Interactions of PCBs with human serum albumin: In vitro spectroscopic study

Abstract

Following absorption, polychlorinated biphenyls (PCBs) bind to albumin and are transported via blood into the target tissues. PCBs then accumulate in tissues and induce a variety of harmful chronic and developmental effects. The aim of the present study is to determine binding parameters, such as binding constant, quenching constant, and number of binding sites for three PCB congeners (PCB118, PCB126 and PCB153) in complex with human serum albumin (HSA). The binding parameters for the complexes of HSA-PCB118, HSA-PCB126, and HSA-PCB153 excited at 280 nm were compared with those excited at 295 nm. Quenching (static and dynamic) of HSA fluorescence was analyzed based on the Stern-Volmer method. Binding (Ka) constants were calculated according to the Scatchard method and analysis of non-linear regression was based on a two-component model with the Lavenberg–Marquardt algorithm. For all analyzed complexes, a single independent class of binding site for PCB congeners was found in HSA subdomain IIA. Tyrosine residues appear to play the most prominent role in binding of PCB126 to HSA, while tryptophan-214 played a dominant role in interactions of PCB153 with HSA. Among studied PCB congeners, PCB118 formed the most stable complexes with HSA. These results illustrate the importance of studies targeting the binding of PCBs to serum albumin as part of the strategy to understand and protect against toxicity of these environmental toxicants.

Sulfation of Lower Chlorinated Polychlorinated Biphenyls Increases Their Affinity for the Major Drug-Binding Sites of Human Serum Albumin

“…47 Ligand-bound crystal structures for the 66.5kDa protein show the various drug-, fatty acid-, ion-, and heme-binding sites of HSA, 48 and many methods have been employed to determine binding parameters. 41, 49–51 In our present studies, we have measured the displacement of site-selective fluorescent probes from the two major drug-binding sites on HSA (i.e., Site I and Site II) as described by Sudlow et al 40 In this examination of LC-PCBs and their hydroxylated and sulfated metabolites, the displacement of: 5-dimethylamino-1-naphthalenesulfonamide (DNSA) for Site I and dansyl L-proline (DP) for Site II, shown in Figure 1, was used. 40 The displacement of these probes from their respective binding sites has been used to determine site-selectivity for ligands as well as to provide relative estimates of their binding affinities.…”

“…49, 50 Interestingly, a separate study of PCB 118, 126, and 153 found that these compounds bound with high affinity to Sudlow Site I, with no binding to Site II. 51 These seemingly contradictory conclusions may stem from the differences in the design of the studies. 51 Although the approach reported here does not assess total protein binding, the high affinity binding of hydroxylated and sulfated LC-PCBs to HSA measured in this study underscores the importance that binding to human serum albumin may play in their subsequent distribution and effective half-lives in the body.…”

Hydroxylated and sulfated metabolites of lower chlorinated PCBs bind with high affinity to human serum albumin and exhibit selective toxicity to neuronal cells

“…The results of these few studies, however, are sometimes contradictory. [163][164][165] Neurotoxic effects of PCB exposure…”

“…163,165 One study, however, determined that binding occurred at Site I. 164 These seemingly contradictory conclusions stem from the differences in the studies. The latter study was based on a non-selective probe and the analysis of the intrinsic fluorescence of HSA, which can be misleading relates to the importance that albumin plays in the transplacental transfer of drugs and other compounds to the developing fetus.…”

“…The binding of PCB 153 and the PCB 180 to HSA was determined using a combination of intrinsic fluorescence, probe displacement and molecular modelling. It was determined that both compounds bound to a single site of HSA, Sudlow Site II, and that binding was dominated by hydrophobic This work employed the intrinsic fluorescence of HSA and the use of a nonspecific fluorescent probe as well as molecular modelling 164. ApproachThe interest in LC-PCB sulfates and their high affinity for the thyroid hormone binding protein transthyretin suggests that other thyroid hormone binding proteins such as HSA may also bind these sulfates with high affinity.…”