One of the newer areas of barrier method research is the development of microbicides -- substances that destroy or incapacitate infection-causing organisms, including bacteria, viruses and parasites.
Microbicides may offer a female-controlled method of STD prevention that does not require partner knowledge or cooperation. Also, microbicides may or may not have spermicidal properties, allowing women to prevent disease but not pregnancy -- an option that is not available to condom or spermicide users.
While couples may want to prevent pregnancy at certain times in their lives, "the desire to prevent infection is consistent throughout your life," says Dr. Penelope J. Hitchcock, chief of the STD branch of the National Institute of Allergy and Infectious Diseases (NIAID) in the United States. "Program managers have been focusing on family planning and limiting the number of children, but we also have to realize that preservation of fertility is an important component of reproductive health."
NIAID is one of several organizations working to develop microbicides. With NIAID funding, the University of Pittsburgh will soon begin safety and efficacy studies of microbicides containing lactobacilli, bacteria that occur naturally in the vagina. Lactobacilli produce hydrogen peroxide, which scientists believe prevents the spread of infections. The University of Pittsburgh study will examine the use of lactobacilli suppositories among adolescents.
"Adolescents have typically been excluded from research," says Dr. Sharon L. Hillier, the study's principal investigator. "If we are going to think of solutions that will work in preventing STDs, we will have to target the group that is most at risk. We have to determine whether they will use an intervention, and how they will use it. We can benefit from knowledge of their behaviors."
The study will follow more than 900 adolescent women at an urban health clinic for one year. Researchers will try to determine whether use of the lactobacilli suppositories alters microorganisms that normally occur in the vagina, whether the suppositories decrease the incidence of bacterial vaginosis and gonorrhea compared to use of a placebo, and whether use of the suppository has any effect on acquisition of other STDs.
The U.S.-based Population Council also is conducting research to develop new microbicides and has completed safety trials among women on microbicides containing sulfated polysaccharides. These substances occur naturally in the human body, coating the cells and connective tissues. Scientists believe that polysaccharides, which have been shown in vitro to inhibit HIV, may coat the epithelial surface of the vagina with a film that repels HIV and HIV-infected cells. Polysaccharides, which are used as food additives, are non-detergents and may produce less irritation than currently available spermicides.
"What we want is something that is not absorbed when it gets into the vagina," says Dr. David Phillips, who is conducting the research at the Population Council. "Since these compounds are very large in size, they're not easily absorbed by the body. They are generally found throughout nature, so they would be an inexpensive and stable source for microbicides."
The Population Council's studies have examined women's preferences about delivery systems, including film, gels, and suppositories. "One of the take-home messages is that any kind of vaginal product is going to have to be formulated in multiple ways," said Christa Coggins of the Population Council. "There is not going to be one product that will meet every woman's needs."
FHI, NIAID, National Institute of Child Health and Human Development, ReProtect Llc., and Johns Hopkins University are working to evaluate a buffer gel that would offer protection against STDs, including HIV. This product, which would contain substances similar to some of the gel agents found in shampoos and soaps, would maintain the pH levels in the vagina even in the presence of semen, which normally neutralizes the vagina's acidity.
A buffer gel that maintains the acidity in the vagina could have numerous benefits, researchers say. Many types of enveloped viruses, including a strain of HIV, are inactivated by increases in acidity. Bacteria, including the type that causes gonorrhea, are killed when acid levels increase. "Trojan Horse" leukocytes -- the HIV-infected cells in semen and cervical mucus that may enhance the transmission of HIV -- appear to lose motility and viability and stop producing HIV when exposed to an acidic environment. And sperm are rapidly killed by mild acidity. The buffer gel is odorless, colorless and inexpensive, and it does not eliminate the lactobacilli, which help produce the acidity in the vagina.
Plant extracts, including gossypol (cottonseed oil) and neem, have been investigated for their microbicidal effects by the South to South Cooperation in Reproductive Health, based in Brazil. With gossypol, researchers are trying to develop a way to contain the substance in a gelatin capsule that could be inserted into the vagina. Creams and pessaries made from neem, which grows abundantly in the tropics, have been shown to be both spermicidal and microbicidal. However, initial safety studies among humans were discontinued because the odor was unacceptable to users and because it took too long for neem products to dissolve in the vagina. New formulations, with reduced odor, are being tested.
Other substances that are being studied as potential vaginal microbicides are synthetic protegrins, small proteins that occur in the white blood cells and have been shown in vitro to inactivate HIV, herpes, gonorrhea, chlamydia and other bacterial STDs; C31G, a substance in mouthwash that is both spermicidal and microbicidal; N-docosanol, an alcohol that blocks some enveloped viruses; and squalamine, a steroid-based compound that may be effective against bacterial and viral STDs.
Also, a modified version of beta-lactoglobulin, a protein found in the dairy product called whey, has blocked HIV transmission in human cells in test tube experiments at the New York Blood Center. The modified protein, called B69, does not seem to affect sperm.
The interest in microbicides has been fostered, in part, by the need for a female-controlled method that offers women protection against STDs. The best protection currently available is latex condoms, which men control. Yet, while microbicides have been discussed as a method that will benefit women, the development of these products may protect men from contracting STDs as well, Dr. Hitchcock suggests. And they may be more appealing than condoms to use.
-- Barbara Barnett
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