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Biomedical subjects

M Jacobs

Publications and source records attributed to M Jacobs.

At least 109 records · Page 6Linked to original sources
PubMed1995

A dinucleotide mutation in dihydrodipicolinate synthase of Nicotiana sylvestris leads to lysine overproduction.

By applying a mutagenesis/selection procedure to obtain resistance to a lysine analog, S-(2-aminoethyl)L-cysteine (AEC), a lysine overproducing mutant in Nicotiana sylvestris was isolated. Amino acid analyses performed throughout plant development and of different organs of the N. sylvestris RAEC-1 mutant, revealed a developmental-dependent accumulation of free lysine. Lysine biosynthesis in the RAEC-1 mutant was enhanced due to a lysine feedback-desensitized dihydrodipicolinate synthase (DHDPS). Several molecular approaches were undertaken to identify the nucleotide change in the dhdps-r1 gene, the mutated gene coding for the lysine-desensitized enzyme. The enzyme was purified from wild-type plants for amino end microsequencing and 10 amino acids were identified. Using dicotyledon dhdps probes, a genomic fragment was cloned from an enriched library of DNA from the homozygote RAEC-1 mutant plant. A dhdps cDNA, putatively full-length, was isolated from a tobacco cDNA library. Nucleotide sequence analyses confirmed the presence of the previously identified amino end preceded by a chloroplast transit peptide sequence. Nucleotide sequence comparisons, enzymatic and immunological analyses revealed that the tobacco cDNA corresponds to a normal type of DHDPS, lysine feedback-regulated, and the genomic fragment to the mutated DHDPS, insensitive to lysine inhibition. Functional complementation of a DHDPS-deficient Escherichia coli strain was used as an expression system. Reconstruction between the cDNA and genomic fragment led to the production of a cDNA producing an insensitive form of DHDPS. Amino acid sequence comparisons pointed out, at position 104 from the first amino acid of the mature protein, the substitution of Asn to Ileu which corresponds to a dinucleotide mutation. This change is unique to the dhdps-r1 gene when compared with the wild-type sequence. The identification of the nucleotide and amino acid change of the lysine-desensitized DHDPS from RAEC-1 plant opens new perspectives for the improvement of the nutritional value of crops and possibly to develop a new plant selectable marker.

Amino Acid Sequence↗
PubMed1995

A model to predict the histopathology of human stroke using diffusion and T2-weighted magnetic resonance imaging.

BACKGROUND AND PURPOSE: We sought to identify MRI measures that have high probability in a short acquisition time to predict, at early time points after onset of ischemia, the eventual development of cerebral infarction in clinical patients who suffer occlusion of a cerebral artery. METHODS: We developed an MR tissue signature model based on experimentally derived relationships of the apparent diffusion coefficient of water (ADCw) and T2 to ischemic brain tissue histopathology. In eight stroke patients we measured ADCw and T2 intensity using diffusion-weighted echo-planar imaging (DW-EPI). Tissue signature regions were defined, and theme maps of the ischemic focus at subacute time points after stroke onset were generated. RESULTS: Five MR signatures were identified in human stroke foci: two that may predict either cell recovery or progression to necrosis, one that may mark the transition to cell necrosis, and two that may be markers of established cell necrosis. CONCLUSIONS: An MR tissue signature model of ischemic histopathology using ADCw and T2 can now be tested for its potential to predict reversible and identify irreversible cellular damage in human ischemic brain regions.

Aged↗
PubMed1995

Substance use among schizophrenic outpatients: prevalence, course, and relation to functional status.

The prevalence and course of alcohol and drug use were examined in a longitudinal, retrospective study of 100 schizophrenic outpatients. During the 18 month study period, problem substance use (abuse and dependence) was not associated with differential attrition from outpatient treatment. Thirty to forty percent of subjects were using drugs or alcohol during any evaluation period. The overall level of substance use and problem use of alcohol, marijuana, and other drugs remained stable, while problem use of cocaine and multiple substances increased over time. Problem substance use was associated with lower functional status and the detrimental effect of problem substance use appeared to increase with time. These findings underscore the need to address substance use problems in the context of outpatient schizophrenia treatment.

Adult↗
PubMed1995

Combined modalities in the treatment of head and neck cancers.

The higher the T and N stages at diagnosis of head and neck cancer, the lower the proportion of patients who achieve complete, durable local control and the lower the survival. These cancers and their treatments often produce considerable anatomic distortion, affecting function, nutritional status, and appearance. New treatment approaches for locally and regionally advanced head and neck cancers are thus needed to improve survival, quality of life, or both. Combined-modality approaches show promise. Induction chemotherapy and subsequent radiotherapy produce results equivalent to aggressive surgery but allow for better organ function and speech. Induction chemotherapy and radiotherapy are superior to radiotherapy alone. Concurrent chemotherapy and radiotherapy may produce additive or synergistic interactions but increase toxicities. Some studies suggest that concurrent chemotherapy and radiotherapy significantly improves survival over radiotherapy alone in regionally advanced disease. Drug selection criteria have included enhancement of radiation cytotoxicity, effect on cellular kinetics, and, possibly, single-agent antitumor activity. The platinum compounds are of interest, especially in combination with other chemotherapy agents, like 5-fluorouracil and paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ). Concurrent carboplatin and radiotherapy produced a 77-week duration of survival in responders in a University of Maryland Cancer Center study. A study of concurrent carboplatin/bleomycin/radiotherapy had to be halted because of severe bleomycin-induced mucositis. The results in this small group suggest that attenuating mucositis would be desirable. In a subsequent trial, paclitaxel, which shows considerable activity against head and neck cancers, was substituted for bleomycin. Data from the seven patients accrued thus far are too immature to define response. The study continues to accrue patients.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1994

Membrane binding properties of the factor IX gamma-carboxyglutamic acid-rich domain prepared by chemical synthesis.

The fully gamma-carboxylated peptides based upon the complete and truncated Gla/aromatic amino acid stack domains of human Factor IX were prepared by solid phase peptide synthesis using Fmoc (N-(9-fluorenyl)methoxycarbonyl) chemistry. A 47-residue peptide Factor IX-(1-47) and a 42-residue peptide Factor IX-(1-42), both containing 12 residues of L-gamma-carboxyglutamic acid, were purified by high performance liquid chromatography and oxidized to form the disulfide bond. Quantitative gamma-carboxyglutamic acid analysis of Factor IX-(1-47) and Factor IX-(1-42) indicated the presence of 12.1 and 11.2 gamma-carboxyglutamic acid residues/mol of peptide, respectively; no glutamic acid was detected. As monitored by fluorescence quenching, calcium ions induced the prototypical conformational transition in Factor IX-(1-47), but not in Factor IX-(1-42), that is observed with Factor IX. Half-maximal quenching of the intrinsic fluorescence of Factor IX-(1-47) was observed at Ca(II) concentrations of about 50 microM. Factor IX-(1-47) bound to the conformation-specific antibodies, anti-Factor IX:Mg(II) and anti-Factor IX:Ca(II)-specific in the presence of metal ions. Factor IX-(1-47) bound to phospholipid membranes, as monitored by energy transfer from intrinsic fluorophores to dansyl (5-dimethylaminonaphthalene-1-sulfonyl)-phosphatidylethanolamine incorporated into a lipid bilayer composed of phosphatidylserine:phosphatidylcholine. In contrast, Factor IX-(1-42) bound poorly to these same membranes. Factor IX-(1-47) did not inhibit Factor XIa activation of Factor IX but did inhibit the activation of Factor X by Factor IXa bound to Factor VIII in the presence of calcium ions and phospholipid. These results show that phospholipid membrane binding is a property of the Gla/aromatic amino acid stack domain and that the Factor IX-(1-47) peptide, prepared by chemical synthesis, preserves the membrane binding properties and the metal-induced conformational transitions observed in native Factor IX. These results indicate that Factor IX-(1-47) but not Factor IX-(1-42) is a suitable model for structural studies of Factor IX-membrane interaction.

1-Carboxyglutamic Acid↗
PubMed1994

Sequential psychomotor skills development in laparoscopic colon surgery.

OBJECTIVES: To quantify the complexity of each of three skills used in laparoscopic colon surgery and to quantify the relative complexity of seven laparoscopic colon procedures on a graduated complexity scale. DESIGN: Five surgeons used a scale of 1 through 6 to measure the relative complexity of three laparoscopic skills (intracorporeal mobilization, intracorporeal devascularization, and intracorporeal anastomosis) to assess the relative difficulty of seven laparoscopic procedures (right colon resection, sigmoid colon resection, low anterior resection, Hartmann's procedure, left colon resection, abdominoperineal resection, and transverse colon resection) using detailed evaluation of their first 100 laparoscopic colon resections. SETTING: Three private community hospitals. MAIN OUTCOME MEASURES: The complexities of intracorporeal mobilization, intracorporeal devascularization, and intracoporeal anastomosis were recorded for seven laparoscopic colon procedures. RESULTS: The least complex procedure was right colon resection, followed in increasing complexity by sigmoid colon, Hartmann's procedure, low anterior resection, abdominoperineal resection, left colon resection, and transverse colon resection. The addition of each laparoscopic skill increased the complexity during each procedure. All three skills were not required for every procedure. CONCLUSIONS: Since all procedures do not require all three skills, skills can be learned sequentially if patients are chosen judiciously. A sequence of laparoscopic procedures performed by surgeons is recommended. The relative complexities for each procedure suggest an outline (map) for surgeons to use during laparoscopic colon surgery.

Abdomen↗
PubMed1994

Alteration in vascular reactivity in isolated aortic rings from portal vein-constricted rats.

It has been suggested that increased production of nitric oxide by an inducible nitric oxide synthase isoenzyme is important in the pathogenesis of the vascular abnormalities seen in human beings and animals with portal hypertension. We investigated this hypothesis by studying the in vitro vascular reactivity of isolated aortic rings from portal vein-constricted and sham-operated rats. Aortic rings from portal vein-constricted rats exhibited significantly impaired contractility to phenylephrine and potassium chloride compared with control rats. Preincubation with the nitric oxide synthase inhibitor nitro-L-arginine methyl ester significantly increased contractility to phenylephrine and potassium chloride in both portal-hypertensive and control tissues, with greater effect in the portal-hypertensive rings. Despite nitro-L-arginine methyl ester, maximal contractions were still significantly smaller in the portal-hypertensive tissues. Vascular relaxation evoked by acetylcholine, but not by the endothelium-independent vasodilator glyceryl trinitrate, was significantly impaired in the portal-hypertensive group. Our results demonstrate significant impairment in vascular function in aortic rings in this model of portal hypertension. The addition of a nitric oxide synthase inhibitor partly corrected these changes, suggesting that although nitric oxide is likely an important mediator, other factors may also be involved in the pathogenesis of these alterations in vascular function.

Acetylcholine↗
PubMed1994

Molecular analysis of the aspartate kinase-homoserine dehydrogenase gene from Arabidopsis thaliana.

The gene encoding Arabidopsis thaliana aspartate kinase (ATP:L-aspartate 4-phosphotransferase, EC 2.7.2.4) was isolated from genomic DNA libraries using the carrot ak-hsdh gene as the hybridizing probe. Two genomic libraries from different A. thaliana races were screened independently with the ak probe and the hsdh probe. Nucleotide sequences of the A. thaliana overlapping clones were determined and encompassed 2 kb upstream of the coding region and 300 bp downstream. The corresponding cDNA was isolated from a cDNA library made from poly(A)(+)-mRNA extracted from cell suspension cultures. Sequence comparison between the Arabidopsis gene product and an AK-HSDH bifunctional enzyme from carrot and from the Escherichia coli thrA and metL genes shows 80%, 37.5% and 31.4% amino acid sequence identity, respectively. The A. thaliana ak-hsdh gene is proposed to be the plant thrA homologue coding for the AK isozyme feedback inhibited by threonine. The gene is present in A. thaliana in single copy and functional as evidenced by hybridization analyses. The apoprotein-coding region is interrupted by 15 introns ranging from 78 to 134 bp. An upstream chloroplast-targeting sequence with low sequence similarity with the carrot transit peptide was identified. A signal sequence is proposed starting from a functional ATG initiation codon to the first exon of the apoprotein. Two additional introns were identified: one in the 5' non-coding leader sequence and the other in the putative chloroplast targeting sequence. 5' sequence analysis revealed the presence of several possible promoter elements as well as conserved regulatory motifs. Among these, an Opaque2 and a yeast GCN4-like recognition element might be relevant for such a gene coding for an enzyme limiting the carbon-flux entry to the biosynthesis of several essential amino acids. 3' sequence analysis showed the occurrence of two polyadenylation signals upstream of the polyadenylation site. This work is the first report of the molecular cloning of a plant ak-hsdh genomic sequence. It describes a promoter element that may bring new insights to the regulation of the biosynthesis of the aspartate family of amino acids.

Amino Acid Sequence↗
PubMed1994

Isolation of a poplar and an Arabidopsis thaliana dihydrodipicolinate synthase cDNA clone.

A poplar DHDPS cDNA clone has been isolated by functional rescue of the dapA-deficient AT997 mutant of Escherichia coli. By sequence comparison between the poplar and maize DHDPS cDNAs, two oligonucleotides were designed to perform polymerase chain reaction (PCR) on Arabidopsis thaliana genomic DNA. The PCR fragment was subsequently used to isolate an Arabidopsis DHDPS genomic and cDNA clone.

Amino Acid Sequence↗
PubMed1994

Laparoscopic-assisted sigmoid colectomy and low anterior resection.

Laparoscopic-assisted sigmoid colectomy or low anterior resection was undertaken in 30 selected patients. The median age was 51 (range, 30-85) years. Eight patients had previous abdominal surgery: four hysterectomies, two appendectomies, and two cholecystectomies. There was no mortality. Complications occurred in three patients. One patient developed a wound infection, there was one iliac artery injury, and one postoperative bleed, which did not require transfusion. Eighteen patients were operated on for primary cancer of the colon and 12 patients for benign disease. Technical aspects are described in detail. The average hospital stay was four days with most patients receiving oral analgesics by the second postoperative day. Laparoscopic colon resection can be an alternative to open surgery.

Colectomy↗
PubMed1994

Altered prostacyclin synthesis by aortae from hepatic portal vein-constricted rats: evidence for effects on protein kinase C and calcium.

To investigate the mechanisms causing reduced systemic vascular reactivity to vasoconstrictor agents in portal hypertension, we studied receptor- and signal-transduction-linked PGI2 (a vasodilator) synthesis (measured as 6-oxo-PGF1 alpha by radioimmunoassay) in the aorta (ex vivo) of portal vein-constricted rats. PGI2 synthesis was stimulated by adrenaline (via heterogeneous alpha-adrenoceptors), phorbol ester dibutyrate (a protein kinase C activator), arachidonic acid (the substrate for PGI2 synthesis) and the Ca2+ ionophore A23187 (A23187) and thapsigargin (both of which elevate intracellular Ca2+, which in turn elicits the release of arachidonic acid). The release of PGI2 by the aortae of rats with portal hypertension in comparison to sham-operated controls was: 1) enhanced in response to adrenaline, 2) reduced in response to phorbol ester dibutyrate, A23187 and thapsigargin and 3) unchanged in response to arichidonic acid. These data indicate that in aortae from rats with experimental portal hypertension: i) there are no changes in the enzymes involved in PGI2 synthesis (cyclooxygenase, PGI2 synthase), ii) there is a specific increase in adrenoceptor-linked PGI2 synthesis in aortae which may contribute to arterial vasodilation in this experimental model and 3) the diminished response of PGI2 synthesis to A23187, phorbol ester dibutyrate and thapsigargin indicates that there is a generalised attenuation of protein kinase C activator activity and of Ca2+. Since Ca2+ is a key component of excitation-contraction coupling and protein kinase C activator has been implicated in mediating this event, attenuation of these systems may also explain, at least in part, the known reduced vasoactivity of aortae from rats with portal hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Differential interactions of promoter elements in stress responses of the Arabidopsis Adh gene.

The Adh (alcohol dehydrogenase, EC 1.1.1.1.) gene from Arabidopsis thaliana (L.) Heynh. can be induced by dehydration and cold, as well as by hypoxia. A 1-kb promoter fragment (CADH: -964 to +53) is sufficient to confer the stress induction and tissue-specific developmental expression characteristics of the Adh gene to a beta-glucuronidase reporter gene. Deletion mapping of the 5' end and site-specific mutagenesis identified four regions of the promoter essential for expression under the three stress conditions. Some sequence elements are important for response to all three stress treatments, whereas others are stress specific. The most critical region essential for expression of the Arabidopsis Adh promoter under all three environmental stresses (region IV: -172 to -141) contains sequences homologous to the GT motif (-160 to -152) and the GC motif (-147 to -144) of the maize Adh1 anaerobic responsive element. Region III (-235 to -172) contains two regions shown by R.J. Ferl and B.H. Laughner ([1989] Plant Mol Biol 12: 357-366) to bind regulatory proteins; mutation of the G-box-1 region (5'-CCACGTGG-3', -216 to -209) does not affect expression under uninduced or hypoxic conditions, but significantly reduces induction by cold stress and, to a lesser extent, by dehydration stress. Mutation of the other G-box-like sequence (G-box-2: 5'-CCAAGTGG-3', -193 to -182) does not change hypoxic response and affects cold and dehydration stress only slightly. G-box-2 mutations also promote high levels of expression under uninduced conditions. Deletion of region I (-964 to -510) results in increased expression under uninduced and all stress conditions, suggesting that this region contains a repressor binding site. Region II (-510 to -384) contains a positive regulatory element and is necessary for high expression levels under all treatments.

Alcohol Dehydrogenase↗
PubMed1994

Response of recurrent brain metastases in malignant melanoma to 5-fluorouracil and interferon-alpha therapy.

A 36-year-old woman underwent removal of a stage II malignant melanoma from the left ankle in 1985. A single brain metastasis to the right frontal lobe was removed in July 1986. Postoperatively, she received 5-fluorouracil, cisplatin, and etoposide (VP-16) in conjunction with radiation therapy. She achieved remission until March 1988, when left hemiparesis occurred suddenly. Computed tomography and magnetic resonance scans revealed multiple brain metastases. She was treated with a combination of 5-fluorouracil, 1,000 mg/m2 in a 24-hour continuous IV infusion for 5 days; interferon-alpha, 10 million units in subcutaneous injection daily for 10 days; and oral cimetidine, 1,200 mg daily for 7 days. This regimen, repeated every 4 to 6 weeks for four cycles, was well tolerated, with complete remission of neurological deficits and resolution of the lesions seen on the brain scans until she died 11 months later of intracranial hemorrhage secondary to severe thrombocytopenia.

Adult↗
PubMed1994

An electrophysiological study on children and young adults with Alport's syndrome.

Alport's syndrome is characterised by progressive haematuric nephritis and high tone sensorineural hearing loss. Ocular signs are variable, the most consistent findings being anterior lenticonus and retinal flecks in the macula and mid peripheral areas. Previous electrophysiological studies on patients with Alport's syndrome have mostly been on adult patients undergoing haemodialysis, or after renal transplantation. A group of young patients with Alport's syndrome were studied to assess if early electrophysiological changes were detectable. A total of 20 patients (15 males and five females) between the ages of 3.5 and 22 years (mean 12.7 (years) were examined and compared with control subjects. Visual evoked potentials and electroretinograms were obtained following flash and pattern reversal stimulation. Electro-oculograms were also recorded. No significant electrophysiological changes were found in any of the 20 patients, including four who had visible fundus changes.

Adolescent↗