Uptake and output of various forms of choline by organs of the conscious chronically catheterized sheep

Intermediate metabolites and molecular correlates of one‑carbon and nutrient metabolism differ in tissues from Holstein fetuses

Methionine and folate cycles along with transsulfuration comprise the one‑carbon metabolism (OCM) pathway. Amino acids and other nutrients feed into OCM, which is central to cellular function. mRNA abundance, proteins (Western blotting), and metabolites (GC-MC) associated with OCM were used to characterize these mechanisms in fetal tissues. Liver, whole intestine, and semitendinosus muscle were harvested from fetuses in 6 multiparous Holstein cows (37 kg milk/d, 100 d gestation). Data were analyzed using PROC MIXED (SAS 9.4). Protein abundance of BHMT was greatest (P < 0.01) in liver suggesting active remethylation of homocysteine to methionine. This idea was supported by the greater (P < 0.05) mRNA of CBS, BHMT, MTR, SHMT1, and MAT1A (encoding OCM enzymes) in liver. The antioxidant protein GPX3 had greatest (P < 0.05) abundance in liver, whereas the glutathione-transferase GSTM1 was 5-fold greater (P < 0.05) in intestine than liver and muscle. Greatest concentrations of glycine, serine, and taurine along with lower cysteine underscored the relevance of OCM in fetal liver. Phosphoethanolamine concentration was greatest (4-fold, P < 0.05) in intestine and along with the greatest (P < 0.05) mRNA of SLC44A1 (choline transporter), CHKA, and CEPT1 underscored the importance of the CDP-choline pathway. Greatest (P < 0.05) mRNA of PPARA, CPT1A, and HMGCS2 along with lower PCK1 in liver highlighted a potential reliance on fatty acid oxidation. In contrast, greater (P < 0.05) concentration of myo-inositol in muscle and intestine suggested both tissues rely on glucose as main source of energy. Future research should address how environmental inputs such as maternal nutrition alter these pathways in fetal tissues and their phenotypic outcomes.

Effects of Rumen-Protected Choline on Growth Performance, Carcass Characteristics and Blood Lipid Metabolites of Feedlot Lambs

Simple Summary

Choline is important for animal health, due to its involvement in the synthesis of vital molecules in the body. Several feed materials used in animal nutrition contain choline, but this naturally occurring choline is rapidly degraded in the rumen, therefore, it should be offered as rumen-protected choline (RPC) in ruminant animal species. Here we describe the results of a study that we performed with the aim of evaluating the effect of RPC on growth, carcass, and some blood metabolites in feedlot lambs. RPC supplementation did not significantly affect dry-matter intake, weight gain, gain:feed ratio, or carcass weights. Interestingly, RPC supplementation was associated with lower blood triglycerides and increased backfat thickness and yield grade, thus suggesting an effect of RPC on lipid metabolism. RPC supplementation was also associated with a reduced height to the shoulder and longissimus muscle area, suggesting an inhibitory effect of RPC on growth. The results of this study do not support the use of RPC supplementation to improve animal performance or carcass characteristics in feedlot lambs.

Abstract

Choline is an essential nutrient for animals, but dietary choline is degraded in the rumen, and thus, should be offered as rumen-protected choline (RPC) in ruminants. In this article, we investigate the effect of RPC supplementation in feedlot lambs. Forty intact male Saint Croix lambs (average: 20.3 kg, 3–4 months of age) on a high grain-low roughage base feed were randomly assigned to four treatments (0, 0.1, 0.2, and 0.3% RPC on dry-matter basis; n = 10 per group). RPC was offered for 90 days after 15 days of adaptation. RPC supplementation was not associated with significant differences in dry matter intake, weight gain, gain:feed ratio, carcass weights, and the dressing percentages. There was a linear decrease in height to the shoulder (p = 0.013) and longissimus muscle area (p = 0.051) with higher RPC levels, and a higher backfat thickness and yield grade with 0.3% RPC compared to 0.1% RPC (p < 0.05). Blood triglycerides concentrations were higher in control (0% RPC) compared to 0.3% RPC (p = 0.008). The lack of significant effects on growth performance and the results on backfat thickness and yield grade, may indicate undesirable effects associated with RPC supplementation. More research is needed to establish the needs and specific quantities of RPC supplementation in feedlot lambs.

Comparative mammalian choline metabolism with emphasis on the high-yielding dairy cow

The present review examines the importance of choline in dairy cow nutrition. Choline is an essential nutrient for mammals when excess methionine and folate are not available in the diet. The requirement for choline can be met by dietary choline and by transmethylation reactions. Two types of functions for choline are known: functions of cholineper se; functions as a methyl donor. The two principal methyl donors in animal metabolism are betaine, a metabolite of choline, and S-adenosyl-methionine, a metabolite of methionine. Choline and methionine are interchangeable with regard to their methyl group-furnishing functions. In adult ruminants, choline is extensively degraded in the rumen; for this reason dietary choline contributes insignificantly to the choline body pool and methyl group metabolism is generally conservative with a relatively low rate of methyl catabolism and an elevated rate ofde novosynthesis of methyl groups via the tetrahydrofolate system. In dairy ruminants, the dietary availability of choline is still low, but the output of methylated compounds in milk is high, and precursors from the tetrahydrofolate pathway are limiting, especially at the onset of lactation. Therefore choline may be a limiting nutrient for milk production in high-yielding dairy cows.

Interaction between cytotoxic effects of gamma-radiation and folate deficiency in relation to choline reserves

The search for non-toxic radio-protective drugs has yielded many potential agents but most of these compounds have certain amount of toxicity. Recent studies have indicated that bio-molecules such as folate and choline might be of radio-protective value as they are, within broad dose ranges, non-toxic to humans and experimental animals. The objective of the present study was to investigate choline dependent adaptive response to potential synergistic cytotoxic effect of folate deficiency and gamma-radiation. Male Swiss mice maintained on folate sufficient diet (FSD) and folate free diet (FFD) based on AIN-93M formula, were subjected to 1-4Gy total body gamma-irradiation. To investigate liver DNA damage, apurinic/apyrimidinic sites (AP sites) were quantified. A significant increase in liver DNA AP sites with concomitant depletion of liver choline reserves was observed when gamma-radiation was combined with folate deficiency. Further work in this direction suggested that cytotoxic interaction between folate deficiency and gamma radiation might induce utilization of choline and choline containing moieties by modifying levels of key regulatory enzymes dihydrofolate reductase (DHFR) and choline oxidase (ChoOx). Another major finding of these studies is that significant liver damage at higher doses of radiation (3-4Gy), might release considerable amounts of choline reserves to serum. In conclusion, a plausible interpretation of the present studies is that folate deprivation and gamma-radiation interact to mobilize additional choline reserves of hepatic tissue, for redistribution to other organs, which could not be utilized by folate deficiency alone. Present results clearly indicated a distinct choline pool in liver and kidney tissues that could be utilized by folate deficient animals only under radiation stress conditions.

Phosphoethanolamine N-methyltransferase (PMT-1) catalyses the first reaction of a new pathway for phosphocholine biosynthesis in Caenorhabditis elegans

The development of nematicides targeting parasitic nematodes of animals and plants requires the identification of biochemical targets not found in host organisms. Recent studies suggest that Caenorhabditis elegans synthesizes phosphocholine through the action of PEAMT (S-adenosyl-L-methionine:phosphoethanolamine N-methyltransferases) that convert phosphoethanolamine into phosphocholine. Here, we examine the function of a PEAMT from C. elegans (gene: pmt-1; protein: PMT-1). Our analysis shows that PMT-1 only catalyses the conversion of phosphoethanolamine into phospho-monomethylethanolamine, which is the first step in the PEAMT pathway. This is in contrast with the multifunctional PEAMT from plants and Plasmodium that perform multiple methylations in the pathway using a single enzyme. Initial velocity and product inhibition studies indicate that PMT-1 uses a random sequential kinetic mechanism and is feedback inhibited by phosphocholine. To examine the effect of abrogating PMT-1 activity in C. elegans, RNAi (RNA interference) experiments demonstrate that pmt-1 is required for worm growth and development and validate PMT-1 as a potential target for inhibition. Moreover, providing pathway metabolites downstream of PMT-1 reverses the RNAi phenotype of pmt-1. Because PMT-1 is not found in mammals, is only distantly related to the plant PEAMT and is conserved in multiple parasitic nematodes of humans, animals and crop plants, inhibitors targeting it may prove valuable in human and veterinary medicine and agriculture.

An animal model of systemic carnitine deficiency produced by haemodialysis of sheep

1. Sheep, which had previously been surgically prepared with cannulae in various vessels to monitor substrate and metabolite exchanges across all the major organs, were connected to a haemodialysis machine and their blood was dialysed at an average rate of 6.23 ml/min/kg body weight. 2. Dialysis for 4 hr reduced the blood free carnitine concentrations to approx. 50% of the initial values and the concentrations returned to the initial values after 18 hr recovery. 3. Carnitine balance studies showed that approx. twice the amount of carnitine lost from the blood during dialysis passed into the dialysate indicating that carnitine was also lost from the extracellular fluid. 4. The average blood concentration of short-chain acylcarnitines did not vary significantly during dialysis or during the recovery phase. However, an output of short-chain acylcarnitines by the liver at 3 and 18 hr recovery and an uptake by the hind-body at 18 hr recovery was observed. 5. These results suggest that haemodialysis of sheep provides a useful model of systemic carnitine deficiency and suggest that treatment with acetylcarnitine or propionylcarnitine could be an efficient means of supplying carnitine in carnitine replacement therapy.

Determination of creatinine in whole blood, plasma, and urine by high-performance liquid chromatography

A sensitive method for the specific determination of creatinine in whole blood, plasma, and urine with high precision and accuracy is described. Samples were deproteinized by addition of acetonitrile and analyzed by high-performance liquid chromatography using a cation-exchange column with a mobile phase of 9% acetonitrile in 40 mM ammonium phosphate (pH 4.0). The recoveries of creatinine added to blood and plasma were almost complete, ranging from 99 to 101%. The coefficients of variation were very small, 1.6% for blood and plasma and 1.5% for urine. Samples can be assayed in 11-min intervals subsequent to the initial injection. As little as 2 microliter of blood or plasma or 0.02 microliter of urine is sufficient for chromatographic analysis. The present method was successfully used for the accurate measurement of small arterial-venous differences of creatinine concentrations in blood across body organs and showed that in the sheep creatinine is produced in the muscles and is excreted by the kidneys. The method is also suitable for routine analysis of creatinine in clinical laboratories.

Effects of estradiol-17 beta on the net hepatic extraction of triglyceride in vivo in fed and fasted sheep

The effects of estrogen and fasting on hepatic metabolism were studied by an arteriovenous difference technique in six multicatheterized ewes. In each experiment samples were collected during fed and 3- and 5-day fasted states before, and 10 to 17 days after the animals had been implanted with 550 mg of estradiol-17 beta. The implants elevated plasma estradiol five- to seven-fold. Plasma concentrations of insulin and triglyceride (TG) were increased (P less than 0.01) by 131% and 62% respectively by estradiol in fed sheep. Concurrent circulating concentrations of glucose, glycerol, free fatty acids, and beta-hydroxybutyrate were unaffected. During fasting estradiol elevated circulating concentrations of beta-hydroxybutyrate slightly, while levels of other metabolites and insulin were not different from fasted controls. In fed animals estradiol had no effect on the net hepatic uptake (NHU) of TG or glycerol but during fasting estradiol reduced the NHU of TG and glycerol by 47% and 31% (P less than 0.01) respectively. In addition, estradiol reduced the net hepatic production of beta-hydroxybutyrate in fed, but not in fasted animals. Net hepatic exchanges of glucose, or FFA were not affected by estradiol in either the fed or fasted state. Fasting increased the NHU of TG (P less than 0.05) and glycerol (P less than 0.01). The results of this study suggest that estradiol, at physiological concentrations, has lipotropic and anti-ketogenic effects on the ruminant liver. However, the anti-ketogenic effect is not apparent in fasted animals. Secondly, it appears that the hepatic lipidosis which often occurs in ruminants during negative energy balance is due largely to an increase in the NHU of circulating TG.

Choline biosynthesis in sheep. Evidence for extrahepatic synthesis

1. Choline production by various tissues of the sheep was measured by determining venous and arterial free choline concentrations in blood samples taken from various vessels in conscious multicannulated sheep. 2. Significant production of free choline occurred in the upper and lower body regions, and specifically in the heart, brain and hind-limb muscles of sheep, but there was no significant uptake or output of phosphatidylcholine across these tissues, as determined by arterio-venous differences. 3. In contrast, in the rat there were no significant arterio-venous differences in the concentrations of free choline or phosphatidylcholine across the hind-body. 4. Synthesis of phosphatidylcholine from endogenous phosphatidylethanolamine and S-adenosyl-L-[methyl-14C]methionine was measured in experiments in vitro using microsomal preparations from a variety of sheep and rat tissues. 5. The biosynthetic activity was highest in liver from sheep and rats, although the activity in sheep microsomal preparations was about one-quarter of that in rat microsomal preparations. 6. Microsomal preparations from sheep lung, kidney, gut epithelium, brain, heart and skeletal muscles also showed considerable biosynthetic activity, but in the rat the activity was virtually confined to the liver. 7. Overall, the results show a significant production of choline in extrahepatic tissues of the sheep, with skeletal muscle contributing some 60% of this extrahepatic activity. Thus the extrahepatic production of choline in the sheep, together with the extensive reutilization of bile choline, can explain the maintenance of the large endogenous body pool of choline in this species.

Degradation of dipalmitoyl phosphatidylcholine by isolated rat granular pneumocytes and reutilization for surfactant synthesis

We investigated metabolic utilization of exogenous (modelled after lung surfactant) phospholipids by granular pneumocytes in primary culture. Cells were incubated for 21, 65, and 140 min with [3H-methyl]dipalmitoylphosphatidylcholine (DPPC) containing liposomes prepared from synthetic lipids. Radioactivity in cellular phosphatidylcholine (PC) declined steadily to 50% of the total trypsin-resistant cell-associated radioactivity. The proportion of radioactivity increased with time in cytidine-5'-diphosphate-choline and phosphorylcholine, which suggested reutilization of choline for PC synthesis. Cells incubated with liposomes for 2 h revealed that of the total cell-associated radioactivity, 7% was in lamellar bodies and 10% in the microsomal fraction. The lipid-associated radioactivity was 24% in "soluble," 96% in lamellar bodies, and 92% in the microsomal fraction. Percent of total PC label recovered in disaturated PC of microsomal fractions decreased (slope = -5.27%/h) with time of incubation (r = 0.67). Incubation of cells with liposomes containing ([3H-methyl]choline-[14C]palmitoyl) DPPC led to altered isotope ratios in both lamellar bodies and microsomes. These observations indicate that granular pneumocytes degrade exogenous PC and resynthesize PC from degradation products.

The enterohepatic recycling of bile choline in sheep

1. Measurement of unesterified choline in blood samples taken from five conscious multi-cannulated sheep indicated a significant production of unesterified choline by the alimentary tract, as judged by the portal venous minus arterial difference and significant uptake by the liver, as judged from the portal venous minus hepatic venous and arterial minus hepatic venous differences. 2. A mean liver blood flow rate of 1.68 +/- 0.22 1/min for the five sheep was determined by bromosulphophthalein clearance and, combined with the differences in unesterified choline across organs, gave a production rate of free choline of 9.1 mmol/day by the alimentary tract and an uptake by the liver of 13.2 mmol/day. 3. Infusion of [methyl-3H]choline chloride into the portal vein of a sheep over 1 hr and subsequent isolation of the bile for several days showed over 70% cumulative recovery of the radioactivity in the choline moiety of bile phosphatidylcholine over a 120 hr period. 4. Subsequent infusion 17 days later of bile lipid [3H]choline via a duodenal fistula also gave approx. 70% cumulative recovery of radioactivity in the choline moiety of newly secreted bile phosphatidylcholine in 120 hr. 5. These results show a very extensive enterohepatic recirculation of bile choline in the sheep, which is in contrast to the situation in monogastric animals.

De novo sn-glycerol-3-phosphorylcholine synthetase activity in lung and muscle and its subcellular location

The activity of glycerophosphorylcholine synthetase, a newly discovered enzyme involved in the synthesis of acyl-specific phosphatidylcholines, is reported in rat lung and muscle. Its subcellular location appears to be mitochondrial. The implication of these findings in the synthesis of lung surfactant and the pathology of muscular dystrophy are discussed.

Impaired biosynthesis of highly unsaturated phosphatidylcholines: a hypothesis on the molecular etiology of some muscular dystrophies

A brief review of the literature concerning the synthesis of phosphatidylcholine and phosphatidylethanolamine in muscle suggests that the cytidine pathways are replaced by the recently proposed acyl-specific de novo and salvage glycerolphosphodiester pathways (Infante, 1984) in fully differentiated muscle. An analysis of published data suggests an impaired synthesis of 4,7,10,13,16,19-docosahexaenoic phosphatidylcholine, at the level of de novo sn-3-glycerolphosphorylcholine synthesis, as the primary defect in Duchenne and (dy) murine muscular dystrophies. This phosphatidylcholine species is postulated to be required for optimum sarcoplasmic Ca2+ transport activity. It is proposed that this impairment initiates the secondary series of events which lead to the observed pathology of these diseases. Based on some predictions of the hypothesis, potential diagnosis and treatments are suggested.