ATTOMOLE DETECTION OF 3H IN BIOLOGICAL SAMPLES USING ACCELERATOR MASS-SPECTROMETRY - APPLICATION IN LOW-DOSE, DUAL-ISOTOPE TRACER STUDIES IN CONJUNCTION WITH C-14 ACCELERATOR MASS-SPECTROMETRY

This is the first demonstration of the use of accelerator mass spectro metry (AMS) as a tool for the measurement of H-3 With attomole (10(-18 ) mol) sensitivity in a biological study. AMS is an analytical techniq ue for quantifying rare isotopes with high sensitivity and precision a nd 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 corre lation with liquid scintillation counting. The mean coefficient of var iation of H-3 AMS based upon the analysis of separately prepared aliqu ots of these samples was 12%. The sensitivity for H-3 detection in tis sue, protein, and DNA was approximately 2-4 amol/mg of sample. This hi gh sensitivity is comparable to detection limits for C-14-labeled carc inogens 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 le vels of H-3-labeled 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (P hIP) and C-14-labeled 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (M eIQx) in rat liver tissue and bound to liver DNA and protein 4.5 h fol lowing acute administration of individual or coadministered doses in t he 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-pr otein and -DNA adduct levels were higher than PhIP adduct levels, whic h is consistent with their respective carcinogenicity in this organ. C oadministration of PhIP and MeIQx did not demonstrate any measurable s ynergistic effects compared to administration of these compounds indiv idually. 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.