BOTH PROSTAGLANDIN E(2) AND NITRIC-OXIDE SEQUENTIALLY MEDIATE THE TUMOR-NECROSIS-FACTOR ALPHA-INDUCED INHIBITION OF SURFACTANT SYNTHESIS BYHUMAN TYPE-II PNEUMOCYTES

Background: Tumor necrosis factor alpha (TNF-alpha)-induced inhibition of surfactant synthesis seems to participate in the pathogenesis of t he adult respiratory distress syndrome. Objectives: To examine the abi lity of human type II pneumocytes to produce nitric oxide (NO) in the presence of TNF-alpha and, in addition, to explore the role of this ra dical in the transduction of the cytokine signal. Design: Multiple org an donors were the source of lung tissue specimens. Type II pneumocyte s were isolated by enzymatic digestion, adherence separation of macrop hages, and gradient purification. After 24-h preculture, cells were cu ltured for 24 hours in the presence or absence of TNF-alpha (100 ng/mL ), sodium nitroprusside (100 mu mol/L), N-omega-nitro-L-arginine methy l ester (NAME) (1 mmol/L), methylene blue (10 mu mol/L), 8-bromo-3',5' -cyclic guanosine monophosphate (8-Br-cGMP) (1 mmol/L), prostaglandin E(2) (PGE(2)) (0.1 mu mol/L), indomethacin (30 mu mol/L), and combinat ions. The NO release to the medium and cGMP and PGE(2) contents of the cells were measured. Results: The incorporation of C-14-labeled gluco se (D-[U-C-14]glucose) into phosphatidylcholine and phosphatidylglycer ol was selectively inhibited either by 8-Br-cGMP or in the presence of TNF-alpha, PGE(2), or nitroprusside, all of which caused an increase in the intracellular levels of cGMP. The inhibitory effect of TNF-a! w as partially reverted by indomethacin, NAME, N-monomethyl arginine, or methylene blue. The inhibitory effect of PGE, was partially reverted by NAME, while that of nitroprusside was reverted by methylene blue, b ut not by indomethacin. Tumor necrosis factor alpha induced an increas e in PGE(2) (4.31 +/- 0.27 vs 1.65 +/- 0.17-pg/mu g protein, n = 10, P < .01) and cGMP (0.238 +/- 0.012 vs 0.109 +/- 0.014-pmol/mu g protein , n = 10, P < .01) cell content and in the NO release to the medium (3 .10 +/- 0.14 vs 1.19 +/- 0.11-nmol/mu g protein, n = 10, P < .01). The basal NO release to the medium was also increased in the presence of PGE(2). The NAME, which blocked NO generation and cGMP increase, did n ot affect PGE(2) production in response to TNF-alpha. However, indomet hacin, which blocked PGE(2) production, also blunted NO generation and cGMP increase. Conclusions: The NO generation, secondary to PGE(2) pr oduction, seems responsible for the TNF-alpha-induced inhibition of ph osphatidylcholine synthesis by human type II pneumocytes. Nitric oxide seems to exert this effect through activation of guanylyl cyclase.