Octanoate and nonaoate oxidation increases 50-80% over the first two days of life in piglet triceps brachii and gracilis muscle strips.

An in vitro muscle strip incubation system was developed to measure the rate of catabolism of 1 mmol/L [1-(14)C]octanoate, 1 mmol/L [1-(14)C]nonanoate, 1 mmol/L [9-(14)C]nonanoate, and 10 mmol/L [U-(14)C]glucose by measuring the recovery of (14)CO(2). Muscle strips (13 mm × 1.5 mm, ~50 mg) were isolated from triceps brachii and gracilis muscles of newborn and 2-d-old, small (<950 g) and large (>1450 g) piglets. The position of the (14)C label in the substrate affected the rate and amount of recovery in (14)CO(2). Therefore, comparisons were made between age groups (0 vs. 2 d old) within substrates but limited across substrates to comparisons of [1-(14)C]-labeled fatty acids. The medium-chain fatty acid (MCFA) oxidation rates [pmol/(h · mg)] in muscle strips isolated from piglets from the 2 weight groups (<950 and >1450 g) did not differ (P > 0.99), there was a trend towards a difference between triceps brachii and gracilis muscle (P = 0.09; data not shown), and there were no significant interactions involving pig weight or muscle type; therefore, results were pooled across these factors. During the first 2 d of life, MCFA oxidation [pmol/(h • · mg muscle strip)] increased (P < 0.05) 50-80%, but the glucose oxidation rate did not change (P > 0.82). By d 2, the oxidation rate of nonanoate as represented by the one carbon was 25% greater than for octanoate (P < 0.05). The conversion of [9-(14)C]nonanoate to (14)CO(2) indicated that muscle had the capacity to oxidize the propionyl-CoA produced by ß-oxidation of nonanoate and that odd-chain C-9 MCFA provided anabolic carbon to the citric acid cycle.

Consideration of betaine and one-carbon sources of N5-methyltetrahydrofolate for use in homocystinuria and neural tube defects.

A major focus in attempts to ameliorate homocystinuria and neural tube defects is supplementation of the diet with B vitamins. The metabolic defect in these cases may be due in part to a deficiency of methyl groups. B vitamin supplementation supports the need for enzyme cofactors but cannot provide substrate in the form of methyl groups. l-Methionine is an essential amino acid and is required for protein synthesis, but it also plays a unique role in metabolism as S-adenosylmethionine, which is the primary methyl donor in metabolism. The observation that l-homocysteine, which is produced in the metabolism of l-methionine, is remethylated 2-4 times before it is destroyed is key to understanding the possibility of a methyl group deficiency. This suggests that the requirement for methyl groups (ie, S-adenosylmethionine) may be 2-4 times that for methionine in support of protein synthesis. l-Homocysteine can be remethylated to form l-methionine by betaine or N(5)-methyltetrahydrofolate. Betaine and one-carbon sources that lead to the production of N(5)-methyltetrahydrofolate and the remethylation of l-homocysteine to form l-methionine should be considered along with B vitamin supplementation in the treatment of homocystinuria and neural tube defects.

Role of S-adenosylmethionine, folate, and betaine in the treatment of alcoholic liver disease: summary of a symposium.

This report is a summary of a symposium on the role of S-adenosylmethionine (SAM), betaine, and folate in the treatment of alcoholic liver disease (ALD), which was organized by the National Institute on Alcohol Abuse and Alcoholism in collaboration with the Office of Dietary Supplements and the National Center for Complementary and Alternative Medicine of the National Institutes of Health (Bethesda, MD) and held on 3 October 2005. SAM supplementation may attenuate ALD by decreasing oxidative stress through the up-regulation of glutathione synthesis, reducing inflammation via the down-regulation of tumor necrosis factor-alpha and the up-regulation of interleukin-10 synthesis, increasing the ratio of SAM to S-adenosylhomocysteine (SAH), and inhibiting the apoptosis of normal hepatocytes and stimulating the apoptosis of liver cancer cells. Folate deficiency may accelerate or promote ALD by increasing hepatic homocysteine and SAH concentrations; decreasing hepatic SAM and glutathione concentrations and the SAM-SAH ratio; increasing cytochrome P4502E1 activation and lipid peroxidation; up-regulating endoplasmic reticulum stress markers, including sterol regulatory element-binding protein-1, and proapoptotic gene caspase-12; and decreasing global DNA methylation. Betaine may attenuate ALD by increasing the synthesis of SAM and, eventually, glutathione, decreasing the hepatic concentrations of homocysteine and SAH, and increasing the SAM-SAH ratio, which can trigger a cascade of events that lead to the activation of phosphatidylethanolamine methyltransferase, increased phosphatidylcholine synthesis, and formation of VLDL for the export of triacylglycerol from the liver to the circulation. Additionally, decreased concentrations of homocysteine can down-regulate endoplasmic reticulum stress, which leads to the attenuation of apoptosis and fatty acid synthesis.

Blood D-(-)-3-hydroxybutyrate concentrations after oral administration of trioctanoin, trinonanoin, or tridecanoin to newborn rhesus monkeys (Macaca mulatta).

Premature newborn infants are born with limited stores of glycogen and fat. Energy, such as medium-chain triglycerides (MCT), which can spare the use of body protein as metabolic energy, may be beneficial. This study compares MCT containing C8, C9, or C10 fatty acids as oral sources of energy for newborn rhesus monkeys (Macaca mulatta). On day 1 of life, 4 groups of 5 monkeys were given a single dose of water or MCT by nasogastric tube. The dose provided approximately 80% of the expected energy requirement. Plasma C8:0, C9:0, and C10:0 fatty acids and whole-blood D-(-)-3-hydroxybutyrate (3HB) concentrations were measured at 0, 1, and 3 h after dosing. Concentrations of free fatty acids (C8, C9, or C10) and ketone (3HB) increased with time after the dose. At 1 and 3 h, concentrations of C8 and C9 did not differ, but C9 was greater than C10. At 1 h, blood 3HB concentrations due to C8 triglyceride were higher than C9 or C10 (503 versus 174 and 225 µmol/L respectively). As MCT chain length increased from C8 to C10, blood concentration of 3HB decreased. Odd-chain MCT (C9 versus C8) resulted in lower whole-blood ketone (3HB), perhaps due to C9 metabolism or the rate of release or uptake of fatty acids. These results have implications for the use of MCT in nutritional supplements for preterm infants.

Unique aspects of lysine nutrition and metabolism.

Lysine nutrition is unique among indispensable amino acids in that it can be conserved and can be fed 12 h out of phase (delayed supplement) with the other dietary amino acids. In piglets, high levels (2-6%) of L-lysine added to a 10% protein diet can be tolerated without obvious detrimental effects. In both rat and piglet liver preparations, the first enzyme in the saccharopine-dependent pathway of lysine catabolism, lysine alpha-ketoglutarate reductase (LKR), is found only in the mitochondrial matrix. For Lys catabolism to occur, Lys must first enter the matrix of the mitochondrion. LKR, saccharopine dehydrogenase, mitochondrial lysine uptake, and lysine oxidation (LOX) all increased>3-fold in rats fed high levels of dietary protein (up to 60%). The activities of mitochondrial Lys uptake and LOX were similar when expressed as mmol/(d.100 g body weight). Thus, LOX can be a proxy for mitochondrial Lys uptake. Piglet liver LKR and LOX increase 5- to 10-fold when piglets are fed high-protein (50 or 75%) diets. In both the rat and piglet, after adapting to the high protein diet, the activity of LKR is 400-500 times that of LOX, suggesting that Lys uptake by a transporter(s) is rate limiting. Quantitative 24-h dietary infusion studies in piglets revealed that>80% of the Lys infused (4% of the diet) could not be recovered in the urine or body or accounted for by calculated Lys oxidation based on liver activity of LOX. Other pathways and tissues may account for the Lys oxidation in piglets.

The contribution of body protein to the supply of energy in starved newborn piglets is not preferentially suppressed by intravenous provision of glucose and fat.

Newborn piglets were used to study body protein preservation because it is critical to the survival of premature infants. Quantitative estimates of endogenous fuel use were obtained from 12 to 72 h of age in male piglets. Of the 40 piglets used (1300 +/- 205 g, mean +/- SD), 16 served as a 12-h-old body composition reference (R), 16 were starved (S) and received water only, and 8 received supplemental energy (E), obtaining 70% [210 kJ/(kg x d)] of their resting energy requirement as an i.v. mixture of glucose and Intralipid (65:35 energy ratio). Urine was collected continuously from the bladder via an umbilical urachal catheter. Total body water, glycogen, lipid, ash, and Kjeldahl-N were determined on whole-pig homogenates. Comparative slaughter was used to estimate the disappearance of body constituents of S and E pigs from 12 to 72 h of age. Midpoint body weight was used in these calculations. Supplemental energy decreased use of all body energy sources as indicated by the decrease in body dry matter disappearance, 41.6 +/- 8.8 vs. 25.5 +/- 5.9 g/kg (P = 0.0021) and protein (urinary N excretion), 995 +/- 508 vs. 329 +/- 135 mg/kg (P = 0.0119) over 60 h. Supplemental energy did not preferentially spare the percentage of the resting energy expenditure supplied by endogenous body protein (protein 37.6% +/- 9.6 vs. 41.7% +/- 10.4; lipid 25.7% +/- 5.2 vs. 20% +/- 4.1; glycogen 36.8% +/- 7.5 vs. 38.3% +/- 9.9; S vs. E) because it made up approximately 40% of the total in food-deprived and supplemented piglets.

Recovery of (15)n in the body, urine, and gas phase of piglets infused intravenously with (15)n L-alanine from 12-72 hours of age.

Previous studies of nitrogen metabolism provided evidence suggesting that nitrogen excretory product(s) not measured by standard methods of analysis escape detection. To determine whether (15)N could be recovered quantitatively in the body, urine, or expired gas, newborn piglets (n = 16; 1.47 +/- 0.27 kg) were infused intravenously with (15)N L-alanine from 12 to 72 h of age at a rate providing 25% of the piglets' resting energy expenditure and a (15)N abundance of 2.3 (n = 4), 2.8 (n = 10), or 3.3 (n = 2) atom percent. To investigate the possibility of gaseous nitrogen excretion, 4 piglets infused with (15)N L-alanine were housed in a closed circuit respiration system initially flushed with an 80% argon:20% O(2) mixture. The gas composition of the system was monitored at 12-h intervals throughout the experiment. Mean total recovery of (15)N was 93.3 +/- 2.8% and was significantly different from 100% (P < 0.001). To determine whether (15)N recovery was altered by metabolism, 2 piglets (1.34 +/- 0.13 kg) were killed 6 min after a bolus i.v. infusion of (15)N L-alanine (97.96 +/- 1.13 atom percent). Mean recovery of (15)N in the bodies of these piglets was 101.5 +/- 1.6% and was not different from 100%. No change in chamber gas (28)N(2) (P = 0.0969) or (29)N(2) (P = 0.08565) over 72 h was evident. The inability to recover 6.7 +/- 2.8% of infused (15)N suggests that a nitrogen-containing excretory product or metabolite may be escaping detection, but the discrepancy cannot be explained by gaseous nitrogen ((28)N(2), (29)N(2), or (30)N(2)) excretion.