BritishJoumalo/Plastic Suraerv(1991),44,21&214
The effects of ultraviolet radiation on wound healing S. F. Davidson, S. K. Brantley and S. K. Das Division of Plastic Surgery, Department of Surgery, University of Mississippi Medical Center, Jackson, Mississippi, USA SUMMARY. The effects of prior ultraviolet light exposure on wound tensile strength and skin histology were evaluated in the hairless guinea pig model. Hairless guinea pigs (strain IAF/HA-HO) were irradiated with either UVA (80 J/cm’) or UVB (0.46 J/cm”) every other day for 16 weeks. Following cessation of treatment, a standard dorsal wound was made in each animal, allowed to heal, and mechanically tested to failure at 21 days. Serial 4 mm punch biopsies were obtained prior to the initial exposure and at 2,4,8,12 and 16 weeks. Histological examination with haematoxylin and eosin, trichrome and elasthr stains was performed. In comparison to the unexposed control group, wound tensile strength was significantly less in the UVA- and UVB-irradiated animals. Histological examination revealed a marked endothelial swelling and eoainophilic Miltration in the irradiated groups. These results indicate that repeated exposure to even moderate doses of non-ionisingradiation alters normal skin structure and adversely affects subsequent wound tensile strength in this model.
Electromagnetic
In recent years, increased public interest and scientific studies have been prompted by reports of ultravioletinduced skin cancer (Van Der Leun, 1984). Public campaigns have discouraged long-term exposure to midday sun and other high levels of ultraviolet radiation that result in skin erythema or discomfort (MacKie, 1987). However, many people continue to expose themselves to high doses of solar radiation and new sources of artificial ultraviolet radiation, i.e. tanning booths, with photoaging an undesirable consequence. While tanning has been associated with health and beauty, the long-term sequelae are not as attractive. The purpose of the present study was to examine the histological structure and wound tensile strength of healing skin following UVR exposure at two different wavelengths. Ultraviolet light is of higher energy, shorter wavelength than visible light (400-700 nm). In 1932, Coblentz divided the ultraviolet spectrum into three regions on the basis of wavelength, relation to visible light and effect on human skin (Coblentz, 1932) (Fig. 1). This nomenclature has prevailed but the subdivisions are arbitrary and ranges may vary somewhat in the literature (Parrish et al., 1978). The shortest wavelength in the ultraviolet spectrum, UVC (200-290 nm), is emitted from germicidal lamps and is toxic to one-cell organisms. It also constitutes a major component of extraterrestrial light; however, it is almost completely absorbed by the atmosphere and little actually reaches the earth’s surface (MacKie, 1987). UVB (29%315 nm) has been termed the sunburn spectrum. Like UVC, it is largely absorbed by the atmosphere but sufficient amounts do pass through to produce erythema in human skin. UVB was long considered to be solely responsible for UV skin damage and UV carcinogenesis. This band is absorbed
Spectrum
Vio,et
200
Visible
Red
300
Wavelength in Nanometers
Fig. 1 Figure l-Divisions
of the electromagnetic spectrum.
primarily in the epidermis with little dermal penetration. Thus, UVB-induced skin damage has been reported to be limited largely to the epidermis (Diffey, 1982; Kligman et al., 1985). Systemic immunological changes and a reduction in epidermal growth factor receptor sites also result from UVB exposure (Letvin et al., 1980). UVA (315400 nm) was initially considered innocuous because of the increased energy needed (1000 x ) in the UVA range to elicit either a germicidal or an erythrogenic effect when compared to UVB radiation of the same dose (Hawk, 1983). Recently UVA has been shown to induce skin cancer and is believed to be responsible for 80% of the cytotoxic effects of solar UV (Diffey, 1985 ; Whitman et al., 1985). The more penetrating UVA passes easily through the atmosphere and most sunscreens. In fair-skinned Caucasians, up to 50% of the dose passes through the epidermis to be absorbed by the dermis (Parrish et al., 1978; Kligman et al., 1985). Artificial sources of this 210
211
The Effects of Ultraviolet Radiation on Wound Healing
wavelength are used for psoralen phototherapy (PUVA) and it is the primary wavelength emitted in newer tanning booths (Diffey, 1985; MacKie, 1987). Additional detrimental effects reported include the augmentation of the effect of UVB and the induction of photosensitivity (Parrish et al., 1978; Letvin et al., 1980; Van Der Leun, 1984; Whitman et al., 1985; Hersey et al., 1988). It appears that while many have claimed UVA to be safe, published data indicate otherwise. In the present study, the hairless guinea pig was used to compare skin structure and wound tensile strength following exposure to UVA (98.1%) and UVB radiation with those of a non-irradiated control group. Materials and methods
Thirty 10 week old female hairless guinea pigs (IAF/ HA-HO) from the Charles River breeding stock were divided into three groups of 10: UVA, UVB and a control group. The Psorolite Model 2001 (Psorolite Corporation, Columbia, South Carolina) with interchangeable fluorescent bulbs provided the radiation. Spectral analysis was obtained with an Optica Model 742 spectrometer at a distance of 6 inches. The UVA source consisted of a bank of six Voltarc fluorescent bulbs (ERE-HO, F7V) at a distance of 6 inches. A dose of 80 J/cm* was given every other day for 16 weeks, for a total dose of 4560 J/cm*. This represented two MEDs (minimal erythema dose) per day in the guinea pig (Whitman et al., 1985). The UVB source consisted of a bank of six Voltarc fluorescent bulbs (BL-HO, B8V) at a distance of 6 inches. A dose of 0.46 J/cm* (two MEDs) was given every other day for 16 weeks, for a total dose of 25.76 J/cm*. Both spectra are shown in Figure 2. Histology Biopsies (4 mm) from the dorsal skin were taken prior to exposure and at 2,4,8, 12 and 16 weeks. Standard 1.0 0.8
haematoxylin and eosin, elastin and trichrome sections were prepared from each specimen. Mean epidermal thickness was calculated from five measurements in each of the 180 biopsy sections using a stage micrometer. Wound tensile strength Following the lbweek exposure period, further exposures were stopped and a 6 cm dorsal midline incision was made and carried down through the panniculus camosus with a scalpel. Standard closure of the wound was achieved by the same surgeon with interrupted sutures (4-O nylon) spaced 0.5 cm apart. The sutures were removed at 14 days and the wounds were allowed to heal for 21 days. The animals were then anaesthetised and a 3 x 5 cm section of skin and panniculus camosus containing the wound was excised and divided into five strips (1 cm) tangential to the original wound. Mechanical testing was performed with an MTS 812 closed-loop servo hydraulic mechanical testing system (piston rate 10 mmfsec) in air @23”C to breaking (Smith er al., 1986). To obtain a measurement of stress, the surface area of the healing surface was calculated following testing. Each specimen was placed vertically between blocks of cucumber and frozen with medium containing haematoxylin to improve contrast. The specimen was sectioned to wound surface and the surface photographed with two standard reference points at 5 X magnification. The area of the wound surface was determined from the photographs with a Zeiss Videoplan II (Smith et al., 1986). Results
Gross obseruations All 30 animals did well throughout the irradiation period, and weight gain did not differ between the groups. Gross examination revealed only darker ear and foot pigmentation in the irradiated animals, with no gross evidence of skin damage in any group. Following wounding, a wound infection in a UVB animal necessitated its exclusion from the study. An average weight loss of 10% of original body weight was seen in all groups following wounding.
0.8 0.7
Wound tensile strength
0.6 0.5 0.4 0.3 0.2 0.1 0.0 250
265
280
295
310
325
340
355
370
385
303.0nm @ 365.0nm
-
UVB Spectrum
Peak Value = 2.37E-04 @
-
UVA Spectrum
Peak
Value
= 3.11E-04
Fig. 2 Figure 2-Spectra
of UVA and UVB light sources.
400
Wound tensile strength (breaking stress) is derived by dividing the force by the surface area. Wound tensile strength was determined to be significantly less in the irradiated groups in comparison to the control group. There were significant differences (p
The effects of ultraviolet radiation on wound healing S. F. Davidson, S. K. Brantley and S. K. Das Division of Plastic Surgery, Department of Surgery, University of Mississippi Medical Center, Jackson, Mississippi, USA SUMMARY. The effects of prior ultraviolet light exposure on wound tensile strength and skin histology were evaluated in the hairless guinea pig model. Hairless guinea pigs (strain IAF/HA-HO) were irradiated with either UVA (80 J/cm’) or UVB (0.46 J/cm”) every other day for 16 weeks. Following cessation of treatment, a standard dorsal wound was made in each animal, allowed to heal, and mechanically tested to failure at 21 days. Serial 4 mm punch biopsies were obtained prior to the initial exposure and at 2,4,8,12 and 16 weeks. Histological examination with haematoxylin and eosin, trichrome and elasthr stains was performed. In comparison to the unexposed control group, wound tensile strength was significantly less in the UVA- and UVB-irradiated animals. Histological examination revealed a marked endothelial swelling and eoainophilic Miltration in the irradiated groups. These results indicate that repeated exposure to even moderate doses of non-ionisingradiation alters normal skin structure and adversely affects subsequent wound tensile strength in this model.
Electromagnetic
In recent years, increased public interest and scientific studies have been prompted by reports of ultravioletinduced skin cancer (Van Der Leun, 1984). Public campaigns have discouraged long-term exposure to midday sun and other high levels of ultraviolet radiation that result in skin erythema or discomfort (MacKie, 1987). However, many people continue to expose themselves to high doses of solar radiation and new sources of artificial ultraviolet radiation, i.e. tanning booths, with photoaging an undesirable consequence. While tanning has been associated with health and beauty, the long-term sequelae are not as attractive. The purpose of the present study was to examine the histological structure and wound tensile strength of healing skin following UVR exposure at two different wavelengths. Ultraviolet light is of higher energy, shorter wavelength than visible light (400-700 nm). In 1932, Coblentz divided the ultraviolet spectrum into three regions on the basis of wavelength, relation to visible light and effect on human skin (Coblentz, 1932) (Fig. 1). This nomenclature has prevailed but the subdivisions are arbitrary and ranges may vary somewhat in the literature (Parrish et al., 1978). The shortest wavelength in the ultraviolet spectrum, UVC (200-290 nm), is emitted from germicidal lamps and is toxic to one-cell organisms. It also constitutes a major component of extraterrestrial light; however, it is almost completely absorbed by the atmosphere and little actually reaches the earth’s surface (MacKie, 1987). UVB (29%315 nm) has been termed the sunburn spectrum. Like UVC, it is largely absorbed by the atmosphere but sufficient amounts do pass through to produce erythema in human skin. UVB was long considered to be solely responsible for UV skin damage and UV carcinogenesis. This band is absorbed
Spectrum
Vio,et
200
Visible
Red
300
Wavelength in Nanometers
Fig. 1 Figure l-Divisions
of the electromagnetic spectrum.
primarily in the epidermis with little dermal penetration. Thus, UVB-induced skin damage has been reported to be limited largely to the epidermis (Diffey, 1982; Kligman et al., 1985). Systemic immunological changes and a reduction in epidermal growth factor receptor sites also result from UVB exposure (Letvin et al., 1980). UVA (315400 nm) was initially considered innocuous because of the increased energy needed (1000 x ) in the UVA range to elicit either a germicidal or an erythrogenic effect when compared to UVB radiation of the same dose (Hawk, 1983). Recently UVA has been shown to induce skin cancer and is believed to be responsible for 80% of the cytotoxic effects of solar UV (Diffey, 1985 ; Whitman et al., 1985). The more penetrating UVA passes easily through the atmosphere and most sunscreens. In fair-skinned Caucasians, up to 50% of the dose passes through the epidermis to be absorbed by the dermis (Parrish et al., 1978; Kligman et al., 1985). Artificial sources of this 210
211
The Effects of Ultraviolet Radiation on Wound Healing
wavelength are used for psoralen phototherapy (PUVA) and it is the primary wavelength emitted in newer tanning booths (Diffey, 1985; MacKie, 1987). Additional detrimental effects reported include the augmentation of the effect of UVB and the induction of photosensitivity (Parrish et al., 1978; Letvin et al., 1980; Van Der Leun, 1984; Whitman et al., 1985; Hersey et al., 1988). It appears that while many have claimed UVA to be safe, published data indicate otherwise. In the present study, the hairless guinea pig was used to compare skin structure and wound tensile strength following exposure to UVA (98.1%) and UVB radiation with those of a non-irradiated control group. Materials and methods
Thirty 10 week old female hairless guinea pigs (IAF/ HA-HO) from the Charles River breeding stock were divided into three groups of 10: UVA, UVB and a control group. The Psorolite Model 2001 (Psorolite Corporation, Columbia, South Carolina) with interchangeable fluorescent bulbs provided the radiation. Spectral analysis was obtained with an Optica Model 742 spectrometer at a distance of 6 inches. The UVA source consisted of a bank of six Voltarc fluorescent bulbs (ERE-HO, F7V) at a distance of 6 inches. A dose of 80 J/cm* was given every other day for 16 weeks, for a total dose of 4560 J/cm*. This represented two MEDs (minimal erythema dose) per day in the guinea pig (Whitman et al., 1985). The UVB source consisted of a bank of six Voltarc fluorescent bulbs (BL-HO, B8V) at a distance of 6 inches. A dose of 0.46 J/cm* (two MEDs) was given every other day for 16 weeks, for a total dose of 25.76 J/cm*. Both spectra are shown in Figure 2. Histology Biopsies (4 mm) from the dorsal skin were taken prior to exposure and at 2,4,8, 12 and 16 weeks. Standard 1.0 0.8
haematoxylin and eosin, elastin and trichrome sections were prepared from each specimen. Mean epidermal thickness was calculated from five measurements in each of the 180 biopsy sections using a stage micrometer. Wound tensile strength Following the lbweek exposure period, further exposures were stopped and a 6 cm dorsal midline incision was made and carried down through the panniculus camosus with a scalpel. Standard closure of the wound was achieved by the same surgeon with interrupted sutures (4-O nylon) spaced 0.5 cm apart. The sutures were removed at 14 days and the wounds were allowed to heal for 21 days. The animals were then anaesthetised and a 3 x 5 cm section of skin and panniculus camosus containing the wound was excised and divided into five strips (1 cm) tangential to the original wound. Mechanical testing was performed with an MTS 812 closed-loop servo hydraulic mechanical testing system (piston rate 10 mmfsec) in air @23”C to breaking (Smith er al., 1986). To obtain a measurement of stress, the surface area of the healing surface was calculated following testing. Each specimen was placed vertically between blocks of cucumber and frozen with medium containing haematoxylin to improve contrast. The specimen was sectioned to wound surface and the surface photographed with two standard reference points at 5 X magnification. The area of the wound surface was determined from the photographs with a Zeiss Videoplan II (Smith et al., 1986). Results
Gross obseruations All 30 animals did well throughout the irradiation period, and weight gain did not differ between the groups. Gross examination revealed only darker ear and foot pigmentation in the irradiated animals, with no gross evidence of skin damage in any group. Following wounding, a wound infection in a UVB animal necessitated its exclusion from the study. An average weight loss of 10% of original body weight was seen in all groups following wounding.
0.8 0.7
Wound tensile strength
0.6 0.5 0.4 0.3 0.2 0.1 0.0 250
265
280
295
310
325
340
355
370
385
303.0nm @ 365.0nm
-
UVB Spectrum
Peak Value = 2.37E-04 @
-
UVA Spectrum
Peak
Value
= 3.11E-04
Fig. 2 Figure 2-Spectra
of UVA and UVB light sources.
400
Wound tensile strength (breaking stress) is derived by dividing the force by the surface area. Wound tensile strength was determined to be significantly less in the irradiated groups in comparison to the control group. There were significant differences (p
