Wellness Foods + Supplements 1/2022

AMD and micronutrients
centre of the retina. The macula lutea (Latin
for “yellow spot”) located here is a place with
a particularly high density of photoreceptor
cells (Fig. 1). The macula owes its yellow
colour to the antioxidant and UV light filtering
pigments lutein and zeaxanthin, which are
contained in 1.000-fold higher concentrations
in this area, compared to blood levels.
About 100,000 cone photoreceptors with
their outer segments are arranged in an
area with a diameter of about 3 mm. Due to
the effect of the concentrated light, around
10,000 outer segments have to be renewed
every night, which can only take place by a
particularly intensive metabolism. Over time,
insoluble degradation products are increasingly
deposited and accumulate in the
retina. A prominent representative of these
residues from proteins and fats is called lipofuscin.
In conjunction with UV light, lipofuscin
catalyses the formation of free radicals.
These are reactive oxygen species that
damage surrounding tissue. With a particularly
powerful radical scavenging system, the
eye can defend itself against oxidative stress.
With increasing age, the capacity of the antioxidative
mechanisms decreases significantly.
Age-related macular degeneration
Age-related macular degeneration (AMD)
is a disease of the retina and the choroid
behind it. It usually appears in the form
of visual disturbances, which appear in a
bending of straight lines and in image failures
in areas of the field of vision. Due to
the increased accumulation of lipofuscin in
the retina, the function of the visual cells is
increasingly impaired and they eventually
die off. The patchy disappearance of larger
and larger areas (“geographic atrophy”), in
the advanced stage, is a common cause of severe vision loss in old
age. AMD comes in two forms. The so-called dry form of the disease
accounts for about 80 % of cases. In this form, the ability to see is
increasingly impaired in the central field of vision. In the wet form
of the disease, flat vascular membranes also form under the retina,
which tend to bleed. This can quickly lead to reading blindness. Due
to the demographic development, the number of people affected by
AMD is increasing significantly. In industrialized countries, the disease
is the main cause of blindness in people over 50, followed by glaucoma
and diabetic retinopathy. In Germany, about 12 % of the population
are affected by early stages of AMD. In contrast, about 0.2%
suffer a late form of macular degeneration characterized by choroidal
neovascularization (new blood vessel formation in the retina) with
fibrosis and formation of scars (in wet AMD) or geographic atrophy
(in dry AMD). (1)
The role of mitochondria in AMD
Mitochondria are cell organelles enclosed by a double membrane
in which oxidative phosphorylation, i. e. energy production using
oxygen, takes place. As the “power plants of the cells”, mitochondria
are responsible for generating more than 90% of the energy of
metabolism in the form of adenosine triphosphate (ATP). Anaerobic
processes can only produce 2 moles of ATP per mole of glucose.
Aerobic energy production via the respiratory chain located in the
mitochondria can generate 36 moles of ATP from one mole of
glucose. The mitochondria therefore enable energy production to be
18 times more efficient. Electrons are transferred from complex I and
complex II of the respiratory chain to coenzyme Q10, which transfers
them to complex III and via cytochrome C to complex IV. The electrons
are brought to a lower energy level and the released energy is
used to pump protons through the membrane to build up an electrochemical
gradient. At complex IV, the electrons are transferred to
oxygen to form water while consuming protons. The excess protons
between the inner and outer membrane are broken down at complex
V in order to regenerate ATP from ADP and phosphorus with the
energy gained (Fig. 2).
Reactions with oxygen also produce relevant amounts of oxygen radicals
in the mitochondria. By transferring electrons to oxygen, superoxide
radicals (O 2
-) are formed in a magnitude of about two percent of
the oxygen converted. Antioxidants such as coenzyme Q10 and anti-
H +
H +
H +
H +
e
Cyt C
Complex
Q10
Complex
e Complex Komplex Complex
I e e
e III
IV
V
Complex
II
NADH NAD+
O 2 2H 2 O
Succinate Fumarate
ADP+P ATP +H
H +
H +
H +
H + 2 O
Fig. 2: The energy from our food is used via the respiratory chain to pump electrons across the inner mitochondrial membrane. At
complex V, the proton gradient is broken down and the released energy is used to regenerate ATP, the cell's energy carrier.
No. 1 April/May 2022
27