15.1 Epidemiological Study . . . 380 15.2 Molecular Mechanisms of Tobacco Smoke-Induced
Skin Aging . . . 380 15.2.1 Effects of Tobacco Smoke on Skin Models In Vitro 381 15.2.3 Effect of Tobacco Smoke In Vivo . . . 381 15.3. Some Molecular Mechanisms and Protective
Factors . . . 382 15.4. Conclusions . . . 383 References . . . 383
Contents Chapter
Tobacco Smoke and Skin Aging
Akimichi Morita
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15.1 Epidemiological Study
As early as 1971, Daniell (1971) found that tobacco smoking has a deleterious effect on the skin, and smoker’s wrinkles are typical clinical features of smokers. A recent epide- miological study has clearly shown that tobacco smoking is one of the numerous factors contributing to premature skin aging, which is dependent on age, sex, pigmentation, sun exposure history, alcohol consumption, and other factors (Ernster et al. 1995; Frances 1998; Grady and Ernster 1992; Kadunce et al. 1991). In a further cross-section study, sun exposure, pack years of smoking history, and potential confounding variables were as- sessed by questionnaire. Facial wrinkles were quantified using the Daniell score. Logistic statistic analysis of the data revealed that age, pack year, and sun exposure independently contributed to facial wrinkle formation (Yin et al. 2001a). In this survey, age (OR = 7.5, 95% CI = 1.87–30.16), pack year (OR = 5.8, 95% CI = 1.72–19.87), and sun exposure (OR = 2.65, 95% CI = 1.0–7.0) were independently contributing to the facial wrinkles, as estimated by a logistic regression analysis model. Using silicone rubber replicas com- bined with computerized image processing, an objective measurement of skin’s topogra- phy, the association between wrinkle formation and tobacco smoking was investigated.
Sixty-three volunteers were enrolled by assessing their skin replicas and in an attempt to elucidate the association between tobacco smoking and wrinkles (Yin et al. 2001b).
The replica analysis showed that the depth (Rz) and variance (Rv) of furrows (Rv) in sub- jects with smoking history ≥35 pack years were significantly higher than nonsmokers (p<0.05). The lines of furrows (Rl) in subjects with smoking history were significantly lower than nonsmokers (p<0.05) (Yin et al. 2000a; 2001b).
Tobacco smoking, which is regarded as another an important environmental factor, can potentially cause “tobacco wrinkles” (Daniell 1971), although chronic exposure of skin to ultraviolet (UV) radiation results in marked alterations in the structure and com- position of the epidermis and dermis, i.e., photoaging (Fisher et al. 1999; Grether-Beck 1997; Wenk et al. 2001). In a recent study, tobacco smoking per se or when smoking combined with UV exposure were strong predictors of skin aging (Leung and Harvey 2002).
15.2 Molecular Mechanisms of Tobacco Smoke-Induced Skin Aging
Tobacco smoking probably exerts its deleterious effects on skin directly through its ir- ritant components on the epidermis and indirectly on the dermis via the blood circula- tion (Frances 1998; Lofroth 1989). The decreased stratum corneum moisture of the face contributes to facial wrinkling because of the direct toxicity of the smoke. Pursing the lips during smoking with contraction of facial muscles and squinting because of the ir- ritating of smoke may cause the formation of wrinkling around the mouth and in the crow’s foot area (Smith and Fenske 1996). The changes in the dermis of macromolecular metabolism have been brought into focus as a major factor leading to skin aging (Uitto et al. 1989). Specifically, it has been demonstrated that accumulation of elastosis material is accompanied by degradation of matrix protein, which is mediated by matrix metal- loproteinases (MMPs) in skin aging. The molecular alteration in the dermis includes the
decrease of collagen synthesis, induction of MMPs, abnormal accumulation of elastic fibers, and proteoglycans (Fisher and Voorhees 1998; Shuster 2001; Yin et al. 2000b).
15.2.1 Effects of Tobacco Smoke on Skin Models In Vitro
The biosynthesis of new collagen was decreased significantly by tobacco smoke extracts in cultured skin fibroblasts (Yin et al. 2006). The studies also showed that the production of both procollagen types I and III, the precursors of collagen, were significantly de- creased from the supernatant of cultured fibroblast treated with tobacco smoke extracts, using Western blot analysis (Yin et al. 2006). This result indicated that the final produc- tion of collagen secreted into the medium as reduced, regardless of the rate of collagen synthesis in the cell tested in 3H-proline incorporation.
Although elastic fibers account for only 2–4% of extracellular matrix, these provide elasticity and resilience to normal skin. Tobacco smoke extracts induced the significant increase in tropoelastin mRNA in cultured skin fibroblasts. Accumulation of abnormal elastic material (termed solar elastosis) is the prominent histopathologic alterations in photoaged skin (Montagna et al. 1989; Tsuji 1987). Boyd et al. (1999) reported that to- bacco smoking could facilitate smoke’s elastosis of the subjects with an average of 42 pack years of tobacco smoking. In an in vitro study using cultured skin fibroblasts, tobacco smoke extracts induced elevation of tropoelastin. This might be attributed to premature skin aging.
The expressions of MMP-1 and MMP-3 mRNA, extracellular matrix (ECM)-as- sociated members of the MMPs gene family, were induced in cultured skin fibroblast stimulated with tobacco smoke extracts in a dose-dependent manner (Yin et al. 2000b).
These results support the concept that MMPs are primary mediators of connective tissue damage in skin exposed to tobacco smoke extracts and of the premature skin aging. In addition, expression of TIMP-1 and TIMP-3 remained unchanged (Yin et al. 2000b). By inducing the expressions of MMP-1 and MMP-3, but not the induction of tissue inhibi- tor of MMPs, tobacco smoke extracts could alter their ratio in favor of the induction of MMPs and appears to result in a more degradative environment that produces loss of cu- taneous collagen (Yin et al. 2000b). In addition, MMPs comprise a family of degradative enzymes, which are responsible for the degradation of extracellular matrix components such as native collagen, elastin fibers, and various proteoglycans. MMP-3 and MMP-7 may play a key role in the degradation of elastin and proteoglycans (Saarialho-Kere et al.
1999). MMP-7 was increased in fibroblasts induced by tobacco smoke extract.
15.2.3 Effect of Tobacco Smoke In Vivo
In a clinical study, significant higher levels of MMP-1 mRNA were observed in the but- tock skin of smokers, compared with nonsmokers, using quantitative real-time PCR (Lahmann et al. 2001). The elevated enzyme should lead to the degradation of collagen, elastic fibers, and proteoglycans. Therefore, the observations in dermal connective tissue induced by the treatments of tobacco suggested an imbalance between the biosynthesis and degradation, with less repair capacity on the face of the ongoing degradation, which
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leads to loss of collagen and elastic fibers, manifesting clinically as aging appearance of skin.
Although staining of skin specimen and biochemical analysis of photodamaged skin demonstrated increased glycosaminoglycan content of sun-damaged skin, the under- lying molecular pathogenesis remains unclear. Versican, the large chondroitin sulfate (CS) proteoglycan, has been identified in the dermis in association with elastic fibers, which contain a hyaluronic acid-binding domain. The core protein has been postulated to play a role in molecular interactions and specifically, to facilitate the binding of these macromolecules to other matrix components or cytokines such as transforming growth factor (TGF) (Fisher et al. 1989). Decorin, a small CS proteoglycan, has been shown to codistribute with collagen fibers and postulated to function in cell recognition, possible by connecting extracellular matrix components and cell surface glycoproteins (Zimmer- mann and Ruoslahti 1989). Targeted disruption of decorin synthesis in mice resulted in a significant reduction in the tensile strength of skin (Danielson et al. 1997). There was a decrease in the proportion of large chondroitin sulfate proteoglycan (versican) and a concomitant increase in the proportion of small dermatan sulfate proteoglycan (decorin) as a function of age as reported by Carrino et al. (2000). Ito et al. (2001) also observed that versican was stained strongly in young rats and faintly in old rats. On the other hand, decorin was faintly stained in the young rats and distinctly stained in the old rats. There were several reports concerning the changes of proteoglycans on photoaging, especially UVB irradiation (Bernstein et al. 1995; Margelin et al. 1993). The analysis of new synthesized proteoglycans showed a marked increase after UVB radiation in mice (Margelin et al. 1993). Versican and decorin immunostaining increased in photoaged tissue samples, accompanied by similar alterations in gene expression (Bernstein et al.
1995). Tobacco smoke extracts decreased both versican protein and mRNA levels in cul- tured akin fibroblasts. However, tobacco smoke extract exposure resulted in a significant increase of decorin. These results have a similar to those observed in photoaging.
15.3. Some Molecular Mechanisms and Protective Factors
Based on experimental evidence, a working model for UVA damage skin was proposed in which UV irradiation gene expression was mediated via the generation of singlet oxy- gen through a pathway involving activation of transcription factor AP-2 (Grether-Beck 1997). In order to define whether the reactive oxygen species (ROS) were involved in upregulation of MMPs induced by tobacco, sodium azide (NaN3), l-ascorbic acid, and vitamin E, which are potent quenchers of singlet oxygen and other ROS, were employed.
NaN3, l-ascorbic acid, and vitamin E abrogated the induction of MMPs after exposure of fibroblast to tobacco smoke extract. Among the antioxidant reagents, l-ascorbic acid most obviously diminished the increase in MMP-1 expression level on exposure of fibro- blasts to tobacco smoke extracts (Yin et al. 2000b). This points at that ROS were most probable responsible for the enhanced induction of MMPs by tobacco smoke extract.
The transforming growth factor-β1 (TGF-β1) is a multifunctional cytokine that regulates cell proliferation and differentiation, tissue remodeling, and repair (Massague 1998). TGF-β1 is a potent growth inhibitor in the epidermis, playing an important role in maintenance of tissue homeostasis. In the dermis, however, TGF-β1 acts as a posi- tive growth factor, inducing the synthesis of extracellular matrix proteins. TGF-β signals
through a heteromeric complex of type I/II TGF-β receptors, which initiate signal trans- duction (Kadin 1994; Piek 1999). A recent report showed that UV irradiation can cause downregulation of TGF-β type II receptor mRNA and protein, and induction of Smad7 mRNA and protein in human skin (Quan et al. 2001).
Tobacco smoke extracts induced the latent form TGF-β, not the active form, assayed by enzyme-linked immunosorbent assay (ELISA), in the supernatants of cultured skin fibroblasts (Yin et al. 2003). The induction of endogenous TGF-β1 from tobacco-ex- posed cells contributes to the intracellular defense capacity. Fibroblasts responses to TGF-β1 are mediated through its active form binding to the cell surface receptor. To- bacco smoke extracts blocked cellular responsiveness to TGF-β1 through the induction of nonfunctional latent form and downregulation of TGF-β1 receptor (Yin et al. 2003).
Exogenous addition of TGF-β1 might be useful to stimulate the collagen production or to protect against the deleterious effects of tobacco smoke.
15.4. Conclusions
Tobacco smoke contains numerous compounds, with at least 3,800 constituents (Batsch et al. 1993). Just which constituents that contributed to the damage of connective tissue are still unclear. The tobacco-induced skin aging provides a tool for studying the effects of smoking. Also, detailed knowledge may provide a motivation to stop smoking, espe- cially among those who are more concerned about their appearances than the potential internal damage associated with smoking.
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