Use of S-adenosylmethionine as an index of methionine recycling in rat liver slices

Serum Lipid, Amino Acid and Acylcarnitine Profiles of Obese Cats Supplemented with Dietary Choline and Fed to Maintenance Energy Requirements

Obesity is a health concern for domestic cats. Obesity and severe energy restriction predispose cats to feline hepatic lipidosis. As choline is linked to lipid metabolism, we hypothesized that dietary choline supplementation would assist in reducing hepatic fat through increased lipoprotein transport and fatty acid oxidation. Twelve obese cats (body condition score [BCS] ≥ 8/9) were split into two groups. Cats were fed a control (n = 6; 4587 mg choline/kg dry matter [DM]) or a high choline diet (n = 6; 18,957 mg choline/kg DM) for 5 weeks, for adult maintenance. On days 0 and 35, fasted blood was collected, and the body composition was assessed. Serum lipoprotein and biochemistry profiles, plasma amino acids and plasma acylcarnitines were analyzed. The body weight, BCS and body composition were unaffected (p > 0.05). Choline increased the serum cholesterol, triacylglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, very low-density lipoprotein cholesterol and plasma methionine (p < 0.05) and decreased the serum blood urea nitrogen and alkaline phosphatase (p < 0.05). Choline also reduced the plasma acylcarnitine to free carnitine ratio (p = 0.006). Choline may assist in eliminating hepatic fat through increased fat mobilization and enhanced methionine recycling.

Studies on the protective effects of betaine against oxidative damage during experimentally induced restraint stress in Wistar albino rats

Stress can be defined as physical and psychological modifications that disrupt the homeostasis and the balance of organisms. Stress is known as one of the most important reasons of several diseases. In the present study, the anti-stress effect of betaine was evaluated with reference to its antioxidant property. Wistar albino rats were divided into four groups such as control, betaine, restraint stress (6 h/day for 30 days), and betaine + restraint stress. The oxidative damage was assessed by measuring the protein and corticosterone in plasma, lipid peroxidation, non-enzymic (reduced glutathione), and enzymic antioxidants (glutathione peroxidase, glutathione-S-transferase, catalase, and superoxide dismutase) in the lymphoid organs of thymus and spleen. Followed by the induction of restraint stress, the non-enzymic and enzymic antioxidants were significantly decreased with concomitant increase observed in the levels of corticosterone and lipid peroxidation. Oral pretreatment with betaine (250 mg/kg body weight daily for a period of 30 days) significantly (P < 0.001) prevented the restraint stress-induced alterations in the levels of protein and corticosterone in plasma of experimental groups of rats. It counteracted the restraint stress-induced lipid peroxidation and maintained the antioxidant defense system in the lymphoid tissues at near normal. The findings suggest that betaine possesses significant anti-stress activity, which may be due to its antioxidant property.

Effects of choline deficiency and methotrexate treatment upon rat liver

Choline deficiency and treatment with methotrexate (MTX) both are associated with fatty infiltration of the liver. Choline, methionine, and folate metabolism are interrelated and converge at the regeneration of methionine from homocysteine. MTX perturbs folate metabolism, and it is possible that it also influences choline metabolism. We fed rats a choline deficient diet for 2 weeks and/or treated them with methotrexate (MTX; 0.1 mg/kg daily). Choline deficiency lowered hepatic concentrations of choline (to 43% control), phosphocholine (PCho; to 18% control), glycerophosphocholine (GroPCho; to 46% control), betaine (to 30% control), phosphatidylcholine (PtdCho; to 62% control), methionine (to 80% control), and S-adenosylmethionine (AdoMet; to 57% control), while S-adenosylhomocysteine (AdoHcy) and triacylglycerol concentrations increased (to 126% and 319% control, respectively). MTX treatment alone lowered hepatic concentrations of PCho (to 48% control), GroPCho (to 69% control), betaine (to 55% control), and AdoMet (to 75% control). The addition of MTX treatment to choline deficiency resulted in a larger decrease in AdoMet concentrations (to 75% control) and larger increases in AdoHcy and triacylglycerol concentrations (to 150% and 500% control, respectively) than was observed in choline deficiency alone. Livers from MTX-treated animals used radiolabeled choline to make the same metabolites as did livers from controls (most of the label was converted to PCho and betaine). In choline deficient animals, most of the labeled choline was converted to PtdCho. Therefore, MTX depleted hepatic PCho, GroPCho, and betaine by a mechanism that was different from that of choline deficiency. MTX increased the extent of fatty infiltration of the liver in choline deficient rats, and choline deficiency and MTX treatment damaged hepatocytes as measured by leakage of alanine aminotransferase activity. Our data are consistent with the hypothesis that the fatty infiltration of the liver associated with MTX treatment occurs because of a disturbance in choline metabolism.

Betaine in human nutrition

Betaine is distributed widely in animals, plants, and microorganisms, and rich dietary sources include seafood, especially marine invertebrates ( approximately 1%); wheat germ or bran ( approximately 1%); and spinach ( approximately 0.7%). The principal physiologic role of betaine is as an osmolyte and methyl donor (transmethylation). As an osmolyte, betaine protects cells, proteins, and enzymes from environmental stress (eg, low water, high salinity, or extreme temperature). As a methyl donor, betaine participates in the methionine cycle-primarily in the human liver and kidneys. Inadequate dietary intake of methyl groups leads to hypomethylation in many important pathways, including 1) disturbed hepatic protein (methionine) metabolism as determined by elevated plasma homocysteine concentrations and decreased S-adenosylmethionine concentrations, and 2) inadequate hepatic fat metabolism, which leads to steatosis (fatty accumulation) and subsequent plasma dyslipidemia. This alteration in liver metabolism may contribute to various diseases, including coronary, cerebral, hepatic, and vascular diseases. Betaine has been shown to protect internal organs, improve vascular risk factors, and enhance performance. Databases of betaine content in food are being developed for correlation with population health studies. The growing body of evidence shows that betaine is an important nutrient for the prevention of chronic disease.

Effect of acute betaine administration on hepatic metabolism of S-amino acids in rats and mice

Alterations of hepatic glutathione level by betaine were observed previously. In this study effects of betaine administration (1000 mg/kg, i.p.) on S-amino acid metabolism in rats and mice were investigated. Hepatic glutathione level decreased rapidly followed by marked elevation in 24 hr. Concentrations of S-adenosylmethionine, S-adenosylhomocysteine, and methionine were increased whereas cystathionine decreased significantly, suggesting that homocysteine generated in the methionine cycle is preferentially remethylated to methionine rather than being utilized for synthesis of cysteine. Hepatic cysteine concentration declined immediately, but plasma cysteine increased. Effect of betaine on hepatic cysteine uptake was estimated from the difference in cysteine concentration in major blood vessels connected to liver. Cysteine concentration either in the portal vein or abdominal aorta was not altered, however, a significant increase was noted in the hepatic vein, indicating that hepatic uptake of cysteine was decreased by betaine treatment. Activities of glutamate cysteine ligase, cystathionine beta-synthase, and cystathionine gamma-lyase were elevated in 24 hr. Pretreatment with propargylglycine, an irreversible inhibitor of cystathionine gamma-lyase, did not abolish the betaine-induced reduction of hepatic glutathione in 4 hr, however, the elevation at t=24 hr was blocked completely. In conclusion the present results indicate that betaine administration induces time-dependent changes on hepatic metabolism of S-amino acids. Betaine enhances metabolic reactions in the methionine cycle, but inhibits cystathionine synthesis and cysteine uptake, leading to a decrease in supply of cysteine for glutathione synthesis. Reduction in glutathione is subsequently reversed due to induction of cysteine synthesis and glutamate cysteine ligase activity.

Diethyl maleate, an in vivo chemical depletor of glutathione, affects the response of male and female rats to arsenic deprivation

An experiment was performed to determine the effect of diethyl maleate (DEM), an in vivo depletor of glutathione, on the response of male and female rats to arsenic deprivation. A 2 x 2 x 2 factorially arranged experiment used groups of six weanling Sprague-Dawley rats. Dietary variables were arsenic at 0 or 0.5 microgram/g and DEM at 0 or 0.25%; the third variable was gender. Animals were fed for 10 wk a casein-ground corn based diet that contained amounts of calcium, phosphorus, and magnesium similar to the AIN-76 diet. DEM supplementation increased blood arsenic in both male and female rats; female rats had the greatest amount of arsenic in whole blood. Although female rats in general had a lower concentration of glutathione in liver, those fed no supplemental DEM, regardless of their arsenic status, had the lowest amounts. Compared to males, female rats had a lower activity of liver glutathione S-transferase (GST). Arsenic deprivation decreased, and DEM supplementation increased liver GST activity in both male and female rats. Lung GST activity was also increased by DEM supplementation in male, but not female, rats. The most striking finding of the study was that compared to males, females had extremely elevated kidney calcium concentrations, and that the elevation was exacerbated by arsenic deprivation. DEM supplementation also exacerbated the accumulation of calcium in the kidney of the female rats. The response of the rat to both DEM and arsenic was, for many variables, dependent on gender. This gender dependence may be explained by the differences in methionine metabolism between male and female rats. Thus, arsenic deprivation apparently can manifest itself differently depending on gender.

Choline: an important nutrient in brain development, liver function and carcinogenesis

Choline is required to make certain phospholipids which are essential components of all membranes. It is a precursor for biosynthesis of the neurotransmitter acetylcholine and also is an important source of labile methyl groups. Much attention has been given to the effect of supplemental choline upon brain function, i.e., enhancement of acetylcholine synthesis and release. In addition, choline supplements administered to rats in utero or shortly after birth permanently after brain function. The mechanisms for this effect is unknown and under investigation at this time. Healthy humans fed diets deficient in choline, and humans fed parenterally have decreased plasma choline concentrations and develop liver dysfunction that is similar to that seen in choline-deficient animals. In experimental animals, fatty liver occurs in choline deficiency because phosphatidylcholine synthesis is required for very low-density lipoprotein secretion. This accumulation of lipids in liver may explain why choline-deficient rats spontaneously develop hepatocarcinoma. We found that choline deficiency was associated with the accumulation of 1,2-diacylglycerol, an activator of protein kinase C. Several lines of evidence indicate that cancers might develop secondary to abnormalities in protein kinase C-mediated signal transduction.

Effect of choline deficiency on S-adenosylmethionine and methionine concentrations in rat liver

Choline and C1 metabolism pathways intersect at the formation of methionine from homocysteine. Hepatic S-adenosylmethionine (AdoMet) concentrations are decreased in animals ingesting diets deficient in choline, and it has been suggested that this occurs because the availability of methionine limits AdoMet synthesis. If the above hypothesis is correct, changes in hepatic AdoMet concentrations should relate in some consistent manner to changes in hepatic methionine concentrations. Rats were fed on a choline-deficient or control diet for 1-42 days. Hepatic choline concentrations in control animals were 105 nmol/g, and decreased to 50% of control after the first 7 days on the choline-deficient diet. Hepatic methionine concentrations decreased by less than 20%, with most of this decrease occurring between days 3 and 7 of choline deficiency. Hepatic AdoMet concentrations decreased by 25% during the first week, and continued to decrease (in total, by over 60%) during each subsequent week during which animals consumed a choline-deficient diet. Hepatic S-adenosylhomocysteine (AdoHcy) concentrations increased by 50% when animals consumed a choline-deficient diet. AdoHcy is formed when AdoMet is utilized as a methyl donor. In summary, choline deficiency can deplete hepatic stores of AdoMet under dietary conditions that only minimally decrease the availability of methionine within liver. Thus decreased availability of methionine may not have been the only mechanism whereby choline deficiency lowers hepatic AdoMet concentrations. We suggest that increased utilization of AdoMet might also have occurred.

Brain tumor protein synthesis and histological grades: a study by positron emission tomography (PET) with C11-L-Methionine

Brain protein synthesis may be evaluated in vivo by a PET three compartment methionine model. 14 human brain tumor patients were studied. Protein synthesis rate (PSR) was increased in any glial tumor even in low grades, but this increase was statistically more important in anaplastic tumor. Radiotherapy action was evaluated in two patients. Local tumoral PSR was reduced to normal brain PSR after treatment. No difference was seen in normal cortex contralateral to the lesion between pre and post radiotherapy examination. 11 C-L-Methionine incorporation measured by PET looks as a very sensitive method for studying tumor metabolism and treatment effects.

Comparative studies on the methionine synthesis in sheep and rat tissues

The important features of the enzymes involved in methionine synthesis in sheep were found to be the low activity of betaine-homocysteine methyltransferase and the high activity of 5-methyltetrahydrofolate-homocysteine methyltransferase. The rate of the methionine synthesis in sheep liver was significantly lower than that in rats due to the low activity of hepatic betaine-homocysteine methyltransferase. The hepatic methionine recycling was stimulated by the addition of betaine in both species. These results indicate that in sheep 5-methyltetrahydrofolate-homocysteine methyltransferase plays a significant role in hepatic methionine synthesis along with betaine-homocysteine methyltransferase. In contrast, in the rat hepatic system methionine synthesis is virtually dependent on betaine-homocysteine methyltransferase.