Changes in Blood Manganese Concentration and MRI T1 Relaxation Time During 180 Days of Stainless Steel Welding-Fume Exposure in Cynomolgus Monkeys

Magnetic resonance imaging T1 indices of the brain as biomarkers of inhaled manganese exposure

Excessive exposure to manganese (Mn) is linked to its accumulation in the brain and adverse neurological effects. Paramagnetic properties of Mn allow the use of magnetic resonance imaging (MRI) techniques to identify it in biological tissues. A critical review was conducted to evaluate whether MRI techniques could be used as a diagnostic tool to detect brain Mn accumulation as a quantitative biomarker of inhaled exposure. A comprehensive search was conducted in MEDLINE, EMBASE, and PubMed to identify potentially relevant studies published prior to 9 May 2022. Two reviewers independently screened identified references using a two-stage process. Of the 6452 unique references identified, 36 articles were retained for data abstraction. Eligible studies used T1-weighted MRI techniques and reported direct or indirect T1 measures to characterize Mn accumulation in the brain. Findings demonstrate that, in subjects exposed to high levels of Mn, deposition in the brain is widespread, accumulating both within and outside the basal ganglia. Available evidence indicates that T1 MRI techniques can be used to distinguish Mn-exposed individuals from unexposed. Additionally, T1 MRI may be useful for semi-quantitative evaluation of inhaled Mn exposure, particularly when interpreted along with other exposure indices. T1 MRI measures appear to have a nonlinear relationship to Mn exposure duration, with R1 signal only increasing after critical thresholds. The strength of the association varied depending on the regions of interest imaged and the method of exposure measurement. Overall, available evidence suggests potential for future clinical and risk assessment applications of MRI as a diagnostic tool.

The schizophrenia risk locus in SLC39A8 alters brain metal transport and plasma glycosylation

A common missense variant in SLC39A8 is convincingly associated with schizophrenia and several additional phenotypes. Homozygous loss-of-function mutations in SLC39A8 result in undetectable serum manganese (Mn) and a Congenital Disorder of Glycosylation (CDG) due to the exquisite sensitivity of glycosyltransferases to Mn concentration. Here, we identified several Mn-related changes in human carriers of the common SLC39A8 missense allele. Analysis of structural brain MRI scans showed a dose-dependent change in the ratio of T2w to T1w signal in several regions. Comprehensive trace element analysis confirmed a specific reduction of only serum Mn, and plasma protein N-glycome profiling revealed reduced complexity and branching. N-glycome profiling from two individuals with SLC39A8-CDG showed similar but more severe alterations in branching that improved with Mn supplementation, suggesting that the common variant exists on a spectrum of hypofunction with potential for reversibility. Characterizing the functional impact of this variant will enhance our understanding of schizophrenia pathogenesis and identify novel therapeutic targets and biomarkers.

Recent Updates on Acquired Hepatocerebral Degeneration

BACKGROUND

Acquired hepatocerebral degeneration (AHD) refers to a chronic neurological syndrome in patients with advanced hepatobiliary diseases. This comprehensive review focuses on the pathomechanism and neuroimaging findings in AHD.

METHODS

A PubMed search was performed using the terms "acquired hepatocerebral degeneration," "chronic hepatocerebral degeneration," "Non-Wilsonian hepatocerebral degeneration," "cirrhosis-related parkinsonism," and "manganese and liver disease."

RESULTS

Multiple mechanisms involving the accumulation of toxic substances such as ammonia or manganese and neuroinflammation may lead to widespread neurodegeneration in AHD. Clinical characteristics include movement disorders, mainly parkinsonism and ataxia-plus syndrome, as well as cognitive impairment with psychiatric features. Neuroimaging studies of AHD with parkinsonism show hyperintensity in the bilateral globus pallidus on T1-weighted magnetic resonance images, whereas molecular imaging of the presynaptic dopaminergic system shows variable findings. Ataxia-plus syndrome in AHD may demonstrate high-signal lesions in the middle cerebellar peduncles on T2-weighted images.

DISCUSSION

Future studies are needed to elucidate the exact pathomechanism and neuroimaging findings of this heterogeneous syndrome.

Extrapyramidal system neurotoxicity: animal models

The central nervous system's extrapyramidal system provides involuntary motor control to the muscles of the head, neck, and limbs. Toxicants that affect the extrapyramidal system are generally clinically characterized by impaired motor control, which is usually the result of basal ganglionic dysfunction. A variety of extrapyramidal syndromes are recognized in humans and include Parkinson's disease, secondary parkinsonism, other degenerative diseases of the basal ganglia, and clinical syndromes that result in dystonia, dyskinesia, essential tremor, and other forms of tremor and chorea. This chapter briefly reviews the anatomy of the extrapyramidal system and discusses several naturally occurring and experimental models that target the mammalian (nonhuman) extrapyramidal system. Topics discussed include extrapyramidal syndromes associated with antipsychotic drugs, carbon monoxide, reserpine, cyanide, rotenone, paraquat, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and manganese. In most cases, animals are used as experimental models to improve our understanding of the toxicity and pathogenesis of these agents. Another agent discussed in this chapter, yellowstar thistle poisoning in horses, however, represents an important spontaneous cause of parkinsonism that naturally occurs in animals. The central focus of the chapter is on animal models, especially the concordance between clinical signs, neurochemical changes, and neuropathology between animals and people.

Manganese in cerebrospinal fluid and blood plasma of patients with amyotrophic lateral sclerosis

Neurotoxic properties of manganese (Mn) are well documented. It is less known that Mn contributes to the development of neurodegenerative disorders in the general population. This study presents Mn data from patients with amyotrophic lateral sclerosis (ALS) in a well-defined cohort diagnosed by electrophysiological methods. Cerebrospinal fluid (CSF) and plasma were collected from patients and controls. Mn concentrations were analyzed by high-resolution inductively coupled plasma mass spectrometry. Concentrations of Mn were significantly higher in ALS CSF (median 5.67 μg/L) than in CSF from controls (median 2.08 μg/L). Also, ALS CSF Mn concentrations were higher than ALS plasma Mn concentrations (median 0.91 μg/L), suggesting transport of Mn into the central nervous system. The properties of barrier systems between blood and the brain are discussed and the possibility of Mn accumulation contributing to the relentless course of ALS is introduced.

Gene expression profiling in the lung tissue of cynomolgus monkeys in response to repeated exposure to welding fumes

Many in the welding industry suffer from bronchitis, lung function changes, metal fume fever, and diseases related to respiratory damage. These phenomena are associated with welding fumes; however, the mechanism behind these findings remains to be elucidated. In this study, the lungs of cynomolgus monkeys were exposed to MMA-SS welding fumes for 229 days and allowed to recover for 153 days. After the exposure and recovery period, gene expression profiles were investigated using the Affymetrix GeneChip Human U133 plus 2.0. In total, it was confirmed that 1,116 genes were up-or downregulated (over 2-fold changes, P\0.01) for the T1 (31.4 ± 2.8 mg/m3) and T2 (62.5 ± 2.7 mg/m3) dose groups. Differentially expressed genes in the exposure and recovery groups were analyzed, based on hierarchical clustering, and were imported into Ingenuity Pathways Analysis to analyze the biological and toxicological functions. Functional analysis identified genes involved in immunological disease in both groups. Additionally, differentially expressed genes in common between monkeys and rats following welding fume exposure were compared using microarray data, and the gene expression of selected genes was verified by real-time PCR. Genes such as CHI3L1, RARRES1, and CTSB were up-regulated and genes such as CYP26B1, ID4, and NRGN were down-regulated in both monkeys and rats following welding fume exposure. This is the first comprehensive gene expression profiling conducted for welding fume exposure in monkeys, and these expressed genes are expected to be useful in helping to understand transcriptional changes in monkey lungs after welding fume exposure.

Isolation and characterization of a Mn(II)-oxidizing Bacillus strain from the demosponge Suberites domuncula

In this study we demonstrate that the demosponge Suberites domuncula harbors a Mn(II)-oxidizing bacterium, a Bacillus strain, termed BAC-SubDo-03. Our studies showed that Mn(II) stimulates bacterial growth and induces sporulation. Moreover, we show that these bacteria immobilize manganese on their cell surface. Comparison of the 16S rDNA sequence allowed the grouping of BAC-SubDo-03 to the Mn-precipitating bacteria. Analysis of the spore cell wall revealed that it contains an Mn(II)-oxidizing enzyme. Co-incubation studies of BAC-SubDo-03 with 100 μM MnCl₂ and >1 μM of CuCl₂ showed an increase in their Mn(II)-oxidizing capacity. In order to prove that a multicopper oxidase-like enzyme(s) (MCO) exists in the cell wall of the S. domuncula-associated BAC-SubDo-03 Bacillus strain, the gene encoding this enzyme was cloned (mnxG-SubDo-03). Sequence alignment of the deduced MCO protein (MnxG-SubDo-03) revealed that the sponge bacterium clusters together with known Mn(II)-oxidizing bacteria. The expression of the mnxG-SubDo-03 gene is under strong control of extracellular Mn(II). Based on these findings, we assume that BAC-SubDo-03 might serve as a Mn reserve in the sponge providing the animal with the capacity to detoxify Mn in the environment. Applying the in vitro primmorph cell culture system we could demonstrate that sponge cells, that were co-incubated with BAC-SubDo-03 in the presence of Mn(II), show an increased proliferation potential.

Biomarkers of manganese intoxication

Manganese (Mn), upon absorption, is primarily sequestered in tissue and intracellular compartments. For this reason, blood Mn concentration does not always accurately reflect Mn concentration in the targeted tissue, particularly in the brain. The discrepancy between Mn concentrations in tissue or intracellular components means that blood Mn is a poor biomarker of Mn exposure or toxicity under many conditions and that other biomarkers must be established. For group comparisons of active workers, blood Mn has some utility for distinguishing exposed from unexposed subjects, although the large variability in mean values renders it insensitive for discriminating one individual from the rest of the study population. Mn exposure is known to alter iron (Fe) homeostasis. The Mn/Fe ratio (MIR) in plasma or erythrocytes reflects not only steady-state concentrations of Mn or Fe in tested individuals, but also a biological response (altered Fe homeostasis) to Mn exposure. Recent human studies support the potential value for using MIR to distinguish individuals with Mn exposure. Additionally, magnetic resonance imaging (MRI), in combination with noninvasive assessment of γ-aminobutyric acid (GABA) by magnetic resonance spectroscopy (MRS), provides convincing evidence of Mn exposure, even without clinical symptoms of Mn intoxication. For subjects with long-term, low-dose Mn exposure or for those exposed in the past but not the present, neither blood Mn nor MRI provides a confident distinction for Mn exposure or intoxication. While plasma or erythrocyte MIR is more likely a sensitive measure, the cut-off values for MIR among the general population need to be further tested and established. Considering the large accumulation of Mn in bone, developing an X-ray fluorescence spectroscopy or neutron-based spectroscopy method may create yet another novel non-invasive tool for assessing Mn exposure and toxicity.

Manganese (Mn) and iron (Fe): interdependency of transport and regulation

Manganese (Mn) and iron (Fe) are transition metals that are crucial to the appropriate growth, development, function, and maintenance of biological organisms. Because of their chemical similarity, in organisms ranging from bacteria to mammals they share and compete for many protein transporters, such as the divalent metal transporter-1. As such, during conditions of low Fe, abnormal Mn accumulation occurs. Conversely, when Mn concentrations are altered, the homeostasis and deposition of Fe and other transition metals are disrupted. Our lab has undertaken a series of studies in rats involving pregnant dams, neo- and perinatal pups, and adult animals. Animals were exposed to various concentrations of dietary Fe and/or Mn, and protein transporter expression, blood Mn and Fe concentrations, brain transition metal concentrations, and temporal brain deposition patterns were examined. As a result, we have demonstrated the importance of the interdependence of the transport of Mn and Fe, and established brain metal concentrations in several longitudinal studies. The purpose of this review is to examine these studies in their entirety and highlight the importance of monitoring the deposition and accumulation of both Mn and Fe when designing future studies related to either dietary or environmental changes in transition metal levels. Finally, this review will provide information about various transport proteins currently under investigation in the research community related to Fe and Mn regulation and transport.

Recovery from welding-fume-exposure-induced MRI T1 signal intensities after cessation of welding-fume exposure in brains of cynomolgus monkeys

The shortening of the MRI T1 relaxation time, indicative of a high signal intensity in a T1-weighted MRI, is known as a useful biomarker for Mn exposure after short-term welding-fume exposure. A previous monkey experimental study found that the T1 relaxation times decreased time-dependently after exposure, and a visually detectable high signal intensity appeared after 150 days of exposure. The nadir for the shortening of the T1 relaxation time was also previously found to correspond well with the blood Mn concentration in welders, suggesting a correlation between a prolonged high blood Mn concentration and shortened T1 relaxation time. Accordingly, to clarify the clearance of the brain Mn concentration after the cessation of welding-fume exposure, cynomolgus monkeys were assigned to 3 groups-unexposed, low dose (31 mg/m(3) total suspended particulate (TSP), 0.9 mg Mn/m(3)), and high dose (62 mg/m(3) TSP, 1.95 mg Mn/m(3))-and exposed to manual metal-arc stainless steel (MMA-SS) welding fumes for 2 h per day for 8 mo in an inhalation chamber system equipped with an automatic fume generator. After reaching the peak MRI T1 signal intensity (shortest T1 relaxation time), the monkeys were allowed to recover by ceasing the welding-fume exposure. Within 2 mo, the MRI T1 signal intensities for the exposed monkeys returned to nearly the same level as those for the unexposed monkeys, indicating the potential for recovery from a high MRI T1 signal intensity induced by welding-fume exposure, even after prolonged exposure. Clearance of the Mn tissue concentration was also demonstrated in the globus pallidus, plus other tissues from the brain, liver, spleen, and blood. In contrast, there was no clearance of the lung concentrations of Mn, indicating that a soluble form of Mn was transported to the blood and brain. Therefore, the solubility of Mn in welding fumes would appear to be an important determinant as regards the retention of blood Mn levels and brain tissue Mn concentrations in welders.

Twenty-Eight-Day Inhalation Toxicity Study of Silver Nanoparticles in Sprague-Dawley Rats

The antibacterial effect of silver nanoparticles has resulted in their extensive application in health, electronic, and home products. Thus, the exposed population continues to increase as the applications expand. Although previous studies on silver dust, fumes, and silver compounds have revealed some insights, little is yet known about the toxicity of nano-sized silver particles, where the size and surface area are recognized as important determinants for toxicity. Thus, the inhalation toxicity of silver nanoparticles is of particular concern to ensure the health of workers and consumers. However, the dispersion of inhalable ambient nano-sized particles has been an obstacle in evaluating the effect of the inhalation of nano-sized particles on the respiratory system. Accordingly, the present study used a device that generates silver nanoparticles by evaporation/condensation using a small ceramic heater. As such, the generator was able to distribute the desired concentrations of silver nanoparticles to chambers containing experimental animals. The concentrations and distribution of the nanoparticles with respect to size were also measured directly using a differential mobility analyzer and ultrafine condensation particle counter. Therefore, the inhalation toxicity of silver nanoparticles was tested over a period of 28 days. Eight-week-old rats, weighing about 283 g for the males and 192 g for the females, were divided into 4 groups (10 rats in each group): a fresh-air control, a low-dose group (1.73 x 10(4)/cm3), a middle-dose group (1.27 x 10(5)/cm3), and a high-dose group (1.32 x 10(6) particles/cm3, 61 microg/m3). The animals were exposed to the silver nanoparticles for 6 h/day, 5 days/wk, for a total of 4 wk. The male and female rats did not show any significant changes in body weight relative to the concentration of silver nanoparticles during the 28-day experiment. Plus, there were no significant changes in the hematology and blood biochemical values in either the male or female rats. Therefore, the initial results indicated that exposure to silver nanoparticles at a concentration near the current American Conference of Governmental Industrial Hygienists (ACGIH) silver dust limit (100 microg/m3) did not appear to have any significant health effects.

Pulmonary Toxicity and Recovery from Inhalation of Manual Metal Arc Stainless Steel Welding Fumes in Rats

The objectives of this study were to examine the lung injury and inflammation caused by manual metal arc stainless steel (MMA-SS) welding fume inhalation and to evaluate the recovery process. Sprague-Dawley rats were exposed to MMA-SS welding fumes for 2 h per day in a whole-body exposure chamber, with a total suspended particulate (TSP) concentration of 51.4 ± 2.8 mg/m³ (low dose) or 84.6 ± 2.9 mg/m³ (high dose) for 30 days. The animals were sacrificed after 30 days of exposure as well as after a 30-day recovery period. To assess the inflammatory or injury responses, cellular and biochemical parameters as well as cytokines were assayed in the bronchoalveolar lavage fluid (BALF). MMA-SS welding fume exposure led to a significant elevation in the number of alveolar macrophages (AM) and polymorphonuclear cells (PMN). Additionary, the values of β-nacetyl glucosaminidase (β-NAG) and lactate dehydrogenase (LDH) in the BALF were increased in the exposed group when compared to controls. After 30 days of recovery from exposure, a significant reduction in inflammatory parameters of BALF was observed between the exposed and recovered groups. Slight, but significant elevations were noted in the number of AM and PMN in the recovered groups, and AM that had been ingested fume particles still remain in the lungs. In conclusion, these results indicated that welding fumes induced inflammatory responses and cytotoxicity in the lungs of exposed rats. Fume particles were not fully cleared from lungs even after a 30-day recovery period.

Comparison of high MRI T1 signals with manganese concentration in brains of cynomolgus monkeys after 8 months of stainless steel welding-fume exposure

Several pharmacokinetic studies on inhalation exposure to manganese (Mn) have already demonstrated that Mn readily accumulates in the olfactory and brain regions. However, a shortening of the magnetic resonance imaging (MRI) T1 relaxation time or high T1 signal intensity in specific sites of the brain, including the globus pallidus and subcortical frontal white matter, as indicative of tissue manganese accumulation has not yet been clearly established for certain durations of known doses of welding-fume exposure in experimental animals. Accordingly, to investigate the movement of manganese after welding-fume exposure, six cynomolgus monkeys were acclimated and assigned to three dose groups: unexposed, low dose (31 mg/m(3) total suspended particulate [TSP], 0.9 mg/m(3) of Mn), and high dose (62 mg/m(3) TSP, 1.95 mg/m(3) of Mn) of total suspended particulate. The primates were exposed to manual metal arc stainless steel (MMA-SS) welding fumes for 2 h per day in an inhalation chamber system equipped with an automatic fume generator. Magnetic resonance imaging (MRI) studies were conducted before the initiation of exposure and thereafter every month. The tissue Mn concentrations were then measured after a plateau was reached regarding the shortening of the MRI T1 relaxation time. A dose-dependent increase in the Mn concentration was found in the lungs, while noticeable increases in the Mn concentrations were found in certain tissues, such as the liver, kidneys, and testes. Slight increases in the Mn concentrations were found in the caudate, putamen, frontal lobe, and substantia nigra, while a dose-dependent noticeable increase was only found in the globus pallidus. Therefore, the present results indicated that a shortening of the MRI T1 relaxation time corresponded well with the Mn concentration in the globus pallidus after prolonged welding-fume exposure.