Dietary olive (Olea europaea) leaf extract suppresses oxidative stress and modulates intestinal expression of antioxidant- and tight junction-related genes in common carp (Cyprinus carpio)

Abstract

The present study was conducted in order to evaluate the effects of various levels of dietary olive leaf extract (OLE) on growth performance, whole body lipid peroxidation, and intestinal expression of hsp70 and antioxidant- and tight junction-related genes in common carp. Common carp juveniles (15 g) were fed with four diets, i.e. control and three diets supplemented with 0.1% (0.1E), 0.5% (0.5E) and 1% (1E) OLE for eight weeks. The results revealed that there was no significant difference in growth performance and feed efficiency between the control and OLE-treated groups (p > 0.05). There was no change in oxidative conditions among the treatments after one week, but the control group showed oxidative stress after eight weeks. The 0.1E and 0.5E treatments showed significantly suppressed oxidative stress (p < 0.05). After one week, there was no difference in sod gene expression among the treatments; cat showed down-regulation and up-regulation in the 0.1E and 1E treatments, respectively; gr showed up-regulation in the 0.5E and 1E treatments. After eight weeks, the 0.1E showed down-regulation; whereas, the 0.5E showed up-regulation in the antioxidant-related gene expressions compared to the control; the 1E treatment showed diverse changes in the gene expressions at this time. The 1E treatment had significantly lower hsp70 gene expression compared to the control after one week; however, after eight weeks, the 0.1E and 0.5E treatments showed significant down-regulation in the gene expression compared to the control and 1E treatments. Compared to the control group, the 0.1E (occl, cld3 and cld7) and 0.5E (occl and cld3) treatments showed up-regulation in tight junction-related gene expressions after one week. After eight weeks, there was no significant difference in occl and cld3 gene expressions among the treatments, but cld7 showed significant up-regulation along with the increase in dietary OLE supplementation. It is concluded that dietary OLE had no noticeable influence on common carp growth performance, but modulated gene expression of antioxidant enzyme and attenuated oxidative stress after 8 weeks.