Seasonal variation of peroxisomal enzyme activities and peroxisomal structure in mussels Mytilus galloprovincialis and its relationship with the lipid content

Variations in structure and function of peroxisomes in digestive tissues of marine mussels have been proposed to be valid biomarkers of environmental contamination by organic xenobiotics. The aim of the present work was to st udy the seasonal variations in peroxisomal enzyme activities, catalase, pal mitoyl-CoA oxidase (AOX) and D-amino acid oxidase (DAOX) and peroxisomal st ructure in mussels. Peroxisomal changes were related to the seasonal variat ion in the contents of neutral lipids in the digestive gland as the lipid m etabolism in mussels is subjected to seasonal variations linked to the repr oductive cycle and food intake. Significant higher catalase activities were recorded from April to June when compared to the rest of the year and AOX activity was also markedly induced during the late winter and spring (Febru ary to May) with maximal activities in April. DAOX activity did not vary se asonally, the highest activities being measured in November, February and M ay. Stereological studies of peroxisomes in digestive tubule cells revealed significantly higher volume, surface and numerical densities in animals co llected in spring and summer. Changes in peroxisomal volume density were fo und to be significantly and positively correlated with changes in AOX and c atalase activities. The peroxisomal structure and enzyme activities were ne gatively correlated with the lipid contents of digestive tubules. In April, the volume density occupied by neutral lipids was higher in duct epithelia while previously it was higher in digestive tubule epithelia. This trend w as maintained during the period in which peroxisomes were more abundant unt il July. In the following September, digestive tubules recovered their lipi d load. It is concluded that seasonal changes related to food intake and re productive cycle induce changes in peroxisomal parameters that can be compa red to typical peroxisome proliferation, with a 25-fold increase in AOX act ivity and an 8-fold increase in the peroxisomal numerical density in early spring. (C) 1999 Elsevier Science Inc. All rights reserved.