Polymorphisms in the parasite genes for pfcrt and pfmdr-1 as molecular markers for chloroquine resistance in Plasmodium falciparum in Lambaréné, Gabon

An in vitro study on the differentiated metabolic mechanism of chloroquine-resistant Plasmodium falciparum using high-resolution metabolomics

Chloroquine (CQ) is an important drug used therapeutically for treatment of malaria. However, due to limited number of studies on metabolic targets of chloroquine (CQ), it is difficult to attribute mechanisms underlying resistance associated with usage of this drug. The present study aimed to investigate the metabolic signatures of CQ-resistant Plasmodium falciparum (PfDd2) compared to CQ-sensitive Plasmodium falciparum (Pf3D7). Both Pf3D7 and PfDd2 were treated with CQ at 200 nM for 48 hr; thereafter, the harvested red blood cells (RBCs) and media were subjected to microscopy and high-resolution metabolomics (HRM). Glutathione, γ-L-glutamyl-L-cysteine, spermidine, inosine monophosphate, alanine, and fructose-1,6-bisphosphate were markedly altered in PfDd2 of RBC. In the media, cysteine, cysteic acid, spermidine, phenylacetaldehyde, and phenylacetic acid were significantly altered in PfDd2. These differential metabolic signatures related signaling pathways of PfDd2, such as oxidative stress pathway and glycolysis may provide evidence for understanding the resistance mechanism and pathogenesis of the CQ-resistant parasite.

Monitoring of efficacy, tolerability and safety of artemether-lumefantrine and artesunate-amodiaquine for the treatment of uncomplicated Plasmodium falciparum malaria in Lambaréné, Gabon: an open-label clinical trial

Background

Malaria remains a major public health problem, affecting mainly low-and middle-income countries. The management of this parasitic disease is challenged by ever increasing drug resistance. This study, investigated the therapeutic efficacy, tolerability and safety of artemether–lumefantrine (AL) and artesunate–amodiaquine (AS–AQ), used as first-line drugs to treat uncomplicated malaria in Lambaréné, Gabon.

Methods

A non-randomized clinical trial was conducted between October 2017 and March 2018 to assess safety, clinical and parasitological efficacy of fixed-doses of AL and AS–AQ administered to treat uncomplicated Plasmodium falciparum malaria in children aged from 6 months to 12 years. After 50 children were treated with AL, another 50 children received ASAQ. The 2009 World Health Organization protocol for monitoring of the efficacy of anti‑malarial drugs was followed. Molecular markers msp1 and msp2 were used to differentiate recrudescence and reinfection. For the investigation of artemisinin resistant markers, gene mutations in Pfk13 were screened.

Results

Per-protocol analysis on day 28 showed a PCR corrected cure rate of 97% (95% CI 86–100) and 95% (95% CI 84–99) for AL and AS–AQ, respectively. The most frequent adverse event in both groups was asthenia. No mutations in the kelch-13 gene associated with artemisinin resistance were identified. All participants had completed microscopic parasite clearance by day 3 post-treatment.

Conclusion

This study showed that AL and AS–AQ remain efficacious, well-tolerated, and are safe to treat uncomplicated malaria in children from Lambaréné. However, a regular monitoring of efficacy and a study of molecular markers of drug resistance to artemisinin in field isolates is essential.

Trial registration ANZCTR, ACTRN12616001600437. Registered 18 November, http://www.anzctr.org.au/TrialSearch.aspx?searchTxt=ACTRN12616001600437p&isBasic=True

Prospective Clinical Trial Assessing Species-Specific Efficacy of Artemether-Lumefantrine for the Treatment of Plasmodium malariae, Plasmodium ovale, and Mixed Plasmodium Malaria in Gabon

Treatment recommendations for Plasmodium malariae and Plasmodium ovale malaria are largely based on anecdotal evidence. The aim of this prospective study, conducted in Gabon, was to systematically assess the efficacy and safety of artemether-lumefantrine for the treatment of patients with uncomplicated P. malariae or P. ovale species monoinfections or mixed Plasmodium infections. Patients with microscopically confirmed P. malariae, P. ovale, or mixed-species malaria with at least one of these two Plasmodium species were treated with an oral, fixed-dose combination of artemether-lumefantrine for 3 consecutive days. The primary endpoints were per-protocol PCR-corrected adequate clinical and parasitological response (ACPR) on days 28 and 42. Tolerability and safety were recorded throughout the follow-up period. Seventy-two participants (42 male and 30 female) were enrolled; 62.5% of them had PCR-corrected mixed Plasmodium infections. Per protocol, PCR-corrected ACPR rates were 96.6% (95% confidence interval [CI], 91.9 to 100) on day 28 and 94.2% (95% CI, 87.7 to 100) on day 42. Considering Plasmodium species independently from their coinfecting species, day 42 ACPR rates were 95.5% (95% CI, 89.0 to 100) for P. falciparum, 100% (exact CI, 84.6 to 100) for P. malariae, 100% (exact CI, 76.8 to 100) for P. ovale curtisi, and 90.9% (95% CI, 70.7 to 100) for P. ovale wallikeri Study drug-related adverse events were generally mild or moderate. In conclusion, this clinical trial demonstrated satisfying antimalarial activity of artemether-lumefantrine against P. ovalewallikeri, P. ovale curtisi, P. malariae, and mixed Plasmodium infections, with per-protocol efficacies of 90% to 100% and without evident tolerability or safety concerns. (This trial was registered in the clinical study database ClinicalTrials.gov under the identifier NCT02528279.).

Pfcrt 76T and pfmdr1 86Y allele frequency in Plasmodium falciparum isolates and use of self-medication in a rural area of Gabon

BACKGROUND

Studies showed that chloroquine resistance may revert to sensitivity after its withdrawal mainly detected by a significant decrease of Plasmodium falciparum pfcrt 76T and pfmdr1 86Y alleles. Besides, self-medication is considered as a key factor of antimalarial drug resistance expansion. Thus, pfcrt 76T and pfmdr1 86Y allele frequency and its relationship with antimalarial drug self-medication was analyzed in P. falciparum isolates collected in Gabon.

METHODS

Samples were collected from febrile children screened for P. falciparum infection in 2005 and 2008 at the regional hospital of Oyem. Self-use of antimalarial drugs before the day of consultation was recorded. Polymorphic codons 76 and 86 of pfcrt and pfmdr1 genes were analyzed by PCR-RFLP.

RESULTS

The frequency of pfcrt 76T mutant allele was greater than 70.0% in 2005 and 2008. Wild type isolates were 1.7-fold more prevalent in 2008. The prevalence of pfmdr1 86Y mutant allele was comparable between 2005 and 2008 (p=0.1); the proportion of wild type allele reached 20.5% in 2008. The frequency of wild type allele pfcrt K76 or pfmdr1 N86 was higher among patients without anti-malarial drug self-medication compared to those who used it.

CONCLUSIONS

An increase of the frequency of P. falciparum wild type allele pfcrt 76K and pfmdr1 86N was observed within a short period after chloroquine withdrawal. The proportion of mutant genotypes is still high, mainly among patients using self-medication with antimalarial drugs.

Prospective evaluation of artemether-lumefantrine for the treatment of non-falciparum and mixed-species malaria in Gabon

Background

The recommendation of artemisinin combination therapy (ACT) as first-line treatment for uncomplicated falciparum malaria is supported by a plethora of high quality clinical trials. However, their recommendation for the treatment of mixed-species malaria and the large-scale use for the treatment of non-falciparum malaria in endemic regions is based on anecdotal rather than systematic clinical evidence.

Methods

This study prospectively observed the efficacy of artemether-lumefantrine for the treatment of uncomplicated non-falciparum or mixed-species malaria in two routine district hospitals in the Central African country of Gabon.

Results

Forty patients suffering from uncomplicated Plasmodium malariae, Plasmodium ovale or mixed-species malaria (including Plasmodium falciparum) presenting at the hospital received artemether-lumefantrine treatment and were followed up. All evaluable patients (n = 38) showed an adequate clinical and parasitological response on Day 28 after oral treatment with artemether-lumefantrine (95% confidence interval: 0.91,1). All adverse events were of mild to moderate intensity and completely resolved by the end of study.

Conclusions

This first systematic assessment of artemether-lumefantrine treatment for P. malariae, P. ovale and mixed-species malaria demonstrated a high cure rate of 100% and a favourable tolerability profile, and thus lends support to the practice of treating non-falciparum or mixed-species malaria, or all cases of malaria without definite species differentiation, with artemether-lumefantrine in Gabon.

Trial Registration

ClinicalTrials.gov Identifier: NCT00725777

A thirteen-year analysis of Plasmodium falciparum populations reveals high conservation of the mutant pfcrt haplotype despite the withdrawal of chloroquine from national treatment guidelines in Gabon

Background

Chloroquine resistance (CR) decreased after the removal of chloroquine from national treatment guidelines in Malawi, Kenia and Tanzania. In this investigation the prevalence of the chloroquine resistance (CQR) conferring mutant pfcrt allele and its associated chromosomal haplotype were determined before and after the change in Gabonese national treatment guidelines from chloroquine (CQ) to artesunate plus amodiaquine (AQ) in 2003.

Methods

The prevalence of the wild type pfcrt allele was assessed in 144 isolates from the years 2005 - 07 by PCR fragment restriction digest and direct sequencing. For haplotype analysis of the chromosomal regions flanking the pfcrt locus, microsatellite analysis was done on a total of 145 isolates obtained in 1995/96 (43 isolates), 2002 (47 isolates) and 2005 - 07 (55 isolates).

Results

The prevalence of the mutant pfcrt allele decreased from 100% in the years 1995/96 and 2002 to 97% in 2005 - 07. Haplotype analysis showed that in 1995/96 79% of the isolates carried the same microsatellite alleles in a chromosomal fragment spanning 39 kb surrounding the pfcrt locus. In 2002 and 2005 - 07 the prevalence of this haplotype was 62% and 58%, respectively. Pfcrt haplotype analysis showed that all wild type alleles were CVMNK.

Conclusion

Four years after the withdrawal of CQ from national treatment guidelines the prevalence of the mutant pfcrt allele remains at 97%. The data suggest that the combination of artesunate plus AQ may result in continued selection for the mutant pfcrt haplotype even after discontinuance of CQ usage.

Molecular surveillance of drug-resistant Plasmodium falciparum in two distinct geographical areas of Nigeria

Drug resistance against P. falciparum has been recognized as the crucial obstacle to curbing mortality and morbidity from malaria. We therefore determined the baseline distribution of pfcrt and pfmdr1 genes associated with resistance to chloroquine and pfdhfr gene associated with resistance to pyrimethamine in P. falciparum isolates collected from two geographically distinct areas of Nigeria. We use RT-PCR assays and sequencing to determine the prevalence of these mutations. The combined prevalence of pfcrt T76 mutation in the two sites was 92.3% with 86% from Osogbo compared to 93% from Lafia. Sequencing analysis of the (Pfcrt) K76T haplotype (amino acids 72-76) revealed CVIET as the only resistance haplotype present in the two areas. The frequency of pfmdr1 polymorphisms was higher in Lafia (39%) compared to that in Osogbo (35%) and the combined prevalence from the two sites was 45.5%. The prevalence of the pfdhfr triple mutant alleles was high in both locations. The Osogbo vs Lafia prevalence for pfdhfr mutations was 84% vs 91%, 88% vs 87% and 96% vs 96% for I51, R59 and N108, respectively. None of the samples from the two locations had the T108 mutation. The combined prevalence of pfcrt and pfmdr1 in Osogbo and Lafia was 44.2% with a risk ratio of 0.4164 while the combined prevalence of pfcrt, pfmdr1 and pfdhfr was 40.4% with a risk ratio of 1.081. These results strongly suggest the widespread distribution of CQ and pyrimethamine resistance without any marked distinction between the two locations.

Rapid detection of Pfcrt and Pfmdr1 mutations in Plasmodium falciparum isolates by FRET and in vivo response to chloroquine among children from Osogbo, Nigeria

Background

Chloroquine (CQ) has been in use in Africa for a long time. Because of misuse, this drug has now lost its efficacy due to the emergence of resistance strains in most parts of Africa. Recently, it was shown that after chloroquine has been withdrawn from the market, chloroquine-sensitive Plasmodium falciparum re-emerged and chloroquine could again be used successfully as an antimalarial. Surveillance of parasite populations is, therefore, important to decide whether chloroquine could be re-introduced.

Methods

To estimate the prevalence of the most pivotal polymorphisms, including Pfcrt K76T, Pfmdr1 N86Y and Pfmdr1 Y184F mutations, and their contributions to the outcome of CQ treatment, isolates from Osogbo Western Nigeria were tested using the Fluorescence Resonance Energy Transfer (FRET) method on a real-time PCR instrument.

Results

116 children with acute uncomplicated P. falciparum malaria infections were treated with the standard dosage of CQ and followed-up for 28 days. Blood samples were collected on filter paper at enrollment and during follow-up for identification of parasite carrying the chloroquine resistant transporter (pfcrt) and P. falciparum-multi drug resistance (pfmdr1) gene mutations. Parasitological assessment of response to treatment showed that 62% of the patients were cured and 38% failed the CQ treatment. The presence of single mutant pfcrt (T76) alleles (P = 0.003) and in combination with mutant pfmdr1 Y86 (P = 0.028) was significantly associated with in vivo CQR. No other mutation on its own or in combinations was significantly associated with treatment outcome. Mutant pfcrt was more prevalent in both pre- and post-treatment isolates. No association was observed between age or initial level of parasitaemia and chloroquine treatment outcome.

Conclusion

The result established the usefulness and accuracy of real time PCR in pfcrt and pfmdr1 mutation detection and also give further evidence to the reliability of the pfcrt T76 point mutation as a molecular marker for CQ resistance.

No variation in the prevalence of point mutations in the Pfcrt and Pfmdr1 genes in isolates from Gabonese patients with uncomplicated or severe Plasmodium falciparum malaria

In Lambaréné (Gabon), where a high level of Plasmodium falciparum resistance to chloroquine has been reported, we assessed the relationship between polymorphisms in the P. falciparum chloroquine resistance transporter (Pfcrt) and multidrug resistance-1 (Pfmdr1) genes and the clinical severity of malaria. Ninety-one and 60 P. falciparum isolates from children with uncomplicated or severe malaria were collected in 1996 and 2002, respectively. Single nucleotide mutations at codon 76 in the Pfcrt gene and at codons 86, 184, 1034, 1042, and 1246 in the Pfmdr1 gene were assessed by PCR-RFLP. All P. falciparum isolates presented the Pfcrt K76T mutation, whatever the clinical status. A high prevalence (>80%) of the Pfmdr1 86Tyr and 184Phe mutations was detected at both time points and in both clinical groups. We did not identify any specific mutation in the Pfmdr1 gene associated with the severity of disease, and the multiplicity of P. falciparum infection was also similar in both groups. Our results showed no change in the polymorphism of Pfcrt and Pfmdr1 genes in P. falciparum isolates collected in 1996 and 2002, and the severity of the disease was not associated with specific mutations neither in the Pfcrt nor in the Pfmdr1 genes in the study site.

Antimalarial activity of a synthetic endoperoxide (RBx-11160/OZ277) against Plasmodium falciparum isolates from Gabon

OZ277 is a newly developed, fully synthetic endoperoxide antimalarial that we tested against field isolates from Gabon. A comparison of activities of OZ277 with artesunate, mefloquine, and chloroquine showed OZ277 to be highly active against all parasite isolates. Artesunate and mefloquine also showed potent antiparasitic activity, but all isolates were chloroquine resistant.

An efficient PCR–SSCP-based method for detection of a chloroquine resistance marker in the PfCRT gene of Plasmodium falciparum

The spread of chloroquine resistance throughout the world poses a major problem in combating malaria. In the present study, an efficient polymerase chain reaction-single strand conformational polymorphism (PCR--SSCP)-based assay detected the PfCRT K76T point mutation, which is a marker for chloroquine resistance. For the first time, we have used a PCR--SSCP-based technique to identify the mutation in a single-step labelling reaction during PCR and SSCP gel electrophoresis. This assay is 100% efficient, giving no false-positive or -negative results, and can be carried out within a short bench time. We have successfully analysed 120 natural isolates using the PCR-SSCP method for detection of the chloroquine resistance marker and found 91 of the 120 samples to show the PfCRT T76 mutation, and 71% (65 of the 91 samples) showed a positive correlation with chloroquine resistance from the clinical data of the patients. The PCR-SSCP technique can also be applied for the detection of new haplotypes of the PfCRT gene and surveillance of chloroquine-resistant malaria in malaria-endemic localities around the world.

In vivo chloroquine resistance and prevalence of the pfcrt codon 76 mutation in Plasmodium falciparum isolates from the Republic of Congo

Chloroquine (CQ) resistance in Plasmodium falciparum has been particularly associated with mutations in the pfcrt gene. The present study was carried out in the malaria hyperendemic town of Brazzaville (Republic of Congo, Central Africa) where CQ is still recommended and used as a first-line drug for P. falciparum malaria. We assessed the efficacy of CQ in vivo, and the association between pfcrt mutation at codon 76 and treatment outcome in 50 children with uncomplicated malaria. The failure rate on day 28 was 95.7% and the pfcrt K76T mutation was present in 100% of isolates. No variation in the multiplicity of infection was observed in pre- and post-treatment isolates. In further 87 isolates from uncomplicated patients not treated with CQ, the mutation was detected in 98.5% of isolates. This study confirms the high level of in vivo resistance to CQ and shows the high prevalence of pfcrt K76T mutation in the Republic of Congo.

[Real-time PCR for detection of molecular markers of resistance in Plasmodium falciparum]

Plasmodium falciparum drug resistance is a major problem in malaria endemic areas. Molecular markers and in vitro tests have been developed to study and monitor drug resistance. However, none used alone, can provide sufficient data concerning the level of drug resistance and to issue precise guideline for drug use policies in endemic areas. We propose real-time PCR for the simultaneous detection of pfcrt and pfmdr1 genes mutations. The aim of this study was not to provide definitive data concerning the rate of mutations in an endemic area, but to describe a powerful method allowing the detection of major pfmdr1 and pfcrt mutations.

Reassessment of the resistance of Plasmodium falciparum to chloroquine in Gabon: implications for the validity of tests in vitro vs. in vivo

Increasing resistance of Plasmodium falciparum to antimalarial drugs presents a major risk factor for people living in endemic areas of tropical Africa. In Lambaréné, Gabon, regular surveillance of chloroquine sensitivity of P. falciparum in vitro has been carried out since 1992 using the WHO standard microtest. Results indicated that from 1994 onwards chloroquine resistance in vitro decreased significantly and that by 2000, about 70% of parasite isolates seemed to be sensitive to chloroquine in vitro. In 2001, we conducted a clinical study to reassess the efficacy of chloroquine in vivo for the treatment of uncomplicated P. falciparum malaria. Twenty-six patients aged 4-15 years were included in this study. Most unexpectedly, the study demonstrated high-grade resistance to chloroquine in vivo (failure rate on day 28 of 100%). As a consequence, tests of parasite susceptibility to chloroquine in vitro were repeated using the same protocol except for the replacement of previously used commercially available predosed WHO culture plates by independently dosed plates. All tested P. falciparum isolates were highly resistant to chloroquine, correlating well with our clinical findings. We concluded that high level resistance of P. falciparum to chloroquine persists in the study area. Neglect or absence of quality controls of essential test material can lead to invalid study results and wrong conclusions and should always be suspected in the case of major fluctuations in the sensitivity patterns of an antimalarial drug in vitro. In addition, our results highlight the supreme value of tests in vivo in providing reliable estimates of the efficacy of an antimalarial in a specific area.