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

Protein Oxidative Modifications in Neurodegenerative Diseases: From Advances in Detection and Modelling to Their Use as Disease Biomarkers

Oxidation-reduction post-translational modifications (redox-PTMs) are chemical alterations to amino acids of proteins. Redox-PTMs participate in the regulation of protein conformation, localization and function, acting as signalling effectors that impact many essential biochemical processes in the cells. Crucially, the dysregulation of redox-PTMs of proteins has been implicated in the pathophysiology of numerous human diseases, including neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. This review aims to highlight the current gaps in knowledge in the field of redox-PTMs biology and to explore new methodological advances in proteomics and computational modelling that will pave the way for a better understanding of the role and therapeutic potential of redox-PTMs of proteins in neurodegenerative diseases. Here, we summarize the main types of redox-PTMs of proteins while providing examples of their occurrence in neurodegenerative diseases and an overview of the state-of-the-art methods used for their detection. We explore the potential of novel computational modelling approaches as essential tools to obtain insights into the precise role of redox-PTMs in regulating protein structure and function. We also discuss the complex crosstalk between various PTMs that occur in living cells. Finally, we argue that redox-PTMs of proteins could be used in the future as diagnosis and prognosis biomarkers for neurodegenerative diseases.

Applications of human and bovine serum albumins in biomedical engineering: A review

Serum albumin, commonly recognized as a predominant major plasma protein, is ubiquitously distributed among vertebrates, demonstrating versatility and widespread accessibility. Numerous studies have discussed the composition and attributes of human and bovine serum albumin; nonetheless, few systematic and comprehensive summaries on human and bovine serum albumin exist. This paper reviews the applications of human and bovine serum albumin in biomedical engineering. First, we introduce the differences in the structure of human and bovine serum albumin. Next, we describe the extraction methods for human and bovine serum albumin (fractionation process separation, magnetic adsorption, reverse micellar (RM) extraction, and genetic engineering) and the advantages and disadvantages of recently developed extraction methods. The characteristics of different processing forms of human and bovine serum albumin are also discussed, concomitantly elucidating their intrinsic properties, functions, and applications in biomedicine. Notably, their pivotal functions as carriers for drugs and tissue-engineered scaffolds, as well as their contributions to cell reproduction and bioimaging, are critically examined. Finally, to provide guidance for researchers in their future work, this review summarizes the current state of human and bovine serum albumin research and outlines potential future research topics.

Albumin of People with Diabetes Mellitus Is More Reduced at Low HbA1c

Oxidative stress is involved in the development, progression, and complications of diabetes mellitus (DM). Oxidative modification of human serum albumin's cysteine-34 is a marker for oxidative stress-related pathological conditions. We aimed to evaluate the redox state of albumin in patients with DM to investigate possible correlations with age, diabetes duration, and disease control status. Plasma aliquots were collected from 52 participants (26 type 1 and 26 type 2 DM). Patients were divided into two groups according to their glycated hemoglobin levels less than or equal to and greater than 58 mmol/L. Albumin redox state was assessed with high-performance liquid chromatography by fractionating it into human mercaptalbumin (HMA) and human nonmercaptalbumin 1 and 2 (HNA1 and HNA2). Albumin redox fractions were differently related to the age of study participants. In age-matched T1DM and T2DM groups, the albumin redox state was essentially the same. Irreversibly oxidized HNA2 was positively correlated with diabetes duration, especially in the T1DM group. HNA was increased in people with an increased HbA1c (>58 mmol/mol). Our results support the hypothesis that oxidative stress plays a crucial role in DM pathogenesis and emphasize the importance of diabetes control on systemic oxidative burden.

Beyond the amyloid cascade: An update of Alzheimer's disease pathophysiology

Alzheimer's disease (AD) is a multi-etiology disease. The biological system of AD is associated with multidomain genetic, molecular, cellular, and network brain dysfunctions, interacting with central and peripheral immunity. These dysfunctions have been primarily conceptualized according to the assumption that amyloid deposition in the brain, whether from a stochastic or a genetic accident, is the upstream pathological change. However, the arborescence of AD pathological changes suggests that a single amyloid pathway might be too restrictive or inconsistent with a cascading effect. In this review, we discuss the recent human studies of late-onset AD pathophysiology in an attempt to establish a general updated view focusing on the early stages. Several factors highlight heterogenous multi-cellular pathological changes in AD, which seem to work in a self-amplifying manner with amyloid and tau pathologies. Neuroinflammation has an increasing importance as a major pathological driver, and perhaps as a convergent biological basis of aging, genetic, lifestyle and environmental risk factors.

Feasibility, safety, and tolerability of two modalities of plasma exchange with albumin replacement to treat elderly patients with Alzheimer's disease in the AMBAR study

BACKGROUND

In the Alzheimer Management by Albumin Replacement (AMBAR) study, mild-to-moderate Alzheimer's disease (AD) patients were treated with a plasma exchange (PE) program. Feasibility and safety of PE in this specific population are poorly understood and were analyzed in detail in this study.

METHODS

Qualified patients were treated with 6 weeks of weekly conventional therapeutic plasma exchange (TPE) with albumin replacement followed by monthly low-volume plasma exchange (LVPE) for 12 months. The patients were divided into four groups: placebo (sham PE treatment), low-albumin (20 g), low-albumin + intravenous immunoglobulin (IVIG) (10 g), and high-albumin (40 g) + IVIG (20 g). Adverse events (AEs) were recorded and analyzed for all PE treatment groups and PE modalities.

RESULTS

PE procedure-related AEs were more common in the active treatment groups (16.9% out of 1283 TPE and 12.5% out of 2203 LVPE were associated with at least one AE, a similar rate than in other PE indications) than in the placebo group (0.7% out of 1223 sham PE). Percentage of procedures with at least one AEs was higher with central venous access compared to peripheral venous access in all three active treatment groups (20.1% vs 13.1%, respectively).

CONCLUSION

The TPE and LVPE procedures used in the AMBAR study on mild-to-moderate AD population were as safe and feasible as in other therapeutic applications of PE or routine plasmapheresis.

Plasma Exchange in Alzheimer's Disease

Therapeutic plasma exchange (TPE) has traditionally been used to selectively remove pathologic contents including autoantibodies, abnormal proteins, immune complexes, or toxins from a patient's plasma. In addition to the removal of molecular contributors to disease, fluid replacement and infusion of beneficial plasma constituents including albumin can be tapered based on the pathophysiologic mechanisms of the offending disease. This treatment modality has shown efficacy in symptomatic relief and slowing of disease progression for various neurologic, immunologic, and hematologic diseases. This review outlines the rationale for TPE in the treatment of Alzheimer's Disease (AD) through a potential mechanism leveraging the concentration gradient of amyloid β peptides and the infusion of albumin, and critically reviews the clinical evidence for treatment of AD using TPE and albumin replacement. This review also highlights potential sources of bias that must be considered in conjunction with the evidence of efficacy for the use of TPE in AD.

Redox State of Human Serum Albumin in Multiple Sclerosis: A Pilot Study

Like in many other pathologies, oxidative stress is involved in the development of neurodegenerative disorders. Human serum albumin (HSA) is the main protein in different body fluids including cerebrospinal fluid (CSF). By its redox state in terms of cysteine-34, albumin serves as marker for oxidative burden. We aimed to evaluate the redox state of HSA in patients with multiple sclerosis in serum and CSF in comparison to controls to identify possible correlations with disease activity and severity. Samples were stored at -70 °C until analysis by HPLC for the determination of albumin redox state in terms of the fractions of human mercaptalbumin (HMA), human nonmercaptalbumin1 (HNA1), and human nonmercaptalbumin2 (HNA2). Albumin in CSF showed significantly higher fractions of the reduced form HMA and decreased HNA1 and HNA2. There was no difference between albumin redox states in serum of patients and controls. In CSF of patients HNA2 showed a trend to higher fractions compared to controls. Albumin redox state in serum was associated with physical disability in remission while albumin redox state in CSF was related to disease activity. Thus, albumin redox state in serum and CSF of patients in relation to disease condition merits further investigation.

Severe and long-lasting alteration of albumin redox state by plasmapheresis

Plasmapheresis (PE) is an established form of therapeutic apheresis (TA). Purpose of this longitudinal prospective single center study was to investigate the effect of PE on albumin redox state (ARS), as infusion of commercial albumin during PE may alter albumin oxidation which has an impact on its functional properties and oxidative stress level. 43 subjects with autoimmune-mediated neurological disorders were included. 20 subjects in the experimental group received five treatments of PE. 13 subjects received five treatments of immunoadsorption and 10 subjects received no TA as controls. ARS was determined before and after TA and 12 days after the last TA by fractionating it into human mercaptalbumin (HMA), human non-mercaptalbumin 1 (HNA-1), and human non-mercaptalbumin 2 (HNA-2) by high-performance liquid chromatography. Irreversibly oxidised HNA-2 increased over the course of five PE treatments from 2.8% (IQR 1.3–3.7%) to 13.6% (IQR 10.9–15.9) (P < 0.01) and remained elevated 12 days after the last PE procedure (7.7% IQR 7.1–10.5, P < 0.05). The study showed for the first time that PE exerts a severe and long-lasting alteration on ARS indicating a new adverse effect of PE, that may influence oxidative stress level.

Neuropsychological, neuropsychiatric, and quality-of-life assessments in Alzheimer's disease patients treated with plasma exchange with albumin replacement from the randomized AMBAR study

INTRODUCTION

We report the effects of plasma exchange (PE) with albumin replacement on neuropsychological, neuropsychiatric, and quality-of-life (QoL) outcomes in mild-to-moderate Alzheimer's disease (AD) patients in a phase 2b/3 trial (Alzheimer's Management by Albumin Replacement [AMBAR] study).

METHODS

Three hundred forty-seven patients were randomized into placebo (sham-PE) and three PE-treatment arms with low/high doses of albumin, with/without intravenous immunoglobulin (IVIG). Specific test measurements were performed at baseline; month 2 (weekly conventional PE); months 6, 9, and 12 (monthly low-volume PE [LVPE]); and month 14.

RESULTS

The PE-treated mild-AD cohort improved their language fluency and processing speed versus placebo at month 14 (effect sizes: >100%; P-values: .03 to .001). The moderate-AD cohort significantly improved short-term verbal memory (effect sizes: 94% to >100%; P-values: .02 to .003). The progression of the neuropsychiatric symptoms of PE-treated was similar to placebo. Mild-AD patients showed improved QoL (P-values: .04 to .008).

DISCUSSION

PE-treated AD patients showed improvement in memory, language abilities, processing speed, and QoL-AD. No worsening of their psychoaffective status was observed.

A simple colorimetric assay to determine the concentration and proportion of human mercaptalbumin

Objectives

Design and methods

Results

Conclusions

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Concentrations of the reduced form of human serum albumin (human mercaptalbumin) were measured by a colorimetric assay using Michler's Hydrol.

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The assay uses the total thiol concentration to approximate the human mercaptalbumin concentration.

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Accuracy was improved by alkylating part of the samples and canceling the contribution of the non-thiol component to the colorimetric changes.

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Combining Michler's Hydrol assay with bromocresol purple assay enabled us to obtain the proportions of mercaptalbumin and non-mercaptalbumin, which correlated with HPLC as a reference method.

Human serum albumin in neurodegeneration

Serum albumin (SA) exists in relatively high concentrations, in close contact with most cells. However, in the adult brain, except for cerebrospinal fluid (CSF), SA concentration is relatively low. It is mainly produced in the liver to serve as the main protein of the blood plasma. In the plasma, it functions as a carrier, chaperon, antioxidant, source of amino acids, osmoregulator, etc. As a carrier, it facilitates the stable presence and transport of the hydrophobic and hydrophilic molecules, including free fatty acids, steroid hormones, medicines, and metal ions. As a chaperon, SA binds to and protects other proteins. As an antioxidant, thanks to a free sulfhydryl group (-SH), albumin is responsible for most antioxidant properties of plasma. These functions qualify SA as a major player in, and a mirror of, overall health status, aging, and neurodegeneration. The low concentration of SA is associated with cognitive deterioration in the elderly and negative prognosis in multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). SA has been shown to be structurally modified in neurological conditions such as Alzheimer's disease (AD). During blood-brain barrier damage albumin enters the brain tissue and could trigger epilepsy and neurodegeneration. SA is able to bind to the precursor agent of the AD, amyloid-beta (Aβ), preventing its toxic effects in the periphery, and is being tested for treating this disease. SA therapy may also be effective in brain rejuvenation. In the current review, we will bring forward the prominent properties and roles of SA in neurodegeneration.

Clinical Significance of Albumin- and Bilirubin-Based Biomarkers in Glaucoma: A Retrospective Case-Control Study

Glaucoma is the second leading cause of global blindness. The etiology of glaucoma is complicated. In addition to elevated intraocular pressure (IOP), several other mechanisms have been implicated in pathogenesis, such as oxidative stress and systemic inflammation. Serum albumin (ALB) and bilirubin (BIL) have been reported to have potent antioxidant properties and contribute to maintain redox homeostasis in various diseases. However, associations between these parameters and glaucoma remain mostly unknown. Here, we conducted a retrospective case-control study, revealing that serum ALB, total BIL (TBIL), and indirect BIL (IBIL) levels were markedly lower in glaucoma patients than those in healthy controls. Furthermore, the neutrophil-to-ALB (NAR), neutrophil-to-TBIL (NTBR), and neutrophil-to-IBIL (NIBR) ratios were greatly higher in glaucoma. Additionally, interestingly, lower ALB and BIL levels and higher NAR, NTBR, and NIBR were associated with severer glaucomatous visual impairment, and NAR, NTBR, and NIBR showed good accuracy as diagnostic tests for glaucoma severity, suggesting these indices might be useful as discriminative biomarkers for disease severity. Our current findings demonstrate associations between ALB, BIL, NAR, NTBR, NIBL, and glaucoma. It might be useful to use NAR, NTBR, and NIBR as predictive markers for disease severity and employ ALB/BIL as alternative therapy or adjuvant medicines in glaucoma patients.

Interactions of intrinsically disordered proteins with the unconventional chaperone human serum albumin: From mechanisms of amyloid inhibition to therapeutic opportunities

Human Serum Albumin (HSA), the most abundant protein in plasma, serves a diverse repertoire of biological functions including regulation of oncotic pressure and redox potential, transport of serum solutes, but also chaperoning of misfolded proteins. Here we review how HSA interacts with a wide spectrum of client proteins including intrinsically disordered proteins (IDPs) such as Aβ, the islet amyloid peptide (IAPP), alpha synuclein and stressed globular proteins such as insulin. The comparative analysis of the HSA chaperone - client interactions reveals that the amyloid-inhibitory function of HSA arises from at least four emerging mechanisms. Two mechanisms (the monomer stabilizer model and the monomer competitor model) involve the direct binding of HSA to either IDP monomers or oligomers, while other mechanisms (metal chelation and membrane protection) rely on the indirect modulation by HSA of other factors that drive IDP aggregation. While HSA is not the only extracellular chaperone, given its abundance, HSA is likely to account for a significant fraction of the chaperoning effects in plasma, thus opening new therapeutic opportunities in the context of the peripheral sink hypothesis.

Oxidative Modification of Proteins: From Damage to Catalysis, Signaling, and Beyond

Significance: The systematic investigation of oxidative modification of proteins by reactive oxygen species started in 1980. Later, it was shown that reactive nitrogen species could also modify proteins. Some protein oxidative modifications promote loss of protein function, cleavage or aggregation, and some result in proteo-toxicity and cellular homeostasis disruption. Recent Advances: Previously, protein oxidation was associated exclusively to damage. However, not all oxidative modifications are necessarily associated with damage, as with Met and Cys protein residue oxidation. In these cases, redox state changes can alter protein structure, catalytic function, and signaling processes in response to metabolic and/or environmental alterations. This review aims to integrate the present knowledge on redox modifications of proteins with their fate and role in redox signaling and human pathological conditions. Critical Issues: It is hypothesized that protein oxidation participates in the development and progression of many pathological conditions. However, no quantitative data have been correlated with specific oxidized proteins or the progression or severity of pathological conditions. Hence, the comprehension of the mechanisms underlying these modifications, their importance in human pathologies, and the fate of the modified proteins is of clinical relevance. Future Directions: We discuss new tools to cope with protein oxidation and suggest new approaches for integrating knowledge about protein oxidation and redox processes with human pathophysiological conditions. Antioxid. Redox Signal. 35, 1016-1080.

Serum Albumin in Health and Disease: Esterase, Antioxidant, Transporting and Signaling Properties

Being one of the main proteins in the human body and many animal species, albumin plays a decisive role in the transport of various ions-electrically neutral and charged molecules-and in maintaining the colloidal osmotic pressure of the blood. Albumin is able to bind to almost all known drugs, as well as many nutraceuticals and toxic substances, largely determining their pharmaco- and toxicokinetics. Albumin of humans and respective representatives in cattle and rodents have their own structural features that determine species differences in functional properties. However, albumin is not only passive, but also an active participant of pharmacokinetic and toxicokinetic processes, possessing a number of enzymatic activities. Numerous experiments have shown esterase or pseudoesterase activity of albumin towards a number of endogeneous and exogeneous esters. Due to the free thiol group of Cys34, albumin can serve as a trap for reactive oxygen and nitrogen species, thus participating in redox processes. Glycated albumin makes a significant contribution to the pathogenesis of diabetes and other diseases. The interaction of albumin with blood cells, blood vessels and tissue cells outside the vascular bed is of great importance. Interactions with endothelial glycocalyx and vascular endothelial cells largely determine the integrative role of albumin. This review considers the esterase, antioxidant, transporting and signaling properties of albumin, as well as its structural and functional modifications and their significance in the pathogenesis of certain diseases.

Serum Albumin: A Multifaced Enzyme

Human serum albumin (HSA) is the most abundant protein in plasma, contributing actively to oncotic pressure maintenance and fluid distribution between body compartments. HSA acts as the main carrier of fatty acids, recognizes metal ions, 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 esterase, enolase, glucuronidase, and peroxidase (pseudo)-enzymatic activities. HSA-based catalysis is physiologically relevant, affecting the metabolism of endogenous and exogenous compounds including proteins, lipids, cholesterol, reactive oxygen species (ROS), and drugs. Catalytic properties of HSA are modulated by allosteric effectors, competitive inhibitors, chemical modifications, pathological conditions, and aging. HSA displays anti-oxidant properties and is critical for plasma detoxification from toxic agents and for pro-drugs activation. The enzymatic properties of HSA can be also exploited by chemical industries as a scaffold to produce libraries of catalysts with improved proficiency and stereoselectivity for water decontamination from poisonous agents and environmental contaminants, in the so called “green chemistry” field. Here, an overview of the intrinsic and metal dependent (pseudo-)enzymatic properties of HSA is reported to highlight the roles played by this multifaced protein.

Therapeutic plasma exchange with albumin: a new approach to treat Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is a chronic neurodegenerative disease and the most common cause of dementia. It has a complex pathophysiology that is not yet completely understood, where multiple central, systemic, and environmental factors play a key role in disease progression. Understanding the multifactorial nature of AD is paramount to formulate new therapies.

AREAS COVERED

The authors reviewed the role of the amyloid-β-binding, antioxidant, and immunomodulatory properties of albumin in AD and the use of therapeutic plasma exchange (PE) in neurology. The results from the Alzheimer Management By Albumin Replacement (AMBAR) trial that combined the use of PE with albumin replacement in patients with mild-to-moderate AD, are also analyzed.

EXPERT OPINION

Findings from the AMBAR study provide encouraging results in the treatment of AD with PE and albumin replacement, especially in patients at the moderate stage of the disease, who showed less cognitive decline from baseline compared with placebo in most of the variables analyzed. Further research is warranted to ascertain the possible mechanisms of action underlying these results. Different cohorts of patients that may also benefit from this treatment, such as those with mild cognitive impairment or other types of dementia, could also be the target of additional studies.

Recent Advancements in Electrochemical Biosensors for Alzheimer's Disease Biomarkers Detection

Background

It is estimated that the average time between the diagnosis of Alzheimer’s disease (AD) and the patient’s death is 5-9 years. Therefore, both the initial phase of the disease and the preclinical state can be included in the critical period in disease diagnosis. Accordingly, huge progress has recently been observed in biomarker research to identify risk factors for dementia in older people with normal cognitive functions and mild cognitive impairments.

Methods

Electrochemical biosensors are excellent analytical tools that are used in the detection of AD biomarkers as they are easy to use, portable, and can do analysis in real time.

Results

This review presents the analytical techniques currently used to determine AD biomarkers in terms of their advantages and disadvantages; the most important clinical biomarkers of AD and their role in the disease. All recently used biorecognition molecules in electrochemical biosensor development, i.e., receptor protein, antibodies, aptamers and nucleic acids, are summarized for the first time. Novel electrochemical biosensors for AD biomarker detection, as ideal analytical platforms for point-of-care diagnostics, are also reviewed.

Conclusion

The article focuses on various strategies of biosensor chemical surface modifications to immobilize biorecognition molecules, enabling specific, quantitative AD biomarker detection in synthetic and clinical samples. In addition, this is the first review that presents innovative single-platform systems for simultaneous detection of multiple biomarkers and other important AD-associated biological species based on electrochemical techniques. The importance of these platforms in disease diagnosis is discussed.

Ischemia-Modified Albumin: Origins and Clinical Implications

Albumin is one of the most abundant proteins in the body of mammals: about 40% of its pool is located in the intravascular space and the remainder is found in the interstitial space. The content of this multifunctional protein in blood is about 60-65% of total plasma proteins. A decrease in its synthesis or changes of functional activity can destabilize oncotic blood pressure, cause a violation of transporting hormones, fatty acids, metals, and drugs. Albumin properties change under ischemic attacks associated with oxidative stress, production of reactive oxygen species, and acidosis. Under these conditions, ischemia-modified albumin (IMA) is generated that has a reduced metal-binding capacity, especially for transition metals, such as copper, nickel, and cobalt. The method of determining the cobalt-binding capability of HSA was initially proposed to evaluate IMA level and then licensed as an ACB test for routine clinical analysis for myocardial ischemia. Subsequent studies have shown the viability of the ACB test in diagnosing other diseases associated with the development of oxidative stress. This review examines recent data on IMA generation mechanisms, describes principles, advantages, and limitations of methods for evaluation of IMA levels, and provides detailed analysis of its use in diagnostic and monitoring therapeutic efficacy in different diseases.

Emerging insights into the role of albumin with plasma exchange in Alzheimer's disease management

Alzheimer's disease (AD) is a neurodegenerative process that inexorably leads to progressive deterioration of cognition function and, ultimately, death. Central pathophysiologic features of AD include the accumulation of extracellular plaques comprised of amyloid-β peptide (Aβ) and the presence of intraneuronal neurofibrillary tangles. However, a large body of evidence suggests that oxidative stress and inflammation are major contributors to the pathogenesis and progression of AD. To date, available pharmacologic treatments are only symptomatic. Clinical trials focused on amyloid and non-amyloid-targeted treatments with small molecule pharmacotherapy and immunotherapies have accumulated a long list of failures. Considering that around 90 % of the circulating Aβ is bound to albumin, and that a dynamic equilibrium exists between peripheral and central Aβ, plasma exchange with albumin replacement has emerged as a new approach in a multitargeted AD therapeutic strategy (AMBAR Program). In plasma exchange, a patient's plasma is removed by plasmapheresis to eliminate toxic endogenous substances, including Aβ and functionally impaired albumin. The fluid replacement used is therapeutic albumin, which acts not only as a plasma volume expander but also has numerous pleiotropic functions (e.g., circulating Aβ- binding capacity, transporter, detoxifier, antioxidant) that are clinically relevant for the treatment of AD. Positive results from the AMBAR Program (phase 1, 2, an 2b/3 trials), i.e., slower decline or stabilization of disease symptoms in the most relevant clinical efficacy and safety endpoints, offer a glimmer of hope to both AD patients and caregivers.

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.

Oxidized Albumin as a Mediator of Kidney Disease

Renal diseases are a global health concern, and nearly 24% of kidney disease patients are overweight or obese. Particularly, increased body mass index has been correlated with oxidative stress and urinary albumin excretion in kidney disease patients, also contributing to increased cardiovascular risk. Albumin is the main plasma protein and is able to partially cross the glomerular filtration barrier, being reabsorbed mainly by the proximal tubule through different mechanisms. However, it has been demonstrated that albumin suffers different posttranslational modifications, including oxidation, which appears to be tightly linked to kidney damage progression and is increased in obese patients. Plasma-oxidized albumin levels correlate with a decrease in estimated glomerular filtration rate and an increase in blood urea nitrogen in patients with chronic kidney disease. Moreover, oxidized albumin in kidney disease patients is independently correlated with higher plasma levels of transforming growth factor beta (TGF-β1), tumor necrosis factor (TNF-α), and interleukin (IL)-1β and IL-6. In addition, oxidized albumin exerts a direct effect on neutrophils by augmenting the levels of neutrophil gelatinase-associated lipocalin, a well-accepted biomarker for renal damage in patients and in different experimental settings. Moreover, it has been suggested that albumin oxidation occurs at early stages of chronic kidney disease, accelerating the patient requirements for dialytic treatment during disease progression. In this review, we summarize the evidence supporting the role of overweight- and obesity-induced oxidative stress as a critical factor for the progression of renal disease and cardiovascular morbimortality through albumin oxidation.

The Universal Soldier: Enzymatic and Non-Enzymatic Antioxidant Functions of Serum Albumin

As a carrier of many biologically active compounds, blood is exposed to oxidants to a greater extent than the intracellular environment. Serum albumin plays a key role in antioxidant defence under both normal and oxidative stress conditions. This review evaluates data published in the literature and from our own research on the mechanisms of the enzymatic and non-enzymatic activities of albumin that determine its participation in redox modulation of plasma and intercellular fluid. For the first time, the results of numerous clinical, biochemical, spectroscopic and computational experiments devoted to the study of allosteric modulation of the functional properties of the protein associated with its participation in antioxidant defence are analysed. It has been concluded that it is fundamentally possible to regulate the antioxidant properties of albumin with various ligands, and the binding and/or enzymatic features of the protein by changing its redox status. The perspectives for using the antioxidant properties of albumin in practice are discussed.

Human Serum Albumin-Inspired Glycopeptide-Based Multifunctional Inhibitor of Amyloid-β Toxicity

In Alzheimer's disease (AD), insoluble Aβ42 peptide fragments self-aggregate and form oligomers and fibrils in the brain, causing neurotoxicity. Further, the presence of redox-active metal ions such as Cu2+ enhances the aggregation process through chelation with these Aβ42 aggregates as well as generation of Aβ42-mediated reactive oxygen species (ROS). Herein, we have adopted a bioinspired strategy to design and develop a multifunctional glycopeptide hybrid molecule (Glupep), which can serve as a potential AD therapeutic. This molecule consists of a natural metal-chelating tetrapeptide motif of human serum albumin (HSA), a β-sheet breaker peptide, and a sugar moiety for better bioavailability. We performed different biophysical and docking experiments, which revealed that Glupep not only associates with Aβ42 but also prevents its self-aggregation to form toxic oligomers and fibrils. Moreover, Glupep was also shown to sequester out Cu2+ from the Aβ-Cu2+ complex, reducing the ROS formation and toxicity. Besides, this study also revealed that Glupep could protect PC12-derived neurons from Aβ-Cu2+-mediated toxicity by reducing intracellular ROS generation and stabilizing the mitochondrial membrane potential. All these exciting features show Glupep to be a potent inhibitor of Aβ42-mediated multifaceted toxicity and a prospective therapeutic lead for AD.

A randomized, controlled clinical trial of plasma exchange with albumin replacement for Alzheimer's disease: Primary results of the AMBAR Study

Introduction

This phase 2b/3 trial examined the effects of plasma exchange (PE) in patients with mild‐to‐moderate Alzheimer's disease (AD).

Methods

Three hundred forty‐seven patients (496 screened) were randomized (1:1:1:1) into three PE treatment arms with different doses of albumin and intravenous immunoglobulin replacement (6‐week period of weekly conventional PE followed by a 12‐month period of monthly low‐volume PE), and placebo (sham).

Results

PE‐treated patients performed significantly better than placebo for the co‐primary endpoints: change from baseline of Alzheimer's Disease Cooperative Study–Activities of Daily Living (ADCS‐ADL; P = .03; 52% less decline) with a trend for Alzheimer's Disease Assessment Scale–Cognitive Subscale (ADAS‐Cog; P = .06; 66% less decline) scores at month 14. Moderate‐AD patients (baseline Mini‐Mental State Examination [MMSE] 18‐21) scored better on ADCS‐ADL (P = .002) and ADAS‐Cog (P = .05), 61% less decline both. There were no changes in mild‐AD patients (MMSE 22‐26). PE‐treated patients scored better on the Clinical Dementia Rating Sum of Boxes (CDR‐sb) (P = .002; 71% less decline) and Alzheimer's Disease Cooperative Study‐Clinical Global Impression of Change (ADCS‐CGIC) (P < .0001; 100% less decline) scales.

Discussion

This trial suggests that PE with albumin replacement could slow cognitive and functional decline in AD, although further studies are warranted.

Human CNS barrier-forming organoids with cerebrospinal fluid production

Cerebrospinal fluid (CSF) is a vital liquid, providing nutrients and signaling molecules and clearing out toxic by-products from the brain. The CSF is produced by the choroid plexus (ChP), a protective epithelial barrier that also prevents free entry of toxic molecules or drugs from the blood. Here, we establish human ChP organoids with a selective barrier and CSF-like fluid secretion in self-contained compartments. We show that this in vitro barrier exhibits the same selectivity to small molecules as the ChP in vivo and that ChP-CSF organoids can predict central nervous system (CNS) permeability of new compounds. The transcriptomic and proteomic signatures of ChP-CSF organoids reveal a high degree of similarity to the ChP in vivo. Finally, the intersection of single-cell transcriptomics and proteomic analysis uncovers key human CSF components produced by previously unidentified specialized epithelial subtypes.

Intestinal Permeability and Oral Absorption of Selected Drugs Are Reduced in a Mouse Model of Familial Alzheimer's Disease

Compared with the significant number of studies reporting altered abundance and function of drug transporters at the blood-brain barrier (BBB) in Alzheimer's disease (AD), the impact of AD on the abundance of intestinal drug transporters and the subsequent effects on oral drug absorption have received little attention. We have reported the altered abundance of some small intestinal drug transporters in a familial mouse model of AD; however, whether this leads to altered oral drug absorption is unknown. The current study examined plasma concentrations of caffeine and diazepam (markers for transcellular passive transport), digoxin (P-glycoprotein substrate), and valsartan (multidrug resistance-associated protein 2 substrate) following oral administration to 8-10 month old female wild-type (WT) and APPswe/PSEN1dE9 (APP/PS1) transgenic mice, a commonly used mouse model of familial AD. The plasma exposure of valsartan and digoxin was significantly (p < 0.05) lower in APP/PS1 animals compared with WT mice, whereas the plasma concentrations of the passive transcellular markers caffeine and diazepam did not significantly differ between the two genotypes. To assess whether the reduced oral absorption of valsartan and digoxin was due to decreased intestinal transport, the ex vivo transport of the previously mentioned drugs and mannitol (a marker of paracellular transport) across the jejunum of WT and APP/PS1 mice was assessed over 120 min. In line with the in vivo absorption studies, the permeability of caffeine and diazepam did not significantly differ between WT and APP/PS1 mice. The permeability of ³H-digoxin through the APP/PS1 mouse jejunum was lower than that measured through the WT jejunum; the average amount (relative to dose applied) permeating the tissue over 120 min was 0.22 ± 0.11% (mean ± SD) for the APP/PS1 jejunum and 0.85 ± 0.3% for the WT jejunum. A 1.9-fold reduction in the average amount of valsartan permeating the jejunum of APP/PS1 mice relative to that of WT mice was also detected. Although no apparent morphological alterations were observed in the jejunal tissue of APP/PS1 mice, the permeability of ¹⁴C-mannitol across the jejunum from APP/PS1 mice was lower than that across the WT jejunum (P_app= 10.7 ± 3.7 × 10^-6 and 6.0 ± 3.4 × 10^-6 cm/s, respectively), suggesting tightened paracellular junctions in APP/PS1 mice. These studies are the first to demonstrate, in APP/PS1 mice, reduced intestinal permeability and the absorption of drugs commonly prescribed to people with AD for their comorbidities. If these findings translate to people with AD, then modified dosing regimens may be necessary for selected drugs to ensure that their plasma concentrations remain in the effective range.

Aging-Related and Gender Specific Albumin Misfolding in Alzheimer's Disease

Aging-related protein misfolding and aggregation may play critical roles in the pathogenesis of numerous diseases. In the brain, extracellular aggregated amyloid-β (Aβ) is closely related to the death of neurons in individuals with Alzheimer's disease (AD). Albumin-Aβ binding is important in preventing Aβ fibril aggregation. However, because albumin is the most abundant and important antioxidant in the circulation, aging-related oxidative stress could have a significant effect on the molecular conformation and binding capacities of albumin. To investigate the link between misfolded albumin and AD, we developed fluorescent assays to determine the effects of misfolded albumin on membrane integrity in the presence of a lipolytic, inflammatory response-like enzyme, secretory phospholipase A2 (sPLA2). We found that misfolded albumin increased degradation of phospholipids in highly fluid bilayer membranes in the presence of sPLA2 due to hydrophobic effects of misfolded albumin. High amounts of misfolded albumin were present in sera of elderly (average 74 years) versus young (average 24 years) subjects (p < 0.0001). Albumin in cerebrospinal fluid (CSF) of elderly subjects, though present in small concentrations, had a 2- to 3-fold increased capacity to promote sPLA2-catalyzed membrane phospholipid degradation as compared with the same amount of albumin in serum (p < 0.0001). In addition, the fatty acid binding capacity of albumin in CSF from female subjects was considerably lower than values obtained for men, especially for individuals diagnosed with AD (p = 0.0006). This study suggests that inflammation, misfolded albumin and/or other dysfunctional proteins, and changes in membrane fluidity could alter cell membrane integrity and homeostasis and contribute to the pathogenesis of aging-related dementia and AD.

Effect of CTerm of human albumin on the aggregation propensity of Aβ1-42 peptide: a potential of mean force study

Alzheimer's disease (AD) is the most common progressive neurodegenerative brain disorder. It is characterized by the presence of extracellular aggregated fibrillary form of amyloid beta (Aβ) peptide and intraneuronal neurofibrillary tangles caused by the hyperphosphorylation of tau protein. Monomeric form of Aβ peptide in α-conformation is not toxic but it can undergo self-aggregation to form β-conformation which is neurotoxic. The most promising approach to combat AD is to prevent the self-aggregation of Aβ peptide. Recently, it has been reported that C-terminal (CTerm) of human albumin (HA) binds to the Aβ_1-42 peptide and impairs the Aβ_1-42 aggregation and promotes disassembly of Aβ_1-42 aggregates. In this work, using potential of mean force (PMF) and binding free energy (BFE) calculations, we have demonstrated the effect of CTerm of HA on the dimerization of Aβ_1-42 peptide. From the PMF profile, we noticed Aβ_1-42-CTerm Heterodimer (10.99 kcal mol - 1) complex to have higher disassociation energy than Aβ_1-42-Aβ_1-42 homodimer (2.23 kcal mol - 1) complex. And also from the BFE calculations, we found that the binding affinity between Aβ_1-42 peptide and CTerm (ΔG_bind = -32.27 kcal mol - 1 from MM-GBSA and ΔG_bind = -2.83 kcal mol - 1 from MM-PBSA (molecular mechanics-Poisson - Boltzmann surface area)) to be stronger than the Aβ_1-42 peptide and another Aβ_1-42 peptide (ΔG_bind = -16.20 kcal mol - 1 from MM-GBSA and ΔG_bind = -1.95 kcal mol - 1 from MM-PBSA). In this study, our findings from PMF and BFE analysis of the two complexes provide salient structural, binding and unbinding features and thermodynamics that support the ability of CTerm of HA in affecting the dimerization of Aβ_1-42. Communicated by Ramaswamy H. Sarma.

Albumin Exchange in Alzheimer's Disease: Might CSF Be an Alternative Route to Plasma?

Amyloid β (Aβ) in brain parenchyma is thought to play a central role in the pathogenesis of Alzheimer's disease (AD). Aβ is transported from the brain to the plasma via complex transport mechanisms at the blood-brain barrier (BBB). About 90-95% of plasma Aβ may be bound to albumin. Replacement of serum albumin in plasma has been proposed as a promising therapy for AD. However, the efficacy of this approach may be compromised by altered BBB Aβ receptors in AD, as well as multiple pools of Aβ from other organs in exchange with plasma Aβ, competing for albumin binding sites. The flow of interstitial fluid (ISF) into cerebrospinal fluid (CSF) is another major route of Aβ clearance. Though the concentration of albumin in CSF is much lower than in plasma, the mixing of CSF with ISF is not impeded by a highly selective barrier and, hence, Aβ in the two pools is in more direct exchange. Furthermore, unlike in plasma, Aβ in CSF is not in direct exchange with multiple organ sources of Aβ. Here we consider albumin replacement in CSF as an alternative method for therapeutic brain Aβ removal and describe the possible advantages and rationale supporting this hypothesis.

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.