Simple sensitive microbioassay for adenine arabinoside and hypoxanthine arabinoside in human plasma

Previous methods using low- or high-pressure liquid chromatography and UV absorbance for quantitation of arabinosides in plasma can practically detect only ≥200 ng of adenine arabinoside and ≥100 ng of hypoxanthine arabinoside per ml, and they require expensive equipment and expert technical assistance. The authors describe in this report a simple quantitative microbioassay for arabinosides in human plasma based on their ability to inhibit the cytopathic effect of vaccinia virus in an adenosine deaminase-free cell culture system. Using prior separation of nucleosides in plasma by thin-layer chromatography, followed by the microbioassay, the authors quantitated adenine arabinoside with a sensitivity of ~4ng/ml and hypoxanthine arabinoside at ~625 ng/ml. This assay method is simple, sensitive, and reproducible, requires small plasma samples, measures biological activity, and is adaptable to routine use. It is an important tool for evaluating the pharmacology of adenine arabinoside and Ara-AMP in patients in current clinical trials.