Characterising the role of actin and PI (3) kinases in endocytosis in the malaria parasite Plasmodium falciparum

Includes bibliographical references (leaves 94-103).By contrast to mammalian cells, very little is known about endocytosis in the malaria parasite. However, endocytosis via the cytostome is required by the parasite to ingest haemoglobin from its host cytosol which it transports within double membrane vesicles to the digestive vacuole, where digestion occurs and metabolites are used mostly for nutritional purposes. To gain a deeper understanding of the molecular basis and mechanisms of this vital process, a panel of inhibitors was used to inhibit the actin cytoskeleton and PI (3) kinases in the parasite. In this study Cytochalasin D and Latrunculin A, which depolymerise and prevent actin fimalment formation, Jasplakinolide, which stabilises actin filaments, and Wormannin and LY294002, which inhibit PI 93) kinase, were used to study actin disrupting and PI (3) kinase inhibiting drug effects on haemoglobin endocytosis and transport vesicle trafficking within the malaria parasite Plasmodium falciparum

Characterizing population pharmacokinetic/pharmacodynamic relationships in pulmonary tuberculosis infected adults using nonlinear mixed effects modelling

This pharmacokinetic sub-study was nested within the phase-III OFLOTUB study investigating the shortening of tuberculosis treatment. A total of 343 adults enrolled in Benin, Guinea, Senegal, and South Africa were randomized to receive rifampicin, isoniazid, pyrazinamide, and ethambutol in the standard 6-month control regimen or the 4-month test regimen where gatifloxacin replaced ethambutol. The pharmacokinetics of all drugs was described at first dose and steady-state using nonlinear mixed-effects modelling, and individual exposures were summarised as area under the concentration-time curve (AUC0-24) and peak concentration. Autoinduction of rifampicin metabolism was characterized with a semi-mechanistic enzyme turn-over model. Gatifloxacin dose was evaluated using Monte Carlo simulations. Lastly, Classification & Regression Tree (CART) analysis techniques were used to identify factors predictive of 2-month culture conversion or 24-month long-term composite outcome. Consistent with literature findings, approximately 73.0, 43.0, 0.3, 6.0 and 0.0% of patients failed to achieve previously reported target concentrations for rifampicin, isoniazid, pyrazinamide, ethambutol, and gatifloxacin, respectively

Actin is required for endocytic trafficking in the malaria parasite Plasmodium falciparum

The intra-erythrocytic stages of the malaria parasite endocytose large quantities of the surrounding erythrocyte cytoplasm and deliver it to a digestive food vacuole via endocytic vesicles. Digestion provides amino acids for parasite protein synthesis and is required to maintain the osmotic integrity of the host cell. The parasite endocytic pathway has been described morphologically by electron microscopy, but the molecular mechanisms that mediate and regulate it remain elusive. Given the involvement of actin in endocytosis in other eukaryotes, we have used actin inhibitors to assess the requirement for this protein in the endocytic pathway of the human malaria parasite, Plasmodium falciparum. Treatment of cultures with cytochalasin D did not affect haemoglobin levels in the parasites when co-administered with protease inhibitors, and neither did it affect the uptake of the endocytic tracer horseradish peroxidase, suggesting the absence of actin in the mechanism of endocytosis. However, in the absence of protease inhibitors, treated parasites contained increased levels of haemoglobin due to an accumulation of enlarged endocytic vesicles, as determined by immunofluorescence and electron microscopy, suggesting a role for actin in vesicle trafficking, possibly by mediating vesicle maturation and/or fusion to the digestive vacuole. In contrast to cytochalasin D, treatment with jasplakinolide led to an inhibition of endocytosis, an accumulation of vesicles closer to the plasma membrane and a marked concentration of actin in the parasite cortex. We propose that the stabilization of cortical actin filaments by jasplakinolide interferes with normal endocytic vesicle formation and migration from the cell periphery

A semimechanistic pharmacokinetic-enzyme turnover model for rifampin autoinduction in adult tuberculosis patients.

The currently recommended doses of rifampin are believed to be at the lower end of the dose-response curve. Rifampin induces its own metabolism, although the effect of dose on the extent of autoinduction is not known. This study aimed to investigate rifampin autoinduction using a semimechanistic pharmacokinetic-enzyme turnover model. Four different structural basic models were explored to assess whether different scaling methods affected the final covariate selection procedure. Covariates were selected by using a linearized approach. The final model included the allometric scaling of oral clearance and apparent volume of distribution. Although HIV infection was associated with a 30% increase in the apparent volume of distribution, simulations demonstrated that the effect of HIV on rifampin exposure was slight. Model-based simulations showed close-to-maximum induction achieved after 450-mg daily dosing, since negligible increases in oral clearance were observed following the 600-mg/day regimen. Thus, dosing above 600 mg/day is unlikely to result in higher magnitudes of autoinduction. In a typical 55-kg male without HIV infection, the oral clearance, which was 7.76 liters · h⁻¹ at the first dose, increased 1.82- and 1.85-fold at steady state after daily dosing with 450 and 600 mg, respectively. Corresponding reductions of 41 and 42%, respectively, in the area under the concentration-versus-time curve from 0 to 24 h were estimated. The turnover of the inducible process was estimated to have a half-life of approximately 8 days in a typical patient. Assuming 5 half-lives to steady state, this corresponds to a duration of approximately 40 days to reach the induced state for rifampin autoinduction

Evaluation of initial and steady-state gatifloxacin pharmacokinetics and dose in pulmonary tuberculosis patients by using monte carlo simulations.

A 4-month regimen of gatifloxacin with rifampin, isoniazid, and pyrazinamide is being evaluated for the treatment of tuberculosis in a phase 3 randomized controlled trial (OFLOTUB). A prior single-dose study found that gatifloxacin exposure increased by 14% in the combination. The aims of the study are to evaluate the initial and steady-state pharmacokinetics of gatifloxacin when daily doses are given to patients with newly diagnosed drug-sensitive pulmonary tuberculosis as part of a combination regimen and to evaluate the gatifloxacin dose with respect to the probability of attaining a pharmacokinetic/pharmacodynamic target. We describe the population pharmacokinetics of gatifloxacin from the first dose to a median of 28 days in 169 adults enrolled in the OFLOTUB trial in Benin, Guinea, Senegal, and South Africa. The probability of achieving a ratio of ≥125 for the area under the concentration time curve to infinity (AUC0-∞) for the free fraction of gatifloxacin over the MIC (fAUC/MIC) was investigated using Monte Carlo simulations. The median AUC0-∞ of 41.2 μg · h/ml decreased on average by 14.3% (90% confidence interval [CI], -90.5% to +61.5%) following multiple 400-mg daily doses. At steady state, 90% of patients achieved an fAUC/MIC of ≥125 only when the MIC was <0.125 μg/ml. We conclude that systemic exposure to gatifloxacin declines with repeated daily 400-mg doses when used together with rifampin, isoniazid, and pyrazinamide, thus compensating for any initial increase in gatifloxacin levels due to a drug interaction. (The OFLOTUB study has been registered at ClinicalTrials.gov under registration no. NCT00216385.)

PfPI3K, a phosphatidylinositol-3 kinase from Plasmodium falciparum, is exported to the host erythrocyte and is involved in hemoglobin trafficking

Polyphosphorylated phosphoinositides (PIPs) are potent second messengers, which trigger a wide variety of signaling and trafficking events in most eukaryotic cells. However, the role and metabolism of PIPs in malaria parasite Plasmodium have remained largely unexplored. Our present studies suggest that PfPI3K, a novel phosphatidylinositol-3-kinase (PI3K) in Plasmodium falciparum, is exported to the host erythrocyte by the parasite in an active form. PfPI3K is a versatile enzyme as it can generate various 3′-phosphorylated PIPs. In the parasite, PfPI3K was localized in vesicular compartments near the membrane and in its food vacuole. PI3K inhibitors wortmannin and LY294002 were effective against PfPI3K and were used to study PfPI3K function. We found that PfPI3K is involved in endocytosis from the host and trafficking of hemoglobin in the parasite. The inhibition of PfPI3K resulted in entrapment of hemoglobin in vesicles in the parasite cytoplasm, which prevented its transport to the food vacuole, the site of hemoglobin catabolism. As a result, hemoglobin digestion, which is a source of amino acids necessary for parasite growth, was attenuated and caused the inhibition of parasite growth

A differential response to antihypertensive therapy in African men and women: Insights from the CREOLE Trial

Background: We sought to address the paucity of data to support the evidence-based management of hypertension to achieve optimal blood pressure (BP) control on a sex-specific basis in Africa. Methods: We undertook a post hoc analysis of the multicenter, randomized CREOLE (Comparison of Three Combination Therapies in Lowering Blood Pressure in Black Africans) Trial to test the hypothesis that there would be clinically important differences in office BP control between African men and women. We compared the BP levels of 397 and 238 hypertensive women (63%, 50.9 ± 10.5 years) and men (51.2 ± 11.3 years) from 10 sites across sub-Saharan Africa who completed baseline and 6-month profiling according to their randomly allocated antihypertensive treatment. Results: Overall, 442/635 (69.6%) participants achieved an office BP target of \u3c140/90 mm Hg at 6 months; comprising more women (286/72.0%) than men (156/65.5%) (adjusted odds ratio [OR] 1.59, 95% confidence interval [CI] 1.07–2.39; P = 0.023). Women randomized to amlodipine–hydrochlorothiazide (HCTZ) (adjusted OR 3.03, 95% CI 1.71–5.35; P \u3c 0.001) or amlodipine–perindopril (adjusted OR 2.62, 95% CI 1.49–4.58; P = 0.01) were more likely to achieve this target compared with perindopril–HCTZ. Among men, there were no equivalent treatment differences—amlodipine–HCTZ (OR 1.54, 95% CI 0.76–3.12; P = 0.23) or amlodipine–perindopril (OR 1.32, 95% CI 0.65–2.67; P = 0.44) vs. perindopril–HCTZ. Among the 613 participants (97%) with 24-hour ambulatory BP monitoring, women had significantly lower systolic (124.1 ± 18.1 vs. 127.3 ± 16.9; P = 0.028) and diastolic (72.7 ± 10.4 vs. 75.1 ± 10.5; P = 0.007) BP levels at 6 months compared with men. Conclusions: These data suggest clinically important differences in the therapeutic response to antihypertensive combination therapy among African women compared with African men