Probiotic modulation of the neonatal gut-lung axis in the regulation of early respiratory function

The gut -lung axis represents bidirectional communication between the gastrointestinal and respiratory systems that contributes to immune regulation and inflammatory homeostasis. This study evaluated the effects of probiotic-conditioned media (PCM) and live probiotics on epithelial barrier function, inflammatory responses, oxidative stress, and mitochondrial function using Caco-2 intestinal epithelial and A549 pulmonary epithelial cell models under inflammatory conditions.

Cells were treated with 20% PCM or live probiotics at a multiplicity of infection (MOI) of 50:1 and exposed to LPS (1 μg/mL) or TNF-α (10 ng/mL). Barrier integrity was evaluated using transepithelial electrical resistance (TEER) and FITC-dextran permeability assays. Reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨm), inflammatory and tight junction gene expression, and SCFA concentrations were assessed using DCFH-DA staining, JC-1 staining, qPCR, and GC-MS, respectively. All experiments comprised three independent biological replicates (n=3), with data presented as mean ± SD and analyzed using one-way ANOVA followed by Tukey's post hoc multiple-comparison test.

Probiotic treatment increased TEER from 318 ± 21 Ω·cm² with LPS to 468 ± 23 Ω·cm² with 20% PCM and reduced ROS from 198 ± 12% to 118 ± 8%. Live probiotics produced comparable responses, restoring TEER to 482 ± 20 Ω·cm² and reducing ROS to 115 ± 7% in Caco-2 cells. ΔΨm increased from 0.82 ± 0.08 with LPS to 1.52 ± 0.11 with PCM. Acetate and butyrate concentrations increased to 6.8 ± 0.5 and 1.5 ± 0.2 mM, respectively. SCFA analysis showed increased acetate (6.8 ± 0.5 vs. 2.2 ± 0.3 mM) and butyrate (1.5 ± 0.2 vs. 0.5 ± 0.1 mM) in the 20% PCM group compared with the control condition (p<0.01). Compared with the LPS-treated inflammatory condition, probiotic treatment reduced the levels of the pro-inflammatory cytokines IL-6 and TNF-α by approximately 50%, while IL-10 expression increased to 1.8 ± 0.2-fold (p<0.05).

Collectively, probiotics and PCM supported epithelial protection by improving barrier integrity and attenuating inflammatory and oxidative responses, with increased SCFA production representing a potential contributing mechanism.