Inhibition of p38 mitogen activated protein kinase increases lipopolysaccharide induced inhibition of apoptosis in neutrophils by activating extracellular signal-regulated kinase.

BACKGROUND: Prolonged polymorphonuclear neutrophil (PMN) survival has been implicated in tissue injury after sepsis. Previously we reported that lipopolysaccharide (LPS) inhibits PMN apoptosis via the activation of the extracellular signal-regulated kinase (ERK). Conversely, the p38 mitogen activated protein kinase (MAPK) pathway is involved in the spontaneous apoptosis of PMNs. The interaction between these 2 pathways and their ability to regulate apoptosis during sepsis remain largely undefined. We hypothesize that there is interaction between the ERK and p38 pathways during sepsis. METHODS: PMNs were isolated from healthy volunteers by Ficoll gradient centrifugation and red blood cell sedimentation. Cells were then pretreated for 1 hour with the ERK inhibitor (PD98059, 10 micromol/L), p38 inhibitor (SB203580, 1 micromol/L), or vehicle. After treatment with LPS, apoptosis and MAPK activity were correlated. RESULTS: LPS stimulation significantly inhibits PMN apoptosis compared with unstimulated cells. Furthermore, inhibition of ERK significantly abrogates this effect, whereas inhibition of p38 augments LPS induced inhibition of apoptosis. Elk-1 phosphorylation (ERK target) is significantly increased by LPS alone and by inhibition of the p38 pathway during LPS stimulation. This correlates with ERK phosphorylation by Western blot. CONCLUSIONS: These data show that p38 inhibition enhances ERK activity during endotoxemia. Furthermore, these data suggest that cooperation between ERK and p38 MAPK pathways dictates the apoptotic potential of PMNs during inflammatory states.

Heat shock protein 27 inhibits apoptosis in human neutrophils.

BACKGROUND: Prolonged neutrophil(PMN) survival has been implicated in tissue injury following sepsis. A variety of bacterial products have been identified which inhibit PMN apoptosis including lipopolysaccharide(LPS). Extracellular heat shock proteins(Hsp) have recently been identified as potent regulatory signals for the innate immune system during the inflammatory response. We hypothesized that Hsp 27 can affect PMN phenotype with respect to apoptosis and cytokine profile. MATERIALS AND METHODS: PMN were isolated from the peripheral blood of healthy human volunteers by red blood cell sedimentation and gradient centrifugation. Cells were placed in media and cultured for 18 h with and without recombinant human Hsp 27 at various concentrations. In parallel experiments, PMN were stimulated with LPS, a known inhibitor of PMN apoptosis, for comparison. Apoptosis was quantified using annexin V and propidium iodide staining with flow cytometric analysis. Culture supernatants were assayed for secretion of TNF-alpha, IL-10, and IL-12. RESULTS: Hsp 27 significantly inhibits PMN apoptosis [control; 81.8 +/- 3.6%, vs Hsp 27, 60.4 +/- 4.1% p < 0.05]. The reduction is similar to that signaled by LPS, alone. Together their effect is not synergistic. The Hsp 27 response is dose-dependent. Hsp 27 does not induce secretion of TNF-alpha, IL-10, or IL-12, whereas LPS does signal IL-12 and TNF-alpha secretion. CONCLUSION: These data demonstrate that exogenous Hsp 27 may play a role in neutrophil-mediated tissue injury during trauma and sepsis via its ability to inhibit neutrophil apoptosis. However, Hsp 27 does not significantly alter neutrophil phenotype with respect to cytokine production profile.

The liver as an immune organ.

Systemic inflammation contributes to significant morbidity in the ICU. With its ability to generate antiinflammatory acute-phase proteins, cytokines via Kupffer cells, and recently acknowledged resident lymphocytes, the liver provides a central regulatory role in inflammation. The liver has constant exposure to foreign material as a result of gut translocation and first-pass metabolism from the bloodstream. Consequently, the balance between hepatic activation and tolerance becomes an important factor in the host response to inflammation. Interventions and therapies that can assess and modulate these hepatic functions can improve outcomes for ICU patients.

Inhibited neutrophil apoptosis: proteasome dependent NF-kappaB translocation is required for TRAF-1 synthesis.

Neutrophil (PMN) apoptosis regulates local and systemic inflammation during sepsis. Tumor necrosis factor receptor-associated factors (TRAFs) have been implicated as mediators of apoptosis; however, the signaling pathways for their production in stimulated PMN are unclear. We hypothesize that NF-kappaB translocation is necessary for the induction of TRAF-1 in PMNs with prolonged survival. Neutrophils were isolated from the blood of healthy volunteers by Ficoll gradient centrifugation and red blood cell sedimentation. Neutrophil NF-kappaB was inhibited with a proteasome inhibitor, PSI-I. Cells were treated with PSI-I (30 microM) or vehicle (DMSO 0.2%) for 50 min then incubated over an 18-h time course with LPS (10 to 1000 ng/mL), tumor necrosis factor alpha (TNFalpha) (2 to 20 ng/mL) or control media. In vitro apoptosis was quantified by propidium iodide FACS analysis. Total cellular TRAF-1 was detected by Western blot analysis of cell lysates. Steady state TRAF-1 mRNA was detected by RPA. NF-kappaB activity was determined by Western blot analysis for nuclear p65. Means and standard errors were calculated; data were analyzed by ANOVA. Lipopolysaccharide (LPS) and TNFalpha increased PMN nuclear p65 and steady state TRAF-1 mRNA. Apoptosis was inhibited by TNFalpha and LPS at 12 and 18 h (P < 0.01). Incubation of cells in the NF-kappaB inhibitor PSI-I blocked LPS and TNFalpha-induced inhibition of apoptosis (P < 0.05) and the induction of both nuclear p65 and TRAF-1 mRNA. These data demonstrate that inhibition of PMN apoptosis and TRAF-1 induction by LPS and TNFalpha is NF-kappaB dependent.

Activated neutrophils induce nitric oxide production in Kupffer cells.

Neutrophils (PMN) are proposed to contribute to hepatic dysfunction during sepsis. Transmigrating PMN have been demonstrated to adhere to and injure parenchymal cells (hepatocytes); however, the effect of sepsis-activated PMN on hepatic macrophages or Kupffer cells (KC) is poorly characterized. We hypothesize that PMN influence KC inflammatory mediator production, including nitric oxide. Rodent KC were co-cultured with PMN obtained from controls (Norm-PMN) or endotoxemic rats [lipopolysaccharide (LPS)-PMN] for 18 h. After an 18-h incubation, supernatants and cell lysates of the KC were analyzed for nitric oxide (NO) production. Co-cultures with LPS-PMN/KC demonstrated significantly increased production of nitrite and up-regulation of inducible nitric oxide synthase (iNOS) protein compared to KC alone or Norm-PMN/KC co-cultures. Immunohistochemistry revealed preferential iNOS protein staining in the cytoplasm of KC cultured with LPS-PMN compared to controls. Nitrite production in co-cultures of KC and LPS-PMN where cell contact was inhibited by a cell impermeable but diffusable membrane was significantly reduced. These data provide evidence that KC can be stimulated directly by activated PMN for production of NO. Further, they suggest another mechanism by which PMN modulate hepatic function during sepsis.

Enhancing hepatocyte adhesion by pulsed plasma deposition and polyethylene glycol coupling.

Decreased hepatocyte adhesion to polymeric constructs limits the function of tissue engineered hepatic assist devices. We grafted adhesion peptides (RGD and YIGSR) to polycaprolactone (PCL) and poly-L-lactic acid (PLLA) in order to mimic the in vivo extracellular matrix and thus enhance hepatocyte adhesion. Peptide grafting was done by a novel technique in which polyethylene glycol (PEG)-adhesion peptide was linked to allyl-amine coated on the surface of PCL and PLLA by pulsed plasma deposition (PPD). Peptide grafting density, quantified by radio-iodinated tyrosine in YIGSR, was 158 fmol/cm(2) on PLLA and 425 fmol/cm(2) on PCL surfaces. The adhesion of hepatocytes was determined by plating 250,000 hepatocytes/well (test substrates were coated on 12 well plates) and quantifying the percentage of adhered cells after 6 h by MTT assay. Adhesion on PCL surfaces was significantly enhanced (p < 0.05) by both YIGSR (percentage of adhered cells = 53 +/- 7%) and RGD (53 +/- 12%) when compared to control surfaces (31 +/- 8%). Hepatocyte adhesion on PLLA was significantly (p < 0.05) enhanced on PLLA-PEG-RGD surfaces (76 +/- 14%) compared to control surfaces (42 +/- 19%) and more (68 +/- 25%) but not statistically significant (p = 0.15) on PLLA-PEG-YIGSR surfaces compared to control surfaces. These results indicate that hepatocyte adhesion to PCL and PLLA based polymeric surfaces can be enhanced by a novel adhesion peptide grafting technique using pulsed plasma deposition and PEG cross-linking.

Induction of global anergy rather than inhibitory Th2 lymphokines mediates posttrauma T cell immunodepression.

Depressed mitogen-induced IL-2 and IFN-gamma responses after severe mechanical or thermal injury are postulated to result from an expansion of Th2 lymphocytes with concomitant excessive production of IL-4 and/or IL-10. Here, we simultaneously assessed proliferation and Th1 (IFN-gamma) versus Th2 (IL-10, IL-4) lymphokine production in trauma patients' isolated T cells stimulated in a costimulation sufficient, antigen presenting cell independent system (anti CD3 + anti-CD4). T cells with depressed proliferation and IL-2 production simultaneously lost IL-4, IL-10, and IFN-gamma protein and mRNA responses. Exogenous IL-12 addition did not restore IFNgamma responses, but exogenous IL-2 partially restored IL-4, IFN-gamma, and IL-10 production. Although initially partially restored by exogenous IL-2 or stimulation with PMA + ionomycin, patient T cells with persisting anergy progressively lost even these lymphokine and proliferative responses. Development of global T cell anergy was not a result of lost T cell viability or protein synthesis, since it corresponded to predominance of anergic T cells with upregulated expression of CD11b, but downregulated CD28 and CD3 expression. Thus, the subset of posttrauma patients whose isolated T cells become unresponsive experienced progressively worsening global anergy, mediated not by an increased production of Th2 lymphokines, but possibly by T cell incapacity to be activated through TCR triggering or Ca(2+) mobilization.

Inhibition of neutrophil apoptosis after severe trauma is NFkappabeta dependent.

BACKGROUND: Systemic inflammation may inhibit neutrophil (PMN) apoptosis and promote multiple organ dysfunction syndrome. We hypothesize that severe trauma causes dysregulation of PMN apoptosis. METHODS: Neutrophils were isolated from trauma patients (24-72 hours after injury; n = 16) and controls (healthy volunteers) and incubated for 18 hours. In separate experiments, control cells were treated +/- the nuclear factor kappa beta (NFkappabeta) inhibitor pyrrolidinithiocarbamate then incubated with 25% patient or control plasma. Apoptosis was quantified by enzyme-linked immunosorbent assay for histone-associated DNA and annexin V fluorescence-activated cell sorter. NFkappabeta activation was determined by Western blot for phosphorylated I kappabeta. RESULTS: Apoptosis was inhibited in trauma patient PMN. Neutrophil apoptosis correlated with multiple organ dysfunction syndrome score, Acute Physiology and Chronic Health Evaluation II, and platelet count. Patient plasma inhibited apoptosis and induced phosphorylation of I kappabeta in control cells. Inhibition of PMN apoptosis by patient plasma was blocked by pretreatment with pyrrolidinithiocarbamate. CONCLUSION: NFkappabeta-dependent inhibition of neutrophil apoptosis occurs after trauma. Early inhibition of PMN apoptosis is dependent on the magnitude of injury.

Inhibition of alveolar neutrophil immigration in endotoxemia is macrophage inflammatory protein 2 independent.

BACKGROUND: Altered transendothelial migration and delayed apoptosis of neutrophils (PMN) have been implicated as contributing to infection in patients with gram-negative sepsis. Macrophage inflammatory protein 2 (MIP-2) signals PMN immigration and may alter other PMN functions. We tested the hypothesis that sequential endotoxin challenge in vivo alters PMN apoptosis and chemotactic responses. MATERIALS AND METHODS: Endotoxemia was induced in male Wistar rats (250 g) via intraperitoneal (IP) administration of LPS (4 mg/kg). After 18 h, intratracheal (IT) injection of LPS (400 microg/kg) was performed. Control animals received saline injections. Four hours after IT-LPS, circulating and bronchoalveolar lavage (BAL) PMN were isolated. PMN yields were calculated, and apoptosis was quantified after 18 h in culture by annexin V-fluorescein isothiocyanate FACS analysis. BAL MIP-2 concentrations were determined by ELISA. PMN chemotaxis to MIP-2 and IL-8 was determined using a fluorescent in vitro migration assay. RESULTS: Endotoxemia (IP-LPS) significantly decreases BAL PMN yield in response to an in vivo IT-LPS challenge. IT-LPS inhibits BAL PMN apoptosis to the same extent as sequential IP/IT-LPS. Alveolar MIP-2 concentrations are similar in the two groups. In vitro migration to IL-8 and MIP-2 was inhibited in PMN from endotoxemic versus control animals. CONCLUSIONS: These data demonstrate that endotoxemia inhibits PMN migration despite similar MIP-2 concentrations in the alveolus. Sequential insults do not affect the inhibition of apoptosis. In vitro, PMN from endotoxemic animals display impaired chemotaxis to MIP-2 and interleukin-8. This may result in an inadequate host defense that contributes to increased ICU-acquired pneumonia in septic patients.

Temporal bone fractures: otic capsule sparing versus otic capsule violating clinical and radiographic considerations.

OBJECTIVE: To assess the practicality and utility of the traditional classification system for temporal bone fracture (transverse vs. longitudinal) in the modern Level I trauma setting and to determine whether a newer system of designation (otic capsule sparing vs. otic capsule violating fracture) is practical from a clinical and radiographic standpoint. METHODS: The University of Massachusetts Medical Center Trauma Registry was reviewed for the years 1995 to 1997. Patients identified as sustaining closed head injury were reviewed for basilar skull fracture and temporal bone fracture. Clinical and radiographic records were evaluated by using the two classification schemes. RESULTS: A total of 2,977 patients were treated at the trauma center during this time. Ninety (3%) patients sustained a temporal bone fracture. The classic characterization of transverse versus longitudinal fracture (20% vs. 80%, respectively) was unable to be determined in this group; therefore, clinical correlation to complications using that paradigm was not possible. By using the otic capsule violating versus sparing designation, an important difference in clinical sequelae and intracranial complications became apparent. Compared with otic capsule sparing fractures, patients with otic capsule violating fractures were approximately two times more likely to develop facial paralysis, four times more likely to develop CSF leak, and seven times more likely to experience profound hearing loss, as well as more likely to sustain intracranial complications including epidural hematoma and subarachnoid hemorrhage. CONCLUSION: The use of a classification system for temporal bone fractures that emphasizes violation or lack of violation of the otic capsule seems to offer the advantage of radiographic utility and stratification of clinical severity, including severity of Glasgow Coma Scale scores and intracranial complications such as subarachnoid hemorrhage and epidural hematoma.

Mitogen-activated protein kinases signal inhibition of apoptosis in lipopolysaccharide-stimulated neutrophils.

BACKGROUND: Neutrophil (PMN) apoptosis is critical to the resolution of infection and the limitation of inflammation. Bacterial endotoxin (lipopolysaccharide [LPS]) inhibits PMN apoptosis and activates the p38 mitogen-activated protein kinase (MAPK) signal cascade. The role of p38 and other MAPKs (ERK and SAPK/JNK) in regulating PMN apoptosis after LPS stimulation is unknown. We hypothesize that MAPK activation by LPS signals inhibition of PMN apoptosis. METHODS: PMNs were isolated from the blood of healthy human volunteers and incubated with PD98059 (ERK inhibitor), SB203580 (p38 inhibitor), or 0.1% dimethyl sulfoxide (vehicle) for 1 hour before treatment with LPS (0, 10, or 1000 ng/mL). Neutrophil MAPK activation was determined by Western blot analysis for phosphorylated p38, ERK, and SAPK/JNK. Apoptosis was quantified by flow cytometry with use of propidium iodide and annexin V. RESULTS: LPS inhibited PMN apoptosis and activated p38 and ERK in a dose- and time-dependent fashion. SAPK/JNK was not activated by LPS. Treatment of cells with ERK inhibitor before LPS stimulation abrogated LPS signaled inhibition of PMN apoptosis. Conversely, p38 inhibition with SB203580 augmented inhibition of apoptosis by LPS. CONCLUSIONS: These data demonstrate opposing roles of MAPKs in mediating PMN apoptosis after LPS stimulation. We conclude that LPS signal transduction by ERK inhibits PMN apoptosis while activation of p38 promotes apoptosis.

Hepatocyte polyunsaturated fatty acid enrichment increases acute phase protein synthesis.

BACKGROUND: The production of acute phase proteins by the liver is critical for homeostasis and recovery after injury. Polyunsaturated fatty acids, specifically of the n-3 family, have demonstrated anti-inflammatory properties that promote recovery; however, the effects of these fatty acids on acute phase protein synthesis have not been fully evaluated. METHODS: The synthesis of the acute phase proteins alpha-2 macroglobulin and lipopolysaccharide binding protein was studied in hepatocyte-Kupffer's cell cocultures from Wistar rats. Cultures were endotoxin stimulated after enrichment with albumin complexed arachidonic acid (20:4n-6) or docosahexaenoic acid (22:6n-3). Protein synthesis was analyzed by [35S]-methionine labeling or Western blotting. Culture interleukin-6 levels were determined. RESULTS: Both polyunsaturated fatty acids increase hepatocyte synthesis of acute phase proteins alpha 2-macroglobulin and lipopolysaccharide binding protein compared with controls; however, the response in the docosahexaenoic acid (22:6n-3) treated cultures was significant (P < .05 vs control). Interleukin-6 was also increased in the polyunsaturated fatty acid cultures compared with controls (P < .05) vs control). Cellular phospholipids were significantly enriched with the individual supplemented fatty acids (P < .05 vs bovine serum albumin). CONCLUSIONS: Polyunsaturated fatty acids have the capability to increase in vitro acute phase protein synthesis. This may contribute to the observed anti-inflammatory effect of n-3 polyunsaturated fatty acid enrichment.

Liposomes modulate Kupffer cell endotoxin response.

OBJECTIVES: To test the hypothesis that pretreatment with liposomes enriched with the omega 3 fatty acid docosahexaenoic acid (22:6 omega 3) will alter the Kupffer's cell and systemic cytokine (tumor necrosis factor and interleukin-6) response to endotoxin challenge, and to demonstrate alterations in Kupffer's cell phospholipid fatty acid composition after in vivo liposome treatment. DESIGN: Nonrandomized controlled laboratory investigation in Wistar rats. INTERVENTIONS: Animals were assigned to three pretreatment groups: no liposomes; liposomes, 100 mg/kg; or liposomes, 400 mg/kg given by bolus intravenous injection with the animals under inhalation anesthesia. Eighteen hours after liposome treatment, each group was challenged with Escherichia coli lipopolysaccharide (3 mg/kg intraperitoneally in 10 mL of lactated Ringer's solution) or lactated Ringer's solution only. In a separate set of experiments, Kupffer's cells were obtained from animals pretreated with liposome, 400 mg/kg, or controls and challenged with lipopolysaccharide (1, 100, or 10(4) ng/mL) in vitro. OUTCOME MEASURES: Serum and Kupffer's cell supernatant tumor necrosis factor and interleukin-6 bioactivity, Kupffer's cell phospholipid fatty acid composition, survival, and liver histologic findings. RESULTS: In vivo liposome pretreatment (400 mg/kg) resulted in significant increases in serum tumor necrosis factor and interleukin-6 levels 90 minutes after intraperitoneal lipopolysaccharide challenge (P < .05 vs no liposomes). Kupffer's cells isolated from liposome-treated animals (400 mg/kg) compared with untreated controls release significantly more tumor necrosis factor and interleukin-6 after lipopolysaccharide stimulation in vitro in a dose-dependent response (P < .05). Liposome treatment increased total polyunsaturated fatty acid, total omega 3, and docosahexaenoic acid 22:6 omega 3 content in Kupffer's cell phospholipids compared with untreated controls. Survival 24 hours after lipopolysaccharide challenge was reduced by liposome (400 mg/kg) pretreatment (P < .05 by chi 2 test). Livers from each treatment group demonstrated focal areas of hepatocyte necrosis and inflammatory cells. CONCLUSION: Liposome pretreatment increases the circulating and Kupffer's cell cytokine response to endotoxemia, increases Kupffer's cell polyunsaturated fatty acid content, and is associated with reduced survival.

Interleukin-6 production after thermal injury: evidence for nonmacrophage sources in the lung and liver.

BACKGROUND: Thermal injury induces circulating levels of interleukin-6 (IL-6). The liver and lung have been proposed as major sources of IL-6 after injury; however, multiple cell types within these organs are capable of IL-6 production. In these experiments we further characterize cellular sources of IL-6 after thermal injury by examining tissue macrophage response in the liver and lung and IL-6 production of cultured pulmonary microvascular endothelial cells (PMECs). METHODS: Serum, liver and lung tissue, and tissue macrophage IL-6 response was determined in Wistar rats subjected to a 35 to 40% total body surface area scald injury. Cultured PMEC IL-6 production was determined after treatment with serum from the burned animals. IL-6 bioactivity was assayed by 7TD1 proliferation, and IL-6 messenger RNA levels were determined by reverse transcriptase-polymerase chain reaction. Alveolar macrophages were obtained by bronchoalveolar lavage. Kupffer cells and PMECs were obtained by enzyme digestion of liver and lungs. RESULTS: Burn increases circulating IL-6 activity through postburn day 3 (388 +/- 50 units/0.1 ml versus 80 +/- 12 units/0.1 ml in controls). Burn increases lung and liver IL-6 messenger RNA without concurrent increase in the alveolar macrophages or Kupffer cells and persists in the lung after bronchoalveolar lavage. PMECs cultured in the presence of postburn day 3 serum (10% vol) release more IL-6 activity (1118 +/- 333 units/culture versus sham rat serum with 288 +/- 146 units/culture) than control cultures and have more readily detectable levels of IL-6 messenger RNA. CONCLUSIONS: Non-tissue macrophage sources including microvascular endothelium may be a contributing source of IL-6 in the lung after thermal injury.

Augmented tumor necrosis factor response to lipopolysaccharide after thermal injury is regulated posttranscriptionally.

BACKGROUND AND OBJECTIVE: Thermal injury has been shown to enhance macrophage sensitivity to lipopolysaccharide (LPS), resulting in augmented tumor necrosis factor alpha (TNF-alpha) production. This study was designed to examine whether enhanced TNF-alpha response after thermal injury and LPS stimulation is regulated at the level of transcription. DESIGN: Tumor necrosis factor alpha release in alveolar macrophages harvested from sham- or thermal-injured Wistar rats was determined using an L929 cytotoxicity bioassay on days 1, 3, and 5 following 40% scald burn and incubation for 24 hours with LPS (0 or 10 micrograms/mL). Separate groups of rats underwent intraperitoneal injection of LPS (5 mg/kg) 3 days following sham or thermal injury. Lung tissue RNA was isolated and probed for TNF-alpha messenger RNA (mRNA), using nuclease protection analysis. Finally, pooled alveolar macrophages were harvested 3 days following sham or thermal injury and cultured in the presence or absence of LPS (10 micrograms/mL) for 4 hours. The RNA from the pooled alveolar macrophages was extracted and probed for TNF-alpha mRNA levels. RESULTS: Thermal injury alone did not significantly increase alveolar macrophage TNF-alpha bioactivity, whole-lung TNF-alpha mRNA levels, or pooled alveolar macrophages TNF-alpha mRNA levels when compared with levels in sham-injured rats. However, alveolar macrophages from postburn day 3 (PBD 3) demonstrated increased sensitivity to LPS (10 micrograms/mL) compared with alveolar macrophages from sham-injured animals undergoing similar LPS treatment (2365 +/- 1011 vs 169 +/- 79 ng/mL; P < .05). Whole-lung mRNA levels in both sham-injured and PBD-3 rats receiving intraperitoneal LPS, while elevated approximately 2.5-fold from those of non-LPS treated rats, were not different from each other. Finally, pooled alveolar macrophages from sham-injured and PBD-3 rats cultured in the presence of LPS had approximately 1.7-fold and threefold increased TNF-alpha mRNA levels, respectively, compared with alveolar macrophages not cultured with LPS. CONCLUSIONS: Thermal injury induces priming of alveolar macrophages, resulting in significant increases in macrophage TNF-alpha production after exposure to LPS. The majority of this effect appears to be regulated at a posttranscriptional level, since there were only moderate increases in TNF-alpha mRNA levels after LPS stimulation, which did not coincide with large differences in bioactivity.

Acute-phase hepatocytes regulate liver sinusoidal cell mediator production.

BACKGROUND: Overproduction of liver sinusoidal cell (LCS) mediators in response to endotoxemia or gram-negative infection that follows tissue injury may contribute to hepatic dysfunction. OBJECTIVE: To better define the role of hepatocyte-derived acute-phase reactants in the regulation of sinusoidal cell mediator production following sequential insults, we tested the hypothesis that interleukin-6 (IL-6) prestimulation alters hepatocyte regulation of lipopolysaccharide (LPS)-stimulated sinusoidal cell tumor necrosis factor (TNF), IL-6, and nitric oxide production. METHODS: Hepatocytes and LSCs were isolated from Wistar rats, and in vitro responses were compared between LSCs alone and hepatocyte-LSC cocultures. Cocultures and LSCs alone were sequentially stimulated with IL-6 (5000 U/mL) then LPS (dose-response), and culture supernatants were analyzed for TNF (L929 cytolysis), IL-6 (7TD1 proliferation), and nitric oxide (Griess reaction). Induction of acute-phase protein synthesis by the stimulation of hepatocytes with IL-6 and dexamethasone (0.1 mumol/L) was assayed by methionine radiolabeling and SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Coculture levels of messenger RNA for TNF-alpha and IL-6 were examined by RNA extraction and reverse transcriptase polymerase chain reaction with specific primers. RESULTS: Interleukin-6 and dexamethasone signal hepatocyte acute-phase protein synthesis. Prestimulation of cocultures, but not of LSCs alone, with IL-6 inhibits LPS-stimulated IL-6 and nitric oxide production significantly. Bioactivity of TNF is reduced to a lesser extent. Polymerase chain reaction analysis demonstrated similar levels of TNF and IL-6 message following sequential stimulation. CONCLUSIONS: Interleukin-6-stimulated acute-phase hepatocytes limit LPS-stimulated coculture cytokine bioactivity and nitric oxide production. This hepatocyte response may provide a local counterregulatory mechanism to limit LSC-mediated injury.

Burn injury enhances alveolar macrophage endotoxin sensitivity.

Systemic activation of inflammatory cascades has been implicated in the pathogenesis of the multiple organ dysfunction syndrome. To begin to determine whether dysregulation of macrophage cytokine expression after burn plays a role in organ failure, we examined tumor necrosis factor alpha bioactivity of liver and lung macrophages under two conditions: (1) at 1, 3, 5, and 7 days after 40% scald burn, and (2) after sequential insult consisting of 40% scald burn followed by in vitro incubation with endotoxin. Burn alone did not significantly alter alveolar macrophage or Kupffer cell tumor necrosis factor alpha bioactivity at any of the timepoints examined. Sequential insult did not result in significant changes in Kupffer cell tumor necrosis factor alpha, but tumor necrosis factor alpha was increased 11.1 times in alveolar macrophages harvested on postburn day 3. Therefore macrophage cytokine responses to thermal injury are apparently both tissue-specific and time-dependent.

Sequential insult enhances liver macrophage-signaled hepatocyte dysfunction.

Injury results in altered hepatocyte protein synthesis including the production of acute-phase reactants. Evidence suggests that these hepatocyte products regulate macrophage function; however, their role in liver macrophage-mediated hepatocyte dysfunction following a second insult is poorly characterized. We hypothesize that IL-6-stimulated hepatocyte products alter liver macrophage responses to lipopolysaccharide, contributing to enhanced hepatocyte dysfunction. To test this hypothesis, hepatocytes, obtained by liver collagenase digestion, were treated with rIL-6 (murine, 300 units/ml) for 24 hr, and then liver macrophages, obtained by perfusion and pronase digestion, were added to establish cocultures. Cocultures were then stimulated with endotoxin (LPS, Escherichia coli O111:B4, 10 micrograms/ml) and hepatocyte dysfunction was assessed by determining secretory protein synthesis ([35S]methionine labeling, trichloracetic acid precipitation, and SDS-PAGE) and energy metabolism [mitochondrial respiration using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) dye]. Cultures of hepatocytes alone stimulated with IL-6, LPS, or sequential IL-6 followed by LPS demonstrate no difference in total secretory protein synthesis or mitochondrial respiration. In contrast, hepatocyte-liver macrophage cocultures demonstrate significantly reduced total secretory protein synthesis following sequential IL-6 followed by LPS ([35S]methionine cpm x 10(3): control, 33.8 +/- 8.5; LPS, 25.8 +/- 6.3; IL-6/LPS, 15.7 +/- 6.4; P < 0.05 vs control). This effect is specific to IL-6 since sequential TNF-alpha followed by LPS did not result in significant suppression of secretory protein synthesis. One-dimensional SDS-PAGE of labeled coculture secretory proteins demonstrates qualitative changes following sequential insult in vitro compared to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Omega 3 polyunsaturated fatty acids as modulators of cellular function in the critically ill.

Continued improvement in outcome in ICU patients with the hypermetabolism-organ failure syndrome require a better understanding of the disease process. Current research is focusing on altered regulation at the cell membrane and nuclear levels. Cell culture models have provided insight into one possible mechanism, that of altered cell-cell communication with dysregulation of the associated parenchyma. Alteration of the PUFA content of the membrane of macrophages with omega 3 PUFA can be easily induced and maintained, and can alter cell membrane physical characteristics and how the membrane responds to LPS-stimulated prostanoid release. There is also an associated alteration in the release of monokine. These changes are associated with improvements in T lymphocyte response to antigen and in outcome from septic peritonitis. The precise mechanisms through which these effects occur are the subject of investigations, as are the clinical implications. Nonetheless, nutrient pharmacology with omega 3 PUFA may be a promising area of research that will have clinical applicability in ICU patients.

Hepatic acute phase protein synthesis is indirectly regulated by tumor necrosis factor.

It has been proposed that tumor necrosis factor (TNF) is a direct regulator of postinjury hepatic protein synthesis. To test this hypothesis we investigated the total protein and specific acute phase protein synthesis response of murine hepatocytes to stimulation with mu-rTNF-alpha in vivo and in vitro. Total hepatocyte secretory protein synthesis was assessed by incorporation of [35-S] methionine into TCA-precipitated protein; and acute phase protein synthesis was assessed by induction of a 23-kD acute phase protein marker and by suppression of albumin synthesis determined by SDS-PAGE and autoradiography. We found that rTNF in vivo (8,000 units, IP injection) was associated with reduced total hepatocyte secretory protein synthesis (29 +/- 10%), increased synthesis of the 23-kD acute phase reactant (4.1 +/- 1.6-fold), and decreased albumin synthesis (0.68 +/- 0.2-fold) compared to saline-injected control animals. The in vitro stimulation of cultured murine hepatocytes directly with rTNF failed to demonstrate changes in total secretory protein synthesis or 23-kD protein; however, it did result in significant suppression of albumin synthesis (0.82 +/- 0.1-fold). In additional experiments, hepatocytes:nonparenchymal cell co-cultures stimulated with lipopolysaccharide (LPS) demonstrated protein synthesis changes similar to the in vivo TNF response including increased 23-kD protein and decreased albumin synthesis. These co-cultures demonstrated TNF production; however, addition of TNF antiserum during LPS stimulation had no effect on either 23-kD protein or albumin synthesis, despite the complete neutralization of TNF activity in the co-culture supernatants.(ABSTRACT TRUNCATED AT 250 WORDS)