Effect of a free radical scavenger on nitric oxide release in microvessels

Abstract

Background

Superoxides impair nitric oxide (NO) bioactivity; however, the dynamics of NO release in the peripheral microcirculation remain unknown. We investigated the effect of a free-radical scavenger (edaravone) on dynamic NO release and the expression of eNOS and iNOS in microvessels.

Methods and results

An electrochemical microsensor was positioned at the iliac artery bifurcation of the rat abdominal aorta, and NO release was measured in response to edaravone. A bio-imaging model was also used to obtain images of NO release from microvessels. Moreover, eNOS expression and iNOS expression were investigated in inflammatory and non-inflammatory models. NO was observed in association with microvessels in the mesentery. NO release in the aorta was significantly greater with edaravone than with placebo in the non-inflammatory model (P < 0.05). Acetylcholine-induced NO release with edaravone was greater than with placebo in both models. Bio-imaging showed greater NO release from arterioles than from venules. eNOS expression with edaravone was greater than with placebo with or without inflammation. iNOS expression was increased by inflammation, but edaravone inhibited this increase.

Conclusion

These results support the critical role of NO in the microcirculation and suggest that free-radical scavenging increases the bioavailability of NO in the microcirculation via eNOS upregulation.

Introduction

The majority of reactive oxygen species (ROS) generated in vivo are removed by antioxidants or antioxidative enzymes. However, excessive generation of ROS can result in oxidation of critical biogenic substances such as DNA, lipids, enzymes, and proteins (Lau et al., 2008). Many reports show that oxidative damage of these biogenic substances can lead to problems such as the development of atherosclerosis (Barry-Lane et al., 2001, Griendling et al., 2000, Ozono et al., 2007). The level of oxidized low-density lipoproteins (LDLs) is believed to increase with increased oxidative stress and these oxidized LDLs contribute to the development of human coronary artery plaque, disturb vascular endothelial cells, and affect the accumulation of inflammatory cells (Ehara et al., 2001, Meisinger et al., 2005). They may also contribute to plaque destabilization (Ehara et al., 2001, Meisinger et al., 2005). Atherosclerotic progress is followed by damage to the microcirculation, which results in impaired blood flow and the formation of basic arteriosclerotic lesions. This damage to the microcirculation has a major impact on the production and release of vasorelaxation factors such as prostacyclin (Fleming et al., 1996, Gryglewski et al., 2001), nitric oxide metabolites (NOx) (Gryglewski et al., 2001), and endothelium-derived hyperpolarizing factors (Fleming et al., 1996). Nitric oxide (NO) is an essential gas mediator that regulates blood flow in the microcirculation in response to tissue metabolism (i.e., the consumption of oxygen) via vasorelaxation. It also has a platelet-antiaggregating effect (Arnal, 1997).

3-Methyl-1-1-phenyl-2-pyrazolin-5-one (edaravone), a free-radical scavenger, has been used clinically in Japan for the treatment of cerebral infarction since 2001, and it has been reported to improve clinical outcomes in patients with ischemic stroke (Group, 2003, Tanaka, 2002, Xi et al., 2007). Experimental studies have revealed that edaravone decreases oxidative stress (Zhang et al., 2005), and its neuroprotective effects are indisputable (Watanabe et al., 1994, Yoneda et al., 2003).

We examined the influence of ROS on NO release and on nitric oxide synthase (NOS) expression in endothelial cells in vivo by using the free-radical scavenger edaravone.