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Biomedical subjects

J Cohen

Publications and source records attributed to J Cohen.

At least 721 records · Page 40Linked to original sources
PubMed1994

Rescue of human embryos by micromanipulation.

This chapter evaluates clinical micromanipulation techniques aimed at rescuing abnormally developing zygotes and cleaved embryos. First, the possibility of reversing dispermic zygotes to a normal biparental diploid state was evaluated by extracting the distal pronucleus (that furthest from the polar body). The ratio of X:Y was determined in both groups of embryos by assessing a minimum of two blastomeres using duplex PCR or multiple colour FISH. The ratio of embryos containing only an X chromosome and those with X as well as Y chromosomes in the intact dispermic zygotes was 1.0:2.6, which is similar to the theoretical ratio of 1:3. This ratio was 1.0:1.5 in dispermic zygotes from which the distal pronuclei were removed. Although the ratio of X:Y was altered following removal of distal pronuclei, suggesting frequent targeting of male pronuclei, accidental removal of the female pronucleus could not be excluded. In a second set of mouse experiments, it was shown that the hatching process of embryos that develop with excessive amounts of degenerate material is adversely affected. It was shown that removal of such extracellular material by micromanipulation potentially reverted the hatching process. It was also indicated that immediate removal of the degenerate tissue was more beneficial than that following prolonged co-culture. Assisted hatching is probably the most frequently applied clinical embryo micromanipulation procedure. The outcome of assisted hatching is dependent largely on the mode by which the zona pellucida is breached, the size of the artificial gap and the thickness of the zona pellucida. Embryos with zonae thicker than 17 microns rarely implant. Zona drilling could be detrimental in embryos with thin zonae (< 12 microns). Superficial zona thinning has not enhanced implantation. These observations led to a routine procedure called selective assisted hatching, which involves measuring the zonae before zona drilling and replacement on day 3 of development. This appears to be most successful in older women and those with elevated basal FSH levels. Selective assisted hatching is routinely applied in consenting patients whose embryos have thick zonae, slow development or excessive fragmentation (> 20%). Zona drilling of all embryos, regardless of zona thickness, is being performed in patients aged over 40 years and in those with repeated failures or elevated basal FSH levels. Results in the first group of more than 900 patients indicate that nearly one-quarter of human embryos have the ability to implant.

Animals↗
PubMed1994

Renin inhibitors: C-terminal oxetanes as potent transition-state mimics.

A novel transition-state mimic containing a C-terminal oxetane has been developed. Renin inhibitors incorporating this fragment exhibit enhanced potency against human plasma renin at physiological pH. The binding affinity of this new species has allowed size reductions at other sites.

Dipeptides↗
PubMed1994

The parental origin of the distal pronucleus in dispermic human zygotes.

The purpose of this investigation was to determine the parental origin of the pronucleus furthest from the second polar body (the distal pronucleus) in dispermic human zygotes. Intact dispermic embryos (n = 53) and those from which the distal pronucleus (n = 50) was removed at the zygote stage were biopsied after cleavage. Blastomeres were sexed using either coamplification of X and Y probes using a duplex polymerase chain reaction (PCR), or simultaneous fluorescence in situ hybridisation (FISH) with directly fluorochrome-labelled probes for chromosomes X, Y and 18. The ratio X/Y was determined in both groups of embryos by assessing a minimum of two blastomeres. If the pronuclei in dispermic zygotes are topographically in a fixed position, the X/Y ratio should change from 1:3 in dispermic embryos to 1:1 in enucleated ones. The ratio of embryos containing only an X chromosome and those with X as well as Y chromosomes in the intact dispermic zygotes was 1.0:2.3 which is similar to the theoretical ratio of 1:3. This ratio was 1.0:1.3 in dispermic zygotes from which the distal pronuclei were removed. This ratio is not significantly different from the 1:1 ratio based on a statistical analysis with a sample size of 50. These sex ratios would have been considered different if more than 200 enucleations had been performed. Although the ratio X/Y was altered following removal of distal pronuclei, suggesting frequent targeting of male pronuclei, accidental removal of the female pronucleus could not be excluded. This indicates that enucleation of dispermic zygotes could produce high yields of gynogenetic and androgenetic embryos for research purposes. Clinical application aimed at producing biparental zygotes may be hazardous, since mosaicism was common among enucleated embryos.

Cell Nucleus↗
PubMed1994

Pathogenesis and potential strategies for prevention and treatment of septic shock: an update.

Septic shock is mediated by complex interactions of cells, cytokines, and humoral pathways. Clinical therapeutic strategies aimed at inhibiting selected pathways have been efficacious in subsets of patients. Experimental studies focusing on the activities of single cytokines have contributed to the understanding of the complex pathophysiology of septic shock. More precise delineation of the roles of each mechanism contributing to pathogenesis will permit the identification of subsets of patients who might benefit from particular therapeutic strategies and will guide the development of additional approaches to prevention and treatment.

Cytokines↗
PubMed1994

Inhibition of nitric oxide synthase in experimental gram-negative sepsis.

Nitric oxide (NO) has been proposed as a mediator of hypotension in septic shock. The aim of this study was to determine whether an inhibitor of NO production, NG-monomethyl-L-arginine (L-NMMA), was able to protect against death in two murine models of experimental gram-negative sepsis. L-NMMA (3-300 mg kg-1) did not improve survival in intravenous or intraperitoneal models of sepsis. Seven h after intravenous infection, L-NMMA (100 mg/kg-1) reduced serum nitrite plus nitrate levels (NO breakdown products) from 774 microM in control-treated animals to 282 microM in L-NMMA-treated animals (P < .001). This compared to a level of 103 microM in uninfected mice. L-NMMA produced little change in bacterial load following infection and did not increase hepatic damage, as measured by serum levels of ornithine carbamoyltransferase. Thus, while L-NMMA may reverse the hyporesponsiveness of peripheral circulation in sepsis, it was unable to prevent death in these models of gram-negative septic shock.

Amino Acid Oxidoreductases↗
PubMed1994

Monospermic polyploidy and atypical embryo morphology.

Monospermic cleavage-arrested human embryos were analysed by fluorescence in-situ hybridization using specific DNA probes for chromosomes X, Y and 18 simultaneously. Two groups of monospermic polyploid embryos could be distinguished: (i) embryos (n = 13) with only one large cell surrounded by smaller blastomere-sized extracellular fragments. These embryos were polyploid and frequently polyploid mosaic. (ii) Embryos developing from larger than normal oocytes were triploid or triploid mosaics (n = 4). Atypical morphology was not seen in eight other polyploid monospermic embryos. The atypical morphologies described here are quite rare, but are genetically uniform. Polyspermic embryos are the only other known example of a dual genetic-morphological abnormality.

Blastomeres↗
PubMed1994

Healthy deliveries from biopsied human embryos.

Preimplantation genetic diagnosis was performed in 122 embryos obtained by IVF from 11 patients carriers of haemophilia, Duchenne's muscular dystrophy, Barth's syndrome, cystic fibrosis, Pelizaeus-Merzbacher syndrome or Rett's syndrome. After multiplex polymerase chain reaction (PCR) or fluorescence in situ hybridization (FISH) analysis with multiple probes, 28 embryos diagnosed as not affected were replaced. Of these, eight implanted (28%) and produced three ongoing pregnancies, three deliveries of four babies and a biochemical pregnancy. However, one case screened for cystic fibrosis was misdiagnosed and the pregnancy was terminated. In order to evaluate the efficiency of multiplex PCR, 55 non-replaced embryos were reassessed by PCR or by FISH. Identical results were obtained in all cases. However, one embryo which had only X-chromosome specific amplification by PCR was found to be XO in all its cells by FISH. Although multiplex PCR is demonstrated to be reliable for sexing of human embryos, FISH has the additional advantages of supplying ploidy assessment while not being affected by contamination.

Biopsy↗
PubMed1994

The human zygote inherits its mitotic potential from the male gamete.

The control of centrosome and centriole duplication and formation of a single bipolar spindle during syngamy is different from that of somatic cells. If centrosomes from both gametes become functional, mosaicism could be induced following the formation of abnormal spindles. The centrosome used for development in most species is paternally inherited, with the exception of the mouse. Single and double centrioles within centrosomes in human zygotes have been described. Interpretation of data suggests that sperm centrioles are associated with further development. Here we provide evidence that the human sperm centrosome controls the first mitotic divisions after fertilization. Mosaicism and ploidy were determined in blastomeres derived from four groups of embryos: (i) dispermic zygotes, (ii) enucleated dispermic zygotes, (iii) monospermic zygotes in which the second polar body was retained (digynic), and (iv) enucleated monospermic digynic zygotes. Results prove that dispermic zygotes do not have bipolar spindles and become mosaic. This is determined by an extranuclear factor, since removal of a single pronucleus does not correct the abnormal division. Monospermic digynic embryos become triploid, indicating that the three pronuclei are organized in a single spindle and a single centrosome is active. Removal of one pronucleus from such zygotes causes the embryo to revert to a normal diploid state. These findings have consequences for the study of parthenogenesis, androgenesis and gynogenesis in the human.

Animals↗
PubMed1994

Monozygotic twinning in the human is associated with the zona pellucida architecture.

Six cases of identical twin pregnancies which occurred in 2163 cycles of in-vitro fertilization during a 3 year period are reported. Monozygosity was confirmed when the number of fetuses exceeded the number of embryos replaced (n = 4) or when two concepti were observed in a single amniotic sac (n = 2). Each of the reported pregnancies resulted from replacement of embryos either with naturally thin zonae pellucidae or embryos whose zonae had been breached during micromanipulation for assisted fertilization (subzonal sperm insertion) or assisted hatching. That such cases exclusively gave rise to monozygosity suggests a link between the physical state of the zona pellucida, hatching, and generation of identical twins.

Blastocyst↗
PubMed1994

Chromosome mosaicism in human embryos.

In the human, mosaicism may occur before implantation; but, to determine when it first occurs, it is necessary to study the chromosomal complement of all blastomeres. Full karyotypes of blastomeres from 2- to 8-cell human embryos by conventional karyotyping of metaphase spreads are difficult to obtain. The aim of this study was to assess the stage at which mosaicism occurred in preimplantation human embryos through use of fluorescence in situ hybridization (FISH) with multiple probes. All or most blastomeres from 2- to 12-cell human embryos were analyzed by FISH using probes for gonosomes and chromosome 18. FISH was performed on blastomeres from 117 morphologically normal monospermic embryos that were not transferred after preimplantation diagnosis because of their risk of carrying X-linked disease; 20 (17.1%) of these embryos were mosaic. Another group of 163 arrested or morphologically abnormal monospermic embryos were also analyzed by FISH; 47 (28.8%) of these embryos were mosaic. In addition, 37 dispermic embryos were analyzed, and 28 (75.7%) of these were found to be mosaic. Mosaicism first occurred at the second cleavage division when the monospermic embryo was mostly diploid and at the first cleavage division when the embryo was mostly haploid, polyploid, or dispermic.

Blastomeres↗
PubMed1994

Identification of the nucleic acid binding domain of the rotavirus VP2 protein.

The bovine rotavirus VP2 protein is the major component of the core and forms the most internal layer surrounding the dsRNA genome. We have constructed recombinant baculoviruses expressing truncated VP2 proteins. The nucleic acid binding activity of these truncated proteins was tested by North-Western blotting experiments with single-stranded and double-stranded probes. The nucleic acid binding domain in VP2 was localized between amino acids 1 to 132. Recombinant proteins bound single-stranded and double-stranded nucleic acids, but showed less affinity for double-stranded RNA and DNA. Interactions of VP2 with the genome were investigated in viral single-shelled particles by u.v.-cross-linking. In these experiments, only VP2 protein bound the genomic RNA in purified single-shelled particles.

Animals↗
PubMed1994

Identification of cytotoxic T cell epitopes on the VP3 and VP6 rotavirus proteins.

It has been shown previously that the viral glycoprotein VP7 is a major target of cytotoxic T lymphocytes (CTLs) induced by bovine rotavirus RF in C57BL/6 mice. Here we show that these RF-specific CTLs recognize target cells infected with a recombinant vaccinia virus (rVV) expressing the SA11 (simian rotavirus) VP6 but not those infected with rVVs that express RF VP1, VP2 or VP3 core proteins. After immunization of mice with insect cells infected with recombinant baculoviruses that express the corresponding RF proteins a strong specific CTL response was generated against target cells infected with VP6 rVV and VP3 rVV, a weak one against the VP2 rVV but none against the VP1 rVV. Kb-restricted CTL epitopes were identified on VP6 and VP3 using allele-specific motifs. When peptides corresponding to these epitopes were used to restimulate in vitro the spleen cells from RF-immunized mice, CTLs specific for each peptide and its corresponding rVV were induced.

Animals↗
PubMed1994

Transitions between routes of administration of regular amphetamine users.

A sample of 301 regular amphetamine users was interviewed regarding transitions between routes of administration of amphetamines. Use of amphetamines by injecting was widespread, with two-thirds (67%) of subjects having injected the drug during the preceding 6 months. Needle-sharing was common, with 41% of injectors having shared a needle in the month preceding interview. A transition to regular amphetamine injecting from other routes of administration was reported by 40% of subjects, with males being twice as likely to report such a transition. The median number of such transitions was one. The main reasons given by subjects for the transition to injecting were liking the "rush" from injecting, and seeing it as a more economical and a healthier way to use. A small proportion of subjects (9%) reported a transition away from injecting amphetamines, with a median of one such transition. The most common reason given for abandoning injecting was concern about vascular damage. Interventions to encourage safer use of amphetamines need to address the misconceptions that injecting is more economical and more healthy, and to emphasize the vascular problems associated with injecting.

Adolescent↗
PubMed1994

The use of benzodiazepines among regular amphetamine users.

The relationship between benzodiazepine and regular amphetamine use was examined in a sample of 301 regular amphetamine users. Benzodiazepine use was widespread, with 37% of subjects having used them in the month preceding interview, and 55% in the preceding 6 months. Injectors of amphetamines were more likely to have ever used, and to be currently using, benzodiazepines. Comparisons of benzodiazepine users with other subjects indicated that benzodiazepine users had higher levels of polydrug use and psychopathology, as well as poorer health and social functioning than non-users. The odds of benzodiazepine using injectors having injected with a borrowed used needle in the preceding month were 3.8 times of those of non-benzodiazepine-using injectors. These results are consistent with studies of other groups of illicit drug users, such as heroin users, in indicating that benzodiazepine use is associated with greater levels of risk and psycho-social dysfunction.

Adolescent↗