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G Boss

Publications and source records attributed to G Boss.

9 recordsLinked to original sources
PubMed1998

Stereoselective biotransformation of the selective serotonin reuptake inhibitor citalopram and its demethylated metabolites by monoamine oxidases in human liver.

Citalopram (CIT) is an antidepressive drug of the group of selective serotonin reuptake inhibitors (SSRIs). The tertiary amine CIT is given as a racemic drug, but its pharmacological activity resides mainly in S-CIT. CIT is metabolised by cytochrome P450 (CYP) to N-demethylcitalopram (DCIT) and N-didemethylcitalopram (DDCIT). The citalopram propionic acid derivative (CIT-PROP) is another, but pharmacologically inactive, metabolite, the formation of which has been poorly characterised but is postulated to occur by deamination of CIT, DCIT and/or DDCIT. The aim of the present investigation was to study the formation of the enantiomers of CIT-PROP from CIT and its two N-demethylated metabolites, DCIT and DDCIT, in an in vitro incubation system (microsomal and cytosolic fractions) obtained from human livers. The production of CIT-PROP was measured by a stereospecific HPLC method. Incubation of rac-CIT, rac-DCIT and rac-DDCIT (500 microM each, separately) in the presence (or absence) of NADP showed that CIT-PROP formation was substrate-dependent and essentially NADP-independent. Monoamine oxidases (MAO) type A and B and aldehyde oxidase were identified as the probable enzymes involved in the formation of CIT-PROP from CIT, DCIT and DDCIT. Indeed, the irreversible monoamine oxidase type A inhibitor clorgyline and the irreversible monoamine oxidase type B inhibitor selegiline (both at 0.5 microM in the incubation mixture) inhibited CIT-PROP formation, depending on the substrate, up to 70% and 88%, respectively. The participation of aldehyde oxidase in the subsequent step is suggested by the inhibition caused by menadione (50 microM) in CIT-PROP formation. Preliminary experiments suggest the presence of four unknown metabolites, probably products of deamination, which were detected in plasma and urine samples of patients treated with CIT as well as in in vitro biotransformations. Their presence confirms the importance of deamination in the biotransformation of CIT and its demethylated metabolites, especially in the brain where, in contrast to the liver, the role of cytochrome P450 appears to be low.

Adult↗
PubMed1997

Proliferation of human malignant astrocytomas is dependent on Ras activation.

Overexpression and activation of receptor tyrosine kinases, such as platelet derived growth factor receptors (PDGFRs) and epidermal growth factor receptor (EGFR), leads to proliferation of human malignant astrocytoma cells. Although oncogenic mutations affecting Ras are not prevalent in human malignant astrocytomas, we have investigated whether levels of activated Ras.GTP might be elevated in these tumors secondary to the mitogenic signals originating from activated receptor tyrosine kinases. In support of this hypothesis high levels of Ras.GTP, similar to those found in oncogenic Ras transformed fibroblasts, were present in four established human malignant astrocytoma cell lines which express PDGFRs and EGFR, and 20 operative malignant astrocytoma specimens. Stimulation of PDGFR's and EGFR's induced tyrosine phosphorylation of the Shc adaptor protein and its association with Grb2, suggesting a mechanism by which Ras may be activated in human malignant astrocytoma cells. Furthermore, blocking Ras activation by expression of the Ha-Ras-Asn17 dominant-negative mutant, or by farnesyl transferase inhibitors, decreased in vitro proliferation of the human astrocytoma cell lines. These results support the hypothesis that proliferative signals from receptor tyrosine kinases expressed by human malignant astrocytoma cells utilize the Ras mitogenic pathway. Pharmacological inhibitors of the Ras pathway may therefore be of therapeutic value in these presently terminal tumors.

Alkyl and Aryl Transferases↗
PubMed1996

Ras-GTP levels are elevated in human NF1 peripheral nerve tumors.

Neurofibromin, the gene product of NF1, is a Ras GTPase Activating Protein. The absence of neurofibromin leads to increased levels of Ras-GTP, which contributes to the proliferation of NF1 neurogenic sarcoma cell lines. Whether this pathogenic mechanism is applicable to benign and malignant peripheral nerve tumours from NF1 and non NF1 patients is not known, due to lack of a tissue based assay. We have adapted a colorimetric enzymatic assay for determining levels of Ras bound guanine nucleotides in tissues. Ras-GTP levels were increased in NF1 neurogenic sarcomas (15 times) and benign NF1 neurofibromas (four times), compared to non NF1 schwannomas. Neurofibromin was not expressed in NF1 sarcomas, in support of its important negative Ras regulatory role in the pathogenesis of NF1 peripheral nerve tumors.

Base Sequence↗
PubMed1992

Enzymic hydrolysis of nicotinate esters: comparison between plasma and liver catalysis.

1. The enzymic hydrolysis of a wide series of nicotinic acid esters was investigated using human and rat plasma, and purified hog liver carboxylesterase, and compared with previously published data from rat liver microsomes. Esterase activities were always found to obey Michaelis-Menten kinetics. 2. Rat liver microsomal and plasma enzyme velocities were six orders of magnitude smaller than those of purified hog liver carboxylesterase, and three orders smaller than human plasma activities, but the Km values were of the same magnitude. 3. The binding of nicotinate esters to human plasma esterases, and purified hog liver carboxylesterase, appears to depend mainly on hydrophobic and steric factors.

Animals↗
PubMed1991

Structure-metabolism relationships in the hydrolysis of nicotinate esters by rat liver and brain subcellular fractions.

Rat liver and brain subcellular esterase activities toward nicotinic acid esters were studied, under varying conditions, such as pH, organic solvents, protein concentration, duration of incubation, and substrate concentration. Esterases in each subcellular fraction displayed activities that obey Michaelis-Menten kinetics, although subcellular fractions are heterogeneous. The Km values were of the same magnitude, and the Vmax values were lower in microsomes than in cytosol of the liver. Brain activities normalized to protein concentration, were much lower than liver activities, aromatic nicotinates being the best substrates in both tissues. Myelin and brain mitochondria of nerve-ending and neuroglial origin display esterase activity toward phenyl nicotinate. In contrast to brain esterases, liver esterases appear homogeneous, and esterase activities in both tissues react differently to changes in pH. Qualitative and quantitative structure-metabolism relationships are not suggestive of tissue-specific ester hydrolysis.

Animals↗
PubMed1990

Inotropic interventions during myocardial "stunning" in the pig.

To study the effects of inotropic interventions on myocardial "stunning," we subjected pigs to 12 minutes of left anterior descendents (LAD) coronary artery occlusion followed by 2 hours of reperfusion. Measurements were made of segmental shortening (SS%), myocardial blood flow (MBF), adenine nucleotides, the extent of ultrastructural damage, and granulocyte accumulation. Three groups of pigs were compared: control (CON) (N = 6), isoproterenol infused (ISO) (N = 6), and pretreated with triiodothyronine (T3) (30 micrograms/kg ip) (N = 5). Inotropic reserve was tested with a bolus of Ca++. During reperfusion, SS% in the CON reperfused segments showed a relatively constant decrement of 75% throughout the reperfusion period but no alteration in the inotropic reserve. In the ISO group, SS% was maintained at preocclusion levels, but there was a small but significant decrease in the inotropic reserve. In the T3 group, SS% was reduced more than 90% and showed no response to the Ca++. Myocardial blood flow was maintained at control levels in the CON and ISO groups during reperfusion but was greatly reduced in the T3 group. The ATP was reduced 36% in CON, 39% in ISO, and further reduced to 87% of control in the T3 group. Mitochondrial damage in the CON and ISO groups was 5 and 10%, respectively, and reversible, but there was 86% irreversible damaged mitochondria in the T3 group. Using a monoclonal antibody against pig granulocytes, the presence and quantitation of adherent granulocytes were determined. There was no accumulation of granulocytes. These data suggest that some forms of myocardial adrenergic augmentation during stunning may have adverse consequences. Thus, the strength, duration, and types of stimulation may be critical to the preservation of the myocardium in the treatment of myocardial stunning.

Adenosine Diphosphate↗
PubMed1984

High-performance liquid chromatographic separation of the enantiomers of anti-inflammatory 2-arylpropionates: suitability of the method for in vitro metabolic studies.

The enantiomers of 2-phenylpropionic acid, 2-(2-naphthyl)propionic acid, 2-(4-biphenyl)propionic acid and six anti-inflammatory congeners were separated by high-performance liquid chromatography via their diastereoisomeric derivatives with (S)-(-)-1-phenylethylamine. In agreement with a general rule, the diastereoisomers derived from the (R)-acids are less polar and elute first. Structural factors influencing the resolution are discussed. Good calibrations were obtained for R/S ratios and total (R + S) concentrations of flurbiprofen and naproxen added to inactivated rat liver preparations. The method is suitable for in vitro metabolic studies of chiral 2-arylpropionates.

Animals↗