The role and mechanism of protein post­translational modification in vascular calcification (Review).

Vascular calcification is closely associated with morbidity and mortality in patients with chronic kidney disease, atherosclerosis and diabetes. In the past few decades, vascular calcification has been studied extensively and the findings have shown that the mechanism of vascular calcification is not merely a consequence of a high-phosphorus and high-calcium environment but also an active process characterized by abnormal calcium phosphate deposition on blood vessel walls that involves various molecular mechanisms. Recent advances in bioinformatics approaches have led to increasing recognition that aberrant post-translational modifications (PTMs) play important roles in vascular calcification. This review presents the latest progress in clarifying the roles of PTMs, such as ubiquitination, acetylation, carbamylation and glycosylation, as well as signaling pathways, such as the Wnt/ß-catenin pathway, in vascular calcification.

Antibody profiles in the mosaic of "seronegative" APS syndrome.

Clinical manifestations, as distinct from thrombotic and obstetric morbidity, were recently included in the update of classification criteria of the antiphospholipid syndrome (APS). However, the existence of several patients with clinical manifestations suggestive of APS, but negative for criteria antiphospholipid antibodies (aPLs) [anti-cardiolipin antibodies (aCL), anti-ß2-glycoprotein I antibodies (aß2-GPI) and lupus anticoagulant] may suggest an update of diagnostic criteria. In this study, we analyzed the prevalence of six non-criteria aPLs in a large monocentric cohort of patients with seronegative APS (SN-APS), to investigate their possible diagnostic role. aCL IgA, aß2-GPI IgA and aß2-GPI Domain 1 antibodies were detected by chemiluminescence, anti-phosphatidylserine/prothrombin (aPS/PT) IgG, anti-vimentin/cardiolipin (aVim/CL) IgG and anti-carbamylated-ß2-glycoprotein I (aCarb-ß2-GPI) IgG by ELISA in sera from 144 SN-APS patients. In SN-APS patients, aCL IgA were detected in 4/144 (2.77%), aß2-GPI IgA in 2/144 (1.39%), aß2-GPI-Domain 1 in 1/144 (0.69%), aPS/PT in 16/144 (11.11%), aVim/CL in 37/144 (25.69%) and aCarb-ß2-GPI in 43/144 patients (29.86%). Patients negative for all non-criteria aPL assays were 77/144 (53.47%). Notably, the Venn diagram showed that aCarb-ß2-GPI together with aVim/CL represented the prevalent combination of positive antibodies. In SN-APS patients, aCL IgA were associated with recurrent thrombosis (OR11.48; p=0.03); in obstetric SN-APS patients, aPS/PT were significantly associated with foetal deaths (OR4.84; p=0.01), aVim/CL with spontaneous abortions (OR2.71; p=0.016). This study indicates that aPS/PT, aVim/CL and aCarb-ß2-GPI antibodies may represent useful tools to identify "seronegative" APS patients, who are negative for criteria aPLs, supporting the need to make testing for non-criteria aPLs more accessible in patients with SN-APS.

Structures of wild-type and a constitutively closed mutant of connexin26 shed light on channel regulation by CO2.

Connexins allow intercellular communication by forming gap junction channels (GJCs) between juxtaposed cells. Connexin26 (Cx26) can be regulated directly by CO2. This is proposed to be mediated through carbamylation of K125. We show that mutating K125 to glutamate, mimicking the negative charge of carbamylation, causes Cx26 GJCs to be constitutively closed. Through cryo-EM we observe that the K125E mutation pushes a conformational equilibrium towards the channel having a constricted pore entrance, similar to effects seen on raising the partial pressure of CO2. In previous structures of connexins, the cytoplasmic loop, important in regulation and where K125 is located, is disordered. Through further cryo-EM studies we trap distinct states of Cx26 and observe density for the cytoplasmic loop. The interplay between the position of this loop, the conformations of the transmembrane helices and the position of the N-terminal helix, which controls the aperture to the pore, provides a mechanism for regulation.

Comparative CKD risk prediction using homocitrulline and carbamylated albumin: two circulating markers of protein carbamylation.

BACKGROUND: Protein carbamylation, a post-translational protein modification primarily driven by urea, independently associates with adverse clinical outcomes in patients with CKD. Biomarkers used to quantify carbamylation burden have mainly included carbamylated albumin (C-Alb) and homocitrulline (HCit, carbamylated lysine). In this study, we aimed to compare the prognostic utility of these two markers in order to facilitate comparisons of existing studies employing either marker alone, and to inform future carbamylation studies. METHODS: Both serum C-Alb and free HCit levels were assayed from the same timepoint in 1632 individuals with CKD stages 2-4 enrolled in the prospective Chronic Renal Insufficiency Cohort (CRIC) study. Adjusted Cox proportional hazard models were used to assess risks for the outcomes of death (primary) and end stage kidney disease (ESKD) using each marker. C-statistics, net reclassification improvement, and integrated discrimination improvement were used to compare the prognostic value of each marker. RESULTS: Participant demographics included mean (SD) age 59 (11) years; 702 (43%) females; 700 (43%) white. C-Alb and HCit levels were positively correlated with one another (Pearson correlation coefficient 0.64). Higher C-Alb and HCit levels showed similar increased risk of death (e.g., the adjusted hazard ratio [HR] for death in the 4th carbamylation quartile compared to the 1st was 1.90 (95% confidence interval [CI] 1.35-2.66) for C-Alb, and 1.89 [1.27-2.81] for HCit; and on a continuous scale, the adjusted HR for death using C-Alb was 1.24 [1.11 to 1.39] per standard deviation increase, and 1.27 [1.10-1.46] using HCit). Both biomarkers also had similar HRs for ESKD. The C-statistics were similar when adding each carbamylation biomarker to base models (e.g., for mortality models, the C-statistic was 0.725 [0.707-0.743] with C-Alb and 0.725 [0.707-0.743] with HCit, both compared to a base model 0.723). Similarities were also observed for the net reclassification improvement and integrated discrimination improvement metrics. CONCLUSIONS: C-Alb and HCit had similar performance across multiple prognostic assessments. The markers appear readily comparable in CKD epidemiological studies.

A novel DNase assay reveals low DNase activity in severe asthma.

Secreted deoxyribonucleases (DNases), such as DNase-I and DNase-IL3, degrade extracellular DNA, and endogenous DNases have roles in resolving airway inflammation and guarding against autoimmune responses to nucleotides. Subsets of patients with asthma have high airway DNA levels, but information about DNase activity in health and in asthma is lacking. To characterize DNase activity in health and in asthma, we developed a novel kinetic assay using a Taqman probe sequence that is quickly cleaved by DNase-I to produce a large product signal. We used this kinetic assay to measure DNase activity in sputum from participants in the Severe Asthma Research Program (SARP)-3 (n = 439) and from healthy controls (n = 89). We found that DNase activity was lower than normal in asthma [78.7 relative fluorescence units (RFU)/min vs. 120.4 RFU/min, P < 0.0001]. Compared to patients with asthma with sputum DNase activity in the upper tertile activity levels, those in the lower tertile of sputum DNase activity were characterized clinically by more severe disease and pathologically by airway eosinophilia and airway mucus plugging. Carbamylation of DNase-I, a post-translational modification that can be mediated by eosinophil peroxidase, inactivated DNase-I. In summary, a Taqman probe-based DNase activity assay uncovers low DNase activity in the asthma airway that is associated with more severe disease and airway mucus plugging and may be caused, at least in part, by eosinophil-mediated carbamylation.NEW & NOTEWORTHY We developed a new DNase assay and used it to show that DNase activity is impaired in asthma airways.

Neutrophils in Inflammatory Bone Diseases.

PURPOSE OF REVIEW: In this review, we summarize the current evidence that suggests that neutrophils play a key role in facilitating damage to local bone structures. RECENT FINDINGS: Neutrophil infiltration is a hallmark of inflammatory bone diseases such as rheumatoid arthritis (RA) and periodontitis disease (PD). Both of these human diseases are marked by an imbalance in bone homeostasis, favoring the degradation of local bone which ultimately leads to erosions. Osteoclasts, a multinucleated resident bone cell, are responsible for facilitating the turnover of bone and the bone damage observed in these diseases. The involvement of neutrophils and neutrophil extracellular trap formation have recently been implicated in exacerbating osteoclast function through direct and indirect mechanisms. We highlight a recent finding that NET proteins such as histones and elastase can generate non-canonical, inflammatory osteoclasts, and this process is mediated by post-translational modifications such as citrullination and carbamylation, both of which act as autoantigens in RA. It appears that NETs, autoantibodies, modified proteins, cytokines, and osteoclasts all ultimately contribute to local and permanent bone damage in RA and PD. However, more studies are needed to fully understand the role of neutrophils in inflammatory bone diseases.

Accumulation of Carbamylation-Derived Products in Aneurysmal Aorta.

INTRODUCTION: Carbamylation is a nonenzymatic post-translational modification of proteins characterized by the binding of isocyanic acid to amino groups of proteins, which leads to the alteration of their properties. An increase in serum carbamylation-derived products, including homocitrulline (HCit), has been shown to be associated with the development of cardiovascular diseases. METHODS: HCit was quantified by LC-MS/MS within extracts of aneurysmal and control human aortas. A mouse model of aortic aneurysm (ApoE-/- mice perfused with angiotensin II and fed with sodium cyanate) was used to evaluate the role of carbamylation in aneurysm development. RESULTS: HCit quantification showed a greater heterogeneity of values in aneurysmal aortas in comparison with control ones. At the maximum diameter of dilation, HCit values were significantly higher (+94%, p < 0.05) compared with less dilated areas. No differences were observed according to aneurysm size or when comparing ruptured and unruptured aneurysms. No significant effect of carbamylation on aneurysm development was observed using the animal model. CONCLUSIONS: These results evidenced the accumulation of HCit within aneurysmal aortas but do not allow concluding about the exact participation of protein carbamylation in the development of human abdominal aortic aneurysms.

Analysis of a macrophage carbamylated proteome reveals a function in post-translational modification crosstalk.

BACKGROUND: Lysine carbamylation is a biomarker of rheumatoid arthritis and kidney diseases. However, its cellular function is understudied due to the lack of tools for systematic analysis of this post-translational modification (PTM). METHODS: We adapted a method to analyze carbamylated peptides by co-affinity purification with acetylated peptides based on the cross-reactivity of anti-acetyllysine antibodies. We also performed immobilized-metal affinity chromatography to enrich for phosphopeptides, which allowed us to obtain multi-PTM information from the same samples. RESULTS: By testing the pipeline with RAW 264.7 macrophages treated with bacterial lipopolysaccharide, 7,299, 8,923 and 47,637 acetylated, carbamylated, and phosphorylated peptides were identified, respectively. Our analysis showed that carbamylation occurs on proteins from a variety of functions on sites with similar as well as distinct motifs compared to acetylation. To investigate possible PTM crosstalk, we integrated the carbamylation data with acetylation and phosphorylation data, leading to the identification 1,183 proteins that were modified by all 3 PTMs. Among these proteins, 54 had all 3 PTMs regulated by lipopolysaccharide and were enriched in immune signaling pathways, and in particular, the ubiquitin-proteasome pathway. We found that carbamylation of linear diubiquitin blocks the activity of the anti-inflammatory deubiquitinase OTULIN. CONCLUSIONS: Overall, our data show that anti-acetyllysine antibodies can be used for effective enrichment of carbamylated peptides. Moreover, carbamylation may play a role in PTM crosstalk with acetylation and phosphorylation, and that it is involved in regulating ubiquitination in vitro. Video Abstract.

Distribution and clinical significance of anti-carbamylation protein antibodies in rheumatological diseases among the Chinese Han population.

Objective: Several studies have demonstrated that anti-carbamylation protein antibodies (Anti-CarPA) are persistent in patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), systemic sclerosis (SSC), primary Sjögren's syndrome (pSS), and interstitial lung disease associated with RA (RA-ILD). However, the relationship between anti-CarPA and other rheumatic diseases (RDs) and non-RA-ILD is not known till now. This study sought to examine the presence of anti-CarPA in Chinese Han patients with RDs and its clinical significance. Methods: The study included 90 healthy controls (HCs) and 300 patients with RDs, including RA, SLE, polymyositis/dermatomyositis (PM/DM), pSS, SSC, spondyloarthritis (SpA), anti-neutrophil cytoplasmic autoantibodies associated with vasculitis (AAV), undifferentiated connective tissue disease (UCTD), and Behcet's disease (BD). Antibodies against carbamylated human serum albumin were detected using commercial enzyme-linked immunosorbent assay kits. Correlations between clinical and laboratory parameters were analyzed. Result: Serum levels of anti-CarPA in RA (34.43 ± 33.34 ng/ml), SLE (21.12 ± 22.23 ng/ml), pSS (16.32 ± 13.54 ng/ml), PM/DM (30.85 ± 17.34 ng/ml), SSC (23.53 ± 10.70 ng/ml), and UCTD (28.35 ± 21.91 ng/ml) were higher than those of anti-CarPA in the HCs (7.30 ± 5.05 ng/ml). The concentration of serum anti-CarPA was higher in patients with rheumatic disease-related interstitial lung disease (RD-ILD), especially RA-ILD, PM/DM-ILD, and pSS-ILD. Patients with RD-ILD who tested positive for anti-CarPA were more likely to have a more severe radiographic classification (grades II, p = 0.045; grades III, p = 0.003). Binary logistic regression analysis suggested that anti-CarPA had an association with ILD in RA (p = 0.033), PM/DM (p = 0.039), and pSS (p = 0.048). Based on receiver operating characteristics (ROC) analysis, anti-CarPA cutoffs best discriminated ILD in RA (>32.59 ng/ml, p = 0.050), PM/DM (>23.46 ng/ml, p = 0.038), and pSS (>37.08 ng/ml, p = 0.040). Moreover, serum levels of anti-CarPA were correlated with antibodies against transcription intermediary factor 1 complex (anti-TIF1) (R = -0.28, p = 0.044), antibodies against glycyl-transfer ribonucleic acid synthetase (anti-EJ) (R = 0.30, p = 0.031), and antibodies against melanoma differentiation-associated gene 5 (anti-MDA5) (R = 0.35, p = 0.011). Conclusion: Serum anti-CarPA could be detected in patients with RA, PM/DM, pSS, SSC, and UCTD among the Chinese Han population. And it may also assist in identifying ILD in patients with RA, PM/DM, and pSS, which emphasized attention to the lung involvement in anti-CarPA-positive patients.

Comparison of homocitrulline and carbamylated albumin as biomarkers of carbamylation reactions in hemodialyzed patients.

To describe the association between levels of homocitrulline (HCit) and the degree of albumin carbamylation in a cohort of hemodialyzed patients. Plasma total and protein-bound HCit concentrations in samples from hemodialyzed patients included in NICOREN trial were determined by LC-MS/MS at baseline and after 24 weeks of treatment with either sevelamer or nicotinamide. HCit concentrations at all timepoints and in both groups were positively and significantly correlated with the degree of albumin carbamylation. Plasma concentrations of total HCit, protein-bound HCit and carbamylated albumin did not decrease after 24 weeks of treatment with either sevelamer or nicotinamide. The present results demonstrate that plasma total and protein-bound HCit concentrations were closely associated with albumin carbamylation in hemodialyzed patients. Therefore, total and protein-bound HCit concentrations might be valuable biomarkers of the overall intensity of protein carbamylation in this context. Given the less complex and time-consuming analytical methods required, these markers should be favored in future clinical studies of carbamylation reaction.

The Microbiome and Protein Carbamylation: Potential Targets for Protein-Restricted Diets Supplemented with Ketoanalogues in Predialysis Chronic Kidney Disease.

In chronic kidney disease (CKD), metabolic derangements resulting from the interplay between decreasing renal excretory capacity and impaired gut function contribute to accelerating disease progression and enhancing the risk of complications. To protect residual kidney function and improve quality of life in conservatively managed predialysis CKD patients, current guidelines recommend protein-restricted diets supplemented with essential amino acids (EAAs) and their ketoanalogues (KAs). In clinical studies, such an approach improved nitrogen balance and other secondary metabolic disturbances, translating to clinical benefits, mainly the delayed initiation of dialysis. There is also increasing evidence that a protein-restricted diet supplemented with KAs slows down disease progression. In the present review article, recent insights into the role of KA/EAA-supplemented protein-restricted diets in delaying CKD progression are summarized, and possible mechanistic underpinnings, such as protein carbamylation and gut dysbiosis, are elucidated. Emerging evidence suggests that lowering urea levels may reduce protein carbamylation, which might contribute to decreased morbidity and mortality. Protein restriction, alone or in combination with KA/EAA supplementation, modulates gut dysbiosis and decreases the generation of gut-derived uremic toxins associated, e.g., with cardiovascular disease, inflammation, protein energy wasting, and disease progression. Future studies are warranted to assess the effects on the gut microbiome, the generation of uremic toxins, as well as markers of carbamylation.

Posttranslational modifications in psoriatic arthritis: A systematic literature review.

BACKGROUND AND AIMS: Psoriatic arthritis (PsA) is an inflammatory complex condition. Posttranslational modifications influence almost all aspects of normal cell biology and pathogenesis. The aim of this systematic review was to collect all published evidence regarding posttranslational modifications in PsA, and the main outcome was to evaluate an association between disease outcomes and specific posttranslational modifications in PsA. METHODS: A systematic electronic search was performed in Medline, PubMed, Cochrane, Virtual Health Library, and Embase databases. A total of 587 articles were identified; 59 were evaluated after removing duplicates and scanning, of which 47 were included. A descriptive analysis was conducted, with results grouped according to the type of posttranslational modification evaluated. The protocol was registered at the PROSPERO database. RESULTS: Seven posttranslational modifications were identified: citrullination, carbamylation, phosphorylation, glycosylation, acetylation, methylation, and oxidative stress. Anti-citrullinated peptide and anti-carbamylated protein have been evaluated in rheumatoid arthritis. There is now information suggesting that these antibodies may be helpful in improving the diagnosis of PsA and that they may demonstrate a correlation with worse disease progression (erosions, polyarticular involvement, and poor treatment response). Glycosylation was associated with increased inflammation and phosphorylation products related to the expression of SIRT2 and pSTAT3 or the presence of Th17 and cytokine interleukin-22, suggesting a possible therapeutic target. CONCLUSIONS: Posttranslational modifications often play a key role in modulating protein function in PsA and correlate with disease outcomes. Citrullination, carbamylation, phosphorylation, glycosylation, acetylation, methylation, and oxidative stress were identified as associated with diagnosis and prognosis.

High expression level of homocitrulline is correlated with seborrheic keratosis and skin aging

Abstract Backgroud Homocitrulline (Hcit), is involved in the pathological processes of some diseases. However, the role and function of Hcit (CBL) in human skin remains largely obscure. Objective To investigate the correlation of the level of Hcit in seborrheic keratosis, skin aging, and its clinical significance. Methods Immunohistochemistry was used to analyze the level of Hcit in skin lesions of seborrheic keratosis (SK), unaffected skin (distant 0.5 centimeters from SK lesion), and normal skin of healthy subjects in the control group. ELISA test was used to detect the serum level of CBL in SK patients and healthy subjects of different ages. Results Hcit was mainly localized in the nucleus of epidermal cells. In healthy control skin, the expression of Hcit increased with age and showed a positive correlation with age (the correlation coefficient was 0.806, p = 0.0002). The expressional level of Hcit in SK lesions was higher than that in healthy control skin (Z = −3.703, p = 0.0002). The serum level of CBL in healthy subjects and in SK patients increased with age (the correlation coefficient were 0.5763, p = 0.0032; 0.682, p = 0.004. respectively). The serum level of CBL in SK patients was higher than that in healthy subjects (Z = −2.19, p = 0.030). Study limitations The small serum sample size in the study. Conclusion The high expressional level of Hcit is correlated with seborrheic keratosis and skin aging. HCit may be one of the potential biomarkers of skin aging.

Altered ureido protein modification profiles in seminal plasma extracellular vesicles of non-normozoospermic men.

Introduction: Extracellular vesicles (EVs) have been recognized as key players in numerous physiological functions. These vesicles alter their compositions attuned to the health and disease states of the organism. In men, significant changes in the proteomic composition(s) of seminal plasma EVs (sEVs) have already been found to be related to infertility. Methods: Methods: In this study, we analyze the posttranslational configuration of sEV proteomes from normozoospermic (NZ) men and non-normozoospermic (non-NZ) men diagnosed with teratozoospermia and/or asthenozoospermia by unbiased, discovery-driven proteomics and advanced bioinformatics, specifically focusing on citrulline (Cit) and homocitrulline (hCit) posttranscriptional residues, both considered product of ureido protein modifications. Results and discussion: Significant increase in the proteome-wide cumulative presence of hCit together with downregulation of Cit in specific proteins related to decisive molecular functions have been encountered in sEVs of non-NZ subjects. These findings identify novel culprits with a higher chance of affecting fundamental aspects of sperm functional quality and define potential specific diagnostic and prognostic non-invasive markers for male infertility.

Potential interference of in vitro carbamylation on C-reactive protein laboratory measurement.

Carbamylation is a nonenzymatic post-translational modification observed during the reaction between cyanate and amino acids and/or proteins that may occur during some pathologies such as chronic kidney disease. Evidence suggests that carbamylation may interfere with the quantification of some analytes measured using immunoturbidimetric assays. C-reactive protein (CRP) is an inflammatory response protein that is commonly quantified through immunoturbidimetry in clinical laboratories. Because the presence of modified proteins in serum can lead to impaired quantification, this study aimed to verify the impact of in vitro carbamylation on the measurement of CRP in a CRP standard solution and serum pool. The samples were incubated with 150 nM, 150 µM, or 150 mM potassium cyanate (KOCN) or 20, 100, or 500 mg/dL urea at 37 °C for 24 h. CRP concentrations were measured using an immunoturbidimetric assay. The results showed a 61%-72% decrease in the CRP detection rate after incubation with KOCN. Incubation with urea resulted in a 0.7%-8% lower CRP detection rate. The results of this study indicate that high concentrations of cyanate can lead to falsely decreased CRP levels, as measured by immunoturbidimetry.

Carbamylated lipoproteins in diabetes.

Diabetic dyslipidemia is characterized by quantitative and qualitative abnor-malities in lipoproteins. In addition to glycation and oxidation, carbamylation is also a post-translational modification affecting lipoproteins in diabetes. Patients with type 2 diabetes (T2D) exhibit higher levels of carbamylated low-density lipoproteins (cLDL) and high-density lipoproteins (cHDL). Accumulating evidence suggests that cLDL plays a role in atherosclerosis in diabetes. cLDL levels have been shown to predict cardiovascular events and all-cause mortality. cLDL facilitates immune cell recruitment in the vascular wall, promotes accumulation of lipids in macrophages, and contributes to endothelial dysf-unction, endothelial nitric oxide-synthase (eNOS) inactivation and endothelial repair defects. Lastly, cLDL induces thrombus formation and platelet aggregation. On the other hand, recent data have demonstrated that cHDL serum level is independently associated with all-cause and cardiovascular-related mortality in T2D patients. This relationship may be causative since the atheroprotective properties of HDL are altered after carbamylation. Thus, cHDL loses the ability to remove cholesterol from macrophages, to inhibit monocyte adhesion and recruitment, to induce eNOS activation and to inhibit apoptosis. Taken together, it seems very likely that the abnormalities in the biological functions of LDL and HDL after carbamylation contribute to atherosclerosis and to the elevated cardiovascular risk in diabetes.

Measurement of Homocitrulline, A Carbamylation-derived Product, in Serum and Tissues by LC-MS/MS.

Carbamylation corresponds to the nonenzymatic binding of isocyanic acid to protein amino groups and participates in protein molecular aging, characterized by the alteration of their structural and functional properties. Carbamylated proteins exert deleterious effects in vivo and are involved in the progression of various diseases, including atherosclerosis and chronic kidney disease. Therefore, there is a growing interest in evaluating the carbamylation rate of blood or tissue proteins, since carbamylation-derived products (CDPs) constitute valuable biomarkers in these contexts. Homocitrulline, formed by isocyanic acid covalently attaching to the ε-NH2 group of lysine residue side chain, is the most characteristic CDP. Sensitive and specific quantification of homocitrulline requires mass spectrometry-based methods. This article describes a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of homocitrulline, with special emphasis on preanalytical steps that allow quantification of total or protein-bound homocitrulline in serum or tissue samples. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Sample pretreatment for the quantification of homocitrulline by LC-MS/MS Alternate Protocol: Preanalytical steps for the quantification of homocitrulline in tissue samples Basic Protocol 2: LC-MS/MS quantification of homocitrulline Basic Protocol 3: LC-MS/MS quantification of lysine in hydrolysates.

Sodium zirconium cyclosilicate and metabolic acidosis: Potential mechanisms and clinical consequences.

Metabolic acidosis is frequent in chronic kidney disease (CKD) and is associated with accelerated progression of CKD, hypercatabolism, bone disease, hyperkalemia, and mortality. Clinical guidelines recommend a target serum bicarbonate ≥ 22 mmol/L, but metabolic acidosis frequently remains undiagnosed and untreated. Sodium zirconium cyclosilicate (SZC) binds potassium in the gut and is approved to treat hyperkalemia. In clinical trials with a primary endpoint of serum potassium, SZC increased serum bicarbonate, thus treating CKD-associated metabolic acidosis. The increase in serum bicarbonate was larger in patients with more severe pre-existent metabolic acidosis, was associated to decreased serum urea and was maintained for over a year of SZC therapy. SZC also decreased serum urea and increased serum bicarbonate after switching from a potassium-binding resin in normokalemic individuals. Mechanistically, these findings are consistent with SZC binding the ammonium ion (NH4+) generated from urea by gut microbial urease, preventing its absorption and, thus, preventing the liver regeneration of urea and promoting the fecal excretion of H+. This mechanism of action may potentially result in benefits dependent on corrected metabolic acidosis (e.g., improved well-being, decreased catabolism, improved CKD mineral bone disorder, better control of serum phosphate, slower progression of CKD) and dependent on lower urea levels, such as decreased protein carbamylation. A roadmap is provided to guide research into the mechanisms and clinical consequences of the impact of SZC on serum bicarbonate and urate.

Serum carboxymethyllysine concentration is associated with erosive hand osteoarthritis.

OBJECTIVE: Carboxymethyllysine (CML) and homocitrulline (HCit) are the products of two non-enzymatic post-translational modifications of protein, a process related to age. We investigated whether serum CML and HCit concentrations were associated with hand osteoarthritis (HOA), especially erosive HOA. DESIGN: Serum CML and HCit were measured by using liquid chromatography coupled with tandem mass spectrometry at inclusion in 386 patients included in the DIGItal Cohort Design (DIGICOD) cohort. We investigated whether serum CML and/or HCit concentrations were associated with erosive HOA or with HOA clinical and radiological features. Moreover, we compared the tissular concentrations of CML and HCit in OA and non-OA cartilage from proximal interphalangeal and metacarpo-phalangeal (MCP) joints from human cadaveric donors. RESULTS: Median (IQR) serum CML concentration was lower in patients with erosive HOA than those with non-erosive HOA (178.7 [157.1-208.8] vs 194.7 [168.9-217.1] µmol/mol Lys, P = 0.002), but median HCit concentration did not differ between the groups (193.9 [162.9-232.0] vs 193.9 [155.9-224.6] µmol/mol Lys). Cartilage HCit and CML concentrations were not correlated with clinical features. Serum CML concentration was higher in OA than non-OA MCPs (7.0 vs 4.0 mmol/mol Lys, P = 0.01). CONCLUSIONS: Serum CML concentration was lower in erosive HOA than non-erosive HOA, and cartilage CML concentration was higher in OA than non-OA cartilage. These results encourage further studies to test whether serum CML could be a new prognostic biomarker in HOA.

High expression level of homocitrulline is correlated with seborrheic keratosis and skin aging.

BACKGROUD: Homocitrulline (Hcit), is involved in the pathological processes of some diseases. However, the role and function of Hcit (CBL) in human skin remains largely obscure. OBJECTIVE: To investigate the correlation of the level of Hcit in seborrheic keratosis, skin aging, and its clinical significance. METHODS: Immunohistochemistry was used to analyze the level of Hcit in skin lesions of seborrheic keratosis (SK), unaffected skin (distant 0.5 centimeters from SK lesion), and normal skin of healthy subjects in the control group. ELISA test was used to detect the serum level of CBL in SK patients and healthy subjects of different ages. RESULTS: Hcit was mainly localized in the nucleus of epidermal cells. In healthy control skin, the expression of Hcit increased with age and showed a positive correlation with age (the correlation coefficient was 0.806, p = 0.0002). The expressional level of Hcit in SK lesions was higher than that in healthy control skin (Z = -3.703, p = 0.0002). The serum level of CBL in healthy subjects and in SK patients increased with age (the correlation coefficient were 0.5763, p = 0.0032; 0.682, p = 0.004. respectively). The serum level of CBL in SK patients was higher than that in healthy subjects (Z = -2.19, p = 0.030). STUDY LIMITATIONS: The small serum sample size in the study. CONCLUSION: The high expressional level of Hcit is correlated with seborrheic keratosis and skin aging. HCit may be one of the potential biomarkers of skin aging.