Biomedical subjects

J Klein

Publications and source records attributed to J Klein.

At least 433 records · Page 24Linked to original sources

PubMed1993

Glutamate activates phospholipase D in hippocampal slices of newborn and adult rats.

Phospholipase D (PLD) is activated by many neurotransmitters in a novel signal transduction pathway. In the present work, PLD activity was studied comparatively in hippocampal slices of newborn and adult rats. Basal PLD activity in adult rats was almost three times higher than in newborn rats. In newborn rats, L-glutamate and 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) time- and concentration-dependently enhanced the formation of [3H]phosphatidylpropanol ([3H]PP) and of [3H]phosphatidic acid in the presence of 2% propanol. N-Methyl-D-aspartate and kainate (both 1 mM) caused small, but significant increases (approximately 50%), whereas alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (100 microM) was ineffective. Maximally effective concentrations of glutamate (1 mM) and of 1S,3R-ACPD (300 microM) increased the PLD activity to almost 300% of basal activity; the EC50 values were 199 and 47 microM, respectively. Glutamate receptor antagonists, such as DL-2-amino-3-phosphonopropionic acid (AP3), DL-2-amino-5-phosphonovaleric acid, and kynurenate (all 1 mM) did not inhibit the glutamate-evoked increase of PP formation. In slices of adult rats, the response to 1S,3R-ACPD was significant, but small, whereas glutamate was effective only in the presence of the glutamate uptake inhibitor L-aspartate-beta-hydroxamate. It is concluded that glutamate activates PLD in rat hippocampus through an AP3-resistant metabotropic receptor. This effect is subject to ontogenetic development, with one important factor being glutamate uptake.

Aging↗

PubMed1993

Intestinal epithelial cells contribute to the enhanced generation of platelet activating factor in ulcerative colitis.

Generation of platelet activating factor by intestinal mucosal epithelial cells and lamina propria mononuclear cells was evaluated to elucidate the possible role of this mediator in the pathogenesis of inflammatory bowel disease. Epithelial and lamina propria mononuclear cells were isolated from surgical specimens from control, Crohn's disease, and ulcerative colitis patients. Platelet activating factor was extracted from highly purified cell preparations with 80% ethanol after stimulation with and without 0.2 uM calcium ionophore A23187 and was measured by platelet aggregation assay. Both cell types generated platelet activating factor activity and this was generally comparable for epithelial and lamina propria cells. Basal and stimulated platelet activating factor activity of epithelial and lamina propria cells from ulcerative colitis but not Crohn's disease patients was appreciably higher than that of control. Stimulation with calcium ionophore increased appreciably platelet activating factor activity in lamina propria cells from all groups. In contrast, only epithelial cells from ulcerative colitis showed an appreciable increase after calcium ionophore induction. These results suggest that epithelial cells are important contributors to intestinal platelet activating factor generation under normal and inflammatory conditions and that epithelial cells actively play a part in the pathogenesis of ulcerative colitis.

Adolescent↗

PubMed1993

The molecular descent of the major histocompatibility complex.

In the last few years, more than 500 primate major histocompatibility complex (Mhc) genes or parts thereof have been sequenced. The extraordinary sequence information is used here to draw conclusions about the manner of Mhc evolution. The Mhc genes are found to evolve at a relatively slow rate with the regularity of a clock. It takes from 1 to 6 million years for a new mutation to be incorporated into an Mhc allele, and the mutation rate is comparable to that of most other primate genes. The nonsynonymous sites coding for the peptide-binding region (PBR) are under relatively weak positive selection pressure (selection coefficient of a few percent only); the nonsynonymous non-PBR sites are under moderate negative selection pressure. The positive pressure is probably provided by parasites and is responsible for the trans-species persistence of allelic lineages at functional Mhc loci for more than 40 million years.

Alleles↗

PubMed1993

Synthesis and application of new microcarriers for animal cell culture. Part I: Design of polystyrene based microcarriers.

In this work (Part I), surface modified styrene polymers as new microcarrier material for animal cell culture were extensively investigated. The first synthesis steps--carried out by chloromethylation, sulphonation and nitration of the polystyrene matrix--resulted in precursors with a defined surface layer thickness. The obtained hydrophobic bulk phase showed a limited absorption of hydrophilic media components compared to polysaccharides matrices like dextran. By varying reaction conditions for microcarrier synthesis and/or by using similar styrene type polymer matrices like polyvinyltoluene, the specific density (1.028-1.05 g/cm3) of the microcarrier matrix was adjusted without problems. Chemical varying of the microcarrier surface by reaction of the precursors with different amines, saccharides or proteins led to new microcarriers with optimal conditions for cell adhesion and cell growth. All biological investigations were carried out with a BHK 21 (c-13) cell line. Detailed results will be discussed and summarized in Part II of this work.

Amines↗

PubMed1993

Synthesis and application of new microcarriers for animal cell culture. Part II: Application of polystyrene microcarriers.

In this work (Part II) the application of new polystyrene based microcarriers in cell culture technology is demonstrated. Carriers with a variety of surface modifications were tested as a growth support for cell line BHK 21. The growth behavior of the cells and cell to surface attachment were compared to Cytodex 3 (Pharmacia), which was used as a reference carrier. To select carriers with growth supporting surfaces, broad screening in petri dish experiments was carried out. Candidates with the highest growth rates were investigated in spinner flash experiments in further detail. Polystyrene carrier with a surface modification like triethylamine, maltamine or N-methylglucosamine were able to support growth as good or better as the reference carrier Cytodex 3. Economies of ingredients and ease in laboratory handling could make amine-modified polystyrenes a competitive alternative to currently commercially available microcarrier types.

Animals↗

PubMed1993

Intrapleural streptokinase as adjunctive treatment for persistent empyema in pediatric patients.

Successful treatment of persistent empyema by intrapleural streptokinase is described in five pediatric patients. Their ages ranged from 18 months to 7 years. All experienced dramatic improvement in the resolution of their empyemas following intrapleural streptokinase. Improved chest tube drainage occurred concurrently with clinical improvement. Intrapleural instillation of streptokinase appears to be a safe adjunctive therapeutic tool to facilitate drainage of persistent empyema in the small number of pediatric patients in whom it has been employed. Additional study will be required to further assess the long-term therapeutic efficacy and consequences of intrapleural streptokinase therapy.

Chest Tubes↗

PubMed1993

Managed competition in Minnesota.

The state of Minnesota Employee Group Insurance Program is one of the longest-operating examples of the managed competition approach to health insurance purchasing. The program, now in its fifth year of managed competition, has achieved many of the outcomes projected by managed competition theorists, including significant savings in health care costs and expansion of managed care in rural areas. The program's experience may offer insights into the potential success of managed competition in other settings.

Competitive Medical Plans↗

PubMed1993

Ritanserin, imipramine, and placebo in the treatment of dysthymic disorder.

Fifty outpatients with dysthymic disorder (DSM-III) were divided by double-blind randomized assignment into three groups given ritanserin, imipramine, and placebo, respectively. The trial was of 7 weeks' duration; by week 6, imipramine was clearly superior to placebo, whereas by week 7, both drugs caused significantly more improvement than the placebo. Although imipramine had slightly greater efficacy than ritanserin, it also had significantly more side effects. This was particularly evident in the higher dropout rate with imipramine. The efficacy and side effect profile of ritanserin makes it well tolerated and acceptable with dysthymic patients who, although they do not respond as quickly as patients with major depressive disorder, do show significant improvement, given sufficient time.

Adult↗

PubMed1993

Effect of GVHD on the recovery of NK cell activity and LAK precursors following BMT.

The mechanism by which GVHD augments the graft-versus-leukemia (GVL) effect of marrow transplants has not been ascertained. One possibility involves the secondary activation of natural killer (NK) cells by cytokines released during the GVHD process. To evaluate this possibility we have compared NK activity and lymphokine-activated killer cell precursor (LAKp) frequencies in serially sampled PBMC from recipients of unmanipulated autologous or allogeneic marrow with and without active GVHD. NK activity recovered rapidly after BMT and was elevated during episodes of acute GVHD. However, NK activity did not differ between recipients of autologous or allogeneic marrow without GVHD nor was NK activity increased in association with chronic GVHD. Endogenously-activated NK cells were detected only in recipients of allogeneic marrow but this did not correlate with GVHD status. In contrast to NK activity, LAKp frequencies fell below the control range during the first 8 weeks after BMT. By 9-14 weeks the median LAKp frequency was normal and did not differ between the three groups then or later after transplant. We conclude that acute GVHD may serve to increase the lytic activity of NK cells but does not result in increased LAKp. LAKp frequencies are below normal during the first two months after BMT, a finding not previously recognized from bulk culture LAK studies. The role of LAK effectors in GVL may involve more the degree of cellular activation rather than the number of cells activated.

Acute Disease↗

PubMed1993

Comparison of the pharmacokinetics of 1,2-dimethyl-3-hydroxypyrid-4-one (L1) in healthy volunteers, with and without co-administration of ferrous sulfate, to thalassemia patients.

Given the mortality and morbidity associated with acute iron intoxication, effective iron chelation which is easily administered in an emergency situation would be ideal. The pharmacokinetics of L1 were examined in 5 healthy adult male volunteers to assess its potential for use in acute iron overload. Ferrous sulfate (600 mg), L1 (900 mg), and ferrous sulfate and L1 were administered on three separate days, each one week apart. On each test day, blood samples were collected at regular intervals for the measurement of plasma L1 and total iron. Pharmacokinetic values were calculated. The data were also compared to that obtained in 10 patients with beta-thalassemia and chronic iron overload. In the normal volunteers, a 20% decrease in the area under the concentration time curve of plasma iron and of plasma L1 was demonstrated when they were co-administered. There was no change in urinary iron excretion when L1 was given with iron (p = 0.414). The elimination half-life of L1 in the thalassemia patients (137.65 +/- 48.65 min) was significantly longer than that in the healthy volunteers (77.56 +/- 13.0) (p = 0.0047) due to larger apparent volume of distribution. In all of the iron-overloaded individuals L1 resulted in increased urinary iron excretion. None of the other pharmacokinetic variables compared were significantly different between these two groups. These studies indicate that at levels below saturation, transferrin does not allow L1 to remove absorbed iron in healthy volunteers, whereas in thalassemia patients, who are beyond saturation of their iron binding capacity, the drug binds iron and promotes its excretion.

Adolescent↗

PubMed1993

Synergistic effect of nicotinamide and choline administration on extracellular choline levels in the brain.

Experimental studies indicate that the availability of free choline is a rate-limiting step for acetylcholine synthesis in central cholinergic neurons, especially when the release of acetylcholine is increased. In the present study we applied the microdialysis technique to measure the concentration of extracellular choline in the rat hippocampus. The i.p. injection of 6, 20 and 60 mg/kg of choline chloride led to short-lasting elevations of the basal choline efflux (1.78 pmol/min) by 14, 26 and 131%. N-Methylnicotinamide, a metabolite of nicotinamide, has been reported to inhibit the outward transport of choline from the cerebrospinal fluid to the blood. The s.c. injection of 5 and 10 mmol/kg of nicotinamide caused increases of extracellular choline by 54 and 113%, respectively, and choline levels remained elevated for several hr. Moreover, the administration of 10 mmol/kg of nicotinamide dramatically potentiated the effects of exogenous choline administration on choline availability in the central nervous system. The effects of 6 and 20 mg/kg of choline chloride were increased by a factor of more than 10-fold when determined as area under the curve. Additional experiments demonstrated that neither nicotinamide nor N-methylnicotinamide (100 microM) have an influence on the uptake, metabolism or release of choline in the hippocampal slice preparation. It is likely, therefore, that nicotinamide, after metabolic conversion in the brain to N-methylnicotinamide, leads to a blockade of choline clearance from the brain. The combined administration of choline and of a choline transport blocker analogous to nicotinamide may be of potential use in central cholinergic dysfunction.

Animals↗

PubMed1993

Trans-specific Mhc polymorphism and the origin of species in primates.

The major histocompatibility complex (Mhc) is a cluster of loci controlling the specific immune response in vertebrates. Mhc alleles often differ by a large number of nucleotide substitutions, some of which began to accumulate before the emergence of extant species. We have applied the theory of allelic genealogy to the primate Mhc genes with the aim of estimating the size of the founding populations. The calculations indicate that the long-term effective population size of the studied species was between 10(4) and 10(5) individuals and that it most likely never dropped below 10(3) individuals.

Alleles↗

PubMed1992

Major histocompatibility complex class II genes of zebrafish.

Twenty cDNA clones derived from beta-chain-encoding class II genes of the zebrafish (Brachydanio rerio) major histocompatibility complex (MHC) have been sequenced. They fall into three groups identifying three loci of expressed genes. The length and organization of these genes are similar to those of their mammalian homologs. Amplification by polymerase chain reaction and sequencing of genomic DNA from zebrafish collected at different locations in India indicate the existence of a fourth group of sequences (fourth locus). A high degree of polymorphism at the B. rerio MHC loci and concentration of variability to the putative peptide-binding region of the beta 1-domain-encoding part of the gene are also indicated. Large genetic distances between alleles suggest trans-specific evolution of fish MHC polymorphism. Zebrafish genes appear to be derived from a different ancestor than the various class II gene families of other vertebrates. In spite of great sequence divergence between fish and mammalian MHC genes, there seems to be a striking conservation in their overall organization.

Animals↗

PubMed1992

Quinone reduction and redox cycling catalysed by purified rat liver dihydrodiol/3 alpha-hydroxysteroid dehydrogenase.

A highly active preparation of rat liver dihydrodiol/3 alpha-hydroxysteroid dehydrogenase was obtained using a newly developed, rapid purification scheme involving affinity chromatography on Red Sepharose. Depending on the coenzyme present, the purified enzyme was found to catalyse the oxidation of dihydrodiols and steroids or the reduction of substrates with carbonyl or quinone moieties. Using a wide range of synthetic quinones derived from polycyclic aromatic hydrocarbons (PAHs), we observed a pronounced regioselectivity of the quinone reductase activity. Good substrates were the o-quinones of phenanthrene, benz(a)anthracene, chrysene and benzo(a)pyrene with the quinonoid moiety in the K-region which were reduced at rates of 1-10 mumol/min.mg enzyme. 1,4-Benzoquinone, naphthalene-1,2-quinone and benz(a)anthracene-8,9-quinone were also reduced at high rates. In contrast, alkyl-substituted quinones such as duroquinone and menadione were poor substrates for the enzyme. During the enzymatic reduction of several o-quinones, but not 1,4-benzoquinone, we observed the oxidation of large amounts of NADPH and the consumption of molecular oxygen which is indicative of a redox-cycling process. Thus, the reduction of quinones of PAHs may lead to a facilitated conjugation and excretion of these highly lipophilic compounds, but may also initiate toxic processes due to the formation of reactive oxygen species.

Animals↗

PubMed1992

Dihydrodiol dehydrogenase activities of rabbit liver are associated with hydroxysteroid dehydrogenases and aldo-keto reductases.

1. Dihydrodiol dehydrogenase activities were investigated in rabbit liver. Using a five-step purification scheme, eight isoenzymes of dihydrodiol dehydrogenase with isoelectric points of 5.55-9.3 and promoter molecular masses of 34-35 kDa were purified to apparent homogeneity and designated CF-1 to CF-6, CM-1 and CM-2. 2. CF-1 and CF-2 had near-neutral isoelectric points of 7.4 and 6.8 and molecular masses of about 125 kDa in the native state. Both enzymes readily accepted NAD+ as well as NADP+ as coenzymes, had relatively low Km values of 0.33 mM and 0.47 mM for benzene dihydrodiol and resembled previously described carbonyl reductases in their substrate specificity towards ketones and quinones. 3. CF-5 and CF-6 had acidic isoelectric points of 5.9 and 5.55 and native molecular masses of approximately 60 kDa. They displayed a strong preference for NADP(H) as coenzyme and had high Km and Vmax with benzene dihydrodiol. Since these enzymes reduced p-nitrobenzaldehyde and glucuronic acid efficiently, they appeared to be closely related to aldehyde reductase. 4. CF-4 had a high 3 alpha-hydroxysteroid dehydrogenase activity for the diagnostic substrate androsterone, a moderate activity for other 3 alpha-hydroxysteroids as well as 17 alpha-hydroxysteroids, and relatively low activities for 3 beta-hydroxysteroids and 17 beta-hydroxysteroids. CF-5 and CM-1 had high 17 beta-hydroxysteroid dehydrogenase activity for the diagnostic substrate 5 alpha-dihydrotestosterone, and low to moderate activities for other 17 beta-hydroxysteroids as well as 3 alpha-hydroxysteroids. 5. The isoenzyme CM-2 had an isoelectric point of 9.3 and was a very active quinone reductase with phenanthrene-9,10-quinone as substrate. It was potently inhibited by phenobarbital. 6. We conclude that the dihydrodiol dehydrogenase activities of rabbit liver are associated with aldehyde and carbonyl reductase and with 3 alpha-hydroxysteroid and 17 beta-hydroxysteroid dehydrogenases.

Alcohol Oxidoreductases↗

PubMed1992

Bracteomania, an inflorescence anomaly, is caused by the loss of function of the MADS-box gene squamosa in Antirrhinum majus.

Anomalous flowering of the Antirrhinum majus mutant squamosa (squa) is characterized by excessive formation of bracts and the production of relatively few and often malformed or incomplete flowers. To study the function of squamosa in the commitment of an inflorescence lateral meristem to floral development, the gene was cloned and its genomic structure, a well as that of four mutant alleles, was determined. SQUA is a member of a family of transcription factors which contain the MADS-box, a conserved DNA binding domain. In addition, we analysed the temporal and spatial expression pattern of the squa gene. Low transcriptional activity of squa is detectable in bracts and in the leaves immediately below the inflorescence. High squa transcript levels are seen in the inflorescence lateral meristems as soon as they are formed in the axils of bracts. Squa transcriptional activity persists through later stages of floral morphogenesis, with the exception of stamen differentiation. Although necessary for shaping a normal racemose inflorescence, the squa function is not absolutely essential for flower development. We discuss the function of the gene during flowering, its likely functional redundancy and its possible interaction with other genes participating in the genetic control of flower formation in Antirrhinum.

Alleles↗

PubMed1992

The effects of cardiac transplantation and cyclosporine therapy on digoxin pharmacokinetics.

Most patients needing cardiac transplantation are treated with digoxin for heart failure. Because of its narrow therapeutic range, even recommended doses of digoxin may cause severe toxicity. Several drugs, including quinidine, amiodarone, verapamil, and propafenone can interact with digoxin, leading to toxic accumulation of the glycoside. The authors have recently reported two cases of severe digitalis toxicity after the initiation of cyclosporine treatment in patients awaiting cardiac transplantation. A preliminary study on two additional patients suggested that cyclosporine reduced the plasma clearance and volume of distribution of digoxin. To assess the mechanism of this interaction, the authors studied digoxin pharmacokinetics in patients awaiting cardiac transplantation and again after the surgery, during chronic cyclosporine therapy. To separate the effects of transplantation and cyclosporine on digoxin pharmacokinetics, pharmacokinetic studies were subsequently performed in dogs to allow controlled experimental conditions for evaluation of the digoxin-cyclosporine interaction.

Administration, Oral↗

PubMed1992

Hair analysis of cocaine: differentiation between systemic exposure and external contamination.

Cocaine has been shown to accumulate in hair of admitted users. Before using this test to verify cocaine use, however, it is crucial to differentiate between systemic exposure and external contamination from being in contact with crack smoke. In the present studies, the authors document that pyrolysis of crack results in hair accumulation of cocaine, but not its benzoylecgonine metabolite, whereas after admitted cocaine use both species are detectable in hair. External contamination with crack smoke is washable, whereas systemic exposure is not. The authors suggest these two criteria to distinguish systemic exposure from external contamination.

Animals↗