March 2, 2001 -- Although condoms may have their drawbacks, they are effective when used properly in preventing both pregnancy and sexually transmitted diseases. But what if a single pill could protect against both? New research reported in the March 2 issue of Science helps explain how the body fights STDs and may hold the key to developing contraceptives for men that enhance these defense mechanisms.
"A condom in pill form is the final goal of my research," scientist Yong-Lian Zhang, PhD, tells WebMD. "This report is just the beginning." Zhang is a professor of molecular biology at the Shanghai Institute for Biological Sciences of the Chinese Academy of Sciences.
Zhang and his colleagues discovered a fragment of rat DNA that codes for a unique protein called Bin1b. This protein resembles in structure and function other immune system regulators called defensins, which kill bacteria, viruses, and other infectious agents. Unlike the other defensins, Bin1b is found only in the epididymis, a male sex organ involved in sperm production.
"Both the male and female reproductive tract are open to the outside and are consequently subject to challenge by a variety of infectious organisms," Ken Roberts, PhD, tells WebMD. "It makes sense that nature would provide a mechanism of defense against these challenges." Roberts, who was not involved in the study, is an assistant professor of urologic surgery at the University of Minnesota in Minneapolis.
"While the protein they are studying is in the epididymis and has antibacterial effects, the claim of it being a condom in pill form is very premature," Joe Scobey, PhD, tells WebMD after reviewing the study. He is a cell biologist at the University of Pittsburgh.
"A condom provides two functions in that it is used as both a contraceptive and a prophylactic," Michael A. Laing, PhD, a molecular biologist at McMaster University in Hamilton, Ontario, tells Web MD. "The authors have only addressed its function as an antimicrobial and only in a very limited way. It would be premature to suggest that Bin1b has the potential to be used as a contraceptive."
Sexually transmitted bacteria and viruses, including the HIV virus that causes AIDS, collect in the epididymis, where Bin1b may act as a natural defense. Additional evidence for this role is that inflammation of the epididymis, which is associated with STDs, increases levels of Bin1b. The researchers also found that Bin1b killed bacteria in culture.
"I do not think the antimicrobial activity is the sole function of this gene in the epididymis," says Zhang, who is continuing to study Bin1b's role in fertility.
As levels of Bin1b increase during sexual maturation and decrease during aging, it may be important in fertility by affecting sperm maturation, storage, and protection. Drugs that act on Bin1b might therefore be useful as male contraceptives while protecting against STDs -- at least in rats.
Defensins in humans appear to kill bacteria and viruses, immobilize sperm, and prevent fertilized eggs from implanting in the uterine wall. Since the DNA coding for Bin1b has similar genetic sequences in chimpanzees and even humans, discoveries in the rat might potentially apply to the human after considerable additional drug development and testing.
But the experts WebMD interviewed are skeptical about the claim that Bin1b may immobilize sperm simply because it is structurally similar to other defensins. "It would be like saying that because oranges are high in vitamin C and apples are also fruits, they must also be high in vitamin C," Scobey says.
One of the problems involved in using a protein such as Bin1b in pill form would be getting it into the epididymis in high enough quantities to be effective. "Without meaning to be facetious, these pills in all likelihood would have to be taken as suppositories rather than orally," Laing says.
Scobey's suggestions are "to focus research efforts on the properties of unique proteins that do act upon sperm and to discover ways in which these proteins can be exploited to affect male fertility."
Chances are this is a long way off. Latex condoms were first mass-produced around 1850 as a contraceptive and were promoted during World War II to keep the troops free of syphilis and other STDs. With the development of antibiotics and oral contraceptives, the condom fell out of favor -- at least until AIDS reared its ugly head.
"One could certainly call Bin1b 'nature's condom,' since it may very well act as a [contraceptive] in the epididymis," Roberts says. "We may be able to take advantage of this, and perhaps other, natural defense mechanisms to develop new and better [agents] to prevent infection of the reproductive tract."
Though researchers have developed male birth control pills, it will take at least three to four years of testing before any are available on the market. Condoms are often touted as the best defense against AIDS short of abstinence, and they prevent pregnancy without having the potentially dangerous side effects of drugs.