Iron Prevents Hypoxia-Associated Inflammation Through the Regulation of Nuclear Factor-κB in the Intestinal Epithelium

Research Progress on the Mechanism of Intestinal Barrier Damage and Drug Therapy in a High Altitude Environment

The plateau is a typical extreme environment with low temperature, low oxygen and high ultraviolet rays. The integrity of the intestinal barrier is the basis for the functioning of the intestine, which plays an important role in absorbing nutrients, maintaining the balance of intestinal flora, and blocking the invasion of toxins. Currently, there is increasing evidence that high altitude environment can enhance intestinal permeability and disrupt intestinal barrier integrity. This article mainly focuses on the regulation of the expression of HIF and tight junction proteins in the high altitude environment, which promotes the release of pro-inflammatory factors, especially the imbalance of intestinal flora caused by the high altitude environment. The mechanism of intestinal barrier damage and the drugs to protect the intestinal barrier are reviewed. Studying the mechanism of intestinal barrier damage in high altitude environment is not only conducive to understanding the mechanism of high altitude environment affecting intestinal barrier function, but also provides a more scientific medicine treatment method for intestinal damage caused by the special high altitude environment.

Chlamydia trachomatis L2/434/Bu Favors Hypoxia for its Growth in Human Lymphoid Jurkat Cells While Maintaining Production of Proinflammatory Cytokines

The role of lymphocytes as a cornerstone of the inflammatory response in the invasive pathogenesis of Chlamydia trachomatis (Ct) LGV (L1-3) infection is unclear. Therefore, we assessed whether the adaptation of CtL2 to immortal lymphoid Jurkat cells under hypoxic conditions occurred through proinflammatory cytokine profile modification. The quantities of inclusion-forming units with chlamydial 16S rDNA confirmed that CtL2 grew well under hypoxic rather than normoxic conditions in the cells. Confocal microscopic imaging and transmission electron microscopy revealed the presence of bacterial progeny in the inclusions and showed that the inclusions were larger under hypoxic rather than normoxic conditions; this was supported by the results of 3D image construction. Furthermore, PCR-based analysis of proinflammatory cytokines revealed that the gene expression levels under hypoxic conditions were significantly higher than those under normoxic conditions. In particular, the expression of two genes (CXCL8 and CXCR3) was significantly diminished under normoxic conditions. Taken together, the results indicated that hypoxia promoted CtL2 growth in Jurkat cells while maintaining the levels of proinflammatory cytokines. Thus, Ct LGV infection in lymphocytes under hypoxic conditions might be crucial to a complete understanding of the invasive pathogenesis.

The ROS/GRK2/HIF-1α/NLRP3 Pathway Mediates Pyroptosis of Fibroblast-Like Synoviocytes and the Regulation of Monomer Derivatives of Paeoniflorin

Hypoxia is an important factor in the development of synovitis in rheumatoid arthritis (RA). The previous study of the research group found that monomeric derivatives of paeoniflorin (MDP) can alleviate joint inflammation in adjuvant-induced arthritis (AA) rats by inhibiting macrophage pyroptosis. This study revealed increased levels of hypoxia-inducible factor- (HIF-) 1α and N-terminal p30 fragment of GSDMD (GSDMD-N) in fibroblast-like synoviocytes (FLS) of RA patients and AA rats, while MDP significantly inhibited their expression. Subsequently, FLS were exposed to a hypoxic environment or treated with cobalt ion in vitro. Western blot and immunofluorescence analysis showed increased expression of G protein-coupled receptor kinase 2 (GRK2), HIF-1α, nucleotide-binding oligomerization segment-like receptor family 3 (NLRP3), ASC, caspase-1, cleaved-caspase-1, and GSDMD-N. Electron microscopy revealed FLS pyroptosis after exposure in hypoxia. Next, corresponding shRNAs were transferred into FLS to knock down hypoxia-inducible factor- (HIF-) 1α, and in turn, NLRP3 and western blot results confirmed the same. The enhanced level of GSDMD was reversed under hypoxia by inhibiting NLRP3 expression. Knockdown and overexpression of GRK2 in FLS revealed GRK2 to be a positive regulator of HIF-1α. Levels of GRK2 and HIF-1α were inhibited by eliminating excess reactive oxygen species (ROS). Furthermore, MDP reduced FLS pyroptosis through targeted inhibition of GRK2 phosphorylation. According to these findings, hypoxia induces FLS pyroptosis through the ROS/GRK2/HIF-1α/NLRP3 pathway, while MDP regulates this pathway to reduce FLS pyroptosis.

HIF-1 mediated activation of antimicrobial peptide LL-37 in type 2 diabetic patients

Abstract

Infections are common in patients with diabetes, but increasing antibiotic resistance hampers successful bacterial clearance and calls for alternative treatment strategies. Hypoxia-inducible factor 1 (HIF-1) is known to influence the innate immune defense and could therefore serve as a possible target. However, the impact of high glucose on HIF-1 has received little attention and merits closer investigation. Here, we show that higher levels of proinflammatory cytokines and CAMP, encoding for the antimicrobial peptide cathelicidin, LL-37, correlate with HIF-1 in type 2 diabetic patients. Chemical activation of HIF-1 further enhanced LL-37, IL-1β, and IL-8 in human uroepithelial cells exposed to high glucose. Moreover, HIF-1 activation of transurethrally infected diabetic mice resulted in lower bacterial load. Drugs activating HIF-1 could therefore in the future potentially have a therapeutic role in clearing bacteria in diabetic patients with infections where antibiotic treatment failed.

Key messages

• Mohanty et al. “HIF-1 mediated activation of antimicrobial peptide LL-37 in type 2 diabetic patients.”

• Our study highlights induction of the antimicrobial peptide, LL-37, and strengthening of the innate immunity through hypoxia-inducible factor 1 (HIF-1) in diabetes.

• Our key observations are:

1. HIF-1 activation increased LL-37 expression in human urothelial cells treated with high glucose. In line with that, we demonstrated that patients with type 2 diabetes living at high altitude had increased levels of the LL-37.

2. HIF-1 activation increased IL-1β and IL-8 in human uroepithelial cells treated with high glucose concentration.

3. Pharmacological activation of HIF-1 decreased bacterial load in the urinary bladder of mice with hereditary diabetes.

• We conclude that enhancing HIF-1 may along with antibiotics in the future contribute to the treatment in selected patient groups where traditional therapy is not possible.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-021-02134-7.

Neutrophil-to-Lymphocyte Ratio and Erythropoietin Resistance among Maintenance Hemodialysis Patients

INTRODUCTION

Neutrophil lymphocyte ratio (NLR) and platelet lymphocyte ratio (PLR) are recent prognostic biomarkers associated with inflammation. Increased erythropoiesis resistance index (ERI) may predict the risk of all-cause and cardiovascular mortality in hemodialysis (HD) patients. However, the roles of NLR and PLR in erythropoietin (EPO) responsiveness remain unclear in HD patients. This study aims to investigate the relationship between NLR and PLR and EPO responsiveness in maintenance HD patients.

METHODS

A total of 299 HD patients were included in this survey. Laboratory data and demographic details were collected. EPO responsiveness was evaluated by ERI. Pearson correlation analysis and logistic regressions were conducted to evaluate the factors that may be associated with EPO responsiveness.

RESULTS

The EPO responsiveness was positively related to ferritin and negatively related to serum albumin, lymphocytes, and hemoglobin. A multivariate linear regression revealed that only NLR (standardized β = 0.13, p = 0.024) but not PLR (standardized β = 0.107, p = 0.063) was correlated with a higher ERI.

CONCLUSION

A higher NLR level was shown to be a cheaper method to predict worse EPO responsiveness in HD patients.

Hypoxia Reduces the Transcription of Fibrotic Markers in the Intestinal Mucosa

Introduction

Intestinal fibrosis, characterized by excessive deposition of extracellular matrix proteins, is a common and severe clinical complication of inflammatory bowel disease (IBD). However, the mechanisms underlying fibrosis remain elusive, and currently, there are limited effective pharmacologic treatments that target the development of fibrosis. Hypoxia is one of the key microenvironmental factors influencing intestinal inflammation and has been linked to fibrosis.

Objective

In the present study, we sought to elucidate the impact of hypoxia on fibrotic gene expression in the intestinal mucosa.

Methods

Human volunteers, IBD patients, and dextran sulphate sodium-treated mice were exposed to hypoxia, and colonic biopsies were collected. The human intestinal epithelial cell line Caco-2, human THP-1 macrophages, and primary human gut fibroblasts were subjected to hypoxia, and changes in fibrotic gene expression were assessed.

Results

Human volunteers subjected to hypoxia presented reduced transcriptional levels of fibrotic and epithelial-mesenchymal transition markers in the intestinal mucosa. IBD patients showed a trend towards a decrease in tissue inhibitor of metalloproteinase 1 protein expression. In mice, hypoxic conditions reduced the colonic expression of several collagens and matrix metalloproteinases. Hypoxic Caco-2 cells, THP-1 cells, and primary gut fibroblasts showed a significant downregulation in the expression of fibrotic and tissue remodelling factors.

Conclusions

Stabilization of hypoxia-inducible factors might represent a novel therapeutic approach for the treatment of IBD-associated fibrosis.

Influence of iron manipulation on hypoxic pulmonary vasoconstriction and pulmonary reactivity during ascent and acclimatization to 5050 m

KEY POINTS

Iron acts as a cofactor in the stabilization of the hypoxic-inducible factor family, and plays an influential role in the modulation of hypoxic pulmonary vasoconstriction. It is uncertain whether iron regulation is altered in lowlanders during either (1) ascent to high altitude, or (2) following partial acclimatization, when compared to high-altitude adapted Sherpa. During ascent to 5050 m, the rise in pulmonary artery systolic pressure (PASP) was blunted in Sherpa, compared to lowlanders; however, upon arrival to 5050 m, PASP levels were comparable in both groups, but the reduction in iron bioavailability was more prevalent in lowlanders compared to Sherpa. Following partial acclimatization to 5050 m, there were differential influences of iron status manipulation (via iron infusion or chelation) at rest and during exercise between lowlanders and Sherpa on the pulmonary vasculature.

ABSTRACT

To examine the adaptational role of iron bioavailability on the pulmonary vascular responses to acute and chronic hypobaric hypoxia, the haematological and cardiopulmonary profile of lowlanders and Sherpa were determined during: (1) a 9-day ascent to 5050 m (20 lowlanders; 12 Sherpa), and (2) following partial acclimatization (11 ± 4 days) to 5050 m (18 lowlanders; 20 Sherpa), where both groups received an i.v. infusion of either iron (iron (iii)-hydroxide sucrose) or an iron chelator (desferrioxamine). During ascent, there were reductions in iron status in both lowlanders and Sherpa; however, Sherpa appeared to demonstrate a more efficient capacity to mobilize stored iron, compared to lowlanders, when expressed as a Δhepcidin per unit change in either body iron or the soluble transferrin receptor index, between 3400-5050 m (P = 0.016 and P = 0.029, respectively). The rise in pulmonary artery systolic pressure (PASP) was blunted in Sherpa, compared to lowlanders during ascent; however, PASP was comparable in both groups upon arrival to 5050 m. Following partial acclimatization, despite Sherpa demonstrating a blunted hypoxic ventilatory response and greater resting hypoxaemia, they had similar hypoxic pulmonary vasoconstriction when compared to lowlanders at rest. Iron-infusion attenuated PASP in both groups at rest (P = 0.005), while chelation did not exaggerate PASP in either group at rest or during exaggerated hypoxaemia ( P I O 2  = 67 mmHg). During exercise at 25% peak wattage, PASP was only consistently elevated in Sherpa, which persisted following both iron infusion or chelation. These findings provide new evidence on the complex interplay of iron regulation on pulmonary vascular regulation during acclimatization and adaptation to high altitude.

High Erythropoiesis Resistance Index Is a Significant Predictor of Cardiovascular and All-Cause Mortality in Chinese Maintenance Hemodialysis Patients

Background

Renal anemia is a common complication of hemodialysis patients. Erythropoietin (EPO) hyporesponsiveness has been recognized as an important factor to poor efficacy of recombinant human erythropoietin in the treatment of renal anemia. More importantly, increased erythropoiesis resistance index (ERI) may be associated with inflammation and increased mortality.

Objective

The objective of this research was to investigate correlated factors of EPO responsiveness and to clarify the relationships between EPO hyporesponsiveness and cardiovascular mortality and all-cause mortality among maintenance hemodialysis patients.

Methods

This prospective cohort study enrolled 276 maintenance hemodialysis patients for a 55-month follow-up to investigate the factors related to ERI and its relationship to all-cause mortality and cardiovascular mortality.

Results

ERI was positively correlated with predialysis serum high-sensitivity C-reactive protein (r = 0.234, p < 0.001), alkaline phosphatase (r = 0.134, p = 0.028), and ferritin (r = 0.155, p = 0.010) and negatively correlated with albumin (r = −0.206, p < 0.001) and creatinine (r = −0.232, p < 0.001). As multiple linear regression showed, predialysis serum albumin, high-sensitivity C-reactive protein, ferritin, and creatinine were independent correlated factors of ERI (p < 0.05). Kaplan–Meier curves showed that the cumulative incidences of both cardiovascular mortality and all-cause mortality were significantly higher in patients with ERI > 11.04 IU/kg/w/g/dL (both p < 0.01). The high ERI group was significantly associated with higher risk for all-cause mortality (OR 1.781, 95% CI 1.091 to 2.910, p = 0.021) and cardiovascular mortality (OR 1.972, 95% CI 1.139 to 3.417, p = 0.015) after adjusting for confounders.

Conclusions

Predialysis serum albumin, high-sensitivity C-reactive protein, ferritin, and creatinine were independent correlated factors of EPO responsiveness among maintenance hemodialysis patients. Patients with higher ERI values had a higher all-cause mortality rate and cardiovascular mortality rate.

Enterotoxigenic Escherichia coli Heat-Stable Toxin Increases the Rate of Zinc Release from Metallothionein and Is a Zinc- and Iron-Binding Peptide

Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in children in low- to middle-income countries. Previous studies have identified heat-stable enterotoxin (ST)-producing ETEC as one of the major diarrhea-causing pathogens in children younger than five years. In this study, we examined iron and zinc binding by both human and porcine ST variants and determined how host metallothionein could detoxify ST. We found that ST purified from ETEC culture supernatants eluted as a doublet during C18 reverse-phase chromatography. Leading edge fractions of the ST doublet were found to be devoid of iron, while trailing edge fractions of the ST doublet were found to contain measurable iron. Next, we found that purified ST could be reconstituted with iron under reducing and anaerobic conditions, and iron-bound ST attenuated the induction of cGMP in T84 epithelial cells. Moreover, we demonstrated that supernatants of ETEC 214-4 grown under increasing iron concentrations were only able to induce cGMP at iron concentrations greater than 5 μM. In vitro studies also demonstrated that ST binds zinc, and once bound, zinc removal from ST required denaturing conditions. Zinc-bound ST also failed to induce cGMP. We found that ST contributes disulfide bonds to the perceived oxidized glutathione pool, increases the rate of zinc release from metallothionein, and can be detoxified by metallothionein. Lastly, we showed ST induces transcriptional changes in genes previously shown to be regulated by deferoxamine. These studies demonstrate ST ETEC pathogenesis may be tied intimately to host mucosal metal status.IMPORTANCE Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in children in low- to middle-income countries, deployed military personnel, and travelers to regions of endemicity. The heat-stable toxin (ST) is a small nonimmunogenic secreted peptide with 3 disulfide bonds. It has been appreciated that dietary disulfides modulate intestinal redox potential and that ST could be detoxified using exogenous reductants. Using biochemical and spectroscopic approaches, we demonstrated that ST can separately bind iron and zinc under reducing conditions, thereby reducing ST toxicity. Moreover, we demonstrated that ST modulates the glutathione (GSH)/oxidized glutathione (GSSG) ratio and that ST should be considered a toxin oxidant. ST can be detoxified by oxidizing zinc-loaded metallothionine, causing free zinc to be released. These studies help lay a foundation to understand how diarrheal pathogens modulate intestinal redox potential and may impact how we design therapeutics and/or vaccines for the pathogens that produce them.

Dietary iron deficiency impaired intestinal immune function of on-growing grass carp under the infection of Aeromonas hydrophila: Regulation of NF-κB and TOR signaling

Iron is an important mineral element for fish. In this study, we investigated the influences of dietary iron deficiency on intestinal immune function as well as underlying signaling of on-growing grass carp (Ctenopharyngodon idella). Fish were fed with six graded level of dietary iron for sixty days, and a fourteen days' challenge test under infection of Aeromonas hydrophila thereafter. Results showed that compared with optimal iron level, iron deficiency increased enteritis morbidity, decreased lysozyme (LZ) and acid phosphatase (ACP) activities, complement 3 (C3), C4 and immunoglobulin M (IgM) concentrations and down-regulated mRNA levels of hepcidin, liver expressed antimicrobial peptide 2A (LEAP-2A), LEAP-2B, Mucin2, β-defensin-1, anti-inflammatory cytokines transforming growth factor β1 (TGF-β1), TGF-β2, interleukin 4/13A (IL-4/13A), IL-4/13B, IL-10, IL-11 and IL-15, inhibitor of κBα (IκBα), target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1), whereas up-regulated mRNA levels of pro-inflammatory cytokines IL-1β, interferon γ2 (IFN-γ2), IL-8, IL-12p35, IL-12p40 and IL-17D, nuclear factor kappa B (NF-κB) p65, IκB kinases α (IKKα), IKKβ and eIF4E-binding protein (4E-BP) in intestine of on-growing grass carp, indicating that iron deficiency impaired intestinal immune function of fish under infection of A. hydrophila. Besides, iron excess also increased enteritis morbidity and impaired immune function of fish under infection of A. hydrophila. In addition, the effect of ferrous fumarate on intestinal immune function of on-growing grass carp is more efficient than ferrous sulfate. Finally, based on ability against enteritis, LZ activities in mid intestine and distal intestine, we recommended adding 83.37, 86.71 and 85.39 mg iron/kg into diet, respectively.