Review Article: GLP-1 Receptor Agonists and Glucagon/GIP/GLP-1 Receptor Dual or Triple Agonists—Mechanism of Action and Emerging Therapeutic Landscape in MASLD

Abstract

Background:

Metabolic dysfunction-associated steatotic liver disease (MASLD) is primarily managed through diet and lifestyle modifications. However, these behavioural interventions alone may not achieve disease regression or remission, and maintaining long-term adherence is challenging. Incretin mimetics and other gastrointestinal hormones targeting the pleiotropic pathophysiological pathways underlying MASLD have now emerged as promising disease-modifying therapies.

Aims:

This is a comprehensive review summarising the role of glucagon-like peptide-1 (GLP-1) receptor agonists and glucagon/glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptor dual or triple agonists in the treatment of metabolic dysfunction-associated steatohepatitis (MASH).

Methods:

Only clinical trials with endpoints assessed by liver histology were included for a robust evaluation of therapeutic efficacy.

Results:

Recent evidence from phase 2 clinical trials for MASH demonstrated that pharmacological agents based on GLP-1 receptor agonism are effective in improving disease activity. Additionally, tirzepatide and survodutide showed potential clinical benefits in reducing fibrosis. Other cardiometabolic benefits observed include weight loss and improvements in glycaemic control and lipid profile. Adherence to treatment may be limited by gastrointestinal side effects, though they were found to be generally mild to moderate in severity. An interim analysis of the semaglutide phase 3 trial confirmed its efficacy in improving steatohepatitis and demonstrated its potential to improve fibrosis.

Conclusions:

GLP-1 receptor agonists, alone or in combination with GIP and/or glucagon receptor agonists, represent promising, effective pharmacotherapies for the treatment of MASLD/MASH. Larger and longer-duration clinical trials are needed to further evaluate the efficacy and safety of GIP receptor and glucagon receptor agonism.

1 |. Introduction

Metabolic dysfunction-associated steatotic liver disease (MASLD) is characterised by intrahepatic lipid accumulation combined with the presence of at least one cardiometabolic risk factor (e.g., overweight/obesity, type 2 diabetes, hypertension, and dyslipidaemia). MASLD can progress to advanced forms of liver disease due to inflammation and fibrosis, including metabolic dysfunction-associated steatohepatitis (MASH) and subsequently cirrhosis [1, 2]. Fibrosis stage has consistently emerged as the strongest predictor of major adverse liver outcomes (MALOs) and all-cause mortality among individuals with MASLD [2–4]. Additionally, increasing fibrosis severity is associated with a higher risk of major adverse cardiovascular events (MACEs), highlighting the inter-relatedness of clinical outcomes among MASLD and associated diseases [5].

MASLD and associated cardiometabolic diseases, mainly obesity and type 2 diabetes, share common pathogenesis in insulin resistance [6, 7]. Under normal physiologic conditions, the liver, skeletal muscle, and adipose tissue regulate metabolic homeostasis by storing glucose and triglycerides up to a certain individualised threshold [8]. Insulin plays a pivotal role in this regulation via insulin-sensitive tissues: promoting hepatic glycogen synthesis and inhibiting glycogenolysis; stimulating redistribution of glucose transporter type 4 to the skeletal muscle cell and adipocyte plasma membranes for glucose uptake and glycogen synthesis and triglyceride production, respectively, and storage; suppressing lipolysis in white adipose tissue (WAT), thereby decreasing circulating free fatty acids (FFAs) [7, 9, 10]. In MASLD, lipid storage in WAT in excess of the adiposity threshold contributes to adipocyte insulin resistance [8]. The consequences are an impairment in nutrient storage and an increase in lipolysis with systemic release of FFAs, cytokines, and extracellular vesicles directed to the liver despite circulating hyperinsulinemia [11]. Concurrently, in insulin-resistant states, increased circulating levels of insulin stimulate hepatic lipogenic enzymes and increase de novo hepatic lipogenesis, exacerbating hepatic steatosis, inflammation, and fibrosis [6, 12]. Hepatic steatosis further disrupts insulin-mediated suppression of hepatic gluconeogenesis, a process that accounts for 90% of endogenous glucose production [13, 14]. Glycaemic dysregulation, the loss of insulin-mediated paracrine regulation of glucagon, and decrements in glucose disposal into insulin-resistant skeletal muscle contribute to circulating hyperglycaemia and perpetuate insulin resistance in MASLD [6, 15]. Given the pathogenic association between insulin resistance and MASLD, and overlap with obesity and type 2 diabetes, glucose-lowering agents targeting insulin resistance, adipose tissue dysfunction, and the incretin system have been studied for treatment of MASLD/MASH [11]. Notably, the incretin effect—amplification of post-prandial insulin secretion—is attenuated in MASLD/MASH, type 2 diabetes, and obesity [16]. Hypothesised causes include: reduction in endogenous glucagon-like peptide-1 (GLP-1) levels in patients with MASLD and type 2 diabetes, reduction of glucose-dependent insulinotropic polypeptide (GIP) receptors or substrates involved in GIP signalling, and increased hepatic expression of dipeptidyl peptidase-4 (DPP-4), an enzyme that degrades GLP-1, diminishing systemic levels of active GLP-1 [16–18].

GLP-1 receptor agonists, alone or in combination with GIP and/or glucagon receptor agonists, have now emerged as promising pharmacotherapies for the treatment of metabolic disorders, including MASLD/MASH as well as obesity and type 2 diabetes. Importantly, recently published retrospective cohort studies using healthcare databases have suggested a potential beneficial effect of GLP-1 receptor agonists on long-term adverse liver outcomes, including cirrhosis, hepatic decompensation, and hepatocellular carcinoma [19, 20]. However, these findings require confirmation in randomised controlled trials. This narrative review summarises the role of incretin mimetics, individually or in combination therapy, in the treatment of MASLD/MASH—highlighting the pathophysiology and mechanisms of action, recent evidence from phase 2 and 3 MASH clinical trials, and clinical benefits.

2 |. Literature Search

Electronic databases, including PubMed and ClinicalTrials.gov, were searched up until June 2024 for relevant references. The primary search terms included: NAFLD or NASH or MASLD or MASH AND incretin therapies or GLP-1 receptor agonists or GIP receptor agonists or glucagon receptor agonists or dual agonism or triple agonism. Only clinical trials with endpoints assessed by liver histology were included for robust evaluation of therapeutic efficacy. References cited in reviewed articles were also searched. Data from reviewed articles were summarised in this narrative review.

3 |. Pathophysiology

Incretin hormones, including GLP-1 and GIP, are gut peptides released after meal intake and are responsible for as much as 70% of post-prandial glucose-dependent insulin secretion from endocrine pancreatic beta-cells and regulation of glucagon secretion to control glucose homeostasis [21–23]. Beyond their insulinotropic effects, incretin hormones have pivotal roles in tissues and organs expressing associated receptors, including the pancreas, adipose tissue, bone, heart and central nervous system [24, 25]. Overall, incretin hormones contribute to energy balance by suppressing glucagon secretion, delaying gastric emptying, and promoting satiety through direct actions on the central nervous system [24, 25].

3.1 |. GLP-1 Receptor Agonism

GLP-1 is primarily synthesised in the intestinal endocrine L-cells with the highest density in the distal ileum. GLP-1 is secreted at both a continuous basal rate during the fasting or inter-prandial state and in a bolus fashion during the postprandial state [23]. The apical surface of the L-cell is in contact with the gut lumen, and thus intestinal nutrients—fatty acids, glucose, and proteins and amino acids—stimulate GLP-1 secretion [26]. GLP-1 is also synthesised in the brain stem and transported to different regions of the central nervous system [27]. After entering the general circulation, GLP-1 binds to G-protein coupled receptors in pancreatic and extra-pancreatic tissues, including the enteric and central nervous systems, kidney, lung, heart, and endothelial and vascular smooth muscle cells [27]. The pathophysiology of GLP-1 receptor agonism is displayed in Figure 1.

FIGURE 1 |.

Pathophysiology of receptor glucagon-like peptide 1 agonism. Glucagon-like peptide-1 receptor agonism ameliorates MASLD/MASH at distinct points during pathogenesis. While the predominant actions of enhancing insulin sensitivity and weight loss result in a reduction of hepatic steatosis (green), certain activities mitigate inflammation (red) and fibrosis (blue). ECM = extra-cellular matrix, FFAs = free fatty acids, VLDL = very low-density lipoprotein. Created with BioRender.com.

3.1.1 |. Effects on Hepatic Metabolism

The primary mechanisms by which GLP-1 receptor agonists improve hepatic steatosis are linked to the reduction in food intake and body weight [27, 28]. However, GLP-1 also has tissue-specific actions that ameliorate the pathways by which caloric intake and insulin resistance promote the development of MASLD and progression to MASH [27].

In disordered energy homeostasis, circulating nutrient surplus and decreased adipose tissue storage cause the flux of FFAs to the liver, in turn leading to the development of hepatic steatosis [29]. GLP-1 acts via synergistic pathways to reduce liver fat content and inflammation: (1) potentiation of beta-cell insulin secretion, resulting in increased adipose tissue nutrient intake and buffering circulating FFAs away from hepatic storage; (2) inhibition of de novo lipogenesis—a major contributor to hepatic triglyceride accumulation—via downregulation of involved genes; (3) improvement in adipose tissue sensitivity to lipotoxic metabolites and pro-inflammatory mediators which reduces their circulating presence; (4) decrease in enterocyte chylomicron production and secretion responsible for direct transport of triglycerides to the liver; (5) reduction of hepatic very low-density lipoproteins (VLDL) production which transport triglycerides to other tissues [27, 29, 30]. These mechanisms contribute to the therapeutic benefits of GLP-1 based therapies in mitigating hepatic steatosis and improving overall lipid homeostasis [27, 29].

Glucose homeostasis is a parallel goal of GLP-1 receptor agonism [31]. Studies support the role of GLP-1 in paracrine regulation—increase in pancreatic insulin secretion and decrease in glucagon secretion leading to non-hepatic skeletal muscle glucose disposal (uptake) in the initial prandial state and increased hepatic glucose disposal in the postprandial state [32]. Increased insulin secretion leads to insulin-mediated suppression of hepatic glucose production [28, 29]. Central nervous system-mediated suppression of hepatic glucose production via GLP-1 circuits is noted in murine studies, but less certain in humans [27]. By inhibiting hepatic glucose production and promoting glucose uptake, GLP-1 receptor agonism counteracts dysregulated glucose metabolism—deterring insulin resistance in MASLD.

GLP-1 receptor agonists have demonstrated anti-inflammatory effects, impacting systemic and hepatic inflammation [27, 33]. Increased circulating levels of proinflammatory cytokines—TNF-alpha, IL-1 beta, and IL-6—notably impair insulin secretion and promote pancreatic beta-cell apoptosis in patients with type 2 diabetes [34]. In both animal models and clinical trials, treatments with incretin-mimetics attenuate the expression of these cytokines, resulting in reduced circulation of inflammatory markers and increased expression of anti-inflammatory mediators [34–36]. Clinical trials of GLP-1 receptor agonists in MASH have noted reduced levels of liver enzymes, markers of liver injury, and improved histologic markers of inflammation, although the precise anti-inflammatory mechanisms independent of concurrent improvements in metabolic parameters remain unclear [27, 30]. Proposed mechanisms include: (1) reduction in hepatic steatosis which counteracts lipotoxicity that triggers cell death; (2) GLP-1 induction of proteins regulating cell stress responses and apoptosis; (3) GLP-1 mediated reduction in hepatic macrophage infiltration [34, 35].

Thus, GLP-1 therapies promise anti-inflammatory benefit in dysregulated metabolic states otherwise marked by chronic inflammation.

Hepatic fibrosis is the primary determinant of clinical outcomes in patients with MASLD [37]. Hepatic fibrosis is characterised by the accumulation of the extracellular matrix (ECM)—a network of macromolecular proteins that under normal physiological conditions maintains tissue homeostasis, but in excess leads to fibrosis [38]. Hepatic fibrosis ultimately potentiates hepatocyte and overall liver dysfunction, but fibrosis is in principle reversible [27, 37, 38]. Although liraglutide administration in obese mice did not show significant histologic improvement in observed fibrosis scores, the study may highlight the biological basis of fibrosis regression, noting reduced expression of genes associated with ECM expansion (alpha-smooth muscle actin, hydroxyproline) and fibrosis [27, 39].

3.1.2 |. Effects on Extra-Hepatic Metabolism

GLP-1 receptors have broad distribution in extra-pancreatic tissues, accounting for the pleiotropic effects of GLP-1 receptor agonism in the treatment of MASLD [27, 40]. These effects primarily focus on mechanisms for weight loss [40]. GLP-1 acts in the central nervous system to encourage satiety and reduce food intake [24]. The nucleus of the solitary tract (NTS) located in the brainstem, regulates meal size and frequency by integrating neural signals via vagal afferents from the gastrointestinal tract that are stimulated by gastric stretch receptors and gut peptides such as cholecystokinin, ghrelin, and leptin (primary mechanism), gustatory input from the tongue, hormonal modulation by gut peptides, and direct nutrient sensing [41, 42]. GLP-1 producing preproglucagon-expressing neurons (PPG is cleaved into GLP-1) are located almost exclusively in NTS and project to CNS nuclei relevant for energy balance [43, 44]. Energy balance is regulated in the central nervous system ‘command center’—the hypothalamus, specifically the arcuate nucleus, which is responsible for sensing energy status and controlling caloric intake and expenditure through orexigenic and anorexigenic neuropeptides [45, 46]. The arcuate nucleus is comprised of pro-opiomelanocortin (POMC)/cocaine-and-amphetamine-regulated transcript (CART) neurons that express GLP-1 receptors [47]. Depolarization of POMC/CART neurons in response to circulating adiposity signals leads to down-stream effects of appetite suppression and deferred initiation of meals, and is increasingly stimulated via GLP-1 [47, 48]. These neurons further project to the lateral parabrachial nucleus where meal termination is regulated [48]. The impact of central GLP-1 on food regulation is also appreciated to extend beyond homeostatic (or metabolic, need based) food intake. Key mesolimbic reward areas, like the ventral tegmental area (VTA) and nucleus accumbens (NAc), are innervated by the GLP-1 producing neurons in the NTS, potentially allowing hindbrain GLP-1 to modulate reward behaviour directly [44]. Injection of GLP-1 RA into the NAc in animal models yields a reduction in food intake with possible lack of preference for high-energy/fat food if presented with choices [44, 49]. GLP-1 acts via both hunger-driven and non-homeostatic pathways to centrally mediate appetite suppression, which is a significant contributor to weight loss—an important modulator of hepatic steatosis regression and MASH resolution [27, 40]. The central actions of GLP-1 underline its role in the integrated control of metabolism and behaviour, as well as a treatment strategy for disorders of maladaptive reward behaviours (chronic hyperphagia and substance abuse). Delayed gastric emptying may also contribute to appetite reduction. GLP-1 is traditionally seen as an ‘ileal brake’ hormone since it responds to nutrients in the ileal lumen and inhibits gastric and proximal intestinal motility, which are associated with acute appetite suppression [48, 50]. GLP-1 mostly acts locally in the gut wall due to rapid inactivation after release from intestinal L cells, and activates local intestinofugal neurons that in turn stimulate gastric sympathetic neurons, leading to gastric relaxation and fullness [51]. GLP-1 inhibition of proximal intestinal smooth muscle decreases absorption of nutrients and lowers plasma glucose and triglyceride levels, thereby reducing insulin secretion and improving insulin sensitivity [52]. The effect on gastric emptying diminishes over time with continuous exposure, primarily with long-acting agents that result in tachyphylaxis due to sustained receptor agonism [48, 53]. Short-acting agents retain their gastric inhibitory effects as they cause only intermittent exposure to pharmacologic concentrations of GLP-1 receptor agonists [48, 53].

Treatment with GLP-1 receptor agonists alone may not reach metabolic targets, particularly since therapeutic potential is limited by gastrointestinal side effects such as nausea and vomiting, which hinder dose escalation [48, 53]. Newer therapies are sought to maintain the benefits of sustained GLP-1R activation while minimising side effects and enhancing metabolic homeostasis –combining GLP-1RA with GIP-RA may expand its therapeutic index [45].

3.2 |. GIP Receptor Agonism

GIP is secreted by intestinal K cells in the proximal duodenum and, similarly to GLP-1, plays a key role in regulating post-prandial blood glucose homeostasis and lipid metabolism [23, 54]. GLP-1 and GIP have different receptor expression patterns, suggesting that the two hormones have both similar and different physiologic activities [23, 55]. Although GLP-1 and GIP share an insulinotropic effect and promote expansion of beta-cell mass, they have contrary effects on postprandial glucagon secretion—the former suppresses glucagon response and the latter enhances it during hypoglycaemic or euglycaemic states [23, 56]. Furthermore, while GLP-1 has clinically relevant effects on the gastrointestinal tract, for example, gastric emptying, and central nervous system to regulate appetite and satiety, GIP has a primary role promoting tissue storage of triglycerides [23, 55]. Notably, high-fat diets induce secretion of GIP, and hypersecretion potentially promotes excessive visceral and hepatic lipid accumulation [54]. Understanding how GIP receptor activation in target tissues—pancreatic islets, central nervous system and adipose tissue—regulates physiological and clinical outcomes is necessary [23].

Glucose-dependent insulinotropic polypeptide receptor agonism for treating metabolic conditions was initially dismissed due to concerns that GIP receptor agonists (GIP RA) fail to stimulate insulin secretion in patients with type 2 diabetes, stimulate glucagon secretion worsening hyperglycaemia, and contribute to obesity [57]. Antithetical activation of both GIP and GLP-1 receptors has offered a promising approach for the treatment of metabolic conditions due to their combined effects in enhancing insulin secretion, reducing energy consumption, and improving insulin sensitivity both directly and indirectly compared to GLP-1 receptor mono-agonism [45, 57]. As such, unimolecular co-agonists have been the primary area of clinical relevance. The pathophysiology of GIP receptor agonism is displayed in Figure 2.

FIGURE 2 |.

Pathophysiology of glucose-dependent insulinotropic peptide receptor agonism. Glucose-dependent insulinotropic peptide receptor agonism primarily prevents hepatic steatosis through amplification of insulin secretion and potent activity in adipocyte tissue to buffer fatty acids and mitigate ectopic fat deposition. FFAs = free fatty acids, GLP-1 = glucose-like peptide 1, WAT = white adipose tissue. Created with BioRender.com.

3.2.1 |. Effects on Hepatic Metabolism

GIP largely plays an indirect but crucial role in hepatic metabolic regulation. Adipose tissue insulin resistance is implicated in the pathogenesis of metabolic abnormalities in MASLD, leading to hepatic lipid accumulation and disordered glucose homeostasis [58]. GLP-1 alone may mitigate these effects by modulating insulin levels to improve adipocyte storage, reducing hepatic insulin resistance, and decreasing de novo lipogenesis [23, 27, 30]. The additive effect of GIP on insulin secretion is due to direct activity in beta cells and indirect mediation of alpha-to-beta-cell communication—in fact, GIP is responsible for a substantial if not greater insulin response to glucose intake than GLP-1 [22, 59]. Unfortunately, this synergy is lost in prolonged hyperglycaemic states due to selective dysfunction in GIP signalling—downregulation of GIPR mRNA and accelerated receptor degradation—whereas sensitivity to GLP-1 remains intact [22, 23]. Achieving euglycemia can restore GIP activity; thus, dual GIP receptor and GLP-1R agonism can enhance insulin secretion by first improving beta-cell sensitivity to GIP, followed by additive insulinotropic effects from dual incretin signalling [22, 59]. Both GLP-1 and GIP action further promote insulin secretion through actions that increase pancreatic beta cell mass and inhibit apoptosis [23].

Beyond insulin secretion, recent findings indicate that GIPR agonism may enhance peripheral insulin sensitivity independently of GLP-1R activity [22, 60]. Chronic administration of tirzepatide has demonstrated improved insulin sensitivity in obese mice, characterised by increased glucose uptake into adipose tissue [60]. Given that GIP receptor is predominantly expressed in adipose tissue but not in muscle or liver, this action promotes favourable fat storage patterns and potentially mitigates ectopic fat deposition [57].

Glucose-dependent insulinotropic polypeptide also plays an important role in promoting dietary lipid storage and lipid handling [23]. Unlike the GLP-1 receptor, the GIP receptor is expressed in WAT and is hypothesized to enhance adipocytes ability to clear dietary triglycerides and improve long-term lipid storage by facilitating the healthy expansion of WAT [45, 54]. In type 2 diabetes, the lipid-buffering capacity of WAT is dysregulated due to nutrient surplus in excess of adipose storage capacity, reduced insulin-mediated suppression of FFAs release, lowered adipose tissue perfusion, and impaired recruitment of lipoprotein lipase (LPL) which is responsible for hydrolysis and uptake of triglycerides [45]. In human studies, GIP promotes lipid disposal by enhancing triglycerides clearance through increased WAT blood flow, increased adipocyte insulin sensitivity, and recruitment of insulin-sensitive LPL, and resultant triglycerides synthesis and storage in WAT [45, 61]. GIP also facilitates WAT expansion through hypertrophy of existing adipocytes and differentiation of preadipocytes [45, 62]. The outcome is decreased circulating FFAs following surplus caloric intake, limiting lipid spillover into ectopic regions and improvement in systemic insulin sensitivity [45].

3.2.2 |. Effects on Extra-Hepatic Metabolism

GIP is widely expressed in the central nervous system, in particular hypothalamic regions that regulate food seeking and promote nausea, such that its local activity may provide a combined metabolic benefit with GLP-1 by reducing energy intake [63]. Studies in high-fat fed mice show that combined GIP and GLP-1 administration leads to greater anorexia and weight loss than either agent alone [45, 64, 65]. Multiple hypothesised mechanisms by which GIP RA perform synergistically with GLP-1RA are described: (1) activation of hypothalamic GIPR+ cells reduces food intake; (2) GIPR expression in oligodendrocytes which play a role in regulation of the blood–brain barrier may enhance GLP-1 access to target hypothalamic areas; (3) local inhibitory neurons expressing GIP receptor may modulate emetic responses from GLP-1 receptor activation [63, 64, 66]. GIP may enhance weight loss by directly targeting its receptor in the central nervous system to regulate appetite, enhancing GLP-1’s anorectic action, and reducing drug-induced nausea in order to improve the tolerability of and compliance to GLP-1 receptor agonists [45].

3.3 |. Glucagon Receptor Agonism

Glucagon is a peptide hormone secreted by pancreatic alpha cells in response to hypoglycaemia and suppressed by physiologic levels of glucose [67]. Its release is mediated by paracrine control from neighbouring pancreatic beta cells, exemplified by the inhibitory effect of insulin on glucagon exocytosis [67]. Glucagon plays a primary role in the counter-regulation of hypoglycaemia by promoting hepatic glycogenolysis and gluconeogenesis in order to maintain adequate plasma glucose levels [68]. Conditions hallmarked by pathologic hyperglycaemia and insulin resistance, such as type 2 diabetes and obesity, present with hyperglucagonemia; thus, initial interest focused on glucagon antagonism as antihyperglycaemic therapy [68]. In fact, glucagon sensitivity may even be impaired in individuals with steatotic liver disease, disrupting the liver–alpha cell axis [69]. However, glucagon receptor signalling in hepatic and extra-hepatic tissues has been shown to decrease hepatic steatosis, stimulate glucose-dependent insulin secretion, and improve energy balance through appetite suppression and energy expenditure—physiologic activities that counteract the development of MASLD. In fact, glucagon secretion has been inversely related to steatosis progression [70]. As a newer basis for MASLD/MASH therapy, glucagon receptor agonists have been combined with incretin-based agonists to leverage complementary physiologic activities and balance negative effects of glucagon activation [71]. The pathophysiology of glucagon receptor agonism is displayed in Figure 3.

FIGURE 3 |.

Pathophysiology of glucagon receptor agonism. Glucagon receptor agonism impacts the development of hepatic steatosis (green) via enhancing hypolipidemic activities in the liver and achieving a negative energy balance for more potent weight loss. Glucagon receptor agonism is hypothesized to ameliorate inflammation (red) and fibrosis (blue). FFA = free fatty acid. Created with BioRender.com.

3.3.1 |. Effects on Hepatic Metabolism

Whereas GLP-1 and GIP receptors are not expressed in hepatocytes, the glucagon receptor is abundantly expressed in hepatic tissue, facilitating hypolipidaemic activities in the liver [71]. Increased de novo lipogenesis and attenuated mitochondrial fatty acid oxidation potentiate hepatic lipid accumulation [27]. Glucagon signalling in hepatocytes suppresses intermediaries in fatty acid synthesis and prompts catabolism of FFAs, leading them to beta-oxidation and degradation, thereby diverting them from storage as triglycerides and eventual release in the form of VLDL [72]. In preclinical models, comparison of cotadutide, a glucagon/GLP-1 dual RA, and liraglutide demonstrated superior reduction of hepatic de novo lipogenesis and enhancement of hepatocyte mitochondrial oxidative capacity (similar to levels stimulated by glucagon mono-agonism—suggesting restoration of mitochondrial function is a glucagon-specific benefit) [39]. Additionally, glucagon signalling increases the secretion of follistatin, a glycoprotein that counteracts hepatic lipid uptake and synthesis [70, 73]. Inhibition of glucagon receptor signalling has been associated with an increased risk of fatty liver, underscoring the protective role of glucagon in the development and progression of hepatic steatosis [72, 74]. In the above animal model, cotadutide administration was associated with reduction of hepatic inflammation and fibrosis, as indicated by decreases in quantitative measures of liver fibrosis, circulating collagen markers, and inflammatory/pro-fibrotic genes [39]. While hypothesised to improve hepatocyte mitochondrial function and turnover, decrease mitochondrial oxidative stress, and decrease stellate cell activation, the anti-inflammatory and anti-fibrotic benefits of glucagon receptor agonism are more likely a consequence of overall reduction in hepatic steatosis [28, 75].

One point bearing mention is the glucagon-mediated paracrine interaction between alpha and beta cells. Pancreatic islet alpha cells release factors, like glucagon, that stimulate beta cell function and increase glucose-dependent insulin secretion [76]. In fact, glucagon acts upon both beta-cell glucagon and GLP-1 receptors [76]. This particular step in glucose homeostasis is vital for the modulation of species-specific glycaemic set points, for example, blood glucose levels are tightly balanced in humans with metabolic regulatory organs balancing the production and utilisation of glucose to return glycaemic levels to a set point of around 90 mg/dL [77]. While the paracrine activities of glucagon complement incretin-mediated insulin secretion, the non-overlapping functions of these peptides in other tissues, such as increased appetite suppression and energy expenditure, provide even more significant benefit in combination treatments [71].

3.3.2 |. Effects on Extra-Hepatic Metabolism

The metabolic role of glucagon includes inducing satiation, acting as a terminating factor for meal intake [78, 79]. Glucagon secretion increases quickly following food intake and is directed primarily to the liver in order to stimulate hepatic glycogenolysis during meals [78]. Early studies of hepatic-portal glucagon infusions in rodents reduced the size of spontaneous meal intake without affecting intermeal intervals, indicating a contribution to meal termination rather than postprandial satiety [79, 80]. Glucagon signals satiation to the central nervous system via the hepatic branch of the abdominal vagus nerve, as vagotomy or lesions in the nucleus tractus solitarius (NTS) in the brainstem prevent glucagon’s inhibiting effect on feeding [78, 81, 82]. Increased energy expenditure must complement reduced food intake in order to maintain weight loss since physiological compensatory adaptations protect against major weight decrement: decreased caloric intake leads to increased hunger, lower sensitivity to satiety factors, and a reduced metabolic rate [83, 84]. Therefore, the primary hypothesised benefit of adding glucagon receptor agonism to incretin-based receptor agonism is its ability to increase resting energy expenditure [84, 85].

Glucagon influences energy balance in order to modulate body weight via facultative thermogenesis—increased heat production primarily in brown adipose tissue (BAT) and skeletal muscle when heat-saving mechanisms such as piloerection cannot maintain body temperature within a physiologic range [86]. Glucagon stimulates energy expenditure in the following ways: (1)—activation of BAT via direct glucagon receptor activity and indirect fibroblast growth factor 21 (FGF 21)-dependent pathways with downstream effects of increased oxygen consumption (an indirect measure of heat production); (2)—’browning’ of WAT such that adipocytes take on intermediate functional characteristics between brown and white adipocytes, including thermogenesis; (3)—enhancement of skeletal muscle thermogenesis; (4)—raising metabolic rate as evidenced by an increase in daily calorie expenditure following acute glucagon infusion [84, 86–88]. Consequently, the magnitude of weight loss benefit in multi-agonist therapies has shown dependence on glucagon activity: a balanced ratio of GLP-1 and glucagon receptors co-agonism achieves maximal weight loss without hyperglycaemia in contrast to dual-agonists with lower glucagon receptor potency or enhanced glucagon receptor activity [89].

Studying GLP-1, GIP, and glucagon triple RA for the treatment of MASLD/MASH follows the success of mono- and dual-agonists helping patients with type 2 diabetes and obesity achieve clinical targets by offering advantages of each constitutive component while minimising the risk of undesirable effects. Tri-agonism is founded on the following approach: GLP-1 receptor agonism promotes weight, which glucagon receptor agonism enhances through supplementary mechanisms, while GLP-1 and GIP receptor agonism stimulates insulin secretion and protects against hyperglycaemic risk [71]. The hyperglycaemia buffer of dual-incretin action is a particularly important benefit as it allows for more potent development of the glucagon constituent in drug formulation in order to promote greater weight loss [90]. Successful murine studies have shown that triagonists, in comparison to dual-incretin co-agonists, more effectively reduced adipose tissue, hepatic steatosis, plasma cholesterol and improved glucose tolerance while achieving a favourable energy balance by increasing energy expenditure and decreasing food intake [91, 92]. A phase 2 trial of triagonist retatrutide, including 338 adults with obesity compared to placebo over 48 weeks, reported a 24.2% average weight reduction—the highest weight loss from a pharmacologic agent—and improvements in cardiometabolic parameters, as well as a MASLD sub-study of 98 patients with 90% of participants showing normalisation of liver triglyceride content by magnetic resonance imaging proton density fat fraction (MRI-PDFF) following treatment with the two highest doses of the drug [93–95]. Collectively, triagonism therapy promises sufficient reversal of metabolic syndrome while also directly affecting hepatic lipid metabolism and MASH-related inflammation and fibrosis.

4 |. Emerging Data From Mash Clinical Trials

In clinical trials for MASH, the U.S. Food and Drug Administration (FDA) currently accepts two histological endpoints for accelerated approval: (1) resolution of MASH without worsening of fibrosis, and (2) improvement in fibrosis by at least one stage without worsening of MASH [96]. These endpoints reflect key therapeutic goals in the management of MASH and are used as proxies for long-term clinical benefit. Phase 2 and phase 3 clinical trials for MASLD/MASH with GLP-1 receptor agonists and glucagon/GIP/GLP-1 receptor dual or triple agonists, using biopsy to assess hepatic endpoints, are summarised in Table 1.

TABLE 1 |.

Summary of phase 2 and phase 3 clinical trials for MASLD/MASH with GLP-1 receptor agonists and glucagon/GIP/GLP-1 receptor dual or triple agonists, using biopsy to assess hepatic endpoints.

Intervention	Mechanism of action	Study design (ClinicalTrials.gov number)	Recruitment status	Study population	Duration	Dosing	Results
Liraglutide	GLP-1 RA	Phase 2 (LEAN, NCT01237119)	Completed	N = 52 with MASH	48 weeks	1.8 mg and placebo once-daily s.c.	39% resolution of MASH without worsening of fibrosis; 26% improvement in fibrosis (no statistically significant).
Semaglutide	GLP-1 RA	Phase 2 (NCT02970942)	Completed	N = 320 with biopsy-proven MASH and F1-F2-F3	72 weeks	0.1 mg, 0.2 mg, 0.4 mg, and placebo once-daily s.c.	36%–59% resolution of MASH without worsening of fibrosis; 32%–49% improvement in fibrosis without worsening of MASH (no statistically significant).
		Phase 3 (ESSENCE, NCT04822181)	Ongoing	N = 1197 with biopsy-proven MASH and F2-F3	240 weeks	2.4 mg and placebo once-weekly s.c.	In the first 800 participants (interim analysis at week 72): 62.9% resolution of MASH without worsening of fibrosis; 36.8% improvement in fibrosis without worsening of MASH
Pemvidutide	Glucagon/GLP-1 dual RA	Phase 2 (IMPACT, NCT05989711)	Ongoing	N = 190 with MASH F2-F3	24 weeks	1.2 mg, 1.8 mg, and placebo once-weekly s.c.	Not applicable
Tirzepatide	GIP/GLP-1 dual RA	Phase 2 (SYNERGY-NASH, NCT04166773)	Completed	N = 190 with MASH F2-F3	52 weeks	5 mg, 10 mg, 15 mg, and placebo once-weekly s.c.	44%–62% resolution of MASH without worsening of fibrosis; 51%–55% improvement in fibrosis without worsening of MASH
Survodutide	Glucagon/GLP-1 dual RA	Phase 2 (NCT04771273)	Completed	N = 293 with biopsy-proven MASH and F1-F2-F3	48 weeks	2.4 mg, 4.8 mg, 6 mg, and placebo once-weekly s.c.	43%–62% improvement in MASH without worsening of fibrosis; 34%–36% improvement in fibrosis
Efocipegtrutide	Glucagon/GIP/GLP-1 triple RA	Phase 2 (HM-TRIA-201, NCT04505436)	Ongoing	N = 240 with biopsy-proven MASH and F1-F2-F3	52 weeks	2 mg, 4 mg, 6 mg, and placebo once-weekly s.c.	Not applicable

Abbreviations: ALT, alanine aminotransferase; GIP, gastric inhibitory polypeptide; GLP-1, glucagon-like peptide 1; MASH, metabolic dysfunction-associated steatohepatitis; NAS, NAFLD activity score; PDFF, proton density fat fraction; RA, receptor agonist; s.c., subcutaneous.

4.1 |. GLP-1 Receptor Agonists

Liraglutide is a GLP-1 receptor agonist that is currently approved for the treatment of type 2 diabetes and obesity. The phase 2, double-blind trial of liraglutide included 52 participants with biopsy-proven MASH (LEAN, NCT01237119) aged 18–70 years, with or without type 2 diabetes, and with a BMI > 25 kg/m² at screening [97]. Eligible subjects were randomised 1:1 to liraglutide 1.8 mg (N = 26) once-daily subcutaneously or placebo (N = 26) for 48 weeks. Participants underwent liver biopsy at the beginning and at the end of the 48 weeks period. The primary endpoint of resolution of MASH without worsening of fibrosis was achieved in 39% and 9% of participants in the 1.8 mg and placebo groups, respectively (p = 0.019). Fewer participants in the liraglutide group had fibrosis progression than in the placebo group (9% vs. 36%, respectively; p = 0.04), but there was no statistically significant difference in improvement in fibrosis between the two groups (26% vs. 14%, respectively; p = 0.46). The mean percent weight loss was 5.5% in the liraglutide group vs. 0.7% in the placebo group (p = 0.003). An improvement in HbA1c was also observed in the liraglutide group (mean absolute change −5.7 mmol/mol; p = 0.03). The incidence of gastrointestinal side effects was higher in the liraglutide group compared to the placebo group (nausea: 46% vs. 38%; diarrhoea: 38% vs. 19%; constipation: 27% vs. 0%; vomiting: 19% vs. 12%), but most were mild to moderate in severity. Treatment discontinuation due to side effects occurred in 8% and 4% of participants receiving liraglutide and placebo, respectively. No cases of liver failure, hepatitis, or pancreatitis were reported during the trial.

Semaglutide is a GLP-1 receptor agonist that is also currently approved for the treatment of type 2 diabetes and obesity. The phase 2, double-blind trial of semaglutide included 320 participants with biopsy-proven MASH and fibrosis stage F1-F2-F3 (NCT02970942) aged 18–75 years, with or without type 2 diabetes, and with a BMI > 25 kg/m² at screening [98]. Eligible subjects were randomised 3:3:3:1:1:1 to semaglutide 0.1 mg (N = 80), 0.2 mg (N = 78), or 0.4 mg (N = 82) once-daily subcutaneously or placebo (N = 80) for 72 weeks. Participants underwent liver biopsy at the beginning and at the end of the 72-week period. The primary endpoint of resolution of MASH without worsening of fibrosis was achieved in 40%, 36%, 59%, and 17% of participants in the 0.1, 0.2, 0.4 mg, and placebo groups, respectively (p < 0.001 for semaglutide 0.4 mg vs. placebo). There was no statistically significant difference in the secondary endpoint of ≥ 1 stage improvement in fibrosis without worsening of MASH (49%, 32%, 43%, and 33% in the 0.1, 0.2, 0.4 mg, and placebo groups, respectively; p = 0.48 for semaglutide 0.4 mg vs. placebo). The mean percent weight loss was 13% in the 0.4 mg group vs. 1% in the placebo group. A dose-dependent reduction in HbA1c levels was also reported in participants receiving semaglutide, with or without type 2 diabetes. The incidence of gastrointestinal side effects was higher in the 0.4 mg group compared to the placebo group (nausea: 42% vs. 11%; diarrhoea: 20% vs. 14%; constipation: 22% vs. 12%; vomiting: 15% vs. 2%). Gastrointestinal side effects were the most common reason for discontinuation, but discontinuation occurred in only 4% of participants receiving semaglutide. The incidence of hepatic events was similar across all treatment groups. Gallbladder-related disorders occurred in a higher percentage of participants receiving semaglutide compared to those on placebo (6%, 5%, and 7% in the 0.1, 0.2, and 0.4 mg groups, respectively, vs. 2% in the placebo group). No cases of acute pancreatitis were reported.

The phase 3, double-blind trial (ESSENCE, NCT04822181) of semaglutide is still ongoing. Participants aged ≥ 18 years with biopsy-proven MASH and fibrosis stage F2-F3 are randomised 2:1 to semaglutide 2.4 mg once-weekly subcutaneously or placebo for 240 weeks (N = 1197). Primary endpoints are resolution of MASH without worsening of fibrosis, improvement in fibrosis with no worsening of MASH, and cirrhosis-free survival. Long-term outcomes will be assessed over 240 weeks. A planned interim analysis at week 72 of the first 800 participants (part 1) evaluated the trial’s primary endpoints (semaglutide group, N = 534; placebo group, N = 266) [99]. Resolution of MASH without worsening of fibrosis was achieved in 62.9% of participants in the semaglutide group compared to 34.3% of those in the placebo group (p < 0.001). Improvement in fibrosis with no worsening of MASH was achieved in 36.8% of participants in the semaglutide group compared to 22.4% of those in the placebo group (p < 0.001). As expected, improvements in body weight and cardiometabolic parameters, including HbA1c, high-sensitivity C-reactive protein, and lipid profile, were observed. The mean percent weight loss was 10.5% in the semaglutide group compared to 2% in the placebo group (p < 0.001). There were also improvements in liver enzymes and non-invasive fibrosis markers, including a 20% decrease in liver stiffness by VCTE, a 0.6 units decrease in enhanced liver fibrosis (ELF) score, and a 17% decrease in N-terminal propeptide of type III collagen (Pro-C3) biomarker (p < 0.001). The most common side effects with semaglutide were gastrointestinal and had a higher incidence compared to placebo (nausea: 36.2% vs. 13.2%; diarrhoea: 26.9% vs. 12.2%; constipation: 22.2% vs. 8.4%; vomiting: 18.6% vs. 5.6%), but only 13.4% were serious in severity. Treatment discontinuation due to side effects occurred in 3% of participants with both semaglutide and placebo. Gallbladder-related adverse events were reported in 2.5% of semaglutide-treated participants and in 1.5% of participants on placebo. Three (< 1%) cases of acute pancreatitis were reported. Long-term outcome results are expected in quarter 2 of 2028. Lastly, the phase 2, double-blind trial of semaglutide in cirrhosis included 71 adults with biopsy-confirmed MASH-related cirrhosis, aged 18–75 years, with or without type 2 diabetes, and BMI ≥ 27 kg/m² (NCT03987451). Eligible subjects were randomised 2:1 to semaglutide 2.4 mg once-weekly subcutaneously (N = 47) or placebo (N = 24) for 48 weeks. The primary endpoint was ≥ 1 stage improvement in fibrosis with no worsening of MASH, assessed by biopsy in the intention-to-treat population. Although there was no statistically significant difference between the two groups in the proportion of patients who achieved the primary endpoint or MASH resolution, no safety concerns were raised in this population [100].

4.2 |. GIP/GLP-1 Receptor Dual Agonists

Tirzepatide is a once-weekly GIP and GLP-1 receptor dual agonist that is currently approved for the treatment of type 2 diabetes and obesity. The phase 2, double-blind, dose-finding trial of tirzepatide included 190 participants with biopsy-proven MASH and fibrosis stage F2-F3 (SYNERGY-NASH, NCT04166773) aged 18–80 years, with or without type 2 diabetes, and with a BMI ≥ 27 kg/m² and ≤ 50 kg/m² [101]. Eligible subjects were randomised 1:1:1:1 to tirzepatide 5 mg (N = 47), 10 mg (N = 47), or 15 mg (N = 48) once-weekly subcutaneously or placebo (N = 48) for 52 weeks. Participants underwent liver biopsy at the beginning and at the end of the 52 weeks period. The primary endpoint of resolution of MASH without worsening of fibrosis was achieved in 44%, 56%, and 62% of participants in the 5, 10, and 15 mg groups, respectively, compared to 10% of those in the placebo group (p < 0.001 for all tirzepatide-treated groups vs. placebo). The secondary endpoint of ≥ 1 stage improvement in fibrosis with no worsening of MASH was achieved in 55%, 51%, and 51% of participants in the 5, 10, and 15 mg groups, respectively, compared to 30% of those in the placebo group (p < 0.05 for all tirzepatide-treated groups vs. placebo). Looking at the imaging data, there was a clinically significant reduction in liver fat content based on magnetic resonance imaging proton density fat fraction (MRI-PDFF) ranging from 41.3% to 57% in participants receiving tirzepatide compared to 9.8% of placebo (p < 0.05 for all tirzepatide-treated groups vs. placebo). Iron-corrected T1 (cT1) reduction was also observed in participants receiving tirzepatide and it was clinically significant as well, ranging from 70.7 msec to 107.2 msec (p < 0.05 for all tirzepatide-treated groups vs. placebo). A reduction of liver stiffness by VCTE was also observed within 1 year of treatment with tirzepatide, ranging from 3.1 kPa to 3.5 kPa (p < 0.05 for all tirzepatide-treated groups vs. placebo). Similarly, a significant reduction in ELF (ranging from 0.45 to 0.50) and Pro-C3 (ranging from 40.1 to 45.7 μg/L) biomarkers was observed (p < 0.001 for all tirzepatide-treated groups vs. placebo). The mean percent weight loss was 10.7%, 13.3%, and 15.6% in the 5, 10, and 15 mg groups, respectively, compared to 0.8% in the placebo group (p < 0.001 for all tirzepatide-treated groups vs. placebo). Notably, subjects with type 2 diabetes were likely to have a lower weight loss, but it was still up to 13.7% in the 15 mg group compared to 1.3% in the placebo group (p < 0.001). The most common side effects with tirzepatide were gastrointestinal and had a higher incidence compared to placebo (nausea: 44% vs. 12%; diarrhoea: 27% vs. 23%; constipation; 15% vs. 6%; vomiting: 15% vs. 2%), but most (> 90%) were mild to moderate in severity. Treatment discontinuation due to side effects occurred in 4% of participants with both tirzepatide and placebo. Progression to cirrhosis was observed in 3% and 4% of tirzepatide and placebo groups, respectively. No participant developed hepatic decompensation and there was no evidence of drug-induced liver injury. Gallbladder-related adverse events were reported in 3% of tirzepatide-treated participants and in 2% of participants on placebo. No cases of acute pancreatitis were reported.

4.3 |. Glucagon/GLP-1 Receptor Dual Agonists

Pemvidutide is a once-weekly glucagon receptor/GLP-1 receptor dual agonist under development for the treatment of MASH and obesity. The phase 2, double-blind trial (IMPACT, NCT05989711) is ongoing. Participants aged 18–75 years with biopsy-proven MASH and fibrosis stage F2-F3, with or without type 2 diabetes, and BMI ≥ 27.0 kg/m², are randomised 1:2:2 to pemvidutide 1.2 mg or 1.8 mg once-weekly subcutaneously or placebo for 24 weeks (estimated enrolment: N = 190). Primary endpoints are resolution of MASH without worsening of fibrosis and ≥ 1 stage improvement in fibrosis without worsening of MASH. The estimated study completion is expected in September 2025. Results from the extension study of the phase 1b trial (NCT05292911), including 64 participants with MRI-PDFF ≥ 10% and BMI ≥ 28.0 kg/m², showed that 50%, 44%, and 60% of subjects with ALT ≥ 30 IU/L at baseline achieved a simultaneous reduction in MRI-PDFF ≥ 30% and ALT ≥ 17 IU/L after 24 weeks at pemvidutide 1.2, 1.8, and 2.4 mg, respectively, compared to 0% of those on placebo [102].

Survodutide is a once-weekly glucagon receptor/GLP-1 receptor dual agonist with approximately 8-fold higher activity for the GLP-1 receptor than for the glucagon receptor [103]. The phase 2, double-blind, dose-finding trial of survodutide included 293 participants with biopsy-proven MASH and fibrosis stage F1-F2-F3 (NCT04771273) aged 18–80 years, with or without type 2 diabetes, and with a BMI ≥ 25 kg/m² [104]. Eligible subjects were randomised 1:1:1:1 to survodutide 2.4 mg (N = 73), 4.8 mg (N = 72), or 6 mg (N = 74) once-weekly subcutaneously or to placebo (N = 74) for 48 weeks. Participants underwent liver biopsy at the beginning and at the end of the 48-week period. The primary endpoint of improvement in MASH without worsening of fibrosis was achieved in 47%, 62%, and 43% of participants in the 2.4 mg, 4.8 mg, and 6 mg groups, respectively, as compared to 14% of those in the placebo group (p < 0.001 for all survodutide-treated groups vs. placebo). The secondary endpoint of ≥ 1 stage improvement in fibrosis was achieved in 34%, 36%, and 34% of subjects in the 2.4 mg, 4.8 mg, and 6 mg groups, respectively, as compared to 22% of those in the placebo group. Looking at the imaging data, a clinically significant reduction in liver fat content based on MRI-PDFF ranged from 57% to 67% in participants receiving survodutide compared to 14% of those on placebo. The absolute weight loss was 10.2, 12.9, and 13.1 kg in the 2.4, 4.8, and 6 mg groups, respectively, compared to 0.6 kg in the placebo group. Notably, an improvement in HbA1c of up to 0.8% was also reported in those receiving survodutide, suggesting that the glycaemic benefits due to GLP-1 receptor agonism are maintained with survodutide despite also having glucagon receptor agonism. The most common side effects with survodutide were gastrointestinal and had a higher incidence compared to placebo (nausea: 66% vs. 23%; diarrhoea: 49% vs. 23%; constipation: 21% vs. 15%; vomiting: 41% vs. 4%). Treatment discontinuation due to gastrointestinal side effects occurred in 16% of participants receiving survodutide compared to 1.4% of those on placebo.

4.4 |. Glucagon/GIP/GLP-1 Receptor Triple Agonists

Efocipegtrutide is a once-weekly glucagon/GIP/GLP-1 receptor triple agonist under investigation for the treatment of MASH. The phase 2, double-blind trial (HM-TRIA-201, NCT04505436) is still ongoing in the US and Korea. Adults with biopsy-proven MASH and fibrosis stage F1–F2–F3, with or without type 2 diabetes, and with MRI-PDFF ≥ 8% at screening are randomised 1:1:1:1 to efocipegtrutide 2, 4, and 6 mg once-weekly subcutaneously or placebo for 52 weeks (estimated enrolment: N = 240). The primary endpoint is resolution of MASH without worsening of fibrosis. The estimated study completion is expected in November 2025.

5 |. Clinical Benefits of GLP-1 Receptor Agonists and Combined Therapies on MASLD Comorbidities

The clinical benefits of GLP-1 receptor agonists and combined therapies on MASLD comorbidities are presented in Figure 4. Tirzepatide (Zepbound) has received recent FDA approval for chronic weight management alongside GLP-1 receptor agonist liraglutide (Saxenda) and semaglutide (Wegovy), following the demonstration of over 20% mean weight loss achieved in non-diabetic patients with obesity [105–110]. In addition to well-described effects on obesity and type 2 diabetes, GLP-1 receptor agonists have ameliorated cardiovascular events, and ongoing studies are evaluating the safety of dual-agonists [111]. The LEADER, REWIND, and SUSTAIN-6 trials of respective liraglutide 1.8 mg/daily (or maximum tolerated dose), once-weekly dulaglutide 1.5 mg, and once-weekly semaglutide 0.5 mg or 1.0 mg administration in patients with type 2 diabetes and cardiovascular disease or risk factors found decreased hazard ratios ranging from 0.74 to 0.88 for the primary composite endpoint first occurrence of death from cardiovascular causes, nonfatal myocardial infarction, or nonfatal stroke [112–114]. Only the REWIND trial was designed to demonstrate superiority in comparison to placebo [112]. The SELECT trial demonstrated an up to 20% relative risk reduction in major adverse cardiac events (3-point MACE) and all-cause mortality following administration of once-weekly semaglutide 2.4 mg in patients with atherosclerotic cardiovascular disease (ASCVD) but without type 2 diabetes; subsequently in March 2024, the FDA approved semaglutide for reduction of cardiovascular events in patients with ASCVD and overweight or obese habitus [115, 116].

FIGURE 4 |.

Clinical evidence of glucagon-like peptide 1 receptor agonists and combined therapies on MASLD comorbidities. The following generic incretin-based therapies have been studied with select positive outcomes for cardiometabolic co-morbidities associated with MASLD/MASH and are listed with the relevant referenced trials and studied doses. Therapies outlined by a grey box are FDA-approved for treatment of the associated conditions. ASCVD = atherosclerotic cardiovascular disease, HFpEF = heart failure with preserved ejection fraction, HFrEF = heart failure with reduced ejection fraction, MASH = metabolic dysfunction-associated steatohepatitis, MASLD = metabolic dysfunction-associated steatotic liver disease. Created with BioRender.com.

Treatment with GLP-1 receptor agonists has also raised interest in their therapeutic effect on heart failure-related outcomes. In a meta-analysis of four randomised, placebo–controlled trials involving 3743 patients with a history of heart failure with mildly reduced or preserved ejection fraction (HFpEF), once-weekly semaglutide (2.4 mg in STEP-HFpEF, STEP-HFpEF DM, and SELECT; 1.0 mg in FLOW) reduced the rate of worsening heart failure events, that is, first occurrence of hospitalisation or urgent visit for heart failure often requiring intravenous therapy, but did not affect cardiovascular mortality alone [115, 117–120]. Notably, patients with a BMI ≥ 35 kg/m² experienced greater benefits than those with lower BMI, potentially underscoring the benefit derived from targeting obesity-related metabolic drivers of heart failure rather than modulation of myocardial loading or neurohormonal mediation [118, 121]. GLP-1 receptor agonists effect on heart failure outcomes has differed by heart failure subtype. Data from the FIGHT and LIVE trials, inclusive of patients with median left ventricular ejection fraction of 25% and ≤ 45%, respectively, associated GLP-1 receptor agonists use with neutral or even harmful effects in patients with heart failure with reduced ejection fraction (HFrEF): liraglutide 1.8 mg/daily administration did not improve mortality and rehospitalisation in patients with advanced heart failure, left ventricular function, or exercise capacity stable among chronic heart failure patients, and suggested an increase in cardiac events [122, 123]. However, a pre-specified analysis of the SELECT trial examining the effect of GLP-1 receptor agonists vs. placebo on composite heart failure outcomes saw benefit in patients with heart failure regardless of subtype [121]. GLP-1 receptor agonists use has not yet obtained FDA approval for use in either subtype of heart failure (HfpEF, HfrEF), awaiting targeted studies to demonstrate a benefit in cardiovascular mortality.

GLP-1 receptor agonists and combination therapies have demonstrated benefit in the treatment of obstructive sleep apnoea (OSA), a disease characterised by repetitive episodes of partial or complete upper airway collapse, through the effects of weight loss—reduction of upper airway and neck adiposity which can compress the airway and visceral adiposity which can reduce lung volumes [124, 125]. In the SCALE Sleep Apnea trial, liraglutide 3.0 mg/daily led to a mean reduction in apnoea-hypopnea index (AHI) of 12.2 events per hour compared to 6.1 events per hour in the placebo group [126]. In the SURMOUNT-OSA program of two phase 3 trials, once-weekly tirzepatide 10 or 15 mg was administered to patients with obesity not established on positive airway pressure (PAP) therapy (trial 1) and receiving PAP therapy (trial 2) [127]. Trials 1 and 2 observed a mean reduction in AHI of 25.3 and 29.3 events per hour with tirzepatide compared to 5.3 and 5.5 events per hour with placebo, respectively, and an average overall body weight reduction of up to 20% from baseline in the tirzepatide groups [127]. Notably, the observed improvements were present regardless of PAP therapy use, highlighting an important adjunct benefit of GLP-1RA and combined therapies to standard of care OSA treatments. Predicated on the findings of the SURMOUNT-OSA program, the FDA approved the use of tirzepatide for OSA in December 2024 [128].

GLP-1 receptor agonists also offer renal protective effects for patients with diabetic nephropathy. In the first dedicated trial of renal outcomes in type 2 diabetes, once-weekly semaglutide 1.0 mg demonstrated a 24% risk reduction of the composite primary endpoint—the onset of kidney failure, at least a 50% reduction in the estimated glomerular filtration rate (eGFR) from baseline, or death from kidney-related or cardiovascular causes—and slowed significant eGFR decline (9.3% vs. 12.1%) over 3.4 years [120]. The trial was terminated early as the pre-specified interim analysis met criteria for efficacy [129]. The FDA approved the use of semaglutide to decrease the risk of kidney failure and disease progression, as well as death from cardiovascular disease in adults with type 2 diabetes and chronic kidney disease in January 2025 based on outcomes of the FLOW trial [130].

Currently, evidence regarding the impact of GLP-1 receptor agonists on major adverse liver outcomes (MALOs) in diabetic populations derives primarily from large retrospective cohort studies. In a large analysis using the TriNetX database including 15,176 propensity-matched pairs of patients with type 2 diabetes and MASLD, initiation of GLP-1 receptor agonists was associated with a significantly lower risk of composite MALOs compared to sodium-glucose cotransporter 2 inhibitors (adjusted hazard ratio [aHR] 0.84) [131]. Specifically, GLP-1 receptor agonists use was linked to a reduced incidence of hepatic decompensation (aHR 0.83) and a lower risk of all-cause mortality (aHR 0.84) [131]. These real-world findings suggest a potential hepatoprotective effect of GLP-1 receptor agonists. However, the retrospective nature of the analysis limits definitive conclusions.

Novel use of GLP-1 receptor agonists and combined therapies in neuropsychiatric diseases, such as addiction treatment, and neurological disorders are future areas of research [132]. In preclinical models, GLP-1 receptor agonists modulate alcohol consumption and related behaviours, including reducing alcohol intake, suppressing alcohol-seeking behaviours, and alleviating withdrawal symptoms in rodents [133]. Reduced desire for alcohol use has been reported among patients taking GLP-1 receptor agonists or dual-agonists for the treatment of obesity [134]. A retrospective cohort study of electronic health records of 83,825 patients with obesity demonstrated that semaglutide use compared with other anti-obesity medications is associated with a 50%–56% lower risk for both the incidence and recurrence of alcohol use disorder [135]. A small clinical trial of 127 patients that evaluated exenatide compared to placebo as an adjunct to standard cognitive-behavioural therapy for alcohol use disorder reported significant reduction in heavy drinking days and total alcohol intake only in a subgroup of patients with obesity [136]. Importantly, in this study, exenatide significantly attenuated fMRI alcohol cue reactivity in the ventral striatum and septal area, which are crucial brain areas for drug reward and addiction, demonstrating the pathophysiologic rationale for efficacy [136]. The need for clinical validation of novel uses of GLP-1 receptor agonists and combined therapies to treat neuropsychiatric diseases remains.

6 |. Conclusion

Pleiotropic mechanisms influence the pathogenesis of MASLD/MASH and related co-morbidities. Combination incretin-based therapies target parallel injury pathways, leveraging the complementary benefits of constitutive peptides while ameliorating adverse effects of mono-agonism that could limit treatment efficacy. Recent evidence from phase 2 clinical trials for MASH demonstrated that pharmacological agents based on GLP-1 receptor agonism are effective in improving disease activity, that is, steatohepatitis. Additionally, tirzepatide and survodutide showed potential clinical benefits in reducing fibrosis. Other cardiometabolic benefits observed include weight loss and improvements in glycaemic control and lipid profile. Adherence to treatment may be limited by gastrointestinal side effects, though they were found to be generally mild to moderate in severity. An interim analysis of the semaglutide phase 3 trial confirmed its efficacy in improving steatohepatitis and demonstrated its potential to improve fibrosis. Larger and longer-duration clinical trials are needed to further evaluate the efficacy and safety of GIP receptor and glucagon receptor agonism. Finally, combination therapies—including GLP-1 receptor agonists paired with agents targeting complementary pathways such as fibroblast growth factor 21 (FGF21) analogues [137]—are poised to shape a promising and diverse treatment landscape for MASH. Clinical developments in GLP-1 receptor agonists and combined therapies offer an opportunity to individualise MASLD/MASH treatment based on desired hepatic effects, comorbidities and patient characteristics.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.