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Amodiaquin accumulation by mouse erythrocytes infected with Plasmodium berghei
Abstract:
[14C]amodiaquin accumulation by washed erythrocyte preparations was characterized to permit comparisons with chloroquine accumulation. Erythrocytes infected with Plasmodium berghei CS (chloroquine-susceptible) accumulate amodiaquin by a saturable process that has an apparent dissociation constant for amodiaquin of 7.6 X 10(-8) M and is competitively inhibited by chloroquine, quinine and quinacrine, as is the process of chloroquine accumulation. Within experimental error, the K1 of 8 X 10(-7) M estimated for chloroquine is the same regardless of whether the drug being accumulated is [14C]amodiaquin or [14C]chloroquine. Likewise, the K1 for amodiaquin is the same regardless of which drug is being accumulated. In addition, glucose stimulates and hydrogen ion, cold or interruption of glycolysis inhibits amodiaquin as well as chloroquine accumulation. These findings are evidence that a single process serves to accumulate both drugs. In the absence of substrate, erythrocytes infected with P. berghei CR (chloroquine-resistant) accumulate twice as much amodiaquin as chloroquine, and they accumulate more amodiaquin than do erythrocytes infected with P. berghei CS. These differences occur because P. berghei CR infects polychromatophilic erythrocytes possessing a high-affinity, substrate-independent process of accumulation to which amodiaquin has greater access than chloroquine. In the presence of glucose, amodiaquin accumulation by erythrocytes infected with P. berghei CR, when plotted as a function of amodiaquin concentration in the medium, describes a sigmoid curve.
Insights
Amodiaquine and chloroquine accumulate in malaria-infected erythrocytes via a shared, saturable process. Chloroquine-resistant parasites exhibit altered accumulation due to erythrocyte type, affecting amodiaquine uptake.
Area of Science:
- Pharmacology
- Malariology
- Cell Biology
Background:
- Antimalarial drug accumulation in erythrocytes is crucial for treatment efficacy.
- Understanding drug transport mechanisms can reveal resistance pathways.
- Amodiaquine and chloroquine are vital antimalarial drugs with distinct resistance profiles.
Purpose of the Study:
- To characterize [14C]amodiaquine accumulation in Plasmodium berghei-infected erythrocytes.
- To compare amodiaquine and chloroquine accumulation mechanisms.
- To investigate the basis for differential drug accumulation in chloroquine-susceptible and resistant malaria.
Main Methods:
- Washed erythrocyte preparations infected with Plasmodium berghei (CS and CR strains) were used.
- Drug accumulation was measured using radiolabeled [14C]amodiaquine and [14C]chloroquine.
- Kinetic parameters (dissociation constant, inhibition constants) were determined under various conditions (pH, temperature, glycolysis inhibitors, glucose).
Main Results:
- A single, saturable process mediates the accumulation of both amodiaquine and chloroquine.
- This shared process is competitively inhibited by chloroquine, quinine, and quinacrine.
- Glucose stimulates, while low pH, cold, and glycolysis inhibition impair accumulation of both drugs.
- Chloroquine-resistant parasites showed significantly higher amodiaquine accumulation than chloroquine.
- This difference is attributed to the infection of polychromatophilic erythrocytes by resistant strains, possessing a high-affinity, substrate-independent accumulation process.
Conclusions:
- A common transport mechanism exists for amodiaquine and chloroquine accumulation in erythrocytes.
- Drug resistance in Plasmodium berghei CR is linked to erythrocyte-specific accumulation processes.
- Amodiaquine exhibits greater access to this high-affinity accumulation pathway than chloroquine.