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PubMed1993

Utilization of ketone bodies by chick brain and spinal cord during embryonic and postnatal development.

Lipid synthesis from acetoacetate and 3-hydroxybutyrate was studied in chick embryo from 15 to 21 days and in chick neonate from 1 to 21 days. Embryonic spinal cord showed higher ability than brain to incorporate acetoacetate into total lipids, although a sharp decrease was found at hatching. 3-Hydroxybutyrate incorporation into total lipids was also higher in spinal cord than in brain, especially during the embryonic period. Phospholipids were the main lipids formed in both tissues from both precursors. An appreciable percentage of radioactivity was also recovered as free cholesterol, especially during the embryonic phase. The developmental patterns of amino acid synthesis from acetoacetate and 3-hydroxybutyrate were similar in both tissues: a clear increase after hatching was followed by a decrease at day 4 of neonatal life. Acetoacetate was a better substrate for amino acid synthesis than 3-hydroxybutyrate during the embryonic development in both tissues. Oxidation of both precursors to CO2 strongly decreased between 15 and 21 days of embryonic development both in brain and spinal cord.

3-Hydroxybutyric Acid↗
PubMed2004

Enantioselective reduction of carbonyl compounds by whole-cell biotransformation, combining a formate dehydrogenase and a (R)-specific alcohol dehydrogenase.

A whole-cell biotransformation system for the reduction of prochiral carbonyl compounds, such as methyl acetoacetate, to chiral hydroxy acid derivatives [methyl (R)-3-hydroxy butanoate] was developed in Escherichia coli by construction of a recombinant oxidation/reduction cycle. Alcohol dehydrogenase from Lactobacillus brevis catalyzes a highly regioselective and enantioselective reduction of several ketones or keto acid derivatives to chiral alcohols or hydroxy acid esters. The adh gene encoding for the alcohol dehydrogenase of L. brevis was expressed in E. coli. As expected, whole cells of the recombinant strain produced only low quantities of methyl (R)-3-hydroxy butanoate from the substrate methyl acetoacetate. Therefore, the fdh gene from Mycobacterium vaccae N10, encoding NAD+-dependent formate dehydrogenase, was functionally coexpressed. The resulting two-fold recombinant strain exhibited an in vitro catalytic alcohol dehydrogenase activity of 6.5 units mg-1 protein in reducing methyl acetoacetate to methyl (R)-3-hydroxy butanoate with NADPH as the cofactor and 0.7 units mg-1 protein with NADH. The in vitro formate dehydrogenase activity was 1.3 units mg-1 protein. Whole resting cells of this strain catalyzed the formation of 40 mM methyl (R)-3-hydroxy butanoate from methyl acetoacetate. The product yield was 100 mol% at a productivity of 200 micromol g-1 (cell dry weight) min-1. In the presence of formate, the intracellular [NADH]/[NAD+] ratio of the cells increased seven-fold. Thus, the functional overexpression of alcohol dehydrogenase in the presence of formate dehydrogenase was sufficient to enable and sustain the desired reduction reaction via the relatively low specific activity of alcohol dehydrogenase with NADH, instead of NADPH, as a cofactor.

Acetoacetates↗
PubMed1990

Effects of ketone bodies on carbohydrate metabolism in non-insulin-dependent (type II) diabetes mellitus.

The ability of ketone bodies to suppress elevated hepatic glucose output was investigated in eight postabsorptive subjects with non-insulin-dependent diabetes mellitus (NIDDM). Infusion of sodium acetoacetate alone (20 mumols/kg/min) for 3 hours increased total serum ketones (beta-hydroxybutyrate and acetoacetate) to approximately 6 mmol/L, but did not reduce plasma glucose (14.0 +/- 0.8 to 12.3 +/- 0.9 mmol/L) or isotopically determined hepatic glucose output (17.5 +/- 1.4 to 12.7 +/- 1.0 mumols/kg/min) more than saline alone. Plasma C-peptide concentrations were unchanged, while serum glucagon increased from 131 +/- 13 to 169 +/- 24 ng/mL (P less than .015) and free fatty acids were suppressed by 43% (0.35 +/- 0.08 to 0.20 +/- 0.06 mmol/L, P less than .025). When sodium acetoacetate was infused with somatostatin (0.10 micrograms/kg/min) to suppress glucagon and insulin secretion, the decrease in both plasma glucose (13.3 +/- 0.9 to 10.2 +/- 0.7 mmol/L) and hepatic glucose output (17.2 +/- 1.6 to 9.4 +/- 0.6 mumols/kg/min) was greater than either acetoacetate or somatostatin infusion alone. Infusion of equimolar amounts of sodium bicarbonate had no effect on glucose metabolism. In conclusion, these results demonstrate that ketone bodies can directly suppress elevated hepatic glucose output in NIDDM independent of changes in insulin secretion, but only when the concomitant stimulation of glucagon secretion is prevented. Ketone bodies also suppress adipose tissue lipolysis in the absence of changes in plasma insulin and may serve to regulate their own production.

Acetoacetates↗
PubMed1996

Ketoacids attenuate glucose uptake in human trophoblasts isolated from first-trimester chorionic villi.

OBJECTIVE: The objective of this study was to evaluate the hypothesis that ketoacids (acetoacetic acid and beta-hydroxybutyrate) diminish glucose transport in trophoblasts cultured from first-trimester chorionic villi. STUDY DESIGN: First-trimester trophoblasts were obtained by transabdominal chorionic villus sampling for subsequent cytogenetic analysis. The cells were established as a continuous line exhibiting trophoblast characteristics. Trophoblasts were cultured in Ham's F12/Dulbecco's modified Eagle's medium (1:1) supplemented with 15% fetal bovine serum. Experiments were initiated by a 24-hour preincubation in serum-free Ham's F12/Dulbecco's modified Eagle's medium followed by incubation with ketoacids (acetoacetic acid and beta-hydroxybutyrate, 0 to 10 mmol/L) in the presence or absence of insulin-like growth factor-I (100 ng/ml). The cells were challenged with 2-deoxy-[1,2-3H]D-glucose (0.1 mmol/L) for 5 minutes and then cell-associated radioactivity was measured. Total ribonucleic acid was extracted from cells incubated with ketoacids in the presence or absence of insulin-like growth factor-I, and Northern blots were probed with a phosphorus 32-labeled complementary deoxyribonucleic acid fragment encoding the rat GLUT 1. RESULTS: Ketoacids caused a dose-dependent inhibition of glucose transport. At 5 mmol/L acetoacetic acid there was a > 50% reduction in the rate of glucose transport in both control and insulin-like growth factor-I-treated cells. The diminution in glucose uptake by trophoblasts was not due to cellular toxicity of the ketoacids because there was no significant difference in trypan blue exclusion or lactate dehydrogenase release between control and ketoacid-treated cells. Northern analysis revealed that the steady-state expression of GLUT1 messenger ribonucleic acid was diminished in ketone-treated cells, but this effect was overcome by coincubation of cultures with insulin or insulin-like growth factor-I. CONCLUSIONS: These results indicate that ketoacids can suppress the uptake of glucose into first-trimester human trophoblasts. Because ketoacidosis in pregnant women with diabetes mellitus is a frequent clinical consequence of poor metabolic control, it is possible that elevated levels of acetoacetic acid and beta-hydroxybutyrate may impair the transport of glucose across the placental trophoblast and into the fetal circulation.

Acetoacetates↗
PubMed1971

Ketone-body utilization by adult and suckling rat brain in vivo.

1. Ketone-body utilization in fed and starved adult and suckling rats has been investigated by measuring arterio-venous differences across the brain. Venous blood was collected from the confluence of sinuses and arterial blood from the femoral artery in adult rats and by cardiac puncture in suckling rats. 2. During starvation the arterio-venous difference of ketone bodies increased in proportion to their concentrations in the blood and reached a value of 0.16mm at 48h. At a given concentration of the respective ketone bodies the arterio-venous differences of acetoacetate were about twice those of 3-hydroxybutyrate. 3. Fed rats in which the concentrations of ketone bodies were raised by intravenous infusion of sodium acetoacetate had the same arterio-venous differences as starved rats at corresponding ketone-body concentrations. Thus the ability of the rat brain to utilize ketone bodies is independent of the nutritional state. 4. The concentrations of glucose, acetoacetate and 3-hydroxybutyrate were much lower in the brain than in the arterial blood. The measured (blood concentration)/(brain concentration) ratio was 4.4 for glucose, 4.5 for acetoacetate and 8.1 for 3-hydroxybutyrate in 48h-starved rats. 5. The mean arterio-venous difference of glucose across the brain was 0.51mm in fed rats and 0.43mm in 96h-starved rats. 6. Conversion of glucose into lactate rose from negligible values in the fed state to 0.2mm after 48h starvation and decreased to zero after 96h starvation. 7. In 16-22-day-old suckling rats the arterio-venous differences of ketone bodies across the brain were also proportional to the ketone-body concentration, but they were about 3-4 times greater than in adult rats at the same blood ketone-body concentration. 8. Arterio-venous differences of glucose were about the same in adult and suckling rats. 9. The brain of fed suckling rats formed more lactate from glucose than fed adult rats. 10. The results indicate that ketone bodies are major metabolic fuels of the brain of the suckling rat under normal conditions.

Acetoacetates↗
PubMed1973

D-3-hydroxybutyrate dehydrogenase from Rhodopseudomonas spheroides. Kinetics of radioisotope redistribution at chemical equilibrium catalysed by the enzyme in solutions.

1. The reversible NAD(+)-linked oxidation of d-3-hydroxybutyrate to acetoacetate in 0.1m-sodium pyrophosphate buffer, pH8.5, at 25.0 degrees C, catalysed by d-3-hydroxybutyrate dehydrogenase (d-3-hydroxybutyrate-NAD(+) oxidoreductase, EC 1.1.1.30), was studied kinetically at chemical equilibrium by monitoring radioisotope redistribution with sodium dl-hydroxy[3-(14)C]butyrate and [4-(3)H]NAD(+)(labelled in the nicotinamide ring). 2. When all substrates are maintained at concentrations approaching saturation (approx. 3-50 times the K(m) values) the first-order rate constant for the enzyme-catalysed interconversion of NAD(+) and NADH is much smaller than that for the enzyme-catalysed interconversion of d-3-hydroxybutyrate and acetoacetate. 3. The rate of interconversion of NAD(+) and NADH increases initially with increasing concentrations of d-3-hydroxybutyrate and acetoacetate (ratio of concentrations maintained constant), passes through a maximum and approaches closely to zero at saturating concentrations of the latter substrates. 4. The rates of interconversion of NAD(+) and NADH and of d-3-hydroxybutyrate and acetoacetate increase with increasing concentration of NAD(+) (up to 66 times its K(m) value) and NADH (up to 180 times its K(m) value) (ratio of the concentrations of the nicotinamide nucleotides maintained constant). 5. These findings support the description of this catalysis as an ordered Bi Bi mechanism with no detectable alternative pathway, in which the interconversion of the central ternary complexes is not rate-limiting, and provide no evidence for the formation of dead-end complexes. 6. The solubility of 2,4-dinitrophenylhydrazine in HCl exhibits an acidity optimum, the maximum solubility at 25.0 degrees C (3.8mg/ml, 19mm) occurring at 2.29m-HCl; in solutions of this acidity acetone 2,4-dinitrophenylhydrazone is relatively insoluble (0.098mg/ml, 0.413mm).

Acetoacetates↗
PubMed1976

Effect of hyperphenylalaninaemia on lipid synthesis from ketone bodies by rat brain.

The effect of hyperphenylalaninaemia on the metabolism of ketone bodies in vivo and in vitro by developing rat brain was investigated. The incorporation in vivo of [14C]acetoacetate into cerebral lipids was decreased by both chronic (for 3 days) and acute (for 6h) hyperphenylalaninaemia induced by injecting phenylalanine into 1-week-old rats. In studies in vitro it was observed that the incorporation of the radioactivity from [14C]acetoacetate and 3-hydroxy[14C]butyrate into cerebral lipids was inhibited by phenyl-pyruvate, but not by phenylalanine. Phenylpyruvate also inhibited the incorporation of 3H from 3H2O into lipids by brain slices metabolizing either 3-hydroxybutyrate or acetoacetate in the presence of glucose. These findings suggest that the decrease in the incorporation in vivo of [14C]acetoacetate into cerebral lipids in hyperphenylalaninaemic rats is most likely caused by phenylpyruvate and not by phenylalanine. Phenylpyruvate as well as phenylalanine had no inhibitory effects on ketone-body-catabolizing enzymes, namely 3-hydroxybutyrate dehydrogenase, 3-oxo acid CoA-transferase and acetoacetyl-CoA thiolase, in rat brain. Phenylpyruvate but not phenylalanine inhibited the activity of the 2-oxoglutarate dehydrogenase complex from rat and human brain. These findings suggest that the metabolism of ketone bodies is impaired in brains of untreated phenylketonuric patients, and in turn may contribute to the diminution of mental development and function associated with phenylketonuria.

Acetoacetates↗
PubMed1976

Effects of ketone bodies on amino acid metabolism in isolated rat diaphragm.

1. Diaphragms from 48h-starved rats were incubated in Krebs-Ringer bicarbonate medium at 37degreesC for 30min and then transferred into new medium and incubated for 1, 2 and 3 h. 2. The amount of free amino acids found at the end of each time of incubation was larger than the amount at the beginning of incubation, indicating that in this system proteolysis is prevailing. 3. The diaphragms was releasing mainly alanine and glutamine into the incubation medium. 4. Within the periods of incubation the release and metabolism of free amino acids was proceeding at a constant rate. 5. Addition of sodium DL-3-hydroxybutyrate decreased the tissue content of several amino acids, among which were tyrosine and phenylalanine, suggesting that proteolysis was decreased by ketone bodies. 6. In the presence of glucose (10mM) and branched-chain amino acids (0.5mM), sodium DL-3-hydroxybutyrate at concentrations of 4 or 6 mM resulted in 30% decrease in tissue alanine content and a 20% decline in alanine release. Release of taurine and glutamine was decreased by 19 and 16% respectively with 6 mM-sodium DL-3-hydroxybutyrate. Addition of sodium acetoacetate (1-3mM) also resulted in a 20-35% decrease in tissue content of alanine, glutamine and taurine and in a 15-24% decrease of alanine and glutamine release. Smaller decreases (less than 15%) in the release of glycine, threonine, proline, serine and aspartate were also observed in the presence of sodium DL-3-hydroxybutyrate or sodium acetoacetate. 7. Substitution of pyruvate (1.0mM) for glucose in the presence of acetoacetate restored alanine and glutamine production to control values. In the presence of acetoacetate, pyruvate also increased the tissue content of aspartate by 77% and decreased the tissue content of glutamate by 30%. 8. It is suggested that in diaphragms from starved rats, ketone bodies (a) in the absence of other substrates inhibit protein catabolism and (b) in the presence of glucose and branched-chain amino acids decrease alanine and glutamine production, by inhibiting glycolysis.

Acetoacetates↗
PubMed1976

Effect of ischaemic limb injury on the rates of metabolism of ketone bodies in starved rats.

1. Rats starved for 30h were injected with trace amounts of [3-14C]acetoacetate and beta-hydroxy[3-14C]butyrate 1h after ischaemic limb injury in a 20 degrees C environment, and the concentrations and radioactivities of blood ketone bodies were determined at intervals. 2. Starvation alone raised the rates of production and utilization of beta-hydroxybutyrate plus acetoacetate about 3.7-fold, but lowered their metabolic clearance rates by about 50%. In the starved rat ketone-body oxidation could account for up to 30% of whole body O2 consumption. 3. Injury in starved rats lowered the rates of production and utilization of both beta-hydroxybutyrate and acetoacetate, the combined fall of about 37% slightly exceeding the concomitant fall in whole-body O2 consumption. The concentration of beta-hydroxybutyrate decreased after injury, but its metabolic clearance rate was unaltered; the concentration of acetoacetate rose slightly and its metabolic clearance rate fell.

Acetoacetates↗
PubMed1978

Formation and utilization of 3-hydroxy-3-methylglutarate in liver mitochondria of starved and streptozotocin-diabetic rats.

Kidney and liver mitochondria of rat, rabbit and guinea pig are able to transform 3-hydroxy-3-methylglutarate into acetoacetate, whereas ox liver mitochondria and rat mitochondria of heart, diaphragm and brain do not exhibit such an activity. Starvation and streptozotocin treatment decreases the formation of acetoacetate from 3-hydroxy-3-methylglutarate. Addition of acetoacetate and succinate to the incubation media of mitochondria results in a decrease in the transformation of 3-hydroxy-3-methylglutarate into acetoacetate. A 3-hydroxy-3-methylglutaryl-CoA hydrolase is present in rat liver mitochondria; the activity does not show appreciable changes after starvation or streptozotocin treatment.

Acetoacetates↗
PubMed1979

The metabolism of 4-methyl-2-oxopentanoate in rat pancreatic islets.

1. Radioactively labelled 4-methyl-2-oxopentanoate was taken up by isolated pancreatic islets in a concentration- and pH-dependent manner and led to the intracellular accumulation of labelled amino acid and to a decrease in the intracellular pH. Uptake of 4-methyl-2-oxopentanoate did not appear to be either electrogenic or Na+-dependent. The islet content of 2-oxo acid radioactivity was not affected by either 2-cyano-3-hydroxy-cinnamate (10mM) or pyruvate (10mM), although both these substances inhibited the oxidation of [U-14C]4-methyl-2-oxopentanoate by islet tissue. 2. 4-Methyl-2-oxopentanoate markedly stimulated islet-cell respiration, ketone-body formation and biosynthetic activity. The metabolism of endogenous nutrients by islets appeared to be little affected by the compound. 3. Studies with the 3H- and 14C-labelled substrate revealed that 4-methyl-2-oxopentanoate was incorporated by islets into CO2, water, acetoacetate, L-leucine and to a lesser extent into islet protein and lipid. Carbon atoms C-2, C-3 and C-4 of the acetoacetate produced were derived from the carbon skeleton of the 4-methyl-2-oxopentanoate, but the acetoacetate carboxy group was derived from the incorporation of CO2. These results, and consideration of the relative rates of 14CO2 and acetoacetate formation from 1-14C-labelled as opposed to U-14C-labelled 4-methyl-2-oxopentanoate, led to the conclusion that the pathway of catabolism of this 2-oxo acid in pancreatic islets is identical with that described in other tissues. The amination of 4-methyl-2-oxopentanoate by islets was attributed to the presence of a branched-chain amino acid aminotransferase (EC 2.6.1.42) activity in the tissue. Although glutamate dehydrogenase activity was demonstrated in islet tissue, the reductive amination of 2-oxoacids did not seem to be of importance in the formation of leucine from 4-methyl-2-oxopentanoate. 4. The results of experiments with respiratory inhibitors and uncouplers, and the finding that 14CO2 production and islet respiration were linked in a 1:1 stoicheiometry suggested that 4-methyl-2-oxopentanoate catabolism was coupled to mitochondrial oxidative phosphorylation. The catabolism of 4-methyl-2-oxopentanoate in islet tissue appeared to be regulated at the level of the initial 2-oxo acid dehydrogenase (EC 1.2.1.25) reaction.

Acetoacetates↗
PubMed1983

Effect of fatty acids and ketones on the activity of pyruvate dehydrogenase in skeletal-muscle mitochondria.

The presence of palmitoyl-L-carnitine and acetoacetate (separately) decreased flux through pyruvate dehydrogenase in isolated mitochondria from rat hind-limb muscle. The effect of acetoacetate was dependent on the presence of 2-oxoglutarate and Ca2+. Palmitoylcarnitine, but not acetoacetate, also decreased the mitochondrial content of active dephospho-pyruvate dehydrogenase (PDHA). This effect was large only in the presence of EGTA. Addition of Ca2+-EGTA buffers stabilizing pCa values of 6.48 or lower gave near-maximal values of PDHA content, irrespective of the presence of fatty acids or ketones when mitochondria were incubated under the same conditions used for the flux studies, i.e. at low concentrations of pyruvate. There was, however, a minor decrement in PDHA content in response to palmitoylcarnitine oxidation when the substrate was L-glutamate plus L-malate. Measurement of NAD+, NADH, CoA and acetyl-CoA in mitochondrial extracts in general showed decreases in [NAD+]/[NADH] and [CoA]/[acetyl-CoA] ratios in response to the oxidation of palmitoylcarnitine and acetoacetate, providing a mechanism for both decreased PDHA content and feedback inhibition of the enzyme in the PDHA form. However, only changes in [CoA]/[acetyl-CoA] ratio appear to underlie the decreased PDHA content on addition of palmitoylcarnitine when mitochondria are incubated with L-glutamate plus L-malate (and no pyruvate) as substrate. The effect of palmitoylcarnitine oxidation on flux through pyruvate dehydrogenase and on PDHA content is less marked in skeletal-muscle mitochondria than in cardiac-muscle mitochondria. This may reflect the less active oxidation of palmitoylcarnitine by skeletal-muscle mitochondria, as judged by State-3 rates of O2 uptake. In addition, Ca2+ concentration is of even greater significance in pyruvate dehydrogenase interconversion in skeletal-muscle mitochondria than in cardiac-muscle mitochondria.

Acetoacetates↗
PubMed1997

Effects of ketone bodies on astrocyte amino acid metabolism.

The effects of acetoacetate and 3-hydroxybutyrate on glial amino acid metabolism were studied in primary cultures of astrocytes. The exchange of nitrogen among amino acids was measured with 15N as a metabolic probe and gas chromatography-mass spectrometry as a tool with which to quantify isotope abundance. Addition of either acetoacetate or 3-hydroxybutyrate (5 mM) to the incubation medium did not alter the initial rate of appearance of [15N]glutamate in the glia, but it did inhibit transamination of glutamate to [15N]aspartate. Addition of acetoacetate also inhibited formation of [2-(15)N]glutamine, but 3-hydroxybutyrate had a stimulatory effect. The presence in the medium of sodium acetate (5 mM) was also associated with diminished production of [15N]aspartate and [2-(15)N]glutamine with [15N]glutamate as precursor. Studies with [2-(15)N]glutamine as precursor indicated that treatment of the astrocytes with ketone bodies did not alter flux through the glutaminase pathway. Nor did the presence of the ketone bodies reduce significantly the flux of nitrogen from [15N]GABA to [2-(15)N]glutamine when the former species served as a metabolic tracer. The concentration of internal citrate increased in the presence of acetoacetate, 3-hydroxybutyrate, and acetate. Studies with purified sheep brain glutamine synthetase showed that citrate inhibited this enzyme. These findings are considered in terms of the known anticonvulsant effect of a ketogenic diet.

3-Hydroxybutyric Acid↗
PubMed1996

Carboxylation of epoxides to beta-keto acids in cell extracts of Xanthobacter strain Py2.

A novel enzymatic reaction involved in the metabolism of aliphatic epoxides by Xanthobacter strain Py2 is described. Cell extracts catalyzed the CO2-dependent carboxylation of propylene oxide (epoxypropane) to form acetoacetate and beta-hydroxybutyrate. The time courses of acetoacetate and beta-hydroxybutyrate formaton indicate that acetoacetate is the primary product of propylene oxide carboxylation and that beta-hydroxybutyrate is a secondary product formed by the reduction of acetoacetate. Analogous C5 carboxylation products were identified with 1,2-epoxybutane as the substrate. In the absence of CO2, propylene oxide and 1,2-epoxybutane were isomerized to form acetone and methyl ethyl ketone, respectively, as dead-end products. The carboxylation of short-chain epoxides to beta-keto acids is proposed to serve as the physiological reaction for the metabolism of aliphatic epoxides in Xanthobacter strain Py2.

3-Hydroxybutyric Acid↗
PubMed1970

Effect of ethanol on ketone metabolism.

Ketonuria has been observed in alcoholics. To study the mechanism of this effect, healthy, volunteers were given adequate diets (36% of calories as lipid and 15% as protein) for 18 days, with isocaloric replacement of carbohydrate (46% of calories) by either ethanol or additional fat. The latter resulted in a high fat diet, with 82% of calories as lipid. After about 1 wk of alcohol, massive and persistent ketonuria developed. Compared with the control period, there was a 30-fold increase in fasting blood acetoacetate and beta-hydroxybutyrate (P < 0.001). With the high fat diet, acetoacetate and beta-hydroxybutyrate increased 8- to 10-fold (P < 0.001). In the postprandial state, ethanol also induced hyperketonemia, but less markedly than when ethanol followed an overnight fast. With low fat diets (5% of calories), alcohol (46% of total calories) did not induce ketonuria or hyperketonemia, suggesting that a combination of alcohol and dietary fat is necessary. The addition of alcohol to rat liver slices did not affect ketogenesis. In rats pretreated with alcohol for 3 days, however, ketonemia developed, hepatic glycogen was decreased, and liver slices (incubated with palmitate-(14)C and glucose) had a significant increase in acetoacetate production, when compared to carbohydrate pretreated controls. Alcohol pretreatment or addition of alcohol in vitro had no effect on acetoacetate utilization by rat diaphragms, and decreased only slightly the conversion of beta-hydroxybutyrate-(14)C to (14)CO(2). Thus, the hyperketonemia and ketonuria observed after alcohol consumption cannot be attributed to an immediate effect of alcohol, but is the consequence of a delayed change in intermediary metabolism characterized by increased hepatic ketone production from fatty acids, possibly linked to ethanol-induced glycogen depletion and depression of citric acid cycle activity.

Acetoacetates↗
PubMed1991

Substrate utilization for phosphatidylcholine synthesis by type II pneumocytes of neonatal rats.

Type II pneumocytes isolated from neonatal rat lungs, using an isolation procedure developed for adult rats, were found to be phenotypically stable and metabolically active in culture. The cells, purified by metrizamide gradient centrifugation and differential adherence, were capable of synthesizing phospholipids from 14C-labeled choline, palmitate, glucose, and acetoacetate. Regardless of the 14C-labeled substrates used, greater than two thirds of the radioactivity incorporated into phosphatidylcholine was recovered in disaturated phosphatidylcholine, the major component of surfactant phospholipids. The incorporation of palmitate into phosphatidylcholine and other phospholipids (i.e. phosphatidyl-ethanolamine, -glycerol, -serine, and -inositol) indicates that the neonatal type II cells have the capacity to produce surfactant lipids. The neonatal cells preferentially utilized acetoacetate over glucose as a precursor of phospholipids. In the adult type II cells, glucose was incorporated into phospholipids more rapidly than acetoacetate. The rate of glucose incorporation in the neonatal cells was enhanced by exogenous insulin. The preferential utilization of acetoacetate by the neonatal type II cells is consistent with the stimulated acetoacetyl CoA synthetase pathway in the lung. The depressed glucose incorporation into phospholipid, on the other hand, may be attributed to insulin insufficiency in the neonate.

Acetoacetates↗
PubMed1987

Modulation of the glucagon-dependent induction of phosphoenolpyruvate carboxykinase by adenosine, but not ketone bodies or ammonia in rat hepatocyte cultures. Possible significance for the zonal heterogeneity of liver parenchyma.

In primary cultures of rat hepatocytes the glucagon-dependent induction of phosphoenolpyruvate carboxykinase was studied in the presence of putative local hormone and substrate modulators which form clear concentration gradients during liver passage such as adenosine, ketone bodies and ammonia. 1) Adenosine inhibited the induction of phosphoenolpyruvate carboxykinase in a concentration-dependent manner between 50 and 200 microM up to 4 h after glucagon application; AMP had similar, adenine, inosine and guanosine had no effect. Adenosine was almost totally metabolized by the liver cells during the first 4 h of the induction period. The inhibitory action of adenosine was also observed using dibutyryl-cAMP or 8-bromo-cAMP as inducer; it could not be prevented by the adenosine receptor antagonist caffeine nor could it be mimicked by the selective adenosine receptor agonist N6-(phenylisopropyl)adenosine. 2) Acetoacetate suppressed the induction of phosphoenolpyruvate carboxykinase in a concentration-dependent manner between 5 and 20mM during the first 4 h after glucagon addition. beta-Hydroxybutyrate showed no effect. Neither starting with acetoacetate nor with beta-hydroxybutyrate did the cell cultures establish the thermodynamic equilibrium between the two compounds. 3) Ammonia did not affect induction of phosphoenolpyruvate carboxykinase at concentrations up to 2mM. Ammonia was converted to urea within the first 4 h; yet it remained at clearly hyperphysiological concentrations in the medium during that period. It is concluded that the glucagon-dependent induction of phosphoenolpyruvate carboxykinase was modulated by the local hormone adenosine via a mechanism not involving adenylate cyclase and by acetoacetate via an unknown mechanism. The inhibitory action of adenosine may, that of acetoacetate can hardly be physiologically relevant.

Acetoacetates↗
PubMed1986

Quantification of analyte and interferent by multipoint analysis.

We have investigated the application of multipoint kinetic curve-fitting methods to the determination of an analyte in the presence of a single interferent. Our model system for the analyte-interferent was creatinine-acetoacetate as determined with the kinetic Jaffé method. We examined the utility of the following multipoint approaches: simultaneous equations, multivariable linear regression, and iterative multivariable nonlinear regression. With appropriate restrictions, all approaches could detect acetoacetate interference and quantify both creatinine and acetoacetate. A two-stage linear regression approach was both versatile and computationally simple. Interferent was detected in the first stage, and both analyte and interferent were quantified in the second stage if the interferent was assumed known and an adequate fit of the model to the data was obtained. Using the two-stage linear regression model, we obtained results for 10 ketotic patients that correlated well with results by enzymatic methods for creatinine (r = 0.976) and acetoacetate (r = 0.995); we also demonstrated that creatinine could be quantified in the presence of the antibiotic cefoxitin.

Acetoacetates↗