Crosstalk between oxidative stress and inflammatory pathways: Natural therapeutic approaches for diabetic wound healing

Abstract

Oxidative stress and inflammation are closely interrelated processes that are pivotal to the impaired wound healing associated with diabetes. Chronic hyperglycemia in diabetic patients induces excessive reactive oxygen species (ROS) production, which triggers heightened inflammatory responses. The resulting inflammation exacerbates oxidative damage, delays wound closure, and intensifies tissue injury, thereby creating a detrimental cycle that disrupts normal wound healing. Recent research has increasingly focused on the therapeutic potential of natural products in modulating oxidative stress and inflammation to enhance diabetic wound healing. Natural compounds, such as polyphenols, flavonoids, and terpenoids, have demonstrated significant efficacy in reducing oxidative damage and modulating inflammatory pathways. These bioactive agents exhibit potent antioxidant activity by scavenging ROS and enhancing endogenous antioxidant defenses while concurrently inhibiting the release of proinflammatory cytokines. Additionally, natural therapies have been shown to promote angiogenesis, enhance collagen synthesis, and improve fibroblast function, further facilitating wound repair. This review provides insights into the complex interplay between oxidative stress and inflammation in diabetic wound healing and evaluates the therapeutic potential of natural products as adjunctive treatments. Further clinical investigations are essential to validate the efficacy and safety of these natural interventions for diabetic wound management.

Key Words: Diabetic wound healing; Oxidative stress; Inflammation; Natural medicines; Signaling pathways

Core Tip: Oxidative stress and inflammation significantly impede wound healing in diabetes through a complex interactive mechanism. Natural therapeutic agents, including polyphenols, flavonoids, and terpenoids, have shown promise in mitigating oxidative damage and inflammatory responses and promoting angiogenesis, collagen deposition, and fibroblast function. This review highlights the intricate crosstalk between oxidative stress and inflammatory pathways in diabetic wound healing and underscores the potential of natural products as adjunctive therapies, emphasizing the need for further clinical validation to establish their efficacy and safety.

INTRODUCTION

Diabetic foot ulcers (DFUs) are defined as full-thickness skin lesions located below the ankle in individuals with diabetes and are frequently accompanied by peripheral neuropathy and/or peripheral artery disease, with increased risks of infection and ischemia[1]. As of 2021, approximately 537 million adults aged between 20 and 79 years worldwide were affected by diabetes mellitus[2]. Each year, approximately 4 million diabetic patients develop DFUs, and the treatment costs of DFUs are nearly equal to the total costs associated with all other diabetic complications combined[3,4]. The pathogenesis and progression of DFUs involve complex interactions between hyperglycemia, inflammation, and oxidative stress (OS). Excessive OS exacerbates insulin resistance (IR), impairs glucose control and triggers inflammatory responses, leading to the release of proinflammatory cytokines. These processes result in vascular and nerve damage, immune dysfunction, and ultimately delayed wound healing. Critically, the crosstalk between OS and inflammation creates a self-sustaining, detrimental cycle that disrupts the delicate balance between antioxidant and anti-inflammatory defenses and significantly hinders the healing of diabetic chronic wound (DCW)[5].

Natural medicines, renowned for their favorable safety profiles and pharmacological activities, have demonstrated efficacy in alleviating OS, improving local microcirculation, and promoting wound healing[6]. Conventional treatment of DFUs primarily involves surgical debridement, pressure offloading, restoration of blood flow, and infection control[7]. With the growing global recognition of traditional Chinese medicine (TCM), natural medicines, an integral component of TCM, have emerged as valuable adjuncts in the management of DFUs[8]. This review aims to summarize the key factors affecting diabetic wound healing and to elucidate how natural medicines modulate OS and inflammation in DFUs. The goal of this study was to provide a theoretical foundation for DFUs prevention and treatment and to provide a reference for the clinical application of adjunctive therapies.

MECHANISMS OF NORMAL AND IMPAIRED WOUND HEALING

Wound healing is a highly orchestrated biological process that involves the coordinated action of multiple cell types, molecular mediators, signaling pathways, and immune and biological systems. This process encompasses distinct yet overlapping phases, including hemostasis, inflammation, tissue proliferation, and remodeling[9].

During wound formation, tissue damage disrupts the local microenvironment and causes vascular injury, resulting in bleeding. The body rapidly initiates hemostasis through a series of coordinated mechanisms, including platelet aggregation, vasoconstriction, coagulation factor activation, complement activation, and the initiation of inflammatory responses, ultimately leading to the formation of a blood clot and stabilization of the wound site.

Following coagulation, the wound transitions into the inflammatory phase, which typically lasts 1-4 days. During this stage, the complement cascade is activated, leading to a series of molecular events that promote neutrophil recruitment at the wound site. Neutrophils play pivotal roles in phagocytosing bacteria, foreign bodies, and necrotic tissue, thereby preventing infection. Concurrently, macrophages are activated and secrete elevated levels of proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), IL-6, IL-12, and IL-23, while they secrete lower levels of IL-10. This cytokine milieu initiates a complex inflammatory cascade and enables a degree of self-regulation within the wound microenvironment[10,11].

After the resolution of inflammation, the wound enters the proliferative phase. During this stage, several key processes take place: (1) Granulation tissue formation: Newly formed granulation tissue, which is composed of small blood vessels and fibroblasts, begins to develop at the wound site. The recruitment of these cells is mediated by growth factors such as transforming growth factor-beta (TGF-β) and platelet-derived growth factor, which are secreted by inflammatory cells and platelets. Granulation tissue provides essential nutritional support for wound healing and serves as a structural scaffold for subsequent tissue repair; (2) Epithelialization: Epithelial cells at the wound margin proliferate and migrate across the wound bed, ultimately forming a new skin barrier. This process is stimulated by various growth factors, including hepatocyte growth factor, fibroblast growth factor, and members of the epidermal growth factor family[12]. Once epithelial cells converge, migration ceases, and basement membrane formation begins to stabilize the newly formed epithelial layer; and (3) Collagen deposition: Collagen, produced by fibroblasts, is critical throughout all stages of wound healing and gradually imparts structural support to the wound. As collagen accumulates, the tensile strength of the wound increases; however, the ultimate strength depends on the duration and specific location of the repair. While collagen improves the structural integrity of the wound, full restoration to preinjury strength is rarely achieved because of inevitable tissue remodeling during the healing process.

The final phase of wound healing is the remodeling phase, which is characterized by long-term tissue maturation and reorganization. During this stage, extracellular matrix (ECM) synthesis, neovascularization, and remodeling occur concurrently. The remodeling phase is prolonged, often lasting from 1-2 years or even longer. Although wounds gradually recover tensile strength and partial function, full restoration to the native physiological state is rarely achieved. Ultimately, repair results in the formation of scar tissue, which may be associated with partial functional impairment[13].

CROSSTALK BETWEEN OS AND INFLAMMATION IN DIABETIC WOUNDS

Diabetic wounds are more complex than normal wounds, as multiple aspects of the healing process are disrupted by factors such as hyperglycemia, bacterial infection, ischemia-hypoxia, vascular dysfunction, impaired synthesis of nicotinamide adenine dinucleotide (NAD⁺), and chronic inflammation[14]. These factors can act synergistically to exacerbate tissue damage, ultimately resulting in delayed wound healing.

Role of inflammation in diabetic wounds

Chronic inflammation is a hallmark of diabetic wounds, reflecting both the underlying disease state and a critical barrier to effective wound repair. This persistent inflammatory condition disrupts the normal injury response, prolonging the inflammatory phase and impairing the transition to the proliferative phase, thereby hindering progression through the normal stages of wound healing[15].

During the early stages of wound healing, damage-associated molecular patterns, hydrogen peroxide, chemokines, and other signaling molecules establish gradients that guide neutrophils to the wound site for pathogen clearance. However, hyperglycemia impairs chemokine expression, thereby slowing neutrophil-mediated elimination of pathogens[16]. Monocytes subsequently migrate to the wound bed, where they differentiate into macrophages and assume specialized roles. A key event marking the transition from the inflammatory to the proliferative phase is the shift of macrophages from the proinflammatory M1 phenotype to the anti-inflammatory M2 phenotype. Persistent hyperglycemia, however, suppresses the expression of glycolytic rate-limiting enzymes and associated pathways in macrophages, resulting in diminished phagocytic and antimicrobial capacity[17]. In chronic diabetic wounds, the M1 phenotype is predominant, whereas anti-inflammatory M2 macrophages are relatively rare. This imbalance leads to the sustained secretion of proinflammatory cytokines, including TNF-α, IL-1β, IL-6, IL-12, and IL-23[18]. Mechanistically, M1 macrophages activate reduced coenzyme II and the NAD⁺ phosphate (NADPH) oxidase system, enhancing reactive oxygen species (ROS) production to combat pathogens, but this also disrupts normal wound healing. In the diabetic ulcer environment, upstream receptors such as the toll-like receptors (TLRs) family are significantly upregulated, intensifying myeloid differentiation primary response gene 88 (MyD88) signaling and promoting nuclear factor kappa-B (NF-κB) pathway activation. This cascade interferes with the release of interferons, inflammatory cytokines, and chemokines[15]. NF-κB activation further stimulates the assembly and activation of the NLRP3 inflammasome, thereby contributing to the immune-inflammatory response. Common metabolic byproducts in diabetes, such as advanced glycation end-products (AGEs), bind to receptor of AGEs (RAGEs), activating both the NF-κB and mitogen-activated protein kinase (MAPK) pathways and increasing the release of proinflammatory cytokines. These signaling molecules form a positive feedback loop, perpetuating inflammation and exacerbating the inflammatory phenotype[19]. Ultimately, hyperglycemia-induced inflammation impairs angiogenesis, limiting oxygen and nutrient delivery and thereby sustaining a chronic inflammatory microenvironment within the wound.

Role of OS in diabetic wounds

The pathological state of diabetic wounds leads to excessive production of O^2-, triggering OS. Moreover, the imbalance between free radicals and antioxidants in the body exacerbates the overproduction of ROS. The accumulation of ROS then leads to cellular and tissue damage, subsequently delaying the wound healing process. OS, through various mechanisms, such as skin damage, neuropathy, ischemic lesions, and local infections, further impairs the healing process of diabetic wounds[20]. Wounds in diabetic patients appear to be more susceptible to excessive OS and damage, both at the wound periphery and in the central wound tissue. The activity of antioxidants, such as glutathione (GSH), GSH peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT), is reduced in local tissues, whereas the level of the oxidant malondialdehyde (MDA) is elevated. These changes reflect a diminished antioxidant capacity in diabetic wounds[21]. Excessive accumulation of ROS is considered a hallmark factor in the delayed healing of DCW. In the early stages of wound healing, moderate ROS expression promotes angiogenesis, whereas excessive ROS and antioxidant defense deficiencies in DCW lead to prolonged nonhealing[22]. ROS can regulate the migration and proliferation of fibroblasts and keratinocytes by activating MAPK signaling pathways, such as the p38 MAPK, JNK, and ERK pathways[23]. Persistent OS accelerates the senescence of fibroblasts, endothelial cells, keratinocytes, and mesenchymal stem cells, which significantly hinders the wound healing process, including granulation tissue formation. Elevated expression of AGEs in the diabetic wound microenvironment can induce excessive ROS production upon binding to receptors on endothelial cell surfaces[24]. Moreover, ROS can impair the activation of hypoxia-inducible factor-1/vascular endothelial growth factor (VEGF), leading to insufficient angiogenesis and causing local ischemia[25]. Additionally, ROS can damage wound contraction, prolong the inflammatory response, and hinder the proliferation of the ECM. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a critical transcription factor involved in wound healing through the regulation of angiogenesis and antioxidant gene expression. When the regulation of genes encoding heme oxygenase 1 and NAD(P)H dehydrogenase quinone 1 is insufficient, antioxidant responses are weakened, leading to elevated ROS levels[26,27]. The microenvironment induces increased expression of matrix metalloproteinases, stalling re-epithelialization, whereas activation of the Nrf2 signaling pathway significantly increases TGF-β1 in keratinocytes and reduces MMP9 synthesis[28,29]. Additionally, OS responses can impact the healing of diabetic wounds by activating the NF-κB, TGF-β, phosphoinositide 3-kinase/protein kinase B, and Janus kinase/signal transducer and activator of transcription (STAT) signaling pathways[30,31] (Figure 1). Many studies have shown that the Nrf2 and NF-κB signaling pathways are more critical for the regulation of inflammation and OS and that these pathways interact with each other[28]. For example, tanshinone II_A has the capacity to concomitantly stimulate the Nrf2/antioxidant response element pathway and suppress the NF-κB pathway, thereby ameliorating neuropathic pain in diabetic rats[32]. Nrf2 can bind to the negative regulator kelch-like ECH-associated protein 1 (Keap1) to form a protein complex. Its downstream target HO-1 can inhibit the phosphorylation of IκB, a p65 site in the NF-κB pathway, by binding to it and attenuating the inflammatory response[33,34].

Figure 1 Crosstalk between oxidative stress and inflammatory signaling pathways. AGE: Advanced glycation end-products; ARE: Antioxidant response element; ERK: Extracellular signal-regulated kinase; HMGB1: High mobility group box 1; IRAK: Interleukin-1 receptor-associated kinase; JAK: Janus kinase; JNK: C-Jun N-terminal kinase; Keap1: Kelch-like ECH-associated protein 1; MAPK: Mitogen-activated protein kinase; MEK: Mitogen-activated extracellular signal-regulated kinase; NF-κB: Nuclear factor kappa-B; NEMO: NF-κB essential modulator; Nrf2: Nuclear factor erythroid 2-related factor 2;PI3K: Phosphoinositide 3-kinase; STAT3: Signal transducer and activator of transcription 3; TAB: TAK1-binding protein; TAK: Transforming growth factor-β activated kinase; TLR: Toll-like Receptor; TRAF6 TNF receptor-associated factor 6; Tyk2: Tyrosine kinase 2. Created in BioRender.

Additionally, NF-κB has been found to suppress the transcriptional activity of Nrf2. Research indicates that the p65 subunit of NF-κB hinders the Nrf2/ARE pathway[35], promotes the translocation of Keap1 to the nucleus, diminishes the binding of Nrf2 to its DNA sequence counterpart, and increases the ubiquitination of Nrf2[36]. Many DFUs studies have focused on the relationship between Nrf2 and the NF-κB signaling pathway. For example, nanoparticle gauze incorporating a blend of gallocatechin has been shown to mitigate OS and inflammation while enhancing wound healing in diabetic rats through modulation of the Nrf2/HO-1 and TLR4/NF-κB pathways[37].

Mutual reinforcement of OS and inflammation

Oxidative reactions and inflammation are protective mechanisms of self-regulation that help maintain a certain balance under physiological conditions. Diabetic wounds are disrupted by external factors, such as metabolic disorders and harmful stimuli, making it difficult for the inflammatory state to subside. As a result, reactive molecules such as oxygen free radicals, ROS, and reactive nitrogen species (RNS) exceed the body's antioxidant defense capacity, leading to damage to cells, tissues, and organs. These data indicate that hyperglycemia triggers the formation of free radicals and disrupts the endogenous antioxidant defense system through the mitochondrial electron transport chain, glucose autoxidation, and the polyol pathways. Combined, these pathways increase the levels of ROS and RNS in the body, with the mitochondrial electron transport chain being the primary source of ROS production. The electron transport chain (ETC) primarily involves enzyme complexes I-IV, cytochrome c, and coenzyme Q. A small amount of superoxide products, including O^2-, hydrogen peroxide (H₂O₂), and hydroxyl radicals, are continuously generated in enzyme complexes I and III. SOD, CAT, and GPx catalyze the conversion of superoxide products into oxygen and water[38]. When excessive accumulation of superoxide products such as ROS occurs, the cellular antioxidant capacity is reduced, and the body's inflammatory response intensifies[39,40]. ROS play a central role in the interaction between inflammation and oxidative reactions, and their overproduction further leads to IR and impaired insulin secretion, thereby exacerbating the metabolic disorder cycle and promoting the progression of diabetic complications[41].

OS and inflammatory responses often interact with each other. OS can promote the onset of inflammation by activating signaling pathways such as the NF-κB and MAPK pathways. Oxygen free radicals stimulate immune cells directly or indirectly, causing them to secrete inflammatory mediators that initiate both local and systemic inflammatory responses. In turn, the inflammatory response can increase the activity of local inflammatory cells, such as neutrophils and macrophages, leading to the production of more ROS. Hyperglycemia impairs the process of monocyte recruitment to wounds, and changes in the immune microenvironment lead to macrophage polarization toward the proinflammatory M1 phenotype, enhancing the inflammatory response and increasing oxidative damage. Additionally, during pathogen phagocytosis, inflammatory cells release large amounts of oxygen free radicals. These free radicals are used to eliminate pathogens but may also cause oxidative damage to normal cells in the body. In diabetic wounds, the reduced activity of GSH-Px and SOD weakens the ability to eliminate free radicals, leading to increased oxidative damage. Furthermore, inflammatory cells release enzymes (such as NADPH oxidase and peroxisomal enzymes) to increase ROS production, further exacerbating OS. Continuous activation of the inflammatory response and increased OS result in worsened tissue damage and disease progression in wounds. In diabetic wounds, the elevated expression of AGEs and excessive oxidation of the AGE-RAGE axis activate NF-κB, increasing the transcription of various inflammatory factors and adhesion molecules, which promotes macrophage polarization toward the M1 type[42]. OS can also activate the NLRP3 inflammasome, inducing the release of proinflammatory cytokines such as IL-1β and IL-18. The excessive release of inflammatory cytokines leads to sustained inflammation in the wound area, and this chronic inflammation not only damages the tissue but also increases OS, creating a vicious cycle. Studies have shown that inhibiting the AGE-NF-κB-NLRP3 axis can enhance anti-inflammatory, antioxidant, and proangiogenic responses, thereby promoting diabetic wound healing[43].

AGEs reduce the bioavailability of endothelial nitric oxide and lead to excessive production of ROS, thereby impairing fibroblast and keratinocyte proliferation, as well as collagen deposition, ultimately hindering wound repair[42]. In chronic diabetic wounds, due to the influence of inflammation and OS, various proteases and proinflammatory factors are excessively expressed, disrupting the ECM environment of skin tissue. This impairs angiogenesis, epithelial regeneration, and ECM synthesis. By modulating the Nrf2 signaling pathway, the expression of antioxidant enzymes can be increased, whereas the secretion of proinflammatory cytokines can be suppressed, thereby accelerating reepithelialization and promoting wound healing[44,45].

Owing to excessive inflammation, sustained hyperglycemia, and dysregulated oxidative function, diabetic wounds promote the colonization of various microorganisms, creating a pathological microenvironment for biofilm infections. High levels of OS in diabetic wounds significantly alter the wound microbiome. These bacteria severely impair healing and may lead to amputations[46]. Reports indicate that, by clearing ROS and regulating bacterial activity, OS and biofilm infections can be suppressed, thus promoting wound healing[47].

Studies on patients with DFUs have also confirmed that OS and excessive inflammation are critical factors affecting wound healing. Elevated levels of inflammatory factors and oxidative products exacerbate impaired glucose metabolism, vascular lesions, and wound ulceration[48] (Figure 2). DFUs patients exhibit significantly reduced antioxidant capacity, accompanied by marked inflammatory responses. Therefore, antioxidant and anti-inflammatory drugs have become primary therapeutic strategies for diabetic wound treatment[5,49]. A gel that combines the dual effects of improving oxidative damage and reducing inflammation has been shown to promote tissue repair and vascular regeneration in DCW[50]. Currently, an increasing number of studies are focusing on anti-inflammatory and antioxidant strategies, which have gradually become effective approaches for the treatment of diabetic wounds.

Figure 2 Interactions between oxidative stress and inflammation in diabetic wounds. Hyperglycemia-induced oxidative stress and inflammation synergistically disrupt multiple stages of the wound healing process, including immune cell recruitment, angiogenesis, fibroblast activation, and extracellular matrix remodeling. These processes impair re-epithelialization and prolong chronic wound states. The interplay between M1/M2 macrophage polarization, ischemia, biofilm formation, and mesenchymal stem cell dysfunction further reinforces a self-perpetuating cycle of delayed tissue repair within the diabetic microenvironment. HIF: Hypoxia-inducible factor; HMOX-1: Heme oxygenase 1; IGF: Insulin-like growth factor; KGF: Keratinocyte growth factor; MMP: Matrix metalloproteinase; ROS: Reactive oxygen species; TIMP: Tissue inhibitor of metalloproteinases; VEGF: Vascular endothelial growth factor. Created in BioRender.

NATURAL MEDICINES TARGETING OS AND INFLAMMATION IN DIABETIC WOUNDS

Natural medicines have a wide range of pharmacological activities, many of which exhibit significant potential in promoting diabetic wound healing by effectively reducing free radical levels, mitigating oxidative damage through antioxidant effects, regulating the balance of inflammatory factors and inhibiting excessive inflammatory responses. Depending on their molecular structure, natural medicines can be categorized into various types (Figure 3).

Figure 3 Natural compounds and their mechanisms in promoting diabetic wound healing. T-AOC: Total antioxidant capacity; MCP-1: Monocyte chemoattractant protein-1; GCLC: Glutamate-cysteine ligase; 8-OHdG: 8-oxo-2'-deoxyguanosine; TRX: Thioredoxin; SIRT1/PGC-1α: Silent information regulator/Peroxisome proliferator-activated receptor-γ coactivator-1α; AMP-AMPK: Adenosine 5‘-monophosphate-activated protein kinase; G-CSF: Granulocyte colony-stimulating factor; M-CSF: Macrophage colony-stimulating factor; ECAR: Extracellular acidification rate; glycoPER: Glycolytic proton efflux rate; Rho/ROCK: Ras homolog gene/Rho-associated coiled-coil-forming protein kinase; STAT6: Signal transducer and activator of transcription 6; HOMA-IR: Homeostatic model assessment of insulin resistance; ASC: Apoptosis - associated speck - like protein containing a CARD; PPAR-γ: Peroxisome proliferator-activated receptor gamma; Bcl: B-cell lymphoma; TAS: Total antioxidant status; TOS: Total oxidant status; CXCL: C-X-C Motif chemokine ligand; IFN-γ: Interferon-γ; 8-iso-PG: 8-isoprostane; VCAM-1: Vascular cell adhesion molecule 1; COX2: Cyclooxygenase-2.

Flavonoids

Flavones: Baicalin (BAI) and baicalein, bioactive molecules found in Scutellaria baicalensis, are common flavonoid compounds containing phenolic hydroxyl groups that exhibit antioxidant and anti-inflammatory properties. Studies have shown that BAI can effectively alleviate diabetic conditions in patients, significantly increasing the levels of GSH-Px, SOD, and CAT while reducing MDA levels. Additionally, BAI notably inhibits the infiltration of inflammatory cells such as T lymphocytes, neutrophils, and macrophages[51]. It exerts its anti-inflammatory and antioxidant regulatory effects by upregulating the p62-Keap1-Nrf2 signaling cascade, thereby suppressing the expression of proinflammatory biomarkers and enhancing antioxidant enzyme synthesis[52]. When BAI is used to treat diabetic wounds, it can perform the aforementioned functions, resulting in enhanced epithelialization and the formation of a new vascular network[53].

Diabetic neuropathy is one of the mechanisms leading to the progression of DFU. Baicalein has been shown to improve neuronal function. It exerts protective effects on diabetic peripheral neuropathy by reducing superoxide levels, lowering the expression of inflammatory mediators, and enhancing the antioxidant and anti-inflammatory defense systems[54]. In recent years, macrophages have emerged as key targets for treating DFU, as they play crucial roles in balancing the inflammatory response. These data suggest that baicalein can disrupt the Keap1-Nrf2 interaction by competitively binding to the DGR/Kelch domain of Keap1, thereby activating the antioxidant transcriptional program, inhibiting ROS production, and alleviating OS damage. This further modulates the wound healing process[55].

Flavonols: Quercetin (Que) is a flavonoid compound widely found in the stems, flowers, leaves, buds, seeds, and fruits of many plants. It has anti-diabetic, anti-inflammatory, antioxidant, antimicrobial, and wound healing properties[56]. Que interacts with the redox reactions of the ETC, affecting its membrane potential, and can also influence ATP production through oxidative phosphorylation. As an antioxidant, Que reduces ROS production, decreases apoptosis, and alleviates mitochondrial damage[57]. Experiments have shown that Que can alleviate vascular calcification by slowing OS and mitochondrial fission[58], and it also regulates macrophage reprogramming through its impact on OS[59]. Another study indicated that Que can suppress ROS production by modulating the microbiome and reducing the levels of proinflammatory mediators, thereby increasing the expression of various endogenous antioxidants and exerting protective effects on tissues[60,61]. Que promotes angiogenesis, cell proliferation, and collagen deposition, making it a promising molecule for the treatment of DFU. However, its poor permeability and low oral bioavailability limit its effectiveness in the prevention and treatment of DFU[62]. To overcome these limitations, researchers have developed modified formulations, such as Que hydrogels[63] and Que nanocomposites[64], which maximize the antioxidant and anti-inflammatory properties as well as accelerate wound healing.

Rutin, a flavonoid glycoside widely found in plants, exerts its antidiabetic effects by reducing the levels of ROS, AGE precursors, and inflammatory cytokines, with significant effects on diabetes and its complications[65]. Intraperitoneal injection of rutin significantly improves weight loss and metabolic disorders in diabetic rats and further promotes wound healing by inhibiting the activity of inflammatory cells and increasing the production of antioxidant enzymes[66]. Similarly, the local application of rutin nanoparticles to diabetic wounds significantly accelerates the wound healing process by restoring antioxidant capacity and reducing inflammation[67].

Polymethoxylated Flavones: Nobiletin, a polymethoxyflavonoid found in certain citrus fruits, is a highly lipophilic, bioavailable, and low-toxicity compound. Nobiletin has excellent antidiabetic effects, improving lipid deposition, OS, and inflammation through the Nrf2 signaling pathway[68,69]. Additionally, nobiletin can inhibit the expression of inflammatory factors, alleviate neurotoxicity, enhance antioxidant capacity, and promote neuronal cell survival[70], thereby improving neuropathy associated with DFU.

Isoflavone: Calycosin-7-glucoside (CG), an isoflavonoid isolated from Astragalus, has been shown to increase ROS production, reduce the mitochondrial membrane potential, and induce apoptosis through mitochondrial pathways. Thioredoxin 1 (TRX1) is an important redox-regulating protein, and CG can increase OS by inhibiting TRX1 expression in a dose-dependent manner[71]. Furthermore, studies have shown that CG can promote monocyte recruitment and reduce the mitochondrial glycolysis rate via the ROS/AMPK/STAT6 pathway, inducing M2 macrophage polarization and thereby accelerating diabetic wound healing[72].

Puerarin (PR), an isoflavonoid extracted from Pueraria lobata, can delay the progression of diabetes and its complications by lowering blood glucose, improving IR, inhibiting inflammation, reducing OS, and preventing the formation of AGEs[73]. PR promotes M2 macrophage polarization and inhibits the activation of inflammatory pathways in high-glucose cultures by suppressing the NF-κB and MAPK signaling cascades, thereby exerting therapeutic effects on diabetic wounds[74]. Leveraging these properties, researchers have combined PR with emerging technologies such as hydrogels to develop optimized multifunctional dressings. These dressings, which incorporate natural drugs, can respond more effectively to OS and inflammation, thus accelerating the healing process of chronic diabetic wounds[75,76].

Genistein, an isoflavonoid from the plant estrogen family, possesses antioxidant and anti-inflammatory properties. Intervention with genistein in fructose-fed rats significantly reduces OS markers and proinflammatory factors[77]. Furthermore, it improves fasting blood glucose levels and ensures the rapid transition from the inflammatory phase to the proliferative phase of wound healing in diabetic mice by regulating early-stage inflammatory factors (TNF-α, iNOS, Cyclooxygenase 2, and NF-κB) and the antioxidant defense system (Nrf2, HO-1, GPX, and CAT)[78].

Phenols

Polyphenols: Curcumin (Cur), a polyphenolic compound extracted from turmeric roots, regulates inflammatory factors through the NF-κB signaling pathway, reduces OS levels, and improves pancreatic β-cell function, thus exerting protective effects against diabetes-related complications[79]. Reports have indicated that Cur has great potential in the treatment of DFU. Cur-loaded nanoparticles effectively improve diabetic wound infections caused by methicillin-resistant Staphylococcus aureus[80]. Despite its poor water solubility, low bioavailability, and chemical instability, Fan et al[81] developed a composite hydrogel of Cur, which effectively scavenges reactive ROS, downregulates IL-1β, and upregulates platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31), expression, thereby promoting angiogenesis and collagen deposition and accelerating wound healing. Another Cur-loaded thermosensitive hydrogel demonstrated excellent biological stability, enhancing antioxidant effects while remodeling the microenvironment necessary for DFU healing[82].

Kaempferol (Kae), a natural polyphenol derived primarily from the rhizomes of the ginger family plant Kaempferia, is also a type of flavonols, has been found to directly scavenge peroxynitrite and hydroxyl radicals (secondary metabolites of OS) at low concentrations while increasing the expression of antioxidant enzymes at relatively high concentrations[83]. Kae can also reduce hyperglycemia, OS, and inflammation markers by activating the AGE-RAGE axis[84]. A study by Yao et al[85] revealed that Kae alleviates OS and inflammation induced by H₂O₂ and paraquat, inhibits the activation of inflammatory pathways, and increases antioxidant levels by increasing Nrf2 and HO-1 protein levels, thereby protecting blood vessels from damage. Furthermore, Kae-loaded electrospun dressings exhibit favorable wound healing effects on diabetic wounds by modulating MMP9 and macrophage polarization[86]. When combined with lecithin-chitosan, the dressings further enhance lipophilicity and mucosal adhesion, thereby improving the healing effect[87].

Xanthones: Mangiferin, a glucosylxanthone extracted from plants in the Anacardiaceae and Gentianaceae families, has a wide range of biological activities, including antioxidant, antidiabetic, antiviral, anticancer, and anti-inflammatory effects. It prevents cellular damage by alleviating OS-induced apoptosis and regulating MAPK-mediated inflammation[88]. Nrf2, a redox-sensitive transcription factor, is commonly activated by mangiferin. Through the activation of the Nrf2 signaling pathway, mangiferin reduces the synthesis of oxidative products and dose-dependently inhibits the generation of ROS under high-glucose conditions. Additionally, it promotes the regeneration of damaged vascular networks in hyperglycemic environments[89]. Owing to its poor solubility in both water and lipids, mangiferin has low bioavailability; however, the formulation can be altered to improve its solubility[90]. Lwin et al[91] demonstrated that, when mangiferin gel is applied to diabetic rat wounds, it improves wound conditions and accelerates the healing process by modulating angiogenic factors, inflammatory markers, and OS biomarkers.

Terpenoids

Diterpenoids: Salvia miltiorrhiza contains a variety of diterpene compounds, primarily lipophilic tanshinones, including tanshinone II_A, cryptotanshinone, tanshinone I, and dihydrotanshinone, which have low toxicity and high efficacy. These compounds exhibit a wide range of pharmacological activities, such as antioxidant, anticoagulant, antimicrobial, antiviral, anti-inflammatory, and immunosuppressive effects[92]. Dihydrotanshinone inhibits the secretion of inflammatory factors and the occurrence of OS in vivo through the high mobility group box 1 protein/TLR4/NAD⁺ oxidase 4 pathway, thereby attenuating apoptosis[93]. Tanshinone II_A reduces ROS and MDA production in LPS-treated mice and promotes SOD expression, mitigating OS and inflammation in endothelial cells by activating the Nrf2 signaling pathway[94]. Additionally, nanoparticles loaded with tanshinone II_A show enhanced antimicrobial properties, reducing wound infections and promoting tissue repair[95]. Cryptotanshinone improves the inflammatory response and OS under high-glucose conditions. When applied to diabetic wounds, it inhibits leukocyte infiltration, increases vascular density, and promotes wound healing by facilitating fibroblast transformation and enhancing ECM remodeling[96,97].

Triterpenes: Asiaticoside, a triterpenoid saponin compound isolated from Centella asiatica, has various pharmacological effects, including antioxidant, anti-inflammatory, and antiulcer activities. Centella extract alleviates tissue damage in diabetic pathological environments through its antioxidant and anti-inflammatory actions[98]. The combination of asiaticoside and NO modulates the Wnt/β-catenin signaling pathway; inhibits bacterial growth at the wound site; reduces inflammation; and increases the expression of VEGF, iNOS, eNOS, and CD34, thus accelerating diabetic wound healing[99]. In tissue repair, it also suppresses fibroblast proliferation, thereby preventing the formation of hypertrophic scars, and can be subsequently applied to individuals prone to scarring[99].

Quinones

Emodin and rhein are both anthraquinone compounds. Emodin alleviates OS and inflammation induced by high glucose in cells[100]. It mediates the NF-κB signaling pathway by inhibiting the p65-NF-κB complex and increasing the proportion of M2 macrophages. Additionally, it increases the expression levels of collagen III, fibronectin, and α-SMA, thereby accelerating wound healing through increased ECM synthesis and granulation tissue formation[101]. Rhein also exerts anti-inflammatory and antioxidant effects to alleviate high-glucose-induced damage, and it can prevent and treat diabetes by improving IR. When combined with chitosan, rhein enhances its anti-inflammatory and antimicrobial properties, effectively reducing tissue inflammation, promoting collagen deposition, and accelerating diabetic wound healing[102].

Alkaloids

Isoquinoline alkaloids: Berberine (BBR) is an alkaloid isolated from the Ranunculaceae plant Coptis chinensis. It has various biological activities, including the regulation of glucose and lipid metabolism and anti-inflammatory and antioxidant effects. BBR enhances insulin sensitivity and increases insulin receptor expression in a dose-and time-dependent manner[103]. Nanoparticles loaded with BBR demonstrate effective antioxidant and anti-inflammatory activities in LPS-induced mouse macrophages, reducing the gene expression of TNF-α and iNOS and decreasing ROS and NO production[104]. Another BBR -modified hydrogel also has excellent moisturizing, anti-inflammatory, and antioxidant properties, and when applied to diabetic wounds, it accelerates the regeneration of epithelial tissue[105].

Piperidine alkaloids: Matrine, an alkaloid found in plants of the Sophora genus, effectively alleviates OS damage to organs and also reduces the production of inflammatory mediators[106]. The potent anti-inflammatory effects of matrine can mitigate the inflammatory response around wounds, reducing ROS generation. Exosome vesicles loaded with matrine can synergistically enhance the anti-inflammatory efficacy of matrine and promote the formation of new tissue and blood vessels during wound healing[107].

Vanillamide alkaloids: Capsaicin, the main pungent component of chili peppers, is volatile and has a strong irritating odor. It has antioxidant, antidiabetic, antitumor, and analgesic properties. The dual actions of capsaicin, as an antioxidant and a dicarbonyl scavenger, contribute to its antiglycation effects[108]. Capsaicin can counteract the depletion of antioxidants and antioxidant enzymes and reduce the elevated levels of lipid oxidation products[109,110]. Owing to its good metabolic activity on the skin, capsaicin can maximize its advantages when applied topically. Capsaicin-based topical formulations, such as ointments or patches, are widely used for pain management, such as for alleviating peripheral neuropathic pain in patients with DFU[111,112]. Although current studies have demonstrated that capsaicin can enhance the healing of conventional wounds by suppressing inflammatory responses, its therapeutic potential in the treatment of diabetic wounds remains to be further elucidated[113].

Steroids

β-Sitosterol (BSIT) is a plant sterol widely found in various plant oils, nuts, and seeds in nature. It has antibacterial, anti-inflammatory, antioxidant, and antihyperglycemic activities. BSIT alleviates lipid metabolism disorders and combats OS and inflammation by regulating the TGF-β1/Nrf2/SIRT1/p53 signaling pathway[114,115]. The data indicate that the MAPK, mTOR, and VEGF signaling pathways are more enriched in wounds treated with β-sitosterol. Additionally, it can aid in diabetic wound healing by regulating M2 macrophage polarization and angiogenesis[116].

Other natural compounds

Other compounds, such as polysaccharides derived from carbohydrates, including Bai Ji polysaccharide[117], astragalus polysaccharide[118], lycopene from carotenoids[119], and cinnamaldehyde from aldehydes[120,121], all exhibit good antioxidant and anti-inflammatory effects. The potential of these compounds in promoting wound healing is currently being investigated.

CLINICAL APPLICATIONS AND CHALLENGES OF NATURAL MEDICINES

Studies on the clinical application of natural medicines have gradually increased in recent years; for example, 8% capsaicin patches can moderately relieve peripheral nerve pain in diabetic foot[122]. Nanohydrogels embedded with Que and oleic acid significantly reduce wound healing time after application to diabetic wounds[123]. The treatment of diabetic foot is a multidisciplinary comprehensive process that usually requires a combination of wound care, anti-infection, blood glucose control, angiogenesis, surgical intervention and other measures. A single natural medicine may not be able to address the complex pathological state of diabetic foot comprehensively; therefore, in clinical treatment, multiple medicines are used in combination according to certain compatibility rules, that is, compound medicine in TCM. For example, in a study of 720 DFU patients, topical cortex phellodendron compound fluid significantly accelerated wound healing and improved clinical efficacy[124]. Another prospective randomized, double-blind, placebo-controlled study revealed that a drug (NF3) consisting of Astragali Radix and Rehmanniae Radix reduces the expression of inflammatory factors and improves limb neuropathy and wound healing efficiency when administered orally[125]. Shengji Ointment promotes fresh granulation growth and skin regeneration and maintains a traumatized regenerative environment after intervention in patients with Wagner grade 3-4 DFUs[126]. There are also reports of natural medicine injections being administered via the Zusanli (ST36) acupuncture point for the treatment of diabetic peripheral neuropathy. However, these trials are of low quality and need to be further investigated[127] (Table 1). At present, in clinical application in China, in addition to the use of conventional drug therapy, most natural medicine-based methods, combined with massage, acupoint injections, foot baths, fumigation, moxibustion and other TCM integrated treatment modalities, can significantly improve the healing rate of wounds[128].

Table 1 Clinical evidence for natural medicine-based therapies in diabetic wound management.

Drugs	Composition	Dosage form	Condition	n (experiment/control)	Study design	Treatment		Clinical effect	ChiCTR/NCT number	Ref.
						Experimental	Control
CPCF	Cortex Phellodendri (huangbai), Forsythia suspensa (lianqiao), Lonicera japonica Thunb (rendong), Taraxacum mongolicum Hand.-Mazz. (pugongying), Scolopendra (wugong)	Fluid	DFU	540/180	RCT	CPCF	Kangfuxin solution	Angiogenesis, tissue repair, wound healing	ChiCTR-IPR-15007182	[124]
Two-herb recipe (NF3)	Astragali Radix (huangqi), Rehmanniae Radix (shengdi)	Granules	DFU	8/8	RCT	NF3	Placebo	Fibroblast regeneration, angiogenesis and anti-inflammation	NCT01389362	[125]
Shengji ointment	Testudinis Carapax et Plastrum (guijia), Rehmanniae Radix (dihuang), Angelicae Sinensis Radix (danggui), Gypsum Fibrosum (shigao), Calamina (luganshi)	Ointment	DFU (Wagner grade 3-4)	54/126	RCT	Shengji ointment and bromelain	Hydrocolloid dressing	Granulation tissue regeneration	ChiCTR2000039327	[126]
Nano-hydrogel embedded with quercetin and oleic acid	Quercetin and oleic acid	Hydrogel	DFU	28/28	RCT	Nano-hydrogel embedded with quercetin and oleic acid	Hyaluronic acid	Reduce pain, improve tissue viscoelasticity, accelerated wound healing	-	[123]
Capsaicin 8% patch	Capsaicin	Patch	Diabetic peripheral neuropathy	186/183	RCT	Capsaicin 8% patch	Placebo patch	Reduce pain, relieve diabetic peripheral neuropathy symptoms	NCT01533428	[122]

CPCF: Cortex phellodendri compound fluid; RCT: Randomized clinical trial; DFU: Diabetic foot ulcers.

Although natural medicines show some potential in the treatment of diabetic foot, especially anti-inflammatory antioxidants, most reports on natural medicines are concentrated in Chinese journals, and international journals lack sufficient data from high-quality, randomized controlled, long-term clinical studies. This led us to be unable to adequately demonstrate the long-term effects of natural medicines in the treatment of diabetic foot.

The treatment of diabetic wounds often requires the localized application of natural drugs; however, achieving uniformity in dosage and concentration for such local application remains a challenge. Discrepancies in the origins and extraction techniques of natural drug components can result in variations in efficacy among different batches of the same drug, thereby complicating the standardization of drug formulations, which is a key obstacle in clinical translation. The optimal efficacy of natural drugs typically hinges on the appropriate dosage and administration route. Nonetheless, certain natural drugs encounter issues of limited bioavailability and solubility, impeding drug absorption and necessitating refinement or alteration of drug delivery methods to increase their efficacy. These challenges, in turn, have impeded the widespread clinical adoption of these drugs.

CONCLUSION

Diabetic wounds are characterized by OS and inflammation due to the hyperglycemic and hypoxic environment, which leads to disruptions in the antioxidant and anti-inflammatory systems[129]. Therefore, accelerating wound healing in diabetic patients requires both blood glucose control and the suppression of inflammation and OS. Natural medicines are widely sourced and exhibit significant antioxidant and anti-inflammatory effects. Moreover, in treating DFU, these compounds demonstrate numerous shared properties beyond anti-inflammatory and antioxidant effects. For instance, tanshinone, asiaticoside, and matrine all promote angiogenesis; curcumin and quercetin enhance collagen deposition; and tanshinone and curcumin exhibit antibacterial properties. They are more cost-effective and efficient, with fewer side effects, which has garnered increasing attention in recent years for diabetic wound research. In particular, flavonoids typically feature phenolic hydroxyl groups within their molecular structure, enabling them to directly counteract free radicals by forming stable intermediates (oxides or peroxides). These products exhibit reduced reactivity, thereby mitigating oxidative damage[130]. Moreover, flavonoids can impede the function of inflammation-associated enzymes. Certain flavonoids, such as isoprenoid flavonoids and flavonols, exhibit a broad spectrum of activity by inhibiting numerous microbial virulence factors. Additionally, they demonstrate synergistic effects with antibiotics, effectively suppressing biofilm formation on diabetic wounds[131]. Furthermore, the encapsulation and applicability of flavonoids render them suitable for use as carriers in innovative drug delivery systems, which can enhance healing mechanisms and increase bioavailability[132]. For example, Que has many therapeutic advantages in wounds, but its low water solubility, poor permeability, poor oral bioavailability and other characteristics limit its application in DFU; however, by combining nanocarriers, polymer nanoparticles, nanofibers, hydrogels and other methods, its solubility and skin permeability can be improved so that the composition can better penetrate through the stratum corneum and remain in the dermis of the skin. Such modifications would enhance the efficacy of Que, which can also be combined with other compounds to exert stronger healing effects[133]. Although these studies are still in the preclinical stage, on the basis of the results of existing studies, natural pharmaceutical compounds still have great potential to treat DFU. As a result, drug development is gradually focusing on identifying new targeted therapies from natural products that can provide safer and more effective treatments for diabetes and its complications[134]. The combined use of multiple natural compounds can further enhance therapeutic efficacy. For example, the synergistic effects of Cur, resveratrol, and Que can mitigate inflammation and OS induced by hyperglycemia and aging conditions[135]. In addition to these applications, the use of novel carriers, such as hydrogels[136], chitosan[137], and exosomes[138], for the delivery of natural drugs can synergistically enhance effects, enable targeted delivery, reduce drug toxicity, improve drug solubility and bioavailability, and strengthen the anti-inflammatory and antioxidant effects of natural medicines. This approach can effectively promote granulation tissue formation and accelerate healing in diabetic wounds. As research into natural medicines has progressed, they have demonstrated significant therapeutic potential through multiple pathways in the treatment of diabetic wounds, offering effective adjunctive therapy, with their full potential warranting further exploration and development.