Chemical constituents of plants from the genus Rhododendron

Rhododendron luteum Sweet Flower Supercritical CO2 Extracts: Terpenes Composition, Pro-Inflammatory Enzymes Inhibition and Antioxidant Activity

Terpenes are plant secondary metabolites known for their anti-inflammatory and antioxidant activities. According to ethnobotanical knowledge, Rhododendron luteum Sweet was used in traditional medicine against inflammation. The present study was conducted to determine the triterpene profile and antioxidant and anti-inflammatory activity of supercritical CO2 (SC-CO2) extracts of Rhododendron luteum Sweet flower (RLF). An LC-APCI-MS/MS analysis showed the presence of eight pentacyclic triterpenes and one phytosterol in the extracts obtained with pure CO2 as well as CO2 with the addition of aqueous ethanol as a co-solvent. Among the compounds detected, oleanolic/ursolic acid, β-sitosterol and 3β-taraxerol were the most abundant. The extract obtained with pure SC-CO2 was additionally subjected to HS-SPME-GC-FID-MS, which revealed more than 100 volatiles, mainly eugenol, β-phenylethanol, dodecane, β-caryophyllene, estragole and (Z)- and (E)-cinnamyl alcohol, followed by δ-cadinene. The extracts demonstrated significant hyaluronidase inhibition and exhibited varying modes of lipoxygenase and xanthine oxidase inhibitory activities. The studies of RLF have shown that their SC-CO2 extracts can be a rich source of triterpenes with anti-inflammatory potential.

Chemistry, biosynthesis, and theranostics of antioxidant flavonoids and polyphenolics of genus Rhododendron: an overview

The genus Rhododendron is an ancient and most widely distributed genus of the family Ericaceae consisting of evergreen plant species that have been utilized as traditional medicine since a very long time for the treatment of various ailments including pain, asthma, inflammation, cold, and acute bronchitis. The chemistry of polyphenolics isolated from a number of species of the genus Rhododendron has been investigated. During the currently designed study, an in-depth study on the phytochemistry, natural distribution, biosynthesis, and pharmacological properties including their potential capability as free radical scavengers has been conducted. This work provides structural characteristics of phenolic compounds isolated from the species of Rhododendron with remarkable antioxidant potential. In addition, biosynthesis and theranostic study have also been encompassed with the aims to furnish a wide platform of valuable information for designing of new drug entities. The detailed information including names, structural features, origins, classification, biosynthetic pathways, theranostics, and pharmacological effects of about 171 phenolics and flavonoids isolated from the 36 plant species of the genus Rhododendron with the antioxidant potential has been covered in this manuscript. This study demonstrated that species of Rhododendron genus have excellent antioxidant activities and great potential as a source for natural health products. This comprehensive review might serve as a foundation for more investigation into the Rhododendron genus.

From petals to healing: consolidated network pharmacology and molecular docking investigations of the mechanisms underpinning Rhododendron arboreum flower's anti-NAFLD effects

Rhododendron arboreum: Sm., also known as Burans is traditionally used as an anti-inflammatory, anti-diabetic, hepatoprotective, adaptogenic, and anti-oxidative agent. It has been used since ancient times in Indian traditional medicine for various liver disorders. However, the exact mechanism behind its activity against NAFLD is not known. The aim of the present study is to investigate the molecular mechanism of Rhododendron arboreum flower (RAF) in the treatment of NAFLD using network pharmacology and molecular docking methods. Bioactives were also predicted for their drug-likeness score, probable side effects and ADMET profile. Protein-protein interaction (PPI) data was obtained using the STRING platform. For the visualisation of GO analysis, a bioinformatics server was employed. Through molecular docking, the binding affinity between potential targets and active compounds were assessed. A total of five active compounds of RAF and 30 target proteins were selected. The targets with higher degrees were identified through the PPI network. GO analysis indicated that the NAFLD treatment with RAF primarily entails a response to the fatty acid biosynthetic process, lipid metabolic process, regulation of cell death, regulation of stress response, and cellular response to a chemical stimulus. Molecular docking and molecular dynamic simulation exhibited that rutin has best binding affinity among active compounds and selected targets as indicated by the binding energy, RMSD, and RMSF data. The findings comprehensively elucidated toxicity data, potential targets of bioactives and molecular mechanisms of RAF against NAFLD, providing a promising novel strategy for future research on NAFLD treatment.

How generalist insect herbivores respond to alien plants? The case of Aphis fabae-Myzus persicae-Rhododendron ponticum

BACKGROUND

The enemy release hypothesis (ERH) predicts that alien plant species are unsuitable hosts for native phytophagous insects. However, the biotic resistance hypothesis (BRH) predicts that generalist herbivores may prefer an alien plant over their common host plant. In this study, we have tested these two hypotheses by comparing the potential colonization of the invasive Pontic rhododendron (Rhododendron ponticum L.) versus the common rearing host plants by two generalist aphid species (Aphis fabae and Myzus persicae). We assessed (i) the probing behavior using the electrical penetration graph (EPG) technique and (ii) survival and fecundity in Petri dishes.

RESULTS

The results showed the inability of A. fabae and Myzus persicae to immediately colonize R. ponticum. Despite their ability to feed on this invasive plant, the two aphid species hardly survived and poorly reproduced.

CONCLUSION

Our results are consistent with the ERH, since R. ponticum appeared as an unsuitable host for native phytophagous insects. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

An updated review of the genus Rhododendron since 2010: Traditional uses, phytochemistry, and pharmacology

Rhododendron, the largest genus of Ericaceae, consists of approximately 1000 species that are widely distributed in Europe, Asia, and North America but mainly exist in Asia. Rhododendron plants have not only good ornamental and economic value but also significant medicinal potential. In China, many Rhododendron plants are used as traditional Chinese medicine or ethnic medicine for the treatment of respiratory diseases, pain, bleeding and inflammation. Rhododendron is known for its abundant metabolites, especially diterpenoids. In the past 13 years, a total of 610 chemical constituents were reported from Rhododendron plants, including 222 diterpenoids, 122 triterpenoids, 103 meroterpenoids, 71 flavonoids and 92 other constituents (lignans, phenylpropanoids, phenolic acids, monoterpenoids, sesquiterpenoids, coumarins, steroids, fatty acids). Moreover, the bioactivities of various extracts and isolates, both in vitro and in vivo, were also investigated. Our review summarized the research progress of Rhododendron regarding traditional uses, phytochemistry and pharmacology in the past 13 years (2010 to December 2022), which will provide new insight for prompting further research on Rhododendron application and drug development.

Grayanotoxin I variation across tissues and species of Rhododendron suggest pollinator-herbivore defence trade-offs

Grayanotoxin I (GTX I) is a major toxin in leaves of Rhododendron species, where it provides a defence against insect and vertebrate herbivores. Surprisingly, it is also present in R. ponticum nectar, and this can hold important implications for plant-pollinator mutualisms. However, knowledge of GTX I distributions across the genus Rhododendron and in different plant materials is currently limited, despite the important ecological function of this toxin. Here we characterise GTX I expression in the leaves, petals, and nectar of seven Rhododendron species. Our results indicated interspecific variation in GTX I concentration across all species. GTX I concentrations were consistently higher in leaves compared to petals and nectar. Our findings provide preliminary evidence for phenotypic correlation between GTX I concentrations in defensive tissues (leaves and petals) and floral rewards (nectar), suggesting that Rhododendron species may commonly experience functional trade-offs between herbivore defence and pollinator attraction.

Traditional uses, phytochemistry, pharmacology, toxicology, and quality control of Rhododendron dauricum L. leaves: A comprehensive review

ETHNOPHARMACOLOGICAL RELEVANCE

Rhododendron dauricum L. is a traditional herb mainly distributed in the northeast China, Mongolia, Korea Peninsula, and Russia Far East. The dried leaves of Rhododendron dauricum L. (LRD), generally known "Man Shan Hong" have been traditionally applied as folk medicines to treat fever, copious phlegm, asthma, acute and chronic bronchitis, sore throat, dysentery, diabetes mellitus, cancer, and hypertension. To date, no comprehensive review on R. dauricum leaves has been published.

AIM OF THE STUDY

Recent progresses in traditional use, phytochemistry, pharmacology, toxicology, and quality control of R. dauricum leaves are systematically presented and critically evaluated in order to provide scientifical basis for its reasonable utilization and further study.

MATERIALS AND METHODS

All information about R. dauricum leaves were retrieved from internet scientific databases including Sci-Finder, Web of Science, PubMed, CNKI, Google Scholar, Elsevier, Wiley, ACS publications, SpringerLink, and the Chinese Pharmacopoeia between 1970 and 2022. Plant names were validated by "The Plant List" (http://www.theplantlist.org/).

RESULTS

So far, 114 structurally diverse compounds have been isolated and identified from LRD, mainly including flavonoids, diterpenoids, triterpenoids, meroterpenoids, phenols, and 54 volatile components were identified from the essential oils of LRD. Among these, flavonoids are considered as characteristic components and major bioactive phytochemicals. The crude extracts and compounds from LRD have been reported to possess broad pharmacological effects including antitussive and expectorant, anti-inflammatory, anti-HIV, antibacterial, and cytotoxic effects, etc. CONCLUSIONS: As a traditional herb medicine, LRD have been used popularly. On the one hand, traditional uses of LRD provide valuable directions for current research; on the other hand, modern phytochemical and pharmacological studies verify the traditional uses to make its reasonable utilization. However, several defects such as active components determination, in vivo and clinical pharmacological evaluation, toxicology assessment, and quality control of LRD need further study.

Worldwide distribution and clinical characteristics of mad honey poisoning cases

OBJECTIVES

Mad honey poisoning is a common public health problem that can be seen in many parts of the world. In this study, the symptoms and clinical findings of mad honey poisoning cases and their distribution worldwide were investigated based on current data.

METHODS

PubMed, Scopus, Web of Science and Google Scholar databases were searched. The demographic characteristics of the cases, clinical findings, amount of consumed honey, duration of hospitalization, and data of the region where mad honey was produced were recorded.

RESULTS

900 cases were identified. The majority of poisoning cases (91.44%) were reported from mad honey produced in Turkey, Nepal (4.67%) came second and Korea (1.56) third. The majority of cases in Turkey were due to honey produced in the Black Sea Region. It was also determined that the mad honey was produced in the west Black Sea Region in most of the cases (35.22%), followed by the east Black Sea Region with a rate of 33.22%. In poisonous cases, it was determined that the mad honey was mostly produced in Rize, followed by Trabzon and Kastamonu, respectively. The most common signs of mad honey poisoning were bradycardia (88.48%) and hypotension (76.04%).

CONCLUSION

The majority of cases have been reported from Turkey. When examining where the mad honey was produced in Turkey, it was seen that the western Black Sea Region came first, and the eastern Black Sea Region came second. Rize came first among the provinces, followed by Trabzon and Kastamonu. There is a parallelism between the distribution of mad honey poisoning cases and the distribution areas of Rhododendron species. However, although Rhododendron species show a widespread distribution throughout the world, why the majority of the cases were reported from Turkey draws attention as an issue that needs to be investigated.

Risks for human health related to the presence of grayanotoxins in certain honey

The European Commission asked EFSA for a scientific opinion on the risks for human health of the presence of grayanotoxins (GTXs) in 'certain honey' from Ericaceae plants. The risk assessment included all structurally related grayananes occurring with GTXs in 'certain' honey. Oral exposure is associated with acute intoxication in humans. Acute symptoms affect the muscles, nervous and cardiovascular systems. These may lead to complete atrioventricular block, convulsions, mental confusion, agitation, syncope and respiratory depression. For acute effects, the CONTAM Panel derived a reference point (RP) of 15.3 μg/kg body weight for the sum of GTX I and III based on a BMDL10 for reduced heart rate in rats. A similar relative potency was considered for GTX I. Without chronic toxicity studies, an RP for long-term effects could not be derived. There is evidence for genotoxicity in mice exposed to GTX III or honey containing GTX I and III, showing increased levels of chromosomal damage. The mechanism of genotoxicity is unknown. Without representative occurrence data for the sum of GTX I and III and consumption data from Ericaceae honey, acute dietary exposure was estimated based on selected concentrations for GTX I and III reflecting concentrations measured in 'certain' honeys. Applying a margin of exposure (MOE) approach, the estimated MOEs raised health concerns for acute toxicity. The Panel calculated the highest concentrations for GTX I and III below which no acute effects would be expected following 'certain honey' consumption. The Panel is 75% or more certain that the calculated highest concentration of 0.05 mg for the sum of GTX I and III per kg honey is protective for all age groups regarding acute intoxications. This value does not consider other grayananes in 'certain honey' and does not cover the identified genotoxicity.

Rhodomollosides A and B, glycosides of methyl everninate from the aerial parts of Rhododendron molle

Two new glycosides of methyl everninate, rhodomollosides A (1) and B (2), were isolated from the aerial parts of a medicinal plant Rhododendron molle. The structures of 1 and 2 were elucidated on the basis of detailed spectroscopic analyses as well as HPLC analyses for thiazolidine derivatives of their sugar moieties. The sugar moiety of rhodomolloside A (1) was elucidated to be a rare monosaccharide, D-allose, while rhodomolloside B (2) was assigned as a D-glucoside of methyl everninate. Furthermore, they were evaluated for their cytotoxicity against RAW264.7 cells, and for their inhibitory effects with a lipopolysaccharide (LPS)-stimulated murine macrophages RAW 264.7 cells model.

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.

Two new diterpenoids from the stems of Rhododendron dauricum as GABAA receptor agonists

Two new diterpenoids, dauricumins A (1) and B (2), together with two known aromatic meroterpenoids (3 and 4), were isolated from the petroleum ether soluble fraction of the stems from Rhododendron dauricum through an HPLC-MS-SPE-NMR combination strategy. The absolute configurations of 1 and 2 were elucidated by ECD calculations and [Rh₂ (OCOCF₃)₄]-induced CD spectrum analysis. In a membrane potential FLIPR assay, confluentin (4) showed an agonistic effect on GABA_A receptor (EC₅₀ = 20 µM).

Minor terpenoids from the stems and twigs of Rhododendron ovatum

Four minor undescribed terpenoids, including a monoterpenoid (1) and three triterpenoids (3, 6 and 7), together with 26 known terpenoids were isolated from the stems and twigs of Rhododendron Ovatum. Their structures were identified by extensive spectroscopic analyses and electronic circular dichroism (ECD) techniques. Compound 10 showed excellent cytotoxicity against human colon cancer cell (HCT-116) with IC₅₀ value of 2.56 μM. Compounds 9 and 19 exhibited partly inhibitory effects on nitric oxide production stimulated by lipopolysaccharide-induced neuroinflammation in microglia cells at 10 μM with inhibition ratios of 39.70% and 28.08%, respectively.

Selection and Evaluation of Candidate Reference Genes for Quantitative Real-Time PCR in Aboveground Tissues and Drought Conditions in Rhododendron Delavayi

There has been no systematic identification and screening of candidate reference genes for normalization of quantitative real-time PCR (qRT-PCR) results in Rhododendron delavayi to date. Therefore, the present study used GAPDH, Act, EF1, Tub-, Tub-5, UEC1, TATA, TATA-2, UEP, TIP41, and Ubiquitin to predict their stabilities on different aboveground tissues (matured leaves (ML), stem tips (STM), and flower buds (FB)) at different developmental stages (young and adult plants) using five statistical algorithms: Delta Ct method, BestKeeper, geNorm, Normfinder, and RefFinder. The findings were confirmed using ML obtained from plants that had been stressed by drought. By using RefFinder with ML samples collected under drought conditions, it was determined that the top five most stable reference genes were GAPDH > UEC1 > Actin > Tubulin- > Tubulin—5, whereas the least stable reference gene was Ubiquitin. In addition, under control conditions, UEC1, UEC2, Actin, and GAPDH were selected as the highest stable potential reference genes at the juvenile stage of R. delavayi with ML and STM. When ML and STM were combined with drought-stressed samples, TIP41, GAPDH, or their combination proved to be the most effective qRT-PCR primers. The findings will aid in the improvement of the precision and reliability of qRT-PCR data and laying the groundwork for future gene functional studies in R. delavayi.

Rhododendron arboreum: A Critical Review on Phytochemicals, Health Benefits and Applications in the Food Processing Industries

Abstract:

Rhododendron is a resourceful, evergreen shrub or a small tree with an ornate display of scarlet red or pale pink flowers that belongs to the family Ericaceae. Rhododendron plants are traditionally used to treat numerous human ailments like blood dysentery, headache, asthma, cough, stomachache, fever, inflammation and fungal infections. Rhododendron also has economic, medicinal, and pharmacological importance. Rhododendron has been regarded as a rich source of secondary metabolites. Apart from aesthetic and sacred values, from past times, Rhododendron juice was prepared from the flowers to curb allergies, treat diabetes and deal with inflammations. Recent studies have shown several promising activities particularly relaxant, digestive enzyme, antioxidant, antimicrobial, antispasmodic, anticancer and antagonistic effects. With the rapidly growing popularity of Rhododendron arboreum, it is important to have a comprehensive reference for its nutritional benefits with the growing search for natural and healthy foods. This work aimed to review the recent advances in research carried out to date for the purposive evaluation of the nutritional quality and potential health benefits of Rhododendron arboreum for its utilization in food processing industries for composing novel value- added products, to achieve high consumer acceptability and health benefits.

Natural plant toxins in honey: An ignored threat to human health

Consumers often believe that "natural food" is harmless, however naturally occurring toxins in food represent a health risk to humans. Honey as a natural, nutritious sweetener, is one of the most commonly consumed foods throughout the world. However, food safety concerns for honey arise when honeybees collect nectar from poisonous plants such as Rhododendron sp., Coriaria arborea, and Tripterygium wilfordii Hook F. Such honey contains natural plant toxins. Humans may develop intoxication symptoms after consuming toxic honey; in some cases, it can be fatal. As a result, toxic honey poses an often-ignored threat to public health. Typical plant toxins such as grayanotoxins, triptolides, tutin and pyrrolizidine alkaloids, have been identified in toxic honey. Although different toxic honeys elicit similar symptoms, such as vomiting, nausea, and dizziness, the mechanism of toxicity may be different. Thus, it is necessary to determine the exact toxicity mechanism of different toxins to further develop effective antidotes and cures. Another important challenge is preventing toxic honey from entering the food chain. Liquid chromatography-mass spectrometry has a wide range of applications in the detection of different toxins due to its accuracy and simplicity. More methods, however, are urgently needed to detect multiple plant-derived toxins in honey and its derivatives. Developing uniform international standards for toxin detection during quarantine using advanced techniques is critical for preventing human consumption of toxic honey.

LC-ESI-MS/MS Characterization of Concentrated Polyphenolic Fractions from Rhododendron luteum and Their Anti-Inflammatory and Antioxidant Activities

The high biological potential of polyphenols encourages the search for new natural sources of and biomedical applications for these compounds. Rhododendron luteum Sweet was previously reported to contain pharmaceutically active polyphenols. The present research investigates the polyphenolic fractions in R. luteum leaves, including a determination of the free and bound phenolic acid and flavonoid contents and their anti-inflammatory and antioxidant activities. LC-ESI-MS/MS (liquid chromatography/electrospray ionization triple quadrupole mass spectrometry) analysis revealed a great abundance of free (e.g., 5-O-caffeoylquinic acid, ferulic acid, protocatechuic acid, catechin, and dihydromyricetin) and bound (e.g., caffeic acid, p-coumaric, protocatechuic acid, myricetin, quercetin) phenolics. The R. luteum samples exhibited high anti-inflammatory potential in lipoxygenase (IC50: 0.33 ± 0.01-2.96 ± 0.06 mg dry extract (DE)/mL) and hyaluronidase (IC50: 78.76 ± 2.09 - 429.07 ± 31.08 µg DE/mL) inhibition capacity assays. Some samples also had the ability to inhibit cyclooxygenase 1 (IC50: 311.8 ± 10.95 µg DE/mL) and cyclooxygenase 2 (IC50: 53.40 ± 5.07; 608.09 ± 14.78 µg DE/mL). All fractions showed excellent antioxidant activity in the Oxygen Radical Absorbance Capacity (ORAC) assay (5.76-221.81 g Trolox/g DE), ABTS•+ radical scavenging ability (0.62 ± 0.03 - 5.09 ± 0.23 g Trolox/g DE), and moderate ion (Fe2+) chelating power. This paper expands our knowledge of the phytochemistry and pharmacological activity of R. luteum polyphenols. It reveals, for the first time, the presence of dihydromyricetin, afzelin, and laricitrin in the plant material. It indicates biologically active polyphenolic fractions that should be further investigated or which could be efficiently used in pharmaceutical, cosmetic, or nutraceutical applications.

Ethnobotanical study of traditionally used medicinal plants of Pauri district of Uttarakhand, India

ETHNOPHARMACOLOGICAL RELEVANCE

The indigenous knowledge of medicinal plants is important part of primary health care system in almost every society, especially the far-flung areas. These areas, one of the last storehouses of traditional knowledge are under the constant threat of losing this valuable information as it moves from one generation to another through word of mouth. Modernization, migration, education, and changing socio-economic status of people also affect the perpetuality of traditional knowledge. Therefore, time-to-time updation of information regarding the ethnomedicinal plants must be carried out so that any addition to the traditional knowledge is recorded and further phytochemical and pharmacological studies may be conducted for developing new drugs.

AIM OF THE STUDY

The study aimed at documenting the traditional knowledge and practices about the medicinal plants used by the inhabitants of Pauri district of Uttarakhand. Besides, the study strives to identify plants for future phytochemical and pharmacological studies.

MATERIAL AND METHODS

The information was collected through semi-structured questionnaire from 98 informants distributed in 15 villages of Pauri. The data was analyzed for use-reports (UR), frequency of citation (FC) and informant consensus factor (F_IC).

RESULTS

In the present study, total 236 species belonging to 80 families and 188 genera were found to treat 82 ailments. Asteraceae (23 species), Rosaceae (16 species) and Lamiaceae (13 species) were the most represented families. Correlation and regression analysis between the local flora and present study reveals that Poaceae, Fabaceae, and Asteraceae were the main outlier species having more representatives in local flora than medicinally important species. Herbs (57.2%) were the most frequently used life forms, and leaves (24.5%) the most commonly utilized plant parts. All the plants were collected from the natural resources and none of them was under cultivation. Nearly 76% of the total drugs were administered orally. The informants divulged 1556 use-reports. The most utilized species based on frequency of citation were Urtica dioica L. (44), Bergenia ciliata Haworth (38), Viola canescens Wall. (38), Rhododendron arboretum Smith (32), and Ocimum tenuiflorum L. (30). All the disorders were grouped into 13 ailment categories based on ICPC-2 classification. The main ailment categories as per Informant Consensus Factor (F_IC) were digestive (F_IC, 0.83), urological (F_IC, 0.83) and cardiovascular (F_IC, 0.81) disorders. A comparative analysis between the present and other local and regional studies show that as many as 13 species were new record for the state of Uttarakhand.

CONCLUSION

The inhabitants of Pauri have good knowledge of medicinal plants. Although the therapeutic value of most of the preferred medicinal plants has already been validated, some medicinal plants lack proper scientific validation. We recommend further phytochemical investigations and pharmacological validations of Begonia picta Smith, Citrus pseudolimon Tanka, Cotoneaster rotundifolia Wall., Heracleum canescens Lindl., Parochetus communis Buch-Ham., Pittosporum napaulense DC., and Plantago erosa Wall.

Sagan Dalya Tea, a New "Old" Probable Adaptogenic Drug: Metabolic Characterization and Bioactivity Potentials of Rhododendron adamsii Leaves

Adams' rhododendron (Rhododendron adamsii Rehder) or Sagan Dalya tea is a famous Siberian evergreen medical plant of the Ericaceae family used in traditional medicines of Buryats, Yakuts, and Mongols as a tonic, stimulant, and adaptogenic drug. The high popularity of R. adamsii coupled with poor scientific knowledge prompted the addressing of gaps related to metabolic and biomedical data of Sagan Dalya tea. The application of solid-phase extraction and liquid chromatography-mass spectrometric techniques for the metabolomic study of R. adamsii leaf extracts resulted in the identification of more than 170 compounds, including carbohydrates, organic acids, simple phenol glycosides, triterpene glycosides, flavonoids, prenylated phenols, benzoic acid derivatives, hydroxycinnamates, dihydrochalcones, catechins, and procyanidins, most of which were identified for the first time in the plant. Extended surveys of the seasonal content of all detected compounds prove that specific metabolite variations reflect the bioactivity of R. adamsii extracts. Regarding in vitro methods, the expressed antioxidant potential of R. adamsii extracts was investigated via radical-scavenging, nitric oxide scavenging, and ferrous (II) ion chelating assays. The animal-based swimming to exhaustion test demonstrates the stimulating influence of R. adamsii extract on physical performance and endurance, concluding that the drug could act as an adaptogen. Thus, Sagan Dalya tea (R. adamsii) has confirmed its "old" application as a tonic remedy and requires further precise study as a novel adaptogenic plant.

The Rhododendron Plant Genome Database (RPGD): a comprehensive online omics database for Rhododendron

Background

The genus Rhododendron L. has been widely cultivated for hundreds of years around the world. Members of this genus are known for great ornamental and medicinal value. Owing to advances in sequencing technology, genomes and transcriptomes of members of the Rhododendron genus have been sequenced and published by various laboratories. With increasing amounts of omics data available, a centralized platform is necessary for effective storage, analysis, and integration of these large-scale datasets to ensure consistency, independence, and maintainability.

Results

Here, we report our development of the Rhododendron Plant Genome Database (RPGD; http://bioinfor.kib.ac.cn/RPGD/), which represents the first comprehensive database of Rhododendron genomics information. It includes large amounts of omics data, including genome sequence assemblies for R. delavayi, R. williamsianum, and R. simsii, gene expression profiles derived from public RNA-Seq data, functional annotations, gene families, transcription factor identification, gene homology, simple sequence repeats, and chloroplast genome. Additionally, many useful tools, including BLAST, JBrowse, Orthologous Groups, Genome Synteny Browser, Flanking Sequence Finder, Expression Heatmap, and Batch Download were integrated into the platform.

Conclusions

RPGD is designed to be a comprehensive and helpful platform for all Rhododendron researchers. Believe that RPGD will be an indispensable hub for Rhododendron studies.

Multiple Biological Activities of Rhododendron przewalskii Maxim. Extracts and UPLC-ESI-Q-TOF/MS Characterization of Their Phytochemical Composition

Backgroud:Rhododendron przewalskii Maxim. is an evergreen shrub that is used as a traditional medicine in China. However, the modern pharmacology and the chemical components of this plant has not been studied. In this paper, we aimed to investigate the antifungal, anti-inflammatory and antioxidant activities and underlying mechanism of its aqueous and ethanol extracts, and analyze their chemical composition and active compounds of R. przewalskii.

Methods: The antifungal activity was determined in vitro, and anti-inflammatory and antioxidant activities and underlying mechanism of its aqueous and ethanol extracts were evaluated in vitro and in RAW 264.7 cells. The chemical composition were analyzed using UPLC-ESI-Q-TOF/MS, and the contents of six compounds were determined via HPLC.

Results: Both extracts of R. przewalskii showed promising anti-inflammatory activity in vitro; decreased the production of four inflammatory cytokines, namely, nitric oxide, IL-1β, IL-6 and TNF-ɑ, in RAW 264.7 cells induced by lipopolysaccharide; and exhibited weak cytotoxicity. The extracts significantly scavenged DPPH radicals, superoxide radicals and hydroxyl radicals to exert antioxidant effects in vitro. The two extracts also exhibited cellular antioxidant activity by increasing superoxide dismutase and CAT activities and decreasing malondialdehyde content in RAW 264.7 cells induced by LPS. However, the antifungal activity of the two extracts was weak. Nine flavonoids were identified by UPLC-ESI-Q-TOF/MS. Of these, six compounds were analyzed quantitatively, including avicularin, quercetin, azaleatin, astragalin and kaempferol, and five compounds (myricetin 3-O-galactoside, paeoniflorin, astragalin, azaleatin and kaempferol) were found in this species for the first time. These compounds demonstrated antioxidant activities that were similar to those of the R. przewalskii extracts and were thought to be the active compounds in the extracts.

Conclusion:R. przewalskii extracts presented promising anti-inflammatory and antioxidant activities. The extracts contained amounts of valuable flavonoids (8.98 mg/g fresh material) that were likely the active compounds in the extract contributing to the potential antioxidant activity. These results highlight the potential of R. przewalskii as a source of natural antioxidant and anti-inflammatory agents for the pharmaceutical industry.

A new pentacyclic triterpenoid from the leaves of Rhododendron dauricum L. with inhibition of NO production in LPS-induced RAW 264.7 cells

A new pentacyclic triterpenoid, 3-oxo-urs-11,13(18)-dien-28-oic acid (1), along with twelve known triterpenoids, α-amyrin (2), 19α-hydroxy-α-amyrin (3), triptohypol E (4), uvaol (5), 2α,3α-dihydroxyurs-11-en-13β,28-olide (6), 3β-hydroxyurs-11-en-13β,28-olide (7), ursolic acid (8), asiatic acid (9), oleanolic acid (10), aegiceradienol (11), obtusalin (12) and betulinic acid (13) were isolated from the leaves of Rhododendron dauricum L. Their structures were established from spectroscopic data and comparison with reported values. Among them, compounds 3, 4, 6, 7 and 11 were isolated from the Ericaceae family for the first time. Compounds 2, 5, 9, 12 and 13 were obtained from R. dauricum for the first time. Additionally, compounds 6, 10 and 11 significantly inhibited the levels of NO in LPS-stimulated RAW 264.7 cells at 3 μM.

De novo transcriptome sequencing of Rhododendron molle and identification of genes involved in the biosynthesis of secondary metabolites

BACKGROUND

Rhododendron molle (Ericaceae) is a traditional Chinese medicinal plant, its flower and root have been widely used to treat rheumatism and relieve pain for thousands of years in China. Chemical studies have revealed that R. molle contains abundant secondary metabolites such as terpenoinds, flavonoids and lignans, some of which have exhibited various bioactivities including antioxidant, hypotension and analgesic activity. In spite of immense pharmaceutical importance, the mechanism underlying the biosynthesis of secondary metabolites remains unknown and the genomic information is unavailable.

RESULTS

To gain molecular insight into this plant, especially on the information of pharmaceutically important secondary metabolites including grayanane diterpenoids, we conducted deep transcriptome sequencing for R. molle flower and root using the Illumina Hiseq platform. In total, 100,603 unigenes were generated through de novo assembly with mean length of 778 bp, 57.1% of these unigenes were annotated in public databases and 17,906 of those unigenes showed significant match in the KEGG database. Unigenes involved in the biosynthesis of secondary metabolites were annotated, including the TPSs and CYPs that were potentially responsible for the biosynthesis of grayanoids. Moreover, 3376 transcription factors and 10,828 simple sequence repeats (SSRs) were also identified. Additionally, we further performed differential gene expression (DEG) analysis of the flower and root transcriptome libraries and identified numerous genes that were specifically expressed or up-regulated in flower.

CONCLUSIONS

To the best of our knowledge, this is the first time to generate and thoroughly analyze the transcriptome data of both R. molle flower and root. This study provided an important genetic resource which will shed light on elucidating various secondary metabolite biosynthetic pathways in R. molle, especially for those with medicinal value and allow for drug development in this plant.

Influence of Accelerated Solvent Extraction Conditions on the LC-ESI-MS/MS Polyphenolic Profile, Triterpenoid Content, and Antioxidant and Anti-lipoxygenase Activity of Rhododendron luteum Sweet Leaves

Evaluation of native plant resources and their efficient use is one of the current trends in phytochemistry. The main aim of the present study was to investigate the biological activities of different Rhododendron luteum Sweet leaf extracts obtained with the use of accelerated solvent extraction using different solvents and extraction temperatures. All extracts were subjected to bioactivity assays, which revealed considerable anti-lipoxygenase (23.07-90.13% lipoxygenase inhibition) and antiradical potential. All samples exhibited high 2,2-diphenyl-1-picrylhydrazyl (DPPH^•) (234.18-621.90 mg Trolox equivalents (TE)/g) and 2,2'-azino-bis-3(ethylbenzthiazoline-6-sulphonic acid) (ABTS^•+) (88.79-349.41 mg TE/g) scavenging activity, high antioxidant potential in the Oxygen Radical Absorbance Capacity (ORAC) assay (495.77-1011.59 mg TE/g), and moderate ion chelating (Fe2+) capacity. The chemical profile of each sample was determined using liquid chromatography/electrospray ionization triple quadrupole mass spectrometry (LC-ESI-MS/MS) and spectrophotometric procedures. Twenty-three compounds representing seven polyphenol subclasses were detected and quantified, including some phenolic acids and flavonoids that had not been previously reported for this plant material. It was shown that 5-O-caffeoylquinic acid, protocatechuic acid, catechin, quercetin and its glycosides (hyperoside, isoquercetin, quercitrin), and pentacyclic triterpenes were the dominant secondary metabolites in R. luteum leaves. The antioxidant activity was found to be strongly related to different polyphenol groups and total triterpene content, while the anti-lipoxygenase potential was highly dependent on catechin.

Genetic Diversity and Population Structure of Rhododendron rex Subsp. rex Inferred from Microsatellite Markers and Chloroplast DNA Sequences

Genetic diversity is vital to the sustainable utilization and conservation of plant species. Rhododendron rex subsp. rex Lévl. is an endangered species endemic to the southwest of China. Although the natural populations of this species are facing continuous decline due to the high frequency of anthropogenic disturbance, the genetic information of R. rex subsp. rex is not yet elucidated. In the present study, 10 pairs of microsatellite markers (nSSRs) and three pairs of chloroplast DNA (cpDNAs) were used in the elucidation of the genetic diversity, population structure, and demographic history of 11 R. rex subsp. rex populations. A total of 236 alleles and 12 haplotypes were found. A moderate genetic diversity within populations (HE = 0.540 for nSSRs, Hd = 0.788 for cpDNA markers), high historical and low contemporary gene flows, and moderate genetic differentiation (nSSR: FST = 0.165***; cpDNA: FST = 0.841***) were detected among the R. rex subsp. rex populations. Genetic and geographic distances showed significant correlation (p < 0.05) determined by the Mantel test. The species exhibited a conspicuous phylogeographical structure among the populations. Using the Bayesian skyline plot and species distribution models, we found that R. rex subsp. rex underwent a population demography contraction approximately 50,000-100,000 years ago. However, the species did not experience a recent population expansion event. Thus, habitat loss and destruction, which result in a population decline and species inbreeding depression, should be considered in the management and conservation of R. rex subsp. rex.

Two novel flavonoids from the leaves of Rhododendron dauricum L. with their inhibition of TNF-α production in LPS-induced RAW 264.7 cells

Two new flavonoids, (2S)-6,8-dimethyl-5,7,3',4'-tetrahydroxyflavanone 4'-O-β-D-glucopyranoside (1) and quercetin 3-O-β-D-(6''-p-methoxybenzoyl)-galactopyranoside (2), together with ten known flavonoids (3-12) were isolated from the leaves of Rhododendron dauricum L. The structures of the flavonoids were characterized from spectroscopic data (1D and 2D NMR and HR-ESI-MS). The isolated flavonoids were evaluated for their inhibitory effects on the production of tumour necrosis factor (TNF)-α in LPS-stimulated RAW 264.7 cells. Compound 11 exhibited inhibitory activity against TNF-α production with an IC₅₀ value of 46.2 ± 1.2 µM.

Synthesis, characterization and cellular mineral absorption of nanoemulsions of Rhododendron arboreum flower extracts stabilized with gum arabic

To assess the cellular mineral uptake and oxidative stability of flower extract, a nanoscale gum arabic stabilized Rhododendron arboreum flower extract emulsion was formulated. Four different concentrations of flower extract (1-5%) were used for the optimization of the nanoemulsion. A significant (P < 0.05) difference was observed in average droplet size (43.51-55.87 nm) of the nanoemulsion. FTIR spectrum confirmed mainly C=C, aliphatic C-H, aliphatic and aromatic galacto-proteins, and polymeric-OH groups present in nanoemulsion. Smooth type of nanoemulsion was confirmed by inverted light microscopy. Ionic strength was evaluated and significant (P < 0.05) increase in particles size was attributed, whereas significant (P < 0.05) decrease in zeta potential was observed by increased NaCl concentration. Iron and calcium showed a non-significant difference in terms of mineral bioavailability. Calcium revealed significantly higher cellular uptake (52.11%) in comparison with iron (50.25%) and zinc (45.32%) during transwell assay. Higher cellular iron uptake unveiled a satisfactory amount of ferritin content.

Chemical composition of essential oils from four Rhododendron species and their repellent activity against three stored-product insects

The objective of this work was to analyze four essential oils (EOs) from Rhododendron species in China and evaluate their repellent activity against Tribolium castaneum, Lasioderma serricorne, and Liposcelis bostrychophila adults. These four EOs from Rhododendron species, including R. capitatum, R. przewalskii, R. mucronulatum, and R. micranthum, were obtained by hydrodistillation. Major components of four EOs were identified as sesquiterpenoids by GC-MS. The relatively high components included cedrene (22.20%), borneol (36.64%), 4-(2,3,4,6-tetramethylphenyl)-3-buten-2-one (27.74%), and germacrene D (27.60%). Repellent activity of EOs from Rhododendron species was investigated against T. castaneum, L. serricorne, and L. bostrychophila adults for the first time. In this study, EOs had demonstrated their repellent activities against three stored-product insects in 2- and 4-h exposure. The above results can not only provide comprehensive utilization of plant resources of Rhododendron genus but also establish a very good perspective of novel application to control stored-product insects.

Grayanane Diterpenoids from the Leaves of Rhododendron auriculatum and Their Analgesic Activities

Twenty-four grayanane diterpenoids (1-24) including 12 new ones (1-12) were isolated from Rhododendron auriculatum. The structures of the new grayanane diterpenoids (1-12) were defined via extensive spectroscopic data analysis. The absolute configurations of compounds 2-4, 10-12, 14, and 16 were established by single-crystal X-ray diffraction analysis, and electronic circular dichroism data were used to define the absolute configurations of auriculatols D (8) and E (9). Auriculatol A (1) is the first example of a 5,20-epoxygrayanane diterpenoid bearing a 7-oxabicyclo[4.2.1]nonane motif and a trans/cis/cis/cis-fused 5/5/7/6/5 pentacyclic ring system. Auriculatol B (2) is the first example of a 3α,5α-dihydroxy-1-βH-grayanane diterpenoid. 19-Hydroxy-3-epi-auriculatol B (6) and auriculatol C (7) represent the first examples of 19-hydroxygrayanane and grayan-5(6)-ene diterpenoids, respectively. Diterpenoids 1-24 showed analgesic activities in the writhing test induced by HOAc, and 2, 6, 10, 13, 19, and 24 at a dose of 5.0 mg/kg exhibited significant analgesic effects (inhibition rates >50%). Grayanane diterpenoids grayanotoxins I (19) and IV (24) at doses of 0.2 and 0.04 mg/kg showed more potent analgesic activities than morphine.

Determination of histological, immunohistochemical and biochemical effects of acute and chronic grayanotoxin III administration in different doses in rats

Grayanotoxin (GTX)-III is a Na-channel neurotoxin. Grayanotoxins can be found in the nectar, pollen, and other plant parts of the Rhododendron genus plants from the Ericaceae family. It is widely believed that honey produced from these plants, which are concentrated in the Black Sea region, is traditionally characterized as enhancing sexual performance. It is thought that the effective factor is dose for this compound, which has both beneficial and toxic effects reported. Therefore, it is aimed to evaluate the histological, immunohistochemical, and biochemical effects of acute and chronic impact of GTX-III in different doses on testes tissue in this study. For this purpose, 100 Sprague-Dawley male rats were divided into 5 separate groups for acute and chronic research. While dose groups were (control, 0.1, 0.2, 0.4, ve 0.8 μg/kg/bw) for experimental groups, a single dose (i.p.) was administered for acute impact whereas the same doses were administered daily for 3 weeks to assess chronic effect. At the end of the experiment, Johnsen testicular biopsy scoring was performed on testicular tissue samples, seminiferous tubule diameters were measured, and apoptotic cells were evaluated by TUNEL method. Testosterone, LH, and FSH levels were measured by ELISA method in serum and tissue specimens. It was found that Johnsen score of acute doses was significantly lower than the control group, and the diameter of the seminiferous tubules decreased significantly in acute and chronic dose-administered groups compared to the control. Hemorrhage, epithelial shedding, irregularity in seminiferous epithelium, and vacuolization were observed in acute and chronic dose-administered groups, and increase in apoptotic cells was determined. Hormone levels varied depending on the dose. In conclusion, it was found that dose-dependent acute and chronic effects of GTX-III are different, and this factor should be taken into account in studies to be carried out due to the adverse effects of high doses.

Grayanotoxin I Intoxication in Pet Pigs

Contaminated honey is a common cause of grayanotoxin intoxication in humans. Intoxication of animals, especially cattle, is usually due to ingestion of plants of the Ericaceae family, such as Rhododendron. Here, we report the ingestion of Pieris japonica as the cause of grayanotoxin I intoxication in 2 miniature pigs that were kept as pets. The pigs showed sudden onset of pale oral mucosa, tachycardia, tachypnea, hypersalivation, tremor, and ataxia that progressed to lateral recumbency. The pathological examination of one pig revealed no specific indications for intoxication except for the finding of plant material of Pieris japonica in the intestine. Grayanotoxin I was identified in the ingested plant, gastric content, blood, liver, bile, kidney, urine, lung, and skeletal muscle via HPLC-MS/MS. Grayanotoxin I should be considered as a differential etiological diagnosis in pigs with unspecific signs and discovery of ingested plant material as the only indication in the pathologic examination.

The draft genome assembly of Rhododendron delavayi Franch. var. delavayi

Rhododendron delavayi Franch. is globally famous as an ornamental plant. Its distribution in southwest China covers several different habitats and environments. However, not much research had been conducted on Rhododendron spp. at the molecular level, which hinders understanding of its evolution, speciation, and synthesis of secondary metabolites, as well as its wide adaptability to different environments. Here, we report the genome assembly and gene annotation of R. delavayi var. delavayi (the second genome sequenced in the Ericaceae), which will facilitate the study of the family. The genome assembly will have further applications in genome-assisted cultivar breeding. The final size of the assembled R. delavayi var. delavayi genome (695.09 Mb) was close to the 697.94 Mb, estimated by k-mer analysis. A total of 336.83 gigabases (Gb) of raw Illumina HiSeq 2000 reads were generated from 9 libraries (with insert sizes ranging from 170 bp to 40 kb), achieving a raw sequencing depth of ×482.6. After quality filtering, 246.06 Gb of clean reads were obtained, giving ×352.55 coverage depth. Assembly using Platanus gave a total scaffold length of 695.09 Mb, with a contig N50 of 61.8 kb and a scaffold N50 of 637.83 kb. Gene prediction resulted in the annotation of 32 938 protein-coding genes. The genome completeness was evaluated by CEGMA and BUSCO and reached 95.97% and 92.8%, respectively. The gene annotation completeness was also evaluated by CEGMA and BUSCO and reached 97.01% and 87.4%, respectively. Genome annotation revealed that 51.77% of the R. delavayi genome is composed of transposable elements, and 37.48% of long terminal repeat elements (LTRs). The de novo assembled genome of R. delavayi var. delavayi (hereinafter referred to as R. delavayi) is the second genomic resource of the family Ericaceae and will provide a valuable resource for research on future comparative genomic studies in Rhododendron species. The availability of the R. delavayi genome sequence will hopefully provide a tool for scientists to tackle open questions regarding molecular mechanisms underlying environmental interactions in the genus Rhododendron, more accurately understand the evolutionary processes and systematics of the genus, facilitate the identification of genes encoding pharmaceutically important compounds, and accelerate molecular breeding to release elite varieties.

Leaf trichomes and foliar chemistry mediate defence against glasshouse thrips; Heliothrips haemorrhoidalis (Bouché) in Rhododendron simsii

Herbivore defence mechanisms are a costly diversion of resources away from growth and reproduction. Thus time-limited and tissue specific expression in critical plant parts is more efficient as defined by optimal defence theory. Surprisingly little is known about Rhododendron herbivore defence but it may be mediated by combined chemical and physical mechanisms. Rhododendron simsii Planch. survives cyclic infestations of a leaf-feeding thrips, Heliothrips haemorrhoidalis (Bouché), which severely damage mature leaves but avoid terminal young leaves suggesting specific, localised defence expression. We examined correlations between the distribution of thrips and feeding damage with density of trichomes and the concentration of the diterpenoid, grayanotoxin I, a compound implicated in but not previously reported to mediate invertebrate defence in Rhododendron. Our data show that as leaves matured the number of thrips and area of feeding damage increased as trichome density and grayanotoxin I concentration decreased, this inverse correlation suggesting trichomes and grayanotoxin I mediate defence in younger leaf tissue. Grayanotoxin I was tested against H. haemorrhoidalis and was toxic to immature life stages and repellent to the adult thrips, reducing numbers of first instars emerging on leaves when applied at ecologically relevant concentrations. This work demonstrates that the pattern of defensive traits in foliage of a species of Rhododendron is key to its ability to tolerate cyclic infestations of a generalist herbivore, effectively conserving vital tissues required for growth and reproduction.

Effects of Mad Honey on Some Biochemical Parameters in Rats

The aims of this study were to determine grayanotoxin (GTX-III) toxin level in mad honey using liquid chromatography-tandem mass spectrometry and examine the dynamic changes of certain biochemical parameters in blood serum of rats that consumed mad honey. For the experimental animal study, 20 Sprague-Dawley female rats were divided into 5 groups of 4 rats each, with one group being the control group (Group 1) and the others being the experimental groups (Groups 2-5). Groups 2, 3, 4, and 5 were, respectively, given mad honey extract at doses of 0.3, 0.6, 1.2, and 2.4 mg/g body weight/day via oral gavage for 8 days. According to results, the quantity of GTX-III found in the honey sample as 39.949 ± 0.020 μg GTX-III/g honey, and the biochemical analysis of the tested parameters (aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, alkaline phosphatase, creatine kinase, and creatine kinase muscle and brain) showed a significant elevation with increasing concentration of honey. In conclusion, the use of increasing concentrations of Rhododendron honey was seen as a source of enzymatic symptoms.

Acute effects of grayanotoxin in rhododendron honey on kidney functions in rats

The aim of the study is to evaluate the acute biochemical and histological changes in rat kidneys after treatment with grayanotoxin (GTX) of rhododendron honey (RH). A total of 60 Sprague-Dawley female rats were divided into five groups of 12 rats each, one being a control group (group 1) and group 2 was treated with 0.015 mg/kg/bw of GTX standard preparation via intraperitoneal injection. Groups 3, 4, and 5 were given RH at doses of 0.1, 0.5, and 2.5 g/kg/bw, respectively, via oral gavage. Compared to the control group, significant increases were observed in glucose, blood urea nitrogen (BUN), and creatinine levels of the GTX-injected groups after 1 h. However, in low dose RH group, such an increase was not observed and had a normal appearance histologically. Therefore, low dose (1 g/kg/bw) of RH produces no acute adverse effects on renal functions of rats.

A Novel Class of Plant Type III Polyketide Synthase Involved in Orsellinic Acid Biosynthesis from Rhododendron dauricum

Rhododendron dauricum L. produces daurichromenic acid, the anti-HIV meroterpenoid consisting of sesquiterpene and orsellinic acid (OSA) moieties. To characterize the enzyme responsible for OSA biosynthesis, a cDNA encoding a novel polyketide synthase (PKS), orcinol synthase (ORS), was cloned from young leaves of R. dauricum. The primary structure of ORS shared relatively low identities to those of PKSs from other plants, and the active site of ORS had a unique amino acid composition. The bacterially expressed, recombinant ORS accepted acetyl-CoA as the preferable starter substrate, and produced orcinol as the major reaction product, along with four minor products including OSA. The ORS identified in this study is the first plant PKS that generates acetate-derived aromatic tetraketides, such as orcinol and OSA. Interestingly, OSA production was clearly enhanced in the presence of Cannabis sativa olivetolic acid cyclase, suggesting that the ORS is involved in OSA biosynthesis together with an unidentified cyclase in R. dauricum.

Antinociceptive Grayanoids from the Roots of Rhododendron molle

Nine new grayanoids (1-9), together with 11 known compounds, were isolated from the roots of Rhododendron molle. The structures of the new compounds (1-9) were determined on the basis of spectroscopic analysis, including HRESIMS, and 1D and 2D NMR data. Compounds 4, 6, 12, and 14-20 showed significant antinociceptive activities in an acetic acid-induced writhing test. In particular, 14 and 15 were found to be more potent than morphine for both acute and inflammatory pain models and 100-fold more potent than gabapentin in a diabetic neuropathic pain model.

Antioxidative phytochemicals from Rhododendron oldhamii Maxim. leaf extracts reduce serum uric acid levels in potassium oxonate-induced hyperuricemic mice

Background

Some of the genus Rhododendron was used in traditional medicine for arthritis, acute and chronic bronchitis, asthma, pain, inflammation, rheumatism, hypertension and metabolic diseases and many species of the genus Rhododendron contain a large number of phenolic compounds and antioxidant properties that could be developed into pharmaceutical products.

Methods

In this study, the antioxidative phytochemicals of Rhododendron oldhamii Maxim. leaves were detected by an online HPLC–DPPH method. In addition, the anti-hyperuricemic effect of the active phytochemicals from R. oldhamii leaf extracts was investigated using potassium oxonate (PO)-induced acute hyperuricemia.

Results

Six phytochemicals, including (2R, 3R)-epicatechin (1), (2R, 3R)-taxifolin (2), (2R, 3R)-astilbin (3), hyposide (4), guaijaverin (5), and quercitrin (6), were isolated using the developed screening method. Of these, compounds 3, 4, 5, and 6 were found to be major bioactive phytochemicals, and their contents were determined to be 130.8 ± 10.9, 105.5 ± 8.5, 104.1 ± 4.7, and 108.6 ± 4.0 mg per gram of EtOAc fraction, respectively. In addition, the four major bioactive phytochemicals at the same dosage (100 mmol/kg) were administered to the abdominal cavity of potassium oxonate (PO)-induced hyperuricemic mice, and the serum uric acid level was measured after 3 h of administration. H&E staining showed that PO-induced kidney injury caused renal tubular epithelium nuclear condensation in the cortex areas or the appearance of numerous hyaline casts in the medulla areas; treatment with 100 mmol/kg of EtOAc fraction, (2R, 3R)-astilbin, hyposide, guaijaverin, and quercitrin significantly reduced kidney injury. In addition, the serum uric acid level was significantly suppressed by 54.1, 35.1, 56.3, 56.3, and 53.2 %, respectively, by the administrations of 100 mmol/kg EtOAc fraction and the derived major phytochemicals, (2R, 3R)-astilbin, hyposide, guaijaverin, and quercitrin, compared to the PO group. The administration of 10 mg/kg benzbromarone, a well-known uricosuric agent, significantly reduced the serum uric acid level by 45.5 % compared to the PO group.

Conclusion

The in vivo decrease in uric acid was consistent with free radical scavenging activity, indicating that the major phytochemicals of R. oldhamii leave extracts and the derived phytochemicals possess potent hypouricemic effects, and they could be potential candidates for new hypouricemic agents.

Mad honey intoxication: A systematic review on the 1199 cases

Mad honey, produced by honeybees from the nectars of Rhododendron genus (R. ponticum and R. luteum) flowers, is widely used in indigenous medicine, especially in the treatment of hypertension and sexual dysfunction. However, the consumption of this honey can result in intoxication soon after. The diagnosis of honey poisoning and a full understanding of its treatment is important for both effective and immediate treatment, and also for the prevention of unnecessary costs. Upon the evaluation of approximately 34 years of case reports between 1981 and 2014, it was found that the cases of poisoning were more frequently reported in males (75.17%) and between the ages 41 to 65. The most common complaints related to honey poisoning were dizziness, nausea, presyncope and the ECG findings were: sinus bradycardia (79.58%), complete atrioventricular block (45.83%), atrioventricular block (30.91%), ST-segment elevation (22.63%), and nodal rhythm (11.27%), As a result of the evaluation of 1199 cases, it was found that no deaths were reported. The patients were most frequently treated with 0.5 mg atropine (37.79%), 1 mg atropine (49.73%), salin (iv fluid) (65.35%), and generally the patients were discharged within 24 h after recovery.

Assessment of cytotoxicity exerted by leaf extracts from plants of the genus Rhododendron towards epidermal keratinocytes and intestine epithelial cells

Background

Rhododendron leaf extracts were previously found to exert antimicrobial activities against a range of Gram-positive bacteria. In this study, we investigated which of the extracts with these antimicrobial properties would be best suited for further exploitation. Specifically, the project aims to identify biologically active compounds that affect bacterial but not mammalian cells when applied in medical treatments such as lotions for ectopic application onto skin, or as orally administered drugs.

Methods

Different concentrations of DMSO-dissolved remnants of crude methanol Rhododendron leaf extracts were incubated for 24 h with cultured epidermal keratinocytes (human HaCaT cell line) and epithelial cells of the intestinal mucosa (rat IEC6 cell line) and tested for their cytotoxic potential. In particular, the cytotoxic potencies of the compounds contained in antimicrobial Rhododendron leaf extracts were assessed by quantifying their effects on (i) plasma membrane integrity, (ii) cell viability and proliferation rates, (iii) cellular metabolism, (iv) cytoskeletal architecture, and (v) determining initiation of cell death pathways by morphological and biochemical means.

Results

Extracts of almost all Rhododendron species, when applied at 500 μg/mL, were potent in negatively affecting both keratinocytes and intestine epithelial cells, except material from R. hippophaeoides var. hippophaeoides. Extracts of R. minus and R. racemosum were non-toxic towards both mammalian cell types when used at 50 μg/mL, which was equivalent to their minimal inhibitory concentration against bacteria. At this concentration, leaf extracts from three other highly potent antimicrobial Rhododendron species proved non-cytotoxic against one or the other mammalian cell type: Extracts of R. ferrugineum were non-toxic towards IEC6 cells, and extracts of R. rubiginosum as well as R. concinnum did not affect HaCaT cells. In general, keratinocytes proved more resistant than intestine epithelial cells against the treatment with compounds contained in Rhododendron leaf extracts.

Conclusions

We conclude that leaf extracts from highly potent antimicrobial R. minus and R. racemosum are safe to use at 50 μg/mL in 24-h incubations with HaCaT keratinocytes and IEC6 intestine epithelial cells in monolayer cultures. Extracts from R. rubiginosum as well as R. concinnum or R. ferrugineum are applicable to either keratinocytes or intestinal epithelial cells, respectively. Beyond the scope of the current study, further experiments are required to identify the specific compounds contained in those Rhododendron leaf extracts that exert antimicrobial activity while being non-cytotoxic when applied onto human skin or gastrointestinal tract mucosa. Thus, this study supports the notion that detailed phytochemical profiling and compound identification is needed for characterization of the leaf extracts from specific Rhododendron species in order to exploit their components as supplementary agents in antimicrobial phyto-medical treatments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-015-0860-8) contains supplementary material, which is available to authorized users.