Paecilomyces cicadae: a systematic overview of the biological activities and potential mechanisms of its active metabolites

ABSTRACT
 The microbe Paecilomyces cicadae (Miquel) Samson (P. cicadae) is an asexual strain of Cordyceps cicadae (C. cicadae) used in traditional Chinese medicine. Due to the abundance of secondary metabolites found in cultured metabolites, including polysaccharides, hyaluronic acid, ergosterol peroxide, and active nucleosides, P. cicadae and/or C. cicadae exhibit several therapeutic activities, including immunoregulatory, antioxidant, and anti-diabetic effects. Given the great attention for health care and the desirable medical value of C. cicadae and/or P. cicadae, they are becoming potential alternatives of Cordyceps sinensis (C. sinensis). Although there are many studies on P. cicadae/C. cicadae, most of them are experimental research articles. There are limited reviews to summarize the latest researches on P. cicadae/C. cicadae. This review mainly focuses on the metabolites, physiological activities and mechanisms of action of P. cicadae and/or C. cicadae. This review can serve as a theoretical basis for the more efficient use of this medicinal fungus.

Although there are many studies on P. cicadae/C.cicadae, most of them are experimental research articles.There are limited reviews to summarize the latest researches on P. cicadae/C.cicadae.This review mainly focuses on the metabolites, physiological activities and mechanisms of action of P. cicadae and/or C. cicadae.We hope to this paper could provide theoretical basis for future researchers.In addition, cicada flowers were also included in the study.

Metabolic actives
The studies of fungal metabolic actives have gathered a lot of attention ever since Byerrum first reported the antitumor activity of polysaccharides in mushrooms in the 1960s (Byerrum et al., 1957).Numerous pieces of literatures have revealed recently that the metabolic actives of some fungi have hypoglycemic (Dai et al., 2015), immunomodulatory (Yu et al., 2018), antiviral (Li et al., 2021c;Verma, 2022;Zhu et al., 2020a), anti-inflammatory (Qi et al., 2021;Xu & Du, 2020), antioxidant (Zhu et al., 2018), and antitumor effects (Tian et al., 2019;Zhang et al., 2021c).The active ingredients of various medicinal fungi are also being used increasingly in medicine, food, biology, cosmetics, and other fields.We summarized some typical outcomes for various polysaccharides, proteins, extracts, and other active substances in fungi (Table 1).

Polysaccharides
A class of polymeric carbohydrates known as polysaccharides is composed of at least 10 monosaccharides that are linked by glycosidic bonds.Polysaccharides have the general formula C x (H 2 O) y , where x is often a significant value between 200 and 2500.The general formula can also be written as (C 6 H 10 O 5 ) n , where n is usually between 40 and 3000.The repeating units in the polymer backbone are usually six-carbon monosaccharides.
Polysaccharides are one kind of the main active components in mushrooms (Won et al., 2011).They are structurally diverse macromolecules that serve a variety of roles in many biological processes.The distinct advantages of polysaccharides are their excellent safety and easy availability.Furthermore, growing evidences have suggested that natural polysaccharides can directly scavenge reactive oxidative free radicals (ROS) (Asker et al., 2009), increase cell viabilities (Vinderola et al., 2006), and boost immunity in cells (Yamada et al., 1997).In 1982, researchers discovered for the first time the structure of P. cicadae polysaccharides.The galactomannan in P. cicadae was isolated by Japanese researchers (Ukai et al., 1983).Its relative molecular weight is 27 000, making it a kind of water-soluble polysaccharides.It is composed of D-mannose and D-galactose in a 4:3 ratio.The P. cicadae polysaccharides were subsequently isolated using a chromatographic column by Ren et al. (Ren et al., 2014), who discovered that mannose (43.2%), rhamnose (32.1%), xylose (14.5%), and arabinose (10.2%) made up the majority of its structure.According to Li et al. (Li, He, et al., 2016a), the primary structural characteristics of P. cicadae polysaccharides were rhamnose, arabinose, fucose, xylose, mannose, glucose, and galactose with a molar ratio of 0.63:13.1:1.30:21.3:46.5:6.0:10.22.Although different structures were identified, there are three kinds of monosaccharides, mannose, galactose, and arabinose, are usually existed.
Recently, it has been discovered that a significant amount of hyaluronic acid was detected in the fermentation broth of P. cicadae (Tan et al., 2007), which has gathered people's attention.It may be another source to obtain hyaluronic acid economically, and conveniently.Hyaluronic acid ((C 14 H 21 NO 11 )n, Figure 1, 1) is a polymer, nonprotein, acidic mucopolysaccharide, whose structural units are acetylglucosamine and glucuronic acid (Chandrashekar, 2006;Hedén et al., 2020).Hyaluronic hacid exhibits substantial health benefits for the body, such as strong water retention properties.It plays roles in cell proliferation, wound healing, migration, and differentiation, which makes it an important biomedical raw material (Donejko et al., 2015;Mandal et al., 2018).According to Tan et al. (2007), an optimal fermentation medium composition for hyaluronic acid was obtained, those were 6% lactose, 0.5% beef extract, and yeast extract in a 1:1 and 0.1% magnesium sulfate.The yield of hyaluronic acid could reach up to 11.35 mg/mL.Furthermore, the process of extracting hyaluronic acid from P. cicadae has also been studied (Huang & Tian, 2009).
The physical and biological properties of polysaccharides are influenced by many important factors, one of which is molecular weight.It is reported that high-molecular-weight polysaccharides are necessary for their immunomodulatory and antitumor activities (Ren et al., 2012;Suarez et al., 2006).However, some low-weight molecular polysaccharides can also exhibit strong biological functions (He et al., 2020;Li et al., 2021b;Yuan et al., 2020).C. cicadae polysaccharides have strong antioxidant and hypoglycemic properties with a molecular weight of 60.7 kDa (Tang et al., 2022).JCH-3, a relatively low-weight molecular polysaccharide isolated from C. cicadae, had excellent immunoregulatory activities, compared to JCH-1 and JCH-2, according to Xu et al (Xu et al., 2020).A similar result was observed when we discussed the anti-inflammatory properties of Ganoderma lucidum (G.lucidum) polysaccharides of low weight (Liu et al., 2018).
The biological activities may be affected by the high proportion of monosaccharides in polysaccharides.According to Yang et al. (2020d), The antioxidant activity of the polysaccharides was significantly influenced by the content of uronic acid.In general, neutral polysaccharides are thought to have a higher free radical scavenging capacity than acidic polysaccharides.Another literature reported that C. cicadae polysaccharides with high ratios of uronic acid, arabinose, and galactose were considered to have significant contributions to antioxidant activity (Wang et al., 2022).
Furthermore, the composition of monosaccharides in polysaccharides were also closely related to the biological activities (Su & Li, 2020;Xu et al., 2019;Yiyong & Yiting, 2018).Mannose, glucose, and galactose were found to positively impact on the antioxidant activity of cicada polysaccharides (Tang et al., 2022).Additionally, polysaccharide conformations are another element that can influence biological activity.According to Surenjav et al., the antitumor biological activity of polysaccharides with a single flexible chain was significantly lower than that of natural triple helix lentinan (Surenjava et al., 2006).
It is intriguing and important to study the chemical structure of polysaccharides, the composition of monosaccharides, molar ratio of parent compounds and their biological activities.The other parameters that influence the activities are also eager to be found out.
Among them, adenosine is frequently used as a typical compound for determining nucleoside levels since it has a base that contains nitrogen.When adenosine is used as a raw material or precursor in synthesizing cordycepin, it serves as a key quality index for measuring cicada flowers.Here, we discussed the typical nucleosides existed in P. cicadae and/or C. cicadae.Cordycepin (C 10 H 13 N 5 O 3 , Figure 1, 8) as received a lot of attention for its great therapeutic potential.It is also called 3'-deoxyadenosine (Frederiksen et al., 1965), and is an important secondary metabolite in Cordyceps species such as Cordyceps militaris (C.militaris) (Cunningham et al., 1950) and Cordyceps sinensis (C.sinensis).Additionally, it is present in the broth and mycelium of P. cicadae (Li et al., 2007).

Cordycepin
Cordycepin combines with certain adenosine receptor and activates downstream biomarkers to perform biological activities subsequently.According to the reports, Cordycepin can interact with A1, A2A, A2B and A3 adenosine receptors subtypes to exert benefits such as anti-inflammation, anti-virus, cell repair, and protection of liver, kidney, heart, and brain (Cao et al., 2017;Chen et al., 2014;Ravani et al., 2017;Sheth et al., 2014).It can also inhibit protein synthesis and cell adhesion by altering intracellular signal transduction (Varani et al., 2011).
Previously, the fruiting body of C. militaris was mostly used to extract natural cordycepin.However, the needs of the industry could not be met by this production process because it had complicated cultural conditions and a low cordycepin yield.The chemical production of cordycepin has been reported since the 1960s, giving it a preliminary development in the field (Hansske & Robins, 1985;Kwon et al., 2003;Ohno et al., 1984).Adenosine is typically used as a raw material to undergo a sequence of reactions in acidic or alkaline conditions.However, several chemical methods have limitations that make them unsuitable for industrial production, including high costs, environmental pollution, complex processes, and poor yields.Later studies of biological cordycepin synthesis methods, such as enzymatic production and fermentation, have been reported.
Researchers have made great contributions to improving cordycepin yield in C. militaris, such as spore hybridization and mutagenesis technology (Kang et al., 2017;Masuda et al., 2014;Wongsa et al., 2020).P. cicadae can also be found to obtain cordycepin from the mycelium, with a relatively high content (Li et al., 2007).The medium components were closely related to cordycepin yield.
Although the health benefits of cordycepin have been recognized but the commercial products of cordycepin is rare.The fruit bodies or the mycelia of C. militaris have been successfully commercialized for medicinal and health products, and even for direct consumption as edible mushroom in supermarket.Up to 2023, there are 43 health foods made from Cordyceps approved by the Ministry of Health of the People's Republic of China.Among them, there are at least two medicinal products made from C. militaris: C. militaris mycelia powder (Z20030034) and capsule (Z20030035) manufactured by Jilin Zhongsheng Pharmaceutical Co., Ltd.(Dong et al., 2015).
HEA is a potent antioxidant, anti-inflammatory, and hypoglycemic compound with various therapeutic properties, including anti-diabetes, renal protection, anti-inflammatory, antitumor, and sedative effects (Li et al., 2019a;Lu et al., 2015;Meng et al., 2015;Zheng et al., 2018).Studies show that HEA has anti-inflammatory benefits by increasing antioxidant enzyme activity, inhibiting lipid peroxidation, and lowering pro-inflammatory factors like IL-6, IL-1β, TNFα, and NF-kB (Wang et al., 2019a).Additionally, HEA can inhibit H 2 O 2 -induced cell damage by lowering ROS production to restore or preserve mitochondrial function (Zhang, Wu, et al., 2019a).Studies demonstrated that cicada HEA has significant hypoglycemic and hypolipidemic effects on type 2 diabetic rats (Sun et al., 2021), and can be used as a supplement to diabetes management and reduce the many diabetic complications in genetically obese mice (Li et al., 2019a).

Cordycepic acid
Cordycepic acid (C 6 H 14 O 6 , Figure 1, 11) is a polyol-structured isomer of quinic acid, also known as 1,3,4,5-tetrahydroxycyclohexanoic acid.Cordycepic acid was initially isolated from C. sinensis in 1957 (Chatterjee et al., 1957).The composition of the crystalline substance was determined to be D-mannitol (Chatterjee et al., 1957).The content of cordycepic acid is one of the key factors used to evaluate the quality of C. sinensis.
In addition, the fermentation broths, the mycelia, and the fruiting bodies of C. cicadae, P. cicadae, and C. militaris, all contain cordycepic acid (Dong et al., 2012;Dou et al., 2013;Raethong et al., 2020;Shi et al., 2022).Xia et al. (2014) discussed the contents of cordycepic acid in the fruiting bodies of different strains, and found that the fruiting body of P. cicadae had a high concentration of cordycepic acid; it may contain up to 78.19 mg/g, which is higher than that in C. sinensis (77.27 mg/g), C. militaris (43.36 mg/g), and natural C. cicadae (53.6 ± 1.16 mg/g).Apart from the different strains, the contents in fruiting bodies also change as progress through their growth stages and are influenced by various fermentation factors, including carbon sources, nitrogen sources, and inorganic salts (Dou et al., 2013;Raethong et al., 2020;Shi et al., 2022).Additionally, the parameters in solid fermentation, such as the medium, light and humidity were also affected cordycepic acid contents (Curran, 1980).
As an immunosuppressive agent, myriocin has the potential to be clinically effective.In vivo and in vitro experiments have revealed that it is 10-100 times more potent than the immunosuppressive agent cyclosporine A (CsA), with fewer adverse effects to the kidneys (Fujita et al., 1994).In addition, the antitumor effect of myriocin is proved by Choi et al. (2014).It was shown that ISP-1 can activate DR4 pathway and induce apoptosis of lung cancer cells.
Researches will be performed to continue to discover the unknown secondary metabolites with pharmacologic effects.

Biological activities
Metabolites have been reported to have a wide range of biological activities, such as immunoregulatory, antibacterial, antioxidant, and antitumor activities.In the study, we comprehensively summarized the pharmacological effects and their mechanisms of these metabolites derived from P. cicadae and/or C. cicadae (Table 3).Here, we discussed in detail based on each pharmacological effect.

Immunoregulatory activity
It has been observed that polysaccharides originating from microorganisms or plants can improve immunity by activating macrophages or enhancing the synthesis of cytokines and immunoglobulins (Huang et al., 2016;Li et al., 2017c;Shen et al., 2017).Polysaccharide is one of the most abundant and bioactive components found in mushroom fruit bodies, cultured mycelia, and fermentation broths (Chen et al., 2021).It interacts with receptors on the cell surface, affects the expression of some signaling biomarkers, and then increases the production of immune factors or antibodies, so as to play a role in regulating the immune function of the body (Jiang et al., 2010).
The polysaccharides from P. cicadae and/or C. cicadae have been reported to have immunomodulatory properties (Jin et al., 2008;Tian et al., 2022;Xu et al., 2018).They can regulate the NF-κB/MAPK signaling pathway to improve cellular immunity (Tian et al., 2022) and the TLR4 signaling (Kim et al., 2011) pathway to increase dendritic cell maturation.We are all aware that an excessive increase in inflammatory cytokines can cause inflammation, but an increase in cytokines within a reasonable range can stimulate cellular immunity.High doses of polysaccharides have been shown to significantly increase serum levels of TNF-α, IL-1β, IL-6, IL-10, NO, or immunoglobulin A levels, activating the cellular immune response and enhancing cellular immunity (Jin et al., 2008;Wang et al., 2022;Xu et al., 2018).
Similar to the study on the regulation of intestinal flora by polysaccharides from Grifola frondosa (Li et al., 2019b), polysaccharides from P. cicadae can regulate the systemic immune response by elevating the relative abundance of beneficial bacteria (Lactobacillus) and the concentration of short-chain fatty acids in the intestine (Wan et al., 2022).C. cicadae polysaccharides have been reported to have the abilities in improving metabolic disorders and reducing liver oxidative stress by increasing glutathione peroxidase (GSH-Px), SOD, and catalase (CAT) activities and decreasing lipid peroxidation (MDA) levels (Zhang et al., 2021).In addition, P. cicadae polysaccharides can affect cellular proliferative activities and their immune-enhancing activity.Figure 4 showed the general reported mechanisms of immune regulation of C. cicadae and/or P. cicadae in detail.
As a source of polysaccharides, C. cicadae spores are also being researched.The active ingredients found in C. cicadae spores are typically believed to be nearly identical to those found in C. cicadae mycelia and C. cicadae fermentation broth (Sun et al., 2017;Wang et al., 2017a).Polysaccharides in spores have also been reported to have immune-enhancing properties (Fu et al., 2019;Sun et al., 2017;Wang et al., 2017c).Similar to lentinan, C. cicadae spore polysaccharides could protect mice given the immunosuppressive drug cyclophosphamide by increasing macrophage phagocytic activity and regulating the secretion of cytokines and immunoglobulins (Zheng et al., 2022).

Antitumor activities
Numerous studies have extensively explored the antitumor properties of P. cicadae and C. cicadae.Several tumor cells were used as the assessment model, including renal cancer cells (He et al., 2018), gastric cancer cells (Xie et al., 2019), liver cancer cells (Wang et al., 2014a), and cervical cancer cells (Xu et al., 2021a) to evaluate the mechanisms of the components from P. cicadae or C. cicadae.Several components have been claimed to have antitumor properties, including EP, adenine, uridine, adenosine, HEA, polysaccharides, and certain organic solvent extracts from fruiting bodies, mycelia, and fermentation broth.
How cancer cells are out of the regulation of cell proliferation was the important question to be answered by the researchers.The two most important mechanisms of antitumor action are apoptosis and cell cycle arrest.However, the fundamental driving forces are very diverse depending on the various elements or components.
EP, a secondary metabolite of P. cicadae, was discovered to have antitumor activity by He et al. (2018).It was reported that EP promoted apoptosis, inhibited migration and invasion, blocked the cell cycle, and prevented DNA replication and mitosis (He et al., 2018).The ethanol extract of C. cicadae, with adenine, uridine, adenosine, and HEA presented, showed antitumor effect by the mechanism of cell cycle arrest, MMP depolarization, Ca 2+ overload, over-expressed Bax, AIF, caspase-8, caspase-6, and caspase-3 and decreased Bcl-2 (Xie et al., 2019).The polysaccharide extracts from C. cicadae spore powders have antitumor properties comparable to those of Ganoderma lucidum spores (Wang et al., 2012a;Zhu et al., 2012).These extracts can significantly lower the expression of β-catenin and N-cadherin and inhibit Wnt/β-catenin signaling and caspase-mediated mitochondrial apoptosis pathways (Sun et al., 2017).Additionally, C. cicadae may also have an impact on G2/M arrest to obtain the antitumor impact.Besides, C. cicadae polysaccharides could upregulate the expression of P53 (Xu et al., 2021a) and downregulate the expression of cyclin E, cyclin A, and CDK2, which prevented Hela cells from proliferating.
To maximize the antitumor benefits, some researchers have suggested combining natural elements from P. cicadae and C. cicadae with medicines like cisplatin, adriamycin, and cyclophosphamide (Cai et al., 2010;Jin et al., 2008).Various outcomes were obtained.Cai et al. (2010) found that the combination of polysaccharides and adenosine had specific antitumor effects in vitro.While the addition of polysaccharides did not strengthen the antitumor activity of adriamycin or cisplatin.Another study (Jin et al., 2008) found that combining P. cicadae with cyclophosphamide synergistically enhanced antitumor activity.
These studies have demonstrated the potential for P. cicadae and C. cicadae to serve as sources of natural antitumor drugs.Exploring the synergies of the combination of natural extracts and chemical compounds is a meaningful direction.

Antioxidant and anti-aging activities
Several mechanisms, such as reducing capacity, inhibiting chain initiation, binding transition metal ion catalysts, peroxides decomposition, and radical scavenging, can be used to explain the antioxidant and anti-aging activities.The cellular assessment of antioxidant activities involves the enzyme capacities (SOD, CAT, GSH-Px, etc.), lipid peroxidation products levels (malondialdehyde, lipofuscin, etc.), and the accumulation of ROS.The antioxidant effect, which has an anti-aging impact, is attained by raising or lowering these levels.
Numerous studies have shown that P. cicadae and/or C. cicada have free radical scavenging abilities (He et al., 2010;Ren et al., 2014;Wang et al., 2019b).According to (2019b), the polysaccharides from C. cicada scavenged hydroxyl radicals at various concentrations in a dose-dependent manner.The significant antioxidant properties of P. cicadae polysaccharides and C. cicadae fruiting body polysaccharides were also demonstrated by assessing DPPH free radical, superoxide radical, and hydroxyl radical scavenging capacities in the tube (Ren et al., 2014).He et al. (2010) also documented the ability of P. cicadae polysaccharides to scavenge DPPH, superoxide, and hydroxyl radicals.
The protective and repairing effects on oxidative stress damage models also reflect the antioxidant and anti-aging capacities of the sample.On H 2 O 2 -induced oxidative damage in PC12 cells, the protective effect of HEA was reported (Zhang, Wu, et al., 2019a).Compared to the damaged model, HEA could boost intracellular antioxidant enzyme activity and cell viability, decrease dehydrogenase release, and limit the ROS production and lipid peroxidation production.In addition, the decrease in inflammatory cytokines such as IL-6, IL-1β, TNF-α, and NF-кB was observed.Animal experiments supported the antioxidant properties of polysaccharides from C. cicadae.It was reported that polysaccharides from C. cicadae spores can boost SOD, CAT, and GSH-Px activities, indicating that they have the antioxidant capacity and hepatoprotective activities (Zhang et al., 2021).Another study found that C. cicadae polysaccharides were crucial in prolonging the lifespan of Drosophila, probably because of the upregulated expression genes associated with antioxidants such as CAT and SOD1 (Zhu et al., 2020b).
Hyaluronan (HA) in cells is a natural component in the skin that helps absorb moisture from the skin surface.The lack of HA results in skin water loss, sagging, increased wrinkles and decreased elasticity.Shao et al. (2023) found that C. cicadae extract promoted HA synthesis in fibroblasts, and the extract was rich in polysaccharides, and five alditols (mainly mannitol).
In addition, it is reported that C. cicadae and P. cicadae showed potential therapeutic benefits in rats with adenine-induced chronic renal failure, increasing SOD activity and decreasing MDA and GSH (Li et al., 2018).Additionally, the serum levels of BUN and Crea were significantly decreased, and TP, ALB, RBC, HCT, and HGB were increased.These results suggested that C. cicadae and P. cicadae can inhibit oxidative stress and enhance antioxidant capacity to exert renal protective effects.
These findings show that P. cicadae and C. cicadae may be investigated as potential natural antioxidants and used as new dietary supplements to delay aging.

Anti-inflammatory effect
There are lots of factors, such as physical damage, metabolic disorders, infection-related factors, oxidative stress, and chemical substances, can cause inflammation (Salminen et al., 2022;Tilg et al., 2020).It is also well accepted that inflammation is linked with oxidative stress.Oxidative stress refers to elevated intracellular levels of ROS that is considered to be the most potent inflammatory mediators (Shin et al., 2008).Antioxidants play a significant role in reducing inflammation (Waxman K. 1996).The increase of antioxidant enzymes in cells can prevent acute and chronic inflammatory reactions, exert anti-inflammatory effects on the eyes, protect the kidneys, and have anti-diabetic properties.
Lipopolysaccharide (LPS)-induced inflammation, in vitro cell lines and in animals, represents a standard paradigm for studying inflammation.The anti-inflammatory mechanisms of the active substances may be involved in the increased expression of antioxidant enzymes, reduced the deposition of peroxide, and the decrease of the secretion of pro-inflammatory factors (Table 2).Figure 5 displays the general mechanisms of the antiinflammatory effects of P. cicadae and/or C. cicadae.
It is reported that some therapeutic anti-inflammatory compounds are derived from C. cicadae and P. cicadae.An excellent anti-inflammatory impact of HEA on human bodies is thought to exist.In vivo and in vitro studies (Lu et al., 2015;Wang et al., 2019a;Zheng et al., 2018) have been performed to prove its anti-inflammatory properties.HEA can increase the activity of antioxidant enzymes in kidney tissues, including glutathione (GSH), catalase (CAT), and SOD.Some pro-inflammatory mediators (TNF-α, IL-6, IL-1β, NF-κB, and TGF-β1) (Wang et al., 2019a) can also be decreased in a dosedependent manner.
Additionally, hepatoprotective and renal protective activities of C. cicadae polysaccharides are also partly due to their anti-inflammatory mechanism.It can reduce renal interstitial fibrosis in rats with diabetic nephropathy by reducing inflammation and managing issues with intestinal flora (Yang et al., 2020b).C. cicadae polysaccharides can also play roles in the treatment of liver dysfunction by anti-inflammation and FOOD AND AGRICULTURAL IMMUNOLOGY against oxidative damage in a rat model of metabolic syndrome induced by a high-sugar and high-fat diet (Zhang et al., 2021).
The Toll-like receptor (TLR) signaling pathway plays a key role in inflammation.TLR4 is an important transmembrane pattern-recognition receptor and has been extensively documented in a variety of inflammatory conditions.The stimulation of TLR4 initiates a series of signaling cascades that result in the activation of nuclear factor κB (NF-κB), interferon β regulatory factor 3 (IRF3), and mitogen-activated protein kinases (MAPKs) which mediates the upregulation of inflammatory cytokine gene expression leading to an inflammatory response (Shim et al., 2013;Sugiyama et al., 2016).HEA can inhibit TLR4-mediated NF-κB signaling pathway to reduce the proinflammatory response induced by LPS (Lu et al., 2015).HEA also obviously decreased LPS-induced inflammatory cytokine level in RAW 264.7 cells and TGF-β1-induced fibroblast activation in NRK-49F cells by modulating NF-κB and TGF-β1/Smad signaling (Zheng et al., 2018).

Anti-diabetic effect
Diabetes is a global epidemic that caused by either insufficient insulin production from the pancreas (type 1), or when the body cannot effectively utilize the insulin it produces (type 2) (World Health Organization, 1999).Drugs that regulate blood sugar and reduce insulin resistance are the mainstays of treatment for diabetes (Evans & Krentz, 1999;Guo et al., 2016).However, these drugs may cause several adverse reactions, such as hypoglycemia, lactic acidosis, and ketoacidosis (Li et al., 2004).The use of natural ingredients is considered an appropriate alternative medicine for treating diabetes and its associated complications (Day, 1998).
According to Day (1998), C. cicadae exhibited a hypoglycemic impact in a mouse model of type 1 diabetes induced by alloxan.A recent study has shown that HEA in C. cicadae can improve glucose tolerance and exhibits hypoglycemic effects on type 2 diabetes (Li et al., 2019a).A study compared the anti-diabetic benefits of P. cicadae and Astragalus membranaceus, and was reported that P. cicadae was more effective at postponing the onset of diabetic nephropathy than Astragalus membranaceus, in which the PI3K/AKT/mTOR signaling pathway played important roles (Yang et al., 2020a).Researches will be performed continuedly to understand the underlying mechanisms and advance the application.

Antibacterial activity
Antibiotics will be used to treat bacteria using traditional antibacterial methods, but overuse of these drugs will result in bacterial resistance (Martínez, 2012;Yang et al., 2020a).Numerous reports have indicated that natural fermentation metabolites have antibacterial activity, including crude proteins and polysaccharides obtained from fungi and traditional Chinese medicines (Keypour et al., 2008;Kim et al., 2001).
According to the report, the crude proteins in the fermentation broth of P. cicadae can destroy the cell membrane structure of E. coli and alter the composition of entire cells or membrane proteins (Cen et al., 2021).Both of the extracellular and intracellular polysaccharides from C. cicadae have been demonstrated to have antibacterial activities.It was discovered that pathogenic microorganisms, including Escherichia coli, Klebsiella pneumoniae, Vivrio choler, Pseudomonas aeruginosa, Vibrio alginolyticus, Staphylococcus aureus, Vibrio parahaemolyticus, and Streptococcus pneumonia were significantly inhibited by both of the extraand intracellular polysaccharides (Sharma et al., 2015).In addition, the inhibition rate of intracellular polysaccharides was marginally higher than that of extracellular polysaccharides.
Cordycepin was reported to have antibacterial activity by Ahn et al. (2000).It can inhibit the growth of Clostridium paraputrificum and Clostridium perfringens, but have no effect on Bifidobacterium spp.and Lactobacillus spp.(Ahn et al., 2000).

Conclusion and future perspectives
The advantages of low toxicity and simple cultivation make natural P. cicadaethe same genus as C. sinensisa desirable species.It is expected to serve as a replacement for C. sinensis.Due to the limited natural resources and challenging artificial cultivation of P. cicadae, the use of modern biological fermentation technology to cultivate artificial P. cicadae mycelium has almost become the only and fundamental way to solve the problem.
The review primarily described the main active components, physiological functions, and mechanisms of P. cicadae and C. cicadae.We also provided a scientific summary of their typical therapeutic effects.
Recent studies have demonstrated that its extracts have positive therapeutic and health-promoting effects, particularly in inflammation-mediated diseases like diabetes, kidney disease, obesity, and cancer.We hope this will gives us a theoretical basis to use medicinal fungi more effectively.
Future research will be required to determine the exact functional mechanisms of the active ingredients from P. cicadae and/or C. cicadae.The efficacy and safety of single or combined use still need researchers' attention.In addition, there is a need to advance the industrialization of active substance preparation.

Disclosure statement
No potential conflict of interest was reported by the author(s).

Figure 1
Figure 1 Continued

Figure 4 .
Figure 4.The general mechanism of immune regulation of C. cicadae and/or P. cicadae.The immunomodulatory effect exerts in two ways.① C. cicadae and/or P. cicadae polysaccharides can regulate the systemic immune response by increasing the relative abundance of beneficial bacteria (e. g.Lactobacillus) and the concentration of short-chain fatty acids in the intestine; ② C. cicadae polysaccharides can alleviate metabolic disorders and reduce liver oxidative stress by changing the activities of enzymes and reducing the levels of inflammatory factors.

Table 1 .
Functions and mechanisms of active substances in some fungi.Chemical structures of compounds extracted from P. cicadae and/or C. cicadae.The active metabolites of P. cicadae/C.cicadae are classified into six major categories, namely polysaccharides, nucleoside compounds, ergosterol and its peroxides, cordycepin acid, myriocin, and other compounds.

Table 2 .
Display the anti-inflammatory mechanisms and pharmacological activities of Cordycepin.

Table 3 .
Pharmacological effects and their mechanisms of the metabolic actives derived from P. cicadae and/or C. cicadae.