Inhibition of Enzyme Activities by Free Fatty Acids

Targeting PHB2 mediated mitophagy alleviates non-esterified fatty acid-induced mitochondrial dysfunction in bovine mammary epithelial cells

Mitochondrial dysfunction has been reported to occur in the mammary gland of dairy cows suffering from ketosis. Prohibitin 2 (PHB2) plays a crucial role in regulating mitophagy, which clears impaired mitochondria to maintain normal mitochondrial function. Therefore, the current study aimed to investigate how PHB2 mediates mitophagy, thereby influencing mitochondrial function in the bovine mammary epithelial cell MAC-T. First, mammary gland tissue and blood samples were collected from healthy cows (control; n = 15, BHB <0.6 mM) and cows with clinical ketosis (CK; n = 15, BHB >3.0 mM). Compared with the control group, the CK group exhibited lower dry matter intake (DMI), milk production, milk protein, milk lactose, and serum glucose. In contrast, milk fat, serum nonesterified fatty acids (NEFA) and BHB were greater in CK group. The protein abundance of PHB2, peroxisome proliferator activated receptor-γ coactivator-1α (PGC-1α), mitofusin 2 (MFN2) in whole cell lysates (WCL), as well as PHB2, sequestosome-1 (SQSTM1, also called p62), microtubule-associated protein 1 light chain 3-II (LC3-II), and ubiquitinated proteins in mitochondrial fraction were significantly lower in the CK group. ATP content of mammary gland tissue in CK group was lower than that of healthy cows. Second, MAC-T were cultured and treated with NEFA (0, 0.3, 0.6, 1.2 mM). MAC-T treated with 1.2 mM NEFA displayed decreased protein abundance of PHB2, PGC-1α, MFN2 in WCL, as well as protein abundance of PHB2, p62, LC3-II, and ubiquitinated proteins in mitochondrial fraction. The content of ATP and JC-1 aggregates in 1.2 mM NEFA group were lower than in the 0 mM NEFA group. Additionally, 1.2 mM NEFA disrupted the fusion between mitochondria and lysosomes. MAC-T were then pretreated with 100 nM rapamycin, followed by treatment with or without NEFA. Rapamycin alleviated impaired mitophagy and mitochondria dysfunction induced by 1.2 mM NEFA. Third, MAC-T were transfected with small interfering RNA to silence PHB2 or a plasmid for overexpression of PHB2, followed by treatment with or without NEFA. The silencing of PHB2 aggravated 1.2 mM NEFA induced impaired mitophagy and mitochondrial dysfunction, whereas the overexpression of PHB2 alleviated these effects. Overall, this study provides evidence that PHB2, in regulation of mitophagy, is a mechanism for bovine mammary epithelial cells to counteract NEFA-induced mitochondrial dysfunction.

Acceptors and Effectors Alter Substrate Inhibition Kinetics of a Plant Glucosyltransferase NbUGT72AY1 and Its Mutants

One of the main obstacles in biocatalysis is the substrate inhibition (SI) of enzymes that play important roles in biosynthesis and metabolic regulation in organisms. The promiscuous glycosyltransferase UGT72AY1 from Nicotiana benthamiana is strongly substrate-inhibited by hydroxycoumarins (inhibitory constant Ki < 20 µM), but only weakly inhibited when monolignols are glucosylated (Ki > 1000 µM). Apocarotenoid effectors reduce the inherent UDP-glucose glucohydrolase activity of the enzyme and attenuate the SI by scopoletin derivatives, which could also be achieved by mutations. Here, we studied the kinetic profiles of different phenols and used the substrate analog vanillin, which has shown atypical Michaelis-Menten kinetics in previous studies, to examine the effects of different ligands and mutations on the SI of NbUGT72AY1. Coumarins had no effect on enzymatic activity, whereas apocarotenoids and fatty acids strongly affected SI kinetics by increasing the inhibition constant Ki. Only the F87I mutant and a chimeric version of the enzyme showed weak SI with the substrate vanillin, but all mutants exhibited mild SI when sinapaldehyde was used as an acceptor. In contrast, stearic acid reduced the transferase activity of the mutants to varying degrees. The results not only confirm the multi-substrate functionality of NbUGT72AY1, but also reveal that the enzymatic activity of this protein can be fine-tuned by external metabolites such as apocarotenoids and fatty acids that affect SI. Since these signals are generated during plant cell destruction, NbUGT72AY1 likely plays an important role in plant defense by participating in the production of lignin in the cell wall and providing direct protection through the formation of toxic phytoalexins.

Protein-lipid complexes: molecular structure, current scenarios and mechanisms of cytotoxicity

Some natural proteins can be complexed with oleic acid (OA) to form an active protein-lipid formulation that can induce tumor-selective apoptosis. The first explored protein was human milk α-lactalbumin (α-LA), called HAMLET when composed with OA in antitumor form. Several groups have prepared active protein-lipid complexes using a variety of approaches, all of which depend on target protein destabilization or direct OA-protein incubation to alter pH to acid or alkaline condition. In addition to performing vital roles in inflammatory processes and immune responses, fatty acids can disturb different metabolic pathways and cellular signals. Therefore, the tumoricidal action of these complexes is related to OA rather than the protein that keeps OA in solution and acts as a vehicle for transferring OA molecules to tumor cells. However, other studies have suggested that the antitumor efficacy of these complexes was exerted by both protein and OA together. The potential is not limited to the anti-tumor activity of protein-lipid complexes but extends to other functions such as bactericidal activity. The protein shell enhances the solubility and stability of the bound fatty acid. These protein-lipid complexes are promising candidates for fighting various cancer types and managing bacterial and viral infections.

Origins of the difference between food folate analysis results obtained by LC-MS/MS and microbiological assays

To investigate the often reported disagreement in food folate quantitation between the microbiological assay and high-performance liquid chromatography methods, different foods were analyzed both by a microbiological assay and by a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. For the LC-MS/MS analysis we emphasize the need for complete deconjugation of polyglutamic folate forms. Moreover, our results revealed no need for an additional enzyme treatment except in the deconjugation step. To check the efficiency of deconjugation without additional sample preparations, the amount of diglutamates was quantified and samples were screened for additional polyglutamates. A thorough investigation of a substance with a polyglutamate chain deconjugated like the folates revealed that it was an oxidation product of 5-methyltetrahydrofolate, a pyrazino-s-triazine called MeFox in previous reports. The latter is not microbiologically active and, therefore, does not contribute to the amount of total folates. But we found it is commonly present in foods, especially in those low in ascorbic acid. The microbiological assay showed different responses to the single vitamers. Therefore, it was necessary to perform calibration with the folate that had the highest portion in the folate distribution. The investigations showed that both methods can provide similar results when they both include a deconjugation step. This is particularly important for LC-MS/MS but probably also for the microbiological assay. Additionally, consideration of the folate distribution was found to be crucial for the accurate calibration of the microbiological assay.

Chlorinated Phospholipids and Fatty Acids: (Patho)physiological Relevance, Potential Toxicity, and Analysis of Lipid Chlorohydrins

Chlorinated phospholipids are formed by the reaction of hypochlorous acid (HOCl), generated by the enzyme myeloperoxidase under inflammatory conditions, and the unsaturated fatty acyl residues or the head group. In the first case the generated chlorohydrins are both proinflammatory and cytotoxic, thus having a significant impact on the structures of biomembranes. The latter case leads to chloramines, the properties of which are by far less well understood. Since HOCl is also widely used as a disinfecting and antibacterial agent in medicinal, industrial, and domestic applications, it may represent an additional source of danger in the case of abuse or mishandling. This review discusses the reaction behavior of in vivo generated HOCl and biomolecules like DNA, proteins, and carbohydrates but will focus on phospholipids. Not only the beneficial and pathological (toxic) effects of chlorinated lipids but also the importance of these chlorinated species is discussed. Some selected cleavage products of (chlorinated) phospholipids and plasmalogens such as lysophospholipids, (chlorinated) free fatty acids and α-chloro fatty aldehydes, which are all well known to massively contribute to inflammatory diseases associated with oxidative stress, will be also discussed. Finally, common analytical methods to study these compounds will be reviewed with focus on mass spectrometric techniques.

Low-density lipoprotein-mediated delivery of docosahexaenoic acid selectively kills murine liver cancer cells

AIM

The natural omega-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA), has recently been credited for possessing anticancer properties. Herein, we investigate the cytotoxic actions of DHA-loaded low-density lipoprotein (LDL) nanoparticles in normal and liver cancer cells.

MATERIALS & METHODS

LDL-DHA nanoparticles were prepared and subjected to extensive biophysical characterization. The therapeutic utility of LDL-DHA nanoparticles was evaluated in normal and malignant murine hepatocyte cell lines, TIB-73 and TIB-75, respectively.

RESULTS & DISCUSSION

The engineered LDL-DHA nanoparticles possessed enhanced physical and oxidative stabilities over native LDL and free DHA. Dose-response studies showed that therapeutic doses of LDL-DHA nanoparticles that completely killed TIB-75 were innocuous to TIB-73. The selective induction of lipid peroxidation and reactive oxygen species in the cancer cells was shown to play a central role in LDL-DHA nanoparticle-mediated cytotoxicity.

CONCLUSION

In summary, these findings indicate that LDL-DHA nanoparticles show great promise as a selective anticancer agent against hepatocellular carcinoma.

Two unsaturated fatty acids with potent α-glucosidase inhibitory activity purified from the body wall of sea cucumber (Stichopus japonicus)

One therapeutic approach for preventing diabetes mellitus and obesity is to retard the absorption of glucose via inhibition of α-glucosidase. Two unsaturated fatty acids with strong α-glucosidase inhibitory activity, 7(Z)-octadecenoic acid (1) and 7(Z),10(Z)-octadecadienoic acid (2), were purified from the body wall of Stichopus japonicus. IC(50) values of compounds 1 and 2 were 0.51 and 0.67 μg/mL against Saccharomyces cerevisiae α-glucosidase and 0.49 and 0.60 μg/mL against Bacillus stearothermophilus α-glucosidase, respectively. These compounds mildly inhibited rat-intestinal sucrase and maltase. In addition, both compounds showed a mixed type of inhibition against S. cerevisiae α-glucosidase and were very stable under thermal and acidic conditions up to 60 min. The K(I) and K(IS) values of compounds 1 and 2 were 0.44 and 0.22 μg/mL, and 0.39 and 0.13 μg/mL, respectively.

PRACTICAL APPLICATION

One therapeutic approach for preventing diabetes mellitus is to retard the absorption of glucose via inhibition of α-glucosidase. In this study, 2 fatty acids with strong α-glucosidase-inhibitory activity, 7(Z)-octadecenoic acid and 7(Z),10(Z)-octadecadienoic acid, were purified and identified from sea cucumber. Therefore, sea cucumber fatty acids can potentially be developed as a novel natural nutraceutical for the management of type-2 diabetes.

Metabolism in ischemic muscles before and after treatment with glucose-insulin-potassium infusion

Arteriosclerosis, arterial thrombosis and emboli in the lower extremities of man result in metabolic disorders in the muscles due to a deficit between oxygen required and oxygen made available. Furthermore, diminished perfusion pressure results in diminished exchange of substrates and electrolytes across the capillary walls. In the muscle cells there is a depression of glycolytic enzyme function and a stimulation of lipid activity, resulting in accumulation of free fatty acids and acidosis within the cells. In order to increase R.Q. in the muscles in question, infusion of glucose-insulin-potassium were installed via a catheter introduced into the superior vena cava for 3 days. Following this, muscle samples showed significant increase of carbohydrate metabolism as compared to lipid metabolism and nearly normalization of intracellular content of free fatty acids. This was accompanied by improvement of the clinical condition of the patients and loss of pain in the extremities affected.

Experimental and computational studies investigating trehalose protection of HepG2 cells from palmitate-induced toxicity

Understanding the mechanism of saturated fatty acid-induced hepatocyte toxicity may provide insight into cures for diseases such as obesity-associated cirrhosis. Trehalose, a nonreducing disaccharide shown to protect proteins and cellular membranes from inactivation or denaturation caused by different stress conditions, also protects hepatocytes from palmitate-induced toxicity. Our results suggest that trehalose serves as a free radical scavenger and alleviates damage from hydrogen peroxide secreted by the compromised cells. We also observe that trehalose protects HepG2 cells by interacting with the plasma membrane to counteract the changes in membrane fluidity induced by palmitate. The experimental results are supported by molecular dynamics simulations of model cell membranes that closely reflect the experimental conditions. Simulations were performed to understand the specific interactions between lipid bilayers, palmitate, and trehalose. The simulations results reveal the early stages of how palmitate induces biophysical changes to the cellular membrane and the role of trehalose in protecting the membrane structure.

Inhibition of energy metabolism in cerebral cortex of young rats by the medium-chain fatty acids accumulating in MCAD deficiency

Patients affected by medium-chain acyl CoA dehydrogenase (MCAD) deficiency, a frequent inborn error of metabolism, suffer from acute episodes of encephalopathy. However, the mechanisms underlying the neuropathology of this disease are poorly known. In the present study, we investigated the in vitro effect of the medium-chain fatty acids (MCFA), at concentrations varying from 0.01 to 3 mM, accumulating in MCAD deficiency on some parameters of energy metabolism in cerebral cortex of young rats. (14)CO(2) production from [U(14)] glucose, [1-(14)C] acetate and [1,5-(14)C] citrate was evaluated by incubating cerebral cortex homogenates from 30-day-old rats in the absence (controls) or presence of octanoic acid, decanoic acid or cis-4-decenoic acid. OA and DA significantly reduced (14)CO(2) production from acetate by around 30-40%, and from glucose by around 70%. DA significantly reduced (14)CO(2) production from citrate by around 40%, while OA did not affect this parameter. cDA inhibited (14)CO(2) production from all tested substrates by around 30-40%. The activities of the respiratory chain complexes and of creatine kinase were also tested in the presence of DA and cDA. Both metabolites significantly inhibited cytochrome c oxidase activity (by 30%) and complex II-III activity (DA, 25%; cDA, 80%). Furthermore, only cDA inhibited complex II activity (by 30%), while complex I-III and citrate synthase were not affected by these MCFA. On the other hand, only cDA reduced the activity of creatine kinase in total homogenates, as well as in mitochondrial and cytosolic fractions from cerebral cortex (by 50%). The data suggest that the major metabolites which accumulate in MCAD deficiency, with particular emphasis to cDA, compromise brain energy metabolism. We presume that these findings may contribute to the understanding of the pathophysiology of the neurological dysfunction of MCAD deficient patients.

Inhibition of fatty acid synthesis in bovine mammary homogenate by palmitic acid is not a detergent effect

Supplemental fat fed to dairy cows affects the fat composition of milk by reducing the yield of mammary synthesized fatty acids. The effect has been attributed to a potential allosteric inhibition of acetyl coenzyme-A, a key enzyme in fatty acid synthesis. In vitro experiments have demonstrated an inhibition of fatty acid synthesis when long-chain fatty acids are added to incubations. However, in vitro inhibition can result from a nonspecific detergent effect arising from an inherent physical property of fatty acids. An allosteric role for palmitic acid has not been tested in bovine mammary tissue. The objective of this experiment was to test the hypothesis that palmitic acid is an allosteric inhibitor of fatty acid synthesis in mammary tissue. We tested for a detergent effect by including a synthetic detergent, sodium dodecyl sulfate, under identical incubation conditions. A subcellular supernatant fraction of mammary tissue was used for incubations in the present experiment. The incubation system produced free fatty acids in a linear fashion for time and protein content. Results indicated that fatty acid synthesis was affected by the addition of palmitic acid to the incubations but not by caprylic acid, a short-chain fatty acid. Sodium dodecyl sulfate did not affect fatty acid synthesis at the concentrations used. The results of the present experiment indicate that palmitic acid inhibited fatty acid synthesis, and the effect was not the result of a detergent effect.

Metabolic cardiomyopathies

The energy needed by cardiac muscle to maintain proper function is supplied by adenosine Ariphosphate primarily (ATP) production through breakdown of fatty acids. Metabolic cardiomyopathies can be caused by disturbances in metabolism, for example diabetes mellitus, hypertrophy and heart failure or alcoholic cardiomyopathy. Deficiency in enzymes of the mitochondrial beta-oxidation show a varying degree of cardiac manifestation. Aberrations of mitochondrial DNA lead to a wide variety of cardiac disorders, without any obvious correlation between genotype and phenotype. A completely different pathogenetic model comprises cardiac manifestation of systemic metabolic diseases caused by deficiencies of various enzymes in a variety of metabolic pathways. Examples of these disorders are glycogen storage diseases (e.g. glycogenosis type II and III), lysosomal storage diseases (e.g. Niemann-Pick disease, Gaucher disease, I-cell disease, various types of mucopolysaccharidoses, GM1 gangliosidosis, galactosialidosis, carbohydrate-deficient glycoprotein syndromes and Sandhoff's disease). There are some systemic diseases which can also affect the heart, for example triosephosphate isomerase deficiency, hereditary haemochromatosis, CD 36 defect or propionic acidaemia.

Long chain fatty acids inhibit and medium chain fatty acids activate mammalian cardiac hexokinase

We investigated the effect of non-esterified fatty acids (FAs) on bovine heart hexokinase (type I: ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1). Long chain FAs (C14 to C20) inhibited the enzyme in a way that correlated positively with both the chain length and the degree of unsaturation. Medium chain FA with 12 or less carbons activated hexokinase in a chain length dependent manner with the greater activation shown by laurate. The activation constant of laurate was 91.5 microM with a maximal activation of 60.3%. Oleate caused a maximal decrease in specific activity of 25% with an inhibition constant of 79 microM. Using the fluorescent probe cis-parinarate, we found a saturable binding site with K(d) of 3.5 microM. Oleate competed the fluorescent probe from the protein with a K(d) of 1.4 microM. Medium chain FAs did not compete the probe from HK. The binding of fatty acid to the protein appears to be entropically driven as indicated by an Arrhenius analysis (DeltaS=+231.6 J mol(-1) deg(-1)). The presence of oleate significantly increased the K(ATP)(m) from 0.47 mM to 0.89 mM while the K(glucose)(m) in the presence of the FA (0.026+/-0.003 mM) was not significantly different from the control (0.014+/-0.004 mM). A decrease in V(max) values in the presence of oleate indicated that a mixed allosteric inhibition was operating.

Differential effects of cis and trans fatty acids on insulin release from isolated mouse islets

In vitro and in vivo studies in animals have shown that elevated levels of free fatty acids (FFAs) induce impaired beta-cell function corresponding to the abnormalities observed in non-insulin-dependent diabetes mellitus (NIDDM). Previously, it was demonstrated that the chain length and degree of unsaturation are of importance for the insulinotropic effect of fatty acids. However, it is not known if the spatial configuration of the fatty acid influences beta-cell function. The present study examines whether cis and trans fatty acids acutely influence insulin release and glucose oxidation in isolated mouse islets in the same way and to the same extent. Thus, we studied the impact of both cis and trans forms of C 18:1 fatty acids. We found that cis and trans vaccenic acid (cis and trans C 18:1 delta11), as well as oleic acid (cis C 18:1 delta9) and elaidic acid (trans 18:1 delta9), caused a dose-dependent increase in glucose (16.7 mmol/L)-stimulated insulin secretion during static islet incubations. The maximal stimulatory effect for cis and trans vaccenic acid and for oleic and elaidic acid was observed at concentrations of 2.0 and 3.0 mmol/L, respectively. The trans isomers, trans vaccenic and elaidic acid, elicited a higher maximal insulin output than the respective cis isomers, cis vaccenic and oleic acid. In the presence of another insulin secretagogue, L-leucine, trans vaccenic but not elaidic acid caused a higher response than their cis isomeric fatty acids. The higher potency of trans fatty acids compared with the cis forms was confirmed in perifusion experiments. Both cis and trans C 18:1 fatty acids stimulated insulin secretion in a glucose-dependent manner. Also, glucose oxidation was influenced differentially by the isomers of fatty acids. Glucose oxidation at 16.7 mmol/L glucose was significantly inhibited by oleic and cis vaccenic acid compared with elaidic and trans vaccenic acid, respectively. In summary, our results demonstrate that the fatty acid spatial configuration modulates glucose oxidation and insulin secretion in mouse beta cells.

Intravenous lipid infusion results in myocardial lipid droplet accumulation combined with reduced myocardial performance in heparinized rabbits

The question addressed in this study was whether a relation between myocardial lipid droplet accumulation and depressed myocardial function existed following intralipid infusion for 45 min in open chest, anaesthetized rabbits. One group of rabbits (n = 8) received intralipid infusion whereas a control group (n = 8) received sodium chloride. Local myocardial performance was obtained by sonomicrometry and the fractional volume of myocardial lipid droplets was measured by morphometric methods. The fractional volume of lipid droplets was 0.667 +/- 0.116% in the intralipid group compared with 0.318 +/- 0.080% in the control group (P < 0.03). Cardiac output and stroke volume fell 26% (P < 0.0001) and 34% (P < 0.0001), respectively, as a result of intralipid infusion. However, myocardial blood flow obtained by radiolabelled microspheres remained unchanged. Local myocardial function was reduced for both segments after intralipid infusion; maximal systolic shortening was reduced from 15.63 +/- 1.45 to 12.07 +/- 1.55% (P < 0.002) in the circumferential segment and from 9.46 +/- 1.17 to 7.40 +/- 0.53% (P < 0.05) in the longitudinal segment. The end-diastolic length of the circumferential segment was reduced by 3% (P < 0.05) after intralipid infusion. The reduced end-diastolic length of circumferential segments together with unchanged left ventricular end-diastolic pressure might indicate reduced left ventricular end-diastolic compliance. We conclude that acute intralipid infusion in rabbits results in myocardial lipid droplet accumulation and depressed local myocardial function.

Effects of L-carnitine and palmitoylcarnitine on membrane fluidity of human erythrocytes

Amphiphilic compounds such as long-chain acyl carnitine accumulate in ischemic myocardium and potentially contribute to the myocardial damage, and the role of carnitine in protecting the heart against ischemic damage is interesting. It has been reported that palmitoylcarnitine causes alterations in the membrane molecular dynamics, so this study was designed to investigate whether L-carnitine had a stabilizing effect of membrane fluidity using the spin-label technique. Human erythrocytes were spin-labeled with 5-doxylstearic acids, and membrane fluidity was quantified by measuring the change in the order parameter S. The administration of palmitoylcarnitine (100 microM) altered the membrane fluidity of erythrocytes and caused significant morphological changes. L-carnitine (2mM) decreased the alteration of the fluidity of erythrocytes incubated with palmitoylcarnitine (100 microM), and improved the morphological changes in erythrocytes. These results show that L-carnitine has a stabilizing effect of membrane fluidity as a result of interaction with the palmitoylcarnitine which has a detergent effect.

Nonesterified fatty acid accumulation and release during heart muscle-cell (myocyte) injury: modulation by extracellular "acceptor"

Long-chain nonesterified fatty acid (NEFA) accumulation in the heart muscle cell (myocyte) and NEFA release to the extracellular milieu are considered contributors to the pathogenesis of myocardial injury in a number of cardiovascular disease states. Reported here is a study of the factors which influence and control the interactions among NEFA formation, intracellular NEFA accumulation, and NEFA release to the extracellular compartment by the irreversibly injured myocyte. Under conditions of metabolic inhibition, neonatal rat myocytes in primary monolayer culture became virtually depleted of ATP within 8 h. The metabolically inhibited myocytes evidenced membrane phospholipid degradation and a resultant net accumulation of NEFA produced thereby in the extracellular medium. However, under conditions of nutrient deprivation, the injured myocytes retained the NEFA produced from phospholipid catabolism intracellularly and did not release it to the culture medium, although the extent of myocyte ATP depletion was the same as it had been from metabolic inhibition. Serum could elicit, in a concentration-dependent fashion, the quantitative release of NEFA from metabolically inhibited myocytes to the culture medium but did not influence the net production of NEFA by the injured cells. Similarly, NEFA release from nutrient-deprived myocytes incubated in serum-free, substrate-free medium or in physiological buffer could be induced by supplementing the medium or buffer with bovine serum albumin (BSA), and the extent of NEFA release, but not NEFA formation, was dependent upon the extracellular BSA concentration. No manipulations to media other than changing their serum content or supplementing them with BSA were found to influence the disposition of NEFA produced during phospholipid catabolism in the irreversibly injured, ATP-depleted myocyte. Therefore, although progressive metabolic compromise in the myocyte was correlated with increasing, net NEFA formation, the distribution of the NEFA between the intracellular and the extracellular compartments was not determined by the magnitude of ATP loss or by the nature or duration of at least two injury stimuli, metabolic inhibition and nutrient deprivation. Rather, the net release of NEFA from the ATP-depleted myocyte to the culture medium and the consequent reduction of intracellular myocyte NEFA overload were critically and causally dependent upon the presence and concentration of extracellular NEFA "acceptor". The influence of acceptor on the mobilization of NEFA from the injured myocyte has implications regarding the use of NEFA release as an index of myocyte pathology and could serve to modify the progression and extent of myocardial injury in vivo.

Sarcolemmal phospholipid fatty acid composition and permeability

In this study, the mechanism of ischaemia-induced increased sarcolemmal permeability, as manifested by release of intracellular enzymes, was investigated. The role of changes in the sarcolemmal phospholipid bilayer in this process was evaluated by experimental modulation of the phospholipid fatty acid composition. The isolated perfused rat heart subjected to low-flow hypoxia, was used as a model of global ischaemia. Glucose as well as saturated (palmitate) and unsaturated (linoleate) long-chain fatty acids were used as substrates. Hearts perfused with palmitate or linoleate (1.5 mM, fatty acid/albumin ratio, 3.4) showed a significantly higher rate of lactate dehydrogenase release in both control and ischaemic conditions than hearts perfused with glucose (10 mM). Lactate dehydrogenase release in the fatty acid-perfused hearts was associated with a significant increase in the percentage unsaturation of the sarcolemmal phospholipid fatty acids. Glucose-perfused hearts, on the other hand, showed only minor changes in the sarcolemmal phospholipid fatty acid composition. Attempts to correlate enzyme release directly with an increase in the percentage unsaturation of phospholipid fatty acids failed, since enzyme release was also stimulated in control fatty-acid-perfused hearts which (when compared with glucose) contained a higher percentage saturated phospholipid fatty acids. The results suggest that myocardial ischaemia, apart from changes in the sarcolemmal phospholipid fatty acid composition, also induces several other changes in sarcolemmal composition (e.g., cholesterol loss) which may affect is permeability for macromolecules.

Ionization and phase behavior of fatty acids in water: application of the Gibbs phase rule

The phase behavior of several medium-chain (10- and 12-carbon) and long-chain (18-carbon) fatty acids in water was examined as a function of the ionization state of the carboxyl group. Equilibrium titration curves were generated above and below fatty acid and acid-soap chain melting temperatures and critical micelle concentrations, and the phases formed were characterized by X-ray diffraction, 13C NMR spectroscopy, and phase-contrast and polarized light microscopy. The resulting titration curves were divided into five regions: (i) at pH values less than 7, a two-phase region containing oil or fatty acid crystals and an aqueous phase; (ii) at pH approximately 7, a three-phase region containing oil, lamellar, and aqueous (or fatty acid crystals, 1:1 acid-soap crystals, and aqueous) phases; (iii) between pH 7 and 9, a two-phase region containing a lamellar fatty acid/soap (or crystalline 1:1 acid-soap) phase in an aqueous phase; (iv) at pH approximately 9, a three-phase region containing lamellar fatty acid-soap (or crystalline 1:1 acid-soap), micellar, and aqueous phases; and (v) at pH values greater than 9, a two-phase region containing micellar and aqueous phases. Interpretation of the results using the Gibbs phase rule indicated that, for oleic acid/potassium oleate, the composition of the lamellar fatty acid/soap phase varied from approximately 1:1 to 1:3 un-ionized to ionized fatty acid species. In addition, constant pH regions observed in titration curves were a result of thermodynamic invariance (zero degrees of freedom) rather than buffering capacity. The results provide insights into the physical states of fatty acids in biological systems.(ABSTRACT TRUNCATED AT 250 WORDS)

A physical-chemical model for cellular uptake of fatty acids: prediction of intracellular pool sizes

If the uptake of fatty acids by liver is a physical, not a biological, process, then the size and location of the intrahepatic pool of fatty acids can be predicted from uptake rates and thermodynamic data. The purpose of the experiments in this paper was to test the accuracy of this idea. Rat livers were perfused with palmitate bound to albumin, and the total amounts of palmitate removed from the perfusate were measured at 3-s intervals. The intrahepatic pools of palmitate calculated from these data were 13.8 and 23.0 nmol/g of liver at ratios of palmitate/albumin (mol/mol) (afferent side) of 2/1 and 4/1, respectively, in the steady state. The intrahepatic pools of palmitate calculated from the distributions of palmitate between membranes, H2O, albumin, and fatty acid binding protein and the measured first-order rate constants for acyl-CoA ligases in mitochondria and microsomes were 12.1 and 34.6 nmol/g for perfusate ratios of palmitate/albumin of 2/1 and 4/1, in the steady state. Intrahepatic pools of palmitate measured after establishment of a steady-state rate of uptake were 15.0 and 31.8 nmol/g for these ratios of palmitate/albumin of 2/1 and 4/1.

Compartmentation and functional mechanisms in myocardial failure and myocardial infarction

Changes in compartmentation and specific mechanism in acute myocardial failure due to global ischemia and in regional myocardial ischemia in dog hearts are described. Ischemic failure was produced by periodic arrest of flow to supported heart preparations perfused with a fluorocarbon (FC-43). Sarcolemmal vesicles (SL) prepared from ischemic failing heart preparations exhibited diminished Ca++ binding and phosphorylation. TA-064, a beta-1-agonist partially abolished the reduction in Ca++ binding and phosphorylation of SL vesicles. The addition of cyclic-AMP (cAMP) and of protein kinase (PK) increased phosphorylation of SL vesicles obtained from non failing heart preparations. Combination of cAMP and of PK had the greatest effect. In contrast to myocardial failure, myocardial infarction is known to produce a large variety of specific disturbances in intermediary cardiac metabolism. Apparently in ischemic failing heart preparations, Ca++ binding and phosphorylation by SL are deficient. The results with TA-064 and isoproterenol suggest that phosphorylation of SL may play a role in the positive inotropic effect of beta-1-agonists.

Synthesis of wax esters by a cell-free system from barley (Hordeum vulgare L.)

Experimental evidence for a membranebound microsomal ester synthetase from Bonus barley primary leaves is reported. The results are consistent with at least two mechanisms for the synthesis of barley wax esters: an acyl-CoA-fattyalcohol-transacylase-type reaction and an apparent direct esterification of alcohols with fatty acids. Biosynthesis of wax esters was not specific with regard to the chain length of the tested alcohols. The microsomal preparation readily catalyzed the esterification of C16-, C18-, C22- or C24-labelled alcohols with fatty acids of endogenous origin. Exogenous long-chain alcohols were exclusively incorporated into the alkyl moieties of the esters. Addition of ATP, CoA and-or free fatty acids was not effective in stimulating or depressing the esterifying activity of the microsomal fraction. Partial solubilization of the ester synthetase was obtained using phosphate-buffered saline.

Inhibition of the hormone-sensitive lipase in adipose tissue by long-chain fatty acyl coenzyme A

The effects of free fatty acids and fatty acyl esters of coenzyme A and carnitine on the activity of a hormone-sensitive lipase preparation made from pigeon adipose tissue were determined. Oleic acid (100 microM) resulted in a 40% inhibition of lipase activity. A more potent inhibition of lipase activity was seen with long-chain fatty acyl CoA compounds. The concentration required for half-maximal inhibition with oleoyl CoA and palmitoyl CoA was 25-40 microM, whereas palmitoyl carnitine stimulated lipase activity. Activated lipase preparations (preincubated with Mg2+, ATP, cyclic AMP and protein kinase) were 4-6 times more sensitive to inhibition by oleoyl CoA than were nonactivated preparations. An increase in cellular levels of fatty acyl coenzyme A could, therefore, contribute to the feedback inhibition of lipolysis in adipose tissue.

Mammalian skeletal muscle: long-lasting contractures and potentiated tetani produced by conditioning with weak acid anions

Reversible contractures can be induced in slow mammalian muscles by manipulations that probably generate a long-lasting alkalinization of the muscle cell interior. Such contractures reach about 1/4 of the tetanic force, P0, and last 10 times longer than potassium contractures. While in contracture, the muscle fibers have high resting potentials so that they can be electrically stimulated. Tetanic force is then increased and added to that of the contracture so that total force may reach 2 P0. This level of potentiation has not been reached by any previously-known method.

Myocardial triglycerides increased by fasting. Effects of hypoxia on contractility and enzymatic release

The effect of fasting on the mechanics of contraction was studied in the isolated perfused rat heart, in oxygenated and hypoxic conditions. Animals were subjected to 48 h of fasting, a condition which produces augmented endogenous triglycerides (TG). Normal and fasted rats were submitted to a 10-min period of hypoxia, which depressed peak tension (Tp), maximal rate of contraction (Tc), and relaxation (Tr); all three parameters recovered with reoxygenation. However, Tp and Tc of hearts of fasted animals were less affected by hypoxia, and Tp, Tc, and Tr attained higher levels during reoxygenation compared with hearts of normally fed animals. These results suggest that as triglycerides are augmented, they might have a beneficial action on the hypoxic heart, though other unknown effects of fasting cannot be discarded. LDH was the only cardiac enzyme whose release in the perfusion medium significantly increased in hypoxic hearts, irrespective of the fasting state of the animal. The positive correlation between LDH and an index of relative recovery (IH) for Tp, Tc, and Tr, indicate that not only hypoxia but a good recovery are necessary to yield high LDH values.

Inhibition of desaturation of palmitic, linoleic and eicosa-8,11,14-trienoic acids in vitro by isomeric cis-octadecenoic acids

The effects of the positional isomers of cis-18 : 1 acids on the desaturation of 18 : 2 omega 6 leads to 18 : 3 omega 6 (delta 6 desaturase), 20 : 3 omega 6 leads to 20 : 4 omega 6 (delta 5 desaturase) and 16 : 0 leads to 16 : 1 (delta 9 desaturase) were investigated using essential fatty acid deficient rat liver microsomes. The isomeric cis-18 : 1 acids were found to be inhibitory for the delta 6, delta 5 and delta 9 desaturases, and the position of the double bond is important in determining the degree of inhibition. The effects of the several cis-18 : 1 isomers on delta 6 and delta 5 desaturases were parallel in magnitude exept for the cis-delta isomer which gave 17.5% inhibition for delta 6 desaturase and no inhibition for delta 5 desaturase. The strongest inhibitor for delta 6 desaturase (cis-delta 8 18 : 1) was also the most potent inhibitor for delta 5 desaturase, and the weakest inhibitor for delta 6 desaturase (cis-delta 3 18 : 1) was the least effective inhibitor on delta 5 desaturase. The delta 9 desaturase was maximally inhibited by cis-delta 10 and delta 11 18 : 1 isomers. The cis-18 : 1 acid isomers in partially hydrogenated edible fats may have effects on the lipid metabolism through their inhibitory effects on the desaturases.

Inhibition of adenine nucleotide translocase by oleoylcarnitine, oleoylcoa and oleate in isolated arterial mitochondria

Adenine nucleotide translocase (AdNT) activity was studied in isolated mitochondria from normal rabbit aortas. The enzyme was inhibited by oleic acid, oleoylCoA, and oleoylcarnitine with 50% inhibition occurring at 5 muM, 6 muM and 14 muM, respectively (corresponding to 8, 10, and 23 nmol/mg protein). PalmitoylCoA and palmitoylcarnitine displayed similar potency to oleylCoA and oleoylcarnitine. The possibility that inhibition by fatty acid, acylCoA, and acylcarnitine could be attributed to non-specific detergency effects seems remote in that these compounds were more potent inhibitors of AdNT than equimolar concentrations of laurylsulfate. In addition, by use of the fluorescent probe N-phenyl-1-naphthylamine, it was shown that under the experimental conditions, inhibition of AdNT occurred at concentrations not exceeding a critical micelle concentration (CMC). Specificity was also suggested in that octanoylCoA was a weak inhibitor of AdNT and acetylcarnitine, butyrylcarnitine, cholesteryl oleate, and sphingomyelin were not inhibitory to the enzyme. In contrast to the observed inhibition of arterial AdNT by oleoylCoA and oleoylcarnitine, AdNT in isolated rabbit and rat heart mitochondria was inhibited only by oleoylCoA.

The effect of isomeric trans-18:1 acids on the desaturation of palmitic, linoleic and eicosa-8,11,14-trienoic acids by rat liver microsomes

The inhibitory effects of the positional isomers of trans-18:1 acids on the desaturation of palmitic acid to palmitoleic (delta 9-desaturase), linoleic to gamma-linolenic (delta 6-desaturase) and eicosa-8,11,14-trienoic to arachidonic acid (delta 5-desaturase) were investigated. These trans-18:1 acids were found to be inhibitory for the microsomal delta 6-, delta 9- and delta 5-desaturases of rat liver. The position of the double bond in the trans-18:1 acids seems to be important in determining the degree of inhibition. At inhibitor/substrate ratio of 3:1, the delta 6-desaturase was most strongly inhibited by trans-delta 3, -delta 4, -delta 7 and -delta 15-18:1 isomers, whereas the delta 9-desaturase was most strongly inhibited by trans-delta3, -delta 5, -delta 7, -delta 10, -delta 12, -delta 13 and -delta 16 isomers. At inhibitor/substrate ratio of 6:1, the delta 5-desaturase was most strongly inhibited by delta 3-, delta 9-, delta 13- and delta 15-isomers. When 18:0 was added to the incubations of 16:0, 18:2 and 20:3 at the same I/S ratios used for the trans-18:1 acids, weak inhibition for delta 9- desaturase and no inhibition for delta 5- and delta 6-desaturases was observed.

Beneficial effect of practolol in preventing adrenaline-induced systemic and myocardial metabolic changes

The aim of the study was to investigate whether the beta blocking agent, practolol, is able to modify some of the metabolic and hormonal responses and the local myocardial changes evoked by an excess of adrenaline similar to that seen after acute coronary occlusion. Adrenaline (1.2 micrograms/kg/min) and practolol (1 mg/kg) were infused concurrently to anaesthetized intact dogs for 5 h. Blood free fatty acid and triiodothyronine levels were measured initially and after 2, 4 and 5 h of infusion. At the end of the infusion the myocardium was subjected to biochemical, histoenzymatic and electron microscopic examination. The results were compared with those obtained in dogs infused with adrenaline alone and with saline alone. Practolol reduced the adrenaline-induced increase in free fatty acids and a fall in triiodothyronine in the blood. Myocardial acetate accumulation and ATP decrease were both reduced by practolol. Histoenzymatic and electron microscopic changes were less. These effects of practolol upon systemic and myocardial disturbances induced by the excess of adrenaline indicate that it might be effective in modifying any excessive adrenergic response which may occur in acute myocardial infarction.

Toxicity of free fatty acids for cultured rat heart muscle and endothelioid cells. I. Saturated long-chain fatty acids

Capric (C10:0), lauric (C12:0), myristic (C14:0), palmitic (C16:0), stearic (C18:0) and arachidic (C20:0) acids were compared for their toxic effects upon cultured rat heart muscle and endothelioid cells. The free fatty acids (FFA) were found to albumin (6:1) and tested at 5 x 10(-5)M. Reduction of cell viability (51Cr release) and in situ mitochondrial and lysosomal labilization were used as indices of injury. Reduction in viability of both cell types was produced by palmitic, stearic or arachidic acids, but only after exposures of from 12 to 36 h. These FFA also produced needle-like cytoplasmic inclusions. Mitochondria and lysosomes were labilized after shorter exposures. Capric, lauric and myristic acids, were relatively non-toxic, and protected endothelioid cell lysosomes from labilization.