Influence of Two Depuration Periods on the Activity and Transcription of Antioxidant Enzymes in Tilapia Exposed to Repeated Doses of Cylindrospermopsin under Laboratory Conditions

Abstract

The cyanobacterial toxin Cylindrospermopsin (CYN), a potent protein synthesis inhibitor, is increasingly being found in freshwater bodies infested by cyanobacterial blooms worldwide. Moreover, it has been reported to be implicated in human intoxications and animal mortality. Recently, the alteration of the activity and gene expression of some glutathione related enzymes in tilapias (Oreochromis niloticus) exposed to a single dose of CYN has been reported. However, little is known about the effects induced by repeated doses of this toxin in tilapias exposed by immersion and the potential reversion of these biochemical alterations after two different depuration periods (3 or 7 days). In the present study, tilapias were exposed by immersion to repeated doses of a CYN-containing culture of Aphanizomenon ovalisporum during 14 days, and then were subjected to depuration periods (3 or 7 days) in clean water in order to examine the potential reversion of the effects observed. The activity and relative mRNA expression by real-time polymerase chain reaction (PCR) of the antioxidant enzymes glutathione peroxidase (GPx) and soluble glutathione-S-transferases (sGST), and also the sGST protein abundance by Western blot analysis were evaluated in liver and kidney of fish. Results showed significant alterations in most of the parameters evaluated and their recovery after 3 days (GPx activity, sGST relative abundance) or 7 days (GPx gene expression, sGST activity). These findings not only confirm the oxidative stress effects produced in fish by cyanobacterial cells containing CYN, but also show the effectiveness of depuration processes in mitigating the CYN-containing culture toxic effects.

Effects of depuration on histopathological changes in tilapia (Oreochromis niloticus) after exposure to cylindrospermopsin

“…Saker et al () firstly investigated CYN accumulation and depuration in the freshwater mussel Anodonta cygnea . Concerning fish, short depuration periods (3 and 7 days) managed to recover from the oxidative damages induced in tilapia by exposure to A. ovalisporum cells containing CYN and 7‐deoxy‐CYN for 7 and 14 days, at biochemical and molecular levels (Guzmán‐Guillén et al, ; Ríos et al, ). Moreover, the reversion of the histopathological alterations induced in the present work is generally in accordance with the one observed in brain of fish undergoing the same conditions, where after 3 days of depuration histopathological damages still persisted, but practically disappeared after 7 days (Guzmán‐Guillén et al, ).…”

“…According to the latter hypothesis, in our work during the first days of depuration, the intestinal alterations are still present because GST and GSH are working in conjugation with CYN for its elimination. Indeed, this is what happened in liver of the same fish in previous works, evidenced by decreases in GST activity, protein and gene expression and GSH content, that did not recover until 7 days of depuration (Ríos et al, ; Guzmán‐Guillén et al, ), as well as the normal intestinal histopathology in the present work. So we could assume these parameters followed the same tendency in intestines.…”

“…According to Yokoyama and Park (), a decline in the production of detoxification enzymes might decrease the depuration rate constant for MC‐LR in U. douglasiae . In the case of our fish, the opposite process might be occurring, with an increased metabolism of CYN in the cleaning period, as shown in a previous study by glutathione peroxidase and glutathione S‐transferase (GST) relative gene expressions and GST activity and relative abundance, all still developed in liver and kidney after 7 days of depuration (Ríos et al, ). Thus, this fact may increase the depuration rate in these organs of fish, as these detoxifying systems are efficient allowing the degradation of CYN to other less or non‐toxic products by metabolic processes.…”

“…Several studies have demonstrated the effectiveness of depuration against oxidative stress in fish and clams exposed to various contaminants such as polychlorinated biphenyls, pesticides, polycyclic aromatic hydrocarbons and metals, among others (Ferreira et al, ; Özcan Oruç, ; Freitas et al, ; Gagnaire et al, ). However, the effect of depuration of cyanotoxins in aquatic organisms has been neglected, being more abundant with MCs or nodularin (NOD) (Sahin et al, ; Ozawa et al, ; Yokoyama and Park, ; Xie et al, ; Mohamed and Hussein, ; Kankaanpää et al, ; Tricarico et al, ; Galanti et al, ), and scarcer with CYN (Saker et al, ; Ríos et al, ; Guzmán‐Guillén et al, ). There is a need to further investigate the effectiveness of short‐term depuration in removing toxins from fish and thus the potential use of this process as a protective health strategy in aquaculture (Al‐Ghais, ).…”

A multiparameter investigation into adverse effects of aflatoxin on Oreochromis niloticus health status

“…Among enzymatic systems, glutathione S-transferase (GST) and glutathione peroxidase (GPx) constitute essential components of cellular detoxification systems that defend cells against ROSs (Ren et al, 2009), hence play a major protective mechanism against oxidative stress (Almar et al, 1998). Both GST and GPx mRNA expressions have been used as biomarkers of exposure to environmental pollution/toxicity, as the mRNA levels represent a snapshot of the cell activity at a given time; and in many instances, single gene mRNA expressions can be useful biomarkers of stress in organisms (Fisher et al, 2006;Espinoza et al, 2012;Rios et al, 2014;Zheng et al, 2014). Furthermore, AFB1 chronic exposure may result in malnutrition, poor growth, suppressed immune response, physiological disorders as well as histological changes (Allameh et al, 2005;Lewis et al, 2005;Selim et al, 2013;Zychowski et al, 2013).…”