CARBON-MONOXIDE CONTRIBUTES TO THE CYTOKINE-INDUCED INHIBITION OF SURFACTANT SYNTHESIS BY HUMAN TYPE-II PNEUMOCYTES

Background: An increase in cyclic guanosine 3',5'- monophosphate (cGMP ) due to nitric oxide generation is known to participate in the mediat ion of the tumor necrosis factor alpha (TNF-alpha) effect in type II c ells. Because guanylyl cyclase can be activated also by carbon monoxid e (CO), in this study we examined the ability of human type II pneumoc ytes to produce CO in the presence of cytokines and the relative contr ibution of this molecule to the TNF-alpha and interleukin 1 effects. D esign: Type II pneumocytes were isolated from cadaveric multiple-organ donors by enzymatic digestion. adherence separation of macrophages, a nd gradient purification. After preculture for 24 hours, cells were cu ltured for 24 hours in the presence or absence of TNF-alpha, interleuk in 1, sodium nitroprusside, N-omega-nitro-L-arginine, CO, hemin, zinc- protoporphyrin type IX, deferoxamine mesylate, S-adenosyl-L-methionine , alpha-tocopherol, methylene blue (a guanylyl cyclase inhibitor), 8-b romine-cGMP, and combinations of these reagents. Both CO (picomole per microgram of protein) and nitric oxide release to the medium and the cGMP (picomole per microgram of protein) content of the cells were mea sured. In a different set of experiments, D-glucose labeled with radio active carbon (C-14) was added to the medium, and the labeling of seve ral lipid fractions was determined (picomole per microgram of protein) . Results: D-[C-14]glucose incorporation into phosphatidylcholine, the main surfactant component, was selectively inhibited in the presence of cytokines, CO, sodium nitroprusside, or 8-bromine-cGMP. The inhibit ory effect of TNF-alpha was partially reversed by N-omega-nitro-L-argi nine, deferoxamine, or alpha-tocopherol and totally reversed by methyl ene blue, Tumor necrosis factor or induced an increase in cGMP cell co ntent and in the CO and nitric oxide release to the medium. Hemin incr eased CO and cGMP production and decreased phosphatidylcholine synthes is. Zinc-protoporphyrin type IX, an inhibitor of heme oxygenase, and a ll 3 antioxidants, which inhibited CO production, also antagonized the TNF-alpha effect on cGMP and phosphatidylcholine synthesis. Conclusio ns: Intracellular cGMP increase due to an endogenous generation of bot h CO and nitric oxide mediates the cytokine-induced inhibition of surf actant synthesis by type II pneumocytes. Both lipid peroxidation and h eme oxygenase activity are sources for the observed CO production.