Central effect of aprotinin, a serine protease inhibitor, on blood pressure in spontaneously hypertensive and Wistar-Kyoto rats

Opioid receptor function is regulated by post-endocytic peptide processing

Most neuroendocrine peptides are generated in the secretory compartment by proteolysis of the precursors at classical cleavage sites consisting of basic residues by well studied endopeptidases belonging to the subtilisin superfamily. In contrast, a subset of bioactive peptides is generated by processing at non-classical cleavage sites that do not contain basic residues. Neither the peptidases responsible for non-classical cleavages nor the compartment involved in such processing has been well established. Members of the endothelin-converting enzyme (ECE) family are considered good candidate enzymes because they exhibit functional properties that are consistent with such a role. In this study we have explored a role for ECE2 in endocytic processing of δ opioid peptides and its effect on modulating δ opioid receptor function by using selective inhibitors of ECE2 that we had identified previously by homology modeling and virtual screening of a library of small molecules. We found that agonist treatment led to intracellular co-localization of ECE2 with δ opioid receptors. Furthermore, selective inhibitors of ECE2 and reagents that increase the pH of the acidic compartment impaired receptor recycling by protecting the endocytosed peptide from degradation. This, in turn, led to a substantial decrease in surface receptor signaling. Finally, we showed that treatment of primary neurons with the ECE2 inhibitor during recycling led to increased intracellular co-localization of the receptors and ECE2, which in turn led to decreased receptor recycling and signaling by the surface receptors. Together, these results support a role for differential modulation of opioid receptor signaling by post-endocytic processing of peptide agonists by ECE2.

Aprotinin in Cardiac Surgery: A Review of Conventional and Novel Mechanisms of Action

Induction of the coagulation and inflammatory cascades can cause multiorgan dysfunction after cardiopulmonary bypass (CPB). In light of these observations, strategies that can stabilize the coagulation process as well as attenuate the inflammatory response during and after cardiac surgery are important. Aprotinin has effects on hemostasis. In addition, aprotinin may exert multiple biologically relevant effects in the context of cardiac surgery and CPB. For example, it decreases neutrophil and macrophage activation and chemotaxis, attenuates release and activation of proinflammatory cytokines, and reduces oxidative stress. Despite these perceived benefits, the routine use of aprotinin in cardiac surgery with CPB has been called into question. In this review, we examined this controversial drug by discussing the classical and novel pathways in which aprotinin may be operative in the context of cardiac surgery.

Role of tissue plasminogen activator/plasmin cascade in delayed neuronal death after transient forebrain ischemia

We studied the possible involvement of the tissue plasminogen activator (t-PA)/plasmin system on both delayed neuronal death in the hippocampus and the associated enhancement of locomotor activity in rats, after transient forebrain ischemia induced by a four-vessel occlusion (FVO). Seven days after FVO, locomotor activity was abnormally increased and, after 10 days, pyramidal cells were degraded in the CA1 region of the hippocampus. FVO increased the t-PA antigen level and its activity in the hippocampus, which peaked at 4 h. Both the enhanced locomotor activity and the degradation of pyramidal cells were significantly suppressed by intracerebroventricular injection of aprotinin, a plasmin inhibitor, at 4 h but not during FVO. These results suggest the importance of the t-PA/plasmin cascade during the early pathological stages of delayed neuronal death in the hippocampus following transient forebrain ischemia.

Substance P attenuates gastric mucosal hyperemia after stimulation of sensory neurons in the rat stomach

BACKGROUND/AIMS

Sensory neurons in the stomach mucosa are closely apposed to mast cells and blood vessels. Mucosal hyperemia, after exposure to capsaicin, is mediated by calcitonin gene-related peptide (CGRP) from these neurons, which also contain substance P (SP). However, the role of this peptide in blood flow regulation remains unclear. Therefore, this study examines the effect of SP on capsaicin-induced mucosal hyperemia and mast cells.

METHODS

Gastric mucosal blood flow was measured with laser Doppler flow velocimetry in chambered rat stomachs. SP, aprotinin (serine protease inhibitor), and ketotifen (mast cell stabilizer) were infused into the splenic artery of rats. Mast cells were counted by microscopy.

RESULTS

Mucosal exposure to capsaicin (640 mumol/L) evoked a 70% increase in mucosal blood flow, which was abolished by SP, whereas aprotinin infused with SP and pretreatment with ketotifen before SP infusion restored the hyperemic response. Morphometry showed that ketotifen inhibited mast cell degranulation in SP-treated animals. Preservation of mast cells in SP-treated rats was linearly correlated to increased mucosal blood flow after exposure to capsaicin.

CONCLUSIONS

These data suggest that SP participates in regulation of gastric mucosal blood flow by activation of mast cells most likely by releasing proteases from mast cells that cleave and inactivate CGRP.