Induction of Cytochrome P450 1a1 and 1b1 by Photooxidized Tryptophan in Transformed Human Keratinocytes

Ultraviolet A light induces DNA damage and estrogen-DNA adducts in Fuchs endothelial corneal dystrophy causing females to be more affected

Fuchs endothelial corneal dystrophy (FECD) is a leading cause of corneal endothelial (CE) degeneration resulting in impaired visual acuity. It is a genetically complex and age-related disorder, with higher incidence in females. In this study, we established a nongenetic FECD animal model based on the physiologic outcome of CE susceptibility to oxidative stress by demonstrating that corneal exposure to ultraviolet A (UVA) recapitulates the morphological and molecular changes of FECD. Targeted irradiation of mouse corneas with UVA induced reactive oxygen species (ROS) production in the aqueous humor, and caused greater CE cell loss, including loss of ZO-1 junctional contacts and corneal edema, in female than male mice, characteristic of late-onset FECD. UVA irradiation caused greater mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) damage in female mice, indicative of the sex-driven differential response of the CE to UVA, thus accounting for more severe phenotype in females. The sex-dependent effect of UVA was driven by the activation of estrogen-metabolizing enzyme CYP1B1 and formation of reactive estrogen metabolites and estrogen-DNA adducts in female but not male mice. Supplementation of N-acetylcysteine (NAC), a scavenger of reactive oxygen species (ROS), diminished the morphological and molecular changes induced by UVA in vivo. This study investigates the molecular mechanisms of environmental factors in FECD pathogenesis and demonstrates a strong link between UVA-induced estrogen metabolism and increased susceptibility of females for FECD development.

Acute exposure to solar simulated ultraviolet radiation affects oxidative stress-related biomarkers in skin, liver and blood of hairless mice

The ultraviolet (UV) region of solar radiation is a critical factor in the initiation and development of a number of skin diseases. However, it is not only skin which is directly exposed to solar light that is affected by UV radiation, through low molecular weight mediators, generated upon irradiation, "non-skin" tissues can also be affected. The aim of this study was to examine in detail, the acute effects of UVA and UVB wavebands on hairless mice. Female SKH-1 hairless mice were exposed to a single dose of UVB (200, 800 mJ/cm(2)) or UVA (10, 20 J/cm(2)) using a solar simulator. The effects on haematological parameters, activity and/or expression of antioxidant enzymes, level of glutathione (GSH), markers of oxidative damage (lipid peroxidation and carbonylated proteins) were analysed in erythrocytes, plasma, liver and whole skin homogenates. No macroscopic changes were observed either 4 or 24 h after UVA/UVB exposure. The blood count showed a significant increase in leukocyte number and reduction of platelets 4 h following UVA and UVB irradiation, which disappeared 24 h after irradiation except for the higher UVA dose. Changes in oxidative stress-related parameters, particularly activity of catalase (CAT) and superoxide dismutase (SOD) and level of GSH and lipid peroxidation products, were found in skin, erythrocytes and liver. The expression of several enzymes (CAT, SOD, glutathione transferase (GST), nicotinamide adenine dinucleotide (phosphate) quinone oxidoreductase (NQO1) and hem oxygenase-1 (HO-1)) in skin was affected following UVA and UVB radiation. Increase in carbonylated proteins was found in plasma and skin samples.

Solar radiation induced skin damage: review of protective and preventive options

PURPOSE

Solar energy has a number of short- and long-term detrimental effects on skin that can result in several skin disorders. The aim of this review is to summarise current knowledge on endogenous systems within the skin for protection from solar radiation and present research findings to date, on the exogenous options for such skin photoprotection.

RESULTS

Endogenous systems for protection from solar radiation include melanin synthesis, epidermal thickening and an antioxidant network. Existing lesions are eliminated via repair mechanisms. Cells with irreparable damage undergo apoptosis. Excessive and chronic sun exposure however can overwhelm these mechanisms leading to photoaging and the development of cutaneous malignancies. Therefore exogenous means are a necessity. Exogenous protection includes sun avoidance, use of photoprotective clothing and sufficient application of broad-spectrum sunscreens as presently the best way to protect the skin. However other strategies that may enhance currently used means of protection are being investigated. These are often based on the endogenous protective response to solar light such as compounds that stimulate pigmentation, antioxidant enzymes, DNA repair enzymes, non-enzymatic antioxidants.

CONCLUSION

More research is needed to confirm the effectiveness of new alternatives to photoprotection such as use of DNA repair and antioxidant enzymes and plant polyphenols and to find an efficient way for their delivery to the skin. New approaches to the prevention of skin damage are important especially for specific groups of people such as (young) children, photosensitive people and patients on immunosuppressive therapy. Changes in public awareness on the subject too must be made.

Inhibition of procarcinogen-bioactivating human CYP1A1, CYP1A2 and CYP1B1 enzymes by melatonin

Administration of melatonin to rodents decreases the incidence of tumorigenesis initiated by benzo[a]pyrene or 7,12-dimethylbenz[a]anthracene, which requires bioactivation by cytochrome P450 enzymes, such as CYP1A1, CYP1A2 and CYP1B1, to produce carcinogenic metabolites. The present study tested the hypothesis that melatonin is a modulator of human CYP1 catalytic activity and gene expression. As a comparison, we also investigated the effect of melatonin on the catalytic activity of CYP2A6, which is also a procarcinogen-bioactivating enzyme. Melatonin (3-300 microm) decreased 7-ethoxyresorufin O-dealkylation catalyzed by human hepatic microsomes and recombinant CYP1A1, CYP1A2 and CYP1B1, whereas it did not affect coumarin 7-hydroxylation catalyzed by hepatic microsomes or recombinant CYP2A6. Melatonin inhibited CYP1 enzymes by mixed inhibition, with apparent K(i) values (mean +/- S.E.M.) of 59 +/- 1 (CYP1A1), 12 +/- 1 (CYP1A2), 14 +/- 2 (CYP1B1) and 46 +/- 8 microm (hepatic microsomes). Additional experiments indicated that melatonin decreased benzo[a]pyrene hydroxylation catalyzed by hepatic microsomes and CYP1A2 but not by CYP1A1 or CYP1B1. Treatment of MCF-10A human mammary epithelial cells with melatonin (up to 300 microm) did not affect basal or benzo[a]pyrene-inducible CYP1A1 or CYP1B1 gene expression. Consistent with this finding, melatonin did not influence reporter activity in aryl hydrocarbon receptor-dependent pGudluc6.1-transfected MCF-10A cells treated with or without benzo[a]pyrene, as assessed in an in vitro cell-based luciferase reporter gene assay. Overall, melatonin is an in vitro inhibitor of human CYP1 catalytic activity, and it may be useful to develop potent analogues of melatonin as potential cancer chemopreventive agents that block CYP1-mediated chemical carcinogenesis.

Role of mitogen-activated protein kinases in aryl hydrocarbon receptor signaling

Human populations are increasingly exposed to a number of environmental pollutants such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls and dioxins. These compounds are activators of the aryl hydrocarbon receptor (AhR) that controls the expression of many genes including those for detoxification enzymes. The regulatory mechanisms of AhR are multi-factorial and include phosphorylation by various protein kinases. Significant progress in the research of mitogen-activated protein kinases (MAPKs) has been achieved in the last decade. Isolated reports have been published on the role of MAPKs in AhR functions and vice versa, with activation of MAPKs by AhR ligands. This mini-review summarizes current knowledge on the mutual interactions between MAPKs and AhR. The majority of studies has been done on cancer-derived cell lines that have impaired cell cycle regulation and lacks the complete detoxification apparatus. We emphasize the importance of the future studies that should be done on non-transformed cells to distinguish the role of MAPKs in cancer and normal cells. Primary cultures of human or rodent hepatocytes that are equipped with a fully functional biotransformation battery or xenobiotics-metabolizing extra-hepatic tissues should be the models of choice, as the results in our experiments confirm.

Differential regulation of hepatic cytochrome P450 monooxygenases in streptozotocin-induced diabetic rats

The present investigation was carried out to study the expression of major cytochrome P450 (CYP) isozymes in streptozotocin-induced diabetes with concomitant insulin therapy. Male Sprague-Dawley rats were randomly assigned to untreated control, streptozotocin-induced diabetic, insulin-treated groups and monitored for 4 weeks. Uncontrolled hyperglycemia in the early phase of diabetes resulted in differential regulation of cytochrome P450 isozymes. CYP1B1, CYP1A2, heme oxygenase (HO)-2 proteins and CYP1A2-dependent 7-ethoxyresorufin O-deethylase (EROD) activity were upregulated in the hepatic microsomes of diabetic rats. Insulin therapy ameliorated EROD activity and the expression of CYP1A2, CYP1B1 and HO-2 proteins. In addition, CYP2B1 and 2E1 proteins were markedly induced in the diabetic group. Insulin therapy resulted in complete amelioration of CYP2E1 whereas CYP2B1 protein was partially ameliorated. By contrast, CYP2C11 protein was decreased over 99% in the diabetic group and was partially ameliorated by insulin therapy. These results demonstrate widespread alterations in the expression of CYP isozymes in diabetic rats that are ameliorated by insulin therapy.

Silybin and dehydrosilybin inhibit cytochrome P450 1A1 catalytic activity: A study in human keratinocytes and human hepatoma cells

The flavonolignan silybin and its derivative dehydrosilybin have been proposed as candidate UV-protective agents in skin care products. This study addressed the effect of silybin and dehydrosilybin on the activity of cytochrome P450 isoform CYP1A1 in human keratinocytes (HaCaT) and human hepatoma cells (HepG2). CYP1A1 catalytic activity was assessed as O-deethylation of 7-ethoxyresorufin using fluorescence detection. Silybin and dehydrosylibin inhibited basal and dioxin-inducible CYP1A1 catalytic activity in both cell lines used. The inhibitory effect of tested compounds was more pronounced in HaCaT cells than in HepG2 cells, and dehydrosilybin was a much stronger inhibitor than silybin. Analyses on CYP1A1 human recombinant protein yielded IC(50) values of 22.9 +/- 4.7 micromol/L and 0.43 +/- 0.04 micromol/L for silybin and dehydrosilybin, respectively. Since CYP1A enzymes are some of the most prominent actors in the process of chemically induced carcinogenesis, the inhibitory activity of the flavonolignans tested against CYP1A1 favors their use as cytoprotective agents in terms of skin and hepatic metabolism. In addition, the capability of dehydrosilybin to inhibit CYP1A1 in submicromolar concentrations makes this compound a potential biological probe in CYP1A1 analyses.

Endogenous UVA-photosensitizers: mediators of skin photodamage and novel targets for skin photoprotection

Endogenous chromophores in human skin serve as photosensitizers involved in skin photocarcinogenesis and photoaging. Absorption of solar photons, particularly in the UVA region, induces the formation of photoexcited states of skin photosensitizers with subsequent generation of reactive oxygen species (ROS), organic free radicals and other toxic photoproducts that mediate skin photooxidative stress. The complexity of endogenous skin photosensitizers with regard to molecular structure, pathways of formation, mechanisms of action, and the diversity of relevant skin targets has hampered progress in this area of photobiology and most likely contributed to an underestimation of the importance of endogenous sensitizers in skin photodamage. Recently, UVA-fluorophores in extracellular matrix proteins formed posttranslationally as a consequence of enzymatic maturation or spontaneous chemical damage during chronological and actinic aging have been identified as an abundant source of light-driven ROS formation in skin upstream of photooxidative cellular stress. Importantly, sensitized skin cell photodamage by this bystander mechanism occurs after photoexcitation of sensitizers contained in skin structural proteins without direct cellular photon absorption thereby enhancing the potency and range of phototoxic UVA action in deeper layers of skin. The causative role of photoexcited states in skin photodamage suggests that direct molecular antagonism of photosensitization reactions using physical quenchers of photoexcited states offers a novel chemopreventive opportunity for skin photoprotection.