[Clinical analysis and genetic diagnosis of three children with Isoleucine metabolic disorders due to variants of HSD17B10 and ACAT1 genes]

OBJECTIVE

To explore the clinical, biochemical and genetic characteristics of three children with Isoleucine metabolic disorders due to variants of HSD17B10 and ACAT1 genes.

METHODS

Two children with 17β hydroxysteroid dehydrogenase 10 (HSD17B10) deficiency and a child with β-ketothiolase deficiency (BKD) diagnosed at Shanghai Children's Hospital between 2014 and 2021 were selected as the study subjects. Clinical data of the children were collected. The children were subjected to blood acylcarnitine, urinary organic acid and genetic testing, and candidate variants were analyzed with bioinformatic tools.

RESULTS

The main symptoms of the three children had included epilepsy, developmental delay, hypotonia and acidosis. Their blood acylcarnitine methylcrotonyl carnitine (C5:1), 3-hydroxyisovalerylcarnitine (C5-OH) and 3-hydroxybutylcarnitine (C4OH) were increased to various extents, and urine organic acids including methyl crotonylglycine and 2-methyl-3-hydroxybutyric acid were significantly increased. Child 1 and child 2 were respectively found to harbor a c.347G>A (p.R116Q) variant and a c.274G>A (p.A92T) variant of the HSD17B10 gene, and child 3 was found to harbor compound heterozygous variants of the ACAT1 gene, namely c.547G>A (p.G183R) and a c.331G>C (p.A111P). Among these, the c.274G>A (p.A92T) and c.331G>C (p.A111P) variants were unreported previously. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), they were respectively classified as variant of unknown significance (PP3_Strong+PM2_supporting) and likely pathogenic (PM3+PM2_Supporting+PP3_Moderate+PP4).

CONCLUSION

Both the HSD17B10 deficiency and BKD can lead to Isoleucine metabolism disorders, which may be difficult to distinguish clinically. Genetic testing can further confirm the diagnosis. Discoveries of the HSD17B10: c.274G>A (p.A92T) variant and the ACAT1: c.331G>C (p.A111P) variant have enriched the mutational spectrum of the two diseases.

Genetic, biochemical, and clinical spectrum of patients with mitochondrial trifunctional protein deficiency identified after the introduction of newborn screening in the Netherlands

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is included in many newborn screening (NBS) programs. Acylcarnitine-based NBS for LCHADD not only identifies LCHADD, but also the other deficiencies of the mitochondrial trifunctional protein (MTP), a multi-enzyme complex involved in long-chain fatty acid β-oxidation. Besides LCHAD, MTP harbors two additional enzyme activities: long-chain enoyl-CoA hydratase (LCEH) and long-chain ketoacyl-CoA thiolase (LCKAT). Deficiency of one or more MTP activities causes generalized MTP deficiency (MTPD), LCHADD, LCEH deficiency (not yet reported), or LCKAT deficiency (LCKATD). To gain insight in the outcomes of MTP-deficient patients diagnosed after the introduction of NBS for LCHADD in the Netherlands, a retrospective evaluation of genetic, biochemical, and clinical characteristics of MTP-deficient patients, identified since 2007, was carried out. Thirteen patients were identified: seven with LCHADD, five with MTPD, and one with LCKATD. All LCHADD patients (one missed by NBS, clinical diagnosis) and one MTPD patient (clinical diagnosis) were alive. Four MTPD patients and one LCKATD patient developed cardiomyopathy and died within 1 month and 13 months of life, respectively. Surviving patients did not develop symptomatic hypoglycemia, but experienced reversible cardiomyopathy and rhabdomyolysis. Five LCHADD patients developed subclinical neuropathy and/or retinopathy. In conclusion, patient outcomes were highly variable, stressing the need for accurate classification of and discrimination between the MTP deficiencies to improve insight in the yield of NBS for LCHADD. NBS allowed the prevention of symptomatic hypoglycemia, but current treatment options failed to treat cardiomyopathy and prevent long-term complications. Moreover, milder patients, who might benefit from NBS, were missed due to normal acylcarnitine profiles.

Thermo-sensitive mitochondrial trifunctional protein deficiency presenting with episodic myopathy

Mitochondrial trifunctional protein (MTP) is involved in long-chain fatty acid β-oxidation (lcFAO). Deficiency of one or more of the enzyme activities as catalyzed by MTP causes generalized MTP deficiency (MTPD), long-chain hydroxyacyl-CoA dehydrogenase deficiency (LCHADD), or long-chain ketoacyl-CoA thiolase deficiency (LCKATD). When genetic variants result in thermo-sensitive enzymes, increased body temperature (e.g. fever) can reduce enzyme activity and be a risk factor for clinical decompensation. This is the first description of five patients with a thermo-sensitive MTP deficiency. Clinical and genetic information was obtained from clinical files. Measurement of LCHAD and LCKAT activities, lcFAO-flux studies and palmitate loading tests were performed in skin fibroblasts cultured at 37°C and 40°C. In all patients (four MTPD, one LCKATD), disease manifested during childhood (manifestation age: 2-10 years) with myopathic symptoms triggered by fever or exercise. In four patients, signs of retinopathy or neuropathy were present. Plasma long-chain acylcarnitines were normal or slightly increased. HADHB variants were identified (at age: 6-18 years) by whole exome sequencing or gene panel analyses. At 37°C, LCHAD and LCKAT activities were mildly impaired and lcFAO-fluxes were normal. Remarkably, enzyme activities and lcFAO-fluxes were markedly diminished at 40°C. Preventive (dietary) measures improved symptoms for most. In conclusion, all patients with thermo-sensitive MTP deficiency had a long diagnostic trajectory and both genetic and enzymatic testing were required for diagnosis. The frequent absence of characteristic acylcarnitine abnormalities poses a risk for a diagnostic delay. Given the positive treatment effects, upfront genetic screening may be beneficial to enhance early recognition.

SIRT3 controls brown fat thermogenesis by deacetylation regulation of pathways upstream of UCP1

OBJECTIVE

Brown adipose tissue (BAT) is important for thermoregulation in many mammals. Uncoupling protein 1 (UCP1) is the critical regulator of thermogenesis in BAT. Here we aimed to investigate the deacetylation control of BAT and to investigate a possible functional connection between UCP1 and sirtuin 3 (SIRT3), the master mitochondrial lysine deacetylase.

METHODS

We carried out physiological, molecular, and proteomic analyses of BAT from wild-type and Sirt3KO mice when BAT is activated. Mice were either cold exposed for 2 days or were injected with the β3-adrenergic agonist, CL316,243 (1 mg/kg; i.p.). Mutagenesis studies were conducted in a cellular model to assess the impact of acetylation lysine sites on UCP1 function. Cardiac punctures were collected for proteomic analysis of blood acylcarnitines. Isolated mitochondria were used for functional analysis of OXPHOS proteins.

RESULTS

Our findings showed that SIRT3 absence in mice resulted in impaired BAT lipid use, whole body thermoregulation, and respiration in BAT mitochondria, without affecting UCP1 expression. Acetylome profiling of BAT mitochondria revealed that SIRT3 regulates acetylation status of many BAT mitochondrial proteins including UCP1 and crucial upstream proteins. Mutagenesis work in cells suggested that UCP1 activity was independent of direct SIRT3-regulated lysine acetylation. However, SIRT3 impacted BAT mitochondrial proteins activities of acylcarnitine metabolism and specific electron transport chain complexes, CI and CII.

CONCLUSIONS

Our data highlight that SIRT3 likely controls BAT thermogenesis indirectly by targeting pathways upstream of UCP1.

3-Hydroxy-fatty acid analysis by gas chromatography-mass spectrometry

The mitochondrial fatty acid beta-oxidation is integral to normal cellular metabolism and maintenance of cellular energy supplies. Disorders of this pathway interrupt the body's ability to deal with fasting states, as well as compromising the functioning of organs and systems whose high-energy requirements utilize fats for a continuous energy source, such as heart and skeletal muscle. This method quantitatively measures intermediate metabolites of fatty acid beta-oxidation, specifically the 3-hydroxy-fatty acids produced by the third step in the pathway. The method is useful for helping to diagnose disorders of the pathway, especially defects in the L-3-hydroxyacyl CoA dehydrogenases. Serum or plasma samples are used for routine clinical evaluation; however, measurement of 3-hydroxy-fatty acid intermediates in fibroblast cell culture media and in samples from mice also allows the method to be used for research into fatty acid oxidation and interconnected pathways. The method is a stable isotope dilution, electron impact ionization gas chromatography/mass spectrometry (GC/MS) procedure.

Four weeks one-leg training and high fat diet does not alter PPARalpha protein or mRNA expression in human skeletal muscle

Fatty acid metabolism is influenced by training and diet with exercise training mediating this through activation of nuclear hormone receptor peroxisome proliferator-activated receptor alpha (PPARalpha) in skeletal muscle. This study investigated the effect of training and high fat or normal diet on PPARalpha expression in human skeletal muscle. Thirteen men trained one leg (T) four weeks (31.5 h in total), while the other leg (UT) served as control. During the 4 weeks six subjects consumed high fat (FAT) diet and seven subjects maintained a normal (CHO) diet. Biopsies were obtained from vastus lateralis muscle in both legs before and after training. After the biopsy, one-leg extension exercise was performed in random order with both legs 30 min at 95% of workload max. A training effect was evident as citrate synthase activity increased (P < 0.05) by 15% in the trained, but not the control leg in both groups. During exercise respiratory exchange ratio was lower in FAT (0.86 +/- 0.01, 0.83 +/- 0.01, mean +/- SEM) than CHO (0.96 +/- 0.02, 0.94 +/- 0.03) and in UT than T legs, respectively. The PPARalpha protein (144 +/- 44, 104 +/- 28, 79 +/- 15, 79 +/- 14, % of pre level) and PPARalpha mRNA (69 +/- [2, 2], 78 +/- [7, 6], 92 +/- [22, 18], 106 +/- [21, 18], % of pre level, geometric mean +/- SEM) expression remained unchanged by diet and training in FAT (UT, T) and CHO (UT, T), respectively. After the training and diet CS, HAD, PPARalpha, UCP2, UCP3 and mFABP mRNA content remained unchanged, whereas GLUT4 mRNA was lower in both groups and LDHA mRNA was lower (P < 0.05) only in FAT.

IN CONCLUSION

4 weeks one leg knee extensor training did not affect PPARalpha protein or mRNA expression. Furthermore, higher fat oxidation during exercise after fat rich diet was not accompanied by an increased PPARalpha protein or mRNA expression after 4 weeks.

Inborn errors of isoleucine degradation: a review

Three inborn errors have been identified in the pathway of isoleucine degradation. Deficiency of beta-ketothiolase (beta-KT, also known as T2, mitochondrial acetoacetyl-CoA thiolase and acetyl-CoA acetyltransferase 1) is a well-described disorder which presents with acute episodic ketoacidosis. In contrast, short/branched-chain acyl-CoA dehydrogenase (SBCAD) and 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiencies are recently described and relatively rare defects which present with predominantly neurological manifestations, although acute metabolic decompensation may occur in the early newborn period. Careful examination of urine organic acids is required for identification and differential diagnosis of these disorders, with awareness that the abnormalities may be subtle and variable. Tandem MS analysis of acylcarnitines may reveal elevated C5 (SBCAD) or C5:1 and/or OH-C5 species (MHBD and beta-KT deficiencies) but the abnormalities are non-diagnostic and may be intermittent or absent. Confirmation of diagnosis is therefore advisable by specific enzyme assay and/or mutation analysis of the ACAT1 (beta-KT), ACADSB (SBCAD) or HADH2 (MHBD) genes. The latter is located on the X chromosome, accounting for the milder clinical phenotype in females. If beta-KT deficiency is diagnosed early and treated by fasting avoidance and modest protein restriction, ketoacidosis episodes can be prevented and the prognosis is excellent. The role of treatment in SBCAD deficiency remains unclear pending further delineation of its clinical phenotype and pathogenicity, particularly regarding asymptomatic individuals detected by expanded newborn screening. The ineffectiveness of isoleucine restriction in MHBD deficiency is consistent with the additional roles of this multifunctional enzyme in sex steroid and neurosteroid metabolism and its interaction with amyloid-beta peptide.

Peroxisomal fatty acid beta-oxidation is not essential for virulence of Candida albicans

Phagocytic cells form the first line of defense against infections by the human fungal pathogen Candida albicans. Recent in vitro gene expression data suggest that upon phagocytosis by macrophages, C. albicans reprograms its metabolism to convert fatty acids into glucose by inducing the enzymes of the glyoxylate cycle and fatty acid beta-oxidation pathway. Here, we asked whether fatty acid beta-oxidation, a metabolic pathway localized to peroxisomes, is essential for fungal virulence by constructing two C. albicans double deletion strains: a pex5Delta/pex5Delta mutant, which is disturbed in the import of most peroxisomal enzymes, and a fox2Delta/fox2Delta mutant, which lacks the second enzyme of the beta-oxidation pathway. Both mutant strains had strongly reduced beta-oxidation activity and, accordingly, were unable to grow on media with fatty acids as a sole carbon source. Surprisingly, only the fox2Delta/fox2Delta mutant, and not the pex5Delta/pex5Delta mutant, displayed strong growth defects on nonfermentable carbon sources other than fatty acids (e.g., acetate, ethanol, or lactate) and showed attenuated virulence in a mouse model for systemic candidiasis. The degree of virulence attenuation of the fox2Delta/fox2Delta mutant was comparable to that of the icl1Delta/icl1Delta mutant, which lacks a functional glyoxylate cycle and also fails to grow on nonfermentable carbon sources. Together, our data suggest that peroxisomal fatty acid beta-oxidation is not essential for virulence of C. albicans, implying that the attenuated virulence of the fox2Delta/fox2Delta mutant is largely due to a dysfunctional glyoxylate cycle.

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiency: an X-linked inborn error of isoleucine metabolism that may mimic a mitochondrial disease

We describe three patients, from two Spanish families, with 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiency, a recently described X-linked neurodegenerative inborn error of isoleucine metabolism. Two of them are males with severe lactic acidosis suggestive of a mitochondrial encephalopathy, and the third is a female who was less severely affected, suggesting skewed X-inactivation. Molecular studies revealed a new missense mutation, 740A-->G, in one family and a previously described mutation, 388C-->T, in the other, causing the amino acid substitutions N247S and R130C, respectively. Both male patients died, one of them despite treatment with an isoleucine-restricted diet, but the disease has remained stable in the female patient after 1 y of treatment.

Inhibition of energy metabolism by 2-methylacetoacetate and 2-methyl-3-hydroxybutyrate in cerebral cortex of developing rats

Mitochondrial beta-ketothiolase and 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiencies are inherited neurometabolic disorders affecting isoleucine catabolism. Biochemically, beta-ketothiolase deficiency is characterized by intermittent ketoacidosis and urinary excretion of 2-methyl-acetoacetate (MAA), 2-methyl-3-hydroxybutyrate (MHB) and tiglylglycine (TG), whereas in MHBD deficiency only MHB and tiglylglycine accumulate. Lactic acid accumulation and excretion are also observed in these patients, being more pronounced in MHBD-deficient individuals, particularly during acute episodes of decompensation. Patients affected by MHBD deficiency usually manifest severe mental retardation and convulsions, whereas beta-ketothiolase-deficient patients present encephalopathic crises characterized by metabolic acidosis, vomiting and coma. Considering that the pathophysiological mechanisms responsible for the neurological alterations of these disorders are unknown and that lactic acidosis suggests an impairment of energy production, the objective of the present work was to investigate the in vitro effect of MAA and MHB, at concentrations varying from 0.01 to 1.0 mmol/L, on several parameters of energy metabolism in cerebral cortex from young rats. We observed that MAA markedly inhibited CO2 production from glucose, acetate and citrate at concentrations as low as 0.01 mmol/L. In addition, the activities of the respiratory chain complex II and succinate dehydrogenase were mildly inhibited by MAA. MHB, at 0.01 mmol/L and higher concentrations, strongly inhibited CO2 production from all tested substrates, as well as the respiratory chain complex IV activity. The other activities of the respiratory chain were not affected by these metabolites. The data indicate a marked blockage in the Krebs cycle and a mild inhibition of the respiratory chain caused by MAA and MHB. Furthermore, MHB inhibited total and mitochondrial creatine kinase activities, which was prevented by the use of the nitric-oxide synthase inhibitor L-NAME and glutathione (GSH). These data indicate that the effect of MHB on creatine kinase was probably mediated by oxidation or other modification of essential thiol groups of the enzyme by nitric oxide and other by-products derived from this organic acid. In contrast, MAA did not affect creatine kinase activity. Taken together, these observations indicate that aerobic energy metabolism is inhibited by MAA and to a greater extent by MHB, a fact that may be related to lactic acidaemia occurring in patients affected by MHBD and beta-ketothiolase deficiencies. If the in vitro effects detected in the present study also occur in vivo, it is tempting to speculate that they may contribute, at least in part, to the neurological dysfunction found in these disorders.

Spastic diplegia and periventricular white matter abnormalities in 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency, a defect of isoleucine metabolism: differential diagnosis with hypoxic-ischemic brain diseases

A 19-month-old boy with 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiency, a defect of isoleucine degradation, had cognitive and motor development delay, spastic diplegia, dysmorphism, and occipital periventricular white matter lesions on MRI scan of the brain. The urinary accumulation of the isoleucine metabolites 2-methyl-3-hydroxybutyrate and tiglylglycine was only moderate under basal conditions. These abnormalities became more pronounced after a 100mg/kg oral isoleucine challenge. Enzyme studies showed a markedly decreased activity of MHBD in fibroblasts and lymphocytes. Sequence analysis of the involved X-chromosome gene (HADH2), revealed the presence of 364C -->G mutation in the patient. His mother was heterozygous for the 364C-->G mutation, whereas the mutation was not found in the other members of the family (father, brother, and sister). This report indicates that an enzyme defect in the metabolism of branched-chain fatty acid oxidation and isoleucine may present features resembling sequelae of neonatal hypoxic-ischemic brain injury. All patients with MHBD deficiency identified so far are characterized by a neurologic phenotype rather than ketoacidotic attacks, unlike patients with the related isoleucine defect beta-ketothiolase deficiency.

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency: impaired catabolism of isoleucine presenting as neurodegenerative disease

We describe a further case of recently reported 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiency, a disorder of isoleucine metabolism. The development of pronounced brain atrophy and symmetrical alterations of the basal ganglia were observed and the importance of specific enzymatic tests is emphasized, which should be performed if urinary metabolites suggest impaired catabolism of isoleucine.

Expanded substrate screenings of human and Drosophila type 10 17beta-hydroxysteroid dehydrogenases (HSDs) reveal multiple specificities in bile acid and steroid hormone metabolism: characterization of multifunctional 3alpha/7alpha/7beta/17beta/20beta/21-HSD

17beta-hydroxysteroid dehydrogenases (17beta-HSDs) catalyse the conversion of 17beta-OH (-hydroxy)/17-oxo groups of steroids, and are essential in mammalian hormone physiology. At present, eleven 17beta-HSD isoforms have been defined in mammals, with different tissue-expression and substrate-conversion patterns. We analysed 17beta-HSD type 10 (17beta-HSD10) from humans and Drosophila, the latter known to be essential in development. In addition to the known hydroxyacyl-CoA dehydrogenase, and 3alpha-OH and 17beta-OH activities with sex steroids, we here demonstrate novel activities of 17beta-HSD10. Both species variants oxidize the 20beta-OH and 21-OH groups in C21 steroids, and act as 7beta-OH dehydrogenases of ursodeoxycholic or isoursodeoxycholic acid (also known as 7beta-hydroxylithocholic acid or 7beta-hydroxyisolithocholic acid respectively). Additionally, the human orthologue oxidizes the 7alpha-OH of chenodeoxycholic acid (5beta-cholanic acid, 3alpha,7alpha-diol) and cholic acid (5beta-cholanic acid). These novel substrate specificities are explained by homology models based on the orthologous rat crystal structure, showing a wide hydrophobic cleft, capable of accommodating steroids in different orientations. These properties suggest that the human enzyme is involved in glucocorticoid and gestagen catabolism, and participates in bile acid isomerization. Confocal microscopy and electron microscopy studies reveal that the human form is localized to mitochondria, whereas Drosophila 17beta-HSD10 shows a cytosolic localization pattern, possibly due to an N-terminal sequence difference that in human 17beta-HSD10 constitutes a mitochondrial targeting signal, extending into the Rossmann-fold motif.

Oxidative 3alpha-hydroxysteroid dehydrogenase activity of human type 10 17beta-hydroxysteroid dehydrogenase

In vitro enzyme assays have demonstrated that human type 10 17beta-hydroxysteroid dehydrogenase (17beta-HSD10) catalyzes the oxidation of 5alpha-androstane-3alpha,17beta-diol (adiol), an almost inactive androgen, to dihydrotestosterone (DHT) rather than androsterone or androstanedione. To further investigate the role of this steroid-metabolizing enzyme in intact cells, we produced stable transfectants expressing 17beta-HSD10 or its catalytically inactive Y168F mutant in human embryonic kidney (HEK) 293 cells. It was found that DHT levels in HEK 293 cells expressing 17beta-HSD10, but not its catalytically inactive mutant, will dramatically increase if adiol is added to culture media. Moreover, certain malignant prostatic epithelial cells have more 17beta-HSD10 than normal controls, and can generate DHT, the most potent androgen, from adiol. This event might promote prostate cancer growth. Analysis of the 17beta-HSD10 sequence shows that this enzyme does not have any ER retention signal or transmembrane segments and has not originated by divergence from a retinol dehydrogenase. The data suggest that the unique mitochondrial location of this HSD [Eur. J. Biochem. 268 (2001) 4899] does not prevent it from oxidizing the 3alpha-hydroxyl group of a C19 sterol in living cells. The experimental results lead to the conclusion that mitochondrial 17beta-HSD10 plays a significant part in a non-classical androgen synthesis pathway along with microsomal retinol dehydrogenases.

Differentiation-dependent expression of 17beta-hydroxysteroid dehydrogenase, type 10, in the rodent testis: effect of aging in Leydig cells

Expression of the new 17beta-hydroxysteroid dehydrogenase (HSD), type 10 (17beta-HSD-10), formerly known as endoplasmic reticulum-associated amyloid-binding protein, has been investigated in the testes of various mammals under normal and perturbed conditions. Results show that 17beta-HSD-10 is a major product of both fetal and adult-type Leydig cells. In the former, protein persists until late in postnatal development; and in the short-day hamster model, it does not disappear when Leydig cells involute. During puberty in the rat, immunohistochemical staining for 17beta-HSD-10 in adult-type Leydig cells first becomes evident on d 20, increasing to maximal staining intensity by d 35. In the rat, but not in the mouse or any other species examined, there is also staining in late spermatids. Examination of testes from rats subjected to perinatal treatment with either a GnRH antagonist or low and high doses of diethylstilbestrol revealed that expression of 17beta-HSD-10 follows closely Leydig cell differentiation status, correlating with 3beta-HSD expression in a previous study. In aging (23 months) rat testes, Leydig cell (but not germ cell) immunostaining for 17beta-HSD-10 is markedly reduced. 17beta-HSD-10 seems to preferentially convert 3alpha-androstanediol into dihydrotestosterone, and estradiol to estrone. Thus, perinatal expression of this enzyme in fetal Leydig cells may contribute to protecting these cells from estrogens and encourage androgen formation.

3-Hydroxy-2-methylbutyryl-CoA dehydrogenase deficiency

A boy now 8 years old presented at 21 months of age with developmental arrest, followed by regression, cortical blindness and myoclonic seizures. Urine organic acid analysis revealed 3-hydroxy-2-methylbutyric acid and tiglyglycine; 3-ketothiolase enzyme activity was normal and he was subsequently found to have 3-hydroxy-2-methylbutyryl-CoA dehydrogenase deficiency.

2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency in a 23-year-old man

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase (EC 1.1.1.178) deficiency is a recently described defect of isoleucine catabolism. The disorder is characterized by normal early development followed by a progressive loss of mental and motor skills. Deterioration may be rapid or may follow a slower decline with a possible stabilization of the disorder on a low-protein diet and appropriate medication. We report a 23-year-old man with 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency with a very mild clinical course. He had apparently normal early development and remained relatively well until the age of 6 years, when he contracted measles. Following this illness, his motor skills and school progress deteriorated. At 15 years he had significant dysarthria, and generalized rigidity with some dystonic and unusual posturing. He was then treated with a low-protein high-carbohydrate diet with a good response in terms of balance and gait. At 18 years he was given benzhexol (Artane), increased slowly from 2 mg to 6 mg daily, resulting in improvement in tremor and dystonia. At 23 years he can dress himself and works in sheltered employment but remains severely dysarthric.

Clinical variability in 3-hydroxy-2-methylbutyryl-CoA dehydrogenase deficiency

We report the identification of two new 7-year-old patients with 3-hydroxy-2-methylbutyryl-CoA dehydrogenase deficiency, a recently described inborn error of isoleucine metabolism. The defect is localized one step above 3-ketothiolase, resulting in a urinary metabolite pattern similar to that seen for deficiency of the latter. One patient has progressive neurodegenerative symptoms, whereas the clinical phenotype of the other patient is characterized by psychomotor retardation without loss of developmental milestones. A short-term biochemical response to an isoleucine-restricted diet was observed in both children.

Abundant type 10 17 beta-hydroxysteroid dehydrogenase in the hippocampus of mouse Alzheimer's disease model

A full-length cDNA of mouse type 10 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD10) was cloned from brain, representing the accurate nucleotide sequence information that rendered possible an accurate deduction of the amino acid sequence of the wild-type enzyme. A comparison of sequences and three-dimensional models of this enzyme revealed that structures previously reported by other groups carry either a truncated or mutated amino-terminal sequence. Fusion of the first 11 residues of the wild-type enzyme to the green fluorescent protein directed the reporter protein into mitochondria. Thus, the N-terminus was identified as a mitochondrial targeting signal that accounts for the intracellular localization of the mouse enzyme. This enzyme is normally associated with mitochondria, not with the endoplasmic reticulum as suggested by its trivial name 'endoplasmic reticulum-associated amyloid-beta biding protein (ERAB)'. After its C-terminal region was used to raise rabbit anti-17 betaHSD10 antibodies, immunogold electron microscopy showed that an abundance of this enzyme could be found in hippocampal synaptic mitochondria of betaAPP transgenic mice, but not in normal controls. High levels of this enzyme may disrupt steroid hormone homeostasis in synapses and contribute to synapse loss in the hippocampus of the mouse Alzheimer's disease model.

[Diagnostic approach and treatment of inherited mitochondrial fatty acid oxidation disorders]

Inherited mitochondrial fatty acid oxidation disorders are a complex set of genetically-based diseases in which up to 22 different entities are currently recognized. Their incidence is probably underestimated because a high level of diagnostic suspicion is required for their detection. Their clinical spectrum and prognosis are variable. In recent years knowledge of these diseases and improved treatment have reduced associated mortality. A common characteristic of all these diseases is hypoketotic hypoglycemia, although this is not constant and does not appear in the short-chain disorders and, sometimes, does not even appear in the medium-chain disorders. Cardiac or skeletal myopathy combined and/or hepatic involvement at periods of metabolic decompensation are typical, since these tissues depend on fatty acid oxidation. Diagnosis has been simplified by the study of acylcarnitines in blood, even in periods of metabolic stability. Determination of acylglycines, organic acids, carnitines, free fatty acids and 3-hydroxy-fatty acids, together with enzymic and genetic studies, complete the diagnosis. In certain circumstances, a provocation test should be carried out. Treatment basically consists of avoiding fasting, restricting fatty acid uptake and increasing carbohydrate uptake, depending on the type of metabolic disorder. Pharmacological treatment may also be added (carnitine, riboflavine or carbamylglutamate).

beta-Amyloid and its binding protein in the hippocampus of diabetic mice: effect of APP17 peptide

The objective of this study was to investigate whether changes in Abeta and ERAB exist in the brain of diabetic mice, and to observe the effects of APP17 peptide. The numbers of neurons stained by APP17 peptide Abeta1-40 Abeta1-42 Abeta1-16 and ERAB antibodies in the brain of diabetic mice was increased compared with normal mice. Staining in APP17 peptide-protected mice was similar to normal mice. We conclude that increased Abeta1-42 and ERAB is an important cause of neuronal degeneration in diabetic encephalopathy. APP17 peptide retards neuronal degeneration by regulating the metabolism of Abeta.

Identification of amyloid-beta binding sites using an antisense peptide approach

The amyloid-beta (A beta) peptide is a cytotoxic peptide implicated in the pathology of Alzheimer's disease (AD). Catalase and the endoplasmic reticulum A beta binding dehydrogenase (ERAB) are both inhibited by characterized fragments of the A beta peptide. In order to target such proteins it is essential to determine which components of these enzymes interact with A beta. This study reports the use of antisense peptide methodology to identify specific A beta-binding domains. Synthetic peptides corresponding to the regions of catalase and ERAB identified showed specific binding to A beta and also prevented A beta cytotoxicity. Antisense peptide methodology has identified A beta recognition sequences and may also be applied to the identification of novel A beta protein interactions to identify targets for use in the treatment of AD.

[Analysis of the polymorphisms of the AACT, ERAB and NACP genes in 15 patients with Alzheimer's disease]

OBJECTIVE

To analyze the polymorphisms of the AACT, ERAB and NACP genes in Han Chinese Alzheimer's disease (AD) patients.

METHODS

Denaturant gradient gel electrophoresis (DGGE) was used to scan all DNA fragments of 3 genes mentioned above in AD group (15 cases) and elderly control group (241 cases).

RESULTS

A25G and G39A substitutions were found in the AACT gene. The gene frequency of A25G was 80% in the AD group and 47% in the control group (P < 0.05). The gene frequency of G39A genotype was 13% in the AD group and 0.4% in the control group (P < 0.01). The allele (39) frequencies were also significantly different between the two groups (P < 0.01). We did not find any points with polymorphism in the ERAB and NACP genes.

CONCLUSION

A25G and G39A substitutions in the AACT gene are probably one of the risk factors to AD in Han Chinese.

Progressive infantile neurodegeneration caused by 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency: a novel inborn error of branched-chain fatty acid and isoleucine metabolism

We report a novel inborn error of metabolism identified in a child with an unusual neurodegenerative disease. The male patient was born at term and recovered well from a postnatal episode of metabolic decompensation and lactic acidosis. Psychomotor development in the first year of life was only moderately delayed. After 14 mo of age, there was progressive loss of mental and motor skills; at 2 years of age, he was severely retarded with marked restlessness, choreoathetoid movements, absence of directed hand movements, marked hypotonia and little reaction to external stimuli. Notable laboratory findings included marked elevations of urinary 2-methyl-3-hydroxybutyrate and tiglylglycine without elevation of 2-methylacetoacetate, mild elevations of lactate in CSF and blood, and a slightly abnormal acylcarnitine profile. These abnormalities became more apparent after isoleucine challenge. Enzyme studies showed absent activity of 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) in the mitochondrial oxidation of 2-methyl branched-chain fatty acids and isoleucine. Under dietary isoleucine restriction, neurologic symptoms stabilized over the next 7 months.

Lack of quinone reductase activity suggests that amyloid-beta peptide/ERAB induced lipid peroxidation is not directly related to production of reactive oxygen species by redoxcycling

Mitochondrial type II hydroxyacyl-CoA dehydrogenase (ERAB) has recently been shown to mediate amyloid-beta peptide (Abeta) induced apoptosis and neurodegeneration. The precise mechanism of cell death induction is unknown, however, Abeta inhibits ERAB activities and as a result of ERAB-Abeta interactions, enhanced formation of lipid peroxidation products occur. The possibility that ERAB mediates quinone reduction is therefore investigated, thus giving the potential of redoxcycling and production of reactive oxygen species, leading to lipid peroxidation. Recombinant human ERAB was produced in a bacterial expression system and enzymological properties were evaluated. Using several orthoquinones as substrates, no ERAB mediated quinone reductase activity was found either in the presence or absence of Abeta, suggesting that the observed in vivo lipid peroxidation is a result of other mechanisms than redoxcycling by quinones.

The gene for the Alzheimer-associated beta-amyloid-binding protein (ERAB) is differentially expressed in the testicular Leydig cells of the azoospermic by w/w(v) mouse

In order to discover possible new testicular paracrine factors involved in the establishment of spermatogenesis, a modified differential display reverse transcription, polymerase chain reaction (DDRT-PCR) procedure was used to detect gene transcripts preferentially expressed in the testes of the azoospermic w/w(v) mutant mouse. One of the differentially expressed gene products showed partial similarity to members of the short-chain alcohol dehydrogenase family of enzymes. This cDNA fragment was used to obtain the full-length mouse cDNA sequence, which initially showed moderate similarity to a 20beta-steroid dehydrogenase from lower organisms, and later shown to have >85% similarity to a novel endoplasmic-reticulum-associated-binding protein (ERAB) from the human brain, implicated in Alzheimer's disease. A recently cloned bovine sequence also of high similarity suggests that this molecule might also represent an isozyme of 3-hydroxyacyl-CoA dehydrogenase. Using the mouse cDNA as probe, northern hybridization showed enrichment of the transcript to the testicular Leydig cells, and showed a specific approximately 20-fold enrichment in the azoospermic mouse testis. The level of the testicular ERAB transcript does not seem to change through puberty, suggesting that a lack of germ cells alone is not responsible for the up-regulation in the w/w(v) testis. Using the three-dimensional coordinates of the published 20beta-hydroxysteroid dehydrogenase structure as template, it was additionally possible to construct a molecular model of the novel protein which showed it to have a very similar structure to this enzyme, including the substrate-binding domain.

ERAB contains a putative noncleavable signal peptide

The 42-residue amyloid beta protein (Abeta42) has been shown to be toxic to neurons and is believed to play a key causative role in Alzheimer's disease (AD). A search for Abeta binding proteins that can mediate its toxicity resulted in the identification of the endoplasmic-reticulum (ER) associated Abeta binding protein (ERAB) which was also shown to be involved in Abeta induced apoptosis. The primary report indicated that a signal sequence is absent in ERAB suggesting that it is bound to the cytoplasmic aspect of cellular membranes. Abeta is generated in the lumen of secretory organelles and released into the medium resulting in its separation from ERAB by a membrane barrier. After computer analysis of the ERAB sequence, we have detected a putative signal peptide that can direct the protein into the secretory pathway. This signal sequence was found in human, rodent, and bovine ERAB suggesting that it is a type II integral membrane protein in vertebrates. This topology can explain the binding of Abeta to ERAB. Our finding that an integral membrane form of ERAB can bind to Abeta in the lumen of transport vesicles and other cytoplasmic receptors provides a basis for understanding its role in AD.

scully, an essential gene of Drosophila, is homologous to mammalian mitochondrial type II L-3-hydroxyacyl-CoA dehydrogenase/amyloid-beta peptide-binding protein

The characterization of scully, an essential gene of Drosophila with phenocritical phases at embryonic and pupal stages, shows its extensive homology with vertebrate type II L-3-hydroxyacyl-CoA dehydrogenase/ERAB. Genomic rescue demonstrates that four different lethal mutations are scu alleles, the molecular nature of which has been established. One of them, scu3127, generates a nonfunctional truncated product. scu4058 also produces a truncated protein, but it contains most of the known functional domains of the enzyme. The other two mutations, scu174 and scuS152, correspond to single amino acid changes. The expression of scully mRNA is general to many tissues including the CNS; however, it is highest in both embryonic gonadal primordia and mature ovaries and testes. Consistent with this pattern, the phenotypic analysis suggests a role for scully in germ line formation: mutant testis are reduced in size and devoid of maturing sperm, and mutant ovarioles are not able to produce viable eggs. Ultrastructural analysis of mutant spermatocytes reveals the presence of cytoplasmic lipid inclusions and scarce mitochondria. In addition, mutant photoreceptors contain morphologically aberrant mitochondria and large multilayered accumulations of membranous material. Some of these phenotypes are very similar to those present in human pathologies caused by beta-oxidation disorders.

An intracellular protein that binds amyloid-beta peptide and mediates neurotoxicity in Alzheimer's disease

Amyloid-beta is a neurotoxic peptide which is implicated in the pathogenesis of Alzheimer's disease. It binds an intracellular polypeptide known as ERAB, thought to be a hydroxysteroid dehydrogenase enzyme, which is expressed in normal tissues, but is overexpressed in neurons affected in Alzheimer's disease. ERAB immunoprecipitates with amyloid-beta, and when cell cultures are exposed to amyloid-beta, ERAB inside the cell is rapidly redistributed to the plasma membrane. The toxic effect of amyloid-beta on these cells is prevented by blocking ERAB and is enhanced by overexpression of ERAB. By interacting with intracellular amyloid-beta, ERAB may therefore contribute to the neuronal dysfunction associated with Alzheimer's disease.

The human peroxisomal multifunctional protein involved in bile acid synthesis: activity measurement, deficiency in Zellweger syndrome and chromosome mapping

The dehydrogenation of 24R,25R-varanoyl-CoA, the physiological intermediate formed during the peroxisomal breakdown of the bile acid intermediate trihydroxycoprostanic acid, was studied in human liver. The reaction appeared to be catalyzed by two different enzymes. A first one, present in the cytosol, did not discriminate between the four possible varanoyl-CoA isomers and did not require the CoA moiety. The second enzymic activity was associated with peroxisomes and acted only on the 24R,25R-isomer, in which the 24-hydroxy group possesses the D-configuration. The D-specific dehydrogenase is part of a 79 kDa protein which represents the human counterpart of a recently discovered second multifunctional protein in rat liver peroxisomes, named multifunctional protein 2 (MFP-2). Human MFP-2, like its rat counterpart, is also responsible for the formation (by hydratation) of 24R,25R-varanoyl-CoA. A deficiency of MFP-2 in Zellweger liver could be demonstrated immunologically by using antibodies against the rat enzyme and enzymically -- after removal of the cytosol -- by using 24R,25R-varanoyl-CoA. The gene coding for MFP-2 was mapped to chromosome 5q2.3.

Changes in skeletal muscle morphology and biochemistry after cardiac transplantation

Skeletal muscle biopsies (vastus lateralis) were performed in 12 patients (mean age 47 +/- 11 years) before and at 3 and 12 months after cardiac transplantation. Fiber type analysis revealed a predominance of type II fibers before cardiac transplantation (66 +/- 10%); the ratio did not change after transplantation. Fiber cross-sectional area increased by 35% to 39% in all fiber types by 12 months after cardiac transplantation. Fiber cross-sectional area, however, remained below the reported normal values. The number of capillaries surrounding each fiber did not change after cardiac transplantation. Skeletal muscle enzyme activity of phosphofructokinase, citrate synthase, and beta-hydroxyacyl coenzyme A dehydrogenase increased by 26%, 47%, and 63%, respectively, after cardiac transplantation (p < 0.05). Peak oxygen uptake also increased significantly after cardiac transplantation (19.5 +/- 8.1 ml/kg/min at 12 months vs 9.8 +/- 1.4 ml/kg/min before transplant, p < 0.01); however, uptake remained 40% below that of predicted. Thus, significant improvement in skeletal muscle morphology and biochemistry occurs in the first year after cardiac transplantation in association with improved exercise capacity. Recovery, however, may be incomplete, which could explain residual impairment of exercise capacity in these patients.

NATURE OF BUTYRATE OXIDATION BY MYCOPLASMA HOMINIS

VanDemark, P. J. (Cornell University, Ithaca, N.Y.), and P. F. Smith. Nature of butyrate oxidation by Mycoplasma hominis. J. Bacteriol. 89:373-377. 1965.-Cell-free extracts of butyrate - grown Mycoplasma hominis strain O7, though lacking thiokinase activity on butyric acid, were found to activate butyrate via an acetyl-butyric thiophorase. These extracts also contained an aceto-coenzyme A (CoA) kinase, a butyryl-CoA dehydrogenase, a crotonase, a reduced nicotinamide adenine dinucleotide-specific beta-hydroxybutyryl-CoA dehydrogenase, and a thiolase. Thiolase activity was stimulated by the addition of magnesium ions. The presence of these enzyme activities in this Mycoplasma species supports the hypothesis that a fatty acid oxidation represents an energy source for the nonfermentative pleuropneumonia-like organisms.

Changing stereochemistry for a metabolic pathway in vivo. Experiments with the peroxisomal beta-oxidation in yeast

The biosphere is inherently built of chiral molecules, and once their metabolism is established, the stereochemical course of the reactions involved is seen to remain highly conserved. However, by replacing the yeast peroxisomal multifunctional enzyme (MFE), which catalyzes the second and third reactions of beta-oxidation of fatty acids via D-3-hydroxyacyl-CoA intermediates, with rat peroxisomal MFE, which catalyzes the same reactions via L-3-hydroxy intermediates, it was possible to change the chiralities of the intermediates in a major metabolic pathway in vivo. Both stereochemical alternatives allowed the yeast cells to grow on oleic acid, implying that when the beta-oxidation pathways evolved, the overall function was the determining factor for the acquisition of MFEs and not the stereospecificities of the reactions themselves.

Fatty acid beta-oxidation in glyoxysomes. Characterization of a new tetrafunctional protein (MFP III)

We describe a new form of a multifunctional protein possessing the enzyme activities of delta 3, delta 2-enoyl-CoA isomerase, 3-hydroxyacyl-CoA epimerase, L-3-hydroxyacyl-CoA dehydrogenase and L-3-hydroxyacyl-CoA forming 2-trans-enoyl-CoA hydratase. This isoform, characterized by a molecular mass of 81 kDa and an isoelectric point above pH 9, was designated MFP III. Along with the tetrafunctional 76.5 kDa MFP II and the trifunctional 74 kDa MFP I, MFP III participates in degradation of fatty acid in glyoxysomes during mobilization of fat reserves. In combination with thiolase, MFP III encompasses all activities to degrade 3-cis-enoyl-CoAs to acetyl-CoA.

Domains of the tetrafunctional protein acting in glyoxysomal fatty acid beta-oxidation. Demonstration of epimerase and isomerase activities on a peptide lacking hydratase activity

Peroxisomes from different eukaryotic organisms house a multifunctional protein acting in fatty acid beta-oxidation. In plant glyoxysomes, one of the isoforms of this protein contains the activities of L-3-hydroxyacyl-CoA hydrolyase (EC 4.2.1.17), L-3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.211), D-3-hydroxyacyl-CoA epimerase, and delta 3,delta 2-enoyl-CoA isomerase (EC 5.3.3.8). This was demonstrated after molecular cloning of a cDNA coding for a protein of 79047 Da and its bacterial expression. Chromatographic purification yielded a monomeric protein exhibiting all four activities. In addition, mutant forms were prepared, and peptides representing single domains were purified. Peptides containing the N-terminal region showed D-3-hydroxyacyl-CoA epimerase and delta 3,delta 2-enoyl-CoA isomerase activities but lacked 2-trans-enoyl-CoA hydratase and L-3-hydroxyacyl-CoA dehydrogenase activities. Using the N-terminal fragment, we demonstrated that the D-3-hydroxyacyl-CoA converting activity is actually an epimerase rather than part of a combined water eliminating and water attaching system. The C-terminal half of the multifunctional protein represents the dehydrogenase domain.

Peroxisomal multifunctional beta-oxidation protein of Saccharomyces cerevisiae. Molecular analysis of the fox2 gene and gene product

The gene encoding the multifunctional protein (MFP) of peroxisomal beta-oxidation in Saccharomyces cerevisiae was isolated from a genomic library via functional complementation of a fox2 mutant strain. The open reading frame consists of 2700 base pairs encoding a protein of 900 amino acids. The predicted molecular weight (98,759) is in close agreement with that of the isolated polypeptide (96,000). Analysis of the deduced amino acid sequence revealed similarity to the MFPs of two other fungi but not to that of rat peroxisomes or the multifunctional subunit of the Escherichia coli beta-oxidation complex. The FOX2 gene was overexpressed from a multicopy vector (YEp352) in S. cerevisiae and the gene product purified to apparent homogeneity. A truncated version of MFP lacking 271 carboxyl-terminal amino acids was also overexpressed and purified. Experiments to study the enzymatic properties of the wild-type MFP demonstrated an absence of activities originally assigned to an MFP of S. cerevisiae (crotonase, L-3-hydroxyacyl-CoA dehydrogenase, and 3-hydroxyacyl-CoA epimerase), whereas two other activities were found: 2-enoyl-CoA hydratase 2 (converting trans-2-enoyl-CoA to D-3-hydroxyacyl-CoA) and D-3-hydroxyacyl CoA dehydrogenase (converting D-3-hydroxyacyl-CoA to 3-ketoacyl-CoA). The truncated form contained only the D-3-hydroxyacyl-CoA dehydrogenase activity. These results clearly demonstrate that the beta-oxidation of fatty acids in S. cerevisiae follows a previously unknown stereochemical course, namely it occurs via a D-3-hydroxyacyl-CoA intermediate.

Enzymatic assay for 3-hydroxyacyl-CoA and 2-trans-enoyl-CoA intermediates of beta-oxidation

An enzymatic assay is presented for determining 3-hydroxyacyl-CoA and 2-trans-enoyl-CoA esters in tissue samples. The procedure includes extraction of acyl-CoA esters from frozen tissue samples with chloroform/methanol, stochiometric oxidation of the acyl esters to 3-keto-acyl-CoAs with 3-hydroxyacyl-CoA dehydrogenase in the presence or absence of enoyl-CoA hydratase, and an enzymatic cycling amplification of NADH produced for fluorometric determination. The procedure allows measurement of these intermediates of beta-oxidation at the picomole level. The method has been used successfully to measure the concentrations of 3-hydroxyacyl-CoA and 2-trans-enoyl-CoA esters in isolated rat hearts perfused with glucose or oleate or under anoxia.

Structure of L-3-hydroxyacyl-coenzyme A dehydrogenase: preliminary chain tracing at 2.8-A resolution

The conformation of L-3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35) has been derived from electron-density maps calculated at 2.8-A resolution with phases obtained from two heavy-atom derivatives and the bound coenzyme, NAD. Like other dehydrogenases, 3-hydroxyacyl-CoA dehydrogenase is a double-domain structure, but the bilobal nature of this enzyme is more pronounced than has been previously observed. The amino-terminal domain, which comprises approximately the first 200 residues, is responsible for binding the NAD cofactor and displays considerable structural homology with the dinucleotide binding domains observed in other NAD-, NADP-, and FAD-dependent enzymes. The carboxyl-terminal domain, comprising the remaining 107 residues, appears to be all alpha-helical and bears little homology to other known dehydrogenases. The subunit-subunit interface in the 3-hydroxyacyl-CoA dehydrogenase dimer is formed almost exclusively by residues in the smaller helical domain. A difference map between the apo and holo forms of the crystalline enzyme has been interpreted in terms of the NAD molecule being bound in a typically extended conformation. The location of the coenzyme binding site, along with the structural homology to other dehydrogenases, makes it possible to speculate about the location of the binding site for the fatty acyl-CoA substrate.

The metabolic transformations of columbinic acid and the effect of topical application of the major metabolites on rat skin

The metabolism of columbinic acid by various fatty acid oxidizing enzyme systems was studied. A cyclooxygenase product, 9-hydroxy-(5E,10E,12Z)-octadecatrienoic acid, was formed nearly quantitatively by ram seminal vesicle microsomes and in small amounts by washed human platelets. The major lipoxygenase product from washed human platelets, soybean lipoxygenase, and neonatal rat epidermal homogenate was 13-hydroxy-(5E,9Z,11E)-octadecatrienoic acid, although lesser quantities of other isomers differing in the double bond configurations were also identified by ultraviolet spectrophotometry and gas chromatography-mass spectroscopy. Topical application of the major lipoxygenase product to paws of essential fatty acid-deficient rats resulted in nearly as complete resolution of the scaly dermatitis as did the application of columbinic acid itself; the cyclooxygenase product was not at all effective.

Evidence for a negative modulating effect of erucic acid on the peroxisomal beta-oxidation enzyme system and biogenesis in rat liver

In male rats fed a 30 cal% high-erucic acid (22:1 (13) (cis] rapeseed oil diet for 4 weeks a transient, small increase in peroxisomal beta-oxidation was observed in liver homogenates and isolated peroxisomes after approximately 1 week. Morphometric analysis revealed a progressive decrease in the average size of the liver peroxisomes (by approx. 20%), as well as their volume fraction (by more than 40%). A negative dose-response was observed when peroxisomal beta-oxidation was determined in animals fed rapeseed oil diets with a variable content of erucic acid. When erucic acid was given as subcutaneous injections the peroxisomal beta-oxidation decreased, in both liver homogenates and isolated peroxisomes. In contrast to recent proposals, our findings indicate that the amount of erucic acid cannot account for the small increase in peroxisomal beta-oxidation observed in the liver of rats adapted to a diet containing 30 cal% rapeseed oil with a high content of this fatty acid. In fact, by the selected criteria erucic acid seems to have a negative modulating effect on both the peroxisomal beta-oxidation enzyme system and biogenesis.

Effects of marine oil diet on peroxisomes and mitochondria of rat liver. A combined biochemical and morphometric study

Feeding male rats a high cal% partially hydrogenated marine oil diet induced a response in the parenchymal liver cells at the cellular as well as the subcellular level. An adaptation in the lipid metabolism is indicated by an accumulation of triglycerides and a hypertrophy of the liver cells, and a rather selective increase (4.9-fold) in the specific activity of peroxisomal beta-oxidation. In addition, a slight proliferation of peroxisomes was observed; the volume fraction and the total number of peroxisomes increased 1.5-fold. The peroxisomes, however, preserved the biochemical and morphological homogeneity characteristic of peroxisomes in normal controls. At the mitochondrial level, a gradual development of megamitochondria was observed as the principal morphological change, with a 1.6-fold increase in the average size. The functional significance of this change remains to be determined. The effects of a partially hydrogenated marine oil diet on parenchymal liver cells appears to be manifestations with multiple causal factors. The high content of very long-chain trans fatty acids is of particular significance for the peroxisomal changes. An essential fatty acid deficiency, enforced by the presence of trans fatty acids in the diet, is most likely the determining factor for the development of megamitochondria.

Polydispersity of rat liver peroxisomes induced by the hypolipidemic and carcinogenic agent clofibrate

1. The present study has confirmed that the hypolipidemic and carcinogenic agent clofibrate induces a marked increase in the specific activity of some peroxisomal marker enzymes in rat liver homogenates, notably of the palmitoyl-CoA dependent dehydrogenase and catalase activities. 2. Clofibrate was found to induce a marked polydispersity of the peroxisomes as determined by analytical differential centrifugation of homogenates and morphometric analysis of hepatocytes. 3. Two major populations of peroxisomes were detected by analytical differential centrifugation under conditions which reduce the hydrostatic pressure effects on the organelle to a minimum. Using urate oxidase as the marker enzyme, the S4,B-values of the two populations were estimated to 1 1 860 S and 4240 S, both different from that of the homogenous population of peroxisomes in the control animals (S4,B approximately equal to 6680 S). The 4240 S-population induced by clofibrate revealed a high specific activity relative to that of of urate oxidase and particularly relative to that of catalase, which was very low. In addition, a less distinct population of particles (870 S lees than S lees than 4240 S) contained more than 50% of the total particle-bound palmitoyl-CoA dependent dehydrogenase activity sedimented at a centrifugal effect of t integral of 0 rmp(2)dt = 1.5 x 10(10) min(-1), but not urate oxidase and catalase activities. This fraction was not observed in the homogenates of normal rats. As in the normal controls, the palmitoyl-CoA dependent dehydrogenase activity was found to be particle-bound (S greater than 870 S). 4. Morphometric analyses of randomly selected hepatocytes revealed that after clofibrate treatment the relative volume fraction of the peroxisomes increased by a factor of 5.5 and thier average diameter and volume by a factor of 1.3 and 2.1, respectively. Furthermore, the frequency of electron-dense matrix cores decreased on clofibrate treatment. In contrast, no change was observed in the average size of the mitochondria, and their relative volume fraction increased only by a factor of 1.2. 5. The clofibrate induced changes in eh morphological and biochemical properties of rat liver peroxisomes appears to be a very useful model system in which to study the biogenesis as well as the biochemical and physiological role(s) of this organelle in mammalian cells.