Effects of high-fat diet and fasting on levels of acyl-coenzyme a binding protein in liver, kidney, and heart of rat

Abstract

Acyl-coenzyme A (CoA) binding protein (ACBP) is a 10-kd protein that binds acyl-CoA moieties and stimulates medium-chain fatty acid synthesis by goat mammary gland fatty acid synthetase. Its exact role in intermediary lipid metabolism has not been fully elucidated. It is hypothesized that ACBP is directly involved in the metabolism of lipid. In the present study, purified rat liver ACBP was used to generate a polyclonal antisera for radioimmunoassay of ACBP in tissue specimens isolated from fasted rats and rats fed normal rat chow and a high-fat diet. In addition, purified ACBP was used to examine its effect on the activity of mitochondrial outer membrane (OM) carnitine palmitoyltransferase (CPT 0). Fasting for 24 hours significantly decreased tissue levels of ACBP in the liver (69.0 ± 7.2 v 46.7 ± 5.0 pg/ng DNA), whereas feeding of a high-fat diet for 48 hours caused ACBP levels to increase (69.0 ± 7.2 v 103.9 ± 18.0). Hepatic levels of this protein continued to increase and remained elevated with prolonged exposure to the high-fat diet (28 days). A similar pattern of change was observed in the kidney, but the magnitude of change was less. Heart ACBP did not respond acutely to the high-fat diet, but did increase after prolonged exposure (28 days). Fasting had no effect on ACBP levels in kidney and heart. Addition of ACBP to an in vitro assay system significantly increased the activity of CPT 0 (from 5.2 ± 0.8 to 72.1 ± 5.3 nmol palmitoylcarnitine formed · min −1 · mg −1 protein) when measured under inhibiting concentrations of palmitoyl-CoA (40 μmol/L). These data indicate that liver ACBP is capable of responding acutely to changes in diet, suggesting that this protein may serve a regulatory role in cellular lipid metabolism.