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Biochemical effects of the hypoglycaemic compound pent--4-enoic acid and related non-hypoglycaemic fatty acids.

1. The effects of the hypoglycaemic compound, pent-4-enoic acid, and of four structurally related non-hypoglycaemic compounds (pentanoic acid, pent-2-enoic acid, cyclopropanecarboxylic acid and cyclobutanecarboxylic acid), on the oxidation of saturated fatty acids by rat liver mitochondria were determined. 2. The formation of (14)CO(2) from [1-(14)C]palmitate was strongly inhibited by 0.01mm-pent-4-enoic acid. 3. The inhibition of oxygen uptake was less than that of (14)CO(2) formation, presumably because fumarate was used as a sparker. 4. The oxidation of [1-(14)C]-butyrate, -octanoate or -laurate was not strongly inhibited by 0.01mm-pent-4-enoic acid. 5. The other four non-hypoglycaemic compounds did not inhibit the oxidation of any saturated fatty acid when tested at 0.01mm concentration, though they all inhibited strongly at 10mm. 6. The oxidation of [1-(14)C]-myristate and -stearate, but not of [1-(14)C]decanoate, was strongly inhibited by 0.01mm-pent-4-enoic acid. 7. The oxidation of [1-(14)C]palmitate was about 50% carnitine-dependent under the experimental conditions used. 8. The percentage inhibition of [1-(14)C]palmitate oxidation by pent-4-enoic acid was the same whether carnitine was present or not. 9. Acetoacetate formation from saturated fatty acids was inhibited by 0.1mm-cyclopropanecarboxylic acid to a greater extent than their oxidation. 10. The other compounds tested inhibited acetoacetate formation from saturated fatty acids proportionately to the inhibition of oxidation. 11. Possible mechanisms for the inhibition of long-chain fatty acid oxidation by pent-4-enoic acid are discussed. 12. There was a correlation between the ability to inhibit long-chain fatty acid oxidation and hypoglycaemic activity in this series of compounds.

Acetoacetates↗

Molecular heterogeneity of variant isovaleryl-CoA dehydrogenase from cultured isovaleric acidemia fibroblasts.

Variants of isovaleryl-CoA dehydrogenase (IVDHase, EC 1.3.99.10) in 15 isovaleric acidemia fibroblast lines were analyzed using [35S]methionine labeling, immunoprecipitation with anti-rat IVDHase antiserum, and NaDodSo4/polyacrylamide gel electrophoresis. Five distinct variants of IVDHase were detected. The molecular size of variant 1 (43 kDa) was indistinguishable from that of normal IVDHase (43 kDa), although the activity of this enzyme was as deficient (0-2.2% of normal control) as that of any other variant. It was synthesized as a precursor (45 kDa), which is the case for normal IVDHase. Variant 2 was synthesized as a 42-kDa precursor, but only a small portion of it was processed to the mature variant form (40 kDa). Variant 3 (41 kDa) was synthesized as a 43-kDa precursor. Variant 4 (40 kDa) was synthesized as a 42-kDa precursor that was readily processed to the mature form. In cells with variant 5, no material that crossreacted with the anti-rat IVDHase antibody was detected. These results suggest that variant 1 may be due to a point mutation, while variants 2-4 may be encoded by a different mutant IVDHase allele that causes the premature termination of translation, although other complex mechanisms are possible. A deletion, a nonsense mutation close to the NH2 terminus or an extremely labile mRNA may give rise to variant 5.

Amino Acid Metabolism, Inborn Errors↗

Molecular basis of isovaleric acidemia and medium-chain acyl-CoA dehydrogenase deficiency.

Our early study of isovaleric acidemia (IVA) indicated that isovaleryl-CoA is dehydrogenated by an enzyme that is specific for isovaleryl-CoA. We subsequently identified and purified isovaleryl-CoA dehydrogenase (IVD) and 2-methyl-branched chain acyl-CoA dehydrogenase, which were previously unknown. We also purified and characterized three previously known acyl-CoA dehydrogenases. Five acyl-CoA dehydrogenases share similar molecular features and reaction mechanisms, indicating a close evolutionary relationship. Using the tritium release assay and [35S]methionine labeling/immunoprecipitation, we showed that IVA is due to a mutation of IVD. We also demonstrated that there are at least 5 distinct forms of mutant IVD, indicating an extensive molecular heterogeneity. Furthermore, we cloned cDNAs encoding IVD and medium-chain acyl-CoA dehydrogenases. The comparison of their complete primary sequences revealed a high degree of homology, indicating that these enzymes belong to a gene family, the acyl-CoA dehydrogenase family.

Acyl-CoA Dehydrogenases↗

L-carnitine therapy in isovaleric acidemia.

Isovaleric acidemia, resulting from isovaleryl-coenzyme A dehydrogenase deficiency, is associated with marked reduction of free carnitine in both plasma and urine. Fast atom bombardment-mass spectrometry, hydrolysis, and gas chromatography/mass spectrometry have unequivocally identified the existence of isovalerylcarnitine, a new metabolite specific for this disorder. Administration of equimolar amounts of glycine or L-carnitine separately with leucine demonstrated that isovaleryl-coenzyme A is removed by supplemental L-carnitine in the form of isovalerylcarnitine as effectively as it is by glycine, in the form of isovalerylglycine. When L-carnitine is given alone, excretion of isovalerylglycine decreases in preference to enhanced excretion of isovalerylcarnitine and hippurate. Treatment with L-carnitine alone has proven effective in preventing further hospitalizations in a patient with this genetic disorder.

Amino Acid Metabolism, Inborn Errors↗

Nutritional & pharmacologic management of hyperlipoproteinemia.

The results of the nutritional intervention on one of the twenty MRFIT centers is presented. The reduction in cholesterol was 5.78% after four years. Those results were compared with the changes found in serum cholesterol with a similar diet and the administration of either clofibrate or gemfibrozil. The reduction with clofibrate remained at 5%. However with gemfibrozil the reduction in cholesterol was 16%. The HDL level rose in half of these patients treated with either clofibrate or gemfibrozil. The results without concurrent dietary restriction usually show a greater reduction in VLDL and a greater rise in HDL than we found when nutritional and pharmacologic intervention were combined.

Cholesterol↗

Effect of gemfibrozil on serum lipids in man.

The effect of gemfibrozil, a new lipid-lowering agent, was studied in 22 patients. Each patient served as his own control in a double blind study. The administration of gemfibrozil, for a period of 24 months, 1200 mg daily, reduced mean serum triglyceride levels by 45.6% (p less than 0.001) and mean serum cholesterol levels by 8.3% (p less than 0.001). Mean serum HDL cholesterol was increased by 32.3% (p less than .0001) and mean serum LDL cholesterol levels were decreased by 11.4% (p less than 0.01). Mean serum VLDL cholesterol was decreased by 45.9% (p less than 0.001). A 3-hour glucose-tolerance test was done in each patient during a placebo-control period and during the administration of gemfibrozil. Mean plasma glucose was moderately increased during the administration of gemfibrozil at all points on the glucose tolerance curve, and to levels of significance at one (p less than 0.05) and two hours (p less than 0.02). There was no effect of the drug on serum immunoreactive insulin. No subjective side effects were apparent.

Adult↗

Changing plasma and urinary organic acid levels in a patient with isovaleric acidemia during an attack.

Organic acids in plasma and urine of a patient with isovaleric acidemia were measured serially during a severe ketoacidotic attack. Urinary ketone bodies, lactic acid and 2-hydroxy-n-butyric acid changed in parallel with the plasma isovaleric acid concentration, which was correlated closely with the severity of the clinical symptoms. A 2-day lag was observed between the time of the peak plasma isovaleric acid level and that of the highest urinary excretion of 3-hydroxyisovaleric acid, methylsuccinic acid, mesaconic acid and 2-hydroxyisobutyric acid, the total quantity of which amounted to one-third of that of isovalerylglycine on the 4th day of the attack. Urinary isovalerylglycine excretion remained at a plateau for 4 days after the highest level of plasma isovaleric acid was observed. The decrease of urinary hippuric acid excretion during the attack continued until the patient had recovered enough to be able to eat. Benzoic acid administration concomitant with leucine and glycine canceled the effect of glycine in lessening the rise of plasma isovaleric acid concentration after a leucine load.

Amino Acid Metabolism, Inborn Errors↗

The treatment of isovaleric acidemia with glycine supplement.

Although dietary leucine restriction and supplemental glycine are used to treat patients with isovaleric acidemia [deficient isovaleryl-CoA-dehydrogenase (E.C.1.3.99.10)], little quantitative information is available regarding their optimum relationship. Herein we compare different glycine supplements and quantitate isovalerylglycine produced in two patients with clinically different forms of isovaleric acidemia during restricted leucine intake and during oral leucine loading. We found that under stable conditions of leucine restriction, 150 mg glycine/kg/day is an optimum glycine supplement and that glycine supplements of more than 250 mg/kg/day may result in reduced isovalerylglycine production; that when isovaleric acid accumulation is increased, glycine supplements to 600 mg/kg/day will increase isovalerylglycine production; and that the phenotype of isovaleric acidemia is related not only to the extent of impaired isovaleryl-CoA dehydrogenase, but also the ability to detoxify accumulated isovaleryl CoA to isovalerylglycine.

Carbon Dioxide↗

Cerebellar hemorrhage complicating isovaleric acidemia: a case report.

Isovaleric acidemia (IVA) is an inborn error of leucine metabolism, resulting in an accumulation of isovaleric acid in the body fluids. The neuropathologic findings in an 11-day-old infant with IVA consisted of diffuse cerebral edema, massive cerebellar hemorrhage, upward transtentorial herniation, and focal degeneration of clusters of glial cells in white and gray matter. Although abnormal myelination has been described in different aminoacidopathies, the above findings have not been reported previously in IVA.

Acidosis↗