Pharmacokinetics of bisphenol A released from a dental sealant

Bisphenol A and related compounds in dental materials

CONTEXT

Dental sealants and composite filling materials containing bisphenol A (BPA) derivatives are increasingly used in childhood dentistry. Evidence is accumulating that BPA and some BPA derivatives can pose health risks attributable to their endocrine-disrupting, estrogenic properties.

OBJECTIVES

To systematically compile and critically evaluate the literature characterizing BPA content of dental materials; to assess BPA exposures from dental materials and potential health risks; and to develop evidence-based guidance for reducing BPA exposures while promoting oral health.

METHODS

The extant toxicological literature and material safety data sheets were used as data sources.

RESULTS

BPA is released from dental resins through salivary enzymatic hydrolysis of BPA derivatives, and BPA is detectable in saliva for up to 3 hours after resin placement. The quantity and duration of systemic BPA absorption is not clear from the available data. Dental products containing the bisphenol A derivative glycidyl dimethacrylate (bis-GMA) are less likely to be hydrolyzed to BPA and have less estrogenicity than those containing bisphenol A dimethacrylate (bis-DMA). Most other BPA derivatives used in dental materials have not been evaluated for estrogenicity. BPA exposure can be reduced by cleaning and rinsing surfaces of sealants and composites immediately after placement.

CONCLUSIONS

On the basis of the proven benefits of resin-based dental materials and the brevity of BPA exposure, we recommend continued use with strict adherence to precautionary application techniques. Use of these materials should be minimized during pregnancy whenever possible. Manufacturers should be required to report complete information on the chemical composition of dental products and encouraged to develop materials with less estrogenic potential.

Urinary, circulating, and tissue biomonitoring studies indicate widespread exposure to bisphenol A

BACKGROUND

Bisphenol A (BPA) is one of the highest-volume chemicals produced worldwide, and human exposure to BPA is thought to be ubiquitous. Thus, there are concerns that the amount of BPA to which humans are exposed may cause adverse health effects. Importantly, results from a large number of biomonitoring studies are at odds with the results from two toxicokinetic studies.

OBJECTIVE

We examined several possibilities for why biomonitoring and toxicokinetic studies could come to seemingly conflicting conclusions.

DATA SOURCES

We examined > 80 published human biomonitoring studies that measured BPA concentrations in human tissues, urine, blood, and other fluids, along with two toxicokinetic studies of human BPA metabolism.

DATA EXTRACTION AND SYNTHESIS

The > 80 biomonitoring studies examined included measurements in thousands of individuals from several different countries, and these studies overwhelmingly detected BPA in individual adults, adolescents, and children. Unconjugated BPA was routinely detected in blood (in the nanograms per milliliter range), and conjugated BPA was routinely detected in the vast majority of urine samples (also in the nanograms per milliliter range). In stark contrast, toxicokinetic studies proposed that humans are not internally exposed to BPA. Some regulatory agencies have relied solely on these toxicokinetic models in their risk assessments.

CONCLUSIONS

Available data from biomonitoring studies clearly indicate that the general population is exposed to BPA and is at risk from internal exposure to unconjugated BPA. The two toxicokinetic studies that suggested human BPA exposure is negligible have significant deficiencies, are directly contradicted by hypothesis-driven studies, and are therefore not reliable for risk assessment purposes.

UK National Clinical Guidelines in Paediatric Dentistry: Use of fissure sealants including management of the stained fissure in first permanent molars

International Journal of Paediatric Dentistry 2010 Summary.  The process of guideline production began in 1994, resulting in first publication in 1997. Each guideline has been circulated to all Consultants in Paediatric Dentistry in the UK, to the Council of the British Society of Paediatric Dentistry (BSPD), and to people of related specialties recognised to have expertise in the subject. The final version of the guideline is produced from a combination of this input and thorough review of the published literature. The intention is to encourage improvement in clinical practice and to stimulate research and clinical audit in areas where scientific evidence is inadequate. Evidence underlying recommendations is scored according to the SIGN classification and guidelines should be read in this context. For those wishing further detail, the process of guideline production in the UK is described in the International Journal of Paediatric Dentistry 1997; 7: 267-268. This guideline is an update on the previously published BSPD policy document on fissure sealants. (Nunn et al., Int J Paed Dent 2000; 10: 174-177).

Molecular toxicology of substances released from resin-based dental restorative materials

Resin-based dental restorative materials are extensively used today in dentistry. However, significant concerns still remain regarding their biocompatibility. For this reason, significant scientific effort has been focused on the determination of the molecular toxicology of substances released by these biomaterials, using several tools for risk assessment, including exposure assessment, hazard identification and dose-response analysis. These studies have shown that substances released by these materials can cause significant cytotoxic and genotoxic effects, leading to irreversible disturbance of basic cellular functions. The aim of this article is to review current knowledge related to dental composites' molecular toxicology and to give implications for possible improvements concerning their biocompatibility.

Bisphenol A levels in blood depend on age and exposure

We present two approaches to estimate blood concentrations of Bisphenol A (BPA). Simple kinetic principles were applied to calculate steady state plasma concentrations. A physiologically based model was used to simulate the blood concentration time profile in several age groups exploring the influence of not yet fully developed metabolic capacity on the blood concentrations in the newborn. Both approaches gave concordant results and are in excellent agreement with experimental results [Völkel, W., Colnot, T., Csanady, G.A., Filser, J.G., Dekant, W., 2002. Metabolism and kinetics of bisphenol A in humans at low doses following oral administration. Chem. Res. Toxicol. 15, 1281-1287]. The predictions also agree with published results obtained with a different physiologically based model. According to model simulations, BPA is present in the blood of the normal population at concentrations several orders of magnitude lower than most measurements reported in the literature. At the same external exposure level, the newborn is predicted to have 3 times greater blood concentration than the adult. This is due to the not yet fully developed glucuronidation activity in the newborn, not fully compensated by the unimpaired sulfation pathway. For the highest measured external BPA exposure, the predicted blood concentrations of 2.6 pg/ml (steady state concentration) and 8.2 pg/ml (peak concentration) in the adult are lower than the in vitro concentrations at which inhibiting adiponectin release from human adipocytes and stimulation of beta-cell production and secretion were observed.

Bisphenol A directly targets tubulin to disrupt spindle organization in embryonic and somatic cells

There is increasing concern that animal and human reproduction may be adversely affected by exposure to xenoestrogens that activate estrogen receptors. There is evidence that one such compound, Bisphenol A (BPA), also induces meiotic and mitotic aneuploidy, suggesting that these kinds of molecules may also have effects on cell division. In an effort to understand how Bisphenol A might disrupt cell division, a phenotypic analysis was carried out using sea urchin eggs, whose early embryonic divisions are independent of zygotic transcription. Fertilized Lytechinus pictus eggs exposed to BPA formed multipolar spindles resulting in failed cytokinesis in a dose-dependent, transcriptionally independent manner. By use of novel biotinylated BPA affinity probes to fractionate cell-free extracts, tubulin was identified as a candidate binding protein by mass spectrometry, and BPA promoted microtubule polymerization and centrosome-based microtubule nucleation in vitro but did not appear to display microtubule-stabilizing activity. Treatment of mammalian cells demonstrated that BPA as well as a series of Bisphenol A derivatives induced ectopic spindle pole formation in the absence of centrosome overduplication. Together, these results suggest a novel mechanism by which Bisphenol A affects the nucleation of microtubules, disrupting the tight spatial control associated with normal chromosome segregation, resulting in aneuploidy.

Derivation of a bisphenol A oral reference dose (RfD) and drinking-water equivalent concentration

Human exposure to bisphenol A (BPA) is due to that found in the diet, and BPA and its metabolites were detected at parts per billion (or less) concentrations in human urine, milk, saliva, serum, plasma, ovarian follicular fluid, and amniotic fluid. Adverse health effects in mice and rats may be induced after parenteral injection or after massive oral doses. Controlled ingestion trials in healthy adult volunteers with 5 mg d16-BPA were unable to detect parent BPA in plasma despite exquisitely sensitive (limit of detection = 6 nM) methods, but by 96 h 100% of the administered dose was recovered in urine as the glucuronide. The extensive BPA glucuronidation following ingestion is not seen after parenteral injection; only the parent BPA binds plasma proteins and estrogen receptors (ER). The hypothesis that BPA dose-response may be described by a J- or U-shape curve was not supported by toxicogenomic data collected in fetal rat testes and epididymes (after repeated parenteral exposure at 2-400,000 microg/kg-d), where a clear monotonic dose-response both in the numbers of genes and magnitude of individual gene expression was evident. There is no clear indication from available data that the BPA doses normally consumed by humans pose an increased risk for immunologic or neurologic disease. There is no evidence that BPA poses a genotoxic or carcinogenic risk and clinical evaluations of 205 men and women with high-performance liquid chromatography (HPLC)-verified serum or urinary BPA conjugates showed (1) no objective signs, (2) no changes in reproductive hormones or clinical chemistry parameters, and (3) no alterations in the number of children or sons:daughters ratio. Results of benchmark dose (BMD10 and BMDL10) calculations and no-observed-adverse-effect level (NOAEL) inspections of all available and reproducible rodent studies with oral BPA found BMD and NOAEL values all greater than the 5 mg/kg-d NOAELs from mouse and rat multigeneration reproduction toxicity studies. While allometric and physiologically based pharmacokinetic (PBPK) models were constructed for interspecies scaling of BPA and its interaction with ER, multigeneration feeding studies with BPA at doses spanning 5 orders of magnitude failed to identify signs of developmental toxicity or adverse changes in reproductive tract tissues; the 5-mg/kg-d NOAELs identified for systemic toxicity in rats and mice were less than the oral NOAELs for reproductive toxicity. Thus, it is the generalized systemic toxicity of ingested BPA rather than reproductive, immunologic, neurobehavioral, or genotoxic hazard that represents the point of departure. Using U.S. Environmental Protection Agency (EPA) uncertainty factor guidance and application of a threefold database uncertainty factor (to account for the fact that the carcinogenic potential of transplacental BPA exposure has yet to be fully defined and comprehensive neurobehavioral and immunotoxicologic evaluations of BPA by relevant routes and at relevant doses have yet to be completed) to the administered dose NOAEL results in an oral RfD of 0.016 mg/kg-d. Assuming the 70-kg adult consumes 2 L of water each day and adopting the default 20% U.S. EPA drinking water relative source contribution yields a 100 microg/L BPA total allowable concentration (TAC).

In vitro and in vivo studies on the toxicity of dental resin components: a review

In vitro and in vivo studies have clearly identified that some components of restorative composite resins, adhesives, and resin-modified glass ionomer cements are toxic. The mechanisms of cytotoxicity are related firstly to the short-term release of free monomers occurring during the monomer-polymer conversion. Secondly, long-term release of leachable substances is generated by erosion and degradation over time. In addition, ion release and proliferation of bacteria located at the interface between the restorative material and dental tissues are also implicated in the tissue response. Molecular mechanisms involve glutathione depletion and reactive oxygen species (ROS) production as key factors leading to pulp or gingival cell apoptosis. Experimental animal approaches substantiate the occurrence of allergic reactions. There is a large gap between the results published by research laboratories and clinical reports.

Microarray analysis of bisphenol A-induced changes in gene expression in human oral epithelial cells

Bisphenol A (BPA) is a common ingredient in dental materials. However, its potential adverse effects on the oral cavity are unknown. The purpose of this study is to identify the genes responding to BPA in a human oral epithelial cell line using DNA microarray. Of the 10,368 genes examined, changes in mRNA levels were detected in seven genes: five were up-regulated and two were down-regulated. The expression levels of the calcium channel, voltage-dependent, L-type, alpha 1C subunit (CACNA1C), cell death activator CIDE-3 (CIDE-3), haptoglobin-related protein (HPR), importin 4 (IPO4), and POU domain, class 2 and transcription factor 3 (POU2F3) were significantly up-regulated in the cells exposed to 100 mM BPA. The spermatogenesis-associated, serine-rich 2 (SPATS2) and HSPC049 protein (HSPC049) were significantly down-regulated. The detailed knowledge of the changes in gene expression obtained using microarray technology will provide a basis for further elucidating the molecular mechanisms of the toxic effects of BPA in the oral cavity.

High-performance liquid chromatographic determination of unreacted monomers and other residues contained in dental composites

HPLC method was developed for determination of bisphenol A diglycidyl methacrylate (bis-GMA), bisphenol A diglycidyl acrylate (bis-GA), bisphenol A dimethacrylate (bis-DMA), glycidylmethacrylate (GMA) and triethylenglycol dimethacrylate (TEGDMA). Separation was carried out on a reversed phase Omnisphere 5 C18 column with a gradient mobile phase of CH3CN/H2O. UV detection was set at 205 nm and 275 nm parallel. The limits of quantification were found. The method has been applied for quantification of unreacted monomers trapped in polymer network of fillings.

Effect of prenatal exposure to bisphenol A on the serum testosterone concentration of rats at birth

In the rat, testosterone (T) in the neonatal period plays an important role in sexual differentiation and there is a serum T surge in male rats 2 hours after birth. Pregnant female rats were exposed to various doses of bisphenol A (BPA) from gestational day 1 (GD1) through 2 hours after parturition. About half of the BPA-exposed and control dams were subjected to cesarean section on GD22. The male fetuses on GD22 were immediately sacrificed and blood was collected. The other half of the BPA-treated and control dams delivered at GD23 (parturition day). The male pups were sacrificed 2 hours after birth. Serum T concentration was determined by radioimmunoassay (RIA). The BPA concentration in the fetal serum on GD22 increased inversely to the T levels in the serum. The T concentration in the pups' serum 2 hours after birth decreased inversely to the BPA concentration in the serum. However, there were no differences in the serum T concentration among the various doses of BPA. These results suggest that exposure to BPA in utero inhibits the T surge in the neonatal period and we speculate that exposure to BPA in utero disrupts the endocrine environment in the neonatal male.

Human exposure to bisphenol A (BPA)

The plastic monomer and plasticizer bisphenol A (BPA) is one of the highest volume chemicals produced worldwide. BPA is used in the production of polycarbonate plastics and epoxy resins used in many consumer products. Here, we have outlined studies that address the levels of BPA in human tissues and fluids. We have reviewed the few epidemiological studies available that explore biological markers of BPA exposure and human health outcomes. We have examined several studies of levels of BPA released from consumer products as well as the levels measured in wastewater, drinking water, air and dust. Lastly, we have reviewed acute metabolic studies and the information available about BPA metabolism in animal models. The reported levels of BPA in human fluids are higher than the BPA concentrations reported to stimulate molecular endpoints in vitro and appear to be within an order of magnitude of the levels needed to induce effects in animal models.

Orthodontic materials research and applications: part 2. Current status and projected future developments in materials and biocompatibility

The purpose of this 2-part opinion article was to project the developments expected to occur in the next few years in orthodontic materials research and applications. Part 1 reviewed developments in bonding to enamel. Part 2 looks at other orthodontic materials applications and explores emerging research strategies for probing the biological properties of materials. In the field of metallic brackets, expansion of the use of titanium alloys with improved hardness and nickel-free steels with better corrosion resistance and increased hardness is expected. Manufacturing techniques might be modified to include laser-welding methods and metal injection molding. Esthetic bracket research will involve the synthesis of high-crystallinity biomedical polymers with increased hardness and stiffness, decreased water sorption, and improved resistance to degradation. New plastic brackets might incorportate ceramic wings. Fiber-reinforced composite archwires, currently experimental, could soon be commercially available, and long-term applications of shape-memory plastics might become viable. Advancements in elastomeric materials will result in polymers with reduced relaxation, broader use of fluoride-releasing elastomers with decreased relaxation, and large-scale film coating of elastomers to decrease reactivity, water sorption, and degradation. Finally, biocompatibility assessments will incorporate testing of potential endocrinological action. New polymer formulations might be tested in adhesive and plastic bracket manufacturing, based on benzoic ring-free monomers to avoid the adverse effects of the estrogenic molecule bisphenol-A.

FDI report on adverse reactions to resin-based materials

Resin-based restorative materials are considered safe for the vast majority of dental patients. Although constituent chemicals such as monomers, accelerators and initiators can potentially leach out of cured resin-based materials after placement, adverse reactions to these chemicals are rare and reaction symptoms commonly subside after removal of the materials. Dentists should be aware of the rare possibility that patients could have adverse reactions to constituents of resin-based materials and be vigilant in observing any adverse reactions after restoration placement. Dentists should also be cognisant of patient complaints about adverse reactions that may result from components of resin-based materials. To minimise monomer leaching and any potential risk of dermatological reactions, resin-based materials should be adequately cured. Dental health care workers should avoid direct skin contact with uncured resin-based materials. Latex and vinyl gloves do not provide adequate barrier protection to the monomers in resin-based materials.

Assessment of bisphenol-A release from orthodontic adhesives

INTRODUCTION

The aim of this study was to quantitatively characterize the bisphenol-A (BPA) released from orthodontic adhesives after artificial accelerated aging.

METHODS

A chemically cured, no-mix adhesive and a visible light-cured adhesive were bonded to 40 stainless steel brackets divided in 2 groups of 20 brackets each. In total, 3 series of specimens were prepared for each adhesive-bracket group. All specimens were immersed in alcohol to induce accelerated aging. Samples of eluent removed from each group at 1 day and at 1, 3, and 5 weeks after aging were processed with high-pressure liquid chromatography; all assays were performed in triplicate, and the results were averaged.

RESULTS

No trace of BPA was identified for either adhesive across all time intervals, implying that, if present, the amount of BPA did not exceed the detection limit of the analytical technique (0.1 ppm or 0.1 microg/L).

CONCLUSIONS

BPA release from light-cured or chemically cured, no-mix adhesives did not reach the 0.1 ppm level. Estrogenicity assays are required to clarify the potential estrogenicity of adhesives, whereas formulation of benzoic ring-free, high molecular weight monomers might eliminate the concerns associated with the use of Bis-GMA.

Toxicokinetics of bisphenol A in rats, monkeys and chimpanzees by the LC–MS/MS method

We examined the toxicokinetics of bisphenol A (BPA) in F344 rats, cynomolgus monkeys and chimpanzees. Serum BPA levels were quantified using the LC-MS/MS method. After oral administration at 10 mg/kg, the maximum concentration in the serum (C(max)) and the area under the serum concentration curve (AUC) of BPA in cynomolgus monkeys and chimpanzees were greater than in rats. After oral administration at 100 mg/kg, AUC during the first 4h (AUC(0-->4h)) in cynomolgus monkeys was greater than in rats. In rats, the serum BPA levels were increased again 6h or later after oral administration at each dose, which suggested the enterohepatic circulation of BPA in rats. After subcutaneous administration at 10 mg/kg, the AUCs were ranked in the following order: cynomolgus monkeys>chimpanzees>rats, and C(max) in cynomolgus monkeys was greater than in rats and chimpanzees. After subcutaneous administration at 100 mg/kg to cynomolgus monkeys and rats, both the C(max) and AUCs in cynomolgus monkeys were greater than in rats. In all species, the oral administration of BPA resulted in much lower C(max) and AUCs than subcutaneous administration at the corresponding doses, indicating the low bioavailability of oral administration. This result suggests that BPA undergoes an extensive first-pass metabolism in these animal species. AUCs of subcutaneous administration and the AUC (0-->4h) of oral administration in the two primates were greater than that in rats. Because the systemic clearance for BPA is assumed to be dependent on the hepatic blood flow-rate, the high AUCs in primates are considered to be due to the lower systemic clearance by a lower hepatic blood flow-rate in primates than in rats. In addition, the toxicokinetics of the metabolites of BPA were examined. After the oral administration of 10 mg/kg BPA, both C(max) and AUCs of BPA metabolites were ranked in the following order: cynomolgus monkeys>chimpanzees>rats, and the terminal elimination half-life (T(1/2)) in rats was greater than that in cynomolgus monkeys and chimpanzees, suggesting the enterohepatic circulation of BPA in rats. From these results, the systemic clearance of BPA in primates is considered to be close to that in humans due to the similarity of the hepatic blood flow-rate. Furthermore, the major elimination route of BPA metabolites in primates is assumed to be renal excretion, as in humans, because the enterohepatic circulation that was observed in rats was not observed. In conclusion, primates are thought to be served as a valuable surrogate model for the toxicokinetics of BPA in humans.

Quantitation of bisphenol A and bisphenol A glucuronide in biological samples by high performance liquid chromatography-tandem mass spectrometry

Bisphenol A (BPA) is a weak estrogen. Pharmacokinetic studies of BPA have demonstrated a rapid and extensive metabolism of BPA to the nonestrogenic BPA-monoglucuronide (BPA-gluc). Some investigators have reported that BPA was found at parts per billion concentrations in the tissues or urine of humans without known exposure to BPA. This work developed a rapid and sensitive method for the determination of BPA and BPA-gluc in plasma and urine based on liquid chromatography-tandem mass spectrometry. The liquid chromatography-electrospray ionization-tandem mass spectrometry method for quantitation of BPA and BPA-gluc uses stable isotope-labeled internal standards. A linear ion trap mass spectrometer permits identification and quantitation of BPA-gluc and BPA without sample workup. Development of separation conditions reduced the BPA-background in solvent samples to below 2.5 pmol/ml for BPA. Limit of quantitation (LOQ) for BPA in control urine was 15 pmol/ml; LOQ for BPA-gluc was 65 pmol/ml. Application of the method to urine samples from human subjects (n = 6) after administration of 25 microg of BPA/person (estimated maximum human daily intake) permitted the determination of excretion kinetics for BPA-gluc; BPA was below the LOD in all except two of the samples. In urine or blood samples of human subjects (n = 19) without intentional exposure to BPA, BPA concentrations were always below the limit of detection ( approximately 2.5 pmol/ml) with or without prior glucuronidase treatment. The results show that care is required for analysis of BPA and its major metabolite BPA-gluc. The LOD obtained and the absence of detectable levels of BPA in samples from individuals suggests that general exposure of humans to BPA is much lower than the worst-case exposure scenario developed.

Bisphenol-A induces cell cycle delay and alters centrosome and spindle microtubular organization in oocytes during meiosis

Bisphenol-A (BPA) is a widely used environmental estrogen-like chemical that has a weak estrogenic activity. This study aimed to test the potential inhibitory effects of BPA on meiotic cell cycle progression, centrosomes and spindle integrity in mouse cumulus-oocyte complexes (COCs). They were exposed to BPA (10-30 microM; 2.3-6.8 ppm) during meiosis-I and the formation of metaphase-II (M-II) spindle. Exposure to BPA during meiosis-I caused a dose-dependent retardation/inhibition of cell cycle progression; 74 and 61% of cells reached metaphase-I (M-I) in the presence of 10 and 30 microM BPA, respectively, (81% in controls, P<0.001). A more striking delay was noted when oocytes were exposed to BPA during the formation of M-II spindle, i.e. 61 and 41% of cells (94% in controls, P<0.001) reached M-II while the remaining cells remained at M-I. Depending on dose, both (i) loosening and elongation of meiotic spindles and (ii) compaction and dispersion of pericentriolar material (PCM) were noted in all samples, all of which resulted in a series of spindle abnormalities. Interestingly, no chromosome was detected in the first polar body after the 10 and 30 microM BPA treatments. When the cells were freed from BPA exposure at 10 and 30 microM, 70 and 61%, of the cells succeeded in reaching M-II (93% in controls, P<0.001), respectively. In conclusion, one mode of action of BPA is a moderately severe yet reversible delay in the meiotic cell cycle, possibly by a mechanism that degrades centrosomal proteins and thus perturbs the spindle microtubule organization and chromosome segregation.

Salivary bisphenol-A levels detected by ELISA after restoration with composite resin

Bisphenol-A diglycidylether methacrylate (Bis-GMA), which is synthesized from bisphenol-A (BPA), a compound with exogenous endocrine disrupter action, is widely used as a dental material. During clinical filling with sealants and composite resins, the compounds are solidified by polymerization and then used. However, it has been noted that unpolymerized monomers may become dissolved in saliva. In this study using a competitive ELISA system, we investigated the changes in the BPA concentration in saliva after restoration with composite resins. Commercial composite resins from nine companies were tested. Mixed saliva was collected from 21 subjects. Based on the dynamics of salivary BPA detected by this ELISA system, we concluded that several tens to 100 ng/ml of BPA were contained in saliva after filling teeth with composite resin but that sufficient gargling can remove it from the oral cavity. Our data suggest that sufficient gargling after treatment is important for risk management.

Leached components from dental composites and their effects on fertility of female mice

This study investigated the effects of leached components from a resin-based dental composite (Z-100) and bisphenol A (BPA) on female mouse fertility. Leached components or BPA (5, 25 and 100 microg kg(-1)) were administered intragastrically daily to the test and distilled water to the control groups for 28 d. Female mice were then mated with sexually mature untreated males and their fertility was assessed. The results revealed a significant reduction in the number of pregnancies--54.5% vs. 100% (control)--in mice treated with the leached components from the dental composite, which also showed an increase of 142% in relative ovary weights. Exposure to 25 and 100 microg kg(-1) BPA resulted in significant increases in the total number of resorptions out of the total number of implantations and significant increases in relative uterine weights. Relative ovarian weights were significantly increased at the highest dose. High performance liquid chromatography analysis showed that tri-(ethylene glycol)-dimethacrylate (TEG-DMA) was the major leached component (total: 5945 microg ml(-1)) from the composite, followed by bisphenol A glycerolate dimethacrylate (BIS-GMA) (total: 2097 microg ml(-1)) and BPA (total: 78 microg ml(-1)). The results suggest that leached components from the dental composite used and commercially purchased BPA have adverse effects on the fertility and reproductive system of female mice.

Leachability of plasticizer and residual monomer from commercial temporary restorative resins

OBJECTIVES

This study was performed to determine the compositions of commercial temporary restorative resins and to evaluate the leachability of plasticizer and residual monomer from them.

METHODS

The chemicals in four commercial temporary restorative resins (Dura Seal, Fit Seal, Plast Seal Quick, and Poly Seal) were detected by GCMS and HPLC. The amounts of plasticizers and residual monomers that leached from cured resin samples immersed in ethanol for 1 h to 14 d were determined by HPLC.

RESULTS

Phthalate esters used as plasticizers contained 40-55 wt% either di-n-butyl phthalate (DBP) or butyl phthalyl butyl glycolate. The resin monomer included methyl methacrylate (MMA) or a mixture of MMA and 2-hydroxyethyl methacrylate (HEMA); 1,3-butanediol dimethacrylate was added as a cross-linking agent. Each resin contained 40-60 wt% monomer. The amounts of phthalate esters leached increased with immersion time up to 7 d, reaching 120-190 microg/mg, and did not change subsequently. The residual monomers leached gradually for up to 3d and did not change subsequently. The amount of leached residual monomer (MMA, HEMA) was 20-90 microg/mg after 3d storage. More than 50% of the leachable plasticizers and monomers were eluted from the cured resins within 24 and 3 h, respectively.

CONCLUSIONS

The amounts of leached plasticizers and residual monomers were extremely large compared with the concentrations of endocrine disrupters and their potentially genotoxic effects. Therefore, it is very important to evaluate the leachability of these compounds from temporary restorative resins.

Parent bisphenol A accumulation in the human maternal-fetal-placental unit

Bisphenol A (BPA), an endocrine disruptor, is employed in the manufacture of a wide range of consumer products. The suggestion that BPA, at amounts to which we are exposed, alters the reproductive organs of developing rodents has caused concern. At present, no information exists concerning the exposure of human pregnant women and their fetuses to BPA. We therefore investigated blood samples from mothers (n = 37) between weeks 32 and 41 of gestation. Afer the births, we also analyzed placental tissue and umbilical cord blood from the same subjects. We developed a novel chemical derivatization-gas chromatography/mass spectrometry method to analyze parent BPA at concentrations < 1 micro g/mL in plasma and tissues. Concentrations of BPA ranged from 0.3 to 18.9 ng/mL (median = 3.1 ng/mL) in maternal plasma, from 0.2 to 9.2 ng/mL (median = 2.3 ng/mL) in fetal plasma, and from 1.0 to 104.9 ng/g (median = 12.7 ng/g) in placental tissue. BPA blood concentrations were higher in male than in female fetuses. Here we demonstrate parent BPA in pregnant women and their fetuses. Exposure levels of parent BPA were found within a range typical of those used in recent animal studies and were shown to be toxic to reproductive organs of male and female offspring. We suggest that the range of BPA concentrations we measured may be related to sex differences in metabolization of parent BPA or variable maternal use of consumer products leaching BPA.

Effects of bisphenol A on adult male mouse fertility

The aim of this investigation was to evaluate the effect of bisphenol A (BPA), a contaminant of resin-based dental composites and sealants, on the fertility of male mice. Forty adult male Swiss mice were divided into four groups of 10. BPA (5, 25 and 100 micro g kg(-1) [corrected] was administered intragastrically daily to the mice in the test groups and distilled water to the control group for 28 d. Male fertility was assessed by mating each mouse with two untreated females. Females mated with male mice having ingested 25 and 100 micro g kg(-1) [corrected] BPA showed a significant reduction in pregnancy rates. Furthermore, the total number of resorptions out of the total number of implantations was significantly increased in females impregnated with males having ingested all three doses of BPA. Males having ingested 25 and 100 micro g kg(-1) [corrected] BPA showed a significant reduction in testicular sperm counts and in the efficiency of sperm production. Epididymal sperm counts were also significantly reduced in males that had ingested BPA. There were significant reductions in the absolute weights of the testes and seminal vesicles. These results suggest that male fertility and reproduction is impaired by bisphenol A.

Maternal-fetal disposition of bisphenol a in pregnant Sprague-Dawley rats

This study describes the maternal-fetal disposition of bisphenol A and its distribution into the placenta and amniotic fluid after iv injection (2 mg/kg) to pregnant Sprague-Dawley rats. Bisphenol A was distributed extensively to the placenta and fetus, with their respective AUC values 4.4- and 2.2-fold greater than AUC for the maternal serum. In contrast, the distribution of bisphenol A into the amniotic fluid was low, with the mean amniotic fluid-to-maternal serum AUC ratio of 0.2. The decay curves of bisphenol A in the placenta, fetus, and amniotic fluid paralleled that of the maternal serum during the terminal elimination phase. A five-compartment open model consisting of the maternal central, maternal peripheral, placental, fetal, and amniotic fluid compartments was used to describe the disposition of bisphenol A in pregnant rats, with the elimination occurring from the maternal central and fetal compartments. Based on this model, bisphenol A delivered to the placenta was transferred primarily to the fetus [kpf/(kpf + kpc + kpa) = 65.4 %], with the remaining fraction transported to the maternal central (33.2%) and amniotic fluid (1.4%) compartments. Bisphenol A was eliminated from the amniotic fluid by the fetal (63.9%) and placental (36.1%) routes. On the other hand, bisphenol A was eliminated from the fetus primarily by the placental route back to mother [kfp/(kfp + kfa + kfo) = 100%], with the amniotic route playing an insignificant role in fetal elimination. The percent contribution of the fetal elimination to the total elimination in the maternal-fetal unit was 0.0% [CLfoAUCfetus/(CLcoAUCmaternal serum + CLfoAUCfetus)]. The pharmacokinetic model used in this study provides insights into the routes of elimination of bisphenol A in the maternal-fetal rat upon maternal administration.

Stability of bisphenol A, triethylene-glycol dimethacrylate, and bisphenol A dimethacrylate in whole saliva

OBJECTIVES

This study investigated the stability of compounds of dental sealant materials in a salivary matrix.

METHODS

Various amounts of bisphenol A (BPA), bisphenol A dimethacrylate (BIS-DMA) or triethylene-glycol dimethacrylate (TEGDMA) were added to whole salivary samples, and stored at -70 degrees C or -20 degrees C for up to 4 months. In other experiments, four separate whole salivary or water samples with BIS-DMA (200 ng/ml) were incubated for 0, 1, 2, 4 or 24h at 37 degrees C. Levels of analytes were determined by capillary gas chromatography/mass spectrophotometry (GC/MS) and high-performance liquid chromatography (HPLC).

RESULTS

BPA was stable under all tested conditions. Samples originally containing BIS-DMA had high levels of BPA and almost no BIS-DMA after 4 months at -20 degrees C. Salivary samples incubated at 37 degrees C originally containing only BIS-DMA (200 ng/ml) demonstrated rapid decreases of BIS-DMA and increases of BPA. By 24h, the mean BIS-DMA concentration fell to 21.8 (25) ng/ml, while BPA increased to 100 (48) ng/ml. Only slight decreases in BIS-DMA and no BPA were present in the water samples incubated at 37 degrees C. BPA, BIS-DMA, and TEGDMA were stable if salivary samples were stored at -70 degrees C. Acidification of salivary samples prevented the breakdown of BIS-DMA.

SIGNIFICANCE

BIS-DMA is converted rapidly to BPA in the presence of whole saliva. This could account for the findings of BPA in clinical samples collected after the placement of certain sealant products. Decreasing salivary pH and temperature can slow this process and this method should be used for clinical studies of salivary BPA leached from restorative materials.

Elution of bisphenol-A from hemodialyzers consisting of polycarbonate and polysulfone resins

This study deals with bisphenol-A (BPA) analysis of the BPA-derived polymer pellets, polycarbonate (PC) and polysulfone (PS), and in the hemodialyzer casings made of PC, and the leaching of BPA from commercially available hemodialyzers into water and bovine serum, using HPLC, GC-MS, and LC-MS analyses, and NMR spectroscopy. Total contents of BPA in polymer pellets of each resin were 4.0 and 7.2 microg/g (PC) and 34.5 microg/g (PS). Amounts of BPA released from hemodialyzer PC casings lacking PS hollow-fiber were 11.7 and 13.7 ng/casing by water extraction, and 296 and 345 ng/casing by methanol extraction. On the other hand, BPA of 3.78 to 141.8 ng/module was recovered using water circulation of hemodialyzers, and 140.7 to 2,090 ng/module was detected when bovine serum was used as a circulation solvent. The elution profiles using various concentrations of ethanol/water mixtures indicated that a 17.2% (v/v) ethanol solution rather than bovine serum can be used as an extraction solvent, where a similar amount of BPA as with bovine serum circulation was eluted from the hemodialyzer. Thus, this solvent may be useful for evaluating BPA elution from hemodialyers under similar conditions to medical use.

TCE Meta-Analyses: Wartenberg et al.'s Response

Comments on Trichloroethylene and Cancer: Epidemiologic Evidence by Daniel Wartenberg, Daniel Reyner, and Cheryl Siegel Scott. Environ Health Perspect 108(suppl 2):161-176 (2000).