Benchmarking the urinary transplant metabolome of kidney transplant recipients using healthy organ donors.

BACKGROUND

Kidney transplantation is the only curative treatment for end-stage kidney disease, providing markedly improved outcomes over dialysis. In search of optimized long-term outcomes, recent studies have demonstrated alterations in the metabolic state of kidney transplant recipients (KTRs) may contribute to chronic graft outcomes. Here, we sought to benchmark metabolic perturbations associated with the post-transplant state using a set of extensively characterized kidney transplant donors as healthy control.

METHODS

In this cross-sectional, single-center study, we used untargeted GC-MS to profile the 24 h urine from 121 stable KTRs (0.2-38.9 yrs post-transplant) and 94 extensively screened healthy potential kidney donors (HC) from the TransplantLines Biobank and Cohort Study. We assessed group differences using linear models adjusted for baseline covariates including eGFR, and the multivariable OPLS-DA model for global separation. ROC analysis was performed on the top discriminants. GlobalTest Pathway enrichment was used to map differentially abundant metabolites in metabolic pathways from the KEGG database.

RESULTS

In KTRs, 28 metabolites were significantly altered compared to HC; 13 of which were elevated and 15 decreased in KTRs. Among them, methylmalonic acid (AUROC 0.886), citric acid (AUROC 0.870), and glycolic acid (AUROC 0.804) were all reduced in KTRs and showed the strongest in-sample separation between the groups. OPLS-DA achieved good group separation (R2Y = 0.733, Q2 = 0.621) with no signs of overfitting. Twenty pathways were significantly perturbed, led by the TCA cycle, glyoxylate and dicarboxylate metabolism and branched-chain amino acid degradation. Sensitivity analyses examining alternative normalizations, excluding patients with diabetes or proteinuria, adjusting for statin use, and stratifying by eGFR and transplant vintage, were highly concordant with the main analysis (Spearman ρ > 0.87 for all pairwise comparisons).

CONCLUSION

Urinary metabolic profiles in KTRs are consistent with alterations in TCA cycle, glyoxylate and dicarboxylate metabolism, and branched chain amino acid degradation after transplantation. Although causality cannot be established from this cross-sectional design, these findings may reflect altered energy metabolism in the post-transplant state.