The Important Role of Volatile Components From a Traditional Chinese Medicine Dayuan-Yin Against the COVID-19 Pandemic

Aromatic Chinese herbs have been used to prevent plagues since ancient times. Traditional Chinese medicine has unique advantages in the prevention and treatment of epidemic diseases. According to the traditional Chinese medicine treatment plan in the National COVID-19 Diagnosis and Treatment Plan (Trial Seventh Edition) of the National Health Commission, Chinese patent medicines or prescriptions rich in aromatic Chinese herbs are selected for prevention and treatment during the period of medical observation, clinical treatment, and recovery of confirmed COVID-19 patients. Some local health committees or traditional Chinese medicine administrations recommend a variety of other ways of using traditional aromatic Chinese herbs to prevent and cure COVID-19. These involve external fumigation, use of moxibustion, and wearing of sachet. The efficacy of aromatic Chinese herbs plays a decisive role in the prevention and treatment of COVID-19. The unique properties, chemical composition, and mechanism of action of aromatic Chinese herbs are worthy of extensive and in-depth experimental and clinical research. The findings are expected to provide a reference for follow-up treatment of novel coronavirus and the development of corresponding drugs. In 2003, Dayuan-Yin produced excellent results in the treatment of the SARS virus. Individually, 112 confirmed cases were administered this drug between January and April 2003, and more than 93.7% of the patients showed noticeable mitigation of the symptoms, as well as recovery. Dayuan-Yin also was selected as one of the nationally recommended prescriptions for the COVID-19. Based on the national recommendation of Dayuan-Yin prescription, this review discusses the role of volatile components in the prevention and treatment of COVID-19, and speculates the possible mechanism of action, so as to provide a basis for the prevention and treatment of COVID-19.


INTRODUCTION BIOACTIVE VOLATILE COMPONENTS OF DAYUAN-YIN
Most of the volatile components of Dayuan-Yin have been elucidated, and their structures are well established (Table 1). However, there are no data on volatile components extracted from Areca catechu L. Based on clinical evidence of therapeutic results with Dayuan-Yin, we summarized its potential bioactive volatile components in the treatment of COVID-19. The biological benefits of Dayuan-Yin seem to involve anti-inflammatory, antiviral, antibacterial, and immunomodulatory effects ( Table 2).

Anti-Viral Effect
In autopsy studies and animal models, COVID-19 manifests mainly as acute viral pneumonia leading to respiratory failure (Chan et al., 2020;Yao et al., 2020). Antiviral drugs have been used to treat common cold, fever and influenza viruses by destroying the viral surface structure and inhibiting its entry (Hsieh et al., 2012), suggesting that antiviral drugs can be used for COVID-19. Unfortunately, no specific antiviral treatment has been recommended for COVID-19 treatment because of insufficient evidence from randomized trials (Hung et al., 2020). It has been shown that many re-purposed drugs have effects against close relatives of SARS-COV-2, such as bcoronavirus, in vitro. Furthermore, lopinavir and many interferons, especially interferon beta, have moderate effects against SARS-COV in vitro and can be used in combination with ribavirin (Chen et al., 2004;Chan et al., 2013). Administration of antiviral drugs soon after symptoms appear reduces the release of virus in respiratory secretions of patients with COVID-19, thereby decreasing their infectivity to others. Targeted preventive treatment for contacts reduces their risk of infection (Welliver et al., 2001;Oriol and Bonaventura, 2020).

Anti-Inflammatory Effect
The levels of proinflammatory factors i.e. IL-2, IL-7, IL-10, GCSF, IP10, MCP1, mip1a, and TNF -a in the plasma of critically-ill patients were higher than those in plasma of patients who were not in intensive care, suggesting that "cytokine storm" is closely related to the severity of COVID-19 . Cytokine storm is a very prominent pathophysiological feature of COVID-19 infection (Lin et al., 2020). Extensive endothelial barrier disruption and uncontrolled cytokine storm promote uncontrolled inflammatory response which is the basis of the core mechanism underlying acute respiratory distress syndrome (ARDS) (Huang et al., 2017), although this phenotype varies among individuals. Experimental models of acute lung injury (ALI) and human genome-wide association studies of ARDS indicate that cytokine storm plays an essential role in the pathophysiology of ARDS ( Biondi et al., 1986;Huang et al., 2017). Moreover, the most common and severe complication of COVID-19 is ARDS (Huang et al., 2017). Therefore, an understanding of the cytokine storm that aggravates ARDS in COVID-19 may lead to early and effective intervention in critically-ill COVID-19 patients. It seems necessary to directly inhibit inflammatory response in the lungs because cytokine storm can be alleviated with inflammatory therapy (Cao P. et al., 2020). Previous studies have shown the benefits of antiinflammatory drugs in lung disease: they slow down impairment of lung function, reverse the inflammatory parameters nearly back to normal values, and improve patients' survival (Konstan et al., 2011;Lubamba et al., 2011). Ibuprofen, a popular antiinflammatory drug, is recommended for airway inflammation in cystic fibrotic lung disease (Flume et al., 2007). Studies have shown

Anti-inflammatory activity
Pogostemon cablin (Blanco) Benth. volatile oils Patchoulene: cyclin E↓, cyclin B↓, CDK1↓; the subsequent S-phase arrest, IFN-gamma↓, IL-10↓  Pogostemon cablin (Blanco) Benth. volatile oils: TNF-a↓, IL-6↓, IL-10↑, NP-SH↑ (Chen et al., 2015) Patchoulene: regulates on the balance between Nrf2 and NF-kB p65 signaling pathways (Yang et al., 2018) Patchoulene: vitro neutrophil fMLP chemotaxis↓, phagocytic activity↑; ear edema↑, myeloperoxidase (MPO) activity↑  that long-term prediagnostic use of nonaspirin NSAIDs (e.g., ibuprofen) is associated with a significant reduction in lung cancer survival (Brasky et al., 2012). In addition, barictinib, fedratinib, and ruxolitinib are active and selective JAK inhibitors which have been approved for rheumatoid arthritis and myelofibrosis. All three drugs are effective anti-inflammatory agents, and as JAK-STAT signaling inhibitors, they may be effective against the consequences of elevated levels of cytokines (including interferon-g) usually observed in patients with COVID-19 (Stebbing et al., 2020). The UK is currently conducting a randomized evaluation of COVID-19 treatment (recovery) trial, based on the announcement on June 16, 2020, that dexamethasone had been shown to significantly improve the prognosis of COVID-19 patients receiving respiratory support (Recovery, Randomised Evaluation of COVid-19 therapy trial, 2020). Dexamethasone is a glucocorticoid which can be used as a synthetic form of the natural hormone cortisol (Cain and Cidlowski, 2017). It has the same anti-inflammatory effect as cortisol. It inhibits the release of inflammatory chemokines by immune cells, thereby improving the prognosis of patients by reducing the severity of ARDS (Lester et al., 2020). In European patients, low-dose dexamethasone reduces mortality by 33% in critically patients requiring invasive ventilation (Lim et al., 2020). However, the implementation of appropriate dexamethasone use in low-and-middle-income countries has been a challenge. For example, corticosteroids may cause sepsis in some prevalent parasitic infections in Africa (Nutman, 2020). Therefore, the use of dexamethasone in African patients who have not been  b-eudesmol has two-way regulation of gastrointestinal motility, which may be anticholinergic or directly acting on gastrointestinal smooth muscle. (Wang et al., 2002) Hinesol: H + , K + -ATPase activity↓ (Kanako et al., 2000 (Guo et al., 2005) Falcarindiol inhibited DC maturation by blocking the canonical pathway of nuclear factor-kappaB and phosphorylated p38. (Mitsui et al., 2010) Falcarindiol inhibit Pseudomonas aeruginosa by repressing virulencerelated genes, including the T3SS; quorum sensing synthase genes lasIR and rhlIR; lasB; motility-related genes fliC and fliG; and phenazine synthesis genes phzA1 and phzA2.   diagnosed with COVID-19 may lead to unexpected consequences (Brotherton et al., 2020). During the treatment of COVID-19, Dayuan-Yin also reduces the severity of ARDS by inhibiting the release of inflammatory chemokines from immune cells. As a classic prescription in ancient China, Dayuan-Yin can play a safe and effective role in the treatment of respiratory infections in a more adverse environment. Thus, it can avoid such problems in a large extent. Anti-inflammatory property is widespread in various sources of volatile components. Several data have found that 1,8-cineole significantly improved lung function and health conditions, and reduced dyspnea in patients with asthma, acute bronchus, and chronic obstructive pulmonary disease (COPD). Moreover, it significantly reduced the frequency of cough in patients with acute bronchitis, and alleviated frequent exacerbations in patients with COPD and frequent exacerbations, notably (Worth et al., 2009;Worth and Dethlefsen, 2012;Fischer and Dethlefsen, 2013;Vogelmeier et al., 2018). In a mouse model of LPS-induced acute pulmonary inflammation, 1,8-cineole upregulated IL-10 in lung tissues, and decreased the expressions of TNF-a, IL-1b, NF-kB's subunit p65 and TLR4 (Zhao et al., 2014). Moreover, 1,8-cineole was shown to inhibit LTB4 and PGE2 (pathways of AA-metabolism in human blood monocytes) in bronchial asthma in vitro (Juergens et al., 1998b). In addition, 1,8-cineole decreased levels of TNFa, IL-1b, leukotriene B4, and thromboxane B2 in human blood monocytes in vitro (Juergens et al., 1998a).
Pogostone, a bioactive component extracted from Pogostemon cablin (Blanco) Benth., reduced the total population of T cells under ConA stimulation by blocking T cell proliferation via downregulation of cyclin E, cyclin B, and CDK1. Subsequent S-phase arrest inhibited the production of IFN-gamma and IL-10 . Simultaneously, pogostone pretreatment mitigated ethanolinduced gastric ulcer in rats by downregulation of IL-6 and TNFalpha, and upregulation of IL-10 and non-protein-sulfhydryl (NP-SH) groups in the gastric mucosa (Chen et al., 2015). In lung disease, pogostone exerted potent protective effects against lipopolysaccharide-induced acute lung injury in mice by decreasing TNF-a-induced cell injury in A549 cells through modulation of the balance between Nrf2 and NF-kB-p65 signaling pathways (Yang et al., 2018). Pogostone significantly inhibited the protein and mRNA expressions of proinflammatory mediators such as TNF-a, IL-6, IL-1b, NO, and PGE2. Pogostone also significantly reduced LPS-induced mortality in mice, suppressed the production of proinflammatory mediators in serum. And it attenuated liver and lung injury via downregulation of the mRNA expressions of inflammatory mediators in multiple organs due to inhibition of activation of NF-kB and phosphorylation of p38 MAPK (Li et al., 2014). Pre-treatment with pogostone markedly mitigated LPS-induced acute lung injury in mice, improved survival, attenuated histological alterations in the lungs, reduced MPO and MDA levels, decreased the wet/dry weight ratio of lungs, and down-regulated proinflammatory mediators, such as TNF-a, IL-1 beta and IL-6. Furthermore, pretreatment with pogostone enhanced the Nrf2dependent genes NQO-1, GCLC, and HO-1, but suppressed the NF-kappa B regulated genes TNF-alpha, IL-1 beta, and IL-6. The mechanism involved in the protective effect of pogostone was correlated with its regulation of the balance between Keap1-Nrf2 and NF-kappa B signaling pathways . Moreover, volatile oils from Pogostemon cablin contain a bioactive component named b-patchoulene which has been shown to significantly decrease mortality and lung wet/dry weight ratio of mice, and mitigate pathological changes in lungs, when compared to model group. It suppressed LPS-induced activation of NF-kappa B, and markedly upregulated Nrf2 and miR-146a (Chen et al., 2017).

Anti-Oxidative Properties
Oxidative stress and inflammation form a positive feedback cycle (Mittal et al., 2014). In lung disease, excessive inflammation and oxidative stress lead to adverse outcomes. For instance, patients with COPD are usually affected by other diseases (Rabe and Watz, 2017). Several mechanisms in lung inflammation and oxidative stress destroy DNA and lead to an imbalance between tissue repair and cell proliferation, which seems to promote the link between COPD and lung cancer (Wilson et al., 2008;Houghton, 2013;Durham and Adcock, 2015). Under normal conditions, the production and elimination of ROS maintain a crucial balance between oxidation and antioxidation (Cao et al., 2019). In such a balance, the signal pathways are regulated, and cell proliferation can be guaranteed. When inflammatory factors destroy this balance, oxidative stress enhances the maturation of proinflammatory factors, leading to oxidative damage to cells and multisystem diseases (Sies, 2015;Kruk et al., 2019). Antioxidant drugs have been used in lung diseases. For example, antioxidants have been recommended for reduction of mortality or prevention of organ damage in animal models of acute lung injury induced by lipophilic acids (Hsu et al., 2006;Zhu et al., 2020). Vitamin C has also been shown to reduce the incidence of pneumonia in several controlled trials for human subjects (Hemila, 2017).
The essential oil of Magnolia officinalis Rehder & E.H. Wilson exerts antioxidant effect by scavenging 1,1-diphenyl-2picrylhydrazyl (DPPH) radical and superoxide anion radical. The essential oil contains b-eucalyptol with a hydroxyl group which can provide hydrogen atom for scavenging DPPH radical. Moreover, with increase in volatile oil concentration, the antioxidant capacity gradually increased (Guo, 2012). The essential oil from Atractylodes lancea (Thunb.) DC. showed a strong antioxidant effect in vitro and indicated by DPPH-radical scavenging property, with an IC 50 of 288.7 mg/ml. Moreover, it inhibited lipid peroxidation, and affected total antioxidant capacity (T-AOC) in the serum and organ tissues of mice . In short-term cigarette smoke (CS)induced acute lung inflammation, 1,8-cineole decreased oxidative stress involving reactive oxygen species, by increasing superoxide dismutase and catalase, while reducing levels of malondialdehyde, inflammation, and the NF-kappa B p65 subunit (Kennedy-Feitosa et al., 2016).

Antibacterial Properties
The major components of Pogostemon cablin (Blanco) Benth. are carvacrol (47.5%) and p-cymene (15.2%). It completely inhibits the growth of E. coli at a level of 0.05% (Lin et al., 2016). The essential oil of Atractylodes lancea (Thunb.) DC. exhibited antibacterial effects against Gram-positive and Gram-negative bacteria due to the cell membrane . In chronic Zhang et al. Dayuan-Yin Against the COVID-19 Pandemic Frontiers in Pharmacology | www.frontiersin.org September 2020 | Volume 11 | Article 583651 rhinosinusitis, 1,8-cineole suppressed the growth of S. aureus, Escherichia coli, Moraxella catarrhalis due to downregulation of significant and critical players in biofilm generation (Agra, Sara, and s B ) (Schürmann et al., 2019). On the other hand, the major constituent of the essential oil of Atractylodes lancea (Thunb.) DC. is b-eudesmol. In terms of intestinal flora, b-eudesmol has two-way regulation for gastrointestinal motility: anticholinergic pathway and direct effect on gastrointestinal smooth muscle. Antibacterial effect is an essential pharmacological property of volatile compounds (Houdkova et al., 2017;Riad et al., 2020). Secondary bacterial co-infection is common in patients with COVID-19 infection, and it leads to adverse prognosis (Macintyre et al., 2018). At present, many antibiotics have been used in the treatment of COVID-19. For example, Shufeng Jiedu Capsule (SFJD) prevents acute upper respiratory tract infection and positively affects fever, cough, and headache. Studies have shown that SFJD significantly reduced the levels of serum PGE2, IL-1 b, and TNF-a in rats with acute pharyngitis (Qian, 2019). Being a popular antiviral and antibacterial drug, SFJD is one of the drugs for COVID-19 treatment in China (Pan X. et al., 2020). In addition, Shuanghuanglian (SHL) is a popular anti-bacterial drug. It has various pharmacological potential such as antibacterial, antiviral, and immune-enhancing properties which can be exploited in the treatment of acute upper respiratory tract infection (Zhang et al., 2013). Preliminary studies in vitro showed that SHL oral liquid inhibited SARS-COV-2. Indeed, SHL has been used to carry out clinical research on COVID-19 in Shanghai Public Health Clinical Center and Tongji Hospital Affiliated to Huazhong University of Science and Technology (Pan X. et al., 2020).
The antibacterial effects of volatile components of Dayuan-Yin are not limited to upper respiratory tract infections: these volatile components also regulate intestinal flora, treat gastric ulcers, and improve gastrointestinal symptoms. Human gut microbes are the "second genome" of the human body (Backhed et al., 2005;Gill et al., 2006;Cani and Delzenne, 2007). The composition of intestinal flora is closely related to human health status, and it plays an essential role in maintaining physiological balance (Schuijt et al., 2016). It has been confirmed that intestinal flora reduces ventilatorassociated pneumonia and enteritis by enhancing the function of primary alveolar macrophages (Bradley et al., 2019). Patients with COVID-19 showed intestinal microbial malnutrition and decreased microbial flora levels of some probiotics such as Lactobacillus and Bifidobacterium. The latest version of novel coronavirus pneumonia diagnosis and treatment plan released by the People's Republic of China National Health Council suggests that intestinal microbiota should be used in severe and critical cases to maintain intestinal micro ecological balance (General Office of the National., Health Commission of the people's Republic of China. et al., 2020).

EFFECTS OF NON-VOLATILE COMPONENTS
Apart from the biological effects of the volatile components mentioned above, other non-volatile components of Dayuan-Yin also have abundant pharmacological properties.  (Zhang T. T. et al., 2014) (Mitsui et al., 2010). Falcarindiol inhibited the growth of Pseudomonas aeruginosa by repressing virulencerelated genes, including the T3SS; quorum sensing synthase genes lasIR and rhlIR; lasB; motility-related genes fliC and fliG; and phenazine synthesis genes phzA1 and phzA2 .
It is obvious that Dayuan-Yin exerts extensive biological properties such as antiviral, anti-inflammatory, antioxidative, and antibacterial effects. It can be inferred that Dayuan-Yin may play an essential role in preventing COVID-19 pandemic.

SUMMARY AND FUTURE PROSPECTS
At present, there are no conventional drugs that can cure COVID-19 (Cao B. et al., 2020). However, according to data collected by the National Health Commission of the people's Republic of China, clinical practice in Chinese hospitals have reported that traditional Chinese medicine has a definite therapeutic effect in the early stages of COVID-19 infection . As a significant part of medical practice, Chinese medicine has been used to treat human diseases for more than 5,000 years (Li and Kan, 2017). In recent decades, volatile compounds extracted from medicinal plants have attracted more and more attention due to their important biological effects such as antiviral, anti-inflammatory, and antibacterial properties. Besides, they are non-toxic and have few side effects, making them suitable for use as drugs. This review discussed the potential role of traditional Chinese medicine in terms of volatile components. The antiinflammatory, antiviral, antibacterial and immunomodulatory effects of these volatiles seem to play the most critical roles in treating patients infected with COVID-19. However, there are still lack of clinical trials on Dayuan-Yin. These need to be done in future.
In China, the situation of COVID-19 pandemic prevention and control has improved. The national pandemic situation has been controlled. However, with the resumption of factory work, re-opening of shopping malls, and resumption of transportation, the cross-flow of personnel has increased significantly, and the probability of close contact between people has increased tremendously too. In particular, with likelihood of increase in imported cases from abroad, the epidemic prevention and control should not be relaxed. It is essential to improve the ability of the human body to withstand infection. In addition to frequent washing of hands, wearing masks, social distancing and other measures, the "Chinese medicine sachet" can be used as an essential means of prevention. This stems from a very important theory of traditional Chinese medicine, namely "treating predisease". This idea in traditional Chinese medicine originated in the Yin and Shang Dynasties, took shape in Zhouyi, and formed in Huangdi Neijing . Chinese doctors in the past dynasties attached great importance to the prevention and treatment of diseases. They emphasized the prevention of diseases first, especially infectious diseases (Lian et al., 2020). Wearing Chinese medicine sachet is another special treatment of "treating pre-disease" . Chinese medicine sachet has been used to prevent disease since ancient times. In this method, aromatic Chinese medicine is put into a unique bag and worn on the chest to prevent respiratory diseases. This is known as "Xiangpei therapy" (Zhang Q. et al., 2014). From the perspective of modern medicine, the medicinal fragrance (i.e., volatile oil components) of Chinese medicine sachet stimulates the nasal mucosa, promotes the secretion of immunoglobulins, and kills all kinds of viruses at the same time, thereby playing multiple roles in regulating immune function, and exerting antibacterial and anti-viral effects (Lvy and Bai, 2017). Interestingly, early intervention with aromatic Chinese medicine blocks the course of diseases and relieves symptoms in clinical practice through oral administration, external fumigation, and moxibustion (Lun and Chen, 1987;Chen et al., 2013). Aromatic Chinese medicine dispels exterior pathogenic factors, regulates qi, activates blood circulation, breaks blood stasis, and disperses nodules. The application of aromatic Chinese medicine embodies the theory of "internal disease and external treatment" of traditional Chinese medicine (Hu et al., 2010). Since the outbreak of COVID-19, fumigation has been used for air disinfection to prevent the spread of the virus. In the clinical treatment period, the application of moxibustion plays the role of anti-inflammatory agent, regulates immune function, and prevents deterioration of the patients (Zhang, 2012;Liu K. et al., 2020). Some local health committees or Chinese medicine administration bureaus are actively involved in promoting aromatic traditional Chinese medicine as an anti-epidemic, as well as the use of fumigation or Chinese medicine sachet to prevent and control COVID-19 .
There is no doubt that the pharmacological effects of volatile components of traditional Chinese medicine are beneficial in the global fight against COVID-19. However, each TCM prescription has multiple goals and links in the treatment of diseases, making it difficult to clearly and thoroughly explain its mechanism in a short period. More research should be carried out on volatile components of traditional Chinese medicine to elucidate the associated regulatory mechanism, evaluate possible side effects, and conduct standard clinical trials. The insights provided in this review may help ease the COVID-19 pandemic worldwide.

AUTHOR CONTRIBUTIONS
Q-wH and JW are the corresponding authors on the study. X-rZ and T-nL are first authors and responsible for collecting materials and writing the paper. Y-yR, Y-jZ, and H-yL helped in organizing the information and edited the article pictures. All authors contributed to the article and approved the submitted version.

FUNDING
This work is financially supported by the Xinglin Scholar Talent Promotion Plan of Chengdu University of Traditional Chinese Medicine (QNXZ2018023, XSGG2019008).

ACKNOWLEDGMENTS
We are indebted to our alma mater, Chengdu University of Traditional Chinese Medicine for provided convenience in the collection of documents. Thanks for all the help from everyone in our lab.