Effect of methotrexate on long-chain fatty acid metabolism in liver of rats fed a standard or a defined, choline-deficient diet

The fetal origins of memory: the role of dietary choline in optimal brain development

Fetal nutrition sets the stage for organ function in later life. In this review we discuss the fetal and neonatal origins of brain function. Numerous research observations point to the importance of choline for the developing fetus and neonate. This essential nutrient is involved in 1-carbon metabolism and is the precursor for many important compounds, including phospholipids, acetylcholine, and the methyl donor betaine. Dietary intake of choline by the pregnant mother and later by the infant directly affects brain development and results in permanent changes in brain function. In rodents, perinatal supplementation of choline enhances memory and learning functions, changes that endure across the lifespan. Conversely, choline deficiency during these sensitive periods results in memory and cognitive deficits that also persist. Furthermore, recent studies suggest that perinatal choline supplementation can reduce the behavioral effects of prenatal stress and the cognitive effects of prenatal alcohol exposure in offspring. The likely mechanism for these effects of choline involves DNA methylation, altered gene expression, and associated changes in stem cell proliferation and differentiation. The currently available animal data on choline and hippocampal development are compelling, but studies are needed to determine whether the same is true in humans.

Genetic variation of folate-mediated one-carbon transfer pathway predicts susceptibility to choline deficiency in humans

Choline is a required nutrient, and some humans deplete quickly when fed a low-choline diet, whereas others do not. Endogenous choline synthesis can spare some of the dietary requirement and requires one-carbon groups derived from folate metabolism. We examined whether major genetic variants of folate metabolism modify susceptibility of humans to choline deficiency. Fifty-four adult men and women were fed diets containing adequate choline and folate, followed by a diet containing almost no choline, with or without added folate, until they were clinically judged to be choline-deficient, or for up to 42 days. Criteria for clinical choline deficiency were a more than five times increase in serum creatine kinase activity or a >28% increase of liver fat after consuming the low-choline diet that resolved when choline was returned to the diet. Choline deficiency was observed in more than half of the participants, usually within less than a month. Individuals who were carriers of the very common 5,10-methylenetetrahydrofolate dehydrogenase-1958A gene allele were more likely than noncarriers to develop signs of choline deficiency (odds ratio, 7.0; 95% confidence interval, 2.0-25; P < 0.01) on the low-choline diet unless they were also treated with a folic acid supplement. The effects of the C677T and A1298C polymorphisms of the 5,10-methylene tetrahydrofolate reductase gene and the A80C polymorphism of the reduced folate carrier 1 gene were not statistically significant. The most remarkable finding was the strong association in premenopausal women of the 5,10-methylenetetrahydrofolate dehydrogenase-1958A gene allele polymorphism with 15 times increased susceptibility to developing organ dysfunction on a low-choline diet.

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.

Studies on methotrexate effects on testicular steroidogenesis in rats

The effects of single dose, 4 consecutive days, 4 and 8 weekly doses of methotrexate (MTX) treatment (3 mg/kg body weight, intramuscularly) with and without leucovorin (LCN) supplementation (0.3 mg/kg body weight, intramuscularly) on serum testosterone titres, total, free and esterified cholesterol concentrations and steroidogenic enzymes, viz. 3beta- and 17beta-hydroxy steroid dehydrogenase activities were studied in adult albino rats. MTX treatment caused a marked reduction in serum testosterone titres in all the treatment groups in a duration-dependent manner. LCN supplementation did not restore serum testosterone titres to normalcy. Total and free cholesterol concentrations remained unaltered in both MTX and MTX + LCN treated groups. On the other hand, a marked increase in esterified cholesterol concentration was evident only in weekly dose treatment groups. The specific activities of 3beta- and 17beta-hydroxy steroid dehydrogenase were markedly diminished in both MTX and MTX + LCN treated groups. The results suggest the inhibitory effect of MTX on steroidogenesis.

Sources of triacylglycerol accumulation in livers of rats fed a cholesterol-supplemented diet

The source of free fatty acids (FFA) and the pathways contributing to the accumulation of neutral fats in livers of rats fed a cholesterol-enriched diet were investigated in this report. Supplementation with 1% cholesterol in the diet for four weeks resulted in hepatomegaly in the rats. The contents of cholesterol and triacylglycerols (TG) per gram liver measured in rats fasted overnight increased by 48 mg (approximately tenfold) and 66 mg (approximately fourfold), respectively. The activities of glycerophosphate acyltransferase and diacylglycerol acyltransferase, the two key enzymes for TG synthesis in liver microsomes, were found to increase by 23 and 19%, respectively, in the cholesterol-fed rats. The secretion of plasma TG present predominantly in very low density lipoprotein was found to decrease by approximately 30%. The incorporation of tritium from tritiated water in liver FFA increased by twofold in rats fed the cholesterol-supplemented diet, whereas the activity of CPT I in liver mitochondria decreased by 23%. The uptake of plasma FFA in vivo in livers of fasted rats maintained on the cholesterol-supplemented diet decreased by 60%. Our data thus indicate that the excess TG accumulated in livers of rats fed the cholesterol-enriched diet resulted from increased synthesis and decreased secretion of TG. To meet the demand of fatty acids for this purpose, de novo lipogenesis increased, whereas beta-oxidation decreased. Although difference in the uptake of extrahepatic FFA may be discounted, a difference in the uptake of chylomicron remnants between the control and cholesterol-fed rats may not be ruled out.

Fatty acid metabolism in liver of rats treated with hypolipidemic sulphur-substituted fatty acid analogues

The purpose of this study was to investigate early biochemical changes and possible mechanisms via which alkyl(C12)thioacetic acid (CMTTD, blocked for beta-oxidation), alkyl(C12)thiopropionic acid (CETTD, undergo one cycle of beta-oxidation) and a 3-thiadicarboxylic acid (BCMTD, blocked for both omega- (and beta-oxidation) influence the peroxisomal beta-oxidation in liver of rats. Treatment of rats with CMTTD caused a stimulation of the palmitoyl-CoA synthetase activity accompanied with increased concentration of hepatic acid-insoluble CoA. This effect was already established during 12-24 h of feeding. From 2 days of feeding, the cellular level of acid-insoluble CoA began to decrease, whereas free CoASH content increased. Stimulation of [1-14C]palmitoyl-CoA oxidation in the presence of KCN, palmitoyl-CoA-dependent dehydrogenase (termed peroxisomal beta-oxidation) and palmitoyl-CoA hydrolase activities were revealed after 36-48 h of CMTTD-feeding. Administration of BCMTD affected the enzymatic activities and altered the distribution of CoA between acid-insoluble and free forms comparable to what was observed in CMTTD-treated rats. It is evident that treatment of peroxisome proliferators (BCMTD and CMTTD), the level of acyl-CoA esters and the enzyme activity involved in their formation precede the increase in peroxisomal and palmitoyl-CoA hydrolase activities. In CMTTD-fed animals the activity of cyanide-insensitive fatty acid oxidation remained unchanged when the mitochondrial beta-oxidation and carnitine palmitoyltransferase operated at maximum rates. The sequence and redistribution of CoA and enzyme changes were interpreted as support for the hypothesis that substrate supply is an important factor in the regulation of peroxisomal fatty acid metabolism, i.e., the fatty acyl-CoA species appear to be catabolized by peroxisomes at high rates only when uptake into mitochondria is saturated. Administration of CETTD led to an inhibition of mitochondrial fatty acid oxidation accompanied with a rise in the concentration of acyl-CoA esters in the liver. Consequently, fatty liver developed. The peroxisomal beta-oxidation was marginally affected. Whether inhibition of mitochondrial beta-oxidation may be involved in regulation of peroxisomal fatty acid metabolism and in development of fatty liver should be considered.

Effects of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate on peroxisomal activities and enzyme activities involved in lipid metabolism in rat liver

The effects of 12-O-tetradecanoylphorbol 13-acetate (TPA) on hepatic lipids and key enzymes involved in esterification, hydrolysis and oxidation of long-chain fatty acids at increasing doses were investigated in rats. TPA administration tended to decrease the mitochondrial activities of palmitoyl-CoA synthetase and carnitine palmitoyltransferase. The microsomal palmitoyl-CoA synthetase activity was increased. TPA administration was also associated with a dose-dependent increase of glycerophosphate acyltransferase activity both in the mitochondrial and microsomal fractions in particular. The data are consistent with a decreased catabolism of long-chain fatty acids at the mitochondrial level, and an increased capacity for esterification of fatty acids in the microsomal fraction. Peroxisomal beta-oxidation was increased about 2-fold in the peroxisome-enriched fraction of TPA-treated rats while the catalase and urate oxidase activities were only marginally affected. TPA administration revealed elevated capacity for hydrolysis of palmitoyl-CoA and palmitoyl-L-carnitine in the microsomal fraction. Neither increased cytosolic palmitoyl-CoA hydrolase activity nor increased hydroxylation of lauric acid nor changes of the hepatic content of cytochrome P-450 isoenzymic forms were observed in the TPA-treated animals. There was no induction of the protein content of the bifunctional enoyl-CoA hydratase. Thus, TPA behaves more like choline-deficient diet and ethionine treatment than well-known peroxisome proliferators. It seems possible that TPA selectively stimulated the peroxisomal activities, i.e., peroxisomal beta-oxidation rather than evoking a peroxisome proliferation capacity.

Alkylthio acetic acids (3-thia fatty acids)--a new group of non-beta-oxidizable peroxisome-inducing fatty acid analogues--II. Dose-response studies on hepatic peroxisomal- and mitochondrial changes and long-chain fatty acid metabolizing enzymes in rats

The activity of key enzymes involved in oxidation and esterification of long-chain fatty acids was investigated after male Wistar rats were treated with different doses of sulfur substituted fatty acid analogues, 1,10-bis(carboxymethylthiodecane) (BCMTD, non-beta-oxidizable and non-omega-oxidizable), 1-mono(carboxymethylthiotetradecane) (CMTTD, trivial name, alkylthio acetic acid, non-beta-oxidizable) and 1-mono(carboxyethylthiotetradecane) (CETTD trivial name, alkylthio propionic acid, beta-oxidizable). The sulfur substituted dicarboxylic acid and the alkylthio acetic acid induced in a dose-dependent manner the mitochondrial, microsomal and especially the peroxisomal palmitoyl-CoA synthetase activity, the mitochondrial and cytosolic palmitoyl-CoA hydrolase activity, the mitochondrial and especially the microsomal glycerophosphate acyltransferase activity and the peroxisomal beta-oxidation, especially revealed in the microsomal fraction. Morphometric analysis of randomly selected hepatocytes revealed that BCMTD and CMTTD treatment increased the number, size and volume fraction of peroxisomes and mitochondria. Thus, the observed changes in the specific activity of fatty acid metabolizing enzymes with multiple subcellular localization can partly be explained as an effect of changes in the s-values of the organelles as proliferation of mitochondria and peroxisomes occurred. The most striking effect of the alkylthio propionic acid was the formation of numerous fat droplets in the liver cells and enhancement of the hepatic triglyceride level. This was in contrast to BCMTD treatment which decreased the hepatic triglyceride content. In conclusion, the results provide evidence that administration of non-beta-oxidizable fatty acid analogues had much higher in vivo potency in inducing hepatomegaly and key enzymes involved in fatty acid metabolism, including proliferation of peroxisomes and mitochondria than is exhibited in the beta-oxidizable, alkylthio propionic acid. Moreover, the dicarboxylic acid was apparently three to six times more potent than the alkylthio acetic acid in inducing peroxisomal beta-oxidation and peroxisome proliferation when considered on a mumol/day basis. As palmitic acid and hexadecanedioic acid only marginally affected these hepatic responses, it is conceivable that the potency of the selected compounds as proliferators of peroxisomes and inducers of the associated enzymes depends on their accessibility for beta-oxidation.