Stéphane Jaisson

Homocitrulline as marker of protein carbamylation in hemodialyzed patients

BACKGROUNDnHomocitrulline (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.nnnMETHODSnSerum 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.nnnRESULTSnMean HCit concentrations reached 1000μmol/mol Lysine before initiation of HD therapy and decreased by 50% within 6months 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.nnnCONCLUSIONnHCit 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.

Early Formation of Serum Advanced Glycation End-Products in Children with Type 1 Diabetes Mellitus: Relationship with Glycemic Control.

OBJECTIVESnTo quantify serum advanced glycation end-products (AGEs) at the onset of type 1 diabetes mellitus and to determine their potential usefulness as retrospective indicators of glycemic balance.nnnSTUDY DESIGNnCarboxymethyllysine (CML) and pentosidine concentrations were determined by liquid chromatography-tandem mass spectrometry in 3 groups of children with type 1 diabetes mellitus: group (Gr) 1, subjects included at disease onset (nxa0=xa036); Gr2, subjects with diabetes of 5xa0years duration (nxa0=xa048); Gr3, subjects with diabetes of 10xa0years duration and in control subjects (nxa0=xa033). Hemoglobin A1c (HbA1c) values were recorded over the entire course of treatment for assessing long-term glycemic balance.nnnRESULTSnSerum AGE concentrations were increased in all groups of subjects with diabetes compared with control subjects, but were highest in Gr1 (for CML: 0.155, 0.306, 0.219, and 0.224xa0mmol/mol Lys in control, Gr1, Gr2, and Gr3 subjects, respectively; for pentosidine: 312, 492, 365, and 403xa0nmol/mol Lys, respectively). AGE concentrations were closely correlated with HbA1c values (rxa0=xa00.78 for CML; rxa0=xa00.49 for pentosidine). In Gr2 and Gr3, the overall glycemic balance estimated by average HbA1c values was positively correlated with CML and pentosidine concentrations, especially in the first year of follow-up.nnnCONCLUSIONnOur results indicate that AGE concentrations are elevated in serum at the time of diabetes mellitus diagnosis, suggesting that the deleterious role of AGEs in the development of long-term complications should be taken into account even at the initial stages of the disease. Moreover, in some circumstances, AGEs could serve as surrogate markers of HbA1c for monitoring glycemic control.

Protein Carbamylation: Chemistry, Pathophysiological Involvement, and Biomarkers

Protein carbamylation refers to a nonenzymatic modification, which consists in the binding of isocyanic acid on protein functional groups. This reaction is responsible for the alteration in structural and functional properties of proteins, which participate in their molecular aging. Protein molecular aging is now considered a molecular substratum for the development of chronic and inflammatory diseases, including atherosclerosis, chronic kidney disease, or rheumatoid arthritis. As a consequence, carbamylation-derived products have been proposed as interesting biomarkers in various pathological contexts and appropriate analytical methods have been developed for their quantification in biological fluids. The purpose of this review is (i) to describe the biochemical bases of the carbamylation reaction, (ii) to explain how it contributes to protein molecular aging, (iii) to provide evidence of its involvement in aging and chronic diseases, and (iv) to list the available biomarkers of carbamylation process and the related analytical methods.

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

Carbamylation corresponds to the non‐enzymatic 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 to evaluate 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 attaches 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 unit describes a liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method for the quantification of homocitrulline, with special emphasis on pre‐analytical steps that allow quantification of total or protein‐bound homocitrulline in serum or tissue samples.