March 2001, Vol. 7, No. 1

Biomedical Research
Nonoxynol-9 Rapidly Exfoliates Rectal Epithelium

New findings, deemed “sobering” by the Population Council scientists who conducted the research, suggest that products containing the spermicide nonoxynol-9 may increase the risk of HIV infection when used during rectal intercourse. David M. Phillips, of the Council’s Center for Biomedical Research, and his colleagues found that nonoxynol-9 caused the rapid exfoliation of epithelium when applied rectally.

Surveys in the United States have shown that 41 percent of men who have sex with men try to use products containing nonoxynol-9 as lubricants during rectal sex. This practice stems in part from a belief that such products may act as microbicides, protecting against infection with HIV. In addition to its ability to kill sperm, nonoxynol-9 (N-9) has been shown to inactivate viruses, including HIV, in vitro and can protect Rhesus macaques from vaginal infection with SIV, a simian virus related to HIV. The results of a clinical trial reported in 2000, however, showed that the use of products containing N-9 increased the likelihood of HIV infection in women. Other studies, done by Phillips and his colleagues, showed that N-9 caused mouse rectal epithelial cells to slough off and made mice highly susceptible to infection with herpes simplex virus-2, a virus structurally similar to HIV.

Testing N-9 in humans
After obtaining these results in mouse studies, Phillips and his team set out to determine the effect of N-9 on human rectal epithelium. The scientists compared the effects of two over-the-counter gels containing N-9—K-Y^® Plus and ForPlay^®—and two gels that do not contain N-9—methyl cellulose and Carraguard™, the Population Council’s leading microbicide candidate. Carraguard is made from carrageenan. (In 2000, Council researchers began conducting expanded safety and acceptability trials of Carraguard among women in South Africa and Thailand. The placebo used for comparison in these trials is methyl cellulose.)

Phillips and his colleagues examined rectal saline lavage specimens taken from four randomly chosen study participants: three men and one woman. Each participant was given a kit that contained the four test products in unmarked containers. Before applying any of the products, the study participants took a baseline lavage specimen, rinsing the rectum with saline and depositing the specimen in a collection vial containing fixative. Next, the participants applied the first formulation rectally and retained it for 15 minutes, then performed a lavage and collected the specimen. Eight to ten hours later, participants collected another lavage specimen. Each product was tested in this way, with participants allowing at least 72 hours between experiments. A total of 36 specimens were collected.

The four specimens collected 15 minutes after the application of K-Y Plus and two of the specimens collected 15 minutes after the application of ForPlay held contents the scientists termed “dramatically different” from the other specimens. These specimens contained hundreds of convoluted sheets of epithelial cells, large enough to be seen with the naked eye. Each sheet typically contained hundreds of cells. The specimens collected after the application of K-Y Plus, which is 2 percent N-9, contained far more cells than the specimens collected after the application of ForPlay, which is 1 percent N-9.

When the scientists examined these six specimens microscopically, they found that each sheet contained columnar and goblet cells, varieties of cells typical of rectal epithelial morphology. In contrast, the other specimens were composed primarily of unidentifiable amorphous material, plant cell walls, bacteria, and an occasional epithelial cell.

“Removal of the rectal epithelium may enhance HIV infection because the primary target cells of HIV, lymphocytes and macrophages, are located in the lamina propria immediately below the gut epithelium,” Phillips concluded. “We therefore caution against the use of N-9-containing products during rectal intercourse.”

These findings challenge the conclusions of other scientists who recently found that Advantage 24^®, a product containing N-9 at 3.5 percent, was not associated with rectal epithelial disruption. The researchers came to this conclusion on the basis of rectal tissue biopsies taken 12 hours after the application of Advantage 24. Phillips and his colleagues argue that the gastrointestinal epithelium rapidly repairs itself. Thus, biopsies taken 12 hours after N-9 application would not accurately show how the chemical damages rectal epithelium. This contention is supported both by the team’s previous mouse studies, which showed that mouse rectal epithelium recovered from N-9-induced damage in one hour, and by the current research, which showed epithelial damage 15 minutes after N-9 application, but no sloughing of epithelium eight to ten hours after N-9 application.

Still, Phillips acknowledges that more research is needed. “We’re working to prove more convincingly—with larger sample sizes—that use of N-9 during anal sex is risky. We’d also like to determine more precisely the length of time needed for rectal epithelial repair. One paper won’t do it.”

Source
Phillips, David M., Clark L. Taylor, Vanaja R. Zacharopoulos, and Robin A. Maguire. 2000. “Nonoxynol-9 causes rapid exfoliation of sheets of rectal epithelium,” Contraception 62(3): 149–154.

Outside funding
The Bill and Melinda Gates Foundation, the Andrew W. Mellon Foundation, and the Rockefeller Foundation

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