Atenolol offers better protection than clonidine against cardiac injury in kainic acid-induced status epilepticus

BACKGROUND AND PURPOSE

Status epilepticus is increasingly associated with cardiac injury in both clinical and animal studies. The current study examined ECG activity for up to 48 h following kainic acid (KA) seizure induction and compared the potential of atenolol and clonidine to attenuate this cardiac pathology.

EXPERIMENTAL APPROACH

Sprague-Dawley rats (male, 300-350 g) were implanted with ECG and electrocorticogram electrodes to allow simultaneous telemetric recordings of cardiac and cortical responses during and after KA-induced seizures. Animals were randomized into saline controls, and saline vehicle-, clonidine- or atenolol-pretreated KA groups.

KEY RESULTS

KA administration in the saline-pretreated group produced an immediate bradycardic response (maximal decrease of 28 ± 6%), coinciding with low-level seizure activity. As high-level seizure behaviours and EEG spiking increased, tachycardia also developed, with a maximum heart rate increase of 38 ± 7% coinciding with QTc prolongation and T wave elevation. Both clonidine and atenolol pretreatment attenuated seizure activity and reduced KA-induced changes in heart rate, QTc interval and T wave amplitude observed during both bradycardic and tachycardic phases in saline-pretreated KA animals. Clonidine, however, failed to reduce the power of EEG frequencies. Atenolol and to a lesser extent clonidine attenuated the cardiac hypercontraction band necrosis, inflammatory infiltration, and oedema at 48 h after KA, relative to the saline-KA group.

CONCLUSIONS AND IMPLICATIONS

Severe seizure activity in this model was clearly associated with altered ECG activity and cardiac pathology. We suggest that modulation of sympathetic activity by atenolol provides a promising cardioprotective approach in status epilepticus.

Leukocyte telomere length in patients with schizophrenia: A meta-analysis

Schizophrenia has been suggested as a syndrome of accelerated aging. Telomere length (TL) decrease is considered one biological marker associated with age and can be accelerated by pathological characteristics present in schizophrenia. Several studies evaluated TL in schizophrenia, but the results are still controversial. The aim of this study was to conduct a meta-analysis of the existing results of TL in leukocytes of individuals with schizophrenia compared to healthy controls. A search was performed in PubMed, using the keywords 'telomere schizophrenia' and 'telomere psychosis'. We included data from original articles that measured TL in leukocytes of human patients with schizophrenia and healthy control subjects. 45 articles were found, but only 7 met our criteria. Telomere length of controls was not statistically different from that of patients with schizophrenia (p=0.07). Crossvalidation with the leave-one-out method resulted in a significant model (p=0.03) in which TL of individuals with schizophrenia is smaller than control (SMD=0.38; 95% CI=[0.05, 0.72]). We also propose a biological pathway through which schizophrenia could promote telomere erosion and how antipsychotics might compensate this loss. There are few studies made on this subject with diverse methodology and heterogeneous sample. Some articles did not consider other possible influences on TL. Overall our results suggest that TL is decreased in schizophrenia. Although this is consistent with the idea of accelerated aging, schizophrenia is a complex disease and there are several factors that influence TL that should be controlled in future studies.

Low-dose GYKI-52466: prophylactic preconditioning confers long-term neuroprotection and functional recovery following hypoxic-ischaemic brain injury

Experimental preconditioning provides beneficial outcomes in conditions such as cardiac surgery, brain surgery and stroke. Here we evaluated the protective effects of low-dose subcutaneous GYKI-52466 preconditioning in a rat model of hypoxic-ischaemic (HI) brain injury. Male Sprague-Dawley rats (postnatal day 26) were administered saline or GYKI-52466 (GYKI; 3-mg/kg, 90 min; 1-mg/kg, twice in 120 min; or 0.5-mg/kg, thrice in 180 min) prior to left common carotid artery occlusion. Animals were allowed to recover for 2h, and then placed in a hypoxia chamber (8% O₂/92% N₂; 33 ± 1°C) for 1h. A sham surgery group received saline without HI. Seizure activity was scored during hypoxia and sensorimotor tests performed before surgery and at 1, 7, 14 and 90 days post-HI. On days 14 and 90 brains were fixed and sectioned for the assessment of infarct size and ventricular enlargement. Low-dose GYKI-52466 preconditioning significantly reduced infarct volume and ventricular enlargement relative to saline-treated controls at day 14 after HI. On day 90, tissue loss was significantly reduced by GYKI 3-mg/kg compared to saline. Foot-faults, paw use asymmetry, and postural reflex scores were significantly improved in all GYKI treatment groups. Our results show that GYKI-52466 is effective at doses well-below, and at pre-administration intervals well-beyond previous studies, and suggest that a classical blockade of ionotropic AMPA receptors does not underlie its neuroprotective effects. Low-dose GYKI-52466 preconditioning represents a novel, prophylactic strategy for neuroprotection in a field almost devoid of effective pharmaceuticals.

Spectral analysis of electrocorticographic activity during pharmacological preconditioning and seizure induction by intrahippocampal domoic acid

Previously we have shown that low-dose domoic acid (DA) preconditioning produces tolerance to the behavioral effects of high-dose DA. In this study, we used electrocorticography (ECoG) to monitor subtle CNS changes during and after preconditioning. Young adult male Sprague-Dawley rats were implanted with a left cortical electrode, and acute recordings were obtained during preconditioning by contralateral intrahippocampal administration of either low-dose DA (15 pmoles) or saline, followed by a high-dose DA (100 pmoles) challenge. ECoG data were analyzed by fast Fourier transformation to obtain the percentage of baseline power spectral density (PSD) for delta to gamma frequencies (range: 1.25-100 Hz). Consistent with previous results, behavioral analysis confirmed that low-dose DA preconditioning 60 min before a high-dose DA challenge produced significant reductions in cumulative seizure scores and high level seizure behaviors. ECoG analysis revealed significant reductions in power spectral density across all frequency bands, and high-frequency/high-amplitude spiking in DA preconditioned animals, relative to saline controls. Significant correlations between seizure scores and ECoG power confirmed that behavioral analysis is a reliable marker for seizure analysis. The reduction of power in delta to gamma frequency bands in contralateral cortex does not allow a clear distinction between seizure initiation and seizure propagation, but does provide objective confirmation that pharmacological preconditioning by DA reduces network seizure activity.

In vivo seizure induction and affinity studies of domoic acid and isodomoic acids-D, -E and -F

Domoic acid and its isomers are produced via algal blooms and are found in high concentrations in shellfish. Here, we assessed the acute seizurogenic potencies of isomers-D, -E and -F and their binding affinities at heterogeneous populations of KA receptors from rat cerebrum. In addition, binding affinities of all six isomers (Iso-A through -F) were assessed at AMPA receptors. Radioligand displacement studies indicated that the seizurogenic potency of Iso-F (E-configuration) closely correlates with its affinities at both KA and AMPA receptors, whereas isomers-D (Z) and -E (E), which exhibit distinctly lower seizurogenic potencies, are quite weak displacers. Previously observed functional potencies for isomers-A, -B and -C (Sawant et al., 2008) correlated with AMPA receptor affinities observed here. Taken together, these findings call into question previous structure-activity rules. Significantly, in our hands, Iso-D was ten-fold less potent than Iso-F. To further explain observed links between structural conformation and functional potency, molecular modeling was employed. Modeling results closely matched the rank order of potency and binding data observed. We further assessed the efficacy of isomers-D, -E and -F as pharmacological preconditioning agents. Acute preconditioning with low-dose Iso-D, -E or -F, before high-dose DA failed to impart behavioural tolerance. This study has shed new light on structural conformations affecting non-NMDA ionotropic glutamate receptor binding and functional potency, and provides a foundation for future work in areas of AMPA and KA receptor modeling.

Mutations of the E1beta subunit gene (PDHB) in four families with pyruvate dehydrogenase deficiency

Pyruvate dehydrogenase complex (PDC) deficiencies are a major cause of primary lactic acidosis. Most cases result from mutations of the gene for the pyruvate dehydrogenase E1alpha subunit (PDHA1), with fewer cases resulting from mutations in genes for E3, E3-binding protein, E2, and the E1beta subunit (PDHB). We have found four cases of PDHB mutations among 83 analyzed cases of PDC deficiency. In this series, PDHB mutations were found to be about 10% as frequent as PDHA1 mutations. All cases were diagnosed by low PDC activity, with normal E2 and E3 activities. These included a 6.5-year-old male (consanguineous, homozygous R36C); a neonatal female who died soon after birth, (compound heterozygous C306R/D319V), a 26-year-old female (heterozygous I142M/W165S), and a 13month old female (consanguineous, homozygous Y132C) who is a sibling of a previously published case. Their ethnic background is diverse (Caucasian, Arab, and African American descent). All cases had lactic acidosis and developmental delay. Three cases had agenesis of the corpus callosum, seizures, and hypotonia; one died within the first year of life. These clinical findings are similar to those of PDHA1 deficiency, except that ataxia was more frequent in PDHA1 cases and consanguinity was found only in PDHB families. PDC activity in lymphocytes from six parents is normal, who all are heterozygous carriers for the respective mutations. Immunoreactivity of E1beta was markedly reduced in one case and showed a slightly larger form of E1beta in one case. Computer analysis predicts that: R36C affects the interaction of several amino acids resulting in conformational change, C306R affects interaction of the two beta subunits, D319 is in the interface of E1 and E2, I142M affects conformation around a K ion affecting stability of the beta subunit, W165S affects hydrophobic interaction between the beta subunits, and Y132C affects interaction between the beta subunits. All of these residues are conserved in E1beta across species, and Y132 is also conserved in other TPP-requiring enzymes. These observations support the conclusion that these are pathogenic mutations.

Isodomoic acids A and C exhibit low KA receptor affinity and reduced in vitro potency relative to domoic acid in region CA1 of rat hippocampus

Several natural isomers of the seizurogenic neurotoxin domoic acid (DA) have been found to occur at up to mg/kg levels in shellfish. The aim of the current study was to assess the neurotoxic potency of isodomoic acids A and C (Iso-A and Iso-C), recently isolated from commercial shellfish. Hippocampal slices were obtained from young adult rats and maintained in a tissue recording chamber. Synaptically evoked population spikes were recorded in region CA1 before and after exposure to DA or its isomers. Both Iso-A and Iso-C produced transient neuronal hyperexcitability followed by a dose-dependent suppression of population spikes, but were, respectively, 4- and 20-fold less potent than DA (spike area: EC50 DA=237 nM; Iso-A=939 nM; Iso-C=4.6 microM). In the hippocampus, DA preconditioning induces tolerance to subsequent DA toxicity. However, in the present study neither Iso-A nor Iso-C were effective as preconditioning agents. Competitive binding studies using homomeric GluR6 kainate (kainic acid, KA) receptors showed the affinity of Iso-A to be 40-fold lower than DA (Ki DA=3.35 nM; Iso-A=130 nM). Together with earlier work showing Iso-C affinity at GluR6 receptors to be 240-fold lower than DA, our results suggest that neuroexcitatory effects of Iso-A in CA1 may involve both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and KA receptors, while Iso-C likely involves the activation of AMPA receptors alone.

A novel mutation in the mitochondrial tRNA(Ser(AGY)) gene associated with mitochondrial myopathy, encephalopathy, and complex I deficiency

PURPOSE

To identify molecular defects in a girl with clinical features of MELAS (mitochondrial encephalomyopathy and lactic acidosis) and MERRF (ragged-red fibres) syndromes.

METHODS

The enzyme complex activities of the mitochondrial respiratory chain were assayed. Temporal temperature gradient gel electrophoresis was used to scan the entire mitochondrial genome for unknown mitochondrial DNA (mtDNA) alterations, which were then identified by direct DNA sequencing.

RESULTS

A novel heteroplasmic mtDNA mutation, G12207A, in the tRNA(Ser(AGY)) gene was identified in the patient who had a history of developmental delay, feeding difficulty, lesions within her basal ganglia, cerebral atrophy, proximal muscle weakness, increased blood lactate, liver dysfunction, and fatty infiltration of her muscle. Muscle biopsy revealed ragged red fibres and pleomorphic mitochondria. Study of skeletal muscle mitochondria revealed complex I deficiency associated with mitochondrial proliferation. Real time quantitative PCR analysis showed elevated mtDNA content, 2.5 times higher than normal. The tRNA(Ser(AGY)) mutation was found in heteroplasmic state (92%) in the patient's skeletal muscle. It was not present in her unaffected mother's blood or in 200 healthy controls. This mutation occurs at the first nucleotide of the 5' end of tRNA, which is involved in the formation of the stem region of the amino acid acceptor arm. Mutation at this position may affect processing of the precursor RNA, the stability and amino acid charging efficiency of the tRNA, and overall efficiency of protein translation.

CONCLUSION

This case underscores the importance of comprehensive mutational analysis of the entire mitochondrial genome when a mtDNA defect is strongly suggested.

Client-centred assessment and the identification of meaningful treatment goals for individuals with a spinal cord injury

STUDY DESIGN

Retrospective analysis.

OBJECTIVES

(1) Describe the self-care, productivity and leisure problems identified by individuals with a spinal cord injury (SCI) during rehabilitation, (2) describe the perceived level of satisfaction and performance with self-care, productivity and leisure activities following an SCI, (3) quantify the relationship between the Canadian occupational performance measure (COPM), a client-centred, individualized measure of function, and the functional independence measure (FIM).

SETTING

Tertiary rehabilitation centre, spinal cord injury unit, GF Strong Rehabilitation Centre, Vancouver, Canada.

METHODS

Health records from 41 individuals with an SCI admitted between 2000 and 2002 were reviewed. Information was obtained from assessments performed on admission and discharge. Self-care, productivity and leisure problems identified by individuals with an SCI were described and their perceived level of performance and satisfaction was calculated. The relationship between the COPM and the FIM was measured by the Pearson product correlation.

RESULTS

Self-care goals were identified most frequently (79%) followed by productivity (12%) and leisure (9%) goals. The top three problems identified by individuals with an SCI were functional mobility (including transfers and wheelchair use), dressing and grooming. A fair relationship was found between the COPM and the FIM (r between 0.351 and 0.514, P<0.05).

CONCLUSIONS

The results highlight the importance of including a client-centred outcome measure in the assessment of individuals with an SCI. Initial support is provided for use of the COPM in individuals with an SCI.

Comparison of the in vitro and in vivo neurotoxicity of three new sources of kainic acid

Historically, all commercially available kainic acid has been derived from a single biological source using a consistent method of extraction and purification. That source became unavailable in 1995. Recently, three new commercial suppliers of kainic acid have made the product available, but the source of the material and the purification processes used differ. Our objective was to systematically compare the response produced by each of these new sources of kainic acid using three established neurobiological techniques: neuronal cell culture, hippocampal slice electrophysiology, and whole animal behavioural toxicity. Results in all three systems indicated no overall differences between the three formulations, although studies in both cerebellar neuron cultures and whole animal toxicity testing in mice, revealed some significant differences that may imply subtle differences in receptor selectivity and/or potency. We conclude that all three sources of kainic acid are viable alternatives to traditional kainate but they may not be identical. Until further information becomes available researchers may want to avoid using the three formulations interchangeably, and take note of the source of kainic acid when evaluating literature describing results from other laboratories.

Autosomal dominant acute necrotizing encephalopathy

OBJECTIVE

To define the clinical and biochemical abnormalities of an autosomal dominant form of acute encephalopathy.

METHODS

The clinical details of 11 affected family members in comparison with 63 unaffected relatives were analyzed.

RESULTS

Affected children become comatose after onset of a febrile illness. Outcomes include full recovery, permanent neurologic impairment, and death. Recurrences produce more severe impairments. Lesions of necrotizing encephalopathy of the thalamus and brainstem are present on autopsy and MRI. Oxidative phosphorylation of intact mitochondria from a muscle biopsy shows loose coupling. Unaffected family members, including obligate carriers, share no clinical characteristics, demonstrating incomplete penetrance.

CONCLUSIONS

Characteristic pathology and MRI findings define this disorder of autosomal dominant acute encephalopathy. Leigh syndrome and sporadic acute necrotizing encephalopathy share similarities but are distinct.

AMPA/kainate and group-I metabotropic receptor antagonists infused into different brain areas impair memory formation of inhibitory avoidance in rats

Several lines of evidence suggest that glutamate receptors are involved in memory processing. To examine the role of non-N-methyl-D-aspartate (non-NMDA) glutamate receptors on memory consolidation, rats were bilaterally implanted with cannulae aimed at the CA1 region of the dorsal hippocampus (CA1), entorhinal cortex (ENTO), posterior parietal cortex (PPC) or the basolateral nucleus of the amygdala (BLA), and trained in a one-trial step-down inhibitory avoidance task. At different times after training, the alpha-amino 3-hydroxy-5 methyl 4-isoxazole propionate (AMPA) receptor blocker, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (1.0 microg/side), or the metabotropic type-I receptor antagonist, 2-amino-3-phosphonopropionic acid (AP3) (1.0 microg/side), were infused into the above-mentioned structures. CNQX produced retrograde amnesia when infused into BLA or CA1 0, 30, 90 or 180 min post-training but not at later times. AP3 blocked memory consolidation when administered into CA1 0, 30 or 180 min post-training, while in BLA, it was amnestic only when given 0 or 30 min after the training session. CNQX and AP3 had no effect on memory when administered into ENTO or PPC at any time. Our data suggest that the consolidation of the avoidance memory requires intact non-NMDA receptor function in the hippocampus and the basolateral nucleus of the amygdala, but not necessarily in the entorhinal and parietal cortex, for long periods after training.

Domoic acid-induced hippocampal CA1 hyperexcitability independent of region CA3 activity

Domoic acid (DOM) is a potent agonist of AMPA and kainic acid (KA) receptors in the CNS and is known to produce seizures acutely, and lasting excitotoxic damage in several brain regions. While the excitotoxic effects of DOM are well documented, its seizurogenic properties are less clear. In this study, we assessed the acute effects of DOM and KA in region CA1 of intact rat hippocampal slices (CA3-on) and in slices lacking region CA3 (CA3-off). Orthodromic Schaffer collateral-evoked CA1 field potentials (population spikes and somal EPSP's) were monitored during DOM and KA (10-500 nM) administration. In CA3-off slices both KA and DOM produced immediate increases in CA1 population spike amplitude. With prolonged exposure, lasting dose-dependent reductions in spike amplitude and EPSP slope were observed, possibly due to depolarising conduction block following excessive AMPA/KA receptor activation; DOM was several-fold more potent than KA in this regard. Population spike threshold did not vary with DOM, but in CA3-on slices a dose-dependent steepening of the I/O curve and increase in maximum spike amplitude was seen. CA1 hyperexcitability, as evidenced by the appearance of prominent second and third population spikes, was equivalently increased across a range of DOM concentrations in both CA3-on and CA3-off slices and, in general, DOM-induced CA1 hyperexcitability was not enhanced by the presence of CA3 for any of the other variables assessed in this study. These findings show that DOM directly promotes neuronal hyperactivity in region CA1, presumably due to tonic AMPA and/or KA-receptor mediated depolarization, and further suggests that DOM-induced hyperactivity in the recurrently networked, AMPA/KA-receptor rich region CA3 does not contribute to the onset and spread of limbic seizures during relatively mild DOM intoxication.

NOESY on neurotoxins: NMR and conformational assignments of picrotoxins

Nuclear Overhauser effect spectroscopy (NOESY) gave full assignments of the 1H-NMR spectra of the picrotoxane neurotoxins tutin, hyenanchin, picrotoxinin and picrotin, as well as the solution conformations of these compounds, consistent with molecular modelling. Fully assigned 13C-NMR data are reported.

Mutations in the X-linked pyruvate dehydrogenase (E1) alpha subunit gene (PDHA1) in patients with a pyruvate dehydrogenase complex deficiency

Defects in the pyruvate dehydrogenase (PDH) complex are an important cause of primary lactic acidosis, a frequent manifestation of metabolic disease in children. Clinical symptoms can vary considerably in patients with PDH complex deficiencies, and almost equal numbers of affected males and females have been identified, suggesting an autosomal recessive mode of inheritance of the disease. However, the great majority of PDH complex deficiencies result from mutations in the X-linked pyruvate dehydrogenase (E1) alpha subunit gene (PDHA1). The major factors that contribute to the clinical variation in E1alpha deficiency and its resemblance to a recessive disease are developmental lethality in some males with severe mutations and the pattern of X-inactivation in females. To date, 37 different missense/nonsense and 39 different insertion/deletion mutations have been identified in the E1alpha subunit gene of 130 patients (61 females and 69 males) from 123 unrelated families. Insertion/deletion mutations occur preferentially in exons 10 and 11, while missense/nonsense mutations are found in all exons. In males, the majority of missense/nonsense mutations are found in exons 3, 7, 8 and 11, and three recurrent mutations at codons R72, R263 and R378 account for half of these patients with missense/nonsense mutations (25 of 50). A significantly lower number of females is found with missense/nonsense mutations (25). However, 36 females out of 55 affected patients have insertion/deletion mutations. The total number of female and male patients is thus almost the same, although a difference in the distribution of the type of mutations is evident between both sexes. In many families, the parents of the affected patients were studied for the presence of the PDHA1 mutation. The mutation was never present in the somatic cells of the father; in 63 mothers studied, 16 were carriers (25%). In four families, the origin of the new mutation was determined to be twice paternal and twice maternal.

A neurophysiological method of rapid detection and analysis of marine algal toxins

We have examined the effectiveness of the in vitro rat hippocampal slice preparation as a means of rapidly and specifically detecting the marine algal toxins saxitoxin, brevetoxin, and domoic acid and have identified toxin-specific electrophysiological signatures for each. Brevetoxin (PbTX3, 50-200 nM) produced a significant reduction in orthodromic population spike amplitude which was quick to reverse during a 50 min wash-out, while antidromic population spikes and field EPSPs exhibited only slight reductions, and fibre spiof orthodrokes showed no change at all. Domoic acid (100 nM) produced a robust, reversible increase in amplitude mic spikes, and the appearance of multiple spikes (i.e., epileptiform activity) within minutes of toxin wash-in. Other notable features of the domoic acid signature included a significant decrease in amplitude of the field EPSPs, and a complete absence of effect on either antidromic or fibre spikes. Fifty nanomolar saxitoxin (PSP) abolished all responses in all slices. Only antidromic spikes showed any recovery during wash-out. Field EPSP and fiber spike analysis further demonstrated that the preparation is capable of reliably detecting saxitoxin in a linearly responsive fashion at toxin concentrations of 25-200 nM, and tests of naturally contaminated shellfish confirmed the utility of this assay as a screening method for PSP. Our findings suggest that the in vitro hippocampal slice preparation has potential in the detection and analysis of three marine algal toxins important to the shellfish industry.

High-affinity [3H] kainic acid binding to brain membranes: a re-evaluation of ligand potency and selectivity

[3H]Kainic acid ([3H]KA) is a widely used tool for studying the KA class of excitatory amino acid receptors. [3H]KA of significantly higher specific activity has become available permitting use of radioligand concentrations below the dissociation constant (K(D)) of the high-affinity binding site. We employed low radioligand (0.05-0.2 nM) and receptor concentrations (0.01 nM) to gain new insights into the binding characteristics of the high-affinity KA binding site in a standard preparation of lyzed synaptosomal membranes from the cerebral cortex of male Sprague-Dawley rats. Under these conditions, KA binds to a single class of high-affinity sites with a K(D) of 1.0+/- 0.3 nM. The potencies of competing agents are considerably higher than published reports. Specifically, domoic acid, glutamate, and glutamine exhibit IC(50) values for displacing [3H]KA of 0.37+/-0.02, 94+/-13, and 1500+/-500 nM, respectively. Domoate (1 microM) was tested against a panel of 32 central nervous system binding sites and found to be inactive at each, indicating this toxin displays considerable selectivity. This study illustrates the remarkable potency of domoic acid and underlines the importance of performing radioligand binding studies at concentrations of constituents that permit characterization of high-affinity interactions.

Characterization of the regulatory region of the human testis-specific form of the pyruvate dehydrogenase alpha-subunit (PDHA-2) gene

The alpha-subunit of human pyruvate dehydrogenase (E(1)) is encoded by two separate genes. The gene located on chromosome X (PDHA-1) is expressed in somatic tissues, whereas the second gene (PDHA-2), located on chromosome 4, is expressed only in post-meiotic spermatogenic cells. A genomic fragment harboring the human gene encoding PDHA-2 has been isolated and approximately 800 nucleotides of the promoter region have been characterized. Functional studies of the promoter indicate the presence of both enhancer and repressor elements that are common to other genes that are only expressed in mature sperm.

Molecular characterization of pyruvate carboxylase deficiency in two consanguineous families

Pyruvate carboxylase (PC) is a biotinylated mitochondrial enzyme that catalyzes the conversion of pyruvate to oxaloacetate. Children with inborn errors of PC metabolism have lactic acidosis, hypoglycemia, and mental retardation. The variable severity of the clinical phenotype is dependent on both genetic and environmental factors. Two consanguineous families with moderate forms of PC deficiency were characterized at the biochemical and molecular levels. In both families, the probands were found to have low PC activity (range, 2-25% of control) in blood lymphocytes and skin fibroblasts associated with either diminished or normal protein levels. In the first case, sequencing of patient-specific PC cDNA demonstrated a T to C substitution at nucleotide 434, which causes a valine to alanine change at amino acid residue 145. Direct sequencing of the parents showed that they are heterozygous for this mutation. In the second family, a brother and sister had mental retardation and episodes of severe lactic/ketoacidosis in early childhood. In these cases, a C to T substitution at nucleotide 1351 results in a cysteine for arginine substitution at amino acid residue 451; the parents were also found to be heterozygous for this mutation. In both families, no other mutations were found, and both substitutions occurred in relatively conserved amino acid residues. These mutations, located in the biotin carboxylase domain, provide a unique opportunity to analyze how natural occurring mutations affect PC function.

Primary hypothyroidism mimicking a pituitary macroadenoma

Pituitary macroadenomas occur infrequently in children and can present with visual dysfunction or endocrinopathy. Occasionally, primary end-organ failure can cause reactive enlargement of the pituitary gland that may be clinically and radiographically indistinguishable from pituitary macroadenoma. The authors describe an example of reactive pituitary hyperplasia from primary hypothyroidism that mimicked a pituitary macroadenoma in a child. Recognition of this entity, which responds to medical therapy, is important because it can spare patients unnecessary surgery.

Deficiency of dihydrolipoamide dehydrogenase due to two mutant alleles (E340K and G101del). Analysis of a family and prenatal testing

A male child with metabolic acidosis was diagnosed as having dihydrolipoamide dehydrogenase (E3) deficiency. E3 activity of the proband's cultured fibroblasts and blood lymphocytes was 3-9% of normal, while in the parent's lymphocytes it was about 60% of normal. The proband's pyruvate dehydrogenase complex (PDC) and the alpha-ketoglutarate dehydrogenase complex activities from cultured skin fibroblasts were 12% and 6% of normal, respectively. PDC activity in the parents cultured fibroblasts was 25-31% of normal. Western and Northern blot analyses showed similar quantities of E3 protein and mRNA in cultured fibroblasts from the proband and his parents. DNA sequencing of cloned full-length E3 cDNAs, from the proband and the parents, showed two mutations on different alleles of proband were inherited from the parents. One mutation is a three nucleotide (AGG) deletion, from the mother, resulting in deletion of Gly101 in the FAD binding domain. The other mutation is a nucleotide substitution (G to A), from the father, leading to substitution of Lys for Glu340 in the central domain. The same deletion mutation was found in E3 cDNA from a chorionic villus sample and cultured fibroblasts obtained from the mother's subsequent offspring. This finding illustrates the possibility of successful prenatal diagnosis of E3 deficiency utilizing mutations characterized prior to initiation of pregnancy.

Outcome of pyruvate dehydrogenase deficiency treated with ketogenic diets. Studies in patients with identical mutations

Inborn errors of the pyruvate dehydrogenase complex (PDC) are associated with lactic acidosis, neuroanatomic defects, developmental delay, and early death. PDC deficiency is a clinically heterogeneous disorder, with most mutations located in the coding region of the X-linked alpha subunit of the first catalytic component, pyruvate dehydrogenase (E1). Treatment of E1 deficiency hs included cofactor replacement, activation of PDC with dichloroacetate, and ketogenic diets. In this report, we describe the outcome of ketogenic diet treatment in seven boys with E1 deficiency. These patients were divided into two groups based on their mutations (R349H, three patients; and R234G, four patients, two sibling pairs). All seven patients received ketogenic diets with varying degrees of carbohydrate restriction. Clinical outcome was compared within each group and between siblings as related to the intensity and duration of dietary intervention. Subjects who either had the diet initiated earlier in life or who were placed on greater carbohydrate restriction had increased longevity and improved mental development. Based on the improved outcomes of patients with identical mutations, it appears that a nearly carbohydrate-free diet initiated shortly after birth may be useful in the treatment of E1 deficiency.

Glucocorticoid receptor activation lowers the threshold for NMDA-receptor-dependent homosynaptic long-term depression in the hippocampus through activation of voltage-dependent calcium channels

The effects of the glucocorticoid receptor agonist RU-28362 on homosynaptic long-term depression (LTD) were examined in hippocampal slices obtained from adrenal-intact adult male rats. Field excitatory postsynaptic potentials were evoked by stimulation of the Schaffer collateral/commissural pathway and recorded in stratum radiatum of area CA1. Low-frequency stimulation (LFS) was delivered at LTD threshold (2 bouts of 600 pulses, 1 Hz, at baseline stimulation intensity). LFS of the Schaffer collaterals did not produce significant homosynaptic LTD in control slices. However, identical conditioning in the presence of the glucocorticoid receptor agonist RU-28362 (10 microM) produced a robust LTD, which was blocked by the selective glucocorticoid antagonist RU-38486. The LTD induced by glucocorticoid receptor activation was dependent on N-methyl-D-aspartate (NMDA) receptor activity, because the specific NMDA receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) blocked the facilitation. However, the facilitation of LTD was not due to a potentiation of the isolated NMDA receptor potential by RU-28362. The facilitation of LTD by RU-28362 was also blocked by coincubation of the L-type voltage-dependent calcium channel (VDCC) antagonist nimodipine. Selective activation of the L-type VDCCs by the agonist Bay K 8644 also facilitated LTD induction. Both nimodipine and D-AP5 were effective in blocking the facilitation of LTD by Bay K 8644. These results indicate that L-type VDCCs can contribute to NMDA-receptor-dependent LTD induction.

Protean manifestations of mitochondrial diseases: a minireview

PURPOSE

Mitochondrial abnormalities are major causes of human disease. Pearson syndrome illustrates many features of abnormal mitochondrial function and genetics.

DESIGN

Mitochondria from adenosine triphosphate (ATP) via five multienzyme complexes of the electron transport chain and oxidative phosphorylation, composed from a blend of nuclear and mitochondrial gene products. Mitochondrial DNA (mtDNA) is small (16.6 kb), encoding some subunits of these complexes as well as transfer RNA (tRNA) and ribosomal RNA, but is replicated and transcribed by nuclear encoded polymerases. Multiple copies of mtDNA are passed on to progeny cells via the cytoplasm, accounting for maternal inheritance. Normal and mutant mtDNA can coexist within the same cell (heteroplasmy); when the proportion of mutant mtDNA exceeds a threshold, cellular function is impaired, resulting in disease.

RESULTS AND CONCLUSIONS

MtDNA abnormalities include point mutations, deletions, and depletion. Point mutations in an enzyme subunit cause a specific disorder, whereas point mutations in the tRNAs result in general impairment of protein synthesis and are associated with a variety of disorders. Large mtDNA deletions, initially described in Kearns-Sayre syndrome (KSS), were found soon thereafter in Pearson syndrome. Survivors of Pearson syndrome have gone on to develop KSS. A whole spectrum of disease forms, ranging from isolated sideroblastic anemia to combined Pearson and KSS, are associated with deletions of mtDNA. Diagnosis of mitochondrial disorders depends on clinical suspicion, enhanced by evidence of abnormal mitochondrial structure, number, and/or function. Effective treatment for mitochondrial disorders is very limited, including correction of the metabolic milieu, activation of enzyme activity by drugs or cofactors, and removal of reactive oxygen species.

Identification of two mutations in a compound heterozygous child with dihydrolipoamide dehydrogenase deficiency

An infant girl with elevated blood lactate, pyruvate, and plasma branched-chain amino acids was diagnosed with dihydrolipoamide dehydrogenase (E3; dihydrolipoamide: NAD+ oxidoreductase, EC 1.8.1.4) deficiency. Activities of the pyruvate dehydrogenase complex and E3 from patient were 26 and 2% of controls in blood lymphocytes, and 11 and 14% in cultured skin fibroblasts, respectively. Western blot analysis demonstrated that the amount of E3 protein in fibroblasts from the patient and her father was about half of controls, while Northern blot analysis showed normal amounts of E3 RNA. DNA sequencing of cloned full-length E3 cDNAs from the patient revealed two mutations in separate alleles. One is a single base insertion of an extra adenine in the last codon of the leader peptide sequence (TAC-->TAAC) leading to a nonsense mutation which results in the premature termination of the precursor E3 polypeptide (Y35X). The other is a missense mutation due to substitution of guanine for adenine, causing an Arg-->Gly substitution at amino acid 460 of the mature protein (R460G) which triggers the loss of E3 activity probably by structural change in the E3 dimer. DNA sequencing of E3 cDNAs from the parents demonstrated that the nonsense mutation was inherited from the father and the missense mutation was inherited from the mother.

Parathyroid hormone resistance and B cell lymphopenia in propionic acidemia

The mechanisms of hypocalcemia, recurrent infections and hypogammaglobulinemia associated with metabolic decompensation of propionic acidemia due to propionyl-CoA carboxylase deficiency have not been defined. A 7-week-old infant with this disorder presented with severe hypocalcemia and B cell lymphopenia during an episode of metabolic acidosis and hyperammonemia. Hypocalcemia (1.1 mmol l-1) was associated with elevated serum intact parathyroid hormone (122 ng l-1), hyperphosphatemia, hypophosphaturia and hypercalcuria, indicating parathyroid hormone resistance. B cell lymphopenia (20 cells microliters-1) was associated with transient neutropenia, anemia and subsequent hypogamma-globulinemia (IgG < 294 mg dl-1, IgM < 8 mg dl-1, IgA < 8 mg dl-1), while T cells were normal. Parathyroid hormone resistance and B cell lymphopenia resolved following treatment with hemodialysis, diet and carnitine. These complications may be due to interference with parathyroid hormone renal tubular action and B cell maturation/proliferation by accumulated organic acids.

Distinction of dicarboxylic aciduria due to medium-chain triglyceride feeding from that due to abnormal fatty acid oxidation and fasting in children

Increased amounts of dicarboxylic acids are excreted in human urine under conditions of medium-chain triglyceride (MCT) feeding, abnormal fatty acid oxidation (FAO) and fasting. Criteria to distinguish dicarboxylic aciduria originating from MCT feeding and other conditions are needed in urinary organic acid profiling for detecting inborn errors of metabolism. Patterns of dicarboxylic aciduria in children under various conditions were compared. The relative amounts of medium-chain saturated dicarboxylic acids in urine are not reliable for identifying MCT-induced dicarboxylic aciduria. On the other hand, low ratios of unsaturated to saturated dicarboxylic acids (<0.1) and 3- hydroxydecenedioic to 3-hydroxydecanedioic acids were found to be useful in identifying dicarboxylic aciduria due to MCT ingestion. Additional unique features of dicarboxylic aciduria from MCT are low ratios of 3-hydroxydodecanedioic to 3-hydroxydecanedioic acid (<0.14) and 3-hydroxyadipic to adipic acid (<0.02).

Three new mutations of the pyruvate dehydrogenase alpha subunit: a point mutation (M181V), 3 bp deletion (-R282), and 16 bp insertion/frameshift (K358SVS-->TVDQS)

Three novel mutations in the coding region of E1 alpha gene were found in three PDC-deficient male patients, including a missense mutation (M181V), a 3 bp deletion (AGA, corresponding to R282), and a 16 bp insertion (CAGTGGATCAAGTTTA), causing a frameshift starting with lysine 358 and resulting in decrease of both E1 subunits.

LTD: many means to how many ends?

Several forms of long-term synaptic depression (LTD) have been identified in the hippocampus. Although these LTDs differ in their methods of induction, it remains unclear whether they converge upon some final common mechanism(s) of expression. In the present paper we review critical aspects of heterosynaptic and homosynaptic LTD induction and consider those findings relevant to the expression of each. In addition, we suggest several experimental approaches which may be of benefit in addressing the commonality of LTD expression mechanisms.

Cooperative interactions among afferents govern the induction of homosynaptic long-term depression in the hippocampus

Prolonged periods of low-frequency stimulation have been shown to produce a robust, long-term synaptic depression (LTD) in both hippocampus and visual cortex. In the present study we have examined the extent to which interactions among afferents govern the induction of homosynaptic LTD in young-adult rats in hippocampal region CA1 in vitro. Field excitatory postsynaptic potentials were assessed before and after conditioning stimulation consisting of two 10-min trains of low-frequency stimulation (LFS; 1 Hz) of the Schaffer collateral/commissural pathway. LFS at an intensity producing a 0.5-mV response did not produce significant synaptic depression. However, LFS administered at a higher intensity resulted in significant input-specific LTD of a 0.5-mV test response. Picrotoxin, which also facilitates depolarization of CA1 neurons, significantly enhanced the magnitude of LTD after LFS at 0.5 mV. In addition, LFS at 0.5 mV in normal perfusion medium (no picrotoxin) produced only small changes in synaptic efficacy when either of two converging pathways was conditioned separately but produced a robust LTD when both pathways were conditioned simultaneously. This cooperative LTD was reversibly blocked by prior administration of 100 microM DL-aminophosphonovaleric acid but not by 20 microM nimodipine. Taken together, these results suggest that cooperative interactions among afferents contribute to voltage-dependent processes underlying the induction of homosynaptic LTD.

Gene regulation and genetic defects in the pyruvate dehydrogenase complex

The mammalian pyruvate dehydrogenase complex (PDC) is subject to both short-term (product inhibition and covalent modification) and long-term (increases in total activity and protein mass) regulation mediated by dietary and hormonal treatments. Recent advances in the isolation and characterization of the complementary DNAs as well as genes encoding several components of mammalian PDC have facilitated studies concerning long-term regulation of PDC. Analyses of the promoter-regulatory regions of the two human PDC genes show characteristics of both facultative and housekeeping gene promoters, indicating complex transcriptional regulation. Deficiency of PDC activity causes a wide range of neurological disabilities. A spectrum of genetic defects in PDC components has been reported; however, the most frequent defects are associated with the pyruvate dehydrogenase component. Heterogeneity in pyruvate dehydrogenase deficiency has been shown to occur at both protein and messenger RNA levels, and several mutations in pyruvate dehydrogenase have been identified. Dietary treatments such as ketogenic diets and vitamin supplements as well as dichloroacetate treatment have been utilized to treat PDC deficiency, but their efficacy requires further evaluation.

Primary amino acid sequence and structure of human pyruvate carboxylase

Pyruvate carboxylase (PC) (pyruvate:carbon dioxide ligase (ADP-forming), EC 6.4.1.1.), a nuclear-encoded mitochondrial enzyme, catalyzes the conversion of pyruvate to oxaloacetate. We have isolated and characterized cDNAs spanning the entire coding region of human PC. The sequence of human PC has an open reading frame of 3537 nucleotides which encodes for a polypeptide with a length of 1178 amino acids. The identity of the cDNA as PC is confirmed by comparison to PC cDNAs of other species and sequenced peptide fragments of mammalian PC. The M(r) of the full length precursor protein is 129,576 and that of the mature apoprotein is 127,370. RNA blot analysis from a variety of human tissues demonstrates that the highest level of PC mRNA is found in liver corresponding to this tissue's high level of PC activity. Based on homology with other biotin-containing proteins, the ATP, pyruvate, and biotin-binding sites can be identified. One of two patients with documented PC deficiency was found to be missing PC mRNA, further confirming the identity of this cDNA.

MRI, clinical, and biochemical features of partial pyruvate carboxylase deficiency

We report a boy with a partial deficiency of pyruvate carboxylase as documented in enzyme assays of skin fibroblasts, lymphocytes, and hepatic tissue. Magnetic resonance imaging at age 20 months demonstrated a leukodystrophic process involving the brain stem and subcortical white matter, which, except for the brain stem, improved after biotin treatment. The lymphocyte pyruvate carboxylase activity of both heterozygous parents slightly increased after receiving oral biotin for 1 month, but a definitive enzymatic response to biotin was not confirmed in our patient. At age 6 years, he is dysarthric with a spastic quadriparesis despite improvements in development and myelination. This is the first demonstration of magnetic resonance imaging changes in this disease.

Flip side of synaptic plasticity: long-term depression mechanisms in the hippocampus

There is growing interest in the phenomenon of long-term depression (LTD) of synaptic efficacy that, together with long-term potentiation (LTP), is a putative information storage mechanism in mammalian brain. In neural network models, multiple learning rules have been used for LTD induction. Similarly, in neurophysiological studies of hippocampal synaptic plasticity, a variety of activity patterns have been effective at inducing LTD, although experimental paradigms are still being optimized. In this review the authors summarize the major experimental paradigms and compare what is known about the mechanisms of LTD induction. Although all paradigms appear to initiate a cascade of events leading to an elevated level of Ca2+ postsynaptically, the extent to which these paradigms involve common expression mechanisms has not yet been tested. The authors discuss several critical experiments that would address this latter issue. Numerous questions about the properties and mechanisms of LTD(s) in the hippocampus remain to be answered, but it is clear that LTD has finally arrived, and will soon be attracting attention equal to its flip side, LTP.

Comparison of associative and non-associative conditioning procedures in the induction of LTD in CA1 of the hippocampus

Recent reports have indicated that weak activity in a test input, negatively correlated (out-of-phase) with tetanization of a separate, converging input, produces an NMDA-independent, associative long-term depression (LTD) of the test input synapses, in hippocampal field CA1 (Stanton and Sejnowski, 1989; Stanton et al., 1991). Associative LTD has also been observed in the dentate gyrus, in vivo, but only following "priming" of the test path with 5 Hz stimulation prior to associative conditioning (Christie and Abraham, 1992b). We have used these stimulus protocols, in vitro, in order to compare the induction of non-associative and associative LTD in field CA1 of the adult rat hippocampus. Stimulation in normal solution evoked a small non-associative LTD, but no associative LTD. Addition of picrotoxin to the medium facilitated the induction of NMDA-dependent non-associative LTD, but not associative LTD. Previously potentiated pathways were not different from naive pathways in expression of LTD of either kind. Finally, 'priming' stimulation (5 Hz) of the test pathway produced a weak, selective enhancement of associative LTD that was, however, not significantly greater than non-associative LTD. These results indicate that, for our experimental conditions, negatively correlated co-activity during afferent tetanization does not induce a substantial associative LTD in area CA1.

Mechanisms of neuronal death in brain aging and Alzheimer's disease: role of endocrine-mediated calcium dyshomeostasis

This paper reviews evidence that brain aging and Alzheimer's disease (AD) are somehow closely related and that the hippocampus (CA1) is highly vulnerable to cell loss under both conditions. In addition, two current lines of evidence on the mechanisms of hippocampal cell loss with aging are considered, including studies of neuronal calcium dysregulation and studies of cumulative glucocorticoid (GC) neurotoxicity. Moreover, recent electrophysiological studies have shown that excess glucocorticoid activation of hippocampal neurons increases the influx of calcium through voltage-activated calcium channels. Second messenger systems may mediate the steroid modulation of calcium channels. Therefore, it is hypothesized that excess glucocorticoid activation and neuronal calcium dysregulation may be two phases of a single process that increases the susceptibility of neurons to neurodegeneration during aging and Alzheimer's disease.

Hippocampal glucocorticoid receptor activation enhances voltage-dependent Ca2+ conductances: relevance to brain aging

Glucocorticoids (GCs) activate several biochemical/molecular processes in the hippocampus through two receptor types. In addition, GCs influence cognitive behaviors and hippocampal neural activity and can also increase the rate of aging-dependent cell loss in the hippocampus. However, the ionic mechanisms through which GCs modulate hippocampal neuronal function are not well understood. We report here direct evidence that activation of cytosolic steroid receptors, specifically of the type II GC receptor, can enhance voltage-dependent Ca2+ conductances in brain neurons. Ca2+ current was assessed by current-clamp measures of Ca2+ action potentials and by sharp electrode voltage-clamp analyses of voltage-sensitive currents in cesium-, tetrodotoxin-, and tetraethylammonium-treated CA1 neurons in hippocampal slices. Both Ca2+ action potentials and voltage-activated Ca2+ currents (N- and L-like) were increased by 2-hr exposure to the synthetic GC receptor agonist, RU 28362. This effect of RU 28362 was blocked by coincubation with cycloheximide, indicating that the GC receptor-Ca2+ channel interaction depends on de novo protein synthesis. Dysregulated calcium homeostasis is also viewed as a candidate mechanism in brain aging. Thus, present results are consistent with the hypothesis that excessive GC-receptor activation and resultant increased Ca2+ influx may be two sequential phases of a brain-aging process that results initially in impairment of function and eventually in neuronal loss.

A mutation in the E1 alpha subunit of pyruvate dehydrogenase associated with variable expression of pyruvate dehydrogenase complex deficiency

Defects in pyruvate dehydrogenase, the first catalytic component of the pyruvate dehydrogenase complex, are the most common cause of pyruvate dehydrogenase complex deficiency. A family with variable pyruvate dehydrogenase complex deficiency had been described in which cultured skin fibroblasts of affected family members had normal pyruvate dehydrogenase complex activity, but different tissues and blood lymphocytes had significantly diminished activities. Enzymatic activity and immunoblot studies indicated that pyruvate dehydrogenase was affected. Further evidence is presented here showing that the defect affecting pyruvate dehydrogenase complex activity is posttranscriptional. Sequencing of the coding region of the alpha-subunit of pyruvate dehydrogenase revealed a point mutation in the codon for amino acid 234 resulting in a substitution of glycine for arginine. Study of other members of the family suggested that this mutation is inherited in a sex-linked mode. The point mutation is located in a highly conserved region of the pyruvate dehydrogenase alpha-subunit gene that contains both hydrophobic and positively charged amino acid residues. Variable expression of pyruvate dehydrogenase complex deficiency in this case may be due to instability of the pyruvate dehydrogenase heterotetramer in specific tissues because of a disruption in subunit-subunit interaction.

Mutations and polymorphisms in the pyruvate dehydrogenase E1 alpha gene

We present an update on mutations and polymorphisms in the human X chromosome located pyruvate dehydrogenase E1 alpha gene. A total of 20 different mutations are tabulated. The mutations include deletions, insertions, and point mutations. Certain sequences seem particularly prone to mutation. Most of the mutations are found in exons 10 and 11. Furthermore, four of the mutations are seen in unrelated patients. Little is known about how the mutations affect the structure or function of the pyruvate dehydrogenase complex.

Lactic acidosis and mitochondrial disorders

Characterization of the biochemical basis of various inherited disorders associated with lactic acidosis has increased dramatically in recent years. These include defects of enzymes of gluconeogenesis, pyruvate oxidation, and electron transport. Clinical manifestations of these disorders show great variation and overlap, frequently involving the central nervous system as well as skeletal and cardiac muscle. Several of these enzymes are large complexes of subunits encoded by multiple genes; the electron transport chain complexes include subunits encoded by both nuclear and mitochondrial genes. This great complexity complicates analysis of specific mutations, despite considerable progress in defining the primary structure of component proteins and their genes. With few exceptions, treatment of disorders associated with congenital lactic acidosis remains unsatisfactory.

Urinary 3-hydroxydicarboxylic acids in pathophysiology of metabolic disorders with dicarboxylic aciduria

Dicarboxylic aciduria occurs during increased mobilization or inhibited beta-oxidation of fatty acids. In these conditions, a number of 3-hydroxydicarboxylic acids are excreted in the urine. These 3-hydroxydicarboxylic acids include 3-hydroxyadipic (3OHDC6), 3-hydroxyoctanedioic (3OHDC8), 3-hydroxydecanedioic (3OHDC10), 3-hydroxydodecanedioic (3OHDC12), and a number of unsaturated homologues. The metabolic origin of these 3-hydroxydicarboxylic acids is from the omega-oxidation of 3-hydroxy fatty acids. Subsequent beta-oxidation of the dicarboxylates yields lower-chain 3-hydroxydicarboxylic acids. A new defect in fatty acid oxidation characterized by increased urinary ratios of 3OHDC6, 3OHDC12, and unsaturated 3OHDC14s relative to 3OHDC10 is described. This pattern is consistent with a defect in long-chain 3-hydroxyacyl-CoA dehydrogenase (LHAD), which was confirmed by enzyme assay in fibroblasts. In contrast, patients with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency had lower ratios of 3OHDC6 and 3OHDC8 to 3OHDC10, consistent with a decreased activity of MCAD. Nonketotic dicarboxylic aciduria, other than MCAD and LHAD deficiencies, is shown to have a normal 3-hydroxydicarboxylic acid profile when compared with fasting normal controls. Since increased excretion of 3-hydroxydicarboxylic acids was observed in all patients with dicarboxylic aciduria, an increased excretion of these compounds is not an adequate criterion to suspect a defect in 3-hydroxyacyl-CoA dehydrogenases. The analysis of the metabolite ratios (3OHDC6 and 3OHDC12 relative to 3OHDC10) is a more useful indicator for defects in LHAD.

Chronic stress-induced acceleration of electrophysiologic and morphometric biomarkers of hippocampal aging

There is increasing evidence that experimental interventions that alter adrenal corticosteroid plasma concentrations can modulate aging changes in the rodent hippocampus. However, there still is very little evidence that elevation of endogenous corticosteroid levels within physiological ranges, such as occurs during chronic stress, can accelerate hippocampal aging-like changes. In addition, almost all prior intervention studies of corticosteroid effects on brain biomarkers of aging have utilized morphologic measures of aging, and it is not yet clear whether electrophysiologic biomarkers of hippocampal aging can also be accelerated by conditions that elevate corticosteroids. In the present studies, specific pathogen-free rats of three ages (4, 12, and 18 months at the start) were trained for 6 months (4 hr/d, 5 d/week) in a two-way shuttle escape task, using low intensity foot shock. This task induces "anxiety" stress, because animals receive little actual shock, but chronic training in the task has been shown to elevate plasma corticosteroids and to downregulate hippocampal corticosteroid receptors. At the end of 6 months, animals were allowed to recover for 3 weeks and were then assessed in acute, anesthetized preparations on a battery of hippocampal neurophysiological markers known to separate young from aged animals (frequency potentiation, synaptic excitability thresholds, EPSP amplitude). The brains were then fixed and sectioned for quantification of neuronal density in field CA1 (a highly consistent anatomic marker of hippocampal aging). The pattern of stress effects differed considerably across age groups. The two younger stress groups exhibited increased evidence of aging-like neurophysiologic change, but exhibited no indications of accelerated neuronal loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal urinary excretion of unsaturated dicarboxylic acids in patients with medium-chain acyl-CoA dehydrogenase deficiency

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most frequently described metabolic disorder of fatty acid oxidation in humans. Acute episodes are usually characterized biochemically by the appearance of nonketotic dicarboxylic aciduria. In addition, other abnormal metabolites, such as suberylglycine, n-hexanoylglycine, 3-phenylpropionylglycine, and octanoylcarnitine, are excreted in the urine. Urinary organic acids were determined using dual capillary column gas-liquid chromatography and gas-liquid chromatography/mass spectrometry. In three cases of MCAD deficiency we observed a disproportionate increase in the excretion of unsaturated dicarboxylic acids compared to either fasting control children with expected ketotic dicarboxylic aciduria or patients with nonketotic dicarboxylic aciduria not associated with MCAD deficiency. The most significant increase was in the urinary excretion of cis-4-decendioic acid. Additionally, the urinary excretions of cis-3-octenedioic and cis-5-decenedioic acids were slightly decreased whereas the excretion of cis-5-dodecenedioic acid was increased. These data are consistent with the notion that as a result of MCAD deficiency the metabolic oxidation of unsaturated fatty acids such as linoleate and oleate is inhibited more than saturated fatty acids.

Genetic defects in human pyruvate dehydrogenase

The nature of PDC deficiency has been characterized at the levels of total and component catalytic activities as well as at the levels of component proteins and specific mRNAs. Defects in 14 cases were shown to involve the E1 component, and there was one case each of an apparent E2 and E3 deficiency. Defects involving the E1 component exhibit heterogeneous expression of E1 proteins and mRNAs, indicating that different types of mutations cause E1 deficiency. E1 deficiencies can occur either in the presence or absence of E1 proteins, representing catalytic mutations or mutations affecting the expression of E1 proteins, respectively. In every case where the content of E1 proteins is reduced, both the E1 alpha and the E1 beta peptides are simultaneously affected. This is likely to be due to rapid degradation of any E1 peptide that is not complexed into the alpha 2 beta 2 conformation. Among subjects with reduced levels of both E1 peptides, some had normal amounts of specific E1 alpha and E1 beta mRNAs. In these subjects, the primary mutations affect either translational or post-translational processes leading to the formation of mature E1 proteins in the mitochondria. In contrast, two cases of simultaneous reduction of both E1 alpha and E1 beta proteins had decreases in the amounts of E1 alpha mRNA only. Mutations in these cases may impair the transcription, nuclear processing, or stability of E1 alpha mRNA. E1 deficiency may manifest in a variable manner. Further characterization of this phenomenon might provide insight into the discrepancy between the clinical severity of the defect and the residual level of PDC catalytic activity. Available information indicates that the E1 alpha gene is located on the X chromosome, but sex distribution of E1 alpha defects suggests that the mode of inheritance may not follow a simple X-linked pattern. The availability of specific PDC antibodies and cDNA clones, as well as the application of molecular biological techniques, should facilitate the characterization of the molecular basis of various PDC deficiencies. This information should provide better understanding of the function of PDC, pathophysiology of PDC deficiency, and mechanisms of inheritance and expression of these genes.