L-Homoarginine and its AGXT2-metabolite GOCA in chronic kidney disease as markers for clinical status and prognosis.

Plasma concentrations of L-homoarginine (hArg) are an emerging marker for clinical status and prognosis in renal and cardiovascular disease. Lowered hArg concentrations are associated with higher risk for these conditions, although a clear pathophysiological explanation for this association has not been established. Baseline plasma samples of patients with different stages of chronic kidney disease (CKD) (n = 527) were obtained from the CARE FOR HOMe study and were analyzed for hArg and, for the first time, its metabolite 6-guanidino-2-oxocaproic acid (GOCA) by isotope dilution LC-MS/MS methods. GOCA is converted from hArg by the enzyme alanine:glyoxylate aminotransferase 2 (AGXT2), which is also in the focus of current cardiovascular research. hArg levels ranged from 0.20-4.01 µmol/L with a median of 1.42 µmol/L, whereas GOCA levels were 0.08-25.82 nmol/L with a median of 1.45 nmol/L. hArg levels in the highest tertile (≥ 1.71 µmol/L) were associated with significantly lower risk for reaching the renal (hazard ratio 0.369, 95% confidence interval 0.028-0.655) or cardiovascular (HR 0.458, CI 0.295-0.712) endpoints in univariate Cox regression analysis. Inversely, GOCA levels in the highest tertile (≥ 2.13 nmol/L) were associated with increased renal (HR 3.807, CI 1.963-7.381) and cardiovascular (HR 1.611, CI 1.041-2.495) risk. A decreased ratio between hArg and GOCA predicted even more pronounced the risks for renal (HR 0.178, CI 0.087-0.363) and cardiovascular (HR 0.447, CI 0.281-0.709) events. However, adjustment for the confounders eGFR and albuminuria attenuated these findings. A pathophysiological role of an increased activity of AGXT2 in CKD should be evaluated in future clinical studies.