Cylindrospermopsin toxicity in mice following a 90-d oral exposure

Cylindrospermopsin (CYN) is a toxin associated with numerous species of freshwater cyanobacteria throughout the world. It is postulated to have caused an episode of serious illnesses in Australia through treated drinking water, as well as lethal effects in livestock exposed to water from farm ponds. Toxicity included effects indicative of both hepatic and renal dysfunction. In humans, symptoms progressed from initial hepatomegaly, vomiting, and malaise to acidosis and hypokalemia, bloody diarrhea, and hyperemia in mucous membranes. Laboratory animal studies predominantly involved the intraperitoneal (i.p.) route of administration and confirmed this pattern of toxicity with changes in liver enzyme activities and histopathology consistent with hepatic injury and adverse renal effects. The aim of this study was designed to assess subchronic oral exposure (90 d) of purified CYN from 75 to 300 µg/kg/d in mouse. At the end of the dosing period, examinations of animals noted (1) elevated organ to body weight ratios of liver and kidney at all dose levels, (2) treatment-related increases in serum alanine aminotransferase (ALT) activity, (3) decreased blood urea nitrogen (BUN) and cholesterol concentrations in males, and (4) elevated monocyte counts in both genders. Histopathological alterations included hepatocellular hypertrophy and cord disruption in the liver, as well as renal cellular hypertrophy, tubule dilation, and cortical tubule lesions that were more prominent in males. A series of genes were differentially expressed including Bax (apoptosis), Rpl6 (tissue regeneration), Fabp4 (fatty acid metabolism), and Proc (blood coagulation). Males were more sensitive to many renal end points suggestive of toxicity. At the end of exposure, toxicity was noted at all dose levels, and the 75 µg/kg group exhibited significant effects in liver and kidney/body weight ratios, reduced BUN, increased serum monocytes, and multiple signs of histopathology indicating that a no-observed-adverse-effect level could not be determined for any dose level.

柱孢藻毒素（Cylindrospermopsin, CYN）是一种广泛分布于全球多种淡水蓝藻物种所产生的毒素。据推测，该毒素曾通过处理后的饮用水在澳大利亚引发大规模严重疾病暴发，并导致接触农场池塘水体的家畜出现致死性中毒反应。其毒性表现出肝肾功能损伤的典型特征。在人体中，中毒症状呈渐进性发展：初期表现为肝肿大、呕吐与全身不适，后续可进展为酸中毒、低钾血症、血性腹泻及黏膜充血。现有动物实验多采用腹腔注射（intraperitoneal, i.p.）染毒途径，通过检测肝酶活性变化与组织病理学改变，证实了该毒素所致肝损伤与肾毒性的病理特征。本研究旨在评估纯化柱孢藻毒素以75~300 μg/kg/d的剂量对小鼠进行90天亚慢性经口染毒的毒性效应。染毒周期结束后，动物检测结果显示：① 各剂量组小鼠的肝、肾脏器体重比均显著升高；② 血清丙氨酸氨基转移酶（alanine aminotransferase, ALT）活性呈现染毒剂量依赖性升高；③ 雄性小鼠的血尿素氮（blood urea nitrogen, BUN）与胆固醇浓度出现降低；④ 雌雄小鼠的单核细胞计数均有所上升。组织病理学观察可见肝脏出现肝细胞肥大与肝索结构破坏，肾脏则表现为肾细胞肥大、肾小管扩张及皮质肾小管病变，其中雄性小鼠的肾脏病变更为显著。转录组分析显示，一系列基因出现差异表达：包括介导细胞凋亡的Bax、参与组织再生的Rpl6、调控脂肪酸代谢的Fabp4以及参与凝血过程的Proc。雄性小鼠对多项反映肾毒性的检测终点更为敏感。全剂量组均观察到毒性效应，其中75 μg/kg剂量组即出现肝/肾脏器体重比异常、血尿素氮降低、血清单核细胞计数升高及多组织病理学改变，提示本研究中未发现无可见有害作用水平（no-observed-adverse-effect level, NOAEL）。