Subchronic, Low-Level Intraperitoneal Injections of Manganese (IV) Oxide and Manganese (II) Chloride Affect Rat Brain Neurochemistry

Manganese in autism spectrum disorder and attention deficit hyperactivity disorder: The state of the art

The objective of the present narrative review was to synthesize existing clinical and epidemiological findings linking manganese (Mn) exposure biomarkers to autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD), and to discuss key pathophysiological mechanisms of neurodevelopmental disorders that may be affected by this metal. Existing epidemiological data demonstrated both direct and inverse association between Mn body burden and ASD, or lack of any relationship. In contrast, the majority of studies revealed significantly higher Mn levels in subjects with ADHD, as well as direct relationship between Mn body burden with hyperactivity and inattention scores in children, although several studies reported contradictory results. Existing laboratory studies demonstrated that impaired attention and hyperactivity in animals following Mn exposure was associated with dopaminergic dysfunction and neuroinflammation. Despite lack of direct evidence on Mn-induced neurobiological alterations in patients with ASD and ADHD, a plethora of studies demonstrated that neurotoxic effects of Mn overexposure may interfere with key mechanisms of pathogenesis inherent to these neurodevelopmental disorders. Specifically, Mn overload was shown to impair not only dopaminergic neurotransmission, but also affect metabolism of glutamine/glutamate, GABA, serotonin, noradrenaline, thus affecting neuronal signaling. In turn, neurotoxic effects of Mn may be associated with its ability to induce oxidative stress, apoptosis, and neuroinflammation, and/or impair neurogenesis. Nonetheless, additional detailed studies are required to evaluate the association between environmental Mn exposure and/or Mn body burden and neurodevelopmental disorders at a wide range of concentrations to estimate the potential dose-dependent effects, as well as environmental and genetic factors affecting this association.

Punicalagin's Protective Effects on Parkinson's Progression in Socially Isolated and Socialized Rats: Insights into Multifaceted Pathway

Parkinson's disease (PD) is a gradual deterioration of dopaminergic neurons, leading to motor impairments. Social isolation (SI), a recognized stressor, has recently gained attention as a potential influencing factor in the progress of neurodegenerative illnesses. We aimed to investigate the intricate relationship between SI and PD progression, both independently and in the presence of manganese chloride (MnCl2), while evaluating the punicalagin (PUN) therapeutic effects, a natural compound established for its cytoprotective, anti-inflammatory, and anti-apoptotic activities. In this five-week experiment, seven groups of male albino rats were organized: G1 (normal control), G2 (SI), G3 (MnCl2), G4 (SI + MnCl2), G5 (SI + PUN), G6 (MnCl2 + PUN), and G7 (SI + PUN + MnCl2). The results revealed significant changes in behavior, biochemistry, and histopathology in rats exposed to SI and/or MnCl2, with the most pronounced effects detected in the SI rats concurrently exposed to MnCl2. These effects were associated with augmented oxidative stress biomarkers and reduced antioxidant activity of the Nrf2/HO-1 pathway. Additionally, inflammatory pathways (HMGB1/RAGE/TLR4/NF-ᴋB/NLRP3/Caspase-1 and JAK-2/STAT-3) were upregulated, while dysregulation of signaling pathways (PI3K/AKT/GSK-3β/CREB), sustained endoplasmic reticulum stress by activation PERK/CHOP/Bcl-2, and impaired autophagy (AMPK/SIRT-1/Beclin-1 axis) were observed. Apoptosis induction and a decrease in monoamine levels were also noted. Remarkably, treatment with PUN effectively alleviated behaviour, histopathological changes, and biochemical alterations induced by SI and/or MnCl2. These findings emphasize the role of SI in PD progress and propose PUN as a potential therapeutic intervention to mitigate PD. PUN's mechanisms of action involve modulation of pathways such as HMGB1/RAGE/TLR4/NF-ᴋB/NLRP3/Caspase-1, JAK-2/STAT-3, PI3K/AKT/GSK-3β/CREB, AMPK/SIRT-1, Nrf2/HO-1, and PERK/CHOP/Bcl-2.

Brain circuits activated by female sexual behavior evaluated by manganese enhanced magnetic resonance imaging

Magnetic resonance imaging (MRI) allows obtaining anatomical and functional information of the brain in the same subject at different times. Manganese-enhanced MRI (MEMRI) uses manganese ions to identify brain activity, although in high doses it might produce neurotoxic effects. Our aims were to identify a manganese dose that does not affect motivated behaviors such as sexual behavior, running wheel and the rotarod test. The second goal was to determine the optimal dose of chloride manganese (MnCl₂) that will allow us to evaluate activation of brain regions after females mated controlling (pacing) the sexual interaction. To achieve that, two experiments were performed. In experiment 1 we evaluated the effects of two doses of MnCl₂, 8 and 16 mg/kg. Subjects were injected with one of the doses of MnCl₂ 24 hours before the test on sessions 1, 5 and 10 and immediately thereafter scanned. Female sexual behavior, running wheel and the rotarod were evaluated once a week for 10 weeks. In experiment 2 we followed a similar procedure, but females paced the sexual interaction once a week for 10 weeks and were injected with one of the doses of MnCl₂ 24 hours before the test and immediately thereafter scanned on sessions 1, 5 and 10. The results of experiment 1 show that neither dose of MnCl₂ induces alterations on sexual behavior, running wheel and rotarod. Experiment 2 demonstrated that MEMRI allow us to detect activation of different brain regions after sexual behavior, including the olfactory bulb (OB), the bed nucleus of the stria terminalis (BNST), the amygdala (AMG), the medial preoptic area (MPOA), the ventromedial hypothalamus (VMH), the nucleus accumbens (NAcc), the striatum (STR) and the hippocampus (Hipp) allowing the identification of changes in brain circuits activated by sexual behavior. The socio sexual circuit showed a higher signal intensity on session 5 than the reward circuit and the control groups indicating that even with sexual experience the activation of the reward circuit requires the activation of the socio sexual circuit. Our study demonstrates that MEMRI can be used repeatedly in the same subject to evaluate the activation of brain circuits after motivated behaviors and how can this activation change with experience.

Risk Factors for Brain Health in Agricultural Work: A Systematic Review

Certain exposures related to agricultural work have been associated with neurological disorders. To date, few studies have included brain health measurements to link specific risk factors with possible neural mechanisms. Moreover, a synthesis of agricultural risk factors associated with poorer brain health outcomes is missing. In this systematic review, we identified 106 articles using keywords related to agriculture, occupational exposure, and the brain. We identified seven major risk factors: non-specific factors that are associated with agricultural work itself, toluene, pesticides, heavy metal or dust exposure, work with farm animals, and nicotine exposure from plants. Of these, pesticides are the most highly studied. The majority of qualifying studies were epidemiological studies. Nigral striatal regions were the most well studied brain area impacted. Of the three human neuroimaging studies we found, two focused on functional networks and the third focused on gray matter. We identified two major directions for future studies that will help inform preventative strategies for brain health in vulnerable agricultural workers: (1) the effects of moderators such as type of work, sex, migrant status, race, and age; and (2) more comprehensive brain imaging studies, both observational and experimental, involving several imaging techniques.

Manganese-induced hyperactivity and dopaminergic dysfunction depend on age, sex and YAC128 genotype

Manganese (Mn) is an essential micronutrient but is neurotoxic in excess. Environmental and genetic factors influence vulnerability to Mn toxicity, including sex, age, and the autosomal dominant mutation that causes Huntington disease (HD). To better understand the differential effects of Mn in wild-type (WT) versus YAC128 mice, we examined impacts of Mn exposure across different ages and sexes on disease-relevant behavioral tasks and dopamine dynamics. Young (3-week) and aged (12-month) WT and YAC128 mice received control (70 ppm) or high (2400 ppm) Mn diet for 8 weeks followed by a battery of behavioral tasks. In young female WT mice, high Mn diet induced hyperactivity across two independent behavioral tasks. Changes in the expression of tyrosine hydroxylase (TH) were consistent with the behavioral data in young females such that elevated TH in YAC128 on control diet was decreased by high Mn diet. Aged YAC128 mice showed the expected disease-relevant behavioral impairments in females and decreased TH expression, but we observed no significant effects of Mn diet in either genotype of the aged group. Fast-scan cyclic voltammetry recorded dopamine release and clearance in the nucleus accumbens of eight-month-old WT and YAC128 mice following acute Mn exposure (3×/1 week subcutaneous injections of 50 mg/kg MnCl[2]-tetrahydrate or saline). In WT mice, Mn exposure led to faster dopamine clearance that resembled saline treated YAC128 mice. Mn treatment increased dopamine release only in YAC128 mice, possibly indirectly correcting the faster dopamine clearance observed in saline treated YAC128 mice. The same exposure paradigm led to decreased dopamine and serotonin and metabolites (3-MT, HVA and 5-HIAA) in striatum and increased glutamate in YAC128 mice but not WT mice. These studies confirm an adverse effect of Mn in young, female WT animals and support a role for Mn exposure in stabilizing dopaminergic dysfunction and motivated behavior in early HD.

Chronic Manganese Administration with Longer Intervals Between Injections Produced Neurotoxicity and Hepatotoxicity in Rats

Abstract

Subacute exposure to manganese (Mn) produced Parkinson’s disease-like syndrome called Manganism. Chronic onset and progression are characteristics of Manganism, therefore, this study aimed to examine Mn toxicity following chronic exposures. Male Sprague-Dawley rats were injected Mn²⁺ 1 and 5 mg/kg, every 10 days for 150 days (15 injections). Animal body weight and behavioral activities were recorded. At the end of experiments, the brain and liver were collected for morphological and molecular analysis. Chronic Mn exposure did not affect animal body weight gain, but the high dose of Mn treatment caused 20% mortality after 140 days of administration. Motor activity deficits were observed in a dose-dependent manner at 148 days of Mn administration. Immunofluorescence double staining of substantia nigra pars compacta (SNpc) revealed the activation of microglia and loss of dopaminergic neurons. The chronic neuroinflammation mediators TNFα, inflammasome Nlrp3, Fc fragment of IgG receptor IIb, and formyl peptide receptor-1 were increased, implicating chronic Mn-induced neuroinflammation. Chronic Mn exposure also produced liver injury, as evidenced by hepatocyte degeneration with pink, condensed nuclei, indicative of apoptotic lesions. The inflammatory cytokines TNFα, IL-1β, and IL-6 were increased, alone with stress-related genes heme oxygenase-1, NAD(P)H:quinone oxidoreductase-1 and metallothionein. Hepatic transporters, such as multidrug resistant proteins (Abcc1, Abcc2, and Abcc3) and solute carrier family proteins (Slc30a1, Slc39a8 and Slc39a14) were increased in attempt to eliminate Mn from the liver. In summary, chronic Mn exposure produced neuroinflammation and dopaminergic neuron loss in the brain, but also produced inflammation to the liver, with upregulation of hepatic transporters.

Graphic Abstract

Electronic supplementary material

The online version of this article (10.1007/s11064-020-03059-2) contains supplementary material, which is available to authorized users.

Maintaining Translational Relevance in Animal Models of Manganese Neurotoxicity

Manganese is an essential metal, but elevated brain Mn concentrations produce a parkinsonian-like movement disorder in adults and fine motor, attentional, cognitive, and intellectual deficits in children. Human Mn neurotoxicity occurs owing to elevated exposure from occupational or environmental sources, defective excretion (e.g., due to cirrhosis), or loss-of-function mutations in the Mn transporters solute carrier family 30 member 10 or solute carrier family 39 member 14. Animal models are essential to study Mn neurotoxicity, but in order to be translationally relevant, such models should utilize environmentally relevant Mn exposure regimens that reproduce changes in brain Mn concentrations and neurological function evident in human patients. Here, we provide guidelines for Mn exposure in mice, rats, nematodes, and zebrafish so that brain Mn concentrations and neurobehavioral sequelae remain directly relatable to the human phenotype.

Carnosine Mitigates Manganese Mitotoxicity in an In Vitro Model of Isolated Brain Mitochondria

Purpose: Manganese (Mn) is a neurotoxic chemical which induces a wide range of complications in the brain tissue. Impaired locomotor activity and cognitive dysfunction are associated with high brain Mn content. At the cellular level, mitochondria are potential targets for Mn toxicity. Carnosine is a dipeptide abundantly found in human brain. Several pharmacological properties including mitochondrial protecting and antioxidative effects have been attributed to carnosine. The current study aimed to evaluate the effect of carnosine treatment on Mn-induced mitochondrial dysfunction in isolated brain mitochondria.

Methods: Mice brain mitochondria were isolated based on the differential centrifugation method and exposed to increasing concentrations of Mn (10 µM-10 mM). Carnosine (1 mM) was added as the protective agent. Mitochondrial indices including mitochondrial depolarization, reactive oxygen species (ROS) formation, mitochondrial dehydrogenases activity, ATP content, and mitochondrial swelling and permeabilization were assessed.

Results: Significant deterioration in mitochondrial indices were evident in Mn-exposed brain mitochondria. On the other hand, it was found that carnosine (1 mM) treatment efficiently prevented Mn-induced mitochondrial impairment.

Conclusion: These data propose mitochondrial protection as a fundamental mechanism for the effects of carnosine against Mn toxicity. Hence, this peptide might be applicable against Mn neurotoxicity with different etiologies (e.g., in cirrhotic patients).

Airborne manganese exposure and neurobehavior in school-aged children living near a ferro-manganese alloy plant

Excessive exposure to Mn can lead to its accumulation in the brain with neurotoxic consequences. In children, elevated Mn has been associated with deficits in certain neuropsychological domains such as cognition, motor function, memory and attention, and in some instances, hyperactivity and behavioral problems. The aim of this study was to evaluate behavioral effects in school-aged children living near a ferro-manganese alloy plant and examine their association with Mn exposure. Occipital hair, toenails and blood samples were collected from 225 children (7-12 years old) enrolled in four elementary schools with different levels of exposure to Mn, based on dust Mn deposition rates. Full data set collection was completed and run from 165 children. Mn in hair (MnH), toenails (MnTn), blood (MnB) and blood lead levels (PbB) were determined by graphite furnace atomic absorption spectrometry. Children's behavior was assessed with the Child Behavior Check List (CBCL) reported by parents. Median levels and range of MnH, MnT and MnB were, respectively, 0.73 µg/g (0.16-8.79), 0.84 µg/g (0.15-9.29) and 8.98 μg/L (1.51-40.43). Median and range of PbB were 1.2 µg/dL (0.2-15.6). MnH and MnB were not associated with any scale of the CBCL behavior scores. We found a positive association between logMnTn and raw total CBCL score (β = 10.17, p = 0.034), adjusting for sex, age, maternal IQ and logPbB. Analyses using Generalized Additive Model showed non-linear associations between MnTn and externalizing behavior (p = 0.035), as well as with the related subscales: aggressive behavior (p = 0.045) and rule-breaking behavior (p = 0.024). Further positive associations were observed between MnTn and thought problems (p = 0.031) and social problems (p = 0.027). These findings corroborate previous studies showing an association between Mn exposures and externalizing behavior. Our results suggest that toenail Mn, as a biomarker of environmental exposure, is associated with disruptive behavior in children living near a ferro-manganese alloy plant.