Assessment of Purple Loosestrife (Lythrum salicaria L.) Extracts from Wild Flora of Transylvania: Phenolic Profile, Antioxidant Activity, In Vivo Toxicity, and Gene Expression Variegation Studies

<b>Background:</b> Purple loosestrife (<i>Lythrum salicaria</i> L.) is a medicinal plant native to the spontaneous Romanian flora. The aim of this study was to investigate the phenolic profile, total phenolic content (TPC), and antioxidant capacity (AC) of two <i>L. salicaria</i> L. extracts, a hydro-methanolic extract (LSmet-1) and a hydro-ethanolic extract (LSeth-2), and their putative toxicity, as well as the effect on eye pigment content in the case of <i>Drosophila melanogaster</i> of an extract derived from LSmet-1 (LSmet-3). To the best of our knowledge, this is the first study to evaluate the influence of <i>L. salicaria</i> L. extracts on cytotoxicity and the expression of genes as determined by eye pigment levels, using a <i>D. melanogaster</i>-based model system. <b>Methods:</b> High-performance liquid chromatography was carried out to investigate the chemical composition of the extracts. Spectrophotometric methods were used to estimate their TPC and AC. Cytotoxicity was evaluated using an in vivo <i>D. melanogaster</i> diet-dependent viability assay and eye pigments of <i>w^m4h</i> males, suitable for position-effect variegation studies, which were quantified by a spectrophotometric method. <b>Results:</b> The results indicated that the main phenolic compounds were gallic acid, resveratrol, and rutin in LSmet-1, whereas in LSeth-2, gallic acid and quercetin were the most relevant. LSmet-1 had a higher TPC compared to LSeth-2. Both extracts exhibited notable efficacy in the applied in vitro antioxidant tests. The viability of flies on normal media increased in a concentration-dependent manner at lower concentrations, with the extract being toxic at higher concentrations. On a high-sugar diet, even lower concentrations were toxic. All tested concentrations influenced the eye pigment content. <b>Conclusions:</b> Our study brings new findings on <i>L. salicaria</i> L. extracts, suggesting the need for further investigation before introducing them in therapy.