Arnaud Friggeri

miR-147, a microRNA that is induced upon Toll-like receptor stimulation, regulates murine macrophage inflammatory responses.

Toll-like receptors (TLRs) are major receptors that enable inflammatory cells to recognize invading microbial pathogens. MicroRNAs are small non-coding RNAs that play important regulatory roles in a variety of biological processes. In this study, we found that a microRNA, miR-147, was induced upon stimulation of multiple TLRs and functioned as a negative regulator of TLR-associated signaling events in murine macrophages. We first demonstrated that the NMES1 transcript was a functional primary miR-147. miR-147 was induced in LPS-stimulated mouse macrophages and under in vivo conditions in the lungs of LPS-treated mice. Expression of miR-147 was greater after cellular activation by TLR4 than after engagement of either TLR2 or TLR3, suggesting that maximal induction of miR-147 required activation of both NF-κB and IRF3. TLR4-induced miR-147 expression was both MyD88- and TRIF-dependent. The miR-147 promoter was responsive to TLR4 stimulation and both NF-κB and STAT1α bound to the miR-147 promoter. miR-147 mimics or induced expression of miR-147 decreased, whereas miR-147 knockdown increased inflammatory cytokine expression in macrophages stimulated with ligands to TLR2, TLR3, and TLR4. These data demonstrate a negative-feedback loop in which TLR stimulation induces miR-147 to prevent excessive inflammatory responses.

Exposure to Hydrogen Peroxide Induces Oxidation and Activation of AMP-activated Protein Kinase

Although metabolic conditions associated with an increased AMP/ATP ratio are primary factors in the activation of 5′-adenosine monophosphate-activated protein kinase (AMPK), a number of recent studies have shown that increased intracellular levels of reactive oxygen species can stimulate AMPK activity, even without a decrease in cellular levels of ATP. We found that exposure of recombinant AMPKαβγ complex or HEK 293 cells to H2O2 was associated with increased kinase activity and also resulted in oxidative modification of AMPK, including S-glutathionylation of the AMPKα and AMPKβ subunits. In experiments using C-terminal truncation mutants of AMPKα (amino acids 1–312), we found that mutation of cysteine 299 to alanine diminished the ability of H2O2 to induce kinase activation, and mutation of cysteine 304 to alanine totally abrogated the enhancing effect of H2O2 on kinase activity. Similar to the results obtained with H2O2-treated HEK 293 cells, activation and S-glutathionylation of the AMPKα subunit were present in the lungs of acatalasemic mice or mice treated with the catalase inhibitor aminotriazole, conditions in which intracellular steady state levels of H2O2 are increased. These results demonstrate that physiologically relevant concentrations of H2O2 can activate AMPK through oxidative modification of the AMPKα subunit. The present findings also imply that AMPK activation, in addition to being a response to alterations in intracellular metabolic pathways, is directly influenced by cellular redox status.

Assessing fluid responsiveness in critically ill patients: False-positive pulse pressure variation is detected by Doppler echocardiographic evaluation of the right ventricle

Objectives:To determine whether peak systolic velocity of tricuspid annular motion assessed by tissue Doppler echocardiography (Sta), a right ventricular function parameter, can discriminate patients with true- and false-positive pulse pressure variation. Pulse pressure variation is used to predict fluid responsiveness in mechanically ventilated patients. However, this parameter has been reported to be falsely positive, especially in patients with right ventricular dysfunction. Design:A prospective study. Setting:Medical and surgical intensive care unit of a university hospital. Patients:Thirty- five mechanically ventilated patients hospitalized for >24 hrs with a pulse pressure variation of >12%. Interventions:Doppler echocardiography (including measurement of Sta and stroke volume) was performed before and after infusion of 500 mL of colloid solution. Patients were classified into two groups according to their response to fluid infusion: responders (at least 15% increase in stroke volume) and nonresponders. Measurements and Main Results:Twenty-three patients (66%) were responders (true-positive group) and 12 (34%) were nonresponders (false-positive group). Before volume expansion, Sta was statistically lower in the nonresponder group (0.13 [0.04] vs. 0.20 [0.05], p = .0004). The area under the curve of the receiver operating characteristic curve was 0.87 (95% confidence interval, 0.74-1). In patients with pulse pressure variation of >12%, a Sta cutoff value of 0.15 m/s discriminated between responders and nonresponders with a sensitivity of 91% (80-100) and a specificity of 83% (62-100). Conclusions:A Sta value of <0.15 m/s seems to be an accurate parameter to detect false-positive pulse pressure variation. Echocardiography should therefore be performed before fluid infusion in patients with pulse pressure variation of >12%.

Skin antisepsis with chlorhexidine–alcohol versus povidone iodine–alcohol, with and without skin scrubbing, for prevention of intravascular-catheter-related infection (CLEAN): an open-label, multicentre, randomised, controlled, two-by-two factorial trial

BACKGROUND Intravascular-catheter-related infections are frequent life-threatening events in health care, but incidence can be decreased by improvements in the quality of care. Optimisation of skin antisepsis is essential to prevent short-term catheter-related infections. We hypothesised that chlorhexidine-alcohol would be more effective than povidone iodine-alcohol as a skin antiseptic to prevent intravascular-catheter-related infections. METHODS In this open-label, randomised controlled trial with a two-by-two factorial design, we enrolled consecutive adults (age ≥18 years) admitted to one of 11 French intensive-care units and requiring at least one of central-venous, haemodialysis, or arterial catheters. Before catheter insertion, we randomly assigned (1:1:1:1) patients via a secure web-based random-number generator (permuted blocks of eight, stratified by centre) to have all intravascular catheters prepared with 2% chlorhexidine-70% isopropyl alcohol (chlorhexidine-alcohol) or 5% povidone iodine-69% ethanol (povidone iodine-alcohol), with or without scrubbing of the skin with detergent before antiseptic application. Physicians and nurses were not masked to group assignment but microbiologists and outcome assessors were. The primary outcome was the incidence of catheter-related infections with chlorhexidine-alcohol versus povidone iodine-alcohol in the intention-to-treat population. This study is registered with ClinicalTrials.gov, number NCT01629550 and is closed to new participants. FINDINGS Between Oct 26, 2012, and Feb 12, 2014, 2546 patients were eligible to participate in the study. We randomly assigned 1181 patients (2547 catheters) to chlorhexidine-alcohol (594 patients with scrubbing, 587 without) and 1168 (2612 catheters) to povidone iodine-alcohol (580 patients with scrubbing, 588 without). Chlorhexidine-alcohol was associated with lower incidence of catheter-related infections (0·28 vs 1·77 per 1000 catheter-days with povidone iodine-alcohol; hazard ratio 0·15, 95% CI 0·05-0·41; p=0·0002). Scrubbing was not associated with a significant difference in catheter colonisation (p=0·3877). No systemic adverse events were reported, but severe skin reactions occurred more frequently in those assigned to chlorhexidine-alcohol (27 [3%] patients vs seven [1%] with povidone iodine-alcohol; p=0·0017) and led to chlorhexidine discontinuation in two patients. INTERPRETATION For skin antisepsis, chlorhexidine-alcohol provides greater protection against short-term catheter-related infections than does povidone iodine-alcohol and should be included in all bundles for prevention of intravascular catheter-related infections. FUNDING University Hospital of Poitiers, CareFusion.

HMGB1 inhibits macrophage activity in efferocytosis through binding to the αvβ3-integrin

Phagocytosis of apoptotic cells is critical to resolution of inflammation. High mobility group box 1 protein (HMGB1), a mediator of inflammation, has been shown to diminish phagocytosis through binding to phosphatidylserine (PS) exposed on the surface of apoptotic neutrophils. However, it is currently unknown whether HMGB1 also modulates the activity of receptors involved in PS recognition on the surface of phagocytes. In the present studies, we found that preincubation of macrophages with HMGB1 decreased their ability to engulf apoptotic neutrophils or thymocytes. Preincubation of macrophages with HMGB1 prevented the enhancement of efferocytosis resulting from exposure to milk fat globule EGF factor 8 (MFG-E8), an opsonin that bridges PS and α(v)β(3) as well as α(v)β(5)-integrins on the surface of phagocytes. The inhibitory effect of HMGB1 on the phagocytic activity of macrophages was prevented by preincubation of HMGB1 with soluble α(v)β(3), but not with soluble α(v)β(5). HMGB1 colocalized with the β(3)-integrin on the cell membrane of macrophages and bound to soluble α(v)β(3), but not to soluble α(v)β(5). HMGB1 suppressed the interaction between MFG-E8 and α(v)β(3). HMGB1 also inhibited intracellular signaling events, including ERK phosphorylation and Rac-1 activation, which are activated in macrophages during phagocytosis of apoptotic cells. These results demonstrate that HMGB1 blocks α(v)β(3)-dependent recognition and uptake of apoptotic cells.

Enterococci increase the morbidity and mortality associated with severe intra-abdominal infections in elderly patients hospitalized in the intensive care unit

OBJECTIVES Enterococci may increase morbidity and mortality in elderly patients with intra-abdominal infections (IAIs) hospitalized in the intensive care unit (ICU). PATIENTS AND METHODS A single-centre, retrospective evaluation of an ICU database (1997-2007) of elderly ICU patients (≥75 years) with a severe IAI was performed. Demographics, severity scores, underlying diseases, microbiology and outcomes were recorded. Patients with enterococci isolated in peritoneal fluid (E+ group) were compared with those lacking enterococci in peritoneal fluid (E- group). Stepwise multivariate logistic regression was used to identify independent factors associated with mortality. RESULTS One hundred and sixty patients were included (mean ± SD age 82 ± 5 years; n = 72 in the E+ group). The E+ group was more severely ill than the E- group, with higher Simplified Acute Physiologic Score 2 (61 ± 20 versus 48 ± 16, P = 0.0001) and Sequential Organ Failure Assessment scores (8 ± 3 versus 5 ± 3, P = 0.0001), a greater postoperative infection rate (58.3% versus 34.1%, P = 0.01), a higher incidence of inappropriate empirical antimicrobial therapies (33.3% versus 19.3%, P = 0.04), a longer duration of mechanical ventilation (11.8 ± 10.9 versus 7.8 ± 10.2 days, P = 0.02) and greater vasopressor use (7.2 ± 7.1 versus 3.3 ± 4.1 days, P = 0.001). ICU mortality was higher in the E+ group than in the E- group (54.2% versus 38.6%, P = 0.05). In the multivariate analysis, E+ status was independently associated with mortality (odds ratio 2.24; 95% confidence interval 1.06-4.75; P = 0.03). CONCLUSIONS In severely ill, elderly patients in the ICU for an IAI, the isolation of enterococci was associated with increased disease severity and morbidity and was an independent risk factor for mortality.

The C-terminal acidic tail is responsible for the inhibitory effects of HMGB1 on efferocytosis

HMGB1 was described originally as a nuclear protein involved in DNA binding and transcriptional regulation. However, HMGB1 also has an extracellular role as a potent mediator of inflammation and can diminish the uptake of apoptotic cells by phagocytes, a process called efferocytosis. To explore the mechanism responsible for the ability of HMGB1 to inhibit efferocytosis, we examined the role of the C‐terminal acidic tail, a region of HMGB1 that has been shown to participate in specific intramolecular interactions. Deletion of the C‐terminal tail abrogated the ability of HMGB1 to decrease murine macrophage ingestion of apoptotic neutrophils and to diminish phagocytosis‐induced activation of Erk and Rac‐1 in macrophages. We found that RAGE plays a major role in efferocytosis, and deletion of the C‐terminal tail of HMGB1 prevented binding of HMGB1 to RAGE but not to other macrophage receptors involved in efferocytosis, such as the αVβ3 integrin. Whereas HMGB1 decreased ingestion of apoptotic neutrophils significantly by alveolar macrophages under in vivo conditions in the lungs of mice, this effect was lost when the C‐terminal acidic tail was absent from HMGB1. These results demonstrate that the HMGB1 C‐terminal tail is responsible for the inhibitory effects of HMGB1 on phagocytosis of apoptotic neutrophils under in vitro and in vivo conditions.

Intracellular HMGB1 Negatively Regulates Efferocytosis

High mobility group box 1 (HMGB1) is a highly conserved protein with multiple intracellular and extracellular functions, including transcriptional regulation, as well as modulation of inflammation, cell migration, and ingestion of apoptotic cells. In these experiments, we examined a potential role for intracellular HMGB1 in modulating phagocytosis. We found that phagocytosis of apoptotic cells resulted in translocation of HMGB1 into the cytoplasm and extracellular space. Transient or stable inhibition of HMGB1 expression in bone marrow-derived macrophages or fibroblasts resulted in increased phagocytosis of apoptotic thymocytes and apoptotic neutrophils. Knockdown of HMGB1 was associated with enhanced activation of Rac-1 and cytoskeletal rearrangement. Intracellular events involved in phagocytosis and upstream of Rac-1 activation, such as phosphorylation of ERK and focal adhesion kinase (FAK), were increased after knockdown of HMGB1. Inhibition of Src kinase activity prevented the increase in phosphorylation of FAK and ERK present during phagocytosis in HMGB1 knockdown cells, and also abrogated the enhancement in phagocytosis associated with HMGB1 knockdown. Interaction between Src and FAK in the cytoplasm of HMGB1 knockdown fibroblasts was enhanced compared with that present in control fibroblasts. Under in vitro conditions, the presence of HMGB1 diminished interactions between purified FAK and Src. These studies demonstrate a novel role for HMGB1 in the regulation of phagocytosis. In particular, these experiments show that intracellular HMGB1, through associating with Src kinase and inhibiting interactions between Src and FAK, diminishes the phagocytic ability of macrophages and other cell populations.

Impact of 30 mg/kg amikacin and 8 mg/kg gentamicin on serum concentrations in critically ill patients with severe sepsis

OBJECTIVES Low first-dose peak serum concentrations of amikacin and gentamicin are commonly reported in ICU patients. The present study aimed to assess whether 30 mg/kg amikacin or 8 mg/kg gentamicin achieved target concentrations in ICU patients with severe sepsis. PATIENTS AND METHODS Sixty-three ICU patients (Simplified Acute Physiology Score II = 43 ± 16) with severe sepsis and an indication for intravenous amikacin (n = 47) or gentamicin (n = 16) were included. The first (30 mg/kg amikacin; 8 mg/kg gentamicin) and subsequent doses and corresponding peak concentrations (30 min after the completion of an infusion) were recorded. French guideline target concentrations were ≥60 and ≥30 mg/L for amikacin and gentamicin, respectively. A target pharmacokinetic/pharmacodynamic ratio of 10 × MIC was also measured. RESULTS Pulmonary, abdominal and urinary tract infections were diagnosed in 56 patients. Infection was confirmed in 37 patients (59%). The targeted first-dose peak concentration was achieved in 37/63 patients (59%) [amikacin 36/47 (77%) and gentamicin 1/16 (6%)], and 59/63 patients (94%) achieved the pharmacokinetic/pharmacodynamic ratio using the MIC data that were available from 21 patients. However, the second dose of aminoglycoside was withheld because of high trough concentrations in nearly half of patients who did not have renal dysfunction. CONCLUSIONS In this study, 30 mg/kg amikacin and 8 mg/kg gentamicin led to target peak serum concentrations in 59% of patients.

Extracellular Histones Inhibit Efferocytosis

The uptake and clearance of apoptotic cells by macrophages and other phagocytic cells, a process called efferocytosis, is a major component in the resolution of inflammation. Increased concentrations of extracellular histones are found during acute inflammatory states and appear to contribute to organ system dysfunction and mortality. In these studies, we examined the potential role of histones in modulating efferocytosis. We found that phagocytosis of apoptotic neutrophils or thymocytes by macrophages was significantly diminished in the presence of histones H3 or H4, but not histone H1. Histone H3 demonstrated direct binding to macrophages, an effect that was diminished by preincubation of macrophages with the opsonins growth arrest-specific gene 6 (Gas6) and milk fat globule-epidermal growth factor (EGF) 8 (MFG-E8). Incubation of histone H3 with soluble αVβ5 integrin and Mer, but not with αVβ3, diminished its binding to macrophages. Phagocytosis of apoptotic cells by alveolar macrophages in vivo was diminished in the presence of histone H3. Incubation of histone H3 with activated protein C, a treatment that degrades histones, abrogated its inhibitory effects on efferocytosis under both in vitro and in vivo conditions. The present studies demonstrate that histones have inhibitory effects on efferocytosis, suggesting a new mechanism by which extracellular histones contribute to acute inflammatory processes and tissue injury.