The use of stable carbon isotopes as a means of studying energy flow is increasing in ecology and paleoecology. However, secondary fractionation and turnover of stable isotopes in animals are poorly understood processes. This study shows that tissues of the gerbil (Meriones unguienlatus) have different δC values when equilibrated on corn (C) or wheat (C) diets with constant C/C contents. Lipids were depleted 3.0‰ and hair was enriched 1.0‰ relative to the C diet. Tissue δC values were ranked hair>brain>muscle>liver>fat. After changing the gerbils to a wheat (C) diet, isotope ratios of the tissues shifted in the direction of the δC value of the new diet. The rate at which carbon derived from the corn diet was replaced by carbon derived from the wheat diet was adequately described by a negative exponential decay model for all tissues examined. More metabolically active tissues such as liver and fat had more rapid turnover rates than less metabolically active tissues such as hair. The half-life for carbon ranged from 6.4 days in liver to 47.5 days in hair.The results of this study have important implications for the use of δC values as indicators of animal diet. Both fractionation and turnover of stable carbon isotopes in animal tissues may obscure the relative contributions of isotopically distinct dietary components (such as C vs. C, or marine vs. terrestrial) if an animal's diet varies through time. These complications deserve attention in any study using stable isotope ratios of animal tissue as dietary indicators and might be minimized by analysis of several tissues or products covering a range of turnover times.

Endemic (Balkan) nephropathy (EN),environmental mutagen ͉ p53 mutation ͉ urothelial cancer ͉ DNA adduct

p73 has significant homology to p53. However, tumor-associated up-regulation of p73 and genetic data from human tumors and p73-deficient mice exclude a classical Knudson-type tumor suppressor role. We report that the human TP73 gene generates an NH2 terminally truncated isoform. ΔNp73 derives from an alternative promoter in intron 3 and lacks the transactivation domain of full-length TAp73. ΔNp73 is frequently overexpressed in a variety of human cancers, but not in normal tissues. ΔNp73 acts as a potent transdominant inhibitor of wild-type p53 and transactivation-competent TAp73. ΔNp73 efficiently counteracts transactivation function, apoptosis, and growth suppression mediated by wild-type p53 and TAp73, and confers drug resistance to wild-type p53 harboring tumor cells. Conversely, down-regulation of endogenous ΔNp73 levels by antisense methods alleviates its suppressive action and enhances p53- and TAp73-mediated apoptosis. ΔNp73 is complexed with wild-type p53, as demonstrated by coimmunoprecipitation from cultured cells and primary tumors. Thus, ΔNp73 mediates a novel inactivation mechanism of p53 and TAp73 via a dominant-negative family network. Deregulated expression of ΔNp73 can bestow oncogenic activity upon the TP73 gene by functionally inactivating the suppressor action of p53 and TAp73. This trait might be selected for in human cancers.

Balkan endemic nephropathy is a chronic tubulointerstitial disease frequently accompanied by urothelial cell carcinomas of the upper urinary tract. This disorder has recently been linked to exposure to aristolochic acid, a powerful nephrotoxin and human carcinogen. Following metabolic activation, aristolochic acid reacts with genomic DNA to form aristolactam-DNA adducts that generate a unique TP53 mutational spectrum in urothelium. The aristolactam-DNA adducts are concentrated in the renal cortex, thus serving as biomarkers of internal exposure to aristolochic acid. Here, we present molecular epidemiologic evidence relating carcinomas of the upper urinary tract to dietary exposure to aristolochic acid. DNA was extracted from the renal cortex and urothelial tumor tissue of 67 patients that underwent nephroureterectomy for carcinomas of the upper urinary tract and resided in regions of known endemic nephropathy. Ten patients from non-endemic regions with carcinomas of the upper urinary tract served as controls. Aristolactam-DNA adducts were quantified by 32P-post-labeling, the adduct was confirmed by mass spectroscopy, and TP53 mutations in tumor tissues were identified by chip-sequencing. Adducts were present in 70% of the endemic cohort and in 94% of patients with specific A:T to T:A mutations in TP53. In contrast, neither aristolactam-DNA adducts nor specific mutations were detected in tissues of patients residing in non-endemic regions. Thus, in genetically susceptible individuals, dietary exposure to aristolochic acid is causally related to endemic nephropathy and carcinomas of the upper urinary tract.

This study was designed to establish the TP53 mutational spectrum of aristolochic acid (AA), examined in the context of endemic (Balkan) nephropathy, an environmental disease associated with transitional cell (urothelial) carcinomas of the upper urinary tract (UUC). Tumor tissue was obtained from residents of regions in Bosnia, Croatia and Serbia where endemic nephropathy has been prevalent for over 50 years. Fifty-nine TP53 mutations were detected in 42 of the 97 tumors analyzed. Mutational spectra were dominated by A:T to T:A transversions with the mutated adenines located almost exclusively on the nontranscribed strand. This marked strand bias is attributed to selective processing of aristolactam-dA adducts by transcription-coupled nucleotide excision repair. Hotspots for A:T to T:A mutations include codons 131 and 179 and the 5 0 -AG acceptor splice site of intron 6. The unique TP53 mutational signature for AA identified in this study can be used to explore the hypothesis that botanical products containing this human carcinogen and nephrotoxin are responsible, in part, for the high prevalence of UUC and chronic renal disease in countries where Aristolochia herbal remedies traditionally have been used for medicinal purposes.