Metformin Hydrochloride Reduces Vocal Fold Fibrosis via AMPK

Study Background and Research Question

Vocal fold fibrosis is a persistent clinical challenge, often arising after trauma, surgery, or chronic inflammation of the vocal cords. The resultant scar tissue disrupts vocal fold pliability and vibratory function, leading to chronic dysphonia and impaired quality of life, particularly in individuals dependent on professional voice use. Current interventions, including voice therapy, corticosteroid injections, cell therapies, and surgical procedures, frequently yield incomplete or temporary outcomes and can carry significant risks or side effects. Thus, there is an ongoing need for safe, mechanism-driven therapeutic strategies that can restore both the structure and function of the injured vocal fold tissue.

Metformin Hydrochloride (Metformin HCl), a well-characterized AMPK signaling pathway modulator, has demonstrated efficacy in fibrotic diseases of the lung and kidney, with mechanistic links to the inhibition of hepatic gluconeogenesis and attenuation of pathological tissue remodeling. Building on this foundation, the present study (Cai et al., 2024) investigates whether Metformin HCl can mitigate vocal fold fibrosis, and if these effects are mediated through AMPK activation.

Key Innovation from the Reference Study

The central innovation of this research lies in establishing direct evidence that Metformin HCl reduces fibrotic remodeling in vocal fold tissue by activating the AMPK signaling pathway. While previous studies had suggested antifibrotic effects of metformin in other organ systems, this is the first report to demonstrate its efficacy in a preclinical model of vocal fold injury. Notably, the work provides mechanistic detail at both histological and molecular levels, linking reduced collagen deposition and fibroblast activation to AMPK pathway engagement, and thereby offering a targeted route for future antifibrotic therapies in laryngeal tissue.

Methods and Experimental Design Insights

The investigative team employed a bifurcated experimental approach combining in vivo and in vitro systems. In the animal model, vocal fold injury was induced in New Zealand White rabbits, followed by systemic administration of metformin via intraperitoneal injection at 250 mg/kg two weeks post-injury. Four weeks after injury, excised vocal folds were subjected to detailed analysis:

• Histological assessment using Masson's trichrome staining to quantify collagen deposition and tissue architecture.
• Immunohistochemistry, qPCR, and Western blotting to evaluate the expression of fibrosis-related markers (COL1A1, α-SMA) and key signaling molecules.

For mechanistic insight, primary vocal fold fibroblasts were isolated and cultured in vitro. Cells were treated with 10 μM metformin, with or without TGF-β1 (10 ng/mL) to induce a fibrotic phenotype. To clarify the role of AMPK, cells were co-treated with Compound C (10 μM), a specific AMPK inhibitor. Molecular readouts included expression levels of extracellular matrix (ECM) proteins and signaling effectors (COL1A1, α-SMA, TGF-β, Smad2, Smad3) associated with fibrosis and AMPK pathway activation.

Core Findings and Why They Matter

According to the reference study, systemic treatment with Metformin HCl significantly improved the structural integrity of the vocal fold lamina in injured rabbits, as evidenced by reduced collagen accumulation and restoration of native tissue architecture. At the molecular level, metformin markedly decreased the expression of COL1A1 and α-SMA—canonical markers of activated fibroblasts and myofibroblast differentiation—both in vivo and in vitro. Notably, the activation of the AMPK signaling pathway by metformin correlated with suppression of TGF-β/Smad2/3 signaling, a central axis driving fibrogenesis in various tissues.

In vitro, the antifibrotic effect of metformin was abrogated by the AMPK inhibitor Compound C, confirming that AMPK activation is necessary for metformin's modulation of fibrotic gene expression in vocal fold fibroblasts. Collectively, these findings delineate a mechanistic sequence wherein metformin acts as a fatty acid oxidation promoter and lipid biosynthesis attenuator, ultimately restraining fibrotic progression through AMPK-dependent inhibition of ECM protein synthesis and fibroblast activation.

Comparison with Existing Internal Articles

This work extends prior evidence of metformin’s antifibrotic and anti-ossific actions in musculoskeletal and metabolic models. For example, earlier research (Metformin Suppresses Tendon Ossification via Nr4a1/Wnt/β-catenin Inhibition) demonstrated that Metformin HCl inhibits heterotopic ossification in tendon by modulating Nr4a1 and Wnt/β-catenin signaling, implicating a broader regulatory effect on pathological tissue remodeling. Similarly, a mechanistic review (Metformin Hydrochloride: Mechanistic Insights & Translational Impact) outlined the compound’s dual role in metabolic and bone biology via AMPK signaling and suppression of collagen and ECM protein synthesis.

The present study is unique in its focus on vocal fold tissue, but the underlying mechanisms—AMPK activation, inhibition of fibrogenic signaling pathways, and modulation of fibroblast phenotype—are conserved across tissue types. This cross-domain congruence reinforces the rationale for exploring Metformin HCl as a versatile tool in fibrosis and tissue regeneration research, as also highlighted in a related article (Metformin Hydrochloride Mitigates Vocal Fold Fibrosis via AMPK).

Limitations and Transferability

While the findings are compelling, certain limitations should be recognized. The rabbit model recapitulates key aspects of vocal fold injury and fibrosis, but differences in healing dynamics and immune responses may limit direct extrapolation to human laryngeal biology. The dosing regimen and intraperitoneal administration route, though effective for preclinical proof-of-concept, may differ from clinically feasible strategies such as oral or localized delivery. Additionally, long-term safety and potential off-target effects of high-dose metformin in laryngeal tissues were not addressed.

Transferability to other fibrotic contexts appears plausible, given the shared involvement of TGF-β/Smad and AMPK signaling across organ systems. However, further studies are required to validate efficacy in chronic, established scar models and to explore combinatorial approaches with current standard-of-care treatments.

Protocol Parameters

• In vivo metformin administration: Intraperitoneal injection of 250 mg/kg, initiated two weeks post-injury in rabbits; tissue analysis at four weeks post-injury.
• In vitro fibroblast assay: Metformin at 10 μM, with TGF-β1 (10 ng/mL) to induce fibrosis; Compound C (10 μM) used to inhibit AMPK and confirm pathway involvement.
• Marker analysis: Expression levels of COL1A1, α-SMA, TGF-β, Smad2, and Smad3 assessed via qPCR and Western blotting; collagen deposition visualized by Masson's trichrome staining.
• Suggested workflow adaptation: For translational or mechanistic studies, dosing and timing should be adjusted based on species, route of administration, and desired fibrosis model.

Research Support Resources

For investigators interested in reproducing or extending these findings, Metformin Hydrochloride (Metformin HCl) (SKU B1970) is available as a research-grade reagent. This compound is supplied as a solid, is water- and DMSO-soluble, and is widely used in studies of AMPK signaling, hepatic gluconeogenesis inhibition, and fibrotic disease mechanisms. Preparation in DMSO with warming or sonication is recommended to achieve desired working concentrations, as outlined in the product information. Use of a validated reagent such as APExBIO’s Metformin HCl can support robust and reproducible workflows in both in vitro and in vivo fibrosis models.