Regressive or lethal lead encephalopathy in the suckling rat. Correlation of lead levels and morphological findings

Lead encephalopathy was produced in immature Sprague-Dawley rats with an intraperitoneal (IP) injection of 60 micrograms/g body weight of lead acetate administered daily from the fifth day after birth. Macroscopic and light microscopic study of the nervous system, estimations of the blood-brain barrier permeability to proteins and brain water content were performed every two days thereafter. Lead levels in total blood, plasma, and several brain areas were measured at the same intervals by flameless atomic absorption spectrometry. Electron microscopic study of the cerebellum was done 2, 6, and 12 days after beginning lead administration. After two days of lead administration and before any pathological change occurred the increase in lead level was greater in the cerebellum than in other brain areas. After four to six days, hemorrhagic lead encephalopathy developed and was most prominent in regions with higher lead levels. From day 11 to 14, there were two possible courses: a) improvement of the clinical status and morphological findings in 25% of the animals, or b) progression of abnormal clinical signs and death. Cerebral edema, both intra- and extracellular, may have contributed to the fatal evolution. The mechanism of this edema appeared complex and may have involved resorption failure. Good correlations were observed among progression of the clinical signs, high water content in the brain, morphological evidence of cerebral edema, and a high cerebellar lead level. In contrast, high blood lead levels could be associated with clinical improvement, normal brain water content, and regression of the pathological findings. These data suggest that differences in evolution are more likely related to differences in the development of resistance of the cerebral capillary to lead, or in the efflux of lead, rather than to the blood lead concentrations.

Influence of lead poisoning on ultrastructural changes in the body wall of Eisenia foetida (Savigny), Oligochaeta. II. Long action of different concentration of lead on ultrastructural changes in the cells of the body wall

The studies were performed on earthworms collected from March to September in the vicinity of Katowice. The earthworms were breed in Petri dishes on soil to which lead nitrate was added in the following concentrations 0.025, 0.10, 0.50 mg/g of soil. For the performed studies small specimen were taken from behind the citellum in which was lead histochemically evaluated. Tissue specimen taken from the citellum of the experimental animals were investigated in electronmicroscope. It has been found that lead accumulates in the sarcoplasm of the muscle fibres but not in the cell organells. Lead concentrations in the cells appear as regular crystals with membranaceous cover. The lead compounds used in the experiments does not provoke structural changes in the contractile elements of the muscle fibres, they induce only some deformations of mitochondria and hyperactivity of the glandular cells of the epithelium.

Ultrastructural and ultrahistochemical investigations of lead-induced intranuclear inclusion bodies in rat kidney

The morphogenesis of intranuclear inclusion bodies in the proximal convoluted tubules of rat kidney is studied in chronic lead poisoning. In early stages electron dense particles and fibrillar structures in connection with interchromatin granules were observed. The fully developed inclusion bodies showed an electron dense core from which fibrils project outwards forming an irregular coronal framework. By the sulphide silver method for the demonstration of heavy metals an intense reaction was observed in the outer areas of the fibrillar corona after digestion using DNase.

[Neurotoxic occupational substances: I. Metals and their compounds. A literature review of the years 1970 to 1982]

The knowledge of the neurotoxicity to the peripheral nervous system of arsenic, lead, thallium and mercury as well as their compounds is reviewed according to the literature of the period 1970-1982. - First acute and chronic intoxications are described with special reference of the neurological symptoms. Then we review the results of electromyographic, neurophysiological and histological investigations. Field studies in occupationally exposed groups and evaluation of dose-response-relationships are specified in detail. Further the presented results are discussed according to aspects in occupational medicine. The following conclusions can be drawn: Neuropathies after arsenic intoxications are characterized by symmetric sensory symptoms as usually numbness and paresthesiae of the distal extremities, but the neurophysiological and histological studies showed a great variety of results. In a former study a significant dose-response-relationship between arsenic load and evidence of neuropathy in workers was demonstrated. The onset of impairments of the peripheral nervous system caused by chronic lead exposure is discussed controversially. Some reports showed a dose-response-relationship between a slowering of nerve conduction velocities and an increase of the lead body burden. Proposals of threshold values ranged between 50 to 80 micrograms lead/dl blood. Other authors did not confirm these results. Longitudinal studies are, with one exception, not available at present. Thus a relevant evaluation, particularly regarding relevance and prognosis of a mild slowering of nerve conduction velocity, can not be given now. The neurotoxicity of mercury and its compounds is well demonstrated. In case of the metal and the inorganic compounds a direct damage of the peripheral nerve is possible, whereas for organic compounds the pathophysiological mechanism is unclear. Studies concerning dose-response-relationships as well as evaluation of threshold values in chronically exposed workers are limited. It seems at present not possible to define a threshold value for the neurotoxic effects of mercury according to peripheral nervous system. Thallium caused peripheral neuropathy is described in many casuistics But to our knowledge there are no reports of neurophysiological studies in occupationally exposed groups.

Changes in Schwann cells and vessels in lead neuropathy

Transmission electron microscopy (TEM) of peripheral nerve in rats receiving 6% lead carbonate for 4-10 weeks provided evidence of a specific Schwann cell injury, associated with demyelination. Intranuclear inclusions in Schwann cells appeared within 2 weeks of administration of a lead-containing diet. Swelling of Schwann cells and disintegration of their cytoplasm was evident at 4 weeks. Distinctive electron-dense inclusions appeared in both Schwann and endothelial cells during the period of intoxication and were ultrastructurally identical to pathognomonic inclusions of lead poisoning seen in renal tubular epithelial cells. Scanning microscopy (SEM) with electron-probe microanalysis was used to identify the lead-containing deposits. In addition to Schwann cell changes, vessels revealed endothelial cell injury and alteread permeability to macromolecules. Since morphologic changes of Schwann cells precede the development of altered vascular permeability and endoneurial edema, it appears that lead gains access to the endoneurium prior to the development of altered vascular permeability, suggesting that edema and altered endoneurial fluid pressure are epiphenomena that supervene after demyelination occurs. Remyelination, Schwann cell proliferation and formation of onion bulbs are manifestations of persistent toxic injury to myelin-sustaining cells, resulting in chronic demyelination.

Development of resistance to lead encephalopathy during maturation in the rat pup

The purpose of this study was to determine the maturational period during which the rat pup becomes resistant to the toxic effects of lead on the brain. Pups were fed lead, as lead acetate, by esophageal catheter for 14 days beginning at various ages between 14-24 days. The daily lead doses, which produced a hemorrhagic cerebellar encephalopathy in at least 50% of pups, were 400 micrograms Pb/g body weight for animals fed from 14 days of age, 800 micrograms/g for animals fed from 16 days, and 1600 micrograms/g for animals fed from 18 days. In contrast, pups fed even higher lead doses beginning at 20 days showed only a patchy cerebellar edema by light microscopy while pups fed from 24 days had normal cerebellums by light microscopy. The encephalopathic lead doses in the younger pups resulted in the same cerebellar lead concentrations (about 30 micrograms/g protein) as the higher lead doses fed pups beginning at 20 ot 24 days. When corrected for blood lead concentrations, the cerebellar lead concentrations were 20-25% higher in the encephalopathic compared to the older encephalopathy-resistant animals. This difference may be accounted for by cerebellar hemorrhages in the younger animals. Polarographic studies showed inhibition of respiration in cerebellar slices from animals fed lead from 14 days of age but not in animals fed from 20 or 24 days of age. Our results that, during the encephalopathy-sensitive age period, a critical cerebellar concentration of lead is associated with the encephalopathy. Resistance to lead encephalopathy in older animals, with similar cerebellar lead concentrations, may be related to a capacity to sequester lead in new cellular locations away from its site of action on aerobic energy metabolism.

The proteins of lead-induced intranuclear inclusion bodies

Characteristic intranuclear inclusion bodies have been isolated from the kidney cortex of lead-intoxicated rats. A protein has been identified which appears to be unique to the inclusion bodies. It was not detected in kidney or liver from normal rats, suggesting that it is induced by lead. However, sequestration of an extant protein by lead remains a possibility. The protein has an apparent molecular weight of 32,000 and an isoelectric point of 6.3. Although traces of related proteins were identified by 125I-tryptic peptide maps, these may be artifacts because they do not occur in some preparations. Identification of this protein provides an opportunity to characterize the molecular interactions between lead and the inclusion bodies. It has been suggested that the inclusion bodies have a protective effect in lead-intoxicated animals. The induction or sequestration of a unique protein lends support to this proposal.

Morphometric effects of postnatal lead exposure on hippocampal development of the 15-day-old rat

Neurotoxic sequelae of developmental lead exposure suggest that the hippocampus may be affected. Therefore, rats received low-level exposure via the milk of dams drinking 0.2% lead acetate beginning at parturition, and mid-dorsal sections of the hippocampus and dentate gyrus (DG) from 15-day-old pups were examined by light and electron microscopy. Lead exposure did not reduce body weight nor produce obviously abnormal vascularity or signs of cytotoxicity in the hippocampal formation, and total numbers per section of dentate granule cells or CA3 pyramidal cells were not reduced. On the other hand, lead exposure reduced neuropil development as evidenced both by reduced areas of the dentate hilus and dentate infrapyramidal stratum moleculare and by increased number of hilar CA3 pyramidal cells per unit area. Also, lead exposure reduced numbers of several types of synaptic profiles per unit area in the suprapyramidal mossy fiber zone. Complex invaginated (CI) profiles, assumed to be mature mossy fiber boutons, were characterized by multiple membrane densities and deep invaginations around dendritic spines of pyramidal cells. Complex noninvaginated (CN) boutons exhibited bag-like profiles with multiple membrane densities. Smaller, less numerous, simple (S) profiles contacted either dendritic trunks (ST) or spines (SS). Lead exposure reduced the numerical density of any of the profiles in the deep (close to stratum pyramidale) part of the proximal (close to DG) region of the suprapyramidal mossy fiber zone, but did not alter the numerical density of any of the profiles in the superficial (distal to stratum pyramidale) parts of either proximal or distal (close to CA1) regions. Average size of CN profiles in the distal region was increased by lead exposure. The pattern of effects suggests that low-level lead exposure during development preferentially affects later developing structures within the hippocampal formation, rather than affecting mature structures.

Additive statistical effects of cadmium and lead on heart-related disease in a North Carolina autopsy series

The association of heart-related mortality with tissue cadmium and lead in a study of autopsies performed on persons who resided in a soft-water, leached-soil area of North Carolina was examined. Liver cadmium concentrations and aortic lead level were indices of these elements. Both cadmium and lead levels had statistically significant correlations with cause of death (heart-related disease vs. non-heart-related disease, excluding cancer). Although cause of death was significantly associated with age, the association with cadmium and lead persisted after statistical adjustment for the effect of age. The combined effects of cadmium and lead provided sufficient information in an additive model to predict cause of death correctly for 80% of the cases, with age contributing insignificantly. These findings indicate the intimate relation of these two trace metals with increased risk of heart-related mortality, even in light of known conventional causes of such deaths.

Intracellular localization of lead in tissues of the mute swan

The aim of this study was to examine the ultrastructure of kidney, liver, blood and intestine of a lead-poisoned bird and compare these with tissues of a healthy bird. From these results it was hoped to reveal that any abnormalities observed were due to lead poisoning and consequently suitable sections were also selected for X-ray analysis. Renal intranuclear inclusions were present in the lead-poisoned swan. X-ray analysis clearly demonstrated that these granules consist of an amorphous mass of lead probably as lead phosphate. Large numbers of electron dense granules were observed in the liver of the lead-poisoned bird and occasionally in the healthy swans liver. X-ray analysis demonstrated that these granules contain iron. Some of the red blood cells of the lead-poisoned swan have opaque granules associated with the plasma membrane, these were not observed in the healthy swan.

Retardation of Schwann cell division and axonal regrowth following nerve crush in experimental lead neuropathy

In experimental lead neuropathy, Schwann cells undergo segmental demyelination and possible cell death and, concurrently, remyelination and multiplication to create new internodes of myelin and onion bulb formations. In rats fed 4% lead carbonate for three months, the ability of Schwann cells to divide (percentage showing mitotic figures, labeling index, n total number per millimeter of fascicular length of nerve) was studied serially for four weeks. Schwann cell events were also compared in sural nerve distal to crush with and without resection of an intervening length of nerve. In both cases, Schwann cell multiplication as a result of axotomy was retarded in lead-intoxicated as compared to control animals. On the average, regrown myelinated axons four weeks after and 10 mm below the point of crush in lead-treated animals were similar in number and smaller in caliber, but they exhibited a normal relationship of myelin thickness to axonal area compared with control animals. These studies provide evidence that Schwann cell division and axonal regrowth after crush are retarded in experimental lead neuropathy.

Ultrastructural changes in the kidneys of rabbits treated with lead acetate

Electron microscopical studies were carried out on the kidneys of rabbits given s.c. injections of 0 (control), 0.25 or 0.50 mg lead acetate/kg b.w. 3 times a week during 14 weeks. At the end of the experimental period the animals had lead blood levels of 60, 500 and 600 micrograms/l whole blood respectively. Treatment-related renal changes were found in the proximal tubules; they consisted of a dose-related increase in the amount of lysosomes in epithelial cells of the convoluted part, and of severely damaged cells and loss of brush border in the straight part. There was also an increase in lysosomal tubular inclusions, which are considered characteristic of lysosomes of the proximal tubular cells of the rabbit kidney. The significance of these findings for assessing the risk of occupational exposure to lead is briefly discussed.

[Toxic occupational liver diseases. Therapeutic effects of silymarin]

We considered two groups, one of 35 and the other of 20 patients, with occupational toxic hepatopathy caused by various toxic substances (mostly solvents, paints and glues). The patients were mostly suffering from chronic or subacute forms. We considered the work conditions in the anamnesis, the period of exposure and most important laboratory parameters of hepatic function checked before and after treatment with Silymarin (420 mg/die/os) for the first group and with "placebo" for the second group. Five patients of the first group were diagnosed by biopsy. The treatment with Silymarin has shown slight variations in some parameters. The therapeutic effect is probably not dependent upon the kind of pathogen noxa; it seems instead to be more evident when the exposure period is shorter. The group "placebo" does not show significant variations.

Histological effects and lead concentrations in tissues of adult male ringed turtle doves that ingested lead shot

Adult male ringed turtle doves (Streptopelia risoria) were administered 0 or 4-110 mg lead shot and/or were exposed to cold temperatures (6 +/- 1 degrees C). Five of the seven doves that ingested shot and were exposed to cold died. Doves that ingested shot and were not exposed to cld (21 +/- 1 degrees C) had no mortality after 9 d, but several birds had seizures. Tissues were examined microscopically for lesion. Doves ingesting shot consistently had Pb intranuclear inclusion bodies in cells of the proximal convoluted tubules, except if death occurred 48 h after shot ingestion. In such cases as in cold-exposed, Pb-treated birds), intracytoplasmic inclusions were detected. Hemosiderin loading in kupffer cells and rarely in hepatocytes was observed in doves ingesting Pb whether they were exposed to a normal temperature or to cold. it appeared that ingestion of shot could abruptly disturb spermatogenesis in ringed turtle doves. The seminiferious tubules were often devoid of spermatozoa in doves ingesting Pb.

Gingival pigmentation as the sole presenting sign of chronic lead poisoning in a mentally retarded adult

A diagnosis of chronic lead poisoning in a mentally retarded adult with pica was initially proposed because of the presence of a "lead line" on the patient's gingiva. The patient had no other signs or symptoms suggestive of her toxic state. Lead poisoning is reviewed from the standpoint of epidemiology, pathophysiology, clinical and oral manifestations, and diagnostic procedures. Dentists working with children or mentally retarded patients should be aware of the increased incidence of lead poisoning in these patient populations and the importance of oral findings and lead-screening techniques in the detection of lead poisoning.

New knowledge on the origin, function and fate of osteoclasts

The most recent findings on the origin, life-span and fate of the osteoclast can be summarized as follows. Osteoclasts originate from progenitor, mononuclear, lymphoid cells which reach the bone surface through the bloodstream. Osteoclasts resorb bone by secreting lysosomal enzymes and procollagenase in the osteoclast-bone interspace. The organic components of the matrix (first interfibrillary substance, then collagen fibrils) are digested in the extracellular space. Dislodged crystals and residual organic constituents are then phagocytosed and collected in cytoplasmic vacuoles where they are completely solubilized. The ruffled border and the adjacent "clear" zone constitute the resorbing apparatus, whose development is roughly proportional to osteoclast activity. Osteoclast nuclei are continuously incorporated and shed, so that individual cells are continuously renewed. This makes the life-span of the osteoclast extremely difficult to determine. The life of each individual osteoclast might theoretically continue as long as the stimulus to resorption persists and sufficient bone matrix is available. Primary abnormalities of the osteoclasts can induce pathologic skeletal changes, as in the case of osteopetrosis and Paget's disease of bone. Conversely, skeletal abnormalities may damage osteoclasts, as in the case of lead intoxication. When this happens, osteoclasts are essentially characterized by an underdeveloped ruffled border, pyknotic nuclei, detachment from the bone matrix and, finally, shrinkage and fragmentation. It is not yet known whether these changes only occur in pathologic conditions, or whether they are the alterations which lead senescent osteoclasts to death even in normal bone.

Drug- and heavy metal--induced hyperpigmentation

Several categories of chemical and pharmacologic agents can cause alterations in cutaneous pigmentation, although the mechanisms differ and in several instances may be unknown. Fixed drug eruptions appear to have alteration of the basement membrane zone with incontinence of epidermal pigment as the mechanism of hyperpigmentation. Heavy metals produce increased pigmentation in part from deposition of metal particles and in part from an increase in epidermal melanin production. The antimalarials may bind to melanin. The phenothiazines and minocycline produce pigmentation from deposition of the drug. The mechanism, site, and nature of the pigment occurring with antineoplastic agents is not well understood, but the location is most likely predominantly epidermal. Clofazimine (Lamprene) alteration in pigmentation appears to result from deposition of the drug in subcutaneous fat.