COPD is a common respiratory disease in clinical practice, and its risk factors include advancing age, long-term smoke irritation, high incidence, and mortality, with continuous airflow restriction being the main pathological characteristic. Relevant statistics (Fang et al., 2018) show that there are approximately 100 million patients with COPD and increasing incidences of COPD in China. According to the World Health Organization, COPD may become the third leading cause of mortality worldwide by 2030 (Kim et al., 2021). Acute exacerbation of COPD (AECOPD) refers to a clinical event characterized by worsening of respiratory symptoms in patients with COPD, leading to changes in symptoms beyond the daily variation range and drug treatment regimens, which is critical for treating COPD disease. This results in reduced quality of life of patients, accelerated decline of lung function, and increased mortality rate of hospitalized patients (Baqdunes et al., 2021; Celli et al., 2021). Presently, there is no effective treatment for AECOPD; therefore, exploring effective prevention and treatment of COPD is one of the most urgent demands of the medical field worldwide.

The respiratory tract constantly exchanges gases with the environment; hence, it is also a system with bacterial colonization. Studies on respiratory microbiota remain in the initial stages. Reportedly, the pulmonary microbiota is closely related to the host’s autoimmune function and participates in the regulation of the immune microenvironment (Cao et al., 2023; Wu et al., 2023). The lungs were presumed to be sterile in healthy individuals; however, owing to the continuous development of medical science and technology, 16S rRNA sequencing has revealed microbial communities detected in the lungs of healthy individuals (Ramsheh et al., 2021; Yagi et al., 2021). The human microbiome includes all forms of microorganisms and their genomes residing within the body of an individual at a specific time, such as in the gut and other mucosal surfaces including the skin, mouth, airways, and vagina (Anand and Mande, 2018, Shi et al., 2021). Ecological imbalance refers to any compositional changes in the microbiome compared with that of healthy individuals (Shi et al., 2021). The low diversity of microbial communities indicates ecological imbalance (Valdes et al., 2018), whereas high diversity is often associated with health and temporal stability (Leitao Filho et al., 2019; Vaughan et al., 2019; Shi et al., 2021).

SJQJD is a medicinal formulation composed of 30 g of mori cortex, 15 g of chrysanthemi indici flos, 40 g of semen benincasae, 20 g of trichosanthis pericarpium, 20 g of pheretima, 20 g of fritillariae cirrhosae bulbus, 50 g of phragmitis rhizoma, 150 g of plantaginis semen, 20 g of concretio silicea bambusae, and 10 g of glycyrrhizae radix et rhizoma. SJQJD exerts considerable clinical effects on patients with COPD presenting phlegm-heat obstructing lung (Yee et al., 2022); however, the specific mechanism underlying SJQJD-mediated treatment of COPD remains unclear. Herein, we constructed a COPD rat model and investigated the effects of SJQJD on the pulmonary microbiota of COPD rats through 16S rRNA sequencing. Modern pharmacology indicates that the extract of mori cortex has a regulatory effect on oxidative stress (Zhai et al., 2022), chrysanthemi indici flos, trichosanthis pericarpium, pheretima, fritillariae cirrhosae bulbus, phragmitis rhizoma all exhibit anti-inflammatory activity (Park et al., 2016; Liu et al., 2020; Tian et al., 2020; Li et al., 2022; Liu et al., 2024), plantaginis semen has the function of regulating lipid metabolism and immune response (Sun et al., 2019; Ren et al., 2021), glycyrrhizae radix et rhizoma has anti-inflammatory and detoxifying effects (Li et al., 2019; Jiang et al., 2022). These physiological processes are involved in various stages of physiological pathology. However, there is currently limited research by semen benincaae and concretio silicea bambusae.

COPD is a chronic inflammatory disease characterized by persistent restriction of the small airways, and it often affects multiple systems. Studies predict that because of the increasing number of smokers and population aging, the annual COPD-associated mortality and number of patients may exceed 5.4 million (GBD 2017 Causes of Death Collaborators, 2018) by the 2060s. Acute exacerbation, leading to frequent medical visits, hospitalizations, and changes in medication regimens, is a major cause of mortality in patients with COPD (Wu et al., 2014; Vogelmeier et al., 2017; Hua et al., 2020; Li et al., 2021). Microbial cultures indicate that the lung microbiota is related to COPD pathogenesis (Shi et al., 2021), and the advances in metagenomic technologies have further validated this conclusion (Karakasidis et al., 2023).

SJQJD is a hospital-prepared medication formulation reviewed by the drug regulatory authority. Clinical studies have shown the good therapeutic effects of SJQJD when used in combination with Western medicine to treat phlegm-heat obstructed lung-type community-acquired pneumonia. Reportedly, the combined treatment of SJQJD with Western medicine for bronchiectasis can effectively improve the lung function, forced vital capacity (FVC), forced expiratory volume in the 1^st second (FEV1), and FEV1/FVC levels of the patients, with a total effective rate of 97.50%, compared with 85.00% in the control group (P < 0.05) (Dong et al., 2018). Additionally, clinical research on patients with phlegm-heat congested lung-type AECOPD has shown (Huang et al., 2021) that after treatment with SJQJD in combination with Western medicine, the T lymphocyte subgroup cluster of differentiation (CD)4⁺ and the CD4⁺/CD8⁺ ratio increased, compared with those before the treatment, and CD8⁺ reduced, indicating the significantly better optimization in the combined treatment group than that in the Western medicine control group (P < 0.05). This suggested that SJQJD might improve the immune function of patients, thereby enhancing their resistance. These findings imply that SJQJD may exert its therapeutic effect on COPD by altering the lung microenvironment and consequently modulating the lung microbiota.

Herein, a COPD rat model was constructed through a combined approach of cigarette smoke exposure and intratracheal LPS instillation, which is a widely used model for COPD. The COPD model group showed structural disorder with considerable inflammatory cell infiltration and epithelial goblet cell proliferation. However, the SJQJD administration reversed these phenomena, indicating its interventional effects on COPD. Moreover, SJQJD improved pulmonary inflammation.

The lung microbiome plays an important role in maintaining stability within the lungs. The airways of patients with COPD often harbor Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis, which in severe cases can be colonized by Klebsiella pneumoniae, Pseudomonas aeruginosa, and other Gram-negative bacteria. Various factors affect the composition of the respiratory microbiota, including the anatomy of the airways, gender, age, and the immune function of the host (Whiteside et al., 2021). In healthy individuals, the lung microbiota is transient and can be regulated by normal lung defense mechanisms, such as bronchial epithelial cilia movements, coughing, and the immune function of the host. Under healthy conditions, the regional growth conditions generally do not support the extensive proliferation of bacteria, resulting in relatively fewer bacteria. However, inflammatory responses increase the vascular permeability of the airways, providing abundant nutrients, such as amino acids, vitamins, carbon sources, and iron, for bacterial reproduction. Inflammation damages epithelial cells, exposing the basement membrane matrix and promoting bacterial adhesion. Similar to the gut microbiota, dysbiosis of the lung microbiota promotes the persistent progression of COPD (Bowerman et al., 2020). Reduced microbial diversity has been associated with COPD exacerbation events (Sze et al., 2012; Wang et al., 2019; Enaud et al., 2020; Su et al., 2022). Herein, the results showed that the microbial abundance and diversity in the COPD model group were significantly reduced, and SJQJD could considerably reverse this phenomenon, suggesting its role in improving the lung microbiota.

The family Mycoplasmataceae includes prokaryotic bacteria such as Mycoplasma and genital Ureaplasma that are pathogenic to humans (Wood et al., 2021). Reportedly, mycoplasmas are one of the common pathogens in patients with COPD (14%) (Lieberman et al., 2001, 2002). Mycoplasmas can evade the host immune system, induce apoptosis, generate free radicals, and cause oxidative-reductive imbalance in the cellular glutathione potential through pro-inflammatory cytokines, thus leading to AECOPD (Sessa et al., 2009; Papaetis et al., 2010). The family Bacillaceae includes rod-shaped, endospore-forming, Gram-positive bacteria (Liu et al., 2015). They are widely found in nature, including both pathogenic and beneficial strains (Hathout et al., 2000). However, their specific role in COPD remains unelucidated. Reportedly, the increase of Bacillus in the mouse lungs can aggravate local inflammatory response, resulting in more severe pulmonary emphysema (Richmond et al., 2018), which suggests that Bacillus may be a risk factor for COPD. Moreover, a considerably higher population of Bacillaceae has been reported in the rat lungs treated with particulate matter 2.5, a COPD-inducing factor, compared with that in the control (Laiman et al., 2023). Furthermore, lower levels of Bacillus have been detected in the sputum of patients with COPD (Simpson et al., 2016), indicating that Bacillus may play a protective role in COPD. The results of this study indicated a low abundance of Bacillaceae in the COPD model, whereas it was considerably higher in the control and SJQJD treatment groups, suggesting that Bacillaceae may have a role in combating COPD. Reportedly, most members of the Lachnospiraceae family in the gut are associated with decreased lung function; however, the abundances of some members are markedly reduced in COPD (Bowerman et al., 2020; Chiu et al., 2021). To date, only a few studies are on the distribution and role of Lachnospiraceae in the lungs. Herein, we discovered Lachnospiraceae to be a marker of the microbiota, with a high abundance in the control and SJQJD groups and a low abundance in the model group, suggesting the regulatory role of its members in COPD in the lungs. Lachnospiraceae members can metabolize dietary fiber into short-chain fatty acids (SCFAs), and the SCFA levels are positively correlated with the severity of COPD because of their participation in the maturation process of immune cells, which then exert local and systemic anti-inflammatory effects (Jang et al., 2020; Song et al., 2023). The above evidence suggests that Lachnospiraceae likely regulate the pulmonary microenvironment and local immune function through their metabolic products.

Furthermore, our study only presented the above results at the animal level. The identification of biomarkers still needs further validation in clinical human specimens. In addition, this article also has certain limitations, as it only observed changes in lung microbiota and did not further verify whether these changes will be involved in the occurrence and development of COPD, as well as the specific mechanisms involved in the process. These are the topics that we need to delve deeper into in the future.

The findings of this study show that SJQJD can improve COPD in rats. Pulmonary microbiome analysis combined with machine learning identified Mycoplasmataceae, Bacillaceae, and Lachnospiraceae as potential key biomarkers for SJQJD intervention in COPD; however, more in-depth studies are required to elucidate their specific mechanisms and clinical significance.

The 16S sequencing data involved in this article has been uploaded to the figshare database, which can be obtained through the link: https://figshare.com/articles/dataset/16s_sequencing_data_of_Sangju_Qingjie_Detection_SJQJD_on_pulmonary_microbiota_in_COPD_rats/25156670.

The animal study was approved by Experimental Animal Ethics Committee of Nankai Hospital in Tianjin. The study was conducted in accordance with the local legislation and institutional requirements.

ZL: Conceptualization, Data curation, Visualization, Writing – original draft. YH: Conceptualization, Data curation, Project administration, Writing – review & editing. CH: Writing – original draft. XL: Writing – review & editing.