Moreover considering that several polyphenols and flavonoids
Moreover, considering that Isotretinoin several polyphenols and flavonoids (i.e. chalcones, flavanones, resveratrol derivatives, ellagic acid) are reported to inhibit tyrosinase and elastase (Pillaiyar et al., 2017; Xing et al., 2016; Wittenauer et al., 2015), the relations between enzyme inhibitory activities and total phenolic and flavonoid content were statistically investigated.
In particular, Pearson correlation test was performed to correlate the percentage of enzymatic inhibition (showed by the extracts at 50 μg/mL) to the phenolic and flavonoid content, respectively. Although the found correlations were not strong, in all cases r was comprised between and 1, indicating a positive correlation between increasing total phenolic and flavonoid content and both enzymatic inhibitory activities (Fig. 2A and B). The highest positive correlation (r = 0.3535 and P = 0.0003) was found between tyrosinase inhibition and total phenolic content.
Discussion In search for natural products endowed with elastase and tyrosinase inhibitory activity, a hundred plant extracts were in vitro tested against these two enzymes. The samples were harvested in different geographical areas (Table 1), and the majority of them are plants of ethnobotanical relevance (Khare, 2004; Guarrera, 2006; Nadembega et al., 2011). A documented ethnobotanical use is not available only for five out of the tested plants, namely: Centaurea horrida Badarò, Hypericum scruglii, Ferula arrigonii Bocchieri, Limonium morisianum and Plagius flosculosus (L.) S. Alavi & V. H. Heywood, which are endemic plants of Sardinia Island (Italy). Seventeen, out of a hundred samples, were selected as the most promising and their IC50 of enzymatic inhibition were investigated. Among them, eleven resulted strongly active on both enzymes; five were able to inhibit only tyrosinase and one was strongly active only against elastase. Leaves extract of Pistacia lentiscus emerged as the most potent elastase inhibitor and, together with Cytinus hypocistis (aerial parts) and Limonium morisianum (aerial parts), it showed also the lowest IC50 of tyrosinase inhibition. P. lentiscus is used in Mediterranean traditional medicine in form of infusion or decoction to treat a wide number of diseases, such as stomachache, eyes infections, burn skin, bronchitis (Bouasla and Bouasla, 2017). Flavonoids, phenolic acids, and their derivatives such as myricetin glycoside, catechin, β-glucogallin, quercitrin gallate were identified as the most abundant phytoconstituents of this plant (Rodríguez-Pérez et al., 2013). Those compounds might play a role in the elastase inhibitory activity showed by this plant (Melzig et al., 2001). Interestingly, L. morisianum is an endemic and exclusive plant of Sardinia and recently some information about its phytochemical profile and anti HIV-1 activity were reported (Sanna et al., 2018a). Myricetin, myricetin 3-O-rutinoside, myricetin-3-O-(6″-O-galloyl)-β-d-galactopyranoside, (-)-epigallocatechin 3-O-gallate, tryptamine, ferulic and phloretic acids were isolated from its aerial parts. Some of the tested samples were obtained from plant species belonging to the same genus, this allowed further considerations concerning their bioactivities. In particular, according to the statistical analysis, Pistacia lentiscus leaves resulted more potent elastase inhibitor than leaves of Pistacia terebinthus (P < 0.05) (Fig. 1A), while no differences were found between their activity against tyrosinase (Fig. 2A). Cistus salvifolius was significantly more potent against elastase than Cistus monspeliensis, while, also in this case, no differences were found between their tyrosinase inhibitory activities. Hypericum hircinum was significantly more active against elastase than Hypericum scruglii (P < 0.05). Hypericum scruglii was found not active against tyrosinase, thus it is more promising to develop a cosmetic product endowed with selective anti-wrinkle activity. H. scruglii resulted enriched in phloroglucinols, which were proved able to inhibit the HIV-1 replication in cell based assays (Sanna et al., 2018b).