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DOI: 10.1039/D0NP00023J (Review Article) Nat. Prod. Rep., 2021, 38, 83-102

Terpenoids from the medicinal mushroom Antrodia camphorata: chemistry and medicinal potential†

Yi Kuang , Bin Li , Zilong Wang , Xue Qiao * and Min Ye *
State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, 38 Xueyuan Road, Beijing 100191, China. E-mail: qiaoxue@bjmu.edu.cn; yemin@bjmu.edu.cn; Fax: +86-10-8280-2024; Tel: +86-10-8280-1516

Received 30th April 2020

First published on 28th July 2020

Abstract

Covering: up to February 2020

Antrodia camphorata is a medicinal mushroom endemic to Taiwan for the treatment of intoxication, liver injury, cancer, and inflammation. Owing to its rare occurrence and potent pharmacological activities, efforts have been devoted to identify its bioactive constituents, especially terpenoids. Since 1995, a total of 162 terpenoids including triterpenoids, meroterpenoids, sesquiterpenoids, diterpenoids, and steroids have been characterized. The ergostane-type triterpenoids (antcins) and meroterpenoids (antroquinonols) are characteristic constituents of A. camphorata. The terpenoids show anti-cancer, hepatoprotective, anti-inflammatory, anti-diabetic, and neuroprotective activities. This review summarizes the research progress on terpenoids in A. camphorata during 1995–2020, including structural diversity, resources, biosynthesis, pharmacological activities, metabolism, and toxicity. The medicinal potential of the terpenoids is also discussed.

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Yi Kuang

Yi Kuang received her Master's degree in 2012 from Peking University Health Science Center. She is currently a PhD candidate in Prof. Min Ye's group at the School of Pharmaceutical Sciences, Peking University. Her research focuses on pharmacological activities of natural products from traditional Chinese medicines, particularly Antrodia camphorata.

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Bin Li

Bin Li obtained his Master's degree in Chinese Materia Medica in 2016 from Beijing University of Chinese Medicine. He joined Prof. Min Ye's group at Peking University and obtained his PhD degree in June 2020. His doctoral research focused on isolation and structural modification of bioactive natural products from Antrodia camphorata.

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Zilong Wang

Zi-Long Wang obtained his Bachelor's degree in resources & development of traditional Chinese medicines in 2017 from College of Chinese Medicinal Materials, Jilin Agricultural University. Currently, he is a PhD candidate in Pharmacognosy at School of Pharmaceutical Sciences, Peking University, under the supervision of Prof. Min Ye. His research mainly focuses on the biosynthesis of natural products from medicinal plants.

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Xue Qiao

Xue Qiao is an Associate Professor at the School of Pharmaceutical Sciences, Peking University. She received her BSc (2007), MSc (2009) and PhD (2012) degrees from Peking University. She worked as a visiting scientist in John Innes Centre (UK) during 2016–2018. Her research interests are focused on chemical analysis of Chinese herbal medicines, and biosynthetic routes to produce bioactive natural products. She has authored 52 scientific publications as the first or corresponding author in journals such as J. Am. Chem. Soc., Angew. Chem. Int. Ed., and Anal. Chem.

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Min Ye

Min Ye is a Professor in Pharmacognosy at the School of Pharmaceutical Sciences, Peking University. He obtained his PhD degree in 2003 at Peking University, and then completed his postdoctoral researches at Peking University, Louisiana State University, and Yale University School of Medicine (2003–2007). He joined the faculty of Peking University as an Associate Professor in December 2007, and was promoted to Full Professor in 2012. His current research interests are focused on (1) elucidation of the effective components of traditional Chinese medicines, and (2) biosynthesis and biocatalysis of natural products.

1 Introduction

Antrodia camphorata (Polyporaceae family) is a rare and precious medicinal fungus in Taiwan, well known by local people as “Niu-Chang-Chih” (Fig. 1). It grows restrictedly on the decaying empty trunk of Cinnamomum kanehirai Hayata (Lauraceae), an endangered aromatic tree also endemic to Taiwan. This fungus was firstly reported in 1990 as Ganoderma comphoratum, and was then renamed as Antrodia cinnamomea.1,2 In 1997, G. comphoratum and A. cinnamomea were found to be conspecific, and this fungus was given the new name Antrodia camphorata (M. Zang & C. H. Su) Sheng H. Wu, Ryvarden & T. T. Chang.3 In 2004, morphological and genetic features indicated this species belonged to a new genus Taiwanofungus, and it was named Taiwanofungus camphoratus.4 This genus was then reinstated as Antrodia by analyzing the ITS region of the ribosomal RNA gene (rDNA).5 Now, the widely accepted official name for this mushroom is Antrodia camphorata, while A. cinnamomea and T. camphoratus are also used.
image file: d0np00023j-f1.tif
Fig. 1 Pictures of Antrodia camphorata. (A) Wild fruiting bodies; (B) dish cultures; (C and D) cutting wood cultures.

A. camphorata has been used as a folk medicine in Taiwan by the aborigines for alcohol intoxication treatment for a long history.6 It is also used as a herbal medicine or dietary supplement to treat various diseases including cancer, liver injury, inflammation, diarrhea, abdominal pain, hypertension, and itchy skin.7 For example, 12% cancer patients in Taiwan tend to use A. camphorata as an adjuvant therapeutic agent or nutrient during cancer treatment. The wild A. camphorata is very rare because C. kanehirai is the only host. The price for the wild fruiting bodies could reach $15[thin space (1/6-em)]000–25[thin space (1/6-em)]000 per kg.8 Thus, several cultivation techniques have been developed to meet the increasing market demands.9

The chemical constituents of A. camphorata include terpenoids, maleic and succinic acid derivatives, benzenoids, benzoquinone derivatives, lignans, and polysaccharides.10 Among them, the terpenoids possess noticeable medicinal potential. For instance, the meroterpenoid antroquinonol is under phase II clinical trial against non-small cell lung cancer (ClinicalTrials.gov identifier: NCT02047344) (Table S1†).11 Previous reviews have summarized the bioactive constituents, biological activities, biosynthesis, or fermentation techniques of A. camphorata.6–15 The present review article focuses on the chemistry and medicinal potential of terpenoids in A. camphorata. Research progress during 1995–2020 in structural diversity, resources, biosynthesis, pharmacological activities, metabolism, and toxicity is summarized, and future perspectives are discussed.

2 Structural diversity

To date, a total of 162 terpenoids (1–162) have been reported from A. camphorata. Most of them were isolated from the fruiting bodies and mycelia, and a few were from the culture broth. According to the chemical skeletons, they can be classified into ergostane-type triterpenoids (1–75), lanostane-type triterpenoids (76–103), meroterpenoids (104–129), sesquiterpenoids (130–133), diterpenoids (134–140), and steroids (141–162). Among them, the most characteristic compounds for A. camphorata are ergostane-type triterpenoids (antcins) and meroterpenoids (antroquinonol and derivatives).

2.1 Ergostane-type triterpenoids

Most Antrodia ergostanes possess a unique C29 skeleton with an α-CH3 group at C-4, and a 24-exo-methylene-26-oic acid side chain at C-17β. Moreover, they usually occur as C-25 epimeric pairs (25R- and 25S-forms) (Fig. 2).
image file: d0np00023j-f2.tif
Fig. 2 Structures of (25R)-antcin A (1) and (25S)-antcin A (2).

Antcins A, B, and C were reported as the first ergostanes from A. camphorata in 1995.16 Thus far, a total of 75 ergostane-type triterpenoids (1–75) have been isolated and identified (Table 1). The most abundant ones are 25R/S-antcin B (3/4), 25R/S-antcin C (5/6), 25R/S-antcin H (14/15), and 25R/S-antcin K (18/19).17 For most of the Antrodia ergostanes, the A/B and C/D rings are both trans-fused (Fig. 3). The structural diversity lies in the oxidative substitutions. C-3, C-7, and C-11 are the most frequently oxidated positions, with a ketone group or α/β-OH at C-3, ketone or α/β-OH(OAc) at C-7, and ketone at C-11. C-4, C-12, and C-15 are occasionally substituted with a β-OH, α-OH (β-OH in a few cases), and α-OH, respectively. Some of them occur as methyl or ethyl esters at C-26. Most of the ergostanes possess a Δ8 double bond, with a few exceptions containing conjugated Δ7,9(11) double bonds. The ergostanes could be classified according to the oxidation degree of the tetracyclic skeleton.

Table 1 Ergostane-type triterpenoids 1–75 from Antrodia camphorataa
No. Compounds Formula MW Source References
a *The compounds were isolated as C-25 epimeric mixtures. F, fruiting body; M, mycelium; D, dish culture.
1 (25R)-Antcin A C29H42O4 454 F&M 16 and 17
2 (25S)-Antcin A C29H42O4 454 F&M 16 and 17
3 (25R)-Antcin B (zhankuic acid A) C29H40O5 468 F 16 and 23
4 (25S)-Antcin B (zhankuic acid A) C29H40O5 468 F 16 and 23
5 (25R)-Antcin C C29H42O5 470 F 16 and 23
6 (25S)-Antcin C C29H42O5 470 F 16 and 23
7 (25R)-Antcin D (zhankuic acid F) C29H40O6 484 F&D 18 and 19
8 (25S)-Antcin D (zhankuic acid F) C29H40O6 484 F&D 18 and 19
9 (25R)-Antcin E C29H40O4 452 F&D 18 and 19
10 (25S)-Antcin E C29H40O4 452 F&D 18 and 19
11 Antcin F* C29H40O5 468 F&D 18 and 19
12 (25R)-Antcin G C31H44O6 512 F&D 18 and 24
13 (25S)-Antcin G C31H44O6 512 F&D 18 and 24
14 (25R)-Antcin H (zhankuic acid C) C29H42O6 486 F 23 and 25
15 (25S)-Antcin H (zhankuic acid C) C29H42O6 486 F 23 and 25
16 (25R)-Antcin I (zhankuic acid B) C29H42O5 470 F&M 17 and 25
17 (25S)-Antcin I (zhankuic acid B) C29H42O5 470 F&M 17 and 25
18 (25R)-Antcin K C29H44O6 488 F&M 23 and 28
19 (25S)-Antcin K C29H44O6 488 F&M 23 and 28
20 Methyl antcinate A* C30H44O4 468 F 20
21 Methyl antcinate B* C30H42O5 482 F 20
22 Methyl antcinate G* C32H46O6 526 F 19
23 Methyl antcinate H* C30H44O6 500 F 19
24 Ethyl anticinate B* (zhankuic acid D) C31H44O5 496 F 26
25 Ethyl anticinate H* (zhankuic acid E) C31H46O6 514 F 26
26 Methyl antcinate K* C30H46O6 502 F 29
27 Methyl antcinate N* C30H46O6 502 F 29
28 Camphoratin A* (antcin N) C29H44O6 488 F 21
29 Camphoratin B* C29H44O5 472 F 21
30 Camphoratin C* C29H42O6 486 F 21
31 Camphoratin D* C29H42O6 486 F 21
32 Camphoratin E* C30H44O5 484 F 21
33 Camphoratin F* C30H44O5 484 F 21
34 (25R)-Camphoratin G C29H42O5 470 F&D 18 and 21
35 (25S)-Camphoratin G C29H42O5 470 F&D 18 and 21
36 Camphoratin H C29H44O2 424 F 21
37 Camphoratin J* C30H44O4 468 F 21
38 Antcamphin A C24H36O5 404 F 22
39 Antcamphin B C26H36O4 412 F 22
40 Antcamphin C C29H42O3 438 F 22
41 Antcamphin D C29H42O3 438 F 22
42 Antcamphin E (25S) C29H42O6 486 F 22
43 Antcamphin F (25R) C29H42O6 486 F 22
44 Antcamphin G (25S) C30H44O6 500 F 22
45 Antcamphin H (25R) C30H44O6 500 F 22
46 Antcamphin I (25R) C29H40O6 484 F 22
47 Antcamphin J (25S) C29H40O6 484 F 22
48 Antcamphin K (25S) C29H44O5 472 F 22
49 Antcamphin L (25R) C29H44O5 472 F 22
50 (25R)-Antcamphin N C29H42O6 486 D 18
51 (25S)-Antcamphin N C29H42O6 486 D 18
52 (25R)-Antcamphin O C29H44O7 504 D 18
53 (25S)-Antcamphin O C29H44O7 504 D 18
54 (25R)-Antcamphin P C29H42O6 486 D 18
55 (25S)-Antcamphin P C29H42O6 486 D 18
56 (25R)-Antcamphin Q C29H42O6 486 D 18
57 (25S)-Antcamphin Q C29H42O6 486 D 18
58 (25R)-Antcamphin R C31H44O6 512 D 18
59 (25S)-Antcamphin R C31H44O6 512 D 18
60 (25R)-Antcamphin S C31H46O5 498 D 18
61 (25S)-Antcamphin S C31H46O5 498 D 18
62 Antcamphin T C30H44O5 484 D 18
63 Antcamphin U C31H46O5 498 D 18
64 Antcamphin V C33H48O6 540 D 18
65 Antcamphin W* C30H40O5 480 D 18
66 Antcamphorol B C28H44O5 460 D 27
67 Antcamphorol C C28H44O5 460 D 27
68 Antcamphorol D (25R) C28H42O6 474 D 27
69 Antcamphorol E (25S) C28H42O6 474 D 27
70 Antcamphorol F C29H44O2 424 D 27
71 Antcamphorol G C29H44O2 424 D 27
72 Antcamphorol H C29H46O2 426 D 27
73 Antcamphorol I C29H44O 408 D 27
74 Antcamphorol J C29H44O3 440 D 27
75 Antcamphorol K C29H44O3 440 D 27


image file: d0np00023j-f3.tif
Fig. 3 Structures of ergostanes 3–75.
2.1.1 Di-oxidated Δ8-ergostanes. This type of ergostanes possess two carbonyl groups at C-3 and C-11 (1, 2, 9, 10, 20, 36, 37, 40, 41).16–22 Among them, antcin A (1/2) is considered as the biosynthetic precursor of other ergostanes, and 37 is the only Antrodia ergostane with a 14-βH.21 Compounds 9, 10, and 65 are further dehydrated to form a Δ14 double bond. Camphoratin H (36) possesses a methyl instead of a carboxyl group at C-26. Antcamphins C and D (40, 41) are the first pair of cis–trans isomers of ergostane-type triterpenoids containing an aldehyde group.22
2.1.2 Tri-oxidated Δ8-ergostanes. A total of 29 ergostanes from A. camphorata are oxidized at C-3, C-11, and C-7 or C-14 by ketone, α/β-OH, or α/β-OAc groups.16–27 Among them, 21, 22, 24, 32, 33, and 60–64 are methyl or ethyl esters. Antcamphins K/L (48/49) are the only Antrodia Δ8-ergostanes with a 3β-OH.22 (25R/S)-Antcin B (3/4) and (25R/S)-antcin C (5/6) are the first C-25 epimeric pairs that are separated.23 Antcin F (11) contain a Δ14 double bond. For antcamphorols J and K (74, 75), C-26 is a methyl group. Compounds 12/13 and 58/59 are isomers, only differing in the stereo-configuration of 7-OAc. Compounds 34/35 are deacetylated derivatives of 12/13. For 16/17, C-7 and C-11 are ketones, and C-3 is substituted with an α-OH. Compound 29 is a derivative of 16/17, with a β-OH at C-7.
2.1.3 Tetra-oxidated Δ8-ergostanes. A total of 25 ergostanes are tetra-oxidated. Among them, ten compounds (18, 19, 26, 30, 42–45, 50, 51) are 3,4,7,11-oxidated ergostanes, and another ten compounds (14, 15, 23, 25, 27, 28, 46, 47, 56, 57) are 3,7,11,12-oxidated.18,19,21–23,25–29 Aside from C-3, C-7, and C-11, compounds 7/8, 31 and 54/55 are also substituted with a 14α-OH or 15α-OH. (25R/S)-Antcamphin N (50/51) contain a Δ14 double bond. These compounds usually have high polarity and show good solubility in aqueous methanol.
2.1.4 Penta-oxidated Δ8-ergostanes. (25R/S)-Antcamphin O (52/53) are oxidated at C-3, C-4, C-7, C-11 and C-12, and are the most highly oxidated ergostanes from A. camphorata.18
2.1.5 Δ7,9(11)-Ergostanes. These ergostanes (70–73) harbor a Δ7,9(11) backbone, with two methyl groups substituted at C-25. The absolute configuration for antcamphorol F (70) was determined by single-crystal X-ray diffraction.27
2.1.6 Norergostanes. Although most of the Antrodia ergostanes possess a C29 skeleton, norergostanes with C24, C26, or C28 skeletons have also been reported.22,27 Compounds 38 and 39 have a C24 and C26 skeleton, respectively, and 66/67 are a pair of E-/Z-isomers with a C28 skeleton. Antcamphorols D and E (68, 69) possess similar structures with (25R/S)-antcin K (18/19), only missing the methyl group at C-4.
2.1.7 Structural characterization of ergostanes. In the UV spectra, the Antrodia ergostanes show a characteristic absorption maximum at around 254 nm (Δ8(9), 11-oxo) or 274 nm (7-oxo, Δ8(9), 11-oxo) (Fig. 4). Their NMR spectra also show characteristic features. The 1H NMR spectra usually display five methyl signals (δH 0.62–2.12) and two terminal olefinic signals (H2-28, δH 4.82–5.25). The 13C NMR spectra show 29 carbon signals, including five methyl groups, one olefinic methylene group (C-28, δC 107.0–111.8), one to three ketone carbonyl groups (C-3/C-7/C-11, δC 199.1–212.4), and one carboxyl group (C-26, δC 176.9–177.6). Some diagnostic NMR signals could be used to determine the location and stereo-configuration of hydroxyl groups (Fig. 5A).22 For instance, H-3α (peak width at half height W1/2 = 28.4–33.5) shows a remarkably broader peak than H-3β (W1/2 = 8.1–8.8) due to the axial–axial couplings of H-3α with H-2 and H-4. This evidence could be used to determine the configuration of 3-OH.
image file: d0np00023j-f4.tif
Fig. 4 Typical UV spectra of ergostanes and lanostanes.30

image file: d0np00023j-f5.tif
Fig. 5 The applications of NMR spectroscopy for structural characterization of Antrodia triterpenoids. (A) 1H NMR to determine the stereo-configuration of H-3 of ergostanes. (B) 1H NMR combined with a chiral derivatizing reagent (AT) to determine the absolute configuration of C-25 of (25S)-antcin G (13). (C) 1H and 13C NMR to differentiate Δ7,9(11) and Δ8(9) lanostanes.22,23

The C-25 epimers of Antrodia ergostanes exhibit very similar physicochemical properties. They were obtained as a mixture in many early literatures. These epimers could be separated by supercritical fluid chromatography (SFC) using chiral or achiral packing materials.30 The epimers of hydrophilic ergostanes like antcin K (18/19) could also be separated by reversed-phase HPLC. In recent publications, most new ergostanes were isolated as pure optical forms using these techniques.

The absolute configurations for C-25 were determined using a chiral derivatizing reagent-based method for the first time by Du et al. in 2012.23 The carboxyl group at C-26 reacts with (R)- and (S)-1-(9-anthryl)-2,2,2-trifluoroethanonyl (AT) to obtain a pair of diasteromeric esters, and the absolute configuration of C-25 could be established by comparing the 1H NMR signals for surrounding protons of the two esters. For instance, for (25S)-antcin G (13), the signals for CH3-18 and CH3-21 (L2 group) of the (R)-AT-ester shifted upfield more significantly than signals of the (S)-AT-ester due to the anisotropic effect of AT anthracene group, thus leading to ΔδR–S < 0 (Fig. 5B).31

2.2 Lanostane-type triterpenoids

Lanostane-type triterpenoids are a group of tetracyclic triterpenoids derived from lanosterol, which is widely present in fungal species including Ganoderma lucidum, Poria cocos, Laetiporus sulphureus, Inonotus obliquus, and Daedalea dick-insii.32 They possess trans-junctions of A/B and C/D rings, a gem-dimethyl group at C-4, β-oriented methyl groups at C-10 and C-13, an α-oriented methyl group at C-14, and a β-oriented side chain at C-17. Most of the Antrodia lanostanes possess a C31 or C30 skeleton, with a hydroxyl or ketone group at C-3, and a carboxyl group at C-21 or C-26. They usually contain Δ8 and Δ7,9(11) double bonds, and occur as a pair, which are difficult to be separated. For some compounds, C-7 is substituted with a hydroxyl or ketone group, and C-15 has an α-OH/OAc group. The Antrodia lanostanes have lower degrees of oxidation than Ganoderma lanostanes like ganoderic acids, though their structures are very similar.33

Thus far, a total of 28 lanostanes (76–103) have been isolated from A. camphorata (Table 2). Eburicol (76) is the first one reported from this species, and the most abundant ones are eburicoic acid (77), sulphurenic acid (78), dehydroeburicoic acid (83), and dehydrosulphurenic acid (84).

Table 2 Lanostane-type triterpenoids 76–103 from Antrodia camphorataa
No. Compounds Formula MW Source References
a *The compounds were isolated as C-25 epimeric mixtures. F, fruiting body; M, mycelium; D, dish culture.
76 Eburicol (24-methylenedihydrolanosterol) C31H52O 440 F 20
77 Eburicoic acid C31H50O3 470 F 28
78 Sulphurenic acid C31H50O4 486 F 28
79 Versisponic acid D C33H52O5 528 F 28
80 Antcamphin X C31H48O4 484 D 18
81 Eburicone C31H50O 438 D 18
82 24-Methylenelanost-8-ene-3β,15α,21-triol C31H52O3 472 F 22
83 Dehydroeburicoic acid C31H48O3 468 F 26
84 Dehydrosulphurenic acid C31H48O4 484 F 26
85 15α-Acetyl-dehydrosulphurenic acid C33H50O5 526 F 26
86 Dehydroeburiconic acid C33H48O5 524 D 18
87 24-Methylenelanosta-7,9(11)-diene-3-one C31H48O 436 D 18
88 3β,15α-Dihydroxylanosta-7,9(11),24-trien-21-oic acid C30H46O4 470 F 28
89 Ganoderic acid Sz C30H44O3 452 F&M 34
90 Ganoderic acid S C32H48O5 512 F&M 34
91 Ganodermadiol C30H48O2 440 F&M 34
92 3,7,11-Trioxo-5α-lanosta-8,24(E)-dien-26-oic acid C30H42O5 482 F&M 34
93 Methyl 11α-hydroxy-3,7-dioxo-5α-lanosta-8,24(E)-dien-26-oate C31H46O5 498 F&M 34
94 11α-Hydroxy-3,7-dioxolanost-8,24(E)-dien-26-oic acid C30H44O5 484 F&M 35
95 Lanosta-8,24-diene-3,21-diol C30H50O2 442 F&M 34
96 Methyl-3,7,11,12,15,23-hexaoxo-5α-lanost-8-en-26-oate* C31H40O8 540 F&M 34
97 Ethyl-3,7,11,12,15, 23-hexaoxo-5α-lanost-8-en-26-oate* C32H42O8 554 F&M 34
98 7β-Hydroxy-3,11,15,23-tetraoxo-27ξ-lanosta-8,16-dien-26-oic acid* C30H40O7 512 F&M 35
99 15-O-Acetylganolucidate A* C32H46O7 542 F&M 35
100 Antcamphorol A C31H50O3 470 D 27
101 Hypocrellol A C30H48O3 456 D 18
102 Ethyl lucidenate A C29H42O6 486 F&M 35
103 Ethyl lucidenate F C29H40O6 484 F&M 35

2.2.1 C31 Δ24(28)-lanostanes. Twelve compounds belong to this type, including 76–87 (Fig. 6).18,20,22,26,28 They possess a C31 skeleton with a 24-methylene side chain. The methyl group at C-21 could be oxidized to a hydroxymethyl or carboxyl group.
image file: d0np00023j-f6.tif
Fig. 6 Structures of lanostanes 76–87.
2.2.2 C30 Δ24-lanostanes. This type (88–95) usually possesses a C30 skeleton with a Δ24 double bond, and the methylene at C-24 is absent (Fig. 7).28,34,35 Compound 90 is the only Antrodia lanostane with a 3α-OH.
image file: d0np00023j-f7.tif
Fig. 7 Structures of lanostanes 88–99.
2.2.3 C30 23-oxo-lanostanes. Compounds 96–99 contain a ketone group at C-23, and C-24 is saturated (Fig. 7).34,35 It is also noteworthy that all of them except for 99 possess a ketone group at C-15, which is rare for Antrodia lanostanes.
2.2.4 C-21–C-24-epoxy lanostanes. Compounds 100 and 101 possess a C-21–C-24-epoxy ring at C-17 (Fig. 8).18,27 Compound 100 is an unprecedented C31 lanostane-type triterpenoid featuring a methyl group at C-15, and the absolute configuration was determined using single-crystal X-ray diffraction.27
image file: d0np00023j-f8.tif
Fig. 8 Structures of lanostanes 100–103.
2.2.5 Norlanostanes. Compounds 102 and 103 have a C27 skeleton, and both compounds are ethyl esters (Fig. 8).35
2.2.6 Structural characterization of lanostanes. The Δ7,9(11) and Δ8 backbones could be easily differentiated according to the maximal UV absorptions (∼242 nm vs. ∼198 nm) (Fig. 4). The Δ7,9(11) lanostanes show two additional olefinic signals in the 1H NMR spectra (δH 5.34–5.88). In the 13C NMR spectra, the Δ8 lanostanes show two alkene signals at δC 134.1–135.7, and the Δ7,9(11) lanostanes show four signals at δC 116.0–147.4 (Fig. 5C).

2.3 Meroterpenoids (antroquinonol and derivatives)

Antroquinonols are characteristic constituents of A. camphorata. They may originate from the combination of an orsellinic acid-derived C7 cyclohexenone and a C15 sesquiterpene unit, and thus belong to meroterpenoids. So far, 26 antroquinonols (104–129) have been isolated from the n-hexane extract of this mushroom (Table 3).36–46 Antroquinonol (104) was the first compound of this type reported from A. camphorata in 2007, followed by antroquinonol B (105) and 4-acetyl-antroquinonol B (106).36–38 Similar structures have also been reported from other fungi.39 Antroquinonol and its derivatives have attracted extensive attention due to their significant antitumor activities, which have been tested in clinical trials. Recently, the total synthesis of (±)-antroquinonol has been achieved, through a concise and efficient route.40,41
Table 3 Meroterpenoids 104–129 from Antrodia camphorataa
No. Compounds Formula MW Source References
a F, fruiting body; M, mycelium; B, culture broth.
104 Antroquinonol C24H38O4 390 F&M 36
105 Antroquinonol B C24H36O6 420 M 37
106 4-Acetylantroquinonol B C26H38O7 462 B 37
107 Antroquinonol C C25H40O5 420 M 42
108 Antroquinonol D C23H36O3 360 F&M 43
109 Antrocamol LT1 C24H38O5 406 M 44
110 Antrocamol LT2 C26H40O6 448 M 44
111 Antrocamol LT3 C24H38O5 406 M 44
112 4-Acetylantrocamol LT3 (4-acetylantroquinonol H) C26H40O6 448 M 45
113 Antroquinonol L C23H32O3 356 B 38
114 Antroquinonol N C24H34O5 402 B 38
115 Antroquinonol O C23H36O5 392 B 38
116 Antroquinonol P C24H38O6 422 B 38
117 Antroquinonol Q C26H40O7 464 B 38
118 Antroquinonol R C23H36O6 408 B 38
119 Antroquinonol S C23H34O5 390 B 38
120 Antroquinonol T C26H42O8 482 B 38
121 Antroquinonol U C24H36O7 436 B 38
122 Antroquinonol V C24H38O5 406 B 38
123 Antroquinonol W C24H40O5 408 B 38
124 Antroquinonol X C23H32O3 356 B 38
125 Ubiquinone Q3 C24H34O4 386 B 38
126 Antroubiquinol A C23H32O5 388 M 46
127 4-Acetylantroquinonol I C26H40O6 448 M 46
128 4-Acetylantroquinonol J C26H42O6 450 M 46
129 4-Acetylantroquinonol K C26H40O7 464 M 46

Most of the antroquinonols bear a cyclohexenone ring, a methoxyl group at C-2, a methyl at C-6, and Δ2, Δ8 and Δ12 double bonds (Fig. 9). Among them, 105, 106, 119, and 126 contain a γ-lactone ring at the side chain, and 106 is one of the most abundant meroterpenoids in A. camphorata. Compounds 113, 114 and 125 possess a 1,4-benzoquinone ring, while 124 contains a benzopyran ring.


image file: d0np00023j-f9.tif
Fig. 9 Structures of meroterpenoids 104–129.

2.4 Sesquiterpenoids, diterpenoids, and steroids

A total of four sesquiterpenoids (130–133) including a sesquiterpene lactone, a naphthalenecarboxaldehyde, a nerolidol, and a cadinol, and seven labdane diterpenoids (134–140) have been reported from A. camphorata (Fig. 10, Table S2 and Fig. S1†). As a unique drimane-type sesquiterpenoid with potent anticancer activities, the total synthesis of antrocin (130) has been reported.47 While steroids and terpenoids are generally considered as two different classes of natural products, the 22 steroids (141–162) from A. camphorata were collected into this review article due to the close biosynthetic relationships. Among the steroids, ergosterol (141) is a major constituent of A. camphorata.
image file: d0np00023j-f10.tif
Fig. 10 Structures of sesquiterpenoids (130–133), diterpenoid 134, and steroid 141.

3 Resources and quality evaluation

Due to the increasing demands and special growing conditions, different cultivation techniques for A. camphorata have been developed, including cutting wood culture, dish culture, submerged fermentation, and solid support culture.8 Different cultivation techniques and conditions may lead to remarkably different chemical profiles (Fig. 11).17,48 The cutting wood cultures grow on the wood of Cinnamomum trees. The chemical constituents are the most similar to the wild growing mushroom, though the cultivation may take 2–3 years and the cost is high. The submerged fermentations use mixed nutrients and natural extracts as the media, and the solid support cultures use grains or agricultural by-products as the substrates. Their cultivation duration is short (several weeks). It is generally considered that these two types of cultures contain low amounts of triterpenoids and high amounts of polysaccharides. However, the addition of certain nutrients may remarkably increase the production of triterpenoids.9 The dish cultures usually grow on agar media containing different nutrients in petri dishes, and the cultivation duration is relatively short. More importantly, its chemical constituents are similar to those of cutting wood cultures, and it is suitable for large-scale production. Moreover, chemical constituents for the fruiting bodies and the mycelia of the fungus may also vary remarkably. Thus, it is important to evaluate the quality of Antrodia samples.
image file: d0np00023j-f11.tif
Fig. 11 UPLC/UV chromatograms of triterpenoids in different cultures of Antrodia camphorata (250 nm). Adapted from ref. 17.

For sample extraction, aqueous organic solvents like 50% methanol may be used to extract the ergostanes, and methanol or ethanol needs to be used for the lanostanes, because the Antrodia lanostanes usually have lower polarities than the ergostanes.17 A number of methods have been developed for the analysis of triterpenoids in A. camphorata. The C-25 epimeric ergostane mixtures could be separated by supercritical fluid chromatography, capillary electrophoresis, or reversed-phase liquid chromatography.23,30,49 Our group developed a UHPLC/DAD/qTOF-MS method to characterize 49 triterpenoids in A. camphorata, and 31 compounds were confirmed by comparing with reference standards. Moreover, the contents of 18 major triterpenoids in 15 batches of A. camphorata samples were determined by UPLC/UV or SFC/MS. The highest contents for the most important compounds are listed as follows: 25R/S antcin B (3/4, 17.8 mg g−1), 25R/S antcin C (5/6, 20.4 mg g−1), 25R/S antcin H (14/15, 31.3 mg g−1), 25R/S antcin K (18/19, 53.5 mg g−1), eburicoic acid (77, 13.9 mg g−1), sulphurenic acid (78, 23.8 mg g−1), dehydroeburicoic acid (83, 30.1 mg g−1), and dehydrosulphurenic acid (84, 26.6 mg g−1). This was the first time that the contents of pure optical forms for 25R-/S-ergostane epimers were quantitatively determined.17

4 Biosynthesis of triterpenoids and antroquinonols

4.1 Genome and transcriptome analysis

The first genome draft (32.15 Mb, 9254 genes) of A. camphorata was reported in 2014.50 A new 29.7 Mb genome analysis was published in 2018.51 The genomes of related mushrooms like Postia placenta, Ganoderma lucidum, and Ganoderma australe have also been sequenced.52–54 Although A. camphorata is morphologically and chemically similar to Ganoderma species, it is evolutionarily closer to the brown-rot fungus P. placenta. The genome data (730.7 Mb) of Cinnamomum kanehirae, the native host of A. camphorata, has been published recently.55 Two peroxidases may contribute to the wood degradation and colonization capacity of the fungus in this unique habitat.56 The transcriptomes of both fruiting body and mycelium of Antrodia camphorata have been reported.50,51,57 These data are valuable to study the growth, development, biosynthesis, and parasitic mechanisms of A. camphorata.

4.2 Biosynthesis of antroquinonols

Antroquinonols have a highly similar structural skeleton to coenzyme Q (CoQ).58 They may originate from the combination of an orsellinic acid-derived C7 cyclohexenone and a C15 sesquiterpene, which are from the polyketide or shikimate pathway and the mevalonate pathway, respectively (Fig. 12). The polyketide synthase gene pks63787 may participate in the biosynthesis of orsellinic acid, a possible precursor for the benzoquinone ring (Table S3†).59,60 On the other hand, 4-hydroxybenzoic acid from the shikimate pathway was reported as a precursor for antroquinonol (104).61Ac-mvd, a mevalonate pyrophosphate decarboxylase gene, may be involved in its upstream biosynthesis.62 The γ-lactone ring of 4-acetylantroquinonol B (106) was proposed to form before the aromatic farnesylation, by condensation of the terminal carboxyl group with the hydroxyl group, or by cyclization of the oxidized terpene.58,63
image file: d0np00023j-f12.tif
Fig. 12 Proposed biosynthesis pathways for antroquinonols and triterpenoids in Antrodia camphorata. SQS, squalene synthase; SQE, squalene monooxygenase or epoxidase; Coq2/3/6, coenzyme Q2/3/6; IPP, isopentenyl diphosphate; GPP, geranyl diphosphate; FPP, farnesyl diphosphate; OA, orsellinic acid; DMQ0, demethoxy-coenzyme Q0; 4-HBA, 4-hydroxybenzoic acid; FOA, 3-farnesyl-orsellinic acid; FHB, 3-farnesyl-4-hydroxybenzoic acid. *, genes characterized from A. camphorata; ▲, similar genes from yeast.15,58,61

4.3 Biosynthesis of triterpenoids

The triterpenoids are derived from the mevalonate pathway. AcOSC is a 2,3-oxidosqualene cyclase (OSC) of A. camphorata catalyzing the formation of lanosterol. Lanosterol could be further oxidized to form lanostane-type triterpenoids (Table S3†).64 The biosynthetic genes for ergostanes are not clear yet, though they have been proposed to be derived from lanostanes. AcCyp51, encoding a sterol 14α-demethylase, was reported as a functional gene in the biosynthesis of ergostanes.65 Besides, ten potential triterpenoid P450 genes have been discovered for high expression during the formation of fruiting bodies, though their functions have not been characterized.66 The proposed biosynthetic pathway for triterpenoids in A. camphorata is shown in Fig. 12.

4.4 Biosynthesis of other terpenoids

Ten terpenoid synthases have been characterized from A. camphorata. They could utilize GPP or FPP to form mono- and sesqui-terpenoids, respectively. They may be involved in the biosynthesis of antrocin (130).67

4.5 Elicitors for triterpenoid and antroquinonol production

Many strategies have been reported to improve the terpenoids production in A. camphorata. The content of 4-acetylantroquinonol B (106) was significantly improved by adding to the culture medium precursor compounds, including 4-hydroxybenzoic acid, vanillic acid, 2,4-dihydroxybenzoic, 2,4,5-trimethoxybenzaldehyde, coenzyme Q0, coenzyme Q10, or nerolidol.68,69 The production of antroquinonols could also be improved when orsellinic acid, camphorwood leach liquor, soybean oil, or H2O2 were added.70,71 The content of antroquinonol (104) in the submerged fermentation could reach 80.1 mg L−1.72 Moreover, monoterpene, tangerine oil, red light, or α-terpineol could act as elicitors for the biosynthesis of triterpenoids.73–75

5 Pharmacological activities and medicinal potential

A. camphorata has been used for hepatoprotection and alcohol intoxication treatment by Taiwan local residents for a long history. A plenty of investigations have been reported on the pharmacological activities and mechanisms of A. camphorata extracts and the major compounds. These researches were summarized here with special focus on triterpenoids and antroquinonols with medicinal potential (Fig. 13).
image file: d0np00023j-f13.tif
Fig. 13 The bioactivities (A) and proposed mechanisms (B) of A. camphorata compounds.

5.1 Anti-cancer activities

The extracts and compounds of A. camphorata exhibited a broad spectrum of anticancer activities on different types of cancer, including bladder cancer, breast cancer, liver cancer, lung cancer, pancreatic cancer, squamous cell carcinoma, leukemia, and adenocarcinoma (Table S4†). For in vitro experiments, the IC50 values ranged from 2.36–170 μg mL−1.76–84 Some results were proved by in vivo experiments. For example, the treatment with an ethanol extract of fruiting bodies (0.9 g kg−1, p.o., for 2 weeks) could inhibit the proliferation and migration of murine leukemia WEHI-3 cells and their tumorigenicity in a BALB/c mice allograft tumor model, via reducing p-ERK1/2, p-Akt and MMP-9, and upregulating p21 and p27.79 A clinical research reported that the dish cultured fruiting bodies (5 to 10 g d−1 for 6 months) prolonged survival of an 88-year-old patient with small cell lung cancer.85

Antroquinonol (104), 4-acetylantroquinonol B (106), and antroquinonol D (108) exhibited anticancer effects against many cell lines, including colon cancer, lung cancer, liver cancer, breast cancer, and glioblastoma cancer, mainly through AMPK/mTOR and JAK-STAT pathways.38,43,86–90 For instance, 4-acetylantroquinonol B (2.5 mg kg−1, i.p., for 6 weeks) exhibited anticancer effects in colorectal cancer xenograft nude mice, via regulation of Lgr5/Wnt/β-catenin and JAK-STAT pathways.88 Due to its potent antitumor activities, a number of clinical studies on antroquinonol have been conducted (Table S1†). The phase I clinical trial of Hocena® (the trade name of antroquinonol) against NSCLC started in 2010, and the phase II trial started in 2013 in the US and Taiwan (ClinicalTrial.gov: NCT01134016, NCT02047344). The study indicated that antroquinonol at up to 600 mg daily for 4 weeks was generally safe.91

Triterpenoids and sesquiterpenoids from A. camphorata also showed potent anticancer effects. Dehydroeburicoic acid (83) possessed cytotoxicities against HL-60 and U87MG cancer cells with IC50 values of 3.4 and 25.7 μM, respectively.92,93 It could suppress tumor size in HL60 xenografted female immune-deficient athymic mice through DNA damaging and mitochondrial dysfunction. Antcins B, H, K (3/4, 14/15, 18/19) and methyl antcinates A, B (20, 21) exhibited promising cytotoxic activities against liver, colon, oral, and breast cancer cells with IC50 values of 22.3–78.0 μM.94–100 The potential mechanism was through suppression of apoptosis via endoplasmic reticulum stress, and suppression of integrin-mediated adhesion, migration, and invasion (Fig. 14). Antrocin (130) exhibited antitumor effects on lung cancer and breast cancer cells both in vitro and in vivo.101,102


image file: d0np00023j-f14.tif
Fig. 14 Proposed mechanism of action of antcins B (3/4), H (14/15), K (18/19), and methyl antcinate A (20) in the suppression of cancer.95–99

Furthermore, A. camphorata possessed synergistic anti-tumor effects with chemotherapeutic agents like mitomycin, cisplatin, trichostatin A, amphotericin B, paclitaxel, sorafenib, 5-fluorouracil, and methotrexate.103–109 For instance, an ethanol extract of A. camphorata significantly increased the tumor inhibition efficacy of sorafenib to 52% on Huh-7 xenograft NOD-SCID mice (100 mg kg−1 extract and 2.5 mg kg−1 sorafenib, i.p., 7 weeks), by targeting mitogen-activated protein (MAP) kinases, modulating cyclin proteins expression, and inhibiting cancer cell invasion.108 Antcin H (14/15, 20 mg kg−1, intratumorally, every other day for 24 days) could enhance the cytotoxicity of low-dose methotrexate (0.5 mg kg−1), significantly suppress tumor growth from 43% to 72%, and prolong the survival from 93.5 days to 106.5 days on Raji lymphoma xenograft NOD-SCID mice, via inhibiting LMP1-induced JAK/STAT related signalling.110 Antrocin (130, 100 mg kg−1) effectively enhanced the radiosensitivity on LAPC4-KD xenografted male BALB/c-nu mice, decreasing tumor size from 76.4% to 88.2% through inhibiting PI3K/AKT and MAPK signalling pathways.111 Our group found that (25R)-antcamphin R (58) and dehydrosulphurenic acid (84) at 20 μM could remarkably enhance the cytotoxicity of paclitaxel (10 nM) against HL60 cells, with inhibition rates increased from 19.6% to 58.2% and 70.6%, respectively.18

5.2 Hepatoprotective activities

The hepatoprotective activities of A. camphorata and its terpenoids have been studied extensively using different hepatotoxicity models. These models were induced by alcohol, galactosamine/TNF-α, acetaminophen (APAP), thioacetamide, carbon tetrachloride (CCl4), lipopolysaccharide (LPS), concanavalin A, or 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) (Table S5†). The proposed mechanisms were summarized in Fig. 15.
image file: d0np00023j-f15.tif
Fig. 15 Proposed mechanisms of action of A. camphorata on alcohol or toxicant induced liver injury.112,113,115–119 AC, Antrodia camphorata extract; 3/4, antcin B; 18/19, antcin K; 77, eburicoic acid; 83, dehydroeburicoic acid; 148, ergostatrien-3β-ol.

The fermented mycelia of A. camphorata (0.5–1.0 g kg−1, p.o., for 4 weeks) reduced liver fibrosis induced by CCl4 in rats by scavenging free radical formation.112 Petri-dish cultured A. camphorata (0.3, 0.6, 1.2 g kg−1, p.o., for 30 days) could protect alcohol-induced hepatic injury in Kunming mice by reducing the serum levels of triglyceride (TG), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and malondialdehyde (MDA).113

Antcin H (14/15, 25 and 50 mg kg−1, i.p.) could protect against liver injury in both galactosamine/TNF-α and APAP-induced mice models, reducing the ALT and glutathione (GSH) levels, through disruption of the binding of p-JNK to Sab, which interfered with the ROS-dependent self-sustaining activation of MAPK cascade.114 Our group screened the protective activities of 26 Antrodia triterpenoids (20 μM) on CCl4-induced HepG2 cell injury model. The compounds could increase the cell viabilities from 50% to >80%. Among them, antcins B and K (3/4, 18/19) (50 mg kg−1, p.o., for 7 days) ameliorated CCl4-induced liver injury in mice, decreasing ALT and AST levels and the incidence of liver necrosis. The activities were even more potent than silymarin.115 Eburicoic acid (77) and dehydroeburicoic acid (83) (20 mg kg−1, i.p., for 7 weeks) could protect against CCl4-induced acute hepatic damage in male ICR mice via antioxidant and anti-inflammatory mechanisms.116 The in vivo protective effects of antcin C (5/6) and antroquinonol (104) against AAPH and alcohol-induced acute liver damages have also been reported.117,118 Furthermore, Antrodia compounds also exhibited significant hepatoprotective effects on chronic mice models. For instance, antrosterol (148) (1, 5, 10 mg kg−1, p.o., for 4 weeks) reduced serum and liver lipids of alcohol-diet fed mice by regulating lipid homeostasis, antioxidant capability, alcohol metabolism, and anti-inflammation.119 It lowered fibrosis related gene expressions, as well as the serum levels of AST, ALT, TNF-α, and IL-1β.

5.3 Anti-inflammatory activities

Inflammation is caused by a variety of stimuli, and could lead to a plenty of diseases.120A. camphorata possesses promising anti-inflammatory activities. The methanol extracts of both solid-state-cultured mycelia and wood-cultured fruiting bodies (300 mg kg−1, i.p., for 2 weeks) alleviated hyperoxia-induced lung injury in transgenic mice (NF-κB-luciferase+/+), reducing neutrophil infiltration, lung edema, ROS generation, and the expression of IL-6, TNF-α, IL-1β, IL-8, IKKα/β and iNOS.121 The methanol extract of solid-state-cultured mycelia (50, 250 mg kg−1, p.o., for 5 weeks) reduced Dermatogoides pteronyssinus-induced airway hyperresponsiveness in pathogen-free male BALB/c mice. It could reduce total serum IgE level, recruit inflammatory cells to the bronchoalveolar lavage fluid through cytokine downregulation and Th1/Th2/Th17 response modulation, and exert synergistic effects on multiple targets to relieve asthma symptoms.122

The total triterpenoids extract (5–20 mg kg−1, p.o., for 35 days) reduced inflammation to promote wound healing on streptozotocin (STZ) induced hyperglycemia-diabetes mice.123 Eburicoic acid, dehydroeburicoic acid, and ergostatrien-3β-ol (148) (10 mg kg−1, i.p., single dose) decreased the paw edema in ICR mice induced by carrageenan, via increasing the activities of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx).124,125 Antcins A and B exhibited potent inhibition against N-formylmethionyl-leucyl-phenylalanine (fMLP)-induced superoxide production with IC50 values of below 10 μM.126 A number of lanostanes significantly suppressed NO production in LPS-treated murine macrophage RAW 264.7 cells with IC50 values of below 10 μM.35

5.4 Anti-diabetic activities

The ethanol extract of A. camphorata increased high glucose-induced insulin secretion dose-dependently through peroxisome proliferator-activated receptor-γ (PPAR-γ) pathway, and protected from ER stress-induced apoptosis in MIN6 cells.127 The nanoencapsulated triterpenoid extracts of dish-cultured A. camphorata were evaluated in high-fat diet (HFD) and STZ-induced diabetic rats.128 Oral treatment of 4–20 mg kg−1 for 6 weeks significantly reduced fasting glucose and serum insulin levels.

The triterpenoids, such as antcin K, eburicoic acid, dehydroeburicoic acid, sulphurenic acid (78), and ergostatrien-3β-ol (148) also displayed antidiabetic and antihyperlipidemic effects in palmitate-treated C2C12 myotubes and in HFD or STZ-induced diabetic mice.129–133 Eburicoic acid could significantly prevent the decrease of phospho-Akt (p-Akt) expression levels in the C2C12 myotubes caused by palmitate. It could also decrease the relative weights of epididymal white adipose tissue and visceral fat from 6–8% to 3–4% (10–40 mg kg−1, p.o., for 4 weeks), reduce the levels of blood glucose, triglyceride, total cholesterol, insulin and leptin, and increase adiponectin levels in HFD mice.129 Dehydroeburicoic acid (10–40 mg kg−1, p.o., for 4 weeks) could markedly decrease blood glucose levels by 42.6–46.5% and reduce the levels of triglyceride and total cholesterol in STZ-induced diabetic mice, via regulation of GLUT4, PPARα, FAS, and phosphorylation of AMPK.132 A number of Antrodia triterpenoids (20 μM) exhibited significant ROS scavenging activities (63.9–70.5%) in high glucose-induced HUVECs.27

5.5 Neuroprotective activities

The extract of A. camphorata fruiting bodies showed significant neuroprotective activities in Aβ40-treated PC-12 cells. Furthermore, the extract (79.45 mg kg−1, p.o., for 28 days) could improve memory and learning abilities of Aβ40 infusion induced Alzheimer's disease (AD) model rats.134 Antroquinonol (7.2, 34.2 mg kg−1, p.o., for 2 months) could improve learning and memory in the Morris water maze test of amyloid precursor protein transgenic AD model mice, reduce hippocampal Aβ levels, and reduce the degree of astrogliosis. It increased Nrf2 expression and reduced histone deacetylase 2 (HDAC2) expression in the hippocampus.135 Moreover, a number of Antrodia diterpenoids exhibited neuroprotective activities in vitro by protecting neurons from Aβ damage.136

5.6 Miscellaneous activities

Immunomodulatory and anti-angiogenic activities have been reported for A. camphorata. While the immunomodulatory activities are mainly related with polysaccharides,137,138 methyl antcinate K (26, 50 μM) was reported as the first natural triterpenoid to promote the ability of dendritic cells (DCs) to prime Th2 responses, and can potentially be used to enhance immune responses and modulate DC function in immunotherapy.29 The ethanol extract of A. camphorata produced anti-angiogenic effects in mice by inhibiting the vascular endothelial growth factor receptor 2 (VEGFR2) signalling pathway.139

5.7 Metabolism and pharmacokinetics

The metabolism and pharmacokinetics of triterpenoids in A. camphorata were firstly reported in 2015 by our group. After oral administration of the ethanol extract, 18 triterpenoids and 8 biotransformed metabolites were detected in rats plasma by UHPLC/qTOF-MS.140 The ergostanes and Δ7,9(11) lanostanes, but not the Δ8 lanostanes, could be absorbed into circulation. High-polarity ergostanes (antcins H and K) and Δ7,9(11) lanostanes were metabolically stable. Meanwhile, low-polarity ergostanes (antcins B and C) undertook hydrogenation (C-3 or C-7 carbonyl groups) or hydroxylation reactions to produce polar metabolites. Moreover, the pharmacokinetics of 14 triterpenoids and 2 metabolites were simultaneously monitored by LC/MS/MS in rats after oral administration of the ethanol extract (1.0 g kg−1). The ergostanes were absorbed and eliminated rapidly, whereas the lanostanes remained in the plasma at a low concentration for a relatively long time. In a mice xenograft S180 tumor model, antcin H (14/15) could be detected in the tumor tissue following oral administration of A. camphorata extract.141 A Caco-2 cell monolayer model was used to test the intestinal absorption properties of 14 triterpenoids from A. camphorata.142 Most ergostanes exhibited high permeability. Antcins A, B, C, H and K could pass through the monolayer via passive transcellular diffusion, and showed high PAB and PBA values (>2.5 × 10−5 cm s−1). Meanwhile, the lanostanes including dehydrosulphurenic acid, 15α-acetyldehydrosulphurenic acid, dehydroeburicoic acid, and eburicoic acid exhibited poor permeability.

The metabolism and pharmacokinetics of antroquinonol have been studied in human and rats. A clinical study evaluated the pharmacokinetics of antroquinonol in patients with metastatic non-small-cell lung cancer after oral administration. These patients received escalating doses (50–600 mg) of once-daily antroquinonol in 4 week cycles (up to 3 cycles).91 Antroquinonol was rapidly eliminated following single and multiple administrations (T1/2 1.30–4.33 h). The Tmax of plasma concentration was 1.00–3.70 h after a single-dose, and 1.92–4.05 h after a multiple-dose treatment. In rats, four metabolites of antroquinonol were isolated from the urine after oral treatment, and their structures were identified by NMR spectroscopic analysis. All the metabolites had a cleaved side chain with a terminal carboxyl group. This catabolic reaction was similar to the cleavage of cholesterol side chain.143

5.8 Toxicity

A. camphorata showed no obvious toxicity in several animal toxicity studies.144–146 Male and female BALB/c mice were orally treated with a water extract of A. camphorata (up to 1666.67 mg per kg per day) for 90 consecutive days, and no significant differences were observed between the control and treatment groups.144 In another study, the 90 day oral toxicity of submerged cultures of A. camphorata was assessed in male and female Sprague-Dawley rats. No significant toxicities were observed for A. camphorata at a dose of 3000 mg per kg per day.145

Hocena® (antroquinonol) showed a safe dosage from 50 to 600 mg daily for 4 weeks in 13 NSCLC subjects.147 No all-cause mortality or serious adverse events were reported. Other adverse events included diarrhea, vomiting, and nausea. Another study reported 36 patients with metastatic non-small-cell lung cancer that received escalating doses of once-daily antroquinonol in 4 week cycles.91 The study indicated that antroquinonol at up to 600 mg daily was basically safe. No mortalibites or serious adverse events were reported, and the most common adverse events were diarrhea, vomiting, and nausea.

Thus far, no reports are available on the toxicity of ethanol extracts of A. camphorata, which mainly consist of triterpenoids. The toxicity of major bioactive triterpenoids such as antcins B, C, H and K, and dehydroeburicoic acid has yet to be studied.

6 Conclusions and future perspectives

A. camphorata is a popular dietary supplement and a promising natural medicine. In the past three decades, 162 terpenoids have been identified from A. camphorata. Among them, ergostane- and lanostane-type triterpenoids, as well as antroquinonols (meroterpenoids) are the major bioactive constituents. Chemical or enzymatic modifications could be used to expand structural diversity of the terpenoids, and to improve their physicochemical and pharmacological properties as drug candidates. For example, hydroxylation or glycosylation may improve solubility, bioavailability, and bioactivity of the triterpenoids.148

Based on the bioactivities, pharmacokinetics, and natural abundances, the most promising terpenoids in A. camphorata for medicinal development include the anti-cancer agents antroquinonol (104), 4-acetylantroquinonol B (106), and antrocin (130), together with the hepatoprotective compounds antcin B (3/4), antcin C (5/6), antcin H (14/15), antcin K (18/19), eburicoic acid (77), sulphurenic acid (78), dehydroeburicoic acid (83), dehydrosulphurenic acid (84), and ergostatrien-3β-ol (148). Potential of the triterpenoids for the treatment of cancer, diabetes, and hyperlipidemia is also noticeable. However, our understanding on detailed mechanisms of actions and molecular targets of the pure compounds is still limited, particularly the mechanisms different from those of currently known drugs. In-depth basic research will benefit the development and clinical use of A. camphorata. It is encouraging that A. camphorata and antroquinonol show good safety in both animal and human studies. Toxicities of the major bioactive triterpenoids need to be evaluated in the future.

It is also encouraging that different cultivation techniques have been developed to produce A. camphorata at a large scale. This is important for sustainable development of this precious mushroom. Preparation of the pure compounds still mainly relies on traditional extraction and isolation. Fortunately, efficient chemical synthetic routes have been established for antroquinonols and antrocin. For the production of complex triterpenoids, synthetic biology may be a promising approach, though the biosynthetic studies are still in an early stage.

7 Conflicts of interest

The authors declare that there are no conflicts of interest.

8 Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 81725023, 81891010/81891011, 81921001), the National Key Research and Development Program of China (No. 2017YFC1700405), and Beijing Natural Science Foundation (No. JQ18027). We wish to thank PhD students Ya-qun Zhang and Hui-fei Su of the Ye group for critically reading the manuscript, and Mr Jen-Yu Lo at Honest & Humble Biotechnology Co., Ltd. (New Taipei City, Taiwan) for providing the samples shown in Fig. 1.

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Footnote

† Electronic supplementary information (ESI) available: Tables S1–S5 and Fig. S1. See DOI: 10.1039/d0np00023j
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