New and Interesting Benefits with New Molecules in Obesity and Type 2 Diabetes

2.1 Genetic and epigenetic influences

Recent studies have reinforced the significant role of genetics in obesity. Monogenic forms, resulting from single-gene mutations, and polygenic obesity, involving multiple genetic variants, contribute to individual susceptibility [1, 2]. Epigenetic modifications, influenced by environmental factors, further modulate gene expression related to adiposity and metabolic regulation [3, 4]. These insights underscore the intricate interplay between genetic predisposition and environmental exposures in obesity development [5].

2.2 Adipose tissue dysfunction and inflammation

Adipose tissue is now recognized as an active endocrine organ. In obesity, adipocyte hypertrophy and hyperplasia lead to hypoxia and subsequent inflammation [7, 8]. This state is characterized by increased infiltration of immune cells, particularly macrophages, which shift from an anti-inflammatory (M2) to a pro-inflammatory (M1) phenotype. The resulting chronic low-grade inflammation disrupts adipokine secretion, notably decreasing adiponectin and increasing leptin levels, contributing to systemic insulin resistance and metabolic dysregulation [9, 10].

2.3 Neuroendocrine regulation and appetite control

The central nervous system, especially the hypothalamus, plays a pivotal role in energy homeostasis. Recent research has elucidated how dysregulation in neuroendocrine pathways affects appetite and satiety signals [10, 11]. Alterations in hormones such as ghrelin, peptide YY, and glucagon-like peptide-1 (GLP-1) have been implicated in disrupted hunger cues, promoting excessive caloric intake and weight gain [12, 13, 14].

2.4 Gut microbiota and metabolic interactions

Advancements in metagenomics have highlighted the gut microbiota’s influence on obesity. Dysbiosis, or microbial imbalance, affects energy harvest from the diet and modulates inflammatory pathways. Specific microbial profiles have been associated with increased adiposity, suggesting that targeting the microbiome could offer novel therapeutic avenues for obesity management [13, 14].

2.5 Insulin resistance and metabolic complications

Obesity-induced inflammation and adipokine imbalance contribute to the development of insulin resistance. This condition impairs glucose uptake in peripheral tissues, elevating blood glucose levels and increasing the risk of type 2 diabetes mellitus (T2DM) [6, 7]. Understanding the molecular mechanisms linking obesity to insulin resistance is essential for developing targeted treatments to mitigate associated metabolic complications [9, 10].

2.6 Environmental and lifestyle factors

Beyond biological mechanisms, environmental and lifestyle factors significantly influence obesity prevalence. Sedentary behavior, high-calorie diets, and socio-economic determinants interact with genetic predispositions, exacerbating weight gain [3, 12]. Public health strategies focusing on lifestyle modifications remain critical components in addressing the obesity epidemic (Figure 2) [15].

2.7 Therapeutic implications and future directions

The deepening understanding of obesity’s pathophysiology has paved the way for innovative therapeutic approaches. Pharmacological agents targeting specific pathways, such as GLP-1 receptor agonists, have shown promise in weight management [16, 17]. Additionally, personalized medicine, considering individual genetic and microbiome profiles, holds potential for more effective interventions. Ongoing research is essential to translate these insights into clinical practice, aiming to curb the global obesity crisis [18, 19, 20, 21, 22, 23], in conclusion, the past two years have yielded significant insights into the multifaceted pathophysiology of obesity. Integrating genetic, inflammatory, neuroendocrine, and environmental perspectives is essential for developing comprehensive strategies to combat this pervasive health issue. Continued interdisciplinary research and public health initiatives are imperative to address the complexities of obesity and its associated comorbidities [9, 13].

3.1 GLP-1 receptor agonists

GLP-1 RAs mimic the incretin hormone GLP-1, enhancing insulin secretion, suppressing glucagon release, delaying gastric emptying, and promoting satiety. These actions collectively improve glycemic control while addressing obesity-related complications in T2DM. Semaglutide, liraglutide, and dulaglutide are among the most studied GLP-1 RAs, demonstrating significant reductions in HbA1c and body weight in clinical trials [25, 26, 27]. Furthermore, GLP-1 RAs have shown cardiovascular protective effects, reducing the risk of major adverse cardiovascular events (MACE) in high-risk patients [28].

On the other hand, recent research has also explored higher doses and innovative delivery methods, such as oral semaglutide, to enhance patient adherence [28, 29, 30]. These advancements further cement the role of GLP-1 RAs as cornerstone therapies for T2DM management.

3.2 GIP receptor agonists

Glucose insulinotrophic peptide (GIP), another incretin hormone, stimulates insulin secretion in a glucose-dependent manner. However, its insulinotropic effect is diminished in individuals with T2DM. Novel therapies targeting GIP receptors aim to restore its regulatory role in glucose homeostasis. Studies have revealed that GIP can enhance β-cell function, particularly when combined with GLP-1 receptor activation, creating synergistic effects [29].

Dual GLP-1/GIP receptor agonists, such as tirzepatide, have emerged as groundbreaking therapies. Tirzepatide has demonstrated superior efficacy compared to GLP-1 RAs alone, achieving unprecedented reductions in HbA1c and body weight while maintaining a favorable safety profile [30].

3.3 Glucagon receptor agonists

While glucagon traditionally plays a counter-regulatory role by increasing hepatic glucose production, recent studies have identified its potential in energy expenditure and lipid metabolism. Dual GLP-1/glucagon receptor agonists, such as cotadutide, exploit these properties, combining glucagon’s lipolytic effects with GLP-1-mediated glycemic control [31, 32]. This dual mechanism offers a promising approach to managing both T2DM and obesity.

Furthermore, triagonists targeting GLP-1, GIP, and glucagon receptors are under investigation, aiming to maximize metabolic benefits. Early trials have shown significant improvements in weight loss and glycemic control, suggesting a transformative potential in T2DM treatment [30].

3.4 Therapeutic implications and future directions

The integration of incretin-based therapies into clinical practice has redefined the treatment paradigm for T2DM. GLP-1, GIP, and glucagon receptor agonists not only improve glycemic control but also address obesity and cardiovascular risk factors, critical components of the T2DM disease burden [31].

Future research is focused on optimizing these therapies through dose refinement, combination regimens, and personalized medicine approaches. Additionally, understanding the long-term effects and safety profiles of these agents remains essential to their widespread adoption.

4.1 Mechanism of action

GLP-1 RAs target the GLP-1 receptor, a member of the G-protein-coupled receptor family, predominantly expressed in pancreatic β-cells, the gastrointestinal tract, and the central nervous system. Activation of this receptor leads to increased intracellular cyclic AMP (cAMP), enhancing glucose-stimulated insulin secretion and suppressing glucagon release in a glucose-dependent manner. These effects improve glycemic control while minimizing the risk of hypoglycemia [32].

In addition to their pancreatic effects, GLP-1 RAs delay gastric emptying and act on hypothalamic centers to reduce appetite, contributing to weight loss. Their cardiovascular benefits, including improved endothelial function and anti-inflammatory effects, further support their role in reducing cardiovascular risks in T2DM patients [33].

4.2 Pharmacokinetics and pharmacodynamics

GLP-1 RAs vary in their pharmacokinetic properties, influencing dosing regimens and patient adherence. Short-acting agents, such as exenatide twice daily, predominantly target postprandial glucose levels due to transient receptor activation.

Long-acting agents, including liraglutide, dulaglutide, and semaglutide, provide sustained receptor activation, effectively lowering fasting and postprandial glucose levels [30].

4.3 Pharmacology of the most important GLP-1 RAs

Exenatide: A synthetic version of exendin-4 with a half-life of 2–4 hours, requiring twice-daily administration. It was the first GLP-1 RA introduced and primarily reduces postprandial glucose excursions [34].

Liraglutide: A long-acting analog with a half-life of approximately 13 hours, requiring once-daily administration. It has demonstrated cardiovascular benefits in addition to glycemic control [35].

Dulaglutide: Engineered as a fusion protein with a half-life of 5 days, allowing for once-weekly dosing. Its molecular structure reduces renal clearance and immunogenicity.

Semaglutide: Available as a weekly injection or daily oral formulation. It has shown superior efficacy in weight reduction and HbA1c control compared to other GLP-1 Ras.

Albiglutide and Lixisenatide: These agents provide alternative options with varying pharmacodynamic profiles, targeting specific patient populations [36].

4.4 Clinical efficacy

Head-to-head trials consistently demonstrate significant reductions in HbA1c (0.5–1.5%) and body weight (3–6 kg) across GLP-1 RAs, with semaglutide often showing the greatest efficacy. Cardiovascular outcome trials (CVOTs) such as LEADER and SUSTAIN-6 highlight their role in reducing MACE [35, 36].

4.5 Safety and tolerability

Gastrointestinal side effects, including nausea and vomiting, are the most common adverse events, often transient and dose-dependent. Rare but serious concerns, such as pancreatitis and gallbladder disease, require further investigation. Their favorable risk-benefit profile, however, supports widespread use [33].

4.6 Emerging trends

The development of dual and triple agonists targeting GLP-1, GIP, and glucagon receptors, such as tirzepatide, represents an exciting frontier. These agents aim to amplify metabolic benefits, achieving superior glycemic control and weight loss [37]. In conclusion, GLP-1 receptor agonists are transformative in managing T2DM and obesity. Their diverse pharmacological profiles, robust efficacy, and safety establish them as essential therapies. Ongoing innovation, particularly with multi-agonist therapies, promises to further enhance their clinical utility.

5.1 Mechanism of action

GLP-1 and GIP are incretin hormones that play crucial roles in glucose homeostasis. GLP-1 enhances glucose-dependent insulin secretion, suppresses glucagon release, delays gastric emptying, and promotes satiety. GIP also stimulates insulin secretion in a glucose-dependent manner but has a less pronounced effect on glucagon suppression and gastric emptying. Dual agonists activate both receptors, potentially amplifying these beneficial effects. Notably, the simultaneous activation of GLP-1 and GIP receptors may lead to improved insulin sensitivity and more substantial reductions in body weight compared to GLP-1 receptor agonists alone.

5.2 Pharmacokinetics and pharmacodynamics

Tirzepatide is the most advanced dual GLP-1/GIP receptor agonist, administered as a once-weekly subcutaneous injection. It exhibits a half-life conducive to weekly dosing, facilitating patient adherence. Clinical trials have demonstrated that tirzepatide significantly reduces HbA1c levels and body weight in patients with T2DM. The pharmacodynamic profile of tirzepatide indicates enhanced insulin secretion, improved insulin sensitivity, and reduced food intake, contributing to its efficacy in glycemic control and weight management [38].

5.3 Clinical efficacy

In clinical studies, tirzepatide has shown superior efficacy in lowering HbA1c and body weight compared to existing GLP-1 receptor agonists. For instance, patients treated with tirzepatide achieved mean HbA1c reductions exceeding 2% and weight loss up to 12 kg over 40 weeks. These outcomes suggest that dual agonism may offer advantages over selective GLP-1 receptor activation, particularly in patients requiring substantial weight reduction alongside glycemic control [39, 40].

5.4 Safety and tolerability

The safety profile of dual GLP-1/GIP receptor agonists is generally consistent with that of GLP-1 receptor agonists, with gastrointestinal adverse events such as nausea, vomiting, and diarrhea being the most commonly reported side effects. These symptoms are typically transient and dose-dependent. Ongoing studies are assessing the long-term safety of these agents, including their cardiovascular outcomes and potential risks associated with chronic use [41, 42, 43, 44, 45].

5.5 Emerging therapies

Beyond tirzepatide, other dual agonists are under investigation. For example, CT-388 is a novel dual GLP-1 and GIP receptor modulator designed for once-weekly subcutaneous administration. Early-phase clinical trials have reported significant weight loss with CT-388, indicating its potential as an effective treatment for obesity and T2DM. In conclusion, Dual GLP-1 and GIP receptor agonists represent a significant advancement in the pharmacotherapy of T2DM and obesity. By leveraging the complementary actions of GLP-1 and GIP, these agents offer enhanced glycemic control and weight reduction compared to existing therapies. Ongoing research will further elucidate their long-term efficacy and safety profiles, potentially expanding their therapeutic applications [46].

6.1 Mechanism of action

Triple agonists simultaneously activate GLP-1, GIP, and glucagon receptors, leading to a multifaceted metabolic response. Activation of GLP-1 receptors enhances insulin secretion, inhibits glucagon release, slows gastric emptying, and promotes satiety. GIP receptor activation further stimulates insulin secretion and may have direct effects on adipose tissue, enhancing lipid metabolism. Glucagon receptor activation increases energy expenditure by promoting hepatic glucose production and lipolysis. The combined activation of these receptors results in improved glycemic control and significant weight reduction.

7.1 Pharmacokinetics and pharmacodynamics

Triple agonists are typically administered via subcutaneous injection. The pharmacokinetic profiles are designed to allow for once-weekly dosing, enhancing patient compliance. These agents exhibit a balanced activity across GLP-1, GIP, and glucagon receptors, ensuring a coordinated metabolic response. The pharmacodynamic effects include enhanced insulin secretion, reduced appetite, increased energy expenditure, and improved lipid metabolism, contributing to their efficacy in obesity and T2DM treatment [48].

7.2 Safety and tolerability

The safety profile of triple agonists is generally consistent with that of GLP-1 receptor agonists. Common adverse events include gastrointestinal symptoms such as nausea, vomiting, and diarrhea, which are typically transient and diminish over time. No significant safety concerns have been reported in clinical trials to date; however, long-term studies are necessary to fully assess their safety profile. In conclusion, triple-action agonists targeting GLP-1, GIP, and glucagon receptors represent a novel and promising approach in the treatment of obesity and T2DM. The synergistic effects of these hormones offer significant advantages in terms of weight loss and glycemic control. Ongoing clinical trials and future research will further elucidate their therapeutic potential and long-term safety [49, 50].

8.1 Cardiovascular benefits

GLP-1 receptor agonists have demonstrated cardioprotective properties in both diabetic and non-diabetic populations. These effects include reduced MACE, improved endothelial function, and decreased arterial stiffness. For example, the LEADER trial with liraglutide showed a 13% reduction in MACE among high-risk patients with T2DM [51]. Similarly, tirzepatide, a dual GIP and GLP-1 receptor agonist, has shown reductions in cardiovascular risk biomarkers, such as triglycerides and C-reactive protein, further highlighting its cardiometabolic benefit [52].

8.2 Anti-inflammatory and immune modulation

Chronic inflammation is a hallmark of obesity and T2DM, contributing to insulin resistance and cardiovascular disease. GLP-1 receptor activation has been linked to reduced levels of inflammatory markers such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α). Moreover, dual and triple agonists that incorporate GIP and glucagon receptor targeting have shown enhanced anti-inflammatory effects. For instance, tirzepatide has demonstrated superior reductions in inflammatory markers compared to GLP-1 receptor agonists alone, indicating a synergistic interaction between GIP and GLP-1 pathways [53, 54].

8.3 Effects on energy expenditure and fat metabolism

Glucagon receptor agonists play a pivotal role in increasing energy expenditure and promoting lipolysis. This complements the satiety-inducing and appetite-suppressing effects of GLP-1 and GIP receptor activation. Triple agonists such as retatrutide have shown unprecedented reductions in body weight in clinical trials, with up to 24% reductions observed in phase 2 studies. This effect is attributed to a balanced stimulation of energy expenditure, appetite suppression, and enhanced lipid metabolism [55, 56].

8.4 Renal protection

Emerging evidence suggests that GLP-1 receptor agonists may confer renoprotective effects by reducing albuminuria and preserving glomerular filtration rates (GFR). These benefits are thought to be mediated through improvements in hemodynamic regulation, reductions in oxidative stress, and anti-inflammatory actions. Dual agonists, such as tirzepatide, may amplify these effects, although long-term studies are needed to confirm these findings [57, 58, 59].

8.5 Neuroprotective effects

GLP-1 receptor agonists also exhibit potential neuroprotective benefits, including improved cognitive function and reduced neuroinflammation. Preclinical studies indicate that GLP-1 receptor activation can mitigate amyloid-beta accumulation and improve synaptic plasticity, suggesting a role in delaying neurodegenerative diseases such as Alzheimer’s disease. While data on dual and triple agonists are limited, their broader metabolic effects may enhance neuroprotection (Figure 3) [60, 61].