Biomedical Engineering Reference
In-Depth Information
Unfortunately, the feasibility of an analytical determination of thionein was in those
days beyond the lab's reach.
The high nickel levels just reported forces to a parenthesis on statistics. If a
series of samples is analyzed and concentrations, not necessarily as aberrant as those
just reported are present in the cohorts,
blind statistics
will remove these values as
outliers
. However, it might be for a serendipitous scientist a fruitful hint!
Hypersensitivity to nickel is not uncommon and clinical aspects are easy to rec-
ognize. Nickel subsulfides (
Ni
3
S
2
) are carcinogenic after phagocytosis but soluble
Ni(II) in nontoxic concentrations is not (or weakly) carcino- or mutagenic.
Most of the discussion of metals was directly or indirectly referring to load-
bearing applications. A more gentle application was the use of stainless steel stents.
Coronary stenting is a current practice in cardiology. In-stent restenosis is a com-
plication which impairs the success of stenting. Delayed hypersensitivity to nickel
and molybdenum was suspected to be part of the inflammatory process and one
of the triggering factors in restenosis, an obvious suspicion. However, despite the
intense contact of blood with the device, restenoses were predominantly observed
in patients with negative patch test to nickel [
148
]. Is it simply explained by damage
of the stent's surface by wear and/or corrosion?
Chromium.
The pure metal is mainly used in the plating industry and in corrosion-
resistant alloys. Hypersensitivity to chromium is not frequent. It is mainly known
from occupational allergies (cement industry) and the most common source of
allergy is the leather of shoes (chromium sulfate is used in the final stage of tan-
ning and increases the average chain length of collagen). Although the sensitivity to
this element is not frequent, below we report on one. The radioactive isotope
51
˛
Cr
has been used extensively in medicine for labeling cells in vivo (
) and,
at least to our knowledge, no allergic reactions were accompanying this application.
The most stable oxidation states of chromium are Cr(III) or Cr(VI).
12
T
1=2
D 27:7d
Under
physiological conditions (pH
D
7.4), Cr(VI) exists mainly as the tetrahedral chro-
mate ion CrO
2
4
. Under physiological conditions, it is a fairly strong oxidant:
CrO
2
4
e
D
OH
C 4
H
2
O
C 3
Cr
.
OH
/
3
C 5
(4.9)
with
V. Target tissues after intravenous exposure to Cr(VI) and Cr(III)
are liver, kidneys and lungs. Cr(VI) is taken up by erythrocytes and becomes bound
to hemoglobin. Cr(III) is bound to serum proteins. Cellular uptake of Cr(III) is
very poor, whereas Cr(VI) passes the cell membrane by simple diffusion. Chro-
mates were known to be carcinogenic for workers in the plating industry. However,
chromium dissolved from alloys, either by oxidation of the metal or by dissolution
of the oxide skin of the metal or alloy, is Cr(III). If Cr(VI) is present (oxidized
by peroxides?), it is metabolized by substances such as ascorbic acid, thiols, glu-
tathione and many other reducing agents Cr(III) forms thousands of octahedral
complexes with O, N, S, C and halides as donor ligands and will travel through
E
0
D0:13
12
The oxidation state of elements are given in Appendix A
.
