People with diets rich in fruits and vegetables have a reduced risk of developing various diseases, including neurodegenerative diseases. Some of the chemicals in these beneficial foods are antioxidants, which are called plant “biopesticides” and are believed to be chemical defenses developed by plants to protect themselves from insects and other invaders.
At much lower doses of the plant chemicals than would be toxic doses, the chemicals stimulate adaptive cellular stress-response pathways that are in many cells, including neurons. These pathways are termed “neurohormetic” or “preconditioning” pathways. Neurohormesis is a means by which nerve cells are induced to prepare themselves to meet minor stress and prevent disease. A mild stress is placed on cells that enhances their ability to deal with greater stresses.
Some “biopesticides” are flavonoids, such as rotenone and myricetin, terpenoids such as farnesol and camphor, alkaloids such as strychnine, nicotine and caffeine, indoles such as indole-3-acetonitrite, glucosinolates such as 2-pentylethyl isothiocyanate, coumarins such as xanthotoxin and coumarin, phenylpropanols such as myristicin and eugenol, and cardenolides such as digitoxin. At high doses these chemicals are carcinogens and neurotoxins but, at low doses these chemicals are beneficial.
In nerve cells some of the chemicals that act to stimulate neurohormetic pathways are nitric oxide, calcium (Ca2+), glutamate and carbon monoxide. They stimulate neurogenesis, synaptic plasticity and resistance to injury and disease. The following factors stimulate the hormetic pathways:
Dietary energy restriction.
Metabolic stress such as ischemia.
“Medicines are toxins taken at low doses.” They produce what is called a biphasic response depending on the dose given. This fact is given as evidence that the effects of these chemicals is not just as antioxidants. Micromolar concentrations of antioxidants are necessary for them to scavenge free radicals. At much lower concentrations, they have neuroprotective activity. Kainic acid and domoic acid are toxins produced in algae, which can cause nerve cell death and seizures, but at much lower doses, they are neuroprotective.
Some of the neurohormetic chemicals are antioxidant enzymes, neurotrophic factors, protein chaperones and other proteins. There are even changes in gene expression which increase the resistance to stress.
Cells are protected from stress by plant chemicals, such as resveratrol, sulforaphanes, circumin, catechins, allium, other sulfur compounds and hypericin, by stimulation of the neurohormetic chemicals. The beneficial effect is believed to be more than just antioxidant effects. Large amounts of sulforaphanes are found in broccoli sprouts and have been found to protect retinal cells from ultraviolet damage, which causes macular degeneration.
Curcumin from the roots of the herb Curcuma longa is used in curry. Consumption of curcumin protects the nervous tissue of the brain from damage from ischemia and traumatic injury by a hormesis mechanism.
The protection of green tea catechins against cancer is from a hormesis mechanism.
Allium and allicin of onions and garlic are organosulfur compounds that protect the nervous system by hormesis mechanisms.
Hypericin from St. John’s Wort protects the nervous system from stress with hormesis mechanisms.
CONCLUSION: Chemicals found in fruits and vegetables have been found to be of benefit in neurological disease. Some of these are alpha-tocopherol, lycopene, resveratrol, Ginkgo biloba and extracts of ginseng. At low doses these chemicals can be used therapeutically to stimulate “hormesis” pathways in cells that prepare cells to deal with greater stress by stimulating beneficial chemical pathways.
NOTE: The hormesis explanation for the benefits of low dose compounds found in food sounds strangely like some of the ideas behind homeopathy. Hormesis has not been accepted into traditional medicine, possibly, because of its association with homeopathy, which was marginalized in the United States in the early 1900’s. Hormesis does have a place in toxicology and teaches that biological chemicals may have one set of effects at a certain dose, but they remarkably different effects at a much lower dose. Read more about hormesis.
The quote that “medicines are toxins taken at low doses” is a reflection of the lesson taught to the ancient Greek god, Asclepius, by the Gorgon that every poison is a medicine if used in the right way. The blood of the Gorgon was poison, but the Gorgon taught Asclepius how to use it as medicine.
To read the author’s abstract of the article click on the link of the author’s title of the article above.