Inhalation of Nitric Oxide Prevents Ischemic Brain Damage in Experimental Stroke by Selective Dilatation of Collateral Arterioles

Abstract

Rationale: Stroke is the third most common cause of death in industrialized countries. The main therapeutic target is the ischemic penumbra, potentially salvageable brain tissue that dies within the first few hours after blood flow cessation. Hence, strategies to keep the penumbra alive until reperfusion occurs are needed.Objective: To study the effect of inhaled nitric oxide on cerebral vessels and cerebral perfusion under physiological conditions and in different models of cerebral ischemia. Methods and Results:This experimental study demonstrates that inhaled nitric oxide (applied in 30% oxygen/70% air mixture) leads to the formation of nitric oxide carriers in blood that distribute throughout the body. This was ascertained by in vivo microscopy in adult mice. Although under normal conditions inhaled nitric oxide does not affect cerebral blood flow, after experimental cerebral ischemia induced by transient middle cerebral artery occlusion it selectively dilates arterioles in the ischemic penumbra, thereby increasing collateral blood flow and significantly reducing ischemic brain damage. This translates into significantly improved neurological outcome. These findings were validated in independent laboratories using two different mouse models of cerebral ischemia and in a clinically relevant large animal model of stroke. Key Words: collateral blood flow Ⅲ ischemic penumbra Ⅲ ischemic stroke Ⅲ nitric oxide inhalation E very year stroke is responsible for the death of 5.5 million people. 1 Despite its high incidence and mortality, clinical therapeutic options are still limited. 2 Research efforts to find novel treatment strategies focus primarily on rescuing the ischemic penumbra, the viable tissue surrounding the nonviable infarct core. In the penumbra, blood flow is critically reduced but still suffices to sustain neuronal integrity for several hours. The delayed nature of cell death in the penumbra leaves a unique window of opportunity for therapeutic interventions. If adequate cerebral perfusion is re-established sufficiently fast, then penumbral tissue can be effectively saved. 3 Therefore, penumbral reperfusion at the earliest possible time is the most critical factor in determining neurological outcome and in preventing mortality after stroke. 4 Conclusions:

Monitoring Stroke Progression: In Vivo Imaging of Cortical Perfusion, Blood—Brain Barrier Permeability and Cellular Damage in the Rat Photothrombosis Model

“…4-Amino-5-methylamino-2',7'-difluorofluorescein diacetate (Molecular Probes) was topically applied (concentration: 50 to 200 μmol/l, 30 minutes incubation) 18 before PT for baseline imaging and ∼ 3 hours after PT to detect NO (n = 5).…”

“…Despite the recent development of new small molecule indicators, most data still originate from in vitro models. 48 Recently, DAF-FM was successfully used to detect NO formation in the arterial and venous cerebral circulation after transient medial cerebral artery occlusion in the mice brain in vivo, 18 yet it is still to be uncovered which cells produce NO. 24 We report increased NO levels in the peri-ischemic brain, mostly in close vicinity to the arterial wall, suggesting a major nonneuronal contribution to NO formation.…”

Nitric Oxide: Considerations for the Treatment of Ischemic Stroke

“…Nitric oxide inhalation is a clinically approved treatment that has few side effects that might positively influence the outcome following ischemic stroke. Terpolilli et al (2011) recently demonstrated an effect of iNO on the cerebrovasculature using in vivo microscopy. In their studies under physiological conditions, iNO led to a significant dilatation of cerebral venules, most probably due to an oxygentension-dependent mechanism.…”

Miniature Imaging Device with a Portable Processing System for Fluorescence Detection of Nitric Oxide in Living

“…On the other hand, NO is also used as a medical treatment, such as for the treatment of newborn infants with hypoxemic respiratory failure (5) and to prevent ischemic stroke. (6) Therefore, many techniques, such as chemiluminescence (7) and electron paramagnetic resonance (EPR) spectroscopy, (8) have been developed. Although these methods can detect NO in the nM range, they cannot be applied to in vivo research owing to toxicity from chemical reactions and the large size of the equipment.…”

“…In small animals, this method is widely used for NO detection. For example, Terpolilli et al (6) studied the functions of NO to prevent ischemic brain damage. However, it is difficult for use in the long-term detection of NO in animals because of the restriction of a microscope, which requires a fixed area and is bulky in size.…”