Hydroxyl radical production via NADPH oxidase in rat striatum due to carbon monoxide poisoning

Mechanisms and therapeutic targets of carbon monoxide poisoning: A focus on reactive oxygen species

Carbon monoxide (CO) poisoning presents a substantial public health challenge that necessitates the identification of its pathological mechanisms and therapeutic targets. CO toxicity arises from tissue hypoxia-ischemia secondary to carboxyhemoglobin formation, and cellular damage mediated by CO at the cellular level. The mitochondria are the major targets of neuronal damage caused by CO. Under normal physiological conditions, mitochondria produce reactive oxygen species (ROS), which are byproducts of aerobic metabolism. While low ROS levels are crucial for essential cellular functions, including signal transduction, differentiation, responses to hypoxia and immunity, transcriptional regulation, and autophagy, excess ROS become pathological and exacerbate CO poisoning. This review presents the evidence of elevated ROS being associated with the progression of CO poisoning. Antioxidant treatments targeting ROS removal have been proven effective in mitigating CO poisoning, underscoring their therapeutic potential. In this review, we highlight the latest advances in the understanding of the role and the clinical implications of ROS in CO poisoning. We focus on cellular sources of ROS, the molecular mechanisms underlying mitochondrial oxidative stress, and potential therapeutic strategies for targeting ROS in CO poisoning.

Carbon Monoxide: A Pleiotropic Redox Regulator of Life and Death

Despite recent technological progress, carbon monoxide poisoning is still one of the leading causes of domestic and industrial morbidity and mortality. The brain is particularly vulnerable to CO toxicity, and thus the majority of survivors develop delayed movement and cognitive complications. CO binds to haemoglobin in erythrocytes, preventing oxygen delivery to tissues, and additionally inhibits mitochondrial respiration. This renders the effect of CO to be closely related to hypoxia reperfusion injury. Oxygen deprivation, as well as CO poisoning and re-oxygenation, are shown to be able to activate the production of reactive oxygen species and to induce oxidative stress. Here, we review the role of reactive oxygen species production and oxidative stress in the mechanism of neuronal cell death induced by carbon monoxide and re-oxygenation. We discuss possible protective mechanisms used by brain cells with a specific focus on the inhibition of CO-induced ROS production and oxidative stress.

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Carbon Monoxide Poisoning: From Microbes to Therapeutics

Carbon monoxide (CO) poisoning leads to 50,000-100,000 emergency room visits and 1,500-2,000 deaths each year in the United States alone. Even with treatment, survivors often suffer from long-term cardiac and neurocognitive deficits, highlighting a clear unmet medical need for novel therapeutic strategies that reduce morbidity and mortality associated with CO poisoning. This review examines the prevalence and impact of CO poisoning and pathophysiology in humans and highlights recent advances in therapeutic strategies that accelerate CO clearance and mitigate toxicity. We focus on recent developments of high-affinity molecules that take advantage of the uniquely strong interaction between CO and heme to selectively bind and sequester CO in preclinical models. These scavengers, which employ heme-binding scaffolds ranging from organic small molecules to hemoproteins derived from humans and potentially even microorganisms, show promise as field-deployable antidotes that may rapidly accelerate CO clearance and improve outcomes for survivors of acute CO poisoning.

Carbon monoxide neurotoxicity is triggered by oxidative stress induced by ROS production from three distinct cellular sources

Carbon monoxide (CO) poisoning is one of the leading causes of toxic mortality and morbidity. We have studied the generation of reactive oxygen species in cortical neurons in culture in response to toxic doses of CO exposure. Fluorescence microscopy was used to measure the rate of free radical generation, lipid peroxidation, GSH level and also mitochondrial metabolism. We have found that toxic concentrations of CO released from CORM-401 induced mitochondrial depolarisation and inhibition of NADH dependent respiration to a lesser degree than when compared to ischaemia. Energy collapse was not observed within 40 min of CO exposure. We have found that CO induces the generation of reactive oxygen species resulting in lipid peroxidation and a decrease in GSH via three different mechanisms: from mitochondria during the first minutes of CO exposure, from xanthine oxidase at around 20 min exposure due to energy deprivation, and considerable ROS production from NADPH oxidase in the post CO exposure period (re-oxygenation). Inhibition of these different phases with mitochondrial antioxidants, inhibitors of xanthine oxidase, or NADPH oxidase, protected neurons and astrocytes against CO-induced oxidative stress and cell death. The most profound effect was seen during NADPH oxidase inhibition. Thus, oxidative stress has a remarkably significant role in CO-induced neuronal cell death and preventing its occurrence during reoxygenation is of great importance in the consideration of a positive, neurologically protective therapeutic outcome for CO exposed patients.

Carbon Monoxide (CO), Nitric Oxide, and Hydrogen Sulfide Signaling During Acute CO Poisoning

Major toxic effects of acute carbon monoxide (CO) poisoning result from increases in reactive oxygen species (ROS) and reactive nitrogen species (RNS) producing oxidative stress. The importance of altered nitric oxide (NO) signaling in evoking increases in RNS during CO poisoning has been established. Although there is extensive literature describing NO and hydrogen sulfide (H2S) signaling in different types of cells under normal conditions, how CO poisoning-evoked deregulation of additional NO signaling pathways and H2S signaling pathways could result in cell injury has not been previously considered in detail. The goal of this article was to do this. The approach was to use published data to describe signaling pathways driven by CO bonding to different ferroproteins and then to collate data that describe NO and H2S signaling pathways that could interact with CO signaling pathways and be important during CO poisoning. Arteriolar smooth muscle cells—endothelial cells located in the coronary and some cerebral circulations—were used as a model to illustrate major signaling pathways driven by CO bonding to different ferroproteins. The results were consistent with the concept that multiple deregulated and interacting NO and H2S signaling pathways can be involved in producing cell injury evoked during acute CO poisoning and that these pathways interact with CO signaling pathways.

Mitochondrial toxins potentiate hydroxyl radical production in rat striatum during carbon monoxide poisoning

Hydroxyl radical (•OH) production in the rat striatum during carbon monoxide (CO) poisoning, which inhibits complex IV, was enhanced synergistically by malonate, a mitochondrial complex II inhibitor, but not N-methyl-4-phenylpyridinium or NaCN, complex I and IV inhibitors, respectively. No such enhancement appeared in the case of NaCN combined with malonate. Intrastriatal dopamine, which is involved in •OH production by malonate, did not synergistically enhance CO-induced •OH production. Diphenyleneiodonium, a nonselective NADPH oxidase inhibitor, partly suppressed the potentiation of CO-induced •OH production by malonate. Impairment of mitochondrial functions might potentiate oxidative stress and intensify CO toxicity in the brain.

Blockade of the renin-angiotensin system suppresses hydroxyl radical production in the rat striatum during carbon monoxide poisoning

Oxidative stress has been suggested to play a role in brain damage during carbon monoxide (CO) poisoning. Severe poisoning induced by CO at 3000 ppm, but not 1000 ppm, enhances hydroxyl radical (˙OH) production in the rat striatum, which might be mediated by NADPH oxidase (NOX) activation associated with Ras-related C3 botulinum toxin substrate (Rac) via cAMP signaling pathway activation. CO-induced ˙OH production was suppressed by antagonists of angiotensin II (AngII) type 1 receptor (AT1R) and type 2 receptor (AT2R) but not an antagonist of the Mas receptor. Suppression by an AT1R antagonist was unrelated to peroxisome proliferator-activated receptor γ. Angiotensin-converting enzyme inhibitors also suppressed CO-induced ˙OH production. Intrastriatal AngII at high concentrations enhanced ˙OH production. However, the enhancement of ˙OH production was resistant to inhibitors selective for NOX and Rac and to AT1R and AT2R antagonists. This indicates a different mechanism for ˙OH production induced by AngII than for that induced by CO poisoning. AT1R and AT2R antagonists had no significant effects on CO-induced cAMP production or ˙OH production induced by forskolin, which stimulates cAMP production. These findings suggest that the renin-angiotensin system might be involved in CO-induced ˙OH production in a manner independent of cAMP signaling pathways.