Kidneys of mice with hereditary tyrosinemia type I are extremely sensitive to cytotoxicity

Children with hereditary tyrosinemia type 1 (HT1) suffer from liver failure, renal tubular dysfunction, and rickets. The disease is caused by deficiency of fumarylacetoacetate hydrolase (FAH), the last enzyme of tyrosine catabolism, and leads to accumulation of the toxic substrate fumarylacetoacetate (FAA) in hepatocytes and renal proximal tubular cells. Patients are treated with 2-(2-nitro-4-trifluoro-methylbenzoyl)-1,3 cyclohexanedione (NTBC), which prevents accumulation of FAA by blocking an enzyme upstream of FAH. Liver transplantation is performed when patients do not respond to NTBC or develop hepatocellular carcinoma. This reduces the tyrosine load for the kidney but does not abolish renal exposure to locally produced FAA. To investigate the pathogenesis of liver and kidney damage induced by tyrosine metabolites, we challenged FAH-deficient mice with various doses of homogentisic acid (HGA), a precursor of FAA. Injecting NTBC-treated Fah-/- mice with low doses of HGA caused renal damage and death of renal tubular cells, as was shown by histologic analyses and deoxynucleotidyl transferase-mediated dUDP nick-end labeling (TUNEL) assay but did not lead to liver damage. In addition, kidney function, but not liver function, was affected after exposure to low doses of HGA. Administration of high doses of HGA led to massive cell death in both the liver and kidneys. Resistance to HGA-induced cell death was seen after withdrawing NTBC from Fah-/- mice. The finding that the kidneys of Fah-/- mice are especially sensitive to damage induced by low doses of HGA underscores the need to perform careful monitoring of the kidney function of tyrosinemia patients undergoing any form of treatment.