Activation of PPARα by Oral Clofibrate Increases Renal Fatty Acid Oxidation in Developing Pigs

Abstract

The objective of this study was to evaluate the effects of peroxisome proliferator-activated receptor α (PPARα) activation by clofibrate on both mitochondrial and peroxisomal fatty acid oxidation in the developing kidney. Ten newborn pigs from 5 litters were randomly assigned to two groups and fed either 5 mL of a control vehicle (2% Tween 80) or a vehicle containing clofibrate (75 mg/kg body weight, treatment). The pigs received oral gavage daily for three days. In vitro fatty acid oxidation was then measured in kidneys with and without mitochondria inhibitors (antimycin A and rotenone) using [1-14C]-labeled oleic acid (C18:1) and erucic acid (C22:1) as substrates. Clofibrate significantly stimulated C18:1 and C22:1 oxidation in mitochondria (p < 0.001) but not in peroxisomes. In addition, the oxidation rate of C18:1 was greater in mitochondria than peroxisomes, while the oxidation of C22:1 was higher in peroxisomes than mitochondria (p < 0.001). Consistent with the increase in fatty acid oxidation, the mRNA abundance and enzyme activity of carnitine palmitoyltransferase I (CPT I) in mitochondria were increased. Although mRNA of mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme A synthase (mHMGCS) was increased, the β-hydroxybutyrate concentration measured in kidneys did not increase in pigs treated with clofibrate. These findings indicate that PPARα activation stimulates renal fatty acid oxidation but not ketogenesis.

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

“…Moreover, the developmental increase could be amplified further by addition of clofibrate into the milk diet, without altering kidney size (weight) or growth performance of the piglets. Similar results were observed from sow-raised pigs receiving an oral gavage of clofibrate in our previous study [13]. 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 induction of renal fatty acid oxidation via activation of PPARα occurred with the same pattern as observed in the liver of neonatal pigs [19]. Although renal β-oxidation was increased as previously observed [13], the increase had a minimal impact on ketogenesis probably due to a limited activity of HMGCS, owing to a posttranscriptional defect described in pigs [20]. Because of the diminished ketogenesis observed in neonatal pigs [21], we have been interested in the effects of modifying CAC anaplerosis and ketogenesis on fatty acid utilization, especially when β-oxidation is induced by PPARα activation.…”

“…Recently we explored the effect of clofibrate on renal fatty acid oxidation in newborn pigs and confirmed that PPARα-mediated mechanisms are active [13]. Renal fatty acid oxidation in both mitochondria and peroxisomes was increased with oral administration of clofibrate (75 mg/kg body weight), and the natural developmental increase was greatly amplified [13]. The amplification induced by PPARα signaling may have great significance for preventing the development of the free fatty acid-associated renal disease.…”

“…Hence, the neonatal pig is commonly used as model for human pediatric nutrition and metabolism [12]. Recently we explored the effect of clofibrate on renal fatty acid oxidation in newborn pigs and confirmed that PPARα-mediated mechanisms are active [13]. Renal fatty acid oxidation in both mitochondria and peroxisomes was increased with oral administration of clofibrate (75 mg/kg body weight), and the natural developmental increase was greatly amplified [13].…”

“…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.…”