Chemical Constituents and Biological Activity Profiles on Pleione (Orchidaceae)

Phenolic phytochemistry, in vitro, in silico, in vivo, and mechanistic anti-inflammatory and antioxidant evaluations of Habenaria digitata

Excessive and imbalance of free radicals within the body lead to inflammation. The objective of the current research work was to explore the anti-inflammatory and antioxidant potential of the isolated compounds from Habenaria digitata. In this study, the isolated phenolic compounds were investigated for in vitro and in vivo anti-inflammatory potential along with the antioxidant enzyme. The anti-inflammatory and antioxidant potential of the phenolic compounds was assayed via various enzymes like COX-1/2, 5-LOX and ABTS, DPPH, and H2O2 free radical enzyme inhibitory assay. These compounds were also explored for their in vivo antioxidant activity like examining SOD, CAT, GSH-Px, and MDA levels in the brain, heart, and liver. The anti-inflammatory potential was evaluated using the carrageenan-induced pleurisy model in mice. On the basis of initial screening of isolated compounds, the most potent compound was further evaluated for the anti-inflammatory mechanism. Furthermore, the molecular docking study was also performed for the potent compound. The phenolic compounds were isolated and identified by GC-MS/NMR analysis by comparing its spectra to the library spectra. The isolated phenolic compounds from H. digitata were 5-methylpyrimidine-24,4-diol (1), 3,5-dihydroxy-6-methyl-2,3-dihydropyran-4-one (2), 2-isopropyl-5-methylphenol (3), 3-methoxy-4-vinylphenol (4), and 2,6-dimethoxy-4-vinylphenol (5). In in vitro antioxidant assay, the most potent compound was compound 1 having IC50 values of 0.98, 0.90, and 5 μg/mL against ABTS, DPPH, and H2O2, respectively. Similarly, against COX1/2 and 5-LOX ,compound 1 was again the potent compound with IC50 values of 42.76, 10.70, and 7.40 μg/mL. Based on the in vitro results, compound 1 was further evaluated for in vivo antioxidant and anti-inflammatory potential. Findings of the study suggest that H. digitata contains active compounds with potential anti-inflammatory and antioxidant effects. These compounds could be screened as drug candidates for pharmaceutical research, targeting conditions associated with oxidative stress and inflammatory conditions in medicinal chemistry and support their ethnomedicinal use for inflammation and oxidative stress.

Signaling pathways regulated by natural active ingredients in the fight against exercise fatigue-a review

Exercise fatigue is a normal protective mechanism of the body. However, long-term fatigue hinders normal metabolism and exercise capacity. The generation and recovery from exercise fatigue involves alterations in multiple signaling pathways, mainly AMPK, PI3K/Akt, Nrf2/ARE, NF-κB, PINK1/Parkin, and BDNF/TrkB, as well as MAPK signaling pathways that mediate energy supply, reduction of metabolites, oxidative stress homeostasis, muscle fiber type switching, and central protective effects. In recent studies, a rich variety of natural active ingredients have been identified in traditional Chinese medicines and plant extracts with anti-fatigue effects, opening up the field of research in new anti-fatigue drugs. In this review we give an overview of the signaling pathways associated with the activity of natural food active ingredients against exercise fatigue. Such a comprehensive review is necessary to understand the potential of these materials as preventive measures and treatments of exercise fatigue. We expect the findings highlighted and discussed here will help guide the development of new health products and provide a theoretical and scientific basis for future research on exercise fatigue.

Dendrobium as a new natural source of bioactive for the prevention and treatment of digestive tract diseases: A comprehensive review with future perspectives

BACKGROUND

The incidence of diseases related to the digestive tract is on the rise, with many types of complex etiologies. Dendrobium nobile Lindl. is a famous Traditional Chinese Medicine (TCM) rich in many bioactives proven to be beneficial in several health diseases related to inflammation and oxidative stress.

PURPOSE

At present, despite the availability of various therapeutic clinical drugs used for the treatment of digestive tract diseases, resistance emergence and existence of several side effects warrant for the developing of novel drugs for improved effects on digestive tract diseases.

METHODS

"Orchidaceae", "Dendrobium", "inflammation", "digestive tract", and "polysaccharide" were used as search terms to screen the literature. The therapeutic use of Dendrobium related to digestive tract diseases relative to known polysaccharides and other bioactive compounds were derived from online databases, including Web of Science, PubMed, Elsevier, Science Direct, and China National Knowledge Infrastructure, as well as relevant information on the known pharmacological actions of the listed phytochemicals.

RESULTS

To better capitalize upon Dendrobium for preventing and treating diseases related to digestive tract, this review summarizes bioactives in Dendrobium reported of potential in digestive tract diseases management and their underlying action mechanisms. Studies revealed that Dendrobium encompasses diverse classes including polysaccharides, phenolics, alkaloids, bibenzyls, coumarins, phenanthrene and steroids, with polysaccharide as the major class. Dendrobium exerts various health effects on a variety of disease related to the digestive tract. Action mechanisms involve antioxidant, anti-inflammatory, anti-apoptotic, antioxidant, anticancer, alongside the regulation of some key signaling pathways.

CONCLUSION

Overall, Dendrobium appears as a promising TCM source of bioactives that has the potential to be further developed into nutraceuticals for digestive tract diseases compared to current drug treatments. This review highlights for Dendrobium potential effects with future perspectives for needed future research to maximize the use of bioactive compounds from Dendrobium for digestive tract disease treatment. A compile of Dendrobium bioactives is also presented alongside methods for their extraction and enrichment for potential incorporation in nutraceuticals.

Origin and diversification of a Himalayan orchid genus Pleione

Pleione is an orchid endemically distributed in high mountain areas across the Hengduan Mountains (HDM), Himalayas, Southeast Asia and South of China. The unique flower shapes, rich colors and immense medicinal importance of Pleione are valuable ornamental and economic resources. However, the phylogenetic relationships and evolutionary history of the genus have not yet been comprehensively resolved. Here, the evolutionary history of Pleione was investigated using single-copy gene single nucleotide polymorphisms and chloroplast genome datasets. The data revealed that Pleione could be divided into five clades. Discordance in topology between the two phylogenetic trees and network and D-statistic analyses indicated the occurrence of reticulate evolution in the genus. The evolution could be attributed to introgression and incomplete lineage sorting. Ancestral area reconstruction suggested that Pleione was originated from the HDM. Uplifting of the HDM drove rapid diversification by creating conditions favoring rapid speciation. This coincided with two periods of consolidation of the Asian monsoon climate, which caused the first rapid diversification of Pleione from 8.87 to 7.83 Mya, and a second rapid diversification started at around 4.05 Mya to Pleistocene. The interaction between Pleione and climate changes, especially the monsoons, led to the current distribution pattern and shaped the dormancy characteristic of the different clades. In addition to revealing the evolutionary relationship of Pleione with orogeny and climate changes, the findings of this study provide insights into the speciation and diversification mechanisms of plants in the East Asian flora.

Genetic relationship of Pleione based on the chloroplast genome

Pleione (Orchidaceae) is a very famous horticultural plant with a high international reputation for its unique flower shape and abundant color. The small difference in morphological characteristics among Pleione species caused by weak reproductive isolation and easy hybridization makes the taxonomic status of individual species very confusing. Chloroplast (cp) genome information is of great significance for the study of plant phylogeny and taxonomy. In this study, the cp genomes of Pleione were sequenced and the complete cp structure and sequence characteristics of 19 species were compared and analyzed. The cp genome of Pleione species exhibited a conserved tetrad structure and each species encoded 135 protein-coding genes, 38 tRNA and 8 RNA genes. The cp genome sizes of 19 Pleione were 157964-159269 bp and the length of LSC, SSC and IR were 85953-87172 bp, 18499-18712 bp, 26459-26756 bp, respectively. Palindromic and forward repeats accounted for a high proportion and the SSRs were mainly mononucleotide repeats in Pleione. Analysis of chloroplast sequence differences indicated that the differences in coding regions were smaller than those in non-coding regions, and the variation in LSC and SSC regions was greater than that in IR regions. Phylogenetic analysis showed that all Pleione species inferred from the cp genome were clustered together and received high support. However, the genetic relationship of Pleione plants is different from the current update system of this genus. Therefore, the demarcation of Pleione interspecific relationships still needs further investigation due to the lack of sufficient evidence. The cp genome serves as valuable information for the identification of Pleione species and the study of phylogenetic relationships.

Podophyllotoxin and its derivatives: Potential anticancer agents of natural origin in cancer chemotherapy

The use of plant secondary metabolites has gained considerable attention among clinicians in the prevention and treatment of cancer. A secondary metabolite isolated mainly from the roots and rhizomes of Podophyllum species (Berberidaceae) is aryltetralin lignan - podophyllotoxin (PTOX). The purpose of this review is to discuss the therapeutic properties of PTOX as an important anticancer compound of natural origin. The relevant information regarding the antitumor mechanisms of podophyllotoxin and its derivatives were collected and analyzed from scientific databases. The results of the analysis showed PTOX exhibits potent cytotoxic activity; however, it cannot be used in its pure form due to its toxicity and generation of many side effects. Therefore, it practically remains clinically unusable. Currently, high effort is focused on attempts to synthesize analogs of PTOX that have better properties for therapeutic use e.g. etoposide (VP-16), teniposide, etopophos. PTOX derivatives are used as anticancer drugs which are showing additional immunosuppressive, antiviral, antioxidant, hypolipemic, and anti-inflammatory effects. In this review, attention is paid to the high potential of the usefulness of in vitro cultures of P. peltatum which can be a valuable source of lignans, including PTOX. In conclusion, the preclinical pharmacological studies in vitro and in vivo confirm the anticancer and chemotherapeutic potential of PTOX and its derivatives. In the future, clinical studies on human subjects are needed to certify the antitumor effects and the anticancer mechanisms to be certified and analyzed in more detail and to validate the experimental pharmacological preclinical studies.

Interaction of PKR with STCS1: an indispensable step in the biosynthesis of lunularic acid in Marchantia polymorpha

Unlike bibenzyls derived from the vascular plants, lunularic acid (LA), a key precursor for macrocyclic bisbibenzyl synthesis in nonvascular liverworts, exhibits the absence of one hydroxy group within the A ring. It was hypothesized that both polyketide reductase (PKR) and stilbenecarboxylate synthase 1 (STCS1) were involved in the LA biosynthesis, but the underlined mechanisms have not been clarified. This study used bioinformatics analysis with molecular, biochemical and physiological approaches to characterize STCS1s and PKRs involved in the biosynthesis of LA. The results indicated that MpSTCS1s from Marchantia polymorpha catalyzed both C2→C7 aldol-type and C6→C1 Claisen-type cyclization using dihydro-p-coumaroyl-coenzyme A (CoA) and malonyl-CoA as substrates to yield a C6-C2-C6 skeleton of dihydro-resveratrol following decarboxylation and the C6-C3-C6 type of phloretin in vitro. The protein-protein interaction of PKRs with STCS1 (PPI-PS) was revealed and proved essential for LA accumulation when transiently co-expressed in Nicotiana benthamiana. Moreover, replacement of the active domain of STCS1 with an 18-amino-acid fragment from the chalcone synthase led to the PPI-PS greatly decreasing and diminishing the formation of LA. The replacement also increased the chalcone formation in STCS1s. Our results highlight a previously unrecognized PPI in planta that is indispensable for the formation of LA.

Biomass and Active Compounds Accumulation of the Medicinal Orchid Pleione bulbocodioides in Response to Light Intensity and Irrigation Frequency

Pseudobulbs of Pleione species are widely used as traditional medicine in Asian countries, but the mechanism of active compound accumulation remains unclear. In the present study, we investigated the accumulation of biomass and three active compounds (dactylorhin A, militarine and batatasin III) of Pleione bulbocodioides in response to different light intensities and irrigation frequencies. We found that single high light (65 % of full sunlight) or drought stress (14-day irrigation interval) increased active compounds accumulation but the combined effect of these two treatments decreased the total content of these three active compounds. This decrease was due to the plants under combined stress having a significantly lower photosynthetic rate, leaf area and longevity, leading to a dramatic decrease in pseudobulb biomass. Among all treatments, the highest total content of active compounds was observed in plants subjected to the high light level with a high water level (3-day irrigation interval), and plants under medium light intensity (30 % of full sunlight) also had considerable content of active compounds accumulation. To balance the quality and quantity of Pleione pseudobulbs during artificial cultivation, 30∼65 % of full sunlight with the avoidance of drought stress is recommended. Our results suggest the accumulation of the three active compounds is significantly influenced by light intensity and irrigation frequency, which may contribute to the artificial cultivation and quality control of medicinal Pleione.

A Walk Through the Maze of Secondary Metabolism in Orchids: A Transcriptomic Approach

Orchids have a huge reservoir of secondary metabolites making these plants of immense therapeutic importance. Their potential as curatives has been realized since times immemorial and are extensively studied for their medicinal properties. Secondary metabolism is under stringent genetic control in plants and several molecular factors are involved in regulating the production of the metabolites. However, due to the complex molecular networks, a complete understanding of the specific molecular cues is lacking. High-throughput omics technologies have the potential to fill up this lacuna. The present study deals with comparative analysis of high-throughput transcript data involving gene identification, functional annotation, and differential expression in more than 30 orchid transcriptome data sets, with a focus to elucidate the role of various factors in alkaloid and flavonoid biosynthesis. Comprehensive analysis of the mevalonate (MVA) pathway, methyl-d-erythritol 4-phosphate (MEP) pathway, and phenylpropanoid pathway provide specific insights to the potential gene targets for drug discovery. It is envisaged that a positive stimulation of these pathways through regulation of pivotal genes and alteration of specific gene expression, could facilitate the production of secondary metabolites and enable efficient tapping of the therapeutic potential of orchids. This further would lay the foundation for developing strategies for genetic and epigenetic improvement of these plants for development of therapeutic products.

Identification and Characterization of Two Bibenzyl Glycosyltransferases from the Liverwort Marchantia polymorpha

Liverworts are rich in bibenzyls and related O-glycosides, which show antioxidant activity. However, glycosyltransferases that catalyze the glycosylation of bibenzyls have not yet been characterized. Here, we identified two bibenzyl UDP-glucosyltransferases named MpUGT737B1 and MpUGT741A1 from the model liverwort Marchantia polymorpha. The in vitro enzymatic assay revealed that MpUGT741A1 specifically accepted the bibenzyl lunularin as substrate. MpUGT737B1 could accept bibenzyls, dihydrochalcone and phenylpropanoids as substrates, and could convert phloretin to phloretin-4-O-glucoside and phloridzin, which showed inhibitory activity against tyrosinase and antioxidant activity. The results of sugar donor selectivity showed that MpUGT737B1 and MpUGT741A1 could only accept UDP-glucose as a substrate. The expression levels of these MpUGTs were considerably increased after UV irradiation, which generally caused oxidative damage. This result indicates that MpUGT737B1 and MpUGT741A1 may play a role in plant stress adaption. Subcellular localization indicates that MpUGT737B1 and MpUGT741A1 were expressed in the cytoplasm and nucleus. These enzymes should provide candidate genes for the synthesis of bioactive bibenzyl O-glucosides and the improvement of plant antioxidant capacity.

Two new bibenzyls from Pleione grandiflora (Rolfe) Rolfe and their antioxidant activity

Two new bibenzyls (1 and 2) were isolated from the pseudobulbs of Pleione grandiflora (Rolfe) Rolfe along with six known compounds, including isoarundinin I (3), isoarundinin II (4), bulbocodin D (5), batatasin III (6), 5,3'-dihydroxy- 4-(p-hydroxybenzyl)-3-methoxybibenzyl (7) and shancigusin F (8). Their structures were established on the basis of spectroscopic methods. These compounds showed potent DPPH free radical scavenging effects with IC₅₀ values ranging from 49.72 ± 0.35 μM to 65.41 ± 0.49 μM.

Mycorrhizal Fungal Partners Remain Constant during a Root Lifecycle of Pleione bulbocodioides (Orchidaceae)

Mycorrhizal mutualisms are vital for orchids through germination to adulthood. Fungal species diversity and community composition vary across seasons and plant development stages and affect plant survival, adaptation, and community maintenance. Knowledge of the temporal turnover of mycorrhizal fungi (OMF) remains poorly understood in the eco-physiologically diverse orchids (especially in epiphytic orchids), although it is important to understand the function and adaptation of mycorrhizae. Some species of Pleione are epiphytic plants with annual roots and may recruit different fungal partners during their root lifecycle. Based on continuous samplings of Pleione bulbocodioides during a whole root lifecycle, we characterized the fungal temporal dynamics using Illumina sequencing of the ITS2 region. Our data showed that the plants of P. bulbocodioides were quickly colonized by OMF at root emergence and had a constant OMF composition throughout one root lifecycle, although the OMF richness declined with root aging after a peak occurrence during root elongation. In contrast, the richness of root-inhabiting fungal endophytes kept increasing with root aging and more drastic turnovers were found in their species compositions. Our findings of OMF temporal turnover contribute to further understanding of mycorrhizal associations and adaptation of Orchidaceae and will benefit orchid resource conservation and utilization.

Discovery of glucosyloxybenzyl 2-hydroxy-2-isobutylsuccinates with anti-inflammatory activities from Pleione grandiflora

Six new glucosyloxybenzyl 2-hydroxy-2-isobutylsuccinates, pleionesides A-F (1-6), along with two known compounds (7, 8) were obtained from the pseudobulbs of Pleione grandiflora (Rolfe) Rolfe. The structures and absolute configurations of new compounds were established by HRESIMS and NMR data, along with acidic hydrolysis and alkaline hydrolysis experiments. Compounds 1-6 were tested for their anti-inflammatory activities on LPS-induced BV2 microglial cells. Amoung them, 2, 4 and 5 showed moderate activities with IC₅₀ values of 73.4, 32.8 and 57.1 μM, respectively, compared with the positive control quercetin with an IC₅₀ value of 28.3 μM.

Phytochemical profiling of bioactive compounds, anti-inflammatory and analgesic potentials of Habenaria digitata Lindl.: Molecular docking based synergistic effect of the identified compounds

ETHNOPHARMACOLOGICAL RELEVANCE

Members of Orchidaceae family has a long history in herbal and Chinese medicines. Members of this family are most commonly famous in the management of inflammation and analgesia in folk medicine. Habenaria digitata, an unexplored specie of Orchidaceae is found in North areas of Pakistan and is used by the local population for the management of analgesia and inflammation.

AIM OF THE STUDY

Based on the effective outcomes of the natural products as alternative therapies, we have evaluated Habenaria digitata for the management of analgesia and inflammation. The aim of the designed project is to provide a scientific basis of using this plant for the management of analgesia and inflammation.

MATERIALS AND METHODS

The H. digitata crude extract (Hd.Cr) and subfractions, i.e. n-hexane (Hd.Hex), chloroform (Hd.Chf), ethyl acetate (Hd.EtAc), n-butanol (Hd.Bt) and aqueous (Hd.Aq) were used. The GC-MS analysis was used for the identification of phytochemicals. The plants samples were subjected to cyclooxygenase (COX 2) and lipoxygenase (5-LOX) enzymes assays. The hot plate model, acetic acid induced writhing and formalin induced paw licking models were used for in-vivo analgesic studies. The in-vivo anti-inflammatory potential was determined with carrageenan induced paw edema test. Molecular docking studies of the identified compounds were carried out by using Molecular Operating Environment (MOE, 2016.08).

RESULTS

The GC-MS analysis confirmed sixty-five compounds in Hd.Cr. Among the fractions, Hd.Chf and Hd.EtAc displayed highest activities. The observed IC₅₀ values were 21.30 and 32.39 μg/ml against COX 2 while 14.42and 16.40 μg/ml for 5-LOX respectively. The in-vivo inflammatory and analgesic studies were pre-requisited with acute toxicity tests. In carrageenan induced inflammation, Hd.Chf excelled the standard drug aspirin by giving 62.92% inhibition of paw edema at 4^th h. Similarly, at highest concentration (75 mg/kg) of acetic acid induced analgesia, Hd.Chf was more potent than the standard drug. In formalin method, Hd.Chf exhibited 85.81% inhibition at phase-I and 74.15% at Phase-II. In hot plate model, Hd.Chf exhibited average reaction time of 10.90 at 15, 30, 45 and 60 min intervals. Docking studies supported our results and confirm the synergistic effects of phytochemicals.

CONCLUSIONS

Our experimental results concluded that H. digitata contains several bioactive compounds. These bioactive compounds synergistically have therapeutic efficacy for the management of inflammation and analgesia. We have confirmed both of these potentials from the in-vitro and in-vivo experiments. Moreover, it is also obvious that the chloroform and ethyl acetate fractions are rich in these bioactive compounds. Specifically, the Hd.Chf is observed to be more practical in all the tested models of analgesia and inflammation. Computed binding energies of the compounds revealed that all the compounds have synergistic effect to prevent analgesia and inflammation.

Xylochemical Synthesis and Biological Evaluation of Shancigusin C and Bletistrin G

The biological activities of shancigusin C (1) and bletistrin G (2), natural products isolated from orchids, are reported along with their first total syntheses. The total synthesis of shancigusin C (1) was conducted by employing the Perkin reaction to forge the central stilbene core, whereas the synthesis of bletistrin G (2) was achieved by the Wittig olefination followed by several regioselective aromatic substitution reactions. Both syntheses were completed by applying only renewable starting materials according to the principles of xylochemistry. The cytotoxic properties of shancigusin C (1) and bletistrin G (2) against tumor cells suggest suitability as a starting point for further structural variation.

Chemical Constituents of Species in the Genus Pleione (Orchidaceae) and the Implications from Molecular Phylogeny

Pleiones are popular ornamental orchids and different species of Pleione are long being used as traditional medicine in many Asian countries. However, previous chemical investigations of the genus Pleione are restricted to only a few species. In the present study, high performance liquid chromatography (HPLC) fingerprint of Pleione plants was established, which in particular, eight common peaks were confirmed in 16 species/hybrids. Three of the compounds corresponding to the chromatographic peaks were identified by electrospray ionization tandem mass spectrometry (ESI-tandem-MS). HPLC analysis confirmed the studied taxa shared most of chemical compounds but the content of chemical compounds was significantly different between species. Comparison of hierarchical clustering result with phylogenetic tree revealed that closely related species have higher similarities in chemical constituents. In consideration of low chemical similarity between spring-flowering and autumn-flowering species, we suggest a discrimination of these two groups during medicinal use of the genus Pleione. Species with a large pseudobulb and with high content of a certain compound should be given priority in future artificial cultivation and medicinal cultivar breeding. We hope our findings will contribute to the quality control and promote conservation of such endangered plant group.

Orchids and their mycorrhizal fungi: an insufficiently explored relationship

Orchids are associated with diverse fungal taxa, including nonmycorrhizal endophytic fungi as well as mycorrhizal fungi. The orchid mycorrhizal (OM) symbiosis is an excellent model for investigating the biological interactions between plants and fungi due to their high dependency on these symbionts for growth and survival. To capture the complexity of OM interactions, significant genomic, numerous transcriptomic, and proteomic studies have been performed, unraveling partly the role of each partner. On the other hand, several papers studied the bioactive metabolites from each partner but rarely interpreted their significance in this symbiotic relationship. In this review, we focus from a biochemical viewpoint on the OM dynamics and its molecular interactions. The ecological functions of OM in plant development and stress resistance are described first, summarizing recent literature. Secondly, because only few studies have specifically looked on OM molecular interactions, the signaling pathways and compounds allowing the establishment/maintenance of mycorrhizal association involved in arbuscular mycorrhiza (AM) are discussed in parallel with OM. Based on mechanistic similarities between OM and AM, and recent findings on orchids' endophytes, a putative model representing the different molecular strategies that OM fungi might employ to establish this association is proposed. It is hypothesized here that (i) orchids would excrete plant molecule signals such as strigolactones and flavonoids but also other secondary metabolites; (ii) in response, OM fungi would secrete mycorrhizal factors (Myc factors) or similar compounds to activate the common symbiosis genes (CSGs); (iii) overcome the defense mechanism by evasion of the pathogen-associated molecular patterns (PAMPs)-triggered immunity and by secretion of effectors such as small inhibitor proteins; and (iv) finally, secrete phytohormones to help the colonization or disrupt the crosstalk of plant defense phytohormones. To challenge this putative model, targeted and untargeted metabolomics studies with special attention to each partner's contribution are finally encouraged and some technical approaches are proposed.

Lignans and Their Derivatives from Plants as Antivirals

Lignans are widely produced by various plant species; they are a class of natural products that share structural similarity. They usually contain a core scaffold that is formed by two or more phenylpropanoid units. Lignans possess diverse pharmacological properties, including their antiviral activities that have been reported in recent years. This review discusses the distribution of lignans in nature according to their structural classification, and it provides a comprehensive summary of their antiviral activities. Among them, two types of antiviral lignans—podophyllotoxin and bicyclol, which are used to treat venereal warts and chronic hepatitis B (CHB) in clinical, serve as examples of using lignans for antivirals—are discussed in some detail. Prospects of lignans in antiviral drug discovery are also discussed.