Genetic strain differences in platelet aggregation of laboratory mice

Strain differences in the drug transport capacity of intestinal glucose transporters in Sprague-Dawley versus Wistar rats, C57BL/6J versus Kunming mice

Designing oral drug delivery systems using intestinal glucose transporters (IGTs) may be one of the strategies for improving oral bioavailability of drugs. However, little is known about the biological factors affecting the drug transport capacity of IGTs. Gastrodin is a sedative drug with a structure very similar to glucose. It is a highly water-soluble phenolic glucoside. It can hardly enter the intestine through simple diffusion but exhibits good oral bioavailability of over 80%. We confirmed that gastrodin is absorbed via the intestinal glucose transport pathway. It has the highest oral bioavailability among the reported glycosides' active ingredients through this pathway. Thus, gastrodin is the most selective drug substrate of IGTs and can be used to evaluate the drug transport capacity of IGTs. Obviously, strain is one of the main biological factors affecting drug absorption. This study firstly compared the drug transport capacity of IGTs between SD rats and Wistar rats and between C57 mice and KM mice by pharmacokinetic experiments and single-pass intestinal perfusion experiments of gastrodin. Then, the sodium-dependent glucose transporter type 1 (SGLT1) and sodium-independent glucose transporters type 2 (GLUT2) in the duodenum, jejunum, ileum and colon of these animals were quantified using RT-qPCR and Western blot. The results showed that the oral bioavailability of gastrodin in Wistar rats was significantly higher than in SD rats and significantly higher in KM mice than in C57 mice. Gastrodin absorption significantly differed among different intestinal segments in SD rats, C57 mice and KM mice, except Wistar rats. RT-qPCR and Western blot demonstrated that the intestinal expression distribution of SGLT1 and GLUT2 in SD rats and C57 mice was duodenum ≈ jejunum > ileum > colon. SGLT1 expression did not differ among different intestinal segments in KM mice, whereas the intestinal expression distribution of GLUT2 was duodenum ≈ jejunum ≈ ileum > colon. However, the expression of SGLT1 and GLUT2 did not differ among different intestinal segments in Wistar rats. It was reported that the intestinal expression distribution of SGLT1 and GLUT2 in humans is duodenum > jejunum > ileum > colon. Hence, the intestinal expression distribution of SGLT1 and GLUT2 of SD rats and C57 mice was more similar to that in humans. In conclusion, the drug transport capacity of IGTs differs in different strains of rats and mice. SD rats and C57 mice are more suitable for evaluating the pharmacokinetics of glycosides' active ingredients absorbed via the intestinal glucose transport pathway.

Comparative study of platelet aggregation and secretion induced by Bothrops jararaca snake venom and thrombin

Victims of Bothrops jararaca snakebites manifest bleedings, blood incoagulability, platelet dysfunction, and thrombocytopenia, and the latter has been directly implicated in the genesis of hemorrhagic diathesis. We addressed herein the direct effects of B. jararaca venom (BjV) on ex vivo platelet aggregation and granule secretion in washed human and mouse platelets. BjV directly aggregated platelets, but the extent of platelet aggregation was lower in human than mouse platelets. On the other hand, BjV (24.4 μg/mL) and thrombin (0.1 U/mL) induced a similar extent of ATP and platelet factor 4 (PF4) secretion in both species. BjV-induced platelet aggregation was independent of the platelet dense body content, as in pearl mouse (Ap3b1^-/-) platelets, whose dense bodies are deficient in adenine nucleotides and serotonin, the extent of platelet aggregation was superior to that induced in BALB/c or C57BL/6 mice. BjV-induced β-hexosaminidase secretion in human platelets was less intense than that evoked by thrombin, and the contrary was observed in mouse platelets. Irreversible inactivation of platelet cyclooxygenase 1 by acetylsalicylic acid did not reduce BjV-induced platelet aggregation. BjV exerted no cytotoxic activity in human and mouse platelets, as evaluated by lactate dehydrogenase loss. Eptifibatide, which inhibits the binding of fibrinogen to platelet glycoprotein complex GPIIb-IIIa, differently blocked BjV-induced platelet aggregation in mice and humans. BjV-induced platelet aggregation did not depend on snake venom serine proteinases nor metalloproteinases in mice, whilst serine proteinases were rather important for platelet aggregation in humans. Our results show that BjV induces direct activation, aggregation, and secretion in human and mouse platelets, but it exerts diverse responses in them, which should be considered in comparative studies to understand pathophysiological events during Bothrops envenomation.

Murine strain differences in hemostasis and thrombosis and tissue factor pathway inhibitor

INTRODUCTION

Differences among murine strains often lead to differential responses in models of human disease. The aim of the current study was to investigate whether differences exist among strains in models of hemostasis and thrombosis and whether these differences are reflected in differences in the tissue factor (TF) pathway.

METHODS

We examined baseline hemostatic parameters and the response to FeCl3-induced arterial thrombosis and a tail vein bleeding model in C57BL/6J (C57), 129S1/SvImJ (129S), and Balb/cJ (BalbC) mice. Finally, we examined TF and tissue factor pathway inhibitor (TFPI) activities in blood and expression in vascular tissue to determine whether these factors covary with a thrombotic phenotype.

RESULTS

No differences were observed in PT or aPTT among strains. 129S mice had lower platelet counts (p<0.001). BalbC had an increased rate of occlusion (mean occlusion time of 330+/-45 sec) in a FeCl(3)-induced model of thrombosis when compared to C57 (1182+/-349 sec) or 129 S (1442+/-281 sec) (p<0.05). Similarly, BalbC demonstrated reduced blood loss in tail bleeding experiments when compared to C57 and 129S. Vascular expression of TF and TFPI content did not correlate with the thrombotic phenotype of BalbC. However, circulating TFPI activities were lower in BalbC compared to both C57 and 129S mice. When normalized to circulating TF activities, BalbC had lower circulating TFPI activity than C57 and 129S, and there was a significant correlation between tail bleeding and normalized TFPI activity (r=0.67).

CONCLUSIONS

These data suggest that there are significant differences among strains in thrombosis and hemostasis and that circulating TFPI activity correlates with these differences.

Higher levels of collagen and facilitated healing protect against ventricular rupture following myocardial infarction

The mechanism of cardiac rupture after MI (myocardial infarction) is not fully understood. Rupture has not been reported in most laboratory species, including the rat, but does occur in mice. We have reported previously that beta2-TG mice (transgenic mice with cardiac-restricted overexpression of beta2-adrenergic receptors) had a lower incidence of rupture compared with NTG (non-transgenic) littermates. We hypothesized that the difference in the incidence of rupture between rodents and specific mouse strains is due to the difference in collagen content following MI. In the present study, we compared the difference in matrix remodelling post-MI between beta2-TG and NTG mice and between mice and rats. MI was induced by ligation of the left main coronary artery. Following MI, tensile strength, insoluble and soluble collagen content and gelatinase expression were determined in the infarcted and non-infarcted myocardium. Better preserved tensile strength measured as TTR [tension-to-rupture; 88+/-14 and 58+/-3% of the respective sham group values for beta2-TG compared with NTG mice (P<0.05); 108+/-7 and 32+/-4% of the respective sham group values for rats compared with 129sv mice (P<0.01)] and less severe acute infarct expansion after MI were found in rats compared with mice or in beta2-TG compared with NTG mice. These differences were associated with a higher content of pre-existing fibril collagen in the normal myocardium of beta2-TG compared with NTG mice (1.6-fold) or rats compared with 129sv mice (2-fold) and an accelerated fibrotic healing in the infarcted myocardium. Additionally, a less pronounced increase in MMP-9 (matrix metalloproteinase-9) activity was observed in the infarcted myocardium of rats compared with 129sv mice. We conclude that a higher collagen level is associated with facilitated fibrotic healing of an infarct and preserves the tensile strength of infarcted myocardium, thereby preventing cardiac rupture and acute ventricular remodelling.

Circadian variations in coagulation and fibrinolytic factors among four different strains of mice

This study examined circadian variation in coagulation and fibrinolytic parameters among Jcl:ICR, C3H/HeN, BALB/cA, and C57BL/6J strains of mice. Plasma plasminogen activator inhibitor 1 (PAI-1) levels fluctuated in a circadian manner and peaked in accordance with the mRNA levels at the start of the active phase in all strains. Fibrinogen mRNA levels peaked at the start of rest periods in all strains, although plasma fibrinogen levels remained constant. Strain differences in plasma antithrombin (AT) activity and protein C (PC) levels were then identified. Plasma AT activity was circadian rhythmic only in Jcl:ICR, but not in other strains, although the mRNA levels remained constant in all strains. Levels of plasma PC and its mRNA fluctuated in a circadian manner only in Jcl:ICR mice, whereas those of plasma prothrombin, factor X, factor VII, prothrombin time (PT), and activated partial thrombin time (APTT) remained constant in all strains. These results suggest that genetic heterogeneity underlies phenotypic variations in the circadian rhythmicity of blood coagulation and fibrinolysis. The circadian onset of thrombotic events might be due in part to the rhythmic gene expression of coagulation and fibrinolytic factors. The present study provides fundamental information about mouse strains that will help to understand the circadian variation in blood coagulation and fibrinolysis.

In vivo response to vascular injury in the absence of factor IX: Examination in factor IX knockout mice

INTRODUCTION

Recently, in vitro models of coagulation have called into question the traditional conception of Factor IX as an intrinsic pathway protein, essential to propagation of coagulation but not central to the initiation of hemostatic plug, which has been thought instead to involve TF/FVIIa interactions with factor X and platelets. We hypothesized that the activation of factor IX, and its role in a factor IXa/FVIIa "tenase" complex leading to thrombin generation, plays a more important role than that of TF/FVIIa complex activation of factor X in the early hemostatic response to vascular injury. In vivo modeling is possible because of the generation of factor IX(-/-) mice.

MATERIALS AND METHODS

We used two models of arterial vascular injury, histological examination following mechanical carotid artery disruption and intravital microscopy of a mesenteric arteriole subsequent to ferric chloride arteriolar injury to examine mice having complete deficiency of factor IX (FIX(-/-)).

RESULTS

Both injury models demonstrate that platelet rich thrombi /hemostatic plug in FIX(-/-) mice is dramatically reduced as compared to wild type mice under conditions of high shear; in fact, no platelet thrombi (>20 mum) were observed in the intravital experiments. Interestingly, the platelet defect is more striking than that described in mice lacking fibrinogen and/or von Willebrand factor.

CONCLUSIONS

The results suggest TF/FVIIa-->FX pathway is insufficient for effective platelet aggregation in the presence of high flow, requiring factor IX at the convergence of both intrinsic and extrinsic pathways. Following platelet adhesion, factor IX is required for normal platelet aggregation in vivo, as well as thrombin generation and propagation of occlusive thrombus at the site of vascular injury.