Diabetic foot ulcers (DFU) represent one of the most severe complications of diabetes, affecting nearly 30% of diabetic patients and leading to high amputation rates and mortality. Despite current treatment approaches including surgical debridement and biomaterial applications, the limited efficacy of existing therapies has created an urgent need for novel therapeutic agents. Recent research has identified narirutin, a bioactive flavonoid isolated from citrus fruits, as a promising candidate for diabetic wound healing through its unique mechanism of action involving metabolic reprogramming.
Metabolic Dysfunction in Diabetic Wound Healing
The healing process of diabetic wounds differs significantly from normal wound repair due to several pathological factors. In the diabetic microenvironment, hyperglycemia, hypoxia, and pH abnormalities impair the normal transition of macrophages from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype. This disruption leads to prolonged inflammation and deficient pro-proliferative cytokine production, ultimately resulting in angiogenesis dysfunction and delayed wound healing.
Macrophages play pivotal roles throughout the wound repair process, initially eliminating pathogens and cellular debris during the inflammatory phase, then transitioning to promote tissue repair during the proliferation phase. However, in diabetic conditions, this critical phenotypic switch is compromised, contributing to chronic wound states.
Narirutin's Mechanism of Action
Research has demonstrated that narirutin effectively promotes diabetic wound healing through a sophisticated mechanism involving metabolic reprogramming of macrophages. The compound activates the AMPK/Mfn2 signaling pathway, which serves as a crucial regulator of cellular energy metabolism.
AMPK functions as an important intracellular energy sensor responsible for glucose and lipid metabolism, while Mfn2, located in the mitochondrial outer membrane, regulates mitochondrial fusion and fission to maintain organelle function. Through this pathway, narirutin enhances oxidative phosphorylation (OXPHOS) while suppressing glycolysis, leading to increased production of α-ketoglutarate and reduced lactate levels.
This metabolic shift is particularly significant because M1 macrophages primarily rely on glycolysis for energy production, generating lactate as a pro-inflammatory metabolite. In contrast, M2 macrophages utilize OXPHOS, producing α-ketoglutarate, which acts as an anti-inflammatory effector. By promoting this metabolic transition, narirutin facilitates the crucial macrophage phenotype switch from M1 to M2.
Experimental Validation
In vitro studies using bone marrow-derived macrophages (BMDMs) demonstrated that narirutin treatment effectively reversed high glucose-induced inflammatory responses. The compound reduced expressions of pro-inflammatory markers including TNF-α, IL-1β, CD86, and iNOS, while increasing anti-inflammatory markers such as TGF-β, IL-4, CD206, and Arg-1.
Mechanistic studies revealed that inhibition of AMPK or silencing of Mfn2 abolished narirutin's beneficial effects, confirming the critical role of the AMPK/Mfn2 pathway. The treatment also enhanced the expression of key OXPHOS enzymes including CPT-1A and IDH3 while reducing glycolytic enzyme LDH expression.
Enhanced Angiogenesis and Wound Healing
Beyond its effects on macrophage metabolism, narirutin demonstrated significant pro-angiogenic properties. The compound enhanced proliferation, migration, and tube formation abilities of human umbilical vein endothelial cells (HUVECs) when co-cultured with narirutin-treated macrophages. This effect was mediated through activation of the VEGFR2/PI3K/Akt/HIF-1α pathway, a crucial growth-promoting signaling cascade.
The pro-angiogenic effects were attributed to narirutin's ability to create a regenerative microenvironment by switching macrophages from the M1-related inflammatory state to the M2-related regenerative phenotype, which promotes blood vessel formation essential for wound healing.
In Vivo Efficacy and Safety
Animal studies using a diabetic wound model confirmed narirutin's therapeutic potential. Both low-dose (60 mg/kg) and high-dose (120 mg/kg) narirutin treatments significantly accelerated wound closure compared to control groups. Histological analysis revealed enhanced collagen deposition, reduced inflammatory cell infiltration, and improved tissue organization in treated animals.
Importantly, narirutin demonstrated excellent safety profiles with no observed toxicity to major organs including heart, liver, spleen, lung, and kidney. Blood biochemical tests showed no alterations in AST, ALT, or creatinine levels, indicating good tolerability.
The treatment also promoted local angiogenesis, as evidenced by increased CD31 expression (a vessel marker) and improved blood perfusion measured by laser speckle contrast imaging. These findings support narirutin's dual mechanism of action in both reducing inflammation and promoting tissue regeneration.
Clinical Implications and Future Directions
The discovery of narirutin's mechanism represents a significant advancement in understanding diabetic wound healing. Unlike traditional anti-inflammatory approaches, narirutin's strategy of promoting metabolic reprogramming addresses the fundamental cellular dysfunction underlying diabetic wounds.
The compound's ability to simultaneously target multiple aspects of wound healing - including inflammation resolution, metabolic correction, angiogenesis promotion, and collagen synthesis - makes it a particularly attractive therapeutic candidate. Its natural origin from citrus fruits also suggests potential advantages in terms of safety and accessibility.
These findings provide scientific basis for the potential clinical application of narirutin in diabetic wound management. The research establishes metabolic reprogramming as a viable therapeutic strategy and identifies the AMPK/Mfn2 pathway as a key target for future drug development efforts.
The study represents the first comprehensive investigation of narirutin's effects on diabetic wound healing through metabolic reprogramming, opening new avenues for treating this challenging clinical condition. Further research will be needed to optimize dosing regimens and evaluate long-term efficacy in clinical settings.
