Search PubMed⌕ Search

Biomedical subjects

S Mihm

Publications and source records attributed to S Mihm.

At least 37 records · Page 2Linked to original sources
PubMed1995

Modulation of transcription factor NF kappa B activity by intracellular glutathione levels and by variations of the extracellular cysteine supply.

HIV-infected individuals and SIV-infected rhesus macaques have, on the average, decreased plasma cysteine and cystine concentrations and decreased intracellular glutathione levels. We now show that a depletion of intracellular glutathione in a human T cell line (Molt-4) inhibits the activation and nuclear translocation of the transcription factor NF kappa B, whereas incubation with increasing extracellular concentrations of cysteine inhibits the DNA-binding and transactivating activity of NF kappa B. Because inhibition of DNA-binding activity is associated with increasing intracellular glutathione disulfide levels and GSSG can be shown to inhibit the DNA-binding activity directly in cell-free systems, our studies suggest that GSSG is a physiologically relevant inhibitor in intact cells also. NF kappa B controls many immunologically important genes, so our studies suggest that the immune system may be sensitive not only against a cysteine and glutathione deficiency but also against an excess of cysteine.

Acetylcysteine↗
PubMed1995

Cryoglobulinemia in chronic hepatitis C virus infection: prevalence, clinical manifestations, response to interferon treatment and analysis of cryoprecipitates.

Chronic hepatitis C virus infection can be associated with mixed cryoglobulinemia and systemic vasculitis. The pathogenesis remains poorly understood. 55 consecutive patients with chronic HCI infection (anti-HCV- and serum HCV RNA-positive) were studies prospectively. Cryoglobulinemia was detected in 28 patients (51%) with a mean cryocrit level of 2.2%. Clinical symptoms of vasculitis were encountered in six patients. Compared to those HCV-infected patients without cryoglobulinemia the following distinctive features were observed in the presence of cryoglobulinemia: increased age (p<0.02), female preponderance (p<0.002), longer-lasting HCV infection (mean of 10.7 vs. 4.7 yrs), higher prevalence of cirrhosis (42.8 vs. 0%), increased serum concentration of IgM and increased rheumatoid factor activity, decreased concentration of serum C4 (each p<0.05). The response to interferon treatment was similar in patients with and without cryoglobulinemia. When cryoprecipitates were analyzed by immunofixation, type II cryoglobulinemia was present in 1/3 and type III in 2/3 of patients. By SDS-PAGE four different proteins were demonstrable in cryoprecipitates each identified by immunoblotting as IgG and IgM heavy or light chains respectively. Cryoprecipitate IgGs were shown to react with HCV structural as well a non-structural proteins in a recombinant immunoblotting assay (RIBA). In contrast, cryoprecipitate IgMs reacted only to the HCV core protein c22-3. HCV RNA was detected in cryoprecipitates without a significant enrichment when compared to the corresponding serum or supernatant HCV RNA content. Given the monoclonality of some cryoprecipitate IgM and their reactivity to HCV core, a cross-reactivity to IgG was postulated. In fact, when performing a computer-assisted search for sequence homology, a motif within the core protein (EGLGWAGWL, conserved in HCV genotypes) was identified homologous to a sequence of IgG heavy chains. Thus, temperature-dependent affinity changes of IgM anti-HCV core (nonapeptide) and ensuing complex formation with IgG via binding to the homologous IgG sequence could be a mechanism of cryoprecipitate formation.

Adult↗
PubMed1994

Distinct effects of glutathione disulphide on the nuclear transcription factor kappa B and the activator protein-1.

Oxidative conditions potentiate the activation of the nuclear transcription factor kappa B (NF kappa B) and the activator protein-1 (AP-1) in intact cells, but inhibit their DNA binding activity in vitro. We now show that both the activation of NF kappa B and the inhibition of its DNA binding activity is modulated in intact cells by the physiological oxidant glutathione disulphide (GSSG). NF kappa B activation in human T lineage cells (Molt-4) by 12-O-tetradecanoyl-phorbol 13-acetate was inhibited by dithiothreitol, and this was partly reversed by the glutathione reductase inhibitor 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or by hydrogen peroxide, indicating that GSSG may be required for NF kappa B activation. These effects of BCNU and hydrogen peroxide were not seen in glutathione-depleted cells. However, NF kappa B and AP-1 activation were potentiated by dithiothreitol if added to cell cultures 1 h after the phorbol ester, indicating that a shift of redox conditions may support optimal oxidative activation with minimal inhibition of DNA binding. The elevation of intracellular GSSG levels by BCNU before stimulation suppressed the chloramphenicol acetyltransferase expression dependent on NF kappa B but increased that dependent on AP-1. This selective suppression of NF kappa B was also demonstrable by electrophoretic mobility shift assays. In vitro, GSSG inhibited the DNA binding activity of NF kappa B more effectively than that of AP-1, while AP-1 was inhibited more effectively by oxidized thioredoxin.

Animals↗
PubMed1994

Effect of glutathione depletion and oral N-acetyl-cysteine treatment on CD4+ and CD8+ cells.

HIV-infected individuals and SIV-infected rhesus macaques have, on the average, decreased plasma cysteine and cystine concentrations and decreased intracellular glutathione levels. We show that the cysteine supply and the intracellular glutathione levels have a strong influence on the T cell system. A study of healthy human subjects revealed that persons with intracellular glutathione levels of 20-30 nmol/mg protein had significantly higher numbers of CD4+ T cells than persons with either lower or higher glutathione levels. Persons who moved during a 4-week observation period from the optimal to the suboptimal range (10-20 nmol/mg) experienced, on the average, a 30% decrease in CD4+ T cell numbers. This decrease was prevented by treatment with N-acetyl-cysteine (NAC). NAC caused this relative increase of CD4+ T cell numbers in spite of decreasing glutathione levels and not by increasing the glutathione level. Our studies suggest that the immune system may be exquisitely sensitive not only against a cysteine and glutathione deficiency but also against an excess of cysteine.

Acetylcysteine↗
PubMed1994

Functions of glutathione and glutathione disulfide in immunology and immunopathology.

Even a moderate increase in the cellular cysteine supply elevates the intracellular glutathione (GSH) and glutathione disulfide (GSSG) levels and potentiates immunological functions of lymphocytes in vitro. At low GSSG levels, T cells cannot optimally activate the immunologically important transcription factor NF kappa B, whereas high GSSG levels inhibit the DNA binding activity of NF kappa B. The effects of GSSG are antagonized by reduced thioredoxin (TRX). As the protein tyrosine kinase activities p56lck and p59fyn are activated in intact cells by hydrogen peroxide, they are likely targets for GSSG action. These redox-regulated enzymes trigger signal cascades for NF kappa B activation and transduce signals from the T cell antigen receptor, from CD4 and CD8 molecules, and from the IL-2 receptor beta-chain. The effector phase of cytotoxic T cell responses and IL-2-dependent functions are inhibited even by a partial depletion of the intracellular GSH pool. As signal transduction is facilitated by prooxidant conditions, we propose that the well-known immunological consequences of GSH depletion ultimately may be results of the accompanying GSSG deficiency. As HIV-infected patients and SIV-infected rhesus macaques have, on the average, significantly decreased plasma cyst(e)ine and intracellular GSH levels, we also hypothesize that AIDS may be the consequence of a GSSG deficiency as well.

Amino Acid Sequence↗
PubMed1992

HIV-induced cysteine deficiency and T-cell dysfunction--a rationale for treatment with N-acetylcysteine.

Markedly decreased plasma cystine and cysteine concentrations have been found in HIV-infected patients at all stages of the disease and in SIV-infected rhesus macaques. The elevated glutamate levels found in the same patients aggravate the cysteine deficiency by inhibiting the membrane transport activity for cystine. The intact immune system appears to require a delicate balance between pro-oxidant and antioxidant conditions, maintained by a limited and well-regulated supply of cysteine. This balance is obviously disturbed in HIV infection and may contribute to the pathogenesis of AIDS.

Acetylcysteine↗
PubMed1991

Requirement for prooxidant and antioxidant states in T cell mediated immune responses.--Relevance for the pathogenetic mechanisms of AIDS?

The discovery of decreased plasma cysteine and cystine levels and elevated plasma glutamate levels in HIV-infected patients has led to intense investigations into the role of cysteine in T cell-mediated immune responses. A large body of evidence indicates that certain aspects of the T cell response require the action of active oxygen derivatives while other aspects of the response require the action of antioxidants such as cysteine and glutathione (GSH). The prooxidant and antioxidant states may be required sequentially at different times during T cell activation. The extremely weak cystine transport activity of T cells together with oxidizing metabolites from inflammatory microenvironments appear to be important factors that support the prooxidant state. The relatively high cystine transport activity of the antigen-presenting macrophages, in contrast, provides these cells with a "cysteine pumping" function that allows the antigen binding T cells in their vicinity to shift to the antioxidant state. The difference between the membrane transport activities for cysteine of T cells and macrophages thus appears to be the key element of a mechanism that facilitates both, the prooxidant state of T cells and their regulated shift to the antioxidant state. When T cells do not receive sufficient amounts of cysteine, the intracellular GSH levels and rates of DNA synthesis activity decrease, and the cells may suffer from various manifestations of oxidative damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMed1991

Modulation of lymphocyte functions and immune responses by cysteine and cysteine derivatives.

Mitogenically stimulated human peripheral blood lymphocytes and T cell clones were found to have weak membrane transport activity for the disulfide cystine but strong membrane transport activity for the thiol amino acid cysteine. Cysteine, however, is represented at the lowest concentration among all protein-forming amino acids in the blood plasma. Complementary laboratory experiments have shown that the cysteine supply is indeed limiting for important lymphocyte functions. Proliferative responses of mitogenically stimulated lymphocytes and T-cell clones and the activation of cytotoxic T cells in allogeneic mixed lymphocyte cultures are strongly influenced by small variations in the extracellular cysteine concentration even in the presence of relatively high and approximately physiologic concentrations of cystine. Cysteine can be substituted by N-acetylcysteine but not by cystine. The more detailed analysis revealed that the extracellular supply of cysteine influences strongly the intracellular level of glutathione (GSH) and also the activity of the transcription factor NF kappa B that regulates the expression of several immunologically relevant genes. In vitro experiments including double-chamber experiments with macrophages and lymphocytes revealed, moreover, that cysteine plays an important role as a regulatory mediator between these cell types. The cysteine supply is impaired directly or indirectly in several pathologic conditions that are associated with immunodeficiencies, including the acquired immune deficiency syndrome (AIDS). Cysteine or cysteine derivatives may therefore be considered for the treatment of patients with HIV-1 infection.

Animals↗
PubMed1991

Inhibition of HIV-1 replication and NF-kappa B activity by cysteine and cysteine derivatives.

HIV-1 proviral DNA contains two binding sites for the transcription factor NF-kappa B. HIV-1-infected individuals have, on average, abnormally high levels of tumour necrosis factor alpha (TNF alpha) and abnormally low plasma cysteine levels. We therefore investigated the effects of cysteine and related thiols on HIV-1 replication and NF-kappa B expression. The experiments in this report show that cysteine or N-acetylcysteine (NAC) raise the intracellular glutathione (GSH) level and inhibit HIV-1 replication in persistently infected Molt-4 and U937 cells. However, inhibition of HIV-1 replication appears not to be directly correlated with GSH levels. Cysteine and NAC also inhibit NF-kappa B activity as determined by electrophoretic mobility shift assays and chloramphenicol acetyl-transferase (CAT) gene expression under control of NF-kappa B binding sites in uninfected cells. This suggests that the cysteine deficiency in HIV-1-infected individuals may cause an over-expression of NF-kappa B-dependent genes and enhance HIV-1 replication. NAC may be considered for the treatment of HIV-1-infected individuals.

Acetylcysteine↗
PubMed1991

Immunomodulatory action of eicosanoids and other small molecular weight products of macrophages.

There is an increasing body of evidence that T cell-mediated immune response is regulated by a variety of small molecular weight products of macrophages. One of the best known immunoregulatory products in this context is prostaglandin E2 (PGE2) which is known to regulate both T cell and macrophage functions. Recently, ornithine, cysteine, and lactate have also been recognized as immunoregulatory mediators. In analogy to the hormone-like cytokines and lymphokines, all these substances are produced by immunologically relevant cells (macrophages) at a variable and regulated rate; and they have been shown to regulate the functional activities of other cells (T cells and macrophages). This brief review describes the key observations that underscore the important regulatory role of these metabolites in physiological and pathological conditions.

Cysteine↗
PubMed1990

Interleukin-2 mRNA expression, lymphokine production and DNA synthesis in glutathione-depleted T cells.

The stimulation of DNA synthesis in lymphocyte populations was previously shown to depend strongly on the intracellular glutathione (GSH) level. Since T cell growth is known to depend on interleukin 2 (IL-2), the experiments in this report were designed to determine whether intracellular GSH depletion may inhibit IL-2 production or the IL-2 dependent DNA synthesis. Our experiments revealed that IL-2 production and DNA synthesis of mitogenically stimulated splenic T cells have indeed different requirements for GSH. The addition of relatively high concentrations of GSH (5 mM) to cultures of concanavalin A (Con A)-stimulated splenic T cells was found to augment strongly the DNA synthesis but inhibited the production of IL-2. Moderate intracellular GSH levels, however, are apparently not inhibitory for IL-2 production, since intracellular GSH depletion by cysteine starvation or by graded concentrations of DL-buthionine sulfoximine (BSO) had virtually no effect on IL-2-specific mRNA expression and the production of T cell growth factor (TCGF). The DNA synthesis activity, in contrast, was strongly suppressed after GSH depletion with either method. As in cultures of splenic T cells, GSH depletion had no substantial effect on the induction of IL-2 mRNA and TCGF production in several mitogenically stimulated T cell clones. Taken together, our experiments suggest that complex immune response may operate best at intermediate GSH levels that are not too high to inhibit IL-2 production but sufficient to support DNA synthesis.

Animals↗
PubMed1989

Downregulation of T cell growth factor production by ornithine decarboxylase and its product putrescine: D,L-alpha-difluoromethylornithine suppresses general protein synthesis but augments simultaneously the production of interleukin-2.

Treatment of EL-4 lymphoma cells with tetradecanoylphorbol-acetate (TPA), a well-known activator of protein kinase C, induces the production of the T cell growth factor interleukin-2 (IL-2) and the expression of IL-2-specific mRNA within 4-8 h. This system is an ideal model for studies on the induction of a differentiated function in a homogeneous lymphoid cell population by a defined signal. TPA induces also an increase of ornithine decarboxylase (ODC) activity and elevates the intracellular concentrations of putrescine and polyamines within 4-8 h. A similar increase of intracellular putrescine and polyamine concentrations can be achieved by administration of 2 mM putrescine to the culture medium. However, putrescine cannot induce the production of IL-2 in the absence of TPA and cannot reconstitute the IL-2 production in cultures with PGE2 or cyclosporine A, i.e., two well-known immunosuppressive substances which inhibit ODC activity. Putrescine has rather a counter-regulatory effect as concluded from the observation that the TPA-induced TCGF production and IL-2-specific mRNA expression are augmented (superinduced) by the ODC inhibitor D,L-alpha-difluoromethylornithine (DFMO) and again suppressed after the administration of putrescine or polyamines to DFMO-treated cultures. The glycolytic activity, general protein synthesis [( 3H]leucine incorporation), and the cell cycle progression from G2/M to G1, in contrast, are inhibited by DFMO and reconstituted by putrescine. This demonstrates that the cells are able to sacrifice to a large extent several vital functions including their general protein synthesis and to devote themselves at the same time to a fulminant production of their functionally most relevant protein IL-2. This process is downregulated by ODC and its product putrescine. A correlation between increased IL-2 production and accumulation of cells in the G2/M phase was also observed in cultures treated with hydroxyurea or with a combination of amethopterin and adenosine.

Adjuvants, Immunologic↗