Sulfur Compounds Inhibit High Glucose-Induced Inflammation by Regulating NF-κB Signaling in Human Monocytes

Metabolite-derived damage-associated molecular patterns in immunological diseases

Damage-associated molecular patterns (DAMPs) are typically derived from the endogenous elements of necrosis cells and can trigger inflammatory responses by activating DAMPs-sensing receptors on immune cells. Failure to clear DAMPs may lead to persistent inflammation, thereby contributing to the pathogenesis of immunological diseases. This review focuses on a newly recognized class of DAMPs derived from lipid, glucose, nucleotide, and amino acid metabolic pathways, which are then termed as metabolite-derived DAMPs. This review summarizes the reported molecular mechanisms of these metabolite-derived DAMPs in exacerbating inflammation responses, which may attribute to the pathology of certain types of immunological diseases. Additionally, this review also highlights both direct and indirect clinical interventions that have been explored to mitigate the pathological effects of these DAMPs. By summarizing our current understanding of metabolite-derived DAMPs, this review aims to inspire future thoughts and endeavors on targeted medicinal interventions and the development of therapies for immunological diseases.

Glucose Promotes EMMPRIN/CD147 and the Secretion of Pro-Angiogenic Factors in a Co-Culture System of Endothelial Cells and Monocytes

Vascular complications in Type 2 diabetes mellitus (T2DM) patients increase morbidity and mortality. In T2DM, angiogenesis is impaired and can be enhanced or reduced in different tissues ("angiogenic paradox"). The present study aimed to delineate differences between macrovascular and microvascular endothelial cells that might explain this paradox. In a monoculture system of human macrovascular (EaHy926) or microvascular (HMEC-1) endothelial cell lines and a monocytic cell line (U937), high glucose concentrations (25 mmole/L) increased the secretion of the pro-angiogenic factors CD147/EMMPRIN, VEGF, and MMP-9 from both endothelial cells, but not from monocytes. Co-cultures of EaHy926/HMEC-1 with U937 enhanced EMMPRIN and MMP-9 secretion, even in low glucose concentrations (5.5 mmole/L), while in high glucose HMEC-1 co-cultures enhanced all three factors. EMMPRIN mediated these effects, as the addition of anti-EMMPRIN antibody decreased VEGF and MMP-9 secretion, and inhibited the angiogenic potential assessed through the wound assay. Thus, the minor differences between the macrovascular and microvascular endothelial cells cannot explain the angiogenic paradox. Metformin, a widely used drug for the treatment of T2DM, inhibited EMMPRIN, VEGF, and MMP-9 secretion in high glucose concentration, and the AMPK inhibitor dorsomorphin enhanced it. Thus, AMPK regulates EMMPRIN, a key factor in diabetic angiogenesis, suggesting that targeting EMMPRIN may help in the treatment of diabetic vascular complications.

Methylsulfonylmethane protects against lethal dose MRSA-induced sepsis through promoting M2 macrophage polarization

BACKGROUND

Multi-drug-resistant bacterial infections, which have become a global threat, lack effective treatments. The discoveries of non-antibiotics with different modes of antibacterial action, such as methylsulfonylmethane (MSM), are a promising new treatment for multi-drug-resistant pathogens.

METHODS

We constructed a mouse peritonitis infection model to evaluate the effects of MSM against methicillin-resistant Staphylococcus aureus (MRSA) infection. The time-kill kinetics of MSM against MRSA and the effect of MSM on the integrity of bacterial cell membrane were measured. Viability effects of MSM on THP1 cells were performed by CCK-8 cytotoxicity assay. Systematic inflammatory factor levels of mice were detected using ELISA. The immune response of peritoneal macrophages during MRSA-infection was evaluated using RNA sequencing. Gene Ontology function, Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses, and correlation analyses were applied to analysis RNA sequencing data. RT-qPCR, western blotting and flow cytometry were performed to analysis the gene and protein expression levels of macrophages.

RESULTS

In in vitro experiments, MSM did not show significant killing effects on the growth of MRSA directly and did not destroy bacterial membrane integrity. MSM also displayed no significant effects on the proliferative capacity of THP1 cells. However, MSM treatment protected mice against a lethal dose MRSA-infection and decreased systemic inflammation. MSM upregulated metabolic pathway in peritoneal macrophages, especial glycolysis, during MRSA infection. MSM increased the expression of M2 markers (such as Arg1), promoted phosphorylation of STAT3 (which regulates M2 polarization), and decreased the expression of M1 markers in peritoneal macrophages. Additionally, MSM treatment increased the expression of H3K18 lactylation specific target genes, including Arg1. GNE-140, the LDHA-specific inhibitor of glycolysis, blocked the MSM-induced Arg1 expression in this disease model.

CONCLUSIONS

MSM protects against MRSA infection through immunomodulation. MSM promotes the expression of Arg1 by lactate-H3K18la pathway to control macrophage to M2 polarization; it firstly provides therapeutic potential for drug-resistant infections and sepsis.

Gymnemic acid protects murine pancreatic β-cells by moderating hyperglycemic stress-induced inflammation and apoptosis in type 1 diabetic rats

Type 1 diabetes is a chronic immune-mediated disease caused by pancreatic β-cell dysfunction with consequent severe insulin deficiency. Exacerbated blood glucose levels can cause oxidative stress in the pancreatic β-cells, which leads to inflammation, and apoptosis resulting in islet dysfunction. Although massive studies have been carried out to elucidate the causative factors for β-cell damage in diabetes, the therapeutic approach to pancreatic β-cell damage has not been extensively studied. Hence, the present study has been designed to delineate the role of gymnemic acid (GA) in protecting pancreatic β-cells in diabetic animals, with special reference to inflammation and apoptosis. Our data revealed that the treatment with GA significantly reverted the alteration in both biochemical and histochemical observations in young diabetic rats. Moreover, treatment with the GA downregulates the expression of proinflammatory markers (nuclear factor-κB, tumor necrosis factor-α, interleukin-[IL]-6, and IL-1β), proapoptotic proteins (Bax, cytochrome c, and cleaved caspase-3), as well as upregulates the expression of antiapoptotic protein Bcl-2 in diabetic rats. These findings suggest that the anti-inflammatory and antiapoptotic nature of GA mitigates β-cell damage in hyperglycemic rats.

Methylsulfonylmethane ameliorates inflammation via NF-κB and ERK/JNK-MAPK signaling pathway in chicken trachea and HD11 cells during Mycoplasma gallisepticum infection

Mycoplasma gallisepticum (MG) is an avian pathogen that commonly causes respiratory diseases in poultry. Methylsulfonylmethane (MSM) is a sulfur-containing natural compound that could alleviate inflammatory injury through its excellent anti-inflammatory and antioxidant properties. However, it is still unclear whether MSM prevents MG infection. The purpose of this study is to determine whether MSM has mitigative effects on MG-induced inflammatory injury in chicken and chicken like macrophages (HD11 cells). In this research, White Leghorn chickens and HD11 cells were used to build the MG-infection model. Besides, the protective effects of MSM against MG infection were evaluated by detecting MG colonization, histopathological changes, oxidative stress and inflammatory injury of trachea, and HD11 cells. The results revealed that MG infection induced inflammatory injury and oxidative stress in trachea and HD11 cells. However, MSM treatment significantly ameliorated oxidative stress, partially alleviated the abnormal morphological changes and reduced MG colonization under MG infection. Moreover, MSM reduced the mRNA expression of proinflammatory cytokines-related genes and decreased the number of death cells under MG infection. Importantly, the protective effects of MSM were associated with suppression of nuclear factor-kappa B (NF-κB) and extracellular signal-related kinases (ERK)/Jun amino terminal kinases (JNK)-mitogen-activated protein kinases (MAPK) pathway in trachea and HD11 cells. These results proved that MSM has protective effects on MG-induced inflammation in chicken, and supplied a better strategy for the protective intervention of this disease.

Iron Metabolism as a Potential Mechanism for Inducing TRAIL-Mediated Extrinsic Apoptosis Using Methylsulfonylmethane in Embryonic Cancer Stem Cells

Embryonic cancer stem cells (CSCs) can differentiate into any cancer type. Targeting CSC using natural compounds is a good approach as it suppresses cancer recurrence with fewer adverse effects, and methylsulfonylmethane (MSM) is a sulfur-containing compound with well-known anticancer activities. This study determined the mechanistic aspects of the anticancer activity of MSM. We used Western blotting and real-time qPCR for molecular signaling studies and conducted flow cytometry for analyzing the processes in cells. Our results suggested an inhibition in the expression of CSC markers and Wnt/β-catenin signaling. MSM induced TRAIL-mediated extrinsic apoptosis in NCCIT and NTERA-2 cells rather than an intrinsic pathway. Inhibition of iron metabolism-dependent reactive oxygen species (ROS) generation takes part in TRAIL-mediated apoptosis induction by MSM. Suppressing iron metabolism by MSM also regulated p38/p53/ERK signaling and microRNA expressions, such as upregulating miR-130a and downregulating miR-221 and miR-222, which resulted in TRAIL induction and thereby extrinsic pathway of apoptosis. Hence, MSM could be a good candidate for neoadjuvant therapy by targeting CSCs by inhibiting iron metabolism.

New Insights into the Pivotal Role of Iron/Heme Metabolism in TLR4/NF-κB Signaling-Mediated Inflammatory Responses in Human Monocytes

Iron metabolism and heme biosynthesis are essential processes in cells during the energy cycle. Alteration in these processes could create an inflammatory condition, which results in tumorigenesis. Studies are conducted on the exact role of iron/heme metabolism in induced inflammatory conditions. This study used lipopolysaccharide (LPS)- or high-glucose-induced inflammation conditions in THP-1 cells to study how iron/heme metabolism participates in inflammatory responses. Here, we used iron and heme assays for measuring total iron and heme. We also used flow cytometry and Western blotting to analyze molecular responses. Our results demonstrated that adding LPS or high-glucose induced iron formation and heme synthesis and elevated the expression levels of proteins responsible for iron metabolism and heme synthesis. We then found that further addition of heme or 5-aminolevulinic acid (ALA) increased heme biosynthesis and promoted inflammatory responses by upregulating TLR4/NF-κB and inflammatory cytokine expressions. We also demonstrated the inhibition of heme synthesis using succinylacetone (SA). Moreover, N-MMP inhibited LPS- or high-glucose-induced inflammatory responses by inhibiting TLR4/NF-κB signaling. Hence, iron/heme metabolism checkpoints could be considered a target for treating inflammatory conditions.

Regulation of Carbohydrate-Responsive Metabolic Genes by Histone Acetylation and the Acetylated Histone Reader BRD4 in the Gene Body Region

Studies indicate that induction of metabolic gene expression by nutrient intake, and in response to subsequently secreted hormones, is regulated by transcription factors binding to cis-elements and associated changes of epigenetic memories (histone modifications and DNA methylation) located in promoter and enhancer regions. Carbohydrate intake-mediated induction of metabolic gene expression is regulated by histone acetylation and the histone acetylation reader bromodomain-containing protein 4 (BRD4) on the gene body region, which corresponds to the transcribed region of the gene. In this review, we introduce carbohydrate-responsive metabolic gene regulation by (i) transcription factors and epigenetic memory in promoter/enhancer regions (promoter/enhancer-based epigenetics), and (ii) histone acetylation and BRD4 in the gene body region (gene body-based epigenetics). Expression of carbohydrate-responsive metabolic genes related to nutrient digestion and absorption, fat synthesis, inflammation in the small intestine, liver and white adipose tissue, and in monocytic/macrophage-like cells are regulated by various transcription factors. The expression of these metabolic genes are also regulated by transcription elongation via histone acetylation and BRD4 in the gene body region. Additionally, the expression of genes related to fat synthesis, and the levels of acetylated histones and BRD4 in fat synthesis-related genes, are downregulated in white adipocytes under insulin resistant and/or diabetic conditions. In contrast, expression of carbohydrate-responsive metabolic genes and/or histone acetylation and BRD4 binding in the gene body region of these genes, are upregulated in the small intestine, liver, and peripheral leukocytes (innate leukocytes) under insulin resistant and/or diabetic conditions. In conclusion, histone acetylation and BRD4 binding in the gene body region as well as transcription factor binding in promoter/enhancer regions regulate the expression of carbohydrate-responsive metabolic genes in many metabolic organs. Insulin resistant and diabetic conditions induce the development of metabolic diseases, including type 2 diabetes, by reducing the expression of BRD4-targeted carbohydrate-responsive metabolic genes in white adipose tissue and by inducing the expression of BRD4-targeted carbohydrate-responsive metabolic genes in the liver, small intestine, and innate leukocytes including monocytes/macrophages and neutrophils.

Natural Sulfurs Inhibit LPS-Induced Inflammatory Responses through NF-κB Signaling in CCD-986Sk Skin Fibroblasts

Lipopolysaccharide (LPS)-induced inflammatory response leads to serious damage, up to and including tumorigenesis. Natural mineral sulfur, non-toxic sulfur (NTS), and methylsulfonylmethane (MSM) have anti-inflammatory activity that may inhibit LPS-induced inflammation. We hypothesized that sulfur compounds could inhibit LPS-induced inflammatory responses in CCD-986Sk skin fibroblasts. We used Western blotting and real-time PCR to analyze molecular signaling in treated and untreated cultures. We also used flow cytometry for cell surface receptor analysis, comet assays to evaluate DNA damage, and ELISA-based cytokine detection. LPS induced TLR4 activation and NF-κB signaling via canonical and protein kinase C (PKC)-dependent pathways, while NTS and MSM downregulated that response. NTS and MSM also inhibited LPS-induced nuclear accumulation and binding of NF-κB to proinflammatory cytokines COX-2, IL-1β, and IL-6. Finally, the sulfur compounds suppressed LPS-induced ROS accumulation and DNA damage in CCD-986Sk cells. These results suggest that natural sulfur compounds could be used to treat inflammation and may be useful in the development of cosmetics.