Chemical constituents, biological activities and anti‐rheumatoid arthritic properties of four citrus essential oils

Abstract

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease with predominant synovitis that has no complete cure or preventive treatment. Citrus essential oils, used in natural fragrances, contain a variety of functional ingredients that are worthy of investigation for their potential as natural anti‐inflammatory drug sources. In this study, essential oils were hydro distilled from the peels of four citrus species: Citrus sinensis (L.) Osbeck (CSEOs), Citrus paradisi Macfad. (CPEOs), Citrus limon (L.) Osbeck (CLEOs) and Citri Reticulatae Pericarpium (CREOs). Altogether, 81 compounds were identified using gas chromatography–mass spectrometry (GC–MS), of which d‐limonene (17.96%–94.66%) was an abundant component of all four oils. The stable 1,1‐diphenyl‐2‐pyrrole hydrazine (DPPH) free radical test showed that all four essential oils had excellent antioxidant properties (IC50, 0.76–13.86 μg/mL). Furthermore, the oils remarkably increased the first G1 phase of the cell cycle, which inhibited the pro‐inflammatory factor expression. An immunohistochemical analysis indicated that the four essential oils inhibited the expression of tumor necrosis factor‐α and cyclooxygenase‐2 and they exhibited anti‐inflammatory activity in a rat model that was similar to that of the common drug, Ibuprofen. These results show that the CSEOs, CPEOs, CLEOs, and CREOs have significant antirheumatic activities and thus have great potential in developing functional food or drugs for treating RA.

Integrated HS-GC–IMS and UPLC-Q-Orbitrap HRMS-based metabolomics revealed the characteristics and differential volatile and nonvolatile metabolites of different citrus peels

“…Na Liu et al noted that citrus peels mainly contained volatile and nonvolatile metabolites ( Liu et al, 2021 ). The volatile compounds, such as esters, alcohols, aldehydes, ketones, sulfides, and terpenes, exhibit strong pharmacological bioactivities, such as antimicrobial ( Lin et al, 2021 , Lin et al, 2021 ), antioxidant ( Vitalini et al, 2021 ), anti-inflammatory (C. Li et al, 2022 ), anti-melanoma ( Kulig et al, 2022 ), and anti-cancer properties ( Tundis et al, 2023 ). D-limonene was reported to alleviate phlegm accumulation and inhibit cancer cells ( Vigushin et al, 1998 ).…”