Moreover Hypericum perforatum L was also included in the
Moreover, Hypericum perforatum L. was also included in the initial screening, showing only a weak percentage of inhibition on both enzymes. In fact, it was not selected among the most active plants. The phytochemical profiles of these three Hypericum species were already reported to be significantly different; in the same study their inhibitory activity against α-glucosidase was investigated and also in that case, H. perforatum proved to be less potent than the other two Hypericum species (Mandrone et al., 2017). The lack of cytotoxicity already reported for the hydroalcoholic extracts of these Hypericum species (Mandrone et al., 2017) make them even more promising for cosmetic purposes.
A further discussion deserved to be done also on the differences in bioactivity showed by extracts obtained from different organs of the same plant source (Table 1). In particular, both extracts of fruits and Illumina for 50 ng DNA of Myrtus communis were tested. Both fruits and leaves were active against tyrosinase, even though fruits resulted more active (P < 0.05) (Fig. 1B), and only fruits were found active against elastase. Conversely, whereas Arbutus unedo leaves exhibited remarkable elastase and tyrosinase inhibitory activities, no enzymatic inhibition was shown by the extract obtained from its fruits.
A. unedo is a source of arbutin, a glycosylate hydroquinone, which is already known as skin-whitening agent (Degen, 2016). However, it inhibits the monophenolase function of this enzyme (Hori et al., 2004), while, in this work, the inhibition of its diphenolase function was evaluated. This data suggests that the presence of active metabolites other than arbutin (i.e. flavonoids) (Castaldi et al., 2009) might contribute to A. unedo (leaves) anti-ageing and skin-whitening properties.
In the case of Pistacia lentiscus, fruits and leaves extracts were both strongly active against tyrosinase, with no significant differences in their IC50 values, while only leaves were found active against elastase.
Roots and leaves of Vitellaria paradoxa were both selected among the most active samples, showing no significant differences between their IC50 values of tyrosinase and elastase inhibition (Fig. 1A and B). Vitellaria paradoxa is known as shea tree and it is very important for food and cosmetic industries. The most investigated and important product obtained from this plant is the butter extracted of the kernel, which is endowed with anti-inflammatory and antioxidant properties (Honfo et al., 2014). Saponins, tannins, and alkaloids were found in its roots, stem bark, and leaves even though these organs remain still poorly investigated (Ndukwe et al., 2007).
Conclusions A hundred extracts obtained from plants collected in India, Africa and Mediterranean area were screened as elastase and tyrosinase inhibitors. Seventeen extracts were selected as the most promising, and among them eleven resulted strongly active on both enzymes; five were able to inhibit only tyrosinase and one was strongly active only against elastase. Noteworthy, among the most active plants selected, two are endemic of Sardinia Island, namely: Hypericum scruglii and Limonium morisianum. The plants active against both enzymes are potentially suitable to develop skin-whitening agents, endowed with additional anti-wrinkles effect. In particular, the following 10 plants potently inhibited both enzymes: Arbutus unedo (leaves), Cistus salvifolius (aerial parts), Cistus monspeliensis (aerial parts), Cytinus hypocistis (aerial parts), Hypericum hircinum (aerial parts), Limonium morisianum (aerial parts), Pistacia terebinthus (leaves), Pistacia lentiscus (leaves), Myrtus communis (fruits), and Vitellaria paradoxa (leaves and roots). Hypericum scruglii (aerial parts) resulted a strong and selective elastase inhibitor, suggesting its potential use as ingredient for selective anti-wrinkles cosmetics. Azadirachta indica (leaves), Cochlospermum tinctorium (leaves), Khaya senegalensis (leaves), Myrtus communis (leaves) and Pistacia lentiscus (fruits) showed activity only against tyrosinase, resulting of particular interest to develop skin-whitening agents with no anti-wrinkle effect, eventually ideal for youngest skins.