Attomole detection of 3H in biological samples using accelerator mass spectrometry:: Application in low-dose, dual-isotope tracer studies in conjunction with 14C accelerator mass spectrometry

This is the first demonstration of the use of accelerator mass spectrometry (AMS) as a tool for the measurement of H-3 With attomole (10(-18) mol) sensitivity in a biological study. AMS is an analytical technique for quantifying rare isotopes with high sensitivity and precision and has been most commonly used to measure C-14 in both the geosciences and more recently in biomedical research. AMS measurement of serially diluted samples containing a H-3-labeled tracer showed a strong correlation with liquid scintillation counting. The mean coefficient of variation of H-3 AMS based upon the analysis of separately prepared aliquots of these samples was 12%. The sensitivity for H-3 detection in tissue, protein, and DNA was approximately 2-4 amol/mg of sample. This high sensitivity is comparable to detection limits for C-14-labeled carcinogens using C-14 AMS and demonstrates the feasibility of H-3 AMS for biomedical studies. One application of this technique is in low-dose, dual-isotope studies in conjunction with C-14 AMS. We measured the levels of H-3-labeled 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and C-14-labeled 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in rat liver tissue and bound to liver DNA and protein 4.5 h following acute administration of individual or coadministered doses in the range of 4-5100 pmol/kg of body weight. Levels of PhIP and MeIQx in whole tissue and bound to liver protein were dose-dependent. MeIQx-protein and -DNA adduct levels were higher than PhIP adduct levels, which is consistent with their respective carcinogenicity in this organ. Coadministration of PhIP and MeIQx did not demonstrate any measurable synergistic effects compared to administration of these compounds individually. These studies demonstrate the application of AMS for the low-level detection of H-3 in small biological samples and for its use in conjunction with C-14 AMS for dual-labeling studies.