Metformin prevents airway hyperreactivity in rats with dietary obesity

Eosinophil biology from the standpoint of metabolism: implications for metabolic disorders and asthma

Eosinophils, recognized for their immune and remodeling functions and participation in allergic inflammation, have recently garnered attention due to their impact on host metabolism, especially in the regulation of adipose tissue. Eosinophils are now known for their role in adipocyte beiging, adipokine secretion, and adipose tissue inflammation. This intricate interaction involves complex immune and metabolic processes, carrying significant implications for systemic metabolic health. Importantly, the interplay between eosinophils and adipocytes is bidirectional, revealing the dynamic nature of the immune-metabolic axis in adipose tissue. While the homeostatic regulatory role of eosinophils in adipose tissue is appreciated, this relationship in the context of obesity or allergic inflammation is much less understood. Mechanistic details of eosinophil-adipose interactions, especially the direct regulation of adipocytes by eosinophils, are also lacking. Another poorly understood aspect is the metabolism of the eosinophils themselves, encompassing metabolic shifts during eosinophil subset transitions in different tissue microenvironments, along with potential effects of host metabolism on the programming of eosinophil hematopoiesis and the resulting plasticity. This review consolidates recent research in this emerging and fascinating frontier of eosinophil investigation, identifying unexplored areas and presenting innovative perspectives on eosinophil biology in the context of metabolic disorders and associated health conditions, including asthma.

Metformin use is associated with decreased asthma exacerbations in adolescents and young adults

RATIONALE

Metformin is a commonly used antidiabetes medication with suggested anti-inflammatory and antioxidative effects. Metformin use has been associated with lower risk of asthma exacerbations and hospitalizations in adults. Here, we aimed to evaluate how asthma exacerbation rates changed after adolescents and young adults were prescribed metformin, and to learn if those changes were related to metformin prescription adherence.

METHODS

Using secondary data of patients between 12 and 20 years old with asthma diagnosis and a metformin prescription from the Arkansas All Payers Claim Database and Arkansas School body mass index (BMI) database, we estimated the change in annualized asthma exacerbation rates after metformin prescription. We also evaluated the association of prescription adherence to the changes in those rates using univariate and multivariate regression models.

RESULTS

A total of 464 patients met inclusion criteria. Outpatient exacerbation rates decreased after metformin prescription (13.4% only before vs. 7.8% only after, p = .009), and the annualized rate decreased more after metformin prescription as adherence increased (rank r = -.165, p < .001). After adjusting for potential confounders-age, sex, BMI, and inhaled corticoid steroid use-the strength of the association was attenuated.

CONCLUSIONS

Asthma exacerbation rates decreased after metformin prescription, but a larger sample of patients who have experienced exacerbations and including patients with asthma who have not been prescribed metformin is needed to better know whether these decreases are driven by metformin use.

Obesity-Associated Non-T2 Mechanisms in Obese Asthmatic Individuals

Obesity and asthma are two common health issues that have shown increased prevalence in recent years and have become a significant socioeconomic burden worldwide. Obesity increases asthma incidence and severity. Obese asthmatic individuals often experience increased exacerbation rates, enhanced airway remodeling, and reduced response to standard corticosteroid therapy. Recent studies indicate that obesity-associated non-T2 factors such as mechanical stress, hyperinsulinemia, systemic inflammation, adipose tissue mediators, metabolic dysregulation, microbiome dysbiosis, and high-fat-diet are responsible for increased asthma symptoms and reduced therapeutic response in obese asthmatic individuals. This manuscript reviews the recent findings highlighting the role of obesity-associated factors that contribute to airway hyper-reactivity, airway inflammation and remodeling, and immune cell dysfunction, consequently contributing to worsening asthma symptoms. Furthermore, the review also discusses the possible future therapies that might play a role in reducing asthma symptoms by diminishing the impact of obesity-associated non-T2 factors.

Metformin regulates the effects of IR and IGF-1R methylation on mast cell activation and airway reactivity in diabetic rats with asthma through miR-152-3p/DNMT1 axis

BACKGROUND/AIM

Metformin is a drug for treating type 2 diabetes mellitus (T2DM). Recently, metformin has been shown to reduce the risks of asthma-associated outcomes and asthma deterioration, thereby holding promise as a superior medicine for diabetic patients with asthma. However, the mechanism by which metformin reduces diabetic asthma is yet to be clarified. This study aimed at ascertaining the downstream molecules underlying the effect of metformin on the activation of mast cells (MCs) and airway reactivity in a concomitant diabetic and asthmatic rat model.

METHODS

A T2DM model was induced utilizing a high-fat diet and streptozotocin. Then, 10% ovalbumin was utilized to stimulate asthma-like pathology in the T2DM rats. RBL-2H3 cells were induced by anti-dinitrophenyl-specific immunoglobulin E for constructing an in vitro model. Luciferase assay and RNA immunoprecipitation (IP) assay were conducted to identify the interaction between microRNA-152-3p (miR-152-3p) and DNA methyltransferase 1 (DNMT1), while chromatin IP to identify the binding of DNMT1 to insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF-1R) promoters. The effects of metformin on both pathological changes in vivo and biological behaviors of cells were evaluated. Using gain- and loss-of-function approaches, we assessed the role of the two interactions in the metformin-induced effect.

RESULTS

It was suggested that metformin could impede the MC activation and airway resistance in the concomitant diabetic and asthmatic rats. Additionally, metformin downregulated IR and IGF-1R through DNMT1-dependent methylation to repress MC activation and airway resistance. DNMT1 was testified to be a target gene of miR-152-3p. Furthermore, miR-152-3p-induced silencing of DNMT1 was blocked by metformin, hence restraining MC activation and airway resistance.

CONCLUSION

The findings cumulatively demonstrate that metformin downregulates IR/IGF-1R to block MC activation and airway resistance via impairing the binding affinity between miR-152-3p and DNMT1.

Maternal high-fat diet increases airway sensory innervation and reflex bronchoconstriction in adult offspring

Children born to obese mothers are prone to develop asthma and airway hyperresponsiveness, but the mechanisms behind this are unclear. Here we developed a mouse model of maternal diet-induced obesity that recapitulates metabolic abnormalities seen in humans born to obese mothers. Offspring of dams fed a high-fat diet (HFD) showed increased adiposity, hyperinsulinemia, and insulin resistance at 16 wk of age despite being fed only a regular diet (RD). Bronchoconstriction induced by inhaled 5-hydroxytriptamine was also significantly increased in offspring of HFD-fed versus RD-fed dams. Increased bronchoconstriction was blocked by vagotomy, indicating this reflex was mediated by airway nerves. Three-dimensional (3-D) confocal imaging of tracheas collected from 16-wk-old offspring showed that both epithelial sensory innervation and substance P expression were increased in the offspring of HFD-fed dams compared with offspring of RD-fed dams. For the first time, we show that maternal high-fat diet increases airway sensory innervation in offspring, leading to reflex airway hyperresponsiveness.NEW & NOTEWORTHY Our study reveals a novel potential mechanism, by which maternal high-fat diet increases the risk and severity of asthma in offspring. We found that exposure to maternal high-fat diet in mice leads to hyperinnervation of airway sensory nerves and increased reflex bronchoconstriction in offspring fed a regular diet only. These findings have important clinical implications and provide new insights into the pathophysiology of asthma, highlighting the need for preventive strategies in this patient population.

The function, mechanisms, and clinical applications of metformin: potential drug, unlimited potentials

Metformin has been used clinically for more than 60 years. As time goes by, more and more miraculous effects of metformin beyond the clinic have been discovered and discussed. In addition to the clinically approved hypoglycemic effect, it also has a positive metabolic regulation effect on the human body that cannot be ignored. Such as anti-cancer, anti-aging, brain repair, cardiovascular protection, gastrointestinal regulation, hair growth and inhibition of thyroid nodules, and other nonclinical effects. Metformin affects almost the entire body in the situation taking it over a long period, and the preventive effects of metformin in addition to treating diabetes are also beginning to be recommended in some guidelines. This review is mainly composed of four parts: the development history of metformin, the progress of clinical efficacy, the nonclinical efficacy of metformin, and the consideration and prospect of its application.

Insulin increases sensory nerve density and reflex bronchoconstriction in obese mice

Obesity-induced asthma responds poorly to all current pharmacological interventions, including steroids, suggesting that classic, eosinophilic inflammation is not a mechanism. Since insulin resistance and hyperinsulinemia are common in obese individuals and associated with increased risk of asthma, we used diet-induced obese mice to study how insulin induces airway hyperreactivity. Inhaled 5-HT or methacholine induced dose-dependent bronchoconstriction that was significantly potentiated in obese mice. Cutting the vagus nerves eliminated bronchoconstriction in both obese and nonobese animals, indicating that it was mediated by a neural reflex. There was significantly greater density of airway sensory nerves in obese compared with nonobese mice. Deleting insulin receptors on sensory nerves prevented the increase in sensory nerve density and prevented airway hyperreactivity in obese mice with hyperinsulinemia. Our data demonstrate that high levels of insulin drives obesity-induced airway hyperreactivity by increasing sensory innervation of the airways. Therefore, pharmacological interventions to control metabolic syndrome and limit reflex-mediated bronchoconstriction may be a more effective approach to reduce asthma exacerbations in obese and patients with asthma.

Metformin Alleviates Airway Hyperresponsiveness in a Mouse Model of Diet-Induced Obesity

Obese asthma is a unique phenotype of asthma characterized by non-allergic airway hyperresponsiveness (AHR) and inflammation which responds poorly to standard asthma therapy. Metformin is an oral hypoglycemic drug with insulin-sensitizing and anti-inflammatory properties. The objective of the current study was to test the effect of metformin on AHR in a mouse model of diet-induced obesity (DIO). We fed 12-week-old C57BL/6J DIO mice with a high fat diet for 8 weeks and treated them with either placebo (control, n = 10) or metformin (n = 10) added in drinking water (300 mg/kg/day) during the last 2 weeks of the experiment. We assessed AHR, metabolic profiles, and inflammatory markers after treatments. Metformin did not affect body weight or fasting blood glucose, but significantly reduced serum insulin (p = 0.0117). Metformin reduced AHR at 30 mg/ml of methacholine challenge (p = 0.0052) without affecting baseline airway resistance. Metformin did not affect circulating white blood cell counts or lung cytokine mRNA expression, but modestly decreased circulating platelet count. We conclude that metformin alleviated AHR in DIO mice. This finding suggests metformin has the potential to become an adjuvant pharmacological therapy in obese asthma.