Inhibition of microsomal prostaglandin E synthase-1 ameliorates acute lung injury in mice

High-throughput single-cell analysis reveals Omp38-specific monoclonal antibodies that protect against Acinetobacter baumannii infection

Infections caused by Acinetobacter baumannii (A. baumannii) have emerged as a global public health concern because of high pathogenicity of this bacterium. Monoclonal antibodies (mAbs) have a lower likelihood of promoting drug resistance and offer targeted treatment, thereby reducing potential adverse effects; however, the therapeutic potential of mAbs targeting A. baumannii has not been fully characterized. In this study, mAbs against the outer membrane proteins (OMPs) of A. baumannii were isolated in a high-throughput manner. The ability of Omp38-specific mAbs to bind to A. baumannii strains from diverse sources was confirmed via enzyme-linked immunosorbent assay (ELISA). Intravenous administration of the Omp38-specific mAbs significantly improved the survival rate and reduced the bacterial load in a mouse model of lethal A. baumannii infection. Flow cytometry and ELISA confirmed that immune cell infiltration and cytokine production, respectively, decreased in a mouse model of sublethal A. baumannii infection. In addition, analysis of the Omp38-mAb C3 binding conformation revealed the potential mechanism of broad-spectrum binding activity of this mAb against A. baumannii. Taken together, these findings indicate that mAbs against Omp38 facilitate bacterial clearance from host, minimize inflammatory mediator release and reduce host damage, highlighting the potential of Omp38-specific mAbs in the clinical treatment of A. baumannii infection.

FlaA N/C attenuates radiation-induced lung injury by promoting NAIP/NLRC4/ASC inflammasome autophagy and inhibiting pyroptosis

BACKGROUND

Radiation-induced lung injury (RILI) is the most common complication experienced by patients with thoracic tumors after radiotherapy. Among patients receiving thoracic tumor radiotherapy, 14.6-37.2% develop RILI. RILI is characterized by an acute inflammatory response; however, the exact mechanism remains unclear and an ideal drug is still lacking. In this study, we investigated the protective effects of flagellin A with linked C- and N-terminal ends (FlaA N/C) against the development of RILI.

METHODS

Mice and bronchial epithelial cells were exposed to radiation (15 Gy) after FlaA N/C treatment. Lung injury, bronchial epithelial cell injury, and RILI were assessed by histological evaluation in vivo and cell viability and cell death detection in vitro. Pyroptosis was assessed by western blotting (WB), immunofluorescence (IF), and immunohistochemistry (IHC). To explore the molecular mechanisms by which FlaA N/C inhibits RILI, conditional Beclin 1 (Beclin1+/-) and NLR family CARD domain-containing protein 4 (Nlrc4)-knockout (Nlrc4-/-) mice were generated. An autophagy inhibitor was used for in vitro cell assays, and pyroptosis indicators were detected. Data were analyzed using one-way analysis of variance.

RESULTS

FlaA N/C attenuated radiation-induced lung tissue damage, pro-inflammatory cytokine release, and pyroptosis in vivo and cell viability, cell death, and pyroptosis in vitro. Mechanistically, FlaA N/C activated the neuronal apoptosis inhibitory protein (NAIP)/NLRC4/apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) inflammasome, which was then degraded during Beclin 1-mediated autophagy. Deletion of the FlaA N/C D0 domain reversed the inhibitory effect of FlaA N/C on radiation-induced pyroptosis in vivo and in vitro. Similarly, Nlrc4-knockout in vivo or inhibition of autophagy in vitro eliminated the protective effects of FlaA N/C against radiation-induced pyroptosis.

CONCLUSIONS

These results indicate that FlaA N/C attenuates RILI by promoting NAIP/NLRC4/ASC inflammasome autophagy and inhibiting pyroptosis. This study provides a potential approach for RILI intervention.

Dipeptidyl peptidase-4 inhibitor linagliptin reduces inflammatory response, ameliorates tissue edema formation, and improves survival in severe sepsis

BACKGROUND

Excessive inflammation in sepsis causes microvascular dysfunction associated with organ dysfunction and high mortality. The present studies aimed to examine the therapeutic potential of linagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor in a clinically relevant polymicrobial sepsis model in mice.

METHODS

Sepsis was induced by cecal ligation and puncture (CLP). Mice were grouped into: Sham control+vehicle; Group 2: CLP+vehicle; Group 3: CLP+dexamethasone (10 mg/kg, s.c.) given 6 h after CLP; Group 4: CLP+linagliptin (1 mg/kg, s.c.) given 6 h after CLP. The experiment was terminated 24 hours after CLP in two experimental sets. Seven-day survival following CLP was determined in a third experimental set.

RESULTS

Treatment with linagliptin inhibited DPP-4 activity, increased the levels of active forms of endogenous gastric inhibitory polypeptide and glucagon-like peptide-1, without affecting the blood glucose levels in CLP mice. Compared to vehicle treatment, administration of linagliptin reduced sepsis-induced tissue hyper permeability as evidenced by a reduction in vascular Evans blue leakage, prevented edema formation in the lung, heart, liver and kidney. Furthermore, linagliptin or dexamethasone reduced sepsis-induced proinflammatory cytokine and chemokine production, such as IL-1β, IL-2, IL-10, IL-23, IL-27, VCAM-1, eotaxin, MDC, MCSF1, GCP-2, and NGAL. Importantly, administration of linagliptin improved the 7-day survival rate following CLP in mice. RNA sequencing in lung and heart revealed that linagliptin attenuated key inflammatory pathways including TNF alpha (via NFκB) and IL6/JAK/STAT3 signaling and activated interferon signaling in the heart.

CONCLUSIONS

Linagliptin treatment can attenuate the inflammatory response, protect against severe sepsis-induced vascular hyperpermeability, reduce multiorgan injury, and most importantly, improve the survival.

A critical role for HNF4α in polymicrobial sepsis-associated metabolic reprogramming and death

In sepsis, limited food intake and increased energy expenditure induce a starvation response, which is compromised by a quick decline in the expression of hepatic PPARα, a transcription factor essential in intracellular catabolism of free fatty acids. The mechanism upstream of this PPARα downregulation is unknown. We found that sepsis causes a progressive hepatic loss-of-function of HNF4α, which has a strong impact on the expression of several important nuclear receptors, including PPARα. HNF4α depletion in hepatocytes dramatically increases sepsis lethality, steatosis, and organ damage and prevents an adequate response to IL6, which is critical for liver regeneration and survival. An HNF4α agonist protects against sepsis at all levels, irrespectively of bacterial loads, suggesting HNF4α is crucial in tolerance to sepsis. In conclusion, hepatic HNF4α activity is decreased during sepsis, causing PPARα downregulation, metabolic problems, and a disturbed IL6-mediated acute phase response. The findings provide new insights and therapeutic options in sepsis.

STING-Dependent Sensing of Self-DNA Driving Pyroptosis Contributes to Radiation-Induced Lung Injury

PURPOSE

Radiation therapy (RT) is indispensable for managing thoracic carcinomas. However, its application is limited by radiation-induced lung injury (RILI), one of the most common and fatal complications of thoracic RT. Nonetheless, the exact molecular mechanisms of RILI remain poorly understood.

METHODS AND MATERIALS

To elucidate the underlying mechanisms, various knockout mouse strains were subjected to 16 Gy whole-thoracic RT. RILI was assessed by quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, histology, western blot, immunohistochemistry, and computed tomography examination. To perform further mechanistic studies on the signaling cascade during the RILI process, pulldown, chromatin immunoprecipitation assay, and rescue assays were conducted.

RESULTS

We found that the cGAS-STING pathway was significantly upregulated after irradiation exposure in both the mouse models and clinical lung tissues. Knocking down either cGAS or STING led to attenuated inflammation and fibrosis in mouse lung tissues. NLRP3 is hardwired to the upstream DNA-sensing cGAS-STING pathway to trigger of the inflammasome and amplification of the inflammatory response. STING deficiency suppressed the expressions of the NLRP3 inflammasome and pyroptosis-pertinent components containing IL-1β, IL-18, GSDMD-N, and cleaved caspase-1. Mechanistically, interferon regulatory factor 3, the essential transcription factor downstream of cGAS-STING, promoted the pyroptosis by transcriptionally activating NLRP3. Moreover, we found that RT triggered the release of self-dsDNA in the bronchoalveolar space, which is essential for the activation of cGAS-STING and the downstream NLRP3-mediated pyroptosis. Of note, Pulmozyme, an old drug for the management of cystic fibrosis, was revealed to have the potential to mitigate RILI by degrading extracellular dsDNA and then inhibiting the cGAS-STING-NLRP3 signaling pathway.

CONCLUSIONS

These results delineated the crucial function of cGAS-STING as a key mediator of RILI and described a mechanism of pyroptosis linking cGAS-STING activation with the amplification of initial RILI. These findings indicate that the dsDNA-cGAS-STING-NLRP3 axis might be potentially amenable to therapeutic targeting for RILI.

The anti-inflammatory and vasoprotective properties of mPGES-1 inhibition offer promising therapeutic potential

INTRODUCTION

Prostaglandin E2 (PGE2) is produced by cyclooxygenases (COX-1/2) and the microsomal prostaglandin E synthase 1 (mPGES-1). PGE2 is pro-inflammatory in diseases such as rheumatoid arthritis, cardiovascular disorders, and cancer. While Nonsteroidal anti-inflammatory drugs (NSAIDs) targeting COX can effectively reduce inflammation, their use is limited by gastrointestinal and cardiovascular side effects resulting from the blockade of all prostanoids. To overcome this limitation, selective inhibition of mPGES-1 is being explored as an alternative therapeutic strategy to inhibit PGE2 production while sparing or even upregulating other prostaglandins. However, the exact timing and location of PGH2 conversion to PGD2, PGI2, TXB2 or PGF2α, and whether it hinders or supports the therapeutic effect of mPGES-1 inhibition, is not fully understood.

AREAS COVERED

The article briefly describes prostanoid history and metabolism with a strong focus on the vascular effects of prostanoids. Recent advances in mPGES-1 inhibitor development and results from pre-clinical and clinical studies are presented. Prostanoid shunting after mPGES-1 inhibition is highlighted and particularly discussed in the context of cardiovascular diseases.

EXPERT OPINION

The newest research demonstrates that inhibition of mPGES-1 is a potent anti-inflammatory treatment strategy and beneficial and safer regarding cardiovascular side effects compared to NSAIDs. Inhibitors of mPGES-1 hold great potential to advance to the clinic and there are ongoing phase-II trials in endometriosis.

Analgesic effects of a highly selective mPGES-1 inhibitor

The growing opioid use and overdose crisis in the US is closely related to the abuse of pain medications. Particularly for postoperative pain (POP), ~ 310 million major surgeries are performed globally per year. Most patients undergoing surgical procedures experience acute POP, and ~ 75% of those with POP report the severity as moderate, severe, or extreme. Opioid analgesics are the mainstay for POP management. It is highly desirable to develop a truly effective and safe non-opioid analgesic to treat POP and other forms of pain. Notably, microsomal prostaglandin E2 (PGE₂) synthase-1 (mPGES-1) was once proposed as a potentially promising target for a next generation of anti-inflammatory drugs based on studies in mPGES-1 knockouts. However, to the best of our knowledge, no studies have ever been reported to explore whether mPGES-1 is also a potential target for POP treatment. In this study, we demonstrate for the first time that a highly selective mPGES-1 inhibitor can effectively relieve POP as well as other forms of pain through blocking the PGE₂ overproduction. All the data have consistently demonstrated that mPGES-1 is a truly promising target for treatment of POP as well as other forms of pain.

Nonacidic thiophene-based derivatives as potential analgesic and design, synthesis, biological evaluation, and metabolic stability study

Nonsteroidal anti-inflammatory drugs represent one of the most popularly used classes of drugs. However, their long-term administration is associated with various side effects including gastrointestinal ulceration. One of the major reasons of NSAIDs ulcerogenicity is direct damage of the epithelial lining cells by the acidic moieties present in many drugs. Another drawback for this acidic group is its rapid metabolism and clearance through Phase II conjugation. Three series of thiophene and thienopyrimidine derivatives were designed and synthesized as nonacidic anti-inflammatory agents. In vivo testing of their analgesic activity indicated that compounds 2b and 7a-d showed higher PI values than that of the positive control drugs, indomethacin and celecoxib. The latter compounds 2b and 7a-d were subjected to further anti-inflammatory activity testing where they showed comparable percentage edema inhibition to that of indomethacin and celecoxib. Compounds 2b, 7a, 7c, and 7d inhibited PGE2 synthesis by 61.10%-74.54% (71.47% for indomethacin, and 80.11% for celecoxib). The same compounds inhibited the expression of rat mPGES-1 and cPGES3 by 74%-83% (77% for indomethacin, and 82% for celecoxib) and 48%-70% (62% for indomethacin, and 70% for celecoxib), respectively. The stability of the most active compound 2b in Nonenzymatic gastrointestinal fluids and in human plasma was tested. Additionally, studying the metabolic stability of compound 2b in S9 rat liver fraction showed that it displayed a slow in vitro clearance with half-life time 1.5-fold longer than indomethacin. The metabolites of 2b were predicted via UPLC-MS/MS. In silico ADMET profiling study was also included.

Anti-inflammatory effects of N-Acetylcysteine and Elaeagnus angustifolia extract on acute lung injury induced by λ-carrageenan in rat

N-Acetylcysteine (NAC) is a chemical compound with anti-inflammatory and antioxidant activity and acts as a free radical scavenger. Elaeagnus angustifolia (EA) is a plant native to the western part of Iran, with antioxidant and anti-inflammatory properties. The present study been taken evaluated the protective effect afforded by EA and NAC extracts on carrageenan-induced acute lung injury in Wistar rats. In this study, 42 rats were randomly assigned into seven groups. NAC and EA extracts were orally administered once/day for 21 continuous days. Pulmonary damage was induced by intratracheal injection of 100 μl of 2% λ-Carrageenan on day 21. Twenty-four hours post-surgery, the rats were euthanized and the samples were collected. Pretreatment with NAC and EA extracts reduced the total and differential cell accumulation as well as IL-6, and TNF-α cytokines. Antioxidant indicators demonstrate that in the groups receiving NAC and EA extract, MDA decreased while thiol and antioxidant capacity elevated. Treatment with NAC and EA significantly reduced Carrageenan-induced pathological pulmonary tissue injury. NAC and EA extract has protective effects on acute carrageenan-induced lung injury.

Microsomal prostaglandin E2 synthase-1 and its inhibitors: Molecular mechanisms and therapeutic significance

Inflammation is closely linked to the abnormal phospholipid metabolism chain of cyclooxygenase-2/microsomal prostaglandin E₂ synthase-1/prostaglandin E₂ (COX-2/mPGES-1/PGE₂). In clinical practice, non-steroidal anti-inflammatory drugs (NSAIDs) as upstream COX-2 enzyme activity inhibitors are widely used to block COX-2 cascade to relieve inflammatory response. However, NSAIDs could also cause cardiovascular and gastrointestinal side effects due to its inhibition on other prostaglandins generation. To avoid this, targeting downstream mPGES-1 instead of upstream COX is preferable to selectively block overexpressed PGE₂ in inflammatory diseases. Some mPGES-1 inhibitor candidates including synthetic compounds, natural products and existing anti-inflammatory drugs have been proved to be effective in in vitro experiments. After 20 years of in-depth research on mPGES-1 and its inhibitors, ISC 27864 have completed phase II clinical trial. In this review, we intend to summarize mPGES-1 inhibitors focused on their inhibitory specificity with perspectives for future drug development.

Effects of microsomal prostaglandin E synthase-1 (mPGES-1) inhibition on resistance artery tone in patients with end stage kidney disease

BACKGROUND

Inhibition of the microsomal prostaglandin (PG) E₂ synthase (mPGES-1) introduces a promising anti-inflammatory treatment approach by specifically reducing PGE₂ . The microvasculature is a central target organ for early manifestations of cardiovascular disease. Therefore, a better understanding of the prostaglandin system and characterising the effects of mPGES-1 inhibition in this vascular bed are of interest.

EXPERIMENTAL APPROACH

The effects of mPGES-1 inhibition on constriction and relaxation of resistance arteries (Ø100-400μm) from patients with end stage kidney disease (ESKD) and controls (Non-ESKD) were studied using wire-myography in combination with immunological and mass-spectrometry based analyses.

KEY RESULTS

Inhibition of mPGES-1 in arteries from ESKD patients and Non-ESKD controls significantly reduced adrenergic vasoconstriction, which was not affected by the COX-2 inhibitors NS-398 and Etoricoxib or the COX-1/COX-2 inhibitor Indomethacin, tested in Non-ESKD controls. Correspondingly, a significant increase of acetylcholine-induced dilatation was observed for mPGES-1 inhibition only. In IL-1β treated arteries, inhibition of mPGES-1 significantly reduced PGE₂ levels while PGI₂ levels remained unchanged. In contrast, COX-2 inhibition blocked the formation of both prostaglandins. Blockage of PGI₂ signaling with an IP receptor antagonist did not restore the reduced constriction, neither did blocking of PGE₂ -EP4 or signaling through PPARγ. A biphasic effect was observed for PGE₂ , inducing dilatation at nmol and constriction at μmol concentrations. Immunohistochemistry demonstrated expression of mPGES-1, COX-1, PGIS, weak expression for COX-2 as well as receptor expression for PGE₂ (EP1-4), thromboxane (TP) and PGI₂ (IP) in ESKD and Non-ESKD.

CONCLUSION

Our study demonstrates vasodilating effects following mPGES-1 inhibition in human microvasculature and suggests that several pathways besides shunting to PGI₂ may be involved.