In vivo interaction between mouse liver lysosomes and chloroquine
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Abstract:
Particles sedimenting at 27,000 g X 10 min (MLCQ) were separated from liver homogenates of mice injected with chloroquine (CQ). The MLCQ contained most of the drug recovered in the organ as well as 50% of the liver aryl sulphatase activity. The release of CQ from MLCQ was studied in some physicochemical conditions, and in the presence of various agents known to modify membrane composition and stability. At pH 7.4, the equilibrium between free and bound CQ depended on the dilution of the MLCQ, and the time to reach equilibrium was strongly influenced by the temperature of incubation. Several agents causing membrane disruption and lysosomal enzyme leakage, such as osmotic shock, sonication and digitonin, had little effect on the CQ release. Acid and alkaline buffers, 0.55 M KCl and 0.1% Triton X-100 caused, instead, the immediate release of most of the bound CQ. Concentrations of digitonin causing the release of aryl sulphatase activity had little effect on bound CQ, suggesting that the drug is retained in lysosomes by forces and/or structures different in nature from those retaining most of the lysosomal enzyme activity. We think that the CQ trapped in lysosomes is bound to high affinity sites in membranous structures which are particularly altered by agents known to extract peripheral proteins from biological membranes or to change the conformation of molecular structures.
Insights
Chloroquine (CQ) primarily binds to lysosomal structures within liver cells. Agents disrupting membranes had minimal effect, suggesting unique binding mechanisms for CQ.
Area of Science:
- Cell Biology
- Pharmacology
- Biochemistry
Background:
- Chloroquine (CQ) is an antimalarial drug with lysosomotropic properties.
- Understanding CQ's intracellular localization and binding is crucial for its therapeutic and toxicological effects.
Purpose of the Study:
- To investigate the physicochemical conditions governing chloroquine binding to subcellular particles in mouse liver.
- To elucidate the nature of the interaction between chloroquine and lysosomal structures.
Main Methods:
- Isolation of particulate fractions (MLCQ) from mouse liver homogenates after chloroquine administration.
- Studying chloroquine release from MLCQ under various conditions (pH, temperature, dilution) and in the presence of different agents.
- Assessing the release of aryl sulphatase activity as a marker for lysosomal integrity.
Main Results:
- MLCQ contained the majority of hepatic chloroquine and significant aryl sulphatase activity.
- Chloroquine release was dependent on MLCQ dilution and incubation temperature at pH 7.4.
- Agents causing lysosomal disruption (osmotic shock, sonication, digitonin) showed minimal chloroquine release.
- Acid/alkaline buffers, high salt (KCl), and Triton X-100 induced rapid chloroquine release.
Conclusions:
- Chloroquine is retained in lysosomes by mechanisms distinct from those binding most lysosomal enzymes.
- CQ likely binds to high-affinity sites on membranous structures within lysosomes.
- These binding sites are sensitive to agents altering peripheral protein association or molecular conformation.