Cocaine and cocaethylene binding to human placenta in vitro, ,

Objective: The aim of the study was to determine the binding profiles of cocaine and its ethyl homolog, cocaethylene, in human placenta. Study design: Pooled whole human placental homogenates supplemented with either nonlabeled cocaine or cocaethylene over the concentration range 10 to 5000 × 10–7 mol/L were submitted for equilibrium dialysis. Drug concentrations were measured by high-pressure liquid chromatography. Scatchard analysis of the data was performed. Results: A high-affinity, low-capacity binder was identified for cocaine (equilibrium constant of association, 3.68 × 105 L/mol; concentration of binding sites, 4.36 × 10–6 mol/L) and for cocaethylene (equilibrium constant of association, 2.42 × 104 L/mol; concentration of binding sites, 2.65 × 10–5 mol/L). Also, a low-affinity, high-capacity binder was noted for cocaine (equilibrium constant of association, 1.93 × 103 L/mol; concentration of binding sites, 5.28 × 10–4 mol/L) and for cocaethylene (equilibrium constant of association, 2.15 × 102 L/mol; concentration of binding sites, 2.65 × 10–3 mol/L). The concentration of binding sites expressed as moles per gram of placenta was as follows: high-affinity binder (cocaine, 4.36 × 10–8; cocaethylene, 2.65 × 10–7) and low-affinity binder (cocaine, 5.28 × 10–6; cocaethylene, 2.65 × 10–5). Up to 59% of cocaine and up to 42% of cocaethylene was bound. Conclusion: Human placenta may serve as a depot for cocaine and cocaethylene.