Carnitine palmitoyltransferase I control of acetogenesis, the major pathway of fatty acid β-oxidation in liver of neonatal swine

Abstract

Lin X, Shim K, Odle J. Carnitine palmitoyltransferase I control of acetogenesis, the major pathway of fatty acid ␤-oxidation in liver of neonatal swine. Am J Physiol Regul Integr Comp Physiol 298: R1435-R1443, 2010. First published March 17, 2010 doi:10.1152/ajpregu.00634.2009.-To examine the regulation of hepatic acetogenesis in neonatal swine, carnitine palmitoyltransferase I (CPT I) activity was measured in the presence of varying palmitoyl-CoA (substrate) and malonyl-CoA (inhibitor) concentrations, and [1-14 C]-palmitate oxidation was simultaneously measured. Accumulation rates of 14 C-labeled acetate, ketone bodies, and citric acid cycle intermediates within the acid-soluble products were determined using radio-HPLC. Measurements were conducted in mitochondria isolated from newborn, 24-h (fed or fasted), and 5-mo-old pigs. Acetate rather than ketone bodies was the predominant radiolabeled product, and its production increased twofold with increasing fatty acid oxidation during the first 24-h suckling period. The rate of acetogenesis was directly proportional to CPT I activity. The high activity of CPT I in 24-h-suckling piglets was not attributable to an increase in CPT I gene expression, but rather to a large decrease in the sensitivity of CPT I to malonyl-CoA inhibition, which offset a developmental decrease in affinity of CPT I for palmitoyl-CoA. Specifically, the IC 50 for malonyl-CoA inhibition and Km value for palmitoyl-CoA measured in 24-h-suckling pigs were 1.8-and 2.7-fold higher than measured in newborn pigs. The addition of anaplerotic carbon from malate (10 mM) significantly reduced 14 C accumulation in acetate (P Ͻ 0.003); moreover, the reduction was much greater in newborn (80%) than in 24-h-fed (72%) and 5-mo-old pigs (55%). The results demonstrate that acetate is the primary product of hepatic mitochondrial ␤-oxidation in Sus scrofa and that regulation during early development is mediated primarily via kinetic modulation of CPT I. acetate; anaplerosis; carnitine palmitoyltransferase I activity; ketone bodies; mitochondria; Sus scrofa IT IS WELL ESTABLISHED THAT hepatic long-chain fatty acid oxidation is acutely controlled by a system in which carnitine palmitoyltransferase I (CPT I) is regulated allosterically by a change in malonyl-CoA concentration and/or the sensitivity to malonyl-CoA inhibition. This regulatory mechanism dictates fatty acid flux into mitochondria and controls the rates of ␤-oxidation and ketogenesis based on the animal's physiological status. The neonatal period represents a physiological state characterized by marked enhancement of fatty acid oxidation and ketogenesis. Both humans and rats present a significant hyperketonemia during the suckling period (40). Evidence confirms that the physiological hyperketonemia is a result of the high hepatic ketogenic rate in neonates consuming a diet (i.e., milk) that is high in fat and low in carbohydrate. In fact, more than 90% of the non-CO 2 carbon derived from fatty acid oxidation in liver homogenates is ketone bodies (21). Wh...

Transplacental induction of fatty acid oxidation in term fetal pigs by the peroxisome proliferator-activated receptor alpha agonist clofibrate

“…The measurements followed the same procedure as described previously by Lin et al [5]. Specifically, liver homogenates (~40 mg) were incubated in 25 mL Erlenmeyer flasks with a final of volume of 2 mL of the reaction medium with or without addition of antimycin A (50 μmol/L) and rotenone (10 μmol/L) described as previously [13] for determining peroxisomal β-oxidation by inhibition of the electron transport chain of oxidative phosphorylation.…”

“…However, results from previous studies show that over 85% of the fatty acids taken up by newborn pig hepatocytes are re-esterified but not oxidized [4]. In addition, 80% of the acetyl-CoA produced from fatty acid β-oxidation in mitochondria and/or peroxisomes is converted to acetate rather than ketone bodies [5]. These results indicate that newborn pigs have a limited capacity to oxidize milk fat for energy production at birth.…”

Clofibrate Increases Long-Chain Fatty Acid Oxidation by Neonatal Pigs

“…The synthesized TGs were purified by alkaline/ ethanolic extraction, and purity ($95%) was confirmed chromatographically using an HPLC system (Waters) equipped with a photodiode array detector (19). The synthesis of [1-14 C]oleic acid and erucic acid TGs followed the same procedure as described above using [1][2][3][4][5][6][7][8][9][10][11][12][13][14] (21). The schedule and duration of the expired CO 2 collection was patterned following the study by Heo et al (20), and the pigs were killed by American Veterinary Medical Association-approved electrocution when the experiment ended, after 24 h of collection.…”

“…Furthermore, >90% of oleate taken up by piglet hepatocytes is re-esterified with limited flux through b-oxidation (4), and suckling pigs remain hypoketonemic despite elevated dietary fat (5,6). Studies in liver tissue demonstrated that at least 75% of the acetyl-CoA generated from hepatic FA b-oxidation is converted to acetate rather than ketone bodies (7). These observations imply unique aspects of FA metabolism and its regulation in neonatal pigs.…”

A Genome Scan for Selection Signatures in Pigs

“…Taking the 0–4.41 Mb selection region of SSC2 detected in Songliao, Yorkshire and Rongchang for instance, two QTLs influencing backfat thickness and leaf fat in the carcass and meat and carcass quality were mapped in this region. Simultaneously, this region also overlapped with the carnitine palmitoyltransferase 1A (CPT1A) gene, which plays an important role in the regulation of fatty acid metabolism in newborn pig [36], as shown in Table 4. Again for ear morphology, a series of QTLs related to ear erectness in Yorkshire, ear size in Landrace and ear weight in Rongchang were separately found to overlap with the 32.51–33.01 Mb selection regions in Landrace and Yorkshire on SSC5, and 38.40–39.45 Mb in Yorkshire and 33.36–35.00 Mb in Rongchang on SSC7.…”