Perinatal 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure sensitizes offspring to angiotensin II-induced hypertension

Research progress on the correlation between gut microbiota and preeclampsia: microbiome changes, mechanisms and treatments

Preeclampsia is a specific disease during pregnancy and is a significant factor in the increased mortality in perinatal women. Gut microbiota, an intricate and abundant microbial community in the digestive tract, is crucial for host metabolism, immunity, and nutrient absorption. The onset and progression of preeclampsia are closely correlated with the changes in maternal gut microbiota. Research purpose was to compile the existing bits of present scientific data and to close the gap in the knowledge of changes in gut microbiota in preeclampsia and their association with preeclampsia. We searched studies from two electronic databases (PubMed and Web of Science) included from 2014 to 2023. This review is divided into three parts. In the first part, the author elaborates longitudinal differences of maternal gut microbiota during different gestation periods. In the second part, we discuss that gut microbiota can lead to the occurrence of preeclampsia by systemic immune response, influencing the release of active peptides, short-chain fatty acids, trimethylamine-N-oxide (TMAO) and other metabolites, vascular factors and Microorganism-immune axis. In the third part, we proposed that a high-fiber diet combined with drugs and microecological regulators may be therapeutic in enhancing or preventing the emergence and evolution of preeclampsia, which needs further exploration. Although the pathogenesis of preeclampsia is still nebulous and there is no clear and valid clinical treatment, our study provides new ideas for the pathogenesis, prevention and treatment of preeclampsia.

Developmental Exposure to Endocrine Disrupting Chemicals and Its Impact on Cardio-Metabolic-Renal Health

Developmental origin of health and disease postulates that the footprints of early life exposure are followed as an endowment of risk for adult diseases. Epidemiological and experimental evidence suggest that an adverse fetal environment can affect the health of offspring throughout their lifetime. Exposure to endocrine disrupting chemicals (EDCs) during fetal development can affect the hormone system homeostasis, resulting in a broad spectrum of adverse health outcomes. In the present review, we have described the effect of prenatal EDCs exposure on cardio-metabolic-renal health, using the available epidemiological and experimental evidence. We also discuss the potential mechanisms of their action, which include epigenetic changes, hormonal imprinting, loss of energy homeostasis, and metabolic perturbations. The effect of prenatal EDCs exposure on cardio-metabolic-renal health, which is a complex condition of an altered biological landscape, can be further examined in the case of other environmental stressors with a similar mode of action.

Prenatal exposure to propylparaben at human-relevant doses accelerates ovarian aging in adult mice

Embryonic exposure to environmental chemicals may result in specific chronic diseases in adulthood. Parabens, a type of environmental endocrine disruptors widely used in pharmaceuticals and cosmetics, have been shown to cause a decline in women's reproductive function. However, whether exposure to parabens during pregnancy also negatively affect the ovarian function of the female offspring in adulthood remains unclear. This study aims to investigate the effects of prenatal propylparaben (PrP) exposure on the ovarian function of adult mice aged 46 weeks, which is equivalent to the age of 40 years in women. Pregnant ICR mice were intraperitoneally injected with human-relevant doses of PrP (i.e., 0, 7.5, 90, and 450 mg/kg/day) during the fetal sex determination period-from embryonic day E7.5 to E13.5. Our results revealed that ovarian aging was accelerated in PrP-exposed mice at 46 weeks, with altered regularity of the estrous cycle, decreased serum estrogen (E2) and progesterone (P4) levels, reduced size of the primordial follicle pool, and increased number of atretic follicles. It was found that prenatal exposure to human-relevant doses of PrP exacerbated ovarian oxidative stress, inflammation, and fibrosis, which promoted follicular atresia by activating the mitochondrial apoptosis pathway. To compensate, the depletion of primordial follicles was also accelerated by activating the PI3K/AKT/mTOR signaling pathway in PrP-exposed mice. Moreover, PrP induced hypermethylation of CpG sites in the promoter region of Cyp11a1 (a 17.16-64.28% increase) partly led to the disrupted steroidogenesis, and the altered methylation levels of imprinted genes H19 and Peg3 may also contribute to the phenotypes observed. These remarkable findings highlight the embryonic origin of ovarian aging and suggest that a reduced use of PrP during pregnancy should be advocated.

Perinatal Resveratrol Therapy to Dioxin-Exposed Dams Prevents the Programming of Hypertension in Adult Rat Offspring

Exposure to environmental chemicals during pregnancy and lactation is a contributing factor in gut microbiota dysbiosis and linked to programming of hypertension. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic dioxin, induces toxic effects by mediating aryl hydrocarbon receptor (AHR). Resveratrol, a potent antioxidant with prebiotic properties, can possess high affinity for AHR and protect against TCDD-activated AHR attack. We examined whether perinatal resveratrol therapy prevents offspring hypertension programmed by maternal TCDD exposure and whether its beneficial effects are related to reshaping gut microbiota and antagonizing AHR-mediated T helper 17 (TH17) cells responses using a maternal TCDD exposure rat model. Pregnant Sprague-Dawley rats were given a weekly oral dose of TCDD 200 ng/kg for four doses (T), 50 mg/L of resveratrol in drinking water (CR), TCDD + resveratrol (TR), or vehicle (C) in pregnancy and lactation periods. Male offspring (n = 7–8/group) were sacrificed at the age of 12 weeks. Perinatal TCDD exposure caused elevated blood pressure in adult male offspring, which resveratrol supplementation prevented. Additionally, the TCDD-induced programming of hypertension is coincided with the activation of AHR signaling, TH17-induced renal inflammation, and alterations of gut microbiota compositions. Conversely, TCDD-mediated induction of AHR signaling and TH17 responses were restored by maternal resveratrol supplementation. Furthermore, maternal resveratrol supplementation prevented the programming of hypertension and was related to increased genera Bacteroides, ASF356, and Lachnoclostridium. Taken together, these results suggest that the interplay between gut microbiota, AHR-mediated TH17 responses, and renal inflammation in the gut and kidneys may play an important role in the action of resveratrol against TCDD-induced programming of hypertension.

Maternal 3,3-Dimethyl-1-Butanol Therapy Protects Adult Male Rat Offspring against Hypertension Programmed by Perinatal TCDD Exposure

Maternal exposure to environmental pollutants affects fetal development, which can result in hypertension in adulthood. Gut microbiota-derived metabolite trimethylamine (TMA), trimethylamine-N-oxide (TMAO), and short chain fatty acids (SCFAs) have been associated with hypertension. We tested a hypothesis that maternal 3,3-Dimethyl-1-butanol (DMB, a TMA inhibitor) therapy prevents 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure-induced hypertension in adult offspring relevant to alterations of gut microbiota-derived metabolites, the mediation of aryl hydrocarbon receptor (AHR) signaling, and the renin-angiotensin system (RAS). Pregnant Sprague-Dawley rats were given weekly oral dose of TCDD 200 ng/kg for four doses (T), 1% DMB in drinking water (D), TCDD + DMB (TD), or vehicle (C) in pregnancy and lactation periods. Male progeny (n = 8/group) were sacrificed at the age of 12 weeks. Perinatal TCDD exposure caused hypertension in adult male offspring coinciding with reduced α-diversity, increased the Firmicutes to Bacteroidetes ratio, less abundant beneficial bacteria, impaired SCFA receptors' expression, the activation of AHR signaling, and the aberrant activation of the RAS. Treatment with DMB during pregnancy and lactation rescued hypertension induced by perinatal TCDD exposure. This was accompanied by reshaping gut microbiota, mediating TMA-TMAO metabolic pathway, increasing acetic acid and its receptors, and restoring the AHR and RAS pathway. Our data provide new insights into the therapeutic potential of DMB, a microbiome-based metabolite treatment, for the prevention of hypertension of developmental origins.

Developmental and lifelong dioxin exposure induces measurable changes in cardiac structure and function in adulthood

Congenital heart disease (CHD) is the most common congenital abnormality. A precise etiology for CHD remains elusive, but likely results from interactions between genetic and environmental factors during development, when the heart adapts to physiological and pathophysiological conditions. Further, it has become clearer that early exposure to toxins that do not result in overt CHD may be associated with adverse cardiac outcomes that are not manifested until later life. Previously, interference with endogenous developmental functions of the aryl hydrocarbon receptor (AHR), either by gene ablation or by in utero exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent AHR ligand, was shown to cause structural, molecular and functional cardiac abnormalities and altered heart physiology in mouse embryos. Here, we show that continuous exposure to TCDD from fertilization throughout adulthood caused male mice to underperform at exercise tolerance tests compared to their control and female counterparts, confirming previous observations of a sexually dimorphic phenotype. Renin-angiotensin stimulation by angiotensin II (Ang II) caused measurable increases in blood pressure and left ventricle mass, along with decreased end diastolic volume and preserved ejection fraction. Interestingly, TCDD exposure caused measurable reductions in the myocardial hypertrophic effects of Ang II, suggesting that endogenous AHR signaling present in adulthood may play a role in the pathogenesis of hypertrophy. Overall, the findings reported in this pilot study highlight the complex systems underlying TCDD exposure in the development of cardiac dysfunction in later life.

AHR canonical pathway: in vivo findings to support novel antihypertensive strategies

Essential hypertension (HTN) is a disease where genetic and environmental factors interact to produce a high prevalent set of almost indistinguishable phenotypes. The weak definition of what is under the umbrella of HTN is a consequence of the lack of knowledge on the players involved in environment-gene interaction and their impact on blood pressure (BP) and mechanisms. The disclosure of these mechanisms that sense and (mal)adapt to toxic-environmental stimuli might at least determine some phenotypes of essential HTN and will have important therapeutic implications. In the present manuscript, we looked closer to the environmental sensor aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor involved in cardiovascular physiology, but better known by its involvement in biotransformation of xenobiotics through its canonical pathway. This review aims to disclose the contribution of the AHR-canonical pathway to HTN. For better mirror the complexity of the mechanisms involved in BP regulation, we privileged evidence from in vivo studies. Here we ascertained the level of available evidence and a comprehensive characterization of the AHR-related phenotype of HTN. We reviewed clinical and rodent studies on AHR-HTN genetic association and on AHR ligands and their impact on BP. We concluded that AHR is a druggable mechanistic linker of environmental exposure to HTN. We conclude that is worth to investigate the canonical pathway of AHR and the expression/polymorphisms of its related genes and/or other biomarkers (e.g. tryptophan-related ligands), in order to identify patients that may benefit from an AHR-centered antihypertensive treatment.

Targeting on Gut Microbiota-Derived Metabolite Trimethylamine to Protect Adult Male Rat Offspring against Hypertension Programmed by Combined Maternal High-Fructose Intake and Dioxin Exposure

Gut microbiota-dependent metabolites, in particular trimethylamine (TMA), are linked to hypertension. Maternal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure or consumption of food high in fructose (HFR) can induce hypertension in adult offspring. We examined whether 3,3-maternal dimethyl-1-butanol (DMB, an inhibitor of TMA formation) therapy can protect adult offspring against hypertension arising from combined HFR and TCDD exposure. Pregnant Sprague-Dawley rats received regular chow or chow supplemented with fructose (60% diet by weight) throughout pregnancy and lactation. Additionally, the pregnant dams received TCDD (200 ng/kg BW orally) or a corn oil vehicle on days 14 and 21 of gestation, and days 7 and 14 after birth. Some mother rats received 1% DMB in their drinking water throughout pregnancy and lactation. Six groups of male offspring were studied (n = 8 for each group): regular chow (CV), high-fructose diet (HFR), regular diet+TCDD exposure (CT), HFR+TCDD exposure (HRT), high-fructose diet+DMB treatment (HRD), and HFR+TCDD+DMB treatment (HRTD). Our data showed that TCDD exacerbates HFR-induced elevation of blood pressure in male adult offspring, which was prevented by maternal DMB administration. We observed that different maternal insults induced distinct enterotypes in adult offspring. The beneficial effects of DMB are related to alterations of gut microbiota, the increase in nitric oxide (NO) bioavailability, the balance of the renin-angiotensin system, and antagonization of aryl hydrocarbon receptor (AHR) signaling. Our findings cast new light on the role of early intervention targeting of the gut microbiota-dependent metabolite TMA, which may allow us to prevent the development of hypertension programmed by maternal excessive fructose intake and environmental dioxin exposure.

Review of the Effects of Perinatal Exposure to Endocrine-Disrupting Chemicals in Animals and Humans

Maternal exposure to endocrine-disrupting chemicals (EDCs) is associated with long-term hormone-dependent effects that are sometimes not revealed until maturity, middle age, or adulthood. The aim of this study was to conduct descriptive reviews on animal experimental and human epidemiological evidence of the adverse health effects of in utero and lactational exposure to selected EDCs on the first generation and subsequent generation of the exposed offspring. PubMed, Web of Science, and Toxline databases were searched for relevant human and experimental animal studies on 29 October 29 2018. Search results were screened for relevance, and studies that met the inclusion criteria were evaluated and qualitative data extracted for analysis. The search yielded 73 relevant human and 113 animal studies. Results from studies show that in utero and lactational exposure to EDCs is associated with impairment of reproductive, immunologic, metabolic, neurobehavioral, and growth physiology of the exposed offspring up to the fourth generation without additional exposure. Little convergence is seen between animal experiments and human studies in terms of the reported adverse health effects which might be associated with methodologic challenges across the studies. Based on the available animal and human evidence, in utero and lactational exposure to EDCs is detrimental to the offspring. However, more human studies are necessary to clarify the toxicological and pathophysiological mechanisms underlying these effects.

2,7-Dibromocarbazole interferes with tube formation in HUVECs by altering Ang2 promoter DNA methylation status

2,7-Dibromocarbazole (2,7-DBCZ) is one of the most frequently detected polyhalogenated carbazoles (PHCZs) in the environmental media. 2,7-DBCZ has attracted public attention for its potential for dioxin-like toxicity and cardiovascular toxicity. However, researches on the potential mechanism of angiogenesis inhibition by 2,7-DBCZ is still insufficient. Herein, human umbilical vein endothelial cells (HUVECs) were applied to explore the angiogenic effect of 2,7-DBCZ and the potential underlying mechanisms. 2,7-DBCZ significantly inhibited tube formation in HUVECs in the non-toxic concentration range. PCR array showed that 2,7-DBCZ reduced the expression proportion between VEGFs and Ang2, thereby inhibiting tube formation in HUVECs. Then, small RNA interference and DNA methylation assays were adopted to explore the potential mechanisms. It has been found that angiopoietin2 (Ang2)-silencing recovered the tube formation inhibited by 2,7-DBCZ. The DNA methylation status of Ang2 promoter also showed a demethylation tendency after exposure. In conclusion, 2,7-DBCZ could demethylate the Ang2 promoter to potentiate Ang2 expression, thus altering angiogenic phenotype of HUVECs by reducing the proportion between Ang2 and VEGFs. The data presented here can help to guide safety measures on the use of dioxin-like PHCZs for their potential adverse effects and provide a method for identifying the relevant biomarkers to assess their cardiovascular toxicity.

In utero dioxin exposure and cardiometabolic risk in the Seveso Second Generation Study

BACKGROUND/OBJECTIVES

In utero exposure to endocrine-disrupting compounds such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) may alter risk of obesity and related metabolic disease later in life. We examined the relationship of prenatal exposure to TCDD with obesity and metabolic syndrome (MetS) in children born to a unique cohort of TCDD-exposed women resulting from a 1976 explosion in Seveso, Italy.

SUBJECTS/METHODS

In 2014, nearly 40 years after the explosion, we enrolled 611 post-explosion offspring, 2 to 39 years of age, in the Seveso Second Generation Study. In utero TCDD exposure was defined primarily as TCDD concentration measured in maternal serum collected soon after the explosion and alternately as TCDD estimated at pregnancy. We measured height, weight, waist circumference, body fat, blood pressure, and fasting blood levels of lipids and glucose, which were combined to assess body mass index (BMI) and MetS.

RESULTS

Children (314 female, 297 male) averaged 23.6 (±6.0) years of age. Among the 431 children ≥18 years, a 10-fold increase in initial maternal TCDD concentration was inversely associated with BMI in daughters (adj-β = -0.99 kg/m2; 95% CI -1.86, -0.12), but not sons (adj-β = 0.41 kg/m2; 95% CI -0.35, 1.18) (p-int = 0.02). A similar relationship was found in the younger children (2-17 years); a 10-fold increase in initial maternal TCDD was inversely associated with BMI z-score (adj-β = -0.59 kg/m2; 95% CI -1.12, -0.06) among daughters, but not sons (adj-β = 0.04 kg/m2; 95% CI -0.34, 0.41) (p-int = 0.03). In contrast, in sons only, initial maternal TCDD was associated with increased risk for MetS (adj-RR = 2.09, 95% CI 1.09, 4.02). Results for TCDD estimated at pregnancy were comparable.

CONCLUSIONS

These results suggest prenatal TCDD exposure alters cardiometabolic endpoints in a sex-specific manner. In daughters, in utero TCDD is inversely associated with adiposity measures. In sons, in utero TCDD is associated with increased risk for MetS.

Maternal Resveratrol Therapy Protects Male Rat Offspring against Programmed Hypertension Induced by TCDD and Dexamethasone Exposures: Is It Relevant to Aryl Hydrocarbon Receptor?

Hypertension can originate from early-life adverse environmental in utero exposure to dexamethasone (DEX) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Since DEX and TCDD are related to the aryl hydrocarbon receptor (AHR) signaling pathway, we examined whether resveratrol, an AHR modulator and antioxidant, could prevent programmed hypertension via regulating AHR signaling and oxidative stress. Groups of four-month-old male rat offspring were studied (n = 7⁻8 per group): control, DEX (0.1 mg/kg i.p. from a gestational age of 16 to 22 days), TCDD (200 ng/kg in four once-weekly oral doses), DEX + TCDD, and DEX + TCDD + R (resveratrol 0.05% in drinking water throughout pregnancy and lactation). Maternal TCDD exposure aggravated prenatal DEX-induced hypertension in adult male offspring, which maternal resveratrol therapy prevented. Maternal TCDD exposure aggravated DEX-induced oxidative damage in offspring kidneys, which was prevented by resveratrol therapy. Maternal resveratrol therapy decreased asymmetric and symmetric dimethylarginine (ADMA and SDMA) levels, thereby preventing combined DEX and TCDD exposure-induced programmed hypertension. Increases in renal Ahrr and Cyp1a1 expression induced by DEX + TCDD exposure were restored by resveratrol therapy. The beneficial effects of resveratrol on DEX + TCDD-induced hypertension relate to reduced renal mRNA expression of Ren, Ace, and Agtr1a expression. Thus, the beneficial effects of resveratrol on DEX + TCDD-induced hypertension include reduction of oxidative stress, restoration of nitric oxide (NO) bioavailability, blockade of the renin⁻angiotensin system (RAS), and antagonizing AHR signaling pathway.

Persistent Organochlorine Pollutants in Plasma, Blood Pressure, and Hypertension in a Longitudinal Study

Persistent organochlorine pollutants (POPs) have shown to be involved in the atherosclerotic process and to cause endothelial cell dysfunction. To assess longitudinally whether plasma concentrations of different POPs were associated with blood pressure and risk of hypertension in middle-aged women and men. Study subjects were 850 participants in the VIP (Västerbotten Intervention Programme) with 2 blood samples and blood pressure measurements, 10 years apart, during 1990 to 2003 (baseline) and during 2000 to 2013 (follow-up). Dioxin-like and nondioxin-like polychlorinated biphenyls (DL-PCBs, NDL-PCBs) and p,p'-dichlorodiphenyldichloroethylene (DDE) were measured. Associations were assessed using generalized estimating equations. At baseline sampling 49% and at follow-up 64% had hypertension. DL-PCBs and DDE, but not NDL-PCBs or hexachlorobenzene, were associated with hypertension. Only the association for DL-PCBs remained statistically significant after lipid-standardization and adjustment for body mass index and total serum lipids. The multivariable-adjusted odds ratio of hypertension based on repeated measurements were 1.52 (95% confidence interval, 1.08-2.13) for DL-PCBs (third versus first tertile of lipid-standardized POPs). In stratified adjusted analyses, odds ratio for those born after 1950 increased to 3.99 (95% confidence interval, 2.15-7.43), whereas no association was observed among those born earlier. Based on repeated measurements, the accumulated exposure to DL-PCBs and DDE, although less clear for the latter, may disrupt the normal blood pressure levels and increase the odds of hypertension. Moreover, individuals experiencing early-life POP exposure may be at elevated risk of vascular POP effects.

Relationship between serum trimethylamine N-oxide and exposure to dioxin-like pollutants

Trimethylamine N-oxide (TMAO) is a diet and gut microbiota-derived metabolite that has been linked to cardiovascular disease risk in human studies and animal models. TMAO levels show wide inter and intra individual variability in humans that can likely be accounted for by multiple factors including diet, the gut microbiota, levels of the TMAO generating liver enzyme Flavin-containing monooxygenase 3 (FMO3) and kidney function. We recently found that dioxin-like (DL) environmental pollutants increased FMO3 expression to elevate circulating diet-derived TMAO in mice, suggesting that exposure to this class of pollutants might also contribute to inter-individual variability in circulating TMAO levels in humans. To begin to explore this possibility we examined the relationship between body burden of DL pollutants (reported by serum lipid concentrations) and serum TMAO levels (n = 340) in the Anniston, AL cohort, which was highly exposed to polychlorinated biphenyls (PCBs). TMAO concentrations in archived serum samples from the Anniston Community Health Survey (ACHS-II) were measured, and associations of TMAO with 28 indices of pollutant body burden, including total dioxins toxic equivalent (TEQ), were quantified. Twenty-three (22 after adjustment for multiple comparisons) of the 28 indices were significantly positively associated with TMAO. Although the design of ACHS-II does not enable quantitative assessment of the contributions of previously known determinants of TMAO variability to this relationship, limited multivariate modeling revealed that total dioxins TEQ was significantly associated with TMAO among females (except at high BMIs) but not among males. Our results from this cross-sectional study indicate that exposure to DL pollutants may contribute to elevated serum TMAO levels. Prospective longitudinal studies will be required to assess the joint relationship between DL pollutant exposures, other determinants of TMAO, and health outcomes.

Chronic cardiovascular disease-associated gene network analysis in human umbilical vein endothelial cells exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The association of dioxin exposure with increased morbidity or mortality of chronic cardiovascular diseases (CVDs) has been established by many epidemiological studies. However, the precise global gene expression alterations caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the cardiovascular system need to be further elucidated. In this study, we profiled the gene expression of human umbilical vein endothelial cells (HUVECs) exposed to different concentrations of TCDD by high-throughput sequencing. Expression of 1,838 genes was changed significantly after TCDD stimulation. The FunDO analysis suggested that some CVDs were highly associated with TCDD treatment, including atherosclerosis, thromboangiitis obliterans, pulmonary arterial hypertension (PAH), and hypertension. KEGG pathway analysis showed that many genes in the signaling pathways of vascular smooth muscle contraction and apoptosis were altered distinctly. In addition, we revealed evidence regarding the gene network changes of chronic CVDs including atherosclerosis, thrombosis, myocardial infarction (MI), hypertension, and PAH in TCDD-exposed HUVECs. We found that gene expression of β1-adrenoceptors (ADRB1), β2-adrenoceptors (ADRB2), endothelin-converting enzyme 1 (ECE1), and endothelin-1 gene (EDN1) that are involved in the blood pressure regulation pathway decreased apparently under TCDD treatment. Moreover, the transcripts of interleukin 1 beta (IL-1β) and tumor necrosis factor α (TNFα), which are related to atherosclerosis, were up-regulated by TCDD stimulation. In addition, the transcripts of Homo sapiens collagen, type IV, alpha 1 (COL4A1), and isoforms that trigger the MI pathway were up-regulated after TCDD exposure. Finally, we found enhanced platelet-derived growth factor (PDGF) and signal transducer and activator of transcription 5 (Stat5) expression with TCDD treatment in endothelial cells, which are involved in PAH induced by vascular injury.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Oxidative status in the macula densa modulates tubuloglomerular feedback responsiveness in angiotensin II-induced hypertension

AIM

Tubuloglomerular feedback (TGF) is an important mechanism in control of signal nephron glomerular filtration rate. The oxidative stress in the macula densa, primarily determined by the interactions between nitric oxide (NO) and superoxide (O2-), is essential in maintaining the TGF responsiveness. However, few studies examining the interactions between and amount of NO and O2- generated by the macula densa during normal and hypertensive states.

METHODS

In this study, we used isolated perfused juxtaglomerular apparatus to directly measure the amount and also studied the interactions between NO and O2- in macula densa in both physiological and slow pressor Angiotensin II (Ang II)-induced hypertensive mice.

RESULTS

We found that slow pressor Ang II at a dose of 600 ng kg(-1) min(-1) for two weeks increased mean arterial pressure by 26.1 ± 5.7 mmHg. TGF response increased from 3.4 ± 0.2 μm in control to 5.2 ± 0.2 μm in hypertensive mice. We first measured O2- generation by the macula densa and found it was undetectable in control mice. However, O2- generation by the macula densa increased to 21.4 ± 2.5 unit min(-1) in Ang II-induced hypertensive mice. We then measured NO generation and found that NO generation by the macula densa was 138.5 ± 9.3 unit min(-1) in control mice. The NO was undetectable in the macula densa in hypertensive mice infused with Ang II.

CONCLUSIONS

Under physiological conditions, TGF response is mainly controlled by the NO generated in the macula densa; in Ang II induced hypertension, the TGF response is mainly controlled by the O2- generated by the macula densa.

Circulating levels of p,p'-DDE are related to prevalent hypertension in the elderly

BACKGROUND

Polychlorinated biphenyls (PCBs) and dioxin given to experimental animals increase the blood pressure. We therefore investigated if circulating levels of persistent organic pollutants (POPs) were related to hypertension in a population-based sample of men and women.

METHODS

One thousand and sixteen subjects aged 70 years were investigated in the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. Twenty-three POPs were analyzed using high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). Hypertension was defined as a systolic blood pressure ≥140mmHg or a diastolic blood pressure ≥90mmHg, and/or use of antihypertensive medication.

RESULTS

Seven hundred and thirty-two subjects (72%) showed hypertension. When the POPs were treated as continuous variables and adjusted for gender only, two PCBs with a low number of chlorine atoms (PCB 105 and 118) were related to prevalent hypertension. Also the OC pesticide p,p'-DDE was related to hypertension. The strongest of these associations was seen for p,p'-DDE (OR 1.35 for a 1 SD change, 95% CI 1.17-1.56, p<0.0001). Following further adjustment also for BMI, smoking status, education level and exercise habits, only p,p'-DDE was still significantly related to hypertension (OR 1.23 for a 1 SD change, 95% CI 1.06-1.43, p=0.006).

CONCLUSION

In this cross-sectional analysis of an elderly population, high levels of circulating levels of p,p'-DDE were associated with prevalent hypertension, further strengthening the experimental findings that POPs might influence blood pressure.

Enhanced expression and activity of Nox2 and Nox4 in the macula densa in ANG II-induced hypertensive mice

NAD(P)H oxidase (Nox)2 and Nox4 are the isoforms of Nox expressed in the macula densa (MD). MD-derived superoxide (O₂⁻), primarily generated by Nox2, is enhanced by acute ANG II stimulation. However, the effects of chronic elevations in ANG II during ANG II-induced hypertension on MD-derived O₂⁻ are unknown. We infused a slow pressor dose of ANG II (600 ng·min⁻¹·kg⁻¹) for 2 wk in C57BL/6 mice and found that mean arterial pressure was elevated by 22.3 ± 3.4 mmHg (P < 0.01). We measured O₂⁻ generation in isolated and perfused MDs and found that O₂⁻ generation by the MD was increased from 9.4 ± 0.9 U/min in control mice to 34.7 ± 1.8 U/min in ANG II-induced hypertensive mice (P < 0.01). We stimulated MMDD1 cells, a MD-like cell line, with ANG II and found that O₂⁻ generation increased from 921 ± 91 to 3,687 ± 183 U·min⁻¹·10⁵ cells⁻¹, which was inhibited with apocynin, oxypurinol, or NS-398 by 46%, 14%, and 12%, respectively. We isolated MD cells using laser capture microdissection and measured mRNA levels of Nox. Nox2 and Nox4 levels increased by 3.7 ± 0.17- and 2.6 ± 0.15-fold in ANG II-infused mice compared with control mice. In MMDD1 cells treated with Nox2 or Nox4 small interfering (si)RNAs, ANG II-stimulated O₂⁻ generation was blunted by 50% and 41%, respectively. In cells treated with p22(phox) siRNA, ANG II-stimulated O₂⁻ generation was completely blocked. In conclusion, we found that a subpressor dose of ANG II enhances O₂⁻ generation in the MD and that the sources of this O₂⁻ are primarily Nox2 and Nox4.

Development of cardiac hypertrophy by sunitinib in vivo and in vitro rat cardiomyocytes is influenced by the aryl hydrocarbon receptor signaling pathway

Sunitinib (SUN) is a new tyrosine kinase inhibitor that possesses both anti-angiogenic and anti-tumor activities. Although SUN has improved survival rate in cancer patients, cardiotoxicity has been reported as a significant side effect. Several studies suggested a role for the aryl hydrocarbon receptor (AhR) and its regulated genes such as cytochrome P4501A1 (CYP1A1) in the pathogenesis of heart failure and cardiac hypertrophy. To test the hypothesis that SUN induces cardiac hypertrophy through the modulation of AhR, Wistar albino rats were treated for 15 and 30 days with increasing doses of SUN (25, 50, and 100 mg/kg), whereas at the in vitro level, rat cardiomyocyte H9c2 cells were incubated with SUN (1, 2.5, and 5 μM). Thereafter, cardiac hypertrophy parameters were determined at the biochemical, histopathology, and gene expression levels. SUN treatment causes increase in cardiac enzymes, changes in histopathology, and induction in several hypertrophic markers. This was associated with proportional increase in the CYP1A1 gene in a concentration- and time-dependent manner. The direct involvement of AhR in the SUN-induced cardiac hypertrophy in H9c2 cells was supported by the ability of resveratrol, an AhR antagonist, to block the SUN-induced hypertrophy and the ability of SB203580, a novel AhR agonist, to potentiate SUN-induced hypertrophic genes. This is the first demonstration that SUN induces hypertrophic genes in vivo and in vitro rat cardiomyocyte through AhR/CYP1A1-mediated mechanism.

Can persistent organic pollutants and plastic-associated chemicals cause cardiovascular disease?

During the last decade, associations between persistent organic pollutants (POPs), such as polychlorinated biphenyls, dioxins and pesticides, and cardiovascular (CV) risk factors and overt CV disease (CVD) have been reported in humans. Recently, associations between plastic-associated chemicals (PACs), such as bisphenol A and phthalates, and CVD have also begun to emerge. Several approaches to evaluating such associations have been used: accidents with a high level of exposure, occupational exposure studies, geographical studies of subjects living near a contaminated area and traditional case-control or cohort studies with measurements of circulating levels of different environmental contaminants in the general population. Exposure to POPs has consistently been associated with diabetes using all the approaches described above, including prospective studies. The evidence regarding associations between exposure to POPs and other CV risk factors, such as hypertension, obesity and lipids, is less strong and is mainly based on cross-sectional data. Associations between overt CVD and POPs have been reported using all the above approaches, but prospective data from population-based studies are still lacking to provide firm evidence of an important and independent role of POP exposure in the pathogenesis of CVD. Nevertheless, taken together, current evidence suggests that further longitudinal and experimental studies should be conducted to investigate the effect of exposure to both POPs and PACs, such as bisphenol A and phthalates.

In utero exposure to benzo(a)pyrene predisposes offspring to cardiovascular dysfunction in later-life

In utero exposure of the fetus to benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon, is thought to dysregulate cardiovascular development. To investigate the effects of in utero B(a)P exposure on cardiovascular development, timed-pregnant Long Evans Hooded (LEH) rats were exposed to diluent or B(a)P (150, 300, 600 and 1200 μg/kg/BW) by oral gavage on embryonic (E) days E14 (the metamorphosing embryo stage) through E17 (the 1st fetal stage). There were no significant effects of in utero exposure to B(a)P on the number of pups born per litter or in pre-weaning growth curves. Pre-weaning profiles for B(a)P metabolite generation from cardiovascular tissue were shown to be dose-dependent and elimination of these metabolites was shown to be time-dependent in exposed offspring. Systolic blood pressure on postnatal day P53 in the middle and high exposure groups of offspring were significantly elevated as compared to controls. Microarray and quantitative real-time PCR results were directly relevant to a biological process pathway in animal models for "regulation of blood pressure". Microarray and quantitative real-time PCR analysis revealed upregulation of mRNA expression for angiotensin (AngII), angiotensinogen (AGT) and endothelial nitric oxide synthase (eNOS) in exposed offspring. Biological network analysis and gene set enrichment analysis subsequently identified potential signaling mechanisms and molecular pathways that might explain the elevated systolic blood pressures observed in B(a)P-exposed offspring. Our findings suggest that in utero exposure to B(a)P predispose offspring to functional deficits in cardiovascular development that may contribute to cardiovascular dysfunction in later life.

Impact of 2,3,7,8-tetrachlorodibenzo-p-dioxin on cutaneous wound healing

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a representative of a large group of polyhalogenated aromatic hydrocarbons that are widespread environmental contaminants. Administration of TCDD to laboratory animals or cultured cells results in a number of adverse effects that are well documented. For example, the effects of TCDD observed in developing organisms indicate that exposure to this class of environmental contaminants significantly alters embryo morphogenesis. However, it is not clear whether tissue regeneration in adult animals may be similarly affected. With this in mind, we examined the impact of TCDD exposure on wound healing using a murine cutaneous wound healing model. Our results indicate that TCDD exposure did not significantly alter the time needed for wound closure. However, in the TCDD-treated mice, a significant decrease in tensile strength in the healed wounds was observed which is indicative of an aberrantly healed wound. Immunostaining revealed that exposure to TCDD increased the population of macrophages detected within the wounded tissue at the latter stages of wound healing. Our findings support the idea that exposure to environmental contaminants such as TCDD is proinflammatory in the wounded tissue, disrupts normal healing and ultimately produces in a poorly healed wound.

Endothelial cell-specific aryl hydrocarbon receptor knockout mice exhibit hypotension mediated, in part, by an attenuated angiotensin II responsiveness

Hypotension in aryl hydrocarbon receptor knockout mice (ahr(-/-)) is mediated, in part, by a reduced contribution of angiotensin (Ang) II to basal blood pressure (BP). Since AHR is highly expressed in endothelial cells (EC), we hypothesized that EC-specific ahr(-/-) (ECahr(-/-)) mice would exhibit a similar phenotype. We generated ECahr(-/-) mice by crossing AHR floxed mice (ahr(fx/fx)) to mice expressing Cre recombinase driven by an EC-specific promoter. BP was assessed by radiotelemetry prior to and following an acute injection of Ang II or chronic treatment with an angiotensin converting enzyme inhibitor (ACEi). ECahr(-/-) mice were hypotensive (ECahr(+/+): 116.1±1.4; ECahr(-/-): 107.4±2.0 mmHg, n=11, p<0.05) and exhibited significantly different responses to Ang II and ACEi. While Ang II increased BP in both genotypes, the increase was sustained in ECahr(+/+), whereas the increase in ECahr(-/-) mice steadily declined. Area under the curve analysis showed that Ang II-induced increase in diastolic BP (DBP) over 30 min was significantly lower in ECahr(-/-) mice (ECahr(+/+) 1297±223 mmHg/30 min; ECahr(-/-)(AUC): 504±138 mmHg/30 min, p<0.05). In contrast, while ACEi decreased BP in both genotypes, the subsequent rise in DBP after treatment was significantly delayed in the ECahr(-/-) mice. ECahr(-/-) mice also exhibited reduced vascular and adipose Ang II type 1 receptor (AT1R) expression, and reduced aortic Ang II-dependent vasoconstriction in the presence of vascular adipose. Taken together these data suggest that hypotension in ECahr(-/-) mice results from reduced vascular responsiveness to Ang II that is influenced by AT1R expression and adipose.

2,3,7,8-Tetrachlorodibenzo-p-dioxin and beta-naphthoflavone induce cellular hypertrophy in H9c2 cells by an aryl hydrocarbon receptor-dependant mechanism

Cigarette smoke is a major risk factor for cardiovascular diseases. It contains thousands of compounds that activate the aryl hydrocarbon receptor (AhR). In addition, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most potent AhR ligand, has been shown to cause cardiotoxic effects in several in vivo models. Although induction of CYP1 family is the most important effect of AhR activation, the role of CYP1 induction in mediating the cardiotoxic effect of TCDD is usually overlooked. Therefore, we investigated whether AhR activation causes a hypertrophic effect in H9c2 cells and we related this effect to changes in CYP gene expression. In the current study, the cardiac derived H9c2 cells were treated with two AhR ligands, TCDD and beta-naphthoflavone (BNF), for 24 and 48h. The expression of the hypertrophic markers, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), and several CYP genes were measured by real-time PCR. Treatment of H9c2 cells with TCDD or BNF for 24h caused a significant induction of CYP1A1, CYP1B1, and CYP4A1; however, there was no change in the expression of other genes. On the other hand, treatment of the cells with TCDD or BNF for 48h caused a significant induction of the hypertrophic markers, ANP and BNP, and several CYP genes such as CYP1A1, CYP1B1, CYP2E1, CYP2J3, and CYP4F4 parallel to a significant increase in the cell surface area. Neither TCDD nor BNF increased the oxidative stress in H9c2 cells at all concentrations tested. Interestingly, resveratrol, an AhR antagonist, protected the cells from TCDD-induced hypertrophy. In conclusion, AhR ligands caused a hypertrophic effect in H9c2 cells which was associated with induction of several CYP genes which can be prevented by resveratrol.

Overview of developmental heart defects by dioxins, PCBs, and pesticides

The developing cardiovascular system is a sensitive target of many environmental pollutants, including dioxins, dioxin-like polychlorinated biphenyls (PCBs), and some pesticides such as methyl parathion. Laboratory research has utilized a variety of vertebrate models to elucidate potential mechanisms that mediate this cardioteratogenicity and to establish the sensitivity of different species for predicting potential risk to environmental and human health. Studies of dioxin and dioxin-like PCBs have illustrated that piscine, avian, and mammalian embryos exhibit cardiovascular structural changes and functional deficits, although the specific characteristics vary among the individual models. Piscine models typically exhibit reduced blood flow, altered heart looping, and reduced heart size and contraction rate. The chick embryo exhibits extensive cardiac dilation, thinner ventricle walls, and reduced responsiveness to chronotropic stimuli, while the murine embryo exhibits reduced heart size. It is notable that in all models the dioxin-associated cardioteratogenicity is associated with increases in cardiovascular apoptosis and decreases in cardiocyte proliferation. While the cardiotertogenicity in piscine and avian species is associated with overt morbidity and mortality, that is not the case for the murine embryo. However, murine offspring exposed during development to dioxin exhibit cardiac hypertrophy and an increased sensitivity to a second cardiovascular insult in adulthood. Thus, although the mammalian embryo is less sensitive to cardiovascular defects by dioxin and dioxin-like compounds, developmental exposure increases the risk of cardiovascular disease later in life. The impact of developmental exposure to dioxin-like chemicals on human cardiovascular disease susceptibility is not known. However, recent animal research has confirmed human epidemiology studies that dioxin exposure in adulthood is associated with hypertension and cardiovascular disease.