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Purpose: RPR 102341 is structurally similar to the fluoroquinolone class of antibiotics. Because some fluoroquinolones have been shown to inhibit theophylline metabolism, concomitant administration may increase plasma levels of theophylline resulting in serious adverse effects. The purpose of this study was to determine if RPR 102341 affects theophylline metabolism in vitro and, thus, predict whether a clinically significant drug interaction is likely to occur. In addition, the effect of RPR 102341 on phenacetin O-deethylase activity was determined to address the enzymatic basis of a potential drug interaction., Methods: The in vitro theophylline metabolism assay was conducted according to a modification of a published procedure. The phenacetin O-deethylase assay was conducted according to a modification of a published procedure., Results: The rate of conversion of theophylline to 3-methylxanthine in human liver microsomes in the presence of 100 microM and 500 microM RPR 102341 was 93.6 and 106 percent of the control reactions, respectively. The formation of 1-methylxanthine was 97.6 and 100 percent of the control, and 1.3-dimethyluric acid formation was 88.9 and 95.2 percent of control at 100 microM and 500 microM RPR 102341, respectively. In agreement, RPR 102341 caused no inhibition of human liver CYP1A2-catalyzed phenacetin O-deethylase activity. Finally, no inhibition was observed when RPR 102341 was incubated with human liver microsomes and an NADPH regenerating system prior to the addition of theophylline., Conclusions: Based on these studies, RPR 102341 is not expected to cause significant drug interactions with theophylline.

In vitro methods were used to identify the cytochrome P450 (CYP) enzyme(s) involved in S-mephenytoin N-demethylation. S-Mephenytoin (200 microM) was incubated with human liver microsomes, and nirvanol formation was quantitated by reversed-phase HPLC. S-Mephenytoin N-demethylase activity in a panel of human liver microsomes ranged 35-fold from 9 to 319 pmol/min/mg protein and correlated strongly with microsomal CYP2B6 activity (r = 0.91). Additional correlations were found with microsomal CYP2A6 and CYP3A4 activity (r = 0.88 and 0.74, respectively). Microsomes prepared from human beta-lymphoblastoid cells transformed with individual P450 cDNAs were assayed for S-mephenytoin N-demethylase activity. Of 11 P450 isoforms (P450s 1A1, 1A2, 2A6, 2B6, 2E1, 2D6, 2C8, 2C9, 2C19, 3A4, and 3A5) tested, only CYP2B6 catalyzed the N-demethylation of S-mephenytoin with an apparent K(m) of 564 microM. Experiments with P450 form-selective chemical inhibitors, competitive substrates, and anti-P450 antibodies were also performed. Troleandomycin, a mechanism-based CYP3A selective inhibitor, and coumarin, a substrate for CYP2A6 and therefore a potential competitive inhibitor, failed to inhibit human liver microsomal S-mephenytoin N-demethylation. In contrast, orphenadrine, an inhibitor of CYP2B forms, produced a 51 +/- 4% decrease in S-mephenytoin N-demethylase activity in human liver microsomes and a 45% decrease in recombinant microsomes expressing CYP2B6. Also, both CYP2B6-marker 7-ethoxytrifluoromethylcoumarin O-deethylase and S-mephenytoin N-demethylase activities were inhibited by approximately 65% by 5 mg anti-CYP2B1 IgG/mg microsomal protein. Finally, polyclonal antibody inhibitory to CYP3A1 failed to inhibit S-mephenytoin N-demethylase activity. Taken together, these studies indicate that the N-demethylation of S-mephenytoin by human liver microsomes is catalyzed primarily by CYP2B6.

The brain uptake and biotransformation of remacemide hydrochloride [(+/-)-2-amino-N-(1-methyl-1,2-diphenylethyl)acetamide monohydrochloride; FPL 12924AA] were studied in the rat. The brain uptake indices (BUI) for remacemide and its pharmacologically active metabolite FPL12495 [(+/-)-1-methyl-1,2-diphenylethylamine monohydrochloride] were 51 and 130%, respectively. The BUI of [14C] remacemide and [14C]FPL12495 were not affected by increasing amounts of unlabeled remacemide or FPL12495, respectively. Likewise, the BUI of remacemide was not affected by dl-amphetamine or beta-phenethylamine. A mixture of [3H]remacemide hydrochloride (3H label in the glycine moiety) and [14C]remacemide hydrochloride (14C label in 1,2-diphenyl-2-aminopropane moiety) was administered by intracarotid injection. The ratio of 14C/3H in the brain was equal to that in the injection mixture, indicating that remacemide enters the brain intact. HPLC analysis of brain extracts of rats given [14C] remacemide hydrochloride by intracarotid injection revealed that 97.8 +/- 0.2% (mean +/- SD) of the radioactivity was present as remacemide, whereas 1.9 +/- 0.2% of the radioactivity was present as FPL12495. Finally, in vitro studies revealed that remacemide is hydrolyzed by whole-brain homogenates to the pharmacologically active metabolite FPL12495. Data indicate that remacemide enters the brain by passive diffusion and undergoes deglycination at the blood-brain barrier or within the brain to give FPL12495.

In the past, the comparison of results of studies on malignant lymphomas has been biased by the use of different classifications of the diseases and to an even greater extent by subjective interpretation in the classification of the tumour cells. To overcome these short-comings, we have developed cytometric features specifically for automated recognition of cell images from high grade malignant non-Hodgkin's lymphomas (NHL) and reactive lymphoid lesions. This study used a colour TV-microscope system, high resolution scanning (13.3 pixel/microns), and image processing to study a total of 3600 lymphoid cells from 15 high grade malignant NHL and three tonsils. Sixteen out of 64 features, especially developed for image analysis in cytological preparations, have been evaluated. Because of a considerable overlap of all the single features, no feature on its own allows reliable discrimination. But, multivariant analysis of suitable feature combinations resulted in reliable identification and discrimination of the most frequently occurring cell types. We show that the lymphocytes, centrocytes, centroblasts, immunoblasts and lymphoblasts, as they are defined by subjective morphological criteria in the Kiel-classification of malignant NHL, also form distinctive subpopulations on the basis of their objective mathematical cell features. Furthermore, we have shown that there are distinctive differences between the lymphoma cells and their benign counterparts derived from reactive lymphoid lesions.

The tendency toward extremely high variability among relaxins derived from purportedly closely related species has come to an abrupt end with the discovery of quasi-porcine relaxin in the minke whale (Balaenoptera acutorostrata) and the Bryde's whale (Balaenoptera edeni). An aqueous abstract of the corpora lutea of the two baleen whales contained significant amounts of relaxin-like activity as determined by a mouse bioassay and by cross-reactivity with anti-pig relaxin antibodies. The activity could be isolated and purified to homogeneity. Sequence analysis revealed that both whale relaxins differed from each other by about 3 residues, whereas the relaxin of B. edeni differed at only one position from that of pig relaxin. The similarity appears to include even the chain length heterogeneity observed at the C-terminal end of the B chain in porcine relaxin which is produced by a peculiar mode of connecting peptide removal from the pro-hormone. This finding may well represent one of the better documented challenges to the current paradigm of molecular evolution.