Effects of Dietary Anaplerotic Carbon Sources and Ketogenic Fatty Acids on Hepatic Fatty Acid Oxidation in Neonatal Pigs
Authors: Zhao Jinan , Pike Brandon , Zhang Yong , Sabin Sean , Smith Andrew , Zhu Yongwen , Odle Jack , Xi Lin 
Published: June 2021

Feeding clofibrate (a PPARα pharmaceutical agonist) to newborn pigs greatly increases hepatic fatty acid oxidation by stimulating the activities of the key enzymes (CPTI and HMGCS) in β‐oxidation and ketogenesis. This study was conducted to investigate whether increasing Krebs cycle activity and ketogenic capacity would benefit the fatty acid oxidation induced by the PPARα agonist. Suckling newborn pigs (N=48) from 6 litters were assigned randomly into 8 treatment groups based on body weight (1.31±.2 kg) following a 2 (± clofibrate) × 4 (+succinate, valerate, hexonate or 2‐methylpentanoate (2MPA)) factorial design. Pigs were fed a basal milk replacer containing either 0 or 0.35% of clofibrate with supplementation of 5% glycerol‐succinate (GS), triglycerides of valerate (triC5), hexanate (triC6), or 2MPA (tri2MPA). As supplemented, milk formula were isocaloric and given to the pigs 3Xper d for 5 d. Fatty acid oxidation was examined in fresh homogenates of liver collected on d 6 using [1‐14C] palmitic acid (1 mM). The measurements were performed in the absence or presence of carnitine (1mM) or L659699 (1.6 μM), inhibitor of 3‐hydroxy‐3‐methylglutaryl‐CoA synthase, and iodoacetamide (50 μM) inhibitor of acetoacetate synthesis. Total hepatic palmitate oxidation (14C accumulated in CO2 and acid soluble products (ASP)) was on average 2.2 fold higher from pigs fed clofibrate than without clofibrate (P < 0.0001). Supplementation of GS, triC5, triC6 or tri2MPA to the diets had no significantly impacts on the hepatic palmitate oxidation (P = 0.57). However, the dietary treatments significantly changed the distributions of 14C accumulation between in CO2 and ASP regardless of clofibrate supplementation. The 14C accumulation in CO2 in homogenates from pigs fed tri2MPA without clofibrate was 72% and 57% higher than in homogenates from pigs fed GS and triC5 (P<0.006). Liver homogenates from pigs fed triC6 also had higher 14C accumulation in CO2 compared with pigs fed GS. No difference was detected between tri2MPA and triC6 treatments. Clofibrate increased 14C accumulation in CO2 in pigs fed all diets (P > 0.0001), but the increase was greater from pigs fed diets containing triC6, triC5 and GS than tri2MPA (P<0.0001). No differences were observed among pigs fed triC6, triC5 and GS. Inclusion of carnitine in the incubations increased 14C accumulation in both CO2 and ASP by 2.6 fold in pigs, regardless of clofibrate treatment. Addition of either L659699 or iodoacetamide had no impact palmitate oxidation rate. The results indicate that dietary supplementation of extra anaplerotic carbon sources and ketogenic fatty acids modifies the metabolism of acetyl‐CoA (product of β‐oxidation) via changing TCA cycle activity, but the modification has no impact on the hepatic fatty acid oxidative capacity induced by PPARα activation. The availability of carnitine in the milk is a key element to maintain robust fatty acid oxidation rate during the neonatal period.

Support or Funding Information

Supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2015‐67015‐23245