Role of ABC transporter MRPA, gamma-glutamylcysteine synthetase and ornithine decarboxylase in natural antimony-resistant isolates of Leishmania donovani.
OBJECTIVE
The resistance of clinical isolates of Leishmania donovani to sodium antimony gluconate (SAG), the mainstay of treatment in Indian visceral leishmaniasis, has become a critical issue in India. The present work investigates the mechanism of resistance to SAG in parasites isolated from patients who are unresponsive to SAG.


RESULTS
Susceptibility to SAG as determined in vitro with intracellular amastigotes correlated well with the clinical response. The ABC transporter gene MRPA was amplified in resistant field isolates as part of an extrachromosomal circle. Co-amplification of the pterin reductase gene (PTR1) and MRPA suggests amplification of the H locus in SAG-resistant isolates. Amplification of MRPA was correlated to increased RNA as determined by real-time PCR. MRPA is an ABC-thiol transporter, and cysteine and glutathione were increased in the resistant isolates. Ornithine decarboxylase (a rate limiting enzyme in polyamine biosynthesis), and gamma-glutamylcysteine synthetase (a rate limiting enzyme in glutathione biosynthesis), the two building blocks of the main cellular thiol trypanothione, were overexpressed in some of the resistant isolates.


CONCLUSIONS
A variety of resistance mechanisms to SAG, most of them consistent with a model based on the study of resistance in vitro, were present in clinical isolates from the same geographical region.
Mukherjee
Angana
A
School of Life Sciences, Jawaharlal Nehru University, New Delhi - 110 067, India.
Padmanabhan
Prasad K
PK
Singh
Sushma
S
Roy
Gaétan
G
Girard
Isabelle
I
Chatterjee
Mitali
M
Ouellette
Marc
M
Madhubala
Rentala
R
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000967:Antimony Sodium Gluconate / Q000494:pharmacology* / Q000627:therapeutic use; D000981:Antiprotozoal Agents / Q000494:pharmacology* / Q000627:therapeutic use; D015153:Blotting, Western; D004351:Drug Resistance; D005721:Glutamate-Cysteine Ligase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007893:Leishmania donovani / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D007898:Leishmaniasis, Visceral / Q000188:drug therapy / Q000469:parasitology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D009955:Ornithine Decarboxylase / Q000235:genetics / Q000378:metabolism*; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013438:Sulfhydryl Compounds / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D000981:Antiprotozoal Agents; D008562:Membrane Glycoproteins; C106891:PgpA protein, Leishmania; D015800:Protozoan Proteins; D013438:Sulfhydryl Compounds; D009955:Ornithine Decarboxylase; D005721:Glutamate-Cysteine Ligase; D000967:Antimony Sodium Gluconate