Lead exposure effect on angiotensin II renal vasoconstriction

Perfluoroalkyl substances (PFAS) and lead (Pb) as "cardiovascular disruptors" in 9-11-year-old children living in Syracuse, New York, United States

OBJECTIVE

Per- and polyfluoro-alkyl substances (PFAS) and lead (Pb) are ubiquitous environmental toxicants with apparent impact on cardiovascular disease (CVD) risk. As one possible mechanism for this increased risk, we have previously demonstrated an association between Pb exposure and heightened cardiovascular reactivity to acute psychological stress, a CVD risk factor. The present study expands this approach and considers both PFAS and Pb exposures (and the possible interaction).

METHODS

We assessed 14 serum PFAS and whole blood Pb concentrations in a sample of 9-11 year-old children (N = 291; 43.2% White, 56.8% Black; 53.5% female). We measured cardiovascular functioning at rest and during psychological stress as well as multiple indicators of subclinical CVD including resting blood pressure (BP), carotid-femoral pulse wave velocity (cfPWV), carotid intima-media thickness (cIMT), and left ventricular mass (LVM). Data analysis included general linear modeling as well as a non-parametric approach to study metal mixtures, specifically Bayesian Kernel Machine Regression (BKMR).

RESULTS

Significant interactions between different PFAS and with Pb suggest the importance of considering toxicant mixtures when assessing potential disruption of the cardiovascular system. The pattern of findings suggests that greater "vascular reactivity" (elevated BP and vascular resistance during acute psychological stress) was associated with higher concentrations of perfluorononanoic acid (PFNA), perfluorohexane sulfonate (PFHxS), and Pb, but only when perfluorooctanoic acid (PFOA) was concurrently elevated. With respect to subclinical outcomes, increasing perfluorodecanoic acid (PFDA) was associated with greater cIMT (β = 0.21, p = 0.010).

CONCLUSION

To our knowledge this is the first study to consider how PFAS exposures might affect cardiovascular functioning and subclinical disease. Although a complex pattern of associations emerged, it does appear that PFAS and Pb can be classified as "cardiovascular disruptors" in children. Further research is needed to replicate these novel findings and determine whether these disruptions produce future cardiovascular disease.

Increased endothelial nitric oxide production after low level lead exposure in rats involves activation of angiotensin II receptors and PI3K/Akt pathway

BACKGROUND

Lead induces endothelial dysfunction and hypertension in humans and animals. Seven-day exposure to a low dose in rats reduces vasocontractile responses and increases nitric oxide (NO) bioavailability. We hypothesized that this occurs by angiotensin II receptors (AT1/AT2) activation.

MATERIALS AND RESULTS

Wistar rats were exposed to lead acetate (1 st dose 4 μg/100 g, subsequent dose 0.05 μg/100 g/day i.m., 7 days) or saline (control group). Lead acetate exposure reduced the phenylephrine vascular response. Pre-incubations with NO synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) or phosphatidylinositol 3-kinase (PI3K) inhibitor (wortmannin) increased the contractile response in aortas from lead-treated rats. Pre-incubation with AT2 antagonist (PD123319) restored normal vascular contraction, and both PD123319 or AT1 antagonist (losartan) impeded the potentiated effects of L-NAME and wortmannin. Reinforcing those findings, increased NO bioavailability was blunted by AT1 and AT2 antagonists without summative effect when co-incubated. Finally, to test whether activation of AT1 could upregulate AT2 to increase NO bioavailability rats were simultaneously exposed to lead acetate and treated with losartan (15 mg/kg/day, orally given). Losartan prevented changes on vascular reactivity and endothelial modulation in lead-exposed group. Moreover, incubation with PD123319 had no more effects in aortic from losartan-treated rats.

CONCLUSION

Our results suggest that low-dose lead acetate exposure induces an increase of NO involving mainly AT2 receptor activation and the PI3K/Protein Kinase B (PI3K/Akt) pathway. Additionally, we suggest that AT1 activation plays a role in AT2 upregulation, probably as a protective mechanism. Altogether, these effects might contribute to preserving endothelial function against the harmful effects by lead in the vascular system.

Effect of LA on the Growth and Development of the Main Organs in Female Mice

Effects of lead acetate (LA) on the growth and development of major organs in female mice were studied. Female mice were divided randomly into four treatment groups and one control group. In treatment groups, mice were injected with different concentrations of LA solution every 2 days; whereas control-group mice received equal volumes of sterile normal saline. Body weight (BW) and symptoms were recorded every 2 days. After LA exposure, mice were executed by cervical dislocation and main organs (heart, liver, spleen, lung, kidney) collected for evaluation of morphologic and histologic changes. LA could greatly affect increases in BW, and BW decreased with increasing dose and time of exposure to LA. Compared with the control group, organ coefficients in treatment groups were of the order kidney and spleen > liver and lung > heart and demonstrated obvious dose-time effects. LA exposure could damage the heart, liver, spleen, lung, and kidney. Damage to the kidney and spleen was the most severe, followed by that to the liver, heart, and lung. Damage was aggravated with increasing doses and exposure time to LA in an obvious dose-time relationship; when LA dose was ≥20 mg/kg, the growth and development of mice were obviously inhibited. These results suggest that long-term exposure to low-dose LA can result in universal pathologic damage to mouse organs and that severity is dependent on the dose and duration of LA exposure.

Centrally acting drug moxonidine decreases reactive oxygen species via inactivation of the phosphoinositide-3 kinase signaling in the rostral ventrolateral medulla in hypertensive rats

OBJECTIVE

Centrally acting antihypertensive action of moxonidine is a result of activation of Imidazoline-1 receptor (I1R) in the rostral ventrolateral medulla (RVLM). Hypertension shows an increase in reactive oxygen species (ROS) in the RVLM. The present objective was to determine the phosphoinositide-3 kinase (PI3K) signaling pathway involved in the effect of moxonidine on ROS generation in the RVLM of spontaneously hypertensive rat (SHR).

METHODS

Wistar-Kyoto rats and SHR received intracisternal infusion (2 weeks) of tested agents which were subjected to subsequent experiments. In-situ ROS in the RVLM was evaluated by the oxidative fluorescence dye. Western blot and PCR analysis were performed to detect the expression levels of PI3K signaling pathway. Lentivirus was injected bilaterally into the RVLM for silencing PI3K signaling.

RESULTS

ROS production in the RVLM was dose-dependently reduced in SHRs treated with infusion of moxonidine (20 nmol/day), which was prevented by the I1R antagonist efaroxan but not by the α2-adrenoceptor antagonist yohimbine. Moxonidine pretreatment significantly blunted cardiovascular sensitivity to injection of tempol (5 nmol) or angiotensin II (10 pmol) into the RVLM in SHR. Expression levels of PI3K/Akt, nuclear factor kappa-B (NFκB), NADPHase (NOX4), and angiotensin type I receptor (AT1R) in the RVLM were markedly decreased in SHR treated with moxonidine. Infection of lentivirus containing PI3K shRNA in the RVLM effectively prevented effects of moxonidine on cardiovascular activity and expression levels of Akt, NFκB, NOX4, and AT1R.

CONCLUSION

The centrally antihypertensive drug moxonidine decreases ROS production in the RVLM through inactivation of the PI3K/Akt signaling pathway in hypertension.

Associations of blood heavy metal levels with intraocular pressure

PURPOSE

Whether or which blood heavy metal levels (BHMLs) influence elevating intraocular pressure (IOP) are unknown. We examined the relationship among blood lead, mercury, and cadmium levels, blood pressure (BP), and IOP and assessed whether BP mediates these BHMLs-IOP associations.

METHODS

We analyzed data on 8371 adult (≥20 years) from the Korea National Health and Nutrition Examination Survey from 2008 to 2012. Mediation analysis was used to examine the contribution of BP to the BHMLs-IOP relationship.

RESULTS

IOP and three BHMLs were significantly associated with systolic and diastolic BP. But IOP was associated with only blood lead and mercury levels. BP significantly mediated lead-IOP and mercury-IOP associations: BP accounted for 20.5% and 14.2% of the association with IOP. Blood lead and mercury levels were significantly associated with IOP.

CONCLUSIONS

BP significantly mediates the effects of those blood lead and mercury levels on IOP outcome. Prospective studies are needed to further examine the causal pathway from BHMLs to IOP elevation.

Exercise Training Improves the Altered Renin-Angiotensin System in the Rostral Ventrolateral Medulla of Hypertensive Rats

The imbalance between angiotensin II (Ang II) and angiotensin 1-7 (Ang 1-7) in the brain has been reported to contribute to cardiovascular dysfunction in hypertension. Exercise training (ExT) is beneficial to hypertension and the mechanism is unclear. This study was aimed to determine if ExT improves hypertension via adjusting renin angiotensin system in cardiovascular centers including the rostral ventrolateral medulla (RVLM). Spontaneously hypertensive rats (SHR, 8 weeks old) were subjected to low-intensity ExT or kept sedentary (Sed) for 12 weeks. Blood pressure elevation coupled with increase in age was significantly decreased in SHR received ExT compared with Sed. The results in vivo showed that ExT significantly reduced or increased the cardiovascular responses to central application of sarthran (antagonist of Ang II) or A779 (antagonist of Ang 1-7), respectively. The protein expression of the Ang II acting receptor AT1R and the Ang 1-7 acting receptor Mas in the RVLM was significantly reduced and elevated in SHR following ExT, respectively. Moreover, production of reactive oxygen species in the RVLM was significantly decreased in SHR following ExT. The current data suggest that ExT improves hypertension via improving the balance of Ang II and Ang 1-7 and antioxidative stress at the level of RVLM.

Lead Induces Apoptosis and Histone Hyperacetylation in Rat Cardiovascular Tissues

Acute and chronic lead (Pb) exposure might cause hypertension and cardiovascular diseases. The purpose of this study was to evaluate the effects of early acute exposure to Pb on the cellular morphology, apoptosis, and proliferation in rats and to elucidate the early mechanisms involved in the development of Pb-induced hypertension. Very young Sprague-Dawley rats were allowed to drink 1% Pb acetate for 12 and 40 days. Western blot analysis indicated that the expression of proliferating cell nuclear antigen (PCNA) decreased in the tissues of the abdominal and thoracic aortas and increased in the cardiac tissue after 12 and 40 days of Pb exposure, respectively. Bax was upregulated and Bcl-2 was downregulated in vascular and cardiac tissues after 40 days of Pb exposure. In addition, an increase in caspase-3 activity was observed after 40 days of exposure to Pb. In terms of morphology, we found that the internal elastic lamina (IEL) of aorta lost the original curve and the diameter of cardiac cell was enlarged after 40 days. Furthermore, the exposure led to a marked increase in acetylated histone H3 levels in the aortas and cardiac tissue after 12 and 40 days, than that in the control group. These findings indicate that Pb might increase the level of histone acetylation and induce apoptosis in vascular and cardiac tissues. However, the mechanism involved need to be further investigated.

Cardiovascular responses to lead are biphasic, while methylmercury, but not inorganic mercury, monotonically increases blood pressure in rats

Cardiovascular diseases, such as heart attack and stroke, are the major cause of death worldwide. It is well known that a high number of environmental and physiological risk factors contribute to the development of cardiovascular diseases. Although risk factors are additive, increased blood pressure (hypertension) is the greatest risk factor. Over the last two decades, a growing number of epidemiological studies associate environmental exposure to lead or mercury species with hypertension. However, cardiovascular effects beyond blood pressure are rarely studied and thresholds for effect are not yet clear. To explore effects of lead or mercury species on the cardiovascular system, normal male Wistar rats were exposed to a range of doses of lead, inorganic mercury or methylmercury through the drinking water for four weeks. High-resolution ultrasound was used to measure heart and vascular function (carotid artery blood flow) at baseline and at the end of the exposure, while blood pressure was measured directly in the femoral artery at the end of the 4-week exposure. After 4 weeks, blood pressure responses to lead were biphasic. Low lead levels decreased blood pressure, dilated the carotid artery and increased cardiac output. At higher lead doses, rats had increased blood pressure. In contrast, methylmercury-exposed rats had increased blood pressure at all doses despite dilated carotid arteries. Inorganic mercury did not show any significant cardiovascular effects. Based on the current study, the benchmark dose level 10% (BMDL10s) for systolic blood pressure for lead, inorganic mercury and methylmercury are 1.1, 1.3 and 1.0 μg/kg-bw/d, respectively. However, similar total mercury blood levels attributed to inorganic mercury or methylmercury produced strikingly different results with inorganic mercury having no observable effect on the cardiovascular system but methylmercury increasing systolic and pulse pressures. Therefore, adverse cardiovascular effects cannot be predicted by total blood mercury level alone and the mercury species of exposure must be taken into account.

Modified natural clinoptilolite detoxifies small mammal's organism loaded with lead I. Lead disposition and kinetic model for lead bioaccumulation

Zeolites, especially clinoptilolites, have wide application in removing heavy metals from different solutions and wastewater. The detoxification capacity of the clinoptilolite sorbent KLS-10-MA, a modified natural Bulgarian zeolite, applied as a food supplement in conditions of an ecotoxicological experiment with conventional food and lead was demonstrated for the first time. Laboratory mice, inbred imprinting control region strain, were used in a 90-day ecotoxicological experiment. Animals were divided into four experimental groups. Lead bioaccumulations in exposed and non-supplemented/supplemented with KLS-10-MA animals were compared. As additional control, healthy animals non-exposed to Pb were fed with conventional forage mixed with 12.5% KLS-10-MA. The dietary inclusion of the sorbent reduced Pb concentrations in exposed and supplemented mice by 84%, 89%, 91%, 77%, and 88% in carcass, liver, kidneys, bones, and feces, respectively. A mathematical model was proposed to outline the common trends of bone Pb bioaccumulation in exposed and non-supplemented/supplemented animals. Characteristic parameters of the kinetics of Pb concentrations were determined. Based on the model, the coefficient of absorption of Pb by gastrointestinal mucosa in the supplemented mice was found-η = 3.53% (versus η = 15% in non-supplemented ones). The present study clearly indicates that there is a realistic perspective to create a new drug based on modified natural clinoptilolites in cases of chronic heavy metal intoxication, without negatively affecting the environment.

Modified natural clinoptilolite detoxifies small mammal's organism loaded with lead II: genetic, cell, and physiological effects

The detoxification capacity of the clinoptilolite modification KLS-10-MA used as food additive in small mammals, chronically lead-exposed, was proven for the first time. The modified clinoptilolite was prepared based on natural Bulgarian clinoptilolite deposits. As a powder, it was mechanically mixed at 12.5% concentration with the conventional forage for small rodents. Lead in the form of aqueous solution of Pb(NO(3))(2) was diluted in the drinking water. In the ecotoxicological experiment covering 90 days, imprinting control region laboratory mice were used. They were allocated into four groups: group 1, (control): animals fed with conventional food for small rodents and water; group 2: animals fed with conventional food + clinosorbent KLS-10-MA and water; group 3: animals fed with conventional food and water + Pb(NO(3))(2); and group 4: animals fed with conventional food + KLS-10-MA and water + Pb(NO(3))(2). A group of non-exposed healthy animals was fed with conventional forage mixed with KLS-10-MA to prove eventual toxicity of the sorbent and influence on growth performance. The changes in the chromosome structure, mitotic index, erythrocyte form, erythropoiesis, and body weight gain were recorded. On day 90, the following relations were established: Pb-exposed and clinoptilolite-supplemented mice exhibited 2.3-fold lower chromosome aberrations frequency, 2.5-fold higher mitotic index, and 1.5-fold higher percentage normal erythrocytes 1.3-fold higher body weight compared to Pb-exposed and unsupplemented animals. The obtained data showed that the sorbent is practically non-toxic. The results of the present study encourage a further elaboration of a reliable drug based on the tested substance in the cases of chronic lead intoxication.

Hydroethidine- and MitoSOX-derived red fluorescence is not a reliable indicator of intracellular superoxide formation: another inconvenient truth

Hydroethidine (HE; or dihydroethidium) is the most popular fluorogenic probe used for detecting intracellular superoxide radical anion. The reaction between superoxide and HE generates a highly specific red fluorescent product, 2-hydroxyethidium (2-OH-E(+)). In biological systems, another red fluorescent product, ethidium, is also formed, usually at a much higher concentration than 2-OH-E(+). In this article, we review the methods to selectively detect the superoxide-specific product (2-OH-E(+)) and the factors affecting its levels in cellular and biological systems. The most important conclusion of this review is that it is nearly impossible to assess the intracellular levels of the superoxide-specific product, 2-OH-E(+), using confocal microscopy or other fluorescence-based microscopic assays and that it is essential to measure by HPLC the intracellular HE and other oxidation products of HE, in addition to 2-OH-E(+), to fully understand the origin of red fluorescence. The chemical reactivity of mitochondria-targeted hydroethidine (Mito-HE, MitoSOX red) with superoxide is similar to the reactivity of HE with superoxide, and therefore, all of the limitations attributed to the HE assay are applicable to Mito-HE (or MitoSOX) as well.