Abstract
Hypericum L. (Hypericaceae) extracts have been used for their therapeutic effects; however, not much is known about the immunomodulatory activity of essential oils extracted from this plant. We isolated essential oils from the flowers and leaves of H. perforatum and analyzed their chemical composition and innate immunomodulatory activity. Analysis of flower (HEOFl) versus leaf (HEOLv) essential oils using gas chromatography–mass spectrometry revealed that HEOFl was comprised mainly of monoterpenes (52.8%), with an abundance of oxygenated monoterpenes, including cis-p-menth-3-en-1,2-diol (9.1%), α-terpineol (6.1%), terpinen-4-ol (7.4%), and limonen-4-ol (3.2%), whereas the sesquiterpenes were found in trace amounts. In contrast, HEOLv was primarily composed of sesquiterpenes (63.2%), including germacrene D (25.7%) and β-caryophyllene (9.5%). HEOLv also contained oxygenated monoterpenes, including terpinen-4-ol (2.6%), while monoterpene hydrocarbons were found in trace amounts. Both HEOFl and HEOLv inhibited neutrophil Ca2+ mobilization, chemotaxis, and reactive oxygen species (ROS) production, with HEOLv being much more active than HEOFl. Furthermore, the pure sesquiterpenes germacrene D, β-caryophyllene, and α-humulene also inhibited these neutrophil responses, suggesting that these compounds represented the active components of HEOLv. Although reverse pharmacophore mapping suggested that potential protein targets of germacrene D, β-caryophyllene, bicyclogermacrene, and α-humulene could be PIM1 and mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MAPKAK2), a kinase binding affinity assay did not support this finding, implying that other biological targets are involved. Our results provide a cellular and molecular basis to explain at least part of the beneficial immunotherapeutic properties of the H. perforatum essential oils.
Highlights
Hypericum L. (Hypericaceae) is comprised of approximately 500 species that can be found around the world
The chemical composition of H. perforatum essential oils has been reported previously in several publications [9,11,32,33,34,35,36,37,38,39], there is a wide variation in the reported levels of secondary metabolites from different H. perforatum plant samples
Few studies have investigated flower and leaf essential oils separately, and there are no publications on the chemical composition of essential oils from H. perforatum collected in the Rocky Mountain region of the United States
Summary
Hypericum L. (Hypericaceae) is comprised of approximately 500 species that can be found around the world. Various products from Hypericum species have been used as antidepressant, sedative, diuretic, antiphlogistic, analgesic, astringent, and antipyretic remedies in Europe, America, Africa, and Asia [1,2,3,4,5,6,7,8]. H. perforatum L. has been widely used in many countries in antibacterial, antiviral, anti-inflammatory, antinociceptive, or analgesic remedies [4]. Extracts from this herb have been reported as a therapeutic remedy for burns, skin wounds, cuts, stomach aches, and ulcers [5]. H. perforatum extracts have been reported to have anti-angiogenic, anti-fibroblastic, and antioxidant properties [6,7,8]. Hypericum essential oils are rich sources of monoterpenes, sesquiterpenes, and their oxygenated derivatives (reviewed in [9] and Table 1, which has a listing of the more recent H. perforatum essential oil data published after this review)
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