3.3.1. Antioxidant Activity

The results of the antioxidant activities of the extract are presented in Table 2. The human body is constantly exposed to external factors that contribute to the development of reactive oxygen species (ROS), resulting in oxidative stress. Studies have confirmed the contribution of oxidative stress to the onset of various diseases such as cancer, inflammatory processes and skin diseases such as acne vulgaris. Currently, there is a trend towards using antioxidants from a natural origin due to the accumulation of synthetic antioxidants in the body [34,35]. Nitric oxide plays a central role in the regulation of several physiological processes in the human body. However, nitric oxide that is a product of sodium nitroprusside has a strong nitrosonium (NO+) character that can change and interfere with the normal function of several cellular processes [16]. Pro-inflammatory cytokines and bacterial cell wall components have been linked with the overproduction and release of increased amounts of nitric oxide. The increased nitric oxide free radicals are involved in the onset of inflammation associated with diseases such as acne vulgaris and post-inflammatory hyperpigmentation [36].

*Sideritis perfoliata* displayed a moderate nitric oxide scavenging activity with an IC50 of 266.0 ± 7.1 μg/mL (Table 2). The noteworthy free radical scavenging activity for *S. perfoliata* can be attributed to the high phenolic content of *Sideritis* spp. [37]. Previous studies done by Zengin et al. [37] speculated the significant nitric oxide scavenging activity of *S. galatica* to be due to the presence of tocopherols, carotenoids and ascorbic acid in the plant extract.

Phongpaichit et al. [38] reported an extract with an IC50 between 10 and 50 μg/mL to have a significant antioxidant capacity. In the present study, *S. perfoliata* displayed noteworthy antioxidant activity with an IC50 of 23.9 ± 0.85 μg/mL. Studies done by Güvenç et al. [39] on the DPPH antioxidant potential of various *Sideritis* spp, confirmed the free radical scavenging potential of flavonoids together with phenylethanoid glycosides present in these species.

The estimation of the total antioxidant capacity of an extract uses a combination of different antioxidant parameters. These include determining the reducing capacity of the extract against a specific free radical agent such as ammonium molybdate as well as calculating the phenolic content of the extract. High phenolic content is associated with high antioxidant capacity [17,40]. The *S. perfoliata* extract had significantly lower phenol content than that of the positive control gallic acid, while showing a significantly higher capacity to scavenge the ammonium molybdate free radical when compared with gallic acid. This means that the *S. perfoliata* extract has an overall moderate antioxidant capacity.
