Pharmacological and toxicological activities of α-humulene and its isomers: A systematic review

Control of pathogenic bacterial biofilm associated with acne and the anti-inflammatory potential of an essential oil blend

Acne is one of the most common skin conditions worldwide, with multifactorial origins it affects areas of the skin with hair follicles and sebaceous glands that become clogged. Bacterial incidence aggravates treatment due to resistance to antimicrobial agents and production of virulence factors such as biofilm formation. Based on these information, this study aims to conduct in vitro evaluations of the antibacterial activity of essential oils (EOs), alone and in combination, against Propionibacterium acnes, Staphylococcus aureus, and Staphylococcus epidermidis in planktonic and biofilm forms. This study also assessed the anti-inflammatory potential (TNF-α) and the effects of EOs on the viability of human keratinocytes (HaCaT), murine fibroblasts (3T3-L1), and bone marrow-derived macrophages (BMDMs). Of all EOs tested, 13 had active action against P. acnes, 9 against S. aureus, and 9 against S. epidermidis at concentrations of 0.125-2.0 mg/mL. Among the most active plant species, a blend of essential oil (BEOs) was selected, with Cymbopogon martini (Roxb.) Will. Watson, Eugenia uniflora L., and Varronia curassavica Jacq., the latter due to its anti-inflammatory action. This BEOs showed higher inhibition rates when compared to chloramphenicol against S. aureus and S. epidermidis, and higher eradication rates when compared to chloramphenicol for the three target species. The BEOs did not affect the cell viability of cell lines evaluated, and the levels of TNF-α decreased. According to these results, the BEOs evaluated showed potential for the development of an alternative natural formulation for the treatment of acne.

The Clinical Translation of α-humulene - A Scoping Review

α-humulene, a sesquiterpene found in essential oils of various plant species, has garnered interest due to its potential therapeutic applications. This scoping review aims to consolidate α-humulene's evidence base, informing clinical translation, and guiding future research directions. A scoping review was conducted of EMBASE, MEDLINE, and PubMed databases up to 14th July 2023. All studies describing original research on α-humulene extraction, as well as pre-clinical and clinical research, were included for review. Three hundred and forty articles were analysed. α-humulene yields ranged from negligible to 60.90% across plant species. In vitro experiments demonstrated cytotoxicity against adenocarcinomas (such as colorectal, pulmonary, breast, prostatic, lung, and ovarian), with varying responses in other cell models. Mechanistic insights revealed its involvement in mitochondrial dysfunction, diminished intracellular glutathione levels, and the induction of oxidative stress. In rodent studies, oral administration of α-humulene at 50 mg/kg reduced inflammation markers in paw oedema and ovalbumin-induced airway inflammation. Intraperitoneal administration of α-humulene (50 - 200 mg/kg) exhibited cannabimimetic properties through cannabinoid 1 and adenosine A2a receptors. α-humulene also exhibited a multitude of properties with potential scope for therapeutic utilisation. However, there is a paucity of studies that have successfully translated this research into clinical populations with the associated disease. Potential barriers to clinical translation were identified, including yield variability, limited isolation studies, and challenges associated with terpene bioavailability. Consequently, rigorous pharmacokinetic studies and further mechanistic investigations are warranted to effectively uncover the potential of α-humulene.

Salvia verticillata (L.)-Biological Activity, Chemical Profile, and Future Perspectives

Species belonging to the genus Salvia, Lamiaceae, have been deeply involved in the folk medicine of different nations since ancient times. Lilac sage, or Salvia verticillata L. (S. verticillata) is a less studied species from the genus. However, it seems to have a prominent potential for the future drug discovery strategies of novel phytopharmaceuticals. This review aims to summarise the data on the biological activity and the phytochemical profile of extracts and essential oils derived from S. verticillata. This review is based on data from 57 in vitro and in vivo studies. The chemical profile of S. verticillata includes different synergic compounds like phenolic acids, flavonoids, terpenes, and salvianolic acids. Although some small amounts of salvianolic acid B were found in S. verticillata extracts, the major compound among the salvianolic acids is salvianolic acid C, a compound associated with the potential for improving liver fibrosis, cardio- and hepatoprotection, and the inhibition of SARS-CoV-2 infection. The cannabinoid type 2 receptor agonist β-caryophyllene is one of the major compounds in S. verticillata essential oils. It is a compound with a prominent potential in regenerative medicine, neurology, immunology, and other medical fields. The in vivo and the in vitro studies, regarding S. verticillata highlighted good antioxidant potential, anti-inflammatory, antibacterial, and antifungal activity. S.verticillata was also reported as a potential source of drug candidates for the treatment of neurodegenerative diseases such as Alzheimer's disease, because of the inhibitory activity on the acetylcholinesterase. However, the number of studies in this direction is limited.

Opportunities, Challenges, and Scientific Progress in Hemp Crops

The resurgence of cannabis (Cannabis sativa L.) has been propelled by changes in the legal framework governing its cultivation and use, increased demand for hemp-derived products, and studies recognizing the industrial and health benefits of hemp. This has led to the creation of novel high-cannabidiol, low-Δ9-tetrahydrocannabinol varieties, enabling hemp crop expansion worldwide. This review elucidates the recent implications for hemp cultivation in Europe, with a focus on the legislative impacts on the cultivation practices, prospective breeding efforts, and dynamic scientific landscape surrounding this crop. We also review the current cultivars' cannabinoid composition of the European hemp market and its major differences with that of the United States.

Sesquiterpene-evoked phytochemical toxicity in PC12 neuronal cells reveals a variable degree of oxidative stress and alpha-tocopherol and glutathione-dependent protection

Phytochemicals are often promoted generally as antioxidants and demonstrate variable levels of reactive oxygen species (ROS) sequestration in vitro, which attributes to their neuroprotective bioactivity. Sesquiterpenes from cannabis and essential oils may demonstrate bifunctional properties towards cellular oxidative stress, possessing pro-oxidant activities by generating ROS or scavenging ROS directly. Sesquiterpenes can also oxidize forming sesquiterpene oxides, however the relative contribution they make to the bioactivity or cytotoxicity of complex botanical extracts more generally is unclear, while selected cannabis-prevalent terpenes such as β-caryophyllene may also activate cannabinoid receptors as part of their biological activity. In the present study, we investigated selected sesquiterpenes β-caryophyllene and humulene and their oxidized forms (β-caryophyllene oxide and zerumbone, respectively) against established antioxidants (ascorbic acid, α-tocopherol, and glutathione) and in the presence of cannabinoid receptor 1 and cannabinoid receptor 2 antagonists, to gain a better understanding of the molecular and cellular mechanisms of neuroprotection versus neurotoxicity in semi-differentiated rat neuronal phaeochromocytoma (PC12) cells. Our results demonstrate that the sesquiterpenes β-caryophyllene, humulene and zerumbone possess concentration-dependent neurotoxic effects in PC12 cells. Both β-caryophyllene- and humulene-evoked toxicity was unaffected by CB1 or CB2 receptor antagonism, demonstrating this occurred independently of cannabinoid receptors. Both glutathione and α-tocopherol were variably able to alleviate the concentration-dependent loss of PC12 cell viability from exposure to β-caryophyllene, humulene and zerumbone. During 4-hour exposure to sesquiterpenes only modest increases in ROS levels were noted in PC12 cells, with glutathione co-incubation significantly inhibiting intracellular ROS production. However, significant increases in ROS levels in PC12 cells were demonstrated during 24-hour incubation with either antioxidants or sesquiterpenes individually, and with additive toxicity exhibited in combination. Overall, the results highlight a concentration-dependent profile of sesquiterpene neurotoxicity independent of cannabinoid receptors and dissociated from the formation of reactive oxygen species as a marker or correlate to the loss of cell viability.

Potential anti-inflammatory biomarkers from Myrtaceae essential oils revealed by untargeted metabolomics

Many species from Myrtaceae have traditionally been used in traditional medicine as anti-inflammatory, antimicrobial, antidiarrheal, antioxidant and antirheumatic, besides in blood cholesterol reduction. In the present work, the anti-inflammatory activity of essential oils from eighteen Myrtaceae spp. were evaluated according to their ex-vivo anti-inflammatory activity in human blood, and the corresponding biomarkers were determined using untargeted metabolomics data and multivariate data analysis. From these studied species, six displayed anti-inflammatory activity with percentage rates of inhibition of PGE2 release above 70%. Caryophyllene oxide (1), humulene epoxide II (2), β-selinene (3), α-amorphene (4), α-selinene (5), germacrene A (6), β-bisabolene (7), α-muurolene (8), α-humulene (9), β-gurjunene (10), myrcene (11), β-elemene (12), α-cadinol (13), α-copaene (14), E-nerolidol (15) and ledol (16) were annotated as potential anti-inflammatory biomarkers. The results obtained in this study point to essential oils from species of the Myrtaceae family as a rich source of anti-inflammatory agents.

Anticancer effect of terpenes: focus on malignant melanoma

Melanoma is a highly aggressive and life-threatening form of skin cancer that accounts for a significant proportion of cancer-related deaths worldwide. Although conventional cancer therapies, such as surgical excision, chemotherapy, and radiation, have been used to treat malignant melanoma, their efficacy is often limited due to the development of resistance and adverse side effects. Therefore, there is a growing interest in developing alternative treatment options for melanoma that are more effective and less toxic. Terpenes, a diverse group of naturally occurring compounds of plant origin, have emerged as potential anticancer agents due to their ability to inhibit tumor growth and induce apoptosis in cancer cells. In this review, the current understanding of the anticancer effects of terpenes (including, thymoquinone, β-elemene, carvacrol, limonene, α-pinene, β-caryophyllene, perillyl alcohol, taxol, betulinic acid, α-bisabolol, ursolic acid, linalool, lupeol, and artesunate) was summarized, with a special focus on their potential as therapeutic agents for malignant melanoma.

Volatile secondary metabolites of a traditional herb Cajanus lineatus (Wight & Arn.) Maesen (Janglitur) from India

The hydro-distilled volatile components were obtained from the herb (leaf and stem) of Cajanus lineatus (Wight & Arn.) Maesen (Syn: Atylosia lineata Wight & Arn.) of the family Fabaceae, commonly known as Janglitur in India, and the essential oil was analysed for the first time using GC-FID and GC-MS. Sixty-two compounds were identified from the herb oil of C. lineatus. The major compounds were identified as β-caryophyllene (10.6%) and α-humulene (10.3%). The oil was found to be rich in sesquiterpene hydrocarbons (51.5%) type compounds.

Metabolomic Approach Based on Analytical Techniques for the Detection of Secondary Metabolites from Humulus lupulus L. Dried Leaves

Currently, the leaves of the hop plant (Humulus lupulus L.) are an unexploited and still little-investigated agricultural by-product. In our study, with the aim of exploring the metabolome of dried hop leaves (Chinook cultivar), a metabolomic approach was applied using multiple analytical tools such as SPME/GC-MS, GC-MS, PTR-ToF-MS, and NMR to identify the secondary metabolites. The obtained results showed the presence of a high number of components belonging to different chemical classes. In fact, thanks to the multi-methodological approach, volatile organic compounds (VOCs) with low molecular weight, terpenic compounds, fatty acids, sugars, amino acids, organic acids, and alcohols have been detected and identified. Among the revealed terpenes in the untreated matrix, the sesquiterpenes α-humulene, β-caryophyllene, and α-copaene were the most abundant. Among the saturated and unsaturated fatty acids, palmitic and linolenic acids, respectively, were those with the highest relative percentages. Particularly relevant was the sugar content, where sucrose was the main exponent while glutamate and asparagine were the principal detected amino acids. Conversely, alcohols and organic acids were the least abundant compound classes, and xanthohumol was also identified in the methanolic extract.

Cistus albidus L.-Review of a Traditional Mediterranean Medicinal Plant with Pharmacological Potential

Cistus albidus L. (Cistaceae) is a medicinal plant that has been used therapeutically since ancient times in the Mediterranean basin for its important pharmacological properties. The ability of C. albidus to produce large quantities of a wide range of natural metabolites makes it an attractive source of raw material. The main constituents with bioactive functions that exert pharmacological effects are terpenes and polyphenols, with more than 200 identified compounds. The purpose of this review is to offer a detailed account of the botanical, ethnological, phytochemical, and pharmacological characteristics of C. albidus with the aim of encouraging additional pharmaceutical investigations into the potential therapeutic benefits of this medicinal plant. This review was carried out using organized searches of the available literature up to July 2023. A detailed analysis of C. albidus confirms its traditional use as a medicinal plant. The outcome of several studies suggests a deeper involvement of certain polyphenols and terpenes in multiple mechanisms such as inflammation and pain, with a potential application focus on neurodegenerative diseases and disorders. Other diseases such as prostate cancer and leukemia have already been researched with promising results for this plant, for which no intoxication has been reported in humans.

A New Essential Oil from the Leaves of Gynoxys rugulosa Muschl. (Asteraceae) Growing in Southern Ecuador: Chemical and Enantioselective Analyses

An essential oil, distilled from the leaves of the Andean species Gynoxys rugulosa Muschl., is described in the present study for the first time. The chemical composition was qualitatively and quantitatively determined by GC-MS and GC-FID, respectively. On the one hand, the qualitative composition was obtained by comparing the mass spectrum and the linear retention index of each component with data from literature. On the other hand, the quantitative composition was determined by calculating the relative response factor of each constituent, according to its combustion enthalpy. Both analyses were carried out with two orthogonal columns of nonpolar and polar stationary phases. A total of 112 compounds were detected and quantified with at least one column, corresponding to 87.3-93.0% of the whole oil mass. Among the 112 detected components, 103 were identified. The main constituents were α-pinene (5.3-6.0%), (E)-β-caryophyllene (2.4-2.8%), α-humulene (3.0-3.2%), germacrene D (4.9-6.5%), δ-cadinene (2.2-2.3%), caryophyllene oxide (1.6-2.2%), α-cadinol (3.8-4.4%), 1-nonadecanol (1.7-1.9%), 1-eicosanol (0.9-1.2%), n-tricosane (3.3-3.4%), 1-heneicosanol (4.5-5.8%), n-pentacosane (5.8-7.1%), 1-tricosanol (4.0-4.5%), and n-heptacosane (3.0-3.5%). Furthermore, an enantioselective analysis was carried out on the essential oil, by means of two cyclodextrin-based capillary columns. The enantiomers of α-pinene, β-pinene, sabinene, α-phellandrene, β-phellandrene, linalool, α-copaene, terpinen-4-ol, α-terpineol, and germacrene D were detected, and the respective enantiomeric excess was calculated.

Psidium guajava L.: From byproduct and use in traditional Mexican medicine to antimicrobial agent

Mexico is one of the largest guava producers in the world, so it has access to a huge amount of waste and byproducts obtained after the industrial processing of the fruit. This review discusses the potential recovery of this residue for its application as an antimicrobial agent, considering the phytochemical composition, the bioactivity reported in-vivo and in-vitro, and the toxicology of the plant. Nowadays there is a growing demand for more natural and safer products, so the use of guava extracts is an interesting initiative, especially due to its availability in the country, its wide variety of traditional uses, and its phytochemical profile. This review highlights the importance and potential antimicrobial use of this plant in today's world.

Active Compounds with Medicinal Potential Found in Maxillariinae Benth. (Orchidaceae Juss.) Representatives-A Review

Orchids are widely used in traditional medicine for the treatment of a whole range of different health conditions, and representatives of the Neotropical subtribe Maxillariinae are not an exception. They are utilized, for instance, for their spasmolytic and anti-inflammatory activities. In this work, we analyze the literature concerning the chemical composition of the plant extracts and secretions of this subtribe's representatives published between 1991 and 2022. Maxillariinae is one of the biggest taxa within the orchid family; however, to date, only 19 species have been investigated in this regard and, as we report, they produce 62 semiochemicals of medical potential. The presented review is the first summary of biologically active compounds found in Maxillariinae.

High-yield α-humulene production in Yarrowia lipolytica from waste cooking oil based on transcriptome analysis and metabolic engineering

BACKGROUND

α-Humulene is an important biologically active sesquiterpene, whose heterologous production in microorganisms is a promising alternative biotechnological process to plant extraction and chemical synthesis. In addition, the reduction of production expenses is also an extremely critical factor in the sustainable and industrial production of α-humulene. In order to meet the requirements of industrialization, finding renewable substitute feedstocks such as low cost or waste substrates for terpenoids production remains an area of active research.

RESULTS

In this study, we investigated the feasibility of peroxisome-engineering strain to utilize waste cooking oil (WCO) for high production of α-humulene while reducing the cost. Subsequently, transcriptome analysis revealed differences in gene expression levels with different carbon sources. The results showed that single or combination regulations of target genes identified by transcriptome were effective to enhance the α-humulene titer. Finally, the engineered strain could produce 5.9 g/L α-humulene in a 5-L bioreactor.

CONCLUSION

To the best of our knowledge, this is the first report that converted WCO to α-humulene in peroxisome-engineering strain. These findings provide valuable insights into the high-level production of α-humulene in Y. lipolytica and its utilization in WCO bioconversion.

Fermentative α-Humulene Production from Homogenized Grass Clippings as a Growth Medium

Green waste, e.g., grass clippings, is currently insufficiently recycled and has untapped potential as a valuable resource. Our aim was to use juice from grass clippings as a growth medium for microorganisms. Herein, we demonstrate the production of the sesquiterpene α-humulene with the versatile organism Cupriavidus necator pKR-hum on a growth medium from grass clippings. The medium was compared with established media in terms of microbial growth and terpene production. C. necator pKR-hum shows a maximum growth rate of 0.43 h-1 in the grass medium and 0.50 h-1 in a lysogeny broth (LB) medium. With the grass medium, 2 mg/L of α-humulene were produced compared to 10 mg/L with the LB medium. By concentrating the grass medium and using a controlled bioreactor in combination with an optimized in situ product removal, comparable product concentrations could likely be achieved. To the best of our knowledge, this is the first time that juice from grass clippings has been used as a growth medium without any further additives for microbial product synthesis. This use of green waste as a material represents a new bioeconomic utilization option of waste materials and could contribute to improving the economics of grass biorefineries.

Engineering the oleaginous yeast Candida tropicalis for α-humulene overproduction

Background

α-Humulene is a plant-derived monocyclic sesquiterpenoid with multiple pharmacological activities, and far-reaching potential for the development of new drugs. Currently, the production of α-humulene is typically achieved via plant extraction, which is not sustainable and limited by low yields. The oleaginous yeast Candida tropicalis has recently emerged as a valuable host for producing high-value-added chemicals. However, the potential of C. tropicalis for terpenoid production has not been exploited.

Results

In this study, C. tropicalis was engineered for de novo synthesis of α-humulene from glucose. To improve α-humulene production, the codon-optimised α-humulene synthase gene and the entire endogenous farnesyl diphosphate synthesis pathway were co-overexpressed. Furthermore, bottlenecks in the α-humulene synthase pathway were identified and relieved by overexpressing α-humulene synthase, acetoacetyl-CoA thiolase and NADH-dependent HMG-CoA reductase. Combined with fermentation medium optimisation, the engineered strain produced 195.31 mg/L of α-humulene in shake flasks and 4115.42 mg/L in a bioreactor through fed-batch fermentation, a 253- and 5345-fold increase over the initial production, respectively.

Conclusions

This study demonstrates the potential of C. tropicalis for α-humulene production, and presents a platform for the biosynthesis of other terpenoids.

Phytochemicals and Biological Activities of Garcinia atroviridis: A Critical Review

Garcinia atriviridis Griff ex T. Anders (G. atroviridis) is one of the well-known species of the genus Garicinia that is native to Thailand, Myanmar, Peninsular Malaysia, and India. G. atroviridis is a perennial medium-sized tree that has a wide range of values, from food to medicinal use. Different parts of G. atroviridis are a great source of bioactive substances that have a positive impact on health. The extracts or bioactive constituents from G. atroviridis have demonstrated various therapeutic functions, including antioxidant, antimicrobial, anticancer, anti-inflammatory, antihyperlipidemic, and anti-diabetic. In this paper, we provide a critical review of G. atroviridis and its bioactive constituents in the prevention and treatment of different diseases, which will provide new insight to explore its putative domains of research.

Hemp (Cannabis sativa L., Kompolti cv.) and Hop (Humulus lupulus L., Chinook cv.) Essential Oil and Hydrolate: HS-GC-MS Chemical Investigation and Apoptotic Activity Evaluation

In this study, essential oils (EOs) and hydrolates (Hys) from Italian hemp (Cannabis sativa L. Kompolti cv.) and hop (Humulus Lupulus L., Chinook cv.) supply chains were chemically characterized and tested to investigate their apoptotic potential for the first time. Headspace–Gas Chromatography–Mass Spectrometry (HS-GC-MS) techniques were performed to describe their volatile chemical profile, highlighting a composition rich in terpene derivatives such as monoterpenes and sesquiterpenes among which β-myrcene, limonene, β-caryophyllene and α-humulene were the main constituents of EOs; in contrast, linalool, cis-p-menth-2,8-dien-1-ol, terpinen-4-ol, α-terpineol, caryophyllene oxide, and τ-cadinol were found in the Hys. The cytotoxicity activity on human leukemia cells (HL60), human neuroblastoma cells (SH-SY5Y), human metastatic adenocarcinoma breast cells (MCF7), human adenocarcinoma breast cells (MDA), and normal breast epithelial cell (MCF10A) for the EOs and Hys was studied by MTT assay and cytofluorimetric analysis and scanning and transmission electron microscopy were performed to define ultrastructural changes and the mechanism of cells death for HL 60 cells. An induction of the apoptotic mechanism was evidenced for hemp and hop EOs after treatment with the corresponding EC₅₀ dose. In addition, TEM and SEM investigations revealed typical characteristics induced by the apoptotic pathway. Therefore, thanks to the integration of the applied methodologies with the used techniques, this work provides an overview on the metabolomic profile and the apoptotic potential of hemp and hop EOs and, for the first time, also of Hys. The findings of this preliminary study confirm that the EOs and Hys from Cannabis and Humulus species are sources of bioactive molecules with multiple biological effects yet to be explored.

Preliminary Study on Phytochemical Constituents and Biological Activities of Essential Oil from Myriactis nepalensis Less

In response to the need for novel therapeutic strategies to combat the development of microbial resistance, plant essential oils may represent a promising alternative source. This study set out to characterize the chemical composition and assess the antibacterial potential of Myriactis nepalensis Less. essential oil (MNEO). Essential oil isolated from M. nepalensis by hydrodistillation was analyzed using a GC–MS technique. The antibacterial properties of MNEO alone and combined with antibiotics (chloramphenicol and streptomycin) were tested via the disc diffusion, microbroth dilution, and checkerboard methods. MNEO was represented by oxygenated sesquiterpenes (60.3%) and sesquiterpene hydrocarbons (28.6%), with caryophyllene oxide, spathulenol, humulene epoxide II, β-elemene, neointermedeol, and β-caryophyllene as the main compounds. MNEO exhibited a strong antibacterial effect against Gram-positive bacteria, with MIC and MBC values of 0.039 mg/mL and 0.039–0.156 mg/mL, respectively, and synergistic effects were observed in both combinations with chloramphenicol and streptomycin. Furthermore, the antibiofilm and cytotoxic activities of MNEO were also evaluated. The crystal violet assay was used for quantification of Staphylococcus aureus biofilm formation, and an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay was conducted to determine cell viability. The results revealed MNEO could dose-dependently inhibit Staphylococcus aureus biofilm formation and possessed potential cytotoxic on both normal and cancer cells (IC50 values from 13.13 ± 1.90 to 35.22 ± 8.36 μg/mL). Overall, the results indicate that MNEO may have promising applications in the field of bacterial infections.

Health Benefits of the Diverse Volatile Oils in Native Plants of Ancient Ironwood-Giant Cactus Forests of the Sonoran Desert: An Adaptation to Climate Change?

We document the species richness and volatile oil diversity in Sonoran Desert plants found in the Arizona Uplands subdivision of this binational USA/Mexico region. Using floristics, we determined that more than 60 species of 178 native plants in the ancient ironwood-giant cactus forests emit fragrant biogenic volatile organic compounds (BVOCs), especially with the onset of summer monsoons. From these desert species, more than 115 volatile oils have been identified from one biogeographic region. For the 5 BVOCs most commonly associated with "forest bathing" practices in Asian temperate forests, at least 15 Sonoran Desert plant species emit them in Arizona Uplands vegetation. We document the potential health benefits attributed to each of 13 BVOCs in isolation, but we also hypothesize that the entire "suite" of BVOCs emitted from a diversity of desert plants during the monsoons may function synergistically to generate additional health benefits. Regular exposure to these BVOC health benefits may become more important to prevent or mitigate diseases of oxidative stress and other climate maladies in a hotter, drier world.