Effects of Clausena lansium leaves volatile oil emulsion against Staphylococcus aureus in mice via autophagy modulation.

Abstract

Background: Volatile oil from fresh Clausena lansium (Lour.) Skeels (Rutaceae) (common name Wampee) has been previously extracted by our group from fresh C. lansium leaf and its components were qualitative and quantitatively analyzed by GC-MS. It altered the cell membrane permeability of Staphylococcus aureus and reduced the levels of inflammation factors. However, previous in vivo reports on the anti-inflammatory and the antibacterial properties against S. aureus are scarce.

Hypothesis/purpose: To evaluate the protective in vivo effects of Wampee leaves volatile oil emulsion (WVOE) against S. aureus-induced pneumonia and elucidate the underlying mechanisms of action.

Methods: Wild-type and nucleotide oligomerization domain-like receptor protein 3 (NLRP3)-deficient mice were used. Mice were treated with WVOE for 7 days, and subjected to S. aureus infection by nasal administration on day 5 for 48 h. Lung and blood samples were collected for assessing lung damage and protein abundance. Lung bacterial load, wet/dry ratio, C-reactive protein (CRP) levels, inflammatory cytokines secretion, and lung histopathological injury were examined.

Results: WVOE effectively reduced lung bacterial load, wet/dry ratio, and CRP levels increased following S. aureus infection in mice. WVOE decreased the secretion of inflammatory cytokines (IL-6 and TNF-α) and lung histopathological injury, and suppressed the NF-κB pathway and NLRP3 inflammasome activation. NLRP3^-/- mice exhibited lower bacterial load, inflammatory cytokines levels and lung histopathological injury compared with mice in the model group. Autophagy was enhanced in S. aureus-infected mice, with higher levels of p-mTOR, Beclin-1, Atg 16L1, Atg7, p62, p-p62, and LC3II. WVOE administration restored the autophagy related protein levels. Autophagy was inhibited in NLRP3^-/- mice of the control and model groups, and WVOE lost its ability to regulate the autophagy-related proteins enhanced upon S. aureus infection. WVOE enhanced autophagy to alleviate lung injury by inhibiting NLRP3-targeted P62. Furthermore, compared with the 3MA + model group, WVOE reduced the bacterial load and CRP levels, pulmonary septa narrowing, and congestion. NLRP3 protein expression increased due to autophagy inhibition. WVOE exerted a pharmacological effect through the PI3K/AKT/mTOR pathway.

Conclusion: WVOE regulated the PI3K/AKT/mTOR pathway and enhanced autophagy, with NLRP3 playing a crucial role. WVOE exhibited protective effects against S. aureus-induced pneumonia by inhibiting NLRP3 inflammasome activation and enhancing autophagy. These findings expand the understanding of antibacterial properties of WVOE, and provide novel insights into the therapeutic potential of WVOE in managing S. aureus infections.