Microcystin-LR Induced Reactive Oxygen Species Mediate Cytoskeletal Disruption and Apoptosis of Hepatocytes in Cyprinus carpio L.

Jinlin Jiang,Xiaorong Wang,Jing Xu,Zhengjun Shan,Deyang Kong,Weili Xu,Junying Zhou,Matias A Avila

doi:10.1371/journal.pone.0084768

Abstract

Microcystins (MCs) are a group of cyclic hepatotoxic peptides produced by cyanobacteria. Microcystin-LR (MC-LR) contains Leucine (L) and Arginine (R) in the variable positions, and is one of the most common and potently toxic peptides. MC-LR can inhibit protein phosphatase type 1 and type 2A (PP1 and PP2A) activities and induce excessive production of reactive oxygen species (ROS). The underlying mechanism of the inhibition of PP1 and PP2A has been extensively studied. The over-production of ROS is considered to be another main mechanism behind MC-LR toxicity; however, the detailed toxicological mechanism involved in over-production of ROS in carp (Cyprinus carpio L.) remains largely unclear. In our present study, the hydroxyl radical (•OH) was significantly induced in the liver of carp after a relatively short-term exposure to MC-LR. The elevated reactive oxygen species (ROS) production may play an important role in the disruption of microtubule structure. Pre-injection of the antioxidant N-acetyl-cysteine (NAC) provided significant protection to the cytoskeleton, however buthionine sulfoximine (BSO) exacerbated cytoskeletal destruction. In addition, the elevated ROS formation induced the expression of apoptosis-related genes, including p38, JNKa, and bcl-2. A significant increase in apoptotic cells was observed at 12 - 48 hours. Our study further supports evidence that ROS are involved in MC-LR induced damage to liver cells in carp, and indicates the need for further study of the molecular mechanisms behind MC-LR toxicity.

Highlights

Microcystins (MCs) are a group of cyanobacterial toxins comprised of more than 80 variants
The intensity of OH in the group treated with 50 μg/kg of MC-LR was significantly increased at 5h and 12 h after MC-LR exposure, compared to the control group (p < 0.05, p < 0.01)
Signal intensity of OH was seen in the control group, indicating that OH can be produced under normal physiological conditions

Summary

Introduction

Microcystins (MCs) are a group of cyanobacterial toxins comprised of more than 80 variants. Previous studies have shown that the death of large numbers of fish during outbreaks of cyanobacterial bloom is associated with the production of MCs and with several special conditions, including high water temperature, high pH, high concentration of ammonia and nitrogen, and low dissolved oxygen [2]. MC exposure can cause histopathological changes in various organs, including the liver, kidney, gill, intestine, and heart. It can alter the activity of various enzymes in the fish. The long-term accumulation of toxins in fish will definitely produce harmful effects, and may affect human health through the food chain [4,5,6,7,8,9]

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