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Biomedical subjects

A M Lennon

Publications and source records attributed to A M Lennon.

At least 19 recordsLinked to original sources
PubMed2003

Review of the current status of tooth whitening with the walking bleach technique.

Internal bleaching procedures such as the walking bleach technique can be used for whitening of discoloured root-filled teeth. The walking bleach technique is performed by application of a paste consisting of sodium perborate-(tetrahydrate) and distilled water (3% H2O2), respectively, in the pulp chamber. Following a critical review of the scientific literature, heating of the mixture is contra-indicated as the risk of external cervical resorption and the formation of chemical radicals is increased by application of heat. An intracoronal dressing using 30% H2O2 should not be used in order to reduce the risk of inducing cervical resorption. This review provides advice based on the current literature and discusses how the walking bleach technique can lead to successful whitening of non-vital root-filled teeth without the risks of side-effects.

Borates↗
PubMed2003

Peritoneal involvement in stage II colon cancer.

A pathologist (K.S.) reviewed histologic slides for peritoneal involvement by tumor cells for 118 patients with stage II colon cancer. Patients were followed up for a median of 6 years. Tumor cells were found free in the peritoneal space in 16 cases (13.6%). The presence of cancer cells free in the peritoneal space was associated with lymphovascular invasion (P = .001) and neural invasion (P < .001). The overall 5-year survival was 80% in the patient population, but was 39% and 86% for those with and without tumor cells free in the peritoneal space, respectively (P < .0001). Multivariate analysis confirmed that free tumor cells within the peritoneal space (P < .0001) and lymphovascular invasion (P = .007) were related independently to outcome. Peritoneal involvement with tumor cells free in the peritoneal space in stage II colon cancer is a powerful indicator of outcome; patients have a survival similar to that for patients with stage III disease.

Adult↗
PubMed2001

Clinical applications and outcomes of using indicators of risk in caries management.

The aim of this review was to systematically assess clinical evidence in the literature to determine the predictive validity of currently available multivariate caries risk-assessment strategies (including environmental, sociodemographic, behavioral, microbiological, dietary/nutritional, and/or salivary risk factors) in: 1) primary teeth; 2) coronal surfaces of permanent teeth; and 3) root surfaces of permanent teeth. We identified 1,249 articles in the search, and selected 169 for full review. Inclusion and exclusion criteria were established prior to commencement of the literature search. Papers that conformed to these criteria were included (n = 15 for primary teeth; n = 22 for permanent teeth; and n = 6 for root surfaces), and 126 papers were excluded. Included articles were grouped by study design as: longitudinal, retrospective, and cross-sectional. The predictive validity of the models reviewed depended strongly on the caries prevalence and characteristics of the population for which they were designed. In many instances, the use of a single predictor gave equally good results as the use of a combination of predictors. Previous caries experience was an important predictor for all tooth types.

Adolescent↗
PubMed2001

Problem-based learning and the dental school library.

A major curriculum revision involving the utilization of problem-based learning was implemented at Indiana University School of Dentistry in the summer of 1997. Two of the main goals of this new student-centered curriculum were to promote critical thinking skills and to encourage a desire for lifelong learning, both of which were anticipated to increase student use of the library. This study examined circulation at the library for three years immediately prior to, and for three years immediately following, the curricular change. Results show that library circulation has increased significantly since the pedagogical change. This suggests that students in the new curriculum place more emphasis on the library as a learning resource than did their traditional curriculum counterparts.

Analysis of Variance↗
PubMed2000

Defective MHC class II expression in an MHC class II deficiency patient is caused by a novel deletion of a splice donor site in the MHC class II transactivator gene.

MHC class II deficiency patients are mutated for transcription factors that regulate the expression of major histocompatibility complex (MHC) class II genes. Four complementation groups (A-D) are defined and the gene defective in group A has been shown to encode the MHC class II transactivator (CIITA). Here, we report the molecular characterization of a new MHC class II deficiency patient, ATU. Cell fusion experiments indicated that ATU belongs to complementation group A. Subsequent mutation analysis revealed that the CIITA mRNA lacked 84 nucleotides. This deletion was the result of the absence of a splice donor site in the CIITA gene of ATU. As a result of this novel homozygous genomic deletion, ATU CIITA failed to transactivate MHC class II genes. Furthermore, this truncated CIITA of ATU did not display a dominant negative effect on CIITA-mediated transactivation of various isotypic MHC class II promoters.

Antigens, Differentiation, B-Lymphocyte↗
PubMed1999

Regulation of type 3 iodothyronine deiodinase expression in cultured rat astrocytes: role of the Erk cascade.

The type 3 iodothyronine deiodinase (D3) metabolizes thyroid hormones to inactive metabolites in many tissues, including the brain. In the present studies, we have examined the mechanisms by which T3 (T3), retinoic acid, 12-O-tetradecanoyl phorbol 13-acetate (TPA), and basic fibroblast growth factor (bFGF) induce D3 expression in primary cultures of neonatal rat astrocytes. In untreated cells, D3 messenger RNA (mRNA) was essentially undetectable by Northern analysis and RT-PCR. However, all four agents induced expression of a 2.4-kb D3 transcript as well as D3 activity. Induction of D3 by TPA and bFGF was more rapid than that by T3 and retinoic acid, and T3 potentiated the stimulatory effects of TPA and bFGF. D3 induction by TPA was blocked by GF 109203X, an inhibitor of protein kinase C. In addition, the effects of TPA and bFGF were partially prevented by PD 98059, a specific inhibitor of MEK and the Erk signaling cascade. These studies demonstrate that multiple growth factors and hormones regulate D3 activity in cultured astrocytes by inducing D3 mRNA expression. In addition, the stimulatory effects of TPA and bFGF on D3 mRNA and activity appear to be mediated at least in part by activation of the MEK/Erk signaling cascade.

Animals↗
PubMed1998

Regulation of the cyanide-resistant alternative oxidase of plant mitochondria. Identification of the cysteine residue involved in alpha-keto acid stimulation and intersubunit disulfide bond formation.

The cyanide-resistant alternative oxidase of plant mitochondria is a homodimeric protein whose activity can be regulated by a redox-sensitive intersubunit sulfhydryl/disulfide system and by alpha-keto acids. After determining that the Arabidopsis alternative oxidase possesses the redox-sensitive sulfhydryl/disulfide system, site-directed mutagenesis of an Arabidopsis cDNA clone was used to individually change the two conserved Cys residues, Cys-128 and Cys-78, to Ala. Using diamide oxidation and chemical cross-linking of the protein expressed in Escherichia coli, Cys-78 was shown to be: 1) the Cys residue involved in the sulfhydryl/disulfide system; and 2) not required for subunit dimerization. The C128A mutant was stimulated by pyruvate, while the C78A mutant protein had little activity and displayed no stimulation by pyruvate. Mutating Cys-78 to Glu produced an active enzyme which was insensitive to pyruvate, consistent with alpha-keto acid activation occurring through a thiohemiacetal. These results indicate that Cys-78 serves as both the regulatory sulfhydryl/disulfide and the site of activation by alpha-keto acids. In light of these results, the previously observed effects of sulfhydryl reagents on the alternative oxidase of isolated soybean mitochondria were re-examined and were found to be in agreement with a single sulfhydryl residue being the site both of alpha-keto acid activation and of the regulatory sulfhydryl/disulfide system.

Amino Acid Substitution↗
PubMed1998

CIITA B-cell-specific promoter suppression in MHC class II-silenced cell hybrids.

In this study, various sets of somatic cell hybrids, generated by the fusion of epithelial cell lines with B-lymphoblastoid cell lines, were analyzed for the expression of major histocompatibility complex (MHC) class II antigens. We first demonstrate, in human and mouse intraspecies hybrids, the coordinate suppression of MHC class II, Ii (invariant chain) and HLA-DM gene transcription, and the release of the silencing by the addition of interferon gamma. Using interspecies hybrids, the segregation of human chromosomes allowed us to establish that MHC class II extinction is linked to the presence in the hybrids of the chromosomes from the epithelial fusion partner. Moreover, our data provide evidence that the expression pattern of MHC class II mRNA is correlated with that of the class II transactivator (CIITA), suggesting that CIITA is the actual target of the silencing. To gain further insight into the suppression phenomenon we performed luciferase assays which show that silencing affects the activity of the B-cell-specific promoter of CIITA. These results therefore demonstrate that the MHC class II gene silencing in somatic cell hybrids is due to an active suppression of one of the promoters of the CIITA gene, mediated by the epithelial cell fusion partner.

Animals↗
PubMed1997

Expression of the type II iodothyronine deiodinase in cultured rat astrocytes is selenium-dependent.

The iodothyronine deiodinases are a family of selenoproteins that metabolize thyroxine and other thyroid hormones to active and inactive metabolites in a number of tissues including brain. Using primary cultures of rat astroglial cells as a model system, we demonstrate that the mRNA for the type II iodothyronine deiodinase (DII) selenoenzyme is rapidly and markedly induced by forskolin and 8-bromo-cAMP. The induction of DII activity, however, was significantly impaired by culturing cells in selenium-deficient medium for 7 days. Under such conditions, the addition of selenium resulted in a rapid increase in cAMP-induced DII activity that was dose-dependent, with maximal effects noted within 2 h. Cycloheximide blocked this effect of selenium on restoring cAMP-induced DII activity, whereas actinomycin D did not. These data demonstrate that the DII selenoenzyme is expressed in cultured astrocytes and that the induction of DII activity by cAMP analogues appears to be mediated, at least in part, by pretranslational mechanisms. Furthermore, selenium deprivation impairs the expression of DII activity at the level of translation.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1997

Isolation of a B-cell-specific promoter for the human class II transactivator.

The class II transactivator (CIITA) is essential for the expression of major histocompatibility complex (MHC) class II antigens. The tissular patterns of CIITA and MHC class II gene expression are tightly correlated: CIITA mRNA is highly expressed in B cells, and is induced by interferon gamma (IFN-gamma) in macrophage and epithelial cell lines. We first isolated two overlapping cosmids encoding human CIITA which, when co-transfected, are able to restore MHC class II expression in a B-lymphoblastoid cell line (B-LCL) defective for CIITA. Subsequently, a 1.8 kilobase (kb) fragment of the CIITA promoter was isolated and sequenced. A motif presenting a strong similarity to an initiator was detected, as well as putative binding sites for Sp1, GATA-2, LyF-1, ets-1, AP1, and MZF1 transcription factors, and two GAS motifs. When introduced in front of a luciferase reporter gene, this promoter is able to direct a high luciferase activity in a human B-LCL. In contrast, luciferase expression was not stimulated after IFN-gamma treatment when the construct was transfected in macrophage or in epithelial cell lines. However, an induction of the human CIITA gene was observed in mouse macrophage and fibrosarcoma cell lines, when the cells were transfected with a cosmid containing the human CIITA gene, but lacking the 1.8 kb promoter described above. Taken together, these data suggest the existence of an intragenic promoter driving an IFN-gamma-inducible expression of CIITA.

B-Lymphocytes↗
PubMed1994

Induction of type III-deiodinase activity in astroglial cells by retinoids.

Thyroid hormones and retinoic acid (RA) are important modulators of growth, development, and differentiation. Type III deiodinase (D-III), which catalyzes thyroid hormones degradation in the brain and in cultured astroglial cells, is induced in astroglial cells by multiple pathways, including cAMP, 12.0-tetradecanoylphorbol-13-acetate (TPA), fibroblast growth factors, and thyroid hormones themselves. In the present study, the effects of retinoids on D-III activity were examined in astroglial cells cultures in a chemically defined medium devoid of hormones and growth factors. Incubation of astroglial cells with 5 microM all-trans-RA caused up to 200-fold increase in D-III activity, which reached a plateau after 48 h. The retinoid-induced increase in D-III activity was concentration dependent (0.5 microM all-trans-RA and 9-cis-RA producing half-maximal effect). Retinol was effective at physiological concentrations (1 and 10 microM). The 48 h effects of 5 microM all-trans-RA and 10 nM thyroid hormones on D-III activity were at least additive. Addition of 2 nM acidic fibroblast growth factor or 1 mM 8-bromo-cAMP for the last 8 h of a 48 h incubation with 5 microM all-trans-RA did not alter the induction by all-trans-RA, whereas 0.1 microM TPA in the same conditions produced an additive effect with all-trans-RA. All-trans-RA (5 microM) had little or no effect on type II deiodinase, the enzyme which catalyzes the activation of thyroxine to 3,5,3'-triiodothyronine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

12-O-tetradecanoylphorbol 13-acetate and fibroblast growth factor increase the 30-kDa substrate binding subunit of type II deiodinase in astrocytes.

Type II 5'-deiodinase (D-II) catalyzes the intracellular conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the brain. The D-II activity in astroglial cell cultures is induced by several pathways including cyclic AMP (cAMP), 12-O-tetradecanoylphorbol 13-acetate (TPA), and fibroblast growth factors (FGFs). We have examined the effect of TPA and FGFs on the 30-kDa substrate binding subunit of D-II, by affinity labeling with N-bromoacetyl-[125I]T4 in astroglial cells. TPA (0.1 microM), 20 ng/ml acidic FGF (aFGF), and 1 mM 8-bromo cyclic AMP all caused an increase in the 30-kDa protein. cAMP induced the greatest increase (fivefold) followed by TPA (3.2-fold) and FGF (2.8-fold). Glucocorticoids acted synergistically with cAMP and aFGF and promoted the effect of TPA. Affinity labeling was competitively inhibited by bromoacetyl-T4 > bromoacetyl-T3 > T4 > reverse T3 > iopanoic acid > T3 > 3,5,3'-triiodothyroacetic acid. The effect of TPA (0.1 microM) was maximum at 8 h and then gradually decreased. aFGF (20 ng/ml) plus heparin (17 micrograms/ml) induced a maximal 30-kDa increase at 8 h, which stayed stable for up to 24 h. The effect of aFGF was concentration dependent. Of the other growth factors studied, only basic FGF and platelet-derived growth factor induced small increases in the 30-kDa protein. Epidermal growth factor had little effect. In vitro labeling of cAMP, TPA, and aFGF-stimulated cell sonicates resulted in an increase in the 30-kDa protein that paralleled the increase in D-II activity.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1994

Sulfation after deiodination of 3,5,3'-triiodothyronine in rat cultured astrocytes.

The metabolism of [125I]T3 by rat astrocytes in culture was analyzed by Sephadex LH-20 chromatography and HPLC. The conjugates isolated on LH-20 were not hydrolyzed by glucuronidase, indicating the absence of glucuroconjugates. 3,3'-Diiodothyronine (3,3'T2) sulfate (3,3'T2-S) was the main product that accumulated in the medium over the T3 concentration explored (10 pM to 10 nM). The identity of the peak eluted as 3,3'T2-S was ascertained by its hydrolysis with sulfatase and the generation of 3,3'T2 identified by HPLC. 3'-Monoiodothyronine sulfate was also found in cells treated with 1 microM retinoic acid, i.e. with high type III deiodinase activity. No T3 sulfate (T3-S) was found as a metabolite of T3. Astrocytes did not break down 1 nM [125I]T3-S added to the medium. Astrocytes pretreated for 3 days with 10 nM T3 showed increased production of 3,3'T2-S from 10 nM [125I]T3. Exogenous [125I]3,3'T2 (20 nM) was conjugated to 3,3'T2-S released into the medium. Pretreatment of astrocytes with 10 nM T3 did not alter the production of 3,3'T2-S from 3,3'T2. Thus, T3 is metabolized in astrocytes by direct 5-deiodination, followed by sulfation. Whereas T3 induces its own deiodination and type III deiodinase activity, T3 does not regulate the sulfation of its main metabolite, 3,3'T2. This demonstration of sulfation of iodothyronines in cells originating from the brain raises the question of the role of this TH metabolic pathway in the brain.

Animals↗
PubMed1992

Purification and characterization of rat brain cytosolic 3,5,3'-triiodo-L-thyronine-binding protein. Evidence for binding activity dependent on NADPH, NADP and thioredoxin.

A rat brain cytosolic 3,5,3'-triiodo-L-thyronine-(T3)-binding protein (CTBP) was purified using, successively, carboxymethyl-Sephadex, DEAE-Spherodex, T3-Sepharose-4B affinity chromatography and Sephacryl S-200. The molecular mass determined by SDS/PAGE wa 58 kDa. The binding characteristics determined by Scatchard analysis revealed a single class of binding sites with a Ka of 1.56 nM-1 and a maximal binding capacity of 7500 nmol T3/g protein. The relative binding affinities of iodothyronine analogues were D-T3 > L-T3 > L-T4 > 3,3'-5-triiodothyroacetic acid > reverse T3. The optimum pH for binding was 7.5. Purified brain CTBP was reversibly inactivated by charcoal. NADPH, NADP and thioredoxin restored binding activity to a level higher than that of the control; this effect was concentration dependent. Maximal activation was observed at 25 nM NADPH. NADP was effective only in the presence of 1 mM dithiothreitol; maximal activity was obtained at 10 nM NADP. At concentrations higher than 50 nM NADP, the binding gradually decreased. Thioredoxin in the presence of 1 mM dithiothreitol activated CTBP; maximal binding was obtained with 4 microM thioredoxin. In the presence of NADPH, NADP or thioredoxin the maximal binding capacity increased 2-4 times and the Ka was 2.6 nM-1. These results show that the activity of purified cytosolic brain T3-binding protein may be modulated by NADPH, NADP or thioredoxin.

Animals↗
PubMed1992

Induction of type III deiodinase activity in astroglial cells by thyroid hormones.

The type III deiodinase (D-III) activity in astroglial cells is induced by multiple pathways activated by cAMP, 12-O-tetradecanoylphorbol-13-acetate (TPA), and fibroblast growth factors (FGFs). This study examines the effects of thyroid hormones on D-III activity in astroglial cells with or without induction by these factors. Addition of 10 nM T3 to the culture medium caused a slow increase in D-III activity, which reached a plateau after 48 h. This increase was concentration dependent (maximal response at 10 nM). Doses as low as 0.3 nM caused significant increases in D-III activity. The effect of T3 was reversible. A dose of 10 nM L-T3, D-T3, T4, 3,5,3'-triiodothyroacetic, or 3'-isopropyl-3,5-diiodothyronine produced 5- to 15-fold increases in D-III activity after 48 h. In contrast, 10 nM L-thyronine, 3-monoiodothyronine, 3,3'-diiodothyronine, 3,5-diiodothyronine, and rT3 were without effect. A dose of 10 nM T3 or T4 amplified the D-III activity stimulated by 0.1 microM TPA, 20 ng/ml acidic FGF, or 1 mM 8-bromo-cAMP 3- to 8-fold. Otherwise, T3 rapidly inhibited D-II activity. This inhibition was concentration dependent, with a half-maximal effect around 10 nM. In conclusion, thyroid hormones induce D-III activity and potentiate the D-III activity induced by cAMP, TPA, and FGFs in astroglial cells. These reversible effects together with inhibition of D-II activity may contribute to protect the brain against hyperthyroidism.

Animals↗
PubMed1988

Characterization of a cytosolic triiodothyronine binding protein in atrium and ventricle of rat heart with different sensitivity toward thyroid hormone levels.

Cytosolic T3-binding protein (CTBP) has been identified in both the ventricle and atrium of adult rat hearts. Its biochemical characteristics and concentration have been determined in the two tissues as a function of thyroid hormone level. In both tissues association and dissociation constants were, respectively, k+1 = 1.3 x 10(8) M-1/min and k-1 = 0.025 min-1. Scatchard analysis of T3 equilibrium binding data revealed a single class of binding sites (Ka = 3.8 x 10(8) M-1). The maximal binding capacity (MBC) was 1400 fmol/mg protein in the ventricle and 730 fmol/mg protein in the atrium. The apparent mol wt of CTBP, determined by gel filtration, was 63.000. Among the thyroid hormone analogs tested in ventricular cytosol, D-T3 had the highest affinity, followed by L-T3, L-T4, 3,3',5-triiodothyroacetic acid, and rT3. These characteristics were very similar to those previously described for rat brain, and dog and rat liver and kidney CTBP. In hypothyroid rats MBC was only increased in the atrium (50-100%); after a single injection of T4 (2 micrograms/10 g BW 3 or 18 h before death) values returned to normal in the atrium and declined in the ventricle (-35%). During postnatal development, the highest MBC value (2000 fmol T3/mg protein) was observed in atria on day 10, i.e. when the serum T4 level was still low, and in the ventricle on day 30 (4000 fmol T3/mg protein) when the serum T4 level was at its highest. Binding affinities were similar in the two tissues at all ages studied. It was twice as high in both these tissues during the first week of development than in adulthood. These results favor a thyroid hormone down-regulation of the binding capacity of CTBP that would be more sensitive to the hormone in the atrium than in the ventricle.

Aging↗
PubMed1985

Cellular location of cytosolic triiodothyronine binding protein in primary cultures of fetal rat brain.

The evolution of a cytosolic triiodothyronine (T3) binding protein was studied in primary cultures of fetal rat brain. These cultures exhibited neuronal characteristics during the first week. T3 binding activity in cell supernatants increased during this period from 39 +/- 7 (mean +/- SD) to 159 +/- 24 fmoles T3/culture flask. A similar increase was observed in the soluble proteins. After day 8, neuronal death occurred and glial cells multiplied and differentiated. On day 11 an 86% drop in the binding activity was observed (24 +/- 7 fmoles T3/culture flask); the pool of soluble proteins remained stable. Scatchard analysis revealed two types of binding site in both 7- and 14-day cultured cell cytosols. Binding affinities were similar in both cytosols (KA1 approximately 1.5 X 10(9) M-1, KA2 approximately 1 X 10(8) M-1); in contrast, the number of sites was 4-fold smaller in 14-day cytosols. In subcultures mostly composed of glial cells, almost the same affinities were measured, but the numbers of both types of sites were 20 times smaller than in 7-day cells. These results show that in cell cultures from embryonic rat telencephalon, cytosolic T3 binding protein is mainly located in the neurons.

Animals↗