Department of Physics, University of Arkansas, Fayetteville, AR 72701, USA.
Malar J. 2012 Aug 8;11:267. doi: 10.1186/1475-2875-11-267.
Haemozoin crystals, produced by Plasmodium during its intra-erythrocytic asexual reproduction cycle, can generate UV light via the laser-induced, non-linear optical process of third harmonic generation (THG). In the current study the feasibility of using haemozoin, constitutively stored in the parasite's food vacuole, to kill the parasite by irradiation with a near IR laser was evaluated.
Cultured Plasmodium parasites at different stages of development were irradiated with a pulsed NIR laser and the viability of parasites at each stage was evaluated from their corresponding growth curves using the continuous culture method. Additional testing for germicidal effects of haemozoin and NIR laser was performed by adding synthetic haemozoin crystals to Escherichia coli in suspension. Cell suspensions were then irradiated with the laser and small aliquots taken and spread on agar plates containing selective agents to determine cell viability (CFU).
Parasites in the late-trophozoites form as well as trophozoites in early-stage of DNA synthesis were found to be the most sensitive to the treatment with -4-log reduction in viability after six passes through the laser beam; followed by parasites in ring phase (-2-log reduction). A -1-log reduction in E. coli viability was obtained following a 60 min irradiation regimen of the bacteria in the presence of 1 μM synthetic haemozoin and a -2-log reduction in the presence of 10 μM haemozoin. Minimal (≤ 15%) cell kill was observed in the presence of 10 μM haemin.
Laser-induced third-harmonic generation by haemozoin can be used to inactivate Plasmodium. This result may have clinical implications for treating severe malaria symptoms by irradiating the patient's blood through the skin or through dialysis tubing with a NIR laser.
疟原虫在其红细胞内无性繁殖周期中产生的疟色素晶体可以通过激光诱导的非线性光学过程三谐波产生（THG）产生紫外光。在目前的研究中，评估了通过用近红外激光照射恒定位点在寄生虫食物泡中的疟色素晶体来杀死寄生虫的可行性。
用脉冲近红外激光照射处于不同发育阶段的培养疟原虫，用连续培养法从相应的生长曲线评估每个阶段寄生虫的存活率。通过将合成的疟色素晶体添加到悬浮的大肠杆菌中，对疟色素和近红外激光的杀菌效果进行了额外的测试。然后用激光照射细胞悬浮液，并取少量悬液涂在含有选择性试剂的琼脂平板上，以确定细胞存活率（CFU）。
处于晚期滋养体形式的寄生虫以及处于 DNA 合成早期阶段的滋养体对该处理最敏感，经过六次通过激光束后，存活率降低了 4 个对数级；其次是处于环状阶段的寄生虫（降低 2 个对数级）。在存在 1 μM 合成疟色素的情况下，对细菌进行 60 分钟的照射方案后，大肠杆菌的存活率降低了 1 个对数级；在存在 10 μM 疟色素的情况下，存活率降低了 2 个对数级。在存在 10 μM 血红素的情况下，观察到的细胞杀伤最小（≤15%）。
疟色素的激光诱导三谐波产生可用于灭活疟原虫。这一结果可能对通过用近红外激光透过皮肤或通过透析管照射患者的血液来治疗严重疟疾症状具有临床意义。
