PHOSPHOLIPID SURFACTANT ADSORPTION BY RESPIRABLE QUARTZ AND IN-VITRO EXPRESSION OF CYTOTOXICITY AND DNA-DAMAGE

Respirable-sized quartz was treated with a saline dispersion of dipalm itoyl phosphatidylcholine (DPPC), a primary component of pulmonary sur factant, to model the adsorption of phospholipid surfactant onto quart z dust following particle deposition in the bronchoalveolar region of the lung. Control and surfactant-treated dusts were used to challenge lavaged rat pulmonary macrophages in vitro over a 1-week period, to de termine the effects of adsorbed surfactant on the expression of quartz cytotoxicity and genotoxicity. DNA damage was determined by the singl e cell gel electrophoresis 'comet' assay. Untreated quartz induced DNA damage, increasing with dose and with time of incubation of dust with macrophages over a 5 day period. DPPC treatment of quartz suppressed DNA damage through 1 day of macrophage challenge. DNA damage then incr eased over a 5 day period, to approximately half the positive control (untreated quartz) values. Cytotoxicity was measured by trypan blue dy e exclusion and by the Live-Dead(R) fluorescence assay for cell viabil ity. Cytotoxicity of surfactant-treated quartz measured one day after challenge of lavaged macrophages was suppressed to values near those o f the negative controls, and then increased over a 1 week incubation p eriod to levels near those expressed by native quartz positive control s. Quartz similarly treated with dioleoyl phosphatidylcholine mixed wi th DPPC substituted in one acyl group with a boron-containing fluoresc ent chromophore was used with confocal microscopy to measure particle- associated fluorescent surfactant in cells. Approximately half of the fluorescence intensity was lost over a I week period following challen ge of lavaged macrophage. Results are discussed in terms of a model of restoration of quartz particle surface toxicity as prophylactic surfa ctant is removed from particle surface by cellular enzymatic digestion processes. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved .