Characterization of the redox components of transplasma membrane electron transport system from Leishmania donovani promastigotes

Unnatural Direct Interspecies Electron Transfer Enabled by Living Cell-Cell Click Chemistry

Direct interspecies electron transfer (DIET) is essential for maintaining the function and stability of anaerobic microbial consortia. However, only limited natural DIET modes have been identified and DIET engineering remains highly challenging. In this study, an unnatural DIET between Shewanella oneidensis MR-1 (SO, electron donating partner) and Rhodopseudomonas palustris (RP, electron accepting partner) was artificially established by a facile living cell-cell click chemistry strategy. By introducing alkyne- or azide-modified monosaccharides onto the cell outer surface of the target species, precise covalent connections between different species in high proximity were realized through a fast click chemistry reaction. Remarkably, upon covalent connection, outer cell surface C-type cytochromes mediated DIET between SO and RP was achieved and identified, although this was never realized naturally. Moreover, this connection directly shifted the natural H2 mediated interspecies electron transfer (MIET) to DIET between SO and RP, which delivered superior interspecies electron exchange efficiency. Therefore, this work demonstrated a naturally unachievable DIET and an unprecedented MIET shift to DIET accomplished by cell-cell distance engineering, offering an efficient and versatile solution for DIET engineering, which extends our understanding of DIET and opens up new avenues for DIET exploration and applications.

Effect of capsaicin on the protozoan parasite Trypanosoma cruzi

Trypanosoma cruzi is the causative agent of Chagas disease. There are only two approved treatments, both of them unsuitable for the chronic phase, therefore the development of new drugs is a priority. Trypanosoma cruzi arginine kinase (TcAK) is a promising drug target since it is absent in humans and it is involved in cellular stress responses. In a previous study, possible TcAK inhibitors were identified through computer simulations resulting the best compounds capsaicin and cyanidin derivatives. Here, we evaluate the effect of capsaicin on TcAK activity and its trypanocidal effect. Although capsaicin produced a weak enzyme inhibition, it had a strong trypanocidal effect on epimastigotes and trypomastigotes (IC50 = 6.26 µM and 0.26 µM, respectively) being 20-fold more active on trypomastigotes than mammalian cells. Capsaicin was also active on the intracellular cycle reducing by half the burst of trypomastigotes at approximately 2 µM. Considering the difference between the concentrations at which parasite death and TcAK inhibition occur, other possible targets were predicted. Capsaicin is a selective trypanocidal agent active in nanomolar concentrations, with an IC50 57-fold lower than benznidazole, the drug currently used for treating Chagas disease.

Characterization of Transplasma Membrane Electron Transport Chain in Wild and Drug-Resistant Leishmania donovani Promastigote and Amastigote

BACKGROUND

Leishmania donovani (L. donovani) is one of the parasites that cause leishmaniasis. The mechanisms by which L. donovani fights against adverse environment and becomes resistant to drugs are not well understood yet.

OBJECTIVE

The present study was designed to evaluate the effects of different regulators on the modulation of Transplasma Membrane Electron Transport (transPMET) systems of susceptible and resistant L. donovani cells.

MATERIALS AND METHODS

Effects of UV, different buffers, and electron transport inhibitors and stimulators on the reduction of α-lipoic acid (ALA), 1,2-naphthoquinone-4-sulphonic acid (NQSA) and ferricyanide were determined.

RESULTS AND DISCUSSION

ALA reductions were inhibited in susceptible, sodium antimony gluconate (SAG)-resistant and paromomycin (PMM)-resistant AG83 amastigote cells, and stimulated in susceptible and SAG-resistant AG83 promastigote cells upon UV exposure. The results indicate that UV irradiation almost oppositely affect ALA reductions in amastigotes and promastigotes. ALA reductions were stimulated in sensitive and inhibited in resistant GE1 amastigotes upon UV exposure. Susceptible amastigotes and promastigotes inhibited, and resistant amastigotes and promastigotes stimulated NQSA reduction under UV irradiation. Thus, susceptible and drug-resistant amastigotes and promastigotes are different in the reduction of ALA. Susceptible and resistant AG83 amastigotes and promastigotes inhibited the ferricyanide reductions upon UV exposure, which indicates, there is no such difference in ferricyanide reductions among susceptible as well as resistant AG83 amastigotes and promastigotes. The reductions of extracellular electron excerptors in susceptible promastigotes requires the availability of Na⁺ and Cl^- ions for maximal activity but susceptible amastigotes are mostly not dependent on the availability of Na⁺ and Cl^- ions. Both in promastigotes and amastigotes, reductions of electron acceptors were strongly inhibited by carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone. Furthermore, antimycin A, rotenone and capsaicin markedly inhibited the reductions of electron acceptors in promastigotes, but not in amastigotes.

CONCLUSION

Results of this study suggest that the transPMET system is functionally different in wild and resistant strains of L. donovani.

Correlation between glucose uptake and membrane potential in Leishmania parasites isolated from DCL patients with therapeutic failure: a proof of concept

Besides infection with drug-resistant parasites, therapeutic failure in leishmaniasis may be caused by altered drug pharmacokinetics, re-infection, and host immunologic compromise. Our aim has been to evaluate if relapses that occur in patients suffering from diffuse cutaneous leishmaniasis (DCL) associate with changes in the fitness of infecting organisms. Therefore, in isolates from patients suffering DCL, we correlated glucose uptake and plasma membrane potential and compared the results with those obtained from reference strains. The data demonstrate that Leishmania parasites causing DCL incorporate glucose at an efficient rate, albeit without significant changes in the plasma membrane potential as their corresponding reference strains. The isolate that did not change its accumulation rate of glucose compared to its reference strain expressed a less polarized membrane potential that was insensitive to mitochondrial inhibitors, suggesting a metabolic dysfunction that may result in glycolysis being the main source of ATP. The results constitute a proof of concept that indicates that parasites causing DCL adapted well to drug pressure and expressed an increased fitness. That is, that in Leishmania mexicana and Leishmania amazonensis, parasites isolated from DCL patients, a strong modification of the parasite physiology might occur. As consequences, the parasites adapted well to drug pressure, increased their fitness, and they had an efficient glucose uptake rate albeit not significant changes in membrane potential as their corresponding reference strains. Further validation of the concepts herein established and whether or not the third isolate corresponds with a drug-resistant phenotype need to be demonstrated at the genetic level.

alpha-Lipoic acid modulates thiol antioxidant defenses and attenuates exercise-induced oxidative stress in standardbred trotters

Several micronutrient supplementation strategies are used to cope with oxidative stress, although their benefits have recently been questioned. The aim of the present study was to examine the effects of DL-alpha-lipoic acid (LA) in response to acute exercise and during recovery in horses. Six standardbred trotters were tested on the treadmill before and after 5-week LA supplementation (25 mg/kg body weight/day). According to electron paramagnetic resonance measurements, strenuous aerobic exercise increased significantly free radical formation in the gluteus medius muscle, which was prevented by LA supplementation. The activities of thioredoxin reductase and glutathione reductase in muscle were significantly increased in LA-treated horses, but neither LA nor exercise affected muscle thioredoxin activity. LA increased the concentration of total glutathione in muscle at rest and during recovery. Treatment with LA blunted the exercise-induced increase in plasma oxygen radical absorbance capacity and decreased the post-exercise levels of lipid hydroperoxides in plasma and malondialdehyde in plasma and in muscle. These findings suggest that LA enhances thiol antioxidant defences and decreases exercise-induced oxidative stress in skeletal muscle.

Monensin causes dose dependent inhibition of Mycobacterium avium subspecies paratuberculosis in radiometric culture

Background

Mycobacterium avium subspecies paratuberculosis (MAP) causes a chronic wasting diarrheal disease in ruminants called Johne's disease, that is evocative of human inflammatory bowel disease (IBD). Agents used to treat IBD, called "anti-inflammatories", immuno-modulators" and "immuno-suppressants" inhibit MAP growth in culture. We concluded that, unknowingly, the medical profession has been treating MAP since sulfasalazine's introduction in 1942. Monensin, called a "Growth Enhancer" in cattle, ameliorates Johne's disease without a documented mechanism of action. We hypothesized that Monensin would inhibit MAP in culture.

Methods

Using the radiometric ¹⁴CO₂ Bactec^® system, that expresses mycobacterial growth in arbitrary growth index (GI) units, we studied the effect of Monensin on the growth kinetic of MAP isolated from humans with IBD ("Dominic", "Ben" & UCF-4) and cattle with Johne's disease (303 & ATCC 19698.) Results are expressed as percent inhibition of cumulative GI (%–ΔcGI).

Results

The positive control Clofazimine inhibits every strain tested. The negative controls Cycloheximide & Phthalimide, have no inhibition on any MAP strain. Monensin has dose dependent inhibition on every MAP strain tested. The most susceptible human isolate was UCF-4 (73% – ΔcGI at 1 μg/ml) and bovine isolate was 303 (73% – ΔcGI at 4 μg/ml.) Monensin additionally inhibits M. avium ATCC 25291 (87% – ΔcGI at 64 μg/ml) & BCG (92% – ΔcGI at 16 μg/ml).

Discussion

We show that in radiometric culture the "Growth Enhancer" Monensin causes dose dependent inhibition of mycobacteria including MAP. We posit that the "Growth Enhancer" effect of Monensin may, at least in part, be due to inhibition of MAP in clinical or sub-clinical Johne's disease.

Is dihydrolipoic acid among the reductive activators of parasite CysHis proteases?

Activities of mature CysHis proteases depend upon relative rates of oxidations vs. reductions of catalytic sulfur by multiple enzymatic and non-enzymatic reactions. CysHis peptidolysis is inhibited by Fe3+ but not Fe2+. Others report the paradox that malarial parasites require exogenous free lipoic acid (LA) from human host, although the apicoplast organelle produces it. Extra-cellular LA disulfide can be taken up and reduced to dihydrolipoic acid (DHLA) by reductases of any cell type. Here, the opposing effects of DHLA vs. Fe3+ on the falcipain-2 hemoglobinase were investigated employing Z-Phe-Arg-AMC substrate. Despite limited solubility, non-regenerated DHLA (10 microM, threshold 2 microM) was found to be the most potent activator of the air-inactivated (sulfoxygenated) protease discovered thus far. Activation was preemptively opposed by Fe3+, but not Fe2+. However, cruzain from T. cruzi, and cathepsin B from mammal were indistinguishable in their responsiveness to DHLA and Fe redox. Thus, DHLA activation vs. Fe3+ inhibition is not unique to falcipain-2 or apicomplexans but is rather a primordial feature of CysHis peptidolysis. Free LA and/or unassociated lipoylated enzyme subunits could be among multiple pathways shuttling reducing equivalents to reduction of proteins, including CysHis proteases. It is discussed that opposing DHLA-Fe3+ modification of plasmodial proteolysis might be a specialized adaptation to intra-erythrocytic growth.

Leishmania amazonensis: Anionic currents expressed in oocytes upon microinjection of mRNA from the parasite

Transport mechanisms involved in pH homeostasis are relevant for the survival of Leishmania parasites. The presence of chloride conductive pathways in Leishmania has been anticipated since anion channel inhibitors limit the proton extrusion mediated by the H+ATPase, which is the major regulator of intracellular pH in amastigotes. In this study, we used Xenopus laevis oocytes as a heterologous expression system in which to study the expression of ion channels upon microinjection of polyA mRNA from Leishmania amazonensis. After injection of polyA mRNA into the oocytes, we measured three different types of currents. We discuss the possible origin of each, and propose that Type 3 currents could be the result of the heterologous expression of proteins from Leishmania since they show different pharmacological and biophysical properties as compared to endogenous oocyte currents.