Depression is a debilitating neuropsychological disorder that impairs daily functioning and is characterized by a constant sense of melancholy, loss of interest, and intellectual disability. Globally, major depression disorder (MDD) and dysthymia are responsible for approximately 46.9 million disabilities annually, with over 800,000 suicidal deaths mostly accompanied by neurological and psychiatric disorders such as MDD (Li et al., 2022a; Moitra et al., 2022). The number of patients with depression reached 542 million in 2015, with an 18.4% global increase between 2005 and 2015 (Disease and Prevalence, 2016). Due to the effects of coronavirus disease 2019, the number of patients with depression worldwide increased by 27.6% and depression is estimated to become the leading cause of death by 2030 (COVID-19 Mental Disorders Collaborators, 2021). Therefore, discovering efficient and safe treatment modalities is currently highly needed. There are three main interventions for treating depression that are currently used: 1) pharmaceutical antidepressants, such as SNRIs and SSRIs, among others; 2) research-based psychotherapy, such as cognitive behavioral therapy and interpersonal psychotherapy; and 3) physical therapy, such as vagus nerve stimulation or repeated transcranial magnetic stimulation. However, about one-third of patients still do not achieve remission after four consecutive antidepressant trials, and at least 50%–80% of patients still exist recurrence, with a progressive increase in severity and frequency, this mainly attributed to increased resistance in depression (Borbely et al., 2022). Furthermore, patients’ resistance to antidepressants is often accompanied by high levels of serum inflammatory factors such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) (Beurel et al., 2020). Heightened inflammation can also exacerbate mood disorders such as anxiety and anhedonia, as well as somatic symptoms such as insomnia and gastrointestinal disorders (Kiecolt-Glaser et al., 2015). Thus, it is still necessary to find or develop antidepressant treatments with high-efficiency and fewer side effects.

Traditional Chinese Medicine (TCM) operates on the understanding that the human body is an organic whole, and the viscera coordinate with each other in function and influence each other in pathology (Xiang-yu et al., 2021). The pathogenesis of depression as viewed in TCM is a disorder of the Shao Yang pivot and dysfunction of Yin and Yang. Shao Yang is the pivot for the rise and fall of the Qi movement; Shao Yang dysfunction leads to depression and insomnia. When the Shao Yang channel restrains the Qi, the body will feel cold and physically heavy and patients will show appetite loss (Hanying et al., 2022). CLM is a TCM prescription derived from “Shang Han Lun” that is prescribed to treat mental diseases caused by the imbalance of the pivot of Shao Yang and the loss of Yin and Yang. It has the effects of mediating the Shao Yang pivot and tranquilizing the mind (Wan et al., 2021). Numerous studies have shown that CLM contributes to improvements in dementia, insomnia, anxiety, and depression (Yuanwen et al., 2022). Although the efficacy and safety of CLM for the treatment of depression have been evaluated in many studies, determining a reliable basis for evidence-based medicine is difficult due to deviations in the included studies, literature updates, and inconsistencies in patient grouping and comorbidities (Li et al., 2018; Wan et al., 2021). The potential mechanism behind CLM’s antidepressant effect may be related to the inhibition of N-methyl-D-aspartate (NMDA) receptors to increase hippocampal synaptic plasticity, positively regulation of neuronal apoptosis, and inhibition of neuroinflammation (Liu et al., 2010; Wang et al., 2018; Lizhi et al., 2021). However, owing to the intricacy of the compound constituents, particularly the molecular target mechanisms of its active substances, the mechanisms associated with its antidepressant effect remain unclear. As a novel discipline, network pharmacology can effectively and systematically explore correlations between traditional Chinese medicine substances, targets, and diseases by constructing a variety of network models comprehensively using multiple platforms and technologies to help explore potential mechanisms (Chen et al., 2018).

Based on the above background, CLM has a wide range of antidepressant efficacy, but with still a lack of clinical evidence, and its antidepressant mechanism is still unclear due to the complexity of TCM compound ingredients. Therefore, this study aimed to assess clinical evidence on the efficacy of CLM in patients with depression using a meta-analysis and to explore its underlying antidepressant molecular mechanisms via network pharmacology.

At present, the pathological mechanisms of depression mainly involve the monoamine hypothesis, hypothalamus–pituitary–adrenal axis hyperactivity, neuroplasticity and neurogenesis, structural and functional brain changes, and inflammation (Malhi and Mann, 2018). However, due to the unclear pathophysiological mechanisms of depression, one-third of patients face treatment resistance or adverse reactions to common treatments, and the treatment of depression still faces challenges (Dodd et al., 2021). CLM is derived from “Shang Han Lun” and has a significant effect on depression. However, due to the complexity of its components, the mechanism of action of this prescription has not been fully clarified. The results of present study indicated that the antidepressant efficacy of CLM, whether administered alone or in combination with antidepressants, was significantly higher than that of antidepressants alone. In addition, whether in CLM alone or CLM + SSRI/SNRI, the symptoms of depression, anxiety, and insomnia in patients with depression were significantly improved comparing antidepressants alone. CLM and CLM + SSRI also showed fewer adverse reactions than SSRI alone. Five compounds in CLM and seven of its key targets were shown to be related to antidepressant activity in the present analysis.

CLM has extensive neural activities in the treatment of depression, anxiety, insomnia, and neurocognitive disorders (Niitsu et al., 2013). A meta-analysis of CLM’s efficiency and safety in treating post-stroke depression revealed that, regardless of the length of the treatment period, CLM showed better efficacy than an antidepressant group. Additionally, in the group receiving CLM combined with pharmaceutical antidepressants, the incidence of adverse reactions such as abnormal blood or urine routine tests, abnormal liver function, sleeplessness, and digestive tract pain was dramatically decreased (Wan et al., 2021). In addition, a correlation has been shown between depression, anxiety, and insomnia; the association between insomnia and feelings of self-disgust was fully mediated by anxiety and depression (Ypsilanti et al., 2018). This means that a good treatment strategy for patients with depression seems to be relieving anxiety and insomnia while adjusting mood. In the present findings, compared with antidepressants, both CLM alone and combined with SSRI/SNRI markedly reduced the scores of HAMD and SDS. For anxiety and insomnia, we conducted a meta-analysis of HAMA, SAS, and PSQI scores, results indicated that the synergistic effect of CLM and SSRI was significantly better than that of SSRI alone. In addition, due to the limited literature on CLM alone and CLM + SNRI, the synergistic effect of CLM alone or with SNRI may need further exploration. However, for overall efficacy in anxiety, CLM alone or in combination is not inferior to antidepressants alone. In terms of adverse reactions, whether CLM alone or in combination with SSRI, the incidence of adverse reactions is significantly fewer than that of SSRI alone. It is worth noting that the incidence of adverse reactions in CLM combined with SNRI is the same as that of SNRI alone, which may be the reason for only including one trial. Therefore, CLM could not only improve the symptoms of depression, anxiety, and insomnia, but can also reduce the incidence of adverse responses caused by commonly used antidepressants, especially in combination with SSRI.

Depression and inflammation are intertwined; heightened inflammation exacerbates not only physical symptoms such as pain sensitivity, fatigue, and anhedonia but also psychological symptoms such as negative mood, loss of appetite, and feelings of inferiority (Kiecolt-Glaser et al., 2015). Levels of proinflammatory cytokines in peripheral blood were shown to be significantly increased in patients with major depressive disorder, such as IL-6, TNF-α and IL-1β (Howren et al., 2009; Dowlati et al., 2010; Liu et al., 2012). Moreover, nonsteroidal anti-inflammatory drugs could significantly reduce depressive symptoms compared to placebo treatment (Kohler et al., 2014). Therefore, anti-inflammatory treatments may be effective for depression. The present results indicated that CLM dramatically decreased the levels of TNF-α and IL-6 in the peripheral blood of patients with depression compared to antidepressant treatment groups.

In order to further investigate the aforementioned putative mechanisms of CLM’s anti-depressant effects, network pharmacology was conducted. We intersected 416 therapeutic targets from 1490 depression targets and 2356 targets of CLM compound components. According to the H-C-T network, the top five active ingredients were stigmasterol, quercetin, β-stiosterol, coumestrol, and stepholidine. Recent research has shown that oral and intraperitoneal treatment of stigmasterol and β-stiosterol significantly reduced immobility time in tail suspension and forced swimming tests in rat models of depression, and its antidepressant activity might be mediated by the glutamatergic systems (Zhao et al., 2016; Ghosh et al., 2022). Quercetin has been reported to inhibit inflammation and attenuate depression-like behavior by regulating PI3K/AKT/NF-κB and promoting mitophagy in a lipopolysaccharide-induced mouse model of depression (Han et al., 2021; Sun et al., 2021). Monoamine oxidase A inhibitors, as third-line antidepressants, are widely used in clinics, and coumestrol has been proven to be a selective and competitive monoamine oxidase A inhibitor (Seong et al., 2022). As a specific dopamine receptor D1 agonist, stepholidine could activate the PKA/mTOR pathway to upregulate the expression of synaptogenesis-related proteins and exert antidepressant effects (Zhang et al., 2017). The above research provides a pharmacological basis for the clinical efficacy of CLM in depression, although the effect of CLM on depression has been revealed directly or indirectly through the above ingredients, due to the complexity of the ingredients, the specific mechanisms have not been clarified. Therefore, we assessed the relevant pathways for CLM in the treatment of depression using KEGG and GO enrichment analyses.

Research has confirmed that inflammation induced by glial cells is an important mechanism leading to depression. Neuroglial cells can regulate neuron electrical activity and even death by adjusting synaptic plasticity and integrating and transmitting synaptic information (Perez-Catalan et al., 2021). This may explain the anti-inflammatory and antidepressant mechanism of CLM, where GO analysis showed that the antidepressant effect of CLM mainly plays a protective role by regulating the inflammatory response. In addition, at the level of CC and MF, CLM mainly plays a role in synaptic spines, synapses, membrane rafts, and nuclear envelope by combining with enzymes and neurotransmitters. The present KEGG analysis of CLM also pointed to neuroinflammation, which involves the PI3K/Akt, JAK-STAT, and NF-κB signaling pathways. The PI3K/Akt signaling pathway is involved in synaptic plasticity, learning and memory, and inflammation, which are important in the pathogenesis of depression (Matsuda et al., 2019). Enzymatic activity of PI3K and Akt was shown to be decreased in patients with depression, which may lead to neuron loss, decreased neuroplasticity, and dysregulation of neurotrophic factors (Karege et al., 2011). Evidence has also shown that activation of Akt signaling can alleviate stress-induced depressive behaviors in mice by inhibiting neuroinflammation and increasing neurotrophic factors (Xian et al., 2019). Accordingly, by activating Akt signaling, CLM was shown to reverse the abnormal expression of AMPA and NMDA receptors in the prefrontal cortex of depressed mice (Wang et al., 2018). The JAK-STAT and NF-κB signaling pathways are downstream cascade signals of the PI3K/Akt pathway and both play key roles in cell proliferation, differentiation, migration, and apoptosis. The involvement of the JAK/STAT pathway in synaptic plasticity has been confirmed to depend on the activation of NMDA receptors in the hippocampal CA1 region (Nicolas et al., 2012). Therefore, we speculate that the antidepressant effect of CLM may be related to the activation of PI3K/Akt and its downstream signaling pathways, inhibition of inflammatory storms, and protection of neurons.

Notably, the therapeutic efficacy of ketamine, an NMDA receptor antagonist, has highlighted the emerging data linking the regulation of NMDA to the etiology of depression. More significantly, increases in proinflammatory cytokines (such as IL-1, IL-6, and TNF-α) have been directly associated with JAK-STAT activation. Antidepressants may work by decreasing proinflammatory cytokines via modulation of the JAK/STAT pathway, and they may also improve somatic symptoms, anhedonia, and low energy levels (Malemud and Miller, 2008). The NF-κB signaling pathway contributes to the pathogenesis of neurodegenerative diseases, with the PI3K/Akt pathway as its major upstream component (Dong et al., 2016). Activation of the PI3K/Akt signaling pathway has been reported to significantly reduce the nuclear translocation of NF-κB and the activation of microglia, thus inhibiting neuronal apoptosis and inflammation (Zhu et al., 2018). Although CLM likely exerts anti-depressant effects via the PI3K/Akt, JAK/STAT, NF-κB, or apoptosis signaling pathways, it remains urgently necessary to clarify the therapeutic targets of CLM, which may contribute to the development of novel therapeutic strategies.

Next, according to the PPI network and molecular docking analyses, MAPK3, TP53, MAPK1, STAT3, and PI3KR1 were potential antidepressant targets of CLM. Similar to the above results from the network pharmacology analysis, stigmasterol showed high binding energy with PI3KR1, suggesting that CLM alleviates depression via modulation of the PI3K/Akt signaling pathway. In summary, the above evidence suggests that CLM is a safe and effective antidepressant prescription with multiple pathways and targets. Its mechanism is likely related to the regulation of neuronal synaptic plasticity, inflammation, and apoptosis.

This study still exist limitations. The treatment time was not explored on anti-depression efficacy. Secondly, it is still shallow that the evidence for selecting serum IL-6 and TNF-α as inflammation indicators. On the one hand, it is limited by available studies, on the other hand, other indicators such as serum IL-1β and CRP also affect the resistance to antidepressants. Meanwhile, the increase in these indicators also indicates more severe disease course outcomes and more extensive somatization symptoms (Kiecolt-Glaser et al., 2015). Furthermore, the number of trials included in this study was insufficient to clearly state the specific efficacy of some subgroup analyses such as HAMA and SAS, so part results have to be roughly concluded by assessing the comprehensive efficacy of CLM alone or in combination with antidepressants. Then, part of literature included by allocation concealment and blinding is not yet clear. TCM has the characteristics of personalized treatment, which is limited to the unique odor and color, making it difficult to implement blind methods. In addition, screening the active ingredients based on OB and DL may exist inconsistency with the precise ingredients, and the predicted targets are likely to be limited by the hot spots of current research. Finally, the specific mechanism in this study still needs to be verified by further vivo and vitro experiments.

This study analyzed the effectiveness and mechanism of CLM in the treatment of depression. Our findings revealed that compared to antidepressants, CLM had better clinical efficacy and fewer side effects, especially in combination with SSRI. Its mechanism in treating depression may be related to regulating neuronal synaptic plasticity, inhibiting neuroinflammation, and improving neuronal damage. Stigmasterol, β-stiosterol, and coumestrol, three components of CLM. may play antidepressant roles via the targets of PIK3R1, MAPK3, and AKT1. The PI3K/Akt signaling pathway may be one of the main pathways for CLM to achieve its antidepressant effect.