Chemical Composition and Assessment of the Anti-Inflammatory, Antioxidant, Cytotoxic and Skin Enzyme Inhibitory Activities of Citrus sinensis (L.) Osbeck Essential Oil and Its Major Compound Limonene

Essential oils (EOs) from species have attracted attention for their diverse properties, including anti-inflammatory, antioxidant and cytotoxic effects, which address critical health challenges such as chronic diseases and skin disorders. (L.) Osbeck, which is a widely cultivated citrus fruit, is attracting increasing attention in the field of medicinal research due to its richness of limonene (comprising approximately 85-90% of the oil). This study investigates the chemical profile of CS-EO and biological activities of CS-EO and limonene. This study used gas chromatography-mass spectrometry (GC-MS), confirming limonene as the predominant compound (70.15%) along with other minor constituents, including thujene (10.52%), myrcene (5.54%) and α-pinene (2.81%). The biological activities of CS-EO and limonene were examined, specifically focusing on their antioxidant, anti-inflammatory, cytotoxicity and dermatoprotective effects. Antioxidant potential was evaluated using DPPH, FRAP and beta-carotene assays, with CS-EO and limonene exhibiting comparable efficacy. Anti-inflammatory properties were assessed via inhibition assays of prostaglandin E2 (PGE2) and nitric oxide (NO) production, showing significant reductions in LPS-stimulated macrophages treated by CS-EO or limonene. Cytotoxicity testing on various cell lines indicated selective activity of the tested compounds, with low toxicity observed on human skin fibroblasts. Limonene and CS-EO were highly effective on HepG2 cellules, with IC values of 0.55 ± 0.01 µg/mL and 15.97 ± 1.20 µg/mL, respectively. Dermatoprotective effects were further confirmed using enzymes, where CS-EO and limonene showed remarkable inhibitory potential against elastase (IC of 65.72 ± 1.92 and 86.07 ± 1.53 µg/mL, respectively) and tyrosinase (IC of 102 ± 2.16 and 78.34 ± 1.15 µg/mL, respectively) enzymes compared to quercetin used as a standard (IC of 111.03 ± 0.1 and 124.22 ± 0.07 µg/mL, respectively). The findings of this study suggest the potential for the development of new therapeutic approaches based on CS-EO, which could be applicable in the pharmaceutical, cosmetic and nutraceutical fields and have protective benefits for skin health.