Amoebicidal activity of essential oils and essential oil-based microemulsions of Aloysia citrodora Ortega ex Pers., Cymbopogon winterianus Jowitt ex Bor and Ocimum gratissimum L. against Acanthamoeba polyphaga trophozoites.

AIMS: Evaluate the in vitro efficacy of the essential oils derived from Aloysia citrodora (Verbenaceae), Cymbopogon winterianus (Poaceae), and Ocimum gratissimum (Lamiaceae) against Acanthamoeba polyphaga trophozoites. Additionally, microemulsions formulated with these essential oils, along with their major components, were analyzed. METHODS AND RESULTS: The prepared microemulsions were characterized using polarized light microscopy and rheological techniques. The amoebicidal activity was determined by measuring the inhibitory concentration (IC50). Flow cytometry was employed to detect membrane damage and alterations in trophozoites size. The results revealed transparent and thermodynamically stable microemulsions. The essential oil from O. gratissimum exhibited a lower IC50, with values of 280.66 µg mL-1 and 47.28 µg mL-1 after 24 and 48 hours, respectively. When microemulsions containing essential oils were tested, the IC50 values exhibited a reduction of over 80% after 24 hours. Particularly, eugenol, a constituent of the O. gratissimum essential oil, displayed higher amoebicidal activity. The essential oils also caused damage to the cell membrane, resulting in the subsequent death of the trophozoites. CONCLUSIONS: The EOs of A. citrodora, C. winterianus, and O. gratissimum and their microemulsions showed antiparasitic effect against A. polyphaga trophozoites, representing promising alternatives for the treatment of diseases caused by this protozoan.

Effect of 3-Carene and the Micellar Formulation on Leishmania (Leishmania) amazonensis.

Leishmaniases are neglected tropical diseases caused by obligate intracellular protozoa of the genus Leishmania. The drugs used in treatment have a high financial cost, a long treatment time, high toxicity, and variable efficacy. 3-Carene (3CR) is a hydrocarbon monoterpene that has shown in vitro activity against some Leishmania species; however, it has low water solubility and high volatility. This study aimed to develop Poloxamer 407 micelles capable of delivering 3CR (P407-3CR) to improve antileishmanial activity. The micelles formulated presented nanometric size, medium or low polydispersity, and Newtonian fluid rheological behavior. 3CR and P407-3CR inhibited the growth of L. (L.) amazonensis promastigote with IC50/48h of 488.1 ± 3.7 and 419.9 ±1.5 mM, respectively. Transmission electron microscopy analysis showed that 3CR induces multiple nuclei and kinetoplast phenotypes and the formation of numerous cytosolic invaginations. Additionally, the micelles were not cytotoxic to L929 cells or murine peritoneal macrophages, presenting activity on intracellular amastigotes. P407-3CR micelles (IC50/72 h = 0.7 ± 0.1 mM) increased the monoterpene activity by at least twice (3CR: IC50/72 h >1.5 mM). These results showed that P407 micelles are an effective nanosystem for delivering 3CR and potentiating antileishmanial activity. More studies are needed to evaluate this system as a potential therapeutic option for leishmaniases.

Thermosensitive system formed by poloxamers containing carvacrol: An effective carrier system against Leishmania amazonensis.

The drugs used in the treatment of leishmaniasis show problems concerning side effects and toxicity. As a result, the search for new actives is necessary, and natural products like carvacrol - 5-isopropyl-2-methylphenol, become a relevant alternative. To enable the use of carvacrol as an antileishmanial agent, thermosensitive hydrogels were developed from poloxamer triblock copolymers 407 (P407) and 188 (P188). Carvacrol-free and carvacrol-containing hydrogels were obtained from P407 alone and from the mixture of P407 and P188. The hydrogels were subjected to Differential scanning calorimetry, Small-angle X-ray scattering, Scanning electron microscopy, and Rheology analysis. The activity of hydrogels and carvacrol isolated against promastigotes and intracellular amastigotes of Leishmania amazonensis and their cytotoxicity in mammalian cells was determined. The sol-gel transition temperature for the binary hydrogel containing carvacrol (HG407/188CA) was 37.04 ± 1.35 °C. HG407/188CA presented lamellar structure at temperatures of 25 °C and 37 °C. HG407/188CA and carvacrol presented IC50 against Leishmania amazonensis promastigotes of 18.68 ± 1.43 µg/mL and 23.83 ± 3.32 µg/mL, respectively, and IC50 against Leishmania amazonensis amastigotes of 35.08 ± 0.75 µg/mL and 29.32 ± 0.21 µg/mL, respectively. HG407/188CA reduced the toxicity of carvacrol in all mammalian cells evaluated, raising the CC50 in murine peritoneal macrophages from 40.23 ± 0.21 µg/mL to 332.6 ± 4.89 µg/mL, obtaining a Selectivity Index (SI) of 9.5 against 1.37 of the isolated carvacrol. HG407/188CA provided higher selectivity of carvacrol for the parasite. Thus, the binary hydrogel obtained may enable the use of carvacrol as a potential antileishmanial agent.

Nisin Induces Cell-Cycle Arrest in Free-Living Amoebae Acanthamoeba castellanii.

PURPOSE: Acanthamoeba spp. are free-living amoebas with worldwide distribution and play an important role as disease-causing agents in humans. Drug inability to completely eradicate these parasites along with their toxic effects suggest urgent need for new antimicrobials. Nisin is a natural antimicrobial peptide produced by Lactococcus lactis. Nisin is also the only bacteriocin approved for use in food preservation. In this work, we analyzed the effect of nisin on the growth of Acanthamoeba castellanii trophozoites. METHODS: A total of 8 × 104 trophozoites were exposed to increasing concentrations of nisin to determine its activity. Changes in cell membrane and cellular cycle of trophozoites were investigated by flow cytometry, and nisin cytotoxicity in mammalian cells was evaluated in L929 cells by MTT method. RESULTS: After 24 h exposure to increasing nisin concentrations, an IC50 of 4493.2 IU mL-1 was obtained for A. castellanii trophozoites. However, after 72 h a recovery in amoebic growth was observed, and it was no longer possible to determine IC50. Flow cytometry analysis showed that nisin has no effect on the membrane integrity. Treatment with nisin induced cell-cycle arrest during G1 and S phases in A. castellanii trophozoites, which recovered their growth after 72 h. CONCLUSION: This is one of the first studies showing the effect of internationally approved nisin against A. castellanii trophozoites. Nisin caused cell-cycle arrest in trophozoites, momentarily interfering with the DNA replication process. The data highlight the amoebostatic activity of nisin, and suggest its use as an adjuvant for the treatment of infections caused by Acanthamoeba spp.