Prenatal and preschool age lead exposure: relationship with size

This report examines possible adverse effects on size and growth associated with subclinical prenatal and preschool age lead exposure in an urban cohort followed prospectively from birth through early childhood. Measurements of weight, stature (length), and head circumference were obtained at birth and during five subsequent in-home assessments. Prenatal lead exposure was assessed by cord (n = 185) and maternal (n = 162) blood lead levels at delivery. Preschool blood lead samples were obtained at ages six months (n = 151), two years (n = 165), three years (n = 165), and four years, ten months (n = 164). Multivariate longitudinal analyses incorporating adjustment for covariates revealed no statistically significant adverse effects of prenatal lead exposure on either neonatal size or on subsequent growth through age four years, ten months. Similarly, no statistically significant adverse effects were found between the preschool lead indices derived from blood collected at or after age two years and ensuing size measurements. We also found no evidence for an interaction between pre- and postnatal lead exposure. A marginal inverse association was exhibited between blood lead at six months and subsequent measures of head circumference. Limitations in the implications of this result in the context of many nonsignificant tests were discussed.

Reversible Schwann cell hypertrophy in lead neuropathy

Schwann cell hypertrophy is an early change observed in lead-induced neuropathy in the rat. In order to quantify this cell hypertrophy, a morphometric analysis of Schwann cell cytoplasmic and nuclear areas and their relationship to the cross-sectional area of the associated myelinated fibre was performed. The study was carried out on sural and peroneal nerves from three groups of adult rats. Group I was intoxicated with 4% lead acetate in the drinking water for 6 weeks; group II animals were treated as in group I and then restored to standard laboratory conditions for 30 days; and group III were controls. The results showed that: (a) after 6 weeks of lead exposure, cytoplasmic and nuclear areas were significantly greater in intoxicated, compared with control rats; (b) after 30 days recovery, Schwann cell cytoplasmic and nuclear areas did not differ from control rats.

Electrophysiologic study in acute lead poisoning

A 2-month-old girl with acute lead poisoning demonstrated electrophysiologic evidence of neurotoxicity. Motor nerve conduction studies of the median, ulnar, peroneal, and posterior tibial nerves revealed both axonal and demyelinating neuropathy. Somatosensory evoked potential studies of median and posterior tibial nerves demonstrated evidence of cortical involvement. Brainstem auditory evoked potential study disclosed the possibility of acoustic nerve involvement but no evidence of a brainstem lesion. Postmortem examination revealed cerebral edema and focal segmental demyelination of the median nerve.

Cellular and molecular toxicity of lead in bone

To fully understand the significance of bone as a target tissue of lead toxicity, as well as a reservoir of systemic lead, it is necessary to define the effects of lead on the cellular components of bone. Skeletal development and the regulation of skeletal mass are ultimately determined by the four different types of cells: osteoblasts, lining cells, osteoclasts, and osteocytes. These cells, which line and penetrate the mineralized matrix, are responsible for matrix formation, mineralization, and bone resorption, under the control of both systemic and local factors. Systemic components of regulation include parathyroid hormone, 1,25-dihydroxyvitamin D3, and calcitonin: local regulators include numerous cytokines and growth factors. Lead intoxication directly and indirectly alters many aspects of bone cell function. First, lead may indirectly alter bone cell function through changes in the circulating levels of those hormones, particularly 1,25-dihydroxyvitamin D3, which modulate bone cell function. These hormonal changes have been well established in clinical studies, although the functional significance remains to be established. Second, lead may directly alter bone cell function by perturbing the ability of bone cells to respond to hormonal regulation. For example, the 1,25-dihydroxyvitamin D3-stimulated synthesis of osteocalcin, a calcium-binding protein synthesized by osteoblastic bone cells, is inhibited by low levels of lead. Impaired osteocalcin production may inhibit new bone formation, as well as the functional coupling of osteoblasts and osteoclasts. Third, lead may impair the ability of cells to synthesize or secrete other components of the bone matrix, such as collagen or bone sialoproteins (osteopontin). Finally, lead may directly effect or substitute for calcium in the active sites of the calcium messenger system, resulting in loss of physiological regulation. The effects of lead on the recruitment and differentiation of bone cells remains to be established. Compartmental analysis indicates that the kinetic distribution and behavior of intracellular lead in osteoblasts and osteoclasts is similar to several other cell types. Many of the toxic effects of lead on bone cell function may be produced by perturbation of the calcium and cAMP messenger systems in these cells.

Age and gender influence on lead accumulation in root dentine of human permanent teeth

143 permanent teeth of individuals aged 14-60 yr from a non-occupationally exposed population in northern Israel were analysed for lead accumulation in a atomic absorption spectrophotometer graphite-furnace. A significant correlation was established between lead level and age. No gender correlation was found. The results suggest that any study dealing with lead accumulation in different populations has to compare groups of the same age range, ignoring the sex of the individuals.

The small intestinal enterocytes of rats during lead poisoning: the application of the Timm sulphide silver method and an ultrastructural study

Young male rats were divided into 3 groups which received approximately 100 mg of a lead acetate/kg b.w. per day in their drinking water during 2, 30 and 60 d, respectively. Samples from the jejunum were processed for transmission electron microscopy (TEM), and after 60 d of exposure blocks of tissue were also processed to evaluating the Timm sulphide silver reaction sites in the epithelial absorptive cells in TEM according to Dancher and Zimmer (5). The ultrastructure of enterocytes in poisoned rats at 2 days was similar to the controls. A marked feature of about one third of the rat enterocytes exposed to lead for 30 d was the presence of numerous, small rough-membraned vesicles and prominent, dilated Golgi complexes in their cytoplasm. Most of the enterocytes at the 60th d of lead-exposed rats had a vacuolated cytoplasm associated with the prominent Golgi complexes and vacuoles of various size. They also had pleomorphic rough-membraned vesicles and dilated cisternae of the RER. The presence of the Timm reaction deposits has been observed on the microvillar surface of the brush border in connection with the enterocyte plasma membrane, and in the extracellular space between epithelial cells. Furthermore, Timm precipitates were found in extravascular spaces surrounding capillaries, between endothelial cells, and in the capillary lumen.

Lead poisoning and brain cell function

Exposure to excessive amounts of inorganic lead during the toddler years may produce lasting adverse effects upon brain function. Maximal ingestion of lead occurs at an age when major changes are occurring in the density of brain synaptic connections. The developmental reorganization of synapses is, in part, mediated by protein kinases, and these enzymes are particularly sensitive to stimulation by lead. By inappropriately activating specific protein kinases, lead poisoning may disrupt the development of neural networks without producing overt pathological alterations. The blood-brain barrier is another potential vulnerable site for the neurotoxic action of lead. Protein kinases appear to regulate the development of brain capillaries and the expression of the blood-brain barrier properties. Stimulation of protein kinase by lead may disrupt barrier development and alter the precise regulation of the neuronal environment that is required for normal brain function. Together, these findings suggest that the sensitivity of protein kinases to lead may in part underlie the brain dysfunction observed in children poisoned by this toxicant.

The histopathology of tissue lead retention

An experimental murine model of chronic lead retention is established. This model excludes joint communication and synovial fluid solubility of lead ions recognized in human gunshot injury. Degenerative changes in the visceral organs and bone appear in these mice 30 days after implantation of lead spheres in the subcutaneous tissues of the posterior body wall. Degeneration, necrosis and interstitial fibrosis of the lung, kidney and remodeling of femoral bone are noted during the course of the experiment (120 days). It is concluded that the systemic diffusion of lead ions from a central focus is related to the development of an absorptive circulatory mechanism around the retained peripheral lead mass.

Developmental exposure to organic lead causes permanent hippocampal damage in Fischer-344 rats

The long-term consequences of neonatal exposure to triethyl lead, the putative neurotoxic metabolite of the anti-knock gasoline additive tetraethyl lead, were examined with respect to central nervous system (CNS) development. We presently report a series of studies in which exposure of neonatal rats to organic lead produces profound CNS damage in adulthood as indicated by dose-dependent, persistent behavioral hyperreactivity as well as dose-dependent, preferential, and permanent damage to the hippocampus. General morphological parameters of brain development were not altered. Pharmacological probes of neurotransmitter system integrity suggested a functional and dose-dependent relationship between this behavioral hyperreactivity and hippocampal damage via cholinergic, but not dopaminergic, pathways. Furthermore, these alterations were not accompanied by long-term alterations in motor activity and were not attributable to the presence of lead in adult neural tissue. Finally, these behavioral, anatomical, and pharmacological indices of developmental exposure to organic lead were dissociable from any effects of early undernutrition. These data collectively indicate that organolead compounds may pose a potent neurotoxic threat to the developing CNS.

Influence of fixation procedures on the microanalysis of lead-induced intranuclear inclusions in rat kidney

Using Laser Microprobe Mass Analysis (LAMMA), we studied the chemical composition of lead-induced intranuclear inclusions in rat kidney tissue prepared by three different wet chemical fixation procedures for transmission electron microscopy. Fixation with glutaraldehyde-Na2S gave the same results as fixation with glutaraldehyde only: a high lead concentration could be detected. Therefore, for lead strongly bound to proteins, precipitation procedures are not essential. Post-fixation with osmium tetroxide drastically changed the composition of the inclusions: the lead concentration decreased substantially, while sodium, calcium, and barium were introduced. The osmium tetroxide fixative was found to be the source of the contamination. It also contained aluminum, and we suggest that other proteins (e.g., in neurofibrillary tangles) might be able to take up Al out of solution and that care must be exercised in interpreting the microanalytical results of osmium-fixed material. For the microanalysis of the lead inclusions, fixation with glutaraldehyde only provides a good compromise between preservation of the ultrastructure and maintenance of the element distribution.

Dose-related proximal tubular dysfunction in male rats chronically exposed to lead

Male Wistar rats were given 0.5 and 2% lead acetate in drinking water for 2 months, 1% lead acetate for 3 months and sodium acetate equimolar to 2% lead acetate for 3 months. Glucose, total proteins, lactate dehydrogenase (LDH), lysozyme and beta 2-microglobulin (beta 2-m) were measured in 24-h urine every month. Kidney weight and histology were also examined. At the three doses, lead exposure produced a significant elevation of the kidney weight. No significant change in urinary parameters was observed in rats given 0.5% lead acetate. Exposure to 1% lead acetate increased the urinary excretion of beta 2-m only. At the 2% lead acetate dose the elevation of beta 2-m excretion was accompanied by an increased urinary output of glucose, total proteins, lysozyme and LDH. Observations of the kidneys by light microscopy were in agreement with these biochemical findings. The nephrotoxic effect of acetate was excluded by the lack of biochemical or histological effects of sodium acetate on the kidney. It is concluded that a proximal tubular dysfunction is induced in rats chronically exposed to high doses of lead.

Comparison between electrophysiologic and morphologic changes in lead induced peripheral neuropathy in rats

Compound nerve action potential (CNAP) of the mixed peripheral nerve is composed of A alpha beta, A delta, and C potentials. All components of CNAPs in the sciatic nerve were recorded by stimulating the tibial nerve of both control and lead-poisoned rats. Marked decrease of nerve conduction velocity and prolonged duration were found in A alpha beta and A delta fibers especially in large myelinated A alpha beta fibers. The amplitude decreased in A alpha beta potential, but the area did not change. In C potential produced by activation of unmyelinated fibers, nerve conduction velocity slightly decreased, but the amplitude and area did not significantly change. Pathologic correlates revealed prominent segmental demyelination with significant decrease of large myelinated fiber densities. Minimal axonal degeneration of unmyelinated fibers was present. We can conclude that electrophysiologic changes in the lead-poisoned rats correlate with pathologic changes in them.

Microscopic examination of hippocampal slices after short-term lead exposure in vitro

By using light microscopic, electron microscopic and morphometric methods 450 microns thick slices of guinea pig hippocampus were studied after 5-hr incubation as controls in normal media and after incubation in media containing 40 microM lead acetate. Pyramidal neurons of the CA1 region and the granule cells of the fascia dentata were well preserved in the center of the slice, whereas neuronal structures in outer parts of the slice were either vacuolated or hyperchromatic and shrunken. Most of the CA4 neurons were lytic except for a few in the center of the slice. Morphometric analysis of the pyramidal layer of CA1 yielded approximately 55% well-preserved pyramidal neurons both in lead-exposed slices and in slices incubated in normal media. Electron microscopic examination of the CA1 region demonstrated no ultrastructural changes of lead-exposed slices compared to control. In conclusion, the reduction of evoked neuronal activities in the CA1 region of hippocampal slices during short-term lead exposure in vitro appears not to be linked to a specific neuropathological lesion.

The effects of long-term lead intoxication on the nervous system of the chicken

In order to study the possible etiologic role of lead in human motor neuron disease we produced chronic lead intoxication in the chicken by daily administration of lead acetate. Control animals received sodium acetate. During life, periodic measurements were made of motor function, motor nerve conduction velocity and response amplitude. After sacrifice, histologic analysis was performed on spinal cord, peripheral nerve and muscle. A syndrome was produced characterized by a fall in motor response amplitude, spinal motor neuron degeneration, motor axonal loss and atrophy of muscle, similar to that seen in human motor neuron diseases.

The effect of chronic lead intoxication in mature chickens

In a study of chronic lead intoxication in mature chickens, blood lead levels were significantly lower in hens than in roosters receiving the same oral dose of lead. It was then shown that eggshells from lead-treated hens contained 6-12 times the lead concentration of eggshells from control hens. Similarly, the lead content of egg yolks from treated hens was significantly higher than yolks from controls. Lead-treated hens laid significantly more eggs during the period of observation of nearly 3 years because of the increased frequency of laying cycles, which was almost three times that of control hens. A further observation was histologic damage to the mature testes of the rooster.

Neuronal depletion of the amygdala resembles the learning deficits induced by low level lead exposure in rats

The behavioral deficits observed after lead exposure have been related to limbic system dysfunction. In a previous study it was shown that the neurotoxicity of lead could not be explained by the damage of the hippocampus alone. The purpose of the present investigation was to use behavioral comparisons to test the hypothesis that the intrinsic neurons of several nuclei of the amygdala, where lead has been found to accumulate, can be a target of the effects of the metal as well. A group of rats were maternally and permanently exposed to lead (750 ppm in the diet as lead acetate). Another group of equally aged and housed rats, never experimentally exposed to lead, were injected ibotenic acid into the amygdala. All groups plus sham-operated and unoperated controls were tested in the open field, the radial arm maze, and a passive avoidance task. The results showed that lead exposure (both permanent and maternal) and amygdalectomy produced a) no effect on locomotor activity, b) impairments in the acquisition phase of the radial maze, and c) impairments in passive avoidance. These results suggest an involvement of the amygdala in the neurotoxic action of lead, but not as the only brain structure. The deficits in permanently lead-exposed rats are more pronounced than in only maternally-exposed animals suggesting a longlasting, but not totally irreversible effect of early lead exposure.

Cytophotometric investigations on a chronic tubular nephropathy simulating preneoplastic condition

Cytophotometric investigations were performed on the atypical renal tubular epithelium of a young man who died of renal failure, possibly due to chronic lead exposure. The aim of this analysis was to determine whether nuclear atypia indicates incipient malignancy or is a type of so-called "benign atypias". DNA histogram, showing euploid polyploidy supports the latter view and the dysplastic epithelial lesion is not even considered to be a preneoplastic condition.

Use of an in vitro system to study the effects of lead on astrocyte-endothelial cell interactions: a model for studying toxic injury to the blood-brain barrier

We investigated the effect of inorganic lead on the interaction of immature rat astrocytes and bovine adrenal endothelial cells. The two cell types were cultured alone and in coculture in the presence or absence of lead acetate for up to 1 week. A battery of cell specific markers was used for cell identification. Newborn Sprague-Dawley rat brain astrocytes were more sensitive than bovine adrenal endothelial cells to the cytotoxic effects of 10-50 microM lead acetate, as demonstrated by a decrease in cell number and by the presence of intracellular vacuoles and detached cells. The number of astrocytes decreased to 50% of control after 4 days in culture at a concentration of 10 microM lead. In contrast, a mitogenic effect of lead was observed on the endothelial cells at this concentration, with an increase in cell number to 110% of control. In coculture, the two cell types demonstrated a distinctive cellular organization and the astrocytes were less sensitive to the cytotoxic effects of lead than when they were cultured alone. A lead-enhanced induction of a neural capillary enzyme activity, gamma-GTP, was detected histochemically in the coculture system. These results are consistent with a maturing or differentiating effect of the endothelial cells on the astrocytes, making them less susceptible to lead and mature enough to induce gamma-GTP activity in the endothelial cells.

Recovery of the early cellular changes induced by lead in rat peripheral nerves after withdrawal of the toxin

A morphological and quantitative investigation was carried out in the peripheral nerves of adult rats, which were first exposed to 4% lead acetate in the drinking water and then restored to standard laboratory conditions. After six weeks of continuous lead exposure, the only cells involved were Schwann cells (SC) and endothelial cells (EC). As compared to age-matched controls, the most conspicuous changes observed by light and electron microscopy in these cells included the presence of nuclear inclusion bodies (NIB), cytoplasmic hypertrophy, mitochondrial abnormalities, an increased number of myelin-derived SC intracytoplasmic structures, and vesiculation of myelin sheaths. By counting the number of nuclear profiles containing NIB in semithin sections stained with basic fuchsin and methylene blue, we found that SC from predominantly cutaneous (sural) nerves were less vulnerable to lead than SC from mixed (peroneal) and muscular (tibial) nerves. With respect to EC, however, no significant differences were found among these three nerves. After termination of lead exposure, we observed a gradual decrease of most of the above cellular changes, which finally disappeared at day 30 post-intoxication. However, the number of myelin-related SC cytoplasmic bodies still remained above normal levels at the time of the termination of the experiment (60 days post-intoxication). The nature of the changes induced by lead in peripheral nerve cells as well as the rapid and nearly complete recovery suggest that they reflect a compensatory response to overcome the adverse effects of the lead on cell metabolism.

Lead arthritis and lead poisoning following bullet wounds: a clinicopathologic, ultrastructural, and microanalytic study of two cases

Bullet wounds causing lead synovitis in the wrist and knee are reported in two patients, one of whom also developed clinical plumbism. Very high lead levels in the synovial fluid are believed to be responsible for toxicity changes that occurred in the synovium and bone. Ultrastructurally, these alterations included the formation of nuclear lead inclusions, dilation, and degranulation of the rough endoplasmic reticulum and deposition of crystalline precipitates in the matrix of the mitochondria in macrophages, osteoclasts, and synoviocytes, as well as the development of cytoplasmic lead inclusions in osteoclasts. Energy-dispersive x-ray elemental analysis (EDXEA) indicated that the nuclear inclusions contained only lead, whereas precipitates within the mitochondria and elsewhere in the cytoplasm were composed of complexes containing lead, calcium, and phosphorus. Similarly constituted extracellular complexes were incorporated into newly formed trabecular bone laid down as a physiologic response to the bullet lodged within the wrist bones. This bone subsequently exhibited defects in bone resorption, which were characterized by depressed osteoclastic function and a unique lesion termed incomplete osteocytic osteolysis. The genesis of this latter lesion is uncertain. The sequestration of the partially degraded bone fragments containing lead complexes into the marrow and eventually into the joint spaces and synovium permitted the recycling of bone lead, and this may have played an important role in inducing clinical plumbism in one of the patients in this study.

Ultrastructural aspects of the small intestinal lead toxicology. Part I: Surface ultrastructure of the small intestine mucosa in rats with lead acetate poisoning

The effects of low concentration of lead acetate on the apical surface of the jejunal enterocytes were studied. Young male rats were divided into 2 groups which received 0.01% lead acetate solution in drinking water during 30 and 60 d respectively. Blood lead concentrations of poisoned rats were elevated to 30.33 micrograms Pb/100 ml at d 30 of intoxication, then slightly depressed at the end of experiment. Weight gain was impaired only in the 60-d group in comparison with controls. Samples from jejunum were processed for scanning electron microscopy using a critical point drying method and gold evaporation. The fine structure of the surface enterocytes was always determined in the epithelial bands above the levels of crypts nearly half a distance from crypt to villous top. The shape of the jejunal villi in poisoned rats was similar to that in non-poisoned rats. A marked feature of the rats' jejunum exposed to heavy metal for 30 d was a rough appearance of the surface villi, probably associated with distortion of the glycocalyx layer. Extensive areas with degenerative lesions were observed on the surface of the most villi on the 60th d of intoxication. Microvilli of enterocytes distributed within these areas were deformed and sometimes could be completely absent. All enterocytes exhibited various degrees of glycocalyx disturbance. It was concluded that the pronounced toxic effects of lead were related to modification of biochemical properties of the surface coat of enterocytes. This abnormal function of the glycocalyx could result in damage and microvillous malformations.