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ROS: A Step Closer to Elucidating Their Role in the Etiology ofLight-Induced Skin Disorders Homer S. BlackDepartment of Dermatology, Baylor College of Medicine, Houston, Texas, USA Free radicals are chemical species characterized by an free radical scavenging. In addition, there are a number of odd number of orbital electrons, or by pairs of electrons of pathologies where lipid oxidation has been shown to similar directional spin isolated singly in separate orbitals.
increase with no concurrent exacerbation of disease Consequently, most of these agents are highly reactive and development and sometime to occur concomitantly with usually exhibit an extremely short half-life, although due to amelioration of the disorder (Rhodes et al, 1995). Thus, the steric and resonance effects, some exceptions occur. For relevance of these indirect responses to the pathology of example, the diradical, molecular oxygen, exists in the triplet state (3O2) and is an essential element of normal Recent advances in a number of analytical techniques, metabolism of aerobic organisms. Even under normal especially free radical spin trapping, have held promise to circumstances, however, the controlled reduction of oxygen advance our knowledge of free radical roles in disease.
occurs and leads to the formation of the major reactive Froncisz et al (1989) provided construction details, engi- oxygen species (ROS), i.e., superoxide anion, hydrogen neering characteristics, and spectroscopic performance peroxide, and hydroxyl radical. Singlet oxygen, although data of a loop-gap resonator for the electron spin technically not a free radical, is highly reactive and may resonance (ESR) detection of spin labels. A low-frequency produce biological effects similar to those of other ROS. In ESR spectrometer has been employed to measure free addition to ROS, organisms may be subjected to a wide radical reactions in living mice (Utsumi et al, 1995). Free array of other free radicals, including those of both radical production in tissues of a living animal, the first exogenous and endogenous origin. This is particularly true report of such a direct measurement, employed low- of the skin. Almost every major class of cellular chemical frequency paramagnetic resonance, in combination with in constituent (e.g., lipids, nucleic acids, and proteins) is vivo spin trapping, to detect hydroxyl markers produced subject to radical attack, providing a rationale for the from ionizing radiation in the tumor of a living mouse involvement of free radical reactions in the pathophysiology (Halpern et al, 1995). He et al (2001), using a specially of a wide spectrum of disorders. Although the idea that free designed bridged loop-gap surface resonator, described in radical-mediated reactions might be responsible for some vivo imaging of free radicals in human subjects with the use of the deleterious effects observed in actinically exposed of topically applied nitroxide spin labels and ESR. Using skin is now accepted as fait accompli, it was at first various oxygen-sensitive nitroxide spin labels and ESR, it received with due skepticism. Certainly, it had been clearly was found that trap intensity corresponded to irradiance demonstrated that radicals resulted after UV radiation of and penetration of UVB and UVA in human skin biopsies excised skin (Pathak and Stratton, 1968). But the reason for (Herrling et al, 2003). In this issue of the Journal, Takeshita this caution was based upon the fact that methodology and colleagues, in a carefully controlled study, have required for rigorous testing for involvement of free radicals employed the griseofulvin-induced protoporphyria mouse in pathogenesis had not advanced to the stage that lent model and in vivo ESR spectrometry to examine ROS itself well to in vivo measurement (Black, 1987). Thus, the generation and their potential role in this photosensitive gradual acceptance of free radical involvement in specific disorder (2004). Although porphyrias may exhibit an indeter- cutaneous disorders came largely from a considerable body minate pattern of inheritance, they represent a group of of circumstantial evidence based upon indirect lines of diseases that result from deficiencies in specific enzymes in investigation involving the major participants in such reac- heme biosynthesis that takes place in the erythropoietic tions, i.e., pro-oxidants, free radicals, and anti-oxidants.
system and liver (Cox, 1997). Accumulation of heme Examples include the amelioration of symptoms or a precursors leads to a distinct syndrome of cutaneous disease state by antioxidants, or the measurement of lipid photosensitivity, thought to result partly from photodynamic oxidation. With respect to the former, it is becoming clear reactions of ROS with porphyrins (Buettner and Oberley, that antioxidant function is more complex, producing 1980). Edema and erythema occur within a few minutes physiological responses that may or may not result from after light exposure. The griseofulvin-induced protopor-phyria mouse model has been thoroughly documented andis employed as a standard model for the study of Erythro-poietic protoporphyria (Konrad et al, 1975). If, indeed, ROS Abbreviations: DFO, desferr loxamine meystate; ESR, electron spinresonance; ROS, reactive oxygen species Copyright r 2004 by The Society for Investigative Dermatology, Inc.
reaction of protoporphyrin, then in vivo generation of these generation, their possible role in a number of photosensi- agents would have to be detected in the skin of griseofulvin- tivity disorders, as well as in the evaluation of antioxidants induced protoporphyria. This was approached by using and sunscreens in radical scavenging.
L-band ESR spectrometry with a loop-gap resonator tomeasure the systemically administered probe (carbamoyl- PROXYL)1 throughout a mouse, i.e., whole-body measure-ments. A surface resonator was then attached to the skin Address correspondence to: Homer S. Black, site to be examined, and ESR spectra were obtained.
Department of Dermatology, Baylor College of Medicine, Houston,Texas 77030, USA.
Comparison of ESR signal intensity after administration ofthe carbamoyl-PROXYL probe, and sensitivity mappingof the surface resonator, indicated that the ESR signaldetected with the surface resonator came mainly from the probe distributed in the skin. The intensities of the low-fieldpeaks were used to calculate signal decay. A good HS: Potential involvement of free radical reactions in ultraviolet light- mediated cutaneous damage. Photochem Photobiol 46:213–221, 1987 correlation between enhanced nitroxyl signal decay and Buettner GR, Oberley LW: The apparent production of superoxide and hydroxyl ROS generation had previously been demonstrated (Miura radicals by hematoporphyrins and light as seen by spin-trapping. FEBS et al, 1995). Measurements were taken in griseofulvin-fed Cox T M: Erythropoietic protoporphyria. J Inherit Metab Dis 20:258–269, 1997 mice and controls, before and after irradiation with a 300-W Froncisz W, Oles T, Hyde JS: Murine L-band ESR loop-gap resonator. J Magn tungsten lamp, and after administration of saline control or ROS inhibitors. Light irradiation increased the signal decay Halpern HJ, Yu C, Barth E, et al: In situ detection, by spin trapping, of hydroxyl rate (an indication of ROS formation) significantly in the radical markers produced from ionizing radiation in the tumor of a livingmouse. Proc Natl Acad Sci USA 92:796–800, 1995 griseofulvin-fed mice but had little effect on this parameter He G, Samonilov A, Kuppusamy P, et al: In vivo EPR imaging of the distribution in control mice. Conversely, when the light was switched off, and metabolism of nitroxide radicals in human skin. J Magn Reson there was a rapid deceleration of the decay rate to the original level, i.e., the decay rate responded quickly and Herrling T, Fuchs J, Rehberg J, et al: UV-induced free radicals in skin detected by ESR spectroscopy and imaging using nitroxides. Free Radic Biol Med reversibly to light irradiation. Furthermore, superoxide dismutase, catalase, and the iron-chelating agent, DFO, Konrad K, Honigsmann H, Gschnait F, et al: Mouse model for protoporphyria. II.
when given intravenously prior to ESR measurement, Cellular and subcellular events in the photosensitivity flare of the skin.
J Invest Dermatol 65:300–310, 1975 suppressed the rate of signal decay in irradiated griseoful- Miura Y, Hamada A, Utsumi H: In vivo ESR studies of antioxidant activity on free vin-fed mice in a concentration-dependent manner but had radical reaction in living mice under oxidative stress. Free Radic Res no effect on decay rate in non-irradiated mice.
Although speculation remains regarding the precise Pathak MA, Stratton K: Free radicals in human skin before and after exposure to light. Arch Biochem Biophys 123:468–476, 1968 mechanism(s) of ROS action in this light-sensitive disorder, Proctor PH, Reynolds ES: Free radicals and disease in man. Physiol Chem Phys this is a report of in vivo detection of light-induced ROS in the skin of a living animal and makes an important Rhodes LE, Durham BH, Fraser WD, et al: Dietary fish oil reduces basal and contribution to fulfilling the criteria for acceptance of free 2 levels in skin and increases the threshold to provocation of polymorphic light eruption. J Invest Dermatol 105:532– radical participation in a disease state (Proctor and Reynolds, 1984) . The development of the surface resonator Takeshita K, Takajo T, Hirata H, Ono M, Utsumi H: In vivo oxygen radical proto- as an analytical tool for the detection of in vivo radical porphyria model mouse with visible light exposure: An L-Band ESR study.
J Invest Dermatol 122:1463–1470, 2004 generation in the skin should be, as the authors note, Utsumi H, Ichikawa K, Takeshita K: In vivo ESR measurements of free radical extremely valuable in dermatology for examination of ROS reactions in living mice. Toxicol Lett 82–83:561–565, 1995 13-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl, a stable nitroxide radical employed as a spin probe. It may also act asa superoxide dismutase (SOD) mimic compound. Thus, theincreased decay rate of this redox probe after light exposure ofskin in griseofulvin-fed mice supports the involvement of ROSspecies in mediation of symptoms in this photosensitive model.

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