Splenectomy ablates endotoxin-induced IFNgamma response in rats

Distinguishing the Concentration- vs. Bioaccumulation-Dependent Immunological and Metabolic Effects of Clofazimine

The antimycobacterial drug clofazimine (CFZ) is used as a single agent at high doses, to suppress the exaggerated inflammation associated with leprosy. Paradoxically, increasing doses of CFZ leads to bioaccumulation of CFZ in the spleen and other organs under physiologically relevant dosing regimens, without accompanying dose-dependent elevation in the concentrations of the circulating drug in the blood. In long-term oral dosing regimens, CFZ induces immunological and metabolic changes resulting in splenomegaly, while the mass of other organs decreases or remains unchanged. As an organ that extensively sequesters CFZ as insoluble drug precipitates, the spleen likely influences drug-induced inflammatory signaling. To probe the role of systemic drug concentrations vs. drug bioaccumulation in the spleen, healthy mice were treated with six different dosing regimens. A subgroup of these mice underwent surgical splenectomies prior to drug treatment to assess the bioaccumulation-dependent changes in immune system signaling and immune-system-mediated drug distribution. Under increasing drug loading, the spleen was observed to grow up to six times in size, sequestering over 10% of the total drug load. Interestingly, when the spleen was removed prior to CFZ administration, drug distribution in the rest of the organism was unaffected. However, there were profound cytokine elevations in the serum of asplenic CFZ-treated mice, indicating that the spleen is primarily involved in suppressing the inflammatory signaling mechanisms that are upregulated during CFZ bioaccumulation. Thus, beyond its role in drug sequestration, the spleen actively modulates the systemic effect of CFZ on the immune system, without impacting its blood concentrations or distribution to the rest of the organism.

Enhanced Bacteremia in Dextran Sulfate-Induced Colitis in Splenectomy Mice Correlates with Gut Dysbiosis and LPS Tolerance

Because both endotoxemia and gut dysbiosis post-splenectomy might be associated with systemic infection, the susceptibility against infection was tested by dextran sulfate solution (DSS)-induced colitis and lipopolysaccharide (LPS) injection models in splenectomy mice with macrophage experiments. Here, splenectomy induced a gut barrier defect (FITC-dextran assay, endotoxemia, bacteria in mesenteric lymph nodes, and the loss of enterocyte tight junction) and gut dysbiosis (increased Proteobacteria by fecal microbiome analysis) without systemic inflammation (serum IL-6). In parallel, DSS induced more severe mucositis in splenectomy mice than sham-DSS mice, as indicated by mortality, stool consistency, gut barrier defect, serum cytokines, and blood bacterial burdens. The presence of green fluorescent-producing (GFP) E. coli in the spleen of sham-DSS mice after an oral gavage supported a crucial role of the spleen in the control of bacteria from gut translocation. Additionally, LPS administration in splenectomy mice induced lower serum cytokines (TNF-α and IL-6) than LPS-administered sham mice, perhaps due to LPS tolerance from pre-existing post-splenectomy endotoxemia. In macrophages, LPS tolerance (sequential LPS stimulation) demonstrated lower cell activities than the single LPS stimulation, as indicated by the reduction in supernatant cytokines, pro-inflammatory genes (iNOS and IL-1β), cell energy status (extracellular flux analysis), and enzymes of the glycolysis pathway (proteomic analysis). In conclusion, a gut barrier defect after splenectomy was vulnerable to enterocyte injury (such as DSS), which caused severe bacteremia due to defects in microbial control (asplenia) and endotoxemia-induced LPS tolerance. Hence, gut dysbiosis and gut bacterial translocation in patients with a splenectomy might be associated with systemic infection, and gut-barrier monitoring or intestinal tight-junction strengthening may be useful.

The Effect of Curcumin on an Animal Intestinal Ischemia/Reperfusion Model for Bacterial Translocation and Inflammatory Response

Ischemia/reperfusion (IR) injury of the intestine is a major problem in abdominal pathological condition and is associated with a high morbidity and mortality. The purpose of the study is to investigate the effects of curcumin on the bacterial translocation incidence and inflammatory response in rats submitted to bowel ischemia reperfusion injury. Thirty-two Wistar albino rats with a weight of 200 to 250 g were used in the study. They were randomly divided into 3 groups (n = 10 for each group): sham only operated group(group I); IR group (group II); and IR + curcumin treatment group (group III). Curcumin (curcumin from Curcuma longa) 20 mg/kg/day was given orally to the curcumin group. All animals were given 109 E. Coli by orogastric intubation 12 hours before sampling. Seventy-two hours after the first operation, mesenteric lymph node and blood samples were obtained and cultured. Blood samples of 2 mL were obtained for a polymerase chain reaction study. A piece of terminal ileum was also sampled for histopathologic examination. Mesenteric lymph node and blood cultures of all control animals were positive for microbiological growth, and polymerase chain reaction results were positive in seven of the eight rats. Histopathologically, edema, vasodilatation and inflammatory cell infiltration were found to be less in the other groups in comparison to the control group. Curcumin reduced bacterial translocation in blood, hepatocellular damage, and plasma cytokine levels. Curcumin reduced the incidence of bacterial translocation in intestinal I/R. rats. These results suggest that Curcumin would be clinically useful in the treatment of intestinal I/R injury.

Role of the spleen in the development of steatohepatitis in high-fat-diet-induced obese rats

Obesity is considered a systemic low-grade inflammatory state. Although the spleen is the main immune organ with a close anatomical relationship with the liver, its role in the progression of fatty liver disease remains uncertain. Therefore, we sought to clarify the functional role of the spleen in the development of steatohepatitis in high-fat (HF)-diet-induced obese rats. Male Sprague-Dawley rats were fed HF food and divided into two groups, a splenectomy (SPX) group and a sham-operation (Sham) group. The liver and abdominal white adipose tissue (WAT) were removed one and six months after surgery, and we evaluated the effects of SPX on WAT and HF-induced fatty liver. SPX rats exhibited worse dyslipidemia and inflammatory changes in WAT one month after surgery. Hepatic steatosis and inflammation were accelerated by SPX, based on the time after surgery. At one month after surgery, the tissue triglyceride content increased in SPX rats, compared with Sham controls (P < 0.05). The liver histology also showed a worsening of steatosis in those rats. At six months after SPX, dramatic inflammatory and fibrotic changes were observed in liver tissue sections. Hepatic carnitine palmitoyltransferase-1 was suppressed at one and six months after SPX (P < 0.05 for each). WAT and liver tissue levels of inflammatory markers such as tumor necrosis factor-α, and the expression of Kupffer cells were all increased at six months in SPX rats, compared with Sham controls (P < 0.05 for each). Our results indicate that the preservation of the spleen contributes to the prevention of the progression of hepatic steatosis to steatohepatitis in obese rats.

Involvement of remnant spleen volume on the progression of steatohepatitis in diet-induced obese rats after a splenectomy

AIM

  This study investigated the correlation between remnant spleen volume after splenectomy (SPX) and the degree of hepatic steatosis and/or inflammation.

METHODS

  Male Sprague-Dawley rats were fed HF food and divided into three groups: sham-operation (Sham) group, a hemisplenectomy (H-SPX) group, and a total-splenectomy (T-SPX) group. Serum was collected and livers removed 12 weeks after surgery. We measured serum lipid markers and evaluated liver changes by comparing the three groups. Additionally, we examined liver changes 24 weeks after SPX.

RESULTS

  Serum triglyceride and free fatty acid levels after SPX were higher than those of sham controls, and a significant difference was found between T-SPX and the other groups (P < 0.05 for each). Increased intrahepatic fat accumulation was shown in SPX rats along with lower residual spleen volume; this fat accumulation after SPX was accelerated in rats at 24 weeks. Additionally, liver inflammatory changes, including an increase in the Kupffer cell population and pro-inflammatory cytokine production, as well as a high level of oxidative stress, were observed in the liver sections from SPX rats, which correlated significantly with less volume of the residual spleen. Also, an increase in pro-inflammatory cytokine content and a decrease in anti-inflammatory cytokine content were shown in the residual spleen from H-SPX rats, as compared to those of sham controls (P < 0.05 for each).

CONCLUSION

  These results indicate the importance of preserving splenic tissue. This residual spleen may play an important role in preventing the progression from diet-induced hepatic steatosis to steatohepatitis.

A hepatic protein, fetuin-A, occupies a protective role in lethal systemic inflammation

Background

A liver-derived protein, fetuin-A, was first purified from calf fetal serum in 1944, but its potential role in lethal systemic inflammation was previously unknown. This study aims to delineate the molecular mechanisms underlying the regulation of hepatic fetuin-A expression during lethal systemic inflammation (LSI), and investigated whether alterations of fetuin-A levels affect animal survival, and influence systemic accumulation of a late mediator, HMGB1.

Methods and Findings

LSI was induced by endotoxemia or cecal ligation and puncture (CLP) in fetuin-A knock-out or wild-type mice, and animal survival rates were compared. Murine peritoneal macrophages were challenged with exogenous (endotoxin) or endogenous (IFN-γ) stimuli in the absence or presence of fetuin-A, and HMGB1 expression and release was assessed. Circulating fetuin-A levels were decreased in a time-dependent manner, starting between 26 h, reaching a nadir around 24–48 h, and returning towards base-line approximately 72 h post onset of endotoxemia or sepsis. These dynamic changes were mirrored by an early cytokine IFN-γ-mediated inhibition (up to 50–70%) of hepatic fetuin-A expression. Disruption of fetuin-A expression rendered animals more susceptible to LSI, whereas supplementation of fetuin-A (20–100 mg/kg) dose-dependently increased animal survival rates. The protection was associated with a significant reduction in systemic HMGB1 accumulation in vivo, and parallel inhibition of IFN-γ- or LPS-induced HMGB1 release in vitro.

Conclusions

These experimental data suggest that fetuin-A is protective against lethal systemic inflammation partly by inhibiting active HMGB1 release.

Regulation of lipopolysaccharide-induced inflammatory response and endotoxemia by beta-arrestins

Beta-arrestins are scaffolding proteins implicated as negative regulators of TLR4 signaling in macrophages and fibroblasts. Unexpectedly, we found that beta-arrestin-1 (beta-arr-1) and -2 knockout (KO) mice are protected from TLR4-mediated endotoxic shock and lethality. To identify the potential mechanisms involved, we examined the plasma levels of inflammatory cytokines/chemokines in the wild-type (WT) and beta-arr-1 and -2 KO mice after lipopolysaccharide (LPS, a TLR4 ligand) injection. Consistent with lethality, LPS-induced inflammatory cytokine levels in the plasma were markedly decreased in both beta-arr-1 and -2 KO, compared to WT mice. To further explore the cellular mechanisms, we obtained splenocytes (separated into CD11(b+) and CD11(b-) populations) from WT, beta-arr-1, and -2 KO mice and examined the effect of LPS on cytokine production. Similar to the in vivo observations, LPS-induced inflammatory cytokines were significantly blocked in both splenocyte populations from the beta-arr-2 KO compared to the WT mice. This effect in the beta-arr-1 KO mice, however, was restricted to the CD11(b-) splenocytes. Our studies further indicate that regulation of cytokine production by beta-arrestins is likely independent of MAPK and IkappaBalpha-NFkappaB pathways. Our results, however, suggest that LPS-induced chromatin modification is dependent on beta-arrestin levels and may be the underlying mechanistic basis for regulation of cytokine levels by beta-arrestins in vivo. Taken together, these results indicate that beta-arr-1 and -2 mediate LPS-induced cytokine secretion in a cell-type specific manner and that both beta-arrestins have overlapping but non-redundant roles in regulating inflammatory cytokine production and endotoxic shock in mice.

NK but not CD1-restricted NKT cells facilitate systemic inflammation during polymicrobial intra-abdominal sepsis

Evidence suggests that NK and NKT cells contribute to inflammation and mortality during septic shock caused by cecal ligation and puncture (CLP). However, the specific contributions of these cell types to the pathogenesis of CLP-induced septic shock have not been fully defined. The goal of the present study was to determine the mechanisms by which NK and NKT cells mediate the host response to CLP. Control, NK cell-deficient, and NKT cell-deficient mice underwent CLP. Survival, cytokine production, and bacterial clearance were measured. NK cell trafficking and interaction with myeloid cells was also studied. Results show that mice treated with anti-asialoGM1 (NK cell deficient) or anti-NK1.1 (NK/NKT cell deficient) show less systemic inflammation and have improved survival compared with IgG-treated controls. CD1 knockout mice (NKT cell deficient) did not demonstrate decreased cytokine production or improved survival compared with wild type mice. Trafficking studies show migration of NK cells from blood and spleen into the inflamed peritoneal cavity where they appear to facilitate the activation of peritoneal macrophages (F4-80(+)GR-1(-)) and F4-80(+)Gr-1(+) myeloid cells. These findings indicate that NK but not CD1-restricted NKT cells contribute to acute CLP-induced inflammation. NK cells appear to mediate their proinflammatory functions during septic shock, in part, by migration into the peritoneal cavity and amplification of the proinflammatory activities of specific myeloid cell populations. These findings provide new insights into the mechanisms used by NK cells to facilitate acute inflammation during septic shock.

Obstructive jaundice promotes intestinal-barrier dysfunction and bacterial translocation: experimental study

BACKGROUND

Although clinical and experimental studies have demonstrated a correlation between obstructive jaundice and the development of sepsis, the mechanism has not been fully elucidated.

PURPOSE

The aim of this study was to investigate the influence of biliary obstruction on bacterial translocation as a possible source of infection in cases of obstructive jaundice.

MATERIAL AND METHODS

Two groups of 12 Wistar rats were examined: rats subjected to common bile duct (CBD) ligation (group A) and rats subjected to a sham operation (group B). After 7 days, blood samples were taken and liver, spleen, and mesenteric lymph nodes (MLNs) from the ileocecal area were removed, divided into small pieces, and cultured. Quantitative culture results were determined by the number of colony-forming units (CFU) per milliliter of homogenate. Bacterial translocation was defined as the presence of a positive culture of MLNs, blood, liver, and/or spleen. Samples for histopathological examination were taken from the mucosa of the ileum and the colon and evaluated for inflammatory and destructive changes.

RESULTS

There was no evidence of bacterial translocation to MLNs, blood, spleen, or liver detected in any of the 12 sham-operated control rats. In contrast, bacterial translocation was demonstrated in 8 of the 12 CBD-ligated rats (P < 0.01). In all eight cases in which translocation occurred, Escherichia coli were cultured from the MLNs. There were no histological changes in the mucosal samples of the control animals. In the CBD-ligated rats, hyperemia, vacuolization, reduction of goblet cells, decreased mitotic activity, and infiltration by lymphocytes and polymorphonuclear leukocytes (PMNLs) were detected. Cases in which translocation occurred were significantly associated with decreased mitotic activity in the colon (r = -0.5, P < 0.01) and higher infiltration by PMNLs in the ileum (r = -0.62, P < 0.05).

CONCLUSION

Obstructive jaundice in a rat model predisposes to bacterial translocation. This suggests a mechanism whereby jaundiced patients are susceptible to septic complication.

The role of the spleen in laparoscopy-associated inflammatory response

BACKGROUND

Carbon dioxide (CO(2)) pneumoperitoneum alters the inflammatory response in animal models of sepsis. The spleen is a key organ in inflammation and its removal was predicted to modify this effect.

METHODS

The acute phase inflammatory response to lipopolysaccharide (LPS) challenge in male rats was examined for the effects of splenectomy (spx) and the technique of removal (open or laparpscopic). A series of experiments compared LPS-only controls with LPS injection 2 or 9 days following open spx, lap CO2 spx, open sham, or lap CO2 sham. The method of splenectomy was studied by randomization to control, open spx, lap CO2 spx, lap helium (He) spx, or lap air spx with LPS challenge on postoperative day 2. Serum levels of tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (INF-gamma) and, interleutin (IL) 10 were collected at multiple time points, assayed by commercial enzyme-linked immunosorbent assay, analyzed by analysis of variance.

RESULTS

Levels of TNF-alpha at 1.5 were significantly lower following open sham than following lap sham (p < 0.05). Splenectomy drastically reduced INF-gamma and TNF-alpha levels compared to controls (p < 0.05) on postoperative day 2. No method of spx preserved TNF-alpha or INF-gamma responses. Recovery of TNF-alpha response on day 9 was delayed in the spx groups.

CONCLUSIONS

Splenectomy dramatically reduces TNF-alpha and INF-gamma responses to LPS challenge, although by different mechanisms. Pneumoperitoneum-mediated modulation of the septic inflammatory response is partially dependent on the spleen.

IL-10 Plasma Levels are Elevated After LPS Injection in Splenectomized A/J Mice1

BACKGROUND

Splenectomy is clinically indicated in certain cases of hypersplenism and splenic trauma. However, it is associated with serious complications, in particular, reduced clearance of encapsulated organisms and a high incidence of sepsis, which has been coined overwhelming post-splenectomy sepsis (OPSS). In addition to the role of the spleen in the clearance of microorganisms, this organ may be involved in regulation of the inflammatory response. We investigated the effect of splenectomy on the inflammatory process induced by LPS in a murine model that resembles, in part, the pathophysiological aspects of sepsis.

MATERIALS AND METHODS

Male mice (8-weeks-old) from different inbred strains were randomized into three groups: splenectomized (SPX), sham operated (SHAM), and non-operated controls (NoOp). After 9 days of recovery, mice were injected with LPS (15 mg/kg) and cytokine plasma levels were measured by ELISA at 1.5 or 6 h after injection. Peritoneal macrophages (PMphi) were isolated from the three groups, and cytokine production was evaluated after incubation with LPS in culture conditions.

RESULTS

IL-10 plasma levels were elevated in SPX A/J mice (6.7 +/- 0.4 mug/ml) after injection of LPS (15 mg/kg) compared to NoOp A/J mice (4.2 +/- 0.2 mug/ml, P < 0.05). Similar elevation in IL-10 plasma levels was detected in SPX DBA/2J mice as compared to NoOp DBA/2J mice, but not in C57BL/6J and BALB/cJ mice. In contrast, SPX AKR mice displayed lower IL-10 levels than NoOp mice. PMphis from SPX A/J mice produced elevated levels of IL-10 compared to PMphis from SHAM or NoOp A/J mice, mimicking the in vivo observations.

CONCLUSION

Our data suggest that the spleen plays an important role in modulating the inflammatory process induced by LPS, extending beyond passive clearance of encapsulated organisms. In addition, the contribution of the spleen to the inflammatory process may be influenced by the genetic background.

Bench to bedside: HMGB1-a novel proinflammatory cytokine and potential therapeutic target for septic patients in the emergency department

Overwhelming gram-negative bacterial infection and life-threatening systemic inflammation are widespread problems in critically ill emergency department patients. Currently, the treatment of these patients is largely supportive, focusing on antibiotics, fluids, hemodynamic and ventilatory support, and intensive monitoring. The only Food and Drug Administration-approved pharmaceutical agent for the treatment of sepsis is activated protein C, with its use largely relegated to the intensive care unit. The subject thus remains an active area of exploration for emergency medicine research. During sepsis and inflammation, innate immune cells release excessive amounts of proinflammatory cytokines such as tumor necrosis factor (TNF) and interleukin-1beta. If delivered early enough, anti-TNF antibodies can be an effective therapy in experimental models of septic shock. Anti-TNF antibodies have been developed for clinical use in rheumatoid arthritis and Crohn's disease. However, anti-TNF treatment for sepsis has been difficult to achieve in the clinical setting, perhaps because TNF's early release and transient appearance in the serum create a narrow therapeutic window. An alternative strategy would be to identify "late" mediators that may be clinically more accessible. High mobility group box 1 (HMGB1), a protein previously known only as a nuclear transcription factor, is now implicated as a late mediator of sepsis. Targeting late mediators of lethal systemic inflammation represents a novel approach that may widen the therapeutic window and lead to new strategies for inhibiting the deleterious effects of the inflammatory cascade. Here the authors review the studies that led to the discovery of HMGB1 as a late mediator of systemic inflammation and discuss the possibility of HMGB1 as a therapeutic target for septic patients in the emergency department.

Enhanced interferon-gamma production and bacterial clearance in the liver of splenectomized mice in the models of Escherichia coli injection or intestinal obstruction

Although several studies have reported that splenectomy increases susceptibility to bacterial infections, other reports have indicated that splenectomy does not induce such susceptibility. To clarify this discrepancy, we studied the effects of splenectomy in the models of lipopolysaccharide (LPS) or Escherichia coli challenge and intestinal obstruction, focusing on cytokine production and bacterial clearance in the liver. Using C57BL/6 mice at 4 weeks after splenectomy or a sham operation, either LPS or E. coli was injected or an intestinal obstruction was made to examine the mortality, serum cytokine levels, cytokine production of the liver mononuclear cells (MNCs), and bacterial clearance in the liver. As a result, no differences were observed in survival rates after LPS or E. coli challenge between the mice with and without splenectomy. However, in a model of intestinal obstruction, splenectomized mice survived significantly longer than the sham-operated mice. Liver MNCs from splenectomized mice produced a significantly larger amount of interferon-gamma compared with those from sham-operated mice. Furthermore, bacterial counts in the liver at 2 h after E. coli injection and at 24 h after intestinal obstruction were significantly decreased in splenectomized mice compared with sham-operated mice. In conclusion, splenectomy does not impair host defense against bacteria infection provided that recovery is sufficient to allow compensatory processes in the liver to occur.

Mast cells and resistance to peritoneal sepsis after burn injury

A mouse model of burn injury demonstrates increasing mortality to an infectious challenge in the form of cecal ligation and puncture (CLP) reaching a peak at 10 days after injury. Because it is widely believed that peritoneal mast cells play an important role in the defense against peritoneal sepsis, we wished to explore the possibility that peritoneal mast cell dysfunction contributed to increased CLP mortality after burn injury. Kit(W-v) C57BL/6 mice, which were shown to lack peritoneal mast cells by cytospin and flow cytometry, and normal littermate control animals were subjected to 25% burn or sham burn injury and 10 days later underwent CLP. Burn injured Kit(W-v) and normal littermates had a high CLP mortality when compared with sham-injured Kit(W-v) and normal littermates (P < 0.003), but the sham- and burn-injured Kit(W-v) and normal littermate animals did not differ from one another with respect to CLP mortality. This result prompted a comparison of CLP mortality in untreated WBB6F1 Kit(W/W-v) mice, known to be mast cell deficient, and normal littermate controls, as well as untreated C57BL/6 Kit(W-v) and normal littermates. The WBB6F1 Kit(W/W-v) mice showed significantly increased mortality after CLP as compared with the littermate controls (P = 0.03), whereas both C57BL/6 Kit(W-v) and littermate controls had very low mortality after CLP. A study of peritoneal cell populations 24 h after CLP failed to reveal an obvious cause for the difference in CLP survival between the two mast cell-deficient strains. Tumor necrosis factor-alpha (TNF-alpha) measurements in peritoneal fluid showed appreciable amounts of TNF-alpha in the littermate controls of both strains and little in the fluid obtained from the mast cell-deficient animals of both strains. We conclude that peritoneal mast cell dysfunction is unlikely to be a major cause of decreased resistance to peritoneal sepsis in burn-injured animals and that the importance of peritoneal mast cells in combating peritoneal sepsis in the mouse appears to be strain dependent.

IFN-gamma induces high mobility group box 1 protein release partly through a TNF-dependent mechanism

We recently discovered that a ubiquitous protein, high mobility group box 1 protein (HMGB1), is released by activated macrophages, and functions as a late mediator of lethal systemic inflammation. To elucidate mechanisms underlying the regulation of HMGB1 release, we examined the roles of other cytokines in induction of HMGB1 release in macrophage cell cultures. Macrophage migration inhibitory factor, macrophage-inflammatory protein 1beta, and IL-6 each failed to significantly induce the release of HMGB1 even at supraphysiological levels (up to 200 ng/ml). IFN-gamma, an immunoregulatory cytokine known to mediate the innate immune response, dose-dependently induced the release of HMGB1, TNF, and NO, but not other cytokines such as IL-1alpha, IL-1beta, or IL-6. Pharmacological suppression of TNF activity with neutralizing Abs, or genetic disruption of TNF expression (TNF knockout) partially (50-60%) inhibited IFN-gamma-mediated HMGB1 release. AG490, a specific inhibitor for Janus kinase 2 of the IFN-gamma signaling pathway, dose-dependently attenuated IFN-gamma-induced HMGB1 release. These data suggest that IFN-gamma plays an important role in the regulation of HMGB1 release through a TNF- and Janus kinase 2-dependent mechanism.

Differential induction of hepatic dysfunction after intraportal and intravenous challenge with endotoxin and Staphylococcal enterotoxin B

We have previously shown that systemic infusion of the bacterial toxins Staphylococcal enterotoxin B (SEB) and endotoxin (LPS) induces hepatic dysfunction as measured by decreased biliary indocyanine green (ICG) excretion. In this study, we compare the effects of these bacterial toxins after infusion into the portal and systemic circulation and directly measure biliary bile acid excretion as a measure of cholestasis. We hypothesized that bacterial toxins infused into the portal vein would induce greater hepatic dysfunction than toxins infused into the systemic circulation. Using a chronically catheterized rat model, biliary bile acid excretion was directly measured after infusion of LPS at 10 and 100 microg/kg with and without 50 microg/kg SEB into the portal vein (IPV) or inferior vena cava (IV) at baseline, and at 6 and 24 h. We found that when LPS was infused alone, only IPV administration caused a significant decrease in bile acid excretion at 6 h. There was no change in bile acid excretion after IV administration of LPS. In contrast, when the combination of LPS and SEB was infused, both IV and IPV administration significantly decreased bile acid excretion at 6 and 24 h. At 6 h post-LPS and -SEB administration, the decrease in bile acid excretion was significantly greater after IPV than IV administration. There was no site-specific difference in IFN-gamma release after infusion of toxins. However, peak TNFalpha release was decreased in IPV-infused rats [10 microg/kg (P < 0.05) or 100 microg/kg (P = ns) LPS with SEB] compared with the same doses in IV-infused rats. These data question the role of systemic TNF-alpha and IFN-gamma in regulating hepatic dysfunction and suggest a differential functional response of the liver to systemic and gut-derived septic events. This study also further explains the frequent development of liver dysfunction in patients with sepsis, multisystem organ failure, and other diseases with altered intestinal permeability.