mezerein and n-dodecane

Responses of various cells of the epidermis and dermis to topically applied agents have been implicated in the mechanism of multistage mouse tumorigenesis. These responses have been discussed almost entirely in the context of a single promoter treatment, although tumor expression is dependent on multiple applications. Responses of keratinocytes, epidermal dendritic non-keratinocytes and dermal leukocytes were therefore recorded following multiple topical applications of the potent complete tumor-promoting agent 12-O-tetradecanoylphorbol-13-acetate (TPA). In order to assess the importance of the response of individual cell types to the mechanisms and stages of promotion, responses to TPA were compared with those to agents with low complete promoting activity, but significant activity in individual stages of multistage promotion models. These included 4-O-methyl-TPA, a stage 1 promoting agent, mezerein and n-dodecane, stage 2 promoting agents of apparently different mechanism of action, and ethyl phenylpropiolate (EPP), a highly inflammatory stage 3 promoting agent. In agreement with previous findings, TPA induced a persistent epidermal hyperplasia and an increase in dark keratinocytes, although a similar finding was made for EPP and n-dodecane. The response to n-dodecane was significantly delayed, however, and that to EPP was accompanied by focal epidermal destruction and inflammation. The response to n-dodecane contrasted with that found for mezerein, supporting the suggestion that their mechanisms of action are distinct. Multiple treatments of 4-O-methylTPA caused no increase in dark cells, and mezerein induced no increase in numbers of pyknotic cells, whereas increases were expected in both cases on the basis of single dose experiments. Of the agents examined, only TPA induced a decrease in pale dendritic epidermal cells in the absence of marked toxicity, supporting the previous proposal that prolonged effects on this cell type are important in the promotion process. Some degree of persistent dermal leukocyte infiltration was observed with all agents excepting 4-O-methylTPA, although the extent of the response and its cellular characteristics appeared strongly dependent on the agent applied. In the case of TPA small mononuclear cells, neutrophils and macrophages all provided significant contributions to the total infiltrate. A similar phenomenon was observed with n-dodecane and EPP, with an additional increase in eosinophils which was not observed with

Topics: Acetone; Alkanes; Alkynes; Animals; Carcinogens; Diterpenes; Epidermis; Female; Langerhans Cells; Leukocytes; Male; Mice; Mice, Inbred Strains; Skin; Terpenes; Tetradecanoylphorbol Acetate

n-Dodecane, a previously little-studied tumor-promoting agent and mezerein, a diterpenoid natural product, have both been reported to have activity primarily in Stage II of two stage tumor promotion in SENCAR mouse skin. Histological changes in this tissue were therefore investigated in response to these agents in order to determine whether changes could be identified which were common to Stage II promotion by both compounds, and specific in this respect compared to those induced by the complete promoting agent 12-O-tetradecanoylphorbol-13-acetate (TPA). All three agents were applied at doses which have previously been found active in multistage tumorigenesis studies in this strain. A single dose of 50 mg dodecane induced no increase in the number of interfollicular cell layers or epidermal thickness, nor any observable inflammation, 6-144 h after application. In contrast, marked increases were predictably observed with TPA and mezerein, maximal responses occurring after 48-72 h. n-Dodecane induced no increase in the number of keratinocytes with dense cytoplasm and increased affinity for basophilic dyes (dark cells), only TPA demonstrating this activity. The alkane likewise did not increase the number of pyknotic basal keratinocytes indicating that toxicity would not account for the low Stage I activity of this agent in the way proposed for mezerein which was the most active in this respect, inducing a significant increase 48 h after treatment. Like TPA and mezerein, n-dodecane induced a significant increase in large intra-mitochondrial densities. Forty-eight to seventy-two hours after application, dodecane induced a significant decrease in the numbers of dendritic epidermal cells, a response which was also observed for TPA and mezerein, although occurring somewhat more rapidly. All three agents appeared to induce these cells to retract their characteristic processes. After four applications of n-dodecane the number of epidermal cell layers and mitotic index were equal to or greater than those observed with TPA. These findings show that in SENCAR epidermis the previously uncharacterized tumor-promoting agent n-dodecane induced essentially no histologic changes in mouse skin in common with mezerein, a second agent with activity primarily in Stage II of two stage tumor promotion, which were not also shown by the complete promoter TPA. The only characteristic specific to Stage II promoting agents therefore remains an inability to induce increased numbers of

Topics: Alkanes; Animals; Carcinogens; Diterpenes; Epidermal Cells; Epidermis; Female; Mice; Mice, Inbred Strains; Microscopy, Electron; Mitochondria; Mitotic Index; Skin; Terpenes; Tetradecanoylphorbol Acetate; Time Factors

Application of the alkane n-dodecane to the dorsal skin of 6-8 week old female SENCAR mice initiated with 10 nmol dimethylbenz[a]anthracene led to papilloma formation in the majority of treated animals. Compared to the potent phorbol diester 12-O-tetradecanoylphorbol-13-acetate (TPA), n-dodecane was several orders of magnitude less potent on a dose basis, and maximal papilloma response required more extended application (22 weeks for 50 mg dodecane compared to 12 weeks for 2 micrograms TPA). In two-stage promotion experiments n-dodecane appeared to act as a stage II promoting agent at appropriate doses, being comparable in activity to mezerein--an agent with well-characterized activity of this type. Dodecane, unlike mezerein, did not induce the formation of a significant number of pyknotic cells, however, suggesting that the weak promoting activity of dodecane in stage 1 was not a result of toxicity. In comparison with TPA, both mezerein and n-dodecane at promoting doses induced less sustained hyperplasia in SENCAR mouse skin, a finding also consistent with the proposal that n-dodecane is principally active in stage II of two-stage promotion models. Both agents induced ornithine decarboxylase activity in SENCAR mouse skin, the maximal induction being observed at apparently the same time after a single application.

Topics: Acetone; Alkanes; Animals; Cocarcinogenesis; Diterpenes; Female; Mice; Papilloma; Skin Neoplasms; Terpenes; Tetradecanoylphorbol Acetate