Lead increases inositol 1,4,5-trisphosphate levels but does not interfere with calcium transients in primary rat astrocytes

Lead (Pb) Exposure Enhances Expression of Factors Associated with Inflammation

The human immune system is constantly exposed to xenobiotics and pathogens from the environment. Although the mechanisms underlying their influence have already been at least partially recognized, the effects of some factors, such as lead (Pb), still need to be clarified. The results of many studies indicate that Pb has a negative effect on the immune system, and in our review, we summarize the most recent evidence that Pb can promote inflammatory response. We also discuss possible molecular and biochemical mechanisms of its proinflammatory action, including the influence of Pb on cytokine metabolism (interleukins IL-2, IL-4, IL-8, IL-1b, IL-6), interferon gamma (IFNγ), and tumor necrosis factor alpha (TNF-α); the activity and expression of enzymes involved in the inflammatory process (cyclooxygenases); and the effect on selected acute phase proteins: C-reactive protein (CRP), haptoglobin, and ceruloplasmin. We also discuss the influence of Pb on the immune system cells (T and B lymphocytes, macrophages, Langerhans cells) and the secretion of IgA, IgE, IgG, histamine, and endothelin.

Assessment of soil lead exposure in children in Shenyang, China

Soil lead pollution is serious in Shenyang, China. The paper brings together the soil work, the bioaccessibility, and the blood lead data to assess the soil lead exposure in children in Shenyang, China. Approximately 15.25% of the samples were above China Environment Protection Agency guideline concentration for soil Pb to protect human from health risk (350 mgkg(-1)). Pb concentrations varied among use scenarios. The main lead contamination sources are industry emission and automobile exhaust. Bioaccessibility also varied among use scenarios. Children, who ingested soil from industrial area, public parks, kindergarten playground, and commercial area, are more susceptible to soil lead toxicity. The industrial area soil samples presented higher bioaccessibility compared to the other use scenario soil samples contaminated by automobile exhaust. The result also suggested a most significant linear relationship between the level of Pb contamination and the amount of Pb mobilized from soil into ingestion juice. Soil pH seemed to have insignificant influence on bioaccessibility in the present study. Bioaccessibility was mainly controlled by other factors that are not investigated in this study. A linear relationship between children blood lead and soil intestinal bioaccessibility was present in the study. Children who are 4-5 years old are more likely to demonstrate the significant relationship between soil lead bioaccessibility and blood lead as their behaviors place them at greatest risk of soil lead toxicity, and their blood lead levels are more likely to represent recent exposure.

Low blood lead levels do not appear to be further reduced by dietary supplements

OBJECTIVE

Our objective was to evaluate the association of dietary intakes of selected micronutrients and blood lead (PbB) concentrations in female adults and in children.

DESIGN

With longitudinal monitoring, we measured daily intakes of the micronutrients calcium, magnesium, sodium, potassium, barium, strontium, phosphorus, zinc, iron (limited data), and copper from 6-day duplicate diets (2-13 collections per individual) and PbB concentrations. Participants were three groups of females of child-bearing age (one cohort consisting of 21 pregnant subjects and 15 nonpregnant controls, a second cohort of nine pregnant migrants), and one group of 10 children 6-11 years of age.

RESULTS

Mean PbB concentrations were <5 microg/dL. A mixed linear model that included only group and time accounted for 5.9% of the variance of the PbB measurements; neither the effect of time nor the effect of group was significant. The model containing all of the micronutrients (except iron, for which there was a great deal of missing data), along with time and group, accounted for approximately 9.2% of the variance of PbB; this increase was not statistically significant. There was, however, a significant association of PbB with phosphorus, magnesium, and copper when all micronutrients were included in the statistical analysis, perhaps reflecting a synergistic effect.

CONCLUSIONS

In contrast to most previous studies, we found no statistically significant relationships between the PbB concentrations and micronutrient intake. In adults and older children with low PbB concentrations and minimal exposure to Pb, micronutrient supplementation is probably unnecessary.

Relationship between blood lead concentration and dietary intakes of infants from 3 to 12 months of age

Data from a study of mother-infant pairs of low socioeconomic status living in Albany County, NY, were analyzed to determine the influence of diet and nutrition on the blood lead level of infants during the first year of life. Children's diets were assessed at 3-month intervals using a 24-h diet recall as reported by the primary caregiver. The potential impact of dietary consumption of protein, iron, zinc, calcium, vitamin D, and fat, as well as serum vitamin D and ferritin on blood lead levels at 6 and 12 months of age was examined with multivariable statistical analyses, controlling for other influences on lead levels. Neonates' blood lead levels were low at birth (geometric mean=1.6 microg/dL), and none were elevated (> or = 10 microg/dL). By 12 months, the mean blood lead for this sample was 5.1 microg/dL, and 18% of the sample had an elevated blood lead level. We observed significant inverse relationships between infants' 6-month lead level and their intake of zinc, iron, and calcium. At 12 months, low iron intake continued to be associated with higher lead levels, although zinc and calcium did not. Protein had a paradoxical effect, being associated with lower lead at 6 months, but higher lead at 12 months. Serum vitamin D and ferritin were not associated with lead levels, nor was vitamin supplement use. The results reported here emphasize the value of key minerals in the diet to reduce lead absorption during early infancy.

Mobilization of intracellular calcium in kidney epithelial cells is inhibited by lead

The effect of lead (Pb) on intracellular calcium (Cai) after stimulation with agonists was studied in Madin-Darby canine kidney (MDCK) cells. In response to the agonist ADP, the levels of Cai increased by approximately threefold in MDCK cells bathed in a buffer with calcium (Ca) or in a buffer with nominal Ca. Pb inhibited the response to ADP in MDCK cells bathed in either buffer. The inhibition by Pb was observed after a 5 and 20-min exposure to Pb, but not after 2-min. Very high concentrations of ADP did not reverse the effects of Pb. Concentrations of Pb of 1 microM or more inhibited the response to ADP. Similarly, the response to bradykinin was also inhibited by Pb. Protein kinase C did not play a role since the protein kinase C inhibitor GF 109203X did not reverse the effects of Pb. Interestingly, MDCK cells treated with Pb at concentrations above 1 microM, for periods of 5-20 min, displayed elevated levels of inositol 1,4,5-trisphosphate. In conclusion, Pb inhibits mobilization of Cai after agonist stimulation by a mechanism that is unrelated to the type of agonist used. Evidence is presented suggesting that the inhibition is due to increases in levels of inositol 1,4,5-trisphosphate, which possibly decreases the amount of Cai available for mobilization.

Lead targets GRP78, a molecular chaperone, in C6 rat glioma cells

Exposure to potentially neurotoxic levels of lead (Pb) occurs in about 9% of American children under 6 years of age. Astroglia in the brain serve as a Pb depot, sequestering Pb and preventing its contact with the more sensitive neurons. Astroglia have the capacity to adapt to Pb exposure, and as such are able to tolerate relatively high intracellular Pb accumulation. This tolerance mechanism has yet to be defined in biochemical terms. In the present study, we present evidence that glucose-regulated protein (GRP78), a molecular chaperone in the ER, participates directly or indirectly in the tolerance mechanism. Exposure of cultured C6 rat glioma cells, an astroglia-like cell line, to 1 microM Pb acetate for 1 week raised the intracellular levels of two proteins, one of which was identified by sequence analysis as GRP78. GRP78 accumulation started within 1 day and progressed with time of exposure. Studies in vitro showed that GRP78 bound tightly to affinity columns with Pb(2+) as the affinity ligand and bound weakly when either Zn(2+) or Ni(2+) replaced the Pb(2+). The reduced form of GSH and BSA did not compete with GRP78 to chelate Pb(2+). However, the heavy metal binding domain (HMB) of Menkes protein competed with GRP78 for chelating Pb(2+). The data provide evidence that GRP78 may be a component of the Pb tolerance mechanism through its direct interaction with Pb(2+). Its increased synthesis could be part of the adaptive response to Pb exposure.

Molecular mechanisms of lead neurotoxicity

Epidemiological studies have shown a strong relationship between the level of lead in blood and bone as assessed by performance on IQ tests and other psychometric tests. Approximately 1 out of 10 children in the United States have blood lead levels above 10 microg/dl, which has been established as the level of concern. Studies on experimental animals exposed to lead after birth have shown learning deficits at similar blood lead levels. Since learning requires the remodeling of synapses in the brain, lead may specifically affect synaptic transmission. Although the molecular targets for lead are unknown, a vast amount of evidence accumulated over many years has shown that lead disrupts processes that are regulated by calcium. Our laboratory has been studying the effect of lead on protein kinase C, a family of isozymes some of which require calcium for activity. We and others have shown that picomolar concentrations of lead can replace micromolar concentrations of calcium in a protein kinase C enzyme assay. Furthermore, lead activates protein kinase C in intact cells and induces the expression of new genes by a mechanism dependent on protein kinase C. We propose that the learning deficits caused by lead are due to events regulated by protein kinase C that most likely occur at the synapse.

Alteration of rat submandibulary gland secretion of protein, calcium and N-acetyl-beta-D-glucosaminidase activity by lead

1. Effects of various doses of long-term lead treatment (0.01%, 0.04% and 0.05%) on rat submandibular saliva were investigated in this study. 2. Both submandibular ducts were cannulated intraorally with polyethylene tubes and saliva was collected from anesthetized lead treated and control rats using pilocarpine as secretagogue. 3. Saliva protein concentration was found to be reduced in lead (0.04%)- and (0.05%)-treated groups. 4. Saliva calcium concentration had a significant reduction only in the lead (0.05%)-treated group. 5. The secretion of the lysosomal enzyme, N-acetyl-beta-D-glucosaminidase (NAG) in saliva decreased significantly in the lead (0.04%)- and (0.05)-treated groups. Specific activity of the enzyme showed an increase in these treated groups. 6. Good correlations were found between saliva protein concentration and NAG activity, saliva protein and calcium concentrations and calcium concentration and NAG activity. 7. There was a correlation between blood and submandibular saliva lead levels, and the saliva/blood ratio was approximately constant for all treated groups. 8. With respect to the ability of lead to substitute for calcium in several intracellular regulatory events, explanation for these alterations in submandibular saliva composition can be made.