Development of mammalian embryos exposed to mixed-size nanoparticles

Inhaled or ingested ultrafine nanoparticles and their effects on early pregnancy remain polemic. The objectives of the study were: (a) to determine the embryotoxic effects of nanoparticles at the 2-cell stage and (b) to localize the internalized nanoparticles in the blastocyst. Thawed mouse 2-cell embryos (no. = 128) were exposed to either mixed-size polystyrene-based nanoparticles (11 million/ml) or control G1.3 medium and assessed after 72 hours. Additionally, blastocysts (no. = 146) were exposed to nanoparticles and analyzed. The results showed that the nanoparticles did not inhibit 2-cell embryo development to the blastocyst stage (89.4 vs 96.8%; treated vs control). There were no differences in hatching (34.8 vs 43.5%), implantation (13.6 vs 24.2%) and degeneration (10.6 vs 3.2%). Delayed exposure to nanoparticles showed similar percent hatching (40.7 vs 47.3%) and implantation (17.6 vs 20.0%). Although nanoparticles were internalized, embryo development was not inhibited suggesting a lack of embryotoxicity. During hatching, the larger nanoparticles adhered to the extruding blastocyst, preferentially on trophoblasts, but interference was insignificant. Exposure to polystyrene-based nanoparticles at the concentration tested are not associated with embryonic loss.

Comet assay of cumulus cell DNA status and the relationship to oocyte fertilization via intracytoplasmic sperm injection

This paper postulates that in the ovary, the close association between the cumulus cells and the oocytes permits the fertilizing ability of the oocytes to be determined indirectly through cumulus cell DNA status. The objective was to use a modified comet assay to analyse cumulus cell DNA and relate the data to oocyte fertilization after intracytoplasmic sperm injection (ICSI) procedures. Oocytes were retrieved (n = 15 cases) and free-floating cumulus cells were pooled and smeared on clear glass slides to dry. Meanwhile, the denuded oocytes were injected with spermatozoa and fertilization was assessed, followed by embryo transfer. The fixed cumulus cells were stained in acridine orange, coated with a mini-gel agarose layer, lysed in alkaline buffer and electrophoresis performed. Analyses of fluorescent cell images (n = 449) showed that the tail moment was positively correlated to the percentage of fertilization after ICSI (r = 0.567, P < 0.05). In contrast, there was no correlation between tail moment and number of oocytes retrieved, total ampoules used, endometrial thickness and age of patient. The results suggested that the competence of the oocytes was associated with the cumulus cell DNA status. A unique feature here was the comet assay for archived material with obvious advantages.

Updating quality control assays in the assisted reproductive technologies laboratory with a cryopreserved hamster oocyte DNA cytogenotoxic assay

PURPOSE

Despite advances in assisted reproduction, there is no progress in quality control bioassays. The objectives were to develop a comet assay to measure DNA fragmentation in thawed cryopreserved oocytes and compare this assay with one-cell mouse embryo bioassay.

METHODS

Thawed hamster oocytes from a commercial source were incubated in culture media with either 0-, 50-, or 100-microM hydrogen peroxide, or, in media exposed to different contact materials and unknown proficiency analytes. Incubation time was 1.5 h at 37 degrees C. The oocytes were dried, fixed, stained with acridine orange, embedded in a mini-agarose layer and electrophoresis was carried out. Fluorescent images were analyzed. The results were compared with standard one-cell mouse assay data.

RESULTS

The 100-microM hydrogen peroxide treatment caused greatest DNA fragmentation in the hamster oocytes at Hours 1 and 2. A dose response was observed. Intraassay coefficient of variation was 5.7%. Only one of the five materials tested passed both assays. The data for the unknown proficiency analytes were similar for both assays.

CONCLUSIONS

The oocyte comet assay demonstrated DNA fragmentation in the presence of toxic substances. The detection of toxicity in two materials that passed the mouse bioassay suggested increased sensitivity in the new assay. The oocyte comet assay and the mouse bioassay results matched in the proficiency test. However, more studies are still needed to determine optimal sensitivity.

A simple comet assay for archived sperm correlates DNA fragmentation to reduced hyperactivation and penetration of zona-free hamster oocytes

OBJECTIVE

To correlate sperm variables with sperm DNA fragmentation, as assessed by using a modified alkaline comet assay for sperm smears.

DESIGN

The comet assay was adapted for fixed sperm smears (59 cases), and the level of DNA fragmentation was determined.

SETTING

Clinical and academic research environment.

PATIENT(S)

59 patients undergoing fertility treatment.

INTERVENTION(S)

Sperm samples leftover from IVF procedures were fixed and processed for the comet assay.

MAIN OUTCOME MEASURE(S)

Sperm head DNA density and sperm variables.

RESULT(S)

A correlation was observed between increased sperm head DNA fragmentation and decreased penetration of zona-free hamster oocytes. Heat-induced hyperactive motility decreased as DNA fragmentation increased. The DNA fragmentation did not correlate with percentages of intact acrosome, normality, maturity, and strict normal morphology.

CONCLUSION(S)

The advantages of the comet assay for archived cells include simplicity, low intraassay coefficient of variation, and low performance cost; in addition, DNA analysis can be carried out at leisure. Low DNA damage was associated with higher hyperactivation and oocyte penetration, suggesting that failed fertilization was linked to compromised DNA integrity in the sperm. Exploration of compounds to repair damaged DNA is warranted.

Spermac stain analysis of human sperm acrosomes

OBJECTIVE

To study the association between low percentages of intact sperm acrosomes and fertilization failures in conventional IVF procedures.

DESIGN

A retrospective study.

SETTING

Clinical and academic research environment.

PATIENT(S)

Patients undergoing treatment of infertility.

INTERVENTION(S)

Sperm cells were fixed and stained using the Spermac stain.

MAIN OUTCOME MEASURE(S)

Percentages of intact acrosomes and fertilization.

RESULT(S)

There was a significant association between specimens with <40% intact acrosomes and failed conventional IVF procedures. Among the 29 cases with <40% intact acrosomes, 9 cases (31%) resulted in zero penetration of the oocytes. The mean (+/-SEM) percentage of fertilization was lower in the abnormal acrosome group (43.3% +/- 6.5%) than in the normal acrosome group (64.1% +/- 5.6%). The status of the sperm acrosome was not correlated with the results of fertilization in intracytoplasmic sperm injection procedures.

CONCLUSION(S)

Sperm with low percentages of intact acrosomes were associated with failed fertilization. The Spermac stain was useful for assessing acrosomes and identifying possible male factor infertility problems. The results suggested that a minimum percentage of sperm with intact acrosomes are needed for fertilization to occur in vitro.

Enhanced fertility after heat-induced hyperactivation

OBJECTIVE

To determine sperm hyperactivation, kinematic parameters, and fertilizing capacity after pretreating sperm at 40 degrees C for 4 hours.

DESIGN

Prospective study involving pooled donor sperm that were colloid washed and incubated at either 23 degrees C (control) or 40 degrees C (heat-treated) for 4 hours as pretreatment. After incubation, analyses were performed with a computer-assisted sperm analyzer, whereas separate portions of sperm were evaluated with the sperm penetration assay at 37 degrees C.

SETTING

Clinical and academic research environment.

PATIENT(S)

Cryopreserved-thawed sperm from different donors (n = 5).

MAIN OUTCOME MEASURE(S)

Sperm kinematic and fertilizing parameters.

RESULT(S)

Heat pretreatment of sperm resulted in over 22 times higher hyperactive motility at hour 4 compared with the control. The other kinematic parameters were also different. The heat-pretreated sperm group had a significantly higher percent penetration of zona-free oocytes with more swollen sperm heads per oocyte and enhanced sperm binding.

CONCLUSION(S)

The results showed that hyperactivation was induced by pretreatment of sperm with 40 degrees C heat, suggesting the involvement of heat factors in hyperactivation. The fertilizing capacity of sperm may be improved by the mild heat pretreatment when marked by the presence of heat-induced hyperactivation.

Heat-induced hyperactivation

PURPOSE

The objectives of this study were (1) to determine the sperm hyperactivation and related kinematic parameters at 40 degrees C after using four sperm wash procedures and (2) to correlate the heat-induced hyperactivation data with cases of clinical pregnancies from either artificial insemination or standard in vitro fertilization (IVF).

METHODS

Semen samples (n = 51) were collected by ejaculation, and semen analyses were carried out to determine the pretreatment data. Sperm kinematic measurements were performed using the Hamilton Thorn HTM-C computer-aided sperm analyzer. Hyperactivation was determined using the sort module on the HTM-C. Membrane integrity was assessed using the hypoosmotic sperm swelling procedure. Sperm morphology and acrosomal status were also determined using the Spermac stain. Each semen specimen was divided and processed through either the swim-up wash, the 1-h test-yolk buffer (TYB) wash, the 1 mg/ml pentoxifylline stimulant procedure, or the two-layer 90:47% gradient colloidal solution procedure. The washed sperm were incubated at 25 or at 40 degrees C for 4 hr. After incubation, kinematic parameters were assessed for the posttreatment data. Semen specimens were obtained on different occasions for artificial insemination or standard IVF. Data from intracytoplasmic sperm injection cases were not included to avoid confounding factors. Live births and/or pregnancies with fetal heart-beat examined by ultrasound were considered clinical pregnancies.

RESULTS

Heat-induced hyperactive motility was significantly higher in sperm of the male partner of pregnant (n = 7) patients compared with nonpregnant (n = 44) patients (mean +/- SE, 10.0 +/- 3.3 versus 5.5 +/- 0.8%) after TYB processing followed by 4 hr of incubation at 40 degrees C. This was also observed after colloid (Percoll) processing (11.6 +/- 4.6 versus 5.8 +/- 0.8%). There were no differences in hyperactivation after 4 hr at 23 degrees C between pregnant and nonpregnant cases. Parameters such as count, volume, motility, viability, and acrosomal status were not different for the groups. However, the percentage of sperm with normal morphology (WHO classification) was twice as high in the pregnant group versus the nonpregnant group.

CONCLUSIONS

Heat-induced hyperactivation was associated with fertile sperm and was predictive of pregnancy obtained after artificial insemination or IVF. The association was evident only after TYB or Percoll sperm processing. The study could not confirm the finding of significant decreases in motility after heat treatment of sperm derived from infertile males. The mechanism for heat-induced hyperactivation did not involve membrane integrity or the sperm acrosome, although an involvement of heat shock proteins was postulated. Interestingly, there were no pregnancies when sperm did not exhibit heat-induced hyperactivation.

Correlation between intact sperm acrosome assessed using the Spermac stain and sperm fertilizing capacity

Accurate determination of sperm acrosomal status is important in fertility studies. The objective was to correlate the percentage of intact acrosome assessed using the new Spermac stain with the capacity of sperm to fertilize oocytes. Sperm specimens were processed either by centrifuge wash, 48:95 Percoll gradient or test yolk buffer (TYB) wash, and tested using the zona-free hamster oocyte assay. The results indicated a correlation between the percentage of sperm with intact acrosome reaction and the percentage of sperm penetrating the oocytes in the TYB-washed group. The data suggest the usefulness of the Spermac stain for assessing the acrosomal status and in predicting the fertilizing capacity of the sperm.