Targeting negative energy balance with calorie restriction and mitochondrial uncoupling in db/db mice

Obesity and mitochondrial uncoupling - an opportunity for the carbon monoxide-based pharmacology of metabolic diseases

Obesity, a chronic and progressive disease with a complex etiology, remains a significant global health challenge. Despite advancements in lifestyle interventions, pharmacological therapies, and bariatric surgery, substantial barriers to effective and sustained obesity management persist. Resistance to weight loss and gradual weight regain are commonly reported, limiting the long-term success of both non-pharmacological and pharmacological strategies. A possible contributor is metabolic adaptation, a phenomenon characterized by reduced metabolic rate and energy expenditure following weight loss, which hinders therapeutic efficacy. To address these challenges, increasing attention has been directed toward strategies that counteract maladaptive mechanisms by modulating metabolic rate and enhancing energy expenditure. One promising approach involves mitochondrial uncoupling, where electron transport and oxygen consumption are disconnected from ATP synthesis, promoting energy dissipation. Preclinical studies have demonstrated the potential of various chemical compounds with uncoupling activity as anti-obesity agents. Additionally, carbon monoxide (CO) has emerged as a significant gaseous signaling molecule in human physiology, with anti-inflammatory, antioxidative, and cytoprotective properties. Advances in CO-based pharmacology have led to the development of controlled-release CO donors, enabling precise therapeutic application. Experimental studies suggest that CO modulates mitochondrial bioenergetics, induces mild mitochondrial uncoupling, and regulates mitochondrial biogenesis. By integrating these findings, this review uniquely connects scientific threads, offering a comprehensive synthesis of current knowledge while proposing innovative directions in mitochondrial, metabolic and CO-based pharmacological research. It highlights the potential of CO-based pharmacology to regulate metabolic rate, support weight loss, and address obesity-related dysfunctions, thus suggesting novel pathways for advancing obesity treatment.

Systematic Review and Meta-analysis of Randomized Clinical Trials Comparing Time-Restricted Eating With and Without Caloric Restriction for Weight Loss

CONTEXT

Although it is well established that caloric restriction (CR) is the primary driver of weight loss, circadian-driven metabolic benefits have been recognized as possibly enhancing the effects of CR. Time-restricted eating (TRE) has emerged as a promising approach in this context.

OBJECTIVE

We conducted a systematic review and meta-analysis to compare the effects of TRE with isocaloric diet controls (analysis 1) and non-isocaloric controls (analysis 2) on anthropometric and body-composition parameters in adults with overweight or obesity.

DATA SOURCES

A search was carried out in the Medline, LILACS, Embase, and CENTRAL databases using Medical Subject Heading (MeSH) and similar terms such as "Obesity," "Obesity, Abdominal," "Time-restricted eating," "Body weight," "Changes in body weight," and others.

DATA EXTRACTION

We included 30 studies involving a total of 1341 participants. Studies were screened based on titles and abstracts followed by full-text reading, and data were extracted from eligible studies using a pre-established form. All these steps were performed by 2 authors independently and blinded, with discrepancies resolved by a third author.

DATA ANALYSIS

The results of main findings revealed that, in studies using non-isocaloric controls, the TRE group showed significant reductions in body weight (BW) (mean difference [MD]: -2.82 kg; 95% CI: -3.49, -2.15), fat mass (FM) (MD: -1.36 kg; 95% CI: -2.09, -0.63), and fat-free mass (FFM) (MD: -0.86 kg; 95% CI: -1.23, -0.49). In studies that used isocaloric control strategies, the TRE group showed significant reductions in BW (MD: -1.46 kg; 95% CI: -2.65, -0.26), FM (MD: -1.50 kg; 95% CI: -2.77, -0.24), and FFM (MD: -0.41 kg; 95% CI: -0.79, -0. 03).

CONCLUSION

TRE yields favorable anthropometric and clinical outcomes, even when intake is isocaloric between the intervention and control groups. This result suggests that circadian effects may enhance the impact of CR on excess weight.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42022301594.

Integrative metabolism in MASLD and MASH: Pathophysiology and emerging mechanisms

The liver acts as a central metabolic hub, integrating signals from the gastrointestinal tract and adipose tissue to regulate carbohydrate, lipid, and amino acid metabolism. Gut-derived metabolites, such as acetate and ethanol and non-esterified fatty acids from white adipose tissue, influence hepatic processes, which rely on mitochondrial function to maintain systemic energy balance. Metabolic dysregulation caused by obesity, insulin resistance, and type 2 diabetes disrupts these pathways, leading to metabolic dysfunction-associated steatotic liver disease (MASLD) and steatohepatitis (MASH). In this review, we explore the metabolic fluxes within the gut-adipose tissue-liver axis, focusing on the pivotal role of de novo lipogenesis, dietary substrates like glucose and fructose, and changes in mitochondrial function during MASLD progression. We also highlight the contributions of white adipose tissue insulin resistance and impaired mitochondrial dynamics to hepatic lipid accumulation. Further understanding how the interplay between substrate flux from the gastro-intestinal tract integrates with adipose tissue and intersects with structural and functional alterations to liver mitochondria will be important to identify novel therapeutic targets and advance the treatment of MASLD and MASH.

Hyperglucagonemia and glucagon hypersecretion in early type 2 diabetes result from multifaceted dysregulation of pancreatic mouse α-cells

Hyperglucagonemia has been implicated in the pathogenesis of type 2 diabetes (T2D). In contrast to β-cells, studies on the function of the pancreatic α-cell in T2D are scarce. Consequently, the processes underlying hyperglucagonemia and α-cell dysfunction are largely unknown, limiting the appropriate design of specific pharmacological and therapeutic strategies. In the current study, we aimed to analyze the alterations of the pancreatic α-cell and its glucagon responses in diabetic db/db mice at early stages of the disease. In this context of glucose intolerance, hyperinsulinemia, and β-cell dysfunction, hyperglucagonemia was only present at fed conditions and was associated with insulin resistance. Yet, we found that the glucagon-to-insulin ratio in db/db mice did not change with fed or fasted states, further supporting that the metabolic regulation of glucagon release was impaired. Pancreatic β-cell dysfunction in db/db mice was manifested by increased basal secretion from isolated islets along with reduced insulin content. In contrast, α-cells from diabetic animals presented upregulated secretion and islet content of glucagon compared with controls. Electrophysiological analysis of dispersed α-cells revealed that altered secretion was not the result of impaired exocytosis. Instead, we found defective regulation of Ca2+ signaling by glucose. Besides these functional alterations, we also observed augmented α-cell mass in diabetic mice, which was accompanied by disrupted islet cytoarchitecture as well as increased α-cell size and number, without pieces of evidence of upregulated proliferation. Overall, these findings indicate that hyperglucagonemia in early T2D results from multifaceted α-cell deregulation in mice.

Biochemical basis and therapeutic potential of mitochondrial uncoupling in cardiometabolic syndrome

Mild uncoupling of oxidative phosphorylation is an intrinsic property of all mitochondria, allowing for adjustments in cellular energy metabolism to maintain metabolic homeostasis. Small molecule uncouplers have been extensively studied for their potential to increase metabolic rate, and recent research has focused on developing safe and effective mitochondrial uncoupling agents for the treatment of obesity and cardiometabolic syndrome (CMS). Here, we provide a brief overview of CMS and cover the recent mechanisms by which chemical uncouplers regulate CMS-associated risk-factors and comorbidities, including dyslipidemia, insulin resistance, steatotic liver disease, type 2 diabetes, and atherosclerosis. Additionally, we review the current landscape of uncoupling agents, focusing on repurposed FDA-approved drugs and compounds in advanced preclinical or early-stage clinical development. Lastly, we discuss recent molecular insights by which chemical uncouplers enhance cellular energy expenditure, highlighting their potential as a new addition to the current CMS drug landscape, and outline several limitations that need to be addressed before these agents can successfully be introduced into clinical practice.

Beneficial effects of MGL-3196 and BAM15 combination in a mouse model of fatty liver disease

BACKGROUND AND AIM

Metabolic dysfunction-associated steatohepatitis (MASH) is a metabolic disorder with limited treatment options. The thyroid hormone receptor (THR)-β agonist resmetirom/MGL-3196 (MGL) increases liver fat oxidation and has been approved for treating adult MASH. However, over 60% of patients receiving MGL treatment do not achieve MASH resolution. Therefore, we investigated the potential for combination therapy of MGL with the mitochondrial uncoupler BAM15 to improve fatty liver disease outcomes in the GAN mouse model of MASH.

METHODS

C57BL/6J male mice were fed GAN diet for 38 weeks before stratification and randomization to treatments including MGL, BAM15, MGL + BAM15, or no drug control for 8 weeks. Treatments were admixed in diet and mice were pair-fed to control for drug intake. Treatment effectiveness was assessed by body weight, body composition, energy expenditure, glucose tolerance, tissue lipid content, and histological analyses.

RESULTS

MGL + BAM15 treatment resulted in better efficacy versus GAN control mice than either monotherapy in the context of energy expenditure, liver fat loss, glucose control, and fatty liver disease activity score. Improvements in ALT, liver mass, and plasma cholesterol were primarily driven by MGL, while improvements in body fat were primarily driven by BAM15. No treatments altered liver fibrosis.

CONCLUSIONS

MGL + BAM15 treatment had overall better efficacy to improve metabolic outcomes in mice fed GAN diet than either monotherapy alone. These data warrant further investigation into combination therapies of THR-β agonists and mitochondrial uncouplers for the potential treatment of disorders related to fatty liver, obesity, and insulin resistance.

Liver-Selective Imidazolopyrazine Mitochondrial Uncoupler SHD865 Reverses Adiposity and Glucose Intolerance in Mice

Excess body fat is a risk factor for metabolic diseases and is a leading preventable cause of morbidity and mortality worldwide. There is a strong need to find new treatments that decrease the burden of obesity and lower the risk of obesity-related comorbidities, including cardiovascular disease and type 2 diabetes. Pharmacologic mitochondrial uncouplers represent a potential treatment for obesity through their ability to increase nutrient oxidation. Herein, we report the in vitro and in vivo characterization of compound SHD865, the first compound to be studied in vivo in a newly discovered class of imidazolopyrazine mitochondrial uncouplers. SHD865 is a derivative of the furazanopyrazine uncoupler BAM15. SHD865 is a milder mitochondrial uncoupler than BAM15 that results in a lower maximal respiration rate. In a mouse model of diet-induced adiposity, 6-week treatment with SHD865 completely restored normal body composition and glucose tolerance to levels like those of chow-fed controls, without altering food intake. SHD865 treatment also corrected liver steatosis and plasma hyperlipidemia to normal levels comparable with chow-fed controls. SHD865 has maximal oral bioavailability in rats and slow clearance in human microsomes and hepatocytes. Collectively, these data identify the potential of imidazolopyrazine mitochondrial uncouplers as drug candidates for the treatment of obesity-related disorders.

ARTICLE HIGHLIGHTS

Beneficial effects of simultaneously targeting calorie intake and calorie efficiency in diet-induced obese mice

Semaglutide is an anti-diabetes and weight loss drug that decreases food intake, slows gastric emptying, and increases insulin secretion. Patients begin treatment with low-dose semaglutide and increase dosage over time as efficacy plateaus. With increasing dosage, there is also greater incidence of gastrointestinal side effects. One reason for the plateau in semaglutide efficacy despite continued low food intake is due to compensatory actions whereby the body becomes more metabolically efficient to defend against further weight loss. Mitochondrial uncoupler drugs decrease metabolic efficiency, therefore we sought to investigate the combination therapy of semaglutide with the mitochondrial uncoupler BAM15 in diet-induced obese mice. Mice were fed high-fat western diet (WD) and stratified into six treatment groups including WD control, BAM15, low-dose semaglutide without or with BAM15, and high-dose semaglutide without or with BAM15. Combining BAM15 with either semaglutide dose decreased body fat and liver triglycerides, which was not achieved by any monotherapy, while high-dose semaglutide with BAM15 had the greatest effect on glucose homeostasis. This study demonstrates a novel approach to improve weight loss without loss of lean mass and improve glucose control by simultaneously targeting energy intake and energy efficiency. Such a combination may decrease the need for semaglutide dose escalation and hence minimize potential gastrointestinal side effects.

Supplementation with Jatobá-do-cerrado flour (Hymenaea stigonocarpa Mart.) decreases hypothalamic inflammation and improves obesity parameters in rats on a high-fat diet

To evaluate the impact of jatobá-do-cerrado flour on nutritional, inflammatory, and oxidative stress markers, an study was conducted using male Wistar rats. These animals were allocated into four groups: a standard diet (Control), a high-fat diet (HFD), a diet with jatobá-do-cerrado flour (JCF), and a combination of high-fat diet and jatobá-do-cerrado flour (HFD + JCF). Comprehensive evaluations included food intake, cytokine concentrations, and redox status indicators. HFD group exhibited increased caloric intake and fat mass, elevated circulating IL-6, and heightened lipid peroxidation markers. This group also showed increased hypothalamic concentrations of IL-6, TNFα, and lipid peroxidation. In contrast, the HFD + JCF group showed reduced caloric intake, fat mass, and improvements in redox balance and inflammatory markers both in the blood and hypothalamus. SUMMARY: In the current study, we evaluated the potential of Jatobá-do-cerrado flour in mitigating the effects of a high-fat diet in adult Wistar rats. The addition of fat to the animals' diet for 63 days induced obesity, dyslipidemia, as well as an increase in inflammatory and lipid peroxidation markers, both in the blood and hypothalamus. Conversely, supplementation with Jatobá-do-Cerrado flour showed anti-obesogenic effects and these may be associated with the reduction of inflammation and oxidative stress. Therefore, supplementation with this flour has the potential to be a functional food for the treatment or prevention of obesity.

BAM15 as a mitochondrial uncoupler: a promising therapeutic agent for diverse diseases

Subcellular organelles dysfunction is implicated in various diseases, including metabolic diseases, neurodegenerative diseases, cancer, and cardiovascular diseases. BAM15, a selective mitochondrial uncoupler, has emerged as a promising therapeutic agent due to its ability to enhance mitochondrial respiration and metabolic flexibility. By disrupting the coupling between electron transport and ATP synthesis, BAM15 dissipates the proton gradient, leading to increased mitochondrial respiration and energy expenditure. This review provides a comprehensive overview of BAM15, including its mechanism of action and potential therapeutic applications in diverse disease contexts. BAM15 has shown promise in obesity by increasing energy expenditure and reducing fat accumulation. In diabetes, it improves glycemic control and reverses insulin resistance. Additionally, BAM15 has potential in non-alcoholic fatty liver disease, sepsis, and cardiovascular diseases by mitigating oxidative stress, modulating inflammatory responses, and promoting cardioprotection. The safety profile of BAM15 is encouraging, with minimal adverse effects and remarkable tolerability. However, challenges such as its high lipophilicity and the need for alternative delivery methods need to be addressed. Further research is necessary to fully understand the therapeutic potential of BAM15 and optimize its application in clinical settings.