Leishmaniasis is an infectious parasitic disease that is caused by protozoa of the genus Leishmania, a member of the Trypanosomatidae family. Leishmaniasis is classified by the World Health Organization as a neglected tropical disease that is responsible for millions of deaths worldwide. Although there are many possible treatments for leishmaniasis, these treatments remain mostly ineffective, expensive, and long treatment, as well as causing side effects and leading to the development of resistance. For novel and effective treatments to combat leishmaniasis, many research groups have sought to utilize natural products. In addition to exhibiting potential as therapeutic compounds, natural products may also contribute to the development of new drugs based on their chemical structures. This review presents the most promising natural products, including crude extracts and isolated compounds, employed against Leishmania spp.

Host nutritional status directly interferes with immunity and/or susceptibility to infectious diseases. To understand the mechanisms behind this relationship, the use of animal models and feeding protocols is necessary. In the literature, studies reporting marasmic malnutrition in mice are not common. In this context, the objective of this study was to validate a feed methodology that mimics marasmic malnutrition, examining the nutritional, biochemical, and hematological status in BALB/c mice. Weaned BALB/c mice were or were not fed a Restricted diet (36.26% carbohydrate, 8.79% protein, 4.95% fat, and 7.62 kJ/100 g). Some malnourished mice underwent a refed process with a Control diet (65.93% carbohydrate, 24.18% protein, 9.89% fat, and 15.24 kJ/100 g). The nutritional status of the mice was evaluated through phenotypic markers and hematological and biochemical parameters. Our results showed that the Restricted diet was able to induce mild malnutrition in mice, resulting in mouse weight loss of 12%, which could be reversed after refeeding. Malnourished mice demonstrated slow body growth and low body mass index (BMI) values. Malnourished mice also showed physical and behavioral changes, a reduction of 47.5% in leukocyte counts and a 2-fold increase in cholesterol levels. In conclusion, our feeding protocol was able to generate mild malnutrition and cause changes in the nutritional status of mice that could be similar to those observed in marasmic malnutrition.

Leishmania infantum infantum (LII) is one of the species that causes visceral leishmaniasis (VL) in the Old World, while L. infantum chagasi (LIC) is present in the New World. Few studies address biological differences or the behavior of these strains during infection. These parasites live inside cells of their hosts, continuously evading microbicidal mechanisms and modulating the immune responses of these cells. One of the mechanisms used by these protozoa involves the L-arginine metabolism. Understanding the differences between Leishmania species and establishing an improved murine model for study of leishmaniasis are matters of extreme importance. Thereby, the objectives of this work were to analyze the biological and molecular differences between two Leishmania infantum strains (LII and LIC) and the degree of susceptibility to infection of mice with different genetic backgrounds. The infectivity in vivo and in vitro of LII and LIC strains was evaluated in BALB/c and Swiss Webster mice, as well the NOS and ARG activities. The LII strain was more infective than the LIC strain both in vivo and in vitro. In animals infected by the LII and LIC strains, differences in NOS and ARG activities occurred. In vitro, promastigotes of LII isolated from BALB/c and Swiss Webster mice showed higher ARG activity than LIC promastigotes during the growth curve. However, no difference was observed in intracellular NO production by promastigotes of these strains. The ARG gene sequences were compared, and those of both strains were identical. However, despite the similarity, the strains showed different expression levels of this gene. It can be concluded that although L. chagasi strains are considered identical to L. infantum strains from a molecular point of view, these strains have different biological behavior.

Given the lack of investments, structure, and difficulty of metabolite isolation, promising natural product studies do not progress to preclinical studies, such as pharmacokinetics. 2′-Hydroxyflavanone (2HF) is a flavonoid that has shown promising results in different types of cancer and leishmaniasis. For accurate quantification of 2HF in BALB/c mouse blood, a validated HPLC-MS/MS method was developed. Chromatographic analysis was performed using C18 (5μm, 150 mm × 4.6 mm). The mobile phase consisted of water containing 0.1% formic acid, acetonitrile, and methanol (35/52/13 v/v/v) at a flow rate and total running time of 0.8 mL/min and 5.50 min, respectively, with an injection volume of 20 µL. 2HF was detected by electrospray ionization in negative mode (ESI-) using multiple reaction monitoring (MRM). The validated bioanalytical method showed satisfactory selectivity without significant interference for the 2HF and IS. In addition, the concentration range between 1 and 250 ng/mL showed good linearity (r = 0.9969). The method showed satisfactory results for the matrix effect. Precision and accuracy intervals varied between 1.89% and 6.76% and 95.27% and 100.77%, respectively, fitting the criteria. No degradation of 2HF in the biological matrix was observed since stability under freezing and thawing conditions, short duration, postprocessing, and long duration showed deviations less than 15%. Once validated, the method was successfully applied in a 2HF oral pharmacokinetic study with mouse blood, and the pharmacokinetic parameters were determined. 2HF demonstrated a Cmax of 185.86 ng/mL, a Tmax of 5 min, and a half-life (T1/2) of 97.52 min.

17Leishmania infantum infantum (LII) is one of the species that causes visceral 18 leishmaniasis (VL) in the Old World, while L. infantum chagasi (LIC), and is present 19 in the New World. Few studies address the biological differences, as well as the 20 behaviour of these strains during infection. These parasites live inside the cells of 21 their hosts, continuously evading the microbicidal mechanisms and modulating the 22 immune response of these cells. One of the mechanisms used by these protozoa 23 involves the L-arginine metabolism. Given the importance of the understanding of 2 24 differences between Leishmania species, as well as establishing a better murine 25 model to study leishmaniases, the objectives of this work were to analyse the 26 biological and molecular differences between two Leishmania infantum strains (LII 27 and LIC) and the degree of susceptibility of mice with different genetic backgrounds 28 to infection, as well as to understand the role of arginase (ARG)/nitric oxide synthase 29 (NOS) in the parasite-host relationship. The infectivity in vivo and in vitro of LII and 30 LIC was performed in BALB/c and Swiss Webster mice, as well the NOS and ARG 31 activities. The LII strain showed more infective than the LIC strain both in vivo and 32 in vitro. In animals infected by both strains, a difference in NOS and ARG activities 33 occurred. In vitro, promastigotes of LII isolated from BALB/c and Swiss Webster mice 34 showed higher ARG activity than the LIC during the growth curve, however, no 35 difference was observed in intracellular NO production by promastigotes between 36 these strains. A comparison of the sequences of the ARG gene was made and both 37 strains were identical. However, despite the similarity, the strains showed different 38 expression of this gene. It can be concluded that although L. chagasi strains are 39 considered identical to L. infantum strains, both have different biological behaviour. 40 41 Keywords: Leishmania species, L-arginine, arginase, nitric oxide synthase 42 43 3 47 attributed to them, which can manifest in various forms with different symptoms 48 depending on the infecting species and the host immune response. The main forms 49 of the disease are cutaneous, mucocutaneous and visceral leishmaniases (VL), the 50 latter being the most lethal manifestation with almost 0.5 million new cases each 51year, if not treated the mortality rate can reach 100% in two years [1,2] . 52Leishmania infantum is one of the species that causes VL and is present in 53 the Mediterranean Basin, as well as in the Middle East and South Asia. Some years 54 ago, L. chagasi was considered a new species of Leishmania causing visceral 55 leishmaniasis in the New World. However, after genetic sequencing studies, 56L. chagasi was considered identical to L. infantum, being denominated L. infantum 57 (syn. L. chagasi) [3] . Nevertheless, further studies showing antigenic differences 58 between both strains, they have considered as two subspecies L. infantum infantum 59 in the Old Wor...