The systemic and pulmonary LPS binding protein response to intratracheal lipopolysaccharide. Shock. 2009;31:212-217. [PMID: 18520704 DOI: 10.1097/SHK.0b013e31817c0d7d]

Association of low-grade inflammation caused by gut microbiota disturbances with osteoarthritis: A systematic review

Background

Currently, many studies have been published on the relationship between the gut microbiome and knee osteoarthritis. However, the evidence for the association of gut microbiota with knee osteoarthritis has not been comprehensively evaluated.

Objective

This review aimed to assess existing results and provide scientific evidence for the association of low-grade inflammation caused by gut microbiota disturbances with knee osteoarthritis.

Methods

This study conducted an extensive review of the current literature using four databases, PubMed, EMBASE, Cochrane Library and Web of Science before 31 December 2021. Risk of bias was determined using ROBINS and SYRCLE, and quality of evidence was assessed using GRADE and CAMADARES criteria. Twelve articles were included.

Results

Studies have shown that a high-fat diet leads to a disturbance of the gut microbiota, mainly manifested by an increase in the abundance of Firmicutes and Proteobacteria, a decrease in Bacteroidetes, and an increase in the Firmicutes/ Bacteroidetes ratio. Exercise can reverse the pattern of gain or loss caused by high fat. These changes are associated with elevated levels of serum lipopolysaccharide (LPS) and its binding proteins, as well as various inflammatory factors, leading to osteoarthritis (OA).

Conclusion

This systematic review shows that a correlation between low-grade inflammation caused by gut microbiota disturbances and severity of knee osteoarthritis radiology and dysfunction. However, there was a very small number of studies that could be included in the review. Thus, further studies with large sample sizes are warranted to elucidate the association of low-grade inflammation caused by gut microbiota disturbances with osteoarthritis, and to explore the possible mechanisms for ameliorating osteoarthritis by modulating gut microbiota.

Inhibitory effects of lactoferrin on pulmonary inflammatory processes induced by lipopolysaccharide by modulating the TLR4-related pathway

This study tested the ability of lactoferrin to modulate pulmonary inflammation. To construct in vitro and in vivo inflammatory lung models, cells from the human lung adenocarcinoma cell line (A549) were exposed to lipopolysaccharide (LPS, 1 µg/mL), and mice (CD-1) were intratracheally administered LPS [10 mg/kg of body weight (BW), tracheal lumen injection], respectively. The A549 cells were preincubated with lactoferrin (10 mg/mL), and the mice were intraperitoneally injected with lactoferrin (100 mg/kg of BW), followed by LPS treatment. The concentrations of proinflammatory cytokines (IL-1β and TNF-α) in culture medium of A549 cells and in bronchoalveolar lavage fluid of the mice were determined using enzyme-linked immunosorbent assays. The toll-like receptor 4-related pathway (TLR4/MyD88/IRAK1/TRAF6/NFκB) was determined at gene and protein expression levels in A549 cells and mouse lung tissue. Results showed that LPS treatment significantly elevated the concentrations of IL-1β and TNF-α in the A549 cell culture medium and in bronchoalveolar lavage fluid of the mice; it also elevated both the mRNA and protein expressions of TLR4 and the TLR4 downstream factors in A549 cells and mouse lung tissue. Nevertheless, lactoferrin apparently depressed the releases of IL-1β and TNF-α from A549 cells and lung tissues stimulated by LPS, and significantly suppressed the TLR4 signaling pathway. Lactoferrin also promoted the enhancement of miR-146a expression in A549 cells and mouse lung tissue. Moreover, 100°C heating for 3 min caused total loss of the previously listed bioactivity of lactoferrin. Collectively, we proved that lactoferrin intervened in LPS-induced inflammation in the pulmonary cell model and in the mouse model, through inhibiting the TLR4-related pathway.

Liver-lung interactions in acute respiratory distress syndrome

Patients with liver diseases are at high risk for the development of acute respiratory distress syndrome (ARDS). The liver is an important organ that regulates a complex network of mediators and modulates organ interactions during inflammatory disorders. Liver function is increasingly recognized as a critical determinant of the pathogenesis and resolution of ARDS, significantly influencing the prognosis of these patients. The liver plays a central role in the synthesis of proteins, metabolism of toxins and drugs, and in the modulation of immunity and host defense. However, the tools for assessing liver function are limited in the clinical setting, and patients with liver diseases are frequently excluded from clinical studies of ARDS. Therefore, the mechanisms by which the liver participates in the pathogenesis of acute lung injury are not totally understood. Several functions of the liver, including endotoxin and bacterial clearance, release and clearance of pro-inflammatory cytokines and eicosanoids, and synthesis of acute-phase proteins can modulate lung injury in the setting of sepsis and other severe inflammatory diseases. In this review, we summarized clinical and experimental support for the notion that the liver critically regulates systemic and pulmonary responses following inflammatory insults. Although promoting inflammation can be detrimental in the context of acute lung injury, the liver response to an inflammatory insult is also pro-defense and pro-survival. A better understanding of the liver–lung axis will provide valuable insights into new diagnostic targets and therapeutic strategies for clinical intervention in patients with or at risk for ARDS.

Pulmonary inflammation-induced alterations in key regulators of mitophagy and mitochondrial biogenesis in murine skeletal muscle

Background

Both mitophagy, a selective mechanism for clearance of mitochondria, and mitochondrial biogenesis are key processes determining mitochondrial content and oxidative capacity of the musculature. Abnormalities in these processes could therefore contribute to deterioration of peripheral muscle oxidative capacity as observed in e.g. chronic obstructive pulmonary disease. Although it has been suggested that inflammatory mediators can modulate both mitophagy and mitochondrial biogenesis, it is unknown whether acute pulmonary inflammation affects these processes in oxidative and glycolytic skeletal muscle in vivo. Therefore, we hypothesised that molecular signalling patterns of mitochondrial breakdown and biogenesis temporally shift towards increased breakdown and decreased biogenesis in the skeletal muscle of mice exposed to one single bolus of IT-LPS, as a model for acute lung injury and pulmonary inflammation.

Methods

We investigated multiple important constituents and molecular regulators of mitochondrial breakdown, biogenesis, dynamics, and mitochondrial content in skeletal muscle over time in a murine (FVB/N background) model of acute pulmonary- and systemic inflammation induced by a single bolus of intra-tracheally (IT)-instilled lipopolysaccharide (LPS). Moreover, we compared the expression of these constituents between gastrocnemius and soleus muscle.

Results

Both in soleus and gastrocnemius muscle, IT-LPS instillation resulted in molecular patterns indicative of activation of mitophagy. This coincided with modulation of mRNA transcript abundance of genes involved in mitochondrial fusion and fission as well as an initial decrease and subsequent recovery of transcript levels of key proteins involved in the molecular regulation of mitochondrial biogenesis. Moreover, no solid differences in markers for mitochondrial content were found.

Conclusions

These data suggest that one bolus of IT-LPS results in a temporal modulation of mitochondrial clearance and biogenesis in both oxidative and glycolytic skeletal muscle, which is insufficient to result in a reduction of mitochondrial content.

Integrative Physiology of Pneumonia

Pneumonia is a type of acute lower respiratory infection that is common and severe. The outcome of lower respiratory infection is determined by the degrees to which immunity is protective and inflammation is damaging. Intercellular and interorgan signaling networks coordinate these actions to fight infection and protect the tissue. Cells residing in the lung initiate and steer these responses, with additional immunity effectors recruited from the bloodstream. Responses of extrapulmonary tissues, including the liver, bone marrow, and others, are essential to resistance and resilience. Responses in the lung and extrapulmonary organs can also be counterproductive and drive acute and chronic comorbidities after respiratory infection. This review discusses cell-specific and organ-specific roles in the integrated physiological response to acute lung infection, and the mechanisms by which intercellular and interorgan signaling contribute to host defense and healthy respiratory physiology or to acute lung injury, chronic pulmonary disease, and adverse extrapulmonary sequelae. Pneumonia should no longer be perceived as simply an acute infection of the lung. Pneumonia susceptibility reflects ongoing and poorly understood chronic conditions, and pneumonia results in diverse and often persistent deleterious consequences for multiple physiological systems.

Biomarkers of inflammation - LBP and TLR- predict progression of knee osteoarthritis in the DOXY clinical trial

OBJECTIVE

To evaluate systemic inflammatory biomarkers in symptomatic knee osteoarthritis (OA) and their association with radiographic and biochemical OA progression.

METHODS

Lipopolysaccharide (LPS) binding protein (LBP), soluble Toll-like receptor 4 (sTLR4) and interleukin 6 (IL-6) were measured in plasma of 431 knee OA patients from the doxycycline (DOXY) trial at baseline and 18 months. Plasma lipopolysaccharide and lipopolysaccharide binding protein (LBP) were also measured at 12 months. As a biochemical indicator of disease activity and OA progression, urinary (u) C-telopeptide of Type II collagen (uCTX-II) was measured in samples collected at baseline and 18 months. Change over 16 months in radiographic tibiofemoral joint space width (JSW in mm) and joint space narrowing (JSN≥0.5 mm) were used to indicate radiographic OA progression. Change over 18 months for uCTX-II was used as a secondary outcome. Both univariate and multivariable regression analyses were performed to test the association between Z-score transformed biomarkers and outcomes.

RESULTS

Baseline LBP and time-integrated concentration (TIC) of LBP over 12 and 18 months were associated with worsening joint space width (JSW) (parameter estimates: -0.1 to -0.07) and JSN (OR: 1.32 to 1.42) adjusting for treatment group, age, body mass index (BMI) and corresponding baseline radiographic measures. Baseline sTLR4 and TIC over 18 months were associated with change in uCTX-II over 18 months (adjusted parameter estimates: 0.0017 to 0.0020). Results were not modified by treatment with doxycycline.

CONCLUSION

Plasma LBP and sTLR4 were associated with knee OA progression over 16-18 months. These results lend further support for a role of systemic low-grade inflammation in the pathogenesis of knee OA progression.

Comparative pharmacokinetic study of pyranocoumarins and khellactone in normal and acute lung injury rats after oral administration of Peucedanum praeruptorum Dunn extracts using a rapid and sensitive liquid chromatography-tandem mass spectrometry method

Pyranocoumarins are the main constitutes in Peucedanum praeruptorum Dunn and possess various biological activities. In this article, we developed and validated a rapid and sensitive liquid chromatography-tandem mass spectrometry method for the targeted quantification of the pyranocoumarins, praeruptorin A, praeruptorin B and praeruptorin E, and khellactone, which is a common metabolite of these pyranocoumarins in rat plasma samples. We then performed a comparative pharmacokinetic study of these pyranocoumarins and khellactone in normal and lipopolysaccharide-induced acute lung injury (ALI) in rats following oral administration of P. praeruptorum Dunn extracts. Calibration curves gave desirable linearity (r > 0.99) and the lower limit of quantifications were sufficient for quantitative analysis. The precision and accuracy were assessed by intra-batch and inter-batch assays, and the relative standard deviations were all within 10.23% and the accuracy (relative error) was between -5.52% and 8.68%. The extraction recoveries, matrix effects and stability were also acceptable. The pharmacokinetic study revealed that the area under the concentration-time curve (0-t) of khellactone in ALI rats was significantly decreased compared with the normal rats. Meanwhile, the systemic exposures of these pyranocoumarins were slightly higher in the ALI rats than those in normal rats were. The pharmacokinetic study in the pathological state might provide information that was more comprehensive to guide the clinical usage of P. praeruptorum Dunn.

The Lung-Liver Axis: A Requirement for Maximal Innate Immunity and Hepatoprotection during Pneumonia

The hepatic acute-phase response (APR), stimulated by injury or inflammation, is characterized by significant changes in circulating acute-phase protein (APP) concentrations. Although individual functions of liver-derived APPs are known, the net consequence of APP changes is unclear. Pneumonia, which induces the APR, causes an inflammatory response within the airspaces that is coordinated largely by alveolar macrophages and is typified by cytokine production, leukocyte recruitment, and plasma extravasation, the latter of which may enable delivery of hepatocyte-derived APPs to the infection site. To determine the functional significance of the hepatic APR during pneumonia, we challenged APR-null mice lacking hepatocyte signal transducer and activator of transcription 3 (STAT3) and v-rel avian reticuloendotheliosis viral oncogene homolog A (RelA) with Escherichia coli in the airspaces. APR-null mice displayed ablated APP induction, significantly increased mortality, liver injury and apoptosis, and a trend toward increased bacterial burdens. TNF-α neutralization reversed hepatotoxicity, but not mortality, suggesting that APR-dependent survival is not solely due to hepatoprotection. After a milder (nonlethal) E. coli infection, hepatocyte-specific mutations decreased APP concentrations and pulmonary inflammation in bronchoalveolar lavage fluid. Cytokine expression in airspace macrophages, but not other airspace or circulating cells, was significantly dependent on APP extravasation into the alveoli. These data identify a novel signaling axis whereby the liver response enhances macrophage activation and pulmonary inflammation during pneumonia. Although hepatic acute-phase changes directly curb injury induced by TNF-α in the liver itself, APPs downstream of these same signals promote survival in association with innate immunity in the lungs, thus demonstrating a critical role for the lung-liver axis during pneumonia.

Activation of Hepatic STAT3 Maintains Pulmonary Defense during Endotoxemia

Pneumonia and infection-induced sepsis are worldwide public health concerns. Both pathologies elicit systemic inflammation and induce a robust acute-phase response (APR). Although APR activation is well regarded as a hallmark of infection, the direct contributions of liver activation to pulmonary defense during sepsis remain unclear. By targeting STAT3-dependent acute-phase changes in the liver, we evaluated the role of liver STAT3 activity in promoting host defense in the context of sepsis and pneumonia. We employed a two-hit endotoxemia/pneumonia model, whereby administration of 18 h of intraperitoneal lipopolysaccharide (LPS; 5 mg/kg of body weight) was followed by intratracheal Escherichia coli (10(6) CFU) in wild-type mice or those lacking hepatocyte STAT3 (hepSTAT3(-/-)). Pneumonia alone (without endotoxemia) was effectively controlled in the absence of liver STAT3. Following endotoxemia and pneumonia, however, hepSTAT3(-/-) mice, with significantly reduced levels of circulating and airspace acute-phase proteins, exhibited significantly elevated lung and blood bacterial burdens and mortality. These data suggested that STAT3-dependent liver responses are necessary to promote host defense. While neither recruited airspace neutrophils nor lung injury was altered in endotoxemic hepSTAT3(-/-) mice, alveolar macrophage reactive oxygen species generation was significantly decreased. Additionally, bronchoalveolar lavage fluid from this group of hepSTAT3(-/-) mice allowed greater bacterial growth ex vivo. These results suggest that hepatic STAT3 activation promotes both cellular and humoral lung defenses. Taken together, induction of liver STAT3-dependent gene expression programs is essential to countering the deleterious consequences of sepsis on pneumonia susceptibility.

Evaluation of optimized continuous venovenous hemodiafiltration therapy efficiency in severe burn patients with sepsis

As an initial factor, sepsis and multiple organ dysfunction syndrome (MODS) caused by sepsis are the principal causes of death in burned patients. In this report, we measured the levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-8 in severely burned patients with sepsis after the initiation of continuous vein-vein hemodiafiltration (CVVHDF) to evaluate the clinical usefulness of CVVHDF on the removal of key mediators. The vital sign indices, such as the heart rate (HR), respiration (R) and central venous pressure (CVP), were recorded at 0 and 42 h in each group. Further, the laboratory examinations indexes, such as the white blood cell count, blood sugar, serum sodium, blood urea nitrogen and serum creatinine, were detected in venous blood samples. Twenty-two severely burned patients suffering from sepsis were randomized into the control group (A, n = 11) and the experimental group (B, n = 11). The patients in group A underwent conventional treatment, and those in group B received conventional+CVVHDF treatment. The vital signs, such as the HR, R, and CVP, and laboratory examination indices, such as the blood cell count, blood sugar, serum sodium, blood urea nitrogen, and serum creatinine, dropped significantly in group B compared with those in group A at 42 h (P < 0.05). The plasma levels of TNF-α, IL-6 and IL-8 were measured at 0, 12, 18, 24, 36 and 42 h after the start of CVVHDF and at the same time points after the patients were diagnosed with sepsis in group A. The plasma levels of TNF-α in group B decreased by 32% at 18 h after the start of CVVHDF and decreased by 43% at 42 h after the start of CVVHDF; however, these levels were increased compared with the normal values (P < 0.01). The plasma levels of IL-6 decreased at 18 h after the start of CVVHDF (0.274 ± 0.137 ng/ml). Following a brief increase at 24 h, the plasma levels of IL-6 again decreased continuously until the end of the investigation (0.192 ± 0.119 ng/ml). The plasma levels of IL-8 in group B decreased by 56% at 18 h after the start of CVVHDF, but they were increased compared with the normal values (P < 0.01). The plasma levels of IL-8 in group B decreased by 70% at 42 h after the start of CVVHDF, but they were increased compared with the normal values (P < 0.01). The MODS incident was 4 of 11 in group A compared with 1 of 11 in group B (P < 0.01). In conclusion, CVVHDF can effectively reduce the levels of TNF-α, IL-6 and IL-8 as well as the MODS incidence in patients with serious burns.

Hfe deficiency impairs pulmonary neutrophil recruitment in response to inflammation

Regulation of iron homeostasis and the inflammatory response are tightly linked to protect the host from infection. Here we investigate how imbalanced systemic iron homeostasis in a murine disease model of hereditary hemochromatosis (Hfe^−/− mice) affects the inflammatory responses of the lung. We induced acute pulmonary inflammation in Hfe^−/− and wild-type mice by intratracheal instillation of 20 µg of lipopolysaccharide (LPS) and analyzed local and systemic inflammatory responses and iron-related parameters. We show that in Hfe^−/− mice neutrophil recruitment to the bronchoalveolar space is attenuated compared to wild-type mice although circulating neutrophil numbers in the bloodstream were elevated to similar levels in Hfe^−/− and wild-type mice. The underlying molecular mechanisms are likely multifactorial and include elevated systemic iron levels, alveolar macrophage iron deficiency and/or hitherto unexplored functions of Hfe in resident pulmonary cell types. As a consequence, pulmonary cytokine expression is out of balance and neutrophils fail to be recruited efficiently to the bronchoalveolar compartment, a process required to protect the host from infections. In conclusion, our findings suggest a novel role for Hfe and/or imbalanced iron homeostasis in the regulation of the inflammatory response in the lung and hereditary hemochromatosis.

Of microbes and meals: the health consequences of dietary endotoxemia

The human intestinal tract comprises a rich and complex microbial ecosystem. This intestinal microbota provides a large reservoir of potentially toxic molecules, including bacterial endotoxin (ie, lipopolysaccharide [LPS]). This potent inflammatory molecule is detectable in the circulation of healthy individuals, and levels transiently increase following ingestion of energy-rich meals. Chronic exposure to circulating endotoxin has been associated with obesity, diabetes, and cardiovascular disease. Western-style meals augment LPS translocation and by this mechanism may contribute to the pathogenesis of these diseases. By contrast, the gut and other organs have evolved mechanisms to detoxify endotoxin and neutralize the potentially inflammatory qualities of circulating endotoxin. Of specific interest to clinicians is evidence that acute postprandial elevation of circulating endotoxin is dependent on meal composition. In this review, the authors present an overview of the biochemical and cellular mechanisms that lead to endotoxemia, with emphasis on the interplay between microbial and nutrition determinants of this condition. The link between endotoxemia, diet, and changes in the intestinal microbiota raise the possibility that dietary interventions can, at least in part, ameliorate the detrimental outcomes of endotoxemia.

Old and new findings on lipopolysaccharide-binding protein: a soluble pattern-recognition molecule

LBP [LPS (lipopolysaccharide)-binding protein] was discovered approximately 25 years ago. Since then, substantial progress has been made towards our understanding of its function in health and disease. Furthermore, the discovery of a large protein family sharing functional and structural attributes has helped in our knowledge. Still, key questions are unresolved, and here an overview on the old and new findings on LBP is given. LBP is an acute-phase protein of the liver, but is also synthesized in other cells of the organism. While LBP is named after the ability to bind to LPS of Gram-negative bacteria, it also can recognize other bacterial compounds, such as lipopeptides. It has been shown that LBP is needed to combat infections; however, the main mechanism of action is still not clear. New findings on natural genetic variations of LBP leading to functional consequences may help in further elucidating the mechanism of LBP and its role in innate immunity and disease.

Hematological and acute-phase responses to diet-induced obesity in IL-6 KO mice

Obesity is associated with chronic inflammation and elevated levels of IL-6. The role of IL-6 in induction of acute-phase proteins and modulation of hematological responses has been demonstrated in models of inflammation and aging, but not in obesity. We hypothesized that IL-6 is necessary to regulate the acute-phase response and hematological changes associated with diet-induced obesity (DIO) in mice. Feeding a 60%kcal/fat diet for 13 weeks to C57BL6 WT male mice induced a significant increase in IL-6 expression in visceral adipose tissue (VAT), but not liver, compared to mice fed chow diet. Significantly elevated IL-6 levels were present in the peritoneal lavage fluid, but not plasma, of DIO compared to lean mice. A comparable degree of obesity, hepatomegaly, hyperleptinemia, VAT inflammation and insulin resistance was observed in DIO WT and IL-6 KO mice compared to WT and KO mice fed chow diet. Significant leukocytosis was observed in DIO WT but not DIO KO mice compared to lean groups. A significant reduction in platelet counts, without alterations in platelet size, percentage of circulating reticulated platelets and number of bone marrow megakaryocytes, was present in DIO KO mice compared to each other group. Hepatic expression of thrombopoietin was comparable in each group, with DIO WT and KO mice having reduced VAT expression compared to lean mice. Lean KO mice had significantly elevated plasma levels of thrombopoietin compared to each other group, whereas liver-associated thrombopoietin levels were comparable in each group. Deficiency of IL-6 resulted in blunted hepatic induction of the acute-phase protein serum amyloid A-1, whereas expression of hepcidin-1 and -2, LPS-binding protein, ceruloplasmin, plasminogen activator inhibitor-1 and thrombospondin-1 was IL-6-independent. In conclusion, in the absence of overt metabolic alterations, IL-6 modulates leukocytosis, thrombopoiesis and induction of SAA-1, but not other acute-phase proteins in obese mice.

NF-κB and STAT3 signaling hubs for lung innate immunity

Innate immune responses to lung pathogens involve the coordinated expression of myriad affector and effector molecules of innate immunity, which must be induced and appropriately regulated in response to diverse stimuli generated by microbes or the infected host. Many intercellular and intracellular signaling pathways are involved, but we propose NF-κB and STAT3 transcription factors to be especially important signaling hubs for integrating these pathways to orchestrate effective host defense without excessive inflammatory injury.

Significance of SOCS-1 expression changes in the liver of endotoxemic mice and endotoxin-tolerant mice

AIM: To investigate SOCS-1 (suppressor of cytokine signaling-1) expression changes in the liver of endotoxemic mice and endotoxin-tolerant mice and to explore the relationship between SOCS-1 expression and endotoxin tolerance.

METHODS: The mouse models of endotoxemia and endotoxin tolerance were established by lipopolysaccharide (LPS) pretreatment. At different time points after LPS pretreatment, the level of serum TNF-α was detected by enzyme-linked immunosorbent assay (ELISA), the expression levels of TNF-α and SOCS-1 mRNAs in the liver were detected by reverse transcription-polymerase chain reaction (RT-PCR), the pathological and ultrastructural changes in liver tissue were observed, and SOCS-1 protein expression in liver tissue was detected by immunohistochemistry.

RESULTS: After LPS stimulation, the levels of serum TNF-α and hepatic TNF-α and SOCS-1 mRNAs began to increase at 1 h, peaked at 3 h, and then decreased gradually to the normal level. In contrast, serum TNF-α and hepatic TNF-α mRNA levels showed no significant changes in mice treated with PBS. No SOCS-1 mRNA expression was detected in control mice (P < 0.01). At 3 h, serum TNF-α and hepatic TNF-α mRNA levels were significantly lower in endotoxin-tolerant mice than in endotoxin-intolerant mice (693.38 ng/L ± 95.2 ng/L vs 1110.24 ng/L ± 164.33 ng/L, P < 0.01; 97.96 ± 19.67 vs 139.14 ± 31.17, P < 0.05), while hepatic SOCS-1 mRNA level was significantly higher in endotoxin-tolerant mice than in endotoxin-intolerant mice (91.58 ± 12.94 vs 52.82 ± 6.96, P < 0.01). Pathological and histological changes in the liver of endotoxemic mice included fatty degeneration and necrosis, while the major ultrastructural change was presence of activated Kupffer cells whose phagocytic function was enhanced. Hepatic SOCS-1 protein expression could be detected by immunohistochemistry.

CONCLUSION: SOCS-1 mRNA expression in liver tissue is enhanced markedly in endotoxin-tolerant mice. Close associations are noted among hepatic SOCS-1 mRNA expression, Kupffer cell activation and endotoxin tolerance.

Chronic pulmonary LPS tolerance induces selective immunosuppression while maintaining the neutrophilic response

LPS challenge causes potent activation of innate immunity. Because LPS is ubiquitously present in ambient air, repeated inhalation may lead to activation of the pulmonary immune response. If this activation is unregulated, chronic LPS inhalation would lead to persistent inflammation and organ damage. We hypothesized that the lung uses the mechanism of LPS tolerance to maintain the balance between hypoinflammatory and hyperinflammatory states. We developed a model of chronic pulmonary LPS tolerance induced by pulmonary exposure to 1 microg LPS for 4 consecutive days. Mice were challenged with 10 microg of LPS 24 h later. TNF-alpha protein was significantly decreased in the bronchoalveolar lavage fluid of tolerant versus nontolerant mice, whereas IL-6 levels were significantly increased in the tolerant group. Tolerant mice were also protected from airway hyperresponsiveness. M2 and M3 muscarinic receptor mRNA was significantly decreased in the lungs of tolerant mice, suggesting a mechanism for the decreased airway hyperresponsiveness. CXCL2 was significantly reduced in tolerant mice, but CXCL1 was equivalent between groups. No difference was seen in neutrophil recruitment to the alveolar space. Interestingly, LPS tolerance does not confer cross-tolerance to the Toll-like receptor (TLR) 2 stimulus Pam3Cys. TNF-alpha and IL-6 concentrations were significantly increased in LPS-tolerant mice challenged with Pam3Cys; however, chemokine concentrations were unaffected. Our data show that repeated LPS inhalation results in differential regulation of cytokines but does not inhibit neutrophil recruitment. This unrestricted neutrophil recruitment may represent a mechanism by which individuals may be protected from pulmonary bacterial infection and pneumonia.

Endotoxin-induced translocation of interleukin-6 from lungs to the systemic circulation

It is widely postulated that systemic inflammation related to lung infections is largely caused by cytokine translocation from the lungs into the systemic circulation but there is a paucity of animal models to evaluate this hypothesis. In this proof-of-concept study, we developed a murine model to determine whether interleukin (IL)-6, a primary inflammatory cytokine, translocates following airway exposure to endotoxin. We collected central venous blood from the right atrium and arterial blood from the aorta simultaneously at 4 h and 24 h following intratracheal exposure to endotoxin (25 microg) and measured IL-6 in the serum and broncho-alveolar lavage (BAL) fluid (n = 33 mice). We repeated the experiment following 3 d of treatment with dexamethasone (n = 31 mice). Without stimulation, there was no significant arteriovenous gradient (3 pg/ml with interquartile range [IQR] of 3-5 pg/ml in arterial versus 18 pg/ml with IQR of 8-24 pg/ml in venous serum; P = 0.86). A significant arteriovenous difference was observed by 4 h post-exposure to endotoxin (2813 pg/ml with IQR of 1578-4316 pg/ml in arterial versus 1282 pg/ml with IQR of 778-2699 pg/ml in venous serum; P50.0001). The rise in the BAL IL-6 levels correlated with the increases in the arterial serum levels (P50.0001). Administration of intraperitoneal dexamethasone for 3 d attenuated the increased arteriovenous gradient. This murine model facilitates the estimation of cytokine translocation across the lungs and evaluation of compounds to modulate this gradient.

Mechanisms of the hepatic acute-phase response during bacterial pneumonia

The acute-phase response is characterized by increased circulating levels of acute-phase proteins (APPs) generated by the liver. During bacterial pneumonia, APPs correlate with the severity of disease, serve as biomarkers, and are functionally significant. The kinetics and regulatory mechanisms of APP induction in the liver during lung infection have yet to be defined. Here we show that APP mRNA transcription is induced in the livers of mice whose lungs are infected with either Escherichia coli or Streptococcus pneumoniae, and that in both cases this induction occurs in tandem with activation in the liver of the transcription factors signal transducer and activator of transcription 3 (STAT3) and NF-kappaB RelA. Interleukin-6 (IL-6) deficiency inhibited the activation of STAT3 and the induction of select APPs in the livers of pneumonic mice. Furthermore, liver RelA activation and APP induction were reduced for mice lacking all signaling receptors for tumor necrosis factor alpha and IL-1. In a murine hepatocyte cell line, knockdown of either STAT3 or RelA by small interfering RNA inhibited cytokine induction of the APP serum amyloid A-1, demonstrating that both transcription factors were independently essential for the expression of this gene. These data suggest that during pneumonia caused by gram-negative or gram-positive bacteria, the expression of APPs in the liver depends on STAT3 activation by IL-6 and on RelA activation by early-response cytokines. These signaling axes may be critical for integrating systemic responses to local infection, balancing antibacterial host defenses and inflammatory injury during acute bacterial pneumonia.