Essential Oil Composition, Antioxidant Activity and Leaf Micromorphology of Five Tunisian <i>Eucalyptus</i> Species

<i>Eucalyptus</i> species have been widely employed in the projects of reforestation in Tunisia. Although their ecological functions are controversial, these plants are indeed important to counteract soil erosion, and represent a fast-growing source of fuelwood and charcoal wood. In the present study, we considered five <i>Eucalyptus</i> species, namely <i>Eucalyptus alba</i>, <i>E. eugenioides</i>, <i>E. fasciculosa</i>, <i>E. robusta</i>, and <i>E. stoatei</i> cultivated in the Tunisian <i>Arboreta</i>. The aim was to carry out the micromorphological and anatomical characterization of the leaves, the extraction and phytochemical profile of the essential oils (EOs), and the evaluation of their biological properties. Four of the EOs showed the prevalence of eucalyptol (1,8-cineole) varying from 64.4 to 95.9%, whereas <i>a</i>-pinene predominated in <i>E. alba</i> EO (54.1%). These EOs showed in vitro antioxidant activity, and reduced the oxidative cellular stress as shown by their activity on reactive oxygen species (ROS) production, and modulation of the expression of antioxidant enzymes, such as glutamate-cysteine ligase (GCL) and heme oxygenase-1 (Hmox-1). Moreover, the EOs inhibited the production of nitric oxide (NO), showing anti-inflammatory activity. The data collected suggest that these EOs may be considered a promising therapeutic strategy for inflammation-based diseases and may represent an additional value for the economy of Tunisia.