Sequential histological changes and mast cell response in skin during chemically-induced carcinogenesis

Dihydrolipoic acid inhibits skin tumor promotion through anti-inflammation and anti-oxidation

alpha-Lipoic acid (LA) has been intensely investigated as a therapeutic agent for several diseases, including hepatic disorder and diabetic polyneuropathy. However, the effects of LA or its reduced form, dihydrolipoic acid (DHLA), on cancer chemoprevention has never been reported. In the present study, we examined the effects of DHLA/LA on the production of nitric oxide (NO) by inducible NO synthase (iNOS) and the formation of prostaglandin E2 (PGE(2)) by cyclooxygenase-2 (COX-2), two important mediators associated with inflammation. DHLA/LA significantly inhibited lipopolysaccharide (LPS)-induced NO and PGE(2) formation in RAW 264.7 cells. Meanwhile, treatment with DHLA/LA suppressed the expression of iNOS protein but, unexpectedly, did not affect or increase the expression of COX-2 protein. The in vivo anti-inflammatory and antitumor-promoting activities were evaluated by a topical 12-O-tetradecanoylphorbol 13-acetate (TPA) application to mouse skin with measurement of edema formation, epidermal thickness and hydrogen peroxide production. DHLA significantly inhibited the priming and activation stages of skin inflammation induced by a double TPA application, by decreasing the inflammatory parameters. Furthermore, DHLA inhibited DMBA (0.3 micromol)/TPA (2.0 nmol)-induced skin tumor formation by reducing the tumor incidence and tumor multiplicity. When applied topically onto the shaven backs of mice prior to TPA, DHLA markedly inhibited the expression of iNOS protein. DHLA also strongly and directly inhibited COX-2 activity. These results suggest that DHLA can be a possible chemopreventive agent in inflammation-associated tumorigenesis.

Conjugated linoleic acid induces mast cell recruitment during mouse mammary gland stromal remodeling

Conjugated linoleic acid (CLA) is a dietary chemopreventive agent that induces apoptosis in the mammary adipose vascular endothelium and decreases mammary brown adipose tissue (BAT) and white adipose tissue (WAT). To determine onset and extent of stromal remodeling, we fed CD2F1/Cr mice diets supplemented with 1 or 2 g/100 g mixed CLA isomers for 1-7 wk. BAT loss, collagen deposition, and leukocyte recruitment occurred in the mouse mammary fat pad, coincident with an increase in parenchymal-associated mast cells in mice fed both levels of CLA. Feeding experiments with purified isomers (0.5 g/100 g diet) demonstrated that these changes were induced by trans-10, cis-12 CLA (10,12-CLA), but not by cis-9, trans-11 CLA (9,11-CLA). This stromal remodeling did not require tumor necrosis factor (TNF)-alpha, a major cytokine in mast cells, as TNF-alpha null mice demonstrated collagen deposition, increased leukocytes, and BAT loss in the mammary fat pad in response to 10,12-CLA. To test the hypothesis that mast cells recruited in response to 10,12-CLA were required for stromal remodeling, Steel mice (WBB6F1/J-kit(W)/kit(W-V)), which lack functional mast cells, were examined for their stromal response to 10,12-CLA. Both wild-type and Steel mice showed a significantly increased leukocytic adipose infiltrate, collagen deposition, and decreased adipocyte size, although BAT was maintained in Steel mice. These results demonstrate that 10,12-CLA induces an inflammatory and fibrotic phenotype in the mouse mammary gland stroma that is independent of TNF-alpha or mast cells and suggest caution in the use of 10,12-CLA for breast cancer chemoprevention.

Acacetin suppressed LPS-induced up-expression of iNOS and COX-2 in murine macrophages and TPA-induced tumor promotion in mice

Acacetin (5,7-dihydroxy-4'-methoxyflavone), a flavonoid compound, has anti-peroxidative and anti-inflammatory effects. In this study, we investigated the inhibitory effects of acacetin and a related compound, wogonin, on the induction of NO synthase (NOS) and COX-2 in RAW 264.7 cells activated with lipopolysaccharide (LPS). Acacetin markedly and actively inhibited the transcriptional activation of iNOS and COX-2. Western blotting, reverse transcription-polymerase chain reaction (PCR), and real-time PCR analyses demonstrated that acacetin significantly blocked protein and mRNA expression of iNOS and COX-2 in LPS-inducted macrophages. Treatment with acacetin reduced translocation of nuclear factor-kappa B (NF kappa B) subunit and the dependent transcriptional activity of NF kappa B. The activation of NF kappa B was inhibited by prevention of the degradation of inhibitor kappa B (I kappa B). Furthermore, acacetin inhibited LPS-induced phosphorylation as well as degradation of I kappa B alpha. We further investigated the roles of tyrosine kinase, phosphatidylinositiol 3-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK) in LPS-induced macrophages. We found that acacetin also inhibited LPS-induced activation of PI3K/Akt and p44/42, but not p38 MAPK. After initiation of 7,12-dimethlybene[a]anthracene (DMBA), applying acacentin topically before each 12-O-tetradecanoylphorbol 13-acetat (TPA) treatment was found to reduce the number of papillomas at 20 weeks. Taken together, these results show that acacetin down regulates inflammatory iNOS and COX-2 gene expression in macrophages by inhibiting the activation of NF kappa B by interfering with the activation PI3K/Akt/IKK and MAPK, suggesting that acacetin is a functionally novel agent capable of preventing inflammation-associated tumorigenesis.

Inflammation in epithelial skin tumours: old stories and new ideas

The essential contribution of inflammation to tumour development and progression has gained increasing acceptance. For epithelial skin cancer, the observation that tumours arise in sites of chronic irritation and inflammation dates back to 1828 and has stimulated a whole field of research. Chemically-induced mouse skin tumours requiring inflammatory agents such as 12-O-tetradecanoylphorbol 13-acetate (TPA) for tumour-promotion have greatly contributed to our understanding of multi-stage carcinogenesis and have given important insights into the functional interaction between inflammatory micro-environment and epithelial tumour, especially when used in combination with transgenic animals. Data from these and additional new model systems clearly emphasise that the tumour-promoting micro-environment is indispensable for tumour formation and progression. It strongly resembles the wound and is largely orchestrated by inflammatory cells allowing tumour cells to co-opt signalling molecules of the innate immune system to promote their growth, invasion and metastasis. Consequently, anti-inflammatory drugs are of great clinical interest in prevention and treatment of epithelial skin cancers.

Lysosomal glycosidases and their natural substrates in major salivary glands of hamsters treated with 7,12-dimethylbenzanthracene (DMBA)

Oro-maxillofacial diseases may influence structure and function of salivary glands. In this study, 32 hamsters were treated with topical application of 7,12-dimethylbenzanthracene (DMBA) on the buccal pouch. After 16 weeks, the animals were killed and the major salivary glands extracted. The activities of some lysosomal glycosidases and their natural substrates were measured to understand how the carcinogenetic stress and the inflammatory reaction could influence the physiology of the salivary glands. Large differences were observed in lysosomal activities among treated and untreated animals. Similarly, large differences were shown in the concentration of natural substrates, including sialic acids. These results suggest that inflammation and/or tumors induce profound changes in the biology of the salivary glands.

Human mast cells produce matrix metalloproteinase 9

Extracellular matrix-destructive enzymes, like matrix metalloproteinases (MMP), have been recognized in the process of inflammation and tissue remodeling and repair. The affected tissues often contain markedly increased numbers of mast cells. Although mast cells are capable of activating latent collagenase and proMMP, it has so far been unknown whether human mast cells themselves produce and secrete MMP9. In this study, MMP9 production by cord blood-derived cultured human mast cells and HMC-1 human mast cells was examined by reverse-transcriptase PCR, gelatin zymography and Western blot analysis using an antibody against MMP9. Cultured mast cells and HMC-1 cells treated with phorbol 12-myristate 13-acetate were shown to express MMP9 mRNA, and the cultured conditioned media from these cells showed gelatinolytic activity, identical with MMP9. Immunohistochemical examination was performed to detect MMP9 in tissue mast cells; mast cells localized in the skin, lung and synovial tissue showed strongly positive reactions for MMP9. Thus, these findings indicate that human mast cells can produce MMP9, which might contribute to extracellular matrix degradation and absorption in the process of allergic and nonallergic responses.

Topical tretinoin increases dermal mast cells, induces epidermal mast cell growth factor (c-kit ligand) and modulates its distribution in hairless mice

In previous studies we have noted that mast cells are increased in tretinoin-treated photoaged hairless mouse skin. Because UV radiation is known to increase mast cell numbers, we were interested in whether tretinoin alone would modulate the mast cell population in unirradiated mice. Animals were treated topically with 0.05% tretinoin, 5 days a week, for 2, 4, 6, 8 and 10 weeks. Untreated and vehicle controls were included. Biopsies were processed for light microscopy and stained with toluidine blue. Mast cells in the upper and lower dermis were scored separately under high magnification. After 2 weeks of tretinoin, mast cells in the upper dermis were significantly increased, as indicated by the appearance of small, moderately metachromatically granulated cells near the dermal-epidermal junction. Mast cells in the lower dermis, the site of a granulomatous reaction, were large, densely granular and significantly increased after 6 weeks of treatment. Immunohistochemical evaluation for mast cell growth factor (MGF) revealed a marked increase in keratinocyte cytoplasmic staining by week 2. After 4-6 weeks, membrane-associated or intercellular staining was evident. Cells in the upper dermis also showed membrane reactivity for MGF. By 8-10 weeks, epidermal MGF reactivity had dissipated in the more basal keratinocytes. These findings show that topical tretinoin can induce epidermal MGF along with an associated mast cell hyperplasia. It is suggested that the two populations of dermal mast cells may have different functions.

Dermal mast cell granules bind interstitial procollagenase and collagenase

In order to identify structures in human skin that bind collagenase, sections from frozen or paraffin-embedded skin were incubated with either procollagenase or activated collagenase. After washing, bound procollagenase or collagenase was detected by immunofluorescence microscopy. In normal skin, procollagenase bound only to isolated granular dermal cells that were identified as mast cells on the basis of staining with fluoresceinated avidin and pinacyanol erythrosinate. When mast cells were degranulated by exposure to the ionophore A23187, extracellular granules bound procollagenase. Of various pathologic conditions examined, the highest binding of procollagenase occurred in specimens of urticaria pigmentosa. Procollagenase bound to granular cells and to abundant granules scattered throughout the dermis. Binding could be abolished by pre-treatment of tissue sections with heparinase or by pre-incubation of procollagenase with soluble heparin, suggesting that heparin is the binding agent in the granules. Activated collagenase also bound to dermal mast cells but in addition bound strongly to the dermal collagen. Enzymatic activity of activated collagenase was not inhibited by heparin in concentrations up to 10 mg/ml. There is evidence that mast cell tryptase can contribute to procollagenase activation. This study further supports a role for mast cells in collagenolysis by demonstrating that heparin from mast cells binds procollagenase and possibly serves as a reservoir for procollagenase, which may then subsequently be activated.

Mast cells and matrix degradation at sites of tumour invasion in rat mammary adenocarcinoma

Significant numbers of mast cells have been demonstrated histologically around the periphery of the invasive rat mammary adenocarcinoma 13672NF. The number of mast cells at microfoci along the tumour:host tissue junction was significantly greater than that found in normal mammary tissues, and few mast cells were detected within the tumour itself. Mast cell degranulation, often associated with disruption and lysis of the connective tissue matrix, was a common feature in later stages of tumour proliferation. When soluble products derived from purified rat peritoneal mast cells were added to monolayer cultures of rat stromal fibroblasts or tumour cells they stimulated a significant increase in total collagenase production, and the mast cell products were also capable of activating the latent collagenases thus produced. Histological examination indicated that degradation of local collagenous matrix was a common feature of mast cell degranulation, an observation possibly explained by the release of mast cell enzymes and/or the potential of this cell to modulate the expression of collagenolytic activity by surrounding cells. These observations suggest that, at least in some tumours, mast cells contribute to the connective tissue breakdown commonly associated with tumour invasiveness and metastatic spread.

Proliferation of mast cells in normal and DMBA-treated mouse skin

To examine the pattern of proliferation of mast cells in the skin of Swiss Webster mice, single or multiple pulses of 3H-thymidine, autoradiography and selective staining techniques were combined to detect DNA synthesis. A very low labelling index was found for the mast cells of normal skin but alteration of the mast-cell population using the chemical carcinogen dimethylbenzathracene led to increased labelling of mast cells. A series of studies of experimentally altered skin showed a pattern of mast cell labelling which suggested derivation of new mast cells by local self-replication. The labelling pattern indicated that mast cells labelled after 1 h divided to produce 2 daughter cells and that the rate of increase in the number of labelled mast cells following repeated labelling for up to 20 days was linear. These data do not suggest major recruitment of mast cells from a distant source during this period.