Metallothioneins contribution to the response of bivalve mollusk to xenobiotics

Abstract

Estimation of cellular thiols metallothioneins (MTs) sensitivity to continuous pressure of environmental chemical ‘cocktail’ of xenobiotics needs investigation in correct model experiments. The aim of this study was to elucidate MT s contribution into bivalve mollusk response to co-exposure to xenobiotics and elevated temperature. We treated the mussels Unio tumidus Philipson, 1788 (Unionidae) with drugs diclofenac (Dc, 2 nM), nifedipine (Nf, 2 nM) or with organophosphonate herbicide glyphosate (Gl, formulation Roundup MAX, 79 nM) separately at 18°C and in combination at 18°C (DcNfGl) and 25°C (DcNfGl+T) during 14 days. MTs were isolated from digestive gland by size-exclusion chromatography. The concentration of MTs in the tissue was assessed according to metals (Zn, Cu, Cd) in the eluted peak of MTs (MT-Me) and thiols (MT-SH) content. Tissue redox status was assessed using lactate/pyruvate ratio. The assay of cells viability was based on the lysosomes ability of hemocytes to concentrate the Neutral Red (NR) dye. It was found, that MT-SH content in the digestive gland was increased under all exposures. Treatment with Dc increased the level of MT-Me, whereas treatment with Gl decreased it and increased lactate/pyruvate ratio. Nf decreased this ratio by elevating pyruvate level and increased lysosomal membrane stability in hemocytes. At co-exposure to xenobiotics and elevated temperature the number of hemocytes with nuclear abnormalities was increased indicating the exceeding of organisms’ adaptive limits. Multivariate statistical analyses showed negative correlations in pairs MT-SH/MT-Me and MT-SH/pyruvate and distinguished Gl and DcNfGl+T exposed groups from other groups.

Keywords

• metallothioneins
• diclofenac
• nifedipine
• roundup
• redox state
• bivalve mollusk