Monoterpenes:
Essence of a Cancer Cure
From The April 1999 Issue of Nutrition Science News
By Cindy L.A. Jones, Ph.D.
Essential oils, the highly concentrated volatile, aromatic essences of plants, are a mainstay
of aromatherapy but are also used in flavoring, perfumes and even as solvents. Researchers
now think that two components of orange oil and lavender oil are a good bet to prevent and
treat cancer.
Most essential oils contain monoterpenes—compounds that contain 10 carbon molecules often
arranged in a ring. Monoterpenes are formed in the mevalonic acid pathway in plants.
This is the same pathway that makes cholesterol in animals and humans. Early on, cancer
researchers realized that some aspects of cholesterol metabolism were involved in cancer
growth. They then discovered that plant monoterpenes interfered with animal cholesterol
synthesis, thereby reducing cholesterol levels and reducing tumor formation in animals.1
Limonene and Perillyl Alcohol
Two widely studied monoterpenes are being evaluated for their anticancer activity—limonene
from orange peel (Citrus sinensis) and perillyl alcohol from lavender (Lavandula angustifolia).
Because limonene and perillyl affect the pathway that produces cholesterol, they can inhibit
cholesterol synthesis, thereby eliminating a minor contributor to cancer formation.2
Monoterpenes also increase the levels of liver enzymes involved in detoxifying carcinogens, an effect that
decreases the possibility carcinogens will cause cellular damage.2
In addition, monoterpenes stimulate apoptosis, a cellular self-destruction mechanism triggered
when a cell's DNA is badly damaged.3 This safety feature is generally activated before a cell
becomes cancerous. Finally, monoterpenes inhibit protein isoprenylation.
The cell uses this process to help a protein—in this case the ras protein involved in cell
growth—find its proper location within the cell.4 If ras is not in the right place, it
becomes overactive and can spur cancerous cell growth.
Where Do They Come From?
Most plant matter contains a
wide variety of monoterpenes.
Rich sources include:
- herbs
- spices
- wine
- essential oils
- eggs
- olive & palm oil
- rice bran oil
- barley oil
- dairy products
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Laboratory animal studies demonstrate that these two monoterpenes inhibit the formation of
chemically induced breast, colon, liver, skin and pancreatic tumors.5
For example, animals fed a diet containing 5 percent orange peel oil had a significantly reduced
risk of developing mammary tumors when treated with the chemical tumor inducer DMBA.6
Similarly, animals fed a 5-percent limonene diet had less chance of mammary tumor growth.
Researchers noticed that in this experiment rat tumors also regressed, suggesting limonene
may treat existing cancer as well as prevent it.
New drugs typically undergo three phases of clinical tests, each more rigorous than the
previous: Phase I trials establish a toxic human dose, phase II trials determine a
therapeutic dose and how it is metabolized, and phase III trials determine drug
effectiveness. Extensive animal studies are done before phase I trials begin.
Phase I trials have so far shown that limonene is well tolerated by cancer patients
and has little toxicity.7 Phase II trials, to test how well
limonene actually works to reduce cancer, are under way at several institutions
including the National Cancer Institute (NCI) in Bethesda, Md.
In other research, perillyl alcohol, a related compound, was found to be five times as
active as limonene in regressing tumors.7 A diet of 2.5 percent perillyl alcohol caused
75 percent of chemically induced rat mammary tumors to regress.8 Perillyl alcohol is
now being tested in NCI-sponsored phase I clinical trials as a treatment for advanced
breast, ovarian and prostatic cancers at the University of Wisconsin, Madison.9
Researchers speculate that perillyl alcohol may also be effective against pancreatic cancer,
which is extremely difficult to treat.10
The amount of monoterpenes needed to prevent cancer in humans is not established.
Toxicity studies are incomplete, but the high doses required for chemotherapy may
cause kidney damage and gastrointestinal problems. Both orange and lavender essential
oils are safe to ingest; in fact, orange oil is a common food additive used for flavoring.
Few drugs have been developed that effectively treat cancer, so NCI is constantly
searching for potential drug candidates. Many of these candidates, like limonene and
perillyl alcohol, are natural products from herbs. For now though, these two
concentrated substances remain in the realm of the laboratory—the doses being
used in clinical trials are intended for treating cancer and must be monitored by a physician.
Cindy L.A. Jones, Ph.D., is a Denver writer, consultant and educator who
specializes in biochemistry and molecular biology.
References
- Elson CE, Yu SG. The chemoprevention of cancer by mevalonate-derived constituents of fruits and vegetables. J Nutr 1994;124:607-14.
- Gould MN. Cancer chemoprevention and therapy by monoterpenes. Environ Health Perspect 1997;105:S977-9.
- Mills JJ, et al. Induction of apoptosis in liver tumors by the monoterpene perillyl alcohol. Cancer Res 1995; 55:979-83.
- Hohl RJ. Monoterpenes as regulators of malignant cell proliferation. In: American Institute for Cancer Research. Dietary Phytochemicals in Cancer Prevention and Treatment. New York: Plenum Press;1996.
- Elson CE. Suppression of mevalonate pathway activities by dietary isoprenoids: protective roles in cancer and cardiovascular disease. J Nutr 1995;125:1666S-72S.
- [Anonymous]. Clinical Development Plan: l-Perillyl Alcohol, J Cellular Biochem 1996;26S:137-48.
- Crowell PL, et al. Antitumor effects of limonene and perillyl alcohol against pancreatic and breast cancer. In: American Institute for Cancer Research. Dietary Phytochemicals in Cancer Prevention and Treatment. New York: Plenum Press;1996.
- Vigushin DM, et al. Phase I and pharmacokinetic study of d-limonene in patients with advanced cancer. Cancer Research Campaign Phase I/II Clinical Trials Committee. Cancer Chemother & Pharmacol 1998;42:111-17.
- Ziegler J. Raloxifen, retinoids and lavender: "me too" tamoxifen alternatives under study. J Natl Canc Inst 1996;88:1100-1.
- Stark MJ, et al. Chemotherapy of pancreatic cancer with the monoterpene perillyl alcohol. Cancer Letters 1995; 96:15-21.
Please contact me for additional information.
Debbie Allen, CNT, CNHP
Silver Director, Young Living
Call: 800-769-7923
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