ANP Increases Zn2⁺ Accumulation During Reperfusion in Ex Vivo and In Vivo Hearts.

Abstract

Objective: Atrial natriuretic peptide (ANP) and Zn^2⁺ have been shown to confer cardioprotection against ischemia/reperfusion (I/R) injury. Zn^2⁺ alleviates myocardial hypertrophy and pulmonary hypertension by regulating ANP expression, but its precise role in ANP-mediated cardioprotection remains unclear. This study aimed to investigate whether ANP protects the heart during reperfusion by modulating Zn^2⁺ levels and to explore the underlying mechanisms involved.

Methods: In this study, we utilized an isolated reperfused heart model in rats, as well as wild-type (WT) and ANP knockout (ANP^-/-) mouse models, for in vivo I/R experiments. For clinical investigations, plasma samples were collected from 216 patients with ischemia-related diseases. Evans blue and TTC staining, radioimmunoassay, ICP‒OES, echocardiography, Hydro-Cy3-mediated ROS detection, and Western blotting were employed to evaluate the effect of ANP on Zn^2⁺ homeostasis.

Results: Plasma ANP levels were significantly elevated in patients with ST-elevation myocardial infarction (STEMI), non-ST-elevation myocardial infarction (NSTEMI), and heart failure (HF). ANP secretion increased during reperfusion, rather than infarction, both ex vivo and in vivo, promoting Zn^2⁺ accumulation in reperfused tissue. ANP and Zn^2⁺ protected mitochondria and reduced infarct size; these effects were reversed by the Zn^2⁺ chelator TPEN. In WT and ANP^-/- mice, EF% and FS% decreased after reperfusion, with ANP^-/- mice exhibiting significantly worse cardiac function. ANP pretreatment alone improved cardiac function, but combined pretreatment with ANP and TPEN decreased EF% and FS% while increasing LVID. Reperfusion increased ROS levels in both WT and ANP^-/- hearts, which were reduced by ANP pretreatment. I/R injury elevated Zn^2⁺ transporter 8 (ZnT8) expression, an effect that was counteracted by ANP, although this effect was reversed by TPEN. Hypoxia-inducible factor 1-alpha (HIF-1α) expression was elevated in I/R rats and ANP^-/- mice, and it was inhibited by both Zn^2⁺ and ANP pretreatment. However, the HIF-1α inhibitor 2-Me did not reverse the effect of ANP on ZnT8 expression. Additionally, ANP increased PI3K expression in both WT and ANP^-/- I/R mice, but this effect was blocked by the PI3K inhibitor LY294002.

Conclusions: ANP modulates Zn^2⁺ homeostasis during reperfusion injury by downregulating ZnT8 through the PI3K signalling pathway, thereby reducing myocardial I/R injury.