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Published on: July 14, 2016
The renal phenotype of allopurinol-treated HPRT-deficient mouse
Cristina Zennaro1, Federica Tonon1, Paola Zarattini2
1Department of Medical, Surgery and Health Sciences, Università degli Studi di Trieste, Trieste, Italy.
Abstract:
Excess of uric acid is mainly treated with xanthine oxidase (XO) inhibitors, also called uricostatics because they block the conversion of hypoxanthine and xanthine into urate. Normally, accumulation of upstream metabolites is prevented by the hypoxanthine-guanine phosphoribosyltransferase (HPRT) enzyme. The recycling pathway, however, is impaired in the presence of HPRT deficiency, as observed in Lesch-Nyhan disease. To gain insights into the consequences of purine accumulation with HPRT deficiency, we investigated the effects of the XO inhibitor allopurinol in Hprt-lacking (HPRT-/-) mice. Allopurinol was administered in the drinking water of E12-E14 pregnant mothers at dosages of 150 or 75 microg/ml, and mice sacrificed after weaning. The drug was well tolerated by wild-type animals and heterozygous HPRT+/- mice. Instead, a profound alteration of the renal function was observed in the HPRT-/- model. Increased hypoxanthine and xanthine concentrations were found in the blood. The kidneys showed a yellowish appearance, diffuse interstitial nephritis, with dilated tubules, inflammatory and fibrotic changes of the interstitium. There were numerous xanthine tubular crystals, as determined by HPLC analysis. Oil red O staining demonstrated lipid accumulation in the same location of xanthine deposits. mRNA analysis showed increased expression of adipogenesis-related molecules as well as profibrotic and proinflammatory pathways. Immunostaining showed numerous monocyte-macrophages and overexpression of alpha-smooth muscle actin in the tubulointerstitium. In vitro, addition of xanthine to tubular cells caused diffuse oil red O positivity and modification of the cell phenotype, with loss of epithelial features and appearance of mesenchymal characteristics, similarly to what was observed in vivo. Our results indicate that in the absence of HPRT, blockade of XO by allopurinol causes rapidly developing renal failure due to xanthine deposition within the mouse kidney. Xanthine seems to be directly involved in promoting lipid accumulation and subsequent phenotype changes of tubular cells, with activation of inflammation and fibrosis.
Insights
In Lesch-Nyhan disease models, blocking xanthine oxidase (XO) with allopurinol leads to kidney failure. This occurs because of xanthine crystal buildup, causing lipid accumulation and cell changes in the kidneys.
Area of Science:
- Nephrology
- Biochemistry
- Pharmacology
Background:
- Xanthine oxidase (XO) inhibitors treat excess uric acid by blocking urate production.
- Hypoxanthine-guanine phosphoribosyltransferase (HPRT) normally prevents metabolite buildup.
- HPRT deficiency, seen in Lesch-Nyhan disease, impairs this recycling pathway.
Purpose of the Study:
- Investigate the effects of XO inhibition on purine accumulation in HPRT-deficient mice.
- Examine the renal consequences of allopurinol treatment in HPRT-/- mice.
Main Methods:
- Administered allopurinol to pregnant Hprt-/- mice and their offspring.
- Assessed renal function, metabolite concentrations (HPLC), and kidney histology.
- Analyzed gene expression (mRNA) and protein markers (immunostaining) in kidney tissues.
- Performed in vitro studies using tubular cells exposed to xanthine.
Main Results:
- Allopurinol caused severe renal dysfunction in HPRT-/- mice, unlike wild-type or HPRT+/- mice.
- Elevated blood hypoxanthine and xanthine levels were observed.
- Kidneys exhibited interstitial nephritis, tubular dilation, inflammation, fibrosis, and xanthine crystal deposition.
- Xanthine deposits correlated with lipid accumulation and tubular cell changes (epithelial-to-mesenchymal transition).
- Increased expression of adipogenesis, profibrotic, and proinflammatory markers was noted.
Conclusions:
- In HPRT deficiency, allopurinol-induced XO blockade leads to renal failure via xanthine deposition.
- Xanthine accumulation promotes lipid deposition and tubular cell dedifferentiation.
- These changes activate inflammatory and fibrotic processes in the kidney.
