Metabolic profiling in children and young adults with autosomal dominant polycystic kidney disease

Abstract

Autosomal dominant polycystic kidney disease (ADPKD) is the most commonly inherited kidney disease. Although children with ADPKD show normal renal function, cyst development is already occurring. In this study, we aimed to identify markers and associated molecular pathways of disease progression in children and young adults with ADPKD. Plasma samples were collected during a 3-year randomized, double-blind, placebo-controlled, phase III clinical trial that was designed to test the efficacy of pravastatin on slowing down ADPKD progression in pediatric patients. Samples from 58 patients were available at baseline and at the 3-year endpoint of the study, respectively. Furthermore, plasma samples from 98 healthy children were used as controls. Metabolomic analysis was performed using liquid chromatography-tandem mass spectrometry and differences in metabolic profiles over time and within study groups were evaluated. While pravastatin therapy led to a decrease in a percent change of total kidney volume (HtTKV) in ADPKD patients, it had minimal effects on metabolite changes. Oxidative stress, endothelial dysfunction, inflammation and immune response were the most affected signaling pathways that distinguished healthy from diseased children. Pathway analysis revealed that metabolites in the arginine metabolism (urea and nitric oxide cycles), asparagine and glutamine metabolism, in the methylation cycle and kynurenine pathway were significantly changed between healthy and children with ADPDK and continued to diverge from the control levels while the disease progressed. Detected metabolite changes were primarily governed by disease progression, and less by pravastatin treatment. Identified metabolic pathways, from arginine and asparagine to kynurenine metabolism could present therapeutic targets and should be further investigated for potential to treat ADPKD progression at an early stage.

Figure 1

(A) Principal component analysis scores plot of healthy children (N = 98) versus children with ADPKD (N = 78) revealed a clear separation between the groups at baseline. Ellipses represent 95% confidence intervals for each individual group on the PCA plot. (B) Factor change in metabolite intensity between patients with ADPKD and healthy subjects (at baseline; presented only those with minimum of 50% change) and (C) pathway enrichment analysis of metabolites that were significantly different (after Bonferroni correction) between healthy children and children with ADPKD at baseline. The color and size of each dot were associated with the -log (p) value and pathway impact value, respectively, where a small p value and high pathway impact value indicate the pathway is greatly influenced (large red node). (D) Receiver operating curve (ROC) biomarker analysis of metabolites identified in ADPKD at baseline versus healthy subjects revealed thirty-seven metabolites with area under the curve (AUC) values of above 0.90.

Figure 2

(A) Pearson correlation coefficients and (B) pathway enrichment analysis of plasma metabolites that significantly correlated with HtTKV at baseline in pediatric ADPKD patients (N = 78, after adjustment for age, gender and race).

Figure 3

(A) Principal component analysis between pediatric ADPKD patients at the baseline (0 months) and after 36 months of treatment (group A = pravastatin, N = 31, group B = placebo, N = 27) and (B) Pearson correlation coefficients between the percent change HtTKV to a percent change in metabolites (significant after adjustment to age, gender, race (placebo, N = 27) as well as treatment group (both groups combined = ALL, N = 58). Percent change was calculated by normalizing the change over time (Δ(36–0) months) to the corresponding baseline. Ellipses represent 95% confidence intervals for each individual group on the PCA plot.

Figure 4

Summary of metabolic reprogramming observed in patients with ADPKD: changes in activity of NO and urea cycles, aspartate/asparagine and glutamine/glutamate cycles and methylation/ methionine cycles. Arrows indicate directional changes (increase/decrease) with lighter arrows expressing less pronounced changes. ADMA: asymmetric dimethylarginine, ARG: arginase1, ASNase: asparaginase, ASNS: asparagine synthetase, ASS1: argininosuccinate synthase 1, eNOS: endothelial nitric oxide synthase, GLSase: glutaminase, GS: glutamine synthetase, ODC: ornithine decarboxylase, SAM: S-adenosylmethionine, SAH: S-adenosylhomocysteine, SAHH: S-adenosylhomocysteine hydrolase.