Since Mn 2+ is chemically more stable than Mn 3+ in the body, Mn is mainly incorporated into metalloenzymes in the form of Mn 2+ 20, 21. While Mn has many oxidation states, Mn 2+ and Mn 3+ are the two common species found in human body 19. Due to the incomplete development of the blood-brain barrier (BBB), neonates are at a higher risk of Mn toxicity compared with adult rats 15– 18. Of note, consumption of contaminated water from domestic wells has also been found to be a source of Mn toxicity 13, 14. The use of methylcyclopentadienyl Mn tricarbonyl (MMT) as an antiknock agent increases Mn exposure in people living in urban, dense traffic zones 11, 12. Other subsets of population which can be exposed to high levels of Mn include infants fed formulas based on cow or soy milk 3, and patients receiving prolonged exposure to total parenteral nutrition 10. The Bureau of Labor Statistics estimated about 400,000 people to be working in welding-related occupations in the U.S in 2015 9. Over the last few decades, welding, mining, and smelting have been recognized as high-risk occupations for developing Mn toxicity 8. These workers displayed symptoms of motor and cognitive deficiencies, tremors, gait disturbances and hallucinations 7. Historically, chronic Mn encephalopathy was first recognized among workers engaged in grinding of Mn ores. However, more common cases of human pathologies associated with Mn result from excessive exposure to this metal, rather than from Mn deficiency 5, 6, raising a huge concern in public health. Mn deficiency, although rare, is characterized by weight loss, poor bone formation, and reduced fertility 4. Dietary sources of Mn include nuts, legumes, seafood and tea. In addition, the metal is also involved in the physiological regulation of blood sugar, bone growth, blood clotting, and the immune system 3. Manganese (Mn) is an essential transition metal, which serves a vital role as a cofactor for various metabolic and antioxidant enzymes 1, 2.
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