Comprehensive Genomic Discovery of Non-Coding Transcriptional Enhancers in the African Malaria Vector Anopheles coluzzii

Almost all regulation of gene expression in eukaryotic genomes is mediated by the action of distant non-coding transcriptional enhancers upon proximal gene promoters. Enhancer locations cannot be accurately predicted bioinformatically because of the absence of a defined sequence code, and thus functional assays are required for their direct detection. Here we used a massively parallel reporter assay, Self-Transcribing Active Regulatory Region sequencing (STARR-seq), to generate the first comprehensive genome-wide map of enhancers in Anopheles coluzzii, a major African malaria vector in the Gambiae species complex. The screen was carried out by transfecting reporter libraries created from the genomic DNA of 60 wild A. coluzzii from Burkina Faso into A. coluzzii 4a3A cells, in order to functionally query enhancer activity of the natural population within the homologous cellular context. We report a catalog of 3,288 active genomic enhancers that were significant across three biological replicates, 74% of them located in intergenic and intronic regions. The STARR-seq enhancer screen is chromatin-free and thus detects inherent activity of a comprehensive catalog of enhancers that may be restricted in vivo to specific cell types or developmental stages. Testing of a validation panel of enhancer candidates using manual luciferase assays confirmed enhancer function in 26 of 28 (93%) of the candidates over a wide dynamic range of activity from two to at least 16-fold activity above baseline. The enhancers occupy only 0.7% of the genome, and display distinct composition features. The enhancer compartment is significantly enriched for 15 transcription factor binding site signatures, and displays divergence for specific dinucleotide repeats, as compared to matched non-enhancer genomic controls. The genome-wide catalog of A. coluzzii enhancers is publicly available in a simple searchable graphic format. This enhancer catalogue will be valuable in linking genetic and phenotypic variation, in identifying regulatory elements that could be employed in vector manipulation, and in better targeting of chromosome editing to minimize extraneous regulation influences on the introduced sequences.

Importance: Understanding the role of the non-coding regulatory genome in complex disease phenotypes is essential, but even in well-characterized model organisms, identification of regulatory regions within the vast non-coding genome remains a challenge. We used a large-scale assay to generate a genome wide map of transcriptional enhancers. Such a catalogue for the important malaria vector, Anopheles coluzzii, will be an important research tool as the role of non-coding regulatory variation in differential susceptibility to malaria infection is explored and as a public resource for research on this important insect vector of disease.

Leucine-Rich Immune Factor APL1 Is Associated With Specific Modulation of Enteric Microbiome Taxa in the Asian Malaria Mosquito Anopheles stephensi

The commensal gut microbiome is contained by the enteric epithelial barrier, but little is known about the degree of specificity of host immune barrier interactions for particular bacterial taxa. Here, we show that depletion of leucine-rich repeat immune factor APL1 in the Asian malaria mosquito Anopheles stephensi is associated with higher midgut abundance of just the family Enterobacteraceae, and not generalized dysbiosis of the microbiome. The effect is explained by the response of a narrow clade containing two main taxa related to Klebsiella and Cedecea. Analysis of field samples indicate that these two taxa are recurrent members of the wild Anopheles microbiome. Triangulation using sequence and functional data incriminated relatives of C. neteri and Cedecea NFIX57 as candidates for the Cedecea component, and K. michiganensis, K. oxytoca, and K.sp. LTGPAF-6F as candidates for the Klebsiella component. APL1 presence is associated with host ability to specifically constrain the abundance of a narrow microbiome clade of the Enterobacteraceae, and the immune factor may promote homeostasis of this clade in the enteric microbiome for host benefit.

Gene copy number and function of the APL1 immune factor changed during Anopheles evolution

Background

The recent reference genome assembly and annotation of the Asian malaria vector Anopheles stephensi detected only one gene encoding the leucine-rich repeat immune factor APL1, while in the Anopheles gambiae and sibling Anopheles coluzzii, APL1 factors are encoded by a family of three paralogs. The phylogeny and biological function of the unique APL1 gene in An. stephensi have not yet been specifically examined.

Methods

The APL1 locus was manually annotated to confirm the computationally predicted single APL1 gene in An. stephensi. APL1 evolution within Anopheles was explored by phylogenomic analysis. The single or paralogous APL1 genes were silenced in An. stephensi and An. coluzzii, respectively, followed by mosquito survival analysis, experimental infection with Plasmodium and expression analysis.

Results

APL1 is present as a single ancestral gene in most Anopheles including An. stephensi but has expanded to three paralogs in an African lineage that includes only the Anopheles gambiae species complex and Anopheles christyi. Silencing of the unique APL1 copy in An. stephensi results in significant mosquito mortality. Elevated mortality of APL1-depleted An. stephensi is rescued by antibiotic treatment, suggesting that pathology due to bacteria is the cause of mortality, and indicating that the unique APL1 gene is essential for host survival. Successful Plasmodium development in An. stephensi depends upon APL1 activity for protection from high host mortality due to bacteria. In contrast, silencing of all three APL1 paralogs in An. coluzzii does not result in elevated mortality, either with or without Plasmodium infection. Expression of the single An. stephensi APL1 gene is regulated by both the Imd and Toll immune pathways, while the two signaling pathways regulate different APL1 paralogs in the expanded APL1 locus.

Conclusions

APL1 underwent loss and gain of functions concomitant with expansion from a single ancestral gene to three paralogs in one lineage of African Anopheles. We infer that activity of the unique APL1 gene promotes longevity in An. stephensi by conferring protection from or tolerance to an effect of bacterial pathology. The evolution of an expanded APL1 gene family could be a factor contributing to the exceptional levels of malaria transmission mediated by human-feeding members of the An. gambiae species complex in Africa.

Influence of genetic polymorphism on transcriptional enhancer activity in the malaria vector Anopheles coluzzii

Enhancers are cis-regulatory elements that control most of the developmental and spatial gene expression in eukaryotes. Genetic variation of enhancer sequences is known to influence phenotypes, but the effect of enhancer variation upon enhancer functional activity and downstream phenotypes has barely been examined in any species. In the African malaria vector, Anopheles coluzzii, we identified candidate enhancers in the proximity of genes relevant for immunity, insecticide resistance, and development. The candidate enhancers were functionally validated using luciferase reporter assays, and their activity was found to be essentially independent of their physical orientation, a typical property of enhancers. All of the enhancers segregated genetically polymorphic alleles, which displayed significantly different levels of functional activity. Deletion mutagenesis and functional testing revealed a fine structure of positive and negative regulatory elements that modulate activity of the enhancer core. Enhancer polymorphisms segregate in wild A. coluzzii populations in West Africa. Thus, enhancer variants that modify target gene expression leading to likely phenotypic consequences are frequent in nature. These results demonstrate the existence of naturally polymorphic A. coluzzii enhancers, which may help explain important differences between individuals or populations for malaria transmission efficiency and vector adaptation to the environment.

The Anopheles gambiae 2La chromosome inversion is associated with susceptibility to Plasmodium falciparum in Africa

Chromosome inversions suppress genetic recombination and establish co-adapted gene complexes, or supergenes. The 2La inversion is a widespread polymorphism in the Anopheles gambiae species complex, the major African mosquito vectors of human malaria. Here we show that alleles of the 2La inversion are associated with natural malaria infection levels in wild-captured vectors from West and East Africa. Mosquitoes carrying the more-susceptible allele (2L+^a) are also behaviorally less likely to be found inside houses. Vector control tools that target indoor-resting mosquitoes, such as bednets and insecticides, are currently the cornerstone of malaria control in Africa. Populations with high levels of the 2L+^a allele may form reservoirs of persistent outdoor malaria transmission requiring novel measures for surveillance and control. The 2La inversion is a major and previously unappreciated component of the natural malaria transmission system in Africa, influencing both malaria susceptibility and vector behavior.

First identification of Rickettsia helvetica in questing ticks from a French Northern Brittany Forest

Tick-borne rickettsiae are considered to be emerging, but data about their presence in western Europe are scarce. Ixodes ricinus ticks, the most abundant and widespread tick species in western Europe, were collected and tested for the presence of several tick-borne pathogens in western France, a region never previously explored in this context. There was a high tick abundance with a mean of 4 females, 4.5 males, and 23.3 nymphs collected per hour per collector. Out of 622 tested ticks, specific PCR amplification showed the presence of tick symbionts as well as low prevalence of Borrelia burgdorferi (0.8%), Bartonella spp. (0.17%), and Anaplasma phagocytophilum (0.09%). The most prevalent pathogen was Rickettsia helvetica (4.17%). This is the first time that this bacteria has been detected in ticks in this region, and this result raises the possibility that bacteria other than those classically implicated may be involved in rickettsial diseases in western France.

Evolution of GOUNDRY, a cryptic subgroup of Anopheles gambiae s.l., and its impact on susceptibility to Plasmodium infection

The recent discovery of a previously unknown genetic subgroup of Anopheles gambiae sensu lato underscores our incomplete understanding of complexities of vector population demographics in Anopheles. This subgroup, named GOUNDRY, does not rest indoors as adults and is highly susceptible to Plasmodium infection in the laboratory. Initial description of GOUNDRY suggested it differed from other known Anopheles taxa in surprising and sometimes contradictory ways, raising a number of questions about its age, population size and relationship to known subgroups. To address these questions, we sequenced the complete genomes of 12 wild-caught GOUNDRY specimens and compared these genomes to a panel of Anopheles genomes. We show that GOUNDRY is most closely related to Anopheles coluzzii, and the timing of cladogenesis is not recent, substantially predating the advent of agriculture. We find a large region of the X chromosome that has swept to fixation in GOUNDRY within the last 100 years, which may be an inversion that serves as a partial barrier to contemporary gene flow. Interestingly, we show that GOUNDRY has a history of inbreeding that is significantly associated with susceptibility to Plasmodium infection in the laboratory. Our results illuminate the genomic evolution of one of probably several cryptic, ecologically specialized subgroups of Anopheles and provide a potent example of how vector population dynamics may complicate efforts to control or eradicate malaria.

An Evolution-Based Screen for Genetic Differentiation between Anopheles Sister Taxa Enriches for Detection of Functional Immune Factors

Nucleotide variation patterns across species are shaped by the processes of natural selection, including exposure to environmental pathogens. We examined patterns of genetic variation in two sister species, Anopheles gambiae and Anopheles coluzzii, both efficient natural vectors of human malaria in West Africa. We used the differentiation signature displayed by a known coordinate selective sweep of immune genes APL1 and TEP1 in A. coluzzii to design a population genetic screen trained on the sweep, classified a panel of 26 potential immune genes for concordance with the signature, and functionally tested their immune phenotypes. The screen results were strongly predictive for genes with protective immune phenotypes: genes meeting the screen criteria were significantly more likely to display a functional phenotype against malaria infection than genes not meeting the criteria (p = 0.0005). Thus, an evolution-based screen can efficiently prioritize candidate genes for labor-intensive downstream functional testing, and safely allow the elimination of genes not meeting the screen criteria. The suite of immune genes with characteristics similar to the APL1-TEP1 selective sweep appears to be more widespread in the A. coluzzii genome than previously recognized. The immune gene differentiation may be a consequence of adaptation of A. coluzzii to new pathogens encountered in its niche expansion during the separation from A. gambiae, although the role, if any of natural selection by Plasmodium is unknown. Application of the screen allowed identification of new functional immune factors, and assignment of new functions to known factors. We describe biochemical binding interactions between immune proteins that underlie functional activity for malaria infection, which highlights the interplay between pathogen specificity and the structure of immune complexes. We also find that most malaria-protective immune factors display phenotypes for either human or rodent malaria, with broad specificity a rarity.

Anopheles gambiae and Anopheles coluzzii are the primary mosquito vectors of human malaria in West Africa. Both of these closely related species efficiently transmit the disease, although they display ecological differences. Previous work showed that A. coluzzii displays distinct genetic patterns in genes important for mosquito immunity. Here, we use this genetic pattern as a filter to examine a panel of potential immune genes, and show that the genetic pattern is strongly predictive for genes that play a functional role in immunity when tested with malaria parasites.

The kdr-bearing haplotype and susceptibility to Plasmodium falciparum in Anopheles gambiae: genetic correlation and functional testing

Background

Members of the Anophelesgambiae species complex are primary vectors of human malaria in Africa. It is known that a large haplotype shared between An. gambiae and Anophelescoluzzii by introgression carries point mutations of the voltage-gated sodium channel gene para, including the L1014F kdr mutation associated with insensitivity to pyrethroid insecticides. Carriage of L1014F kdr is also correlated with higher susceptibility to infection with Plasmodium falciparum. However, the genetic mechanism and causative gene(s) underlying the parasite susceptibility phenotype are not known.

Methods

Mosquitoes from the wild Burkina Faso population were challenged by feeding on natural P. falciparum gametocytes. Oocyst infection phenotypes were determined and were tested for association with SNP genotypes. Candidate genes in the detected locus were prioritized and RNAi-mediated gene silencing was used to functionally test for gene effects on P. falciparum susceptibility.

Results

A genetic locus, Pfin6, was identified that influences infection levels of P. falciparum in mosquitoes. The locus segregates as a ~3 Mb haplotype carrying 65 predicted genes including the para gene. The haplotype carrying the kdr allele of para is linked to increased parasite infection prevalence, but many single nucleotide polymorphisms on the haplotype are also equally linked to the infection phenotype. Candidate genes in the haplotype were prioritized and functionally tested. Silencing of para did not influence P. falciparum infection, while silencing of a predicted immune gene, serine protease ClipC9, allowed development of significantly increased parasite numbers.

Conclusions

Genetic variation influencing Plasmodium infection in wild Anopheles is linked to a natural ~3 megabase haplotype on chromosome 2L that carries the kdr allele of the para gene. Evidence suggests that para gene function does not directly influence parasite susceptibility, and the association of kdr with infection may be due to tight linkage of kdr with other gene(s) on the haplotype. Further work will be required to determine if ClipC9 influences the outcome of P. falciparum infection in nature, as well as to confirm the absence of a direct influence by para.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0924-8) contains supplementary material, which is available to authorized users.

ZIPCO, a putative metal ion transporter, is crucial for Plasmodium liver-stage development

The malaria parasite, Plasmodium, requires iron for growth, but how it imports iron remains unknown. We characterize here a protein that belongs to the ZIP (Zrt-, Irt-like Protein) family of metal ion transport proteins and have named ZIP domain-containing protein (ZIPCO). Inactivation of the ZIPCO-encoding gene in Plasmodium berghei, while not affecting the parasite's ability to multiply in mouse blood and to infect mosquitoes, greatly impairs its capacity to develop inside hepatocytes. Iron/zinc supplementation and depletion experiments suggest that ZIPCO is required for parasite utilization of iron and possibly zinc, consistent with its predicted function as a metal transporter. This is the first report of a ZIP protein having a crucial role in Plasmodium liver-stage development, as well as the first metal ion transporter identified in Plasmodium pre-erythrocytic stages. Because of the drastic dependence on iron of Plasmodium growth, ZIPCO and related proteins might constitute attractive drug targets to fight against malaria.

Differences in gene transcriptomic pattern of Plasmodium falciparum in children with cerebral malaria and asymptomatic carriers

The mechanisms underlying the heterogeneity of clinical malaria remain largely unknown. We hypothesized that differential gene expression contributes to phenotypic variation of parasites which results in a specific interaction with the host, leading to different clinical features of malaria. In this study, we analyzed the transcriptomes of isolates obtained from asymptomatic carriers and patients with uncomplicated or cerebral malaria. We also investigated the transcriptomes of 3D7 clone and 3D7-Lib that expresses severe malaria associated-variant surface antigen. Our findings revealed a specific up-regulation of genes involved in pathogenesis, adhesion to host cell, and erythrocyte aggregation in parasites from patients with cerebral malaria and 3D7-Lib, compared to parasites from asymptomatic carriers and 3D7, respectively. However, we did not find any significant difference between the transcriptomes of parasites from cerebral malaria and uncomplicated malaria, suggesting similar transcriptomic pattern in these two parasite populations. The difference between isolates from asymptomatic children and cerebral malaria concerned genes coding for exported proteins, Maurer's cleft proteins, transcriptional factor proteins, proteins implicated in protein transport, as well as Plasmodium conserved and hypothetical proteins. Interestingly, UPs A1, A2, A3 and UPs B1 of var genes were predominantly found in cerebral malaria-associated isolates and those containing architectural domains of DC4, DC5, DC13 and their neighboring rif genes in 3D7-lib. Therefore, more investigations are needed to analyze the effective role of these genes during malaria infection to provide with new knowledge on malaria pathology. In addition, concomitant regulation of genes within the chromosomal neighborhood suggests a common mechanism of gene regulation in P. falciparum.

Diverged alleles of the Anopheles gambiae leucine-rich repeat gene APL1A display distinct protective profiles against Plasmodium falciparum

Functional studies have demonstrated a role for the Anopheles gambiae APL1A gene in resistance against the human malaria parasite, Plasmodium falciparum. Here, we exhaustively characterize the structure of the APL1 locus and show that three structurally different APL1A alleles segregate in the Ngousso colony. Genetic association combined with RNAi-mediated gene silencing revealed that APL1A alleles display distinct protective profiles against P. falciparum. One APL1A allele is sufficient to explain the protective phenotype of APL1A observed in silencing experiments. Epitope-tagged APL1A isoforms expressed in an in vitro hemocyte-like cell system showed that under assay conditions, the most protective APL1A isoform (APL1A(2)) localizes within large cytoplasmic vesicles, is not constitutively secreted, and forms only one protein complex, while a less protective isoform (APL1A(1)) is constitutively secreted in at least two protein complexes. The tested alleles are identical to natural variants in the wild A. gambiae population, suggesting that APL1A genetic variation could be a factor underlying natural heterogeneity of vector susceptibility to P. falciparum.

Abstract P6-04-12: Novel selective estrogen receptors degraders regress tumors in pre-clinical models of endocrine-resistant breast cancer

80% of all breast cancers express the estrogen receptor alpha (ERα) and thus are treated with anti-hormonal therapies that directly block ER function (e.g. Tamoxifen) or hormone synthesis (Aromatase Inhibitors). While these therapies are initially effective, acquired resistance invariably emerges. Importantly, the majority of these tumors continue to depend on ERα for growth and survival. The emerging evidence that ERα can signal in both a ligand-dependent and ligand-independent manner supports the development of agents that are not only competitive ERα antagonists but also reduce steady state levels of the receptor and thus limit both modes of signaling.

We have identified novel, non-steroidal ERα antagonists that induce degradation of ERα in breast cancer cell lines at picomolar concentrations resulting in significant reduction in steady state ERα protein levels. Using peptide-based conformational profiling, we show that these Selective Estrogen Receptor Degraders (SERDs) induce estrogen receptor conformations that are distinct from both fulvestrant and tamoxifen indicating a unique mechanism of action. This unique biological profile coupled with good oral pharmacokinetics produces tumor regressions in both tamoxifen-sensitive and -resistant models of breast cancer in vivo. Recent pre-clinical and clinical data indicate that PI3K pathway signaling can contribute to the endocrine resistant state. In a preclinical model of tamoxifen resistant breast cancer in which SERD monotherapy only produces tumor growth inhibition, SERD therapy in combination with torc1/2 inhibition results in frank tumor regressions. These orally bioavailable SERDs hold promise as a next generation therapy for the treatment of ER+ breast cancer as monotherapy, as well as in combination with agents that target other pathways involved in both intrinsic and acquired endocrine resistance.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-04-12.

Validation of BdCCp2 as a marker for Babesia divergens sexual stages in ticks

Babesiosis is a tick-transmitted disease of mammalian hosts, caused by the intraerythrocytic protozoan parasites of the genus Babesia. Transmission of Babesia parasites from the vertebrate host to the tick is mediated by sexual stages, the gametocytes which are the only intraerythrocytic stages that survive and develop inside the vector. Very few data are available concerning these parasite stages and some markers are needed in order to refine our knowledge of Babesia life cycle inside the tick and to permit the monitoring of parasite transmission from vertebrate to vector. We previously identified some potential markers of the Babesia divergens gametocytes using an in silico post-genomic approach based on sequence identity between the available genomes of Plasmodium and Babesia spp. Here, one of the identified proteins, BdCCp2, was validated as a marker of sexual stages of B. divergens, in infected ticks challenged with antisera directed against recombinant BdCCp2 protein. The BdCCp2 protein was detected by Western blot in some infected ticks, as a discrete band of approximately 171 kDa, while no signal was detected in the laboratory-reared non-infected tick. BdCCp2 was also detected, by immunohistochemical analyses, in piriform or ovoid bodies, measuring 2.5-4.5 μm in diameter, in the gut of partially engorged ticks that were experimentally infected. This molecular marker can then be used in the future to characterize and analyze the biology of B. divergens gametocytes.

The effects of ultrasound on organoclay dispersion in the PP matrix

PP/MMT nanocomposites were prepared by solution intercalation using sonication and quiescent conditions, and the effects on the morphological, thermal and mechanical properties were evaluated by WAXD, TEM, DMA, TGA and DSC analyses. The present study aims to clarify the effects of ultrasound use on the organoclay surface with different amounts of organic modifiers and on the exfoliation processes. The sonication process decreased around of 200 nm the aspect ratio of C15A organoclay. Besides, the effectiveness of the ultrasound process was only achieved with the C15A system because there is a small energetic barrier between their layers (clay with larger d 001). The sonication process increased the exfoliation and distribution of the C15A platelets in the PP matrix, increasing by 5% its reinforcement capacity. However, for I44P system, the use of ultrasound did not show any significant effect on the morphology and consequently on the final properties of the PP matrix. The T(c) temperature and the thermal stability of the PP nanocomposites were increased, independent of the clay type or of the ultrasound use.

The novel putative transporter NPT1 plays a critical role in early stages of Plasmodium berghei sexual development

Transmission of Plasmodium species from a mammalian host to the mosquito vector requires the uptake, during an infected blood meal, of gametocytes, the precursor cells of the gametes. Relatively little is known about the molecular mechanisms involved in the developmental switch from asexual development to sexual differentiation or the maturation and survival of gametocytes. Here, we show that a gene coding for a novel putative transporter, NPT1, plays a crucial role in the development of Plasmodium berghei gametocytes. Parasites lacking NPT1 are severely compromised in the production of gametocytes and the rare gametocytes produced are unable to differentiate into fertile gametes. This is the earliest block in gametocytogenesis obtained by reverse genetics and the first to demonstrate the role of a protein with a putative transport function in sexual development. These results and the high degree of conservation of NPT1 in Plasmodium species suggest that this protein could be an attractive target for the development of novel drugs to block the spread of malaria.

Effect of the novel anti-androgen ARN-509 on response and seizure in castration-resistant prostate cancer models

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Background: ARN-509 is a second-generation anti-androgen discovered in a screen to identify full androgen receptor (AR) antagonists in the context of AR over-expressing prostate cancer cells, a model for castration resistant prostate cancer (CRPC). It has been reported that other second-generation anti-androgens, MDV3100 and BMS-641988, can induce seizures at high dose in pre-clinical species and man and that this is mediated through antagonism of the CNS-based GABAA receptor. To define the clinical potential of ARN-509, we carried out a comprehensive assessment of its in vitro and in vivo activity in validated models of CRPC and assessed its seizure inducing potential.

Methods: ARN-509 and MDV3100 were profiled in a series of assays to monitor both on- and off-target activity. Comparative in vivo efficacy in the LNCaP/AR mouse xenograft model of CRPC and pharmacokinetics were determined. Seizure inducing potential was assessed in an acute pentylenetetrazol (PTZ) infusion model.

Results: In vivo, in the LNCaP/AR model of CRPC, an ARN-509 dose of 10 mg/kg/day exhibited tumors regressions equivalent in frequency and magnitude to a 30 mg/kg/day dose of MDV3100. Tumor re-growth following once daily dosing (30 mg/kg) for 28 days revealed that ARN-509 treated tumors exhibited a more durable response than MDV3100 treated tumors as evidenced by a significantly longer time to re-growth. At doses that yielded equivalent degree of tumor regression, the steady state plasma and brain levels were significantly lower for ARN-509 (10 mg/kg) than MDV3100 (30 mg/kg). ARN-509 and MDV3100 exhibit similar binding affinity to the GABAA receptor; IC50 3.0 and 2.7 mM, respectively. In vivo seizure potential of ARN-509 and MDV3100 was assessed in an acute PTZ infusion model in mice. MDV3100 was found to produce a dose dependant lowering of seizure threshold, while ARN-509 had no effect at any dose tested.

Conclusions: ARN-509 is a second-generation anti-androgen with significant efficacy and an appropriate safety profile that supports its clinical development in both CRPC and earlier stages of prostate cancer. ARN-509 is currently in a phase I/II study in CRPC patients.

[Table: see text]

A cryptic subgroup of Anopheles gambiae is highly susceptible to human malaria parasites

Population subgroups of the African malaria vector Anopheles gambiae have not been comprehensively characterized owing to the lack of unbiased sampling methods. In the arid savanna zone of West Africa, where potential oviposition sites are scarce, widespread collection from larval pools in the peridomestic human habitat yielded a comprehensive genetic survey of local A. gambiae population subgroups, independent of adult resting behavior and ecological preference. A previously unknown subgroup of exophilic A. gambiae is sympatric with the known endophilic A. gambiae in this region. The exophilic subgroup is abundant, lacks differentiation into M and S molecular forms, and is highly susceptible to infection with wild Plasmodium falciparum. These findings might have implications for the epidemiology of malaria transmission and control.

In silico and biological survey of transcription-associated proteins implicated in the transcriptional machinery during the erythrocytic development of Plasmodium falciparum

Background

Malaria is the most important parasitic disease in the world with approximately two million people dying every year, mostly due to Plasmodium falciparum infection. During its complex life cycle in the Anopheles vector and human host, the parasite requires the coordinated and modulated expression of diverse sets of genes involved in epigenetic, transcriptional and post-transcriptional regulation. However, despite the availability of the complete sequence of the Plasmodium falciparum genome, we are still quite ignorant about Plasmodium mechanisms of transcriptional gene regulation. This is due to the poor prediction of nuclear proteins, cognate DNA motifs and structures involved in transcription.

Results

A comprehensive directory of proteins reported to be potentially involved in Plasmodium transcriptional machinery was built from all in silico reports and databanks. The transcription-associated proteins were clustered in three main sets of factors: general transcription factors, chromatin-related proteins (structuring, remodelling and histone modifying enzymes), and specific transcription factors. Only a few of these factors have been molecularly analysed. Furthermore, from transcriptome and proteome data we modelled expression patterns of transcripts and corresponding proteins during the intra-erythrocytic cycle. Finally, an interactome of these proteins based either on in silico or on 2-yeast-hybrid experimental approaches is discussed.

Conclusion

This is the first attempt to build a comprehensive directory of potential transcription-associated proteins in Plasmodium. In addition, all complete transcriptome, proteome and interactome raw data were re-analysed, compared and discussed for a better comprehension of the complex biological processes of Plasmodium falciparum transcriptional regulation during the erythrocytic development.

Population diversity and antibody selective pressure to Plasmodium falciparum MSP1 block2 locus in an African malaria-endemic setting

Background

Genetic evidence for diversifying selection identified the Merozoite Surface Protein1 block2 (PfMSP1 block2) as a putative target of protective immunity against Plasmodium falciparum. The locus displays three family types and one recombinant type, each with multiple allelic forms differing by single nucleotide polymorphism as well as sequence, copy number and arrangement variation of three amino acid repeats. The family-specific antibody responses observed in endemic settings support immune selection operating at the family level. However, the factors contributing to the large intra-family allelic diversity remain unclear. To address this question, population allelic polymorphism and sequence variant-specific antibody responses were studied in a single Senegalese rural community where malaria transmission is intense and perennial.

Results

Family distribution showed no significant temporal fluctuation over the 10 y period surveyed. Sequencing of 358 PCR fragments identified 126 distinct alleles, including numerous novel alleles in each family and multiple novel alleles of recombinant types. The parasite population consisted in a large number of low frequency alleles, alongside one high-frequency and three intermediate frequency alleles. Population diversity tests supported positive selection at the family level, but showed no significant departure from neutrality when considering intra-family allelic sequence diversity and all families combined. Seroprevalence, analysed using biotinylated peptides displaying numerous sequence variants, was moderate and increased with age. Reactivity profiles were individual-specific, mapped to the family-specific flanking regions and to repeat sequences shared by numerous allelic forms within a family type. Seroreactivity to K1-, Mad20- and R033 families correlated with the relative family genotype distribution within the village. Antibody specificity remained unchanged with cumulated exposure to an increasingly large number of alleles.

Conclusion

The Pfmsp1 block2 locus presents a very large population sequence diversity. The lack of stable acquisition of novel antibody specificities despite exposure to novel allelic forms is reminiscent of clonal imprinting. The locus appears under antibody-mediated diversifying selection in a variable environment that maintains a balance between the various family types without selecting for sequence variant allelic forms. There is no evidence of positive selection for intra-family sequence diversity, consistent with the observed characteristics of the antibody response.

Fine pathogen discrimination within the APL1 gene family protects Anopheles gambiae against human and rodent malaria species

Genetically controlled resistance of Anopheles gambiae mosquitoes to Plasmodium falciparum is a common trait in the natural population, and a cluster of natural resistance loci were mapped to the Plasmodium-Resistance Island (PRI) of the A. gambiae genome. The APL1 family of leucine-rich repeat (LRR) proteins was highlighted by candidate gene studies in the PRI, and is comprised of paralogs APL1A, APL1B and APL1C that share ≥50% amino acid identity. Here, we present a functional analysis of the joint response of APL1 family members during mosquito infection with human and rodent Plasmodium species. Only paralog APL1A protected A. gambiae against infection with the human malaria parasite P. falciparum from both the field population and in vitro culture. In contrast, only paralog APL1C protected against the rodent malaria parasites P. berghei and P. yoelii. We show that anti-P. falciparum protection is mediated by the Imd/Rel2 pathway, while protection against P. berghei infection was shown to require Toll/Rel1 signaling. Further, only the short Rel2-S isoform and not the long Rel2-F isoform of Rel2 confers protection against P. falciparum. Protection correlates with the transcriptional regulation of APL1A by Rel2-S but not Rel2-F, suggesting that the Rel2-S anti-parasite phenotype results at least in part from its transcriptional control over APL1A. These results indicate that distinct members of the APL1 gene family display a mutually exclusive protective effect against different classes of Plasmodium parasites. It appears that a gene-for-pathogen-class system orients the appropriate host defenses against distinct categories of similar pathogens. It is known that insect innate immune pathways can distinguish between grossly different microbes such as Gram-positive bacteria, Gram-negative bacteria, or fungi, but the function of the APL1 paralogs reveals that mosquito innate immunity possesses a more fine-grained capacity to distinguish between classes of closely related eukaryotic pathogens than has been previously recognized.

The African malaria vector mosquito Anopheles gambiae possesses immune mechanisms that can protect it against infection with malaria parasites, which kill more than one million people per year. Much work studying mosquito response to malaria has used model rodent malaria parasites that do not infect people, but are in the same genus and overall share most major features with the human parasites. Here, we show that the immune response used by A. gambiae to protect itself against infection by human and rodent malaria parasites utilizes different immune signaling pathways. A family of proteins called APL1 appears to be responsible for the ability of the mosquito to distinguish between the human or rodent malaria parasites. An individual APL1 relative is required for protection against the human malaria parasite but has no effect against the rodent parasite, and another APL1 relative is required for protection against rodent but not human malaria. This represents the finest ability yet demonstrated of mosquito immunity to distinguish between relatively similar pathogens, and highlights the distinct nature of mosquito response against human as compared to rodent malaria parasites.

LISP1 is important for the egress of Plasmodium berghei parasites from liver cells

Most Apicomplexa are obligatory intracellular parasites that multiply inside a so-called parasitophorous vacuole (PV) formed upon parasite entry into the host cell. Plasmodium, the agent of malaria and the Apicomplexa most deadly to humans, multiplies in both hepatocytes and erythrocytes in the mammalian host. Although much has been learned on how Apicomplexa parasites invade host cells inside a PV, little is known of how they rupture the PV membrane and egress host cells. Here, we characterize a Plasmodium protein, called LISP1 (liver-specific protein 1), which is specifically involved in parasite egress from hepatocytes. LISP1 is expressed late during parasite development inside hepatocytes and locates at the PV membrane. Intracellular parasites deficient in LISP1 develop into hepatic merozoites, which display normal infectivity to erythrocytes. However, LISP1-deficient liver-stage parasites do not rupture the membrane of the PV and remain trapped inside hepatocytes. LISP1 is the first Plasmodium protein shown by gene targeting to be involved in the lysis of the PV membrane.

Dynamic RNA profiling in Plasmodium falciparum synchronized blood stages exposed to lethal doses of artesunate

Background

Translation of the genome sequence of Plasmodium sp. into biologically relevant information relies on high through-put genomics technology which includes transcriptome analysis. However, few studies to date have used this powerful approach to explore transcriptome alterations of P. falciparum parasites exposed to antimalarial drugs.

Results

The rapid action of artesunate allowed us to study dynamic changes of the parasite transcriptome in synchronous parasite cultures exposed to the drug for 90 minutes and 3 hours. Developmentally regulated genes were filtered out, leaving 398 genes which presented altered transcript levels reflecting drug-exposure. Few genes related to metabolic pathways, most encoded chaperones, transporters, kinases, Zn-finger proteins, transcription activating proteins, proteins involved in proteasome degradation, in oxidative stress and in cell cycle regulation. A positive bias was observed for over-expressed genes presenting a subtelomeric location, allelic polymorphism and encoding proteins with potential export sequences, which often belonged to subtelomeric multi-gene families. This pointed to the mobilization of processes shaping the interface between the parasite and its environment. In parallel, pathways were engaged which could lead to parasite death, such as interference with purine/pyrimidine metabolism, the mitochondrial electron transport chain, proteasome-dependent protein degradation or the integrity of the food vacuole.

Conclusion

The high proportion of over-expressed genes encoding proteins exported from the parasite highlight the importance of extra-parasitic compartments as fields for exploration in drug research which, to date, has mostly focused on the parasite itself rather than on its intra and extra erythrocytic environment. Further work is needed to clarify which transcriptome alterations observed reflect a specific response to overcome artesunate toxicity or more general perturbations on the path to cellular death.

Plasmodium falciparum transcriptome analysis reveals pregnancy malaria associated gene expression

BACKGROUND

Pregnancy-associated malaria (PAM) causing maternal anemia and low birth weight is among the multiple manifestations of Plasmodium falciparum malaria. Infected erythrocytes (iEs) can acquire various adhesive properties that mediate the clinical severity of malaria. Recent advances on the molecular basis of virulence and immune evasion have helped identify var2csa as a PAM-specific var gene.

METHODOLOGY/PRINCIPAL FINDINGS

The present study presents a genome-wide microarray transcript analysis of 18 P. falciparum parasite isolates freshly collected from the placenta. The proportion of PAM over-expressed genes located in subtelomeric regions as well as that of PAM over-expressed genes predicted to be exported were higher than expected compared to the whole genome. The identification of novel parasite molecules with specificity to PAM and which are likely involved in host-pathogen interactions and placental tropism is described. One of these proteins, PFI1785w, was further characterized as the product of a two-exon PHIST gene, and was more often recognized by serum samples from P. falciparum-exposed women than from men.

CONCLUSIONS/SIGNIFICANCE

These findings suggest that other parasite proteins, such as PFI1785w, may contribute beside VAR2CSA to the pathogenesis of PAM. These data may be very valuable for future vaccine development.

Rosetting is associated with increased Plasmodium falciparum in vivo multiplication rate in the Saimiri sciureus monkey

Severe Plasmodium falciparum malaria in African children is associated with high peripheral parasite densities and high rate of rosette-forming parasites. To explore the relationship between rosette formation and parasite density in vivo, we compared the multiplication rate of a rosette-forming variant (varO) of the Palo Alto line with a sibling non-rosetting variant (varR) in splenectomized Saimiri monkeys. The multiplication rate of varO parasites was 1.5-fold higher than that of the varR variant. This indicates that rosetting is indeed associated with high parasite multiplication efficiency in vivo and, as such, may contribute to the high parasite densities observed in severe malaria.

Serial Analysis of Gene Expression in Plasmodium berghei salivary gland sporozoites

BACKGROUND

The invasion of Anopheles salivary glands by Plasmodium sporozoites is an essential step for transmission of the parasite to the vertebrate host. Salivary gland sporozoites undergo a developmental programme to express genes required for their journey from the site of the mosquito bite to the liver and subsequent invasion of, and development within, hepatocytes. A Serial Analysis of Gene Expression was performed on Anopheles gambiae salivary glands infected or not with Plasmodium berghei and we report here the analysis of the Plasmodium sporozoite transcriptome.

RESULTS

Annotation of 530 tag sequences homologous to Plasmodium berghei genomic sequences identified 123 genes expressed in salivary gland sporozoites and these genes were classified according to their transcript abundance. A subset of these genes was further studied by quantitative PCR to determine their expression profiles. This revealed that sporozoites modulate their RNA amounts not only between the midgut and salivary glands, but also during their storage within the latter. Among the 123 genes, the expression of 66 is described for the first time in sporozoites of rodent Plasmodium species.

CONCLUSION

These novel sporozoite expressed genes, especially those expressed at high levels in salivary gland sporozoites, are likely to play a role in Plasmodium infectivity in the mammalian host.

Whole-transcriptome analysis of Plasmodium falciparum field isolates: identification of new pathogenicity factors

BACKGROUND

Severe malaria and one of its most important pathogenic processes, cerebral malaria, involves the sequestration of parasitized red blood cells (pRBCs) in brain postcapillary venules. Although the pathogenic mechanisms underlying malaria remain poorly characterized, it has been established that adhesion of pRBCs to endothelial cells (ECs) can result in cell apoptosis, which in turn may lead to disruption of the blood-brain barrier. The nature of the parasite molecules involved in the pathogenesis of severe malaria remains elusive.

METHODS

Whole-transcriptome profiling of nonapoptogenic versus apoptogenic parasite field isolates obtained from Gabonese children was performed with pan-genomic Plasmodium falciparum DNA microarrays; radiolabeled instead of fluorescent cDNAs were used to improve the sensitivity of signal detection.

RESULTS

Our methods allowed the identification of 59 genes putatively associated with the induction of EC apoptosis. Silencing of Plasmodium gene expression with specific double-stranded RNA was performed on 8 selected genes; 5 of these, named "Plasmodium apoptosis-linked pathogenicity factors" (PALPFs), were found to be linked to parasite apoptogenicity. Of these genes, 2 might act via parasite cytoadherence.

CONCLUSION

This is the first attempt to identify genes involved in parasite pathogenic mechanisms against human ECs. The finding of PALPFs illuminates perspectives for novel therapeutic strategies against cerebral complications of malaria.

PDE5 inhibitors beyond erectile dysfunction

The phosphodiesterase type-5 (PDE5) inhibitors sildenafil, vardenafil and tadalafil are widely used first-line therapy for erectile dysfunction (ED). Since the advent of sildenafil in 1998, more than 40 million men worldwide have been successfully treated with these compounds. The safety and high tolerability of PDE5 inhibitors make them an attractive tool to investigate further physiological functions of PDE5, for example the modulation of intracellular cyclic GMP (cGMP) pools. As cGMP is a key component of intracellular signaling this may provide novel therapeutic opportunities beyond ED even for indications in which chronic administration is necessary. The approval of sildenafil for the treatment of pulmonary hypertension in 2005 was a notable success in this area of research. A number of other potential new indications are currently in various phases of preclinical research and development. In recent years, extensive but very heterogeneous information has been published in this field. The aim of this review is to summarize existing preclinical and clinical knowledge and critically discuss the evidence to support potential future indications for PDE5 inhibitors.

Rapid dissemination of Plasmodium falciparum drug resistance despite strictly controlled antimalarial use

BACKGROUND

Inadequate treatment practices with antimalarials are considered major contributors to Plasmodium falciparum resistance to chloroquine, pyrimethamine and sulfadoxine. The longitudinal survey conducted in Dielmo, a rural Senegalese community, offers a unique frame to explore the impact of strictly controlled and quantified antimalarial use for diagnosed malaria on drug resistance.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted on a yearly basis a retrospective survey over a ten-year period that included two successive treatment policies, namely quinine during 1990-1994, and chloroquine (CQ) and sulfadoxine/pyrimethamine (SP) as first and second line treatments, respectively, during 1995-1999. Molecular beacon-based genotyping, gene sequencing and microsatellite analysis showed a low prevalence of Pfcrt and Pfdhfr-ts resistance alleles of Southeast Asian origin by the end of 1994 and their effective dissemination within one year of CQ and SP implementation. The Pfcrt resistant allele rose from 9% to 46% prevalence during the first year of CQ reintroduction, i.e., after a mean of 1.66 CQ treatment courses/person/year. The Pfdhfr-ts triple mutant rose from 0% to 20% by end 1996, after a mean of 0.35 SP treatment courses/person in a 16-month period. Both resistance alleles were observed at a younger age than all other alleles. Their spreading was associated with enhanced in vitro resistance and rapidly translated in an increased incidence of clinical malaria episodes during the early post-treatment period.

CONCLUSION/SIGNIFICANCE

In such a highly endemic setting, selection of drug-resistant parasites took a single year after drug implementation, resulting in a rapid progression of the incidence of clinical malaria during the early post-treatment period. Controlled antimalarial use at the community level did not prevent dissemination of resistance haplotypes. This data pleads against reintroduction of CQ in places where resistant allele frequency has dropped to a very low level after CQ use has been discontinued, unless drastic measures are put in place to prevent selection and spreading of mutants during the post-treatment period.

Transcriptome analysis of antigenic variation in Plasmodium falciparum--var silencing is not dependent on antisense RNA

A microarray analysis of Plasmodium falciparum selected to express different var genes suggests that antisense transcripts are not responsible for the transcriptional silencing of non-expressed var genes.

Background

Plasmodium falciparum, the causative agent of the most severe form of malaria, undergoes antigenic variation through successive presentation of a family of antigens on the surface of parasitized erythrocytes. These antigens, known as Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) proteins, are subject to a mutually exclusive expression system, and are encoded by the multigene var family. The mechanism whereby inactive var genes are silenced is poorly understood. To investigate transcriptional features of this mechanism, we conducted a microarray analysis of parasites that were selected to express different var genes by adhesion to chondroitin sulfate A (CSA) or CD36.

Results

In addition to oligonucleotides for all predicted protein-coding genes, oligonucleotide probes specific to each known var gene of the FCR3 background were designed and added to the microarray, as well as tiled sense and antisense probes for a subset of var genes. In parasites selected for adhesion to CSA, one full-length var gene (var2csa) was strongly upregulated, as were sense RNA molecules emanating from the 3' end of a limited subset of other var genes. No global relationship between sense and antisense production of var genes was observed, but notably, some var genes had coincident high levels of both antisense and sense transcript.

Conclusion

Mutually exclusive expression of PfEMP1 proteins results from transcriptional silencing of non-expressed var genes. The distribution of steady-state sense and antisense RNA at var loci are not consistent with a silencing mechanism based on antisense silencing of inactive var genes. Silencing of var loci is also associated with altered regulation of genes distal to var loci.

Potency, selectivity, and consequences of nonselectivity of PDE inhibition

Phosphodiesterases (PDEs) play a decisive role in cyclic nucleotide-mediated intracellular signaling. As PDEs are expressed in a variety of tissues, selectivity is a prerequisite for a therapeutically applicable PDE inhibitor. Sildenafil, vardenafil, and tadalafil are selective for PDE5, with vardenafil exhibiting the highest potency and minimal inhibition of other PDEs, with the exception of PDE6. Tadalafil is extremely selective for PDE5, but also potently inhibits PDE11, an enzyme with unknown physiological function. As PDE1 is expressed in the brain, myocardium, and vascular smooth muscle cells, nonselectivity with respect to this enzyme (selectivity: tadalafil>vardenafil>sildenafil) may result in vasodilation and tachycardia. Inhibition of PDE6 (selectivity: tadalafil>vardenafil congruent with sildenafil), which is expressed only in retina and functions in visual transduction, can transiently disturb vision. PDE5 inhibitors may also indirectly inhibit PDE3 by increasing cyclic guanosine monophospate levels, thereby elevating heart rate and vasodilation while inhibiting platelet aggregation.

Vardenafil preclinical trial data: potency, pharmacodynamics, pharmacokinetics, and adverse events

Vardenafil potently inhibits human phosphodiesterase 5 (PDE5) with an IC50 of 0.7 nM. Enhancement of nitric oxide (NO)-induced erections in rabbits by 0.1 mg/kg vardenafil is limited by its pharmacokinetic properties (Tmax=1 h; T1/2=1.2 h), although erectile effects have been observed after 7 h. In humans, vardenafil is rapidly absorbed (Tmax approximately 40 min) and more slowly metabolized (T1/2 approximately 4 h), with an absolute bioavailability of 14.5% (vs 40% for sildenafil). Although the consumption of high-fat meals does not affect the drug's relative bioavailability, it retards intestinal absorption. Coadministration of CYP3A4 inhibitors such as ritonavir can affect hepatic metabolism. M1, an active metabolite of vardenafil, is a four-fold-less potent inhibitor of PDE5 than its parent compound, contributing approximately 7% to vardenafil's overall efficacy. The side effects of all selective PDE5 inhibitors commonly include vasodilation, small reductions in blood pressure, headache, and nasal congestion.

Pro-erectile effect of vardenafil: in vitro experiments in rabbits and in vivo comparison with sildenafil in rats

OBJECTIVES

To assess pro-erectile responses to vardenafil, a new selective PDE5 inhibitor, in vitro in isolated rabbit corpora cavernosa, and in vivo in anaesthetized rats.

METHODS

Rabbit cavernosal strips were precontracted with 10 microM phenylephrine. Dose-response relaxation curves to cumulative dosings of vardenafil (1 nM-10 microM) were constructed alone and in the presence of 10 mM L-NAME. Relaxation responses to electrical field stimulation (EFS) (2 Hz, 2 ms, 10 V) were compared in control preparations and in the presence of vardenafil (1-10 nM). Male Sprague-Dawley rats were anaesthetized with urethane and prepared for measurement of blood pressure and intracavernous pressure. Erectile responses (ICPmax/dBP x 100) to cavernous nerve submaximal stimulation (10 Hz, 1 ms, 0.45-1.6 V) were determined before, and 3, 10 and 23 min after i.v. administration of saline, vardenafil or sildenafil (0.1, 1 mg/kg).

RESULTS

Vardenafil was effective in relaxing precontracted rabbit cavernosal strips (IC50 54 +/- 18 nM). This relaxing activity was partially antagonized with 10 mM L-NAME, increasing the IC50 to 620 +/- 81 nM. Vardenafil significantly increased (more than 4 times) relaxation of precontracted rabbit cavernosal strips to EFS at 10 nM. In anaesthetized rats, erectile responses were significantly facilitated 3 and 13 min after 0.1 and 1 mg/kg vardenafil was administered. In contrast, 1 mg/kg sildenafil only significantly increased erectile responses at 3 min post-injection.

CONCLUSIONS

Vardenafil relaxes rabbit corpus cavernosum in vitro and is effective at a lower dose than sildenafil in facilitating erectile responses to cavernous nerve stimulation in anaesthetized rats.

Vardenafil enhances clitoral and vaginal blood flow responses to pelvic nerve stimulation in female dogs

The relaxation of the smooth muscle in the vagina and clitoris and the increase of blood flow into these organs is thought to be essential in the female sexual response. Vardenafil is a type 5 phosphodiesterase (PDE5) inhibitor that potentiates the nitric oxide (NO)/cGMP pathway facilitating penile smooth muscle relaxation and improving penile erection in men. Although the potentiation of the NO/cGMP pathway through PDE5 inhibitors can clearly enhance blood flow into the penis and is used in the therapy of male sexual dysfunction, there is controversy about the efficacy of these agents in improving female sexual function. The aim of this work was to evaluate the effects of vardenafil on the increase of blood flow into the vagina and clitoris induced by pelvic nerve electrical stimulation (PNES) in a female dog model. Application of PNES produced consistent and frequency-related increased blood flow into the vagina and clitoris of anesthetized female dogs. The magnitude and duration of the blood flow responses to PNES were variable among the different animals but remained stable over time within the same animal. The intravenous administration of vardenafil (1 mg/kg) significantly potentiated the increases in blood flow produced by PNES into the vagina (381.4 and 206.2% of control response at 5 and 10 Hz, respectively, P<0.01, n=6) and clitoris (379.4 and 238.5% of control response at 5 and 10 Hz, respectively, P<0.01, n=6) 20 min after administration. The significant enhancement of PNES-induced responses was maintained 50 min (224.5 and 181.0%, P<0.01 in vagina; 294.8 and 258.9%, P<0.05 in clitoris) and 80 min after vardenafil administration (209.5 and 156.9%, P<0.05 in vagina; 268.9 and 194.9%, P<0.05 in clitoris). Here we present a feasible model for research into female sexual function. Our results show that vardenafil effectively potentiates the blood flow responses to PNES in the genitalia of female dogs. These results emphasize the role of the NO/cGMP pathway in the local vasodilatory response in female sexual organs and provide a rationale for testing PDE5 inhibitors, such as vardenafil, as a treatment for certain forms of female sexual dysfunction.

Vardenafil reverses erectile dysfunction induced by paroxetine in rats

Selective serotonin reuptake inhibitors (SSRIs) are associated with a high incidence of impotence. Paroxetine is an extensively used SSRI that has been shown to impair erectile function in patients, to induce erectile dysfunction and to inhibit nitric oxide synthase (NOS) activity and NO production in animal models. NO is a key mediator of penile erection. Vardenafil is a type 5 phosphodiesterase inhibitor that potentiates NO-mediated responses in isolated trabecular smooth muscle and penile erection in men in clinical trials. The aim of this study was to evaluate the effects of vardenafil on the impairment of erectile responses produced by paroxetine in the rat model. Application of cavernosal nerve electrical stimulation (CNES) produced frequency-related intracavernosal pressure (ICP) increases, which were inhibited by the NOS inhibitor N(G)-nitro-L-arginine (0.3 mg/kg) and potentiated by vardenafil (0.3 mg/kg). Acute paroxetine treatment (10 mg/kg) significantly reduced ICP-responses to CNES. This inhibition was completely reversed by vardenafil (0.3 mg/kg) administration. The results show that the erectile dysfunction induced by paroxetine in rats can be effectively treated with vardenafil, suggesting that the use of this compound could be a reasonable therapeutic approach to treating erectile dysfunction associated with SSRI administration.

BAY 41-2272: a stimulator of soluble guanylyl cyclase induces nitric oxide-dependent penile erection in vivo

OBJECTIVES

To determine the effectiveness of BAY 41-2272 on penile erections in an in vivo rabbit model. The nitric oxide (NO)-dependent increase of intracellular cyclic guanosine monophosphate (cGMP) by cGMP-phosphodiesterase (PDE5) inhibition has been shown to be an effective mechanism in the treatment of erectile dysfunction. Direct, NO-independent stimulation of soluble guanylyl cyclase should also lead to elevated cGMP levels in tissues and could be an attractive alternative therapeutic option for the treatment of erectile dysfunction. BAY 41-2272 is a novel non-NO-based direct stimulator of soluble guanylyl cyclase that activates purified enzyme in a synergistic fashion with NO.

METHODS

BAY 41-2272 was administered to conscious rabbits intravenously (IV) and orally (PO). Erection was assessed in a time-dependent manner by measuring the length of the uncovered penile mucosa. Erections were evaluated in the absence and presence of NO (with intravenous sodium nitroprusside [SNP] as the NO donor).

RESULTS

BAY 41-2272 only induced weak penile erections in conscious rabbits after IV (1 mg/kg) and PO (10 mg/kg) administration in the absence of an NO donor. However, the efficacy of BAY 41-2272 was potentiated by the simultaneous administration of SNP. Through simultaneous SNP administration, the effective doses of BAY 41-2272 were reduced significantly (minimal effective dose 0.1 mg/kg IV and 1 mg/kg PO).

CONCLUSIONS

The results of this study clearly demonstrated the effect of BAY 41-2272 on penile erection in the conscious rabbit model after PO and IV administration. The time-course and onset of erection was concurrent with the stimulation by exogenous NO (SNP), suggesting that this new pharmacologic mechanism of soluble guanylyl cyclase stimulation could be used in the treatment of erectile dysfunction. Because the effect is increased by SNP, it can be expected that BAY 41-2272 would have enhanced activity during sexual arousal, when NO is produced endogenously.

Three multigene families in Plasmodium parasites: facts and questions

Multigene families optimise fitness by providing a set of related genes with possibly different temporal and/or topological expression patterns. We analyse here the structural organisation and sequence diversity of the rDNA, sera and var C Plasmodium falciparum families, and discuss their consequences for parasite biology. The low rDNA copy number, which reduces reshuffling, is probably the corollary of the need for functionally distinct rRNAs in the insect and in the vertebrate host. The unusual intra-genome and population rDNA sequence diversity results in cells equipped with mosaic ribosome sets. The functional constraints are such that ribosome compatibility could influence parasite fitness and contribute to population structuring. Unlike the dispersed rDNA units, the sera family is arranged as a tandem gene cluster, with seven contiguous similar genes, and one more distantly related paralog. We address the question of the inclusion criteria in family definition. We discuss the results concerning the SERA proteins expression and function in the context of the long overlooked multigene family. The var C module is shared by var genes, 'orphan' var C and var C pseudogenes. Analysis of 125 var C deduced protein sequences highlights a well-conserved framework, including putative phosphorylation sites, consistent with the proposed function of mediating interaction with cytoskeletal proteins. The 5' and 3' flanking sequences of the var C pseudogenes are heterogeneous. In contrast, the flanking sequences of the uninterrupted var C modules show remarkable conservation. This is interesting in view of the silencing activity of the var intronic sequence on var expression. The 5' flanking sequence dichotomy reported for internal and sub-telomeric var genes extends to the 3' flanking sequences. This has profound implications for transcription regulation and generation of diversity. The var C family suggests a role for pseudogenes as a diversity reservoir and in genome dynamics by promoting ectopic recombination.

The phosphodiesterase inhibitory selectivity and the in vitro and in vivo potency of the new PDE5 inhibitor vardenafil

We investigated the potency and the selectivity profile of vardenafil on phosphodiesterase (PDEs) enzymes, its ability to modify cGMP metabolism and cause relaxation of penile smooth muscle and its effect on erections in vivo under conditions of exogenous nitric oxide (NO) stimulation. PDE isozymes were extracted and purified from human platelets (PDE5) or bovine sources (PDEs 1, 2, 3, 4 and 6). The inhibition of these PDEs and of human recombinant PDEs by vardenafil was determined. The ability to potentiate NO-mediated relaxation and influence cGMP levels in human corpus cavernosum strips was measured in vitro, and erection-inducing activity was demonstrated in conscious rabbits after oral administration together with intravenous doses of sodium nitroprusside (SNP). The effects of vardenafil were compared with those of the well-recognized PDE5 inhibitor, sildenafil (values for sildenafil in brackets). Vardenafil specifically inhibited the hydrolysis of cGMP by PDE5 with an IC50 of 0.7 nM (6.6 nM). In contrast, the IC50 of vardenafil for PDE1 was 180 nM; for PDE6, 11 nM; for PDE2, PDE3 and PDE4, more than 1000 nM. Relative to PDE5, the ratios of the IC50 for PDE1 were 257 (60), for PDE6 16 (7.4). Vardenafil significantly enhanced the SNP-induced relaxation of human trabecular smooth muscle at 3 nM (10 nM). Vardenafil also significantly potentiated both ACh-induced and transmural electrical stimulation-induced relaxation of trabecular smooth muscle. The minimum concentration of vardenafil that significantly potentiated SNP-induced cGMP accumulation was 3 nM (30 nM). In vivo studies in rabbits showed that orally administered vardenafil dose-dependently potentiated erectile responses to intravenously administered SNP. The minimal effective dose that significantly potentiated erection was 0.1 mg/kg (1 mg/kg). The selectivity for PDE5, the potentiation of NO-induced relaxation and cGMP accumulation in human trabecular smooth muscle and the ability to enhance NO-induced erection in vivo indicate that vardenafil has the appropriate properties to be a potential compound for the treatment of erectile dysfunction. Vardenafil was more potent and selective than sildenafil on its inhibitory activity on PDE5.