Trace element concentration in human brain. Activation analysis of cobalt, iron, rubidium, selenium, zinc, chromium, silver, cesium, antimony and scandium

Metal mixtures associate with higher amyotrophic lateral sclerosis risk and mortality independent of genetic risk and correlate to self-reported exposures: a case-control study

Background

The pathogenesis of amyotrophic lateral sclerosis (ALS) involves both genetic and environmental factors. This study investigates associations between metal measures in plasma and urine, ALS risk and survival, and exposure sources.

Methods

Participants with and without ALS from Michigan provided plasma and urine samples for metal measurement via inductively coupled plasma mass spectrometry. Odds and hazard ratios for each metal were computed using risk and survival models. Environmental risk scores (ERS) were created to evaluate the association between exposure mixtures and ALS risk and survival and exposure source. ALS (ALS-PGS) and metal (metal-PGS) polygenic risk scores were constructed from an independent genome-wide association study and relevant literature-selected SNPs.

Results

Plasma and urine samples from 454 ALS and 294 control participants were analyzed. Elevated levels of individual metals, including copper, selenium, and zinc, significantly associated with ALS risk and survival. ERS representing metal mixtures strongly associated with ALS risk (plasma, OR=2.95, CI=2.38-3.62, p<0.001; urine, OR=3.10, CI=2.43-3.97, p<0.001) and poorer ALS survival (plasma, HR=1.42, CI=1.24-1.63, p<0.001; urine, HR=1.52, CI=1.31-1.76, p<0.001). Addition of the ALS-PGS or metal-PGS did not alter the significance of metals with ALS risk and survival. Occupations with high potential of metal exposure associated with elevated ERS. Additionally, occupational and non-occupational metal exposures associated with measured plasma and urine metals.

Conclusion

Metals in plasma and urine associated with increased ALS risk and reduced survival, independent of genetic risk, and correlated with occupational and non-occupational metal exposures. These data underscore the significance of metal exposure in ALS risk and progression.

Trace elements dyshomeostasis in liver and brain of weanling mice under altered dietary selenium conditions

BACKGROUND

A balanced diet containing selenium (Se) and other trace elements is essential for normal development and growth. Se has been recognized as an essential trace element; however, its interaction with other elements has not been fully investigated. In the present study, sodium (Na), magnesium (Mg), potassium (K), calcium (Ca), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), Se and rubidium (Rb), were analysed in liver and brain regions under altered dietary Se intake in weanling mice to identify major discriminatory elements.

METHODS

The study investigated the effects of different levels of Se intake on the elemental composition in liver and brain tissues of weaned mice. After 24 weeks of feeding with Se adequate, deficient, and excess diets, elemental analysis was performed on the harvested tissues using Inductively coupled plasma mass spectrometry (ICP-MS). Statistical analysis that included analysis of covariance (ANCOVA), correlation coefficient analysis, principal component analysis, and partial least squares discriminant analysis were performed.

RESULTS

The ANCOVA showed statistically significant changes and correlations among the analysed elements under altered dietary Se status. The multivariate analysis showed differential changes in elements in liver and brain regions. The results suggest that long-term dietary Se alternations lead to dyshomeostasis in trace elements that are required in higher concentrations compared to Se. It was observed that changes in the Fe, Co, and Rb levels were similar in all the tissues studied, whereas the changes in Mg, Cr, and Mn levels were different among the tissues under altered dietary Se status. Additionally, the changes in Rb levels correlated with the dietary Se intake but had no relation with the tissue Se levels.

CONCLUSIONS

The findings suggest interactions between Mg, Cr, Mn, Fe, Co, and Se under altered Se status may impact cellular functions during postnatal development. However, the possible biological significance of alterations in Rb levels under different dietary Se paradigms needs to be further explored.

Serum cobalt and chromium concentration following total hip arthroplasty: a Bayesian network meta-analysis

The present systematic review investigated the concentration of chromium (Cr) and cobalt (Co) in serum in patients who have undergone total hip arthroplasty (THA). The first outcome of interest was to investigate the mean concentration in serum of Cr and Co using different material combinations and to verify whether their concentrations change significantly using different patterns of head and liner in THA. The second outcome of interest was to investigate whether the time elapsed from the index surgery to the follow-up, BMI, sex, and side exert an influence on the mean concentration of Cr and Co in serum in patients who have undergone THA. The following material combinations were investigated (head-liner): Ceramic-Co Cr (CoCr), CoCr-CoCr, CoCr-Polyethylene, CoCr high carbide-CoCr high carbide. Data from 2756 procedures were retrieved. The mean length of follow-up was 69.3 ± 47.7 months. The ANOVA test evidenced good comparability in age, length of follow-up, BMI, and sex (P > 0.1). In patients who have undergone THA, the mean concentration in the serum of Co ranged between 0.5 µg/L and 3.5 µg/L, and the mean concentration of Cr from 0.6 to 2.6 µg/L. The difference in the concentration of Co and Cr in serum is strictly related to the implant configuration, with the coupling CoCr-CoCr showing the highest and CoCr-Polyethylene showing the lowest concentration. Patient characteristics, BMI, sex, side and the time elapsed from the index surgery to the last follow-up did not exert a significant influence on the concentration of Co and Cr in serum in patients who have undergone total hip arthroplasty (THA).

Toward revising dietary zinc recommendations for children aged 0 to 3 years: a systematic review and meta-analysis of zinc absorption, excretion, and requirements for growth

CONTEXT

The Food and Agriculture Organization of the United Nations and the World Health Organization are updating their dietary zinc recommendations for children aged 0 to 3 years.

OBJECTIVE

The aim of this review was to retrieve and synthesize evidence regarding zinc needs for growth as well as zinc losses, absorption, and bioavailability from the diet.

DATA SOURCES

MEDLINE, Embase, and Cochrane Library databases were searched electronically from inception to August 2020. Studies assessing the above factors in healthy children aged 0 to 9 years were included, with no limits on study design or language.

DATA EXTRACTION

Ninety-four studies reporting on zinc content in tissue (n = 27); zinc absorption (n = 47); factors affecting zinc bioavailability (n = 30); and endogenous zinc losses via urine, feces, or integument (n = 40) met the inclusion criteria. Four reviewers extracted data and two reviewers checked for accuracy.

DATA ANALYSES

Studies were synthesized narratively, and meta-analyses of zinc losses and gains as well the subgroups of age, type of feeding, country's income, and molar ratio of phytate to zinc were conducted. Meta-analysis revealed an overall mean (95%CI) urinary and endogenous fecal zinc excretion of 17.48 µg/kg/d (11.80-23.15; I2 = 94%) and 0.07 mg/kg/d (0.06-0.08; I2 = 82%), respectively, with a mean fractional zinc absorption of 26.75% (23.69-29.81; I2 = 99%). Subgrouping by age revealed differences in mean values associated with the transition from milk-based diets to solid food during the first 3 years of life.

CONCLUSION

This review synthesizes data that may be used to formulate zinc requirements in young children. Results should be interpreted with caution because of considerable heterogeneity in the evidence.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD42020215236.

Long-term Cognitive Trajectory After Total Joint Arthroplasty

IMPORTANCE

Individuals with total joint arthroplasty (TJA) have long-term exposure to metal-containing implants; however, whether long-term exposure to artificial implants is associated with cognitive function is unknown.

OBJECTIVE

To compare long-term cognitive trajectories in individuals with and without TJA.

DESIGN, SETTING, AND PARTICIPANTS

This population-based cohort study assessed serial cognitive evaluations of 5550 participants (≥50 years of age) from the Mayo Clinic Study of Aging between November 1, 2004, and December 31, 2020.

EXPOSURES

Total joint arthroplasty of the hip or the knee.

MAIN OUTCOMES AND MEASURES

Linear mixed-effects models were used to compare the annualized rate of change in global and domain-specific cognitive scores in participants with and without TJA, adjusting for age, sex, educational level, apolipoprotein E ε4 carrier status, and cognitive test practice effects.

RESULTS

A total of 5550 participants (mean [SD] age at baseline, 73.04 [10.02] years; 2830 [51.0%] male) were evaluated. A total of 952 participants had undergone at least 1 TJA of the hip (THA, n = 430) or the knee (TKA, n = 626) before or after entry into the cohort. Participants with TJA were older, more likely to be female, and had a higher body mass index than participants without TJA. No difference was observed in the rate of cognitive decline in participants with and without TJA until 80 years of age. A slightly faster cognitive decline at 80 years or older and more than 8 years from surgery was observed (b = -0.03; 95% CI, -0.04 to -0.02). In stratified analyses by surgery type, the faster decline was observed primarily among older participants with TKA (b = -0.04; 95% CI, -0.06 to -0.02).

CONCLUSIONS AND RELEVANCE

In this cohort study, long-term cognitive trajectories in individuals with and without TJA were largely similar except for a slightly faster decline among the oldest patients with TKA; however, the magnitude of difference was small and of unknown clinical significance.

Psychiatric Disorders and Genotoxicity Following Primary Metal on Polyethylene Total Hip Arthroplasty and Their Correlation to Cobalt/Chromium Levels

Introduction

Hip arthroplasty (HA) using implantable metal components is among the commonest orthopedic interventions. However, it can be followed by several complications following corrosion and the release of metal ions. Several studies proved that damaged genomic DNA may contribute to the pathophysiology of mental disorders.

Aim

The current work aims to evaluate the psychiatric disorders in metal on polyethylene hip arthroplasty (MOP-HA) patients and its correlation to cobalt/chromium (Co/Cr) levels and genotoxicity.

Methods

The work was a longitudinal follow-up study including 34 adults with unilateral primary MOP-HA meeting the inclusion and exclusion criteria. Preoperatively, 6, 12-months-postoperatively, patients were examined for cognitive impairment using mini-mental-state-examination (MMSE), depression using major-depressive-inventory (MDI), and blood samples were collected for estimation of Co/Cr, detection of genotoxicity by single-cell-gel-electrophoresis (comet assay) and serum 8-hydroxy-2'-deoxyguanosine (8-OHdG).

Results

Cognitive impairment was reported in 18.5% and 14.8% at 6-months, and 12-months postoperative, respectively. Depressive disorder was recorded in 22.2% at 6-months and 14.8% at 12-months postoperative. The marginal homogeneity tests proved a non-significant difference. There was a non-significant difference in preoperative, 6-months, 12-months postoperative MMSE, and MDI scores. There were significantly increased Co/Cr levels at 6-months postoperative. The levels decreased at 12-months postoperative, however, still significantly higher than preoperative values. There was a significant increase in serum 8-OHdG and the levels were positively correlated to cobalt levels at both 6 and 12-months-postoperative. There was a non-significant difference among preoperative, 6-months, and 12-months postoperative comet assay measurements.

Conclusion

From previous findings, we can conclude that will-functioning MOP hip arthroplasty can induce increased ion levels and positively correlated increase in biochemical markers of genotoxicity (8-OHdG).

Quantification of the Intrinsic T1 and T2 of Heschl's Gyri with MR Fingerprinting

PURPOSE

The human primary auditory cortex is located in the Heschl's gyrus (HG). To assess the intrinsic MR property in the gray matter of the HG (GM-HG) with T1 and T2 values using a commercially available MR fingerprinting (MRF) technique.

METHODS

The subjects were 10 healthy volunteers (with 20 HGs; mean age, 31.5 years old; range, 25-53 years old). Coronal T1 and T2 maps were obtained with commercially available MRF using a 3-Tesla MR system. Two radiologists measured the T1 and T2 values of the GM-HG, the GM in the superior temporal gyrus (GM-STG), and the GM in the middle temporal gyrus (GM-MTG) by drawing a ROI on coronal maps.

RESULTS

For both radiologists, the mean T1 and T2 values of the GM-HG were significantly lower than those in the GM-STG or GM-MTG (P < 0.01). The interobserver reliability using the intraclass correlation coefficients (ICC) (2,1) showed strong agreement for the measurement of the T1 and T2 values (ICCs =⃥ 0.80 and 0.78 for T1 and T2 values, respectively).

CONCLUSION

The T1 and T2 values on MRF for the GM-HG were lower than those for the GM-STG and GM-MTG, likely reflecting a higher myelin content and iron deposition in the GM-HG. Quantitative measurements using the MRF can clarify cortical properties with high reliability, which may indicate that MRF mapping provides new insights into the structure of the human cortical GM.

ICP-MS Multi-Elemental Analysis of the Human Meninges Collected from Sudden Death Victims in South-Eastern Poland

Metals perform many important physiological functions in the human body. The distribution of elements in different tissues is not uniform. Moreover, some structures can be the site of an accumulation of essential or toxic metals, leading to multi-directional intracellular damage. In the nervous system, these disorders are especially dangerous. Metals dyshomeostasis has been linked to a variety of neurological disorders which end up leading to permanent injuries. The multi-elemental composition of the human brain is still the subject of numerous investigations and debates. In this study, for the first time, the meninges, i.e., the dura mater and the arachnoid, were examined for their elemental composition by means of inductively coupled plasma mass spectrometry (ICP-MS). Tissue samples were collected post mortem from those who died suddenly as a result of suicide (n = 20) or as a result of injuries after an accident (n = 20). The interactions between 51 elements in both groups showed mainly weak positive correlations, which dominated the arachnoid mater compared to the dura mater. The study showed differences in the distribution of some elements within the meninges in the studied groups. The significant differences concerned mainly metals from the lanthanide family (Ln), macroelements (Na, K, Ca, Mg), a few micronutrients (Co), and toxic cadmium (Cd). The performed evaluation of the elemental distribution in the human meninges sheds new light on the trace metals metabolism in the central nervous system, although we do not yet fully understand the role of the human meninges.

Current understanding of hexavalent chromium [Cr(VI)] neurotoxicity and new perspectives

Hexavalent chromium [Cr(VI)] is a global environmental pollutant that increases risk for several types of cancers and is increasingly being recognized as a neurotoxicant. Traditionally, the brain has been viewed as a largely post-mitotic organ due to its specialized composition of neurons, and consequently, clastogenic effects were not considered in neurotoxicology. Today, we understand the brain is composed of at least eight distinct cell types - most of which continue mitotic activity throughout lifespan. We have learned these dividing cells play essential roles in brain and body health. This review focuses on Cr(VI), a potent clastogen and known human carcinogen, as a potentially neurotoxic agent targeting mitotic cells of the brain. Despite its well-established role as a human carcinogen, Cr(VI) neurotoxicity studies have failed to find a significant link to brain cancers. In the few studies that did find a link, Cr(VI) was identified as a risk for gliomas. Instead, in the human brain, Cr(VI) appears to have more subtle deleterious effects that can impair childhood learning and attention development, olfactory function, social memory, and may contribute to motor neuron diseases. Studies of Cr(VI) neurotoxicity with animal and cell culture models have demonstrated elevated markers of oxidative damage and redox stress, with widespread neurodegeneration. One study showed mice exposed to Cr(VI)-laden tannery effluent exhibited longer periods of aggressive behavior toward an "intruder" mouse and took longer to recognize mice previously encountered, recapitulating the social memory deficits observed in humans. Here we conducted a critical review of the available literature on Cr(VI) neurotoxicity and synthesize the collective observations to thoroughly evaluate Cr(VI) neurotoxicity - much remains to be understood and recognized.

Reference values for trace element levels in the human brain: A systematic review of the literature

Some trace elements (TE) are eminently toxic for humans (e.g., Al, Pb, Hg, Cd) and its presence in the central nervous system has been linked to the etiology of neurodegenerative diseases (ND). More recently, the focus has shifted to the potential role of the imbalances on essential TE levels (e.g., Fe, Cu, Zn, Se) within the brain tissue, and they have also been identified as potentially responsible for the cognitive decline associated with normal ageing and the development of some ND, although their definite role remains unclear. Accurately, well-defined reference values for TE levels in human body fluids and tissues are indispensable to identify possible disturbances in individual cases. Moreover, since the brain is a highly heterogeneous organ, with anatomically and physiologically very different areas, a detailed mapping of TE distribution across the brain tissue of normal individuals, with an in-depth analysis of TE levels in the different brain regions, is a mandatory prior work so that the results obtained from patients suffering from ND and other brain diseases can be interpreted. This review aims to compile and summarize the available data regarding TE levels in the different human brain regions of "normal" (non-diseased) individuals in order to contribute to the establishment of robust reference values. Fifty-four studies, published since 1960, were considered. The results showed a great variability between different studies. The potential sources of this variability are discussed. The need for increased harmonization of experimental strategies is highlighted in order to improve the comparability of the data obtained.

Role of zinc in neonatal growth and brain growth: review and scoping review

This manuscript includes (1) a narrative review of Zinc as an essential nutrient for fetal and neonatal growth and brain growth and development and (2) a scoping review of studies assessing the effects of Zinc supplementation on survival, growth, brain growth, and neurodevelopment in neonates. Very preterm infants and small for gestational age infants are at risk for Zinc deficiency. Zinc deficiency can cause several complications including periorificial lesions, delayed wound healing, hair loss, diarrhea, immune deficiency, growth failure with stunting, and brain atrophy and dysfunction. Zinc is considered essential for oligodendrogenesis, neurogenesis, neuronal differentiation, white matter growth, and multiple biological and physiological roles in neurobiology. Data support the possibility that the critical period of Zinc delivery for brain growth in the mouse starts at 18 days of a 20-21-day pregnancy and extends during lactation and in human may start at 26 weeks of gestation and extend until at least 44 weeks of postmenstrual age. Studies are needed to better elucidate Zinc requirement in extremely low gestational age neonates to minimize morbidity, optimize growth, and brain growth, prevent periventricular leukomalacia and optimize neurodevelopment. IMPACT: Zinc is essential for growth and brain growth and development. In the USA, very preterm small for gestational age infants are at risk for Zinc deficiency. Data support the possibility that the critical period of Zinc delivery for brain growth in the mouse starts at 18 days of a 20-21-day pregnancy and extends during lactation and in human may start at 26 weeks' gestation and extend until at least 44 weeks of postmenstrual age. Several randomized trials of Zinc supplementation in neonates have shown improvement in growth when using high enough dose, for long duration in patients likely to or proven to have a Zinc deficiency. Studies are needed to better elucidate Zinc requirement in extremely low gestational age neonates to minimize morbidity, optimize growth and brain growth, prevent periventricular leukomalacia and optimize neurodevelopment.

Multi-element Analysis of Brain Regions from South African Cadavers

Trace elements are vital for a variety of functions in the brain. However, an imbalance can result in oxidative stress. It is important to ascertain the normal levels in different brain regions, as such information is still lacking. Therefore, this study aimed to provide baseline trace element concentrations from a South African population, as well as determine trace element differences between sex and brain regions. Samples from the caudate nucleus, putamen, globus pallidus and hippocampus were analysed using inductively coupled plasma mass spectrometry. Aluminium, antimony, arsenic, barium, boron, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, mercury, molybdenum, nickel, phosphorus, potassium, selenium, silicon, sodium, strontium, vanadium and zinc were assessed. A multiple median regression model was used to determine differences between sex and regions. Twenty-nine male and 13 female cadavers from a Western Cape, South African population were included (mean age 35 years, range 19 to 45). Trace element levels were comparable to those of other populations, although magnesium was considerably lower. While there were no sex differences, significant anatomical regional differences existed; the caudate nucleus and hippocampus were the most similar, and the globus pallidus and hippocampus the most different. In conclusion, this is the first article to report the trace element concentrations of brain regions from a South African population. Low magnesium levels in the brain may be linked to a dietary deficiency, and migraines, depression and epilepsy have been linked to low magnesium levels. Future research should be directed to increase the dietary intake of magnesium.

Concentrations of Essential Trace Metals in the Brain of Animal Species-A Comparative Study

The essential trace metals iron, zinc, and copper have a significant physiological role in healthy brain development and function. Especially zinc is important for neurogenesis, synaptogenesis, synaptic transmission and plasticity, and neurite outgrowth. Given the key role of trace metals in many cellular processes, it is important to maintain adequate levels in the brain. However, the physiological concentration of trace metals, and in particular zinc, in the human and animal brain is not well described so far. For example, little is known about the trace metal content of the brain of animals outside the class of mammals. Here, we report the concentration of iron, zinc, and copper in fresh brain tissue of different model-species of the phyla Chordata (vertebrates (mammals, fish)), Annelida, Arthropoda (insects), and Mollusca (snails), using inductively coupled plasma mass-spectrometry (ICP-MS). Our results show that the trace metals are present in the nervous system of all species and that significant differences can be detected between species of different phyla. We further show that a region-specific distribution of metals within the nervous system already exists in earthworms, hinting at a tightly controlled metal distribution. In line with this, the trace metal content of the brain of different species does not simply correlate with brain size. We conclude that although the functional consequences of the controlled metal homeostasis within the brain of many species remains elusive, trace metal biology may not only play an important role in the nervous system of mammals but across the whole animal kingdom.

Tensor-valued diffusion MRI differentiates cortex and white matter in malformations of cortical development associated with epilepsy

Objective:

Delineation of malformations of cortical development (MCD) is central in presurgical evaluation of drug-resistant epilepsy. Delineation using magnetic resonance imaging (MRI) can be ambiguous, however, because the conventional T₁- and T₂-weighted contrasts depend strongly on myelin for differentiation of cortical tissue and white matter. Variations in myelin content within both cortex and white matter may cause MCD findings on MRI to change size, become undetectable, or disagree with histopathology. The novel tensor-valued diffusion MRI (dMRI) technique maps microscopic diffusion anisotropy, which is sensitive to axons rather than myelin. This work investigated whether tensor-valued dMRI may improve differentiation of cortex and white matter in the delineation of MCD.

Methods:

Tensor-valued dMRI was performed on a 7 T MRI scanner in 13 MCD patients (age = 32 ± 13 years) featuring periventricular heterotopia, subcortical heterotopia, focal cortical dysplasia, and polymicrogyria. Data analysis yielded maps of microscopic anisotropy that were compared with T₁-weighted and T₂-fluid-attenuated inversion recovery images and with the fractional anisotropy from diffusion tensor imaging.

Results:

Maps of microscopic anisotropy revealed large white matter-like regions within MCD that were uniformly cortex-like in the conventional MRI contrasts. These regions were seen particularly in the deep white matter parts of subcortical heterotopias and near the gray-white boundaries of focal cortical dysplasias and polymicrogyrias.

Significance:

By being sensitive to axons rather than myelin, mapping of microscopic anisotropy may yield a more robust differentiation of cortex and white matter and improve MCD delineation in presurgical evaluation of epilepsy.

Analysis of Trace Elements in Human Brain: Its Aim, Methods, and Concentration Levels

Trace elements play a crucial role in many biochemical processes, mainly as components of vitamins and enzymes. Although small amounts of metal ions have protective properties, excess metal levels result in oxidative injury, which is why metal ion homeostasis is crucial for the proper functioning of the brain. The changes of their level in the brain have been proven to be a risk factor for Alzheimer's, Parkinson's, and Huntington's diseases, as well as amyotrophic lateral sclerosis. Therefore, it is currently an important application of various analytical methods. This review covers the most important of them: inductively coupled ground mass spectrometry (ICP-MS), flame-induced atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (GFAAS), optical emission spectrometry with excitation in inductively coupled plasma (ICP-OES), X-ray fluorescence spectrometry (XRF), and neutron activation analysis (NAA). Additionally, we present a summary of concentration values found by different research groups.

Effects of Excess Cr3+ on Trace Element Contents in the Brain and Serum in Chicken

This study aimed to investigate the effects of chromic chloride (CrCl₃) on Ca, Mg, Mn, Fe, Cu, and Zn contents in the brain and serum of chicken. Seventy-two chickens were randomly divided into four groups and treated with different doses of CrCl₃ via drinking water: 0, 1/8, 1/4, and 1/2 LD₅₀ for 42 days. The contents of the elements were evaluated through inductively coupled plasma mass spectrometry. Results showed that Cr contents in the brain and serum were higher than those in the control groups, although no significant dose-dependent changes (P > 0.05) in brain of the Cr-treated groups were observed at 42 days. As exposure time was prolonged and CrCl₃ dosage was increased, Ca contents increased (P < 0.05). Mg and Cu contents in serum decreased; by contrast, Mg and Cu contents initially increased and then decreased in the brain. Fe and Zn contents in the serum increased; conversely, Fe and Zn contents in the brain decreased. CrCl₃ exposure did not significantly affect Mn contents at 14 or 28 days, but significantly decreased (P < 0.05) at 42 days. Therefore, excess Cr³⁺ intake can disrupt absorption and deposition of other trace elements in the brain and serum; the blood-brain barrier may prevent the accumulation of these elements in the brain exposed to CrCl₃.

Alkali metals levels in the human brain tissue: Anatomical region differences and age-related changes

The link between trace elements imbalances (both "toxic" and "essential") in the human brain and neurodegenerative disease has been subject of extensive research. More recently, some studies have highlighted the potential role of the homeostasis deregulation of alkali metals in specific brain regions as key factor in the pathogenesis of neurodegenerative diseases such as multiple sclerosis and Alzheimer's disease. Using flame atomic emission spectrometry and inductively coupled plasma-mass spectrometry after microwave-assisted acid digestion of the samples, alkali metals (Na, K, Li, Rb and Cs) were determined in 14 different areas of the human brain (frontal cortex, superior and middle temporal gyri, caudate nucleus, putamen, globus pallidus, cingulated gyrus, hippocampus, inferior parietal lobule, visual cortex of the occipital lobe, midbrain, pons, medulla and cerebellum) of adult individuals (n=42; 71±12, range: 50-101 years old) with no known history and evidence of neurodegenerative, neurological or psychiatric disorder. Potassium was found as the most abundant alkali metal, followed by Na, Rb, Cs and Li. Lithium, K and Cs distribution showed to be quite heterogeneous. On the contrary, Rb and Na appeared quite homogeneously distributed within the human brain tissue. The lowest levels of Na, K, Rb and Li were found in the brainstem (midbrain, medulla and pons) and cerebellum, while the lowest levels of Cs were found in the frontal cortex. The highest levels of K (mean±sd; range 15.5±2.5; 8.9-21.8mg/g) Rb (17.2±6.1; 3.9-32.4μg/g and Cs (83.4±48.6; 17.3-220.5ng/g) were found in putamen. The highest levels of Na and Li were found in the frontal cortex (11.6±2.4; 6.6-17.1mg/g) and caudate nucleus (7.6±4.6 2.2-21.3ng/g), respectively. Although K, Cs and Li levels appear to remain largely unchanged with age, some age-related changes were observed for Na and Rb levels in particular brain regions (namely in the hippocampus).

Anatomical regional differences in selenium levels in the human brain

The role of selenium in human brain physiology, as well as in aging and neurodegenerative processes, remains unclear. Thus, the aim of this study was to establish the "normal" (reference) levels for selenium in the human brain, as well as anatomical regional differences and age-related changes. Using inductively coupled plasma-mass spectrometry after sample microwave-assisted acid digestion, selenium levels were measured in 14 different areas of the brain of adult individuals (n = 42; 71 ± 12, range 50-101 years old) without a known history of neurodegenerative, neurological, or psychiatric disorders. In the whole data set (n = 588; 42 individuals × 14 brain areas), selenium levels ranged from 552 to 1435 ng/g, with a mean ± SD content of 959 ± 178 ng/g (dry weight basis). Selenium distribution across the different brain areas was heterogeneous, with the highest levels in the putamen, parietal inferior lobule, and occipital cortex and the lowest expression in the medulla and cerebellum. Selenium levels were unchanged with aging. Compared with the age-matched control group, significantly increased levels of selenium were found in the globus pallidus, superior temporal gyrus, and frontal cortex of Parkinson's disease (n = 1) and Alzheimer's disease (n = 2) patients. This study provides new data on the anatomical regional differences in selenium levels in the human brain, which will aid future interpretation of studies examining brain tissue affected by neurodegenerative (and other) brain diseases.

Selenoproteins in nervous system development and function

Selenoproteins are a distinct class of proteins that are characterized by the co-translational incorporation of selenium (Se) in the form of the 21st amino acid selenocysteine. Selenoproteins provide a key defense against oxidative stress, as many of these proteins participate in oxidation-reduction reactions neutralizing reactive oxygen species, where selenocysteine residues act as catalytic sites. Many selenoproteins are highly expressed in the brain, and mouse knockout studies have determined that several are required for normal brain development. In parallel with these laboratory studies, recent reports of rare human cases with mutations in genes involved in selenoprotein biosynthesis have described individuals with an assortment of neurological problems that mirror those detailed in knockout mice. These deficits include impairments in cognition and motor function, seizures, hearing loss, and altered thyroid metabolism. Additionally, due to the fact that oxidative stress is a key feature of neurodegenerative disease, there is considerable interest in the therapeutic potential of selenium supplementation for human neurological disorders. Studies performed in cell culture and rodent models have demonstrated that selenium administration attenuates oxidative stress, prevents neurodegeneration, and counters cell signaling mechanisms known to be dysregulated in certain disease states. However, there is currently no definitive evidence in support of selenium supplementation to prevent and/or treat common neurological conditions in the general population. It appears likely that, in humans, supplementation with selenium may only benefit certain subpopulations, such as those that are either selenium-deficient or possess genetic variants that affect selenium metabolism.

Anatomical region differences and age-related changes in copper, zinc, and manganese levels in the human brain

Using inductively coupled plasma-mass spectrometry after samples microwave-assisted acid digestion, zinc (Zn), copper (Cu), and manganese (Mn) levels were measured in 14 different areas of the human brain of adult individuals (n = 42; 71 ± 12, range 50-101 years old) without a known history of neurodegenerative, neurological, or psychiatric disorder. The main goals of the work were to establish the "normal" (reference) values for those elements in the human brain and to evaluate the age-related changes, a prior and indispensable step in order to enlighten the role of trace element (TE) in human brain physiology and their involvement in aging and neurodegenerative processes. Considering the mean values for the 14 regions, Zn (mean ± sd; range 53 ± 5; 43-61 μg/g) was found at higher levels, followed by Cu (22 ± 5; 10-37 μg/g) and Mn (1.3 ± 0.3; 0.5-2.7 μg/g). The TE distribution across the brain tissue showed to be quite heterogeneous: the highest levels of Zn were found in the hippocampus (70 ± 10; 49-95 μg/g) and superior temporal gyrus (68 ± 10; 44-88 μg/g) and the lowest in the pons (33 ± 8; 19-51 μg/g); the highest levels of Cu and Mn were found in the putamen (36 ± 13; 21-76 μg/g and 2.5 ± 0.8; 0.7-4.5 μg/g, respectively) and the lowest in the medulla (11 ± 6; 2-30 μg/g and 0.8 ± 0.3; 0.2-1.8 μg/g, respectively). A tendency for an age-related increase in Zn and Mn levels was observed in most brain regions while Cu levels showed to be negatively correlated with age.

Brain structure and function in patients after metal-on-metal hip resurfacing

BACKGROUND AND PURPOSE

Hip prostheses that use a metal-on-metal articulation expose the brain to elevated metal concentrations that, in acute excess due to prosthesis malfunction, is associated with neurologic damage, including visual and hearing loss and motor deficits. Here, we examined whether chronic exposure to lower elevated metal levels, typical of well-functioning prostheses, also affects brain structure and function.

MATERIALS AND METHODS

We compared brain volumes, metal deposition, and gray matter attenuation by MR imaging and clinical neurologic function in patients 8 years after receiving a metal-on-metal hip resurfacing versus a matched group of patients with the same duration exposure to a conventional hip prosthesis.

RESULTS

Twenty-nine patients (25 men; mean, age 59±7 years) after metal-on-metal hip resurfacing and 29 patients (25 men; 59±8 years) after total hip arthroplasty were compared. Whole blood cobalt and chromium concentrations were 5-10 times higher in the metal-on-metal hip resurfacing group (P<.0001). Occipital cortex gray matter attenuation tended to be lower (P<.005 uncorrected, P>.05 corrected), and the optic chiasm area tended to be lower (mean difference, -2.7 mm2; P=.076) in the metal-on-metal hip resurfacing group. Subgroup analyses in 34 patients (17 per group), after exclusion of primary ocular pathology, showed the same trend in gray matter attenuation in the occipital cortex and basal ganglia and a smaller optic chiasm in the metal-on-metal hip resurfacing group (mean difference, -3.9 mm2; P=.048). No other structural or functional differences were found between the groups.

CONCLUSIONS

Chronic exposure to metal-on-metal hip resurfacing is associated with subtle structural change in the visual pathways and the basal ganglia in asymptomatic patients.

Assessment of trace elements in human brain using inductively coupled plasma mass spectrometry

Recent brain research reveals a major role of trace elements in various diseases such as multiple sclerosis, Alzheimer's and Wilson's disease. The majority of published tissue concentrations dates back decades, and was assessed with various methods. Little is known about hemispherical differences, the correlation of trace elements or age-dependent changes in the human brain. Thus, the aim of this study was to examine trace element concentrations in different human brain regions after whole brain formalin fixation. 549 samples of 13 brain regions were investigated in 11 deceased subjects without known history of brain pathology. Regional wet-to-dry mass ratios and concentrations of iron, copper, magnesium, manganese, calcium and zinc were determined using inductively coupled plasma mass spectrometry. Cortical gray matter revealed higher water content (wet-to-dry mass ratios 5.84-6.40) than white matter regions (wet-to-dry mass ratios 2.95-3.05). Element concentrations displayed specific regional differences. Good linear correlation of concentrations between elements was found for iron/copper as well as for manganese/magnesium (Spearman's rank correlation coefficient 0.74 and 0.65, respectively). Significant inter-hemispherical differences were found for copper in occipital white matter, for magnesium and calcium in putamen and for iron and copper in temporal white matter. An age dependent increase was seen in cortical gray matter for calcium, for magnesium in all regions except in cortical gray matter, for copper in substantia nigra and for zinc in occipital cortex. The presented trace element concentrations can serve as a fundamental basis for further brain research. Wet-to-dry mass ratios allow a comparison with reference data from other studies.

Friedreich's ataxia causes redistribution of iron, copper, and zinc in the dentate nucleus

Friedreich's ataxia (FRDA) causes selective atrophy of the large neurons of the dentate nucleus (DN). High iron (Fe) concentration and failure to clear the metal from the affected brain tissue are potential risk factors in the progression of the lesion. The DN also contains relatively high amounts of copper (Cu) and zinc (Zn), but the importance of these metals in FRDA has not been established. This report describes nondestructive quantitative X-ray fluorescence (XRF) and "mapping" of Fe, Cu, and Zn in polyethylene glycol–dimethylsulfoxide (PEG/DMSO)-embedded DN of 10 FRDA patients and 13 controls. Fe fluorescence arose predominantly from the hilar white matter, whereas Cu and Zn were present at peak levels in DN gray matter. Despite collapse of the DN in FRDA, the location of the peak Fe signal did not change. In contrast, the Cu and Zn regions broadened and overlapped extensively with the Fe-rich region. Maximal metal concentrations did not differ from normal (in micrograms per milliliter of solid PEG/DMSO as means ± S.D.): Fe normal, 364 ± 117, FRDA, 344 ± 159; Cu normal, 33 ± 13, FRDA, 33 ± 18; and Zn normal, 32 ± 16, FRDA, 33 ± 19. Tissues were recovered from PEG/DMSO and transferred into paraffin for matching with immunohistochemistry of neuron-specific enolase (NSE), glutamic acid decarboxylase (GAD), and ferritin. NSE and GAD reaction products confirmed neuronal atrophy and grumose degeneration that coincided with abnormally diffuse Cu and Zn zones. Ferritin immunohistochemistry matched Fe XRF maps, revealing the most abundant reaction product in oligodendroglia of the DN hilus. In FRDA, these cells were smaller and more numerous than normal. In the atrophic DN gray matter of FRDA, anti-ferritin labeled mostly hypertrophic microglia. Immunohistochemistry and immunofluorescence of the Cu-responsive proteins Cu,Zn-superoxide dismutase and Cu⁺⁺-transporting ATPase α-peptide did not detect specific responses to Cu redistribution in FRDA. In contrast, metallothionein (MT)-positive processes were more abundant than normal and contributed to the gliosis of the DN. The isoforms of MT, MT-1/2, and brain-specific MT-3 displayed only limited co-localization with glial fibrillary acidic protein. The results suggest that MT can provide effective protection against endogenous Cu and Zn toxicity in FRDA, similar to the neuroprotective sequestration of Fe in holoferritin.

ZIP4 is a novel molecular marker for glioma

BACKGROUND

Dysregulated zinc transport has been observed in many cancers. However, the status of zinc homeostasis and the expression profile of zinc transporters in brain and brain tumors have not been reported.

METHODS

The gene profiles of 14 zinc importers (ZIPs) and 10 zinc exporters (ZnTs) in patients with glioma were studied by investigating the association between the zinc transporters and brain tumor characteristics (tumor grade and overall survival time). Three independent cohorts were analyzed to cross-validate the findings: the Chinese Glioma Genome Atlas (CGCA) cohort (n = 186), the US National Cancer Institute Repository for Molecular Brain Neoplasia Data (REMBRANDT) cohort (n = 335), and The University of Texas (UT) cohort (n = 34).

RESULTS

The expression of ZIP3, 4, 8, 14, ZnT5, 6, and 7 were increased, and the expression of ZnT10 was decreased in grade IV gliomas, compared with grade II gliomas. Among all 24 zinc transporters, ZIP4 is most significantly associated with tumor grade and overall survival; this finding is consistent across 2 independent cohorts (CGCA and REMBRANDT) and is partially validated by the third cohort (UT). High ZIP4 expression was significantly associated with higher grade of gliomas and shorter overall survival (hazard ratio = 1.61, 95% confidence interval = 1.02-2.53, P = .040 in CGCA cohort; hazard ratio = 1.32, 95% confidence interval = 1.08-1.61, P = .007 in REMBRANDT cohort).

CONCLUSIONS

Dysregulated expression of zinc transporters is involved in the progression of gliomas. Our results suggest that ZIP4 may serve as a potential diagnostic and prognostic marker for gliomas.

Deep ocean mineral water accelerates recovery from physical fatigue

Background

Deep oceans have been suggested as a possible site where the origin of life occurred. Along with this theoretical lineage, experiments using components from deep ocean water to recreate life is underway. Here, we propose that if terrestrial organisms indeed evolved from deep oceans, supply of deep ocean mineral water (DOM) to humans, as a land creature, may replenish loss of molecular complexity associated with evolutionary sea-to-land migration.

Methods

We conducted a randomized, double-blind, placebo-controlled crossover human study to evaluate the effect of DOM, taken from a depth of 662 meters off the coast of Hualien, Taiwan, on time of recovery from a fatiguing exercise conducted at 30°C.

Results

The fatiguing exercise protocol caused a protracted reduction in aerobic power (reduced VO_2max) for 48 h. However, DOM supplementation resulted in complete recovery of aerobic power within 4 h (P < 0.05). Muscle power was also elevated above placebo levels within 24 h of recovery (P < 0.05). Increased circulating creatine kinase (CK) and myoglobin, indicatives of exercise-induced muscle damage, were completely eliminated by DOM (P < 0.05) in parallel with attenuated oxidative damage (P < 0.05).

Conclusion

Our results provide compelling evidence that DOM contains soluble elements, which can increase human recovery following an exhaustive physical challenge.

The molecular basis of memory

We propose a tripartite biochemical mechanism for memory. Three physiologic components are involved, namely, the neuron (individual and circuit), the surrounding neural extracellular matrix, and the various trace metals distributed within the matrix. The binding of a metal cation affects a corresponding nanostructure (shrinking, twisting, expansion) and dielectric sensibility of the chelating node (address) within the matrix lattice, sensed by the neuron. The neural extracellular matrix serves as an electro-elastic lattice, wherein neurons manipulate multiple trace metals (n > 10) to encode, store, and decode coginive information. The proposed mechanism explains brains low energy requirements and high rates of storage capacity described in multiples of Avogadro number (N(A) = 6 × 10(23)). Supportive evidence correlates memory loss to trace metal toxicity or deficiency, or breakdown in the delivery/transport of metals to the matrix, or its degradation. Inherited diseases revolving around dysfunctional trace metal metabolism and memory dysfunction, include Alzheimer's disease (Al, Zn, Fe), Wilson's disease (Cu), thalassemia (Fe), and autism (metallothionein). The tripartite mechanism points to the electro-elastic interactions of neurons with trace metals distributed within the neural extracellular matrix, as the molecular underpinning of "synaptic plasticity" affecting short-term memory, long-term memory, and forgetting.

The future of susceptibility contrast for assessment of anatomy and function

The magnetic properties of tissues affect MR images and differences in magnetic susceptibility can be utilized to provide impressive image contrast. Specifically, phase images acquired with gradient echo MRI provide unique and superb contrast which reflects variations in the underlying tissue composition. There is great interest in extracting tissue susceptibility from image data since magnetic susceptibility is an intrinsic tissue property that reflects tissue composition much more closely than MRI phase. Still, this major tissue contrast mechanism is largely unexplored in magnetic resonance imaging because non-conventional reconstruction and dipole deconvolution are required to quantitatively map tissue susceptibility properly. This short review summarizes the current state of susceptibility contrast and susceptibility mapping and aims to identify future directions.

[Normal aging and imaging correlations]

Age-related structural, functional and biochemical changes of the brain can be visualized by neuroimaging methods. Physiological aging of the brain has to be clearly distinguished from pathological alterations of the brain for reliable and early diagnoses of neurodegenerative diseases. Concerning the speed of the cerebral aging process, significant inter-individual differences can be observed. In general, aging is associated with a decline of cognitive functions. Simultaneously, a decay of the average brain volume, especially in the frontal lobe accompanies the process of aging. Correspondingly, a strong susceptibility for age-related degeneration has been observed in the fronto-striato-thalamic network. Due to increasing age the white matter is affected by a progressive loss of fiber integrity mirrored in a significant decay of the fractionated anisotropy (FA) measured by diffusion tensor imaging (DTI). Age-related degeneration of the white matter further leads to a growing number of T2 hyperintense white-matter lesions. Aging also influences the cerebral perfusion pattern leading to a perceptible decay of the global cerebral blood flow (CBF) and blood volume (CBV). During life, iron accumulates in the brain, predominantly in the globus pallidus and in the substantia nigra. By 1H-MR spectroscopy, a decrease of N-acetyl-aspartate (NAA) as a correlate for reduced neuronal metabolism is found in the brain of elderly individuals.

Role of selenium on calcium signaling and oxidative stress-induced molecular pathways in epilepsy

Epilepsy is one of the oldest neurological conditions known to humankind. It is known that oxidative stress and generation of reactive oxygen species are a cause and consequence of epileptic seizures. Although recent years have seen tremendous progress in the molecular biology and metabolism of selenium, we still know little about the cell type-specific and temporal pattern of selenium and its derivatives in the brain of epileptic humans and experimental animals. It has been suggested that some antiepileptic drug therapies such as valproic acid, deplete the total body selenium level and selenium-dependent glutathione peroxidase (GSH-Px) activity although therapy with a new epileptic drug, topiramate, activated GSH-Px activity in epileptic animals and humans. An observation of lower blood or tissue selenium level and GSH-Px activity in epileptic patients and animals compared to controls in recent publications may support the proposed crucial role of selenium level and GSH-Px activity in the pathogenesis of epilepsy. Selenium is incorporated into an interesting class of molecules known as selenoproteins that contain the modified amino acid, selenocysteine. There are signs of selenium and selenoprotein deficiency in the pathogenesis of epilepsy. In conclusion, there is convincing evidence for the proposed crucial role of selenium and deficiency of GSH-Px enzyme activity in epilepsy pathogenesis. Blood GSH-Px activities could be a reliable indicator of selenium deficiency in patients with epilepsy.

Mapping brain metals to evaluate therapies for neurodegenerative disease

The brain is rich in metals and has a high metabolic rate, making it acutely vulnerable to the toxic effects of endogenously produced free radicals. The abundant metals, iron and copper, transfer single electrons as they cycle between their reduced (Fe(2+) , Cu(1+) ) and oxidized (Fe(3+) , Cu(2+) ) states making them powerful catalysts of reactive oxygen species (ROS) production. Even redox inert zinc, if present in excess, can trigger ROS production indirectly by altering mitochondrial function. While metal chelators seem to improve the clinical outcome of several neurodegenerative diseases, their mechanisms of action remain obscure and the effects of long-term use are largely unknown. Most chelators are not specific to a single metal and could alter the distribution of multiple metals in the brain, leading to unexpected consequences over the long-term. We show here how X-ray fluorescence will be a valuable tool to examine the effect of chelators on the distribution and amount of metals in the brain.

Identification of two phospholipid hydroperoxide glutathione peroxidase (gpx4) genes in common carp

The monomeric selenoprotein, phospholipid hydroperoxide glutathione peroxidase (GPx4) is an essential member of the antioxidant defense system. This paper describes the identification of two gpx4 genes (gpx4a and gpx4b) from somatic tissues of common carp (Cyprinus carpio). The two sequences exhibited 78% and 79% identity at the DNA and the predicted protein level, respectively. The gpx4a transcript was detected in all examined tissues of unstressed animals, with the highest level in the liver. The gpx4b expression was low relative to that of gpx4a in the liver, heart, muscle and brain, and was virtually undetected in the kidney. However, in the olfactory lobe gpx4b was expressed at a fairly high level, the ratio gpx4a/gpx4b being approximately 2:1. Cold shock and Cd(2+) exposure influenced the gpx4a expression to only a slight extent, whereas gpx4b was greatly down-regulated following Cd(2+) exposure.

Systems genetics analysis of iron regulation in the brain

Iron imbalances in the brain, including excess accumulation and deficiency, are associated with neurological disease and dysfunction; yet, their origins are poorly understood. Using systems genetics analysis, we have learned that large individual differences exist in brain iron concentrations, even in the absence of neurological disease. Much of the individual differences can be tied to the genetic makeup of the individual. This genetic-based differential regulation can be modeled in genetic reference populations of rodents. The work in our laboratory centers on iron regulation in the brain and our animal model consists of 25 BXD/Ty recombinant inbred mouse strains. By studying naturally occurring variation in iron phenotypes, such as tissue iron concentration, we can tie that variability to one or more genes by way of quantitative trait loci (QTL) analysis. Moreover, we can conduct genetic correlation analyses between our phenotypes and others previously measured in the BXD/Ty strains. We have observed several suggestive QTL related to ventral midbrain iron content, including one on chromosome 17 that contains btbd9, a gene that in humans has been associated with restless legs syndrome and serum ferritin. We have also observed gene expression correlations with ventral midbrain iron, including btbd9 expression and dopamine receptor expression. In addition, we have observed significant correlations between ventral midbrain iron content and dopamine-related phenotypes. The following is a discussion of iron regulation in the brain and the contributions a systems genetics approach can make toward understanding the genetic underpinnings and relation to neurological disease.

Synchrotron X-ray fluorescence reveals abnormal metal distributions in brain and spinal cord in spinocerebellar ataxia: a case report

For the first time, synchrotron rapid-scanning X-ray fluorescence (RS-XRF) was used to simultaneously localize and quantify iron, copper, and zinc in spinal cord and brain in a case of spinocerebellar ataxia (SCA). In the normal medulla, a previously undescribed copper enrichment was seen associated with spinocerebellar fibers and amiculum olivae. This region was virtually devoid of all metals in the SCA case. Regions with neuronal loss and gliosis in the cerebellar cortex, inferior olivary, and dentate nuclei and areas showing loss of myelinated fibers were also low in all metals in SCA compared to control. In contrast, the ventral columns of the spinal cord that exhibited only moderate myelin pallor had increased metal levels. Iron and zinc were also elevated in the globus pallidus pars externa in SCA relative to control. We hypothesize that metals increase as part of the initial neurodegenerative process, but once degeneration is advanced, the metal levels drop. This implies a role for multiple metals in SCA neurodegeneration, but further study is required to establish a causative role. We suggest that if these findings are generally true of at least some cases of SCA, not only iron but also copper and zinc should be considered as possible therapeutic targets.

Genetics of iron regulation and the possible role of iron in Parkinson's disease

Parkinson's disease (PD) is acknowledged as the second most common neurodegenerative disorder after Alzheimer's Disease. Older age may be the only unequivocal risk factor for PD although the male to female ratio is consistently greater than 1 in populations of European ancestry. Characteristic features of PD include dopaminergic neuron death in the substantia nigra (SN) pars compacta, accumulation of alpha-synuclein inclusions known as Lewy bodies in the SN, and brain iron accumulation beyond that observed in non-PD brains of a similar age. In this review article, we will provide an overview of human and animal studies investigating the contributions of iron in PD, a summary of human studies of iron-related genes in PD, a review of the literature on the genetics of iron metabolism, and some hypotheses on possible roles for iron in the pathogenic processes of PD including potential interactions between iron and other factors associated with Parkinson's disease.

Studies on the pathogenesis of Parkinson's disease in Japan

Studies on the pathogenesis of nigral cell death in Parkinson's disease (PD) are reviewed. Discussions are focused mainly on studies performed by Japanese investigators because of the purpose of this issue. We and other groups found a decrease in complex I of the mitochondrial electron transfer complex in the substantia nigra of patients with PD, and in addition to complex I deficiency, we reported loss of alpha-ketoglutarate dehydrogenase complex of the tricarboxylic acid cycle (TCA cycle) by immunohistochemistry. Thus mitochondrial respiratory failure and resultant energy crisis appear to be one of the most important mechanisms that lead nigral neurons to cell death. The primary cause of mitochondrial respiratory failure has not been elucidated yet; however, environmental neurotoxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) may be responsible for nigral cell death in PD; in this respect a number of candidate toxins including tetrahydroisoquinolines and beta-carbolines have extensively been studied for nigral as well as mitochondrial toxicity. Recent progress in this field is also reviewed. Even if an environmental neurotoxin is involved in PD, exposure to such a neurotoxin alone may not account for its pathogenesis, as most of us are probably being exposed to the same toxin. Therefore, genetic predisposition appears to be essential for the development of PD. The genetic predisposition may involve hepatic detoxifying enzymes for such neurotoxins, the transport mechanism of those toxins to the brain, bioactivation of those toxins in the brain, the uptake mechanism to the nigral neurons, and the activity levels of target enzymes or proteins; all of these factors are being extensively studied in many laboratories at a molecular level.

The neuromelanin of human substantia nigra: structure, synthesis and molecular behaviour

The pigmented neurons of the substantia nigra (SN) are typically lost in Parkinson's disease: however the possible relationship between neuronal vulnerability and the presence of neuromelanin (NM) has not been elucidated. Early histological studies revealed the presence of increasing amounts of NM in the SN with aging in higher mammals, showed that NM granules are surrounded by membrane, and comparatively evaluated the pigmentation of SN in different animal species. Histochemical studies showed the association of NM with lipofuscins. However, systematic investigations of NM structure, synthesis and molecular interactions have been undertaken only during the last decade. In these latter studies, NM was identified as a genuine melanin with a strong chelating ability for iron and affinity for compounds such as lipids, pesticides, and MPP+. The affinity of NM for a variety of inorganic and organic toxins is consistent with a postulated protective function for NM. Moreover, the neuronal accumulation of NM during aging, and the link between its synthesis and high cytosolic concentration of catechols suggests a protective role. However, its putative neuroprotective effects could be quenched in conditions of toxin overload.

Quantitative T2 in the occipital lobe: the role of the CPMG refocusing rate

PURPOSE

To investigate the dependence of occipital gray and white matter T(2) on the Carr-Purcell-Meiboom-Gill (CPMG) refocusing interval, thereby testing the basis of a novel functional magnetic resonance imaging (fMRI) method for blood volume quantification, and addressing recent questions surrounding T(2) contrast in the occipital lobe.

MATERIALS AND METHODS

A CPMG sequence with 1 x 1 x 5 mm(3) resolution was used to quantify T(2) in a single axial slice at the midlevel of the occipital lobe in 23 healthy adult volunteers. Refocusing intervals of 8, 11, and 22 msec were compared. A Bayesian classifier was used to classify a 1 x 1 x 1 mm(3) T(1)-weighted three-dimensional data set into gray matter, white matter, and cerebrospinal fluid, with an average 95% a posteriori probability used as the threshold for inclusion into a tissue-specific region of interest (ROI).

RESULTS

The usual T(2) contrast between the gray and white matter (i.e., T(2GM) > T(2WM)) was observed, with a highly significant effect of tissue type on the estimated T(2) (P < 10(-5)). The observed T(2) gradually decreased with increasing refocusing interval, for a decrease of 3.3 +/- 1.5 msec in gray matter and 3.0 +/- 1.5 msec in white matter between the 8 and 22 msec refocusing interval acquisitions.

CONCLUSION

The observed T(2) shortening is consistent with the effect of the dramatic decrease in T(2) of partly deoxygenated blood on this range of refocusing rates.

Selenium and selenoproteins in the brain and brain diseases

Over the past three decades, selenium has been intensively investigated as an antioxidant trace element. It is widely distributed throughout the body, but is particularly well maintained in the brain, even upon prolonged dietary selenium deficiency. Changes in selenium concentration in blood and brain have been reported in Alzheimer's disease and brain tumors. The functions of selenium are believed to be carried out by selenoproteins, in which selenium is specifically incorporated as the amino acid, selenocysteine. Several selenoproteins are expressed in brain, but many questions remain about their roles in neuronal function. Glutathione peroxidase has been localized in glial cells, and its expression is increased surrounding the damaged area in Parkinson's disease and occlusive cerebrovascular disease, consistent with its protective role against oxidative damage. Selenoprotein P has been reported to possess antioxidant activities and the ability to promote neuronal cell survival. Recent studies in cell culture and gene knockout models support a function for selenoprotein P in delivery of selenium to the brain. mRNAs for other selenoproteins, including selenoprotein W, thioredoxin reductases, 15-kDa selenoprotein and type 2 iodothyronine deiodinase, are also detected in the brain. Future research directions will surely unravel the important functions of this class of proteins in the brain.

Lead-exposed increase in movement behavior and brain lipid peroxidation in fish

Lipid peroxides formation and motor activity were studied in fish under lead exposure for a period of 30 days. The in vitro studies of lead exposure were also performed in fish brain homogenates. Spontaneous motor activity of fish was affected by lead exposure (50 microg/L). The behaviors were increased in fish during the first three days with jerky movements and then as spontaneous movements between 16 and 30 days of lead exposure. Lipid peroxidation, which is measured as thiobarbituric acid reactive species, was increased by 52% on 15 days and 156% on 30 days of lead exposure (50 microg/L). The effects of lead exposure (50 microg) were also observed in in vitro fish brain homogenates (1 mL, 5% w/v) alone, in presence of pro-oxidant system (as iron 100 microg) or anti-oxidant system (as alpha-tocopherol, 100 microg). Steady state increments of lipid peroxidation were apparent up to the concentration of 40 microg of lead treatment in brain homogenates, which subsequently attained a plateau up to the treatment of 100 microg lead. Lead at the concentration of 50 microg promoted lipid peroxidation by 225%. Iron-induced lipid peroxidation was 135% as compared to control. Lead neurotoxicity was further aggravated by iron by 33%, while the combined impact was 476% higher when compared with the control (i.e., untreated brain homogenates). Alpha-tocopherol reduced the levels of lipid peroxidation by 31%. Moreover, treatment of alpha-tocopherol also suppressed the lead neurotoxicity by 53%. These findings suggest that lead intoxication increases spontaneous motor activity and lipid peroxides in brain of fish in chronic exposure. I, therefore, speculate that presence of iron may accentuate lead neurotoxicity, while on the other hand, treatment with biological anti-oxidant alpha-tocopherol may provide relief from lead neurotoxicity.

Heschl and superior temporal gyri: low signal intensity of the cortex on T2-weighted MR images of the normal brain

PURPOSE

To study the normal signal intensity pattern in the primary auditory cortex (first Heschl gyrus [HG]) and the surrounding cortices in the superior temporal gyrus (STG) and middle temporal gyrus (MTG) on T2-weighted magnetic resonance (MR) images.

MATERIALS AND METHODS

Coronal T2-weighted fast spin-echo MR images in 30 neurologically normal patients (60 hemispheres) were retrospectively analyzed. Two raters evaluated the cortical signal intensity of the first HG and the neighboring STG and compared them with those of the MTG and the subcortical white matter. The cortical signal intensities between the first HG and the STG were also directly compared. Coronal MR images, which included images of the anterior and posterior halves of the first HG, were evaluated separately.

RESULTS

All first HGs were hypointense to the MTG and were either iso- or hypointense to the STG. Cortical hypointensity was especially prominent in the posterior half; the first HG was isointense to the white matter in 33 (55%) hemispheres. The STG was hypointense to the MTG in 54 (90%) hemispheres and in the anterior halves of 36 (60%) hemispheres.

CONCLUSION

These findings demonstrate lower signal intensity of the cortex on T2-weighted images in the first HG and surrounding STG compared with that of the MTG.

The influence of neonatal nutrition on behavioral development: a critical appraisal

Specific nutrients appear to modify the metabolism of neurotransmitters, which are endogenous regulators of neurogenesis, neural migration, and synaptogenesis during both embryonic and early postnatal life. This has led to the question of whether, by affecting neurotransmission, malnutrition during the early neonatal period affects behavioral development. The literature based on animal models suggests that nutrient deficiencies during early life influence neurotransmission and, in some instances, also affect behavioral outcomes. A clear answer to the question, however, remains elusive. This can be attributed to the complexity of the process of brain development, where changes at a cellular level may not necessarily translate into changes at a behavioral level. Future investigations in this important area of research should work toward refinement of the design of behavioral experiments so that these studies can contribute to the understanding of the putative mechanisms involved.

Multielemental analysis of human fetal tissues using inductively coupled plasma-mass spectrometry

Inductively coupled plasma-mass spectrometry (ICP-MS) was used to study the distribution of 26 major and trace elements in six tissues from 21 human fetuses aged 16-22 wk. Brain, lung, spleen, kidney, heart, and liver were analyzed following a microwave oven digestion step carried out according to clean techniques designed for ultratrace metal analyses. Precision and accuracy controls were conducted using standard reference material #1577b Bovine Liver. Significant differences among tissues were found for most of the elements. Essential trace elements seem to be increasingly retained as fetal tissues mature and become physiologically functional. The ranges of concentrations measured in fetal tissues at this stage of development are generally lower and much narrower than in adult tissues. The age of the fetus, which is not given in most studies, as well as the different techniques and levels of quality assurance could be responsible for the discrepancies in the trace metal concentrations reported here and in the literature. Intratissue homogeneity was also assessed in five human fetal brains. Frontal, occipital, parietal and temporal lobes, striatum, hippocampus, and thalamus were isolated and analyzed separately. No significant differences were found in the distribution of any of the elements at this stage of development. Because of the relatively narrow ranges of concentrations found for most elements, we believe that the results presented in this study represent the inorganic fingerprint of the main tissues of normal fetuses at midpregnancy for the Greater Montreal area.