Urinary Metabolomics from a Dose-Fractionated Polymyxin B Rat Model of Acute Kidney Injury

Background Polymyxin B remains an important antimicrobial against multi-drug resistant bacteria; however, kidney injury is often a treatment limiting event with kidney failure rates that range from 5-13%. Methods Samples were obtained from a previously conducted study of male Sprague-Dawley rats that received dose fractionated polymyxin B (12 mg/kg/day subcutaneously) once daily (QD), twice daily (BID), and thrice daily (TID) for three days. In the original study, urinary biomarkers and kidney histopathology scores were determined. Urine was sampled daily and analyzed for urinary metabolites via 1H NMR analysis. Unsupervised Principal Components Analysis was applied for exploratory data analysis to identify trends and outliers in the spectral data. Then, supervised Orthogonal Partial Least Square Discriminant Analysis was applied to classify the samples collected in different days and identify metabolic differences during the treatment. Metabolomes were compared across study groups (i.e. those receiving QD, BID, TID, and control) using a mixed-effects models. Spearman correlation was performed for injury biomarkers and the metabolome. Results A total of 27 rats contributed 77 urinary samples; n=25 rats were included that were treated with Polymyxin B and n=2 received saline. Pre-dosing samples clustered well and were characterized by higher amounts of citrate, 2-oxoglutarate, and Hippurate. On day 1 post treatment, day 1 samples showed higher taurine; day 3 samples had higher lactate, acetate and creatine. Taurine was the only metabolite significantly increased in both BID and TID compared to QD group. Taurine on day 1 correlated with increasing histopathology scores (Spearman’s rho = 0.4167, P=0.038) and KIM-1 (Spearman’s rho =0.4052, P=0.036); whereas KIM-1 on day one and day 3 did not reach significance with histopathology (Spearman’s rho = 0.3248, P=0.11 and Spearman’s rho = 0.3739, P=0.066). Conclusion Polymyxin B causes increased amounts of urinary taurine on day 1 which then normalizes to baseline concentrations. Taurine may provide one of the earlier signals of acute kidney damage caused by polymyxin B.