Broncho-alveolar lavage procedure extract compounds from surrounding tissue

Abstract

Broncho-alveolar lavage (BAL) is routinely used for collection of cells from the alveolar space and for sampling of epithelial lining fluid (ELF) in lungs in preclinical studies. Urea is present in all tissue at the same concentration and therefore is commonly used as a dilution marker of the BAL fluid to calculate back to compound concentration in ELF.

The aim of the present study was to investigate the accuracy of ELF concentration determination and the possible extraction from surrounding tissue of compounds with diverse physicochemical properties, using different BAL volumes and repeated BAL procedure.

Propranolol, diazepam, indomethacin, AZD4721, and anakinra were delivered as an intravenous (IV) bolus dose followed by an IV infusion for 4 h to reach steady state. BAL was performed with 1 mL, 4 mL, or repeatedly with 4 mL and samples from BAL, plasma and lung tissue were taken for bioanalysis.

Repeated BAL procedure revealed significant extraction from tissue as the concentration in sequential BAL fluid samples decreased slowly: >60% of the concentration of propranolol in the first BAL fluid sample was still present in the fifth sample of BAL fluid. BAL procedure with 4 mL resulted in more extraction of urea as well as compounds from tissue and/or blood compared to BAL procedure with 1 mL. Small molecules (propranolol, diazepam, indomethacin, AZD4721) were extracted from tissue to a higher degree than the large protein drug anakinra.

The present study clearly demonstrates that BAL procedure results in extraction of urea and compounds from surrounding tissue and the procedure is therefore not fit for the purpose of determination of compound concentrations in ELF.