Inhibition of Leishmania arginase leads to a decrease in parasite growth and infectivity and thus represents an attractive therapeutic strategy. We evaluated the inhibitory potential of selected naturally occurring phenolic substances on Leishmania infantum arginase (ARGLi) and investigated their antileishmanial activity in vivo. ARGLi exhibited a V_max of 0.28 ± 0.016 mM/min and a K_m of 5.1 ± 1.1 mM for L-arginine. The phenylpropanoids rosmarinic acid and caffeic acid (100 µM) showed percentages of inhibition of 71.48 ± 0.85% and 56.98 ± 5.51%, respectively. Moreover, rosmarinic acid and caffeic acid displayed the greatest effects against L. infantum with IC₅₀ values of 57.3 ± 2.65 and 60.8 ± 11 μM for promastigotes, and 7.9 ± 1.7 and 21.9 ± 5.0 µM for intracellular amastigotes, respectively. Only caffeic acid significantly increased nitric oxide production by infected macrophages. Altogether, our results broaden the current spectrum of known arginase inhibitors and revealed promising drug candidates for the therapy of visceral leishmaniasis.

Context: Leishmania amazonensis is the main agent of diffuse cutaneous leishmaniasis, a disease characterized by lesional polymorphism and the commitment of skin surface. Previous reports demonstrated that the Citrus genus possess antimicrobial activity. Objective: This study evaluated the anti-L. amazonensis activity of Citrus sinensis (L.) Osbeck (Rutaceae) extracts. Materials and methods: Citrus sinensis dried leaves were subjected to maceration with hexane (CH), ethyl acetate (CEA), dichloromethane/ethanol (CD/Et – 1:1) or ethanol/water (CEt/W – 7:3). Leishmania amazonensis promastigotes were treated with C. sinensis extracts (1–525 μg/mL) for 120 h at 27 °C. Ultrastructure alterations of treated parasites were evaluated by transmission electron microscopy. Cytotoxicity of the extracts was assessed on RAW 264.7 and J774.G8 macrophages after 48-h treatment at 37 °C using the tetrazolium assay. In addition, Leishmania-infected macrophages were treated with CH and CD/Et (10–80 μg/mL). Results: CH, CD/Et and CEA displayed antileishmanial activity with 50% inhibitory activity (IC₅₀) of 25.91 ± 4.87, 54.23 ± 3.78 and 62.74 ± 5.04 μg/mL, respectively. Parasites treated with CD/Et (131.2 μg/mL) presented severe alterations including mitochondrial swelling, lipid body formation and intense cytoplasmic vacuolization. CH and CD/Et demonstrated cytotoxic effects similar to that of amphotericin B in the anti-amastigote assays (SI of 2.16, 1.98 and 1.35, respectively). Triterpene amyrins were the main substances in CH and CD/Et extracts. In addition, 80 μg/mL of CD/Et reduced the number of intracellular amastigotes and the percentage of infected macrophages in 63% and 36%, respectively. Conclusion: The results presented here highlight C. sinensis as a promising source of antileishmanial agents.

Background/Objectives: The anti-Leishmania potential of Curcuma longa and its derivatives, such as curcuminoids, is well-established, yet their mechanisms of action remain underexplored. This study investigates the inhibitory effects of C. longa extracts and curcumin on Leishmania infantum arginase, a key enzyme in polyamine and trypanothione biosynthesis, and evaluates their antiparasitic activity. Methods: Extracts were prepared via rhizome successive maceration with hexane (HEXCURC), dichloromethane (DCCURC), and ethanol (ETOHCURC) and chemically characterized by a combination of chromatographic and spectrometric methods. The inhibition of recombinant L. infantum arginase (LiARG) was assessed by urea quantification, while molecular docking explored interactions between the main compounds annotated in the extracts and the enzyme’s active site. Biological activity was tested against L. infantum promastigotes, intracellular amastigotes, and mammalian cells. Results: LC-MS and GC-MS revealed curcuminoids and turmerones as main compounds annotated in the extracts. DCCURC, HEXCURC, and curcumin showed the strongest LiARG inhibition (IC₅₀ = 10.04, 14.4, and 17.55 μg/mL, respectively). Docking analysis revealed that curcumin, demethoxycurcumin, and bisdemethoxycurcumin bind near the active site, with binding energies of –3.43, –4.14, and –3.99 kcal/mol, respectively. Curcumin demonstrated superior anti-promastigote activity (IC₅₀ = 15.01 μg/mL) and selectivity (SI = 12.7) compared to the extracts. It also significantly reduced amastigote burden in infected macrophages (IC₅₀ = 13.6 μg/mL). Conclusions: This is the first report demonstrating that C. longa extracts and curcumin inhibit LiARG. These findings support curcumin’s potential as a lead compound for developing multi-target therapies against leishmaniasis, combining enzyme inhibition with direct antiparasitic effects.

Leishmania amazonensis, a cause of cutaneous leishmaniasis in Brazil, is a neglected disease with toxic and inconsistently effective treatments. The parasite’s survival depends on managing oxidative stress, making redox-regulating enzymes potential therapeutic targets. Geopropolis, a resinous product from native stingless bees, shows promising antiparasitic effects. This study aims to evaluate the anti-L. amazonensis activity of geopropolis produced by Melipona bicolor, M. marginara, M. mondury, and M. quadrifasciata (two samples), targeting enzymes responsible for the parasite’s redox balance. Ethanol extracts of geopropolis produced by each bee (BCRL, MRGT, MNDY, MNDA(1), and MNDA(2), respectively) were analyzed for total phenolics and flavonoids. Promastigotes and axenic amastigotes were treated with various extract concentrations, and parasite viability was assessed using the resazurin reduction method. Cytotoxicity was tested on peritoneal macrophages, RAW 264.7, VERO cell lines (MTT assay), and erythrocytes (hemolysis assay). Additionally, mitochondrial dehydrogenase activity, reactive oxygen species (ROS) production, the inhibition of recombinant arginase, and autophagic activity were also evaluated in treated parasites. MRGT showed the highest levels of phenolics (762 mg GAE/g) and flavonoids (345 mg QE/g). MDRY was more effective against promastigote and axenic amastigote forms (IC₅₀ = 168 and 19.7 µg/mL, respectively). MRGT showed lower cytotoxicity against RAW 264.7 and VERO (CC₅₀ = 654 µg/mL and 981 µg/mL, respectively). Erythrocytes exhibited reduced sensitivity to MNDA(2) (HC₅₀ = 710 µg/mL). The activity of dehydrogenases and LiARG was reduced by treating the parasites with the extracts following the induction of ROS and autophagic activity. These results highlight geopropolis extracts as a source of substances with anti-L. amazonensis activity capable of inducing oxidative stress on the parasite.