ADP‐degrading enzymes inhibit platelet activation in bile duct‐ligated rats

Abstract

Summary. Background: The effect of cholestatic liver disease on primary hemostasis function remains ill-defined. Objectives: To determine platelet function and identify the mechanisms involved in the observed platelet function in cholestatic rats. Methods: Platelet function was studied in a model of 2-week bile duct ligation and compared to that in sham-operated rats with and without a storage pool defect. Results: ADP-induced and collagen-induced platelet aggregation were clearly impaired following bile duct ligation (P < 0.01 for areas under the curve). Crossover experiments, with sham platelets in bile ductligated plasma and vice versa, demonstrated that this is due to inhibition by a plasmatic factor, as sham platelets aggregated less in cholestatic plasma (P < 0.03) and to an equal extent as platelets from bile duct-ligated rats when they were in the same sham or cholestatic plasma. Moreover, in bile duct-ligated rats, platelet ultrastructure was unaffected and platelet aggregation was similar to that of sham platelets when resuspended in the same plasma (P-value not significant). Aditionally, studies in storage pool-deficient rats showed no role of platelet exhaustion. The plasmatic factor causing impaired aggregation was shown to be increased total activity of ADP-degrading enzymes upon bile duct ligation (P < 0.01), as there was no decreased aggregation with a stable ADP analog in bile duct-ligated rats (P-value not significant vs. sham-operated rats). Furthermore, preincubation of plasma from bile duct-ligated rats with ADP decreased aggregation more than was seen with sham plasma (P < 0.01). Conclusions: Bile duct ligation does not affect intrinsic platelet function, but impairs platelet activation via release of ADP-degrading enzymes in the circulation.

Extracellular Ca2+ modulates ADP‐evoked aggregation through altered agonist degradation: implications for conditions used to study P2Y receptor activation

“…It has previously been reported that in blood from patients with elevated leucocyte counts, degradation of ADP is accelerated and aggregation in response to ADP is reduced due to increased NTPDase levels (Pulte et al , 2007; Glenn et al , 2008). Moreover, in a rat model of cholestatic liver disease where plasma ectonucleotidase activity is enhanced, reduced aggregation was exhibited in response to ADP and low dose collagen (which is dependent on ADP secretion) (Witters et al , 2010). Conversely, individuals demonstrating reduced ectonucleotidase expression may have more reactive platelets and be more susceptible to thrombotic events.…”

Bile Acids Do Not Contribute to the Altered Calcium Homeostasis of Platelets from Rats with Biliary Cirrhosis

“…The underlying mechanisms for altered platelet function in cholestasis are unclear. Several mechanisms have been suggested (Bowen et al, 1988; Pihusch et al, 2002; Atucha et al, 2007; Witters et al, 2010; Tripodi et al, 2011), including an intrinsic change in platelet function, e.g., increased aggregation resulting from altered intracellular calcium (Ca 2+ ) homeostasis or decreased aggregation due to a storage pool deficiency, the effect of a plasmatic factor such as bile acids or bilirubin or because of the effect of release of ADP-degrading enzymes in the circulation. Regarding platelet activation, the necessary increase in cytoplasmic Ca 2+ levels, both by release from internal stores and entry of extracellular Ca 2+ , has been reported to be defective both in experimental models of liver cirrhosis and patients (Bandi et al, 1997; Atucha et al, 2007; Annie-Jeyachristy et al, 2008).…”

Defective Platelet Activation and Bleeding Complications upon Cholestasis in Mice

“…Inhibited platelet activation was found by Witters and colleagues who analyzed bile duct ligated rats as well [51]. The authors provided evidence for ADP-degrading enzymes that inhibit platelet activation upon cholestasis in rats.…”