Introduction: 2,8 dihydroxyadenine(DHA)nephropathy is a rare but severe nephropathy due to autosomic recessive mutation of the adenosine phosphoribosyl transferase enzyme. The main clinical manifestations are kidney stone and chronic kidney disease attributed to the tubular precipitation of DHA crystals. Late diagnosis leads frequently to end-stage renal disease and even kidney graft loss. Diagnosis is achieved by the presence of DHA in urine (crystalluria) or in kidney biopsy (Infrared spectroscopic analyses), and is confirmed by genetic analyses. Xanthine oxydase inhibitors, allopurinol and febuxostat, inhibit DHA formation and prevent the development of CKD progression at early stages. The purpose of the study is to assess (I) whether DHA crystals promote tissular inflammation and (II) whether anti-inflammatory drugs could improve renal function.
Methods: Clinical study: 17 kidney biopsies from 12 patients affected by DHA nephropathy have been analyzed to assess renal lesions and inflammatory infiltrate.
In vitro study: Murine macrophages (RAW 264.7 cell line) have been exposed to DHA and sodium urate (MSU) crystals to assess inflammatory response.
In vivo study-1: An air-pouch murine model has been performed to assess the inflammatory response to DHA and MSU crystals in vivo.
In vivo study-2: A murine model of DHA nephropathy (adenine-enriched food) has been performed to test whether anakinra or dexamethasone could improve renal function and histological lesions, in addition to the conventional treatment (allopurinol).
Results: Crystallites were frequently associated with tubulo-interstitial damages: tubular necrosis in all biopsies (n=17), tubular atrophy and interstitial fibrosis in 82% (n=14) and diffuse interstitial inflammation in 53% (n=9). Of notice, granuloma-like structures were observed in 88% of the cases (n=15). These granuloma contained giant and multinucleated cells developed specifically around tubule remnants containing crystallites.
In vitro: In both groups, crystal endocytosis was observed in both cases at 24 hrs. Between 72 and 144 hrs, only macrophages exposed to DHA generated ball-like structures with giant, multinucleated, and dendritic cells surrounding crystalline deposits, mimicking the granuloma observed in vivo. Macrophages exposure to DHA increased TNF-alpha (TNF-α) and to a lesser extent interleukin-1 beta (IL-1β) synthesis.
In vivo: DHA crystals increased dramatically inflammatory cells recruitment and IL-1β local production in the air-pouch model. In the DHA nephropathy model, mice exposed to allopurinol during 14 days had an improvement of renal function in comparison to control mice. Allopurinol reduced the amount of crystalline deposits in kidneys (assessed by CT-scan and 2D morphometric analyses). The addition of dexamethasone or anakinra to allopurinol during 14 days did not reduce crystalline deposits but resulted in a significant improvement of renal function and inflammatory markers, especially in the anakinra-treated group.
Conclusion: Renal function recovery remains partial and delayed when xanthine oxidase inhibitors are used to treat DHA nephropathy. The evidence that DHA nephropathy is an inflammatory and granulomatous disease, and the significant effect of dexamethasone or anakinra in experimental models suggest that patients could benefit of a short-term anti-inflammatory treatment to cure renal granulomatous disease in addition to xanthine oxidase inhibitors.