Interference of Plasticizers on Plasma Protein Binding Measurements

Accurate measurement of plasma protein binding (PPB) is of critical importance in drug discovery. Methodologies for PPB measurement continue to evolve to address the challenges of highly bound compounds. In order to generate high quality PPB data, it is crucial to not only apply state-of-the-art methods and highly sensitive and selective detectors, but also use high-quality plasma. In this study, we found that plasticizers, leaching from polyvinyl chloride (PVC) plasma storage bags, interfered with drug binding to both human α1-acid glycoprotein (AAG) and human serum albumin (HSA). Several AAG and HSA binding drugs were used to probe the differences in PPB using blood/plasma collected and stored in PVC bags or glass tubes through vacutainers. The results showed that plasma collected using vacutainers into the glass tubes has lower plasma fraction unbound (f_u,p) values than those from the PVC bags. The f_u,p differences can be as high as 32-fold. Hence, it is recommended to use vacutainers and glass tubes rather than PVC bags, for blood collection and plasma storage. Plasma from animal species collected using polypropylene syringes into polyethylene tubes showed no differences in f_u,p from plasma collected using vacutainers into glass tubes. Not all compounds are sensitive to plasticizer interference for PPB. It is therefore important to select appropriate positive controls for f_u,p measurement, such as warfarin for HSA and imatinib for AAG, to monitor the quality of plasma and minimize the interference from plasticizers.