Effect of vasoactive amines on Weibel-Palade bodies in capillary endothelial cells

Early angiopoietin-2 levels after onset predict the advent of severe pancreatitis, multiple organ failure, and infectious complications in patients with acute pancreatitis

BACKGROUND

Acute pancreatitis is a severe condition that requires early identification of patients at risk of developing potentially lethal complications. Current clinical scoring systems and biochemical parameters are insufficient. In this study, we aimed to assess whether early plasma Angiopoietin-2 (Ang-2) is associated with adverse outcomes in patients with predicted severe acute pancreatitis (SAP).

STUDY DESIGN

This analysis is a substudy of the PROPATRIA trial (probiotics vs placebo in patients with predicted SAP). The Ang-2 levels were measured prospectively in plasma in the first 5 days after admission in 115 patients.

RESULTS

Early Ang-2 levels were higher in patients who developed SAP: 6.4 vs 3.1 μg/L (p < 0.001) and also were higher in patients who developed multiorgan failure in the first week (p = 0.001) and after the first week (p = 0.049). Furthermore, high Ang-2 levels were associated with infectious complications in the first week (p < 0.001) and after the first week (p < 0.001). Finally, plasma Ang-2 was significantly higher in patients who died (p < 0.001) and in patients who developed bowel ischemia (p < 0.001). As a predictor of adverse outcomes, plasma Ang-2 was superior to a number of current scores, such as the APACHE II score, the Imrie score, C-reactive protein, lipopolysaccharide binding protein, and procalcitonin.

CONCLUSIONS

In the setting of this randomized controlled trial, early plasma Ang-2 was found to be an accurate predictor of SAP, multiorgan failure, and infectious complications. As a biomarker, it did outperform all of the investigated conventional predictors that are currently used in clinical practice.

Angiopoietins: a link between angiogenesis and inflammation

The angiopoietin (Ang)-Tie ligand-receptor system has a key regulatory role in regulating vascular integrity and quiescence. Besides its role in angiogenesis, it is an important regulator in numerous diseases including inflammation. Ang-1-mediated Tie2 activation is required to maintain the quiescent resting state of the endothelium. Agonistic Ang-1 functions are antagonized by Ang-2, which is believed to inhibit Ang-1-Tie2 signaling. Ang-2 destabilizes the quiescent endothelium and primes it to respond to exogenous stimuli, thereby facilitating the activities of inflammatory (tumor necrosis factor and interleukin-1) and angiogenic (vascular endothelial growth factor) cytokines. Intriguingly, Ang-2 is expressed weakly by the resting endothelium but becomes strongly upregulated following endothelial activation. Moreover, endothelial cells store Ang-2 in Weibel-Palade bodies from where it can be made available quickly following stimulation, suggesting a role of Ang-2 in controlling rapid vascular adaptive processes. This suggests that Ang-2 is the dynamic regulator of the Ang-Tie2 axis, thereby functioning as a built-in switch controlling the transition of the resting quiescent endothelium towards the activated responsive endothelium.

Long-term effects of erythropoietin on platelet serotonin storage and platelet aggregation in hemodialysis patients with reference to ketanserin treatment

Correction of uremic platelet serotonin (5-HT) storage pool deficiency is one of the very early hemostatic effects of erythropoietin (Epo) therapy. In this work, platelet 5-HT with relation to primary hemostasis was studied in 15 hemodialysis patients treated with Epo for 8 months. Moreover, effects of ketanserin, a blocker of platelet and vascular smooth muscle cell 5-HT2A receptors, in these patients were followed. The parameters studied were compared with relevant values in healthy controls and in hemodialysis patients not treated with Epo, and remeasured in the long-term Epo patients after a 14-day oral ketanserin trial. Platelet 5-HT content in the eighth month of Epo therapy was not different from the one in untreated patients. Ristocetin- and collagen-induced platelet aggregation were enhanced in comparison with both control groups, as opposed to unaltered response to ADP and arachidonic acid. Fibrinogen concentration was lower than in the untreated group. An inverse correlation between ADP-induced platelet aggregation and the skin bleeding time (r=-0.536, p<0.05) and a positive one between the former and platelet 5-HT (r=0.644, p<0.01) were found. Platelet count correlated positively with both platelet 5-HT (r=0.823, p<0.0002) and ADP-induced platelet aggregation (r=0.596, p<0.02). Ketanserin produced a decrease in ristocetin-induced platelet aggregation, fibrinogen, and prolongation of the bleeding time. The first two of the changes correlated positively with their pre-ketanserin values (r=0.923, p<0.00001 and r=0.839, p< 0.0001, respectively). Post-ketanserin, positive correlations between depressed ristocetin- and arachidonic acid-induced platelet aggregation (r=0.760, p<0.005), and between collagen- and corresponding values of arachidonic acid- (r=0.622, p<0.02), ADP-induced platelet aggregation (r=0.396, p<0.01), and platelet 5-HT (r=0.654, p<0.05) were found. Efficient hemostasis in hemodialysis patients on protracted Epo therapy is, in part, dependent on enhanced platelet aggregability. Correction of platelet 5-HT storage pool deficiency is not evident in this stage but 5-HT still influences complex mechanisms of primary hemostasis. Ketanserin is of anticoagulant value in these patients but its effects must be weighted against possible exacerbation of the anemia.