Could a Pill Protect Like a Condom?
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.