Regulation of mitochondrial fatty acid β-oxidation in human: what can we learn from inborn fatty acid β-oxidation deficiencies?

Integrated Transcriptome Analysis of miRNAs and mRNAs in the Skeletal Muscle of Wuranke Sheep

MicroRNAs (miRNAs) are regarded as important regulators in skeletal muscle development. To reveal the regulatory roles of miRNAs and their target mRNAs underlying the skeletal muscle development of Wuranke sheep, we investigated the miRNA and mRNA expression profiles in the biceps femoris of these sheep at the fetal (3 months of gestation) and 3- and 15-month-old postnatal stages. Consequently, a total of 1195 miRNAs and 24,959 genes were identified. Furthermore, 474, 461, and 54 differentially expressed miRNAs (DEMs) and 6783, 7407, and 78 differentially expressed genes (DEGs) were detected among three comparative groups. Functional analysis demonstrated that the target mRNAs of the DEMs were enriched in multiple pathways related to muscle development. Moreover, the interactions among several predicted miRNA-mRNA pairs (oar-miR-133-HDAC1, oar-miR-1185-5p-MYH1/HADHA/OXCT1, and PC-5p-3703_578-INSR/ACTG1) that potentially affect skeletal muscle development were verified using dual-luciferase reporter assays. In this study, we identified the miRNA and mRNA differences in the skeletal muscle of Wuranke sheep at different developmental stages and revealed that a series of candidate miRNA-mRNA pairs may act as modulators of muscle development. These results will contribute to future studies on the function of miRNAs and their target mRNAs during skeletal muscle development in Wuranke sheep.

RNF152 Suppresses Fatty Acid Oxidation and Metastasis of Lung Adenocarcinoma by Inhibiting IRAK1-Mediated AKR1B10 Expression

Lung adenocarcinoma (LUAD) is a common subtype of primary lung cancer. Fatty acid oxidation plays a key role in LUAD development by providing energy for tumor cells. This study aimed to identify the role of ring finger protein 152 (RNF152) in LUAD. RNF152 was down-regulated in LUAD, and low RNF152 expression correlated with a poor prognosis in LUAD patients. RNF152 overexpression inhibited the proliferation and malignant phenotype of LUAD cells, whereas RNF152 knockdown exerted an opposite effect. Tumor cells overexpressing RNF152 showed less fatty acid oxidation compared with control cells, whereas RNF152 knockdown induced fatty acid uptake and oxidation. Further analysis revealed the binding reaction between RNF152 and interleukin-1 receptor-associated kinase 1 (IRAK1). RNF152 reduced the stability of IRAK1 in LUAD cells by promoting its ubiquitination. RNF152-overexpressed tumor cells exhibited a significantly lower level of Aldo-Keto reductase family 1 member 10 (AKR1B10), whereas up-regulation of IRAK1 restored the expression of AKR1B10 in RNF152-overexpressed cells. Furthermore, up-regulation of IRAK1 eliminated the antitumor effect of RNF152 in LUAD cells. Mouse xenograft models confirmed the inhibitory effect of RNF152 on the tumorigenesis and metastasis of LUAD. Taken together, RNF152 played a tumor suppressive role in LUAD by promoting IRAK1 ubiquitination and IRAK1-mediated down-regulation of AKR1B10, thereby reversing the malignant phenotype of LUAD.

Effects of L-carnitine supplementation on glucolipid metabolism: a systematic review and meta-analysis

Background: L-carnitine supplementation has been utilized against glucolipid metabolism disruption. However, to the best of our knowledge, no meta-analysis process has analyzed the effects of L-carnitine supplementation on insulin resistance, fasting blood glucose, lipid metabolism, and liver enzyme levels in adults. Methods: Through the analysis and screening of 12 221 studies, 15 studies were selected from eligible trials for meta-analysis. Meta-analysis was performed in a random effect model with heterogeneity determined by I², and subgroup analyses were used to further identify the source of heterogeneity. Result: The results showed significant effects of L-carnitine on FBG (MD = -4.94 mg dL^-1, 95% CI: -7.07 to -2.82), insulin (MD = -0.99 μU mL^-1, 95% CI: -1.41 to -0.56), HOMA-IR (MD = -0.58, 95% CI: -0.77 to -0.38), TG (MD = -11.22 mg dL^-1, 95% CI: -19.21 to -3.22), TC (MD = -6.45 mg dL^-1, 95% CI: -9.95 to -2.95, LDLc (MD = -8.28 mg dL^-1, 95% CI: -11.08 to -5.47), and ALT (MD = -19.71 IU L^-1, 95% CI: -36.45 to -2.96). However, no significant effect of L-carnitine supplementation was observed in HDLc (MD = -0.77 mg dL^-1, 95% CI: -0.10 to -1.63) or AST (MD = -11.05 IU L^-1, 95% CI: -23.08 to 0.99). The duration of carnitine supplementation was negatively associated with mean differences in FBG, as assessed by meta-regression. Conclusion: The current meta-analysis revealed that L-carnitine may have favorable effects on glucolipid profile, especially insulin, FBG, HOMA-IR, TG, TC, LDLc, and ALT levels.

Insights from comparative transcriptome analysis in the responses of Pb-tolerant fungi Curvularia tsudae to Pb stress

The fungus Curvularia tsudae can survive in environments that are extremely contaminated by heavy metals; however, the underlying molecular mechanisms of heavy metal tolerance are not clear. In this study, we determined the effects of lead (Pb) stress on the growth of C. tsudae and used RNA-Seq to identify significant genes and biological processes involved. The present study showed that C. tsudae had an outstanding resistant capacity to Pb stress and could survive at a concentration of 1600 mg L-1 Pb. Although an obvious inhibition on the growth was observed, the fungus exhibited tolerance as it continued to grow at a Pb concentration of 1600 mg L-1 for seven days. A total of 9997 (9020 up and 977 down) differentially expressed genes (DEGs) were detected in the mycelium of C. tsudae at Pb free (0 mg L-1) and Pb stressed samples. Pathway enrichment analysis identified several biological processes for managing Pb stress. Genes involved in carbohydrate metabolism tended to be modulated in response to Pb stress, while amino acids and the lipid metabolism would also be induced by Pb stress, and up-regulated genes involved in antioxidant substances and ABC transporters may be committed to high Pb tolerance. Our study contributes to the current literature on C. tsudae response to Pb stress and provides a useful reference for fungi as bioremediators in heavy metal-contaminated environments.

GC-MS metabolomics reveals dysregulated lipid metabolic pathways and metabolites in diabetic testicular toxicity: Therapeutic potentials of raffia palm (Raphia hookeri G. Mann & H. Wendl) wine

ETHNOPHARMACOLOGICAL RELEVANCE

Raffia palm (Raphia hookeri G. Mann & H. Wendl) wine (RPW) is a natural beverage obtained from the R. hookeri consumed for refreshment and medicinal purposes. For medicinal purposes, it is used singly or as macerating agent for other medicinal plants for the treatment of several diseases.

AIM

This study investigates the effect of Raffia palm wine on dysregulated lipid metabolic pathways in testicular tissues of type 2 diabetic (T2D) rats.

METHODS

Raffia palm wine (150 and 300 mg/kg bodyweight) was administered to two T2D groups respectively, another T2D group was not administered treatment and served as negative control, while metformin served as the standard drug. After 6 weeks of treatment, the rats were sacrificed, and the testes collected. After weighing, the organs were homogenized in 20% methanol/ethanol and centrifuged at 20,000 g to extract the lipid metabolites.

RESULTS

GC-MS analysis of the supernatants revealed an alteration of the metabolites on induction of T2D, with concomitant generation of 10 metabolites. Raffia palm wine inhibited the T2D-generated metabolites while replenishing cholesterol and squalene levels, with concomitant generation of 7 and 8 metabolites for low and high dose treatment respectively. Pathway enrichment analysis of the metabolites revealed a decreased level of steroid biosynthesis and increased level of fatty acid biosynthesis. Raffia palm wine inactivated glycerolipid, fatty acid, and arachidonic acid metabolisms, fatty acid biosynthesis and fatty acid elongation in mitochondria pathways, and activated pathways for plasmalogen synthesis, mitochondrial beta-oxidation of long chain saturated fatty acids.

CONCLUSION

The replenishment and generation of these metabolites and additional ones as well as activation of pathways involved in energy generation, phospholipids, antioxidant activity, steroidogenesis and spermatogenesis suggest a therapeutic effect of Raffia palm wine against hyperglycemic-induced testicular dysfunction.

Mitochondrial Fatty Acid β-Oxidation and Resveratrol Effect in Fibroblasts from Patients with Autism Spectrum Disorder

Patients with autism spectrum disorder (ASD) may have an increase in blood acyl-carnitine (AC) concentrations indicating a mitochondrial fatty acid β-oxidation (mtFAO) impairment. However, there are no data on systematic mtFAO analyses in ASD. We analyzed tritiated palmitate oxidation rates in fibroblasts from patients with ASD before and after resveratrol (RSV) treatment, according to methods used for the diagnosis of congenital defects in mtFAO. ASD participants (N = 10, 60%; male; mean age (SD) 7.4 (3.2) years) were divided in two age-equivalent groups based on the presence (N = 5) or absence (N = 5) of elevated blood AC levels. In addition, electron transport chain (ETC) activity in fibroblasts and muscle biopsies and clinical characteristics were compared between the ASD groups. Baseline fibroblast mtFAO was not significantly different in patients in comparison with control values. However, ASD patients with elevated AC exhibited significantly decreased mtFAO rates, muscle ETC complex II activity, and fibroblast ETC Complex II/III activity (p < 0.05), compared with patients without an AC signature. RSV significantly increased the mtFAO activity in all study groups (p = 0.001). The highest mtFAO changes in response to RSV were observed in fibroblasts from patients with more severe symptoms on the Social Responsiveness Scale total (p = 0.001) and Awareness, Cognition, Communication and Motivation subscales (all p < 0.01). These findings suggested recognition of an ASD patient subset characterized by an impaired mtFAO flux associated with abnormal blood AC. The study elucidated that RSV significantly increased fibroblast mtFAO irrespective of plasma AC status, and the highest changes to RSV effects on mtFAO were observed in the more severely affected patients.

Identification of novel diagnostic biomarkers in endometrial cancer using targeted metabolomic profiling

PURPOSE

Endometrial cancer (EC) is the most common gynecological malignancy with high disease burden especially in advanced stages of the disease. Our study investigated the metabolomic profile of EC patient's serum with the aim of identifying novel diagnostic biomarkers that could be used especially in early disease detection.

MATERIAL AND METHODS

Using targeted metabolomic serum profiling based on HPLC-TQ/MS, women with EC (n ​= ​15) and controls (n ​= ​21) were examined for 232 endogenous metabolites.

RESULTS

Top performing biomarkers included ceramides, acylcarnitines and 1-methyl adenosine. Top 4 biomarkers combined achieved 94% sensitivity with 75% specificity with AUC 92.5% (CI 90.5-94.5%). Individual markers also provided significant predictive values: C16-ceramide achieved sensitivity 73%, specificity 81%, AUC 0.83, C22-ceramide sensitivity 67%, specificity 81%, AUC 0.77, hydroxyhexadecenoylcarnitine sensitivity 60%, specificity 96%, AUC 0.76 and 1-methyladenosine sensitivity 67%, specificity 81%, AUC 0.75. The individual markers, however, did not reach the high sensitivity and specificity of the 4-biomarker combination.

CONCLUSIONS

Using mass spectrometry targeted metabolomic profiling, ceramides, acylcarnitines and 1-methyladenosine were identified as potential diagnostic biomarkers for EC. Additionally, these identified metabolites may provide additional insight into cancer cell metabolism.

Electron transfer flavoprotein and its role in mitochondrial energy metabolism in health and disease

Electron transfer flavoprotein (ETF) is an enzyme with orthologs from bacteria to humans. Human ETF is nuclear encoded by two separate genes, ETFA and ETFB, respectively. After translation, the two subunits are imported to the mitochondrial matrix space and assemble into a heterodimer containing one FAD and one AMP as cofactors. ETF functions as a hub taking up electrons from at least 14 flavoenzymes, feeding them into the respiratory chain. This represents a major source of reducing power for the electron transport chain from fatty acid oxidation and amino acid degradation. Transfer of electrons from the donor enzymes to ETF occurs by direct transfer between the enzyme bound flavins, a process that is tightly regulated by the polypeptide chain and by protein:protein interactions. ETF, in turn relays electrons to the iron sulfur cluster of the inner membrane protein ETF:QO, from where they travel via the FAD in ETF:QO to ubiquinone, entering the respiratory chain at the level of complex III. ETF recognizes its dehydrogenase partners via a recognition loop that anchors the protein on its partner followed by dynamic movements of the ETF flavin domain that bring redox cofactors in close proximity, thus promoting electron transfer. Genetic mutations in the ETFA or ETFB genes cause the Mendelian disorder multiple acyl-CoA dehydrogenase deficiency (MADD; OMIM #231680). We here review the knowledge on human ETF and investigations of the effects of disease-associated missense mutations in this protein that have promoted the understanding of the essential role that ETF plays in cellular metabolism and human disease.

SOCS2 Inhibits Mitochondrial Fatty Acid Oxidation via Suppressing LepR/JAK2/AMPK Signaling Pathway in Mouse Adipocytes

Suppressor of cytokine signaling 2 (SOCS2) plays an important role in fat deposition, skeletal muscle, central nervous system development, and mitochondria biogenesis. Nevertheless, the regulatory mechanisms of SOCS2 on mitochondrial fatty acid oxidation (FAO) remain unclear. Leptin could inhibit food intake and increase thermogenesis through leptin receptor (LepR), which was present in the hypothalamus and certain peripheral organs, including adipose tissue. With strong interest, we focused on the connection between leptin and SOCS2 and their effect on FAO in adipocytes. In our study, we found that the mRNA level of SOCS2 and the protein levels of PGC-1α, CPT-1b, FAT, and p-ACC were elevated by leptin in the inguinal adipose tissue of mice. On the contrary, the protein levels of FABP4, FATP1, and FAS were declined. The genes related to fatty acid oxidation such as PGC-1α, NRF-1, TFAM, CPT-1b, AOX1, COX2, and UCP2 were attenuated by SOCS2, but elevated by leptin. Moreover, fatty acid oxidation enzyme MCAD, LCAD, and Cyt C levels were reduced in response to SOCS2. These reductions correspond well with the reduced release of free fatty acid and the reduction of mitochondrial complexes I and III by SOCS2. Furthermore, JAK2/AMPK pathway-specific inhibitors could block the mitochondrial FAO; hence, this pathway was implied to have a potential impact on FAO. Together, these studies suggested that SOCS2 had a negative effect on mitochondrial fatty acid oxidation, and the LepR/JAK2/AMPK pathway played a crucial role in this process.

[Dysfunctions of mitochondrial fatty acid β-oxidation in rare and common diseases]

Dysfunctions of mitochondrial fatty acid ß-oxidation (ß-FAO) in various tissues represent a hallmark of many common disorders, and are acknowledged to play an essential role in the pathogenesis of diabetes, obesity, and cardiac diseases. Moreover, inborn defects in ß-FAO form a large family of rare diseases with variable phenotypes, ranging from fatal multi-organ failure in the newborn to isolated adult onset myopathy. These pathologies highlight the critical role of ß-FAO in many tissues with high-energy demand (heart, muscle, liver, kidney). Furthermore, and unexpectedly, very recent data unveiled the possible involvement of ß-FAO in instructing complex non energy-related functions, such as chromatin modification, control of neural stem cell activity, or survival and fate of cancer cells. Pharmacological targeting of ß-FAO by small molecules might therefore open new avenues for the treatment of various rare or common diseases.

Metformin regulates lipid metabolism in a canine model of atrial fibrillation through AMPK/PPAR-α/VLCAD pathway

Background

Atrial lipid metabolic remodeling is critical for the process of atrial fibrillation (AF). Abnormal Fatty acid (FA) metabolism in cardiomyocytes is involved in the pathogenesis of AF. MET (Metformin), an AMPK (AMP-activated protein kinase) activator, has been found to be associated with a decreased risk of AF in patients with type 2 diabetes. However, the specific mechanism remains unknown.

Methods

Fifteen mongrel dogs were divided into three groups: SR, ARP (pacing with 800 beats/min for 6 h), ARP plus MET (treated with MET (100 mg/kg/day) for two weeks before pacing). We assessed metabolic factors, speed limiting enzymes circulating biochemical metabolites (substrates and products), atrial electrophysiology and accumulation of lipid droplets.

Results

The expression of AMPK increased in the ARP group and significantly increased in the MET+ARP group comparing to the SR group. In the ARP group, the expressions of PPARα、PGC-1α and VLCAD were down-regulated, while the concentration of free fatty acid and triglyceride and the lipid deposition in LAA (left atrial appendage) increased. Moreover, AERP and AERPd have also been found abnormally in this process. Pretreatment with MET before receiving ARP reversed the alterations aforementioned.

Conclusions

The FA metabolism in LAA is altered in the ARP group, mainly characterized by the abnormal expression of the rate-limiting enzyme. Metformin reduces lipid accumulation and promotes β-oxidation of FA in AF models partially through AMPK/PPAR-α/VLCAD pathway. Our study indicates that MET may inhibit the FA lipid metabolic remodeling in AF.

Nuclear Peroxisome Proliferator-Activated Receptors (PPARs) as Therapeutic Targets of Resveratrol for Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by defective social communication and interaction and restricted, repetitive behavior with a complex, multifactorial etiology. Despite an increasing worldwide prevalence of ASD, there is currently no pharmacological cure to treat core symptoms of ASD. Clinical evidence and molecular data support the role of impaired mitochondrial fatty acid oxidation (FAO) in ASD. The recognition of defects in energy metabolism in ASD may be important for better understanding ASD and developing therapeutic intervention. The nuclear peroxisome proliferator-activated receptors (PPAR) α, δ, and γ are ligand-activated receptors with distinct physiological functions in regulating lipid and glucose metabolism, as well as inflammatory response. PPAR activation allows a coordinated up-regulation of numerous FAO enzymes, resulting in significant PPAR-driven increases in mitochondrial FAO flux. Resveratrol (RSV) is a polyphenolic compound which exhibits metabolic, antioxidant, and anti-inflammatory properties, pointing to possible applications in ASD therapeutics. In this study, we review the evidence for the existing links between ASD and impaired mitochondrial FAO and review the potential implications for regulation of mitochondrial FAO in ASD by PPAR activators, including RSV.

A new AMPK activator, GSK773, corrects fatty acid oxidation and differentiation defect in CPT2-deficient myotubes

Carnitine palmitoyl transferase 2 (CPT2) deficiency is one of the most common inherited fatty acid oxidation (FAO) defects and represents a prototypical mitochondrial metabolic myopathy. Recent studies have suggested a pivotal role of adenosine monophosphate-activated protein kinase (AMPK) in skeletal muscle plasticity and mitochondrial homeostasis. Thus, we tested the potential of GSK773, a novel direct AMPK activator, to improve or correct FAO capacities in muscle cells from patients harboring various mutations. We used controls' and patients' myotubes and studied the parameters of FAO metabolism, of mitochondrial quantity and quality and of differentiation. We found that AMPK is constitutively activated in patients' myotubes, which exhibit both reduced FAO and impaired differentiation. GSK773 improves or corrects several metabolic hallmarks of CPT2 deficiency (deficient FAO flux and C16-acylcarnitine accumulation) by upregulating the expression of CPT2 protein. Beneficial effects of GSK773 are also likely due to stimulation of mitochondrial biogenesis and induction of mitochondrial fusion, by decreasing dynamin-related protein 1 and increasing mitofusin 2. GSK773 also induces a shift in myosin heavy chain isoforms toward the slow oxidative type and, therefore, fully corrects the differentiation process. We establish, through small interfering RNA knockdowns and pharmacological approaches, that these GSK773 effects are mediated through peroxisome proliferator-activated receptor gamma co-activator 1-alpha, reactive oxygen species and p38 mitogen-activated protein kinase, all key players of skeletal muscle plasticity. GSK773 recapitulates several important features of skeletal muscle adaptation to exercise. The results show that AMPK activation by GSK773 evokes the slow, oxidative myogenic program and triggers beneficial phenotypic adaptations in FAO-deficient myotubes. Thus, GSK773 might have therapeutic potential for correction of CPT2 deficiency.

Central role of obesity in endothelial cell dysfunction and cardiovascular risk

SUMMARY Atherosclerosis is the leading cause of mortality in the contemporary world. The critical role of the endothelial cells (EC) in vascular homeostasis, the metabolic changes that take place when the cell is activated, and the elements involved in these processes have been widely explored over the past years. Obesity and its impact, promoting a rise in blood levels of free fatty acids (FAs) are often associated with atherosclerosis and cardiovascular mortality. However, the mechanisms that promote cardiovascular structural changes and adaptive changes in the ECs, particularly in the context of obesity, are little known. Here, we reviewed studies that assessed the metabolic adaptations of healthy and dysfunctional ECs during exposure to FAs, as well as the epidemiological perspectives of cardiovascular structural changes in obesity. Finally, we explored the role of new agents – sphingolipids, dietary unsaturated fatty acids and sodium-glucose cotransporter-2 inhibitors (iSGLT2) – in atherosclerosis and their relationship with obesity.

The carnitine system and cancer metabolic plasticity

Metabolic flexibility describes the ability of cells to respond or adapt its metabolism to support and enable rapid proliferation, continuous growth, and survival in hostile conditions. This dynamic character of the cellular metabolic network appears enhanced in cancer cells, in order to increase the adaptive phenotype and to maintain both viability and uncontrolled proliferation. Cancer cells can reprogram their metabolism to satisfy the energy as well as the biosynthetic intermediate request and to preserve their integrity from the harsh and hypoxic environment. Although several studies now recognize these reprogrammed activities as hallmarks of cancer, it remains unclear which are the pathways involved in regulating metabolic plasticity. Recent findings have suggested that carnitine system (CS) could be considered as a gridlock to finely trigger the metabolic flexibility of cancer cells. Indeed, the components of this system are involved in the bi-directional transport of acyl moieties from cytosol to mitochondria and vice versa, thus playing a fundamental role in tuning the switch between the glucose and fatty acid metabolism. Therefore, the CS regulation, at both enzymatic and epigenetic levels, plays a pivotal role in tumors, suggesting new druggable pathways for prevention and treatment of human cancer.

A proteomic-based investigation of potential copper-responsive biomarkers: Proteins, conceptual networks, and metabolic pathways featuring Penicillium janthinellum from a heavy metal-polluted ecological niche

Filamentous fungi‐copper (Cu) interactions are very important in the formation of natural ecosystems and the bioremediation of heavy metal pollution. However, important issues at the proteome level remain unclear. We compared six proteomes from Cu‐resistant wild‐type (WT) Penicillium janthinellum strain GXCR and a Cu‐sensitive mutant (EC‐6) under 0, 0.5, and 3 mmol/L Cu treatments using iTRAQ. A total of 495 known proteins were identified, and the following conclusions were drawn from the results: Cu tolerance depends on ATP generation and supply, which is relevant to glycolysis pathway activity; oxidative phosphorylation, the TCA cycle, gluconeogenesis, fatty acid synthesis, and metabolism are also affected by Cu; high Cu sensitivity is primarily due to an ATP energy deficit; among ATP generation pathways, Cu‐sensitive and Cu‐insensitive metabolic steps exist; gluconeogenesis pathway is crucial to the survival of fungi in Cu‐containing and sugar‐scarce environments; fungi change their proteomes via two routes (from ATP, ATP‐dependent RNA helicases (ADRHs), and ribosome biogenesis to proteasomes and from ATP, ADRHs to spliceosomes and/or stress‐adapted RNA degradosomes) to cope with changes in Cu concentrations; and unique routes exist through which fungi respond to high environmental Cu. Further, a general diagram of Cu‐responsive paths and a model theory of high Cu are proposed at the proteome level. Our work not only provides the potential protein biomarkers that indicate Cu pollution and targets metabolic steps for engineering Cu‐tolerant fungi during bioremediation but also presents clues for further insight into the heavy metal tolerance mechanisms of other eukaryotes.

Living on the edge: substrate competition explains loss of robustness in mitochondrial fatty-acid oxidation disorders

Background

Defects in genes involved in mitochondrial fatty-acid oxidation (mFAO) reduce the ability of patients to cope with metabolic challenges. mFAO enzymes accept multiple substrates of different chain length, leading to molecular competition among the substrates. Here, we combined computational modeling with quantitative mouse and patient data to investigate whether substrate competition affects pathway robustness in mFAO disorders.

Results

First, we used comprehensive biochemical analyses of wild-type mice and mice deficient for medium-chain acyl-CoA dehydrogenase (MCAD) to parameterize a detailed computational model of mFAO. Model simulations predicted that MCAD deficiency would have no effect on the pathway flux at low concentrations of the mFAO substrate palmitoyl-CoA. However, high concentrations of palmitoyl-CoA would induce a decline in flux and an accumulation of intermediate metabolites. We proved computationally that the predicted overload behavior was due to substrate competition in the pathway. Second, to study the clinical relevance of this mechanism, we used patients’ metabolite profiles and generated a humanized version of the computational model. While molecular competition did not affect the plasma metabolite profiles during MCAD deficiency, it was a key factor in explaining the characteristic acylcarnitine profiles of multiple acyl-CoA dehydrogenase deficient patients. The patient-specific computational models allowed us to predict the severity of the disease phenotype, providing a proof of principle for the systems medicine approach.

Conclusion

We conclude that substrate competition is at the basis of the physiology seen in patients with mFAO disorders, a finding that may explain why these patients run a risk of a life-threatening metabolic catastrophe.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-016-0327-5) contains supplementary material, which is available to authorized users.

Medium-chain acyl-Coenzyme A dehydrogenase deficiency (MCADD): a cause of severe hypoglycaemia in an apparently well child

Medium-chain acyl-Coenzyme A dehydrogenase deficiency (MCADD) is a disorder of fatty acid β oxidation inherited in an autosomal recessive manner. The enzyme is useful in hepatic ketogenesis, a major source of energy once hepatic glycogen stores become depleted during prolonged fasting. It is a cause of hypoketotic hypoglycaemia in a previously well child. MCADD is not part of newborn screening in Ireland; children are likely to be missed if routine hypoglycaemic screen is not instituted when blood glucose level is below 2.6 mmol/L. This is a case of an otherwise healthy 23-month-old baby girl who presented with severe hypoglycaemia with some initial diagnostic dilemma.

Ketogenic diet and childhood neurological disorders other than epilepsy: an overview

INTRODUCTION

In the last years, ketogenic diet (KD) has been experimentally utilized in various childhood neurologic disorders such as mitochondriopathies, alternating hemiplegia of childhood (AHC), brain tumors, migraine, and autism spectrum disorder (ASD). The aim of this review is to analyze how KD can target these different medical conditions, highlighting possible mechanisms involved. Areas covered: We have conducted an analysis on literature concerning KD use in mitochondriopathies, AHC, brain tumors, migraine, and ASD. Expert commentary: The role of KD in reducing seizure activity in some mitochondriopathies and its efficacy in pyruvate dehydrogenase deficiency is known. Recently, few cases suggest the potentiality of KD in decreasing paroxysmal activity in children affected by AHC. A few data support its potential use as co-adjuvant and alternative therapeutic option for brain cancer, while any beneficial effect of KD on migraine remains unclear. KD could improve cognitive and social skills in a subset of children with ASD.

Ketogenic diets: from cancer to mitochondrial diseases and beyond

BACKGROUND

The employment of dietary strategies such as ketogenic diets, which force cells to alter their energy source, has shown efficacy in the treatment of several diseases. Ketogenic diets are composed of high fat, moderate protein and low carbohydrates, which favour mitochondrial respiration rather than glycolysis for energy metabolism.

DESIGN

This review focuses on how oncological, neurological and mitochondrial disorders have been targeted by ketogenic diets, their metabolic effects, and the possible mechanisms of action on mitochondrial energy homeostasis. The beneficial and adverse effects of the ketogenic diets are also highlighted.

RESULTS AND CONCLUSIONS

Although the full mechanism by which ketogenic diets improve oncological and neurological conditions still remains to be elucidated, their clinical efficacy has attracted many new followers, and ketogenic diets can be a good option as a co-adjuvant therapy, depending on the situation and the extent of the disease.

Bi-allelic Truncating Mutations in TANGO2 Cause Infancy-Onset Recurrent Metabolic Crises with Encephalocardiomyopathy

Molecular diagnosis of mitochondrial disorders is challenging because of extreme clinical and genetic heterogeneity. By exome sequencing, we identified three different bi-allelic truncating mutations in TANGO2 in three unrelated individuals with infancy-onset episodic metabolic crises characterized by encephalopathy, hypoglycemia, rhabdomyolysis, arrhythmias, and laboratory findings suggestive of a defect in mitochondrial fatty acid oxidation. Over the course of the disease, all individuals developed global brain atrophy with cognitive impairment and pyramidal signs. TANGO2 (transport and Golgi organization 2) encodes a protein with a putative function in redistribution of Golgi membranes into the endoplasmic reticulum in Drosophila and a mitochondrial localization has been confirmed in mice. Investigation of palmitate-dependent respiration in mutant fibroblasts showed evidence of a functional defect in mitochondrial β-oxidation. Our results establish TANGO2 deficiency as a clinically recognizable cause of pediatric disease with multi-organ involvement.

Metabolic Encephalopathy and Lipid Storage Myopathy Associated with a Presumptive Mitochondrial Fatty Acid Oxidation Defect in a Dog

A 1-year-old spayed female Shih Tzu presented for episodic abnormalities of posture and mentation. Neurological examination was consistent with a bilaterally symmetric multifocal encephalopathy. The dog had a waxing-and-waning hyperlactemia and hypoglycemia. Magnetic resonance imaging revealed bilaterally symmetric cavitated lesions of the caudate nuclei with less severe abnormalities in the cerebellar nuclei. Empirical therapy was unsuccessful, and the patient was euthanized. Post-mortem histopathology revealed bilaterally symmetric necrotic lesions of the caudate and cerebellar nuclei and multi-organ lipid accumulation, including a lipid storage myopathy. Malonic aciduria and ketonuria were found on urinary organic acid screen. Plasma acylcarnitine analysis suggested a fatty acid oxidation defect. Fatty acid oxidation disorders are inborn errors of metabolism documented in humans, but poorly described in dogs. Although neurological signs have been described in humans with this group of diseases, descriptions of advanced imaging, and histopathology are severely lacking. This report suggests that abnormalities of fatty acid metabolism may cause severe, bilateral gray matter necrosis, and lipid accumulation in multiple organs including the skeletal muscles, liver, and kidneys. Veterinarians should be aware that fatty acid oxidation disorders, although potentially fatal, may be treatable. A timely definitive diagnosis is essential in guiding therapy.

Mitochondrial dysfunction in fatty acid oxidation disorders: insights from human and animal studies

Patients affected by FAOD commonly present with hepatopathy, cardiomyopathy, skeletal myopathy and encephalopathy. Human and animal evidences indicate that mitochondrial functions are disrupted by fatty acids and derivatives accumulating in these disorders, suggesting that lipotoxicity may contribute to their pathogenesis.

Mitochondrial fatty acid oxidation (FAO) plays a pivotal role in maintaining body energy homoeostasis mainly during catabolic states. Oxidation of fatty acids requires approximately 25 proteins. Inherited defects of FAO have been identified in the majority of these proteins and constitute an important group of inborn errors of metabolism. Affected patients usually present with severe hepatopathy, cardiomyopathy and skeletal myopathy, whereas some patients may suffer acute and/or progressive encephalopathy whose pathogenesis is poorly known. In recent years growing evidence has emerged indicating that energy deficiency/disruption of mitochondrial homoeostasis is involved in the pathophysiology of some fatty acid oxidation defects (FAOD), although the exact underlying mechanisms are not yet established. Characteristic fatty acids and carnitine derivatives are found at high concentrations in these patients and more markedly during episodes of metabolic decompensation that are associated with worsening of clinical symptoms. Therefore, it is conceivable that these compounds may be toxic. We will briefly summarize the current knowledge obtained from patients and genetic mouse models with these disorders indicating that disruption of mitochondrial energy, redox and calcium homoeostasis is involved in the pathophysiology of the tissue damage in the more common FAOD, including medium-chain acyl-CoA dehydrogenase (MCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies. We will also provide evidence that the fatty acids and derivatives that accumulate in these diseases disrupt mitochondrial homoeostasis. The elucidation of the toxic mechanisms of these compounds may offer new perspectives for potential novel adjuvant therapeutic strategies in selected disorders of this group.

Mitochondrial dysfunction and seizures: the neuronal energy crisis

Seizures are often the key manifestation of neurological diseases caused by pathogenic mutations in 169 of the genes that have so far been identified to affect mitochondrial function. Mitochondria are the main producers of ATP needed for normal electrical activities of neurons and synaptic transmission. Additionally, they have a central role in neurotransmitter synthesis, calcium homoeostasis, redox signalling, production and modulation of reactive oxygen species, and neuronal death. Hypotheses link mitochondrial failure to seizure generation through changes in calcium homoeostasis, oxidation of ion channels and neurotransmitter transporters by reactive oxygen species, a decrease in neuronal plasma membrane potential, and reduced network inhibition due to interneuronal dysfunction. Seizures, irrespective of their origin, represent an excessive acute energy demand in the brain. Accordingly, secondary mitochondrial dysfunction has been described in various epileptic disorders, including disorders that are mainly of non-mitochondrial origin. An understanding of the reciprocal relation between mitochondrial dysfunction and epilepsy is crucial to select appropriate anticonvulsant treatment and has the potential to open up new therapeutic approaches in the subset of epileptic disorders caused by mitochondrial dysfunction.

Redox signalling and mitochondrial stress responses; lessons from inborn errors of metabolism

Mitochondria play a key role in overall cell physiology and health by integrating cellular metabolism with cellular defense and repair mechanisms in response to physiological or environmental changes or stresses. In fact, dysregulation of mitochondrial stress responses and its consequences in the form of oxidative stress, has been linked to a wide variety of diseases including inborn errors of metabolism. In this review we will summarize how the functional state of mitochondria -- and especially the concentration of reactive oxygen species (ROS), produced in connection with the respiratory chain -- regulates cellular stress responses by redox regulation of nuclear gene networks involved in repair systems to maintain cellular homeostasis and health. Based on our own and other's studies we re-introduce the ROS triangle model and discuss how inborn errors of mitochondrial metabolism, by production of pathological amounts of ROS, may cause disturbed redox signalling and induce chronic cell stress with non-resolving or compromised cell repair responses and increased susceptibility to cell stress induced cell death. We suggest that this model may have important implications for those inborn errors of metabolism, where mitochondrial dysfunction plays a major role, as it allows the explanation of oxidative stress, metabolic reprogramming and altered signalling growth pathways that have been reported in many of the diseases. It is our hope that the model may facilitate novel ideas and directions that can be tested experimentally and used in the design of future new approaches for pre-symptomatic diagnosis and prognosis and perhaps more effective treatments of inborn errors of metabolism.