PDTC and NO suppress CC chemokine production in TNF-α-stimulated human pulmonary microvascular endothelial cells

Human neutrophil-pulmonary microvascular endothelial cell interactions in vitro: differential effects of nitric oxide vs. peroxynitrite

Sepsis-induced acute lung injury is characterized by activation and injury of pulmonary microvascular endothelial cells (PMVEC), increased neutrophil-PMVEC adhesion and migration, and trans-PMVEC high-protein edema. Inducible NO synthase (iNOS) inhibits septic murine neutrophil migration in vivo and in vitro. The effects of NO in human neutrophil-PMVEC interactions are not known. We isolated human PMVEC using magnetic bead-bound anti-PECAM antibody. Confluent PMVEC at passage 3-4 were co-cultured with human neutrophils for assessment of neutrophil-PMVEC adhesion, and trans-PMVEC neutrophil migration and Evans-Blue dye-labeled albumin leak. Two NO donors (spermine-NONOate, S-nitroso-N-acetylpenicillamine) attenuated both cytomix-enhanced neutrophil-PMVEC adhesion by 64+/-14% (p<0.01) and 32+/-3% (p<0.05), respectively, and cytomix-induced trans-PMVEC neutrophil migration by 85+/-16% (p<0.01) and 43+/-5% (p<0.01), respectively. Correspondingly, iNOS inhibition with 1400W enhanced cytomix-stimulated neutrophil migration by 52+/-3% (p<0.01), but had no effect on neutrophil-PMVEC adhesion. Conversely, a peroxynitrite donor (SIN-1) increased both neutrophil-PMVEC adhesion (38+/-2% vs. 14+/-1% control, p<0.01) and trans-PMVEC neutrophil migration; with both effects were completely inhibited by scavenging of NO, superoxide, or peroxynitrite (p<0.05 for each). Scavenging of peroxynitrite also eliminated cytomix-induced neutrophil adhesion and migration. Blocking CD18-dependent neutrophil adhesion prevented cytomix-stimulated trans-PMVEC EB-albumin leak (p<0.05), while inhibiting neutrophil migration paradoxically enhanced cytomix-stimulated EB-albumin leak (11+/-1% vs. 7+/-0.5%, p<0.01). FMLP-induced neutrophil migration had no effect on trans-PMVEC EB-albumin leak. In summary, we report differential effects, including the inhibitory action of NO and stimulatory effect of ONOO(-) on human neutrophil-PMVEC adhesion and trans-PMVEC migration under cytomix stimulation. Moreover, neutrophil-PMVEC adhesion, but not trans-PMVEC migration, contributes to human PMVEC barrier dysfunction.

Inducible NO synthase (iNOS) in human neutrophils but not pulmonary microvascular endothelial cells (PMVEC) mediates septic protein leak in vitro

Sepsis-induced acute lung injury (ALI) is characterized by injury of the pulmonary microvascular endothelial cells (PMVEC) leading to high-protein pulmonary edema. Inducible NO synthase (iNOS) mediates trans-PMVEC protein leak in septic mice in vivo and in murine PMVEC under septic conditions in vitro, but the role of iNOS in human PMVEC protein leak has not been addressed. We hypothesized that iNOS in human neutrophils, but not human PMVEC, mediates septic trans-PMVEC protein leak in vitro. We isolated human PMVEC from lung tissue using magnetic bead-bound anti-PECAM antibody and assessed Evans blue albumin leak across human PMVEC monolayers under septic conditions in the presence/absence of human neutrophils. PMVEC were used at passages 3-4, seeded on 3 mum Transwell inserts and grown to confluence. Cytomix-stimulated trans-PMVEC albumin leak was not attenuated by pre-treatment with 1400 W, a selective iNOS inhibitor, or l-NAME, a non-selective NOS inhibitor. In neutrophil-PMVEC co-culture, basal unstimulated trans-EB-albumin leak was 0.6+/-0.3%, which was increased by cytomix stimulation to 11.5+/-4.4%, p<0.01. Cytomix-stimulated EB-albumin leak in neutrophil-PMVEC co-cultures was inhibited by pre-treatment with 1400 W (3.8+/-1.0%, p<0.05) or l-NAME (4.0+/-1.1%, p<0.05). Pre-treatment of neutrophil-PMVEC co-cultures with PEG-SOD (superoxide scavenger) and FeTPPS (peroxynitrite scavenger) also significantly attenuated neutrophil-dependent cytomix-stimulated leak (4.7+/-3.0%, p<0.05; 0.5+/-1.0%, p<0.01, respectively). In conclusion, trans-human PMVEC albumin leak under septic conditions is dependent on iNOS activity specifically in neutrophils, but not in PMVEC themselves. Septic neutrophil-dependent trans-PMVEC albumin leak may be mediated by peroxynitrite.