Leukotriene B₄mediates macrophage influx and pulmonary hypertension in bleomycin-induced chronic neonatal lung injury

Abstract

Ee MT, Kantores C, Ivanovska J, Wong MJ, Jain A, Jankov RP. Leukotriene B4 mediates macrophage influx and pulmonary hypertension in bleomycin-induced chronic neonatal lung injury. Am J Physiol Lung Cell Mol Physiol 311: L292-L302, 2016. First published June 17, 2016 doi:10.1152/ajplung.00120.2016.-Systemically-administered bleomycin causes inflammation, arrested lung growth, and pulmonary hypertension (PHT) in the neonatal rat, similar to human infants with severe bronchopulmonary dysplasia (BPD). Leukotrienes (LTs) are inflammatory lipid mediators produced by multiple cell types in the lung. The major LTs, LTB4 and cysteinyl LTs, are suggested to contribute to BPD, but their specific roles remain largely unexplored in experimental models. We hypothesized that LTs are increased in bleomycin-induced BPD-like injury, and that inhibition of LT production would prevent inflammatory cell influx and thereby ameliorate lung injury. Rat pups were exposed to bleomycin (1 mg·kg Ϫ1 ·day Ϫ1 ip) or vehicle (control) from postnatal days 1-14 and were treated with either zileuton (5-lipoxygenase inhibitor), montelukast (cysteinyl LT1 receptor antagonist), or SC57461A (LTA4 hydrolase inhibitor) 10 mg·kg Ϫ1 ·day Ϫ1 ip. Bleomycin led to increased lung content of LTB4, but not cysteinyl LTs. Bleomycininduced increases in tissue neutrophils and macrophages and lung contents of LTB4 and tumor necrosis factor-␣ were all prevented by treatment with zileuton. Treatment with zileuton or SC57461A also prevented the hemodynamic and structural markers of chronic PHT, including raised pulmonary vascular resistance, increased Fulton index, and arterial wall remodeling. However, neither treatment prevented impaired alveolarization or vascular hypoplasia secondary to bleomycin. Treatment with montelukast had no effect on macrophage influx, PHT, or on abnormal lung structure. We conclude that LTB4 plays a crucial role in lung inflammation and PHT in experimental BPD. Agents targeting LTB4 or LTB4-mediated signaling may have utility in infants at risk of developing BPD-associated PHT. rat; newborn; inflammation; lung injury THE SURVIVAL OF EXTREMELY low-birth-weight infants has improved over recent decades, but at the cost of a high risk of developing chronic lung injury, known as bronchopulmonary dysplasia (BPD) (3). Chronic pulmonary hypertension (PHT) is common in infants with severe BPD, heralding a greatly increased morbidity and mortality (11,31,34,47). The pathogenesis of BPD is multifactorial, with upregulation of inflammatory mediators leading to, or caused by, infiltration of inflammatory cells playing a major role (38,43,46). However, the specific mediators contributing to inflammatory neonatal lung injury remain unclear, and there are presently no effective treatments.Leukotrienes (LTs) are potent lipid mediators, first described in 1979 by Borgeat and Samuelsson (5) as a new lineage of arachidonic acid-derived metabolites. LTs are produced by, recruit, and activate immune cells, thus initiating, augmenting, and sustaining tissue in...

Sodium nitrite augments lungS-nitrosylation and reverses chronic hypoxic pulmonary hypertension in juvenile rats

“…We have previously reported that LTA4H inhibition prevented vascular remodeling and chronic PHT in bleomycinexposed neonatal rats (16). In the present study, we observed that rescue NaNO 2 significantly decreased lung LTB4 content (product of LTA4H epoxy hydrolase activity) and that rescue therapy with SC57461A partially reversed chronic hypoxic PHT.…”

“…There are several limitations to this study. First, it is likely that multiple SNO protein modifications contributed to NaNO 2 -mediated reversal of chronic PHT; however, we chose to explore LTA4H as a candidate because of amenability to pharmacological inhibition and the known effects of the leukotriene pathway in mediating PHT (16). Of the other candidate SNO proteins identified, all may contribute to the pathogenesis of chronic PHT (modulators of actin depolymerization, oxidative stress, cell survival) and warrant further exploration.…”

“…Rat pups received daily subcutaneous NaNO 2 (5, 10, 20, or 50 mg/kg in 0.9% saline vehicle; 5 l per g body wt) or vehicle alone from PNDs 1-21 to determine the dose of NaNO2 that maximally prevented chronic PHT without significantly (Ͼ5%) increasing blood methemoglobin (MetHb). For rescue treatment studies, rats received daily subcutaneous NaNO2 (20 mg/kg), which was determined to be the dose that best met the above criteria, or SC57461A (LTA4H inhibitor) at a dose (10 mg· kg Ϫ1 ·day Ϫ1 sc) previously reported by our group to be effective in neonatal rats (16) or vehicle (0.9% saline or 20% DMSO in PBS, respectively) from PND 14 to PND 21. Separate animals were exposed to chronic hypoxia with or without iNO 20 ppm.…”

Leukotriene biosynthetic enzymes as therapeutic targets

“…Further investigations pointed to a critical role of LTB 4 in the disease process. Thus, studies in several rat models of PH as well as cells and tissue samples from patients with PH revealed elevated levels of LTB 4 , both systemically and locally in lung tissue, and high levels of LTA4H were observed in accumulated macrophages (113)(114)(115). At a functional level, macrophage-derived LTB 4 was shown to induce apoptosis of pulmonary artery endothelial cells as well as proliferation and hypertrophy of pulmonary smooth muscle cells (113).…”

Emerging therapeutics in pulmonary hypertension

“…Moreover, it was shown that bleomycin treatment leads to LTB4-meidated macrophage influx and PH. Inhibition of LTB4 formation with zileuton (5-lipoxygenase inhibitor) and SC57461A (LTA4H inhibitor) prevented the development of PH in rat pups exposed to bleomycin (36). Currently, the effect of bestatin (ubenimex) is being examined in a phase 2 clinical trial (LIBERTY Study) in patients with PAH (NCT02664558).…”