In 2007, a group of experts critically analyzed hundreds of publications on bisphenol A (BPA), including the evidence for low dose effects. Here, we have updated these evaluations to determine the strength of the evidence for low dose effects of BPA. Based on the cut-offs for “low doses” established previously (i.e., the lowest observed adverse effect level [LOAEL], or 50 mg/kg/day for mammalian studies), we identified more than 450 low dose studies. Using an integrative approach, we examined five endpoints in depth that had evidence from two or more study types (in vitro, in vivo laboratory animal, and human). Based on all available studies, we are confident that consistent, reproducible, low dose effects have been demonstrated for BPA. We conclude that the doses that reliably produce effects in animals are 1–4 magnitudes of order lower than the current LOAEL of 50 mg/kg/day and many should be considered adverse.

Bisphenol A (BPA) is a ubiquitous plasticizing agent used in the manufacturing of polycarbonate plastics and epoxy resins. There is well-documented and broad human exposure to BPA. The potential risk that BPA poses to the human health has attracted much attention from regulatory agencies and the general public, and has been extensively studied. An emerging and rapidly growing area in the study of BPA’s toxicity is its impact on the cardiovascular (CV) system. Recent epidemiological studies have shown that higher urinary BPA concentration in humans is associated with various types of CV diseases, including angina, hypertension, heart attack and coronary and peripheral arterial disease. Experimental studies have demonstrated that acute BPA exposure promotes the development of arrhythmias in female rodent hearts. Chronic exposure to BPA has been shown to result in cardiac remodeling, atherosclerosis, and altered blood pressure in rodents. The underlying mechanisms may involve alteration of cardiac Ca²⁺ handling, ion channel inhibition/activation, oxidative stress, and genome/transcriptome modifications. In this review, we discuss these recent findings that point to the potential CV toxicity of BPA, and highlight the knowledge gaps in this growing research area.

There is wide-spread human exposure to bisphenol A (BPA), a ubiquitous estrogenic endocrine disruptor that has been implicated as having potentially harmful effects on human heart health. Higher urine BPA concentrations have been shown to be associated with cardiovascular diseases in humans. However, neither the nature nor the mechanism(s) of BPA action on the heart are understood. The rapid (<7 min) effects of BPA and 17β-estradiol (E2) in the heart and ventricular myocytes from rodents were investigated in the present study. In isolated ventricular myocytes from young adult females, but not males, physiological concentrations of BPA or E2 (10⁻⁹ M) rapidly induced arrhythmogenic triggered activities. The effects of BPA were particularly pronounced when combined with estradiol. Under conditions of catecholamine stimulation, E2 and BPA promoted ventricular arrhythmias in female, but not male, hearts. The cellular mechanism of the female-specific pro-arrhythmic effects of BPA and E2 were investigated. Exposure to E2 and/or BPA rapidly altered myocyte Ca²⁺ handling; in particular, estrogens markedly increased sarcoplasmic reticulum (SR) Ca²⁺ leak, and increased SR Ca²⁺ load. Ryanodine (10⁻⁷ M) inhibition of SR Ca²⁺ leak suppressed estrogen-induced triggered activities. The rapid response of female myocytes to estrogens was abolished in an estrogen receptor (ER) β knockout mouse model. Physiologically-relevant concentrations of BPA and E2 promote arrhythmias in a female-specific manner in rat hearts; the pro-arrhythmic actions of estrogens are mediated by ERβ-signaling through alterations of myocyte Ca²⁺ handling, particularly increases in SR Ca²⁺ leak. Our study provides the first experimental evidence suggesting that exposure to estrogenic endocrine disrupting chemicals and the unique sensitivity of female hearts to estrogens may play a role in arrhythmogenesis in the female heart.

Previously we showed that 17β-estradiol (E₂) and/or the xenoestrogen bisphenol A (BPA) alter ventricular myocyte Ca²⁺ handing, resulting in increased cardiac arrhythmias in a female-specific manner. In the present study, the roles of estrogen receptors (ER) in mediating the rapid contractile and arrhythmogenic effects of estrogens were examined. Contractility was used as an index to assess the impact of E₂ or BPA on Ca²⁺ handling in rodent ventricular myocytes. The concentration-response curve for the stimulatory effects of BPA and E₂ on female myocyte was inverted-U shaped. Detectable effects for each compound were observed at 10⁻¹²m, and the most efficacious concentrations for each were at 10⁻⁹m. Sensitivity to E₂ and BPA was not observed in male myocytes and was abolished in myocytes from ovariectomized females. Analysis using protein-conjugated E₂ suggests that these rapid actions are induced by membrane-associated receptors. Analysis using selective ER agonists and antagonists and a genetic ERβ knockout mouse model showed that ERα and ERβ have opposing actions in myocytes and that the balance between ERβ and ERα signaling is the prime regulator of the sex-specific sensitivity toward estrogens. The response of female myocytes to E₂ and BPA is dominated by the stimulatory ERβ-mediated signaling, and the absence of BPA and E₂ responsiveness in males is due to a counterbalancing-suppressive action of ERα. We conclude that the sex-specific sensitivity of myocytes to estrogens and the rapid arrhythmogenic effects of BPA and estradiol in the female heart are regulated by the balance between ERα and ERβ signaling.

Background: The need for mechanistic understanding of nonmonotonic dose responses has been identified as one of the major data gaps in the study of bisphenol A (BPA). Previously we reported that acute exposure to BPA promotes arrhythmogenesis in female hearts through alteration of myocyte Ca2+ handling, and that the dose response of BPA was inverted U-shaped. Objective: We sought to define the cellular mechanism underlying the nonmonotonic dose response of BPA in the heart. Methods: We examined rapid effects of BPA in female rat ventricular myocytes using video-edge detection, confocal and conventional fluorescence imaging, and patch clamp. Results: The rapid effects of BPA in cardiac myocytes, as measured by multiple end points, including development of arrhythmic activities, myocyte mechanics, and Ca2+ transient, were characterized by nonmonotonic dose responses. Interestingly, the effects of BPA on individual processes of myocyte Ca2+ handling were monotonic. Over the concentration range of 10–12 to 10–6 M, BPA progressively increased sarcoplasmic reticulum (SR) Ca2+ release and Ca2+ reuptake and inhibited the L-type Ca2+ current (ICaL). These effects on myocyte Ca2+ handling were mediated by estrogen receptor (ER) β signaling. The nonmonotonic dose responses of BPA can be accounted for by the combined effects of progressively increased SR Ca2+ reuptake/release and decreased Ca2+ influx through ICaL. Conclusion: The rapid effects of BPA on female rat cardiac myocytes are characterized by nonmonotonic dose responses as measured by multiple end points. The nonmonotonic dose response was produced by ERβ-mediated monotonic effects on multiple cellular Ca2+ handling processes. This represents a distinct mechanism underlying the nonmonotonicity of BPA’s actions. Citation: Liang Q, Gao X, Chen Y, Hong K, Wang HS. 2014. Cellular mechanism of the nonmonotonic dose response of bisphenol A in rat cardiac myocytes. Environ Health Perspect 122:601–608; http://dx.doi.org/10.1289/ehp.1307491

Transmural electrical dispersion determines the repolarization sequence across the ventricular wall, and plays an important role in the development of arrhythmias under pathological conditions. While it is clear that the transmural gradient of the transient outward current (I_to) underlies the dramatic difference in phase 1 repolarization across the ventricle, its contribution to the transmural action potential duration (APD) dispersion is not clear. We investigated this problem using the dynamic clamp technique in canine ventricular myocytes. The dynamic clamp allows quantitative ‘insertion’ of simulated conductances in real, biological cells, bridging pure computer modelling and experimental electrophysiology. ‘Insertion’ of an epicardial level of I_to in endocardial cells produced a prominent phase 1 repolarization and a ‘spike‐and‐dome’ action potential morphology, but did not significantly affect the APD. Increasingly larger I_to densities prolonged, and then dramatically shortened the endocardial APD. We also used the dynamic clamp to subtract, or ‘block’ the native I_to in epicardial cells. Such ‘blockade’ eliminated the epicardial action potential notch, but had no significant effect on the APD. We conclude that I_to, while being a key regulator of phase 1 repolarization, does not significantly affect the APD of canine ventricular myocytes, and that the I_to gradient is not a significant contributor to the transmural APD dispersion in the canine ventricle. By allowing computer simulation on a biological background, the dynamic clamp is a new and effective tool to study the ionic basis of the electrical properties of cardiac cells.