Davies K P, Zahner H, Köhler P
Institute of Parasitology, University of Zürich, Switzerland.
Exp Parasitol. 1989 May;68(4):382-91. doi: 10.1016/0014-4894(89)90123-9.
It is suggested that the recently developed benzothiazole and amoscanate derivatives with antifilarial activity exert their action in vitro by an inhibition of mitochondrial-derived respiration. It was confirmed that the drugs CGP 20376, 21835, 20308, 21306, and 6140 cause a rapid immobilization in vitro of the adult filarial worm, Litomosoides carinii, the time required being similar to rotenone at the same concentration. The other drugs investigated, CGPs 20309, 21833, 24589, 23518, and 13231, were also effective; however, they required much longer incubation times. Submitochondrial particles (SMP) were prepared from Ascaris muscle and rat liver. The concentration of drug causing 50% inhibition of respiration (IC50) was calculated. It was found that the drugs most rapidly inhibiting respiration have IC50s for NADH oxidase of less than 25 microM in both Ascaris and rat liver SMP. This effect on SMP respiration could be overcome by using succinate as a substrate, indicating the site of inhibition to be within complex I of the mitochondrial respiratory chain. Further experiments showed that whereas the respiratory chain's NADH:ferricyanide reductase was unaffected by these drugs, there were pronounced effects on both Ascaris and rat liver NADH:quinone reductase activity. This suggests that the inhibition within complex I occurs after the flavoprotein dehydrogenase, but before the site of the quinone reduction. The other compounds examined, which had a slower effect on motility, also showed inhibition of the NADH oxidase, but not to as great an extent as the aforementioned compounds. The compounds most active against motility were also most effective at inhibiting respiration in intact adult L. carinii. Analysis of the aerobic end products produced by L. carinii showed that acetate production was greatly reduced even in the presence of low concentrations of the drugs. There was also a slight decrease in lactate production. However, a direct effect on the glycolytic pathway was ruled out by two observations. One, that the production of lactate from cell-free extracts of L. carinii is unaffected by the presence of the drugs, and secondly, that a protozoan, Giardia lamblia, reliant on glycolysis for energy production, can survive for long periods of time in the presence of high concentrations of the drugs. A correlation can be observed between the time for immobilization of the filarial worm and the strength of inhibition of mitochondrial respiration. Therefore, it is suggested that, at least in vitro, the mechanism of toxicity of these antifilarials in L. carinii is due to the blocking of the respiratory chain at a site similar to that of rotenone.
有人提出，最近开发的具有抗丝虫活性的苯并噻唑和氨甲酰苯胺衍生物在体外通过抑制线粒体呼吸发挥作用。已证实药物CGP 20376、21835、20308、21306和6140能在体外迅速使成年丝虫卡里尼丝虫固定，所需时间与相同浓度的鱼藤酮相似。研究的其他药物CGP 20309、21833、24589、23518和13231也有效；然而，它们需要更长的孵育时间。从蛔虫肌肉和大鼠肝脏制备了亚线粒体颗粒（SMP）。计算了引起50%呼吸抑制（IC50）的药物浓度。发现在蛔虫和大鼠肝脏SMP中，对呼吸抑制最快的药物对NADH氧化酶的IC50小于25 microM。使用琥珀酸作为底物可以克服对SMP呼吸的这种影响，表明抑制位点在线粒体呼吸链的复合体I内。进一步的实验表明，虽然呼吸链的NADH：铁氰化物还原酶不受这些药物影响，但对蛔虫和大鼠肝脏的NADH：醌还原酶活性都有显著影响。这表明复合体I内的抑制发生在黄素蛋白脱氢酶之后，但在醌还原位点之前。所检测的其他化合物对运动的影响较慢，也显示出对NADH氧化酶的抑制，但程度不如上述化合物。对运动最具活性的化合物在抑制完整成年卡里尼丝虫的呼吸方面也最有效。对卡里尼丝虫产生的需氧终产物的分析表明，即使在低浓度药物存在下，乙酸盐的产生也大大减少。乳酸的产生也略有减少。然而，两项观察结果排除了对糖酵解途径的直接影响。一是卡里尼丝虫无细胞提取物中乳酸的产生不受药物存在的影响，二是一种依赖糖酵解产生能量的原生动物贾第虫在高浓度药物存在下可以存活很长时间。可以观察到丝虫固定时间与线粒体呼吸抑制强度之间的相关性。因此，有人提出，至少在体外，这些抗丝虫药对卡里尼丝虫的毒性机制是由于在与鱼藤酮相似的位点阻断呼吸链。
