The pattern of early lung parenchymal and air space injury following acute blood loss

Dexmedetomidine-ketamine combination mitigates acute lung injury in haemorrhagic shock rats

AIM OF THE STUDY

Upregulation of pulmonary inflammatory molecules is crucial in mediating the development of acute lung injury induced by haemorrhagic shock. Dexmedetomidine and ketamine possess potent anti-inflammatory capacity. We sought to elucidate whether dexmedetomidine, ketamine, or dexmedetomidine-ketamine combination could mitigate acute lung injury in haemorrhagic shock rats.

METHODS

Fifty adult male Sprague-Dawley rats were randomized to the sham-instrumented, haemorrhagic shock (HS), HS plus dexmedetomidine (HS-D), HS plus ketamine (HS-K), or HS plus dexmedetomidine-ketamine (HS-D+K) group (n=10 in each group). Haemorrhagic shock was induced by blood withdrawing and the mean blood pressure was maintained at 40-45mmHg for 120min. Resuscitation was then performed by infusion of shed blood/saline mixtures. After monitoring for another 8h, rats were sacrificed.

RESULTS

Histology findings and lung injury score analysis revealed moderate lung injury in rats of the HS, HS-D, and HS-K groups, whereas those of the HS-D+K group revealed mild lung injury. The effects of haemorrhagic shock on increasing cell number and protein concentration in bronchoalveolar lavage fluid as well as water content, leukocyte infiltration, and myeloperoxidase activity of lung tissues were significantly attenuated by dexmedetomidine-ketamine combination but not by dexmedetomidine or ketamine alone. Dexmedetomidine-ketamine combination, but not dexmedetomidine or ketamine alone, also significantly inhibited haemorrhagic shock-induced upregulation of pulmonary inflammatory molecules, including nitric oxide, prostaglandin E(2), chemokine (e.g., macrophage inflammatory protein-2), and cytokines [e.g., interleukin (IL)-1beta, and IL-6].

CONCLUSIONS

Dexmedetomidine-ketamine combination mitigates acute lung injury in haemorrhagic shock rats.

A temporal study of gene expression in rat lung following fixed-volume hemorrhage

Previous studies have indicated that hemorrhage may predispose the lung to respiratory distress syndrome. Gene expression profiling with oligonucleotide microarrays was used to evaluate the genetic responses of the lung to hemorrhage. Conscious rats, chronically instrumented with a catheter and telemetry device to record blood pressure, heart rate, and temperature, had 40% of their estimated blood volume removed at a rate of 1 ml/min over 7-10 min. Groups of three or more rats were euthanized at 1, 3, 6, 16, 24, 48, or 72 h following hemorrhage. Two additional groups were unmanipulated controls and instrumented animals with sham hemorrhage. Total RNA was isolated from lung, reverse-transcribed to cDNA, fluorescently labeled, and hybridized to oligonucleotide microarrays probing 5,671 rat genes. After hemorrhage, statistically detectable alteration of expression was seen in approximately 0.8% of the genes at some time during the 72-h test period (vs. sham hemorrhage) as determined by false discovery rate statistics in the statistical analysis of microarrays program. A subset was confirmed by RT-PCR analysis. Hemorrhage influenced genes that regulate intracellular signaling and structure, growth factors, and hormonal receptors. There also appeared to be increased expression of genes that may mediate sequestration of neutrophils and mononuclear cells from the circulation. This hemorrhage model, although producing severe hemodynamic alterations, avoided mortality and histological evidence of lung damage, a feature intended to help ensure reliable evaluation of gene expression. These results indicate that gene expression profiling with microarrays provides a new tool for exploring the response of a tissue to systemic blood loss.

Hemorrhagic shock resuscitation with a low molecular weight starch reduces neutrophil-endothelial interactions and vessel leakage in vivo

BACKGROUND

The polymorphonuclear neutrophil (PMN) has been implicated in the pathogenesis of endothelial cell (EC) damage and organ injury following hemorrhagic shock. Pentastarch (PTS), a low substituted medium molecular weight (MW) colloid, improves hemodynamics in hypovolemic shock and cardiac surgery. No data exist comparing the immunomodulation of PTS and Ringer's lactate (RL) on the activation of PMN in hemorrhagic shock in vivo.

METHODS

Using an in vivo murine hemorrhagic shock model (blood withdrawal to maintain 50 mmHg x 45 min), circulating PMN were observed every 15 minutes using intravital microscopy on cremaster muscle. EC-PMN interactions (videorecorded and subsequently analyzed blindly), vessel leakage (live epifluorescence after injection of 50 mg/kg fluorescent albumin) and PMN expression of L-selectin (immunofluorescent monoclonal antibodies and flow cytometry) were evaluated in three resuscitation groups: PTS (7.14 mL/kg 10% pentastarch/0.9% NaCl + shed blood, n = 13), RL (RL [2 x shed blood volume] + shed blood, n = 13) and SHAM (0 hemorrhage, 0 resuscitation, n = 9). Significance was evaluated by ANOVA with Bonferroni correction.

RESULTS

PMN rolling was significantly diminished in PTS and SHAM as compared to RL animals at all time points. Similar differences were found in PMN adherence to EC at most time points onwards from 15 minutes following resuscitation. In vivo vessel permeability was lowest in SHAM and PTS animals (mean 0.274 +/- 0.07 and 0.356 +/- 0.15, respectively, p > 0.05) and highest in RL animals (0.667 +/- 0.09, p < 0.001 vs PTS or SHAM). PMN L-selectin expression tended to be higher in the RL group than either SHAM and PTS groups. There were no flow-mechanics differences between groups (vessel diameter, mean red cell velocity, shear stress, shear rate).

CONCLUSIONS

10% pentastarch reduces RL-associated EC-PMN interactions and vessel leakage following hemorrhagic shock. These results support the use of low MW starches to resuscitate hemorrhagic shock, potentially reducing PMN-mediated tissue injury.

A low level of TNF-alpha mediates hemorrhage-induced acute lung injury via p55 TNF receptor

Acute lung injury after hemorrhagic shock (HS) is associated with the expression of tumor necrosis factor (TNF)-alpha in the lung. However, the role of TNF-alpha and its receptors in this pulmonary disorder remains obscure. This study examined the temporal relationship of pulmonary TNF-alpha production to neutrophil accumulation during HS and determined the role of TNF-alpha in neutrophil accumulation and lung leak. HS was induced in mice by removal of 30% of total blood volume. Lung TNF-alpha was measured by ELISA. Neutrophil accumulation was detected by immunofluorescent staining, and microvascular permeability was assessed using Evans blue dye. Although HS induced a slight and transient increase in lung TNF-alpha, neutrophil accumulation preceded the increase in TNF-alpha. However, lung neutrophil accumulation and lung leak were abrogated in TNF-alpha knockout mice, and both were restored by administration of recombinant TNF-alpha to TNF-alpha knockout mice before HS. Neutrophil accumulation and lung leak were abrogated in mice lacking the p55 TNF-alpha receptor, but neither was influenced by p75 TNF-alpha receptor knockout. This study demonstrates that a low level of pulmonary TNF-alpha is sufficient to mediate HS-induced acute lung injury during HS and that the p55 TNF-alpha receptor plays a dominant role in regulating the pulmonary inflammatory response to HS.

Augmented metalloproteinase activity and acute lung injury in copper-deficient rats

Dietary copper is required for normal function of >30 mammalian enzyme systems. Copper deficiency causes a number of cardiovascular defects as well as impaired immune cell function. Little is known regarding the effects of copper deficiency on acute inflammatory responses, but this topic is relevant because many members of the Western population receive less than the recommended dietary allowance of copper. In the current studies, we investigated the effects of dietary copper deficiency on acute lung injury induced by intrapulmonary deposition of IgG immune complexes. Weanling male Long-Evans rats were fed diets either adequate (5.6 microg/g) or deficient (0.3 microg/g) in copper. IgG immune complex lung injury was greatly increased in copper-deficient rats as determined by lung vascular leakage of albumin and histopathology. However, no change was observed in either the lung content of tumor necrosis factor-alpha or lung neutrophil accumulation. Lungs from copper-deficient rats had much higher levels of matrix metalloproteinase (MMP)-2 and MMP-9 than did copper-adequate control animals. This increased activity was not attributable to alveolar macrophages or neutrophils. These data suggest that the augmented lung injury caused by copper deficiency is due to increased pulmonary MMP-2 and MMP-9 activity and not a generalized amplification of the inflammatory response.

Detrimental effects of complement activation in hemorrhagic shock

The complement system has been implicated in early inflammatory events and a variety of shock states. In rats, we measured complement activation after hemorrhage and examined the hemodynamic and metabolic effects of complement depletion before injury and worsening of complement activation after hemorrhage and resuscitation [with a carboxypeptidase N inhibitor (CPNI), which blocks the clearance of C5a]. Rats were bled to a mean arterial pressure of 30 mmHg for 50 min and were then resuscitated for 2 h. Shock resulted in significant evidence of complement consumption, with serum hemolytic activity being reduced by 33% (P < 0.05). Complement depletion before injury did not affect hemorrhage volume (complement depleted = 28 +/- 1 ml/kg, complement intact = 29 +/- 1 ml/kg, P = 0.74) but improved postresuscitation mean arterial pressure by 37 mmHg (P < 0.05) and serum bicarbonate levels (complement depleted = 22 +/- 3 meq/ml, complement intact = 13 +/- 8 meq/ml, P < 0.05). Pretreatment with CPNI was lethal in 80% of treated animals vs. the untreated hemorrhaged group in which no deaths occurred (P < 0.05). In this model of hemorrhagic shock, complement activation appeared to contribute to progressive hypotension and metabolic acidosis seen after resuscitation. The lethality of CPNI during acute blood loss suggests that the anaphylatoxins are important in the pathophysiological events involved in hemorrhagic shock.