Page 478 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

VetBooks.ir Chapter 30

Manganese

Dejan Milatovic and Ramesh C. Gupta

INTRODUCTION AND BACKGROUND Mn deficiency can be linked to silent heat, reduced con-
ception, abortions, reduced birth weight, an increased per-
Manganese (Mn) is a naturally occurring trace metal
centage of male calves, paralysis and skeletal damage in
commonly found in the environment. It is the twelfth
calves. Mn deficiency can cause delayed estrus, reduced
most abundant element in the earth’s crust, present in
fertility, and spontaneous abortions in mares. Foals are
rocks, soil, water, and food. It does not occur naturally
born with skeletal deformities and muscle contractures,
in a pure state and the most important Mn-containing
such as asymmetry of the skull, curvature of the vertebral
minerals are oxides, carbonates, and silicates (Post,
column, shortened limb bones, enlarged joints, and con-
1999). As a transition metal, Mn exists in more than five tracture of neck muscles. In dogs, Mn deficiency can
21 31
valence states, with a majority as Mn or Mn .Mn is
cause crooked and shortened soft bones (Puls, 1994).
abundantly found in the environment, including rocks,
Despite its essentiality, Mn overexposure can cause a
soil,water,and food,withthe highest concentrations
variety of toxic effects in humans and animals. Mn has
typically in nuts, cereals, grains, fruits, vegetables, and
been linked to a peculiar extrapyramidal syndrome in
tea. Mn is a component of certain aluminum alloys, par-
occupational workers since 1837. Since then, incidences
ticularly those used in the manufacture of soft drink
of Mn poisoning, especially in mines and steel factories,
cans. Inorganic Mn is also used in dry cell batteries, ani-
have been reported in many countries (Wang et al.,
mal feed, brick coloring, and fertilizers (Aschner et al.,
1989; Lucchini et al., 2009; Racette et al., 2012; Chen
1999; ATSDR, 2000; Corathers, 2001; O’Neal
et al., 2014). Fortunately, in the last three decades there
and Zheng, 2015). Organic Mn is used as a fuel additive
has been a declining trend even in developing countries.
and in fungicides, such as mancozeb and maneb
Mn poisoning can occur in animals or humans if the
(ATSDR, 2000; Kaiser, 2003).
exposure level of Mn exceeds the normal levels in the
Mn is an essential element for maintaining the proper
environment. Toxicity can also occur if either the dietary
function and regulation of many biochemical and cellular
concentration exceeds the maximal tolerable levels or if
reactions (Takeda, 2003) that are critical for humans, ani-
dietary intake of other minerals is marginal (Hartman
mals, and plants (Takeda, 2003; Tarale et al., 2016). It is
et al., 1955; Ivan and Hidiroglou, 1980; Southern and
required for growth and development and plays a role in
Baker, 1983; Baker and Halpin, 1991; Hauser et al.,
immune response, blood sugar homeostasis, adenosine tri-
1994). The brain, in particular, is highly susceptible to
phosphate (ATP) regulation, digestion, bone growth,
Mn toxicity. Excessive accumulation of Mn in specific
reproduction, and lactation. It is a necessary component
brain areas, such as the substantia nigra, the globus palli-
of numerous metalloenzymes, such as Mn superoxide dis-
dus and the striatum, produce neurotoxicity leading to a
mutase, arginase, phosphoenol-pyruvate carboxylase, and
degenerative brain disorder, referred to as manganism.
glutamine synthase (Aschner and Aschner, 2005). As a
In addition to neurological effects, Mn accumulation is
result, dietary deficiency of Mn is known to affect several
also associated with reproductive and developmental
enzymes, including glycosyltransferases, xylosyltrans-
effects. High-dose exposure to Mn has been associated
ferases, arginase, and mitochondrial superoxide dismutase
with increased fetal brain Mn concentrations (Kontur
(NRC, 2005). The dietary requirement of Mn is 10 ppm
and Fechter, 1985) although several studies have
in rats and mice, 40 ppm in guinea pigs, 20 ppm in pigs,
reported an ability of the placenta to reduce systemic
28 30 ppm in chickens, 20 ppm in beef cattle and
delivery of Mn to the fetal brain. Moreover, Mn plays a
40 ppm in dairy cattle. Practically, Mn deficiency occurs
role in the modulation of the immune system, and in pro-
more frequently in cattle, pigs, and poultry. In ruminants,
tein, lipid and carbohydrate metabolism (Addess et al.,
Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00030-1
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