EFFECT OF FREE FATTY ACIDS ON BINDING OF DRUGS BY BOVINE SERUM ALBUMIN, BY HUMAN SERUM ALBUMIN AND BY RABBIT SERUM

¹ Departments of Medicine and Biochemistry, Emory University School of Medicine, Atlanta, Georgia

Do plasma free fatty acids inhibit the binding of other ligands by serum albumin, and if so, at what serum FFA concentration does this effect become manifest? To investigate these questions bovine serum albumin (BSA) and human serum albumin (HSA) were prepared with either 7, 3.5 or <0.05 mol of palmitate or oleate per mol of protein. These preparations correspond to serum free fatty acids (FFA) concentrations of 4000, 2000 and <30 µEq/l. By the dialysis-equilibrium technique, the capacity of these albumin preparations to bind some or all of these ligands was measured: Salicylate, octanoate, bromsulfophthalein (BSP), phenylbutasone, sulfadiasine, thiopental, bishydroxycoumarin and diphenyihydantoin. Analysis of SCatchard plots shows that Salicylate, octanoate, BSP and phenylbutazone occupied three classes of binding site in BSA, whereas for sulfadiasine, bisbydroxycoumarin, thiopental and diphenylhydantoin only one type of binding site was detected. The binding of all eight ligands to BSA was inhibited by palmitate at a molar ratio of 7. The inhibition affected either the number of binding sites in a particular class available to the ligand, or the association constant for the interaction of the site with the ligand or both. Binding to salicylate, octanoate, sulfadiasine, thiopental and diphenylhydantoin was markedly reduced, with 50% or more reduction in number of clasa 1 sites available, whereas binding of BSP, phenylbutasone and bishydroxycoumarin was less inhibited, the number of available class 1 sites being preserved. The inhibitory effect of oleate at a molar ratio of 7 on the binding properties of BSA for salicylate, octanoate and diphenylhydantoin was closely similar to that of 7 mol of palmitate. Palmitate at a molar ratio of 3.5 inhibited the binding of salicylate and octanoate to BSA, but the effect was only a small fraction of that observed with 7 mol of palmitate; 3.5 mol of plamitate did not inhibit binding of diphenylhydantoin. The binding of salicylate, octanoate and diphenylhydantoin to HSA containing 7, 3.5 or <0.05 mol of FFA was qualitatively similar to that observed with the corresponding series of BSA preparations. The binding of salicylate, octanoate and diphenylhydantoin by rabbit sera with FFA concentrations ranging between 300 and 3000 and 3000 µEq/l was also measured; these sara were obtained by injecting the animals with graded doses of the lipolytic hormone adrenocorticotropin. Below the concentration 1700 µEq/l, FFA did not inhibit binding capacity of the serum detestably. concentrations above 2200 µEq/l were consistently associated with a 20 to 26% reduction in the binding of all three ligands. These experiments suggest that serum FFA in the concentration range of 2000 to 4000 µEq/l have a general inhibitory effect on the capacity of serum albumin to bind many ligands of widely different structure, but that at concentrations below 2000 µEq/l this effect is minor or absent.