Deciphering interleukin-18 in diabetes and its complications: Biological features, mechanisms, and therapeutic perspectives

Interleukin-18 (IL-18), a potent and multifunctional pro-inflammatory cytokine, plays a critical role in regulating β-cell failure, β-cell death, insulin resistance, and various complications of diabetes mellitus (DM). It exerts its effects by triggering various signaling pathways, enhancing the production of pro-inflammatory cytokines and nitric oxide (NO), as well as promoting immune cells infiltration and β-cells death. Abnormal alterations in IL-18 levels have been revealed to be strongly associated with the onset and development of DM and its complications. Targeting IL-18 may present a novel and promising approach for DM therapy. An increasing number of IL-18 inhibitors, including chemical and natural inhibitors, have been developed and have been shown to protect against DM and diabetic complications. This review provides a comprehensive understanding of the production, biological functions, action mode, and activated signaling pathways of IL-18. Next, we shed light on how IL-18 contributes to the pathogenesis of DM and its associated complications with links to its roles in the modulation of β-cell failure and death, insulin resistance in various tissues, and pancreatitis. Furthermore, the therapeutic potential of targeting IL-18 for the diagnosis and treatment of DM is also highlighted. We hope that this review will help us better understand the functions of IL-18 in the pathogenesis of DM and its complications, providing novel strategies for DM diagnosis and treatment.

Identification of potential novel targets for treating inflammatory bowel disease using Mendelian randomization analysis

BACKGROUND

Inflammatory bowel disease (IBD) is a complex autoimmune disorder, although some medications are available for its treatment. However, the long-term efficacy of these drugs remains unsatisfactory. Therefore, there is a need to develop novel drug targets for IBD treatment.

METHODS

We conducted two-sample Mendelian randomization (MR) analysis using Genome-Wide Association Study (GWAS) data to assess the causal relationships between plasma proteins and IBD and its subtypes. Subsequently, the presence of shared genetic variants between the identified plasma proteins and traits was explored using Bayesian co-localization. Phenome-wide MR was used to evaluate evaluated adverse effects, and drug target databases were examined for therapeutic potential.

RESULTS

Using the Bonferroni correction (P < 3.56e-05), 17 protein-IBD pairs were identified. Notably, the genetic associations of IBD shared a common variant locus (PP.H4 > 0.7) with five proteins (MST1, IL12B, HGFAC, FCGR2A, and IL18R1). As a subtype of IBD, ulcerative colitis shares common variant loci with FCGR2A, IL12B, and MST1. In addition, we found that ANGPTL3, IL18R1, and MST1 share a common variant locus with Crohn's disease. Furthermore, phenome-wide MR analysis revealed that except for ANGPTL3, no other proteins showed potential adverse effects. In the drug database, identified plasma proteins such as FCGR2A and IL18R1 were found to be potential drug targets for the treatment of IBD and its subtypes.

CONCLUSION

Six proteins (FCGR2A, IL18R1, MST1, HGFAC, IL12B, and ANGPTL3) were identified as potential drug targets for the treatment of IBD and its subtypes.

Causal effects of inflammatory protein biomarkers on inflammatory diseases

Many circulating proteins are associated with the presence or severity of disease. However, whether these protein biomarkers are causal for disease development is usually unknown. We investigated the causal effect of 21 well-known or exploratory protein biomarkers of inflammation on 18 inflammatory diseases using two-sample Mendelian randomization. We identified six proteins to have causal effects on any of 11 inflammatory diseases (FDR < 0.05, corresponding to P < 1.4 × 10^–3). IL-12B protects against psoriasis and psoriatic arthropathy, LAP-TGF-β-1 protects against osteoarthritis, TWEAK protects against asthma, VEGF-A protects against ulcerative colitis, and LT-α protects against both type 1 diabetes and rheumatoid arthritis. In contrast, IL-18R1 increases the risk of developing allergy, hay fever, and eczema. Most proteins showed protective effects against development of disease rather than increasing disease risk, which indicates that many disease-related biomarkers are expressed to protect from tissue damage. These proteins represent potential intervention points for disease prevention and treatment.

Haematological profile of COVID-19 patients from a centre in Singapore

BACKGROUND

Haematological markers such as absolute lymphopenia have been associated with severe COVID-19 infection. However, in the literature to date, the cohorts described have typically included patients who were moderate to severely unwell with pneumonia and who required intensive care stay. It is uncertain if these markers apply to a population with less severe illness. We sought to describe the haematological profile of patients with mild disease with COVID-19 admitted to a single centre in Singapore.

METHODS

We examined 554 consecutive PCR positive SARS-COV-2 patients admitted to a single tertiary healthcare institution from Feb 2020 to April 2020. In all patients a full blood count was obtained within 24 h of presentation.

RESULTS

Patients with pneumonia had higher neutrophil percentages (66.5 ± 11.6 vs 55.2 ± 12.6%, p < 0.001), lower absolute lymphocyte count (1.5 ± 1.1 vs 1.9 ± 2.1 x109/L, p < 0.011) and absolute eosinophil count (0.2 ± 0.9 vs 0.7 ± 1.8 × 109/L, p = 0.002). Platelet counts (210 ± 56 vs 230 ± 61, p = 0.020) were slightly lower in the group with pneumonia. We did not demonstrate significant differences in the neutrophil-lymphocyte ratio, monocyte-lymphocyte ratio and platelet-lymphocyte ratio in patients with or without pneumonia. Sixty-eight patients (12.3%) had peripheral eosinophilia. This was more common in migrant workers living in dormitories.

CONCLUSION

Neutrophilia and lymphopenia were found to be markers associated with severe COVID-19 illness. We did not find that combined haematological parameters: neutrophil-lymphocyte ratio, monocyte-lymphocyte ratio and platelet-lymphocyte ratio, had any association with disease severity in our cohort of patients with mild-moderate disease. Migrant workers living in dormitories had eosinophilia which may reflect concurrent chronic parasitic infection.

Alpha-Lipoic Acid Plays a Role in Endometriosis: New Evidence on Inflammasome-Mediated Interleukin Production, Cellular Adhesion and Invasion

Endometriosis is an estrogen-linked gynecological disease defined by the presence of endometrial tissue on extrauterine sites where it forms invasive lesions. Alterations in estrogen-mediated cellular signaling seems to have an essential role in the pathogenesis of endometriosis. Higher estrogen receptor (ER)-β levels and enhanced ER-β activity were detected in endometriotic tissues. It is well known that ER-β interacts with components of the cytoplasmic inflammasome-3 (NALP-3), the NALP-3 activation increases interleukin (IL)-1β and IL-18, enhancing cellular adhesion and proliferation. Otherwise, the inhibition of ER-β activity suppresses the ectopic lesions growth. The present study aims to investigate the potential effect of α-lipoic acid (ALA) on NALP-3 and ER-β expression using a western blot analysis, NALP-3-induced cytokines production by ELISA, migration and invasion of immortalized epithelial (12Z) and stromal endometriotic cells (22B) using a 3D culture invasion assay, and matrix-metalloprotease (MMPs) activity using gelatin zymography. ALA significantly reduces ER-β, NALP-3 protein expression/activity and the secretion of IL-1β and IL-18 in both 12Z and 22B cells. ALA treatment reduces cellular adhesion and invasion via a lower expression of adhesion molecules and MMPs activities. These results provide convincing evidence that ALA might inhibit endometriosis progression.

Molecularly Distinct NLRP3 Inducers Mediate Diverse Ratios of Interleukin-1β and Interleukin-18 from Human Monocytes

Inflammasomes cleave and activate interleukin- (IL-) 1β and IL-18 which have both shared and unique biological functions. IL-1β is an important mediator of the acute phase response to infections and tissue damage, whereas IL-18 takes part in activation and tailoring of the adaptive immune response. While IL-1β has served as the prototypic indicator of inflammasome activation, few studies have compared the potential differences in IL-1β and IL-18 production during inflammasome activation. Since these cytokines partake in different immune pathways, the involvement of inflammasome activity in different conditions needs to be described beyond IL-1β production alone. To address a potential heterogeneity in inflammasome functionality, ATP, chitosan, or silica oxide (SiO₂) were used to induce NLRP3 inflammasome activation in THP-1 cells and the subsequent outcomes were quantified. Despite using doses of the inflammasome inducers yielding similar release of IL-1β, SiO₂-stimulated cells showed a lower concentration of released IL-18 compared to ATP and chitosan. Hence, the cells stimulated with SiO₂ responded with a distinctly different IL-18 : IL-1β ratio. The difference in the IL-18 : IL-1β ratio for SiO₂ was constant over different doses. While all downstream responses were strictly dependent on a functional NLRP3 inflammasome, the differences did not depend on the level of gene expression, caspase-1 activity, or pyroptosis. We suggest that the NLRP3 inflammasome response should be considered a dynamic process, which can be described by taking the ratio between IL-1β and IL-18 into account and moving away from an on/off perspective of inflammasome activation.

Inhibition of the IL-18 Receptor Signaling Pathway Ameliorates Disease in a Murine Model of Rheumatoid Arthritis

Interleukin (IL)-18 expression in synovial tissue correlates with the severity of joint inflammation and the levels of pro-inflammatory cytokines. However, the role of the IL-18/IL-18 receptor-alpha (Rα) signaling pathway in autoimmune arthritis is unknown. Wild-type (WT) and IL-18Rα knockout (KO) mice were immunized with bovine type II collagen before the onset of arthritis induced by lipopolysaccharide injection. Disease activity was evaluated by semiquantitative scoring and histologic assessment. Serum inflammatory cytokine and anticollagen antibody levels were quantified by an enzyme-linked immunosorbent assay. Joint cytokine and matrix metalloproteinases-3 levels were determined by a quantitative polymerase chain reaction. Splenic suppressors of cytokine signaling (SOCS) were determined by Western blot analysis as indices of systemic immunoresponse. IL-18Rα KO mice showed lower arthritis and histological scores in bone erosion and synovitis due to reductions in the infiltration of CD4+ T cells and F4/80+ cells and decreased serum IL-6, -18, TNF, and IFN-γ levels. The mRNA expression and protein levels of SOCS3 were significantly increased in the IL-18Rα KO mice. By an up-regulation of SOCS, pro-inflammatory cytokines were decreased through the IL-18/IL-18Rα signaling pathway. These results suggest that inhibitors of the IL-18/IL-18Rα signaling pathway could become new therapeutic agents for rheumatoid arthritis.

Lipopolysaccharide-Induced Acute Kidney Injury Is Dependent on an IL-18 Receptor Signaling Pathway

The proinflammatory cytokine interleukin (IL)-18 is an important mediator of the organ failure induced by endotoxemia. IL-18 (known as an interferon-gamma (IFN-γ) inducing factor), and other inflammatory cytokines have important roles in lipopolysaccharide (LPS)-induced acute kidney injury (AKI). We investigated the effect of inflammatory cytokines and Toll-like receptor 4 (TLR4) expression, an event that is accompanied by an influx of monocytes, including CD4⁺ T cells and antigen-presenting cells (APCs) in IL-18Rα knockout (KO) mice and wild-type (WT) mice after LPS injection. In the acute advanced phase, the IL-18Rα KO mice showed a higher survival rate and a suppressed increase of blood urea nitrogen, increased levels of proinflammatory cytokines such as IFN-γ and IL-18, the infiltration of CD4⁺ T cells and the expression of kidney injury molecule-1 as an AKI marker. In that phase, the renal mRNA expression of the M1 macrophage phenotype and C-C chemokine receptor type 7 as the maturation marker of dendritic cells (DCs) was also significantly decreased in the IL-18Rα KO mice, although there were small numbers of F4/80⁺ cells and DCs in the kidney. Conversely, there were no significant differences in the expressions of mRNA and protein TLR4 after LPS injection between the WT and IL-18Rα KO groups. Our results demonstrated that the IL-18Rα-mediated signaling pathway plays critical roles in CD4⁺ T cells and APCs and responded more quickly to IFN-γ and IL-18 than TLR4 stimulation in the pathogenesis of LPS-induced AKI.

The role of IL-18 in type 1 diabetic nephropathy: The problem and future treatment

Diabetic vascular complication is a leading cause of diabetic nephropathy, a progressive increase in urinary albumin excretion coupled with elevated blood pressure leading to declined glomerular filtration and eventually end stage renal failure. There is growing evidence that activated inflammation is contributing factor to the pathogenesis of diabetic nephropathy. Meanwhile, IL-18, a member of the IL-1 family of inflammatory cytokines, is involved in the development and progression of diabetic nephropathy. However, the benefits derived from the current therapeutics for diabetic nephropathy strategies still provide imperfect protection against renal progression. This imperfection points to the need for newer therapeutic agents that have potential to affect primary mechanisms contributing to the pathogenesis of diabetic nephropathy. Therefore, the recognition of IL-18 as significant pathogenic mediators in diabetic nephropathy leaves open the possibility of new potential therapeutic targets.

Inflammosome in the human endometrium: further step in the evaluation of the "maternal side"

OBJECTIVE

To investigate the expression of inflammosome components (NALP-3, associated speck-like protein containing a CARD [ASC]) and their activation (caspase-1, interleukin [IL]-1β, and IL-18 secretion) in the human endometrium from fertile and women with history of recurrent pregnancy loss (RPL).

DESIGN

Experimental study.

SETTING

University hospital.

PATIENT(S)

Ten fertile women (control group [CTR]) and 30 women with RPL.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Endometrial samples were collected by hysteroscopy during the putative window of implantation and evaluated for chronic endometrial inflammation by hystopathological analysis. Inflammosome expression was analysed by immunohystochemical staining (27 RPL and 10 CTR women). The expression of NALP-3 and ASC protein was quantified by Western blot (30 RPL and 10 CTR women). Caspase-1 activation and IL-1β and IL-18 secretion was quantified by ELISA (30 RPL and 10 CTR women).

RESULT(S)

We observed a significantly increased expression of inflammasome NALP-3 and ASC protein, an increased activation of caspase-1, and increased levels of IL-1β and IL-18 in RPL endometrium compared with CTR.

CONCLUSION(S)

Abnormal activation of endometrial innate immunity by means of inflammosome, stimulated by pathogen- or damage-associated molecular patterns, may represent an additional mechanism, currently not investigated, negatively interfering with endometrial receptivity. More studies are required [1] to identify the primary trigger of endometrial inflammosome activation and its clinical impact in the occurrence of RPL; and [2] to validate the inflammosome components as a novel family of endometrial biomarkers and promising therapeutic targets in RPL.

The ratio of plasma interleukin-18 is a sensitive biomarker for acute kidney injury after liver transplantation

BACKGROUND

Acute kidney injury (AKI) is common after liver transplantation (OLT) and is associated with high morbidity and mortality. Previous studies have shown that interleukin-18 (IL-18) levels are associated with AKI. The purpose of this study was to determine whether plasma IL-18 levels were early predictors for AKI after liver transplantation.

METHODS

Plasma samples were obtained from 26 patients who underwent OLT at induction of anesthesia (T1), 1 hour after the surgical incision (T2), the time of reperfusion (T3), as well as 1 (T4), 2 (T5), and 4 hours (T6) after reperfusion. Samples were also obtained at 24 hours after surgery (T7). The AKI criteria were taken according to the Acute Kidney Injury Network criteria.

RESULTS

Twelve patients (46%) developed AKI after OLT. The area under the receiver operating curve of plasma IL-18 concentrations (T4/T1) to predict AKI occurrence was 0.842 at T5, 0.905 at T6, 0.726 at T7, and 0.726 at T5 to T7.

CONCLUSION

Plasma IL-18 concentrations taken 1 hour after reperfusion were predictive of AKI. Therefore, changing IL-18 ratio may be an early predictor for AKI after OLT.

Protection from inflammatory organ damage in a murine model of hemophagocytic lymphohistiocytosis using treatment with IL-18 binding protein

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening condition due to the association of an infectious agent with lymphocyte cytotoxicity defects, either of congenital genetic origin in children or presumably acquired in adults. In HLH patients, an excess of lymphocyte or macrophage cytokines, such as IFN-γ and TNFα is present in serum. In animal models of the disease, IFN-γ and TNF-α have been shown to play a central pathogenic role. In humans, unusually high concentrations of IL-18, an inducer of IFN-γ, and TNF-α have been reported, and are associated with an imbalance between IL-18 and its natural inhibitor IL-18 binding protein (IL-18BP) resulting in an excess of free IL-18. Here we studied whether IL-18BP could reduce disease severity in an animal model of HLH. Mouse cytomegalovirus infection in perforin-1 knock-out mice induced a lethal condition similar to human HLH characterized by cytopenia with marked inflammatory lesions in the liver and spleen as well as the presence of hemophagocytosis in bone marrow. IL-18BP treatment decreased hemophagocytosis and reversed liver as well as spleen damage. IL-18BP treatment also reduced both IFN-γ and TNF-α production by CD8(+) T and NK cells, as well as Fas ligand expression on NK cell surface. These data suggest that IL-18BP is beneficial in an animal model of HLH and in combination with anti-infectious therapy may be a promising strategy to treat HLH patients.

Responses of IL-18- and IL-18 receptor-deficient pancreatic islets with convergence of positive and negative signals for the IL-18 receptor

Pancreatic islets contain cells that produce IL-18 and cells that express IL-18 receptors. In experimentally induced diabetes, islet failure correlates with IL-18 levels and diabetes is delayed with blockade of endogenous IL-18. We studied islet-derived IL-18 and responses to IL-18 in a mouse model of islet allograft transplantation. In vitro, IL-18-stimulated islets produced nitric oxide, which closely matched islet apoptosis. By neutralizing IL-18 activity with IL-18 binding protein (IL-18BP), we observed that islets produce bioactive IL-18. In vivo, transgenic mice overproducing IL-18BP (IL-18BP-Tg) exhibited delayed hyperglycemia induced by beta cell toxic streptozotocin. Similarly, cultured IL-18BP-Tg islets were protected from streptozotocin-induced apoptosis. In the transplant model, islets grafted from WT to IL-18BP-Tg mice achieved prolonged normoglycemia (P = 0.031). Improved graft function was also observed by using IL-18-deficient islets transplanted into WT recipients, demonstrating that endogenous, islet-derived IL-18 mediates IL-18-driven graft damage. Unexpectedly, islets from mice deficient in IL-18 receptor alpha chain (IL-18R) exhibited rapid graft failure (P = 0.024; IL-18- versus IL-18R-deficient grafts in WT recipients). In related studies, IL-18R-deficient splenocytes and macrophages produced 2- to 3-fold greater amounts of IL-18, TNFalpha, macrophage inflammatory protein 1, macrophage inflammatory protein 2, and IFNgamma upon stimulation with Con A, Toll-like receptor 2 agonist, or anti-CD3 antibodies. These data reveal a role for islet-derived IL-18 activity during inflammation-mediated islet injury. Importantly, discrepancies between IL-18- and IL-18R-deficient cells suggest that IL-18Ralpha chain is used by an inflammation-suppressing signal.