Variability in antioxidant/detoxification enzymes of Sinonovacula constricta exposed to benzo[a]pyrene and phenanthrene
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants of petrogenic and pyrogenic origin that are widespread in marine and coastal environments (Rocha et al., 2012). Benzo[a]pyrene(B(a)P), a probable human carcinogen (Laffon et al., 2006) is widely used as a reference compound in studies on the toxicity of PAHs in natural communities (Aoya et al., 2003). Phenanthrene (PHE) is a priority PAH, and, although not mutagenic or carcinogenic, it is commonly used as a model substrate for studies on metabolism of carcinogenic PAHs (Zhang et al., 2014).
Antioxidant defenses are sensitive to environmental contamination and can be used as biological indicators of aquatic environmental health (Sturve et al., 2008). The defense mechanisms mainly allow metabolization, detoxification, sequestration, excretion and antioxidant protection to help the organisms to live under stress (Kaur and Kaur, 2015). Bioaccumulation of toxic substances triggers redox reactions generating free radicals that induce biochemical alterations in organism's tissues (Woo et al., 2006). B(a)P and PHE can cause oxidative stress by inducing a high level of reactive oxygen species (ROS), which could be related to cellular damage and apoptosis (Bo et al., 2014). Antioxidant enzyme systems are a well-developed regulatory mechanism scavenging ROS for protective mechanisms and avoid oxidative stress, including non-enzymatic small antioxidant molecules (such as reduced glutathione (GSH)) and a cascade of enzymes (such as superoxide dismutase (SOD) (Ren et al., 2015). Antioxidant/detoxification enzymes thus play a crucial role in maintaining organism homeostasis and their induction reflects a specific response to pollutants (Lavradas et al., 2016, Tsangaris et al., 2010, Schmidt et al., 2013). Therefore, antioxidant/detoxification enzymes have been proposed as biomarkers of contaminant-mediated oxidative stress in a vary from aquatic organisms (Regoli et al., 1998). An integrated biomarker response index (IBR) was developed to assess aquatic environmental quality based on the response from antioxidant enzymes to pollutants (Serafim et al., 2012). The IBR index can be useful for the quantitative assessment of the toxicological effects of PHE on Morula granulate (Bhagat et al., 2016).
Bivalve mollusks, owing to their feeding behavior, readily take up lipophilic organic contaminants, such as PAHs, from the marine environment, with a variety of physiological effects (Livingstone et al., 1995). In this study, an attempt has been made to select the biomarker enzyme for assessing B(a)P and PHE effects on biotransformation in Sinonovacula constricta, an Agamaki clam (an economically important shellfish in Asia). Levels of antioxidant/detoxification enzymes were estimated in gills as an indicator of the stress after 15 days exposure to B(a)P and PHE. The experiment was to ascertain the time taken for reversals of enzyme activity to normal after exposure to these two PAH. Little work has been done on the effect of PAH on antioxidant/detoxification enzymes of clams. Therefore, this work holds great importance for environmental risk assessment. A group of frequently used oxidative stress biomarkers (SOD, CST, GSH, EROD, and AHH) were selected for biochemical assays, and the integrated biomarker response (IBR) index was applied to assess the comprehensive effects of the different exposures to B(a)P and PHE.
Section snippets
Chemicals
B(a)P (purity, 99%) and PHE (CAS# 85-01-8) were purchased from the Sigma Company. Acetone was used as the vehicle to dissolve the chemical. All other chemicals and solvents were of analytical grade.
Animals and treatments
Healthy S. constricta averaging 14.62 ± 2.26 cm in body length, were obtained from a commercial farm in Qidong, Jiangsu, China. The clams were subjected to an acclimation period of one week in plastic tanks of 100 L capacities before the exposure test. The tanks were containing aerated seawater (salinity
B(a)P and PHE experiment
The effect of exposure to B(a)P on activities of antioxidant enzymes (SOD, GST, GSH, AHH and EROD) in the tissues of gills of S. constricta was shown in Fig. 1, Fig. 2. During the experiment, the activities of AHH, EROD, SOD and GST in the tissues of gills increased and then came into equilibrium. GSH contents in the tissues of gills tended to alter slightly (p > 0.05), while a significant decrease (p < 0.05) occurred in the tissues of gills exposed to 4.5 μg L− 1 B(a)P and PHE after 3 days.
The correlation analysis with B(a)P and PHE on detoxification metabolism parameters in S. constricta tissues
As shown in
Discussion
Antioxidant responses are often induced by exposure to reactive oxygen species or contaminants(Fernández et al., 2012). Some authors suggested that PAHs and other organic compounds contaminants can induce ROS inciting oxidative stress and even lipid peroxidation with changing the antioxidant enzymes in molluscan bivalves (Bebianno and Barreira, 2009). Our experimental results demonstrated that 15 d exposure to B(a)P and PHE, induced oxidative damage to gills of S. constricta as there was a
Conclusion
In conclusion, this study revealed both similarities and differences of time-, concentration-, and inducer-dependent EROD, GST, AHH, SOD and GSH responses of the target organs, gills of clams. This was the case of both B(a)P and PHE, while biochemical parameters responded much more strongly to B(a)P than to PHE. How relevant such organ differences are with respect to metabolism and toxicity of the xenobiotics, remains to be evaluated.
Acknowledgments
This work was supported by the Special Scientific Research Funds for Central Non-profit Institutes, Chinese Academy of Fishery Sciences (No. 2014A02XK01), the Special Scientific Research Funds for Central Non-profit Institutes, Chinese Academy of Fishery Sciences (No. 2014T06), National Modern Agricultural Industry Technology System Construction Project (No.·CARS-48), and Professional Project on Special Key Technology for Oil Spill for Ministry of Agriculture (No. 2012-NZ-5739).
References (37)
- et al.
Enzymatic and cellular responses in relation to body burden of PAHs in bivalve molluscs: a case study with chronic levels of North Sea and Barents Sea dispersed oil
Mar. Pollut. Bull.
(2009) - et al.
Effects of environmental pollution in caged mussels Mytilus galloprovincialis
Mar. Environ. Res.
(2013) - et al.
Relationships between tissue concentrations of polycyclic aromatic hydrocarbons and antioxidative responses of marine mussels, Perna viridis
Aquat. Toxicol.
(2001) - et al.
Assessment of the mechanisms of detoxification of chemical compounds and antioxidant enzymes in the digestive gland of mussels, Mytilus galloprovincialis, from Mediterranean coastal sites
Chemosphere
(2012) - et al.
Glutathione S-transferases the first enzymatic step in mercapturic acid formation
J. Biol. Chem.
(1974) - et al.
A fluoremetric method for determination of oxidized and reduced glutathione in tissues
Anal. Biochem.
(1976) - et al.
Variability in antioxidant/detoxification enzymes of Labeo rohita exposed to an azo dye, acid black (AB)
Comp. Biochem. Physiol. C
(2015) Generation of superoxide radical during autoxidation of hydroxylamine and an assay for superoxide dismutase
Arch. Biochem. Biophys.
(1978)- et al.
Monitoring of the impact of prestige oil spill on Mytilus galloprovincialis from Galician coast
Environ. Int.
(2006) - et al.
Metabolites analysis, metabolic enzyme activities and bioaccumulation in the clam Ruditapes philippinarum exposed to benzo[a]pyrene
Ecotoxicol. Environ. Saf.
(2014)