Short-term treatment with nitrate is not sufficient to induce in vivo antithrombotic effects in rats and mice

Direct comparison of inorganic nitrite and nitrate on vascular dysfunction and oxidative damage in experimental arterial hypertension

Arterial hypertension is one of the major health risk factors leading to coronary artery disease, stroke or peripheral artery disease. Dietary uptake of inorganic nitrite (NO₂^-) and nitrate (NO₃^-) via vegetables leads to enhanced vascular NO bioavailability and provides antihypertensive effects. The present study aims to understand the underlying vasoprotective effects of nutritional NO₂^- and NO₃^- co-therapy in mice with angiotensin-II (AT-II)-induced arterial hypertension. High-dose AT-II (1 mg/kg/d, 1w, s. c.) was used to induce arterial hypertension in male C57BL/6 mice. Additional inorganic nitrite (7.5 mg/kg/d, p. o.) or nitrate (150 mg/kg/d, p. o.) were administered via the drinking water. Blood pressure (tail-cuff method) and endothelial function (isometric tension) were determined. Oxidative stress and inflammation markers were quantified in aorta, heart, kidney and blood. Co-treatment with inorganic nitrite, but not with nitrate, normalized vascular function, oxidative stress markers and inflammatory pathways in AT-II treated mice. Of note, the highly beneficial effects of nitrite on all parameters and the less pronounced protection by nitrate, as seen by improvement of some parameters, were observed despite no significant increase in plasma nitrite levels by both therapies. Methemoglobin levels tended to be higher upon nitrite/nitrate treatment. Nutritional nitric oxide precursors represent a non-pharmacological treatment option for hypertension that could be applied to the general population (e.g. by eating certain vegetables). The more beneficial effects of inorganic nitrite may rely on superior NO bioactivation and stronger blood pressure lowering effects. Future large-scale clinical studies should investigate whether hypertension and cardiovascular outcome in general can be influenced by dietary inorganic nitrite therapy.

Effect of quinolinic acid - A uremic toxin from tryptophan metabolism - On hemostatic profile in rat and mouse thrombosis models

PURPOSE

We aimed to determine the effect of quinolinic acid (QA) on hemostasis in rat and mouse models of thrombosis.

MATERIAL AND METHODS

Wistar rats (male, n = 72) received QA dissolved in drinking water in doses of 3, 10, 30 mg/kg or pure drinking water (vehicle control group -VEH) for 14 days. On the 14^th day of the experiment the effect of QA on hemostasis was evaluated using electrically induced arterial thrombosis model. The following parameters were measured: thrombus weight, hematology, thromboelastometric (ROTEM) parameters, TXA₂ and 6-keto-PGF_1α concentration, coagulation and fibrinolytic markers activity and concentration. GFP mice (male, n = 30) were assigned to the group receiving QA (30 mg/kg) or VEH for 14 days and to the group receiving: single intravenous dose of QA (30 mg/kg) or VEH or the same dose of QA and anti-CD31 (platelet endothelial cell adhesion molecule-1, PECAM-1) antibody conjugated with Alexa Fluor 647. The effect of QA on hemostasis was evaluated in the model of laser-induced injury of mesentery vein using intravital confocal microscopy.

RESULTS

Administering QA for 14 days resulted in a divergent, depending on dose, increase in concentration of active form of tPA and PAI-1 and concentration of total PAI-1 and PAP complexes in rats' plasma. In turn, administering QA for 14 days in mice revealed its prothrombotic activity, while single-dose IV administration revealed its antithrombotic activity, through the up-regulation of PECAM-1 expression.

CONCLUSIONS

We demonstrated the first evidence for the opposite biological effects of QA on hemostasis in rat and mouse thrombosis models.

Multiorgan Development of Oxidative and Nitrosative Stress in LPS-Induced Endotoxemia in C57Bl/6 Mice: DHE-Based In Vivo Approach

Detection of free radicals in tissues is challenging. Most approaches rely on incubating excised sections or homogenates with reagents, typically at supraphysiologic oxygen tensions, to finally detect surrogate, nonspecific end products. In the present work, we explored the potential of using intravenously (i.v.) injected dihydroethidine (DHE) to detect superoxide radical (O₂ ^∙-) abundance in vivo by quantification of the superoxide-specific DHE oxidation product, 2-hydroxyethidium (2-OH-E⁺), as well as ethidium (E⁺) and DHE in multiple tissues in a murine model of endotoxemia induced by lipopolysaccharide (LPS). LPS was injected intraperitoneally (i.p.), while DHE was delivered via the tail vein one hour before sacrifice. Tissues (kidney, lung, liver, and brain) were harvested and subjected to HPLC/fluorescent analysis of DHE and its monomeric oxidation products. In parallel, electron spin resonance (EPR) spin trapping was used to measure nitric oxide (^∙NO) production in the aorta, lung, and liver isolated from the same mice. Endotoxemic inflammation was validated by analysis of plasma biomarkers. The concentration of 2-OH-E⁺ varied in the liver, lung, and kidney; however, the ratios of 2-OH-E⁺/E⁺ and 2-OH-E⁺/DHE were increased in the liver and kidney but not in the lung or the brain. An LPS-induced robust level of ^∙NO burst was observed in the liver, whereas the lung demonstrated a moderate yet progressive increase in the rate of ^∙NO production. Interestingly, endothelial dysfunction was observed in the aorta, as evidenced by decreased ^∙NO production 6 hours post-LPS injection that coincided with the inflammatory burden of endotoxemia (e.g. elevated serum amyloid A and prostaglandin E₂). Combined, these data demonstrate that systemic delivery of DHE affords the capacity to specifically detect O₂ ^∙- production in vivo. Furthermore, the ratio of 2-OH-E⁺/E⁺ oxidation products in tissues provides a tool for comparative insight into the oxidative environments in various organs. Based on our findings, we demonstrate that the endotoxemic liver is susceptible to both O₂ ^∙--mediated and nonspecific oxidant stress as well as nitrosative stress. Oxidant stress in the lung was detected to a lesser extent, thus underscoring a differential response of liver and lung to endotoxemic injury induced by intraperitoneal LPS injection.