Serum and Platelet Lipoamide Dehydrogenase in Friedreich's Ataxia

Mitochondrial Alpha-Keto Acid Dehydrogenase Complexes: Recent Developments on Structure and Function in Health and Disease

The present work delves into the enigmatic world of mitochondrial alpha-keto acid dehydrogenase complexes discussing their metabolic significance, enzymatic operation, moonlighting activities, and pathological relevance with links to underlying structural features. This ubiquitous family of related but diverse multienzyme complexes is involved in carbohydrate metabolism (pyruvate dehydrogenase complex), the citric acid cycle (α-ketoglutarate dehydrogenase complex), and amino acid catabolism (branched-chain α-keto acid dehydrogenase complex, α-ketoadipate dehydrogenase complex); the complexes all function at strategic points and also participate in regulation in these metabolic pathways. These systems are among the largest multienzyme complexes with at times more than 100 protein chains and weights ranging up to ~10 million Daltons. Our chapter offers a wealth of up-to-date information on these multienzyme complexes for a comprehensive understanding of their significance in health and disease.

Changes in mitochondrial glutathione levels and protein thiol oxidation in ∆yfh1 yeast cells and the lymphoblasts of patients with Friedreich's ataxia

Friedreich's ataxia (FRDA) is a neurodegenerative disease caused by low levels of the mitochondrial protein frataxin. The main phenotypic features of frataxin-deficient human and yeast cells include iron accumulation in mitochondria, iron-sulfur cluster defects and high sensitivity to oxidative stress. Frataxin deficiency is also associated with severe impairment of glutathione homeostasis and changes in glutathione-dependent antioxidant defenses. The potential biological consequences of oxidative stress and changes in glutathione levels associated with frataxin deficiency include the oxidation of susceptible protein thiols and reversible binding of glutathione to the SH of proteins by S-glutathionylation. In this study, we isolated mitochondria from frataxin-deficient ∆yfh1 yeast cells and lymphoblasts of FRDA patients, and show evidence for a severe mitochondrial glutathione-dependent oxidative stress, with a low GSH/GSSG ratio, and thiol modifications of key mitochondrial enzymes. Both yeast and human frataxin-deficient cells had abnormally high levels of mitochondrial proteins binding an anti-glutathione antibody. Moreover, proteomics and immunodetection experiments provided evidence of thiol oxidation in α-ketoglutarate dehydrogenase (KGDH) or subunits of respiratory chain complexes III and IV. We also found dramatic changes in GSH/GSSG ratio and thiol modifications on aconitase and KGDH in the lymphoblasts of FRDA patients. Our data for yeast cells also confirm the existence of a signaling and/or regulatory process involving both iron and glutathione.

Problems in the congenital lactic acidoses

The congenital lactic acidosis form a heterogeneous group of inborn errors that includes defects of gluconeogenesis, the pyruvate dehydrogenase complex, the Krebs cycle and the respiratory chain. These disorders are not easily classified because of the absence of specific metabolites, difficulties in providing suitable tissue specimens and technical problems with the enzyme assays. The commonest causes of lactic acidosis due to inborn errors are the deficiencies of glucose-6-phosphatase and fructose bisphosphatase, which present with hypoglycaemia, lactic acidosis and hepatomegaly. Pyruvate carboxylase and phosphoenolpyruvate deficiencies vary considerably in both clinical expression and biochemical findings. Neurological symptoms predominate in defects of the pyruvate dehydrogenase complex, and some cases of the spinocerebellar ataxias may be due to partial defects of the pyruvate and 2-oxoglutarate dehydrogenase complexes.

Friedreich's ataxia: electrophysiologic and histologic findings in patients and relatives

Peripheral nerve conduction velocity and cortical evoked potentials were investigated in 48 patients with Friedreich's disease and in 35 relatives. There were 14 patients and 2 relatives who underwent sural nerve biopsy. In the patients sensory conduction velocity was moderately slowed, whereas sensory responses were markedly reduced. Nerve biopsy showed a severe loss of large myelinated fibers and no demyelination. On teased nerve fiber preparations, most fibers presented uniformly short internodes. No correlation was seen between sensory conduction findings or histologic abnormalities and clinical disability. In patients SSEP changes, which were constant, and VEPs, which were frequently involved, were unrelated to the severity or duration of clinical disability. There were 14 relatives who showed clinical signs of Friedreich's disease. Slightly decreased distal conduction velocity along sensory fibers was observed in more than half of the relatives. Nerve biopsy was noncontributory. In conclusion, we could not determine whether the abnormalities observed in the siblings were an expression of a heterozygotic condition, or whether they were early signs of the disease.

Exclusion of the Friedreich ataxia gene from chromosome 19

Friedreich ataxia, a progressive neurodegenerative disorder, is an autosomal recessive disease with a carrier frequency of 1/110 in the United Kingdom. The pathophysiological basis for the disease is not known and the chromosomal location of the mutation remains unidentified. As part of an attempt to map the mutation using linked DNA markers, we demonstrate that the Friedreich ataxia gene is excluded from human chromosome 19. This study also demonstrates that the insulin receptor, which maps to chromosome 19 and may be associated with abnormal biochemical features in some patients, is not the basic defect.

The inherited ataxias

Clinical, biochemical, and genetic studies have brought clarity to many issues concerning the inherited ataxias. The classification, diagnosis, and therapy of hereditary ataxias are now better understood although many questions remain. Basic defects are identified in some disorders.

Familial intermittent ataxia with possible X-linked recessive inheritance. Two patients with abnormal pyruvate metabolism and a response to acetazolamide

Five males in one kindred suffered from intermittent ataxia and one female may have been more mildly affected. The pattern of inheritance strongly suggests X-linkage. Cerebral pathology in one case had some features of Leigh's disease. A defect in pyruvate metabolism was found in two cases. Acetazolamide gave a temporary clinical and biochemical improvement in two cases.

Friedreich ataxia and low pyruvate carboxylase activity in liver and fibroblasts

Biochemical studies in liver, muscle, and cultured fibroblasts were carried out in seven patients with Friedreich ataxia. Lowered activity of pyruvate carboxylase was shown in liver and cultured fibroblasts in all instances.

[Glutamate and GABA concentration in the brain and cerebrospinal fluid of rats treated with phosphatidylcholine]

Phosphatidylcholine increases CNS concentrations of acetylcholine. In rats we investigated whether or not phosphatidylcholine also influences the neurotransmitters glutamate and GABA. In 17 rats 1.5 gram/kg Lethicon perorally was administered daily for 2 weeks, 15 rats served as controls. In tissue from frontal cortex, striatum, substantia nigra, cerebellar cortex no significant differences between treated and untreated animals were found in glutamate or GABA concentrations. A central nervous interaction between the cholinergic system and the neurotransmitters glutamate and GABA, therefore, could not be demonstrated after 2 weeks of phosphatidylcholine intake.

Optimal conditions for the assay of lipoamide dehydrogenase in homogenized human platelets

Widely different method have been used to assay lipoamide dehydrogenase in tissues from patients with neurological diseases. We have re-examined conditions of assay in homogenized human platelets in the light of results of optimal and inhibitory conditions others have found for the purified pig and rat liver enzymes. Optimal conditions in homogenized platelets for the forward, physiological direction were pH 8.0, 2-4 mmol/l dihydrolipoamide and 1.6-2 mmol/l NAD+ and for the reverse reaction, pH 7.3, 1.2-2 mmol/l lipoamide and 0.125-0.2 mmol/l NADH. Km values by the Lineweaver-Burke method were approximately 420 mumol/l dihydrolipoamide, 180 mumol/l NAD+, 600 mumol/l lipoamide and 27 mumol/l NADH. The optimal conditions and Km values are similar to those reported for the purified pig and rat enzymes. Assays by the present methods should therefore reflect the activity of lipoamide dehydrogenase and not the effects of substrate or cofactor inhibition nor the effects of other, interfering enzyme activities.

Oral lecithin and linoleic acid in Friedreich's ataxia: I. Design of the study, material and methods

A clinical and biochemical evaluation of twenty-two patients with Friedreich's Ataxia and ten normal controls was undertaken in 1980 to assess the effect of lecithin and linoleic acid supplements on the course of the disease. The trial consisted of two consecutive six months periods on either supplements in a double-blind crossover fashion. Clinical appraisal was performed with regards to the following parameters: joints mobility, muscle strength, equilibrium, coordination, motor accuracy, speech and numerous day to day activities. Blood samples were obtained at the beginning and in the course of the trial for enzymatic determinations. This paper describes the methodology of the study.

Choline chloride in the treatment of cerebellar and spinocerebellar ataxia

The use of orally administered choline chloride in the treatment of cerebellar and spinocerebellar ataxia was investigated by a short-term double-blind crossover trial in 20 patients with ataxia. These patients, who include 7 with Friedreich's ataxia, 7 with mixed spinocerebellar ataxia and 6 will primary cerebellar degeneration received placebo and 6g/day or 12g/day of choline with crossover at 6 weeks. Serum choline levels were measured 1 h after the first daily dose. Mild but significant improvement in upper limb co-ordination was noted in 3 patients with Friedreich's ataxia, 3 with mixed ataxia and 4 patients with primary cerebellar degeneration. Improvement in gait and lower limb co-ordination was observed in only 2 patients (one with cerebellar ataxia and 1 with mixed ataxia) There was no correlation between serum choline levels and clinical response to choline. Choline chloride produces a mild but functionally significant improvement in motor co-ordination in some patients with cerebellar and spinocerebellar ataxia.

Friedreich's ataxia 1980. An overview of the physiopathology

Phase three of the Quebec Cooperative Study of Friedreich's Ataxia was devoted to an understanding of the physiopathology of individual symptoms on the basis of previously discovered biochemical leads. The present paper attempts to pull these results together by presenting, as a hypothesis, a unifying scheme of possible interactions and relationships. The central core of this hypothesis is the demonstration in Friedreich's ataxia of a state of mitochondrial energy deprivation. This is indirectly responsible for such associated and important symptoms as muscle weakness, dying-back neuropathy, scoliosis and hypertrophic cardiomyopathy. Secondarily, and possibly as an independent but linked-event, the entry of glucose into cells and pyruvate oxidation, are slowed down, favoring the development of diabetes. As a consequence, tissue concentrations of glutamic acid and aspartic acid are decreased, particularly in more vulnerable areas such as the cerebellum, brain stem and dorsal root ganglia. This tissue deficiency in putative excitatory neurotransmitters is directly responsible for the symptom of ataxia. This conclusion is reinforced by the correction of the ataxia in experimental animals, by the intraventricular injection of the same amino acids, and not by the injection of other stimulants of motricity. The observed mitochondrial energy deprivation could be the metabolic consequence of major changes in the linoleic acid (18.2) composition of inner mitochondrial membrane phospholipids, such as cardiolipin. Such decreases in membrane 18:2 could be the result of interference with the normal incorporation of this fatty acid to lipoproteins and/or cell membranes. It is at this level that the search for the specific enzyme defect in Friedreich's ataxia is continuing.

Correlation between serum lipoamide dehydrogenase activity and phosphatidylcholine therapy in Friedreich's ataxia

Serum lipoamide dehydrogenase activity and kinetics were studied in nine patients with Friedreich's ataxia before and three months after therapy with oral lecithin. Results disclosed a significant reduction in LAD inhibition by NADH in all patients after therapy. Three patients normalized their increased Km for lipoamide and one patient showed the opposite results after therapy. Two patients ceased lecithin after one month. All seven patients who remained in the trial group and one additional patient, showed subjective and objective signs of improvement in physical resistance. This study has offered some biochemical basis for the apparent clinical improvement in patients with Friedreich's ataxia who undergo lecithin therapy.

Friedreich's ataxia in northern Italy: I. Clinical, neurophysiological and in vivo biochemical studies

Eighteen patients with the presumptive diagnosis of Friedreich's ataxia were studied. Clinical, neurophysiological and biochemical data were concordant in 14 patients and led to the diagnosis of typical Friedreich's ataxia in this group of patients. The remaining 4 patients differed from the typical patients in several respects, but mainly in the cardiological findings. It is concluded that no single clinical or laboratory finding is typical of F.A. Multidisciplinary approaches are essential to the diagnosis of Friedreich's ataxia.

Active pyruvate dehydrogenase in platelets from Friedreich's ataxia patients

Pyruvate dehydrogenase (PDH) activity was measured in platelets from 10 patients with Friedreich's ataxia, and 10 age-matched healthy control subjects. Both total PDH and active PDH activity were measured. There were no significant differences between the two groups.

Effect of asparagine, glutamine and insulin on cerebral amino acid neurotransmitters

Treatment of rats with asparagine or glutamine caused substantial increases in glutamine concentrations in cerebellum and medulla oblongata. Insulin treatment caused a diminution of glutamate and GABA in these regions of brain. Since it is now well-established that glutamine is a very efficient precursor of the neurotransmitter pool of glutamate in mammalian brain, treatment with asparagine or glutamine could be of therapeutic (replacement) value in the treatment of neurological disorders such as Friedreich's ataxia, in which cerebral glutamate concentrations have been found to be diminished.

Friedreich's ataxia. I. Clinical, neurophysiological and in vivo biochemical studies

Eighteen patients with the presumptive diagnosis of Friedreich's ataxia were studied. Clinical, neurophysiological and biochemical data were concordant in 14 patients and led to the diagnosis of typical Friedreich's ataxia in this group of patients: the remaining 4 patients differed from the typical patients in several respects but mainly in the cardiological findings. It is concluded that so far no single clinical or laboratory finding is typical of F.A.. Multidisciplinary approaches are essential to the diagnosis of Friedreich's ataxia.

An investigation of pyruvate metabolism in patients with cerebellar and spinocerebellar degeneration

This study extends previous observations of pyruvate metabolism in the spino-cerebellar degenerations by screening for abnormalities of pyruvate oxidation using the rise in blood pyruvate after an oral glucose load and examining the activity of the lipoamide dehydrogenase (LAD) moeity of the pyruvate dehydrogenase complex in the serum of 31 patients with Friedreich's ataxia, hereditary spastic ataxia and primary cerebellar degeneration. Serum LAD activity was significantly reduced in 10 Friedreich's ataxia patients when compared to controls and to 10 patients with spastic ataxia, thus confirming previous studies. Two patients with Friedreich's ataxia and 2 with primary cerebellar degeneration had abnormal blood pyruvate curves after oral glucose loading. The findings suggest that abnormal pyruvate oxidation occurs in some cases of Friedreich's ataxia and primary cerebellar degeneration and that the abnormality of pyruvate metabolism is not necessarily reflected in the serum LAD activity of these patients. The relevance of these findings to the heterogeneity of the hereditary ataxias is discussed.

Pyruvate dehydrogenase, lipoamide dehydrogenase and citrate synthase activity in fibroblasts from patients with Friedreich's and Charlevoix-Saguenay ataxia

The activity of lipoamide dehydrogenase and two closely related enzymes was studied simultaneously in early, mild, and late passage fibroblast cultures. Friedreich's ataxia fibroblasts tended to lose pyruvate dehydrogenase and citrate synthase activities, while lipoamide dehydrogenase activity remained constant with aging of the cells. Mean pyruvate dehydrogenase activity was lower over-all in fibroblasts from ataxics. Mean citrate synthase activity was higher in ataxic fibroblasts. Present tissue culture media do not represent the best conditions in which to reproduce cofactor binding defects such as those found in other genetic diseases with structural enzyme mutations.