3.3.2. Elastase Inhibition

The connective tissue of the skin has the main component of elastic fibres known as elastin. Elastic fibres and collagenous fibres in the skin create a network and they develop in the epidermis. Elastin is degraded by elastase; therefore, inhibition of the elastase enzyme can retain the elasticity of the skin [41]. *Sideritis perfoliata* showed significant inhibition of the enzyme elastase, with an IC50 value of 57.18 ± 3.22 μg/mL (Table 2). Ursolic acid was used as the positive control, the IC50 value was 18.45 ± 2.23 μg/mL. No elastase inhibition has been reported previously for *S. perfoliata* and species in the same genus. The IC50 value of 57.18 ± 3.22 μg/mL indicates good enzyme inhibition, meaning that the plant has the potential to maintain skin elasticity. Lee et al. [41] studied the elastase inhibition of *Areca catechu*, and reported noteworthy activity, with an IC50 value of 42.4 μg/mL. In 2013, Ndlovu et al. [42] investigated the elastase inhibition of *Peltophorum africanum*, they reported the plant to be a potential enzyme inhibitor with an IC50 of 55.83 μg/mL.

According to the Gas Chromatography-Mass Spectrometry (GC-MS) results, the essential oil of *S. perfoliata* is characterized by the presence of monoterpenes, which are known to inhibit the activity of the elastase enzyme, according to Kacem and Meraihi [43]. They investigated the elastase inhibition of the essential oil extracted from seeds of *Nigella sativa* (L.) and reported that the main components of the essential oil were p-cymene, thymoquinone, carvone, thymol and carvacrol, which are monoterpenes. These monoterpenes had IC50 values between 12 and 104 μM.
