The source of acetyl coenzyme A for acetylcholine synthesis in the perfused rat phrenic nerve-hemidiaphragm

ATP-citrate lyase deficiency in the mouse

ATP-citrate lyase (Acly) is one of two cytosolic enzymes that synthesize acetyl-coenzyme A (CoA). Because acetyl-CoA is an essential building block for cholesterol and triglycerides, Acly has been considered a therapeutic target for hyperlipidemias and obesity. To define the phenotype of Acly-deficient mice, we created Acly knockout mice in which a beta-galactosidase marker is expressed from Acly regulatory sequences. We also sought to define the cell type-specific expression patterns of Acly to further elucidate the in vivo roles of the enzyme. Homozygous Acly knockout mice died early in development. Heterozygous mice were healthy, fertile, and normolipidemic on both chow and high fat diets, despite expressing half-normal amounts of Acly mRNA and protein. Fibroblasts and hepatocytes from heterozygous Acly mice contained half-normal amounts of Acly mRNA and protein, but this did not perturb triglyceride and cholesterol synthesis or the expression of lipid biosynthetic genes regulated by sterol regulatory element-binding proteins. The expression of acetyl-CoA synthetase 1, another cytosolic enzyme for producing acetyl-CoA, was not up-regulated. As judged by beta-galactosidase staining, Acly was expressed ubiquitously but was expressed particularly highly in tissues with high levels of lipogenesis, such as in the livers of mice fed a high-carbohydrate diet. beta-Galactosidase staining was intense in the developing brain, in keeping with the high levels of de novo lipogenesis of the tissue. In the adult brain, beta-galactosidase staining was in general much lower, consistent with reduced levels of lipogenesis; however, beta-galactosidase expression remained very high in cholinergic neurons, likely reflecting the importance of Acly in generating acetyl-CoA for acetylcholine synthesis. The Acly knockout allele is useful for identifying cell types with a high demand for acetyl-CoA synthesis.

Chemistry and biochemistry of (-)-hydroxycitric acid from Garcinia

(-)-Hydroxycitric acid [(-)-HCA] is the principal acid of fruit rinds of Garcinia cambogia, Garcinia indica, and Garcinia atroviridis. (-)-HCA was shown to be a potent inhibitor of ATP citrate lyase (EC 4.1.3.8), which catalyzes the extramitochondrial cleavage of citrate to oxaloacetate and acetyl-CoA: citrate + ATP + CoA --> acetyl-CoA + ADP + P(i) + oxaloacetate. The inhibition of this reaction limits the availability of acetyl-CoA units required for fatty acid synthesis and lipogenesis during a lipogenic diet, that is, a diet high in carbohydrates. Extensive animal studies indicated that (-)-HCA suppresses the fatty acid synthesis, lipogenesis, food intake, and induced weight loss. In vitro studies revealed the inhibitions of fatty acid synthesis and lipogenesis from various precursors. However, a few clinical studies have shown controversial findings. This review explores the literature on a number of topics: the source of (-)-HCA; the discovery of (-)-HCA; the isolation, stereochemistry, properties, methods of estimation, and derivatives of (-)-HCA; and its biochemistry, which includes inhibition of the citrate cleavage enzyme, effects on fatty acid synthesis and lipogenesis, effects on ketogenesis, other biological effects, possible modes of action on the reduction of food intake, promotion of glycogenesis, gluconeogenesis, and lipid oxidation, (-)-HCA as weight-controlling agent, and some possible concerns about (-)-HCA, which provides a coherent presentation of scattered literature on (-)-HCA and its plausible mechanism of action and is provocative of further research.

Effects of organophosphates on presynaptic events in the vascularly perfused phrenic nerve-hemidiaphragm preparation from the rat

A vascularly perfused phrenic nerve-hemidiaphragm preparation from the rat was developed to study effects of physostigmine and some organophosphate inhibitors on the synthesis and release of endogenous and deuterium-labelled (choline--D9) acetylcholine (ACh) as well as the presynaptic uptake of choline. Choline and ACh were determined by combined gas chromatography/mass spectrometry. Without stimulation the endogenous levels of ACh were 320 pmole/hemidiaphragm for unlabelled and less than 1 pmole/hemidiaphragm of deuterium-labelled ACh. After stimulation at 15 Hz for 1 hr, 460 pmole/hemidiaphragm of unlabelled and 15 pmole/hemidiaphragm of deuterium-labelled ACh were found. Without stimulation the release of unlabelled ACh was 6 pmole/min/hemidiaphragm and for deuterium-labelled 0.2 pmole/min/hemidiaphragm. Evoked release (15 Hz, 1 hr) was 22 pmole/min/hemidiaphragm for unlabelled and 1.8 pmole/min/hemidiaphragm for deuterium labelled ACh. During stimulation and treatment with high concentrations (10(-5)-10(-4) M) of soman, DFP and Vx the level of unlabelled endogenous ACh increased, but the level of deuterium labelled ACh decreased in the diaphragm. During stimulation and treatment with these inhibitors the release of both unlabelled and labelled ACh decreased. During treatment with high concentrations (10(-5)-10(-4) M) of sarin and physostigmine there were no changes in endogenous levels or release of unlabelled or deuterium labelled ACh. The different effects of cholinesterase inhibitors are probably linked to the synthesis and release mechanism of ACh rather than to the choline uptake mechanism.

Ethanol interaction with drug acetylation in vivo and in vitro

The acute effect of ethanol on sulfadimidine or procainamide pharmacokinetics was studied in healthy drug-free volunteers. Ethanol treatment increased the elimination rate, as well as the amount of acetylated drug measured in blood and urine. No changes of apparent volume of distribution or renal drug clearance were found. In three out of seven slow acetylators tested, the rate of acetylation increased so noticeably after ethanol that they would otherwise have been classified as rapid acetylators. Using suspensions of isolated rat liver parenchymal cells, the effect of ethanol, acetate, citrate, pyruvate, and L(-)carnitine on acetylation of sulfanilamide and procainamide was studied. Ethanol treatment enhanced sulfanilamide acetylation, whereas the acetylation of procainamide was unchanged. Acetate, citrate, and pyruvate treatment enhanced the acetylation of both drugs. Acetate treatment increased both Km and Vmax of both sulfanilamide and procainamide acetylation. In rat liver homogenates, acetyl-CoA increased the rate of sulfanilamide acetylation in a dose-dependent manner.

Acetylcoenzyme A and acetylcholine in slices of rat caudate nuclei incubated with (-)-hydroxycitrate, citrate, and EGTA

The effects of (-)-hydroxycitrate (OHC) and citrate on the concentration of acetylcoenzyme A (acetyl-CoA) and acetylcholine (ACh) in the tissue and on the release of ACh into the medium were investigated in experiments on slices of rat caudate nuclei incubated in media with 6.2 or 31.2 mM K+, 0 or 2.5 mM Ca2+, and 0, 1, or 10 mM EGTA. OHC diminished the concentration of acetyl-CoA in the slices under all conditions used; in experiments with 2.5 mM OHC, the concentration of acetyl-CoA was lowered by 25-38%. Citrate, in contrast, had no effect on the level of acetyl-CoA in the tissue. Although both OHC and citrate lowered the concentration of ACh in the slices during incubations with 6.2 mM K+ and 1 mM EGTA, they had different effects on the content of ACh during incubations in the presence of Ca2+. The concentration of ACh in the slices was increased by citrate during incubations with 2.5 mM Ca2+ and 31.2 or 6.2 mM K+, but it was lowered or unchanged by OHC under the same conditions. The release of ACh into the medium was lowered or unchanged by OHC and lowered, unchanged, or increased by citrate. It is concluded that most effects of OHC on the metabolism of ACh can be explained by the inhibition of ATP-citrate lyase; with glucose as the main metabolic substrate, ATP-citrate lyase appears to provide about one-third of the acetyl-CoA used for the synthesis of ACh. Experiments with citrate indicate that an increased supply of citrate may increase the synthesis of ACh. The inhibitory effect of citrate on the synthesis of ACh, observed during incubations without Ca2+, is interpreted to be a consequence of the chelation of intracellular Ca2+; this interpretation is supported by the observation of a similar effect caused by 10 mM EGTA.