N6022 attenuates cerebral ischemia/reperfusion injury-induced microglia ferroptosis by promoting Nrf2 nuclear translocation and inhibiting the GSNOR/GSTP1 axis

Stroke poses a significant risk of mortality, particularly among the elderly population. The pathophysiological process of ischemic stroke is complex, and it is crucial to elucidate its molecular mechanisms and explore potential protective drugs. Ferroptosis, a newly recognized form of programmed cell death distinct from necrosis, apoptosis, and autophagy, is closely associated with the pathophysiology of ischemic stroke. N6022, a selective inhibitor of S-nitrosoglutathione reductase (GSNOR), is a "first-in-class" drug for asthma with potential therapeutic applications. However, it remains unclear whether N6022 exerts protective effects in ischemic stroke, and the precise mechanisms of its action are unknown. This study aimed to investigate whether N6022 mitigates cerebral ischemia/reperfusion (I/R) injury by reducing ferroptosis and to elucidate the underlying mechanisms. Accordingly, we established an oxygen-glucose deprivation/reperfusion (OGD/R) cell model and a middle cerebral artery occlusion/reperfusion (MCAO/R) mouse model to mimic cerebral I/R injury. Our data, both in vitro and in vivo, demonstrated that N6022 effectively protected against I/R-induced brain damage and neurological deficits in mice, as well as OGD/R-induced BV2 cell damage. Mechanistically, N6022 promoted Nrf2 nuclear translocation, enhancing intracellular antioxidant capacity of SLC7A11-GPX4 system. Furthermore, N6022 interfered with the interaction of GSNOR with GSTP1, thereby boosting the antioxidant capacity of GSTP1 and attenuating ferroptosis. These findings provide novel insights, showing that N6022 attenuates microglial ferroptosis induced by cerebral I/R injury through the promotion of Nrf2 nuclear translocation and inhibition of the GSNOR/GSTP1 axis.

GSNOR and ALDH2 alleviate traumatic spinal cord injury

Traumatic spinal cord injury (SCI) enhances the activity of S-nitrosoglutathione reductase (GSNOR) and inhibits the mitochondrial aldehyde dehydrogenase 2 (ALDH2) activity, resulting in prolonged and sustained pain and functional deficits. This study's objective was to test the hypotheses that GSNOR's specific inhibitor N6022 mitigates pain and improves functional recovery in a mouse model of SCI. Furthermore, the degree of recovery is enhanced and the rate of recovery is accelerated by an ALDH2 activator Alda-1. Using both wild-type and GSNOR^-/^- mice, the SCI model deployed for groups was contusion at the T9-T10 vertebral level. The enzymatic activity of GSNOR and ALDH2 was measured, and the expression of GSNOR and ALDH2 was determined by western blot analysis. Functional improvements in experimental animals were assessed with locomotor, sensorimotor, and pain-like behavior tests. Wild-type SCI animals had enhanced GSNOR activity and decreased ALDH2 activity, leading to neurovascular dysfunction, edema, and worsened functional outcomes, including locomotor deficits and pain. Compared to wild-type SCI mice, GSNOR^-/^- mice had better functional outcomes. Monotherapy with either GSNOR inhibition by N6022 or enhanced ALDH2 activity by Alda-1 correlated well with functional recovery and lessened pain. However, combination therapy provided synergistic pain-relieving effects and more significant functional recovery compared with monotherapy. Conclusively, dysregulations in GSNOR and ALDH2 are among the causative mechanisms of SCI injury. Either inhibiting GSNOR or activating ALDH2 ameliorates SCI. Combining the specific inhibitor of GSNOR (N6022) with the selective activator of ALDH2 (Alda-1) provides greater protection to the neurovascular unit and confers greater functional recovery. The study is novel, and the combination therapy (N6022 + Alda-1) possesses translational potential.

Targeting GSNOR for functional recovery in a middle-aged mouse model of stroke

The nitric oxide (NO) metabolome and the NO metabolite-based neurovascular protective pathways are dysregulated after stroke. The major NO metabolite S-nitrosoglutahione (GSNO) is essential for S-nitrosylation-based signaling events and the inhibition of S-nitrosoglutahione (GSNO)-metabolizing enzyme GSNO reductase (GSNOR) provides protective effects following cardiac ischemia. However, the role of GSNOR and GSNOR inhibition-mediated increased GSNO/S-nitrosylation is not understood in neurovascular diseases such as stroke. Because age is the major risk factor of stroke and recovery in aged stroke patients is low and slow, we investigated the efficacy of GSNOR inhibition using a GSNOR selective inhibitor N6022 in a clinically relevant middle-aged cerebral ischemia and reperfusion (IR) mouse model of stroke. N6022 (5 mg/kg; iv) treatment of IR mice at 2 h after reperfusion followed by the treatment of the same dose daily for 3 days reduced the infarct volume and decreased the neurological score. Daily treatment of IR animals with N6022 for 2 weeks significantly improved neurological score, brain infarctions/atrophy, survival rate, motor (measured by cylinder test) and cognitive (evaluated by novel object recognition test) functions which paralleled the decreased activity of GSNOR, reduced levels of peroxynitrite and decreased neurological score. These results are the first evidence of a new pathway for the treatment of stroke via the inhibition of GSNOR. Based on the efficacy of N6022 in the stroke animal model and its use in human therapeutic studies without toxicity, we submit that GSNOR is a druggable target, and N6022 is a promising drug candidate for human stroke therapy.

S-Nitrosoglutathione Mimics the Beneficial Activity of Endothelial Nitric Oxide Synthase-Derived Nitric Oxide in a Mouse Model of Stroke

BACKGROUND

The nitric oxide (NO)-producing activity of endothelial nitric oxide synthase (eNOS) plays a significant role in maintaining endothelial function and protecting against the stroke injury. However, the activity of the eNOS enzyme and the metabolism of major NO metabolite S-nitrosoglutathione (GSNO) are dysregulated after stroke, causing endothelial dysfunction. We investigated whether an administration of exogenous of GSNO or enhancing the level of endogenous GSNO protects against neurovascular injury in wild-type (WT) and eNOS-null (endothelial dysfunction) mouse models of cerebral ischemia-reperfusion (IR).

METHODS

Transient cerebral ischemic injury was induced by middle cerebral artery occlusion (MCAO) for 60 minutes in male adult WT and eNOS null mice. GSNO (0.1 mg/kg body weight, intravenously) or N6022 (GSNO reductase inhibitor, 5.0 mg/kg body weight, intravenously) was administered 30 minutes before MCAO in preinjury and at the reperfusion in postinjury studies. Brain infarctions, edema, and neurobehavioral functions were evaluated at 24 hours after the reperfusion.

RESULTS

eNOS-null mice had a higher degree (P< .05) of injury than WT. Pre- or postinjury treatment with either GSNO or N6022 significantly reduced infarct volume, improved neurological and sensorimotor function in both WT and eNOS-null mice.

CONCLUSION

Reduced brain infarctions and edema, and improved neurobehavioral functions by pre- or postinjury GSNO treatment of eNOS knock out mice indicate that GSNO can attenuate IR injury, likely by mimicking the eNOS-derived NO-dependent anti-ischemic and anti-inflammatory functions. Neurovascular protection by GSNO/N6022 in both pre- and postischemic injury groups support GSNO as a promising drug candidate for the prevention and treatment of stroke injury.

Effect of the S-nitrosoglutathione reductase inhibitor N6022 on bronchial hyperreactivity in asthma

RATIONALE

Patients with asthma demonstrate depletion of the endogenous bronchodilator GSNO and upregulation of GSNOR.

OBJECTIVES

An exploratory proof of concept clinical study of N6022 in mild asthma to determine the potential bronchoprotective effects of GSNOR inhibition. Mechanistic studies aimed to provide translational evidence of effect.

METHODS

Fourteen mild asthma patients were treated with intravenous N6022 (5 mg) or placebo and observed for 7 days, with repeated assessments of the provocative dose of methacholine causing a 20% fall in FEV1 (methacholine PC₂₀ FEV1), followed by a washout period and crossover treatment and observation. In vitro studies in isolated eosinophils investigated the effect of GSNO and N6022 on apoptosis.

MEASUREMENTS AND MAIN RESULTS

This was a negative trial as it failed to reach its primary endpoint, which was change from baseline in methacholine PC₂₀ FEV1 at 24 h. However, our exploratory analysis demonstrated significantly more two dose-doubling increases in PC₂₀ FEV1 for N6022 compared with placebo (21% vs 6%, P < 0.05) over the 7-day observation period. Furthermore, a significant treatment effect was observed in the change in PC₂₀ FEV1 from baseline averaged over the 7-day observation period (mean change: +0.82 mg/ml [N6022] from 1.34 mg/ml [baseline] vs -0.18 mg/ml [placebo] from 1.16 mg/ml [baseline], P = 0.023). N6022 was well tolerated in mild asthmatics. In vitro studies demonstrated enhanced eosinophilic apoptosis with N6022.

CONCLUSIONS

In this early phase exploratory proof of concept trial in asthma, N6022 did not significantly alter methacholine PC₂₀ FEV1 at 24 h, but did have a treatment effect at 7 days compared to baseline. Further investigation of the efficacy of S-nitrosoglutathione reductase inhibition in a patient population with eosinophilic asthma is warranted.

Discovery of s-nitrosoglutathione reductase inhibitors: potential agents for the treatment of asthma and other inflammatory diseases

S-Nitrosoglutathione reductase (GSNOR) regulates S-nitrosothiols (SNOs) and nitric oxide (NO) in vivo through catabolism of S-nitrosoglutathione (GSNO). GSNOR and the anti-inflammatory and smooth muscle relaxant activities of SNOs, GSNO, and NO play significant roles in pulmonary, cardiovascular, and gastrointestinal function. In GSNOR knockout mice, basal airway tone is reduced and the response to challenge with bronchoconstrictors or airway allergens is attenuated. Consequently, GSNOR has emerged as an attractive therapeutic target for several clinically important human diseases. As such, small molecule inhibitors of GSNOR were developed. These GSNOR inhibitors were potent, selective, and efficacious in animal models of inflammatory disease characterized by reduced levels of GSNO and bioavailable NO. N6022, a potent and reversible GSNOR inhibitor, reduced bronchoconstriction and pulmonary inflammation in a mouse model of asthma and demonstrated an acceptable safety profile. N6022 is currently in clinical development as a potential agent for the treatment of acute asthma.