treated with Lenvatinib: A Multicenter Cohort Study

We aimed to investigate the impact of the controlling nutritional status (CONUT) score, an immuno-nutritional biomarker, on the prognosis of patients with hepatocellular carcinoma (HCC) treated with lenvatinib (LEN). This retrospective study enrolled 164 patients with HCC and treated with LEN (median age 73 years, Barcelona Clinic Liver Cancer (BCLC) stage B/C 93/71). Factors associated with overall survival (OS) were evaluated using multivariate and decision tree analyses. OS was calculated using the Kaplan–Meier method and analyzed using the log–rank test. Independent factors for OS were albumin–bilirubin grade 1, BCLC stage B, and CONUT score <5 (hazard ratio (HR) 2.9, 95% confidence interval (CI) 1.58–5.31, p < 0.001). The CONUT score was the most important variable for OS, with OS rates of 70.0% and 29.0% in the low and high CONUT groups, respectively. Additionally, the median survival time was longer in the low CONUT group than in the high CONUT group (median survival time not reached vs. 11.3 months, p < 0.001). The CONUT score was the most important prognostic variable, rather than albumin–bilirubin grade and BCLC stage, in patients with HCC treated with LEN. Accordingly, immuno-nutritional status may be an important factor in the management of patients with HCC treated with LEN.

A Simplified Method for Simultaneous Determination of α-Lipoic Acid and Low-Molecular-Mass Thiols in Human Plasma

α-Lipoic acid, glutathione, cysteine, and cysteinylglycine can be applied as therapeutic agents in civilization diseases such as diabetes mellitus, cardiovascular diseases, and cancers. On the other hand, a higher concentration of homocysteine can result in health problems and has been indicated as an independent risk factor for cardiovascular disease and accelerated atherosclerosis. Here, the first simplified HPLC-UV assay that enables simultaneous determination of α-lipoic acid and low-molecular-mass thiols in plasma, reduces the number of steps, shortens the total time of sample preparation, and limits the amount of single-use polypropylene laboratory materials is described. The assay is based on reversed-phase high performance liquid chromatography with UV detection and simultaneous reduction of disulfide bound with tris(2-carboxyethyl)phosphine and the selective pre-column derivatization of the thiol group with 1-benzyl-2-chloropyridinium bromide. Linearity in the detector responses for plasma samples were observed in ranges: 0.12-5.0 nmol mL^-1 for α-lipoic acid; 2.0-20.0 nmol mL^-1 for glutathione, cysteinylglycine, and homocysteine; and 40.0-400.0 for cysteine. The LODs for α-lipoic acid and low-molecular-mass thiols were 0.08 and 0.12 nmol mL^-1, respectively, while LOQs were 0.12 and 0.16 nmol mL^-1, respectively. The usefulness of the proposed method has been proven by its application to real samples.

A 2D HPLC-MS/MS method for several antibiotics in blood plasma, plasma water, and diverse tissue samples

An analytical method using 2D high-performance liquid chromatography followed by tandem mass spectrometry for the quantification of the beta-lactam antibiotics amoxicillin, flucloxacillin, piperacillin, benzylpenicillin, the beta-lactamase inhibitors clavulanic acid, and tazobactam, as well as the macrolide antibiotic clindamycin, is presented. All analytes were measured in human plasma, while amoxicillin, clavulanic acid, flucloxacillin, and clindamycin were also analyzed in human tissue samples. Because of its high-protein binding, additionally, the free fraction of flucloxacillin was measured after ultrafiltration. As internal standards, deuterated forms of the beta-lactams were used. Sample preparation for all matrices was protein precipitation followed by online extraction on a TurboFlow MAX column, while sample separation was performed on an Accucore XL C18 column. Calibration curves were linear over 0.2-25 mg/kg for the tissue samples and 0.05-20 mg/l for the free fraction of flucloxacillin. In plasma, the calibration curves for amoxicillin and piperacillin were linear over 3.125-125 mg/l, for clavulanic acid and tazobactam over 1-40 mg/l, for benzylpenicillin 0.25-40 mg/l, and for flucloxacillin and clindamycin over 1.5-60 mg/l and 0.05-8 mg/l respectively. In plasma and plasma ultrafiltrate, inaccuracy and imprecision for any analyte were always less than 15%. In tissue, the accuracy and precision varied up to 16%, respectively, 20%, when various tissues were analyzed using a calibration in water. Graphical abstract.

Impaired albumin function: a novel potential indicator for liver function damage?

Albumin is the most abundant plasma protein and albumin infusion is commonly used. Conventionally, the biologic and therapeutic effects of albumin have been thought to be due to its oncotic properties. However, albumin has a variety of biologic functions, including molecular transport, anti-oxidation, anti-inflammation, endothelial stabilisation, anti-thrombotic effects, and the adjustment of capillary permeability. Despite this, the functions of albumin have not been thoroughly investigated. Recent studies have shown non-alcoholic fatty liver disease (NAFLD), viral hepatitis, cirrhosis, and liver failure to be associated with impairments in albumin function, which are associated with impairments in liver function and disease prognosis. Post-translational modifications of albumin cause structural modifications that affect protein function. Recently, the concentration of albumin associated with normal function, the 'efficient albumin concentration', has been attracting more interest. In addition, although many biologic markers, including albumin concentration, are widely used for the assessment of early liver dysfunction in patients with liver diseases, the predictive values are unsatisfactory. However, clinical evidence has suggested that albumin function may represent a novel biomarker of early impairment in liver function. In this review, we summarise the factors affecting albumin function and discuss the clinical significance of impairments in albumin function in various liver diseases.Key messagesThe importance of albumin depends not only on its concentration, but also on its various physiological functions.Impaired albumin function has been reported in a variety of liver diseases, and is associated with disease severity and prognosis, thereby proposing the concept of 'effective albumin concentration'.Albumin dysfunction occurs earlier than other conventional indicators, and albumin dysfunction may be a new biomarker of early impairment in liver function.Many exogenous and endogenous factors lead to post-translational modifications of albumin, which alters the three-dimensional structure of albumin, resulting in a decrease in its biological activity.

Top-Down Proteomics Applied to Human Cerebrospinal Fluid

Cerebrospinal fluid (CSF) is the fluid of choice to study pathologies and disorders of the central nervous system (CNS). Its composition, especially its proteins and peptides, holds the promise that it may reflect the pathological state of an individual. Traditionally, proteins and peptides in CSF have been analyzed using bottom-up proteomics technologies in the search of high proteome coverage. However, the limited protein sequence coverage of this technology means that information regarding post-translational modifications (PTMs) and alternative splice variants is lost. As an alternative technology, top-down proteomics offers low to medium proteome coverage, but high protein coverage enabling almost a full characterization of the proteins' primary structure. This allows us to precisely identify distinct molecular forms of proteins (proteoforms) as well as naturally occurring bioactive peptide fragments, which could be of critical biological relevance and would otherwise remain undetected with a classical proteomics approach.Here, we describe various strategies including sample preparation protocols, off-line intact protein prefractionation, and LC-MS/MS methods together with data analysis pipelines to analyze cerebrospinal fluid (CSF) by top-down proteomics. However, there is not a unique or standardized method and the selection of the top-down strategy will depend on the exact goal of the study. Here, we describe various top-down proteomics methods that enable rapid protein characterization and may be an excellent companion analytical workflow in the search for new protein biomarkers in neurodegenerative diseases.

Increased Albumin Oxidation in Cerebrospinal Fluid and Plasma from Alzheimer's Disease Patients

Background:

Oxidative stress in the brain and peripheral systems is considered a major player in Alzheimer’s disease (AD). Albumin is the main transporter and the main extracellular antioxidant in the human body.

Objective:

Here we explore for the first time the oxidation status of cerebrospinal fluid (CSF) and plasma albumin in AD in comparison to healthy subjects.

Methods:

Plasma and CSF samples were obtained from mild-moderate AD patients and control healthy age-matched donors. Albumin redox state forms (reduced: HMA; reversibly oxidized: HNA1; irreversibly oxidized: HNA2) were determined by HPLC. Albumin post-translational modifications (PTM) analysis was performed by mass spectrometry.

Results:

HPLC showed less HMA in AD plasma than in controls (54.1% versus 65.2% ; p < 0.0001), mainly at expense of HNA1 (42.8% versus 32.5% ; p < 0.0001). In AD CSF, HMA was drastically decreased compared to controls (9.6% versus 77.4% ; p < 0.0001), while HNA2 was increased (52.8% versus 7.4% ; p < 0.0001). In AD patients but not in healthy controls, CSF albumin was much more irreversibly oxidized than in plasma (close to 20-fold increase in HNA2). PTM analysis showed that AD CSF albumin samples behave as a differentiated cluster, thus confirming the albumin oxidative pattern observed by HPLC.

Conclusion:

CSF albumin oxidation in AD patients was dramatically increased comparing to healthy controls, while in plasma this increase was smaller. CSF albumin in AD patients was much more oxidized than in plasma, but this effect was not observed in healthy controls. These results suggest that albumin oxidation, especially in CSF, and its role in AD deserves further investigation.

Redox equilibrium of serum apolipoprotein E3: a buffering effect of disulfide-linked complexes against oxidative stress on apolipoprotein E3-containing lipoproteins

Reversible redox modification of cysteine thiols is crucial for protecting proteins from irreversible detrimental change. However, the physiological significance of the redox modification of apolipoprotein (apo) E is unclear. Here, we hypothesized that the disulfide-linked complexes of apoE3 corresponding to the representative reversible-modified apoE3 play a protective role against oxidative stress. The effects of disulfide bond formation on oxidative stress on apoE3 were evaluated with a band-shift assay. Maleimide-labeled apoE3 and unlabeled apoE3 were defined as the reduced (r)-apoE3 and non-reduced (nr)-apoE3 forms, respectively. Hydrogen peroxide-induced oxidation decreased for reduced-form apoE (r-apoE3) but increased for nr-apoE3. Induction of apoE3-AII complex formation with excess of apoAII markedly suppressed the oxidative stress-induced increase in nr-apoE3 (P<0.001) and enhanced homodimer formation. The apoE3-AII complex was more dominant in high-density lipoprotein (HDL) than in very low-density lipoprotein. Under oxidative stress, HDL showed a significant decrease, rather than an increase, in nr-apoE3 levels with a concomitant significant increase in apoE3-AII levels (P<0.005). This finding suggests that the majority of nr-apoE3 in HDL exists in a reversible oxidized form. The apoE3-AII complex, formed from the reversible oxidized apoE3, is beneficial for maintaining the redox equilibrium of apoE3 by preventing the modification of apoE3 to its irreversible oxidized form. The apoE3-AII complex may be possibly implicated in the pathophysiology of various apoE-related diseases.

A Data Mining-based Prognostic Algorithm for NAFLD-related Hepatoma Patients: A Nationwide Study by the Japan Study Group of NAFLD

The prognosis of patients with nonalcoholic fatty liver disease-related hepatocellular carcinoma (NAFLD-HCC) is intricately associated with various factors. We aimed to investigate the prognostic algorithm of NAFLD-HCC patients using a data-mining analysis. A total of 247 NAFLD-HCC patients diagnosed from 2000 to 2014 were registered from 17 medical institutions in Japan. Of these, 136 patients remained alive (Alive group) and 111 patients had died at the censor time point (Deceased group). The random forest analysis demonstrated that treatment for HCC and the serum albumin level were the first and second distinguishing factors between the Alive and Deceased groups. A decision-tree algorithm revealed that the best profile comprised treatment with hepatectomy or radiofrequency ablation and a serum albumin level ≥3.7 g/dL (Group 1). The second-best profile comprised treatment with hepatectomy or radiofrequency ablation and serum albumin levels <3.7 g/dL (Group 2). The 5-year overall survival rate was significantly higher in the Group 1 than in the Group 2. Thus, we demonstrated that curative treatment for HCC and serum albumin level >3.7 g/dL was the best prognostic profile for NAFLD-HCC patients. This novel prognostic algorithm for patients with NAFLD-HCC could be used for clinical management.

New Insights About Albumin and Liver Disease

Decompensated liver cirrhosis has a dismal prognosis, with an overall survival of 2-4 years, which is worse than for many oncological diseases. Albumin is an important tool in the management of patients with cirrhosis, since it decreases for less than half the risk for post-paracentesis cardiocirculatory dysfunction and mortality associated with spontaneous bacterial infection, as well as, it triplicates the response to terlipressin in patients with hepatorenal syndrome. Recently, research on albumin has been a hot topic, with important new insights such as the characterization of the pleiotropic effects of albumin (which surpass its oncotic properties) and the concept of effective albumin concentration. In fact, patients with liver cirrhosis present posttranslational modifications on albumin that compromises its function. Those modified albumin forms were proved to have prognostic value and its knowledge may change the paradigm of albumin treatment. In this review, we critically summarize the latest evidence on the potential benefits of albumin in patients with end-stage liver disease.

Alterations in conformational state of albumin in plasma in chronic hemodialyzed patients

OBJECTIVE

In chronic hemodialyzed (CH) patients the balance between production of reactive oxygen species and antioxidant defense system is disturbed and shifted towards oxidative conditions. The properties of albumin in CH patients were studied before hemodialysis (HD) and post-HD.

METHODS

Two oxidants were applied, organic t-butyl hydroperoxide (t-BOOH) and inorganic hydroperoxide (H2O2), for oxidation of albumin molecules. By comparison, albumin from healthy donors was also modified by both oxidants. The thiol content in albumin was determined by the Ellman method. Albumin properties were evaluated with the spin labelling technique using two covalently bound spin labels, maleimide (MSL) and iodoacetamide (ISL), and fatty acid spin probe, 16-doxylstearic acid (16-DS).

RESULTS

A decrease in thiols level in HD albumin was greater than in control albumin. The t-BOOH modified the microenvironment at the binding site of MSL and ISL in control albumin molecules to a greater extent than hydrogen peroxide. Control albumin treated with t-BOOH and H2O2 showed an increase in the mobility of 16-DS. However, no changes were observed in albumin from CH patients treated with either of the oxidizing agents.

CONCLUSION

Both oxidants induced strong conformational changes in albumin from healthy volunteers, but were less effective or ineffective in modification of albumin derived from CH patients. These results show that albumin from CH patients is highly modified in vivo and is not vulnerable to oxidation in the same way as normal albumin.

Non-oncotic properties of albumin. A multidisciplinary vision about the implications for critically ill patients

INTRODUCTION

Effective resuscitation with human albumin solutions is achieved with less fluid than with crystalloid solutions. However, the role of albumin in today's critical care unit is also linked to its multiple pharmacological effects. Areas covered: The potential clinical benefits of albumin in select populations of critically ill patients like sepsis seem related to immunomodulatory and anti-inflammatory effects, antibiotic transportation and endothelial stabilization. Albumin transports many drugs used in critically ill patients. Such binding to albumin is frequently lessened in critically ill patients with hypoalbuminemia. These changes could result in sub-optimal treatment. Albumin has immunomodulatory capacity by binding several bacterial products. Albumin also influences vascular integrity, contributing to the maintenance of the normal capillary permeability. Moreover, the albumin molecule encompasses several antioxidant properties, thereby significantly reducing re-oxygenation injury, which is especially important in sepsis. In fact, most studies of albumin administration are a combination of a degree of resuscitation with a degree of maintenance or supplementation of albumin. Expert commentary: The potential clinical benefits of the use of albumin in selected critically ill patients such as sepsis seem related to its immunomodulatory and anti-inflammatory effects, antioxidant properties, antibiotic transportation and endothelial stabilization. Additional studies are warranted to further elucidate the underlying physiologic and molecular rationale.

Abundance matters: role of albumin in diabetes, a proteomics perspective

INTRODUCTION

Human serum albumin (HSA) is a multifaceted protein with vital physiological functions. It is the most abundant plasma protein with inherent capability to bind to diverse ligands, and thus susceptible to various post-translational modifications (PTMs) which alter its structure and functions. One such PTM is glycation, a non-enzymatic reaction between reducing sugar and protein leading to formation of heterogeneous advanced glycation end products (AGEs). Glycated albumin (GA) concentration increases significantly in diabetes and is implicated in development of secondary complications. Areas covered: In this review, we discuss in depth, formation of GA and its consequences, approaches used for characterization and quantification of GA, milestones in GA proteomics, clinical relevance of GA as a biomarker, significance of maintaining abundant levels of albumin and future perspectives. Expert commentary: Elevated GA levels are associated with development of insulin resistance as well as secondary complications, in healthy and diabetic individuals respectively. Mass spectrometry (MS) based approaches aid in precise characterization and quantification of GA including early and advanced glycated peptides, which can be useful in prediction of the disease status. Thus GA has evolved to be one of the best candidates in the pursuit of diagnostic markers for prediction of prediabetes and diabetic complications.

In-vivo oxidized albumin- a pro-inflammatory agent in hypoalbuminemia

Hypoalbuminemia of Hemodialysis (HD) patients is an independent cardiovascular risk factor, however, there is no mechanistic explanation between hypoalbuminemia and vascular injury. In the event of oxidative stress and inflammation to which HD patients are exposed, albumin is oxidized and undetected by common laboratory methods, rendering an apparent hypoalbuminemia. We wanted to show that these circulating modified oxidized albumin molecules cause direct vascular damage, mediating inflammation. Once these in-vivo albumin modifications were reduced in- vitro, the apparent hypoalbuminemia concomitantly with its inflammatory effects, were eliminated. Albumin modification profiles from 14 healthy controls (HC) and 14 HD patients were obtained by mass spectrometry (MS) analyses before and after reduction in- vitro, using redox agent 1,4 dithiothreitol (DTT). Their inflammatory effects were explored by exposing human umbilical endothelial cells (HUVEC) to all these forms of albumin. Albumin separated from hypoalbuminemic HD patients increased endothelial mRNA expression of cytokines and adhesion molecules, and augmented secretion of IL-6. This endothelial inflammatory state was almost fully reverted by exposing HUVEC to the in-vitro reduced HD albumin. MS profile of albumin modifications peaks was similar between HD and HC, but the intensities of the various peaks were significantly different. Abolishing the reversible oxidative modifications by DTT prevented endothelial injury and increased albumin levels. The irreversible modifications such as glycation and sulfonation show low intensities in HD albumin profiles and are nearly unobserved in HC. We showed, for the first time, a mechanistic link between hypoalbuminemia and the pro-inflammatory properties of in-vivo oxidized albumin, initiating vascular injury.

Sepsis and septic shock: Pathogenesis and treatment perspectives

The majority of bacteremias do not develop to sepsis: bacteria are cleared from the bloodstream. Oxygen released from erythrocytes and humoral immunity kill bacteria in the bloodstream. Sepsis develops if bacteria are resistant to oxidation and proliferate in erythrocytes. Bacteria provoke oxygen release from erythrocytes to arterial blood. Abundant release of oxygen to the plasma triggers a cascade of events that cause: 1. oxygen delivery failure to cells; 2. oxidation of plasma components that impairs humoral regulation and inactivates immune complexes; 3. disseminated intravascular coagulation and multiple organs' failure. Bacterial reservoir inside erythrocytes provides the long-term survival of bacteria and is the cause of ineffectiveness of antibiotics and host immune reactions. Treatment perspectives that include different aspects of sepsis development are discussed.

Structural and functional integrity of human serum albumin: Analytical approaches and clinical relevance in patients with liver cirrhosis

Human serum albumin (HSA) is the most abundant circulating plasma protein. Besides a significant contribution to the osmotic pressure, it is also involved in the fine regulation of many other physiological processes, including the balance of the redox state, the inflammatory and/or immunological responses, and the pharmacokinetic and pharmacodynamics of many drugs. Growing evidence suggests that HSA undergoes structural and functional damage in diseases characterized by an enhanced systemic inflammatory response and oxidative stress, as it occurs in chronic liver disease. Based on their clinical relevance, this review provides a summary of the most common post-translational modifications affecting HSA structural integrity and functions and their clinical relevance in the field of liver disease. The review also provides a critical description of the analytical approaches employed for the investigation of conformational alterations and the identification/quantitation of specific post-translational modifications affecting HSA. Finally, the analytical methods available for the assessment of two of the most clinically relevant non-oncotic properties of HSA, namely the binding capacity and the antioxidant activity, are critically reviewed. Among the available techniques particular attention is given to those proposed for the in vitro and in vivo investigation of structurally modified albumin.

Oxidation of human serum albumin exhibits inter-individual variability after an ultra-marathon mountain race

The aim of this study was to examine the oxidation of human serum albumin (HSA) caused by oxidative stress following exhaustive and demanding exercise, such as an ultra-marathon race. For this purpose, blood samples from 12 adult runners who underwent a 103 km mountain ultra-marathon race were collected before the race, and also at 24, 48 and 72 h post-race. HSA was partially purified using affinity chromatography and consequently subjected to western blot analysis in order to determine the levels of disulfide dimers indicating oxidation. For reasons of comparison, the results were correlated with those from a previous study, in which the same samples were analyzed using different oxidative stress markers. The results revealed a good correlation between albumin dimers and protein carbonyls at all time points, while there was also a significant correlation with static oxidation reduction potential at 24 h, and a negative correlation with capacity oxidation reduction potential at 24 and 48 h. In addition, an individual analysis of albumin dimers exhibited great inter-individual differences, indicating the variation of HSA oxidation between different athletes. Namely, in some athletes, HSA seemed to be the main oxidation target of serum proteins, while in other athletes, there was even a reduction of HSA. This inter-individual variability in the oxidation of HSA may suggest that different interventions (e.g., through diet) may be required in order to confront the effects on athletes following strenuous exercise. On the whole, this study suggests the importance of the assessment of albumin dimers as a predictive marker for exercise-induced oxidative stress.

Clinical Implications Associated With the Posttranslational Modification-Induced Functional Impairment of Albumin in Oxidative Stress-Related Diseases

Recent research findings indicate that the posttranslational modification of human serum albumin (HSA) such as oxidation, glycation, truncation, dimerization, and carbamylation is related to certain types of diseases. We report herein on a simple and rapid analytical method, using an electrospray ionization time-of-flight mass spectrometry technique, that allows posttranslational modifications of HSA to be quantitatively and qualitatively evaluated with a high degree of sensitivity. In patients with chronic liver disease, chronic renal disease, and diabetes mellitus, an increase in the level of oxidized cysteine-34 (Cys-34) of HSA accompanied by a decrease in the level of reduced Cys-34 was observed. The redox status of Cys-34 was correlated with ligand binding and the antioxidative functions of HSA. Available evidence indicates that monitoring the redox state of Cys-34 not only could be a useful marker for evaluating the progression of disease and its complications but also would permit therapeutic efficacy to be predicted. The redox state of Cys-34 was also used as an index of the quality of HSA preparations. These data suggest that monitoring the posttranslational modifications of HSA can be important, because the function of HSA is related not only to its serum concentration but also to the preservation of its structural integrity under disease conditions.