Collagenase, a matrix metalloproteinases (MMPs), is a key regulator in the photoaging process of skin due to the reactive oxygen species generated after exposure to ultraviolet A (UVA). Flavonoid compounds have been demonstrated to possess antioxidant properties, and could be useful in the prevention of photoaging. In this study, to investigate the structure-activity relationship of flavonoid compounds on their antioxidant property and inhibitory effects against the MMP activity, the effects of several flavonoids; myricetin, quercetin, kaempferol, luteolin, apigenin and chrysin, on the reactive oxygen species scavengering activity and inhibitory effect against the MMP activity were examined in vitro and in human dermal fibroblasts induced by UVA. The relative order of antioxidative efficacy, as determined using the 1, 1-diphenyl-2-picrylhydrazyl (DPPH) method and the xanthine/xanthine oxidase system, was as follows; flavones: luteolin > apigenin > chrysin, flavonols: myricetin > quercetin > kaempferol, and correlated with the respective number of OH group on their B-ring. In good correlation with the antioxidant properties, the flavonoids inhibited the collagenase activities, in a dose-dependent manner, and the MMP expression. These results suggested the UVA induced antioxidative activity and inhibitory effects of flavonoids on the collagenase in human dermal fibroblasts depends on the number of OH group in the flavonoid structure, and those with a higher number of OH group may be more useful in the prevention of UV stressed skin aging.

Free radicals and reactive oxygen species (ROS), which are generated by UV irradiation, may cause serious injury to skin cell membranes, DNA and functional proteins. In addition, these agents stimulate the expressions of matrix metalloproteinases (MMPs), which can degrade most components of the extracellular matrix (ECM), including collagen. In order to develop new anti-photoaging agents, five major components from the extract of Fraxinus chinensis extract (FCE) were identified. Two of the major components of FCE were found to be esculin (11.2%) and esculetin (1.9%). FCE (IC50: 50.0 microg/mL 1, 1-diphenyl-2-picrylhydrazyl (DPPH); 19.8 microg/mL, superoxide anion radical) and esculetin (IC50: 2.1 microg/mL DPPH; 0.6 microg/mL, superoxide anion radical) showed strong antioxidative activities. Of the compounds tested, esculetin showed the strongest scavenging activity against DPPH radicals, followed by superoxide anions from the xanthine/xanthine oxidase system. The intracellular ROS scavenging activity showed that oxidation of 5-(6-)-chloromethyl-2', 7'-dichlorodihydrofluorescein diacetate (CM-H2DCFDA) was effectively inhibited by esculetin, with potent free radical scavenging activity was also shown in UVB-irradiated human dermal fibroblasts (HDFs). Moreover, treatment of UVA-irradiated HDFs with esculetin resulted in dose-dependent decreases in the expression levels of MMP-1 mRNA and protein. From these results, FCE and one of its components, esculetin, were predicted to be potentially useful as ingredients in cosmetics for protecting against photoaging.

Superoxide radical scavenging activity and DPPH radical scavenging activity were assessed in order to evaluate the antioxidant effect of the Sorbus commixta Hedl. extract (SCoE). SCoE was also treated with several carbohydrate-hydrolytic enzymes that significantly increased the total phenol and flavonoid composition of SCoE. The enzymatically treated SCoE was then assessed for antioxidative activity. The most efficient radical scavenging activity was observed when SCoE was treated with -glucanase. The radical scavenging activity of beta-glucanase-treated SCoE (beta-GSCoE) enhanced the viability of human dermal fibroblasts (HDFs) exposed to ultraviolet (UV) light. The intracellular reactive oxygen species (ROS) scavenging activity of beta-GSCoE was assessed using UVB (20 mJ/cm2)-irradiated HDFs. UVB irradiation increased dichlorofluorescein (DCF) fluorescence, which was measured by a 5-(6-)chloromethyl-2',7'- dichlorodihydrofluorescein diacetate (CM-H2DCFDA). DCF-fluorescence was significantly decreased in the beta-GSCoE-containing culture medium, suggesting that beta-GSCoE scavenges free radicals. The protective effect was further verified by assessing the expression of matrix metalloproteinase-1 (MMP-1) in UVA-irradiated HDFs. The treatment of UVA-irradiated HDFs with beta-GSCoE resulted in a dose-dependent decrease in the expression level of MMP-1 protein and mRNA. These results suggest that beta-GSCoE may mitigate the effects of photoaging in skin by reducing UV-induced adverse skin reactions.

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