A clindamycin acetylated derivative with reduced antibacterial activity inhibits articular hyperalgesia and edema by attenuating neutrophil recruitment, NF-κB activation and tumor necrosis factor-α production

We recently demonstrated that clindamycin exhibits activities in acute and chronic models of pain and inflammation. In the present study, we investigated the effects of clindamycin and a clindamycin acetylated derivative (CAD) in models of acute joint inflammation and in a microbiological assay. Joint inflammation was induced in mice by intraarticular (i.a.) injection of zymosan or lipopolysaccharide (LPS). Clindamycin or CAD were administered via the intraperitoneal route 1 h before zymosan or LPS. Paw withdrawal threshold, joint diameter, histological changes, neutrophil recruitment, tumor necrosis factor-α (TNF-α) production and phosphorylation of the IκBα and NF-κB/p65 were evaluated. In vitro assays were used to measure the antibacterial activity of clindamycin and CAD and also their effects on zymosan-induced TNF-α production by RAW264.7 macrophages. Clindamycin exhibited activity against Staphylococcus aureus and Salmonella Typhimurium ATCC® strains at much lower concentrations than CAD. Intraarticular injection of zymosan or LPS induced articular hyperalgesia, edema and neutrophil infiltration in the joints. Zymosan also induced histological changes, NF-κB activation and TNF-α production. Responses induced by zymosan and LPS were inhibited by clindamycin (200 and 400 mg/kg) or CAD (436 mg/kg). Both clindamycin and CAD inhibited in vitro TNF-α production by macrophages. In summary, we provided additional insights of the clindamycin immunomodulatory effects, whose mechanism was associated with NF-κB inhibition and reduced TNF-α production. Such effects were extended to a clindamycin derivative with reduced antibacterial activity, indicating that clindamycin derivatives should be investigated as candidates to drugs that could be useful in the management of inflammatory and painful conditions.

Combination therapy with budesonide and N-acetylcysteine ameliorates LPS-induced ALI by attenuating neutrophil recruitment through the miR-196b-5p/Socs3 molecular axis

Background

Neutrophil infiltration accelerates the inflammatory response and is highly correlated to the development of acute lung injury (ALI). Budesonide (BUD) and N-acetylcysteine (NAC) both inhibit the inflammatory response to alleviate ALI, so we further investigated whether their combination is better for ALI.

Methods

In this study, we investigated the effect and mechanism of Combined BUD and NAC therapy on LPS-induced ALI. Rat ALI model and neutrophil abnormal activation model were established by lipopolysaccharide (LPS). BUD and NAC were treated alone or in combination, or cells were transfected with miR-196b-5p mimic or si-Socs3 to evaluate the efficacy and mechanism of BUD and NAC alone or in combination. Histopathological observation of lungs was performed by Hematoxylin Eosin (HE) staining. The quantity of neutrophils and inflammatory factors level in bronchoalveolar lavage fluid (BALF) were determined by Richter-Gimza complex stain and Enzyme-Linked Immunosorbnent Assay (ELISA), respectively. ReverseTranscription-PolymeraseChainReaction (RT–qPCR) was utilized to assess miR-196b-5p and inflammatory factor mRNA levels. The expression level of Socs3 was detected by immunohistochemistry or Western Blot.

Results

BUD and NAC combined treatment had a better effect on neutrophil recruitment and inflammatory response in LPS-induced ALI than did BUD and NAC alone. Transfection of the miR-196b-5p mimic reversed the effect of combined BUD and NAC. In conclusion, the combination of BUD and NAC is a better treatment for ALI.

Conclusions

Combination therapy with BUD and NAC ameliorates LPS-induced ALI by attenuating neutrophil recruitment through the miR-196b-5p/Socs3 molecular axis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-022-02185-7.

Endothelial cell-targeting, ROS-ultrasensitive drug/siRNA co-delivery nanocomplexes mitigate early-stage neutrophil recruitment for the anti-inflammatory treatment of myocardial ischemia reperfusion injury

Neutrophils serve as a key contributor to the pathophysiology of myocardial ischemia reperfusion injury (MIRI), because the unregulated activation and infiltration of neutrophils lead to overwhelming inflammation in the myocardium to cause tissue damage. Herein, endothelial cell-targeting and  reactive oxygen species (ROS)-ultrasensitive nanocomplexes (NCs) were developed to mediate efficient co-delivery of VCAM-1 siRNA (siVCAM-1) and dexamethasone (DXM), which cooperatively inhibited neutrophil recruitment by impeding neutrophil migration and adhesion. RPPT was first synthesized via crosslinking of PEI 600 with ditellurium followed by modification with PEG and the endothelial cell-targeting peptide cRGD. RPPT was allowed to envelope the DXM-loaded PLGA nanoparticles and condense the siVCAM-1. After systemic administration in rats experiencing MIRI, the cRGD-modified NCs efficiently targeted and entered the inflamed endothelial cells, wherein RPPT was sensitively degraded by over-produced ROS to trigger intracellular siVCAM-1 release and potentiate the VCAM-1 silencing efficiency. As a consequence of the complementary function of DXM and siVCAM-1, the NCs notably mitigated neutrophil infiltration into ischemic myocardium, provoking potent anti-inflammatory efficacy to reduce MIRI and recover cardiac function. The present study offers an effective approach for the controlled co-delivery of siRNA and drug cargoes, and it also highlights the importance of multi-dimensional manipulation of neutrophils in anti-inflammatory treatment. STATEMENT OF SIGNIFICANCE: The unregulated activation and infiltration of neutrophils lead to overwhelming inflammation in the myocardium after myocardial ischemia reperfusion injury (MIRI). Here, endothelial cell-targeting and ROS-ultrasensitive nanocomplexes (NCs), comprised of PLGA NPs decorated with cRGD-poly(ethylene glycol) (PEG)-modified, ditellurium-crosslinked PEI (RPPT), were developed to mediate efficient co-delivery of VCAM-1 siRNA (siVCAM-1) and dexamethasone (DXM). DXM and siVCAM-1 with complementary functions inhibited both the migration and adhesion of neutrophils, efficiently interventing the neutrophil recruitment and interrupting the self-amplified inflammation cascade in the injured myocardium. The molecular design of RPPT renders an effective example for constructing polymeric materials with high ROS sensitivity, and it resolves the critical dilemma related to polycation-mediated siRNA delivery, such as siRNA encapsulation versus release, and transfection efficiency versus toxicity.

Vitamin D Enhances Neutrophil Generation and Function in Zebrafish (Danio rerio)

Vitamin D (VD) is a major regulator of calcium metabolism in many living organisms. In addition, VD plays a key role in regulating innate and adaptive immunity in vertebrates. Neutrophils constitute an important part of the first line of defense against invading microbes; however, the potential effect of VD on neutrophils remains elusive. Thus, in this study zebrafish in different developmental stages were utilized to identify the potential role of VD in the basal homeostasis and functions of neutrophils. Our results showed that addition of exogenous VD3 promoted granulopoiesis in zebrafish larvae. Reciprocally, neutrophil abundance in the intestine of adult zebrafish with a cyp2r1 mutant, lacking the capacity to 25-hydroxylate VD, was reduced. Moreover, VD-mediated granulopoiesis was still observed in gnotobiotic zebrafish larvae, indicating that VD regulates neutrophil generation independent of the microbiota during early development. In contrast, VD was incapable to influence granulopoiesis in adult zebrafish when the commensal bacteria were depleted by antibiotic treatment, suggesting that VD might modulate neutrophil activity via different mechanisms depending on the developmental stage. In addition, we found that VD3 augmented the expression of il-8 and neutrophil recruitment to the site of caudal fin amputation. Finally, VD3 treatment significantly decreased bacterial counts and mortality in zebrafish infected with Edwardsiella tarda (E. tarda) in a neutrophil-dependent manner. Combined, these findings demonstrate that VD regulates granulopoiesis and neutrophil function in zebrafish immunity.

A role for mast cells and mast cell tryptase in driving neutrophil recruitment in LPS-induced lung inflammation via protease-activated receptor 2 in mice

OBJECTIVE

This study aims to investigate the role of protease-activated receptor (PAR) 2 and mast cell (MC) tryptase in LPS-induced lung inflammation and neutrophil recruitment in the lungs of C57BL/6 mice.

METHODS

C57BL/6 mice were pretreated with the PAR2 antagonist ENMD-1068, compound 48/80 or aprotinin prior to intranasal instillation of MC tryptase or LPS. Blood leukocytes, C-X-C motif chemokine ligand (CXCL) 1 production leukocytes recovered from bronchoalveolar lavage fluid (BALF), and histopathological analysis of the lung were evaluated 4 h later. Furthermore, we performed experiments to determine intracellular calcium signaling in RAW 264.7 cells stimulated with LPS in the presence or absence of a protease inhibitor cocktail or ENMD-1068 and evaluated PAR2 expression in the lungs of LPS-treated mice.

RESULTS

Pharmacological blockade of PAR2 or inhibition of proteases reduced neutrophils recovered in BALF and LPS-induced calcium signaling. PAR2 blockade impaired LPS-induced lung inflammation, PAR2 expression in the lung and CXCL1 release in BALF, and increased circulating blood neutrophils. Intranasal instillation of MC tryptase increased the number of neutrophils recovered in BALF, and MC depletion with compound 48/80 impaired LPS-induced neutrophil migration.

CONCLUSION

Our study provides, for the first time, evidence of a pivotal role for MCs and MC tryptase in neutrophil migration, lung inflammation and macrophage activation triggered by LPS, by a mechanism dependent on PAR2 activation.

Exosomal KRAS mutation promotes the formation of tumor-associated neutrophil extracellular traps and causes deterioration of colorectal cancer by inducing IL-8 expression

Background

Colorectal cancer (CRC) remains one of the leading causes of cancer-related death. The current study aimed to elucidate the mechanism by which exosomes carrying KRAS mutant contribute to neutrophil recruitment as well as the formation of the neutrophil extracellular trap (NET) in CRC.

Methods

APC-WT and APC-KRAS^G12D mouse models were initially developed. Peripheral blood, spleen, bone marrow (BM) and mesenteric lymph nodes (mLN) were isolated to detect neutrophil content. Then, APC-WT and APC-KRAS^G12D mice were injected with exosomes isolated from APC-WT and APC-KRAS^G12D mice. The ratio of neutrophils, NETs formation and IL-8 protein content were subsequently quantified in colon tissues. DKs-8 (wild type) and DKO-1 (KRAS mutant) cells were employed for in vitro experimentation. Then, DKs-8 cells were cultured with exosome-treated PMA stimulated neutrophil-forming NETs culture medium, with cell viability, invasion, migration, and adhesion evaluated.

Results

Compared with APC-WT mice, the numbers of polyps and neutrophils in the peripheral blood, spleen and mLNs were increased in APC-KRAS^G12D mice, accompanied with increased NET formation, IL-8 expression and exosomes. Meanwhile, IL-8 upregulation, neutrophil recruitment and NET formation were observed in the mice injected with exosomes derived from APC-KRAS^G12D. The in vitro investigation results revealed that more NETs were formed in the presence of DKO-1-Exos, which were inhibited by DNAse. In addition, DKs-8- and DKO-1 cells-derived exosomes could adhere to NETs under static conditions in vitro. Exosomal KRAS mutants were noted to exert stimulatory effects on the IL-8 production and NET formation to promote the growth of CRC cells.

Conclusion

The results provide evidence suggesting that exosomes may transfer mutant KRAS to recipient cells and trigger increases in IL-8 production, neutrophil recruitment and formation of NETs, eventually leading to the deterioration of CRC.

Intravascular adhesion and recruitment of neutrophils in response to CXCL1 depends on their TRPC6 channels

Abstract

Here we report a novel role for TRPC6, a member of the transient receptor potential (TRPC) channel family, in the CXCL1-dependent recruitment of murine neutrophil granulocytes. Representing a central element of the innate immune system, neutrophils are recruited from the blood stream to a site of inflammation. The recruitment process follows a well-defined sequence of events including adhesion to the blood vessel walls, migration, and chemotaxis to reach the inflammatory focus. A common feature of the underlying signaling pathways is the utilization of Ca²⁺ ions as intracellular second messengers. However, the required Ca²⁺ influx channels are not yet fully characterized. We used WT and TRPC6^−/− neutrophils for in vitro and TRPC6^−/− chimeric mice (WT mice with WT or TRPC6^−/− bone marrow cells) for in vivo studies. After renal ischemia and reperfusion injury, TRPC6^−/− chimeric mice had an attenuated TRPC6^−/− neutrophil recruitment and a better outcome as judged from the reduced increase in the plasma creatinine concentration. In the cremaster model CXCL1-induced neutrophil adhesion, arrest and transmigration were also decreased in chimeric mice with TRPC6^−/− neutrophils. Using atomic force microscopy and microfluidics, we could attribute the recruitment defect of TRPC6^−/− neutrophils to the impact of the channel on adhesion to endothelial cells. Mechanistically, TRPC6^−/− neutrophils exhibited lower Ca²⁺ transients during the initial adhesion leading to diminished Rap1 and β₂ integrin activation and thereby reduced ICAM-1 binding. In summary, our study reveals that TRPC6 channels in neutrophils are crucial signaling modules in their recruitment from the blood stream in response to CXCL1.

Key point

Neutrophil TRPC6 channels are crucial for CXCL1-triggered activation of integrins during the initial steps of neutrophil recruitment.

Zebrafish, a model to develop nanotherapeutics that control neutrophils response during inflammation

Neutrophils are crucial modulators of the inflammation process, and their uncontrolled response worsens several chronic pathologies. The p38 mitogen-activated protein kinases (MAPKs) activity is critical for normal immune and inflammatory response through the regulation of pro-inflammatory cytokines synthesis. In this work, we study the effect of hybrid lipid-polymer nanoparticles loaded with the p38 MAPK inhibitor SB203580 in an acute and chronic inflammatory model in zebrafish containing a transgenic neutrophil cell line that constitutively expresses a green fluorescent protein. We identify the existence of at least two neutrophils subpopulation involved in the response during the acute inflammation triggered; a first-responder p38α-independent subset and a second-responder p38α-dependent subset. In the case of chronic inflammation, neutrophils recruited in the intestine only during the inflammation process, migrate in a p38α-dependent manner. Likewise, we establish that SB203580-loaded in NPs exerts their action during at least a double period than the inhibitor administers directly in both types of inflammation. Our results demonstrate the exceptional potential of the zebrafish as an inflammatory model for studying novel nanotherapeutics that selectively inhibit the neutrophils response, and to identify functional neutrophils subpopulations involved in the inflammation process.

Toll-Like Receptor 3 Signaling Contributes to Regional Neutrophil Recruitment in Cultured Human Glomerular Endothelial Cells

BACKGROUND

Given the importance of neutrophil recruitment in the pathogenesis of glomerulonephritis (GN), the representative neutrophil chemoattractant C-X-C motif chemokine 1 (CXCL1)/GROα and the adhesion molecule E-selectin in glomerular endothelial cells (GECs) play a pivotal role in the development of GN. Endothelial Toll-like receptor 3 (TLR3) is thought to be involved in the inflammatory response via innate immunity. However, the role of endothelial TLR3 signaling in the expression of neutrophil chemoattractants and adhesion molecules remains to be elucidated. Thus, we aimed to examine this issue.

METHODS

We treated normal human GECs with polyinosinic-polycytidylic acid (poly IC), an authentic double-stranded RNA, and analyzed the expressions of CXCL1 and E-selectin using quantitative real-time reverse transcription-polymerase chain reaction, western blotting, and enzyme-linked immunosorbent assay. To further elucidate the poly IC-induced signaling pathway, we subjected the cells to RNA interference against TLR3, interferon (IFN)-β, nuclear factor (NF)-κB p65, and IFN regulatory factor (IRF) 3. We also used immunofluorescence to examine the endothelial expression of CXCL1 in biopsy specimens from patients with crescentic and non-crescentic purpura nephritis (PN).

RESULTS

We found that the activation of TLR3 induced the endothelial expression of CXCL1 and E-selectin, and that this involved TLR3, -NF-κB, IRF3, and IFN-β. Intense endothelial CXCL1 expression was observed in biopsy specimens from patients with crescentic PN.

CONCLUSION

These findings support a role for glomerular antiviral innate immunity in the pathogenesis of GN. Intervention of glomerular TLR3 signaling may therefore be a suitable therapeutic strategy for treating GN in the future.

Mono Sodium Urate Crystal-induced Peritonitis for in vivoAssessment of Inflammasome Activation

Due to its particulate material, mono-sodium urate (MSU) crystals are potent activators of the NOD-like receptor NLRP3. Upon activation, NLRP3 induces the formation of inflammasome complexes, which lead to the production and release of mature IL-1β. Bioactive IL-1β is a potent activator of innate immune responses and promotes recruitment of inflammatory cells, including neutrophils from the blood into damaged/inflamed tissues. This protocol describes a method to study in vivo inflammasome activation via intraperitoneal injection of MSU crystals. MSU-injection results in a drastic increase of intraperitoneal IL-1β levels, promoting neutrophil infiltration. Early-stage neutrophil numbers correlate with the amount of released IL-1β and can be used as a read-out for the extent of in vivo inflammasome activation. In addition, this protocol might also be used as a sterile peritonitis model, to investigate mechanisms of neutrophil recruitment to the peritoneum, or as a means to obtain large numbers of in vivo activated neutrophils.

Hepatic acute phase response protects the brain from focal inflammation during postnatal window of susceptibility

Perinatal inflammation is known to contribute to neurodevelopmental diseases. Animal models of perinatal inflammation have revealed that the inflammatory response within the brain is age dependent, but the regulators of this variation remain unclear. In the adult, the peripheral acute phase response (APR) is known to be pivotal in the downstream recruitment of leukocytes to the injured brain. The relationship between perinatal brain injury and the APR has not been established. Here, we generated focal inflammation in the brain using interleukin (IL)-1β at postnatal day (P)7, P14, P21 and P56 and studied both the central nervous system (CNS) and hepatic inflammatory responses at 4 h. We found that there is a significant window of susceptibility in mice at P14, when compared to mice at P7, P21 and P56. This was reflected in increased neutrophil recruitment to the CNS, as well as an increase in blood-brain barrier permeability. To investigate phenomena underlying this window of susceptibility, we performed a dose response of IL-1β. Whilst induction of endogenous IL-1β or intercellular adhesion molecule (ICAM)-1 in the brain and induction of a hepatic APR were dose dependent, the recruitment of neutrophils and associated blood-brain barrier breakdown was inversely proportional. Furthermore, in contrast to adult animals, an additional peripheral challenge (intravenous IL-1β) reduced the degree of CNS inflammation, rather than exacerbating it. Together these results suggest a unique window of susceptibility to CNS injury, meaning that suppressing systemic inflammation after brain injury may exacerbate the damage caused, in an age-dependent manner.

Suppression of NLRP3 attenuates hemorrhagic transformation after delayed rtPA treatment in thromboembolic stroke rats: Involvement of neutrophil recruitment

BACKGROUND

Inflammation and neutrophils play pivotal roles in hemorrhagic transformation (HT) after recombinant tissue plasminogen activator (rtPA) treatment in stroke; however, the contribution of Nod-like receptor protein 3 (NLRP3), a key component of the innate immune system, is not yet known. This study aimed to explore the role of NLRP3 in the delayed rtPA-induced HT and its association with the neutrophil recruitment.

METHODS

Rats were subjected to thromboembolic focal cerebral ischemia and delayed rtPA treatment at 4 h after ischemia to mimic HT. NLRP3 short hairpin RNAs (shRNA) were administered 72 h before ischemia. Additionally, rabbit anti-rat neutrophil serum (inducing neutropenia) was administered before cerebral ischemia. The infarct volume, edema volume, neurological deficit, hemorrhages, blood-brain barrier (BBB) integrity and brain neutrophil recruitment were evaluated at 24 h after cerebral ischemia.

RESULTS

Our results demonstrated that delayed rtPA treatment at 4 h after ischemia promoted the expression of NLRP3 in neurons, microglia and endothelial cells, degradation of BBB components, and HT. NLRP3 knockdown significantly attenuated NLRP3 expression, BBB disruption, and HT. It also improved neurological functions and reduced neutrophil recruitment. Rabbit anti-rat neutrophil serum, like NLRP3 shRNA, reduced hemorrhage score and hemorrhage volumes after rtPA treatment. Furthermore, the anti-rat neutrophil serum combined with NLRP3 shRNA didn't further increase the protective effect on HT compared to rabbit anti-rat neutrophil serum used alone.

CONCLUSIONS

Together, our data suggest that NLRP3 inhibition can reduce neutrophil recruitment, which may contribute to the inhibitory effect on HT.

Inhibition of leukotriene B4 synthesis protects against early brain injury possibly via reducing the neutrophil-generated inflammatory response and oxidative stress after subarachnoid hemorrhage in rats

Leukotriene B4 (LTB4) is a highly potent neutrophil chemoattractant and neutrophils induces inflammatory response and oxidative stress when they recruit to and infiltrate in the injuried/inflamed site, such as the brain parenchyma after aneurysmal subarachnoid hemorrhage (SAH). This study is to investigate the potential effects of inhibition of LTB4 synthesis on neutrophil recruitment, inflammatory response and oxidative stress, as well as early brain injury (EBI) in rats after SAH. A pre-chiasmatic cistern SAH model of rats was used in this experiment. SC 57461A was used to inhibit LTB4 synthesis via intracerebroventricular injection. The brain tissues of temporal lobe after SAH were analyzed. Neuronal injury, brain edema and neurological function were evaluated to investigate the development of EBI. We found that inhibition of LTB4 synthesis after SAH could reduce the level of myeloperoxidase, alleviate the inflammatory response and oxidative stress, and reduce neuronal death in the brain parenchyma, and ameliorate brain edema and neurological behavior impairment at 24h after SAH. These results suggest that inhibition of LTB4 synthesis might alleviate EBI after SAH possibly via reducing the neutrophil-generated inflammatory response and oxidative stress.

IL-1β, IL-18, and eicosanoids promote neutrophil recruitment to pore-induced intracellular traps following pyroptosis

Inflammasomes activate caspase-1, initiating a lytic form of programmed cell death termed pyroptosis, which is an important innate immune defense mechanism against intracellular infections. We recently demonstrated in a mouse infection model of pyroptosis that instead of releasing bacteria into the extracellular space, bacteria remain trapped within the pyroptotic cell corpse, termed the pore-induced intracellular trap (PIT). This trapping mediates efferocytosis of the PIT and associated bacteria by neutrophils; bacteria are subsequently killed via neutrophil ROS. Using this pyroptosis model, we now show that the pro-inflammatory cytokines IL-1β and IL-18 and inflammatory lipid mediators termed eicosanoids are required for effective clearance of bacteria downstream of pyroptosis. We further show that IL-1β, IL-18, and eicosanoids affect this in part by mediating neutrophil recruitment to the PIT. This is in addition to our prior findings that complement is also important to attract neutrophils. Thus, the PIT initiates a robust and coordinated innate immune response involving multiple mediators that attract neutrophils to efferocytose the PIT and its entrapped bacteria.

Abnormal cannabidiol attenuates experimental colitis in mice, promotes wound healing and inhibits neutrophil recruitment

Background

Non-psychotropic atypical cannabinoids have therapeutic potential in a variety of inflammatory conditions including those of the gastrointestinal tract. Here we examined the effects of the atypical cannabinoid abnormal cannabidiol (Abn-CBD) on wound healing, inflammatory cell recruitment and colitis in mice.

Methods

Colitis was induced in CD1 mice by a single intrarectal administration of trinitrobenzene sulfonic acid (TNBS, 4 mg/100 μl in 30 % ethanol) and Abn-CBD and/or the antagonists O-1918 (Abd-CBD), AM251 (CB₁ receptor) and AM630 (CB₂ receptor), were administered intraperitoneally (all 5 mg/kg, twice daily for 3 days). The degree of colitis was assessed macro- and microscopically and tissue myeloperoxidase activity was determined. The effects of Abn-CBD on wound healing of endothelial and epithelial cells (LoVo) were assessed in a scratch injury assay. Human neutrophils were employed in Transwell assays or perfused over human umbilical vein endothelial cells (HUVEC) to study the effect of Abn-CBD on neutrophil accumulation and transmigration.

Results

TNBS-induced colitis was attenuated by treatment with Abn-CBD. Histological, macroscopic colitis scores and tissue myeloperoxidase activity were significantly reduced. These effects were inhibited by O-1918, but not by AM630, and only in part by AM251. Wound healing of both HUVEC and LoVo cells was enhanced by Abn-CBD. Abn-CBD inhibited neutrophil migration towards IL-8, and dose-dependently inhibited accumulation of neutrophils on HUVEC.

Conclusions

Abn-CBD is protective against TNBS-induced colitis, promotes wound healing of endothelial and epithelial cells and inhibits neutrophil accumulation on HUVEC monolayers. Thus, the atypical cannabinoid Abn-CBD represents a novel potential therapeutic in the treatment of intestinal inflammatory diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-016-0129-0) contains supplementary material, which is available to authorized users.

Neutrophil-mediated inflammation in the pathogenesis of Clostridium difficile infections

Clostridium difficile is the most important cause of nosocomial infectious diarrhea in the western world. C. difficile infections are a major healthcare burden with approximately 500,000 new cases every year and an estimated annual cost of nearly $1 billion in the U.S. Furthermore, the infections are no longer restricted to health care facilities, and recent studies indicate spread of C. difficile infection to the community as well. The clinical spectrum of C. difficile infection ranges from asymptomatic colonization to severe diarrhea, fulminant colitis and death. This spectrum results from a complex interplay between bacterial virulence factors, the colonic microbiome and the host inflammatory response. The overall vigor of host inflammatory response is believed to be an important determinant of C. difficile disease severity, and a more robust immune response is associated with worse outcomes. Neutrophils are the primary cells that respond to C. difficile invasion and neutrophilic inflammation is the hallmark of C. difficile-associated disease. In this review, we will focus on the role of neutrophils (infiltration to infected tissue, pathogen clearance and resolution of inflammation) in the immuno-pathogenesis of C. difficile-associated disease (CDAD).

Neutrophils and arthritis: Role in disease and pharmacological perspectives

The inflammatory response in the joint can induce an intense accumulation of leukocytes in the tissue that frequently results in severe local damage and loss of function. Neutrophils are essential cells to combat many pathogens, but their arsenal can contribute or aggravate articular inflammation. Here we summarized some aspects of neutrophil biology, their role in inflammation and indicated how the modulation of neutrophil functions could be useful for the treatment of different forms of arthritis.

Visualization of Signaling Molecules During Neutrophil Recruitment in Transgenic Mice Expressing FRET Biosensors

A number of chemical mediators regulate neutrophil recruitment to inflammatory sites either positively or negatively. Although the actions of each chemical mediator on the intracellular signaling networks controlling cell migration have been studied with neutrophils cultured in vitro, how such chemical mediators act cooperatively or counteractively in vivo remains largely unknown. To understand the mechanisms regulating neutrophil recruitment to the inflamed intestine in vivo, we recently generated transgenic mice expressing biosensors based on FRET (Förster resonance energy transfer) and set up two-photon excitation microscopy to observe the gastrointestinal tract in living mice. By measuring FRET in neutrophils, we showed activity changes of protein kinases in the neutrophils recruited to inflamed intestines. In this chapter, we describe the protocol used to visualize the protein kinase activities in neutrophils of the inflamed intestine of transgenic mice expressing the FRET biosensors.

Leukocyte function-associated antigen-1 deficiency impairs responses to polymicrobial sepsis

AIM: To determine the role of leukocyte function-associated antigen-1 (LFA-1) in polymicrobial sepsis model in mice.

METHODS: Cecal ligation and puncture model was used to study polymicrobial sepsis in wild type and LFA-1 knockout (KO) (= CD11a KO) mice. Their survivals were examined. Neutrophil recruitment to the abdominal cavity, bacterial tissue load and bacterial killing by neutrophils, tissue cytokine profiles, and serum cytokines were examined. Apoptosis of tissues was assessed using cleaved-caspase 3 and TUNNEL staining. The recruitment of neutrophils to various tissues was assessed using myeloperoxidase staining or measuring myeloperoxidase activity.

RESULTS: LFA-1 deficiency significantly decreased survival (P = 0.0024) with the reduction of neutrophil recruitment to the abdominal cavity and higher bacterial load in blood. It was also associated with increased apoptosis in spleen and more organ injuries probed by interleukin-6 mRNA level. However, the deficiency of LFA-1 did not prevent neutrophil recruitment to lung, liver, spleen or kidney, which suggested the existence of LFA-1 independent recruitment mechanism in these organs.

CONCLUSION: LFA-1 deficiency did not attenuate neutrophil recruitment to various organs to adequately mitigate secondary tissue injury in sepsis. It was associated with decreased neutrophil recruitment to the abdominal cavity, higher bacterial load, leading to increased mortality in an abdominal, polymicrobial sepsis.

Endothelial Cx40 limits myocardial ischaemia/reperfusion injury in mice

AIMS

Gap junctions are indispensable for the function of heart and blood vessels by providing electrical coupling and direct cell-to-cell transfer of small signalling molecules. Gap junction channels between neighbouring cells are composed of 12 connexins (Cx). Changes in Cx43 expression, localization, and channel properties in cardiomyocytes contribute to infarction and reperfusion injury of the heart. It is increasingly recognized that deleterious consequences of ischaemia/reperfusion (IR) are modulated by the inflammatory response and endothelial function. The role of the endothelial connexins, i.e. Cx40 and Cx37, in cardiac IR injury is, however, not known.

METHODS AND RESULTS

Following 30 min ischaemia and 24 h reperfusion, we found a significant increase in myocardial infarct size in mice with endothelial-specific deletion of Cx40 (Cx40del), but not in Cx37-deficient mice. The cardioprotective effect of endothelial Cx40 was associated with a decrease in neutrophil infiltration. Moreover, beneficial effects of endothelial Cx40 were not observed in isolated Langendorff-perfused hearts, suggesting direct involvement of endothelial-leucocyte interactions in the cardiac injury. Single-dose administration of methotrexate, a CD73 activator, reduced infarct size and neutrophil infiltration into the infarcted myocardium in Cx40del but not in control mice. Similar to Cx40del mice, CD73-deficient mice showed increased sensitivity to cardiac IR injury, which could not be conversed by methotrexate.

CONCLUSION

Endothelial Cx40, but not Cx37, is implicated in resistance of the heart to IR injury by activation of the CD73 pathway. Thus, the Cx40-CD73 axis may represent an interesting target for controlling reperfusion damage associated with revascularization in coronary disease.

The receptor for activated complement factor 5 (C5aR) conveys myocardial ischemic damage by mediating neutrophil transmigration

Tissue loss after myocardial ischemia with reperfusion (MI/R) is in part conveyed by neutrophil recruitment to post-ischemic myocardium. Strategies to prevent reperfusion injury would help to limit myocardial damage. The receptor for activated complement factor 5 (C5aR) plays a prominent role in inflammation. We examine the effects of C5aR-deficiency on reperfusion injury after MI/R. C5aR(-/-)-mice and their C57BL/6- (WT) littermates underwent transient myocardial ischemia followed by different time points of reperfusion. Infarct size and leukocyte infiltration were determined. Expression of C5aR, inflammatory cytokines and adhesion molecules were analyzed by real-time RT-PCR. Leukocyte-endothelial interactions were assessed by low-shear adhesion- and transmigration-assays in vitro. Myocardial C5aR mRNA expression was 2.8-fold increased by ischemia. Infarct size per area-at-risk and leukocyte recruitment into infarctions were reduced in C5aR(-/-)-compared to WT-mice as well as in WT mice treated with the C5aR-antagonist JPE1375. IL-6, IL-1β, ICAM-1 and VCAM-1 expression were not different, while TNFα expression was reduced in C5aR(-/-)-mice after MI/R. In vitro, C5aR on leukocytes is required for effective transendothelial migration but not adhesion. Expression of MMP9 and JAM-A, molecules that are involved in leukocyte transmigration, were reduced in C5aR(-/-) mice in vivo. Genetic C5aR deficiency blunts the inflammatory response in murine MI/R resulting in reduced inflammatory cell recruitment, which is due to a C5aR-dependent effect on leukocyte transmigration across inflamed endothelium into the ischemic myocardium. This effect could be related to MMP9- and JAM-A expression in response to ischemia and reperfusion.

An in vitro study on the modulation of the neutrophil adhesive behavior by soluble fibrinogen

Fibrinogen constitutes an important plasma glycoprotein involved in hemostasis and in inflammation. Previously, we have shown that at physiological concentrations, soluble fibrinogen is able to modulate the pattern of neutrophil activation. This led us to propose that under these conditions, fibrinogen could as well interfere with the adhesive behaviour of circulating neutrophils which is of utmost importance in their recruitment to the vascular wall during inflammatory processes. To address our working hypothesis, in vitro adhesion assays were here performed in a flow chamber by using primary cultures of human umbilical vein endothelial cells (HUVEC) and neutrophils isolated from peripheral venous blood of healthy human donors. In the presence of a physiological concentration of soluble fibrinogen (300 mg/dL), we observed that despite the number of neutrophils rolling on an activated endothelium was not affected, their rolling velocity was increased in comparison to that of non-activated neutrophils. Consequently as expected, the number of fibrinogen-treated neutrophils adhering to activated HUVEC monolayers was significantly diminished. Overall, we have here demonstrated that at least in vitro, soluble fibrinogen under physiological concentrations is able to modulate the interaction of neutrophils with the vascular endothelium. In vivo studies will enable us in the future to study the physiological relevance of these findings and further to understand the mechanisms underlying this function.

Evaluation of tumour necrosis factor-alpha and interleukin-1beta in an experimental pyelonephritis model induced with planktonic and biofilms cells of Pseudomonas aeruginosa

Urinary tract infections may induce severe inflammation, transient impairment in renal function and scar formation, ranging in severity from acute symptomatic pyelonephritis to chronic pyelonephritis, and have the potential to lead to renal failure and death. In the present study, the relationship between production of tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), neutrophil recruitment, bacterial colonization and tissue damage was investigated using a mouse model of acute ascending pyelonephritis induced with planktonic and biofilm cells of Pseudomonas aeruginosa. Neutrophil influx correlated with rise in TNF-alpha and IL-1beta, indicating an association between these cytokines and neutrophil infiltration. However, biofilm cells of P aeruginosa induced higher levels of TNF-alpha and IL-1beta leading to higher neutrophil infiltration causing tissue damage, assessed in terms of malondialdehyde, lactate dehydrogenase and glutathione content, which may have contributed to bacterial persistence compared with their planktonic counterparts. The results of the present investigation suggest that exaggerated cytokine production during P aeruginosa-induced pyelonephritis causes tissue damage operative through neutrophil recruitment leading to bacterial persistence in host tissues. The findings of the present study may be relevant for the better understanding of disease pathophysiology and for the future developments of preventive strategies against pyelonephritis based on anti-inflammatory intervention.