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| Does injury to mitochondria - the cell's powerhouse
- cause aging? |
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How do we control mitochondrial damage? |
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There are a variety of substances in the body that serve to control damage
to mitochondria. These include antioxidants and the enzyme SOD (superoxide
dismutase). DNA repair mechanisms also play a role. Scientists are now seeking
ways to improve the efficacy of these compounds or processes to reduce the
cellular damage associated with mitochondrial damage.
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Antioxidants |
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A number of naturally occurring compounds have antioxidant activity; they
can scavenge and neutralize the potentially damaging oxidative compounds.
Glutathione is one such antioxidant found in mitochondria. When glutathione
is artificially depleted from cells, oxidative damage increases. The level
of glutathione in mitochondria might be even more important than the level
of glutathione in the rest of the cell. Mitochondrial glutathione levels
diminish more with age than do the levels in the rest of the cell. This
decline seems to make mitochondria more susceptible to oxidative damage.
Ascorbic acid, or vitamin C, is another naturally occurring antioxidant
with protective powers. In aged cells, the activity of certain enzymes
decreases in mitochondria. But in one study adding ascorbate to aged cells
in a growth medium - in effect, "feeding" the cells vitamin
C - reduced the rate of loss of these enzymes. Vitamin E, or tocopherol,
is a third antioxidant known to help prevent the mitochondrial oxidative
damage. Research has shown that overproduction of mitochondrial oxidants,
with subsequent membrane damage, is observed in vitamin E-deficient cells.
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SOD |
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Enzymes can also serve as antioxidants. Mitochondria produce an antioxidant
enzyme called "superoxide dismutase" (SOD), which helps defang superoxide
ions, an especially dangerous type of oxidant molecule. The importance
of SOD in protecting mitochondria from oxidant damage was convincingly
demonstrated in a study of animals genetically manipulated to produce
half the normal amount of SOD. Increased oxidative damage was observed
in the deficient mitochondria, along with alterations in their mitochondrial
function.
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DNA Repair |
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Scientists have known for a long time that nuclear DNA has an elaborate
collection of enzymes that proofread and correct mistakes and gaps in
the nucleic acid sequence. For many years, mitochondria were assumed to
not be as fortunately endowed. However, mitochondria are now known to
have the ability to repair some errors in their DNA. Preserving, and perhaps
stimulating, this activity might be one means of preventing age-related
deterioration in mitochondrial DNA.
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