Carbamylation is a general process involved in protein molecular ageing due to 
the nonenzymatic binding of isocyanic acid, mainly generated by urea 
dissociation, to free amino groups. In vitro experiments and clinical studies 
have suggested the potential involvement of carbamylated proteins (CPs) in 
chronic kidney disease (CKD) complications like atherosclerosis, but their 
metabolic fate in vivo is still unknown. To address this issue, we evaluated 
protein carbamylation in the plasma and tissues of control and 75% 
nephrectomised C57BL/6J mice by LC-MS/MS assay of homocitrulline, the major 
carbamylation-derived product (CDP). A basal level of carbamylation was 
evidenced under all conditions, showing that carbamylation is a physiological 
process of protein modification in vivo. CP plasma concentrations increased in 
nephrectomized vs. control mice over the 20 weeks of the experiment (e.g. 335 ± 
43 vs. 167 ± 19 μmol homocitrulline/mol lysine (p<0.001) 20 weeks after 
nephrectomy). Simultaneously, CP content increased roughly by two-fold in all 
tissues throughout the experiment. The progressive accumulation of CPs was 
specifically noted in long-lived extracellular matrix proteins, especially 
collagen (e.g. 1264 ± 123 vs. 726 ± 99 μmol homocitrulline/mol lysine (p<0.01) 
in the skin of nephrectomized vs. control mice after 20 weeks of evolution). 
These results show that chronic increase of urea, as seen in CKD, increases the 
carbamylation rate of plasma and tissue proteins. These results may be 
considered in the perspective of the deleterious effects of CPs demonstrated in 
vitro and of the correlation evidenced recently between plasma CPs and 
cardiovascular risk or mortality in CKD patients.