Bibliometric, taxonomic, and medicinal perspectives of Ganoderma neo-japonicum Imazeki: A mini review

ABSTRACT

Ganoderma, a traditional medicine in Asian countries, has been used to prevent and treat various ailments for centuries. Ganoderma neo-japonicum (synonym Ganoderma bambusicola), also known as purple Lingzhi, is a species that is currently underutilised when compared to Ganoderma lucidum (Lingzhi). However, in recent decades, this mushroom has garnered significant attention due to its ethnomedicinal uses, especially in Southeast Asia regions like Malaysia. The taxonomy and nomenclature of this mushroom have been extensively studied. Numerous publications have reported that G. neo-japonicum displays a variety of medicinal properties, including antioxidation, anticancer, anti-hyperglycaemic, genoprotective, hepatoprotective, neuritogenic, and antidiabetic effects, both in vitro and in vivo. With the surge of research findings on this mushroom, this review aims to provide a systematic bibliometric analysis of G. neo-japonicum, published between 1991 to 2021. Additionally, the taxonomic description of this mushroom is discussed in detail. Our review reveals that G. neo-japonicum contains polysaccharides (α/β-D-glucans), triterpenoids, and sterols/ergosterol. However, the existing literature suggests that these active compounds have not yet been explored to their full potential as drug candidates. Moreover, most of the studies are preclinical and have several drawbacks. In conclusion, G. neo-japonicum possesses valuable pharmacological activities that merit further exploration.

KEYWORDS:

• Ganoderma neo-japonicum
• Ganoderma bambusicola
• purple reishi
• bibliometric analysis
• taxonomy
• domestication
• anticancer

1. Introduction

Malaysia remains a natural reservoir for macrofungi with myriad health benefits (Samsudin and Abdullah 2019). Nevertheless, many wild edible species have been neglected due to the gradual loss of ancestral knowledge within the indigenous communities. The traditional use of macrofungi (mushrooms) is often undocumented. Preserving this eroding knowledge thus becomes of utmost importance as it holds great potential for drug discovery.

Oriental medicine has long used the genus Ganoderma, which contains more than 400 species worldwide (Richter et al. 2015). Numerous pharmacological activities of Ganoderma, including anticancer, anti-hyperglycaemia, anti-inflammation, antioxidant, and antivirus, have been extensively evaluated (Wang et al. 2020). Despite its profound medicinal values, the traditional use of Ganoderma is relatively sparse in Malaysia, as indigenous communities commonly prefer other genera like Amauroderma, Lignosus, Microporus, and Xylaria (Lee et al. 2009; Foo et al. 2018). Malaysia hosts a variety of Ganoderma species (Lee et al. 2012). However, only G. applanatum (Pers.) Pat., G. neo-japonicum Imazeki, and G. lucidum (Curt.: Fr.) Karst are consumed among indigenous tribes in Malaysia (Ayu et al. 2019), implying that some related species with ethnomycological potential may have been overlooked.

In recent years, Ganoderma neo-japonicum Imazeki [Bull. Tokyo Sci. Mus., 1:37 (1939)] is drawing considerable attention from researchers (Tan et al. 2015). This endemic polypore is found in several Asian nations, including China, Japan, and Korea (Tan et al. 2015). It is a saprophytic species that feeds on dead coniferous trees (Hapuarachchi et al. 2019). In Malaysia, G. neo-japonicum (“cendawan senduk”) is well-recognised by ethnic tribes including “Bateq”, “Jahai”, “Jakun”, “Kensiu”, “Kintak”, “Lanoh”, “Semai”, “Temiar”, and “Temuan” (Tan et al. 2015). It is prepared as a tonic for different ailments, such as joint discomfort, cancer, fever, and asthma. It also serves as a topical preparation to aid in wound healing. Such therapeutic claims are encouraging enough to merit scientific validation. Unfortunately, although it is non-poisonous, consumption of G. neo-japonicum was linked to cases of reversible pancytopenia in Korea (Yoon et al. 2011).

The fruiting season of G. neo-japonicum occurs between May and October every year (Tan et al. 2015). The abundance of basidiocarps is highly affected by regional climate and habitat availability. Given its unique growth cycle, commercial foraging alone is far insufficient to support the surge in market demand. Hence, domestication has become crucial to ensure a sustainable harvest and thus mitigate supply shortages. Successful cultivation of G. neo-japonicum on bag logs was reported by Tan et al. (2015). However, the cultivated strain possessed a different antioxidant power as compared to the wild strain. This finding aligns with the outcomes demonstrated by Lignosus rhinocerotis (Cooke) Ryvarden (Jamil et al. 2017), suggesting that an improved cultural process is warranted to retain the bioactivity of G. neo-japonicum.

There are scattered publications about G. neo-japonicum research. On this basis, through bibliometric analysis, the present review aims to uncover the historical exploration and identify the emerging research trend on G. neo-japonicum. This review also discusses the domestication and medicinal properties of G. neo-japonicum.

2. Bibliometric analysis

Bibliometric analysis is widely accepted as an essential tool for monitoring the state of a research domain (Chan et al. 2020; Moral-Muñoz et al. 2020; Tang et al. 2022). It involves a quantitative evaluation of published works in a specific discipline or subject area. In this study, the bibliometric analysis was performed by retrieving publications from several data sources such as Scopus, Web of Science, Dimension, and PubMed, in April 2022. The search string included terms [title-abstract-keywords] of “Ganoderma neo-japonicum” or “Ganoderma neojaponicum”; but was not limited to article type, country, date, and language. After removing duplicates, a total of 36 articles were found between 1991 and 2021 (Figure 1); Scopus represented the most comprehensive database (n = 32), followed by Dimension (n = 28), Web of Science (n = 27), and PubMed (n = 20). These articles consisted of original papers (n = 34), reviews (n = 1), and conference abstracts (n = 1); published in English, Korean, and Russian languages (Table 1).

Figure 1. A venn diagram illustrating the number of articles (n) deposited in four reputed databases, namely Scopus, Web of Science, Dimension, and PubMed, with coverage of Ganoderma neo-japonicum study.

Table 1. List of journals for ganoderma neo-japonicum research output between 1991 and 2021.

No.	Journals	Publishers	^aPublication counts, n			^bCitation counts
			A	R	OP
1.	International Journal of Medicinal Mushrooms	Begell House			4	28
2.	Mycobiology	Korean Society of Mycology			3	27 (D)
3.	Phytochemistry	Elsevier			3	216
4.	Applied Biochemistry and Biotechnology	Springer			1	18
5.	Biologie in Unserer Zeit	Wiley			1	1
6.	Bioprocess and Biosystems Engineering	Springer			1	22
7.	Biotechnology and Applied Biochemistry	Wiley			1	4
8.	BMC Complementary and Alternative Medicine	BioMed Central			1	45
9.	Chiang Mai Journal of Science	Chiang Mai University			1	5
10.	Clinical Toxicology	Taylor & Francis			1	8
11.	Electronic Journal of Biotechnology	Elsevier			1	16
12.	International Journal of Antimicrobial Agents	Elsevier	1			0 (WoS)
13.	International Journal of Nanomedicine	Dove Medical Press			1	187
14.	Izvestiya Vuzov-prikladnaya Khimiya I Biotekhnologiya	Irkutsk National Research Technical University			1	1 (WoS)
15.	Journal of Applied Biological Chemistry	The Korean Society for Applied Biological Chemistry			1	8
16.	Journal of Bioscience and Bioengineering	Elsevier			1	3
17.	Journal of Ethnopharmacology	Elsevier			1	96
18.	Journal of Medicinal Food	Mary Ann Liebert			1	36
19.	Journal of Natural Products	American Chemical Society			1	42
20.	Journal of Traditional and Complementary Medicine	Elsevier			1	39
21.	Microbiology (Russian Federation)	Springer			1	2
22.	Mycosphere	Guizhou Key Laboratory of Agricultural Biotechnology			1	19
23.	Nutrition and Cancer	Taylor & Francis			1	0
24.	Phytotaxa	Magnolia press			1	4
25.	Scientific Reports	Nature			1	23
26.	The Korean Journal of Mycology	The Korean Society of Mycology			1	2 (D)
27.	Toxicon	Elsevier		1		45
28.	Tropical Biomedicine	Malaysian Society of Parasitology and Tropical Medicine			1	0
29.	Turkish Journal of Botany	Tubitak Scientific & Technical Research Council Turkey			1	1

^aRetrieved from four reputed databases, including Scopus, Web of Science, Dimension and PubMed. A, Abstract; R, Review; OP, Original paper.

^bRetrieved from Scopus database unless otherwise stated. D: Dimension; WoS: Web of Science.

The publication counts (n) over a recent 31-year period can be preliminarily divided into two phases (Figure 2): A lag phase (from 1991 to 2008, where n ≤ 1) and a log phase (from 2009 to 2021, where n ≥ 2). Despite the low productivity in the early years, the upward trend depicted in Figure 2 suggested that G. neo-japonicum has gained increasing attention since 2009. Malaysia emerged as the most prolific country in G. neo-japonicum research, contributing about 35% of total publication counts (Figure 3). The research output of Western countries was relatively poorer compared to that of South Korea, Japan, and Taiwan, China. Based on the co-authorship mapping, the mutual writing relationship among countries remained very sparse (Figure 3), underscoring a need for international collaborations to boost current research productivity. Notable crossover collaborations have been evident between Malaysia and South Korea, Vietnam, and Russia, as well as Germany, France, the United States, and Australia. Meanwhile, all the articles (n = 36) were dispersed across 29 different journals (Table 1), according to Bradford’s law of scattering (Tang et al. 2022). Core journals encompassed “International Journal of Medicinal Mushrooms” (n = 4), “Mycobiology” (n = 3), and “Phytochemistry” (n = 3). “Phytochemistry” with 216 citation counts (representing nearly 24% of the total) stood out as the most influential journal for G. neo-japonicum study.

Figure 2. Publication counts of Ganoderma neo-japonicum study reported from 1991 to 2021 (a 31-year time span). The line curve indicates annual cumulative frequency (right axis).

Figure 3. Contributions by country to Ganoderma neo-japonicum research in Scopus database. The country co-authorship network was visualised via citespace software (version 6.1.R1). The connection among nodes (countries) represented a mutual writing relationship, and the strength was indicated by line shade.

3. Taxonomy

The genus Ganoderma Karst. is widely distributed in both temperate and tropical areas (Richter et al. 2015). There are 419 epithets in Species Fungorum (http://www.speciesfungorum.org/Names/Names.asp; retrieval date: April 2022) and 511 records in Mycobank (http://www.mycobank.org/; retrieval date: April 2022).

Principally, Ganoderma comprises species with both “laccate” (subgen. Ganoderma) and “dull” [subgen. Elfvingia (Karst.) Imazeki] pileal surfaces. However, its species delimitation based on morphological traits can be challenging (Richter et al. 2015). Besides having overlapping appearances, Ganoderma shows high morphological variability due to geographic and climatic influences, causing its taxonomical status to be controversial. Moreover, the lack of standardised taxonomic criteria has resulted in a confusing nomenclature within the genus (Richter et al. 2015). Under such circumstances, DNA fingerprinting has emerged as an essential tool for discriminating between Ganoderma species. The useful gene markers include internal transcribed spacer region (ITS), large subunit ribosomal RNA (LSU), second-largest subunit of RNA-polymerase II (RPB2), translation elongation factor 1-α (TEF1α), partial ß-tubulin II (TUB2), and (Stielow et al. 2015).

Ganoderma neo-japonicum is well recognised by its laccate basidiocarp and long slender stipe (Lee 1981; Hattori and Ryvarden 1994). Based on the phylogenetic analysis (TUB2 sequences), it was shown to form a distinct cluster along with related species such as Ganoderma resinaceum Boud. and G. valesiacum Boud (Park et al. 2012a, 2012b). Likewise, concordant phylogenies inferred from ITS sequences have been generated by using the same strain in Korea (Park et al. 1999, 2012a, 2012b) or other representative strains originating in Japan (Wu et al. 2020), Laos (Hapuarachchi et al. 2019), Myanmar (Hapuarachchi et al. 2019), and Taiwan, China (Wang and Yao 2005). Taxonomic assessments on global Ganoderma have further demonstrated that G. neo-japonicum is segregated from G. boninense Pat., G. sichuanense Zhao & Zhang, and G. sinense Zhao et al. (Jargalmaa et al. 2017; Thawthong et al. 2017; Fryssouli et al. 2020; He et al. 2021).

In truth, G. neo-japonicum has been misidentified due to morphological similarities with Ganoderma bambusicola Wu et al., which shares a shiny reddish-black pileus and a long concolorous stipe (Wu et al. 2020). Both species have similar-sized basidiospores with smooth walls and narrow inter-wall pillars as described by Tsivileva et al. (2016), nonetheless, G. neo-japonicum differs in having a heterogeneous pileal context. Upon revisiting the genomic dataset (Table 2), several native “G. neo-japonicum” strains from Laos (Hapuarachchi et al. 2019), Myanmar (Hapuarachchi et al. 2019), and Taiwan, China (Hsieh and Yeh 2004; Wang and Yao 2005) were found to be conspecific with G. bambusicola (Wu et al. 2020). These misidentified strains share a host preference behaviour analogous to the Malaysian G. neo-japonicum found on dead bamboo clumps (Schizostachyum brachycladium) (Tan et al. 2015). However, the phylogenetic relationship between G. neo-japonicum (Malaysia) and G. bambusicola (Taiwan, China) remains inconclusive, necessitating further validation.

Table 2. Taxon identities of Ganoderma neo-japonicum.

No.	GenBank accession numbers		Vouchers/strains	Geographic origin	Specimen type
	ITS	TUB2
1.	AY593866*	-	AS 5.541, Type 1 (=ATCC 76540, BCRC 36094)	Taiwan, China	Culture
2.	AY593867*	-	AS 5.541, Type 2 (=ATCC 76540, BCRC 36094)	Taiwan, China	Culture
3.	-	-	ATCC 76539 (=BCRC 36049)*	Taiwan, China	Culture
4.	JQ520193 (=AF110725)	JQ675646	ASI 7032	Korea	Herbarium
5.	-	-	KLUM 1231	Malaysia	Herbarium
6.	-	-	KLUM 61076	Malaysia	Herbarium
7.	KT318596	-	-	China	Culture
8.	KT318597	-	-	China	Culture
9.	KT318598	-	-	China	Culture
10.	MK345443*	-	GACP14091006	Myanmar	Herbarium
11.	MK345444*	-	GACP17062350	Laos	Herbarium
12.	-	-	SIEbgm	Vietnam	Culture
13.	-	-	SIEbidoup	Vietnam	Culture
14.	MN957784	-	FFPRI WD-1285 (=MAFF 420115)	Japan	Herbarium
15.	MN957785	-	FFPRI WD-1532	Japan	Herbarium

*Presently designated as G. bambusicola sp. nov (Wu et al. 2020).

Abbreviation: ITS, internal transcribed spacer region; TUB2, partial ß-tubulin II.

4. Domestication

The domestication of Ganoderma has been introduced to fulfill the expanding worldwide market demand (Hapuarachchi et al. 2018). Species like G. lucidum, G. resinaceum, G. sichuanense, and G. tropicum (Jungh.) Bres. are now commercially cultivated as reliable sources of medicinal materials.

Collecting wild G. neo-japonicum presents challenges due to its unique growth cycle and host preference. In this context, Jo et al. (2010) were the first to attempt artificial cultivation of G. neo-japonicum using the bag method. The yield (dried fruiting bodies) obtained was 52–61 g per 2.4 kg substrate (90% oak sawdust and 10% rice bran). Subsequently, some patented refinements were made using a culture bottle containing larch sawdust, corn cob meal, and rice bran (3:1:1 ratio) under specific conditions: Illuminance, 500 lux; temperature, 23 °C; and humidity, 90% (Inose and Yamamoto 2013, 2015). The authors reported a yield of dried fruiting bodies at 35–60 g dried per 470 g substrate. A revisited study even found that the use of lignocellulosic substrates, particularly rubberwood sawdust, shortened mycelial colonisation (≈40 days) and primordial formation (≈60 days) in a 500 g substrate bag (Tan et al. 2015).

Apart from fruiting bodies, cultural factors for biomass production of G. neo-japonicum have been elucidated over the past decades. Typically, the pure colony manifests as a white mycelial mat with brownish-yellow pigmentation on solid agar media (Hsieh and Yeh 2004). Its hyphal anatomy is characterised by generative hyphae bearing (with or without) clam connections, nonbranched or moderately branched skeletal hyphae, and relatively thin binding hyphae (Tsivileva et al. 2016). Several physiological assays have found that G. neo-japonicum mycelia exhibit optimal growth on malt extract agar (MEA, enriched with 40 g/L glucose) at pH 6 and 24–28 °C (Hsieh and Yeh 2004). Growth could be further improved upon supplementation of brown sugar and spent yeast at a carbon/nitrogen (C/N) ratio of 1.74 (Ubaidillah et al. 2015), corresponding to the impact of media composition on G. neo-japonicum’s colony development (Tsivileva et al. 2016).

Submerged fermentation provides an alternative way of acquiring biomass and bioactive metabolites from Ganoderma (Zhou et al. 2012). To produce G. neo-japonicum ergothioneine (an antioxidant), optimal yields have been achieved in a formulated fungal growth medium (FGM, pH 4.5) containing methionine (Lee et al. 2009, 2010). Likewise, its phenolic content has been significantly enhanced by adding tryptophan and yeast to FGM under similar cultural conditions (Park and Lee 2010). Immunomodulatory polysaccharides have been produced in a stirred tank bioreactor with the following settings: aeration rate, 1.3 vessel volumes per minute (vvm); agitation speed, 160 r/min; and thermal point, 27 °C. Although various extracellular enzymatic activities, including amylase, avicelase, ß-glucosidase, cellulose, laccase, ligninase, pectinase, protease, and xylanase, were detected in G. neo-japonicum (Hsieh and Yeh 2004; Jo et al. 2011), the production of such enzymes remains inadequate due to elusive cultural conditions.

5. Medicinal properties

Despite a longstanding history in Oriental medicine, numerous Ganoderma species remain underexplored for their medicinal and pharmaceutical benefits. These unexplored species, including G. neo-japonicum, offer a promising avenue for further research and discovery in the field of medicine.

5.1. Functional molecules in G. neo-japonicum

Ganoderma neo-japonicum is one of the underappreciated species with significant ethnomedicinal potential. Its nutritional constituents include carbohydrates, dietary fibre, protein, and trace elements (Subramaniam et al. 2020). This polypore also produces bioactive substances, such as ergothioneine (Lee et al. 2009) and phenolic compounds (Park and Lee 2010), which contribute to its compelling antioxidant capacity (Subramaniam et al. 2014, 2017). G. neo-japonicum possesses phenolic compounds like catechin, chlorogenic acid, gallic acid, p-coumaric acid, protocatechuic acid, quercetin, and vanillin (Park and Lee 2010). In line with this, both the wild and cultivated strains have been shown to have potent free radical scavenging activity (Tan et al. 2015), comparable to that of G. lucidum (Veljović et al. 2017; Kolniak-Ostek et al. 2022) and G. Lingzhi (Dong et al. 2019).

Like other Ganoderma species (Baby et al. 2015; Galappaththi et al. 2023), sporadic studies have unveiled the diverse array of secondary metabolites (1–21, Figure 4) produced by G. neo-japonicum (Table 3). Hirotani et al. (1991) initially reported the isolation of two drimane sesquiterpenoids (crytoporic acids H and I) from this polypore. Thereafter, the isolation of lanostanoids (ganoderal A and ganodermadiol) and steroids (2β,3α,9α-trihydroxyergosta-7,22-diene, ergosta-7,22-dien-3-one, ergosta-7,22-dien-3β-ol, ergosta-7,22-dien-3β-yl palmitate, and ergosta-4,6,8(14),22-tetraen-3-one) was conducted by Gan et al. (1998). Bui et al. (2014) isolated another steroid called ergosterol (ergosta-5,7,22-trien-3-ol). A recent phytochemical screening further identified the presence of 47 lanostane-type triterpenoids in G. neo-japonicum (Zhang et al. 2023). This versatile chemical profile has been found in G. applanatum, G. lucidum, and G. tsugae Murr (Hapuarachchi et al. 2017), which are significantly associated with anticancer properties (Hsu et al. 2008; Li et al. 2017; Elkhateeb et al. 2018). Likewise, G. neo-japonicum has imposed a strong cytotoxic effect on human hepatomas (Bui et al. 2014) and adenocarcinomas (Lau et al. 2021).

Figure 4. Myco-constituents found in Ganoderma neo-japonicum (1–21).

Table 3. Myco-nutrient screening of Ganoderma neo-japonicum extracts with potent bioactivities.

No	Compound	Molecular formula	Classification	Spectroscopic assessment	Specimen (preparations)	References
(1)	Cryptoporic acid H	C21H32O7	Terpenoids (Sesquiterpenoid)	NMR	Culture broth (Ethyl acetate)	Hirotani et al. (1991)
(2)	Cryptoporic acid I	C21H32O8	Terpenoid (Sesquiterpenoid)	NMR	Culture broth (Ethyl acetate)	Hirotani et al. (1991)
(3)	Ganoderal A	C30H44O2	Terpenoid (Triterpenoid)	NMR IR ESI-MS	Air-dried fruiting bodies (Elution of dichloromethane extract, with cyclohexane/dichloromethane at1:4)	Gan et al. (1998)
				LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with dichloromethane at 1:1, subfraction-c purified with petroleum ether/ethyl acetate at 8:1–6:1)	Zhang et al. (2023)
(4)	Ganodermadiol (Ganoderol B)	C30H48O2	Terpenoid (Triterpenoid)	NMR IR ESI-MS	Air-dried fruiting bodies (Elution of dichloromethane extract, with cyclohexane/dichloromethane at 1:6)	Gan et al. (1998)
				NMR ESI-MS	Air-dried fruiting bodies (Elution of ethyl acetate extract, with methanol/chloroform at 1:1, subfraction-3 purified with hexane/ethyl acetate at 4:1)	Bui et al. (2014)
(5)	2β,3α,9α-Trihydroxyergosta-7,22-diene	C28H46O3	Steroid (Ergostane)	NMR IR ESI-MS	Air-dried fruiting bodies (Elution of dichloromethane extract, with cyclohexane/methanol at 2:1)	Gan et al. (1998)
(6)	Ergosta-7,22-dien-3-one	C28H44O	Steroid (Cholestane)	NMR IR ESI-MS	Air-dried fruiting bodies (Elution of dichloromethane extract, with cyclohexane/dichloromethane at 1:1)	Gan et al. (1998)
				GC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with hexane at 1:10)	Lau et al. (2021)
(7)	Ergosta-7,22-dien-3β-ol	C28H46O	Steroid (Cholestane)	NMR IR ESI-MS	Air-dried fruiting bodies (Elution of dichloromethane extract, with cyclohexane/dichloromethane at 1:1)	Gan et al. (1998)
				NMR ESI-MS	Air-dried fruiting bodies (Elution of ethyl acetate extract, with methanol/chloroform at 1:1, subfraction-2 purified with hexane/ethyl acetate at 6:1)	Bui et al. (2014)
(8)	Ergosta-7,22-dien-3β-yl palmitate	C44H76O2	Steroid (Ester)	NMR IR ESI-MS	Air-dried fruiting bodies (Elution of dichloromethane extract, with cyclohexane/dichloromethane at 5:1)	Gan et al. (1998)
(9)	Ergosta-4,6,8(14),22-tetraen-3-one	C28H40O	Steroid (Ergostane)	NMR IR ESI-MS	Air-dried fruiting bodies (Elution of dichloromethane extract, with cyclohexane/dimethyl ketone at 1:0.3)	Gan et al. (1998)
				NMR ESI-MS	Air-dried fruiting bodies (Elution of ethyl acetate extract, with methanol/chloroform at 1:1, subfraction-1 purified with hexane/ethyl acetate at 8:1)	Bui et al. (2014)
(10)	Ergosta-5,7,22-trien-3β-ol (Ergosterol)	C28H44O	Steroid (Ergostane)	NMR ESI-MS	Air-dried fruiting bodies (Elution of ethyl acetate extract, with methanol/chloroform at 1:1, subfraction-2 purified with hexane/ethyl acetate at 6:1)	Bui et al. (2014)
				GC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with hexane at 1:10)	Lau et al. (2021)
(11)	5α-Ergosta-7,22-dien-3β-ol (Stellasterol)	C28H46O	Steroid (Ergostane)	GC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with hexane at 1:10)	Lau et al. (2021)
(12)	Linoleyl alcohol	C18H34O	Fatty ester	GC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with hexane at 1:10)	Lau et al. (2021)
(13)	Proscillaridin A	C30H42O8	Steroid	LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with chloroform at 1:10)	Lau et al. (2021)
(14)	1,25-Dihydroxyvitamin D3 3-glycoside	C33H54O8	Sterol lipid (Secosteroid)	LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with chloroform at 1:10)	Lau et al. (2021)
(15)	Ganoderic acid S	C32H48O5	Terpenoid (Triterpenoid)	LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with chloroform at 1:10)	Lau et al. (2021)
				LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with dichloromethane at 1:1, subfraction-c purified with petroleum ether/ethyl acetate at 8:1–6:1)	Zhang et al. (2023)
(16)	Lucidenic acid L	C27H38O7	Terpenoid (Triterpenoid)	LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with dichloromethane at 1:1, subfraction-c purified with petroleum ether/ethyl acetate at 8:1–6:1)	Zhang et al. (2023)
(17)	Ganoderiol D	C30H48O5	Terpenoid (Triterpenoid)	LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with dichloromethane at 1:1, subfraction-c purified with petroleum ether/ethyl acetate at 8:1–6:1)	Zhang et al. (2023)
(18)	Ganoderic acid beta	C30H44O6	Terpenoid (Triterpenoid)	LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with dichloromethane at 1:1, subfraction-c purified with petroleum ether/ethyl acetate at 8:1–6:1)	Zhang et al. (2023)
(19)	Ganoderic acid F	C32H42O9	Terpenoid (Triterpenoid)	LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with dichloromethane at 1:1, subfraction-c purified with petroleum ether/ethyl acetate at 8:1–6:1)	Zhang et al. (2023)
(20)	Ganoderenic acid B	C30H42O7	Terpenoid (Triterpenoid)	LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with dichloromethane at 1:1, subfraction-c purified with petroleum ether/ethyl acetate at 8:1–6:1)	Zhang et al. (2023)
(21)	Ganodermanontriol	C30H48O4	Terpenoid (Triterpenoid)	LC-MS	Air-dried fruiting bodies (Elution of ethanol extract, with dichloromethane at 1:1, subfraction-c purified with petroleum ether/ethyl acetate at 8:1–6:1)	Zhang et al. (2023)

NMR, Nuclear magnetic resonance; IR, Infrared; ESI-MS, Electrospray ionisation-mass spectrometry; GC-MS, Gas chromatography-mass spectrometry; LC-MS, Liquid chromatography-mass spectrometry.

5.2. Apoptotic and anti-cancer properties

B-cell lymphoma-2 (BCL-2) protein is implicated in various malignancies via its regulation of apoptosis (Warren et al. 2019). Consistent with previous findings on G. lucidum (Li et al. 2017) and G. tsugae (Elkhateeb et al. 2018), Lau et al. (2021) demonstrated that G. neo-japonicum serves as a competitive inhibitor of BCL-2 and thus induces apoptosis in colonic carcinoma cells. The authors identified four potential compounds with inhibitory effects against BCL-2, including stellasterol, proscillaridin A, 1,25-dihydroxyvitamin D3, and linoleyl alcohol.

In their follow-up study, apart from cell death, G. neo-japonicum was shown to trigger cell cycle arrest in colonic carcinoma cells, under both normal and hyperglycaemic conditions (Lau et al. 2022). Furthermore, this polypore was concomitantly found to diminish high-glucose-induced glutathione, thereby enforcing lethal oxidative stress on the carcinoma cells (Lau et al. 2022). G. neo-japonicum, as a fungal material, holds the feasibility for synthesising silver nanoparticles to combat breast cancer through DNA damage (Gurunathan et al. 2013).

5.3. Hepato- and genoprotective effects

Ganoderma neo-japonicum can be a protective agent against liver illness. Lin et al. (1995) reported its hepatoprotective effects by reducing serum levels of glutamic oxaloacetic transaminase (GOT) and lactic dehydrogenase (LDH) in a carbon tetrachloride (CCl₄)-injured rat model. The CCl₄-mediated lipid peroxidation was impaired partly due to its potent free radical scavenging activity. In addition, Tan et al. (2018) highlighted the genoprotective effects of G. neo-japonicum on hydrogen peroxide (H₂O₂)-damaged macrophage cells. According to the study, ethanol extracts of wild basidiocarps imposed superior protection against H₂O₂-induced DNA damage compared to aqueous extracts of wild basidiocarps, as well as domesticated basidiocarps. Nonetheless, both the aqueous and ethanol extracts of mycelia from the submerged culture showed no appreciable DNA repair ability (Tan et al. 2018). It is postulated that variances in their protective effects and cellular DNA repair capacity may be attributed to factors such as growing conditions and substrate types.

5.4. Anti-viral, anti-inflammatory and immunomodulating effects

Enterovirus A71 (EVA71) and coxsackievirus A16 (CV-A16) are the culprits behind hand, foot, and mouth disease (HFMD). Despite ongoing HFMD outbreaks, there are currently no vaccines or antiviral drugs tailored to combat the enteroviruses responsible for HFMD. However, in a recent study, G. neo-japonicum was found to impede enterovirus infection and replication in human primary oral fibroblast cells (Ang et al. 2021). The most potent extract, S2, demonstrated virucidal activities with the presence of active polysaccharides.

Ubaidillah et al. (2015) took steps to isolate and characterise intracellular polysaccharides (IPSs) and extracellular polysaccharides (EPSs) from G. neo-japonicum. Both IPSs and EPSs were observed to increase the proliferation and phagocytosis activities of RAW264.7 macrophages. An oral toxicity test unveiled no significant adverse effects in Sprague-Dawley rats that were fed on dried G. neo-japonicum mycelium (Ubaidillah et al. 2015), suggesting the potential use of its polysaccharides as immunomodulating agents to activate the innate immune system in the fight against infectious diseases.

Moreover, G. neo-japonicum was corroborated to possess anti-inflammatory effects that support cellular longevity (Zhang et al. 2023). It effectively mitigated lipopolysaccharide (LPS)-induced inflammation by downregulating the mRNA levels of pro-inflammatory cytokines, such as TNF-α, IL-1β, and IL-6, resulting in a concurrent decrease in the expression of nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). It also suppressed the LPS-mediated oxidative stress through the inhibition of reactive oxygen species. Upon further investigation, these anti-inflammatory activities were found to be significantly associated with the deactivation of the nuclear factor-kappa B (NF-κB) and the activation of the nuclear factor erythroid 2-related factor 2 (NRF2)/haem oxygenase-1 (HO-1) signalling pathways.

5.5. Neuritogenic effect

Age-related neurodegenerative illnesses are believed to be strongly influenced by neuronal senescence, associated with reduced levels of nerve growth factor (NGF). There is a growing focus on the search for neuroactive compounds that can mimic the activity of NGF (Sabaratnam et al. 2013).

Ganoderma neo-japonicum has undergone testing to assess its ability to promote neurite outgrowth in developing mouse neuroblastoma (N2a) cells (Phan et al. 2013). For possible embryo- and neuro-toxic effects, in vitro cytotoxicity was studied using mouse embryonic fibroblast (BALB/3T3) and N2a cells, respectively. The aqueous extracts of G. neo-japonicum stimulated neurite outgrowth in N2a cells, with average neurite-bearing cells ranging from 26.4% to 29.6%. The neurite outgrowth activities, at a dosage of 20 µg/mL, even showed no significant difference from other medicinal mushrooms with superior neuritogenic characteristics, particularly, Hericium erinaceus (Bull.) Persoon (Phan et al. 2013). It was also been confirmed absence of embryotoxic and neurotoxic effects in BALB/3T3 and N2a cells.

Seow et al. (2013) investigated the neuritogenic effects of aqueous extracts of G. neo-japonicum on pheochromocytoma cells (PC12). The study showed that G. neo-japonicum promotes neuritogenesis via mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 (MEK/ERK1/2) and phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signalling pathways.

5.6. Anti-hyperglycaemic effects

The ethanol extract of wheat grains fermented with G. neo-japonicum mycelia was found to exhibit an insulin-like effect in 3T3-L1 adipocytes, where it increased adipogenesis and exerted modest anti-epinephrine-induced lipolytic activities (Subramaniam et al. 2015). The ethanol extract also upregulated the expression of target genes such as adiponectin, peroxisome proliferator-activated receptor gamma (PPAR), glucose transporter 4 (GLUT4), and hormone-sensitive lipase (HSL).

Meanwhile, G. neo-japonicum hot aqueous extract (AE-3) was demonstrated to have anti-glycaemic properties, as evidenced by α-amylase and α-glucosidase enzyme inhibition assays (Subramaniam et al. 2017). A purified polysaccharide fraction (PF) was separated from AE-3 by column chromatography. Fourier transform infrared spectroscopic assessment of the purified polysaccharide fraction (PF) confirmed the presence of typical polysaccharide bands with an estimated β-glucan content of 39.26%.

Subsequently, Subramaniam et al. (2020) isolated β-D-glucan polysaccharide from G. neo-japonicum and reported its ability to induce insulin-independent adipogenesis in 3T3-L1 adipocytes. This β-D-glucan, designated as “GNJP”, stimulated glucose uptake and adiponectin release while inhibiting lipid formation. Most recently, GNJP has been tested for its potential in treating obesity-induced type 2 diabetes mellitus (T2DM) in mice. The supplementation of GNJP at a dosage of 50 mg/kg body weight was found to inhibit weight gain and liver steatosis (Subramaniam et al. 2023). Moreover, it improved serum lipid profile and glucose tolerance, leading to the successful attenuation of hyperglycaemia and hyperinsulineamia. The increased HSL and decreased Akt-1 and PPAR gene expressions may have contributed to the prevention of obesity and lipid dysregulation. Therefore, supplementing with an appropriate amount of GNJP holds promise for preventing metabolic abnormalities and obesity-induced T2DM.

6. Future prospectives

One of the challenges that are persistent in the development of G. neo-japonicum study is its domestication process, even though a pilot-scale study was reported (Tan et al. 2015). Cultivating a new mushroom species is a complicated procedure that depends on temperature, moisture, soil type, habitat, and spore management. Other potential hurdles might include the non-availability of raw materials (particularly spawn and compost), irregular fluctuating production, perishable nature, lack of knowledge about improved cultivation technology, lengthy and cumbersome methods of compost preparation, and limited post-harvest processing options. Thus, G. neo-japonicum research in the future should focus on improving and refining solid-state fermentation (cultivation) of the basidiocarps.

Besides that, the discovery of new chemical compositions (e.g. novel terpenoids) from this mushroom, whether from mycelial extract or basidiocarps, should be closely followed up. Pre-clinical research should involve carefully planned animal studies. To establish pharmacological effects for human use, there is an urgent need for high-quality clinical data. We lack clinical investigations into the safety and effectiveness of G. neo-japonicum, its interactions with foods and beverages, its actions with chronic usage, teratogenicity, mutagenicity, and genotoxicity. Supporting clinical trials for drug formulations of G. neo-japonicum is essential to broaden its acceptance and understanding in the medical community. This will help in harnessing the potential benefits of this mushroom and making it more accessible for therapeutic applications.

7. Limitations

Data collection for our bibliometric study was carried out in April 2022 and upon re-searching the publication in 2023, we found an additional study done in this period. This could be due to the inconclusive nomenclature of this mushroom. However, to mitigate any potential bias, we included the discussion of both Ganoderma neo-japonicum Imazeki and Ganoderma bambusicola sp. nov., so that scholars would benefit from this comprehensive review.

8. Conclusions

The nomenclature of G. neo-japonicum and G. bambusicola remains a subject of debate due to their similar lustrous “dark reddish brown to purplish black” pileus surface and a long blackish stipe, although G. neo-japonicum differs from the latter in having a uniform pileal context. Notably, G. bambusicola is exclusively known to grow on bamboo roots (Wu et al. 2020). Since its widespread use in tribal and local communities in various Asian countries, particularly Malaysia, research on G. neo-japonicum has made substantial progress. Various investigations from several perspectives have elucidated the mushroom’s biological properties, including anticancer, antidiabetic, antiviral, and immunomodulating actions (Table 4). Research on chemical composition has shed light on the mushroom’s active compounds, including phenolics that contribute to its compelling antioxidative effect, and polysaccharides which are important immunomodulatory agents. Despite successful domestication, G. neo-japonicum has not made much headway in the industrial sector. It is believed that this medicinal mushroom, like G. lucidum, can be effectively cultivated, although this would necessitate additional research and refining, such as substrate formulation and quality spawn production. There are opportunities to expand the cultivation of G. neo-japonicum, leveraging cutting-edge technology for mass production.

Table 4. A summary of medicinal properties of Ganoderma neo-japonicum in the literature.

Medicinal parts	Indications	In vitro/in vivo	Reference
Mycelial extract	Potent antioxidant	In vitro	Subramaniam et al. (2014)
	Potent antioxidant	In vitro	Tan et al. (2015)
	Greener agent to biosynthesize silver nanoparticles; possess cytotoxic effect towards human breast cancer cells	In vitro	Gurunathan et al. (2013)
	No indication of oral toxicity test on rats (2,000 mg/kg body weight/day dosage of dried mycelium)	In vivo	Ubaidillah et al. (2015)
	Geno-protective effect	In vitro	Tan et al. (2018)
	Adipogenic, anti-lipolytic, and adipogenesis in 3T3-LI adipocytes	In vitro	Subramaniam et al. (2015)
Basidiocarp (fruiting body) extract	Potent antioxidant	In vitro	Tan et al. (2015)
	Induced cytotoxic effect and apoptosis on colonic carcinoma cells	In vitro	Lau et al. (2021)
	Management of hyperglycaemia-associated colorectal cancer	In vitro	Lau et al. (2022)
	Free radical scavenging activity; anti-hepatoxic activity	In vivo	Lin et al. (1995)
	Cyto-protection on murine RAW264.7 macrophage; DNA repair ability	In vitro	Tan et al. (2018)
	Antiviral effect against enteroviruses that cause hand, foot, and mouth disease	In vitro	Ang et al. (2021)
	The polysaccharides increase the proliferation and phagocytosis activities of macrophages (immune-stimulating effect)	In vitro	Ubaidillah et al. (2015)
	No indication of embryo- and neurotoxic effect	In vitro	Phan et al. (2013)
	Neurite outgrowth stimulatory effects on neuroblastoma cells	In vitro	Phan et al. (2013)
	Neurite outgrowth stimulatory effects on rat pheochromocytoma cells	In vitro	Seow et al. (2013)
	Anti-hyperglycaemic effect by a purified polysaccharide fraction	In vitro	Subramaniam et al. (2017)
	Induction of insulin-independent adipogenesis by isolated (1,3)(1,6)-β-D-glucan polysaccharide	In vitro	Subramaniam et al. (2020)
	Attenuation of hyperglycaemia and hyperinsulineamia in C57BL/6J mice	In vivo	Subramaniam et al. (2023)

Acknowledgments

The authors would like to thank Mr. Shamsudin Fatani Mohamad, Health and Safety Environment Manager (retired) who introduced this indigenous medicinal mushroom, “cendawan senduk”.

Disclosure statement

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

Additional information

Funding

This work was supported by Postgraduate Research Grant (PG 245-2015B), Universiti Malaya (UM), UM High Impact Research Grant UM-MOE UM.C/625/1/HIR/MOHE/ASH/01 (H-23001-G000008), and UM.C/625/1/HIR/MOE/SC/02 from the Ministry of Education, Malaysia.