Early events in naphthalene-induced acute Clara cell toxicity - II. Comparison of glutathione depletion and histopathology by airway location

One of the presumed roles of intracellular glutathione (GSH) is the protect ion of cells from injury by reactive intermediates produced by the metaboli sm of xenobiotics. To establish whether GSH depletion is a critical step in the initiation of events that lead to cytotoxicity by P450-activated cytot oxicants, naphthalene, a well-defined Clara cell cytotoxicant, was administ ered to mice (200 mg/kg) by intraperitoneal injection. Shortly after inject ion (1, 2, and 3 h), intracellular GSH content was assessed by high perform ance liquid chromatography or quantitative epifluorescent imaging microscop y and compared with the degree of cytotoxicity as assessed by high resoluti on histopathology. In highly susceptible airways (distal bronchioles), GSH decreased by 50% in 1 h. Cytoplasmic vacuolization was not visible until 2 h, when GSH had decreased by an additional 50%. By 3 h, cytoplasmic blebbin g was extensive. In minimally susceptible airways (lobar and proximal bronc hi), GSH depletion varied widely within the population; a small proportion of the cells lost greater than 50% of their GSH by 2 h and a significant pe rcentage of the cells retained most of their GSH throughout the entire 3 h. Cytoplasmic vacuolization was apparent in some of the cells at 2 h but not visible in any cells at 3 h. We conclude that (1) loss of intracellular GS H is an early event that precedes initial signs of cellular damage in Clara cell cytotoxicity; (2) this pattern of loss in relation to early injury is found both in highly susceptible and minimally susceptible airway sites; ( 3) there is wide cell-to-cell heterogeneity in the response; (4) the hetero geneity in the response profile varies between populations in highly suscep tible and minimally susceptible sites; and (5) once the intracellular GSH c oncentration within the entire cell population drops below a certain thresh old, the initial phase of injury becomes irreversible.