Chemical Composition and Potential Properties in Mental Illness (Anxiety, Depression and Insomnia) of Agarwood Essential Oil: A Review

Analysis of fungal composition in different layers of Bantou agarwood-forming trunk of Aquilaria sinensis revealing presence of Aspergillus-inhibiting substances in agarwood sites

Objective

The objective of this study was to analyse fungal composition and exploit application potential in the Bantou (BT) agarwood-forming trunk of Aquilaria sinensis.

Methods

BT agarwood is a naturally formed agarwood that was collected after cutting. Total genomic DNA of the fungi in BT agarwood was extracted by the hexadecyltrimethy ammonium bromide (CTAB) method, followed by PCR amplification and library construction. The effective tags were obtained by the HiSeq2500 platform, and the data were subjected to bioinformatics and statistical analyses.

Results

A total of 7 850 040 effective tags were obtained, Ascomycota was the most abundant fungus at the phylum level, with a relative abundance of 56.36%-61.44%, followed by Basidiomycota, with a relative abundance of 10.49%-20.39%. Dothideomycetes, Agaricomycetes and Sordariomycetes were dominant at the class level, accounting for 26.21%-33.88%, 8.40%-17.66%, and 18.41%-24.11%, respectively. Lignosphaeria, Phaeoacremonium and Hermatomyces were dominant at the genus level, with relative abundances of 6.25%-7.64%, 1.95%-9.05% and 1.5%-5.4%, respectively. Diversity and richness analysis showed that the fungal composition in the agarwood formation sites (agarwood layer, upper agarwood layer and lower agarwood layer) were significantly lower than those in the decomposing layer and the healthy layer. That is, the fungal diversity and richness were significantly reduced during agarwood formation by the action of open wounds. The fungal community structure in the decomposing layer and agarwood formation sites obviously differed from that in the healthy layer. The number of Aspergillus taxa in agarwood formation sites decreased significantly (healthy layer is 0.5%, decomposing layer is 0.022%, upper agarwood layer is 0.012%, agarwood layer is 0.01%, and lower agarwood layer is 0.013%), indicating that agarwood may contain potential substances to inhibit the growth of Aspergillus.

Conclusion

Agarwood from agarwood formation sites contains potential substances that inhibit Aspergillus, which provides valuable information for the control of the genus of Aspergillus.

Agarwood leaf ethanol extract provides neuroprotective properties and promotes cholinergic differentiation of HT22 hippocampal neurons

Neurodegenerative diseases, characterized by the loss or damage of neurons, represent a growing global health concern. Plants are a rich source of naturally occurring compounds with immense therapeutic potential. Among them, Aquilaria crassna (commonly known as agarwood) is a precious fragrant plant extensively used in cosmetics, perfumes, and traditional Asian medicine. However, its neuroprotective role, particularly in neuroregeneration, has been minimally explored. This study aimed to investigate the therapeutic potential of agarwood leaves in promoting neuroregeneration, with a focus on cholinergic function and neural differentiation. To identify bioactive compounds, a comprehensive LC-MS analysis was conducted on agarwood ethanolic extract (AWE). The phytochemicals detected were further evaluated using in silico methods to predict their interaction with receptor proteins linked to neurodegenerative diseases. Virtual screening revealed that several compounds in AWE exhibited strong binding affinities to receptors such as sigma-1, TrkB, Nogo-66, and p75NTR, providing insights into the potential mechanisms underlying its neuroprotective effects. The in-silico findings were validated through in vitro experiments using HT-22 mouse hippocampal cells as a model. AWE treatment led to a dose-dependent increase in the expression of marker proteins associated with neural differentiation and regeneration, including neuronal nuclei (NeuN), growth-associated protein 43 (GAP43), synaptophysin (Syn), brain-derived neurotrophic factor (BDNF), and the sigma-1 receptor. Additionally, AWE enhanced the expression of specific markers for cholinergic neurons, demonstrating its influence on neuronal development and synaptic function. These findings provide compelling evidence of AWE's neuroprotective properties, highlighting its potential as a therapeutic agent for neurodegenerative diseases.

Dynamic Environmental Interactions Shape the Volatile Compounds of Agarwood Oils Extracted from Aquilaria sinensis Using Supercritical Carbon Dioxide

Aquilaria spp. are a highly valuable plant species found in the Chinese herbal medicine and agarwood fragrance supplement industries for fumigation, combustion and perfume. The phytochemical composition of agarwood oils (extracts) was derived from Aquilaria sinensis and its subspecies 'Qi-Nan' using supercritical CO2 extraction technology. Gas chromatography connected with a mass spectrometry apparatus was employed for qualitative and quantitative analyses. Comparing the agarwood oils from six planting areas, 12 common components were obtained, among which sesquiterpenes and chromones had the highest relative content. Genetic and environmental factors had the greatest impact on the three chromones, especially on 2-phenyl-4H-chromen-4-one. According to the PCA and PLS-DA models, the 'Qi-Nan' was derived from a variety selected from the native A. sinensis, and the difference in the volatile components was able to indirectly prove that it was genetically heterogeneous with the native A. sinensis. Using the 73 components obtained from GC-MS analysis, the VIP values and S-plots were generated using the OPLS-DA model. Seven components with VIP values > 1.0 were selected from two groups of agarwood oils of the native A. sinensis and 'Qi-Nan' subspecies. In addition, by analyzing 12 common components, the differential components with VIP values > 1 were 2-phenyl-4H-chromen-4-one and 2-(4-methoxyphenethyl)-4H-chromen-4-one. Chromones were the main component of agarwood oils extracted by supercritical CO2, and 2-phenyl-4H-chromen-4-one could be used as a volatile marker, especially in the 'Qi-Nan' subspecies, where this marker exhibited more prominent characteristics.

Antidepressant Activity of Agarwood Essential Oil: A Mechanistic Study on Inflammatory and Neuroprotective Signaling Pathways

Background: Depression ranks among the most severe mental health conditions, and poses a burden on global health. Agarwood, an aromatic medicinal plant, has shown potential for improving mental symptoms. As a common folk medicine, agarwood has been applied as an alternative method for mental disorders such as depression through aromatherapy. Previous studies have found that the therapeutic effects of agarwood aromatherapy are primarily related to its volatile components. This study aimed to examine the antidepressant properties and underlying mechanisms of agarwood essential oil (AEO), a collection of the volatile components of agarwood utilized through aromatherapy inhalation and injection administration in mice. Methods: A lipopolysaccharide (LPS)-induced inflammatory depression model was used to evaluate the effects of AEO inhalation and injection on depression-like symptoms. Behavioral assessments included the open-field, tail suspension, and forced swimming tests. Western blot (WB) and ELISA techniques were used to further verify the mechanistic insights. Results: In the LPS-induced depression-like model, AEO inhalation and injection significantly improved depression-like symptoms, decreased immobility duration in both the tail suspension and forced swimming tests in model mice, and reduced the levels of inflammatory cytokines IL-1β, IL-6, and TNF-α. WB experiments demonstrated that AEO inhibited the NF-κB/IκB-α inflammatory pathway and activated the BDNF/TrkB/CREB pathway in the hippocampus of the LPS-depression model mice. Notably, AEO extracted by hydrodistillation was more effective in alleviating LPS-induced depressive-like behaviors than using supercritical CO2 fluid extraction. Conclusions: Both the inhalation and the injection administration of AEO exerted notable antidepressant effects, potentially associated with reducing inflammation levels in the brain, downregulating inflammatory NF-κB/IκB-α, and upregulating the neuroprotective BDNF/TrkB/CREB signaling pathway. In the future, it is necessary to further determine the pharmacodynamic components, key targets and specific molecular mechanisms of AEO's antidepressant effects so as to provide more support for the neuroprotective research of medicinal plants.

Visualization OPLS class models of GC-MS-based metabolomics data for identifying agarwood essential oil extracted by hydro-distillation

The composition of natural substances varies with plant species and cultivation environment factors, which is also a complex problem. A total of 127 substances of agarwood essential oils (AEOs) extracted by hydro-distillation were identified by GC-MS analysis. Among the components obtained from AEOs, sesquiterpenes and small molecule aromatic substances were the main components, and there were significantly fewer chromones. The aromatic compound 4-phenyl-2-butanone was the only common component. The VIP value and S-plot generated by the OPLS-DA model based on the comparison of regional groups or pairwise genotypes showed up to 26 potential markers at VIP > 1. The more common components of agarwood, such as sesquiterpenes α-guruene, agarospirol, guaiol, γ-eudesmol and chromone 2-phenylethyl-4H-chromen-4-one, contributed the most to the VIP value. Supervised OPLS-DA was better than that of PLS-DA, providing a reference for the quality evaluation of AEOs. This method emphasizes providing more information and obtaining additional information when combined with appropriate multivariate modeling and effective visualization of specific labeled metabolites for identification.

Sesquiterpenoids in Agarwood: Biosynthesis, Microbial Induction, and Pharmacological Activities

Agarwood, derived from the Aquilaria genus, is widely utilized in perfumery, traditional medicine, and cultural practices throughout Asia. Agarwood is rich in terpenes, especially sesquiterpenes, which are considered to be the source of its rare and exquisite fragrance. This Review consolidates recent research on sesquiterpene biosynthesis in agarwood and the influence of fungi on these processes, alongside a discussion of the potential medicinal value of agarwood sesquiterpenes. This Review commences by elucidating the general biosynthesis of sesquiterpenes and identifying the main enzymes and transcription factors involved in the production of agarwood sesquiterpenes. This Review also summarizes the fungi associated with agarwood and highlights how commensal fungi stimulate agarwood and sesquiterpene production. We then scrutinize the pharmacological properties of sesquiterpenes, underscoring their anti-inflammatory and antimicrobial effects, which are closely linked to cellular signaling pathways, such as the NF-κB and MAPK pathways. Additionally, we review the potential therapeutic benefits of agarwood essential oil for its antidepressant properties, which are linked to the regulation of stress-related neurochemical and hormonal pathways. This Review also addresses the challenges of sustainable agarwood production, highlighting issues such as overharvesting and habitat loss while discussing the potential strategy of harnessing microbes in agarwood production to support the ecological preservation of wild resources. By advancing our knowledge of agarwood and sesquiterpene characteristics, we propose potential directions for the future application and sustainable development of agarwood research.

Nerolidol reduces depression-like behavior in mice and suppresses microglia activation by down-regulating DNA methyltransferase 1

Modern medicine has unveiled that essential oil made from Aquilaria possesses sedative and hypnotic effects. Among the chemical components in Aquilaria, nerolidol, a natural sesquiterpene alcohol, has shown promising effects. This study aimed to unravel the potential of nerolidol in treating depression. Chronic unpredictable mild stress (CUMS) was utilized to induce depression-like behavior in mice, and open field test, sucrose preference, and tail suspension test was conducted. The impacts of nerolidol on the inflammatory response, microglial activation, and DNA methyltransferase 1 (DNMT1) were assessed. To study the regulatory role of DNMT1, lipopolysaccharide (LPS) was used to treat BV2 cells, followed by the evaluation of cell viability and DNMT1 level. Additionally, the influence of DNMT1 overexpression on BV2 cell activation was determined. Behavioral analysis revealed that nerolidol reduced depression-like behavior in mice. Nerolidol reduced the levels of inflammatory factors and microglial activation caused by CUMS. Nerolidol treatment was found to reduce DNMT1 levels in mouse brain tissue and it also decrease the LPS-induced increase in DNMT1 levels in BV2 cells. DNMT1 overexpression reversed the impacts of nerolidol on the inflammation response and cell activation. This study underscores the potential of nerolidol in reducing CUMS-induced depressive-like behavior and inhibiting microglial activation by downregulating DNMT1. These findings offer valuable insights into the potential of nerolidol as a therapeutic option for depression.

The anxiolytic and circadian regulatory effect of agarwood water extract and its effects on the next generation; zebrafish modelling

Anxiety is one of the most common psychiatric symptoms worldwide. Studies show that there is an increase of >25 % in the prevalence of anxiety with the onset of the COVID-19 pandemic process. Due to the various side effects of drugs used in the treatment of anxiety, interest in natural therapeutic alternatives has increased. Agarwood is a plant used as a natural therapeutic due to its sedative effect as well as many effects such as antioxidant and antibacterial. Although there are many studies with agarwood, comprehensive behavioral studies, including the next generation, are limited. In present study, zebrafish fed with diets containing 10-100 ppm water extract of Agarwood (AWE) for 3 and 8 weeks were exposed to predator stress using Oscar fish in order to test the potential anxiolytic effect of AWE. At the end of the period, zebrafish exposed to predator stress were subjected to anxiety and circadian tests. Histopathological evaluation and immunofluorescent analyzes of BDNF and 5HT4-R proteins were performed in the brains of zebrafish. The effects on the next generation were examined by taking offspring from zebrafish. According to the results, it was observed that AWE had a healing effect on anxiety-like behaviors and on the disrupted circadian rhythm triggered by the predatory stress it applied, especially in the 8 weeks 100 ppm group. Interestingly, it was also found to be effective in offspring of zebrafish fed diets with AWE.

Five new sesquiterpenoids from agarwood of Aquilaria sinensis

Five new eudesmane-type sesquiterpenoids (aquisinenoids F-J (1-5)) and five known compounds (6-10) were isolated from the agarwood of Aquilaria sinensis. Their structures, including absolute configurations, were identified by comprehensive spectroscopic analyses and computational methods. Inspired by our previous study on the same kinds of skeletons, we speculated that the new compounds have anticancer and anti-inflammatory activities. The results did not show any activity, but they revealed the structure-activity relationships (SAR).