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Biomedical subjects

A Meister

Publications and source records attributed to A Meister.

At least 91 records · Page 5Linked to original sources
PubMed1991

Suppression of human immunodeficiency virus expression in chronically infected monocytic cells by glutathione, glutathione ester, and N-acetylcysteine.

The effects of glutathione (GSH), glutathione ester (GSE), and N-acetyl-L-cysteine (NAC) on the induction of human immunodeficiency virus (HIV) expression were investigated in the chronically infected monocytic U1 cell line, a previously described cellular model for HIV latency. U1 cells constitutively express low levels of virus, which can be increased by phorbol 12-myristate 13-acetate (PMA), tumor necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), and other inducers. GSH, GSE, and NAC suppressed in a dose-dependent fashion the induction of HIV expression mediated by PMA, TNF-alpha, and IL-6, in the absence of cytotoxic or cytostatic effects. Reverse transcriptase activity, inducible by PMA, TNF-alpha, or IL-6, was decreased by 80-90% after pretreatment with GSH, GSE, or NAC. The induction of total HIV protein synthesis was also decreased appreciably after pretreatment with GSH, GSE, or NAC. The accumulation of HIV mRNA was substantially suppressed after pretreatment with NAC but to a lesser extent after pretreatment with GSH or GSE. Although PMA induces the expression of TNF-alpha in U1 cells, the suppressive effect of GSH, GSE, and NAC on PMA-induced HIV expression in U1 cells was not associated with the inhibition of TNF-alpha expression. The present findings, which elucidate relationships between cellular GSH and HIV expression, suggest that therapy with thiols may be of value in the treatment of HIV infection.

Acetylcysteine↗
PubMed1991

Glutathione deficiency produced by inhibition of its synthesis, and its reversal; applications in research and therapy.

Glutathione, which is synthesized within cells, is a component of a pathway that uses NADPH to provide cells with their reducing milieu. This is essential for (a) maintenance of the thiols of proteins (and other compounds) and of antioxidants (e.g. ascorbate, alpha-tocopherol), (b) reduction of ribonucleotides to form the deoxyribonucleotide precursors of DNA, and (c) protection against oxidative damage, free radical damage, and other types of toxicity. Glutathione interacts with a wide variety of drugs. Despite its many and varied cellular functions, it is possible to achieve therapeutically useful modulations of glutathione metabolism. This article emphasizes an approach in which the synthesis of glutathione is selectively inhibited in vivo leading to glutathione deficiency. This is achieved through use of transition-state inactivators of gamma-glutamylcysteine synthetase, the enzyme that catalyzes the first and rate-limiting step of glutathione synthesis. The effects of marked glutathione deficiency, thus produced in the absence of applied stress, include cellular damage associated with severe mitochondrial degeneration in a number of tissues. Such glutathione deficiency is not prevented or reversed by giving glutathione. The cellular utilization of GSH involves its extracellular degradation, uptake of products, and intracellular synthesis of GSH. This is a normal pathway by which cysteine moieties are taken up by cells. Glutathione deficiency induced by inhibition of its synthesis may be prevented or reversed by administration of glutathione esters which, in contrast to glutathione, are readily transported into cells and hydrolyzed to form glutathione intracellularly. Research derived from this model has led to several potentially useful therapeutic approaches, one of which is currently in clinical trial. Thus, certain tumors, including those that exhibit resistance to several drugs and to radiation, are sensitized to these modalities by selective inhibition of glutathione synthesis. An alternative interpretation is suggested which is based on the concept that some resistant tumors have high capacity for glutathione synthesis and that such increased capacity may be as significant or more significant in promoting the resistance of some tumors than the cellular levels of glutathione. Therapeutic approaches are proposed in which normal cells may be selectively protected against toxic antitumor agents and radiation by cysteine- and glutathione-delivery compounds. Current studies suggest that research on other modulations of glutathione metabolism and transport would be of interest.

Animals↗
PubMed1991

Exocrine pancreas transcription factor 1 binds to a bipartite enhancer element and activates transcription of acinar genes.

Exocrine pancreas (XP) enhancers, which contain a conserved core sequence, are active only in XP cells. A core enhancer-binding activity also appears to be restricted to XP nuclei. Here we describe the properties of a factor, purified approximately 100,000-fold from pancreas nuclei, which displays core enhancer-binding activity. It is not identical to previously characterized factors and is termed exocrine pancreas transcription factor 1 (XPF-1). In the highly purified preparation, only a single major protein of 60 kDa was detected by silver staining on sodium dodecyl sulfate-gels and by UV cross-linking. XPF-1 binds to the core enhancer of all tested XP genes and not to a mutant sequence which is inactive in vivo. High-affinity binding sites are bipartite. The results of competition binding and UV-cross-linking assays suggest that XPF-1 interacts with both motifs. XPF-1 selectively stimulates transcription of core enhancer templates in an in vitro transcription system. We hypothesize that XPF-1 plays a role in activation of the transcription of XP-specific genes.

Amylases↗
PubMed1990

Cellular glutathione as a determinant of sensitivity to mercuric chloride toxicity. Prevention of toxicity by giving glutathione monoester.

Depletion of glutathione (GSH) by treatment of mice with buthionine sulfoximine (BSO), an effective inhibitor of gamma-glutamylcysteine synthetase, markedly enhanced (about 10-fold) the lethal and renal toxicity of mercuric chloride. The lethal toxicity of HgCl2 was prevented by administration of GSH monoester; this was observed in mice pretreated with BSO and given a low dose of HgCl2, and also in untreated mice that were given a much higher dose of HgCl2. In contrast, administration of GSH did not protect. Since administered GSH is not transported effectively into cells, whereas GSH monoester is transported and split intracellularly to GSH, the findings indicate that protection against HgCl2 requires intracellular GSH. The experimental approaches used here suggest that cellular GSH is a major determinant of sensitivity to HgCl2 toxicity, and also that administration of GSH esters may be useful for prevention of HgCl2 toxicity.

Animals↗
PubMed1990

Transport into brain of buthionine sulfoximine, an inhibitor of glutathione synthesis, is facilitated by esterification and administration of dimethylsulfoxide.

Buthionine sulfoximine (BSO), an inhibitor of glutathione synthesis, is poorly transported into the brain of adult mice, and only a slight decrease (approximately 10%) in the level of brain glutathione is found 30-60 min after intraperitoneal administration of BSO. When BSO is given as the ethyl ester, the brain level of BSO increases substantially after 5-15 min, and the glutathione level decreases by about 25% after 30-60 min. When BSO or its ester is given in 15% dimethylsulfoxide solution the brain levels of BSO are increased significantly and the brain glutathione levels are decreased by 20-35%. These observations suggest procedures that may be useful in decreasing the glutathione levels of the brains of adult animals. The finding that administration of BSO ethyl ester led to about a 25% decrease in the brain level of glutathione within 15 min suggests that a fraction of brain glutathione turns over very rapidly and may therefore be of special physiological significance.

Animals↗
PubMed1990

Amino acid sequence of rat kidney gamma-glutamylcysteine synthetase.

gamma-Glutamylcysteine synthetase catalyzes the first step in the synthesis of glutathione. The enzyme isolated from rat kidney has two subunits (heavy, Mr 73,000; and light, Mr 27,700) which may be dissociated by treatment with dithiothreitol. The heavy subunit exhibits all of the catalytic activity of the isolated enzyme and also feedback inhibition by glutathione. The light subunit has no known function and may not be an integral part of the enzyme. cDNA clones encoding rat kidney gamma-glutamylcysteine synthetase were isolated from a lambda gt11 cDNA library by immunoscreening with antibody against the isolated enzyme and further screening with oligonucleotide probes derived from several peptides whose sequences were determined by the Edman method. The nucleotide sequence of the mRNA for the heavy subunit was deduced from the sequences of the cDNA of three such clones. The sequence, which codes for 637 residues (Mr 72,614), contains all four of the independently determined peptide sequences (approximately 100 residues). This amino acid sequence shows extremely low overall similarity to that of gamma-glutamylcysteine synthetase isolated from Escherichia coli.

Amino Acid Sequence↗
PubMed1990

Changes in auditory evoked brain potentials during ultra-low frequency whole-body vibration of man or of his visual surround.

Auditory evoked brain potentials (AEP) were recorded from nine healthy male subjects during three types of condition: A - subject and visual field stationary; B - subject vibrated (z-axis, 0.6 Hz, 1.85 ms-2 rms), visual field stationary; C - subject stationary, visual field vibrated (as for B). The visual surround was confined to a checkerboard pattern in front of the subject. Auditory stimuli (1000 Hz, 86 dB, interstimulus interval 7 s) were delivered via headphones to evoke AEP. Vibration-synchronous activity in the EEG was eliminated by a subtraction technique. In comparison with condition A, conditions B and C caused an attenuation of P2 and N1P2 components of AEP together with an increased latency of N1. Effects of conditions B and C did not differ. Direct vestibular stimulation and mechanisms specific for whole-body vibration were rejected as modes of action. The AEP-changes and the subjective evaluation of experimental conditions, arousal and performance, as well as symptoms of kinetosis (motion sickness) suggest a sensory mismatch, leading to a "latent kinetosis" with de-arousal, as the dominating mechanism by which the processing of information was affected. This suggestion was supported by an additional pilot study. Under real working conditions a similar effect can be expected during relative motion between the driver and his visual surround, i.e. even with perfect vibro-isolation of the driver's seat.

Adult↗
PubMed1990

High-affinity transport of glutathione is part of a multicomponent system essential for mitochondrial function.

Glutathione, an essential cellular antioxidant required for mitochondrial function, is not synthesized by mitochondria but is imported from the cytosol. Rat liver mitochondria have a multicomponent system that underlies the remarkable ability of mitochondria to take up and retain glutathione. At external glutathione levels of less than 1 mM, glutathione is transported into the mitochondrial matrix by a high-affinity component (Km, approximately 60 microM; V max, approximately 0.5 nmol/min per mg of protein), which is saturated at levels of 1-2 mM and stimulated by ATP. Another component has lower affinity (Km, approximately 5.4 mM; Vmax, approximately 5.9 nmol/min per mg of protein) and is stimulated by ATP and ADP. Both components are inhibited by carbonylcyanide p-(trifluoromethoxy)phenylhydrazone (FCCP), glutamate, and ophthalmic acid. Increase of extramitochondrial glutathione promotes uptake and exchange; the intermembranous space seems to function as a recovery zone that promotes efficient recycling of matrix glutathione. The findings are in accord with in vivo data showing that (i) rapid exchange occurs between mitochondrial and cytosolic glutathione, (ii) lowering of cytosolic glutathione levels (produced by administration of buthionine sulfoximine) decreases export of glutathione from mitochondria to cytosol, and (iii) administration of glutathione esters increases glutathione levels in mitochondria more than those in the cytosol.

Animals↗
PubMed1990

Identification of a highly reactive threonine residue at the active site of gamma-glutamyl transpeptidase.

gamma-Glutamyl transpeptidase [(5-glutamyl)-peptide:amino-acid 5-glutamyltransferase, EC 2.3.2.2], an enzyme of major importance in glutathione metabolism, was inactivated by treating it with L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-[3-14C]isoxazoleacetic acid. This selective reagent binds stoichiometrically to the enzyme; more than 90% of the label was bound to its light subunit. Enzymatic digestion of the light subunit gave a 14C-labeled peptide that corresponds to amino acid residues 517-527 of the enzyme and two incomplete digestion products that contain this labeled peptide moiety. The radioactivity associated with this peptide was released with threonine-523 during sequencing by the automated gas-phase Edman method. The light subunit contains 14 other threonine residues and a total of 19 serine residues; these were not labeled. Threonine-523 is situated in the enzyme in an environment that greatly increases its reactivity, indicating that other amino acid residues of the enzyme must also participate in the active-site chemistry of the enzyme.

Amino Acid Sequence↗
PubMed1990

Glutathione is required for intestinal function.

Glutathione (GSH) deficiency produced in mice by giving buthionine sulfoximine leads to severe degeneration of the epithelial cells of the jejunum and colon. This is prevented by giving GSH monoester (orally or i.p.) and also by giving GSH (orally, but not i.p.). The i.p. administration leads to high plasma levels of GSH but does not appreciably increase GSH levels in intestinal mucosa or pancreas. These and previous studies on lens, lung, lymphocytes, liver, heart, and skeletal muscle indicate that there is very little, if any, transport of intact GSH from plasma to these tissues. Cells can use extracellular GSH by a pathway involving its cleavage, uptake of products and intracellular GSH synthesis. Epithelial cells of the gastrointestinal tract may use this pathway and can also take up lumenal GSH (which arises partly from the bile) by a mechanism(s) that may involve transport of dipeptides or of GSH. It is suggested that biliary GSH normally functions in the protection of intestinal mucosa. Administration of GSH may be protective of the gastrointestinal epithelium and may also serve as a good source of cysteine moieties for intracellular GSH synthesis in the gastrointestinal tract and in other tissues. Administration of GSH delivery agents such as GSH esters is more effective than administration of GSH in increasing cellular and mitochondrial levels of GSH.

Animals↗
PubMed1990

Glutathione regulates activation-dependent DNA synthesis in highly purified normal human T lymphocytes stimulated via the CD2 and CD3 antigens.

Regulation of proliferation of normal human T lymphocytes (T cells) by glutathione (GSH) was explored with T-cell activation models that do not require accessory cell signals. L-Buthionine-(S,R)-sulfoximine (BSO), which inactivates gamma-glutamylcysteine synthetase and therefore inhibits GSH synthesis, inhibited proliferation elicited by monoclonal antibodies directed at cluster designation 2 (CD2) and CD3 antigens, or by sn-1,2-dioctanoylglycerol and ionomycin. L-Buthionine-(R)-sulfoximine, which does not inactivate gamma-glutamylcysteine synthetase, did not affect proliferation. BSO-induced inhibition of accessory cell-independent T-cell proliferation was not reversed by recombinant human interleukin 2, despite activation-dependent expression of interleukin 2 receptor alpha by T cells treated with BSO. However, BSO-associated inhibition of T-cell proliferation was reversed by GSH or GSH ester. These studies, which show that GSH can directly modulate proliferation of highly purified T cells, suggest that GSH is essential for steps close to or at DNA synthesis. The availability of methods for decreasing and for increasing GSH levels suggest therapies to produce (i) immunosuppression (of value in organ transplantation), and (ii) immunopotentiation (of potential value in treatment of immunodeficiency states such as AIDS).

Antibodies, Monoclonal↗
PubMed1990

Protection against cisplatin toxicity by administration of glutathione ester.

The role of cellular glutathione in the prevention of toxicity due to the anti-cancer drug cisplatin (cis-diamminedichloroplatinum) was explored in mice treated with buthionine sulfoximine (BSO), a selective inhibitor of gamma-glutamylcysteine synthetase (and therefore of glutathione synthesis), and with glutathione and glutathione monoisopropyl ester. Pretreatment of mice with BSO enhanced the lethal toxicity of cisplatin by about twofold. Administration of glutathione ester (dose, 2.5-7.5 mmol/kg) protected against lethal cisplatin toxicity; glutathione was also effective, but much less so. Glutathione ester, in contrast to glutathione, is effectively transported into cells and split to glutathione intracellularly. The previous findings that administered glutathione does not protect against lethal toxicity due to cadmium ions and mercuric ions, whereas glutathione ester does, suggest that intracellular glutathione is required for protection against these heavy metal ions. That administration of glutathione has a protective effect on cisplatin toxicity suggests that the toxic effects of cisplatin may be exerted both intracellularly and extracellularly, and that extracellular glutathione (or its degradation products) may form a complex with cisplatin extracellularly. The finding that glutathione ester is more effective than glutathione in protecting against the toxicity of cisplatin suggests that use of glutathione ester may be therapeutically advantageous.

Animals↗
PubMed1990

Pan: a transcriptional regulator that binds chymotrypsin, insulin, and AP-4 enhancer motifs.

Two cDNAs were cloned that encode proteins (Pan-1 and Pan-2, with predicted molecular masses of 67.4 and 67.7 kD, respectively) that bind to a conserved transcriptional regulatory element present in pancreatic exocrine genes. The cDNAs are virtually identical in the region that encodes the amino-terminal 525 amino acids; they differ only by a 3-nucleotide insertion that results in the addition of a single amino acid. The cDNAs, however, code for related, but divergent, carboxy-terminal regions. Expression of the cloned cDNAs in HeLa cells activates expression of a cotransfected chimeric gene containing multimers of the pancreatic conserved element linked to a minimal promoter. Pan-1 and Pan-2 bind to the consensus sequence CAC/GCTGT/C, the CACCTGTC motif, which is present in transcriptional control elements of several genes. Both Pan-1 and Pan-2 bind to related motifs present in the rat insulin enhancer as well as a DNA segment containing the SV40 AP-4 element. The Pan-1 and Pan-2 cDNAs display extensive sequence identity with partial cDNA clones encoding E12 and E47, which bind to the immunoglobulin kappa E2 cis-active element, and may be derived from the same gene. These factors belong to a set of genetically distinct molecules, including AP-4 and MLTF, that bind to the CACCTGTC motif or related sequences. The Pan/E12,E47 proteins also show structural similarity with the Drosophila daughterless protein, MyoD, Myogenin, and Myf-5.

Amino Acid Sequence↗
PubMed1990

[The perceptibility of a microwave field under experimental conditions].

The development of effects caused physical environmental factors on subjective images and on behaviour of exposed persons generally presupposes the perceptibility of the factors concerned via receptors. Though there are no indications regarding the existence of specific receptors for electromagnetic fields as yet, one or the other person is certain of being able to notice the presence of electromagnetic fields. The perceptibility of microwave fields and related effects on short-term subjective effects have been tested in an experimental series. We found a) significant differences in the studied effects between experimental and control situations, b) stability of effects in retests, c) increasing correct indications concerning the presence of fields after several training sessions. Subjects could be discriminated regarding the individual level of effects. Moreover female versus male subjects showed different levels of correct indications of fields. The most important symptoms related to field detection are listed.

Double-Blind Method↗
PubMed1989

The chymotrypsin enhancer core. Specific factor binding and biological activity.

A 20-base pair (bp) conserved sequence present in the 5'-flanking regions of genes highly expressed in the exocrine pancreas forms part of the enhancers of the rat amylase 2A, chymotrypsin B, and elastase I genes. Factor(s) that interact with the conserved DNA sequence of the rat chymotrypsin B gene in vitro have been detected in extracts from acinar cells but not in three other cell lines tested. Transfection experiments suggest that the acinar cell factor(s) recognizing this enhancer core sequence are transcriptional activators. Multimers of a 28-bp sequence located by DNase I protection are capable of activating heterologous promoters in acinar cells. In vitro competition binding and methylation interference analyses indicate protein-DNA interactions at two distinct sites 10 base pairs apart on the DNA. This interaction is identical in extracts from cultured acinar cells as well as from whole pancreas tissue. The presence of two contiguous binding motifs on the same face of the DNA suggests that two (multiple) factors cooperate in the transcriptional regulation of this gene. We term these factors CACCTG pan-1 and TTTCCC pan-1. A factor with the binding specificity of the adenovirus major late transcription factor (MLTF) cross-reacts with the factor CACCTG pan-1 in vitro. However, the distribution of this factor in the various cells does not correlate with the activity of the enhancer core element in vivo. Further, conversion of the chymotrypsin sequence into a consensus MLTF site by three-point mutations abolished enhancer activity in acinar cells. Thus, the MLTF-like factor cannot substitute functionally for the factor CACCTG pan-1 and may act as an inhibitor of chymotrypsin enhancer function.

Animals↗
PubMed1989

Glutathione monoesters.

Glutathione monoesters in which the glycine carboxyl group is esterified are effective cellular glutathione delivery agents because they are readily transported into cells and are deesterified intracellularly. In contrast, glutathione itself is not effectively transported into cells. Detailed procedures are given for the preparation of such esters from glutathione and the corresponding alcohol using hydrogen chloride or sulfuric acid as the catalyst.

Carboxylic Acids↗