Improving the Function of Cryopreserved Sperm
Although sperm cryopreservation has provided many new options in the treatment of infertility, it's possibilities could be exploited more fully if sperm could be better protected from damage caused by the freezing process. When cryopreservation damages sperm, it impairs their fertilizing capacity, with the result that pregnancy rates with frozen semen are lower than those achieved with fresh semen.
Improving freezing methods to protect sperm is an important research focus in the Cleveland Clinic Center for Advanced Research in Human Reproduction and Infertility. We have had success with adding the chemical pentoxifylline to the samples before cryopreservation.
Our previous research demonstrated that pentoxifylline stimulates motility and improves motion characteristics in highly motile sperm isolated from ordinary, fresh sperm samples. The chemical appears to work by two mechanisms: first, by increasing intracellular concentrations of CAMP, which boosts motility and the acrosome reaction; and second, by scavenging damaging oxygen-free radicals, which are known to impair sperm function.
Treating fresh sperm with pentoxifylline has been shown to increase success with in vitro fertilization (IVF) and intrauterine insemination (IUI). However, sperm samples vary considerably in their reaction to pentoxifylline, with about 10% failing to respond at all. In addition, previous studies of the agent have used only highly motile sperm selected from fresh semen samples, and, therefore, the possible results in ordinary assisted reproduction protocols were not clear.
In a recent study, we added pentoxifylline to semen, cryopreserved the samples in liquid nitrogen for 48 hours, and assessed post-thaw sperm function. We focused on the effect on the acrosome reaction, a strong indicator of fertilizing capacity and one of the functions most affected by the freeze-thaw process.
In the treated and untreated samples, cryopreservation impaired sperm motility and motion characteristics. Treatment with pentoxifylline did not improve the percentage of sperm that were motile after thawing; in fact, motility was slightly poorer in the treated group.
Pentoxifylline treatment, however, did confer two important advantages. It reduced the frequency of acrosome loss caused by the freeze-thaw process, and it increased the rate at which post-thaw spermatozoa underwent further acrosome reactions, including spontaneous reactions and those induced by calcium ionophore challenge.
These findings may suggest that pentoxifylline has a third mechanism of action, the protection of sperm membranes from damage caused by freezing. The acrosome reaction rate is highly predictive of success rates with IVF; and pentoxifylline may, therefore, have the potential to improve the fertilizing capacity of cryopreserved sperm in procedures such as intrauterine insemination and in vitro fertilization.
Center for Reproductive Medicine
The Cleveland Clinic
9500 Euclid Avenue, Desk A19
Cleveland OH 44195