141 research outputs found

    Characterization of DNA Sequences that Confer Complement Resistance in \u3ci\u3eLeishmania chagasi\u3c/i\u3e

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    Serial passage of axenically cultured Leishmania chagasi promastigotes results in a progressive diminution in resistance to complement-mediated lysis (CML), whereas high CML resistance is seen in infectious metacyclic promastigotes from the sandfly vector as well as metacyclic-like promastigotes within low-passage cultures at stationary growth phase. As we previously reported, in a screen seeking to identify novel genes involved in CML resistance: (1) a genomic cosmid library derived from DNA of CML-resistant L. chagasi promastigotes was transfected into highpassage (constitutively CML-sensitive) L. chagasi promastigotes; (2) transformants were screened for acquisition of CML-resistance; (3) multiple cosmid-transfectants exhibited partial CML resistance; and (4) the sequence for one of the cosmids (Cosmid 51) was determined. This report extends the analysis of Cosmid 51, and identifies by deletion analysis a subregion of the cosmid insert that is critical to the CML-resistance phenotype of Cosmid 51 transformants. We also report the sequence determination and initial CML-resistance activity of another cosmid that also confers partial resistance to CML

    Characterization of DNA Sequences that Confer Complement Resistance in \u3ci\u3eLeishmania chagasi\u3c/i\u3e

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    Serial passage of axenically cultured Leishmania chagasi promastigotes results in a progressive diminution in resistance to complement-mediated lysis (CML), whereas high CML resistance is seen in infectious metacyclic promastigotes from the sandfly vector as well as metacyclic-like promastigotes within low-passage cultures at stationary growth phase. As we previously reported, in a screen seeking to identify novel genes involved in CML resistance: (1) a genomic cosmid library derived from DNA of CML-resistant L. chagasi promastigotes was transfected into highpassage (constitutively CML-sensitive) L. chagasi promastigotes; (2) transformants were screened for acquisition of CML-resistance; (3) multiple cosmid-transfectants exhibited partial CML resistance; and (4) the sequence for one of the cosmids (Cosmid 51) was determined. This report extends the analysis of Cosmid 51, and identifies by deletion analysis a subregion of the cosmid insert that is critical to the CML-resistance phenotype of Cosmid 51 transformants. We also report the sequence determination and initial CML-resistance activity of another cosmid that also confers partial resistance to CML

    Trypanosoma brucei aquaglyceroporin 2 is a high-affinity transporter for pentamidine and melaminophenyl arsenic drugs and the main genetic determinant of resistance to these drugs.

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    OBJECTIVES: Trypanosoma brucei drug transporters include the TbAT1/P2 aminopurine transporter and the high-affinity pentamidine transporter (HAPT1), but the genetic identity of HAPT1 is unknown. We recently reported that loss of T. brucei aquaglyceroporin 2 (TbAQP2) caused melarsoprol/pentamidine cross-resistance (MPXR) in these parasites and the current study aims to delineate the mechanism by which this occurs. METHODS: The TbAQP2 loci of isogenic pairs of drug-susceptible and MPXR strains of T. brucei subspecies were sequenced. Drug susceptibility profiles of trypanosome strains were correlated with expression of mutated TbAQP2 alleles. Pentamidine transport was studied in T. brucei subspecies expressing TbAQP2 variants. RESULTS: All MPXR strains examined contained TbAQP2 deletions or rearrangements, regardless of whether the strains were originally adapted in vitro or in vivo to arsenicals or to pentamidine. The MPXR strains and AQP2 knockout strains had lost HAPT1 activity. Reintroduction of TbAQP2 in MPXR trypanosomes restored susceptibility to the drugs and reinstated HAPT1 activity, but did not change the activity of TbAT1/P2. Expression of TbAQP2 sensitized Leishmania mexicana promastigotes 40-fold to pentamidine and >1000-fold to melaminophenyl arsenicals and induced a high-affinity pentamidine transport activity indistinguishable from HAPT1 by Km and inhibitor profile. Grafting the TbAQP2 selectivity filter amino acid residues onto a chimeric allele of AQP2 and AQP3 partly restored susceptibility to pentamidine and an arsenical. CONCLUSIONS: TbAQP2 mediates high-affinity uptake of pentamidine and melaminophenyl arsenicals in trypanosomes and TbAQP2 encodes the previously reported HAPT1 activity. This finding establishes TbAQP2 as an important drug transporter

    Trypanosoma brucei gambiense group 1 is distinguished by a unique amino acid substitution in the HpHb receptor implicated in human serum resistance

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    Trypanosoma brucei rhodesiense (Tbr) and T. b. gambiense (Tbg), causative agents of Human African Trypanosomiasis (sleeping sickness) in Africa, have evolved alternative mechanisms of resisting the activity of trypanosome lytic factors (TLFs), components of innate immunity in human serum that protect against infection by other African trypanosomes. In Tbr, lytic activity is suppressed by the Tbr-specific serum-resistance associated (SRA) protein. The mechanism in Tbg is less well understood but has been hypothesized to involve altered activity and expression of haptoglobin haemoglobin receptor (HpHbR). HpHbR has been shown to facilitate internalization of TLF-1 in T.b. brucei (Tbb), a member of the T. brucei species complex that is susceptible to human serum. By evaluating the genetic variability of HpHbR in a comprehensive geographical and taxonomic context, we show that a single substitution that replaces leucine with serine at position 210 is conserved in the most widespread form of Tbg (Tbg group 1) and not found in related taxa, which are either human serum susceptible (Tbb) or known to resist lysis via an alternative mechanism (Tbr and Tbg group 2). We hypothesize that this single substitution contributes to reduced uptake of TLF and thus may play a key role in conferring serum resistance to Tbg group 1. In contrast, similarity in HpHbR sequence among isolates of Tbg group 2 and Tbb/Tbr provides further evidence that human serum resistance in Tbg group 2 is likely independent of HpHbR functio

    Regioselective palladium-catalyzed ring-opening reactions of C1-substituted oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylates

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    Abstract Palladium-catalyzed ring-opening reactions of C1 substituted 7-oxanorbornadiene derivatives with aryl iodides were investigated. The optimal conditions for this reaction were found to be PdCl 2 (PPh 3 ) 2 , ZnCl 2 , Et 3 N and Zn in THF. Both steric and electronic factors played a role in the outcome of the reaction as increasing the steric bulk on the bridgehead carbon decreased the yield. These reactions were found to be highly regioselective, giving only one of the two possible regioisomers in all cases. A diverse collection of novel, highly substituted biphenyl derivatives were obtained. 23

    Six-month outcomes of a web-based intervention for users of amphetamine-type stimulants: Randomized controlled trial

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    Background: The use of amphetamine-type stimulants (ATS) places a large burden on health services.Objective: The aim was to evaluate the effectiveness of a self-guided Web-based intervention (“breakingtheice”) for ATS users over 6 months via a free-to-access site.Methods: We conducted a randomized trial comparing a waitlist control with a fully automated intervention containing 3 modules derived from cognitive behavioral therapy and motivation enhancement. The main outcome was self-reported ATS use in the past 3 months assessed at 3- and 6-month follow-ups using the Alcohol, Smoking, and Substance Involvement Screening Test (ASSIST). Secondary outcomes were help-seeking intentions (general help-seeking questionnaire), actual help seeking (actual help-seeking questionnaire), psychological distress (Kessler 10), polydrug use (ASSIST), quality of life (European Health Interview Survey), days out of role, and readiness to change. Follow-up data were evaluated using an intention-to-treat (ITT) analysis with a group by time interaction.Results: We randomized 160 people (intervention: n=81; control: n=79). At 6 months, 38 of 81 (47%) intervention and 41 of 79 (52%) control participants provided data. ATS scores significantly declined for both groups, but the interaction effect was not significant. There were significant ITT time by group interactions for actual help seeking (rate ratio [RR] 2.16; d=0.45) and help-seeking intentions (RR 1.17; d=0.32), with help seeking increasing for the intervention group and declining for the control group. There were also significant interactions for days completely (RR 0.50) and partially (RR 0.74) out of role favoring the intervention group. However, 37% (30/81) of the intervention group did not complete even 1 module.Conclusions: This self-guided Web-based intervention encouraged help seeking associated with ATS use and reduced days out of role, but it did not reduce ATS use. Thus, this program provides a means of engaging with some sections of a difficult-to-reach group to encourage treatment, but a substantial minority remained disengaged.Trial Registration: Australian and New Zealand Clinical Trials Registry: ACTRN12611000947909;https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=343307 (Archived by WebCite athttp://www.webcitation.org/6Y0PGGp8q).URL http://dx.doi.org/10.2196/jmir.3778</a

    Feasibility of novel adult tuberculosis vaccination in South Africa: a cost-effectiveness and budget impact analysis.

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    Early trials of novel vaccines against tuberculosis (TB) in adults have suggested substantial protection against TB. However, little is known about the feasibility and affordability of rolling out such vaccines in practice. We conducted expert interviews to identify plausible vaccination implementation strategies for the novel M72/AS01E vaccine candidate. The strategies were defined in terms of target population, coverage, vaccination schedule and delivery mode. We modelled these strategies to estimate long-term resource requirements and health benefits arising from vaccination over 2025-2050. We presented these to experts who excluded strategies that were deemed infeasible, and estimated cost-effectiveness and budget impact for each remaining strategy. The four strategies modelled combined target populations: either everyone aged 18-50, or all adults living with HIV, with delivery strategies: either a mass campaign followed by routine vaccination of 18-year olds, or two mass campaigns 10 years apart. Delivering two mass campaigns to all 18-50-year olds was found to be the most cost-effective strategy conferring the greatest net health benefit of 1.2 million DALYs averted having a probability of being cost-effective of 65-70%. This strategy required 38 million vaccine courses to be delivered at a cost of USD 507 million, reducing TB-related costs by USD 184 million while increasing ART costs by USD 79 million. A suitably designed adult TB vaccination programme built around novel TB vaccines is likely to be cost-effective and affordable given the resource and budget constraints in South Africa
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