SNPiP Activating the Non-Neuronal Cardiac Cholinergic System Possesses Characteristic Pharmacokinetics and Tissue Distribution in Rats

Background/Objectives: The non-neuronal cardiac cholinergic system (NNCCS) is known to synthesize ACh independently of the parasympathetic nervous system, thereby regulating cardiac homeostasis, which includes sustainability of energy metabolism, anti-inflammatory and anti-ischemic properties, electrical stability, and mitochondrial calcium handling. Given these beneficial functions of NNCCS, we were prompted to search for an inducer. One such inducer is SNPiP, a novel low-molecular-weight chemical compound developed by us. SNPiP accelerates ACh synthesis in the heart via cGMP elevation and, intriguingly, enhances diastolic function, increasing cardiac output and end-systolic pressure without elevating heart rate. However, the pharmacokinetics of SNPiP remain unknown, which led us to conduct the present study. Methods and Results: We found that the half-life of SNPiP in the blood was extremely short, similar to that of a nitric oxide (NO) donor, S-nitroso-N-acetyl-DL-penicillamine. This short half-life is caused by the rapid distribution of SNPiP into organs, including the heart, kidney, and liver. In addition, once transferred into blood cells, SNPiP itself became stable and remained intact for up to 1 h. Moreover, the short half-life was partly explained by the rapid degradation of SNPiP and concomitant loss of the nitroso group in the blood. Notably, when rats were treated with SNPiP, NO levels in the heart elevated bimodally: immediately after administration and again about 12 h later, coinciding with the previous report of NNCCS upregulation and accelerated ACh synthesis with NO production. Importantly, our previous transcriptome analysis of SNPiP-treated hearts supports these findings, as it revealed upregulation of diastolic function-related genes and proteins. Conclusions: Collectively, these results clarify the pharmacokinetics of SNPiP and demonstrate that, despite a shorter half-life, SNPiP is efficiently distributed to the heart, where it confers beneficial effects through induction of NNCCS.