This study examined the anti-inflammatory and endothelial function-enhancing effects of proprotein convertase subtilisin/kexin 9 (PCSK9) inhibitor therapy in the early phase after acute myocardial infarction (AMI) by assessing changes in tumor necrosis factor-α (TNF-α) levels and the L-arginine/asymmetric-dimethylarginine (ADMA) ratio. This retrospective, single-center cohort study included patients who underwent successful timely primary percutaneous coronary intervention (PCI) for first-onset AMI between September 2017 and March 2018. The PCSK9 inhibitor group comprised patients who received 75 mg alirocumab up to 7 days after AMI, while the standard therapy group comprised patients who did not. We evaluated the change in TNF-α levels and the L-arginine/ADMA ratio at the time of hospital admission and prior to discharge. PCSK9 inhibitor therapy in the early phase after AMI suppressed TNF-α levels (standard therapy group, 1.64 ± 2.14 pg/mL vs. PCSK9 inhibitor group, 0.26 ± 0.33 pg/mL
p = 0.033) and increased the L-arginine/ADMA ratio (standard therapy group, - 13.0 ± 39.7 vs. PCSK9 inhibitor group, 23.2 ± 39.7
p = 0.042). Upon multiple regression analysis adjusted for sex, age, and peak creatine kinase levels, PCSK9 inhibitor therapy was associated with TNF-α suppression (p = 0.025
β = - 0.235, 95% confidence interval [CI], - 0.436 to - 0.033). The L-arginine/ADMA ratio was also analyzed using multiple regression, adjusted for sex, age, peak creatine kinase levels, and smoking, showing a significant improvement in the ratio (p = 0.018
β = 41.913, 95% CI, 10.337-73.491). Moreover, a weak negative correlation was suggested between the change in TNF-α levels and the change in L-arginine/ADMA ratio (r = - 0.393, p = 0.058). PCSK9 inhibitor therapy in the early phase after AMI suppresses TNF-α levels and improves the L-arginine/ADMA ratio, potentially indicating anti-inflammatory and endothelial function-enhancing effects.