Dr Daniel Imoedemhe, a consultant in reproductive medicine and endocrinology, working in Saudi Arabia, told the annual meeting of the European Society of Human Reproduction and Embryology, that for the first time studies on human embryos fertilized with air-dried sperm have shown that the new technique does not impair the early stages of embryo cell division
Dr Imoedemhe, from Erfan and Bagedo Hospitals, Centre for Assisted Reproduction, Jeddah, said that in the past it was believed that sperm "died" when allowed to dry in air because they were no longer motile and therefore unable to penetrate an egg. "But with the technique intracytoplasmic sperm injection (ICSI), the loss of motility doesn't necessarily mean the loss of ability to fertilize an egg, since this is largely dependent on the DNA (genetic material) that is tightly packed into the sperm head. We believe our study confirms that sperm DNA is resistant to damage by air drying."
Established methods of sperm preservation require special freezing equipment that needs careful programming to deliver controlled cooling so that the sperm are not destroyed by cooling too fast or too slowly. Sperm also need to be stored with a cryoprotectant (a special chemical that protects sperm from the adverse effects of cooling to low temperatures), which then needs to be removed prior to use.
Sperm are stored in large liquid Nitrogen tanks that require regular top-ups to ensure that they remain in the desired condition. The tanks are expensive, large and occupy a great deal of laboratory space. In the current system, in order to prevent mis-identification during recovery from storage tanks, a rigorous labelling and coding system is required.
"These methods are time-consuming and cumbersome compared to our simple technique of air-drying that just requires re-suspension before use," said Dr Imoedemhe. "The process can be further simplified by allowing patients to take responsibility for storing their air-dried sperm at home."
The new air-drying technique involves smearing a sample pellet of washed sperm on to a glass slide and then leaving it to dry for two to three hours in a laminar flow cabinet that allows a directional flow of filtered air to ensure that the sample remained uncontaminated by airborne dust or micro-organisms. The dried sperm can then be stored at normal room temperature or in a normal refrigerator and do not seem to require any other special storage conditions. Just prior to injection by ICSI into an egg, the sperm film can be re-suspended with a large drop of special biological medium (similar to that in which the eggs are held in order to avoid osmotic changes).
The present study compared early embryos that had been formed from 24 oocytes subjected to ICSI with re-suspended dried sperm (the experimental group) with 108 oocytes that that had been subjected to ICSI with fresh sperm (the therapeutic group). The study involved nine couples where the eggs taken from wives were injected with their husband's sperm.
Researchers found that drying did not prevent the sperm from taking part in the first stages of fertilization that are considered signs of normal development as 92 % of the eggs underwent the formation of two pronuclei (microscopically visible structures can be seen in the egg representing the genetic contributions from the mother and father) in the egg and 86% developed into cleaved embryos (the early stages of cell division).
But although drying did not seem to interfere with fertilization, it was found that 72 hours after sperm injection, the therapeutic group (eggs fertilized with fresh un-dried sperms) had significantly more embryos advancing to the eight or more cell stage than the experimental group (air dried sperm) - 50.5% versus 18.2%.
However Dr Imoedemhe believes this may have more to do with the differences in experimental procedure necessitated by the difficulty of acquiring fresh mature eggs for the experimental group, than the effects of air-drying. In the treatment group all the eggs were mature (at metaphase II), whereas in the air-dried group the eggs were immature (at metaphase I) and had to be matured outside before ICSI. It is thought that such immature eggs may have less potential for development after fertilization compared to normally matured eggs.
"We are greatly encouraged that even under these experimental conditions out of 24 oocytes in the air-dried group, two embryos developed to the blastocyst stage - this is the last free floating stage of development before implantation in the uterine cavity. It's thought that only the best quality embryos can continue developing outside the body to this stage," he said.
Dr Imoedemhe believes the widespread introduction of air drying would allow stored sperm to be transported without the need for specialized equipment, relieve laboratories of the responsibility of caring for preserved sperm and allow decisions and responsibilities for disposal to be borne by owners in the privacy of their own homes.
Storing sperm at home also removes fear of the potential transmission of HIV and other viral diseases (often expressed by patients) if samples from infected individuals were stored inadvertently with those from uninfected people.
Dr Imoedemhe said the next stage is to test the air-drying technique in mature (metaphase II) eggs to see whether division happens at the same rate as with fresh sperm and then to carry out pre-implantation studies on resulting embryos to ensure no adverse genetic effects have been induced by sperm drying.
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