Anti-parasitic activity of a chimeric peptide Cecropin A (2−8)-Melittin (6−9) (CM11) against tachyzoites of Toxoplasma gondii and the BALB/c mouse model of acute toxoplasmosis

Toxoplasmosis is a zoonotic disease that infects most animals, including humans. Pyrimethamine/sulfadiazine is the standard treatment for toxoplasmosis. Although this treatment has been successful, it is often associated with side effects that cannot be tolerated. Therefore, various compounds have been proposed as alternative treatments for toxoplasmosis. Antimicrobial peptides (AMPs) act on various pathogens, from viruses to protozoa.

The purpose of the present study was to evaluate the effects of CM11 on in vitro and in vivo Toxoplasma gondii infection. For in vitro experiments, VERO cells were treated with different concentrations of CM11 (1–128 μg/ml) compared to sulfadiazine (SDZ) (0.78–100 μg/ml). MTT and lactate dehydrogenase (LDH) assays evaluated the cell viability and plasma membrane integrity. Then, the inhibitory concentration (IC₅₀) values were determined for treating tachyzoites of T. gondii before or on cells previously infected. Annexin V-FITC/propidium iodide (PI) staining was used to distinguish viable and apoptotic cells. The effect of CM11, SDZ, and a combination of CM11 and SDZ was evaluated in the BALB/c mouse model of acute toxoplasmosis.

CM11 was effective on tachyzoites of T. gondii and had a time and dose-dependent manner. The results of the MTT assay showed that the CC₅₀ values of CM11 and SDZ were estimated at 17.4 µg/ml and 62.3 µg/ml after 24-h, respectively. The inhibitory concentration (IC₅₀) of CM11 and SDZ on infected cells was estimated at 1.9 µg/ml and 1.4 µg/ml after 24-h, respectively. The highest rate of apoptosis (early and late) in high concentrations of SDZ and CM11 was determined for tachyzoites (2.13 % and 13.88 %), non-infected VERO cells (6.1 % and 19.76 %), and infected VERO cells (7.45 % and 29.9 %), respectively. Treating infected mice with CM11 and a combination of CM11 and SDZ had increased survival time.

Based on the mentioned results, it can be concluded that CM11 has a beneficial effect on tachyzoites of T. gondii in vitro. The result of the mouse model suggests that CM11, either alone or in combination with other chemotherapeutic agents, could be a potential therapeutic for toxoplasmosis. Hence, antimicrobial peptides could be applied as promising anti-toxoplasma agents for treating toxoplasmosis.