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

<b>Background/Objectives</b>: <i>Larix decidua</i> 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 <i>L. decidua</i> extract, evaluate its in vitro antioxidant capacity, and investigate its therapeutic and prophylactic effects on oxidative-nitrosative stress and inflammation. <b>Methods</b><i>: L. decidua</i> 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. <b>Results</b>: 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, <i>L. decidua</i> 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. <b>Conclusions</b>: The ethanolic <i>Larix decidua</i> 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 <i>L. decidua</i> needle preparations as polyphenol-rich nutraceutical/functional ingredient candidates within preventive and adjunct nutrition strategies targeting oxidative stress-driven inflammation.