Chemical variability of Rhododendron tomentosum (Ledum palustre) essential oils and their pro-apoptotic effect on lymphocytes and rheumatoid arthritis synoviocytes

Bioactive Lignan Glycosides in Stems of Marsh Rosemary (Rhododendron tomentosum): Non-Targeted Screening and Identification Using Two-Stage Analytical Strategy

Rhododendron tomentosum is a widespread evergreen shrub used in folk medicine due to the high biological activity of its secondary metabolites, including lignans, that has not been sufficiently studied, and overcoming this problem requires advanced analytical techniques. This study proposes a two-stage analytical strategy for non-targeted screening and identification of lignans in plant extracts that involves the detection of specific lignan-related structures by 2D NMR and the establishment of corresponding fragment ions for further mass spectrometry analysis (HPLC-ESI-MS/MS). The polyphenolic fraction of R. tomentosum stem extract was the object of the study. Eight secoisolariciresinol-type lignans (xylosides, glucosides, and rhamnoside), including one previously unknown compound (5-methoxysecoisolariciresinol 9-xyloside), were identified for the first time. The structures of the five compounds were additionally confirmed by preparative HPLC isolation and NMR studies. All of the obtained compounds had antioxidant activity (FRAP and DPPH) similar to that of ascorbic acid. The proposed analytical strategy can be considered an efficient tool for rapid and reliable group screening and identification of lignan derivatives in plant extracts. Its application in the study of R. tomentosum extracts has revealed a number of lignan glycosides that may contribute to the medicinal properties of the plant.

Elicited Production of Essential Oil with Immunomodulatory Activity in Salvia apiana Microshoot Culture

Salvia apiana Jepson is an endemic North American species characterized by a rich phytochemical profile including abietane-type diterpenoids, phenolic acids, flavonoids, and thujone-free essential oil (EO). The current study was aimed at increasing EO production in bioreactor-grown S. apiana microshoot culture through biotic elicitation using chitosan, ergosterol, and yeast extract (YE). Additionally, the immunomodulatory effects of the major volatile constituent of white sage-1,8-cineole-as well as EOs obtained from both S. apiana microshoots and leaves of field-grown plants, were assessed. EOs were isolated via hydrodistillation and analyzed by GC/MS and GC/FID. Biological assays included flow cytometric evaluation of the proliferation and apoptosis rates of human CD4 and CD8 T lymphocytes, obtained from healthy volunteers and subjected to different concentrations of EOs and 1,8-cineole. Elicitation with 100 mg/L YE improved the production of EO in S. apiana microshoots by 9.4% (1.20% v/m). EOs from both microshoots and leaves of field-grown plants, as well as 1,8-cineole, demonstrated dose-dependent anti-proliferative and pro-apoptotic effects on CD4+ and CD8+ T cells. These findings highlight the potential of S. apiana microshoot cultures capable of producing EO with significant immunomodulatory activity.

Phytochemical Profiling and Biological Activities of Rhododendron Subsect. Ledum: Discovering the Medicinal Potential of Labrador Tea Species in the Northern Hemisphere

Rhododendron subsect. Ledum is a distinct taxonomic subdivision within the genus Rhododendron, comprising a group of evergreen shrubs and small trees. This review will comprehensively analyse the phytochemical profiles and biological properties of the Rhododendron subsect. Ledum species subsect. Ledum consists of eight plant species indigenous to temperate and subarctic regions of the Northern Hemisphere, collectively known as Labrador tea. Recent investigations have concentrated on the phytochemical constituents of these plants due to limited data, emphasizing their evergreen nature and potential industrial significance. This review summarizes their major phytochemical constituents, including flavonoids, phenolic acids, and terpenoids, and discusses their potential biological activities, such as antioxidant, anti-inflammatory, antimicrobial, antitumor, hypoglycemic, hepatoprotective, neuroprotective, and cardioprotective effects. Traditional uses of these plant species align with scientific findings, emphasizing the significance of these plants in traditional medicine. However, despite promising results, gaps exist in our understanding of specific compounds' therapeutic effects, necessitating further research for comprehensive validation. This review serves as a valuable resource for researchers, identifying current knowledge, uncertainties, and emerging trends in the study of the Rhododendron subsect. Ledum species.

Chemical Composition and Antiplasmodial Activity of the Essential Oil of Rhododendron subarcticum Leaves from Nunavik, Québec, Canada

Dwarf Labrador tea, Rhododendron subarcticum Harmaja, is a popular medicinal plant in use by First Nations of Northern Canada, but its phytochemistry has remained largely unexplored. We have isolated and characterized the essential oil from a population of this species harvested near the treeline in Nunavik, Québec. Analyses by gas chromatography-mass spectrometry (GC-MS) and gas chromatography/flame-ionization detection (GC/FID) led to the identification of 53 compounds; the main secondary metabolites were ascaridole (64.7% of the total FID area) and p-cymene (21.1%). Such a composition resembles a chemotype observed for R. tomentosum, a close relative found mainly in Europe and Asia, but has never been attributed to R. subarcticum. Growth inhibition assays against different strains of Plasmodium falciparum (3D7, Dd2), the parasite responsible for the most severe form of malaria, were conducted with either the R. subarcticum's essential oil or the isolated ascaridole. Our results show that the essential oil's biological activity can be attributed to ascaridole as its IC₅₀ is more than twice that of ascaridole [ascaridole's IC₅₀ values are 147.3 nM (3D7) and 104.9 nM (Dd2)].

Essential Oils from Six Aromatic Plants of Langtang National Park: Insights on Their Chemical Constituents via GC-MS Analysis

The present work aims to provide an insight on the chemical constituents of essential oils obtained from six aromatic plants of the Langtang National Park (LNP), Nepal. LNP harbors an enriched biodiversity of medicinal and aromatic plants (MAPs). The composition of essential oils obtained from Rhododendron anthopogon D. Don, Artemisia dubia Wall. ex Besser, Boenninghausenia albiflora (Hook.) Rchb. ex Meisn., Elsholtzia fruticosa (D. Don) Rehder, Juniperus recurva Buch.-Ham. ex D. Don and Rhododendron setosum D. Don, were analyzed by Gas Chromatography-Mass Spectrometry (GC-MS). The essential oils were extracted via the hydrodistillation method using the Clevenger apparatus. GC-MS analysis showed that E-caryophyllene, α-pinene, γ-terpinene, β-pinene and δ-cadinene in Rhododendron anthopogon; santolina-triene, β-cubebene and sabinene in Artemisia dubia; β-myrcene, β-cubebene, E-β-ocimene and bicyclogermacrene in Boenninghausenia albiflora; perillene, eucalyptol and β-pinene in Elsholtzia fruticosa; δ-3-carene, cadina-1(6),4-diene and δ-cadinene in Juniperus recurva; trans-sabinyl acetate, sabinene, α-elemol and germacrene D in Rhododendron setosum are the principal components. The major compounds in the essential oil were monoterpenes and sesquiterpenes, representing almost 80% to 90% of the total constituents of the essential oil. In comparison to the previous studies, the results showed a significant difference in the qualitative composition of the essential oil. This is also the first report on the study of chemical constituents from the essential oil of R. setosum. Despite hosting a plethora of MAPs, only a limited number of studies have been carried out to identify their chemical and biological properties. Hence, further investigations on the MAPs of the Langtang region are highly essential to identify the major chemical constituents and explore their biological activities.

Chemical constituents, antibacterial, acaricidal and anti-inflammatory activities of the essential oils from four Rhododendron species

As the ornamental plants and traditional medicines, Rhododendron przewalskii, R. anthopogonoides, R. thymifolium, and R. capitatum are widely distributed in western China. In this paper, the essential oils from these four species were extracted by supercritical extraction and the components were analyzed using headspace solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS), the antibacterial, acaricidal and anti-inflammatory activities were investigated. Results showed that R. thymifolium (RTEO) contained the highest yield of 0.99% with 246 compounds, followed by R. capitatum (RCEO, 0.81%) with 290 chemicals, R. anthopogonoides (RAEO, 0.57%) with 302 compounds and R. przewalskii (RPEO, 0.30%) with 294 components. They also exhibited the safety at given doses and have the anti-inflammatory in vitro and in vivo tests via inhibiting the cytokines productions, the acaricidal and antibacterial activities also were found. 4-Hydroxy-3-methylacetophenone from RPEO, α-pinene and β-pinene from RAEO, β-farnesene and germacrone from RTEO, and benzylacetone from RCEO, as main and active components, inhibited the NO content in RAW 264.7 cells induced by LPS. These results indicated that four essential oils have certain medicinal value and laid the foundation for the development of these species as raw materials for the pharmaceutical and perfume industries.

Chemical Composition and Immunomodulatory Activity of Essential Oils from Rhododendron albiflorum

Rhododendron (Ericaceae) extracts contain flavonoids, chromones, terpenoids, steroids, and essential oils and are used in traditional ethnobotanical medicine. However, little is known about the immunomodulatory activity of essential oils isolated from these plants. Thus, we isolated essential oils from the flowers and leaves of R. albiflorum (cascade azalea) and analyzed their chemical composition and innate immunomodulatory activity. Compositional analysis of flower (REO_Fl) versus leaf (REO_Lv) essential oils revealed significant differences. REO_Fl was comprised mainly of monoterpenes (92%), whereas sesquiterpenes were found in relatively low amounts. In contrast, REO_Lv was primarily composed of sesquiterpenes (90.9%), with a small number of monoterpenes. REO_Lv and its primary sesquiterpenes (viridiflorol, spathulenol, curzerene, and germacrone) induced intracellular Ca²⁺ mobilization in human neutrophils, C20 microglial cells, and HL60 cells transfected with N-formyl peptide receptor 1 (FPR1) or FPR2. On the other hand, pretreatment with these essential oils or component compounds inhibited agonist-induced Ca²⁺ mobilization and chemotaxis in human neutrophils and agonist-induced Ca²⁺ mobilization in microglial cells and FPR-transfected HL60 cells, indicating that the direct effect of these compounds on [Ca²⁺]_i desensitized the cells to subsequent agonist activation. Reverse pharmacophore mapping suggested several potential kinase targets for these compounds; however, these targets were not supported by kinase binding assays. Our results provide a cellular and molecular basis to explain at least part of the beneficial immunotherapeutic properties of the R. albiflorum essential oils and suggest that essential oils from leaves of this plant may be effective in modulating some innate immune responses, possibly by inhibition of neutrophil migration.

Essential Oils and Bioactive Components against Arthritis: A Novel Perspective on Their Therapeutic Potential

Essential oils (EOs) are known to possess a number of beneficial properties. Their antimicrobial, anti-inflammatory, antioxidant, antidiabetic, and cancer-preventing activities have been extensively reported. Due to their wide use as food preservers and additives, as well as their use in agriculture, perfumes, and make-up products, these complex mixtures of volatile compounds have gained importance from a commercial point of view, not only in the pharmaceutical industry, but also in agronomic, food, cosmetic, and perfume industries. An analysis of the recent scientific literature allowed us to highlight the presence of an increasing number of studies on the potential antiarthritic properties of EOs and their main constituents, which seems to suggest a new interesting potential therapeutic application. The aim of this review is to examine the current knowledge on the beneficial effects of essential oils in the treatment of arthritic diseases, providing an overview of the reports on the in vivo and in vitro effects of EOs. Furthermore, this review critically examines the recent findings on the potential roles of the main components of EOs in the exerted beneficial effects. Obtained negative results are also reported.

Toxic, Radical Scavenging, and Antifungal Activity of Rhododendron tomentosum H. Essential Oils

The chemical composition of eight (seven shoot and one inflorescence) essential oils (EOs) of Rh. tomentosum H. plants growing in Eastern Lithuania is reported. The plant material was collected during different phases of vegetation (from April to October). The oils were obtained by hydrodistillation from air-dried aerial parts (leaves and inflorescences). In total, up to 70 compounds were identified by GC−MS and GC (flame-ionization detector, FID); they comprised 91.0 ± 4.7%–96.2 ± 3.1% of the oil content. Sesquiterpene hydrocarbons (54.1 ± 1.5%–76.1 ± 4.5%) were found to be the main fraction. The major compounds were palustrol (24.6 ± 2.6%–33.5 ± 4.4%) and ledol (18.0 ± 2.9%–29.0 ± 5.0%). Ascaridol isomers (7.0 ± 2.4%–14.0 ± 2.4% in three oils), myrcene (7.2 ± 0.3% and 10.1 ± 1.3%), lepalol (3.3 ± 0.3% and 7.9 ± 3.0%), and cyclocolorenone isomers (4.1 ± 2.5%) were determined as the third main constituents. The toxic activity of marsh rosemary inflorescence and shoot oils samples was evaluated using a brine shrimp (Artemia sp.) bioassay. LC₅₀ average values (11.23–20.50 µg/mL) obtained after 24 h of exposure revealed that the oils were notably toxic. The oil obtained from shoots gathered in September during the seed-ripening stage and containing appreciable amounts of palustrol (26.0 ± 2.5%), ledol (21.5 ± 4.0%), and ascaridol (7.0 ± 2.4%) showed the highest toxic activity. Radical scavenging activity of Rh. tomentosum EOs depended on the plant vegetation stage. The highest activities were obtained for EOs isolated from young shoots collected in June (48.19 ± 0.1 and 19.89 ± 0.3 mmol/L TROLOX (6-hydroxy-2,5,7,8-tetra-methylchromane-2-carboxylic acid) equivalent obtained by, respectively, ABTS^•+ (2,2′-amino-bis(ethylbenzothiazoline-6-sulfonic acid) diammonium salt) and DPPH^•(2,2-diphenyl-1-picrylhydrazyl) assays). Agar disc diffusion assay against pathogenic yeast Candida parapsilosis revealed the potential antifungal activity of EOs. An alternative investigation of antifungal activity employed mediated amperometry at yeast Saccharomyces cerevisiae-modified electrodes. The subjection of yeast cells to vapors of EO resulted in a three to four-fold increase of electrode responses due to the disruption of yeast cell membranes.