Leishmania (Viannia) braziliensis: influence of successive in vitro cultivation on the expression of promastigote proteinases

Virulence factors of Leishmania parasite: Their paramount importance in unraveling novel vaccine candidates and therapeutic targets

Leishmaniasis is a neglected tropical disease and remains a global concern for healthcare. It is caused by an opportunistic protozoan parasite belonging to the genus Leishmania and affects millions worldwide. This disease is mainly prevalent in tropical and subtropical regions and is associated with a high risk of public morbidity and mortality if left untreated. Transmission of this deadly disease is aggravated by the bite of female sand-fly vectors (Phlebotomus and Lutzomyia). With time, significant advancement in leishmaniasis-related research has been carried out to cope with the disease burden. Still, the Leishmania parasite has also co-evolved with its host and adapted successfully within the host's lethal milieu/environment. Thus, understanding and knowledge of various leishmanial virulence factors responsible for the parasitic infection are essential for exploring drug targets and vaccine candidates. The present review elucidates the importance of virulence factors in pathogenesis and summarizes the major leishmanial virulence molecules contributing to the parasitic infection during host-pathogen interaction. Furthermore, we have also elaborated on the potential contribution of leishmanial virulence proteins in developing vaccine candidates and exploring novel therapeutics against this parasitic disease. We aim to represent a clearer picture of parasite pathogenesis within the human host that can further aid in unraveling new strategies to fight against the deadly infection of leishmaniasis.

Synthesis and matched molecular pair analysis of covalent reversible inhibitors of the cysteine protease CPB

Cysteine protease B (CPB) can be targeted by reversible covalent inhibitors that could serve as antileishmanial compounds. Here, sixteen dipeptidyl nitrile derivatives were synthesized, tested against CPB, and analyzed using matched molecular pairs to determine the effects of stereochemistry and p-phenyl substitution on enzyme inhibition. The compound (S)-2-(((S)-1-(4-bromophenyl)-2,2,2-trifluoroethyl)amino)-N-(1-cyanocyclopropyl)-3-phenylpropanamide (5) was the most potent CPB inhibitor (pKi = 6.82), which was also selective for human cathepsin B (pKi < 5). The inversion of the stereochemistry from S to R was more detrimental to potency when placed at the P2 position than at P3. The p-Br derivatives were more potent than the p-CH₃ and p-OCH₃ derivatives, probably due to intermolecular interactions with the S3 subsite.

Detection of Metalloproteases and Cysteine Proteases RNA Transcripts of Leishmania (Leishmania) infantum in Ear Edge Skin of Naturally Infected Dogs

Leishmania spp. proteases have been proposed as virulence factors contributing to adaptive success these parasites to the mammalian hosts. Since these enzymes are poorly studied in naturally infected dogs, this work aims to show the differences in metalloprotease and cysteine proteases gene expression in ear edge skin of dogs naturally infected by Leishmania (Leishmania) infantum. A cohort of dogs (n = 20) naturally infected by L. (L.) infantum was clinically classified as asymptomatic, oligosymptomatic, and polysymptomatic and the parasite load range estimated. The analysis of proteases expression by RT-PCR in the ear edge skin was also assessed, suggesting more transcripts of proteases in cDNA samples from polysymptomatic dogs than oligosymptomatic and asymptomatic ones. Metalloprotease RT-PCR assays yielded products (202 bp) in all assessed cDNA dog samples. In contrast, cysteine proteases transcripts (227 bp) had shown to be better detected in cDNA samples of polysymptomatic dogs, compared with cDNA samples from asymptomatic and oligosymptomatic dogs. Predictive in silico assays suggested that secondary structures of metalloproteasee mRNAs can be more stable than cysteine proteases at the skin temperature of dogs. Evidence is presented that during natural infection of dogs by L. (L.) infantum, this parasite produces transcripts of metalloprotease and cysteine protease RNA in the skin from asymptomatic, oligosymptomatic, and polysymptomatic dogs.

Mapping Alterations Induced by Long-Term Axenic Cultivation of Leishmania amazonensis Promastigotes With a Multiplatform Metabolomic Fingerprint Approach

Leishmaniases are widespread neglected diseases with an incidence of 1.6 million new cases and 40 thousand deaths per year. Leishmania parasites may show distinct, species-specific patterns of virulence that lead to different clinical manifestations. It is well known that successive in vitro passages (SIVP) lead to the attenuation of virulence, but neither the metabolism nor the pathways involved in these processes are well understood. Herein, promastigotes of a virulent L. amazonensis strain recently isolated from mice was compared to SIVP derived and attenuated promastigotes, submitted to 10, 40, and 60 axenic passages and named R10, R40, and R60, respectively. In vitro assays and in vivo tests were performed to characterize and confirmed the attenuation profiles. A metabolomic fingerprint comparison of R0, R10, and R60 was performed by means of capillary electrophoresis, liquid and gas chromatography coupled to mass spectrometry. To validate the metabolomic data, qPCR for selected loci, flow cytometry to measure aPS exposure, sensitivity to antimony tartrate and ROS production assays were conducted. The 65 identified metabolites were clustered in biochemical categories and mapped in eight metabolic pathways: ABC transporters; fatty acid biosynthesis; glycine, serine and threonine metabolism; β-alanine metabolism; glutathione metabolism; oxidative phosphorylation; glycerophospholipid metabolism and lysine degradation. The obtained metabolomic data correlated with previous proteomic findings of the SVIP parasites and the gene expression of 13 selected targets. Late SIVP cultures were more sensitive to Sb^III produced more ROS and exposed less phosphatidylserine in their surface. The correspondent pathways were connected to build a biochemical map of the most significant alterations involved with the process of attenuation of L. amazonensis. Overall, the reported data pointed out to a very dynamic and continuous metabolic reprogramming process, accompanied by changes in energetic, lipid and redox metabolisms, membrane remodeling and reshaping of parasite-host cells interactions, causing impacts in chemotaxis, host inflammatory responses and infectivity at the early stages of infection.

B-1 lymphocytes are able to produce IL-10, but is not pathogenic during Leishmania (Leishmania) amazonensis infection

Over the years research has found an association between B lymphocytes and pathogenesis during Leishmania sp. infections. Recently we demonstrated that B-2 lymphocytes are the main producers of IL-10 during L. amazonensis infection, and that the disease severity in BALB/c mice was attributed to these IL-10-producing B-2 lymphocytes. Here, we aim to understand the role of peritoneal B-1 lymphocytes in the pathogenesis of L. amazonensis infection. We found that infection resulted in a decrease in the number of B-1a lymphocytes and increase in B-1b lymphocytes in the peritoneal cavity of WT BALB/c mice but not in B lymphocyte deficient mice (BALB/Xid) mice. In vitro interaction between B-1 lymphocytes and L. amazonensis showed that the amastigote form of the parasite was able to induce higher levels of IL-10 in B-1 lymphocytes derived from infected BALB/c mice than the promastigote. Moreover, B-1 lymphocytes derived from infected mice produced more IL-10 than B-1 lymphocytes derived from naïve mice under amastigote interaction. However, the repopulation of BALB/Xid mice with B-1 lymphocytes from WT BALB/c mice did not affect the lesion development. Together, these results suggest that although B-1 lymphocytes are able to produce IL-10 during in vitro interaction with L. amazonensis, they are not directly related to pathogenesis in vivo.

Dipeptidyl nitrile derivatives have cytostatic effects against Leishmania spp. promastigotes

Cysteine proteases are involved in critical cell processes to the protozoa from Leishmania genus, and their inhibition is a therapeutic alternative to treat the disease. In this work, derivatives of dipeptidyl nitriles acting as reversible covalent inhibitors of cysteine proteases were studied as cytostatic agents. The proteolytic activity inside the living and lysed parasite cells was quantified using a selective substrate for cysteine proteases (Z-FR-MCA) from Leishmania amazonensis and L. infantum. The overall proteolytic activity of intact cells and even cell extracts was only marginally affected at high concentrations, with the observation of cytostatic activity and cell cycle arrest of promastigotes. However, the cytotoxic effects were only observed for infected J774 macrophages, which impaired further analysis of the amastigote infection. Therefore, the proteolytic inhibition in intact L. amazonensis and L. infantum promastigotes had no relationship to the cytostatic activity, which emphasizes that these dipeptidyl nitriles act through another mechanism of action.

Evidence of Subpopulations with Distinct Biological Features Within a Leishmania (Viannia) braziliensis Strain

The present study demonstrates that the Leishmania (Viannia) braziliensis strain MCAN/BR/1998/R619 is composed of multiple subpopulations with measurable distinctions. Single parasites were separated from a culture of promastigotes in stationary phase by cell sorting and then cultivated as subpopulations. Subsequently, these subpopulations were evaluated for features of in vitro growth, infectivity to murine macrophages and proteinase gene expression. The first evidence of distinct characteristics was observed during the in vitro cultivation of isolated subpopulations, as distinct clusters of patterns were formed among the cultures, indicating the existence of quantifiable fluctuations in metrics. Further, when infecting murine macrophages, the subpopulations induced distinct patterns of production of immune response mediators. While some subpopulations mainly induced the production of IL-1β, IL-6 and TNF-α, others induced the production of IL-12p70 and nitric oxide. Finally, amastigotes of these subpopulations had higher expression of proteinase genes than promastigotes. Additionally, cysteine proteinase, serine proteinase, metalloproteinase and aspartic proteinases were differentially expressed in promastigote and amastigote forms. These data suggest the existence of distinct profiles for the L. (V.) braziliensis MCAN/BR/1998/R619 strain and subpopulations that could drive the success of parasite adaptation to the environments that they inhabit.

Increasing in cysteine proteinase B expression and enzymatic activity during in vitro differentiation of Leishmania (Viannia) braziliensis: First evidence of modulation during morphological transition

Leishmania (Viannia) braziliensis presents adaptive protease-dependent mechanisms, as cysteine proteinases B (CPB). This study investigates the expression of three cpb gene isoforms and CPB enzymatic activity during the parasite differentiation. Relative expression levels of LbrM.08.0810 gene were assessed, exhibiting a higher quantity of transcripts in the logarithmic promastigotes phase than in the stationary promastigotes phase (>1.5 times). The cbp gene tends to decrease during acid pH shock and increases when the temperature rises (>1.3 times). LbrM.08.0820 and LbrM.08.0830 genes exhibited similar expression profiles to LbrM.08.0810 gene, with lower levels being observed overall. The proteolytic activity exhibits a gradual increase during the parasite's differentiation with low levels in samples of logarithmic promastigotes phase (3.2 ± 0.08 mmol min^-1 mg protein^-1) to a peak of activity after 72 h of incubation at 32 °C (4.2 ± 0.026 mmol min^-1 mg protein^-1) followed by a subsequent decrease of 68 % of peak activity levels after 96 h of incubation at 32 °C (2.8 ± 0.37 mmol min^-1 mg protein^-1). These activities were also measured in the presence of selective inhibitors for cysteine proteinases, such as Z-Phe-Phe-fluoromethyl ketone and trans-epoxysuccinyl-L-leucylamido(4-guanidino)butane, demonstrating their source as cathepsin-like proteinases. To the best of our knowledge, this report presents the first description of a modulation of cathepsin L-like expression during the L. (V.) braziliensis in vitro differentiation induced by acid pH and high temperature.

Why strategies to control Leishmania spp. multiplication based on the use of proteinase inhibitors should consider multiple targets and not only a single enzyme

The use of proteinases as targets to develop novel chemotherapies against Leishmania spp. infections is a very promising strategy. Based on a previous study by Goyal et al. [J Mol Model (2014) 20:2099], we discuss herein the idea that only a combined treatment with distinct proteinase inhibitors would be an effective antileishmanial therapy.