Human serum albumin is the most abundant protein in the blood serum. Albumin determines the protein binding characteristics for majority of drugs. It is a common practice that the human albumin is replaced by the cheaper and safer bovine albumin, with the assumption that they have identical binding properties, in the binding studies. We here report a case in which the anti-inflammatory drug ibuprofen exhibited different effects on displacing the calcium channel blocker nifedipine from its binding to bovine and human albumins. Ultrafiltration technique was used to separate free from bound nifedipine, and HPLC method was used to analyze its concentrations. The binding parameters were calculated using Scatchard analysis. Nifedipine binding profile to bovine albumin, with no ibuprofen, revealed that the drug has only one class of specific binding sites with n=1 and k = 5.4 x 104 M-1. However, binding studies of nifedipine in presence of ibuprofen revealed significant difference in the binding profile between bovine and human albumins. Moreover, the interaction of nifedipine with bovine albumin was found to be dependent on the ibuprofen concentration. In presence of lower ibuprofen concentrations, up to 83 µM, nifedipine molar binding ratio (r) was found to initially increase rather than decreasing. At higher Ibuprofen concentrations, r started to decrease. On the other hand, the displacement of nifedipine from human albumin exhibited no such initial increase in the molar binding ratio. This displacement-profile difference was observed at two different nifedipine concentrations of 10 and 20 µM.
Keywords: Bovine albumin, drug interaction, human albumin, ibuprofen, mutual binding, nifedipine, partial displacement, Scatchard plot, ultrafiltration.