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Carmen Mendoza

Publications and source records attributed to Carmen Mendoza.

12 recordsLinked to original sources
PubMed2004

Caspase-dependent and -independent DNA fragmentation in Sertoli and germ cells from men with primary testicular failure: relationship with histological diagnosis.

BACKGROUND: Germ cell elimination and sperm DNA fragmentation in men with primary testiculopathies involve apoptosis-related processes whose mechanisms are poorly understood. This study examines the participation of typical (caspase-dependent) and atypical (caspase-independent) pathways in these processes. METHODS: Caspase activity and DNA fragmentation were evaluated in Sertoli and germ cells from 63 men with non-obstructive azoospermia and with different histological diagnoses who were undergoing testicular biopsy for an assisted reproduction attempt. In eight of these men, phosphatidylserine externalization was also examined. RESULTS: The percentage of Sertoli cells showing caspase activity and DNA fragmentation was low and uniform in all diagnoses. In germ cells that remained tightly associated with Sertoli cells despite vigorous mechanical treatment, the incidence of both caspase activity and DNA fragmentation was high, particularly in men with maturation arrest. In Sertoli cell-free germ cells, high incidence of DNA fragmentation contrasted with low incidence of caspase activity and phosphatidylserine externalization. CONCLUSIONS: In men with primary testicular failure, apoptosis of Sertoli cells is insignificant. Some germ cells undergo caspase-dependent apoptosis, show phosphatidylserine externalization and are tightly associated with Sertoli cells. Other germ cells show caspase-independent DNA fragmentation, do not externalize phosphatidylserine and lack a tight association with Sertoli cells.

Apoptosis↗
PubMed2003

Microfilament disruption is required for enucleation and nuclear transfer in germinal vesicle but not metaphase II human oocytes.

OBJECTIVE: To evaluate the usefulness of microfilament disruption before enucleation and nuclear transfer in human oocytes at different stages of maturation. DESIGN: Prospective experimental study. SETTING: Private clinics. PATIENT(S): Infertile couples undergoing assisted reproduction attempts. INTERVENTION(S): Oocyte enucleation and nuclear transfer, activation of reconstructed oocytes. MAIN OUTCOME MEASURE(S): Oocyte survival, nuclear transfer efficacy, activation outcomes. RESULT(S): Survival rate and nuclear transfer efficacy of germinal vesicle oocytes exposed to the microfilament disrupting agent cytochalasin B before enucleation were 88% and 80%, respectively. These figures dropped, respectively, to 8% and 2% when cytochalasin treatment was omitted. By contrast, cytochalasin-treated and -untreated metaphase II oocytes showed similar survival rate (87% vs. 90%) and nuclear transfer efficacy (78% vs. 87%). This also applied to metaphase II oocytes matured in vitro from the germinal vesicle stage. Cytochalasin treatment did not affect activation rate of reconstructed oocytes, but it increased the occurrence of oocytes with multiple female pronuclei. CONCLUSION(S): Microfilament disruption before enucleation is required for germinal vesicle oocytes but not for metaphase II oocytes.

Actin Cytoskeleton↗
PubMed2002

Pharmacological concentrations of follicle-stimulating hormone and testosterone improve the efficacy of in vitro germ cell differentiation in men with maturation arrest.

OBJECTIVE: To examine whether in vitro differentiation of germ cells from men with maturation arrest is improved by augmenting FSH and T concentrations above the values effective in samples from men with normal spermatogenesis. DESIGN: Prospective, controlled in vitro study. SETTING: Private assisted reproduction centers and a university department. PATIENT(S): Men with meiotic or postmeiotic maturation arrest. INTERVENTION(S): Testicular spermatid extraction, in vitro culture of testicular biopsy samples, intraoocyte injection of elongated spermatids, embryo culture and transfer. MAIN OUTCOME MEASURE(S): Progression of in vitro germ cell differentiation, fertilization, and pregnancy outcomes with in vitro cultured germ cells. RESULT(S): In some cases of meiotic and postmeiotic maturation arrest, more advanced germ cell stages were achieved by in vitro culture in the presence of 500 IU/L FSH as compared with 50 IU/L FSH. The beneficial effect of 500 IU/L FSH was further potentiated by a simultaneous increase of T concentration from 1 to 10 microM. Fertilizations with germ cells recovered after incubation with these pharmacological hormone concentrations gave rise to viable embryos and the births of five healthy babies. CONCLUSION(S): Pharmacological concentrations of FSH and T are beneficial for in vitro maturation of germ cells from some men with in vivo maturation arrest.

Biopsy↗
PubMed2002

Use of a modified intracytoplasmic sperm injection technique to overcome sperm-borne and oocyte-borne oocyte activation failures.

OBJECTIVE: To examine whether sperm-borne and oocyte-borne oocyte activation failures can be overcome by mechanical means that entail modifying the ICSI technique. DESIGN: Case report series. SETTING: Private clinics. PATIENT(S): Six infertile couples undergoing ICSI. INTERVENTION(S): Standard ICSI and modified ICSI based on mechanical manipulation that facilitated entry of calcium into the oocyte. MAIN OUTCOME MEASURE(S): Fertilization rate and pregnancy outcome. RESULT(S): In three cases of sperm-borne and three cases of oocyte-borne oocyte activation deficiencies, the modified ICSI technique enabled normal fertilization and development of embryos with good morphology. In terms of fertilization, the efficacy of modified ICSI was similar to use of a calcium ionophore, without producing extensive embryo fragmentation during postfertilization development. Term pregnancies resulting in the birth of normal children were achieved with the modified ICSI technique in five cases. CONCLUSION(S): Sperm-borne and oocyte-borne oocyte activation failures can be overcome by modifying the ICSI technique. The modification obviates the need to use insufficiently tested and potentially harmful drugs.

Adult↗
PubMed2002

Paternal effects acting during the first cell cycle of human preimplantation development after ICSI.

BACKGROUND: The ability of human embryos to undergo normal development has been shown previously to be subject to strong paternal (sperm-derived) effects. This study was undertaken to determine whether paternal influences on human embryo quality are detectable as early as the first cell cycle after fertilization. METHODS: The quality of zygotes and cleaving embryos resulting from sibling donor oocytes fertilized by sperm from different patients were compared in a donor oocyte-sharing programme. RESULTS: Fertilizations with sperm from certain individuals repeatedly resulted in the formation of high proportions of zygotes with abnormal pronuclear morphology that subsequently tended to cleave slowly and to show extensive fragmentation and blastomere irregularities. This phenomenon was observed with oocytes from two different donors for each of these individuals and contrasted with normal developmental performance of embryos resulting from sibling oocytes fertilized by sperm from other men with similar basic sperm characteristics. Fertilization rates were not related to these differences. CONCLUSIONS: These data point to a very early onset of paternal effects that condition human embryo development. These effects may be both of genetic (related to the minor gene activity of the male pronucleus) or epigenetic (related to the sperm-derived oocyte-activating factor or sperm centrosome) origin.

Adult↗
PubMed2002

Effects of exogenous LH administration during ovarian stimulation of pituitary down-regulated young oocyte donors on oocyte yield and developmental competence.

BACKGROUND: The role of exogenous LH supplementation in ovarian stimulation is a matter of debate. Here we evaluate the impact of exogenous LH on oocyte yield and developmental competence in an oocyte donation programme. METHODS: Oocyte donors were randomized (computer-generated randomization list) to groups stimulated with FSH alone or with a combination of FSH and LH after pituitary down-regulation with a GnRH agonist administered in the mid-luteal phase. RESULTS: In donors with deep suppression of pituitary LH (<1 IU/l) before the beginning of ovarian stimulation, the inclusion of exogenous LH resulted in an increase in the number of mature oocytes and good-quality zygotes and embryos as well as higher implantation rates when compared with stimulation with FSH alone. In contrast, the inclusion of exogenous LH in the stimulation of donors with pre-stimulation serum LH of >or=1 IU/l impaired embryo morphology and lowered the implantation rate, although it increased the number of metaphase II oocytes. CONCLUSIONS: The inclusion of exogenous LH to the ovarian stimulation protocol can have beneficial or detrimental effects on oocyte yield and quality, depending on the level of endogenous LH. These data support the concept of a 'window' for LH requirement in ovarian stimulation.

Adult↗
PubMed2002

Follicular fluid markers of oocyte developmental potential.

BACKGROUND: Concentrations of certain substances in follicular fluid (FF) are related to fertilization outcome and early post-fertilization development. The study aim was to identify FF markers with which to predict embryo implantation potential. METHODS: Concentrations of selected hormones, cytokines and growth factors in individual FF samples obtained during assisted reproduction treatment were related with treatment outcomes. RESULTS: Mean concentrations of LH, growth hormone (GH), prolactin (PRL), 17beta-estradiol (E2) and insulin-like growth factor (IGF)-I were higher, and that of interleukin-1 (IL-1) was lower, in treatment attempts leading to a clinical pregnancy as compared with those in which no pregnancy was established. Concentrations of FSH, progesterone, tumour necrosis factor-alpha and IGF-II were similar in successful and unsuccessful attempts. In successful attempts, LH and GH levels were higher in those follicles from which oocytes giving rise to transferred embryos (i.e. embryos with best morphology and fastest cleavage rate) originated, as compared with other follicles from which a mature oocyte was recovered but was cryopreserved for later use. CONCLUSIONS: FF levels of LH, GH, PRL, E2, IGF-I and IL-1 may serve to analyse cases of repeated assisted reproduction failures and to assess effects of modifications of the ovarian stimulation protocol.

Adult↗
PubMed2002

Caspase activity in preimplantation human embryos is not associated with apoptosis.

BACKGROUND: Previous studies on mammalian preimplantation embryos have suggested an association between caspase activation, blastomere fragmentation and apoptosis. However, some reports on human embryos questioned the causal relationship between blastomere fragmentation and apoptosis, and information about the presence and activity of caspases in human embryos is lacking. METHODS: A fluorochrome-labelled universal caspase inhibitor was used to visualize active caspases in blastomeres and fragments of preimplantation human embryos. RESULTS: Caspase activity was detected only after fertilization, and was rare in blastomeres but frequent in fragments. The incidence of caspase activity in blastomeres and fragments was stable between the 2-cell and 12-cell stages. Caspase-positive blastomeres were only seen in poor-morphology embryos. The percentage of caspase-positive fragments was increased in embryos with multinucleated blastomeres but was unrelated to embryo morphology. Moreover, caspase-positive fragments detached from healthy blastomeres that were isolated by embryo biopsy and subsequently underwent mitotic division in culture. CONCLUSIONS: These data suggest that caspases in preimplantation human embryos are involved in developmental processes unrelated to cell death.

Apoptosis↗
PubMed2002

In-vitro effects of FSH and testosterone withdrawal on caspase activation and DNA fragmentation in different cell types of human seminiferous epithelium.

BACKGROUND: Caspases are downstream elements of apoptosis-mediating pathways initiated by the Fas ligand/Fas receptor system which is supposed to play a central role in the regulation of apoptosis in the human seminiferous epithelium. However, caspase activity in different cell types of this epithelium has never been addressed. METHODS AND RESULTS: We evaluated caspase activity and DNA integrity in Sertoli and germ cells within in-vitro cultured segments of human seminiferous tubules after induction of apoptosis by FSH or testosterone withdrawal. FSH withdrawal increased the incidence of DNA fragmentation in meiotic (primary spermatocytes) and post-meiotic (spermatids) germ cells without producing any detectable effect on caspase activity in these cells and without affecting DNA integrity or caspase activity in Sertoli cells. Testosterone withdrawal stimulated caspase activity and produced DNA fragmentation in Sertoli cells, but showed only a weak effect on DNA fragmentation in germ cells and did not alter germ cell caspase activity. CONCLUSIONS: These findings confirm the central role of caspases in apoptosis of Sertoli cells. However, they also suggest that acute apoptosis of germ cells in the adult human testis occurs in a caspase-independent way and is controlled by Sertoli cells via an as yet undetermined mechanism.

Apoptosis↗
PubMedDate not supplied

Luteinizing hormone affects uterine receptivity independently of ovarian function.

Previous studies have suggested that LH, in addition to its well-known effects on the ovary, may exert direct effects on the uterus. This study evaluated the effects of mid-cycle administration of human chorionic gonadotrophin (HCG), which signals through the LH receptor, on endometrial thickness and uterine receptivity in two groups of women lacking ovarian activity and receiving embryos from an oocyte donation programme. Patients in one group still had ovulatory cycles, but their ovarian function was suppressed by pituitary down-regulation with a gonadotrophin-releasing hormone (GnRH) agonist in the embryo transfer cycle, resulting in low endogenous LH concentrations. Patients in the other group were menopausal women whose pituitary function was not down-regulated in the embryo transfer cycle and whose endogenous LH concentrations were thus high. Patients in each of the two groups were randomized into two subgroups. Patients in one subgroup were given 5000 IU of HCG 2 days before oocyte recovery in the corresponding donor. Patients in the other subgroup received placebo at the same time. Oocytes from each donor were randomly distributed between one patient from the HCG subgroup and one patient from the placebo subgroup in each patient group. Endometrial growth and secretory transformation were stimulated by sequential treatment with oestradiol valerate and progesterone. In women with low endogenous LH receiving placebo, endometrial thickness stopped increasing at the beginning of secretory transformation. Mid-cycle HCG administration resulted in a continuous increase in endometrial thickness through this period, improved the implantation rate after embryo transfer in these women (30.6 versus 20.7%) and augmented the number of multiple pregnancies. No similar stagnation of endometrial thickness and no effects of mid-cycle HCG administration on endometrial thickness, the implantation rate and the number of multiple pregnancies were found in women with high endogenous LH. It is concluded that endometrial maturation is disturbed in women with low endogenous LH but can be rescued by mid-cycle stimulation of LH receptor with exogenous HCG in the absence of ovarian activity.

Adult↗
PubMedDate not supplied

Somatic cell haploidization: an update.

Oocyte donation is the only method of treating female sterility caused by complete absence of oocytes, with the loss of genetic motherhood. Genetic fatherhood of males with complete absence of spermatozoa can only be restored by assisted reproduction treatment if sperm precursor cells belonging to the male germline can still be recovered from the testis. Otherwise, sperm donation is the only available solution. Somatic nucleus haploidization after injection into previously enucleated donor oocytes (diploid-to-haploid reduction) might enable the reconstruction of new oocytes carrying the complete nuclear genome of female patients lacking their own oocytes. Such newly formed oocytes could subsequently be fertilized by spermatozoa from the patient's husband. In cases of male infertility with complete absence of the germline, the patient's somatic cell nuclei could be injected into the oocytes without previous enucleation, and somatic nucleus haploidization would occur in the presence of the original female nucleus (triploid-to-diploid reduction), hopefully leading to the formation of a diploid embryo. Both interventions differ substantially from cloning because embryos are formed by syngamy with the male and female genomes originating from the two genetic parents, as in natural fertilization. Ultrastructural remodelling of mouse somatic cell nucleoli can be achieved in enucleated metaphase II mouse oocytes. Haploidization has also been attempted with Sertoli cells and with fibroblasts, both of which are also available in male patients. Experiments are currently under way to assess the regularity of chromatid segregation during somatic nucleus haploidization.

Animals↗