Flavonoids from Piper Species as Promising Antiprotozoal Agents against Giardia intestinalis. Structure-Activity Relationship and Drug-Likeness Studies

Diarrhea diseases caused by the intestinal protozoan parasite Giardia intestinalis are a major global health burden. Moreover, there is an ongoing need for novel anti-Giardia drugs due to drawbacks with currently available treatments. This paper reports on the isolation and structural elucidation of six new flavonoids (1-6), along with twenty-three known ones (7-29) from the Piper species. Their structures were established by spectroscopic and spectrometric techniques. Flavonoids were tested for in vitro antiprotozoal activity against Giardia intestinalis trophozoites. In addition, structure-activity relationship (SAR) and in silico ADME studies were performed to understand the pharmacophore and pharmacokinetic properties of these natural compounds. Eight flavonoids from this series exhibited remarkable activity in the micromolar range. Moreover, compound 4 was identified as having a 40-fold greater antiparasitic effect (IC50 61.0 nM) than the clinical reference drug, metronidazole (IC50 2.5 µM). This antiprotozoal potency was coupled with an excellent selectivity index (SI 233) on murine macrophages and in silico drug-likeness. SAR studies revealed that the substitution patterns, type of functional group, and flavonoid skeleton played an essential role in the activity. These findings highlight flavonoid 4 as a promising candidate to develop new drugs for the treatment of Giardia infections.

Evaluating the Potential of Ursolic Acid as Bioproduct for Cutaneous and Visceral Leishmaniasis

Leishmaniasis affects around 12 million people worldwide and is estimated to cause the ninth-largest disease burden. There are three main forms of the disease, visceral (VL), cutaneous (CL), and mucocutaneous (MCL), leading to more than one million new cases every year and several thousand deaths. Current treatments based on chemically synthesized molecules are far from ideal. In this study, we have tested the in vitro and in vivo efficacy of ursolic acid (UA), a multifunctional triterpenoid with well-known antitumoral, antioxidant, and antimicrobial effects on different Leishmania strains. The in vitro antileishmanial activity against the intracellular forms was six and three-fold higher compared to extracellular forms of L. amazonensis and L. infantum, respectively. UA also showed to be a potent antileishmanial drug against both VL and CL manifestations of the disease in experimental models. UA parenterally administered at 5 mg/kg for seven days significantly reduced the parasite burden in liver and spleen not only in murine acute infection but also in a chronic-infection model against L. infantum. In addition, UA ointment (0.2%) topically administered for four weeks diminished (50%) lesion size progression in a chronic infection model of CL caused by L. amazonensis, which was much greater than the effect of UA formulated as an O/W emulsion. UA played a key role in the immunological response modulating the Th1 response. The exposure of Leishmania-infected macrophages to UA led to a significant different production in the cytokine levels depending on the Leishmania strain causing the infection. In conclusion, UA can be a promising therapy against both CL and VL.

Leishmaniasis in the major endemic region of Plurinational State of Bolivia: Species identification, phylogeography and drug susceptibility implications

The Plurinational State of Bolivia is one of the Latin American countries with the highest prevalence of leishmaniasis, highlighting the lowlands of the Department of La Paz where about 50% of the total cases were reported. The control of the disease can be seriously compromised by the intrinsic variability of the circulating species that may limit the efficacy of treatment while favoring the emergence of resistance. Fifty-five isolates of Leishmania from cutaneous and mucocutaneous lesions from patients living in different provinces of the Department of La Paz were tested. Molecular characterization of isolates was carried out by 3 classical markers: the rRNA internal transcribed spacer 1 (ITS-1), the heat shock protein 70 (HSP70) and the mitochondrial cytochrome b (Cyt-b). These markers were amplified by PCR and their products digested by the restriction endonuclease enzymes AseI and HaeIII followed by subsequent sequencing of Cyt-b gene and ITS-1 region for subsequent phylogenetic analysis. The combined use of these 3 markers allowed us to assign 36 isolates (65.5%) to the complex Leishmania (Viannia) braziliensis, 4 isolates (7, 27%) to L. (Viannia) lainsoni. and the remaining 15 isolates (23.7%) to a local variant of L. (Leishmania) mexicana. Concerning in vitro drug susceptibility the amastigotes from all isolates where highly sensitive to Fungizone^® (mean IC₅₀ between 0.23 and 0.5μg/mL) whereas against Glucantime^® the sensitivity was moderate (mean IC₅₀ ranging from 50.84μg/mL for L. (V.) braziliensis to 18.23μg/mL for L. (L.) mexicana. L. (V.) lainsoni was not sensitive to Glucantime^®. The susceptibility to miltefosine was highly variable among species isolates, being L. (L.) mexicana the most sensitive, followed by L. (V.) braziliensis and L. (V.) lainsoni (mean IC₅₀ of 8.24μg/mL, 17.85μg/mL and 23.28μg/mL, respectively).

Synthesis and antileishmanial activity of C7- and C12-functionalized dehydroabietylamine derivatives

Abietane-type diterpenoids, either naturally occurring or synthetic, have shown a wide range of pharmacological actions, including antiprotozoal properties. In this study, we report on the antileishmanial evaluation of a series of (+)-dehydroabietylamine derivatives functionalized at C7 and/or C12. Thus, the activity in vitro against Leishmania infantum, Leishmania donovani, Leishmania amazonensis and Leishmania guyanensis, was studied. Most of the benzamide derivatives showed activities at low micromolar concentration against cultured promastigotes of Leishmania spp. (IC50 = 2.2-46.8 μM), without cytotoxicity on J774 macrophage cells. Compound 15, an acetamide, was found to be the most active leishmanicidal agent, though it presented some cytotoxicity on J774 cells. Among the benzamide derivatives, compounds 8 and 10, were also active against L. infantum intracellular amastigotes, being 18- and 23-fold more potent than the reference compound miltefosine, respectively. Some structure-activity relationships have been identified for the antileishmanial activity in these dehydroabietylamine derivatives.

Triazolopyridopyrimidines: an emerging family of effective DNA photocleavers. DNA binding. Antileishmanial activity

Triazolopyridopyrimidines 3-phenyl-6,8-di(2-pyridyl)-[1,2,3]triazolo[5',1':6,1]pyrido[2,3-d]pyrimidine (1a), 6,8-di(pyridin-2-yl)-[1,2,3]triazolo[1',5':1,6]pyrido[2,3-d]pyrimidine (1b) and 3-methyl-6,8-di(2-pyridyl)-[1,2,3]triazolo[5',1':6,1]pyrido[2,3-d]pyrimidine (1c) were prepared and their electrochemical and luminescence properties were studied in depth. The DNA binding ability of this series of compounds has been investigated by means of UV-vis absorption and fluorescence titrations, steady-state emission quenching with ferrocyanide as well as viscosity measurements. Results have shown that triazolopyridopyrimidine 1a interacts strongly at DNA grooves. This compound also displays preferential binding to GC-rich sequences and the ability to photooxidize guanine. Moreover, these studies have revealed the key role of the phenyl substituent at the triazole ring in the binding affinity of 1a-c. Compounds 1b and 1c did not show appreciable propensity for DNA binding, however these triazolopyridopyrimidines demonstrated to present photoinduced DNA cleavage activity, 1b being more active than 1c. DNA photocleavage mediated by these compounds takes place mainly through single strand scission events and, in a minor extent, through double strand cuts. Mechanistic investigations using radical scavengers showed that both 1b and 1c generate reactive oxygen species (singlet oxygen, superoxide and hydroxyl radicals) upon irradiation. Both type I and type II mechanisms are involved in the photocleavage process. Furthermore, compounds 1a-c were tested for their antiprotozoal activity against four different Leishmania spp. (L. infantum, L. braziliensis, L. guyanensis and L. amazonensis). Triazolopyridopyrimidines 1a and 1c resulted to be more active and selective than the reference drug (miltefosine) in vitro against L. infantum amastigotes. Compound 1a exhibited high leishmanicidal activity against L. infantum spleen forms in the in vivo test.

In vitro and in vivo antileishmanial and trypanocidal studies of new N-benzene- and N-naphthalenesulfonamide derivatives

We report in vivo and in vitro antileishmanial and trypanocidal activities of a new series of N-substituted benzene and naphthalenesulfonamides 1-15. Compounds 1-15 were screened in vitro against Leishmania infantum , Leishmania braziliensis , Leishmania guyanensis , Leishmania amazonensis , and Trypanosoma cruzi . Sulfonamides 6e, 10b, and 10d displayed remarkable activity and selectivity toward T. cruzi epimastigotes and amastigotes. 6e showed significant trypanocidal activity on parasitemia in a murine model of acute Chagas disease. Moreover, 6e, 8c, 9c, 12c, and 14d displayed interesting IC50 values against Leishmania spp promastigotes as well as L. amazonensis and L. infantum amastigotes. 9c showed excellent in vivo activity (up to 97% inhibition of the parasite growth) in a short-term treatment murine model for acute infection by L. infantum. In addition, the effect of compounds 9c and 14d on tubulin as potential target was assessed by confocal microscopy analysis applied to L. infantum promastigotes.

Synthetic oxoisoaporphine alkaloids: in vitro, in vivo and in silico assessment of antileishmanial activities

Leishmaniasis is a growing health problem worldwide. As there are certain drawbacks with the drugs currently used to treat human leishmaniasis and resistance to these drugs is emerging, there is a need to develop novel antileishmanial compounds, among which isoquinoline alkaloids are promising candidates. In this study, 18 novel oxoisoaporphine derivatives were synthesized and their possible antileishmanial activity was evaluated. The in vitro activity of these derivatives against Leishmania amazonensis axenic amastigotes was first evaluated, and the selected compounds were then tested in an inhibition assay with promastigotes of L. infantum, L. braziliensis, L. amazonensis and L. guyanensis, and with intracellular amastigotes of L. infantum and L. amazonensis. Finally, the most active compounds, OXO 1 (2,3-dihydro-7H-dibenzo[de,h]quinolin-7-one) and OXO 13 (2,3,8,9,10,11-hexahydro-7H-dibenzo[de,h]quinolin-7-one), were tested in BALB/c mice infected with L. infantum. Treatment of mice at a dose of 10 mg/kg with OXO 1 yielded significant reductions (p<0.05) in parasite burden in liver and spleen (99% and 78%, respectively) whereas with OXO 13 were not significant. Although previous reports suggest that this family of molecules displays inhibitory activity against monoamine oxidase A and acetylcholinesterase, these enzymes were not confirmed as targets for antileishmanial activity on the basis of the present results. However, after development of a new bioinformatics model to analyze the Leishmania proteome, we were able to identify other putative targets for these molecules. The most promising candidates were four proteins: two putative pteridine reductase 2 (1MXF and 1MXH), one N-myristoyltransferase (2WUU) and one type I topoisomerase (2B9S).

Nuclease activity and ultrastructural effects of new sulfonamides with anti-leishmanial and trypanocidal activities

Our aim was to evaluate the in vitro efficacy of a series of N-benzenesulfonamides of amine substituted aromatic rings, sulfonamides 1-6, against Trypanosoma cruzi and Leishmania spp. and to compare their trypanocidal and leishmanicidal profile. In order to elucidate the probable mechanism of action, the interaction of selected sulfonamides with pUC18 plasmid DNA was investigated by nuclease activity assays. In addition, the cellular targets of these sulfonamides in treated parasites were also searched by transmission and scanning electron microscopy. The most active compounds 4-nitro-N-pyrimidin-2-ylbenzenesulfonamide 1a and 4-chloro-N-5-methyl-thiazol-2-yl-benzenesulfonamide 2d displayed significant in vitro activity against Leishmania spp. promastigotes, without toxicity to J774 macrophages. Selected sulfonamides 1a, 4-nitro-N-pyrazin-2-yl-benzenesulfonamide 1n and 2d were also active against Leishmania infantum intracellular amastigotes. Compounds 1n and 2d showed nuclease activity in the presence of copper salt analogous to our previous results with sulfonamide 1a. Mechanistic data reveal the involvement of a redox process. Evidence for the formation of reactive oxygen species (ROS) responsible for DNA strand scission is provided for sulfonamides 1a, 1n and 2d. Transmission electron microscopic (TEM) analysis of L. infantum promastigotes treated with compounds 1a, 1n and 2d shows an overall cellular disorganization effects which are mainly addressed to DNA bearing structures such as the nucleus, mitochondria and kinetoplast. Disruption of double nuclear membrane and loss of cellular integrity along with accumulation of cytoplasmic electrodense bodies were also frequently observed.