Low-frequency ultrasound alleviates pulmonary inflammation induced by Klebsiella pneumoniae in mice by inhibiting the TNFR1/NF-κB pathway

Background: Therapeutic ultrasound has been found to promote tissue healing and reduce inflammation in non-infectious diseases, but its efficacy in infectious inflammation remains unclear. Here, we employ the mice pneumonia model to explore the anti-inflammatory effects of low-frequency ultrasound (LFU) and elucidate its potential molecular mechanisms.

Methods: Pneumonia in mice was induced by intratracheal instillation of 100 μL of a 4.5 × 10⁸ CFU/mL Klebsiella pneumoniae (Kp) Bacterial suspension. A single LFU treatment (29.36 kHz, 270 mW/cm², 10 min) was applied to the chest of mice at 6 or 48 h after Infection. Biological samples were collected for gene, protein, and cellular experiments.

Results: LFU demonstrated good anti-inflammatory effects in mice during the recovery phase of Kp Infection (48 h after Infection). Although LFU alone had no bactericidal effects, it slightly reduced the pathological score of lung injury and significantly decreased the infiltration of CD45⁺ leukocytes. Additionally, the protein levels of TNF-α, GM-CSF and COX-2 in the bronchoalveolar lavage fluid were significantly reduced. Bulk RNA-sequencing results showed that the TNF Receptor (TNFR)/NF-κB pathway was up-regulated after Kp Infection, which was suppressed after LFU treatment. Western blot and immunofluorescence revealed LFU significantly reduced the protein levels of TNFR1, p-p65, and nuclear p65. The anti-inflammatory effect of LFU was comparable to a 20 mg/kg NF-κB Inhibitor and superior to a 15 mg/kg TNFR antagonist.

Conclusion: LFU exerts anti-inflammatory effects by inhibiting the TNFR1/NF-κB pathway during the recovery period of Kp Infection, reducing inflammatory transcription and thereby decreasing the release of inflammatory factors.

Anti-inflammatory; Klebsiella pneumoniae; Low-frequency ultrasound; TNFR/NF-κB.