Biomedical subjects

G Pons

Publications and source records attributed to G Pons.

At least 37 records · Page 2Linked to original sources

PubMed1990

Nitrofurantoin excretion in human milk.

Six lactating white healthy women (26-36 years old, weighing 45-58 kg) were treated with 50 mg nitrofurantoin tablets, a urinary antiseptic. They received either 50 mg (group I; n = 3) or 100 mg (group II; n = 3) 3 times a day (09.00, 16.00, 19.00 h) for 24 h, 2-5 days after the delivery of a full-term neonate. The study was performed on the 4th dose at 09.00 h just before breakfast. Milk samples were collected before, 3 and 6 h after the nitrofurantoin administration with an Egnell SMB breast pump. The complete milk samples were collected from each breast, and pooled. 5 ml venous blood samples were drawn before, 1, 2, 3 and 6 h after nitrofurantoin administration. Plasma and milk nitrofurantoin concentrations were measured by HPLC. Apparent elimination half-life and apparent plasma clearance were the same in both groups, 0.8 +/- 0.09 h and 27.6 +/- 5.57 l/h, respectively. Nitrofurantoin was not detectable in the milk just before the 4th administration. The amount excreted in the milk within 6 h after nitrofurantoin administration was 22-57 micrograms (I) and 61-284 micrograms (II) which represents 0.05-0.11% (I) and 0.06-0.28 (II) of the nitrofurantoin dose. The nitrofurantoin concentration ratio of the breast milk to the plasma collected at 3 h was 2.2 +/- 1.2 (I) and 2.3 +/- 1.6 (II). These results show that nitrofurantoin excretion in human milk is low: below 0.12 (I) and 0.29% (II). It suggested that breast-fed newborn infants from mothers treated with nitrofurantoin would be exposed to small amounts of drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Sequence of rat skeletal muscle phosphoglycerate mutase cDNA.

A cDNA clone coding rat skeletal muscle phosphoglycerate mutase was isolated from a rat muscle lambda gt10 cDNA library and its sequence was determined. The deduced protein possesses 252 amino acids and is 94% homologous with respect to human muscle phosphoglycerate mutase. No amino acids changes occur at the active site and structural predictions suggest strong conformational homologies with other enzymes of the mutase family.

Amino Acid Sequence↗

PubMed1989

Dihydrolipoamide dehydrogenase: functional similarities and divergent evolution of the pyridine nucleotide-disulfide oxidoreductases.

Dihydrolipoamide dehydrogenase (E3) is the common component of the three alpha-ketoacid dehydrogenase complexes oxidizing pyruvate, alpha-ketoglutarate, and the branched-chain alpha-ketoacids. E3 also participates in the glycine cleavage system. E3 belongs to the enzyme family called pyridine nucleotide-disulfide oxidoreductases, catalyzing the electron transfer between pyridine nucleotides and disulfide compounds. This review summarizes the information available for E3 from a variety of species, from a halophilic archaebacterium which has E3 but no alpha-ketoacid dehydrogenase complexes, to mammalian species. Evidence is reviewed for the existence of two E3 isozymes (one for pyruvate dehydrogenase complex and alpha-ketoglutarate dehydrogenase complex and the other for branched-chain alpha-ketoacid dehydrogenase complex) in Pseudomonas species and for possible mammalian isozymes of E3, one associated with the three alpha-ketoacid dehydrogenase complexes and one for the glycine cleavage system. The comparison of the complete amino acid sequences of E3 from Escherichia coli, yeast, pig, and human shows considerable homologies of certain amino acid residues or short stretches of sequences, especially in the specific catalytic and structural domains. Similar homology is found with the limited available amino acid sequence information on E3 from several other species. Sequence comparison is also presented for other member flavoproteins [e.g., glutathione reductase and mercury(II) reductase] of the pyridine nucleotide-disulfide oxidoreductase family. Based on the known tertiary structure of human glutathione reductase it may be possible to predict the domain structures of E3. Additionally, the sequence information may help to better understand a divergent evolutionary relationship among these flavoproteins in different species.

Amino Acid Sequence↗

PubMed1989

Zolpidem excretion in breast milk.

Five, lactating, healthy white women were treated with a single 20 mg tablet of zolpidem 3-4 days after the delivery of a full term baby. The drug was administered at 20.00 h, 30 min after dinner, and milk samples were collected before and 3, 13 and 16 h. Venous blood 5 ml was taken before and 1.5, 3, 13, 16 h after zolpidem administration. The apparent elimination half life, estimated from plasma zolpidem concentrations was 2.6 h. The amount of zolpidem excreted in the milk at 3 h ranged between 0.76 and 3.88 micrograms, which represented 0.004 to 0.019% of the administered dose; no detectable (below 0.5 ng/ml) zolpidem was found in the milk at subsequent sampling times. The ratio of the zolpidem concentrations in breast milk and plasma at 3 h was 0.13. The apparent breast milk clearance of zolpidem, calculated from the ratio of the total amount of zolpidem excreted in milk to its AUC in plasma was 1.48 ml/h. The results show that the excretion of zolpidem in human milk is very low (below 0.02%) and that most of it takes place during the first 3 h following drug intake.

Adult↗

PubMed1989

Maturation of AFMU excretion in infants.

The maturation of the N-acetyltransferase-dependent AFMU production from caffeine was studied during infancy. The group of children (N = 14) consisted of 4 premature newborn infants and ten 1-19 month-old infants who received caffeine citrate solution for the treatment and prevention of apnea. Caffeine, AFMU, 1X and 9 other metabolites were measured in urine using HPLC. The AFMU/1X ratio did not vary significantly in this population with increasing age. In one of the infants serially studied, the AFMU/1X ratio increased dramatically between 6 and 12 months of age. This observation suggests that the maturation of N-acetyltransferase activity is not completed before 1 year of age implying that acetylator status cannot reliably be determined before that age. Patients studied before 1 year of age whose AFMU/1X ratio was below 0.4 may be either true slow acetylators or still immature fast acetylators.

Acetylation↗

PubMed1989

Molecular biology of the human pyruvate dehydrogenase complex: structural aspects of the E2 and E3 components.

The availability of the primary amino acid sequences of the E2 of PDC, alpha-KGDC and BCKADC from several prokaryotic and eukaryotic species has allowed us to compare the structural aspects of human PDC-E2 with those of the E2 components from the other complexes. The PDC-E2 components from all the species examined so far contain three structurally identifiable regions: the lipoyl-bearing domain, the E3-binding site, and the catalytic domain. The primary structure of the lipoyl-bearing domain shows considerable variation in its size, ranging from one to three repeating units of approximately 110 amino acids, but essentially preserving its function in the E2 components. In contrast, the sizes of the E3-binding site and the catalytic domain of PDC-E2 from several species are essentially similar and show considerable conservation of specific amino acid residues. Obviously, additional studies are warranted to better understand the structure-function relationships of these domains and the evolutionary conservation of PDC-E2 in different species. Similarly, the availability of the primary amino acid sequences of E3 from several prokaryotes and eukaryotes has also permitted comparison of the structural domains of these proteins with that of the known structure of human GR, a flavoprotein member of the pyridine nucleotide-disulfide oxidoreductase family. Four structural domains (FAD, NAD+, central, and interface domains) have been identified in the E3 components. On the basis of the comparison of the secondary structural elements of GR and E3, the core structure of these two proteins are shown to be similar. It is hoped that further analysis of E3 using site-directed mutagenesis and determination of its crystal structure will provide better insight into its structure-function relationships.

Amino Acid Sequence↗

PubMed1989

[Atrioventricular block, a complication of radiotherapy of the mediastinum].

Cardiac complications of mediastinal irradiation usually concern the pericardium, the ventricular myocardium and the coronary arteries. We report the case of a 42-year old woman who experienced a syncopal atrioventricular (AV) block 12 years after irradiation of a mediastinal Hodgkin's lymphoma. Electrophysiological recordings showed infranodal conduction disturbances. A review of the literature yielded only 12 cases of syncopal radiation-induced AV block. This case highlights the risk of syncopal AV blocks occurring a long time after mediastinal irradiation and leading to severe damage of the His bundle and its branches. The presence, as in our patient, of an associated right ventricular outflow tract stenosis confirms the importance and severity of radiation-induced cardiac lesions.

Adult↗

PubMed1989

[Use of the labelling of drugs with stable isotopes in clinical pharmacology in children].

There are only few studies available in the literature, using drugs labelled with stable isotopes in pediatric clinical pharmacology. However, the stable isotope methods are of great potential interest. These sensitive methods allow to quantitate drugs in small volumes of biological fluid with great specificity. They are innocuous and allow in vivo drug metabolic studies. Using 1-3 15N, 2 13C labelled theophylline, it has been possible to demonstrate N7-theophylline methylation into caffeine in premature neonates while this metabolic pathway is virtually not existent in adults. Stable isotope techniques allow to study intraindividual changes in kinetic parameters of drugs during maintenance therapy without discontinuing the drug. For instance, auto-induction of carbamazepine metabolism was demonstrated in children using stable isotope-labelled carbamazepine in serial pharmacokinetic studies during maintenance therapy. They also make bioavailability studies possible in children. These methods make possible new non invasive studies like CO2 breath test. Using 1-3-7 13C-caffeine we demonstrated the feasibility of the CO2 breath test in young infants and described the maturation of the N-demethylation pathway for caffeine. The correlation between the rate of 13C-CO2 elimination and caffeine plasma clearance indicates that the CO2 breath test is a non invasive method useful for measuring caffeine N-demethylation and that this test might theoretically be used for monitoring caffeine treatment.

Child↗

PubMed1988

Nucleotide sequence of a cDNA for the dihydrolipoamide acetyltransferase component of human pyruvate dehydrogenase complex.

Deoxynucleotide sequencing of a cDNA for the dihydrolipoamide acetyltransferase (PDC-E2) component of human pyruvate dehydrogenase complex (PDC) revealed an open reading frame of 1848 base pairs corresponding to a leader sequence of 54 amino acids and a mature protein of 561 amino acids (59,551 Da). Both an amino-terminal lipoyl-bearing domain and a carboxy-terminal catalytic domain are present in the deduced amino acid sequence. The lipoyl-bearing domain contains two repeating units of 127 amino acids, each harboring one lipoic acid-binding lysine. Thus, mammalian PDC-E2 differs as to the number of lipoic acid-binding sites from other dihydrolipoamide acyltransferases in both prokaryotic and eukaryotic organisms.

Acetyltransferases↗

PubMed1988

Induction of dihydrolipoamide dehydrogenase in 3T3-L1 cells during differentiation.

The activity and turnover of dihydrolipoamide dehydrogenase (E3), the common component of the three 2-oxoacid dehydrogenase complexes, were measured during the differentiation of 3T3-L1 preadipocytes into 3T3-L1 adipocytes. The specific activity of E3 increased approx. 3-4-fold in 3T3-L1 adipocytes differentiated under a regimen of insulin, dexamethasone and 3-isobutyl-1-methylxanthine for 48 h, followed by insulin alone thereafter. A rabbit antibody to pig heart E3 quantitatively precipitated the enzyme from 3T3-L1 adipocytes. By using immunoprecipitation and gel electrophoresis, a 3.3-fold increase was observed in E3 protein in 3T3-L1 adipocytes as compared with 3T3-L1 preadipocytes, on a DNA basis. Pulse-labelling experiments with L-[35S]methionine revealed a 3.5-fold increase in the rate of synthesis of E3 in 3T3-L1 adipocytes compared with that observed in 3T3-L1 preadipocytes. In contrast, the apparent half-lives of the E3 in 3T3-L1 preadipocytes (43 h) and 3T3-L1 adipocytes (33 h) were not significantly different. Therefore, the 3-4-fold increase in the specific activity of E3 in 3T3-L1 adipocytes resulted from an increased rate of synthesis of the enzyme.

Adipose Tissue↗

PubMed1988

Maturation of caffeine metabolic pathways in infancy.

The maturation of the different pathways of caffeine metabolism was studied during infancy. The group of children (n = 14) consisted of four premature newborn infants and 10 older infants who received caffeine citrate solution. Caffeine and 11 of its metabolites were measured by HPLC. Total demethylation and N3- and N7-demethylation increase exponentially with postnatal age; the plateau is reached by 120 days and accounts for 58.6%, 90.5%, and 79.3%, respectively. N1-demethylation shows no variation with postnatal age. It is suggested that N3-demethylation is more important in young infants than in adults and that maturation of N1-demethylation occurs later than 19 months of age. 8-Hydroxylation is mature as early as 1 month of age and may be higher in infants than in adults. Acetylation is not mature before at least 1 year of age. Differences in maturation rate of acetylation may be related in part to genetic acetylator status.

Acetylation↗

PubMed1988

Heterogeneous expression of protein and mRNA in pyruvate dehydrogenase deficiency.

Deficiency of pyruvate dehydrogenase [pyruvate:lipoamide 2-oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1], the first component of the pyruvate dehydrogenase complex, is associated with lactic acidosis and central nervous system dysfunction. Using both specific antibodies to pyruvate dehydrogenase and cDNAs coding for its two alpha and beta subunits, we characterized pyruvate dehydrogenase deficiency in 11 patients. Three different patterns were found on immunologic and RNA blot analyses. (i) Seven patients had immunologically detectable crossreactive material for the alpha and beta proteins of pyruvate dehydrogenase. (ii) Two patients had no detectable crossreactive protein for either the alpha or beta subunit but had normal amounts of mRNA for both alpha and beta subunits. (iii) The remaining two patients also had no detectable crossreactive protein but had diminished amounts of mRNA for the alpha subunit of pyruvate dehydrogenase only. These results indicate that loss of pyruvate dehydrogenase activity may be associated with either absent or catalytically inactive proteins, and in those cases in which this enzyme is absent, mRNA for one of the subunits may also be missing. When mRNA for one of the subunits is lacking, both protein subunits are absent, suggesting that a mutation affecting the expression of one of the subunit proteins causes the remaining uncomplexed subunit to be unstable. The results show that several different mutations account for the molecular heterogeneity of pyruvate dehydrogenase deficiency.

Acidosis, Lactic↗

PubMed1988

Cloning and cDNA sequence of the dihydrolipoamide dehydrogenase component human alpha-ketoacid dehydrogenase complexes.

cDNA clones comprising the entire coding region for human dihydrolipoamide dehydrogenase (dihydrolipoamide:NAD+ oxidoreductase, EC 1.8.1.4) have been isolated from a human liver cDNA library. The cDNA sequence of the largest clone consisted of 2082 base pairs and contained a 1527-base open reading frame that encodes a precursor dihydrolipoamide dehydrogenase of 509 amino acid residues. The first 35-amino acid residues of the open reading frame probably correspond to a typical mitochondrial import leader sequence. The predicted amino acid sequence of the mature protein, starting at the residue number 36 of the open reading frame, is almost identical (greater than 98% homology) with the known partial amino acid sequence of the pig heart dihydrolipoamide dehydrogenase. The cDNA clone also contains a 3' untranslated region of 505 bases with an unusual polyadenylylation signal (TATAAA) and a short poly(A) track. By blot-hybridization analysis with the cDNA as probe, two mRNAs, 2.2 and 2.4 kilobases in size, have been detected in human tissues and fibroblasts, whereas only one mRNA (2.4 kilobases) was detected in rat tissues.

Amino Acid Sequence↗

PubMed1988

Gentamicin monitoring in neonates.

The elimination of gentamicin (G) was studied in 103 neonates (30 premature) during the first month of life after 2.5 mg/kg i.v. (as infusion) over 20-30 min. G plasma levels, measured by EMIT assay, were obtained before and at 1, 2, 3, and 6 h after infusion. We derived individual first-order kinetic parameters and designed optimal dose regimens. G plasma clearance, half-life, and recommended dose (mg/kg/h) changed exponentially with postnatal age during the first 14 days of life. No significant changes in kinetic values were noted during the first 3 days of life; however, they varied linearly with gestational age when they were measured during this period. Apgar score at 10 min and blood urea nitrogen significantly influenced the same parameters. The predictive value of a designed dose regimen was evaluated at steady-state, after dosage adjustment using two plasma concentration values: the minimum plasma concentration was below 2 mg/L in 93% of the patients; the plasma concentration observed within 1 h after completion of the infusion was (mean +/- SD) 5.33 +/- 0.97 mg/L. Our data suggest that 2.5 mg/kg every 12 h is appropriate in most neonates except for 0-2-day-old premature infants who require 2.5 mg/kg every 18 h. Monitoring of G plasma levels is advisable in infants with low Apgar score and/or renal failure.

Age Factors↗

PubMed1988

Developmental changes of caffeine elimination in infancy.

Five neonates (4 premature) and 16 infants (6 prematurely born), 15-588 days old, received caffeine as citrate salt for apnea. Plasma samples were collected 0, 2, 4, 6 h after a dose and before the next scheduled one. Patients 8 and 9 were serially studied. Caffeine plasma concentrations were determined using HPLC. The caffeine elimination half-life and clearance varied linearly with gestational age and exponentially with postnatal age, the plateau being reached during the second trimester of life. Dose regimen guidelines as a function of postnatal age were derived from individually calculated doses and dosing intervals in order to achieve, at steady state, a caffeine mean plasma concentration of 11 mg/l with a minimum of 7.5 mg/l and a maximum of 14.5 mg/l. We suggest dosing intervals for infants before 1 month, 1-2 months, 2-4 months and after 4 months to be equal to 24, 12, 8 and 6 h, respectively. The individual recommended dose varies from 2 to 10 mg/kg (as caffeine base) making caffeine monitoring mandatory in infants.

Aging↗

PubMed1988

Maturation of caffeine N-demethylation in infancy: a study using the 13CO2 breath test.

Four premature neonates and eight infants 1-19 months old received caffeine for apnea. The usual morning oral dose was substituted by 1,3,7 13C-trimethylxanthine (13C-tri CAF) as the citrate salt. Five breath samples were collected the day before (day 1) and the day of 13C-tri CAF administration (day 2). Plasma (after each breath collection) and urine were collected on day 2. 13C-CO2 exhalation was determined by isotope ratio mass spectrometry. Caffeine and its metabolites were measured using high-pressure liquid chromatography. Assessment of the labeled CO2 in the breath revealed no detectable 13C-tri CAF N-demethylation activity in infants before 45 wk postconceptional age. However, demethylation (as urinary metabolites) has been detected before that age. Two-, 4-, and 6-h cumulative excretion of 13C-tri CAF as 13C-CO2 increased with postnatal age and correlated with caffeine plasma clearance (r = 0.840, p less than 0.01). These results were consistent with those obtained for urinary metabolites. In one infant (19 months old) the cumulative excretion of 13C-CO2 while crying was 65% of the value observed during quiet breathing. The measurement of caffeine demethylation using the caffeine CO2 breath test is feasible in infants and is a safe and noninvasive method to determine age related changes in P4501-dependent N-demethylase activity.

Apnea↗

PubMed1987

Rat liver mitochondria contain two immunologically distinct dihydrolipoamide dehydrogenases.

We have raised antisera against dihydrolipoamide dehydrogenase. One antigen was isolated from purified bovine kidney pyruvate dehydrogenase complex (PDC). The other antigen was a commercial preparation of porcine heart dihydrolipoamide dehydrogenase (E3) which did not first involve purification of the alpha-keto acid dehydrogenase complex(es). Both antibody preparations cross-reacted with the E3 components of PDC, alpha-ketoglutarate dehydrogenase complex, and branched-chain keto acid dehydrogenase complex. This demonstrates the immunological identity of the E3 components. These sera totally precipitated E3 activity from the purified complexes, from purified preparations of E3, and from extracts of rat heart and kidney mitochondria. The two sera vary in their reaction with rat liver mitochondrial extracts: the anti PDC-E3 serum left residual E3 activity (approximately 50% of the original) that was precipitable by the anti-E3 anti-serum. This indicates that liver contains two immunologically distinct forms of E3. Metabolic assays measuring the differential effects of the two sera on the glycine decarboxylation reaction suggest that the form which is immunologically nonreactive with the anti-PDC-E3 serum could represent the E3 involved in the glycine cleavage system.

Animals↗

PubMed1987

Isolation of a cDNA clone for the dihydrolipoamide acetyltransferase component of the human liver pyruvate dehydrogenase complex.

Dihydrolipoamide acetyltransferase (E2) forms the structural core of pyruvate dehydrogenase complex. A cDNA clone (lambda E2-1) for mammalian E2 was identified from a human liver lambda gt11 library using anti-E2 serum. Affinity-selected antibodies using the fusion protein from lambda E2-1 immuno-reacted specifically with E2 of purified pyruvate dehydrogenase complex on immuno-blot analysis. The cDNA insert was approximately 2.3 kb in length with an internal EcoR1 site generating 1.4 and 0.9 kb fragments. A synthetic 17-mer oligodeoxynucleotide mixture based on the amino acid sequence surrounding the lipoic acid-containing lysine residue in bovine kidney E2 hybridized with the 2.3 kb cDNA insert and the 1.4 kb fragment.

Acetyltransferases↗