Lead: intestinal absorption and bone mobilization during lactation

Lead exposure in American black bears increases with age and big game harvest density

Hunting has multiple consequences for wildlife, and it can be an important source of environmental pollution. Most big game hunters use lead (Pb) ammunition that shed metal fragments in the tissues of harvested animals. These Pb fragments become available to scavengers when hunters discard contaminated slaughter remains in the environment. This exposure route has been extensively studied in avian scavengers, but few studies have investigated Pb exposure from ammunition in mammals. Mammalian scavengers, including American black bears (Ursus americanus), frequently use slaughter remains discarded by hunters. The objective of this study was to investigate whether big game harvest density influenced long-term Pb exposure in American black bears from Quebec, Canada. Our results showed that female black bears had higher tooth Pb concentrations in areas with higher big game harvest densities, but such relationship was not evident in males. We also showed that older bears had higher tooth Pb concentrations compared to younger ones. Overall, our study showed that Pb exposure increases with age in black bears and that some of that Pb likely comes from bullet fragments embedded in slaughter remains discarded by hunters. These results suggest that hunters may drive mammalian scavengers into an evolutionary trap, whereby the long-term benefits of consuming slaughter remains could be negated due to increased Pb exposure.

The content of toxic elements in hair of dairy cows as an indicator of productivity and elemental status of animals

The study was conducted on a model of dairy cows of the Holstein breed. At the first stage of research, the elemental composition of cow hair was studied (n = 198). Based on this study, the percentile intervals of chemical elements concentrations in hair were established; values of 25 and 75 percentiles were determined, and they were considered as "physiological standard." At the second stage, the elemental composition of hair from the upper part of withers of highly productive Holstein cows during the period of increasing milk yield was analyzed (n = 47). The elemental composition of biological substrates was studied according to 25 indicators, using the methods of atomic emission and mass spectrometry (AES-ICP and MS-ICP). An assessment of productivity parameters of cows depending on the level of toxic elements in hair revealed a negative statistically significant relationship with the level of lead. Lead content in hair was negatively correlated with the yield of fat (r = - 0.50), protein (r = - 0.37), and dry matter (r = - 0.48) in milk. Based on these data, cows were divided into three groups: group I, with Pb concentration in hair 0.0245-0.0449 mg/g, group II-between 0.0495 and 0.141 mg/kg, and in group III-between 0.145 and 0.247 mg/g. It was established that increasing Pb content decreases daily production of milk fat by 18.8 (P ≤ 0.05) and 25.3% (P ≤ 0.05), protein by 9.7 (P ≤ 0.05) and 10.7% (P ≤ 0.05), and dry matter by 8.0 and 13.0% (P ≤ 0.05) in cows. Average daily milk yield, adjusted for 1% of fat, decreased by 19.2 (P ≤ 0.05) and 25.3% (P ≤ 0.05), respectively. As the concentration of lead in hair increased, the content of toxic elements (Al, As, Cd, Hg, Pb, Sn, Sr) increased from 0.07 to 0.235 mmol/kg in group I, in group II from 0.082 to 0.266 mmol/kg, and in group III-from 0.126 to 0.337 mmol/kg. It was concluded that it is necessary to further study the use of physiological standard indicators of the content of toxic chemical elements in hair of dairy cows to increase productivity and maintain animal health and to create an effective system of individual health monitoring of highly productive cattle.

Participation of phospholipase-A2 and sphingomyelinase in the molecular pathways to eryptosis induced by oxidative stress in lead-exposed workers

The increment of eryptosis in lead-exposed workers has been associated with oxidative stress, having as the main mediator [Ca²⁺]_i. However, other molecules could participate as signals, such as PLA₂ and SMase, which have been proposed to increase PGE₂ and ceramides, both involved in the increment of PS externalization due to osmotic stress. To study the role of these enzymes in lead intoxication, we studied 30 lead exposed workers and 27 non-lead exposed individuals. We found, compared to non-exposed subjects, lead intoxication characterized by high blood lead concentration (median = 39.1 μg/dL), and low δ-ALAD activity (median = 348 nmol of porphobilinogen/h/mL); oxidative stress with high lipid peroxidation (median = 1.31 nmol of malondialdehyde/mL) and low TAC (median = 370 mM Trolox equivalents); a higher enzymatic activity of PLA₂ (median = 518 AFU/mg) and SMase (median = 706 AFU/mg) and higher eryptosis (median = 0.92% PS externalization). Correlation and conditional probability analyses permit to associate oxidative stress and eryptosis with high PLA₂ activity. However, high SMase activity was only associated with PLA₂ activity. The role of these enzymes in the signal path to eryptosis induced by oxidative stress in lead-exposed workers is discussed.

Blood lead, calcium, and phosphorus in women with preeclampsia in Edo State, Nigeria

The authors investigated the effect of blood lead (BPb) and its relationship with calcium and phosphorus in the development of preeclampsia in Nigeria. Blood samples were collected from 59 preclamptics, 150 normal pregnant, and 122 nonpregnant women. Blood lead and serum Ca and P were determined. Blood lead was significantly higher (p < .001), whereas serum Ca and P were significantly lower (p < .001) in preclamptics than in normal pregnant women (60.2 ± 12.8 vs 26.3 ± 8.0 μg/dL for Pb, 1.39 ± 0.33 vs 2.03 ± 0.22 mmol/L for Ca, and 0.76 ± 0.10 vs 0.99 ± 0.13 mmol/L for P, respectively). There was significant increase (p < .05) in BPb and decreases (p < .01) in serum Ca and P in pregnant women than in nonpregnant women (35.7 ± 18.0 vs 13.1 ± 6.4 μg/dL for Pb, 1.85 ± 0.33 vs 2.33 ± 0.20 mmol/L for Ca, and 0.93 ± 0.38 vs 1.24 ± 0.26 mmol/L for P). Also, BPb was negatively correlated with serum Ca and, P, and positively correlated with systolic and diastolic blood pressures in pregnancy (r = -.804 for Ca, r = -.728 for P, r = .908 for SBP, and r = .842 for DBP) and preeclampsia (p < .01). It appears that increase in blood lead, which parallels decreases in serum calcium and phosphorus, may be related to the development and progression of preeclampsia in this environment.

Vitamin-E reduces the oxidative damage on delta-aminolevulinic dehydratase induced by lead intoxication in rat erythrocytes

Lead intoxication induces oxidative damage on lipids and proteins. In the present paper we study in vivo and in vitro the antioxidant effect of vitamin-E and trolox, on the oxidative effects of lead intoxication in rat erythrocytes. Vitamin-E simultaneously administered to erythrocytes treated with lead was capable to prevent the inhibition of delta-aminolevulinic dehydratase activity and lipid oxidation. Partial but important protective effects were found when vitamin-E was administered either after or before lead exposure in rats. In vitro, the antioxidant trolox protected delta-ALA-D activity against damage induced by lead or menadione. These results indicate that vitamin-E could be useful in order to protect membrane-lipids and, notably, to prevent protein oxidation produced by lead intoxication.

Effects of 1,25-dihydroxicolecalciferol and dietary calcium–phosphate on distribution of lead to tissues during growth

The susceptibility to the toxic effects of lead (Pb) is mainly mediated by age and nutritional and hormonal status, and children are among the most vulnerable to them. During growth, an increase in calcium, phosphate and vitamin D in diet is recommended to enhance calcium and phosphate intestinal absorption and bone deposit. Calcium and phosphate reduce lead intestinal absorption, and 1,25-dihydroxicolecalciferol (1,25(OH)2D3) (active metabolite of vitamin D) increases both lead and calcium intestinal absorption. However, the effects of 1,25(OH)2D3 on lead bone deposit and redistribution to soft tissues are not well known. In this study, we examined the effects of calcium-phosphate diet supplementation and the administration of 1,25(OH)2D3 on Pb distribution to soft tissue and bone in growing rats exposed to Pb. Rats (21 days old) were exposed for 28 days to 100 ppm of Pb solution in drinking water. Calcium and phosphate in diet were increased from 1 to 2.5% and from 0.65 to 1.8%, respectively, and 1,25(OH)2D3 was administrated by intraperitoneal injection of 7.2 ng/kg every 7 days. Between 21 and 49 days, the body weight increased about 5 times. The results showed that high calcium-phosphate diet led to lower Pb concentration in blood and in bone, but Pb liver and kidney concentrations increased, which indicates that absorption and bone deposit redistribution of Pb decreased. On the other hand, no effect of this diet rich in calcium-phosphate in Pb concentration was observed in brain. Blood and bone Pb concentrations increased even more when the high calcium-phosphate diet included 1,25(OH)2D3. In the rats treated only with 1,25(OH)2D3, blood and bone Pb concentrations were lower. Higher concentrations of lead in the soft organs were observed also in rats treated under a high calcium-phosphate diet plus 1,25(OH)2D3 administration. The above mentioned results suggested that 1,25(OH)2D3 induces an increased absorption and redistribution of Pb, and therefore, it may enhance systemic damage in Pb-exposed growing animals.

Toxicity of environmental lead and the influence of intestinal absorption in children

Exposure to metals, particularly lead, remains a widespread issue that is associated with historical and current industrial practices. Whereas the toxic properties of metals are well described, exposure to metals per se is only one of many factors contributing to elevated blood metal concentrations and their consequent health effects in humans. The absorbed dose of metal is affected by geochemical, biochemical, and physiological parameters that influence the rate and extent of absorption. In children, the interplay among these factors can be of critical importance, especially when biochemical and physiological processes might not have matured to their normal adult status. Such immaturity represents an elevated risk to metal-exposed children because they might be more susceptible to enhanced absorption, especially via the oral route. This review brings together the more recent findings on the physiological mechanisms of metal absorption, especially lead, and examines several models that can be useful in assessing the potential for metal uptake in children.

The effects of dietary calcium during lactation on lead in bone mobilization: implications for toxicology

Under a normal 1.0% calcium (Ca) concentration in the diet during and after chronic lead (Pb) intoxication, there was a significant increment in the concentration of Pb in the blood, kidney, liver and brain during lactation, parallel to a decrement of Pb in the bone. The increment of Pb in the brain was accompanied by an enhanced lipid oxidation (increase in conjugated dienes). During lactation, on the first 14 days, when dietary Ca was reduced to 0.05%, bone Ca concentration was decreased by 15%, bone resorption measured as acid phosphatase activity in plasma increased three times and Pb bone concentration dropped by 30%. Under a 0.05% Ca in the diet in the nonlactating rats, Ca in the bone decreases also, but there were neither increments in bone resorption nor Pb efflux from the bone. These results suggested that Pb efflux in the bone was related to bone resorption during lactation. Interestingly, when dietary Ca was enhanced to 2.5% in lactating rats, Ca concentration in the bone increased by 21%, but resorption did not decrease and Pb bone concentration decreased by 28%, enhancing toxicity. In the control Pb-exposed nonlactating rats under a 2.5% Ca in the diet, Ca concentration in the bone was increased (18%), and Pb concentration in the bone was unaltered. Since Ca metabolism changes drastically in humans during pregnancy and lactation, and it is likely that bone Pb is mobilized and transferred to the more available compartments of the maternal circulation, the increment in daily intake of Ca during lactation could enhance Pb efflux from the bone.

The role of anion exchange in the uptake of Pb by human erythrocytes and Madin-Darby canine kidney cells

Anion exchange (AE) plays a critical role in regulating intracellular pH in erythrocytes and epithelial cells and has been suggested to facilitate the transport of lead (Pb) across the erythrocyte cell membrane. In this study we examined the role of AE in the uptake of Pb by human erythrocytes and by Madin-Darby canine kidney (MDCK) cells, the kidney epithelial cell line. Functional AE in MDCK cells was evidenced by: increased uptake of SO(4)(2-) at pH 6.0 over pH 7.0, and inhibition of SO(4)(2-) uptake by the AE inhibitor 4, 4'-diisothiocyanostilbene-2, 2'- disulfonic acid (DIDS) as well as by non-halide anions. Accumulation of Pb into MDCK cells was time and temperature dependent. DIDS inhibited uptake of Pb into human erythrocytes but not MDCK cells. In conclusion, uptake of Pb into erythrocytes but not kidney epithelial cells occurs through AE.

Lead and calcium transport in human erythrocyte

In this paper we report the lead (Pb) and calcium (Ca) uptake by erythrocyte ghosts. In both cases the transport was carried out by a passive transport system with two kinetic components (Michaelis-Menten and Hill). Pb and Ca were capable of inhibiting the transport of the other metal in a non-competitive way. Under hyperpolarization, the uptakes of Ca and Pb were enhanced and the Michaelis-Menten component prevailed. Both Ca and Pb uptakes were inhibited by N-ethyl-maleimide to the same extent. These results indicate that Pb and Ca share the same permeability pathway in human erythrocytes and that this transport system is electrogenic.

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.

Effect of lead on the calcium transport in human erythrocyte

In this paper we study the calcium uptake in the erythrocyte, a non-excitable cell. This uptake is performed through a passive transport system with two kinetic components (Michaelis-Menten and Hill). The uptake of calcium seems to be driven by voltage through its electrophoretical effect. Lead is capable of inhibiting calcium uptake in a non-competitive manner. As it has been described in other systems, lead is also capable of inhibiting calcium efflux by inhibiting Ca(Mg)-ATPase. Under physiological conditions, the function of ATPase reduces the effect of lead on calcium influx. However, in chronic intoxication a small increment of intracellular calcium is observed, indicating that lead is affecting calcium efflux mainly. We discuss the effects of lead on calcium equilibrium in erythrocytes.

Effect of acute lead treatment on coproporphyrinogen oxidase activity in HepG2 cells

Acute toxic effects of lead were evaluated on porphyrin synthesis and coproporphyrinogen oxidase (CO) activity in an in vitro model, using HepG2 cells, a hepatoma cell line of human origin. Lead concentrations for exposure treatments were 0.5, 1.0, 2.5, 5.0 microM. No significant changes were found in treated cells with respect to uroporphyrin cellular or media concentrations. Cellular protoporphyrin increased in dose response shape, but no changes in extracellular content were found. Extracellular coproporphyrin concentration increased in a dose response manner without changes in cellular content. The CO activity was depressed in dose response shape, reaching 62% of control activity at 5.0 microM of lead treatment. The CO activity in Pb-treated cells was recovered after dithiothreitol (DTT) treatment, suggesting that sulphydryl groups play an essential role in the enzyme activity. The dose-response increase of coproporphyrin secretion accompanied by the depression of CO activity supports the suggestion that lead causes CO inhibition, as observed in this cellular model.

Effects of micronutrients on metal toxicity

There is growing evidence that micronutrient intake has a significant effect on the toxicity and carcinogenesis caused by various chemicals. This paper examines the effect of micronutrient status on the toxicity of four nonessential metals: cadmium, lead, mercury, and arsenic. Unfortunately, few studies have directly examined the effect of dietary deficiency or supplementation on metal toxicity. More commonly, the effect of dietary alteration must be deduced from the results of mechanistic studies. We have chosen to separate the effect of micronutrients on toxic metals into three classes: interaction between essential micronutrients and toxic metals during uptake, binding, and excretion; influence of micronutrients on the metabolism of toxic metals; and effect of micronutrients on secondary toxic effects of metals. Based on data from mechanistic studies, the ability of micronutrients to modulate the toxicity of metals is indisputable. Micronutrients interact with toxic metals at several points in the body: absorption and excretion of toxic metals; transport of metals in the body; binding to target proteins; metabolism and sequestration of toxic metals; and finally, in secondary mechanisms of toxicity such as oxidative stress. Therefore, people eating a diet deficient in micronutrients will be predisposed to toxicity from nonessential metals.