Bacterial translocation in multiple organ failure: Cause or epiphenomenon still unproven

The Effect of Elevated Intra-Abdominal Pressure on TLR4 Signaling in Intestinal Mucosa and on Intestinal Bacterial Translocation in a Rat

BACKGROUND

Recent evidence suggests that elevated intra-abdominal pressure (IAP) may adversely affect the intestinal barrier function. Toll-like receptor 4 (TLR-4) is responsible for the recognition of bacterial endotoxin or lipopolysaccharide and for initiation of the Gram-negative septic shock syndrome. The objective of the current study was to determine the effects of elevated IAP on intestinal bacterial translocation (BT) and TLR-4 signaling in intestinal mucosa in a rat model.

METHODS

Male Sprague-Dawley rats were randomly assigned to one of two experimental groups: sham animals (Sham) and IAP animals who were subjected to a 15 mmHg pressure pneumoperitoneum for 30 minutes. Rats were sacrificed 24 hours later. BT to mesenteric lymph nodes, liver, portal vein blood, and peripheral blood was determined at sacrifice. TLR4-related gene and protein expression (TLR-4; myeloid differentiation factor 88 [Myd88] and TNF-α receptor-associated factor 6 [TRAF6]) expression were determined using real-time PCR, western blotting, and immunohistochemistry.

RESULTS

Thirty percent of sham rats developed BT in the mesenteric lymph nodes (level I) and 20% of control rats developed BT in the liver and portal vein (level II). abdominal compartment syndrome (ACS) rats demonstrated an 80% BT in the lymph nodes (Level I) and 40% BT in the liver and portal vein (Level II). Elevated BT was accompanied by a significant increase in TLR-4 immunostaining in jejunum (51%) and ileum (35.9%), and in a number of TRAF6-positive cells in jejunum (2.1%) and ileum (24.01%) compared to control animals. ACS rats demonstrated a significant increase in TLR4 and MYD88 protein levels compared to control animals.

CONCLUSIONS

Twenty-four hours after the induction of elevated IAP in a rat model, increased BT rates were associated with increased TLR4 signaling in intestinal mucosa.

Bacterial translocation: overview of mechanisms and clinical impact

Bacterial translocation (BT) is a phenomenon in which live bacteria or its products cross the intestinal barrier. Gut translocation of bacteria has been shown in both animal and human studies. BT and its complications have been shown clearly to occur in animal models, but its existence and importance in humans has been difficult to ascertain. We review the mechanisms of BT and its clinical impact based on the current literature.

Intestinal Permeability and Cytokine Inflammatory Response in Multiply Injured Patients

In experimental settings, the increased intestinal permeability (IP) following severe trauma is associated with increased serum concentrations of cytokines. Multiply injured patients are susceptible to the development of multiple organ failure (MOF). The aim of this study was to determine if altered IP after trauma was associated with upregulation of cytokines and if cytokines and IP influenced the development of MOF. In 30 multiply injured patients, IP was measured on days 2 and 4 after injury using the lactulose-mannitol (L-M) test, and the levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and IL-8 were determined simultaneously. The L-M ratio increased significantly from 0.049 (0.017-0.133) on day 2 to 0.150 (0.059-0.339) on day 4 (p < 0.02) On day 4, a significant correlation was also found between the L-M ratio and IL-6 (r = 0.43, p < 0.03). The IL-6 level on days 2 and 4 was significantly (p < 0.01 and p < 0.03, respectively) higher in MOF patients than in those without MOF, as was the TNF-alpha level on day 4 significantly higher (p < 0.04) in MOF patients. IP increases following multiple trauma, and on day 4 it correlates with the IL-6 level. However, in patients who develop MOF only cytokines are invariably increased, with IL-6 alone being significantly increased on both measurements in these patients.

Adverse Effects of Increased Intra-abdominal Pressure on Small Bowel Structure and Bacterial Translocation in the Rat

BACKGROUND

The purpose of this study was to evaluate the effects of elevated intra-abdominal pressure (IAP) on intestinal structures and bacterial translocation in the rat.

MATERIALS AND METHODS

Forty-two male Sprague-Dawley rats were randomly divided into three experimental groups of 14 rats each: the sham group underwent insertion of a balloon-tipped catheter; the IAP-15 group was subjected to a 15 mm Hg pneumoperitoneum for 60 minutes; and the IAP-25 group was subjected to a 25 mm Hg pneumoperitoneum for 60 minutes. Intestinal structural changes (bowel circumference, overall bowel and mucosal weight, mucosal DNA and protein, villus height, and crypt depth) and bacterial translocation to mesenteric lymph nodes, liver, spleen, portal blood, and peripheral blood were determined 24 hours following pneumoperitoneum.

RESULTS

IAP-15 and IAP-25 rats demonstrated a significant decrease in: bowel and mucosal weight in the duodenum, jejunum, and ileum; mucosal DNA and protein in the jejunum and ileum; villus height in the jejunum: and crypt depth in the jejunum and ileum compared to the sham rats. Bacterial translocation was demonstrated in 60% of IAP-15 rats and in 80% of IAP-25 rats.

CONCLUSION

Elevated IAP results in mucosal injury of the gut, causing mucosal hypoplasia, and increases bacterial translocation.

Pathogenesis of multiple organ dysfunction syndrome: gut origin, protection, and decontamination

Clinical and experimental studies performed over the past several decades have implicated bacterial and endotoxin translocation (BET) from the gut to distant organs in the pathogenesis of multiple organ dysfunction syndrome (MODS). Experimental studies in animals directed at maintaining the integrity of the intestinal mucosa have shown efficacy in preventing BET and the induction of distant inflammatory processes, suggesting that the egress of bacteria and their surface endotoxins might be pivotal in inducing MODS. However, clinical studies have failed to convincingly recapitulate these beneficial effects. Selective digestive decontamination, although it effectively decreases rates of respiratory infection, has failed to reduce MODS in critically ill patients and, except in certain patient subsets, has had no demonstrable effect on mortality. Nevertheless, the gut is an immunologically active organ that, irrespective of BET occurrence, appears to contribute significantly to the development of distant organ dysfunction following ischemia/reperfusion injury. Resuscitation strategies aimed at minimizing the inflammatory effects of gut-derived mediators, such as toxic oxygen species, appear promising in preventing the development of distant organ injury in the critically ill patient.

Pathogenesis of malaria and clinically similar conditions

There is now wide acceptance of the concept that the similarity between many acute infectious diseases, be they viral, bacterial, or parasitic in origin, is caused by the overproduction of inflammatory cytokines initiated when the organism interacts with the innate immune system. This is also true of certain noninfectious states, such as the tissue injury syndromes. This review discusses the historical origins of these ideas, which began with tumor necrosis factor (TNF) and spread from their origins in malaria research to other fields. As well the more established proinflammatory mediators, such as TNF, interleukin-1, and lymphotoxin, the roles of nitric oxide and carbon monoxide, which are chiefly inhibitory, are discussed. The established and potential roles of two more recently recognized contributors, overactivity of the enzyme poly(ADP-ribose) polymerase 1 (PARP-1) and the escape of high-mobility-group box 1 (HMGB1) protein from its normal location into the circulation, are also put in context. The pathogenesis of the disease caused by falciparum malaria is then considered in the light of what has been learned about the roles of these mediators in these other diseases, as well as in malaria itself.