Time to harmonize mitochondrial syndrome nomenclature and classification: A consensus from the North American Mitochondrial Disease Consortium (NAMDC)

OBJECTIVE

To harmonize terminology in mitochondrial medicine, we propose revised clinical criteria for primary mitochondrial syndromes.

METHODS

The North American Mitochondrial Disease Consortium (NAMDC) established a Diagnostic Criteria Committee comprised of members with diverse expertise. It included clinicians, researchers, diagnostic laboratory directors, statisticians, and data managers. The Committee conducted a comprehensive literature review, an evaluation of current clinical practices and diagnostic modalities, surveys, and teleconferences to reach consensus on syndrome definitions for mitochondrial diseases. The criteria were refined after manual application to patients enrolled in the NAMDC Registry.

RESULTS

By building upon published diagnostic criteria and integrating recent advances, NAMDC has generated updated consensus criteria for the clinical definition of classical mitochondrial syndromes.

CONCLUSIONS

Mitochondrial diseases are clinically, biochemically, and genetically heterogeneous and therefore challenging to classify and diagnose. To harmonize terminology, we propose revised criteria for the clinical definition of mitochondrial disorders. These criteria are expected to standardize the diagnosis and categorization of mitochondrial diseases, which will facilitate future natural history studies and clinical trials.

Metabolic reprogramming during hyperammonemia targets mitochondrial function and postmitotic senescence

Ammonia is a cytotoxic metabolite with pleiotropic molecular and metabolic effects, including senescence induction. During dysregulated ammonia metabolism, which occurs in chronic diseases, skeletal muscle becomes a major organ for nonhepatocyte ammonia uptake. Muscle ammonia disposal occurs in mitochondria via cataplerosis of critical intermediary metabolite α-ketoglutarate, a senescence-ameliorating molecule. Untargeted and mitochondrially targeted data were analyzed by multiomics approaches. These analyses were validated experimentally to dissect the specific mitochondrial oxidative defects and functional consequences, including senescence. Responses to ammonia lowering in myotubes and in hyperammonemic portacaval anastomosis rat muscle were studied. Whole-cell transcriptomics integrated with whole-cell, mitochondrial, and tissue proteomics showed distinct temporal clusters of responses with enrichment of oxidative dysfunction and senescence-related pathways/proteins during hyperammonemia and after ammonia withdrawal. Functional and metabolic studies showed defects in electron transport chain complexes I, III, and IV; loss of supercomplex assembly; decreased ATP synthesis; increased free radical generation with oxidative modification of proteins/lipids; and senescence-associated molecular phenotype–increased β-galactosidase activity and expression of p16^INK, p21, and p53. These perturbations were partially reversed by ammonia lowering. Dysregulated ammonia metabolism caused reversible mitochondrial dysfunction by transcriptional and translational perturbations in multiple pathways with a distinct skeletal muscle senescence-associated molecular phenotype.

Possible Bioenergetic Biomarker for Chronic Cancer-Related Fatigue

BACKGROUND

Cancer-related fatigue is a highly prevalent, debilitating, and persistent symptom experienced by patients receiving cancer treatments. Up to 71% of men with prostate cancer receiving radiation therapy experience acute and persistent CRF. There is neither an effective therapy nor a diagnostic biomarker for cancer-related fatigue. This pilot study aimed to discover potential biomarkers associated with chronic cancer-related fatigue in men with prostate cancer receiving radiation therapy.

METHODS

We used a longitudinal repeated-measures research design. Twenty men with prostate cancer undergoing radiation therapy completed all study visits. Cancer-related fatigue was evaluated by a well-established and validated questionnaire, the Patient-Reported Outcomes Measurement Information System-Fatigue (PROMIS-F) Short Form. In addition, peripheral blood mononuclear cells (PBMC) were harvested to quantify ribonucleic acid (RNA) gene expression of mitochondria-related genes. Data were collected before, during, on completion, and 24 months postradiation therapy and analyzed using paired t-tests and repeated measures analysis of variance.

RESULTS

The mean of the PROMIS-F T-score was significantly increased over time in patients with prostate cancer, remaining elevated at 24 months post-radiation therapy compared to baseline. A significant downregulated BC1 ubiquinol-cytochrome c reductase synthesis-like (BCS1L) was observed over time during radiation therapy and at 24 months postradiation therapy. An increased PROMIS-F score was trended with downregulated BCS1L in patients 24 months after completing radiation therapy.

DISCUSSION

This is the first evidence to describe altered messenger RNA for BCS1L in chronic cancer-related fatigue using the PROMIS-F measure with men receiving radiation therapy for prostate cancer.

CONCLUSION

Our results suggest that PBMC messenger RNA for BCS1L is a potential biomarker and therapeutic target for radiation therapy-induced chronic cancer-related fatigue in this clinical population.

Exercise training and diet-induced weight loss increase markers of hepatic bile acid (BA) synthesis and reduce serum total BA concentrations in obese women

Regular exercise has profound metabolic influence on the liver, but effects on bile acid (BA) metabolism are less well known. BAs are synthesized exclusively in the liver from cholesterol via the rate-limiting enzyme cholesterol 7 alpha-hydroxylase (CYP7A1). BAs contribute to the solubilization and absorption of lipids and serve as important signaling molecules, capable of systemic endocrine function. Circulating BAs increase with obesity and insulin resistance, but effects following exercise and diet-induced weight loss are unknown. To test if improvements in fitness and weight loss as a result of exercise training enhance BA metabolism, we measured serum concentrations of total BAs (conjugated and unconjugated primary and secondary BAs) in sedentary, obese, insulin-resistant women (N = 11) before (PRE) and after (POST) a ∼14-wk exercise and diet-induced weight loss intervention. BAs were measured in serum collected after an overnight fast and during an oral glucose tolerance test (OGTT). Serum fibroblast growth factor 19 (FGF19; a regulator of BA synthesis) and 7-alpha-hydroxy-cholesten-3-one (C4, a marker of CYP7A1 enzymatic activity) also were measured. Using linear mixed-model analyses and the change in V̇O_2peak (mL/min/kg) as a covariate, we observed that exercise and weight loss intervention decreased total fasting serum BA by ∼30% (P = 0.001) and increased fasting serum C4 concentrations by 55% (P = 0.004). C4 was significantly correlated with serum total BAs only in the POST condition, whereas serum FGF19 was unchanged. These data indicate that a fitness and weight loss intervention modifies BA metabolism in obese women and suggest that improved metabolic health associates with higher postabsorptive (fasting) BA synthesis. Furthermore, pre- vs. postintervention patterns of serum C4 following an OGTT support the hypothesis that responsiveness of BA synthesis to postprandial inhibition is improved after exercise and weight loss.NEW & NOTEWORTHY Exercise and weight loss in previously sedentary, insulin-resistant women facilitates a significant improvement in insulin sensitivity and fitness that may be linked to changes in bile acid metabolism. Diet-induced weight loss plus exercise-induced increases in fitness promote greater postabsorptive bile acid synthesis while also sensitizing the bile acid metabolic system to feedback inhibition during a glucose challenge when glucose and insulin are elevated.

Relationships between expression of BCS1L, mitochondrial bioenergetics, and fatigue among patients with prostate cancer

Introduction: Cancer-related fatigue (CRF) is the most debilitating symptom with the greatest adverse side effect on quality of life. The etiology of this symptom is still not understood. The purpose of this study was to examine the relationship between mitochondrial gene expression, mitochondrial oxidative phosphorylation, electron transport chain complex activity, and fatigue in prostate cancer patients undergoing radiotherapy (XRT), compared to patients on active surveillance (AS).

Methods: The study used a matched case–control and repeated-measures research design. Fatigue was measured using the revised Piper Fatigue Scale from 52 patients with prostate cancer. Mitochondrial oxidative phosphorylation, electron-transport chain enzymatic activity, and BCS1L gene expression were determined using patients’ peripheral mononuclear cells. Data were collected at three time points and analyzed using repeated measures ANOVA.

Results: The fatigue score was significantly different over time between patients undergoing XRT and AS (P<0.05). Patients undergoing XRT experienced significantly increased fatigue at day 21 and day 42 of XRT (P<0.01). Downregulated mitochondrial gene (BC1, ubiquinol-cytochrome c reductase, synthesis-like, BCS1L, P<0.05) expression, decreased OXPHOS-complex III oxidation (P<0.05), and reduced activity of complex III were observed over time in patients with XRT. Moreover, increased fatigue was significantly associated with downregulated BCS1L and decreased complex III oxidation in patients undergoing XRT.

Conclusion: Our results suggest that BCS1L and complex III in mitochondrial mononuclear cells are potential biomarkers and feasible therapeutic targets for acute XRT-induced fatigue in this clinical population.

Alterations of skeletal muscle bioenergetics in a mouse with F508del mutation leading to a cystic fibrosis-like condition

High energy expenditure is reported in cystic fibrosis (CF) animal models and patients. Alterations in skeletal muscle oxidative capacity, fuel utilization, and the creatine kinase-phosphocreatine system suggest mitochondrial dysfunction. Studies were performed on congenic C57BL/6J and F508del (Cftr^tm1kth) mice. Indirect calorimetry was used to measure gas exchange to evaluate aerobic capacity during treadmill exercise. The bioenergetic function of skeletal muscle subsarcolemmal (SSM) and interfibrillar mitochondria (IFM) was evaluated using an integrated approach combining measurement of the rate of oxidative phosphorylation by polarography and of electron transport chain activities by spectrophotometry. CF mice have reduced maximal aerobic capacity. In SSM of these mice, oxidative phosphorylation was impaired in the presence of complex I, II, III, and IV substrates except when glutamate was used as substrate. This impairment appeared to be caused by a defect in complex V activity, whereas the oxidative system of the electron transport chain was unchanged. In IFM, oxidative phosphorylation and electron transport chain activities were preserved, whereas complex V activity was reduced, in CF. Furthermore, creatine kinase activity was reduced in both SSM and IFM of CF skeletal muscle. The decreased complex V activity in SSM resulted in reduced oxidative phosphorylation, which could explain the reduced skeletal muscle response to exercise in CF mice. The decrease in mitochondrial creatine kinase activity also contributed to this poor exercise response.

ATAD3A oligomerization causes neurodegeneration by coupling mitochondrial fragmentation and bioenergetics defects

Mitochondrial fragmentation and bioenergetic failure manifest in Huntington’s disease (HD), a fatal neurodegenerative disease. The factors that couple mitochondrial fusion/fission with bioenergetics and their impacts on neurodegeneration however remain poorly understood. Our proteomic analysis identifies mitochondrial protein ATAD3A as an interactor of mitochondrial fission GTPase, Drp1, in HD. Here we show that, in HD, ATAD3A dimerization due to deacetylation at K135 residue is required for Drp1-mediated mitochondrial fragmentation. Disturbance of ATAD3A steady state impairs mtDNA maintenance by disrupting TFAM/mtDNA binding. Blocking Drp1/ATAD3A interaction with a peptide, DA1, abolishes ATAD3A oligomerization, suppresses mitochondrial fragmentation and mtDNA lesion, and reduces bioenergetic deficits and cell death in HD mouse- and patient-derived cells. DA1 treatment reduces behavioral and neuropathological phenotypes in HD transgenic mice. Our findings demonstrate that ATAD3A plays a key role in neurodegeneration by linking Drp1-induced mitochondrial fragmentation to defective mtDNA maintenance, suggesting that DA1 might be useful for developing HD therapeutics.

Huntington’s disease leads to mitochondrial fragmentation and bioenergetic failure, although how the two events are connected is poorly understood. Here, Zhao et al. identify ATAD3A as a molecular linker and show that a peptide inhibitor of ATAD3A oligomerization suppresses HD phenotypes.

Integrated mitochondrial function and cancer-related fatigue in men with prostate cancer undergoing radiation therapy

Introduction

Fatigue experienced by cancer patients is one of the most common symptoms with the greatest adverse effect on quality of life, but arguably the least understood. The purpose of this study was to explore changes in integrated mitochondrial function and fatigue in non-metastatic prostate cancer patients receiving localized radiation therapy (XRT).

Materials and methods

We proposed a mitochondrial bioenergetics mechanism of radiation-induced fatigue linking impaired oxidative phosphorylation (OXPHOS) through complex III and decreased adenosine triphosphate (ATP) production as consequences of XRT. Integrated mitochondrial function was measured as mitochondrial OXPHOS from patients’ peripheral blood mononuclear cells. Fatigue was measured using the revised Piper Fatigue Scale. Data were collected before (day 0) and at day 21 of XRT.

Results

At day 21 of XRT, fatigue symptom intensified in 15 prostate cancer patients (P<0.05). Mitochondrial OXPHOS complex III-linked and uncoupled complex III rates were significantly decreased in mononuclear cells at day 21 during XRT compared to that before XRT (P<0.05). Additionally, increased fatigue appeared to be associated with decreased OXPHOS complex III-linked respiration in patients undergoing XRT.

Conclusion

Fatigue was associated with OXPHOS complex III-linked oxidation and a defect in oxidation starting at complex III in mononuclear cell mitochondria was revealed at day 21 of XRT in 15 prostate cancer patients. Complex III is a potential target for pharmacological and, in particular, nutraceutical interventions, eg, Q10, for design of interventions for CRF.

Mitofusin 2 Regulates Axonal Transport of Calpastatin to Prevent Neuromuscular Synaptic Elimination in Skeletal Muscles

Skeletal muscles undergo atrophy in response to diseases and aging. Here we report that mitofusin 2 (Mfn2) acts as a dominant suppressor of neuromuscular synaptic loss to preserve skeletal muscles. Mfn2 is reduced in spinal cords of transgenic SOD1^G93A and aged mice. Through preserving neuromuscular synapses, increasing neuronal Mfn2 prevents skeletal muscle wasting in both SOD1^G93A and aged mice, whereas deletion of neuronal Mfn2 produces neuromuscular synaptic dysfunction and skeletal muscle atrophy. Neuromuscular synaptic loss after sciatic nerve transection can also be alleviated by Mfn2. Mfn2 coexists with calpastatin largely in mitochondria-associated membranes (MAMs) to regulate its axonal transport. Genetic inactivation of calpastatin abolishes Mfn2-mediated protection of neuromuscular synapses. Our results suggest that, as a potential key component of a novel and heretofore unrecognized mechanism of cytoplasmic protein transport, Mfn2 may play a general role in preserving neuromuscular synapses and serve as a common therapeutic target for skeletal muscle atrophy.

Analyzing mitochondrial function in human peripheral blood mononuclear cells

Mitochondrial oxidative phosphorylation (OXPHOS) is responsible for producing most of the adenosine triphosphate required by eukaryotic cells. Lymphocytes make up the majority of the peripheral blood mononuclear cells. Peripheral blood mononuclear cells are readily obtainable, providing an ideal sample to monitor systemic changes and understand molecular signaling mechanisms in disease processes. Mitochondrial energy metabolism of lymphocyte has been used to screen for OXPHOS disorders. While there are increasing studies of lymphocyte OXPHOS, few studies examined activity of electron transport chain of lymphocyte mitochondria. We present an optimal protocol to harvest fresh peripheral blood mononuclear cells from human whole blood, determine integrated mitochondrial function, and analyze electron transport chain complex activity. Analyzing integrated mitochondrial function using OXPHOS provides data to uncover defects in the transport of substrates into the mitochondria, generation of reducing equivalents, the electron transport chain, and coupling to the production of adenosine triphosphate. The optimal conditions to harvest peripheral blood mononuclear cells were using blood anticoagulated with ethylenediaminetetraacetic acid, processed utilizing Lymphoprep™, and washed in phosphate buffered saline, all at room temperature. Using isolated peripheral blood mononuclear cells, integrated mitochondrial function and the activities of electron transport chain were determined.

Investigating the link of ACAD10 deficiency to type 2 diabetes mellitus

The Native American Pima population has the highest incidence of insulin resistance (IR) and type 2 diabetes mellitus (T2DM) of any reported population, but the pathophysiologic mechanism is unknown. Genetic studies in Pima Indians have linked acyl-CoA dehydrogenase 10 (ACAD10) gene polymorphisms, among others, to this predisposition. The gene codes for a protein with a C-terminus region that is structurally similar to members of a family of flavoenzymes-the acyl-CoA dehydrogenases (ACADs)-that catalyze α,β-dehydrogenation reactions, including the first step in mitochondrial FAO (FAO), and intermediary reactions in amino acids catabolism. Dysregulation of FAO and an increase in plasma acylcarnitines are recognized as important in the pathophysiology of IR and T2DM. To investigate the deficiency of ACAD10 as a monogenic risk factor for T2DM in human, an Acad-deficient mouse was generated and characterized. The deficient mice exhibit an abnormal glucose tolerance test and elevated insulin levels. Blood acylcarnitine analysis shows an increase in long-chain species in the older mice. Nonspecific variable pattern of elevated short-terminal branch-chain acylcarnitines in a variety of tissues was also observed. Acad10 mice accumulate excess abdominal adipose tissue, develop an early inflammatory liver process, exhibit fasting rhabdomyolysis, and have abnormal skeletal muscle mitochondria. Our results identify Acad10 as a genetic determinant of T2DM in mice and provide a model to further investigate genetic determinants for insulin resistance in humans.

Defects in skeletal muscle subsarcolemmal mitochondria in a non-obese model of type 2 diabetes mellitus

Skeletal muscle resistance to insulin is related to accumulation of lipid-derived products, but it is not clear whether this accumulation is caused by skeletal muscle mitochondrial dysfunction. Diabetes and obesity are reported to have a selective effect on the function of subsarcolemmal and interfibrillar mitochondria in insulin-resistant skeletal muscle. The current study investigated the role of the subpopulations of mitochondria in the pathogenesis of insulin resistance in the absence of obesity. A non-obese spontaneous rat model of type 2 diabetes mellitus, (Goto-Kakizaki), was used to evaluate function and biochemical properties in both populations of skeletal muscle mitochondria. In subsarcolemmal mitochondria, minor defects are observed whereas in interfibrillar mitochondria function is preserved. Subsarcolemmal mitochondria defects characterized by a mild decline of oxidative phosphorylation efficiency are related to ATP synthase and structural alterations of inner mitochondria membrane but are considered unimportant because of the absence of defects upstream as shown with polarographic and spectrophometric assays. Fatty acid transport and oxidation is preserved in both population of mitochondria, whereas palmitoyl-CoA increased 25% in interfibrillar mitochondria of diabetic rats. Contrary to popular belief, these data provide compelling evidence that mitochondrial function is unaffected in insulin-resistant skeletal muscle from T2DM non-obese rats.

Effect of Maternal Obesity on Placental Lipid Metabolism

Obese women, on average, give birth to babies with high fat mass. Placental lipid metabolism alters fetal lipid delivery, potentially moderating neonatal adiposity, yet how it is affected by maternal obesity is poorly understood. We hypothesized that fatty acid (FA) accumulation (esterification) is higher and FA β-oxidation (FAO) is lower in placentas from obese, compared with lean women. We assessed acylcarnitine profiles (lipid oxidation intermediates) in mother-baby-placenta triads, in addition to lipid content, and messenger RNA (mRNA)/protein expression of key regulators of FA metabolism pathways in placentas of lean and obese women with normal glucose tolerance recruited at scheduled term Cesarean delivery. In isolated trophoblasts, we measured [3H]-palmitate metabolism. Placentas of obese women had 17.5% (95% confidence interval: 6.1, 28.7%) more lipid than placentas of lean women, and higher mRNA and protein expression of FA esterification regulators (e.g., peroxisome proliferator-activated receptor γ, acetyl-CoA carboxylase, steroyl-CoA desaturase 1, and diacylglycerol O-acyltransferase-1). [3H]-palmitate esterification rates were increased in trophoblasts from obese compared with lean women. Placentas of obese women had fewer mitochondria and a lower concentration of acylcarnitines, suggesting a decrease in mitochondrial FAO capacity. Conversely, peroxisomal FAO was greater in placentas of obese women. Altogether, these changes in placental lipid metabolism may serve to limit the amount of maternal lipid transferred to the fetus, restraining excess fetal adiposity in this population of glucose-tolerant women.

Parkinson's disease-associated pathogenic VPS35 mutation causes complex I deficits

Defect in the complex I of the mitochondrial electron-transport chain is a characteristic of Parkinson's disease (PD) which is thought to play a critical role in the disease pathogenesis. Mutations in vacuolar protein sorting 35 (VPS35) cause autosomal dominant PD and we recently demonstrated that pathogenic VPS35 mutations cause mitochondrial damage through enhanced mitochondrial fragmentation. In this study, we aimed to determine whether pathogenic VPS35 mutation impacts the activity of complex I and its underlying mechanism. Indeed, VPS35 D620N mutation led to decreased enzymatic activity and respiratory defects in complex I and II in patient fibroblasts. While no changes in the expression of the complex I and II subunits were noted, the level of assembled complex I and II as well as the supercomplex was significantly reduced in D620N fibroblasts. Importantly, inhibition of mitochondrial fission rescued the contents of assembled complexes as well as the functional defects in complex I and II. Overall, these results suggest that VPS35 D620N mutation-induced excessive mitochondrial fission leads to the defects in the assembled complex I and supercomplex and causes bioenergetics deficits.

Hyperammonaemia-induced skeletal muscle mitochondrial dysfunction results in cataplerosis and oxidative stress

KEY POINTS

Hyperammonaemia occurs in hepatic, cardiac and pulmonary diseases with increased muscle concentration of ammonia. We found that ammonia results in reduced skeletal muscle mitochondrial respiration, electron transport chain complex I dysfunction, as well as lower NAD⁺ /NADH ratio and ATP content. During hyperammonaemia, leak of electrons from complex III results in oxidative modification of proteins and lipids. Tricarboxylic acid cycle intermediates are decreased during hyperammonaemia, and providing a cell-permeable ester of αKG reversed the lower TCA cycle intermediate concentrations and increased ATP content. Our observations have high clinical relevance given the potential for novel approaches to reverse skeletal muscle ammonia toxicity by targeting the TCA cycle intermediates and mitochondrial ROS.

ABSTRACT

Ammonia is a cytotoxic metabolite that is removed primarily by hepatic ureagenesis in humans. Hyperammonaemia occurs in advanced hepatic, cardiac and pulmonary disease, and in urea cycle enzyme deficiencies. Increased skeletal muscle ammonia uptake and metabolism are the major mechanism of non-hepatic ammonia disposal. Non-hepatic ammonia disposal occurs in the mitochondria via glutamate synthesis from α-ketoglutarate resulting in cataplerosis. We show skeletal muscle mitochondrial dysfunction during hyperammonaemia in a comprehensive array of human, rodent and cellular models. ATP synthesis, oxygen consumption, generation of reactive oxygen species with oxidative stress, and tricarboxylic acid (TCA) cycle intermediates were quantified. ATP content was lower in the skeletal muscle from cirrhotic patients, hyperammonaemic portacaval anastomosis rat, and C2C12 myotubes compared to appropriate controls. Hyperammonaemia in C2C12 myotubes resulted in impaired intact cell respiration, reduced complex I/NADH oxidase activity and electron leak occurring at complex III of the electron transport chain. Consistently, lower NAD⁺ /NADH ratio was observed during hyperammonaemia with reduced TCA cycle intermediates compared to controls. Generation of reactive oxygen species resulted in increased content of skeletal muscle carbonylated proteins and thiobarbituric acid reactive substances during hyperammonaemia. A cell-permeable ester of α-ketoglutarate reversed the low TCA cycle intermediates and ATP content in myotubes during hyperammonaemia. However, the mitochondrial antioxidant MitoTEMPO did not reverse the lower ATP content during hyperammonaemia. We provide for the first time evidence that skeletal muscle hyperammonaemia results in mitochondrial dysfunction and oxidative stress. Use of anaplerotic substrates to reverse ammonia-induced mitochondrial dysfunction is a novel therapeutic approach.

Sterol regulatory element-binding protein-1 (SREBP-1) is required to regulate glycogen synthesis and gluconeogenic gene expression in mouse liver

Sterol regulatory element-binding protein-1 (SREBP-1) is a key transcription factor that regulates genes in the de novo lipogenesis and glycolysis pathways. The levels of SREBP-1 are significantly elevated in obese patients and in animal models of obesity and type 2 diabetes, and a vast number of studies have implicated this transcription factor as a contributor to hepatic lipid accumulation and insulin resistance. However, its role in regulating carbohydrate metabolism is poorly understood. Here we have addressed whether SREBP-1 is needed for regulating glucose homeostasis. Using RNAi and a new generation of adenoviral vector, we have silenced hepatic SREBP-1 in normal and obese mice. In normal animals, SREBP-1 deficiency increased Pck1 and reduced glycogen deposition during fed conditions, providing evidence that SREBP-1 is necessary to regulate carbohydrate metabolism during the fed state. Knocking SREBP-1 down in db/db mice resulted in a significant reduction in triglyceride accumulation, as anticipated. However, mice remained hyperglycemic, which was associated with up-regulation of gluconeogenesis gene expression as well as decreased glycolysis and glycogen synthesis gene expression. Furthermore, glycogen synthase activity and glycogen accumulation were significantly reduced. In conclusion, silencing both isoforms of SREBP-1 leads to significant changes in carbohydrate metabolism and does not improve insulin resistance despite reducing steatosis in an animal model of obesity and type 2 diabetes.

Design and implementation of the first randomized controlled trial of coenzyme CoQ₁₀ in children with primary mitochondrial diseases

We report the design and implementation of the first phase 3 trial of CoenzymeQ₁₀ (CoQ₁₀) in children with genetic mitochondrial diseases. A novel, rigorous set of eligibility criteria was established. The trial, which remains open to recruitment, continues to address multiple challenges to the recruitment of patients, including widely condoned empiric use of CoQ₁₀ by individuals with proven or suspected mitochondrial disease and skepticism among professional and lay mitochondrial disease communities about participating in placebo-controlled trials. These attitudes represent significant barriers to the ethical and scientific evaluation--and ultimate approval--of nutritional and pharmacological therapies for patients with life-threatening inborn errors of energy metabolism.

Novel ETF dehydrogenase mutations in a patient with mild glutaric aciduria type II and complex II-III deficiency in liver and muscle

We describe a 22-year-old male who developed severe hypoglycemia and lethargy during an acute illness at 4 months of age and subsequently grew and developed normally. At age 4 years he developed recurrent vomiting with mild hyperammonemia and dehydration requiring frequent hospitalizations. Glutaric aciduria Type II was suspected based upon biochemical findings and managed with cornstarch, carnitine and riboflavin supplements. He did not experience metabolic crises between ages 4-12 years. He experienced recurrent vomiting, mild hyperammonemia, and generalized weakness associated with acute illnesses and growth spurts. At age 18 years, he developed exercise intolerance and proximal muscle weakness leading to the identification of multiple acyl-CoA dehydrogenase and complex II/III deficiencies in both skeletal muscle and liver. Subsequent molecular characterization of the ETFDH gene revealed novel heterozygous mutations, p.G274X:c.820 G > T (exon 7) and p.P534L: c.1601 C > T (exon 12), the latter within the iron sulfur-cluster and predicted to affect ubiquinone reductase activity of ETFDH and the docking of ETF to ETFDH. Our case supports the concept of a structural interaction between ETFDH and other enzyme partners, and suggests that the conformational change upon ETF binding to ETFDH may play a key role in linking ETFDH to II/III super-complex formation.

Inflammatory Breast Cancer as a Model Disease to Study Tumor Angiogenesis: Results of a Phase IB Trial of Combination SU5416 and Doxorubicin

PURPOSE

We used inflammatory breast cancer (IBC) as a model disease to investigate biological changes associated with an antiangiogenesis agent, SU5416, combined with doxorubicin.

EXPERIMENTAL DESIGN

Patients with stage IIIB or IV IBC were treated neoadjuvantly with the combination of SU5416 and doxorubicin for induction therapy. The dose of SU5416 (administered on days 1 and 4, every 3 weeks) and doxorubicin (administered on day 1 every 3 weeks) were escalated in cohorts of three patients starting at 110 and 60 mg/m2, respectively, for a total of five cycles leading up to mastectomy. Patients underwent serial assessment (pharmacokinetic sampling, biopsy of breast, tumor blood flow dynamic contrast-enhanced magnetic resonance imaging, plasma angiogenesis, and endothelial cell damage markers) prior to treatment, at the end of cycles no. 2 and no. 5, and after mastectomy.

RESULTS

Eighteen patients were enrolled; neutropenia was dose-limiting, and overall median survival was not reached (50 months of study follow-up). Four patients (22%) experienced congestive heart failure, which resolved and were likely attributable to a smaller volume of distribution and higher Cmax of doxorubicin in combination with SU5416. We did observe a significant decline in tumor blood flow using Kep calculated by Brix (pretreatment versus post-cycle no. 5; P = 0.033), trend for a decline in tumor microvessel density after treatment, and low baseline levels of soluble intracellular adhesion molecule were associated with improved event-free survival.

CONCLUSIONS

This study showed evidence of an unfavorable cardiac interaction between SU5416 and doxorubicin, which prohibits further investigation of this combination. However, this study supports the importance of using IBC as a model for investigating angiogenesis inhibitors.

cis-3,4-Methylene-heptanoylcarnitine: characterization and verification of the C8:1 acylcarnitine in human urine

Acylcarnitine profiles have been used to diagnose specific inherited metabolic diseases. For some acylcarnitines, however, the detailed structure of their acyl group remains a question. One such incompletely characterized acylcarnitine is cis-3,4-methylene-heptanoylcarnitine. To investigate this problem, we isolated the "C8:1" acylcarnitine from human urine, transesterified it to form its acyl picolinyl ester, and characterized it by GC/EI-MS. These results were compared to GC/EI-MS results from authentic standards we synthesized (cis-3,4-methylene-heptanoylcarnitine, trans-2-octenoylcarnitine, 3-octenoylcarnitine, cis-4-octenoylcarnitine, and trans-4-octenoylcarnitine). Only cis-3,4-methylene-heptanoylcarnitine matched the urinary "C8:1" acylcarnitine. The standards were then spiked in human urine, converted to pentafluorophenacyl esters, and detected by HPLC/MS. cis-3,4-Methylene-heptanoylcarnitine exactly matched the "C8:1" acylcarnitine in urine, whereas none of the other C8:1 acylcarnitine standards matched. Based on the data from GC/EI-MS and HPLC/MS, the "C8:1" acylcarnitine in human urine is shown to be cis-3,4-methylene-heptanoylcarnitine.

Picolinyl ester fragmentation mechanism studies with application to the identification of acylcarnitine acyl groups following transesterification

Acyl picolinyl esters provide excellent data to identify the structures of acyl groups. However, the mechanisms for the formation of fragment ions from picolinyl esters are unsettled. Proposed structures for fragment ions have focused on long-chain groups and may not accommodate results from medium- and short-chain acyl groups. Using deuterium-labeled organic acids, we have investigated the mechanisms for the formation of fragment ions. Based on these studies, we propose a new mechanism that is consistent with the experimental data. We then tested the mechanisms by analyzing selected acylcarnitines. Transesterification of acylcarnitines was performed by reaction with 3-pyridylcarbinol and potassium tert-butoxide in dichloromethane to produce acyl picolinyl esters. The picolinyl esters were separated and detected by gas chromatography/electron ionization-mass spectrometry. Each mass spectrum contained a series of peaks with m/z differences of 12, 13, or 14 u depending on the acyl group's chemical structure. The position of an unsaturated bond or branched methyl in the acyl group of acylcarnitine can be readily determined.

Phase I study of the EGFR tyrosine kinase inhibitor erlotinib in combination with docetaxel and radiation in locally advanced squamous cell cancer of the head and neck (SCCHN)

5545

Background: EGFR is highly expressed in SCCHN, representing a promising therapeutic target. Erlotinib (E) is an EGFR tyrosine kinase inhibitor that may potentiate the efficacy of concurrent radiation (RT) and docetaxel (D). We sought to establish the MTD, toxicities and preliminary efficacy of the combination of RT, D and E in patients (pts) with SCCHN. Methods: Patients with previously untreated stage III-IVB SCCHN were enrolled in a phase I dose-escalating study with standard once-daily RT (70.2 Gy, 1.8 Gy/day), weekly D for the duration of RT and daily E for two weeks prior, during and up to two years following RT. 4 dose levels (DL) were evaluated [D (mg/m2)/E (mg): 15/50, 15/100, 20/100, 20/150]. A 3+3 escalation design was followed. Pharmacokinetic studies (PK) were performed. Results: A total of 23 patients were enrolled (6 pts at each DL 1–3, 5 pts at DL4). Primary site: oral cavity (n = 1), pharynx (n = 15) and larynx (n = 7). 20 patients (87%) had stage IV disease. Three dose-limiting toxicities were observed, 1 at each DL (1–3), including a death within 30 days from last treatment (DL1), grade 3 mucositis resulting in holding RT (>5 days) (DL2) and grade 4 mucositis (DL3). No DLT to date on DL4 with 3/5 pts evaluable. In patients enrolled at DL 1–3 (n = 18), post concurrent chemoRT, best response was CR (n = 15), not evaluable (n = 2), death on study (n = 1). 3/3 pts who underwent planned neck dissection had a pathologic CR. 9 patients are currently receiving adjuvant E and 1 has completed the 2-year course. 3 patients have relapsed. Interpatient variability of E peak plasma concentrations measured after the first dose was observed at all dose levels: 458 ± 173 ng/mL (DL1), 686 ± 364 (DL2), 1017 ± 241 (DL3), 833 ± 222 (DL4) (mean ± s.d., n = 6, 6, 6, 2 at DL1–4 respectively). Adjuvant erlotinib plasma concentration data will be presented separately. No significant PK interaction of erlotinib with docetaxel was noted. Conclusions: The combination of daily erlotinib with weekly docetaxel and RT for pts with stage III-IVB SCCHN is feasible and active. A phase II trial is planned. Supported in part by NIH grants nos. CA62502 and M01 RR-000080.

No significant financial relationships to disclose.

Structural differences in two biochemically defined populations of cardiac mitochondria

To determine whether there are structural differences in two topologically separated, biochemically defined mitochondrial populations in rat heart myocytes, the interior of these organelles was examined by high-resolution scanning electron microscopy. On the basis of a count of 159 in situ subsarcolemmal mitochondria (SSM, i.e., those that directly abut the sarcolemma), these organelles possess mainly lamelliform cristae (77%), whereas the cristae in in situ interfibrillar mitochondria (IFM, i.e., those situated between the myofibrils, n = 300) are mainly tubular (55%) or a mixture of tubular and lamelliform (24%). Isolated SSM (n = 374), similar to their in situ counterparts, have predominantly lamelliform cristae (75%). The proportions of crista types in isolated IFM (n = 337) have been altered, with only 20% of these organelles retaining exclusively tubular cristae, whereas 58% are mixed; of the latter, lamelliform cristae predominate. This finding suggests that, in contrast to SSM, the cristae in IFM are structurally plastic, changing during isolation. These observations on >1,000 organelles provide the first quantitative morphological evidence for definitive differences between the two populations of cardiac mitochondria.

The role of carnitine in normal and altered fatty acid metabolism

Carnitine is a low-molecular-weight compound obtained from the diet that also is biosynthesized from the essential amino acids lysine and methionine. Carnitine has been identified in a variety of mammalian tissues and has an obligate role in the mitochondrial oxidation of long-chain fatty acids through the action of specialized acyltransferases. Other roles for carnitine include buffering of the acyl coenzyme A (CoA)-CoA ratio, branched-chain amino acid metabolism, removal of excess acyl groups, and peroxisomal fatty acid oxidation. The growing body of evidence about carnitine function has led to increased understanding and identification of disorders associated with altered carnitine metabolism. Disorders of fatty acid oxidation and metabolism typically are associated with primary and secondary forms of carnitine deficiency. These disorders, which include increased lipolysis, increased lipid peroxidation, accumulation of acylcarnitines, and altered membrane permeability, have significant consequences for patients with myocardial diseases and kidney failure. Therapeutic administration of carnitine shows promise in treating selected groups of patients who have altered carnitine homeostasis, resulting in improved cardiac function, increased exercise capacity, reduced muscle cramps, and reduced intradialytic complications.

Isolation of hepatic mitochondrial contact sites: previously unrecognized inner membrane components

An improved, fast, and relatively simple procedure for isolation of hepatic mitochondrial contact sites is described. These contact sites include conventional outer membrane, but the inner membrane component (which we term fusion patches) has a unique biochemical composition characterized by a clustering of three specific inner membrane proteins of 54, 52, and 31 kDa identified by proteomics, respectively, as the alpha and beta subunits of ATP synthase and the liver isoform of adenine nucleotide transferase. The contact site fraction was prepared using a discontinuous sucrose gradient from crude outer membranes derived from swollen/shrunk rat liver mitochondria. The resultant contact sites were analyzed using a continuous sucrose density gradient, revealing an apparent heterogeneity due to varying amounts of retained fusion patches in relation to the unvarying outer membrane component. By electron microscopy, contact sites consist of small vacuoles that contain one or several tiny vesicles, many of which are composed of multiple, closely packed lamellae. The contact site subfraction morphology is consistent with the biochemical variation. Thus, contact sites are not haphazard fusions of outer and inner membrane, but consist in part of regions of inner membrane of novel composition (fusion patches) and of conventional outer membrane.

Rat liver mitochondrial contact sites and carnitine palmitoyltransferase-I

In hepatic mitochondria, the outer membrane enzyme, carnitine palmitoyltransferase-I (CPT-I), appears to colocalize with contact sites. We have prepared contact sites that are essentially devoid of noncontact site membranes. The contact site fraction has a high specific activity for CPT-I and contains a protein at 88 kDa that is recognized by antibodies directed at two different peptide epitopes on CPT-I. Similarly long-chain acyl-CoA synthetase (LCAS) specific activity is high in this fraction; a protein at 79 kDa is recognized by an antibody against LCAS. Although activity of carnitine palmitoyltransferase-II (CPT-II) is present, it is not enriched in the contact site fraction, and a protein of 68 kDa weakly reacted with anti-CPT-II antibody. Likewise, carnitine-acylcarnitine translocase (CACT) protein is present, but at a somewhat reduced level. Using an analytical continuous sucrose gradient, we demonstrate that the activities of CPT-I and LCAS and their associated immunoreactive proteins are present in a constant amount throughout the contact site subfractions. The enzymatic activity of CPT-II and its associated immunoreactive protein, as well as immunoreactive CACT, is absent in the lighter density gradient subfractions and is present in the higher density subfractions only in trace amounts. This heterogeneity of the contact site fraction is due to unvarying amounts of outer membrane and increasing amounts of attached inner membrane with increasing density of the subfractions.

Fatty acid import into mitochondria

The mitochondrial carnitine system plays an obligatory role in beta-oxidation of long-chain fatty acids by catalyzing their transport into the mitochondrial matrix. This transport system consists of the malonyl-CoA sensitive carnitine palmitoyltransferase I (CPT-I) localized in the mitochondrial outer membrane, the carnitine:acylcarnitine translocase, an integral inner membrane protein, and carnitine palmitoyltransferase II localized on the matrix side of the inner membrane. Carnitine palmitoyltransferase I is subject to regulation at the transcriptional level and to acute control by malonyl-CoA. The N-terminal domain of CPT-I is essential for malonyl-CoA inhibition. In liver CPT-I activity is also regulated by changes in the enzyme's sensitivity to malonyl-CoA. As fluctuations in tissue malonyl-CoA content are parallel with changes in acetyl-CoA carboxylase activity, which in turn is under the control of 5'-AMP-activated protein kinase, the CPT-I/malonyl-CoA system is part of a fuel sensing gauge, turning off and on fatty acid oxidation depending on the tissue's energy demand. Additional mechanism(s) of short-term control of CPT-I activity are emerging. One proposed mechanism involves phosphorylation/dephosphorylation dependent direct interaction of cytoskeletal components with the mitochondrial outer membrane or CPT-I. We have proposed that contact sites between the outer and inner mitochondrial membranes form a microenvironment which facilitates the carnitine transport system. In addition, this system includes the long-chain acyl-CoA synthetase and porin as components.

A 22 kDa polyanion inhibits carnitine-dependent fatty acid oxidation in rat liver mitochondria

The transport of activated fatty acids across the mitochondrial outer membrane has not been fully addressed. A polyanion (M(n)=22 kDa) inhibited the ADP-stimulated carnitine-dependent oxidation of both palmitoyl-CoA and palmitate plus CoA as well as mitochondrial hexokinase binding. In contrast, the oxidation of palmitoylcarnitine plus malate, as well as glutamate oxidation, was essentially unaffected. Mitochondrial carnitine palmitoyltransferase-1 was not inhibited by the polyanion. The data suggest an additional component in carnitine-dependent mitochondrial fatty acid oxidation, possibly porin.

Genetic disorders of carnitine metabolism and their nutritional management

Carnitine functions as a substrate for a family of enzymes, carnitine acyltransferases, involved in acyl-coenzyme A metabolism and as a carrier for long-chain fatty acids into mitochondria. Carnitine biosynthesis and/or dietary carnitine fulfill the body's requirement for carnitine. To date, a genetic disorder of carnitine biosynthesis has not been described. A genetic defect in the high-affinity plasma membrane carnitine-carrier(in) leads to renal carnitine wasting and primary carnitine deficiency. Myopathic carnitine deficiency could be due to an increase in efflux moderated by the carnitine-carrier(out). Defects in the carnitine transport system for fatty acids in mitochondria have been described and are being examined at the molecular and pathophysiological levels. the nutritional management of these disorders includes a high-carbohydrate, low-fat diet and avoidance of those events that promote fatty acid oxidation, such as fasting, prolonged exercise, and cold. Large-dose carnitine treatment is effective in systemic carnitine deficiency.

A phase I trial of radiotherapy and simultaneous 24-hour paclitaxel in patients with locally advanced head and neck squamous cell carcinoma

Preclinical studies have demonstrated that tumor cells exposed to paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) for protracted periods (ie, 24 hours) and then irradiated undergo enhanced radiation-induced cell kill. Importantly, paclitaxel-induced tumor cell mitotic arrest at the time of radiation was associated with the enhanced cell kill. At the Case Western Reserve Cancer Center, we have conducted a phase I trial in 24 patients with either locally advanced or recurrent/metastatic head and neck squamous cell carcinoma to evaluate the clinical and pharmacologic effects of a 24-hour paclitaxel infusion combined with radiotherapy. The maximum tolerated dose was < or =75 mg/m2. Dose-limiting toxicity was febrile granulocytopenia. Mucositis was significant and necessitated the use of enteral feeding tubes in the majority of patients. All patients with locally advanced disease demonstrated either a complete response or major partial response. At a median follow-up of 13.4 months, disease has relapsed in only two of 22 patients with locally advanced disease. Pharmacokinetic studies revealed that a dose of > or =75 mg/m2 achieved near steady-state mean paclitaxel plasma concentrations greatly exceeding the threshold concentrations shown to alter microtubule function and induce tumor cell mitotic arrest in vitro. Pharmacodynamic studies performed at 21 to 26 hours after initiation of infusion demonstrated that a dose of > or =75 mg/m2 uniformly induced tumor cell mitotic arrest and oral epithelial mitotic arrest. The pharmacologic data and outcome results provide a strong rationale for the continued use of a 24-hour paclitaxel infusion and concurrent radiation for the treatment of newly diagnosed, locally advanced head and neck squamous cell carcinoma in an experimental setting.

Influence of age, performance status, body weight, and tumor type in individuals with cancer on the disposition of warfarin and its enantiomers: Department of Veterans Affairs cooperative study number 75

Plasma warfarin and its R,S enantiomer concentrations, one-stage prothrombin times, and mean daily warfarin doses were analyzed in 196 patients given warfarin. These individuals were part of a controlled clinical trial that examined the effect of warfarin as an adjuvant to "standard" treatment in a variety of malignancies. Neither the plasma warfarin concentration nor the daily warfarin dose required to produce a given degree of prothrombin-time prolongation was influenced by age or body weight in these subjects. When the data were analyzed by performance status, we noted several variations of interest. Individuals with different tumor types demonstrated disparities in warfarin disposition. Patients with colorectal cancer, for example, required lower mean daily warfarin doses to achieve a given degree of one-stage prothrombin time prolongation. Analysis of warfarin enantiomers (R,S) in a selected group of patients demonstrated a lower-than-normal ratio (2:1) for the colorectal cancer group (1.42:1) because of an apparent decrease in the plasma R component. In contrast, patients with head and neck cancer demonstrated a ratio of 2.85:1, and the R component was elevated. Warfarin disposition and the effect of warfarin on vitamin K-dependent clotting factor production were altered in the patients with cancer reported in this study. The mechanisms for these alterations are complex and not completely understood.

Furosemide kinetics in patients with hepatic cirrhosis with ascites

Furosemide, 20 mg, was given intravenously as a bolus to seven patients with cirrhotic ascites and a 10-mg intravenous bolus dose was given to three normal subjects. Furosemide concentrations were measured by a specific high-performance liquid chromatographic analytic method. The median plasma elimination half-life (t1/2), volume of distribution at a steady state (VdSS), and VDarea of furosemide were 0.70 hr, 91 ml/kg, and 119 ml/kg in normal subjects. In the cirrhotic patients elimination t1/2 and Vd at steady state doubled and the Vdarea of furosemide was almost double that of the normal. There were no differences in plasma clearance or renal and nonrenal clearance between patients and controls, but five of the seven patients had lower renal clearances than controls. The water and sodium response to furosemide was directly related to the urinary furosemide excretion rate. We identified a subset of cirrhotic patients who responded poorly (125 ml/hr urinary output in the first 4 hr after furosemide compared to 300 ml/hr in the other patients and 400 ml/hr in the controls) to furosemide. These "poor responders" had the lowest renal clearance of furosemide and the lowest urinary furosemide excretion rates. Our data indicate that furosemide kinetics are altered in patients with cirrhotic ascites and lack of response in a subset of these patients is due to lack of delivery of furosemide to the renal site of its action.

Combined partial deficiency of muscle carnitine palmitoyltransferase and carnitine with autosomal dominant inheritance

The authors studied a 53 year old woman and her 22 year old son with episodes of paroxysmal muscle cramps and dark urines lasting several hours related to high fat diet and strenuous physical exercise beginning on both at age 14 years. The father, paternal uncle, paternal grandfather and another son of the mother also had paroxysmal muscle cramps. The two studied cases showed normal findings for physical evaluation, blood lactate after ischemic exercise, and muscle histology (light and electron microscopy). The serum creatine kinase was elevated in the son and normal in the mother. However, 72 hour fasting significantly raised the serum creatine kinase level in both cases. Plasma concentration of ketone bodies and acid soluble acyl-carnitine increased normally with prolonged fasting. The biochemical evaluation of the muscle tissue revealed intact anaerobic glycolysis and normal glycogen content but combined partial deficiency of muscle carnitine palmitoyltransferase and carnitine in both cases.