Biomedical subjects

Henri Brunengraber

Publications and source records attributed to Henri Brunengraber.

At least 19 recordsLinked to original sources

PubMed2006

Localization of the pre-squalene segment of the isoprenoid biosynthetic pathway in mammalian peroxisomes.

Previous studies have indicated that the early steps in the isoprenoid/cholesterol biosynthetic pathway occur in peroxisomes. However, the role of peroxisomes in cholesterol biosynthesis has recently been questioned in several reports concluding that three of the peroxisomal cholesterol biosynthetic enzymes, namely mevalonate kinase, phosphomevalonate kinase, and mevalonate diphosphate decarboxylase, do not localize to peroxisomes in human cells even though they contain consensus peroxisomal targeting signals. We re-investigated the subcellular localization of the cholesterol biosynthetic enzymes of the pre-squalene segment in human cells by using new stable isotopic techniques and data computations with isotopomer spectral analysis, in combination with immunofluorescence and cell permeabilization techniques. Our present findings clearly show and confirm previous studies that the pre-squalene segment of the cholesterol biosynthetic pathway is localized to peroxisomes. In addition, our data are consistent with the hypothesis that acetyl-CoA derived from peroxisomal beta-oxidation of very long-chain fatty acids and medium-chain dicarboxylic acids is preferentially channeled to cholesterol synthesis inside the peroxisomes without mixing with the cytosolic acetyl-CoA pool.

Acetyl-CoA C-Acetyltransferase↗

PubMed2006

Competition between acetate and oleate for the formation of malonyl-CoA and mitochondrial acetyl-CoA in the perfused rat heart.

We previously showed that, in the perfused rat heart, the capacity of n-fatty acids to generate mitochondrial acetyl-CoA decreases as their chain length increases. In the present study, we investigated whether the oxidation of a long-chain fatty acid, oleate, is inhibited by short-chain fatty acids, acetate or propionate (which do and do not generate mitochondrial acetyl-CoA, respectively). We perfused rat hearts with buffer containing 4 mM glucose, 0.2 mM pyruvate, 1 mM lactate, and various concentrations of either (i) [U-(13)C]acetate, (ii) [U-(13)C]acetate plus [1-(13)C]oleate, or (iii) unlabeled propionate plus [1-(13)C]oleate. Using mass isotopomer analysis, we determined the contributions of the labeled substrates to the acetyl moiety of citrate (a probe of mitochondrial acetyl-CoA) and to malonyl-CoA. We found that acetate, even at low concentration, markedly inhibits the oxidation of [1-(13)C]oleate in the heart, without change in malonyl-CoA concentration. We also found that propionate, at a concentration higher than 1 mM, decreases (i) the contribution of [1-(13)C]oleate to mitochondrial acetyl-CoA and (ii) malonyl-CoA concentration. The inhibition by acetate or propionate of acetyl-CoA production from oleate probably results from a competition for mitochondrial CoA between the CoA-utilizing enzymes.

Acetates↗

PubMed2006

Parenteral and enteral metabolism of anaplerotic triheptanoin in normal rats.

A new chronic treatment for inherited disorders of long-chain fatty acid oxidation involves administering up to one-third of dietary calories as triheptanoin, a medium-odd-chain triglyceride (Roe CR, Sweetman L, Roe DS, David F, and Brunengraber H. J Clin Invest 110: 259-269, 2002). Heptanoate and C(5)-ketone bodies derived from its partial oxidation in liver are precursors of anaplerotic propionyl-CoA in peripheral tissues. It was hypothesized that increasing anaplerosis in peripheral tissues would boost energy production. In the present study, we tested the potential of a triheptanoin emulsion as an intravenous nutrient. Normal rats were infused with triheptanoin intravenously or intraduodenally at up to 40% of caloric requirement. The blood concentration ratio (heptanoate/C(5)-ketone bodies) was high with intravenous and low with intraduodenal triheptanoin infusion. During intravenous infusion of triheptanoin, lipolysis was stimulated but appeared compensated by fatty acid reesterification. During intraduodenal infusion of triheptanoin, lipolysis was not stimulated. Our data support the hypothesis that intravenous triheptanoin could be used to treat decompensated patients with long-chain fatty acid oxidation disorders.

Animals↗

PubMed2005

Differential effects of heptanoate and hexanoate on myocardial citric acid cycle intermediates following ischemia-reperfusion.

In the normal heart, there is loss of citric acid cycle (CAC) intermediates that is matched by the entry of intermediates from outside the cycle, a process termed anaplerosis. Previous in vitro studies suggest that supplementation with anaplerotic substrates improves cardiac function during myocardial ischemia and/or reperfusion. The present investigation assessed whether treatment with the anaplerotic medium-chain fatty acid heptanoate improves contractile function during ischemia and reperfusion. The left anterior descending coronary artery of anesthetized pigs was subjected to 60 min of 60% flow reduction and 30 min of reperfusion. Three treatment groups were studied: saline control, heptanoate (0.4 mM), or hexanoate as a negative control (0.4 mM). Treatment was initiated after 30 min of ischemia and continued through reperfusion. Myocardial CAC intermediate content was not affected by ischemia-reperfusion; however, treatment with heptanoate resulted in a more than twofold increase in fumarate and malate, with no change in citrate and succinate, while treatment with hexanoate did not increase fumarate or malate but increased succinate by 1.8-fold. There were no differences among groups in lactate exchange, glucose oxidation, oxygen consumption, and contractile power. In conclusion, despite a significant increase in the content of carbon-4 CAC intermediates, treatment with heptanoate did not result in improved mechanical function of the heart in this model of reversible ischemia-reperfusion. This suggests that reduced anaplerosis and CAC dysfunction do not play a major role in contractile and metabolic derangements observed with a 60% decrease in coronary flow followed by reperfusion.

Animals↗

PubMed2005

Probing peroxisomal beta-oxidation and the labelling of acetyl-CoA proxies with [1-(13C)]octanoate and [3-(13C)]octanoate in the perfused rat liver.

We reported previously that a substantial fraction of the acetyl groups used to synthesize malonyl-CoA in rat heart is derived from peroxisomal beta-oxidation of long-chain and very-long-chain fatty acids. This conclusion was based on the interpretation of the 13C-labelling ratio (malonyl-CoA)/(acetyl moiety of citrate) measured in the presence of substrates that label acetyl-CoA in mitochondria only (ratio < 1.0) or in both mitochondria and peroxisomes (ratio > 1.0). The goals of the present study were to test, in rat livers perfused with [1-(13C)]octanoate or [3-(13C)]octanoate, (i) whether peroxisomal beta-oxidation contributes acetyl groups for malonyl-CoA synthesis, and (ii) the degree of labelling homogeneity of acetyl-CoA proxies (acetyl moiety of citrate, acetate, beta-hydroxybutyrate, malonyl-CoA and acetylcarnitine). Our data show that (i) octanoate undergoes two cycles of peroxisomal beta-oxidation in liver, (ii) acetyl groups formed in peroxisomes contribute to malonyl-CoA synthesis, (iii) the labelling of acetyl-CoA proxies is markedly heterogeneous, and (iv) the labelling of C1+2 of beta-hydroxybutyrate does not reflect the labelling of acetyl-CoA used in the citric acid cycle.

Acetates↗

PubMed2005

Pyruvate carboxylase deficiency: clinical and biochemical response to anaplerotic diet therapy.

A six-day-old girl was referred for severe hepatic failure, dehydratation, axial hypotonia, and both lactic acidosis and ketoacidosis. Biotin-unresponsive pyruvate carboxylase deficiency type B was diagnosed. Triheptanoin, an odd-carbon triglyceride, was administrated as a source for acetyl-CoA and anaplerotic propionyl-CoA. Although this patient succumbed to a severe infection, during the six months interval of her anaplerotic and biochemical management, the following important observations were documented: (1) the immediate reversal (less than 48 h) of major hepatic failure with full correction of all biochemical abnormalities, (2) on citrate supplementation, the enhanced export from the liver of triheptanoin's metabolites, namely 5 carbon ketone bodies, increasing the availability of these anaplerotic substrates for peripheral organs, (3) the demonstration of the transport of C5 ketone bodies-representing alternative energetic fuel for the brain-across the blood-brain barrier, associated to increased levels of glutamine and free gamma-aminobutyric acid (f-GABA) in the cerebrospinal fluid. Considering that pyruvate carboxylase is a key enzyme for anaplerosis, besides the new perspectives brought by anaplerotic therapies in those rare pyruvate carboxylase deficiencies, this therapeutic trial also emphasizes the possible extended indications of triheptanoin in various diseases where the citric acid cycle is impaired.

Autopsy↗

PubMed2004

Peroxisomal and mitochondrial oxidation of fatty acids in the heart, assessed from the 13C labeling of malonyl-CoA and the acetyl moiety of citrate.

We previously showed that a fraction of the acetyls used to synthesize malonyl-CoA in rat heart derives from partial peroxisomal oxidation of very long and long-chain fatty acids. The 13C labeling ratio (malonyl-CoA)/(acetyl moiety of citrate) was >1.0 with 13C-fatty acids, which yields [13C]acetyl-CoA in both mitochondria and peroxisomes and < 1.0 with substrates, which yields [13C]acetyl-CoA only in mitochondria. In this study, we tested the influence of 13C-fatty acid concentration and chain length on the labeling of acetyl-CoA formed in mitochondria and/or peroxisomes. Hearts were perfused with increasing concentrations of labeled docosanoate, oleate, octanoate, hexanoate, butyrate, acetate, or dodecanedioate. In contrast to the liver, peroxisomal oxidation of 1-13C-fatty acids in heart does not form [1-13C]acetate. With [1-13C]docosanoate and [1,12-13C2]dodecanedioate, malonyl-CoA enrichment plateaued at 11 and 9%, respectively, with no detectable labeling of the acetyl moiety of citrate. Thus, in the intact rat heart, docosanoate and dodecanedioate appear to be oxidized only in peroxisomes. With [1-13C]oleate or [1-13C]octanoate, the labeling ratio >1 indicates the partial peroxisomal oxidation of oleate and octanoate. In contrast, with [3-13C]octanoate, [1-13C]hexanoate, [1-13C]butyrate, or [1,2-13C2]acetate, the labeling ratio was <0.7 at all concentrations. Therefore, in rat heart, (i) n-fatty acids shorter than 8 carbons do not undergo peroxisomal oxidation, (ii) octanoate undergoes only one cycle of peroxisomal beta-oxidation, (iii) there is no detectable transfer to the mitochondria of acetyl-CoA from the cytosol or the peroxisomes, and (iv) the capacity of C2-C18 fatty acids to generate mitochondrial acetyl-CoA decreases with chain length.

Acetyl Coenzyme A↗

PubMed2004

In vitro modeling of fatty acid synthesis under conditions simulating the zonation of lipogenic [13C]acetyl-CoA enrichment in the liver.

In the companion report (Bederman, I. R., Reszko, A. E., Kasumov, T., David, F., Wasserman, D. H., Kelleher, J. K., and Brunengraber, H. (2004) J. Biol. Chem. 279, 43207-43216), we demonstrated that, when the hepatic pool of lipogenic acetyl-CoA is labeled from [13C]acetate, the enrichment of this pool decreases across the liver lobule. In addition, estimates of fractional synthesis calculated by isotopomer spectral analysis (ISA), a nonlinear regression method, did not agree with a simpler algebraic two-isotopomer method. To evaluate differences between these methods, we simulated in vitro the synthesis of fatty acids under known gradients of precursor enrichment, and known values of fractional synthesis. First, we synthesized pentadecanoate from [U-13C3]propionyl-CoA and four gradients of [U-13C3]malonyl-CoA enrichment. Second, we pooled the fractions of each gradient. Third, we diluted each pool with pentadecanoate prepared from unlabeled malonyl-CoA to simulate the dilution of the newly synthesized compound by pre-existing fatty acids. This yielded a series of samples of pentadecanoate with known values of (i) lower and upper limits for the precursor enrichment, (ii) the shape of the gradient, and (iii) the fractional synthesis. At each step, the mass isotopomer distributions of the samples were analyzed by ISA and the two-isotopomer method to determine whether each method could correctly (i) detect gradients of precursor enrichment, (ii) estimate the gradient limits, and (iii) estimate the fractional synthesis. The two-isotopomer method did not identify gradients of precursor enrichment and underestimated fractional synthesis by up to 2-fold in the presence of gradients. ISA uses all mass isotopomers, correctly identified imposed gradients of precursor enrichment, and estimated the expected values of fractional synthesis within the constraints of the data.

Acetyl Coenzyme A↗

PubMed2004

Zonation of labeling of lipogenic acetyl-CoA across the liver: implications for studies of lipogenesis by mass isotopomer analysis.

Measurement of fractional lipogenesis by condensation polymerization methods assumes constant enrichment of lipogenic acetyl-CoA in all hepatocytes. mass isotopomer distribution analysis (MIDA) and isotopomer spectral analysis (ISA) represent such methods and are based on the combinatorial analyses of mass isotopomer distributions (MIDs) of fatty acids and sterols. We previously showed that the concentration and enrichment of [13C]acetate decrease markedly across the dog liver because of the simultaneous uptake and production of acetate. To test for zonation of the enrichment of lipogenic acetyl-CoA, conscious dogs, prefitted with transhepatic catheters, were infused with glucose and [1,2-13C2]acetate in a branch of the portal vein. Analyses of MIDs of fatty acids and sterols isolated from liver, bile, and plasma very low density lipoprotein by a variant of ISA designed to detect gradients in precursor enrichment revealed marked zonation of enrichment of lipogenic acetyl-CoA. As control experiments where no zonation of acetyl-CoA enrichment would be expected, isolated rat livers were perfused with 10 mm [1,2-13C2]acetate. The ISA analyses of MIDs of fatty acids and sterols from liver and bile still revealed a zonation of acetyl-CoA enrichment. We conclude that zonation of hepatic acetyl-CoA enrichment occurs under a variety of animal models and physiological conditions. Failure to consider gradients of precursor enrichment can lead to underestimations of fractional lipogenesis calculated from the mass isotopomer distributions. The degree of such underestimation was modeled in vitro, and the data are reported in the companion paper (Bederman, I. R., Kasumov, T., Reszko, A. E., David, F., Brunengraber, H., and Kelleher, J. K. (2004) J. Biol. Chem. 279, 43217-43226).

Acetates↗

PubMed2004

Regulation of malonyl-CoA concentration and turnover in the normal heart.

The goal of this study was to test the relationship between malonyl-CoA concentration and its turnover measured in isolated rat hearts perfused with NaH(13)CO(3). This turnover is a direct measurement of the flux of acetyl-CoA carboxylation in the intact heart. It also reflects the rate of malonyl-CoA decarboxylation, i.e. the only known fate of malonyl-CoA in the heart. Conditions were selected to result in stable malonyl-CoA concentrations ranging from 1.5 to 5 nmol.g wet weight-(1). The malonyl-CoA concentration was directly correlated with the turnover of malonyl-CoA, ranging from 0.7 to 4.2 nmol.min(-) (1).g wet weight(-1) (slope = 0.98, r(2) = 0.94). The V(max) activities of acetyl-CoA carboxylase and of malonyl-CoA decarboxylase exceeded the rate of malonyl-CoA turnover by 2 orders of magnitude and did not correlate with either concentration or turnover of malonyl-CoA. However, conditions of perfusion that increased acetyl-CoA supply resulted in higher turnover and concentration, demonstrating that malonyl-CoA turnover is regulated by the supply of acetyl-CoA. The only condition where the activity of malonyl-CoA decarboxylase regulated malonyl-CoA kinetics was when the enzyme was pharmacologically inhibited, resulting in increased malonyl-CoA concentration and decreased turnover. Our data show that, in the absence of enzyme inhibitors, the rate of acetyl-CoA carboxylation is the main determinant of the malonyl-CoA concentration in the heart.

Acetyl Coenzyme A↗

PubMed2004

Peroxisomal fatty acid oxidation is a substantial source of the acetyl moiety of malonyl-CoA in rat heart.

Little is known about the sources of acetyl-CoA used for the synthesis of malonyl-CoA, a key regulator of mitochondrial fatty acid oxidation in the heart. In perfused rat hearts, we previously showed that malonyl-CoA is labeled from both carbohydrates and fatty acids. This study was aimed at assessing the mechanisms of incorporation of fatty acid carbons into malonyl-CoA. Rat hearts were perfused with glucose, lactate, pyruvate, and a fatty acid (palmitate, oleate or docosanoate). In each experiment, substrates were (13)C-labeled to yield singly or/and doubly labeled acetyl-CoA. The mass isotopomer distribution of malonyl-CoA was compared with that of the acetyl moiety of citrate, which reflects mitochondrial acetyl-CoA. In the presence of labeled glucose or lactate/pyruvate, the (13)C labeling of malonyl-CoA was up to 2-fold lower than that of mitochondrial acetyl-CoA. However, in the presence of a fatty acid labeled in its first acetyl moiety, the (13)C labeling of malonyl-CoA was up to 10-fold higher than that of mitochondrial acetyl-CoA. The labeling of malonyl-CoA and of the acetyl moiety of citrate is compatible with peroxisomal beta-oxidation forming C(12) and C(14) acyl-CoAs and contributing >50% of the fatty acid-derived acetyl groups that end up in malonyl-CoA. This fraction increases with the fatty acid chain length. By supplying acetyl-CoA for malonyl-CoA synthesis, peroxisomal beta-oxidation may participate in the control of mitochondrial fatty acid oxidation in the heart. In addition, this pathway may supply some acyl groups used in protein acylation, which is increasingly recognized as an important regulatory mechanism for many biochemical processes.

Animals↗

PubMed2004

Investigations by mass isotopomer analysis of the formation of D-2-hydroxyglutarate by cultured lymphoblasts from two patients with D-2-hydroxyglutaric aciduria.

D-2-Hydroxyglutaric aciduria is an inborn error of metabolism first described in 1980. To date, more than 40 patients have been diagnosed with this disease. To identify the metabolic precursor of D-2-hydroxyglutarate (D-2-HG), cultured human lymphoblasts from two patients with D-2-HG aciduria were grown in culture medium supplemented with [U-(13)C(6)]glucose or [(2)H(5)]glutamate. Mass isotopomer distribution measurements of D-2-HG, 2-ketoglutarate (2-KG) and citrate were performed by gas chromatography-mass spectrometry. The mass isotopomer distributions in D-2-HG, 2-KG and citrate, following [U-(13)C(6)]glucose and [(2)H(5)]glutamate incubations, revealed that 2-KG interconverts rapidly to D-2-HG and that D-2-HG is formed within the mitochondria.

Cell Line↗

PubMed2004

New secondary metabolites of phenylbutyrate in humans and rats.

Phenylbutyrate is used to treat inborn errors of ureagenesis, malignancies, cystic fibrosis, and thalassemia. High-dose phenylbutyrate therapy results in toxicity, the mechanism of which is unexplained. The known metabolites of phenylbutyrate are phenylacetate, phenylacetylglutamine, and phenylbutyrylglutamine. These are excreted in urine, accounting for a variable fraction of the dose. We identified new metabolites of phenylbutyrate in urine of normal humans and in perfused rat livers. These metabolites result from interference between the metabolism of phenylbutyrate and that of carbohydrates and lipids. The new metabolites fall into two categories, glucuronides and phenylbutyrate beta-oxidation side products. Two questions are raised by these data. First, is the nitrogen-excreting potential of phenylbutyrate diminished by ingestion of carbohydrates or lipids? Second, does competition between the metabolism of phenylbutyrate, carbohydrates, and lipids alter the profile of phenylbutyrate metabolites? Finally, we synthesized glycerol esters of phenylbutyrate. These are partially bioavailable in rats and could be used to administer large doses of phenylbutyrate in a sodium-free, noncaustic form.

Adult↗

PubMed2003

Quantifying rates of protein synthesis in humans by use of 2H2O: application to patients with end-stage renal disease.

A method is introduced for quantitating protein synthetic rates in humans by use of (2)H(2)O. Its validity was tested in subjects with end-stage renal disease. Six clinically stable subjects, hemodialyzed three times weekly, ingested (2)H(2)O to a body water (2)H enrichment of approximately 0.4%. On dialysis, body water enrichment declined to approximately 0.1%. Enrichment of the alpha-hydrogen of plasma free alanine was also approximately 0.4% before and approximately 0.1% after dialysis. Beta-hydrogen enrichment was approximately 80-100% of alpha-hydrogen enrichment. (2)H(2)O was ingested to replace (2)H(2)O removed after each dialysis for 15-51 days, returning enrichment to approximately 0.4%. Enrichment of alanine from plasma albumin gradually increased, with again approximately 80-100% as much (2)H in beta- as in alpha-hydrogens. With continued dialyses, without (2)H(2)O replacement, alanine from albumin enrichment gradually declined, whereas free alanine and water enrichments were negligible. The fractional albumin synthesis rate, calculated from the increase in enrichment in alanine from albumin, was 4.0 +/- 0.5%/day, and from the decrease, 4.6 +/- 0.2%/day. Thus body water enrichment in a subject given (2)H(2)O can be maintained constant long term. A rapid exchange, essentially complete, occurs between the hydrogens of alanine and body water. An integrated measure over a long period of albumin's synthetic rate can be estimated from both the rise in enrichment of alanine from the protein during (2)H(2)O ingestion and fall on (2)H(2)O withdrawal, while the subject's living routine is uninterrupted. Estimates are in subjects with renal disease, but the method should be applicable to estimates of protein synthetic rates in normal subjects and in other pathological states.

Adult↗

PubMed2003

Assessing the reversibility of the anaplerotic reactions of the propionyl-CoA pathway in heart and liver.

While a number of studies underline the importance of anaplerotic pathways for hepatic biosynthetic functions and cardiac contractile activity, much remains to be learned about the sites and regulation of anaplerosis in these tissues. As part of a study on the regulation of anaplerosis from propionyl-CoA precursors in rat livers and hearts, we investigated the degree of reversibility of the reactions of the propionyl-CoA pathway. Label was introduced into the pathway via NaH13CO3, [U-13C3]propionate, or [U-13C3]lactate + [U-13C3]pyruvate, under various concentrations of propionate. The mass isotopomer distributions of propionyl-CoA, methylmalonyl-CoA, and succinyl-CoA revealed that, in intact livers and hearts, (i) the propionyl-CoA carboxylase reaction is slightly reversible only at low propionyl-CoA flux, (ii) the methylmalonyl-CoA racemase reaction keeps the methylmalonyl-CoA enantiomers in isotopic equilibrium under all conditions tested, and (iii) the methylmalonyl-CoA mutase reaction is reversible, but its reversibility decreases as the flow of propionyl-CoA increases. The thermodynamic dis-equilibrium of the combined reactions of the propionyl-CoA pathway explains the effectiveness of anaplerosis from propionyl-CoA precursors such as heptanoate.

Acyl Coenzyme A↗

PubMed2003

Post-ischemic treatment with dipyruvyl-acetyl-glycerol decreases myocardial infarct size in the pig.

The beneficial effects of pyruvate in organ reperfusion injury have been documented, however the therapeutic use of pyruvate has been hindered by the lack of an appropriate delivery method. Pyruvic acid is unstable and high rates of sodium pyruvate infusion are toxic. Dipyruvyl-acetyl-glycerol (DPAG) ester was developed as a novel method for intravenous pyruvate delivery at a high rate without sodium overload. We tested the ability of DPAG to reduce myocardial infarct size when administered after severe myocardial ischemia in an anesthetized open-chest pig model of ischemia-reperfusion injury. Ischemia was induced by total occlusion of the distal 2/3 of the left anterior descending coronary artery for one hour, followed by two hours of reperfusion. Animals were either untreated (n = 7), or treated with intravenous DPAG (8.0 mg/kg(-1). min(-1), n = 8) during the two hours of reperfusion. Infarct size was measured on blinded samples using tetrazolium staining. The DPAG treated group had elevated pyruvate levels (0.82 +/- 0.07 mM) and reduced infarct size (20.1 +/- 4.2% of the volume at risk, compared to 30.8 +/- 4.6% in the untreated animals (p < 0.05)), with no difference in blood pressure or heart rate between groups. In conclusion, an intravenous infusion of DPAG safely increases arterial pyruvate concentration and reduces myocardial infarct size following myocardial ischemia.

Animals↗

PubMed2002

Quantitative assessment of anaplerosis from propionate in pig heart in vivo.

Normal cardiac metabolism requires continuous replenishment (anaplerosis) of catalytic intermediates of the citric acid cycle. Little is known about the quantitative aspects of propionate as a substrate of in vivo anaplerosis; therefore, we measured the rate of propionate entry into the citric acid cycle in hearts of anesthetized pigs. [U-(13)C(3)]propionate (0.25 mM) was infused in a coronary artery branch for 1 h via an extracorporeal perfusion circuit, and cardiac biopsies were analyzed for the mass isotopomer distribution of citric acid cycle intermediates. Infusion of propionate did not affect myocardial oxygen consumption, heart rate, or contractile function. In the infused territory, propionate infusion did not affect uptake of glucose and lactate but decreased free fatty acid uptake by one-half (P < 0.05). Propionate extraction and uptake were 57.4 +/- 3.3% and 0.078 +/- 0.009 micromol x min(-1) x g(-1). Anaplerosis from propionate, calculated from the mass isotopomer distribution of succinate, accounted for 8.9 +/- 1.3% of the citric acid cycle flux. Propioylcarnitine release accounted for only 0.033 +/- 0.002% of propionate uptake. Methylcitrate did not accumulate. Thus administration of a low concentration of propionate appears to be a convenient and safe way to boost anaplerosis in the heart.

Animals↗

PubMed2002

Probing the link between citrate and malonyl-CoA in perfused rat hearts.

Little is known about the sources of cytosolic acetyl-CoA used for the synthesis of malonyl-CoA, a key regulator of fatty acid oxidation in the heart. We tested the hypothesis that citrate provides acetyl-CoA for malonyl-CoA synthesis after its mitochondrial efflux and cleavage by cytosolic ATP-citrate lyase. We expanded on a previous study where we characterized citrate release from perfused rat hearts (Vincent G, Comte B, Poirier M, and Des Rosiers C. Citrate release by perfused rat hearts: a window on mitochondrial cataplerosis. Am J Physiol Endocrinol Metab 278: E846-E856, 2000). In the present study, we show that citrate release rates, ranging from 6 to 22 nmol/min, can support a net increase in malonyl-CoA concentrations induced by changes in substrate supply, at most 0.7 nmol/min. In experiments with [U-(13)C](lactate + pyruvate) and [1-(13)C]oleate, we show that the acetyl moiety of malonyl-CoA is derived from both pyruvate and long-chain fatty acids. This (13)C-labeling of malonyl-CoA occurred without any changes in its concentration. Hydroxycitrate, an inhibitor of ATP-citrate lyase, prevents increases in malonyl-CoA concentrations and decreases its labeling from [U-(13)C](lactate + pyruvate). Our data support at least a partial role of citrate in the transfer from the mitochondria to cytosol of acetyl units for malonyl-CoA synthesis. In addition, they provide a dynamic picture of malonyl-CoA metabolism: even when the malonyl-CoA concentration remains constant, there appears to be a constant need to supply acetyl-CoA from various carbon sources, both carbohydrates and lipids, for malonyl-CoA synthesis.

ATP Citrate (pro-S)-Lyase↗