Green Ethanolic Repercolation of Larix decidua Needles: Phytochemical Profiling and In Vivo Modulation of the Oxidative–Nitrosative Axis in Acute Sterile Inflammation

Background/Objectives: Larix decidua has been used in traditional medicine for the treatment of various inflammatory conditions. Although their use has been recognized in alternative medicine, the scientific documentation of the antioxidant and anti-inflammatory potential of ethanolic extracts from its needles remains insufficiently characterized. The present study aimed to characterize the phytochemical profile of the ethanolic L. decidua extract, evaluate its in vitro antioxidant capacity, and investigate its therapeutic and prophylactic effects on oxidative–nitrosative stress and inflammation. Methods: L. decidua needles were extracted using a modified Squibb repercolation method. Polyphenol and flavonoid content were quantified, and individual phenols were identified by HPLC-DAD-ESI⁺. The in vitro antioxidant activity was evaluated using DPPH, FRAP, H₂O₂, and NO scavenging assays. The therapeutic and prophylactic in vivo potential was evaluated in a model of acute inflammation induced with turpentine in male Wistar rats. Serum oxidative markers (TOS, TAC, OSI, MDA, AOPP, 8-OHdG, NO, 3-NT, SH) and inflammatory markers (NFκB-p65, IL-1β, IL-18) were quantified. Results: The extract contained high levels of flavonols and hydroxybenzoic acids; kaempferol glycosides and catechin were the dominant constituents. In vitro, the extract exhibited radical scavenging activities. In vivo, L. decidua attenuated oxidative and nitrosative stress, restored antioxidant defense, and reduced NFκB-p65, IL-1β, and IL-18 levels in a concentration-dependent manner. The L100 concentration most closely approximated the values produced by Trolox and diclofenac. Conclusions: The ethanolic Larix decidua needle extract exerted antioxidant and anti-inflammatory effects in a rat model of acute sterile inflammation, attenuating systemic oxidative–nitrosative stress and pro-inflammatory mediators in a concentration-dependent manner. These preclinical findings support further investigation of standardized L. decidua needle preparations as polyphenol-rich nutraceutical/functional ingredient candidates within preventive and adjunct nutrition strategies targeting oxidative stress-driven inflammation.