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Biomedical subjects

L Frank

Publications and source records attributed to L Frank.

At least 19 recordsLinked to original sources
PubMed1996

BDNF down-regulates neurotrophin responsiveness, TrkB protein and TrkB mRNA levels in cultured rat hippocampal neurons.

Regulation of Trk receptors by their ligands, the neurotrophins, was investigated in dissociated cultures of embryonic day 18 rat hippocampal neurons. Cultures were exposed to brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) or NT-4/5 for 24 h upon plating followed by factor washout. As determined by immunohistochemical staining and phosphotyrosine blotting, the functional responses to acute stimulation with BDNF, NT-3 and NT-4/5, including c-Fos induction and phosphorylation of Trk and extracellular signal-regulated kinase (ERK) proteins, were significantly decreased after 6 days in culture by prior exposure to BDNF. As determined by Western and Northern blot analysis respectively, there was a parallel down-regulation of TrkB protein as well as of trkB and trkC mRNA levels in BDNF-pretreated cultures. Exposure to NT-3 or NT-4/5 at the same concentrations as BDNF did not down-regulate any of the measured cellular responses or TrkB protein and/or trkB and trkC mRNA levels. Regulation of hippocampal neuronal Trkb protein does not appear to be just a development phenomenon, as infusion of BDNF into the hippocampus of adult rats for 6 days produced an 80% decrease in levels of full-length TrkB protein. We thus show that exposure of hippocampal neurons to BDNF, both in culture and in the adult brain, results in down-regulation of TrkB. At least in vitro, this leads to long-term functional desensitization to BDNF, NT-3 and NT-4/5, as well as down-regulation of trkB and trkC mRNA.

Animals↗
PubMed1995

Typhoid fever in the park: epidemiology of an outbreak at a cultural interface.

The number of reported outbreaks of typhoid fever in the United States has recently increased. Only six were reported from 1980-1989, but seven outbreaks were reported in 1990. In August 1990, health officials in Montgomery County, Maryland, were notified of two cases of typhoid fever among persons who had attended both a family picnic attended by 60 persons and a Latin Food Festival attended by 100,000 people. We obtained interviews, blood and stool cultures, and Vi serologies from attendees at and food handlers for the picnic. We defined cases as culture-confirmed or probable. Of the 60 picnic attendees, 24 (40%) had cases, of which 16 were culture confirmed. Those who ate potato salad were at increased risk of disease (17/32 vs. 6/28, relative risk [RR] = 2.5, 95% confidence interval [CI] 1.1-5.4). Picnic attendees who also attended the Latin Food Festival were not at significantly greater risk of disease than those who did not, (11/22 vs. 13/38, RR = 1.5, CI = 0.8-2.7) and we found no evidence of disease among other festival attendees. The potato salad was prepared with intensive handling and without adequate temperature control by a recent immigrant from El Salvador who was asymptomatic, did not attend the picnic, had Salmonella typhi (S. typhi) in her stool, and had elevated Vi antibodies, strongly suggestive of the carrier state. Outbreaks of typhoid fever are a threat for cosmopolitan communities. While currently available control measures are unlikely to prevent all outbreaks, thorough investigation can identify previously unrecognized carriers.

Adolescent↗
PubMed1995

Failure of premature rabbits to increase lung antioxidant enzyme activities after hyperoxic exposure: antioxidant enzyme gene expression and pharmacologic intervention with endotoxin and dexamethasone.

Premature rabbits, unlike full-term rabbits, are unable to mount a protective increase in pulmonary antioxidant enzyme (AOE) activities in response to 48 h of hyperoxic exposure and demonstrate increased pulmonary O2 toxicity compared with full-term rabbits. To examine AOE gene expression of CuZn superoxide dismutase (SOD), Mn SOD, catalase, and glutathione peroxidase in preterm versus term rabbits in response to hyperoxia, 29.5 d preterm rabbits (delivered by hysterotomy) and term rabbits (spontaneously vaginally delivered) were exposed to 48 h of > 90% O2 or room air. Preterm rabbits had a significant increase in CuZn SOD mRNA without corresponding AOE activity increases, suggesting translational/posttranslational inhibition. In full-term rabbits, the magnitude of lung AOE mRNA changes was associated with concordant magnitude changes in activities of CuZn SOD, Mn SOD, and catalase, suggesting pretranslational regulation of AOE gene expression; glutathione peroxidase, however, appears to be regulated translationally/posttranslationally. To investigate potential pharmacologic means of overcoming the susceptibility of the preterm rabbit to O2 toxicity, 29.5 d preterm rabbits received 20-40 micrograms/kg of Salmonella typhimurium endotoxin or diluent S.C. (after birth and at 24 h); in separate experiments, pregnant rabbits received intramuscular injections of dexamethasone (0.01-0.05 mg/kg) or saline on gestational d 27.5 and 28.5 and underwent hysterotomy at 29.5 d.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Positive regulation of pulmonary antioxidant enzyme gene expression by prenatal thyrotropin releasing hormone plus dexamethasone treatment in premature rats exposed to hyperoxia.

Prenatal administration of thyrotropin releasing hormone (TRH) plus dexamethasone (DEX) to pregnant rats produces significantly depressed fetal lung antioxidant enzyme (AOE) activities and AOE mRNA levels in late gestation. Because of this negative regulation of AOE gene expression in the late fetal lung, we hypothesized that hormonally pretreated prematurely delivered rats might demonstrate inferior tolerance to prolonged hyperoxia. Litters of prenatal TRH+DEX-treated and sham-treated prematurely delivered rat pups (gestational d 21 of 22) were randomized to either > 95% O2 or room air for up to 14 d. The right lungs of 2- and 7-d exposure pups were assayed for AOE activities; the left lungs of the same pups were used to quantitate the concentrations of AOE mRNA by solution hybridization. The prenatal TRH+DEX-treated pups were able to induce adaptive lung AOE mRNA and activity responses to hyperoxia by 2 d of exposure; and by 7 d in O2 they showed greater increases in AOE mRNA concentrations and AOE activities in response to hyperoxic challenge compared with the sham-treated controls. Lung lipid surfactant measurements after hyperoxia were not affected by prenatal TRH+DEX treatment. In addition, TRH+DEX-pretreated premature rats did not show the hypothesized increased susceptibility to O2-induced lung damage and lethality, but, in fact, had slightly improved hyperoxic survival (d 3-7 of O2 exposure) compared with sham-treated controls. Exposure to hyperoxia significantly reduced serum triiodothyronine and thyroxine levels in the sham-control pups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Premature rats treated with propylthiouracil show enhanced pulmonary antioxidant enzyme gene expression and improved survival during prolonged exposure to hyperoxia.

In full-term newborn rats, propylthiouracil (PTU) treatment has been previously shown to decrease susceptibility to O2-induced lung damage and improve survival during hyperoxic exposure. However, no differences were found in lung antioxidant enzyme (AOE) activity responses to hyperoxia compared with O2-exposed untreated (control) term rats. To further explore possible pulmonary protective effects of PTU treatment in prematurely delivered animals, we administered PTU (0.015%) in drinking water to timed-pregnant rats for the final 10 d of gestation prior to delivery 1 d before term, and during lactation; control pregnant/nursing rats received untreated water. Both groups of 21-d premature rat pups were randomized to either > 95% O2 or room air exposure after birth for up to 14 d. The left lungs of 7-d exposure pups were used to quantitate the concentrations of AOE mRNA by solution hybridization; the right lungs of the same pups were assayed for AOE activities. PTU treatment resulted in survival rates of O2-exposed preterm rat pups that were consistently higher at all time periods in hyperoxia including 7 d [PTU, 67 of 82 (82%) versus control pups, 58 of 113 (51%); p < 0.001] and 14 d [PTU, 31 of 39 (79%) versus control, 15 of 66 (23%); p < 0.001]. Further evidence of increased tolerance to > 95% O2 in PTU pups included a significant decrease in the incidence of microscopic intraalveolar edema and a significant increase in lung tissue surfactant-related phospholipids compared with O2-exposed control pups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Structural analysis of inositol monophosphatase complexes with substrates.

The structures of ternary complexes of human inositol monophosphatase with inhibitory Gd3+ and either D- or L-myo-inositol 1-phosphate have been determined to 2.2-2.3 A resolution using X-ray crystallography. Substrate and metal are bound identically in each active site of the phosphatase dimer. The substrate is present at full occupancy, while the metal is present at only 35% occupancy, suggesting that Li+ from the crystallization solvent partially replaces Gd3+ upon substrate binding. The phosphate groups of both substrates interact with the phosphatase in the same manner with one phosphate oxygen bound to the octahedrally coordinated active site metal and another oxygen forming hydrogen bonds with the amide groups of residues 94 and 95. The active site orientations of the inositol rings of D- and L-myo-inositol 1-phosphate differ by rotation of nearly 60 degrees about the phosphate ester bond. Each substrate utilizes the same key residues (Asp 93, Ala 196, Glu 213, and Asp 220) to form the same number of hydrogen bonds with the enzyme. Mutagenesis experiments confirm the interaction of Glu 213 with the inositol ring and suggest that interactions with Ser 165 may develop during the transition state. The structural data suggest that the active site nucleophile is a metal-bound water that is activated by interaction with Glu 70 and Thr 95. Expulsion of the ester oxygen appears to be promoted by three aspartate residues acting together (90, 93, and 220), either to donate a proton to the leaving group or to form another metal binding site from which a second Mg2+ coordinates the leaving group during the transition state.

Crystallography, X-Ray↗
PubMed1994

Structural studies of metal binding by inositol monophosphatase: evidence for two-metal ion catalysis.

The structure of inositol monophosphatase has been determined to 2.60 A resolution in complexes with Mn2+ and with Mn2+ and phosphate. In the Mn2+ complex, three metal cations and one Cl were bound in the active site on each of the two subunits of the enzyme. Ligands to the three metals include the side chains of Glu 70, Asp 90, Asp 93, and Asp 220, t he carbonyl group of Ile 92, several solvent molecules and the chloride, which is a ligand to each of the cations. When phosphate is soaked into these Mn2+ cocrystals, one of the three Mn2+ ions is expelled from the active site, leaving metal ions with octahedral and tetrahedral coordination geometry. In addition, the structure of apoinositol monophosphatase was determined to 2.5 A resolution. Residues 70-75, a two-turn helical segment which is involved in metal coordination, moves away from the metal binding site by 2-3 A in the absence of cations. Residues 30-40, which wrap around the metal binding site and interact with the metal indirectly through solvent molecules and protein ligands to the metal, become disordered in the absence of metal. In various metal complexes, segmental mobility is also observed in the residues which form the metal binding sites. The results of these studies of the interaction of inositol monophosphatase with cations suggest that the enzyme accomplishes phosphate ester hydrolysis using two metal ions, one with octahedral and one with tetrahedral coordination geometry. Broad metal-binding specificity appears to result from extensive flexibility in several of the protein segments which contribute metal ligands, from the presence of alternate metal ligands and from metal coordination spheres which include water molecules.

Apoenzymes↗
PubMed1994

Effects of the 21-aminosteroid, U74389F, on bleomycin-induced pulmonary fibrosis in rats.

OBJECTIVE: To determine if a new class of agents, the 21-aminosteroids, which are reportedly potent inhibitors of iron-dependent lipid peroxidation, could protect rats from bleomycin-induced pulmonary fibrosis. SUBJECTS: Fifty-five adult male Sprague-Dawley rats. DESIGN: Prospective, randomized, blinded, controlled trial. INTERVENTIONS: The rats were subjected to intratracheal bleomycin (or saline vehicle), and were then treated with the 21-aminosteroid, U74389F (20 mg/kg/day), or vehicle, for the next 7 days. MEASUREMENTS AND MAIN RESULTS: At 21 days after bleomycin administration, pulmonary fibrosis was assessed histologically as percent of lung fields with evidence of fibrosis. Pulmonary fibrosis was assessed biochemically by measuring pulmonary elastin and hydroxyproline content. To determine if a protective effect of U74389F was linked to the 21-aminosteroid's ability to suppress lipid peroxidation, two products of lipid peroxidation were assayed in the lungs at 7 and 14 days after bleomycin exposure. By histologic assessment, the 21-aminosteroid-treated, bleomycin-exposed animals were found to have significantly decreased the extent of pulmonary fibrosis when compared with the bleomycin control group (mean 48.6 +/- 20.0 [SD] % [n = 9] vs. 68.4 +/- 19.6% [n = 11]; p < .05). In addition, lung elastin was decreased by approximately 75% (p < .05) and hydroxyproline was decreased by approximately 50% (NS) in the 21-aminosteroid-treated group when compared with the bleomycin control group. At 7 and 14 days after bleomycin exposure, all bleomycin-exposed animals had evidence of increased lipid peroxidation (conjugated dienes and thiobarbituric acid-reactive substances), but the 21-aminosteroid-treated, bleomycin-exposed animals had significantly decreased evidence of lipid peroxidation when compared with bleomycin controls. CONCLUSIONS: The 21-aminosteroid can substantially protect animals from bleomycin-induced pulmonary fibrosis and may prove useful in other lung diseases where iron-dependent, free-radical reactions and/or lipid peroxidation are presumed mechanisms of toxicity.

Animals↗
PubMed1994

Development of gas-exchange surface area in rat lung. The effect of alveolar shape.

During development, the surface area of the gas-exchange region of the lung can increase by: (1) expansion, (2) subdivision (septation), (3) replication, or (4) change of shape of the basic gas-exchange units (saccules or alveoli). We evaluated the shape of these units in rat lung from birth to adulthood. A shape factor (phi g) was defined in terms of the surface area (Sg) and the volume (Va) of the average unit, using the expression phi g = SgVa-2/3. We studied the lungs of untreated animals and of animals exposed to or treated with hyperoxia (> 95% O2) and/or dexamethasone, each of which is known to inhibit septation in early postnatal life, and with deferoxamine, which protects the lung against the inhibitory effect of hyperoxia. The values found for the shape factor showed no significant difference with regard to age or treatment. This finding suggests that: (1) saccules and alveoli are formed with a certain predetermined shape (close to a hemisphere), (2) any enlargement with time is isotropic, (3) alveolar shape is insensitive to the drastic treatments used, and (4) change of shape is not a mechanism used to increase the gas-exchange surface area of the developing rat lung.

Age Factors↗
PubMed1994

Comparative responses of premature versus full-term newborn rats to prolonged hyperoxia.

Because fetal rat lungs have lower baseline levels of both surfactant and antioxidant enzymes than full-term newborn rats, we questioned whether prematurely delivered rats might be more susceptible to O2 toxicity than those born at term. In the present studies, prematurely delivered rats (gestational d 21 of 22) and full-term rat pups were simultaneously put in > 95% O2 after birth. Surprisingly, we found that the preterm rats were not more susceptible to O2-induced lung damage and lethality than full-term newborns, but, in fact, the composite percentage of survival was even greater in the preterm pups from 7 to 9 d in hyperoxia and were similar thereafter up to 14 d in high O2. In addition, the preterm rats showed significantly decreased lung wet/dry weight ratios and consistently less severe pathologic evidence of pulmonary edema compared with term rats at 6 and 8 d of O2 exposure. The premature pups demonstrated the capability of inducing pulmonary antioxidant enzyme responses to hyperoxia by 3 d, and had significantly elevated copper-zinc superoxide dismutase, catalase, and glutathione peroxidase activities (and lung surfactant contents) at 6 d of O2 exposure compared with the term rats in O2. The rates of lung total O2 consumption and cyanide-resistant O2 consumption at d 6 in hyperoxia were not different for preterm versus term pups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Comparison of the determination of magnesium by methylthymol blue spectrophotometry and atomic absorption spectrophotometry.

Plasma samples (n = 155) of 30 patients on an intensive ward were analysed for magnesium simultaneously by atomic absorption spectrophotometry (AAS) and methylthymol blue spectrophotometry. Methylthymol blue spectrophotometry was performed at the bedside, using two different multianalysers, Easy ST 1 and Easy ST 2, Merck, D-Darmstadt. Precision was 12.2% (Easy ST 1) and 17.1% (Easy ST 2), and the average value was 0.89 mmol/l, which was above the expected range (0.72-0.88 mmol/l). Accuracy was 16.25% (Easy ST 1) and 8.75% (Easy ST 2). Analyser 2 was more accurate (8.75% versus 6.25%) but less precise (17.1% versus 12.2%) than analyser 1. Precision of AAS was between the expected values of 0.69 and 0.84 mmol/l. Easy ST and AAS gave significantly different values (p < 0.0001) for 155 measurements. Comparison of AAS and methylthymol blue spectrophotometery showed that methylthymol blue spectrophotometry produced higher values than AAS (mean difference 0.186 mmol/l). Furthermore, analyses of 40 samples of a standardized plasma concentration with methylthymol blue spectrophotometry showed a very low precision (15.3%). Easy ST cannot be assigned for urinary measurements of magnesium. Experimentally measured samples gave unaccountable results.

Bromthymol Blue↗
PubMed1994

Propylthiouracil treatment decreases the susceptibility to oxygen radical-induced lung damage in newborn rats exposed to prolonged hyperoxia.

In newborn rats, antenatal thyroid stimulation with thyroid-releasing hormone is associated with developmental decreases in pulmonary antioxidant enzyme activities and decreased survival rates during prolonged hyperoxic exposure, with pathologic evidence of increased O2-induced lung damage. Propylthiouracil (PTU), in addition to its antithyroid effects, reportedly has antioxidant properties. To explore possible pulmonary protective effects from both the antithyroid and antioxidant properties of PTU, we administered PTU (0.015%) in drinking water to timed-pregnant rats for the final 10 d of gestation and during lactation; control rats received untreated water. The survival rate of the PTU-treated pups when placed in more than 95% O2 at birth was consistently higher at all time periods in hyperoxia from 6 d [PTU, 81 of 81 (100%); control pups, 70 of 84 (83%); p < 0.01] to 14 d [PTU, 41 of 53 (77%); control pups = 14 of 56 (25%); p < 0.01]. Further evidence of increased tolerance to more than 95% O2 in PTU pups included a significant decrease in the incidence of microscopic intraalveolar edema, decreased lipid peroxidation (malondialdehyde), and a significant increase in lung tissue surfactant-related phospholipids compared with O2-exposed control pups. No differences were present in lung structural maturation, antioxidant enzyme activity response to hyperoxia, or lung tissue O2 radical formation in more than 95% O2. We conclude that PTU treatment has important postnatal effects that protect newborn rats against oxidant-induced lung injury and lethality during hyperoxia, which may be related to PTU inhibition of thyroid hormone production, effect on O2 metabolism, or its direct antioxidant properties.

Animals↗
PubMed1993

Does lung NAD(P)H:quinone reductase (DT-diaphorase) play an antioxidant enzyme role in protection from hyperoxia?

NAD(P)H:quinone reductase, or DT-diaphorase, has been studied primarily in the liver where it appears to function as an antioxidant-like enzyme in the 2-electron reduction of some quinones to less toxic hydroquinones. This property together with new molecular biology evidence that oxidants such as H2O2 can induce gene transcription of DT-diaphorase provide especially intriguing reasons to examine the possibility that lung DT-diaphorase could have an important antioxidant enzyme role versus pulmonary O2 toxicity during exposure to hyperoxia. We found that similar to the 'classical' lung antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) DT-diaphorase activity increased significantly in the late gestational fetal lung; also its activity was altered in the same way as the antioxidant enzymes by prenatal hormonal treatment. Another similarity is that DT-diaphorase activity was induced in the neonatal animal lung during hyperoxia, but not in the adult animal lung. However, using various drug treatments which markedly increased lung DT-diaphorase activity (e.g., 3-methylcholanthrene, butylated hydroxyanisole, methimazole) we found no improved hyperoxic survival in the treated adult rats. Also, dicumarol treatment, which markedly depressed DT-diaphorase activity, did not diminish the hyperoxic survival rate in an O2-tolerant adult rat model. Thus, we conclude that unlike the classical antioxidant enzymes, increased pulmonary DT-diaphorase activity is probably neither necessary nor sufficient to protect against pulmonary O2 toxicity during hyperoxia.

Aging↗
PubMed1993

The effect of an AMPA antagonist (NBQX) on postischemic neuron loss and protein synthesis in the rat brain.

Two groups of rats were subjected to 12 min of global cerebral ischemia and 6 days recirculation using the four-vessel occlusion model with hypotension and then treated with the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) antagonist NBQX [2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F) quinoxalinedione (Honoré et al. 1988]. One group was used for routine and quantitative histology and immunostaining for glial fibrillary acidic protein (GFAP). The second group was subjected to autoradiographic studies of regional cerebral protein synthesis, with special emphasis on the hippocampus, the frontal cortex, and the thalamus. It was found that neuroprotective treatment with NBQX normalized cerebral protein synthesis rate (CPSR) in all investigated regions 6 days after ischemia. In untreated ischemic animals CPSR was normalized in all regions except for the CA3 and thalamus, where it had increased by 29% and 41%, respectively. Treatment of controls with NBQX had no effect on CPSR after 6 days. The histological investigations revealed that NBQX did not protect vulnerable cells in the dentate hilus and the reticular thalamic nucleus (RTN). In these regions reactive astrocytosis visualized by GFAP immunostaining was equally pronounced in both ischemic and NBQX-treated animals, and most neurons in the RTN were eosinophilic. The 80-100% pyramidal neuron loss in CA1 was accompanied by a high degree of reactive astrocytosis, whereas the NBQX-treated animals showed no signs of astrocytosis in this region. The ischemic CA1 pyramidal layer was also massively invaded by microglia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Negative regulation of antioxidant enzyme gene expression in the developing fetal rat lung by prenatal hormonal treatments.

Prenatal administration of thyrotropin-releasing hormone (TRH) or TRH plus dexamethasone (DEX) to pregnant rats accelerates lung surfactant system development in late gestation, but paradoxically depresses the normal late gestational elevation in fetal lung antioxidant enzyme (AOE) activities (Pediatr Res 30:522, 1991). In these present studies, we tested whether both prenatal hormonal treatments act to depress normal fetal lung AOE development by negative regulation of AOE gene expression. We used solution hybridization to quantitate the concentration of AOE mRNA. Results of the developmental studies revealed significantly decreased lung mRNA concentrations of copper-zinc superoxide dismutase, manganese superoxide dismutase, catalase, and glutathione peroxidase in late gestation as a result of prenatal TRH treatment. The addition of DEX administration did not reverse the lowered expression of lung AOE genes due to TRH treatment, but instead resulted in significant additional decreases in pulmonary AOE mRNA levels at both 21 and 22 d of gestation. The tested AOE mRNA half-lives (stabilities) revealed no significant differences between controls (8.0-10.5 h) and TRH-treated (8.2-9.5 h) and TRH-plus-DEX treatment (7.8-10.7 h) groups. These findings suggest that prenatal treatment with TRH and with TRH plus DEX acts to depress the normal late fetal lung AOE activity elevations by (direct) negative regulation of AOE gene expression, and the decreased AOE expression is likely regulated at the level of gene transcription rather than posttranscriptionally.

Animals↗