Inconsiderate supplementation of iron to treat anemia, without
proper interpretation of lab work including iron indices, may
impair the host’s ability to fight off bacteria such as Salmonella.
Summary: Individuals who do not produce
enough iron are anemic, and often experience fatigue. One common
remedy is for physicians to prescribe an iron infusion to their
anemic patients. This makes sense, but can lead to unexpected
consequences like increasing the risk of food poisons such as
Salmonella. These types of poisons depend on abundant access to
iron. Physicians should be attuned to this dynamic when
determining the strength of iron infusions for their anemic
patients.
Article:
One would think that too much iron is too much iron - whether it
is ingested from particular foods or stored in the body
genetically - and that pathogens such
as Salmonella would grow identically in either
case. It turns out that this is not the case, and that genetic
and dietary forms of hemochromatosis – iron overload – lead to
divergent paths with respect
to Salmonella infection. This is the
conclusion of a recent paper published in Frontiers in
Cellular Infection and Microbiology, authored by
Dr. Manfred Nairz and colleagues.
Many people experience excessive deposits of iron in their
bloodstreams, which is a medical condition known as
hemochromatosis. This most often occurs genetically, affecting
people in adolescence or in adulthood. Excessive iron
accumulation is a concern for many reasons, as the body has no
natural way to dispose of iron. These excessive deposits will
eventually damage tissues and organs. In addition, infections
that enter the body rely upon cellular access to iron as a means
of spreading more rapidly within the infected person’s body than
they could otherwise. For example, the
pathogen Salmonella – which people experience
as a type of food poisoning – feeds upon iron to course
throughout the body.
Although hemochromatosis is commonly genetic it can also result
from repetitive blood transfusions due to an underlying
hematologic disease. It is also possible that some people will
accumulate excessive iron simply from the foods they eat. Many
foods, such as tuna and red meat, are particularly rich in iron.
A person who consumes these iron-laden foods at greater than
typical levels has the potential to develop dietary
hemochromatosis.
The research team infected two different strains of mice
with Salmonella – one strain of mice had
normal levels of iron, the other had an excessive amount of iron
(which is roughly analogous to humans who experience genetic
hemochromatosis). Both strains of mice then received additional
iron orally, as a way to replicate dietary iron overload. The
normal mice, whose main source of excessive iron was only dietary
and not genetic, became particularly susceptible to the spread
of Salmonella. The mice who were genetically
susceptible to accumulating iron actually fared better with
guarding against Salmonella.
This is a counter-intuitive finding, given that the genetically
hemochromatotic mice actually had more iron in their bodies
overall than the mice with dietary iron only. The reason is an
essential difference between genetic and dietary hemochromatosis.
In the genetic version of hemochromatosis there is actually a
deficit of iron in macrophages, which is the cell type
that Salmonella invades and grows within. This
is because iron is distributed elsewhere throughout the mice’s
body in these genetic cases, in great quantities. The shortage of
iron in the macrophage acts as a brake against Salmonella. With
dietary iron overload, on the other hand, much of the iron winds
up in the body’s macrophages. That is exactly
what Salmonella is hoping to find.
The importance of the paper stretches beyond understanding what
makes Salmonella flourish. Many people suffer
from anemia due to an iron deficit, which is the exact opposite
of hemochromatosis. This can lead to fatigue and general
lethargy, and an infusion of iron is one common remedy. An
excessive infusion of iron, alas, is likely to lead to an
increase in Salmonella and other similar
infections. As. Dr. Nairz remarks, “inconsiderate supplementation
of iron to treat anemia, without proper interpretation of lab
work including iron indices, may impair the host’s ability to
fight off bacteria such as Salmonella .”
Physicians should be attuned to this trade-off when treating
anemia or other forms of iron deficit.
END
Corresponding Authors
Manfred Nairz, manfred.nairz@i-med.ac.at
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