Metabolomics to unveil and understand phenotypic diversity between pathogen populations

Visceral leishmaniasis is caused by a parasite called Leishmania donovani, which every year infects about half a million people and claims several thousand lives. Existing treatments are now becoming less effective due to the emergence of drug resistance. Improving our understanding of the mechanisms used by the parasite to adapt to drugs and achieve resistance is crucial for developing future treatment strategies. Unfortunately, the biological mechanism whereby Leishmania acquires drug resistance is poorly understood. Recent years have brought new technologies with the potential to increase greatly our understanding of drug resistance mechanisms. The latest mass spectrometry techniques allow the metabolome of parasites to be studied rapidly and in great detail. We have applied this approach to determine the metabolome of drug-sensitive and drug-resistant parasites isolated from patients with leishmaniasis. The data show that there are wholesale differences between the isolates and that the membrane composition has been drastically modified in drug-resistant parasites compared with drug-sensitive parasites. Our findings demonstrate that untargeted metabolomics has great potential to identify major metabolic differences between closely related parasite strains and thus should find many applications in distinguishing parasite phenotypes of clinical relevance

Metabolic Variation during Development in Culture of Leishmania donovani Promastigotes

The genome sequencing of several Leishmania species has provided immense amounts of data and allowed the prediction of the metabolic pathways potentially operating. Subsequent genetic and proteomic studies have identified stage-specific proteins and putative virulence factors but many aspects of the metabolic adaptations of Leishmania remain to be elucidated. In this study, we have used an untargeted metabolomics approach to analyze changes in the metabolite profile as promastigotes of L. donovani develop during in vitro cultures from logarithmic to stationary phase. The results show that the metabolomes of promastigotes on days 3–6 of culture differ significantly from each other, consistent with there being distinct developmental changes. Most notable were the structural changes in glycerophospholipids and increase in the abundance of sphingolipids and glycerolipids as cells progress from logarithmic to stationary phase

Effects of excess carbon and vibrational properties in ultrafine SiC powders

Structural and vibrational properties are investigated in SiC nanopowders synthesized by a CO2 laser pyrolysis of (SiH4, C2H2) gaseous mixture and thermally treated up to 1800 °C. The structural modifications of the SiC crystallites and the arrangement of the carbon in excess are monitored at different annealing stages. A critical behaviour is revealed in the powder annealed at Ta = 1500 °C through the features of the Raman spectra and the insulating-conductor transition. The significant electric conductivity (σ ≈ 0.05 S cm−1) which appears above Ta is discussed with respect to the powder composition and the interface effects where the carbon in excess seems to play a key role

Nanosized Si/C/N composite powders formed by laser-aerosol coupling

Recently it has been shown that ultrafine preceramic Si/C/N powders in the nanometric range can be obtained by combining the ultrasonic injection of a liquid precursor with the CO2 laser irradiation. At the CEA the first experiments were conducted with hexamethyldisilazane - (CH3)3SiNHSi(CH3)3 - (or HMDS) as the precursor. The aerosol droplets formed by the Pyrosol process are carried out with a flow of argon or argon - ammonia mixture into the beam of a high powered industrial continuous wave CO2 laser. At laboratory scale up to 100cm3/hr of liquid are displaced with a conversion efficiency (liquid → powder) of about 45%. The chemical composition is controlled by varying the synthesis conditions. The C/N atomic ratio changes from 3 (under argon) to 0.35 (under argon + ammonia). The as-formed powders are amorphous, monodispersed and nanosized (<100nm). The effect of heating under nitrogen atmosphere has been studied by various diagnostics (chemical analysis, BET, XRD)

Therapeutic evaluation of free and nanocapsule-encapsulated atovaquone in the treatment of murine visceral leishmaniasis

International audienceThe activities of free atovaquone (ATV) and of poly(D,L-lactide) nanocapsules loaded with the drug, in the treatment of mice with visceral leishmaniasis caused by Leishmania infantum, were compared. Each mouse was infected intravenously with 2 x 10(7) promastigotes, on day 0. On days 15, 17 and 19, most of the infected mice were treated either with free ATV, in a dimethylsulphoxide/cremophor/water mixture, or with the ATV-loaded nanocapsules (at, respectively, 0.2-1.6 and 0.125-1.0 mg ATV/kg, on each treatment day). The rest of the mice were left untreated, as controls. All the mice were killed on day 21 and dissected so that their livers and spleens could be weighed. The liver parasite burdens, evaluated using the Stauber method, indicated that the ATV-loaded nanocapsules were significantly more effective than the free drug. In nanocapsules, for example, a total dose of 3.0 mg ATV/kg reduced liver burdens by 71.3%, whereas treatment with a higher total dose of the free drug (4.8 mg/kg) only cut the number of liver parasites by 34.4%. The dose-response data indicated that livers would have been cleared of parasites if the nanocapsule preparation had been given as three doses each equivalent to 3 mg ATV/kg, whereas the maximum suppression possible with the free drug would have been about 61%, whatever the dose