Genotoxicity assessment and detoxification induction in Dreissena polymorpha exposed to benzo[a]pyrene

Abstract

The use of DNA adduct analysis has previously focused on the use of marine organisms for biomonitoring, whereas similar investigations in freshwater organisms are sparse. In that context, we have investigated the relevance of DNA adducts as biomarkers of genotoxicity in the freshwater mussels Dreissena polymorpha. The objective of the present study is to determine the stability of DNA adducts induced by benzo[a]pyrene (B[a]P) in zebra mussels. Mussels were exposed to dissolved B[a]P (10-100 µg/l) for 4 days. Afterwards, mussels were kept in clean water for 28 days and DNA adduct levels were subsequently measured in two different organs, the digestive glands and the gills, using the (32)P-postlabelling technique. In parallel, the expression of genes involved in the detoxification system was assessed by qPCR (catalase, superoxide dismutase, glutathione S transferase, HSP70, aryl hydrocarbon receptor, P glycoprotein). We observed a higher level of DNA adducts in the digestive glands compared to the gills. Moreover, in gills, the level of DNA adduct was dependent on the B[a]P concentration. The levels of adducts tended to decrease in both organs after 28 days in clean water. In addition, an early induction of HSP70, PgP, AHR and SOD mRNA levels was noticed in the gills compared to the digestive glands. CAT and GST gene expression increased from 12h exposure in both organs. A higher gene expression level of those genes was observed in the gills, except for AHR and CAT genes. Data converge towards the fact that DNA adducts hence represent a very promising biomarker of B[a]P contamination and potentially of exposure to polycyclic aromatic hydrocarbons. In addition, for the first time in this study, B[a]P detoxification system was characterised in D. polymorpha.

Genotoxicity and activation of cellular defenses in transplanted zebra mussels Dreissena polymorpha along the Seine river

“…In the same way, Rocher et al (2006) also observed DNA adduct amounts in zebra mussels collected in stations from the Seine estuary and the Seine Bay around 10 adducts/10 9 nt. The same range of DNA adduct formation was previously noticed in laboratory experiments where D. polymorpha exposed to Benzo[a] pyrene depicted DNA adducts ranging from 1.3 to 5.19 adducts/10 9 nucleotides in gills and from 0.9 to 2.29 adducts/10 9 nucleotides in the digestive glands (Châtel et al, 2012). This was also comparable to marine mussels exposed to the same xenobiotic (Canova et al, 1998;Skarphéinsdóttir et al, 2003;Akcha et al, 2000).…”

“…S3 ribosomal gene was chosen as the reference gene for normalization as previously demonstrated (Contardo-Jara et al, 2010;Châtel et al, 2012). Table 1 Primer sequences (5 0 -3 0 ) used in qRT-PCR.…”

“…Indeed, a few studies in fluvial or lake areas have underlined the interest of using DNA adducts (Pfohl-Leszkowicz et al, 1993;Le Goff et al, 2006;Rocher et al, 2006;Al-Subiai et al, 2012;Cachot et al, 2013) and DNA strand breaks (Binelli et al, 2007;Jha, 2008;Michel et al, 2013) for biological effects evaluation of chemical contamination. DNA adducts formation was observed in both marine mussels (Akcha et al, 2000;Skarphéinsdóttir et al, 2003;Pisoni et al, 2004;Amat et al, 2004;Bocquéné et al, 2004;Rocher et al, 2006) and freshwater mussels (Le Rocher et al, 2006;Châtel et al, 2012), exposed to model PAHs which indicate that these species are able to metabolize benzo[a]pyrene (B[a]P) into reactive metabolites that can bind to DNA and form DNA adducts. Moreover, field experiments have demonstrated a correlation between level of PAHs pollution and formation of DNA adduct in freshwater mussels (Le Rocher et al, 2006).…”

“…Because only few studies have compared the adduct levels in various tissues, we choose to compare those amounts in gills and digestive glands of zebra mussels. In order to confirm the persistence of DNA adduct observed in laboratory experiments (Châtel et al, 2012), mussels were transplanted into three sites of the Seine river and also on the reference site, which correspond to the sampling site, for one and two months. Moreover, expression of some genes implicated in phase I and II detoxification mechanisms as well as biomarkers involved in different metabolic pathways related to xenobiotic exposure were analysed in these mussels.…”

DNA oxidation and DNA repair in gills of zebra mussels exposed to cadmium and benzo(a)pyrene

“…Even though bivalve BaP metabolisation remain lower than in vertebrates, zebra mussel gill cells are able to transform the BaP into active metabolite which can induce DNA lesions such as bulky DNA adducts as we recently observed in gills and digestive gland (Chatel et al 2012). BaP induced DNA SB has been largely observed in bivalve species such as for example Mytilus sp.…”