Amoebicidal activity and chemical composition of Pterocaulon polystachyum (Asteraceae) essential oil.

Acanthamoeba species are free-living amoebae that constitute an etiological agent of Acanthamoeba keratitis, an illness that may cause severe ocular inflammation and blindness and has a very difficult treatment. These molecules that are found in plants may be an alternative for the development of new drugs. Plants of the genus Pterocaulon (Asteraceae) are used in folk medicine as an antiseptic and antifungal agent. In this work, we analyzed Pterocaulon polystachyum essential oil and assessed its amoebicidal activity against Acanthamoeba polyphaga. The leaves of the fresh plant submitted to hydrodistillation yielded 0.15% (w/v) of essential oil that was analyzed by gas chromatography-mass spectrometry being E-sesquilavandulyl acetate as the major component, representing 43.8% of the oil. For the assessment of the amoebicidal activity, concentrations of 20, 10, 5, 2.5, and 1.25 mg/mL of essential oil were tested, being lethal to 100% of the A. polyphaga trophozoites at the concentrations of 10 and 20 mg/mL in 24 and 48 h. The cytotoxic effect of essential oil was also tested in mammalian cells using MTT assay. Amoebicidal activity results are in accordance with previous work in which the lipophilic compounds from this plant were active against Acanthamoeba castellanii. However, further studies with the major component of the essential oil will be carried out.

Acaricidal properties of the essential oil and precocene II obtained from Calea serrata (Asteraceae) on the cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae).

Calea serrata Less. (Asteraceae), an endemic species of south Brazil known as "quebra-tudo", is used in Afro-Brazilian religious rituals and in folk medicine for treating liver disorders. Phytochemical studies of the n-hexane extract of this plant demonstrated the presence of precocene II, a benzopyran derivative known for its insecticidal activity. The aim of this work was to isolate this benzopyran and determine the chemical composition of the essential oil of C. serrata and further to evaluate the acaricidal activity of the essential oil and precocene II against the larvae of Rhipicephalus (Boophilus) microplus. The LC(99.9) and LC(50) values obtained with the oil, which presents precocene II and sesquiterpenes, were 3.94 µL/mL and 0.28 µL/mL, respectively. For precocene II this values were 4.25mg/mL and 1.78 mg/mL, respectively. The results indicate a synergistic interaction between the components of the oil and precocene II.

Acaricidal properties of the essential oil from Hesperozygis ringens (Lamiaceae) on the cattle tick Riphicephalus (Boophilus) microplus.

Hesperozygis ringens (Benth.) Epling (Lamiaceae) is a strongly aromatic plant employed popularly for its antiparasitic properties. The leaves afforded 4% of essential oil constituted mainly by pulegone (86%). Laboratory tests were carried out to determine the toxicity of the essential oil species on engorged females and larvae of the cattle tick Riphicephalus (Boophilus) microplus using the adult immersion test (AIT) and the larval immersion test (LIT). It was observed that the essential oil at the concentration of 50 microL/mL and 25 microL/mL inhibited the egg laying significatively in relation to the controls and the eggs from these treated females were affected by the oil; the hatching was inhibited in 95% and 30%, respectively. In the LIT it was verified that the LC(99.9), LC(50) and LC(1) was 0.541 microL/mL, 0.260 microL/mL and 0.015 microL/mL, respectively. Pulegone, isolated from the oil, showed similar effect on the females and on the larvae, indicating that it is responsible for the oil activity.