title: Kinetic modeling of slow dissociation of bromosulphophthalein from albumin in perfused rat liver: toxicological implications.
abstract: Due to strong binding between organic anions and albumin, the kinetics of the binding process must be carefully considered in biologically-based models used for predictive toxicology applications. Specifically, the slow dissociation rate of an organic anion from the protein may lead to reduced availability of free anion in its flow through the capillaries of an organ. In this work, the effect of the dissociation rate of the anion bromosulphophthalein (BSP) from albumin was studied in isolated, perfused rat livers in the presence of albumin concentrations of 0.25, 1, and 4% (w/v) and an initial BSP concentration of 20 microM. The uptake of BSP from the perfusion medium was modeled using a biologically-based kinetic model of the sinusoidal and intracellular liver compartments. The best fit of the model to data resulted in the prediction of a slow dissociation rate constant for the BSP-albumin of between 0.097 and 0.133 s(-1). Assuming BSP and albumin to be in binding equilibrium in the sinusoidal space, with rapid binding-rate constants, as is often done, produced an unacceptable fit. These results indicate that the strong binding interaction between BSP and albumin, beyond keeping the concentration of free chemical low due to a small equilibrium dissociation constant, can also reduce uptake by an organ due to the slow release of BSP from the protein during passage through the capillaries. The implication of this dissociation-limited condition, when extrapolating to other doses and in-vivo situations, is discussed.
authors.affiliation: Department of Physics, Wright State University, Dayton, Ohio 45435, USA. bfoy@discover.wright.edu
authors.forename: B D
authors.initials: BD
authors.lastname: Foy
authors.forename: C
authors.initials: C
authors.lastname: Toxopeus
authors.forename: J M
authors.initials: JM
authors.lastname: Frazier
mesh_terms: D000818:Animals; D002199:Capillary Permeability / Q000187:drug effects*; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008954:Models, Biological; D010477:Perfusion; D011485:Protein Binding; D051381:Rats; D011916:Rats, Inbred F344; D012709:Serum Albumin / Q000378:metabolism*; D013448:Sulfobromophthalein / Q000493:pharmacokinetics* / Q000494:pharmacology; D013997:Time Factors
chemical_list: D012709:Serum Albumin; D013448:Sulfobromophthalein