Biomedical subjects

P Baumann

Publications and source records attributed to P Baumann.

At least 19 recordsLinked to original sources

PubMed1996

Human Rad51 protein promotes ATP-dependent homologous pairing and strand transfer reactions in vitro.

The human testis Rad51 protein, a structural homolog of E. coli RecA, binds single- and double-stranded DNA and exhibits DNA-dependent ATPase activity. Using circular ssDNA and linear dsDNA (3.0 kb in length), we demonstrate that hRad51 promotes homologous pairing and strand exchange reactions in vitro. Joint molecule formation was dependent upon ATP hydrolysis and DNA homology and was stimulated by the single-strand DNA-binding protein RP-A. In these reactions, the 5' terminus of the complementary strand of the linear duplex was efficiently transferred to the ssDNA. However, under standard conditions, extensive strand exchange was not observed. These results establish hRad51 as a functional homolog of RecA, but indicate that the human protein and its bacterial counterpart differ in their ability to promote extensive strand transfer. It is proposed that hRad51 mediates homology recognition and initiates strand exchange, but that extensive heteroduplex formation in higher organisms requires the actions of additional proteins.

Adenosine Triphosphate↗

PubMed1996

Analytical methods for the quantitative determination of selective serotonin reuptake inhibitors for therapeutic drug monitoring purposes in patients.

Five selective serotonin reuptake inhibitors (SSRIs) have been introduced recently: citalopram, fluoxetine, fluvoxamine, paroxetine and sertraline. Although no therapeutic window has been defined for SSRIs, in contrast to tricyclic antidepressants, analytical methods for therapeutic drug monitoring of SSRIs are useful in several instances. SSRIs differ widely in their chemical structure and in their metabolism. The fact that some of them have N-demethylated metabolites, which are also SSRIs, requires that methods be available which allow therapeutic drug monitoring of the parent compounds and of these active metabolites. most procedures are based on prepurification of the SSRIs by liquid-liquid extraction before they are submitted to separation by chromatographic procedures (high-performance liquid chromatography, gas chromatography, thin layer chromatography) and detection by various detectors (UV, fluorescence, electrochemical detector, nitrogen-phosphorus detector, mass spectrometry). This literature review shows that most methods allow quantitative determination of SSRIs in plasma, in the lower ng/ml range, and that they are, therefore, suitable for therapeutic drug monitoring purposes of this category of drugs.

1-Naphthylamine↗

PubMed1996

Simultaneous determination of plasma levels of fluvoxamine and of the enantiomers of fluoxetine and norfluoxetine by gas chromatography-mass spectrometry.

A gas chromatographic-mass spectrometric method is presented which allows the simultaneous determination of the plasma concentrations of fluvoxamine and of the enantiomers of fluoxetine and norfluoxetine after derivatization with the chiral reagent, (S)-(-)-N-trifluoroacetylprolyl chloride. No interference was observed from endogenous compounds following the extraction of plasma samples from six different human subjects. The standard curves were linear over a working range of 10 to 750 ng/ml for racemic fluoxetine and norfluoxetine and of 50 to 500 ng/ml for fluvoxamine. Recoveries ranged from 50 to 66% for the three compounds. Intra- and inter-day coefficients of variation ranged from 4 to 10% for fluvoxamine and from 4 to 13% for fluoxetine and norfluoxetine. The limits of quantitation of the method were found to be 2 ng/ml for fluvoxamine and 1 ng/ml for the (R)- and (S)-enantiomers of fluoxetine and norfluoxetine, hence allowing its use for single dose pharmacokinetics. Finally, by using a steeper gradient of temperature, much shorter analysis times are obtained if one is interested in the concentrations of fluvoxamine alone.

Fluoxetine↗

PubMed1996

An archaebacterial homologue of the essential eubacterial cell division protein FtsZ.

Life falls into three fundamental domains--Archaea, Bacteria, and Eucarya (formerly archaebacteria, eubacteria, and eukaryotes,. respectively). Though Archaea lack nuclei and share many morphological features with Bacteria, molecular analyses, principally of the transcription and translation machineries, have suggested that Archaea are more related to Eucarya than to Bacteria. Currently, little is known about the archaeal cell division apparatus. In Bacteria, a crucial component of the cell division machinery is FtsZ, a GTPase that localizes to a ring at the site of septation. Interestingly, FtsZ is distantly related in sequence to eukaryotic tubulins, which also interact with GTP and are components of the eukaryotic cell cytoskeleton. By screening for the ability to bind radiolabeled nucleotides, we have identified a protein of the hyperthermophilic archaeon Pyrococcus woesei that interacts tightly and specifically with GTP. Furthermore, through screening an expression library of P. woesei genomic DNA, we have cloned the gene encoding this protein. Sequence comparisons reveal that the P. woesei GTP-binding protein is strikingly related in sequence to eubacterial FtsZ and is marginally more similar to eukaryotic tubulins than are bacterial FtsZ proteins. Phylogenetic analyses reinforce the notion that there is an evolutionary linkage between FtsZ and tubulins. These findings suggest that the archaeal cell division apparatus may be fundamentally similar to that of Bacteria and lead us to consider the evolutionary relationships between Archaea, Bacteria, and Eucarya.

Amino Acid Sequence↗

PubMed1996

Activity of 2-azaspiro[4.5]decane-6-carboxylates as GABA-uptake inhibitors.

Novel GABA analogous spirocyclic amino acid esters 7a-d and 8a-d were prepared and investigated for interaction with GABA-A and GABA-B receptors as well as the GABA uptake system. Starting from known bromoethyl lactones 1 or 2 and arylalkylamines spirocyclic hydroxyalkyl lactams 3a-d and 4a-d were obtained and reduced by LiAlH4 to yield spirocyclic hydroxymethyl pyrrolidines 5a-d and 6a-d. Oxidation by Jones reagent followed by subsequent esterification gave the title compounds 7a-d and 8a-d which represent conformationally restricted analogues of GABA. Whereas the new spirocyclic amino acid esters 7a-d and 8a-d showed no activity at GABA receptors they proved to be active as GABA uptake inhibitors. An examination of the relationship between structure and GABA uptake inhibition revealed a strong dependence of activity upon the length of the alkyl chain in N-arylalkyl substituents and upon the ring size of underlying spirocyclic system.

Animals↗

PubMed1996

The tryptophan biosynthetic pathway of aphid endosymbionts (Buchnera): genetics and evolution of plasmid-associated anthranilate synthase (trpEG) within the aphididae.

The bacterial endosymbionts (Buchnera) from the aphids Rhopalosiphum padi, R. maidis, Schizaphis graminum, and Acyrthosiphon pisum contain the genes for anthranilate synthase (trpEG) on plasmids made up of one or more 3.6-kb units. Anthranilate synthase is the first as well as the rate-limiting enzyme in the tryptophan biosynthetic pathway. The amplification of trpEG on plasmids may result in an increase of enzyme protein and overproduction of this essential amino acid, which is required by the aphid host. The nucleotide sequence of trpEG from endosymbionts of different species of aphids is highly conserved, as is an approximately 500-bp upstream DNA segment which has the characteristics of an origin of replication. Phylogenetic analyses were performed using trpE and trpG from the endosymbionts of these four aphids as well as from the endosymbiont of Schlechtendalia chinensis, in which trpEG occurs on the chromosome. The resulting phylogeny was congruent with trees derived from sequences of two chromosome-located bacterial genes (part of trpB and 16S ribosomal DNA). In turn, trees obtained from plasmid-borne and bacterial chromosome-borne sequences were congruent with the tree resulting from phylogenetic analysis of three aphid mitochondrial regions (portions of the small and large ribosomal DNA subunits, as well as cytochrome oxidase II). Congruence of trees based on genes from host mitochondria and from bacteria adds to previous support for exclusively vertical transmission of the endosymbionts within aphid lineages. Congruence with trees based on plasmid-borne genes supports the origin of the plasmid-borne trpEG from the chromosomal genes of the same lineage and the absence of subsequent plasmid exchange among endosymbionts of different species of aphids.

Amino Acid Sequence↗

PubMed1996

Non-response to citalopram in depressive patients: pharmacokinetic and clinical consequences of a fluvoxamine augmentation.

The effect of comedication with fluvoxamine on the plasma concentrations of the enantiomers of citalopram and its metabolites in dextromethorphan/mephenytoin phenotyped patients pretreated with citalopram (CIT) was studied: seven female patients (45.1 +/- 13.9 years) suffering from a major depressive episode [ICD-10: F32.2 (n = 3 patients), F33.2 (n = 2), F32.10 (n = 1) or F32.11 (n = 1)], who were non-responders to a 3-week treatment with 40 mg/day CIT (From day-21 to day 0) (day 0: MADRS score > or = 12), were co-medicated for another 3 weeks with fluvoxamine (50 mg/day from day 1-7, 100 mg/day from day 14-21). All patients were extensive metabolizers of mephenytoin (CYP2C19) and dextromethorphan (CYP2D6), except one patient, who had a genetic deficiency of CYP2D6. There was a significant increase of the plasma concentrations of S- and R-citalopram from day 0 (27 +/- 14 micrograms/l and 55 +/- 23 micrograms/l, respectively) to day 21 (83 +/- 38 micrograms/l and 98 +/- 44 micrograms/l, respectively), after addition of fluvoxamine (P < 0.02, for each comparison), and the mean ratio S/R-citalopram increased from 0.48 to 0.84. S-Citalopram inhibits more potently 5-HT uptake than R-citalopram: therefore, fluvoxamine increases the pharmacologically more active S-citalopram with some stereoselectivity. According to a previous in vitro study, this pharmacokinetic interaction occurs on the level of CYP2C19, but also of CYP2D6 and CYP3A4 which, in contrast to CYP1A2, contribute to the N-demethylation of citalopram and which are stereoselectively inhibited by fluvoxamine. All but one patient showed clinical improvement by a decrease of the MADRS score by at least 50% and a final score < or = 13 (mean +/- SD: day 0:30.6 +/- 9.2; day 21:11.0 +/- 6.5). Some patients showed minor symptoms, such as nausea and tremor, but the combined treatment was generally well tolerated.

Adult↗

PubMed1996

Replacement of (R)-methadone by a double dose of (R,S)-methadone in addicts: interindividual variability of the (R)/(S) ratios and evidence of adaptive changes in methadone pharmacokinetics.

METHODS: Twenty-two patients receiving (R)-methadone maintenance treatment were switched to a double dose of (R,S)-methadone: blood samples were collected before and after the change, and the concentrations of the enantiomers were measured. In the second period, during racemic methadone treatment, important interindividual variability in the stereoselective disposition of the enantiomers of methadone was measured, with (R)/(S) ratios ranging from 0.63 to 2.40. This point should be taken into account particularly with respect to therapeutic drug monitoring of racemic methadone. RESULTS: A significant decrease P < 0.005 in the mean serum concentration/dose ratios of the active (R)-enantiomer before and after the change was measured (mean 3.97 and 3.33). CONCLUSION: Although of small amplitude (16%), this decrease confirms previously described adaptive changes in methadone pharmacokinetics during racemic methadone maintenance treatment and may necessitate, in some patients, a dose adjustment.

Adult↗

PubMed1996

Ribosomal protein S1 (RpsA) of Buchnera aphidicola, the endosymbiont of aphids: characterization of the gene and detection of the product.

Buchnera aphidicola is a prokaryotic endosymbiont found in specialized cells of the aphid Schizaphis graminum. Many of the previously cloned B. aphidicola genes are preceded by a poor ribosome-binding site. Ribosomal protein S1 (RpsA) allows the translation of messenger RNAs that lack or have a poor ribosome binding site. We have cloned and sequenced a 4.5-kilobase (kb) B. aphidicola DNA fragment containing four open reading frames corresponding to aroA-rpsA-himD-tpiA. The deduced amino acid sequence of B. aphidicola RpsA was 75% identical to that of the Escherichia coli protein. The major difference was in the number of basic amino acids, which were present in higher numbers in B. aphidicola RpsA. Antiserum to E. coli RpsA was prepared and used to detect B. aphidicola RpsA in cell-free extracts of aphids. During the first 12 days of aphid growth there is a slight decrease in the amount of RpsA per unit of aphid weight. The three additional genes found on the 4.5-kb DNA fragment encoded for proteins involved in aromatic amino acid biosynthesis (aroA), DNA bending (himD), and carbohydrate metabolism (tpiA). The presence of these genes in B. aphidicola is additional evidence of its similarity to free-living bacteria.

Amino Acid Sequence↗

PubMed1996

Neuroendocrine effects of a 20-mg citalopram infusion in healthy males. A placebo-controlled evaluation of citalopram as 5-HT function probe.

Pharmacokinetic measurements, neuroendocrine responses, and side effects profiles of intravenous infusions of 20 mg citalopram over 30 minutes during the early afternoon have been studied. Eight healthy male volunteers were enrolled in a placebo- (saline) controlled, single-blind, cross-over protocol. Plasma concentrations of the parent compound showed a double exponential decay. Demethyl and didemethyl metabolites were not detectable, but low concentrations of the propionic acid derivative of citalopram were found. Determination of the citalopram enantiomers yielded a balanced S(+)/R(-) ratio of 0.9 to 1.2. The endocrine response to the drug was characterized by significant increases in plasma prolactin and cortisol. Except for one subject, who developed pronounced side effects, human growth hormone showed a surge following saline that was inhibited following citalopram. Rectal temperature and heart rate were not affected and tolerability was favorable. Because of citalopram's extremely high selectivity for the presynaptic 5-hydroxytryptamine nerve terminals, the present data suggest that it might be a promising tool for the investigation of serotonergic function in the human brain in vivo.

Citalopram↗

PubMed1996

Treatment-resistant schizophrenia: clinical experience with new antipsychotics.

Approximately 20-30% of patients with schizophrenia are resistant to conventional neuroleptics (i.e. are treatment-resistant). Clozapine has been shown to be effective in a proportion of treatment-resistant cases and to have a low side effect profile. However, it can cause agranulocytosis, is sedative and has marked anticholinergic properties. Risperidone, which is effective in chronic schizophrenia and has a low side effect profile and does not require routine blood monitoring, was compared with clozapine in a double-blind comparative study in 86 treatment-resistant patients. Preliminary findings indicate that, at endpoint, risperidone and clozapine were almost equieffective (total PANSS, PANSS subscales and CGI). Both drugs caused few adverse effects, and the severity of extrapyramidal symptoms was no different in the two groups. It is concluded that risperidone could be another drug effective in treatment-resistant schizophrenia. Further, larger trials will be needed to confirm this.

Clozapine↗

PubMed1996

Plasma levels of the enantiomers of thioridazine, thioridazine 2-sulfoxide, thioridazine 2-sulfone, and thioridazine 5-sulfoxide in poor and extensive metabolizers of dextromethorphan and mephenytoin.

Concentrations of total (R) + (S) and of the enantiomers (R) and (S) of thioridazine and metabolites were measured in 21 patients who were receiving 100 mg thioridazine for 14 days and who were comedicated with moclobemide (450 mg/day). Two patients were poor metabolizers of dextromethorphan and one was a poor metabolizer of mephenytoin. Cytochrome P450IID6 (CYP2D6) is involved in the formation of thioridazine 2-sulfoxide (2-SO) from thioridazine and also probably partially in the formation of thioridazine 5-sulfoxide (5-SO), but not in the formation of thioridazine 2-sulfone (2-SO2) from thioridazine 2-SO. Significant correlations between the mephenytoin enantiomeric ratio and concentrations of thioridazine and metabolites suggest that cytochrome P450IIC19 could contribute to the biotransformation of thioridazine into yet-unknown metabolites, other than thioridazine 2-SO, thioridazine 2-SO2, or thioridazine 5-SO. An enantioselectivity and a large interindividual variability in the metabolism of thioridazine have been shown: measured (R)/(S) ratios of thioridazine, thioridazine 2-SO fast eluting (FE), thioridazine 2-SO slow eluting (SE), thioridazine 2-SO (FE+SE), thioridazine 2-SO2, thioridazine 5-SO(FE), and thioridazine 5-SO(SE) were (mean +/- SD) 3.48 +/- 0 .93 (range, 2.30 to 5.80), 0.45 +/- 0.22 (range, 0.21 to 1.20), 2.27 +/- 8.1 (range, 6.1 to 40.1), 4.64 +/- 0.68 (range, 2.85 to 5.70), 3.26 +/- 0.58 (range, 2.30 to 4.30), 0.049 +/- 0.019 (range, (0.021 to 0.087), and 67.2 +/- 66.2 (range, 16.8 to 248), respectively. CYP2D6 is apparently involved in the formation of (S)-thioridazine 2-SO(FE), (R)-thioridazine 2-SO(SE), and also probably (S)-thioridazine 5-SO(FE) and (R)-thioridazine 5-SO(SE).

Adult↗

PubMed1996

Pharmacokinetic fluvoxamine-clomipramine interaction with favorable therapeutic consequences in therapy-resistant depressive patient.

We describe the case of a depressive patient who was a rapid metabolizer of CYP2D6 substrates and a heavy smoker, and who did not respond to several courses of treatment with antidepressants, as a result of unusually low drug-plasma levels. During hospitalization, he did not improve after treatment with clomipramine (150-225 mg/day during three weeks), but showed a response within four days after addition of fluvoxamine (100 mg/day). Plasma levels of clomipramine and desmethylclomipramine changed from 58 ng/ml and 87 ng/ml to 223 ng/ml and 49 ng/ml respectively one week after addition of fluvoxamine. Present knowledge of the role of cytochrome P-450 isozymes, such as CYP1A2, CYP2C19, CYP2D6, and CYP3A4, in the metabolism of psychotropic drugs as well as therapeutic drug-plasma level monitoring may thus help to determine individual treatment.

Antidepressive Agents, Second-Generation↗

PubMed1996

Therapeutic suggestion has not effect on postoperative morphine requirements.

This study was designed to confirm the effect of therapeutic intraoperative auditory suggestion on recovery from anesthesia, to establish the effect of preoperative suggestion, and to assess implicit memory for intraoperative information using an indirect memory task. Sixty consenting unpremedicated patients scheduled for elective gynecologic surgery were randomly divided into three equal groups: Group 1 received a tape of therapeutic suggestions preoperatively, and the story of Robinson Crusoe intraoperatively; Group 2 heard the story of Peter Pan preoperatively and therapeutic suggestions intraoperatively; Group 3 heard the Crusoe story preoperatively and the Peter Pan story intraoperatively. A standardized anesthetic technique was used with fentanyl, propofol, isoflurane, and nitrous oxide. After surgery, all patients received patient-controlled analgesia (PCA) with a standardized regimen. In the 24 h postsurgery, morphine use was recorded every 6 h and at 24 h an indirect memory test (free association) was used to test for memory of the stories. Anxiety scores were measured before surgery and at 6 and 24 h postsurgery. There were no significant differences between groups for postoperative morphine use, pain or nausea scores, anxiety scores, or days spent in hospital after surgery. Seven of 20 patients who heard the Pan story intraoperative gave a positive association with the word "Hook," whereas 2 of 20 who did not hear the story gave such an association. Indirect memory for the Pan story was established using confidence interval (CI) analysis. (The 95% CI for difference in proportion did not include zero). No indirect memory for the Crusoe story could be demonstrated. This study did not confirm previous work which suggested that positive therapeutic auditory suggestions, played intraoperatively, reduced PCA morphine requirements. In contrast, a positive implicit memory effect was found for a story presented intraoperatively.

Adult↗

PubMed1996

A double-blind, placebo-controlled study of citalopram with and without lithium in the treatment of therapy-resistant depressive patients: a clinical, pharmacokinetic, and pharmacogenetic investigation.

Sixty-nine depressive patients (DSM III criteria: 296.2, 296.3, 296.5, 300.4) were treated with 40 to 60 mg citalopram (CIT) daily for 4 weeks. Among them, 45 responded to treatment (improvement > 50% on the 21-item Hamilton Rating Scale for Depression [HAM-D]) and continued their treatment for another week before being released from the study. The 24 nonresponders were randomized and comedicated under double-blind conditions with lithium carbonate (Li) (2 x 400 mg/day) (CIT-Li group) or with placebo (CIT-Pl group) from days 29 to 35. For days 36 to 42, the patients of both subgroups were treated openly with Li (800 mg/day) in addition to the ongoing CIT treatment. On day 35, 6 of 10 patients responded to the CIT-Li combination, whereas 2 of 14 patients only responded to the CIT-Pl combination. This group difference reached significance (p < 0.05) on day 35 with lower HAM-D total scores in the CIT-Li group. No evidence was seen of a pharmacokinetic interaction between CIT and Li, and this combination was well tolerated. Patients were phenotyped with dextromethorphan and mephenytoin at baseline and at day 28. As evaluated at baseline, three patients (responders) were poor metabolizers of dextromethorphan and six patients (three responders and three nonresponders) of mephenytoin. On day 28, the ratio CIT/N-desmethylCIT (DCIT) in plasma was significantly higher in poor than in extensive metabolizers of mephenytoin (p = 0.0001), and there was a significant positive correlation between the metabolic ratio of dextromethorphan and the ratio DCIT/N-didesmethylCIT in plasma (p < 0.001). These findings illustrate the role of CYP2D6 and CYP2C19 in the metabolism of CIT. It can be concluded that Li addition to CIT is effective in patients not responding to CIT alone without any evidence of an accentuation or provocation of adverse events.

Adult↗

PubMed1996

Pharmacology and pharmacokinetics of citalopram and other SSRIs.

Citalopram together with fluoxetine, fluvoxamine, paroxetine and sertraline belong to the group of SSRIs, so named because of their pharmacological action as selective serotonin reuptake inhibitors in rat brain synaptosomes-their potency of inhibiting noradrenaline uptake is low and, from a clinical point of view, irrelevant. In contrast to classical tricyclic antidepressants and some antipsychotics, the SSRIs have little affinity for the dopamine D2 receptors, 5-HT1A and 5-HT2A receptors, alpha 1-receptors, beta-receptors, muscarinic receptors and histamine H1 receptors. Several authors have examined whether SSRIs are ligands of other receptors, including the 5-HT3-5-HT7 receptors and their subtypes, and the NMDA receptor, and whether chronic treatment with SSRIs modifies the affinity and binding capacity of these receptors. The SSRIs differ by their pharmacokinetics and pharmacogenetics of metabolism and by their cytochrome P450 isozyme inhibition properties. Some situations are presented in which plasma level monitoring of SSRIs is recommended, despite the lack of clearly defined "therapeutic windows'.

Animals↗

PubMed1996

Fluoxetine addition to methadone in addicts: pharmacokinetic aspects.

We report nine cases where fluoxetine (FX) (20 mg/day) was added to maintenance treatment with methadone (MTD) (dose range: 30-100 mg) in addicts with affective disorders. MTD plasma levels were measured before and after treatment with FX under steady-state conditions. Among the nine patients, two also received fluvoxamine (FLVX) at different times. Although it is possible that in some patients a moderate FX-MTD interaction occurs, resulting in increased plasma levels of MTD, this interaction is certainly less marked than that between FLVX and MTD and unlikely to have clinical consequences.

Adult↗

PubMed1996

The endosymbiont (Buchnera sp.) of the aphid Diuraphis noxia contains plasmids consisting of trpEG and tandem repeats of trpEG pseudogenes.

Most aphids are dependent for their survival on prokaryotic endosymbionts assigned to the genus Buchnera. Among the functions of Buchnera species is the synthesis of tryptophan, which is required by the aphid host. In Buchnera species from the aphid Diuraphis noxia, the genes for anthranilate synthase (trpEG) were found on a plasmid which consisted of seven tandem repeats of a 3.2-kb unit and one 2.6-kb unit which differed in containing a 0.6-kb deletion. One of the 3.2-kb units contained open reading frames corresponding to trpEG; the remaining units contained trpEG pseudogenes (psi). The nucleotide sequence upstream of trpE contained a region that has characteristics of an origin of replication (ori). Relative to trpB (a chromosomal gene), there were about two copies of the trpEG-containing plasmid. Comparisons of the nucleotide sequences of the 3.2-kb units containing trpEG and psi trpEG indicated that most changes occurred in a 700-nucleotide segment that included the region upstream of trpE and the portion of this gene coding for the N terminus. The consequence of these changes was the silencing of trpEG by inactivation of the putative promoter region and premature termination of the TrpE peptide. In contrast, the nucleotide sequence of the segment corresponding to ori was conserved in the units containing trpEG and psi trpEG. We offer a number of speculations on the evolutionary pressure in this lineage which resulted in the silencing of most of trpEG while still retaining the regions resembling ori.

Animals↗