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

Is Methylglyoxal a Potential Biomarker for the Warburg Effect Induced by the Lipopolysaccharide Neuroinflammation Model?

Methylglyoxal (MG) is considered a classical biomarker of diabetes mellitus and its comorbidities. However, a role for this compound in exacerbated immune responses, such as septicemia, is being increasingly observed and requires clarification, particularly in the context of neuroinflammatory responses. Herein, we used two different approaches (in vivo and acute hippocampal slice models) to investigate MG as a biomarker of neuroinflammation and the neuroimmunometabolic shift to glycolysis in lipopolysaccharide (LPS) inflammation models. Our data reinforce the hypothesis that LPS-induced neuroinflammation stimulates the cerebral innate immune response by increasing IL-1β, a classical pro-inflammatory cytokine, and the astrocyte reactive response, via elevating S100B secretion and GFAP levels. Acute neuroinflammation promotes an early neuroimmunometabolic shift to glycolysis by elevating glucose uptake, lactate release, PFK1, and PK activities. We observed high serum and cerebral MG levels, in association with a reduction in glyoxalase 1 detoxification activity, and a close correlation between serum and hippocampus MG levels with the systemic and neuroinflammatory responses to LPS. Findings strongly suggest a role for MG in immune responses.

Effects of metformin on cancers in experimental and clinical studies: Focusing on autophagy and AMPK/mTOR signaling pathways

Metformin (MET) is a preferred drug for the treatment of type 2 diabetes mellitus. Recent studies show that apart from its blood glucose-lowering effects, it also inhibits the development of various tumours, by inducing autophagy. Various studies have confirmed the inhibitory effects of MET on cancer cell lines' propagation, migration, and invasion. The objective of the study was to comprehensively review the potential of MET as an anticancer agent, particularly focusing on its ability to induce autophagy and inhibit the development and progression of various tumors. The study aimed to explore the inhibitory effects of MET on cancer cell proliferation, migration, and invasion, and its impact on key signaling pathways such as adenosine monophosphate-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), and PI3K. This review noted that MET exerts its anticancer effects by regulating key signalling pathways such as phosphoinositide 3-kinase (PI3K), LC3-I and LC3-II, Beclin-1, p53, and the autophagy-related gene (ATG), inhibiting the mTOR protein, downregulating the expression of p62/SQSTM1, and blockage of the cell cycle at the G0/G1. Moreover, MET can stimulate autophagy through pathways associated with the 5' AMPK, thereby inhibiting he development and progression of various human cancers, including hepatocellular carcinoma, prostate cancer, pancreatic cancer, osteosarcoma, myeloma, and non-small cell lung cancer. In summary, this detailed review provides a framework for further investigations that may appraise the autophagy-induced anticancer potential of MET and its repurposing for cancer treatment.

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.

TRPA1 channel mediates methylglyoxal-induced mouse bladder dysfunction

Introduction: The transient receptor potential ankyrin 1 channel (TRPA1) is expressed in urothelial cells and bladder nerve endings. Hyperglycemia in diabetic individuals induces accumulation of the highly reactive dicarbonyl compound methylglyoxal (MGO), which modulates TRPA1 activity. Long-term oral intake of MGO causes mouse bladder dysfunction. We hypothesized that TRPA1 takes part in the machinery that leads to MGO-induced bladder dysfunction. Therefore, we evaluated TRPA1 expression in the bladder and the effects of 1 h-intravesical infusion of the selective TRPA1 blocker HC-030031 (1 nmol/min) on MGO-induced cystometric alterations. Methods: Five-week-old female C57BL/6 mice received 0.5% MGO in their drinking water for 12 weeks, whereas control mice received tap water alone. Results: Compared to the control group, the protein levels and immunostaining for the MGO-derived hydroimidazolone isomer MG-H1 was increased in bladders of the MGO group, as observed in urothelium and detrusor smooth muscle. TRPA1 protein expression was significantly higher in bladder tissues of MGO compared to control group with TRPA1 immunostaining both lamina propria and urothelium, but not the detrusor smooth muscle. Void spot assays in conscious mice revealed an overactive bladder phenotype in MGO-treated mice characterized by increased number of voids and reduced volume per void. Filling cystometry in anaesthetized animals revealed an increased voiding frequency, reduced bladder capacity, and reduced voided volume in MGO compared to vehicle group, which were all reversed by HC-030031 infusion. Conclusion: TRPA1 activation is implicated in MGO-induced mouse overactive bladder. TRPA1 blockers may be useful to treat diabetic bladder dysfunction in individuals with high MGO levels.

Effects of metformin on acute respiratory distress syndrome in preclinical studies: a systematic review and meta-analysis

Introduction: In this study, we conducted a systematic review and meta-analysis to judge the effects of metformin on acute respiratory distress syndrome (ARDS) in a comprehensive and quantitative manner. Methods: We included studies that tested the effects of metformin on ALI or ARDS in in vivo studies. We excluded literature from which data could not be extracted or obtained. Electronic search was conducted to retrieve relevant literature from public databases, including PubMed, Web of Science, Embase, Scopus, and the Cochrane Central Register of Controlled Trials (inception to July 2023). Moreover, ProQuest Dissertations and Theses Global, Google Scholar, and Baidu scholar were inquired. Retrieved literature was screened and evaluated by pairs of reviewers independently according to pre-stated criteria. The Systematic Review Center for Laboratory Animal Experimentation risk of bias tool was used to evaluate the methodological quality of eligible literature. No restriction was exerted on publication status or language. Results: Fifteen preclinical studies were analyzed in this meta-analysis. Pooled results showed metformin effectively decreased pulmonary wet-to-dry weight ratios [SMD = -2.67 (-3.53 to -1.81), I2 = 56.6%], protein content [SMD = -3.74 (-6.76 to -0.72), I2 = 86.7%] and neutrophils [SMD = -3.47 (-4.69 to -2.26), I2 = 0%] in BALF, pulmonary malondialdehyde [SMD = -1.98 (-3.77 to -0.20), I2 = 74.2%] and myeloperoxidase activity [SMD = -3.15 (-4.79 to -1.52), I2 = 74.5%], lung injury scores [SMD = -4.19 (-5.65 to -2.74), I2 = 69.1%], and mortality at 24 h [RR = 0.43 (0.24-0.76), I2 = 0%] as well as 48 and 72 h. Conclusion: Metformin inhibited pulmonary inflammation and oxidative stress and improved experimental lung injury and survival rates in animal models of ARDS. Results from randomized controlled trials are needed.

Metformin beyond an anti-diabetic agent: A comprehensive and mechanistic review on its effects against natural and chemical toxins

In addition to the anti-diabetic effect of metformin, a growing number of studies have shown that metformin has some exciting properties, such as anti-oxidative capabilities, anticancer, genomic stability, anti-inflammation, and anti-fibrosis, which have potent, that can treat other disorders other than diabetes mellitus. We aimed to describe and review the protective and antidotal efficacy of metformin against biologicals, chemicals, natural, medications, pesticides, and radiation-induced toxicities. A comprehensive search has been performed from Scopus, Web of Science, PubMed, and Google Scholar databases from inception to March 8, 2023. All in vitro, in vivo, and clinical studies were considered. Many studies suggest that metformin affects diseases other than diabetes. It is a radioprotective and chemoprotective drug that also affects viral and bacterial diseases. It can be used against inflammation-related and apoptosis-related abnormalities and against toxins to lower their effects. Besides lowering blood sugar, metformin can attenuate the effects of toxins on body weight, inflammation, apoptosis, necrosis, caspase-3 activation, cell viability and survival rate, reactive oxygen species (ROS), NF-κB, TNF-α, many interleukins, lipid profile, and many enzymes activity such as catalase and superoxide dismutase. It also can reduce the histopathological damages induced by many toxins on the kidneys, liver, and colon. However, clinical trials and human studies are needed before using metformin as a therapeutic agent against other diseases.

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.

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.