TY - JOUR
T1 - The interaction of arsenical drugs with dihydrolipoamide and dihydrolipoamide dehydrogenase from arsenical resistant and sensitive strains of Trypanosoma brucei brucei
AU - Fairlamb, Alan H.
AU - Smith, Keith
AU - Hunter, Karl J.
N1 - Funding Information:
This work was supported by grants from the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases and from the Wellcome Trust. We would like to thank Dr J.R. Guest, University of Sheffield, for provision of the E. coli mutant for the bioassay of lipoic acid derivatives, Dr P. Ulrich of the Rockefeller University for generating the original arsenical-resistant line and Christopher Keating for his technical assistance.
PY - 1992/7
Y1 - 1992/7
N2 - d,l-dihydrolipoamide and d,l-dihydrolipoic acid react to form stable complexes with melarsen oxide with association constants of 5.47 × 109 and 4.51 × 109 M-1, respectively. These complexes possess 6-membered cyclic dithioarsenite rings which are 10-fold less stable than the 5-membered rings found in the trypanocidal drugs melarsoprol and trimelarsen, but 500-fold more stable than the 25-membered macrocyclic ring formed between melarsen oxide and dihydrotrypanothione. l-Lipoic acid concentrations in arsenical sensitive and resistant cloned lines of Trypanosoma brucei brucei have been determined by bioassay using a mutant of Escherichia coli auxotrophic for lipoate. The arsenical resistant strain was found to contain significantly less lipoic acid than the sensitive strain (19.2 ± 4.3 and 9.7 ± 2.9 pmol (108 cells)-1, respectively). The activity of the plasma membrane-associated dihydrolipoamide dehydrogenase was found to be slightly, but significantly increased in the arsenical resistant strain (34.7 ± 1.4 and 47.8 ± 3.7 mU mg-1, respectively). However, the Km for dihydrolipoamide and the inactivation kinetics with melarsen oxide were not significantly different between these strains. Estimates of the ratio of substrate to enzyme are of the order of 12:1 and 6:1 for arsenical sensitive and resistant strains, respectively, suggesting that these components are likely to be intimately associated with each other in the plasma membrane. These findings implicate lipoic acid, but not dihydrolipoamide dehydrogenase, in resistance to arsenical drugs, either through the mechanism of uptake or as the final target of these drugs.
AB - d,l-dihydrolipoamide and d,l-dihydrolipoic acid react to form stable complexes with melarsen oxide with association constants of 5.47 × 109 and 4.51 × 109 M-1, respectively. These complexes possess 6-membered cyclic dithioarsenite rings which are 10-fold less stable than the 5-membered rings found in the trypanocidal drugs melarsoprol and trimelarsen, but 500-fold more stable than the 25-membered macrocyclic ring formed between melarsen oxide and dihydrotrypanothione. l-Lipoic acid concentrations in arsenical sensitive and resistant cloned lines of Trypanosoma brucei brucei have been determined by bioassay using a mutant of Escherichia coli auxotrophic for lipoate. The arsenical resistant strain was found to contain significantly less lipoic acid than the sensitive strain (19.2 ± 4.3 and 9.7 ± 2.9 pmol (108 cells)-1, respectively). The activity of the plasma membrane-associated dihydrolipoamide dehydrogenase was found to be slightly, but significantly increased in the arsenical resistant strain (34.7 ± 1.4 and 47.8 ± 3.7 mU mg-1, respectively). However, the Km for dihydrolipoamide and the inactivation kinetics with melarsen oxide were not significantly different between these strains. Estimates of the ratio of substrate to enzyme are of the order of 12:1 and 6:1 for arsenical sensitive and resistant strains, respectively, suggesting that these components are likely to be intimately associated with each other in the plasma membrane. These findings implicate lipoic acid, but not dihydrolipoamide dehydrogenase, in resistance to arsenical drugs, either through the mechanism of uptake or as the final target of these drugs.
KW - Arsenical drugs
KW - Dihydrolipoamide dehydrogenase
KW - Drug effects
KW - Drug resistance
KW - Lipoic acid
KW - Trypanosoma brucei brucei
UR - http://www.scopus.com/inward/record.url?scp=0026631251&partnerID=8YFLogxK
U2 - 10.1016/0166-6851(92)90024-E
DO - 10.1016/0166-6851(92)90024-E
M3 - Article
C2 - 1501642
AN - SCOPUS:0026631251
SN - 0166-6851
VL - 53
SP - 223
EP - 231
JO - Molecular and Biochemical Parasitology
JF - Molecular and Biochemical Parasitology
IS - 1-2
ER -