Alterations in gut-derived uremic toxins before the onset of azotemic chronic kidney disease in cats

Abstract

Background: Although gut-derived uremic toxins are increased in azotemic chronic kidney disease (CKD) in cats and implicated in disease progression, it remains unclear if augmented formation or retention of these toxins is associated with the development of renal azotemia.

Objectives: Assess the association between gut-derived toxins (ie, indoxyl-sulfate, p-cresyl-sulfate, and trimethylamine-N-oxide [TMAO]) and the onset of azotemic CKD in cats.

Animals: Forty-eight client-owned cats.

Methods: Nested case-control study, comparing serum and urine gut-derived uremic toxin abundance at 6-month intervals between initially healthy cats that developed azotemic CKD (n = 22) and a control group (n = 26) that remained healthy, using a targeted metabolomic approach.

Results: Cats in the CKD group had significantly higher serum indoxyl-sulfate (mean [SD], 1.44 [1.06] vs 0.83 [0.46]; P = .02) and TMAO (mean [SD], 1.82 [1.80] vs 1.60 [0.62]; P = .01) abundance 6 months before the detection of azotemic CKD. Furthermore, logistic regression analysis indicated that indoxyl-sulfate (odds ratio [OR]: 3.2; 95% confidence interval [CI]: 1.2-9.0; P = .04) and TMAO (OR: 3.9; 95% CI: 1.4-11; P = .03) were predictors for the onset of azotemia 6 months before diagnosis. However, renal function biomarkers creatinine, symmetric dimethylarginine, and urinary specific gravity were significantly correlated with indoxyl-sulfate and TMAO abundance, causing a loss in predictive significance after correction for these factors.

Conclusions: Impaired gut-derived uremic toxin handling is apparent at least 6 months before the diagnosis of azotemia, likely reflecting an already ongoing decrease in GFR, tubular function, or both. A direct causal relationship between gut-derived uremic toxicity and the initiation of CKD in cats is still lacking.

Keywords: CKD development; early intervention; feline chronic kidney disease; pathophysiology; uremic toxicity.

FIGURE 1

(1) This prospective nested case‐control study consisted of a healthy population of cats that was followed longitudinally, with assessments conducted at 6‐month intervals. Group 1 consisted of all cats that developed azotemic CKD during the study (further referred to as CKD development cohort). Data on cats that developed CKD was tracked back to 6 and 12 months before their diagnosis (ie, timepoints −12 months, −6 months, and CKD onset). Group 2 consisted of a control cohort of cats that remained healthy throughout 1 year follow‐up. Likewise, data on cats that remained healthy was tracked back to 6 and 12 months before health confirmation (ie, timepoints −12 months, −6 months, and maintained health). (2) Serum and urine samples were collected, followed by chemical extraction according to feline specific optimized and validated methods. (3) Samples from both matrices were analyzed using ultrahigh‐performance liquid chromatography coupled to high‐resolution mass spectrometry (UHPLC‐HRMS). (4) The primary objective of our nested case‐control study was to assess the association between circulating gut‐derived uremic toxins and the development of azotemic CKD, 6 and 12 months before diagnosis. Statistical analyses also aimed to compare metabolite abundance between the CKD development cohort and the healthy cohort (at timepoints −12 months, n = 15 vs n = 26; −6 months, n = 22 vs n = 26 and CKD onset or maintained health, n = 22 vs n = 26). Furthermore, the trend of altering metabolites was evaluated over time in the CKD development cohort (n = 15).

FIGURE 2

Comparisons of (I) serum dietary amino acids tryptophan, tyrosine, carnitine; (II) gut bacterial byproducts indole, p‐cresol, trimethylamine (TMA); (III) related uremic toxins indoxyl‐sulfate, p‐cresyl‐sulfate, trimethylamine‐N‐oxide (TMAO); and (IV) urinary abundance of these compounds between a healthy feline cohort and a cohort of cats developing azotemic CKD over time. Specific comparisons are shown between the healthy cohort and the CKD development cohort at 12 months, 6 months prior, and at the time of azotemic CKD diagnosis or maintained health. Significant P values (<.05) are represented by the symbol * after FDR correction.