Beta-adrenergic receptor density and adenylate cyclase activity in lead-exposed rat brain after cessation of lead exposure

Early-life low-level lead exposure alters anxiety-like behavior, voluntary alcohol consumption and AC5 protein content in adult male and female C57BL/6 J mice

Despite efforts to eradicate sources of environmental lead (Pb), children, predominately in lower socioeconomic areas, are still frequently exposed to unsafe levels of Pb from soils, dust, and water. Human studies suggest that Pb exposure is associated with altered drug consumption in adults; however, there is limited research at comparable exposure levels (blood Pb levels <10 μg/dL). To model how early-life, low-level Pb exposure affects alcohol consumption in adulthood, we exposed postnatal day (PND) 21 C57Bl/6 J mice to either 30 ppm or 0 ppm Lead (IV) Acetate in distilled water until PND 42, and testing began in adulthood. We predicted that mice with early-life Pb exposure would exhibit greater anxiety-like behavior and consume more alcohol in a three-week Drinking-in-the-Dark procedure (20% v/v) and a 24-h two-bottle choice procedure (10% v/v). We also predicted that Pb exposure would decrease whole-brain content of Adenylate Cyclase-5 (AC5), a protein linked to anxiety-like behaviors and alcohol drinking. There was no difference in limited-access binge-like consumption between exposure groups; however, Pb-exposed mice displayed higher two-bottle choice alcohol intake and preference. Furthermore, Pb-exposed mice exhibited greater anxiety-like behaviors in experiments conducted before an alcohol drinking history but not after. Finally, Pb-exposed mice exhibited an upregulation of whole-brain AC5 protein content. However, this difference was not found in the nucleus accumbens, dorsomedial or dorsolateral striatum. These findings conclude that early-life Pb exposure alters voluntary alcohol consumption and whole-brain AC5 protein content in adulthood. Future studies are necessary to further understand the mechanism behind how Pb exposure alters alcohol intake.

Two-Year Responses of Heart Rate and Heart Rate Variability to First Occupational Lead Exposure

[Figure: see text].

Heart rate variability and peripheral nerve conduction velocity in relation to blood lead in newly hired lead workers

OBJECTIVES

Previous studies relating nervous activity to blood lead (BL) levels have limited relevance, because over time environmental and occupational exposure substantially dropped. We investigated the association of heart rate variability (HRV) and median nerve conduction velocity (NCV) with BL using the baseline measurements collected in the Study for Promotion of Health in Recycling Lead (NCT02243904).

METHODS

In 328 newly hired men (mean age 28.3 years; participation rate 82.7%), we derived HRV measures (power expressed in normalised units (nu) in the high-frequency (HF) and low-frequency (LF) domains, and LF/HF) prior to long-term occupational lead exposure. Five-minute ECG recordings, obtained in the supine and standing positions, were analysed by Fourier transform or autoregressive modelling, using Cardiax software. Motor NCV was measured at the median nerve by a handheld device (Brevio Nerve Conduction Monitoring System, NeuMed, West Trenton, NJ, USA). BL was determined by inductively coupled plasma mass spectrometry.

RESULTS

Mean BL was 4.54 µg/dL (IQR 2.60-8.90 µg/dL). Mean supine and standing values of LF, HF and LF/HF were 50.5 and 21.1 nu and 2.63, and 59.7 and 10.9 nu and 6.31, respectively. Orthostatic stress decreased HF and increased LF (p<0.001). NCV averaged 3.74 m/s. Analyses across thirds of the BL distribution and multivariable-adjusted regression analyses failed to demonstrate any association of HRV or NCV with BL.

CONCLUSIONS

At the exposure levels observed in our study, autonomous nervous activity and NCV were not associated with BL.

TRIAL REGISTRATION NUMBER

NCT02243904.

Lead Inhibits Human Sperm Functions by Reducing the Levels of Intracellular Calcium, cAMP, and Tyrosine Phosphorylation

It is well known that there has been a worldwide decrease in human male fertility in recent years. One of the main factors affecting this is environmental pollution. Lead is one of the major heavy metal contaminants that threaten the health of animals and human beings in China. It preferentially accumulates in male reproductive organs and can be up to 10 µM in human seminal plasma. Lead impairs mammalian spermatogenesis and sperm quality in vivo. It also inhibits sperm functions in vitro but the underlying mechanisms remain unclear. Therefore, we aimed to investigate the in vitro toxicity of lead on human sperm functions and to elucidate the underlying mechanisms. Semen samples were collected from 20 healthy volunteers with different careers and backgrounds living in Nanchang, Jiangxi. Human sperm suspensions were treated with different concentrations of lead acetate (0, 0.5, 2.5, 10, 50, and 100 µM) and the viability, motility, capacitation and progesterone-induced acrosome reaction were examined. Treatment with 10-100 µM lead acetate dose-dependently inhibited total and progressive motility measures, capacitation and progesterone-induced acrosome reaction. It also dose-dependently decreased the intracellular concentrations of cyclic adenosine monophosphate (cAMP) and calcium ([Ca(2+)]i), and reduced the tyrosine phosphorylation of sperm proteins, all of which are thought to be key factors in the regulation of sperm function. Our findings suggest that lead inhibits human sperm functions by reducing the levels of sperm intracellular cAMP, [Ca(2+)]i and tyrosine phosphorylation of sperm proteins in vitro.

Blood Lead Below 0.48 μmol/L (10 μg/dL) and Mortality Among US Adults

Background— Blood lead levels above 0.48 μmol/L (10 μg/dL) in adults have been associated with increased risk of cardiovascular, cancer, and all-cause mortality. The objective of the present study was to determine the association between blood lead levels below 0.48 μmol/L and mortality in the general US population.

Methods and Results— Blood lead levels were measured in a nationally representative sample of 13 946 adult participants of the Third National Health and Nutrition Examination Survey recruited in 1988 to 1994 and followed up for up to 12 years for all-cause and cause-specific mortality. The geometric mean blood lead level in study participants was 0.12 μmol/L (2.58 μg/dL). After multivariate adjustment, the hazard ratios (95% CI) for comparisons of participants in the highest tertile of blood lead (≥0.17 μmol/L [≥3.62 μg/dL]) with those in the lowest tertile (<0.09 μmol/L [<1.94 μg/dL]) were 1.25 (1.04 to 1.51; P trend across tertiles=0.002) for all-cause mortality and 1.55 (1.08 to 2.24; P trend across tertiles=0.003) for cardiovascular mortality. Blood lead level was significantly associated with both myocardial infarction and stroke mortality, and the association was evident at levels >0.10 μmol/L (≥2 μg/dL). There was no association between blood lead and cancer mortality in this range of exposure.

Conclusions— The association between blood lead levels and increased all-cause and cardiovascular mortality was observed at substantially lower blood lead levels than previously reported. Despite the marked decrease in blood lead levels over the past 3 decades, environmental lead exposures remain a significant determinant of cardiovascular mortality in the general population, constituting a major public health problem.