Manganese Toxicity

Excerpt

Manganese (Mn) is an environmentally abundant essential metal required for numerous indispensable biochemical processes throughout the human body. Its function arises secondary to its inclusion within protein structures as a cofactor. Without its presence, the human body’s immune function, biochemical regulation of energy consumption, growth potential, coagulation, and hemostatic function, and mechanisms to remove byproducts of aberrant oxidative stress would be significantly diminished.

Optimal nutritional sources of Mn are derived mainly from plants, yet supplementation via vitamins or health products is another notable contribution. Drinking water often contains trace amounts of Mn, with specific cut-offs measured to prevent toxic exposures. Another beneficial source of Mn for infants is via breast milk and formula, which stave off deficiency during their critical developmental period.

Manganese toxicity (manganism) is rarely encountered, yet it is important to recognize the consequence of occupational, accidental, or iatrogenic exposures to Mn. The main toxic effects attributable to this metal are extra-pyramidal side-effects that closely resemble symptoms of Parkinson syndrome. These adverse effects are secondary to its deposition in specific components of the basal ganglia and alteration of dopaminergic neuronal enzyme activity. Other prominent effects include cardiotoxicity, hepatotoxicity, and increased mortality in infants.

The most often documented etiologies for the development of manganism include chronic total parenteral nutrition (TPN) use in critically ill patients, consumption of contaminated well-water, and exposure through work in welding, smelting, and mining. The metal is readily absorbed through the intestinal tract, and absorption is variable based on the level of dietary intake, with biliary and pancreatic metabolism affecting excretion. However, these mechanisms are bypassed with IV administration, owing to the potentiality for manganism with IV preparations containing the essential metal.