Hepatic activities of CYP1A and thiamine-dependent enzymes in Baltic salmon (Salmo salar) alevins suffering from the thiamine deficiency M74

Since 1974, Baltic salmon, Salmo salar, alevins have been affected by the M74 syndrome, a putative thiamine deficiency with associated high mortality levels that may be reduced by thiamine treatment. This study demonstrates that alevins with M74 suffer from lowered activities of the thiamine-dependent enzymes transketolase and α-ketoglutarate dehydrogenase compared to control fish. In addition, cytochrome P4501A-activity (CYP1A; measured as EROD) is lower in M74-affected alevins. Thiamine treatments administered after hatching resulted in increased activities of transketolase, α-ketoglutarate dehydrogenase and CYP1A in the M74 groups, restoring the thiamine-dependent enzyme activities to levels comparable to those of controls. We suggest that low activities of transketolase and α-ketoglutarate dehydrogenase may be responsible for M74-associated mortality. Low transketolase activities may reduce the intracellular availability of ribose 5-phosphate and NADPH. Ribose 5-phosphate is necessary for protein synthesis and NADPH is the cofactor for NADPH-cytochrome P450 reductase. Reduced cellular availability of these compounds may result in the reduced CYP1A-activities observed in this study.