Long-term methylglyoxal intake aggravates murine Th2-mediated airway eosinophil infiltration

Dietary glycation compounds - implications for human health

The term "glycation compounds" comprises a wide range of structurally diverse compounds that are formed endogenously and in food via the Maillard reaction, a chemical reaction between reducing sugars and amino acids. Glycation compounds produced endogenously are considered to contribute to a range of diseases. This has led to the hypothesis that glycation compounds present in food may also cause adverse effects and thus pose a nutritional risk to human health. In this work, the Senate Commission on Food Safety (SKLM) of the German Research Foundation (DFG) summarized data on formation, occurrence, exposure and toxicity of glycation compounds (Part A) and systematically assessed potential associations between dietary intake of defined glycation compounds and disease, including allergy, diabetes, cardiovascular and renal disease, gut/gastrotoxicity, brain/cognitive impairment and cancer (Part B). A systematic search in Pubmed (Medline), Scopus and Web of Science using a combination of keywords defining individual glycation compounds and relevant disease patterns linked to the subject area of food, nutrition and diet retrieved 253 original publications relevant to the research question. Of these, only 192 were found to comply with previously defined quality criteria and were thus considered suitable to assess potential health risks of dietary glycation compounds. For each adverse health effect considered in this assessment, however, only limited numbers of human, animal and in vitro studies were identified. While studies in humans were often limited due to small cohort size, short study duration, and confounders, experimental studies in animals that allow for controlled exposure to individual glycation compounds provided some evidence for impaired glucose tolerance, insulin resistance, cardiovascular effects and renal injury in response to oral exposure to dicarbonyl compounds, albeit at dose levels by far exceeding estimated human exposures. The overall database was generally inconsistent or inconclusive. Based on this systematic review, the SKLM concludes that there is at present no convincing evidence for a causal association between dietary intake of glycation compounds and adverse health effects.

Dietary dicarbonyl compounds exacerbated immune dysfunction and hepatic oxidative stress under high-fat diets in vivo

High-fat diets (HFDs) predispose to obesity and liver dysfunctions, and α-dicarbonyl compounds (α-DCs) present in highly processed foods are also implicated in relevant pathological processes. However, the synergistic harmful effects of α-DCs co-administered with HFDs remain to be elucidated. In this study, 6-week-old C57BL/6 mice were fed with a HFD co-administered with 0.5% methylglyoxal (MGO)/glyoxal (GO) in water for 8 weeks, and multi-omics approaches were employed to investigate the underlying toxicity mechanisms. The results demonstrated that the MGO intervention with a HFD led to an increased body weight and blood glucose level, accompanied by the biological accumulation of α-DCs and carboxymethyl-lysine, as well as elevated serum levels of inflammatory markers including IL-1β, IL-6, and MIP-1α. Notably, hepatic lesions were observed in the MGO group under HFD conditions, concomitant with elevated levels of malondialdehyde. Transcriptomic analysis revealed enrichment of pathways and differentially expressed genes (DEGs) associated with inflammation and oxidative stress in the liver. Furthermore, α-DC intervention exacerbated gut microbial dysbiosis in the context of a HFD, and through Spearman correlation analysis, the dominant genera such as Fusobacterium and Bacteroides in the MGO group and Colidextribacter and Parabacteroides in the GO group were significantly correlated with a set of DEGs involved in inflammatory and oxidative stress pathways in the liver. This study provides novel insights into the healthy implications of dietary ultra-processed food products in the context of obesity-associated disorders.

Methylglyoxal and Advanced Glycation End Products (AGEs): Targets for the Prevention and Treatment of Diabetes-Associated Bladder Dysfunction?

Methylglyoxal (MGO) is a highly reactive α-dicarbonyl compound formed endogenously from 3-carbon glycolytic intermediates. Methylglyoxal accumulated in plasma and urine of hyperglycemic and diabetic individuals acts as a potent peptide glycation molecule, giving rise to advanced glycation end products (AGEs) like arginine-derived hydroimidazolone (MG-H1) and carboxyethyl-lysine (CEL). Methylglyoxal-derived AGEs exert their effects mostly via activation of RAGE, a cell surface receptor that initiates multiple intracellular signaling pathways, favoring a pro-oxidant environment through NADPH oxidase activation and generation of high levels of reactive oxygen species (ROS). Diabetic bladder dysfunction is a bothersome urological complication in patients with poorly controlled diabetes mellitus and may comprise overactive bladder, urge incontinence, poor emptying, dribbling, incomplete emptying of the bladder, and urinary retention. Preclinical models of type 1 and type 2 diabetes have further confirmed the relationship between diabetes and voiding dysfunction. Interestingly, healthy mice supplemented with MGO for prolonged periods exhibit in vivo and in vitro bladder dysfunction, which is accompanied by increased AGE formation and RAGE expression, as well as by ROS overproduction in bladder tissues. Drugs reported to scavenge MGO and to inactivate AGEs like metformin, polyphenols, and alagebrium (ALT-711) have shown favorable outcomes on bladder dysfunction in diabetic obese leptin-deficient and MGO-exposed mice. Therefore, MGO, AGEs, and RAGE levels may be critically involved in the pathogenesis of bladder dysfunction in diabetic individuals. However, there are no clinical trials designed to test drugs that selectively inhibit the MGO-AGEs-RAGE signaling, aiming to reduce the manifestations of diabetes-associated bladder dysfunction. This review summarizes the current literature on the role of MGO-AGEs-RAGE-ROS axis in diabetes-associated bladder dysfunction. Drugs that directly inactivate MGO and ameliorate bladder dysfunction are also reviewed here.

Multifaceted roles of T cells in obesity and obesity-related complications: A narrative review

Obesity is characterized by chronic low-grade inflammatory responses in the adipose tissue, accompanied by pronounced insulin resistance and metabolic anomalies. It affects almost all body organs and eventually leads to diseases such as fatty liver disease, type 2 diabetes mellitus, and atherosclerosis. Recently, T cells have emerged as interesting therapeutic targets because the dysfunction of T cells and their cytokines in the adipose tissue is implicated in obesity-induced inflammation and their complicated onset. Although several recent narrative reviews have provided a brief overview of related evidence in this area, they have mainly focused on either obesity-associated T cell metabolism or modulation of T cell activation in obesity. Moreover, at present, no published review has reported on the multifaceted roles of T cells in obesity and obesity-related complications, even though there has been a significant increase in studies on this topic since 2019. Therefore, this narrative review aims to comprehensively summarize current advances in the mechanistic roles of T cells in the development of obesity and its related complications. Further, we aim to discuss relevant drugs for weight loss as well as the contradictory role of T cells in the same disease so as to highlight key findings regarding this topic and provide a valid basis for future treatment strategies.

Metformin Counteracts the Deleterious Effects of Methylglyoxal on Ovalbumin-Induced Airway Eosinophilic Inflammation and Remodeling

Exposure to methylglyoxal (MGO) increases the levels of receptor for advanced glycation end products (RAGE) and reactive-oxygen species (ROS) in mouse airways, exacerbating the inflammatory responses. Metformin scavenges MGO in plasma of diabetic individuals. We investigated if amelioration by metformin of eosinophilic inflammation reflects its ability to inactivate MGO. Male mice received 0.5% MGO for 12 weeks together or not with 2-week treatment with metformin. Inflammatory and remodeling markers were evaluated in bronchoalveolar lavage fluid (BALF) and/or lung tissues of ovalbumin (OVA)-challenged mice. MGO intake elevated serum MGO levels and MGO immunostaining in airways, which were reduced by metformin. The infiltration of inflammatory cells and eosinophils and levels of IL-4, IL-5 and eotaxin significantly increased in BALF and/or lung sections of MGO-exposed mice, which were reversed by metformin. The increased mucus production and collagen deposition by MGO exposure were also significantly decreased by metformin. In MGO group, the increases of RAGE and ROS levels were fully counteracted by metformin. Superoxide anion (SOD) expression was enhanced by metformin. In conclusion, metformin counteracts OVA-induced airway eosinophilic inflammation and remodeling, and suppresses the RAGE-ROS activation. Metformin may be an option of adjuvant therapy to improve asthma in individuals with high levels of MGO.

RAGE-Dependent Effect of Exogenous Methylglyoxal Intake on Lung Biomechanics in Mice

Methylglyoxal (MG) is a known highly reactive dicarbonyl and precursor to free radicals and advanced glycation end-products (AGEs). It is discussed to be involved in tissue aging and in the pathogenesis of different degenerative diseases. The effect of long-term oral administration of MG, simulating dietary MG intake, on the lung biomechanics of wild type (WT) and receptor for advanced glycation end-products knockout (RAGE-KO) mice was studied using an ex vivo ventilation system starting at the age of 6 months and after feeding for 6 and 12 months with MG. Our results showed that MG was taken up in the circulation and efficiently excreted with urine. The amount of free urinary MG measured after 12 months of feeding was lowered. After 12 months feeding, a significant airway resistance increase accompanied by a decrease of the maximal inspiratory airflow was observed in WT animals. No effect of MG in lung function of RAGE-KO mice could be detected. Despite the evidence that MG entered the systemic circulation, no MG-derived AGE accumulation was detected in the lung lysates in dependency on MG-feeding. Our data indicate that the short-term feeding of MG has little effect in vivo. Only after long-term treatment was MG secretion reduced, leading to tissue impairment.

Negative Effects of Chronic High Intake of Fructose on Lung Diseases

In the modern diet, excessive fructose intake (>50 g/day) had been driven by the increase, in recent decades, of the consumption of sugar-sweetened beverages. This phenomenon has dramatically increased within the Caribbean and Latin American regions. Epidemiological studies show that chronic high intake of fructose related to sugar-sweetened beverages increases the risk of developing several non-communicable diseases, such as chronic obstructive pulmonary disease and asthma, and may also contribute to the exacerbation of lung diseases, such as COVID-19. Evidence supports several mechanisms—such as dysregulation of the renin−angiotensin system, increased uric acid production, induction of aldose reductase activity, production of advanced glycation end-products, and activation of the mTORC1 pathway—that can be implicated in lung damage. This review addresses how these pathophysiologic and molecular mechanisms may explain the lung damage resulting from high intake of fructose.

Blockade of Tyrosine Kinase, LCK Leads to Reduction in Airway Inflammation through Regulation of Pulmonary Th2/Treg Balance and Oxidative Stress in Cockroach Extract-Induced Mouse Model of Allergic Asthma

Asthma is one of the most common inflammatory diseases affecting the airways. Approximately 300 million individuals suffer from asthma around the world. Allergic immune responses in the asthmatic airways are predominantly driven by Th2 cells and eosinophils. Lymphocyte-specific protein tyrosine kinase (LCK) is a non-receptor tyrosine kinase which regulates several key intracellular events through phosphorylation of its substrates. Some of the intracellular signaling pathways activated by LCK phosphorylation help in differentiation of Th2 cells which secrete allergic cytokines that amplify airway inflammation. Therefore, this investigative study was designed to determine the role of LCK in a cockroach extract (CE)-induced airway inflammation murine model of allergic asthma. Further, the effect of a pharmacological LCK inhibitor, A-770041, on allergic airway inflammation and key intracellular pathways in CD4+ T cells was assessed. Our data exhibit that there is an activation of LCK during allergic airway inflammation as depicted by increased p-LCK levels in CD4+ T cells. Activated LCK is involved in the activation of ITK, PLC-γ, GATA3, NFkB, and NFATc1. Activated LCK is also involved in the upregulation of Th2 related cytokines, such as IL-4/IL-5/IL-13 and oxidative stress, and the downregulation of Treg cells. Furthermore, utilization of LCK inhibitor causes the reduction in p-LCK, PLC-γ, GATA3, and NFATc1 as well as Th2 cytokines and oxidative stress. LCK inhibitor causes upregulation of Treg cells in allergic mice. LCK inhibitor also caused a reduction in CE-induced airway inflammation and mucus secretion. Therefore, the inhibition of LCK signaling could be a fruitful approach to adjust allergic airway inflammation through the attuning of Th2/Treg immune responses. This study could lead to the design of newer treatment options for better management of allergic inflammation in asthma.

Inner Shell of the Chestnut (Castanea crenatta) Suppresses Inflammatory Responses in Ovalbumin-Induced Allergic Asthma Mouse Model

The inner shell of the chestnut (Castanea crenata) contains various polyphenols, which exert beneficial biological effects. Hence, we assessed the anti-inflammatory efficacy of a chestnut inner shell extract (CIE) in ovalbumin (OVA)-induced allergic asthma. We intraperitoneally injected 20 ug of OVA with 2 mg of aluminum hydroxide on days 0 and 14. On test days 21, 22, and 23, the mice were treated with aerosolized 1% (w/v) OVA in saline. CIE was administered orally at 100 and 300 mg/kg on days 18–23. CIE significantly reduced inflammatory cytokines and cells and immunoglobulin-E increased by OVA. Anti-inflammatory efficacy was revealed by reduction of inflammatory cell migration and mucus secretion in lung tissue. Further, CIE suppressed the OVA-induced nuclear factor kappa B (NF-κB) phosphorylation. Accordingly, the expression of cyclooxygenase (COX-2), inducible nitric oxide synthase (iNOS), and matrix metalloproteinase-9 (MMP-9) were decreased sequentially in lung tissues. CIE alleviated OVA-induced airway inflammation by restraining phosphorylation of NF-κB and the sequentially reduced expression of iNOS, COX-2, leading to reduced MMP-9 expression. These results indicate that CIE has potential as a candidate for alleviating asthma.

Enhanced RAGE Expression and Excess Reactive-Oxygen Species Production Mediates Rho Kinase-Dependent Detrusor Overactivity After Methylglyoxal Exposure

Methylglyoxal (MGO) is a highly reactive dicarbonyl compound implicated in diabetes-associated diseases. In vascular tissues, MGO induces the formation of advanced glycation end products (AGEs) that bounds its receptor RAGE, initiating the downstream tissue injury. Outside the cardiovascular system, MGO intake produces mouse voiding dysfunction and bladder overactivity. We have sought that MGO-induced bladder overactivity is due to activation of AGE-RAGE-reactive-oxygen species (ROS) signaling cascade, leading to Rho kinase activation. Therefore, female mice received 0.5% MGO orally for 12 weeks, after which in vitro bladder contractions were evaluated in the presence or not of superoxide dismutase (PEG-SOD) or the Rho kinase inhibitor Y27632. Treatment with MGO significantly elevated the serum levels of MGO and fluorescent AGEs, as well as the RAGE immunostaining in the urothelium, detrusor, and vascular endothelium. RAGE mRNA expression in the bladder was also higher in the MGO group. Methylglyoxal significantly increased the ROS production in both urothelium and detrusor smooth muscle, with the increases in detrusor markedly higher than urothelium. The bladder activity of superoxide dismutase (SOD) was significantly reduced in the MGO group. Gene expressions of L-type Ca²⁺ channels, RhoA, ROCK-1, and ROCK-2 in bladder tissues were significantly elevated in the MGO group. Increased bladder contractions to electrical-field stimulation, carbachol α,β-methylene ATP, and extracellular Ca²⁺ were observed after MGO exposure, which was significantly reduced by prior incubation with either PEG-SOD or Y27632. Overall, our data indicate serum MGO accumulation elevates the AGEs levels and activates the RAGE-ROS signaling leading to Rho kinase-induced muscle sensitization, ultimately leading to detrusor overactivity.

Methylglyoxal Exacerbates Lipopolysaccharide-Induced Acute Lung Injury via RAGE-Induced ROS Generation: Protective Effects of Metformin

Purpose

Methylglyoxal (MGO) is a highly reactive dicarbonyl species implicated in diabetic-associated diseases. Acute lung injury (ALI) symptoms and prognosis are worsened by diabetes and obesity. Here, we hypothesized that elevated MGO levels aggravate ALI, which can be prevented by metformin. Therefore, this study evaluated the lung inflammation in lipopolysaccharide (LPS)-exposed mice pretreated with MGO.

Methods

C57Bl/6 male mice treated or not with MGO for 12 weeks were intranasally instilled with LPS (30 µg) to induce ALI, and metformin (300 mg/kg) was given as gavage in the last two weeks of treatment. After 6 h, bronchoalveolar lavage fluid (BALF) and lung tissues were collected to quantify the cell infiltration, cytokine levels, reactive-oxygen species (ROS) production, and RAGE expression.

Results

LPS exposure markedly increased the neutrophil infiltration in BALF and lung tissue, which was accompanied by higher levels of IFN-γ, TNF-α and IL-1β compared with untreated group. MGO treatment significantly increased the airways neutrophil infiltration and mRNA expressions of TNF-α and IL-1β, whereas COX-2 expression remained unchanged. In lung tissues of LPS-exposed mice, MGO treatment significantly increased the immunostaining and mRNA expression of RAGE, and the ROS levels. Serum MGO concentration achieved after 12-week intake was 9.2-fold higher than control mice, which was normalized by metformin treatment. Metformin also reduced the inflammatory markers in response to MGO.

Conclusion

MGO intake potentiates the LPS-induced ALI, increases RAGE expression and ROS generation, which is normalized by metformin. MGO scavengers may be a good adjuvant therapy to reduce ALI in patients with cardiometabolic diseases.

Metformin abrogates the voiding dysfunction induced by prolonged methylglyoxal intake

Methylglyoxal (MGO) is a reactive carbonyl species found at high levels in blood of diabetic patients. The anti-hyperglycemic drug metformin can scavenger MGO and reduce the formation of advanced glycation end products (AGEs). Here, we aimed to investigate if MGO-induced bladder dysfunction can be reversed by metformin. Male C57/BL6 mice received 0.5% MGO in drinking water for 12 weeks, and metformin (300 mg/kg, daily gavage) was given in the last two weeks. The bladder functions were evaluated by performing voiding behavior assays, cystometry and in vitro bladder contractions. MGO intake markedly elevated the levels of MGO and fluorescent AGEs in serum and reduced the mRNA expression and activity of glyoxalase (Glo1) in bladder tissues. Glucose levels were unaffected among groups. MGO intake also increased the urothelium thickness and collagen content of the bladder. Void spot assays in conscious mice revealed an increased void volume in MGO group. The cystometric assays in anesthetized mice revealed increases of basal pressure, non-voiding contractions frequency, bladder capacity, inter-micturition pressure and residual volume, which were accompanied by reduced voiding efficiency in MGO group. In vitro bladder contractions to carbachol, α,β-methylene ATP and electrical-field stimulation were significantly greater in MGO group. Metformin normalized the changes of MGO and AGEs levels, Glo1 expression and activity, urothelium thickness and collagen content. The MGO-induced voiding dysfunction were all restored by metformin treatment. Our findings strongly suggest that the amelioration of MGO-induced voiding dysfunction by metformin relies on its ability to scavenger MGO, preventing its accumulation in blood.

Impact of Albendazole on Cytokine and Chemokine Response Profiles in Echinococcus multilocularis-Inoculated Mice

Objective

Alveolar echinococcosis (AE) is a zoonosis caused by the larval stage of the metacestode Echinococcosis multilocularis with a tumor-like behavior in the targeted organ, especially in the liver. Surgery with albendazole is first-line modality for AE. Drug discontinuation is usually based upon the parasitic viability shown by the positron emission tomography (PET) scan. However, as a demanding and expensive method, it is not widely practiced in majority of the endemic regions. Further understanding on the cytokine and chemokine response profiles in AE patients may provide an interesting insight for potential markers in viability assessment.

Methods

Mice were inoculated with Echinococcus multilocularis intrahepatically to develop the hepatic AE murine model. Oral albendazole administration was then applied for three months after the first inoculation, and peripheral and regional immune cells including type 1 T helper cells (Th), Th2, Th17, regulatory T (Treg) cells, related cytokines, and chemokines were examined.

Results

The hepatic AE lesion was confirmed by ultrasound examination resulting in a successful rate of 70%. Among the 17 cytokines and chemokines detected, plasma levels of IL-23 were significantly higher in E. multilocularis-infected mice when compared to the control group; furthermore, more obvious increasing levels were found after albendazole treatment (p < 0.05). All chemokine levels other than eotaxin and MCP-3 were slightly higher in E. multilocularis-infected mice compared to the control group (p > 0.05). Eotaxin levels were significantly decreased in mice with E. multilocularis infection followed by albendazole treatment (p < 0.05). Both IL-17A and IL-23 expressions in hepatic AE lesions were significantly higher and related with disease activity.

Conclusion

Albendazole administration influenced the balance of immune response and promotes the secretion of proinflammatory factors which is beneficial to parasite clearance. IL-23 seems to be associated with the successful albendazole treatment in mice with E. multilocularis infection; such a change could be translated into clinical application in the near future.

Callicarpa japonica Thunb. ameliorates allergic airway inflammation by suppressing NF-κB activation and upregulating HO-1 expression

ETHNOPHARMACOLOGICAL RELEVANCE

Callicarpa japonica Thunb., as an herbal medicine has been used for the treatment of inflammatory diseases in China and Korea.

MATERIALS AND METHODS

Ultra performance liquid chromatography-photodiode array-quadrupole time-of-flight mass spectrometer (UPLC-PDA-QTof MS) was used to detect the major phenylethanoid glycosides in the C. japonica extract. BALB/c mice were intraperitoneally sensitized by ovalbumin (OVA) (on days 0 and 7) and challenged by OVA aerosol (on days 11-13) to induce airway inflammatory response. The mice were also administered with C. japonica Thunb. (CJT) (20 and 40 mg/kg Per oral) on days 9-13. CJT pretreatment was conducted in lipopolysaccharide (LPS)-stimulated RAW264.7 or phorbol 12-myristate 13-acetate (PMA)-stimulated A549 cells.

RESULTS

CJT administration significantly reduced the secretion of Th2 cytokines, TNF-α, IL-6, immunoglobulin E (IgE) and histamine, and the recruitment of eosinophils in an OVA-exposed mice. In histological analyses, the amelioration of inflammatory cell influx and mucus secretion were observed with CJT. The OVA-induced airway hyperresponsiveness (AHR), iNOS expression and NF-κB activation were effectively suppressed by CJT administration. In addition, CJT led to the upregulation of HO-1 expression. In an in vitro study, CJT pretreatment suppressed the LPS-induced TNF-α secretion in RAW264.7 cells and attenuated the PMA-induced IL-6, IL-8 and MCP-1 secretion in A549 cells. These effects were accompanied by downregulated NF-κB phosphorylation and by upregulated HO-1 expression.

CONCLUSION

These results suggested that CJT has protective activity against OVA-induced airway inflammation via downregulation of NF-κB activation and upregulation of HO-1, suggesting that CJT has preventive potential for the development of allergic asthma.

Alterations in Oral-Nasal-Pharyngeal Microbiota and Salivary Proteins in Mouth-Breathing Children

Mouth breathing induces a series of diseases, while the influence on microbiota of oral cavity and salivary proteins remains unknown. In this study, for the first time, profiles of oral-nasal-pharyngeal microbiota among mouth-breathing children (MB group, n = 10) were compared with paired nose-breathing children (NB group, n = 10) using 16S ribosomal DNA (rDNA) (V3-V4 region) high-throughput sequencing. The differentially expressed salivary proteins were revealed using label-free quantification (LFQ) method, and their associations with bacterial abundance were measured by canonical correspondence analysis (CCA). The overall bacterial profiles differed between the two groups, and the differences were related to the duration of mouth breathing. The diversity of oral-pharyngeal microbiota was significantly higher, and the nasal-pharyngeal species tended to be consistent (unweighted UniFrac, p = 0.38) in the MB group. Opportunistic pathogens were higher in relative abundance as follows: Acinetobacter in the anterior supragingival plaque, Neisseria in unstimulated saliva, Streptococcus pneumoniae in the pharynx, and Stenotrophomonas in the nostrils. The expression level of oxidative-stress-related salivary proteins (lactoylglutathione lyase and peroxiredoxin-5) were upregulated, while immune-related proteins (integrin alpha-M and proteasome subunit alpha type-1) were downregulated in MB group. The differentially expressed proteins were associated with specific bacteria, indicating their potentials as candidate biomarkers for the diagnosis, putatively early intervention, and therapeutic target of mouth breathing. This study showed that mouth breathing influences the oral-nasal-pharyngeal microbiota and enriches certain pathogens, accompanied with the alterations in the salivary environment. Further research on the pathological mechanisms and dynamic changes in longitudinal studies are warranted.