Increased Biosynthesis of CoA in the Liver of Rats Treated with Clofibrate

Abstract

The amounts of CoA in rat liver increased about three fold after treatment with clofibrate. About 10 of total CoA were long‐chain acyl‐CoA in normal rats, and slightly less in clofibrate‐treated animals. The wet weight and protein content of the liver increased by about 25%. From livers of clofibrate‐treated rats, mitochondrial and lysosomal fractions were obtained in increased amounts by conventional tissue fractionation techniques. The supernatants from such livers had rather high activities of marker enzymes for lysosomes and peroxisomes. No changes of the specific activities of the two first enzymes in the degradation pathway for CoA, i.e. acid phosphatase and nucleotide pyrophosphatase, were found in the liver homogenate from clofibrate‐treated rats. In the mitochondrial fraction from such livers, both (contaminating) activities were decreased. The degradation of CoA was increased in the supernatant, however, probably because of an increased leakage of acid phosphatase from lysosomes during the fractionation procedure. The synthesis of CoA from pantothenic acid was estimated by two different methods in vitro: by quantitation of CoA formed and by estimation of the incorporation of [14C]pantothenic acid into CoA. By both methods, CoA synthesis was found to be increased 3–4‐fold in livers from clofibrate‐treated rats. Dephospho‐CoA kinase was found to have a dual localization, with a minor pool in the mitochondrial fraction. This enzyme was only slightly increased in the clofibrate‐treated animals. The activity of pantothenate kinase was more than doubled after clofibrate treatment. This is thought to be the most important factor for the increase of CoA. CoA exerted feed‐back inhibition at this step in liver supernatant from normal and clofibrate‐treated rats.

Effects of clofibrate on the intracellular localization of palmitoyl‐CoA hydrolase and palmitoyl‐L‐carnitine hydrolase in rat liver

“…The marker enzymes (see section 2.4 above) for inner mitochondrial membrane [ 141, mitochondrial matrix [ 151, lysosomes [ 161, peroxisomes [ 171, microsomes [ 181, and plasma membrane [ 191 were distributed as might be expected [4,11]. The cross-contamination between fractions, calculated from the marker enzymes, was low except for the presence of marker enzymes for the mitochondrial outer membrane, peroxisomes and Percentage values microsomes in the particle-free supernatant.…”

“…Male Wistar-M#ll rats (220-340 g) were randomly selected for control and clotibrate-treated groups, and given ordinary, commercial food or the same food containing 0.3% (w/w) clofibrate as in [4]. Both groups were fed lo-14 days before they were killed.…”

Feedback Regulation of Murine Pantothenate Kinase 3 by Coenzyme A and Coenzyme A Thioesters

“…The metabolic state of the animal (fasting or feeding) (15)(16)(17)(18)(19), pathological conditions (diabetes) (23,24), and hypolipidemic drugs (fibrates) (14,19,20) all significantly alter the cellular levels of CoA. These alterations are reflected in concomitant changes in tissue PanK activity (21,22), indicating an important role for PanK expression in controlling the cellular CoA levels. Extracts from livers derived from animals treated with hypolipidemic drugs not only have increased PanK activity, but also, this elevated activity responds differently to CoA and acetyl-CoA regulators when compared with the activity from control livers (8), thus suggesting selective expression of PanK isoforms induced by the drug.…”

Regulation of the Biosynthesis of CoA at the Level of Pantothenate Kinase

“…Table 1 also shows that the inhibitions generally were less pronounced with enzyme from clofibratetreated rats: approximately half for all long-chain acyl-CoA thioesters tested and even less for CoASH and dephosphoCoA (the amount of protein was adjusted to give approximately the same activity without inhibitor as with enzyme from normal-fed rats). This difference from pantothenate kinase from normal rats remained unexplained, but may contribute to the increased hepatic biosynthesis of CoA during clofibrate treatment observed previously [7].…”