Comparative study of the antiviral effect of cultivated and wild olive leaf extracts: The herpes Simplex (HSV) and the Epstein- Barr virus (EBV) as study models

Due to the richness of bioactive compounds, Olea europaea leaf extracts exhibit health effects. The present research evaluated the antioxidant antibacterial, and antiviral effects of leaf extracts obtained from Olea europaea L. var. sativa (OESA) and Olea europaea var. sylvestris (OESY) from Tunisia. LC-DAD-ESI-MS analysis identified different compounds that contributed to the observed biological properties. This work evaluated antioxidant activities in vitro using Phosphomolybdenum assay, the DPPH free radical scavenging assay (DPPH), the Ferric reducing antioxidant power (FRAP) assay, and Scavenging Activity of Nitric Oxide as well as by pretreatment of HeLa cells and PBMC exposed to H2O2. Our findings Olea europaea exhibited antioxidant activity in both chemical and biological tests. Especially, pretreatment of HeLa cells with different extract concentrations conferred protection against lipid peroxidation and modulated activities of two antioxidant enzymes, catalase, SOD, and Glutathione peroxidase. In biological system, Olea europaea exhibited a 50 % cytotoxic concentration evaluated as 15.09 mg/ml and 14.53 mg/ml. Incubation of HeLa cell line with no cytotoxic concentrations resulted in special protection from oxidative stress induced by H2O2, evidenced by a decrease of MDA levels and an increase of antioxidant enzymes activities compared to cells treated with H2O2 alone. In the second part, we study the anti-bacterial and anti-HSV-1 effects. Both OESA and OESY were active against Gram-positive bacteria (MIC values between 7.81 and 15.61 µg/mL and between 15.61 and 31.25 µg/mL against Staphylococcus aureus ATCC 6538 for OESY and OESA, respectively). The antiviral activity against herpes simplex type 1 (HSV-1) was assessed on Vero cells. The cell viability results indicated that Olea europaea leaf extracts were not toxic to cultured Vero cells. The half-maximal cytotoxic concentration (CC50) values for OESA and OESY were 0.2 mg/mL and 0.82 mg/mL, respectively. Furthermore, both a plaque reduction assay and viral entry assay demonstrated antiviral activity. In the third part, we focused on antioxidant activity and antiviral activity against Epstein Barr Virus. During EBV infection, the free radicals increased, triggering lipid oxidation. Therefore, monitoring the secondary lipid peroxidation products was done by measuring malonaldehyde (MDA) and conjugated dienes (DC). As an inductor of the lytic cycle, the simultaneous treatment of Raji cells with OESA and TPA generated a significant decrease in MDA levels and DC (p <0.05). Besides, Raji cells simultaneously exposed to TPA and OESA exhibited a percentage of EBV-positive fluorescence cells lower than TPA treated cells (****P <0.0001). We conclude that Olea europaea leaves antioxidant effects and suggests a potential source of natural antioxidant molecules with possible applications in industry and medicine. In addition, Olea europaea leaf extracts demonstrated a bacteriostatic effect and remarkable antiviral activity. Also, OESA treatment has a protective effect against EBV lytic cycle induction. Keywords: Olea europaea, LC-DAD-ESI-MS analysis antioxidant activity; antimicrobial effect; antiviral activity; herpes simplex virus 1, Epstein Barr Virus