Stimulation of canine cardiac sarcoplasmic reticulum Ca2+ uptake by dihydropyridine Ca2+ antagonists

We examined the effects of four Ca2+ antagonists that possess the ability to bind to calmodulin-felodipine, nitrendipine, prenylamine, and verapamil--as well as the effect of the calmodulin antagonist trifluoperazine on Ca2+ uptake and Ca2+ + Mg2+/ATPase activity in canine cardiac sarcoplasmic reticulum. In the presence of 20-30 microM felodipine and 100-200 microM nitrendipine, Ca2+ uptake increased from 69 nmoles X mg-1 X min-1 to 107 and 108 nmoles X mg-1 X min-1, respectively, with half-maximal stimulation occurring at 7.5 and 28 microM respectively. Ca2+ + Mg2+/ATPase activity was unchanged over the same concentration ranges. In contrast, both Ca2+ uptake and Ca2+ + Mg2+/ATPase activities were inhibited in the presence of 10-100 microM trifluoperazine (IC50 = 25 microM), 10-100 microM prenylamine (IC50 = 35 microM) and 100-200 microM verapamil (inhibition insufficient for IC50 determination). None of the drugs affected membrane permeability to Ca2+ as determined by passive 45Ca2+ efflux in the presence of ethyleneglycol bis(beta-amenoethyl ether)N,N,N1-tetraacetic acid (EGTA). Drug inhibition of calmodulin-dependent turkey gizzard myosin light chain kinase activation in a purified protein system was used as a direct measure of calmodulin antagonism, and felodipine, nitrendipine, trifluoperazine, prenylamine, and verapamil blocked this activation at IC50 values of 9.8, 55, 6.4, 31, and 93 microM respectively. None of the drugs studied, however, had any effect upon endogenous phospholamban phosphorylation in our cardiac sarcoplasmic reticulum preparations. These observations indicate that dihydropyridine Ca2+ antagonists stimulate cardiac sarcoplasmic reticulum Ca2+ uptake in vitro either by increasing the efficiency of the transport process or by inhibiting Ca2+-dependent Ca2+ release, and suggest that these effects do not result from interference with calmodulin-mediated processes.     

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.     

Bioluminescent imaging of drug efflux at the blood–brain barrier mediated by the transporter ABCG2

ATP-binding cassette (ABC) transporters are a group of transmembrane proteins that maintain chemical homeostasis through efflux of compounds out of organelles and cells. Among other functions, ABC transporters play a key role in protecting the brain parenchyma by efflux of xenobiotics from capillary endothelial cells at the blood–brain barrier (BBB). They also prevent the entry of therapeutic drugs at the BBB, thereby limiting their efficacy. One of the key transporters playing this role is ABCG2. Although other ABC transporters can be studied through various imaging modalities, no specific probe exists for imaging ABCG2 function in vivo. Here we show that d-luciferin, the endogenous substrate of firefly luciferase, is a specific substrate for ABCG2. We hypothesized that ABCG2 function at the BBB could be evaluated by using bioluminescence imaging in transgenic mice expressing firefly luciferase in the brain. Bioluminescence signal in the brain of mice increased with coadministration of the ABCG2 inhibitors Ko143, gefitinib, and nilotinib, but not an ABCB1 inhibitor. This method for imaging ABCG2 function at the BBB will facilitate understanding of the function and pharmacokinetic inhibition of this transporter.Provision of nutrients and maintenance of chemical homeostasis in the brain is performed by the endothelial cells of brain capillaries within a neurovascular unit termed the blood–brain barrier (BBB) (1). In contrast to endothelial cells of capillaries elsewhere in the body, those in the brain are joined by tight junctions forming a physiologic barrier. Drug delivery to the brain depends on physicochemical characteristics such as lipophilicity, molecular weight, and ionic state. For many compounds, brain entry is lower than other tissues/organs because of the presence of ATP-binding cassette (ABC) efflux transporters at the apical surface of endothelial cells at the BBB (2, 3). These transporters maintain chemical homeostasis in the brain, and prevent toxins from interfering with neural processes by regulating the compounds that can enter the brain.ABC transporters contribute to the clinical challenge of drug delivery to the brain, and it has been estimated that only 2% of drug discovery compounds can cross the BBB to reach therapeutic targets (4). ABCG2 (also known as breast cancer resistance protein) and ABCB1 (also called P-glycoprotein) are the two most highly expressed efflux transporters at the BBB (5). Altered expression of ABC transporters at the BBB has been associated with a range of pathophysiological conditions (2, 6). ABC efflux transporters at the BBB also play a major role in limiting effective concentrations of chemotherapeutic agents to treat primary and metastatic tumors in the brain (7). ABCG2 has been shown to work in tandem with ABCB1 at the BBB (8, 9). However, its individual contribution is not understood.Molecular imaging allows the measurement of the individual contribution and function of transporters in vivo (10). Efflux of a substrate by transporters at the BBB is reflected by little to no uptake in brain tissue, and when efflux transport is pharmacologically inhibited, increased accumulation occurs (11, 12). Although a number of radiolabeled specific substrates have been developed to study ABCB1 function by using positron emission tomography (PET), no specific probe exists for imaging ABCG2 function at the BBB (13, 14).Whole-animal bioluminescent imaging (BLI) is increasingly used in mouse genetic studies to visualize cellular events (15). The primary reporters used for BLI are the light-generating luciferase enzymes and their substrates, such as firefly luciferase (fLuc) and d-luciferin. It has been reported that ABCG2 expression decreases bioluminescence in fLuc cells compared with control cells (16), and biodistribution studies have reported low distribution of d-luciferin in the brain (17). This suggests that ABCG2 may restrict the entry of d-luciferin at the BBB. We hypothesized that ABCG2 function at the BBB could be examined by using BLI in transgenic mice expressing fLuc in the brain.In this study, we sought to answer two questions. First, is d-luciferin a specific substrate of human and murine ABCG2? To assess this directly, we measured the fluorescence levels of d-luciferin in human and mouse cells that overexpress select ABC transporters. Second, can d-luciferin be used in vivo as a probe to measure ABCG2 function at the BBB? To answer this question, we used BLI to measure the bioluminescence in the brain of fLuc-expressing transgenic mice administered d-luciferin with or without an inhibitor of ABCG2. Our goal was to develop time-course BLI of the mouse brain with a view to understanding the kinetics of ABCG2 activity at the BBB.     

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.