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SCD is a great diet for healthy skin because it eliminates pathogenic bacteria. The most common bacterial toxin is LPS (also known as endotoxin). LPS increase MMP-1 expression. MMP-1 degrades collagen; collagen breakdown leads to wrinkles. Sun exposure and tobacco smoking also increase MMP-1 expression and it was found that MMP-1 might also be important in the skin-aging effects of tobacco smoking and sun exposure.

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1: Lancet. 2001 Mar 24;357(9260):935-6.

Matrix metalloproteinase-1 and skin ageing in smokers.
Lahmann C, Bergemann J, Harrison G, Young AR.

Smokers look older than non-smokers of the same age. We have compared the concentrations of mRNA for matrix metalloproteinase 1 (MMP-1) in the buttock skin of smokers and non-smokers with quantitative real-time polymerase chain reactions. MMP-1 degrades collagen, which accounts for at least 70% of the dry weight of dermis. We report significantly more MMP-1 mRNA in the skin of smokers than non-smokers whereas no difference was seen for the tissue inhibitor of metalloproteinases 1 (TIMP-1) or the housekeeping gene GAPDH (glyceraldehyde-3-phosphate dehydrogenase). We suggest that smoking-induced MMP-1 might be important in the skin-ageing effects of tobacco smoking.

PMID: 11289356 [PubMed

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1: Photodermatol Photoimmunol Photomed. 2001 Aug;17(4):178-83.

Skin aging induced by ultraviolet exposure and tobacco smoking: evidence from epidemiological and molecular studies.
Yin L, Morita A, Tsuji T.

Department of Dermatology, Nagoya City University Medical School, Nagoya, Japan.

To investigate the relationship between these two environmental factors, we have conducted a cross-sectional study of 83 subjects (48 males, 35 females, age range 2395), in which sun exposure, pack-years of smoking history and potential confounding variables were assessed by questionnaire. Facial wrinkles were quantified using the Daniell score. In order to study the molecular mechanism by which smoking caused wrinkle formation, in vitro studies were conducted to assess the alteration of matrix metalloproteinase-1 (MMP-1) mRNA expression in human fibroblasts stimulated with tobacco smoke extract or/and UVA.

Results: Logistic statistic analysis of the data revealed that age [odds ratio (OR)=7.5, 95% confidence interval (CI)=1.8730.16], pack-years (OR=5.8, 95% CI=1.7219.87), and sun exposure (OR=2.65, 95% CI=1.07.0) independently contributed to facial wrinkle formation. When excessive sun exposure (>2 h/day) and heavy smoking (35 pack-years) occurred together, the risk for developing wrinkles was 11.4 times higher than that of non-smokers and those with less sun exposure (<2 h/day) at the same age. The in vitro studies revealed that MMP-1 expression was significantly increased in fibroblasts after the stimulation with either tobacco smoke extract or UVA. Maximum induction was observed when cells were treated with tobacco smoke extract plus UVA, indicating that the two factors act in an additive manner. MMP-1 induction was significantly higher in the low glutathione (GSH) content fibroblast compared to that in the high GSH fibroblast, indicating that the differences in glutathione content define the susceptibility of fibroblasts towards UV- or tobacco smoking-induced MMP-1 expression.

Conclusion: Tobacco smoke and UVA cause wrinkle formation independently of each other. We propose that both factors cause aging of human skin through additive induction of MMP-1 expression.

PMID: 11499540

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1: Arch Oral Biol. 2009 Feb;54(2):146-55. Epub 2008 Nov 4.

Effects of nicotine and lipopolysaccharide on the expression of matrix metalloproteinases, plasminogen activators, and their inhibitors in human osteoblasts.

Katono T, Kawato T, Tanabe N, Tanaka H, Suzuki N, Kitami S, Morita T, Motohashi M, Maeno M.

Nihon University Graduate School of Dentistry, 1-8-13, Kanda Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan.

Lipopolysaccharide (LPS) from periodontopathic bacteria can initiate alveolar bone loss through the induction of host-derived cytokines. Smoking increases the risk and severity of periodontitis. We examined the effects of nicotine and LPS on the expression of matrix metalloproteinases (MMPs), plasminogen activators (PAs), and their inhibitors, including tissue inhibitors of metalloproteinases (TIMPs) and PA inhibitor-1 (PAI-1), in osteoblasts.

Methods

The cells were cultured with or without 10−4M nicotine and 100ng/ml LPS for 12 days or with 100μg/ml polymyxin B, 10−4M d-tubocurarine, 10μmol/ml NS398, or 10−6M celecoxib in the presence of either nicotine or LPS for 12 days. The gene and protein expression levels for MMPs, PAs, TIMPs, and PAI-1 were examined using real-time PCR and ELISAs, respectively. PGE2 production was determined using an ELISA.

Results

The addition of nicotine and/or LPS to the culture medium increased the expression of MMP-1, -2, and -3 and tissue-type PA (tPA); decreased the expression of TIMP-1, -3, and -4; and did not affect expression of TIMP-2 or PAI-1. In the presence of d-tubocurarine or polymyxin B, neither nicotine nor LPS stimulated the expression of MMP-1. In the presence of NS398 or celecoxib, the stimulatory effects of nicotine and LPS on MMP-1 expression were unchanged, but they were unable to stimulate PGE2 production.

Conclusion

These results suggest that nicotine and LPS stimulate the resorption process that occurs during turnover of osteoid by increasing the production of MMPs and tPA and by decreasing the production of TIMPs. Furthermore, they suggest that the stimulatory effect of nicotine and LPS on PGE2 production is independent of their stimulatory effect on MMP-1 expression.

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This quote is coming from the Introduction section.

Stimulation of monocytes with LPS, a surface component of Gram-negative bacteria, induces a number of MMPs including two prominent monocyte MMPs: interstitial collagenase (MMP-1) and gelatinase B (MMP-9). MMP-1 cleaves fibrillar collagens, such as types I, II, and III, resulting in denatured collagens (gelatins) that are further degraded by MMP-9. Additionally, MMP-9 also degrades laminin and type IV collagen, components of the basement membrane. Thus, these enzymes are involved in the connective tissue loss associated with chronic inflammatory diseases as well as the migration of cells out of the blood stream and through the extracellular matrix.