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Biomedical subjects

A Mayer

Publications and source records attributed to A Mayer.

At least 145 records · Page 8Linked to original sources
PubMed1994

Identification of low-level contamination of blood as basis for detection of human immunodeficiency virus (HIV) DNA in anti-HIV-negative specimens.

The significance of detection of human immunodeficiency virus (HIV) DNA by the polymerase chain reaction (PCR) in seronegative or seroconverting (SC) subjects remains controversial. In a previously reported study, we identified a case in which a specimen collected 12 months before seroconversion (pre-SC) was found repeatedly to be PCR positive in three experienced laboratories, while the 6-month pre-SC bleed was PCR-negative; PCR-based human leukocyte antigen (HLA)-DQA and -DRB typing of serial peripheral blood mononuclear cell (PBMC) samples from this case did not indicate a specimen mix-up or labeling error. To further investigate this case, we used HIV env sequence and DNA heteroduplex gel-shift analyses to characterize HIV quasispecies present in serial pre- and post-SC specimens. HIV env sequences and gel-shift pattern analyses from the 12-month pre-SC versus post-SC samples indicated that markedly distinct quasispecies were present, suggesting possible abortive infection followed by reinfection and subsequent seroconversion. However, the HIV burden of this pre-SC sample was very low (1 provirus/10(6) PBMCs), and the quasispecies was highly heterogeneous, findings suggesting long-term rather than recent HIV infection. To test the hypothesis that the index pre-SC sample was PCR positive owing to trace blood contamination during initial processing, we analyzed the three seropositive samples collected on the same date in 1985. One of these samples was highly related to the index pre-SC sample by env sequence and gel-shift methodologies.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1994

The role of brachytherapy in the radiation treatment of malignant tumours.

The magnitude of brachytherapy doses depends on the applied dose rates: high-dose-rate or low-dose-rate techniques. Brachytherapy is usually performed as a complementary modality with megavoltage external beam therapy, but it is also used preoperatively for cancers of the uterine cervix and corpus. The most common localization is reviewed in this paper with special regard to the indications, treatment methods and prognosis of curing for rectal and breast cancer.

Brachytherapy↗
PubMed1993

The prognostic significance of proliferating cell nuclear antigen, epidermal growth factor receptor, and mdr gene expression in colorectal cancer.

BACKGROUND: Proliferating cell nuclear antigen (PCNA), a proliferation marker, epidermal growth factor receptor (EGFR), a glycoprotein that plays a role in tumorigenesis by binding the mitogenic epidermal growth factor, and P-glycoprotein, the mdr gene product, are considered to be of prognostic relevance in different tumor types. Parameters that allow prediction of the course of disease in colorectal cancer would aid the development of improved treatment strategies. METHODS: Immunohistochemical staining was performed on paraffin-embedded sections of 82 colorectal adenocarcinomas and 18 lymph node metastases. EGFR and P glycoprotein expression was evaluated semiquantitatively; PCNA expression was analyzed quantitatively. RESULTS: An inverse relationship between the percentage of PCNA-positive cells and survival times could be demonstrated, survival differed significantly among the quartiles (P < 0.02). The median and range of the percentage of PCNA-positive cells in primary tumors and lymph node metastases were similar. The extent of EGFR expression also revealed significant differences concerning survival times; patients with more than 50% stained tumor cells had a poorer prognosis than those with less than 50% stained cells. P-glycoprotein expression was found to have no influence on survival. CONCLUSIONS: Knowledge of the percentage of PCNA-positive cells could be especially helpful in deciding whether to treat patients with localized disease further because adjuvant chemotherapy affects mainly dividing cells and should, therefore, be more successful in tumors with high proliferative activity.

Adult↗
PubMed1993

Liver transplantation in babies and children with extrahepatic biliary atresia.

Orthotopic liver transplantation (OLT) is a life-saving procedure for end-stage liver failure. We reviewed 39 children (24 girls, 15 boys) who received OLT for biliary atresia from 1987 to 1991. Twenty had unsuccessful portoenterostomy, 6 were referred too late for a drainage operation, and the remaining 13 achieved bile drainage but developed portal hypertension. At transplant 37 had decompensated liver disease with varices (28), ascites (24), encephalopathy (17), and gastrointestinal bleeding (12). The median weight and age at transplant were 8 kg and 12.6 months, respectively. The median waiting time was 65 days. Forty-eight grafts (30 reduced and 18 whole) were performed; graft loss was 33% and 27%, respectively. Of the 30 segmental grafts, 15 were reduced conserving the left lateral segment and hepatic vein (Brisbane technique)--13 were from the left lobe and 2 from the right lobe. The overall subject survival rate is 72%. Eleven deaths occurred: primary nonfunction (3), sepsis (3), perioperative bleed (3), and other causes (2). Early complications included: hepatic artery thrombosis (5), hepatic vein thrombosis (2), bowel perforation (3), biliary leak (3), and acute rejection (8). Later complications were chronic rejection (4) and biliary stricture requiring reconstruction (3). Follow-up at 12 months confirms good quality of life for both child and family with catch up growth and normal development. Technical advances in reduction hepatectomy have allowed us to treat small babies under 1 year with an urgent requirement for OLT, with comparable results to those obtained with whole grafts. In conclusion, in the future size and age need not be a contraindication to OLT in children with biliary atresia.

Biliary Atresia↗
PubMed1993

Chiral separation and detection enhancement of propranolol using automated pre-column derivatization.

In the liquid chromatographic analysis of pharmaceuticals, two challenges are often encountered: detectivity and chiral separations. Propranolol, a beta adrenergic blocker, is a pharmaceutical compound that faces both of these limitations. In this study, both limitations are overcome simultaneously using derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC), a highly fluorescent and chiral reagent. The derivatization is automated using an autosampler with an AutoMix microrobotic feature, which greatly contributes to the efficiency and reproducibility of the method when manipulating microliter volumes of sample and reagents. The method yields excellent separation of the diasteriomers, has a detection limit of 1 picomol, good reproducibility and linearity in the 50-400 pmol range (on column). In addition, this method is simple, requires no elevated temperature, no chiral stationary or mobile phases and can be easily automated.

Chromatography, High Pressure Liquid↗
PubMed1993

Translocation and insertion of precursor proteins into isolated outer membranes of mitochondria.

Nuclear-encoded proteins destined for mitochondria must cross the outer or both outer and inner membranes to reach their final sub-mitochondrial locations. While the inner membrane can translocate preproteins by itself, it is not known whether the outer membrane also contains an endogenous protein translocation activity which can function independently of the inner membrane. To selectively study the protein transport into and across the outer membrane of Neurospora crassa mitochondria, outer membrane vesicles were isolated which were sealed, in a right-side-out orientation, and virtually free of inner membranes. The vesicles were functional in the insertion and assembly of various outer membrane proteins such as porin, MOM19, and MOM22. Like with intact mitochondria, import into isolated outer membranes was dependent on protease-sensitive surface receptors and led to correct folding and membrane integration. The vesicles were also capable of importing a peripheral component of the inner membrane, cytochrome c heme lyase (CCHL), in a receptor-dependent fashion. Thus, the protein translocation machinery of the outer mitochondrial membrane can function as an independent entity which recognizes, inserts, and translocates mitochondrial preproteins of the outer membrane and the intermembrane space. In contrast, proteins which have to be translocated into or across the inner membrane were only specifically bound to the vesicles, but not imported. This suggests that transport of such proteins involves the participation of components of the intermembrane space and/or the inner membrane, and that in these cases the outer membrane translocation machinery has to act in concert with that of the inner membrane.

Biological Transport↗
PubMed1993

An individual with a high prevalence of a tat-defective provirus in peripheral blood.

The first exon of tat was sequenced from 23 provirus genomes randomly amplified directly from an HIV-1-infected individual's peripheral blood. Twelve of the 23 sequences constituted a distinct subset of the quasi-species detected. This subset had in common two inactivating mutations in the tat gene. In addition, two of these defective genomes each had a unique mutation. This is the second instance of a defective early gene being present in a high percentage of the proviruses present in the PBMCs of an HIV-1-infected individual, (the first reported by Martins LP et al.: J Virol 1991;65:4502-4507), and suggests that genomes defective in an early gene can participate in the infectious spread of HIV-1 in vivo.

Base Sequence↗
PubMed1993

Calcium-antagonistic effects of carbamazepine in epilepsies and affective psychoses.

Carbamazepine (CBZ) is known to have beneficial effects in the treatment of epilepsies and in the prophylaxis of affective disorders. Since increased transmembrane calcium fluxes and intracellular calcium concentrations play a key role in the generation of epilepsies and possibly also in the development of these psychiatric disorders the effects of CBZ on epileptic discharges (elicited by caffeine, penicillin and low Mg2+) in CA3 neurons of hippocampal slices were compared with those of the organic calcium antagonist verapamil and found to be almost the same.

Animals↗
PubMed1993

Effects of carbamazepine on action potentials and calcium currents in rat spinal ganglion cells in vitro.

The effects of carbamazepine (CBZ) on action potentials and calcium currents in cultured rat sensory spinal ganglion cells were investigated. CBZ was found to reversibly suppress the calcium-dependent components of action potentials and to reduce the amplitude of the after-hyperpolarizations, while the rising phase and the peak amplitude were hardly changed. Furthermore, CBZ caused a marked reduction in the calcium currents, which in some cells was reversible. The present findings confirm that CBZ has calcium-antagonistic properties.

Action Potentials↗
PubMed1993

[Preoperative low-dose-rate versus high-dose-rate brachytherapy in stage IB cervix cancer. An efficacy study].

In women with stage IB (FIGO) carcinoma of the cervix, the authors investigated the efficacy of the manual low-dose rate (LDR) and afterloading high-dose rate (HDR) technique in terms of local freedom from tumor. It was found that in the 194 patients treated with the low-dose rate LDR-technique (computed dose point A 23.5 GY; point B 4.7 Gy), the surgical specimen was free of tumor in 37%. Among the 161 patients treated with the high-dose rate technique (point A11 Gy; point B 2 Gy), 41% of the surgical specimens were free of tumor. Follow-up examinations in the group receiving LDR-brachytherapy were carried out within a period of between ten and 90 months after treatment (average: 30.76 months). In 84% of the cases, NED was established. In the patient group treated with HDR-brachytherapy, follow-up examinations performed within a period of between six and 42 months after treatment (average 17.17 months), NED was found in 90%.

Adult↗
PubMed1992

Cloning and sequencing of genes encoding the TthHB8I restriction and modification enzymes: comparison with the isoschizomeric TaqI enzymes.

Genes encoding the TthHB8I restriction and modification (R-M) system from Thermus thermophilus HB8 (recognition sequence T decreases CGA) were cloned in Escherichia coli. The genes have the same transcriptional orientation, with the last 13 codons of the methyltransferase (MTase) overlapping the first 13 codons of the endonuclease (ENase). Nucleotide sequence analysis of the TthHB8I ENase revealed a single chain of 263 amino acid (aa) residues that share a 77% identity with the corrected isoschizomeric TaqI ENase. Likewise, the Tth MTase (428 aa) shares a 79% identity with the corrected sequence of the TaqI MTase. This high degree of aa conservation suggests a common origin between the Taq and Tth R-M systems. However, codon usage and G+C content for the R-M genes differed markedly from that of other cloned Thermus genes. This suggests that these R-M genes were only recently introduced into the genus Thermus.

Amino Acid Sequence↗
PubMed1992

Interferon-gamma-induced assembly block in the replication cycle of adenovirus 2: augmentation by tumour necrosis factor-alpha.

Replication of adenovirus 2 (Ad-2) is inhibited in A 549 cells pretreated with interferon-gamma (IFN-gamma). The antiviral effect is synergistically enhanced by the simultaneous presence of tumor necrosis factor-alpha (TNF-alpha) before infection. Under conditions of strong inhibition of virus progeny formation, viral DNA synthesis and [35S]methionine incorporation into most late viral proteins are only marginally impaired. Pulse chase experiments indicate a partial inhibition of processing of viral proteins. Viral proteins are not degraded and capsomeres accumulate in the inhibitor-treated cells. Capsid formation, on the other hand, is strongly inhibited in the cytokine-treated cells. The inhibition of Ad-2 replication in A 549 cells by IFN-gamma and TNF-alpha is caused, therefore, by a block in the maturation of Ad-2.

Adenoviruses, Human↗
PubMed1992

In situ nuclear magnetic resonance of N pulse labels monitors different routes for nitrogen assimilation.

Nuclear magnetic resonance offers the possibility of noninvasive in situ observation of (15)N pulse labeling in the presence of light. In vivo, exclusively the delta-nitrogen of Gln is labeled in the cyanobacterium Microcystis firma when glutamate synthase is inhibited by azaserine. In contrast, the green alga Chlorella fusca is additionally capable of incorporating nitrogen into Glu, thus providing evidence for an anabolic function of glutamate dehydrogenase in this organism.

Journal Article↗
PubMed1992

[The brachytherapy of carcinoma of the external auditory canal].

Brachytherapy is advantageous in the initial carcinomas of external auditory canal. The radiation charge of the surrounding tissues is much lower in spite of millivoltage irradiation because of its higher dosage gradient. It is stated according to the recent experiences and results on seven treated patients, that with LDR treatment of 5 x 10 Gy on consecutive days and with HDR treatment of 6 x 6 Gy on weekly interruptions (in both cases the dose means a depth of 5 mm). It is impossible to give the analysis because of the small number of cases. On base of our own patients it could be proved that lasting recovery of bone involving tumours is due to radical surgery and postoperative millivoltage irradiation.

Brachytherapy↗
PubMed1991

The ubiquitin-activating enzyme, E1, is required for stress-induced lysosomal degradation of cellular proteins.

ts85, a cell line that harbors a mutant thermolabile ubiquitin-activating enzyme, E1, fails to degrade short lived proteins at the restrictive temperature (Ciechanover, A., Finley, D., and Varshavsky, A. (1984) Cell 37, 57-66). However, the involvement of the ubiquitin system in the degradation of long lived proteins (most cellular proteins fall in this category) has not been addressed. In the present study we show that upon shifting the mutant cells to the restrictive temperature, there is no change in the rate of degradation of long lived proteins. In contrast, shifting the wild-type cells (FM3A) to the high temperature is accompanied by a 2-fold increase in the rate of proteolysis of this group of proteins. This heat-induced accelerated degradation can be inhibited completely by NH4Cl and chloroquine. Similarly, exposure of the cells to starvation, a stimulus that activates the autophagic-lysosomal pathway, has no effect on the degradation of long lived proteins in the mutant cells after inactivation of E1. Under the same conditions, the degradation rate in the wild-type cells increases almost 4-fold. Analogous results were obtained using a different cell line that also harbors a thermolabile E1 (ts20 (Kulka, R. G., Raboy, B., Schuster, R., Parag, H. A., Diamond, G., Ciechanover, A., and Marcus, M. (1988) J. Biol. Chem. 263, 15726-15731)). Cycloheximide and 3-methyladenine, known inhibitors of formation of autophagic vacuoles, inhibit the heat-induced accelerated degradation of long lived proteins in wild-type cells. Taken together, the results suggest that 1) heat stress induces enhanced degradation of intracellular proteins; 2) the process occurs most probably in autophagic vacuoles; and 3) activation of ubiquitin is required for the formation of these vacuoles. As there is no change in the basal rate of degradation of intracellular proteins in the mutant cells at the restrictive temperature, it appears that the ubiquitin system is not involved in their breakdown.

Adenine↗
PubMed1991

Separation and detection of DNA polynucleotides using capillary electrophoresis. Application to detection of polymerase chain reaction-amplified human immunodeficiency virus and HLA DNA.

The polymerase chain reaction (PCR) is a technique for rapid amplification of target DNA sequences. During the past several years, a large number of research applications of PCR have appeared, many of which may prove to be useful clinically. We report the use of capillary electrophoresis, a fully automated technique, as an alternative to polyacrylamide gel electrophoresis for the detection of PCR-amplified viral and cellular DNA. We describe conditions for rapid separation, detection, and discrimination of PCR products from the human immunodeficiency virus type 1 gag gene and the HLA-DQ-alpha gene amplified from the human immunodeficiency virus provirus-containing U1.1 cell line. The sensitivity achieved with the use of capillary electrophoresis analysis was roughly equivalent to that of ethidium bromide staining of polyacrylamide gel electrophoresis gels. Further refinement of capillary electrophoresis for automated detection and quantitation of PCR-amplified products should expedite more widespread application of PCR analysis in the clinical laboratory.

DNA↗