Albumin-bound low molecular weight thiols analysis in plasma and carotid plaques by CE

Oxidative Modifications in Advanced Atherosclerotic Plaques: A Focus on In Situ Protein Sulfhydryl Group Oxidation

Although oxidative stress has been long associated with the genesis and progression of the atherosclerotic plaque, scanty data on its in situ effects on protein sulfhydryl group modifications are available. Within the arterial wall, protein sulfhydryls and low-molecular-weight (LMW) thiols are involved in the cell regulation of both Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS) levels and are a target for several posttranslational oxidative modifications that take place inside the atherosclerotic plaque, probably contributing to both atherogenesis and atherosclerotic plaque progression towards complicated lesions. Advanced carotid plaques are characterized by very high intraplaque GSH levels, due to cell lysis during apoptotic and/or necrotic events, probably responsible for the altered equilibrium among protein sulfhydryls and LMW thiols. Some lines of evidence show that the prooxidant environment present in atherosclerotic tissue could modify filtered proteins also by protein-SH group oxidation, and demonstrate that particularly albumin, once filtered, represents a harmful source of homocysteine and cysteinylglycine inside the plaque. The oxidative modification of protein sulfhydryls, with particular emphasis to protein thiolation by LMW thiols and its association with atherosclerosis, is the main topic of this review.

Microbial Redox Regulator-Enabled Pulldown for Rapid Analysis of Plasma Low-Molecular-Weight Biothiols

Although low-molecular-weight (LMW) biothiols function as a disease indicator in plasma, rapidly and effectively analyzing them remains challenging in the extracellular oxidative environment due to technical difficulties. Here, we report a newly designed, affinity pulldown platform using a Bacillus subtilis-derived organic hydroperoxide resistance regulatory (OhrR_BS) protein and its operator dsDNA for rapid and cost-effective analyses of plasma LMW biothiols. In the presence of organic hydroperoxide, LMW biothiols triggered the rapid dissociation of FAM-labeled dsDNA from FLAG-tagged OhrR_BS via S-thiolation of OhrR_BS on anti-FLAG antibody-coated beads, which led to a strong increase of fluorescence intensity in the supernatant after pulldown. This method was easily extended by using a reducing agent to detect free and total LMW biothiols simultaneously in mouse plasma. Unlike free plasma LMW biothiols, total plasma LMW biothiols were more elevated in ΔLDLR mice than those in normal mice. Owing to the rapid dissociation of OhrR/dsDNA complexes in response to LMW biothiols, this pulldown platform is immediately suitable for monitoring rapid redox changes in plasma LMW biothiols as well as studying oxidative stress and diseases in blood.

Homocysteine Modification in Protein Structure/Function and Human Disease

Epidemiological studies established that elevated homocysteine, an important intermediate in folate, vitamin B₁₂, and one carbon metabolism, is associated with poor health, including heart and brain diseases. Earlier studies show that patients with severe hyperhomocysteinemia, first identified in the 1960s, exhibit neurological and cardiovascular abnormalities and premature death due to vascular complications. Although homocysteine is considered to be a nonprotein amino acid, studies over the past 2 decades have led to discoveries of protein-related homocysteine metabolism and mechanisms by which homocysteine can become a component of proteins. Homocysteine-containing proteins lose their biological function and acquire cytotoxic, proinflammatory, proatherothrombotic, and proneuropathic properties, which can account for the various disease phenotypes associated with hyperhomocysteinemia. This review describes mechanisms by which hyperhomocysteinemia affects cellular proteostasis, provides a comprehensive account of the biological chemistry of homocysteine-containing proteins, and discusses pathophysiological consequences and clinical implications of their formation.

Levels of Urinary Trypsin Inhibitor and Structure of Its Chondroitin Sulphate Moiety in Type 1 and Type 2 Diabetes

BACKGROUND

Diabetes mellitus is a global health problem representing the fifth leading cause of mortality and a major risk factor for cardiovascular diseases. In the last years, we reported an association among urinary trypsin inhibitor (UTI), a small proteoglycan that plays pleiotropic roles in many inflammatory processes, and both type 1 and 2 diabetes and developed a method for its direct quantitation and structural characterization.

METHODS

Urine from 39 patients affected by type 1 diabetes, 32 patients with type 2 diabetes, and 52 controls were analysed. UTI was separated from the main glycosaminoglycans physiologically present in urine by anion exchange chromatography, treated for chondroitin sulphate (CS) chain complete depolymerisation, and analysed for both UTI content and CS structure. UTI identification was performed by nano-LC-MS/MS analysis.

RESULTS

We evidenced increased UTI levels, as well as reduced sulphation of its CS moiety in association with diabetes, regardless of both age and medium-term glycaemic control. Furthermore, no association between UTI and albumin excretion rate was found.

CONCLUSIONS

Evidences suggest that UTI levels are not directly correlated with renal function or, otherwise, that they may increase before the onset of renal impairment in diabetes, representing a potential marker for the underlying inflammatory condition.

Derivatization methods for LC–MS analysis of endogenous compounds

Sensitive and reliable analysis of endogenous compounds is critically important for many physiological and pathological studies. Methods based on LC–MS have progressed to become the method of choice for analyzing endogenous compounds. However, the analysis can be challenging due to various factors, including inherent low concentrations in biological samples, low ionization efficiency, undesirable chromatographic behavior and interferences of complex biological. The integration of chemical derivatization with LC–MS could enhance its capabilities in sensitivity and selectivity, and extend its application to a wider range of analytes. In this article, we will review the derivatization strategies in the LC–MS analysis of various endogenous compounds, and provide applications highlighting the impact of these important techniques in the evaluation of pathological events.

Human serum albumin Cys34 oxidative modifications following infiltration in the carotid atherosclerotic plaque

Objectives. To evaluate if the prooxidant environment present in atherosclerotic plaque may oxidatively modify filtered albumin. Methods. Fluorescein-5-maleimide labelled plasma samples and plaque extracts from 27 patients who had undergone carotid endarterectomy were analysed through nonreducing SDS-PAGE for albumin-Cys³⁴ oxidation. Furthermore, degree and pattern of S-thiolation in both circulating and plaque-filtered albumin were assayed. Results. Albumin filtered in the atherosclerotic plaque showed higher levels of Cys³⁴ oxidative modifications than the corresponding circulating form as well as different patterns of S-thiolation. Conclusions. Data indicate that the circulating albumin, once filtered in plaque, undergoes Cys³⁴ oxidative modifications and demonstrate for the first time that albumin is a homocysteine and cysteinylglycine vehicle inside the plaque environment.

Urine bikunin as a marker of renal impairment in Fabry's disease

Fabry's disease is a rare lysosomal storage disorder caused by the deficiency of α-galactosidase A that leads to the accumulation of neutral glycosphingolipids in many organs including kidney, heart, and brain. Since end-stage renal disease represents a major complication of this pathology, the aim of the present work was to evaluate if urinary proteoglycan/glycosaminoglycan excretion could represent a useful marker for monitoring kidney function in these patients at high risk. Quali-quantitative and structural analyses were conducted on plasma and urine from 24 Fabry's patients and 43 control subjects. Patients were sorted for presence and degree of renal impairment (proteinuria/renal damage). Results showed that levels of urine bikunin, also known as urinary trypsin inhibitor (UTI), are significantly higher in patients with renal impairment than in controls. In this respect, no differences were evidenced in plasma chondroitin sulfate isomers level/structure indicating a likely direct kidney involvement. Noteworthy, urine bikunin levels are higher in patients since early symptoms of renal impairment occur (proteinuria). Overall, our findings suggest that urine bikunin level, as well as proteinuria, could represent a useful parameter for monitoring renal function in those patients that do not present any symptoms of renal insufficiency.

Protein sulfhydryl group oxidation and mixed-disulfide modifications in stable and unstable human carotid plaques

Objectives. Oxidative stress has been implicated in the outcome of atherosclerotic plaques. However, at present, no data are available neither on the degree of plaque protein sulfhydryl groups oxidation nor on its relationship with plaque vulnerability. We investigated the entity of protein-SH oxidative modifications, focusing on low molecular weight thiols adduction, in human carotid plaque extracts in relation to plaque stability/instability. Methods. Plaque stability/instability was histologically assessed. The extent of protein-SH oxidative modifications was established by a differential proteomic approach on fluorescein-5-maleimide-labeled plaque extracts and corresponding plasma samples from 48 endarterectomized patients. The analysis on protein thiolation was performed by capillary zone electrophoresis. Results. We observed a higher protein-SH oxidation of both plasma-derived and topically expressed proteins in unstable plaques, partly due to higher levels of S-thiolation. Conversely, in plasma, none of the investigated parameters discriminated among patients with stable and unstable plaques. Conclusions. Our results suggest the presence of a more pronounced oxidative environment in unstable plaques. Identifying specific oxidative modifications and understanding their effects on protein function could provide further insight into the relevance of oxidative stress in atherosclerosis.