Pharmacologic activation of peroxisome proliferator-activating receptor-α accelerates hepatic fatty acid oxidation in neonatal pigs

Abstract

Up-regulation of peroxisome proliferator-activating receptor-α (PPARα) and increasing fatty acid oxidation are important for reducing pre-weaning mortality of pigs. We examined the time-dependent regulatory effects of PPARα activation via oral postnatal clofibrate administration (75 mg/(kg-BW·d) for up to 7 days) on mitochondrial and peroxisomal fatty acid oxidation in pigs, a species with limited hepatic fatty acid oxidative capacity due to low ketogenesis. Hepatic oxidation was increased by 44-147% (depending on fatty acid chain-length) and was attained after only 4 days of clofibrate treatment. Acyl-CoA oxidase (ACO) and carnitine palmitoyltransferase I (CPTI) activities accelerated in parallel. The increase in CPTI activity was accompanied by a rapid reduction in the sensitivity of CPTI to malonyl-CoA inhibition. The mRNA abundance of CPTI and ACO, as well as peroxisomal keto-acyl-CoA thiolase (KetoACoA) and mitochondrial malonyl-CoA decarboxylase (MCD), also were augmented greatly. However, the increase in ACO activity and MCD expression were different from CPTI, and significant interactions were observed between postnatal age and clofibrate administration. Furthermore, the expression of acetyl-CoA carboxylase β (ACCβ) decreased with postnatal age and clofibrate had no effect on its expression. Collectively these results demonstrate that the expression of PPARα target genes and the increase in fatty acid oxidation induced by clofibrate are time- and age-dependent in the liver of neonatal pigs. Although the induction patterns of CPTI, MCD, ACO, KetoACoA, and ACCβ are different during the early postnatal period, 4 days of exposure to clofibrate were sufficient to robustly accelerate fatty acid oxidation.

Effects of Dietary Anaplerotic and Ketogenic Energy Sources on Renal Fatty Acid Oxidation Induced by Clofibrate in Suckling Neonatal Pigs

“…In that study, the amplified β-oxidation was associated with an induction of gene expression and activity of carnitine palmitoyl-transferase I (CPTI), one of the target genes of PPARα [13]. The increased CPTI activity was accompanied by a rapid reduction in the sensitivity of CPTI and an increase in the gene expression of malonyl-CoA decarboxylase (MCD) in the liver of swine [15], suggesting that malonyl-CoA is involved in the regulation of fatty acid catabolism induced by clofibrate. Unlike in the liver, however, the effects of clofibrate on MCD was not detected in the kidneys in this study.…”

“…The CAC intermediate, succinate, was used as a direct anaplerotic carbon source and also due to its role in inhibition of ketogenesis by inactivation of mHMGCS via succinyl-CoA [17]. Although the activity of mHMGCS could not be improved by induction of the gene expression via activation of PPARα [15], we expected that ketone bodies might be produced via the AACD pathway when fatty acid β-oxidation is increased. Indeed, feeding diets containing MCFA increased β-hydroxybutyrate concentration as compared to succinate in kidney tissues, suggesting that the renal ketogenic pathways could be modified by diet.…”

“…The formulated basal milk replacer contained 12.8% of dry matter. Based on our previous study [15], the average clofibrate intake would be~200 mg/kg body weight per day if the average milk intake was 750 mL and the average body weight was 1.65 kg throughout the experimental period. Supplements to the basal diet were offset by reductions in soybean oil so that diets remained iso-caloric.…”

“…Palmitate oxidation was measured in fresh kidney homogenates as previously described [15]. Measurements were conducted using [1-14 C] palmitic acid (0.5 mM, 0.28 kBq/µmol) pre-incubated with or without carnitine (1 mM), L659699 (1.6 µM), an inhibitor of both mitochondrial HMGCS and cytosolic HMGCS [37], or iodoacetamide (50 µM), an inhibitor of acetoacetyl-CoA deacylase (AACD) for acetoacetate synthesis [38].…”

“…For example, addition of malic acid [14] and 2-methylpentanoate (2MPA, unpublished data) in liver homogenates from pigs and rats increased the fatty acid oxidation in vitro and modified the carbon distribution between CO 2 and acid soluble products (ASP). The gene mitochondrial 3-hydroxy-3-methyl-glutaryl-CoA synthase (mHMGCS), coding for the key enzyme of ketogenesis is expressed significantly in liver and kidney after feeding clofibrate, but the ketone body levels in plasma and tissues remain low [13,15]. Because the excess acetyl-CoA generated from the elevated fatty acid β-oxidation needs to divert into the citric acid cycle (CAC) and the ketogenic pathway for further metabolism, the capacities of these pathways are critical for maintaining a high β-oxidative flux.…”