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Biomedical subjects

D L Laskin

Publications and source records attributed to D L Laskin.

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

Alterations in epidermal sulfated proteoglycan production following topical application of the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate to mouse skin.

Topical application of the phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) to mouse skin causes marked changes in epidermal cell growth and differentiation. In the present studies we characterized the production of sulfated proteoglycans in the epidermis following treatment with TPA since these macromolecules are important structural and functional components of the tissue. We found that 35S-sulfate was readily incorporated into mouse epidermal proteoglycans. Sepharose CL-4B column chromatography revealed one major peak of sulfated proteoglycans in this tissue (Kav = 0.4-0.5). Approximately 65% of these proteoglycans were heparan sulfate and 10-20% chondroitin sulfate. Using specific monoclonal antibodies and flow cytometry, we found that the epidermal cells produced chondroitin-4-sulfate, chondroitin-6-sulfate and chondroitin-O-sulfate. Within 24 hr of application of TPA to mice, an increase in glycosaminoglycan content of the epidermis was observed. This was associated with a decrease in 35S-sulfate uptake into the tissue. Although TPA had no effect on the size or relative distribution of the epidermal sulfated proteoglycans, an increase in chondroitin-4-sulfate expression was observed in treated skin. Changes in the production of proteoglycans following TPA treatment may underlie structural alterations that occur in the epidermis during tumor promotion.

Animals↗
PubMed1991

Changes in sulfated proteoglycan production after activation of rat liver macrophages.

Production of extracellular matrix proteins-in particular, the proteoglycans-by macrophages is important in many of their functions, including cell-cell recognition, adhesion and phagocytosis. In this study, we characterized changes in sulfated proteoglycan production by hepatic macrophages following in vivo activation with lipopolysaccharide. We found that both resident Kupffer cells and liver macrophages from lipopolysaccharide-treated rats incorporated [35S]sulfate into proteoglycans. Lipopolysaccharide-activated macrophages incorporated two to three times more of the label than did resident Kupffer cells. In addition, although both cell types produced chondroitin sulfate and heparan sulfate, resident Kupffer cells synthesized more chondroitin sulfate whereas lipopolysaccharide-activated cells produced more heparan sulfate. Using specific antibodies and flow cytometry, we also found that hepatic macrophages produced chondroitin-4-sulfate, chondroitin-6-sulfate and chondroitin-O-sulfate. Lipopolysaccharide-activated macrophages contained more chondroitin-4-sulfate and chondroitin-O-sulfate and less heparan sulfate than did resident Kupffer cells. Both tunicamycin and beta-D-xylosides, inhibitors of sulfated proteoglycan biosynthesis, were found to block phagocytosis by the cells. Taken together, these results suggest that sulfated proteoglycans are important in activation and functional responsiveness of liver macrophages.

Animals↗
PubMed1991

Liver macrophage-mediated cytotoxicity toward mastocytoma cells involves phagocytosis of tumor targets.

Macrophage-mediated cytotoxicity toward tumor cells usually involves extracellular lysis of the targets. In this study, we report that liver macrophages from rats treated with lipopolysaccharide (5 mg/kg, intravenous) also kill certain tumor cell targets by phagocytosis. Liver macrophages were coincubated with P815 mouse mastocytoma cells for 24 to 72 hr at an effector/target ratio of 10:1. Macrophage phagocytosis was characterized by flow cytometry and by light and electron microscopy. For flow-cytometric studies, P815 cells were prelabeled with the fluorescent dye 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate. We found that coincubation of macrophages with labeled targets resulted in a time-dependent increase in macrophage-associated fluorescence, reaching a maximum at 72 hr. This correlated with light-microscopic observations of increased numbers of tumor cells in the macrophages and enhanced macrophage surface area and density. Electron microscopic studies revealed that the initial event in the phagocytic process involved the capture of P815 cells by the pseudopodia of the macrophages. Target cells were then surrounded by lamellipodia, internalized in phagosomes and destroyed. These data, together with previous studies, provide evidence for multiple mechanisms of cytotoxicity mediated by activated liver macrophages.

Animals↗
PubMed1990

Production of hydrogen peroxide by murine epidermal keratinocytes following treatment with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate.

The ability of murine epidermal cells to produce intracellular hydrogen peroxide was analyzed by flow cytometry and the measurement of 2',7'- dichlorofluorescin (DCFH) oxidation. Epidermal cells isolated from acetone-treated CD-1 mice for 24 h were relatively homogeneous in cell size and density and oxidized low levels of DCFH. However, following 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment of mice (10 micrograms; 24 h), two cytokeratin-positive populations of cells were identified that were heterogeneous with respect to size and density. These two TPA-derived cell populations oxidized levels of DCFH that were time and dose dependent and were between 2- and 10-fold higher than levels of DCFH oxidized by cells isolated from acetone-treated mice. The ability of catalase, the enzyme that detoxifies hydrogen peroxide, to suppress DCFH oxidation to control levels suggested that intracellular hydrogen peroxide was responsible for the enhanced rate of DCFH oxidation in epidermal cells isolated from TPA-treated mice. The ability of mouse epidermal keratinocytes to oxidize DCFH in response to TPA treatment was confirmed using a cloned keratinocyte cell line. These results suggest that specific subpopulations of keratinocytes produce elevated levels of intracellular peroxides following treatment with TPA either in vivo or in culture.

Animals↗
PubMed1990

Fluorescence assay for per-cell estimation of cytochrome P-450-dependent monooxygenase activities in keratinocyte suspensions and cultures.

An assay was characterized that facilitated per-cell estimation of cytochrome P-450-dependent monooxygenase activities in whole-cell suspensions and cultures of murine epidermal keratinocytes (MEKs). 7-Ethoxycoumarin O-deethylase (7-ECD), 7-ethoxyresorufin O-deethylase (7-ERD), and 7-pentoxyresorufin O-deethylase (7-PRD) activities were monitored by fluorescent detection of their products. MEKs were made permeable by a freeze-thaw cycle, and xenobiotic metabolism occurred in situ. Analyses of cultured MEKs were made with the cells attached to the culture dishes. Product formation was proportional with MEK cell number and assay time and was dependent upon a NADPH-generating system. The three monooxygenase activities were inhibited to various degrees, in a dose-dependent manner, by the P-450 inhibitors alpha-naphthoflavone and metyrapone. The number of MEKs obtained from a single mouse was sufficient for multiple analyses. The assay was also used to determine monooxygenase activities in whole-cell suspensions of rat hepatocytes. Constitutive per hepatocyte 7-ECD, 7-PRD, and 7-ERD activities were 357-, 96-, and 1926-fold greater, respectively, than the activities measured in suspensions of dorsal MEKs.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1990

Differentiation of U-937 histiocytic lymphoma cells towards mature neutrophilic granulocytes by dibutyryl cyclic adenosine-3',5'-monophosphate.

Treatment of U-937 cells with the cyclic nucleotide analog, dibutyryl cyclic adenosine-3',5'-monophosphate (dBcAMP) induced these cells to differentiate towards granulocytes. dBcAMP produced a dose- and time-dependent inhibition of U-937 cell growth reaching a maximum after 48-h treatment with 500 microM. At this concentration, dBcAMP had no effect on cell viability. Treatment with dBcAMP caused a rapid (within 24 h) decrease in the number of cells in the S phase of the cell cycle, with a concomitant increase in cells in the G0/G1 phase. dBcAMP also induced the appearance of f-met-leu-phe receptors on U-937 cells as well as the ability to produce hydrogen peroxide and superoxide anion. These data suggest that dBcAMP-treated U-937 cells were functionally mature. Using specific monoclonal antibodies and flow cytometry, we found that differentiated U-937 cells expressed the monocytic/granulocytic surface markers MY8 and MAC-1, but not the monocyte specific markers MO2 or MY4. In addition, dBcAMP-treated U-937 cells did not stain for nonspecific esterase, displayed less HLA-DR antibody binding than undifferentiated cells and appeared smaller and more granular. These are all characteristics of mature granulocytes. Taken together our studies indicate that differentiation of U-937 cells is not necessarily limited to the monocytic pathway of development.

Antibodies, Monoclonal↗
PubMed1990

Failure of F-Met-Leu-Phe to induce chemotaxis in differentiated promyelocytic (HL-60) leukemia cells.

Treatment of HL-60 promyelocytic leukemia cells with dibutyryl cyclic adenosine 3',5'-monophosphate (dbcAMP) induced these cells to differentiate toward mature neutrophilic granulocytes (PMN). DbcAMP was found to produce a rapid time- and dose-dependent inhibition of HL-60 cell proliferation, reaching a maximum after 48 hr treatment of the cells with 250-500 microM. This was associated with morphologic alterations consistent with maturing PMN. Using immunofluorescence and flow cytometry, we found that dbcAMP-treated HL-60 cells expressed some, but not all, surface markers characteristic of mature phagocytes. Thus receptors for the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP); the monocyte/granulocyte markers My-8, Mo-1, and Leu-15; as well as the monocyte markers Mo-2 and My-4 were identified on the cells. In contrast, dbcAMP-treated cells did not express the PMN-specific antigen DL1.2. We also found that dbcAMP-treated HL-60 cells produced hydrogen peroxide in response to the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA). However, the magnitude of this response was significantly less than that observed in mature PMN. In contrast, fMLP-stimulated levels of hydrogen peroxide production were comparable in both cell types. In addition, despite the fact that dbcAMP-treated cells expressed fMLP receptors, they did not exhibit directed migration toward this chemotactic peptide. Taken together, these data suggest that dbcAMP-induced differentiation of HL-60 cells is incomplete.

Antigens, Surface↗
PubMed1990

Activation of neutrophils by factors released from alveolar macrophages stimulated with collagen-like polypeptides.

Oxidant-induced injury is associated with breakdown of interstitial collagen and the accumulation of inflammatory cells in the lungs. In previous studies, we demonstrated that phagocyte accumulation is mediated, in part, by chemotactic factors generated from damaged collagen. To determine if alveolar macrophages also mediate the migration of polymorphonuclear leukocytes (PMN) into the lungs, we examined the release of chemotactic factors from alveolar macrophages treated with native or synthetic collagenous peptides. These included fragments of bovine collagen digested with bacterial collagenase (CG) or cyanogen bromide (CB) as well as small molecular weight synthetic polypeptides containing proline (Pro), glycine (Gly), and hydroxyproline (Hyp), the major amino acids that comprise collagen. We found a dose- and time-related generation of PMN chemotactic activity by collagen peptide-treated macrophages. The maximum activity was released 72 h after pretreatment of macrophages for 1 to 3 h with 0.1 to 1 microM CG-, CB-, or (Pro-Pro-Gly)5-peptides. The native peptides derived from CG-digested collagen were more active than synthetic peptides containing Pro and Gly. Neither trypsin digests of bovine serum albumin nor synthetic peptides containing Hyp stimulated chemotactic factor release from macrophages. The alveolar macrophage-derived chemotactic factor was found to lose activity when dialyzed and after heat or trypsin treatment. The release of PMN-activating factors by collagen peptide-treated macrophages was also examined. Alveolar macrophage-conditioned medium was found to stimulate PMN production of reactive oxygen intermediates as well as elastase and gelatinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1989

Activation of bone marrow phagocytes following benzene treatment of mice.

Techniques in flow cytometry/cell sorting were used to characterize the effects of benzene and its metabolites on subpopulations of bone marrow cells. Treatment of male Balb/c mice with benzene (880 mg/kg) or a combination of its metabolites, hydroquinone and phenol (50 mg/kg), resulted in a 30 to 40% decrease in bone marrow cellularity. Flow cytometric analysis revealed two subpopulations of bone marrow cells that could be distinguished by their size and density or granularity. The larger, more dense subpopulation was found to consist predominantly of macrophages and granulocytes as determined by monoclonal antibody binding and by cell sorting. Benzene treatment had no selective cytotoxic effects on subpopulations of bone marrow cells. To determine if benzene treatment activated bone marrow phagocytes, we quantified production of hydrogen peroxide by these cells using the fluorescent indicator dye, 2',7'-dichlorofluorescein diacetate. We found that macrophages and granulocytes from bone marrow of treated mice produced 50% more hydrogen peroxide in response to the phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate than did cells from control animals. It is hypothesized that phagocyte activation and production of cytotoxic reactive oxygen intermediates may contribute to hematotoxicity induced by benzene.

Animals↗
PubMed1988

Functional and biochemical properties of rat Kupffer cells and peritoneal macrophages.

Functional and biochemical techniques were used to further characterize heterogeneity between rat Kupffer cells and peritoneal macrophages. Both macrophage cell types were found to phagocytize antibody coated sheep red blood cells in a time-dependent manner. However, Kupffer cells were two to three times more phagocytic than were peritoneal macrophages. In contrast, the peritoneal cells released significantly more superoxide anion in response to the complement cleavage product, C5a and the phorbol ester tumor promoter, 12-0-tetradecanoyl-phorbol-13-acetate, and produced more hydrogen peroxide than did the liver macrophages. Both cell types responded chemotactically to C5a. These results suggest that macrophages may develop specialized functions depending on the needs of their local environment. Using one and two dimensional SDS-polyacrylamide gel electrophoresis, we also compared the production of newly synthesized proteins by Kupffer cells and peritoneal macrophages. In general, the macrophages were found to produce similar types and numbers of proteins with some exceptions. These included proteins that were unique to peritoneal macrophages and other proteins observed only in Kupffer cells. The production of these proteins in liver macrophages did not appear to correlate with levels of functional activation, but may be more related to the tissue origin of the cells.

Animals↗
PubMed1988

Neutrophil response following intratracheal instillation of collagen peptides into rat lungs.

Inflammatory lung diseases are associated with destruction of interstitial collagen and release of degraded collagen fragments into the lower respiratory tract. To determine whether degraded collagen might be one factor mediating the cellular influx, we measured polymorphonuclear leukocytes (PMN) in bronchoalveolar lavage fluid following intratracheal instillation of collagen peptides. The responses to collagenous peptides derived from collagen digested with bacterial collagenase and to the collagenous-like polytripeptide (proline-proline-glycine) were examined. Both types of collagen peptides were chemotactic for human PMN in vitro. Two days following instillation of 5 mg collagenous peptides, we observed a threefold increase in the percentage of PMN in lavage fluid with a maximum (fivefold) response on day 6. Since other chemoattractants produce a response within hours when instilled intratracheally, we postulated that the late neutrophil influx produced with collagen may be the result of production of a neutrophil chemoattractant by alveolar macrophages. Alveolar macrophages treated with collagenous or collagenous-like peptides released PMN chemotactic factors, and the time course of release of chemotactic activity by alveolar macrophages in vitro correlated with the in vivo finding of a 2-6-day delay in PMN accumulation in the lungs. These observations are consistent with the idea that collagen peptides may stimulate alveolar macrophages to produce chemotactic factors for neutrophils. This mechanism may play a role in the accumulation of phagocytic cells in the lung following injury.

Animals↗
PubMed1987

Differential sensitivity of tumor targets to liver macrophage-mediated cytotoxicity.

Liver macrophages activated in vivo with bacterially derived lipopolysaccharide (LPS) display enhanced chemotaxis, phagocytosis, and oxidative metabolism. To determine if LPS also activates these mononuclear phagocytes for tumor cell killing, we compared the cytotoxic activity of macrophages from livers of rats treated with LPS (5 mg/kg, i.v.) with resident Kupffer cells. We found that both macrophage cell types displayed cytotoxicity towards rat N1S1 hepatoma and RBL-1 basophilic leukemia cells. Cytotoxicity of resident and LPS-activated liver macrophages towards these targets increased with cocultivation time, was dependent on the effector:target cell ratio, and appeared to involve extracellular lysis. No direct correlation between macrophage activation and cytotoxicity was observed towards these targets. While liver macrophages from LPS treated rats were more cytotoxic towards N1S1 cells, resident Kupffer cells were more cytotoxic towards RBL-1 cells. In further studies, resident Kupffer cells were also found to display extracellular cytolytic activity towards mouse P815 mastocytoma cells. In contrast, LPS-activated liver macrophage-mediated killing of these targets involved phagocytosis of intact tumor cells, as evidenced by light and electron microscopy and by uptake of 51Cr-labeled cells. These results suggest that cytotoxicity mediated by liver macrophages depends on the type of macrophage and the nature of the tumor cell target. In addition, cytotoxicity towards tumor targets appears to involve at least two different mechanisms including extracellular cytolysis and phagocytosis.

Animals↗
PubMed1987

Induction of chemotaxis in mouse peritoneal macrophages by activators of protein kinase C.

Two activators of calcium and phospholipid dependent protein kinase (protein kinase C), the tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and the synthetic diacylglycerol, 1-oleoyl-2-acetylglycerol (OAG), were compared as chemotactic agents for mouse peritoneal macrophages. Both of these compounds were found to induce chemotaxis in the macrophages to a similar extent in a time and dose dependent manner. Induction of chemotaxis was observed in the concentration range of 10-100 nM for TPA and 25-250 microM for OAG. Two structurally related synthetic sn 1,2-diacylglycerols, 1,2-dioctanoylglycerol (diC8) and 1,2-didecanoylglycerol (diC10), were also found to be chemotactic for macrophages, while monoacylglycerol (2-monoolein) was inactive. Of the diacylglycerols, OAG was found to be the most active followed by diC8 and diC10. In contrast to TPA, the synthetic diacylglycerols had no effect on superoxide anion release by the cells, suggesting that the mechanism of superoxide anion release by TPA in macrophages is distinct from chemotaxis. Phorbol-12,13-diacetate, a biologically inactive phorbol ester analog that inhibits the binding of TPA to its cellular receptors, inhibited macrophage chemotaxis induced by TPA, the synthetic diacylglycerols, and the complement fragment, C5a. Taken together, our results suggest that chemotaxis in macrophages may be mediated by activation of protein kinase C.

Animals↗
PubMed1986

Chemotactic activity of collagen-like polypeptides for human peripheral blood neutrophils.

Damage to interstitial connective tissue is associated with the rapid accumulation of monocytes and neutrophils at the site of injury. To study the role of collagen fragments in neutrophil migration, we analyzed the chemotactic properties of peptide fragments of bovine collagen digested with bacterial collagenase or cyanogen bromide and small molecular weight synthetic polypeptides containing proline (Pro), hydroxyproline (Hyp), and glycine (Gly), the major amino acids that comprise collagen. Using the Boyden chamber and under agarose techniques, we found that collagen fragments were as potent in inducing chemotaxis in neutrophils as the bacterial-derived peptide f-met-leu-phe. The synthetic polytripeptides (Pro-Pro-Gly)5 and (Pro-Hyp-Gly)5 were found to be equipotent in inducing chemotaxis, producing a maximal induction of chemotaxis at 5-10 nM. This suggests that Hyp, the unique imino acid found in collagen, is not required for chemotactic activity. Increasing the length of the synthetic tripeptide from 5 to 10 subunits decreased its chemotactic activity, while the single tripeptide subunit (Pro-Hyp-Gly)1 was the least active peptide, inducing a maximal response at 100 nM. To study the structural requirements for chemotaxis, Pro-Hyp-Gly tripeptides were synthesized with modifications at the N and C terminals ends. Addition of a methyl group to the carboxyl of Gly to form an ester enhanced the chemotactic activity of the peptide by 50%, while substitutions on the amino terminus with an acetyl group decreased the chemotactic activity by 50%. Substitution on the amino terminus with a Boc group decreased the chemotactic activity by 100%. These results indicate that there are specific structural requirements for chemotaxis induced by peptides having a collagen-like sequence of amino acids.

Chemotactic Factors↗
PubMed1986

Accumulation of activated mononuclear phagocytes in the liver following lipopolysaccharide treatment of rats.

Lipopolysaccharide (LPS) is a toxic bacterial cell wall component that is rapidly cleared from the portal circulation by Kupffer cells. To determine if interaction with LPS causes the accumulation and activation of mononuclear phagocytes (MNP) in the liver, we compared the morphological and functional characteristics of MNP obtained from livers of rats treated with LPS (5 mg/kg, intravenously [IV]) with normal resident Kupffer cells. MNP were isolated from rat livers by combined collagenase/pronase perfusion, selective digestion, and differential centrifugation on a metrizamide gradient. MNP obtained from livers of LPS-treated rats were found to display morphologic and functional characteristics of activated macrophages. These cells were generally larger than resident cells, were highly vacuolated, and adhered to culture dishes more rapidly. Both cell types phagocytized sheep red blood cells (sRBC) in a time-dependent manner, reaching a maximum after 60-75 min incubation with sRBC. However, MNP from livers of LPS-treated rats phagocytized 10-15 times more sRBC than resident Kupffer cells from untreated animals. Employing the Boyden chamber technique, both cell types were also found to be chemotactic to a number of stimuli including the complement fragment, C5a, the tumor promoter, 12-0-tetradecanoyl-phorbol-13-acetate (TPA), and collagenous peptides related to tissue breakdown products. MNP from livers of LPS-treated rats were generally 10-15 times more responsive to the chemoattractants than resident Kupffer cells. In addition, both resident Kupffer cells and MNP from LPS-treated rats were found to release superoxide anion in response to stimulation by C5a and TPA. Taken together these results suggest that LPS treatment of rats leads to the recruitment and activation of MNP in the liver.

Animals↗
PubMed1986

Potential role of activated macrophages in acetaminophen hepatotoxicity. I. Isolation and characterization of activated macrophages from rat liver.

Twenty-four hours following treatment of rats with the analgesic acetaminophen (1.2 g/kg), we observed an infiltration of mononuclear cells into centrilobular regions of the liver in the absence of necrosis. To determine whether acetaminophen induces the accumulation and activation of mononuclear phagocytes, we compared the morphologic and functional characteristics of macrophages obtained from livers of acetaminophen-treated rats with those of resident macrophages (Kupffer cells) from untreated control animals. Macrophages were isolated from rat livers by combined collagenase/pronase perfusion, selective digestion, and differential centrifugation on a metrizamide gradient. Acetaminophen treatment resulted in a twofold increase in macrophage yields from the liver compared with controls. Macrophages isolated from treated animals were generally larger than resident Kupffer cells, were highly vacuolated, and adhered to culture dishes more rapidly. Liver macrophages from both treated and untreated rats phagocytized sheep red blood cells (sRBC) in a time-dependent manner, reaching a maximum after 60-75 min incubation with sRBCs. However, macrophages from livers of acetaminophen-treated rats phagocytized two to three times more sRBC than did resident Kupffer cells. Using the Boyden chamber technique, both macrophage populations were found to be chemotactic to a number of stimuli including the complement fragment, C5a, and synthetic collagenous peptides related to tissue breakdown products. Levels of migration of macrophages from livers of acetaminophen-treated rats were four to seven times greater than those of resident Kupffer cells. In addition, compared with resident Kupffer cells, macrophages from acetaminophen-treated rats released 30% more superoxide anion in response to the stimulus, 12-O-tetradecanoyl-phorbol-13-acetate. Taken together, these results suggest that acetaminophen treatment of rats leads to the recruitment and activation of macrophages in the liver.

Acetaminophen↗
PubMed1986

Potential role of activated macrophages in acetaminophen hepatotoxicity. II. Mechanism of macrophage accumulation and activation.

Treatment of rats with acetaminophen (1.2 g/kg) results in the accumulation of activated macrophages in the centrilobular regions of the liver. To study the mechanism by which these cells accumulate and become activated, we examined the release of chemotactic and activating factors from cultured hepatocytes treated with acetaminophen (10-100 microM). We found a dose- and time-related generation of Kupffer cell and monocyte chemotactic activity by acetaminophen-treated hepatocytes. The maximum response was observed with a 25% dilution of medium collected 24 hr following treatment of hepatocytes with acetaminophen. Using a checkerboard assay, the factor in conditioned medium was determined to induce chemotaxis as well as chemokinesis in both Kupffer cells and monocytes. The hepatocyte-derived chemotactic factor was also found to be stable to freeze-thawing but to lose activity following heat or trypsin treatment. These results, together with our findings that chemotactic activity was eluted in the void volume following Sephadex G-25 size exclusion chromatography, suggested that the chemotactic factor released by hepatocytes is a large molecular weight protein. The release of Kupffer cell activating factors by acetaminophen-treated hepatocytes was also examined. Hepatocyte-conditioned medium was found to stimulate Kupffer cell phagocytosis and superoxide anion release, two characteristics of activated macrophages. These effects were maximal with conditioned medium collected from hepatocytes 24 hr following treatment with 50-100 microM acetaminophen. Acetaminophen alone had no effect on chemotaxis, phagocytosis, or superoxide anion production by Kupffer cells or monocytes. Taken together, these results suggest that macrophage accumulation and activation in the liver following acetaminophen treatment may be mediated, at least in part, by factors released from hepatocytes.

Acetaminophen↗