72–75 Reduced megalin expression leading to impaired receptor-mediated endocytosis is responsible for increased excretion of low molecular weight proteins.76 The carcinogenicity of AA is related to the strong affinity of AA metabolites for the exocyclic amino group of DNA. In vitro studies have shown that

the NAD(P)H:quinone oxidoreductase, cytochrome P450 1A1/2, NADPH:CYP reductase and cyclooxygenase are responsible for activating AA.68,77–79 Upon binding to the adenine residues, AA induces specific AT TA transversion mutations leading to activation of H-ras and overexpression of p53.80,81 This ‘signature mutation’ is not seen in other types of urological malignancies. Elimination of AA involves oxidative conversion of AAI to AA Ia followed by reduction to N-hydroxyaristolactam Ibrutinib Ia. Both AAIa and aristolactam Ia are excreted through the kidneys either as such or as glucuronide, acetate or sulfate conjugate. This pathway is responsible for loss of toxicity and has been dubbed the ‘detoxification pathway’ (Fig. 1).68,82 The enzymes involved in this pathway belong to the cytochrome P450 system.83,84 Cytochrome P450 reductase-null mice exhibit slower AA clearance and higher AAI levels in the kidney and liver.84

Using specific inhibitors of the various components of the CYP family, Sistkova et al.83 found that conversion to AAIa in human hepatic microsome preparations was attributable Deforolimus ic50 to CYP1A. Why not all individuals exposed to AA develop kidney disease or tumours is not known. Postulations include difference

in the dose of ingested AA, degree of absorption BCKDHB and simultaneous consumption of other compounds that potentiate or mitigate AA toxicity by interfering with enzyme activity. Recent work suggests that variation in genes encoding these enzymes may determine individual susceptibility. An increased risk of BEN was shown in individuals who had a G allele at 6989 position of the CYP3A5 gene.85NQO1*2 mutation affected the risk of development of malignancies.85 Better understanding of these pathways might allow us to develop novel strategies to limit or even reverse the toxicities. Such strategies might include decreasing drug accumulation by downregulating transporters; accelerating metabolism or blocking activation by using specific enzyme inducers or inhibitors; modulation of the major effector pathways, for example inhibition of the pro-apoptotic or upregulation of the anti-apoptotic molecules, alteration of calcium efflux, modulation of NO generation; and using growth factors to stimulate regeneration or using molecules to inhibit enzymes that cause tissue destruction (matrix metalloproteinase (MMP)) or fibrosis (TGF-β).