Quantitative measurement of genome-wide DNA methylation by a reliable and cost-efficient enzyme-linked immunosorbent assay technique

DNA methylation, the conversion of cytosine to 5-methylcytosine, is an important epigenetic modification involved in gene regulation. DNA methylation is essential for normal development whereas abnormal methylation has been implicated in pathological conditions including cancer. To evaluate the extent and variation of genome-wide DNA methylation and its changes during cellular differentiation and tumorgenesis as well as the interplay with histone modifications, accurate and reproducible quantification of the genomic DNA methylation level is required. These measurements have so far been achieved only by sophisticated and costly techniques. Here we report the generation of an enzyme-linked immunosorbent assay (methDNA-ELISA) for the accurate quantification of global DNA methylation levels. The linear region of this methDNA-ELISA ranges from 1 to 10%, making it highly suitable for the typical ranges from 2 to 6% in mammalian genomes. This method requires 10 ng of isolated DNA per sample, thus permitting investigation with minimal amounts of DNA previously not applicable for global DNA methylation analysis, e.g., clinical biopsies or cells collected by microdissection.

Stimulatory type A CpG-DNA induces a Th2-like response in human endothelial cells

Unmethylated CpG-DNA motifs from pathogens are detected by the pattern recognition receptor toll-like receptor 9 (TLR9), eliciting an inflammatory immune response. These DNA sequences have been identified as potent immune modifiers and are used as adjuvants in vaccine research. Since we previously found TLR9 expression and function in human endothelial cells, we have here investigated whether endothelial cells play a role in the recognition of respective ligands and whether their response might contribute to vaccination success. We determined the effect of CpG-DNA on the inflammatory response of human endothelial cells of aortic or skin microvascular origin (HAoEC, HDMEC and HMEC-1) and compared the effects to those of two identically treated human macrophage cell lines. Using the same CpG-DNA D19(chimera) sequence in both cell types, we find the known up-regulation of pro-inflammatory cytokines in macrophages but consistent and significant inhibition of the pro-inflammatory response (IL-6, IL-8, and IFN-beta1) in endothelial cells. This inhibition is accompanied by enhanced proliferation and an increase in IL-10 gene expression. This anti-inflammatory response persists even in the presence of pro-inflammatory cytokines and low LPS concentrations, and is overruled only in the presence of relatively high concentrations of LPS. By testing different sequences, we find the strongest response with phosphorothioate bonds. Our results demonstrate an important regulatory function of endothelial cells in inflammatory responses, and the apparent Th2-like endothelial response in the human system may contribute significantly to the adjuvant activity of CpG-DNA.

Comparison of experimental gingivitis with persistent gingivitis: differences in clinical parameters and cytokine concentrations

BACKGROUND AND OBJECTIVE

Experimental gingivitis has been studied extensively as a well-controlled laboratory model of gingivitis. It is unclear, however, how experimental gingivitis compares with persistent plaque and gingivitis in more naturalistic settings. The present study compares both conditions in a randomized controlled design.

MATERIAL AND METHODS

Twenty-six students suffering from plaque and gingivitis were randomly assigned to either a persistent gingivitis or an experimental gingivitis condition. Subjects with persistent gingivitis continued their habitual (i.e. insufficient) oral hygiene behaviour, resulting in persistence of plaque and gingivitis. Experimental gingivitis consisted of initial prophylaxis and subsequent total neglect of oral hygiene. Crevicular interleukin-1beta and interleukin-8 and clinical data were assessed weekly.

RESULTS

After 4 wk, subjects with experimental gingivitis showed significantly more plaque accumulation (p = 0.005), higher interleukin-1beta (p = 0.037), and lower interleukin-8 (p = 0.043) concentrations than subjects with persistent gingivitis. Whereas in experimental gingivitis we observed considerable fluctuations in clinical and immunological parameters over the 4-wk period, persistent gingivitis was characterized by little fluctuation, indicating that we were monitoring an inflammatory steady state.

CONCLUSION

The data indicate that conditions observed after 4 wk of experimental gingivitis are not comparable with persistent gingival inflammation in a naturalistic setting. Results are discussed with respect to current studies, indicating that chronic inflammation may reflect a stage of down-regulated pro-inflammatory response.

The role of nitric oxide

When studying the impact of endothelins (ETs) on physiology and pathophysiology, this needs to be done in the context of nitric oxide (NO) synthesis and action, since these two are closely intertwined in their action. Here, we will review the work demonstrating the crosstalk between endothelin-1 (ET-1) and NO, and the recent developments regarding the role of these two mediators in inflammatory processes. Moreover, we will discuss the role of NO in pro-inflammatory diseases and the potential mechanisms of the anti-inflammatory activity of ET receptor antagonism.

Pathophysiology of cutaneous lupus erythematosus -- novel aspects

The pathophysiology of cutaneous lupus erythematosus (CLE) has been investigated in numerous studies demonstrating that the combination of specific cellular and molecular events is leading to inflammation and tissue damage in this disease. However, a complete understanding of the diverse pathophysiological mechanisms and interactions does not exist. Various environmental factors influence the clinical expression of CLE and a striking relationship has emerged between sunlight exposure and the various subtypes of this disease. In the past years, photoprovocation tests with different ultraviolet (UV) wavelengths have been approved to be an optimal way to evaluate photosensitivity in patients with CLE. Furthermore, research on the pathogenetic mechanisms of UV-induced skin lesions has become an increasingly dynamic field and several new aspects of this disease could be identified. In this review, the impact of UV exposure that contributes to the manifestations of CLE is discussed and recently reported mechanisms in the pathophysiology of this disease are considered including the clearance of apoptotic cells, expression of inducible nitric oxide synthase, function of CD4(+)CD25(+) regulatory T cells, and the role of chemokines for lymphocyte recruitment. Elucidation of the relevant factors might lead to future development of effective strategies to prevent abnormal reactivity in patients with CLE.

Increased apoptosis of neutrophils in a case of clozapine-induced agranulocytosis - a case report

A 45-year-old female suffering from severe chronic schizophrenia of the paranoid type did not respond to typical antipsychotics. Five weeks after starting therapy with clozapine, she developed a clozapine-induced agranulocytosis (CA). Discontinuation of clozapine and treatment with granulocyte colony-stimulating factor (G-CSF) led to normalization of blood neutrophil counts within three weeks. This report suggests enhanced apoptosis of blood neutrophils during the acute phase of CA resulting from enhanced expression of the pro-apoptotic proteins Bax and Bik and from a decrease of the anti-apoptotic BCl-X(L) mRNA. The time course of decline and recovery of neutrophilic cells, as well as the release pattern of endogenous G-CSF, resembles those of chemotherapy-induced neutropenia. The kinetics of CD 34-positive cells mimics that of cytotoxic progenitor cell mobilization, e. g., after cytostatic drug administration. Our findings argue against the hypothesis that clozapine-mediated inhibition of G-CSF or granulocyte-macrophage colony-stimulating factor (GM-CSF) release is involved in CA development. Because clozapine-induced cell death mainly affects the neutrophil lineage, the elucidation of the exact mechanism of CA may open new perspectives for the treatment of psychiatric and possibly hematological disorders.

Ultraviolet A1 radiation induces nitric oxide synthase-2 expression in human skin endothelial cells in the absence of proinflammatory cytokines

Skin exposure to ultraviolet radiation from sunlight causes erythema and edema formation as well as inflammatory responses. As some of these ultraviolet-induced effects are potentially mediated by nitric oxide synthases, we examined the role of cytokines and ultraviolet A1 radiation (340-400 nm) on the expression of the nitric oxide synthase-2 in endothelia of normal human skin biopsies during short-term organ culture as well as expression and activity of the nitric oxide synthase-2 in in vitro cell cultures of human dermal endothelial cells. Both, cytokine challenge (interleukin-1beta + tumor necrosis factor-alpha + interferon-gamma) but also ultraviolet A1 exposure (50 J per cm2) in the absence of cytokines led to the expression of nitric oxide synthase-2 in human skin organ cultures as shown by immunohistochemistry. Moreover, exposing human dermal endothelial cell cultures to proinflammatory cytokines but also to ultraviolet A1 radiation (6-24 J per cm2) in the absence of cytokines resulted in significant nitric oxide synthase-2 mRNA and protein expression as well as enzyme activity. Ultraviolet A1 irradiation of cytokine activated cells led to further increases in nitric oxide synthase-2 mRNA, protein expression, and enzyme activity. Moreover, a reporter gene assay using a human nitric oxide synthase-2 promoter construct provide evidence that ultraviolet A1, in the absence of cytokines, induces nitric oxide synthase-2 expression and activity, as previously shown for cytokines. Thus, the results presented here demonstrate for the first time that in dermal endothelia of human skin ultraviolet A1 radiation alone represents a proinflammatory stimulus sufficient to initiate nitric oxide synthase-2 expression as well as activity comparable with the respective response seen in the presence of proinflammatory cytokines.

Nitric oxide inhibits endothelial IL-1[beta]-induced ICAM-1 gene expression at the transcriptional level decreasing Sp1 and AP-1 activity

BACKGROUND

Nitric oxide (NO) has frequently been shown to inhibit leukocyte adherence to activated endothelium thus displaying anti-adhesive and immunosuppressive activities. A molecular mechanism contributing to this effect is described.

MATERIALS AND METHODS

Primary murine aortic endothelial cells were activated with interleukin (IL)-1beta to express intercellular adhesion molecule-1 (ICAM-1) mRNA in the presence or absence of the physiological spontaneous NO-donor S-nitrosocysteine. Subsequently, semiquantitative RT-PCR and gel shift assays with nuclear extracts were performed to analyse the effects of NO on ICAM-1 mRNA expression and on the activity of transcription factors involved in ICAM-1 transcription. In addition, luciferase reporter gene activity of cytokine-activated cells transiently transfected with an ICAM-1 promoter-luciferase construct and cultured in the presence of the slow-releasing NO-donor DETA/NO was determined.

RESULTS

NO at subtoxic concentrations decreases IL-1beta-induced endothelial ICAM-1 mRNA expression. This inhibition occurs at the transcriptional level, as NO affects IL-1b-induced ICAM-1 promoter activity in transiently transfected cells. Using gel-shift assays and double-stranded oligonucleotide consensus sequences of the known transcription factor binding sites of the ICAM-1 promoter, Sp1 and AP-1 were identified as transcriptional activators of IL-1beta-driven ICAM-1 expression. The DNA binding of both of these transcription factors to specific binding sites of the ICAM-1 promoter was decreased in MAEC exposed to NO.

CONCLUSIONS

Our studies indicate that the anti-adhesive effect of NO concentrations equivalent to high-output NO synthesis is mediated, at least in part, by inhibition of ICAM-1 expression via a concerted action of NO on the redox-sensitive transcriptional activators Sp1 and AP-1. This molecular mechanism may contribute to the anti-inflammatory actions of NO synthesized by the inducible NO synthase.

Nitric oxide inhibits the cochaperone activity of the RING finger-like protein DnaJ

As a consequence of bacterial infection and the ensuing inflammation, expression of the inducible NO synthase results in prolonged synthesis of NO in high concentrations, which among other functions, contributes to the innate defense against the infectious agent. Here we show that NO inhibits the ability of the bacterial cochaperone DnaJ containing a RING finger-like domain to cooperate with the Hsp70 chaperone DnaK in mediating correct folding of denatured rhodanese. This inhibition is accompanied by S-nitrosation of DnaJ as well as by Zn2+ release from the protein. In contrast, NO has no effect on the activity of GroEL, a bacterial chaperone without zinc sulfur clusters. Escherichia coli cells lacking the chaperone trigger factor and thus relying on the DnaJ/DnaK system are more susceptible toward NO-mediated cytostasis than are wild-type bacteria. Our studies identify the cochaperone DnaJ as a molecular target for NO. Thus, an encounter of bacterial cells with NO can impair the protein folding activity of the bacterial chaperone system, thereby increasing bacterial susceptibility toward the defensive attack by the host.

Inducible nitric oxide synthase-derived nitric oxide in gene regulation, cell death and cell survival

Studies from many laboratories have demonstrated the complex role of NO in inflammatory processes. Prolonged exposure to NO shifts the cellular redox potential to a more oxidized state and this is critically regulated by intracellular levels of reduced glutathione. NO-mediated stress will alter gene expression patterns, and the number of genes known to be involved is steadily increasing. Indeed, due to its S-nitrosating activity in the presence of oxygen, NO can modify the activity of transcription factors containing zinc finger motifs or cysteines within the DNA-binding domain. In addition, we are faced with not only NO acting as a powerful inducer of apoptosis or of necrosis in some cells, but also representing an equally powerful protection from cell death in many instances. Some of these apparent discrepancies may be explained by different capacities of cells to cope with the stress of NO exposure. Here, we review our findings on the complex impact of NO on transcriptional regulation of genes, cell death and cell survival. These NO-mediated actions will contribute to a better understanding of the impact of inducible nitric oxide synthase (iNOS) enzyme activity during inflammatory reactions.

Even after UVA-exposure will nitric oxide protect cells from reactive oxygen intermediate-mediated apoptosis and necrosis

Reactive oxygen species (ROS) play a pivotal role in UVA-induced cell damage. As expression of the inducible nitric oxide synthase (iNOS) is a normal response of human skin to UV radiation we examined the role of nitric oxide (NO) as a protective agent during or even after UVA1- or ROS-exposure against apoptosis or necrosis of rat endothelial cells. When added during or up to 2 h subsequent to UVA1 or ROS exposure the NO-donor S-nitroso-cysteine (SNOC) at concentrations from 100-1000 microM significantly protects from both apoptosis as well as necrosis. The NO-mediated protection strongly correlates with complete inhibition of lipid peroxidation (sixfold increase of malonedialdehyde formation in untreated versus 1.2-fold with 1 mM SNOC). NO-mediated protection of membrane function was also shown by the inhibition of cytochrome c leakage in UVA1 treated cells, a process not accompanied by alterations in Bax and Bcl-2 protein levels. Thus, the experiments presented demonstrate that NO exposure during or even after a ROS-mediated toxic insult fully protects from apoptosis or necrosis by maintaining membrane integrity and function.

Nitric oxide interferes with islet cell zinc homeostasis

Zinc is crucial for the biosynthesis, storage, and secretion of insulin in pancreatic islet cells. We have previously presented evidence that NO interferes with cellular Zn(2+) homeostasis and we therefore investigated the influence of chronic NO exposure on the labile islet cell Zn(2+) content. A strong fluorescence activity in a large islet cell subpopulation was found after staining with the Zn(2+)-specific fluorophore Zinquin. Culture for 24 h in the presence of nontoxic concentrations of the slow-releasing NO donor DETA/NO resulted in a significantly reduced Zn(2+)-dependent fluorescence. This appears to be islet specific as in endothelial cells DETA/NO exposure enhanced the Zn(2+)-dependent fluorescence activity in a concentration-dependent manner. These results suggest that NO interferes with cellular Zn(2+) homeostasis, which in islet cells is crucial for proper hormone delivery and thus special cell function.

Amphotericin B severely affects expression and activity of the endothelial constitutive nitric oxide synthase involving altered mRNA stability

The therapeutic use of the antifungal drug amphotericin B (AmB) is limited due to severe side effects like glomerular vasoconstriction and risk of renal failure during AmB administration. As nitric oxide (NO) has substantial functions in renal autoregulation, we have determined the effects of AmB on endothelial constitutive NO synthase (ecNOS) expression and activity in human and rat endothelial cell cultures. AmB used at concentrations of 0.6 to 1.25 microg ml(-1) led to increases in ecNOS mRNA and protein expression as well as NO production. This was the result of an increased ecNOS mRNA half-life. In contrast, incubation of cells with higher albeit subtoxic concentrations of AmB (2.5 - 5.0 microg ml(-1)) resulted in a decrease or respectively in completely abolished ecNOS mRNA and protein expression with a strongly reduced or inhibited ecNOS activity, due to a decrease of ecNOS mRNA half-life. None of the AmB concentrations affected promoter activity as found with a reporter gene construct stably transfected into ECV304 cells. Thus, our experiments show a concentration-dependent biphasic effect of AmB on expression and activity of ecNOS, an effect best explained by AmB influencing ecNOS mRNA stability. In view of the known renal accumulation of this drug the results reported here could help to elucidate its renal toxicity.

Implications of inducible nitric oxide synthase expression and enzyme activity

We summarize here our current knowledge about inducible nitric oxide synthase (NOS) activity in human diseases and disorders. As basic research discovers more and more effects of low or high concentrations of NO toward molecular and cellular targets, successful therapies involving inhibition of NO synthesis or application of NO to treat human diseases are still lacking. This is in part due to the fact that the impact of NO on cell function or death are complex and often even appear to be contradictory. NO may be cytotoxic but may also protect cells from a toxic insult; it is apoptosis-inducing but also exhibits prominent anti-apoptotic activity. NO is an antioxidant but may also compromise the cellular redox state via oxidation of thiols like glutathione. NO may activate specific signal transduction pathways but is also reported to inhibit exactly these, and NO may activate or inhibit gene transcription. The situation may even be more complicated, because NO, depending on its concentration, may react with oxygen or the superoxide anion radical to yield reactive species with a much broader chemical reaction spectrum than NO itself. Thus, the action of NO during inflammatory reactions has to be considered in the context of timing and duration of its synthesis as well as stages and specific events in inflammation.

Lectin-Mediated Drug Targeting: Discrimination of Carbohydrate-Mediated Cellular Uptake between Tumor and Liver Cells with Neoglycoconjugates Carrying Fucose Epitopes Regioselectively Modified in the 3-Position

The circumvention of efficient "carbohydrate traps" in the liver is required for targeting glycoconjugates on tumor cells. As shown in the model system of bovine serum albumin (BSA) conjugates, the nature of R(1)-R(3) of the fucose epitope plays an important role in the discrimination of cellular uptake between tumor and liver cells as well as in the cytotoxic activity.

Zinc finger transcription factors as molecular targets for nitric oxide-mediated immunosuppression: inhibition of IL-2 gene expression in murine lymphocytes

BACKGROUND

Nitric oxide (NO) has frequently been shown to display immunosuppressive activities. We describe here a molecular mechanism contributing to this effect.

MATERIALS AND METHODS

Murine T cell lymphoma EL4-6.1 cells were activated with the physiological stimulus interleukin (IL)-1beta to express IL-2 mRNA in the presence or absence of subtoxic concentrations of the physiological spontaneous NO donor S-nitrosocysteine (SNOC). Subsequently, semiquantitative RT-PCR and gel shift assays with nuclear extracts were performed to analyze the effects of NO on IL-2 mRNA expression and on the activity of the dominant regulating transcription factors Sp1, EGR-1, and NFATc.

RESULTS

NO inhibits IL-1beta-induced IL-2 mRNA expression in EL4-6.1 cells. The suppressive activity of NO was concentration dependent and found to be completely reversible. Importantly, NO at the concentrations used induced neither apoptosis nor necrosis. Dominant regulation of IL-2 gene expression is known to reside in the zinc finger transcription factors Sp1 or EGR-1 and in the non-zinc finger protein NFAT. NO abrogates the DNA binding activities of recombinant Sp1 and EGR-1. More importantly, gel shift assays also showed a lack of DNA binding of native Sp1 derived from NO-treated nuclear extracts and that from NO-treated viable lymphocytes. This effect is selective, as the DNA binding activity of recombinant NFATc was not affected by NO.

CONCLUSION

Inactivation of zinc finger transcription factors by NO appears to be a molecular mechanism in the immunosuppressive activity of NO in mammals, thus contributing to NO-mediated inhibition of IL-2 gene expression after physiological stimuli. The exact understanding of the molecular mechanism leading to NO-mediated, fully reversible suppression of immune reactions may lead to use of this naturally occurring tool as an aid in inflammatory diseases.

Influence of nitric oxide on the intracellular reduced glutathione pool: different cellular capacities and strategies to encounter nitric oxide-mediated stress

Different cell types exhibit huge differences towards the cytotoxic action of NO. In search for an explanation, we used subtoxic concentrations of the NO-donors S-nitrosocysteine (SNOC) for short-term challenge and of (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1,2-diolate (DETA/NO) for longer periods of exposure, respectively, and subtoxic concentrations of the oxidant H2O2 to determine the impact on intracellular reduced glutathione (GSH) concentrations. We find that GSH concentrations are always decreased, but that different cell types show different responses. Incubation of the relatively NO-sensitive murine lymphocytes with both NO-donors, but not with H2O2, resulted in a nearly complete loss of intracellular GSH. Short-term NO-treatment of P815 mastocytoma cells, also sensitive to NO-mediated cell death, decreased GSH to a similar extent only if either glutathione reductase (GSHR) activity or y-glutamylcysteine synthetase (gammaGCS) activity were inhibited concomitantly by specific inhibitors. Long-term NO-treatment of P815 cells, however, resulted in a significant decrease of GSH that could be further enhanced by inhibiting gammaGCS activity. In contrast, neither short-term nor long-term NO-exposure nor H2O2-treatment affected intracellular GSH levels of L929 fibroblasts, which were previously shown to be extremely resistant towards NO, whereas concomitant gammaGCS inhibition, but not GSHR inhibition, completely decreased GSH concentrations. These results show that different cell types use different pathways trying to maintain glutathione concentrations to cope with nitrosative stress, and the overall capability to maintain a critical amount of GSH correlates with susceptibility to NO-induced cell death.

A regulatory defect of constitutive no-synthase in islet endothelial cells correlates with probability of disease manifestation in BBdp rats

AIMS/HYPOTHESIS

Type I (insulin-dependent) diabetes mellitus is characterised by leucocyte infiltration of pancreatic islets and a progressive destruction of insulin-producing beta cells. As endothelial nitric oxide production is known to regulate adhesion molecule expression and leucocyte permeation, we examined the activity and expression of the constitutive nitric oxide synthase (ecNOS) of islet endothelial cells from prediabetic BBdp rats.

METHODS

Cultures of aortic endothelial cells and islet capillary endothelial cells were established from young normoglycaemic BBdp rats, Wistar rats and diabetes-resistant BBdr rats, all matched for age. Nitrite and citrulline production was measured in all culture supernatants as indicators for ecNOS activities. Expression of ecNOS mRNA was assessed by reverse transcription-polymerase chain reaction.

RESULTS

In contrast to those of the aorta, the Wistar rat islet derived endothelial cells exhibited a strong positive correlation of ecNOS activity with the culture medium glucose concentration but none of the BB rat-derived islet endothelial cells showed a similar glucose-responsiveness. Furthermore, at physiological as well as at increased glucose concentrations islet endothelia from all BBdp rats exhibited a considerable decrease in ecNOS activity by a factor of 3 to 6, indicating a specific dysfunction which is also found for the inducible nitric oxide synthase activity after cytokine challenge but effects were less (2.5 to 3 times) dramatic. In contrast, aorta endothelia from all rats exhibited identical ecNOS activities and no glucose responsiveness. We also found a correlation between ecNOS activities and ecNOS-mRNA expression and can exclude the involvement of the inducible isoform.

CONCLUSION/INTERPRETATION

A reproducible and highly significant dysfunction of islet ecNOS expression and activity in young normoglycaemic BBdp rats, which strongly correlates with the probability for disease manifestation is shown.

Nitric oxide fully protects against UVA-induced apoptosis in tight correlation with Bcl-2 up-regulation

A variety of toxic and modulating events induced by UVA exposure are described to cause cell death via apoptosis. Recently, we found that UV irradiation of human skin leads to inducible nitric-oxide synthase (iNOS) expression in keratinocytes and endothelial cells (ECs). We have now searched for the role of iNOS expression and nitric oxide (NO) synthesis in UVA-induced apoptosis as detected by DNA-specific fluorochrome labeling and in DNA fragmentation visualized by in situ nick translation in ECs. Activation with proinflammatory cytokines 24 h before UVA exposure leading to iNOS expression and endogenous NO synthesis fully protects ECs from the onset of apoptosis. This protection was completely abolished in the presence of the iNOS inhibitor L-N5-(1-iminoethyl)-ornithine (0.25 mM). Additionally, preincubation of cells with the NO donor (Z)-1-[N(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-i um-1, 2-diolate at concentrations from 10 to 1000 microM as an exogenous NO-generating source before UVA irradiation led to a dose-dependent inhibition of both DNA strand breaks and apoptosis. In search of the molecular mechanism responsible for the protective effect, we find that protection from UVA-induced apoptosis is tightly correlated with NO-mediated increases in Bcl-2 expression and a concomitant inhibition of UVA-induced overexpression of Bax protein. In conclusion, we present evidence for a protective role of iNOS-derived NO in skin biology, because NO either endogenously produced or exogenously applied fully protects against UVA-induced cell damage and death. We also show that the NO-mediated expression modulation of proteins of the Bcl-2 family, an event upstream of caspase activation, appears to be the molecular mechanism underlying this protection.

Effects of Magnesium Dobesilate on Nitric Oxide Synthase Activity in Endothelial Cells

This study was done to determine the effects of the angioprotective agent dobesilate on expression and activity on the constitutive nitric oxide synthase (ecNOS) in resident endothelial cells, as well as of the inducible nitric oxide synthase (iNOS) in cytokine-activated endothelial cells, by recording, in culture supernatants, the concentrations of citrulline as a reaction product of both enzymes. In capillary, microvascular, and macrovascular endothelial cells, Mg dobesilate incubation (0.25-1 mM) for 24 hours led to a highly significant concentration-correlating increase in ecNOS activities. These increases were not due to iNOS expression, and with cytokine-activated endothelial cell cultures that do express iNOS only moderate effects with little or no concentration dependency were seen. Addition of the NOS inhibitor NG-monomethyl-L-arginine (NMA) significantly suppresses citrulline formation in all cultures as evidence for the enzyme specificity.

Nitric oxide and its implications in skin homeostasis and disease - a review

The recent identification of the nitric oxide synthase (NOS) pathway in various cell types in the skin has provided important insight into the molecular mechanisms underlying regulatory and homeostatic functions of the skin. Many studies also point to perturbations or defects in the signaling cascade of nitric oxide (NO) and reactive nitrogen intermediates as key players in skin disease pathogenesis. A critical role for NO is now established for a subset of human skin diseases, and new mechanism-based therapies may be available in the near future. This remarkable progress and the implications it may have for common forms of skin disease are reviewed here.

Biphasic effect of exogenous nitric oxide on proliferation and differentiation in skin derived keratinocytes but not fibroblasts

Nitric oxide (NO) is known to exert cytotoxic and cytostatic effects in various cells and tissues. Although NO formation in human skin has been convincingly demonstrated, little is known about the NO-mediated effects in skin physiology and pathology. Here, we investigate the influence of NO on proliferation, differentiation, and apoptosis of primary cultures of normal human keratinocytes and fibroblasts. Four different NO donors at concentrations ranging from 0.01 to 5 mM were added every 12 h or 24 h to primary cultures of human keratinocytes and fibroblasts, and cells cultured for up to 3 d in the presence of these compounds. Cultures were examined for necrosis or apoptosis using trypan blue exclusion and in situ nick-translation. Cultures were also screened for the expression of the proliferation marker Ki67 and for an increase in cell numbers using neutral red staining. In addition, keratinocytes were stained for cytokeratin 6 expression to assess differentiation. We find that both keratinocytes and fibroblasts are highly resistant towards necrosis- or apoptosis-inducing effects of NO. In both cell types NO modulates cell growth, albeit in a cell-type specific pattern: cytostasis becomes significant in fibroblasts at concentrations of > or = 0.25 mM of the NO donor. In keratinocytes a biphasic effect is found with increased proliferation at low concentrations ranging from 0.01 to 0.25 mM and cytostasis at concentrations of > or = 0.5 mM. Conversely, expression of cytokeratin 6 is decreased at the lower NO donor concentrations and increased at higher concentrations as an indication of induction of differentiation at higher NO concentrations. Collectively, our results demonstrate that NO modulates proliferation and differentiation in human skin cells, a finding that will help to explain the pathophysiology of human skin diseases. Moreover, these findings suggest that NO generation in human skin diseases is not directly associated with local cell destruction, in contrast to findings in several other human diseases.

Aberrant timing in epidermal expression of inducible nitric oxide synthase after UV irradiation in cutaneous lupus erythematosus

Photosensitivity is a main criterion for the diagnosis of systemic lupus erythematosus (LE), and ultraviolet (UV) irradiation plays a key role in the pathogenesis of cutaneous LE. Patients with a tentative diagnosis of LE are routinely tested for skin lesion development after experimental UV irradiation, providing an ideal opportunity to evaluate early, preclinical events involved in the pathogenesis of LE. Several reports have shown expression of the cytokine-inducible nitric oxide synthase (iNOS) in autoimmune diseases. Therefore, we investigated the role of iNOS expression at mRNA and protein level in the pathogenesis of LE lesions. Skin biopsies from patients with different subtypes of LE were examined, and iNOS expression was found in six of 18 biopsies from cutaneous LE patients and two of three biopsies from systemic LE patients. In biopsies taken 4-20 d after UV irradiation, epidermal iNOS expression was seen in all patients (n = 10) after UVB and in four of 10 patients provoked by UVA. In healthy controls (n = 8) epidermal iNOS expression was detected 24 h after UV irradiation, persisting for another day before subsiding on day 3. In LE patients (n = 8) the exact reverse situation was seen: an iNOS-specific signal was undetectable in keratinocytes for 2 d after UV irradiation, but became positive on day 3 and persisted for up to 25 d in the evolving skin lesions. Our findings demonstrate a time-restricted, UV-induced iNOS expression in human skin; moreover, the results indicate that both the kinetics of iNOS induction as well as the time span of local iNOS expression may be critical to the development of cutaneous LE lesions.

Nitric oxide in human skin: current status and future prospects

The gaseous free radical nitric oxide is an important biologic mediator with physiologic and pathophysiologic roles in nearly every organ system. Because of its unique biologic activity, unusual chemical structure, and unprecedented mechanisms of action, nitric oxide, arguably more than any other natural product, has opened new avenues to investigate cellular processes. Nitric oxide is generated in biologic tissues by specific nitric oxide synthases that metabolize arginine and molecular oxygen to citrulline and nitric oxide. Besides its function as a diffusible messenger in the vasculature and in neurons, nitric oxide also plays a key role in innate immunity and inflammation. Recent progress has allowed the identification of the nitric oxide pathway in several cell types that reside in the skin, including keratinocytes, melanocytes, Langerhans cells, fibroblasts, and endothelial cells. Convincing evidence suggests that nitric oxide synthesis in these cells can be modulated by calcium-mobilizing agonists as well as diverse inflammatory and immune stimuli, and thereby contributes to the pathogenesis of several human skin diseases. Characterization of these intrinsic and extrinsic regulatory stimuli of nitric oxide synthesis has afforded substantial insights into the role of nitric oxide in inflammatory, hyperproliferative, and autoimmune skin diseases, as well as skin cancer, and may ultimately form the basis for future therapeutic intervention. The demonstrable and potential roles of nitric oxide in skin disease pathogenesis and treatment are the subjects of this review.

Dobesilate enhances endothelial nitric oxide synthase-activity in macro- and microvascular endothelial cells

1. Dobesilate is used for normalizing vascular dysfunction in a number of diseases. In search for an effect on endothelial NO production, macrovascular endothelial cells from rat aorta, microvascular endothelial cells from rat exocrine pancreatic tissue, and capillary endothelial cells from rat islets, were cultured in the presence or absence of Mg-Dobesilate. The activity of constitutive nitric oxide synthase (ecNOS) in resident cells as well as of inducible nitric oxide synthase (iNOS) in cytokine-activated cells was measured indirectly by recording the citrulline concentrations in culture supernatants. 2. In each of the different endothelial cells Mg-Dobesilate incubation (0.25-1 mM) for 24 h led to a significant and concentration-dependent increase in ecNOS-activities. With cytokine-activated endothelial cell cultures only moderate effects were seen with little or no concentration-dependency. Addition of the NOS-inhibitor N(G)-monomethyl-L-arginine led to a significant suppression of citrulline formation in all cultures as an evidence for the enzyme specificity of these effects. 3. iNOS- and ecNOS-specific reverse transcription and semi-quantitative polymerase chain reaction (RT-PCR) with RNA from resident or cytokine-activated endothelial cells gave no evidence for an increase in NOS-specific mRNA after Mg-Dobesilate-treatment. Furthermore, Dobesilate-mediated enhancement of NO synthesis in resting endothelial cells was not due to iNOS induction in these cells, as no iNOS-specific signal was found by RT-PCR.

The dominant role of exogenous or endogenous interleukin-1 beta on expression and activity of inducible nitric oxide synthase in rat microvascular brain endothelial cells

In the brain large amounts of nitric oxide are produced in response to various pathological stimuli such as infectious agents, ischemia and trauma. Although it is known that endothelial cells can express the inducible isoform of nitric oxide synthase (iNOS) upon activation, the impact of different cytokines on iNOS expression in rat microvascular endothelial cells remains unclear. We now investigated iNOS mRNA expression and enzyme activity in primary cell cultures of rat microvascular brain endothelial cells after treatment with the proinflammatory cytokines interleukin-1beta (IL-1beta), Tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) alone or in combination. Cells were characterized by immunocytochemistry staining for von-Willebrand-factor and the rat brain endothelial antigen recognized by monoclonal antibody Ox2. iNOS-enzyme activity was determined by measurement of nitrite in the supernatants of cell culture using the Griess-reaction. In addition mRNA expression was analysed by RT-PCR with iNOS and IL-1beta specific primers. All cells in the endothelial cell culture were found to express the antigenic phenotype vWF+/Ox2+/Ox43-, thus identifying the cells as rat brain endothelial cells of microvascular origin. IL-1beta was the only cytokine that as a single stimulus induced iNOS mRNA expression and iNOS-enzyme activity in these endothelial cells. All combinations of two cytokines, including that of TNF-alpha and IFN-gamma--or the triple combination led to expression of iNOS-mRNA and active protein. Cell activation by the combination of TNF-alpha + IFN-gamma led to an early expression of IL-1beta by the endothelial cells suggesting iNOS induction as a consequence of endogenous IL-1beta production under this challenge. The experiments prove that rat brain microvascular endothelial cells express iNOS and produce large amounts of NO under inflammatory conditions. Furthermore, our results indicate a decisive role of IL-1beta in iNOS expression and NO generation.

Nitric oxide-induced expression of C-reactive protein in islet cells as a very early marker for islet stress in the rat pancreas

In searches for marker molecules specifically expressed in nitric oxide-treated islet cells as a means to recognize early events in islet destruction, we now establish the presence of neo-C-reactive protein (neoCRP) in rat islet cells as early as 2 hr after treatment. We detected this altered molecular form of the acute-phase-reactant C-reactive protein (CRP) using immunocytochemistry with an anti-neoCRP-specific monoclonal antibody as well as reverse transcription-polymerase chain reaction with CRP-specific primers and in situ hybridization to demonstrate the presence of CRP-specific mRNA. After induction of a generalized inflammatory reaction in rats with heat-inactivated Corynebacterium parvum in vivo, neoCRP expression in islets is also found and within the pancreas restricted to pancreatic islet cells only. Our findings suggest an early heat-shock-like expression of this molecule in response to local nitrite oxide production or to exogeneously added nitric oxide in islet cells.

Nitric oxide: cytotoxicity versus cytoprotection--how, why, when, and where?

Nitric oxide (NO) has been found to play an important role as a signal molecule in many parts of the organism as well as a cytotoxic effector molecule of the nonspecific immune response. It appears paradoxical that NO on one side acts as a physiological intercellular messenger and on the other side may display cytotoxic activity in vivo. To make things even more complicated, cytoprotective properties of NO are also described. We here review the current understanding of cytotoxic versus cytoprotective effects of NO in mammalian cells and try to highlight the janus-faced properties of this important small molecule.

Nitric oxide mediates intracytoplasmic and intranuclear zinc release

We previously described that NO. leads to destruction of ZnS clusters and release of Zn2+ from various proteins including zinc finger transcription factors. To assess the relevance in living cells, we investigated, whether exogenous NO. leads to an increase of cytoplasmic and nuclear free Zn2+. L929 cells, mouse splenocytes, or rat aorta endothelial cells were labeled with Zinquin-E, a Zn2+-specific fluorophore, and were treated with two different spontaneous NO donors, S-nitrosocysteine or DETA/NO. Both NO donors strongly increased the Zn2+-dependent fluorescence in the cellular cytosol and also in nuclei as compared to controls. NO-dependent Zn2+ release in splenocytes was quantitated by flow cytometry. These results show for the first time, that nitrosative stress mediates intracellular and intranuclear Zn2+ release which may be relevant in altering gene expression patterns.

Endothelial cells as cytotoxic effector cells: cytokine-activated rat islet endothelial cells lyse syngeneic islet cells via nitric oxide

In vivo, each beta cell is located in proximity to at least one capillary islet endothelial cell. Rat aorta and islet endothelial cells can be activated in vitro to express inducible nitric oxide synthase by a cytokine mixture of tumour necrosis factor-alpha, gamma-interferon, and interleukin-1 beta and to produce high concentrations of nitric oxide. We have performed co-culture experiments with rat islet endothelial cells together with isolated syngeneic islet cells at low target:effector ratios with or without previous cytokine challenge of endothelial cultures. Co-cultures were always free of exogenous cytokines, which were removed prior to addition of islet cells. We found that pre-activated, in contrast to resident islet endothelial cells, at a target:effector ratio as low as 1:1 almost completely lysed syngeneic beta and non-beta cells with 24 h of co-culture. Lysis by pre-activated islet endothelial cells was found to be preceded by DNA damage found in 46% of islet cells after 8 h of co-culture with pre-activated vs 7% with resting islet endothelial cells. Lysis was blocked to control levels in the presence of the nitric oxide synthase inhibitor NG-methyl-L-arginine. With the results presented here, we demonstrate for the first time, that activated endothelial lining cells can express effector cell activity and thus can contribute to local tissue destruction, especially in organs that are densely capillarized such as pancreatic islets.

A proinflammatory activity of interleukin 8 in human skin: expression of the inducible nitric oxide synthase in psoriatic lesions and cultured keratinocytes

Psoriasis is a common chronic skin disease mediated by cellular immune mechanisms and characterized by an intense neutrophil cell infiltrate and proliferative activation of epidermal keratinocytes. We have previously described the expression of the inducible nitric oxide synthase (iNOS) in epidermal keratinocytes of psoriatic skin lesions. In this study, the role of iNOS in psoriatic inflammation was explored ex vivo in psoriatic skin biopsies and in vitro in primary cultures of human keratinocytes. Messenger RNA for the iNOS enzyme (iNOS mRNA) was detected by reverse transcriptase polymerase chain reaction in skin biopsies from patients with psoriasis, but not in skin specimens from patients with atopic eczema or from healthy volunteers. As demonstrated by in situ hybridization and immunohistochemistry, expression of iNOS mRNA and its gene product was localized to the epidermal keratinocytes of psoriatic skin lesions. In situ hybridization further revealed a complete colocalization of mRNA expression for iNOS with interleukin (IL) 8 receptor-specific mRNA either in the basal germinative cell layer or at focal sites of ongoing neutrophil inflammation in suprabasal cell layers. Because psoriatic keratinocytes have previously been shown to express mRNA transcripts for IL-8, it seemed reasonable to hypothesize that iNOS expression could be induced in an autocrine loop by IL-8. This hypothesis was substantiated by our in vitro experiments showing that a combination of IL-8 and interferon gamma induces the expression of iNOS-specific mRNA and of the functional enzyme in cultured human keratinocytes. These results suggest an important role for iNOS in concert with IL-8 and its receptor early during the formation of psoriatic lesions.

Streptozotocin is not a spontaneous NO donor

The reaction of streptozotocin with oxymyoglobin was analyzed and compared with results using various compounds that spontaneously generate nitric oxide in solution.

Independent modulation of galactose-specific receptor expression in rat liver cells

The expression of galactose-specific receptors on liver cells from rats at the end of pregnancy and from estrogen-treated animals was studied. The number and distribution of binding sites were estimated on hepatocytes and Kupffer and endothelial cells in vitro as well as in situ by means of protein-gold complexes. Hepatocytes and endothelial cells from pregnant rats showed an increased binding activity of at least three times for hepatocytes and one and a half times for endothelial cells with respect to normal rat livers. The increase in the hepatocyte receptor expression was paralleled by an increase in the level of its specific messenger RNA (mRNA). On Kupffer cells, a decreased number of binding sites, at least three times less than control values, was measured. The correlation between the altered hormonal level during pregnancy and the expression of galactose binding sites was examined in hepatocytes and Kupffer cells isolated from virgin rats treated with the synthetic estrogen diethylstilbesterol. In estrogen-treated rats both the binding sites and the specific mRNA of hepatocytes increased as compared with vehicle-treated or untreated animals. In contrast, in Kupffer cells both the estrogen treatment as well as vehicle-only injection led to a significant reduction in the expression of binding sites as compared with virgin untreated animals. To establish whether the decrease of galactose binding sites in Kupffer cells was related to the activation of macrophages or to the removal of plasma membrane caused by enhanced nonspecific phagocytosis, in situ binding experiments were performed after lipopolysaccharide (LPS)-stimulation or latex-bead phagocytosis. Nonspecific phagocytosis does not affect the binding activity, which instead appears strongly reduced after LPS injection. These findings suggest an independent response of galactose-specific receptor expression systems in the different types of liver cells to modulating agents.

Insulitis and islet-cell antibody formation in rats with experimentally reduced beta-cell mass

We studied the effect of severe reduction of beta-cell mass by 90% pancreatectomy on the immune tolerance to the endocrine pancreas. Four months after subtotal pancreatectomy all LEW.Han rats had developed mononuclear infiltration of islets and 9 of 14 rats were positive for islet-cell antibodies. Electron microscopy revealed lymphocytic invasion of endocrine tissue, lysis of beta cells and phagocytotic macrophages. None of these changes were seen 2 weeks after 90% pancreatectomy or 4 months after 10% pancreatectomy. Weekly substitution of islet antigens in the form of a homogenate of 100 islets into 90% pancreatectomized LEW.Han rats almost completely prevented the development of insulitis and autoantibodies. The dependence of insulitis on T cells was shown when 90% pancreatectomy in LEW.rnu rats (i.e., the congenic athymic nude strain), did not result in islet infiltration. The exocrine tissue remained normal in all experimental groups. During the observation period insulitis was not associated with overt diabetes but was accompanied by substantial enlargement of islets and of beta-cell mass, as shown by morphometry. Suppression of islet inflammation by injection of islet antigens abolished beta-cell regeneration, despite continuing metabolic stress in rats with 90% pancreatectomy. The findings indicate induction of islet autoimmunity in response to 90% but not to 10% pancreatectomy. We conclude that severe reduction of the islet-antigen mass allows the development of T-cell-dependent islet autoimmunity which indicates a loss of immune tolerance. In addition, the data suggest the existence of islet-antigen autoreactive immune cells in rats not genetically predisposed to autoimmune diabetes. Finally, we conclude that selective beta-cell regeneration occurs in association with insulitis.

The content of glutathione and glutathione S-transferases and the glutathione peroxidase activity in rat liver nuclei determined by a non-aqueous technique of cell fractionation

Hepatocellular nuclei require glutathione, glutathione S-transferases (GSTs) and Se-dependent glutathione peroxidase (GPx) for intranuclear protection against damage from electrophiles or products of active oxygen. Data so far available from the literature on nuclei isolated in aqueous systems range from glutathione, GSTs and GPx either being absent altogether to being present in quantities in excess of those in the cytoplasm. This paper describes a small-scale preparation of a nuclear fraction from rat liver by a non-aqueous technique, designed to retain nuclear water-soluble molecules in situ, since low-molecular-mass compounds can diffuse freely into other compartments during aqueous separation. This non-aqueous procedure shows the nucleus to contain glutathione at 8.4 mM and soluble GSTs at 38 micrograms/mg of protein, the enrichment over the homogenate being 1.2-1.4-fold. Se-dependent GPx activity was also present in the nucleus (56 m-units/mg), although with slightly lower activity than in the homogenate (0.7-fold).

Nitric oxide induces apoptosis in mouse thymocytes

Nitric oxide (NO) produced at high concentrations by the inducible NO synthase is an important effector molecule involved in immune regulation and defense. We have examined whether NO represents a signal for triggering apoptosis in thymocytes. Freshly isolated thymocytes were incubated with different chemical NO donors for various intervals. Apoptosis was determined by detection of DNA strand breaks with in situ nick translation. All NO donors induced thymocyte apoptosis with 30% positive thymocytes vs 10% in controls after 8 h. Apoptosis was prevented by addition of ZnSO4. Short-term pre-exposure to NO resulted in protection from apoptosis induced by glucocorticoids comparable with the protective effect of heat shock. Flow cytometry revealed that NO treatment as well as heat shock or dexamethasone incubation is accompanied by reduction in the CD4+ CD8+ thymocyte subpopulation. Apoptosis induction was accompanied by increased expression of p53, as detected by PCR analysis 2 h after NO donor addition. In vivo treatment of mice with endotoxin results in increased thymic apoptosis. Focal apoptosis was found to occur in close proximity to blood vessels 18 h after LPS treatment. Capillary endothelium and dendritic cells adjacent to apoptotic foci were found to stain strongly for inducible NO synthase expression. Furthermore, in an in vitro experiment using cocultures of thymocytes with LPS/cytokine-activated endothelial cells expressing inducible NO synthase, a significantly increased rate of thymocyte apoptosis was found, and this could be prevented completely by inhibiting NO production. Addition of dexamethasone to these cocultures did not lead to a further increase in the percentage of apoptotic thymocytes, underlining the protective effect of NO on dexamethasone-induced apoptosis.

Nitric oxide induces apoptosis in mouse thymocytes

Nitric oxide (NO) produced at high concentrations by the inducible NO synthase is an important effector molecule involved in immune regulation and defense. We have examined whether NO represents a signal for triggering apoptosis in thymocytes. Freshly isolated thymocytes were incubated with different chemical NO donors for various intervals. Apoptosis was determined by detection of DNA strand breaks with in situ nick translation. All NO donors induced thymocyte apoptosis with 30% positive thymocytes vs 10% in controls after 8 h. Apoptosis was prevented by addition of ZnSO4. Short-term pre-exposure to NO resulted in protection from apoptosis induced by glucocorticoids comparable with the protective effect of heat shock. Flow cytometry revealed that NO treatment as well as heat shock or dexamethasone incubation is accompanied by reduction in the CD4+ CD8+ thymocyte subpopulation. Apoptosis induction was accompanied by increased expression of p53, as detected by PCR analysis 2 h after NO donor addition. In vivo treatment of mice with endotoxin results in increased thymic apoptosis. Focal apoptosis was found to occur in close proximity to blood vessels 18 h after LPS treatment. Capillary endothelium and dendritic cells adjacent to apoptotic foci were found to stain strongly for inducible NO synthase expression. Furthermore, in an in vitro experiment using cocultures of thymocytes with LPS/cytokine-activated endothelial cells expressing inducible NO synthase, a significantly increased rate of thymocyte apoptosis was found, and this could be prevented completely by inhibiting NO production. Addition of dexamethasone to these cocultures did not lead to a further increase in the percentage of apoptotic thymocytes, underlining the protective effect of NO on dexamethasone-induced apoptosis.

Inducible nitric oxide synthase and its product nitric oxide, a small molecule with complex biological activities

More and more attention is paid to the radical nitric oxide which is now known to be part of the mammalian physiology and immune system. Nitric oxide is synthesized by one of the most complicated and fascinating enzyme families identified so far. Inducible nitric oxide synthesis after appropriate stimuli has regulatory, cytostatic and/or toxic consequences and may play an important role in the pathophysiology of several diseases.

Glucagon effect on intracellular proteolysis and pericanalicular location of hepatocyte lysosomes in isolated perfused guinea pig livers

In guinea pigs, glucagon choleresis is accompanied by a significant, but transient, stimulation of biliary protein secretion, which can be accounted for mainly by biliary discharge of lysosomal enzymes. To clarify whether intracellular proteolysis--a process regulated by glucagon and taking place predominantly in the lysosomes--may interact with biliary protein secretion, we determined hepatic proteolytic activity and bile secretory function during substrate deprivation, amino acid supplementation, and glucagon administration in isolated perfused guinea pig livers. To further elucidate the nature of transient lysosomal enzyme release into bile during glucagon infusion, we analyzed pericanalicular distribution of lysosomes by quantitative electron microscopy. The results demonstrate that intracellular proteolysis is accompanied by biliary excretion of lysosomal enzymes. Glucagon-induced secretion of these enzymes as well as labeled proteins into bile occurs independent of protein breakdown and cannot be modulated by addition of amino acids as potent inhibitors of intracellular proteolysis. During glucagon administration, bile canalicular area and pericanalicular distribution of secondary lysosomes show a rapid increase, which persists during the entire infusion period and thus does not explain the transient biliary release of lysosomal enzymes. We therefore postulate that regulation of this process must be located beyond the lysosomal compartment, either involving transport processes or intracellular kinetics of lysosome formation or altered fusion kinetics at the bile canalicular membrane compartment. Metabolic and biliary effects of glucagon seem to occur independent of each other and to underly different regulatory mechanisms.