High-Affinity Accumulation of Chloroquine by Mouse Erythrocytes Infected with Plasmodium berghei

Abstract

A B S T R A C T Washed erythrocytes infected with chloroquine-susceptible (CS) or with chloroquine-resistant (CR) P. berghei were used in model systems in vitro to study the accumulation of chloroquine with high affinity. The CS model could achieve distribution ratios (chloroquine in cells: chloroquine in medium) of 100 in the absence of substrate, 200-300 in the presence of 10 mM pyruvate or lactate, and over 600 in the presence of 1 mM glucose or glycerol. In comparable studies of the CR model, the distribution ratios were 100 in the absence of substrate and 300 or less in the presence of glucose or glycerol. The presence of lactate stimulated chloroquine accumulation in the CR model, whereas the presence of pyruvate did not. Lactate production from glucose and glycerol was undiminished in the CR model, and ATP concentrations were higher than in the CS model. Cold, iodoacetate, 2,4-dinitrophenol, or decreasing pH inhibited chloroquine accumulation in both models. These findings demonstrate substrate involvement in the accumulation of chloroquine with high affinity.In studies of the CS model, certain compounds competitively inhibited chloroquine accumulation, while others did not. This finding is attributable to a specific receptor that imposes structural constraints on the process of accumulation. For chloroquine analogues, the position and length of the side chain, the terminal nitrogen atom of the side chain, and the nitrogen atom in the quinoline ring are important determinants of binding to this receptor.

Identification of the acidic compartment of Plasmodium falciparum-infected human erythrocytes as the target of the antimalarial drug chloroquine.

“…However, as expected, at higher CQ concentrations, a slight alkalinization of the food vacuole became apparent. An analogous study of CQ accumulation in Plasmodium berghei attributed the effect of external pH to a non-specific interaction (Fitch et al, 1974).…”

Inhibition of the peroxidative degradation of haem as the basis of action of chloroquine and other quinoline antimalarials

“…Chloroquine resistance is thought to arise, at least in part, from a decreased level of chloroquine uptake, although some studies suggest that an alteration in the drug target may also be involved [30,36,45]. Chloroquine resistance can be reversed in itro and in animal models by co-administration of compounds such as verapamil, chlorpromazine and desipramine [46][47][48].…”

Chloroquine Resistance in Malaria: Accessibility of Drug Receptors to Mefloquine

“…1). We have previously reported that amodiaquine is accumulated more effectively than chloroquine by erythrocytes infected with P. berghei CR (chloroquine resistant) (10) or Plasmodium falciparum CR (5). We now report that mefloquine accumulation is undiminished in erythrocytes infected with P. berghei CR.…”

“…The parasites, the characteristics of erythrocytes infected with them, and the methods used to obtain and prepare infected erythrocytes for study have been described previously (3,12). The P. berghei CR line is resistant to 40 mg of chloroquine per kg of body weight of the mouse daily (12).…”

“…Under conditions that prevail in vivo, however, resistant parasites receive less exposure because the infected erythrocytes fail to accumulate chloroquine avidly (3,5,9,12,14). Consequently, chloroquine resistance in this model may be attributed to reduced exposure of the parasites rather than to ineffectiveness of the drug after it reaches the parasites: This mechanism of resistance provides a basis for explaining how drugs in the same chemotherapeutic class with chloroquine could be effective in the treatment of chloroquine-resistant malaria.…”