Identification of eugenol as the major determinant of GABAA-receptor activation by aqueous Syzygium aromaticum L. (clove buds) extract

Clove Essential Oil: Chemical Profile, Biological Activities, Encapsulation Strategies, and Food Applications

Plants have proven to be important sources for discovering new compounds that are useful in the treatment of various diseases due to their phytoconstituents. Clove (Syzygium aromaticum L.), an aromatic plant widely cultivated around the world, has been traditionally used for food preservation and medicinal purposes. In particular, clove essential oil (CEO) has attracted attention for containing various bioactive compounds, such as phenolics (eugenol and eugenol acetate), terpenes (β-caryophyllene and α-humulene), and hydrocarbons. These constituents have found applications in cosmetics, food, and medicine industries due to their bioactivity. Pharmacologically, CEO has been tested against a variety of parasites and pathogenic microorganisms, demonstrating antibacterial and antifungal properties. Additionally, many studies have also demonstrated the analgesic, antioxidant, anticancer, antiseptic, and anti-inflammatory effects of this essential oil. However, CEO could degrade for different reasons, impacting its quality and bioactivity. To address this challenge, encapsulation is viewed as a promising strategy that could prolong the shelf life of CEO, improving its physicochemical stability and application in various areas. This review examines the phytochemical composition and biological activities of CEO and its constituents, as well as extraction methods to obtain it. Moreover, encapsulation strategies for CEO and numerous applications in different food fields are also highlighted.

The effect of eugenol anesthesia on the electric organ discharge of the weakly electric fish Apteronotus leptorhynchus

Eugenol, the major active ingredient of clove oil, is widely used for anesthesia in fish. Yet virtually nothing is known about its effects on CNS functions, and thus about potential interference with neurophysiological experimentation. To address this issue, we employed a neuro-behavioral assay recently developed for testing of water-soluble anesthetic agents. The unique feature of this in-vivo tool is that it utilizes a readily accessible behavior, the electric organ discharge (EOD), as a proxy of the neural activity generated by a brainstem oscillator, the pacemaker nucleus, in the weakly electric fish Apteronotus leptorhynchus. A deep state of anesthesia, as assessed by the cessation of locomotor activity, was induced within less than 3 min at concentrations of 30-60 µL/L eugenol. This change in locomotor activity was paralleled by a dose-dependent, pronounced decrease in EOD frequency. After removal of the fish from the anesthetic solution, the frequency returned to baseline levels within 30 min. Eugenol also led to a significant increase in the rate of 'chirps,' specific amplitude/frequency modulations of the EOD, during the 30 min after the fish's exposure to the anesthetic. At 60 µL/L, eugenol induced a collapse of the EOD amplitude after about 3.5 min in half of the fish tested. The results of our study indicate strong effects of eugenol on CNS functions. We hypothesize that these effects are mediated by the established pharmacological activity of eugenol to block the generation of action potentials and to reduce the excitability of neurons; as well as to potentiate GABAA-receptor responses.

Clove volatile oil-loaded nanoemulsion reduces the anxious-like behavior in adult zebrafish

BACKGROUND

Clove volatile oil (CVO) and its major compound, eugenol (EUG), have anxiolytic effects, but their clinical use has been impaired due to their low bioavailability. Thus, their encapsulation in nanosystems can be an alternative to overcome these limitations.

OBJECTIVES

This work aims to prepare, characterize and study the anxiolytic potential of CVO loaded-nanoemulsions (CVO-NE) against anxious-like behavior in adult zebrafish (Danio rerio).

METHODS

The CVO-NE was prepared using Agaricus blazei Murill polysaccharides as stabilizing agent. The drug-excipient interactions were performed, as well as colloidal characterization of CVO-NE and empty nanoemulsion (B-NE). The acute toxicity and potential anxiolytic activity of CVO, EUG, CVO-NE and B-NE against adult zebrafish models were determined.

RESULTS

CVO, EUG, CVO-NE and B-NE presented low acute toxicity, reduced the locomotor activity and anxious-like behavior of the zebrafish at 4 - 20 mg kg-1. CVO-NE reduced the anxious-like behavior of adult zebrafish without affecting their locomotor activity. In addition, it was demonstrated that anxiolytic activity of CVO, EUG and CVO-NE is linked to the involvement of GABAergic pathway.

CONCLUSION

Therefore, this study demonstrates the anxiolytic effect of CVO, in addition to providing a new nanoformulation for its administration.

Eugenol promotes appetite through TRP channels mediated-CaMKK2/AMPK signaling pathway

Eugenol is a major component of clove oil. A recent study found that inhalation of eugenol promoted the appetite of mice. However, whether oral ingestion of eugenol promoted appetite is unclear and its mechanism await study. Here, mice were divided into four treatments (n = 20) and fed a basal diet supplemented with 0%, 0.005%, 0.01% and 0.02% eugenol for 4 weeks. In addition, mice (n = 7) were injected intraperitoneally with 3 mg/kg body weight eugenol. Our data showed that feeding mice with 0.01% and 0.02% eugenol promoted their appetite. In addition, the short-term intraperitoneal injection of eugenol enhanced the feed intake in mice within 1 h. Further studies found that dietary eugenol increased orexigenic factors expression and decreased anorexigenic factors expression in mice. We then carried out N38 cell experiments to explore the transient receptor potential (TRP) channels-dependent mechanism of eugenol in promoting appetite. We found that eugenol activated the TRP channels mediated-CaMKK2/AMPK signaling pathway in the hypothalamus and N38 cells. Besides, the inhibition of TRPV1 and AMPK eliminated the upregulation of eugenol on the agouti-related protein level in N38 cells. In conclusion, the study suggested that eugenol promotes appetite through TRPV1 mediated-CaMKK2/AMPK signaling pathway.

Elucidating Pathway and Anesthetic Mechanism of Action of Clove Oil Nanoformulations in Fish

Clove oil (CO), an essential oil of Syzygium aromaticum, has been reported as an anesthetic for many fish species. However, its insoluble properties require a suitable delivery system for its application. In the present study, nanoformulations of CO as a nanoemulsion (CO-NE), a self-microemulsifying drug-delivery system (CO-SMEDDS), and a self-nanoemulsifying drug-delivery system (CO-SNEDDS) were prepared for delivering CO. Zebrafish were used as a fish model to investigate oil pathways. The result shows fluorescence spots of fluorescence-labeled CO accumulate on the gills, skin, and brain. All CO nanoformulations significantly increased penetration flux compared to CO ethanolic solution. Investigation of the anesthetic mechanism of action using a rat brain γ-aminobutyric acid subtype A (GABA_A) receptor-binding test demonstrates that CO and its major compound, eugenol, modulate [³H]muscimol binding. CO-NE exhibited a concentration-dependent binding activity with an EC₅₀ value of 175 µg/mL, significantly higher than CO solution in dimethyl sulfoxide. In conclusion, CO enters the fish through the skin and gills. The anesthetic mechanism of action of CO is based on modulation of [³H] muscimol binding to GABA_A receptors. Among three nanoformulations tested, CO-NE is the most effective at increasing permeability and enhancing the receptor-binding activity of the oil.

Herbal Tea for the Management of Pharyngitis: Inhibition of Streptococcus pyogenes Growth and Biofilm Formation by Herbal Infusions

Herbal teas are becoming popular as functional beverages due to their various health promotional properties. This study aimed at assessing 13 hot water infusions (HWIs) from different herbs against streptococcal pharyngitis (strep throat). Licorice root exhibited the lowest minimum inhibitory concentrations (MIC) of 1.56 mg/mL, followed by barberry root, thyme, and oregano flowering shoots, with a MIC of 3.13 mg/mL. At their respective minimum bactericidal concentrations (MBC), licorice showed the bactericidal effect on S. pyogenes within 12 h after exposure while others need 24 h for a similar outcome. The HWIs exhibited inhibitory activity on biofilm formation, ranging from 1.56 to 6.25 mg/mL, which confirmed by ruptured cells or clusters of dead cell debris observed in scanning electron microscope (SEM). Overall, non-toxic concentrations of efficacious HWIs from licorice root, barberry root, thyme, and oregano flowering shoots may provide potential sources for developing herbal teas or biomedicine for the management of S. pyogenes infections.

Development of a MD-LC-MS/MS Method to Analyze 3 Bioactive Compounds in Huoxuezhitong Rubber Patch and Application to a Pharmacokinetic Study in Rats

Huoxuezhitong rubber patch, a well-known traditional Chinese medicine (TCM) prescription, is utilized to treat pain and inflammation. In this study, a microdialysis-ultra-high-performance liquid chromatography-tandem mass spectrometry (MD-LC-MS/MS) method was designed for the simultaneous determination of active constituents in the rubber patch, such as paeonol (Pae), eugenol (Eug), and piperine (Pip). A microdialysis probe was implanted in the subcutaneous tissue of a rat, which is intended to detect the subcutaneous concentrations of target components. Saline containing 30% ethanol acted as perfusion fluid. Analytes in the microdialysate were completely separated over an ACQITY UPLC RBEH C₁₈ column (2.1mm×100mm, 1.7μm). The mobile phase was composed of 0.01% ammonia aqueous and acetonitrile-0.01% ammonia with gradient elution. The single-run analysis time was 10.0 minutes. The linear regression displayed good linear relationships in the ranges of 0.25-100 ng/mL for paeonol and eugenol and 0.001-5 ng/mL for piperine. The interday and intraday precision of the quality control samples exhibited relative standard deviations (RSD) <13.56%. The accuracy values ranged from -14.92% to 14.00%. The present method was successfully applied in pharmacokinetics studies following dermal administration of Huoxuezhitong rubber patch in rats. Pip's T_max (488.00±150.73) min was greater than that of Pae (186.67±48.44) min and Eug (240.00±138.56) min, and the rank order of t_1/2 was Pae > Pip > Eug. The rank order of AUC_0-720 and C_max was both Eug > Pae > Pip. MRT_0-∞ of Pip was higher than that of Pae and Eug. Eugenol showed a faster elimination and a shorter half-life. Paeonol showed a stronger drug reservoir function after removing the drug source.