A preclinical systematic review and meta-analysis assessing the effect of biological sex in lipopolysaccharide-induced acute lung injury

Abstract

It is unclear what effect biological sex has on outcomes of acute lung injury (ALI). Clinical studies are confounded by their observational design. We addressed this knowledge gap with a preclinical systematic review of ALI animal studies. We searched MEDLINE and Embase for studies of intratracheal/intranasal/aerosolized lipopolysaccharide administration (the most common ALI model) that reported sex-stratified data. Screening and data extraction were conducted in duplicate. Our primary outcome was histological tissue injury and secondary outcomes included alveolar-capillary barrier alterations and inflammatory markers. We used a random-effects inverse variance meta-analysis, expressing data as standardized mean difference (SMD) with 95% confidence intervals (CIs). Risk of bias was assessed using the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) tool. We identified six studies involving 132 animals across 11 independent experiments. A total of 41 outcomes were extracted, with the direction of effect suggesting greater severity in males than females in 26/41 outcomes (63%). One study reported on lung histology and found that male mice exhibited greater injury than females (SMD: 1.61, 95% CI: 0.53-2.69). Meta-analysis demonstrated significantly elevated albumin levels (SMD: 2.17, 95% CI: 0.63-3.70) and total cell counts (SMD: 0.80, 95% CI: 0.27-1.33) in bronchoalveolar lavage fluid from male mice compared with female mice. Most studies had an "unclear risk of bias." Our findings suggest sex-related differences in ALI severity. However, these conclusions are drawn from a small number of animals and studies. Further research is required to address the fundamental issue of biological sex differences in LPS-induced ALI.

Keywords: ALI; ARDS; acute lung injury; acute respiratory distress syndrome; biological sex.

Graphical abstract

Figure 1.

Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) flow diagram detailing study screening and selection.

Figure 2.

Heat map illustrating the direction of effect on acute lung injury outcomes. The direction of the effect is visually represented by color: blue signifies that males had more severe outcomes; red indicates that females had more severe outcomes. The magnitude of the effect size is depicted through the intensity of shading [Tesfaigzi et al. (18); Speyer et al. (19); Card et al. (20); Moitra et al. (21); Puntorieri et al. (22); Mock et al. (23)].

Figure 3.

Meta-analysis of all included studies of LPS-induced lung injury that reported the outcome of albumin leakage (A) and bronchoalveolar lavage fluid (BALF) total protein (B). Data are presented as a forest plot with standardized mean difference and 95% confidence intervals. Effect sizes <0 favor female animals having worse outcomes and >0 favor males having worse outcomes. The I² value represents the statistical heterogeneity [Speyer et al. (19); Moitra et al. (21); Puntorieri et al. (22); Mock et al. (23)].

Figure 4.

Meta-analysis of all included studies of LPS-induced lung injury that reported the outcome of bronchoalveolar lavage fluid (BALF) total cell counts. Data are presented as a forest plot with standardized mean difference and 95% confidence intervals. Effect sizes <0 favor female animals having worse outcomes and >0 favor males having worse outcomes. The I² value represents the statistical heterogeneity [Puntorieri et al. (22); Card et al. (20); Mock et al. (23); Moitra et al. (21)].

Figure 5.

Meta-analysis of all included studies of LPS-induced lung injury reporting bronchoalveolar lavage fluid (BALF) IL-6 (A), TNF-α (B), and IL-1β (C) concentrations. Data are presented as a forest plot with standardized mean difference and 95% confidence intervals. Effect sizes <0 favor female animals having worse outcomes and >0 favor males having worse outcomes. The I² value represents the statistical heterogeneity [Puntorieri et al. (22); Card et al. (20); Speyer et al. (19); Tesfaigzi et al. (18)].

Figure 6.

Meta-analysis of all included studies of LPS-induced lung injury that reported the outcome of total neutrophils (A), total macrophages (B), and tissue myeloperoxidase content (C). Data are presented as a forest plot with standardized mean difference and 95% confidence intervals. Effect sizes <0 favor female animals having worse outcomes and >0 favor males having worse outcomes. The I² value represents the statistical heterogeneity [Speyer et al. (19); Card et al. (20); Puntorieri et al. (22); Tesfaigzi et al. (18); Moitra et al. (21)].

Figure 7.

Risk of bias assessment.