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Natural
Insecticides
You sit down to an attractive green salad. All the ingredients were
purchased at an organic farmers co-op, so you're sure that every
bite must be free of any toxic chemical. Well, not quite. Your salad
is indeed safe and healthy, but it does contain tiny amounts of
natural toxic substances. Here's a sampling of the chemicals that
may be in your salad.
- Neochlorogenic
acid: broccoli, brussels sprouts, kale
- Estragole:
basil
- Caffeic
acid: lettuce, carrots, apples, celery, eggplants, cherries
- p-Hydrazinobenzoate:
mushrooms
- Sinigrin:
cabbage, collard greens, cauliflower, horseradish
These
chemicals are natural insecticides. Plants produce these chemicals
to discourage insects from eating them. At very high doses, much
higher than humans would eat in a normal diet, these natural insecticides
have caused cancers in rodents. Fortunately many plant-eating animals,
including humans, produce enzymes to protect themselves against
natural pesticides.
Enzymes
are proteins that can break large molecules into smaller, simpler
forms that our cells can use or discard. Certain types of biotransformation
enzymes protect our bodies from chemicals in the environment, such
as natural pesticides. Genetic variations in these biotransformation
enzymes are of special interest to researchers at the Center for
Ecogenetics and Environmental Health. These researchers study complex
relationships between genetics, disease, and exposure to toxic chemicals.
For
example, the relationship between humans and chemicals found in
plants (also called phytochemicals) is quite complicated. Substances
that are toxic at high doses can actually be beneficial at low doses.
One such substance is sulfurophane, a chemical found in broccoli,
cabbage, and brussel sprouts. At low doses, such as the levels you’d
be exposed to by eating broccoli for dinner, sulfurophane functions
as an antioxidant, triggering activity by biotransformation enzymes
to battle chemical reactions that can damage human cells.
Opening
the Enzyme Tool Box
Most biotransformation enzymes are multi-purpose, like an adjustable
wrench or a Swiss Army knife. Therefore a relatively small number
of enzymes can tackle the multitude of substances we encounter every
day. For example, a single cup of coffee contains over 1,000 different
chemicals, including natural insecticides, and the average person
has enzymes that can handle all of them. Because biotransformation
enzymes are so versatile, they can de-toxify man-made insecticides
as well as natural ones. (To detoxify a chemical is to make it less
toxic or harmful.)
Although
biotransformation enzymes can de-toxify a broad array of chemicals,
they can be stumped. For example, they may not be able to detoxify
certain poisons, such as strychnine (originally extracted from a
tropical tree). Or they may be overwhelmed by large amounts of less
toxic substances. This may occur if a person spills pesticide on
their skin.
Some
animals have special biotransformation enzymes that allow them to
eat foods that are poisonous to other species. For example, the
larva of the black swallowtail butterfly produces an enzyme that
detoxifies the natural insecticide xanthotoxin, found in plants
in the carrot, parsley, and citrus families. Most insects can't
eat these plants so the black swallowtail larva has few competitors
for its favorite foods.
Toxic
Chemicals and the Environment:
Who Gets Sick?
The amount and types of toxic substances humans can detoxify is
also affected by genetics, because each of us is born with slightly
different biotransformation genes. Basic research into the biotransformation
of xenobiotic chemicals may also help scientists develop antidotes
to poisons and better ways to adjust doses of prescription medicines.
For
example, CEEH researchers have found that persons with a certain
variation in a liver enzyme have trouble processing the drug warfarin.
Warfarin is a powerful drug that helps prevent blood from coagulating,
or clotting. Warfarin is also used in rodent poisons. CEEH researchers
are also studying variations in the way that individuals react to
toxic substances in the environment, including pesticides, solvents,
and methyl mercury.
Genetic
Differences and Disease Risk
CEEH researchers are also trying to determine why people who are
genetically susceptible to a disease only get symptoms when exposed
to a specific chemical. For example, aflatoxin is a natural toxin
produced by a mold that grows on damp peanuts and grains. It can
cause liver cancer, especially in people who already suffer from
liver damage caused by the hepatitis B virus.
Differences
in the way people biotransform aflatoxin affect their risk of getting
liver cancer. Like most molecules, aflatoxin is biotransformed in
stages by a series of enzymes. These enzymes trim and rebuild the
molecule until it reaches a final form that can be safely excreted.
During one of these stages, enzymes in the liver briefly activate
the aflatoxin, making it more toxic. Additional enzymes then de-activate
most of the aflatoxin, making it less harmful. The speed of these
chemical reactions are important because activated aflatoxin can
mutate, or change, cell DNA. If concentrations of activated aflatoxin
builds up in the liver, the resulting mutations can cause liver
cancer.
Center
researchers are studying genetic differences in the enzymes that
activate and de-activate aflatoxin and whether these differences
affect cancer risk. This research may help guide cancer prevention
efforts, particularly in developing nations where aflatoxin exposure
is a serious problem. Many of these nations also have high rates
of hepatitis B infection, which makes their populations even more
susceptible to aflatoxin-caused cancer.
Fortunately
in the United States, aflatoxin exposure is limited, due to careful
food processing and inspection. When aflatoxin is present, levels
are low enough that the body can handle them easily, as it does
the natural insecticides in broccoli and carrots. So feel free to
eat a peanut butter sandwich. Your biotransformation enzymes are
on duty.
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