Definitions

Gossypol

Gossypol

[gos-uh-pawl, -pol]
Gossypol C30H30O8 is a polyphenol derived from the cotton plant (genus Gossypium, family Malvaceae). Gossypol is a polyphenolic aldehyde that permeates cells and acts as an inhibitor for several dehydrogenase enzymes. It is a yellow pigment.

Among other things, it has been tested as a male oral contraceptive in China. In addition to its contraceptive properties, gossypol has also long been known to possess anti-malarial properties. Other researchers are investigating the anti-cancer properties of gossypol.

Biological properties

It has proapoptotic properties, probably due to the regulation of the Bax and Bcl2. It also reversibly inhibits Calcineurin and binds to calmodulin. Inhibits replication of the HIV-1 virus. It is an effective protein kinase C inhibitor.

Contraceptive use

A 1929 investigation in Jiangxi showed correlation between low fertility in males and use of crude cottonseed oil for cooking. The compound causing the contraceptive effect was determined to be gossypol.

In the 1970s, the Chinese government began researching the use of gossypol as a contraceptive. Their studies involved over 10,000 subjects, and continued for over a decade. They concluded that gossypol provided reliable contraception, could be taken orally as a tablet, and did not upset men's balance of hormones.

However, gossypol also had serious flaws. The studies also discovered an abnormally high rate of hypokalemia among subjects. Hypokalemia — low blood potassium levels — is usually the result of kidney malfunction and causes symptoms of fatigue, muscle weakness, and at its most extreme, paralysis. In addition, about 7% of subjects reported effects on their digestive system, and about 12% increased fatigue. Most subjects recovered after stopping treatment and taking potassium supplements. A later study showed that taking potassium supplements during gossypol treatment did not prevent hypokalemia in primates.

In the mid-1990s, the Brazilian pharmaceutical company Hebron announced plans to market a low-dose gossypol pill called Nofertil, but the pill never came to market. Its release was indefinitely postponed due to unacceptably high rates of permanent infertility. Between five and twenty-five percent of the men remained azoospermic up to a year after stopping treatment. The longer the men had taken the drug and the higher their overall dosage, the more likely the men were to have lowered fertility or to become completely infertile. Researchers have suggested that gossypol might make a good non-invasive alternative to surgical vasectomy.

In 1986, the Chinese stopped research because of these side effects.

In 1998, the World Health Organization's Research Group on Methods for the Regulation of Male Fertility recommended that research should be abandoned. In addition to the other side effects, the WHO researchers were concerned about gossypol's toxicity: the toxic dose in primates is less than 10 times the contraceptive dose. This report effectively ended further studies of gossypol as a temporary contraceptive, but research into using it as an alternative to vasectomy continues in Austria, Brazil, Chile, China, the Dominican Republic, and Nigeria.

Oncology Testing

Gossypol is also under investigation as a possible chemotherapy drug especially in its R- state. It is currently believed that gossypol in itself will not kill cancerous cells, however it changes the chemistery within the cancer cell and makes it more suceptible to traditional chemotherapy drugs. Phased trials have been done on resistant prostate and lung cancer. Few results have been published to date so no conclusions can be drawn.

Toxicity

Food and animal agricultural industries must manage cotton-derivative product levels to avoid toxicity. For example, only ruminant microflora can digest gossypol, but only to a certain level, and cottonseed oil must be refined.

Researchers at Texas A&M University have genetically engineered cotton plants that contain very little gossypol in the seed, but still contain the compound in the stems and leaves. This provides protection against pests and diseases, while allowing the seed to be used for oil and meal for human consumption. The plants are modified by RNAi, shutting down the genes for gossypol production in the seed while leaving them unaffected in the rest of the plant. The resulting gossypol-free cottonseed is then suitable as a high-quality protein source suitable for consumption not only by cattle, but also by humans, pigs, chickens, or turkeys, making the plant additionally valuable as a food crop.

References

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