Heparin reacts with and inactivates nitric oxide

Rapid Formation of Methemoglobin via Nitric Oxide Delivery for Potential Use as an MRI Contrast Agent

Contrast-enhanced magnetic resonance angiography is a vital tool for evaluating vascular pathology. However, concerns about the limitations and safety of gadolinium-based contrast agents have led to an interest in alternative agents. Methemoglobin (metHb) increases the T1-weighted signal intensity of the magnetic resonance image of blood and could provide a safe and effective alternative. MetHb can be produced by the reaction of nitric oxide (NO) gas with oxyhemoglobin followed by natural conversion back to hemoglobin by cytochrome b5 reductase. Since rapid production of metHb via NO has not been studied, the effectiveness of producing metHb via NO delivery to blood was evaluated using a hollow-fiber module. MetHb production began immediately and > 90% conversion was achieved within 10 min. MetHb remained stable for at least 90 min when NO delivery was removed following metHb formation. Comparison of experimental data for metHb formation with model predictions showed that only a fraction of the NO delivered was utilized for metHb production, suggesting an additional fast reaction of NO with other blood constituents. Directly delivering NO to blood for the rapid formation of metHb provides a potential platform for producing metHb as an alternative contrast agent.

Development and In Vitro Whole Blood Hemocompatibility Screening of Endothelium-Mimetic Multifunctional Coatings

Multifunctional antithrombotic surface modifications for blood-contacting medical devices have emerged as a solution for foreign surface-mediated coagulation disturbance. Herein, we have developed and evaluated an endothelium-inspired strategy to reduce the thrombogenicity of medical plastics by imparting nitric oxide (NO) elution and heparin immobilization on the material surface. This dual-action approach (NO+Hep) was applied to polyethylene terephthalate (PET) blood incubation vials and compared to isolated modifications. Vials were characterized to evaluate NO surface flux as well as heparin density and activity. Hemocompatibility was assessed in vitro using whole blood from human donors. Compared to unmodified surfaces, blood incubated in the NO+Hep vials exhibited reduced platelet aggregation (15% decrease AUC, p = 0.040) and prolonged plasma clotting times (aPTT = 147% increase, p < 0.0001, prothrombin time = 5% increase, p = 0.0002). Prolongation of thromboelastography reaction time and elevated antifactor Xa levels in blood from NO+Hep versus PET vials suggests some heparin leaching from the vial surface, confirmed by post-blood incubation heparin density assessment. Results suggest NO+Hep surface modification is a promising approach for blood-contacting plastics; however, careful tuning of NO flux and heparin stabilization are essential and require assessment using human blood as performed here.

Antioxidant tempol modulates the increases in tissue nitric oxide metabolites concentrations after oral nitrite administration

Nitric oxide (NO) metabolites have physiological and pharmacological importance and increasing their tissue concentrations may result in beneficial effects. Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) has antioxidant properties that may improve NO bioavailability. Moreover, tempol increases oral nitrite-derived gastric formation of S-nitrosothiols (RSNO). We hypothesized that pretreatment with tempol may further increase tissue concentrations of NO-related species after oral nitrite administration and therefore we carried out a time-dependent analysis of how tempol affects the concentrations of NO metabolites in different tissues after oral nitrite administration to rats. NO metabolites (nitrate, nitrite and RSNO) were assessed by ozone-based reductive chemiluminescence assays in plasma, stomach, aorta, heart and liver samples obtained from anesthetized rats at baseline conditions and 15 min, 30 min, 2 h or 24 h after oral nitrite (15 mg/kg) was administered to rats pretreated with tempol (18 mg/kg) or vehicle 15 min prior to nitrite administration. Aortic protein nitrosation was assessed by resin-assited capture (SNO-RAC) method. We found that pretreatment with tempol transiently enhanced nitrite-induced increases in nitrite, RSNO and nitrate concentrations in the stomach and in the plasma (all P < 0.05), particularly for 15-30 min, without affecting aortic protein nitrosation. Pretreatment with tempol enhanced nitrite-induced increases in nitrite (but not RSNO or nitrate) concentrations in the heart (P < 0.05). In contrast, tempol attenuated nitrite-induced increases in nitrite, RSNO or nitrate concentrations in the liver. These findings show that pretreatment with tempol affects oral nitrite-induced changes in tissue concentrations of NO metabolites depending on tissue type and does not increase nitrite-induced vascular nitrosation. These results may indicate that oral nitrite therapy aiming at achieving increased nitrosation of cardiovascular targets requires appropriate doses of nitrite and is not optimized by tempol.

Heparin-Coated Albumin Nanoparticles for Drug Combination in Targeting Inflamed Intestine

Targeting areas of inflammation offers potential therapeutic and diagnostic benefits by maximizing drug and imaging marker on-target effects while minimizing systemic exposure that can be associated with adverse side effects. This strategy is particularly beneficial in the management of inflammatory bowel disease (IBD). Here an inflammation-targeting (IT) approach based on heparin-coated human serum albumin nanoparticles (HEP-HSA NPs) that utilize the increased intestinal permeability and changes in electrostatic interaction at the site of intestinal inflammation is described. Using small-molecule and biologic drugs as a model for drug combination, the HEP-HSA NPs demonstrate the capacity to load both drugs simultaneously; the dual-drug loaded HEP-HSA NPs exhibit a higher anti-inflammatory effect than both of the single-drug loaded NPs in vitro and selectively bind to inflamed intestine after enema administration in vivo in a murine model of colitis. Importantly, analyses of the physicochemical characteristics and targeting capacities of these NPs indicate that HEP coating modulates NP binding to the inflamed intestine, providing a foundation for future IT-NP formulation development.

Prion, amyloid beta-derived Cu(II) ions, or free Zn(II) ions support S-nitroso-dependent autocleavage of glypican-1 heparan sulfate

Copper are generally bound to proteins, e.g. the prion and the amyloid beta proteins. We have previously shown that copper ions are required to nitrosylate thiol groups in the core protein of glypican-1, a heparan sulfate-substituted proteoglycan. When S-nitrosylated glypican-1 is then exposed to an appropriate reducing agent, such as ascorbate, nitric oxide is released and autocatalyzes deaminative cleavage of the glypican-1 heparan sulfate side chains at sites where the glucosamines are N-unsubstituted. These processes take place in a stepwise manner, whereas glypican-1 recycles via a caveolin-1-associated pathway where copper ions could be provided by the prion protein. Here we show, by using both biochemical and microscopic techniques, that (a) the glypican-1 core protein binds copper(II) ions, reduces them to copper(I) when the thiols are nitrosylated and reoxidizes copper(I) to copper(II) when ascorbate releases nitric oxide; (b) maximally S-nitrosylated glypican-1 can cleave its own heparan sulfate chains at all available sites in a nitroxyl ion-dependent reaction; (c) free zinc(II) ions, which are redox inert, also support autocleavage of glypican-1 heparan sulfate, probably via transnitrosation, whereas they inhibit copper(II)-supported degradation; and (d) copper(II)-loaded but not zinc(II)-loaded prion protein or amyloid beta peptide support heparan sulfate degradation. As glypican-1 in prion null cells is poorly S-nitrosylated and as ectopic expression of cellular prion protein restores S-nitrosylation of glypican-1 in these cells, we propose that one function of the cellular prion protein is to deliver copper(II) for the S-nitrosylation of recycling glypican-1.