Citation:

Chernoff, N., D. Hill, J. Schmid, J. Lang, A. Farthing, AND H. Huang. Dose-response study of microcystin congeners MCLR, MCLA, MCLY, MCRR, and MCYR administered orally to mice. Toxins. MDPI, Basel, Switzerland, 13(2):86, (2021). https://doi.org/10.3390/toxins13020086

Impact/Purpose:

Microcystins (MCs) comprise a group of common freshwater cyanobacterial toxins that adversely affect liver function in mammals and are among the most common toxins found in U.S. freshwaters. The toxicity of five common microcystin congeners (microcystin-LA (MCLA), MCLR, MCLY, MCRR, and MCYR) commonly observed in Hazardous Algal Blooms was evaluated in mice after oral administration. The purpose of the study was to identify the toxic potentials of three of the congeners that have not been previously determined and compare the toxicities of all five. It was determined that there were highly significant degrees of toxicity induced by the different congeners as well as different types of hepatic toxicity. These data demonstrated that MCLA was the most toxic with a LOAEL of 3 mg/kg while MCRR was minimally toxic at levels of 22 mg/kg. These impact of these data is to emphasize the importance of considering the types of MCs in fresh waters where human populations may be exposed.

Description:

Microcystins are common freshwater cyanobacterial toxins that affect liver function. The toxicities of five microcystin congeners (microcystin-LA (MCLA), MCLR, MCLY, MCRR, and MCYR) commonly observed in harmful algal blooms (HABs) were evaluated in BALB/c mice after a single oral administration of doses ranging from those that were no observed adverse effect levels (NOAELs) to lowest observed adverse effect levels (LOAELs). Animals were monitored for changes in behavior and appearance, and euthanized 24 h after dosing. Test endpoints included clinical changes, necropsy observations, and serum indicators of hepatic toxicity and general homeostasis. Doses were 0.5–7 mg/kg MCLA, 0.5–11 mg/kg MCLR, 1–7 mg/kg MCLY, 7–22 mg/kg MCRR, and 3–11 mg/kg MCYR. MCLA at 3 mg/kg elevated liver/body weight ratio and liver score, ALT, AST, and GLDH, indicating hepatic toxicity, reduced serum glucose and highly elevated total serum bilirubin. MCLR and MCLY induced similar effects with LOAELs of 5 mg/kg, although a greater extent and severity of effects were observed in MCLR animals. MCRR exposure at 22 mg/kg was associated with reduced serum glucose. MCYR induced scattered liver effects at 7 mg/kg and reduced serum glucose levels at 5 mg/kg. The results indicate significant differences in congener-induced toxicity after microcystin exposure

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