Torres, Jacob A.

Abstract Background and Aims Patients with ADPKD exhibit an increased prevalence of kidney stones with a significant overrepresentation of uric acid (UA) stones which has led to the previous suggestion that UA may be associated with disease progression in ADPKD. However, available results are controversial and the exact mechanism remains unknown. Since we have previously reported that calcium-based microcrystals worsen ADPKD disease progression we hypothesized that renal UA crystallization could affect PKD disease progression and aimed to investigate this in animal models of PKD and the AD(H)PKD registry at the University Hospital Cologne. Method WT and Pkd1+/− rats were supplemented with UA and the uricase inhibitor oxonic acid from 8 to 10 weeks of age to induce moderate hyperuricemia causing renal UA crystal deposition. This was followed by washout from 10 to 18 weeks to analyze crystal clearance. For additional treatment with the ketone beta-hydroxybutyrate (BHB) and alkaline Citrate, adult rats received a solution containing 2.1% BHB and 13.75 mM tripotassium citrate/16.75 mM citric acid in the drinking water from 14 to 18 weeks of age. Human data including eGFR, UA levels in serum, spot urine and 24-hour urine and urine pH were used from the AD(H)PKD study (Clinical Trials ID: NCT02497521) and analyzed using multivariable linear models. Results UA crystal deposition in Pkd1+/− rats led to significantly increased kidney growth, tubule dilation and UA crystal burden compared to UA-treated WT controls. Dilated tubules exhibited strong TLR-4 expression, NLRP3 activation, recruitment of peritubular macrophages and intraluminal neutrophils undergoing NETosis. Strikingly—although untreated heterozygous Pkd1+/− rats fail to develop a polycystic phenotype—UA-treated Pkd1+/− rats developed polycystic kidney disease after 8 weeks washout period with persistent activation of TLR4, NLRP3, pericystic macrophages and intracystic neutrophils. UA-treated WT rats displayed a normalization of renal tubules. Previously, we demonstrated that treatment with BHB and Citrate can ameliorate PKD disease progression. BHB has been reported to inhibit TLR4-NLRP3 signaling and citrate can prevent UA deposition due to urine alkalinization. Therefore, we induced UA crystal deposition in Pkd1+/− followed by 4 weeks of normal diet to allow crystal clearance, followed by treatment with BHB/Citrate in the drinking water. Remarkably, BHB/Citrate potently inhibited the progression to PKD in Pkd1+/− rats by ameliorating cyst growth, TLR4-NLRP3 activation, and macrophage and neutrophil recruitment. Translational analysis of UA stone forming parameters in the AD(H)PKD patient registry showed a correlation of serum and urine UA concentration with eGFR slope. However, significance of this association was lost after adjusting for eGFR, age and sex. In contrast, analysis of the Marshal lithogenic risk score which combines urine UA with urine pH to predict the risk for UA crystal/stone formation showed a significant and independent impact on eGFR slope. Conclusion Our results suggest that UA exposure is a sufficient environmental hit to induce cystogenesis in a heterozygous Pkd1 rat model. A heterozygous Pkd1 gene mutation as observed in ADPKD patients creates a hyperresponsive renal phenotype upon UA crystal formation leading to exaggerated tubule dilation, persistent inflammation, fibrosis and progression to PKD. Treatment with BHB/Citrate significantly reduces TLR4-NLRP3 activation and macrophage/ neutrophil recruitment leading to a significant amelioration of UA-induced cystogenesis. We conclude that UA crystal deposition could accelerate PKD disease progression by NLRP3-mediated and macrophage/neutrophil-based hyperinflammation. BHB/Citrate could not only prevent UA crystallization but ameliorate UA-associated kidney injury and ADPKD disease progression. Finally, the translational analysis in the AD(H)PKD patient registry suggest that, although not showing serum uric acid as independent risk factor, the lithogenic risk- largely driven by the combination of urine uric acid and urine pH- could be a driver of PKD disease progression.