Energetic costs of pyrene metabolism in isolated hepatocytes of rainbow trout, Oncorhynchus mykiss

The respiratory costs of pyrene exposure and biotransformation were examined in isolated hepatocytes of adult rainbow trout, Oncorhynchus mykiss. Baseline oxygen consumption rates measured at an acclimation temperature of 7.5 degreesC and during an acute temperature increase to 15 degreesC were 10.1 +/- 0.1 and 22.6 +/- 10.4 ng O-2/min/mg cells, respectively. Hepatocytes exposed to pyrene at 1, 5 and 10 mug/ml exhibited concentration-dependent increases in oxygen consumption. Respiration rates of cells exposed to these concentrations at their acclimation temperature were 12.5 +/- 10.1, 14.7 +/- 0.1 and 17.1 =/- 0.2 ng O-2/min/mg cells, respectively. Exposure of cells to pyrene at 15 degreesC also elevated oxygen consumption to a maximum of 34.4 +/- 0.3 ng O-2/min/mg cells, however, the relationship with pyrene concentration was biphasic. The major metabolite identified through a series of solvent extractions, acid hydrolysis, and synchronous fluorometric spectroscopy was conjugated 1-hydroxypyrene. At 7.5 degreesC, increased pyrene metabolism correlated with increased hepatocyte respiration rates. At 15 degreesC, however, pyrene metabolism reached a maximum at 5 mug/ml, suggesting saturation of detoxification enzymes, which correlated with maximum respiration rates at this concentration. Measures of respiration by isolated mitochondria indicated that changes in hepatocyte oxygen consumption were not through direct effects of pyrene on mitochondria. This study indicates that significant respiratory costs may be accrued by teleost hepatocytes actively metabolizing and secreting xenobiotic compounds. (C) 2004 Elsevier B.V. All rights reserved.