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

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

Previously, we have found that intracellular calcium homeostasis is altered in platelets from an experimental model of liver cirrhosis, the bile-duct ligated (BDL) rat; these alterations are compatible with the existence of a hypercoagulable state and related to an enhanced intracellular calcium release evoked by thrombin and an increased amount of calcium stored in the intracellular organelles. In the present study we have investigated the role of bile acids in those alterations of the BDL cirrhotic model. Cholic acid (CA) or deoxycholic acid (DCA) did not change P-selectin expression or platelet aggregation in any group but elevated baseline platelet calcium levels. Incubation with both bile acids reduced calcium release after stimulation with thrombin in the absence of extracellular calcium. Pretreatment with CA but not with DCA reduced significantly thrombin-induced calcium entry in all three experimental groups. The capacitative calcium entry was also significantly lower in platelets pretreated with both bile acids. The simultaneous addition of thapsigargin and ionomycin to estimate the total amount of calcium in platelet internal stores was decreased by pretreatment with both CA and DCA, although these changes were significantly different in the control rats only with CA and in the BDL platelets with DCA. These results indicate that CA and DCA reduce calcium movements in platelets of control and BDL animals, thus suggesting that bile acids do not participate in the alterations observed in the BDL cirrotic model.

Role of homocysteine and folic acid on the altered calcium homeostasis of platelets from rats with biliary cirrhosis

Previously, we have found that intracellular calcium homeostasis is altered in platelets from an experimental model of liver cirrhosis, the bile-duct ligated (BDL) rat; these alterations are compatible with the existence of a hypercoagulable state. Different studies indicate that cholestatic diseases are associated with hyperhomocysteinemia; thus, we hypothetized that it could contribute to those platelet alterations. In the present study, we have investigated the role of homocysteine (HCY) in platelet aggregation and calcium signaling in the BDL model. The effect of chronic folic acid treatment was also analyzed. Acute treatment with HCY increased the aggregation response to ADP and calcium responses to thrombin in platelets of control and BDL rats. Capacitative calcium entry was not altered by HCY. Chronic treatment with folic acid decreased platelet aggregation in control and BDL rats, but this decrease was greater in BDL rats. In folic acid-treated rats, thrombin-induced calcium entry and release were decreased in platelet of control rats but unaltered in BDL rats; however, capacitative calcium entry was decreased in platelets of control and BDL rats treated with folic acid. Reactive oxygen species were produced at higher levels by BDL platelets after stimulation with HCY or thrombin and folic acid normalized these responses. HCY plays a role in the enhanced platelet aggregation response of BDL rats, probably through an enhanced formation of ROS. Folic acid pretreatment normalizes many of the platelet alterations shown by BDL rats.

Bleeding Diathesis in Fawn Hooded Rats-Possible Implications for Invasive Procedures and Refinement Strategies

Simple Summary

The Fawn Hooded (FH) rat population is commonly used in biomedical research. It is widely acknowledged that the FH rat has a bleeding disorder, which may lead to abundant bleeding. However, the clinical consequences of this bleeding disorder have not been described in current literature. During our study, surgical procedures on FH rats led to an unanticipated loss of animals due to abundant bleeding. Adjustments made to minimize the impact of this disorder in animals undergoing invasive procedures are described. It is strongly recommended to take the bleeding diathesis into account when performing invasive procedures in FH rats and to apply the described refinements.

Abstract

The Fawn hooded (FH) rat is commonly used in biomedical research. It is widely acknowledged that the FH rat has a bleeding disorder; leading to abundant bleedings. Although this bleeding disorder is investigated to model the storage pool defect; its impact on commonly performed invasive laboratory procedures has not yet been described. Our research group experienced clinically significant consequences of this bleeding disorder following invasive procedures (including intraperitoneal injections and neurocranial surgery) in the Rjlbm: FH stock. The clinical consequences of the surgical and anesthetic protocols applied; are described including the subsequent procedural refinements applied to minimize the impact of this disorder. It is strongly recommended to take the bleeding diathesis into account when performing invasive procedures in FH rats and to apply the suggested refinement of procedures.

A novel hypothesis for an alkaline phosphatase 'rescue' mechanism in the hepatic acute phase immune response

The liver isoform of the enzyme alkaline phosphatase (AP) has been used classically as a serum biomarker for hepatic disease states such as hepatitis, steatosis, cirrhosis, drug-induced liver injury, and hepatocellular carcinoma. Recent studies have demonstrated a more general anti-inflammatory role for AP, as it is capable of dephosphorylating potentially deleterious molecules such as nucleotide phosphates, the pathogenic endotoxin lipopolysaccharide (LPS), and the contact clotting pathway activator polyphosphate (polyP), thereby reducing inflammation and coagulopathy systemically. Yet the mechanism underlying the observed increase in liver AP levels in circulation during inflammatory insults is largely unknown. This paper hypothesizes an immunological role for AP in the liver and the potential of this system for damping generalized inflammation along with a wide range of ancillary pathologies. Based on the provided framework, a mechanism is proposed in which AP undergoes transcytosis in hepatocytes from the canalicular membrane to the sinusoidal membrane during inflammation and the enzyme's expression is upregulated as a result. Through a tightly controlled, nucleotide-stimulated negative feedback process, AP is transported in this model as an immune complex with immunoglobulin G by the asialoglycoprotein receptor through the cell and secreted into the serum, likely using the receptor's State 1 pathway. The subsequent dephosphorylation of inflammatory stimuli by AP and uptake of the circulating immune complex by endothelial cells and macrophages may lead to decreased inflammation and coagulopathy while providing an early upstream signal for the induction of a number of anti-inflammatory gene products, including AP itself.

Extracellular Ca(2+) modulates ADP-evoked aggregation through altered agonist degradation: implications for conditions used to study P2Y receptor activation

ADP is considered a weak platelet agonist due to the limited aggregation responses it induces in vitro at physiological concentrations of extracellular Ca²⁺ [(Ca²⁺)_o]. Lowering [Ca²⁺]_o paradoxically enhances ADP-evoked aggregation, an effect that has been attributed to enhanced thromboxane A₂ production. This study examined the role of ectonucleotidases in the [Ca²⁺]_o-dependence of platelet activation. Reducing [Ca²⁺]_o from millimolar to micromolar levels converted ADP (10 μmol/l)-evoked platelet aggregation from a transient to a sustained response in both platelet-rich plasma and washed suspensions. Blocking thromboxane A₂ production with aspirin had no effect on this [Ca²⁺]_o-dependence. Prevention of ADP degradation abolished the differences between low and physiological [Ca²⁺]_o resulting in a robust and sustained aggregation in both conditions. Measurements of extracellular ADP revealed reduced degradation in both plasma and apyrase-containing saline at micromolar compared to millimolar [Ca²⁺]_o. As reported previously, thromboxane A₂ generation was enhanced at low [Ca²⁺]_o, however this was independent of ectonucleotidase activity_. P2Y receptor antagonists cangrelor and MRS2179 demonstrated the necessity of P2Y₁₂ receptors for sustained ADP-evoked aggregation, with a minor role for P2Y₁. In conclusion, Ca²⁺-dependent ectonucleotidase activity is a major factor determining the extent of platelet aggregation to ADP and must be controlled for in studies of P2Y receptor activation.