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The unprecedented rise in global ambient temperatures in the last decade has significantly impacted human health, yet how heat exposure affects the development of sarcopenia remains enigmatic. Here, we demonstrate that chronic heat exposure induces skeletal muscle volume loss, leading to muscle strength and functional decline in mice. The microbiota composition of heat‐exposed mice was analyzed using 16S ribosomal DNA analysis. Liquid chromatography‐mass spectrometry (LC–MS) was used to explore the effects of heat exposure on the blood metabolome and to further analyze the correlation between blood metabolism and gut microbiota. Transplantation of microbiota from heat‐exposed mice to germ‐free mice was sufficient to increase adverse effects on skeletal muscle function in the host. Mechanistically, using an untargeted metabolomics strategy, we reveal that altered gut microbiota due to high temperatures is associated with elevated serum levels of homocitrulline. Homocitrulline causes mitochondrial dysfunction in myocytes by exacerbating ferroptosis levels. And Nrf2 activator (Oltipraz) supplementation alleviates muscle atrophy and dysfunction induced by heat exposure. Our findings reveal the detrimental effects of heat exposure on muscle function and provide new strategies for treating sarcopenia. [ABSTRACT FROM AUTHOR]

Abstract 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.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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.

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. [ABSTRACT FROM AUTHOR]

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. 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. 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). 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. [ABSTRACT FROM AUTHOR]

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 nonnormozoospermic (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. [ABSTRACT FROM AUTHOR]

IntroductionExtracellular 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.MethodsMethods: 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 discussionSignificant 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.

Background: The probiotic E. coli Nissle 1917 (EcN) alleviates the progression of various diseases, including colitis and tumors. However, EcN has not been studied in atherosclerosis. The study investigated the effects of EcN on atherosclerosis model mice and the potential mechanisms., Methods: Mice in the high-fat diet (HFD) model were given EcN (1 × 10 9 CFU/g) or homocitrulline (150 mg/L) by oral administration for 12 weeks. The EcN + antibiotic group was set up to investigate the effects of EcN combined with antibiotics on gut microbiota. The control group was utilized as the negative control. Atherosclerosis status, pyroptosis, gut microbiota, and serum metabolites of mice were examined., Results: EcN treatment alleviated HFD-caused atherosclerotic plaque and lipid droplet production. EcN treatment reversed HFD-induced increases in total cholesterol, triglycerides, and low-density lipoprotein levels and decreases in high-density lipoprotein levels. EcN inhibited the HFD-caused rise in the expression of pyroptosis-related indicators (cleaved Caspase 1, GSDMD-N, NLRP3, IL-18, and IL-1β). The antibiotics partially reversed the effects of EcN on the model mice, suggesting that EcN regulated pyroptosis in the model mice through gut microbiota. Probiotic bacteria, such as Lactobacillus and Muribaculum, were mainly enriched in the EcN and EcN + antibiotic groups, while Helicobacter, Alistipes, and Rikenella were depleted, suggesting that EcN and EcN + antibiotics could alleviate disorders of gut microbiota in the model mice. EcN reversed the trend of HFD-induced decrease of some metabolites, such as 2-methyl-5-nitroimidazole-1-ethanol, methionine sulfoxide, and shikimate 3-phosphate, and inhibited the increase of some metabolites, such as kynurenine, oxoadipate, and homocitrulline. In addition, homocitrulline showed the opposite effects of EcN in the model mice. Homocitrulline could bind to pyroptosis-related proteins to aggravate ox-LDL-induced endothelial cell pyroptosis., Conclusion: EcN could alleviate atherosclerosis development by ameliorating HFD-induced disorders of gut microbiota and serum metabolites (such as homocitrulline) to alleviate pyroptosis, which may be associated with homocitrulline/Caspase 1/NLRP3/GSDMD axis. Our study lays the foundation for the development of promising drugs for atherosclerosis in the future., Competing Interests: Conflict of Interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier GmbH.. All rights reserved.)

Aim: Multiple sclerosis (MS) is a demyelinating disease of central nervous system. Myelin basic protein (MBP) is the major protein in the structure of the myelin sheath, and the abnormal autoimmune response to MBP is related to the demiyelinization in MS. This autoimmune response is thought to be related to extensive post-translational modifications that may occur in the primary structure of MBP. Considering the role of post-translational modifications of MBP in the pathogenesis of MS, this study aimed to investigate the role of carbamylation in the pathogenesis of MS by measuring Hcit levels in patients with MS. Materials and Methods: This study included 80 patients with MS according to McDonald criteria by clinicians, and 60 healthy volunteers. Patients were divided into 2 groups as relapsing-remitting multiple sclerosis (RRMS) (n=44) and secondary progressive MS (SPMS) (n=36) according to Expanded Disability Status Scale (EDSS) score evaluated by clinicians. Serum homocitrulline and lysine levels were measured with validated tandem mass spectrometric method. Results: Serum Hcit levels in patients with MS were statistically significantly higher than the healthy controls. Comparison of MS subgroups according to Hcit levels showed that serum Hcit levels were higher in patients with SPMS than in patients with RRMS. Serum Hcit levels were positively correlated with EDSS and disease duration. Conclusion: Serum Hcit levels were significantly elevated in patients with MS. Moreover, there was a correlation between serum Hcit levels and disease activity and duration of disease. [ABSTRACT FROM AUTHOR]

Objective: Peripheral arterial disease (PAH) is a chronic, progressive disease characterized by arterial stenosis or occlusion. Atherosclerosis is the most common cause of PAH (>90%). Carbamylation is one of the post-translational modification mechanisms of proteins and has been identified as a new risk factor for atherosclerosis. The most common carbamylation product known is homocitrulline. Our aim in this study was to contribute to the elucidation of the role of homocitrulline in the diagnosis of PAH. Methods: 70 patients with PAH and 65 individuals without PAH were included in the study. Serum homocitrulline and lysine levels were measured by AB Sciex API 3200 (Applied Biosystems/MDS Sciex) liquid chromatography-tandem mass spectrometry (LC-MS/ MS) device. Various hematological and biochemical parameters of the patients were measured in Beckman Coulter LH 780 and Beckman Coulter AU 5800 (Beckman Coulter, Brea, USA) autoanalyzers, and C-reactive protein (CRP) levels were measured in IMMAGE 800 (Beckman Coulter, Brea, USA) device, respectively. Results: Serum homocitrulline concentrations of patients with PAH were statistically significantly higher than the control group (p<0.001). Receiver Operating Characteristic (ROC) analysis showed that the optimal serum homocitrulline cut-off value was 165.1 µmol / mol lysine (p<0.001) (sensitivity, 71.4% and specificity, 86.7%) for PAH. The area under curve (AUC) value was 0.873 (95% confidence interval: 0.804- 0.925). There was a positive correlation between serum homocitrulline and urea, CRP, the neutrophillymphocyte ratio (NLR) and the platelet-lymphocyte ratio (PLR) levels. Conclusion: Our findings show that homocitrulline levels are significantly elevated in patients with PAH, and homocitrulline may be a useful marker in the early diagnosis of PAH. [ABSTRACT FROM AUTHOR]

Backgrounds Nonalcoholic fatty liver disease (NAFLD) has multiple causes, is triggered by individual genetic susceptibility, environmental factors, and metabolic disturbances, and may be triggered by acquired metabolic stress. The metabolic profiles of NAFLD show significant ethnic differences, and the metabolic characteristics of NAFLD in Chinese individuals are unclear. Our study aimed to identify the metabolites and pathways associated with NAFLD in a Chinese cohort. Methods One hundred participants, including 50 NAFLD patients and 50 healthy controls, were enrolled in this retrospective observational study at Jinling Hospital in Nanjing; serum samples were collected from the patients and healthy subjects. The metabolome was determined in all samples by liquid chromatography-hybrid quadrupole time-of-flight mass spectrometry (LC-Q/TOF-MS). Univariate and multivariate statistical analyses were used to compare the metabolic profiles between the two groups. Results The comparison indicated that the levels of 89 metabolites were different between the two groups. The glycerophospholipid family of metabolites was the most abundant family of metabolites that demonstrated significant differences. L-acetylcarnitine, L-homocitrulline, and glutamic acid were the top three metabolites ranked by VIP score and had favorable effective functions for diagnosis. Moreover, pathway enrichment analysis suggested 14 potentially different metabolic pathways between NAFLD patients and healthy controls based on their impact value. Biological modules involved in the lipid and carbohydrate metabolism had the highest relevance to the conditions of NAFLD. Glycerophospholipid metabolism had the strongest associations with the conditions of NAFLD. Conclusions Our data suggest that the serum metabolic profiles of NAFLD patients and healthy controls are different. L-Homocitrulline was remarkably increased in NAFLD patients.

Objective: Hyperargininemia due to Arginase 1 deficiency is a rare inborn error of the urea cycle with an incidence estimated at 1:950 000. It has typical severe and progressive abnormal neurological features with biochemical findings of hyperargininemia and hyperexcretion of orotic acid. The aim of our study is to review the clinical and biochemical presentations of 4 children diagnosed with Arginase 1 deficiency in Malaysia and compare with the literature review. Design and Methods: We retrospectively reviewed the medical records of 4 patients with molecularly confirmed Arginase 1 deficiency. Patients were identified from a selective high-risk screening of 51 682 symptomatic patients from January 2006 to December 2020. Results: Our patients exhibited heterogeneous clinical presentations with acute and progressive neurological abnormalities and varying degrees of plasma arginine and urine orotic acid excretions. Interestingly, an unusual hyperexcretion of homocitrulline was found in 3 patients. Conclusions: Hyperargininemia due to Arginase 1 deficiency can present acutely and hyperexcretion of homocitrulline can be an additional biochemical feature of Arginase 1 deficiency. [ABSTRACT FROM AUTHOR]

Objectives: Antibodies against carbamylated protein (anti-CarP) were found to be a promising marker to evaluate joint damage and disease activity in patients with rheumatoid arthritis (RA). However, whether anti-CarP antibodies were present in systemic lupus erythematosus (SLE) remained ambiguous. We have therefore undertaken this study to assess the levels of serum anti-CarP antibodies and to evaluate their clinical value in SLE. Methods: Serum levels of antibodies against carbamylated-vimentin (anti-Carp) were measured by enzyme immunosorbent assay in 100 patients with SLE, 76 with RA, 17 with primary Sjögren syndrome (pSS), and 68 healthy controls. Data analyses between anti-Carp antibodies and other laboratory measures were performed using SPSS 24 software for Windows. Results: The levels of serum anti-CarP antibodies in patients with SLE were significantly higher than those in healthy controls. In addition, anti-CarP antibodies were present in SLE patients lacking the disease-specific antibodies, including anti-Smith–negative patients (24.4%, 21/86), anti-dsDNA–negative patients (29.3%, 12/41), anti-nucleosome–negative patients (21.4%, 9/42), and antiribosomal P protein antibody–negative patients (23.7%, 18/76). There were significant differences between the anti-CarP–positive and anti-CarP–negative SLE patients in clinical and laboratory features, such as age, erythrocyte sedimentation rate (ESR), C-reactive protein, rheumatoid factor, third-generation cyclic citrullinated peptide (CCP3), anticardiolipin, D-dipolymer, complement 3, immunoglobulin G (IgG), red blood cell count (RBC) and hemoglobin. After adjusting for age and disease duration, the high levels of anti-CarP antibodies were still correlated with low RBC, hemoglobin and high ESR, IgG and CCP3. Active SLE patients demonstrated higher anti-CarP IgG than inactive patients. Moreover, the levels of anti-CarP were significantly higher in SLE patients with arthralgia and/or arthritis than in those without joint involvement. Conclusions: Anti-CarP antibodies were present in SLE patients and associated with the disease severity. These might provide a potential supplement to other specific autoantibodies for diagnosis of SLE and serve as a promising marker for measuring joint damage in the disease. [ABSTRACT FROM AUTHOR]

Urea cycle disorders (UCD) are inborn errors of ammonia detoxification in which early diagnosis and treatment are critical to prevent metabolic emergencies. Unfortunately, the diagnosis was often and pronounced delayed. To improve diagnosis, we developed herein a liquid chromatography-tandem mass spectrometry method to investigate the disturbance of amino acid profile caused by UCD. The method enabled absolute quantification of 48 amino acids (AAs) within 20 min. Only 2.5 μL plasma was required for the analysis. The lower limits of quantification for most AAs were 0.01 μmol/L. Method accuracies ranged from 89.9% to 113.4%. The within- and between-run coefficients of variation were 0.8–7.7% and 2.6–14.5%, respectively. With this method, age-specific reference values were established for 42 AAs by analyzing 150 samples from normal controls, and patients with different subtypes of UCD were successfully distinguished. The data of patients revealed that UCD not only disturbed the metabolism of urea cycle AAs and induced accumulation of ammonia detoxification AAs, but also interfered the metabolism of some nervous system related AAs, such as pipecolic acid and N -acetylaspartic acid. This data may provide new insight into pathogenesis for UCD. • We developed a method to quantify 48 disease-related amino acids within 20 min. • Only 2.5 μL plasma was required for the analysis. • Age-specific reference values were established for 42 amino acids. • Patients with different types of urea cycle disorders were diagnosed by the method. • New findings related to pathogenesis of urea cycle disorders were obtained. [ABSTRACT FROM AUTHOR]

Background: Identifying frail elderly subjects is of paramount importance in order to conduct a tailored care. The characterization of frailty status is currently based on the collection of clinical data and on the use of various tools such as Fried's criteria, which constitutes a difficult and time-consuming process. Up to now, no biological markers have been described as reliable tools for frailty characterization. We tested the hypothesis that a link between frailty and protein molecular aging existed. This study aimed therefore at determining whether post-translational modification derived products (PTMDPs), recognized as biomarkers of protein aging, were associated with frailty status in elderly subjects. Methods: Frailty status was determined according to Fried's criteria in 250 elderly patients (>65 years old) hospitalized in a short-term care unit. Serum concentrations of protein-bound PTMDPs, including carboxymethyllysine (CML), pentosidine, methylglyoxal-hydroimidazolone-1 and homocitrulline (HCit), were determined by liquid chromatography coupled with tandem mass spectrometry, and tissue content of advanced glycation end-products was assessed by skin autofluorescence (SAF) measurement. Associations between PTMDPs and frailty status were analyzed using logistic regression models. Results: Frail patients had significantly (p<0.01) higher CML, HCit, and SAF values compared to non-frail and pre-frail subjects. By multivariate analysis, only HCit concentrations and SAF values remained associated with frailty status (p=0.016 and p=0.002, respectively), independently of age, comorbidities, renal function, C-reactive protein and albumin concentrations. Conclusions: HCit and SAF are significantly associated with frailty status in elderly subjects. This study suggests that PTMDPs constitute promising biomarkers for identifying frail patients and guiding personalized patient care. [ABSTRACT FROM AUTHOR]

In 2011 a novel autoantibody system, anti-carbamylated protein (anti-CarP) antibodies, was described in rheumatoid arthritis (RA) patients. Anti-CarP antibody positivity associates with a more severe disease course, is observed years before disease onset, and may predict the development of RA in arthralgia patients. Although many clinical observations have been carried out, information on the antigenic targets of anti-CarP antibodies is limited. Most studies on anti-CarP antibodies utilize an ELISA-based assay with carbamylated fetal calf serum (Ca-FCS) as antigen, a complex mixture of proteins. Therefore, we analysed the molecular identity of proteins within Ca-FCS that are recognized by anti-CarP antibodies. Ca-FCS was fractionated using ion exchange chromatography, selecting one of the fractions for further investigation. Using mass-spectrometry, carbamylated alpha-1-antitrypsin (Ca-A1AT) was identified as a potential antigenic target of anti-CarP antibodies in RA patients. A1AT contains several lysines on the protein surface that can readily be carbamylated. A large proportion of the RA patients harbour antibodies that bind human Ca-A1AT in ELISA, indicating that Ca-A1AT is indeed an autoantigen for anti-CarP antibodies. Next to the Ca-A1AT protein, several homocitrulline-containing peptides of A1AT were recognized by RA sera. Moreover, we identified a carbamylated peptide of A1AT in the synovial fluid of an RA patient using mass spectrometry. We conclude that Ca-A1AT is not only a target of anti-CarP antibodies but is also present in the synovial compartment, suggesting that Ca-A1AT recognized by anti-CarP antibodies in the joint may contribute to synovial inflammation in anti-CarP-positive RA. [ABSTRACT FROM AUTHOR]

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., (Copyright © 2022 Sociedade Brasileira de Dermatologia. Published by Elsevier España, S.L.U. All rights reserved.)

The specificities and cross-reactions of antibodies induced by citrulline- and homocitrulline-containing proteins may give implications on the role of citrulline- and homocitrulline-binding antibodies in the pathogenesis and progression of rheumatoid arthritis (RA). Here we use rabbits as an experimental model of antibody development in RA. Thirty-two animals were immunized with peptide antigens containing either homocitrulline or citrulline. The sera were tested for binding to CCP and MCV antigens and to peptide sequences related to carboxyterminal telopeptides of type I and II collagens and containing arginine, citrulline, or homocitrulline. The binding of CCP and MCV antigens to antisera against homocitrulline-containing immunogens could be inhibited by human serum albumin containing homocitrulline, whereas similar binding to sera against citrulline-containing immunogens was not inhibited. The antisera induced with citrulline-containing collagen telopeptides recognized type I collagen-related antigens in a sequence-specific manner, as antibody binding to both citrulline- and homocitrulline-containing peptides was inhibited by corresponding citrullinated and native peptides. In contrast, type II collagen-related peptides were recognized by the antisera in a ureido group-specific manner, as their binding to homocitrulline-containing peptide was inhibited by both citrulline- and homocitrulline-containing, but not native peptide. Binding of the citrullinated type II collagen peptide could only be inhibited by the similarly citrullinated peptide. In conclusion, antibodies induced with citrulline or homocitrulline-containing antigens bound antigens in a ureido group-specific manner, recognizing citrulline and homocitrulline also in other sequences than those used in the original immunization. In competitive situations the amino acid present in the immunization antigen was favored. [ABSTRACT FROM PUBLISHER]

Background Homocitrulline (HCit) is a carbamylation-derived product (CDP) that has been identified as a valuable biomarker of morbidity and mortality in patients with chronic kidney disease (CKD). The aim of this study was to determine whether initiation of hemodialysis therapy (HD) could induce variations of HCit concentrations in CKD patients. Methods Serum HCit concentrations were determined by LC-MS/MS in CKD patients (n = 108) just before (M0) and six months (M6) after the initiation of HD therapy. Results Mean HCit concentrations reached 1000 μmol/mol Lysine before initiation of HD therapy and decreased by 50% within 6 months after HD onset. HCit concentrations remained stable over time as assessed during a 24-months follow-up period. HCit was mostly found in its protein-bound form in HD patients. HCit concentrations obtained at M0 were positively correlated with urea (r = 0.58) and carbamylated hemoglobin (r = 0.41), and are likely to be promising predictive markers of mortality. However, no correlations were found between HCit concentrations and Kt/V values, suggesting that HCit is not a marker of HD efficiency. Conclusion HCit concentrations reflect the intensity of protein carbamylation and are stable over time during HD treatment, making HCit a reliable biomarker in the follow-up of CKD patients. [ABSTRACT FROM AUTHOR]

Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is caused by deficiency of ornithine translocase leading to predominant tissue accumulation and high urinary excretion of ornithine (Orn), homocitrulline (Hcit) and ammonia. Although affected patients commonly present neurological dysfunction manifested by cognitive deficit, spastic paraplegia, pyramidal and extrapyramidal signs, stroke-like episodes, hypotonia and ataxia, its pathogenesis is still poorly known. Although astrocytes are necessary for neuronal protection. Therefore, in the present study we investigated the effects of Orn and Hcit on cell viability (propidium iodide incorporation), mitochondrial function (thiazolyl blue tetrazolium bromide-MTT-reduction and mitochondrial membrane potential-ΔΨ), antioxidant defenses (GSH) and pro-inflammatory response (NFkB, IL-1β, IL-6 and TNF-α) in unstimulated and menadione-stressed cortical astrocytes that were previously shown to be susceptible to damage by neurotoxins. We first observed that Orn decreased MTT reduction, whereas both amino acids decreased GSH levels, without altering cell viability and the pro-inflammatory factors in unstimulated astrocytes. Furthermore, Orn and Hcit decreased cell viability and ΔΨ in menadione-treated astrocytes. The present data indicate that the major compounds accumulating in HHH syndrome impair mitochondrial function and reduce cell viability and the antioxidant defenses in cultured astrocytes especially when stressed by menadione. It is presumed that these mechanisms may be involved in the neuropathology of this disease. [ABSTRACT FROM AUTHOR]

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-NH 2 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., (© 2023 The Authors. Current Protocols published by Wiley Periodicals LLC.)

Background: Carbamylation is a non-enzymatic post-translational modification of proteins characterized by the addition of isocyanic acid to amino groups. As isocyanic acid mainly originates from the spontaneous dissociation of urea, carbamylation rate is increased during renal failure. The aim of the study was to evaluate serum homocitrulline (HCit), which results from the carbamylation of ε-amino groups of lysine (Lys) residues, in acute renal failure (ARF) and to determine if it could be useful for differentiating acute from chronic renal failure (CRF). Methods: In total, 213 patients with renal failure referred to the nephrology department of the university hospital of Reims were included. Patients were classified into three groups: patients with ARF (ARF group, n=39), patients with CRF complicated with ARF (A/CRF group, n=29) and patients with CRF (CRF group, n=145). Serum HCit concentrations were measured by LC-MS/MS. Concentration kinetics of HCit and urea were studied in patients suffering from ARF. The HCit thresholds distinguishing ARF and CRF were investigated. Results: HCit concentrations increased in ARF patients reaching a peak delayed compared to urea concentration peak. HCit concentrations were positively correlated with urea concentrations (r=0.51) and with the time elapsed since the estimated onset of ARF (r=0.57). Serum HCit concentrations were higher (p<0.05) in CRF group compared to ARF group. The receiver operating characteristic curve analysis showed that HCit concentrations <289 μmol/mol Lys were predictive of ARF (Sensitivity: 83%, Specificity: 72%, AUC: 0.856). Conclusions: Our results demonstrate that HCit is a promising biomarker for distinguishing between ARF and CRF patients. [ABSTRACT FROM AUTHOR]

Hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome is an inborn error of metabolism caused by a defect in the transport of ornithine (Orn) into mitochondrial matrix leading to accumulation of Orn, homocitrulline (Hcit), and ammonia. Affected patients present a variable clinical symptomatology, frequently associated with cerebellar symptoms whose pathogenesis is poorly known. Although in vitro studies reported induction of oxidative stress by the metabolites accumulating in HHH syndrome, so far no report evaluated the in vivo effects of these compounds on redox homeostasis in cerebellum. Therefore, the present work was carried out to investigate the in vivo effects of intracerebellar administration of Orn and Hcit on antioxidant defenses (reduced glutathione concentrations and the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glucose-6-phosphate dehydrogenase), lipid oxidation (malondialdehyde concentrations), as well as on the activity of synaptic Na, K-ATPase, an enzyme highly vulnerable to free radical attack, in the cerebellum of adolescent rats. Orn significantly increased malondialdehyde levels and the activities of all antioxidant enzymes, and reduced Na, K-ATPase activity. In contrast, glutathione concentrations were not changed by Orn treatment. Furthermore, intracerebellar administration of Hcit was not able to alter any of these parameters. The present data show for the first time that Orn provokes in vivo lipid oxidative damage, activation of the enzymatic antioxidant defense system, and reduction of the activity of a crucial enzyme involved in neurotransmission. It is presumed that these pathomechanisms may contribute at least partly to explain the neuropathology of cerebellum abnormalities and the ataxia observed in patients with HHH syndrome. [ABSTRACT FROM AUTHOR]

Background: The aim of the study was to describe automated immunoassays for autoantibodies to homocitrulline or citrulline containing telopeptides of type I and II collagen in various disease categories in an early arthritis series. Methods: Serum samples were collected from 142 patients over 16 years of age with newly diagnosed inflammatory joint disease. All samples were analyzed with an automated inhibition chemiluminescence immunoassay (CLIA) using four different peptide pairs, each consisting of a biotinylated antigen and an inhibiting peptide. Assays were performed with an IDS-iSYS analyzer Autoantibodies binding to homocitrulline and citrulline containing C-telopeptides of type I (HTELO-I, TELO-I) and type II collagens (HTELO-II, TELO-II) were analyzed. Results: The mean ratio of HTELO-I inhibition in seropositive and seronegative rheumatoid arthritis (RA) was 3.07 (95% CI 1.41-11.60), p = 0.003, and in seropositive and seronegative undifferentiated arthritis (UA) 4.90 (1.85-14.49), p < 0.001. The respective mean ratios in seropositive and seronegative RA and UA were in TELO-I 8.72 (3.68-58.01), p < 0.001 and 3.13 (1.49-6.16), p = 0.008, in HTELO-II 7.57 (3.18-56.60), p < 0.001 and 2.97 (1.23-6.69), p = 0.037, and in TELO-II 3.01 (1.30-9.51), p = 0.002 and 3.64 (1.86-7.65), p = 0.008. In reactive arthritis, ankylosing spondylitis, psoriatic arthritis and unspecified spondyloarthritis the inhibition levels were similar to those observed in seronegative RA or UA. Conclusions: Autoantibodies binding to homocitrulline or citrulline containing telopeptides of type I and II collagen did not differ significantly. They were highest among patients with seropositive disease and they differentiated seropositive and seronegative arthritis. [ABSTRACT FROM AUTHOR]

Anti-citrullinated protein antibodies (ACPA) are important serological markers in the diagnosis of rheumatoid arthritis (RA) and are part of the recent disease classification criteria. However, there is a strong need for reliable markers for measuring and predicting joint damage and disease activity. Recently, antibodies directed against carbamylated antigens (anti-CarP antibodies) were identified. A total of 120 RA patients were tested for anti-CCP antibodies using different methods and for anti-CarP antibodies using carbamylated fetal calf serum according to the method described by Shi et al. Additionally, ACPA fine specificities (to three citrullinated peptides) were measured. Disease activity was assessed at baseline using the disease activity score 28 (DAS28) in 80 patients. For 40 RA patients, joint erosion score (JES) was established. The median JES was 14.1 with a standard deviation of 11.5. Anti-CarP antibodies were correlated with joint erosion score ( ρ = 0.34, 95 % CI 0.03-0.59; p = 0.0332). No correlation between ACPA and joint erosion score was observed. No individual marker correlated with DAS28. When one ACPA peptide was combined with anti-CarP antibodies in a score (ACPA peptide 1 divided by anti-CarP), a statistically relevant correlation was found ( p = 0.0264). In this small cohort, the presence of anti-CarP antibodies, but not ACPA correlate with joint erosion score. Anti-CarP antibodies combined with ACPA fine specificities correlated with DAS28. Therefore, anti-CarP antibodies might represent a promising marker to predict joint damage and disease activity in RA patients. [ABSTRACT FROM AUTHOR]

Objective. Plasma and synovial myeloperoxidase (MPO) and its products were strongly associated with osteoarthritis (OA) and rheumatoid arthritis (RA). In addition, it is well known that there is a link between oxidative stress and cytokines. The present study aims at investigating the link between synovial MPO (and its products), interleukin (IL)-18, which is involved in the degradation of articular cartilage in RA, and IL-8, which is involved in recruitment and activation of neutrophils during inflammation. Effects of the treatment of RA on the biological parameters were also investigated. Methods. Patients ( n = 105) were studied including 39 patients with OA, 33 with RA and 33 with RA receiving a specific treatment. Disease activity score (DAS-28) was calculated whereas MPO antigen/activity, neutrophils, chloro-tyrosine (Cl-Tyr), homocitrulline (Hcit), IL-8, and IL-18 were measured in synovial fluid (SF) and CRP was measured in serum. Results. DAS-28 and CRP levels were not significantly different between groups. MPO activity, and MPO, Cl-Tyr, and Hcit levels were significantly higher in SF of RA patients than OA patients. MPO specific activity (MPO activity/antigen ratio) was significantly lower in treated than in untreated RA patients as was IL-8. MPO activity and concentration were correlated with IL-8 and IL-18 in untreated but not in treated RA patients. Conclusions. MPO level is related to IL-8 and IL-18 levels in untreated RA patients. A link has been shown between treatment and decrease of IL-8, MPO specific activity and Hcit in SF. The causal role of MPO in SF inflammation and how treatment can affect MPO specific activity need further investigations. [ABSTRACT FROM AUTHOR]