Tara E. Schafer

Estrogenicity of bisphenol A and bisphenol A dimethacrylate in vitro

Although pit and fissure sealants have been utilized extensively in dentistry as a way of preventing occlusal caries, results described by Olea et al. (1996) raised concerns about the safety of sealants and other resin-based dental materials due to the reported presence of bisphenol A (BPA) and its dimethacrylate ester (BPA-DM). Although the release of these compounds from dental materials has not been substantiated by two subsequent studies, we believed it was important to confirm or refute the report that BPA and BPA-DM have estrogenic activity in vitro. We grew breast cancer cells (MCF-7, T-47D, ZR-75-1) known to proliferate under estrogenic stimulation in phenol red-free DMEM containing human serum and concentrations of BPA or BPA-DM ranging from 10(-8)M to 5 x 10(-6)M. After 1 week, plates were harvested for crystal violet or sulforhodamine-B assays, and the optical densities of groups of treated cells were compared with values from control cells. At concentrations at or above 10(-6)M, both BPA and BPA-DM significantly increased cell proliferation (p < 0.05), comparable to the increase seen with 10(-9)M of estrogen. Flow cytometric methods demonstrated that these mitogenic effects occurred within 24 h of exposure to estrogen, BPA, or BPA-DM. The increase in DNA synthesis was analogous to that seen with estrogen stimulation. Thus, we confirmed that BPA and BPA-DM cause cell proliferation at micromolar concentrations that exceed the effective concentrations of estrogen by 1 to 10,000-fold.

Plaque fluoride concentrations are dependent on plaque calcium concentrations

Despite the 1,000-fold difference between the fluoride concentrations ([F]) in dentifrices and fluoridated drinking water, clinical and epidemiological studies have shown that they have similar cariostatic effects. This double-blind, crossover study was done to determine whether the [F] in dental plaque is related more to the [F] of the dentifrice used or to the plaque concentrations of calcium and magnesium. The subjects (n = 13) were adults and residents of a city served with fluoridated drinking water. After 1 week of using a fluoridated dentifrice (940 ppm) or a placebo dentifrice, whole saliva and plaque were collected 1.0 h and approximately 12 h after the last use of the dentifrices. The average salivary [F] after brushing with the F dentifrice was higher than after using the placebo. The average plaque [F] 1.0 h after brushing with the F dentifrice was higher than after using the placebo (p < 0.01), but the difference at 12 h was not significant. Plaque [Ca] and [F] were directly related under all experimental conditions (p = 0.0001). The relationships between plaque [Mg] and [F] were weaker and inconsistent. Based on these findings and reports in the literature it is concluded that, for persons whose drinking water is fluoridated, plaque [F] throughout much of the day is not significantly increased by the use of a fluoridated dentifrice. Instead they are directly related to plaque [Ca]. These findings offer at least a partial explanation for why fluoridated dentifrices and drinking water have similar cariostatic effects.

4-Hydroxytamoxifen-induced cytotoxicity and bisphenol a: Competition for estrogen receptors in human breast cancer cell lines

SummaryIncreasing concerns over the effects of environmental estrogens on wildlife and humans have highlighted the need for screening systems to assess potentially estrogenic effects of test compounds. As a result, in vitro screening methods such as cell proliferation assays using the estrogen-responsive human breast cancer cell line, MCF-7, have been developed. The present study describes an alternative in vitro approach for the assessment of such xenoestrogens, based on estrogenic rescue of MCF-7 cells from antiestrogen-induced cytotoxicity. This method measures the ability of various estrogenic compounds to compete with a known estrogen-receptor-mediated antihormonal drug, 4-hydroxytamoxifen, using the 1-[4,5-dimethylthiazol-2-yl]-3,5-diphenylformazan (MTT) assay to assess mitochondrial activity. Because 4-hydroxytamoxifen treatment of cells results in a dramatic decrease in mitochondrial dehydrogenase activity which is directly related to their estrogen-receptor content, inhibition of this effect with estrogenic compounds represents an estrogen-receptor interaction, or estrogenic rescue. The estrogenic compounds tested include a weak xenoestrogen, bisphernol A (BPA), and two biological estrogens, 17α- and 17β-estradiol. Competitive inhibition of 4-hydroxytamoxifen-induced cytotoxicity by BPA was compared to that of the biological estrogens. The results indicate that the biological estrogens can successfully compete with the antiestrogen in a dose-dependent manner. In addition, the assay is sensitive enough to detect estrogenic rescue by even the very weak xenoestrogen, BPA, albeit at high BPA concentrations. This simple in vitro method could be used as an alternative or second-line screen for potential xenoestrogens.

Mode of drinking fluoridated milk: effect on intraoral fluoride concentrations

OBJECTIVE To determine the effect of the mode of drinking fluoridated milk on salivary and plaque fluoride concentrations. METHODS Fluoridated milk was ingested by 32 children in three ways: (a) directly from the container (1.0 and 5.0 mg F/litre), (b) through a straw with the tip between the lips (5.0 mg F/litre), and (c) with the tip deep in the oral cavity (5.0 mg F/litre). Saliva was collected at baseline and 2, 15, and 40 min and plaque at baseline and 20 min after drinking. Fluoride concentrations were determined using the electrode after HMDS-facilitated diffusion. RESULTS The mode of drinking did not affect fluoride concentrations in saliva or plaque. The average 2-min salivary concentrations were 65 ng F/mL for the 1.0 mg F/litre group and 276 ng F/mL for the three 5.0 mg F/litre groups (P < 0.01). The average of the 15- and 40-min salivary concentrations was 22 ng F/mL for the 1.0 mg F/litre group and 41 ng F/mL for the 5.0 mg F/litre groups (P < 0.01). Plaque concentrations showed the same patterns as in saliva, that is, they were higher in the three 5.0 mg F/litre groups than in the 1.0 mg F/litre group and the differences among the 5.0 mg F/litre groups were not statistically significant. CONCLUSION Salivary and plaque fluoride concentrations were independent of the mode of drinking but directly related to milk fluoride concentrations.