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ALMEIDA, Afonso (2009) Estudos epidemiológicos e resistência
aos antimaláricos em Timor Leste, Dissertação de Doutoramento
no ramo de Ciências Biomédicas, especialidade de Parasitologia.
IHMT. Lisboa.
(Não contém resumo)
BORGES, Sofia Trindade (2009) Identification of genes
determining mefloquine resistence in malalia parasites,
Dissertação de Doutoramento no ramo de Ciências Biomédicas,
especialidade de Parasitologia. IHMT. Lisboa.
Resumo:
Malaria is by far one of the most severe public health problems
worldwide, devastating the lives of millions of people each year. The extensive
use of antimalarial drugs such as chloroquine and mefloquine, has led to the
acquisition of drug resistance by
Plasmodium falciparum
, severely curtailing
global efforts to control malaria. For this reason, much hope is now laid on new
therapeutic approaches based on the use of artemisinin-based combination
therapies (ACTs), which include mefloquine-artesunate, amodiaquine-
artesunate and lumefantrine-artemether. A better understanding of the
underlying mechanisms of drug resistance is therefore imperative to slow or
circumvent the evolution of resistance, to prolong the life span of the current
drugs and to develop new drugs.
In this context, genetic and genomic tools were applied here to the rodent
malaria model
Plasmodium chabaudi
, to exploit the genetic determinants of
resistance to different component drugs of ACTs.
First, the uncloned progeny of a genetic cross between a mefloquine-resistant
mutant (AS-15MF) and a genetically distinct sensitive clone (AJ) was selected
with an optimized dose of mefloquine. The progeny obtained was then
backcrossed here with AJ and the resulting product analysed by Linkage Group
Selection (LGS) to define the signatures of selection arising after treatment with
chloroquine (CQ), mefloquine (MF), lumefantrine (LM) or artemisinin (ART).
Additionally, the critical genome-wide changes accumulated in AS-15MF were
identified by Solexa whole genome re-sequencing.
Results showed that MF, LM and ART selected parasites bearing a duplicated
segment on chromosome 12 which has translocated onto chromosome 4.
Solexa sequence read-coverage analysis showed that this duplicated fragment
extends for >392 kb and contains about 112 genes, including
mdr1
, the gene
encoding the multi-drug resistance P-glycoprotein. The translocated fragment
was precisely mapped on chromosome 4. MF and ART also generated
selection signatures on chromosome 2, containing a mutation in a
deubiquitinating enzyme, encoded by the
ubp1
gene. Unambiguous evidence is
thus provided for the first time to demonstrate that resistance to chemically
distinct components of ACTs share the same underlying genes, highlighting a
possible limitation of these therapies.
Furthermore, a single mutation, unique to AS-15MF, was identified in a gene
encoding a putative lysine decarboxylase. This mutation is not markedly
selected by MF and it does not segregate with MF responses in the progeny
clones of the genetic cross between AS-15MF and AJ, implying that it is not
directly associated with the MF resistance phenotype.