Studtite formation assessed by Raman spectroscopy and 18^{18}O isotopic labeling during the oxidative dissolution of a MOX fuel

The authors thank the technicians from DHA-Atalante facility who strongly participated to this experiment: Loïck Chauvin,Nathalie Vaissières, Manuel Delaville and Maxime Fagard.International audienceThe formation of studtite has been studied during the oxidative dissolution of a MIMAS MOX fuel disc in aerated water enriched in $^{18}$O under a gamma radiation source, coupling Raman spectroscopy and solution analyzes. The use of isotopic labeling allowed following the reactions responsible for the precipitation of studtite. At the beginning of the experiment, different $^{18}$O enrichments in the uranyl and peroxide bonds of the studtite were observed. While the uranyl bond was primarily enriched in $^{18}$O, the peroxide bond contained large amounts of $^{16}$O. This result suggests an oxygen contribution coming from different radiolytic species for each bond: H$_2$O$_2$ and radicals. The comparison with a UO$_2$ sample leached in similar conditions ruled out a role of the Pu alpha self-irradiation in this different behavior. Yet, the influence of the MOX MIMAS heterogeneous microstructure and chemistry is observed with the preferential dissolution of the UO$_2$ grains, the Pu-rich areas being much more stable with regard to the dissolution. In addition, the studtite first precipitates preferentially on the Pu-poor areas of the sample before covering the entire surface, including the plutonium-enriched aggregates, at the end of the experiment

Influence of high spressures on CH4, CO2 and H2S solubility in polyethylene: Experimental and molecular simulation approaches for pure gas and gas mixtures. Modelling of the sorption isotherms

International audienceThe sorption of methane, carbon dioxide and hydrogen sulphide in polyethylene (PE) was investigated. Data were obtained in a large range of pressures from both experiments and molecular simulation. Monte Carlo (MC) simulations in the osmotic ensemble were used to predict gas concentrations in the amorphous polymer phase. An ad hoc constraint in the osmotic simulations was used to mimic the effect of the crystalline phase. The results obtained from MC simulation compared favourably to experimental results and data from literature. Different sorption mechanisms were evidenced in the low to middle gas pressure range as a function of the gas nature. However, the decrease of gas solubility was evidenced at high pressure. It was assigned to a hydrostatic effect and the bulk modulus of the PE amorphous phase was determined. A simple model allowing the accurate description of gas solubility from low to high gas pressure range was proposed. It was shown to accurately describe the different sorption isotherm shapes obtained for PE and the characteristic parameters of the model were determined for each gas

5WBF: a low-cost and straightforward whole blood filtration method suitable for whole-genome sequencing of Plasmodium falciparum clinical isolates

Abstract Background Whole-genome sequencing (WGS) is becoming increasingly helpful to assist malaria control programmes. A major drawback of this approach is the large amount of human DNA compared to parasite DNA extracted from unprocessed whole blood. As red blood cells (RBCs) have a diameter of about 7–8 µm and exhibit some deformability, it was hypothesized that cheap and commercially available 5 µm filters might retain leukocytes but much less of Plasmodium falciparum-infected RBCs. This study aimed to test the hypothesis that such a filtration method, named 5WBF (for 5 µm Whole Blood Filtration), may provide highly enriched parasite material suitable for P. falciparum WGS. Methods Whole blood was collected from five patients experiencing a P. falciparum malaria episode (ring-stage parasitaemia range: 0.04–5.5%) and from mock samples obtained by mixing synchronized, ring-stage cultured P. falciparum 3D7 parasites with uninfected human whole blood (final parasitaemia range: 0.02–1.1%). These whole blood samples (50 to 400 µL) were diluted in RPMI 1640 medium or PBS 1× buffer and filtered with a syringe connected to a 5 µm commercial filter. DNA was extracted from 5WBF-treated and unfiltered counterpart blood samples using a commercial kit. The 5WBF method was evaluated on the ratios of parasite:human DNA assessed by qPCR and by sequencing depth and percentages of coverage from WGS data (Illumina NextSeq 500). As a comparison, the popular selective whole-genome amplification (sWGA) method, which does not rely on blood filtration, was applied to the unfiltered counterpart blood samples. Results After applying 5WBF, qPCR indicated an average of twofold loss in the amount of parasite template DNA (Pf ARN18S gene) and from 4096- to 65,536-fold loss of human template DNA (human β actin gene). WGS analyses revealed that > 95% of the  parasite nuclear and organellar genomes were all covered at ≥ 10× depth for all samples tested. In sWGA counterparts, the organellar genomes were poorly covered and from 47.7 to 82.1% of the nuclear genome was covered at ≥ 10× depth depending on parasitaemia. Sequence reads were homogeneously distributed across gene sequences for 5WBF-treated samples (n = 5460 genes; mean coverage: 91×; median coverage: 93×; 5th percentile: 70×; 95th percentile: 103×), allowing the identification of gene copy number variations such as for gch1. This later analysis was not possible for sWGA-treated samples, as a much more heterogeneous distribution of reads across gene sequences was observed (mean coverage: 80×; median coverage: 51×; 5th percentile: 7×; 95th percentile: 245×). Conclusions The novel 5WBF leucodepletion method is simple to implement and based on commercially available, standardized 5 µm filters which cost from 1.0 to 1.7€ per unit depending on suppliers. 5WBF permits extensive genome-wide analysis of P. falciparum ring-stage isolates from minute amounts of whole blood even with parasitaemias as low as 0.02%

Plasmodium falciparum kelch13 polymorphisms identified after treatment failure with artemisinin-based combination therapy in Niger

Abstract Background Artemisinin-based combination therapy (ACT) is the most effective treatment for malaria, and has significantly reduced morbimortality. Polymorphisms associated with the Plasmodium falciparum Kelch gene (Pfkelch13) have been associated with delayed parasite clearance even with ACT treatment. Methods The Pfkelch13 gene was sequenced from P. falciparum infected patients (n = 159) with uncomplicated malaria in Niger. An adequate clinical and parasitological response (ACPR) was reported in 155 patients. Four (n = 4) patients had treatment failure (TF) that were not reinfections—two of which had late parasitological failures (LPF) and two had late clinical failures (LCF). Results Thirteen single nucleotide polymorphisms (SNPs) were identified of which seven were non-synonymous (C469R, T508S, R515T, A578S, I465V, I437V, F506L,), and three were synonymous (P443P, P715P, L514L). Three SNP (C469R, F506L, P715P) were present before ACT treatment, while seven mutations (C469R, T508S, R515T, L514L, P443P, I437V, I465V) were selected by artemether/lumefantrine (AL)—five of which were non-synonymous (C469R, T508S, R515T, I437V, I465V). Artesunate/amodiaquine (ASAQ) has selected any mutation. One sample presented three cumulatively non-synonymous SNPs—C469R, T508S, R515T. Conclusions This study demonstrates intra-host selection of Pfkelch13 gene by AL. The study highlights the importance of LCF and LPF parasites in the selection of resistance to ACT. Further studies using gene editing are required to confirm the potential implication of resistance to ACT with the most common R515T and T508S mutations. It would also be important to elucidate the role of cumulative mutations

Potent Antiplasmodial Derivatives of Dextromethorphan Reveal the Ent-Morphinan Pharmacophore of Tazopsine-Type Alkaloids

International audienceThe alkaloid tazopsine 1 was introduced in the late 2000s as a novel antiplasmodial hit compound active against Plasmodium falciparum hepatic stages, with the potential to develop prophylactic drugs based on this novel chemical scaffold. However, the structural determinants of tazopsine 1 bioactivity, together with the exact definition of the pharmacophore, remained elusive, impeding further development. We found that the antitussive drug dextromethorphan (DXM) 3, although lacking the complex pattern of stereospecific functionalization of the natural hit, was harboring significant antiplasmodial activity in vitro despite suboptimal prophylactic activity in a murine model of malaria, precluding its direct repurposing against the disease. The targeted N-alkylation of nor-DXM 15 produced a small library of analogues with greatly improved activity over DXM 3 against P. falciparum asexual stages. Amongst these, N-2’-pyrrolylmethyl-nor-DXM 16i showed a 2- to 36-fold superior inhibitory potency compared to tazopsine 1 and DXM 3 against P. falciparum liver and blood stages, with respectively 760 ± 130 nM and 2.1 ± 0.4 μM IC(50) values, as well as liver/blood phase selectivity of 2.8. Furthermore, cpd. 16i showed a 5- to 8-fold increase in activity relative to DXM 3 against P. falciparum stages I-II and V gametocytes, with 18.5 μM and 13.2 μM IC(50) values, respectively. Cpd. 16i can thus be considered a promising novel hit compound against malaria in the ent-morphinan series with putative pan cycle activity, paving the way for further therapeutic development (e.g., investigation of its prophylactic activity in vivo)

Evaluation of two commercial kits and two laboratory-developed qPCR assays compared to LAMP for molecular diagnosis of malaria

International audienceAbstract Background Malaria is an infectious disease considered as one of the biggest causes of mortality in endemic areas. This life-threatening disease needs to be quickly diagnosed and treated. The standard diagnostic tools recommended by the World Health Organization are thick blood smears microscopy and immuno-chromatographic rapid diagnostic tests. However, these methods lack sensitivity especially in cases of low parasitaemia and non-falciparum infections. Therefore, the need for more accurate and reliable diagnostic tools, such as real-time polymerase chain reaction based methods which have proven greater sensitivity particularly in the screening of malaria, is prominent. This study was conducted at the French National Malaria Reference Centre to assess sensitivity and specificity of two commercial malaria qPCR kits and two in-house developed qPCRs compared to LAMP. Methods 183 blood samples received for expertise at the FNMRC were included in this study and were subjected to four different qPCR methods: the Biosynex Ampliquick ® Malaria test, the BioEvolution Plasmodium Typage test, the in-house HRM and the in-house TaqMan qPCRs. The specificity and sensitivity of each method and their confidence intervals were determined with the LAMP-based assay Alethia® Malaria as the reference for malaria diagnosis. The accuracy of species diagnosis of the Ampliquick ® Malaria test and the two in-house qPCRs was also evaluated using the BioEvolution Plasmodium Typage test as the reference method for species identification. Results The main results showed that when compared to LAMP, a test with excellent diagnostic performances, the two in-house developed qPCRs were the most sensitive (sensitivity at 100% for the in-house TaqMan qPCR and 98.1% for the in-house HRM qPCR), followed by the two commercial kits: the Biosynex Ampliquick ® Malaria test (sensitivity at 97.2%) and the BioEvolution Plasmodium Typage (sensitivity at 95.4%). Additionally, with the in-house qPCRs we were able to confirm a Plasmodium falciparum infection in microscopically negative samples that were not detected by commercial qPCR kits. This demonstrates that the var genes of P. falciparum used in these in-house qPCRs are more reliable targets than the 18S sRNA commonly used in most of the developed qPCR methods for malaria diagnosis. Conclusion Overall, these results accentuate the role molecular methods could play in the screening of malaria. This may represent a helpful tool for other laboratories looking to implement molecular diagnosis methods in their routine analysis, which could be essential for the detection and treatment of malaria carriers and even for the eradication of this disease