Intestinal gram-negative bacterial overgrowth in vivo augments the in vitro response of Kupffer cells to endotoxin

Neural control of the spleen as an effector of immune responses to inflammation: mechanisms and treatments

Immune system responses are a vital defense mechanism against pathogens. Inflammatory mediators finely regulate complex inflammatory responses from initiation to resolution. However, in certain conditions, the inflammation is initiated and amplified, but not resolved. Understanding the biological mechanisms underlying the regulation of the immune response is critical for developing therapeutic alternatives, including pharmaceuticals and bioelectronic tools. The spleen is an important immune effector organ since it orchestrates innate and adaptive immune responses such as pathogen clearance, cytokine production, and differentiation of cells, therefore playing a modulatory role that balances pro- and anti-inflammatory responses. However, modulation of splenic immune activity is a largely unexplored potential therapeutic tool that could be used for the treatment of inflammatory and life-threatening conditions. This review discusses some of the mechanisms controlling neuroimmune communication and the brain-spleen axis.

Pathophysiology of sepsis

PURPOSE OF REVIEW

To provide a current overview of sepsis pathophysiology.

RECENT FINDINGS

The emphasis on sepsis pathophysiology has moved away from the pathogen - the initiating factor - and instead is focussed upon the abnormal and exaggerated host response. Instead of targeted eradication of the infection, the host response activates or suppresses multiple downstream pathways, leading to multiple organ dysfunction.

SUMMARY

Sepsis represents a dysregulated host response to infection leading to organ dysfunction. Here, the pathogen triggers an initial exaggerated inflammatory-immune response that leads to activation or suppression of multiple endothelial, hormonal, bioenergetic, metabolic, immune, and other pathways. These, in turn, produce the circulatory and metabolic perturbations resulting in organ dysfunction. This review will provide an overview of underlying mechanisms and propose that these processes, whereas superficially viewed as dysfunctional, may actually be adaptive/protective in the first instance, though spilling over into maladaptation/harm depending on the magnitude of the host response.

A Brazilian regional basic diet-induced chronic malnutrition drives liver inflammation with higher ApoA-I activity in C57BL6J mice

Malnutrition is still considered endemic in many developing countries. Malnutrition-enteric infections may cause lasting deleterious effects on lipid metabolism, especially in children living in poor settings. The regional basic diet (RBD), produced to mimic the Brazilian northeastern dietary characteristics (rich in carbohydrate and low in protein) has been used in experimental malnutrition models, but few studies have explored the effect of chronic RBD on liver function, a central organ involved in cholesterol metabolism. This study aimed to investigate whether RBD leads to liver inflammatory changes and altered reverse cholesterol metabolism in C57BL6/J mice compared to the control group, receiving a standard chow diet. To evaluate liver inflammation, ionized calcium-binding adapter protein-1 (IBA-1) positive cell counting, interleukin (IL)-1β immunohistochemistry, and tumor necrosis factor (TNF)-α and IL-10 transcription levels were analyzed. In addition, we assessed reverse cholesterol transport by measuring liver apolipoprotein (Apo)E, ApoA-I, and lecithin-cholesterol acyltransferase (LCAT) by RT-PCR. Furthermore, serum alanine aminotransferase (ALT) was measured to assess liver function. RBD markedly impaired body weight gain compared with the control group (P<0.05). Higher hepatic TNF-α (P<0.0001) and IL-10 (P=0.001) mRNA levels were found in RBD-challenged mice, although without detectable non-alcoholic fatty liver disease. Marked IBA-1 immunolabeling and increased number of positive-IBA-1 cells were found in the undernourished group. No statistical difference in serum ALT was found. There was also a significant increase in ApoA mRNA expression in the undernourished group, but not ApoE and LCAT, compared with the control. Altogether our findings suggested that chronic RBD-induced malnutrition leads to liver inflammation with increased ApoA-I activity.

Regulatory Function of Buckwheat-Resistant Starch Supplementation on Lipid Profile and Gut Microbiota in Mice Fed with a High-Fat Diet

Buckwheat-resistant starch (BRS) has shown to be a nutrient capable of lowering cholesterol and reducing obesity. In this study, the regulatory effects of tartary buckwheat starch on blood lipid level and gut microbiota (Lactobacillus, Bifidobacterium, Enterococcus, and Escherichia coli) in mice fed with a high-fat diet was investigated. Male C57BL/6 mice were separately fed with a normal diet (CON), a high-fat diet (HFD), and high-fat diet supplemented with buckwheat-resistant starch (HFD+BRS) for 6 weeks. After the feedings, lipid profile, blood glucose, plasma levels of cytokines, short-chain fatty acid content in the colon and intestinal flora of fecal were measured. Furthermore, the antioxidant indices of the liver and duodenum tissues were measured to evaluate the antioxidant capacity of mice. Significantly reduced plasma levels of total cholesterol (TC), triglyceride (TG), glucose, and cytokines were observed in the HFD+BRS group, accompanied by an increased antioxidant capacity in the liver and duodenum. In addition, supplementation with BRS significantly inhibited the increase in plasma lipopolysaccharide, tumor necrosis factor-α, and interleukin-6 levels. Gut microbiota composition was regulated by the supplement of BRS, which promoted the growth of Lactobacillus, Bifidobacterium, and Enterococcus, as well as inhibited the growth of Escherichia coli. In contrast to the HFD group, the content of short-chain fatty acids in mice colon increased in the BRS group. In conclusion, BRS benefited the cholesterol and glucose metabolism, as well as optimized gut microbiota composition in mice fed with a high-fat diet. PRACTICAL APPLICATION: This study identified the beneficial effects of tartary buckwheat-resistant starch on the regulation of blood lipids and intestinal flora in mice fed a high-fat diet. The result of this study will provide a basis for the development of probiotic products supplemented with tartary buckwheat-resistant starch and direction for further research.

The hepatocyte as a microbial product-responsive cell

Much research has focused on the responses to microbial products of immune cells such as monocytes, macrophages, and neutrophils. Although the liver is a primary response organ in various infections, relatively little is known about the antimicrobial responses of its major cell type, the hepatocyte. It is now known that the recognition of bacteria occurs via cell-surface proteins that are members of the Toll-like receptor (TLR) family. In addition, lipopolysaccharide (LPS) is bound by circulating LPS-binding protein (LBP) and presented to cell-surface CD14, which in turn interacts with TLR and transduces an intracellular signal. We investigated the CD14 and TLR2 responses of whole liver and isolated hepatocytes, and demonstrated that these cells can be induced to express the molecules necessary for responses to both Gram-positive and Gram-negative bacteria. Our findings may have clinical implications for pathological states such as sepsis.

Neonatal sepsis: the gut connection

Colonization of the neonatal gut takes place immediately after birth. Bacteria that get colonized are considered to be "normal" flora derived principally from the mother and the immediate environment. However, for some neonates, the colonization of the gut, particularly with potential pathogens, may lead to subsequent infections or sepsis. The immune system and the gut barrier in neonates is vulnerable, with decreased acid secretion, low levels of protective mucous, and decreased motility, particularly in those who are premature and of low birth weight. This makes the neonatal gut especially prone to colonization with aerobic Gram-negative bacilli (GNB). And these GNB may later, under circumstances favorable to them, cause disease in the neonates. In developing countries, it is the GNB that cause the majority of the infections. In addition, the use of antibiotics in the neonatal intensive care unit also triggers colonization with antibiotic-resistant bacteria. This review discusses various aspects of neonatal gut colonization, neonatal sepsis, and tries to gather support to understand the connection between the gut and subsequent sepsis in neonates.

Non-alcoholic fatty liver disease and obesity: Biochemical, metabolic and clinical presentations

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world. Presentation of the disease ranges from simple steatosis to non-alcoholic steatohepatitis (NASH). NAFLD is a hepatic manifestation of metabolic syndrome that includes central abdominal obesity along with other components. Up to 80% of patients with NAFLD are obese, defined as a body mass index (BMI) > 30 kg/m². However, the distribution of fat tissue plays a greater role in insulin resistance than the BMI. The large amount of visceral adipose tissue (VAT) in morbidly obese (BMI > 40 kg/m²) individuals contributes to a high prevalence of NAFLD. Free fatty acids derived from VAT tissue, as well as from dietary sources and de novo lipogenesis, are released to the portal venous system. Excess free fatty acids and chronic low-grade inflammation from VAT are considered to be two of the most important factors contributing to liver injury progression in NAFLD. In addition, secretion of adipokines from VAT as well as lipid accumulation in the liver further promotes inflammation through nuclear factor kappa B signaling pathways, which are also activated by free fatty acids, and contribute to insulin resistance. Most NAFLD patients are asymptomatic on clinical presentation, even though some may present with fatigue, dyspepsia, dull pain in the liver and hepatosplenomegaly. Treatment for NAFLD and NASH involves weight reduction through lifestyle modifications, anti-obesity medication and bariatric surgery. This article reviews the available information on the biochemical and metabolic phenotypes associated with obesity and fatty liver disease. The relative contribution of visceral and liver fat to insulin resistance is discussed, and recommendations for clinical evaluation of affected individuals is provided.

Assessment of the fecal lactobacilli population in patients with hepatitis B virus-related decompensated cirrhosis and hepatitis B cirrhosis treated with liver transplant

This study aims to provide an overview of the diversity of intestinal Lactobacillus among Chinese patients with hepatitis B virus (HBV)-related decompensated cirrhosis and who received liver transplant for hepatitis B cirrhosis. Fecal samples were collected from 38 healthy volunteers, 61 patients with HBV-related decompensated cirrhosis (group LC) and 74 patients who had liver transplant for hepatitis B cirrhosis (group LT). Quantitative polymerase chain reaction technology with species-specific primers was applied to investigate lactobacilli 16S rDNA in crude DNA, extracted from fecal samples. Software package Statistical Package for the Social Sciences and Palaeontological Statistics for Windows was used to analyze the data. Lactobacilli population of the two patient groups was different from the healthy control subjects, principal differences being marked decrease in the population of Lactobacillus rhamnosus (p < 0.001 for both patient groups) and reduction in the frequency of Lactobacillus fermentus (p < 0.001 for group LC and p < 0.01 for group LT). Our findings on the frequency of lactobacilli population suggested decreased diversity in groups LC and LT (compared with the healthy controls (p < 0.001 and p < 0.01, respectively)). Patients tended to have less complex fecal lactobacilli composition than the healthy controls, especially in the group LC.

Involvement of endotoxin in the mortality of mice with gut-derived sepsis due to methicillin-resistant Staphylococcus aureus

MRSA causes a wide diversity of diseases, ranging from benign skin infections to life-threatening diseases, such as sepsis. However, there have been few reports of the pathophysiology and mechanisms of sepsis resulting from the gut-derived origin of MRSA. Therefore, we established a murine model of gut-derived sepsis with MRSA and factors of MRSA sepsis that cause deterioration. We separated mice into four groups according to antibiotic treatment as follows: (i) ABPC 40 mg/kg; (ii) CAZ 80 mg/kg; (iii) CAZ 80 mg/kg + endotoxin 10 microg/mouse; and (iv) saline-treated control groups. Gut-derived sepsis was induced by i.p. injection of cyclophosphamide after colonization of MRSA strain 334 in the intestine. After the induction of sepsis, significantly more CAZ-treated mice survived compared with ABPC-treated and control groups. MRSA were detected in the blood and liver among all groups. Endotoxin levels were significantly lower in the CAZ-treated group compared to other groups. Inflammatory cytokine levels in the serum were lower in the CAZ-treated group compared to other groups. Fecal culture showed a lower level of colonization of E. coli in the CAZ-treated group compared to other groups. In conclusion, we found that CAZ-treatment ameliorates infection and suppresses endotoxin level by the elimination of E. coli from the intestinal tract of mice. However, giving endotoxin in the CAZ-treated group increased mortality to almost the same level as in the ABPC-treated group. These results suggest endotoxin released from resident E. coli in the intestine is involved in clinical deterioration resulting from gut-derived MRSA sepsis.

Chemical modulators of the innate immune response alter gypsy moth larval susceptibility to Bacillus thuringiensis

Background

The gut comprises an essential barrier that protects both invertebrate and vertebrate animals from invasion by microorganisms. Disruption of the balanced relationship between indigenous gut microbiota and their host can result in gut bacteria eliciting host responses similar to those caused by invasive pathogens. For example, ingestion of Bacillus thuringiensis by larvae of some species of susceptible Lepidoptera can result in normally benign enteric bacteria exerting pathogenic effects.

Results

We explored the potential role of the insect immune response in mortality caused by B. thuringiensis in conjunction with gut bacteria. Two lines of evidence support such a role. First, ingestion of B. thuringiensis by gypsy moth larvae led to the depletion of their hemocytes. Second, pharmacological agents that are known to modulate innate immune responses of invertebrates and vertebrates altered larval mortality induced by B. thuringiensis. Specifically, Gram-negative peptidoglycan pre-treated with lysozyme accelerated B. thuringiensis-induced killing of larvae previously made less susceptible due to treatment with antibiotics. Conversely, several inhibitors of the innate immune response (eicosanoid inhibitors and antioxidants) increased the host's survival time following ingestion of B. thuringiensis.

Conclusions

This study demonstrates that B. thuringiensis infection provokes changes in the cellular immune response of gypsy moth larvae. The effects of chemicals known to modulate the innate immune response of many invertebrates and vertebrates, including Lepidoptera, also indicate a role of this response in B. thuringiensis killing. Interactions among B. thuringiensis toxin, enteric bacteria, and aspects of the gypsy moth immune response may provide a novel model to decipher mechanisms of sepsis associated with bacteria of gut origin.

Causes and metabolic consequences of Fatty liver

Type 2 diabetes and cardiovascular disease represent a serious threat to the health of the population worldwide. Although overall adiposity and particularly visceral adiposity are established risk factors for these diseases, in the recent years fatty liver emerged as an additional and independent factor. However, the pathophysiology of fat accumulation in the liver and the cross-talk of fatty liver with other tissues involved in metabolism in humans are not fully understood. Here we discuss the mechanisms involved in the pathogenesis of hepatic fat accumulation, particularly the roles of body fat distribution, nutrition, exercise, genetics, and gene-environment interaction. Furthermore, the effects of fatty liver on glucose and lipid metabolism, specifically via induction of subclinical inflammation and secretion of humoral factors, are highlighted. Finally, new aspects regarding the dissociation of fatty liver and insulin resistance are addressed.

Impact of the indigenous flora in animal models of shock and sepsis

Septicemia is currently the 10th leading cause of death in the United States, and shock and trauma patients are the source of much of the morbidity and mortality associated with septicemia. There is substantial evidence that the composition of the indigenous flora plays an important role in modulating outcome variables in animal models of shock and sepsis. Germ-free animals that lack an indigenous flora are not as susceptible to shock as their conventionally reared counterparts. And, in conventionally reared animals, the composition of the intestinal flora can also modulate outcome in shock and sepsis. For example, certain bacterial species/strains disseminate from the intestinal tract more easily than others, antibiotic-induced alterations of the flora can modulate the incidence of systemic spread, and a certain threshold number of intestinal bacteria facilitates extraintestinal dissemination. The composition of the intestinal flora can also affect intestinal permeability, the production of inflammatory mediators, and the responses of immune cells in extraintestinal sites. And, there is evidence that prior exposure to endotoxin, via either the oral or systemic route, can influence outcome in animals challenged with parenteral endotoxin, a widely used model of endotoxin shock. The general composition of intestinal flora of experimental animals can be characterized with relative ease. This knowledge can aid data interpretation, either to help explain irreproducible or expected results or to verify that observed differences are likely related to the dependent variable studied rather than the composition of the indigenous flora.

Muscularis inflammation and the loss of interstitial cells of Cajal in the endothelin ETB receptor null rat

Endothelin receptor null rats [ETB(-/-)] are a model for long-segment Hirschsprung's disease. These animals have significant intestinal distension (megaileum) proximal to a constricted region of the gastrointestinal tract lacking enteric ganglia. Experiments were performed to determine the pathophysiological changes that occur in these animals and to examine the tunica muscularis as a unique, immunologically active compartment. We observed abnormal intestinal flora in ETB(-/-) rats, which included a marked increase in gram-negative aerobes (Enterobacteriaceae) and anaerobes (Bacteroidaceae) in the distended region of the small intestine. Histochemical observations showed that neutrophilic infiltration was rarely or not observed, but the number of ED2 positive macrophages was increased in the tunica muscularis. Expression of IL-1beta and IL-6 mRNA was also significantly increased, and the level of CD14 (LPS receptors) were increased significantly in the tunica muscularis. Spontaneous phasic contractions were irregular in the distended intestinal regions of ETB(-/-) rats, and this was associated with an increased number of macrophages and damage to interstitial cells of Cajal (ICC) as revealed by using Kit-like immunoreactivity and electron microscopy. These results suggest that ED2-positive resident macrophages may play an important role in the inflammation of tunica muscularis in ETB(-/-) rats. Increased numbers and activation of macrophages may result in damage to ICC networks leading to disordered intestinal rhythmicity in regions of the gut in which myenteric ganglia are intact.

Norepinephrine regulates hepatic innate immune system in leptin-deficient mice with nonalcoholic steatohepatitis

It is not known why natural killer T (NKT) cells, which modulate liver injury by regulating local cytokine production, are reduced in leptin-deficient ob/ob mice. NKT cells express adrenoceptors. Thus, we hypothesize that the low norepinephrine (NE) activity of ob/ob mice promotes depletion of liver NKT cells, thereby sensitizing ob/ob livers to lipopolysaccharide (LPS) toxicity. To evaluate this hypothesis, hepatic NKT cells were quantified in wild-type mice before and after treatment with NE inhibitors, and in dopamine beta-hydroxylase knockout mice (which cannot synthesize NE) and ob/ob mice before and after 4 weeks of NE supplementation. Decreasing NE activity consistently reduces liver NKT cells, while increasing NE has the opposite effect. Analysis of hepatic and thymic NKT cells in mice of different ages demonstrate an age-related accumulation of hepatic NKT cells in normal mice, while liver NKT cells become depleted after birth in ob/ob mice, which have increased apoptosis of hepatic NKT cells. NE treatment inhibits apoptosis and restores hepatic NKT cells. In ob/ob mice with reduced hepatic NKT cells, hepatic T and NKT cells produce excessive T helper (Th)-1 proinflammatory cytokines and the liver is sensitized to LPS toxicity. NE treatment decreases Th-1 cytokines, increases production of Th-2 cytokines, and reduces hepatotoxicity. Studies of CD1d-deficient mice, which lack the receptor required for NKT cell development, demonstrate that they are also unusually sensitive to LPS hepatotoxicity. In conclusion, low NE activity increases hepatic NKT cell apoptosis and depletes liver NKT cells, promoting proinflammatory polarization of hepatic cytokine production that sensitizes the liver to LPS toxicity.

Gut overgrowth with abnormal flora: the missing link in parenteral nutrition-related sepsis in surgical neonates

BACKGROUND AND AIMS

Patients receiving parenteral nutrition are at risk of septicaemia. Intestinal dysmotility and impaired gut immunity due to parenteral nutrition promote bacterial overgrowth. Gut overgrowth with aerobic Gram-negative bacilli (AGNB) impairs systemic immunity. The aim of this study was to determine the potential role of gut overgrowth with AGNB in the pathogenesis of septicaemia related to parenteral nutrition.

METHODS

A prospective 5 y study of surgical infants less than 6 months of age was undertaken. Surveillance samples of the oropharynx and gut were obtained at the start of parenteral nutrition and thereafter twice weekly, to detect AGNB carriage. Blood cultures were taken on clinical indication only.

RESULTS

Two-hundred and eight infants received parenteral nutrition for 6271 days (median 13 days, range 1-512 days). The incidence of AGNB carriage was 42%, whilst the septicaemia rate was 15%. Eighty-four percent of septicaemic infants carried AGNB, whilst 16% never carried AGNB (P<0.005). Carriage developed significantly earlier than septicaemia.

CONCLUSIONS

The incidence of septicaemia was significantly greater in the subset of abnormal carriers. Although gut overgrowth with abnormal flora reflects illness severity, the fact that it preceded septicaemia implicates AGNB overgrowth, per se, as a contributory factor in the development of septicaemia related to parenteral nutrition. Prevention is unlikely to be successful if it ignores the abnormal flora.

Infection rates in surgical neonates and infants receiving parenteral nutrition: a five-year prospective study

We performed a prospective, observational, cohort study on 208 surgical neonates and infants between 1992 and 1997. Surveillance cultures of the oropharynx and rectum were obtained at the start of parenteral nutrition and thereafter twice weekly. Blood cultures were taken on clinical indication only. Microbial translocation was diagnosed when the micro-organisms in the blood were not distinguishable from those carried in the oropharynx and/or rectum. Liver function was monitored weekly and when septicaemia was suspected. The incidence of septicaemia was 15%. The predominant micro-organisms (86%) were the low-level pathogens, coagulase-negative staphylococci and enterococci. Potential pathogens, including aerobic Gram-negative bacilli, were responsible for the remainder. Microbial translocation was responsible for 84% of septicaemic episodes in 76% of patients. The potential pathogens caused septicaemia significantly later than coagulase-negative staphylococci, at a time when liver function was significantly more impaired. In neonates and infants receiving parenteral nutrition, septicaemia is mainly a gut-derived phenomenon and requires novel strategies for prevention.

Interactions mediating bacterial translocation in the immature intestine

Systemic disease caused by transmucosal passage of enterovirulent bacteria and toxins from the gut lumen into the mesenteric lymph nodes (MLN) is reviewed, with particular concern for bacterial interactions in the developing gut of premature newborns. Anaerobic bacteria are rarely observed to translocate to the MLN. Bifidobacterial strains have been tested for their abilities to adhere to enterocyte-like Caco-2 cells in culture. We have investigated the inhibitory effect of adherent human bifidobacterial strains against colonization by a number of diarrheagenic bacteria (Escherichia coli O157; Salmonella typhimurium) and viruses (murine and rhesus rotavirus), in various in vitro and in vivo models. The phagocytic cell (macrophage) may be a key factor in bacterial translocation (BT). Human breast milk contains abundant bioactive substances (immunologic, nutritional) that provide protective effects through inhibition of bacterial overgrowth and BT. New biotherapeutic therapies that stimulate beneficial anaerobic microflora (Lactobacillus, Bifidobacterium) are promising avenues of research to combat BT in disease treatment.

Clinical impact of abnormal gut flora in infants receiving parenteral nutrition

OBJECTIVE

Illness is associated with the carriage of abnormal flora (aerobic Gram-bacilli except E. coli) in the oropharynx and rectum. The aim of this study was to investigate whether carriage of abnormal flora is associated with increased risk of sepsis and septicemia in surgical newborn infants.

METHODS

A 2-year prospective study was carried out on 94 consecutive newborn infants requiring parenteral nutrition (PN) for gastrointestinal abnormalities. Throat and rectal swabs were taken on day 1 of PN and twice weekly. Patients were divided into two groups: abnormal flora (AF; n = 41) and normal flora (NF; n = 53). Sepsis was defined as clinical features of generalized inflammation requiring blood culture. Septicemia was the combination of sepsis and positive blood culture.

RESULTS

Among the infants carrying abnormal flora Pseudomonas and Enterobacter spp. predominated. Duration of PN (AF median 30 days; NF median 9 days), incidence of sepsis (AF 29%; NF 6%), and septicemia (AF 22%; NF 2%) were significantly greater in the group of infants with abnormal flora. Surveillance cultures allow the detection of a subset of infants on PN at high risk of sepsis and septicemia. The degree of gut dysfunction related to the severity of underlying disease determines the duration of PN and the development of abnormal flora. The association between abnormal carriage and increased risk of sepsis and septicemia may be because of the intestinal endotoxin pool known to cause liver impairment and consequent suppression of systemic immunity.

Bacterial endotoxin enhances the hepatotoxicity of allyl alcohol

Lipopolysaccharide (LPS), or bacterial endotoxin, causes liver damage at relatively large doses in rats. Smaller doses, however, may influence the response to other hepatotoxicants. The purpose these studies was to examine the effect of exposure to relatively all doses of LPS on the hepatotoxic response to allyl alcohol, which causes periportal necrosis in laboratory rodents through an known mechanism. Rats were pretreated with LPS (100 micrograms/kg) 2 hr before treatment with a minimally toxic dose of allyl alcohol mg/kg), and liver toxicity was assessed 18 hr later from activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in plasma and from histologic changes in liver sections. Plasma ALT and AST activities were not elevated significantly in rats treated with vehicle, LPS, or allyl alcohol alone, but pronounced increases were observed in rats treated with LPS and allyl alcohol. Significant liver injury occurred as early as 2 hr after allyl alcohol treatment in LPS-pretreated rats and peaked at 6 hr. LPS treatment did not affect the activity of alcohol dehydrogenase and did not affect the rate of production of NADH in isolated livers perfused with allyl alcohol; thus, LPS does not appear to increase the metabolic bioactivation of allyl alcohol into acrolein. On the other hand, pretreatment with 4-methylpyrazole, an inhibitor of alcohol dehydrogenase, abolished the hepatotoxicity of allyl alcohol in LPS-treated rats, indicating that production of acrolein was needed for LPS enhancement of the toxicity of allyl alcohol. Pretreatment of rats with gadolinium chloride (10 mg/kg), a known inactivator of Kupffer cell phagocytic function, decreased LPS augmentation of the response to allyl alcohol. These data indicate that LPS markedly enhances the hepatotoxic response to allyl alcohol. Furthermore, the results suggest that the LPS-induced enhancement of allyl alcohol hepatotoxicity occurs through a Kupffer cell-dependent mechanism.

Antitumor necrosis factor antibodies reduce hepatic steatosis during total parenteral nutrition and bowel rest in the rat

BACKGROUND

In previous studies, we demonstrated the overgrowth of gram-negative bacteria in the gut and an enhanced release of tumor necrosis factor (TNF) by peritoneal macrophages, suggesting that endotoxin, TNF, or both, may act as hepatotoxins to produce hepatic steatosis during total parenteral nutrition (TPN) and bowel rest. The present study attempts to better define the role of each of these two mediators. The first part examines the LD50 for various doses of endotoxin in TPN-treated rats compared with free-feeding and free-feeding saline-infused rats. In the second part we repeatedly administered anti-TNF monoclonal antibodies to rats subjected to TPN and bowel rest.

METHODS

In the first set of experiments, 87 male Sabra rats were randomized into three groups: free-feeding, infused with normal saline, and infused with TPN. On day 7 of the experiment, all rats received an IV injection of endotoxin at various doses (1.5, 2.5, 5.0, 7.5, and 10 mg/kg). The LD50 in the three groups and at the various doses of lipopolysaccharide tested was determined at 24 hours postinjection. In the second set of experiments, 38 male Sabra rats were randomized into three groups: infused with normal saline and fed rat food ad libitum, infused with TPN, and infused with TPN but also receiving monoclonal antibodies against TNF.

RESULTS

Lower endotoxin doses were required to achieve LD50 in the two IV-infused groups (2.5 to 5.0 mg/kg) compared with the free-feeding group (7.5 mg/kg) (p < .03). These findings suggest a moderate increase in susceptibility to the lethal effect of endotoxin in IV-treated rats. The total hepatic fat and triglyceride levels, which were markedly increased in TPN rats, were significantly reduced by using anti-TNF antibodies. Enhanced TNF production by peritoneal macrophages during TPN was completely eliminated by anti-TNF antibodies, probably the result of suppressed TNF production.

CONCLUSIONS

The continuous translocation of endotoxin from gram-negative bacterial overgrowth in the gut during TPN and bowel rest results in enhanced release of TNF by macrophages. TNF causes hepatic dysfunction, portrayed in the present experimental model as hepatic steatosis. TPN-induced hepatic steatosis was significantly reduced by the administration of monoclonal antibodies against TNF-alpha.

Study of plasma and red cell phospholipid fatty acids in extrahepatic cholestatic jaundice

The poor outcome in patients with extrahepatic cholestatic jaundice seems in some way related to reticuloendothelial dysfunction. Similar dysfunction can be caused by abnormal tissue phospholipid fatty acid patterns. Little is, however, known about such patterns in extrahepatic cholestatic jaundice. The phospholipid fatty acid patterns in 42 controls were compared with 42 patients with extrahepatic cholestatic jaundice. Many abnormalities were found. The general pattern was of a fall in polyunsaturated fatty acids and a rise in monounsaturated fatty acids, with a consequent fall in the double bond index (mean number of double bonds per fatty acid) showing an overall rise in saturation. All three major substrates for eicosanoid production were reduced in the jaundiced group. The changes seemed to be associated with jaundice itself, rather than the cause of the jaundice. The central roles of fatty acids in the determination of membrane function and in the provision of substrates of eicosanoid production, mean that these changes may explain some of the reticuloendothelial dysfunction found in extrahepatic cholestatic jaundice.

The hepatotoxicities of endotoxin and ethanol comparisons in vitro using the precision-cut rat liver slice model

Using the precision-cut rat liver slice model, the in vitro toxicities of endotoxin and ethanol, independently and in combination, were evaluated. Hepatotoxicity was assessed by two measures: the leakage of LDH from slice to medium and the ability of slices to reduce a tetrazolium compound, MTT. Ethanol, in concentrations of 1% and greater, exhibited a time and dose dependent hepatotoxicity; MTT reductive capacity was more profoundly affected than LDH leakage. Endotoxin (0.1 to 100 micrograms/ml), however, had only a modest effect on MTT reduction and did not perturb LDH leakage. When combined in vitro, the toxicities of 2% ethanol and various concentrations of endotoxin were additive. Slices prepared from the livers of rats injected ip with endotoxin one day previously sustained considerably more injury (compared to normal rat liver slices) upon subsequent in vitro exposure to either endotoxin or ethanol. Prior in vivo exposure to ethanol, however, did not affect the subsequent in vitro toxicity of endotoxin. Thus, while endotoxin exhibits only subtle toxic effects upon liver slices in vitro, exposure to endotoxin in vivo renders the liver more susceptible to subsequent direct injury by endotoxin or ethanol.

The gastrointestinal tract. The "undrained abscess" of multiple organ failure

OBJECTIVE

This study determined the association between proximal gastrointestinal (GI) colonization and the development of intensive care unit (ICU)-acquired infection and multiple organ failure (MOF) in a population of critically ill surgical patients.

SUMMARY BACKGROUND DATA

ICU-acquired infection in association with progressive organ system dysfunction is an important cause of morbidity and mortality in critical surgical illness. Oropharyngeal and gastric colonization with the characteristic infecting species is common, but its association with ICU morbidity is poorly defined.

METHODS

A prospective cohort study of 41 surgical ICU patients was undertaken. Specimens of gastric and upper small bowel fluid were obtained for quantitative culture; the severity of organ dysfunction was quantitated by a numeric score.

RESULTS

One or more episodes of ICU-acquired infection developed in 33 patients and involved at least one organism concomitantly cultured from the upper GI tract in all but 3. The most common organisms causing ICU-acquired infection--Candida, Streptococcus faecalis, Pseudomonas, and coagulase-negative Staphylococci--were also the most common species colonizing the proximal GI tract. Gut colonization correlated with the development of invasive infection within 1 week of culture for Pseudomonas (90% vs. 13% in noncolonized patients, p < 0.0001) or Staphylococcus epidermidis (80% vs. 6%, p < 0.0001); a weaker association was seen for colonization with Candida. Infections associated with GI colonization included pneumonia (16 patients), wound infection (12 patients), urinary tract infection (11 patients), recurrent (tertiary) peritonitis (11 patients), and bacteremia (10 patients). ICU mortality was greater for patients colonized with Pseudomonas (70% vs. 26%, p = 0.03); organ dysfunction was most marked in patients colonized with one or more of the following: Candida, Pseudomonas, or S. epidermidis.

CONCLUSIONS

The upper GI tract is an important reservoir of the organisms causing ICU-acquired infection. Pathologic GI colonization is associated with the development of MOF in the critically ill surgical patient.

The effect of albumin or crystalloid resuscitation on bacterial translocation and endotoxin absorption following experimental burn injury

Burn injury induces immune suppression and increases susceptibility to infection. Hypoalbuminemia is an early and consistent finding following thermal injury and is independently associated with gastrointestinal dysfunction and increased rates of infectious morbidity. This study assessed the effects of albumin resuscitation on burn-induced immunosuppression, bacterial translocation, and absorption of gut endotoxin. Male Sprague-Dawley rats, presensitized to keyhole limpet hemocyanin (KLH), underwent a 20% dorsal scald burn injury, followed by laparotomy and IVC catheterization for fluid resuscitation. Animals were randomized to one of three resuscitative regimens: Ringer's lactate 3 ml/kg/% burn, Ringer's lactate 9 ml/kg/% burn, or 5% human albumin 3 ml/kg/% burn. Delayed hypersensitivity (DTH) responses to KLH were depressed 24 hr following injury (preburn 8.9 +/- 0.2 mm, post-burn 3.1 +/- 0.3 mm, P less than 0.001) and were significantly lower in animals in whom gram-negative bacterial translocation had occurred (2.3 +/- 0.4 vs 3.6 +/- 0.2 mm, P less than 0.005). Serum albumin levels were lower and rates of gram-negative bacterial translocation higher for those animals receiving low volume crystalloid resuscitation; animals resuscitated with albumin or high volume crystalloid experienced similar degrees of postinjury hypoalbuminemia and bacterial translocation. Uptake of radiolabeled endotoxin was maximal in animals resuscitated with albumin. Bacterial translocation is believed to be responsible for a significant number of late nosocomial infections following trauma. These data suggest that the adequacy of early resuscitation rather than the type of resuscitative solution is the more important factor in minimizing translocation.

The ecology and immunology of the gastrointestinal tract in health and critical illness

Interactions between the indigenous flora of the gastrointestinal tract and immunologically competent cells in the gut mucosa, gut-associated lymphoid tissues and liver play an important role in normal immune homeostasis. The microbial flora of the normal gut is complex, yet remarkably constant over time. The relative sterility of the upper gut is maintained by multiple factors including gastric acid, bile salts, normal motility and mucosal IgA, while the lower gut is densely colonized with a complex flora. An intact Gram-negative flora is a prerequisite for normal immunological maturation. On the other hand, overgrowth of the gut, particularly by Gram-negative bacteria or fungi, facilitates the translocation of bacteria into the host, and results in suppression of T-cell responses and altered hepatic Kupffer cell function. Bacterial overgrowth and the consequences of the interactions of this potentially pathogenic flora with the gut immune system may contribute to the septic state in critical illness, and to the syndrome of multiple organ failure.

Elemental diet alters macrophage function in mice

Administration of a chemically defined liquid elemental diet (ED) induces spontaneous bacterial translocation to mesenteric lymph nodes (MLN) in animal models. The influence of this process on host immunity is unclear. This study evaluated the effects of ED on peritoneal macrophage (PM phi) antimicrobial functions. Conventional C57/BL6 mice and endotoxin-resistant C3H/HeJ mice (n = 60) were randomized to be pair-fed either an ED or regular chow diet (RD) for 14 days. Blood, spleen, liver, and MLN were cultured for bacteria. PM phi were harvested for: percentage Candida albicans (CA) phagocytosis, percentage killing of CA, PM phi superoxide anion (O2-) production, and TNF-dependent macrophage cytotoxicity. Enteral feeding of ED in conventional C57/BL6 mice caused significant bacterial translocation to MLN but not other organs. Significant impairment of CA killing by PM phi occurred in the ED group and was associated with reduced O2- production. Tumor necrosis factor (TNF)-dependent cytotoxicity of PM phi was also decreased. In endotoxin-resistant C3H/HeJ mice, bacterial translocation was not observed and PM phi antifungal functions remained similar in both RD and ED groups. Thus, enteral feeding of an elemental diet downregulates host oxidative and antimicrobial mechanisms and TNF-dependent cytotoxicity in conventional mice which may be secondary to elemental diet-induced bacterial translocation.

Polymyxin B reduces cecal flora, TNF production and hepatic steatosis during total parenteral nutrition in the rat

Hepatic complications are common in patients receiving total parental nutrition (TPN) and who have no underlying liver disease. In the present study we examined the hypothesis that endotoxin (LPS) or possibly TNF derived from the overgrowth of intestinal gram-negative bacteria is responsible for TPN-associated hepatic steatosis, and that bowel decontamination and specific anti-LPS activity of polymyxin B will reduce fatty infiltration of the liver during TPN. Forty-five male Sabra rats underwent jugular vein cannulation, were placed in metabolic cages, and were randomized into five groups. Group I was continuously infused with normal saline and allowed food ad lib, while group II-V were continuously infused with a TPN formula containing 4.25% amino acids and 25% dextrose for a total of 36 calories and 3.0 g protein per 100 g body weight/day. In addition, groups III-IV were also treated by oral polymyxin B while Groups IV and V received a combination of neomycin, metronidazole, and vancomycin (NMV). Thus, Group III received polymyxin B, Group IV received both polymyxin B and NMV, while Group V received NMV only. On Days 7-8 of the study, all animals were sacrificed and spontaneous production of TNF by peritoneal macrophages, bacterial translocation to mesenteric lymph nodes, culture of the cecum, and fat, triglyceride, and cholesterol contents of the liver were determined. All groups infused with TPN exhibited higher levels of total fat, triglycerides, and cholesterol compared to the free feeding control group (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential pathophysiology of bacterial translocation after thermal injury and sepsis

Bacterial translocation (BT) occurs transiently after thermal injury and may result from an ischemic intestinal insult. To evaluate continued intestinal ischemia in the ongoing BT associated with sepsis after injury, rats were randomized to (1) 30% burn injury with Pseudomonas wound infection (BI), (2) BI + fluid resuscitation (BI + Fluid), (3) BI after allopurinol pretreatment to inhibit xanthine oxidase (BI + Allo), or (4) BI after azapropazone pretreatment to inhibit neutrophil degranulation (BI + Aza). On postburn days (PBD) 1, 4, and 7, animals were studied for evidence of BT and intestinal lipid peroxidation. BI + Fluid, BI + Allo, and BI + Aza significantly (p less than 0.05) reduced rates of BT and ileal lipid peroxidation acutely after thermal injury (PBD 1) compared to BI. All four groups had equally high rates of BT associated with the onset of sepsis (PBDs 4 and 7), without evidence of further intestinal lipid peroxidation. These data indicate that the chronic gut barrier failure associated with sepsis after injury occurs independently of continued intestinal ischemia.

Basic studies on ursodeoxycholyl-para-aminobenzoic acid for evaluation of intestinal microflora

A newly synthesized conjugate of ursodeoxycholic acid with para-aminobenzoic acid (PABA) was investigated to determine its suitability for evaluation of enteric bacteria. This compound, PABA-UDCA, was deconjugated by cholylglycine hydrolase to release free PABA, whereas it was completely resistant to deconjugation by pancreatic and intestinal mucosal enzymes. In bacteriologic experiments almost all the microorganisms that split glycocholic acid deconjugated PABA-UDCA. In rat experiments urinary excretions of PABA were measured during 6 h after oral administration of 10 mg PABA-UDCA (PABA-UDCA administration test). Ten control rats excreted 338.5 +/- 13.8 micrograms (mean +/- SE) of PABA; 10 rats with intestinal stagnant loop excreted more (673.6 +/- 70.2 micrograms; P less than 0.01); whereas 10 rats in each of 7 groups pretreated with oral administration of various antibiotics excreted less (P less than 0.001; polymixin B + tinidazole, 14.0 +/- 2.5 micrograms; polymixin B, 224.9 +/- 23.5 micrograms; tinidazole, 42.7 +/- 8.6 micrograms; kanamycin, 50.3 +/- 5.8 micrograms; clindamycin, 57.4 +/- 7.4 micrograms; vancomycin, 70.4 +/- 8.5 micrograms; and paromomycin, 160.4 +/- 16.4 micrograms). This result was reflected by the bacterial mean count of feces. In the PABA-UDCA administration test, after 2 months of feeding with different diets, rats with high-fiber diet (n = 10) excreted less PABA in urine (70.9 +/- 15.9 micrograms; P less than 0.001) than rats on a control diet (n = 10) and a high-protein-high-fat diet (n = 10) (288.9 +/- 34.5 micrograms and 386.7 +/- 61.2 micrograms, respectively). Fecal bacteriologic status was consistently altered. In human volunteers 250 mg PABA-UDCA was tested. Amounts of PABA excreted in urine during 6 h after dosing were 21.11 +/- 2.02 mg in controls (n = 5) and 12.20 +/- 1.01 mg in the group treated with polymixin B plus tinidazole (n = 5; P less than 0.01). No adverse effect was observed. These basic studies indicate that this compound is likely to offer a simple and rapid method for evaluation of the intestinal microorganisms without use of radioisotopes or expensive, special equipment.

Bacterial overgrowth and intestinal atrophy in the etiology of gut barrier failure in the rat

Bacterial translocation occurs in animal models of shock, trauma, sepsis, and parenteral or elemental enteral alimentation. Bowel atrophy and cecal bacterial overgrowth have both been implicated in the pathophysiology of bacterial translocation in many of these models. To further define the etiology of bacterial translocation resulting from dietary manipulations, rats were fed a elemental/defined-formula diet (DFD) for 2 weeks ad libitum and then randomized to either intestinal decontamination with a nonabsorbable antibiotic (neomycin) or no antibiotic treatment. Neomycin treatment significantly (p less than 0.01) reduced the incidence of bacterial translocation after DFD, in association with a significant reduction in the number of cecal gram-negative bacteria. Neither loss of bowel mass after DFD nor bowel composition was affected by oral neomycin. Bacterial translocation after DFD would thus appear to be the result of cecal bacterial overgrowth rather than a loss of a physical intestinal barrier due to atrophy.

The process of microbial translocation

The process of microbial translocation was studied using Candida albicans, Escherichia coli, or endotoxin instilled into Thiry-Vella loops of thermally injured guinea pigs and rats. Translocation of C. albicans occurred by direct penetration of enterocytes by a unique process different from classical phagocytosis. Translocation between enterocytes was not observed. Internalization was associated with a disturbance of the plasma membrane and brush border, but most internalized organisms were not surrounded by a plasma membrane. Passage of the candida into the lamina propria appeared to be associated with disruption of the basal membrane with extrusion of cytoplasm of the cell and candida. Organisms in the lamina propria were commonly phagocytized by macrophages but also were found free in lymphatics and blood vessels. Translocation of E. coli and endotoxin also occurred directly through enterocytes rather than between them, but translocated endotoxin diffused through the lamina propria and muscular wall of the bowel wall by passing between rather than through the myocytes. These descriptive phenomena provide new insight into the role of the enterocyte and intestinal immune cells in the translocation process.

A new simple test for evaluation of intestinal bacteria

We investigated a newly synthesized conjugate of ursodeoxycholic acid with para-aminobenzoic acid (PABA) to determine its suitability to evaluate enteric bacteria. This compound, PABA-UDCA, is deconjugated by cholylglycine hydrolase to release free PABA whereas it is completely resistant to deconjugation by pancreatic and intestinal mucosal enzymes. In bacteriological experiments, almost all of the microorganisms which split glycocholic acid deconjugated this compound. In animal experiments, urinary excretions of PABA were measured for 6 hours following oral administration of 10 mg PABA-UDCA. Ten control rats excreted 338.5 +/- 43.8 micrograms (mean +/- SD) of PABA; 10 rats with intestinal bacterial overgrowth due to enteric stagnant loops excreted more (673.6 +/- 222.1 micrograms; p less than 0.01), whereas 10 rats in each of 8 groups with intestinal antisepsis by oral administration of various antibiotics excreted significantly less (p less than 0.001) (ampicillin + doxycycline + fradiomycin: 18.3 +/- 16.7, polymixin B + tinidazole: 14.0 +/- 8.0, polymixin B: 224.9 +/- 74.3, tinidazole: 42.7 +/- 27.3, kanamycin: 50.3 +/- 18.2, clindamycin: 57.4 +/- 23.3, vancomycin: 70.4 +/- 27.0, and paromomycin: 160.4 +/- 51.9 micrograms). These observations indicate that this compound is likely to offer a simple and rapid method for evaluation of intestinal microorganisms without the use of radioisotopes or expensive, special apparatus.

Bacterial translocation and intestinal atrophy after thermal injury and burn wound sepsis

Bacterial translocation (BT) occurs after thermal injury in rodents in association with intestinal barrier loss. Infection complicating thermal injury may also affect the intestine producing bowel atrophy. To study these relationships, Wistar rats received either 30% scald followed by wound inoculation with Pseudomonas; 30% scald with pair feeding to infected animals; or sham injury as controls. On days 1, 4, and 7 after injury animals were killed with examination of the bowel and culture of the mesenteric lymph nodes (MLN), livers, spleens, and blood. All burned animals demonstrated BT to the MLN on day 1 after injury, but only burn-infected animals had continued BT on days 4 and 7, with progression of BT to the abdominal organs and blood. Burn injury and infection also resulted in significant atrophy of small bowel mucosa temporally associated with continued BT. Thus injury complicated by infection results in prolonged and enhanced bacterial translocation, perhaps due to failure to maintain the mucosal barrier.

Differences between arterial and mixed venous levels of plasma hydroperoxides following major thoracic and abdominal operations

Fatty acid hydroperoxides in the plasma of 18 patients who were undergoing normal postoperative periods following major thoracic or abdominal operations were measured by using a sensitive assay based upon the activation of the cyclooxygenase activity of prostaglandin H synthase. Following major thoracic operations of nine patients, the mean difference between the arterial (0.49 +/- 0.13 microM, mean +/- S.E.M.) and mixed venous (-0.09 +/- 0.12 microM) level of hydroperoxide was 0.58 +/- 0.13 microM (p less than 0.01). In marked contrast to this result, major abdominal operations of nine patients led to a mean difference between the arterial (-0.19 +/- 0.16 microM) and mixed venous (0.46 +/- 0.08 microM) hydroperoxide levels of -0.65 +/- 0.17 microM (p less than 0.01). Both pulmonary and intraabdominal tissues appear capable of generating significant amounts of fatty acid hydroperoxide in response to standard surgical procedures. The A-MV differences suggest that the blood-borne hydroperoxides were rapidly cleared from the circulation by tissue capillary beds.

Total parenteral nutrition and bowel rest modify the metabolic response to endotoxin in humans

Intestinal mucosal atrophy, as induced by total parenteral nutrition (TPN) and/or prolonged bowel rest, is hypothesized to enhance bowel endotoxin (LPS) translocation and may alter host responses to infection. To examine the effect of TPN-induced bowel atrophy on the response to LPS, 12 healthy volunteers were randomized to receive either enteral feedings (ENT, n = 6) or seven days of TPN without oral intake (TPN, n = 6). Enteral or TPN feedings were terminated 12 hours before the study period when a constant dextrose infusion (50 mg/kg/hour) was initiated and continued throughout the subsequent study period. After placement of arterial, hepatic vein, and femoral vein catheters, metabolic parameters were determined before and for six hours after an intravenous E. coli LPS challenge (20 U/kg). Subsequent peak levels of arterial glucagon (ENT, 189 +/- 39 pg/mL; TPN, 428 +/- 48; p less than 0.01), arterial epinephrine (ENT, 236 +/- 52 pg/mL; TPN, 379 +/- 49; p less than 0.05) and hepatic venous cachectin/tumor necrosis factor (cachectin/TNF) (ENT, 250 +/- 56 pg/mL; TPN, 479 +/- 136; p less than 0.05) were significantly higher in the TPN group than in the ENT group. The extremity efflux of lactate (ENT, -16 +/- 4 micrograms/min-100cc tissue; TPN, -52 +/- 13; t = 2 hours; p less than 0.05) and of amino acids (ENT, -334 +/- 77 nmol/min-100cc tissue; TPN, -884 +/- 58; t = 4 hours; p less than 0.05) were higher in the TPN subjects after the endotoxin challenge. Circulating C-reactive Protein (CRP) levels measured 24 hours postendotoxin were also significantly higher in the TPN subjects (ENT, 1.7 +/- 0.2 mg/dL; TPN, 3.2 +/- 0.3; p less than 0.01). Hence the counter-regulatory hormone and splanchnic cytokine responses to LPS were enhanced after TPN and bowel rest. This is associated with a magnified acute-phase response, peripheral amino acid mobilization, and peripheral lactate production. Thus antecedent TPN may influence the metabolic alterations seen in infection and sepsis via both an exaggerated counter-regulatory hormone response as well as an enhanced systemic and splanchnic production of cytokines.

Evidence that rat Kupffer cells stimulate and inhibit hepatocyte protein synthesis in vitro by different mechanisms

Kupffer cell control of hepatocyte protein synthesis may be an important mechanism involved in the regulation of normal liver function and may be one mechanism responsible for the alterations in liver function seen during sepsis. The present series of in vitro experiments compare the response to various inflammatory stimuli of hepatocytes cocultured with Kupffer cells with that of hepatocytes cultured alone. In the absence of inflammatory stimuli, Kupffer cells stimulated hepatocyte protein synthesis. Lipopolysaccharide or gentamicin-killed Escherichia coli triggered Kupffer cell-mediated inhibition of cocultured hepatocyte protein synthesis but had no effect on protein synthesis of hepatocytes cultured alone. Phorbol myristate acetate, muramyl dipeptide, and calcium ionophore had no effect on hepatocytes cultured alone but resulted in a loss of Kupffer cell-mediated stimulation of cocultured hepatocyte protein synthesis without inhibition. Addition of dexamethasone to cocultures prevented the Kupffer cell-mediated inhibition of hepatocyte protein synthesis triggered by lipopolysaccharide, but did not block Kupffer cell-mediated stimulation in the absence of lipopolysaccharide. The data suggest that Kupffer cells can stimulate and inhibit hepatocyte protein synthesis by independent mechanisms. Kupffer cells may be important regulators of hepatocellular function in health and disease.