Discovery of early urinary biomarkers in preclinical study of gentamicin-induced kidney injury and recovery in rats

LC/MS- and NMR-based global metabolomics analyses were utilized to study the changes in rat urine in response to gentamicin treatment. Sprague–Dawley rats were dosed with gentamicin sulfate at 0, 75, 150 or 300 mg/kg/day for one, two or three consecutive days. Four animals from each group were sacrificed to harvest kidney tissue and to collect urine on days 1, 2, 3, 7, 10, 15, 18, 22, 29, 36 and 44 for a total of 11 different time points. Both uni- and multivariate statistical analyses were employed to identify the significantly changed metabolites in urine at the different dose levels and time points. Increases and decreases in amino acids including tyrosine, valine and hydroxyproline reflected histopathology changes of kidney injury development and/or kidney injury recovery. Glucosuria was noted much earlier than changes in the classic kidney function biomarkers, blood urea nitrogen and serum creatinine. Dopamine-related compounds, homovanillic acid sulfate (HVA-SO4) and homoveratric acid sulfate (HVrA-SO4) were significantly increased at early time points and could be early indicators of a renal adaptive response to gentamicin-induced renal injury. Furthermore, the drug efficacy of gentamicin was evaluated through the detection of changes in gut microflora-related compounds (e.g. indole-containing metabolites). Metabolomics was successful in identifying valine, hydroxyproline, HVA-SO4 and HVrA-SO4 that might serve as potential early injury biomarkers or adaptive markers of gentamicin-induced renal injury, and in assessing gentamicin efficacy through changes in compounds reported to be related to gut microflora. However, caution should be taken in direct translation of the biomarkers reported in clinical settings because a much higher dose of gentamicin than the normal therapeutic dose (~1–2 mg/kg) was used to cause kidney damaged.