cis-4-Decenoic and decanoic acids impair mitochondrial energy, redox and Ca(2+) homeostasis and induce mitochondrial permeability transition pore opening in rat brain and liver: Possible implications for the pathogenesis of MCAD deficiency

The Pathogenesis of Very Long-Chain Acyl-CoA Dehydrogenase Deficiency

Living systems require energy to maintain their existence and perform tasks such as cell division. This energy is stored in several molecular forms in nature, specifically lipids, carbohydrates, and amino acids. At a cellular level, energy is extracted from these complex molecules and transferred to adenosine triphosphate (ATP) in the cytoplasm and mitochondria. Within the mitochondria, fatty acid β-oxidation (FAO) and oxidative phosphorylation (OXPHOS) are crucial metabolic processes involved in generating ATP, with defects in these pathways causing mitochondrial disease. Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a fatty acid β-oxidation disorder (FAOD) affecting 1 to 2 individuals per 100,000. Similar to other mitochondrial disorders, there is no cure for VLCADD, with symptomatic treatment comprising dietary management and supplementation with medium-chain fatty acids to bypass the enzyme deficiency. While this addresses the primary defect in VLCADD, there is growing evidence that other aspects of mitochondrial function are also affected in VLCADD, including secondary defects in OXPHOS function. Here, we review our current understanding of VLCADD with a focus on the associated biochemical and molecular defects that can disrupt multiple aspects of mitochondrial function. We describe the interactions between FAO proteins and the OXPHOS complexes and how these interactions are critical for maintaining the activity of both metabolic pathways. In particular, we describe what is now known about the protein-protein interactions between VLCAD and the OXPHOS supercomplex and how their disruption contributes to overall VLCADD pathogenesis.

Fatty acid β-oxidation in brain mitochondria: Insights from high-resolution respirometry in mouse, rat and Drosophila brain, ischemia and aging models

Glucose is the main energy source of the brain, yet recent studies demonstrate that fatty acid oxidation (FAO) plays a relevant role in the pathogenesis of central nervous system disorders. We evaluated FAO in brain mitochondria under physiological conditions, in the aging brain, and after stroke. Using high-resolution respirometry we compared medium-chain (MC, octanoylcarnitine) and long-chain (LC, palmitoylcarnitine) acylcarnitines as substrates of β-oxidation in the brain. The protocols developed avoid FAO overestimation by malate-linked anaplerotic activity in brain mitochondria. The capacity of FA oxidative phosphorylation (F-OXPHOS) with palmitoylcarnitine was up to 4 times higher than respiration with octanoylcarnitine. The optimal concentration of palmitoylcarnitine was 10 μM which corresponds to the total concentration of LC acylcarnitines in the brain. Maximal respiration with octanoylcarnitine was reached at 20 μM, however, this concentration exceeds MC acylcarnitine concentrations in the brain 15 times. F-OXPHOS capacity was highest in mouse cerebellum, intermediate in cortex, prefrontal cortex, and hypothalamus, and hardly detectable in hippocampus. F-OXPHOS capacity was 2-fold lower and concentrations of LC acylcarnitines were 2-fold higher in brain of aged rats. A similar trend was observed in the rat model of endothelin-1-induced stroke, but reduction of OXPHOS capacity was not limited to FAO. In conclusion, although FAO is not a dominant pathway in brain bioenergetics, it deserves specific attention in studies of brain metabolism.

Plasma lipidomics analysis reveals altered profile of triglycerides and phospholipids in children with Medium-Chain Acyl-CoA dehydrogenase deficiency

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most prevalent mitochondrial fatty acid β-oxidation disorder. In this study, we assessed the variability of the lipid profile in MCADD by analysing plasma samples obtained from 25 children with metabolically controlled MCADD (following a normal diet with frequent feeding and under l-carnitine supplementation) and 21 paediatric control subjects (CT). Gas chromatography-mass spectrometry was employed for the analysis of esterified fatty acids, while high-resolution C18-liquid chromatography-mass spectrometry was used to analyse lipid species. We identified a total of 251 lipid species belonging to 15 distinct lipid classes. Principal component analysis revealed a clear distinction between the MCADD and CT groups. Univariate analysis demonstrated that 126 lipid species exhibited significant differences between the two groups. The lipid species that displayed the most pronounced variations included triacylglycerols and phosphatidylcholines containing saturated and monounsaturated fatty acids, specifically C14:0 and C16:0, which were found to be more abundant in MCADD. The observed changes in the plasma lipidome of children with non-decompensated MCADD suggest an underlying alteration in lipid metabolism. Therefore, longitudinal monitoring and further in-depth investigations are warranted to better understand whether such alterations are specific to MCADD children and their potential long-term impacts.

The Physiological and Pathological Role of Acyl-CoA Oxidation

Fatty acid metabolism, including β-oxidation (βOX), plays an important role in human physiology and pathology. βOX is an essential process in the energy metabolism of most human cells. Moreover, βOX is also the source of acetyl-CoA, the substrate for (a) ketone bodies synthesis, (b) cholesterol synthesis, (c) phase II detoxication, (d) protein acetylation, and (d) the synthesis of many other compounds, including N-acetylglutamate-an important regulator of urea synthesis. This review describes the current knowledge on the importance of the mitochondrial and peroxisomal βOX in various organs, including the liver, heart, kidney, lung, gastrointestinal tract, peripheral white blood cells, and other cells. In addition, the diseases associated with a disturbance of fatty acid oxidation (FAO) in the liver, heart, kidney, lung, alimentary tract, and other organs or cells are presented. Special attention was paid to abnormalities of FAO in cancer cells and the diseases caused by mutations in gene-encoding enzymes involved in FAO. Finally, issues related to α- and ω- fatty acid oxidation are discussed.

Disruption of mitochondrial bioenergetics and calcium homeostasis by phytanic acid in the heart: Potential relevance for the cardiomyopathy in Refsum disease

Refsum disease is an inherited peroxisomal disorder caused by severe deficiency of phytanoyl-CoA hydroxylase activity. Affected patients develop severe cardiomyopathy of poorly known pathogenesis that may lead to a fatal outcome. Since phytanic acid (Phyt) concentrations are highly increased in tissues of individuals with this disease, it is conceivable that this branched-chain fatty acid is cardiotoxic. The present study investigated whether Phyt (10-30 μM) could disturb important mitochondrial functions in rat heart mitochondria. We also determined the influence of Phyt (50-100 μM) on cell viability (MTT reduction) in cardiac cells (H9C2). Phyt markedly increased mitochondrial state 4 (resting) and decreased state 3 (ADP-stimulated) and uncoupled (CCCP-stimulated) respirations, besides reducing the respiratory control ratio, ATP synthesis and the activities of the respiratory chain complexes I-III, II, and II-III. This fatty acid also reduced mitochondrial membrane potential and induced swelling in mitochondria supplemented by exogenous Ca²⁺, which were prevented by cyclosporin A alone or combined with ADP, suggesting the involvement of the mitochondrial permeability transition (MPT) pore opening. Mitochondrial NAD(P)H content and Ca²⁺ retention capacity were also decreased by Phyt in the presence of Ca²⁺. Finally, Phyt significantly reduced cellular viability (MTT reduction) in cultured cardiomyocytes. The present data indicate that Phyt, at concentrations found in the plasma of patients with Refsum disease, disrupts by multiple mechanisms mitochondrial bioenergetics and Ca²⁺ homeostasis, which could presumably be involved in the cardiomyopathy of this disease.

Mitochondrial Fatty Acid β-Oxidation Disorders: From Disease to Lipidomic Studies-A Critical Review

Fatty acid oxidation disorders (FAODs) are inborn errors of metabolism (IEMs) caused by defects in the fatty acid (FA) mitochondrial β-oxidation. The most common FAODs are characterized by the accumulation of medium-chain FAs and long-chain (3-hydroxy) FAs (and their carnitine derivatives), respectively. These deregulations are associated with lipotoxicity which affects several organs and potentially leads to life-threatening complications and comorbidities. Changes in the lipidome have been associated with several diseases, including some IEMs. In FAODs, the alteration of acylcarnitines (CARs) and FA profiles have been reported in patients and animal models, but changes in polar and neutral lipid profile are still scarcely studied. In this review, we present the main findings on FA and CAR profile changes associated with FAOD pathogenesis, their correlation with oxidative damage, and the consequent disturbance of mitochondrial homeostasis. Moreover, alterations in polar and neutral lipid classes and lipid species identified so far and their possible role in FAODs are discussed. We highlight the need of mass-spectrometry-based lipidomic studies to understand (epi)lipidome remodelling in FAODs, thus allowing to elucidate the pathophysiology and the identification of possible biomarkers for disease prognosis and an evaluation of therapeutic efficacy.

Evidence that Oxidative Disbalance and Mitochondrial Dysfunction are Involved in the Pathophysiology of Fatty Acid Oxidation Disorders

Mitochondrial fatty acid β-oxidation disorders (FAODs) are a group of about 20 diseases which are caused by specific mutations in genes that codify proteins or enzymes involved in the fatty acid transport and mitochondrial β-oxidation. As a consequence of these inherited metabolic defects, fatty acids can not be used as an appropriate energetic source during special conditions, such as prolonged fasting, exercise or other catabolic states. Therefore, patients usually present hepatopathy, cardiomyopathy, severe skeletal myopathy and neuropathy, besides biochemical features like hypoketotic hypoglycemia, metabolic acidosis, hypotony and hyperammonemia. This set of symptoms seems to be related not only with the energy deficiency, but also with toxic effects provoked by fatty acids and carnitine derivatives accumulated in the tissues of the patients. The understanding of the mechanisms by which these metabolites provoke tissue injury in FAODs is crucial for the developmental of novel therapeutic strategies that promote increased life expectancy, as well as improved life quality for patients. In this sense, the objective of this review is to present evidence from the scientific literature on the role of oxidative damage and mitochondrial dysfunction in the pathogenesis of the most prevalent FAODs: medium-chain acyl-CoA dehydrogenase (MCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies. It is expected that the findings presented in this review, obtained from both animal model and patients studies, may contribute to a better comprehension of the pathophysiology of these diseases.

Recent Advances in the Pathophysiology of Fatty Acid Oxidation Defects: Secondary Alterations of Bioenergetics and Mitochondrial Calcium Homeostasis Caused by the Accumulating Fatty Acids

Deficiencies of medium-chain acyl-CoA dehydrogenase, mitochondrial trifunctional protein, isolated long-chain 3-hydroxyacyl-CoA dehydrogenase, and very long-chain acyl-CoA dehydrogenase activities are considered the most frequent fatty acid oxidation defects (FAOD). They are biochemically characterized by the accumulation of medium-chain, long-chain hydroxyl, and long-chain fatty acids and derivatives, respectively, in tissues and biological fluids of the affected patients. Clinical manifestations commonly include hypoglycemia, cardiomyopathy, and recurrent rhabdomyolysis. Although the pathogenesis of these diseases is still poorly understood, energy deprivation secondary to blockage of fatty acid degradation seems to play an important role. However, recent evidence indicates that the predominant fatty acids accumulating in these disorders disrupt mitochondrial functions and are involved in their pathophysiology, possibly explaining the lactic acidosis, mitochondrial morphological alterations, and altered mitochondrial biochemical parameters found in tissues and cultured fibroblasts from some affected patients and also in animal models of these diseases. In this review, we will update the present knowledge on disturbances of mitochondrial bioenergetics, calcium homeostasis, uncoupling of oxidative phosphorylation, and mitochondrial permeability transition induction provoked by the major fatty acids accumulating in prevalent FAOD. It is emphasized that further in vivo studies carried out in tissues from affected patients and from animal genetic models of these disorders are necessary to confirm the present evidence mostly achieved from in vitro experiments.

Transport of Ca2+ and Ca2+-dependent permeability transition in heart mitochondria in the early stages of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a progressive skeletal muscle disease that is associated with severe cardiac complications in the late stages. Significant mitochondrial dysfunction is reportedly responsible for the development of cardiomyopathy with age. At the same time, adaptive changes in mitochondrial metabolism in cardiomyocytes were identified in the early stages of DMD. In this work, we evaluate the functioning of calcium transport systems (MCU and NCLX), and MPT pore in the heart mitochondria of young dystrophin-deficient mice. As compared to wild-type animals, heart mitochondria of mdx mice have been found to be more efficient both in respect to Ca²⁺ uniport and Na⁺-dependent Ca²⁺ efflux. The data obtained indicate that the increased rate of Ca²⁺ uptake by heart mitochondria of mdx mice may be due to an increase in the ratio of MCU and MCUb subunits. In turn, an increase in the rate of Ca²⁺ efflux from organelles in DMD may be the result of a significant increase in the level of NCLX. Moreover, the heart mitochondria of mdx mice were more resistant to MPT pore opening, which may be due to an increase in the microviscosity of mitochondrial membranes of DMD mice. At the same time, the level of putative MPT pore proteins did not change. The paper discusses the effect of rearrangements of the mitochondrial proteome involved in the transport and accumulation of calcium on the adaptation of this organ to DMD.

Transport of Ca2+ and Ca2+-Dependent Permeability Transition in Rat Liver Mitochondria under the Streptozotocin-Induced Type I Diabetes

Although diabetes mellitus is known to be a disease associated with mitochondrial dysfunction, not everything is clear about mitochondrial Ca2+ transport and Ca2+-induced permeability transition in diabetic cells. The objective of this work was to study the operation of MCU and Ca2+-dependent mitochondrial permeabilization in the liver cells of Sprague-Dawley rats under the streptozotocin-induced type I diabetes. It was shown that two weeks after the induction of diabetes, the rate of Ca2+ uptake by the mitochondria of diabetic animals increased ~1.4-fold. The expression of MCU and MICU1 subunits did not change, yet the quantity of dominant-negative MCUb channel subunits was almost twice as lower. The organelles also became more resistant to the induction of CsA-sensitive MPT pore and less resistant to the induction of CsA-insensitive palmitate/Ca2+-induced pore. The mitochondria of diabetic liver cells also showed changes in the lipid matrix of their membranes. The content of fatty acids in the membranes grew, and microviscosity of the lipid bilayer (assessed with laurdan) increased. At the same time, lipid peroxidation (assessed by the production of malonic dialdehyde) was stimulated. The paper discusses the consequences of the diabetes-related changes in mitochondria in the context of cell physiology.

Medium-chain acyl-coenzyme A dehydrogenase deficiency: Six cases in the Chinese population

BACKGROUND

Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) is a rare autosomal recessive disorder that affects the degradation of medium-chain fatty acids. Few cases of MCADD have been documented to date in mainland China.

METHODS

Medium-chain acyl-coenzyme A dehydrogenase deficiency was diagnosed in six patients (three girls and three boys) from six unrelated Chinese families at ages ranging from 10 days to 3 years old. The diagnosis was confirmed by the identification of a primary biomarker of serum octanoyl-carnitine (C8) and genetic pathogenic mutations.

RESULTS

Only two patients were admitted because of vomiting, diarrhea, myasthenia, and coma; the other four patients were diagnosed via the newborn screening process. Six mutations were found in acyl-CoA dehydrogenase medium chain (ACADM). One mutation (c.727C>T) was novel and the others (c.158G>A, c.387+1delG, c.449_452del, c.1045C>T, and c.1085G>A) have been previously reported.

CONCLUSIONS

Six Chinese cases of MCADD were identified. One novel mutation was found. c.449_452del and c.1085G>A were common mutations in this study.

The protective effects of distal ischemic treatment on apoptosis and mitochondrial permeability in the hippocampus after cardiopulmonary resuscitation

Apoptosis and mitochondrial dysfunction are the main cause of neurological injury after cardiopulmonary resuscitation (CPR). However, the effects of distal ischemic treatments on ischemia induced apoptosis are rarely studied, and the mechanism by which mitochondrial dysfunction contributes to CPR still unclear. A rat model of distal ischemia was established by clipping the right femoral artery. Rats were divided into blank, model, pre distal ischemic treatment, per-treatment, and post-treatment groups. Neurological deficit score was scored to evaluate neurologic function after cardiopulmonary resuscitation for 72 hr. We employed TUNEL and flow cytometry to measure the rate of apoptosis of hippocampal neurons, the integrity of mitochondrial membrane and the degree of mitochondrial permeability transition pore (mPTP) opening. The rate of apoptosis rate of hippocampal CA1 neurons in the pre-treatment and post-treatment groups were significantly lower than that of the model group. Moreover, the integrity of the mitochondrial membrane in the pre-treatment and post-treatment groups was higher than that in the model and per- treatment groups. Furthermore, the degree of mPTP opening was lower in the pre-treatment and post-treatment groups than the untreated and per-treatment groups. Taken together, our results show that ischemic preconditioning and post processing can maintain the integrity of mitochondria, perhaps by inhibiting the opening of mPTP, and reducing apoptosis of hippocampal neurons by regulating expression of apoptosis related proteins after CPR, to improve neurological function. This study highlights a novel target pathway for treatment of CPR.

Advances in the Understanding and Treatment of Mitochondrial Fatty Acid Oxidation Disorders

Purpose of review

This review focuses on advances made in the past three years with regards to understanding the mitochondrial fatty acid oxidation (FAO) pathway, the pathophysiological ramifications of genetic lesions in FAO enzymes, and emerging therapies for FAO disorders.

Recent findings

FAO has now been recognized to play a key energetic role in pulmonary surfactant synthesis, T-cell differentiation and memory, and the response of the proximal tubule to kidney injury. Patients with FAO disorders may face defects in these cellular systems as they age. Aspirin, statins, and nutritional supplements modulate the rate of FAO under normal conditions and could be risk factors for triggering symptoms in patients with FAO disorders. Patients have been identified with mutations in the ACAD9 and ECHS1 genes, which may represent new FAO disorders. New interventions for long-chain FAODs are in clinical trials. Finally, post-translational modifications that regulate fatty acid oxidation protein activities have been characterized that represent important new therapeutic targets.

Summary

Recent research has led to a deeper understanding of FAO. New therapeutic avenues are being pursued that may ultimately cause a paradigm shift for patient care.