Uptake of purines in <i>Plasmodium falciparum</i>-infected human erythrocytes is mostly mediated by the human Equilibrative Nucleoside Transporter and the human Facilitative Nucleobase Transporter

&lt;b&gt;Background&lt;/b&gt;: Plasmodium parasites are unable to synthesize purines de novo and have to salvage them from the host. Due to this limitation in the parasite, purine transporters have been an area of focus in the search for anti-malarial drugs. Although the uptake of purines through the human equilibrative nucleoside transporter (hENT1), the human facilitative nucleobase transporter (hFNT1) and the parasite-induced new permeation pathway (NPP) has been studied, no information appears to exist on the relative contribution of these three transporters to the uptake of adenosine and hypoxanthine. Using the appropriate transporter inhibitors, the role of each of these salvage pathways to the overall purine transport in intraerythrocytic Plasmodium falciparum was systematically investigated. &lt;b&gt;Methods&lt;/b&gt;: The transport of adenosine, hypoxanthine and adenine into uninfected and P. falciparum-infected human erythrocytes was investigated in the presence or absence of classical inhibitors of the hFNT1, hENT1 and NPP. The effective inhibition of the various transporters by the classical inhibitors was verified using appropriate known substrates. The ability of high concentration of unlabelled substrates to saturate these transporters was also studied. &lt;b&gt;Results&lt;/b&gt;: Transport of exogenous purine into infected or uninfected erythrocytes occurred primarily through saturable transporters rather than through the NPP. Hypoxanthine and adenine appeared to enter erythrocytes mainly through the hFNT1 nucleobase transporter whereas adenosine entered predominantly through the hENT1 nucleoside transporter. The rate of purine uptake was approximately doubled in infected cells compared to uninfected erythrocytes. In addition, it was found that the rate of adenosine uptake was considerably higher than the rate of hypoxanthine uptake in infected human red blood cells (RBC). It was also demonstrated that furosemide inhibited the transport of purine bases through hFNT1. &lt;b&gt;Conclusion&lt;/b&gt;: Collectively, the data obtained in this study clearly show that the endogenous host erythrocyte transporters hENT1 and hFNT1, rather than the NPP, are the major route of entry of purine into parasitized RBC. Inhibitors of hENT1 and hFNT1, as well as the NPP, should be considered in the development of anti-malarials targeted to purine transport

Effects of some natural leads on Trypanosoma and Leishmania strains

Well-known medical herbal compounds including apigenin, daidzein, phyllanthin and tyramine were assessed against Trypanosoma and Leishmania protozoans. Two strains of the bloodstream forms of Trypanosoma brucei: s427-WT and TbAT1-B48, and Leishmania major and Leishmania mexicana promastigotes were utilised. Among selected natural compounds, apigenin and daidzein displayed moderate activity against African trypanosomes with EC50 16 µM for wild-type sensitive control strain. Tyramine was not found to be very active for trypanosomes strains while all compounds were found to have trivial activity for the inhibition of Leishmania mexicana strains

Genotypic status of the TbAT1/P2 adenosine transporter of Trypanosoma brucei gambiense isolates from northwestern Uganda following melarsoprol withdrawal

Human African trypanosomiasis (HAT) manifests as a chronic infection caused by &lt;i&gt;Trypanosoma brucei gambiense&lt;/i&gt;, or as a more acute form due to &lt;i&gt;T. b. rhodesiense&lt;/i&gt;. Both manifestations occur in Uganda and melarsoprol use against the former was jeopardised in the 1990s as reports of reduced efficacy increased to the point where it was dismissed as first-line treatment at some treatment centers. Previous work to elucidate possible mechanisms leading to melarsoprol resistance pointed to a P2 type adenosine transporter known to mediate melarsoprol uptake and previously shown to be mutated in significant numbers of patients not responding to the drug. Our present findings indicate that there is a low prevalence of mutants in foci where melarsoprol relapses are infrequent. In addition we observe that at the Omugo focus where the drug was withdrawn as first line over 6 years ago, the mutant alleles have disappeared, suggesting that drug pressure is responsible for fuelling their spread. Thus constant monitoring for mutants could play a key role in cost-effective HAT management by identifying which foci can still use the less logistically demanding melarsoprol as opposed to the alternative drug eflornithine. What is required now is a simple method for identifying such mutants at the point of care, enabling practitioners to make informed prescriptions at first diagnosis

A detailed description of the phenotypic spectrum of North Sea Progressive Myoclonus Epilepsy in a large cohort of seventeen patients

Introduction: In 2011, a homozygous mutation in GOSR2 (c.430G > T; p. Gly144Trp) was reported as a novel cause of Progressive Myoclonus Epilepsy (PME) with early-onset ataxia. Interestingly, the ancestors of patients originate from countries bound to the North Sea, hence the condition was termed North Sea PME (NSPME). Until now, only 20 patients have been reported in literature. Here, we provide a detailed description of clinical and neurophysiological data of seventeen patients. Methods: We collected clinical and neurophysiological data from the medical records of seventeen NSPME patients (5–46 years). In addition, we conducted an interview focused on factors influencing myoclonus severity. Results: The core clinical features of NSPME are early-onset ataxia, myoclonus and seizures, with additionally areflexia and scoliosis. Factors such as fever, illness, heat, emotions, stress, noise and light (flashes) all exacerbated myoclonic jerks. Epilepsy severity ranged from the absence of or incidental clinical seizures to frequent daily seizures and status epilepticus. Some patients made use of a wheelchair during their first decade, whereas others still walked independently during their third decade. Neurophysiological features suggesting neuromuscular involvement in NSPME were variable, with findings ranging from indicative of sensory neuronopathy and anterior horn cell involvement to an isolated absent H-reflex. Conclusion: Although the sequence of symptoms is rather homogeneous, the severity of symptoms and rate of progression varied considerably among individual patients. Common triggers for myoclonus can be identified and myoclonus is difficult to treat; to what extent neuromuscular involvement contributes to the phenotype remains

Prevalence and associated risk factors of urinary schistosomiasis among primary school pupils in the Jidawa and Zobiya communities of Jigawa State, Nigeria

Background: Urogenital schistosomiasis (UgS) is a parasitic disease caused by Schistosoma haematobium and can lead to chronic ill-health. Nigeria is endemic for schistosomiasis, but epidemiology of UgS has not been studied in most states. This study was conceived with the aim to contribute towards an accurate national picture of UgS in Nigeria. The prevalence of UgS and the associated risk factors were for the first time investigated among primary school pupils in Jidawa and Zobiya communities of the Dutse Local Government Area (LGAs) of Jigawa State, Nigeria. Method: Focus group discussions with teachers and parents were conducted. After obtaining written consent from parents, questionnaires were administered to pupils to obtain socio-demographic data and information on water contact activities. Urine samples (279) were collected and processed by the urine filtration technique to evaluate haematuria and the presence of S. haematobium eggs. Results: Prevalences of 65.7% (90/137) and 69.0% (98/142) were recorded in the Jidawa and Zobiya communities, respectively. In both communities, there was a significant association between gender and UgS: 63.3% of the infected pupils were males as compared to 36.7% females (χ2 = 5.42, p = 0.020). Grade 5 students had a significantly higher prevalence (χ2 = 17.919, p = 0.001) (80.0%) compared to those in grades 2, 3, 4, and 6 (63.8%, 66.7%, 61.5%, and 64.6%, respectively). Water contact activities showed that pupils involved in fishing, irrigation, and swimming were at greater risk of becoming infected in Jidawa and Zobiya, with odds ratios (risk factors) of 5.4 (0.994–28.862) and 4.1 (1.709–9.862), respectively (p = 0.05). Conclusion: Both the Jidawa and Zobiya communities of the Dutse LGAs of Jigawa State are hyperendemic for UgS. In collaboration with the State Ministry of Health, mass administration of praziquantel was carried out in the Jidawa and Zobiya communities after this study

Uptake of pentamidine in Trypanosoma brucei brucei is mediated by the P2 adenosine transporter and at least one novel, unrelated transporter

Diamidine drugs such as pentamidine and berenil (diminazene aceturate) are vital drugs for the treatment of early stage human African trypanosomiasis and the corresponding veterinary condition, respectively. The action of diamidines on trypanosomes is critically dependent on their efficient uptake by the parasite. We have therefore investigated the mode of uptake of pentamidine by Trypanosoma brucei brucei, using [125I]iodopentamidine as a permeant. [125I]Iodopentamidine uptake was linear for up to 15 min and inhibited by adenosine with a Ki value of 0.64±0.03 μM, to a maximum of 50-70%. The adenosine-sensitive flux was also inhibited by adenine with a Ki value of 0.44±0.04 μMM. Iodopentamidine uptake was saturable, with the adenosine-insensitive flux displaying a Km of 22±2 μM and a Vmax of 2.2±0.9 pmol(107 cells)−1 s−1, whereas the adenosine-sensitive flux was inhibited by much lower iodopentamidine concentrations. These results clearly demonstrate that iodopentamidine is taken up by at least two different T. b. brucei transporters, an adenosine-sensitive pentamidine transporter (ASPT1) and a low-affinity pentamidine transporter (LAPT1). The identity of these transporters was investigated, and their significance for drug uptake and resistance in African trypanosomes is discussed

Ever-increasing complexities of diamidine and arsenical crossresistance in African trypanosomes

The treatment of both human and veterinary African trypanosomiasis is still, to a large extent, dependent on diamidines and melaminophenyl arsenicals. Sixty years after the introduction of pentamidine, a large effort is being made to develop a new generation of diamidines for the treatment of sleeping sickness. However, given the reports of resistance to both diamidines and melaminophenyl arsenicals from the field, including crossresistance to both classes in single isolates, researchers should proceed with some caution before introducing new diamidines, and a thorough understanding of the causes of resistance and crossresistance will be essentia

Receptors and signal transduction in the pars intermedia of Xenopus laevis

Contains fulltext : mmubn000001_157048519.pdf (publisher's version ) (Open Access)Promotores : E. Roubos en B. Jenks137 p

Cyclic-nucleotide signalling in protozoa

Compared with the impressive progress in understanding signal transduction pathways and mechanisms in mammalian systems, advances in protozoan signalling processes, including cyclic nucleotide metabolism, have been very slow. This is in large part connected to the fact that the components of these pathways are very different in the protozoan parasites, as confirmed by the recently completed genome. For instance, kinetoplastids have no equivalents to the mammalian Class I adenylyl cyclases (ACs) in their genomes nor any of the subunits of the associated G-proteins. The cyclases in kinetoplastid parasites contain a single transmembrane domain, a conserved intracellular catalytic domain and a highly variable extracellular domain - consistent with the expression of multiple receptor-activated cyclases - but no receptor ligands, agonists or antagonists have been identified. Apicomplexan AC and guanylyl cyclase (GC) are even more unusual, potentially being bifunctional, harbouring either a putative ion channel (AC) or a P-type ATPase-like domain (GC) alongside the catalytic region. Phosphodiesterases (PDEs) and cyclic-nucleotide-activated protein kinases are essentially conserved in protozoa, although mostly insensitive to inhibitors of the mammalian proteins. Some of the PDEs have now been validated as promising drug targets. In the following manuscript, we will summarize the existing literature on cAMP and cGMP in protozoa: cyclases, PDEs and cyclic-nucleotide-dependent kinases