Steady-state concentrations of imipramine and its metabolites in relation to the sparteine/debrisoquine polymorphism

Summary Thirty-five imipramine treated patients were phenotyped with regard to polymorphic drug oxidation using sparteine and/or debrisoquine.During treatment with 100 mg imipramine per day the mean steady-state concentrations and ratios in 28 extensive metabolizers were: imipramine 169 nmol/l; desipramine 212 nmol/l; 2-OH-imipramine/imipramine 0.25; 2-OH-desipramine/desipramine 0.57. The corresponding values in two poor metabolizers were: imipramine 455 and 302 nmol/l; desipramine 1148 and 1721 nmol/l; 2-OH-imipramine/imipramine 0.06 and 0.05; 2-OH-desipramine/desipramine: 0.09 and 0.04 respectively.The metabolic ratios (MR) sparteine/dehydrosparteine and debrisoquine/4-OH-debrisoquine (% of dose in 12-h urine samples) correlated poorly with the imipramine steady-state concentrations during administration of 100 mg per day, but quite well with the desipramine steady-state concentrations. Significant negative correlations were found between sparteine and debrisoquine MR and the 2-OH-imipramine/imipramine and 2-OH-desipramine/desipramine ratios.In most patients the initial dose was changed to obtain concentrations in the therapeutic range, and concentrations for imipramine + desipramine of (mean ± SD) 713±132 nmol/l were achieved in 33 patients. The therapeutic dose was 50 mg per day in one poor metabolizer and ranged from 50–400 mg per day in 32 extensive metabolizers. There was a weak negative correlation between sparteine MR and daily dose.Treatment with imipramine inhibited metabolism of both sparteine and debrisoquine (MR values about doubled), but did not affect the interpatient correlations.     

Benzodiazepine suppression of cortisol secretion: a measure of anxiolytic activity?

Clinical studies on spontaneous afternoon cortisol levels in depressed patients revealed that oxazepam given a few hours before blood sampling, may suppress the cortisol levels. This was confirmed in a volunteer study, where oxazepam 30 and 60 mg caused a dose-dependent suppression of the cortisol level only lasting 2 or 3 hours in spite of persisting high oxazepam levels in plasma. Subsequently, a study in 28 depressed patients showed a substantial suppression of afternoon cortisol after oxazepam 45 mg given 2 hrs prior to sampling. It may be postulated that this effect is mediated through GABA-ergic receptors inhibiting the hypothalamic release of corticotropin releasing factor (CRF). This is interesting since CRF may have neurotropic effects related to the behavioral responses to stress, and the inhibitory effect thus may represent a mechanism of action for the anxiolytic effect of benzodiazepines.     

57miRNA regulation during oncogene-induced senescence

Aberrant oncogene activation induces cellular senescence, an irreversible growth arrest which acts as a barrier against tumor formation. To identify miRNAs involved in oncogene-induced senescence we arrayed miRNA expression in primary human fibroblasts (Tig3) following over-expression of B-RAF. 18 miRNA were significantly regulated (P<0.001) 4 days after B-RAF activation; in particular, miR-34a expression increased ∼8-fold. In addition, miR-34a is up-regulated in mouse fibroblasts undergoing replicative senescence. In agreement with previous reports, we find that miR-34a reduces cellular proliferation and induces cell cycle arrest. Using microarrays, we have identified a number of putative miR-34a targets involved in oncogene-induced senescence and we are now evaluating their ability to mediate the cellular effects of miR-34a. Although members of the miR-34 family are known p53 target genes, our data indicate that miR-34a is regulated independently of p53 during oncogene-induced senescence. Hence, miR-34a responds to several independent cancer-related pathways thereby underlining the importance of miR-34a as an important tumor suppressor. We are currently investigating the regulation of miR-34a in normal and senescent cells using ChIP and promoter reporter assays.     

Elevated serum levels of creatine kinase BB in autosomal dominant osteopetrosis type II

Summary Serum levels of creatine kinase isoenzyme BB (CK-BB) were measured spectrophotometrically and by electrophoresis in 17 patients with autosomal dominant osteopetrosis (ADO) and compared with those of age- and sex-matched controls. Eight patients had ADO type I and nine patients had ADO type II. CK-BB was significantly increased (p<0.002) in type II but normal in type I compared with controls. This finding supports heterogeneity of ADO, and it may indicate a potential role for CK-BB as a marker of immature osteoclasts.     

Increased concentrations of heparin cofactor II in diabetic patients, and possible effects on thrombin inhibition assay of antithrombin III

We compared concentrations of antithrombin III (AT-III) in plasma, as determined by an immunological method and by a functional thrombin inhibition method, in the presence of heparin in 160 blood samples from Type I diabetics. Although the correlation was highly significant (P less than 0.001) between the results obtained by the two methods, our data demonstrated that results by the thrombin inhibition assay, 121 (SD 15)%, expressed as percentages of the results for a normal plasma pool, were significantly (P less than 0.001) higher than by the immunoreactive method, 104 (SD 15)%, indicating an overestimation of functionally active AT-III. Concentrations of functionally active AT-III determined by a factor Xa inhibition assay, 105 (SD 13)%, were in the same range as immunoreactive AT-III. Addition of IgG antiserum to normal pooled plasma quenched only about 90% of the AT-III activity determined by the thrombin inhibition assay, but all of the AT-III activity determined by a factor Xa inhibition assay. These results demonstrate that the factor Xa inhibition assay is more specific for the determination of AT-III than the thrombin inhibition assay. We suggest that the high concentrations of heparin cofactor II, 117 (SD 17)%, might have caused an overestimation of AT III in this group of patients with diabetes Type I, and should not be overlooked in other clinical situations.