Effects of D ‐Aspartate Treatment on D ‐Aspartate Oxidase, Superoxide Dismutase, and Caspase 3 Activities in Frog ( Rana esculenta ) Tissues

Although D ‐aspartate ( D ‐Asp) has been recognized to have a physiological role within different organs, high concentrations could elicit detrimental effects on those same organs. In this study, we examined the D ‐aspartate oxidase ( D ‐AspO) activity and the expression of superoxide dismutase 1 (SOD1) and caspase 3 in different tissues of the frog Rana esculenta after chronic D ‐Asp treatment. Our in vivo experiments, consisting of intraperitoneal (ip) injections of D ‐Asp (2.0 μmol/g b.w.) in frogs for ten consecutive days, revealed that all examined tissues can take up and accumulate D ‐Asp. Further, in D ‐Asp treated frogs, i ) the D ‐AspO activity significantly increased in all tissues (kidney, heart, testis, liver, and brain), ii ) the SOD1 expression (antioxidant enzyme) significantly increased in the kidney, and iii ) the caspase 3 level (indicative of apoptosis) increased in both brain and heart. Particularly, after the D ‐Asp treatment we found in both brain and heart (which showed the lowest SOD1 levels) a significant increase of the caspase 3 expression and, vice versa , in the kidney (which showed the highest SOD1 expression) a significant decrease of the caspase 3 expression. Therefore, we speculate that, in frog tissue, D ‐AspO plays an essential role in modulating the D ‐Asp concentration. In addition, exaggerated D ‐Asp concentrations activated SOD1 as cytoprotective mechanism in the kidney, whereas, in the brain and in the heart, where the antioxidant action of SOD1 is limited, caspase 3 was activated.