MECONIUM INDUCES iNOS EXPRESSION, NO PRODUCTION AND ACTIVATION
OF NF-kB IN ALVEOLAR MACROPHAGES
Tullus K1, Li Y-H1, Yan Z-Q2,
Jonsson B1, Brauner A3
1Astrid Lindgren Children’s Hospital, 2Center
for Molecular Medicine, 3Dep. of Clinical Microbiology,
Karolinska Hospital, Stockholm, Sweden
Objective: Meconium aspiration
syndrome (MAS) is characterized by inflammatory changes in the lung
probably mediated by e.g. cytokines, prostaglandin E2 and nitric
oxide (NO). NO is important in a number of biological reactions e.g.
cytotoxity. The purpose of this study was to investigate if meconium could stimulate alveolar
macrophages to produce nitric oxide (NO) and inducible nitric oxide
synthase (iNOS) in vitro and if
dexamethasone and budesonide could downregulate that response. We also
investigated if the transcription factor nuclear factor-kB (NF-kB) could be involved in
the NO production.
Methods: A rat alveolar
macrophage cell line (Nr8383) was exposed to meconium alone, or in combination with dexamethasone, budesonide or g-IFN for 24 hours.
Griess reaction was used to detect NO, RT-PCR to measure iNOS mRNA
expression, EMSA to analyse NF-kB and immunostaining to
locate iNOS and NF-kB
transactivation.
Results: Both LPS
and meconium stimulated the production of NO and expression of iNOS mRNA in
the rat alveolar macrophage cell line in a dose dependent manner. r-IFN promoted and budesonide (10-4M)
and dexamethasone (10-4M) significantly inhibited the NO
production (p<0.05 respectively). Meconium triggered the NF-kB activation and
immunostaining showed translocation of NF-kB into the nuclei of the
macrophages and iNOS protein in the activated cells.
Conclusion: Our findings
show that meconium can stimulate alveolar macrophages to produce NO through
the iNOS system. This could be mediated via the ubiquitous transcription
factor NF-kB which was
activated. Steroids downregulated the NO production.