Nitroxides and a nitroxide-based UV filter have the potential to photoprotect UVA-irradiated human skin fibroblasts against oxidative damage

Modulation of paraoxonase-2 in human dermal fibroblasts by UVA-induced oxidative stress: A new potential marker of skin photodamage

Paraoxonase-2 (PON2) is an intracellular protein, that exerts a protective role against cell oxidative stress and apoptosis. Genetic and environmental factors (i.e. dietary factors, cigarette smoke, drugs) are able to modulate cellular PON2 levels. The effect of ultraviolet A radiation (UVA), the oxidizing component of sunlight, on PON2 in human dermal fibroblasts (HuDe) has not been previously explored. Excessive UVA radiation is known to cause direct and indirect skin damage by influencing intracellular signalling pathways through oxidative stress mediated by reactive oxygen species (ROS) that modulate the expression of downstream genes involved in different processes, e.g. skin photoaging and cancer. The aim of this study was, therefore, to investigate the modulation of PON2 in terms of protein expression and enzyme activity in HuDe exposed to UVA (270 kJ/m2). Our results show that PON2 is up-regulated immediately after UVA exposure and that its levels and activity decrease in the post-exposure phase, in a time-dependent manner (2-24 h). The trend in PON2 levels mirror the time-course study of UVA-induced ROS. To confirm this, experiments were also performed in the presence of a SPF30 sunscreen used as shielding agent to revert modulation of PON2 at 0 and 2 h post-UVA exposure where other markers of photo-oxidative stress were also examined (NF-KB, γH2AX, advanced glycation end products). Overall, our results show that the upregulation of PON2 might be related to the increase in intracellular ROS and may play an important role in mitigation of UVA-mediated damage and in the prevention of the consequences of UV exposure, thus representing a new marker of early-response to UVA-induced damage in skin fibroblasts.

Antioxidants from Plants Protect against Skin Photoaging

Exposure to UV light triggers the rapid generation and accumulation of reactive oxygen species (ROS) in skin cells, with consequent increase in oxidative stress and thus in photoaging. Exogenous supplementation with dietary antioxidants and/or skin pretreatment with antioxidant-based lotions before sun exposure might be a winning strategy against age-related skin pathologies. In this context, plants produce many secondary metabolites to protect themselves from UV radiations and these compounds can also protect the skin from photoaging. Phenolic compounds, ascorbic acid and carotenoids, derived from different plant species, are able to protect the skin by preventing UV penetration, reducing inflammation and oxidative stress, and influencing several survival signalling pathways. In this review, we focus our attention on the double role of oxidants in cell metabolism and on environmental and xenobiotic agents involved in skin photoaging. Moreover, we discuss the protective role of dietary antioxidants from fruits and vegetables and report their antiaging properties related to the reduction of oxidative stress pathways.

Zinc in Wound Healing Modulation

Wound care is a major healthcare expenditure. Treatment of burns, surgical and trauma wounds, diabetic lower limb ulcers and skin wounds is a major medical challenge with current therapies largely focused on supportive care measures. Successful wound repair requires a series of tightly coordinated steps including coagulation, inflammation, angiogenesis, new tissue formation and extracellular matrix remodelling. Zinc is an essential trace element (micronutrient) which plays important roles in human physiology. Zinc is a cofactor for many metalloenzymes required for cell membrane repair, cell proliferation, growth and immune system function. The pathological effects of zinc deficiency include the occurrence of skin lesions, growth retardation, impaired immune function and compromised would healing. Here, we discuss investigations on the cellular and molecular mechanisms of zinc in modulating the wound healing process. Knowledge gained from this body of research will help to translate these findings into future clinical management of wound healing.

Ethanol extract of Dalbergia odorifera protects skin keratinocytes against ultraviolet B-induced photoaging by suppressing production of reactive oxygen species

Dalbergia odorifera T. Chen (Leguminosae), an indigenous medicinal herb, has been widely used in northern and eastern Asia to treat diverse diseases. Here, we investigated the anti-senescent effects of ethanolic extracts of Dalbergia odorifera (EEDO) in ultraviolet (UV) B-irradiated skin cells. EEDO significantly inhibited UVB-induced senescence of human keratinocytes in a concentration-dependent manner, concomitant with inhibition of reactive oxygen species (ROS) generation. UVB-induced increases in the levels of p53 and p21, biomarkers of cellular senescence, were almost completely abolished in the presence of EEDO. Sativanone, a major constituent of EEDO, also attenuated UVB-induced senescence and ROS generation in keratinocytes, indicating that sativanone is an indexing (marker) molecule for the anti-senescence properties of EEDO. Finally, treatment of EEDO to mice exposed to UVB significantly reduced ROS levels and the number of senescent cells in the skin. Thus, EEDO confers resistance to UVB-induced cellular senescence by inhibiting ROS generation in skin cells.

Can nitroxides evoke the Keap1-Nrf2-ARE pathway in skin?

Nitroxides are stable cyclic radicals of diverse size, charge, and lipophilicity. They are cell-permeative, which effectively protects cells, tissues, isolated organs, and laboratory animals from radical-induced damage. The mechanisms of activity through which nitroxides operate are diverse, including superoxide dismutase-mimetic activity, oxidation of semiquinone radicals, oxidation of reduced metal ions, procatalase-mimetic activity, interruption of radical chain reactions, and indirect modulation of NO levels. Nitroxides possess both a nucleophilic (reducing properties) and an electrophilic (oxidizing properties) nature and, therefore, they may affect different cellular pathways. In the current study, a novel mechanism of action by which nitroxides provide skin protection based on their electrophilic nature is suggested. This study shows that nitroxides may act as electrophiles, directly or indirectly, capable of activating the Keap1-Nrf2-ARE pathway in human keratinocytes (HaCaT) and in human skin (human organ culture model). The high potency of oxoammonium cations versus hydroxylamines in activating the system is demonstrated. The mechanism of action by which nitroxides activate the Keap1-Nrf2-ARE pathway is discussed. Understanding the mechanism of activity may expand the usage of nitroxides as a skin protection strategy against oxidative stress-related conditions.

Ultraviolet radiation, aging and the skin: prevention of damage by topical cAMP manipulation

Being the largest and most visible organ of the body and heavily influenced by environmental factors, skin is ideal to study the long-term effects of aging. Throughout our lifetime, we accumulate damage generated by UV radiation. UV causes inflammation, immune changes, physical changes, impaired wound healing and DNA damage that promotes cellular senescence and carcinogenesis. Melanoma is the deadliest form of skin cancer and among the malignancies of highest increasing incidence over the last several decades. Melanoma incidence is directly related to age, with highest rates in individuals over the age of 55 years, making it a clear age-related disease. In this review, we will focus on UV-induced carcinogenesis and photo aging along with natural protective mechanisms that reduce amount of “realized” solar radiation dose and UV-induced injury. We will focus on the theoretical use of forskolin, a plant-derived pharmacologically active compound to protect the skin against UV injury and prevent aging symptoms by up-regulating melanin production. We will discuss its use as a topically-applied root-derived formulation of the Plectranthus barbatus (Coleus forskolii) plant that grows naturally in Asia and that has long been used in various Aryuvedic teas and therapeutic preparations.

Suppression of experimental autoimmune encephalomyelitis by 300-315nm ultraviolet light

Multiple sclerosis (MS) is a chronic debilitating disease, with lowest incidence in equatorial regions and highest incidence in temperate regions. This relationship is believed to be related to sunlight or UV light exposure. Recent evidence with experimental autoimmune encephalomyelitis (EAE), an animal model of MS, established that this suppression is not mediated by vitamin D production. UV is comprised of three general wave bands: UVC (100-280nm), UVB (280-320nm) and UVA (320-400nm). In the present study we used four lamps that emit different wavelengths of UV: (1) broad band UVB (BB-UVB: 280-320nm); (2) narrow band UVB (NB-UVB: 300-315nm); (3) broad band UVA (BB-UVA: 300-400nm); and (4) long wavelength UVA (UVA-1: 340-400nm). The effect of these light sources was studied in vitamin D-sufficient C57BL/6 mice. The NB-UVB largely accounted for the suppression and delay of onset of EAE by BB-UVB. In contrast, UVA-1 failed to suppress EAE severity at low (∼2.5KJ/m(2)), medium (∼5.0KJ/m(2)) and high (∼10.0KJ/m(2)) doses. Serum calcium and 25-(OH)D3 levels were unchanged after both NB-UVB and UVA-1 treatments. The results demonstrate that NB-UVB (300-315nm) is largely responsible for light-induced suppression of EAE and its effect is not via production of vitamin D.

Effective inhibition of skin cancer, tyrosinase, and antioxidative properties by astaxanthin and astaxanthin esters from the green alga Haematococcus pluvialis

Astaxanthin mono- (AXME) and diesters (AXDE) were characterized and examined for anticancer potency with total carotenoids (TC) and astaxanthin (AX) against UV-7,12-dimethylbenz(a)anthracene (DMBA)-induced skin cancer model in rat. At 200 μg/kg bw, AXDE and AXME reduced UV-DMBA-induced tumor incidences up to 96 and 88%, respectively, when compared to AX (66%) and TC (85%). UV-DMBA has been known to generate high levels of free radicals and tyrosinase enzyme, leading to characteristic symptoms of skin pigmentation and tumor initiation. Intriguingly, ~7-fold increase in tyrosinase and 10-fold decrease in antioxidant levels were normalized by AXDE and AXME as opposed to only ~1.4-2.2-fold by AX and TC, respectively. This result together with the appearance of 72 and 58 ng/mL of retinol in the serum of respective AXE-treated (AXDE + AXME) and AX-treated animals suggested that better anticancer potency of AXEs could be due to increased bioavailability.

The effect of cilostazol on the expression of matrix metalloproteinase-1 and type I procollagen in ultraviolet-irradiated human dermal fibroblasts

AIM

Cilostazol is a selective inhibitor of type III phosphodiesterase that inhibits platelet aggregation. Cilostazol is a useful vasodilator, antithrombotic, and cardiotonic agent. Ultraviolet B (UVB) irradiation increases the production of matrix metalloproteinase-1 (MMP-1) during skin photoaging. The UVB-induced increase of MMP-1 results in connective tissue damage, and the skin becomes wrinkled and aged. Here, we investigated the capacity of cilostazol to inhibit MMP-1 expression in UVB-irradiated human dermal fibroblasts.

MAIN METHODS

Cultured human dermal fibroblasts were irradiated with UVB, followed by the addition of cilostazol to the culture medium.

KEY FINDINGS

Post-treatment with cilostazol attenuated UVB-induced production of MMP-1 and prevented the reduction of type I procollagen. Cilostazol inhibited UVB irradiation-induced phosphorylation of the mitogen-activated protein kinase (MAPK) signaling molecules Jun-N-terminal kinase (JNK) and p38 kinase, as well as activator protein-1 (AP-1) in dermal fibroblasts.

SIGNIFICANCE

Overall, these results demonstrate that cilostazol regulates UVB-induced MMP-1 expression and type I procollagen synthesis by inhibiting MAPK signaling and AP-1 activity. Therefore, we suggest that cilostazol may be useful for the prevention and treatment of skin photodamage caused by UVB-irradiation.

Phototoxicity of kava - formation of reactive oxygen species leading to lipid peroxidation and DNA damage

Kava is one of the most widely sold herbal dietary supplements in the United States. It has been reported that, besides exhibiting hepatotoxicity, kava also possesses photosensitivity and induces dermopathy in humans. In this study, we determined that UVA irradiation of kava in the presence of a lipid, methyl linoleate, generated lipid peroxidation which was mediated by singlet oxygen generated during photoirradiation. The six major kavalactones(yangonin, 7,8-dihydrokawa in, kawain, 7,8-dihydromethysticin, methysticin, and 5,6-dehydrokawain) were also studied in parallel; only 5,6-dehydrokawain and yangonin-induced a low level of lipid peroxidation. UVA irradiation of kava in human HaCaT skin keratinocytes induced cytotoxicity which was mediated by oxidative stress, led to DNA strand cleavage, and produced 8-hydroxy-2'-deoxyguanosine (8-OHdG) adduct. Study by the electron spin resonance (ESR) method revealed that UVA irradiation of kava produced singlet oxygen and carbon-centered radicals. The overall results suggest that kava is photocytotoxic and photogenotoxic, both mediated by free radicals generated during photoirradiation.