Antileishmanial activity of Ptilostemon chamaepeuce subsp. cyprius

Phytochemicals from unexplored plant species may be vital to unlocking pharmaceutical antibiotic and antiparasitic discoveries. New compounds need to be discovered to combat antimicrobial resistance. This study aimed to investigate ethanolic leaf extracts from five endemic and four indigenous plants from Cyprus for antibacterial, antileishmanial, and antioxidant activities.

Ethanolic leaf extracts were screened for antibacterial activity using a broth microdilution assay and iodonitrotetrazolium chloride (INT) as a colourimetric redox indicator for determining the minimum inhibitory concentration (MIC) against four Gram-positive and two Gram-negative American Type Culture Collection (ATCC) reference bacteria. Total phenolic content (TPC), total flavonoid content (TFC) and radical scavenging activity assays were performed to screen for antioxidant potential. Leishmania infantum clinical culture (MCAN/CY/2005/CD57) was used to screen the extracts for in vitro antileishmanial activity. Their cytotoxicity in vitro was assessed using the resazurin fluorometric assay with a HepG2 cell line. As an estimate of in vitro toxicity, a brine shrimp lethality assay was performed.

The ethanol extract of Ptilostemon chamaepeuce subsp. cyprius (Greuter) Chrtek & B. Slavik demonstrated antibacterial activity against Enterococcus faecalis (ATCC 29212) with minimum inhibitory concentration (MIC) < 0.625 mg/mL and antileishmanial activity against a clinical isolate of L.infantum (MCAN/CY/2005/CD57) from an infected dog (promastigote IC₅₀ of 105.7 ± 2.5 μg/mL and amastigote IC₅₀ of 118.5 ± 4.3 μg/mL) after 48 h and compared to the activity of the reference drug, miltefosine (IC₅₀ of 3.7 ± 0.1 μg/mL and 18.5 ± 2.3 μg/mL, respectively). Liquid-chromatography-mass spectrometry (LC-MS) analysis revealed the presence of at least five sesquiterpene lactones (STLs) in P. cham. subsp. cyprius ethanolic extract. The main compound, deacylcynaropicrin, based on its high-resolution mass spectrum, is believed to be primarily responsible for the antileishmanial activity observed in vitro. Quercus alnifolia Poech ethanolic extract showed antibacterial activity against four Gram-positive and one Gram-negative bacteria with MIC values of < 0.625 mg/mL, respectively, and antioxidant capacity in DPPH radical scavenging assay with IC₅₀ of 0.155 ± 0.002 mg/mL and compared to ascorbic acid (IC₅₀ of 0.036 ± 0.000 mg/mL) and Trolox (IC₅₀ of 0.047 ± 0.001 mg/mL).

The ethanolic extract of Ptilostemon chamaepeuce subsp. cyprius demonstrated dose-dependent antileishmanial activity. This is the first data report of P.cham. subsp. cyprius and Q.alnifolia ethanolic extracts to indicate antibacterial, antileishmanial and antioxidant activities in preliminary investigations. Moreover, this is the first report on STLs in P. cham. subsp. cyprius, and future studies are needed to confirm if they are responsible for the in vitro antileishmanial activity. These findings highlight the potential of these endemic plants as sources for developing new drugs targeting Gram-positive bacterial infections and leishmaniasis, encouraging further pharmaceutical research.