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

Human tissue lead (Pb) levels and amyotrophic lateral sclerosis: a systematic review and meta-analysis of case–control studies

Aim

To combine the current scientific literature evidence and elucidate the differences of lead (Pb) bioaccumulation in human tissues by comparing amyotrophic lateral sclerosis (ALS) patients and healthy controls.

Methods

We systematically searched for case–control studies on the association of Pb levels with ALS, in human cells, tissues, and body fluids (nervous tissue, muscle, blood, cerebrospinal fluid, urine, skin appendages). Then, we performed a meta-analysis for all the tissues in which at least five case–control studies were available: whole blood (9 studies), serum/plasma (5 studies), and cerebrospinal fluid (CSF) (6 studies). Differences between cases and controls were evaluated using standardized mean difference, and combined estimates were derived using random effect maximum likelihood (REML) meta-analyses.

Results

Among 1734 records, we identified 46 full-text studies, of which 14 case–control studies met the meta-analysis inclusion criteria. We found higher Pb levels in ALS cases than controls in blood (standardized mean difference (SMD) = 0.61; 95% confidence interval (CI) 0.20, 1.01; p = 0.003), plasma/serum (SMD = 0.27; 95% CI − 0.16, 0.70; p = 0.26), and CSF (SMD = 0.53; 95% CI − 0.09, 1.15; p = 0.09).

Conclusions

This work provides further evidence of the association between Pb bioaccumulation and ALS in body fluids. The lack of association studies in solid tissues did not allow a robust meta-analysis. Future prospective studies are needed to clarify the causality in the association of Pb bioaccumulation with ALS.

Stem cells for ALS: An overview of possible therapeutic approaches

Amyotrophic lateral sclerosis (ALS) is an unusual, fatal, neurodegenerative disorder leading to the loss of motor neurons. After diagnosis, the average lifespan ranges from 3 to 5 years, and death usually results from respiratory failure. Although the pathogenesis of ALS remains unclear, multiple factors are thought to contribute to the progression of ALS, such as network interactions between genes, environmental exposure, impaired molecular pathways and many others. The neuroprotective properties of neural stem cells (NSCs) and the paracrine signaling of mesenchymal stem cells (MSCs) have been examined in multiple pre-clinical trials of ALS with promising results. The data from these initial trials indicate a reduction in the rate of disease progression. The mechanism through which stem cells achieve this reduction is of major interest. Here, we review the to-date pre-clinical and clinical therapeutic approaches employing stem cells, and discuss the most promising ones.

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.

Amyotrophic lateral sclerosis: mechanisms and therapeutics in the epigenomic era

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease of the motor neurons, which results in weakness and atrophy of voluntary skeletal muscles. Treatments do not modify the disease trajectory effectively, and only modestly improve survival. A complex interaction between genes, environmental exposure and impaired molecular pathways contributes to pathology in patients with ALS. Epigenetic mechanisms control the hereditary and reversible regulation of gene expression without altering the basic genetic code. Aberrant epigenetic patterns-including abnormal microRNA (miRNA) biogenesis and function, DNA modifications, histone remodeling, and RNA editing-are acquired throughout life and are influenced by environmental factors. Thus, understanding the molecular processes that lead to epigenetic dysregulation in patients with ALS might facilitate the discovery of novel therapeutic targets and biomarkers that could reduce diagnostic delay. These achievements could prove crucial for successful disease modification in patients with ALS. We review the latest findings regarding the role of miRNA modifications and other epigenetic mechanisms in ALS, and discuss their potential as therapeutic targets.

Metal concentrations in cerebrospinal fluid and blood plasma from patients with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal degenerative disorder of motor neurons. The cause of this degeneration is unknown, and different causal hypotheses include genetic, viral, traumatic and environmental mechanisms. In this study, we have analyzed metal concentrations in cerebrospinal fluid (CSF) and blood plasma in a well-defined cohort (n = 17) of ALS patients diagnosed with quantitative electromyography. Metal analyses were performed with high-resolution inductively coupled plasma mass spectrometry. Statistically significant higher concentrations of manganese, aluminium, cadmium, cobalt, copper, zinc, lead, vanadium and uranium were found in ALS CSF compared to control CSF. We also report higher concentrations of these metals in ALS CSF than in ALS blood plasma, which indicate mechanisms of accumulation, e.g. inward directed transport. A pattern of multiple toxic metals is seen in ALS CSF. The results support the hypothesis that metals with neurotoxic effects are involved in the pathogenesis of ALS.

Geographic distribution of amyotrophic lateral sclerosis through motor neuron disease mortality data

Amyotrophic lateral sclerosis (ALS) is a rare and devastating neurological disorder of the adult age with a prognosis of about 2-3 years from the onset of the disease. No clear cause has been identified but it seems to be a multifactorial disease with genetic and environmental components involved. Increments of mortality rates were observed since 1980 both in Italy and in many other countries. The objective of the present study is to describe the distribution of ALS mortality in Italy in the period 1980-2001 detecting single municipalities or clusters with high mortality levels for motor neuron disease (MND). ALS represents the main part (85%) of the MND group which is globally identified by the IX ICD (International Classification of Diseases and Causes of Death) 335.2 code. Death numbers and standardized mortality ratios (SMR) for MND were calculated for all Italian municipalities through the ENEA mortality database system (data source: National Institute of Statistics-ISTAT), using national mortality rates as reference. Subsequently, in order to detect municipal clusters, spatial analysis was performed. Out of the 8,099 Italian municipalities, 132 where characterized by SMR values higher than expected. Moreover 16 clusters with significant high relative risk values (RR) were identified, 12 out of them including only a single municipality. Only 22 of the municipalities with high SMR were included in the clusters. In conclusion, the two different epidemiological methodologies demonstrated to be widely complementary in detecting the geographical distribution of the disease in terms of risk for populations. A first selection of the priority areas where analytical studies should be carried on, in order to identify risk factors associated to ALS, is tentatively suggested.

Metals in motor neuron diseases

Degenerative processes within the nervous system are common features in disease entities such as dementia of Alzheimer type (DAT), Parkinson disease (PD), and amyotrophic lateral sclerosis (ALS). ALS is a neurodegenerative disease with unknown etiology; widespread muscle wasting and respiratory failure lead to death within a few years. Denervation can be detected with electromyography and axonal deterioration monitored by motor unit number estimates. Several suggestions about the cause of ALS have emerged but no solid theory has yet precipitated. Lead or mercury exposure has been suggested. Exposure data alone cannot support this connection. Alterations in metal kinetics may underlie the deterioration of motor function observed in patients with ALS. In this review the role of metals in motor neuron disease is discussed. Both classic studies on exposure and recent understanding of metal binding proteins are considered. Aspects of peak exposure and excretion are merged toward an understanding of metal dynamics in ALS. An overview of chemical and electrophysiological investigations is given in the context of neurodegeneration.

Lead Exposure as a Risk Factor for Amyotrophic Lateral Sclerosis

BACKGROUND

The etiology of amyotrophic lateral sclerosis (ALS) likely involves an environmental component. We qualitatively assessed literature on ALS and lead exposure. Problems of study design make case reports and studies of lead in blood or tissues difficult to interpret. Most previous case-control studies found an association of ALS with self-reported occupational exposure to lead, with increased risks of 2- to >4-fold. However, these results may have been affected by recall bias.

OBJECTIVE

To address inconsistencies among published reports, we used both lead biomarkers and interview data to assess lead exposure, and we evaluated the role of genetic susceptibility to lead.

METHODS

We conducted a case-control study in New England in 1993-1996 with 109 ALS cases and 256 population-based controls. We measured blood and bone lead levels, the latter using X-ray fluorescence, and interviewed participants regarding sources of lead exposure.

RESULTS

In our study, ALS was associated with self-reported occupational lead exposure, with a dose response for cumulative days of exposure. ALS was also associated with blood and bone lead levels, with a 1.9-fold increase in risk for each mug/dl increment in blood lead and a 2.3- to 3.6-fold increase for each doubling of bone lead. A polymorphism in the delta-aminolevulinic acid dehydratase gene was associated with a 1.9-fold increase in ALS risk.

CONCLUSION

These results, together with previous studies, suggest that lead exposure plays a role in the etiology of ALS. An increase in mobilization of lead from bone into blood may play a role in the acute onset of disease.

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.

Lead exposure and amyotrophic lateral sclerosis

BACKGROUND

Previous interview-based studies have suggested that exposure to neurotoxicants including metals might be related to ALS.

METHODS

We evaluated the relation of lead exposure to ALS, using both biological measures and interviews, in a case-control study conducted in New England from 1993 to 1996. Cases (N = 109) were recruited at two hospitals in Boston, MA. Population controls (N = 256) identified by random-digit dialing were frequency-matched to cases by age, sex, and region of residence within New England.

RESULTS

Risk of ALS was associated with self-reported occupational exposure to lead (odds ratio [OR] = 1.9; 95% confidence interval [CI] = 1.1-3.3), with a dose response for lifetime days of lead exposure. Blood and bone lead levels were measured in most cases (N = 107) and in a subset of controls (N = 41). Risk of ALS was associated with elevations in both blood and bone lead levels. ORs were 1.9 (95% CI = 1.4-2.6) for each microg/dl increase in blood lead, 3.6 (95% CI = 0.6-20.6) for each unit increase in log-transformed patella lead, and 2.3 (95% CI = 0.4-14.5) for each unit increase in log-transformed tibia lead.

CONCLUSIONS

These results are consistent with previous reports and suggest a potential role for lead exposure in the etiology of ALS.

Conjugal amyotrophic lateral sclerosis: toxic clustering or change?

We describe a southern Italian couple, married for 28 years, who developed amyotrophic lateral sclerosis (ALS) within 30 months of each other. They had drunk water taken from an artesian well for nearly thirty years. Samples of the water were investigated in the search for heavy metals and pesticides using high performances liquid chromatography, gas chromatography and absorption spectrometry. No heavy metals, pesticides or known environmental toxic substances were found in significant concentration. This would seem to support the view that conjugal ALS in Caucasians is due to mere coincidence.

Trace elements, age, and sex in amyotrophic lateral sclerosis disease

The statistical tests analysis of variance, analysis of covariance, correlation coefficient, Kolmogorov-Smirnov test, t-test, and Tukey test were applied to copper, magnesium, manganese, and zinc content in serum (S) and in cerebrospinal fluid (CSF) of controls and of a sporadic form of Amyotrophic Lateral Sclerosis (ALS) disease. This is carried out in order to evaluate statistically the possible relationships among the trace elements when ALS patients and controls are considered as independent groups, within sex groups and within age decades of both patients and control classes. A statistically significant difference between older controls (age > 40) and ALS patients (age > 40) for copper in CSF, copper in S, manganese in S, and zinc in CSF was found. Statistically significant correlation coefficients within the different classes formed for this study were observed. Within this pool, a correlation of patient group can differ statistically from the corresponding one of controls and vice versa. Thus, this correlation could be characteristic of the group from which is extracted, e.g., the correlation between copper in S and zinc in S, which is characteristic of ALS patients when considered as an independent group as well as members of the male patient class.

Risk factors for motor neuron disease: a case-control study based on patients from the Scottish Motor Neuron Disease Register

In order to identify risk factors for the subsequent development of motor neuron disease (MND) we have carried out a case-control study of incident patients in Scotland, identified using the Scottish Motor Neuron Disease Register. A standard questionnaire was given to 103 patients and the same number of community controls matched on a one to one basis using the general practitioner's (GP) age and sex register. Recall bias was minimised by using GP records to verify the subject's report. There was an overall lifetime excess of fractures in patients, odds ratio (OR) = 1.3 (95% confidence interval (CI), 0.7-2.5) and this was highest in the 5 years before symptom onset (OR = 15, 95% CI, 3.3-654). There was no association with non-fracture trauma but the OR for a manual occupation in patients was 2.6 (95% CI, 1.1-6.3). Both occupational exposure to lead (OR = 5.7, 95% CI, 1.6-30) and solvents/chemicals (OR = 3.3, 95% CI 1.3-10) were significantly more common in patients. No consistent association was found between MND and factors reflecting socioeconomic deprivation in childhood; childhood infections or social class. Our results identify a number of different factors which may contribute to the aetiology of MND.

Motor neuron disease (amyotrophic lateral sclerosis)

Amyotrophic lateral sclerosis is an insidiously developing, adult-onset, progressive anterior horn cell degeneration with associated degeneration of descending motor pathways. It has been recognized as an important clinical syndrome since the middle of the 19th century. Despite increasing clinical and research interest in this condition, its cause remains obscure, even in the broadest terms. Epidemiologic characteristics of the disease have been interpreted as evidence of both genetic and environmental causes. A major change in the view of this disease is the widely developing perception that it is a disease of elderly persons more than of middle-aged adults as was previously taught. Etiologic hypotheses encompass a broad range of postulated pathophysiologic mechanisms, and we review these in detail. The clinical limits of the disease can now be better defined by using modern diagnostic techniques. Although interest in supportive symptomatic therapy is growing, no intervention has yet been shown to modify the biologically determined motor system degeneration.

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,

Abnormal glutamate metabolism in amyotrophic lateral sclerosis

Glutamate levels were determined in the fasting plasma of 22 patients with early-stage primary amyotrophic lateral sclerosis (ALS) and compared to those of healthy and diseased controls. There was a significant increase (by approximately 100%, p less than 0.0005) in the plasma glutamate of the ALS patients as compared with the controls. Oral glutamate loading (60 mg of monosodium glutamate per kilogram of body weight, taken orally after overnight fasting) resulted in significantly greater elevations in the plasma glutamate and aspartate levels in the ALS patients than in the controls. Glutamate, a potentially neuroexcitotoxic compound, is thought to be the transmitter of the corticospinal tracts and certain spinal cord interneurons. A systemic defect in the metabolism of this amino acid may underlie primary ALS.

Epidermal growth factor in human cerebrospinal fluid: reduced levels in amyotrophic lateral sclerosis

Epidermal growth factor (EGF), a mitogenic peptide, is widely distributed within the brain and endocrine cells of the gastro-intestinal tract. Using EGF radioreceptor assay, the EGF level was measured in lumbar cerebrospinal fluid from five patients with amyotrophic lateral sclerosis (ALS) and seven patients with intervertebral disc disease as a control group. The patients with ALS showed reduced EGF levels to 662.4 +/- 207 pg/ml as compared with controls 1013 +/- 182.8 pg/ml (P less than 0.02). These results indicate a possible EGF involvement in the pathogenesis of ALS.

Amyotrophic lateral sclerosis: Part 2. Etiopathogenesis

The pathogenesis of the motor neuronal degeneration in amyotrophic lateral sclerosis (ALS) is unclear, though several possible etiological factors are currently being investigated. A unifying hypothesis will have to explain the diverse geographical occurrence, clinical features, and selective vulnerability and relative resistance of different neuronal populations in the disease. It is possible that different biochemical defects underlie this diversity, or alternatively that the many factors incriminated in the etiology may act upon an underlying genetic-biochemical abnormality to trigger premature neuronal death. Viruses, metals, endogenous toxins, immune dysfunction, endocrine abnormalities, impaired DNA repair, altered axonal transport, and trauma have all been etiologically linked with ALS, but convincing research evidence of a causative role for any of these factors is yet to be demonstrated.

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 in cerebrospinal fluid and its relationship to plasma lead in humans

Lead levels in whole blood, plasma and cerebrospinal fluid (CSF) were determined in 18 patients suffering from Amyotrophic Lateral Sclerosis (ALS) and in 21 subjects hospitalized for neurological investigations. No significant differences were found for blood, plasma and CSF lead concentration between the ALS group and the other patient group. The plasma lead-CSF lead mean ratio was greater than 1 in both groups, while in subjects with a slight degree of blood-CSF barrier impairment a significant decrease of the ratio was demonstrated. A significant relationship between plasma lead and CSF lead levels (r = 0.405; p less than 0.01), but not between whole blood lead and CSF lead levels, was established. Lead levels in CSF were also age-related (r = 0.485; p less than 0.05) in the group of patients not suffering from ALS. In subjects with normal blood-brain barrier permeability, lead in plasma is a good indicator of CSF lead concentration.

Increased manganese level in spinal cords of amyotrophic lateral sclerosis determined by radiochemical neutron activation analysis

The manganese distribution in the cross-section of the cervical, thoracic and lumbar portion of the spinal cords from 7 autopsied cases with amyotrophic lateral sclerosis (ALS) and 6 control subjects were determined by radiochemical neutron activation analysis. It was possible to determine 1 ng levels of manganese content accurately in the small tissues about 1 mg of dried weight using wet ashing and chemical separation after neutron activation. The dried weight of spinal cord was about 1/3 of the wet weight. Manganese concentration in the wet tissue was calculated from the ratio of dried to wet weight. In the anterior horn of the cervical cords of ALS, manganese concentration was the highest; 1.75 +/- 0.39 ng/mg of dried weight and 0.59 +/- 0.09 ng/mg of wet weight, respectively. These were significantly higher (P less than 0.01) compared to those in controls; 1.02 +/- 0.12 ng/mg of dried weight and 0.35 +/- 0.04 ng/mg of wet weight, respectively. The elevation of manganese level in the spinal cords of ALS was more prominent in the anterior horn and lateral column than in the posterior column both in dried and wet tissues. Since manganese inhibits neuronal transmission, it is likely that neurological degenerative changes occur as a result of local disturbances of manganese metabolism in the spinal cord of ALS.

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.

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.