Chloroquine and hydroxychloroquine binding to melanin: Some possible consequences for pathologies.

Area of Science:

• Pharmacology
• Toxicology
• Biochemistry

Background:

• Chloroquine, an antimalarial and immunosuppressive drug, has known toxicities like retinopathy.
• Hydroxychloroquine, a related compound, is less toxic, potentially due to lower melanin accumulation.
• Melanin-rich tissues, like the retina, may accumulate these drugs.

Purpose of the Study:

• To quantify melanin binding of chloroquine and hydroxychloroquine at physiological pH.
• To investigate the link between drug-melanin binding and observed toxicity.
• To assess drug adsorption and desorption kinetics with melanin.

Main Methods:

• Spectrophotometric quantification of chloroquine and hydroxychloroquine binding to melanin.
• Measurement of drug adsorption and desorption rates from melanin.
• Physiological pH conditions were maintained throughout experiments.

Main Results:

• Significant differences in adsorption affinities between chloroquine and hydroxychloroquine to melanin were observed.
• Both drugs exhibited a strong physical attraction to melanin.
• Quantification of adsorption and desorption provides insight into drug-melanin interactions.

Conclusions:

• Differences in melanin binding affinity may explain the varying bioaccumulation and toxicity of chloroquine and hydroxychloroquine in retinal tissues.
• The findings suggest a direct link between drug-melanin interaction and potential adverse effects like retinopathy.