Trauma-hemorrhagic shock mesenteric lymph from rat contains a modified form of albumin that is implicated in endothelial cell toxicity

It has been proposed that factors originating from the gut after severe trauma/shock are introduced into the systemic circulation through the mesenteric lymphatics and are responsible for the cellular injury and inflammation that culminates in acute multiple organ dysfunction syndrome (MODS). Indeed, it has been shown that lymph collected from shocked but not sham-shocked animals causes endothelial cell death, neutrophil activation, and bone marrow (BM) colony growth suppression in vitro. In an attempt to isolate the factor(s) in lymph responsible for endothelial cell toxicity, lymph from shock and sham animals was fractionated by solid phase extraction (SPE) and ion exchange chromatography (IEX). The separation of shock lymph by both methodologies yielded two fractions having major detectable toxicity to endothelial cells, whereas no toxicity was detected from sham lymph separations by either method. Subsequent analysis of each SPE toxic fraction by gel electrophoresis and mass spectrometry suggests the toxicity is associated with a modified form of rat serum albumin (mod-RSA) and multiple lipid-based factors. Therefore, we have been able to demonstrate by two different separation techniques that shock lymph contains two or more factors that may account for the toxicity to endothelial cells. Further investigations are needed to determine the type of RSA modification and the identity of the lipid factors and their role in MODS.

Albumin protects against gut-induced lung injury in vitro and in vivo

OBJECTIVE

Since albumin has the ability to detoxify, we assessed whether low-dose albumin could protect against trauma/hemorrhagic shock (T/HS)-induced endothelial cell, lung, gut, and red blood cell (RBC) injury in vivo and endothelial cell injury in vitro.

SUMMARY BACKGROUND DATA

T/HS cause ischemic insult to the gut, resulting in the release of biologically active factors into the mesenteric lymph, which then cause injury to multiple distant organs.

METHODS

In vitro experiments tested the ability of albumin to reduce the cytotoxicity of mesenteric lymph from male rats subjected to T/HS (laparotomy + MAP 30 mm Hg for 90 minutes) for human umbilical vein endothelial cell (HUVEC). In subsequent in vivo experiments, the ability of albumin given as part of the resuscitation regimen to protect against T/HS-induced injury was tested by comparing the magnitude of injury in T/HS rats receiving human albumin (shed blood + 0.12, 0.24, or 0.36 g/kg) or lactated Ringer's solution (shed blood + 2 x volume of shed blood as LR) with that observed in rats subjected to trauma/sham shock. Rats were killed after a 3-hour recovery period and had lung permeability evaluated by bronchoalveolar lavage and myeloperoxidase assays, intestinal microvillous injury by histology, and RBC deformability using ektacytometry.

RESULTS

Both bovine and human albumin prevented T/HS lymph-induced HUVEC cytotoxicity in vitro, even when added 30 minutes after the lymph (viability 15 +/- 4% to 88 +/- 3%, P < 0.01). In vivo RBC deformability was better preserved by blood plus albumin than blood plus lactated Ringer's solution (P < 0.01). Likewise, albumin administration reduced T/HS-induced lung permeability and neutrophil sequestration in a dose-dependent fashion, with 0.36 g/kg of albumin effecting total lung protection (P < 0.01). In contrast, albumin treatment did not prevent T/HS-induced gut injury.

CONCLUSIONS

Low-dose albumin protects against gut lymph-induced lung, HUVEC, and RBC injury by neutralizing T/HS lymph toxicity.

Red blood cell damage after trauma-hemorrhage is modulated by gender

BACKGROUND

Previous studies have shown that trauma-hemorrhagic shock (T/HS) causes significant alterations in red blood cell (RBC) deformability and shape. Gender is becoming well recognized as a modulating factor in the pathophysiologic response to trauma. We hypothesize that female subjects are more resistant to adverse effects of T/HS on RBC deformability and shape than male subjects because of estrogen protection.

METHODS

Elongation index, a measure of RBC deformability, was examined in six male rats and four groups of female rats at different stages of the estrous cycle (six animals per group) before and 6 hours after T/HS by laser ektacytometry. RBC shape was determined by scanning electron microscopy. Lipid peroxidation was evaluated by measurement of malonyldialdehyde in plasma 6 hours after T/HS.

RESULTS

Male rats had a significant decrease in RBC elongation index after T/HS as compared with preshock values. RBC deformability of the proestrous (PES) and estrous female rats did not decrease after T/HS. Postshock RBC deformability values in metestrous and diestrous female rats did not differ from male rats. Male rats and metestrous and diestrous females had a significant increase in the percentage of abnormally shaped RBCs immediately after shock and during the postresuscitation period. In PES and ES female rats, RBC shape distribution did not significantly change after T/HS. Plasma malonyldialdehyde levels at 6 hours post-T/HS were higher in the male rats than in PES female rats.

CONCLUSION

These data show that high levels of estrogen in female rats are protective against shock-induced RBC damage and suggest that this effect is associated with a decrease in lipid peroxidation.

The role of oxidant-mediated pathways in the cytotoxicity of endothelial cells exposed to mesenteric lymph from rats subjected to trauma-hemorrhagic shock

Because gut-derived factors carried in mesenteric lymph are implicated in multiple organ dysfunction syndrome and have been shown to injure endothelial cells, we investigated several cellular pathways by which this process could occur. To accomplish this, mesenteric lymph (5%, v/v) collected at 1 to 3 h postshock from male rats undergoing trauma (5-cm laparotomy) and hemorrhagic shock (90 min of mean arterial pressure [MAP] of 30 mmHg; T/HS) was tested for endothelial cell cytotoxicity on human umbilical vein endothelial cells (HUVECs). Over 30 pharmacologic agents that had been reported to inhibit endothelial cell death were tested for their ability to prevent T/HS lymph-induced HUVEC cell death. These included agents documented to protect against oxidant-mediated, calcium-mediated, and arachidonic acid pathway-mediated endothelial cell injury and death. These pharmacologic inhibitors were preincubated with HUVECs for 1 h or were added to the HUVECs simultaneously with lymph, and were then incubated for 18 h. Controls were lymph alone, inhibitor alone, or medium alone. Mitochondrial tetrazolium (MTT) and LDH release assays were used to determine cell viability. The inhibitors that significantly protected HUVECs from the cytotoxicity of T/HS lymph (P < 0.001) included the antioxidant combination of vitamins C and E and the antioxidant-lipooxygenase inhibitor nordihydroguaretic acid (NDGA). These agents were equally effective when added simultaneously with lymph or preincubated with the HUVECs, suggesting an extracellular or membrane-bound process. In summary, the inhibitors that provided protection from toxic lymph appear to work at the membrane and are involved in limiting membrane peroxidation. Based on this study, it appears that an oxidant pathway is involved in T/HS lymph-induced endothelial cell injury and death.