The N-Terminal Region of Plasmodium falciparum MSP10 Is a Target of Protective Antibodies in Malaria and Is Important for PfGAMA/PfMSP10 Interaction

Clinical manifestation of malaria is mainly due to intra-erythrocytic development of Plasmodium parasites. Plasmodium falciparum merozoites, the invasive form of the blood-stage parasite, invade human erythrocytes in a complex but rapid process. This multi-step progression involves interactions between parasite and human host proteins. Here we show that antibodies against a vaccine antigen, PfGAMA, co-immunoprecipitate with PfMSP10. This interaction was validated as direct by surface plasmon resonance analysis. We then demonstrate that antibodies against PfMSP10 have growth inhibitory activity against cultured parasites, with the region PfMSP10 R1 that is critical for its interaction with PfGAMA being the key target. We also observe that the PfMSP10 R1 region is highly conserved among African field isolates. Lastly, we show that high levels of antibodies against PfMSP10 R1 associate with reduced risk to clinical malaria in children resident in a malaria endemic region in northern Uganda. Put together, these findings provide for the first time the functional context of the important role of PfGAMA/PfMSP10 interaction in erythrocyte invasion and unveil a novel asexual blood-stage malaria vaccine target for attenuating P. falciparum merozoite invasion.

Malaria transmission-blocking vaccines: wheat germ cell-free technology can accelerate vaccine development

Introduction: Highly effective malaria vaccines are essential component toward malaria elimination. Although the leading malaria vaccine, RTS,S/AS01, with modest efficacy is being evaluated in a pilot feasibility trial, development of a malaria transmission-blocking vaccine (TBV) could make a major contribution toward malaria elimination. Only a few TBV antigens have reached pre-clinical or clinical development but with several challenges including difficulties in the expression of malaria recombinant proteins and low immunogenicity in humans. Therefore, novel approaches to accelerate TBV research to preclinical development are critical to generate an efficacious TBV.Areas covered: PubMed was searched to review the progress and future prospects of malaria TBV research and development. We also reviewed registered trials at ClinicalTrials.gov as well as post-genome TBV candidate discovery research including our efforts.Expert opinion: Wheat germ cell-free protein synthesis technology can accelerate TBV development by overcoming some current challenges of TBV research.

Genomic and biological features of Plasmodium falciparum resistance against antimalarial endoperoxide N-89

Drug resistance of malaria parasites remains a problem affecting antimalarial treatment and control of the disease. We previously synthesized an antimalarial endoperoxide, N-89, having high antimalarial effects in vitro and in vivo. In this study we seek to understand the resistant mechanism against N-89 by establishing a highly N-89-resistant clone, named NRC10H, of the Plasmodium falciparum FCR-3 strain. We describe gene mutations in the parent FCR-3 strain and the NRC10H clone using whole-genome sequencing and subsequently by expression profiling using quantitative real-time PCR. Seven genes related to drug resistance, proteolysis, glycophosphatidylinositol anchor biosynthesis, and phosphatidylethanolamine biosynthesis exhibited a single amino acid substitution in the NRC10H clone. Among these seven genes, the multidrug resistance protein 2 (mdr2) variant A532S was found only in NRC10H. The genetic status of the P. falciparum endoplasmic reticulum-resident calcium binding protein (PfERC), a potential target of N-89, was similar between the NRC10H clone and the parent FCR-3 strain. These findings suggest that the genetic alterations of the identified seven genes, in particular mdr2, in NRC10H could give rise to resistance of the antimalarial endoperoxide N-89.

Fluorinated alkyl-phosphate-based electrolytes with controlled lithium-ion coordination structure

Herein, we propose Li-ion solvation-controlled electrolytes based on non-flammable organic solvent TFEP and an LiFSA salt [TFEP: tris(2,2,2-trifluoroethyl)phosphate, LiFSA: lithium bis(fluorosulfonyl)amide] to allow Li-ion insertion into a graphite electrode for Li-ion batteries. Comprehensive structural study based on (1) infrared (IR)/Raman spectroscopy, (2) high-energy X-ray total scattering (HEXTS), and (3) molecular dynamics (MD) simulation revealed the solvation (or coordination) structures of Li ions in TFEP-based electrolytes at the molecular level. In binary LiFSA/TFEP with a Li salt concentration (c_Li) < 1.0 mol dm^-3, Li ions are coordinated with both TFEP and FSA components; in detail, two TFEP molecules coordinate in an O-donating monodentate manner and one FSA in an O-donating bidentate manner to form [Li(TFEP)₂(bi-FSA)] as the major species. We demonstrated that adding acetonitrile (AN) to the LiFSA/TFEP electrolytes caused structural changes in the Li-ion complexes. The bi-FSA bound to the Li ion changed its coordination mode to mono-FSA, which was induced by solvating AN molecules to Li ions. The redox reaction corresponding to insertion/deinsertion of Li ions into/from the graphite electrode successfully occurred in 1.0 mol dm^-3 LiFSA/TFEP with an AN electrolyte system, while there was no or reduced Li-ion insertion in the electrolyte without AN. We discussed the relationship between the structure and electrode reaction of the Li-ion complexes based on the FSA-coordination characteristics; i.e., in LiFSA/TFEP with the AN system, the mono-FSA bound to the Li ion is easier to decoordinate due to weaker Li⁺mono-FSA^- interactions rather than the Li⁺bi-FSA^- interactions, which mainly contribute to charge-transfer at the electrode/electrolyte interface to allow Li-ion insertion/deinsertion in the graphite anode.

Anti-MSP11 IgG inhibits Plasmodium falciparum merozoite invasion into erythrocytes in vitro

Merozoite surface proteins (MSPs) are considered as promising blood-stage malaria vaccine candidates. MSP3 has long been evaluated for its vaccine candidacy, however, the candidacy of other members of MSP3 family is insufficiently characterized. Here, we investigated Plasmodium falciparum MSP11 (PF3D7_1036000), a member of the MSP3 family, for its potential as a blood-stage vaccine candidate. The full-length protein (MSP11-FL) as well as the N-terminal half-MSP11 (MSP11-N), known to be unique among the MSP3 family members, were expressed by wheat germ cell-free system, and used to raise antibodies in rabbit. Immunoblot analysis of schizont lysates probed with anti-MSP11-N antibodies detected double bands at approximately 40 and 60 kDa, consistent with the previous report thus confirming antibodies specificity. However, inconsistent with previously reported merozoite's surface localization, immunofluorescence assay (IFA) revealed that MSP11 likely localizes to rhoptry neck of merozoites in mature schizonts. After invasion, MSP11 localized to parasitophorous vacuole and thereafter in Maurer's clefts in trophozoites. Anti-MSP11-FL antibody levels were significantly higher in asymptomatic than symptomatic P. falciparum cases in malaria low endemic Thailand. This reconfirmed that anti-MSP11 antibodies play an important role in protection against clinical malaria, as previously reported. Furthermore, in vitro growth inhibition assay revealed that anti-MSP11-FL rabbit antibodies biologically function by inhibiting merozoite invasion of erythrocytes. These findings further support the vaccine candidacy of MSP11.

Antibodies against a Plasmodium falciparum RON12 inhibit merozoite invasion into erythrocytes

Proteins coating Plasmodium merozoite surface and secreted from its apical organelles are considered as promising vaccine candidates for blood-stage malaria. The rhoptry neck protein 12 of Plasmodium falciparum (PfRON12) was recently reported as a protein specifically expressed in schizonts and localized to the rhoptry neck of merozoites. Here, we assessed its potential as a vaccine candidate. We expressed a recombinant PfRON12 protein by a wheat germ cell-free system to obtain anti-PfRON12 antibody. Immunoblot analysis of schizont lysates detected a single band at approximately 40 kDa under reducing conditions, consistent with the predicted molecular weight. Additionally, anti-PfRON12 antibody recognized a single band around 80 kDa under non-reducing conditions, suggesting native PfRON12 forms a disulfide-bond-mediated multimer. Immunofluorescence assay and immunoelectron microscopy revealed that PfRON12 localized to the rhoptry neck of merozoites in schizonts and to the surface of free merozoites. The biological activity of anti-PfRON12 antibody was tested by in vitro growth inhibition assay (GIA), and the rabbit antibodies significantly inhibited merozoite invasion of erythrocytes. We then investigated whether PfRON12 is immunogenic in P. falciparum-infected individuals. The sera from P. falciparum infected individuals in Thailand and Mali reacted with the recombinant PfRON12. Furthermore, human anti-PfRON12 antibodies affinity-purified from Malian serum samples inhibited merozoite invasion of erythrocytes in vitro. Moreover, pfron12 is highly conserved with only 4 non-synonymous mutations in the coding sequence from approximately 200 isolates deposited in PlasmoDB. These results suggest that PfRON12 might be a potential blood-stage vaccine candidate antigen against P. falciparum.

Early first trimester uteroplacental flow and the progressive disintegration of spiral artery plugs: new insights from contrast-enhanced ultrasound and tissue histopathology

STUDY QUESTION

Does the use of a vascular contrast agent facilitate earlier detection of maternal flow to the placental intervillous space (IVS) in the first trimester of pregnancy?

SUMMARY ANSWER

Microvascular filling of the IVS was demonstrated by contrast-enhanced ultrasound from 6 weeks of gestation onwards, earlier than previously believed.

WHAT IS KNOWN ALREADY

During placental establishment and remodeling of maternal spiral arteries, endovascular trophoblast cells invade and accumulate in the lumen of these vessels to form 'trophoblast plugs'. Prior evidence from morphological and Doppler ultrasound studies has been conflicting as to whether the spiral arteries are completely plugged, preventing maternal blood flow to the IVS until late in the first trimester.

STUDY DESIGN, SIZE, DURATION

Uteroplacental flow was examined across the first trimester in human subjects given an intravenous infusion of lipid-shelled octofluoropropane microbubbles with ultrasound measurement of destruction and replenishment kinetics. We also performed a comprehensive histopathological correlation using two separately archived uteroplacental tissue collections to evaluate the degree of spiral artery plugging and evaluate remodeling of the upstream myometrial radial and arcurate arteries.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Pregnant women (n = 34) were recruited in the first trimester (range: 6+3 to 13+6 weeks gestation) for contrast-enhanced ultrasound studies with destruction-replenishment analysis of signal intensity for assessment of microvascular flux rate. Histological samples from archived in situ (Boyd Collection, n = 11) and fresh first, second, and third trimester decidual and post-hysterectomy uterine specimens (n = 16) were evaluated by immunohistochemistry (using markers of epithelial, endothelial and T-cells, as well as cell adhesion and proliferation) and ultrastructural analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

Contrast agent entry into the IVS was visualized as early as 6+3 weeks of gestation with some variability in microvascular flux rate noted in the 6-7+6 week samples. Spiral artery plug canalization was observed from 7 weeks with progressive disintegration thereafter. Of note, microvascular flux rate did not progressively increase until 13 weeks, which suggests that resistance to maternal flow in the early placenta may be mediated more proximally by myometrial radial arteries that begin remodeling at the end of the first trimester.

LIMITATIONS REASONS FOR CAUTION

Gestational age was determined by crown-rump length measurements obtained by transvaginal ultrasound on the day of contrast-enhanced imaging studies, which may explain the variability in the earliest gestational age samples due to the margin of error in this type of measurement.

WIDER IMPLICATIONS OF THE FINDINGS

Our comprehensive in situ histological analysis, in combination with the use of an in vivo imaging modality that has the sensitivity to permit visualization of microvascular filling, has allowed us to reveal new evidence in support of increasing blood flow to the IVS from 6 weeks of gestation. Histologic review suggested the mechanism may be blood flow through capillary-sized channels that form through the loosely cohesive 'plugs' by 7 weeks gestation. However, spiral artery remodeling on its own did not appear to explain why there is significantly more blood flow at 13 weeks gestation. Histologic studies suggest it may be related to radial artery remodeling, which begins at the end of the first trimester.

STUDY FUNDING/COMPETING INTEREST(S)

This project was supported by the Oregon Health and Science University Knight Cardiovascular Institute, Center for Developmental Health and the Struble Foundation. There are no competing interests.

Elastic modulus estimation based on local displacement observation of elastic body

A method is proposed that provides estimates of the spatial variation of elastic moduli using local displacements of the elastic body. A central issue of elastography imaging has been the limited area of measurement. With the proposed method, stiffness parameter estimations are considered as minimization problems using finite-element models. The sparseness of the gradient of tissue elasticity is also exploited to improve estimation accuracy. Simulation experiments show that based on a 5% area of observation of a simple plate model with non-uniform elasticity the spatial variation of Young's modulus is reconstructed to within 5% accuracy. This result suggests that the proposed framework significantly extends the area of estimation overcoming the limitations of conventional elastography techniques.

Assessment of diastolic function of normal fetal heart using dual-gate Doppler

OBJECTIVES

The ratio of mitral peak early diastolic filling to early diastolic mitral annular velocity (E/e') reflects diastolic cardiac function in adults. Dual-gate Doppler (DD) enables measurements of E/e' in the same heart beat. This study was designed to assess the utility of the DD method for measurement of fetal E/e' and determine reference ranges for normal fetuses.

METHODS

This prospective study comprised normal singleton pregnancies undergoing fetal echocardiography between 16 and 36 weeks of gestation. According to the DD method, E-wave velocity on pulsed-wave Doppler and e'-wave on tissue Doppler imaging were measured simultaneously on an apical or basal four-chamber view, and fetal E/e' was calculated. Spearman's correlation coefficient was used to assess the relationship between gestational age (GA) and E-wave and e'-wave velocities and E/e'.

RESULTS

A total of 133 pregnancies were included in this study and all E/e' measurements were successful. Significant correlation was observed between GA and both left ventricular (LV) E/e' (r _s  = -0.666, P < 0.001) and right ventricular (RV) E/e' (r _s  = -0.607, P < 0.001). The regression equations for bilateral E/e' were: LV-E/e' = 17.341 - 0.631GA + 0.008 × GA² (mean ± SD, R ²  = 0.440 ± 1.333); and RV-E/e' = 19.156 - 0.794GA + 0.012GA² (R ²  = 0.419 ± 1.329).

CONCLUSIONS

Bilateral E/e' of normal fetuses, measured using the DD method, decreased with GA, which is considered to be related to myocardial maturity. DD is a useful and convenient method for evaluating fetal E/e' in order to assess diastolic function in the prenatal period. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Trend in unequal geographical distribution of doctors by age and sex in Japan from 2004 to 2014

OBJECTIVES

In Japan, the proportion of female doctors and elderly doctors is increasing as in other countries. We investigated the relationship between doctors' demographic changes and their geographical distribution.

STUDY DESIGN

A national database study.

METHODS

We assessed trends in unequal geographical distribution of the number of doctors by sex and age from 2004 to 2014 in Japan.

RESULTS

The Gini coefficient values for the number of female doctors (0.18) were larger than those for male doctors across all generations (0.13-0.14). The Gini coefficient values for the number of elderly doctors aged 60 years and older (male: 0.12, female: 0.18-0.23) were larger than those for majority age groups aged 40-59 years (male: 0.10, female: 0.16-0.17).

CONCLUSION

The persisting geographical maldistribution of doctors may be associated with demographic changes, such as increase in the number of female doctors.

PV1, a novel Plasmodium falciparum merozoite dense granule protein, interacts with exported protein in infected erythrocytes

Upon invasion, Plasmodium falciparum exports hundreds of proteins across its surrounding parasitophorous vacuole membrane (PVM) to remodel the infected erythrocyte. Although this phenomenon is crucial for the parasite growth and virulence, elucidation of precise steps in the export pathway is still required. A translocon protein complex, PTEX, is the only known pathway that mediates passage of exported proteins across the PVM. P. falciparum Parasitophorous Vacuolar protein 1 (PfPV1), a previously reported parasitophorous vacuole (PV) protein, is considered essential for parasite growth. In this study, we characterized PfPV1 as a novel merozoite dense granule protein. Structured illumination microscopy (SIM) analyses demonstrated that PfPV1 partially co-localized with EXP2, suggesting the protein could be a PTEX accessory molecule. Furthermore, PfPV1 and exported protein PTP5 co-immunoprecipitated with anti-PfPV1 antibody. Surface plasmon resonance (SPR) confirmed the proteins’ direct interaction. Additionally, we identified a PfPV1 High-affinity Region (PHR) at the C-terminal side of PTP5 where PfPV1 dominantly bound. SIM analysis demonstrated an export arrest of PTP5ΔPHR, a PTP5 mutant lacking PHR, suggesting PHR is essential for PTP5 export to the infected erythrocyte cytosol. The overall results suggest that PfPV1, a novel dense granule protein, plays an important role in protein export at PV.