Interim PET response criteria in paediatric non-Hodgkin's lymphoma. Results from a retrospective multicenter reading.

AIM: To evaluate the use and reliability of the PET-based response criteria for interim PET (iPET) in terms of interobserver variability in pediatric and adolescent patients suffering from non-Hodgkin´s lymphoma (NHL). Particular attention was given to the identification of visual cutoff to separate patients with a favourable outcome. PATIENTS, METHODS: Retrospective analysis of PET-datasets of 18 children and adolescents suffering from NHL who underwent iPET after two cycles of chemotherapy for response assessment. Datasets were evaluated and rated in three independent review centers (RC) (blinded-read, intra-center consensus) using a visual 5-point response scale. Ratings were compared to clinical outcome. Pairwise interobserver agreement was analysed with Cohen's kappa-test (κ). Overall agreement (between attended RCs) was assessed with Fleiss' κ-test. RESULTS: Four patients suffered relapse (early, n = 2; late, n = 2). Per region analyses on interobserver variability revealed a "substantial" agreement (Fleiss' κ = 0.618). Per patient analyses revealed concordant iPET-ratings in eight patients: iPET-negative (iPET-), n = 5; iPET-positive (iPET+), n = 2; iPET-inconclusive (iPET±), n = 1. Discordant ratings were found in the remaining patients. Patients with early relapse were concordantly identified using mediastinal blood pool structures (MBPS, score ≥ 3) as visual cutoff between iPET+ or iPET-, respectively. However, patients with late relapse were not concordantly identified taking the MBPS as visual cutoff. CONCLUSION: The iPET interpretation using a dedicated PET-based response scale assured a low interobserver variability in per-region but not in per-patient analyses in a multicenter read. Using a sensitive read out (iPET+, score ≥ 3) a reliable identification of patients suffering relapse was limited to those with early relapse.

Evaluation of interim PET response criteria in paediatric Hodgkin's lymphoma--results for dedicated assessment criteria in a blinded dual-centre read.

BACKGROUND: The aim of this study was to evaluate the use and reliability of the new positron emission tomography (PET)-based response criteria for interim positron emission tomography (iPET) in patients with paediatric Hodgkin's lymphoma (pHL). Particular emphasis was put on interobserver variability and on identification of a visual cut-off defining patients with very low risk for relapse. PATIENTS AND METHODS: The iPET scans of 39 pHL patients were evaluated in two independent centres by two PET-experienced specialists in nuclear medicine (blinded read, centre consensus) each. The iPET scans were interpreted using a 5-point scale and were compared with the outcome. Cohen's kappa-test (κ) was used to analyse the interobserver agreement. RESULTS: Concordant ratings were assessed in 19 patients with iPET-negative findings, in 11 patients with iPET-positive findings and in 2 patients with inconclusive ratings. A 'substantial agreement' between attended centres was achieved (κ = 0.748). All patients suffering relapse were concordantly identified, taking mediastinal blood pool structures (MBPS) as visual cut-off between PET-positive and PET-negative findings, respectively. All pHL patients with uptake lower than or equal to MBPS remained in complete remission. CONCLUSION(S): The iPET interpretation assured low interobserver variability. High sensitivity for identification of pHL patients suffering relapse is achieved if [18F]-fluorodeoxyglucose uptake above the MBPS value is rated as a PET-positive finding.

Influence of vinpocetine on warfarin-induced inhibition of coagulation.

The influence of 14 days of concomitant vinpocetine administration on prothrombin time prolongation of single 25 mg doses of warfarin was investigated. Eighteen male subjects were included in the study. They received 25 mg warfarin the first day. Prothrombin time, warfarin plasma levels and factor VII coagulation time were monitored on days 1-5. Ten mg vinpocetine was administered from day 6 to 24. Another single dose of 25 mg of warfarin was given a second time on day 20. AUC values of prothrombin time, warfarin plasma level and factor VII clotting time curves and appropriate Cmax and tmax plasma levels of days 20-24 were compared with those of days 1-5. The confidence interval limits of the ratio of AUC20-24/AUC1-5 of prothrombin time curves were within the limits of 0.8 and 1.2, so that the formal criteria of equivalent biological activity were met. However, a minute influence probably without clinical implication is likely since both point estimate as well as confidence interval limits were below 1.

Vinpocetine therapy does not change imipramine pharmacokinetics in man.

The influence of vinpocetine on imipramine steady-state plasma levels was investigated in 18 healthy volunteers. Twenty-five mg imipramine were given t.i.d. for a total of 21 days, vinpocetine treatment was started on day 11 with 10 mg t.i.d. and continued until the end of the study. The AUC of imipramine plasma levels were obtained using consecutive imipramine plasma level determinations from samples drawn every 2 h from 8:00 a.m. to 8:00 p.m. by trapezoidal rule. AUCs of day 10 without and of day 21 during concomitant vinpocetine treatment were compared, demonstrating the independence of imipramine's bioavailability from concomitant vinpocetine treatment. There were no indications to assume a changed absorption of imipramine due to vinpocetine as would be reflected in Cmax and tmax values. Imipramine metabolization to the still effective metabolite desipramine shows a huge interindividual variability although it remains constant for the individual. The analysis of this parameter in the course of this study does not suggest that it is changed due to vinpocetine treatment.

Vinpocetine pharmacokinetics in elderly subjects.

The pharmacokinetics of vinpocetine (Eusenium) were investigated in 20 elderly, healthy volunteers. Plasma levels of the drug were determined during one dose interval of either repeated intravenous infusion or oral administration. AUC, Cmax and tmax values were derived for oral application, AUC values in case of intravenous application. Oral administration of 20 mg vinpocetine resulted in 4.60 x 10(-8) mol l-1 h, 1.71 x 10(-8) mol l-1 and 2.33 h for AUC, Cmax and tmax, respectively. The appropriate values for apovincaminic acid were 1.92 x 10(-6) mol l-1 h, 6.39 x 10(-7) mol l-1 and 2.41 h. When 10 mg vinpocetine were infused for 1 h, AUC values for vinpocetine and apovincaminic acid were 3.42 x 10(-7) mol l-1 h and 1.69 x 10(-6) mol l-1 h. Absolute bioavailability of vinpocetine was 6.7%. These data were in good agreement with the literature on young and elderly subjects. Marked deviations of apovincaminic acid kinetics in elderly subjects as described earlier could not be demonstrated in this study.

Glibenclamide steady state plasma levels during concomitant vinpocetine administration in type II diabetic patients.

The influence of vinpocetine on glibenclamide steady state plasma levels was investigated in 18 patients suffering from type II diabetes and symptoms of dementia. During the study patients continued to follow their individual scheme of glibenclamide intake and 10 mg vinpocetine were given t.i.d. from day 2 to 5. Glibenclamid as well as glucose plasma levels were repeatedly determined on the first day of the trial and compared to those on the fifth day where patients had received additional vinpocetine medication for four days. Time point comparisons were employed to exclude clinically relevant changes of glibenclamide bioavailability and kinetics. The data of this trial show that vinpocetine does not interfere with the kinetics of glibenclamide. Thus, it can be concluded that the comedication with vinpocetine does not represent a potential risk for a possible drug interaction in case of antidiabetics treatment with glibenclamide.

Thrombin-like inhibitory action of trypsin and trypsin-like proteases on human platelet adenylate cyclase.

The effects of trypsin, acrosin and a recently described trypsin-like protease from bovine sperm were studied on adenylate cyclase activity in membranes of human platelets. These proteases caused an immediate decrease in adenylate cyclase activity, which was independent of the platelet membrane concentration used and which was constant for up to 20 min of incubation at 25 degrees C. When the incubation was prolonged, the proteases eliminated their own inhibitory action as well as that of the inhibitory hormone epinephrine. The adenylate cyclase inhibition caused by the proteases was strictly dependent on the presence of GTP (EC50 approximately 0.1 microM), whereas in the absence of GTP only minor changes in enzyme activity were observed at the conditions and protease concentrations used. Maximal inhibition caused by the proteases was between 40% and 60%. Half-maximal inhibition by the purified proteases trypsin and acrosin was observed at about 30 ng/ml and 2 micrograms/ml respectively. Inhibition of platelet adenylate cyclase by the proteases was partially additive with that caused by epinephrine, while with thrombin no additivity was observed. The serine protease inhibitor leupeptin blocked the actions of the proteases when added simultaneously with the enzymes, but was ineffective when added later on. Treatment of platelet membranes with the alkylating N-ethylmaleimide at low concentrations and Mn2+ ions (greater than or equal to 1 mM), both agents known to abolish inhibition of adenylate cyclase via the inhibitory guanine-nucleotide-binding protein Gi, eliminated the inhibitory action of the proteases. The data indicate that trypsin and trypsin-like proteases have two opposite effects on the platelet adenylate cyclase system, the well-documented elimination of Gi action and, as shown here, an immediate activation of Gi with subsequent adenylate cyclase inhibition. The data are consistent with the hypothesis that the activation of Gi caused by the proteases is due to an interaction of the proteases with specific cell-surface receptor sites in a manner similar to thrombin.

Evidence for two GTPases activated by thrombin in membranes of human platelets.

Thrombin inhibits adenylate cyclase and stimulates GTP hydrolysis by high-affinity GTPase(s) in membranes of human platelets at almost identical concentrations. Both of these thrombin actions are similar to those observed with agonist-activated alpha 2-adrenoceptors coupling to the inhibitory guanine nucleotide-binding protein N1. However, stimulation of GTP hydrolysis caused by adrenaline (alpha 2-adrenoceptor agonist) and by thrombin at maximally effective concentrations was partially additive, whereas with regard to adenylate cyclase inhibition no additive response was observed. Furthermore, treatment of platelet membranes with pertussis toxin, which inactivates Ni and largely abolishes thrombin- and adrenaline-induced adenylate cyclase inhibition and adrenaline-induced GTPase stimulation, decreased the thrombin-induced stimulation of GTP hydrolysis by only about 30%. Additionally, the thiol reagent N-ethylmalemide (NEM) at rather low concentrations abolished thrombin- and adrenaline-induced stimulation of GTP hydrolysis was decreased by only 30-40% by treatment of platelet membranes with even high concentrations of NEM. Treatment with cholera toxin, which inhibits GTPase activity of the Ns (stimulatory guanine nucleotide-binding) protein, has no effect on thrombin-stimulated GTP hydrolysis. The data suggest that thrombin interaction with its receptor sites in platelet membranes leads to stimulation of two GTP-hydrolysing enzymes. One of these enzymes is apparently Ni and is also activated by agonist-activated alpha 2-adrenoceptors and is inactivated by pertussis toxin and NEM treatment. The other GTP-hydrolysing enzyme activated by thrombin may represent a guanine nucleotide-binding protein apparently involved in the coupling of thrombin receptors to the phosphoinositide phosphodiesterase.

Bradykinin stimulates GTP hydrolysis in NG108-15 membranes by a high-affinity, pertussis toxin-insensitive GTPase.

In membranes of neuroblastoma x glioma hybrid (NG108-15) cells, bradykinin (EC50 approximately equal to 5 nM) stimulates GTP hydrolysis by a high-affinity GTPase (Km approximately equal to 0.2 microM). The octapeptide, des-Arg9-bradykinin, was inactive. Stimulation of GTP hydrolysis by bradykinin and an opioid agonist was partially additive. Treatment of NG108-15 cells with pertussis toxin, which inactivates Ni, eliminated GTPase stimulation by the opioid agonist but not by bradykinin. The data suggest that bradykinin activates in NG108-15 membranes a guanine nucleotide-binding protein which is not sensitive to pertussis toxin and which may be involved in bradykinin-induced stimulation of phosphoinositide metabolism in these cells.

Dual regulation of adenylate cyclase. A signal transduction mechanism of membrane receptors.

The hormone-sensitive adenylate cyclase is a multi-component system embedded in the lipid bilayer of the plasma membrane and serves as a signal transduction system for various membrane receptors. The complete system consists of various receptor molecules, which sensitize the external ligands, the effector enzyme adenylate cyclase, which catalyzes the formation of cyclic AMP from ATP, and two guanine nucleotide-binding regulatory proteins (N or G proteins), which transduce the signals from the receptors to the adenylate cyclase. Depending on the receptor type activated by a ligand, stimulatory or inhibitory, either the stimulatory or the inhibitory N protein is activated and induces stimulation or inhibition of adenylate cyclase with subsequent increase or decrease in cellular cyclic AMP levels. In this paper, the mechanisms of this hormonal signal transduction system and its regulation will briefly reviewed, with some emphasis on the cardiac system.