Changes in the glutathione system of lung cell lines after treatment with hydrocortisone

Abstract

Administration of anti-inflammatory glucocorticoids is a drug option in the therapy of acute respiratory distress syndrome (ARDS), according to present pathophysiological concepts. Surprisingly, glucocorticoids failed to show beneficial effects. This failure is not understood. In this investigation changes in the glutathione system due to hydrocortisone were found to consist of glutathione depletion and lowered glutathione reductase activities in alveolar epithelial type II cells, contrasted with unchanged activities in a fibroblast-like lung cell line. The glutathione system is thought to be the most important cellular antioxidative system and therefore alveolar epithelial type II cells might be more susceptible to oxidative stress after glucocorticoid treatment. As alveolar epithelial type II cells may be important targets in ARDS, because of their functions (stem cells of type I epithelial cells; surfactant synthesis), these changes might provide an explanation for the failure of glucocorticoids. In the present experiments the capability of hydrocortisone-treated alveolar epithelial type II cells to synthesise glutathione was found to be cysteine dependent at physiological concentrations. Transposing this observation to the in vivo situation, it might be expected that glucocorticoid efficacy in ARDS therapy requires co-administration of substances that increase glutathione synthesis, e.g. N-acetylcysteine.

Enhancing Glutathione Synthesis can Decrease Zinc-Mediated Toxicity

“…At the concentrations studied, zinc did not interfere with the assay. The analytical detection limit for glutathione was ≈0.2 nmol per mg of cellular protein [8]. GSSG was determined after GSH had reacted with 2-vinylpyridine (2 per 100 µl of acid cell extract at pH 7) for half an hour.…”

“…Furthermore, toxicity is enhanced when cellular glutathione had been decreased. Additionally, pretreatment of alveolar epithelial cells with glucocorticoids is known to decrease cellular glutathione and such cells are more susceptible to zinc as compared to not pretreated cells [8].…”

“…Oxidized and reduced glutathione were measured, and protein synthesis was calculated by methionine incorporation into acid insoluble cellular material to assess zinc-mediated toxicity. This latter parameter is described as sensitive and early affected after zinc exposure [8,15].…”

Glucocorticoid pretreatment increases toxicity due to peroxides in alveolar epithelial-like cell lines

“…Correspondingly, cellular glutathione was decreased in both alveolar epithelial cell lines, while content was increased in the fibroblast-like line (Walther, 2004). The cellular GR activity of all cell lines was decreased to about 10% or below this level after incubation of cells with toxic concentrations of zinc.…”

“…Furthermore zinc-mediated toxicity is explained by the glutathione depletion (Walther et al, 1999b) and HC is shown to affect the glutathione system by decreasing glutathione and glutathione reductase (GR) in alveolar epithelial cells (Walther, 2004). Therefore it seems probable that the increase ଝ Results of this investigation partly concern to the inaugural dissertation of R.S.…”