Phytochemical and biological characterization of methanolic extracts from Tunisian Rhanterium suaveolens

Background: Among plants rich in natural antioxidant, the genus Rhanterium (Asteraceae) is a widely distributed medicinal plant throughout western North Africa, the Arabian Peninsula, Iraq and Iran, and some Rhanterium species are used in folk medicine. In the context of a research project aimed to investigate plants from North Africa as potential sources of bioactive products useful for healthy purposes, we have studied the phytochemical profile and the biochemical properties of methanolic extracts from different parts (flowers, leaves, and stems) of Tunisian Rhanterium suaveolens. In particular, the study is aimed to analyze the phenolic composition of these extracts and their antioxidant, anti-inflammatory, and skin whitening properties. Methods: The phytochemical analyses were performed using standard colorimetric procedures, HPLC-DAD and HPLC-DAD-ESI-MS. Then, several in vitro cell-free assays have been used to estimate the antioxidant/free radical scavenging capability of the extracts (Folin, TAC-pm, DPPH, TEAC, ORAC, FRAP, β-carotene bleaching, NO scavenging-activity, SOD-like activity, HOCl-induced albumin degradation). Moreover, the methanolic extracts of R. suaveolens were tested to study the capability to in vitro inhibit the tyrosinase diphenolase activity and to in vivo inhibit melanin accumulation in the Zebrafish assay. Finally, the anti-inflammatory potential of these extracts in an in vitro model of acute intestinal inflammation in differentiated Caco-2 cells was evaluated. Results: The R. suaveolens extracts under study appeared particularly rich in flavonols and hydroxycinnamic acids, in particular the flower extracts. The main compounds in all the extracts were quercetin-3-O-glucoside, dicaffeoylquinic acids, quercetin pentoside, and tricaffeoylquinic acid. All extracts appeared endowed with good antioxidant/free radical scavenging properties, being the flower extracts slightly more active than the others. Moreover, R. suaveolens flowers extract was able to inhibit in vitro tyrosinase activity (IC50 61.56 μg/mL), and exhibited (at the concentration of 0.5 and 1 mg/mL) bleaching effects on the pigmentation of zebrafish embryos (72 h post fertilization), without affecting their development and survival. Furthermore, all extracts showed good anti-inflammatory activity in intestinal epithelial cells as demonstrated by the inhibition of TNF-α-induced gene expression of IL-6 and IL-8. Conclusions: R. suaveolens may be considered as a potential source of agents for the treatment of skin disorders, as well as of pathological conditions related to oxidative stress and inflammation.