August 11, 2006

Common Thickener May Block HPV Infections

a microscopic image of HPV HPV up close. Laboratory of Tumor Virus Biology, NIH's National Cancer Institute

Human papillomaviruses (HPVs) are the most common sexually-transmitted infection in the U.S. A new study shows that carrageenan, a common cosmetic and food additive extracted from red algae, may be able to block HPV infections.

There are more than 100 types of HPVs, over 30 of which can be passed between people through sexual conduct. Most HPV infections don't cause any noticeable symptoms and go away on their own, but some HPV types can cause cervical cancers or genital warts. A recent study showed that women can reduce their risk of HPV infection by using condoms consistently, but the method isn't 100% effective. The Food and Drug Administration recently approved a vaccine to prevent infections by four HPV types that together cause about 70% of cervical cancers and 90% of genital warts worldwide. Another vaccine targeting two other HPV types is also under development. However, some types of HPV that aren't targeted by the current vaccines can cause cervical cancer as well. A topical microbicide, a compound that could block HPV infection in the first place, would be a useful addition to the arsenal of anti-HPV weapons.

An international team led by scientists at NIH's National Cancer Institute set out to screen a wide variety of compounds to see if any could inhibit HPV. To do this, they measured the ability of the compounds to inhibit HPV16, a genital HPV type known to cause cancers, from delivering a reporter protein into test cells.

In the July issue of PLoS Pathogens, the researchers report that various types of carrageenan were by far the most potent inhibitors identified in their screen. Carrageenan is an inexpensive gelling agent used as a thickener in a wide variety of cosmetic and food products, ranging from sexual lubricants to infant feeding formulas. Carrageenan was known to inhibit other viruses, including herpes simplex viruses and some strains of human immunodeficiency virus (the virus that causes AIDS), but at much higher concentrations. The researchers discovered that carrageenan blocks binding of HPV to its target cells and may have other mechanisms of action as well.

The team went on to test carrageenan against several other sexually-transmitted HPV types and found that it was equally potent against them. They also tested various sexual lubricant gels in the HPV16 assay to see if any commercial products inhibited HPV. Several of the lubricant products proved to be extremely potent inhibitors.

High-quality carrageenan preparations have a good safety profile for long-term vaginal use, so it's an appealing candidate for use as a topical microbicide to block HPV transmission. However, the test system used in these experiments may not fully represent some aspects of HPV infection in the body. Clinical trials are needed to determine whether carrageenan-based products are effective topical microbicides against genital HPVs.

— by Abby J. Vogel, M.S.

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