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Biomedical subjects

C Mendoza

Publications and source records attributed to C Mendoza.

At least 19 recordsLinked to original sources
PubMed2001

Absorption of iron from unmodified maize and genetically altered, low-phytate maize fortified with ferrous sulfate or sodium iron EDTA.

BACKGROUND: Reducing the phytate content in grains by genetic manipulation is a novel approach to increasing nonheme-iron absorption from mixed diets. Fractional iron absorption from a genetically modified strain of low-phytate maize (LPM) increased significantly, by 50%. OBJECTIVE: We assessed iron absorption from porridges prepared from the same LPM (lpa-1-1 mutant) and unmodified wild-type maize (WTM), both of which were fortified with either ferrous sulfate or sodium iron EDTA. DESIGN: Porridges providing 3.4 mg Fe were fortified with either ferrous sulfate or sodium iron EDTA to provide an additional 1 mg Fe/serving. In 14 nonanemic women, iron absorption was measured as the amount of radioiron incorporated into red blood cells (extrinsic tag method) 12 d after consumption of the study diets. RESULTS: No significant effect of phytate content on iron absorption was found when porridge was fortified with either sodium iron EDTA or ferrous sulfate. Fractional absorption of iron from WTM porridge fortified with sodium iron EDTA (5.73%) was 3.39 times greater than that from the same porridge fortified with ferrous sulfate (1.69%). Fractional absorption of iron from the sodium iron EDTA-fortified LPM porridge (5.40%) was 2.82 times greater than that from LPM porridge fortified with ferrous sulfate (1.91%) (P<0.0001 for both comparisons, repeated-measures analysis of variance). Thus, the previously identified benefit of LPM was no longer detectable when maize porridge was fortified with additional iron. CONCLUSION: Iron was absorbed more efficiently when the fortificant was sodium iron EDTA rather than ferrous sulfate, regardless of the type of maize.

Adult↗
PubMed2000

In-vitro maturation of immature human male germ cells.

Both meiotic and postmeiotic maturation events have been observed to occur in human male germ cells during in-vitro culture. The temperature of 30 degrees C, medium supplementation with follicle-stimulating hormone and testosterone and the maintenance of the original cell-cell associations within explanted segments of the testicular seminiferous tubules are common features of the most efficient culture systems. The in-vitro maturation processes are markedly accelerated as compared to the in-vivo situation, probably due to the abrogation of a checkpoint controlling the full assembly of molecules needed for spermiogenesis. Moreover, both meiotic and postmeiotic maturation processes can be reactivated in vitro in some cases with a complete block of the same processes in vivo. Healthy babies were born after micromanipulation-assisted fertilization with in-vitro matured elongated spermatids from men with complete in-vivo maturation arrest at the round spermatid stage and at the primary spermatocyte stage.

Cell Differentiation↗
PubMed2000

[Knowledge of care activity: another professional factor associated with utilization?].

OBJECTIVES: To analyse the doctors' level of understanding of the use of resources in primary care and the relationship of their understanding to the proper use of resources. SETTING: Primary care in the Autonomous Community of Murcia. DESIGN: Descriptive, crossover study. RESULTS: There was little concordance between the real data contributed by the unit of information and registration of primary care management and data calculated by the doctors themselves. The best-known parameters are frequency of attendance (kappa index = 0.11) and patient pressure (kappa = 0.39). The profile of the doctors did not in general relate to this degree of understanding; it was only observed in a tendency in older doctors (p < 0.001) to overvalue frequency of attendance. The doctors with less understanding used radiology resources more with 164 requests per 1000 inhabitants per year, made more specialist referrals (826 per thousand inhabitants per year) and prescribed more medicines (21 prescriptions per inhabitant per year). Likewise, doctors who used resources most tended to underestimate their use of resources (p < 0.001). CONCLUSIONS: The doctor's understanding of his/her health-care activity and of the resources it involves is scant and independent of the doctor's professional characteristics. This is a factor, which we could call the professional factor, clearly related to resource use.

Clinical Medicine↗
PubMed2000

Time-dependent closed form solutions for fully competitive enzyme reactions.

An analytic formalism developed earlier to describe the time evolution of the basic enzyme reaction is extended to fully competitive systems. Time-dependent closed form solutions are derived for the three nominal cases of competition: even, slow and fast inhibitors, allowing for the first time the complete characterization of the reactions. In agreement with previous work, the time-independent Michaelis-Menten approach is shown to be inaccurate when a fast inhibitor is present. The validity of the quasi-steady-state approximation on which the present framework is based is also revised.

Enzyme Inhibitors↗
PubMed2000

Birth of healthy twins after fertilization with in vitro cultured spermatids from a patient with massive in vivo apoptosis of postmeiotic germ cells.

OBJECTIVE: To examine whether the results of assisted reproduction with the use of elongated spermatids from a man with incomplete arrest of spermiogenesis and a high frequency of apoptosis among postmeiotic germ cells can be improved by germ cell in vitro culture. DESIGN: Case report. SETTING: Private assisted reproduction centers and a university department. PATIENT(S): Man with incomplete spermiogenesis failure. 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): Fertilization rate, embryo morphology, and pregnancy. RESULT(S): An assisted reproduction attempt with viability-selected elongated spermatids from a fresh testicular biopsy sample resulted in a poor fertilization result and embryo quality. Further analysis of the sample used in this attempt showed a high incidence of apoptosis among postmeiotic germ cells. A second attempt was then performed with in vitro culture of testicular cells for 24 hours before spermatid injection. This procedure led to a significant decrease in the frequency of apoptosis among viability-selected spermatids, to improvement of the fertilization rate and embryo quality, and to the birth of healthy twins. CONCLUSION(S): In vitro culture of testicular biopsy samples before assisted reproduction with elongated spermatids may improve the efficacy of treatment in cases of massive in vivo apoptosis of postmeiotic germ cells.

Adult↗
PubMed2000

The activity (calcium oscillator?) responsible for human oocyte activation after injection with round spermatids is associated with spermatid nuclei.

OBJECTIVE: To compare the oocyte-activating ability of whole human round spermatids and their isolated nuclei. DESIGN: Prospective study using sibling oocytes from patients undergoing spermatid conception and intracytoplasmic sperm injection treatment cycles. SETTING: Private assisted reproduction laboratories and a university department. PATIENT(S): Couples with male infertility. INTERVENTION(S): Sibling oocytes were injected either with whole round spermatids or with their isolated nuclei, followed by artificial triggering of oocyte activation with calcium ionophore. Other sibling oocytes were injected either with isolated spermatid cytoplasm or with whole mature spermatozoa. MAIN OUTCOME MEASURE(S): Numbers of activated oocytes and cleaving embryos. RESULT(S): After oocyte activation was boosted with calcium ionophore, whole spermatids and isolated spermatid nuclei were equally effective in supporting oocyte activation and the formation of pronuclei, whereas no control oocyte was activated under the same conditions after injection of isolated spermatid cytoplasmic compartments. Cleavage rates were lower after the injection of isolated spermatid nuclei than after the injection of whole spermatids. CONCLUSION(S): The factor responsible for human oocyte activation after round spermatid injection is associated with spermatid nuclei. The requirement for the artificial trigger (calcium ionophore) suggests that this factor is identical to the male gamete activity previously characterized as calcium oscillator.

Calcium Signaling↗
PubMed2000

Allelotype and loss of heterozygosity around the L-myc gene locus in primary lung cancers.

L-myc S-allele was reported to be associated with metastasis of lung cancer, indicating the existence of a putative tumor suppressor gene around the L-myc locus, in linkage disequilibrium. The relationship between the S-allele and inactivation of some tumor suppressor gene should be indicated by allelic loss. Therefore, we examined the association between the L-myc S-allele and loss of heterozygosity at 11 loci around the L-myc locus (1p34.3) in primary lesions or other biological characteristics in lung cancer. No associations between the S-allele and allelic loss around the L-myc locus or other characteristics were found. According to the deletion map, three shortest regions of overlap between D1S230 and D1S76 were identified. While loss of heterozygosity at SRO1, between D1S2797 and MYCL1, showed no relationship with the pathological stage, it was more frequently observed in squamous cell carcinoma than adenocarcinoma (P=0.019), and associated with high telomerase activity (P=0.046), an indicator of cellular immortality. In conclusion, we found three shortest regions of overlap (SROs) from D1S2797 to pter, and a tumor suppressor gene, which might be associated with suppression of lung cancer development but not with L-myc S-allele, may exist in SRO1.

Adult↗
PubMed2000

Immature germ cell conception-in vitro germ cell manipulation.

Experimental studies in laboratory animals have shown that successful conception can be achieved by fertilizing oocytes with immature male germ cells. This gave rise to the concept that immature germ cells recovered from the testes of azoospermic men with maturation arrest may be used for assisted reproduction. However, in contrast to using germ cells recovered from healthy animals, clinical application to the treatment of male sterility is burdened by inherent defects in germ cells attributable to underlying testicular pathology. The recent introduction of in vitro germ cell culture/manipulation techniques makes it possible, in some cases, to overcome the in vivo maturation arrest by allowing an additional meiotic and post-meiotic differentiation and the selective harvesting of cells devoid of apoptosis-related nuclear and cytoplasmic damage. These techniques enabled the first births of normal infants fathered by azoospermic men with maturation arrest at the primary spermatocyte stage and improved the efficacy of assisted reproduction in men with maturation arrest at the round spermatid stage.

Animals↗
PubMed2000

Chemically and mechanically induced membrane fusion: non-activating methods for nuclear transfer in mature human oocytes.

Most current studies of nuclear transfer in mammalian oocytes have used electrofusion to incorporate donor cell nuclei into enucleated oocyte cytoplasts. However, the application of electrofusion to human oocytes is hampered by the relative ease with which this procedure induces oocyte activation. Here we tested a previously described chemical fusion technique and an original mechanical fusion procedure in this application. Enucleated metaphase II oocytes were first agglutinated with karyoplasts originating from other metaphase II oocytes and then induced to fuse with the use of polyethylene glycol or by micromanipulation with an intracytoplasmic sperm injection (ICSI) micropipette. Both techniques yielded a high frequency of fusion and did not cause oocyte activation. Moreover, the reconstructed oocytes were easily activated by subsequent treatment with ionophore A23187 and 6-dimethylaminopurine. These techniques may be used in attempts to alleviate female infertility due to insufficiency of ooplasmic factors by nuclear transfer from patients' oocytes to enucleated donor oocyte cytoplasts. For eventual future use in human cloning, they would ensure prolonged exposure of transferred nuclei to metaphase promoting factor, which appears to be required for optimal nuclear reprogramming.

Adenine↗
PubMed2000

In-vitro spermatogenesis resumption in men with maturation arrest: relationship with in-vivo blocking stage and serum FSH.

We have shown previously that germ cells recovered from some men with maturation arrest can resume spermatogenesis in vitro and give rise to late elongated spermatids. This study relates the ability of germ cells to differentiate in vitro to the stage at which spermatogenesis is blocked in vivo and to the patient's serum FSH concentration. The presence of germ cells at different stages of spermatogenesis was assessed, before and after culture, by classical cytology, by fluorescence in-situ hybridization and by immunocytochemistry with a germline-specific marker. The proportion of cases of maturation arrest at the primary spermatocyte, secondary spermatocyte and spermatid stage in which in-vitro resumption of meiosis was achieved was 24.3% (9/37), 100% (3/3) and 51.1% (23/45) respectively. Serum FSH concentrations were higher than normal in most cases. However, lower values were measured in patients in whom in-vitro spermatogenesis was achieved compared with those in whom no progression was detected. These data show that, under the conditions of this study, germ cells from men with very high serum FSH concentrations (>20 IU/l) are less likely to resume spermatogenesis in vitro than those coming from men with only moderate increase (10-20 IU/l).

Adult↗
PubMed2000

In-vitro differentiation of germ cells from frozen testicular biopsy specimens.

In some men with germ cell maturation arrest, spermatogenesis can be resumed during in-vitro culture of testicular biopsy samples. In this study, we examined whether similar differentiation events can be induced in cultured germ cells from cryopreserved testicular biopsy specimens. Fresh and cryopreserved aliquots of the same testicular biopsy samples were cultured in medium supplemented with FSH and testosterone. After 24 and 48 h of culture, the progression of spermatogenesis and the percentage of Sertoli cells with DNA damage, detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL), were evaluated. Spermatogenesis progressed in a similar way in fresh and cryopreserved aliquots over the first 24 h of culture. However, in contrast to fresh aliquots, no additional progress of spermatogenesis was detected between the 24 and 48 h time points. The percentage of TUNEL-positive Sertoli cells in fresh aliquots showed only a moderate increase after 24 h of culture, whereas most Sertoli cells from cryopreserved aliquots became TUNEL-positive during the same culture period. These data show that limited progression of spermatogenesis can be achieved by culturing cryopreserved testicular biopsy specimens for 24 h, but no additional benefit can be expected from prolonging the culture beyond this time point.

Biopsy↗
PubMed2000

The effect of FSH on male germ cell survival and differentiation in vitro is mimicked by pentoxifylline but not insulin.

High concentrations of FSH have been shown to boost in-vitro differentiation of germ cells from men with normal spermatogenesis and from some patients with in-vivo maturation arrest. This study shows that the differentiation-promoting effect of FSH is connected to protection against germ cell apoptosis and that both effects can be mimicked by the intracellular cyclic AMP (cAMP)-elevating drug pentoxifylline. On the other hand, a high concentration of insulin, supposed to act at the insulin-like growth factor I receptor, did not exert any effect either on differentiation or apoptosis of germ cells in vitro. These data show that the in-vitro effects of supraphysiological concentrations of FSH on human spermatogenesis are mediated by the classical FSH signal transduction pathway involving cAMP as a second messenger. Pentoxifylline may thus be useful as an alternative means for intracellular cAMP elevation in men with high circulating FSH concentrations leading to desensitization of the FSH receptor.

Acrosome↗
PubMed1999

Stimulation of tyrosine phosphorylation by progesterone and its 11-OH derivatives: dissection of a Ca(2+)-dependent and a Ca(2+)-independent mechanism.

Progesterone has previously been shown to exert non-genomic effects on human spermatozoa by opening plasma membrane ion channels and by stimulating protein tyrosine phosphorylation. Here we examined how these two activities are influenced by 11-hydroxyl substitution of the steroid molecule either in the alpha- or in the beta-configuration. Both the 11alpha-OH and the 11beta-OH derivatives of progesterone were more effective than progesterone in stimulating tyrosine phosphorylation, although 11alpha-OH-progesterone was a markedly weaker Ca(2+)-influx inducing agonist than the other two steroids. In Ca(2+)-containing medium, the agonist activity of the 11alpha-OH derivative was weaker than that of the 11beta-OH derivative, and it was completely abolished by genistein, whereas that of progesterone and its 11beta-OH derivative was inhibited only partly by this drug. In contrast, when applied in Ca(2+)-free medium, the 11alpha-OH derivative was the strongest of the three agonists tested, and the effects of all the three steroids were completely abolished by genistein. These data show that the structural motifs of steroid molecules that are responsible for the stimulation of tyrosine phosphorylation are different from those mediating the steroid action on Ca2+ influx through plasma membrane channels. The synthesis of selective agonists of both activities may lead to the development of new pharmacological agents to be used in the treatment of steroid-dependent pathologies.

Calcium↗
PubMed1999

In vitro fertilization by intracytoplasmic sperm injection.

Intracytoplasmic sperm injection (ICSI) is the latest, and by far the most efficient, variant of micromanipulation-assisted fertilization, whereby a single spermatozoon is selected, aspirated into a microinjection needle and injected to the oocyte cytoplasm. The development of this technique is mainly linked to application in human assisted reproduction for which it enables fertilization with defective spermatozoa that would not otherwise be able to penetrate an oocyte by their proper means. Because ICSI by-passes many steps of the natural fertilization process, it offers an extremely interesting model for the study of basic mechanisms underlying fertilization. This is particularly true for oocyte activation, whose mechanism needs to be revisited in light of the current ICSI research. The massive application of ICSI in human infertility treatment also represents a huge laboratory in which the impact of different genetic and epigenetic anomalies of the male gamete on fertilization and embryonic development can be studied.

Female↗
PubMed1999

Corrigenda.

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Journal Article↗
PubMed1999

In vitro culture facilitates the selection of healthy spermatids for assisted reproduction.

OBJECTIVE: To evaluate the potential usefulness of in vitro culture of germ cells for distinguishing between healthy and apoptotic spermatids. DESIGN: Prospective study. SETTING: Private assisted reproduction laboratories and a university department. PATIENT(S): Men with secretory azoospermia who were candidates for assisted reproductive treatment. INTERVENTION(S): Testicular biopsy samples were cultured in the presence of FSH and testosterone for 48 hours. Germ cell apoptosis before and after culture was evaluated by terminal deoxyribonucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling. MAIN OUTCOME MEASURE(S): The percentage of germ cells at different stages of spermatogenesis that showed apoptosis-related DNA damage. RESULT(S): In fresh samples, high levels of apoptosis were detected at those stages of spermatogenesis at which major developmental blocks occurred, with a maximum at the most advanced stage detected. In contrast, apoptotic cells were considerably less well represented at the most advanced stage after culture. CONCLUSION(S): In addition to the previously described facilitation of spermatid recognition and the progression of cytoplasmic maturation, in vitro culture of germ cells is useful to overcome the danger of inadvertent use of apoptotic spermatids for assisted reproduction.

Apoptosis↗
PubMed1999

Surveying vendors of street-vended food: a new methodology applied in two Guatemalan cities.

Lack of reliable data about street vendors, who are difficult to survey, has hampered efforts to improve the safety of street-vended food. A two-phase method for sampling vendors, surveying first in areas of concentrated vending activity identified by local authorities and second in randomly selected areas, was developed and implemented in two Guatemalan cities where street-vended food had been implicated in cholera transmission. In a 4-day survey in Escuintla, 59 vendors (42 from phase 1, 17 from phase 2) were interviewed. They demonstrated good knowledge of food safety and cholera but unsafe practices, implying that more effective, practical training was needed. In a 6-day survey in Guatemala City, 78 vendors (77 from phase 1, 1 from phase 2) were interviewed. Sixty-eight (87 %) vendors stored water, usually in wide-mouthed vessels prone to contamination; this led to a field test of a new system for safe water storage. Useful information for public health planning and intervention can be gathered rapidly with this new method for surveying street vendors.

Adolescent↗