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Biomedical subjects

H Lucas

Publications and source records attributed to H Lucas.

At least 19 recordsLinked to original sources
PubMed2005

Bioceramics composition modulate resorption of human osteoclasts.

Biomaterials used in bone regeneration are designed to be gradually resorbed by the osteoclast and replaced by new bone formed through osteoblastic activity. The aim of the present study is to analyze the role of osteoclasts in the resorption process. The attachment of human osteoclasts and the appearance of their resorption lacunae, when cultured on either the resorbable crystalline, calcium orthophosphate materials or on the long-term stable bioceramic material was investigated. The resorbable materials contain Ca10[K,Na](PO4)7 (AW-Si) and Ca2KNa(PO4)2 (GB14, GB9 & D9/25) as their main crystal phases, however they differ in their total solubility. These differences result from small variations in the composition. The long-term stable material consist of about 30% fluorapatite beside calcium zirconium phosphate (Ca5(PO4)3F + CaZr4(PO4)6) and shows a very small solubility. AW-Si has an alkali containing crystalline phase, Ca10[K,Na](PO4). While GB14, GB9 and D9/25 contain the crystalline phase Ca2KNa(PO4)2 with small additions of crystalline and amorphous diphosphates and/or magnesium potassium phosphate (GB14). D9/25 and AW-Si is less soluble compared to GB14, and GB9 among the resorbable materials. Resorbable and long-term stable materials vary in their chemical compositions, solubility, and surface morphology. Osteoclasts modified the surface in their attempts to resorb the materials irrespective of the differences in their physical and chemical properties. The depth and morphology of the resorption imprints were different depending on the type of material. These changes in the surface structure created by osteoclasts are likely to affect the way osteoblasts interact with the materials and how bone is subsequently formed.

Biocompatible Materials↗
PubMed2002

Localization of tyrosine phosphorylated proteins in human sperm and relation to capacitation and zona pellucida binding.

Mammalian sperm must undergo a process known as capacitation before fertilization can take place. A key intracellular event that occurs during capacitation is protein tyrosine phosphorylation. The objective of this study was to investigate and visualize protein tyrosine phosphorylation patterns in human sperm during capacitation and interaction with the zona pellucida. The presence of specific patterns was also assessed in relation to the fertilizing capacity of the spermatozoa after in vitro fertilization. Protein tyrosine phosphorylation was investigated by immunofluorescence. Phosphorylation increased significantly with capacitation and was localized mainly to the principal piece of human sperm. Following binding to the zona pellucida, the percentage of sperm with phosphotyrosine residues localized to both the neck and the principal piece was significantly higher in bound sperm than in capacitated sperm in suspension. When the percentage of principal piece-positive sperm present after capacitation was <7%, fertilization rates after in vitro fertilization were reduced. Different compartments of human spermatozoa undergo a specific sequence of phosphorylation during both capacitation and upon binding to the zona pellucida. Tyrosine phosphorylation in the principal and neck piece may be considered a prerequisite for fertilization in humans.

Female↗
PubMed2002

Economic transition should come with a health warning: the case of Vietnam.

STUDY OBJECTIVE: s: To assess the affordability of health care to poor rural households in Vietnam under conditions of transition from a planned to a market economy and, in light of other transitional experience, inform policy on increasing access of the poor to affordable care of acceptable quality. DESIGN: Observational study by cross sectional socioeconomic survey, longitudinal healthcare seeking survey, and qualitative semi-structured interviews and focus group discussions; qualitative follow up over six years. SETTING: Four rural communes in north of Vietnam between 1992 and 1998. SURVEY PARTICIPANTS: 656 households (2995 people) selected by systematic random sampling. MAIN RESULTS: Compared with non-poor households, poor households had significantly lower average per capita rates of healthcare consultation and expenditure (p<0.01 in both cases). Poor households delayed and minimised healthcare seeking, especially of expensive hospital services. Two thirds of average healthcare spending by poor households was on relatively inexpensive but frequent acts of local ambulatory care. The poor restrained their healthcare seeking but not in proportion to income: for households reporting illness, the average proportion of income devoted to health care was 21.9% for the poor compared with 8.2% for the non-poor (p<0.01). To meet healthcare costs, many poor households reduced essential consumption, sold assets and incurred debt, threatening their future livelihood. CONCLUSIONS: In the short-term the poor need exemption from public sector user fees in both primary and hospital care. In the longer run the government budget and prepayment schemes should replace direct user charges in healthcare finance. Transitional economies like Vietnam should preserve the public health services built up under the planned economy. Market reforms that stimulate growth in the economy appear inappropriate to reform of social sectors.

Ambulatory Care↗
PubMed2001

Tnt1 transposition events are induced by in vitro transformation of Arabidopsis thaliana, and transposed copies integrate into genes.

Tissue culture has been shown to induce the transposition of plant transposable elements; their insertion at novel sites results in somaclonal variation. Introduction of the tobacco retrotransposon Tnt1 into Arabidopsis thaliana by co-cultivation of root explants with Agrobacterium tumefaciens induces its transposition at a high frequency, but no transposed copies are found in plants transformed by the in planta procedure. Transposition occurs in the transformed root cells or in the calli derived from them, allowing the regeneration of transformed plants with up to 26 transposed copies of Tnt1. Analysis of Tnt1 integration sites in Arabidopsis shows that the Tnt1 endonuclease does not show any cleavage-site specificity at the sequence level. The insertion sites are unlinked and distributed on all five Arabidopsis chromosomes. The fact that the majority of the integration sites are located in coding regions, and none in repeated sequences, demonstrates the potential of Tnt1 as a tool for gene tagging.

Agrobacterium tumefaciens↗
PubMed2001

The protease and reverse transcriptase of the tobacco LTR retrotransposon Tnt1 are enzymatically active when expressed in Escherichia coli.

The open reading frame (ORF) of the tobacco retrotransposon Tnt1-94 was over-expressed in Escherichia coli to assay its protease and reverse transcriptase (RT) enzymatic activities. In E. coli, Tnt1-94 polyprotein is cleaved off by the element-encoded protease to release a Gag protein with an apparent molecular mass of 37 kDa that forms high-density aggregates. The catalytic site of Tnt1-94 protease (D-T-A) as determined by deletion analysis differs from that of retroviruses and of well-characterized retrotransposons (D-T/S-G). The cleaved or uncleaved ORF of Tnt1-94 displays an exogenous RT activity. Over-expression of plant retrotransposons ORFs in E. coli provides a very useful strategy to assay the enzymatic activities of their proteins and to determine their catalytic sites.

Blotting, Western↗
PubMed2001

Effects of human hydrosalpinx fluid on in-vitro murine fertilization.

Patients with hydrosalpinges show a decrease of both fertility and clinical outcome of IVF and embryo transfer treatment. Several reports have demonstrated the negative effects of hydrosalpinx fluid (HSF) on embryo development and implantation. The aim of this study was to determine whether human HSF, collected from infertile patients, might exhibit a deleterious effect on gametes and fertilization using a murine IVF system. Murine gametes were co-incubated during IVF until first cleavage with human HSF diluted to 50% from four patients (HSF1-4). It was demonstrated that HSF affected fertilization, as determined by the count of the 2-cell embryos. Pre-incubation of spermatozoa with HSF during capacitation significantly lowered the percentage of 2-cell embryos (P < 0.05). While HSF1-3 had no significant effect on motility and viability of spermatozoa, HSF4 almost completely affected their survival. In contrast, pre-incubation of ovulated oocytes surrounded by their cumulus cells with HSF before IVF did not impede first cleavage. Taken together, these results suggest that HSF has a cytotoxic effect on spermatozoa and/or impairs the fertilization process, probably by altering capacitation/acrosome reaction and/or ligand(s)-receptor(s) interactions. Hydrosalpinges may be partly associated with sterility through HSF inhibitory effects on fertilization.

Animals↗
PubMed2000

A novel, rapid, and accurate method for detecting microdeletion involving the DAZ gene in infertile men.

OBJECTIVE: To report on a novel, accurate method for detecting microdeletion involving the DAZ gene in infertile men. DESIGN: Retrospective clinical study. SETTING: University Infertility Center of Cochin Hospital, Paris, France. PATIENT(S): Infertile patients (n = 25) consulting our infertility department during 1998. The patient cohort included subjects with nonobstructive azoospermia and oligoasthenospermia. INTERVENTION(S): Blood samples were collected from each subject. MAIN OUTCOME MEASURE(S): DNA analysis using polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). RESULT(S): We used a new molecular genetic strategy to rapidly identify deletions of the Y chromosome that include the DAZ locus. The experiment consists of amplifying simultaneously exon 4 of the DAZ and DAZLA genes with the use of specific primers that are complementary to intronic sequences of these genes. DGGE was used to separate the two PCR products, with good resolution. In infertile men with a microdeletion of the DAZ gene, this method allows amplification of an internal control when a deletion of that portion of the Yq chromosome is observed on a single amplification. CONCLUSION(S): This PCR-DGGE method for detection of DAZ gene deletion is simple and fast and does not require the use of radioactive elements. Compared with the classic PCR approach, this new method allows the amplification of the DAZLA copy to be used as an effective internal control in infertile men with microdeletion of the DAZ locus. This procedure could be particularly useful in screening for the DAZ locus in the diagnostic workup of nonobstructive azoospermia and severe oligoasthenoteratozoospermia.

Adult↗
PubMed1998

Novel acylguanidine containing thrombin inhibitors with reduced basicity at the P1 moiety.

Replacement of the noragmatine group in thrombin inhibitors with a beta-alanyl-guanidine group resulted in a nearly equipotent and more selective compound 8 despite the fact that the pKa of this P1 moiety is five orders of magnitude lower. Further modification resulted in a nonpeptide inhibitor with this beta-alanyl-guanidine group, compound 28. This is an active and selective thrombin inhibitor and in view of its nonpeptide/low basicity structure selected for further pharmacological studies.

Antithrombins↗
PubMed1998

Myelomeningocele and Waardenburg syndrome (type 3) in patients with interstitial deletions of 2q35 and the PAX3 gene: possible digenic inheritance of a neural tube defect.

From a spina bifida clinic we have identified two patients with a syndrome of myelomeningocele and Waardenburg syndrome type 3 (WS3). The patients each possess a single, de novo, interstitial deletion of chromosome 2 (2q35-36.2), including the PAX3 gene. Deletion of PAX3 was confirmed by fluorescence in situ hybridization (FISH). Analysis with PAX3 and flanking microsatellites shows that the deleted interval of chromosome 2 is of paternal origin and is at least 2 and 6 cM in the two patients. Interstitial deletions in this region result in the Waardenburg syndrome (WS1), but have not been associated with neural tube defects (NTDs). Although other etiologies have not been formally excluded, these patients raise the possibility of a digenic etiology of their NTDs via a genetic interaction of the deleted PAX3 gene with a second unidentified locus.

Child, Preschool↗
PubMed1997

The promoter of the tobacco Tnt1 retrotransposon is induced by wounding and by abiotic stress.

The transcription of the tobacco Tnt1 retrotransposon was previously shown to be induced, in tobacco and in heterologous species, by microbial elicitors and by pathogen infections. We report here that the expression of the Tnt1 promoter is also activated in heterologous species such as tomato and Arabidopsis by wounding, freezing and by other abiotic factors known to induce the plant defence response, such as salicylic acid, CuCl2, or oxidative stress. A similar regulation is observed in tobacco for most treatments. The induction of the Tnt1 promoter expression by wounding remains localized around injury points. In CuCl2-treated Arabidopsis plants, the transcription of Tnt1 is correlated with accumulation of the phytoalexin camalexin and with the expression of the EL13 defence gene. The interest of the Tnt1 promoter as a sensitive indicator of the plant defence responses is discussed.

Arabidopsis↗
PubMed1997

Retrovirus-like end processing of the tobacco Tnt1 retrotransposon linear intermediates of replication.

The tobacco retrotransposon Tnt1 can transpose through an RNA intermediate in the heterologous host Arabidopsis thaliana. We report here the identification and characterization of extrachromosomal linear and circular DNA forms of Tnt1 in this heterologous host. Our results demonstrate that Tnt1 linear intermediates possess two extra base pairs at each end compared with Tnt1's integrated forms. Prior to integration into the host genome, the two terminal nucleotides at the 3' end of these linear intermediates are removed, as in the case of the yeast Ty3 retrotransposon and of retroviruses. Our data, together with those from recent studies of Ty3, reinforce the idea that 3' dinucleotide cleavage is not restricted to retroviral integrases and is probably a feature shared by many different retrotransposons' enzymes.

Base Sequence↗
PubMed1997

[The future of male contraception: immunocontraception by preventing gamete interaction].

This paper summarize the main data relevant to the obtention of contraceptive vaccines based on spermatozoa as well as zona pellucida antigens. The development of novel forms of contraception is one way in which this global population problems can be tackled. The sperm as well as the oocyte antigens are studied as possible contraceptive vaccine candidates are the subject of this review.

Contraceptive Agents, Male↗
PubMed1997

The expression of the tobacco Tnt1 retrotransposon is linked to plant defense responses.

Activation of retrotransposons by stresses and external changes is common in all eukaryotic systems, including plants. The transcription of the tobacco Tnt1 retrotransposon was studied in its natural host as well as in Arabidopsis and tomato. It is activated by factors of microbial origin, by external stresses, and by viral, bacterial, and fungal attacks. Tnt1 expression is linked with the biological responses of the plant to the elicitor or to the pathogen attack and in particular with the early steps of the metabolic pathways leading to the activation of plant defense genes. In most cases, the basic features of Tnt1 regulation in tobacco are maintained in tomato and Arabidopsis, but some host-specific regulations were shown. The U3 region of the Tnt1 LTR contains the major cis-acting components of Tnt1 transcriptional activation in association with the plant defense responses. Furthermore, the Tnt1 U3 region, and especially the tandemly repeated BII boxes, contains several sequences similar to well-characterized motifs involved in the activation of several plant defense genes. The possible origin of Tnt1 regulatory sequences as well as the biological implications of Tnt1 activation by pathogen attacks are discussed.

Arabidopsis↗
PubMed1995

RNA-mediated transposition of the tobacco retrotransposon Tnt1 in Arabidopsis thaliana.

The tobacco (Nicotiana tabacum) retrotransposon Tnt1 was introduced into Arabidopsis thaliana. In this heterologous host plant species, Tnt1 undergoes an RNA-mediated transposition and creates a 5 bp duplication at the insertion sites. This is the first report of transposition of a retrotransposon after introduction into a heterologous host species. Tnt1 transposed during in vitro regeneration of transformed A.thaliana, but no transposition event was detected as happening in T2 and T3 generation plants. Newly synthesized copies of Tnt1 can integrate into coding regions of the host DNA. Our results open up the possibility of using Tnt1 as a new tool for insertional mutagenesis and functional analysis of plant genomes, in addition to the strategies of T-DNA and transposon tagging.

Amino Acid Sequence↗