Endotoxemia in obstructive jaundice. Observations on cause and clinical significance

Administration of Chlorella sp. microalgae reduces endotoxemia, intestinal oxidative stress and bacterial translocation in experimental biliary obstruction

RATIONALE

Endotoxemia has long been documented in obstructive jaundice, and altered intestinal barrier function is considered to be one of the important mechanisms for this phenomenon. The aim of this study was to investigate the role of different microalgae (Chlorella sp. and Spirulina sp.) extracts in intestinal barrier function and oxidative stress in experimentally jaundiced rats.

METHODS

A total of 60 male wistar rats were randomly divided into four groups of 15 each: I, sham operated; II, bile duct ligation (BDL); III, BDL+Chlorella sp.; IV, BDL+Spirulina sp. Rats were fed rat chow or microalgae extracts supplemented enteral diet ten days after sham operation or BDL. Main outcome measures were endotoxin concentrations in plasma, evidence of bacterial translocation (BT) in mesenteric lymph nodes (MLNs) and liver, oxidative stress, and histology.

RESULTS

Compared to the group I, a significant increase in contamined MLNs, liver, and spleen samples and increased endotoxemia were noted in group II (P<0.01) but were significant reduced in group III (P<0.05). There was no significant difference in BT rate between the group II and group IV (P>0.05). Moreover, Chlorella sp. administration protected in jaundiced rats against oxidative stress, as demonstrated by reduction of intestinal lipid peroxidation, increase of the antioxidant reduced glutathione (GSH), and decrease of the oxidized glutathione (GSSG). The intestinal mucosa in control rats was atrophic with significantly decreased villous density and total mucosal thickness. Chlorella sp. caused a significant reduction in villous atrophy compared with controls.

CONCLUSIONS

Chlorella sp. microalgae supplemented enteral diet has significant protective effects on intestinal mucosa barrier in obstructive jaundice, and reduces intestinal translocation of bacteria and endotoxin.

Concordance of endotoxemia with gram-negative bacteremia. A meta-analysis using receiver operating characteristic curves

OBJECTIVE

To apply meta-analysis to compare the concordance between the results of 2 types of limulus amebocyte lysate (LAL) assay, gelation (GLAL) and chromogenic (CLAL), with the detection of gram-negative bacteremia in patients with suspected bacteremia.

DESIGN

Meta-analysis using receiver operating characteristic-based analytical method.

DATA SOURCES

MEDLINE literature search and manual reviews of article bibliographies together with direct approaches to authors of potentially eligible studies.

STUDY SELECTION

The studies that were selected had all included at least 10 patients, of whom at least 2 patients were diagnosed with gram-negative bacteremia, and all had data available for extraction into a contingency table format.

RESULTS

Fifty-six studies (28 GLAL and 28 CLAL studies) met the inclusion criteria. Studies were stratified by type of test (GLAL vs CLAL). Each analysis was repeated with smaller studies excluded. There was no difference between the 2 types of LAL assays. Among the CLAL studies, there was no difference between studies that did versus those that did not use the sepsis syndrome criteria as a basis for patient inclusion. Among 45 studies for which data on the proportion of non-Enterobacteriaceae were available, there was a trend toward higher concordance as this proportion increased.

CONCLUSIONS

The concordance between the LAL test and the detection of gram-negative bacteremia in patients with suspected bacteremia is no higher with the CLAL assay than with the original GLAL version. However, the concordance is higher among studies with a higher proportion of non-Enterobacteriaceae among the gram-negative bacteremia isolates.

Perioperative anti-endotoxin strategies

Lipopolysaccharides from the outer membrane of Gram-negative bacteria are potent stimuli for the production of numerous cytokines by the immune cells. The systemic inflammatory response to these gut-derived endotoxins is therefore dependent on the responsiveness of the immune system. This paper presents results on anti-endotoxin strategies and the responsiveness to endotoxin in animal models of liver failure. Following partial hepatectomy in the normal rat, anti-endotoxin treatment using the enteral endotoxin binder cholestyramine and the bactericidal permeability-increasing protein showed beneficial effects in terms of reducing the exaggerated metabolic and inflammatory responses. Similar beneficial effects of gut endotoxin restriction were found in bile duct ligated rats subjected to a laparotomy. The beneficial effects of anti-endotoxin strategies in these models were explained by completely different mechanisms. In partial hepatectomized rats the effects were explained by the direct inhibition of the stimulatory action of endotoxin on immune cells preventing an exaggerated inflammatory response. In contrast, in postoperative BDL rats the effects of anti-endotoxin therapy were explained by the restoration of endotoxin sensitivity of the immune cells resulting in an inflammatory response necessary for an adequate reaction to surgery. These different mechanism will be discussed in the light of the phenomenon of endotoxin tolerance.

Endotoxemia: methods of detection and clinical correlates

As an assay for endotoxin, the Limulus amebocyte lysate assay has several desirable properties: sensitivity, specificity, and potential for adaptation to a quantitative format. Several modifications have been developed to enhance its potential for clinical application. The modifications that allow quantitative measurement of endotoxin and also improve its application to blood samples are described in this review. In fluids other than blood, the detection of endotoxin with the Limulus amebocyte lysate assay can be used as an aid to identify the presence of gram-negative bacteria, and the assay has established utility. With blood, however, there are a range of factors that interfere with the detection of endotoxemia and there are disparate views with respect to the diagnostic and prognostic significance of the test results. In general, the clinical significance of the finding of endotoxemia broadly parallels the frequency and importance of gram-negative sepsis in the patient groups studied and a decline in endotoxin levels accompanies clinical improvement. However, with therapies designed to reduce levels of endotoxin, or to antagonize its effects, it is unclear whether clinical improvement occurs as a consequence of changes in the levels of endotoxemia.

Inhibition of bacterial translocation in obstructive jaundice by muramyl tripeptide phosphatidylethanolamine in the rat

Obstructive jaundice is frequently associated with septic complications and enteric bacteria have been isolated from both the infectious focus and bile in jaundiced patients. The present study aimed to evaluate bacterial translocation and the influence of a macrophage-stimulant (muramyl tripeptide phosphatidylethanolamine) on bacterial translocation in obstructive jaundice. Male Sprague-Dawley rats were subjected to sham operation (n = 10) or common bile-duct ligation and transection (n = 35). Two weeks later, jaundiced animals received either physiological saline (n = 15), muramyl tripeptide phosphatidylethanolamine liposomes (n = 10) or placebo (empty) liposomes (n = 10) orally, while sham-operated rats received physiological saline, 48 h prior to evaluation of enteric bacterial translocation. Blood, bile and caecal contents were collected and cultured aerobically and anaerobically, as were tissue samples from the liver, spleen and mesenteric lymph nodes. Positive mesenteric lymph node cultures in animals with jaundice + saline (7/15; 47%) and jaundice + placebo liposomes (4/10; 40%) significantly differed (p < 0.05) from sham-operated animals (1/10; 10%) and muramyl tripeptide phosphatidylethanolamine treated animals (0/10). Caecal counts (CFU/g) of Escherichia coli, Lactobacilli and aerobic and microaerobic bacteria did not differ statistically among the groups, although the number of E. coli tended to be higher in jaundiced animals. Thus, liposomal muramyl tripeptide phosphatidylethanolamine inhibits bacterial translocation, probably by activating mucosal macrophages and enhancing reticuloendothelial system function in rats with biliary obstruction.

Endotoxin-induced liver injury after extended hepatectomy and the role of Kupffer cells in the rat

Liver injury by endotoxin given during regeneration following a 70% hepatectomy was examined in Wistar rats. The intravenous administration of endotoxin caused an elevation of the serum GPT level, and severe damage of the remnant liver showing centrilobular necrosis with microthrombi. The highest mortality was induced by the administration of endotoxin to rats 24 h after hepatectomy. Kupffer cells in the regenerative phase of the liver showed an augmented in vitro production of both tumor necrosis factor (TNF) and interleukin-1 (IL-1). The simultaneous administration of heparin and prostagladin E1 (PGE1), which is known to suppress the production of TNF and IL-1, reduced the magnitude of liver injury and the mortality of these rats. The absence of any direct cytotoxic effect of TNF and IL-1 against liver cells suggested that the cytokines, produced by Kupffer cells, play an important but indirect role in the remnant liver injury induced by endotoxin after hepatectomy.

Endotoxin-induced lung hemorrhages in obstructive jaundiced rats

Endotoxemia in patients with biliary obstruction contributes to the high morbidity and mortality rates following surgery. We developed an animal model of disseminated intravascular coagulation (DIC) in rats on which bile duct ligation was performed following an injection of endotoxin (200 micrograms/kg bw). Macroscopic hemorrhages and microthrombi in the lung were found in jaundiced rats 6 hours after the injection of endotoxin and yet these phenomena were not found in non-jaundiced rats following an injection of the same amount of endotoxin. Coagulation studies also revealed characteristic findings of DIC in the jaundiced rats following the injection of endotoxin. This study confirms that obstructive jaundice is one of the main predisposing factors in the course of endotoxin-induced DIC.