Hypoxia-inducible factor 1 in dendritic cells is crucial for the activation of protective regulatory T cells in murine colitis

Dendritic cells (DCs) serve as a bridge between innate and adaptive immunity and help to maintain intestinal homeostasis. Inflammatory bowel disease (IBD) is associated with dysregulation of the mucosal immune response. The concomitant hypoxic inflammation in IBD will activate the transcription factor hypoxia-inducible factor-1 (HIF-1) to also drive gene expression in DCs. Recent studies have described a protective role for epithelial HIF-1 in mouse models of IBD. We investigated the role of HIF-1 in DC function in a dextran sodium sulfate (DSS)-induced model of murine colitis. Wild-type and dendritic cell-specific HIF-1α knockout mice were treated with 3% DSS for 7 days. Knockout of HIF-1α in DCs led to a significantly larger loss of body weight in mice with DSS-induced colitis than in control mice. Knockout mice exhibited more severe intestinal inflammation with increased levels of proinflammatory cytokines and enhanced production of mucin. Induction of regulatory T cells (Tregs) was impaired, and the number of forkhead box P3 (Foxp3) Tregs was diminished by dendritic HIF-1α knockout. Our findings demonstrate that in DCs HIF-1α is necessary for the induction of sufficient numbers of Tregs to control intestinal inflammation.

[Erythropoiesis: Physiology, pathophysiology, and algorithm for classification of the type of anemia]

Erythropoiesis is a continuous process that replaces 1% of all erythrocytes per day. To keep the erythrocyte count within stable limits about 3 million cells/s must be renewed. This enormous turnover requires folic acid and vitamin B12 for proper cell differentiation and iron for sufficient haemoglobin synthesis. In particular, iron metabolism underlies a precise regulation which may be disturbed by chronic bleeding, inflammatory disease or impaired dietary intake. If the loss of red blood cells due to physiological aging or bleeding is not balanced by sufficient erythropoiesis in the bone marrow, anaemia will develop. For the classification of various types of anaemia, a well-established algorithm has been proven useful. This algorithm addresses basic questions such as erythrocyte volume, the underlying mechanism, e.g. whether too many cells are destroyed or new cells are not sufficiently generated, and finally aims to define the main causes for the above identified disturbance of erythropoiesis.

Modulation of the production of erythropoietin by cytokines: in vitro studies and their clinical implications

The etiology of the anemia of chronic disorders is complex. Factors which clearly contribute to the suppression of erythropoiesis are (a) reduced iron availability and (b) stimulation of the synthesis of immunomodulatory peptides such as IL-1, TNF-alpha and IFN-gamma, which inhibit the proliferation of erythrocytic progenitors in the bone marrow. The question as to whether lack of EPO is of general importance in the pathogenesis of the anemia of chronic inflammatory and malignant diseases is still a subject of controversy. The present in vitro studies show that IL-1 and TNF-alpha, but not IFN-gamma significantly lower the pO2-dependent formation of EPO in HepG2 cultures. In addition, clinical examples are given of anomalously low or high EPO levels in association with diseases involving the immune system. It is proposed that monokines and related immunomodulatory peptides could play a role in the control of the production of EPO.

Type I cell ROS kinetics under hypoxia in the intact mouse carotid body ex vivo: a FRET-based study

Reactive oxygen species (ROS) mainly originating from NADPH oxidases have been shown to be involved in the carotid body (CB) oxygen-sensing cascade. For measuring ROS kinetics, type I cells of the mouse CB in an ex vivo preparation were transfected with the ROS sensor construct FRET-HSP33. After 2 days of tissue culture, type I cells expressed FRET-HSP33 as shown by immunohistochemistry. In one population of CBs, 5 min of hypoxia induced a significant and reversible decrease of type I cell ROS levels (n = 9 CBs; P < 0.015), which could be inhibited by 4-(2-aminoethyl)benzensulfonylfluorid (AEBSF), a highly specific inhibitor of the NADPH oxidase subunits p47(phox) and p67(phox). In another population of CBs, however, 5 min of hypoxia induced a significant and reversible increase of ROS levels in type I cells (n = 8 CBs; P < 0.05), which was slightly enhanced by administration of 3 mM AEBSF. These different ROS kinetics seemed to coincide with different mice breeding conditions. Type I cells of both populations showed a typical hypoxia-induced membrane potential (MP) depolarization, which could be inhibited by 3 mM AEBSF. ROS and MP closely followed the hypoxic decrease in CB tissue oxygen as measured with an O2-sensitive dye. We conclude that attenuated p47(phox) subunit activity of the NADPH oxidase under hypoxia is the physiological trigger for type I cell MP depolarization probably due to ROS decrease, whereas the observed ROS increase has no influence on type I cell MP kinetics under hypoxia.

Rocket fuel for the quantification of S-nitrosothiols. Highly specific reduction of S-nitrosothiols to thiols by methylhydrazine

Reduction of S-nitrosothiols to the corresponding thiol function is the key step in analyzing S-nitrosocysteinyl residues in proteins. Though it has been shown to give low yields, ascorbate-dependent reduction is commonly performed in the frequently used biotin-switch technique. We demonstrate that the compound methylhydrazine can act as a specific and efficient reducing agent for S-nitrosothiols. The corresponding thiol function is exclusively generated from low molecular weight and proteinaceous S-nitrosothiols while methylhydrazine failed to reduce disulfides. It was possible to optimize the experimental conditions so that thiol autoxidation is excluded, and high reaction yields (>90%) are obtained for the thiol function. The biotin-switch technique performed with methylhydrazine-dependent reduction shows remarkably improved sensitivity compared to the ascorbate-dependent procedure.

The anemia of the newborn induces erythropoietin expression in the developing mouse retina

The hematopoietic hormone erythropoietin (Epo), regularly produced by the kidneys and the liver, is also expressed in neuronal tissue, where it has been found to mediate paracrine neuroprotective effects. In most studies exploring the rescue effects of Epo, apoptosis was exogenously induced by different cell death stimuli. Herein, we set out to study the expression and function of Epo in physiologically occurring apoptosis in a model of retinal development. We made use of an organotypic retinal wholemount culture system that resembles the physiological in vivo situation with cell connections still retained. Epo mRNA expression in the retina, liver, and kidney showed a significant increase during early development, coinciding with the anemia of the newborn. In the retina of Epo-green fluorescent protein transgenic mice, Epo-expressing cells were identified and found to be distributed in the retinal ganglion cell layer. Treatment of retinal wholemount cultures with recombinant Epo resulted in a significant decrease of apoptotic ganglion cells as well as photoreceptor cells throughout retinal development. Moreover, transforming growth factor-β-induced apoptosis was completely antagonized by Epo when both factors were simultaneously applied. Investigations on the signaling pathway revealed a decrease in Bax mRNA levels in Epo-treated retinal cells. We conclude that Epo exerts wide and prolonged neuroprotective activity in physiologically occurring apoptosis and thus contributes to proper retinal development.

Imaging of the hypoxia-inducible factor pathway: insights into oxygen sensing

The transcription factor complex hypoxia-inducible factor (HIF)-1 controls the expression of most genes involved in adaptation to hypoxic conditions. HIF-1 is a heterodimer composed of oxygen-labile HIF-alpha and constitutively expressed HIF-beta subunits. The oxygen-dependent regulation of HIF-alpha is a multistep process that includes degradation under normoxia but stabilisation, translocation into the nucleus and activation under hypoxic conditions. The present paper summarises the contributions of optical methods to the understanding of oxygen-dependent regulation of the HIF-1 pathway. The tissue- and cell-specific distribution of HIF-alpha was visualised immunohistochemically and by immunofluorescence. Transcriptional activity of HIF-1 was monitored using green fluorescent protein as a reporter under control of hypoxia response elements in living cells, spheroids and tumour tissues in living mice. With cyan and yellow variants of green fluorescent protein fused to HIF subunits and regulatory proteins, subcellular distribution, migration and interaction were imaged in vivo by means of fluorescence recovery after photo-bleaching and fluorescence resonance energy transfer. Noninvasive imaging of these cellular and molecular processes by laser scanning microscopy complements ex vivo molecular biology assays and provides an additional spatial and temporal dimension to the understanding of the HIF-1 pathway.

Antagonism of lipopolysaccharide-induced blood pressure attenuation and vascular contractility

OBJECTIVE

Aim was to assess whether lipopolysaccharide (LPS)-induced decrease of total peripheral resistance depends on Toll-like receptor (TLR)4 signaling and whether it is sensitive to NO-synthase or TLR4 antagonists.

METHODS AND RESULTS

C3H/HeN mice (control), expressing a functional, and C3H/HeJ mice, expressing a nonfunctional TLR4, were compared. LPS (20 mg/kg) was injected i.p. 6 hours before hemodynamic measurements. L-NAME and SMT, inhibitors of NO production, and Eritoran, a TLR4 antagonist, were tested for their impact on vascular contractility. Aortic rings were incubated for 6 hours with or without LPS (1 microg/mL), or with LPS+Eritoran (2 microg/mL) and their phenylephrine-induced contractility was measured using a myograph. The expression of cytokines in aortic tissue was examined by real-time polymerase chain reaction. In control mice LPS induced a significant decrease of blood pressure and an increase of heart rate, whereas C3H/HeJ remained unaffected. LPS induced an increase of cytokine expression and a depression of vascular contractility only in control mice but not in C3H/HeJ. L-NAME and SMT increased contractility in all rings and restored LPS-dependent depression of contractility. Eritoran prevented LPS-induced loss of contractility.

CONCLUSIONS

LPS upregulates cytokine expression via TLR4 and induces attenuation of smooth muscle contractility which can be effectively antagonized.

Organic cation transport in the rat kidney in vivo visualized by time-resolved two-photon microscopy

Secretion of cationic drugs and endogenous metabolites is a major function of the kidney accomplished by tubular organic cation transport systems. A cationic styryl dye (ASP(+)) was developed as a fluorescent substrate for renal organic cation transporters. The dye was injected intravenously and continuously monitored in externalized rat kidneys by time-resolved two-photon laser scanning microscopy. To investigate changes in transport activity, cimetidine, a competitive inhibitor of organic cation transport was co-injected with ASP(+). Shortly after injection, fluorescence increased in peritubular capillaries. Simultaneously, fluorescence was transiently found at the basolateral membrane of the proximal and distal tubules at a higher intensity and shorter wavelength indicating membrane association of ASP(+). Subsequently, intracellular fluorescence increased steeply within 10 s. In the proximal tubules, intracellular fluorescence decreased by 50% within 5 min, while in the distal tubules the fluorescence decreased by only 5% within the same time frame. Intracellular uptake of ASP(+) into proximal tubules was significantly reduced by cimetidine. Our studies show that organic cation transport of the kidney can be visualized in vivo by two-photon laser scanning microscopy.

Nanostructure of specific chromatin regions and nuclear complexes

Spatially modulated illumination (SMI) microscopy is a method of widefield fluorescence microscopy featuring interferometric illumination, which delivers structural information about nanoscale features in fluorescently labeled cells. Using this approach, structural changes in the context of gene activation and chromatin remodeling may be revealed. In this paper we present the application of SMI microscopy to size measurements of the 7q22 gene region, giving us a size estimate of 105+/-16 nm which corresponds to an average compaction ratio of 1:324. The results for the 7q22 domain are compared with the previously measured sizes of other fluorescently labeled gene regions, and to those obtained for transcription factories. The absence of a correlation between the measured and genomic sizes of the various gene regions indicate that a high variability in chromatin folding is present, with factors other than the sequence length contributing to the chromatin compaction. Measurements of the 7q22 region in different preparations and at different excitation wavelengths show a good agreement, thus demonstrating that the technique is robust when applied to biological samples.

ZAP-70 expression is a prognostic factor in chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (B-CLL) is a heterogenous disease with a highly variable clinical course. Recent studies have shown that expression of the protein tyrosine kinase ZAP-70 may serve as a prognostic marker in B-CLL. Employing a semiquantitative RT-PCR assay, we examined purified leukemia B cells of 39 CLL patients for the expression of ZAP-70 mRNA transcripts. Significant ZAP-70 mRNA levels exceeding those found in control samples with 5% T cells were detected in 36% of the CLL cases. Patients in the ZAP-70 positive cohort were characterized by an unfavorable clinical course with a significantly shorter progression-free survival as compared to the ZAP-70-negative patients (64%). These results were confirmed by flow-cytometric analysis of the ZAP-70 protein, and expanded to a larger patient cohort (n=67). A combined statistical analysis of 79 patients showed that the two patient subgroups also differed with regard to overall survival and a panel of known clinical prognostic factors including LDH, thymidine kinase serum levels and expression of the CD38 surface antigen by the leukemic cell clone. The level of ZAP-70 expression did not change over time in the majority of patients where sequential samples were available for analysis.

Hepatic thrombopoietin mRNA is increased in acute inflammation

The plasma concentration of thrombopoietin (TPO) in general is inversely related to the mass of platelets and megakaryocytes. However, reactive thrombocytosis of inflammatory disease is accompanied by elevated TPO levels. To investigate whether the rate of TPO mRNA expression is altered during acute inflammation, rats were injected with bacterial lipopolysaccharide (LPS). After 6 h, total RNA from liver and kidney was reverse transcribed and analyzed by competitive PCR for TPO and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). LPS-treated rats showed a significant increase in hepatic TPO mRNA concentration. The ratio of TPO to GAPDH mRNA was 3.5 +/- 0.6% in the livers of control rats and 8.3 +/- 2.0% in the livers of LPS-treated rats (mean +/- SD). Thus, reactive thrombocytosis of inflammatory disease might result from an increase in hepatic TPO production. Since platelets are involved in the immune reaction, reactive thrombocytosis may be a mechanism of host defense.

Cytosolic Ca(2+) levels and DNA synthesis of human umbilical vein endothelial cell cultures are unresponsive to thrombopoietin treatment

The hormone thrombopoietin (TPO) induces proliferation of megakaryocytic progenitors and augments agonist-induced mobilization of Ca(2+) in platelets. Because the action of TPO is not restricted to the megakaryocytic lineage, we studied the occurrence of TPO receptor mRNA and protein, and effects of TPO on cytosolic Ca(2+) levels and DNA synthesis in human umbilical vein endothelial cell cultures (HUVECs). Polymerase chain reaction following reverse transcription (RT-PCR) of total mRNA revealed that TPO receptor (MPL) mRNA was expressed only at low level in our samples. TPO receptor protein was not detectable in HUVEC lysates investigated by immunoprecipitation and immunoblotting. In contrast to vascular endothelial growth factor (VEGF), TPO did neither alter fura2 fluorescence as a measure of cytosolic Ca(2+) levels nor increase 5-bromo-2'-deoxyuridine incorporation into DNA of HUVECs. In conclusion, our data demonstrate that HUVECs are neither structurally nor functionally responsive to TPO.

Accumulation of HIF-1alpha under the influence of nitric oxide

The key player for adaptation to reduced oxygen availability is the transcription factor hypoxia-inducible factor 1 (HIF-1), composed of the redox-sensitive HIF-1alpha and the constitutively expressed HIF-1beta subunits. Under normoxic conditions, HIF-1alpha is rapidly degraded, whereas hypoxia, CoCl(2), or desferroxamine promote protein stabilization, thus evoking its transcriptional activity. Because HIF-1 is regulated by reactive oxygen species, investigation of the impact of reactive nitrogen species was intended. By using different nitric oxide (NO) donors, dose- and time-dependent HIF-1alpha accumulation in close correlation with the release of NO from chemically distinct NO donors was established. Intriguingly, small NO concentrations induced a faster but transient HIF-1alpha accumulation than higher doses of the same NO donor. In contrast, NO attenuated up-regulation of HIF-1alpha evoked by CoCl(2) in a concentration- and time-dependent manner, whereas the desferroxamine-elicited HIF-1alpha signal remained unaltered. To demonstrate an autocrine or paracrine signaling function of NO, we overexpressed the inducible NO synthase and used a coculture system of activated macrophages and tubular cells. Expression of the NO synthase induced HIF-1alpha accumulation, which underscored the role of NO as an intracellular activator for HIF-1. In addition, macrophage-derived NO triggered HIF-1alpha up-regulation in LLC-PK(1) target cells, which points to intercellular signaling properties of NO in achieving HIF-1 accumulation. Our results show that NO does not only modulate the HIF-1 response under hypoxic conditions, but it also functions as a HIF-1 inducer. We conclude that accumulation of HIF-1 occurs during hypoxia but also under inflammatory conditions that are characterized by sustained NO formation.

Chronic inborn erythrocytosis leads to cardiac dysfunction and premature death in mice overexpressing erythropoietin

The most common cause of an increase of the hematocrit is secondary to elevated erythropoietin levels. Erythrocytosis is assumed to cause higher blood viscosity that could put the cardiovascular system at hemodynamic and rheological risks. Secondary erythrocytosis results from tissue hypoxia, and one can hardly define what cardiovascular consequences are caused by chronic erythrocytosis or hypoxia. Herein, a novel transgenic (tg) mouse line is characterized that is erythrocytotic because of chronic overexpression of the human erythropoietin gene. These mice grow up well, reaching a hematocrit of about 0.80 in adulthood. Blood volume of adult tg mice was markedly increased by 75%. Unexpectedly, blood pressure was not elevated and cardiac output was not decreased. Still, the adult tg mice showed features of cardiac dysfunction with increased heart weight. In vivo, high-frequency echocardiography revealed marked ventricular dilatation that was confirmed by histologic examination. Furthermore, by transmission electron microscopy, a prominent intracellular edema of the cardiomyocytes was seen. Exercise performance of the tg mice was dramatically reduced, unmasking the severity of their compromised cardiovascular function. In addition, life expectancy of the tg mice was significantly reduced to 7.4 months. Our findings suggest that severe erythrocytosis per se results in cardiac dysfunction and markedly reduced life span.

Erythropoietin gene expression in different areas of the developing human central nervous system

Evidence from cell culture and animal experiments suggests a neuroprotective and neurotrophic function of erythropoietin (EPO). We have quantitated the distribution of EPO mRNA expression in the developing human central nervous system (CNS).

PATIENTS AND METHODS

Up to seven biopsies from different areas of the CNS of four preterm fetuses (gestational age 23-37 weeks) were obtained at routine postmortem examinations. EPO mRNA was quantitated by competitive PCR in samples from the CNS, the kidneys, and the liver where the EPO gene is predominantly expressed at this gestational age.

RESULTS

EPO mRNA was most abundant in one sample from the cerebellum (0.29 amol/microg total RNA [amol=10(-18)mol]) and two from the pituitary gland (0.23 amol/microg total RNA), but levels varied considerably. EPO mRNA in the cortex cerebri (median 0.12 amol/microg total RNA; n=4) dominated over the expression in the corpora amygdala (median 0.05 amol/microg total RNA; n=4), the hippocampus (median 0.03 amol/microg total RNA; n=4), or the basal ganglia (median 0.01 amol/microg total RNA; n=3). Only little EPO mRNA (<0.01 and 0.06 amol/microg total RNA) was found in the spinal cord. EPO mRNA levels in the cerebellum, pituitary gland, or the cerebral cortex were within the same range as in the liver (0.03-1.67 amol/microg total RNA; n=4), or the kidneys (0.06-0.79 amol/microg total RNA; n=4).

CONCLUSION

We found the EPO gene expressed throughout the fetal human CNS. Our data provide the basis to discuss a function for EPO in the brain of humans as well.

VEGF production, cell proliferation and apoptosis of human IGR 1 melanoma cells under nIFN-alpha/beta and rIFN-gamma treatment

The effect of natural and recombinant interferons (nIFN, rIFN) on cell growth, apoptosis and the production of vascular endothelial growth factor (VEGF) was investigated in the human melanoma cell line IGR 1. We determined cell proliferation, cell vitality, DNA synthesis, apoptosis, intracellular oxygen radicals (ROS) and VEGF-mRNA as well as VEGF-protein levels. rIFN-gamma significantly inhibited growth by decreasing DNA synthesis and increasing apoptosis. Less pronounced was the growth inhibitory effect of nIFN-beta because an increased rate of apoptosis was outweighed by enhanced DNA synthesis. nIFN-alpha only had minor effects on cell growth parameters. Under long-term incubation (144 h) nIFN-beta decreased, but rIFN-gamma increased production of the angiogen VEGF. Our data underscore the multiple effects of IFNs on melanoma cells and may contribute to the understanding of ambivalent results of melanoma therapy by IFNs. Particularly, the increased VEGF production under long-term treatment with serum IFN levels between 100 and 1,200 IU/ml should be kept in mind.

Nitric oxide affects the production of reactive oxygen species in hepatoma cells: implications for the process of oxygen sensing

Treatment of human hepatoma cells (HepG2) with NO-donors for 24 h inhibited hypoxia-induced erythropoietin (EPO) gene activation. NO was found to increase the production of reactive oxygen species (ROS), the putative signaling molecules between a cellular O2-sensor and hypoxia inducible factor 1 (HIF-1). HIF-1 is the prime regulator of O2-dependent genes such as EPO. NO-treatment for more than 20 h reduced HIF-1-driven reporter gene activity. In contrast, immediately after the addition of NO, ROS levels in HepG2 cells decreased below control values for as long as 4 h. Corresponding to these lowered ROS-levels, HIF-1 reporter gene activity and EPO gene expression transiently increased but were reduced when ROS levels rose thereafter. Our findings of a bimodal effect of NO on ROS production shed new light on the involvement of ROS in the mechanism of O2-sensing and may explain earlier conflicting data about the effect of NO on O2-dependent gene expression.

Pivotal role of reactive oxygen species as intracellular mediators of hyperthermia-induced apoptosis

The effects of cellular antioxidant capacity on hyperthermia (HT)-induced apoptosis and production of antiapoptotic heat shock proteins (HSPs) were investigated in HL-60 cells and in HL-60AR cells that are characterized by an elevated endogenous catalase activity. Exposure of both cell lines to 43 degrees C for 1 h initiated apoptosis. Apoptosis peaked at 3-6 h after heat exposure in the HL-60 cells. Whereas HL-60AR cells were partially protected against HT-induced apoptosis at these early time points, maximal levels of apoptosis were detected later, i.e. 12-18 h after heat exposure. This differential induction of apoptosis was directly correlated to the induction of the antiapoptotic HSP27 and HSP70. In particular, in the HL-60 cells HSP27 was significantly induced at 12-18 h after exposure to 43 degrees C when apoptosis dropped. In contrast, coinciding with the late onset of apoptosis in HL-60AR cells at that time HL-60AR cells lacked a similar HSP response. In line with the higher antioxidant capacity HL-60AR cells accumulated reactive oxygen species to a lesser degree than HL-60 cells after heat treatment. Protection from HT-induced apoptosis as well as diminished heat-induced HSP27 expression was also observed after cotreatment of HL-60 cells with 43 degrees C and catalase but not with superoxide dismutase. These data emphasize the pivotal role of reactive oxygen species for HT induced pro- and antiapoptotic pathways.

Hypoxia and interleukin-1beta stimulate vascular endothelial growth factor production in human proximal tubular cells

BACKGROUND

Vascular endothelial growth factor (VEGF) promotes angiogenesis and inflammatory reactions. VEGF mRNA is detectable in the proximal tubules of inflamed kidneys but not in normals. In other organs VEGF gene expression is induced by hypoxia and cytokines such as interleukin 1 (IL-1). To identify the cellular mechanisms in control of tubular VEGF production, we studied effects of hypoxia and IL-1beta in VEGF mRNA levels, VEGF secretion, and activity of the hypoxia-inducible dimeric transcription factor 1 (HIF-1alpha/beta) in human proximal tubular epithelial cells (PTECs) in primary culture.

METHODS

PTECs were grown in monolayers from human kidneys. Hypoxia was induced by incubation at 3% O2. VEGF mRNA was quantitated by competitive polymerase chain reaction following reverse transcription. VEGF was measured by enzyme-linked immunoassay. HIF-1alpha was demonstrated by Western blot analysis and HIF-1 DNA binding by gel shift assay.

RESULTS

Significant amounts of VEGF mRNA and VEGF protein were measured in PTEC extracts and culture media, respectively. Stimulation of VEGF synthesis at low O2 tension and following IL-1beta treatment was detectable at the protein level only. Nuclear HIF-1alpha protein levels and HIF-1 binding to DNA were also increased under these conditions.

CONCLUSIONS

PTECs in culture produce VEGF. One mechanism of induction appears to be increased DNA binding of HIF-1 to hypoxia-responsive elements in the VEGF gene promoter. In inflammatory diseases of the kidney, tubular cell-derived VEGF may contribute to microvascular leakage and monocyte extravasation.

Hepatocyte-supported serum-free culture of rat liver sinusoidal endothelial cells

BACKGROUND/AIMS

A major problem in rat liver endothelial cell culture is the rapid loss of cells after 48 h. This study aimed to develop a protocol that allowed easy maintenance and proliferation of sinusoidal endothelial cells in serum-free culture for 5-6 days.

METHODS

Cells isolated from adult rat liver by collagenase digestion were purified by centrifugal elutriation and cultured on glutaraldehyde-crosslinked collagen.

RESULTS

At high plating densities cells could be maintained serum-free for 6 days in the presence of hydrocortisone and basic fibroblast growth factor; at lower plating densities medium had to be supplemented with additional growth-promoting factors. Conditioned medium of adult rat hepatocytes proved to be the most effective growth stimulus; it increased thymidine incorporation, DNA content and cell number per dish with a half-maximal effect at 20% (v/v). Cell proliferation was also observed with either vascular endothelial growth factor, phorbol ester or conditioned media from FAO or HEPG2 liver cell lines provided the cultures were additionally supplemented with 1% newborn calf serum. Vascular endothelial growth factor was detected in all conditioned media. In the absence of hepatocyte-conditioned medium, 1% serum helped to maintain cultures; it itself exerted a low proliferative effect. Higher serum concentrations (>5%), however, led to cell loss after 48 h. The numerous sieve plates of 6-h-old cells progressively disappeared during culture and were replaced by randomly distributed pores, which later grouped together at cell-cell borders. More than 90% of the cells endocytosed acetylated low-density lipoprotein.

CONCLUSIONS

The study shows that cultured hepatocytes secrete growth-promoting substances that stimulate in vitro endothelial cell proliferation in the absence of serum; this effect could be mimicked by the combined addition of vascular endothelial growth factor and 1% serum. The new media formulations should facilitate future research on liver endothelial cells in mono- or coculture.

Interleukin-1beta and tumor necrosis factor-alpha stimulate DNA binding of hypoxia-inducible factor-1

The rate of transcription of several genes encoding proteins involved in O(2) and energy homeostasis is controlled by hypoxia-inducible factor-1 (HIF-1), a heterodimeric DNA binding complex composed of alpha and beta subunits. HIF-1 is considered the primary trans-acting factor for the erythropoietin (EPO) and vascular endothelial growth factor (VEGF) genes. Since EPO gene expression is inhibited by the proinflammatory cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), while no such effect has been reported with respect to the VEGF gene, we investigated the effects of IL-1beta and TNF-alpha on the activation of the HIF-1 DNA-binding complex and the amount of HIF-1alpha protein in human hepatoma cells in culture. Under normoxic conditions, both cytokines caused a moderate activation of HIF-1 DNA binding. In hypoxia, cytokines strongly increased HIF-1 activity compared with the effect of hypoxia alone. Only IL-1beta increased HIF-1alpha protein levels. In transient transfection experiments, HIF-1-driven reporter gene expression was augmented by cytokines only under hypoxic conditions. In contrast to their effect on EPO synthesis, neither IL-1beta nor TNF-alpha decreased VEGF production. The mRNA levels of HIF-1alpha and VEGF were unaffected. Thus, cytokine-induced inhibition of EPO production is not mediated by impairment of HIF-1 function. We propose that HIF-1 may be involved in modulating gene expression during inflammation.

Role of tumor necrosis factor alpha in hyperthermia-induced apoptosis of human leukemia cells

We used the human myelomonoblastic leukemia cell line PLB-985 to study the effects of temperatures ranging from 37 degrees C to 43 degrees C for 1 h on the induction of apoptosis and cell cycle distribution in leukemia cells. The threshold temperature for the onset of apoptosis was 42 degrees C. Whereas hyperthermia exerted no effect on the expression of Bcl-2 and Bax, heat induced a >30-fold increase of tumor necrosis factor (TNF) alpha mRNA expression and a significant increase in TNF-alpha protein secretion. This endogenous production of TNF-alpha correlated directly with the temperature-induced apoptode effect. Blocking TNF-alpha expression via treatment with pyrrolidinedithiocarbamate or blocking TNF-alpha activity with neutralizing antibodies abrogated heat-provoked apoptosis. In addition, exposure of cell culture supernatant of heat-treated PLB-985 cells to untreated cells induced an apoptotic effect. These data indicate a TNF-a-mediated self eradication of the leukemia cells after heat exposure. Inducing apoptosis with wild-type TNF-alpha or p55 and p75 protein muteins demonstrated that this effect was mediated by the p55 receptor. Interestingly, the autocrine suicidal loop found in immature leukemia cells was lost after granulocytic differentiation with 0.5% N,N-dimethylformamide. These data should be of critical importance for the understanding of the biological impact of fever as well as for developing therapeutic approaches to malignant diseases

Expression of the thrombopoietin gene in human fetal and neonatal tissues

Thrombopoietin (TPO) regulates megakaryopoiesis and platelet production. In the adult, TPO is mainly produced by the liver and the kidneys. This study focuses on fetal and neonatal TPO mRNA expression. In 26 human fetuses and preterm neonates, samples from liver, kidney, spleen, lung, and bone marrow were extracted for total RNA. We measured platelet counts, TPO serum concentrations by enzyme-linked immunosorbent assay, and TPO mRNA contents by reverse transcription/competitive polymerase chain reaction. TPO mRNA concentrations per microgram total RNA were similar in liver, spleen, and bone marrow, slightly lower in kidney, and significantly lower in lung. When related to gram tissue, TPO mRNA levels were highest in the liver. Considering the total amount of TPO mRNA produced in liver, kidney, and spleen, the liver accounted for 95.3%. No correlations between TPO mRNA expression and serum TPO concentration, blood platelet count, or gestational age were observed. In conclusion, the liver is the primary site of TPO gene expression in human fetuses and neonates. The spleen may contribute to TPO production during fetal life. Like in the adult, TPO mRNA is expressed in fetal bone marrow.

Evidence against a major role for Ca2+ in hypoxia-induced gene expression in human hepatoma cells (Hep3B)

1. The human hepatoma cell line Hep3B is a widely used model for studies of hypoxia-related gene expression. Cytosolic free calcium concentration ([Ca2+]i) has been implicated in cellular oxygen-sensing processes. We investigated whether calcium ions have a significant impact on the production of erythropoietin (EPO) and vascular endothelial growth factor (VEGF). 2. We found that the calcium ionophore ionomycin induced a rapid and sustained increase of [Ca2+]i while thapsigargin, an inhibitor of endoplasmic reticulum calcium ATPase, only caused a 20 % elevation of [Ca2+]i within 10 min after application. However, the calcium content of intracellular stores was considerably reduced by thapsigargin after an incubation period of 24 h. 3. Variations in [Ca2+]o did not result in altered EPO or VEGF secretion rates. Ionomycin decreased EPO production while the lowering of VEGF production was not statistically significant. In the presence of extracellular Ca2+ the membrane permeant calcium chelator BAPTA-AM stimulated the production of EPO (P < 0.05) but not of VEGF while EGTA-AM, a closely related agent, affected neither EPO nor VEGF formation under these conditions. Incubation with thapsigargin resulted in decreased EPO synthesis (P < 0.05) but stimulated VEGF secretion (P < 0.05). 4. In the absence of extracellular calcium, EGTA-AM led to an accumulation of hypoxia-inducible factor-1alpha (HIF-1alpha). This treatment significantly stimulated VEGF synthesis but also decreased EPO secretion (P < 0.05). 5. Our data suggest that the calcium transient and the cytosolic Ca2+ concentration do not play a key role in hypoxia-induced EPO and VEGF production in Hep3B cells.

Effects of neopterin and 7,8-dihydroneopterin on hypoxia-induced renal erythropoietin production

Activation of the human cellular immune system is associated with greatly increased formation of the pteridines neopterin and 7,8-dihydroneopterin. It has been postulated that pteridines play a role in the pathogenesis of the anaemia of inflammation. Herein, we studied effects of pteridines on renal function, primarily on the synthesis of erythropoietin (Epo). The experiments were performed with isolated rat kidneys which were perfused hypoxically (pO2 26 mmHg) at constant pressure (100 mmHg) in a serum-free recirculation system for 3 h. The results show that the rate of the production of Epo was significantly lowered when neopterin or 7,8-dihydroneopterin were added to the perfusate. Neopterin (200 microM) also reduced the renal Epo mRNA level. Both pteridines increased renal vascular resistance. 7,8-Dihydroneopterin lowered urine flow and glomerular filtration rate more potently than neopterin. Renal O2 consumption and parameters of exocrine renal function (fractional reabsorption rates of sodium, glucose and water) were not altered by the pteridines, while the glomerular permeability was greatly increased. These results suggest that activated macrophages may not only inhibit the synthesis of Epo by generating cytokines and reactive O2 species but also by the release of pteridines. In vivo, high concentrations of pteridines in renal tissue may aggravate the anaemia of inflammation.

Effects of pro- and antioxidative compounds on renal production of erythropoietin

The most important stimulus for the enhanced synthesis of erythropoietin (Epo) is a lowered O2 tension in the tissue. However, the mechanism by which an impaired O2 supply is transduced into appropriate Epo production is still not fully understood. Recently, studies in human hepatoma cells (line HepG2) indicate that reactive O2 species are involved in the signal transduction from the cellular O2 sensor to the Epo gene. To clarify the role of reactive O2 species in the regulation of Epo synthesis in the kidney, the principal Epo-producing organ in vivo, we investigated the influence of potent pro- and antioxidants on Epo production in isolated perfused rat kidneys. Under normoxic conditions, the iron chelator desferrioxamine and the antioxidant vitamin A increased renal Epo production, mimicking hypoxic induction. In contrast, supplementation of the perfusion medium of hypoxically perfused kidneys with the prooxidant compounds H2O2 or pyrogallol caused a significant reduction of Epo synthesis. The inhibition of Epo formation by reactive O2 species could be completely antagonized by desferrioxamine and the hydroxyl radical-(OH*)-scavenger tetramethylthiourea. Vitamin A also antagonized the H2O2-dependent inhibition of hypoxically induced Epo synthesis. Interestingly, the addition of the antioxidant vitamin A to hypoxically perfused kidneys also induced Epo production significantly. Our data strongly support the idea that reactive O2 species, especially H2O2, are part of the signaling chain of the cellular O2-sensing mechanism regulating the renal synthesis of Epo.

Oxygen tension modulates beta-globin switching in embryoid bodies

Little is known about the factors influencing the hemoglobin switch in vertebrates during development. Inasmuch as the mammalian conceptus is exposed to changing oxygen tensions in utero, we examined the effect of different oxygen concentrations on beta-globin switching. We used an in vitro model of mouse embryogenesis based on the differentiation of blastocyst-derived embryonic stem cells to embryoid bodies (EBs). Cultivation of EBs at increasing oxygen concentrations (starting at 1% O2) did not influence the temporal expression pattern of embryonic (betaH1) globin compared to the normoxic controls (20% O2). In contrast, when compared to normoxically grown EBs, expression of fetal/adult (betamaj) globin in EBs cultured at varying oxygen concentrations was delayed by about 2 days and persisted throughout differentiation. Quantitation of hemoglobin in EBs using a 2,7-diaminofluorene-based colorimetric assay revealed the appearence of hemoglobin in two waves, an early and a late one. This observation was verified by spectrophotometric analysis of hemoglobin within single EBs. These two waves might reflect the switch of erythropoiesis from yolk sac to fetal liver. Reduced oxygenation is known to activate the hypoxia-inducible factor-1 (HIF-1), which in turn specifically induces expression of a variety of genes among them erythropoietin (EPO). Although EBs increased EPO expression upon hypoxic exposure, the altered beta-globin appearance was not related to EPO levels as determined in EBs overexpressing EPO. Since mRNA from both mouse HIF-1alpha isoforms was detected in all EBs tested at different differentiation stages, we propose that HIF-1 modulates beta-globin expression during development.

The influence of phenobarbital on cytochromes and reactive oxygen species in erythropoietin producing HepG2 cells

Light absorption photometry of HepG2 cells treated with phenobarbital for enhancing the content of cytochrome P-450 and the synthesis of erythropoietin revealed an influence on all cytochromes detectable in the wavelength range between 400 and 620 nm. No correlation was found between specific changes of cytochrome P-450 absorption and increased EPO synthesis as proposed earlier by Fandrey et al. (Life Sci. (1990) 47, 127-134). In the present study, however, the increased erythropoietin synthesis could be related to a decreased intracellular hydroxyl radical level described as crucial for the oxygen regulated gene expression (Kietzmann et al., Biochem. J. (1998) 335, 425-432; Porwol et al., Eur. J. Biochem. (1998) 256, 16-23).

Tumor necrosis factor-alpha production by human hepatoma cell lines is resistant to drugs that are inhibitory to macrophages

Little is known about the potential of immunomodulatory agents to lower tumor necrosis factor-alpha (TNF-alpha) synthesis in tissues of nonmonocytic origin. We studied effects of diverse drugs on the formation of immunoreactive TNF-alpha in the human hepatoma cell lines HepG2 and Hep3B, in which TNF-alpha production was induced by treatment (3 h incubation periods) with interleukin-1beta (IL-1beta, 300 pg/ml) or phorbol myristate acetate (PMA, 100 nmol/l). TNF-alpha production in IL-1beta-stimulated or PMA-stimulated hepatocyte cultures was not altered following the addition of dihydrocortisone (< or = 1 microg/ml), dibutyryl-cAMP (db-cAMP, < or = 100 micromol/l), adenosine (< or = 1 mmol/l), thalidomide (< or = 25 microg/ml), or cyclosporine (< or = 300 ng/ml). TNF-alpha production was inhibited by taurolidine (> or = 300 microg/ml), but this inhibition was associated with reduced cell viability. Pentoxifylline (1 mg/ml) did not influence PMA-induced TNF-alpha production, but it augmented IL-1beta-induced TNF-alpha production. Measurements of TNF-alpha mRNA by RT-PCR indicated that pentoxifylline exerted its effect posttranscriptionally. Additional studies with PMA-treated human whole blood cultures confirmed that pentoxifylline, db-cAMP, and adenosine reduced TNF-alpha production by leukocytes. These results provide first evidence to assume cell type-specific effects of immunomodulatory drugs on TFN-alpha synthesis, which may be relevant with respect to their clinical application.

Erythropoietin mRNA expression in human fetal and neonatal tissue

Based on animal experiments, a switch of the erythropoietin (EPO) production site from the liver in the fetus to the kidneys in the adult has been postulated. To study the switch in humans, we have quantitated EPO mRNA expression in liver, kidney, spleen, and bone marrow of human fetuses and neonates by means of a competitive polymerase chain reaction (PCR). Tissue samples from 66 routine postmortem examinations were obtained. EPO mRNA was expressed in 97% of the tissue specimen derived from the liver (n = 66) and in 93% of those from the kidneys (17 weeks of gestation until 18 months after birth; n = 59). For the first time the EPO gene was found expressed in vivo in human spleen (96% of 64 samples) and in fetal and neonatal bone marrow (81% of 21 samples). EPO mRNA expression in the kidneys increased significantly beyond 30 weeks of gestation (P < .05). Although there was a slight decrease in EPO mRNA content per g liver tissue towards birth, the liver accounted for about 80% of the total body EPO mRNA. The contribution of the spleen and bone marrow were minor compared with liver and kidneys. Our results indicate that in humans the liver is the primary site of EPO gene expression not only in fetal, but also in neonatal life. A significant increase of renal EPO mRNA expression after 30 weeks of gestation might indicate the beginning switch.

Effects of modulators of the production and degradation of hydrogen peroxide on erythropoietin synthesis

Erythropoietin (Epo) synthesis is suppressed in normoxia and stimulated in hypoxia. To test the hypothesis that the cellular H2O2 level is important in the control of Epo synthesis, we have studied effects of modulators of H2O2 generation and degradation on Epo production in human hepatic cell cultures (hepatoma lines HepG2 and Hep3B). In addition, we measured the activities of antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase) in cultures following hypoxia exposure or H2O2 treatment. The results show that the formation of immunoreactive Epo was stimulated in normoxic cultures by treatment with exogenous catalase thus mimicking the effect of hypoxia (24 h incubation periods). Epo production was also stimulated when scavengers of reactive O2 species (tetramethylthiourea, dihydrorhodamine) were added to the cells. On the other hand, stimulators of H2O2 generation (xanthine oxidase, glucose oxidase, NADH, NADPH) lowered Epo production in hypoxic cultures. Hypoxia exposure decreased superoxide dismutase activity and H2O2 treatment reduced catalase activity thus influencing the endogenous antioxidant defense system. These findings support the concept that reactive O2 species, primarily H2O2, act as messengers in the O2-dependent control of the hepatic production of Epo. Changes in the cellular activities of antioxidant enzymes appear to play only a minor role in this process.

Expression of vascular endothelial growth factor during the development of cardiac hypertrophy in spontaneously hypertensive rats

Left ventricular hypertrophy (LVH) is often associated with an impaired maximal coronary blood flow and increases the vulnerability of the heart tissue to ischaemia. In this study, the correlation between coronary blood flow and expression of the vascular endothelial growth factor (VEGF) mRNA was investigated. Using both haemodynamic measurements and analysis of mRNA, we have demonstrated that during development of LVH, in spontaneously hypertensive rats (SHR), an impaired maximal coronary flow at 12 weeks of age is associated with low levels of VEGF mRNA. However, in older SHR (32 weeks) with stabilised hypertrophy and a normal maximal coronary flow response, VEGF mRNA levels are increased 3-fold. These results suggest that the mechanism for the impaired flow, observed in some types of cardiac hypertrophy, might involve an inadequate growth of the coronary vessels due to insufficient activation of the VEGF gene.

The influence of nickel and cobalt on putative members of the oxygen-sensing pathway of erythropoietin-producing HepG2 cells

Cobalt and nickel stimulate, as does hypoxia, the production of erythropoietin (EPO) in HepG2 cells. Under hypoxic conditions, a decrease in the level of intracellular reactive oxygen species (ROS) is thought to stimulate EPO expression. Cobalt and nickel may interact with the putative oxygen sensor by changing the redox state of the central iron atom of heme proteins, similar to the effects of hypoxia. It was investigated, therefore, whether cobalt and nickel interact with hemeproteins or ROS scavenging systems in the control of intracellular ROS level. Cobalt chloride (100 microM, 24 h) oxidized non respiratory as well respiratory hemeproteins and increased the oxygen consumption. In contrast, nickel chloride (300 microM, 24 h) primarily reduced respiratory hemeproteins and decreased the oxygen consumption. In HepG2 cells treated with CoCl2, iron and cobalt were localized in cytosolic granules close to the cell nucleus and in mitochondria at concentrations up to 12 mM or 41 mM, respectively. Intracellular nickel was not measurable. Three-dimensional reconstruction of confocal laser microscopy images revealed hot spots of hydroxyl radical generation by a Fenton reaction at the sites of cytosolic iron accumulation. The .OH levels decreased in cobalt-treated (to 81%) as well as in nickel-treated (to 67%) HepG2 cells, accompanied by an increase of EPO expression to 167% and 150%, respectively. Our results underline the importance of .OH formed by a Fenton reaction for triggerimg EPO production. Identification of the primary hemeprotein being the oxygen sensor was not possible due to the antagonistic effects of cobalt and nickel on the redox state of detectable hemeproteins.

Serum erythropoietin concentration in anaemia of visceral leishmaniasis (kala-azar) before and during antimonial therapy

Serum erythropoietin (Epo) concentrations and variables of red cell and iron status were studied in 27 Sudanese patients who were treated with sodium stibogluconate for visceral leishmaniasis (kala-azar). Blood haemoglobin increased from 6.4 (+/- 1.7 SD) to 9.5 (+/- 1.4) g/dl during treatment. Serum ferritin decreased concomitantly. Serum iron levels were unchanged whereas the total iron binding capacity increased slightly. The pre-treatment serum Epo concentration in relation to the blood haemoglobin concentration was not as high as expected from the one in primary haematological diseases, indicating that there is a relative lack of Epo in anaemic kala-azar patients. Serum Epo further decreased during stibogluconate therapy. The normal dependence of the serum Epo level on the blood haemoglobin concentration was lost during mid-term antimonial treatment, but it recovered thereafter. Cell culture studies with the human hepatoma cells HepG2 showed that stibogluconate (> or = 30 microg/ml) inhibited Epo gene expression. Thus, effective treatment of kala-azar with stibogluconate results in improvement of anaemia, although the drug itself may impair Epo production.

Manganese augments nitric oxide synthesis in murine astrocytes: a new pathogenetic mechanism in manganism?

Since manganese (Mn2+) is known to be sequestered in glial cells, we investigated possible neurotoxic mechanisms involving astrocytes in vitro. Low concentrations of Mn2+ were toxic only in astrocyte-neuronal cocultures but not in pure astrocyte or neuronal cultures. As a possible mediator of manganese-derived neurotoxicity, we measured the production of nitric oxide in astrocytes. Manganese, but not other transition metals, dose dependently increased iNOS mRNA and protein levels and the release of nitric oxide in activated astrocytes. This effect was specific for astrocytes, since we observed no stimulation in microglial cells. The observations suggest that besides the known inhibition of mitochondrial function the neurotoxic effect of manganese in low concentrations might be mediated by the increased production of nitric oxide in astrocytes.

Decreased erythropoietin response in Plasmodium falciparum malaria-associated anaemia

One of the most serious manifestations of Plasmodium falciparum malaria is anaemia. Its established causes are increased red cell destruction and ineffective erythropoiesis. Since proinflammatory cytokines have been shown to suppress the in vitro synthesis of erythropoietin (Epo), we measured serum immunoreactive Epo in 90 Sudanese patients suffering from malaria. Even in severe cases of anaemia (blood haemoglobin < 80 g/l), serum Epo levels rarely exceeded 300 U/l. For comparison, serum Epo was increased up to 12,000 U/l in a reference group of Caucasian patients with anaemia not associated with infection. Moreover, the slope of the log Epo/haemoglobin regression line was less steep in malarial anaemia. Thus, as documented for other chronic inflammatory disorders, there is a relative lack of Epo in malaria-associated anaemia. Treatment with the antimalarial drug chloroquine may aggravate the defect in Epo production, because chloroquine inhibited Epo synthesis when tested in cell culture.

Erythropoietin gene expression is suppressed after lipopolysaccharide or interleukin-1 beta injections in rats

Proinflammatory cytokines play an important role in the pathogenesis of anemia in inflammatory diseases. Interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) have been reported to inhibit the synthesis of erythropoietin (EPO) in vitro. To evaluate the in vivo significance of this observation, we have investigated effects of the administration of bacterial lipopolysaccharide (LPS) and IL-1 beta on renal EPO production in rats. Measurements by competitive reverse-transcription polymerase chain reaction showed that EPO mRNA levels were significantly reduced in the kidneys of normoxic rats 6 h after the injection of LPS (0.1 or 1 mg/kg). In addition, LPS and IL-1 beta (1 microgram/kg) inhibited the increase in EPO mRNA and plasma EPO levels when administered to rats before hypoxia exposure (8% O2 in the inspiratory gas). Evidence for an inflammatory reaction in the kidneys of LPS-treated rats was provided by measurements of greatly elevated renal TNF-alpha mRNA levels. Furthermore, kidneys isolated from LPS-created rats produced less immunoreactive EPO when perfused hypoxically in vitro for 2 h. Thus mediators of the immune response inhibit renal EPO gene expression in vivo, which is relevant with respect to the impaired synthesis of EPO in inflammatory diseases in humans.

Suppression of the oxidative burst in murine microglia by nitric oxide

The effect of nitric oxide (NO) on the oxidative burst was analyzed in purified murine microglial cells in vitro. The generation of reactive oxygen derivatives was monitored with the use of luminol-dependent chemiluminescence. After inducing the endogenous NO production with interleukin 1beta (IL-1beta) and interferon-gamma (IFN-gamma) the superoxide anion release was significantly reduced, which was reversed by the inhibition of the NO synthase. Additionally, chemical NO-releasing compounds reduced the generation of reactive oxygen derivatives rapidly and independently of the pathway used to trigger the oxidative burst. This effect of NO was not mediated via guanylyl cyclase and cGMP, or due to the scavenging of released superoxide anions. This attenuation of superoxide anion generation by NO may limit deleterious effects of the release of reactive oxygen derivatives in tissue inflammation or injury.

Perioperative use of recombinant human erythropoietin in patients refusing blood transfusions. Pathophysiological considerations based on 5 cases

The efficacy of the administration of recombinant human erythropoietin (rHuEPO) in the treatment of anaemia in critically ill surgical patients refusing red cell transfusions requires further documentation. Herein, we report the outcome of 5 consecutive severely anaemic Jehovah's Witness patients (lowest haemoglobin concentration 27 g/1), who were discharged from the hospital in good condition after treatment. RHuEPO (50-280 U/kg body weight) was daily administered to 4 of the patients, who either exhibited preoperative anaemia or developed postoperative anaemia refractory to endogenous EPO probably due to inflammation. RHuEPO treatment was followed by a steep rise in reticulocytes and haemoglobin concentration. The fifth patient, who exhibited no signs of systemic inflammation following emergency hemicolectomy, was also treated with intravenous iron, but not with rHuEPO. His blood haemoglobin concentration rose from 27 g/l to 92 g/l in 3 wk. These observations indicate that the administration of rHuEPO is justified in the management of life-threatening anaemia, although only on a humanitarian basis, because there is no predictor for the possible spontaneous recovery.

Effects of erythropoietin on endothelin-1 synthesis and the cellular calcium messenger system in vascular endothelial cells

A rise in blood pressure is the main side effect of erythropoietin (EPO) treatment in patients with renal anemia. The mechanisms, however, by which EPO may cause hypertension are still unclear. We therefore investigated the effects of EPO on endothelin (ET) synthesis and cytosolic free calcium concentration ([Ca2+]i) in vascular endothelial cells. Porcine endothelial cells were isolated from thoracic aorta, pulmonary artery, and vena cava. Studies were performed with cells of the first subculture. ET concentrations were measured radioimmunologically. Changes in [Ca2+]i were determined with the fluorescent probe fura-2. Cytotoxicity was assessed by sodium 3'-[1-(phenyl-amino-carbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)ben zene sulfonic acid hydrate (XTT) assay. ET synthesis was similar in cells of different vascular origins and was time-dependent, reaching approximately 2 pmol ET/mg protein within 12 h of incubation. EPO (12 to 200 U/mL) stimulated ET release time- and dose-dependently by up to 83.2% (P < .01) within 12 h in the absence of fetal calf serum and heparin. EPO induced an immediate significant rise in [Ca2+]i from 58 +/- 12 nmol/L to 495 +/- 85 nmol/L (P < .01) with a subsequent slow return to 257 +/- 3 nmol/L. During 2 h of incubation, the Ca-ionophore A 23187 (10(-8) mol/L) moderately but significantly stimulated endothelial ET synthesis. However, the Ca-channel blocker verapamil, the intracellular Ca-release blocker TMB-8, and nickel, an unspecific calcium channel blocker, had no consistent effects on [Ca2+]i or ET synthesis. The protein kinase C inhibitor H-7 stimulated basal [Ca2+]i and cellular ET synthesis. The tyrosine kinase inhibitor genistein suppressed the EPO-induced rise in [Ca2+]i and cellular ET synthesis. From these data we conclude that EPO may stimulate ET synthesis in vascular endothelial cells by activation of an EPO-receptor and via intracellular signalling mechanisms that comprise tyrosine kinase activation and a rise in [Ca2+]i. Therefore, the systemic hypertensive effects of EPO may be due at least in part to local stimulation of vascular endothelial ET synthesis via calcium mobilization.

Effects of antioxidant vitamins on renal and hepatic erythropoietin production

An important role in O2 sensing has been assigned to microsomal and membrane-bound b-type cytochromes which generate regulatory reactive O2 species (ROS). Recently, ROS have been shown to suppress the in vitro synthesis of erythropoietin (Epo). We investigated the potential of the antioxidant vitamins A, E and C to enhance renal and hepatic Epo production. Renal effects were studied in isolated serum-free perfused rat kidneys. In control experiments without antioxidant vitamins, Epo secretion amounted to 441 +/- 23 mU/g kidney (mean +/- SEM, N = 5) during the three hour period of hypoxic perfusion (arterial pO2 35 mm Hg). Epo secretion significantly increased to 674 +/- 92 mU/g kidney (N = 7) when vitamins A (0.5 microgram/ml), E (0.5 microgram/ml) and C (10 micrograms/ml) in combination were added to the perfusion medium. The effects of the single vitamins were studied in Epo-producing hepatoma cell cultures (lines HepG2 and Hep3B). Vitamin A induced a dose-dependent increase (half-maximal stimulation at 0.2 microgram/ml) in the production of immunoreactive Epo during 24 hours of incubation (such as 680 +/- 51 U Epo/g cell protein in HepG2 cultures with 3 micrograms/ml retinol acetate compared to 261 +/- 15 U/g in untreated controls; N = 4). In contrast, vitamin E (tested from 0.05 to 500 micrograms/ml) and vitamin C (tested from 2 to 200 micrograms/ml) did not increase Epo production in hepatoma cell cultures. Thus, while vitamins E and C may have the potential to protect cells from oxidative damage, vitamin A exerts a specific stimulation of Epo production. Preliminary evidence suggests that this effect of vitamin A involves increased mRNA levels of hypoxia-inducible factor 1 alpha (HIF-1 alpha).

Cobalt and desferrioxamine reveal crucial members of the oxygen sensing pathway in HepG2 cells

Cobalt and desferrioxamine, like hypoxia, stimulate the production of erythropoietin in HepG2 cells. It is believed that cobalt as well as desferrioxamine interact with the central iron atom of heme proteins by changing their redox state similar to hypoxia. A subsequent decrease of the intracellular H2O2 levels under hypoxia was presumed to be the key event for stimulating erythropoietin production. We therefore investigated whether cobalt and desferrioxamine control the intracellular H2O2 levels that regulate gene expression by interacting with hemeproteins. Deconvolution of light absorption spectra revealed respiratory heme proteins such as cytochrome c, b558 and cytochrome aa3, as well as cytochrome b558, which is a nonrespiratory heme protein found in HepG2 cells. Whereas respiratory heme proteins are located in mitochondria, cytochrome b558 similar to the one described for the neutrophil NADPH oxidase can be visualized in the cell membrane of HepG2 cells by immunohistochemistry. Incubation with cobalt (100 microM/24 hr) interacts predominantly with cytochrome b558 and cytochrome b558. The interaction of cobalt with the respiratory chain results in an increased oxygen consumption of HepG2 cells as revealed by PO2 microelectrode measurements. Desferrioxamine (130 microM/24 hr), however has no influence on the cytochromes. In response to an external application of NADH (1 mM), the membrane bound cytochrome b558 produces two times more O2- than to the external NADPH (1 mM) application. Neither desferrioxamine not cobalt has any influence on the NADH stimulated O2- generation. Incubation with cobalt or with desferrioxamine, however, leads to a decrease of the intracellular H2O2 level as revealed by the dihydrorhodamine 123 technique, perhaps causing the well-known enhanced erythropoietin production. The cobalt-induced H2O2 decrease seems to be caused by an increased activity of the glutathion peroxidase that is also induced under hypoxia. Desferrioxamine, however, leads to an apparent H2O2 decrease only because it seems to inhibit the iron catalyzed reaction of H2O2 with dihydrorhodamine 123, hinting at the occurrence of the Fenton reaction in HepG2 cells. Therefore, it must be determined whether or not degradation products of H2O2 by the Fenton reaction suppress erythropoietin production under normoxia.

Cobalt chloride and desferrioxamine antagonize the inhibition of erythropoietin production by reactive oxygen species

We have recently proposed a H2O2-generating b-type cytochrome as part of the cellular oxygen sensor that controls O2-dependent erythropoietin (Epo) production in the human hepatocellular carcinoma cell line HepG2. H2O2 could act as an intracellular signaling molecule because its production in HepG2 cells is strictly dependent on the pericellular PO2. High cellular levels of H2O2 inhibit hypoxia-induced Epo production while low levels-as under hypoxic conditions-allow full expression of the Epo gene. Since cobalt chloride (CoCl2) and the iron chelator desferrioxamine (DSF) both mimic the hypoxic induction of Epo production we studied the influence of CoCl2 and DSF on the formation and on the action of reactive O2-species with respect to Epo production. Both chemicals reduced the H2O2-dependent 123-dihydrorhodamine fluorescence in HepG2 cells. The inhibition of Epo production by exogenous H2O2 was completely antagonized by DSF. This might indicate that H2O2 exerts its inhibition through a Fenton type reaction. On the other hand, NADPH and pyrogallol which stimulate the production of O2- inhibited Epo production. CoCl2 antagonized their effects. From our results we propose different sites of interaction with the putative signaling chain for DSF and CoCl2. While DSF appears to reduce the action of the H2O2 molecule, CoCl2 might act further upstream through the induction of H2O2-scavenger systems or by interfering with its production.