Henry Jay Forman, Ph.D.
Molecular Pharmacology and Toxicology
Oxidative stress and signal transduction
Exposure to oxidants produced through metabolism of drugs or environmental pollutants can cause alteration of cell function. Surprisingly, these responses are not always due to the damage by these agents but to their acting as or mimicking normal components of signaling processes.
The alveolar macrophage function, the respiratory burst (stimulated superoxide production), is altered by exposure to NO2 and hyperoxia. Such exposure results in the production of hydroperoxides (ROOH) and a,b-unsaturated aldehydes formed from oxidized lipids. ROOH and these aldehydes are responsible for the effects upon cell function. Incubation of macrophages with low [ROOH] enhances the respiratory burst while higher [ROOH] inhibit the burst. Both effects are mediated through alteration of signal transduction involving changes in intracellular free calcium ([Ca2+]i). 4-hydroxynonenal, at levels produced during exposure to NO2, also inhibits the respiratory burst in a Ca2+-independent manner. Our work continues to explore oxidant modulation of Ca2+-dependent components of signal transduction and formation of adducts to signaling components by 4-HNE.
Glutathione (GSH) is an essential endogenous antioxidant. Oxidative stress elevates synthesis and enzymatic activity of g-glutamylcysteine synthetase (GCS), the first enzyme in de novo GSH synthesis through increases in transcription of the catalytic and regulatory subunits of GCS. The increase in GCS activity enhances GSH synthesis and thereby resistance to a greater oxidative stress. The aims of our studies are to identify the functional regulatory elements responsible for increased GCS, to characterize the oxidative stress responsive transcription factors, and to examine the relationship of cellular H2O2, glutathione redox status (GSH/GSSG), glutathione-conjugates, and glutathione-protein mixed disulfides to synthesis of GCS mRNAs and enzymatic activity, and to determine the relationship between increased GSH synthesis and enhanced resistance to oxidative stress.
- Shi, M.M., Kugelman, A., Iwamoto, T., Tian, L. and Forman, H.J. Quinone-induced oxidative stress elevates glutathione and induces g-glutamylcysteine synthetase activity in rat lung epithelial L2 cells. J. Biol. Chem. 269: 26512-26517, (1994).
- Hoyal, C.R., Gozal, E., Zhou, H., Foldenauer, K. and Forman, H.J. Hydroperoxide-mediation of the rat alveolar macrophage respiratory burst is dependent on altered calcium homeostasis. Arch. Biochem. Biophys. 326: 166-171, 1996
- Kaul, N. and Forman, H.J. Activation of NF-kB by the respiratory burst of macrophages Free Radical Biol. Med. (in press)