Solvent effects on terpenoid compositions and antioxidant activities of Cinnamomum camphora (L.) J. Presl extracts and the main antioxidant agent evaluation through in vitro and in vivo assay

Abstract Plant secondary metabolites can protect organisms against oxidative stress caused by adverse environmental conditions. Cinnamomum camphora (L.) J. Presl contains plentiful terpenoids and is subdivided into 5 chemotypes. To develop natural antioxidants using the plant terpenoids, the terpenoid composition and antioxidant abilities of methanol, ethyl acetate, n-hexane and petroleum ether extracts from linalool and eucalyptol chemotypes were investigated, and the solvent effects on in vitro antioxidant activity of 8 main terpenoids were analyzed. Meanwhile, the in vivo effects of two strong antioxidant terpenoids were evaluated. For the two chemotypes, the 4 solvents exhibited the same extracting effects on the terpenoid types, but methanol extracts contained the highest content of terpenoids, which should contribute to their strongest scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radicals. In linalool and eucalyptol chemotype extracts, linalool, eucalyptol, ocimene, α-pinene, D-limonene, terpinene, β-pinene and longifolene were the 8 main terpenoids. Among the 4 solvents, the 8 terpenoids showed the strongest free radical-scavenging activity with methanol as the reaction medium, which might result from strong-polarity methanol easily activating C = C unsaturated bonds in these compounds. This might also contribute to the strongest scavenging activity of methanol extracts against free radicals. Among these main components, ocimene and longifolene separately showed the strongest activity in scavenging DPPH and ABTS free radical. In in vivo assay, the two compounds significantly lowered the reactive oxygen species (ROS) levels in Chlamydomonas reinhardtii, a single-celled model organism, under H2O2 stress, and the lowering effects gradually enhanced with increasing the compound concentration, resulting in the corresponding promoting effect on the algal growth. At the same concentration, longifolene showed the strongest effect on protecting the algal cells against oxidative stress. Therefore, methanol was suitable for extracting terpenoids in natural antioxidant development, and ocimene and longifolene were two strong antioxidant terpenoids without cell toxicity, with the latter having stronger in vivo antioxidant activity. Graphical Abstract