Lysed cell removal promotes frozen-thawed embryo development
Dr. Vibha Rai
01 July 2007
This study by Elliott et al (2007) opens a new debate about the removal of lysed material from frozen thawed embryos. The first such experiment which showed benefits of removing lysed cells was also done on mouse model back in 1993 (Alikani et al, 1993). Many other studies have been performed (Rienzi et al, 2002 and Nagy et al, 2005) with encouraging results. This has led to the regular use of the technique in many clinics around the world on human embryos. It is known as Lysed Cell Removal (LCR
), and involves removing lysed cells that get damaged as a result of freezing at the time of thawing from human embryos. Scientists believe that these damaged cells secrete toxins and sometimes their accumulation at the site may negatively impact the growth of the embryos. Studies have reported highly improved implantation rates using the above technique in their IVF labs (Nagy et al, 2005, Rienzi et al, 2002&2005).
This experiment is a step towards finding the cause of this increased success rate when lysed cells are removed. The lack of consistency in condition to human embryo culture makes the selection of mouse embryos most apt for this study. Murine embryos were thawed at the two-cell stage. The study then looked into the effect of LCR after mechanical lysis (as opposed to natural lysis caused by the detrimental effects of freezing) of the murine embryos
. Mechanical lysis was used to control the degree of damaged cells. The mouse embryos were distributed in three groups Control group
(n=37) with no lysis, Group-1
- (n=40) consisting of cell lysis and removal and finally Group-2
- (n=40) consisting of cell lysis only.
The results of the experiment show that there was no significant difference between the three groups on day two in the mean number of blastomeres both before and after mechanical cell lysis. There was significant difference between group 1 and 2 when embryo development rate was calculated (the number nuclei cell at the blastocyst stage divided by intact blastomere number on day two). There was hardly any difference in the development stage on day three. However day four showed a higher number of embryos had reached the later embryonic development stages of blastocyst and hatching blastocyst. There was highly significant at p value of <0.005 lower growth when control group when compared with group 2 and also a significant difference with a p value of < 0.05 when group one was compared with group 2.
The results showed that more LCR embryos reach blastocyst stage compared to non-LCR embryos. These frozen thawed embryos after LCR showed faster cleavage than even the control group however this was not so significant unlike that reported in human embryos (Rienzi et al, 2002). This is the only study published that looks into the impact of mechanical cell lysis. The use of nuclear staining to check nuclear growth rate gives a better verification of the cell growth after LCR. This study confirms that Assisted hatching
with LCR technique used for human embryos certainly increases quality of embryos and that accumulation of dead cells is a hindrance in the development of the growing embryos. However, the implantation potential of the embryos after mechanical LCR was not verified due to lack of mouse host. This is a drawback in the study and leaves a void that should be looked in future studies. However, it is certainly a step forward towards finding the reason for this increased implantation.
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