Yinhuang decoction alleviates RSV-induced viral pneumonia via TLR4/NF-κB/NLRP3 pathway with colloidal phase as dominant active fractions.

Lonicera japonica Thunb. (JYH) and Scutellaria baicalensis Georgi (HQ) have been widely applied in pharmaceutical products owing to their heat-clearing and toxin-eliminating properties. Clinically, their combination in Yinhuang decoction (YHD) is commonly used to treat upper respiratory tract diseases due to its potent anti-inflammatory effects. However, their efficacy against virus-induced pneumonia and the underlying mechanisms remain poorly understood. This study aimed to investigate the therapeutic effects and mechanisms of YHD on respiratory syncytial virus (RSV)-induced viral pneumonia in mice. Additionally, it sought to isolate and compare different phases of YHD to determine the most effective phase for treatment. YHD was separated into true solution, colloidal, and precipitate phases for characterization. An RSV-infected pneumonia mouse model evaluated lung function, Micro CT, and H&E staining. RT-qPCR quantified viral load, while oxidative stress and inflammation markers were measured. The potential pathways were explored by RT-qPCR, protein blot and immunofluorescence. The results showed that the colloidal phase showed physicochemical properties similar to YHD, forming stable nanoparticles. YHD significantly improved lung function, reduced viral load, and mitigated oxidative stress and inflammation in RSV-infected mice, with the colloidal phase outperforming other phases. Both YHD and the colloidal phase inhibited the TLR4/NF-κB signaling pathway and NLRP3 inflammasome expression. This work highlights the colloidal phase is identified as the optimal phase of YHD, likely due to its stable nanoparticles. This study clarifies YHD's herb-pair compatibility principles from an active phase perspective, providing a scientific basis for its application in preventing and treating viral pneumonia and related diseases.