To make this possible, the technique relies on these little things called agarose beads, which are large carbohydrate particles frequently used for lab testing. The innocuous beads are then coated with a peptide called zona pellucida glycoprotein 2, or ZP2 for short. ZP2 is responsible for binding sperm to eggs, which is a necessary step that leads to conception. During biological conception, an egg’s natural ZP2 coating is what the sperm attach to in order to achieve fertilization.
Matteo Avella and his team tested the ZP2-coated agarose beads in vitro first, and then implanted them in mice. In the lab tests, the scientists inseminated mouse eggs with mouse sperm. Regular agarose beads were introduced to some samples as a control, and the plain beads did not change the fertilization rate at all. Sperm samples that were introduced to eggs with a mixture of beads coated in ZP2 showed a decrease in fertilization by up to seven percent.
During the live mouse tests, Avella confirmed that implanting the ZP2-coated beads was a safe procedure for the mice, whose reproductive and general health were unaffected by the beads. During the trial, the mice mated normally until a litter was conceived, usually six weeks later in ZP2-treated mice than in normal mice. The first litter produced by ZP2-treated mice was smaller than normal, but each litter that followed was of normal size for a typical mouse.
So what’s going on here? In effect, the ZP2-coated beads work as a decoy. Ejaculated sperm seek out the ZP2-coated egg in order to begin reproduction, but Avella’s research suggests that the sperm are equally drawn to the ZP2-coated beads. As the distracted sperm are attached to the ZP2-coated beads, they are kept away from the female’s eggs, preventing fertilization entirely. Additionally, the fact that mice were able to bring healthy litters to term after the ZP2 beads left their system suggests that the technique could be developed into a reversible (temporary) contraceptive method.
On the infertility side, the fact that sperm seek out and attach to the ZP2-coated beads could help researchers boost the chances of successful in vitro fertilization and other assisted reproduction technologies. Instead of having to visually inspect each individual sperm, researchers would be able to identify the strongest sperm that latch on to the ZP2 beads.
While Avella’s research is promising, there is most likely a very long way to go before ZP2-coated beads are approved as a contraceptive option, or an infertility treatment. However, if the technique does make it past a human testing phase with safe and healthy results, ZP2 beads could become a powerful tool in more than one branch of reproductive health.
