Insect vectors' saliva and gut microbiota as a blessing in disguise: probability versus possibility.

Drawing of host blood is a natural phenomenon during the bite of blood-probing insect vectors. Along with the blood meal, the vectors introduce salivary components and a trail of microbiota. In the case of infected vectors, the related pathogen accompanies the aforementioned biological components. In addition to Anopheles gambiae or Anopheles stephensi, the bites of other nonmalarial vectors cannot be ignored in malaria-endemic regions. Similarly, the bite incidence of Phlebotomus papatasi cannot be ignored in visceral leishmaniasis-endemic regions. Even the chances of getting bitten by uninfected vectors are higher than the infected vectors. We have discussed the probability or possibility of uninfected, infected, and/or nonvector's saliva and gut microbiota as a therapeutic option leading to the initial deterrent to pathogen establishment.

Potential Anti-leishmanial Activity of a Semi-purified Fraction Isolated from the Leaves of Parthenium hysterophorus.

PURPOSE: In the present perspective, emergence of resistant strains of Leishmania donovani and severe side effects resulting from the use of conventional anti-leishmanial therapies present an urgent need for developing novel agents against this parasite. We have explored the effectiveness of secondary plant metabolites as alternative choices in the treatment for visceral leishmaniasis (vl). METHODS: The plant Parthenium hysterophorus L. (Asteraceae) was collected from the West Bengal State University Campus, Barasat, West Bengal, India. The leaves of this plant were extracted by different solvents, such as ethyl acetate, water, petroleum ether and hexane. Gas chromatography-mass spectrometry (GC-MS) analysis was also carried out for the identification of compounds in the hexane soluble fraction (PHFd) with substantial anti-leishmanial activities. The antipromastigote activity and cytotoxicity of this fraction were evaluated by the tetrazolium MTT assay. Other biochemical and physiological parameters were studied by microscopic observation and flow cytometric analyses. RESULTS: PHFd showed considerable activity against L. donovani promastigotes (IC50: 20 µg/ml). The PHFd also inhibited in vitro growth of L. major LV39 promastigotes dose dependently with an IC50 of 40 µg/ml. The GC-MS studies of this particular fraction revealed the presence of four major compounds with different retention times (RT) of 26.08, 33.11, 36.41, and 41.20 min. In this study, we also established that PHFd could induce DNA damage and subsequent apoptosis of L. donovani promastigotes with a concomitant increase in generations of reactive oxygen species (ROS) in a time-dependent manner. This fraction was also found to be effective in nitric oxide-mediated inhibition of intracellular amastigotes (IC50:12.5 µg/ml) without any noticeable cytotoxicity towards murine splenocytes in vitro. CONCLUSION: This study provides the basis for additional phytochemical and pharmacological studies on the antiprotozoal applications of P. hysterophorus.

Targeting the Trypanothione Reductase of Tissue-Residing Leishmania in Hosts' Reticuloendothelial System: A Flexible Water-Soluble Ferrocenylquinoline-Based Preclinical Drug Candidate.

Since inception, the magic bullets developed against leishmaniasis traveled a certain path and then dropped down due to either toxicity or the emergence of resistance. The route of administration is also an important concern. We developed a series of water-soluble ferrocenylquinoline derivatives, targeting Leishmania donovani, among which CQFC1 showed the highest efficacy even in comparison to other drugs, in use or used, both in oral and intramuscular routes. It did not induce any toxicity to splenocytes and on hematopoiesis, induced protective cytokines, and did not hamper the drug-metabolizing enzymes in hosts. It acts through the reduction and the inhibition of parasites' survival enzyme trypanothione reductase of replicating amastigotes in hosts' reticuloendothelial tissues. Unlike conventional drugs, this molecule did not induce the resistance-conferring genes in laboratory-maintained resistant L. donovani lines. Experimentally, this easily bioavailable preclinical drug candidate overcame all of the limitations causing the discontinuation of the other conventional antileishmanial drugs.

Selective in vitro inhibition of Leishmania donovani by a semi-purified fraction of wild mushroom Grifola frondosa.

The current study was designed to assess the anti-leishmanial effect of a semi-purified fraction of wild mushroom Grifola frondosa against Leishmania donovani, in vitro. A total of five extracts from three wild mushrooms [Grifola frondosa (family, Meripilaceae) Laetiporus sulphurous (family, Polyporaceae) and Meripilus giganteus (family, Meripilaceae) were explored for novel anti-leishmanial leads against promastigotes. The ethanol extract of G. frondosa was selected as the most efficient against L. donovani promastigotes (IC50: 93.9 µg/mL). A semi-purified fraction was obtained from an active ethanol extract of G. frondosa and found to inhibit the survival of promastigotes of L. donovani (MHOM/IN/83/AG83) significantly (IC50: 20.37 µg/mL) and it also had some effect against L. major LV39 (MRHO/Sv/59/P strain) and L. tropica WR683 (MHOM/SU/58/OD) strains at higher concentrations (IC50: 46.08 µg/mL and 53.79 µg/mL respectively). The semi-purified fraction also interfered in lipid biosynthesis, altered parasite morphology and induced apoptosis in L. donovani promastigotes. The semi-purified fraction was also effective against intracellular amastigotes in infected macrophages and enhanced the release of nitric oxide and pro-inflammatory cytokines, in vitro. Interestingly, the 50% inhibitory concentration of the semi-purified fraction against the intracellular amastigotes (IC50: 2.48 µg/mL) was much lower in comparison to promastigotes (IC50: 20.37 µg/mL). The semi-purified fraction was found to inhibit the intracellular amastigotes slightly more efficiently in comparison to conventional anti-leishmanial drugs; sodium antimony gluconate, amphotericin B, miltefosine and paromomycin and noticeably non-toxic towards host splenocytes. The findings of the present study established that G. frondosa might be a natural resource for development of a new anti-leishmanial lead.

Protective effect of Croton caudatus Geisel leaf extract against experimental visceral leishmaniasis induces proinflammatory cytokines in vitro and in vivo.

In the present state of overwhelming emergence of drug-unresponsive phenotypes of Leishmania donovani and persistent severe toxicity in conventional anti-leishmanial therapy, in search for novel leads, the aim of this study has been fixed to identify the active extract(s) of Croton caudatus Geisel. var. tomentosus Hook effective against the parasitic protozoans in vitro and in vivo. C. caudatus Geisel. is often used by Chakma and Hmar community, the local tribes of north-east India for medicinal and veterinary purposes. Among the five semi-purified extracts tested, C. caudatus leaves, extracted in hexane and subsequently semi-purified in a column packed with silica gel (70-130 µM; mesh size 60 A°) using ethyl acetate-hexane solvent (9:1), was found to be the most effective growth inhibitor (JDHex) against the Leishmania promastigotes and amastigotes. JDHex significantly altered the biochemical parameters (protein, lipid and carbohydrates) in promastigotes followed by the morphological changes, DNA condensation and subsequent apoptosis in L. donovani. In consequent steps, it has been also proved that JDHex reduced the replication of intracellular amastigotes with concomitant release of nitric oxide and pro-inflammatory cytokines, IL-12 and TNF-α in vitro. Significantly, the 50% inhibitory concentration of JDHex was estimated much lower against the intracellular amastigotes (2.5 µg/mL) in comparison to promastigotes (10 µg/mL). JDHex was also found efficient in reducing parasite burden in spleen and liver when treated in vivo and increased the intracellular IFN-γ and decreased the IL-10 in CD4+ T cells in splenocytes of orally treated animals. The results of this study support the importance in exploration of novel anti-leishmanial leads from C. caudatus Geisel. var. tomentosus Hook. against the L. donovani (MHOM/IN/83/AG83) infection. Partial chemical characterization of JDHex revealed the presence of terpenoids. However, the further chemical investigation of JDHex is warranted.