Effect of dietary omega-3 and omega-6 fatty acid sources on PUVA-induced cutaneous toxicity and tumorigenesis in the hairless mouse

The potential of omega-3 fatty acids in the prevention of non-melanoma skin cancer

In toto, there is strong circumstantial evidence from both experimental and clinical studies to support a role for omega-3 FA in the prevention of non-melanoma skin cancer (NMSC). In experimental animal studies there is direct evidence that dietary omega-3 FA inhibits ultraviolet radiation (UVR) carcinogenic expression, with regard to both increased tumor latent period and reduced tumor multiplicity. Equivalent levels of omega-6 FA increase UVR carcinogenic expression. Dietary omega-3 FA dramatically reduces the plasma and cutaneous pro-inflammatory and immunosuppressive PGE(2) levels in mice. Dietary omega-6 FA increases prostaglandin E synthase type 2 (PGE(2)) level. Dietary omega-3 FA significantly reduces the inflammatory response and sustains, or enhances, the delayed type hypersensitivity immune response in mice when compared to an equivalent dietary level of omega-6 FA. Supplementary omega-3 FA significantly increases the UVR-mediated erythema threshold in humans. Supplementary omega-3 FA significantly reduces the level of pro-inflammatory and immunosuppressive PGE(2) levels in Ultraviolet B-irradiated human skin.

Omega 3 but not omega 6 fatty acids inhibit AP-1 activity and cell transformation in JB6 cells

Epidemiological and animal-based investigations have indicated that the development of skin cancer is in part associated with poor dietary practices. Lipid content and subsequently the derived fatty acid composition of the diet are believed to play a major role in the development of tumorigenesis. Omega 3 (omega3) fatty acids, including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), can effectively reduce the risk of skin cancer whereas omega 6 (omega6) fatty acids such as arachidonic acid (AA) reportedly promote risk. To investigate the effects of fatty acids on tumorigenesis, we performed experiments to examine the effects of the omega3 fatty acids EPA and DHA and of the omega6 fatty acid AA on phorbol 12-tetradecanoate 13-acetate (TPA)-induced or epidermal growth factor (EGF)-induced transcription activator protein 1 (AP-1) transactivation and on the subsequent cellular transformation in a mouse epidermal JB6 cell model. DHA treatment resulted in marked inhibition of TPA- and EGF-induced cell transformation by inhibiting AP-1 transactivation. EPA treatment also inhibited TPA-induced AP-1 transactivation and cell transformation but had no effect on EGF-induced transformation. AA treatment had no effect on either TPA- or EGF-induced AP-1 transactivation or transformation, but did abrogate the inhibitory effects of DHA on TPA- or EGF-induced AP-1 transactivation and cell transformation in a dose-dependent manner. The results of this study demonstrate that the inhibitory effects of omega3 fatty acids on tumorigenesis are more significant for DHA than for EPA and are related to an inhibition of AP-1. Similarly, because AA abrogates the beneficial effects of DHA, the dietary ratio of omega6 to omega3 fatty acids may be a significant factor in mediating tumor development.

Fat intake and risk of squamous cell carcinoma of the skin

The varied effects of different classes of dietary fatty acids on carcinogenesis suggest that fatty acid composition is an important determining factor in tumor development. In the present study, we investigated the association between dietary n-3 and n-6 fatty acid intake and risk of squamous cell carcinoma of the skin (SCC). Data were taken from a population-based case-control study of skin SCC in Southeastern Arizona. Our data show a consistent tendency for a lower risk of SCC with higher intakes of n-3 fatty acids [p (for trend) = 0.055]. The adjusted odds ratios for increasing levels of n-3 fatty acids were 0.85 [95% confidence interval (CI) = 0.56-1.27] and 0.71 (95% CI = 0.49-1.00) compared with the lower level as the referent. For the ratio of n-3 to n-6 fatty acids, the odds ratios in successively higher levels were 0.88 (95% CI = 0.59-1.32) and 0.74 (95% CI = 0.51-1.05), suggesting a tendency toward decreased risk of SCC with increased intake of diets with high ratio of n-3 to n-6 fatty acid. More studies are clearly needed to elucidate the function of dietary fatty acids so that recommendations can be made to alter the human diet for cancer prevention, particularly in light of the increasing incidence of SCC of the skin.

Intradermal transfer of caspase-1 (CASP1) DNA into mouse dissects: role of CASP1 in interleukin-1beta associated skin inflammation and apoptotic cell death

Caspase-1 (CASP1) interleukin-1beta (IL-1beta) converting enzyme (ICE) has been cloned as a specific enzyme which activates the biologically inactive pro-form of IL-1beta into biological active IL-1beta. Based on the significant homology to Ced-3, Caenorhabditis elegans apoptotic gene and, proof of apoptotic activity of ICE in rat fibroblasts, ICE was renamed as CASP1. In contrast to in vitro functions, the in vivo significance of high expression of CASP1 in skin remains to be elucidated. We transferred plasmid DNA encoding murine CASP1 with beta-actin promoter into mouse skin. The CASP1 DNA-injected skin, but not skin injected with control plasmid without CASP1, developed localized erythema with subcutaneous nodules. The nodules were associated with marked inflammatory infiltrates. The apoptotic cells detected by the TUNEL method were distributed in and around the inflammatory foci. The plasma IL-1beta level of CASP1 DNA-injected mouse was elevated compared with that of the control DNA-injected mouse. These inflammatory reactions of CASP1 DNA-injected skin were suppressed by treatment with neutralizing anti-murine IL-1beta antibodies, but the TUNEL positive apoptotic cells were still detected. This study clearly demonstrate dual roles of CASP1 in causing IL-1beta associated granulomatous skin infiltration and inducing apoptotic cell death in vivo.