Induction of swelling of liver mitochondria by fatty acids of various chain length

High-Fidelity Drug-Induced Liver Injury Screen Using Human Pluripotent Stem Cell-Derived Organoids

BACKGROUND & AIMS

Preclinical identification of compounds at risk of causing drug induced liver injury (DILI) remains a significant challenge in drug development, highlighting a need for a predictive human system to study complicated DILI mechanism and susceptibility to individual drug. Here, we established a human liver organoid (HLO)-based screening model for analyzing DILI pathology at organoid resolution.

METHODS

We first developed a reproducible method to generate HLO from storable foregut progenitors from pluripotent stem cell (PSC) lines with reproducible bile transport function. The qRT-PCR and single cell RNA-seq determined hepatocyte transcriptomic state in cells of HLO relative to primary hepatocytes. Histological and ultrastructural analyses were performed to evaluate micro-anatomical architecture. HLO based drug-induced liver injury assays were transformed into a 384 well based high-speed live imaging platform.

RESULTS

HLO, generated from 10 different pluripotent stem cell lines, contain polarized immature hepatocytes with bile canaliculi-like architecture, establishing the unidirectional bile acid transport pathway. Single cell RNA-seq profiling identified diverse and zonal hepatocytic populations that in part emulate primary adult hepatocytes. The accumulation of fluorescent bile acid into organoid was impaired by CRISPR-Cas9-based gene editing and transporter inhibitor treatment with BSEP. Furthermore, we successfully developed an organoid based assay with multiplexed readouts measuring viability, cholestatic and/or mitochondrial toxicity with high predictive values for 238 marketed drugs at 4 different concentrations (Sensitivity: 88.7%, Specificity: 88.9%). LoT positively predicts genomic predisposition (CYP2C9∗2) for Bosentan-induced cholestasis.

CONCLUSIONS

Liver organoid-based Toxicity screen (LoT) is a potential assay system for liver toxicology studies, facilitating compound optimization, mechanistic study, and precision medicine as well as drug screening applications.

Inhibition of β-oxidation is not a valid therapeutic tool for reducing oxidative stress in conditions of neurodegeneration

According to recent reports, systemic treatment of rats with methylpalmoxirate (carnitine palmitoyltransferase-1 inhibitor) decreased peroxidation of polyunsaturated fatty acids in brain tissue. This was taken as evidence of mitochondrial β-oxidation in brain, thereby contradicting long-standing paradigms of cerebral metabolism, which claim that β-oxidation of activated fatty acids has minor importance for brain energy homeostasis. We addressed this controversy. Our experiments are the first direct experimental analysis of this question. We fueled isolated brain mitochondria or rat brain astrocytes with octanoic acid, but octanoic acid does not enhance formation of reactive oxygen species, neither in isolated brain mitochondria nor in astrocytes, even at limited hydrogen delivery to mitochondria. Thus, octanoic acid or l-octanoylcarnitine does not stimulate H₂O₂ release from brain mitochondria fueled with malate, in contrast to liver mitochondria (2.25-fold rise). This does obviously not support the possible occurrence of β-oxidation of the fatty acid octanoate in the brain. We conclude that a proposed inhibition of β-oxidation does not seem to be a helpful strategy for therapies aiming at lowering oxidative stress in cerebral tissue. This question is important, since oxidative stress is the cause of neurodegeneration in numerous neurodegenerative or inflammatory disease situations.

The Mitochondrial Permeability Transition Pore: Channel Formation by F-ATP Synthase, Integration in Signal Transduction, and Role in Pathophysiology

The mitochondrial permeability transition (PT) is a permeability increase of the inner mitochondrial membrane mediated by a channel, the permeability transition pore (PTP). After a brief historical introduction, we cover the key regulatory features of the PTP and provide a critical assessment of putative protein components that have been tested by genetic analysis. The discovery that under conditions of oxidative stress the F-ATP synthases of mammals, yeast, and Drosophila can be turned into Ca(2+)-dependent channels, whose electrophysiological properties match those of the corresponding PTPs, opens new perspectives to the field. We discuss structural and functional features of F-ATP synthases that may provide clues to its transition from an energy-conserving into an energy-dissipating device as well as recent advances on signal transduction to the PTP and on its role in cellular pathophysiology.

The mitochondrial permeability transition pore: molecular nature and role as a target in cardioprotection

The mitochondrial permeability transition (PT) - an abrupt increase permeability of the inner membrane to solutes - is a causative event in ischemia-reperfusion injury of the heart, and the focus of intense research in cardioprotection. The PT is due to opening of the PT pore (PTP), a high conductance channel that is critically regulated by a variety of pathophysiological effectors. Very recent work indicates that the PTP forms from the F-ATP synthase, which would switch from an energy-conserving to an energy-dissipating device. This review provides an update on the current debate on how this transition is achieved, and on the PTP as a target for therapeutic intervention. This article is part of a Special Issue entitled "Mitochondria: from basic mitochondrial biology to cardiovascular disease".

The mitochondrial permeability transition pore: a mystery solved?

The permeability transition (PT) denotes an increase of the mitochondrial inner membrane permeability to solutes with molecular masses up to about 1500 Da. It is presumed to be mediated by opening of a channel, the permeability transition pore (PTP), whose molecular nature remains a mystery. Here I briefly review the history of the PTP, discuss existing models, and present our new results indicating that reconstituted dimers of the F_OF₁ ATP synthase form a channel with properties identical to those of the mitochondrial megachannel (MMC), the electrophysiological equivalent of the PTP. Open questions remain, but there is now promise that the PTP can be studied by genetic methods to solve the large number of outstanding problems.

The mitochondrial permeability transition from yeast to mammals

Regulated permeability changes have been detected in mitochondria across species. We review here their key features, with the goal of assessing whether a "permeability transition" similar to that observed in higher eukaryotes is present in other species. The recent discoveries (i) that treatment with cyclosporin A (CsA) unmasks an inhibitory site for inorganic phosphate (Pi) [Basso, E., Petronilli, V., Forte, M.A. and Bernardi, P. (2008) Phosphate is essential for inhibition of the mitochondrial permeability transition pore by cyclosporin A and by cyclophilin D ablation. J. Biol. Chem. 283, 26307-26311], the classical inhibitor of the permeability transition of yeast and (ii) that under proper experimental conditions a matrix Ca(2+)-dependence can be demonstrated in yeast as well [Yamada, A., Yamamoto, T., Yoshimura, Y., Gouda, S., Kawashima, S., Yamazaki, N., Yamashita, K., Kataoka, M., Nagata, T., Terada, H., Pfeiffer, D.R. and Shinohara Y. (2009) Ca(2+)-induced permeability transition can be observed even in yeast mitochondria under optimized experimental conditions. Biochim. Biophys. Acta 1787, 1486-1491] suggest that the mitochondrial permeability transition has been conserved during evolution.

Alleviation of fatty acid and hypoxia-reoxygenation-induced proximal tubule deenergization by ADP/ATP carrier inhibition and glutamate

Kidney proximal tubules develop a severe but highly reversible energetic deficit due to nonesterified fatty acid (NEFA)-induced dissipation of mitochondrial membrane potential (DeltaPsi(m)) during reoxygenation after severe hypoxia. To assess the mechanism for this behavior, we have compared the efficacies of different NEFA for inducing mitochondrial deenergization in permeabilized tubules measured using safranin O uptake and studied the modification of NEFA-induced deenergization by inhibitors of the ADP/ATP carrier and glutamate using both normoxic tubules treated with exogenous NEFA and tubules deenergized during hypoxia-reoxygenation (H/R). Among the long-chain NEFA that accumulate during H/R of isolated tubules and ischemia-reperfusion of the kidney in vivo, oleate, linoleate, and arachidonate had strong effects to dissipate DeltaPsi(m) that were slightly greater than palmitate, while stearate was inactive at concentrations reached in the cells. This behavior correlates well with the protonophoric effects of each NEFA. Inhibition of the ADP/ATP carrier with either carboxyatractyloside or bongkrekic acid or addition of glutamate to compete for the aspartate/glutamate carrier improved DeltaPsi(m) in the presence of exogenous oleate and after H/R. Effects on the two carriers were additive and restored safranin O uptake to as much as 80% of normal under both conditions. The data strongly support NEFA cycling across the inner mitochondrial membrane using anion carriers as the main mechanism for NEFA-induced deenergization in this system and provide the first evidence for a contribution of this process to pathophysiological events that impact importantly on energetics of intact cells.

The mitochondrial permeability transition from in vitro artifact to disease target

The mitochondrial permeability transition pore is a high conductance channel whose opening leads to an increase of mitochondrial inner membrane permeability to solutes with molecular masses up to approximately 1500 Da. In this review we trace the rise of the permeability transition pore from the status of in vitro artifact to that of effector mechanism of cell death. We then cover recent results based on genetic inactivation of putative permeability transition pore components, and discuss their meaning for our understanding of pore structure. Finally, we discuss evidence indicating that the permeability transition pore plays a role in pathophysiology, with specific emphasis on in vivo models of disease.

Mitochondrial energy dissipation by fatty acids. Mechanisms and implications for cell death

For most cell types, fatty acids are excellent respiratory substrates. After being transported across the outer and inner mitochondrial membranes they undergo beta-oxidation in the matrix and feed electrons into the mitochondrial energy-conserving respiratory chain. On the other hand, fatty acids also physically interact with mitochondrial membranes, and possess the potential to alter their permeability. This occurs according to two mechanisms: an increase in proton conductance of the inner mitochondrial membrane and the opening of the permeability transition pore, an inner membrane high-conductance channel that may be involved in the release of apoptogenic proteins into the cytosol. This article addresses in some detail the mechanisms through which fatty acids exert their protonophoric action and how they modulate the permeability transition pore and discusses the cellular effects of fatty acids, with specific emphasis on their role as potential mitochondrial mediators of apoptotic signaling.

Effects of fatty acids on mitochondria: implications for cell death

Fatty acids have prominent effects on mitochondrial energy coupling through at least three mechanisms: (i) increase of the proton conductance of the inner mitochondrial membrane; (ii) respiratory inhibition; (iii) opening of the permeability transition pore (PTP). Furthermore, fatty acids physically interact with membranes and possess the potential to alter their permeability; and they are also excellent respiratory substrates that feed electrons into the respiratory chain. Due to the complexity of their actions, the effects of fatty acids on mitochondrial function in situ are difficult to predict. We have investigated the mitochondrial and cellular effects of fatty acids of increasing chain length and degree of unsaturation in relation to their potential to affect mitochondrial function in situ and to cause cell death. We show that saturated fatty acids have little effect on the mitochondrial membrane potential in situ, and display negligible short-term cytotoxicity for Morris Hepatoma 1C1 cells. The presence of double bonds increases both the depolarizing effects and the cytotoxicity, but these effects are offset by the hydrocarbon chain length, so that more unsaturations are required to observe an effect as the hydrocarbon chain length is increased. With few exceptions, depolarization and cell death are due to opening of the PTP rather than to the direct effects of fatty acids on energy coupling.

Protonophoric activity of fatty acid analogs and derivatives in the inner mitochondrial membrane: a further argument for the fatty acid cycling model

The protonophoric (uncoupling) action of various long-chain fatty acids and their derivatives in mitochondria was investigated as related to their ability for rapid transbilayer movement in the inner mitochondrial membrane (flip-flop) and interaction with the ADP/ATP carrier (AAC). Flip-flop was assessed from a rapid decrease of internal mitochondrial pH. It was found that long-chain unsubstituted fatty acids (with the exception of very-long-chain unbranched homologs) and their thia and oxa analogs performed a rapid flip-flop, inhibited AAC activity and increased proton permeability of the inner mitochondrial membrane, resulting in dissipation of mitochondrial membrane potential and increased resting state respiration. Bipolar fatty acid analogs, i.e., those containing a second carboxylic group or OH group(s) at the hydrocarbon tail, phenyl-substituted fatty acid derivatives, and fatty acid analogs containing strongly ionized sulfonyl or sulfate groups instead of the carboxylic group, did not flip-flop and were not uncoupling, although some of them were weak inhibitors of AAC. These results provide further confirmation of the fatty acid cycling model (V. P. Skulachev, FEBS Lett. 294, 158-162, 1991) in which the protonophoric function of fatty acids is a result of the spontaneous transbilayer passage of undissociated (protonated) molecules of the fatty acid from the external side of the inner mitochondrial membrane to the matrix side and the AAC-mediated transport of the fatty acid anion in the opposite direction.

Effect of fatty acids on energy coupling processes in mitochondria

Long-chain fatty acids are natural uncouplers of oxidative phosphorylation in mitochondria. The protonophoric mechanism of this action is due to transbilayer movement of undissociated fatty acid in one direction and the passage of its anion in the opposite direction. The transfer of the dissociated form of fatty acid can be, at least in some kinds of mitochondrion, facilitated by adenine nucleotide translocase. Apart from dissipating the electrochemical proton gradient, long-chain fatty acids decrease the activity of the respiratory chain by mechanism(s) not fully understood. In intact cells and tissues fatty acids operate mostly as excellent respiratory substrates, providing electrons to the respiratory chain. This function masks their potential uncoupling effect which becomes apparent only under special physiological or pathological conditions characterized by unusual fatty acid accumulation. Short- and medium-chain fatty acids do not have protonophoric properties. Nevertheless, they contribute to energy dissipation because of slow intramitochondrial hydrolysis of their activation products, acyl-AMP and acyl-CoA. Long-chain fatty acids increase permeability of mitochondrial membranes to alkali metal cations. This is due to their ionophoric mechanism of action. Regulatory function of fatty acids with respect to specific cation channels has been postulated for the plasma membrane of muscle cells, but not demonstrated in mitochondria. Under cold stress, cold acclimation and arousal from hibernation the uncoupling effect of fatty acids may contribute to increased thermogenesis, especially in the muscle tissue. In brown adipose tissue, the special thermogenic organ of mammals, long-chain fatty acids promote operation of the unique natural uncoupling protein, thermogenin. As anionic amphiphiles, long-chain fatty acids increase the negative surface charge of biomembranes, thus interfering in their enzymic and transporting functions.

Effect of salicylic acid and calcium on mitochondrial functions

The rapid mitochondrial uptake of calcium followed by slow release in certain pathophysiological states associated with an increase in intracellular calcium, to normalize the cytoplasmic levels of free calcium, provides an important protective mechanism against calcium cellular toxicity. Salicylic acid, an in vivo metabolite of aspirin, inhibits the uptake and enhances the release of calcium by mitochondria, thereby increasing the levels of cytoplasmic free calcium. The Ca2+ induced mitochondrial swelling is enhanced in the presence of salicylic acid and in which turn leads to loss of biosynthesis of ATP. These results suggest that salicylic acid may promote cellular damage in pathophysiological states associated with increase in intracellular free calcium.

Mitochondrial changes and carnitine status in fasting rats

To elucidate mitochondrial morphology and related pathophysiology in the fasting state, liver mitochondrial area, plasma levels of carnitine and non-esterified fatty acids were measured in fed (N = 30) and fasted for 5 days (N = 28) rats. The rats were divided into three groups according to body weight: 100 g-group (aged 5 weeks), 200 g-group (aged 7-8 weeks), 400 g-group (aged 15-16 weeks). Electron microscopy of the liver revealed mitochondrial enlargement in fasted rats. There were significant differences in mitochondrial area measured by digitizer, between fasted groups with 100 g and 200 g body weights and the compatible fed groups. The grade of mitochondrial swelling was inversely proportional to the body weight (i.e. the age). The fasting induced decreased plasma levels of free carnitine and increased plasma levels of acylcarnitine. Plasma free carnitine levels in all fed rats appeared to be directly correlated to the body weight. The above mitochondrial swelling and abnormal carnitine status are hallmarks of Reye's syndrome (RS). These changes are not specific to RS but might be attributable to fasting.

Activation of mitochondrial ATPase as evidence of loosely coupled oxidative phosphorylation in various skeletal muscle disorders. A histochemical fine-structural study

Combined histochemical and biochemical studies have shown, that the histochemical activity of mitochondrial Mg2+-activated ATPase closely correlates with the coupling state of oxidative phosphorylation (Meijer and Vloedman 1980). Using this histochemical method 646 unselected skeletal muscle biopsies have been investigated. Activation of the enzyme, i.e. loosely coupled mitochondria were present either focally or diffusely expressed in 28% of the biopsies irrespective of the underlying disorder. Most often it was found in mitochondrial myopathies and in progressive muscular dystrophy type Duchenne; in a lesser degree it was also present in neurogenic atrophy and in various other disorders. Ninety two percent of all cases with loose coupling showed mitochondrial proliferations. On the other hand in 20% of all cases with mitochondrial proliferations including 19 cases of diffuse mitochondrial myopathy and 3 of progressive external ophthalmoplegia no activation of the enzyme was found. The results show that loose coupling is closely but not absolutely associated with mitochondrial proliferation, it is present in mitochondrial myopathies but also in various other muscular disorders with different pathogenesis.

Effects of 2,4-dinitrophenol on renal ammoniagenesis in the rat

Injection of anesthetized rats with the uncoupling agent, 2,4-dinitrophenol (2,4-DNP) 10 or 20 mg/kg induced a systemic hyperammonemia unaccompanied by blood acid-base status changes and related to an increased release of ammonium from the kidney into the renal vein. Ammonium excretion into the urine did not increase. The renal uptake of circulating glutamine rose. The antiepileptic drug sodium valproate (VPA), a short-chain, branched fatty acid, had the same effects on rat and man. These findings suggest that VPA stimulates renal ammoniagenesis by the same mechanisms as 2,4-DNP.

Mitochondrial myopathy with loosely coupled oxidative phosphorylation in a case of Zellweger syndrome. A cytochemical-ultrastructural study

A newborn female, the second child of consanguineous parents, exhibited general muscle hypotonia, apathy, hepatomegaly and failure to thrive from birth and signs of craniofacial dysmorphia were present. Pipecolic and trihydroxicoprostanoic acid were excreted in the urine and serum transferrin, ferritin and iron were markedly elevated. At the age of 7 weeks the baby died of respiratory insufficiency. Besides malformations of the brain, renal cysts, liver damage with hypoplastic intrahepatic bile ducts and cholestasis, increased storage of iron and cytochemically proven deficiency of peroxisomes in liver and kidney, morphological studied provided evidence of a mitochondrial myopathy in striated muscle with the accumulation of enlarged bizarre mitochondria, showing only minor structural abnormalities. No defects of NADH-reductase, succinate-dehydrogenase or cytochrome-c-oxidase were demonstrated histochemically. Cytochemical-ultrastructural investigation of mitochondrial ATPase revealed activation of the ATP-synthesising enzyme even before the addition of an uncoupler, this indicating loosely coupled oxidative phosphorylation. In addition a high rate of subcellular autophagy with segregation of mitochondria and focal loss of fibrils was present. Muscle damage in Zellweger syndrome appears to be the consequence of complex, interacting metabolic processes. The mitochondrial myopathy thereby induced allows a better understanding of general muscle hypotonia, one of the leading symptoms of this disorder.

Inhibition of oxidative phosphorylation in hepatic and cerebral mitochondria of sodium valproate-treated rats

Rats were treated with intraperitoneal injections of sodium valproate (VPA), either acutely, one injection VPA 200 mg/kg, or chronically, VPA 600 mg/kg/day for 5 days, and the oxygen consumption, MO2, of isolated hepatic and cerebral mitochondria measured. For hepatic mitochondria, Stade IV MO2 decreased by more than 20%, and Stage III MO2 by more than 50%, in the presence of succinate or glutamate-malate substrates. A decoupling agent intensified this inhibition. With cerebral mitochondria, the effects were similar but weaker, for pyruvate-malate or glutamate-malate substrates. These findings suggest that VPA, a short-chain fatty acid, may affect the properties of the internal mitochondrial membrane, although an action on substrate carriers, or on indispensable mitochondrial metabolites, is not excluded. Inhibition of oxidative phosphorylation cannot, however, alone account for hepatotoxicities seen in VPA-treated subjects. These are rare, whereas inhibition of mitochondrial respiration by VPA is consistently observed.

Fatty acid-membrane interactions in isolated cardiac mitochondria and erythrocytes

The effects of long-chain fatty acids on mitochondrial functions and red cell stability were studied. In albumin-containing incubation media, fatty acid distribution between the albumin-bound and the unbound fraction was estimated by calculation. When fatty acids are compared to one another on the basis of identical unbound concentrations, their effectiveness differs by orders of magnitude. Fatty acids stimulate mitochondrial basic oxygen consumption, thus lowering the respiratory control index, without changing the ATP/O ratio at lower concentrations. Lower concentrations increase Ca2+ uptake velocity, but decrease maximal Ca2+ storage capacity. The order of effectiveness of different fatty acids is the same for both oxidative phosphorylation and Ca2+ uptake. The influence of fatty acids on red cell stability in hypotonic media is similar to these effects both in concentration range and in order of effectiveness. The influence of fatty acids on red cell stability and their critical micellar concentrations were investigated because these are general characteristics of 'detergent-like' compounds. Critical micellar concentrations of the fatty acids in physiological salt buffers are, in general, at least 10-fold higher than the concentrations exhibiting membrane effects in vitro. Based on these findings it is suggested that, of the various concentrations reported in literature for myocardial non-esterified fatty acids, only the lowest values are physiologically possible.

Switch on and switch off phenomenon of liver gluconeogenic function in lamprey (Lampetra fluviatilis L.) under the influence of season and temperature

The potential activity of pyruvate carboxylase in lamprey liver is the same as in mammals. However, at certain stages of the life cycle this reaction does not take place because of ATP deficiency in mitochondria. Energy charge potential of liver cells ranges from 0.76 to 0.11 throughout a year. Heat adaptation of lampreys leads to a rapid increase of the ATP level and of the NAD+/NADH ratio in liver. The intensity of gluconeogenesis and glycogen levels are also enhanced. Cold reacclimation reverses the effect. A scheme accounting for the temperature changes in energy status of hepatocytes has been proposed.

Effect of chain length of short-chain fatty acids on their effect on intracranial pressure in rabbits

The short-chain fatty acids propionic, butyric, valeric, isovaleric and octanoic produced elevations in intracranial pressure during intravenous infusion in rabbits. Serum concentrations of these compounds are elevated in patients with Reye's syndrome, and may contribute to the intracranial pressure elevations found in these patients.

Abnormal polyunsaturated fatty acid patterns of serum lipids in Reye's syndrome

Fatty acid patterns of the serum lipids were measured in 17 children with Reye's syndrome (RS). Serial measurements of total serum free fatty acids (FFA) showed that levels were increased during RS and, after recovery, were significantly lower in the patients who survived. Fatty acid patterns of serum FFA, triglycerides, and phospholipids in patients with RS were significantly different from those in controls. In RS the polyunsaturated fatty acid content of phospholipids was less than control values; in the FFA, it was higher. This was consistent with the possible involvement of increased phospholipase activity. The increase in polyunsaturated fatty acids in FFA, the precursors of prostaglandins, suggests that a grossly disturbed prostaglandin pattern may occur in RS. These changes in lipid metabolism may be related to the abnormal hepatic and neurological functions observed in RS.

Fatal lipid storage myopathy with deficiency of cytochrome-c-oxidase and carnitine. A contribution to the combined cytochemical-finestructural identification of cytochrome-c-oxidase in longterm frozen muscle

Two newborn female siblings fell ill with apathy, failure of suckling and a generalized progressive muscular hypotonia. Death occured at the age of 7 weeks, obviously caused by impairment of respiratory musculature. Biochemical studies in one child revealed carnitine deficiency especially in skeletal muscle; hepatic encephalopathy was absent. Both children had a generalized hyperaminoaciduria, an unusual finding in primary carnitine deficiency. Besides fatty metamorphosis of the liver, bilateral hydroureters and tubular calcifications of both kidneys, morphological studies showed a generalized lipid storage myopathy which predominated in Type-I-fibres and was accentuated in the muscles of the neck. Enzymehistochemical electron microscopy in longterm frozen muscle demonstrated that cytochrome-c-oxidase activity was absent not only in myopathic but also in most of the morphological unchanged muscle fibres. Only some fibres and endothelial cells displayed normal activity of mitochondria. Biochemically no cytochrome aa3 (cytochrome-c-oxidase) could be found in skeletal muscle; cytochrome b was almost undetectable. --In newborns with fatal lipid storage myopathy and carnitine deficiency it seems necessary to look for additional defects in the respiratory chain. Enzyme histochemical electron microscopy is a sensitive method in identifying cytochrome-c-oxidase even after a 12 months period of storage.

Cholesterol esterifying enzyme in normal and degenerating peripheral nerve

The cholesterol esterifying enzyme which incorporates exogenous free [1-14C]oleate into cholesteryl ester is present in rat sciatic endoneurium. Cholesterol esterification is optimal at pH 4.8. Exogenous ATP, CoA, and oleyl-CoA do not greatly affect its activity. Various detergents and bile salts are inhibitory. Enzyme activity does not change appreciably during storage at 4 degrees C for up to 4 days or at -70 degrees C for up to 1 month. Of the subcellular fractions, the microsomal fraction exhibits the highest specific activity. Over 75% of enzyme activity is recovered, with equal amounts in the microsomal and soluble fractions. During nerve fiber degeneration an increase (more than fivefold) in cholesterol esterifying activity, which peaks 6 days after crush, is observed. Elevated levels of enzyme activity persist for 90 days after crush, by which time nerve regeneration is well established. Thus, it is concluded that an increase in cholesterol esterifying activity in degenerating nerve is primarily responsible for cholesterol esterification during Wallerian degeneration. The maximum increase in cholesterol esterifying activity is associated temporally with axonal degeneration and, particularly, with the formation of myelin ovoids.

Mitochondrial calcium transport and calcium-activated phospholipase in porcine malignant hyperthermia

The interaction of Ca2+ with mitochondria isolated from longissismus dorsi, a predominantly white skeletal muscle, of normal and malignant hyperthermia pigs was investigated using tightly-coupled preparations. Arrhenius plots of mitochondrial Ca2+ -stimulated respiration for succinate oxidation of malignant hyperthermia pigs showed a transition temperature (Tt) of 26.31 +/- 0.80 degrees C (n = 5), which was decreased by spermine to 15.41 +/- 0.69 degrees C (n = 3), a value very similar to that for normal pigs. No difference in either the Tt or in the activation energy (Ea) was observed between the two types of pigs when ADP was used instead of Ca2+. Mitochondria of malignant hyperthermia pigs were uncoupled at 40 degrees C by exogenous Ca2+ at 1221 +/- 301 (n = 9) nmol Ca2+ per mg proteinn during succinate oxidation and the uncoupled mitochondria showed large amplitude swelling. Both the Ca2+ -induced uncoupling and swelling were prevented by bovine serum albumin and by the phospholipase inhibitors, spermine and tetracaine. In contrast, mitochondria of normal pigs were still tightly coupled even after a total addition of 2313 +/- 287 (n = 5) nmol Ca2+ per mg protein and retained the original condensed configuration in the presence or absence of spermine and tetracaine. Mitochondria of malignant hyperthermia pigs contained significantly (P less than 0.001) higher quantities of endogenous Ca2+ and showed a significantly (P less than 0.001) faster FCCP-induced endogenous Ca2+ efflux rate than normal when monitored spectroscopically with murexide. No significant difference was observed in either the rate of exogenous Ca2+ uptake or in the extent of Ca2+ accumulated in the aerobic steady state during succinate oxidation between the two types of pigs. The rate of mitochondrial Ca2+ efflux of malignant hyperthermia pigs during anaerobiosis was about twice that of normal. Experimental evidence suggests that mitochondria from musculi longissimus dorsi of malignant hyperthermia pigs contained a Ca2+ -stimulated phospholipase A2 (EC 3.1.1.4, phosphatide 2-acylhydrolase), and that this enzyme if present in mitochondria of normal pigs is either latent or in very low concentration. The significance of the Ca2+ -stimulated phospholipase A2 and its association with the enhanced rate of glycolysis in porcine malignant hyperthermia syndrome and in the post-mortem formation of the pale, soft and exudative conditions observed in white skeletal muscles of malignant hyperthermia pigs is discussed.

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.

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

Oleic (C18:1), linoleic (C18:2), linolenic (C18:3) and arachidonic (C20:4) acids were compared for their toxic effects upon cultured rat heart muscle and endothelioid cells. The free fatty acids (FFA) were bound to albumin (6:1) and tested at concentrations from 5 x 10(-5)M to 5 x 10(-4)M. Reduction of cell viability (51Cr release) and in situ mitochondrial and lysosomal labilization were used as indices of injury. Oleic acids was non-toxic at all times and concentrations tested while linoleic acid increased cell death only in muscle cells after 32 h. Arachidonic acid, by contrast, demonstrated significant toxicity as early as 2 h while both linolenic and arachidonic acids produced major injury at longer durations. A detergent effect was excluded as the injury mechanism because of marked differences in the toxicities of the individual FFA. The similarity in the effects of linolenic and arachidonic acids would appear to exclude prostaglandins as responsible toxic products.

Effect of long-chain fatty acids and acyl-CoA on mitochondrial permeability, transport, and energy-coupling processes

The following effects of fatty acids and acyl-CoA thioesters on energy metabolism of mitochondria can now be assumed: (1) Inhibition of adenine nucleotide translocation. This effect may increase the energy state of mitochondria respiring under state 3 conditions and decrease phosphorylation potential in the surrounding medium (the cytoplasm). (2) Increased permeability to monovalent cations. This may lead to a partial energy dissipation due to a futile recycling of K+ (or another cation), namely and energy-dependent uptake and a passive outflow. (3) True uncoupling due to increased permeability to protons. This effect probably occurs at high concentrations of fatty acids only. (4) Substrate effect. Fatty acids in the form of acyl-CoA are excellent respiratory substrates for mitochondria of most tissues. Their oxidation is coupled to the generation of high energy state of the mitochondrial membrane and, consequently, to ATP synthesis.

Circulatory and metabolic effects of glycerol infusion in patients with recent cerebral infarction

The effect of intravenous infusion of 10 per cent glycerol on regional cerebral blood flow (using hydrogen bolus and Xenon-133 (133Xe) clearance methods) and metabolism was investigated in 57 patients with recent cerebral infarction. Hemispheric blood flow (HBF) increased, together with increase in regional cerebral blood flow (rCBF) and cerebral blood volume (rCBV), in foci of brain ischemia. Hemispheric oxygen consumption (HMIO2) decreased together with hemispheric respiratory quotient. Systemic blood levels of glucose, lactate, pyruvate, and triglycerides also increased after glycerol while free fatty acids (FFA) and inorganic phosphate (Pi) decreased. Hemispheric glucose consumption was unaltered after glycerol so that hemispheric glucose to oxygen ratio tended to rise. Pyruvate and lactate production by brain was unchanged. Glycerol moved across the blood brain barrier into brain and cerebrospinal fluid (CSF). Release of FFA and Pi from infarcted brain was reversed by glycerol. Total phosphate balance was maintained actoss brain both before and after glycerol infusion. Triglycerides increased in CSF after glycerol, originating either from cerebral blood or as a result of lipogenesis in cerebral tissue. The EEG Recording and neurological status of the patients improved despite decreased brain oxygen consumption. Results of this study suggest that after intravenous infusion of 10 per cent glycerol in patients with recent cerebral infarction, glycerol rapidly enters the CSF and brain compartments and favorably affects the stroke process in two ways: first, by redistribution of cerebral blood flow with increase in rCBF and rCBV in ischemic brain secondary to reduction in focal cerebral edema; and second glycerol may become an alternative source of energy either by being directly metabolized by the brain, or indirectly, by enhancing lipogenesis, or by both processes. Involvement of glycerol in lipogenesis with esterification to accumulated FFA might lead to improved coupling of oxidative phosphorylation, a hypothesis that fits the finding of improved neuronal function despite further decrease in cerebral hemispheric oxygen consumption.