Human serum albumin

About: Human serum albumin is a research topic. Over the lifetime, 9402 publications have been published within this topic receiving 269029 citations. The topic is also known as: serum albumin & ALB.

The structural basis of camptothecin interactions with human serum albumin : impact on drug stability

Abstract: The intense intrinsic fluorescence emissions from several clinically relevant camptothecin drugs have been exploited in order to study the structural basis of drug binding to human serum albumin. Both HPLC and time-resolved fluorescence spectroscopic methodologies were employed to characterize the associations of camptothecins with HSA in phosphate-buffered saline (pH 7.4) at 37 degrees C. The alpha-hydroxy delta-lactone ring moiety of camptothecin (C), 10-hydroxycamptothecin (HC), 10,11-(methylenedioxy)camptothecin (MC) and 9-chloro-10,11-(methylenedioxy)camptothecin (CMC) was in each case observed to hydrolyze more rapidly and completely in the presence of HSA than in the protein's absence. Binding isotherms constructed by the method of fluorescence lifetime titration showed that HSA bound preferentially the carboxylate forms of C, HC, MC, and CMC over their lactone forms, thereby providing an explanation for the shift to the right in the lactone-carboxylate equilibrium observed for each compound upon HSA addition. In marked contrast, three analogues (SN-38, CPT-11, and topotecan) all displayed enhanced stabilities in the presence of HSA. While the lifetimes of CPT-11, topotecan, and the carboxylate forms of both drugs were insensitive to the addition of HSA, the lifetimes of both SN-38 and its carboxylate form did titrate upon HSA addition. Analysis of binding isotherms constructed for the albumin interactions of SN-38 and its carboxylate form demonstrated a higher overall association constant for the lactone form [640 (M amino acid (aa) residues)-1] relative to the carboxylate form [150 (M aa)-1]. Our studies indicate that specific modifications at the 7- and 9-positions of the quinoline nucleus, such as those contained in CPT-11, topotecan, and SN-38, enhance drug stability in the presence of HSA. In the case of SN-38, the enhanced stability was shown to be due to preferential associations between the drug's lactone form and the blood protein.

Role of fructose in glycation and cross-linking of proteins

Abstract: Incubation of carbohydrate-free human serum albumin (HSA) with fructose in an aqueous buffer at pH 7.4 resulted in glycation of epsilon-amino groups of lysyl residues. A recently developed procedure, involving analysis of hexitol amino acids by high-performance liquid chromatography of phenylthiocarbamyl derivatives, was used to show that 85% of the bound hexose was attached to protein via carbon 2 (C-2). The remainder was attached to protein via carbon 1 (C-1). When incubations were conducted with glucose under identical conditions, all the hexose was attached via C-1. Examination of human ocular lens proteins showed that the majority of the covalently bound hexose was connected to epsilon-amino groups of lysyl residues via C-1; this was attributed mainly to nonenzymatic glucosylation in vivo, which has already been documented. A significant proportion (10-20%) of the bound hexose was connected via C-2. In view of the HSA-hexose incubation results (above), this indicated that the lens proteins had reacted with endogenous fructose; i.e., they had undergone nonenzymatic fructosylation in vivo. The model protein bovine pancreatic ribonuclease A reacted with fructose and glucose at similar rates under physiological conditions. However, covalent, non-disulfide cross-linking, which could be inhibited by D-penicillamine, was induced 10 times more rapidly by fructose than by glucose. It is postulated that some of the protein cross-linking that occurs in vivo is fructose-induced. The possible significance of these processes in diabetic subjects is discussed.

Mycophenolic acid binding to human serum albumin: characterization and relation to pharmacodynamics.

Abstract: Mycophenolate mofetil, the prodrug form of the immunosuppressive agent mycophenolic acid (MPA), is currently in clinical trials evaluating its effectiveness in transplant recipients. In this study, we validated an ultrafiltration system for the reliable measurement of free MPA. Using this technique, we evaluated factors that might be important in modulating the free fraction of this drug. Human serum albumin (HSA), high concentrations of the primary glucuronide metabolite of MPA, and sodium salicylate significantly affected MPA binding. For HSA the mean +/- SE binding capacity (Bmax) and the dissociation constant (Kd) were 1095 +/- 34 mumol/L and 12.98 +/- 0.93 mumol/L, respectively. The dose for 50% inhibition (IC50) of inosine monophosphate dehydrogenase isoform II by MPA increased 5.4-fold as the concentration of HSA added to the enzyme reaction mixture increased from 0 to 50 g/L (0-724 mumol/L). Furthermore, the IC50 MPA concentration for phytohemagglutinin A-stimulated human peripheral blood mononuclear cells increased 4.8-fold when incubations were performed in the presence of 10 g/L (145 mumol/L) HSA vs no added HSA. These data support the hypothesis that the pharmacological activity of MPA is a function of unbound drug concentration.