Carbamoylation of glomerular and tubular proteins in patients with kidney failure: a potential mechanism of ongoing renal damage.
BACKGROUND
Cyanate formed spontaneously from urea carbamoylates non-protonated amino groups of protein, irreversibly altering function, charge and structure. Carbamoylated proteins in renal tissue have not been examined hitherto.


OBJECTIVE
To identify homocitrulline (epsilon-amino-carbamoyl-lysine), a result of in vivo carbamoylation by urea-derived cyanate, from patients with renal disease or in newly transplanted kidneys by immunohistochemistry. To evaluate enzymatic activity of carbamoylated and non-carbamoylated matrix metalloproteinase-2 and correlate this with renal tissue carbamoylated in vivo.


METHODS
Anti-homocitrulline antibody is specific for homocitrulline and was used to identify carbamoylation of epsilon-amino-lysine in renal biopsies from patients with elevated BUN, with isolated proteinuria, and as controls, from normal donors at time of transplantation. Enzymatic activity of matrix metalloproteinase-2 carbamoylated in vitro was evaluated.


RESULTS
Homocitrulline was present in glomerular basement membrane (8/10), mesangium (8/10), tubular epithelium and cytoplasm (7/10) and Bowman's capsule (1/10) in patients with elevated BUN. The discordant patterns of glomerular and tubular localization of homocitrulline versus immune complexes indicated that the carbamoylated proteins were not a component of immune deposits but were modified proteins in renal tissue. No homocitrulline was found in transplanted kidneys (14/15) or in proteinuric patients (2/2). Enzymatic activity of both human and rat matrix metalloproteinase-2 was strongly inhibited in a dose-dependent fashion when incubated with cyanate.


CONCLUSIONS
In situ carbamoylation in proteins occurred in kidneys of patients with renal dysfunction but not in normal newly transplanted kidneys. Decreased enzymatic activity of carbamoylated enzymes may alter specific renal regulatory mechanisms. Carbamoylated proteins with altered function and charge may represent a previously underestimated mechanism in renal pathophysiology.
Kraus
L M
LM
Department of Molecular Science, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA. lkraus@utmem.edu
Gaber
L
L
Handorf
C R
CR
Marti
H P
HP
Kraus
A P
AP
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002219:Carbamates; D002956:Citrulline / Q000031:analogs & derivatives* / Q000378:metabolism*; D003485:Cyanates / Q000378:metabolism / Q000494:pharmacology; D018450:Disease Progression; D005455:Fluorescent Antibody Technique; D006801:Humans; D007150:Immunohistochemistry; D007676:Kidney Failure, Chronic / Q000378:metabolism* / Q000628:therapy; D016030:Kidney Transplantation; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D011506:Proteins / Q000378:metabolism; D051381:Rats
D000596:Amino Acids; D002219:Carbamates; D003485:Cyanates; D011506:Proteins; C001352:homocitrulline; D002956:Citrulline; D020778:Matrix Metalloproteinase 2