Phytochemistry and Biological Activities of Endophytic Fungi from the Meliaceae Family

Meliaceae plants are found worldwide in tropical or subtropical climates. They are important ethnobotanically as sources of traditional medicine, with 575 species and 51 genera. Previous research found that microorganisms are plant pioneers to produce secondary metabolites with diverse compound structures and bioactivities. Several plants of the Meliaceae family contain secondary metabolites isolated from endophytic fungi. Furthermore, related articles from 2002 to 2022 were collected from SciFinder, Google Scholar, and PubMed. About 276 compounds were isolated from endophytic fungi such as terpenoids, polyketides, lactones, pyrones, quinone, anthraquinones, xanthones, coumarines, isocoumarines, resorcylic acid lactones, cytochalasins, aromatics, ester, quinols, alkaloids, nitro compound, fatty acids, and sugars with bioactivities such as antioxidant, antibacterial, antifungal, anti-influenza, neuroprotective activities, anti-HIV, cytotoxic, allelopathic, anti-inflammatory, antifeedant effects, and BSLT toxicity. Meanwhile, secondary metabolites isolated from endophytic fungi were reported as one of the sources of active compounds for medicinal chemistry. This comprehensive review summarizes the ethnobotanical uses and secondary metabolites derived from Meliaceae endophytic fungi.


Introduction
Meliaceae is the mahogany family in tropical and subtropical regions such as the Himalayas, South America, Central America, Africa, South Asia, and Southeast Asia [1]. In this genus, the major secondary metabolites are sesquiterpenoid, triterpenoid, and limonoid, with minor compounds including flavonoid, lignans, chromone, and phenolic [2,3]. Many secondary metabolites that are valuable in pharmaceuticals have been isolated from the endophytic microorganisms of Meliaceae. Endophytes live in plant tissues without causing obvious disease at any time in the host. They produce bioactive substances that enhance the growth of the host plant. Endophytic fungi play important ecological roles in protecting plants from various biotic (pathogen damage) and abiotic stresses (such high salinity, temperature, and drought) [4][5][6].
Due to their extensive biological activities, fungal secondary metabolites possess unique chemical structures and are considered one of the best repositories for drug discovery from natural sources. Many endophytes produce bioactive products that block the growth of other organisms. In some cases, they can synthesize products similar to those produced by plants [7][8][9][10]. Plant growth promotion may be due to the ability to produce more growth-promoting metabolites [11,12]. Endophytic fungi are polyphyletic microorganisms that live in plant tissues, for examples Fusarium fujikuroi, Colletotrichum sp., and Talaromyces verruculosus. Generally, these microbial entities have been ignored as ecosystem

Alkaloids
Penicillium sp. was isolated from the root bark of M. azedarach and grown on sterilized rice. The known alkaloid verruculogen (209) was obtained after chromatographic procedures. Apart from Penicillium sp., A. fumigatus LN-4 obtained from M. azedarach stem bark and cultured in PD liquid medium also yielded this compound [32,46]. In the study conducted by Li et al. [49], brasiliamide A (210) and brasiliamide B (211) were produced from P. brasilianum in the root bark of M. azaderach [47,60].

Alkaloids
Penicillium sp. was isolated from the root bark of M. azedarach and grown on sterilized rice. The known alkaloid verruculogen (209) was obtained after chromatographic procedures. Apart from Penicillium sp., A. fumigatus LN-4 obtained from M. azedarach stem bark and cultured in PD liquid medium also yielded this compound [32,46]. In the study conducted by Li et al. [49], brasiliamide A (210) and brasiliamide B (211) were produced from P. brasilianum in the root bark of M. azaderach [47,60].
In other studies, pycnophorin (7) was evaluated against several fungi, B. cinerea, A. solani, C. gloeosporioides, and G. saubinettii, and active against B. cinerea and A. solani. This compound (7) was also evaluated for several bacteria, such as E. coli, B. subtilis, S. aureus, and B. cereus. However, these compounds were not active against the bacteria (Table S2) [34].
The javanicin (110) was inactive or only slightly active against fungi such as Pythium ultimum, Phytophthora infestans, Botrytis cinerea, and Ceratocystis ulmi but active against Candida albicans, Escherichia coli, Bacillus sp., and Fusarium oxysporum at higher MIC values ranging from 20 to 40 µg/mL [53]. Meanwhile, compound 111 was tested for its bacteriostatic effect on P. aeruginosa and B. subtilis at 7.81 and 31.25 mg/mL, respectively. The bactericidal effect on E. coli, P. aeruginosa, and B. subtilis at 500, 62.50, and 250 mg/mL, respectively, was also analyzed. Compound 113 has no bacteriostatic effect on E. coli and B. subtilis at a dosage of 500 mg/mL and also has no bactericidal effect on P. aeruginosa at 500 mg/mL. Compound 111 was almost completely inactive against E. coli but showed promising activity against P. aeruginosa and B. subtilis  [32]. Compounds 188 and 189 were tested against the same fungi, B. cinerea and A. solani. The results showed that 188 had activity against both fungi, while 189 affected only A. solani [34].

Cytotoxic Activity
Research on cytotoxic activity in endophytic fungi has been widely reported in many compounds with different test methods. More than 140 natural products with varying levels of antitumor activity have been isolated from fungal endophytes. Alkaloids, terpenes, steroids, polyketides, quinones, isocoumarins, esters, and other secondary metabolites are prevalent. The findings can be used to develop new antitumor drugs and endophyte resources [83][84][85][86][87]. Based on the study conducted by Chokpaibon et al., [31] sesquiterpenoid compounds merulin A-C (1-3) were analyzed for their cytotoxic activity against BT474 and SW620. Compound 3 had the highest activity and was continued by 1 and 2.  Table S3.

Antioxidant and α-Glucoside Inhibitory Activity
Natural compounds isolated from endophytic fungi in medicinal plants are a rich source of drugs with various biological activities, including antioxidant properties. According to Kharat and Mendhulkar [88], phenolic compounds are responsible for antioxidant activity. Their presence may also have contributed to the radical scavenging activity observed in this study [88][89][90][91][92][93].

Anti-Inflammatory and Anti-Influenza
Inflammation is a condition in which catabolism takes precedence over anabolism. It can also be defined as a defense mechanism that aids in the elimination of potentially harmful factors and establishes homeostasis in the body. This causes increased blood flow to the site of inflammation due to the increased permeability of capillaries and white blood cells, resulting in symptoms such as redness, swelling, and pain [94,95]. Endophytic fungi are a valuable source of pharmacologically active metabolites, one of which is anti-inflammatory [96,97]. Liu et al. [38] reported that pestaloporinate B (28) had antiinflammatory activity (no inhibition in LpS-induced RAW 264.7 macrophage cells) and IC 50 of 19.0 µM (positive control L -NMMA IC 50 = 40.5 µM).
The influenza virus is one of the most common respiratory tract pathogenic agents, causing significant mortality, morbidity, and economic loss [98]. Alkaloids contain many important chemical compounds used to develop new anti-influenza agents [99]. The alkaloid group is one of the largest groups isolated from endophytic fungi [100]. In this study, 59 alkaloids were isolated. Wang et al. [62] 50 and SI values of the positive control, ribavirin, were 23.1 (±1.7) µg/mL and 32.2, respectively.

Allelophatic Effects on Wheat Triticum Aestivum
Allelopathy is defined as a direct or indirect harmful or beneficial effect of one plant on another through chemical compounds released into the environment [102]. It has been used as a weed control strategy for commercial herbicide-dominated programs. One of the bioactivities of endophytic fungi compounds studied was allelophatic effects on wheat Triticum aestivum (order poales, poaceae) conducted by Rawat et al. [103]. Compounds 64, 162, and 177-182 were evaluated for allelophatic effects on wheat Triticum aestivum. To some extent, all tested compounds inhibited T. aestivum shoot and root elongation with root intensity (RI) values ranging from 0.02 to 0.87 at 6.25 and 100 µM, respectively. The RI value is used as a direction to know the root growth of the individual species and for the sequence analysis. Furthermore, 179, 64, and 182

Neuroprotective Activity
Neuroprotective activity is an action to save or regenerate the nervous system, cells, structures, and functions by preventing damage to the nervous system in neurochemical modulators. Neurological disabilities include a wide range of disorders, such as epilepsy, autism, neuromuscular disorders, brain tumors, cerebral palsy, Parkinson's, and learning disabilities. Previous studies reported that polyketide compounds phomopsol A (91) and B (92) were tested on pC12 cells that cause Parkinson's disease and respectively showed their cell viability results of 76% and 96% at conc. of 40.0 µM with positive control corticosterone 60% at 200.0 µM [55].

Anti-HIV Activity
Compounds phomoxanthones F, G, H, and K were tested in vitro by HIV-I virustransfected 293 T cells. The result showed that phomoxanthone F at the concentration of 20 µM showed a weak inhibitory rate of 16.48 ± 6.67% with the positive control efavirenz, and an inhibitory rate of 88.54 ± 0.45% at the same concentration.

Phytotoxic Activity
The phytotoxic potential of plants and their compounds on other plants is increasingly being studied as a possible alternative to synthetic herbicides for controlling weeds in cropland. Apart from being an antifeedant, compounds from endophytic fungi were also tested for their phytotoxic activity such as compounds 148, 150, 153, and 162 against Digitaria ciliaris, with the most significant result being compound 150.

Enhanced Root Elongation Activity
The activity of a compound can be influenced by the surrounding environment. Compounds 152, 153, 154, 156, and 157 were tested for their activity on root elongation and the results showed that all the tested compounds increased root elongation activity. This is enough to warrant further studies on their mode of action and their role in chemical ecology, including allelopathy.

Conclusions
Meliaceae plant endophytes have been studied thus far for secondary metabolites. All endophytes use extra-cellular hydrolysis to defend against host attacks, invade pathogens, or obtain the host's nutrients. Previous studies found that several of the same compounds were isolated from the host and its endophytes. Endophytic fungi are one of the microorganisms frequently found in plants. A comprehensive review of secondary metabolites (triterpenoids, sesquiterpenoids, alkaloids, flavonoids, quinones, and other compounds) isolated from Meliaceae endophytes and their pharmacological activities has provided information about species identification, compound isolation, and their vital role in medicine, which can be seen from their pharmacological activity. Endophytic fungi isolated from Meliaceae contain secondary metabolites with antioxidant, antibacterial, antifungal, antiinfluenza, cytotoxic, and BSLT toxicity properties. This review provides sufficient evidence that endophytic fungi are potential bioactive plants. Hopefully, this review will contribute to the advancement of endophytic research, particularly in plants of the Meliaceae family.
Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/molecules28020778/s1, Table S1: Secondary Metabolites Derived from Endophytic fungi-Meliaceae; Table S2: Antimicrobial Activity of Compounds that have been evaluated against several fungi and bacteria; Table S3: Cytotoxic Activity of compounds (165-174) against Several Cells.  Data Availability Statement: This study did not report any data.