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.

Renal proximal tubular cells acquire resistance to cell death stimuli in mice with hereditary tyrosinemia type 1.

BACKGROUND: Hereditary tyrosinemia type 1 (HT1), which is associated with severe liver and kidney damage, is caused by deficiency of fumarylacetoacetate hydrolase (FAH), the last enzyme of the tyrosine breakdown cascade. HT1-associated liver and kidney failure can be prevented by blocking an enzyme upstream of FAH in the tyrosine breakdown pathway with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC). FAH knockout mice develop the HT1 phenotype when NTBC treatment is discontinued. METHODS: The occurrence of cell death was investigated in kidneys of Fah(-/-) mice on and off NTBC either unchallenged or injected with 800 mg/kg of homogentisic acid (HGA), an intermediate of tyrosine breakdown. RESULTS: No cell death could be detected in kidneys of Fah(-/-) mice on NTBC. A slight increase of cleaved caspase-3 was the only apoptosis-related feature that could be detected in kidneys of Fah(-/-) mice off NTBC. Challenge of Fah(-/-) mice on NTBC with HGA led to massive death of renal proximal tubular cells, with positive terminal deoxynucleotidyl transferase-mediated deoxyuridine diphosphate (dUDP) nick-end labeling (TUNEL) and DNA fragmentation assays, but hardly any cleavage of caspase-9 and caspase-3. Fah(-/-) mice off NTBC acquired resistance to HGA-induced renal cell death and the kidneys exhibited relatively few features of apoptosis upon challenge with HGA, with a small increase in expression of cleaved caspase-9 and caspase-3. CONCLUSION: Kidneys of adult Fah(-/-) mice, withdrawn from NTBC for 15 days, reveal limited characteristics of apoptosis, and have acquired resistance to a caspase-9- and caspase-3-independent form of cell death provoked by HGA.

Extensive changes in liver gene expression induced by hereditary tyrosinemia type I are not normalized by treatment with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC).

BACKGROUND: Hereditary Tyrosinemia type I, caused by deficiency of fumarylacetoacetate hydrolase (FAH), is characterized by liver and kidney damage. Administration of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) corrects the tyrosinemia phenotype, but does not prevent development of hepatocellular carcinoma. AIM: To gain insight into the pathophysiological changes associated with liver damage induced by tyrosinemia and the preventive action of NTBC on these changes. METHODS: Differential gene expression patterns in livers of tyrosinemia-affected and healthy mice, and of tyrosinemia-affected and NTBC-treated Fah-/- mice were investigated by suppression subtractive hybridization. RESULTS: Transcripts encoding proteins playing a role in protein turnover, growth and proliferation, RNA processing, and signal transduction were primarily induced in tyrosinemia-affected livers. Transcripts mainly contributing to the profile of suppressed genes encode proteins that are secreted by the liver, or are necessary for intermediate metabolism. NTBC treatment fails to normalize the tyrosinemia-induced alterations in expression of transcripts encoding proteins involved in protein turnover, signal transduction, and cell growth and proliferation. CONCLUSIONS: The failure of NTBC to normalize liver gene expression of Fah-/- mice may play a role in rendering the tyrosinemia-affected liver susceptible to development of hepatocellular carcinoma under NTBC treatment.