Cultured Rat Kupffer Cells Research Articles

Abstract 351: Uptake of antibody-drug conjugates by cultured Kupffer cells can predict pharmacokinetics

Abstract Interest in antibody-drug conjugates (ADCs) has increased rapidly in the oncology field over the past several years. Recent advances in the ADC field have been achieved in part by an improved understanding of how conjugation with drug-linkers impacts the biophysical, pharmacokinetic (PK), and biodistribution properties of a monoclonal antibody. Most of these advances have been driven by in vivo preclinical observations, an inevitably low throughput endeavor. A higher throughput in vitro method that would allow some level of predictive power for ADC disposition in vivo would be highly advantageous, requiring less test article and allowing for much faster turnaround. Thus far no such methods for ADCs have been reported, in contrast to the situation for the prediction of the metabolic clearance of small molecule therapeutics, for which cultured hepatocytes are widely used as an in vitro tool. It has been generally assumed that clearance of ADCs is driven by cells of the monocyte phagocytic system, and we recently published immunohistochemistry (IHC) data implicating hepatic sinusoidal endothelium and the resident liver macrophages, Kupffer cells (KCs), in the accelerated clearance of highly-loaded ADCs. We sought to use this observation to develop a convenient assay that might correlate ADC uptake in vitro with in vivo PK. Initial fluorescent microscopy experiments revealed that cultured rat KCs stain intensely when incubated with fluorescently labeled ADCs, but much less so with unconjugated antibody, similar to the observed IHC results. In an effort to further improve the throughput of this method to allow the rapid comparison of many ADCs, we moved to a FACS-based platform to quantify the amount of KC-associated fluorescent conjugate. To quantify the effect of different drug-linkers, we prepared homogeneous ADCs with 8 drugs per antibody and observed that the KC staining intensity varied widely depending upon the characteristics of the drug-linker that was conjugated. KCs incubated with ADCs loaded with vc-PAB-MMAE had a mean fluorescent intensity (MFI) >20 fold higher than unconjugated Antibody. Additionally, ADCs loaded with MMAE that contain a polyethylene glycol (PEG) masking moiety in the linker had a much lower MFI than those without PEG. This FACS method allowed us to compare fluorescent uptake by KCs with ADC clearance determined in vivo. We have observed that ADC uptake by cultured KCs in vitro correlates well with ADC PK, allowing for more rapid assessment of the PK impact of new drug classes, drug-linker designs, and conjugation methodologies. Citation Format: David Meyer, Sara Shum, Mechthild Jonas, Martha Anderson, Joshua Hunter, Nagendra Chemuturi, Nicole Okeley, Robert Lyon. Uptake of antibody-drug conjugates by cultured Kupffer cells can predict pharmacokinetics. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 351.

Hepatotoxicants induce cytokine imbalance in response to innate immune system

In recent years, attention has been paid to innate immune systems as mechanisms to initiate or promote drug-induced liver injury (DILI). Kupffer cells are hepatic resident macrophages and might be involved in the pathogenesis of DILI by release of pro- and anti-inflammatory mediators such as cytokines, chemokines, reactive oxygen species, and/or nitric oxides. The purpose of this study was to investigate alterations in mediator levels induced by hepatotoxic compounds in isolated Kupffer cells and discuss the relation between balance of each cytokine or chemokine and potential of innate immune-mediated DILI. Primary cultured rat Kupffer cells were treated with hepatotoxic (acetaminophen, troglitazone, trovafloxacin) or non-hepatotoxic (pioglitazone, levofloxacin) compounds with or without lipopolysaccharide (LPS). After 24 hr treatment, cell supernatants were collected and various levels of mediators released by Kupffer cells were examined. Although hepatotoxicants had no effect on the LPS-induced tumor necrosis factor-alpha (TNF-α) secretion, they enhanced the release of pro-inflammatory cytokine interleukin-1 beta (IL-1β) and suppressed the anti-inflammatory cytokines interleukin-6 (IL-6) and interleukin-10 (IL-10) induced by LPS. These cytokine shifts were not associated with switching the phenotypes of M1 and M2 macrophages in Kupffer cells. In conclusion, the present study suggested that the levels of some specific cytokines are affected by DILI-related drugs with LPS stimulation, and imbalance between pro- and anti-inflammatory cytokines, induced by the up-regulation of IL-1β and the down-regulation of IL-6 or IL-10, plays a key role in innate immune-mediated DILI.

LIVER X RECEPTOR AGONIST GW3965 DOSE-DEPENDENTLY REGULATES LPS-MEDIATED LIVER INJURY AND MODULATES POSTTRANSCRIPTIONAL TNF-α PRODUCTION AND P38 MITOGEN-ACTIVATED PROTEIN KINASE ACTIVATION IN LIVER MACROPHAGES

Modulation of the host inflammatory response to infection may be a key approach to improve the outcome of patients with sepsis and organ injury. We previously reported that pretreatment of rats with the liver X receptor (LXR) agonist GW3965 reduced the liver injury associated with endotoxemia and attenuated the production of TNF-alpha by rat Kupffer cells. Here, we examine the dose-dependent effect of GW3965 on liver injury and cytokine production in a rat model of endotoxemia and explore the mechanisms underlying TNF-alpha attenuation in Kupffer cells. Low doses of GW3965 (0.1 or 0.3 mg/kg) administered 30 min before infusion of LPS and peptidoglycan significantly attenuated the increase in plasma levels of the liver injury markers alanine aminotransferase and bilirubin (6 h) as well as the inflammatory mediators TNF-alpha (1 h) and prostaglandin E2 (6 h) associated with endotoxemia. In contrast, pretreatment with a higher dose of GW3965 (1.0 mg/kg) had no such effect. Studies in primary cultures of rat Kupffer cells demonstrated that LXR agonist treatment attenuated both the secreted and cell-associated levels of TNF-alpha, whereas TNF-alpha mRNA levels were not altered. Phosphorylated p38 mitogen-activated protein kinase, which plays a major role in production of TNF-alpha at the posttranscriptional level, was attenuated by GW3965 treatment in Kupffer cells. Experiments in murine LXR-deficient Kupffer cells demonstrated enhanced production of TNF-alpha in Kupffer cells from LXR-alpha(-/-) mice when challenged with LPS compared with LXR-beta(-/-) and wild-type Kupffer cells. Taken together, these results argue in favor of a novel mechanism for LXR-mediated attenuation of liver injury by interfering with posttranscriptional regulation of TNF-alpha in Kupffer cells.

Inhibition of tumor necrosis factor alpha secretion in rat Kupffer cells by siRNA: In vivo efficacy of siRNA-liposomes

Tumor necrosis factor alpha (TNF-α), a pro-inflammatory cytokine, plays a key role in the pathogenesis of many inflammatory diseases, including alcoholic liver disease. In the liver, Kupffer cells are the primary source of the cytokine. Obliteration of Kupffer cells or neutralization of TNF-α by anti-TNF-α antibody or by an antisense oligonucleotide prevents ethanol-mediated liver damage. In this study, we report the identification of yet another highly efficacious gene-silencing molecule, the short interfering RNA (siRNA), SSL3, against TNF-α. The efficacies of various siRNA duplexes were tested against TNF-α mRNA in primary cultures of rat Kupffer cells. SSL3 (25 nM) inhibited lipopolysaccharide (LPS)-induced secretion of TNF-α by 55% ( p < 0.005) with a proportionate reduction in TNF-α mRNA; the inhibitory effect lasted for at least 96 h. Four nucleotide mismatches to SSL3 completely abolished the inhibitory effects of SSL3, suggesting the sequence specificity of the siRNA. Further, the in vivo efficacy of SSL3 was assessed following the i.v. administration of two doses (140 μg/kg body weight/day for 2 days) of liposome-encapsulated SSL3. The LPS-induced TNF-α secretion was inhibited by > 60% ( p < 0.05) by SSL3 pre-treatment. These data demonstrate the identification of an siRNA against TNF-α, which, as a liposomal formulation, has therapeutic potential in the treatment of inflammatory diseases mediated by TNF-α.

Short-term Treatment of RAW264.7 Macrophages with Adiponectin Increases Tumor Necrosis Factor-α (TNF-α) Expression via ERK1/2 Activation and Egr-1 Expression

Short-term Treatment of RAW264.7 Macrophages with Adiponectin Increases Tumor Necrosis Factor-α (TNF-α) Expression via ERK1/2 Activation and Egr-1 Expression

Nuclear Factor-κB Mediates Kupffer Cell Apoptosis Through Transcriptional Activation of Fas/FasL 1,2

Nuclear factor (NF)-kappaB is a key transcriptional factor for cell survival, inflammation, and stress response. We demonstrated that Kupffer cell-derived FasL plays a central role in pancreatitis-induced hepatocyte injury. The aim of this study was to determine the role of NF-kappaB in regulating death ligand/receptor pathway in Kupffer cells during conditions that mimic acute pancreatitis. Tissue cultures of rat Kupffer cells were treated with elastase (1 U/L) to mimic pancreatitis before and after infection with AdIkappaB to block activation of NF-kappaB. Tumor necrosis factor (enzyme-linked immunoassay), Fas/FasL, and caspase-3 (Western), tumor necrosis factor and Fas/FasL mRNA (reverse-transcription polymerase chain reaction), and NF-kappaB DNA binding (electrophoretic mobility shift assay) were determined. Apoptosis was measured by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) and DNA fragmentation. Gels were quantified by densitometry. Data (n=3) are mean+/-SEM; student's t test was used for statistical analysis. AdIkappaB infection up-regulated mutated IkappaBalpha that maintained its binding properties to NF-kappaB. Promoter-reporter assay demonstrated that FasL gene promoter was regulated by NF-kappaB. Infection with AdIkappaB attenuated the elastase-induced up-regulation of Fas/FasL (all P<0.01 versus elastase) and NF-kappaB DNA binding but did not affect elastase-induced up-regulation of TNF. AdIkappaB attenuated elastase-induced cleavage of caspase-3, DNA fragmentation and TUNEL staining (all P<0.01 versus elastase). Inhibition of NF-kappaB DNA binding down-regulates Fas/FasL and attenuates elastase-induced apoptosis; however, it has no effect on TNF production, suggesting that regulation of Fas/FasL and TNF may occur via different pathways. The ability of Kupffer cells to autoregulate their stress response by up-regulating their death ligand/receptor and apoptosis warrants further investigation.

Ca2+ requirement of prostanoid but not of superoxide production by rat Kupffer cells

The release of the prostanoids prostaglandin D2 (PGD2), prostaglandin E2 (PGE2) and thromboxane induced by zymosan and phorbol ester in cultured rat Kupffer cells was found to depend on the extracellular concentration of Ca2+ to some extent. Prostanoid formation following the addition of the calcium ionophore A 23187 was totally inhibited when calcium ions were withdrawn from the medium whereas the prostanoid synthesis from added arachidonic acid was independent of Ca2+. A half-maximal rate of PGE2 release by cells treated with zymosan, phorbol ester or A23187 was obtained at 0.6–0.7 μM free extracellular Ca2+ and ≥ 100 μM free Ca2+ was required to stimulate PGE2 formation maximally. The calmodulin antagonist R24571 partially inhibited the release of PGE2 elicited by zymosan and A23187 but not by phorbol ester or arachidonic acid. Verapamil and nifedipine, two calcium channel blockers, had no effect on the formation of PGE2 irrespective of the stimulus. TMB 8 [3,4,5-trimethoxybenzoic acid 8-(diethylamino)-octyl ester] an intracellular calcium antagonist, inhibited the synthesis of PGE2 induced by zymosan and phorbol ester. The superoxide formation following the addition of zymosan and phorbol ester was not influenced by removal of calcium ions from the medium or by addition of the various calcium antagonists. The data presented here suggest that Ca2+-dependent reactions are involved in the synthesis of prostanoids induced by zymosan and phorbol ester and that both extracellular Ca2+ and mobilization of Ca2+ from intracellular stores are needed to induce maximally the production of prostanoids in cultured rat Kupffer cells.

NF-κB mediates apoptosis through FAS/FASL transcriptional activation in kupffer cells

Introduction. NF-κB is a key transcriptional factor for cell survival, inflammation, and immune response. We demonstrated Kupffer cell-derived FasL plays a critical role in pancreatitis-induced liver injury. The aim of this study was to determine the role of NF-κB in regulating death ligand/receptor pathway in Kupffer cells during conditions that mimic acute pancreatitis. Methods. Tissue cultures of rat Kupffer cells were treated with elastase (1 U/L) to mimic pancreatitis before and after transfection with AdIκB, which blocks activation of NF-κB. Transfection with AdLuc served as control. TNF (ELISA), Fas/FasL, and caspase-3 (Western), TNF and Fas/FasL mRNA (RT-PCR), and NF-κB DNA binding activity (EMSA) were determined. Apoptosis was measured by TUNEL and DNA fragmentation. Gels were quantified by densitometry. Data ( n = 3) are mean ± SEM; Student’s t-test was used for statistical analysis. Results. Transfection with AdIκB attenuated the elastase-induced up regulation of Fas/FasL (Table, ∗all P < 0.01 versus elastase) and the activation of NF-κB (Figure) but did not affect elastase-induced up regulation of TNF (data not shown). In addition, AdIκB attenuated elastase-induced cleavage of caspase-3 (Figure), DNA fragmentation, and TUNEL staining (Table, ∗all P < 0.01 versus elastase). Conclusions. Inhibition of NF-κB down regulates Fas/FasL and attenuates elastase-induced apoptosis; however, it has no effect on TNF production, suggesting that regulation of Fas/FasL and TNF may occur via different pathways. The ability of Kupffer cells to autoregulate their stress response by up regulating their death ligand/receptor and apoptosis warrants further investigation.

Iron activates NF-κB in Kupffer cells

Iron exacerbates various types of liver injury in which nuclear factor (NF)-kappaB-driven genes are implicated. This study tested a hypothesis that iron directly elicits the signaling required for activation of NF-kappaB and stimulation of tumor necrosis factor (TNF)-alpha gene expression in Kupffer cells. Addition of Fe2+ but not Fe3+ (approximately 5-50 microM) to cultured rat Kupffer cells increased TNF-alpha release and TNF-alpha promoter activity in a NF-kappaB-dependent manner. Cu+ but not Cu2+ stimulated TNF-alpha protein release and promoter activity but with less potency. Fe2+ caused a disappearance of the cytosolic inhibitor kappaBalpha, a concomitant increase in nuclear p65 protein, and increased DNA binding of p50/p50 and p65/p50 without affecting activator protein-1 binding. Addition of Fe2+ to the cells resulted in an increase in electron paramagnetic resonance-detectable.OH peaking at 15 min, preceding activation of NF-kappaB but coinciding with activation of inhibitor kappaB kinase (IKK) but not c-Jun NH2-terminal kinase. In conclusion, Fe2+ serves as a direct agonist to activate IKK, NF-kappaB, and TNF-alpha promoter activity and to induce the release of TNF-alpha protein by cultured Kupffer cells in a redox status-dependent manner. We propose that this finding offers a molecular basis for iron-mediated accentuation of TNF-alpha-dependent liver injury.

Pancreatitis-Associated Ascitic Fluid Induces Hepatocyte Death Independent of Local Cytokines

Introduction. Kupffer-cell-derived cytokines mediate liver injury, yet macrophage pacification does not abolish hepatocyte injury. We undertook this study to examine the role of pancreatitis-associated ascitic fluid (PAAF) in liver injury. Methods. Pathogen-free PAAF was perfused into healthy rat livers in situ for 60 min ( n = 5, sham = 5, LPS = 5). AST, ALT, LDH, and TNF were measured in the effluent. Primary cultures of rat Kupffer cells or hepatocytes were treated with PAAF; AST, ALT, LDH, and TNF were measured and cell proliferation was determined by MTT assay. A hepatocyte human cell line (CCL-13) was treated with PAAF and apoptosis was measured by flow cytometry. Results. Liver perfusion with PAAF induced a >15-fold increase in AST/ALT/LDH ( P < 0.001 PAAF vs sham), but not in TNF. In vitro, Kupffer cell viability was sharply reduced by PAAF in a dose-dependent manner; however, 5% PAAF (50% viability) did not induce TNF production from Kupffer cells. PAAF induced a multifold increase in AST/ALT/LDH from fresh hepatocytes ( P < 0.001 vs control), which was not attenuated by a protease inhibitor. The CCL-13 cell population was reduced to 15 ± 2% of baseline by PAAF ( P < 0.001 vs control), whereas elastase, trypsin, or TNF had no effect. PAAF increased the percentage of nonviable CCL-13 cells (78 ± 4% vs 28 ± 1%, P < 0.001 vs control). Neither protease inhibitor nor heat inactivation of PAAF altered this pattern of hepatocyte death. Conclusion. PAAF induces direct hepatocyte injury and death by heat-stable factors other than pancreatic enzymes but not via local production of Kupffer-cell-derived cytokines.

Fructose-1,6-Bisphosphate inhibits excess activation of Kupffer cell function induced by endotoxin.

The effect and mechanism of action of fructose-1,6-bisphosphate (FBP) on Kupffer cell activation were studied in vitro. Kupffer cell was activated by isolation procedure alone from the hepatic tissue. In cultured rat Kupffer cells stimulated by endotoxin, treatment with 5-20 mM FBP not only preserved phagocytic activity, but also inhibited secretion of cytokines (tumor necrosis factor-a and interleukin-1beta) and production of nitric oxide (NOx). Moreover, treatment with 10 mM FBP suppressed the elevation in the intracellular Ca2+ concentration on Kupffer cells stimulated by phorbol 12-myristate 13-acetate, which suggested that this effect may be one of the agents that limit the activation of Kupffer cells. The administration of FBP was effective in the prevention of endotoxin-induced hepatopathy, and we suggest that this may have useful clinical applications.

A23187 causes release of inositol phosphates from cultured rat Kupffer cells

The Ca 2+ ionophore A23187 is routinely used to illustrate the extracellular Ca 2+-dependence of a variety of cellular reactions. We found that A23187-induced hydrolysis of phosphoinositides to various inositol phosphates in rat Kupffer cells was accompanied by their release from the cells. The synthesis and release of inositol phosphates was A23187 concentration-dependent (0.5–10 μM), and was apparent at the lowest concentration tested. A23187-induced release of inositol phosphates increased time-dependently, was apparent at 5 s of stimulation and maximal at 20 min. The effects of A23187 were reversed by EGTA. The integrity of the cells was not affected by A23187 treatment as indicated by their exclusion of trypan blue and the lack of release of lactate dehydrogenase. We propose that such effects should be considered while evaluating the Ca 2+-dependence of biological processes based on the actions of A23187.

UPTAKE AND INTRACELLULAR PROCESSING OF PEG-LIPOSOMES AND PEG-IMMUNOLIPOSOMES BY KUPFFER CELLS IN VITRO*

Specific targeting of drugs to for instance tumors or sites of inflammation may be achieved by means of immunoliposomes carrying site-specific antibodies on their surface. The presence of these antibodies may adversely affect the circulation kinetics of such liposomes as a result of interactions with cells of the mononuclear phagocyte system (MPS), mainly represented by macrophages in liver and spleen. The additional insertion of poly(ethylene glycol) chains on the surface of the immunoliposomes may, however, attenuate this effect.We investigated the influence of surface-coupled rat or rabbit antibodies and of PEG on the uptake of liposomes by rat Kupffer cells in culture with 3H-cholesteryloleyl ether as a metabolically stable marker. Additionally, we assessed the effects of surface-bound IgG and PEG on the intracellular processing of the liposomes by the Kupffer cells, based on a double-label assay using the 3H-cholesteryl ether as an absolute measure for liposome uptake and the hydrolysis of the degradable marker cholesteryl-14C-oleate as relative measure of degradation.Attachment of both rat and rabbit antibodies to PEG-free liposomes caused a several-fold increase in apparent size. The uptake by Kupffer cells, however, was 3–4 fold higher for the rat than for the rabbit IgG liposomes. The presence of PEG drastically reduced the difference between these liposome types. Uptake of liposomes without antibodies amounted to only about 10% (non-PEGylated) or less (PEGylated) of that of the immunoliposomes.In contrast to the marked effects of IgG and PEG on Kupffer cell uptake, the rate of intracellular processing of the liposomes remained virtually unaffected by the presence of these substances on the liposomal surface.These observations are discussed with respect to the design of optimally formulated liposomal drug preparations, combining maximal therapeutic efficacy with minimal toxicity.

Suppression of lipopolysaccharide-induced nitric oxide synthase expression by platelet-activating factor receptor antagonists in the rat liver and cultured rat Kupffer cells.

Excessive nitric oxide (NO) generated by hepatic cells in response to lipopolysaccharide (LPS) and inflammatory substances (e.g., platelet-activating factor [PAF]) is a key contributor to the pathophysiological outcomes observed in the liver during sepsis. In rats subjected to liver-focused endotoxemia, inducible nitric oxide synthase (iNOS) levels in the intact liver were elevated by 6 hours; cell-specific expression of iNOS messenger RNA (mRNA) was Kupffer cells (KCs), endothelial cells, and hepatocytes. Elevated serum alanine transaminase (ALT) levels at 6 hours confirmed hepatic damage. Pretreatment of endotoxemic rats with PAF receptor antagonists BN 50739 or WEB 2170 reduced serum ALT and iNOS mRNA levels in the intact liver. Pretreatment of cultured KCs with BN 50739 or WEB 2170 inhibited both LPS and PAF-induced iNOS mRNA formation. In addition, LPS-induced iNOS protein levels in KCs pretreated with BN 50739 or WEB 2170 were decreased. Exposure of KCs to either LPS or PAF caused the translocation of the p65 subunit of nuclear factor kappa B (NF-kappaB) into the nucleus and this process was attenuated by BN 50739 and WEB 2170. There was concomitant inhibition of LPS-dependent degradation of the inhibitory protein IkappaBalpha and increase in intracellular Ca(2+) in KC treated with BN 50739 or WEB 2170. Also, in KCs, LPS was able to induce iNOS mRNA expression independent of CD14. This response was inhibited by pretreatment of KCs with either BN 50739 or WEB 2170. Our findings indicate that PAF receptor antagonists convey protection against hepatocellular injury accompanied by a decrease in nitric oxide (NO) formation in the livers of endotoxemic rats.

Tauroursodeoxycholic acid enhances phagocytosis of the cultured rat Kupffer cell.

Ursodeoxycholic acid is used in the treatment of acute and chronic intrahepatic cholestasis because it ameliorates cholestasis and protects hepatocytes. However, few studies have examined the effect of bile acids on the function of Kupffer cells. The effect of various bile acids on cultured rat Kupffer cells was studied in terms of phagocytic activity in response to latex particles and morphological alterations. Video-enhanced differential interference contrast microscopy was used. Taurochenodeoxycholic acid and taurodeoxycholic acid reduced the number of latex particles incorporated into Kupffer cells, but taurocholic and tauroursodeoxycholic acids enhanced phagocytosis of latex particles. Inhibition of phagocytosis by taurochenodeoxycholic acid or taurodeoxycholic acid was essentially dose dependent. Tauroursodeoxycholic acid also enhanced phagocytosis by Kupffer cells in which phagocytosis had been reduced by pretreatment with taurochenodeoxycholic acid or taurodeoxycholic acid. Incorporated latex particles had a distinct translocation speed of 0.084+/-0.024 microm/s (mean maximum speed+/-SD); the speed was in the same range with tauroursodeoxycholic acid treatment. Tauroursodeoxycholic acid induced a 56% expansion of cytoplasm, associated with increased ruffling and movement of intracellular organelles. These observations suggest that tauroursodeoxycholic acid enhances membrane trafficking without changing translocation speed.

Up-regulation of heme-binding protein 23 (HBP23) gene expression by lipopolysaccharide is mediated via a nitric oxide-dependent signaling pathway in rat Kupffer cells.

Heme-binding protein 23 (HBP23) is a cytosolic protein that binds the prooxidant heme with high affinity and has been implicated in the cellular protection against reactive oxygen species (ROS). Because lipopolysaccharide (LPS) stimulates macrophages to produce large amounts of ROS the gene expression of HBP23 was analyzed during treatment with LPS in cultured rat Kupffer cells (KC). HBP23 was constitutively expressed in KC and up-regulated on the protein and messenger RNA (mRNA) level by LPS with a time response distinct from that of TNFalpha, but in coordination with that of heme oxygenase-1 (HO-1), which is the inducible isoform of the rate-limiting enzyme of heme degradation. A parallel up-regulation of HBP23 and HO-1 mRNA by LPS was also observed in cultured peritoneal macrophages and peripheral blood monocytes. HBP23 mRNA induction by LPS occurred on the transcriptional level as indicated by blocking with actinomycin D. The induction of HBP23 mRNA expression by LPS was preceded by that of the inducible nitric oxide synthase (iNOS) and the production of nitrite in KC. Treatment with the NOS inhibitor NG-monomethyl L-arginine prevented HBP23 mRNA induction by LPS, which was reversed by an excess of L-arginine. Both the nitric oxide (NO)-donor S-nitroso-N-acetylpenicillamine and the peroxynitrite donor SIN-1 increased HBP23 mRNA expression. HBP23 mRNA induction by LPS was down-regulated by interleukin 10 and transforming growth factor beta1 with a NO-independent mechanism. LPS-stimulated KC exhibited marked protection against the cytotoxicity mediated by H2O2. The data suggest that NO and peroxynitrite are major mediators of the LPS-dependent up-regulation of HBP23 in KC.

Involvement of CD95 (Apo-1/Fas) ligand expressed by rat Kupffer cells in hepatic immunoregulation

Background & Aims: CD95 (Apo-1/Fas) ligand suppresses inflammatory responses in immune-privileged organs. In this study, modulation of the hepatic CD95 receptor/ligand system by interferon gamma and cyclosporin A was investigated. Methods: CD95 receptor and ligand expression were measured at the messenger RNA level by using quantitative reverse-transcription polymerase chain reaction and immunocytochemistry in primary cultures of rat Kupffer cells, hepatocytes, and T lymphocytes. Soluble CD95 in culture supernatants was detected by enzyme-linked immunosorbent assay and apoptosis by the TUNEL method. Results: Interferon gamma treatment led to an increase in CD95 ligand messenger RNA levels in Kupffer cells followed by an overexpression of the soluble CD95 receptor. Supernatants derived from 24-hour but not from 48-hour interferon gamma–treated Kupffer cells killed lymphocytes by a CD95-dependent mechanism. Cyclosporin A inhibited CD95 ligand expression in Kupffer cells and lymphocyte killing. In liver parenchymal cells, interferon gamma increased messenger RNA levels of the transmembrane CD95 isoform and sensitivity of these cells toward CD95-mediated apoptosis. Conclusions: The expression pattern of CD95 receptor and ligand in response to interferon gamma points to a coordinated interplay between Kupffer cells, hepatocytes, and T lymphocytes in which Kupffer cells may regulate programmed cell death of T lymphocytes and hepatocytes. GASTROENTEROLOGY 1999;116:666-677

Ultrastructural characterization of isolated rat Kupffer cells by transmission X-ray microscopy.

The ultrastructure of primary cultured rat Kupffer cells was studied using transmission X-ray microscopy as well as transmission electron microscopy. X-ray microscopical images of intact, hydrated Kupffer cells demonstrated structures such as cell nucleus separated by a nuclear membrane and filaments concentrated in the perinuclear area. Within the cytoplasm, a number of vacuoles were visible; some of these were crescent-shaped vacuoles that were half X-ray lucent, half X-ray dense; others were uniformly dense. The number of crescent-shaped vacuoles was predominant. After phagocytosis of haematite particles, enlarged vacuoles containing the ingested material were visible within the cytoplasm of Kupffer cells while crescent-shaped vacuoles were no longer detectable. Densitometric analysis of the two types of vacuole revealed that the X-ray absorption of the uniform vacuole was approximately half that of the dense part of the crescent-shaped vacuoles. This observation led to speculation on the existence of only one type of vacuole in the cytoplasm of Kupffer cells. The different morphological aspects--crescent-shaped versus uniform vacuoles--might be due to different three-dimensional orientation with respect to the image plane. Using transmission electron microscopy, the morphology of vacuoles differed more widely in diameter, density and shape. Two main types of vacuole were identified: electron-lucent and electron-dense. Based on the observation of only one type of vacuole by transmission X-ray microscopy, the different morphological aspects of vacuoles obtained by transmission electron microscopy could be explained by imaging several different sections of a crescent-shaped vacuole. From the present data it can be concluded that transmission X-ray microscopy is a versatile technique that reveals the ultrastructure of intact, unsectioned biological specimens in their aqueous environment, thereby allowing a more comprehensive interpretation of data obtained by transmission electron microscopy.

Nitric oxide mediates the lipopolysaccharide dependent upregulation of the heme oxygenase-1 gene expression in cultured rat Kupffer cells

Background/ Aims: Heme oxygenase catalyzes the rate-limiting enzymatic step of heme degradation. The inducible isoform of heme oxygenase, heme oxygenase-1, is expressed at a low level in most tissues and is upregulated by its substrate heme and various stress stimuli. Kupffer cells which represent the largest population of the body's tissue macrophages serve physiological functions in the defense against various pathogens such as lipopolysaccharide. The goal of the present study was to investigate the heme oxygenase-1 gene expression in Kupffer cells of rat liver and in isolated Kupffer cell cultures during treatment with lipopolysaccharide. Methods: Cryostat sections of normal rat liver were investigated by immunofluorescence double-staining using specific antibodies for rat heme oxygenase-1 and ED2. Isolation and cell culture of Kupffer cells and primary hepatocytes from rat liver, as well as Northern and Western blot analysis, were performed with standard protocols. Results: Heme oxygenase-1 protein was highly expressed in large sinusoidal cells of normal rat liver, which were identified as Kupffer cells by staining with the macrophage surface marker ED2. By contrast, no expression of heme oxygenase-1 was detected in liver parenchymal cells. High expression of heme oxygenase-1 was also found in isolated Kupffer cells in culture by immunocytochemical staining as well as by Western and Northern blot analysis. After treatment of Kupffer cells cultures with lipopolysaccharide, heme oxygenase-1 was upregulated on the protein and mRNA level in a time- and dose-dependent manner. This increase in heme oxygenase-1 expression by lipopolysaccharide was prevented by the nitric oxide inhibitor N G-monomethyl-L-arginine which was reversed by an excess of L-arginine. Various nitric oxide donors up-regulated heme oxygenase-1 mRNA expression in Kupffer cells. Conclusions: The lipopolysaccharide-dependent upregulation of the heme oxygenase-1 gene which is highly expressed in Kupffer cells is mediated by a nitric oxide-dependent mechanism.

Effect of dibutyryl cyclic AMP on phagocytosis and production of nitric oxide and tumor necrosis factor- α in cultured rat Kupffer cells

Dibutyryl cyclic AMP (DBcAMP) is an analogue of cAMP. DBcAMP has many effects on hepatocellular carcinoma, liver cirrhosis, ischemic liver failure and endotoxin-induced inflammatory liver injury. However, little is known about the mechanism of DBcAMP action in Kupffer cells. We examined the effects of DBcAMP on phagocytic activity and production of nitric oxide (NO) and tumor necrosis factor- α (TNF- α) in cultured rat Kupffer cells treated with lipopolysaccharide (LPS). NO concentrations in culture supernatants were measured using an NO analyzer and TNF- α levels were measured with ELISA. Immunofluorescent staining for nuclear factor- κ B (NF- κ B) was visualized using an anti-NF- κ B p65 antibody. DBcAMP premedication had no effect on LPS-stimulated phagocytic activity of Kupffer cells but increased NO production and inhibited TNF- α production in a dose-dependent manner. Genistein did not block, but H-89 did block, the inhibitory effect of DBcAMP on LPS-stimulated TNF- α production in Kupffer cells. We conclude that DBcAMP inhibits LPS-stimulated TNF- α production by activating cyclic AMP-dependent protein kinase. Using immunofluorescent staining for NF- κ B, we demonstrate that the effect of DBcAMP does not involve signal transduction through NF- κ B.