Azithromycin and its non-antibacterial derivative EP317 attenuate select aspects of ventilator-induced lung injury in rats

EP317, an azithromycin-derived compound with negligible antibacterial activity, was designed to retain the immunomodulatory and epithelial barrier enhancing effects of AZM while mitigating the risk of bacterial resistance. This study investigated the effects of AZM and EP317 in a rat model of VILI. Forty-eight rats were divided into six groups (N=8 per group), receiving either placebo, AZM, or EP317 (5 mg/kg daily for seven days), with half of the animals subjected to mechanical ventilation with peak airway pressure at 35 cmH₂O. Both compounds ameliorated pulmonary oedema and enhanced barrier integrity, showing lower wet/dry ratio in lung tissue and decreased total protein in bronchoalveolar lavage fluid (BALF). Cytokine profiling in plasma (L-Selectin, PAI-1, RANTES, MCP-3, IL-6, SCF, IL-17a, RAGE, MIP-3α, IL-13, G-CSF, IL-10, M-CSF, IFN-γ, GRO-KC and MMP9) revealed that both treatments attenuated inflammatory responses, while cytokine levels in BALF in ventilated animals were either unchanged or increased. Survival rates were improved in the treatment groups. Histological analysis indicated increased oedema in ventilated animals, likely due to the high-pressure ventilation, while drug-treated groups exhibited reduced oedema. Global gene expression profiling by RNA sequencing revealed robust upregulation of inflammatory and stress-response pathways in ventilated animals, with partial attenuation following AZM or EP317 pre-treatment. These findings suggest that EP317 and AZM offer protective effects against VILI. EP317 presents a promising alternative to conventional macrolide therapy by circumventing antibiotic resistance concerns.