Selenium - Toxicology of Metals - page 772

5.2.5 Other Diseases for selenomethionine in humans (Bopp et al ., 1982).

A recent study indicates that selenomethionine is
twice as bioavailable as selenite (Xia et al ., 2005).
Inhalation studies on rats show that 94% of selen-
ious acid deposited in the lungs was absorbed within 4
hours. The corresponding value for elemental selenium
was 57% (Medinsky et al ., 1981). Skin absorption was
also noted in this study. A model based on these rat stud-
ies predicted that organ concentrations in man caused
by inhalation of selenious acid or elemental selenium in
urban atmospheres will not contribute signifi cantly to
human body burdens (Medinsky et al ., 1981).

Several diseases are associated with low levels of
selenium in serum or blood. Patients with kwash-
iorkor had low selenium levels and responded better
to feeding when administered selenium simultane-
ously (Burk et al ., 1967). Patients with liver cirrhosis,
especially alcoholic cirrhosis, had very low levels of
selenium in both serum and liver (Aaseth et al ., 1980;
Czuczejko et al ., 2003; Dworkin and Rosenthal, 1984;
Johansson et al ., 1986; Valimaki et al ., 1983). Low serum
selenium has also been seen in patients with celiac dis-
ease, rheumatoid arthritis, cystic fi brosis, and other
degenerative diseases (Aaseth et al ., 1978; Hinks et al .,
1984). Some improvement regarding morning stiffness
was observed in a double-blind study in patients with
rheumatoid arthritis supplemented with selenium and
vitamin E (Aaseth et al ., 1998). Neurological seizures
in infants have been related to low blood Se levels and
were treated with Se supplementation (Ramaekers
et al ., 1994; Weber et al ., 1991). Combined Se and
iodine defi ciency may result in severe myxedematous
cretinism (Zimmermann and Kohrle, 2002).

5.3.2 Distribution

In laboratory animals, there is a rapid distribu-
tion of water-soluble selenium compounds to most
organs. In later phases, the distribution is infl uenced
by the nutritional state of the animal and the dose of
selenium. Rats raised on a low selenium diet accumu-
late and retain selenium, given as a tracer of selenite,
in reproductive organs, brain, and thymus. In blood,
muscle, liver, spleen, kidney, and lung, accumulation
was more transient, and the concentrations decreased
after the fi rst day. The degree of whole-body retention
is inversely related to the dietary level of selenium
(Burk et al ., 1972). After lung absorption, elemental
selenium exhibited the same type of distribution as
selenious acid (Weissman et al ., 1983).
Results from human studies tend to suggest that
disposition of selenium in man is similar to that in
rats and other laboratory animals (Bopp et al ., 1982).
However, there are indications that selenium distribu-
tion among blood components is different. Thus, only
10-15% of erythrocyte selenium in man was associ-
ated with GSH-px activity, whereas the corresponding
value in rats was 75-85% (Beilstein et al ., 1984). Com-
parative long-term studies on the bioavailability of
selenite and selenomethionine in man (Thomson et al .,
1982) and of selenate and selenium-rich wheat or yeast
in rats (Levander et al ., 1983) suggest that organically
bound selenium maintained platelet GSH-px activity
better than selenite or selenate.
Rats were injected intraperitoneally with 75 Se sod-
ium selenite (5 mg/kg), and it was concluded that
selenium in the form of selenite accumulated in the
anterior pituitary gland. The maximum selenium con-
tent was observed after 2 hours, at which time the ante-
rior pituitary gland contained 2.9

5.3 Kinetics

5.3.1 Absorption

Most water-soluble selenium compounds are
effectively absorbed in the gastrointestinal tract, and
neither size of the dose nor nutritional state of the ani-
mal has been shown to infl uence the absorption. Thus,
more than 90% of orally administered selenite or more
than 80% of orally administered selenomethionine or
selenocysteine is absorbed by rats (Bopp et al ., 1982).
Selenium incorporated into animal tissues (Thomson
et al ., 1975) or corn (Cary et al ., 1973) is absorbed by
rats to a high extent, whereas elemental selenium (cf.
Medinsky et al ., 1981) or selenium sulfi de (Cummins
and Kimura, 1971) is poorly absorbed. Selenite is
readily absorbed in mice and dogs, whereas monkeys
seem to have a slower absorption rate (Furchner et al .,
1975). In sheep and cows, values as low as 30-35%
have been obtained; this low rate of absorption might
be due to selenite reduction to elemental selenium by
bacteria in the gastrointestinal tract of ruminants. Both
selenite and selenomethionine are mainly absorbed in
the duodenum (Whanger et al ., 1976). Active uptake
mechanisms for selenomethionine (McConnell and
Cho, 1965) and selenite (Anundi et al ., 1984) have
been indicated in in vitro studies. Studies on man
indicate a less effi cient uptake of selenite than docu-
mented for rats. Forty to eighty percent of a perorally
given dose of selenite may be absorbed. On the other
hand, higher values (75-97%) have been obtained

g/g wet weight. The
selenium content in pituitary glands from untreated
rats was 0.48

µ

µ g/g wet weight (Thorlacius-Ussing and

Jensen, 1988).
Selenoprotein P, which seems to be the only seleno-
protein that contains more than one SeCys, may have