[Conditional inhibition of hemozoin formation by chloroquine in vitro].
OBJECTIVE
To study the characteristics of inhibition on hemozoin formation by chloroquine under in vitro condition.


METHODS
Under different concentrations (0.5-2 mol/L) of sodium acetate (NaAc) and at the pH range of 4.0-5.0, chloroquine was tested for inhibition of beta-hematin (hemozion) formation by using the HPIA (heme polymerization inhibitory activity) assay. The morphology of beta-hematin crystals was determined by light microscopy. Ultraviolet spectrophotometry was employed to measure beta-hematin content, and the size of beta-hematin crystal was analyzed by X-ray diffraction (XRD).


RESULTS
Chloroquine exhibited varied effect on beta-hematin formation, depending on pH value and Na+ concentration. When the NaAc concentration increased from 0.5 mol/L (pH 4.2) to 2 mol/L (pH 4.8), the chloroquine inhibitory effect also increased. Results suggested that there exists a threshold pH, below which the beta-hematin formation escalates and chloroquine inhibition declines, and at or above which chloroquine exerts a stronger inhibitory effect on beta-hematin formation. With the increase of pH from 4.4 to 4.8, the crystallinity and the size of crystal changed from 6.93% and 357 angstrom to 6.32% and 264 angstrom, respectively. When pH reached to 5, no more beta-hematin formed. Chloroquine could reduce the crystallinity and crystal size of beta-hematin at same pH value. Morphology analysis on the samples was consistent with the above results.


CONCLUSIONS
Chloroquine inhibits hemozoin formation only when the pH value is at or above threshold pH.
Institute for Infectious Diseases and Vaccine Development, School of Medicine, Tongji University, Shanghai 200092, China. swksj@tongji.edu.cn
Jun
J
Sun
Bo
B
Chen
Yan-Yu
YY
Long
D000962:Antimalarials / Q000494:pharmacology*; D002738:Chloroquine / Q000494:pharmacology*; D006420:Hemeproteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D066298:In Vitro Techniques; D014961:X-Ray Diffraction
D000962:Antimalarials; D006420:Hemeproteins; C020753:hemozoin; D002738:Chloroquine