Mice, skin-painting studies

In mice skin-painting studies, skin tumors were produced by steam-refined petroleum bitumens, an air-refined bitumen in toluene, two cracking residue bimmens, and a pooled mixmre of steam- and air-blown petroleum bitumens. In contrast, standard roofing petroleum asphalts produced no tumors. 

Pellets of cholesterol containing 2 mg of hydroquinone implanted in mice bladders caused an excessive number of bladder carcinomas. hr other studies, rats fed up to 1% hydroquinone in their diets for 2 years did not develop tumors, nor did hydroquinone initiate significant numbers of tumors in mice skin painting studies. ... 

As summarized by Nessel (1 999), middle distillate fractions (MDFs) have been tested in numerous lifetime mouse skin-painting studies over the last 20 yr. Early mouse skin-painting studies documenting the carcinogenicity of MDFs in mouse skin include those of Lewis et al. (1984) and Biles et al. (1988), as cited by Nessel (1999). MD API 81 -07, a hydrodesulfurized kerosene, was also shown to induce skin tumors in a C3H/HeJ mouse skin-painting 2-yr bioassay in 50% of the animals with a tumor latency of 76 wk (API 1988, as cited by Skisak 1991). 

The role of skin irritation in the development of skin tumors was investigated by Nessel et al. (1998). In lifetime C3F1 mouse skin-painting studies, MDFs, including a straight-run kerosene, were applied neat and in 50% and 28.6% dilutions. Treatment with the neat straight-run kerosene induced skin tumors and skin irritation treatment with the diluted material produced neither... 

Consideration of all the tumorigenic PAHs and their levels in CSC could account for no more than 3% of the observed biological activity in mouse skin-painting studies. In 1961, Wynder and Hoffmann (4312) stated ... 

Despite comments such as these and additional ones in later publications, animal experimentation, particularly mouse skin-painting studies, constituted a substantial part of the bioassays on tobacco smoke. Such bioassays are not only expensive but also extremely time consuming (18 to 24 months). Because of the absence of a positive response in studies of tobacco smoke inhalation by laboratory animals, mouse skin-painting with CSC was selected as the bioassay of choice in the massive decade-long (1970-1980) study conducted by the National Cancer Institute (NCI) on less hazardous cigarettes, a study that involved nearly 100 test cigarettes and 30 standard or reference cigarettes (1329, 1330,1332,1333, 2683). 

Despite observations that NNAs in CSC or NNAs individually induce few, if any, tumors at the application site in mouse skin-painting studies with CSC, they are one of the two classes of tobacco product components to which the prohealth forces continue to devote their major efforts. In 1990, Hoffmann and Hecht (1727) noted ... 

Roffo. .. claimed to have identified benzpyrene in tobacco tar, but this could not be confirmed by Hirst and his coworkers (813), and more recently that substance could not be detected by Waller (25A81). An examination by Eby (25A21) of the tobacco tar used in this study [the mouse skin-painting study by Wynder, Graham, and Croninger (4306a)] did not reveal any spectroscopic evidence of the known carcinogenic hydrocarbons. 

In the NCI study of the third set of experimental cigarettes (1332), the cigarette MSS composition and biological properties (mouse skin-painting studies) of four cigarette samples were compared. These included three samples to each of which had been added individually a specified amount of glycerol (Code No. 80), sugar (Code No. 81), and cocoa (Code No. 82). 

Since B[a]P in CSC acting alone accounts for less than 2% and the total PAH fraction accounts for less than 3% of the observed biological response in mouse skin-painting studies and no supercarcinogenic PAHs is present, additional mechanisms are needed to explain the biological effect The mechanisms of promotion and cocarcinogenesis of tobacco smoke components (phenols, etc.) may explain the observed effect in skin-painting studies with CSC. 

The following contradictory evidence was reported Increasing the B[a]P level in CSC by a factor of 10 produced no increase in the mmorigenicity of CSC [Roe (3310, 3311)]. Increasing the level of B[a]P by a factor of 30 produced no increase in the tumorigenicity of the CSC in mouse skin-painting studies [Lazar etal. (2320)]. 

The tumorigenicity of the cigarette smoke condensate in mouse skin-painting studies. 

Hundreds of rodent skin-painting studies with CSC and its fractions have been conducted since the first successful production of carcinoma in mice painted with CSC [see (4319, 4332 and references cited), Gori (1329, 1330, 1332, 1333), NCI (2683)]. Even in the massive NCI decade-long study, no attempt was made to correlate NNA content with bioassay results. It was assumed, from studies with individual NNAs, that they had little if any influence on CSC tumorigenicity to mouse skin. Millions of dollars and thousands of hours expended since 1953 in conducting bioassays - particularly mouse skin-painting studies - did not adequately define the total tumorigenicity of CSC in laboratory animals. 

Studies with B[a]P and the C31 and C35 saturated hydrocarbons (SHC), where the SHC B[a]P ratio was 200 1 and 100 1, showed that both saturated hydrocarbons exerted a significant inhibiting effect at both levels on the specific tumorigenicity of B[fl]P in mouse skin-painting experiments [4311,4314, see also pp. 330-331 in (4319) and pp. 370-371 in (4332)]. 

This suggestion, coupled with the mouse skin-painting bioassay results reported by Takizawa (3865a) that several simple quinones such as 2,5-cyclohexadiene-l,4-dione (p-benzoquinone), 1,2-naphthalenedione (1,2-naphthoquinone), and 1,4-naphthalenedione (1,4-naphthoquinone) were tumorigenic to mouse skin, raised serious questions about the desirability of adding phenols to the tobacco blend to enhance the odor and flavor of its smoke. Despite the many studies in which benzene was used as the solvent for testing of the tumorigenicity of PAHs, benzene seldom induced tumors in... 

In the early days of the studies on the specific tumorigenicity of various classes of compounds to mouse skin, investigators were intrigued by the activities exhibited by aromatic hydrocarbons, their dihydric phenols, and the quinones corresponding to the dihydric phenols. The results of mouse skin-painting bioassays with various aromatic hydrocarbons ranging in complexity from monocyclic to hexacyclic, their dihydric phenols, and the corresponding quinones are summarized in Table IX.B-1. 

Tumorigenic to mouse skin in skin-painting studies. 

The effect of cellulose added to cigarette filler on cigarette MSS composition and properties in a mouse skin-painting bioassay was examined in the mid-1970s in the NCI study of the first set of cigarettes (1329, 2683). The results are poorly defined because the cellulose was added (as wood pulp) at a 7.5% level to fillers made from the Standard Experimental Blend (SEB I) reconstituted into sheet material at three different densities. 

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