Natural Antidiabetic Agents: Insights into Ericaceae-Derived Phenolics and Their Role in Metabolic and Oxidative Modulation in Diabetes

Diabetes mellitus (DM) is a chronic disease with a growing prevalence worldwide, leading to severe health complications. Current treatment relies on antidiabetic medications, which may have adverse effects, highlighting the need for alternative approaches. Natural compounds, such as phenolic compounds, have shown promise in glucose modulation. The Ericaceae family includes several plants with potential antidiabetic properties. This review examines the pathophysiology of diabetes, chemical composition, and specific Ericaceae species that have demonstrated antidiabetic effects. Studies indicate that Vaccinium species and other Ericaceae plants can lower blood glucose levels and improve insulin sensitivity through mechanisms such as enzyme inhibition. These findings suggest that Ericaceae plants may serve as complementary strategies for diabetes management.

Recent Advances in Grayanane Diterpenes: Isolation, Structural Diversity, and Bioactivities from Ericaceae Family (2018-2024)

Diterpenes represent one of the most diverse and structurally complex families of natural products. Among the myriad of diterpenoids, grayanane diterpenes are particularly notable. These terpenes are characterized by their unique 5/7/6/5 tetracyclic system and are exclusive to the Ericaceae family of plants. Renowned for their complex structures and broad spectrum of bioactivities, grayanane diterpenes have become a primary focus in extensive phytochemical and pharmacological research. Recent studies, spanning from 2018 to January 2024, have reported a series of new grayanane diterpenes with unprecedented carbon skeletons. These compounds exhibit various biological properties, including analgesic, antifeedant, anti-inflammatory, and inhibition of protein tyrosine phosphatase 1B (PTP1B). This paper delves into the discovery of 193 newly identified grayanoids, representing 15 distinct carbon skeletons within the Ericaceae family. The study of grayanane diterpenes is not only a deep dive into the complexities of natural product chemistry but also an investigation into potential therapeutic applications. Their unique structures and diverse biological actions make them promising candidates for drug discovery and medicinal applications. The review encompasses their occurrence, distribution, structural features, and biological activities, providing invaluable insights for future pharmacological explorations and research.

The efficacy and toxicity of grayanoids as analgesics: A systematic review

ETHNOPHARMACOLOGICAL RELEVANCE

Grayanoids are natural diterpenoids that are mostly found in the Ericaceae family, such as Rhododendron molle (Blume) G. Don (Relevant herb: nao yang hua), Rhododendron micranthum Turcz (also known as: zhao shan bai), which have traditionally been used to treat abdominal pain, cephalgia, and rheumatoid arthritis.

AIMS OF THE REVIEW

The review investigated advancements in notable anti-nociception, toxicity, and probable mechanisms of grayanoids. Meanwhile some binding sites of these compounds on voltage-gated sodium channels (VSGCs) were also analyzed and evaluated.

MATERIALS AND METHODS

The substantial grayanoids literature published before 2022, in SCI Finder, PubMed, Science Direct, Springer, Scopus, Wiley Online Library, J-Stage, and other literature databases had been exhaustively consulted and thoroughly screened.

RESULTS

More than 50 compounds in grayanoids exhibited exceptionally significant anti-nociception (intraperitoneal injection, less than 1 mg/kg), and the alteration of several substituents that were closely associated to the change in activity were investigated. Multiple possible mechanisms of analgesic action and toxicity had been proposed, with VSGCs playing a key part in both. As a result, the binding locations of these compounds on VGSCs (mostly grayanotoxin I and III) had been summarized.

CONCLUSIONS

The considerable anti-nociception, toxicity, and probable mechanisms of grayanoids, as well as the investigation of the binding sites on VSGCs, were discussed in this review. Furthermore, the homology of toxicity and anti-nociception of these substances was considered, as well as the possibility of grayanoids being developed as analgesics.

Evaluation of Rhodojaponin III from Rhododendron molle G. Don on oral antinociceptive activity, mechanism of action, and subacute toxicity in rodents

ETHNOPHARMACOLOGICAL RELEVANCE

In Chinese traditional medicine, Rhododendron molle G. Don is a recognized herb to ease pain. Rhodojaponin III (RJ-III) has been identified as the main pharmacological activity and toxic component of the herb; however, oral antinociception and mechanism of RJ-III have not yet been investigated.

AIM OF THE STUDY

The significance of this study is to evaluate the effects of RJ-III on nociceptive and neuropathic pain, and to preliminarily explore the underlying mechanisms and subacute toxicity.

MATERIALS AND METHODS

The antinociception of RJ-III was evaluated by hot plate, tail-immersion, acetic acid writhing, formalin test and chronic constriction injury (CCI) model in rodents. An experimental validation was conducted using whole-cell patch clamp technique based on the most likely mechanisms of action after screening and prediction by molecular docking study. In addition, the oral subacute toxicity of RJ-III was assessed.

RESULTS

Behavioral experiments showed that RJ-III (0.20 mg/kg) reduced the latency of the nociceptive response in the hot plate and tail-immersion tests. Acetic acid and formalin-induced pain were significantly inhibited by RJ-III (0.10 and 0.05 mg/kg, respectively). Furthermore, 0.30 mg/kg of RJ-III improved hyperalgesia in the CCI-induced rats. Based on molecular docking results, electrophysiological experiments were used to demonstrate mild inhibition of voltage-gated sodium channel-related subtypes. Additionally, oral subacute toxicity that may cause leukopenia and abnormal liver function requires further attention in subsequent studies.

CONCLUSION

RJ-III mildly blocks voltage-gated sodium channel to inhibit nociceptive pain and peripheral neuralgia, but 0.375 mg/kg and above may cause side effect after long-term oral administration.

Structurally diverse diterpenoids from Pieris japonica as potent analgesics

Sixteen diterpenoids (1-16) including 10 new ones, pierisjaponins A-J (1-10), were isolated and identified from Pieris japonica, and their structures were classified into eight diverse carbon skeletons. Pierisjaponins A (1) and B (2) represent the first 1,5-seco-grayanane diterpenoid glucosides and only showed 17 carbon resonances instead of 26 carbons in the ¹³C NMR spectra, their structures were finally defined by single-crystal X-ray diffraction, and the unusual NMR phenomena were explained. Pierisjaponin E (5) is the first mollane diterpene glucoside. This is the first time to report ent-labdane (3, 4, and 11) and ent-rosane (15) type diterpenoids from the Ericaceae plants, which provided the precursors of the Ericaceae diterpenoids and enlarged the chemical diversity of Ericaceae diterpenoids. All the 16 isolates showed potent analgesic activities, and this is the first time to describe the analgesic activities of 1,5-seco-grayanane, ent-labdane, mollane, and ent-rosane type diterpenoids. A preliminary structure-activity relationship is discussed, which provided new clues to design novel analgesics based on the Ericaceae diterpenoids.

Micranthanosides I and II, two novel 1,10-secograyanane diterpenoids and their antinociceptive analogues from the leaves and twigs of Rhododendron micranthum

Micranthanosides I and II (1-2), two diterpenoid glucosides featuring a new 1,10-secograyanane skeleton, thirteen new diterpenoid glycosides (3-15), and 21 known analogues were obtained from the ethanol extract of the leaves and twigs of Rhododendron micranthum. Micranthanoside XII (12) represent the first example of 3,5-epoxy-4,5-seco-ent-kaurane diterpenoid. The structures of these compounds were determined by spectroscopic data analysis and quantum chemical calculations. To clarify the chemical basis and provide reference for rational use of this medicinal plant, the antinociceptive and the anti-inflammatory activities of the compounds were tested. In the acetic acid-induced writhing test, compounds 17 and 19 showed significant antinociceptive activity at a dose of 3 mg kg-1 and compounds 2, 6 and 32 showed significant antinociceptive activity at a dose of 10 mg kg-1. Toxic reactions such as nausea and convulsion were observed when 17, 19, 29, and 31 at a dose of 10 mg kg-1 or 30 and 33 at a dose of 1 mg kg-1 were administered. The anti-inflammatory activities of the isolated compounds were evaluated by measuring the inhibitory effects of LPS-induced NO production in BV2 cells. At 10 μM, micranthanoside IX (9) and rhodomicranoside F (26) showed moderate anti-inflammatory activities with inhibition rates of 56.31% and 72.43%, respectively.

Diterpenoids of terrestrial origin

This review covers the isolation and chemistry of diterpenoids from terrestrial sources from 2017.

Antinociceptive Diterpenoids from the Leaves and Twigs of Rhododendron decorum

Three new leucothane-type (1-3), two new micrathane-type (4, 5), eight new grayanane-type diterpenoids (6-13), and four known compounds were obtained from the ethanol extract of the leaves and twigs of Rhododendron decorum. The structures were determined based on NMR spectra, quantum chemical calculations, and X-ray crystallography. The antinociceptive activities of compounds 1, 3, 4, 6, 8, 10-13, and 15-17 were evaluated via the acetic acid-induced writhing test. Compounds 1, 8, 11-13, and 15 exhibited significant antinociceptive activities. In particular, 12 and 15 were found to be effective at doses of 0.8 and 0.08 mg/kg, respectively.