Studies on the development of carnitine palmitoyltransferase and fatty acid oxidation in liver mitochondria of neonatal pigs

Reduced Visceral Fat Weight and Body Weight Due to Ingestion of Fermented Collagen Peptide in High-Fat Diet-Fed Obese Mice

Oral ingestion of collagen hydrolysate has various benecial effects. We developed a novel fermented collagen peptide (FCP), different from the conventional collagen peptides, by fermenting gelatin with Aspergillus sojae. This study aimed to investigate the effect of FCP in inhibiting fat accumulation under high-fat loading. Male C57BL/6J mice were fed a low- or high-fat diet, or a high-fat diet including 5% FCP for 28 d. Body weight, visceral fat weight, adiponectin levels, leptin concentration, fatty acid synthase (FAS) activity, and carnitine palmitoyltransferase 1A (CPT) activity were determined. FCP supplementation was found to significantly decrease the body weight, visceral fat weight, leptin concentration, and FAS activity, and increase adiponectin levels and CPT activity compared to that in the high-fat diet-fed group. In conclusion, FCP intake reduced visceral fat weight and body weight in high-fat diet-fed mice.

Effects of medium chain triglycerides on hepatic fatty acid oxidation in clofibrate-fed newborn piglets

To investigate whether increasing tricarboxylic acid (TCA) cycle activity and ketogenic capacity would augment fatty acid (FA) oxidation induced by the peroxisome proliferator-activated receptor-alpha (PPARα) agonist clofibrate, suckling newborn piglets (n = 54) were assigned to 8 groups following a 2 ( ± clofibrate) × 4 (glycerol succinate [SUC], triglycerides of 2-methylpentanoic acid [T2M], valeric acid [TC5] and hexanoic acid [TC6]) factorial design. Each group was fed an isocaloric milk formula containing either 0% or 0.35% clofibrate (wt/wt, dry matter basis) with 5% SUC, T2M, TC5 or TC6 for 5 d. Another 6 pigs served as newborn controls. Fatty acid oxidation was examined in fresh homogenates of liver collected on d 6 using [1-¹⁴C] palmitic acid (1 mM) as a substrate (0.265 μCi/μmol). Measurements were performed in the absence or presence of L-carnitine (1 mM) or inhibitors of 3-hydroxy-3-methylglutaryl-CoA synthase (L659699, 1.6 μM) or acetoacetate-CoA deacylase (iodoacetamide, 50 μM). Without clofibrate stimulation, ¹⁴C accumulation in CO₂ was higher from piglets fed diets containing T2M and TC5 than SUC, but similar to those fed TC6. Under clofibrate stimulation, accumulation also was higher in homogenates from piglets fed TC5 than all other dietary treatments. Interactions between clofibrate and carnitine or the inhibitors were observed (P = 0.0004) for acid soluble products (ASP). In vitro addition of carnitine increased ¹⁴C-ASP (P < 0.0001) above all other treatments, regardless of clofibrate treatment. The percentage of ¹⁴C in CO₂ was higher (P = 0.0023) in TC5 than in the control group. From these results we suggest that dietary supplementation of anaplerotic and ketogenic FA could impact FA oxidation and modify the metabolism of acetyl-CoA (product of β-oxidation) via alteration of TCA cycle activity, but the modification has no significant impact on the hepatic FA oxidative capacity induced by PPARα. In addition, the availability of carnitine is a critical element to maintain FA oxidation during the neonatal period.

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

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.

Ontogeny and kinetics of carnitine palmitoyltransferase I in hepatopancreas and skeletal muscle of grass carp (Ctenopharyngodon idella)

The ontogeny and kinetics of carnitine palmitoyltransferase I (CPT I) were investigated in hepatopancreas and muscle throughout four developmental stages (newly hatched larvae, 1-month-old juvenile, 3-month-old, and 6-month-old, respectively) of grass carp Ctenopharyngodon idella. In hepatopancreas, the maximal velocity (Vmax) significantly increased from hatching to 1-month-old grass carp and then gradually declined at 6-month-old grass carp. In muscle, CPT I activity was the highest at 1-month-old grass carp, nearly twofold higher than that at hatching (P < 0.05). The Michaelis constant (Km) value was also the highest for 1-month-old in both tested tissues. Carnitine concentrations (FC, AC and TC) were the lowest for 3-month-old grass carp and remained relatively constant in both tissues from fish under the other developmental stages. The FC concentration in hepatopancreas and muscle at four developmental stages were less than the respective Km, indicating that grass carp required supplemental carnitine in their food to ensure that CPT I activity was not constrained by carnitine availability.

Clofibrate increases long-chain fatty acid oxidation by neonatal pigs

BACKGROUND

Utilization of energy-dense lipid fuels is critical to the rapid development and growth of neonates.

OBJECTIVE

To increase efficiency of milk fat utilization by newborn pigs, the effect of clofibrate on in vivo and in vitro long-chain fatty acid (LCFA) oxidation was evaluated.

METHODS

Newborn male pigs were administered 5 mL of vehicle (2% Tween 80) with or without clofibrate (75 mg/kg body weight) once daily via i.g. gavage for 4 d. Total LCFA oxidative capacity was measured in respiration chambers after gastric infusion (n = 5 per treatment) with isoenergetic amounts of [1-(14)C]triglycerides (TGs), either oleic acid (18:1n-9) TG [3.02 mmol/kg body weight (BW)(0.75)] or erucic acid (22:1n-9) TG (2.46 mmol/kg BW(0.75)). Total expired (14)CO2 was collected and quantified at 20-min intervals over 24 h. Hepatic in vitro LCFA oxidation was determined simultaneously using [1-(14)C]oleic acid and erucic acid substrates.

RESULTS

The in vivo 24-h accumulative [1-(14)C]TG oxidation (percentage of energy intake/kg BW(0.75)) tended to increase with clofibrate supplementation (P = 0.10), although there was no difference in the peak or mean utilization rate. The maximal extent of oleic acid TG oxidation was 1.6-fold that of erucic acid TG (P < 0.006). Hepatic in vitro LCFA oxidation increased 61% with clofibrate (P < 0.0008). The increase in mitochondria was 4-fold greater than in peroxisomes. The relative abundance of mRNA increased 2- to 3-fold for hepatic peroxisome proliferator-activated receptor α and its target genes (fatty acyl-coenzyme A oxidase and carnitine palmitoyltransferase) in the pigs that were administered clofibrate (P < 0.04).

CONCLUSION

Clofibrate may improve in vivo LCFA oxidative utilization in neonatal pigs.

Reduced neonatal mortality in Meishan piglets: a role for hepatic fatty acids?

The Meishan pig breed exhibits increased prolificacy and reduced neonatal mortality compared to commercial breeds, such as the Large White, prompting breeders to introduce the Meishan genotype into commercial herds. Commercial piglets are highly susceptible to hypoglycemia, hypothermia, and death, potentially due to limited lipid stores and/or delayed hepatic metabolic ability. We therefore hypothesized that variation in hepatic development and lipid metabolism could contribute to the differences in neonatal mortality between breeds. Liver samples were obtained from piglets of each breed on days 0, 7, and 21 of postnatal age and subjected to molecular and biochemical analysis. At birth, both breeds exhibited similar hepatic glycogen contents, despite Meishan piglets having significantly lower body weight. The livers from newborn Meishan piglets exhibited increased C18∶1n9C and C20∶1n9 but lower C18∶0, C20∶4n6, and C22∶6n3 fatty acid content. Furthermore, by using an unsupervised machine learning approach, we detected an interaction between C18∶1n9C and glycogen content in newborn Meishan piglets. Bioinformatic analysis could identify unique age-based clusters from the lipid profiles in Meishan piglets that were not apparent in the commercial offspring. Examination of the fatty acid signature during the neonatal period provides novel insights into the body composition of Meishan piglets that may facilitate liver responses that prevent hypoglycaemia and reduce offspring mortality.

Oleate metabolism in pig enterocytes is characterized by an increased oxidation rate in the presence of a high esterification rate within two days after birth

Oleate (OLE) is the principle fatty acid (FA) in mammalian colostrum, but its role in the energy supply in enterocytes after birth remains unknown. We investigated the metabolic fate of OLE in pig enterocytes at birth (d0) and after 2 d of suckling (d2). Cellular TG and phospholipids (PL) and FA composition were analyzed. Metabolic end-products of [1-¹⁴C]OLE were measured in enterocyte incubations. We characterized intestinal carnitine palmitoyltransferase 1 (CPT1), the key enzyme of mitochondrial FA oxidation. The TG content was 6.6-fold higher in enterocytes from pigs on d 2 than in those obtained on d 0, whereas the PL content did not differ. The level of OLE in TG and PL increased from 15 and 11% of total FA, respectively, in enterocytes from newborn piglets to 30 and 17%, respectively, in those from d2 pigs. The capacity for OLE utilization was 2.8-fold greater in d2 than in d0 pig enterocytes. The oxidation and esterification rates were enhanced in enterocytes from piglets on d 2 compared to those obtained on d 0, by 4- and 2.6-fold, respectively. The predominant OLE fate was the esterification pathway, representing >85% of OLE metabolized in both groups. The limited OLE oxidation observed at d 2 may result from the presence of a highly malonyl-CoA-sensitive CPT1A, because the half maximal inhibitory concentration for malonyl-CoA was 162 ± 25 nmol/L. This study highlighted the high esterification capacity for OLE in the newborn pig intestine, which may preserve this major colostrum FA for delivery to other tissues.

Serum carnitine, triglyceride and cholesterol profiles in Korean neonates

This study evaluated carnitine and lipid status of fifty Korean newborns. Each subject was assigned to two groups: one according to body weight at birth and the other according to gestational age. Serum total, HDL- and LDL-cholesterol were significantly lower and triacylglycerols were significantly higher, by 14 %, in the low birth weight infant (LBWI, 1310–2490 g) group compared with the normal birth weight infant (NBWI, 2570–4420 g) group. Neither birth weight nor gestational age affected serum total carnitine concentrations. However, serum ASAC (acid-soluble acylcarnitine) concentrations were 43 % higher (P < 0·001) in the LBWI group compared with the NBWI group, and approximately twice as high (P < 0·05) in the 28–32 gestational age group compared with the other gestational age groups. NEC (non-esterified acyl carnitine) fractions were significantly higher in the NBWI and 28–32 week groups (P < 0·001 andP < 0·05); consequently serum acyl/NEC carnitine ratios were four times higher in the LBWI group compared with the NBWI group and 2–3 times higher in the 25–32 week age group compared with the more advanced gestational age groups. Urinary carnitine excretion, including the NEC fraction and total carnitine, was significantly higher (P < 0·001) for LBWI than for NBWI. By gestational age, NEC excretion of the 28–32 week group was significantly (P < 0·05) higher than that of the other two groups, but total carnitine excretion was not different among the groups. This study demonstrated that Korean immature and preterm newborns have higher serum triacylglycerol concentrations but lower carnitine status than NBWI. Therefore, the lower carnitine status and moderately higher triacylglycerols may suggest that LBWI in Korea might be at risk for poor carnitine status and decreased capacity to utilise fatty acids for energy.

Ontogeny of carnitine palmitoyltransferase I activity, carnitine-Km, and mRNA abundance in pigs throughout growth and development

Carnitine palmitoyltransferase (CPT) I catalyzes an important regulatory step in lipid metabolism; however, no studies, to our knowledge, have evaluated the molecular and kinetic [maximal velocity and Michaelis constant (K(m)) for carnitine] ontogeny of CPT I and prevailing tissue concentrations of carnitine in pigs. To this end, hepatic and skeletal muscle tissues were examined at various ages: birth; 24 h; 1, 3, 5, and 8 wk of age; and adult. Hepatic and skeletal muscle CPT I specific activities were low at birth and increased 100 and 70%, respectively, during the first week of life (P < 0.05). Skeletal muscle transcript amounts were 2.7-fold greater (P < 0.001) in 24-h-old pigs relative to newborns, whereas hepatic CPT I mRNA remained constant at each age studied. The apparent K(m) for carnitine decreased 48% (P < 0.05) during the initial 3 wk of life in liver and decreased 40% (P < 0.05) during the first week of life in skeletal muscle. Plasma and liver free carnitine concentrations increased 95 and 62%, respectively, within 24 h after birth (P < 0.05) and hepatic carnitine concentrations remained constant through 5 wk of age. Consequently, hepatic carnitine concentrations were 20-80% greater (P < 0.05) than the K(m) for carnitine during the suckling period. Skeletal muscle carnitine met or exceeded the apparent K(m) for carnitine at each stage of development. Collectively, these findings suggest that postnatal increases in CPT I activity during the suckling period are accompanied by increased tissue carnitine; however, the lack of hepatic CPT I mRNA induction and low activity reported in both tissues prior to 1 wk of age may limit postnatal lipid utilization during the piglet's transition to extra-uterine life.

Differences in survival and neonatal metabolism in lambs from flocks selected for or against staple strength

In the field, we found that lamb mortality was lower (P < 0.01) in a flock selected for wool staple strength (SS+) than in a flock selected against staple strength (SS–), or a random-bred control flock (R); mortality rates calculated from 4200 records were 17.0, 22.8, and 24.1%, respectively. The proportion of twins was similar in all flocks, but birth weights differed (P < 0.01), being 4.40, 4.25, and 4.14 kg, respectively. Biochemical profiles were measured in lambs from 20 ewes from each flock around the time of birth in an animal-house study, to define potential causes of the genetic difference in survival. In the intensive study, birth weight was similar for all groups; however, gestation length was slightly shorter in the SS+ lambs (P < 0.05 for SS+ v. R). All lambs had low plasma concentrations of the essential amino acids and glucose at birth, compared with after suckling. Plasma concentrations of glucose, non-esterified fatty acids (NEFA), and blood urea nitrogen (BUN) at birth differed between lambs from the flocks with the greatest difference in mortality (i.e. SS+ v. R); that is, SS+ lambs had higher concentrations of glucose (1.84 v. 1.23 mm; P < 0.01) and NEFA (1.52 v. 1.08 mm; P < 0.05), and lower concentrations of BUN (7.7 v. 9.7 mm; P < 0.01) at birth, and for the next 9 h. The semimembranosus and semitendinosus muscle of the SS+ lambs also had lower concentrations of ATP (7.4 v. 5.0 μmol/g, respectively) compared with lambs from the other flocks, immediately post-partum. Muscle phosphocreatinine was also slightly lower in the SS+ lambs. No differences between the genotypes were observed in reserves of glycogen, carcass fat, brown adipose tissue, or in neonatal thyroid hormones. In summary, sheep selected for high wool staple strength had lower lamb mortality than the other 2 flocks. This was accompanied by metabolic differences at birth that can be associated with greater metabolic maturity, rather than greater energy reserves.

Hepatic beta-oxidation and carnitine palmitoyltransferase I in neonatal pigs after dietary treatments of clofibric acid, isoproterenol, and medium-chain triglycerides

A suckling piglet model was used to study nutritional and pharmacologic means of stimulating hepatic fatty acid beta-oxidation. Newborn pigs were fed milk diets containing either long- or medium-chain triglycerides (LCT or MCT). The long-chain control diet was supplemented further with clofibric acid (0.5%) or isoproterenol (40 ppm), and growth was monitored for 10-12 days. Clofibrate increased rates of hepatic peroxisomal and mitochondrial beta-oxidation of [1-(14)C]-palmitate by 60 and 186%, respectively. Furthermore, malonyl-CoA sensitive carnitine palmitoyltransferase (CPT I) activity increased 64% (P < 0.05) in pigs receiving clofibrate. Increased CPT I activity was not congruent with changes in message, as elevated abundance of CPT I mRNA was not detected (P = 0.16) when assessed by qRT-PCR. Neither rates of beta-oxidation nor CPT activities were affected by dietary MCT or by isoproterenol treatment (P > 0.1). Collectively, these findings indicate that clofibrate effectively induced hepatic CPT activity concomitant with increased fatty acid beta-oxidation.

Changes in kinetics of carnitine palmitoyltransferase in liver and skeletal muscle of dogs (Canis familiaris) throughout growth and development

This study was conducted to investigate developmental changes in the kinetics of carnitine palmitoyltransferase (CPT) within hepatic and skeletal muscle tissues of the canine species. Carnitine concentrations, CPT activity and the apparent K(m) for carnitine were measured in tissue homogenates from dogs in six age categories: newborn; 24-h-old; 3-, 6- and 9-wk-old; and adult. Hepatic CPT activity was low at birth, increased by 100% during the suckling period (P < 0.05) and then declined after weaning to adult levels. In contrast, CPT activity in muscle continued to increase with age, reaching adult levels after 9 wk. Congruent with CPT activity, nearly identical concentration profiles of liver and muscle acylcarnitines were observed. The apparent K(m) of hepatic CPT for carnitine also paralleled the increase in CPT activity during the suckling period; however, free and total liver carnitine concentrations declined by 50% during this time (P < 0.05). Beginning at 3 wk of age, the hepatic concentration of free carnitine was at or below the apparent K(m) of CPT for carnitine. A similar relationship existed in muscle of young dogs, but in adults, the free carnitine concentration was markedly increased and exceeded the apparent K(m) by 5-fold. Collectively, we infer that fatty acid oxidation capacity increases rapidly after birth in the canine, after ontogenic increases in CPT activity. Furthermore, based on the relatively low tissue carnitine concentrations when compared with the apparent carnitine K(m) of CPT, we suggest that carnitine may have an important role in the regulation of fatty acid oxidation and that increased dietary carnitine may improve fatty acid oxidative capacity in developing dogs.

Differential induction of peroxisomal beta-oxidation enzymes by clofibric acid and aspirin in piglet tissues

Peroxisomal beta-oxidation (POX) of fatty acids is important in lipid catabolism and thermogenesis. To investigate the effects of peroxisome proliferators on peroxisomal and mitochondrial beta-oxidation in piglet tissues, newborn pigs (1-2 days old) were allowed ad libitum access to milk replacer supplemented with 0.5% clofibric acid (CA) or 1% aspirin for 14 days. CA increased ratios of liver weight to body weight (P < 0.07), kidney weight to body weight (P < 0.05), and heart weight to body weight (P < 0.001). Aspirin decreased daily food intake and final body weight but increased the ratio of heart weight to body weight (P < 0.01). In liver, activities of POX, fatty acyl-CoA oxidase (FAO), total carnitine palmitoyltransferase (CPT), and catalase were 2.7-, 2.2-, 1.5-fold, and 33% greater, respectively, for pigs given CA than for control pigs. In heart, these variables were 2.2-, 4.1-, 1.9-, and 1.8-fold greater, respectively, for pigs given CA than for control pigs. CA did not change these variables in either kidney or muscle, except that CPT activity was increased approximately 110% (P < 0.01) in kidney. Aspirin increased only hepatic FAO and CPT activities. Northern blot analysis revealed that CA increased the abundance of catalase mRNA in heart by approximately 2.2-fold. We conclude that 1) POX and CPT in newborn pigs can be induced by peroxisomal proliferators with tissue specificity and 2) the relatively smaller induction of POX in piglets (compared with that in young or adult rodents) may be related to either age or species differences.

Low Activity of Mitochondrial HMG-CoA Synthase in Liver of Starved Piglets Is Due to Low Levels of Protein Despite High mRNA Levels

The unusually low hepatic ketogenic capacity of piglets has been correlated with lack of expression of the mitochondrial HMG-CoA synthase gene. However, we have shown that starvation of 2-week-old piglets increased the mRNA levels of mitochondrial HMG-CoA synthase to a level similar to that observed in starved rats (S. H. Adams, C. S. Alho, G. Asins, F. G. Hegardt, and P. F. Marrero, 1997, Biochem. J. 324, 65-73). We now report that antibodies against pig mitochondrial HMG-CoA synthase detected the pig enzyme in mitochondria of 2-week-old starved piglets and that the pig mitochondrial HMG-CoA synthase cDNA encodes an active enzyme in the eukaryotic cell line Mev-1, with catalytic behavior similar to that of the rat enzyme when expressed in the same system. We also show that low activity of pig mitochondrial HMG-CoA synthase correlates with low expression of the pig enzyme. The discrepancy in mitochondrial HMG-CoA synthase gene expression between the high levels of mRNA and low levels of enzyme was not associated with differences in transcript maturation, which suggests that an attenuated translation of the pig mRNA is responsible for the diminished ketogenic capacity of pig mitochondria.

Carnitine-acylcarnitine translocase deficiency: metabolic consequences of an impaired mitochondrial carnitine cycle

We describe a patient with carnitine-acylcarnitine translocase deficiency (MIM 212138), who presented with neonatal generalized seizures, heart failure, and coma. Laboratory evaluation revealed hypoglycemia, hyperammonemia, lactic acidemia, hyperuricemia, and mild dicarboxylic aciduria. The fact that total plasma carnitine (7.1 micromol/l [20-30]) and free carnitine (1.9 micromol/l [12-18]) were low together with a high acylcarnitine/free carnitine ratio of 2.7 [0.4-1.0] prompted acylcarnitine analysis. This revealed the presence of large amounts of long-chain derivatives including C(16:0), C(16:1), C(18:1), C(18:2). Based on these findings carnitine-acylcarnitine translocase deficiency was suspected which was confirmed by enzyme studies in fibroblasts. The underlying complex metabolic consequences of this defect are reviewed. Prenatal diagnosis was performed in a subsequent pregnancy and a defect ruled out by measurement of carnitine-acylcarnitine translocase activity in cultured chorionic villi cells. As the clinical recognition of a life-threatening fatty acid oxidation disorder may be difficult, defects in this pathway should be considered in any child with coma, an episode of a Reye-like syndrome, and cardiomyopathy. Since routine laboratory tests often do not provide clues about potential disorders and profiles of urinary organic acids may not be characteristic, we recommend to measure free carnitine and acylcarnitines in plasma in any child with hyperammonemia, hypo/hyperketotic hypoglycemia or lactic acidemia for prompt treatment, proper genetic counseling, and potential prenatal diagnosis.

Rates of mitochondrial and peroxisomal beta-oxidation of palmitate change during postnatal development and food deprivation in liver, kidney and heart of pigs

We measured total, mitochondrial and peroxisomal capacities for beta-oxidation of [1-14C]palmitate in homogenates of liver, kidney and heart from pigs within 0.5 h after birth (0 h, unfed) and at 24 h (suckled or unfed), 10 d (suckled or 24-h food-deprived), 21 d (suckled or 24-h food-deprived) and 5 mo (overnight food-deprived) of age. Assays were conducted in the absence (total beta-oxidation) or presence (peroxisomal beta-oxidation) of antimycin A and rotenone. Mitochondrial beta-oxidation was calculated as total minus peroxisomal beta-oxidation. Acid-soluble products (ASP) from incubation of tissue homogenates from 24-h-old unfed pigs with [1-14C]palmitate were analyzed by radio-HPLC. Total and mitochondrial beta-oxidation capacities were greater (P < 0.05) at 24 h after birth in liver, and at 10 d in kidney and heart, than at 0 or 24 h. Peroxisomal beta-oxidation capacity was increased (P < 0. 05) at 24 h after birth in liver and at 10 and 21 d in heart; in kidney, the capacity was higher during the preweaning period than in adults. Across ages, peroxisomal beta-oxidation capacity represented 37 to 51%, 28 to 41%, and 26 to 31% of total beta-oxidation capacity in liver, kidney, and heart, respectively. Food deprivation increased hepatic total beta-oxidation at 10 d and decreased peroxisomal beta-oxidation at 24 h but had no effect in kidney and heart. Regardless of the presence of respiratory inhibitors, 32%, 31 to 40%, and 45 to 50% of palmitate carboxyl carbon in acid-soluble products was accumulated in acetate in liver, kidney, and heart, respectively. We suggest that a high percentage contribution of peroxisomal beta-oxidation may act as a compensatory mechanism for piglets to oxidize milk fatty acids during postnatal development. Furthermore, acetogenesis may be an important fate of acetyl-CoA from beta-oxidation of fatty acids in various piglet tissues.

Gene expression of mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase in a poorly ketogenic mammal: effect of starvation during the neonatal period of the piglet

The low ketogenic capacity of pigs correlates with a low activity of mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase. To identify the molecular mechanism controlling such activity, we isolated the pig cDNA encoding this enzyme and analysed changes in mRNA levels and mitochondrial specific activity induced during development and starvation. Pig mitochondrial synthase showed a tissue-specific expression pattern. As with rat and human, the gene is expressed in liver and large intestine; however, the pig differs in that mRNA was not detected in testis, kidney or small intestine. During development, pig mitochondrial HMG-CoA synthase gene expression showed interesting differences from that in the rat: (1) there was a 2-3 week lag in the postnatal induction; (2) the mRNA levels remained relatively abundant through the suckling-weaning transition and at maturity, in contrast with the fall observed in rats at similar stages of development; and (3) the gene expression was highly induced by fasting during the suckling, whereas no such change in mitochondrial HMG-CoA synthase mRNA levels has been observed in rat. The enzyme activity of mitochondrial HMG-CoA synthase increased 27-fold during starvation in piglets, but remained one order of magnitude lower than rats. These results indicate that post-transcriptional mechanism(s) and/or intrinsic differences in the encoded enzyme are responsible for the low activity of pig HMG-CoA synthase observed throughout development or after fasting.

Hepatic ketogenesis in newborn pigs is limited by low mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase activity

In newborn-pig hepatocytes, the rate of oleate oxidation is extremely low, despite a very low malonyl-CoA concentration. By contrast, the sensitivity of carnitine palmitoyltransferase (CPT) I to malonyl-CoA inhibition is high, as suggested by the very low concentration of malonyl-CoA required for 50% inhibition of CPT I (IC50). The rates of oleate oxidation and ketogenesis are respectively 70 and 80% lower in mitochondria isolated from newborn-pig liver than from starved-adult-rat liver mitochondria. Using polarographic measurements, we showed that the oxidation of oleoyl-CoA and palmitoyl-L-carnitine is very low when the acetyl-CoA produced is channelled into the hydroxymethylglutaryl-CoA (HMG-CoA) pathway by addition of malonate. In contrast, the oxidation of the same substrates is high when the acetyl-CoA produced is directed towards the citric acid cycle by addition of malate. We demonstrate that the limitation of ketogenesis in newborn-pig liver is due to a very low amount and activity of mitochondrial HMG-CoA synthase as compared with rat liver mitochondria, and suggest that this could promote the accumulation of acetyl-CoA and/or beta-oxidation products that in turn would decrease the overall rate of fatty acid oxidation in newborn- and adult-pig livers.

Relationship between hepatic fatty acid oxidation and gluconeogenesis in the fasting neonatal pig

Hepatocytes were isolated from sixteen fasting neonatal pigs and used in two experiments: (1) to determine the effect of various factors on the ability for hepatic oxidation of fatty acids and (2) to clarify the relationship between fatty acid oxidation and glucose synthesis. In Expt 1, newborn pigs were either fasted from birth for 24 h or allowed to suck ad lib. for 3 d followed by a 24 h fast. In the presence of pyruvate, oxidation of octanoate (2 mM) was about 30-fold greater than oleate (1 mM) regardless of age, but glucose synthesis was not enhanced beyond that observed for pyruvate alone. Inclusion of carnitine (1 mM), glucagon (100 nM) or dibutyryl cAMP (50 microM) in the incubation media did not stimulate either fatty acid oxidation (octanoate or oleate) or glucose synthesis. Extending the period of fasting to 48 h (Expt 2) failed to enhance the fatty acid oxidative capacity or glucose synthesis rate. Likewise, the redox potential of the gluconeogenic substrate (lactate v. pyruvate) did not influence glucose synthesis regardless of the oxidative capacity exhibited for fatty acids. These data indicate that fatty acid oxidative capacity is not the first limiting factor to full expression of gluconeogenesis in hepatocytes isolated from fasted newborn pigs.

Effect of colostrum intake on plasma glucose, non-esterified fatty acid and glucoregulatory hormone patterns in the neonatal pig

The effect of colostrum on endocrine and metabolic factors affecting glucose homeostasis was evaluated in 60 neonatal pigs that were fasted, fed (nursed ad libitum) or limit-fed colostrum (25% ad libitum, 4-hr interval feeding). Plasma acquired at birth (t0), and after 10, 20 and 30 hr (t10, t20 and t30, respectively) was analyzed for glucose, non-esterified fatty acids (NEFA), and the glucoregulatory hormones--insulin, glucagon, cortisol, growth hormone and catecholamines. The concentration of glucose and NEFA was similar among treatment groups at birth and increased in proportion to the quantity of colostrum consumed. Pigs fed ad libitum achieved and maintained a higher (greater than or equal to 40%; P less than .01) glucose concentration when compared to fasted neonates. Limit-fed counterparts also achieved and maintained higher levels, with glucose concentration being approximately 20% higher throughout (P less than .05). Fed pigs maintained NEFA concentrations which were approximately 2.5-fold to 4-fold greater than that of fasted pigs (P less than .05). Likewise, limit-fed pigs tended (P = .19) to have elevated NEFA concentrations and a lower (P less than .05) insulin:glucagon molar ratio. An inverse relationship was observed between colostrum intake and plasma concentrations of cortisol and growth hormone. Concentrations of epinephrine and norepinephrine tended (P greater than .10) to be elevated in fed pigs, relative to those of fasted counterparts. Provision of even limited quantities of colostrum is therefore beneficial to the glucoregulatory response in newborn pigs.

Transient carnitine-responsive medium-chain dicarboxylic aciduria in an infant with cholestasis, hypoglycemia and cardiac failure

In a cholestatic infant showing hypoglycemia and cardiac failure, non-ketotic medium-chain dicarboxylic aciduria was disclosed by urinary organic acid analysis. As urinary excretion of long-chain fatty acids was also increased, a defect in beta-oxidation of long-chain fatty acids appeared likely. To try to improve this abnormality, carnitine supplements were given, which led to the complete resolution of clinical and laboratory abnormalities. This is the first reported case of a cholestatic infant who responded to carnitine supplementation. Deficiency of carnitine palmitoyl transferase was suspected as the underlying cause.

Carnitine deficiency

Carnitine is an essential cofactor in the transfer of long-chain fatty acids across the inner mitochondrial membrane. Carnitine is metabolized from lysine, trimethyllysine and butyrobetaine. Butyrobetaine undergoes hydroxylation in the liver, brain and kidney to form carnitine which in turn is transported via the plasma to the heart and skeletal muscle where it is important for allowing beta oxidation of fatty acids. Three clinical forms of carnitine deficiency have been described: myopathic, systemic and mixed forms. Carnitine deficiency results in accumulation of neutral lipid within skeletal muscle, myocardium and liver. Ultrastructurally, myofibrils are disrupted and there is an accumulation of large aggregates of mitochondria and lipid deposits within the skeletal muscle and myocardium. Carnitine therapy has been effective in the treatment of the myopathic and some cases of systemic and mixed forms. Several syndromes of secondary carnitine deficiency have been described; these may be secondary to genetic defects of intermediary metabolism and to other conditions, particularly following hemodialysis.

Fatty acid and glucose utilization in isolated, working fetal pig hearts

Fatty acid uptake and the effects of long- and short-chain fatty acids on glucose utilization were assessed in isolated perfused fetal pig hearts (0.9 gestation) in which oxygenated nutrient buffer was pumped from both ventricles at controlled pressure (55 mmHg, mean arterial pressure) and heart rate (180 beats/min). When either 1.5 mM palmitate or 1.0 mM octanoate was added to buffer containing 10 mM glucose and insulin (100 microU/ml), glucose uptake, as measured by 3H2O production from D-[2-3H]glucose, was suppressed when compared with glucose uptake in the absence of fatty acid. Increased tissue concentrations of glucose 6-phosphate, fructose 6-phosphate, and citrate in hearts perfused with buffer containing octanoate indicated active beta-oxidation and inhibition of phosphofructokinase activity when compared with hearts perfused with glucose alone. In contrast, hearts perfused with buffer containing palmitate showed no increases in these metabolic intermediates. These results suggest that suppression of glucose uptake in the presence of long-chain fatty acid was not the result of phosphofructokinase inhibition but may result from inhibition of glucose transport by palmitate. Determinations of tissue concentrations of free carnitine and carnitine derivatives indicated that, although palmitate underwent esterification to long-chain acyl carnitine in the fetal heart, it failed to undergo extensive beta-oxidation.

Metabolic fate of non-esterified fatty acids in isolated hepatocytes from newborn and young pigs. Evidence for a limited capacity for oxidation and increased capacity for esterification

In hepatocytes isolated from 48 h-old starved of suckling newborn pigs or from 15-day-old starved piglets, the rate of ketogenesis from oleate or from octanoate is very low. This is not due to an inappropriate fatty acid uptake by the isolated liver cells, but results from a limited capacity for fatty acid oxidation. Some 80-95% of oleate taken up is converted into esterified fats, whatever the age or the nutritional conditions. Three lines of indirect evidences suggest that fatty acid oxidation is not controlled primarily by malonyl-CoA concentration in newborn pig liver. Firstly, the addition of glucagon does not increase fatty acid oxidation or ketogenesis. Secondly, the rate of lipogenesis is very low in isolated hepatocytes from newborn pigs. Thirdly, the rates of oxidation and ketogenesis from octanoate are also decreased in isolated hepatocytes from newborn and young piglets. The huge rate of esterification of fatty acids in the liver of the newborn pigs probably represents a species-specific difference in intrahepatic fatty acid metabolism.

Development of fatty acid oxidation in neonatal guinea-pig liver

The capacity of foetal and neonatal liver to oxidize short-, medium- and long-chain fatty acids was studied in the guinea pig. Liver mitochondria from foetal and newborn animals were unable to synthesize ketone bodies from octanoate, but octanoylcarnitine and palmitoylcarnitine were readily ketogenic. The ketogenic capacity at 24 h after birth was as high as in adult animals. Hepatocytes isolated from term animals were unable to oxidize fatty acids, but at 6 h after birth production of 14CO2, acid-soluble products and acetoacetate from 1-14C-labelled fatty acids was 40-50% of the rates at 24 h. At 12 h of age these rates had already reached the 24 h values and did not change during suckling in the first week of life. The activities of hepatic fatty acyl-CoA synthetases, which were minimal in the foetus or at term, increased to maximal values in 12-24 h. The data show that the capacity for beta-oxidation and ketogenesis develops maximally in this species during the first 6-12 h after birth, and appears to be partly dependent on the development of fatty acid-activating enzyme.

Carnitine in human nutrition

The oxidation of long-chain fatty acids is carnitine-dependent. Indeed, only when they are bound to carnitine, in the form of acyl-carnitines, do fatty acids penetrate into the mitochondria to be oxidized. To meet the need for carnitine, animals depend on both endogenous synthesis and an exogenous supply. A diet rich in meat supplies a lot of carnitine, while vegetables, fruits, and grains furnish relatively little. Although it has a low molecular weight and acts at low doses in a vital metabolic pathway, carnitine should not be considered a vitamin, but rather a nutritive substance. Indeed, it seems that the diet of the adult human need not necessarily furnish carnitine: the healthy organism, given a balanced nutrition (sufficiently rich in lysine and methionine), may well be able to meet all its needs. Furthermore, it seems that a reduction of the exogenous supply of carnitine results in a lowering of its elimination in the urine. However, dietary carnitine is more important during the neonatal period. The transition from fetal to extrauterine life is accompanied by an increased role of lipids in meeting energy needs. This change is accompanied by a rise in the body of the levels of carnitine, which is mainly supplied in the maternal milk. Finally, this review briefly surveys the illnesses in which a dietary carnitine supplement proves useful.

Dietary-dependent carnitine deficiency as a cause of nonketotic hypoglycemia in an infant

Recurrent episodes of hypoglycemia, prostration, vomiting, and hepatomegaly were observed in an infant fed a carnitine-free soy formula. The extremely low plasma and urinary carnitine concentrations, elevated plasma free fatty acids, disproportionately low plasma beta hydroxybutyrate, and elevated urinary dicarboxylic acids, in the presence of a fatty liver, suggested that carnitine deficiency was the basis for this child's metabolic disturbance. When the infant was fed an enriched carnitine diet, remarkable clinical, biochemical, and histologic improvement was observed. The possibility that carnitine may be an essential nutrient for some infants is raised by the findings in this patient.

Carnitine deficiency in premature infants receiving total parenteral nutrition

Carnitine plays a significant role in fatty acid utilization and ketone body production. Its availability is especially important during the immediate postnatal period. To determine whether low birth weight infants who cannot be orally fed are at risk of developing carnitine deficiency, we compared the carnitine blood levels and urinary excretion of 12 premature infants (Group A) receiving total parenteral nutrition (TPN) with those of 8 infants of similar gestational age and birth weight (Group B) who received carnitine-containing milk formulas. In Group A, serum levels of total and free carnitine fell after 5 days of carnitine-deficient parenteral nutrition, and urinary excretion was significantly reduced. Serum levels and urinary excretion increased after the onset of oral feedings. The control Group B exhibited no significant changes in carnitine blood levels between the first and fifth days of life, but did show a later increase. Children in Group A had lower carnitine blood levels compared to those in Group B on the fifth day of life. These findings suggest that premature infants are not able to synthesize enough carnitine to maintain blood levels, and that carnitine deficiency can occur following TPN. Further investigation of metabolic consequences secondary to deficient carnitine intake in premature infants is necessary before carnitine supplementation should be considered.

Plasma carnitine levels during intravenous feeding of the neonate

The premature infant has a limited capacity for fatty acid oxidation. This study shows that solutions commonly used for intravenous feedings in the newborn infant contain no carnitine. Infants maintained on this solution have significantly lower total, free, and acylcarnitine levels as compared to when they are fed orally with expressed human milk or a proprietary formula, which is known to contain carnitine. The exogenous supply of carnitine to the premature infant may have a significant influence on the ability to stimulate optimal fatty acid oxidation.