An alteration in glucose metabolism associated with a defect in ketone body metabolism

[Succinyl CoA:3 oxoacid CoA transferase deficiency: A case report]

Background

Succinyl-CoA:3 oxoacid CoA transferase deficiency (SCOTD) is a rare autosomal recessive disease, characterized by altered utilization of ketone bodies, with acute episodes of ketoacidosis.

Clinical case

It is presented the case of a patient with SCOTD, with a first atypical episode accompanied by hyperglycemia, with 4 subsequent episodes with classic manifestations of the disease, presenting with a biochemical pattern of permanent ketonuria with marked elevation of ketone bodies (acetoacetate, 3 beta-hydroxybutyrate) in the study of urinary organic acids by gas chromatography and mass spectrometry, together with the clinical picture granting the diagnosis. It was started a maintenance therapy with a characteristic feeding plan; it was shown an adequate response to treatment, and the absence of permanent ketosis was surmised.

Conclusion

Being a rare disease, the categorization of these patients as diabetic ketoacidosis is frequent. The clinical and biochemical characteristics with ketosis or persistent ketonuria should be analyzed very carefully, especially in patients presenting with hyperglycemia, which is an atypical manifestation of the disease, in order to make an early diagnosis and treatment, positively impacting the prognosis of patients.

Neonatal hypoglycaemia in severe succinyl-CoA: 3-oxoacid CoA-transferase deficiency

Succinyl-CoA: 3-oxoacid CoA-transferase (SCOT) deficiency is an inborn error of ketone body utilization, characterized by intermittent ketoacidotic crises and persistent ketosis. The diagnosis was suspected in a patient who presented with hypoglycaemia, ketoacidosis and coma at 4 days of age. The hypoglycaemic tendency was only observed during the first month of life. A novel macromolecular labelling assay in cultured skin fibroblasts using D-3-hydroxy[3-14C]butyrate supported the diagnosis. Subsequently, 9% residual SCOT activity and undetectable cross-reactive protein were noted in fibroblasts and the patient was found to be homozygous for the G324E SCOT gene mutation. By 7 years of age, recurrent episodes of ketoacidosis superimposed on persistent hyperketonaemia had resulted in over 25 hospitalizations requiring intravenous fluid, glucose and sodium bicarbonate therapy. He has had normal growth but developmental delay and attention deficit-hyperactivity disorder. A continuous intravenous glucose infusion at 38 microlmol (6.8 mg)/kg per min reduced plasma total ketone levels from greater than 1.5 mmol/L to less than 0.5 mmol/L after 48 h. This indicates that patients with SCOT deficiency do not always manifest ketosis with administration of a sufficient amount of carbohydrates, but that even under such conditions hyperketonaemia is difficult to eliminate completely. The presence of hypoglycaemia does not exclude the diagnosis of SCOT deficiency in infancy.

Decreased oxidation of labeled glucose by dissociated brain cells in the presence of fetal bovine serum

The effect of serum on the rate of substrate oxidation by dissociated brain cells in vitro was examined. At a serum protein concentration of approximately 0.55 milligram per milliliter, oxidation of [6-14C]glucose to 14CO2 was decreased more than 50 percent. Oxidation of [3-14C]-3-hydroxybutyrate and [U-14C]glutamine was decreased much less. Serum from cows, rats, horses, and humans produced similar effects, as did serum from young and old animals and from both sexes. The effect on [6-14C]glucose oxidation was proportional to serum protein concentration, and significant inhibitory activity was obtained with dialyzed serum. Heating (80 degrees C for 10 minutes) significantly reduced the inhibitory activity. These results suggest the presence of a factor in serum that can preferentially decrease glucose oxidation. Such a factor would have profound implications for metabolic regulation in vivo and for studies of cells in vitro in which serum is included in the growth medium.

Glycerol oxidation in rat brain: subcellular localization and kinetic characteristics

The oxidation of [1,3-14C] glycerol to 14CO was measured in slices, whole homogenates, and subcellular fractions of rat brain. In all of these tissue preparations, the Lineweaver-Burk plots of glycerol oxidation were biphasic, yielding two apparent Km and V values. Similar kinetic characteristics were obtained with brain homogenates from guinea pig, mouse, rabbit, monkey, and pig. In other tissues of the rat, including heart, kidney, liver, and skeletal muscle, the Lineweaver-Burk plots for glycerol oxidation were not biphasic but were linear. Heating the brain homogenates for five minutes at 5 degrees C caused a 50% decrease in the rate of oxidation of glycerol without a change in the biphasic double reciprocal plot. The addition of purified glycerol kinase (EC 2.7.1.30) to the homogenate caused an increase in the rate of oxidation and resulted in linear Lineweaver-Burke plot. Brain mitochondria were prepared by two different methods, both of which yielded an enrichment of glycerol oxidation. In contrast, the rate of glucose oxidation was higher in homogenates than in mitochondria, and glucose competed with glycerol as substrate only extramitochondrially. The effects of various metabolic inhibitors suggested the participation of intact, coupled mitochondria, of glycolytic enzymes, and of electron transport in the oxidation of glycerol. The data support the primary localization of glycerol oxidation in nonsynaptic mitochondria in brain and the presence in that organelle of enzymes of the Embden-Meyerhoff pathway or an as yet unidentified system for oxidizing this compound.