Antileishmanial effect of silver nanoparticles and their enhanced antiparasitic activity under ultraviolet light

Abstract

Leishmaniasis is a protozoan vector-borne disease and is one of the biggest health problems of the world. Antileishmanial drugs have disadvantages such as toxicity and the recent development of resistance. One of the best-known mechanisms of the antibacterial effects of silver nanoparticles (Ag-NPs) is the production of reactive oxygen species to which Leishmania parasites are very sensitive. So far no information about the effects of Ag-NPs on Leishmania tropica parasites, the causative agent of leishmaniasis, exists in the literature. The aim of this study was to investigate the effects of Ag-NPs on biological parameters of L. tropica such as morphology, metabolic activity, proliferation, infectivity, and survival in host cells, in vitro. Consequently, parasite morphology and infectivity were impaired in comparison with the control. Also, enhanced effects of Ag-NPs were demonstrated on the morphology and infectivity of parasites under ultraviolet (UV) light. Ag-NPs demonstrated significant antileishmanial effects by inhibiting the proliferation and metabolic activity of promastigotes by 1.5- to threefold, respectively, in the dark, and 2- to 6.5-fold, respectively, under UV light. Of note, Ag-NPs inhibited the survival of amastigotes in host cells, and this effect was more significant in the presence of UV light. Thus, for the first time the antileishmanial effects of Ag-NPs on L. tropica parasites were demonstrated along with the enhanced antimicrobial activity of Ag-NPs under UV light. Determination of the antileishmanial effects of Ag-NPs is very important for the further development of new compounds containing nanoparticles in leishmaniasis treatment.

Keywords: Leishmania; leishmaniasis; nanotechnology; parasite.

Figure 1

Characterization of silver nanoparticles: (A) transmission electron microscope (TEM) image at the scale of 20 nm, (B) TEM image at the scale of 50 nm, and (C) size distributions with dynamic light scattering analysis.

Figure 2

Microscopic view of parasites (A) in the control group (not exposed to silver nanoparticles [Ag-NPs]), (B) in the group exposed to Ag-NPs in the dark, and (C) in the group exposed to Ag-NPs under ultraviolet light (Giemsa staining, magnification 100×).

Figure 3

Microscopic views of the effects of silver nanoparticles (Ag-NPs) on metabolic activity of Leishmania tropica promastigotes in the dark: (A) parasites in the control group (not exposed to Ag-NPs), (B) the cytopathic effects of Ag-NPs at 150 μg/mL, and (C) the cytopathic effects of Ag-NPs at 200 μg/mL. Arrows in (A) indicate the formation of formazan crystals and in (B) and (C) indicate the clusters of Ag-NPs (magnification 40×).

Figure 4

Microscopic views of the effects of silver nanoparticles (Ag-NPs) on metabolic activity of Leishmania parasites under ultraviolet light: (A) parasites in the control group (not exposed to Ag-NPs), (B) the cytopathic effects of Ag-NPs at 150 μg/mL, and (C) the cytopathic effects of Ag-NPs at 200 μg/mL. Arrows in (A) indicate the formation of formazan crystals and in (B) and (C) indicate the clusters of Ag-NPs (magnification 40×).

Figure 5

The effects of different concentrations of silver nanoparticles on metabolic activity of Leishmania tropica promastigotes both in the absence and in the presence of ultraviolet (UV) light (I, control group; II, 25 μg/mL; III, 50 μg/mL; IV, 100 μg/mL; V, 150 μg/mL; VI, 200 μg/mL).

Figure 6

Effects of silver nanoparticles (Ag-NPs) on the proliferation of Leishmania tropica promastigotes in the dark and under ultraviolet (UV) light in different incubation periods (I, parasites in control group in the dark; II, parasites exposed to Ag-NPs in the dark; III, parasites in control group exposed to UV light; IV, parasites exposed to Ag-NPs under UV light). Ag-NPs had significant effects on Leishmania parasites in the experiment groups compared with the control groups. The biggest effect was observed in the experiment group exposed to Ag-NPs and UV light.

Figure 7

Microscopic views of macrophages infected or not infected by parasites after being stained with Giemsa. Leishmania tropica promastigotes (A) in the control group held in the dark and (B) in the control group exposed to ultraviolet (UV) light infected the macrophages. (C) L. tropica promastigotes exposed to silver nanoparticles (Ag-NPs) in the dark also infected macrophages, but their infectivity was very low compared with the control groups. (D) L. tropica promastigotes exposed to Ag-NPs under UV light did no infect the macrophages. (Arrows indicate macrophage-infected parasites.)

Figure 8

Effects of different concentrations of silver nanoparticles on the infection index of Leishmania tropica amastigotes both in the absence and in the presence of ultraviolet (UV) light.