Nitric oxide produced by cytokine-activated pulmonary artery smooth muscle cells is cytotoxic to cocultured endothelium

Nitric oxide deficiency in pulmonary hypertension: Pathobiology and implications for therapy

Nitric oxide (NO) is a diffusible gas with diverse roles in human physiology and disease. Significant progress in the understanding of its biological effects has taken place in recent years. This has led to a better understanding of the pathobiology of pulmonary hypertension (PH) and the development of new therapies. This article provides an overview of the NO physiology and its role in the pathobiology of lung diseases, particularly PH. We also discuss current and emerging specific treatments that target NO signaling pathways in PH.

Signal transduction pathways of IL-1beta-mediated iNOS in pulmonary vascular smooth muscle cells

Interleukin (IL)-1beta is an important early mediator of inflammation in pulmonary artery smooth muscle cells. We previously reported that a geranylgeranyltransferase inhibitor elevated basal levels of inducible nitric oxide synthase (iNOS) and enhanced IL-1beta-mediated induction, suggesting that Rac or Rho small G proteins are candidates for antagonism of such induction. In this study, overexpression of constitutively active Rac1 or its dominant negative mutant did not affect IL-1beta induction of iNOS. Alternatively, treatment with Clostridium botulinum C3 exoenzyme, which ADP-ribosylates Rho, was associated with superinduction of iNOS, suggesting an inhibitory role for Rho. IL-1beta activated the three mitogen-activated protein kinase (extracellular signal-regulated kinases 1 and 2, c-Jun NH2-terminal kinase/stress-activated protein kinase, and p38) and the Janus kinase (JAK)-signal transducer and activator of transcription pathways. The former two pathways were not associated with IL-1beta-mediated iNOS induction, whereas the latter two appeared to have inhibitory roles in iNOS expression. These data suggest that a broad intracellular signaling response to IL-1beta in rat pulmonary artery smooth muscle cells results in elevated levels of iNOS that is opposed by the geranylgeranylated small G protein Rho as well as the p38 and JAK2 pathways.

iNOS expression by activated neutrophils from patients with sepsis

BACKGROUND

Enhanced production of nitric oxide (NO) is associated with various inflammatory diseases such as sepsis. Although activated neutrophils are presumably involved in septic organ injury, the expression of inducible nitric oxide synthase (iNOS) by these cells has not been elucidated. The authors investigated whether activated neutrophils in sepsis could induce mRNA for iNOS and produce NO.

METHODS

Peripheral blood neutrophils were obtained from healthy volunteers, and septic patients underwent a surgical operation. The neutrophils of the healthy volunteers were stimulated with lipopolysaccharide (LPS) and/or tumour necrosis factor-alpha (TNF-alpha). The iNOS expression and NO production were examined by the reverse transcription-polymerase chain reaction and Griess method, respectively.

RESULTS

Circulating neutrophils obtained from patients with sepsis expressed higher levels of iNOS mRNA than those from patients with systemic inflammatory response syndrome (SIRS). Resting neutrophils from normal controls did not express iNOS mRNA and thus did not produce NO. After in vitro stimulation with LPS and TNF-alpha, the neutrophils did express iNOS mRNA and thus produce NO.

CONCLUSION

Activated neutrophils may be one source of NO production in sepsis.

Endogenously produced nitric oxide inhibits endothelial cell growth as demonstrated using novel antisense cell lines

Proliferation of endothelial cells is a vital component of vascular repair and angiogenesis. The endothelial cell mediator, nitric oxide (NO) has been reported both to inhibit and to promote endothelial cell proliferation. In this study we have generated cell lines which constitutively express antisense RNA to a region of inducible nitric oxide synthase (iNOS) from a murine endothelial cell line, sEnd-1. In response to stimulation with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) these antisense cells had no detectable RNA for endogenous iNOS, barely detectable iNOS protein and produced 82% less NO than did the control transfected line. Stimulation of the control transfected line caused significant NO production and inhibition of cell growth whereas for the antisense line, producing little NO in response to stimulation, proliferation remained the same as for unstimulated cells. No differences in cell death were observed between unstimulated and LPS/IFN-gamma stimulated cells. The data presented in this study directly demonstrate that NO derived endogenously from iNOS inhibits proliferation of endothelial cells. This approach overcomes problems in other studies where NO donors or non-isoform specific inhibitors of NO synthase have been used.

Effects of short-term nitrogen monoxide inhalation on leukocyte adhesion molecules, generation of reactive oxygen species, and cytokine release in human blood

Increased nitrogen monoxide (NO) concentrations change leukocyte function under a multitude of experimental conditions. NO inhalation is an experimental treatment for lung failure and exposes leukocytes to increased NO concentrations during passage through the lungs. To investigate whether short-term NO inhalation induces lasting changes in the function of circulating human leukocytes, venous blood samples were drawn from eight healthy male volunteers before and at the end of a 35-min period of breathing 40 ppm NO in 30% O(2). The leukocytes in the samples were subsequently analyzed for NO-induced changes in expression of cell surface molecules, generation of reactive oxygen species (ROS), and cytokine production by flow cytometry and ELISA techniques. The results were (1) NO inhalation changed neither the baseline nor the Escherichia coli lipopolysaccharide (LPS)-induced expression of the cell adhesion molecules CD11a, CD11b, CD11c, and CD62L (l-selectin) on neutrophilic granulocytes (PMN) or monocytes (Mo). The expression of CD14 and HLA-DR was also unchanged. (2) The generation of ROS in response to activation with phorbol myristate acetate increased in PMN after NO inhalation; an increase in Mo did not reach significance. (3) Baseline and LPS-stimulated production of IL-1beta decreased after NO inhalation, while the LPS-stimulated production of TNF-alpha increased. No changes in IL-6 production were detected.

Cell-specific differences in ET-1 system in adjacent layers of main pulmonary artery. A new source of ET-1

Endothelin-1 (ET-1) is a potent vasoconstrictor that causes sustained constriction of the pulmonary artery and modulates normal vascular tone. Endothelial cells were thought to be the major source of ET-1, but recent studies show that vascular smooth muscle cells (SMCs) are also capable of its synthesis. We examined the ET-1 and endothelin-converting enzyme-1 (ECE-1) system in cells cultured from two adjacent layers, subendothelial (L1) and inner medial (L2), of normal sheep main pulmonary artery and the response of this system to exogenous ET-1 and transforming growth factor-beta1 (TGF-beta1). End points include assessment of preproET-1 (ppET-1) and ECE-1 gene coexpression, measurement of intracellular and released ET-1, and ECE-1 activity. RT-PCR analysis revealed that ppET-1 and ECE-1 transcripts were greater in L1 than in L2 cells. The L1 cells also synthesized (L1, 3.2 +/- 0.1; L2, 1.2 +/- 0.1 fmol/10(6) cells) and released (L1, 9.2 +/- 0.5; L2, 2.3 +/-0.1 fmol/ml) greater amounts of ET-1 than L2 cells. The L2 cells internalized exogenous ET-1 in a dose-dependent manner (EC(50) 8 nmol/l) and were more responsive to exogenous ET-1 than L1 cells, showing upregulation of both the ppET-1 and ECE genes. TGF-beta1 downregulated ET-1-stimulated ppET-1 and ECE-1 transcripts but only in L2 cells. In addition, L1 cells showed greater ECE-1 activity than L2 cells, and in both, the activity was sensitive to the metalloprotease inhibitor phosphoramidon. We conclude that the ET-1 system in L1 and L2 cells is distinct. The data suggest that the two cell types have diverse functions in the arterial wall; the L1 cells, like endothelial cells, provide a local source of ET-1; and since the L2 cells are more responsive to exogenous ET-1, they are likely to affect normal pulmonary vascular tone.

Pulmonary arterial smooth muscle cells modulate cytokine- and LPS-induced cytotoxicity in endothelial cells

Cytokines and lipopolysaccharide (LPS) are known to be injurious to vascular endothelial cells (ECs), but the influence of adjacent vascular smooth muscle cells (SMCs) on this injury is unknown. Exposure of cultured rat (RPMECs) or human (HPMECs) pulmonary microvascular ECs on tissue culture plastic to a mixture of cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma) and LPS (cytomix) resulted in a significant increase in (51)Cr release to 35-40%. When unstimulated RPMECs were cocultured with cytomix-pretreated rat pulmonary microvascular SMCs (RPMSMCs) there was an increase in (51)Cr release to 8.4%, which was nitric oxide dependent. However, when RPMECs or HPMECs were stimulated in direct contact with their respective SMCs, rather than a further increase in cytomix-induced injury (e.g., >35-40%), (51)Cr release decreased to <10%. This cytoprotection was fully reproduced with fixed RPMSMCs, and partially reproduced by plating HPMECs on gelatin. These data show that the direct toxicity of a cytokine and endotoxin mixture on cultured ECs can be reduced by contact with vascular smooth muscle.

Interleukin-1beta-induced nitric oxide production in rat aortic endothelial cells: inhibition by estradiol in normal and high glucose cultures

Expression of inducible nitric oxide synthase (iNOS) and the resultant increased nitric oxide (NO) production are associated with septic shock, atherosclerosis, and cytokine-induced vascular injury. Estrogen is known to impact vascular injury and vascular tone, in part through regulation of NO production. In the current study, we examined the effect of physiological concentrations of estradiol on interleukin-1beta (IL-1beta)-induced NO production in rat aortic endothelial cells (RAECs). 17Beta-estradiol significantly decreased IL-1beta-induced iNOS protein levels and reduced NO production in RAECs. High glucose (25 mM) elevated the increase in IL-1beta-induced iNOS protein and NO production. Nevertheless, estradiol still inhibited IL-1beta-induced iNOS and NO production even in the presence of high glucose. These data suggest that estradiol may exert its beneficial effects in part by inhibiting induction of endothelial iNOS, a possible mechanism for the protective effect of estradiol against diabetes-associated cardiovascular complications.

The effect of coculture with human smooth muscle cells on the proliferation, the IL-1 beta secretion, the PDGF production and tube formation of human aortic endothelial cells

Endothelial cells (ECs) and smooth muscle cells (SMCs), which are the major component cells of blood vessels, produce various bioactive substances and communicate with each other through them. Although several studies of the interaction between ECs and SMCs have been reported, the effect of coculture with SMCs on ECs is still obscure. To clarify the interaction of ECs and SMCs, we examined the effect of coculture with SMCs on the proliferation, the IL-1 beta secretion, the PDGF production and tube formation of ECs, using the coculture model: transferable wells and collagen gel. IL-1 and PDGF are considered to be related to progression of atherosclerosis. Proliferation and tube formation of ECs are associated with repair of vessels. In the transferable well system coculture with SMCs stimulated the proliferation of ECs, and enhanced the IL-1 beta secretion of ECs and in the collagen gel system coculture with SMCs induced the tube formation of ECs, and appeared to enhance the PDGF production of ECs. In conclusion, the effect of coculture with SMCs on ECs has two conflicting aspects: progression of atheroscleosis and angiogenesis. These results suggest that an imbalance of their effects may lead to pathological events.

Regional variability in preproEndothelin-1 gene expression in sheep pulmonary artery and lung during the onset of air-induced chronic pulmonary hypertension. Participation Of arterial smooth muscle cells

We investigated preproendothelin-1 (ppET-1) gene expression in the main and midregion pulmonary artery, and peripheral lung from control sheep and from animals during the development of the structural and functional changes of air-induced chronic pulmonary hypertension (CPH). Measurement of ET-1 in lung lymph (n = 7) at 1, 4, 8, and 12 d of continuous air embolization (CAE) showed a significant increase from day 4 compared with controls (n = 4). A semiquantitative reverse transcription PCR for ppET-1 gene expression was developed using ovine-specific primers. Control sheep showed strikingly fewer ppET-1 transcripts in the midregion (22.9+/-2.3 ng cDNA equivalents) than in the main pulmonary artery and lung (736.0+/-263.7 and 705.5+/-125.7, respectively). Smooth muscle cells (SMC) isolated from the main and midregion artery of control sheep confirmed these findings and showed higher levels of intracellular ET-1 synthesis in the main versus the midregion artery. Differences in gene expression persisted during CAE. In main pulmonary artery and lung, ppET-1 transcripts fell to < 1% of controls. However, transcripts in the midregion artery showed a gradual increase. Coincubation of SMC from the midregion with ET-1 plus TGF-beta resulted in an increase in intracellular big ET-1 and a decrease in SMC from the main artery. We conclude that SMC from the main and midregion pulmonary artery are phenotypically different and suggest that local synthesis of ET-1 and TGF-beta, and increased levels of ET-1 in lung lymph, regulate ppET-1 gene expression and synthesis in arterial SMC during the development of air-induced CPH.