Cytokine activation through sublethal hemorrhage is protective against early lethal endotoxic challenge

Sophorolipids block lethal effects of septic shock in rats in a cecal ligation and puncture model of experimental sepsis*

OBJECTIVE

Sophorolipids, a family of natural and easily chemoenzymatically modified microbial glycolipids, are promising modulators of the immune response. The potential of the therapeutic effect of sophorolipids was investigated in vivo in a rat model of sepsis and in vitro by analysis of nitric oxide and cytokine production.

DESIGN

Prospective, randomized animal study.

SETTING

Experimental laboratory.

SUBJECTS

Male Sprague-Dawley rats, 200-240 g.

INTERVENTIONS

Intra-abdominal sepsis was induced in vivo in 166 rats via cecal ligation and puncture (CLP); 60 rats were used to characterize the model. The remaining rats were treated with sophorolipids or vehicle (dimethylsulfoxide [DMSO]/physiologic saline) by intravenous (iv) tail vein or intraperitoneal (IP) injection immediately post-CLP (25/group). Survival rates were compared at 36 hrs after surgery. In vitro, macrophages were cultured in lipopolysaccharide (LPS) +/- sophorolipid and assayed for nitric oxide (NO) production and gene expression profiles of inflammatory cytokines. In addition, splenic lymphocytes isolated from CLP rats +/- sophorolipid treatment (three per group) were analyzed for cytokine production by RNase protection assay.

MEASUREMENTS AND MAIN RESULTS

CLP with 16-gauge needles optimized sepsis induction and resultant mortality. Sophorolipid treatment improved rat survival by 34% (iv) and 14% (IP) in comparison with vehicle controls (p < .05 for iv treatment). Sophorolipids decreased LPS-induced macrophage NO production by 28% (p < .05). mRNA expression of interleukin (IL)-1beta was downregulated by 42.5 +/- 4.7% (p < .05) and transforming growth factor (TGF)-beta1 was upregulated by 11.7 +/- 1.5% (p < .05) in splenocytes obtained 6 hrs postsophorolipid treatment. LPS-treated macrophages cultured 36 hrs with sophorolipids showed increases in mRNA expression of IL-1alpha (51.7%), IL-1beta (31.3%), and IL-6 (66.8%) (p < .05).

CONCLUSIONS

Administration of sophorolipids after induction of intra-abdominal sepsis significantly decreases mortality in this model. This may be mediated in part by decreased macrophage NO production and modulation of inflammatory responses.

MAGNOLOL ALTERS THE COURSE OF ENDOTOXIN TOLERANCE AND PROVIDES EARLY PROTECTION AGAINST ENDOTOXIN CHALLENGE FOLLOWING SUBLETHAL HEMORRHAGE IN RATS

The endotoxin tolerance induced by sublethal hemorrhage (SLH) is associated with an initial surge of proinflammatory cytokines such as TNF-alpha. Magnolol, a potent antioxidative herb, is hypothesized to suppress TNF-alpha production after SLH and to alter or attenuate subsequent endotoxin tolerance. A prospective, randomized experimental study was performed. Male Sprague-Dawley rats were randomly segregated into one of four groups. Rats in the Sham/Veh and Sham/Mag groups received a sham operation for SLH and treatment with vehicle or magnolol, respectively. Rats in the SLH/Veh and SLH/Mag groups received SLH and treatment with vehicle or magnolol, respectively. Animals were subjected to endotoxin challenge (EC) at 12, 24, or 36 h after these procedures. Cytokines (TNF-alpha and IL-10), lipid peroxidation, and superoxide dismutase (SOD) activity were measured in lung tissue following SLH. Plasma cytokines were assessed after SLH or EC at different time points, and survival analyses were performed after EC. Plasma and tissue TNF-alpha increased after SLH; this increase was significantly suppressed by magnolol. Additionally, a significant increase in plasma and tissue IL-10 after SLH was observed in the SLH/Mag group. Lipid peroxidation and SOD activity increased after SLH; magnolol suppressed the lipid peroxidation but not the SOD activity. If EC was performed 12 or 24 h after SLH, greater survival with decreased TNF-alpha and increased IL-10 in plasma was observed in the SLH/Mag group. If EC was performed 24 or 36 h after SLH, greater survival with decreased plasma TNF-alpha was observed in the SLH/Veh group. In conclusion, magnolol induces an antiinflammatory response and provides early protection against EC following SLH; however, magnolol attenuates the protraction of endotoxin tolerance and inhibits late protection against EC following SLH.

Cecropin B enhances betalactams activities in experimental rat models of gram-negative septic shock

OBJECTIVE

To investigate the efficacy of imipenem, piperacillin combined with cecropin B in the prevention of lethality in 2 rat models of septic shock. Main outcome measures were bacterial growth in blood and intra-abdominal fluid, endotoxin and TNF-alpha concentrations in plasma, and lethality.

BACKGROUND

Sepsis remains a serious clinical problem despite intense efforts to improve survival. It is a major cause of morbidity and mortality in hospitalized patients. The primary cause of Gram-negative shock results from activation of host effector cells by endotoxin, the lipopolysaccharide (LPS) associated with cell membranes of Gram-negative bacteria.

METHODS

Adult male Wistar rats were given (1). an intraperitoneal injection of 1 mg of Escherichia coli 0111:B4 LPS or (2). 2 x 1010 CFU of E. coli ATCC 25922. All animals were randomized to receive intraperitoneally isotonic sodium chloride solution, 1 mg/kg cecropin B, 20 mg/kg imipenem, and 120 mg/kg piperacillin alone and combined with 1 mg/kg cecropin B. Each group included 20 animals. RESULTS All compounds reduced the lethality when compared with controls. Piperacillin and imipenem significantly reduced the lethality and the number of E. coli in abdominal fluid compared with saline treatment. On the other hand, each betalactam determined an increase of plasma endotoxin and TNF-alpha concentration. Combination between cecropin B and betalactams showed to be the most effective treatment in reducing all variables measured.

CONCLUSION

Cecropin B enhances betalactams activities in Gram-negative sepic shock rat models.

Antiendotoxin activity of protegrin analog IB-367 alone or in combination with piperacillin in different animal models of septic shock

The therapeutic efficacy of protegrin peptide IB-367 was investigated in three rat models of septic shock: (i) rats injected intraperitoneally with 1mg Escherichia coli 0111:B4 lipopolysaccharide, (ii) rats given an intraperitoneal injection of 2 X 10(10) CFU of E. coli ATCC 25922, and (iii) rats in which intra-abdominal sepsis was induced via cecal ligation and puncture. All animals were randomized to receive parenterally isotonic sodium chloride solution, 1mg/kg of IB-367, 60mg/kg piperacillin and 1mg/kg of IB-367 plus 60mg/kg piperacillin. The peptide demonstrated lower level of antimicrobial activity than piperacillin, nevertheless it exhibited the dual properties of antimicrobial and antiendotoxin agent. Finally IB-367 and piperacillin association showed to be the most effective therapeutic approach.

Antiendotoxin activity of antimicrobial peptides and glycopeptides

An animal study was performed to investigate the efficacy of two glycopeptides and two cationic peptides in the prevention of lethality in a septic shock rat model. Adult Wistar rats were given an intraperitoneal injection of 2x10(10) CFU of Escherichia coli ATCC 25922, with the exception of an uninfected control group (C0). Animals were randomized to receive, immediately after bacterial challenge, intraperitoneally isotonic sodium chloride solution (control group C1), 3 mg/Kg teicoplanin (group 1), 7 mg/Kg vancomycin (group 2), 1 mg/Kg colistin (group 3), 1 mg/Kg buforin II (group 4), or 60 mg/Kg piperacillin (group C(PIP)). In addition, four groups (1a, 2a, 3a, and 4a) received the above mentioned drugs in combination with piperacillin. All compounds and combinations significantly reduced the lethality and the number of E. coli in abdominal fluid compared with C1 group, with the exception of the glycopeptides. Colistin and buforin II combined with piperacillin significantly decreased the lethality compared with piperacillin alone. Finally, colistin, buforin II, and teicoplanin significantly reduced plasma endotoxin concentration in comparison with piperacillin and saline treatment. Antimicrobial peptides and teicoplanin act as antiendotoxin agents and enhance the efficacy of piperacillin.

Potential therapeutic role of cationic peptides in three experimental models of septic shock

The therapeutic efficacies of buforin II, indolicidin, and KFFKFFKFF were investigated in three rat models of septic shock: (i) rats injected intraperitoneally with 10 microg of Escherichia coli O111:B4 lipopolysaccharide, (ii) rats given an intraperitoneal injection of 2 x 10(10) CFU of Escherichia coli ATCC 25922, and (iii) rats in which intra-abdominal sepsis was induced via cecal ligation and single puncture. All animals were randomized to receive parenterally isotonic sodium chloride solution, 1 mg of buforin II per kg of body weight, 1 mg of indolicidin per kg, 1 mg of KFFKFFKFF per kg, and 20 mg of imipenem per kg. The main outcome measures were bacterial growth in abdominal exudate and plasma, endotoxin and tumor necrosis factor alpha (TNF-alpha) concentrations in plasma, and lethality. Treatment with all peptides resulted in significant reductions in plasma endotoxin and TNF-alpha concentrations compared with those resulting from the imipenem and saline treatments. On the other hand, imipenem treatment significantly reduced the levels of bacterial growth compared with the reductions achieved with the peptide and saline treatments. All compounds reduced the rates of death compared to that for the controls. Although the peptides demonstrated lower levels of antimicrobial activity than imipenem, they exhibited the dual properties of antimicrobial and antiendotoxin agents.

Induction of early inflammatory gene expression in a murine model of nonresuscitated, fixed-volume hemorrhage

The etiology of many end-organ problems associated with hemorrhage has been attributed to the inflammatory response to hemorrhage. In a murine model of nonresuscitated, fixed-volume hemorrhage, we sought to elucidate the role that hemorrhagic insult alone plays in the generation of the early inflammatory cascade. Differences could be appreciated as early as 1 h post-hemorrhage, with consistent differences detected by 3 h in all of the major cytokine genes studied. Significant upregulation of IL-1beta , IL-6, TNF-alpha, and IL-10 mRNA expression was observed in both the liver and lung samples of mice subjected to fixed-volume hemorrhage when compared with sham-hemorrhaged mice. The cyclooxygenase-2 (COX-2) and inducible nitric oxide synthetase (iNOS) genes also were upregulated in the livers and lungs of hemorrhaged mice. Finally, expression of the genes that encode the Toll-like receptors (TLR)-2 and -4 was increased by hemorrhage. Taken collectively, these data demonstrate that the initial inflammatory cascade associated with hemorrhage occurs within hours after the initial hemorrhagic event, and can be associated with significant modulation of expression of key pro- and anti-inflammatory cytokine, enzyme, and TLR genes, suggesting that these may be possible new therapeutic targets.

Decreased alpha-adrenergic response in the intestinal microcirculation after "two-hit" hemorrhage/resuscitation and bacteremia

BACKGROUND

The two-hit theory of multiple organ dysfunction syndrome proposes that an initial insult primes the host for an altered response to subsequent stimuli. We have previously documented enhanced dilator tone in the small intestine after a two-hit insult; however, the effects on vasoconstrictor function are unknown. We postulated that prior hemorrhage and resuscitation followed by bacteremia would alter microvascular responsiveness to alpha-adrenergic stimulation.

METHODS

Male Sprague-Dawley rats underwent fixed-volume hemorrhage with resuscitation (H/R) or sham procedure (Sham). At 24 or 72 h, in vivo videomicroscopy of the small intestine was performed (inflow A1 and premucosal A3 arterioles). Constrictor function was assessed by topical application of norepinephrine (NE; 10(-8)-10(-6) M) before and 1 h after intravenous Escherichia coli or saline.

RESULTS

Sham, 24 or 72 h H/R, and E. coli alone produced no significant changes in A1 or A3 response to NE. Sequential H/R + E. coli resulted in decreased constrictor response in both A1 (72 h H/R + E. coli-38% from baseline vs Sham - 54%, P < 0.05) and A3 arterioles (-8% vs -51%, P < 0.05) at high doses of NE (10(-6) M).

CONCLUSIONS

Prior H/R primes the intestinal microvasculature for an altered response during a subsequent stress and these effects persist for up to 72 h following H/R. Sequential insults in this two-hit model caused marked hyporesponsiveness to NE. These alterations in control of microvascular tone might contribute to the hemodynamic compromise of sepsis, impair mucosal blood flow, and contribute to the development of MODS.

Tolerance to shock: an exploration of mechanism

OBJECTIVE

To determine if cross-tolerance to septic shock could be induced by a previous insult with sublethal hemorrhage (SLH) and to characterize the mechanisms involved in this induced protective response.

BACKGROUND DATA

It is possible to condition animals by prior SLH such that they tolerate an otherwise lethal hemorrhage. It is also possible to condition animals with low doses of lipopolysaccharide (LPS) so that they survive a "lethal" septic insult. However, a paucity of information exists on cross-tolerance between hemorrhage and sepsis.

METHODS

Rats were made tolerant by conditioning SLH or sham operation. Twenty-four hours later, tolerant and sham rats were exposed to a lethal dose of LPS. To explore the mechanism of tolerance induction, rats were given the macrophage (Mphi) inhibitor CNI-1493 or saline carrier before SLH. Survival and pulmonary vascular injury were determined after LPS. Serum tumor necrosis factor (TNF) levels and splenic Mphi TNF gene expression were measured at several time points.

RESULTS

Prior SLH indeed made rats tolerant and imparted a significant survival benefit and reduction in pulmonary vascular injury after LPS. The tolerance induced by SLH was reversed by Mphi inhibition. Tolerant animals had low serum TNF levels immediately after SLH and reduced circulating TNF levels after LPS. SLH, however, did not inhibit the augmentation of TNF gene expression after LPS.

CONCLUSIONS

Sublethal hemorrhage bestows protection against a lethal LPS challenge. Inhibition of the Mphi attenuated the benefit of the tolerance induced by SLH. Circulating TNF but not TNF gene after LPS is lessened by SLH. This implicates changes in Mphi intracellular signaling in induction of the tolerant state.

Induction of tolerance to hemorrhagic or endotoxic shock involves activation of NF-kappaB

BACKGROUND

Tolerance to hemorrhagic or endotoxic shock can be induced by prior sublethal hemorrhage (SLH). The purpose of this study was to explore whether alterations in signal transduction pathways involving NF-kappaB occur in macrophages (Mphi) following induction of tolerance by SLH.

METHODS

Using a model of SLH previously shown in our lab to impart a survival benefit to subsequent hemorrhagic or endotoxic shock, rats (n = 30) were conditioned by SLH. Peritoneal Mphi were harvested 24 h after conditioning and stimulated with lipopolysaccharide (LPS) (10 microg/mL). Nuclear and cytosolic proteins were isolated 1 h later for determination of NF-kappaB activation by gel-shift assay and IkappaB-alpha by Western blot. TNF mRNA gene expression was measured 4 h after LPS stimulation by reverse transcription/polymerase chain reaction (RT/PCR). TNF protein levels were measured in cellular supernatants by enzyme-linked immunosorbent assay (ELISA) 18 h after LPS. RESULTS. LPS stimulation of sham Mphi increased NF-kappaB activation with corresponding loss of its inhibitor IkappaB-alpha. In contrast, IkappaB-alpha was not detectable following conditioning, and conditioned Mphi had NF-kappaB activation at baseline which increased minimally with LPS stimulation. LPS increased TNF gene expression and significantly increased protein production by both sham and conditioned Mphi, but this increase was greater in the sham-conditioned group.

CONCLUSIONS

The ability of Mphi from animals made tolerant by SLH to produce TNF in vitro is conserved. Nevertheless, these same Mphi exhibit alterations in TNF gene induction and expression as well as signal transduction, specifically, changes in IkappaB-alpha and NF-kappaB activation. This suggests a role for activation of NF-kappaB in the induction of tolerance.

Sublethal hemorrhage blunts the inflammatory cytokine response to endotoxin in a rat model

BACKGROUND

Tolerance to lipopolysaccharide (LPS) induced by previous hemorrhage in mice is associated with a blunted interleukin 1 (IL-1) response, suggesting down-regulation of the cytokine cascade as a possible protective mechanism. This study was undertaken to determine whether prehemorrhage induces attenuation of the cytokine response to sepsis beyond IL-1 in a rat model and whether this response occurs at the level of gene transcription.

METHODS

Sprague-Dawley rats underwent sublethal hemorrhage, lethal intraperitoneal endotoxin, or sublethal hemorrhage with delayed lethal endotoxin. Animals were killed 12 hours after LPS injection or 24 hours after hemorrhage. IL-1 and tumor necrosis factor (TNF) mRNA levels were determined on total splenic RNA using reverse-transcriptase polymerase chain reaction, and serum cytokine levels were determined using enzyme-linked immunosorbent assay.

RESULTS

Animals that received LPS alone mounted an IL-1 and TNF response (RNA and protein) much higher than animals subjected to hemorrhage alone. TNF and IL-1 gene expression and protein levels in prehemorrhaged animals that received LPS, however, were significantly lower than those of animals that received LPS alone.

CONCLUSION

Hemorrhage induces early IL-1 and TNF gene expression, which blunts their subsequent expected increase after endotoxic challenge. These findings validate previously documented immune-modulated protective effects of the first insult in a two-hit model.

Altered vasoconstrictor and dilator responses after a "two-hit" model of sequential hemorrhage and bacteremia

BACKGROUND

The "two-hit" theory of multiple organ dysfunction (MOD) proposes that an initial insult, such as hemorrhage (HEM), primes the host for an abnormal response to a second stress such as infection. The immunologic/inflammatory component of this theory has been well examined; however, the effects on vascular responsiveness are poorly understood. We hypothesized that HEM primes the vasculature for an altered response to a second pathophysiologic stress.

METHODS

Male Sprague-Dawley rats underwent a fixed-volume HEM with resuscitation (H/R) or sham procedure (Sham). At 48 h, animals were given iv E. coli or saline and followed for 1 h. Thoracic aortic rings were then placed in organ baths containing Krebs buffer aerated with 95% O2, 5% CO2. Cumulative dose-response curves to phenylephrine (PHE) and acetylcholine (ACH) were obtained. Maximum force of contraction (Fmax) was measured and pD2 values (receptor sensitivity) were derived.

RESULTS

H/R alone resulted in heightened constrictor tone and blunted dilator tone. E. coli reduced Fmax in response to PHE by 50% in Sham vs 76% in H/R. Receptor sensitivity (pD2) to PHE was reduced to a greater degree in H/R (3-fold vs 2-fold). These animals also had a more pronounced enhancement of ACH receptor sensitivity (7-fold vs 2-fold).

CONCLUSIONS

Hemorrhage primes the vasculature for an altered response to a subsequent stress. When infection is added as a "second hit," responsiveness to adrenergic agents is diminished and dilator tone is increased. These data may explain the cardiovascular derangements seen clinically in patients who develop MODS after major hemorrhage followed sequentially by infection.

Microvascular changes explain the "two-hit" theory of multiple organ failure

OBJECTIVE

The objective was to determine intestinal microvascular endothelial cell control after sequential hemorrhage and bacteremia.

SUMMARY BACKGROUND DATA

Sepsis that follows severe hemorrhagic shock often results in multiple system organ failure (MSOF) and death. The sequential nature of this clinical scenario has led to the idea of a "two-hit" theory for the development of MSOF, the hallmark of which is peripheral vasodilation and acidosis. Acute bacteremia alone results in persistent intestinal vasoconstriction and mucosal hypoperfusion. Little experimental data exist to support the pathogenesis of vascular dysregulation during sequential physiologic insults. We postulate that hemorrhagic shock followed by bacteremia results in altered microvascular endothelial cell control of dilation and blood flow.

METHODS

Rats underwent volume hemorrhage and resuscitation. A sham group underwent the vascular cannulation without hemorrhage and resuscitation, and controls had no surgical manipulation. After 24 and 72 hours, the small intestine microcirculation was visualized by in vivo videomicroscopy. Mean arterial pressure, heart rate, arteriolar diameters, and A1 flow by Doppler velocimetry were measured. Endothelial-dependent dilator function was determined by the topical application of acetylcholine (ACh). After 1 hour of Escherichia coil bacteremia, ACh dose responses were again measured. Topical nitroprusside was then applied to assess direct smooth muscle dilation (endothelial-independent dilator function) in all groups. Vascular reactivity to ACh was compared among the groups.

RESULTS

Acute bacteremia, with or without prior hemorrhage, caused significant large-caliber A1 arteriolar constriction with a concomitant decrease in blood flow. This constriction was blunted at 24 hours after hemorrhage but was restored to control values by 72 hours. There was a reversal of the response to bacteremia in the premucosal A3 vessels, with a marked dilation both at 24 and 72 hours. The sequence of hemorrhage and E. coli resulted in a progressive enhanced reactivity to the endothelial-dependent stimulus of ACh in the A3 vessels at 24 and 72 hours. Reactivity to endothelial-independent smooth muscle relaxation and subsequent vessel dilation was similar for all groups.

CONCLUSIONS

These data indicate that there is altered endothelial control of the intestinal microvasculature after hemorrhage in favor of enhanced dilator mechanisms in premucosal vessels with enhanced constrictor forces in inflow vessels. This enhanced dilator sensitivity is most evident in small premucosal vessels. This experimental finding supports the premise that an initial pathophysiologic stress alters the subsequent microvascular blood flow responses to systemic inflammation. These changes in the intestinal microcirculation are in concert with the "two-hit" theory for MSOF.