Two Balkan Peninsula endemics, Nepeta rtanjensis and N. argolica subsp. argolica, both characterized by specialized metabolite profiles predominated by iridoids and phenolics, are differentiated according to the stereochemistry of major iridoid aglycone nepetalactone (NL). For the first time, the present study provides a comparative analysis of antimicrobial and immunomodulating activities of the two Nepeta species and their major iridoids isolated from natural sources—cis,trans-NL, trans,cis-NL, and 1,5,9-epideoxyloganic acid (1,5,9-eDLA), as well as of phenolic acid rosmarinic acid (RA). Methanol extracts and pure iridoids displayed excellent antimicrobial activity against eight strains of bacteria and seven strains of fungi. They were especially potent against food-borne pathogens such as L. monocytogenes, E. coli, S. aureus, Penicillium sp., and Aspergillus sp. Targeted iridoids were efficient agents in preventing biofilm formation of resistant P. aeruginosa strain, and they displayed additive antimicrobial interaction. Iridoids are, to a great extent, responsible for the prominent antimicrobial activities of the two Nepeta species, although are probably minor contributors to the moderate immunomodulatory effects. The analyzed iridoids and RA, individually or in mixtures, have the potential to be used in the pharmaceutical industry as potent antimicrobials, and in the food industry to increase the shelf life and safety of food products.

Nepeta nuda L., a notable medicinal species in the tradition of the Balkan region, is a rich source of bioactive iridoids and phenolics previously described as high-resolution taxonomical classifiers for the genus Nepeta. However, their potential in investigating intra-species differentiation is here described for the first time. The aim was to recognize the sources of natural chemical diversity and their association with the genetic variability both within and among N. nuda populations in the Central Balkans. Chemical diversity was assessed from methanol extracts and essential oils through untargeted and targeted metabolomics using state-of-the-art analytical tools, covering a broad spectrum of compounds that represent the N. nuda metabolome. We found that chemodiversity primarily resides within populations of N. nuda, and similar results were obtained at the DNA level using microsatellite markers. The low genetic and chemical differentiation of the studied N. nuda populations implies that their metabolomic profiles may be less influenced by geographic distance and variable environmental conditions within the Central Balkans, as they are under the pivotal control of their genetic backgrounds. Screening the distribution of the major bioactive compounds belonging to phenolics (phenolic acids and flavonoids) and iridoids (both aglycones and glycosylated forms), within and among N. nuda populations, is able to guarantee mass spectrometry-based tools for the selection of elite representative genotypes with practical importance. The knowledge acquired will allow us to delve deeper into the molecular background of N. nuda chemical diversity, which is the course of our further work.

Frankincense resin (Boswellia serrata), native to arid regions of India, the Middle East, and parts of Africa, has been highly valued for its medicinal properties. This study evaluated the antimicrobial potential of methanolic extracts of Boswellia serrata resin against Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria monocytogenes. High-performance thin-layer chromatography (HPTLC) coupled with bioautography identified bioactive zones, while Liquid Chromatography–Mass Spectrometry (LC-MS) quantified the phenolic and terpenoid compounds. The cytotoxicity was assessed on HaCaT human keratinocyte cells to evaluate the safety for dermatological applications. The results demonstrated significant antibacterial activity, particularly against S. aureus and L. monocytogenes. The bioautograms revealed that samples from central and southern Serbia showed the highest antimicrobial effect against the tested bacterial strains. The active compounds included 11-keto-β-boswellic acid (up to 3733.96 μg/g), gallic acid (110.93 μg/g), and naringenin (53.13 μg/g). Cytotoxicity assays confirmed non-toxic effects at 10 µg/mL, with sample 6 enhancing the keratinocyte viability by 137%, while higher concentrations (50 µg/mL) showed variable cytotoxicity. These findings highlight the potential of B. serrata resin as a natural antimicrobial agent, particularly against antibiotic-resistant pathogens. Its therapeutic applicability in pharmaceutical and cosmetic formulations is promising provided that dosing ensures a balance between efficacy and safety.

Many specialized metabolites found in plants have significant potential for developing environmentally friendly weed management solutions. This review focuses on the phytotoxic effects of volatile terpenes and phenolic compounds, particularly nepetalactone, an iridoid monoterpenoid from Nepeta species, and phloretin, a dihydrochalcone predominantly found in the genus Malus. We highlight current findings on their herbicidal effects, including morphological, physiological, and biochemical responses in target plants. These results underscore their potential for developing sustainable herbicides that could control weeds with minimal environmental impact. We also discuss their soil persistence and methods to enhance their solubility, chemical stability, and bioavailability. Additionally, the possible effects on non-target organisms, such as pollinators, non-pollinating insects, and soil microbiota, are considered. However, further research and a deeper understanding of their long-term ecological impact, along with a resistance development risk assessment, is essential for the potential development of bioherbicides that could be applied in sustainable weed management practices.

The genus Nepeta is the sole representative in the plant kingdom that produces nepetalactones, a group of iridoids with a unique stereochemistry, which play key roles in plant defense and ecological interactions. This study investigates N. sibirica L., a species rich in cis,trans-nepetalactone and 1,5,9-epi-deoxyloganic acid, aiming to enhance production of these bioactive iridoids by two alternative strategies: transient expression of key iridoid biosynthesis-related genes and fungal elicitation. In vitro treatments with Trichoderma harzianum and T. viride promoted iridoid production in N. sibirica leaves. It appears that regulatory proteins COI1, MYC2, and YABBY5 provoke coordinated upregulation of the early iridoid pathway genes (NsGPPS, NsGES, NsG8H, Ns8HGO), and of NsMLPL, thus stimulating metabolic flux through the iridoid pathway and providing substrates for the downstream steps mediated by NsISY, NsNEPS1, and NsNEPS2. The N. sibirica PRISE orthologue (NsPRISE) is closely related phylogenetically to the Family 1 isoforms known as P5βRs. However, its ISY-like activity was confirmed through in vitro assays with recombinant proteins expressed heterologously in E. coli. Transient overexpression experiments, which comparatively analysed in planta function of homologous NsPRISE and previously characterized ISY and PRISE orthologues from other Nepeta species, suggested possible in vivo residual ISY-like activity of NsPRISE and its involvement in iridoid production. The current study recognized N. sibirica as a plant susceptible to agroinfiltration, with iridoid metabolism that can be induced by pathogen attack, making it an ideal candidate for developing scalable systems for bioactive compounds production.