In Vitro Sensitivities of Plasmodium falciparum to Different Antimalarial Drugs in Uganda

Little is known about resistance of Plasmodium falciparum to antimalarials in Sahelian countries. Here we investigated the drug susceptibilities of fresh isolates collected in Niger post-deployment of artemisinin-based combination therapies (ACTs). We found that the parasites remained highly susceptible to new (dihydroartemisinin, lumefantrine, pyronaridine, and piperaquine) and conventional (amodiaquine and chloroquine) antimalarial drugs. The introduction of ACTs in 2005 and their further deployment nationwide have therefore not resulted in a decrease in P. falciparum susceptibilities to these antimalarials. The WHO estimates that 50% of the world's population is exposed to malaria. In 2010, 216 million cases and more than 650,000 deaths from malaria were reported. Despite a decrease in the number of confirmed cases in some parts of the world, the situation remains heterogeneous and worrying in Africa (1). Together with respiratory infections and diarrheal diseases, malaria is one of the leading causes of death in Niger. Malaria transmission rates are high, with a mean incidence of 80 cases per 1,000 inhabitants. Despite the complementary nature of interventions in the field, which have strengthened in recent years, the number of cases has steadily risen over the last 20 years, reaching three million in 2010 (2, 3). There are several reasons for the deterioration of the public health situation with regard to malaria, and the increase in resistance to antimalarial drugs is considered a key factor. In Niger, infections are currently treated with combinations of drugs including an artemisinin (ART) derivative (artemisinin-based combination treatment, or ACT) (4). Since 2005, ACT has been proposed as the first-line treatment for the management of uncomplicated malaria. The use of such treatments throughout Niger was greatly expanded in 2010 by the implementation of a Global Fund Affordable Malaria Facility mechanism (5). Thereby, the drug pressure exerted on Plasmodium falciparum increases the risk of selection of parasites with altered susceptibility to antimalarials. This seems to be inevitable, as demonstrated by recent observations in Asia, which have revealed the presence of parasites less sensitive to artemisinins (6). The risk of emerging resistance to ACT makes it necessary to monitor the susceptibilities of parasites to antimalarial drugs, particularly those used in combination with artemisinin derivatives, on a regular basis and to search for new molecules with antimalarial activity.In this context, a study was carried out in Niger in 2011, at Gaya in the Dosso region, 250 km south of Niamey (3.44°N, 11.9°E), to evaluate the response of P. falciparum isolates to lumefantrine (LUM) and amodiaquine diphosphate (AQ), both of which are widely used in the ACTs distributed in Niger. In addition, responses to alternative molecules, such as pyronaridine (PYD) and piperaquine (PIP), both currently not available in Niger, as well as dihydroartemisinin (DHA) and chloroquine (CQ), were investigated. P. falciparum is...

supporting

confidence: 82%

Ex Vivo Responses of Plasmodium falciparum Clinical Isolates to Conventional and New Antimalarial Drugs in Niger

Issaka

Salissou

Aliyu

et al. 2013

“…Interestingly, the presence of wild-type pfmdr1-86 has been associated with reduced susceptibility to QN but in association with an increase in the number of pfmdr1 copies (8). However, the isolates we analyzed in the present study have 1 pfmdr1 copy (a finding from our previous work [19]); thus, pfmdr1 point mutations also modulate QN activity, as previously reported (16,21,33).…”

Section: Resultscontrasting

confidence: 53%

In Vitro Activities of Quinine and Other Antimalarials and pfnhe Polymorphisms in Plasmodium Isolates from Kenya

Okombo

Kiara

Rono

et al. 2010

Resistance to the amino alcohol quinine has been associated with polymorphisms in pfnhe, a sodium hydrogen exchanger. We investigated the role of this gene in quinine resistance in vitro in isolates from Kenya. We analyzed pfnhe whole-gene polymorphisms, using capillary sequencing, and pfcrt at codon 76 (pfcrt-76) and pfmdr1 at codon 86 (pfmdr1-86), using PCR-enzyme restriction methodology, in 29 isolates from Kilifi, Kenya, for association with the in vitro activities of quinine and 2 amino alcohols, mefloquine and halofantrine. In vitro activity was assessed as the drug concentration that inhibits 50% of parasite growth (IC 50 ). The median IC 50 s of quinine, halofantrine, and mefloquine were 92, 22, and 18 nM, respectively. The presence of 2 DNNND repeats in microsatellite ms4760 of pfnhe was associated with reduced susceptibility to quinine (60 versus 227 nM for 1 and 2 repeats, respectively; P < 0.05), while 3 repeats were associated with restoration of susceptibility. The decrease in susceptibility conferred by the 2 DNNND repeats was more pronounced in parasites harboring the pfmdr1-86 mutation. No association was found between susceptibility to quinine and the pfcrt-76 mutation or between susceptibility to mefloquine or halofantrine and the pfnhe gene and the pfcrt-76 and pfmdr1-86 mutations. Using previously published data on the in vitro activities of chloroquine, lumefantrine, piperaquine, and dihydroartemisinin, we investigated the association of their activities with pfnhe polymorphism. With the exception of a modulation of the activity of lumefantrine by a mutation at position 1437, pfnhe did not modulate their activities. Two DNNND repeats combined with the pfmdr1-86 mutation could be used as an indicator of reduced susceptibility to quinine.The amino alcohol quinine (QN) remains one of the important drugs against malaria. It is the drug of choice for the treatment of severe malaria, and in most African countries, including Kenya, where artemisinin-based combinations (lumefantrine-artemether, amodiaquine-artesunate) are now first-line treatments, 7-day quinine monotherapy has become the second-line treatment for uncomplicated malaria (44). However, there is evidence of selection and spread of QN-resistant parasites or those with reduced susceptibility to 8,30,34). This observation led to the investigation of artesunate (an artemisinin derivative) as an alternative to QN for the treatment of severe malaria (14). However, this option could now be compromised by the emergence of artemisinin resistance (9).Several studies have been dedicated to understanding the mechanisms of quinine resistance. Polymorphisms in pfmdr, a gene associated with chloroquine (CQ) resistance, modulate QN susceptibility (27,33,36). A mutation of the CQ resistance gene pfcrt at codon 76 (pfcrt-76) has been associated with reduced susceptibility to QN in vitro, although transfection studies have shown conflicting results (16,37). A seminal study on the association of polymorphisms in pfnhe, a sodium hydrogen exchanger gene, a...

“…Moreover, the overall good clinical efficacy of DHA-PPQ in treating falciparum malaria in areas of high prevalence of CQ-resistant parasites argues against a shared resistance mechanism between CQ and PPQ (15,47,48). Besides, most in vitro studies of laboratory strains and field parasite isolates failed to detect marked reductions in PPQ sensitivity in comparison with 3D7 or other laboratory strains (25,27,29,30). In most in vitro and ex vivo studies conducted thus far, there was generally a 3-to 4-fold difference in PPQ sensitivity between the most and least susceptible isolates (Table 2).…”

Section: Discussionmentioning

confidence: 99%

“…Studies using laboratory CQ-sensitive and -resistant lines further support the existence of cross-resistance between CQ and PPQ (25,26). In contrast, recent ex vivo and in vitro drug assays using parasites of diverse origins (but mostly from Africa) did not notice significant correlation of responses to CQ and PPQ (27)(28)(29)(30) but detected significant positive correlations in some studies between the responses to PPQ and other antimalarials such as DHA, pyronaridine, amodiaquine, or doxycycline. Investigations of the PPQ resistance mechanism mostly using the candidate gene approach also produced conflicting results.…”

mentioning

confidence: 89%

In Vitro Sensitivities of Plasmodium falciparum Isolates from the China-Myanmar Border to Piperaquine and Association with Polymorphisms in Candidate Genes

Hao

Jia²,

et al. 2013

eThe recent reports of resistance in Plasmodium falciparum to artemisinin derivatives and their partner drugs demand intensive studies toward understanding the molecular mechanisms of resistance. In this study, we examined the in vitro susceptibility of 63 P. falciparum field isolates collected from the China-Myanmar border area to chloroquine (CQ) and piperaquine (PPQ). Parasite isolates remained highly resistant to CQ, with the geometric mean 50% inhibitory concentration (IC 50 ) of 252.7 nM and a range of 51.9 to 1,052.0 nM. In comparison, these parasites had a geometric mean IC 50 of 28.4 nM for PPQ, with a fairly wide range of 5.3 to 132.0 nM, suggesting that certain parasite isolates displayed relatively high levels of resistance to PPQ. Interestingly, within the 4 years of study, the parasites exhibited a continuous decline in susceptibilities to both CQ and PPQ, and there was a significant correlation between responses to CQ and PPQ (Pearson correlation coefficient ‫؍‬ 0.79, P < 0.0001). Consistent with the CQ-resistant phenotype, all parasites carried the pfcrt K76T mutation, and most parasites had the CVIET type that is prevalent in Southeast Asia. In contrast, pfmdr1 mutations were relatively rare, and no gene amplification was detected. Only the pfmdr1 N1042D mutation was associated with resistance to CQ. For the pfmrp1 gene, four substitutions reached relatively high prevalence of >22%, and the I876V mutation was associated with reduced sensitivity to CQ. However, we could not establish a link between PPQ responses and the polymorphisms in the three genes associated with quinoline drug resistance.