The nitric oxide hypothesis of late preconditioning

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Biochemistry of Signaling Pathways

Background:

• Ischemic preconditioning (PC) exhibits distinct early and late phases, with the late phase lasting several days.
• The late phase of PC is crucial for sustained cardioprotection but its underlying molecular mechanisms remain under investigation.
• Nitric oxide (NO) is a key signaling molecule implicated in various physiological processes, including cardiovascular regulation.

Discussion:

• The 'NO hypothesis of late PC' proposes a dual role for NO: initiating the response on day 1 and mediating protection on day 2.
• This hypothesis involves the sequential activation of endothelial NOS (eNOS) and inducible NOS (iNOS) isoforms, leading to increased NO production.
• The cascade includes reactive oxygen and nitrogen species, protein kinase C epsilon (PKCε) activation, and downstream signaling involving tyrosine kinases and NF-kappa B.

Key Insights:

• On day 1, ischemic stress increases NO and superoxide, forming peroxynitrite (ONOO-), which activates PKCε, initiating the late PC response.
• On day 2, iNOS is upregulated, producing NO that directly protects the myocardium against ischemic injury.
• Tyrosine kinases play a role in modulating iNOS activity on day 2, further refining the protective mechanism.

Outlook:

• The NO hypothesis provides a comprehensive framework for understanding the initiation and mediation of late PC.
• Understanding this pathway has significant pathophysiological implications for myocardial ischemia.
• Clinical applications may involve utilizing NO donors, such as nitrates, for enhanced cardioprotection in patients.