Potential AIDS preventive doubles as a contraceptive
Our best weapon against the spread of AIDS may turn out to be a common gel that’s been used for years in drugs and cosmetics. That’s the hope of a Johns Hopkins University research team, which has devised a microbicide that not only prevents sexually transmitted diseases such as AIDS but acts as a contraceptive too.
Since an AIDS vaccine has proved elusive, public health officials have stepped up development of microbe-killing chemicals. A Rockefeller Foundation study released earlier this year estimated that the introduction of an effective product could avert 2.5 million infections in regions like Africa in the first three years.
The Johns Hopkins microbicide, called BufferGel, is a leading contender.
The odorless ointment’s protective mechanism is based on an elegantly simple bit of high school chemistry: Alkaline compounds neutralize acid -- and other chemicals can reverse that process.
The vaginal area is mildly acidic, with a pH level of 4 (neutral is 7), comparable to the acidity of wine. “That degree of acidity kills sperm, and all sorts of germs,” says Richard Cone, a biophysicist at Johns Hopkins who helped develop the product.
Semen, which is alkaline with a pH between 7 and 8, raises the vaginal pH to 7 for hours. This allows sperm to survive long enough to fertilize an egg and enables germs to infect cells. Based on this, researchers devised a strategy that mimics the vagina’s method of safeguarding against foreign intruders.
They found that a common pharmaceutical compound, which had been used for decades to thicken ointments, was able to preserve vaginal acidity even in the presence of sperm. So they made it into a lubricant gel. “We wanted to use something that had a long track record of safety with no side effects,” says Dr. Thomas Moench, who also helped develop BufferGel.
This latter point is especially significant because of recent disappointment about the once highly touted microbicide nonoxynol-9, approved by the FDA as a contraceptive. A 2000 study revealed that the spermicide promoted, rather than prevented, HIV transmission because it irritated the cells lining the vagina, providing viruses with an entry point through the damaged tissue.
Initial lab tests, conducted in the early ‘90s, indicated BufferGel preserved the acidity of the vagina, thus killing off such sexually transmitted microbes as HIV, norrhea, chlamydia, herpes, syphilis, HPV (human papilloma virus, which causes genital warts and cervical cancer), and trichomaniases, the most common STD. Safety studies on 125 women in the U.S. and abroad were recently completed. A contraceptive trial by the National Institutes of Health is underway in which 975 women who are using a diaphragm in combination with either BufferGel or a conventional spermicide. If all goes well, BufferGel could be on sale in the U.S. within two years.
But the more crucial test, say researchers, will begin in spring, when 8,500 women in the U.S., India and Africa will see if BufferGel can thwart the spread of AIDS. If it’s effective, it will provide an alternative to women whose partners refuse to use condoms. “This puts the control back into a woman’s hands,” says Johns Hopkins’ Cone.
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Disease fighters
Although more than 50 microbicides are under development, only a few, including BufferGel, are nearing tests in the large-scale clinical trials needed for FDA approval.
Another promising candidate is Carruguard, which was developed by the nonprofit Population Council; it’s slated for tests in Africa early next year. Carruguard, which is composed of a seaweed-derived gel that is used as an additive in cosmetics and toothpaste, seems to attach itself to the outer coat of the AIDS virus, making it inactive.
Similarly, Pro2000, a contraceptive gel made by the Lexington, Mass.-based Indevus Pharmaceuticals, interferes with HIV’s ability to enter uninfected cells. Pro2000 is scheduled for tests alongside BufferGel in spring.
