Phytochemical Composition, Antioxidant and Antiproliferative Activities of Citrus hystrix, Citrus limon, Citrus pyriformis, and Citrus microcarpa Leaf Essential Oils against Human Cervical Cancer Cell Line

Abstract

The essential oil derived from <i>Citrus</i> plants has long been used for medicinal purposes, due to its broad spectrum of therapeutic characteristics. To date, approximately 162 <i>Citrus</i> species have been identified, and many investigational studies have been conducted to explore the pharmacological potential of <i>Citrus</i> spp. oils. This study investigated the volatile constituents of essential oil distilled from the leaves of <i>C. hystrix</i>, <i>C. limon</i>, <i>C. pyriformis</i>, and <i>C. microcarpa</i>, using gas chromatography-quadrupole mass spectrometry. A total of 80 secondary compounds were tentatively identified, representing 84.88-97.99% of the total ion count and mainly comprising monoterpene (5.20-76.15%) and sesquiterpene (1.36-27.14%) hydrocarbons, oxygenated monoterpenes (3.91-89.52%) and sesquiterpenes (0.21-38.87%), and other minor chemical classes (0.10-0.52%). In particular, 27 compounds (1.19-39.06%) were detected across all <i>Citrus</i> species. Principal component analysis of the identified phytoconstituents and their relative quantities enabled differentiation of the <i>Citrus</i> leaf oils according to their species, with the loading variables contributing to these metabolic differences being identified. The <i>Citrus</i> leaf oils were tested for their antioxidant and antiproliferative activities using 2,2-diphenyl-1-picryl-hydrazylhydrate (DPPH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. The results indicated that <i>C. limon</i> displayed the highest DPPH radical scavenging ability (IC₅₀ value of 29.14 ± 1.97 mg/mL), while <i>C. hystrix</i> exhibited the lowest activity (IC₅₀ value of 279.03 ± 10.37 mg/mL). On the other hand, all the <i>Citrus</i> oils exhibit potent antiproliferative activities against the HeLa cervical cancer cell line, with IC₅₀ values of 11.66 μg/mL (<i>C. limon</i>), 20.41 μg/mL (<i>C. microcarpa</i>), 25.91 μg/mL (C. <i>hystrix</i>), and 87.17 μg/mL (C. <i>pyriformis</i>).