Search PubMed⌕ Search

Biomedical subjects

F F Becker

Publications and source records attributed to F F Becker.

At least 37 records · Page 2Linked to original sources
PubMed1996

Inhibition of human DNA ligase I activity by zinc and cadmium and the fidelity of ligation.

Heavy metals, including zinc (Zn) and cadmium (Cd), are potentially important genotoxic agents in our environment. Here we report that human DNA ligase I, the major form of the enzyme in replicative cells, is a target for Zn and Cd ions. ZnCl2 at 0.8 mM caused complete inhibition of DNA ligase I activity, whereas only 0.04 mM CdCl2 was required to achieve a similar effect. Both metals affected all three steps of the reaction, namely, the formation of ligase-AMP intermediate, the transfer of the AMP to DNA and the ligation reaction that succeeds the formation of the AMP-DNA complex. Unlike F-ara-ATP and the natural protein inhibitor of DNA ligase-I, these metals may affect different domains of the enzyme. Moreover, these metal ions did not increase the rate of misligation of F-ara-A-modified DNA or mismatched DNA substrates, but considerable misligation was observed for the T:C mispairing. These data support the notion of high fidelity of the human DNA ligases and that the major action of these metal ions on the enzyme is their inhibitory function.

Adenosine Monophosphate↗
PubMed1996

A histological comparison of 50% and 70% glycolic acid peels using solutions with various pHs.

BACKGROUND: Seventy percent glycolic acid solutions are being commonly used as superficial chemical peeling agents. The pH of these solutions ranges from 0.08 to 2.75. The histologic effects of these various pH solutions on human skin have not been studied. OBJECTIVE: The histologic effects of several commercially available glycolic acid solutions at various pHs were examined. METHODS: Test areas of seven glycolic acid solutions were applied to facial skin of two patients. The skin was not prepped for a peel prior to the application of the acid. The solution was left in place for 30 minutes, then neutralized. After 48 hours, a 2-mm punch biopsy was performed and examined histologically. RESULTS: The peeling solutions with a pH below 2 demonstrated the potential to induce crusting and necrosis, which was not seen with the partially neutralized solutions with a pH above 2. The higher concentration acids (70%) created more tissue damage than the lower concentration (50%) when comparing solutions with free acid. CONCLUSION: This study demonstrates that chemical peeling with a 70% free glycolic acid creates more tissue damage than a free glycolic acid. When using a 70% glycolic acid solution, the lower pH products (below pH 2) create more necrosis than the partially neutralized products with a pH above 2. At this time there is no evidence that creating necrosis leads to a more favorable result of the peel. Therefore, the use of partially neutralized glycolic acid solutions seems prudent, since they have a better safety profile than low pH solutions, which contain only free glycolic acid.

Biopsy↗
PubMed1995

Non-uniform spatial distributions of both the magnitude and phase of AC electric fields determine dielectrophoretic forces.

It is well known that the conventional dielectrophoretic force acting on a polarised particle in a non-uniform AC electric field is proportional to the in-phase component of the induced dipole moment and the non-uniformity of the field strength. In contrast, the travelling-wave-dielectrophoretic force that acts on a particle subjected to a travelling electric field is proportional to the out-of-phase component of the induced dipole moment. We derive a theory that unifies the description and interpretation of conventional dielectrophoretic and travelling-wave-dielectrophoretic forces. We show that a particle in a non-uniform AC electric field experiences a dielectrophoretic force due to spatial non-uniformities of the magnitude and the phase of the field interacting, respectively, with the in-phase and out-of-phase components of the induced dipole moment. The theory is used to explain the translational effects observed for particles in the presence of standing, travelling and rotating fields in several experimental electrode configurations. The good agreement found between the experimental observations and the theoretical predictions validate the theory.

Cell Movement↗
PubMed1995

Separation of human breast cancer cells from blood by differential dielectric affinity.

Electrorotation measurements were used to demonstrate that the dielectric properties of the metastatic human breast cancer cell line MDA231 were significantly different from those of erythrocytes and T lymphocytes. These dielectric differences were exploited to separate the cancer cells from normal blood cells by appropriately balancing the hydrodynamic and dielectrophoretic forces acting on the cells within a dielectric affinity column containing a microelectrode array. The operational criteria for successful particle separation in such a column are analyzed and our findings indicate that the dielectric affinity technique may prove useful in a wide variety of cell separation and characterization applications.

Blood↗
PubMed1995

Identification of a brain- and reproductive-organs-specific gene responsive to DNA damage and retinoic acid.

We have identified and sequenced a new gene from human cells that is responsive to DNA damage and retinoic acid treatment, and it is highly expressed in brain and reproductive organs (BRE). This BRE gene encodes an mRNA of 1.7-1.9 kb, with an open reading frame of 1,149 bp, and gives rise to a deduced polypeptide of 383 amino acid residues. Treatment of fibroblast cell with UV and 4-nitroquinoline-1-oxide caused more than 90% and 50% decreases in BRE mRNA, respectively. Similar decreases in BRE expression were observed in RA-treatment of the brain glioma cell U-251 and the promyelocytic cell HL-60. Decrease in BRE mRNA was also observed in a squamous carcinoma cell, 1483, that showed X-ray resistance and has a more aggressive tumorigenic phenotype, but BRE expression was unchanged in cells after growth inhibition. These data indicate that BRE is a house-keeping gene and it may play a role in homeostatis or in certain pathways of differentiation in cells of neural, epithelial and germ line origins.

Amino Acid Sequence↗
PubMed1995

Electrorotational studies of the cytoplasmic dielectric properties of Friend murine erythroleukaemia cells.

Electrorotation (ROT) spectra of Friend murine erythroleukaemia DS19 cells were measured in the frequency range 10 kHz-100 MHz as a function of suspension osmolality and cell differentiation treatment with hexamethylene bisacetamide (HMBA). A minimization program was employed to curve-fit the measured spectra using a single-shell dielectric model, allowing the derivation of cellular interior conductivity and permittivity (valid for the frequency range 10-100 MHz) and the cytoplasmic membrane capacitance (its dependence on the cell differentiation state and suspension osmolality having been reported earlier). Following HMBA treatment, DS19 cells exhibited a slight increment in average interior permittivity and a decrement in interior conductivity, although the changes were not statistically significant. For both untreated and HMBA treated samples, the average interior conductivity increased and permittivity decreased with increasing suspension osmolality. Of significance was that the average permittivity of cell interiors was larger than that of pure water. The electrorotation spectra of freshly prepared cell nuclei were measured, and the derived nuclear dielectric parameters were employed in numerical simulations to investigate the effects of nuclei on the ROT spectra of intact cells. Other cellular internal structures such as mitochondria were also analysed using theoretical simulations. It was concluded that the derived large permittivity values did not result from cell nuclei or mitochondria, and, instead, we suggest that they may arise from the combined effects of several cytoplasmic organelles.

Animals↗
PubMed1994

Changes in Friend murine erythroleukaemia cell membranes during induced differentiation determined by electrorotation.

We used electrorotation measurements to investigate alterations in the plasma membranes of DS19 murine erythroleukaemia cells that accompanied erythropoietic differentiation induced by hexamethylene bisacetamide (HMBA). Following 3 days of HMBA treatment, the mean cell membrane specific capacitance determined from electrorotation spectra of individual, viable cells at physiological tonicity (300 mosmol/kg) fell from 1.74 to 1.53 microF/cm2, in agreement with trends observed earlier by dielectrophoretic measurements on bulk cell populations. Scanning and transmission electron microscopy revealed that the relatively high values found for cell membrane capacitance (> 1 microF/cm2) reflected the large area of plasma membrane associated with complex surface morphology including numerous microvilli. Furthermore, it demonstrated that the fall in membrane capacitance during HMBA treatment correlated with a reduction in the density of these complex surface features. Differences in the mechanical characteristics of the cell membranes of untreated and treated cells were then examined by exposing cells to osmotic stress. The intricacy of membrane morphology intensified with increasing osmolality of the suspending medium and this was reflected in higher specific capacitance values. When the osmolality was increased from 210 to 450 mosmol/kg, the mean membrane capacitance of untreated DS19 cells changed from 1.58 to 2.05 microF/cm2 while that for HMBA-treated cells changed from 1.47 to 1.72 microF/cm2, a significantly smaller response. This demonstrated that cells exposed to 72 h of differentiation treatment had an enhanced mechanical resilience as compared with their untreated counterparts, evidencing the early stages of the development of the membrane skeleton which becomes fully developed in mature erythrocytes. Our findings demonstrate the value of electrorotation measurements as a method for the non-invasive characterisation of viable leukaemic cells and their responses to stimuli and show that the membrane capacitance values so derived reflect membrane morphology.

Acetamides↗
PubMed1994

The preauricular portion of the rhytidectomy incision.

OBJECTIVE: To evaluate the best placement of the preauricular portion of the rhytidectomy incision in the female patient from the aesthetic point of view. DESIGN: Blind, randomized review of close-up photographs of the ear area in 36 patients after rhytidectomy. SETTING: Office surgical suite, accredited by Accreditation Association of Ambulatory Health Care. PARTICIPANTS: Two facial plastic surgeons and two plastic surgeons, all skilled rhytidectomy surgeons. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Participants received close-up photographs of the ear area of 36 patients at least 6 months after rhytidectomy. Eighteen patients had posterior tragal edge incisions and 18 patients had pretragal incisions. Cases were randomized. Participants were asked to rate the preauricular portion of the rhytidectomy incisions overall as to aesthetic results. The categories were excellent, good, average, acceptable, and poor. RESULTS: Results of surveys were collated. Three categories of results were determined: best, acceptable, and poorest. Posterior tragal edge incisions scored higher than pretragal incisions. Those incisions that scored in the best category tended to have a normal contour of the tragus and normal pretragal sulcus. Incisions that scored in the poorest category tended to have a flat posttragal edge with obliteration of the pretragal sulcus. CONCLUSIONS: The incision at the posterior edge of the tragus is preferred over the pretragal incision for female rhytidectomy patients except those with a large, prominent or angulated tragus.

Ear, External↗
PubMed1993

Membrane changes accompanying the induced differentiation of Friend murine erythroleukemia cells studied by dielectrophoresis.

Dielectrophoresis measurements obtained using an image processing technique are reported over the frequency range 1 Hz to 100 kHz for the Friend murine erythroleukemia cell lines DS19 and R1 before and after treatment with hexamethylene bisacetamide and dimethylsulfoxide, agents that induce terminal differentiation in DS19 but not in R1 cells. Data are analyzed according to the single shell dielectric model of the cell. The membrane capacitance was found to fall by 30% and membrane conductivity by a factor of at least 5 when DS19 cells were induced to differentiate. R1 cells showed no such response. While the theoretical model was found to be useful for comparing differences in data for the different cell lines, several significant discrepancies between its predictions and the experimental data were observed, including positive dielectrophoretic collection at frequencies below 20 Hz and a smaller than predicted response to the membrane permeabilizing agents saponin and valinomycin. Factors that may have accounted for these discrepancies include surface charge effecgs, conduction parallel to the plasma membrane surface, and intracellular compartments.

Cell Differentiation↗
PubMed1993

Biochemical characterization of a protein inhibitor for DNA ligase I from human cells. Regulation/replication/repair/recombination.

An inhibitor for DNA ligase I has recently been purified from human cells. This inhibitor of 55-75 kDa forms a reversible complex with DNA ligase I, but has no effect on DNA ligase II and T4 DNA ligase, suggesting that it may play a regulatory role for DNA replication and repair. This report shows that the inhibitor was sensitive to heating at 52 degrees C and to trypsin treatment, indicating that it is a heat-labile protein. The inhibitor affected the ligation of double- and single-strand breaks in natural and synthetic DNA, but had no effect on the formation of the ligase-AMP complex and on the subsequent reaction following the formation of the AMP-DNA complex. These data indicate that the major mechanism of action for the inhibitor is the blocking of the second step of the reaction, in which the AMP moiety is transferred from the ligase-AMP to DNA. The site of interaction for the enzyme is therefore localized in a domain associated with the DNA binding or the AMP-transferring function.

Adenosine Monophosphate↗
PubMed1993

Activation of distinct multidrug-resistance (P-glycoprotein) genes during rat liver regeneration and hepatocarcinogenesis.

The multidrug transporter P-glycoproteins are encoded by three multidrug-resistance (mdr) genes in rodents, designated mdr1a (mdr3), mdr1b (mdr1), and mdr2. Only the first two genes are functionally related to multidrug resistance. Activation of rodent mdr genes during liver regeneration and hepatocarcinogenesis has been reported. In mice, mdr1a is activated in hepatocellular carcinomas (HCCs) produced by various carcinogenic protocols, whereas both mdr1a and mdr2 are activated during liver regeneration. In this communication, we report isolating three gene-specific probes for the rat mdr homologues, which were used as probes in an RNase protection assay to demonstrate that mdr1b mRNA was expressed in HCCs induced by two different protocols. Furthermore, high levels of hepatic mdr1b mRNA but only moderate levels of mdr1a and mdr2 mRNA were seen in preneoplastic lesions in rats treated with 2-acetylaminofluorene. Likewise, highly elevated levels of hepatic mdr1b mRNA but only moderately increased levels of mdr1a and mdr2 mRNA were seen after partial hepatectomy. Nevertheless, the general patterns of tissue-specific expression of these three mdr genes were similar in rats and mice. These results reveal a complex hepatic gene expression pattern during hepatocarcinogenesis and hepatic proliferation for this conserved gene family in rodents.

2-Acetylaminofluorene↗
PubMed1992

Alterations in expression and structure of the DNA repair gene XRCC1.

The repair-associated gene XRCC1 was previously cloned by complementing the hamster mutant EM9, which has a high rate of spontaneous SCE and hypersensitivity to DNA damaging agents. In analyzing XRCC1 gene expression, similar levels of steady-state mRNA were found in normal cells, Bloom's syndrome cells with altered SCE, and in squamous carcinoma cells with differential X-ray sensitivity. An EcoRI restriction fragment-length polymorphism previously identified in XRCC1 did not correlate with the repair phenotypes of these cells. The mRNA of XRCC1 decreased to 20-40% after treatment of cells with a DNA damaging agent. XRCC1 also showed tissue specific expression in rats. The mRNA levels were high in testis (7-8 fold), ovary (3-4 fold) and brain (4-5 fold), when compared with those in intestine, liver and spleen (1-2 fold). These data and the high levels of XRCC1 protein detected in testis indicate that XRCC1 may play an important role in DNA processing during meiogenesis and recombination in germ cells.

Amino Acid Sequence↗
PubMed1992

Identification of a specific inhibitor for DNA ligase I in human cells.

A protein inhibitor for human DNA ligase I has recently been identified. It was copurified with a fraction of the enzymes from HeLa cells through several steps of chromatography. The inhibitor was first identified by the absence of ligation activity of the associated enzyme, while it retained the ability to form the ligase-[32P]AMP adducts. The inhibitor was eluted as a single peak at approximately 0.25-0.30 M NaCl from a Mono S column. It inhibited the ligation of both double-stranded and single-stranded breaks by purified DNA ligase I but not by T4 DNA ligase and DNA ligase II. Subsequent gel-filtration chromatography indicated that this inhibitor, with a molecular mass of 55-75 kDa, could form a complex with DNA ligase I and inhibited the DNA ligation activity. Rechromatography of the ligase I-inhibitor complex in high-salt conditions resulted in the dissociation of the complex and the restoration of enzyme activity, indicating that the physical interaction of inhibitor with DNA ligase I is one of the mechanisms of inhibition. These data indicate that this protein inhibitor for DNA ligase I may play a specific role in regulating DNA ligation during replication, repair, or recombination.

Chromatography, Affinity↗
PubMed1992

Dual mode of inhibition of purified DNA ligase I from human cells by 9-beta-D-arabinofuranosyl-2-fluoroadenine triphosphate.

9-beta-D-Arabinofuranosyl-2-fluoroadenine (F-ara-A) is an analogue of adenosine and deoxyadenosine with potent anti-tumor activity. The mechanism of action for this compound has been elucidated as the inhibition of DNA and RNA synthesis, induction of DNA fragmentation, and genetic damage. This study demonstrated that DNA ligase I, an enzyme involved in DNA replication, is a target for the drug action. F-ara-adenine triphosphate (F-ara-ATP) at 80 microM inhibited the activity of DNA ligase I by more than 90%. In contrast, eight other related nucleoside analogues showed no effect on the enzyme activity at 200 microM. F-ara-ATP inhibited DNA ligation in two distinct ways. First, F-ara-ATP directly interacted with DNA ligase I and inhibited the formation of the ligase-AMP complex. This inhibition could not be reversed when free F-ara-ATP was eliminated from the treated enzyme; however, the addition of pyrophosphate, followed by gel filtration chromatography, restored enzyme activity, indicating that F-ara-ATP bound to the enzyme and altered the AMP-binding site. Secondly, the activity of DNA ligase I was inhibited when F-ara-ATP was incorporated into the 3' terminus of the DNA substrate. The dual mode of inhibition of DNA ligase I by F-ara-ATP indicates that its effect on DNA ligation may be important in the inhibition of DNA synthesis and the cytotoxicity of F-ara-A.

Adenosine Monophosphate↗
PubMed1992

New retractor for open rhinoplasty.

One of the problems often encountered in external rhinoplasty is retraction of the flap. When a wide, double-pronged retractor is used, the tongue of the external rhinoplasty flap falls between the two points, often obscuring the view of the tip-and-dome anatomy. When vein retractor-type instruments are used, they will often slip and do not stay stable. A retractor has been designed for external rhinoplasty that consists of a wide, double-pronged element to elevate the soft tissues of the lower third of the nose above the cartilaginous and bony anatomy, combined with a central, slightly set-back retractor that holds the tongue of the rhinoplasty flap in a secure, retracted position. This has been a significant improvement in retraction for the external rhinoplasty flap.

Humans↗
PubMed1991

Expression of specific UDP-glucuronosyltransferase isoforms in carcinogen-induced preneoplastic rat liver nodules.

The expression of specific UDP-glucuronosyltransferase isoforms in 2-acetylaminofluorane-induced rat liver preneoplastic nodules was studied; livers from pair-fed littermates were used as controls. For comparison, liver and kidney from 3-methylcholanthrene-treated or untreated (control) rats were used. Steady-state UDP-glucuronosyltransferase mRNA levels were determined by Northern blot analysis or in situ hybridization of tissue sections using a 30-mer oligonucleotide specific for the 3-methylcholanthrene-inducible UDP-glucuronosyltransferase (which is active toward 4-nitrophenol) or a double-stranded cDNA probe specific for androsterone-UDP-glucuronosyltransferase. For 3-methylcholanthrene-inducible UDP-glucuronosyltransferase, the mRNA level was very low in control liver; there was a 15-fold increase after 3-methylcholanthrene treatment. This mRNA was present at relatively high concentration in the kidney and there was a threefold increase after 3-methylcholanthrene administration. In livers with preneoplastic nodules 1 mo after cessation of carcinogen administration, this mRNA concentration was approximately 15 times greater than in control liver. Similar changes in the level of the 3-methylcholanthrene-inducible UDP-glucuronosyltransferase were also observed by in situ hybridization of tissue sections. Immunocytochemical studies using an antiserum that recognizes the 3-methylcholanthrene-inducible UDP-glucuronosyltransferase showed a marked increase in the concentration of this isoform in preneoplastic nodules compared with the adjacent nonnodular liver.

2-Acetylaminofluorene↗