Natural Compounds in the Battle against Microorganisms-Linalool

Monoterpenoid synergy: a new frontier in biological applications

Monoterpenoids, compounds found in various organisms, have diverse applications in various industries. Their effectiveness is influenced by the oil's chemical composition, which in turn is influenced by plant genotype, environmental conditions, cultivation practices, and plant development stage. They are used in various industries due to their distinctive odor and taste, serving as ingredients, additives, insecticides, and repellents. These compounds have synergistic properties, resulting in superior combined effects over discrete ones, potentially beneficial for various health purposes. Many experimental studies have investigated their interactions with other ingredients and their antibacterial, insecticidal, antifungal, anticancer, anti-inflammatory, and antioxidant properties. This review discusses potential synergistic interactions between monoterpenoids and other compounds, their sources, and biological functions. It also emphasizes the urgent need for more research on their bioavailability and toxicity, underlining the importance and relevance of this comprehensive study in the current scientific landscape.

Monoterpene linalool restrains gentamicin-mediated acute kidney injury in rats by subsiding oxidative stress, apoptosis, and the NF-κB/iNOS/TNF-α/IL-1β pathway and regulating TGF-β

The clinical use of gentamicin (GM) is restricted by its nephrotoxic effects. This study aimed for the first time to elucidate the ameliorative effects of the monoterpene linalool (Lin) against GM-mediated acute kidney injury in rats. A total of thirty-two rats were subdivided into four equal groups: control (saline), Lin (100 mg/kg/day), GM (100 mg/kg/day), and GM + Lin (100 and 100 mg/kg/day). Lin and GM were intraperitoneally administered for 12 days. Our results illustrated that Lin ameliorated GM-mediated renal histopathological abnormalities and reduced serum urea and creatinine levels in rats exposed to GM. Lin treatment mitigated oxidative stress in nephrotoxic animals as manifested by reducing serum and renal levels of malondialdehyde and increasing the activities of serum and renal glutathione peroxidase and renal catalase. Moreover, Lin markedly inhibited GM-triggered inflammation by downregulating NF-κB, iNOS, TNF-α, and IL-1β and reducing renal myeloperoxidase activity and nitric oxide levels. Interestingly, Lin repressed GM-induced apoptosis, as reflected by a marked downregulation of Bax and caspase-3 expression, concurrent with the upregulation of Bcl2 expression. Finally, Lin administration led to a significant downregulation of TGF-β expression in nephrotoxic animals. In summary, Lin ameliorated GM-mediated nephrotoxicity in rats, at least through its antioxidant, anti-inflammatory, and anti-apoptotic activities and by modulating TGF-β.

Therapeutic potential of the linalool against cadmium-induced testicular tissue damage

Cadmium (Cd) is a heavy metal that has harmful effects and is one of the contaminants found in the environment. Cd exposure causes important pathophysiological processes, such as reproductive toxicity. Linalool (Lnl) is a monoterpene, a component of essential oils known to be produced synthetically. Additionally, Lnl has many important beneficial effects, such as anti-inflammatory and antioxidant effects. The objective of this study is to determine whether Lnl has a healing impact in opposition to testicular tissue damage due to Cd exposure. In the study, 28 male rats were divided at random into four equal groups (n = 7). No treatment was applied to the control group. CdCl2 was applied intraperitoneally to the Cd group at a dose of 3 mg/kg for the first 7 days of the trial. For the Cd + Lnl group, 3 mg/kg CdCl2 was applied intraperitoneally for the first 7 days of the trial, and 100 mg/kg/day Lnl was applied. Upon completion of all applications, the rats were sacrificed and blood samples and testicular tissue were taken. Cd exposure caused histopathological changes, oxidative stress, inflammation, and an increase in apoptotic cells in testicular tissue. However, Cd altered endocrine hormones in the hypothalamic-pituitary-gonad axis. However, Lnl application against Cd exposure was able to regulate the negativity caused by Cd in both testicular tissue and endocrine hormone levels. In conclusion, Lnl may be a potential therapeutic strategy against Cd-induced reproductive toxicity. We believe that Lnl has a high potential for further studies to determine its detailed mechanisms of action and cellular signaling pathways.

Lavandula angustifolia Essential Oil Inhibits the Ability of Fusobacterium nucleatum to Produce Volatile Sulfide Compounds, a Key Components in Oral Malodor

Oral malodor still constitutes a major challenge worldwide. A strong effort is invested in eliminating volatile sulfur compound-producing oral bacteria through organic natural products such as essential oils. Fusobacterium nucleatum is a known volatile sulfur compound-producing bacteria that inspires oral malodor. The aim of the present study was to test the effect of lavender essential oil on the bacterium's ability to produce volatile sulfide compounds, the principal components of oral malodor. Lavender (Lavandula angustifolia) essential oil was extracted by hydrodistillation and analyzed using GC-MS. The minimal inhibitory concentration (MIC) of lavender essential oil on Fusobacterium nucleatum was determined in a previous trial. Fusobacterium nucleatum was incubated anaerobically in the presence of sub-MIC, MIC, and above MIC concentrations of lavender essential oil, as well as saline and chlorhexidine as negative and positive controls, respectively. Following incubation, volatile sulfur compound levels were measured using GC (Oralchroma), and bacterial cell membrane damage was studied using fluorescence microscopy. Chemical analysis of lavender essential oil yielded five main components, with camphor being the most abundant, accounting for nearly one-third of the total lavender essential oil volume. The MIC (4 µL/mL) of lavender essential oil reduced volatile sulfur compound secretion at a statistically significant level compared to the control (saline). Furthermore, the level of volatile sulfur compound production attributed to 1 MIC of lavender essential oil was in the range of the positive control chlorhexidine with no significant difference. When examining bacterial membrane damage, 2 MIC of lavender essential oil (i.e., 8 µL/mL) demonstrated the same, showing antibacterial membrane damage values comparative to chlorhexidine. Since lavender essential oil was found to be highly effective in hindering volatile sulfur compound production by Fusobacterium nucleatum through the induction of bacterial cell membrane damage, the results suggest that lavender essential oil may be a suitable alternative to conventional chemical-based anti-malodor agents.

Flower Power: An Overview on Chemistry and Biological Impact of Selected Essential Oils from Blossoms

Natural raw materials such as essential oils have received more and more attention in recent decades, whether in the food industry, as flavorings and preservatives, or as insecticides and insect repellents. They are, furthermore, very popular as fragrances in perfumes, cosmetics, and household products. In addition, aromatherapy is widely used to complement conventional medicine. This review summarizes investigations on the chemical composition and the most important biological impacts of essential oils and volatile compounds extracted from selected aromatic blossoms, including Lavandula angustifolia, Matricaria recutita, Rosa x damascena, Jasminum grandiflorum, Citrus x aurantium, Cananga odorata, and Michelia alba. The literature was collected from PubMed, Google Scholar, and Science Direct. Blossom essential oils discussed in this work are used in a wide variety of clinical issues. The application is consistently described as safe in studies and meta-analyses, although there are notes that using essential oils can also have side effects, especially dermatologically. However, it can be considered as confirmed that essential oils have positive influences on humans and can improve quality of life in patients with psychiatric disorders, critically ill patients, and patients in other exceptional situations. Although the positive effect of essential oils from blossoms has repeatedly been reported, evidence-based clinical investigations are still underrepresented, and the need for research is demanded.

Linalool Reduces Virulence and Tolerance to Adverse Conditions of Listeria monocytogenes

Listeria monocytogenes, a foodborne pathogen causing listeriosis, poses substantial societal, economic, and public health challenges due to its resistance, persistence, and biofilm formation in the food industry. Exploring subinhibitory concentrations of compounds to target virulence inhibition and increase susceptibility to adverse conditions presents a promising strategy to mitigate its impact of L. monocytogenes and unveils new potential applications. Thus, this study aims to explore the effect of linalool on virulence factors of L. monocytogenes and potential use in the reduction in its tolerance to stressful conditions. This action was analysed considering the use of two sub-inhibitory concentrations of linalool, 0.312 and 0.625 mg/mL. We found that even with the lowest tested concentrations, a 65% inhibition of violacein production by Chromobacterium violaceum, 55% inhibition in biofilm formation by L. monocytogenes and 62% reduction on haemolysis caused by this bacterium were observed. In addition to its impact on virulence factors, linalool diminished the tolerance to osmotic stress (up to 4.3 log reduction after 24 h with 12% NaCl), as well as to high (up to 3.8 log reduction after 15 min at 55 °C) and low temperatures (up to 4.6 log reduction after 84 days with 12% NaCl at 4 °C). Thus, this study paves the way to further investigation into the potential utilization of linalool to mitigate the threat posed by L. monocytogenes in the field of food safety and public health.

Interaction between Enrofloxacin and Three Essential Oils (Cinnamon Bark, Clove Bud and Lavender Flower)-A Study on Multidrug-Resistant Escherichia coli Strains Isolated from 1-Day-Old Broiler Chickens

Avian pathogenic Escherichia coli (APEC) causes a variety of infections outside the intestine. The treatment of these infections is becoming increasingly difficult due to the emergence of multi-drug resistant (MDR) strains, which can also be a direct or indirect threat to humans as consumers of poultry products. Therefore, alternative antimicrobial agents are being sought, which could be essential oils, either administered individually or in interaction with antibiotics. Sixteen field isolates of E. coli (originating from 1-day-old broilers) and the ATCC 25922 reference strain were tested. Commercial cinnamon bark, clove bud, lavender flower essential oils (EOs) and enrofloxacin were selected to assess the sensitivity of the selected E. coli strains to antimicrobial agents. The checkerboard method was used to estimate the individual minimum inhibitory concentration (MIC) for each antimicrobial agent as well as to determine the interactions between the selected essential oil and enrofloxacin. In the case of enrofloxacin, ten isolates were resistant at MIC ≥ 2 μg/mL, three were classified as intermediate (0.5-1 μg/mL) and three as sensitive at ≤0.25 μg/mL. Regardless of the sensitivity to enrofloxacin, the MIC for cinnamon EO was 0.25% v/v and for clove EO was 0.125% v/v. All MDR strains had MIC values for lavender EO of 1% v/v, while drug-sensitive isolates had MIC of 0.5% v/v. Synergism between enrofloxacin and EO was noted more frequently in lavender EO (82.35%), followed by cinnamon EO (64.7%), than in clove EO (47.1%). The remaining cases exhibited additive effects. Owing to synergy, the isolates became susceptible to enrofloxacin at an MIC of ≤8 µg/mL. A time-kill study supports these observations. Cinnamon and clove EOs required for up to 1 h and lavender EO for up to 4 h to completely kill a multidrug-resistant strain as well as the ATCC 25922 reference strain of E. coli. Through synergistic or additive effects, blends with a lower than MIC concentration of enrofloxacin mixed with a lower EO content required 6 ± 2 h to achieve a similar effect.

Chemical composition and biological activities of essential oils of seven Cultivated Apiaceae species

The Apiaceae family contains many species used as food, spice and medicinal purposes. Different parts of plants including seeds could be used to obtain essential (EO) oils from members of the Apiaceae family. In the present study, EOs were components obtained through hydrodistillation from the seeds of anise (Pimpinella anisum), carrot (Daucus carota), celery (Apium graveolens), dill (Anethum graveolens), coriander (Coriandrum sativum), fennel (Foeniculum vulgare), and cumin (Cuminum cyminum). EO constituents were determined with Gas Chromatography/Mass Spectrometry (GC-MS) and Gas Chromatography/Flame Ionization Detector (GC-FID) and their antioxidant capacities were determined with the cupric reducing antioxidant capacity (CUPRAC) and 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) methods. The antimicrobial activity of EOs were tested against four pathogenic bacteria. Phenylpropanoids in anise (94.87%) and fennel (92.52%), oxygenated monoterpenes in dill (67.59%) and coriander (98.96%), monoterpene hydrocarbons in celery (75.42%), mono- (45.42%) and sesquiterpene- (43.25%) hydrocarbons in carrots, monoterpene hydrocarbon (34.30%) and aromatic hydrocarbons (32.92%) in cumin were the major compounds in the EOs. Anethole in anise and fennel, carotol in carrot, limonene in celery, carvone in dill, linalool in coriander, and cumin aldehyde in cumin were predominant compounds in these EOs. The high hydrocarbon content in cumin EO gave high CUPRAC activity (89.07 µmol Trolox g-1), and the moderate monoterpene hydrocarbon and oxygenated monoterpene content in dill EO resulted in higher DPPH activity (9.86 µmol Trolox g-1). The in vitro antibacterial activity of EOs against Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli was evaluated using the agar diffusion method and the minimum bactericidal concentration was determined. Coriander, cumin and dill EOs showed inhibitory effect against all tested strains except P. aeruginosa. While fennel and celery EOs were effective against E. coli and B. cereus strains, respectively, anise and carrot EOs did not show any antibacterial effect against the tested bacteria. Hierarchical Cluster Analysis (HCA) produced four groups based on EO constituents of seven species. The potential adoption of the cultivated Apiaceae species for EO extraction could be beneficial for the wild species that are endangered by over collection and consumption.

Effects of Saccharomyces cerevisiae and Kluyveromyces marxianus on the Physicochemical, Microbial, and Flavor Changes of Sauce Meat during Storage

Saccharomyces cerevisiae (S. cerevisiae) and Kluyveromyces marxianus (K. marxianus) are often used as fermenters in yogurt and alcohol, and have been less studied within meat products. The yeasts were added to sauce meat, and the uninoculated group served as a control in this study to examine and compare the changing patterns of physicochemical and flavor characteristics of S. cerevisiae and K. marxianus on sauce meat during storage. The changes in moisture content, aw, pH, thiobarbituric acid reactive substances (TBARS), and other flavor characteristics were measured in sauce meat during the first, second, fourth, and sixth months after production. The following factors were examined: moisture content, aw, pH, TBARS, peroxide value (POV), acid value (AV), soluble protein (SP), free amino acid (FAA), and volatile flavoring compounds. With VIP > 1 and p < 0.05 as the screening conditions, the partial least squares model (PLS-DA) was used to assess the distinctive flavor components in the sausages. The findings demonstrated that the three groups' changes in sauce meat were comparable during the first two months of storage but differed significantly between the 4th and 6th months. The moisture content, water activity, and pH of the sauce meat decreased gradually with the storage time; TBARS, AV, and FAA increased significantly; SP decreased significantly from 2.61 to 1.72, while POV increased to 0.03 and then decreased to 0.02. The POV and TBARS values of the yeast-infected meat were substantially lower than those of the control group, and the POV and TBARS values of the meat inoculated with S. cerevisiae were particularly decreased (p < 0.05). The POV and TBARS values of SC (S. cerevisiae group) decreased by 49.09% and 40.15%, respectively, compared to CK (the control group) at the time of storage until June. The experimental group (KM: K. marxianus group) significantly increased the SP and FAA values of the sauce meat (p < 0.05) by 32.4% and 29.84% compared to the CK group, respectively. Esters and olefins as well as alcohols and esters were much greater in meat that had been supplemented with S. cerevisiae and K. marxianus than in meat from the control group. In conclusion, inoculating sauce meat with S. cerevisiae can significantly enhance the quality and flavor of sauce meat while it is being stored.

Update on new trends and progress of natural active ingredients in the intervention of Alzheimer's disease, based on understanding of traditional Chinese and Western relevant theories: A review

Alzheimer's disease (AD) is one of the major neurological disorders causing death in the elderly worldwide. As a neurodegenerative disease that is difficult to prevent and cure, the pathogenesis of AD is complex and there is no effective cure. A variety of natural products derived from plants have been reported to have promising anti-AD activities, including flavonoids, terpenes, phenolic acids and alkaloids, which can effectively relieve the symptoms of AD in a variety of ways. This paper mainly reviews the pharmacological activity and mechanisms of natural products against AD. Although the clinical efficacy of these plants still needs to be determined by further high-quality studies, it may also provide a basis for future researchers to study anti-AD in depth.

Promoter characterization of a citrus linalool synthase gene mediating interspecific variation in resistance to a bacterial pathogen

BACKGROUND

Terpenoids play essential roles in plant defense against biotic stresses. In Citrus species, the monoterpene linalool mediates resistance against citrus canker disease caused by the gram-negative bacteria Xanthomonas citri subsp. citri (Xcc). Previous work had associated linalool contents with resistance; here we characterize transcriptional responses of linalool synthase genes.

RESULTS

Leaf linalool contents are highly variable among different Citrus species. "Dongfang" tangerine (Citrus reticulata), a species with high linalool levels was more resistant to Xcc than "Shatian" pummelo (C. grandis) which accumulates only small amounts of linalool. The coding sequences of the major leaf-expressed linalool synthase gene (STS4) are highly conserved, while transcript levels differ between the two Citrus species. To understand this apparent differential transcription, we isolated the promoters of STS4 from the two species, fused them to a GUS reporter and expressed them in Arabidopsis. This reporter system revealed that the two promoters have different constitutive activities, mainly in trichomes. Interestingly, both linalool contents and STS4 transcript levels are insensitive to Xcc infestation in citrus plants, but in these transgenic Arabidopsis plants, the promoters are activated by challenge of a bacterial pathogen Pseudomonas syringae, as well as wounding and external jasmonic acid treatment.

CONCLUSIONS

Our study reveals variation in linalool and resistance to Xcc in citrus plants, which may be mediated by different promoter activities of a terpene synthase gene in different Citrus species.

Biological Activities of Natural Products III

The search for natural products that display biological activity is invariably an attractive research area for scientific centers and teams from around the world [...].

Phytochemical characterization, antioxidant activity and antihypertensive evaluation of Ocimum basilicum L. in l-NAME induced hypertensive rats and its correlation analysis

Ocimum basilicum Linn. (basil) is an aromatic culinary herb that has shown a great potential in therapeutic world. It has many promising pharmacological activities that make it centre for investigations for many researchers. Current study has been planned to determine chemical constituents of basil leaves extracts and their in-vitro and ex-vivo antioxidant and in-vivo antihypertensive potential. GC-MS studies of non-polar extracts showed presence of 75 compounds including monoterpenes, hydrocarbons, sesquiterpenes, triterpenes, phyto-sterols and phthalates. Higher percentages of fatty acids were also identified. The major compounds include linalool (7.65%), terpineol (1.42%), tau-cadinol (13.55%), methyl palmitate (14.24%), palmitic acid (14.31%), linolenic acid (1.30%) and methyl linolenate (17.72%). Electron spray ionization mass spectrometry ESI-HRMS/MS of the polar extracts revealed the presence of alkaloids, phenolic acid, amino acid, coumarin, lignin, flavanoid and terpene derivative. Total phenolic content and total flavonoid content were determined using spectrophotometric technique and calculated as gallic acid equivalents GAE/g dry weight and rutin equivalent RE/g of dry weight respectively. The highest phenolic content and flavonoid content were found in ethyl acetate extract 9.40 mg GAE/g and 15.9 mg RE/g of dry weight. All the extracts showed significant antioxidant activity in DPPH and ABTS cation decolorization assays. Dichloromethane extract possess the highest DPPH scavenging activity, i.e., 64.12% ± 0.23 at concentration of 4 mg/ml. Moreover in ex-vivo studies all the extracts showed prominent effect by inhibiting AAPS induce oxidation in Human erythrocytes being 69.24% ± 0.18 in dichloromethane extract, 64.44% ± 0.04 in ethyl acetate and 53.33% ± 0.09 in acetone extract. The methanol extract of O. basilicum exhibited significant decrease in systolic blood pressure in l-Name induced hypertensive rats at the dose of 50 mg/kg for 28 days. Total phenolic content had a higher linear correlation (r = 0.678) with antihypertensive activity, with a level of significance 95% showing that phenolic compounds in the leaves of the plant has important role in inhibiting l -NAME induced hypertension while flavonoid compounds may play a key role in the antioxidant activities of the plant, through synergism. Conclusively, O. basilicum leaves with bioactive metabolites are a potential source for the development of antihypertensive drugs.

Essential Oils from Origanum vulgare subsp. virens (Hoffmanns. & Link) Ietsw. Grown in Portugal: Chemical Diversity and Relevance of Chemical Descriptors

Origanum vulgare L. is a well-known aromatic and medicinal plant, whose essential oil (EO) has recognised flavouring and medicinal properties. In this study, Origanum vulgare subsp. virens (Hoffmanns. & Link) Ietsw. EOs, isolated from accessions grown in experimental fields, were evaluated. The plant material was grown from rooted cuttings or nutlets (fruits), originally collected in 20 regions in mainland Portugal and harvesting for EO isolation was performed in two years. EOs were isolated by hydrodistillation and analysed by gas chromatography and gas chromatography-mass spectrometry, for EO quantification and identification, respectively. EO yields ranged from <0.05-3.3% for rooted cuttings, with oregano samples obtained in Portalegre and Alandroal, respectively. Ninety-one compounds were identified, mainly grouped in oxygen-containing monoterpenes and monoterpene hydrocarbons. EO agglomerative cluster analysis evidenced two main clusters, with the first subdivided into four subclusters. From the obtained data, the putative O. vulgare subsp. virens chemotypes are carvacrol, thymol and linalool, with γ-terpinene, p-cymene, cis- and trans-β-ocimene also contributing as these EOs chemical descriptors. The comparison between the present data and a survey of the existing literature on Portuguese O. vulgare reinforces the major variability of this species' EOs and emphasises the importance of avoiding wild collections to obtain a defined chemical type of crop production of market relevance.

Antibacterial activity and metabolomic analysis of linalool against bovine mastitis pathogen Streptococcus agalactiae

Streptococcus agalactiae is among the major causative pathogens of bovine mastitis, as well as crucial pathogen leading to human morbidity and mortality. Being a promising natural antibacterial agent, linalool has been broadly applied in medicine and food processing. However, its antibacterial effect against S. agalactiae has barely been elucidated. This study is the first to investigate the antibacterial activity and action mechanism of linalool against S. agalactiae causing bovine mastitis. Linalool exhibited significant antibacterial activity against S. agalactiae, with an inhibition zone diameter of 23 mm and a minimum inhibitory concentration of 1.875 μL/mL. In addition, linalool damaged cell structural integrity of S. agalactiae, leading to the leakage of intracellular components (alkaline phosphatase, nucleic acids and protein). Linalool also exhibited a scavenging effect on biofilm. Moreover, untargeted metabolomics analysis revealed that linalool stress substantially disrupted intracellular metabolism of S. agalactiae. Linalool caused energy metabolism disorder, and obstructed nucleic acid synthesis in S. agalactiae. Furthermore, downregulation of amino acids (e.g., proline, alanine) and upregulation of saturated fatty acids provide strong evidence for linalool induced cell wall and membrane damage. Overall, linalool exhibited strong antibacterial activity against S. agalactiae by destroying the cell structure and disrupting intracellular metabolism. This study provides a new insight and theoretical foundation for linalool application in preventing S. agalactiae infection.

Essential Oils in the Treatment of Various Types of Acne-A Review

Acne is a chronic, common disease that poses a significant therapeutic, psychological and social problem. The etiopathogenesis of this disease is not fully understood. Drugs used in general and external therapy should have anti-seborrhoeic, anticomadogenic, bactericidal, bacteriostatic, and anti-inflammatory properties. Acne treatment is often associated with the long-term use of antibiotics, contributing to the global antibiotic resistance crisis. In order to solve this problem, attention has been paid to essential oils and their terpene components with potent antimicrobial, anti-inflammatory, and antioxidant properties. Research shows that certain essential oils effectively reduce inflammatory acne lesions through mechanisms related to the sebaceous glands, colonization of Cutibacterium acnes, and reactive oxygen species (ROS). An example is tea tree oil (TTO), a more commonly used topical agent for treating acne. TTO has antimicrobial and anti-inflammatory activity. The paper presents the latest scientific information on the activity and potential use of specific essential oils in treating acne. Evidence of antibacterial, anti-inflammatory, and antioxidant activity of several essential oils and their main components was presented, indicating the possibility of using them in the treatment of acne.