# Cosmeceutical Potentials of _Equisetum debile_ Roxb. ex Vaucher Extracts
## 4 Discussion
These compounds, including hypolaetin 8-rhamnoside, naringenin-7-O-\(\beta\)-D-glucuronide, luteolin 7-glucose, and kaempfer, may also be present in EF. Silicon is known to strengthen skin, hair, nails, and bone [36; 37]. In this study, silicon in _E. debile_ extracts was determined by the ICP-OES method. The contents varied between 0.004 and 0.033% (Table 2), which was considerably low because _Equisetum_ spp. are known to accumulate large amounts of silicon, around 5 to 10% as SiO\({}_{2}\)[26]. This could be partly explained by different sample types used in silicon analysis. In this study, silicon contents were investigated from the crude extract and its corresponding fractions rather than the whole plant. However, the results shown in this study were in accordance with the previous study of _E. sylvaticum_ that reported only 0.025% of the total silicon was collectively extracted by a sequential extraction with solvents having different lipophilic properties [35]. This reaffirms that the extraction method in this study was not the optimal option to acquire high yield silicon. However, some minute silicon from _E. debile_ extracts was detected. Among fractions, HF showed the highest silicon content, which was followed by DF, EF, MF, and MR. The results also show that MF yielded lower silicon content than that of HF by 1.83-fold. This could be partly explained by the potential formation of silicon complexes in plant cells. The accumulated silicon in some plants such as rice and cotton are known to form interactions and binding to organic matters in plant tissue [56]. The organic matrices in question might be made from polymers of carbohydrates such as cellulose, hemicellulose, and callose. These polymers are the major components of cell walls and possibly the sites of silicon deposition [57]. Interactions between organic compounds and silicon form complexes that alter silicon solubility. As a result, the silicon becomes less soluble in water and would only be liberated from plant tissue upon harsh treatment with strong acid digestion [35]. Taken together, this study may suggest that silicon might accumulate in _E. debile_ tissue as the complex forms with a variety of solubilities, potentially with a preference of solubility to solvents with a lower range of polarity indices. Melanin is a brown pigment causing skin to darken. Melanin biosynthesis depends on tyrosinase activations. The modulation of tyrosinase is regulated by not only an individual's genetics but also the responses to environmental stresses, particularly UV radiation [6; 8; 11]. Lowering melanin production has been proven to lighten dark skin. Therefore, the skin-whitening property of _E. debile_ extracts was investigated via the inhibition of tyrosinase using a modified dopachrome 96-well plate method. The variation of inhibitory capacities among extracts was associated with solvent polarities and extraction methods (Figure 7 and Table 3). EF exerted the strongest tyrosinase inhibition. It was considerably stronger than that of HF by 114-fold KAE value and 13-fold IC\({}_{50}\) value. The findings in this study agreed with a previous study which reported the ethyl acetate extract from _E. ramsissimum_ showing a protection against melanoma by decreasing melanin via several mechanisms, including inhibition of tyrosinase, oxidation, and expression of melanogenesis-related proteins, microphthalmia-associated transcription factor (MITF), and tyrosinase-related protein 1 and 2 (Trp-1 and Trp-2) [58]. Since _E. debile_ and _E. ramsissimum_ are in the same genus of _Equisetum_, the ethyl acetate extracts from these two horesteals may possess similar phytochemicals that exert similar mechanisms involving melanin. In this study, EF also possessed the highest total phenolic content among all extracts. Phenolics are known to inhibit tyrosinase and the oxidative process [59; 60]. Therefore, the tyrosinase inhibitors in EF could be phenolic compounds. This explanation is also supported by a positive correlation between _E.