Quantitatively evaluating detoxification of the hepatotoxic microcystin-LR through the glutathione (GSH) pathway in SD rats

Abstract

Glutathione (GSH) plays crucial roles in antioxidant defense and detoxification metabolism of microcystin-LR (MC-LR). However, the detoxification process of MC-LR in mammals remains largely unknown. This paper, for the first time, quantitatively analyzes MC-LR and its GSH pathway metabolites (MC-LR-GSH and MC-LR-Cys) in the liver of Sprague-Dawley (SD) rat after MC-LR exposure. Rats received intraperitoneal (i.p.) injection of 0.25 and 0.5 lethal dose 50 (LD 50 ) of MC-LR with or without pretreatment of buthionine-(S,R)-sulfoximine (BSO), an inhibitor of GSH synthesis. The contents of MC-LR-GSH were relatively low during the experiment; however, the ratio of MC-LR-Cys to MC-LR reached as high as 6.65 in 0.5 LD 50 group. These results demonstrated that MC-LR-GSH could be converted to MC-LR-Cys efficiently, and this metabolic rule was in agreement with the data of aquatic animals previously reported. MC-LR contents were much higher in BSO+MC-LRtreated groups than in the single MC-LR-treated groups. Moreover, the ratio of MC-LR-Cys to MC-LR decreased significantly after BSO pretreatment, suggesting that the depletion of GSH induced by BSO reduced the detoxification of MCs. Moreover, MC-LR remarkably induced liver damage, and the effects were more pronounced in BSO pretreatment groups. In conclusion, this study verifies the role of GSH in the detoxification of MC-LR and furthers our understanding of the biochemical mechanism for SD rats to counteract toxic cyanobacteria.

Molecular Mechanism for the Regulation of Microcystin Toxicity to Protein Phosphatase 1 by Glutathione Conjugation Pathway

“… Figure 3 showed MC-GSHs had lower toxicity than their native toxins in the sequence of MCLR (IC 50 = 2.5  μ g/L) > MCRR (IC 50 = 24.4  μ g/L) > MCLR-GSH (IC 50 = 86.6  μ g/L) > MCRR-GSH (IC 50 = 98.7  μ g/L). Similar to previous studies [17, 21], it was not difficult to find that GSH conjugation was an effective way to control the toxicity of MCs. Though the toxicity of MC-GSHs was obviously decreased, the secondary biotoxicity of MC-GSHs was real and nonnegligible.…”

“…However, they had lower intensities than the newly formed ions with MS signals at m/z 1302.8792 and 673.4521/1345.8864. As GSH was about 307.3235 Da, the above MS signals should be attributed to the addition products of GSH to MCLR or MCRR [21]. In addition, a product with MS signal at m/z 613.6493 was also found in both addition samples.…”

PARP1 Is Up-Regulated in Non-small Cell Lung Cancer Tissues in the Presence of the Cyanobacterial Toxin Microcystin

“…Some of the pathways include Glutathione metabolic pathway, AKT signaling, EGFR signaling, response to hypoxia and oxidative stress, Cell cycle regulation, etc. are known to play a critical role in antioxidant defense, detoxification mechanisms, cell survival, proliferation, oncogenesis and NSCLC progression (Wagner and Schmidt, 2011 ; Guo et al, 2015 ). Further, the deregulation of many signaling pathways such as EGF/RAS/RAF/MEK/ERK and PI3K/AKT/mTOR is considered to play a critical role in oncogenesis and cancer progression (Memmott and Dennis, 2010 ).…”

Mechanisms of Microcystin-induced Cytotoxicity and Apoptosis

“…GSH also conjugates with electrophiles and thus participates in the metabolism and detoxification of endogenous compounds and xenobiotic toxicants, as a major detoxification agent in cells. It has been shown that MCs bind to GSH, forming conjugates (MC-GSH) via glutathione S-transferase (GST), as the first step in the detoxification process, followed by degradation to the cysteine conjugates (MC-Cys) [70,71]. The conjugation makes the toxin more soluble in water, supporting the excretion of toxin from the cells and organisms.…”

“…The initial depletion of GSH and subsequent induction of GSH de novo synthesis might suggest a key role of GSH in the detoxification of MC-LR and protection against oxidative stress [55]. There's also evidence that pretreatment of buthionine-(S,R)-sulfoximine (BSO), a specific GSH synthesis inhibitor, significantly reduced the detoxification of MC-LR and enhanced the level of oxidative stress and hepatotoxicity in SD rats [55,64,71].…”