David A. Stumpf

Carnitine deficiency, organic acidemias, and Reye's syndrome

Relative carnitine deficiency is important in the pathophysiology of several disorders, including Reyes syndrome and organic acidemias. In acute clinical crises, carnitine serves as a “buffer,” trapping toxic acyl compounds. Mitochondria1 failure develops in carnitine deficiency when there is insufficient tissue carnitine available to buffer toxic acyl-CoA metabolites. Toxic levels of acyl-Co A impair the citrate cycle, gluconeogenesis, the urea cycle, and fatty-acid oxidation. Carnitine replacement therapy is safe and induces excretion of toxic acyl groups in the urine.

B- and T-cell markers in opsoclonus–myoclonus syndrome Immunophenotyping of CSF lymphocytes

Background: Although many lines of evidence suggest an autoimmune etiology, the pathophysiology of opsoclonus–myoclonus syndrome (OMS) remains poorly understood and no immunologic abnormalities have correlated with neurologic severity. Conventional immunotherapies often do not prevent relapse or permanent sequelae. Objective: To test the cellular immune hypothesis of OMS in a cross-sectional study and determine if CSF lymphocyte subset analysis provides biomarkers of disease activity. Methods: The expression of lymphocyte surface antigens was investigated in CSF and blood of 36 children with OMS and 18 control subjects, using a comprehensive panel of monoclonal antibodies to adhesion and activation proteins in combination with anti-CD3 and anti-CD45 antibodies in four-color fluorescence-activated cell sorting. Results: Although most children with OMS had normal CSF cell counts, they exhibited expansion of CD19+ B-cell (up to 29%) and γδ T-cell (up to 26%) subsets and a lower percentage of CD4+ T-cells and CD4/CD8 ratio, which persisted even years after disease onset and conventional treatments. The percentage of activated CSF T-cells was also higher. Abnormalities correlated with neurologic severity, as scored blinded from videotapes using a 12-item motor scale, and disease duration. No significant differences were found between tumor and no-tumor groups. In children with neuroblastoma, tumor resection or cancer chemotherapy did not alter immunologic abnormalities. Conclusions: CSF B- and T-cell recruitment is linked to neurologic signs in pediatric OMS, which may relate to relapses and disease progression.

Inhibitory effects of sodium valproate on oxidative phosphorylation

Sodium valproate (VP) inhibited oxidative phosphorylation in isolated rat liver mitochondria. State 3 rates of oxygen consumption with glutamate as substrate were 80% of control values at a low VP concentration (24 μM). At 240 μM, there was more than 50% inhibition of glutamate and α-ketoglutarate state 3 rates. Succinate state p rates were 80% of control values, and uncoupling was noted at 2400 μM VP. These VP effects were similar to those of propionate and isovalerate, suggesting a common mechanism of toxicity. Inhibition of mitochondrial oxidative phosphorylation may explain why VP intoxication causes a hepatocerebral disorder that resembles Reye syndrome.

Lipoamide dehydrogenase deficiency with primary lactic acidosis: Favorable response to treatment with oral lipoic acid

An 8-month-old boy with severe lactic acidosis was found to have lipoamide dehydrogenase deficiency. Treatment with thiamine, biotin, bicarbonate, protein restriction, and ketogenic diet failed to alleviate the lactic acidosis. Oral administration of lipoic acid 25 to 50 mg/kg produced dramatic improvement in lactic and pyruvic acidemia, which has continued for 2 years and which has been accompanied by clinical improvement.

Propionate Inhibition of Succinate: CoA Ligase (GDP) and the Citric Acid Cycle in Mitochondria

Summary: Propionate inhibits oxygen consumption by rat liver mitochondria when glutamate, α-ketaglutarate, and succinate are substrates. Carnitine prevents this effect. The pattern of inhibition of 14CO2 release from metabolic intermediates indicates citric acid cycle inhibition between succinate:coenzyme A (CoA) ligase (GDP) and malate dehydrogenase. Propionyl CoA is synthesized from propionate in mitochondria. Propionyl CoA is a potent inhibitor of succinate:CoA ligase with positive cooperativity and half-maximal inhibition at 2 ± 10−4 M propionyl CoA.Speculation: Inhibition of oxidative phosphorylation and the citric acid cycle may produce the Reyes-like syndrome which occurs in propionic acidemia and possibly related organic acid or mitochondrial disorders. Mitochondrial acyl coenzyme A may be increased in these patients and respond favorably to carnitine therapy.

Friedreich ataxia: III. Mitochondrial malic enzyme deficiency.

Polarographic assays of oxidative phosphorylation in muscle mitochondria indicated abnormal pyruvate-malate metabolism in Friedreich ataxia (FA). Pursuing this clue, more specific assays were performed. Mitochondrial malic enzyme (MEm; malate: NADP oxidoreductase) specific activity was 10% of controls in fibroblasts from eight FA patients (p < 0.0001). Cytosolic malic enzyme was modestly increased in FA fibroblasts. Mitochondrial and cytosolic malate dehydrogenase and aspartate aminotransferase, and malate transport on the dicarboxylate and a-ketoglutarate carriers were normal in fibroblasts or leukocytes. MEm activity is normally highest in the nervous system and heart and is important in regulating carbohydrate metabolism. MEm deficiency could cause FA; further studies are required to substantiate this hypothesis.

A monospecific antibody to human sulfatase a preparation, characterization and significance

Abstract A human enzyme, sulfatase A (arylsulfatase A, EC 3.1.6.1), was fractionated from liver and purified by electrofocusing. When injected into rabbits, the enzyme served as an antigen and induced the formation of antibodies. A monospecific antibody was then obtained when this rabbit antiserum was absorbed with human liver fractions which had been isoelectrically focused next to sulfatase A. Reaction kinetics between this anti-sulfatase A and sulfatases A and B were then studied. The activity of the enzyme was enhanced by the antibody under specified conditions. Thereafter, the antibody could be used to purify the enzyme relatively simply and rapidly.

Brain mitochondrial metabolism in experimental thiamine deficiency

Thiamine deficiency causes Wernickes encephalopathy, although the precise mechanism is unknown. We used a low-thiamine diet in conjunction with a thiamine analog, pyrithiamine, as a model of severe thiamine deficiency in rats. We investigated the function of intact, coupled mitochondria isolated from both brain and liver. State 4 respiration did not change in the thiamine-deficient animals. Brain state 3 rates fell in thiamine-deficient animals when pyruvate/malate, alpha-ketoglutarate, or glutamate were used as substrate. Liver state 3 rates were depressed only when pyruvate/malate was substrate. Activities of brain and liver pyruvate dehydrogenase complex and alpha-ketoglutarate dehydrogenase complex were depressed in the thiamine-deficient group. We conclude that the mitochondrial abnormalities resulting from thiamine deficiency are secondary to depression of thiamine-mediated enzyme activity, rather than from a putative role of thiamine in chemiosmotic coupling, and that the resulting abnormalities in ATP synthesis and perhaps in glutamate catabolism result in the irreversible neurologic defect seen in this disease.

L-Carnitine Reduces Brain Injury after Hypoxia-Ischemia in Newborn Rats

Perinatal hypoxia-ischemia remains a significant cause of neonatal mortality and neurodevelopmental disability. Numerous lines of evidence indicate that cerebral ischemic insults disrupt normal respiratory activity in mitochondria. Carnitine (3-hydroxy-4-N-trimethylammonium-butyrate) has an essential role in fatty acid transport in the mitochondrion and in modulating potentially toxic acyl-CoA levels in the mitochondrial matrix. There are no naturally occurring esterases available to reduce the accumulation of acyl-CoA but this process can be overcome by exogenous carnitine. We used a newborn rat model of perinatal hypoxia-ischemia to test the hypothesis that treatment with l-carnitine would reduce the neuropathologic injury resulting from hypoxia-ischemia in the developing brain. We found that treatment with l-carnitine during hypoxia-ischemia reduces neurologic injury in the immature rat after both a 7- and 28-d recovery period. We saw no neuroprotective effect when l-carnitine was administered after hypoxia-ischemia. Treatment with d-carnitine resulted in an increase in mortality during hypoxia-ischemia. Carnitine is easy to administer, has low toxicity, and is routinely used in neonates as well as children with epilepsy, cardiomyopathy, and inborn errors of metabolism. l-Carnitine merits further investigation as a treatment modality for the asphyxiated newborn or as prophylaxis for the at-risk fetus or newborn.

Friedreich's disease V. Variant form with vitamin E deficiency and normal fat absorption

A 30-year-old woman was thought to have Friedreichs disease because of progressive ataxia, dysarthria, and titubation from age 3 years. Her diet was normal, and there were neither symptoms nor laboratory evidence of liver disease or fat malabsorption. Serum vitamin E content and the ratio of serum vitamin E to total serum lipid were very low, but serum vitamin A, cholylglycine, and lipid levels were normal, as was an oral vitamin E tolerance test. Muscle biopsy showed the lysosomal inclusions of vitamin E deficiency. Mitochondria had normal oxidative phosphorylation using polarographic assays. The cause of her vitamin E deficiency was unknown.