Secondary metabolites from the aerial parts of Origanum scabrum Boiss. & Heldr

A GC-MS and LC-HRMS perspective on the chemotaxonomic investigation of the natural hybrid Origanum × lirium and its parents, O. vulgare subsp. hirtum and O. scabrum

INTRODUCTION

The genus Origanum L. (Lamiaceae) is widespread in the Mediterranean region. However, approximately 75% of the species are only encountered in the eastern part. Out of these, a total of nine species (11 taxa) and three natural hybrids occur in Greece. Nevertheless, so far, there is no consensus regarding their precise botanical classification in the literature. In fact, the taxon Origanum × lirium has been proposed both as a separate species as well as natural hybrid between Origanum vulgare subsp. hirtum and Origanum scabrum.

OBJECTIVES

In this scope, the aim of the current study is to shed light on the matter through the investigation of the chemical composition of both the essential oils and the polar extracts of the mentioned taxa, collected from different geographical regions of Greece.

RESULTS

As it was demonstrated by both gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-high-resolution mass spectrometry (LC-HRMS) data, and highlighted by our comparative analysis, it can be stipulated that Origanum × lirium shares its chemotype to a large extent with its parent species concerning both volatile and polar constituents. Additionally, geographical origin conditions stood out as a key factor influencing their chemical composition.

CONCLUSION

Altogether, the present work provides useful information on the chemical composition of the taxa under investigation, while our findings support the opinion that Origanum × lirium should be considered not as a separate species, but rather as a hybrid on the way to becoming a species.

Phytochemical constituents, biological activities, and health-promoting effects of the genus Origanum

Origanum species are mostly distributed around the Mediterranean, Euro-Siberian, and Iran-Siberian regions. Since time immemorial, the genus has popularly been used in Southern Europe, as well as on the American continent as a spice now known all over the world under the name "oregano" or "pizza-spice." Origanum plants are also employed to prepare bitter tinctures, wines, vermouths, beer, and kvass. The major components of Origanum essential oil are various terpenes, phenols, phenolic acids, and flavonoids with predominant occurrence of carvacrol and thymol (with reasonable amounts of p-cymen and -terpinene) or of terpinene-4-ol, linalool, and sabinene hydrate. Many species of Origanum genus are used to treat kidney, digestive, nervous, and respiratory disorders, spasms, sore throat, diabetes, lean menstruation, hypertension, cold, insomnia, toothache, headache, epilepsy, urinary tract infections, etc. Origanum essential oil showed potent bioactivities owing to its major constituents' carvacrol, thymol, and monoterpenes. Several preclinical studies evidenced its pharmacological potential as antiproliferative or anticancer, antidiabetic, antihyperlipidemic, anti-obesity, renoprotective, antiinflammatory, vasoprotective, cardioprotective, antinociceptive, insecticidal, and hepatoprotective properties. Its nanotechnological applications as a promising pharmaceutical in order to enhance the solubility, physicochemical stability, and the accumulation rate of its essential oils have been investigated. However, Origanum has been reported causing angioedema, perioral dermatitis, allergic reaction, inhibition of platelet aggregation, hypoglycemia, and abortion. Conclusive evidences are still required for its clinical applications against human medical conditions. Toxicity analyses and risk assessment will aid to its safe and efficacious application. In addition, elaborate structure-activity studies are needed to explore the potential use of Origanum-derived phytochemicals as promising drug candidates.

Acute toxicity and repellent activity of the Origanum scabrum Boiss. & Heldr. (Lamiaceae) essential oil against four mosquito vectors of public health importance and its biosafety on non-target aquatic organisms

The recent outbreaks of dengue, chikungunya, and Zika virus highlighted the pivotal importance of mosquito vector control in tropical and subtropical areas worldwide. However, mosquito control is facing hot challenges, mainly due to the rapid development of pesticide resistance in Culicidae and the limited success of biocontrol programs on Aedes mosquitoes. In this framework, screening botanicals for their mosquitocidal potential may offer effective and eco-friendly tools in the fight against mosquitoes. In the present study, the essential oil (EO) obtained from the medicinal plant Origanum scabrum was analyzed by GC-MS and evaluated for its mosquitocidal and repellent activities towards Anopheles stephensi, Aedes aegypti, Culex quinquefasciatus, and Culex tritaeniorhynchus. GC-MS analysis showed a total of 28 compounds, representing 97.1 % of the EO. The major constituents were carvacrol (48.2 %) and thymol (16.6 %). The EO was toxic effect to the A. stephensi, A. aegypti, C. quinquefasciatus, and C. tritaeniorhynchus larvae, with LC₅₀ of 61.65, 67.13, 72.45, and 78.87 μg/ml, respectively. Complete ovicidal activity was observed at 160, 200, 240, and 280 μg/ml, respectively. Against adult mosquitoes, LD₅₀ were 122.38, 134.39, 144.53, and 158.87 μg/ml, respectively. In repellency assays, the EOs tested at 1.0, 2.5, and 5.0 mg/cm² concentration of O. scabrum gave 100 % protection from mosquito bites up to 210, 180, 150, and 120 min, respectively. From an eco-toxicological point of view, the EO was tested on three non-target mosquito predators, Gambusia affinis, Diplonychus indicus, and Anisops bouvieri, with LC₅₀ ranging from 4162 to 12,425 μg/ml. Overall, the EO from O. scabrum may be considered as a low-cost and eco-friendly source of phytochemicals to develop novel repellents against Culicidae.