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 rtanjensis Diklić & Milojević (fam. Lamiaceae) is an endemic, critically endangered plant, protected by the law in Serbia. Various biological activities have been ascribed to its major constituents, nepetalactones. In this study we describe for the first time cytotoxic activity of N. rtanjensis essential oil (EO), obtained from field cultivated plants, which was found to be especially rich in trans,cis-nepetalactone. MTT assays indicated that after 72 h of treatment the EO exhibited cytotoxic activity on investigated cancer cell lines: HeLa, K562, A549, LS-174 and MDA-MB-231. Normal cell line (MRC-5) was the least sensitive to the treatment and IC50 value for this cell line was not reached within the tested range of EO concentrations (up to 0.1 μL/mL). Analysis of morphological changes of treated cells confirmed the higher sensitivity of tumor cells than normal cells to the tested EO. Application of N. rtanjensis EO resulted in the appearance of morphological changes in tested cancer cell lines characteristic for apoptotic cell death, and induced perturbations of the cell cycle of HeLa cells. In addition, upregulation of Bax and p53, and downregulation of Bcl-2, and Skp2 genes, involved in apoptotic signalling cascades, confirmed an apoptosis-inducing effect of N. rtanjensis EO on HeLa cells. Presented results highlighted the potential of N. rtanjensis EO in anticancer therapy.