Treatment of cardiomyopathy and rhabdomyolysis in long-chain fat oxidation disorders using an anaplerotic odd-chain triglyceride.

The current dietary treatment of long-chain fatty acid oxidation defects (high carbohydrate with medium-even-chain triglycerides and reduced amounts of long-chain fats) fails, in many cases, to prevent cardiomyopathy, rhabdomyolysis, and muscle weakness. We hypothesized that the apparent defect in energy production results from a depletion of the catalytic intermediates of the citric acid cycle via leakage through cell membranes (cataplerosis). We further hypothesized that replacing dietary medium-even-chain fatty acids (precursors of acetyl-CoA) by medium-odd-chain fatty acids (precursors of acetyl-CoA and anaplerotic propionyl-CoA) would restore energy production and improve cardiac and skeletal muscle function. We fed subjects with long-chain defects a controlled diet in which the fat component was switched from medium-even-chain triglycerides to triheptanoin. In three patients with very-long-chain acyl-CoA dehydrogenase deficiency, this treatment led rapidly to clinical improvement that included the permanent disappearance of chronic cardiomyopathy, rhabdomyolysis, and muscle weakness (for more than 2 years in one child), and of rhabdomyolysis and weakness in the others. There was no evidence of propionyl overload in these patients. The treatment has been well tolerated for up to 26 months and opens new avenues for the management of patients with mitochondrial fat oxidation disorders.

Choice of oils for essential fat supplements can enhance production of abnormal metabolites in fat oxidation disorders.

Patients with mitochondrial long-chain fat oxidation deficiencies are usually treated with diets containing reduced fat and increased carbohydrate, at times via gastrostomy feeding. To ensure adequate intake of essential fatty acids, supplements are provided to their diets using commercially available oils. These oils contain large quantities of non-essential fats that are preferentially oxidized and produce disease-specific metabolites (acyl-CoA intermediates) due to the genetic defect. This study describes the concentrations of these intermediates as reflected by acylcarnitines as well as the % contribution from each of four fatty acids: palmitate, oleate, linoleate, and alpha-linolenate when incubated with fibroblasts from patients with VLCAD, LCHAD, and trifunctional protein (TFP) deficiencies. Palmitate and oleate produce the majority of disease-specific acylcarnitines with these defective cell lines (79-94%) whereas linoleate and linolenate produced less (6-21%). On average, the amount of acylcarnitines decreased with increasing unsaturation (C18:1>C18:2>C18:3:34%>11%>3%, respectively. This relationship may reflect the "gatekeeper" role of carnitine palmitoyltransferase I (CPT I). A diet comparison between Canola and a combination of Flax/Walnut oils revealed that the latter, containing the least amount of non-essential fats, reduced blood acylcarnitine levels by 33-36%. The etiology of the severe peripheral neuropathy of TFP deficiency may result from the unique metabolite, 3-keto-acyl-CoA, after conversion to a methylketone via spontaneous decarboxylation. Essential fatty acid supplementation with oils should consider these findings to decrease production of disease-specific acyl-CoA intermediates.

Variations in IBD (ACAD8) in children with elevated C4-carnitine detected by tandem mass spectrometry newborn screening.

The isobutyryl-CoA dehydrogenase (IBD) enzyme is involved in the degradation of valine. IBD deficiency was first reported in 1998 and subsequent genetic investigations identified acyl-CoA dehydrogenase (ACAD) 8, now IBD, as the gene responsible for IBD deficiency. Only three individuals homozygous or compound heterozygous for variations in the IBD gene have been reported. We present IBD deficiency in an additional four newborns with elevated C(4)-carnitine identified by tandem mass spectrometry (MS/MS) screening in Denmark and the United States. Three showed urinary excretions of isobutyryl-glycine, and in vitro probe analysis of fibroblasts from two newborns indicated enzymatic IBD defect. Molecular genetic analysis revealed seven new rare variations in the IBD gene (c.348C>A, c.400G>T, c.409G>A, c.455T>C, c.958G>A, c.1000C>T and c.1154G>A). Furthermore, sequence analysis of the short-chain acyl-CoA dehydrogenase (SCAD) gene revealed heterozygosity for the prevalent c.625G>A susceptibility variation in all newborns and in the first reported IBD patient. Functional studies in isolated mitochondria demonstrated that the IBD variations present in the Danish newborn (c.409G>A and c.958G>A) together with a previously published IBD variation (c.905G>A) disturbed protein folding and reduced the levels of correctly folded IBD tetramers. Accordingly, low/no IBD residual enzyme activity was detectable when the variant IBD proteins were overexpressed in Chang cells.

Identification of isobutyryl-CoA dehydrogenase and its deficiency in humans.

The acyl-CoA dehydrogenases (ACDs) are a family of related enzymes that catalyze the alpha,beta-dehydrogenation of acyl-CoA esters. Two homologues active in branched chain amino acid metabolism have previously been identified. We have used expression in Escherichia coli to produce a previously uncharacterized ACD-like sequence (ACAD8) and define its substrate specificity. Purified recombinant enzyme had a k(cat)/K(m) of 0.8, 0.23, and 0.04 (microM(-1)s(-1)) with isobutyryl-CoA, (S) 2-methylbutyryl-CoA, and n-propionyl-CoA, respectively, as substrates. Thus, this enzyme is an isobutyryl-CoA dehydrogenase. A single patient has previously been described whose fibroblasts exhibit a specific deficit in the oxidation of valine. Amplified ACAD8 cDNA made from patient fibroblast mRNA was homozygous for a single nucleotide change (905G>A) in the ACAD8 coding region compared to the sequence from control cells. This encodes an Arg302Gln substitution in the full-length protein (position 280 in the mature protein), a position predicted by molecular modeling to be important in subunit interactions. The mutant enzyme was stable but inactive when expressed in E. coli. It was also stable and appropriately targeted to mitochondria, but inactive when expressed in mammalian cells. These data confirm further the presence of a separated ACD in humans specific to valine catabolism (isobutyryl-CoA dehydrogenase, IBDH), along with the first enzymatic and molecular confirmation of a deficiency of this enzyme in a patient.