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

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.

Using Experimental Models to Identify Pathogenic Pathways and Putative Disease Management Targets in Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a common and serious complication of preterm birth. Limited pharmacological and other medical interventions are currently available for the management of severely affected, very preterm infants. BPD can be modelled in preclinical studies using experimental animals, and experimental animal models have been extremely valuable in the development of hallmark clinical management strategies for BPD, including pulmonary surfactant replacement and single-course antenatal corticosteroids. A gradual move away from large animal models of BPD in favor of term-born rodents has facilitated the identification of a multitude of new mechanisms of normal and stunted lung development, but this has also potentially limited the utility of experimental animal models for the identification of pathogenic pathways and putative disease management targets in BPD. Indeed, more recent pharmacological interventions for the management of BPD that have been validated in randomized controlled trials have relied very little on preclinical data generated in experimental animal models. While rodent-based models of BPD have tremendous advantages in terms of the availability of genetic tools, they also have considerable drawbacks, including limited utility for studying breathing mechanics, gas exchange, and pulmonary hemodynamics; and they have a less relevant clinical context where lung prematurity and a background of infection are now rarely present in the pathophysiology under study. There is a pressing need to refine existing models to better recapitulate pathological processes at play in affected infants, in order to better evaluate new candidate pharmacological and other interventions for the management of BPD.

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.

Development and characterization of an animal model of severe pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a serious pathological phenomenon with poor prognosis, which is associated with morphological as well as hemodynamic alteration of the pulmonary circulation. To establish an animal model mimicking severe human PAH, we combined 2 well-described procedures, i.e. exposure to hypobaric chronic hypoxia and administration of monocrotaline hydrochloride in rats. Compared to a single procedure, the combined procedure induced more severe right ventricle hypertrophy and an increase in right ventricle systolic pressure. Histological examination on the combined procedure model revealed a severe medial hypertrophy as well as occlusive vascular changes of the intra-acinar pulmonary arteries with endothelial lesions. It is noteworthy that severe alterations including concentric neointimal thickening, abnormal endothelial proliferation, plexiform lesions and vascular occlusion with fibrin thrombi were observed in the combined pulmonary hypertension model when exposed to a long period of hypoxia. The present data indicate that a combined treatment of monocrotaline injection and hypobaric chronic hypoxia exposure produces more severe hemodynamic changes and histological alterations. Since human PAH diagnosed in clinical practice is often severe, this combined treatment animal model could be useful to identify relevant therapeutic targets acting on both hemodynamic and structural alterations of the pulmonary circulation.

Clarithromycin, montelukast, and pentoxifylline combination treatment ameliorates experimental neonatal hyperoxic lung injury

OBJECTIVE

We aimed to assess the efficiency of clarithromycin, montelukast, and pentoxifylline treatments, alone and in combination, in reducing hyperoxic lung injury at the histopathologic level.

METHODS

The experiment was carried out with 47 newborn rat pups divided into six groups during postnatal days 3 to 13. The rats belonging to group 1 were designated as the control group and kept in room air without exposure to hyperoxia. Group 2 (clarithromycin), group 3 (montelukast), group 4 (pentoxifylline), group 5 (clarithromycin + montelukast + pentoxifylline combination), and group 6 (placebo) were kept in plexiglass chamber and exposed to hyperoxia (88-92%) throughout the experiment. Alveolar surface area percentage, fibrosis, and smooth muscle actin expression were assessed in the lungs, which were resected by thoracotomy on postnatal day 14.

RESULTS

Drug treatments, when used separately, were not detected to be superior to placebo with regard to mean alveolar surface area, fibrosis, and smooth muscle actin expression. Combination treatment resulted in significantly higher mean lung area percentages and lower actin scores with respect to the placebo treatment group (64.0% vs. 50.2%, p=0.002; 0 (0-1) vs. 7 (2-12), p=0.005, respectively).

CONCLUSIONS

It was determined that clarithromycin, montelukast, and pentoxifylline combination treatment is superior to placebo treatment in the newborn rat hyperoxic lung injury model. The present study indicates that combination therapy might be successful in bronchopulmonary dysplasia, which has complex pathophysiologic processes and lacks established efficient treatment strategies.

Influence of lung oxidant and antioxidant status on alveolarization: role of light-exposed total parenteral nutrition

Parenteral multivitamins (MVP) are linked to the generation of peroxides, which cause oxidant injury in lungs associated with alveolar remodelling linked to lung disease of prematurity. This study was to investigate the relationship between alveolar development and lung oxidant-antioxidant status as modulated by the mode of administration of multivitamins with total parenteral nutrition (TPN). Four groups of guinea pig pups received parenteral nutrition differing by 1) mode of MVP admixture: with amino acid solution (AA-MVP) or lipid emulsion (LIP-MVP); 2) light exposure: TPN exposed (LE) or shielded from light (LP). After 2 or 4 days of TPN, vitamins C and E, 8-isoprostaneF2alpha and alveolarization index were determined in lungs and GSSG/GSH in lungs and blood. Exposure to light and the mode of MVP admixture did not influence vitamin E and isoprostane levels. Blood glutathione redox potential was more oxidized in LE and LIP-MVP groups after 4-day infusions, whereas lung redox potential was more reduced in LE groups. LP and LIP-MVP had a beneficial effect, with higher number of alveoli. Globally, results indicate that in this model, alveolarization and modifications in lung redox potential are two independent events induced by light exposed TPN.

Effect of coadministration of parenteral multivitamins with lipid emulsion on lung remodeling in an animal model of total parenteral nutrition

Exposure of parenteral multivitamin solutions (MVP) to ambient light generates peroxides and vitamin loss, and induces initiation of fibrosis and a reduced alveolar count in an animal model of total parenteral nutrition (TPN). Adding MVP to the lipid moiety of TPN prevents lipid peroxidation and vitamin loss. The aim of the study was to compare modes of delivery of MVP on lung procollagen mRNA and alveolar counts. Three-day-old guinea pig pups were infused continuously with one of three intravenous solutions: 1) control = dextrose; 2) AA + MVP = MVP given with the dextrose + amino-acid moiety, in a "piggyback" setup with a lipid emulsion mixed close to the infusion site; and 3) LIP + MVP = same as AA + MVP, except that MVP is given with the lipid emulsion. After 4 days, lungs were prepared for alveolar count (intercept technique) and for quantification of the procollagen/beta-actin mRNA ratio (initial step of fibrosis). Data were compared by ANOVA. The procollagen mRNA was lower (P < 0.05) in animals receiving LIP + MVP than those with AA + MVP. But the two modes of admixture of MVP had the same effect on the alveolar counts, which were lower (P < 0.01) than controls. The mode of delivery of TPN affects lung remodeling. Although LIP + MVP protects against the initiation of lung fibrosis, the absence of a beneficial effect on alveolar counts suggests that these features of lung remodeling are not caused by a unique component of TPN. Specific roles of peroxides, components of MVP, and light exposure on lung remodeling need to be explored before LIP + MVP can be recommended as an alternative mode of parenteral vitamin delivery.

Interaction between Ascorbate and Light-Exposed Riboflavin Induces Lung Remodeling

Light-exposed parenteral multivitamins induce in lungs peroxide-like oxidant responses as well as the initiation of fibrosis. We hypothesized that peroxides generated in light-exposed total parenteral nutrition (TPN) affect lung remodeling. The objective was to assess the specific roles of peroxides, multivitamin preparation (MVP), and light exposure on lung remodeling during TPN. Three-day-old guinea pigs fitted with an indwelling catheter were assigned to the following intravenous regimens: TPN or MVP +/- photoprotection, H(2)O(2)+/- glutathione, MVP +/- metabisulfite, or ascorbic acid +/- riboflavin. Fed animals served as controls. After 4 days, lungs were sampled to determine alveolarization (intercepts), beta-actin mRNA (protection assay), and apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling). Data were analyzed by analysis of variance. The infusion of light-exposed multivitamins induced a 20% lower (p < 0.01) alveolarization index than fed controls, and 3-fold higher (p < 0.01) apoptotic events. This was prevented by photoprotecting TPN. The effect of multivitamins on the alveolarization index was reproduced (p < 0.05) by infusion of light-exposed riboflavin in the presence of vitamin C. The alveolarization index correlated (r(2) = 0.35; p < 0.05) with beta-actin mRNA, suggesting alveolar disruption. Antiperoxides conferred no protection against decreased alveolarization. Lung remodeling induced by exposure of TPN to ambient light is not due to a direct effect of infused peroxides but rather to an interaction between vitamin C and peroxides generated by the exposure of riboflavin to light. It is speculated that this interaction may play a role in the development of chronic lung disease of premature infants who receive TPN and have immature antioxidant defenses.