Volume 62, Issue 1 , Pages 85-95, January 2010
Photorejuvenation induced by 5-aminolevulinic acid photodynamic therapy in patients with actinic keratosis: A histologic analysis
Article Outline
Background
Repeated exposure to ultraviolet radiation from the sun results in premature photoaging. Photodynamic therapy (PDT) has been shown to be effective for treatment of photoaging, although the data from most studies have been based on clinical observation.
Objectives
We investigated whether 5-aminolevulinic acid (ALA)-PDT induced histologic changes suggesting photorejuvenation.
Methods
Fourteen patients with one to three actinic keratoses on the face were treated twice with ALA-PDT by using a 1200 W metal halogen lamp at 1-month intervals. Skin biopsy before and 1 month after the PDT was performed. Twenty-five pairs of specimens were obtained. We examined the specimens with routine and immunohistochemical staining and evaluated the parameters associated with photoaging by using image analysis.
Results
After ALA-PDT, the mean epidermal thickness and dermal inflammatory infiltrate were reduced. The total collagen volume in the dermis significantly increased with expression of type I and III procollagen. The level of transforming growth factor β and transforming growth factor β type II receptors in the epidermis also increased. The elastotic material with co-localizing fibrillin-1 and tropoelastin expression in the dermis decreased after treatment. The expression of matrix metalloproteinases-1, -3, and -12 also decreased.
Limitations
The study was limited by the small sample size.
Conclusions
ALA-PDT resulted in histological changes indicating restoration of photoaged skin. These data suggest that ALA-PDT could be effective for photorejuvenation.
Key words: histologic changes, photodynamic therapy, photorejuvenation
Abbreviations used: AK, actinic keratosis, ALA, 5-aminolevulinic acid, ECM, extracellular matrix, MMP, metalloproteinase, PDT, photodynamic therapy, TβRII, TGF-β type II receptor, TGF-β, transforming growth factor β, TIMP, tissue inhibitor of metalloproteinases, UV, ultraviolet
Introduction
Ultraviolet (UV) irradiation from the sun damages human skin and causes premature skin aging (photoaging).1 Clinically, photoaged skin differs from sun-protected, naturally aged skin; it is thickened and rough, with coarse wrinkles, mottled pigmentation, and precancerous lesions, including actinic keratoses (AK).
There is growing interest in reversing the signs of photoaging. Photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA), a photosensitizing agent, using a variety of lasers and light sources, enhances the treatment of photodamaged skin and associated AK.2, 3 However, the histologic changes that occur after ALA-PDT have not been fully assessed.
The main constituent of dermal extracellular matrix (ECM) is collagen, particularly collagens I and III, which provide skin with its strength and resilience. However, in photoaged skin, the production of procollagen, the precursor of collagen is reduced; an impaired transforming growth factor β (TGF-β)/Smad pathway, caused by UV irradiation, might play a role in the pathology.4, 5 TGF-β is the major regulator of ECM synthesis in human skin; it stimulates fibroblast proliferation in the dermis to enhance collagen synthesis.6 Down-regulation of the TGF-β type II receptor (TβRII) and ensuing lower response of TGF-β by UV radiation result in reduced collagen synthesis.5 Moreover, dermal collagen is destroyed by the UV-induced matrix metalloproteinases (MMPs) in human skin.7 MMP-1 (fibroblast collagenase) is the main enzyme that degrades collagen in the skin.8 Once MMP-1 breaks down collagen, further degradation is followed by MMP-3 (stromelysin 1), and other MMPs.9
Solar elastosis, the deposition of dystrophic elastotic material within the dermis, is also a characteristic of photoaged skin.10 The mechanism causing this damage remains unclear. However, it may be related to the increased production of elastic fibers, which consist of elastin and fibrillin-rich microfibrils.11, 12 The degradation of elastin by MMP-12 (human macrophage metalloelastase) may also contribute to the development of solar elastosis in photoaged skin.13
In the present study, we examined pre- and post-ALA-PDT specimens for AK and determined whether ALA-PDT induced histologic changes reversing the destructive connective tissue events associated with photoaging.
Methods
Skin samples
From December 2006 to February 2008, 14 patients with one to three AKs on the face presenting to our outpatient clinic at the Department of Dermatology were treated with ALA-PDT. The study was approved by the international review board (IRB No. AJIRB-CRO-08-021), and all subjects provided written informed consent. All patients were Korean with Fitzpatrick skin types III to V. Among these subjects were 5 men (35.8%) and 9 women (64.2%). Ages ranged from 52 to 85 years, with a mean age of 62.07 years. The size of the AKs ranged from 1 × 1.5 cm to 2 × 2.5 cm. The clinical appearance of all lesions was similar, and no patient had hyperkeratotic AKs. There was no history of previous treatment for AKs. All patients received the same therapeutic procedure. We mixed 5-ALA (MEDAC GmbH, Hamburg, Germany) only with petrolatum to make the 20% 5-ALA cream, which was applied to the lesions under an occlusive and light-shielding dressing. Scales and crusts were gently removed before application of the cream. Four hours later, the dressings were removed, and the ALA was washed off with 0.9% saline solution. The lesions were illuminated with red light from a noncoherent light source (Waldmann PDT 1200; Waldmann-Medizin-Technik, Villingen-Schwenningen, Germany; emission wavelength, 580∼740 m) at a light dose of 100 J/cm2 and a fluence rate of 100 mW/cm2.
The treatments were performed twice, at 1-month intervals. One month after the last procedure, the response to the PDT was evaluated. Two- to 3-mm punch biopsies were performed for histologic examination to assess the response. Just before initial biopsy, we marked the biopsy site in the AK and took photographs. In the biopsy after photodynamic therapy, we compared the initial photographs and avoided taking adjacent skin so as not to obtain taking scar tissue.
Patients with residual lesions received an additional two cycles of PDT or cryotherapy. The post-cryotherapy specimens were excluded from the analysis. Finally, 25 pairs of skin specimens were obtained.
Histologic analysis
Hematoxylin-eosin (H&E) staining
Skin biopsy specimens were fixed in 10% formalin, embedded in paraffin, and sectioned into 5-μm sections for routine H&E staining. The epidermal thickness, degree of solar elastosis, and inflammatory infiltrate were measured. The epidermal thickness was the mean length between the outer sides of the epidermis, excluding the stratum corneum, and the dermoepidermal junction through the entire section; computer-based software was used for the measurements (Image-Pro Plus, MEDIA CYBERNETICSA, Silver Spring, MD). For analysis of the solar elastosis and the inflammatory infiltrate, the sections were randomized, and examined under an Olympus microscope (Tokyo, Japan) by blinded investigators. One dermatologist and one dermatopathologist scored the samples using a 5-point semiquantitative scale (0 = no staining and 4 = maximal expression within the view) of 3 high-power fields per section; the average score was calculated for each section.
Masson-trichrome staining and Verhoeff elastic staining
Masson-trichrome–stained collagen fibers and Verhoeff-stained elastic fibers were quantified using computer software as mentioned before. For the scanning view of the papillary and upper reticular dermis, low magnification (×100) was used. The epidermis and epidermal appendages were excluded from the fields. The image program assessed the degree of expression of the stained target versus the unstained background, presented as the percent expression.
Immunohistochemical staining
To avoid variability, we stained all samples for each marker simultaneously under the same conditions. Using the immunoperoxidase technique, 5-μm sections from formalin-fixed, paraffin embedded skin samples were stained with antibodies as follows: Rabbit monoclonal anti-procollagen type I antibody (diluted 1:1000, Chemicon, Temecula, CA), rabbit polyclonal anti-procollagen type III antibody (diluted 1:500, Cedarlane Laboratories, Hornby, Ontario, Canada), mouse monoclonal anti-TGF-β antibody (diluted 1:500, Gene Tex, San Antonio, TX), rabbit polyclonal anti-TβRII antibody (diluted 1:100, Springbioscience, Fremont, CA), rabbit polyclonal anti-fibrillin-1 antibody (diluted 1:50, Abcam, Cambridge, UK), rabbit polyclonal anti-tropoelastin antibody (diluted 1:50, Abcam), rabbit polyclonal anti-MMP-1 antibody (diluted 1:50, Neomarkers Inc, Fremont, CA), rabbit monoclonal anti-MMP-3 antibody (diluted 1:100, Epitomics Inc, Burlingame, CA), rabbit monoclonal anti-MMP-12 antibody (diluted 1:100, Epitomics), and mouse monoclonal anti-TIMP-1 antibody (diluted 1:50, Santa Cruz, CA).
For quantitative evaluation of the immunoreactivity of procollagen I, III, TGF-β, and TβRII, the previously mentioned software was used for the immunohistochemically stained sections in the same way it was used for collagen and elastin fiber measurements. TGF-β and TβRII were evaluated in the epidermis where they were predominantly expressed. The expressing pattern of fibrillin-1, tropoelastin, MMP-1, -3, -12, and TIMP-1 were discontinuous, not appropriate to apply computer software. They were evaluated with a semiquantitative scale as mentioned above.
Statistical analysis
A paired Student t test was used to determine statistical significance of the differences between the staining patterns using the SPSS program. All P values were two tailed, and differences were considered significant when the P value was less than .05. Summary data are expressed as the mean ± standard deviation.
Results
Clearance of AKs
The ALA-PDT was tolerated in all patients. During the treatment, variable degrees of erythema and edema occurred, but resolved within a few days. Some patients reported mild to moderate pain, but interruption of procedure or topical anesthesia was not required.
Initially, 23 AKs were detected among the patients. One month after two sessions of PDT, 19 lesions from 11 patients showed a complete response by histologic examination (remission rate, 82.6%). Clinically, there was no significant scarring or pigmentary changes after treatment (Fig 1). Among 3 patients with persistent lesions, one patient with two lesions received two additional PDT treatments; the AKs in the follow-up biopsy resolved. The other two patients underwent cryotherapy twice with liquid nitrogen, and the lesions cleared (Table I).
Fig 1.
Patient 9, with AK on the nose, before (A) and after (B) PDT.Patient showed complete clearance of lesion.
Table I. Baseline characteristics of patients and course of treatment of AKs
| Patient No. | Sex/Age (y) | Location/No. of lesions | PDT results | |
|---|---|---|---|---|
| 1 | M/72 | R cheek/2 | CR | |
| 2 | F/64 | L cheek/1 | CR | |
| 3 | F/85 | L cheek/2 | CR | |
| 4 | F/67 | R cheek/1 | CR | |
| 5 | F/84 | L cheek/1 | CR | |
| 6 | F/80 | Forehead/1, nose/1, L cheek/1 | CR | |
| 7 | M/70 | L cheek/1 | CR | |
| 8 | F/79 | Nose/2 | Non-CR | 2 sessions of PDT → CR |
| 9 | M/75 | Nose/1 | CR | |
| 10 | F/52 | R cheek/2 | CR | |
| 11 | M/64 | L cheek/1, R cheek/1 | CR | |
| 12 | F/77 | R upper eyelid/1, L cheek/1 | Non-CR of cheek lesion | 2 sessions of cryotherapy → CR |
| 13 | F/76 | R cheek/1 | CR | |
| 14 | F/67 | Nose/2 | Non-CR of one lesion | 2 sessions of cryotherapy → CR |
Mean epidermal thickness and inflammatory infiltrates
After treatment, the epidermis of the photodamaged skin became thinner and more even. The mean epidermal thickness in photodamaged facial skin was significantly decreased from 146.10 ± 63.20 μm to 75.26 ± 20.72 μm after treatment (P < .001). In addition, in the pretreatment specimens, there was a large number of infiltrating cells in the dermis that were significantly reduced after treatment. In semiquantitative analysis, the difference was 0.52 ± 1.05 (P < .02).
Total collagen volume
After PDT, almost all biopsy specimens showed impressive collagen deposition in the upper dermis by H&E staining that was more clearly demonstrated by Masson-trichrome staining (Fig 2, A and B).
Fig 2.
Patient 7. A, H&E-stained and (B) Masson-trichrome–stained specimens demonstrated up-regulated collagen fibers in upper dermis after PDT. Specimens on the left are before PDT; specimens on the right are after PDT. (Original magnification: ×200).
Staining with Masson-trichrome demonstrated a 10.49% ± 9.93% average increase of collagen in staining density in the posttreatment than in the pretreatment specimens (P < .001).
Procollagen type I and type III
The expression of collagen precursors was also increased, especially in the papillary dermis and upper reticular dermis. The average increase was significantly different (Fig 3, A-C).
Fig 3.
A, Staining with procollagen type I and (B) procollagen type III antibodies showed increased expression in skin sections after ALA-PDT (patient 10, lesion 1; original magnification: ×200). Specimens on the left are before PDT; specimens on the right are after PDT. C, Demonstration of 18.03% ± 16.41% and 11.50% ± 9.97% average increase in staining density of procollagen type I and type III, respectively (asterisk, P < .05).
TGF-β and TβR II
We investigated whether ALA-PDT affected the expression of TGF-β and TβR II. After treatment, the mean staining density with TGF-β and TβR II antibodies showed a significant increase mainly in the epidermis (Fig 4, A-C).
Fig 4.
A, TGF-β and (B) TβRII (patient 13, original magnification: ×200) were more expressed in the epidermis after ALA-PDT. Specimens on the left are before PDT; specimens on the right are after PDT. C, Mean staining with TGF-β and TβRII antibodies demonstrated a 23.57% ± 15.16% and 6.61% ± 9.56% average increase in staining density, respectively (asterisk, P < .05).
In one patient with two AK lesions that underwent two additional PDT sessions, the mean expression of TGF-β, TβR II, procollagen I, procollagen III, and total collagen increased more proportional to the number of ALA-PDT sessions (Fig 5).
Fig 5.
Patient 8. Mean expression of TGF-β, TβR II, procollagen I, procollagen III, and total collagen volume increased with each session of ALA-PDT.
Elastotic material
In the H&E-stained sections, a marked elastotic mass was visible in the papillary and reticular dermis of the pre-PDT specimens that were pathognomonic for photoaging. After ALA-PDT, there was a tendency for decrease of these elastotic masses compared to the pretreatment specimens. For patient 8 who received 4 treatment sessions, the change was more pronounced (Fig 6, A). Verhoeff elastic stain demonstrated that after the PDT, the thickened and amorphous elastotic materials disappeared and were restored to more normal horizontally arranged fibers in the dermis (Fig 6, B) The semiquantitative scores for solar elastosis decreased from 3.00 ± 0.32 to 2.32 ± 0.90 after treatment. The mean difference was statistically significant in the semiquantitative analysis (0.68 ± 0.69, P < .001).
Fig 6.
Patient 8. Lesion 1. A, After ALA-PDT, solar elastosis was improved (H&E stain; original magnification: ×200) and (B) elastin fiber reorganization was more clearly recognized with Verhoeff's stain (same patient, original magnification: ×400). Specimens on the left are before PDT; specimens on the right are after PDT.
Fibrillin-1 and tropoelastin
In the dermis, expression of fibrillin-1 and tropoelastin were mainly co-localized with elastotic material, found in the epidermis to a lesser extent. After treatment, the immunoreactivity of fibrillin-1 and tropoelastin was reduced along with resolution of the solar elastosis; from 2.56 ± 1.26 to 1.24 ± 0.88 and from 1.88 ± 0.67 to 1.32 ± 0.48 in semiquantitative scales, respectively. The epidermal expression also decreased (Fig 7, A-C).
Fig 7.
Patient 8. Lesion 2. A, Fibrillin-1 and (B) tropoelastin expression decreased in the dermis after treatment (original magnification: ×200). Specimens on the left are before PDT; specimens on the right are after PDT. C, Mean difference was 1.32 ± 0.90 and 0.56 ± 0.58 in the semiquantitative analysis, respectively (asterisk, P < .001).
MMPs and TIMP
We also investigated changes in the MMPs, degradating enzymes of ECM, and TIMP-1, an inhibitor of MMPs. The expression of MMP-1, -3, -12 tended to decrease after treatment. The immunoreactivity of TIMP-I was minimal when evaluated by our method (Fig 8).
Fig 8.
After ALA-PDT, the degree of MMP-1, -3, and -12 expression was reduced by 0.60 ± 0.91, 0.64 ± 0.91, and 0.68 ± 1.14 in the semiquantitative analysis, respectively (asterisk, P < .05).
Discussion
Topical ALA-PDT was originally used for superficial nonmelanoma skin cancers and their precursors. However, other benign diseases, such as acne vulgaris, sebaceous gland hyperplasia, and hidradenitis suppurativa, have been shown to improve with this treatment.14 Moreover, previous studies have demonstrated the effectiveness of ALA-based PDT treatments using a variety of lasers and light sources for photorejuvenation (Table II). However, most prior data have been based on clinical observation, without histopathologic confirmation. Recently, Marmur, Phelps, and Goldberg15 showed that ALA-IPL induced increase of type I collagen fibers in the photodamaged skin by ultrastructural analysis. In addition, Orringer et al16 also demonstrated increase of type I and III procollagen in the photoaged skin after ALA-PDL. The results of the present study provide more precise histopathologic evidence for photorejuvenation with ALA-PDT in patients with AKs.
Table II. Summary of recent studies of ALA-PDT in photorejuvenation
| Authors/Year of publication | Light source | Methods | Results of ALA-PDT |
|---|---|---|---|
| Touma et al2/2004 | Blue light (417 ± 5 nm) | 18.subjects 20% ALA-solution 1, 2, or 3 hr of application | Approximately 90% resolution of AKs and improvement of skin appearance by reducing wrinkling, shallowness, and dyspigmentation |
| Dover et al24/2005 | IPL | 20.subjects 20% ALA-solution 0.5.to 1 hr of application | Significantly greater improvement in global photodamage, mottled pigmentation, and fine lines in the ALA-PDT-IPL group than treatment with IPL-alone group |
| Marmur, Phelps, and Goldberg15/2005∗ | IPL | 7.subjects 20% ALA-solution 1.hr of application | An increase in type I collagen fibers was seen in the ALA-PDT-IPL group than treatment with IPL group alone in electron-microscopic ultrastructural analysis. |
| Lowe and Lowe25/2005 | LED (633 nm) | 6.subjects 5% 5-ALA-cream 0.5.hr of application | Significant treatment response in 4 of 6 subjects (67%) with reduction in fine lines in the periorbital area, and skin softness was shown in all subjects. |
| Gold et al3/2006∗ | IPL | 16.subjects 20% ALA-solution 0.5.to 1 hr of application | Improvement of crow's feet appearance, tactile skin roughness, mottled hyperpigmentation, and telangiectases, and clearance rates of AK lesions were higher in the ALA-PDT-IPL group than in the IPL-alone group |
| Orringer et al16/2008 | PDL | 25.subjects 20% ALA-solution 3.hr of application | Up-regulation of collagen production was shown, with increase in procollagen type I and III mRNA. |
∗Split-face study. |
One may raise the question that the changes of AK cannot be totally equated with photodamage. However, in this study we focused on the changes of the photodamaged tissue, not AK (atypical tumor cells in the epidermis), after PDT. Because the AK is usually induced by long-term sun exposure, all the patients we studied had photodamaged skin as well as AKs.
In photoaged skin, a decrease in type I and III collagen is more prominent than in intrinsic aged skin. Long-term UV exposure induces MMPs that can degrade collagen in human skin9; eventually the total collagen volume in the dermis will decline as a result. In the present study, the expression of MMP-1 and MMP-3 was found to be decreased 1 month after ALA-PDT.
In addition to destruction of mature collagen, UV irradiation impairs synthesis of new collagen, which is reflected by the down-regulation of type I and type III procollagen gene expression.4 The impaired TGF-β/Smad pathway by down-regulation of TβRII contributes to the pathology.5 UV irradiation down-regulates TβRII, which eventually decreases type I procollagen expression in human skin.5 In the present study, the expression of type I and III procollagen, the precursors of collagen, were constitutionally increased after treatment, which reflect the increased synthesis of dermal collagen. In addition, the immunoreactivity of TGF-β as well as TβRII was significantly increased after treatment, which indicates that they may contribute to the reconstitution of the ECM. The increase of dermal collagen, TGF-β and TβR II expression was more significant in patients who received two more additional PDT treatments. This might suggest a cumulative effect of the ALA-PDT on photorejuvenation.
Another prominent feature of photoaged skin is solar elastosis.10 Some studies showed that solar elastosis could relate with increased tropoelastin gene expression11 or an increased expression of fibrillin in the photodamaged skin.12 In addition, degradation of elastic fibers by UV-induced MMP-12 might contribute to the pathology.13 Diverse proteinases from the chronic UV–induced dermal inflammatory infiltrate could also destroy the microfibrils.17 In the present study, ALA-PDT reduced the accumulation of dystrophic elastotic material in the dermis, which resulted in more normal elastin fiber. In addition, tropoelastin and fibrillin-1, which were mainly co-localized with the elastotic materials, showed reduced expression after the PDT. The expression of MMP-12 and dermal inflammatory infiltrates also decreased after treatment, which likely was associated with the changes in the solar elastosis as well.
Our findings showed a decrease in the intensity of MMP-1, -3, and -12 immunostaining following treatment with ALA-PDT. This conflicts with the findings of some other studies that have reported on the effects of ALA-PDT on the expression of MMPs. For example, when normal or scleroderma fibroblast cells were treated with ALA-PDT, the levels of MMP-1 and MMP-3 proteins increased; this was interpreted as antisclerotic effects of ALA-PDT.18 The expressed level of MMPs increased in a time-dependent manner with the maximal induction at 48 hours following the PDT, thereafter with a decreasing tendency. Recently, in an in vivo study of PDT using a pulsed dye laser in human skin, MMP-1 gene expression was acutely elevated and then returned to baseline levels within 24 hours.16 However, it was also shown that MMP-2 expression was down-regulated 24 hours after Hexvix-mediated PDT in a medulloblastoma cell line (TE-671).19
Our results regarding decreased levels of MMPs might be explained as follows. We evaluated the histologic changes 1 month after the PDT, suggesting that the point in time of the assessment might be an important consideration. In addition, various cell lines used in the in vitro studies might differ from results from our in vivo study. TGF-β might play a role as well. TGF-β does not only up-regulate procollagen synthesis, but it also down-regulates the expression of MMPs.20 In the present study, a marked increase of TGF-β expression was noted after the PDT. In addition, a change in the inflammatory infiltrates could affect the decrease in the MMPs. It is known that UV-induced MMPs are secreted by diverse cells, including infiltrated inflammatory cells.21, 22 We found that the inflammatory infiltrates were significantly decreased after the PDT. Therefore, the net effects of the induction of TFG-β and reduction of the degrading enzymes from the inflammatory cells likely contributed to the decreased expression of MMPs after the ALA-PDT.
On the other hand, it is possible that the light source itself might affect the histologic changes in AKs to some degree, and we do not rule out that possibility. There was one study that demonstrated histologic changes of photodamaged skin (however, not with AKs) after illumination with a red noncoherent light source; however, the light source was different from ours.23 We consider that ALA-PDT and the light itself might have induced the histologic changes in the present study.
The present study is limited by the small sample size. In fact, a study carried out on patients matched for age, skin type, size of the lesion, and biopsy site would be ideal. We tried to compare the different parameters in the different skin type groups and different size of biopsy groups; however, the result did not show statistical significance because of the small sample size.
In conclusion, the results of this study provide histologic evidence supporting the beneficial effects of ALA-PDT for photodamaged skin. In photoaged human skin, ALA-PDT induces deposition of collagen, type I and type III procollagen in the dermis, and TGF-β and TβR II expression in the epidermis. In addition, expression of MMP-1 and -3 decreased after ALA-PDT. Solar elastosis was improved, accompanied by decreased expression of tropoelastin, fibrillin-1, and MMP-12. These results suggest that ALA-PDT could be of therapeutic benefit in the treatment of photoaging. Further controlled split-face studies are necessary in order to fully elucidate the mechanism underlying the effects of ALA-PDT on photoaging in human skin.
The authors thank Young-Bae Kim for excellent technical assistance in immunohistochemical procedures.
References
- . Biochemical and molecular changes in photodamaged skin. In: Gilchrest BA editors. Photodamage. Cambridge: Blackwell Science Ltd; 1995;p. 168–184
- . A trial of short incubation, broad-area photodynamic therapy for facial actinic keratoses and diffuse photodamage. Arch Dermatol. 2004;140:33–40
- . Split-face comparison of photodynamic therapy with 5-aminolevulinic acid and intense pulsed light versus intense pulsed light alone for photodamage. Dermatol Surg. 2006;32:795–801discussion 801-803
- c-Jun-dependent inhibition of cutaneous procollagen transcription following ultraviolet irradiation is reversed by all-trans retinoic acid. J Clin Invest. 2000;106:663–670
- . Solar ultraviolet irradiation reduces collagen in photoaged human skin by blocking transforming growth factor-beta type II receptor/Smad signaling. Am J Pathol. 2004;165:741–751
- . Transforming growth factor-beta stimulates alpha 2(I) collagen gene expression through a cis-acting element that contains an Sp1-binding site. J Biol Chem. 1994;269:14828–14834
- Molecular basis of sun-induced premature skin ageing and retinoid antagonism. Nature. 1996;379:335–339
- . Matrix metalloproteinases in skin. Exp Dermatol. 1997;6:199–213
- . How matrix metalloproteinases regulate cell behavior. Annu Rev Cell Dev Biol. 2001;17:463–516
- . Histology of sun-damaged human skin. J Am Acad Dermatol. 1989;21:907–918
- Ultraviolet radiation increases tropoelastin mRNA expression in the epidermis of human skin in vivo. J Invest Dermatol. 2001;116:915–919
- Enhanced elastin and fibrillin gene expression in chronically photodamaged skin. J Invest Dermatol. 1994;103:182–186
- Ultraviolet modulation of human macrophage metalloelastase in human skin in vivo. J Invest Dermatol. 2002;119:507–512
- . Non-oncologic indications for ALA-PDT. J Dermatolog Treat. 2002;13(Suppl 1):S13–S18
- . Ultrastructural changes seen after ALA-IPL photorejuvenation: a pilot study. J Cosmet Laser Ther. 2005;7:21–24
- Molecular effects of photodynamic therapy for photoaging. Arch Dermatol. 2008;144:1296–1302
- . Catabolism of intact fibrillin microfibrils by neutrophil elastase, chymotrypsin and trypsin. FEBS Lett. 1994;351:85–89
- . Influence of 5-aminolevulinic acid and red light on collagen metabolism of human dermal fibroblasts. J Invest Dermatol. 2003;120:325–331
- . Photodynamic effect in medulloblastoma: downregulation of matrix metalloproteinases and human telomerase reverse transcriptase expressions. Photochem Photobiol Sci. 2008;7:76–83
- . The transforming growth factor-beta family. Annu Rev Cell Biol. 1990;6:597–641
- Histological increase in inflammatory infiltrate in sun-exposed skin of female subjects: the possible involvement of matrix metalloproteinase-1 produced by inflammatory infiltrate on collagen degradation. Br J Dermatol. 2000;142:267–273
- . Skin-infiltrating neutrophils following exposure to solar-simulated radiation could play an important role in photoageing of human skin. Br J Dermatol. 2005;152:321–328
- . Clinical trial of a novel non-thermal LED array for reversal of photoaging: clinical, histologic, and surface profilometric results. Lasers Surg Med. 2005;36:85–91
- . Topical 5-aminolevulinic acid combined with intense pulsed light in the treatment of photoaging. Arch Dermatol. 2005;141:1247–1252
- . Pilot study to determine the efficacy of ALA-PDT photo-rejuvenation for the treatment of facial ageing. J Cosmet Laser Ther. 2005;7:159–162
Funding sources: None.
Conflicts of interest: None declared.
PII: S0190-9622(09)00694-X
doi:10.1016/j.jaad.2009.06.025
© 2009 American Academy of Dermatology, Inc. Published by Elsevier Inc All rights reserved.
Volume 62, Issue 1 , Pages 85-95, January 2010
