Hypertension is still a global health issue despite recent advances in pharmacotherapies. Hypertension originates from adverse environmental exposures in early life, formally known as the developmental origins of health and disease (DOHaD) [1
]. Exposures to environmental chemicals, such as endocrine disrupting chemicals (EDCs), during development can increase the risk of cardiovascular disease later in life [2
]. A meta-analysis study of 11 articles reported that EDCs, especially dioxin-related compounds, are associated with the risk of hypertension [3
]. In utero exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic member of EDCs, has been reported to increase the vulnerability of offspring to developing hypertension in adulthood [4
Exposure of the fetus to increased levels of glucocorticoids, resulting from maternal stress or treatment with synthetic glucocorticoids, can cause long-term programmed changes in later life [5
]. We previously reported that prenatal exposure to dexamethasone (DEX), a widely used synthetic glucocorticoid, induced programmed hypertension in adult offspring [6
]. Glucocorticoids have been found to influence the metabolic pathway of TCDD [8
]. On the other hand, both glucocorticoids and TCDD can activate the aryl hydrocarbon receptor (AHR) signaling pathway [9
]. AHR is known to be associated with many different disorders, including hypertension [10
]. Progression in the development of hypertension in adulthood can occur with multiple sequential hits. Since each hit induced by prenatal DEX or TCDD exposure may act synergistically to deteriorate programming effects induced by each other, and because DEX and TCDD are closely linked to the AHR pathway, we postulate that maternal TCDD exposure could promote deleterious effects on prenatal DEX-induced renal programming and hypertension in adult offspring via the mediation of the AHR pathway in this two-hit model.
The kidney is a major organ responsible for blood pressure (BP) control. The developing kidney is vulnerable to adverse early-life environments, which causes long-term morphological and functional changes, namely in renal programming [11
]. Some particular mechanisms, such as nitric oxide (NO) deficiency, oxidative stress, and activation of the renin–angiotensin system (RAS), have been studied in terms of renal programming [11
]. Notably, that AHR pathway has been reported to interact with oxidative stress [14
] and the RAS [15
], two central mechanisms underlying hypertension, to affect BP. However, whether the above-mentioned mechanisms interrelate to induce hypertension of developmental origins in this two-hit model remain unclear.
Under the DOHaD concept, there may be potential for reprogramming strategies aimed at reversing the programming processes, even before the onset of clinical symptoms, and to thereby shift therapeutic interventions from adulthood to early life [16
]. Resveratrol, a natural phytoalexin, has therapeutic potential with a wide range of beneficial effects [17
]. Our recent reports demonstrated that resveratrol prevents hypertension of developmental origins induced by combined pre- and post-natal high-fat diets [18
]. Given that resveratrol is considered as an AHR modulator [19
] and an antioxidant, we thus examined whether maternal resveratrol treatment can protect offspring against combined TCDD and DEX exposure-induced hypertension of developmental origins via the regulation of oxidative stress, NO, RAS, and the AHR signaling pathway.
Given the fact that pregnant women have been increasingly exposed to a growing number of environmental stresses and chemicals in the modern world, our study provides novel insights into the beneficial effects of maternal resveratrol treatment of hypertension induced by developmental exposure to TCDD and DEX through mediation of NO, RAS, and the AHR pathway. The major findings are as follows. (1) Maternal TCDD exposure exacerbates prenatal DEX-induced hypertension in adult male offspring; (2) maternal resveratrol therapy prevents combined DEX and TCDD exposure-induced programmed hypertension, which is related to decreased ADMA and SDMA levels; (3) maternal TCDD exposure aggravates DEX-induced oxidative damage in offspring kidneys, which resveratrol therapy prevented; and (4) the beneficial effects of resveratrol on DEX + TCDD-induced hypertension relates to reduced renal mRNA expression of Ahrr, Ren, Ace, and Agtr1a expression.
Our data are in agreement with previous studies showing that early exposure to either TCDD or DEX increases the vulnerability of offspring to hypertension in later life [4
]. To our knowledge, this study is the first to show that prenatal DEX and maternal TCDD exposure synergistically induced programmed hypertension in male adult offspring. Our results demonstrated that there was a tendency for combined DEX and TCDD to cause a decrease in BW in adult offspring, despite not reaching statistical significance. Similar to our previous reports [6
], prenatal DEX exposure had no effect on adult offspring’s BW. Whether combined DEX and TCDD exposure causes a negative effect on BW in adult offspring requires further evaluation.
Consistent with a number of recent studies which support the importance of oxidative stress relative to programmed hypertension [11
], our data demonstrate that maternal exposure to DEX and TCDD induces oxidative stress and hypertension concurrently. TCDD has been reported to increase BP via increased renal oxidative stress in adult rats [19
]. Our observations provide further evidence that a combination of TCDD and DEX exposure has a synergistic effect on oxidative stress damage. It is possible that a greater degree of oxidative stress contributes to an exacerbation of programmed hypertension.
Oxidative stress is an oxidative shift characterized by dysregulation of NO and reactive oxygen species (ROS). ADMA is considered a major player in causing a NO–ROS imbalance [21
]. The data presented here show that a combination of TCDD and DEX exposure induces an increase in ADMA and SDMA levels and a decrease in the l
-arginine-to-ADMA ratio. Like ADMA, SDMA can inhibit NO production [22
]. Since the l
-arginine-to-ADMA ratio has been used to represent NO bioavailability [23
], our findings imply that combined TCDD and DEX exposure increases ADMA and SDMA, consequently decreasing NO bioavailability, and may be a major mechanism underlying hypertension of developmental origins.
In addition to their effects on oxidative stress, combined TCDD and DEX exposure were also found to activate the RAS. The classical RAS, defined as the ACE-angiotensin (Ang) II-AT1R axis, promotes vasoconstriction and sodium retention, leading to hypertension. In agreement with a previous study showing that perinatal TCDD exposure increases the susceptibility of offspring to Ang II-induced hypertension [4
], we observed that hypertension induced by TCDD exposure related to increased renal Ace
mRNA expression. Consistent with growing evidence that early blockade of RAS in young offspring protects against the development of hypertension [24
], the data presented here support the view that maternal resveratrol therapy reduces renal Ren
, and Agtr1a
expression and thereby blocks the RAS to provide protection against the development of hypertension.
Resveratrol, a natural phytoalexin, has found uses in a broad spectrum of clinical applications, including in the treatment of hypertension [25
]. It has been used to prevent detrimental effects induced by developmental exposure to TCDD [26
]. However, little is known about the protective effects of maternal resveratrol treatment of hypertension induced by in utero TCDD exposure. Our recent report showed that resveratrol prevents hypertension of developmental origins induced by combined pre- and post-natal high-fat consumption via medication of oxidative stress, NO, and the RAS [18
]. This notion is corroborated by our current study, suggesting that the protective effects of maternal resveratrol treatment on DEX + TCDD-induced hypertension are related to a reduction of oxidative stress, increased NO bioavailability, and a blockade of the RAS.
An additional protective mechanism of resveratrol on programmed hypertension in this two-hit model may be related to mediation of the AHR signaling pathway. AHR signaling can be activated by exogenous ligand TCDD to target AHR gene expression, such as Ahrr
]. Significantly increased mRNA expression of Ahrr
in the kidneys of TCDD-exposed rats indicates AHR activation, which appears to be crucial in BP control [10
]. Conversely, increases in renal Ahrr
expression induced by DEX + TCDD exposure were restored by resveratrol therapy. Although glucocorticoid has been reported to induce AHR and its target genes in adult rats [9
], this notion is not supported by the present observations, which showed that prenatal DEX exposure had no effect on the AHR signaling pathway in offspring. These and previous observations suggest that resveratrol may act as an AHR antagonist and inhibit TCDD-induced AHR target gene expression [19
]. As such, whether other AHR antagonists can provide a therapeutic approach to prevent hypertension of developmental origins requires further study and clarification.
Our study has a few limitations worth noting. Although we focus on the kidney in the present study, the protective effect of resveratrol may be attributed to other organs that control BP, such as the vasculature, the heart, and the brain. Additionally, whether NO deficiency, oxidative stress, activation of the RAS, and AHR signaling in other organs and tissues contribute to programmed hypertension requires further clarification. Secondly, we restricted resveratrol therapy to the DEX + TCDD group because resveratrol has no effect on BP in normotensive controls [28
] and the effect of resveratrol therapy on TCDD-exposed offspring has been studied [26
]. Moreover, previous studies in humans have already shown that the bioavailability of resveratrol after oral intake is rather low [29
]. The development of resveratrol formulations with better biotransformation and pharmacologic properties is still a challenging task for clinical translation in the future. Lastly, we did not explore different doses or exposure times for TCDD; given that most exposures are polychemical and dose-dependent, programming effects may vary during different types of developmental exposures.
To summarize, TCDD exposure exacerbates prenatal DEX-induced hypertension of developmental origins in adult male offspring. Several important mechanisms by which maternal resveratrol therapy protects offspring against combined TCDD and DEX exposure-induced programmed hypertension reduce oxidative stress, increase NO bioavailability, block the RAS, and antagonize AHR signaling. It is clear that a better understanding of the types of chemicals, exposure doses, critical windows, and therapeutic durations for reprogramming interventions are required to help pregnant women and their children against increasing environmental stresses and chemicals.