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Biomedical subjects

A Martinez

Publications and source records attributed to A Martinez.

At least 19 recordsLinked to original sources
PubMed1996

A novel entorhinal projection to the rat dentate gyrus: direct innervation of proximal dendrites and cell bodies of granule cells and GABAergic neurons.

Entorhinal fibers to the fascia dentata originating from layer II stellate neurons are known to terminate exclusively in the outer two thirds of the molecular layer, where they innervate distal dendritic portions of dentate neurons. Using anterograde tracing with Phaseolus vulgaris leucoagglutinin, we unraveled a previously unknown entorhinal projection that directly innervates proximal dendritic portions and somata of granule cells and GABAergic neurons. This projection originates from neurons located in entorhinal layers IV-VI of the medial entorhinal area. These fibers enter the outer two thirds of the molecular layer, traverse the inner molecular layer (IML) and granule cell layer, where they form numerous boutons, and finally arborize subjacent to the granule cells. Correlated light and electron microscopy revealed that the boutons formed by these fibers establish asymmetric synapses on dendrites in the IML, on spines and somata of granule cells, and on spineless dendrites subjacent to the granule cell layer. Postembedding immunogold staining indicates that this entorhino-dentate projection is not GABAergic and that it also terminates on GABAergic inhibitory neurons. These data demonstrate that not all entorhino-dentate fibers display a similar high laminar specificity for the outer molecular layer (OML). Although fibers from the superficial layers of the entorhinal cortex terminate exclusively in the OML, entorhinal fibers arising from deeper layers are not confined to laminar boundaries. Finally, the possibility that these supposedly excitatory entorhinal afferents may monosynaptically activate proximal dendrites and somata of dentate neurons needs to be incorporated into contemporary concepts of the hippocampal network.

Animals↗
PubMed1996

Mutational analysis and secondary structure model of the RNP1-like sequence motif of transcription termination factor Rho.

The function of transcription termination factor Rho from Escherichia coli is dependent upon its ability to bind to specific sites on nascent RNA molecules. The roles of 19 individual amino acid residues (Ile49 to Ser67) in and near a phylogenetically conserved sequence segment of Rho that is similar to the RNP1 motif found in many RNA-binding proteins were examined by testing the phenotypic consequences of mutational changes that were introduced into rho by a random-sequence cassette mutagenesis procedure. The tests of each mutant included the ability of the cells to survive at 42 degrees C in the absence of wild-type rho, the efficiency of termination at a Rho-dependent terminator (lambdatR1) in vivo, the relative level of expression of the mutant protein, and the ability of some of the mutant proteins to bind RNA. The results revealed that residues in the RNP1-like sequence of DGFGFLR (residues 60 to 66) were more important than residues 49 to 59 for termination function and RNA binding, and identified three residues that were particularly sensitive to mutation: Asp60, Phe62 and Arg66. The properties of the mutants are consistent with a secondary structure model, derived from phylogenetic analysis, that has the RNP1-like sequence on one of the three beta-strands of an antiparallel beta-sheet with Asp60 and Gly61 in a turn and the side-chains of Phe62, Phe64 and Arg66 accessible on the same face of the beta-structure for interaction with RNA.

Amino Acid Sequence↗
PubMed1996

Residues in the RNP1-like sequence motif of Rho protein are involved in RNA-binding affinity and discrimination.

The termination of transcription in Escherichia coli by action of Rho factor is dependent on the ability of this homohexameric protein to make productive interactions with the nascent RNA molecule to be terminated. The roles of two residues in a phylogenetically conserved sequence motif in the RNA-binding domain of Rho, Asp60 and Phe62, were analyzed by studies of the biochemical properties of pure mutant proteins. F62S Rho had greatly reduced affinity for lambda cro RNA, very poor ability to terminate transcription in vitro by itself and only partial termination activity (at a level consistent with its in vivo defect) in the presence of NusG. D60G Rho had a high affinity for lambda cro RNA but a much lower ability to discriminate against RNA molecules lacking cis-acting Rho-utilization sequences, and a reduced efficiency of termination that was not improved by NusG. These results indicate a major role for Phe62 in stabilizing the binding of Rho to RNA through hydrophobic interactions, while Asp60 provides an electrostatic repulsive force that allows a rapid dissociation of non-productive complexes with RNA.

Adenosine Triphosphatases↗
PubMed1996

Complete analysis of the presenilin 1 gene in early onset Alzheimer's disease.

The presenilin 1 gene has recently been identified as the locus on chromosome 14 which is responsible for a large proportion of early onset, autosomal dominantly inherited Alzheimer's disease (AD). We have elucidated the intron/exon structure of the gene and designed intronic primers to enable direct sequencing of the entire coding region (10 exons) of the presenilin gene in a large number of families. This strategy has enabled us to find a further two novel mutations in the gene. We discuss the distribution of mutations and the proportions of autosomal dominant AD with a mean age of onset below 60 years caused by mutations in this gene.

Alzheimer Disease↗
PubMed1996

Drug delivery systems: water soluble taxol 2'-poly(ethylene glycol) ester prodrugs-design and in vivo effectiveness.

Water soluble 2'-taxol poly(ethylene glycol) (PEG) esters have been synthesized and shown to function in vitro as prodrugs. However, in vivo experiments clearly establish that in order for these prodrugs to behave in a predictable fashion, the molecular weight of PEG must be of such magnitude so as to maintain a t1/2(circulation) > t1/2(hydrolysis). When PEG derivatives of molecular weight approximately 40 kDa were employed with paclitaxel, ca. 4% by weight of paclitaxel was carried by the water soluble prodrug form, and equivalent in vivo toxicity and increased life expectancy in the P388-treated mouse was observed. An effective method for prescreening prodrugs was found to be the acute murine lethality, which reflects the equivalency of the solubilized transport form and the native drug.

Animals↗
PubMed1996

Immunochemical characterization and transacting properties of upstream stimulatory factor isoforms.

The ubiquitous upstream stimulatory factor (USF) transcription factors encoded by two distinct genes (USF1 and USF2) exist under the form of various dimers able to bind E-boxes. We report the molecular cloning and functional characterization of USF2 isoforms, corresponding to a 44-kDa subunit, USF2a, and a new 38-kDa subunit, USF2b, generated by differential splicing. Using specific anti-USF antibodies, we define the different binding complexes in various nuclear extracts. In vivo, the USF1/USF2a heterodimer represents over 66% of the USF binding activity whereas the USF1 and USF2a homodimers represent less than 10%, which strongly suggests an in vivo preferential association in heterodimers. In particular, an USF1/USF2b heterodimer accounted for almost 15% of the USF species in some cells. The preferential heterodimerization of USF subunits was reproduced ex vivo, while the in vitro association of cotranslated subunits, or recombinant USF proteins, appeared to be random. In transiently transfected HeLa or hepatoma cells, USF2a and USF1 homodimers transactivated a minimal promoter with similar efficiency, whereas USF2b, which lacks an internal 67-amino acid domain, was a poor transactivator. Additionally, USF2b was an efficient as USF1 and USF2a homodimers in transactivating the liver-specific pyruvate kinase gene promoter.

Amino Acid Sequence↗
PubMed1996

Phosphorylation of recombinant human phenylalanine hydroxylase: effect on catalytic activity, substrate activation and protection against non-specific cleavage of the fusion protein by restriction protease.

The phosphorylation of human phenylalanine hydroxylase by cyclic AMP-dependent protein kinase was studied using recombinant enzyme expressed as a fusion protein in the pMAL system of Escherichia coli. Using the target sequence of the restriction protease enterokinase (Asp4-Lys) as the linker peptide, 100% full-length human phenylalanine hydroxylase was obtained on protease cleavage. The fusion protein and human phenylalanine hydroxylase were both phosphorylated at Ser-16 with a stoichiometry of 1 mol of Pi/mol of subunit. The rate of phosphorylation of human phenylalanine hydroxylase was inhibited about 40% by the cofactor tetrahydrobiopterin, and this inhibition was completely prevented by the simultaneous presence of L-phenylalanine (i.e. at turnover conditions). Phosphorylated enzyme revealed a 1.6-fold higher specific activity than the non-phosphorylated enzyme form, and it also required a lower concentration of L-Phe for substrate activation. Pre-incubation with L-Phe increased the specific activity of phenylalanine hydroxylase 2- to 4-fold, L-Phe acting with positive cooperativity. Thus, the basic catalytic and regulatory properties of recombinant human phenylalanine hydroxylase, as well as those observed for the enzyme as a fusion protein, are similar to those previously reported for the rat liver enzyme. When the target sequence of the restriction protease factor Xa (Ile-Glu-Gly-Arg) was used as the linker between maltose-binding protein and human phenylalanine hydroxylase, cleavage of the fusion protein gave a mixture of full-length hydroxylase and a truncated form of the enzyme lacking the 13 N-terminal residues. Interestingly, phosphorylation of the fusion protein, before exposure to factor Xa, almost completely protected against secondary cleavage by this restriction protease at Arg-13 of phenylalanine hydroxylase.

Amino Acid Sequence↗
PubMed1996

Detection of anticentromere antibodies using recombinant human CENP-A protein.

OBJECTIVE: To evaluate CENP-A reactivity with anticentromere antibodies (ACA) using recombinant protein (rCENP-A). METHODS: Human CENP-A antigen was overexpressed in insect cells using the baculovirus system. We tested for ACA activity against the full-length recombinant polypeptide by immunoblot and by enzyme-linked immunosorbent assay (ELISA). RESULTS: Of the ACA+ sera studied (n = 38), 95% were positive when tested against the rCENP-A in the ELISA system. Of the ACA- sera (n = 100), only 2% gave false-positive results in the assay. There was good correlation between the recombinant and bona fide antigens in assaying for ACA reactivity. CONCLUSION: CENP-A is a significant ACA target. The availability of the rCENP-A assay is a valuable adjunct to the previously described rCENP-B assay in analyses of the clinical significance of ACA.

Animals↗
PubMed1996

Cocaine is associated with intrauterine fetal death in women with suspected preterm labor.

The objectives of this study were to determine the rate of recent cocaine use in a metropolitan population of predominantly Hispanic and African-American women with suspected preterm labor and to evaluate the impact of recent cocaine use on intrapartum complications in this population. Urine toxicology screens were prospectively obtained on 102 women with suspected preterm labor. The urine screen did not influence management decisions. Gestational age at delivery, birthweight, and intrapartum complications were compared using Student's t-test, chi-square analysis, or Fisher's exact test. The rate of positive urine drug screens for cocaine was 12.7%. Women with positive toxicology were older (27.8 +/- 5.7 versus 22.1 +/- 4.8 years, p = 0.002) and of higher parity (2 [1 to 7] versus 1 [0 to 7], p = 0.0). Women with positive toxicology were more likely to be black (92.3%) than Hispanic (7.7% [p = 0.0004]). They had more advanced cervical dilation at presentation (3 cm [0 to 6] versus 1 cm [0 to 8], p = 0.008), were more likely to be admitted (85% versus 32%, p < 0.0001), but less likely to receive tocolysis due to advanced dilation or pregnancy complication (36% versus 79%, p = 0.0002). There was no difference in gestational age or birthweight at delivery. There was a significantly higher intrauterine fetal death rate in the cocaine positive group (18.2% versus 0%, p = 0.02). These data suggest that recent cocaine use among women with suspected preterm labor is common in only some segments of an urban population and significantly impacts pregnancy outcome.

Adult↗
PubMed1996

Preschoolers of dysphoric mothers.

Dysphoric mothers rated their preschool children as having more internalizing and externalizing behavior problems than children of nondysphoric mothers. Observers rated the dysphoric mothers as having more negative affect during play interactions, although their children's affect was not rated more negatively. The dysphoric mother-infant dyads were also rated as having a poorer quality interaction. These data suggest that mothers' chronic dysphoria (75% were chronically dysphoric) has a negative impact on the mothers' perceptions of their children as well as the mothers' and children's interaction behavior.

Adult↗
PubMed1996

Efficacy of epiroprim (Ro11-8958), a new dihydrofolate reductase inhibitor, in the treatment of acute Toxoplasma infection in mice.

Toxoplasma gondii is a major cause of focal encephalitis in patients with acquired immunodeficiency syndrome. Epiroprim, an inhibitor of dihydrofolate reductase, was evaluated in vitro and in a mouse model of acute infection for activity against T. gondii. The 50% inhibitory concentration (IC50) of epiroprim for T. gondii dihydrofolate reductase was 0.9 micromole, similar to that of pyrimethamine, but epiroprim was 650-fold more selective than pyrimethamine for T. gondii compared with human dihydrofolate reductase. While intraperitoneally administered epiroprim (300 mg/kg/day for 14 days) alone was ineffective in mice acutely infected with the RH strain of T. gondii, 100% survival was seen when it was combined with orally administered sulfadiazine (375 mg/kg/day), which alone was also ineffective. Increases in survival were seen in combination with doses of sulfadiazine as low as 0.375 mg/kg/day. Orally administered epiroprim combined with dapsone also prolonged survival. Thus epiroprim is an active and potentially less toxic alternative pyrimethamine for the treatment of toxoplasmosis.

Acute Disease↗
PubMed1996

Effects of continuous low-dose-rate brachytherapy on the rectum of the rat.

The dose-limiting factor in essentially all curative radiotherapy is damage to normal tissue. In spite of this, our understanding of radiation-induced damage to normal tissue leaves much to be desired. Damage to the rectum is often observed after clinical brachytherapy of pelvic malignancies. A model in which the rectum of the rat is irradiated with a uniform and reproducible dose of brachytherapy irradiation was developed. This system consists of an intracavitary applicator, which is used in conjunction with methods that reduce fecal flow, a jacket that restrains rat movement and a lead-shielded chamber to contain rats during low-dose-rate brachytherapy. Irradiation was applied in 48-h intervals separated by 48-h breaks during which the applicator was removed. Methods to analyze the sequelae of brachytherapy irradiation of the rectum were also developed. The total dose of 0.75 Gy/h continuous low-dose-rate brachytherapy required to produce obstruction in the rat rectum has been measured. The ED50 was 70.6 +/- 4.2 Gy. The length of time between irradiation and obstruction was also correlated with total dose. Other effects on the rectum that were related to dose were diarrhea and rectovaginal fistula. This irradiation system can produce uniform and reliable brachytherapy doses to the rat rectum. The late effects in normal tissues observed in this model are similar to those observed in humans after irradiation of the rectum. The model should be appropriate for analyzing relative changes in the rectum resulting from different dose rates and fractionation schemes relevant to brachytherapy.

Animals↗
PubMed1996

[Results of a randomized study comparing combination of navelbine-cisplatin to combination of vindesine-cisplatin and to navelbine alone in 612 patients with inoperable non-small cell lung cancer].

The combination of vindesine and cisplatin is considered a reference regimen in advanced NSCLC which has yielded a significant improvement in the duration of survival. A phase II study of a new semi-synthetic vinca alkaloid, Navelbine, reported an unusually high 29% response rate in stage III-IV NSCLC and a phase I-II study established the feasibility of the combination of Navelbine and cisplatin. We, therefore, designed a prospective randomized trial to compare Navelbine and cisplatin (NVB-P) to vindesine and cisplatin (VDS-P) and to evaluate whether the best of these regimens affords a survival benefit compared to Navelbine alone (NVB), an outpatient regimen. Forty-five centers included 612 patients in this study: 206 in NVB-P, 200 in VDS-P and 206 in NVB. Navelbine was given at a dose of 30 mg/m2 weekly, cisplatin at 120 mg/m2 on day 1, day 29 and then every 6 weeks and vindesine at 3 mg/m2 weekly for 6 weeks and then every other week. Treatment was continued until progression or toxicity. Patients' characteristics were similar in the three groups with 59% of patients presenting with metastatic disease. An objective response rate was observed in 30% of patients in NVB-P versus 19% in VDS-P (P = .02) and 14% in NVB (P < .001). The median duration of survival was 40 weeks in NVB-P compared to 32 weeks in VDS-P and 31 weeks in NVB. The comparison of survival between the three groups demonstrated an advantage for NVB-P compared to VDS-P (P = .04) and NVB (P = .02). Neutropenia was significantly higher in the NVB-P group (P < .001) and neurotoxicity more frequent with VDS-P (P < .004). Since our results have demonstrated that NVB-P yields a longer survival duration and a higher response rate than VDS-P or NVB alone, with acceptable toxicity, this combination should be considered a reference regimen in advanced NSCLC.

Adult↗
PubMed1996

[Treatment of inoperable non-small cell bronchogenic carcinoma with a combination of cisplatin and vinorelbine--preliminary evaluation].

The optimal therapeutic approach to patients with inoperable non-small-cell carcinoma is still a matter of discussion. The reason is that chemotherapy improves the quality of life only in some patients. It prolongs their life only by several weeks. In recent years in this indication a new cytostatic is tested--vinorelbine which when used in monotherapy achieves a therapeutic response in 16--30%. In clinical trials of phase 2 a combination of vinorelbine and cisplatinum was most effective and therefore it was selected for the third phase of clinical trials. In the Czech Republic a clinical investigation was made with the objective to verify published data on the success of treatment, evaluate undesirable effects and consider whether it is suitable for routine use. Cisplatinum (Platidiam Lachema) was administered--80 mg/m2 on the first day, vinorelbine (Navelbine Pierre Fabre)--30 mg/m2 on the first and eighth day. The cycle was repeated on the 22nd day. All patients were treated for 12 weeks. Then followed the first evaluation and treatment was continued only in patients with regression or stabilization of the disease. In the group of 126 patients in 44 (35%) partial and in 3 (2.3%) complete therapeutic responses were obtained. In 35 (27%) the disease was evaluated during treatment as stabilized, in 38 (30%) of the patients the disease progressed despite treatment. The tolerance of treatment was, when effective antiemetic treatment was used (ondansetrone or granisetrone), relatively satisfactory.

Antineoplastic Agents↗
PubMed1996

Primary graft failure after heart transplantation. Successful recovery with pneumatic biventricular assistance.

A 41-year-old male underwent orthotopic heart transplantation complicated by intraoperative acute allograft failure. The patient required immediate placement of a pneumatic biventricular assist device which was kept for 49 days until graft recovery resulted in successful explantation of the device. The patient was discharged from hospital on postoperative day 112. Management of primary cardiac allograft failure with mechanical ventricular assistance is discussed.

Adult↗
PubMed1995

Neuropeptide Y is a vasoconstrictor and adrenergic modulator in the hamster microcirculation by acting on neuropeptide Y1 and Y2 receptors.

The microvascular effects of neuropeptide Y, and two analogs with preferential affinity for different neuropeptide Y receptor subtypes, were assessed by intravital microscopy on the hamster cheek pouch. The interaction of neuropeptide Y and its analogs with noradrenaline was also studied. Superfusion with 0.1-300 nM neuropeptide Y caused a concentration-dependent reduction in microvascular conductance that was paralleled by reductions in arteriolar and venular diameters. These effects of neuropeptide Y were equipotent with noradrenaline, but slower to develop and longer-lasting than that of noradrenaline. Neuropeptide Y did not affect permeability to macromolecules, as measured by extravasation of fluorescent dextran. The neuropeptide Y Y1 receptor agonist, [Leu31,Pro34]neuropeptide Y, mimicked neuropeptide Y with similar potency but shorter duration, while neuropeptide Y-(13-36), a neuropeptide Y Y2 receptor agonist, was at least 10-fold less potent than neuropeptide Y to induce a delayed and prolonged reduction in microvascular conductance. The joint superfusion of 1 nM neuropeptide Y plus 0.1 mu M noradrenaline did not cause synergism, nor even summation of effects, but reduced the contractile effect of noradrenaline. No synergism was observed after a 10 min priming with 1 nM neuropeptide Y, followed by its joint application with 0.1 mu M noradrenaline, but a significant vasodilation and hyperemia ensued upon stopping noradrenaline application. Priming with 1 nM [Leu31,Pro34]neuropeptide Y prolonged noradrenaline vasoconstriction without evidence of hyperemia. In contrast, priming with 1 nM neuropeptide Y-(13-36) significantly antagonized noradrenaline vasoconstriction. These findings indicate that both neuropeptide Y receptor subtypes are present in arterioles and venules of the hamster, and suggest that their activation with neuropeptide Y induces a rapid (Y1 receptor subtype activation) and a delayed (Y2 receptor subtype activation) vasocontractile response. The interaction with noradrenaline is complex, without evidence for synergism, but neuropeptide Y Y2 receptor activation seems to antagonize noradrenaline and/or to facilitate auto-regulatory vasodilation after the catecholamine-induced vasoconstriction.

Animals↗
PubMed1995

Dosimetric evaluation of the conformation of the multileaf collimator to irregularly shaped fields.

PURPOSE: The goal of this study was to evaluate the dosimetric characteristics of geometric MLC prescription strategies and compare them to those of conventional shielding block. METHODS AND MATERIALS: Circular fields, square fields, and 12 irregular fields for patients with cancer of the head and neck, lung, and pelvis were included in this study. All fields were shaped using the MLC and conventional blocks. A geometric criterion was defined as the amount of area discrepancy between the MLC and the prescription outline. The "least area discrepancy" (LAD) of the MLC conformation was searched by selecting the collimator angle, meanwhile keeping a preselected position along the width of the leaf into the prescribed field. Five LAD conventions were studied. These included the LAD-0, LAD-1/3, LAD-1/2, and LAD-2/3 that inserted the leaves at the 0, 1/3, 1/2, and 2/3 of the leaf end into the prescription field, respectively. In addition, the LAD optimization was applied to the transecting (TRN) approach for leaf conformation that prescribed an equal area of overblocking and underblocking under each leaf. Film dosimetry was performed in a 20 cm polystyrene phantom at 10 cm depth 100 cm from source to axis distance (SAD) for both 6 and 18 MV photons with each of the above MLC conformations and conventional blocks. The field penumbra width, defined as the mean of the separation between the 20% and 80% isodose lines along the normal of the prescription field edge, was calculated using both the MLC and conventional block film dosimetry and compared. In a similar way, the d20 is defined as the mean separation between the 20% isodose line and the prescription field edge, and the d80 is defined as the mean separation between the 80% isodose line and the prescription field edge. RESULTS: The field penumbra width for all MLC conventions was approximately 2 mm larger than that of the conventional block. However, there was a larger variation of the separation distribution in the penumbra region of the irregular fields for the MLC, which had a standard deviation of 1 mm (a factor of 5 larger than the conventional block). The dosimetry for the circular fields showed that the LAD-TRN, LAD-1/2, and LAD-1/3 approximated the conventional blocking well in terms of d20 and d80; however, no single convention produced the best conformation for both measures. The dosimetric result of the patient treatment fields was similar for all sites. The LAD-1/3, LAD-1/2, and LAD-TRN strategies conformed to within 1 to 1.5 mm of the d80 of the conventional block for both 6 MV and 18 MV, respectively. The LAD-1/2 and LAD-TRN conformations were virtually identical, although it is proven analytically that the LAD-1/2 convention has the least overall area discrepancy of all conventions. CONCLUSIONS: The five MLC conformation conventions resulted in similar dosimetric penumbrae for all field shapes studied. The LAD-1/3, LAD-TRN, and LAD-1/2 produced the more favorable approximation to conventional block. The field penumbra width, although useful for evaluating irregular field shapes, could not describe the large local variations in the penumbra along the field edge for the MLC. These local variations could be of clinical concern when they appear near vital organs. However, the variation in a local region can potentially be reduced by minimizing the jaggedness of the leaf steps in that local region. The dosimetric results were useful as guidelines for the clinicians in the evaluation and adjustment of MLC leaf positions.

Head and Neck Neoplasms↗