Effects of UVA and L-ascorbic acid on nuclear factor-kappa B in melanocytes and in HaCaT keratinocytes

UVB-stimulated TNFα release from human melanocyte and melanoma cells is mediated by p38 MAPK

Ultraviolet (UV) radiation activates cell signaling pathways in melanocytes. As a result of altered signaling pathways and UV-induced cellular damage, melanocytes can undergo oncogenesis and develop into melanomas. In this study, we investigated the effect of UV-radiation on p38 MAPK (mitogen-activated protein kinase), JNK and NFκB pathways to determine which plays a major role in stimulating TNFα secretion in human HEM (melanocytes) and MM96L (melanoma) cells. MM96L cells exhibited 3.5-fold higher p38 activity than HEM cells at 5 min following UVA + B radiation and 1.6-fold higher JNK activity at 15–30 min following UVB+A radiation, while NFκB was minimally activated in both cells. Irradiated HEM cells had the greatest fold of TNFα secretion (UVB: 109-fold, UVA + B: 103-fold & UVB+A: 130-fold) when co-exposed to IL1α. The p38 inhibitor, SB202190, inhibited TNFα release by 93% from UVB-irradiated HEM cells. In the UVB-irradiated MM96L cells, both SB202190 and sulfasalazine (NFκB inhibitor) inhibited TNFα release by 52%. Although, anisomycin was a p38 MAPK activator, it inhibited TNFα release in UV-irradiated cells. This suggests that UV-mediated TNFα release may occur via different p38 pathway intermediates compared to those stimulated by anisomycin. As such, further studies into the functional role p38 MAPK plays in regulating TNFα release in UV-irradiated melanocyte-derived cells are warranted.

Differential activation of signaling pathways by UVA and UVB radiation in normal human epidermal keratinocytes

Ultraviolet (UV) radiation from the solar spectrum is a major etiological factor for many cutaneous pathologies including cancer. By understanding changes in cell signaling pathways induced by UVA and UVB, novel strategies for prevention and treatment of UV-related pathologies could be developed. However, much of the information in the literature from various laboratories cannot cross talk because of difficulties associated with the use of ill-defined light sources and physiologically irrelevant light dosimetry. Herein, we have assessed the effect of exposure of normal human epidermal keratinocytes (NHEK) to UVA (2 and 4 J cm(-2)) or UVB (20 and 40 mJ cm(-2)) radiation. Employing western blot analysis, we found that exposure of NHEK to UVB, but not UVA, phosphorylates JNK1/2 at Th(183)/Tyr(185), STAT3 at Ser(727) , AKT at Ser(473) and increases c-Fos expression, whereas exposure to UVA, but not UVB, phosphorylates AKT at Thr(308). UVB as well as UVA exposure leads to increased phosphorylation of (1) ERK1/2 at Th(202)/Tyr(204); (2) p38 at Th(180)/Tyr(204); (3) STAT3 at Tyr(705); (4) mTOR at Thr(2448); and (v) p70S6k at Thr(421) /Ser(424); enhanced expression of PI3K (p85) and c-jun; and nuclear translocation of NFκB proteins. These findings could be considered as a beginning for understanding the differential effects of UVA and UVB in the human skin and may have implications both with respect to risk assessment from exposure to solar UV radiation, and to target interventions against signaling events mediated by UVA and UVB.

Structure activity relationship of antioxidative property of flavonoids and inhibitory effect on matrix metalloproteinase activity in UVA-irradiated human dermal fibroblast

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.

Biological Role of Vitamin C in Keratinocytes

Epidemiological studies have suggested an association between vitamin C (and other antioxidant vitamins) and cancer risk. However, the mechanisms accounting for prevention have not been extensively investigated. In skin, vitamin C (ascorbic acid) exerts different biological roles, including photoprotective effects and participation in collagen synthesis. This paper reports new findings about additional functions of the vitamin. Vitamin C counteracts oxidative stress via transcriptional and post-translational mechanisms; this modulation may interfere with the activity of redox-sensitive transcription factors, commitment to differentiation or cell cycle arrest, and apoptosis in response to DNA damage. All of these vitamin C-mediated responses might be important in different cell types, allowing for the maintenance of body homeostasis.

Inhibition of UVA irradiation-modulated signaling pathways by rutaecarpine, a quinazolinocarboline alkaloid, in human keratinocytes

Matrix metalloproteinases (MMPs), a key component in photoaging of the skin due to exposure to ultraviolet A, appear to be increased by ultraviolet A irradiation-associated generation of reactive oxygen species. In this study, we investigated the effects of synthetic rutaecarpine, which is also found in Evodia rutaecarpa, on the ultraviolet A-induced changes in the expression of gelatinases: matrix metalloproteinase (MMP)-2 and MMP-9 using HaCaT human keratinocytes as a model cellular system. Ultraviolet A irradiation of HaCaT cells increased the gelatinolytic activities of MMP-2 and MMP-9, which was significantly suppressed by the pretreatment with rutaecarpine. In addition, rutaecarpine significantly suppressed the ultraviolet A-induced enhanced expression of MMP-2 and MMP-9 proteins and mRNAs. Rutaecarpine also inhibited the H2O2-induced increase in the expression of MMP-2 and MMP-9. Furthermore, rutaecarpine decreased the ultraviolet A-induced increased generation of reactive oxygen species. Taken together, these results suggest that rutaecarpine inhibited ultraviolet A-induced reactive oxygen species generation, resulting in the enhanced expression of MMP-2 and MMP-9 in human skin cells. These results further suggest that ruetaecarpine may be useful in the prevention of ultraviolet A-induced photoaging.

UVA-mediated activation of signaling pathways involved in skin tumor promotion and progression

Each year more than 1,000,000 cases of non-melanoma skin cancer (NMSC) are diagnosed in the Unites States. Solar radiation has been described as an important etiological factor in the development of NMSC. UVA comprises the largest portion of solar radiation reaching the surface of the earth (90-99%) and has been described to lead to benign tumor formation as well as malignant cancers, squamous cell carcinomas (SCCs). While much research has focused upon the effects of UVB radiation, little is known about UVA-induced signaling pathways and their role in tumor promotion. Here we focus on UVA-mediated activation of mitogen-activated protein kinase (MAPK) pathways and their role in activator protein-1 (AP-1) mediated transcription and cyclooxygenase-2 (COX-2) expression. AP-1 and COX-2 have been found to play a role in angiogenesis in other tissues. We propose UVA-mediated increases in AP-1 and COX-2 may play a role in tumor promotion through increases in interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF). Since MAPKs, specifically p38 and JNK, appear to play a major role in the expression of UVA-induced AP-1 and COX-2, pharmacological inhibitors may be of benefit in the chemoprevention of non-melanoma skin cancer.

Induction of tumor necrosis factor-alpha by UVB: a role for reactive oxygen intermediates and eicosanoids

UVB irradiation induces nuclear factor-kappaB (NF-kappaB) activation, tumor necrosis factor-alpha (TNF-alpha) expression and reactive oxygen intermediates (ROI) in keratinocytes. We investigated whether ROI play a role in UVB-induced TNF-alpha mRNA expression. The antioxidants N-acetyl cysteine, NAC, epigallocathin gallate, EGCG, butylated hydroxyanisole (BHA) and vitamin C could reduce UVB-induced TNF-alpha mRNA levels to various degrees; vitamin E (alpha-tocopherol) had no effect. BHA was the most potent inhibitor. The oxidant tertiary butylated hydroperoxide could effectively induce TNF-alpha mRNA expression. Nordihydroguaiaretic acid (NDGA) and MK-886, inhibitors of lipoxygenase (LOX), and indometacin and quinacrine, inhibitors of cyclooxygenase (COX) and phospholipase A2, respectively, could also reduce UVB-induced TNF-alpha mRNA expression. Inhibition by NDGA was in concordance with the results for BHA. NDGA, indometacin, quinacrine and BHA could also effectively inhibit the inhibitor of NF-kappaB degradation, thereby maintaining NF-kappaB inactivity. In conclusion, we show that ROI are implicated in the induction of TNF-alpha mRNA by UVB and that not all antioxidants are equally effective inhibitors. COX products and more importantly LOX products, which themselves are products of an oxidative metabolism, are the main ROI implicated in this induction of TNF-alpha expression by UVB probably via activation of NF-kappaB.