Diabetic gastrointestinal autonomic neuropathy: Integrating neuronal degeneration and gut microbial dysbiosis

Abstract

Diabetic gastrointestinal autonomic neuropathy (DGAN) is a common and debilitating complication of diabetes, characterized by autonomic dysfunction in the gastrointestinal system. The complex pathophysiology of DGAN involves neuronal injury that is intrinsically linked to gut dysbiosis. Multiple factors, including hyperglycemia, oxidative stress, and inflammation, significantly contribute to neuronal damage, manifesting as symptoms such as delayed gastric emptying, diarrhea, and constipation. Recent studies have demonstrated that patients with diabetes experience substantial alterations in gut microbiota composition, potentially exacerbating gastrointestinal symptoms. Microbial metabolites may modulate neurotransmitter synthesis and release, directly affecting autonomic nerve function, while dysbiosis amplifies oxidative stress and inflammation, further compromising the enteric nervous system and worsening DGAN. Advances in multi-omics technologies now provide deeper insights into molecular mechanisms of DGAN and its interactions with microbiota. Early diagnosis leveraging biomarkers, gut microbiota analysis, and advanced imaging promises more effective interventions. Emerging therapeutic strategies targeting oxidative stress, inflammation, and gut microbiota represent promising approaches for managing DGAN. Future research should focus on large-scale, multi-ethnic studies and therapies targeting specific microbial metabolites to refine diagnosis and treatment approaches.

Key Words: Diabetic neuropathy; Gastrointestinal; Enteric neuropathy; Diabetes; Neuropathy; Gut microbiota; Gut dysbiosis

Core Tip: Diabetic gastrointestinal autonomic neuropathy (DGAN) represents a complex pathophysiological cascade driven by bidirectional interactions between hyperglycemia-induced neuronal injury and gut dysbiosis. Chronic hyperglycemia triggers oxidative stress, inflammatory pathways, and neurotrophic factor deficits, leading to damage of enteric neurons and glia. Concurrently, diabetes-associated dysbiosis reduces microbial diversity and beneficial metabolite production, which further exacerbates neuroinflammation and autonomic dysfunction. Advanced multi-omics approaches reveal these mechanisms, aiding early diagnosis through microbiome profiling and functional synaptic imaging. Therapeutic strategies targeting microbiota restoration, oxidative stress reduction, and neuroprotection show promise. Future research should prioritize large-scale clinical trials and metabolite-targeted interventions to advance personalized management of DGAN.

INTRODUCTION

Diabetic autonomic neuropathy (DAN) is a common chronic complication of diabetes that can affect multiple organ systems. Among its manifestations, diabetic gastrointestinal autonomic neuropathy (DGAN) is often overlooked despite its high prevalence and significant impact on quality of life. It is estimated that up to three-quarters of patients with long-standing diabetes may develop some degree of DGAN, leading to gastrointestinal dysfunction such as gastroparesis, enteropathy, or fecal incontinence[1,2]. Recent clinical data highlight that beyond the well-studied cardiovascular autonomic neuropathy, gastrointestinal autonomic dysfunction significantly contributes to morbidity in diabetes and warrants greater attention[3]. These symptoms not only substantially diminish quality of life but can also destabilize glycemic control (e.g., through erratic nutrient absorption in gastroparesis)[4]. Thus, elucidating the mechanisms of DGAN is crucial for developing targeted therapeutic interventions.

The pathophysiology of DGAN is complex and multifactorial. Chronic hyperglycemia and associated metabolic derangements trigger a cascade of neuronal injuries in both the enteric and autonomic nervous systems (ANS), including oxidative stress, microvascular ischemia, and immune-mediated damage[5,6]. These insults lead to progressive degeneration or dysfunction of the enteric neurons and supporting glial cells that coordinate gastrointestinal motility and secretory functions[7,8]. In parallel, accumulating evidence indicates that diabetes-induced changes in gut function can disrupt the composition and metabolic homeostasis of the gut microbiota, a condition known as dysbiosis. Conversely, gut microbiota alterations may further exacerbate inflammation and impair neural function in the gastrointestinal tract[9,10]. This bidirectional relationship suggests that DGAN represents not only a result of direct neuronal injury but also an integral component of a broader gut–microbiome–nerve axis disturbance[11,12].

In this review, we discuss the pathophysiological mechanisms underlying DGAN, from the initial neuronal injury caused by the diabetic milieu to the subsequent dysregulation of the gut microbiota, and how these factors interact synergistically to drive gastrointestinal dysfunction in diabetes.

AUTONOMIC REGULATION OF GASTROINTESTINAL FUNCTION

ANS plays a central role in coordinating gastrointestinal function through complex bidirectional interactions between sympathetic, parasympathetic, and enteric nervous systems (ENS). The extrinsic ANS regulates gastrointestinal motility, secretion, and blood flow via vagal (parasympathetic) and splanchnic (sympathetic) pathways, while the intrinsic ENS acts as an independent "second brain" embedded within the gut wall[13].

Sympathetic and parasympathetic regulation

Parasympathetic regulation of gastrointestinal function is primarily mediated through the vagus nerve, which enhances gastrointestinal motility and glandular secretion via acetylcholine release. Efferent vagal fibers innervate both the myenteric and submucosal plexuses, promoting relaxation of the proximal stomach (accommodative reflex), stimulating antral contractions, and facilitating pancreatic enzyme secretion[1]. By contrast, sympathetic control, conveyed via splanchnic nerves, generally inhibits gastrointestinal motility and secretion through the release of norepinephrine, which interacts predominantly with alpha adrenergic receptors to redirect blood flow away from the gastrointestinal tract during periods of stress or physical exertion[5]. Additionally, vagal afferent fibers, constituting approximately 80%-85% of the total vagal nerve fibers, transmit mechanical and chemical sensory signals from the gastrointestinal lumen to the nucleus of tractus solitarius in the brainstem, thereby modulating centrally integrated gastrointestinal reflexes and visceral sensation[13].

ENS architecture

The ENS consists of two interconnected ganglionated plexuses: Myenteric plexus (Auerbach’s plexus), situated between the circular and longitudinal muscle layers and primarily responsible for regulating gastrointestinal motility; and the submucosal plexus (Meissner’s plexus), located closer to the mucosa and involved chiefly in controlling secretion and absorption processes[3]. Collectively, these plexuses integrate approximately 400-600 million neurons, comprising intrinsic primary afferent neurons, interneurons, and motor neurons, which secrete a diverse array of neurotransmitters including acetylcholine, nitric oxide, and vasoactive intestinal peptide, and numerous neuropeptides[14]. The myenteric plexus orchestrates coordinated peristaltic movements through ascending excitatory (predominantly cholinergic) and descending inhibitory (primarily nitrergic) neural pathways that regulate the precise timing of muscle contraction and relaxation[15].

ENS-cellular interactions

The ENS operates synergistically with interstitial cells of Cajal (ICCs), which generate and propagate slow-wave potentials crucial for pacing smooth muscle contractions and maintaining gastrointestinal motility rhythms[15]. ICCs function as electrical pacemakers by forming gap junctions with smooth muscle cells, thereby facilitating coordinated contractile activity. Additionally, enteric glial cells (EGCs), which outnumber enteric neurons by approximately 4:1, play essential roles in neuronal support by secreting neuroprotective substances such as glutathione and glial cell line-derived neurotrophic factor (GDNF), modulating mucosal immunity, and preserving epithelial barrier integrity through bidirectional signaling with enteric neurons[14,16,17]. Recent evidence suggests EGCs also participate actively in neurotransmission and neuroinflammatory processes. This integrated ENS-ICC-EGC network autonomously regulates gastrointestinal functions but remains responsive to modulation by extrinsic ANS inputs, thereby enabling adaptive responses to changing physiological demands[13].

MECHANISMS OF NEURONAL INJURY IN DGAN

The complex pathophysiology of neuronal injury in DGAN arises from the interplay of chronic hyperglycemia-induced direct damage, dysregulated inflammation, impaired neurotrophic support, and specific molecular signaling cascades. These mechanisms converge to disrupt enteric neuronal function and survival (Figure 1).

Figure 1 Metabolism-gut microbiota-enteric autonomic nervous system crosstalk. Hyperglycemia-induced direct injury includes activation of the polyol pathway, accumulation of advanced glycation end-products, and mitochondrial dysfunction. Inflammation and immune-mediated injury, involving activation of the nuclear factor kappa B (NF-kB) signaling pathway and increased release of pro-inflammatory cytokines exacerbate neuronal and glial cell apoptosis. Reduced neurotrophic support contributes significantly to neuronal degeneration. These neuronal injuries interact bidirectionally with gut microbiota dysbiosis, which manifests as decreased beneficial bacteria and increased pathogenic bacteria. Altered microbial metabolites, notably reduced short-chain fatty acids (SCFAs) and elevated lipopolysaccharides (LPS), further disrupt the intestinal mucosal barrier and exacerbate inflammation, creating a vicious cycle with neuronal injury. Clinically, these mechanisms collectively lead to gastrointestinal autonomic dysfunction, such as gastroparesis, intestinal dysmotility, and altered nutrient absorption. SIBO: Small intestinal bacterial overgrowth.

Chronic hyperglycemia directly induces damage to enteric neurons through multiple convergent pathogenic mechanisms. First, activation of the polyol pathway results in intracellular sorbitol accumulation and myo-inositol depletion, disrupting neuronal osmotic balance and reducing Na+/K+-ATPase activity essential for maintaining membrane potential[18]. Second, persistent hyperglycemia promotes the formation of advanced glycation end-products (AGEs). Binding of AGEs to the receptor for AGE (RAGE) triggers oxidative stress cascades via NADPH oxidase activation, initiating caspase-3-dependent apoptotic pathways and neuronal cell death[19,20]. Simultaneously, excessive glucose exposure induces mitochondrial dysfunction characterized by enhanced reactive oxygen species production and impaired electron transport chain activity, resulting in reduced ATP availability and compromised axonal transport mechanism[3,16]. Additionally, hyperglycemia-driven microvascular alterations, notably glycation-induced thickening of the vascular basement membrane, reduce endoneurial blood flow and capillary density, exacerbating neuronal damage through ischemic and hypoxic mechanisms[21].

Chronic low-grade inflammation significantly contributes to the pathogenesis of DGAN[20]. Elevated levels of pro-inflammatory cytokines (e.g., interleukin 1 beta [IL-1β], IL-6, tumor necrosis factor alpha [TNF-α]) stimulate nuclear factor kappa B (NF-κB) signaling cascades within EGCs and neurons, intensifying oxidative stress and disrupting essential neuronal-glial interactions[18,22]. Critically, the aforementioned AGE-RAGE engagement, alongside activation of Toll-like receptors (TLRs) by damage-associated molecular patterns, also aberrantly activates the mitogen-activated protein kinase (MAPK) pathway, particularly the c-Jun N-terminal kinase and p38 MAPK subpathways[23,24]. MAPK activation amplifies the release of pro-inflammatory cytokines (including IL-6 and TNF-α), further fueling inflammation and contributing to synaptic dysfunction and neuronal apoptosis. Hyperactivation of the NF-κB pathway, often synergizing with mitochondrial oxidative stress, exacerbates demyelination of autonomic nerve fibers and impairs axonal transport mechanisms[3,25]. Furthermore, autoimmune mechanisms may aggravate autonomic nerve injury through the generation of antibodies directed against ganglionic acetylcholine receptors, intrinsic enteric neurons, and ICCs[1,3].

Impairment of neurotrophic support significantly exacerbates neuronal injury in DGAN. Reduced levels of critical neurotrophic factors, such as GDNF, brain-derived neurotrophic factor (BDNF), and insulin-like growth factor-1, impede neuronal survival, repair, and axonal regeneration[18,26,27]. Hyperglycemia suppresses GDNF expression through inhibition of the phosphoinositide 3-kinase/Akt signaling pathway, directly diminishing neuronal trophic support[24,27]. Apoptosis of EGCs, a key source of neurotrophic factors, further compromises neuroprotection and neuronal viability. This EGC loss is facilitated by dysregulated microRNA-375 expression and subsequent suppression of phosphoinositide-dependent kinase-1, leading to further GDNF depletion[19]. The resultant disruption of essential neuron-glial communication impairs neurotransmission, synaptic plasticity, and coordinated gastrointestinal motility patterns.

Emerging evidence underscores the contribution of epigenetic alterations to DGAN pathogenesis. Aberrant histone modifications, particularly reduced acetylation of histone H3 at lysine 9, have been implicated in the downregulation of neurotrophic factors such as BDNF, impairing Schwann cell function and neuronal support[28]. Non-coding RNAs play significant regulatory roles: MicroRNA-155 and the long non-coding RNA metastasis associated lung adenocarcinoma transcript 1 have been shown to regulate key genes (e.g., C-X-C chemokine receptor type 4), intensifying inflammatory responses and promoting neuronal apoptosis under diabetic conditions[29,30]. Furthermore, hyperglycemia-induced aberrant DNA methylation patterns cause long-term alterations in mitochondrial respiratory chain complex activity and antioxidant defense mechanisms, suggesting a potential role for "epigenetic memory" in sustaining disease progression even after glycemic normalization[31]. These epigenetic insights provide novel mechanistic understanding and identify potential targets for intervention.

GUT DYSBIOSIS IN DGAN

Diabetes-associated alterations in gut microbiota

Patients with type 2 diabetes exhibit distinctive alterations in gut microbiota composition, characterized by decreased microbial diversity and shifts in taxonomic abundance. A prominent feature is a reduced Firmicutes-to-Bacteroidetes ratio, primarily driven by decreased abundance of beneficial butyrate-producing bacteria, such as members of the Lachnospiraceae family and the genus Roseburia, alongside increased prevalence of specific Bacteroidetes species, notably Bacteroides vulgatus and B. stercoris[10,32]. Opportunistic pathogens, including Fusobacterium nucleatum and Escherichia coli, are significantly enriched, while beneficial symbiotic bacteria, particularly Lactobacillus species and Bifidobacterium strains, are markedly reduced[33]. These microbial shifts have been associated with impaired glucose metabolism, insulin resistance and elevated systemic inflammation[34]. DGAN further exacerbates gut dysbiosis, primarily through mechanisms such as delayed gastric emptying, intestinal dysmotility, and small intestinal bacterial overgrowth (SIBO)[35]. Impaired intestinal motility promotes retrograde colonization by potentially pathogenic bacteria, compromising mucosal integrity and barrier function; concurrently, SIBO modifies luminal pH, bile acid metabolism, and nutrient absorption patterns, further destabilizing the microbial ecosystem[36]. Clinical endoscopic evaluations have identified SIBO in approximately 45% of patients with diabetes with gastrointestinal complications, whereas systematic reviews and meta-analyses estimate the overall prevalence of SIBO in diabetes at approximately 29%, significantly higher than in matched non-diabetic controls[37,38].

Neurofunctional implications of microbial dysbiosis

Short-chain fatty acids (SCFAs), produced by gut microbial fermentation of dietary fiber, modulate ENS function via activation of G-protein-coupled receptor 41 (GPR41) and GPR43[39]. These receptors are expressed in submucosal and myenteric ganglia of the ENS, where SCFA binding stimulates enteroendocrine cells to release glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). GLP-1 enhances insulin sensitivity, while PYY suppresses gastrointestinal motility, collectively regulating postprandial glucose metabolism and energy homeostasis. Additionally, activation of GPR41/GPR43 enhances intestinal epithelial tight junction integrity, preventing systemic entry of endotoxins such as lipopolysaccharide (LPS)[40]. The reduced production of SCFAs, especially butyrate, observed in dysbiotic states impairs neuronal signaling within the ENS, compromises gut-brain axis (GBA) communication, and alters vagal afferent sensitivity, thereby exacerbating diabetic neuropathy[41]. Visconti et al[42] proposed that butyrate exerts neuroprotective effects by enhancing neuronal energy metabolism through the AMP-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) signaling pathway. This observation is consistent with the findings of Yang et al[43], whose randomized clinical trial demonstrated that probiotic interventions may partially restore the neuroprotective capacity of SCFAs in patients with diabetes with early autonomic dysfunction. However, in patients with advanced diabetes, the expression of key microbial genes involved in butyrate synthesis, such as butyryl-CoA transferase, is markedly downregulated, significantly attenuating these protective effects. Conversely, elevated levels of LPS, derived from Gram-negative pathogens such as Enterobacteriaceae, induce systemic inflammation through TLR4-dependent signaling pathways, enhancing oxidative stress and neuronal apoptosis[44]. Moreover, dysbiosis-driven polarization of T helper 17 cells and consequent elevation in pro-inflammatory cytokines (e.g., IL-6, TNF-α) can further damage peripheral nerves by increasing permeability of the blood-nerve barrier and promoting macrophage infiltration[5,45]. Notably, the reduction of the mucin-degrading bacterium Akkermansia muciniphila, commonly observed in patients with diabetes, correlates with impaired gut barrier function, increased intestinal permeability, and increased endotoxemia, thereby intensifying neuroinflammatory processes that contribute to autonomic neuropathy progression[46].

GUT-BRAIN AXIS AND VAGAL NERVE IN DGAN

GBA mediates bidirectional communication between the gastrointestinal tract and the central nervous system, primarily through vagal nerve pathways[47,48]. Under physiological conditions, vagal afferent fibers convey visceral sensory information to the nucleus tractus solitarius in the brainstem, while efferent vagal fibers modulate gastrointestinal motility and secretion via cholinergic parasympathetic signaling[49-51]. In diabetes, however, chronic hyperglycemia induces vagal neuropathy, characterized by axonal degeneration, demyelination, and diminished neuronal plasticity within the dorsal motor nucleus of the vagus, consequently impairing efferent signaling pathways and contributing to clinical manifestations such as gastroparesis, postprandial fullness and intestinal dysmotility[52,53]. Simultaneously, DAN disrupts afferent pathways, attenuating satiety signaling and visceral pain perception, which may contribute to dysregulated food intake[54]. Additionally, vagal hypoactivity diminishes the secretion of GLP-1, a hormone pivotal for glycemic regulation, appetite suppression, and modulation of gastric emptying, thus creating a detrimental cycle of metabolic dysregulation and gastrointestinal disturbances[55,56]. These pathological alterations correlate closely with enteric neuronal degeneration, increased oxidative stress, and progressive depletion of ICCs, further aggravating gastrointestinal symptom burden and reducing quality of life in patients with diabetes[57,58] (Figure 2).

Figure 2 Molecular pathways underlying the pathophysiology of diabetic enteric autonomic neuropathy. Persistent hyperglycemia activates multiple pathogenic signaling pathways leading to autonomic neuronal damage. Increased glucose influx activates the polyol pathway, causing intracellular accumulation of sorbitol and fructose, disrupting osmotic balance. Advanced glycation end (AGE)-products accumulate and interact with their receptors, activating downstream signaling pathways such as protein kinase C (PKC), mitogen-activated protein kinase (MAPK), and phosphoinositide 3-kinase (PI3K)/Akt, leading to the activation of nuclear factor kappa B (NF-κB). Additionally, Toll-like receptors (TLRs), particularly TLR4, are activated by lipopolysaccharide (LPS), derived from gut microbiota dysbiosis, further promoting NF-κB activation. NF-κB translocates into the nucleus, triggering DNA damage and promoting transcription of pro-inflammatory cytokines (tumor necrosis factor alpha [TNF-α], interleukin 8 [IL-8], IL-1β). Increased oxidative stress, mediated by NADPH oxidase and impaired mitochondrial function, exacerbates axonal transport dysfunction. Concurrently, gut microbial dysbiosis reduces beneficial bacteria and short-chain fatty acid (SCFA) production, decreasing activation of AMP-activated protein kinase (AMPK) and proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), thus impairing neuronal energy metabolism. Reduced activation of SCFA receptors (G-protein-coupled receptor 41 [GPR41]/GPR43) also diminishes release of gut-derived neuroendocrine factors (glucagon-like peptide 1 [GLP-1], peptide YY [PYY]), impairing gut-brain signaling, appetite regulation, glucose homeostasis, and gastric motility. RAGE: Receptor for advanced glycation end-product; ROS: Reactive oxygen species.

IMPLICATIONS FOR CLINICAL MANAGEMENT

Therapeutic strategies and clinical interventions

Effective management of DGAN requires a multifaceted strategy that addresses glycemic control, symptomatic relief, and modulation of the underlying pathophysiological mechanisms. Pharmacological treatment with prokinetic agents, such as metoclopramide and domperidone, remains a commonly employed approach to enhance gastrointestinal motility[59]. However, concerns regarding their long-term efficacy and potential adverse effects, including extrapyramidal symptoms and cardiac arrhythmias, necessitate cautious monitoring and individualized use[60]. Antioxidant therapy, exemplified by α-lipoic acid, has been reported to ameliorate oxidative stress associated with diabetic neuropathy[61]. Nonetheless, such interventions are generally considered adjunctive rather than primary treatment options in comprehensive DGAN management.

Gastric electrical stimulation (GES) has emerged as a promising therapeutic modality for patients with refractory gastroparesis unresponsive to conventional pharmacological interventions. This approach involves the implantation of a neurostimulator device that delivers low-energy electrical pulses to the gastric wall, thereby enhancing gastric emptying and alleviating symptoms such as nausea and vomiting[62,63]. Additionally, gastric peroral endoscopic myotomy, an endoscopic pyloromyotomy technique targeting pyloric dysfunction, has demonstrated symptomatic benefits in selected patients with gastroparesis, particularly those with documented pyloric spasm or increased pyloric resistance[64,65]. Despite these promising findings, high-quality evidence from large-scale randomized controlled trials evaluating the efficacy and safety of GES and endoscopic interventions remains limited, highlighting the need for further investigation.

Given the established role of gut dysbiosis in the pathogenesis of DGAN, therapeutic strategies targeting the restoration of microbial homeostasis have attracted increasing attention. Probiotics and prebiotics have shown potential in modulating gut microbiota composition, thereby contributing to the alleviation of gastrointestinal symptoms and the improvement of autonomic function[66-68]. Randomized controlled trials have demonstrated that probiotic supplementation with strains such as Lactobacillus and Bifidobacterium may enhance insulin sensitivity and glycemic control by modulating SCFA metabolism[69]. Furthermore, intervention with low-dose fructo-oligosaccharides has been reported to reduce systemic inflammation, as reflected by decreased levels of pro-inflammatory cytokines such as TNF-α. Fecal microbiota transplantation represents an emerging therapeutic option under investigation for its ability to re-establish a healthy gut microbial ecosystem in various metabolic and gastrointestinal disorders, including DGAN[70]. In addition, recent advances in nanotechnology-based drug delivery systems, such as liposomes and polymer-based carriers, have been developed to improve the stability, bioavailability, and gut-targeting efficiency of active compounds, including probiotics and polyphenols. These innovative approaches enable site-specific delivery to affected regions of the gastrointestinal tract while minimizing systemic exposure and associated adverse effects. Nevertheless, critical challenges persist in translating targeted therapies into clinical practice, including substantial heterogeneity in microbial responses, uncertainty regarding optimal treatment duration and dosage regimens, variability among patient populations, and insufficiently defined long-term safety and sustainability of these interventions in real-world settings. Furthermore, the long-term efficacy and clinical relevance of microbiota-targeted therapies for DGAN management require rigorous validation through larger, multi-center, well-designed clinical trials[8].

Early diagnostic strategies of DGAN

Timely identification of DGAN is essential to prevent disease progression and improve clinical outcomes. Conventional diagnostic approaches primarily rely on the assessment of gastrointestinal motility and autonomic function tests[71]. Gastric emptying can be evaluated using scintigraphy, which remains the gold standard diagnostic modality, as well as through alternative methods such as the gastric emptying breath test or wireless motility capsule studies which offer the advantage of concurrent evaluation of regional transit times throughout the gastrointestinal tract[72].

However, these traditional techniques present significant limitations, particularly in their sensitivity for early-stage detection of DGAN. In many cases, autonomic dysfunction may not be identified until advanced stages of neuronal damage have occurred. Therefore, emerging non-invasive diagnostic tools are gaining attention as promising strategies for earlier detection[3]. Electrochemical skin conductance (ESC) measurement, utilizing devices such as Sudoscan, has been recognized as a rapid, non-invasive method for evaluating sudomotor function, which reflects small fiber neuropathy often associated with autonomic dysfunction in diabetes, including DGAN[73,74]. Several studies have confirmed the utility of ESC in detecting autonomic impairment among patients with diabetes, suggesting its potential role as a screening tool for early-stage neuropathy[75,76]. Nevertheless, recent investigations have reported that gastrointestinal and extraintestinal autonomic parameters may not always correlate directly. In particular, only proximal gastrointestinal symptoms were found to be associated with the gastric motility index and cardiovascular reflex test outcomes[74], highlighting the complexity of autonomic involvement across different organ systems and the need for organ-specific assessment approaches.

Advanced imaging techniques have also been applied to improve diagnostic accuracy in gastrointestinal neuropathies. High-resolution magnetic resonance imaging has been utilized to visualize structural alterations within the ENS, providing valuable insights into neural integrity in affected patients[77]. Furthermore, innovative molecular imaging approaches, such as 18F-SynVesT-1 positron emission tomography combined with neurite orientation dispersion and density imaging, enable the assessment of synaptic density and neuronal morphology. These modalities have been employed in experimental studies investigating the relationship between gut microbiota alterations and neuropathic changes[78], revealing correlations between microbiota composition, metabolite profiles, and neuronal integrity.

Additionally, the exploration of molecular biomarkers indicative of neuronal injury and inflammation represents an emerging direction for improving early diagnosis of DGAN. Although significant progress has been made in identifying biomarkers for diabetic peripheral neuropathy, research specifically focusing on reliable molecular indicators for gastrointestinal autonomic neuropathy remains limited[79]. Further investigations are warranted to establish DGAN-specific biomarkers that could facilitate early detection and enable timely therapeutic intervention.

CONCLUSION

The pathophysiological mechanisms of DGAN involve a complex bidirectional interplay between neuronal injury and gut microbiota dysbiosis, wherein these two factors form a self-perpetuating cycle that exacerbates gastrointestinal dysfunction and systemic metabolic disturbances. Accumulating evidence suggests that autonomic neurodegeneration and microbial dysbiosis impair ENS signaling and gastrointestinal motility through convergent mechanisms including oxidative stress, neuroinflammation, and disruption of the intestinal epithelial barrier. Moreover, microbiota-derived metabolites, such as SCFAs and LPS, actively modulate the neuroimmune microenvironment, thereby further aggravating autonomic neuronal damage. These findings indicate that integrated therapeutic strategies simultaneously targeting both neuronal protection and the restoration of microbial homeostasis may represent a paradigm-shifting approach for optimizing the management of DGAN. Future research should focus on integrating neurobiology, microbiome science, metabolomics and advanced computational modelling to systematically elucidate the molecular networks governing neuron–microbiota interactions in DGAN. With the advancement of artificial intelligence (AI), AI-driven multi-omics data analysis may facilitate the identification of DGAN-specific biomarkers, enabling precision stratification and personalized therapeutic strategies. In particular, incorporating insights from epigenetics and immunometabolic regulation may support the development of individualized interventions based on host genotype–microbiome interactions, such as customized probiotic formulations or targeted modulation of microbial metabolites. Restoration of vagal nerve function and plasticity, through pharmacological, electrical, or microbiota-based modulation of GBA, holds promise for reversing gastrointestinal dysmotility associated with DGAN. Concurrently, precision-targeted microbial interventions could contribute to the re-establishment of ENS homeostasis. The development of combination therapies or novel nanotechnology-based delivery systems to enhance treatment efficacy also warrants further exploration. Ultimately, large-scale, multicenter, longitudinal clinical trials are needed to validate the long-term safety and clinical effectiveness of these interdisciplinary approaches in the prevention and management of DGAN and its related complications. Such efforts will be critical for translating basic mechanistic research into precision medicine practices, advancing the care of patients affected by DAN.