Intranasal exposure of manganese induces neuroinflammation and disrupts dopamine metabolism in the striatum and hippocampus

Signal Transduction Associated with Mn-induced Neurological Dysfunction

Manganese (Mn) is a heavy metal that occurs widely in nature and has a vital physiological role in growth and development. However, excessive exposure to Mn can cause neurological damage, especially cognitive dysfunction, such as learning disability and memory loss. Numerous studies on the mechanisms of Mn-induced nervous system damage found that this metal targets a variety of metabolic pathways, for example, endoplasmic reticulum stress, apoptosis, neuroinflammation, cellular signaling pathway changes, and neurotransmitter metabolism interference. This article reviews the latest research progress on multiple signaling pathways related to Mn-induced neurological dysfunction.

Spatial memory impairment is associated with decreased dopamine-β-hydroxylase activity in the brains of rats exposed to manganese chloride

Chronic exposure to manganese compounds leads to accumulation of the manganese in the basal ganglia and hippocampus. High levels of manganese in these structures lead to oxidative stress, neuroinflammation, imbalance of brain neurotransmitters, and hyperactivation of calpains mediating neurotoxicity and causing motor and cognitive impairment. The purpose of this work was to study the effect of excess manganese chloride intake on rats' spatial memory and on dopamine-β-hydroxylase (DβH) activity under conditions of calpain activity suppression. Rats were divided into 3 groups of 10 animals each. Group 1 received MnCl2 (30 days, 5 mg/kg/day, intranasally), group 2 received MnCl2 (30 days, 5 mg/kg/day, intranasally) and calpain inhibitor Cast (184-210) (30 days, 5 µg/kg/day, intranasally), and group 3 received sterile saline (30 days in a volume of 20 μl, intranasally). The spatial working memory was assessed using Morris water maze test. DβH activity was determined by HPLC. We have shown that in response to excessive intake of MnCl2, there was a development of cognitive impairments in rats, which was accompanied by a decrease in DβH activity in the hippocampus. The severity of cognitive impairment was reduced by inhibiting the activity of m-calpain. The protective effect of calpain inhibitors was achieved not through an effect on DβH activity. Thus, the development of therapeutic regimens for the treatment of manganism using dopaminomimetics and/or by inhibiting calpains, must be performed taking into account the manganese-induced decrease of DβH activity and the inability to influence this process with calpain inhibitors.

Neuroprotective Effect of Vitamin D on Behavioral and Oxidative Parameters of Male and Female Adult Wistar Rats Exposed to Mancozeb (manganese/zinc ethylene bis-dithiocarbamate)

The constant exposure of rural workers to pesticides is a serious public health problem. Mancozeb (MZ) is a pesticide  linked to hormonal, behavioral, genetic, and neurodegenerative effects, mainly related to oxidative stress. Vitamin D is a promising molecule that acts as a protector against brain aging. This study aimed to evaluate the neuroprotective role of vitamin D in adult male and female Wistar rats exposed to MZ. Animals received 40 mg/kg of MZ i.p. and 12.5 μg/kg or 25 μg/kg vitamin D by gavage, twice a week, for 6 weeks. The concentration of manganese had a significant increase in the hippocampus of both sexes and in the striatum of females, unlike zinc, which did not show a significant increase. MZ poisoning led to mitochondrial changes in brain tissues and promoted anxiogenic effects, especially in females. Alterations in antioxidant enzymes, mainly in the catalase activity were observed in intoxicated rats. Taken together, our results showed that exposure to MZ leads to the accumulation of manganese in brain tissues, and the behavior and metabolic/oxidative impairment were different between the sexes. Furthermore, the administration of Vitamin D was effective in preventing the damage caused by the pesticide.

Manganese induces S-nitrosylation of PINK1 leading to nerve cell damage by repressing PINK1/Parkin-mediated mitophagy

Chronic exposure to excess manganese (Mn) causes neurotoxicity, which is characterized by Parkinson-like symptoms and referred to as manganism. In the last few decades, mitochondrial damage and subsequent energy failure have been reported to be important mechanisms of Mn toxicity, yet how Mn causes mitochondrial damage remains largely unknown. Here, we demonstrated that Mn induced S-nitrosation of phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1), a master regulator in the mitophagy pathway, results in dysregulation of mitophagy and nerve cell injury in the rat striatum. We cultured primary neurons and used 1400 W, a potent and selective inducible nitric oxide synthase (iNOS) inhibitor, as an intervention to verify the precise mechanism of Mn-induced dysregulation of mitophagy. We demonstrated that Mn-induced S-nitrosylation of PINK1 decreased the phosphorylated level of parkin RBR E3 ubiquitin-protein ligase (Parkin), as well as the translocation of Parkin to damaged mitochondria, which led to the accumulation of damaged mitochondria and mitochondrial-mediated apoptosis. Our findings indicated the unusual connection between nitrative stress and mitochondrial dysfunction in Mn-induced neurotoxicity. These data highlight the role of S-nitrosation of PINK1 in Mn-induced dysregulation of mitophagy and provide a reliable target for the development of specific drugs and the early treatment of manganism, which has important theoretical and practical significance.

Protective effect of calpain inhibitors against manganese-induced toxicity in rats

Development of manganism is a major complication of manganese exposure in which neurological dysfunction is linked to accumulation of metal in the brain. Current therapies do not prevent progression of the disease. Therefore, development of effective therapeutic strategies for treatment of manganism is of utmost importance. Since the hyperactivation of calpain family proteases in CNS during manganism in an animal model is observed, we assumed that inhibition of calpains can suppress the development of Mn-induced neurological disturbances. The goal of this study is to delineate protective effect and the mechanism of neuroprotection of calpain inhibitor in rat model of Mn-induced neurological symptoms. Using the Gait analysis test, we found that chronic intranasal administration of the calpain inhibitor Cast (184-210) (peptide, which is corresponding to the 184-210 amino acid of the endogenous inhibitor of calpains-human calpastatin) to Mn-treated rats contributed to a significant decrease in the severity of gait disorders, although it did not lead to a decrease in the Mn deposition in the striatum and hippocampus. Accordingly to the results of PCR-RT, this effect was accompanied by a partial reduction in the content of neuro-inflammatory markers (IL-1β, TNF-α, NFκB mRNA in the hippocampus and, additionally, IBA-1 mRNA in the striatum), as well as normalization of the content of dopamine and its metabolites in the hippocampus and striatum, which was assessed by HPLC. In striatum cells, the application of Cast (184-210) also led to a significant increase in the production of tyrosine hydroxylase, which was analyzed by immunoblotting method. These findings suggest that calpain inhibitors may be a valid therapeutic agent in manganism.

Novel Pharmacotherapies in Parkinson's Disease

Parkinson’s disease (PD), an age-related progressive neurodegenerative condition, is associated with loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc), which results in motor deficits characterized by the following: akinesia, rigidity, resting tremor, and postural instability, as well as nonmotor symptoms such as emotional changes, particularly depression, cognitive impairment, gastrointestinal, and autonomic dysfunction. The most common treatment for PD is focused on dopamine (DA) replacement (e.g., levodopa = L-Dopa), which unfortunately losses its efficacy over months or years and can induce severe dyskinesia. Hence, more efficacious interventions without such adverse effects are urgently needed. In this review, following a general description of PD, potential novel therapeutic interventions for this devastating disease are examined. Specifically, the focus is on nicotine and nicotinic cholinergic system, as well as butyrate, a short chain fatty acid (SCFA), and fatty acid receptors.