A comparison of drug binding sites on mammalian albumins.

The research focuses on investigating the similarity of drug binding sites on human albumin with those on other mammalian albumins (bovine, dog, horse, sheep and rat). The study indicates that while albumins of bovine, dog, horse, and sheep have binding sites similar to humans, rat albumins present differently.

Research Methodology

• The study used two fluorescent probes, warfarin and dansylsarcosine, which are known to interact with binding sites I and II on human albumins, respectively. The goal was to see whether similar interactions occur on the albumins of bovines, dogs, horses, sheep and rats.
• A variance of factors were studied to ascertain the similarity of these binding sites. These factors are displacement of the probes by ligands that selectively bind to site I (phenylbutazone) and site II (diazepam), the effects of non-esterified fatty acids with varying carbon chain lengths and changes on fluorescence when pH changed, and the inhibition ability of ligands on the hydrolysis of 4-nitrophenyl acetate.

Findings

• The fluorescence of bound warfarin and dansylsarcosine was selectively diminished by phenylbutazone and diazepam respectively on bovine, dog, horse, human and sheep albumins.
• The study found variations in fatty acid effects. Medium chain fatty acids (C1-C12) had a reducing effect on the fluorescence of dansylsarcosine, with maximum inhibition coming from C9 while long chain acids (C12-C20) enhances the fluorescence of warfarin, with maximum increases seen with C12.
• For these albumins, changes in pH from 6 to 9 resulted in an increased fluorescence of warfarin. However, site I ligands (warfarin/phenylbutazone) didn’t have strong effects on 4-nitrophenyl acetate hydrolysis, while site II ligands (dansylsarcosine/diazepam) significantly inhibited this reaction.

Rat Albumins vs Other Mammalian Albumins

• Rat albumins behaved differently from other studied albumins. The fatty acids and pH changes didn’t enhance the fluorescence of warfarin. Also, the differential effects of both site I and II ligands on the fluorescence of warfarin/dansylsarcosine and the hydrolysis of 4-nitrophenyl acetate were less apparent with rat albumins.
• The difference in behaviour suggests that rat albumins have different characteristics when compared to humans, bovines, dogs, horses, and sheep. The binding site of warfarin and, to a lesser degree, the binding site of dansylsarcosine on rat albumin differed from those on other albumins studied.