Flower Extracts of the Invasive Species Prunus serotina Ehrh.: Phytochemical Composition, Protective Effects on Human Plasma Components, and Impact on Neutrophil Functions

Prunus serotina Ehrh. (Rosaceae) is one of the most widespread invasive tree species in Europe. Its abundant floral biomass remains understudied, despite its potential as a source of valuable bioactive compounds. Our study provides a comprehensive phytochemical characterization of P. serotina flower extracts and the first evaluation of their biological activity in models related to inflammation and oxidative stress. Phytochemical composition was analyzed using UHPLC-PDA-ESI-MS3, HPLC-PDA, and spectrophotometric techniques. Over 60 specialized metabolites were fully or partially identified, primarily polyphenolic compounds (flavonols, phenolic acids, proanthocyanidins), and the content of major constituents was quantified using authentic reference standards, providing the most detailed profiling data on P. serotina flowers to date. The total phenolic content of the extracts, obtained using water, 70% ethanol–water, ethyl acetate, and n-butanol, ranged from 119.05 to 144.97 mg/g dw. Biological potential of the extracts was evaluated by assessing their effects on pro-inflammatory cytokine release (TNF-α), the inflammation-related enzyme elastase (ELA-2), and reactive oxygen species (ROS) level in stimulated human immune cells (neutrophils), as well as their ability to enhance plasma antioxidant capacity (NEAC) and protect human plasma proteins and lipids from peroxynitrite-induced damage. At concentrations of 1–100 µg/mL, the extracts decreased TNF-α, ELA-2, and ROS levels by up to 46%, 43%, and 74%, respectively, and reduced 3-nitrotyrosine by up to 72%. These findings highlight the potential of P. serotina biomass as a sustainable source of bioactive compounds for inflammation- and oxidative stress-related disorders, particularly cardiovascular diseases (CVDs). However, further in vivo studies are needed to verify these effects under physiological conditions and assess their pharmacological potential.