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K M Gibson

Publications and source records attributed to K M Gibson.

At least 73 records · Page 4Linked to original sources
PubMed1997

Regulatory adaptation of isoprenoid biosynthesis and the LDL receptor pathway in fibroblasts from patients with mevalonate kinase deficiency.

In a search for the pathophysiologic mechanisms, we estimated isoprenoid synthesis and concentration, cellular growth, and the activity of the LDL receptor pathway in fibroblasts from patients with mevalonate kinase deficiency (MKD), a severe multisystemic disorder of cholesterol and non-sterol isoprenoid biosynthesis. In response to different concentrations of LDL and non-lipoprotein-bound cholesterol, MKD cells partially counteracted their enzyme defect by increased activities of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase (results from earlier studies) and the LDL receptor pathway, responses similar to the pharmacologic effects seen upon administration of HMG-CoA reductase inhibitors. Rates of N-linked protein glycosylation, estimated as the amount of [14C]galactose-labeled macromolecules secreted into cell culture medium, were significantly decreased in MKD fibroblasts in comparison with control cells which may indicate alterations in the dolichol or dolichol phosphate pool. In response to exogenous cholesterol, the major feedback inhibitor of isoprenoid biosynthesis, growth velocities of MKD fibroblasts declined in comparison with control cells, further suggesting an impairment of non-sterol isoprenoid biosynthesis in MKD. Our results suggest an imbalance in the multilevel regulation of the biosynthesis of cholesterol and non-sterol isoprenoids in MKD, representing an additional causative factor responsible for the pre- and postnatal pathology of MKD.

Adaptation, Physiological↗
PubMed1997

The clinical phenotype of succinic semialdehyde dehydrogenase deficiency (4-hydroxybutyric aciduria): case reports of 23 new patients.

OBJECTIVES: To further define the clinical spectrum of the disease for pediatric and metabolic specialists, and to suggest that the general pediatrician and pediatric neurologist consider succinic semialdehyde dehydrogenase (SSADH) deficiency in the differential diagnosis of patients with (idiopathic) mental retardation and emphasize the need for accurate, quantitative organic acid analysis in such patients. PATIENTS: The clinical features of 23 patients (20 families) with SSADH deficiency (4-hydroxybutyric acid-uria) are presented. The age at diagnosis ranged from 3 months to 25 years in the 11 male and 12 female patients; consanguinity was noted in 39% of families. OUTCOME MEASUREMENTS: The following abnormalities were observed (frequency in 23 patients): motor delay, including fine-motor skills, 78%; language delay, 78%; hypotonia, 74%; mental delay, 74%; seizures, 48%; decreased or absent reflexes, 39%; ataxia, 30%; behavioral problems, 30%; hyperkinesis, 30%; neonatal problems, 26%; and electroencephalographic abnormalities, 26%. Associated findings included psychoses, cranial magnetic resonance or computed tomographic abnormalities, and ocular problems in 22% or less of patients. Therapy with vigabatrin proved beneficial to varying degrees in 35% of the patients. Normal early development was noted in 30% of patients. CONCLUSIONS: Our data imply that two groups of patients with SSADH deficiency exist, differentiated by the course of early development. Our recommendation would be that accurate, quantitative organic acid analysis in an appropriate specialist laboratory be requested for any patients presenting with two or more features of mental, motor, or language delay and hypotonia of unknown cause. Such analyses are the only definitive way to diagnose SSADH deficiency; the diagnosis can be confirmed by determination of enzyme activity in white cells from whole blood. We think that increased use of organic acid determination will lead to increased diagnosis of SSADH deficiency and a more accurate representation of disease frequency. As additional patients are identified, we should have a better understanding of both the metabolic and clinical profiles of SSADH deficiency.

Adolescent↗
PubMed1997

Endogenous natriuretic factors 7: biospecificity of a natriuretic gamma-tocopherol metabolite LLU-alpha.

The structural elucidation and mechanism of action of a potential component, LLU-alpha, of what is possibly a multifactorial complex known as "natriuretic hormone" was recently reported [Wechter, W.J. et al. (1996a) Proc. Natl. Acad. Sci. U.S.A. 93: 6002-6007]. "Natriuretic hormone," a long-sought factor, is believed to regulate extracellular fluid volume and consequently be pathomimetic for hypertension, cirrhosis, congestive heart failure and other volume expanded states. The studies reported herein further characterize LLU-alpha. The precursor of the endogenous LLU-alpha was demonstrated to be gamma-tocopherol by radiolabeling studies. The pharmacokinetics of infused rac-LLU-alpha proved to be biphasic (half-lives: 12 min and 6 h). Specificity of the inhibition of the 70 pS potassium channel of the thick ascending limb of the loop of Henle was examined with the natural S-enantiomer being the most potent known inhibitor whereas the analogous alpha-tocopherol metabolite, rac-5-Me-LLU-alpha, showed no inhibition. Rac-LLU-alpha does not inhibit two isozymes of the Na+/K+-ATPase. LLU-alpha is natriuretic acting via inhibition of the 70 pS potassium channel and not Na+/K+-ATPase, the assumed mechanism of action of the "natriuretic hormone." LLU-alpha, a metabolite of a vitamin, if it were found to play a role in the regulation of extracellular fluid volume, would be the second example of a vitamin acting as a precursor for a hormone. Of considerable interest is the fact that this manuscript reports the first biological activity of gamma-tocopherol, a member of the vitamin E complex.

Animals↗
PubMed1997

Post-translational regulation of mevalonate kinase by intermediates of the cholesterol and nonsterol isoprene biosynthetic pathways.

To assess the potential for feedback inhibition by isoprene intermediates in the cholesterol and nonsterol isoprene biosynthetic pathway, we expressed human cDNAs encoding mevalonate kinase (MKase), phosphomevalonate kinase (PMKase), and mevalonate diphosphate decarboxylase (MDDase) as fusion proteins in Escherichia coli DH5alpha, and purified these proteins by affinity chromatography. Several phosphorylated and non-phosphorylated isoprenes were analyzed as inhibitors of the enzymes using a standard spectrophotometric assay. Of the three proteins, only MKase was inhibited through competitive interaction at the ATP-binding site. The intermediates studied (and their relative inhibitory capacity) were: geranylgeranyl-diphosphate (GGPP, C20) > farnesyl-diphosphate (FPP, C15) > geranyl-diphosphate (GPP, C10) > isopentenyl-diphosphate (IPP, C5) > or = 3,3-dimethylallyl-diphosphate (DMAPP, C5) > farnesol (C15) > dolichol-phosphate (DP, C(80-100)). Mevalonate-diphosphate, geraniol, and dolichol were not inhibitors. Our data further define the spectrum of physiologic inhibitors of MKase, and provide the first evidence for feedback inhibition of MKase by a nonsterol isoprene produced by the branched pathway, dolichol-phosphate. These results provide additional evidence that MKase may occupy a central regulatory role in the control of cholesterol and nonsterol isoprene biosynthesis.

Carboxy-Lyases↗
PubMed1996

Molecular cloning of human phosphomevalonate kinase and identification of a consensus peroxisomal targeting sequence.

Two overlapping cDNAs which encode human liver phosphomevalonate kinase (PMKase) were isolated. The human PMKase cDNAs predict a 191-amino acid protein with a molecular weight of 21,862, consistent with previous reports for mammalian PMKase (Mr = 21,000-22,500). Further verification of the clones was obtained by expression of PMKase activity in bacteria using a composite 1024-base pair cDNA clone. Northern blot analysis of several human tissues revealed a doublet of transcripts at approximately 1 kilobase (kb) in heart, liver, skeletal muscle, kidney, and pancreas and lower but detectable transcript levels in brain, placenta, and lung. Analysis of transcripts from human lymphoblasts subcultured in lipid-depleted sera (LDS) and LDS supplemented with lovastatin indicated that PMKase gene expression is subject to regulation by sterol at the level of transcription. Southern blotting indicated that PMKase is a single copy gene covering less than 15 kb in the human genome. The human PMKase amino acid sequence contains a consensus peroxisomal targeting sequence (PTS-1), Ser-Arg-Leu, at the C terminus of the protein. This is the first report of a cholesterol biosynthetic protein which contains a consensus PTS-1, providing further evidence for the concept that early cholesterol and nonsterol isoprenoid biosynthesis may occur in the peroxisome.

Amino Acid Sequence↗
PubMed1996

3-Hydroxy-3-methylglutaryl CoA lyase (HL): mouse and human HL gene (HMGCL) cloning and detection of large gene deletions in two unrelated HL-deficient patients.

3-hydroxy-3-methylglutaryl CoA lyase (HL, EC 4.1.3.4) catalyzes the cleavage of 3-hydroxy-3-methylglutaryl CoA to acetoacetic acid and acetyl CoA, the final reaction of both ketogenesis and leucine catabolism. Autosomal-recessive HL deficiency in humans results in episodes of hypoketotic hypoglycemia and coma. Using a mouse HL cDNA as a probe, we isolated a clone containing the full-length mouse HL gene that spans about 15 kb of mouse chromosome 4 and contains nine exons. The promoter region of the mouse HL gene contains elements characteristic of a housekeeping gene: a CpG island containing multiple Sp1 binding sites surrounds exon 1, and neither a TATA nor a CAAT box are present. We identified multiple transcription start sites in the mouse HL gene, 35 to 9 bases upstream of the translation start codon. We also isolated two human HL genomic clones that include HL exons 2 to 9 within 18 kb. The mouse and human HL genes (HGMW-approved symbol HMGCL) are highly homologous, with identical locations of intron-exon junctions. By genomic Southern blot analysis and exonic PCR, we found 2 of 33 HL-deficient probands to be homozygous for large deletions in the HL gene.

Animals↗
PubMed1996

Late-onset holocarboxylase synthetase deficiency.

We report a 21-month-old female patient whose urine organic acid profile suggested a biotin utilization abnormality consistent with multiple carboxylase deficiency. For most previously reported patients, holocarboxylase synthetase deficiency has correlated with the early-onset variant of multiple carboxylase deficiency; conversely, biotinidase deficiency has been characteristic of the late-onset form. In vitro enzyme studies revealed that our patient suffered from holocarboxylase synthetase deficiency. We suggest that holocarboxylase synthetase deficiency should be considered in the differential diagnosis of older patients in whom there is suspicion of a defect in biotin metabolism.

Biotin↗
PubMed1996

Seizures in a boy with succinic semialdehyde dehydrogenase deficiency treated with vigabatrin (gamma-vinyl-GABA).

Succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal recessive disease involving the catabolism of the neurotransmitter gamma-aminobutyric acid (GABA). The main symptoms include retardation of psychomotor and language development, muscle hypotonia and non-progressive ataxia. Therapy consisting of approximately 75 mg/kg per day of vigabatrin, an irreversible inhibitor of GABA-transaminase, is reported to lead to some improvement of the clinical condition in affected patients. We report on a 12-year-old boy with SSADH deficiency who, when treated with 75 mg/kg per day of vigabatrin, showed marked amelioration of symptoms but also EEG changes and two generalized seizures. On discontinuing vigabatrin therapy, the seizures resolved and the EEG improved, but the patient's clinical condition deteriorated to its pre-treatment state. A stable EEG without the recurrence of seizures as well as renewed improvement of cognitive and behavioural functions was achieved with a reduced vigabatrin dose of 25 mg/kg per day. We conclude that vigabatrin in SSADH deficiency should be administered in a gradually increasing dosage combined with frequent evaluation of the clinical condition and the EEG.

4-Aminobutyrate Transaminase↗
PubMed1996

Clustering of mutations in the biotin-binding region of holocarboxylase synthetase in biotin-responsive multiple carboxylase deficiency.

Holocarboxylase synthetase (HCS) catalyses the biotinylation of the four biotin-dependent carboxylases found in humans. A deficiency in HCS results in biotin-responsive multiple carboxylase deficiency (MCD). We have identified six different point mutations in the HCS gene in nine patients with MCD. Two of the mutations are frequent among the MCD patients analyzed. Four of the mutations cluster in the putative biotin-binding domain as deduced from the corresponding Escherichia coli enzyme and consistent with an explanation for biotin-responsiveness based on altered affinity for biotin. The two others may define an additional domain involved in biotin-binding or biotin-mediated stabilization of the protein.

Amino Acid Sequence↗
PubMed1995

Molecular cloning of the mature NAD(+)-dependent succinic semialdehyde dehydrogenase from rat and human. cDNA isolation, evolutionary homology, and tissue expression.

Three rat brain cDNA clones approximately 3500, 1465, and 1135 base pairs in length encoding succinic semialdehyde dehydrogenase (SSADH; EC 1.2.1.24) were isolated from two cDNA libraries using a polymerase chain reaction derived probe. Restriction mapping and DNA sequencing revealed that the 3.5-kilobase clone contained an 84-base pair (28 amino acid) insert in the coding region. Composite clones encoding mature SSADH predicted proteins with 488 amino acids (M(r) = 52,188) when including the insert and 460 amino acids (M(r) = 48,854) without the insert. The cDNA clones were confirmed by expression of enzyme activity in bacteria and protein sequence data obtained from sequencing purified rat brain SSADH. Two human liver SSADH cDNA clones of 1091 and 899 base pairs were also isolated. Human and rat SSADH share 83 and 91% identity in nucleotide and protein sequence, respectively. Northern blot analysis revealed two differentially expressed SSADH transcripts of approximately 2.0 and 6.0 kilobases in both rat and human tissues. Human genomic Southern blots indicate that the two SSADH transcripts are encoded by a greater than 20-kilobase single copy gene. Mammalian SSADH contains significant homology to bacterial NADP(+)-succinic semialdehyde dehydrogenase (EC 1.2.1.16) and conserved regions of general aldehyde dehydrogenases (EC 1.2.1.3), suggesting it is a member of the aldehyde dehydrogenase superfamily of proteins.

Aldehyde Dehydrogenase↗
PubMed1995

Molecular prenatal diagnosis of 3-hydroxy-3-methylglutaryl CoA lyase deficiency.

We report the first molecular prenatal diagnosis of 3-hydroxy-3-methylglutaryl CoA lyase (HL) deficiency. The proband had a classic but severe presentation with hypoketotic hypoglycaemia and acidosis, secondary mental retardation, and epilepsy, and HL deficiency was documented in cultured fibroblasts. We found him to be homozygous for the frameshift mutation N46fs (+1), which yields a distinct pattern on single-strand conformation polymorphism (SSCP) analysis. In two subsequent pregnancies, molecular prenatal diagnosis was performed using SSCP. In the first, chorionic villus biopsy was normal. In the second pregnancy, amniocentesis revealed an affected fetus. In both pregnancies, the diagnosis was confirmed enzymatically. HL activity was less than 7 per cent of control values in amniocytes and fetal liver of the affected pregnancy. In the second pregnancy, amniotic fluid metabolite measurements by stable isotope dilution-selected ion monitoring mass spectrometry showed greater than 100-fold increases of 3-hydroxy-3-methylglutaric acid and of 3-methylglutaconic acid levels compared with controls.

Amniocentesis↗