How common carp (Cyprinus carpio) avoid oxidative stress during an exposure to a sublethal three-metal (Cu/Cd/Zn) mixture

Abstract

Aquatic environments are subjected to numerous anthropogenic stressors that are much more diverse and variable than those tested in laboratory conditions. So it is important to analyse the effects of metal mixtures to obtain a realistic understanding of the impact of pollution in such natural ecosystems. The impact of a one-week exposure to metal mixture containing copper (Cu), cadmium (Cd) and zinc (Zn) was evaluated in the common carp Cyprinus carpio. The concentrations of metals used in this study represent 10% of the 96 h LC50 of each single metal exposure (Cu = 4.8 µg.L 1; Cd = 2.9 µg.L-1 and Zn = 206.8 µg.L-1). To evaluate the impact of mixture stress at different levels of oxidative processes and to apprehend their time course within one-week exposure, indicators of oxidative stress (malondialdehyde [MDA] level and xanthine oxidase [XO] activity), as well as activities and gene expression of key enzymes involved in antioxidant defense (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx], glutathione reductase [GR] and glutathione-S-transferase [GST]) were measured in gills and liver of C. carpio. In addition, the total antioxidative capacity (TAC) was quantified. No sign of oxidative stress was observed during the experiment, but CAT, GPx, GR and GST activities were significantly reduced in the liver after 7 days of exposure. This suggests a potential decrease of glutathione levels and risk of increased free radicals in case of longer exposure. In the gills, there were no major changes in the TAC or in the activities of antioxidant enzymes but the relative expression of the genes coding for CAT and GR were triggered, suggesting an effect on the transcription processes. These results prove the high tolerance of C. carpio to these levels of metal pollution, at least in this short-term exposure.

Full text

26-30 May 2019
Helsinki, Finland
How common carp (Cyprinus carpio) avoid
oxidative stress during an exposure to a
sublethal three-metal (Cu/Cd/Zn) mixture
Marion.Pillet@uantwerpen.be Pillet, M., Castaldo, G., De Weggheleire, S., Bervoets, L., Blust, R. and De Boeck, G.
Systemic Physiological and Ecotoxicological Research, University of Antwerp, Belgium
Introduction
Objectives:
• investigate the effect of metal mixture on
oxidative stress and antioxidant defense
• understand the time course of these
processes over a week of exposure
M & M
Control
Exposed
Zn = 206.8 µg/L
Cu = 4.8 µg/L
Cd = 2.9 µg/L
d1 d3 d7
Levels of:
•Oxidative stress indicators
= MDA & XO
•Total antioxidative capacity (T-AOC)
Enzyme activity & gene expression of
antioxidant defenses:
•1st line of defense = CAT & SOD
•Glutathione system = GPx, GR & GST
Results &
discussion
•well-studied, economically
important
•bioindicator in environmental
pollution studies
•threatened by metal
contamination
ROS production
Oxidative stress
Tissue damage
Cu Zn
Cd
Cyprinus carpio
Healthy ecosystem
Chemical
pollution Management
Effective
quality standard
Uncertainty of
prediction based
on single
compound /
species toxicity
data
Challenging
assessment
of mixture
stress liver gills
MDA

No sign of oxidative stress during the
one-week experiment
XO
T
-
AOC

Unchanged
Day 1 Day 3 Day 7
GR total activity
(U/g wet weight)
*
ab
a **
b
Day 7 Day 3 Day 1
GR relative expression
ab
a
b
Results for glutathione reductase in liver
liver gills
Enzyme
Gene
Enzyme
Gene
SOD
- - - -
CAT
↘ - - ↗
GPx
↘ - - -
GR
↘ - - ↗
GST
↘ - - -
Different responses
at the gene and
enzyme levels
Glutathione
system most
impacted
Most significant
differences observed
after 3 to 7 days
Day 7 Day 3 Day 1
a
a
b
CAT relative expression
Day 7 Day 3 Day 1
*
CAT total activity
(U/g wet weight)
Results for catalase in liver
Lower enzymes activities may lead to a decrease of glutathione
levels  increase of free radicals?
Oxidative stress is avoided, but only for a short period.
C. carpio is able to cope with short term exposure to metal mixture.
Impact of metal
mixture on
transcription