氯喹在体外对疟色素形成的条件性抑制

目的 研究在体外系统中氯喹对疟原虫疟色素形成抑制作用的特点。 方法 利用光镜和分光光度法观察和检测不同浓度乙酸钠溶液（0.5、1、1.5和2 mol/L）在不同pH值（pH 4.0、4.2、4.4、4.6、4.8和5.0）条件下,氯喹对疟色素基质形态及其生成量的影响,观察疟色素形成基质的形态变化规律。同时,用X-射线衍射分析不同pH条件下氯喹对色素晶体的结晶度及晶体大小的影响。 结果 氯喹抑制疟色素形成的临界pH值随乙酸钠浓度的升高而升高,从0.5 mol/L乙酸钠时的pH 4.2到2 mol/L时的pH 4.8。X-射线衍射分析表明,环境pH值由4.4提高到4.8,疟色素晶体的结晶度和晶体大小也分别从6.93%和357 ?魡下降到6.32%和264 ?魡。当pH值升高到5.0时,β-hematin晶体不再形成。氯喹可降低相同pH条件下β-hematin晶体的结晶度和晶体大小。形态学观察结果与之一致。 结论 体外实验表明,氯喹仅在疟色素形成处于或大于临界pH时,才表现出抑制疟色素形成的作用。

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 β-hematin（hemozion）formation by using the HPIA（heme polymerization inhibitory activity）assay. The morphology of β-hematin crystals was determined by light microscopy. Ultraviolet spectrophotometry was employed to measure β-hematin content, and the size of β-hematin crystal was analyzed by X-ray diffraction（XRD）. Results Chloroquine exhibited varied effect on β-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 β-hematin formation escalates and chloroquine inhibition declines, and at or above which chloroquine exerts a stronger inhibitory effect on β-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 Å to 6.32% and 264Å, respectively. When pH reached to 5, no more β-hematin formed. Chloroquine could reduce the crystallinity and crystal size of β-hematin at same pH value. Morphology analysis on the samples was consistent with the above results. Conclusion Chloroquine inhibits hemozoin formation only when the pH value is at or above threshold pH.