Abnormal tissue distribution of lead in amyotrophic lateral sclerosis

Metals and neurodegenerative diseases. A systematic review

Neurodegenerative processes encompass a large variety of diseases with different pathological patterns and clinical presentation such as Amyotrophic Lateral Sclerosis (ALS), Alzheimer Disease (AD) and Parkinson's disease (PD). Genetic mutations have a known causative role, but the majority of cases are likely to be probably caused by a complex gene-environment interaction. Exposure to metals has been hypothesized to increase oxidative stress in brain cells leading to cell death and neurodegeneration. Neurotoxicity of metals has been demonstrated by several in vitro and in vivo experimental studies and it is likely that each metal could be toxic through specific pathways. The possible pathogenic role of different metals has been supported by some epidemiological evidences coming from occupational and ecological studies. In order to assess the possible association between metals and neurodegenerative disorders, several case-control studies have also been carried out evaluating the metals concentration in different biological specimens such as blood/serum/plasma, cerebrospinal fluid (CSF), nail and hair, often reporting conflicting results. This review provides an overview of our current knowledge on the possible association between metals and ALS, AD and PD as main neurodegenerative disorders.

Motor neuron disease mortality and lifetime petrol lead exposure: Evidence from national age-specific and state-level age-standardized death rates in Australia

BACKGROUND

The age standardized death rate from motor neuron disease (MND) for persons 40-84 years of age in the Australian States of New South Wales, Victoria, and Queensland increased dramatically from 1958 to 2013. Nationally, age-specific MND death rates also increased over this time period, but the rate of the rise varied considerably by age-group. The historic use of lead (Pb) additives in Australian petrol is a candidate explanation for these trends in MND mortality (International Classification of Disease (ICD)-10 G12.2).

METHODS

Leveraging temporal and spatial variation in petrol lead exposure risk resulting from the slow rise and rapid phase-out of lead as a constituent in gasoline in Australia, we analyze relationships between (1) national age-specific MND death rates in Australia and age-specific lifetime petrol lead exposure, (2) annual between-age dispersions in age-specific MND death rates and age-specific lifetime petrol lead exposure; and (3) state-level age-standardized MND death rates as a function of age-weighted lifetime petrol lead exposure.

RESULTS

Other things held equal, we find that a one percent increase in lifetime petrol lead exposure increases the MND death rate by about one-third of one percent in both national age-specific and state-level age-standardized models of MND mortality. Lending support to the supposition that lead exposure is a driver of MND mortality risk, we find that the annual between-age group standard deviation in age-specific MND death rates is strongly correlated with the between-age standard deviation in age-specific lifetime petrol lead exposure.

CONCLUSION

Legacy petrol lead emissions are associated with age-specific MND death rates as well as state-level age-standardized MND death rates in Australia. Results indicate that we are approaching peak lead exposure-attributable MND mortality.

The Expression and Significance of Metallothioneins in Murine Organs and Tissues Following Mercury Vapour Exposure

The fate of inspired mercury vapour (Hg0) is critical in the central nervous system (CNS) where it can circumvent the blood—brain barrier (BBB) at the neuromuscular junction (NMJ) and accumulate indefinitely in motor neurons by retrograde transport. The detoxification of systemic Hg0 by lung and liver requires investigation. We exposed 129/Sv wild-type (Wt) and 129/Sv MT-I, II double knockout (KO) mice to 500 μg Hg0/m3 for 4 hours to investigate the expression of MT in the lung, liver, and spinal cord following Hg0 exposure using unexposed groups as controls. There were congestive changes in liver and lung of both Wt and MT-KO groups of Hg0-treated mice; these changes appeared more pronounced in the MT-KO group. Motor neurons in the spinal cord did not show any pathological changes. Based on expression of MT, liver appears to have a major role in trapping and stabilising mercury. In the spinal cord, MT was expressed in all white matter astrocytes and in some grey matter astrocytes. Notably, motor neurons did not express MT, and the presence of MT could not be demonstrated in the axons of the ventral root. The absence of MT expression in motor neurons and their axons suggests the dependence of the motor system on the detoxifying capacity of liver MTs.

A meta-analysis of observational studies of the association between chronic occupational exposure to lead and amyotrophic lateral sclerosis

OBJECTIVE

The association between occupational exposure to lead and amyotrophic lateral sclerosis (ALS) was examined through systematic review and meta-analyses of relevant epidemiological studies and reported according to PRISMA guidelines.

METHODS

Relevant studies were searched in multiple bibliographic databases through September 2013; additional articles were tracked through PubMed until submission. All records were screened in DistillerSR, and the data extracted from included articles were synthesized with meta-analysis.

RESULTS

The risk of developing ALS among individuals with a history of exposure to lead was almost doubled (odds ratio, 1.81; 95% confidence interval, 1.39 to 2.36) on the basis of nine included case-control studies with specific lead exposure information, with no apparent heterogeneity across included studies (I = 14%). The attributable risk of ALS because of exposure to lead was estimated to be 5%.

CONCLUSIONS

Previous exposure to lead may be a risk factor for ALS.

Exposure to environmental toxicants and pathogenesis of amyotrophic lateral sclerosis: state of the art and research perspectives

There is a broad scientific consensus that amyotrophic lateral sclerosis (ALS), a fatal neuromuscular disease, is caused by gene--environment interactions. In fact, given that only about 10% of all ALS diagnosis has a genetic basis, gene-environmental interaction may give account for the remaining percentage of cases. However, relatively little attention has been paid to environmental and lifestyle factors that may trigger the cascade of motor neuron degeneration leading to ALS, although exposure to chemicals--including lead and pesticides-agricultural environments, smoking, intense physical activity, trauma and electromagnetic fields have been associated with an increased risk of ALS. This review provides an overview of our current knowledge of potential toxic etiologies of ALS with emphasis on the role of cyanobacteria, heavy metals and pesticides as potential risk factors for developing ALS. We will summarize the most recent evidence from epidemiological studies and experimental findings from animal and cellular models, revealing that potential causal links between environmental toxicants and ALS pathogenesis have not been fully ascertained, thus justifying the need for further research.

Analysis of factors that modify susceptibility and rate of progression in amyotrophic lateral sclerosis (ALS)

We conducted case-control and prospective longitudinal studies to examine risk factors and predictors of disease progression for ALS. Ninety-five subjects with ALS and 106 healthy control subjects were enrolled. All subjects completed a risk factor questionnaire at enrollment. The ALS subjects were prospectively followed for one year to define factors that influence the rate of disease progression, measured by rate of change in percent predicted forced vital capacity (%FVC) and the ALS functional rating scale (ALSFRS) score. The association of each potential risk factor with ALS was determined using univariate logistic regression. A random slope model was used to determine the association of each risk factor with disease progression. The demographic characteristics of ALS subjects and controls at enrollment did not differ. Significant risk factors for ALS included reported exposure to lead (p = 0.02) and pesticides (p = 0.03). Disease progression was faster in the ALS subjects having bulbar onset and a shorter time period between onset of symptoms and diagnosis. Pertinent variables not associated with either causation or progression of ALS included physical activity, cigarette smoking and a history of physical trauma or other clinical disorders.

Atrophy of Large Myelinated Motor Axons and Declining Muscle Grip Strength Following Mercury Vapor Inhalation in Mice

The effects of acute mercury vapor (Hg(0)) exposure on the peripheral motor system have not been previously addressed in the literature. Early case studies report that acute exposure in humans can cause symptoms resembling motor neuron disease (MND). Mercury granules can be histochemically demonstrated in the cytoplasm of murine motor neurons following Hg(0) exposure, suggesting it is transported from the neuromuscular junction (NMJ) to the cell body by retrograde axonal transport mechanisms. We considered the hypothesis that morphological damage to the peripheral motor axonal cytoskeleton possibly involving neurofilaments (NFs) follows Hg(0) exposure. Eight-week-old wild type (Wt) 129S/v mice were exposed to 500 microg/m(3) of Hg(0) for 4 h in an experimental vapor exposure chamber. Forelimb grip strength (FGS) was measured over 4-wk intervals prior to removal of the murine phrenic nerves (MPN) 7 mo postexposure. Autometallography of 7-microm-thick spinal-cord sections from Hg(0)-exposed mice confirmed the presence of mercury deposits in ventral horn motor neurons. The morphology of the myelinated motor axons was assessed by computer-assisted image analysis of 1-microm-thick resin cross sections of the MPN. The group exposed to Hg(0) showed a significant reduction in the mean axon caliber, p < .0001. Gaussian spectral analysis of axon diameter distribution showed atrophy principally to large myelinated fibers, a subpopulation of axons that is also affected in MND. This atrophic change was also accompanied by an increased irregularity in axon shape. FGS initially increased with age until 20 wk and then progressively decreased after 22 wk to 36 wk. In conclusion, Hg(0) exposure appears to reduce axon diameter, suggesting axon caliber-determining cytoskeletal components such as neurofilaments may be damaged by heavy metal-induced oxidative stress mechanisms, resulting in functional changes to motor units.

Amyotrophic lateral sclerosis: possible role of environmental influences

This treatise briefly discusses the genetic features of ALS and reviews environmental exposures in sporadic ALS. At least 10 genetic foci are responsible for cases of familial motor neuron disease and more are yet to be discovered. Research into sporadic ALS suggests that abundant factors apparently participate in the disease process. A singular cause and unifying disease and nerve dysfunction in polyneuropathies, a multitude of genetic, toxic, autoimmune, infectious, and systematic processes seem to be at play. The ALS syndrome likely will not be dissimilar.

Urinary excretion of lead and mercury after oral administration of meso-2,3-dimercaptosuccinic acid in patients with motor neurone disease

Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) are progressive neurodegenerative disorders involving motor neurones. The aetiology of the non-familiar forms is still unknown but it has been suggested that long-term exposure to heavy metals such as lead and mercury may play a role in the pathogenesis of these diseases. In 53 patients suffering from ALS (n = 42) and SMA (n = 9) the oral administration of dimercaptosuccinic acid (DMSA, 20 mg/kg) did not result in a greater mobilization of lead and mercury from peripheral depots than in control subjects. Although it cannot be excluded that the amount of lead or mercury excreted after DMSA administration may not be a reflection of the amount accumulated in the motor neurons, this study does not provide support for the hypothesis that heavy metals play a significant role in the occurrence of motor neurone diseases.

Motor neuron disease: a primary disorder of corticomotoneurons?

It has been suggested that the primary site of damage in motor neuron disease (MND) is the cortical motor neuron, with secondary degeneration of spinal motor neurons. To test this hypothesis, we sought to determine if loss of corticomotoneurons in MND precedes spinal motor neuron loss. The density of corticomotoneurons was measured in 18 MND and 9 control cases using 10-microns horizontal sections of motor cortex in the hand/arm region. The density of spinal motor neurons was measured in 10-microns transverse sections of the lower cervical spinal cord. Corticomotoneuron and spinal motor neuron densities were decreased in MND cases compared to controls, but in MND cases there was poor correlation (r2 = 0.06) between corticomotoneuron and spinal motor neuron densities. The results indicate that corticomotoneuron and spinal motor neurons are lost at different rates in different MND patients, and that corticomoteneuron loss is unlikely to be a primary event in MND.

A review of axonal transport of metals

Neurons have efficient mechanisms for the transport of organelles and chemical substances in axons to the nerve terminals and back to the cell bodies. Enzymes involved in transmitter synthesis, peptide transmitters and their precursors are examples of macromolecules that are transported down the axon, anterogradely. For final degradation and possible reuse, many constituents are transported back to the cell body, retrogradely. Retrograde transport is also a pathway by which certain toxins may bypass the blood-brain barrier and accumulate in neurons. In recent years, it has been shown that certain metals may accumulate in neurons following retrograde transport. The metals for which retrograde transport has been demonstrated include lead, cadmium and mercury. In this article recent findings regarding axonal transport of metals are reviewed. The putative mechanisms involved in the uptake of metals into the nerve terminal and the fate of metals in the cell body are outlined. Axonal transport of metals as a possible etiological factor in diseases of the human nervous system is discussed.

Lead uptake in motor axons

In an attempt to determine whether lead (Pb) in striated muscle can be taken up by motor axon, mice were injected intramuscularly with a 5% Pb nitrate solution, and the passage of Pb through the tissues was traced with electron microscopy. Thirty minutes after injection in the tibialis anterior muscle, Pb was seen at the sarcolemma and axolemma of the neuromuscular junction (NMJ) and in the adjacent sarcoplasmic reticulum (SR). Pb was also present in the axoplasm and mitochondria of terminal and preterminal motor axons. The presence of Pb was confirmed with x-ray elemental microanalysis. The results indicate that there is a pathway for intramuscular Pb to enter terminal motor axons. This supports the hypothesis that some forms of motor neuron disease (MND) may be due to axonal uptake and retrograde transport of Pb.

[Motor neuron disease: metabolic evaluation]

The authors studied serum and urinary calcium and phosphorus levels, as well as abnormalities on the spine of 30 patients with motor neuron disease. The authors believe in multifactorial aspects in the pathogenesis of motor neuron disease, calling special attention to toxic and metabolic factors.

The effect of nerve crush and botulinum toxin on lead uptake in motor axons

After lead (Pb) is injected into striated muscle it binds to the sarcolemma of the neuromuscular junction (NMJ) and crosses into the terminal axons of motor neurons. To find out whether this intra-axonal accumulation of Pb is due to active transport or to diffusion down a concentration gradient, Pb uptake into motor axons of mice was studied at active and inactive NMJs. Twenty-four hours after sciatic nerve crush, 0.1 ml of 5% lead nitrate was injected into the tibialis anterior muscle and 30 min later the location of Pb was sought with electron microscopy and X-ray elemental analysis. A greatly reduced amount of Pb entered the axons after nerve crush compared to non-nerve crush animals, indicating that an active NMJ is required for intra-axonal Pb accumulation. To test if Pb could be entering the axon via recycling vesicles, botulinum toxin (BoTx) was injected into the muscle 24 h before Pb injection. There was no difference in intra-axonal Pb uptake in control and BoTx-injected animals, indicating that Pb is unlikely to use recycled vesicles to enter the axon.

Animal models of amyotrophic lateral sclerosis and the spinal muscular atrophies

The causes of human amyotrophic lateral sclerosis (ALS) and the spinal muscular atrophies (SMA) are, almost without exception, unknown. This ignorance has stimulated the search for animal models to obtain insight into the etiology, pathogenesis and biochemical mechanisms underlying the human disorders. None of the 38 animal models, described in this review, provides an exact animal copy of a specific human motor neuron disease. Most of the models reproduce certain structural or physiological aspects of their human counterparts. The various experimental models can be classified according to the pathogenetic mechanism involved and according to the structural changes observed. Models based on experimentally induced disease, include heavy metals and trace elements (lead intoxication in guinea pigs, rabbits, rats, cats and primates; mercury intoxication in rats; aluminium intoxication in rabbits; swayback in goat kids; calcium and magnesium deficient rabbits and primates and calcium deficient cynomolgus monkeys), toxins (IDPN, vincristine, vinblastine, podophyllotoxin, colchicine, maytansine, maytanprine, L-BMAA, lectins, adriamycin), nutritional factors (ascorbic acid deficient guinea pigs), virus infection (spongiform polioencephalomyelitis, attenuated poliovirus, lactate dehydrogenase-elevating virus), and immunological factors (immunization with motor neurons). Hereditary models comprise hereditary canine spinal muscular atrophy, hereditary neurogenic amyotrophy in the pointer dog, Stockard paralysis, Swedish Lapland dog paralysis, "wobbler" mouse, "shaker" calf, and hereditary spinal muscular atrophy in zebra foals, crossbred rabbits,

Epidemiology of amyotrophic lateral sclerosis in the province of Modena, Italy. Influence of environmental exposure to lead

A retrospective study of all admissions to the University of Modena Neurological Department from 1976-1986; 51 cases of amyotrophic lateral sclerosis (ALS) were found. ALS mean annual incidence was 0.78/100,000 inhabitants, while prevalence was 2.35/100,000. Mean age at onset was 61.43 years, mean and median duration of illness were, respectively, 28.83 and 24.5 months, and survival at 5 years post-onset was 24.4%. A tendency to higher incidence and prevalence of ALS in the ceramic district, when compared with those of the rest of the province was found. However, the small number of cases did not allow any conclusive statistical correlation between environmental exposure to lead and frequency of ALS.

Retrograde axonal transport of mercury

Female Wistar rats were injected in the tongue with a small volume of 203Hg and were killed 2 weeks later. The lower brain stem with the hypoglossal nuclei was removed and sectioned in a cryostat. Autoradiography of freeze-dried sections showed labeling of both hypoglossal nuclei. The results are regarded as strong evidence of retrograde axonal transport of mercury in the hypoglossal nerve.

Morbidity and mortality in motor neuron disease: comparison with multiple sclerosis and Parkinson's disease: age and sex specific rates and cohort analyses

The cause of motor neuron disease (MND) remains unknown although recent reports have suggested a possible rise in mortality rate. The present account describes age-specific patterns in morbidity rate and cross-sectional and cohort analyses of mortality rate, and compares these with those in multiple sclerosis and Parkinson's disease. First hospital admission rate for motor neuron disease (a proxy for incidence rates) rose steadily with age in males and females until the age of 75 years or more, but then fell, but only in females. This irregular pattern suggested the possibility of an environmental effect on certain older birth cohorts. The validity of the results was supported by a similar pattern in the two hospital regional authorities studied and the difference between this pattern and that found in multiple sclerosis and Parkinson's disease. Age-specific mortality rates of motor neuron disease between 15 and 64 years for males and females in England and Wales from 1940 to 1982 rose steadily with age. Mortality rates after the age of 65 fell in all female cohorts studied, but only in the earlier male cohorts. Unlike Parkinson's disease there was no strong birth cohort effect. However an analysis of Office of Population Censuses and Surveys (Registrar General) reports has revealed a slight increase in the age-specific mortality rate in both males and females aged 65 and over for successive birth cohorts born since 1900. Neither changes in ICD coding or in diagnostic habits could account for this pattern, which differed from that seen in Parkinson's disease. No such effect was seen in multiple sclerosis.

High accuracy (stable isotope dilution) measurements of lead in serum and cerebrospinal fluid

The concentration of lead in blood, serum, cerebrospinal fluid, and urine was measured in patients with neurological disease and in control subjects including cases of plumbism. A plot of blood lead versus serum lead resembles the familiar curves of blood lead versus either free erythrocyte porphyrin or urinary delta-aminolaevulinic acid in that serum lead is constant up to a blood lead concentration of 40 micrograms/dl (2 mumol/l) and rises steeply thereafter. The serum lead concentrations yield renal clearances in the range 5-22 ml/min in agreement with values obtained with radiolead on man and predicted from animal studies. The lead content of cerebrospinal fluid is consistently less than that of serum, averaging 50% of the serum concentration for blood leads of less than 20 micrograms/dl (1 mumol/l) but rising to 80-90% in cases of plumbism. Patients with motor neurone disease could not be distinguished from those with other neurological diseases on the basis of the lead content of their serum or cerebrospinal fluid.

Lead neuropathy

The still unexplained nature of the neurotropic action of lead has prompted this chronological survey of the course of development of the medical attitude towards the problems of lead neuropathy all along the centuries--from ancient times up to the present. Once a conspicuous, severe, and even frequent clinical type of plumbism, peripheral lead neuropathy has received due attention in the early classics (Tanquerel des Plances, Duchenne, Aran, Remak, Romberg, Erb, etc.) and of the pioneers in industrial medicine (Legge, Aub, Teleky, Hamilton). Even the modern era, however, has not come further than to state that lead produces different neurological effects in different animal species and even in humans--different patterns of neuromuscular involvement. With the advent of electrophysiology, conflicting and inconsistent findings have also appeared, particularly in regard to overt and latent lead neuropathies. Theories regarding the mode and site of the neurotoxic action of lead are reviewed and data which might be used as arguments both in favor and against are presented.

Lead concentrations in blood, plasma, erythrocytes, and cerebrospinal fluid in amyotrophic lateral sclerosis

The purpose of the investigation was to elucidate the repeatedly discussed relationship between chronic lead intoxication and ALS. The following mean lead concentrations were determined in 9 patients with ALS: 8.65 +/- 3,91 micrograms/100 ml in the blood, 0.97 +/- 0.78 microgram/100 ml in the plasma, 19.15 +/- 5.0 micrograms/100 ml in the erythrocytes, and 0.89 +/- 0.44 microgram/100 ml in the cerebrospinal fluid. These values did not differ appreciably from the controls with 7.91 +/- 3.83 micrograms/100 ml (n = 14) in the blood, 1.13 +/- 0.46 microgram/100 ml (n = 10) in the plasma, 18.96 +/- 12.63 micrograms/100 ml (n = 10) in the erythrocytes, and 0.85 +/- 0.91 microgram/100 ml (n = 15) in the cerebrospinal fluid. These findings do not support the assumption of lead poisoning as a pathogenetic factor in ALS.

Epidemiology of motor neuron disease in northern Sweden

All cases of motor neuron disease (MND), encompassing amyotrophic lateral sclerosis (ALS), progressive bulbar paralysis (PBP) and progressive spinal muscular atrophy (PSMA), in northern Sweden, diagnosed between 1969-1980 have been analysed. 128 cases were found, corresponding to an average annual incidence rate of 1.67 per 100,000. The prevalence on December 31, 1980 was 4.8 per 100,000. Age-specific incidence rates were higher in the high age groups with a maximum at 60-64 years for males, at 70-74 years for females and at 65-69 years for the sexes combined. The median age at onset was 61 years. Clustering was not found in mining districts and overrepresentation of miners and stone treaters was not observed. Minor differences in incidence rates, as measured by the standardized morbidity ratio, SMR, were found between the inland, coastal and mountain areas. The median survival time after onset of disease was 32 months for ALS, 30 months for PBP and 70 months for PSMA. The combined survival rate for all MND cases was 28% after 5 years and 15% after 10 years. The male to female ratio was 1.1:1, and 4.7% were familial cases.

Further studies on the erythrocyte uptake of lead in vitro in amyotrophic lateral sclerosis (ALS) patients and controls. Abnormal erythrocyte fragility in ALS

Following our earlier observations on increased plasma concentrations of lead in amyotrophic lateral sclerosis (ALS), the erythrocyte uptake of lead from plasma has been studied in vitro. Whole-blood from ALS patients and controls was incubated after the addition of lead (0.6 mumol/l whole-blood) and plasma lead concentrations were repeatedly determined. Incubation was continued until haemolysis developed. Fairly stable plasma lead concentrations were established at, on the average, 0.5-0.6 mumol/l after 10-30 min and persisted throughout the incubation with no significant difference between ALS- and control samples. Unexpectedly, it was also observed that haemolysis occurred significantly earlier in the ALS- than in the control samples. Plateau levels in plasma lead concentration of the same order as in the present experiments have been observed both in ALS- and control samples in previous experiments with the same technique, where the lead dose added was twice as high, and these plateau levels were about 10 times higher than those observed in vivo in ALS patients and controls. It is therefore suggested that the final plasma lead concentrations in vivo is established by factors other than the erythrocyte uptake and it is improbable that the differences between ALS patients and controls in plasma lead concentration are associated with differences in the degree of lead uptake by the red cells. The increased plasma lead concentrations in ALS patients may instead be caused by increased fragility of the erythrocytes, as manifested by the earlier occurrence of haemolysis in the present experiments. The observation of increased red cell fragility is, however, also of interest as a possible manifestation of a generalized membrane defect.

Abnormal distribution of lead in amyotrophic lateral sclerosis--reestimation of lead in the cerebrospinal fluid

The lead concentration in CSF was determined by flameless atomic absorption spectrophotometry in 16 ALS patients and 22 control cases. The mean values were 0.69 +/- 0.55 (ALS) and 0.41 +/- 0.37 (controls), P < 0.01. This confirms our earlier findings of raised CSF lead levels in ALS but the present values are lower than previously reported for both ALS patients and controls.

Neuromuscular junction macromolecules in the pathogenesis of amyotrophic leteral sclerosis

An hypothesis regarding the pathogenesis of amyotrophic lateral sclerosis is presented, which places emphasis on extraneural cells. Classical experimental denervation is compared and contrasted with motor neuron disease, both from information in the literature as well as concepts deriving from the hypothesis. Background information regarding neuromuscular junction-specific (16S) acetylcholinesterase and a basal lamina-enriched surface glycoprotein (fibronectin) are presented, which suggest not only their mutual interaction, but likely parallel regulation on muscle cell surfaces by the motor nerve. Since 16S acetylcholinesterase likely contains basal lamina-type collagen and fibronectin specifically associates with collagen, a model relating activation of latent collagenase enzyme in amyotrophic lateral sclerosis is described. It is suggested that continued degeneration, including transneuronal effects, of the motor system ensues from random, continuous loss of nerve-muscle adherence resulting from collagen resorption at the neuromuscular junction.

Metals in spinal cord tissue of patients dying of motor neuron disease

To evaluate the role of toxic metals in causing motor neuron disease (MND), we used a photon-excited, energy-dispersive x-ray analytical system to measure the metal content of spinal ventral horn tissue. Specimens were taken from the cervical and lumbar enlargements of 7 patients who died of MND and the results compared with those found in 12 control patients. Anterior horn lead levels were elevated in MND patients compared to controls (mean, 40.7 micrograms/gm versus 14.6 micrograms/gm; p less than 0.05) and lead levels correlated with the duration of illness (r = +0.84, p less than 0.05). Only 2 MND patients had detectable manganese levels (72.3 and 132.2 micrograms/gm) whereas 1 control had detectable manganese (14.3 micrograms/gm). One MND patient had 244 micrograms/gm selenium, but 3 controls had levels of 180, 58, and 62. Patients with the histories of greatest environmental exposure to metals during life exhibited the highest tissue levels of metals after death; despite chelation therapy for about a year, high lead levels remained in their tissue.

Serum protein binding of lead in vitro in amyotrophic lateral sclerosis patients and controls

The binding of lead to serum proteins was studied in vitro in ALS-patients and controls. Serum was incubated with 210Pb, the proteins were separated by isoelectric focusing and the radioactivity in the different protein fractions was determined by liquid scintillation counting. The activity was concentrated in the orosomucoid (acid alpha1-glycoprotein) fraction both in ALS-patients and controls under the present experimental conditions and the capacity of this protein to bind lead was demonstrated in a control experiment. The findings are discussed in relation to our earlier observations on increased concentrations of lead in cerebrospinal fluid and plasma in ALS-patients and the hypothetical role of the retrograde axonal transport in motoneurons in the pathogenesis of ALS. The present observations do not lend support to the idea that the increased plasma concentrations of lead in the disease would be related to qualitative differences in serum protein binding.

Increased plasma levels of lead in patients with amyotrophic lateral sclerosis compared with control subjects as determined by flameless atomic absorption spectrophotometry

The levels of lead in plasma were determined in 16 cases of amyotrophic lateral sclerosis (ALS) and 18 control subjects, using flameless atomic absorption spectrophotometry. The mean values were 0.52+/-0.22 microgram/100ml (ALS) and 0.37+/-0.13 microgram/100ml (controls), the difference is statistically significant (5% level). The values in both groups are lower than reported earlier for normal subjects. The findings are discussed against the background of the possible pathogenetic significance of retrograde axoplasmic flow in ALS.

Capillary permeability in ALS, determined through transcapillary escape rate of 125I-albumin

Since various macromolecules have experimentally been demonstrated to be taken up by the motor end-plates and subsequently transported through retrograde axoplasmic flow, noxious substances may gain entrance to the lower motorneurons through the same route. Consequently, the function of the capillary barrier in skeletal muscle is of interest in diseases of the lower motorneurons. The transcapillary escape of 125I-albumin was determined in six ALS patients. The values fell within the range earlier reported for normals.