Mesenteric lymph is responsible for post-hemorrhagic shock systemic neutrophil priming

BACKGROUND

Hemorrhagic shock-induced splanchnic hypoperfusion has been implicated as a priming event in the two event model of multiple organ failure (MOF). We have previously shown that early postinjury neutrophil (PMN) priming identifies the injured patient at risk for MOF. Recent in vitro studies have demonstrated that postshock mesenteric lymph primes isolated human neutrophils. We hypothesize that lymphatic diversion before hemorrhagic shock abrogates systemic PMN priming and subsequent lung injury.

METHODS

Sprague-Dawley rats (n >or= 5 per group) underwent hemorrhagic shock (MAP 40 mm Hg x 30 min) and resuscitation (shed blood + 2x crystalloid) with and without mesenteric lymphatic duct diversion. Sham animals underwent anesthesia and laparotomy. Whole blood was taken 2 hours after resuscitation, heparinized, and incubated for 5 min at 37 degrees C. Surface expression of CD11b (a marker for PMN priming) was determined by flow-cytometry compared with isotype controls. In addition, lung myeloperoxidase (MPO) was measured for PMN sequestration, and Evans blue lung leak was assessed in the bronchoalveolar lavage fluid in sham, and shock +/- lymph diversion animals.

RESULTS

Hemorrhagic shock resulted in increased surface expression of PMN CD11b relative to sham (23.8 +/- 6.7 vs. 9.9 +/- 0.6). Mesenteric lymphatic diversion before hemorrhagic shock abrogated this effect (8.0 +/- 2.6). Lung PMN accumulation, as assessed by MPO, was greater in the lungs of nondiverted (113 +/- 14 MPO/mg lung) versus sham (55 +/- 4 MPO/mg lung, p < 0.05); lymph diversion reduced lung PMNs to control levels (71 +/- 6.5 MPO/mg lung, p < 0.05). Evans blue lung leak was 1.6 times sham in the hemorrhagic shock group; this was returned to sham levels after lymph diversion (p < 0.05).

CONCLUSION

Post-hemorrhagic shock mesenteric lymph primes circulating PMNs, promotes lung PMN accumulation, and provokes acute lung injury. Lymphatic diversion abrogates these pathologic events. These observations further implicate the central role of mesenteric lymph in hemorrhagic shock-induced lung injury. Characterizing the PMN priming agents could provide insight into the pathogenesis of postinjury MOF and ultimately new therapeutic strategies.

Hypertonic saline activation of p38 MAPK primes the PMN respiratory burst

Investigation of hypertonic saline (HTS) modulation of neutrophils (PMN) cytotoxic responses has generated seemingly contradictory results. Clinically relevant levels of HTS attenuate receptor-mediated p38 MAPK signaling, whereas higher levels activate p38 MAPK. Concurrently, HTS exerts a dose-dependent attenuation of the PMN respiratory burst, most notably at concentrations where p38 MAPK is activated. We hypothesized that HTS-mediated p38 MAPK activation augments the PMN respiratory burst on return to normotonicity. We found that although clinically relevant levels of HTS (Na+ > or = 200 mM) did not activate p38 MAPK, higher concentrations (Na+ > or = 300 mM) resulted in activation comparable with that after PAF stimulation. Transient stimulation with high levels of HTS primed the PMN respiratory burst in response to fMLP and PMA. This effect was attenuated by pretreatment with SB 203580, a p38 MAPK specific inhibitor. We conclude that severe osmotic shock primes the respiratory burst via p38 MAPK signaling, further supporting the role of this signaling cascade in PMN priming.

Post-hemorrhagic shock mesenteric lymph lipids prime neutrophils for enhanced cytotoxicity via phospholipase A2

Hemorrhagic shock induced mesenteric hypoperfusion has long been implicated as a key event in the pathogenesis of the adult respiratory distress syndrome (ARDS) and multiple organ failure (MOF). Previous work links post-hemorrhagic shock mesenteric lymph (PHSML) lipids and neutrophil (PMN) priming in the pathogenesis of ARDS. We hypothesize that gut phospholipase A2 (PLA2) liberates proinflammatory lipids following hemorrhagic shock, which are responsible for enhanced PMN cytotoxicity. Mesenteric lymph was collected from rats (n > or = 5) before hemorrhagic shock, during hemorrhagic shock (MAP 40 mm Hg x 30 min), and after resuscitation (shed blood + 2x lactated Ringers). PMNs were incubated with physiologic concentrations (1-5%, v:v) of (a) buffer control, (b) sham (c) pre-shock lymph, (c) PHSML, (d) PHSML lipid extracts, (e) heat-denatured PSHML, and (f) PHSML harvested after i.v. pretreatment with a known PLA2 inhibitor (quinacrine, 10 mg/kg). PMNs were activated with fMLP (1 micromol), and the maximal rate of superoxide production measured by reduction of cytochrome c. Gut morphology was assessed histologically using hematoxalin and eosin (HE) staining. PHSML and PHSML lipid extracts (5%, v:v) primed for enhanced superoxide production compared to buffer controls (2.5-fold and 3.6-fold), sham (2.5-fold) and pre-shock lymph (2.0-fold). Lymph collected after systemic PLA2 inhibition, in contrast, abrogated the PMN priming response. Gut mucosal morphology, at end-resuscitation, was intact on HE staining both with and without PLA2 inhibition. Heat denaturing the PHSML (eliminating cytokines and complement), on the other hand, did not reduce PMN priming. Physiologic concentrations of PHSML lipids prime the PMN respiratory burst. Lymph priming is diminished with systemic PLA2 inhibition, implicating gut PLA2 as a source of proinflammatory lipids that may be central in the pathogenesis of hemorrhagic shock induced ARDS/MOF.

Cytosolic phospholipase A(2)-mediated ICAM-1 expression is calcium dependent

BACKGROUND

Some human malignancies such as virus-related hepatocellular cancer arise in a setting of chronic inflammation. Upregulation of ICAM-1 is a seminal late event in malignant transformation following chronic inflammation. Cytosolic phospholipase A(2) (cPLA(2)) is a lipid-mediator activated by inflammatory stimuli, which has been shown to mediate ICAM-1 upregulation. As lipid mediators are known to work via calcium-dependent mechanisms in nearly all mammalian cells, we hypothesize that inflammatory-mediated ICAM-1 upregulation is dependent on both cPLA(2) and intracellular calcium.

MATERIALS AND METHODS

HUVEC were chosen as a representative cell line as they emulate hepatic sinusoids and are a well-established cell model. These were grown to confluence in T-25 flasks and stimulated with TNF-alpha or LPS for 6 h. Additional groups were preincubated with AACOCF3 (a specific cPLA(2) inhibitor) or BAPTA A.M. (a specific inhibitor of intracellular Ca(2+)) prior to being exposed to inflammatory stimuli. ICAM-1 expression was determined by mean fluorescent intensity (MFI) as measured by FITC-labeled moAb to ICAM-1 via FACS. The role of intracellular Ca(2+) on cPLA(2) activity was determined by thin-layer chromatography. Groups were compared using ANOVA with Scheffe's post hoc analysis; *P < 0.05 vs control, daggerP < 0.05 vs LPS and TNF-alpha was considered significant; N > or = 4 all experimental groups.

RESULTS

Both cPLA(2) and Ca(2+) inhibition significantly inhibited inflammatory upregulation of ICAM-1. Pretreatment with BAPTA A.M. attenuated HUVEC cPLA(2) activity in response to LPS. These findings suggest that appropriate molecular target suppression may prevent malignant degeneration in the presence of chronic inflammation.

Phospholipase A(2)--derived neutral lipids from posthemorrhagic shock mesenteric lymph prime the neutrophil oxidative burst

BACKGROUND

Our previous work identified posthemorrhagic shock mesenteric lymph (PHSML) lipids as key elements in polymorphonuclear neutrophil (PMN)--provoked acute lung injury. We hypothesize that gut phospholipase A(2) (PLA(2)) is responsible for the generation of proinflammatory lipids in PHSML that primes circulating PMNs for enhanced oxidative burst.

METHODS

Mesenteric lymph was collected from rats (n = 5) before (preshock), during the induction of hemorrhagic shock (mean arterial pressure, 40 mm Hg x 30 minutes), and at resuscitation (shed blood + 2x lactated Ringer's solution). PLA(2) inhibition (quinacrine, 10 mg/kg, intravenously) was given before shock was induced. Extracted lipids were separated by normal phase high-pressure liquid chromatography and resuspended in albumin. PMNs were exposed to a 5% vol:vol concentration of eluted lipids and activated with N-formyl-methionyl-leucyl-phenylalanine (1 micromol/L). Superoxide production was assessed by cytochrome C reduction.

RESULTS

High-pressure liquid chromatography--extracted neutral lipids of lymph collected before hemorrhagic shock did not prime the PMN oxidase, whereas isolated neutral lipids of postshock lymph primed PMNs 2.6- +/- 0.32-fold above baseline (P <.05). PLA(2) inhibition returned PHSML neutral lipid priming to baseline levels.

CONCLUSIONS

PLA(2) inhibition before hemorrhagic shock abrogates the neutrophil priming effects of PHSML through reduction of the accumulation of proinflammatory neutral lipids. Identification of these PLA(2)-dependent lipids provides a mechanistic link that may have therapeutic implications for postshock acute lung injury.

Ionomycin causes activation of p38 and p42/44 mitogen-activated protein kinases in human neutrophils

Many receptor-linked agents that prime or activate the NADPH oxidase in polymorphonuclear neutrophils (PMNs) elicit changes in cytosolic Ca2+ concentration and activate mitogen-activated protein (MAP) kinases. To investigate the role of Ca2+ in the activation of p38 and p42/44 MAP kinases, we examined the effects of the Ca2+-selective ionophore ionomycin on priming and activation of the PMN oxidase. Ionomycin caused a rapid rise in cytosolic Ca2+ that was due to both a release of cytosolic Ca2+ stores and Ca2+ influx. Ionomycin also activated (2 microM) and primed (20-200 nM) the PMN oxidase. Dual phosphorylation of p38 MAP kinase and phosphorylation of its substrate activating transcription factor-2 were detected at ionomycin concentrations that prime or activate the PMN oxidase, while dual phosphorylation of p42/44 MAP kinase and phosphorylation of its substrate Elk-1 were elicited at 0.2-2 microM. SB-203580, a p38 MAP kinase antagonist, inhibited ionomycin-induced activation of the oxidase (68 +/- 8%, P < 0.05) and tyrosine phosphorylation of 105- and 72-kDa proteins; conversely, PD-98059, an inhibitor of MAP/extracellular signal-related kinase 1, had no effect. Treatment of PMNs with thapsigargin resulted in priming of the oxidase and activation of p38 MAP kinase. Chelation of cytosolic but not extracellular Ca2+ completely inhibited ionomycin activation of p38 MAP kinase, whereas chelation of extracellular Ca2+ abrogated activation of p42/44 MAP kinase. These results demonstrate the importance of changes in cytosolic Ca2+ for MAP kinase activation in PMNs.

Secretory phospholipase A2 activity correlates with postinjury multiple organ failure

Postinjury multiple organ failure (MOF) may result from overwhelming systemic hyperinflammation. Secretory phospholipase A2 (sPLA2) produces many inflammatory lipid mediators, and levels have been correlated with both the severity of patient injury and postinjury mortality. The objective of this study was to characterize the plasma activity of sPLA2 type IIa in severely injured patients and to determine whether the activity of this enzyme correlates with the subsequent development of MOF.

PATIENTS

Seventeen severely injured patients at known risk for MOF had blood sampled on postinjury days 0, 1, 2, 3, and 5.

DESIGN

sPLA2 activity was sequentially measured and correlated with MOF scores.

RESULTS

Six patients (35%) developed MOF. In comparison with non-MOF patients, MOF patients had elevated sPLA2 activity beginning 36 hrs postinjury (MOF sPLA2, 2.4 +/- 0.97, vs. non-MOF sPLA2, 0.86 +/- 0.16 active units (AU); p < .05) and continuing over the ensuing 5 days. To rule out the possibility that stored blood components required for patient resuscitation was the source of sPLA2, the sPLA2 was measured in packed red blood cells, platelet concentrates, and fresh frozen plasma over the routine storage time. None of the products tested had elevated levels of sPLA2 compared with fresh plasma from healthy adult volunteers.

CONCLUSIONS

We conclude that increased sPLA2 activity is associated with the development of postinjury MOF.

Hypertonic saline attenuation of the neutrophil cytotoxic response is reversed upon restoration of normotonicity and reestablished by repeated hypertonic challenge

BACKGROUND

Hypertonic saline (HTS) resuscitation, in addition to enhancing hemodynamic recovery, modulates postinjury hyperinflammation in the critically injured. The polymorphonuclear neutrophil (PMN) cytotoxic response, a key element in the pathogenesis of postinjury organ dysfunction, is attenuated under hypertonic conditions. Although plasma Na(+) rises to 180 mmol/L after HTS infusion, baseline levels are reestablished within 24 hours. We hypothesized that HTS attenuation of the PMN cytotoxic response (beta2-integrin expression, elastase release, and O2- production) is reversed upon return to normotonicity, but can be reestablished by repeated HTS challenge.

METHODS

Isolated human PMNs were incubated in HTS (Na(+) = 180 mmol/L) for 5 minutes at 37 degrees C then returned to normotonicity by centrifugation and resuspension in isotonic buffer. Stimulated (PAF) beta2-integrin expression was measured by flow cytometry. Stimulated (PAF/fMLP) elastase release and O2- production were measured by cleavage of N-methoxysuccinyl-Ala-Ala-Pro-Val p-nitroanilide and reduction of cytochrome c (Cyt c). Protein tyrosine phosphorylation in PMN cell lysates was assessed by Western blot.

RESULTS

Clinically relevant levels of HTS induced tyrosine phosphorylation in resting PMNs and attenuated cytotoxic responses. Reestablishment of normotonicity returned these functions to baseline. A repeated HTS challenge after restoration of normotonicity also induced tyrosine phosphorylation and suppressed the cytotoxic response.

CONCLUSIONS

HTS attenuation of the PMN cytotoxic response is reversible but can be reestablished by repeated HTS treatment. This phenomenon may provide the unique opportunity to selectively and temporarily decrease the postinjury inflammatory response when patients are at greatest risk for PMN-mediated tissue damage.

Blood transfusion and the two-insult model of post-injury multiple organ failure

Neutrophils (PMNs) have been implicated in the pathogenesis of multiple organ failure (MOF). The two-insult model of MOF is based on the fundamental concept that two sequential and independent insults that are individually innocuous against the host can cause overwhelming inflammation. The in vitro PMN priming/activation sequence simulates the two-insult model. Our work has demonstrated that transfusion is an early consistent risk factor for post-injury MOF and lysophosphatidylcholines (lyso-PCs) are generated in stored blood components. Additionally, platelet-activating factor (PAF) is a key inflammatory agent produced in severely injured patients. We therefore hypothesize that two events, trauma and transfusion, enhance PMN cytotoxicity irrespective of the sequence. Superoxide (O2-) production was measured by reduction of cytochrome c, adherence to fibrinogen was assessed by the radioactivity of adherent Na2(51)CrO4 (51Cr)-labeled PMNs, and endothelial cell (EC) damage by measuring the radioactivity released from 51Cr-labeled human umbilical vein endothelial cells monolayers. Isolated PMNs were primed with buffer, PAF (2 microM), or lyso-PCs (4.5, 15, and 30 microM) followed by activation with buffer, N-formyl-methionyl-leucyl-phenylalanine (fMLP) (1 microM), PAF (2 microM), or lyso-PCs (4.5, 15, and 30 microM). Neither PAF nor lyso-PCs alone stimulated O2- production. While PAF alone caused PMN adherence, lyso-PCs alone did not allowed PMNs to adhere to fibrinogen. However, both combinations of PAF/lyso-PCs and lyso-PCs/PAF significantly augmented O2- production and PMN adherence. Furthermore, these enhanced PMN cytotoxic responses significantly caused EC damage. These findings suggest that in the scenario of the two-insult model, early or late transfusion administered following trauma can provoke PMN cytotoxicity via priming or activation, thereby increasing the risk of post-injury MOF.

Transfusion-related acute lung injury secondary to biologically active mediators

Transfusion-related acute lung injury is seen following the transfusion of blood components. The reported incidence is approximately 1 in 2000 transfusions. Clinically, it is similar to adult respiratory distress syndrome. The pathophysiology is unclear but has been attributed to HLA antibodies, granulocyte antibodies, and more recently to biologically active mediators in stored blood components. We report a case with laboratory evidence that supports the role of biologically active mediators in the pathogenesis of transfusion-related acute lung injury. To our knowledge, the case reported here is the first to use lipid extractions of patient samples to determine that lipid-priming activity was present at the time transfusion-related acute lung injury was identified clinically.

Plasma from aged stored red blood cells delays neutrophil apoptosis and primes for cytotoxicity: abrogation by poststorage washing but not prestorage leukoreduction

BACKGROUND

Blood transfusion-particularly that of older stored red blood cells (RBCs)--is an independent risk factor for postinjury multiple organ failure. Immunomodulatory effects of RBC transfusion include neutrophil (PMN) priming for cytotoxicity, an effect exacerbated by longer RBC storage times. We have found that delayed PMN apoptosis in trauma patients is provoked by transfusion, independent of injury severity. We hypothesized that aged stored RBCs delay PMN apoptosis, but that prestorage leukodepletion or poststorage washing could abrogate the effect.

METHODS

Healthy volunteers each donated 1 unit of blood. One half was leukodepleted, and RBC units were processed in the usual fashion and stored at 4 degrees C. Aliquots were removed on days 1, 14, 21, and 42 and the plasma fraction isolated. Selected aliquots were washed with normal saline before plasma isolation. PMNs harvested from healthy controls were incubated (5% CO2, 37 degrees C) with unmodified, leukoreduced, or washed RBC plasma (20% plasma/80% RPMI 1640), and apoptosis assessed by morphology after 24 hours. Apoptotic index (apoptotic PMNs/total PMNs) was compared. PMN priming for superoxide release was also assessed after plasma exposure.

RESULTS

PMN apoptosis was delayed by RBCs stored for 21 or 42 days. Prestorage leukodepletion did not alter the effect. However, washing 42-day-old RBCs abrogated the effect. PMN priming for superoxide was provoked by stored packed RBCs in an identical pattern to delayed apoptosis.

CONCLUSION

Plasma from stored RBCs-even if leukoreduced-delays apoptosis and primes PMNs. The effect becomes evident at 21 days and worsens through product outdate (42 days), but may be prevented by poststorage washing. Inflammatory agents contaminating stored blood likely mediate the effect. Modification of transfusion practices (e.g., giving fresher or washed RBCs or blood substitutes) may attenuate adverse immunomodulatory effects of transfusion in trauma patients.

Resuscitation with a blood substitute abrogates pathologic postinjury neutrophil cytotoxic function

BACKGROUND

Resuscitation with oxygen-carrying fluids is critically important in the patient with hemorrhagic shock caused by trauma. However, it is clear that a number of biologic mediators present in stored blood (packed red blood cells [PRBCs]) have the potential to exacerbate early postinjury hyperinflammation and multiple organ failure through priming of circulating neutrophils (PMNs). PolyHeme (Northfield Laboratories, Evanston, IL), a hemoglobin-based substitute that is free of priming agents, provides an alternative. We hypothesized that PMN priming would be attenuated in patients resuscitated with PolyHeme in lieu of stored blood.

METHODS

Injured patients requiring urgent transfusion were given either PolyHeme (up to 20 units) or PRBCs. Early postinjury PMN priming was measured via beta-2 integrin expression, superoxide production, and elastase release.

RESULTS

Treatment groups were comparable with respect to extent of injury and early physiologic compromise. PMNs from patients resuscitated with PRBCs showed priming in the early postinjury period by all three measures. No such priming was evident in patients resuscitated with PolyHeme.

CONCLUSION

The use of a blood substitute in the early postinjury period avoids PMN priming and may thereby provide an avenue to decrease the incidence or severity of postinjury multiple organ failure.

The lipid fraction of post-hemorrhagic shock mesenteric lymph (PHSML) inhibits neutrophil apoptosis and enhances cytotoxic potential

Dysfunctional neutrophil (PMN) apoptosis facilitates hyperinflammatory tissue injury. Previous work has demonstrated that post-hemorrhagic shock mesenteric lymph (PHSML) provokes PMN-mediated acute lung injury in animal models, but the mechanism remains unclear. We have documented that the lipid fraction of PHSML is responsible for PMN priming of the respiratory burst. In this study, we hypothesized that PHSML lipids delay PMN apoptosis and thereby further enhance PMN cytotoxic potential. Mesenteric lymph was collected from rats (n = 5) before (control), during non-lethal hemorrhagic shock (MAP 40 mmHg, 30 min), and during resuscitation (shed blood + 2x crystalloid). Human PMNs were incubated with control, PHSML, PHSML lipid extracts, and heat-treated PHSML (60 degrees C, 30 min.) at 1-10% (v:v) in RPMI 1640 for 24 h. Apoptosis was assessed using acridine orange/ethidium bromide staining and fluorescence microscopy. Priming of the respiratory burst was evaluated by incubating PMNs with (a) control PHSML or (b) PHSML lipid extracts for 24 h and by activating with fMLP (1 micromol/L). PHSML and PHSML lipid extracts (5-10%) inhibited PMN apoptosis. Heat denaturing the PHSML (to eliminate cytokines and complement) had no effect on the inhibition of PMN apoptosis. Similarly, incubation with polymixin B at a concentration that binds endotoxin had no effect. Both the PHSML and PHSML lipids (5%) following 24-h incubation primed the fMLP-activated oxidase. At physiologic concentrations, both PHSML and the lipid fraction of PHSML delay PMN apoptosis and prime the NADPH oxidase. These data further implicate the lipid components of mesenteric lymph as central in the pathogenesis of hemorrhagic shock induced PMN-mediated acute lung injury.

Hypertonic saline inhibits neutrophil (PMN) priming via attenuation of p38 MAPK signaling

Priming of the neutrophil cytotoxic response is central to the pathogenesis of early postinjury multiple organ failure (MOF). Platelet-activating factor (PAF) has been implicated as a key inflammatory mediator in postinjury neutrophil priming and requires p38 MAPK signaling to produce its biologic effects. Hypertonic saline (HTS) resuscitation decreases the postinjury inflammatory response following shock in animals and decreases receptor-mediated neutrophil (PMN) cytotoxic functions in vitro. We hypothesized that HTS attenuates PAF priming of the PMN cytotoxic response by interfering with PAF-mediated p38 MAPK signal transduction. Isolated PMNs were preincubated in isotonic buffer or HTS (Na+ = 180 mM), then primed with PAF. Neutrophil CD11b/CD18 expression was measured by flow cytometry. Receptor-dependent (fMLP), N-formyl-methionyl-leucyl-phenylalanine, fMLP) and receptor-independent (PMA) O2- production was measured by reduction of cytochrome c in resting and PAF primed PMNs. Total p38 MAPK protein PAF-mediated p38 MAPK activation was assessed by western blot of PMN lysates. Clinically relevant levels of HTS attenuated PAF-mediated beta2-integrin expression. While HTS attenuated receptor-dependent (fMLP and PAF/fMLP) O2- production, receptor-independent (PMA) O2- production was unaffected. Conversely, HTS attenuated PAF priming of PMA-mediated O2- production. PAF and HTS did not alter total cellular p38 MAPK content. Clinically relevant levels of HTS alone did not activate p38 MAPK but inhibited PAF mediated p38 MAPK activation. HTS attenuates PAF priming of the PMN cytotoxic response by altering intracellular signal transduction. Therefore, HTS resuscitation may attenuate postinjury PMN priming and ultimately the risk of developing MOF.

Hypertonic saline attenuation of polymorphonuclear neutrophil cytotoxicity: timing is everything

BACKGROUND

The potential to modulate the inflammatory response has renewed interest in hypertonic saline (HTS) resuscitation of injured patients. However, the effect of the timing of HTS treatment with respect to polymorphonuclear neutrophil (PMN) priming and activation remains unexplored. We hypothesized that HTS attenuation of PMN functions requires HTS exposure before priming and activation.

METHODS

Isolated PMN were incubated in HTS (180 mM Na+) before L-alpha-phosphatidylcholine, beta-acetyl-gamma-O-alkyl (PAF)/N-formylmethionyl-leucyl-phenylalanine (fMLP) priming/activation, after priming, or after priming/activation. Superoxide production was measured by the reduction cytochrome c, elastase release by cleavage of AAPV-pNA, and beta2-integrin expression by flow cytometry.

RESULTS

HTS before priming or activation decreased beta2-integrin expression, superoxide production, and elastase release. In contrast, HTS after priming/activation augmented superoxide production and elastase release.

CONCLUSION

The timing of HTS is a key variable in the attenuation of PMN cytotoxic functions. Maximal attenuation of cytotoxicity is achieved before priming, whereas HTS exposure after activation augments cytotoxicity.

Maximal human neutrophil priming for superoxide production and elastase release requires p38 mitogen-activated protein kinase activation

HYPOTHESIS

Neutrophil priming has been implicated in the development of multiple organ failure, although the precise intracellular mechanisms that regulate neutrophil priming remain unclear. Our previous work characterized platelet-activating factor (PAF) priming of human neutrophils for concordant superoxide anion (O2-) generation and elastase degranulation. The p38 mitogen-activated protein kinase (MAPK) is activated by PAF stimulation. We hypothesized that PAF-induced human neutrophil priming for O2- and elastase release is mediated via the p38 MAPK pathway.

DESIGN

Isolated neutrophils from 6 human donors were preincubated with the specific p38 MAPK inhibitor SB 203580 (1 micromol/L) or buffer (control) for 30 minutes. Cells were then primed with PAF (200 nmol/L), followed by receptor-dependent (N-formyl-methionyl-leucyl-phenylalanine, 1 micromol/L) or receptor-independent phorbol myristate acetate (PMA, 100 ng/mL) activation.

SETTING

Urban trauma research laboratory.

PATIENTS

Healthy volunteer donors of neutrophils.

MAIN OUTCOME MEASURES

Maximal rate of O2- generation was measured by superoxide dismutase-inhibitable reduction of cytochrome c and elastase release by the cleavage of N-methoxysuccinyl-Ala-Ala-Pro-Val-p-nitroanilide.

RESULTS

SB 203580 significantly attenuated the generation of O2- and release of elastase from neutrophils activated with N-formyl-methionyl-leucyl-phenylalanine but not with PMA. Independent of the activator receptor status, SB 203580 almost completely blocked the exaggerated neutrophil cytotoxic response due to PAF priming.

CONCLUSIONS

The p38 MAPK pathway is required for maximal PAF-induced neutrophil priming for O2- production and elastase degranulation. Therefore, the MAPK signaling cascade may offer a potential therapeutic strategy to preempt global neutrophil hyperactivity rather than attempt to nullify the end products independently.

Stored red blood cells selectively activate human neutrophils to release IL-8 and secretory PLA2

Packed red blood cell (PRBC) transfusion has been invoked previously with immunosuppression and increased infections, but it has now been demonstrated that stored PRBCs (>14 days) can prime PMNs and provoke multiple organ failure. Recently, the role of PMNs in the genesis of MOF has been extended to their release of inflammatory cytokines, notably IL-1, IL-8, TNFalpha, and secretory phospholipase A2 (sPLA2). We hypothesize that stored PRBCs can act as a second event via stimulating the release of inflammatory cytokines from PMNs. Isolated human PMNs were incubated for 24 h in RPMI with either 20% fresh plasma or plasma from 42 day old PRBC (day of outdate) and release of IL-8, IL-1beta, TNFalpha, and sPLA2 were measured. Plasma from stored PRBCs contained small amounts of IL-8, sPLA2, and TNFalpha (102.1 +/-5.6 pg/ml, 87.6+/-6.0 pg/ml and 9.7+/-.7 pg/ml). Levels of IL-1beta were below detection (<1 pg/ml). Day 42 PRBC plasma stimulated significant PMN release of both IL-8 and sPLA2 as compared to both control and day 0 plasma (*P < .05), but PRBC plasma did not stimulate PMN release of either IL-1beta or TNFalpha. Transfused blood is emerging as an inflammatory agent that is capable of producing PMN priming. In this study we have demonstrated that PRBC plasma selectively activates PMNs to release both IL-8 and sPLA2. Thus, transfusion of PRBCs may represent a preventable inflammatory insult via modification of both blood banking and transfusion practices.

Hypertonic saline resuscitation abrogates neutrophil priming by mesenteric lymph

OBJECTIVE

Neutrophil (PMN) priming after hemorrhagic shock is predictive of the subsequent development of multiple organ failure, but the mechanism remains unknown. Recently, we and others have demonstrated that mesenteric lymph from shock animals resuscitated with lactated Ringer's solution (LR) is not only a potent PMN priming agent but also causes lung injury. Work by others has shown that resuscitation with hypertonic saline (HTS) protects animals from lung injury after hemorrhagic shock. Therefore, we hypothesize that resuscitation with HTS will abolish PMN priming by postshock mesenteric lymph.

METHODS

After mesenteric lymph duct catheterization, male rats underwent hemorrhagic shock (mean arterial pressure of 40 mm Hg for 90 minutes) and resuscitation with shed blood plus either LR (2x volume of shed blood) or 4 mL/kg of 7% HTS (isonatremic). Priming for superoxide by PMN was measured after fMLP (1 microM) activation.

RESULTS

Shock significantly decreased mesenteric lymph flow from preshock levels in both groups. LR resuscitation produced significantly more mesenteric lymph than HTS resuscitation. Mesenteric lymph from LR animals primed PMN for superoxide production, whereas, HTS eliminated this priming.

CONCLUSION

HTS not only decreases postshock mesenteric lymph production, it eliminates PMN priming by mesenteric lymph, suggesting a mechanism for the beneficial effects of HTS resuscitation.

Age of transfused blood is an independent risk factor for postinjury multiple organ failure

BACKGROUND

Blood transfusion has repeatedly been demonstrated to be an independent risk factor for postinjury multiple organ failure (MOF). Previously believed to represent a surrogate for shock, packed red blood cell (PRBC) transfusion has recently been shown to result in neutrophil priming and pulmonary endothelial cell activation. We have previously observed that the generation of inflammatory mediators is related to the length of PRBC unit storage. The purpose of this study was to determine if age of transfused PRBC is a risk factor for the development of postinjury MOF.

METHODS

Using our prospective database of trauma patients at risk for developing MOF, we identified patients who developed MOF (MOF+) and received 6 to 20 units of PRBCs in the first 12 hours following injury. A similar cohort of patients, matched for ISS and transfusion requirement, who did not develop MOF (MOF-) were also identified. The age of each unit of PRBC transfused in the first 6 hours was determined. Multiple logistic regression was performed to determine if age of transfused blood is an independent risk factor.

RESULTS

Sixty-three patients were identified, 23 of whom were MOF+. There was no difference in ISS and transfusion requirement between MOF+ and MOF- groups. MOF+ patients, however, were significantly older (46+/-4.7 years versus 33+/-2.3 years). Moreover, mean age of transfused blood was greater in the MOF+ patients (30.5+/-1.6 days versus 24+/-0.5 days). Similarly, the mean number of units older than 14 and 21 days old were greater in the MOF+ patients. Multivariate analysis identified mean age of blood, number of units older than 14 days, and number of units older than 21 days as independent risk factors for MOF.

CONCLUSION

The age of transfused PRBCs transfused in the first 6 hours is an independent risk factor for postinjury MOF. This suggests that current blood bank processing and storage technique should be reexamined. Moreover, fresh blood may be more appropriate for the initial resuscitation of trauma patients requiring transfusion.

Extracellular signal-related kinase 1/2 and p38 mitogen-activated protein kinase pathways serve opposite roles in neutrophil cytotoxicity

BACKGROUND

Inflammatory stimuli rapidly activate mitogen-activated protein kinases (MAPKs) in neutrophils (PMNs). However, their role in cytotoxic function remains unknown. Elucidating the signals involved in release of cytotoxic agents from PMNs may provide new avenues for therapy in diseases of diminished or excessive PMN function.

HYPOTHESIS

The p38 MAPK and extracellular signal-related kinase 1/2 (ERK1/2) modulate superoxide generation and elastase release in activated human PMNs.

STUDY DESIGN

Isolated human PMNs were incubated with specific inhibitors of MAPK pathways, or vehicle control solution, before activation with the bacterial peptide f-Met-Leu-Phe.

MAIN OUTCOME MEASURES

The rate of superoxide release from activated PMNs was measured by the superoxide dismutase-inhibitable reduction of cytochrome-c. Elastase release from PMNs was determined by cleavage of the substrate Ala-Ala-Pro-Val-pNA.

RESULTS

Superoxide release from activated PMNs was inhibited by blockade of p38 MAPK activation but unaffected by blockade of ERK1/2. Conversely, elastase release was unaffected by p38 MAPK inhibition and increased by ERK1/2 inhibition.

CONCLUSIONS

Activation of p38 MAPK promotes superoxide release from PMNs activated by f-Met-Leu-Phe. The ERK1/2 pathway may serve as a negative feedback mechanism for granule exocytosis.

Cardiopulmonary bypass renders patients at risk for multiple organ failure via early neutrophil priming and late neutrophil disability

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with a systemic inflammatory response syndrome (SIRS) and these patients are recognized to be at increased risk for delayed infectious complications. We have documented that circulating neutrophils (PMNs) from patients manifesting SIRS have evidence of early postinjury priming for cytotoxicity. Consequently, we hypothesized that CPB would result in early postoperative PMN hyperresponsiveness (priming).

MATERIALS AND METHODS

Six patients (mean age 50 +/- 2.9 years) who underwent CPB for CABG had sequential blood samples obtained perioperatively. PMNs were isolated and superoxide anion (O(-)(2)) generation (nmol O(-)(2)/3.75 x 10(5) PMNs/min) was measured by reduction of cytochrome c after exposure to fMLP, C5a, or PMA; elastase release (% total PMN elastase content) was measured by cleavage of AAPV-pNA after exposure to fMLP or C5a.

RESULTS

PMNs were activated for increased elastase release 6 h after initiation of CPB. Significant PMN priming for O(-)(2) production was discovered at 3, 6, and 12 h following CPB and for elastase release at 3 and 6 h after CPB. At 2 to 3 days after CPB, O(-)(2) generation was significantly less than that of the preoperative control. Neutrophil primability with PAF was detected at 6 h after CPB. A similar defect in PAF-primable O(-)(2) production was seen 2 and 3 days post-CPB. Direct PMN interrogation with the receptor-independent activator PMA revealed loss of integrity of the NADPH oxidase at 2 and 3 days following CPB.

CONCLUSIONS

A vulnerable window exists between 3 and 12 h after CPB when PMNs are primed for enhanced cytotoxicity via O(-)(2) production and elastase release. Paradoxically, PMN oxidase integrity becomes deficient 48 h post-CPB, while protease degranulation remains intact. These events render the bypass patient at risk for multiple organ failure via both early PMN-mediated tissue injury and delayed infectious complications.

Neutrophils are primed for cytotoxicity and resist apoptosis in injured patients at risk for multiple organ failure

BACKGROUND

Postinjury multiple organ failure (MOF) is the result of a dysregulated systemic inflammatory response in which primed neutrophils (PMNs) are sequestered in tissues, vulnerable to activation through secondary insults. Apoptosis is critical to the normal clearance of these sequestered PMNs. Conversely, dysfunctional apoptosis prolongs the PMN functional life span, potentially exacerbating PMN-mediated tissue injury and the development of MOF. We hypothesized that severe trauma, in addition to priming PMNs, provokes dysfunctional PMN apoptosis.

METHODS

Neutrophils were harvested daily from 12 severely injured patients at high risk for MOF, cultured for 24 hours, and assessed for apoptosis with use of acridine orange-ethidium bromide staining and fluorescence microscopy. Priming for elastase release was measured in freshly isolated patient PMNs. Plasma from patients was assessed for its ability to delay apoptosis of normal PMNs.

RESULTS

Four patients (33%) had MOF. Neutrophil apoptosis was profoundly delayed in severely injured patients throughout the 5-day study period. Priming for elastase release was augmented concomitantly. Patients' plasma delayed apoptosis of normal PMNs.

CONCLUSION

In patients at high risk for postinjury MOF, PMNs are not only primed for cytotoxicity but also resist apoptosis. The dysfunctional apoptosis is attributed, at least in part, to a plasma-borne mediator. The net effect may facilitate hyperinflammatory organ injury.