A novel hydrolase with a pro-death activity from the protozoan parasite Leishmania major

Genetic Mechanism of Non-Targeted-Site Resistance to Diquat in Spirodela polyrhiza

Understanding non-target-site resistance (NTSR) to herbicides represents a pressing challenge as NTSR is widespread in many weeds. Using giant duckweed (Spirodela polyrhiza) as a model, we systematically investigated genetic and molecular mechanisms of diquat resistance, which can only be achieved via NTSR. Quantifying the diquat resistance of 138 genotypes, we revealed an 8.5-fold difference in resistance levels between the most resistant and most susceptible genotypes. Further experiments suggested that diquat uptake and antioxidant-related processes jointly contributed to diquat resistance in S. polyrhiza. Using a genome-wide association approach, we identified several candidate genes, including a homolog of dienelactone hydrolase, that are associated with diquat resistance in S. polyrhiza. Together, these results provide new insights into the mechanisms and evolution of NTSR in plants.

Anti-proliferative and apoptosis induction activities of curcumin on Leishmania major

Leishmaniasis is a major vector-borne disease triggered by an obligate intracellular protozoan parasite of the genus Leishmania and transmitted by the bite of phlebotomine female sand flies. This parasite causes a wide range of human diseases, from localized self-healing cutaneous lesions to fatal visceral infections. The aim of this study was to investigate the cytotoxic, antiproliferative, and apoptotic effects of curcumin on Leishmania major promastigotes (MHOM/SA/84/JISH) and to assess these effects on the cell cycle of promastigotes. The MTT colorimetric assay was used to evaluate the cytotoxicity and proliferation of promastigotes. Additionally, flow cytometry was used to analyze the cell cycle. The Annexin V/propidium iodide staining technique followed by flow cytometry was used to study the cell death induced by curcumin. In this study curcumin showed a potent antileishmanial effect, exhibiting cytotoxicity against L. major promastigotes. At 80μM, the survival in curcumin treated promastigotes reached 22%; however, the median lethal concentration of curcumin (LC₅₀) was 35μM. The drug exerted its cytotoxic effect by inducing apoptosis. Curcumin-induced cell death in promastigotes reached 82.5% at 80μM concentration. In addition, curcumin delayed the cell cycle in the S-phase inhibiting cell proliferation. Thus, curcumin was shown to be effective against L. major promastigotes. Therefore, curcumin merits further research studies to demonstrate its efficacy in treating cutaneous leishmaniasis.

Chitosan Contribution to Therapeutic and Vaccinal Approaches for the Control of Leishmaniasis

The control of leishmaniases, a complex parasitic disease caused by the protozoan parasite Leishmania, requires continuous innovation at the therapeutic and vaccination levels. Chitosan is a biocompatible polymer administrable via different routes and possessing numerous qualities to be used in the antileishmanial strategies. This review presents recent progress in chitosan research for antileishmanial applications. First data on the mechanism of action of chitosan revealed an optimal in vitro intrinsic activity at acidic pH, high-molecular-weight chitosan being the most efficient form, with an uptake by pinocytosis and an accumulation in the parasitophorous vacuole of Leishmania-infected macrophages. In addition, the immunomodulatory effect of chitosan is an added value both for the treatment of leishmaniasis and the development of innovative vaccines. The advances in chitosan chemistry allows pharmacomodulation on amine groups opening various opportunities for new polymers of different size, and physico-chemical properties adapted to the chosen routes of administration. Different formulations have been studied in experimental leishmaniasis models to cure visceral and cutaneous leishmaniasis, and chitosan can act as a booster through drug combinations with classical drugs, such as amphotericin B. The various architectural possibilities given by chitosan chemistry and pharmaceutical technology pave the way for promising further developments.

Cell death in Leishmania

Leishmaniases still represent a global scourge and new therapeutic tools are necessary to replace the current expensive, difficult to administer treatments that induce numerous adverse effects and for which resistance is increasingly worrying. In this context, the particularly original organization of the Leishmania parasite in comparison to higher eukaryotes is a great advantage. It allows for the development of new, very specific, and thus non-cytotoxic treatments. Among these originalities, Leishmania cell death can be cited. Despite a classic pattern of apoptosis, key mammalian apoptotic proteins are not present in Leishmania, such as caspases, cell death receptors, and anti-apoptotic molecules. Recent studies have helped to develop a better understanding of parasite cell death, identifying new proteins or even new apoptotic pathways. This review provides an overview of the current knowledge on Leishmania cell death, describing its physiological roles and its phenotype, and discusses the involvement of various proteins: endonuclease G, metacaspase, aquaporin Li-BH3AQP, calpains, cysteine proteinase C, LmjHYD36 and Lmj.22.0600. From these data, potential apoptotic pathways are suggested. This review also offers tools to identify new Leishmania cell death effectors. Lastly, different approaches to use this knowledge for the development of new therapeutic tools are suggested: either inhibition of Leishmania cell death or activation of cell death for instance by treating cells with proteins or peptides involved in parasite death fused to a cell permeant peptide or encapsulated into a lipidic vector to target intra-macrophagic Leishmania cells.

A potential acetyltransferase involved in Leishmania major metacaspase-dependent cell death

BACKGROUND

Currently, there is no satisfactory treatment for leishmaniases, owing to the cost, mode of administration, side effects and to the increasing emergence of drug resistance. As a consequence, the proteins involved in Leishmania apoptosis seem a target of choice for the development of new therapeutic tools against these neglected tropical diseases. Indeed, Leishmania cell death, while phenotypically similar to mammalian apoptosis, is very peculiar, involving no homologue of the key mammalian apoptotic proteins such as caspases and death receptors. Furthermore, very few proteins involved in Leishmania apoptosis have been identified.

RESULTS

We identified a protein involved in Leishmania apoptosis from a library of genes overexpressed during Leishmania differentiation during which autophagy occurs. Indeed, the gene was overexpressed when L. major cell death was induced by curcumin or miltefosine. Furthermore, its overexpression increased L. major curcumin- and miltefosine-induced apoptosis. This gene, named LmjF.22.0600, whose expression is dependent on the expression of the metacaspase, another apoptotic protein, encodes a putative acetyltransferase.

CONCLUSIONS

This new protein, identified as being involved in Leishmania apoptosis, will contribute to a better understanding of Leishmania death, which is needed owing to the absence of a satisfactory treatment against leishmaniases. It will also allow a better understanding of the original apoptotic pathways of eukaryotes in general, while evidence of the existence of such pathways is accumulating.