Essential oils in the treatment of respiratory tract diseases highlighting their role in bacterial infections and their anti-inflammatory action: a review

The volatile oil of Hyssopus cuspidatus Boriss. (HVO) ameliorates OVA-induced allergic asthma via inhibiting PI3K/Akt/JNK/P38 signaling pathway and maintaining airway barrier integrity

ETHNOPHARMACOLOGICAL RELEVANCE

Hyssopus cuspidatus Boriss., a classic Uyghur medicine, is used to treat inflammatory lung diseases such as asthma. But the therapeutic effect and mechanism of the volatile oil of Hyssopus cuspidatus Boriss.(HVO) in asthma therapy remain unclear.

AIM OF THE STUDY

We aim to characterize the constituents of HVO, investigate the therapeutic effect in OVA-induced allergic asthmatic mice and further explore the molecular mechanism.

MATERIALS AND METHODS

In this study, we applied two-dimensional gas chromatography quadrupole time-of-flight mass spectrometry (GC × GC-QTOF MS) to identify the ingredients of HVO. We established OVA-induced asthmatic model to investigate the therapeutic effect of HVO. To further explore the potential molecular pathways, we used network pharmacology approach to perform GO and KEGG pathways enrichment, and then built an ingredient-target-pathway network to identify key molecular pathways. Finally, LPS-induced RAW 264.7 macrophages and OVA-induced asthmatic model were used to validate the potential signaling pathways.

RESULTS

GC × GC-QTOF MS analysis revealed the presence of 123 compounds of HVO. The sesquiterpenes and monoterpenes are the main constituents. The in vivo study indicated that HVO suppressed OVA-induced eosinophilic infiltration in lung tissues, inhibited the elevation of IgE, IL-4, IL-5, and IL-13 levels, downregulated the expressions of phosphorylated PI3K, Akt, JNK and P38, and maintained epithelial barrier integrity via reducing the degradation of occludin, Zo-1, Zo-2, and E-cadherin. The in vitro study also revealed an inhibition of NO release and downregulation of phosphorylated PI3K, Akt, JNK and P38 levels.

CONCLUSION

HVO alleviates airway inflammation in OVA-induced asthmatic mice by inhibiting PI3K/Akt/JNK/P38 signaling pathway and maintaining airway barrier integrity via reducing the degradation of occludin, Zo-1, Zo-2, and E-cadherin.

Essential oils for clinical aromatherapy: A comprehensive review

ETHNOPHARMACOLOGICAL RELEVANCE

Aromatherapy, a holistic healing practice utilizing the aromatic essences of plant-derived essential oils, has gained significant attention for its therapeutic potential in promoting overall well-being. Use of phytoconstituent based essential oil has played a significant role in the evolving therapeutic avenue of aromatherapy as a complementary system of medicine.

AIM OF THE STUDY

This comprehensive review article aims to explore the usage of essential oils for aromatherapy, shedding light on their diverse applications, scientific evidence, and safety considerations. Furthermore, the growing interest in using essential oils as complementary therapies in conjunction with conventional medicine is explored, underscoring the significance of collaborative healthcare approaches.

MATERIALS AND METHODS

Literature search was performed from databases like PubMed, ScienceDirect, Scopus, and Bentham using keywords like Aromatherapy, Aromatic Plants, Essential oils, Phytotherapy, and complementary medicine. The keywords were used to identify literature with therapeutic and mechanistic details of herbal agents with desired action.

RESULTS

The integration of traditional knowledge with modern scientific research has led to a renewed interest in essential oils as valuable tools in contemporary healthcare. Various extraction methods used to obtain essential oils are presented, emphasizing their impact on the oil's chemical composition and therapeutic properties. Additionally, the article scrutinizes the factors influencing the quality and purity of essential oils, elucidating the significance of standardization and certification for safe usage. A comprehensive assessment of the therapeutic effects of essential oils is provided, encompassing their potential as antimicrobial, analgesic, anxiolytic, and anti-inflammatory agents, among others. Clinical trials and preclinical studies are discussed to consolidate the existing evidence on their efficacy in treating diverse health conditions, both physical and psychological. Safety considerations are of paramount importance when employing essential oils, and this review addresses potential adverse effects, contraindications, and best practices to ensure responsible usage.

CONCLUSIONS

This comprehensive review provides valuable insights into the exploration of essential oils for aromatherapy, emphasizing their potential as natural and potent remedies for a wide range of ailments. By amalgamating traditional wisdom and modern research, this article aims to encourage further investigation into the therapeutic benefits of essential oils while advocating for their responsible and evidence-based incorporation into healthcare practices.

Essential Oil from Vietnamese Peperomia leptostachya Hook. & Arn. (Piperaceae): Chemical Composition, Antioxidant, Anti-Inflammatory, Cytotoxic Activities, and In Silico Analysis

This study is the first to investigate the chemical composition and antioxidant, anti-inflammatory, and cytotoxic activities of Peperomia leptostachya leaf oil. A yellow oil was obtained through hydro-distillation, with a yield of 0.1% (w/w). The GC-MS analysis revealed 66 compounds, constituting 99.6% of the oil. Sesquiterpene hydrocarbons predominated (70.4%), followed by monoterpene hydrocarbons (13.2%), oxygenated sesquiterpenes (12.4%), non-terpenic compounds (2.0%), and oxygenated monoterpenes (1.6%). Major constituents included germacrene D (25.1%), (E)-caryophyllene (17.4%), bicyclogermacrene (6.6%), α-pinene (6.2%), and β-pinene (4.7%). The assessment of antioxidant capacity via 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging assay yielded a weak effect, with an IC50 value > 100 µg/mL. The inhibition of lipopolysaccharide-induced nitric oxide production in RAW 264.7 cells was quantified using the MTT assay, showing an IC50 value of 15.15 ± 0.68 µg/mL. Furthermore, cytotoxic effects on SK-LU-1 cell line growth were evaluated using the sulforhodamine B assay, resulting in an IC50 value of 37.45 ± 2.43 μg/mL. The anti-inflammatory activity was notable among the analyzed bioactivities of this oil. By employing a computational model, the predominant secondary metabolites in the essential oil were selected as candidates for interaction analysis with cyclooxygenase-2, an enzyme implicated in the inflammatory response. Our findings suggest that P. leptostachya leaf oil could serve as a potential source of natural compounds with prospective therapeutic effects in treating inflammatory conditions.

Is aromatic plants environmental health engineering (APEHE) a leverage point of the earth system?

It is important to note that every ecological niche in an ecosystem is significant. This study aims to assess the importance of medicinal and aromatic plants (MAPs) in the ecosystem from multiple perspectives. A primary model of Aromatic Plants Environmental Health Engineering (APEHE) has been designed and constructed. The APEHE system was used to collect aerosol compounds, and it was experimentally verified that these compounds have the potential to impact human health by binding to AKT1 as the primary target, and MMP9 and TLR4 as secondary targets. These compounds may indirectly affect human immunity by reversing drug resistance in drug-resistant bacteria in the nasal cavity. This is mainly achieved through combined mutations in sdhA, scrA, and PEP. Our findings are based on Network pharmacology and molecular binding, drug-resistance rescue experiments, as well as combined transcriptomics and metabolomics experiments. It is suggested that APEHE may have direct or indirect effects on human health. We demonstrate APEHE's numerous potential benefits, such as attenuation and elimination of airborne microorganisms in the environment, enhancing carbon and nitrogen storage in terrestrial ecosystems, promoting the formation of low-level clouds and strengthening the virtuous cycle of Earth's ecosystems. APEHE also supports the development of transdisciplinary technologies, including terpene energy production. It facilitates the creation of a sustainable circular economy and provides additional economic advantages through urban optimisation, as well as fresh insights into areas such as the habitability of other planets. APEHE has the potential to serve as a leverage point for the Earth system. We have created a new research direction.

Differences in Airway Remodeling and Emphysematous Lesions between Rats Exposed to Smoke from New-Type and Conventional Tobacco Varieties

Genes from Perilla frutescens and Ocimum basilicum were introduced into N. tabacum L. var. HHY via distant hybridization, and the new-type tobacco varieties "Zisu" and "Luole" were developed, with noticeable differences in chemical composition. Smoking is the leading cause of chronic obstructive pulmonary disease (COPD), and its pathogenesis is complex. In the present study, 48 male Sprague-Dawley (SD) rats were randomly divided into four groups, namely, the control, "HHY", "Zisu" and "Luole", and then exposed to fresh air/cigarette smoke (CS) for 30 days and 60 days. The COPD model was constructed, and their health hazards were compared and evaluated. CS from different tobacco varieties influenced rats in varying degrees at the tissue, cell and molecular levels. The rats in the "HHY" group showed obvious symptoms, such as cough and dyspnea, which were less severe in the "Zisu" and "Luole" groups. Pathological and morphological analyses, including scores, MLI, MAN, WAt/Pbm and WAm/Pbm, showed that "Zisu" and "Luole" caused less damage to the airways and lung parenchyma than "HHY". Significant increases in the numbers of total leukocytes and neutrophils in the BALF were found in "HHY" compared to those in "Zisu" and "Luole". Moreover, they caused less oxidative stress and apoptosis in lung tissues, as reflected by indicators such as ROS, MDA, T-AOC, GSH, the apoptotic index and the ratio of Bcl-2 to Bax. "Zisu" and "Luole" even altered the ratios of MMP-9/TIMP-1 and IFN-γ/IL-4 in lung tissues to a lesser degree. These differences between CS-exposed rats may be closely related to the altered expression of Nrf2, p38 MAPK and p-p38 MAPK. Changes in chemical composition via introducing genes from some medicinal plants may be an attractive strategy for tobacco harm reduction.

Antimicrobial Activity of Individual Volatile Compounds from Various Essential Oils

Interest in natural remedies has grown recently due to a variety of public health concerns such as microbial antibiotic resistance. This global health concern necessitates innovative approaches to combat bacterial infections. Building upon established therapeutic uses of essential oils, this research focused on the volatile constituents of essential oils. The volatile antimicrobial activity of these constituents was studied by employing a derivative of a modified disk diffusion assay for quantitative comparisons. This study emphasizes the significance and value of exploring natural compounds as alternatives to traditional antibiotics and provides insights into their mechanisms and applications in contending with bacterial pathogens.

Synthetic polyploidization induces enhanced phytochemical profile and biological activities in Thymus vulgaris L. essential oil

Essential oil from Thymus vulgaris L. has valuable therapeutic potential that is highly desired in pharmaceutical, food, and cosmetic industries. Considering these advantages and the rising market demand, induced polyploids were obtained using oryzalin to enhance essential oil yield. However, their therapeutic values were unexplored. So, this study aims to assess the phytochemical content, and antimicrobial, antioxidant, and anti-inflammatory activities of tetraploid and diploid thyme essential oils. Induced tetraploids had 41.11% higher essential oil yield with enhanced thymol and γ-terpinene content than diploid. Tetraploids exhibited higher antibacterial activity against all tested microorganisms. Similarly, in DPPH radical scavenging assay tetraploid essential oil was more potent with half-maximal inhibitory doses (IC50) of 180.03 µg/mL (40.05 µg TE/mg) than diploid with IC50 > 512 µg/mL (12.68 µg TE/mg). Tetraploids exhibited more effective inhibition of in vitro catalytic activity of pro-inflammatory enzyme cyclooxygenase-2 (COX-2) than diploids at 50 µg/mL concentration. Furthermore, molecular docking revealed higher binding affinity of thymol and γ-terpinene towards tested protein receptors, which explained enhanced bioactivity of tetraploid essential oil. In conclusion, these results suggest that synthetic polyploidization using oryzalin could effectively enhance the quality and quantity of secondary metabolites and can develop more efficient essential oil-based commercial products using this induced genotype.

Possible modulating functions of probiotic Lactiplantibacillus plantarum in particulate matter-associated pulmonary inflammation

Pulmonary disease represents a substantial global health burden. Increased air pollution, especially fine particulate matter (PM2.5) is the most concerned proportion of air pollutants to respiratory health. PM2.5 may carry or combine with other toxic allergens and heavy metals, resulting in serious respiratory allergies and anaphylactic reactions in the host. Available treatment options such as antihistamines, steroids, and avoiding allergens/dust/pollutants could be limited due to certain side effects and immense exposure to air pollutants, especially in most polluted countries. In this mini-review, we summarized how PM2.5 triggers respiratory hyperresponsiveness and inflammation, and the probiotic Lactiplantibacillus plantarum supplementation could minimize the risk of the same. L. plantarum may confer beneficial effects in PM2.5-associated pulmonary inflammation due to significant antioxidant potential. We discussed L. plantarum's effect on PM2.5-induced reactive oxygen species (ROS), inflammatory cytokines, lipid peroxidation, and DNA damage. Available preclinical evidence shows L. plantarum induces gut-lung axis, SCFA, GABA, and other neurotransmitter signaling via gut microbiota modulation. SCFA signals are important in maintaining lung homeostasis and regulating intracellular defense mechanisms in alveolar cells. However, significant research is needed in this direction to contemplate L. plantarum's therapeutic potential in pulmonary allergies.

Metabolite profiling of four Tunisian Eucalyptus essential oils and assessment of their insecticidal and antifungal activities

Aphids (Aphidoidea) and Fusarium spp. are widely recognized as destructive pests that cause significant damage to crops on a global scale. This study aimed to ascertain the chemical composition of essential oils (EOs) of four Tunisian Eucalyptus species and evaluate their toxicity against common aphids and phytopathogenic fungi. The EOs were obtained via hydrodistillation and subsequently analyzed using GC-MS. The chemical composition analysis revealed the presence of five distinct chemical classes in the EOs: monoterpene hydrocarbons (3.8-16.7 %), oxygenated monoterpenes (5.5-86.0 %), sesquiterpene hydrocarbons (0.2-2.2 %), oxygenated sesquiterpenes (4.2-86.7 %), and non-terpene derivatives (0.1-14.1 %).Hierarchical clustering analysis (HCA) and principal component analysis (PCA) of the Eucalyptus leaf EOs highlighted significant differences among them, leading to the generation of distinct HCA clades representing at least twelve major components. The statistical analysis clearly demonstrated a dose-response relationship, indicating the impact of the tested EOs on the growth of insects and fungal mycelium. The observed effects varied due to the variability in the chemical compositions of the EOs. Notably, among the EOs tested, Eucalyptus lesoufii Maiden exhibited particularly potent effects against the targeted insect and fungal species. This research contributes to the ongoing exploration of natural alternatives to chemical pesticides, providing further insights for potential industrial applications. It underscores the versatility of these EOs and their potential as valuable candidates in strategies for pest and disease management.

Culinary spices and herbs in managing early and long-COVID-19 complications: A comprehensive review

Human race is preparing for the upsurge and aftermath of COVID-19 pandemic complicated by novel variants, new waves, variable mortality rate, and post-COVID complications. Despite use of repurposed drugs, symptomatic treatments and licensing of multiple vaccines, the daily number of cases and rate of transmission are significant. Culinary spices and herbs have been historically used in pandemic and non-pandemic times to reduce respiratory viral burden. Specific food items and culinary spices can boost the levels of protective immunity and also offer therapeutic benefits against impervious bugs via well-known as well as less-known but scientifically testable mechanisms. Here, we analyzed the phytochemicals profile of Ayurvedic herbs and inferred from the clinical trials/observational studies to provide a focused and succinct perspective on the relevance of "food-based" traditional decoction to moderate COVID-19 disease and long-COVID via modulation of immunity and reinstatement of homeostasis. We also underscore the druggable targets in pathogenesis of COVID-19 which are relevant to the ongoing clinical trials using spices and herbs. This information will provide a strong scientific rationale for standardization of the traditional herbs-based therapies and adopting the use of herbs, spices, and their formulations for reducing SARS-CoV-2 transmission, long-COVID symptoms, and COVID-19 disease progression.

Antibacterial and anti-corona virus (229E) activity of Nigella sativa oil combined with photodynamic therapy based on methylene blue in wound infection: in vitro and in vivo study

Microbial skin infections, antibiotic resistance, and poor wound healing are major problems, and new treatments are needed. Our study targeted solving this problem with Nigella sativa (NS) oil and photodynamic therapy based on methylene blue (MB-PDT). Antibacterial activity and minimum inhibitory concentration (MIC) were determined via agar well diffusion assay and broth microdilution, respectively. Transmission electron microscopy (TEM) proved deformations in Staphylococcus aureus ATCC 6538. Gas chromatography-mass spectrometry identified useful compounds that were suggested to be responsible for the potency of the oil. NS oil was tested as an antivirus against low pathogenic coronavirus (229E). Therapies examined, MB-PDT, NS, and MB-PDT + NS oil, to accelerate wound healing. The antibacterial efficacy against S. aureus was promising, with a MIC of 12.5% and TEM showing injured cells treated with NS oil. This oil inhibited 229E virus up to 42.85% and 32.14%. All tested therapies were successful in accelerating wound healing. The most successful was combined therapy (MB-PDT + NS oil), with a faster healing time. The combined therapy (MB-PDT + NS oil) reduced bacterial counts, which may be a key factor in accelerating wound healing. Skin wound histology was investigated; blood hematology and biochemical analysis did not change significantly after the safe combination treatment. A combination treatment could facilitate healing in a simple and inexpensive way in the future. Based on the results of the in vitro and in vivo studies, it was determined that NS oil had antibacterial and anti-corona virus activity when used in conjunction with photodynamic treatment based on methylene blue to treat wound infections.

Validation of Broth Macrodilution Volatilization Method for Testing of Essential Oils in Liquid and Vapor Phase: Chemical Composition, Cytotoxicity, and Antibacterial Effect of Indian Medicinal Plants against Pneumonia-Causing Pathogens

Essential oils (EOs) have great potential in inhalation therapy for the treatment of respiratory infections. However, innovative methods for evaluation of antimicrobial activity of their vapors are still needed. The current study reports validation of the broth macrodilution volatilization method for assessment of the antibacterial properties of EOs and shows the growth-inhibitory effect of Indian medicinal plants against pneumonia-causing bacteria in liquid and vapor phase. Among all samples tested, Trachyspermum ammi EO exhibits the strongest antibacterial effect against Haemophilus influenzae, with minimum inhibitory concentrations of 128 and 256 µg/mL in the liquid and vapor phases, respectively. Furthermore, Cyperus scariosus EO is found to be nontoxic to normal lung fibroblasts assessed by modified thiazolyl blue tetrazolium bromide assay. Chemical analysis performed using gas chromatography-mass spectrometry identified α-citral, cyperotundone, and thymol as the main constituents of Cymbopogon citratus, C. scariosus, and T. ammi EOs, respectively. In addition, β-cymene is identified as the major compound of T. ammi EO vapors when analyzed using solid-phase microextraction and gas-tight syringe sampling techniques. This study demonstrates the validity of the broth macrodilution volatilization method for antimicrobial screening of volatile compounds in the vapor phase and suggests the therapeutic potential of Indian medicinal plants in inhalation therapy.

Natural Products for the Prevention and Treatment of Common Cold and Viral Respiratory Infections

The common cold is generally considered a usually harmless infectious disease of the upper respiratory pathway, with mostly mild symptoms. However, it should not be overlooked, as a severe cold can lead to serious complications, resulting in hospitalization or death in vulnerable patients. The treatment of the common cold remains purely symptomatic. Analgesics as well as oral antihistamines or decongestants may be advised to relieve fever, and local treatments can clear the airways and relieve nasal congestion, rhinorrhea, or sneezing. Certain medicinal plant specialties can be used as therapy or as complementary self-treatment. Recent scientific advances discussed in more detail in this review have demonstrated the plant's efficiency in the treatment of the common cold. This review presents an overview of plants used worldwide in the treatment of cold diseases.

Pharmacologic effects approach of essential oils and their components on respiratory diseases

ETHNOPHARMACOLOGICAL RELEVANCE

Essential oils (EOs) are concentrated hydrophobic liquids with volatility and a unique aroma. Formed by aromatic plants as secondary metabolites, EOs have been used as traditional medicines to treat various health problems worldwide. Historical records show that herbs rich in EOs have been widely used to treat respiratory diseases in China, Europe, and many other regions.

AIM OF THE REVIEW

This review summarizes the traditional applications and modern pharmacological mechanisms of EOs derived from aromatic herbs and their active ingredients in respiratory diseases in preclinical and clinical trials through multitarget synergy.

MATERIALS AND METHODS

Information about EOs and respiratory diseases was collected from electronic databases, such as ScienceDirect, Web of Science, PubMed, Google Scholar, Baidu Scholar, and the China National Knowledge Infrastructure (CNKI).

RESULTS

This review presents the preventive and therapeutic effects of EOs on respiratory diseases, including chronic obstructive pulmonary disease, bronchial asthma, acute lung injury, pulmonary infection, and pulmonary fibrosis. The molecular mechanisms of EOs in treating different lung diseases are summarized, including anti-inflammation, anti-oxidation, mucolytic, and immune regulatory mechanisms.

CONCLUSIONS

EOs show potential as supplements or substitutes for treating lung diseases.

Comparative GC Analysis, Bronchodilator Effect and the Detailed Mechanism of Their Main Component; Cinnamaldehyde of Three Cinnamon Species

Cinnamon is one of the most commonly used spices worldwide. In some Arab countries, cinnamon is used with other ingredients to relieve bronchospasm and treatment of airways-related disorders. In the current study, GC, GC-MS and tracheal relaxant effect comparison were performed using the three available types in Saudi Arabia, Cinnamomum verum (Ceylon cinnamon), C. cassia (Chinese cinnamon) and C. loureiroi (Vietnamese cinnamon). The essential oil of C. verum was the most potent in the relaxation of guinea pig isolated tracheal muscles against carbachol (CCh, 1 uM)-evoked bronchospasm at the concentration range from 0.03 to 3 mg/mL followed by C. bureiroi at 0.03 to 5 mg/mL; whereas, C. cassia was the least potent oil. Cinnamaldehyde (1), isolated as the main component of the three oils induced complete relaxation of low K+ (25 mM)-evoked contractions, with mild effect on the contractions evoked by high K+ (80 mM). Pre-incubation of the tracheal tissues with glibenclamide (10 mM) significantly opposed the relaxation of low K+ by cinnamaldehyde. The standard drug, cromakalim also inserted glibenclamide-sensitive inhibition of low K+ without relaxing high K+. These results indicate that cinnamaldehyde acts predominantly by ATP-specific K+ channel opening followed by weak Ca++ antagonistic effects. The obtained results justify the medicinal value of cinnamon oil in respiratory disorders.

Bio-guided chemical characterization and nano-formulation studies of selected edible volatile oils with potentials antibacterial and anti-SARS-CoV-2 activities

The recent pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has opened the door to potential threats of the respiratory system. The discovery of drugs from natural sources is one of the most important strategies for treating the upper respiratory tract. In this study, we investigated the selected formulated EOs activities against Gram-negative (E. coli, K. pneumonia, and P. aeruginosa) and Gram-positive (S. aureus, E. fecalis) bacteria and against the SARS-CoV-2 virus, with the mode of action investigated as anti-SARS-CoV-2. Cinnamomum zeylanicum and Syzygium aromaticum EOs were the most promising antibacterial oils. C. zeylanicum EO showed MIC values of 1, 1, 2, ≤0.5, and 8 µg/mL against E. coli, K. pneumoniae, P. aeruginosa, S. aureus, and E. fecalis, respectively, while S. aromaticum EO showed MIC values of 8, 4, 32, 8, 32 µg/mL against the same organisms. The cytotoxic activity of the oil samples was tested in VERO-E6 cells using (MTT) assay and showed that the safest oil was F. vulgare, then L. nobilis, C. carvi, S. aromaticum, and E. globulus. The most potent antiviral EOs were C. zeylanicum oil and S. aromaticum, with IC₅₀ value of 15.16 and 96.5 µg/mL, respectively. Moreover, the safety index of S. aromaticum EO (26.3) was greater than the oil of C. zeylanicum (7.25). The mechanism by which C. zeylanicum oil exerts its antiviral activity may involve both the virucidal effect and its impact on viral reproduction. The nano-emulsion dosage form of the potent EOs was prepared and re-examined against the same bacterial and viral strains. Finally, the chemical characterization of these promising essential oils was analyzed and identified using the GC-MS approach. To the best of our knowledge, this is the first report concerning the in vitro investigation of anti-SARS-CoV-2 activity of these selected essential oils, along with a proposed mechanism for the potent oil's activity.

Essential Oils and Their Compounds as Potential Anti-Influenza Agents

Essential oils (EOs) are chemical substances, mostly produced by aromatic plants in response to stress, that have a history of medicinal use for many diseases. In the last few decades, EOs have continued to gain more attention because of their proven therapeutic applications against the flu and other infectious diseases. Influenza (flu) is an infectious zoonotic disease that affects the lungs and their associated organs. It is a public health problem with a huge health burden, causing a seasonal outbreak every year. Occasionally, it comes as a disease pandemic with unprecedentedly high hospitalization and mortality. Currently, influenza is managed by vaccination and antiviral drugs such as Amantadine, Rimantadine, Oseltamivir, Peramivir, Zanamivir, and Baloxavir. However, the adverse side effects of these drugs, the rapid and unlimited variabilities of influenza viruses, and the emerging resistance of new virus strains to the currently used vaccines and drugs have necessitated the need to obtain more effective anti-influenza agents. In this review, essential oils are discussed in terms of their chemistry, ethnomedicinal values against flu-related illnesses, biological potential as anti-influenza agents, and mechanisms of action. In addition, the structure-activity relationships of lead anti-influenza EO compounds are also examined. This is all to identify leading agents that can be optimized as drug candidates for the management of influenza. Eucalyptol, germacrone, caryophyllene derivatives, eugenol, terpin-4-ol, bisabolene derivatives, and camphecene are among the promising EO compounds identified, based on their reported anti-influenza activities and plausible molecular actions, while nanotechnology may be a new strategy to achieve the efficient delivery of these therapeutically active EOs to the active virus site.

Achillea fragrantissima Essential Oil: Composition and Detailed Pharmacodynamics Study of the Bronchodilator Activity

The bronchodilator effect of the Achillea fragrantissima essential oil (AFO) was studied in guinea pigs’ tracheas and the influence of drying on the quantity and composition of AFO was studied using GC-MS and GC analyses. AFO produced a complete and potent relaxation against carbachol (CCh), while lower potency and partial efficacy were observed against high K+ (80 mM), thus producing dual inhibitory effects similar to dicyclomine. The anticholinergic-like action was further confirmed when pre-incubation tracheal tissues were used at lower concentrations with AFO displacing the CCh concentration‒response curves (CRCs) to the right in a competitive manner similar to atropine. However, non-parallel shifts in CCh CRCs were observed with higher doses, similar to dicyclomine. Further confirmation of the CCB-like effect was obtained from the non-specific deflection of Ca++ CRCs toward the right using the pre-incubated tissues with AFO in Ca++ free medium, similar to verapamil. When AFO was tested against low K+-mediated contractions to explore the possible involvement of additional antispasmodic mechanism(s), AFO interestingly showed a complete inhibition with a higher potency. This inhibition was found to be sensitive to tetraethylammonium (TEA) and 4-aminopyridine (4-AP), whereas glibenclamide (Gb) remained inactive. These results show that AFO possesses bronchodilator effects predominantly from its anticholinergic and K+ channel activation followed by weak Ca++ channels inhibition.

Antioxidant and Anti-Inflammatory Effects of Thyme (Thymus vulgaris L.) Essential Oils Prepared at Different Plant Phenophases on Pseudomonas aeruginosa LPS-Activated THP-1 Macrophages

Thyme (Thymus vulgaris L.) essential oil (TEO) is widely used as an alternative therapy especially for infections of the upper respiratory tract. TEO possesses antiviral, antibacterial, and antifungal properties. The emerging antibiotic resistance of bacterial strains, including Pseudomonas aeruginosa, has prompted the urge to find alternative treatments. In the present study, we examined the anti-inflammatory and antioxidant effects of thymol, the main compound of TEO, and two TEOs prepared at the beginning and at the end of the flowering period that may make these oils promising candidates as complementary or alternative therapies against P. aeruginosa infections. The activity measurements of the antioxidant enzymes peroxidase (PX), catalase (CAT), and superoxide dismutase (SOD) as well as the determination of total antioxidant capacity of P. aeruginosa-activated THP-1 cells revealed that thymol and both TEOs increased CAT and SOD activity as well as the antioxidant capacity of the THP-1 cells. The measurements of the proinflammatory cytokine mRNA expression and secreted protein level of LPS-activated THP-1 cells showed that from the two TEOs, only TEO prepared at the beginning of the flowering period acted as a potent inhibitor of the synthesis of IL-6, IL-8, IL-β, and TNF-α. Our results suggest that not only thymol, but also the synergism or the antagonistic effects of the additional compounds of the essential oils are responsible for the anti-inflammatory activity of TEOs.

Essential oil nebulization in mild COVID-19(EONCO): Early phase exploratory clinical trial

Background

Medications studied for therapeutic benefits in coronavirus disease 2019 (COVID-19) have produced inconclusive efficacy results except for steroids.

Objective

A prospective randomized open-label, parallel-arm Phase I/II clinical trial was planned to compare essential oil (EO) blend versus placebo nebulization in mild COVID-19.

Methods

A Phase I safety evaluation was carried out in a single ascending and multiple ascending dose study designs. We assessed Phase II therapeutic efficacy on COVID-19 and general respiratory symptoms on days 0, 3, 5, 7, 10, and 14 on the predesigned case record form. Viremia was evaluated on day 0, day 5, and day 10.

Results

Dose-limiting toxicities were not reached with the doses, frequencies, and duration studied, thus confirming the formulation's preliminary safety. General respiratory symptoms (p < 0.001), anosmia (p < 0.05), and dysgeusia (p < 0.001) benefited significantly with the use of EO blend nebulization compared to placebo. Symptomatic COVID-19 participants with mild disease did not show treatment benefits in terms of symptomatic relief (p = 1.0) and viremia clearance (p = 0.74) compared to the placebo. EO blend was found to be associated with the reduced evolution of symptoms in previously asymptomatic reverse transcription polymerase chain reaction (RT-PCR)-positive study participants (p = 0.034).

Conclusion

EO nebulization appears to be a safer add-on symptomatic relief approach for mild COVID-19. However, the direct antiviral action of the EO blend needs to be assessed with different concentrations of combinations of individual phytochemicals in the EO blend.

Essential Oils in Respiratory Mycosis: A Review

Respiratory mycosis is a major health concern, due to the expanding population of immunosuppressed and immunocompromised patients and the increasing resistance to conventional antifungals and their undesired side-effects, thus justifying the development of new therapeutic strategies. Plant metabolites, namely essential oils, represent promising preventive/therapeutic strategies due to their widely reported antifungal potential. However, regarding fungal infections of the respiratory tract, information is disperse and no updated compilation on current knowledge is available. Therefore, the present review aims to gather and systematize relevant information on the antifungal effects of several essential oils and volatile compounds against the main type of respiratory mycosis that impact health care systems. Particular attention is paid to Aspergillus fumigatus, the main pathogen involved in aspergillosis, Candida auris, currently emerging as a major pathogen in certain parts of the world, and Cryptococcus neoformans, one of the main pathogens involved in pulmonary cryptococcosis. Furthermore, the main mechanisms of action underlying essential oils’ antifungal effects and current limitations in clinical translation are presented. Overall, essential oils rich in phenolic compounds seem to be very effective but clinical translation requires more comprehensive in vivo studies and human trials to assess the efficacy and tolerability of these compounds in respiratory mycosis.

Pinus sylvestris L. and Syzygium aromaticum (L.) Merr. & L. M. Perry Essential Oils Inhibit Endotoxin-Induced Airway Hyperreactivity despite Aggravated Inflammatory Mechanisms in Mice

Scots pine (SO) and clove (CO) essential oils (EOs) are commonly used by inhalation, and their main components are shown to reduce inflammatory mediator production. The aim of our research was to investigate the chemical composition of commercially available SO and CO by gas chromatography–mass spectrometry and study their effects on airway functions and inflammation in an acute pneumonitis mouse model. Inflammation was evoked by intratracheal endotoxin and EOs were inhaled three times during the 24 h experimental period. Respiratory function was analyzed by unrestrained whole-body plethysmography, lung inflammation by semiquantitative histopathological scoring, myeloperoxidase (MPO) activity and cytokine measurements. α-Pinene (39.4%) was the main component in SO, and eugenol (88.6%) in CO. Both SO and CO significantly reduced airway hyperresponsiveness, and prevented peak expiratory flow, tidal volume increases and perivascular edema formation. Meanwhile, inflammatory cell infiltration was not remarkably affected. In contrast, MPO activity and several inflammatory cytokines (IL-1β, KC, MCP-1, MIP-2, TNF-α) were aggravated by both EOs. This is the first evidence that SO and CO inhalation improve airway function, but enhance certain inflammatory parameters. These results suggest that these EOs should be used with caution in cases of inflammation-associated respiratory diseases.

Ultrastructural Damages to H1N1 Influenza Virus Caused by Vapor Essential Oils

Influenza viruses are transmitted from human to human via airborne droplets and can be transferred through contaminated environmental surfaces. Some works have demonstrated the efficacy of essential oils (EOs) as antimicrobial and antiviral agents, but most of them examined the liquid phases, which are generally toxic for oral applications. In our study, we describe the antiviral activity of Citrus bergamia, Melaleuca alternifolia, Illicium verum and Eucalyptus globulus vapor EOs against influenza virus type A. In the vapor phase, C. bergamia and M. alternifolia strongly reduced viral cytopathic effect without exerting any cytotoxicity. The E. globulus vapor EO reduced viral infection by 78% with no cytotoxicity, while I. verum was not effective. Furthermore, we characterized the EOs and their vapor phase by the head-space gas chromatography-mass spectrometry technique, observing that the major component found in each liquid EO is the same one of the corresponding vapor phases, with the exception of M. alternifolia. To deepen the mechanism of action, the morphological integrity of virus particles was checked by negative staining transmission electron microscopy, showing that they interfere with the lipid bilayer of the viral envelope, leading to the decomposition of membranes. We speculated that the most abundant components of the vapor EOs might directly interfere with influenza virus envelope structures or mask viral structures important for early steps of viral infection.

Anti-inflammatory response of cardamom extract and prediction of therapeutic window in COVID-19 patients by assessing inflammatory markers using RT-PCR

INTRODUCTION

Molecular diagnostics using RT-PCR has now emerged as the new diagnostic method for clinicians with the dawn of SARS-CoV-2. In India, the popularity and awareness of RT-PCR and particularly the increased availability of testing machines across hospitals has now opened up possibilities of diagnostic tests with RT-PCR. In view of the cytokine storm which is the significant reason for morbidity and mortality of COVID-19 patients, we proposed to test the usefulness of a multiplex RT-PCR test kit that simultaneously measured inflammatory markers namely, IL-6, TNF- α and IL-10 (IFM) all in one tube. The study included a group of patients who were equally allotted to two treatment arms one of which received standard of care along with a food supplement capsule as a natural anti-inflammatory (RECOVEREEZ FORTE™), and the other group received standard of care that included oral Prednisolone tablets in tapered dosage. RECOVEREEZ FORTE™ consists of potent biomolecules from cardamom extract. A natural product with substantial anti-inflammatory action when consumed early at the onset of symptoms is hereby proven by comparing gene expression profile of inflammatory markers with routinely tested inflammatory parameters such as serum IL-6, CRP and LDH. In addition to predicting worse disease outcomes beforehand, RT-PCR assay tests provides an opportunity for identifying therapeutic window aiding in practicing effective treatment strategy for COVID-19. RT-PCR analysis of IFM together being used in a single multiplex kit is being first reported and such a test as a prognosticator for disease progression does seem promising and worthy of clinicians adopting novel testing modalities in clinical practice.

AIM OF THE STUDY

To study the anti-inflammatory response of RECOVEREEZ FORTE™ using RT-PCR based multiplex gene profiling of inflammatory markers in disease prognosis and show its predictability of worsening outcomes and its role in identifying therapeutic window for RECOVEREEZ FORTE™. To show the potentiality of RECOVEREEZ FORTE™ in reducing COVID-19 symptoms and SARS-CoV-2 RT-PCR Ct values of the treatment group.

MATERIALS AND METHODS

This was a short study of a 10-day period where the end point was the negativity of COVID-19 on RT-PCR test or the decline in cycle threshold (Ct) values of the test performed on day 10 when compared to day 0. During the course of the study, patients were given standard treatment and an oral dose of 500 mg of RECOVEREEZ FORTE™ thrice daily, or standard of care and oral Prednisolone in tapered dosage (control group). All essential interventions were included in the standard of care as decided by the attending physician. The RT-PCR results of inflammatory markers were compared to routinely tested parameters such as IL-6, CRP and LDH. Time to clinical improvement was in terms of SARS-CoV-2 RT-PCR test negativity or recovery of COVID-19 symptoms. We enrolled 64 patients, of which 32 were allocated to RECOVEREEZ FORTE ™ group and 32 to the control group.

RESULTS

The RT-PCR analysis of elevated IFM on day 0 corresponded to above normal protein levels of routinely tested parameters such as serum IL-6, CRP and LDH on day 5. Similarly, elevated IFM on day 5 corresponded to above normal protein levels on day 10. Such an association was equally prevalent in both the control group and RECOVEREEZ FORTE™ group, stipulating that RECOVEREEZ FORTE™ may be used as an alternative to steroids. The obtained results indicate that the RT-PCR assessment predicts worse outcomes 5 days earlier. But, the RT-PCR analysis of elevated IFM on day 0 did not correspond to the above normal protein levels of other parameters on day 10. Hence, indicating that the IFM RT-PCR test cannot predict worse outcomes 10 days earlier. Also, RECOVEREEZ FORTE™ when consumed for a period of 10 days normalized LDH values, compared to the control group. Moreover, IFM RT-PCR test identified a 5-day therapeutic window for RECOVEREEZ FORTE™ against inflammation experienced by patients. In addition to the above findings, the authors also observed that majority of the patients belonging to the treatment group showed recovery from symptoms such as fever, cough, sore throat and breathlessness compared to control group by day 5. 12 (37.5%) out of 32 patients and 6 (18.75%) out of 32 patients belonging to the treatment group and control group, respectively, became SARS-CoV-2 negative by day 5, indicating a probable anti-viral action of RECOVEREEZ FORTE™ against SARS-CoV-2.

CONCLUSION

The IFM RT-PCR test possess 5-day early prediction ability and lacks 10-day prediction ability. Treatment with RECOVEREEZ FORTE™ indicates good anti-inflammatory action which is equivalent to steroids. Intake of RECOVEREEZ FORTE ™ for a period of 5 days depicts persistent anti-inflammatory action, recovery of COVID-19 symptoms and a probable anti-viral action. Moreover, an effective normalization of LDH may be rendered by RECOVEREEZ FORTE™ when consumed for a period of 10 days.

Nano-Antibacterials Using Medicinal Plant Components: An Overview

Gradual emergence of new bacterial strains, resistant to one or more antibiotics, necessitates development of new antibacterials to prevent us from newly evolved disease-causing, drug-resistant, pathogenic bacteria. Different inorganic and organic compounds have been synthesized as antibacterials, but with the problem of toxicity. Other alternatives of using green products, i.e., the medicinal plant extracts with biocompatible and potent antibacterial characteristics, also had limitation because of their low aqueous solubility and therefore less bioavailability. Use of nanotechnological strategy appears to be a savior, where phytochemicals are nanonized through encapsulation or entrapment within inorganic or organic hydrophilic capping agents. Nanonization of such products not only makes them water soluble but also helps to attain high surface to volume ratio and therefore high reaction area of the nanonized products with better therapeutic potential, over that of the equivalent amount of raw bulk products. Medicinal plant extracts, whose prime components are flavonoids, alkaloids, terpenoids, polyphenolic compounds, and essential oils, are in one hand nanonized (capped and stabilized) by polymers, lipids, or clay materials for developing nanodrugs; on the other hand, high antioxidant activity of those plant extracts is also used to reduce various metal salts to produce metallic nanoparticles. In this review, five medicinal plants, viz., tulsi (Ocimum sanctum), turmeric (Curcuma longa), aloe vera (Aloe vera), oregano (Oregano vulgare), and eucalyptus (Eucalyptus globulus), with promising antibacterial potential and the nanoformulations associated with the plants' crude extracts and their respective major components (eugenol, curcumin, anthraquinone, carvacrol, eucalyptus oil) have been discussed with respect to their antibacterial potency.

Essential Oil Blends: The Potential of Combined Use for Respiratory Tract Infections

This study investigated the potential efficacy of 369 commercial essential oil combinations for antimicrobial, anti-toxic and anti-inflammatory activity with the aim of identifying synergy among essential oils commonly used in combination by aromatherapists for respiratory purposes. Essential oil combinations were assessed for their antimicrobial activities using a panel of Gram-positive, Gram-negative, and yeast strains associated with respiratory tract infections. The antimicrobial activity was measured by determining the minimal inhibitory concentration (MIC) of microbial growth. The fractional inhibitory concentration index (ΣFIC) was calculated to determine the antimicrobial interactions between the essential oils in the combination. The toxicity of the essential oil combinations was tested in vitro using the brine shrimp lethality assay, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay on RAW 264.7 mouse macrophage cells and A549 lung cancer cell lines. In addition, an inflammatory response was evaluated measuring nitric oxide production. The essential oils, when in combination, demonstrated an increased antimicrobial effect, a reduction in toxicity and provided improved anti-inflammatory outcomes. Five distinct combinations [Cupressus sempervirens (cypress) in combination with Melaleuca alternifolia (tea tree), Hyssopus officinalis (hyssop) in combination with Rosmarinus officinalis (rosemary), Origanum marjorana (marjoram) in combination with M. alternifolia, Myrtus communis (myrtle) in combination with M. alternifolia and Origanum vulgare (origanum) in combination with M. alternifolia] were found to be the most promising, demonstrating antimicrobial activity, reduced cytotoxicity and improved anti-inflammatory effects. With the increased prevalence of respiratory tract infections and the growing antimicrobial resistance development associated with antimicrobial treatments, this study provides a promising complementary alternative for the appropriate use of a selection of essential oil combinations for use in the respiratory tract.

Anti-inflammatory effect of lavender (Lavandula angustifolia Mill.) essential oil prepared during different plant phenophases on THP-1 macrophages

BACKGROUND

Pseudomonas aeruginosa is the most common Gram-negative bacterium associated with nosocomial respiratory infections. Lavender essential oil is mainly used in aromatherapy, but it has several pharmacological and therapeutic properties. Furthermore, it possesses antifungal and antibacterial activities. The anti-inflammatory activity of essential oils may depend on the composition and the ratio of the compounds. The constitution of the essential oils extracted from the different stages of flowering period varies, which makes it plausible that the collection time of the flowers influences the anti-inflammatory effects. Different types of essential oils reduce inflammation acting similarly by modulating the activity and action of the NFκB signalling pathway, which is the major regulator of the transcription of pro-inflammatory cytokines.

METHODS

Lavender essential oils were distilled from lavender plant cultivated in Hungary and the flowers were harvested at the beginning and at the end of flowering period. The experiments were carried out on THP-1 human monocyte/macrophage cell line as in vitro cell culture model for monitoring the effects of lavender essential oils and the main compound linalool on P. aeruginosa LPS stimulated inflammation. The mRNA and protein levels of four pro-inflammatory cytokines, IL-6, IL-1β, IL-8 and TNFα were determined by Real Time PCR and ELISA measurements. The effects of essential oils were compared to the response to two NFκB inhibitors, luteolin and ACHP.

RESULTS

Linalool and lavender essential oil extracted from plants at the beginning of flowering period were successful in decreasing pro-inflammatory cytokine production following LPS pretreatment. In case of IL-8 and IL-1β lavender oil showed stronger effect compared to linalool and both of them acted similarly to NFκB inhibitors. Pretreatments with linalool and lavender essential oil/beginning of flowering period prevented pro-inflammatory cytokine production compared to LPS treatment alone. Although lavender essential oil/end of flowering period decreased IL-6, IL-1β and IL-8 mRNA expression in case of LPS pretreatment, it was not capable to reduce cytokine secretion.

CONCLUSION

Based on our results it has been proven that lavender essential oil extracted at the beginning of flowering period is a potent inhibitor of the synthesis of four pro-inflammatory cytokines IL-6, IL-8, IL-β and TNFα of THP-1 cells. This supports the relevance of the collection of the lavender flowers from early blooming period for essential oil production and for the utilization as an anti-inflammatory treatment.

An Evaluation of the Potential of Essential Oils against SARS-CoV-2 from In Silico Studies through the Systematic Review Using a Chemometric Approach

Essential oils (EOs) and their compounds have attracted particular attention for their reported beneficial properties, especially their antiviral potential. However, data regarding their anti-SARS-CoV-2 potential are scarce in the literature. Thus, this study aimed to identify the most promising EO compounds against SARS-CoV-2 based on their physicochemical, pharmacokinetic, and toxicity properties. A systematic literature search retrieved 1669 articles; 40 met the eligibility criteria, and 35 were eligible for analysis. These studies resulted in 465 EO compounds evaluated against 11 human and/or SARS-CoV-2 target proteins. Ninety-four EO compounds and seven reference drugs were clustered by the highest predicted binding affinity. Furthermore, 41 EO compounds showed suitable drug-likeness and bioactivity score indices (≥0.67). Among these EO compounds, 15 were considered the most promising against SARS-CoV-2 with the ADME/T index ranging from 0.86 to 0.81. Some plant species were identified as EO potential sources with anti-SARS-CoV-2 activity, such as Melissa officinalis Arcang, Zataria multiflora Boiss, Eugenia brasiliensis Cambess, Zingiber zerumbet Triboun & K.Larsen, Cedrus libani A.Rich, and Vetiveria zizanoides Nash. Our work can help fill the gap in the literature and guide further in vitro and in vivo studies, intending to optimize the finding of effective EOs against COVID-19.

The use of chemometric modelling to determine chemical composition-antimicrobial activity relationships of essential oils used in respiratory tract infections

The antimicrobial effects of essential oils are commonly cited within aromatherapeutic texts for use in respiratory tract infections. These essential oils are inhaled or applied to the skin to treat infections and manage symptoms associated with these conditions. A limited number of these essential oils have been scientifically studied to support these claims, specifically, against respiratory pathogens. This study reports on the minimum inhibitory concentration (MIC) of 49 commercial essential oils recommended for respiratory tract infections, and identifies putative biomarkers responsible for the determined antimicrobial effect following a biochemometric workflow. Essential oils were investigated against nine pathogens. Three essential oils, Amyris balsamifera (amyris), Coriandrum sativum (coriander) and Santalum austrocaledonicum (sandalwood) were identified as having greater activity (MIC value = 0.03-0.13 mg/ml) compared to the other essential oils investigated. The essential oil composition of all 49 oils were determined using Gas Chromatography coupled to Mass Spectroscopy (GC-MS) analysis and the GC-MS data analysed together with the antimicrobial data using chemometric tools. Eugenol was identified as the main biomarker responsible for antimicrobial activity in the majority of the essential oils. The ability of a chemometric model to accurately predict the active and inactive biomarkers of the investigated essential oils against pathogens of the respiratory tract was 80.33%.

Chemical composition of essential oils of eight Tunisian Eucalyptus species and their antibacterial activity against strains responsible for otitis

Background

The chemical composition and biological activity of Eucalyptus essential oils have been studied extensively (EOs). A few of them were tested for antibacterial effectiveness against otitis strains. The chemical composition and antibacterial activity of the EOs of eight Tunisian Eucalyptus species were assessed in the present study.

Methods

Hydrodistillation was used to extract EOs from the dried leaves of eight Eucalyptus species: Eucalyptus accedens, Eucalyptus punctata, Eucalyptus robusta, Eucalyptus bosistoana, Eucalyptus cladocalyx, Eucalyptus lesouefii, Eucalyptus melliodora and Eucalyptus wandoo. They are assessed by GC/MS and GC/FID and evaluated for antibacterial activity using agar diffusion and broth microdilution techniques against three bacterial isolates (Haemophilus influenzae, Haemophilus parainfluenzae, Klebsiella pneumoniae) and three reference bacteria strains (Pseudomonas aeruginosa, ATTC 9027; Staphylococcus aureus, ATCC 6538; and Escherichia coli, ATCC 8739). Furthermore, the selected twenty-one major compounds and all values of the inhibition zone diameters were subjected to further statistical analysis using PCA and HCA.

Results

The EO yields of the studied Eucalyptus species range from 1.4 ± 0.4% to 5.2 ± 0.3%. Among all the species studied, E. lesouefii had the greatest mean percentage of EOs. The identification of 128 components by GC (RI) and GC/MS allowed for 93.6% – 97.7% of the total oil to be identified. 1,8-cineole was the most abundant component found, followed by α-pinene, p-cymene, and globulol. The chemical components of the eight EOs, extracted from the leaves of Eucalyptus species, were clustered into seven groups using PCA and HCA analyses, with each group forming a chemotype. The PCA and HCA analyses of antibacterial activity, on the other hand, identified five groups.

Conclusion

The oils of E. melliodora, E. bosistoana, and E. robusta show promise as antibiotic alternatives in the treatment of otitis media.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03379-y.

Possible Tracheal Relaxant and Antimicrobial Effects of the Essential Oil of Ethiopian Thyme Species (Thymus serrulatus Hochst. ex Benth.): A Multiple Mechanistic Approach

The genus Thymus is traditionally used for the treatment of hyperactive airways complaints. The purpose of the current study is to investigate the potential tracheal relaxant effect and possible mechanism(s) of the essential oil of Thymus serrulatus (TS Oil) in isolated guinea pig tracheal tissues. The essential oil was obtained from the fresh erial parts of Thymus serrulatus, and its phyto-components were identified by GC-MS analysis. Guinea pig tracheal preparations were used for testing the tracheal relaxant effect of TS Oil with the determination of the mechanism(s) involved in this relaxation. GC-MS findings reveal that terpenes, fragrance constituents, saponins, and higher fatty acids are present in TS Oil. In isolated guinea pig trachea, TS Oil inhibited carbachol (CCh, 1 µM) and K⁺ (80 mM)-induced contractions in a pattern similar to that of dicyclomine. TS Oil, at 0.3 mg/ml, shifted parallel CCh-curves towards the right, followed by a non-parallel shift at higher concentration (1 mg/ml), thus suppressing maximum response in the same manner as produced by dicyclomine. Pretreatment of tissues with TS Oil (1 and 3 mg/ml) also produced a rightward shift of Ca⁺⁺ concentration-response curves (CRCs) in the same manner as caused by verapamil. Further, TS Oil at low concentrations (0.3 and 1 mg/ml) shifted isoprenaline-induced inhibitory CRCs towards the left and increased cAMP levels in isolated tracheal homogenates similar to papaverine, a phosphodiesterase (PDE) inhibitor. In the antimicrobial assay performed by the agar well diffusion method, TS Oil was found most active against Candida albicans and Staphylococcus aureus where the zone of inhibition measured was 28 mm. Additionally, there was little difference between standard strains of gram-positive and gram-negative bacteria. However, methicillin-resistant S. aureus (MRSA) showed a small zone of inhibition as compared to standard strains (22 mm). From these results, it can be concluded that the essential oil of T. serrulatus has the potential to produce antimicrobial effects while causing tracheal relaxation mediated possibly by anticholinergic effects, Ca⁺⁺ channel blockade, and PDE inhibition whereas additional mechanism(s) cannot be ruled out.

Appropriate use of essential oils and their components in the management of upper respiratory tract symptoms in patients with COVID-19

Introduction

The involvement of the upper respiratory tract is common in COVID-19, and the majority of patients are treated at home with a mild-to-moderate form of the disease. Many approaches based on essential oils have been proposed for the symptomatic treatment of COVID-19. This work aims to outline the potential and safe evidence-based uses of essential oils and their major components for the clinical management of mild respiratory symptoms caused by uncomplicated coronavirus infections, including SARS-CoV-2. Due to their wide use, a focus on the constituents eucalyptol and menthol has been provided.

Methods

An overview of the scientific literature with a critical discussion of retrieved evidence and clinical recommendations.

Results

In general, eucalyptol and essential oils or blends whose content is rich in it, may be used as an integrative remedy for the symptomatic improvement of patients with mild and uncomplicated infections caused by coronaviruses. Menthol is not recommended in patients with COVID-19, due to a potential reduction of the self-perception of dyspnea, which can lead infected patients to underestimate the actual disease severity and to delay medical attention.

Discussion

Based on available evidence, symptomatic remedies for COVID-19, such as essential oils and their isolated compounds, can be useful, but are not an alternative to standard medical therapy and do not exempt patients from following precautionary measures issued by health authorities. Clinical recommendations on the appropriate use of essential oils for the management of upper airway symptoms of COVID-19 are provided. Further studies on the topic are advised.

Gas Chromatography-Mass Spectrometry-Based Classification of 12 Fennel (Foeniculum vulgare Miller) Varieties Based on Their Aroma Profiles and Estragole Levels as Analyzed Using Chemometric Tools

Fennel (Foeniculum vulgare Miller) is a popular aromatic plant native to the Mediterranean basin and cultivated worldwide that is valued for the nutritional and health benefits of its fruits. Headspace solid-phase microextraction of 12 fennel accessions of cultivated (F. vulgare subsp. vulgare) and wild forms (F. vulgare subsp. piperitum) of different origins was carried out for assessing their volatile distribution. Fifty-four volatiles were identified, with ethers amounting for the major class at ca. 52-99% attributed to the abundance of (E)-anethole and estragole. Several subsp. vulgare accessions proved to be excellent sources of the chief aroma (E)-anethole (95.9-98.4%), whereas high levels of estragole at ca. 72% were observed in subsp. piperitum from Minia and Khartoum and must be considered in the safety assessment of fennel. Other volatile classes were detected including ketones, esters, aldehydes, alcohols, and hydrocarbons (monoterpenes, sesquiterpenes, and diterpenes). Fenchone exceeded 15% of the total volatiles in some fennel specimens, linked to a conspicuous bitter aftertaste. The members of subsp. piperitum were more enriched in monoterpene hydrocarbons with sabinene found exclusively in these, while subsp. vulgare comprised a higher content of ethers. Principle component analysis determined isoterpinolene as a special component in subsp. piperitum. In all specimens from the same group, estragole was the most distinguished volatile compound according to the findings from orthogonal partial least squares-discriminant analysis. The highest estimated estragole levels were detected in subsp. piperitum from Minia at 89.8 mg/g. This comparative study provides the first comprehensive insight into volatile profiling of 12 fennel fruit varieties.

Microbial Interkingdom Biofilms and the Quest for Novel Therapeutic Strategies

Fungal and bacterial species interact with each other within polymicrobial biofilm communities in various niches of the human body. Interactions between these species can greatly affect human health and disease. Diseases caused by polymicrobial biofilms pose a major challenge in clinical settings because of their enhanced virulence and increased drug tolerance. Therefore, different approaches are being explored to treat fungal-bacterial biofilm infections. This review focuses on the main mechanisms involved in polymicrobial drug tolerance and the implications of the polymicrobial nature for the therapeutic treatment by highlighting clinically relevant fungal-bacterial interactions. Furthermore, innovative treatment strategies which specifically target polymicrobial biofilms are discussed.

A new phenolic glycoside from Trollius chinensis Bunge with anti-inflammatory and antibacterial activities

A undescribed phenolic glycoside, trochinenol A (1), was isolated from the flowers of Trollius chinensis Bunge and the structure was identified by spectroscopic methods. Its anti-inflammatory and antibacterial effects were investigated by broth microdilution and NF-κB reporter gene assays. Consequently, compound 1 exhibited an appreciable effect against Staphylococcus aureus with the MIC value of 6.25 µg/mL. Besides, it showed moderate effect against TNFα-induced activation of NF-κB pathway.

Effects of Thymus vulgaris L., Cinnamomum verum J.Presl and Cymbopogon nardus (L.) Rendle Essential Oils in the Endotoxin-induced Acute Airway Inflammation Mouse Model

Thyme (TO), cinnamon (CO), and Ceylon type lemongrass (LO) essential oils (EOs) are commonly used for inhalation. However, their effects and mechanisms on inflammatory processes are not well-documented, and the number of in vivo data that would be important to determine their potential benefits or risks is low. Therefore, we analyzed the chemical composition and investigated the activity of TO, CO, and LO on airway functions and inflammatory parameters in an acute pneumonitis mouse model. The components of commercially available EOs were measured by gas chromatography-mass spectrometry. Airway inflammation was induced by intratracheal endotoxin administration in mice. EOs were inhaled during the experiments. Airway function and hyperresponsiveness were determined by unrestrained whole-body plethysmography on conscious animals. Myeloperoxidase (MPO) activity was measured by spectrophotometry from lung tissue homogenates, from which semiquantitative histopathological scores were assessed. The main components of TO, CO, and LO were thymol, cinnamaldehyde, and citronellal, respectively. We provide here the first evidence that TO and CO reduce inflammatory airway hyperresponsiveness and certain cellular inflammatory parameters, so they can potentially be considered as adjuvant treatments in respiratory inflammatory conditions. In contrast, Ceylon type LO inhalation might have an irritant effect (e.g., increased airway hyperresponsiveness and MPO activity) on the inflamed airways, and therefore should be avoided.

Essential oils and its bioactive compounds modulating cytokines: A systematic review on anti-asthmatic and immunomodulatory properties

BACKGROUND

Asthma, the main inflammatory chronic condition affecting the respiratory system, is characterized by hyperresponsiveness and reversible airway obstruction, recruitment of inflammatory cells and excessive production of mucus. Cytokines as biochemical messengers of immune cells, play an important role in the regulation of allergic inflammatory and infectious airway processes. Essential oils of plant origin are complex mixtures of volatile and semi volatile organic compounds that determine the specific aroma of plants and are categorized by their biological activities.

PURPOSE

We reviewed whether essential oils and their bioactive compounds of plant origin could modulate cytokines' immune responses and improve asthma therapy in experimental systems in vitro and in vivo.

METHODS

Electronic and manual search of articles in English available from inception up to November 2018 reporting the immunomodulatory activity of essential oils and their bioactive compounds for the management of asthma. We used PubMed, EMBASE, Scopus and Web of Science. Publications reporting preclinical experiments where cytokines were examined to evaluate the consequence of anti-asthmatic therapy were included.

RESULTS

914 publications were identified and 13 were included in the systematic review. Four articles described the role of essential oils and their bioactive compounds on bronchial asthma using cell lines; nine in vivo studies evaluated the anti-inflammatory efficacy and immunomodulating effects of essential oil and their secondary metabolites on cytokines production and inflammatory responses. The most important immunopharmacological mechanisms reported were the regulation of cytokine production, inhibition of reactive oxygen species accumulation, inactivation of eosinophil migration and remodeling of the airways and lung tissue, modulation of FOXP3 gene expression, regulation of inflammatory cells in the airways and decreasing inflammatory mediator expression levels.

CONCLUSION

Plant derived essential oils and related active compounds have potential therapeutic activity for the treatment of asthma by modulating the release of pro-inflammatory (TNF-α, IL-1β, IL-8), Th17 (IL-17), anti-inflammatory (IL-10), Th1 (IFN-γ, IL-2, IL-12) and Th2 (IL-4, IL-5, IL-6, IL-13) cytokines and the suppression of inflammatory cell accumulation.

Natural Macromolecules as Carriers for Essential Oils: From Extraction to Biomedical Application

Essential oils (EOs) and their main constituents, the terpenes, are widely studied, mostly relating to their antioxidant ability and bioactivity, such as antimicrobial, anticancer, anti-inflammatory, and range of other actions in the living systems. However, there is limited information on their bioavailability, especially upon clinical studies. Having in mind both strong biological effects and health benefits of EOs and their specific physicochemical properties (volatility, lipophilic character, low water solubility or insolubility, viscosity, expressed odor, concentration-dependent toxicity, etc.), there is a need for their encapsulation for target delivery. Encapsulation of EOs and their constituents is the prerequisite for enhancing their oxidative stability, thermostability, photostability, shelf life, and biological activity. We considered various carrier types such a (1) monophase and polyphase polysaccharide hydrogel carriers, (2) polysaccharide-protein carriers, and (3) lipid carriers in the context of physicochemical and engineering factors. Physicochemical factors are encapsulation efficiency, chemical stability under gastric conditions, mechanical stability, and thermal stability of carrier matrices. Choice of carrier material also determines the encapsulation technique. Consequently, the engineering factors are related to the advantage and disadvantage of various encapsulation techniques frequently used in the literature. In addition, it was intended to address the interactions between (1) main carrier components, such as polysaccharides, proteins, and lipids themselves (in order to form chemically and mechanically stable structure); (2) main carrier components with pepsin under gastric conditions (in order to form resistant material under gastric conditions); and (3) main carrier components with EOs (in order to enhance encapsulation efficiency), as a necessary precondition for whole process optimization. Finally, different sources for obtaining natural carrier macromolecules are surveyed, especially the agro-waste materials and agricultural and food by-products. This review article highlights the bioavailability aspects of encapsulated EOs and physicochemical and engineering factors concerning natural macromolecule carriers for their target delivery and application.

Striking essential oil: tapping into a largely unexplored source for drug discovery

Essential oils (EOs) have been used therapeutically for centuries. In recent decades, randomized controlled (clinical) trials have supported efficacy in specific therapeutic indications for a few of them. Some EOs, their components or derivatives thereof have been approved as drugs. Nevertheless, they are still considered products that are mainly used in complementary and alternative medicine. EO components occupy a special niche in chemical space, that offers unique opportunities based on their unusual physicochemical properties, because they are typically volatile and hydrophobic. Here we evaluate selected physicochemical parameters, used in conventional drug discovery, of EO components present in a range of commercially available EOs. We show that, contrary to generally held belief, most EO components meet current-day requirements of medicinal chemistry for good drug candidates. Moreover, they also offer attractive opportunities for lead optimization or even fragment-based drug discovery. Because their therapeutic potential is still under-scrutinized, we propose that this be explored more vigorously with present-day methods.

Much More Than a Pleasant Scent: A Review on Essential Oils Supporting the Immune System

The augmenting acceptance and application of herbal medicine in prevention and treatment of diseases also involve the use of plant essential oils (EOs) through different routes of administration (aromatherapy). Scientific data supporting the efficacy of certain herbal products are continuously growing; however, the cumulative evidence is not always sufficient. The anti-inflammatory properties of EOs have been investigated more extensively and also reviewed in different settings, but so far, our review is the first to summarize the immune-supporting properties of EOs. Our aim here is to synthesize the currently available data on the immune function enhancing effects of EOs. An online search was conducted in the PubMed database, which was terminated at the end of July 2019. Other articles were found in the reference lists of the preselected papers. Studies that applied whole EOs with known components, or single EO constituents under in vitro or in vivo laboratory conditions, or in human studies, and de facto measured parameters related to immune function as outcome measures were included. Two specific fields, EO dietary supplementation for livestock and fish, and forest bathing are also explored. Some EOs, particularly eucalyptus and ginger, seem to have immune function enhancing properties in multiple studies.

Effects of Eucalypt Plant Monoterpenes on Koala (Phascolarctos Cinereus) Cytokine Expression In Vitro

Protective immunity is crucial for survival of any species, though the koala as a specialist feeder adapted to an exclusive diet of eucalypts that contain plant secondary metabolites of varying toxicity and of immunomodulatory property. Being constantly exposed to such dietary chemicals it raises the question of their immune effects in a specialist eucalypt feeder. This study demonstrates that natural levels of circulating eucalypt plant secondary metabolites have dose dependent in vitro effects on cytokine expression of koala peripheral blood mononuclear cells, suggesting a potential trade-off of reduced function in multiple arms of the immune system associated with koala's use of its specialized dietary niche.

Antibacterial activity against porcine respiratory bacterial pathogens and in vitro biocompatibility of essential oils

Bacterial respiratory infections affecting pigs such as pneumonia, pleuropneumonia, and pleurisy, are a major health concern in the swine industry and are associated with important economic losses. This study aimed to investigate the antibacterial activities of essential oils against major swine respiratory pathogens with a view to developing a potential alternative to antibiotics. Their synergistic interactions with the bacteriocin nisin was also examined. Lastly, we assessed the in vitro biocompatibility of the most efficient essential oils using a pig tracheal epithelial cell line. Of the nine essential oils tested, those from cinnamon, thyme, and winter savory were the most active against Streptococcus suis, Actinobacillus pleuropneumoniae, Actinobacillus suis, Bordetella bronchiseptica, Haemophilus parasuis, and Pasteurella multocida, with minimum inhibitory concentrations and minimum bactericidal concentrations ranging from 0.01 to 0.156% (v/v). The main component found in cinnamon, thyme, and winter savory oils were cinnamaldehyde, thymol, and carvacrol, respectively. Treating pre-formed S. suis and A. pleuropneumoniae biofilms with thyme or winter savory oils significantly decreased biofilm viability. We also observed a synergistic growth inhibition of S. suis with mixtures of nisin and essential oils from thyme and winter savory. Concentrations of nisin and cinnamon, thyme and winter savory essential oils that were effective against bacterial pathogens had no effect on the viability of pig tracheal epithelial cells. The present study brought evidence that essential oils are potential antimicrobial agents against bacteria associated with porcine respiratory infections.

Origanum vulgare L. Essential Oil as a Potential Anti-Acne Topical Nanoemulsion-In Vitro and In Vivo Study

Antibiotics are often prescribed in acne treatment; however, Propionibacterium acnes and Staphylococcus epidermidis, the two of the major acne-associated bacteria, developed antibiotic resistance. Essential oils (EOs) present a natural, safe, efficacious and multifunctional alternative treatment. This study aimed to assess the potential anti-acne activity of selected seven EOs commonly used in Mediterranean folk medicine. Antimicrobial activity screening of these oils showed oregano to exhibit the strongest antimicrobial activity with minimum inhibitory concentration (MIC) of 0.34 mg/mL and minimum bactericidal concentration (MBC) of 0.67 mg/mL against P. acnes; and MIC of 0.67 mg/mL and MBC of 1.34 mg/mL against S. epidermidis. The composition of the most effective EOs (oregano and thyme) was determined using gas chromatography-mass spectrometry (GC-MS). Monoterpenoid phenols predominated oregano and thyme EO with thymol percentile 99 and 72, respectively. Thymol showed MIC 0.70 mg/mL against both P. acnes and S. epidermidis whereas MBC was 1.40 and 2.80 mg/mL against P. acnes and S. epidermidis, respectively. Moreover, oregano exhibited the strongest anti-biofilm effect against S. epidermidis with MBIC 1.34 mg/mL and killing dynamic time of 12 and 8 h against P. acnes and S. epidermidis, respectively. Oregano, the most effective EO, was formulated and tested as a nanoemulsion in an acne animal mouse model. The formulation showed superior healing and antimicrobial effects compared to the reference antibiotic. Collectively, our data suggested that oregano oil nanoemulsion is a potential natural and effective alternative for treating acne and overcoming the emerging antibiotic resistance.

Evaluation of Antipneumonic Effect of Philippine Essential Oils Using Broth Microdilution Volatilization Method and Their Lung Fibroblasts Toxicity

Essential oils isolated from six Philippine plant species, namely Alpinia brevilabris C. Presl, Alpinia cumingii K. Schum., Alpinia elegans (C. Presl) K. Schum., Callicarpa micrantha Vidal, Cinnamomum mercadoi S. Vidal, and Piper quinqueangulatum Miq. were assessed for their in vitro growth-inhibitory effect against pneumonia causing bacteria ( Haemophilus influenzae, Streptococcus pneumoniae, and Staphylococcus aureus) using the broth microdilution volatilization method. Additionally, a modified thiazolyl blue tetrazolium bromide assay was performed for evaluation of their cytotoxic activity to human lung cells. All essential oils exhibited some antibacterial efficacy in liquid phase; however, only A. cumingii oil was active in the vapour as well. Both A. cumingii and A. elegans oils showed the most effective antibacterial potential against H. influenzae in liquid medium with the minimum inhibitory concentration of 256 μg/mL. Using dual-column/dual-detector system GC/MS analysis, hedycaryol, β-pinene, caryophyllene epoxide, aristolochene, borneol, and linalool were identified as the major components of A. brevilabris, A. cumingii, A. elegans, C. micrantha, C. mercadoi, and P. quinqueangulatum leaves oils, respectively.

Antibacterial activity evaluation of selected essential oils in liquid and vapor phase on respiratory tract pathogens

BACKGROUND

The increasing number of multidrug-resistant bacteria and the fact of antibiotic resistance is leading to a continuous need for discovering alternative treatments against infections, e.g. in the case of respiratory tract diseases. Essential oils (EOs), because of their volatility, can easily reach both the upper and lower parts of the respiratory tract via inhalation. Therefore, the aim of the present study was the antibacterial evaluation of clove, cinnamon bark, eucalyptus, thyme, scots pine, peppermint, and citronella EOs against respiratory tract pathogens such as Streptococcus pneumoniae, S. mutans, S. pyogenes, Haemophilus influenzae, H. parainfluenzae, and Moraxella catarrhalis. Furthermore, we wanted to compare the antibacterial effect of these EOs in two different test systems to provide data for the development of an appropriate product formulation.

METHODS

Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined with in vitro vapor phase test (VPT) and broth macrodilution test (BDT). The chemical and percentage compositions of the EOs were determined by GC-MS and GC-FID analysis.

RESULTS

Among the EOs, thyme was the most effective against S. mutans (MIC: 0.04 mg/mL in BDT, but cinnamon bark and clove oils also presented high inhibition in liquid medium with MIC values of 0.06 mg/mL and 0.1 mg/mL against S. pneumoniae and S. pyogenes, respectively. M. catarrhalis was the most sensitive to thyme EO (MIC: 0.09 mg/mL). Cinnamon bark EO was the most effective against Haemophilus spp. (MIC: 0.06 mg/mL). In the VPT, cinnamon bark was the most effective oil against all investigated pathogens with MIC values in the range of 15.62-90 μl/L. Surprisingly, the eucalyptus and scots pine showed weak activity against the test bacteria in both test systems.

CONCLUSIONS

The EO of thyme, clove and cinnamon bark may provide promising antibacterial activity against respiratory tract pathogens either in liquid medium or in vapor phase. However, their effect is lower than that of the reference antibiotics. The combination of EOs and antibiotics may be beneficial in the alternative treatment of respiratory tract diseases. In vivo studies are necessary to calculate the effective dose of EOs in patients and determine their possible side effects and toxicity.