Both prostaglandin E2 and nitric oxide sequentially mediate the tumor necrosis factor alpha-induced inhibition of surfactant synthesis by human type II pneumocytes
E. Vara, J. Arias-Diaz, C. Garcia, J. Hernandez and J. L. Balibrea
Department of Biochemistry (Facultad de Medicina), Universidad Complutense, Madrid, Spain.
BACKGROUND: Tumor necrosis factor alpha (TNF-alpha)-induced inhibition of
surfactant synthesis seems to participate in the pathogenesis of the adult
respiratory distress syndrome. OBJECTIVES: To examine the ability 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 radical in the
transduction of the cytokine signal. DESIGN: Multiple organ donors were the
source of lung tissue specimens. Type II pneumocytes were isolated by
enzymatic digestion, adherence separation of macrophages, and gradient
purification. After 24-hour preculture, cells were cultured for 24 hours in
the presence or absence of TNF-alpha (100 ng/mL), sodium nitroprusside (100
mumol/L), N omega-nitro-L-arginine methyl ester (NAME) (1 mmol/L),
methylene blue (10 mumol/L),8-bromo-3',5'-cyclic guanosine monophosphate
(8-Br-cGMP) (1 mmol/L), prostaglandin E2 (PGE2) (0.1 mumol/L), indomethacin
(30 mumol/L), and combinations. The NO release to the medium and cGMP and
PGE2 contents of the cells were measured. RESULTS: The incorporation of
14C-labeled glucose (D-[U-14C]glucose) into phosphatidylcholine and
phosphatidylglycerol was selectively inhibited either by 8-Br-cGMP or in
the presence of TNF-alpha, PGE2, or nitroprusside, all of which caused an
increase in the intracellular levels of cGMP. The inhibitory effect of
TNF-alpha was partially reverted by indomethacin, NAME, N-monomethyl
arginine, or methylene blue. The inhibitory effect of PGE2 was partially
reverted by NAME, while that of nitroprusside was reverted by methylene
blue, but not by indomethacin. Tumor necrosis factor alpha induced an
increase in PGE2 (4.31 +/- 0.27 vs 1.65 +/- 0.17-pg/microgram protein, n =
10, P < .01) and cGMP (0.238 +/- 0.012 vs 0.109 +/- 0.014-pmol/microgram
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/microgram protein, n = 10, P
< .01). The basal NO release to the medium was also increased in the
presence of PGE2. The NAME, which blocked NO generation and cGMP increase,
did not affect PGE2 production in response to TNF-alpha. However,
indomethacin, which blocked PGE2 production, also blunted NO generation and
cGMP increase. CONCLUSIONS: The NO generation, secondary to PGE2
production, seems responsible for the TNF-alpha-induced inhibition of
phosphatidylcholine synthesis by human type II pneumocytes. Nitric oxide
seems to exert this effect through activation of guanylyl cyclase.
