The effect of scutellaria baicalensis and its active ingredients on major depressive disorder: a systematic review and meta-analysis of literature in pre-clinical research

Background: Scutellaria baicalensis, the dry root of scutellaria baicalensis georgi, is a traditional Chinese medicine with long. In clinic, scutellaria baicalensis is commonly used in prescription for the treatment of depression. Additionally, numerous pre-clinical studies have shown that Scutellaria baicalensis and its active constituents are effective for depression. In this study, we aims to systematically review the roles of scutellaria baicalensis in depression and summarize the possible mechanism. Methods: A systematic review and meta-analysis were conducted to analyze the existing studies on the effects of scutellaria baicalensis on depression in animal models. Briefly, we searched electronic databases including Pubmed and Embase for preclinical trial studies from inception to September 2023. The items in each study were evaluated by two independent reviewers, and meta-analyses were performed on scutellaria baicalensis-induced behavioral changes in the study. Finally, random effects model is used to collect data. Results: A total of 49 studies were identified, and 13 studies were included in the final analysis. They all reported the different antidepressant effects of scutellaria baicalensis and the underlying biological mechanisms. Among the included 13 studies, the results of eight articles SPT[SMD = −2.80, 95%CI(-4.03, -1.57), p < 0.01], the results of the nine articles OFT[SMD = −2.38, 95%CI(-3.53, -1.23), p < 0.01], and the results of two articles NSFT[SMD = −2.98, 95%CI(-3.94, -2.02), p < 0.01] were significantly different from the control group. The risk of bias was moderate in all studies, however, there was a significant heterogeneity among studies. Conclusion: These results preliminarily suggest that scutellaria baicalensis can alleviate depressive behaviors and modulate underlying mechanisms, which is expected to be a promising antidepressant.


Introduction
Depression (major depressive disorder), a common mental disease, is manifested by persistent feeling of sadness and loss of interest.This kind of disease can disturb person's ability to work, study, sleep, eat, and enjoy once pleasurable activities.What's more, people with depression possess cognitive behavioral, social dysfunction, and even suicide tendency in severe cases (Vos et al., 2017;Dwyer Jennifer et al., 2020).In recent years, its commonly defined that depression is global burden of disease with high mortality and morbidity, and high disability rate.In America, In 2017, the World Health Organization revealed that there were more than 300 million depression patients in the world, accounting for about 4.4% of the global population (World Health Organization WHO, 2017).Depression accounts for a large share of the global disease burden, with approximately 264 million people globally estimated to suffer from the condition (World Health Organization (WHO)).In China, a cross-sectional epidemiological study from 2013.07 to 2015.03 revealed that the economic burden of China is about 2.5 trillion US dollars, accounting for 10% of the total global disease burden (Jin et al., 2021).A cross-national comparison reported that lifetime prevalence estimates of major depressive disorders ranged from 1.0% (Czech Republic) to 16.9% (United States), with midpoints at 8.3% (Canada) and 9.0% (Chile), while the 12-month prevalence estimates ranged from 0.3% (Czech Republic) to 10% (United States), with midpoints at 4.5% (Mexico) and 5.2% (West Germany) (Kessler Ronald and Bromet Evelyn, 2013).Another cross-sectional survey analysis conducted in USA also pointed that individuals with depression diagnosis have substantial humanistic and economic burden (Jain et al., 2022).In 2015, The World Health Organization ranked depression as the single largest contributor to global disability, accounting for 7.5% of all years lived with disability (World Health Organization WHO, 2017).These epidemiological studies highlight that depressive disorder is a current issue for public health and will be a future challenge.
More and more studies on depression have shown that numerous factors, such as age, genetics, biology, and environment, influence depression morbidity and mortality (Hammen, 2018;Barrenetxea et al., 2022;Mars et al., 2022).Koh et al. reported that the incidence of population (70-80 years) was higher when compared with the population (60-69) (Barrenetxea et al., 2022).Bai et al. also revealed that in the last 3 decades, the incidence rate of depression among older individuals has increased though the age-standard incidence rate of depression has declined in China (Bai et al., 2022).In addition, the impact of other diseases such as cardiovascular diseases, obesity, and hypertension can not be ignored in recent years (Li et al., 2022).Indeed, there is a bidirectional association between cardiovascular diseases (Bobo et al., 2020), obesity (Luppino et al., 2010), hypertension (Jokela et al., 2014) and anxiety.In Korea, Park et al. found that depression increased the risk of ischemic heart disease by 38% and cerebrovascular disease by 46% among older adults through retrospective cohort study (Park et al., 2020).In addition, people with cardiovascular disease have a significantly increased risk of depression (Lesman-Leegte et al., 2009).An overview of a metaanalysis showed that Obese adults were 55 percent more likely to be depressed, and depressed adults were 58 percent more likely to be obese (Luppino et al., 2010).Lu et al. reported that incidence of depression in China were more high in women than that in men, unemployed people than employed, and those who were separated, widowed, or divorced than people who were married or cohabiting (Jin et al., 2021).
Presently, the clinical treatment strategy for depression contains first-line antidepressant drugs, cognitive-behavioral therapy, and physiotherapy (Kverno and Mangano, 2021).And the first-line antidepressant drugs includes selective serotonin reuptake inhibitor (SSRIs, fluoxetine, paroxetine, and sertraline), serotonin and noradrenaline reuptake inhibitor (SNRIs, venlafaxine, and duloxetine), noradrenergic and specific serotonergic antidepressants (NaSSA, mirtazapine), serotonin receptor antagonists and reuptake inhibitors (SARIs, trazodone), monoamine oxidase inhibitor (MAOI, moclobemide), and tricyclic antidepressants (TCA, imipramine) (Plenge et al., 2021).What's more, ketamine (Nikayin et al., 2022) and nitrous oxide (Quach et al., 2022) are also used for the resistant depression.However, the cure rate of first-line antidepressants is low, and the adverse reactions of these drugs are obvious, and a response to conventional antidepressants requires several weeks of treatment and carries a non-negligible risk of suicide.Therefore, there is a major medical need for novel and improved antidepressant treatments.Acupuncture and herbal medicine were also used for the treatment of depression, and herbal medicine were shown to had superior efficacy and safety profiles (Chen and Shan, 2019).
Scutellaria baicalensis georgi is a herbal medicine frequently used in China, and its dry root (common name: Huang-Qin in Chinese) is widely used in prescription for the treatment of depression (Zhang et al., 2015;Lee et al., 2017).The beneficial effects of the root are due to different bioactive compounds in the brain, some of which are able to cross the blood-brain barrier (BBB).As far as it concerns scutellaria baicalensis, this corresponds to the two main flavonoids, namely, baicalin and baicalein, being purified from the plant's dry roots (Wang et al., 2018;Zhao et al., 2019).Previous studies have shown that scutellaria baicalensis has a wide range of pharmacological effects including anti-inflammatory, antioxidative, neuroprotective, antibacterial, and anti-tumor activities (Zhao et al., 2016;Zhou et al., 2016;Zhao Yikai et al., 2018;Yoon et al., 2020).It has been found that Scutellaria baicalensis and its main components baicalin and baicalein have significant antidepression effects and mechanism involves many aspects, such as improving the level of monoamine transmitter brain neurotrophic factor, regulating the HPA axis, anti-inflammation, anti-oxidation and promoting neurogenesis (Hai-Yang et al., 2016;Pazini Francis et al., 2017).In addition, as a traditional medicine, Scutellaria baicalensis has produced neuroprotective effects in various models of Parkinson's disease (Mu X. et al., 2011), Alzheimer's disease (Zhao J. et al., 2018)and so on.Recent studies have shown that baicalin and baicalein, in addition to protecting dopaminergic neurons from mitochondrial and oxidation-related toxicity, may also have a beneficial effect on DA-related brain diseases by increasing DA levels in the brain (Im H. I. et al., 2005;Zhao J. et al., 2018).
At present, accumulating evidence from the pharmacological effect indicated that scutellaria baicalensis may have great potential in treating depression.Nevertheless, up to now, the pre-clinical studies on scutellaria baicalensis for depression have not been systematically evaluated and summarized.In this study, we conducted a rigorous and comprehensive systematic review and meta-analysis of recent literature on the treatment of depression model animals by scutellaria baicalensis, and explored different behavioral changes and potential mechanisms, aiming to provide evidence and guidance for clinical practice.
2 Materials and methods Subsequently, the two researchers (Ying Ma and Xun Zhou) independently reviewed the title/abstract related to the topic.A full-text read was also performed to find the potential documents that met the eligibility criteria.Importantly, any disagreements between the two researchers were resolved through negotiation or thirdparty consensus.

Inclusion and exclusion criteria
Studies were be included when they meet the following criteria: (1) in vivo studies on animal subjects; (2) the animal disease model was depressive disorder model; (3) animals were treated with scutellaria baicalensis or its active components baicalin and baicalin; (4) the data included in the literature were represented by mean and standard (SD) or can be converted to mean and SD.Exclusion criteria are as follows: (1) other types of studies (in vitro studies, case reports, clinical trials, reviews, abstracts or comments), (2) combination with other compounds, (3) not depressive disorder model, ( 5) studies with insufficient data, (6) the sample size of control group and scutellaria treatment group was less than three animals.( 7) plagiarism or duplicate publication of literature.

Data extraction
General data, intervention measures, efficacy indicators, test results and other data of patients were independently extracted by two researchers (Ying Ma and Xun Zhou) according to a unified table and cross-checked.The following information for each study include: (1) the year of publication of the first author's name; (2) characteristics of the animal, including species, number, sex, weight, etc.; (3) the establishment of depression model and anesthesia used in the model; (4) Characteristics of intervention, including dose and route of administration; (5) main outcome indicators and differences between groups.If the main data were lost or displayed in a graphical manner, we would contact the publishers to obtain the original data.The values in the graph were measured by digital ruler software without receiving any reply from the author.

Quality assessment of included studies
The methodological quality of the included studies was evaluated by independently two investigators (Ying Ma and Xun Zhou) according to the Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies (CAMARADES)'s risk of bias tool (Macleod et al., 2004).The terms for quality assessment included 1) peer reviewed publication; 2) control of temperature; 3) random allocation to groups; 4) blinded induction of depression; 5) blinded assessment of behavioral outcome; 6) use of anesthetic without significant intrinsic neuroprotective activity; 7) calculation of the sample size necessary to achieve sufficient power; 8) appropriate animal model which uses animals without relevant comorbidities (aged, diabetic, or hypertensive); 9) compliance with animal welfare Regulations; 10) statement of potential conflict of interests.Any disagreements between the two researchers were resolved through negotiation or third party consensus.

Statistical analysis
Meta-analysis was performed using Review Manager (RevMan v5.3) software.Outcome measures were all expressed as continuous Summary of the process for identifying candidate studies.3 Results

Study selection
In the initial search of databases, 373 literature were retrieved.After eliminating redundant and irrelevant articles, 84 records remained.Subsequently, the investigators screened the titles and abstracts, and 26 studies were exclude.After reviewing the full-text articles carefully, 10 studies were excluded for at least one of the following reasons: (1) metabolites were studied; (2) no relevant outcome; (3) review article.Ultimately, 13 studies were included in this meta analysis.The search strategy built on this study using the PRISMA method (Moher et al., 2009) is described in Figure 1.

Characteristics of included studies
The basic characteristics of the 13 studies were shown in Table 1.The meta-analysis included 270 animals (136 in the model group and 134 in the Scutellaria baicalensis treatment group) in 13 studies.

Methodological quality
The assessment of the quality of these studies included in these work was conducted from CAMARADES.As shown in table 2, the quality score ranged from 6 to 7, with median of 6.615.All of the studies have been peer-reviewed and reported.All studies have reported that animals were randomly divided into groups and blinded assessment of behavioral outcome.In addition, there were no study reported blinded induction of depression.

Effects of scutellaria baicalensis on depression by OFT analysis
In OFT, meta-analysis of nine studies (Xiong et al., 2011;Lee et al., 2013;Zhang et al., 2016;Zhang et al., 2018;Zhang Ruyi et al., 2019;Zhong et al., 2019;Fan et al., 2020;Jia et al., 2021;Zhao et al., 2021)had a total sample size of 170, of which 84 animals received Scutellaria baicalensis and 86 received a vehicle or saline treatment.There was Statistically significant between groups in the number of crossings and rearing, indicating that Scutellaria baicalensis treatment can ameliorate the frequency of crossing and rearing compared with the control group [SMD = −2.38,95%CI(-3.53,-1.23), p < 0.01], as shown in Figure 2C.

Discussion
Depression is a common mental disease associated with high morbidity and huge social burden.Numerous preclinical studies have shown that Scutellaria baicalensis and its active constituents are effective for depression.The aim of this study is to systematically review the roles of scutellaria baicalensis in depression and summarize the possible mechanism.To our knowledge, it is a first systematic review and meta-analysis of preclinical studies on the efficacy of Scutellaria baicalensis and its main components in animal depression model.The results indicated that Scutellaria baicalensis can remarkably safeguard against depression evidenced by improved behavioral changes.And this activities were associated with the regulation of Scutellaria baicalensis on inflammatory responses, oxidative stress, apoptosis, and neurotransmitters production via modulating TrkB-BDNF, PI3K-AKT, MAPK and NF-κB pathways.
In this work, 13 studies were included to assess the efficacy of scutellaria baicalensis on depression.Chronic unpredictability mild stress, corticosterone, rotenone-induced depression model, experimental autoimmune prostatitis (EAP)-induced depression mice model, olfactory bulbectomy (OBX) depression mice model and repeated restraint stress-induced depression rat model were used to study the antidepressant effect of Scutellaria baicalensis, while sucrose preference test (SPT), open field test (OFT), Morris water maze test (MWM), tail suspension test (TST), novelty suppressed feeding test (NSFT), and forced swimming test (FST) were adopted to evaluate the efficacy.
So far, the anti-depressive actvities of scutellaria baicalensis are welly studied, and the commonly used animal models are CUMS (Xiong et al., 2011;Zhang et al., 2016;Zhang et al., 2018;Zhang Ruyi et al., 2019;Liu et al., 2019;Jia et al., 2021)and CORT (Zhang Kuo et al., 2019;Li-Ting et al., 2019;Fan et al., 2020), etc., and one of the criteria to evaluate the success of depression model and the efficacy of anti-depression is behavioral test.Sucrose preference test for evaluating degree of pleasure lack of mice, open field test reflect the spontaneous activity in mice and explore the behavior, forced swimming test and tail suspension test reflects the behavior of the mice desperation, reaction ability of learning and memory in mice water maze experiment, while novelty suppressed feeding test, the variation of the lack of animal euphoria (Lu et al., 2016).In a mouse model of chronic cort-induced depression, baicalin significantly ameliorates behavior change by reducing the time spent in the central area of the open field test and the time spent in the cross maze test with open arms, and increasing the immobile time in the tail suspension test and forced swimming test.(Zhang et al., 2016;Zhang Kuo et al., 2019).On the other hand, Scutellaria baicalensis alleviated depression-like behavior by increasing sucrose consumption and reducing the immobile time of tail suspension and forced swimming tests in mild stress chronic mouse model (CUMS) (Li-Ting et al., 2019;Liu et al., 2019;Zhong et al., 2019).
These results resembled theoretical study.Studies have reported that scutellaria baicalensis may induce the release of monoamine (DA) and enhance GABA-induced signal transduction, thereby increasing cAMP/pERK and PI3K/pAKT signals, and promoting the synthesis and neurogenesis of neurotrophic factors (BDNF and NGF) (Im Heh-In et al., 2005;Mu Xin et al., 2011).Secondly, scutellaria baicalensis plays an anti-inflammatory role by decreasing the levels of inducible nitric oxide synthase, NF-κB and pro-inflammatory cytokines TNF-α, IL-6 and IL-1β (Ma et al., 2015).It is reported that scutellaria baicalensis can also improve mitochondrial membrane potential depolarization and ATP production, and increase AMPK to enhance mitochondrial autophagy and mitochondrial biogenesis, thus playing a protective role in mitochondria (Zhang et al., 2017).It also lowers levels of reactive oxygen species and nitrogen species, increases superoxide dismutase, glutathione, glutathione peroxidase and catalase activities, heat shock protein 70, heme oxygenase-1 and thioredoxin levels, and ultimately reduces lipid peroxidation.The content of malondialdehyde and lipoxygenase are decreased by Scutellaria baicalensis.It also inhibited p-P38, Bax/Bcl-2 ratio, caspase 3, caspase 6, caspase 9, and cytochrome C release, thereby inhibiting apoptosis (Liu et al., 2012;Wang et al., 2013;Li et al., 2019).
This study was screened strictly in accordance with the inclusion criteria, exclusion criteria and literature quality scoring criteria, but there may still be the following limitations that may affect the accuracy of the study: First, the databases searched in this review were all in English, so there may be some deviations; Second, the methodological quality of the included studies was moderate, with none of the studies reporting the blinded induction of depression and the sample size needed to calculate it to obtain sufficient power; Third, the lack of negative studies may lead to overestimation of the true role of Scutellaria baicalensis.Fourthly, in the included studies, there were significant differences in depression modeling method and time, dosage and treatment time of scutellaria baicalensis.

Conclusion
In this preclinical systematic review, scutellaria baicalum can improve the symptoms of anhedonia, reduce the degree of behavioral despair, improve the cognitive ability of mice and play an anti-depressive effect in experimental depression.The mechanism mainly includes antioxidant, anti-inflammatory, neurotransmitter regulation, and inhibition of apoptosis.Therefore, scutellaria baicalensis may be a candidate for further clinical trials of depression.

FIGURE 1
FIGURE 1 , immobility time was dramatically reduced in the Scutellaria baicalensis group versus

FIGURE 2
FIGURE 2 Forest plot of studies investigating the effect of Scutellaria baicalensis on animal behavior.The protective effects of Scutellaria baicalensis on animal behavior by (A) SPT, (B) TST, (C) OFT, (D) NSFT, (E) MWM, and (F) FST analysis.

TABLE 1
Characteristics of studies included in systematic review of antidepressant effects of Scutellaria baicalensis.

TABLE 1 (
Continued) Characteristics of studies included in systematic review of antidepressant effects of Scutellaria baicalensis.CI).If there was no statistical heterogeneity among studies (p ≥ 0.10, I 2 ≤ 5%), fixed-effect model was used for analysis.Otherwise, random effect model is used to analyze.Probability value p < 0.05 was considered statistically significant.

TABLE 2
Quality assessment of studies included in systematic review of antidepressant effects of Scutellaria Baicalensis following modified scale of CAMARADES.