Catabolism of human tissue plasminogen activator in mice

The catabolism of human tissue plasminogen activator (t-PA) was studied in mice. The clearance of t-PA labeled with iodine 125 was rapid (t1/2). The clearance of phenylmethylsulfonyl-125I-t-PA, which is active site-inhibited, was identical to the active enzyme. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that the vast majority of 125I-t-PA injected into the circulation was present as free enzyme and not in a complex with inhibitors. The clearance of 125I-t-PA was unaltered by large molar excesses of several ligands of known clearance specificities, including macroalbumin, asialoorosomucoid, and diisopropylphosphorylthrombin and was also not altered in the presence of a 1,000-fold molar excess of unlabeled t-PA. Organ distribution studies demonstrated that the early rapid clearance of 125I-t-PA occurred in hepatocytes, followed by a later renal phase of clearance. The clearance of 125I-urokinase (UK) also was studied and was very similar in all aspects to the clearance of 125I-t-PA. These results suggest that both t-PA and UK are cleared from the circulation by unique nonsaturable processes localized in the liver that are independent of the proteinase active site.     

The SV stent study: a prospective, multicentre, angiographic evaluation of the BiodivYsio phosphorylcholine coated small vessel stent in small coronary vessels

OBJECTIVE: To evaluate the use of the phosphorylcholine (PC) coated BiodivYsio small vessel (SV) stent in native coronary vessels of small calibre. DESIGN AND SETTING: Prospective, multi-centre, multi-national registry with 6-month clinical and core-lab angiographic follow-up. Adverse events were adjudicated by a Clinical Events Committee (CEC) and included peri-procedural analysis of cardiac enzymes. PATIENTS: Patients with signs or symptoms of ischaemia with an identified target lesion in an epicardial vessel with reference diameter 2.0-2.75 mm were enrolled. Intervention in other epicardial territories in the same patient was permitted. RESULTS: Recruitment of 150 consecutive lesions (in 143 patients) was completed in 19 centres in Europe and Israel. The stent was deployed successfully in all but one lesion. At 6 months, 1 patient (1%) had experienced sudden cardiac death, 4 further patients (3%) had a non-Q wave MI, and a further 24 patients (17%) had repeat revascularisation of a study target vessel. The mean reference vessel diameter prior to stenting was 2.2 mm (S.D. 0.4). Mean minimal luminal diameters at pre-procedure, post procedure and follow-up were 0.6 mm (S.D. 0.3), 2.0 mm (S.D. 0.4) and 1.2 mm (S.D. 0.6), respectively. The late lumen loss index was 0.55 (S.D. 0.53) with a binary restenosis rate of 32%. CONCLUSIONS: In stenting of selected lesions in small vessels, the BiodivYsio SV stent demonstrated high rates of implant success. The rates of major adverse cardiac events (MACE), angiographic restenosis and repeat revascularisation are similar to those reported in other small vessel bare metal stent studies.     

Preparation of polyethylene glycol-tissue plasminogen activator adducts that retain functional activity: characteristics and behavior in three animal species

Conditions were defined for the derivatization of recombinant tissue plasminogen activator (rt-PA) with polyethylene glycol (PEG) so as to retain functional activity as a possible means of producing a t-PA species with a prolonged circulating lifetime. Derivatives with a wide range of retention of activities were prepared by varying the concentration and species of activated PEG. The specific activities of the PEG-rt-PA derivatives were dependent on the method of assay. Assays using preformed fibrin gave higher estimates of retention of activity than assays using soluble components. Plasma elimination studies in mice and rats indicated prolonged circulating lifetimes for the radiolabeled PEG-rt-PA derivatives after a rapid clearance and distribution phase; however, the disappearance of functional activity was much more rapid than the disappearance of radiolabeled material. The PEG-rt-PA derivatives appeared to accumulate in tissues above their interstitial fluid concentrations and were rapidly inactivated, apparently by reaction with the plasma protease inhibitors. These results were consistent with the inactivation of the PEG-rt-PA derivatives in rat plasma in vitro. A somewhat longer half-life (t1/2) of the one derivative studied was observed in dogs (t1/2, 16 minutes) as compared with the rat (t1/2, five minutes). This was sufficient to confer thrombolytic activity upon the derivative (administered by bolus injection) in contrast to native rt-PA. The potential of PEG-modified rt-PA as a long-lived thrombolytic agent in humans will depend, however, on whether there will be a further extension of the t1/2 because of a reduction in clearance and/or a reduction in the rate of inactivation.     

The role of endothelium in factor Xa regulation: the effect of plasma proteinase inhibitors and hirudin

The role of endothelium in the inhibition of human factor Xa was studied in a plasma environment. Human factor Xa can bind to and function on bovine aortic endothelium in a manner similar to that of bovine factor Xa. Approximately 70% of the bound factor Xa is subject to inhibition by plasma proteinase inhibitors, and the remaining 30% is irreversibly bound as part of a 125 Kd membrane-associated complex not subject to proteolytic degradation. The proportion reversibly bound and its rate of release do not alter with changes in calcium, citrate, heparin, or active proteinase inhibitor concentrations. The principal plasma proteinase inhibitor of human factor Xa was antithrombin III, which accounted for 60% to 65% of factor Xa released from endothelium, with alpha 1-proteinase inhibitor inactivating 20% to 25% and alpha 2- macroglobulin approximately 15%. All of the reversibly bound factor Xa was identified in complex with one of these three proteinase inhibitors. The thrombin active-site inhibitor hirudin was found to markedly accelerate the displacement of reversibly bound factor Xa from the endothelium and to associate specifically with factor Xa without a loss of activity toward chromogenic substrates, perhaps accounting for a novel mechanism of anticoagulation.     

Electron microscopic localization of factor-VIII-related antigen in adult human blood vessels

We have localized factor-VIII-related antigen, using immunofluorescence and electron microscopy, in adult human blood vessels. In addition to its presence in endothelial cells, the antigen was localized within subendothelium and the layers of elastic lamina closest to the lumen. Also, we provide the first morphological evidence that factor-VIII- related antigen is associated with collagen fibrils within the vessel wall. These studies suggest that this subendothelial factor-VIII- related antigen may play a role in the adhesion of platelets to subendothelial components following endothelial injury.     

Demographic and clinical predictors of depressive symptoms among incarcerated women

Background  

Imprisonment may lead to the development of mental illness, especially depression. This study examines the clinical and sociodemographic profiles of imprisoned women, identifies indicative signs of depression, and relates these indicators to other variables.     

The Introduction of H2-Receptor Antagonists to Scandinavia: Effects of Experts' Opinions

To evaluate the therapeutic potential of the newly developed proton pump inhibitor lansoprazole in patients with reflux oesophagitis, we performed a double-blind randomized clinical trial comparing 20 mg omeprazole and 30 mg lansoprazole, involving 229 patients at 9 Scandinavian hospitals. The treatment period was 4 or 8 weeks, and main efficacy variables were healing of endoscopic changes, relief of reflux symptoms, and occurrence of adverse events. No significant difference in terms of healing was found, either after 4 or after 8 weeks' treatment. Patients receiving lansoprazole experienced a greater improvement in heartburn after 4 weeks (p = 0.03), and there was a similar trend for acid regurgitation. Lansoprazole was found to be an effective and safe alternative to omeprazole in short-term treatment of moderate reflux oesophagitis.     

Kinetics and 28-day test–retest repeatability and reproducibility of [11C]UCB-J PET brain imaging

[¹¹C]UCB-J is a novel radioligand that binds to synaptic vesicle glycoprotein 2A (SV2A). The main objective of this study was to determine the 28-day test–retest repeatability (TRT) of quantitative [¹¹C]UCB-J brain positron emission tomography (PET) imaging in Alzheimer’s disease (AD) patients and healthy controls (HCs). Nine HCs and eight AD patients underwent two 60 min dynamic [¹¹C]UCB-J PET scans with arterial sampling with an interval of 28 days. The optimal tracer kinetic model was assessed using the Akaike criteria (AIC). Micro-/macro-parameters such as tracer delivery (K₁) and volume of distribution (V_T) were estimated using the optimal model. Data were also analysed for simplified reference tissue model (SRTM) with centrum semi-ovale (white matter) as reference region. Based on AIC, both 1T2k_V_B and 2T4k_V_B described the [¹¹C]UCB-J kinetics equally well. Analysis showed that whole-brain grey matter TRT for V_T, DVR and SRTM BP_ND were –2.2% ± 8.5, 0.4% ± 12.0 and –8.0% ± 10.2, averaged over all subjects. [¹¹C]UCB-J kinetics can be well described by a 1T2k_V_B model, and a 60 min scan duration was sufficient to obtain reliable estimates for both plasma input and reference tissue models. TRT for V_T, DVR and BP_ND was <15% (1SD) averaged over all subjects and indicates adequate quantitative repeatability of [¹¹C]UCB-J PET.