Oral Efficacy of Apigenin against Cutaneous Leishmaniasis: Involvement of Reactive Oxygen Species and Autophagy as a Mechanism of Action

Background

The treatment for leishmaniasis is currently based on pentavalent antimonials and amphotericin B; however, these drugs result in numerous adverse side effects. The lack of affordable therapy has necessitated the urgent development of new drugs that are efficacious, safe, and more accessible to patients. Natural products are a major source for the discovery of new and selective molecules for neglected diseases. In this paper, we evaluated the effect of apigenin on Leishmania amazonensis in vitro and in vivo and described the mechanism of action against intracellular amastigotes of L. amazonensis.

Methodology/Principal Finding

Apigenin reduced the infection index in a dose-dependent manner, with IC₅₀ values of 4.3 μM and a selectivity index of 18.2. Apigenin induced ROS production in the L. amazonensis-infected macrophage, and the effects were reversed by NAC and GSH. Additionally, apigenin induced an increase in the number of macrophages autophagosomes after the infection, surrounding the parasitophorous vacuole, suggestive of the involvement of host autophagy probably due to ROS generation induced by apigenin. Furthermore, apigenin treatment was also effective in vivo, demonstrating oral bioavailability and reduced parasitic loads without altering serological toxicity markers.

Conclusions/Significance

In conclusion, our study suggests that apigenin exhibits leishmanicidal effects against L. amazonensis-infected macrophages. ROS production, as part of the mechanism of action, could occur through the increase in host autophagy and thereby promoting parasite death. Furthermore, our data suggest that apigenin is effective in the treatment of L. amazonensis-infected BALB/c mice by oral administration, without altering serological toxicity markers. The selective in vitro activity of apigenin, together with excellent theoretical predictions of oral availability, clear decreases in parasite load and lesion size, and no observed compromises to the overall health of the infected mice encourage us to supports further studies of apigenin as a candidate for the chemotherapeutic treatment of leishmaniasis.

Leishmaniasis is an important neglected disease caused by protozoa of the genus Leishmania and affects more than 12 million people worldwide. Pentavalent antimonials and amphotericin B have been used for decades to treat leishmaniasis; however, these drugs result in numerous adverse side effects, have variable efficacy and are subject to parasite resistance. The lack of suitable therapy necessitates the development of novel antileishmanial compounds. In this study, we investigated the antileishmanial activity of apigenin in vitro and in vivo and described the mechanism of action against intracellular amastigotes of Leishmania amazonensis. Apigenin reduced the infection index in a dose-dependent manner and increased reactive oxygen species (ROS) generation. Additionally, apigenin induced an increase in the number of macrophages autophagosomes after the infection, surrounding the parasitophorous vacuole, suggestive of the involvement of host autophagy probably due to ROS generation induced by apigenin. Furthermore, treatment with apigenin was also effective in vivo, showing oral bioavailability and significantly reducing lesion sizes and parasite burden without altering serological toxicity markers.

Effect of Apigenin on Leishmania amazonensis Is Associated with Reactive Oxygen Species Production Followed by Mitochondrial Dysfunction

Leishmaniasis is an important neglected disease caused by protozoa of the genus Leishmania that affects more than 12 million people worldwide. Leishmaniasis treatment requires the administration of toxic and poorly tolerated drugs, and parasite resistance greatly reduces the efficacy of conventional medications. Apigenin (1), a naturally occurring plant flavone, has a wide range of reported biological effects. In this study, antileishmanial activity of 1 in vitro was investigated, and its mechanism of action against Leishmania amazonensis promastigotes was described. Treatment with 1 for 24 h resulted in concentration-dependent inhibition of cellular proliferation (IC50 = 23.7 μM) and increased reactive oxygen species (ROS) generation. Glutathione and N-acetyl-l-cysteine protected L. amazonensis from the effects of 1 and reduced ROS levels after the treatment. By contrast, oxidized glutathione did not reduce the levels of ROS caused by 1 by not preventing the proliferation inhibition. Apigenin 1 also induced an extensive swelling in parasite mitochondria, leading to an alteration of the mitochondrial membrane potential, rupture of the trans-Golgi network, and cytoplasmic vacuolization. These results demonstrate the leishmanicidal effect of 1 and suggest the involvement of ROS leading to mitochondrial collapse as part of the mechanism of action.

Reactive oxygen species production by quercetin causes the death of Leishmania amazonensis intracellular amastigotes

The present study reports the mechanism of the antileishmanial activity of quercetin against the intracellular amastigote form of Leishmania amazonensis. Treatment with 1 reduced the infection index in L. amazonensis-infected macrophages in a dose-dependent manner, with an IC₅₀ value of 3.4 μM and a selectivity index of 16.8, and additionally increased ROS generation also in a dose-dependent manner. Quercetin has been described as a pro-oxidant that induces the production of reactive oxygen species, which can cause cell death. Taken together, these results suggest that ROS production plays a role in the mechanism of action of 1 in the control of intracellular amastigotes of L. amazonensis.