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

Abstract

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.

Review: Marsh rosemary (Rhododendron tomentosum Harmaja (ex Ledum palustre Linn) growing in Lithuania) essential oils and their properties

“…Rhododendron tomentosum H. (ex Ledum palustre L.) plant material, the essential oils of which are already investigated [13,[31][32][33][34], was collected mostly in the Eastern part of the country (Rokiškis, Utena, Vilnius and Šalčininkai districts), and in one study [16] a sampling site was not indicated (Fig. 1).…”

“…Anticancer in vitro, using mouse leukemia cells L1210 [5] Anticancer in vitro, using human lympho-blastoid Raji cells [6] Analgesic, using model of acetic acid-induced writhing response in mice [7] Antibacterial in vitro, by broth dilution method, against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae [8] Antidiabetic in vitro, using C2C12 murine skeletal myoblasts and the 3T3-L1 murine preadipocyte cell lines [9] Antidiabetic in vitro, using Caco-2/15 cells; western blot analysis in vivo. Rats, oral glucose tolerance test [10] Antifungal, against Aspergillus niger, Candida albicans, Microsporum canis, Trichophyton rubrum and Trichophyton mentagrophytes [11] Antifungal in vitro, by microbroth dilution method, against Cryptococcus neoformans, Saccharomyces cerevisiae, Aspergillus niger and Candida albicans [12] Antifungal, using agar disc diffusion assay, against Candida parapsilosis [13] Antifungal, using mediated amperometry at Saccharomyces cerevisiae-modified electrodes [13] Antifungicidal, by agar-diffusion method, against Trichoderma harzianum and Penicillium cyclopium [14,15] Anti-inflammatory, by model of lambda-carrageenan-induced paw edema in mice [7] Anti-inflammatory in vivo, using tests of carrageenan-induced edema in rats [8] Anti-inflammatory, using tests of subcutaneous carrageenan injection-induced hind paw oedema in rats [16] Anti-inflammatory in vitro, by prostaglandin biosynthesis assay; PAF-induced exocytosis [17] Antimicrobial Variuos parts of the plant -all aerial parts or separated shoots, inflorescences and seeds -have been chosen for the oils preparation. Plant material was dried at room temperature (20-25°C); different plant organs were separated before drying.…”

“…Hydrodistillation (HD) was performed in a circulatory Clevenger-type apparatus, according to the procedure described in the European Pharmacopoeia. In order to obtain sufficient amounts of wild rosemary EOs, HD time of 2 h was chosen [13,[31][32][33][34], and the procedure time of 4 h up to exhaustion of all oils present in the matrix [16]. Previously, it was proved that the extension of distillation time from 2 to 4 h has increased Rh.…”

“…The content of EO from Lithuania marsh rosemary aerial parts varied from 0.45 to 2.01% (v/w, on a dry weight basis). The lowest contents 0.45 and 0.59% of the oils were obtained for aged (mature) shoots gathered in Rokiškis District [31], and from young shoots collected in April in Samanis for-est marshes (Utena District), respectively [13,32]. The largest quantity (2.0%) of the EO was obtained after 4 h of a hydro-distillation procedure [16].…”

“…Many research works have been devoted to investigate various bioactivities, such as antibacte-rial, anticancer, anti-inflammatory, fungicidal, antioxidant, toxic, etc. properties of marsh rosemary extracts (see Table 1 for details) [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The expectorant and antitussive effect of marsh rosemary tea depends on the presence of ledol in the essential oils [3].…”