Researchers have developed a promising new form of reversible contraception using sticky beads.
When implanted in the uterus of mice, the beads proved to be effective sperm traps, preventing pregnancy. They serve a dual purpose, as they could also be used to select the healthiest sperm for infertility treatments.
To design these special sticky beads, scientists started with agarose beads—large carbohydrates extracted from seaweed used in laboratory testing—and coated them with the same peptide responsible for binding sperm to eggs, known as ZP2, or zona pellucida glycoprotein 2.
Before a sperm cell can fertilize an egg, it first has to bind to an extracellular protein matrix known as zona pellucida, which surrounds the egg. Once sperm identify and bind to the ZP2, they can penetrate the egg and fertilization occurs. The ZP2 is then shed to ensure only one sperm penetrates the egg.
Matteo Avella, a post-doctoral fellow at the National Institute of Health, and his colleagues capitalized on the properties of the ZP2 to develop the sticky beads. Their research was published Wednesday in Science Translational Medicine.
When implanted in the uterus of mice, the beads acted as decoys, trapping the sperm and preventing them from traveling up the reproductive tract.
These sperm-binding beads may also help researchers identify the best sperm to use for assisted reproductive technologies
For their initial proof of concept experiment, Avella's group tested the effects of the sticky beads in vitro, or outside the body. In the lab they took normal mouse eggs and inseminated them with normal mouse sperm. In some samples, the agarose beads were also introduced, but had no effect on fertilization. Once the ZP2 coated beads were added to the mix, however, a decrease in fertilization was observed by as much as 7 percent.
Next, the researchers tried the same experiment in mice. "The beads were implanted into the mice and were well-tolerated, not harming the mice or affecting their reproductive tract and mating behavior," said Dr. Jurrien Dean, a colleague of Avella's.
The mice mated continuously until they produced a litter. The first litter produced by the treated mice was approximately six weeks later than the mice who were not treated. This first litter was also smaller than normal, but each subsequent litter was of normal size—indicating that this method could offer reversible contraception.
So what happens to the beads? According to Dr. Dean, the beads are robust. The team observed no degradation, but the beads were lost over time, presumably via discharge from the reproductive tract.
Since the results show that the ZP2 peptide can be used to decoy sperm, these sperm-binding beads may also help researchers identify the best sperm to use for assisted reproductive technologies (ART), such as in vitro-fertilization. Current technologies rely on visual inspection of each sperm, looking specifically at shape and motility.
Further testing is needed, but these results show that sticky beads could be a new form of contraception, as well as a new tool for infertility treatments.
The ZP2 coating could also be applied to other forms of contraception, such as vaginal rings, to help prevent pregnancy.