Extracellular localization of the diterpene sclareol in clary sage (Salvia sclarea L., Lamiaceae)

Engineering Sclareol Production on the Leaf Surface of Nicotiana tabacum

Sclareol, a diterpene alcohol, is the most common starting material for the synthesis of ambrox, which serves as a sustainable substitute for ambergris, a valuable fragrance secreted by sperm whales. Sclareol has also been proposed to possess antibacterial, antifungal, and anticancer activities. However, in nature, sclareol is only produced by a few plant species, including Cistus creticus, Cleome spinosa, Nicotiana glutinosa, and Salvia sclarea, which limits its commercial application. In this study, we cloned the two genes responsible for sclareol biosynthesis in S. sclarea, labda-13-en-8-ol diphosphate synthase (LPPS) and sclareol synthase (SS), and overexpressed them in tobacco (Nicotiana tabacum L.). The best transgenic tobacco lines accumulated 4.1 μg/cm2 of sclareol, which is comparable to the sclareol production of N. glutinosa, a natural sclareol producer. Thus, sclareol synthesis in tobacco represents a potential alternative means for the production of this high-value compound.

Antiemetic effects of sclareol, possibly through 5-HT3 and D2 receptor interaction pathways: In-vivo and in-silico studies

BACKGROUND

Emesis is a complex physiological phenomenon that serves as a defense against numerous toxins, stressful situations, adverse medication responses, chemotherapy, and movement. Nevertheless, preventing emesis during chemotherapy or other situations is a significant issue for researchers. Hence, the majority view contends that successfully combining therapy is the best course of action. In-vivo analysis offers a more comprehensive grasp of how compounds behave within a complex biological environment, whereas in-silico evaluation refers to the use of computational models to forecast biological interactions.

OBJECTIVES

The objectives of the present study were to evaluate the effects of Sclareol (SCL) on copper sulphate-induced emetic chicks and to investigate the combined effects of these compounds using a conventional co-treatment approach and in-silico study.

METHODS

SCL (5, 10, and 15 mg/kg) administered orally with or without pre-treatment with anti-emetic drugs (Ondansetron (ODN): 24 mg/kg, Domperidone (DOM): 80 mg/kg, Hyoscine butylbromide (HYS): 100 mg/kg, and Promethazine hydrochloride (PRO): 100 mg/kg) to illustrate the effects and the potential involvement with 5HT3, D2, M3/AChM, H1, or NK1 receptors by SCL. Furthermore, an in-silico analysis was conducted to forecast the role of these receptors in the emetic process.

RESULTS

The results suggest that SCL exerted a dose-dependent anti-emetic effect on the chicks. Pretreatment with SCL-10 significantly minimized the number of retches and lengthened the emesis tendency of the experimental animals. SCL-10 significantly increased the anti-emetic effects of ODN and DOM. However, compared to the ODN-treated group, (SCL-10 + ODN) group considerably (p < 0.0001) extended the latency duration (109.40 ± 1.03 s) and significantly (p < 0.01) decreased the number of retches (20.00 ± 0.70), indicating an anti-emetic effect on the test animals. In in-silico analysis, SCL exhibited promising binding affinities with suggesting receptors.

CONCLUSION

SCL-10 exerted an inhibitory-like effect on emetic chicks, probably through the interaction of the 5HT3 and D2 receptors. Further studies are highly appreciated to validate this study and determine the precise mechanism(s) behind the anti-emetic effects of SCL. We expect that SCL-10 may be utilized as an antiemetic treatment in a single dosage form or that it may function as a synergist with other traditional medicines.

Phytosterols Are Involved in Sclareol-Induced Chlorophyll Reductions in Arabidopsis

Sclareol, a diterpene, has a wide range of physiological effects on plants, such as antimicrobial activity; disease resistance against pathogens; and the expression of genes encoding proteins involved in metabolism, transport, and phytohormone biosynthesis and signaling. Exogenous sclareol reduces the content of chlorophyll in Arabidopsis leaves. However, the endogenous compounds responsible for sclareol-induced chlorophyll reduction remain unknown. The phytosterols campesterol and stigmasterol were identified as compounds that reduce the content of chlorophyll in sclareol-treated Arabidopsis plants. The exogenous application of campesterol or stigmasterol dose-dependently reduced the content of chlorophyll in Arabidopsis leaves. Exogenously-applied sclareol enhanced the endogenous contents of campesterol and stigmasterol and the accumulation of transcripts for phytosterol biosynthetic genes. These results suggest that the phytosterols campesterol and stigmasterol, the production of which is enhanced in response to sclareol, contribute to reductions in chlorophyll content in Arabidopsis leaves.

The bioactivities of sclareol: A mini review

Sclareol, a diterpene alcohol isolated from the herbal and flavor plant clary sage (Salvia sclarea L.), is far-famed as the predominant ingredient in the refined oil of Salvia sclarea (L.). The empirical medicine of Salvia sclarea L. focused on various diseases, such as arthritis, oral inflammation, digestive system diseases, whereas the sclareol possessed more extensive and characteristic bioactivities, including anti-tumor, anti-inflammation and anti-pathogenic microbes, even anti-diabetes and hypertension. However, there is a deficiency of literature to integrate and illuminate the pharmacological attributes of sclareol based on well-documented investigations. Interestingly, sclareol has been recently considered as the potential candidate against COVID-19 and Parkinson’s disease. Accordingly, the bioactive attributes of sclareol in cancer, inflammation, even pharmacochemistry and delivery systems are reviewed for comprehensively dissecting its potential application in medicine.

Labdane Diterpenoids from Salvia tingitana Etl. Synergize with Clindamycin against Methicillin-Resistant Staphylococcus aureus

Quorum-sensing (QS) is a regulatory mechanism in bacterial communication, important for pathogenesis control. The search for small molecules active as quorum-sensing inhibitors (QSI) that can synergize with antibiotics is considered a good strategy to counteract the problem of antibiotic resistance. Here the antimicrobial labdane diterpenoids sclareol (1) and manool (2) extracted from Salvia tingitana were considered as potential QSI against methicillin-resistant Staphylococcus aureus. Only sclareol showed synergistic activity with clindamycin. The quantification of these compounds by LC-MS analysis in the organs and in the calli of S. tingitana showed that sclareol is most abundant in the flower spikes and is produced by calli, while manool is the major labdane of the roots, and is abundant also in the leaves. Other metabolites of the roots were abietane diterpenoids, common in Salvia species, and pentacyclic triterpenoids, bearing a γ-lactone moiety, previously undescribed in Salvia. Docking simulations suggested that 1 and 2 bind to key residues, involved in direct interactions with DNA. They may prevent accessory gene regulator A (AgrA) binding to DNA or AgrA activation upon phosphorylation, to suppress virulence factor expression. The antimicrobial activity of these two compounds probably achieves preventing upregulation of the accessory gene regulator (agr)-regulated genes.

Characterization and evolutionary analysis of Cucumber mosaic virus isolate infecting Salvia sclarea in India

Cucumber mosaic virus (CMV) is one of the most widespread viruses that infects a large number of cultivated crops worldwide and causes severe losses. Besides vegetables and ornamental crops, it is also spreading on medicinal and aromatic plants (MAPs) at an alarming rate. Natural occurrence of green mosaic, leaf curling, necrosis, and distortion were observed on the leaves of Salvia sclarea in the experimental field of CSIR-CIMAP, Lucknow, India. Mechanical transmission assay, morphological features, CP gene, and RNA3-based genomic characterization revealed the association of a new CMV isolate with the present disease. Virus is mechanically sap transmissible to the test plants. Transmission electron microscopy showed the presence of isodiametric particles of ~ 28 nm in diameter. Phylogenetic studies revealed that RNA3 (~ 2.2 kb) belongs to the subgroup IA of CMV. Multiple sequence alignment of amino acid sequences showed that MP possesses two unique changes in the RNA-binding domain and CP was found to be the conserved one with one change only. To the best of our knowledge, this is the first report of a CMV isolate infecting S. sclarea.

Sclareol and linalyl acetate are produced by glandular trichomes through the MEP pathway

Sclareol, an antifungal specialized metabolite produced by clary sage, Salvia sclarea, is the starting plant natural molecule used for the hemisynthesis of the perfume ingredient ambroxide. Sclareol is mainly produced in clary sage flower calyces; however, the cellular localization of the sclareol biosynthesis remains unknown. To elucidate the site of sclareol biosynthesis, we analyzed its spatial distribution in the clary sage calyx epidermis using laser desorption/ionization mass spectrometry imaging (LDI-FTICR-MSI) and investigated the expression profile of sclareol biosynthesis genes in isolated glandular trichomes (GTs). We showed that sclareol specifically accumulates in GTs' gland cells in which sclareol biosynthesis genes are strongly expressed. We next isolated a glabrous beardless mutant and demonstrate that more than 90% of the sclareol is produced by the large capitate GTs. Feeding experiments, using 1-¹³C-glucose, and specific enzyme inhibitors further revealed that the methylerythritol-phosphate (MEP) biosynthetic pathway is the main source of isopentenyl diphosphate (IPP) precursor used for the biosynthesis of sclareol. Our findings demonstrate that sclareol is an MEP-derived diterpene produced by large capitate GTs in clary sage emphasing the role of GTs as biofactories dedicated to the production of specialized metabolites.

Sclareol Inhibits Hypoxia-Inducible Factor-1α Accumulation and Induces Apoptosis in Hypoxic Cancer Cells

Purpose: The hypoxia in solid tumors is associated with the resistance to chemo/radiotherapy. Hypoxia-inducible factor-1 (HIF-1) plays a key role in cell remodeling to hypoxia. Therefore, the inhibition of HIF-1 accumulation is considered a hopeful strategy for the treatment of cancer. Here, we aimed to evaluate the geno- and cytotoxicity properties of sclareol, a natural bicyclic diterpene alcohol, on A549 cells in CoCl₂-induced hypoxia.

Methods: The cytotoxicity and apoptosis-inducing properties of sclareol on the A549 cell were evaluated using MTT assay and Annexin V/PI staining, respectively in hypoxia. DAPI staining, DNA ladder, and comet assay were used to evaluate the genotoxicity. Further, the qPCR technique was employed to assess the expression of HIF-1α, HIF-1β, and downstream target genes (GluT1, and Eno1). Finally, the level of HIF-1α protein was evaluated through Western blotting in sclareol-treated cells in hypoxia.

Results: The inhibitory concentration (IC₅₀) of sclareol against A549 cells was 8 μg/mL at 48 hours in hypoxia. The genotoxicity of sclareol was confirmed in the cells treated with sclareol in hypoxia. Sclareol induced ~46% apoptosis and also necrosis in the hypoxic condition. The qPCR analyses showed an enhanced suppression of HIF-1α, HIF-1β, GluT1, and Eno1 due to the sclareol treatment in the hypoxia. Moreover, protein quantification analysis showed dose-dependently degradation of HIF-1α in hypoxia upon treatment with sclareol.

Conclusion: The results obtained here indicate that sclareol possesses dose-dependent cytotoxicity effects against A549 cells in hypoxia through inhibition of HIF-1α protein accumulation, increasing cell sensitivity to intracellular oxygen levels, and disruption of cell adaptation to hypoxia.

Fungal volatiles emitted by members of the microbiome of desert plants are diverse and capable of promoting plant growth

Fungi represent a group of eukaryotic microorganisms that are an important part of the plant microbiome. They produce a vast array of metabolites, including fungal volatile organic compounds (fVOCs). However, the diversity and biological activities of fVOCs emitted by the mycobiota of plants native to arid and semi-arid environments remain under-explored. We characterized the chemical diversity of fVOCs produced by 22 representative members of the microbiome of agaves and cacti using SPME-GC-MS. We further tested the effects of pure compounds on the growth and development of Arabidopsis thaliana and host plants. Members of the Sordariomycetes (nine strains), Eurotiomycetes (three), Dothideomycetes (eight), Saccharomycetes (one) and Mucoromycetes (one) were included in our study. We identified 94 fungal organic volatiles classified into nine chemical classes. Terpenes showed the greatest chemical diversity, followed by alcohols and aliphatic compounds. We discovered that camphene and benzyl benzoate, together with the widely distributed and already tested benzyl alcohol, 2-phenylethyl alcohol and 3-methyl-1-butanol, improved plant growth and development of A. thaliana, Agave tequilana and Agave salmiana. Our studies on the fungal VOCs from desert plants underscore an untapped chemical diversity with promising biotechnological applications.

Genetic Control of Glandular Trichome Development

Plant glandular trichomes are epidermal secretory structures producing various specialized metabolites. These metabolites are involved in plant adaptation to its environment and many of them have remarkable properties exploited by fragrance, flavor, and pharmaceutical industries. The identification of genes controlling glandular trichome development is of high interest to understand how plants produce specialized metabolites. Our knowledge about this developmental process is still limited, but genes controlling glandular trichome initiation and morphogenesis have recently been identified. In particular, R2R3-MYB and HD-ZIP IV transcription factors appear to play essential roles in glandular trichome initiation in Artemisia annua and tomato. In this review, we focus on the results obtained in these two species and we propose genetic regulation models integrating these data.

Therapeutic Potential of Sclareol in Experimental Models of Rheumatoid Arthritis

Previous studies have shown that the natural diterpene compound, sclareol, potentially inhibits inflammation, but it has not yet been determined whether sclareol can alleviate inflammation associated with rheumatoid arthritis (RA). Here, we utilized human synovial cell line, SW982, and an experimental murine model of rheumatoid arthritis, collagen-induced arthritis (CIA), to evaluate the therapeutic effects of sclareol in RA. Arthritic DBA/1J mice were dosed with 5 and 10 mg/kg sclareol intraperitoneally every other day over 21 days. Arthritic severity was evaluated by levels of anti-collagen II (anti-CII) antibody, inflammatory cytokines, and histopathologic examination of knee joint tissues. Our results reveal that the serum anti-CII antibody, cytokines interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, and IL-17, as well as Th17 and Th1 cell population in inguinal lymph nodes, were significantly lower in sclareol-treated mice compared to the control group. Also, the sclareol treatment groups showed reduced swelling in the paws and lower histological arthritic scores, indicating that sclareol potentially mitigates collagen-induced arthritis. Furthermore, IL-1β-stimulated SW982 cells secreted less inflammatory cytokines (TNF-α and IL-6), which is associated with the downregulation of p38-mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), and NF-κB pathways. Overall, we demonstrate that sclareol could relieve arthritic severities by modulating excessive inflammation and our study merits the pharmaceutical development of sclareol as a therapeutic treatment for inflammation associated with RA.

The Diterpene Sclareol Vascular Effect in Normotensive and Hypertensive Rats

BACKGROUND:

The diterpene Sclareol has antimicrobial action, cytotoxic and cytostatic effects and anti-tumor activities. However, researches on the cardiovascular system are scarce.

OBJECTIVE:

This study was designed to investigate the mechanisms involved in the Sclareol cardiovascular effect in normotensive and hypertensive rats.

METHODS:

The arterial hypertension was promoted using 2-kidneys 1-clip model in rats. The effect of sclareol on blood pressure was performed by using three dose (10, 20 and 40 mg/kg). Cumulative dose-response curves for Sclareol were determined for endothelium-intact and endothelium-denuded aortic rings in presence or absence of L-NAME and ODQ. The NOx levels were measure in the plasma sample.

RESULTS:

The Sclareol administration in vivo caused a significant reduction in blood pressure in both groups. In vitro the sclareol promoted relaxation in aorta, with endothelium, pre-contracted to Phe. The inhibitors of the nitric oxide synthase and soluble guanylate cyclase were as efficient as the removal of endothelium, in inhibiting the Sclareol-induced relaxation. Otherwise, it was no change of NOx. Also, for unknown reasons, the Sclareol is not selective for hypertensive animals.

CONCLUSION:

The diterpene Sclareol showed in vivo hypotensive and in-vitro vasodilator effects; The chemiluminescence plasmatic NO analysis showed no significant difference between groups and The Sclareol exhibit better effect on normotensive than hypertensive animals to reduce blood pressure. It is concluded that the diterpenes metabolites would be a promising source prototype for the development of new agents in the cardiovascular therapy.

FUNDAMENTO:

O diterpeno Esclareol tem ação antimicrobiana, efeitos citotóxicos e citostáticos e atividades antitumorais. No entanto, pesquisas sobre o sistema cardiovascular são escassas.

OBJETIVO:

Este estudo foi desenvolvido para investigar os mecanismos envolvidos no efeito cardiovascular de Esclareol em ratos normotensos e hipertensos.

MÉTODOS:

A hipertensão arterial foi promovida utilizando modelo de 2 clones de 1-clipe em ratos. O efeito do esclareol sobre a pressão arterial foi realizado utilizando três doses (10, 20 e 40 mg/kg). As curvas dose-resposta cumulativas para Esclareol foram determinadas para anéis aórticos endotélio-intactos e desprovidos de endotélio na presença ou ausência de L-NAME e ODQ. Os níveis de NOx foram medidos na amostra de plasma.

RESULTADOS:

A administração de Esclareol in vivo causou uma redução significativa na pressão sanguínea em ambos os grupos. In vitro o esclareol promoveu relaxamento na aorta, com endotélio, pré-contraído a Phe. Os inibidores da óxido nítrico sintase e da guanilato ciclase solúvel foram tão eficientes quanto a remoção do endotélio, na inibição do relaxamento induzido por Esclareol. Por outra parte, não houve mudança de NOx. Além disso, por razões desconhecidas, o Sclareol não é seletivo para animais hipertensos.

CONCLUSÃO:

O diterpeno Esclareol apresentou efeitos hipotensores in vivo e vasodilatadores in vitro; A análise de NO plasmático por quimioluminescência não mostrou diferença significativa entre os grupos e O Esclareol exibe melhor efeito sobre os animais normotensos do que hipertensos para reduzir a pressão arterial. Conclui-se que os metabólitos de diterpenos seriam um protótipo de fonte promissora para o desenvolvimento de novos agentes na terapia cardiovascular.

Localization of a defensive volatile 4-hydroxy-4-methylpentan-2-one in the capitate glandular trichomes of Oenothera glazioviana

Glandular trichomes of plants produce a wide variety of secondary metabolites which are considered as major defensive chemicals. The capitate glandular trichomes of Oenothera glazioviana (Onagraceae) were collected with laser microdissection and analyzed by gas chromatography-mass spectrometry. The volatile compound 4-hydroxy-4-methylpentan-2-one (1) was identified. We found that compound 1 displays antimicrobial, insecticidal, and phytotoxic activities. These results suggest that compound 1 might function as a defensive compound in the capitate glandular trichomes of O. glazioviana against pathogens, insect herbivores, and presumably competitive plants as well.

Enzymes for synthetic biology of ambroxide-related diterpenoid fragrance compounds

Ambrox and related ambroxides are highly priced in the fragrance industry, and valued for their delicate odor and fixative properties. Historically, ambrox was obtained from ambergris, a waxy excretion produced by sperm whales, now an endangered species. Synthetic ambroxides have replaced ambergris in perfume manufacture. Plant labdane diterpenoids can serve as starting material for ambroxide synthesis. Among these, the diterpene alcohol sclareol is the major industrial precursor obtained from cultivated clary sage (Salvia sclarea). In plants, a large family of diterpene synthase (diTPS) enzymes controls key reactions in diterpenoid biosynthesis. Advanced metabolite profiling and high-throughput sequencing of fragrant and medicinal plants have accelerated discovery of novel diTPS functions, providing a resource for combinatorial synthetic biology and metabolic engineering approaches. This chapter highlights recent progress on the discovery, characterization, and engineering of plant diTPSs with potential uses in ambroxide production. It features biosynthesis of sclareol, cis-abienol, and diterpene resin acids, as sources of genes and enzymes for diterpenoid bioproducts.

FT-IR, FT-Raman, UV-visible, and NMR spectroscopy and vibrational properties of the labdane-type diterpene 13-epi-sclareol

In this work, FT-IR, FT-Raman, UV-Visible and NMR spectroscopies and density functional theory (DFT) calculations were employed to study the structural and vibrational properties of the labdane-type diterpene 13-epi-sclareol using the hybrid B3LYP method together with the 6-31G(∗) basis set. Three stable structures with minimum energy found on the potential energy curves (PES) were optimized, and the corresponding molecular electrostatic potentials, atomic charges, bond orders, stabilization energies and topological properties were computed at the same approximation level. The complete assignment of the bands observed in the vibrational spectrum of 13-epi-sclareol was performed taking into account the internal symmetry coordinates for the three structures using the scaled quantum mechanical force field (SQMFF) methodology at the same level of theory. In addition, the force constants were calculated and compared with those reported in the literature for similar compounds. The predicted vibrational spectrum and the calculated (1)H NMR and (13)C NMR chemical shifts are in good agreement with the corresponding experimental results. The theoretical UV-Vis spectra for the most stable structure of 13-epi-sclareol demonstrate a better correlation with the corresponding experimental spectrum. The study of the three conformers by means of the theory of atoms in molecules (AIM) revealed different H bond interactions and a strong dependence of the interactions on the distance between the involved atoms. Furthermore, the natural bond orbital (NBO) calculations showed the characteristics of the electronic delocalization for the two six-membered rings with chair conformations.