Hochuekkito attenuates anxiety-like behavior associated with pulmonary inflammation induced by intratracheal lipopolysaccharides in mice

Introduction: We have previously demonstrated that intratracheal lipopolysaccharide (LPS) injection induces significant pulmonary inflammation accompanied by hippocampal microglial activation, indicative of neuroinflammation. Hochuekkito (HET) is a traditional Japanese herbal medicine used to treat various conditions, including mental disorders and physical weakness. We have previously reported that HET ameliorates anxiety-like behaviors induced by intraperitoneal LPS injections in mice. However, its anxiolytic effects on anxiety-like behaviors due to pulmonary inflammation remain poorly understood. Therefore, in the present study, we aimed to investigate the effects of HET on anxiety-like behaviors induced by intratracheal LPS injection in mice. Methods: Mice received HET (1.0 g/kg) once daily for 2 weeks through oral gavage prior to LPS treatment. The light-dark box test was conducted 24 h following LPS injection to assess anxiety-like behaviors. Diazepam, a clinically used anxiolytic, served as a positive control. The lung wet-to-dry weight ratio was determined, and the concentrations of interleukin-6 (IL-6) in the lungs and serum were assessed. Results: mRNA expression levels in LPS-treated mice. Diazepam failed to exert significant effects in LPS-treated mice, whereas HET remained effective under inflammatory conditions. Moreover, LPS injections significantly increased the number of Iba-1-immunoreactive microglial cells in the CA1 region of the hippocampus, whereas this effect was suppressed by treatment with HET. In the bronchoalveolar lavage fluid (BALF), the LPS-induced increase in white blood cell count was significantly reduced by treatment with HET. Furthermore, HET alleviated LPS-induced pulmonary inflammation, as evidenced by decreased lung wet-to-dry weight ratios. Conclusion: This study suggests that inflammation induced by intratracheal LPS injection contributes to anxiety-like behaviors in mice and that IL-6 may play a key role in linking peripheral inflammation to neuroinflammatory responses. The anxiolytic effects of HET appear to be associated, at least in part, with the suppression of IL-6 elevation in both the periphery and the hippocampus, along with attenuation of microglial activation. Our findings suggest that HET may serve as a potential therapeutic agent for anxiety-like behaviors associated with pulmonary inflammation.