Linalool bioactive properties and potential applicability in drug delivery systems

Natural Compounds in the Battle against Microorganisms-Linalool

The purpose of this article is to present recent studies on the antimicrobial properties of linalool, the mechanism of action on cells and detoxification processes. The current trend of employing compounds present in essential oils to support antibiotic therapy is becoming increasingly popular. Naturally occurring monoterpene constituents of essential oils are undergoing detailed studies to understand their detailed effects on the human body, both independently and in doses correlated with currently used pharmaceuticals. One such compound is linalool, which is commonly found in many herbs and is used to flavor black tea. This compound is an excellent fragrance additive for cosmetics, enhancing the preservative effect of the formulations used in them or acting as an anti-inflammatory on mild skin lesions. Previous studies have shown that it is extremely important due to its broad spectrum of biological activities, i.e., antioxidant, anti-inflammatory, anticancer, cardioprotective and antimicrobial. Among opportunistic hospital strains, it is most active against Gram-negative bacteria. The mechanism of action of linalool against microorganisms is still under intensive investigation. One of the key aspects of linalool research is biotransformation, through which its susceptibility to detoxification processes is determined.

Basil (Ocimum basilicum L.) Leaves as a Source of Bioactive Compounds

Basil (Ocimum basilicum L.) is an annual spicy plant generally utilized as a flavouring agent for food. Basil leaves also have pharmaceutical properties due to the presence of polyphenols, phenolic acids, and flavonoids. In this work, carbon dioxide was employed to extract bioactive compounds from basil leaves. Extraction with supercritical CO₂ (p = 30 MPa; T = 50 °C) for 2 h using 10% ethanol as a cosolvent was the most efficient method, with a yield similar to that of the control (100% ethanol) and was applied to two basil cultivars: “Italiano Classico” and “Genovese”. Antioxidant activity, phenolic acid content, and volatile organic compounds were determined in the extracts obtained by this method. In both cultivars, the supercritical CO₂ extracts showed antiradical activity (ABTS^●+ assay), caffeic acid (1.69–1.92 mg/g), linalool (35–27%), and bergamotene (11–14%) contents significantly higher than those of the control. The polyphenol content and antiradical activity measured by the three assays were higher in the “Genovese” cultivar than in the “Italiano Classico” cultivar, while the linalool content was higher (35.08%) in the “Italiano Classico” cultivar. Supercritical CO₂ not only allowed us to obtain extracts rich in bioactive compounds in an environmentally friendly way but also reduced ethanol consumption.

Respiratory Depression as Antibacterial Mechanism of Linalool against Pseudomonas fragi Based on Metabolomics

Linalool showed a broad-spectrum antibacterial effect, but few studies have elucidated the antibacterial mechanism of linalool on Pseudomonas fragi (P. fragi) to date. The present study aimed to uncover the antimicrobial activity and potential mechanism of linalool against P. fragi by determining key enzyme activities and metabolites combined with a high-throughput method and metabolomic pathway analysis. As a result, linalool had excellent inhibitory activity against P. fragi with MIC of 1.5 mL/L. In addition, the presence of linalool significantly altered the intracellular metabolic profile and a total of 346 differential metabolites were identified, of which 201 were up-regulated and 145 were down-regulated. The highlight pathways included beta-alanine metabolism, pantothenic acid and CoA metabolism, alanine, aspartate and glutamate metabolism, nicotinate and nicotinamide metabolism. Overall, linalool could cause metabolic disorders in cells, and the main metabolic pathways involved energy metabolism, amino acid metabolism and nucleic acid metabolism. In particular, the results of intracellular ATP content and related enzymatic activities (ATPase, SDH, and GOT) also highlighted that energy limitation and amino acid disturbance occurred intracellularly. Together, these findings provided new insights into the mechanism by which linalool inhibited P. fragi and theoretical guidance for its development as a natural preservative.

Mixed consortium of microbial inoculants improves yield and essential oil profile of coriander

Coriander (Coriandrum sativum L.), one of the oldest spice plants globally, has wide usage, mainly owing to its essential oil content. This study investigated the effects of rhizobacteria, mycorrhizae, and their combination on the yield and essential oil profile of coriander. The treatments resulted in statistically higher yield properties and essential oil values than the control. The effects of the microorganism treatments on the yield characteristics were not statistically different. However, the treatments significantly affected the essential oil content and yield. While the arbuscular mycorrhizal fungi and combined application of the microorganisms were statistically equal, arbuscular mycorrhizal fungi had a higher value in essential oil content and yield by 0.75% and 11.8 L ha^-1, respectively. The combined application resulted in higher values of linalool (9.47%) and γ-terpinene (6.75%), the components with the highest rate in the essential oil composition. The principal component analysis highlighted the importance of the combined application on the crucial components. In the light of the results, beneficial microorganism treatments were considered significant for yield and essential oil enhancement. Therefore, the wide use of these treatments will highly contribute to coriander cultivation.

Antifungal activity of linalool against fluconazole-resistant clinical strains of vulvovaginal Candida albicans and its predictive mechanism of action

Candida albicans is the most frequently isolated opportunistic pathogen in the female genital tract, with 92.3% of cases in Brazil associated with vulvovaginal candidiasis (VVC). Linalool is a monoterpene compound from plants of the genera Cinnamomum, Coriandrum, Lavandula, and Citrus that has demonstrated a fungicidal effect on strains of Candida spp., but its mechanism of action is still unknown. For this purpose, broth microdilution techniques were applied, as well as molecular docking in a predictive manner for this mechanism. The main results of this study indicated that the C. albicans strains analyzed were resistant to fluconazole and sensitive to linalool at a dose of 256 µg/mL. Furthermore, the increase in the minimum inhibitory concentration (MIC) of linalool in the presence of sorbitol and ergosterol indicated that this molecule possibly affects the cell wall and plasma membrane integrity of C. albicans. Molecular docking of linalool with proteins that are key in the biosynthesis and maintenance of the cell wall and the fungal plasma membrane integrity demonstrated the possibility of linalool interacting with three important enzymes: 1,3-β-glucan synthase, lanosterol 14α-demethylase, and Δ 14-sterol reductase. In silico analysis showed that this monoterpene has theoretical but significant oral bioavailability, low toxic potential, and high similarity to pharmaceuticals. Therefore, the findings of this study indicated that linalool probably causes damage to the cell wall and plasma membrane of C. albicans, possibly by interaction with important enzymes involved in the biosynthesis of these fungal structures, in addition to presenting low in silico toxic potential.

Exploring the medicinally important secondary metabolites landscape through the lens of transcriptome data in fenugreek (Trigonella foenum graecum L.)

Fenugreek (Trigonella foenum-graecum L.) is a self-pollinated leguminous crop belonging to the Fabaceae family. It is a multipurpose crop used as herb, spice, vegetable and forage. It is a traditional medicinal plant in India attributed with several nutritional and medicinal properties including antidiabetic and anticancer. We have performed a combined transcriptome assembly from RNA sequencing data derived from leaf, stem and root tissues. Around 209,831 transcripts were deciphered from the assembly of 92% completeness and an N50 of 1382 bases. Whilst secondary metabolites of medicinal value, such as trigonelline, diosgenin, 4-hydroxyisoleucine and quercetin, are distributed in several tissues, we report transcripts that bear sequence signatures of enzymes involved in the biosynthesis of such metabolites and are highly expressed in leaves, stem and roots. One of the antidiabetic alkaloid, trigonelline and its biosynthesising enzyme, is highly abundant in leaves. These findings are of value to nutritional and the pharmaceutical industry.

Terpenes Combinations Inhibit Biofilm Formation in Staphyloccocus aureus by Interfering with Initial Adhesion

The biofilm is a conglomerate of cells surrounded by an extracellular matrix, which contributes to the persistence of infections. The difficulty in removing the biofilm drives the research for new therapeutic options. In this work, the effect of terpenes (−)-trans-Caryophyllene, (S)-cis-Verbenol, (S)-(−)-Limonene, (R)-(+)-Limonene, and Linalool was evaluated, individually and in combinations on bacterial growth, by assay with resazurin; the formation of biofilm, by assay with violet crystal; and the expression of associated genes, by real-time PCR, in two clinical isolates of Staphyloccocus aureus, ST30-t019 and ST5-t311, responsible for more than 90% of pediatric infections by this pathogen in Paraguay. All combinations of terpenes can inhibit biofilm formation in more than 50% without affecting bacterial growth. The most effective combination was (−)-trans-Caryophyllene and Linalool at a 500 μg/mL concentration for each, with an inhibition percentage of 88%. This combination decreased the expression levels of the sdrD, spa, agr, and hld genes associated with the initial cell adhesion stage and quorum sensing. At the same time, it increased the expression levels of the cap5B and cap5C genes related to the production of capsular polysaccharides. The combinations of compounds tested are promising alternatives to inhibit biofilm formation in S. aureus.

In-Depth Study of Thymus vulgaris Essential Oil: Towards Understanding the Antibacterial Target Mechanism and Toxicological and Pharmacological Aspects

Questions have been raised apropos the emerging problem of microbial resistance, which may pose a great hazard to the human health. Among biosafe compounds are essential oils which captured consumer draw due to their multifunctional properties compared to chemical medication drugs. Here, we examined the chemical profile and the mechanism(s) of action of the Thymus vulgaris essential oil (TVEO) against a Gram-negative bacterium Salmonella enterica Typhimurium ATTCC 10028 (S. enterica Typhimurium ATTCC 10028) and two Gram-positive bacteria Staphyloccocus aureus ATCC 6538 (S. aureus ATCC 6538) and Listeria monocytogenes ATCC 19117 (L. monocytogenes ATCC 19117). Findings showed that TVEO was principally composed of thymol, o-cymene, and γ-terpinene with 47.44, 16.55, and 7.80%, respectively. Molecular docking simulations stipulated that thymol and β-sesquiphellandrene (a minor compound at 1.37%) could target multiple bacterial pathways including topoisomerase II and DNA and RNA polymerases of the three tested bacteria. This result pointed plausible impairments of the pathogenic bacteria cell replication and transcription processes. Through computational approach, the VEGA quantitative structure–activity relationship (QSAR) model, we revealed that among twenty-six TVEO compounds, sixteen had no toxic effects and could be safe for human consumption as compared to the Food and Drug Administration (FDA) approved drugs (ciprofloxacin and rifamycin SV). Assessed by the SwissADME server, the pharmacokinetic profile of all identified TVEO compounds define their absorption, distribution, metabolism, and excretion (ADME) properties and were assessed. In order to predict their biological activity spectrum based on their chemical structure, all TVEO compounds were subjected to PASS (Prediction of Activity Spectra for Substances) online tool. Results indicated that the tested compounds could have multiple biological activities and various enzymatic targets. Findings of our study support that identified compounds of TVEO can be a safe and effective alternative to synthetic drugs and can easily combats hazardous multidrug-resistant bacteria.

Comparative proteomics reveals biochemical changes in Salvia miltiorrhiza Bunge during sweating processing

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia miltiorrhiza Bunge is a bulk medicinal material used in traditional Chinese medicine, that can cure cardiovascular diseases, neurasthenia, and other conditions. Sweating is a frequently used method of processing S. miltiorrhiza for medical applications. We previously demonstrated changes to the metabolic profile of linoleic acid, glyoxylate, and dicarboxylate after Sweating. However, this alteration has not been explained at the molecular level.

MATERIALS AND METHODS

Fresh roots of Salvia miltiorrhiza Bunge were treated by the Sweating processing, and then the tandem mass tag technique was used to compare the proteome difference between Sweating S. miltiorrhiza and non-Sweating S. miltiorrhiza.

RESULTS

We identified a total of 850 differentially expressed proteins after Sweating treatment in S. miltiorrhiza, including 529 upregulated proteins and 321 downregulated proteins. GO enrichment analysis indicated that these differentially expressed proteins are involved in external encapsulating structure, cell wall, oxidoreductase activity, ligase activity, and others. Further analysis showed that CYP450, the pathogenesis-related protein Bet v 1 family, and the peroxidase domain were the major protein domains. KEGG enrichment identified 18 pathways, of which phenylpropanoid biosynthesis is the most important one related to the metabolite profile and is the principal chemical component of S. miltiorrhiza.

CONCLUSION

This study addressed potential molecular mechanisms in S. miltiorrhiza after Sweating, and the findings provide reasons for the changes in biochemical properties and metabolites changes which might cause pharmacological variation at the proteome level.

An update on the progress of microbial biotransformation of commercial monoterpenes

Monoterpenes, a class of isoprenoid compounds, are extensively used in flavor, fragrance, perfumery, and cosmetics. They display many astonishing bioactive properties of biological and pharmacological significance. All monoterpenes are derived from universal precursor geranyl diphosphate. The demand for new monoterpenoids has been increasing in flavor, fragrances, perfumery, and pharmaceuticals. Chemical methods, which are harmful for human and the environment, synthesize most of these products. Over the years, researchers have developed alternative methods for the production of newer monoterpenoids. Microbial biotransformation is one of them, which relied on microbes and their enzymes. It has produced many new desirable commercially important monoterpenoids. A growing number of reports reflect an ever-expanding scope of microbial biotransformation in food and aroma industries. Simultaneously, our knowledge of the enzymology of monoterpene biosynthetic pathways has been increasing, which facilitated the biotransformation of monoterpenes. In this article, we have covered the progress made on microbial biotransformation of commercial monoterpenes with a brief introduction to their biosynthesis. We have collected several reports from authentic web sources, including Google Scholar, Pubmed, Web of Science, and Scopus published in the past few years to extract information on the topic.

Linalool as a Therapeutic and Medicinal Tool in Depression Treatment: A Review

Depression is a prevalent disease worldwide, limiting psychosocial functioning and thequality of life. Linalool is the main constituent of some essential oils from aromatic plants, representing about 70% of these volatile concentrates. Evidence of the linalool activity on the central nervous system, mainly acting as an antidepressant agent, is increasingly abundant. This review aimed to extend the knowledge of linalool's antidepressant action mechanisms, which is fundamental for future research, intending to highlight this natural compound as a new antidepressant phytomedication. A critical analysis is proposed here with probable hypotheses of the synergic mechanisms that support the evidence of antidepressant effects of the linalool. The literature search has been conducted in databases for published scientific articles before December 2020, using relevant keywords. Several pieces of evidence point to the anticonvulsant, sedative, and anxiolytic actions. In addition to these activities, other studies have revealed that linalool acts on the monoaminergic and neuroendocrine systems, inflammatory process, oxidative stress, and neurotrophic factors, such as BDNF, resulting in considerable advances in the knowledge of the etiology of depression. In this context, linalool emerges as a promising bioactive compound in the therapeutic arsenal, capable of interacting with numerous pathophysiological factors and acting on several targets. This review claims to contribute to future studies, highlighting the gaps in the linalool knowledge, such as its kinetics, doses, routes of administration, and multiple targets of interaction, to clarify its antidepressant activity.

Vanadium-doped phosphomolybdic acids as catalysts for geraniol oxidation with hydrogen peroxide

In this work, vanadium-doped phosphomolybdic acids were evaluated as catalysts in green oxidation routes of terpene alcohols with hydrogen peroxide. A series of phosphomolybdic acids containing a variable load of vanadium cations (i.e., V5+ ions) were synthesized, and tested as catalysts in geraniol oxidation, the model molecule selected. All the catalysts were characterized by powder X-ray diffraction, attenuated diffuse reflectance infrared spectroscopy, UV-Vis spectroscopy, thermogravimetric analysis, N2 adsorption-desorption isotherms, scanning electronic microscopy, X-ray dispersive spectroscopy, and n-butylamine potentiometric titration. Various catalysts were evaluated; phosphomolybdic acids with general formulae H3+n PMo12-n V n O40 (n = 0, 1, 2 and 3), and common Brønsted acids (i.e., H2SO4, H3PO4, and p-toluene sulfonic acid). Among them, vanadium monosubstituted phosphomolybdic acid was the most active catalyst and selective toward epoxide. The effect of main reaction variables, such as temperature, load catalyst, and reactant stoichiometry was assessed. Evaluating the effect of substrate, it was verified that only allylic alcohols such as geraniol and nerol were successfully epoxidized, demonstrating that this is a hydroxy group-assisted reaction. The effect of vanadium doping on the physicochemical properties of the phosphomolybdic acid catalysts was evaluated and used to explain their catalytic performance.

The Effect of Bergamot Essential Oil Aromatherapy on Improving Depressive Mood and Sleep Quality in Postpartum Women: A Randomized Controlled Trial

BACKGROUND

The postpartum period is a physiologically and psychologically crucial transition phase for every woman who gives birth. Aromatherapy may improve mood and alleviate sleep challenges. However, few randomized controlled clinical trials have focused on the effect of aromatherapy in postpartum women.

PURPOSE

This study was designed to explore the effect of a bergamot essential oil aromatherapy intervention on depressive mood and sleep quality in postpartum women.

METHODS

This randomized controlled trial used consecutive sampling. The participants were all women in a postpartum care center in eastern Taiwan and were randomly assigned to either the experimental (n = 29) or control (n = 31) group. Bergamot essential oil aroma was used in the experimental group, and pure water aroma was used in the control group. The experimental and control interventions were both performed while the participants were residents at the postpartum care center in the afternoon for 15 minutes each day. Before the aroma intervention, pretests were conducted using the Edinburgh Postnatal Depression Scale and the Postpartum Sleep Quality Scale. The first and second posttests were conducted using the same two scales at 2 and 4 weeks after the intervention, respectively.

RESULTS

At both the first and second posttests, depressive mood was significantly lower (p < .001) in the experimental group than in the control group, supporting the positive effect of the bergamot essential oil aroma intervention on depressive mood in postpartum women. No significant intergroup difference in sleep quality (p > .05) was observed at either the first or second posttest, indicating an uncertain effect of the bergamot essential oil aroma intervention on sleep quality.

CONCLUSIONS/IMPLICATIONS FOR PRACTICE

The results of this study support the effectiveness of bergamot essential oil aromatherapy in alleviating depressive mood in postpartum women. In addition, the results provide a practical reference for clinical postpartum nursing care.

Potential antifungal impact of citral and linalool administered individually or combined with fluconazole against clinical isolates of Candida krusei

Introduction: Candida krusei is recognized as a major fungal pathogen in patients with immunodeficiency disorders. The present study aimed at investigating the anticandidal activities of citral and linalool combined with fluconazole (FLZ) against FLZ-resistant C. krusei strains. Methods: Antifungal activities were evaluated by the broth microdilution (MD) method to determine the minimum inhibitory and fungicidal concentrations (namely, MICs and MFCs) according to the Clinical and Laboratory Standards Institute (CLSI) M27-A3 document. The interactions were further evaluated using fractional inhibitory concentration indices (FICIs) for combinations of citral+FLZ and linalool+FLZ, calculated from checkerboard MD assays. Results: The mean ± standard deviation (SD) MIC values of citral, linalool, and FLZ against the C. krusei isolates were 70.23 ± 17, 150 ± 38.73, and 74.66 ± 36.95 μg/mL, respectively. Some fungicidal activities were also observed for citral (2.5) and linalool (1.53) against the C. krusei isolates. The FICI values of citral+FLZ and linalool+FLZ for the C. krusei isolates ranged from 0.4 to 1.00 and 0.19 to 0.63, respectively. The additive and synergistic interactions of linalool + FLZ were further observed in 12 (57.1%) and 9 (42.9%) C. krusei isolates. However, there was an additive interaction for citral + FLZ in 17 (80.9%) isolates. They also showed a synergistic interaction in only four (19.1%) isolates. Moreover, linalool and citral plus FLZ did not have any antagonistic effect on any isolates. Conclusion: The study findings support the possible capabilities of citral and linalool, as anticandidal agents, and FLZ might be supplemented with citral and/or linalool for treating FLZ-resistant C. krusei infections.

Ultrasonic Extraction of Bioactive Compounds from Green Soybean Pods and Application in Green Soybean Milk Antioxidants Fortification

Green soybean (Glycine max L.) pods (GSP) are agro-industrial waste from the production of frozen green soybean and milk. These pods contain natural antioxidants and various bioactive compounds that are still underutilized. Polyphenols and flavonoids in GSP were extracted by ultrasound technique and used in the antioxidant fortification of green soybean milk. The ultrasound extraction that yielded the highest total polyphenol content and antioxidant activities was 50% amplitude for 10 min. Response surface methodology was applied to analyze an optimum ultrasonic-assisted extraction (UAE) condition of these variables. The highest desirability was found to be 50% amplitude with an extraction time of 10.5 min. Under these conditions, the experimental total phenolic content, total flavonoid content, and antioxidant activity were well matched with the predicted values (R² > 0.70). Fortification of the GSP extracts (1-3% v/v) in green soybean milk resulted in higher levels of bioactive compounds and antioxidant activity in a dose-dependent manner. Procyanidins were found to be the main polyphenols in dried GSP crude extracts, which were present at a concentration of 0.72 ± 0.01 mg/100 g. The addition of GSP extracts obtained by using an ultrasound technique to green soybean milk increased its bioactive compound content, especially procyanidins, as well as its antioxidant activity.

Pulsed Electric Field-Assisted Extraction of Aroma and Bioactive Compounds From Aromatic Plants and Food By-Products

In this work, the effect of pulsed electric field (PEF) pre-treatment on the extractability in green solvents (i. e., ethanol–water mixture and propylene glycol) of target aroma and bioactive compounds, such as vanillin from vanilla pods, theobromine and caffeine from cocoa bean shells, linalool from vermouth mixture, and limonene from orange peels, was investigated. The effectiveness of PEF as a cell disintegration technique in a wide range of field strength (1–5 kV/cm) and energy input (1–40 kJ/kg) was confirmed using impedance measurements, and results were used to define the optimal PEF conditions for the pre-treatment of each plant tissue before the subsequent solid–liquid extraction process. The extracted compounds from untreated and PEF-treated samples were analyzed via GC-MS and HPLC-PDA analysis. Results revealed that the maximum cell disintegration index was detected for cocoa bean shells and vanilla pods (Z_p = 0.82), followed by vermouth mixture (Z_p = 0.77), and orange peels (Z_p = 0.55). As a result, PEF pre-treatment significantly enhanced the extraction yield of the target compounds in both solvents, but especially in ethanolic extracts of vanillin (+14%), theobromine (+25%), caffeine (+34%), linalool (+114%), and limonene (+33%), as compared with untreated samples. Moreover, GC-MS and HPLC-PDA analyses revealed no evidence of degradation of individual compounds due to PEF application. The results obtained in this work suggest that the application of PEF treatment before solid–liquid extraction with green solvents could represent a sustainable approach for the recovery of clean labels and natural compounds from aromatic plants and food by-products.

Anti-Diabetes, Anti-Gout, and Anti-Leukemia Properties of Essential Oils from Natural Spices Clausena indica, Zanthoxylum rhetsa, and Michelia tonkinensis

Essential oils (EOs) of Clausena indica fruits, Zanthoxylum rhetsa fruits, and Michelia tonkinensis seeds were analyzed for their phytochemical profiles and biological activities, including anti-diabetes, anti-gout, and anti-leukemia properties. Sixty-six volatile compounds were identified by gas chromatography–mass spectrometry (GC–MS), in which, myristicin (68.3%), limonene (44.2%), and linalool (49.3%) were the most prominent components of EOs extracted from C. indica, Z. rhetsa, and M. tonkinensis, respectively. In addition, only EOs from C. indica inhibited the activities of all tested enzymes comprising α-amylase (IC₅₀ = 7.73 mg/mL), α-glucosidase (IC₅₀ = 0.84 mg/mL), and xanthine oxidase (IC₅₀ = 0.88 mg/mL), which are related to type 2 diabetes and gout. Remarkably, all EOs from C. indica, Z. rhetsa (IC₅₀ = 0.73 mg/mL), and M. tonkinensis (IC₅₀ = 1.46 mg/mL) showed a stronger anti-α-glucosidase ability than acarbose (IC₅₀ = 2.69 mg/mL), a known anti-diabetic agent. Moreover, the growth of leukemia cell Meg-01 was significantly suppressed by all EOs, of which, the IC₅₀ values were recorded as 0.32, 0.64, and 0.31 mg/mL for EOs from C. indica, Z. rhetsa, and M. tonkinensis, respectively. As it stands, this is the first report about the inhibitory effects of EOs from C. indica and Z. rhetsa fruits, and M. tonkinensis seeds on the human leukemia cell line Meg-01 and key enzymes linked to diabetes and gout. In conclusion, the present study suggests that EOs from these natural spices may be promising candidates for pharmaceutical industries to develop nature-based drugs to treat diabetes mellitus or gout, as well as malignant hematological diseases such as leukemia.

Growth-phase specific regulation of cviI/R based quorum sensing associated virulence factors in Chromobacterium violaceum by linalool, a monoterpenoid

Quorum sensing (QS)-dependent gene regulation in bacteria performs a vital role in synchronization of cell-density-dependent functions. In Chromobacterium violaceum QS-dependent cviI/R regulatory genes are activated during the mid- or late-exponential phase of growth. However, sufficient evidence is lacking on the role of QS inhibitors on gene regulation at different phases of growth. Hence, we report the role of linalool, a natural monoterpenoid on QS mediated gene regulation at different stages of growth in C. violaceum by performing biosensor, growth kinetic and gene expression studies. In vitro and in vivo studies were performed for establishing role of linalool in reducing the virulence and infection by using HEK-293 T cell lines and Caenorhabditis elegans models respectively. C. violaceum CV026 with C₆-HSL was used as control. The results showed linalool to be a QS inhibitor with an estimated IC₅₀ of 63 µg/mL for violacein inhibition. At this concentration the cell density difference (delta OD₆₀₀) of 0.14 from the compound was observed indicating the quorum concentration. The expression of cviI/R was initiated at mid-log phase (~ 18 h) and reached the maximum at 36 h in control whereas in treatment it remained significantly downregulated at all time points. The expression of violacein biosynthetic genes vioA, vioC, vioD and vioE was also downregulated by linalool. Infection studies with linalool showed higher survival rates in HEK-293T cell lines and C. elegans compared to the infection control. Taken together, this study proves linalool to be a QS inhibitor capable of attenuation of QS by controlling the cell density through cviI/R downregulation at the early phase of growth and hence offering scope for its application for controlling infections.

Functional conservation of Anopheline linalool receptors through 100 million years of evolution

Insects rely on olfactory receptors to detect and respond to diverse environmental chemical cues. Detection of semiochemicals by these receptors modulates insect behavior and has a direct impact on species fitness. Volatile organic compounds (VOCs) are released by animals and plants and can provide contextual cues that a blood meal host or nectar source is present. One such VOC is linalool, an enantiomeric monoterpene, that is emitted from plants and bacteria species. This compound exists in nature as one of two possible stereoisomers, (R)-(-)-linalool or (S)-(+)-linalool. In this study, we use a heterologous expression system to demonstrate differential responsiveness of a pair of Anopheline odorant receptors (Ors) to enantiomers of linalool. The mosquitoes Anopheles gambiae and Anopheles stephensi encode single copies of Or29 and Or53, which are expressed in the labella of An. gambiae. (S)-(+)-linalool activates Or29 orthologs with a higher potency than (R)-(-)-linalool, while the converse is observed for Or53 orthologs. The conservation of these receptors across a broad range of Anopheline species suggests they may function in the discrimination of linalool stereoisomers, thereby influencing the chemical ecology of mosquitoes. One potential application of this knowledge would be in the design of novel attractants or repellents to be used in integrated pest management practices.

Metagenomic Study on Chinese Homemade Paocai: The Effects of Raw Materials and Fermentation Periods on the Microbial Ecology and Volatile Components

“Chinese paocai” is typically made by fermenting red radish or cabbage with aged brine (6–8 w/w). This study aimed to reveal the effects of paocai raw materials on fermentation microorganisms by metagenomics sequencing technology, and on volatile organic compounds (VOCs) by gas chromatography–mass spectroscopy, using red radish or cabbage fermented for six rounds with aged brine. The results showed that in the same fermentation period, the microbial diversity in cabbage was higher than that in red radish. Secundilactobacillus paracollinoides and Furfurilactobacillus siliginis were the characteristic bacteria in red radish paocai, whereas 15 species of characteristic microbes were found in cabbage. Thirteen kinds of VOCs were different between the two raw materials and the correlation between the microorganisms and VOCs showed that cabbage paocai had stronger correlations than radish paocai for the most significant relationship between 4-isopropylbenzyl alcohol, α-cadinol, terpinolene and isobutyl phenylacetate. The results of this study provide a theoretical basis for understanding the microbiota and their relation to the characteristic flavors of the fermented paocai.

Variability in the Chemical Composition of a New Aromatic Plant Artemisia balchanorum in Southern Russia

Lemon wormwood Artemisia balchanorum was recently introduced to southern Russia as a new aromatic plant. Based on biological and chemical characteristics, several populations with dominant citral, linalool, and geraniol production were selected for further development and maintained by seed propagation. Chemical analysis of five outstanding populations at three stages of annual development: vegetative, flower buds, and full flowering, confirmed that the seed populations retain the distinct dynamics of the dominant and minor components during the annual cycle and can be used for the commercial production of citral, linalool, and geraniol. Micropropagation in vitro allows for efficient clonal micropropagation and mass reproduction of elite cultivars and promising forms of A. balchanorum on a commercial scale but cannot serve as a source of direct and efficient production of secondary metabolites.

Recent updates on bioactive properties of linalool

Natural products, including essential oils and their components, have been used for their bioactivities. Linalool (2,6-dimethyl-2,7-octadien-6-ol) is an aromatic monoterpene alcohol that is widely found in essential oils and is broadly used in perfumes, cosmetics, household cleaners and food additives. This review covers the sources, physicochemical properties, application, synthesis and bioactivities of linalool. The present study focuses on the bioactive properties of linalool, including anticancer, antimicrobial, neuroprotective, anxiolytic, antidepressant, anti-stress, hepatoprotective, renal protective, and lung protective activity and the underlying mechanisms. Besides this, the therapeutic potential of linalool and the prospect of encapsulating linalool are also discussed. Linalool can induce apoptosis of cancer cells via oxidative stress, and at the same time protects normal cells. Linalool exerts antimicrobial effects through disruption of cell membranes. The protective effects of linalool to the liver, kidney and lung are owing to its anti-inflammatory activity. On account of its protective effects and low toxicity, linalool can be used as an adjuvant of anticancer drugs or antibiotics. Therefore, linalool has a great potential to be applied as a natural and safe alternative therapeutic.

A review on the traditional uses, phytochemistry, and pharmacological activities of clove basil (Ocimum gratissimum L.)

In traditional medicine, Ocimum gratissimum (clove basil) is used in the treatment of various diseases such as diabetes, cancer, inflammation, anaemia, diarrhoea, pains, and fungal and bacterial infections. The present study reviewed the phytochemicals, essential oils, and pharmacological activities of O. gratissimum. The bioactive compounds extracted from O. gratissimum include phytochemicals (oleanolic acid, caffeic acid, ellagic acid, epicatechin, sinapic acid, rosmarinic acid, chlorogenic acid, luteolin, apigenin, nepetoidin, xanthomicrol, nevadensin, salvigenin, gallic acid, catechin, quercetin, rutin, and kaempfero) and essential oils (camphene, β-caryophyllene, α- and β-pinene, α-humulene, sabinene, β-myrcene, limonene, 1,8-cineole, trans-β-ocimene, linalool, α- and δ-terpineol, eugenol, α-copaene, β-elemene, p-cymene, thymol, and carvacrol). Various in vivo and in vitro studies have shown that O. gratissimum and its bioactive constituents possess pharmacological properties such as antioxidant, anti-inflammatory, anticancer, hepatoprotective, antidiabetic, antihypertensive, antidiarrhoeal, and antimicrobial properties. This review demonstrated that O. gratissimum has a strong preventive and therapeutic effect against several diseases. The effectiveness of O. gratissimum to ameliorate various diseases may be attributed to its antimicrobial and antioxidant properties as well as its capacity to improve the antioxidant systems. However, despite the widespread pharmacological activities of O. gratissimum, further experiments in human clinical trial studies are needed to establish effective and safe doses for the treatment of various diseases.

Biological evaluation of linalool on the function of blood vessels

Long-term hypertension leads to alterations in the structure and function of blood vessels, and abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) are important factors for these changes. Linalool is a natural compound extracted from plants. The present study aimed to explore the role and underlying mechanism of linalool in the physiological behavior of VSMCs. Angiotensin II (Ang II) was utilized to treat VSMCs, and MTT and western blotting assays were then employed to detect the effect of linalool on the induced proliferation and migration of VSMCs. The target gene of linalool was predicted by the SwissTargetPrediction website, and its expression level in VSMCs was determined using reverse transcription-quantitative PCR and western blotting. Next, the role of the target gene in the physiological behavior of VSMCs treated with linalool was examined, and the signaling pathway was explored. The results revealed that the proliferation and migration of VSMCs treated with Ang II were significantly promoted, and linalool could alleviate these effects in a dose-dependent manner. Cholinergic receptor muscarinic 3 (CHRM3), as a predicted target, was found to be highly expressed in Ang II-induced VSMCs, and CHRM3 overexpression could prevent the inhibitory effect of linalool on cell proliferation and migration. In addition, its overexpression caused an increase in the expression of proteins related to the MAPK signaling pathway. In conclusion, linalool inhibited the proliferation and migration of Ang II-induced VSMCs and blocked the MAPK signaling pathway by downregulating CHRM3.

Development of Coriandrum sativum Oil Nanoemulgel and Evaluation of Its Antimicrobial and Anticancer Activity

This study is aimed at developing coriander oil into a nanoemulgel and evaluating its antimicrobial and anticancer effects. Coriander (Coriandrum sativum) oil was developed into a nanoemulgel by using a self-nanoemulsifying technique with Tween 80 and Span 80. Hydrogel material (Carbopol 940) was then incorporated into the nanoemulsion and mixed well. After this, we evaluated the particle size, polydispersity index (PDI), rheology, antimicrobial effect, and cytotoxic activity. The nanoemulsion had a PDI of 0.188 and a particle size of 165.72 nm. Interesting results were obtained with the nanoemulgel against different types of bacteria, such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and methicillin-resistant Staphylococcus aureus (MRSA), with a minimum inhibitory concentration (MIC) of 2.3 μg/ml, 3.75 μg/ml, and 6.5 μg/ml, respectively. In addition, the half-maximal inhibitory concentration (IC₅₀) of the nanoemulgel when applying it to human breast cancer cells (MCF-7), hepatocellular carcinoma cells (Hep3B), and human cervical epithelioid carcinoma cells (HeLa) was 28.84 μg/ml, 28.18 μg/ml, and 24.54 μg/ml, respectively, which proves that the nanoemulgel has anticancer effects. The development of C. sativum oil into a nanoemulgel by using a self-nanoemulsifying technique showed a bioactive property better than that in crude oil. Therefore, simple nanotechnology techniques are a promising step in the preparation of pharmaceutical dosage forms.

A network pharmacology-based approach to explore the active ingredients and molecular mechanism of Lei-gong-gen formula granule on a spontaneously hypertensive rat model

Background

Lei-gong-gen formula granule (LFG) is a folk prescription derived from Zhuang nationality, the largest ethnic minority among 56 nationalities in China. It consists of three herbs, namely Eclipta prostrata (L.) L., Smilax glabra Roxb, and Centella asiatica (L.) Urb. It has been widely used as health protection tea for hundreds of years to prevent hypertension in Guangxi Zhuang Autonomous Region. The purpose of this study is to validate the antihypertensive effect of LFG on the spontaneously hypertensive rat (SHR) model, and to further identify the effective components and anti-hypertension mechanism of LFG.

Methods

The effects of LFG on blood pressure, body weight, and heart rate were investigated in vivo using the SHR model. The levels of NO, ANG II, and ET-1 in the serum were measured, and pathological changes in the heart were examined by H&E staining. The main active components of LFG, their corresponding targets, and hypertension associated pathways were discerned through network pharmacology analysis based on the Traditional Chinese Medicine Systems Pharmacology (TCMSP), Traditional Chinese Medicine Integrated Database (TCMID), and the Bioinformatics Analysis Tool for Molecular Mechanism of Traditional Chinese Medicine (BATMAN-TCM). Then the predicted results were further verified by molecular biology experiments such as RT-qPCR and western blot. Additionally, the potential active compounds were predicted by molecular docking technology, and the chemical constituents of LFG were analyzed and identified by UPLC-QTOF/MS technology. Finally, an in vitro assay was performed to investigate the protective effects of potential active compounds against hydrogen peroxide (H₂O₂) induced oxidative damage in human umbilical vein endothelial cells (HUVEC).

Results

LFG could effectively reduce blood pressure and increase serum NO content in SHR model. Histological results showed that LFG could ameliorate pathological changes such as cardiac hypertrophy and interstitial inflammation. From network pharmacology analysis, 53 candidate active compounds of LFG were collected, which linked to 765 potential targets, and 828 hypertension associated targets were retrieved, from which 12 overlapped targets both related to candidate active compounds from LFG and hypertension were screened and used as the potential targets of LFG on antihypertensive effect. The molecular biology experiments of the 12 overlapped targets showed that LFG could upregulate the mRNA and protein expressions of NOS3 and proto-oncogene tyrosine-protein kinase SRC (SRC) in the thoracic aorta. Pathway enrichment analysis showed that the PI3K-AKT signaling pathway was closely related to the expression of NOS3 and SRC. Moreover, western blot results showed that LFG significantly increased the protein expression levels of PI3K and phosphorylated AKT in SHR model, suggesting that LFG may active the PI3K-AKT signaling pathway to decrease hypertension. Molecular docking study further supported that p-hydroxybenzoic acid, cedar acid, shikimic acid, salicylic acid, nicotinic acid, linalool, and histidine can be well binding with NOS3, SRC, PI3K, and AKT. UPLC-QTOF/MS analysis confirmed that p-hydroxybenzoic acid, shikimic acid, salicylic acid, and nicotinic acid existed in LFG. Pre-treatment of HUVEC with nicotinic acid could alleviate the effect on cell viability induced by H₂O₂ and increase the NO level in cell supernatants.

Conclusions

LFG can reduce the blood pressure in SHR model, which might be attributed to increasing the NO level in serum for promoting vasodilation via upregulating SRC expression level and activating the PI3K-AKT-NOS3 signaling pathway. Nicotinic acid might be the potential compound for LFG antihypertensive effect.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-021-00507-1.

Monoterpenoid biosynthesis by engineered microbes

Monoterpenoids are C10 isoprenoids and constitute a large family of natural products. They have been used as ingredients in food, cosmetics and therapeutic products. Many monoterpenoids such as linalool, geraniol, limonene and pinene are volatile and can be found in plant essential oils. Conventionally, these bioactive compounds are obtained from plant extracts by using organic solvents or by distillation method, which are costly and laborious if high purity product is desired. In recent years, microbial biosynthesis has emerged as alternative source of monoterpenoids with great promise for meeting the increasing global demand for these compounds. However, current methods of production are not yet at levels required for commercialization. Production efficiency of monoterpenoids in microbial hosts is often restricted by high volatility of the monoterpenoids, a lack of enzymatic activity and selectivity, and/or product cytotoxicity to the microbial hosts. In this review, we summarize advances in microbial production of monoterpenoids over the past three years with particular focus on the key metabolic engineering strategies for different monoterpenoid products. We also provide our perspective on the promise of future endeavors to improve monoterpenoid productivity.

Synthesis of uniform submicron poly(lactic acid)-based particles/capsules by radical precipitation polymerization

Poly(l-lactic acid) (PLLA) is a well-known biopolymer, usually synthesized via step-growth or ring-opening polymerization from lactic acid or a lactide monomer, respectively. PLLA microspherical particles are produced by dispersion polymerization with a ring-opening lactide monomer using a particular copolymer chain as a stabilizer. This is not easy to achieve when dehydration is needed. Here, a robust and simple synthesis of a nearly monodisperse, submicron PLLA-based particle/capsule was proposed via radical precipitation polymerization without the use of surfactant. A commercial PLLA was first glycolyzed with ethylene glycol to obtain a low molecular weight glycolyzed PLLA (GPLLA). Then, the GPLLA was copolymerized with methacrylic acid and ethylene glycol dimethacrylate monomers using a benzoyl peroxide initiator. Active sites on the GPLLA backbone were generated by hydrogen abstraction of benzoyloxy radicals that further copolymerized before self-assembly to form the polymer particles. Uniform particle size of about 580 nm with a low polydispersity index (PDI) of 0.012 was obtained. This method was also implemented to produce nearly monodisperse capsules containing linalool. The particle size of PLLA-based capsules was about 280 nm with narrow particle size distribution (PDI of 0.120). The PLLA-based capsules effectively inhibited microbial growth of Staphylococcus aureus, Escherichia coli and Candida albicans and were not toxic to human cells.

Effect of the Distillation Time on the Chemical Composition, Antioxidant Potential and Antimicrobial Activity of Essential Oils from Different Cannabis sativa L. Cultivars

Within the unavoidable variability of various origins in the characteristics of essential oils, the aim of this study was to evaluate the effect of the distillation time on the chemical composition and biological activity of Cannabis sativa essential oils (EOs). The dry inflorescences came from Carmagnola, Kompolti, Futura 75, Gran Sasso Kush and Carmagnola Lemon varieties from Abruzzo region (Central Italy), the last two being new cultivar here described for the first time. EOs were collected at 2 h and 4 h of distillation; GC/MS technique was applied to characterize their volatile fraction. The EOs were evaluated for total polyphenol content (TPC), antioxidant capacity (AOC) and antimicrobial activity against food-borne pathogens and spoilage bacteria. The time of distillation particularly influenced EOs chemical composition, extracting more or less terpenic components, but generally enriching with minor sesquiterpenes and cannabidiol. A logical response in ratio of time was observed for antioxidant potential, being the essential oils at 4 h of distillation more active than those distilled for 2 h, and particularly Futura 75. Conversely, except for Futura 75, the effect of time on the antimicrobial activity was variable and requires further investigations; nevertheless, the inhibitory activity of all EOs against Pseudomonas fluorescens P34 was an interesting result.

The methyl jasmonate-responsive transcription factor DobHLH4 promotes DoTPS10, which is involved in linalool biosynthesis in Dendrobium officinale during floral development

Linalool is an aromatic monoterpene produced in the Chinese medicinal plant Dendrobium officinale, but little information is available on the regulation of linalool biosynthesis. Here, a novel basic helix-loop-helix (bHLH) transcription factor, DobHLH4 from D. officinale, was identified and functionally characterized. The expression profile of DobHLH4 was positively correlated with that of DoTPS10 (R² = 0.985, p < 0.01), which encodes linalool synthase that is responsible for linalool production, during floral development. DobHLH4 was highly expressed in petals, and was significantly induced by methyl jasmonate. Analysis of subcellular localization showed that DobHLH4 was located in the nucleus. Yeast one-hybrid and dual-luciferase assays indicated that DobHLH4 bound directly to the DoTPS10 promoter harboring the G-box element, and up-regulated DoTPS10 expression. A yeast two-hybrid screen confirmed that DobHLH4 physically interacted with DoJAZ1, suggesting that DobHLH4 might function in the jasmonic acid-mediated accumulation of linalool. Furthermore, transient overexpression of DobHLH4 in D. officinale petals significantly increased linalool production by triggering linalool biosynthetic pathway genes, especially DoTPS10. We suggest a hypothetical model that depicts how jasmonic acid signaling may regulate DoTPS10 by interacting with DobHLH4 and DoJAZ1. In doing so, the formation of linalool is controlled. Our results indicate that DobHLH4 is a positive regulator of linalool biosynthesis and may be a promising target for in vitro-based metabolic engineering to produce linalool.

Bacterial terpenome

Covering: up to mid-2020 Terpenoids, also called isoprenoids, are the largest and most structurally diverse family of natural products. Found in all domains of life, there are over 80 000 known compounds. The majority of characterized terpenoids, which include some of the most well known, pharmaceutically relevant, and commercially valuable natural products, are produced by plants and fungi. Comparatively, terpenoids of bacterial origin are rare. This is counter-intuitive to the fact that recent microbial genomics revealed that almost all bacteria have the biosynthetic potential to create the C5 building blocks necessary for terpenoid biosynthesis. In this review, we catalogue terpenoids produced by bacteria. We collected 1062 natural products, consisting of both primary and secondary metabolites, and classified them into two major families and 55 distinct subfamilies. To highlight the structural and chemical space of bacterial terpenoids, we discuss their structures, biosynthesis, and biological activities. Although the bacterial terpenome is relatively small, it presents a fascinating dichotomy for future research. Similarities between bacterial and non-bacterial terpenoids and their biosynthetic pathways provides alternative model systems for detailed characterization while the abundance of novel skeletons, biosynthetic pathways, and bioactivies presents new opportunities for drug discovery, genome mining, and enzymology.

Essential oils of spontaneous species of the genus Lavandula from Portugal: a brief review

Spontaneous lavender growing in uncultivated fields in Portugal have been used in traditional medicine for internal and external uses. The essential oils (EOs) of Lavandula stoechas subsp. luisieri are characterized by the presence of trans-α-necrodyl acetate and trans-necrodol. These EOs are able to prevent the generation and deposition of neurotoxic β-amyloid peptide in Alzheimer's disease. The EOs also present antibacterial, anti-fungal, anti-Leishmania, antioxidant, anti-inflammatory and antifeedant effects. In the case of hydrodistillation, the predominant compound of Lavandula viridis EO was 1,8-cineole, nevertheless in the case of supercritical fluid extraction, the main constituent was camphor. In in vitro shoots EOs, 1,8-cineole and α-pinene were the most important compounds. The EOs presented anti-fungal activity particularly against Cryptococcus neoformans and dermatophytes. The antioxidant and anti-protozoal activities of L. viridis EOs were lower than L. stoechas subsp. luisieri EOs, with hydrodistillation being the best method for obtaining samples with higher antioxidant and anti-acetylcholinesterase activities. The presence of fenchone, 1,8-cineole and camphor was a common trace of the Lavandula pedunculata subsp. pedunculata EOs and in in vitro axillary shoots EOs. Lavandula pedunculata subsp. lusitanica EOs were predominantly constituted of fenchone and camphor. The antioxidant activity of L. pedunculata subsp. lusitanica EOs was poorer than other Lavandula EOs from Portugal.

A systematic review on ethnopharmacology, phytochemistry and pharmacological aspects of Thymus vulgaris Linn

Thymus vulgaris Linn. is a medicinal and culinary herb from the Southern European region known for its anti-infective, cardioprotective, gastroprotective, anti-inflammatory, and immunomodulatory activities since the Egyptian era. The reported pharmacological activities of T. vulgaris L. include antibacterial, antioxidant, anti-inflammatory, antiviral, and anti-cancerous activities. In this review, a comprehensive approach is put forth to scrutinize and report the available data on phytochemistry, ethnopharmacology, pharmacology, and toxicology of the plant. The different extracts and essential oil obtained from the plant have been assessed and reported to treat ailments like microbial infections, inflammation, non-communicable diseases like cancer, and sexually transmitted diseases like HIV-1 and Herpes. The literature review has also indicated the use of volatile oils, phenolic acids, terpenoids, flavonoids, saponins, steroids, tannins, alkaloids, and polysaccharides in pharmacotherapy. Applications of these compounds including antidiabetic, anti-Alzheimer's, cardio, neuro and hepatoprotective, anti-osteoporosis, sedative, immunomodulatory, antioxidant, anti-tyrosinase, antispasmodic, antinociceptive, gastroprotective, anticonvulsant, antihypertensive, antidepressant, anti-amnesia, and anti-helminthic activities have been mentioned. Further, based on research gaps, recommendations have been provided to evaluate T. vulgaris L. systematically to develop plant-based drugs, nutraceuticals, and to evaluate their clinical efficiency and safety.

Essential Oils of New Lippia alba Genotypes Analyzed by Flow-Modulated Comprehensive Two-Dimensional Gas Chromatography (GC×GC) and Chemometric Analysis

Lippia alba (Mill.) N. E. Br. (Verbenaceae) is an aromatic shrub whose essential oils have stood out as a promising source for application in several industrial fields. In this study, the essential oils chemical characterization of eight new L. alba genotypes was performed. The selected materials were collected from the Active Germplasm Bank of the Agronomic Institute and the essential oils were extracted by hydrodistillation. Flow-modulated comprehensive two-dimensional gas chromatography coupled to mass spectrometry (GC×GC-MS) was employed for chemical characterization and evaluation of possible co-eluted compounds. In addition, the chemical analyses were submitted to multivariate statistical analyses. From this investigation, 73 metabolites were identified in the essential oils of the genotypes, from which α-pinene, β-myrcene, 1,8-cineole, linalool, neral, geranial, and caryophyllene oxide were the most abundant compounds among the accessions. This is the first report disclosing α-pinene in higher amounts in L. alba (19.69%). In addition, sabinene, trans-verbenol, myrtenol, (E)-caryophyllene, α-guaiene, germacrene D, and α-bulnesene were also found in relevant quantities in some of the genotypes, and myrtenal and myrtenol could be well separated through the second dimension. Such results contributed to the understanding of the chemical composition of those new genotypes, being important to drive a future industrial applicability and studies in genetic breeding.

Linalool Alleviates Aβ42-Induced Neurodegeneration via Suppressing ROS Production and Inflammation in Fly and Rat Models of Alzheimer's Disease

Terpenes are vital metabolites found in various plants and animals and known to be beneficial in the treatment of various diseases. Previously, our group identified terpenes that increased the survival of Alzheimer's disease (AD) model flies expressing human amyloid β (Aβ) and identified linalool as a neuroprotective terpene against Aβ toxicity. Linalool is a monoterpene that is commonly present as a constituent in essential oils from aromatic plants and is known to have anti-inflammatory, anticancer, antihyperlipidemia, antibacterial, and neuroprotective properties. Although several studies have shown the beneficial effect of linalool in AD animal models, the mechanisms underlying the beneficial effect of linalool on AD are yet to be elucidated. In the present study, we showed that linalool intake increased the survival of the AD model flies during development in a dose-dependent manner, while the survival of wild-type flies was not affected even at high linalool concentrations. Linalool also decreases Aβ-induced apoptosis in eye discs as well as the larval brain. Moreover, linalool intake was found to reduce neurodegeneration in the brain of adult AD model flies. However, linalool did not affect the total amount of Aβ42 protein or Aβ42 aggregation. Rather, linalool decreased Aβ-induced ROS levels, oxidative stress, and inflammatory response in the brains of AD model flies. Furthermore, linalool attenuated the induction of oxidative stress and gliosis by Aβ_1-42 treatment in the rat hippocampus. Taken together, our data suggest that linalool exerts its beneficial effects on AD by reducing Aβ42-induced oxidative stress and inflammatory reactions.

Antimicrobial Activity and Proposed Action Mechanism of Linalool Against Pseudomonas fluorescens

In this study, linalool, one of the principal components of essential oils, was used as an antibacterial agent to investigate the antibacterial activity and mechanism of linalool against Pseudomonas fluorescens. The reduction in membrane potential (MP), leakage of alkaline phosphatase (AKP) and the release of macromolecules, including DNA, RNA and protein confirmed that damage to cell wall membrane structure and leakage of cytoplasmic contents were due to the linalool treatment. Furthermore, the decrease of enzyme activity, including the succinate dehydrogenase (SDH), malate dehydrogenase (MDH), pyruvate kinase (PK), and ATPase indicated that linalool could lead to metabolic dysfunction and inhibit energy synthesis. In addition, the activity of respiratory chain dehydrogenase and metabolic activity of respiration indicated that linalool inhibits cellular respiration. These results revealed that linalool had strong antibacterial activity against P. fluorescens via membrane damage, bacterial metabolic and oxidative respiratory perturbations, interfering in cellular functions and even causing cell death. It was suggested that linalool may be a new potential source as food antiseptics in food systems.