Oxygen-induced lung injury in the pre-term guinea pig: the role of leukotriene B4

Antileukotrienes for the prevention and treatment of chronic lung disease in very preterm newborns: a systematic review

BACKGROUND

Very preterm infants are at high risk of developing chronic lung disease, which requires respiratory support and might have long-term sequelae. As lung inflammation plays an important role in pathogenesis, antileukotrienes have been explored in both clinical and animal studies. We aimed to assess the benefits and harms of antileukotrienes for the prevention and treatment of respiratory morbidity and mortality in very preterm newborns.

METHODS

In this systematic review, we included randomized trials and non-randomized studies in humans and animals reporting the effects of antileukotrienes in very preterm infants or other mammals within 10 days of birth. Our pre-specified primary outcomes were all-cause mortality and any harm, and, for the clinical studies, incidence of chronic lung disease. Included studies underwent risk of bias-assessment and data extraction performed by two authors independently. There were no language restrictions.

RESULTS

Fifteen studies totally met our inclusion criteria: one randomized trial and four non-randomized studies in humans and 10 animal studies (five in rodents, two in lambs and one in either guinea pigs, rabbits or caprinae). All five clinical studies used montelukast and had a small sample size, ranging from 4 to 77 infants. The randomized trial (n = 60) found no difference in the incidence of chronic lung disease between the groups. Only one clinical study, which enrolled four very preterm infants and had a critical overall risk of bias, reported long-term outcomes. All other studies had unclear or greater overall risk of bias and meta-analyses were therefore deemed unfeasible. Eight of ten animal studies used leukotriene receptor antagonists as antileukotriene (montelukast in three of ten studies) and seven had an experimental study design (i.e. some animals were not exposed to antileukotrienes but no randomization). Three of the ten animal studies assessed different doses. Animal studies found no effect on the outcomes mortality, growth, or lung function related surrogate outcomes.

CONCLUSIONS

Use of antileukotrienes in very preterm infants to prevent or treat chronic lung disease is not supported by the available evidence. Large randomized trials focusing on outcomes relevant to patients, including long-term outcomes, are needed. Studies should also minimize risk of bias.

Leukotriene B4 mediates macrophage influx and pulmonary hypertension in bleomycin-induced chronic neonatal lung injury

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(-1)·day(-1) 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(-1)·day(-1) ip. Bleomycin led to increased lung content of LTB4, but not cysteinyl LTs. Bleomycin-induced increases in tissue neutrophils and macrophages and lung contents of LTB4 and tumor necrosis factor-α 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.

The efficacy and safety of Montelukast sodium in the prevention of bronchopulmonary dysplasia

Purpose

The purpose of this study was to evaluate the efficacy and safety of Montelukast sodium in the prevention of bronchopulmonarydysplasia (BPD).

Methods

The Interventional study was designed as a multicenter, prospective, and randomized trial, with open labeled and parallel-experimental groups, 66 infants were enrolled and allocated to either the case group (n=30) or the control group (n=36) based on gestational age (GA). Infants in the case group were given Montelukast sodium (Singulair) based on their body weight (BW). Zero week was defined as the start time of the study.

Results

The incidence of moderate to severe BPD was not different between the groups (case group: 13 of 30 [43.3%] vs. control group: 19 of 36 [52.8%], P=0.912). Additionally, secondary outcomes such as ventilation index, mean airway pressure and resort to systemic steroids were not significantly different. There were no serious adverse drug reactions in either group, and furthermore the rate of occurrence of mild drug related-events were not significantly different (case group: 10 of 42 [23.8%] vs. control group: 6 of 48 (15.8%), P=0.414).

Conclusion

Montelukast was not effective in reducing moderate or severe BPD. There were no significant adverse drug events associated with Montelukast treatment.

Pivotal role of the 5-lipoxygenase pathway in lung injury after experimental sepsis

Postsepsis lung injury is a common clinical problem associated with significant morbidity and mortality. Leukotrienes (LTs) are important lipid mediators of infection and inflammation derived from the 5-lipoxygenase (5-LO) metabolism of arachidonate with the potential to contribute to lung damage after sepsis. To test the hypothesis that LTs are mediators of lung injury after sepsis, we assessed lung structure, inflammatory mediators, and mechanical changes after cecal ligation and puncture surgery in wild-type (WT) and 5-LO knockout (5-LO(-/-)) mice and in WT mice treated with a pharmacologic LT synthesis inhibitor (MK886) and LT receptor antagonists (CP105,696 and montelukast). Sixteen hours after surgery, WT animals exhibited severe lung injury (by histological analysis), substantial mechanical impairment (i.e., an increase in static lung elastance), an increase in neutrophil infiltration, and high levels of LTB4, cysteinyl-LTs (cys-LTs), prostaglandin E2, IL-1β, IL-6, IL-10, IL-17, KC (CXCL1), and monocyte chemotactic protein-1 (CCL2) in lung tissue and plasma. 5-LO(-/-) mice and WT mice treated with a pharmacologic 5-LO inhibitor were significantly protected from lung inflammation and injury. Selective antagonists for BLT1 or cys-LT1, the high-affinity receptors for LTB4 and cys-LTs, respectively, were insufficient to provide protection when used alone. These results point to an important role for 5-LO products in sepsis-induced lung injury and suggest that the use of 5-LO inhibitors may be of therapeutic benefit clinically.

5-Lipoxygenase-activating protein (FLAP) inhibitor MK-0591 prevents aberrant alveolarization in newborn mice exposed to 85% oxygen in a dose- and time-dependent manner

Bronchopulmonary dysplasia is characterized by prolonged oxygen dependency due to compromised gas-exchange capability. This is attributable mainly to inadequate and aberrant alveolarization resulting from insults like hyperoxia. Leukotrienes are associated with hyperoxia-induced inhibition of alveolarization. We hypothesized that a 5-lipoxygenase-activating protein (FLAP) inhibitor given while newborn mice were exposed to 85% oxygen would prevent aberrant alveolarization in a dose- and time-dependent manner. Newborn mice were exposed to either room air or hyperoxia for 14 days. Pups were treated with either vehicle or MK-0591 10, 20, or 40 mg/kg subcutaneously daily for days 1-4, 5-9, or 10-14. On day 14, the lungs were inflated, fixed, and stained for histopathological and morphometric analyses. Hyperoxia groups treated with MK-0591 20 or 40 mg/kg during days P1-P4 or P10-P14 showed alveolarization that resembled that of room air controls while untreated hyperoxia groups showed definite evidence of aberrant alveolarization but no inflammation. In a hyperoxia-exposed newborn mice model, a FLAP inhibitor given during critical window periods may prevent aberration of alveolarization in a dose- and time-dependent manner.

On the pulmonary toxicity of oxygen: III. The induction of oxygen dependency by oxygen use

Oxygen is central to the development of neonatal lung injury. The increase in oxygen exposure of the neonatal lung during the onset of extrauterine air breathing is an order of magnitude, from a range of 10-12 to 110-120Torr. The contributions of oxygen and the volume and pressure relationships of ventilatory support to lung injury are not easily distinguished in the clinical setting. Sequential changes in inspired air or 100% oxygen were studied in 536 newborn rabbits without ventilatory support. Bilateral cervical vagotomies (BCV) were performed at 24h post natal to induce ventilatory distress which eventuates in hyaline membrane disease. The sequences applied yielded evidence for an induced state of oxygen dependency from oxygen use which was reflected in differences in survival and the extent of pulmonary injury. The median survival for animals kept in air throughout was 3h. Oxygen before vagotomy or during the first 3h afterwards extended the survival significantly but produced more extensive, more severe, and more rapid lung lesions. Returning animals to air after prior oxygen exposure reduced the number of survivors past 10h and shortened the maximum survival in those groups. These features indicate the development of a dependency of the defense mechanisms on the availability of oxygen at the higher level for metabolic and possibly other aspects of the pulmonary and systemic response to injury, beyond the usual physiological need. Subset analysis revealed additive and latent effects of oxygen and demonstrated a remarkable rapidity in onset of severe lesions under some circumstances, illustrating the toxicity of oxygen per se.

Topical inhibition of nuclear factor-κB enhances reduction in lung edema by surfactant in a piglet model of airway lavage

OBJECTIVE

Acute respiratory distress syndrome is occasionally seen in newborn infants due to a severe inflammatory process in the lungs that affects capillary-alveolar permeability, epithelial integrity, and type I and II pneumocyte function. The aim of this study was to investigate the effect of a topically applied nuclear factor-kappaB inhibitor (IkappaB kinase-NF-kappaB essential modulator binding domain [IKK-NBD] peptide) on gas exchange, lung function, lung fluids, and inflammation in a piglet model of repeated airway lavage that is characterized by surfactant deficiency, lung edema, and an inflammatory response.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Research laboratory of a university children's hospital.

SUBJECTS

A total of 24 anesthetized, mechanically ventilated newborn piglets.

INTERVENTIONS

Repeated airway lavage was carried out until both the Pao2 decreased to approximately 40 mm Hg, while ventilating the piglets with an Fio2 of 0.6, and a peak inspiratory pressure of >/=18 cm H2O was needed to maintain tidal volume at 6 mL/kg. One group of piglets served as a control (n = 8), a second group (S, n = 8) received a porcine surfactant preparation (Curosurf), and a third group received IKK-NBD peptide admixed to surfactant (S+IN, n = 8).

MEASUREMENTS AND MAIN RESULTS

After 6 hrs of mechanical ventilation after intervention, S+IN group piglets showed decreased extravascular lung water (S+IN vs. S, 20 +/- 3 vs. 28 +/- 10 mL/kg; p < .05) and a lesser protein content in the epithelial lining fluid (S+IN vs. S, 38 +/- 5 vs. 50 +/- 5 mg/L; p < .05). Functional residual capacity (S+IN vs. S, 16.7 +/- 6.3 vs. 12.2 +/- 4.3 mL/kg; p < .05), alveolar volume (S+IN vs. S, 5.4 +/- 1.8 vs. 4.6 +/- 1.5 mL/kg; p < .05), and lung mechanics were improved. Bronchoalveolar lavage showed a lesser percentage of polymorphonuclear leukocytes (S+IN vs. S, 70% +/- 6% vs. 82% +/- 3%; p < .01) and a reduction in the chemokine leukotriene B4 (S+IN vs. S, 2.0 +/- 0.6 vs. 3.5 +/- 1.4 pg/mL; p < .01).

CONCLUSIONS

A topically applied nuclear factor-kappaB inhibitor improves lung edema and lung volumes and reduces inflammation in this newborn piglet model of airway lavage.

Montelukast does not protect against hyperoxia-induced inhibition of alveolarization in newborn rats

Impaired lung development has been demonstrated in neonatal animals exposed to hyperoxia. High lung cys-leukotriene levels may be a contributing factor towards the increase in oxygen toxicity. We investigated the effect of cysteinyl-leukotriene inhibition using the receptor antagonist, montelukast (MK, Singulair), on hyperoxia-induced changes in lung parenchymal structure in neonatal rat pups. Rat pups were exposed to 21% O(2) (air) or 50% O(2) (moderate hyperoxia) from days 1-14 after birth, and were administered the cys-leukotriene receptor antagonist MK (1 mg/kg/day) or normal saline from days 4-14. Somatic growth and morphometric measurements were done on day 15. There was a significant increase in bronchoalveolar lavage fluid cysteinyl-leukotriene levels (+61.9%) when animals were exposed to hyperoxia. O(2) exposure significantly decreased the specific internal surface area by 13%. There was a nonsignificant 5.8% and 19.6% increase in mean chord length and mean alveolar diameter, respectively, as well as an 8.6% decrease in lung volume to body weight ratio. Inhibition of only one arm of the arachidonic-acid cascade by MK was not sufficient to prevent these oxygen-induced changes.

Carboxy-substituted cinnamides: a novel series of potent, orally active LTB4 receptor antagonists

A series of carboxy-substituted cinnamides were investigated as antagonists of the human cell surface leukotriene B4 (LTB4) receptor. Binding was determined through measurement of [3H]LTB4 displacement from human neutrophils. Receptor antagonism was confirmed through a functional assay, which measures inhibition of Ca2+ release in human neutrophils. Potent antagonists were discovered through optimization of a random screening hit, a p-(alpha-methylbenzyloxy)cinnamide, having low-micromolar activity. Substantial improvement of in vitro potency was realized by the attachment of a carboxylic acid moiety to the cinnamide phenyl ring through a flexible tether, leading to identification of compounds with low-nanomolar potency. Modification of the benzyloxy substituent, either through ortho-substitution on the benzyloxy phenyl group or through replacement of the ether oxygen with a methylene or sulfur atom, produced achiral antagonists of equal or greater potency. The most potent compounds in vitro were assayed for oral activity using the arachidonic acid-induced mouse ear edema model of inflammation. Several compounds in this series were found to significantly inhibit edema formation and myeloperoxidase activity in this model up to 17 h after oral administration. Representatives of this series have been shown to be potent and long-acting orally active inhibitors of the LTB4 receptor.