# Cosmeceutical Potentials of _Equisetum debile_ Roxb. ex Vaucher Extracts
## 4 Discussion
debile_ total phenolic content and the inhibition activity of tyrosinase (coefficient of determination (R\({}^{2}\)) of 0.8587), as shown in Figure 6. Quercetin previously found in ethyl acetate extract of _E. debile_ might be one of the bioactive phenolics that is responsible for the tyrosinase inhibitory effects [55]. Quercetin could inhibit tyrosinase via several mechanisms, such as the inhibition of monophenolase and diphenolase activities of tyrosinase [59; 61]. It could directly bind to tyrosinase via hydrophobic interaction, leading to the induction of conformational changes and impeding enzymatic activities. Since the active site of tyrosinase contains binuclear copper, inhibitors could chelate the copper ion within active sites, leading to the obstruction of interaction between tyrosine substrate and tyrosinase. Quercetin bearing a catechol structure was previously known to chelate copper ion in tyrosinase active site [61]. Additionally, since hydroxylated flavonoids share structural similarities to tyrosine, it could also compete for tyrosinase [59; 60]. In addition, the phenolic compounds found in CE by LCMS (Q-TOF) qualification analysis, such as hypolaetin 8-rhamoside, naringenin-7-O-\(\beta\)-D-glucuronide, luteolin 7-glucose, and kaempfer, could also be compounds of interest due to their previously reported abilities to exert inhibitions against tyrosinase [62; 63]. Collagens are proteins providing the structural stability of skin. Collagen account for 70-80% of skin weight and are known to be rapidly dismantled by collagenase. The depletion of collagens is a hallmark of wrinkle formation and aging skin [14]. The occurrence of diminishing collagens is strongly associated with UV-induced collagenases. Inhibitions of collagenases have been proved to delay collagen loss [64]. There is still a lack of anti MMP-1 and MMP-2 activity studies in the horsetail plants. This study therefore is the first to assess the inhibition of collagenase via MMP-1 and MMP-2 of _E. debile_ extracts by using EnzChek assay kits. All _E. debile_ extracts exhibited dose-dependent inhibitions against both collagenases, and the inhibition patterns between MMP-1 and MMP-2 were strongly consistent (Figure 8). CE and EF possessed comparative inhibitions and were the most potent against both enzymes. Among the fractions, EF had noticeably higher inhibitions than those of HF by 3.11-fold of IC\({}_{50}\) MMP-1 and 2.84-fold of IC\({}_{50}\) MMP-2. Although EF had similar inhibition potencies relative to CE, it is proposed as a superior extract for anti-wrinkle applications due to the higher refined compounds and richer phenolic contents. The EF's strong collagenase inhibitions could be partly explained by the enriched compositions of TPC. In polyphenol molecules, hydroxyl groups could directly interact with either backbone or other functional group side chains of collagenases. Additionally, the benzene ring of the molecule could form hydrophobic interactions to collagenases. These interactions lead to conformational changes, causing collagenase to be inactivated [64]. Another potential mechanism is that the phenolics directly chelate Zn\({}^{2+}\) in the active site of collagenases since _Equisetum_ plants were reported to have metal-chelating capacities for antioxidant activities [58]. The chelation prevents collagenases from interacting with collagen substrates. As a result, collagen degradation can be avoided, improving the condition of aging skin [47; 60; 65]. In this study, one of the phenolic compounds in _E. debile_ extracts exerting these mechanisms could be quercetin, since it was previously shown to have the inhibitory effects against both the activities of recombinant human MMP-1 (IC\({}_{50}\) of 39.6 \(\upmu\)M) and the induction of MMP-1 in human dermal fibroblasts via several mechanisms. These mechanisms include the inhibitions of extracellular signal-regulated protein kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) [66].