Dual localization and properties of ATP--dependent long-chain fatty acid activation in rat liver mitochondria and the onsequences for fatty acid xidation

Myocardial non-esterified fatty acids during normoxia and ischemia in Langendorff and working rat hearts

In isolated perfused rat hearts, the tissue levels of non-esterified fatty acids (NEFA) decreased during normoxic perfusion for 60 min in the working heart but not in the Langendorff heart. The levels of both saturated and unsaturated NEFA increased during ischemia for 20 min in the working heart but not in the Langendorff heart, although unsaturated NEFA increased in the Langendorff heart when the ischemic period was 40 min. Arachidonic and linoleic acids were the NEFA that accumulated most prominently.

Changes in myocardial nonesterified fatty acids during ischemia and reperfusion in isolated, perfused, working rat hearts

The time course of changes in the myocardial levels of nonesterified fatty acids (NEFA), adenosine triphosphate (ATP), creatine phosphate (CrP) and lactate, and those in the cardiac mechanical function during ischemia and reperfusion was investigated in the isolated, perfused, working rat heart. Ischemia was produced by lowering the afterload pressure from 60 to 0 mm Hg, and reperfusion resulted from raising the afterload pressure to 60 mm Hg. Ischemia stopped the heart beat, and increased the myocardial levels of unsaturated NEFA (such as arachidonic, palmitoleic, and linoleic acids) as a function of the ischemic period; it decreased the myocardial levels of ATP and CrP, and increased the myocardial level of lactate. The level of arachidonic acid increased when the myocardial level of ATP fell below 5 mumol/g dry weight. Reperfusion after ischemia started the heart beat, and restored the mechanical function which depended on the preceding ischemic period. Reperfusion also increased the levels of ATP and CrP and decreased the level of lactate, whereas it further increased the levels of the NEFA that had been elevated by ischemia. The recovery of mechanical function was inversely correlated with the myocardial level of arachidonic acid during ischemia and reperfusion. We concluded that changes in the myocardial levels of NEFA during ischemia and reperfusion are different from those of ATP, CrP, and lactate, and suggest that the myocardial level of arachidonic acid during ischemia and reperfusion can be a sensitive and suitable marker for the recovery of mechanical function during reperfusion.

Inhibition of fatty acid biosynthesis by bezafibrate in different rat cells

Bezafibrate is one of the main drugs used in the treatment of human hyperlipemic diseases. Its action on the biosynthesis of fatty acids has been studied and the following conclusions have been drawn: (1) Lipogenesis from glucose is inhibited in hepatocytes and adipocytes isolated from "refed" rats previously treated with bezafibrate. (2) Lipogenesis from glucose is inhibited by bezafibrate in hepatocytes and adipocytes isolated from "refed" rats. (3) Lipogenesis from glucose is also inhibited by bezafibrate in acini isolated from lactating rats. These results show that bezafibrate is an inhibitor of fatty acid synthesis.

Lipid alterations in isolated, working rat hearts during ischemia and reperfusion: its relation to myocardial damage

Disturbances in lipid metabolism may play an important role in the onset of irreversible myocardial damage. To investigate the effect of ischemia and reperfusion on lipid homeostasis and to delineate its possible consequences for myocardial damage, Krebs-Henseleit-perfused, working rat hearts were subjected to various periods of no-flow ischemia (10 to 90 minutes) with or without 30 minutes of reperfusion. During ischemia, the rise in nonesterified fatty acids (NEFAs) was preceded by the accumulation of substantial amounts of glycerol, indicating the presence of an active triacylglycerol-NEFA cycle. The subsequent rise in NEFAs (from 0.25 to 1.64 mumol/g dry residue wt after 90 minutes [means]) coincided with the reduction of ATP to values lower than 10 mumol/g dry wt and the rise of AMP, a potent inhibitor of acyl-coenzyme A synthetase, to values exceeding 2 mumol/g dry wt, making the latter compound a good candidate to hamper the turnover of endogenous lipids during prolonged ischemia. Reperfusion resulted in an additional rise in NEFAs (up to 4.1 mumol/g dry residue wt after 60 minutes of ischemia). Neither ischemia nor reperfusion resulted in significant decreases in the tissue content of triacylglycerols and the various phospholipids. During reperfusion recovery of stroke volume was still adequate at tissue NEFA levels thought to be incompatible with normal mitochondrial function. A positive correlation (r = 0.81) was found between NEFA content of reperfused hearts and cumulative release of lactate dehydrogenase during reperfusion. Accordingly it is concluded that 1) reperfusion results in additional changes in myocardial lipid homeostasis, 2) the accumulating NEFAs are compartmentalized, possibly at the cellular level, and 3) the accumulation of NEFAs is a sensitive marker for myocardial cell damage.

Compartmentation of dicarboxylic acid beta-oxidation in rat liver: importance of peroxisomes in the metabolism of dicarboxylic acids

Peroxisomal and mitochondrial beta-oxidation of dicarboxylic acids (DCAs) were investigated and compared. When isolated hepatocytes were incubated with DCAs of various chain lengths, H2O2 was derived from peroxisomal beta-oxidation, the rates of its generation being comparable to those seen with monocarboxylic acids (MCAs), whereas the rates of ketone body production, a measure of mitochondrial beta-oxidation, were much lower than those with MCAs. Peroxisomal beta-oxidation measured by cyanide-insensitive NAD reduction exhibited similar chain-length specificities for both dicarboxylyl-CoAs (DC-CoAs) and monocarboxylyl-CoAs (MC-CoAs), except that the activities for DC-CoAs with 10-16 carbon atoms were about half of those of the corresponding MC-CoAs. In contrast, mitochondrial beta-oxidation measured by antimycin A-sensitive O2 consumption had no activity for DCAs. In the study with purified enzymes, the reactivities of mitochondrial carnitine palmitoyltransferase and acyl-CoA dehydrogenase for DC-CoAs were much lower than those for MC-CoAs, while the reactivity of peroxisomal acyl-CoA oxidase for DC-CoAs was comparable to that for the corresponding MC-CoAs. Accordingly, the properties of carnitine palmitoyltransferase and acyl-CoA dehydrogenase must be the rate-limiting factors for mitochondrial beta-oxidation, with the result that DCAs might hardly be oxidized in mitochondria. Comparative study of beta-oxidation capacities of peroxisomes and mitochondria in the liver showed that DC12-CoA was hardly subjected to mitochondrial beta-oxidation, and that the beta-oxidation of DCAs in rat liver, therefore, must be carried out exclusively in peroxisomes.

Kinetics of human spermatozoa long-chain fatty acid: CoASH ligase

The kinetics of long-chain saturated fatty acid activation were studied in the supernatant obtained from Triton-treated human spermatozoa. Sperm long-chain fatty acid: CoASH ligase (AMP) (E.C. 6.2.1.3) was able to activate myristic, palmitic, and stearic acids, but was incapable of utilizing lauric, arachidic, and behenic acids. Peak activity was obtained with palmitic acid. Although the Kms for each fatty acid were similar (4.3 to 5.0 microM), the Vmax was several-fold higher for palmitate. In contrast, ligase from liver homogenates assayed under identical conditions activated lauric through stearic acids, with maximal rates being noted with myristic acid. When compared with nongerminal tissues, sperm ligase appears unique because of its narrower acyl substrate specificity.

Long-chain acyl-CoA synthetase and "outer" carnitine long-chain acyltransferase activities of intact brown adipose tissue mitochondria

1. The activities of long-chain acyl-CoA synthetase (acid: CoA ligase (AMP-forming), EC 6.2.1.3) and the "outer" carnitine long-chain acyltransferase (palmitoyl-CoA: L-carnitine O-palmitoyltransferase, EC 2.3.1.21) have been estimated in intact brown adipose tissue mitochondria. The assay of both enzymes is based on a coupled reaction in which the intramitochondrial (matrix) CoASH is the final acyl acceptor and the oxidation-reduction state of the flavoproteins in the acyl-CoA dehydrogens pathway is used to determine the intramitochondrial level of acyl-CoA. 2. Using endogenous fatty acids as the substrate, the progress curve of acyl-CoA synthetase activity was in most mitochondrial preparations linear within the first 30 s. When initial rates were measured, the Km value for CoASH (2.4 micron) was lower than previously determined for the acyl-CoA synthetase in brown adipose tissue mitochondria as well as in mitochondria of other tissues. The pH activity curve indicates that the unprotonated form of the fatty acids represents the substrate of acyl-CoA synthetase, i.e. similar to the effect of pH on the binding of fatty acids to bovine serum albumin. 3. Experimental evidence is presented that at temperatures higher than the transition temperature of the acyl-CoA synthetase (i.e. Tt = 19 degrees C), this enzymic reaction is rate-limiting in the sequence of coupled reactions leading to beta-oxidation in the mitochondrial matrix. 4. The initial rate of the long-chain acyl-COA synthetase reaction was estimated to v = 119 +/- 16 nmol . min-1 . mg-1 protein (mean +/- S.D., n = 5) at an optimal concentration of palmitate which exceeds that of rat heart mitochondria by a factor of 10.

Effect of chronic hypoxia on hepatic triacylglycerol concentration and mitochondrial fatty acid oxidizing capacity in liver and heart

The effect of moderated hypoxia (50.5 kPa air) and severe hypoxia (40.8 kPa air) in vivo liver and heart triglyceride concentration and mitochondrial respiration rates was studied. Liver triglyceride concentrations increased in severe hypoxia from 7.3 mumol/g wet weight to 23.3 mumol/g wet weight over 7 days. After the period of seven days in severe hypoxia, the palmitate, octanoate and palmitoylcarnitine oxidation rates of mitochondrial suspensions were significantly reduced when the citric acid cycle was operative. No decrease in the fatty acid, fatty acyl-CoA or carnitine derivative oxidation was observed when only the beta oxidation system was studied. Mitochondria isolated from the heart or liver after seven days in severe hypoxia showed reduced respiratory control ratios, the decrease being from the normal 4.9 to 1.9 in the liver mitochondria using succinate as substrate. The reduction in respiratory control was mainly due to lowered State 3 respiration rates. Some reduction in the ratio was also observed in the fasting controls, from 5.8 to 3.4 with succinate. The respiratory control ratio could be partially normalized by the addition of albumin to the isolation medium for the liver mitochondria after severe hypoxia. Under these conditions, however, the State 4 respiration of the mitochondria from the hypoxic animals was higher than that for the controls.

Aspects of long-chain acyl-COA metabolism

1. Long-chain acid: CoA ligase (AMP-forming) (trivial name acyl-CoA synthetase; EC 6.2.1.3) is located at the membranes of the endoplasmic reticulum and the outer membrane of the mitochondria. The latter membrane has by far the highest specific activity. 2. GTP-dependent synthesis of acyl-CoA has a very low activity in liver mitochondria (about 5% of the activity measured with ATP). CTP, ITP, UTP and GTP may all provide energy for fatty acid activation in sonicated mitochondria by formation of ATP from endogenous ADP and AMP. 3. In rat liver palmitoyl-CoA: L-carnitine O-palmitoyltransferase (trivial name carnitine palmitoyltransferase; EC 2.3.1.21) is located at the microsomal membranes and in the inner membrane of the mitochondria. Its activity is increased, in both membranes, during fasting and in thyroxine-treated rats. The extramitochondrial carnitine palmitoyltransferase may capture part of the acyl CoA formed at the endoplasmic reticulum as acyl-carnitine, especially during fasting and other metabolic conditions of high fatty acid turnover. This transport form of activated fatty acid can penetrate the inner mitochondrial membrane (the acyl-CoA barrier) where it can be reconverted to acyl-CoA, providing the substrate for beta-oxidation in the inner membrane-matrix compartment. The small part of the mitochondrial carnitine palmitoyltransferase, described to be present at the external surface of the mitochondrial inner membrane, may have the same function in the transport of acyl-CoA formed at the mitochondrial outer membrane. 4. Isolated rat liver mitochondria can oxidize high concentrations of palmitate or oleate in the absence of carnitine. In this case the fatty acids are activated in the inner membrane-matrix compartment of the mitochondria, probably by a medium-chain acyl-CoA synthetase with wide substrate specificity. Because this enzyme is less active in heart and absent in skeletal muscle, these tissues oxidize long-chain fatty acids in an obligatory carnitine-dependent fashion. Also the liver oxidizes long-chain fatty acids in a carnitine-dependent way if lower fatty acid concentrations are used. In this tissue carnitine stimulates specifically the partial oxidation of fatty acids to beta-hydroxybutyrate and acetoacetate. 5. The activities of acyl-CoA: sn-glycerol-3-phosphate O-acyltransferase (trivial name glycerophosphate acyltransferase; EC 2.3.1.15) and carnitine palmitoyltransferase change in opposite directions during fasting. These activity changes, together with the measured kinetic properties of the enzymes in mitochondria and microsomes, allow a switch (relatively) from lipid synthesis to ketogenesis during fasting. This switch may occur at the level of long-chain acyl-CoA both in the endoplasmic reticulum and in the mitochondria.