Disorders of lipid metabolism in muscle

Clinical Reasoning: A 60-Year-Old Woman With Rapidly Progressive Muscle Weakness and Ophthalmoparesis

The clinical assessment of patients with proximal muscle weakness represents a frequent yet intricate challenge. We present the case of a 60-year-old woman who experienced a progressive, symmetrical weakness in proximal limbs and bulbar muscles over 6 months. Notable clinical findings included bilateral ophthalmoparesis; widespread muscle atrophy; and pronounced weakness in craniobulbar, cervical, and proximal muscles, more severe than in distal ones. We elucidate a methodical diagnostic approach, focusing on constructing a comprehensive differential diagnosis and identifying potential causes of proximal muscle weakness. Special emphasis is placed on exploring the etiologies in cases presenting with both progressive muscle weakness and ophthalmoparesis. We further describe the role of muscle biopsy results and their integration with genetic testing outcomes.

Subtherapeutic Kitasamycin Promoted Fat Accumulation in the Longissimus Dorsi Muscle in Growing-Finishing Pigs

Kitasamycin (KM), a broad-spectrum macrolide antibiotic, has implications for growth performance and residue in animals and humans. This study aimed to explore the effects of different KM doses on intramuscular fat accumulation, cecal microflora, and short-chain fatty acids (SCFAs) using a growing-finishing pig model. Forty-two pigs were divided into three groups: control, subtherapeutic KM (50 mg/kg, KM50), and therapeutic KM (200 mg/kg, KM200) diets over 8 weeks. KM50 led to increased back fat thickness, fat content in the longissimus dorsi muscle (LM), and elevated plasma total cholesterol (TC) levels (p < 0.05), supported by upregulated lipid synthesis gene expression (Acc1, Fas, Scd1) (p < 0.05) in the LM. KM50 altered cecal microflora, reducing Lactobacillus spp. and Bifidobacterium spp. abundance, while increasing SCFA concentrations (acetic acid, propionic acid, total SCFAs) (p < 0.05). KM200 had minimal effects on intestinal weight and density, with increased apparent digestibility of nutrients. These findings highlight the dose-dependent impact of KM on intramuscular fat deposition. Subtherapeutic KM induced ectopic fat deposition, emphasizing potential risks in disease treatment for humans and animals.

Lipid Metabolism, Disorders and Therapeutic Drugs - Review

Different lifestyles have an impact on useful metabolic functions, causing disorders. Different lipids are involved in the metabolic functions that play various vital roles in the body, such as structural components, storage of energy, in signaling, as biomarkers, in energy metabolism, and as hormones. Inter-related disorders are caused when these functions are affected, like diabetes, cancer, infections, and inflammatory and neurodegenerative conditions in humans. During the Covid-19 period, there has been a lot of focus on the effects of metabolic disorders all over the world. Hence, this review collectively reports on research concerning metabolic disorders, mainly cardiovascular and diabetes mellitus. In addition, drug research in lipid metabolism disorders have also been considered. This review explores lipids, metabolism, lipid metabolism disorders, and drugs used for these disorders.

Effect of l-carnitine supplementation on muscle cramps induced by stroke: A case report

l-carnitine, a compound responsible for transportation of acyl groups across cell membranes and modulating intracellular acyl-coenzyme A levels, is reported to reduce muscle cramps in patients with liver cirrhosis and diabetes and those on dialysis. A 79-y-old man with right-sided paralysis was admitted to our hospital and diagnosed with cerebral infarction. Nocturnal leg cramps appeared in the affected side and caused sleep disturbance. Supplementation with l-carnitine reduced the number of nocturnal leg cramps and alleviated sleep disturbance. It also plays an important role in nerve protection and treatment for carnitine deficiency. Patients with stroke-induced paralysis experience muscle wasting, which might reduce pooled carnitine in the affected side. This case suggests that stroke may cause localized carnitine deficiency, and l-carnitine supplementation might be effective for muscle cramps induced by stroke. To the best of our knowledge, this is the first case of l-carnitine supplementation for muscle cramps triggered by cerebral infarction.

Identification of a haplotype associated with cholesterol deficiency and increased juvenile mortality in Holstein cattle

Over the last decades, several genetic disorders have been discovered in cattle. However, the genetic background of disorders in calves is less reported. Recently, German cattle farmers reported on calves from specific matings with chronic diarrhea and retarded growth of unknown etiology. Affected calves did not respond to any medical treatment and died within the first months of life. These calves were underdeveloped in weight and showed progressive and severe emaciation despite of normal feed intake. Hallmark findings of the blood biochemical analysis were pronounced hypocholesterolemia and deficiency of fat-soluble vitamins. Results of the clinical and blood biochemical examination had striking similarities with findings reported in human hypobetalipoproteinemia. Postmortem examination revealed near-complete atrophy of the body fat reserves including the spinal canal and bone marrow. To identify the causal region, we performed a genome-wide association study with 9 affected and 21,077 control animals genotyped with the Illumina BovineSNP50 BeadChip (Illumina Inc., San Diego, CA), revealing a strong association signal on BTA 11. Subsequent autozygosity mapping identified a disease-associated haplotype encompassing 1.01 Mb. The segment of extended homozygosity contains 6 transcripts, among them the gene APOB, which is causal for cholesterol disorders in humans. However, results from multi-sample variant calling of 1 affected and 47 unaffected animals did not detect any putative causal mutation. The disease-associated haplotype has an important adverse effect on calf mortality in the homozygous state when comparing survival rates of risk matings vs. non-risk matings. Blood cholesterol values of animals are significantly associated with the carrier status indicating a codominant inheritance. The frequency of the haplotype in the current Holstein population was estimated to be 4.2%. This study describes the identification and phenotypic manifestation of a new Holstein haplotype characterized by pronounced hypocholesterolemia, chronic emaciation, growth retardation, and increased mortality in young cattle, denominated as cholesterol deficiency haplotype. Our genomic investigations and phenotypic examinations provide additional evidence for a mutation within the APOB gene causing cholesterol deficiency in Holstein cattle.

Lipid storage myopathy with clinical markers of Marfan syndrome: A rare association

Disorders of lipid metabolism can cause variable clinical presentations, often involving skeletal muscle, alone or together with other tissues. A 19-year-old boy presented with a 2-year history of muscle pain, cramps, exercise intolerance and progressive weakness of proximal lower limbs. Examination revealed skeletal markers of Marfan syndrome in the form of increased arm span compared with height, Kyphoscoliois, moderate pectus excavatum, high arched palate and wrist sign. He also had mild neck flexor weakness and proximal lower limb weakness with areflexia. Pathologic findings revealed lipid-laden fine vacuoles in the muscle fibers. Possibility of carnitine deficiency myopathy was considered and the patient was started on carnitine and Co Q. The patient made remarkable clinical improvement over the next 2 months. This case is reported for rarity of the association of clinical markers of Marfan syndrome and lipid storage myopathy and sparse literature on lipid storage myopathy in the Indian context.

Efficacy of L-carnitine in reducing hyperammonaemia and improving neuropsychological test performance in patients with hepatic cirrhosis : results of a randomised trial

OBJECTIVES

To determine the efficacy of L-carnitine in reducing hyperammonaemia and improving neuropsychological performance in patients with hepatic cirrhosis and subclinical hepatic encephalopathy (SHE).

DESIGN

Randomised, parallel group, controlled trial.

PATIENTS AND METHODS

The study enrolled 31 patients with hepatic cirrhosis resulting from hepatitis C and/or hepatitis B, alcohol abuse and other causes. Patients randomised to active treatment, received oral L-carnitine 6 g/day in two divided doses for 4 weeks. Diagnosis of SHE was based on psychometric tests (subtests of the Wechsler Adult Intelligence Scale-Revised and the Halstead-Reitan Neuropsychological Test Battery) carried out at beginning and end of study. Serum ammonia levels were measured before treatment and weekly thereafter.

RESULTS

A total of 27 patients completed the study. Sixteen patients received L-carnitine and 11 served as controls (no treatment). L-carnitine caused rapid and significant reductions in ammonia levels, sustained over the 4-week treatment period (mean reductions 60.1 and 1.4 (μmol/L in the treated and control groups, respectively). Normal ammonia levels were attained in 14 of 16 patients receiving L-carnitine. Based on psychometric test results, seven patients (43.7%) in the L-carnitine group and five (45.5%) in the control group had SHE at baseline. L-carnitine treatment for 4 weeks caused a net overall improvement in psychometric test results compared with controls. No clinically significant adverse events were reported and all patients receiving L-carnitine reported subjective improvements in their condition.

CONCLUSIONS

RESULTS of this preliminary study indicate that L-carnitine reduces hyperammonaemia and improves the clinical symptoms of SHE in patients with hepatic cirrhosis.

Delineating the role of alterations in lipid metabolism to the pathogenesis of inherited skeletal and cardiac muscle disorders: Thematic Review Series: Genetics of Human Lipid Diseases

As the specific composition of lipids is essential for the maintenance of membrane integrity, enzyme function, ion channels, and membrane receptors, an alteration in lipid composition or metabolism may be one of the crucial changes occurring during skeletal and cardiac myopathies. Although the inheritance (autosomal dominant, autosomal recessive, and X-linked traits) and underlying/defining mutations causing these myopathies are known, the contribution of lipid homeostasis in the progression of these diseases needs to be established. The purpose of this review is to present the current knowledge relating to lipid changes in inherited skeletal muscle disorders, such as Duchenne/Becker muscular dystrophy, myotonic muscular dystrophy, limb-girdle myopathic dystrophies, desminopathies, rostrocaudal muscular dystrophy, and Dunnigan-type familial lipodystrophy. The lipid modifications in familial hypertrophic and dilated cardiomyopathies, as well as Barth syndrome and several other cardiac disorders associated with abnormal lipid storage, are discussed. Information on lipid alterations occurring in these myopathies will aid in the design of improved methods of screening and therapy in children and young adults with or without a family history of genetic diseases.

Clinical and genetic analysis of lipid storage myopathies

Causative genes have been identified only in four types of lipid storage myopathies (LSMs): SLC22A5 for primary carnitine deficiency (PCD); ETFA, ETFB, and ETFDH for multiple acyl-coenzyme A dehydrogenation deficiency (MADD); PNPLA2 for neutral lipid storage disease with myopathy (NLSDM); and ABHD5 for neutral lipid storage disease with ichthyosis. However, the frequency of these LSMs has not been determined. We found mutations in only 9 of 37 LSM patients (24%): 3 in SLC22A5; 4 in MADD-associated genes; and 2 in PNPLA2. This low frequency suggests the existence of other causative genes. Muscle coenzyme Q(10) levels were normal or only mildly reduced in two MADD patients, indicating that ETFDH mutations may not always be associated with CoQ(10) deficiency. The 2 patients with PNPLA2 mutations had progressive, non-episodic muscle disease with rimmed vacuoles. This suggests there is a different pathomechanism from other LSMs.

Encephalopathy due to carnitine deficiency in an adult patient with gluten enteropathy

A 48-year-old male patient had two episodes of fever, headache, confusion and seizures following an upper respiratory tract infection. Electroencephalography (EEG) revealed diffuse slowing of background activity. Plasma free carnitine and serum lipid levels were low; fecal fat content and serum antigliadin antibodies were elevated. Duodenal biopsy was compatible with gluten enteropathy. Symptoms improved after the patient was started on a gluten-free diet and carnitine replacement therapy. No recurrence was observed within a four-year follow-up. Carnitine deficiency in adulthood is unusual, and encephalopathy due to carnitine deficiency as a result of celiac disease has not been described previously.

Myopathies

Electrodiagnostic studies are an important adjunct to the clinical examination of a patient with a suspected myopathy; however, the clinical examination is crucial in making an accurate diagnosis, because electrodiagnostic studies have only a limited role in delineating with certainty the underlying myopathic disorder. Hereditary and acquired myopathies are reviewed in this article, with particular emphasis on distinguishing clinical and electrodiagnostic features. The hereditary myopathies that are discussed include the muscular dystrophies and the congenital distal mitochondrial, and metabolic myopathies. Acquired myopathies, including inflammatory, endocrine, and toxic myopathies, as well as those associated with systemic illness, are briefly reviewed.

The effects of increasing exercise intensity on muscle fuel utilisation in humans

1. Contemporary stable isotope methodology was applied in combination with muscle biopsy sampling to accurately quantify substrate utilisation and study the regulation of muscle fuel selection during exercise. 2. Eight cyclists were studied at rest and during three consecutive 30 min stages of exercise at intensities of 40, 55 and 75 % maximal workload (W(max)). A continuous infusion of [U-(13)C]palmitate and [6,6-(2)H(2)]glucose was administered to determine plasma free fatty acid (FFA) oxidation and estimate plasma glucose oxidation, respectively. Biopsy samples were collected before and after each exercise stage. 3. Muscle glycogen and plasma glucose oxidation rates increased with every increment in exercise intensity. Whole-body fat oxidation increased to 32 +/- 2 kJ min(-1) at 55 % W(max), but declined at 75 % W(max) (19 +/- 2 kJ min(-1)). This decline involved a decrease in the oxidation rate of both plasma FFA and triacylglycerol fat sources (sum of intramuscular plus lipoprotein-derived triacylglycerol), and was accompanied by increases in muscle pyruvate dehydrogenase complex activation and acetylation of the carnitine pool, resulting in a decline in muscle free carnitine concentration. 4. We conclude that the most likely mechanism for the reduction in fat oxidation during high-intensity exercise is a downregulation of carnitine palmitoyltransferase I, either by this marked decline in free carnitine availability or by a decrease in intracellular pH.

Disorders of lipid metabolism in skeletal muscle

Lipid storage myopathies are typically present with recurrent episodes of myoglobinuria and hypoglycemia, triggered by fasting or infection. Dilated cardiomyopathy can occur. This article will discuss an approach to lipid storage myopathies and describes various forms of disorders by fatty acid oxidation.

The effects of 3-hydroxy-3-methylglutaryl-CoA reductase inhibition on tissue levels of carnitine and carnitine acyltransferase activity in the rabbit

Recently, a new class of lipid lowering agents [3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors] was introduced into clinical practice. The use of these agents could lead to a secondary deficiency in carnitine, which may manifest clinically as a myalgia/myositis-a side effect that is occasionally seen with this class of drugs. In the present study, we examined the effect of an HMG-CoA reductase inhibitor (lovastatin) on serum and tissue levels of carnitine and carnitine acyltransferase activities in the rabbit. Rabbits (n = 6) were fed chow containing lovastatin (30 mg/d) for 16 wk. Blood was collected and tissues (liver, heart, and skeletal muscle) harvested at sacrifice. Free and total carnitine were measured in serum and tissues by a radioenzymatic method. Carnitine acetyltransferase and carnitine palmitoyltransferase (CPT) activities were determined and expressed relative to DNA. Serum free (24.0 +/- 2.6 vs. 29.4 +/- 3.1 microM) and total (35.1 +/- 4.7 vs. 52.8 +/- 8.8 microM) carnitine levels increased significantly with 16 wk of treatment. This increase in total carnitine was mainly due to an increase in the levels of serum acylcarnitine (12.7 +/- 3.1 vs 26.5 +/- 5.7 microM). Tissue levels of total carnitine were significantly decreased by the treatment. Carnitine acetyltransferase was unaffected by the treatment, whereas there was a significant increase in the activity of CPT in the liver and heart.

Carnitine-dependent changes of metabolic fuel consumption during long-term treatment with valproic acid

Energy metabolism was measured in children receiving long-term treatment with valproic acid. In 8 of 10 randomly selected subjects, the resting respiratory quotient was higher than in age- and sex-matched control subjects (0.91 +/- 0.01 vs 0.87 +/- 0.01; p < 0.05). A shift was observed in fuel consumption, and a significant reduction was found in the amount of fats oxidized (0.68 +/- 0.23 vs 1.18 +/- 0.18 gm.kg-1.day-1), which was accompanied by increased utilization of carbohydrates (5.31 +/- 0.79 vs 3.81 +/- 0.39 gm.kg-1.day-1) in comparison with the control subjects. The resting total energy expenditure was not affected by the treatment. The children with an altered energy consumption pattern (n = 8) received carnitine supplementation for a month; the respiratory quotient then decreased (0.87 +/- 0.02), the oxidation of fats increased (1.42 +/- 0.25), and the consumption of carbohydrates decreased (3.87 +/- 0.79), but no changes in resting energy expenditure were observed. We conclude that carnitine depletion, a known adverse effect of valproic acid administration, may result in inhibited fatty acid oxidation, leading to a shift of substrates utilized from fats to carbohydrates.

Rhabdomyolysis in childhood. A primer on normal muscle function and selected metabolic myopathies characterized by disordered energy production

Patients with rhabdomyolysis present an important clinical problem. In acute episodes immediate treatment may be necessary to prevent significant morbidity and mortality. Evaluation of affected patients necessitates an understanding of basic muscle pathophysiology and of the variety of disturbances that can interfere with muscle energy metabolism. The physician must then pursue a systematic stepwise evaluation (Table 6) that includes obtaining relevant history and laboratory studies, as well as arranging for appropriate provocative testing and muscle biopsy. Once the diagnosis is established, patient and family counseling is necessary, particularly in genetic disorders. Unfortunately, specific therapies have not proven entirely successful, and treatment generally has been directed at reducing the severity of rhabdomyolytic episodes.

Histochemistry of the triceps surae muscle in idiopathic congenital clubfoot

The histochemical composition of the triceps surae muscle was investigated in 13 previously unoperated children (age 9-24 months) with unilateral idiopathic clubfoot. On both the normal and the affected side, the percentage of type I fibers was significantly higher than that of the other fiber types. The muscle biopsies from the clubfoot side showed an increase in their connective tissue content. The affected side showed a nonsignificant higher percentage of type I fibers, whereas the average capillary density and capillary to fiber ratio were significantly lower.

Metabolic myopathy produced by acute inhibition of glyceraldehyde-3-phosphate dehydrogenase with ortho-iodosobenzoic acid

A previously developed model of exercise-induced muscle contracture using iodoacetate to inhibit glyceraldehyde-3-phosphate dehydrogenase in rat hindlimb muscles produced selective type II myofiber damage. Utilizing a modification of the same model system, rats were given intra-aortic ortho-iodosobenzoic acid (700 nmol/kg body weight), which cleaves tryptophanyl peptides from glyceraldehyde-3-phosphate dehydrogenase. Within 2-4 h, spontaneous electrically-silent contracture developed in the injected musculature resulting in a plantar-flexed position of the hindlimb. After 24 h, the extensor digitorum longus and tibialis anterior muscles appeared grossly swollen (edematous) and discolored. Microscopically, the extensor digitorum longus (composed predominantly of type II myofibers) contained many randomly scattered, damaged myofibers, reduced glycogen content, absent glyceraldehyde-3-phosphate dehydrogenase activity, interstitial edema and focal collections of mononuclear phagocytes. Damaged fibers showed degenerative changes and contained stainable intracellular calcium. On modified trichrome-stained sections, an outer red staining rim of material was identifiable in many fibers. The fibers of the soleus muscle (composed predominantly of type I myofibers) were not damaged, indicating a preferential ortho-iodosobenzoic acid effect on type II myofibers.

Type 1 fiber abnormalities in skeletal muscle of patients with hypertrophic and dilated cardiomyopathy: evidence of subclinical myogenic myopathy

Abnormalities of skeletal muscle have been described in patients with dilated and hypertrophic cardiomyopathy. Eleven patients with dilated and eight with hypertrophic cardiomyopathy without overt symptomatic skeletal myopathy underwent extensive neuromuscular studies. Quantitative electromyography showed abnormal reduction of motor unit potential duration, indicative of myogenic myopathy, in four patients (36%) with dilated and in three (37%) with hypertrophic cardiomyopathy. Values were 21% to 40% (mean 28%) lower than those in age-matched normal control subjects. The presence of normal nerve conduction velocities and of normal motor unit fiber density in all patients indicated lack of neurogenic abnormalities. Skeletal muscle biopsy was performed in five patients with dilated and in four with hypertrophic cardiomyopathy. In all nine patients light and electron microscopy showed central hyporeactive cores, selective atrophy and mitochondrial abnormalities of type 1 fibers but not of type 2 fibers. The degree of impairment of left ventricular function in patients with electromyographic abnormalities was similar to that of those without (percent fractional shortening at two-dimensional echocardiography 21 +/- 9 versus 25 +/- 10, ejection fraction at angiography 39 +/- 13% versus 42 +/- 13% and left ventricular end-diastolic pressure 21 +/- 6 versus 21 +/- 8 mm Hg) as well as symptom duration (9 +/- 4 versus 12 +/- 8 months). Thus, subclinical electromyographic alterations indicative of myogenic myopathy are frequent in patients with dilated and hypertrophic cardiomyopathy and are unrelated to the degree of impairment of left ventricular function. The concomitant histologic alterations, characterized by selective type 1 atrophy, are similar to those observed in congenital and idiopathic myopathies, but different from those described in secondary heart failure.

Increase in median power frequency of the myoelectric signal in pathological fatigue

During bicycle ergometry, surface EMG analysis was performed on the m. vastus lateralis in a patient with pathological fatigue (due to skeletal muscle carnitine deficiency). With prolonged, submaximal, exercise (30% VO2 max, 2 h) the median frequency of the power density spectrum increased, despite fatigue and lactate production. This observation questions the general validity of the present concepts on myoelectric aspects of fatigue.

In vivo muscle magnetic resonance spectroscopy in a family with mitochondrial cytopathy: a defect in fat metabolism

In vivo proton and phosphorus magnetic resonance spectroscopy (MRS) studies were performed at 1.5 T on two patients (siblings) diagnosed as having a mitochondrial cytopathy. The clinical diagnosis was based on a complete battery of biochemical tests, electron microscopy and modified Gomori trichrome stain studies of muscle. Proton spectra from the gastrocnemius muscle were recorded using the stimulated echo acquisition mode (STEAM) and the phosphorus spectra were obtained using the depth-resolved surface coil spectroscopy (DRESS) sequence. Proton resonances from neutral fats in the patients were found to be strikingly weak compared to normals. The ratios [PCr]/[ATP] and [PCr]/[Pi] and the pH values, as inferred from the phosphorus MRS, were found to be marginally decreased compared to normals. These studies indicate defective fatty acid metabolism in these two patients. It is, however, not known whether the abnormal mitochondrial ultrastructure represents a primary abnormality or secondary to defective fatty acid metabolism.

A case of carnitine palmitoyltransferase II deficiency in human skeletal muscle

A 20-year-old man was shown to have a deficiency of carnitine palmitoyltransferase (CPT) II in skeletal muscle. The evidence was: (i) there was no significant oxidation of [9,10-3H]-palmitate or of [1-14C]palmitate in mitochondrial fractions from fresh skeletal muscle from the patient; (ii) all the CPT activity in a homogenate of fresh muscle from the patient was overt (CPT I) with no increase in activity after the inner membrane was disrupted; (iii) all the CPT activity in the patient's muscle was inhibited by malonyl-CoA; and (iv) an immunoreactive peptide of 67 kDa corresponding to CPT II, present in mitochondria from controls, was absent in those from the patient.

Metabolic myopathy produced by dinitrofluorobenzene inhibition of creatine phosphokinase

A previously developed animal model of exercise-induced muscle contractures, which utilized intra-aortic injection of iodoacetate (IOA) to inhibit the second stage glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase, showed histological evidence of selective type II muscle fiber involvement with sparing of the type I muscle fibers. A new model has been developed using dinitrofluorobenzene (DNFB) as a selective inhibitor of creatine phosphokinase in a similar, but slightly modified distal aortic injection protocol. Two hours after the injection of a dinitrofluorobenzene solution of 2.22 mg/kg body weight, spontaneous electrically-silent contracture developed in the injected lower extremity, involving principally the soleus muscle. Histologically, selective damage was apparent in the type I muscle fibers, with sparing of the type II muscle fibers. The contrast in findings associated with iodoacetate inhibition of glycolysis or with DNFB inhibition of the phosphocreatine shuttle suggests that type I and type II fibers have markedly different usable pools of readily available ATP: type II fibers must rely on the minute-by-minute replenishment of the usable pool of ATP from glycolysis, while type I fibers must regenerate the usable pool of ATP from phosphocreatine through a creatine phosphokinase-mediated process.

Cramps following exercise

A 13-year old boy presented with a 10-year history of severe muscle cramps experienced an hour after prolonged exercise. There was no history of exercise intolerance or myoglobinuria. A muscle biopsy showed a lipid myopathy and a deficiency of muscle carnitine palmityl transferase. He has responded to a high carbohydrate, low fat diet with added carbohydrate intake preceding extensive exercise. Diagnosis of this entity before an episode of rhabdomyolysis is unusual.

Lipid storage myopathy associated with recurrent Reye syndrome-like attacks, but with a normal carnitine level

A 7-year-old girl developed recurrent episodes of hepatic and cerebral dysfunction which mimicked those in Reye syndrome (RS). Because of mild muscle weakness, she had repeated muscle biopsies which showed markedly increased amounts of lipid droplets, predominantly in type 1 fibers. Liver histological examination showed widespread hepatocellular steatosis. However, diffuse microvesicular fat, seen in RS, was not found in the cytoplasm. The concentrations of free- and acylcarnitine in serum and muscle were within normal ranges. Normal ketogenesis was induced by fasting. Based on the clinical, laboratory, and histopathological findings, our patient was initially thought to have systemic carnitine deficiency. However, the serum and muscle carnitine levels were within normal limits. Although the primary metabolic defect has yet to be elucidated, the present study indicates that lipid storage myopathy in the absence of carnitine deficiency can be complicated with RS-like episodes.

Adult onset systemic carnitine deficiency: favorable response to L-carnitine supplementation

We report the case of a patient who at age 39 first developed an episode of muscle weakness and transient ketoacidosis with biopsy proven fatty infiltration of the liver. Over the next several years, myopathy ensued; biopsy revealed extensive deposition of lipid globules in type 1 muscle fibres. Further investigations established the diagnosis of systemic carnitine deficiency (SCD) with skeletal muscle, hepatic, and cardiac involvement. The patient has benefited from L-carnitine supplementation. Our case represents an unusually late onset of SCD and highlights the necessity, when appropriate, of a high index of suspicion of this rare but treatable disorder.

Secondary mitochondrial pathology

A considerable number of myopathies seem to involve the mitochondria but the various causes may be situated outside the mitochondria. These can be categorized as (1) deficiency; (2) intoxication; (3) disturbed regulatory control; (4) hypoxia; (5) disturbed interaction with other cell organelles and (6) unidentified causes.

Defects of fatty acid oxidation in skeletal muscle

Fatty acids are important substrates for resting and exercising skeletal muscle. Defects of fatty acid oxidation result in muscle pain and weakness, and there is often lipid accumulation in muscle fibres. Only a few of the several possible enzyme defects have been found and some of these have responded to therapy. Some techniques for the investigation of fatty acid oxidation are outlined.

Ultrastructural modifications of muscle in three types of compartment syndrome

The histological and ultrastructural aspects of three cases representing different types of compartment syndromes are analyzed. In the acute syndrome edema is the prominent feature. The two chronic cases are characterized by an accumulation of intermyofibrillar lipid globules. All three have in common mitochondrial enlargement, disorganization of the cristae and paracrystalline inclusions. These pathological findings are discussed in the light of lesions seen in striated muscle ischaemia or in certain metabolic myopathies.

Carnitine palmityltransferase deficiency with permanent weakness

A 16-year-old male had a history of muscle pain and exercise intolerance from the age of six years. At 14 years of age, he experienced the first episode of myoglobinuria and has had eight episodes subsequently. The longest interval between episodes was 14 months. Between attacks he manifested permanent, mild proximal limb weakness, elevated serum creatine kinase activity, and myopathic features indicated by electromyography and muscle biopsies. The muscle carnitine palmityltransferase activity was 30% of normal. This patient demonstrates that carnitine palmityltransferase deficiency can be a progressive disorder leading to permanent weakness. The need for early diagnosis and treatment is stressed.

Carnitine: an overview of its role in preventive medicine

Carnitine (beta-hydroxy-gamma-N-trimethylaminobutyric acid) is required for transport of long-chain fatty acids into the inner mitochondrial compartment for beta-oxidation. Widely distributed in foods from animal, but not plant, sources, carnitine is also synthesized endogenously from two essential amino acids, lysine and methionine. Human skeletal and cardiac muscles contain relatively high carnitine concentrations which they receive from the plasma, since they are incapable of carnitine biosynthesis themselves. Since the discovery of a primary genetic carnitine deficiency syndrome in 1973, carnitine has become the subject of extensive research. It is now recognized that carnitine deficiency may also occur secondary to genetic disorders of intermediary metabolism as well as to a variety of clinical disorders, including renal disease treated by hemodialysis, the renal Fanconi syndrome, cirrhosis, untreated diabetes mellitus, malnutrition, Reye's syndrome, and certain disorders of the endocrine, neuromuscular, and reproductive systems. Administration of the anticonvulsant valproic acid and total parenteral nutrition may also induce hypocarnitinemia. In many instances, the physiological implications of secondary carnitine deficiency have not been resolved. However, evidence for a specific carnitine requirement for the newborn, especially if preterm, is accumulating. Moreover, carnitine administration may have a favorable effect on some forms of hyperlipoproteinemia. Carnitine, now recognized as a conditionally essential nutrient, is a significant factor in preventive medicine.

Skeletal muscle endurance: the effect of increased availability of endogenous long-chain fatty acid fuel

A possible role of intramuscularly derived fatty acid fuel on muscle endurance was investigated in curarized diaphragms of fasted rats. These showed significantly improved endurance during 60 min of intermittent stimulation at 20 Hz in vitro compared with diaphragms of fed control animals. The improved endurance appeared to be related to an increased availability and utilization of fatty acid fuel derived from greatly increased numbers of lipid globules in muscle fibers of fasted animals. The pH of muscles with improved endurance (fasted rats) was not different from that of muscles from fed controls at rest. After 60 min of intermittent stimulation, the muscle pH diminished to the same extent in both groups. Diaphragms of fasted rats that were refed 12 h before testing did not show improved endurance. Epinephrine in the bath abolished the improved endurance of diaphragms of fasted rats. Diaphragms of fasted guinea pigs did not show significantly improved endurance (despite abundant intracellular lipid globules), possibly because of a reduced intracellular carnitine.

Mitochondrial cytopathy with lactic acidosis, carnitine deficiency and DeToni-Fanconi-Debré syndrome

We reported a 6-year-old girl with mitochondrial cytopathy with lactic acidosis. The patient developed hypotonia, hearing loss, mental retardation, short stature, cataracta, hypoparathyroidism, DeToni-Fanconi-Debré syndrome and carnitine deficiency. Histological examination disclosed ragged red fibers and moderate lipid storage in skeletal muscle tissue and several structural abnormalities of mitochondria both in muscle tissue and proximal renal tubules. Biochemical examination of muscle tissue revealed a partial deficiency of pyruvate dehydrogenase complex and normal activities of cytochrome c oxidase, succinate cytochrome c reductase and NADH cytochrome c reductase. This is the first report of mitochondrial cytopathy representing DeToni-Fanconi-Debré syndrome associated with partial deficiency of pyruvate dehydrogenase complex and normal cytochrome c oxidase activity.

Beta-oxidation enzymes in normal human muscle and in muscle from a patient with an unusual form of myopathic carnitine deficiency

In a reported patient with myopathic carnitine deficiency, addition of exogenous carnitine to muscle homogenates failed to correct palmitate oxidation, and oral carnitine was of no clinical benefit. In a muscle biopsy from this patient, we found that, in contrast to the marked deficiency of free carnitine (3% of normal) short- and medium-chain acylcarnitines were in the normal range and long-chain acylcarnitine was increased almost four times. As this result confirmed the hypothesis of a muscle defect of mitochondrial oxidation of palmitate, all eight enzymes of beta-oxidation were measured spectrophotometrically in the muscle extract. None of them was found to be defective. These data suggest that the underlying biochemical abnormality in this patient may be a deficiency of the carnitine-acylcarnitine translocase system or a defective interaction between acyl-CoA dehydrogenase and its flavoprotein coenzyme.

The effects of L- and D-carnitine administration on cardiovascular development of the chick embryo

A single 1.0-ml volume of L- or D-carnitine solution, at several selected mmole concentrations, was applied to the extraembryonic membranes of 3- and 4-day chick embryos in ovo. Hamburger-Hamilton stages of chick development ranged from 17 to 23. During the 17-18th days of incubation, embryos were dissected, and both survival and intracardiac anomaly rates were determined. Only at extremely high doses, both stereoisomers of carnitine exhibited a statistically significant toxigenic effect (p less than 0.001) as measured by a sharp decrease in survival rate when compared to chick Ringer's saline controls. Furthermore, since the anomaly rates became significant only near the LD50's, this indicated that intracardiac anomalies were induced only at toxic doses. Therefore, it is suggested that cardiovascular teratogenicity may be the result of toxicity. Below the LD50, anomaly rates were not significantly different from those of control embryos. In comparison, L- and D-carnitine were significantly different from one another (p less than 0.001) both in survival rate and percent affected embryos at a dose of 0.5 mmole. In summary, exogenous carnitine administration to the chick embryo does not appear to be deleterious to the developing cardiovascular system.

[Muscle carnitine deficiency: report of 8 cases with clinical, electromyographic, histochemical and biochemical studies]

We describe 8 patients with muscle carnitine deficiency, 7 males and 1 female, varying in age from 5 days to 64 years. Seven had decreased muscle strength and all had increased lipids droplets in the muscle biopsy. The symptoms began in the first days of life in three cases, in childhood in two, in adult life in two, while one case was free of symptoms at age 64 (heterozygote?). Some patients had difficulty chewing, dysphagia, hypotonia and splenomegaly; one patient had a fluctuating clinical course. All had elevated serum enzymes, mainly creatine-kinase. The electromyogram showed primary muscle involvement in one case, denervation in two, "mixed" features in two and was not done in three. The muscle biopsy, beside lipid storage, showed denervation in four, chronic myopathy in four and type II fiber atrophy in one. In two cases, histological findings suggested infantile spinal muscle atrophy. One patient appeared to have a systemic form of carnitine deficiency, with severe myocardial involvement and died of heart failure before treatment was initiated. A discussion about clinical findings, metabolism and therapeutic aspects of muscle carnitine deficiency is made.

Effects of L-carnitine loading on the aerobic and anaerobic performance of endurance athletes

L-Carnitine (L-C), a well known physiological carrier across the inner mitochondrial membrane of activated long chain fatty acids and acceptor of acyl groups from acyl-CoA, has been recently synthesised industrially. This has made it possible to study the effects of L-C loading (4 g X d(-1) by mouth over a period of 2 weeks) on the aerobic and anaerobic performance of 6 long distance competitive walkers. As a result of the treatment: 1) mean total, free and esterified serum L-C both at rest and shortly after completing a 120 min walk at about 65% of the individual maximal aerobic power (VO2max) were significantly increased; 2) VO2max increased 6%, from 54.5 +/- 3.7 (S.D.) to 57.8 +/- 4.7 m1O2 X kg(-1) X min(-1) (P less than 0.02); 3) blood lactate concentration (Lab) as a consequence of short bouts repeated exercise (series of 10, 15 and 20 jumps off both feet on a force platform) was unchanged; 4) heart rate, pulmonary ventilation, oxygen consumption, and respiratory quotient in the same conditions as for 1) were unchanged. It is concluded that, in trained athletes, as a consequence of L-C loading VO2max is slightly but significantly raised, probably as a result of an activation of substrate flow through the TCA cycle, whereas the lipid contribution to metabolism in prolonged submaximal exercise remains unchanged.

Mitochondrial myopathies

Mitochondrial myopathies are clinically heterogeneous disorders that can affect multiple systems besides skeletal muscle (mitochondrial encephalomyopathies or cytopathies) and are usually defined by morphological abnormalities of muscle mitochondria. There are a few distinctive syndromes, such as the Kearns-Sayre syndrome; myoclonus epilepsy with ragged-red fibers; and mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes. Biochemically, mitochondrial myopathies can be divided into defects of substrate utilization, oxidation-phosphorylation coupling, and the respiratory chain. Because mitochondria have their own DNA and their own translation and transcription apparatuses, mitochondrial myopathies can be due to defects of either a nuclear or mitochondrial genome and can be transmitted by mendelian or maternal inheritance.

Carnitine deficiency

Carnitine is an essential cofactor in the transfer of long-chain fatty acids across the inner mitochondrial membrane. Carnitine is metabolized from lysine, trimethyllysine and butyrobetaine. Butyrobetaine undergoes hydroxylation in the liver, brain and kidney to form carnitine which in turn is transported via the plasma to the heart and skeletal muscle where it is important for allowing beta oxidation of fatty acids. Three clinical forms of carnitine deficiency have been described: myopathic, systemic and mixed forms. Carnitine deficiency results in accumulation of neutral lipid within skeletal muscle, myocardium and liver. Ultrastructurally, myofibrils are disrupted and there is an accumulation of large aggregates of mitochondria and lipid deposits within the skeletal muscle and myocardium. Carnitine therapy has been effective in the treatment of the myopathic and some cases of systemic and mixed forms. Several syndromes of secondary carnitine deficiency have been described; these may be secondary to genetic defects of intermediary metabolism and to other conditions, particularly following hemodialysis.

Mitochondrial myopathy with diffuse activation and focal deficiency of mitochondrial ATPase and carnitine deficiency

In skeletal muscle from a patient with a mitochondrial myopathy and muscular carnitine deficiency, histochemical analysis demonstrated that mitochondrial ATPase showed activation with loss of latency even before addition of the uncoupler dinitrophenol (DNP). According to combined histochemical and biochemical studies by Meijer and Vloedman (1980), this finding indicates loosely coupled oxidative phosphorylation. After the addition of DNP the reaction intensity was markedly increased, but there were scattered enzyme-deficient fibres in which some residual activity was shown by ultracytochemistry. No defect in mitochondrial enzymes was found in biochemical studies. The enzyme histochemical changes and carnitine deficiency are probably both secondary to an unknown mitochondrial defect. Both the carnitine deficiency and the mitochondrial myopathy remained unchanged following long-term carnitine substitution therapy despite clinical improvement.