A Review on Chemical Constituents and Biological Activities of the Genus Beilschmiedia (Lauraceae)

The current review is aimed to deliver some updates on the ethnobotany, phytochemistry and biological activities of Beilschmiedia species in order to throw more light on their therapeutic potentials and future research priorities. Phytochemical studies on Beilschmiedia genus yielded essential oils, endiandric acid derivatives, amides/alkaloids, lignans/neoligans, flavonoids and miscellaneous compounds, while bioactivity studies revealed that the extracts and compounds displayed a broad spectrum of biological activities. Only 24 species of the genus Beilschmiedia have been studied phytochemically thus far. Therefore, there is a need to ascertain the pharmacological properties of the plant extracts and new compounds from this genus. More studies on the standardization and pharmacology of Beilschmiedia extracts need to be conducted to ascertain new pharmacological properties and their biochemical and physiological mechanisms. Furthermore, detailed preclinical toxicity, bioavailability, pharmacokinetics and pharmacodynamics of extracts of the species and their isolated compounds require additional investigation in order to verify their safety and determine their suitability as sources of some current medicines. Keywords: Beilschmiedia , Lauraceae, ethnobotany, phytochemistry, pharmacology


INTRODUCTION
The genus Beilschmiedia is a pantropical genus of about 287 species mainly in Southeast Asia and Africa. About 81 Beilschmiedia species have been identified in inter-tropical Africa with 41 species in Cameroon alone [1,2]. Plants of the genus Beilschmiedia have been listed in the plant list (2013). 287 of the genus names are accepted and the remaining names are either synonym or unresolved names. Revisional studies of the genus have been made in several regions, such as China, Madagascar, Australia and the Neotropics. In recent years, Kostermans described many new taxa of Beilschmiedia from Malay Peninsular and Southern Thailand [3][4][5][6][7][8][9]. Kochummen also revised Lauraceae and published in Tree Flora of Malaya [10]. Van der Werff studied the genera of Lauraceae in the Flora Malesiana Region and two reports on the synopsis of genus Beilschmiedia in Madagascar have been published [11,12].
The ethnopharmacological history of Beilschmiedia indicates that some species have been used in local medicine to treat various conditions, including uterine tumors, rheumatism, pulmonary disorders, bacterial infections, malaria and tuberculosis [13][14][15][16][17]. Because of their versatile therapeutic traditional uses, extensive phytochemical investigations have been carried out on Beilschmiedia plants which led to isolation of numerous classes of secondary metabolites such as terpenoids, endiandric acid derivatives, essential oils, fatty acids, lignans/neolignans, flavonoids, amide/alkaloids and other components. Endiandric acid derivatives are considered to be the main constituents in Beilschmiedia species and are responsible for many of their biological and pharmacological activities [18][19][20][21][22].
Both in vivo and in vitro experiments have indicated that the Beilschmiedia plant extracts possess a variety of pharmacological aspects with antioxidant, anti-inflammatory, cytotoxicity, antibacterial and antifungal activities [23][24][25][26]. With consideration of the importance of the therapeutic property of this genus to heal various ailments. Therefore a broader range of studies on the bioactivities need to be performed to ascertain the pharmacological properties. These gaps lead to systematic research activities on phytochemicals and pharmacology of genus Beilschmiedia. As extensive studies on Beilschmiedia species have not been conducted, there are thus significant opportunities to discover novel bioactive compounds and beneficial medicinal and pharmacological properties from various extracts of the species are warranted. The available information on various species belonging to the genus Beilschmiedia were collected via electronic search (using Pubmed, SciFinder, Scopus, Google Scholar, JCCC@INSTIRC and Web of Science) and a library search for articles published in peer-reviewed journals.

DISTRIBUTION, BOTANICAL DESCRIPTION AND ETHNOBOTANY
The genus Beilschmiedia comprises more of trees and rarely shrubs, and is usually distinguished from other genera of the Lauraceae by the following characteristics: paniculate or racemose inflorescences that are not strictly cymose at the terminal division, bisexual and trimerous flowers with six equal to subequal tepals, six to nine fertile stamens representing the outer two or three whorls, two-celled anthers, and fruits lacking cupules. This family is also recognized by the simple, alternate, stiff and aromatic elliptic to obovate leaves, and by the fruits often borne in a cup [27]. It is placed in the tribe Cryptocaryeae Nees together with other core genera such as Cryptocarya, Endiandra and Potameia based on the wood and bark anatomy and inflorescence structure [27]. Most of the species grow in tropical climates but few of them are native to the temperate regions. They are widespread in tropical Asia, Africa, Australia, New Zealand, Central America, Caribbean and South America [28]. In the Southeast Asia, the genus can be found in Myanmar, Vietnam, Cambodia, Thailand, Malaysia, Philippines, Indonesia and various islands, such as Sumatra and Java [29]. Beilschmiedia is categorized as a genus of forest trees, predominantly from low to high elevation. B. glauca is found in the upper evergreen forest and rarely found in the lowland evergreen forest, B. maingayi is found in the upper evergreen forest, over 1,200 m altitude, B. membranacea is found in the montane evergreen forest and B. palembanica is found in the lower evergreen forest to the upper evergreen forest. Many species of Beilschmiedia were reported in Bhutan and Sikkim, such as B. gammieana in montane forest with oaks, and broad leaves forest at 1,750 -2,050 m altitude, B. assamica in subtropical forest and broad leaves forest and in temperate zone at 300-1,800 m altitude and B. roxburghiana in subtropical forest at 200 -400 m altitude [30,31].
Available literature and information show that several Beilschmiedia species have been applied as traditional medicines in various parts of the world. This genus has an economic importance in forest products for use as timber and herbal medicine. The most prevalent usages are for treating bone related problems which include arthritis, rheumatism and renal ailments. The important ethnomedicinal properties possessed by this genus can be the basis for further research to determine the phytochemical and pharmacological aspects of the above mentioned genus. The lists of the various medicinal uses of Beilschmiedia species in different parts of the world are shown in Table 1.

CHEMICAL CONSTITUENTS
Systematic phytochemical investigation is important to understand the pharmacology of the species as well as the mechanisms of action and for quality control purposes. The phytochemical studies of various species of the genus have successfully afforded numerous chemical components. They were essential oils, endiandric acid derivatives, amides and alkaloids, lignans and neolignans, flavonoids and also miscellaneous compounds (cyanogenic glycosides, benzopyran, benzenoid, terpenes, benzaldehyde, and fatty acid). The major components of the essential oil compositions from several species of Beilschmiedia species are tabulated in Table 2. The phytochemical studies of Beilschmiedia species are shown in Table 3.

BIOLOGICAL ACTIVITIES
The literature study reveals the need for a thorough investigation of the pharmacological characteristics of the extracts and isolated compounds from Beilschmiedia genus. The biological activities including anti-inflammatory, antioxidant, acetylcholinesterase, anti-αglucosidase, anti-leishmanial, antifungal, antimalarial, anticancer, antitubercular, antiplasmodial, antibacterial and cytotoxicity have been reported in some works. Indeed, the genus Beilschmiedia has been exploited traditionally thus revealed the medicinal variation if possesses. In addition, several species that have been used traditionally to treat some types of ailments have not been investigated for their biological activities at all. Thus, this is an opportunity to find new pharmacological properties from this genus, not to mention promising sources for drugs, such as for cancer, hernia, skin and digestive diseases. Furthermore, the toxicity of the genus members has not been studied from this genus. The information of the qualification of the extracts are very important to be applied as drugs.

Anti-inflammatory activity
A methanol extract of the roots of B. tsangii has shown potent inhibition of NO production, and negative cytotoxicity against RAW 264.7 cells [19]. Huang et al [19] also studied the antiinflammatory activity of several compounds isolated from B. tsangii. They found that endiandramide A-B exhibited significant iNOS inhibitory activity against RAW 264.7 cells at the concentration range of 0.1 -100 μM. A year later, they reported moderate iNOS inhibitory activity for endiandric acid M. They also suggested that endiandramide B and endiandric acids K-M having the same skeleton but with different substituents at C-8, exhibited ascending degrees of iNOS inhibitory activity in the order: endiandramide B (16.40 μM) > endiandric acid M (31.70 μM) > endiandric acid L (39.56 μM) > endiandric acid K (58.21 μM). This suggests that the iNOS potency of the substituent at C-8 could be arranged as N-isobutylamido group > an α,βunsaturated carboxylic acid group > a carboxylic acid group. Endiandric acid M, having four fewer methylenes than endiandric acid L, showed stronger potency than endiandric acid L. This also suggests that fewer methylenes in the alkyl side of endiandric acid analogues result in greater potency of iNOS inhibitory activity [45]. In addition, the mixture extracts of the leaves and of B. erythrophloia showed weak inhibitory activity of NO production at dose of 25 µg/mL [23].

Antibacterial activity
B. cinnamomea root extract demonstrated moderate activity against Enterobacter aerogenes EA294 with minimum inhibitory concentration (MIC) value of 64 µg/mL [55]. Three years later, Fankam et al [25] reported on methanol fruits extract of B. obscura which showed strong activity against Escherichia coli ATCC8739 with MIC value of 16 μg/mL. Besides, another study reported on B. tovarensis wood extract displayed significant results against Staphylococcus aureus and Enterococcus faecalis [52]. Anti-bacterial activity on methoxylated flavonoid derivatives from B. zenkeri, showed that beilschmieflavonoid B displayed the activity against Streptococcus minor with MIC value of 197.5 µM. Pipyahyine that was also isolated from this species, showed moderate activity against Bacillus subtilis and Pseudomonas agarici with MIC of 163 and 81.5 µM, respectively [16].
Talontsi et al [21] and a co-worker identified cryptobeilic acids A-D, tested for anti-bacterial activity and showed that cryptobeilic acid A gave moderate activity against Escherichia coli (MIC value of 10 μM), while cryptobeilic acid B was active against Pseudonamas stutzeri with a MIC value of 10 μM. In another study, Chouna et al [44] reported that beilschmiedic acid C demonstrated the best activity against Bacillus subtilis and Micrococcus luteus with MIC of 89.5, 5.58 and 11.1 µM, respectively. Antibacterial activity on endiandric acid derivatives was further studied by Williams et al [20]. It was observed that beilschmiedic acid A, K and L gave moderate activity against clinical isolate of methicillin-resistant Staphylococcus aureus with MIC values of 10 -11 µM.

Cytotoxicity activity
The in vitro cytotoxicity of the methanol extracts of B. erythrophloia showed weak activity against HUVEC (human umbilical vein endothelial cells), MCF-7 (breast cancer cell) line and HL-60 (human promyelocytic leukemia cell) cell lines, showed weak activity with MIC values reaching more than 100 μg/mL at the range of concentration 25 -500 µg/mL [23]. In another study, the B. acuta fruits, leaves and bark extracts showed the inhibition of CCRF-CEM leukemia cell growth of 65.17, 26.35 and 21.33 %, respectively, as measured by the resazurin reduction assay. In addition, the leaves extract also displayed significant activity towards cell lines HCT116p53 (colon cancer cell), MDA-MB-231 (human breast carcinoma cell) and U87MG (human glioblastoma cell) with IC 50 of 4.79, 6.45, and 7.46 µg/mL, respectively. The bark extract also showed activity against the cell line MDA-MB-231 with an IC 50 value of 6.66 µg/mL [24].
The in vitro cytotoxicity properties of the leaf oil of B. erythrophloia were evaluated against OEC-M1 (human oral squamous cancer cell), J5 (human hepatocellular carcinoma cell), A549 (human lung adenocarcinoma cell), HT-29 (human colon cancer cell), UACC-62 (human melanoma cell) and K562 (human leukemic cell) and shows IC 50 values of 32.6, 48.6, 38.7, 18.9, 5.8, and 6.8 μg/mL, respectively [39]. Williams et al [20] screened the isolated endiandric acids for their in vitro cytotoxicity activity against NCI-H460 (large cell lung carcinoma), PC-3 (prostate adenocarcinoma) and M14 (amelanotic melanoma cell) lines using a MTT-based assay. They managed to find moderate activity of beilschmiedic acid L, I and K against the NCI-H460 cell lines with IC 50 values of 4.4, 5.5 and 5.9 µM, respectively. (-)-Kunstleramide was investigated on MTT assays against A375 (human melanoma cell), HT-29 (human colon adenocarcinoma cell), WRL-68 (normal hepatic cell), A549 and PC-3 cells. The results showed moderate activity among all the tested cell lines with EC 50 values in the range of 44.74 -73.87 μg/mL [47]. Chen et al [50] studied the in vitro cytotoxicity of several compounds isolated from B. tsangii. They found that tsangin A-B, αtocospiro B and beilschmin A displayed from medium to strong activity against the P-388 (murine leukemia cell) line. In addition, αtocospiro B, exhibited the most cytotoxic against the HT-29 cell line. In addition, six alkaloids isolated from B. brevipes were tested for in vitro cytotoxic activity against P-388 cell lines, O, Odimethylcoclaurine exhibited significant cytotoxicity with an IC 50 of 6.5 μg/mL [48].

Anti-plasmodial activity
According to Lenta et al [16] among the methoxylated flavonoid tested for in vitro antiplasmodial activity, 5-hydroxy-7,8dimethoxyflavanone exhibited the most significant activity against Plasmodium falciparum chloroquine-resistant strain W2 giving an IC 50 value of 9.3 µM. The other compounds which showed remarkable activity were pipyahyine and betulinic acid which gave IC 50 values of 3.7 and 5.2 µM, respectively. Talontsi et al [21] studied the anti-plasmodial activity of the isolated endiandric acid derivatives from B. cryptocaryoides. Cryptobeilic acid B exhibited anti-plasmodial activity against the erythrocytic stages of chloroquine-resistant Plasmodium falciparum strain NF54, followed by tsangibeilin B and cryptobeilic acid D at a concentration of 10 μg/mL.

Anti-tubercular activity
Chen et al [15] investigated the in vitro antitubercular effects of the isolates from the leaves of B. tsangii against Mycobacterium tuberculosis 90 -221387. They reported that among the furanoid lignans, beilschmin A-B exhibited potent activity with IC 50 values of 2.5 and 7.5 µM, respectively. Both compounds also exhibited corresponding epoxy-analogues, 4α,5αepoxybeilschmin A-B and this revealed that epoxidation of the C-4,5 bond would result in reduced anti-tubercular activity. In another study of anti-tubercular activity, Yang et al [18] verified that erythrophloin C showed significant activity against Mycobacterium tuberculosis H37Rv (MIC of 50 µg/mL), comparable to ethambutol (MIC of 6.25 μg/mL).

Anti-cancer activity
The anti-apoptotic proteins Bcl-2, Bcl-xL, Bcl-w, Mcl-1, and A1, members of the Bcl-2 family, have become attractive molecular targets for cancer treatment. The discovery of dual inhibitors acting on Bcl-xL and Mcl-1 could play a significant role in cancer treatment. Apart from that, Apel et al [22] had investigated the anti-cancer activity of isolated endiandric acid from B. ferruginea, ferrugineic acid A-K against anti-apoptotic proteins Bcl-xL and Mcl-1 by using a fluorescence polarization assay. Ferrugineic acid B-C and ferrugineic acid J were proved to have significantly exhibited binding affinity for both anti-apoptotic proteins, Bcl-xL.
Meanwhile, ferrugineic acid D showed only a strong inhibiting activity for anti-apoptotic protein, Mcl-1. Considering the weak binding affinity for Mcl-1 of other tested compounds, it could be postulated that the length of the saturated carbon side chain (preferentially five or seven CH 2 groups) associated with a terminal 4hydroxyphenyl ring, play a crucial role for Bcl-xL and Mcl-1 binding affinities.
Mollataghi et al [49] have reported the anti-fungal activity of the new alkaloid, 2-hydroxy-9methoxyaporphine isolated from B. alloiophylla. This compound demonstrated good activity against Candida albicans with MIC value of 8.0 µg/mL. More than a decade ago, Kitagawa et al [34] successfully isolated a bisbenzylisoquinoline alkaloid, (+)-dehatrine from the Indonesian medicinal plant, B. madang. The compound was found to exhibit a potent inhibitory activity against the proliferation of the malarial pathogen, Plasmodium falciparum K1 strain (IC 50 of 0.17 µM), with almost the same activity as quinine (IC 50 of 0.27 µM). Mollataghi et al [49] studied the in vitro α-glucosidase activity of the isolated compounds from B. alloiophylla. Three compounds that were found to have moderate activity, were characterized as oreobeiline, 6epioreobeiline and (S)-3-methoxynordomesticine.
In addition, for cholinesterase and leishmanial activities, the results suggested that 2-hydroxy-9methoxyaporphine, laurotetanine and liriodenine displayed significant acetylcholinesterase (AChE) activity. Meanwhile, the authors deemed that they also possessed significant activity in leishmanial activity.

CONCLUSION
This compilation includes the traditional uses, phytochemical and pharmacological aspects of the genus Beilschmiedia, and especially provides some analysis of the literature published. Some members of the genus are reported to possess medicinal properties and are used to treat various ailments. Endiandric acid derivatives are major constituents of this genus, and are important chemotaxonomic markers used to identify Beilschmiedia plant species from a phytochemical point of view.