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Biomedical subjects

S Linn

Publications and source records attributed to S Linn.

At least 109 records · Page 6Linked to original sources
PubMed1990

Wartime neurosurgical experience in Lebanon, 1982-85. II: Closed craniocerebral injuries.

This report presents 64 patients who sustained military-related closed craniocerebral injuries during the Lebanon conflict of 1982-85, all of whom underwent CT scanning at the initial assessment. Of these, 59% required surgery for removal of hematomas, depressed fractures and for monitoring intracranial pressure, in addition to intensive care management of elevated intracranial pressure and associated insults. CT scan revealed brain concussion only in 23%, depressed fracture in 9%, brain contusion alone in 17%, extracerebral hematomas in 17%, intracerebral hematomas in 11%, and diffuse axonal injury in 22%. Overall mortality was 19%, and the outcome was good in 69%. Various factors affecting survival are discussed, and our findings are compared with those in the literature concerning closed head injuries among civilians. Attention is drawn to the high proportion of diffuse brain injury due to blasts caused by side mines. Despite continued efforts to hasten evacuation from the field and improve the management of warfare-related head trauma, the outcome is still far from satisfactory.

Blast Injuries↗
PubMed1989

DNA polymerases alpha and delta are immunologically and structurally distinct.

The relationship between DNA polymerases alpha and delta are evaluated immunologically by monoclonal antibody specifically against DNA polymerase alpha and murine polyclonal antiserum against calf thymus DNA polymerase delta. DNA polymerases alpha and delta are found to be immunologically distinct. The structural relationship between the proliferating cell nuclear antigen (PCNA)-dependent calf DNA polymerase delta and DNA polymerase alpha from human and calf was analyzed by two-dimensional tryptic peptide mapping of the catalytic polypeptides. The results demonstrate that the catalytic polypeptides of the PCNA-dependent calf polymerase delta and DNA polymerase alpha are distinct, unrelated, and do not share any common structural determinants. The immunological and structural relationship between a recently identified PCNA-independent form of DNA polymerase delta from HeLa cells was also assessed. This PCNA-independent human polymerase delta was found to be immunologically unrelated to human polymerase alpha but to share some immunological and structural determinants with the PCNA-dependent calf thymus polymerase delta.

Antibodies↗
PubMed1989

Purification and characterization of UV endonucleases I and II from murine plasmacytoma cells.

Three endonucleases from murine plasmacytoma cells that specifically nick DNA which was heavily irradiated with ultraviolet (UV) light were resolved by Sephacryl S-200 column chromatography. Two of these, UV endonucleases I and II, were purified extensively. UV endonuclease I appears to be a monomeric protein with a molecular mass of 43 kDa; UV endonuclease II has an S value of 2.9 S, with a corresponding molecular mass estimated at 28 kDa. Both enzymes act as a class I AP endonuclease, cleaving phosphodiester bonds via a beta-elimination mechanism, so as to form an unsaturated deoxyribose at the 3' terminus. Both have thymine glycol DNA glycosylase activity and their substrate specificities generally appear to be overlapping but not identical. UV endonuclease I acts on both supercoiled and relaxed DNAs, whereas II acts only on supercoiled DNA. Both enzymes are active in EDTA, but have different optima for salt, pH, and Triton X-100. Each enzyme is also present in cultured diploid human fibroblasts.

Animals↗
PubMed1989

Characterization of a large form of DNA polymerase delta from HeLa cells that is insensitive to proliferating cell nuclear antigen.

A large form of DNA polymerase delta from HeLa cells was recently purified in this laboratory as a factor required for conservative DNA synthesis in a reconstituted system utilizing UV-irradiated permeabilized human diploid fibroblasts (Nishida, C., Reinhard, P., and Linn, S. (1988) J. Biol. Chem. 263, 501-510). We have now purified this form of the enzyme utilizing its polymerase activity and further characterized it. The enzyme activity sediments at 11.1 S in low salt and 6.8 S in high salt. In both cases, activity cosediments with the major visible peptide displayed by sodium dodecyl sulfate-polyacrylamide gels which has an Mr of 215,000. This value is consistent with the molecular mass calculated from the sedimentation coefficient and gel filtration behavior in high salt. In low salt the apparent molecular mass was approximately double. The enzyme prefers poly(dA).oligo(dT) as template/primer in low salt, with which it has a processivity of several thousand nucleotides in 1 mM MgCl2. At isotonic KCl or potassium phosphate concentrations, the preferred template/primer is activated DNA. Proliferating cell nuclear antigen, also characterized as a DNA polymerase delta auxiliary protein, does not increase the activity of this preparation of the enzyme. An antibody to the proliferating cell nuclear antigen has no inhibitory effect, nor is it able to recognize any peptides in immunoblots of purified enzyme fractions. Under polymerizing conditions, the enzyme removes mismatched, but not matched nucleotides from the 3' terminus of oligo(dT) annealed to poly(dA) suggesting a proofreading function. The properties of this form of DNA polymerase delta distinguish it from other preparations reported in the literature.

Antigens, Neoplasm↗
PubMed1989

High density lipoprotein cholesterol levels among US adults by selected demographic and socioeconomic variables. The Second National Health and Nutrition Examination Survey 1976-1980.

The distribution of serum high density lipoprotein cholesterol (HDL cholesterol) levels was determined on a nationally representative sample of 9,625 adults aged 20-74 years, as part of the Second National Health and Nutrition Examination Survey, 1976-1980 (NHANES II). Mean HDL cholesterol levels were higher in women compared with men (an age-adjusted difference of 8.9 mg/dl for whites and 4.4 mg/dl for blacks). HDL cholesterol levels were higher in blacks compared with whites (an age-adjusted difference of 7.4 mg/dl for men and 2.8 mg/dl for women). All differences were statistically significant (p less than 0.01). These relations remained after stratification by age, income, poverty index, education, body mass index, alcohol consumption, cigarette smoking, and physical activity. For whites, HDL cholesterol levels were highest in the highest category of earnings, whereas blacks generally had lower levels of HDL cholesterol with increased earnings. In a multivariate model, important predictors of higher HDL cholesterol levels were being female, being black, and reporting a higher frequency of alcohol consumption. Less strongly related were age, years of education, and reported high physical activity. Smoking and body mass index were strongly negatively related to HDL cholesterol levels. The findings in this national study support previous findings in selected populations in the United States.

Adult↗
PubMed1989

Neurotraumatological survey in northern Israel. I. Annual and seasonal variations.

A descriptive epidemiological study of neurotraumatology was undertaken over a 4.5-year period at a regional hospital with a referral base of 1,200,000 residents with a single neurosurgical department. The 1,370 patients included in this study were those who required neurosurgical evaluation and treatment. The data base consists of demographic, clinical and radiological features at the time of admission, as well as the hospital course through to discharge. Higher admission rates were noted in spring and summer, although the mechanisms of injury showed variations. Some of the yearly variations can be explained, such as a change in rates of admission of soldiers and Lebanese population. A change from the expected outcome related to the Glasgow Coma Scale in one of the years deserves another quality control study. The main advantage of such a study, apart from the creation of data base, is an online guide for the decision-making process of health facility planning.

Brain Injuries↗
PubMed1989

[Casualties of the Peace for Galilee operation].

Most casualties of the Peace for Galilee operation were hospitalized at the Rambam Medical Center. Data from the medical records of 864 casualties of the first 15 weeks of the conflict were analyzed. 75% of them were battle casualties, and the rest were injured in accidents. Since this is the major central hospital of northern Israel, most of the severe, and about a third of the minor casualties were hospitalized here. Half of the cases reached hospital within 3 hours and 20 minutes of the time of injury. The overall mortality of all casualties, battle and accident, was 2.9%. The mortality among battle casualties who arrived at the hospital alive, was 3.4%.

Accidents↗
PubMed1988

Mitochondrial endonuclease activities specific for apurinic/apyrimidinic sites in DNA from mouse cells.

Endonuclease activity which specifically cleaves baseless (apurinic/apyrimidinic (AP] sites in supercoiled DNA has been purified from mitochondria of the mouse plasmacytoma cell line, MPC-11. Two variant forms separate upon purification; these have small but reproducible differences in catalytic and chromatographic properties, but similar physical properties. Both have a sedimentation coefficient of 4.0, corresponding to a molecular weight of 61,000 (assuming a globular configuration) and a peptide molecular weight of about 65,000 as determined by immunoblot analysis with antiserum raised against the major AP endonuclease from HeLa cells. Thus mitochondrial AP endonuclease appears to be a monomer of about 65 kDa, making it distinguishable from the major AP endonuclease of MPC-11 cells which, like those of other mammalian cells, appears to be a monomer of about 41 kDa. A possible 82-kDa precursor form was also detected by immunoblot analysis of a crude mitochondrial fraction. Mitochondrial AP endonuclease activity is greatly stimulated by divalent cations, has a pH optimum between 6.5 and 8.5, and cleaves the AP site by a class II mechanism to generate a 3'-OH nucleotide residue. These properties resemble those of the major mammalian AP endonucleases but, unlike those enzymes, mitochondrial AP endonuclease activity is neither inhibited by adenine or NAD+ nor stimulated by Triton X-100. Since the mitochondrial activity generates active primer termini for DNA synthesis, it could function in base excision DNA repair; alternatively, it might have a role in eliminating damaged mitochondrial genomes from the gene pool.

Apurinic Acid↗
PubMed1988

DNA-repair reactions by purified HeLa DNA polymerases and exonucleases.

PM2 duplex DNA substrates containing small gaps were utilized to study DNA repair reactions of extensively purified HeLa DNase V (a bidirectional double strand DNA exonuclease) and DNA polymerases beta, gamma (mitochondrial and extramitochondrial), and alpha holoenzyme, and delta as a function of ionic strength. At 50 mM NaCl, DNase V carried out extensive exonucleolytic degradation, and beta-polymerase exhibited strand displacement synthesis. However, at 150 mM NaCl, the DNase appeared only to remove damaged nucleotides from DNA termini while beta-polymerase catalyzed only gap-filling synthesis. When present in equimolar amounts, beta-polymerase and DNase V (which can be isolated as a 1:1 complex) catalyzed more degradation than synthesis at 50 mM NaCl; however, at 150 mM NaCl a coupled very limited nick translation reaction ensued. At physiological ionic strength DNA polymerase alpha holoenzyme was not active upon these substrates. In 15 mM KCl it could fill small gaps and carry out limited nick translation with undamaged DNA, but it could not create a ligatable substrate from UV-irradiated DNA incised with T4 UV endonuclease. Mitochondrial DNA polymerase gamma was more active at 150 mM NaCl than at lower ionic strengths. It readily filled small gaps but was only marginally capable of strand-displacement synthesis. The extramitochondrial form of gamma-polymerase, conversely, was less sensitive to ionic strength; it too easily filled small gaps but was not effective in catalyzing strand displacement synthesis. Finally, DNA polymerase delta was able to fill gaps of several to 20 nucleotides in 0.05 M NaCl, but at higher NaCl concentrations there was little activity. DNA polymerases delta did not demonstrate strand displacement synthesis. Therefore, at physiological ionic strength, it appears that either DNA polymerase beta or extramitochondrial DNA polymerase gamma might aid in short patch DNA repair of nuclear (or transfecting) DNAs, whereas mitochondrial gamma-polymerase might fill small gaps in mitochondrial DNA.

DNA↗
PubMed1988

DNA damage and oxygen radical toxicity.

A major portion of the toxicity of hydrogen peroxide in Escherichia coli is attributed to DNA damage mediated by a Fenton reaction that generates active forms of hydroxyl radicals from hydrogen peroxide, DNA-bound iron, and a constant source of reducing equivalents. Kinetic peculiarities of DNA damage production by hydrogen peroxide in vivo can be reproduced by including DNA in an in vitro Fenton reaction system in which iron catalyzes the univalent reduction of hydrogen peroxide by the reduced form of nicotinamide adenine dinucleotide (NADH). To minimize the toxicity of oxygen radicals, the cell utilizes scavengers of these radicals and DNA repair enzymes. On the basis of observations with the model system, it is proposed that the cell may also decrease such toxicity by diminishing available NAD(P)H and by utilizing oxygen itself to scavenge active free radicals into superoxide, which is then destroyed by superoxide dismutase.

Chemical Phenomena↗
PubMed1988

Toxic DNA damage by hydrogen peroxide through the Fenton reaction in vivo and in vitro.

Exposure of Escherichia coli to low concentrations of hydrogen peroxide results in DNA damage that causes mutagenesis and kills the bacteria, whereas higher concentrations of peroxide reduce the amount of such damage. Earlier studies indicated that the direct DNA oxidant is a derivative of hydrogen peroxide whose formation is dependent on cell metabolism. The generation of this oxidant depends on the availability of both reducing equivalents and an iron species, which together mediate a Fenton reaction in which ferrous iron reduces hydrogen peroxide to a reactive radical. An in vitro Fenton system was established that generates DNA strand breaks and inactivates bacteriophage and that also reproduces the suppression of DNA damage by high concentrations of peroxide. The direct DNA oxidant both in vivo and in this in vitro system exhibits reactivity unlike that of a free hydroxyl radical and may instead be a ferryl radical.

Bacteriophage lambda↗
PubMed1988

De novo and maintenance DNA methylation by a mouse plasmacytoma cell DNA methyltransferase.

A DNA methyltransferase of Mr = 140,000 that is active on both unmethylated and hemimethylated DNA substrates has been purified from the murine plasma-cytoma cell line MPC 11. The maximal rate of methylation was obtained with maintenance methylation of hemimethylated Micrococcus luteus or M13 DNAs. At low enzyme concentrations, the highest rate of de novo methylation occurred with single-stranded DNA or relatively short duplex DNA containing single-stranded regions. Strong substrate inhibition was observed with hemimethylated but not unmethylated DNA substrates. Fully methylated single-stranded M13 phage DNA inhibited neither the de novo nor the maintenance reactions, but unmethylated single-stranded M13 DNA strongly inhibited the maintenance reaction. The kinetics observed with hemimethylated and single-stranded substrates could be explained if the enzyme were to bind irreversibly to a DNA molecule and to aggregate if present in molar excess. Such aggregates would be required for activity upon hemimethylated but not single-stranded DNA. For de novo methylation of duplex DNA, single-stranded regions or large amounts of methyltransferase appear to be required. The relative substrate preference for the enzyme is hemimethylated DNA greater than fully or partially single-stranded DNA greater than fully duplex DNA.

Animals↗
PubMed1988

The mechanisms of action of E. coli endonuclease III and T4 UV endonuclease (endonuclease V) at AP sites.

Treatment of DNA containing AP sites with either T4 UV endonuclease or with E. coli endonuclease III followed by a human class II AP endonuclease releases a putative beta-elimination product. This result suggests that both the T4 endonuclease and E. coli endonuclease III class I AP endonucleases catalyze phosphodiester bond cleavage via a lyase- rather than a hydrolase mechanism. Indeed, we have not detected a class I AP endonuclease which hydrolytically catalyzes phosphodiester bond cleavage. Whereas these enzymes use a lyase-like rather than a hydrolytic mechanism, they nonetheless catalyze phosphodiester bond cleavage. We suggest that the term endonuclease can be properly applied to them.

Bacterial Proteins↗
PubMed1988

DNA repair synthesis in human fibroblasts requires DNA polymerase delta.

When UV-irradiated cultured diploid human fibroblasts were permeabilized with Brij-58 then separated from soluble material by centrifugation, conservative DNA repair synthesis could be restored by a soluble factor obtained from the supernatant of similarly treated HeLa cells. Extensive purification of this factor yielded a 10.2 S, 220,000-dalton polypeptide with the DNA polymerase and 3'- to 5'-exonuclease activities reported for DNA polymerase delta II (Crute, J. J., Wahl, A. F., and Bambara, R. A. (1986) Biochemistry 25, 26-36). Monoclonal antibody to KB cell DNA polymerase alpha, while binding to HeLa DNA polymerase alpha, did not bind to the HeLa DNA polymerase delta. Moreover, at micromolar concentrations N2-(p-n-butylphenyl)-2'-deoxyguanosine 5'-triphosphate (BuPdGTP) and 2-(p-n-butylanilino)-2'-deoxyadenosine 5'-triphosphate (BuAdATP) were potent inhibitors of DNA polymerase alpha, but did not inhibit the DNA polymerase delta. Neither purified DNA polymerase alpha nor beta could promote repair DNA synthesis in the permeabilized cells. Furthermore, under conditions which inhibited purified DNA polymerase alpha by greater than 90%, neither monoclonal antibodies to DNA polymerase alpha, BuPdGTP, nor BuAdATP was able to inhibit significantly the DNA repair synthesis mediated by the DNA polymerase delta. Thus, it appears that a major portion of DNA repair synthesis induced by UV irradiation might be catalyzed by DNA polymerase delta. When xeroderma pigmentosum human diploid fibroblasts were utilized, DNA repair synthesis dependent upon ultraviolet light could be restored by addition of both T4 endonuclease V and DNA polymerase delta, but not by addition of either one alone. This result suggests that cytosol-depleted permeabilized DNA repair-defective human fibroblasts and HeLa DNA polymerase delta might be exploited to provide a functional assay for purifying active DNA repair factors from DNA repair-proficient cells without a preknowledge of their function.

DNA Polymerase II↗
PubMed1988

A reduced rate of bulky DNA adduct removal is coincident with differentiation of human neuroblastoma cells induced by nerve growth factor.

Human SY5Y neuroblastoma cells which were differentiated in culture by treatment with 7S murine nerve growth factor for 5 weeks and selection with aphidicolin (L. Jensen, Dev. Biol. 120:56-64, 1987) demonstrated a considerably slower rate of removal of DNA adducts of benzo[a]pyrene, benzo[a]pyrenediolepoxide, and N7-methylguanine than did undifferentiated mitotic cells. A dramatic decline in unscheduled DNA synthesis induced by UV radiation was similarly observed. DNA polymerase beta and uracil DNA glycosylase were unchanged after differentiation, DNA polymerase alpha and DNA methylase decreased roughly threefold, and total apurinic-apyrimidinic endonuclease activity increased roughly threefold after treatment.

Aphidicolin↗
PubMed1988

Adverse outcomes of pregnancy in women exposed to diethylstilbestrol in utero.

We analyzed data collected by interview and medical record review for 200 women exposed to diethylstilbestrol (DES) and 12,240 unexposed women to evaluate the relation between maternal DES exposure and outcomes of pregnancy. Low birth weight, short gestation, bleeding in the first trimester, toxemia, breech presentation and premature rupture of the membranes occurred more often among the exposed women. These relationships remained statistically significant after the use of linear regression and logistic regression analyses to control for multiple confounding factors. Both exposed women and their physicians should be aware of the possible relationship between maternal exposure to DES and late adverse outcomes of pregnancy. Close medical supervision of these women throughout pregnancy and delivery is recommended.

Demography↗