Survival of Mice with Gastrointestinal Acute Radiation Syndrome through Control of Bacterial Translocation

Radiation-induced eCIRP impairs macrophage bacterial phagocytosis

Macrophages are essential immune cells for host defense against bacterial pathogens after radiation injury. However, the role of macrophage phagocytosis in infection following radiation injury remains poorly examined. Extracellular cold-inducible RNA-binding protein (eCIRP) is a damage-associated molecular pattern that dysregulates host immune system responses such as phagocytosis. We hypothesized that radiation-induced eCIRP release impairs macrophage phagocytosis of bacteria. Adult healthy mice were exposed to 6.5-Gy total body irradiation (TBI). Primary peritoneal macrophages isolated from adult healthy mice were exposed to 6.5-Gy radiation. eCIRP-neutralizing monoclonal antibody (mAb) was added to the cell culture prior to irradiation. Bacterial phagocytosis by peritoneal macrophages was assessed using pHrodo Green-labeled E. coli 7 days after irradiation ex vivo and in vitro. Bacterial phagocytosis was also assessed after treatment with recombinant murine CIRP (rmCIRP). Rac1 and ARP2 protein expression in cell lysates and eCIRP levels in the peritoneal lavage were assessed by Western blotting. Bacterial phagocytosis by peritoneal macrophages was significantly decreased after irradiation compared to controls ex vivo and in vitro. Rac1 and ARP2 expression in the peritoneal macrophages were downregulated after TBI. TBI significantly increased eCIRP levels in the peritoneal cavity. rmCIRP significantly decreased bacterial phagocytosis in a dose-dependent manner. eCIRP mAb restored bacterial phagocytosis by peritoneal macrophages after irradiation. Ionizing radiation exposure impairs bacterial phagocytosis by macrophages after irradiation. Neutralization of eCIRP restores the phagocytic ability of macrophages after irradiation. Our findings elucidate a novel mechanism of immune dysfunction and provide a potential new therapeutic approach for limiting infection after radiation injury.

Recent advances in potential targets for myocardial ischemia reperfusion injury: Role of macrophages

Myocardial ischemia-reperfusion injury (MIRI) is a complex process that occurs when blood flow is restored after myocardium infarction (MI) with exacerbated tissue damage. Macrophages, essential cell type of the immune response, play an important role in MIRI. Macrophage subpopulations, namely M1 and M2, are distinguished by distinct phenotypes and functions. In MIRI, macrophages infiltrate in infarcted area, shaping the inflammatory response and influencing tissue healing. Resident cardiac macrophages interact with monocyte-derived macrophages in MIRI, and influence injury progression. Key factors including chemokines, cytokines, and toll-like receptors modulate macrophage behavior in MIRI. This review aims to address recent findings on the classification and the roles of macrophages in the myocardium, spanning from MI to subsequent MIRI, and highlights various signaling pathways implicated in macrophage polarization underlining the complexity of MIRI. This article will shed light on developing advanced therapeutic strategies for MIRI management.

Characterization of Early and Late Damage in a Mouse Model of Pelvic Radiation Disease

Pelvic radiation disease (PRD), a frequent side effect in patients with abdominal/pelvic cancers treated with radiotherapy, remains an unmet medical need. Currently available preclinical models have limited applications for the investigation of PRD pathogenesis and possible therapeutic strategies. In order to select the most effective irradiation protocol for PRD induction in mice, we evaluated the efficacy of three different locally and fractionated X-ray exposures. Using the selected protocol (10 Gy/day × 4 days), we assessed PRD through tissue (number and length of colon crypts) and molecular (expression of genes involved in oxidative stress, cell damage, inflammation, and stem cell markers) analyses at short (3 h or 3 days after X-ray) and long (38 days after X-rays) post-irradiation times. The results show that a primary damage response in term of apoptosis, inflammation, and surrogate markers of oxidative stress was found, thus determining a consequent impairment of cell crypts differentiation and proliferation as well as a local inflammation and a bacterial translocation to mesenteric lymph nodes after several weeks post-irradiation. Changes were also found in microbiota composition, particularly in the relative abundance of dominant phyla, related families, and in alpha diversity indices, as an indication of dysbiotic conditions induced by irradiation. Fecal markers of intestinal inflammation, measured during the experimental timeline, identified lactoferrin, along with elastase, as useful non-invasive tools to monitor disease progression. Thus, our preclinical model may be useful to develop new therapeutic strategies for PRD treatment.

Potential applications of drug delivery technologies against radiation enteritis

INTRODUCTION

The incidence of abdominal tumors, such as colorectal and prostate cancers, continually increases. Radiation therapy is widely applied in the clinical treatment of patients with abdominal/pelvic cancers, but it often unfortunately causes radiation enteritis (RE) involving the intestine, colon, and rectum. However, there is a lack of suitable treatment options for effective prevention and treatment of RE.

AREAS COVERED

Conventional clinical drugs for preventing and treating RE are usually applied by enemas and oral administration. Innovative gut-targeted drug delivery systems including hydrogels, microspheres, and nanoparticles are proposed to improve the prevention and curation of RE.

EXPERT OPINION

The prevention and treatment of RE have not attracted sufficient attention in the clinical practice, especially compared to the treatment of tumors, although RE takes patients great pains. Drug delivery to the pathological sites of RE is a huge challenge. The short retention and weak targeting of conventional drug delivery systems affect the therapeutic efficiency of anti-RE drugs. Novel drug delivery systems including hydrogels, microspheres, and nanoparticles can allow drugs long-term retention in the gut and targeting the inflammation sites to alleviate radiation-induced injury.

Host antibacterial defense of 6-10 Gy γ-irradiated mice subjected to lentiviral vector-based Gas5 gene therapy

Gut bacteria-associated sepsis is a serious concern in patients with gastrointestinal acute radiation syndrome (GIARS). In our previous studies, all mice exposed to 8 Gy of whole body γ-irradiation (8 Gy GIARS-mice) died by sepsis stemming from bacterial translocation. M1Mϕ located in the bacterial translocation site (i.e., the mesenteric lymph nodes, MLNs) have been characterized as major antibacterial effector cells. However, M2bMϕ, inhibitor cells for M1Mϕ polarization, predominated in the MLNs of these mice. The reduced expression of long noncoding RNA Gas5 was associated with M2bMϕ polarization. In this study, we tried to reduce the mortality rate of 8 Gy GIARS-mice through Gas5 gene transduction using lentivirus (Gas5 lentivirus). After Gas5 lentivirus injection, Gas5 RNA was overexpressed in MLN-F4/80⁺ cells of 8 Gy GIARS-mice, and these cells were identified as non-M2bMϕ. All of the 8 Gy GIARS-mice injected with Gas5 lentivirus survived 30 days or more after irradiation, and bacterial translocation and subsequent sepsis were shown to be minimal in these mice. These results indicate that the antibacterial resistance of 8 Gy GIASR-mice can be restored through the modulation of M2bMϕ located in the bacterial translocation site by Gas5 transduction.

Dose- and Segment-Dependent Disturbance of Rat Gut by Ionizing Radiation: Impact of Tight Junction Proteins

The damaging effect of ionizing radiation (IR) exposure results in the disturbance of the gut natural barrier, followed by the development of severe gastrointestinal injury. However, the dose and application segment are known to determine the effects of IR. In this study, we demonstrated the dose- and segment-specificity of tight junction (TJ) alteration in IR-induced gastrointestinal injury in rats. Male Wistar rats were subjected to a total-body X-ray irradiation at doses of 2 or 10 Gy. Isolated jejunum and colon segments were tested in an Ussing chamber 72 h after exposure. In the jejunum, 10-Gy IR dramatically altered transepithelial resistance, short-circuit current and permeability for sodium fluorescein. These changes were accompanied by severe disturbance of histological structure and total rearrangement of TJ content (increased content of claudin-1, -2, -3 and -4; multidirectional changes in tricellulin and occludin). In the colon of 10-Gy irradiated rats, lesions of barrier and transport functions were less pronounced, with only claudin-2 and -4 altered among TJ proteins. The 2-Gy IR did not change electrophysiological characteristics or permeability in the colon or jejunum, although slight alterations in jejunum histology were noted, emphasized with claudin-3 increase. Considering that TJ proteins are critical for maintaining epithelial barrier integrity, these findings may have implications for countermeasures in gastrointestinal acute radiation injury.

CD34+CD10+CD19− Cells in Patients with Unhealthy Alcohol Use Stimulate the M2b Monocyte Polarization

M2b monocytes commonly isolated from patients with unhealthy alcohol use (Alc) have been described as cells that make the host susceptible to opportunistic infections. CD34⁺CD10⁺CD19⁻ cells are multilineage progenitors of CD19⁺ cells, and we show that the effect of these cells from the peripheral blood on M2b monocyte polarization differed between healthy donors and Alc in this study. In healthy donors, these cells consistently differentiated into high-mobility group box-1 (HMGB1)-nonproducing cells (CD19⁺ cells) in response to retinoic acid (RA). However, owing to the lack of expression of RA receptor (RAR), these cells from Alc failed to differentiate into CD19⁺ cells under the same RA stimulation. Conditioned medium (CM) of these cells from Alc induced the polarization of M2b monocytes, which increases the susceptibility of hosts to opportunistic infections in Alc. When the alcoholic individuals were subjected to 2 weeks of abstinence from alcohol, these cells from Alc recovered their RAR expression and differentiated into CD19⁺ cells. Moreover, the CM of these cells from Alc after abstinence lost its ability to induce M2b monocyte polarization. These results indicate that these cells from Alc have different properties from those of healthy donors. In Alc, these cells without RAR stimulate M2b monocyte polarization through the production of HMGB1.

Gut barrier disruption and chronic disease

The intestinal barrier protects the host against gut microbes, food antigens, and toxins present in the gastrointestinal tract. However, gut barrier integrity can be affected by intrinsic and extrinsic factors, including genetic predisposition, the Western diet, antibiotics, alcohol, circadian rhythm disruption, psychological stress, and aging. Chronic disruption of the gut barrier can lead to translocation of microbial components into the body, producing systemic, low-grade inflammation. While the association between gut barrier integrity and inflammation in intestinal diseases is well established, we review here recent studies indicating that the gut barrier and microbiota dysbiosis may contribute to the development of metabolic, autoimmune, and aging-related disorders. Emerging interventions to improve gut barrier integrity and microbiota composition are also described.

Radiotherapy-Induced Digestive Injury: Diagnosis, Treatment and Mechanisms

Radiotherapy is one of the main therapeutic methods for treating cancer. The digestive system consists of the gastrointestinal tract and the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder). The digestive system is easily impaired during radiotherapy, especially in thoracic and abdominal radiotherapy. In this review, we introduce the physical classification, basic pathogenesis, clinical characteristics, predictive/diagnostic factors, and possible treatment targets of radiotherapy-induced digestive injury. Radiotherapy-induced digestive injury complies with the dose-volume effect and has a radiation-based organ correlation. Computed tomography (CT), MRI (magnetic resonance imaging), ultrasound (US) and endoscopy can help diagnose and evaluate the radiation-induced lesion level. The latest treatment approaches include improvement in radiotherapy (such as shielding, hydrogel spacers and dose distribution), stem cell transplantation and drug administration. Gut microbiota modulation may become a novel approach to relieving radiogenic gastrointestinal syndrome. Finally, we summarized the possible mechanisms involved in treatment, but they remain varied. Radionuclide-labeled targeting molecules (RLTMs) are promising for more precise radiotherapy. These advances contribute to our understanding of the assessment and treatment of radiation-induced digestive injury.

Intestinal mucositis precedes dysbiosis in a mouse model for pelvic irradiation

Pelvic radiotherapy is known to evoke intestinal mucositis and dysbiosis. Currently, there are no effective therapies available to mitigate these injuries, which is partly due to a lack of insight into the events causing mucositis and dysbiosis. Here, the complex interplay between the murine host and its microbiome following pelvic irradiation was mapped by characterizing intestinal mucositis along with extensive 16S microbial profiling. We demonstrated important morphological and inflammatory implications within one day after exposure, thereby impairing intestinal functionality and inducing translocation of intraluminal bacteria into mesenteric lymph nodes as innovatively quantified by flow cytometry. Concurrent 16S microbial profiling revealed a delayed impact of pelvic irradiation on beta diversity. Analysis of composition of microbiomes identified biomarkers for pelvic irradiation. Among them, members of the families Ruminococcaceae, Lachnospiraceae and Porphyromonadaceae were differentially affected. Altogether, our unprecedented findings showed how pelvic irradiation evoked structural and functional changes in the intestine, which secondarily resulted in a microbiome shift. Therefore, the presented in vivo irradiation-gut-microbiome platform allows further research into the pathobiology of pelvic irradiation-induced intestinal mucositis and resultant dysbiosis, as well as the exploration of mitigating treatments including drugs and food supplements.

Hepatic F4/80+ CD11b+ CD68- cells influence the antibacterial response in irradiated mice with sepsis by Enterococcus faecalis

Gut-associated sepsis is a major problem in patients undergoing abdominal radiation therapy; the majority of pathogens causing this type of sepsis are translocated from the gut microbiota. While treating sepsis, bacterial clearance must be achieved to ensure patient survival, and the hepatic immune response is responsible for this process. In particular, Kupffer cells play a crucial role in the hepatic immune response against infectious agents. Recently, two populations of Kupffer cells have been described: liver-resident macrophages (Mϕ) (F4/80+ CD11b- CD68+ cells) and hepatic Mϕ derived from circulating monocytes (F4/80+ CD11b+ CD68- cells). We examined the properties of both types of hepatic Mϕ obtained from irradiated and normal mice and their role in sepsis. Hepatic F4/80+ CD11b- CD68+ cells from both normal and irradiated mice did not show any antibacterial activity. However, F4/80+ CD11b+ CD68- cells from normal mice behaved as effector cells against sepsis by Enterococcus faecalis, although those from irradiated mice lost this ability. Moreover, hepatic F4/80+ CD11b+ CD68- cells from normal infected mice were shown to be IL-12+ IL-10- CD206- CCL1- (considered M1Mϕ), and hepatic F4/80+ CD11b- CD68+ cells from the same mice were shown to be IL-12- IL-10+ CD206+ CCL1- (considered M2aMϕ). When normal mice were exposed to radiation, hepatic F4/80+ CD11b+ CD68- cells altered their phenotype to IL-12- IL-10+ CD206- CCL1+ (considered M2bMϕ), independent of infection, but hepatic F4/80+ CD11b- CD68+ cells remained IL-12- IL-10+ CD206+ CCL1- (M2aMϕ). In addition, hepatic F4/80+ CD11b+ CD68- cells from irradiated mice acquired antibacterial activity upon treatment with CCL1 antisense oligodeoxynucleotides. Therefore, the characteristics of hepatic F4/80+ CD11b+ CD68- cells play a key role in the antibacterial response against gut-associated sepsis.

Glycyrrhizin Protects γ-Irradiated Mice from Gut Bacteria-Associated Infectious Complications by Improving miR-222-Associated Gas5 RNA Reduction in Macrophages of the Bacterial Translocation Site

Gut bacteria-associated sepsis is a serious concern in patients with gastrointestinal acute radiation syndrome (GIARS). In our previous studies, gut bacteria-associated sepsis caused high mortality rates in mice exposed to 6-9 Gy of γ-rays. IL-12⁺CD38⁺ iNOS⁺ Mϕ (M1Mϕ) located in the bacterial translocation site (mesenteric lymph nodes [MLNs]) of unirradiated mice were characterized as host defense antibacterial effector cells. However, cells isolated from the MLNs of GIARS mice were mostly CCL1⁺IL-10⁺LIGHT⁺miR-27a⁺ Mϕ (M2bMϕ, inhibitor cells for the M1Mϕ polarization). Reduced long noncoding RNA Gas5 and increased miR-222 expression in MLN-Mϕ influenced by the irradiation were shown to be associated with M2bMϕ polarization. In this study, the mortality of mice exposed to 7 Gy of γ-rays (7 Gy GIARS mice) was completely controlled after the administration of glycyrrhizin (GL), a major active ingredient in licorice root (Glycyrrhiza glabra). Bacterial translocation and subsequent sepsis were minimal in 7 Gy GIARS mice treated with GL. Increased Gas5 RNA level and decreased miR-222 expression were shown in MLN-Mϕ isolated from 7 Gy GIARS mice treated with GL, and these macrophages did not display any properties of M2bMϕ. These results indicate that gut bacteria-associated sepsis in 7 Gy GIARS mice was controlled by the GL through the inhibition of M2bMϕ polarization at the bacteria translocation site. Expression of Ccl1, a gene required for M2bMϕ survival, is silenced in the MLNs of 7 Gy GIARS mice because of Gas5 RNA, which is increased in these cells after the suppression of miR-222 (a Gas5 RNA expression inhibitor) by the GL.

Prediction and Treatment of Radiation Enteropathy: Can Intestinal Bugs Lead the Way?

Radiation-induced gastrointestinal toxicity is a significant comorbidity affecting many patients with cancer. Intestinal microbial changes are observed in patients suffering from radiation enteropathy, although a causal relationship with disease activity has yet to be proven. Implementation of bacterial profiling in clinical care could improve recognition and management of this debilitating disease.See related article by Reis Ferreira et al., p. 6487.

Macrophages with regulatory functions, a possible new therapeutic perspective in autoimmune diseases

Macrophages are pivotal cells involved in chronic inflammatory and autoimmune diseases. In fact, during these diseases, activated macrophages may play a critical role, promoting the inflammation as well as mediating the damage resolution. This dichotomy is referred to two end-stage phenotypes of macrophages, conventionally known as M1 and M2, playing a pro-inflammatory and anti-inflammatory role, respectively. The M1 macrophages are the mainly subset involved during inflammatory processes, producing pro-inflammatory mediators. Conversely, the M2 macrophages are proposed to contribute to the resolution phase of inflammation, when cells with pro-resolving property are recruited and activated. In fact, this subset of macrophages may activate regulatory T lymphocytes, which play a critical role in the maintenance of peripheral tolerance and preventing the occurrence of autoimmune diseases. On these bases, the polarization toward the M2 phenotype could play a therapeutic role for autoimmune diseases. In this Review we discussed the characteristic of M1 and M2 macrophages, focusing on the immunoregulatory role of M2 cells and their potential ability to control the inflammation and to promote the immunological tolerance.

Food-borne patulin toxicity is related to gut barrier disruption and can be prevented by docosahexaenoic acid and probiotic supplementation

Patulin (PAT) is a mycotoxin widely found in fruits and vegetables. Several reviews and studies have hypothesized that in vivo PAT toxicity is related to gut barrier dysfunction, but evidence for this is not substantial. The goal of the present study was to further demonstrate the role of the gut barrier in food-borne PAT toxicity. In vitro assays showed that PAT exposure induced significant cell death, inhibited the mRNA expressions of tight junction proteins and increased gut permeability in Caco-2 cell monolayers. An acute PAT exposure animal trial reported for the first time an association between PAT-induced disruption of the gut barrier and endotoxemia in mice. Sub-chronic PAT exposure also inhibited the expression of ZO-1 in the gut and induced both intestinal and systematic inflammation in mice. Dietary supplements with previously reported protective effects on the gut barrier, such as docosahexaenoic acid and Lactobacillus plantarum CCFM8610, were able to recover the PAT-induced gut barrier dysfunction and significantly alleviate PAT toxicity in vivo. Another L. plantarum strain, CCFM11, with poor gut barrier modulation ability, failed to exhibit identical protective effects against PAT toxicity to L. plantarum CCFM8610. Our results indicated that PAT-induced disruption of the gut barrier and bacterial translocation may be another toxic mechanism of PAT besides its inherent cytotoxicity. Gut barrier protection may be considered an important target for the prevention of PAT toxicity.

M2b macrophage polarization and its roles in diseases

Macrophages play an important role in a wide variety of physiologic and pathologic processes. Plasticity and functional polarization are hallmarks of macrophages. Macrophages commonly exist in two distinct subsets: classically activated macrophages (M1) and alternatively activated macrophages (M2). M2b, a subtype of M2 macrophages, has attracted increasing attention over the past decade due to its strong immune‐regulated and anti‐inflammatory effects. A wide variety of stimuli and multiple factors modulate M2b macrophage polarization in vitro and in vivo. M2b macrophages possess both protective and pathogenic roles in various diseases. Understanding the mechanisms of M2b macrophage activation and the modulation of their polarization might provide a great perspective for the design of novel therapeutic strategies. The purpose of this review is to discuss current knowledge of M2b macrophage polarization, the roles of M2b macrophages in a variety of diseases and the stimuli to modulate M2b macrophage polarization.