Lead poisoning and the blood-brain barrier

Lead exposure may produce varying degrees of neuropsychiatric manifestations from discrete phenomena, quite often seen in children and as an occupational disease, to the rate fulminant lead encephalopathy. It was determined whether or not damage of the blood-brain barrier permeability in adult rats, as has been demonstrated in neonatal animals exposed to lead, could also play a role. Massive lead exposure did not induce any change in the transfer (facilitated diffusion) of phenylalanine any tyrosine measured by means of the indicator dilution technique. Ultrastructural examination, after application of horseradish peroxidase, did not reveal any pathological changes in the permeability to the tracer. It is concluded that in adult rats, in contrast to neonatal animals, the observed pathological signs clearly seen in the chronically exposed animals must be ascribed to a noxious influence of lead on the extravascular side of the blood-brain barrier.

Liver changes under combined effect of working environmental factors

Liver changes after separate and combined action of vibration (whole body, 100 Hz, 0.1 mm amplitude) and other factors: noise (white noise 105 dB/A), heat (35 degrees C, humidity 45--55% and air velocity 0.2--0.3 ms-1) and lead (lead acetate, 20 mg/kg) were studied in white rats. The exposure lasted for 2 h daily during 10 days (lead was daily applied per os in a water solution). After the treatment in liver homogenates the activity of SucDH, LDH, and ATP-ase, as well as the quantity of soluble proteins (SP) and -SH gr were determined. In fresh frozen liver slices the activity of SucDH, LDH, and ATP-ase were investigated. Liver samples were studied by light and electro-microscopy. The results show that vibration alone did not produce marked changes, but when the other factors acted simultaneously, more expressed alterations in the liver were found. The most pronounced changes were obtained after vibration and lead effect. The histological, histochemical, and electron-microscopic findings support the biochemical data about certain disturbances in the energy supply and utilization in the liver tissue.

Blood nerve barrier in rat and cellular mechanisms of lead-induced segmental demyelination

Feeding of lead carbonate to rats causes widespread and reproducible segmental de- and remyelination of myelinated fibers (MFs) of peripheral nerve. Such segmental demyelination might be explained by increased permeability of endoneurial capillaries to serum containing protein-bound lead. The perineurium of control and lead nerves was impermeable to fluorescein-labeled bovine albumin (FBA) and to horseradish peroxidase (HRP). Epineurial capillaries in both conditions allowed HRP to pass freely between and, to a lesser extent, through endothelial cells. Confirming earlier work, endoneurial capillaries of control rats did not appear to allow HRP to pass between endothelial cells, but allowed some to pass by pinocytosis through endothelial cells where it was taken up by macrophages. Contrary to expectation, flooding of the endoneurium with HRP was seen in only 1 of 36 tissue blocks of lead nerves from rats fed 4% lead carbonate for 7 1/2 and 12 weeks. Abundant HRP reaction product was seen in the epineurium in more than half of these tissue blocks. HRP was not generally found in endoneurial fluid, even in lead nerves with marked edema and widespread segmental de- and remyelination. These findings are against a massive breakdown of the blood nerve barrier, so that HRP passes freely into the endoneurium between endoneurial endothelial cells. It was our impression that HRP reaction product was slightly increased in endoneurial endothelial cells and macrophages of lead nerves as compared to control nerves. These studies suggest that there may be an increased transfer of HRP through endoneurial cells in lead neuropathy. The studies do not provide additional evidence that an altered blood nerve barrier is involved in the development of segmental demyelination in lead neuropathy.

The endoneurial content of lead related to the onset and severity of segmental demyelination

The endoneurial lead and water content was serially evaluated in the nerves of rats fed lead carbonate and related to the onset and severity of segmental demyelination and remyelination. Lead began to accumulate significantly in the endoneurium by 5 days, reached a maximum level (71 microgram/g dry weight) by 34 days, and then fell to the perineurial level (28 microgram/g dry weight) by 3 months. The water content of endoneurium did not become significantly increased until the 50th day. Extensive teased fiber grading of pathologic abnormalities carried out on the same animals showed that segmental demyelination began between the 20th and 35th days and worsened progressively. This provides the first evidence that high endoneurial lead concentration precedes segmental demyelination and nerve edema. It suggests that the random Schwann cell damage is more likely to be due to a direct toxic effect of lead rather than to a factor associated with edema or increased endoneurial pressure. Contrary to our expectations, lead content does not parallel water content, as would be expected if lead entry into the endoneurium were associated with an abrupt breakdown of the blood-nerve barrier. A further new finding is the decrease in endoneurial lead content at a time when edema and the pathologic lesions are progressing. This may suggest the development of lead removal mechanisms.

Changes in endoneurial fluid pressure, permeability, and peripheral nerve ultrastructure in experimental lead neuropathy

The dynamics of endoneurial edema were studied by quantifying endoneurial fluid pressure (EFP) during the development of lead neuropathy and correlating these data with changes in blood-nerve barrier permeability and with morphological alterations in nerves, capillaries, and Schwann cells. EFP measured from the sciatic nerve in control Long-Evans rats was 2.1 +/- 1.0 cm H2O. EFP was significantly elevated 7 weeks after animals were started on a diet containing 6% lead carbonate, and it increased progressively until a plateau in pressure was reached between weeks 9 and 11. Thereafter, EFP gradually returned to normal values. The progressive increase in EFP was highly correlated with the extravasation of osmotically active macromolecules, traced by fluorescein isothiocyanate-dextran compounds of graded molecular weight and by horseradish peroxidase (HRP). Electron microscopy revealed extravasation of HRP between endothelial cells, intranuclear inclusions characteristic of lead poisoning in Schwann cell nuclei, demyelination, and remyelination. The observation of intranuclear inclusions consistent with lead deposition in Schwann cells strengthens the hypothesis that extravasated lead in the interstitial fluid causes direct injury to Schwann cells, giving rise to demyelination. Nerve compliance was determined.

An in vitro study of the effects of lead on an epithelioid cell line

The effects of a growth-inhibiting dose of lead on the cell surface, mitochondria, and vacuoles of RLC-GAI cells, an epithelioid cell line, were examined. The cells were found to begin to retract from the culture dish, becoming rounded in shape as early as 6 hours after lead addition. The rounded cells were found to be more susceptible to osmotic shock than normal cells. Studies with cytochalasin B showed that microfilaments were able to polymerize in the lead-treated rounded cells and microvilli were normal. Calcium did not prevent cell rounding by lead. Lead-induced detachment was reversed when cells were placed in normal medium. Mitochondrial and vacuolar alterations became apparent after several additional days. There was a decrease in the fraction of cytoplasm containing mitochondria and in the amount of cristae surface area in mitochondria. In cells incubated in mainly particulate lead increased numbers of lead-containing vacuoles were also seen.

Electron probe microanalysis of isolated brain capillaries poisoned with lead

The blood-brain barrier has been proposed as an important site for the toxic action of lead in the central nervous system. To investigate this, capillary endothelial cells were isolated from rat cortex and exposed to lead in vitro. Tissue suspensions were then prepared for electron microscopy and X-ray microprobe analysis. In cells exposed in vitro to lead, electron-dense deposits were observed within mitochondria. With X-ray analysis, it was determined that these intramitochondrial deposits contained lead in a non-crystalline matrix. Also, lead appeared to be accumulated in the same intramitochondrial areas as calcium. The results suggest that lead is preferentially sequestered in mitochondria of capillary endothelial cells. Further, this selective localization may be associated with lead-induced disruptions in intracellular calcium metabolism and transepithelial transport processes.

Lead poisoning in monkeys: functional and histopathological alterations of the kidneys

Ten monkeys (Macacus Irus) were given 0--15 mg of lead acetate (in drinking water) 6 days a week for 9 months. Two of the monkeys were also put on a low calcium diet with 6 mg of lead acetate/day. The blood lead level usually increased from the third month according to the dose of lead ingested and more quickly in monkeys deprived of calcium. Some of the monkeys showed signs of alteration in protein glomerular filtration and/or proximal tubular reabsorption. Studies using optical and electron microscopy showed distinct pathological changes in the proximal tubular epithelium where heavy deposits of lead were seen in the nuclei.

Experimental lead paint poisoning in nonhuman primates. III. Pathologic findings

Necropsies were performed on 25 rhesus monkeys, three cebus monkeys and three baboons which had been fed leaded paint or lead acetate at various doses up to 666 days. The 31 test primates and six controls ranged in age from five days to about eight years. In addition, the brains of 13 subadult squirrel monkeys fed lead oxide and two controls were studied grossly and microscopically. Lead content of liver, kidney and brain correlated with clinical outcome and typical histologic changes. Neuropathologic lesions, most severe in the young, occurred in 28 of 43 test primates despite a paucity of neurological signs. Brain lesions were similar to those occurring in human lead encephalopathy and included degenerative and proliferative changes of small vessels, ring hemorrhages, edema, perivascular hyalin droplets, rosette-like deposits of proteinaceous exudates, focal loss of myelin, astrogliosis and necrosis of hippocampal neurons.

A quantitative histological study of the effects of acute triethyl lead poisoning on the adult mouse brain

The effects of a single injection of triethyl lead chloride on the mouse brain was studied 1, 3, 5, 7 and 30 days postinjection using quantitative histological techniques. The total number of glia in the anterior commissure was significantly reduced following injection but by 30 days postinjection had returned to normal. The number of neurons and the number of glia in the indusium griseum did not change significantly. The number of mitotic cells in the subependymal layer fell slightly from 1 to 3 days postinjection then returned to normal 5 days postinjection. The number of pyknotic cells in the subependymal layer did not appear to change following injection. In the anterior commissure the number of mitotic cells fell significantly from 1 to 3 days postinjection and then increased significantly at 5 days postinjection. A similar increase in mitosis was found at 5 days postinjection in the indusium griseum. At 7 days postinjection a significant decrease occurred in pyknotic cells in the anterior commissure and indusium griseum. Changes in the percentage of each type of glial cell present were found 30 days postinjection. This suggests that although the total number of glia may return to normal the number of each type of glial cell present changes following injection of triethyl lead. There was no evidence of cerebral oedema following triethyl lead injection either at the light or electron microscopic level.