Technology Review: Application of Whole-Body Autoradiography in Toxicology

Validation of procedures for quantitative whole-body autoradiography using digital imaging

The objective of this study was to demonstrate that tissue concentrations of radioactivity derived by digital analysis of autoradiograms were comparable to values derived from direct sampling and analysis of tissues. In addition, we describe the preparation and calibration of standards for use in quantitative whole-body autoradiography. For this study, three male Long-Evans hooded rats were administered 14C radioactivity intravenously. The animals were sectioned for whole-body autoradiography, with concomitant sampling of blood and 16 selected tissues. After 3 weeks of film exposure, the optical densities of the resulting autoradiograms were analyzed with a RAS3000 digital imaging system to estimate tissue concentrations of radioactivity. These concentrations were then compared with those obtained by direct analysis of the tissue samples. The concentrations derived from digital analysis of the autoradiograms were very highly correlated with those determined from direct tissue analysis (r = 0.956). Linear regression analysis yielded a straight line with a slope of 0.97 and a goodness of fit (r2) of 0.913. This analysis suggested that there is an approximate 1:1 correlation between concentration values determined by the two methods. Marked differences between the values derived via the two techniques were observed for only three tissues. However, this subset of the data accounted for only 6% of the total data, and the differences were probably due to contamination from adjacent tissues during excision. Overall, the concentrations of radioactivity derived from digital analysis of the autoradiograms were comparable to those derived from direct analysis of tissue samples. The results indicated that the digital analysis procedure for film can serve as a valuable adjunct to conventional tissue analysis for radioactivity.

Comparison of quantitative whole-body autoradiographic and tissue dissection techniques in the evaluation of the tissue distribution of [14C]daptomycin in rats

Quantitative whole-body autoradiography (QWBA) was evaluated and compared to tissue dissection/liquid scintillation counting (TD/LSC) techniques by determining the tissue distribution of radiocarbon in rats following iv administration of the antibiotic [14C]daptomycin (LY146032). QWBA, using computer-assisted video-image analysis, was initially evaluated by characterizing and calibrating commercial standards to blood and brain, kidney, liver, and lung homogenates. Frozen (carboxymethyl)cellulose blocks containing tissue homogenates spiked with [14C]glucose (370-37,000 Bq/g or 10-1000 nCi/g) were sectioned and optical densities (OD) measured. Characterization of QWBA included repeated measures data analysis to determine the significance of tissue type and intra- and inter-section and block variability. Regression models relating OD to radiocarbon concentration were also used to calibrate commercial standards for use in QWBA analyses. Results indicated that there were no substantial differences between OD readings from different tissues; however, the greatest source of variation in OD reading was section thickness. Because quantitative variations were largely attributed to section thickness, an internal standard (IS), consisting of liver homogenates spiked with [14C]glucose, was evaluated as a correction factor. Tissue concentrations of radiocarbon in male Fischer 344 rats were evaluated by QWBA and TD/LSC techniques 0.25 h following a single iv 10 mg/kg dose of [14C]daptomycin. Results indicated that tissue concentrations of radiocarbon obtained by QWBA, normalized using an IS, were comparable to those obtained by TD/LSC.