Ageing muscle repair is a critical biological process that naturally declines with advancing age, leading to progressive muscle weakness, structural degradation, and functional loss. As skeletal muscle ages, individuals experience sarcopenia, characterized by reduced muscle cross-sectional area, increased fibrotic scarring, lipid infiltration, and a preferential loss of fast-twitch glycolytic myofibers responsible for rapid force generation. Muscle regeneration relies on resident stem cells known as satellite cells, which remain quiescent within the extracellular matrix until activated by specific extracellular signaling proteins. Among these local chemical signals, hepatocyte growth factor (HGF) serves as the primary wake-up signal that initiates satellite cell activation, proliferation, and differentiation following mechanical stretch, exercise, or focal physical injury. However, during the normal physiological ageing process, persistent oxidative stress and inflammatory cascades alter the structural integrity of these endogenous signaling molecules. Recent breakthrough research from Kyushu University published in Scientific Reports demonstrates that a novel sulfur-containing compound, lipoic acid trisulfide (LASSS), can effectively protect and supercharge HGF, creating a highly active form termed "Super HGF" that significantly enhances muscle stem cell activation and preserves regenerative potential even under severe oxidative conditions.

Understanding Ageing Muscle Repair Mechanisms

To fully appreciate the therapeutic significance of lipoic acid trisulfide, clinicians must understand the underlying molecular physiology governing skeletal muscle regeneration. Skeletal muscle comprises roughly forty percent of total adult body mass and represents one of the most metabolically active and dynamic organ systems in human physiology. Under healthy physiological conditions, uninjured skeletal muscle maintains satellite cells in a specialized quiescent state beneath the basal lamina. When physical trauma, mechanical overload, or micro-tears occur within muscle myofibers, localized extracellular signaling molecules are immediately liberated from the surrounding extracellular matrix. Hepatocyte growth factor (HGF) acts as the principal ligand that binds directly to c-Met tyrosine kinase receptors located on the cell surface of quiescent satellite cells. This precise ligand-receptor engagement triggers downstream intracellular signaling cascades that break stem cell quiescence, driving satellite cells into active cell cycle division. These activated stem cells multiply rapidly, migrate to the site of cellular damage, and differentiate into myoblasts that ultimately fuse with damaged myofibers or coalesce to form brand-new functional myotubes. In youthful tissue, this regenerative machinery operates with remarkable efficiency, restoring full contractile strength and structural integrity. However, as individuals age, systemic low-grade inflammation, altered cellular redox homeostasis, and cumulative oxidative damage systematically impair this regenerative cascade, leaving muscle tissue vulnerable to progressive atrophy and incomplete recovery after disuse or physical injury.

The Role of HGF Nitration in Muscle Loss

The molecular drivers behind age-related regenerative failure have long been a focal point of geriatric and musculoskeletal research. Previous groundbreaking investigations conducted by Professor Ryuichi Tatsumi's research team at Kyushu University established that age-related muscle decline is not primarily caused by an absolute quantitative deficit of hepatocyte growth factor. Instead, the protein undergoes a specific, irreversible post-translational chemical modification known as protein-tyrosine nitration. During chronic oxidative stress and age-associated inflammatory states, reactive nitrogen species add nitro groups specifically to tyrosine residues located at positions Y198 and Y250 within the HGF molecule. Crucially, these specific tyrosine sites reside directly within the active binding domain that HGF utilizes to dock onto the c-Met receptor on satellite cells. Once nitrated, HGF loses its native three-dimensional conformational flexibility and docking affinity, rendering it functionally inert—analogous to a rusted key that can no longer turn inside its corresponding lock. Because nitrated HGF cannot successfully engage c-Met receptors, satellite cells fail to receive the necessary activation signal and remain trapped in a dormant or senescent state. Consequently, injured or overloaded muscle tissue cannot effectively repair itself, facilitating the gradual accumulation of fibrotic connective tissue, intramuscular adipose tissue, and irreversible loss of high-power fast-twitch motor units in elderly patients.

Lipoic Acid Trisulfide and Super HGF Formation

In an effort to prevent or reverse this nitration-induced inactivation, the research team investigated sulfur-rich antioxidant molecules capable of modulating protein redox chemistry. Specifically, they examined two distinct trisulfides: glutathione trisulfide (GSSSG) and lipoic acid trisulfide (LASSS). Trisulfides represent an intriguing class of sulfur compounds containing three sequentially linked sulfur atoms capable of participating in unique biological sulfur-exchange and redox reactions. While initial laboratory experiments demonstrated that both GSSSG and LASSS could modestly reduce protein nitration at tyrosine sites Y198 and Y250, neither compound fully restored normal receptor-binding kinetics at standard molar ratios. However, when researchers increased the molar ratio of LASSS to HGF to 1:8000, an extraordinary biochemical phenomenon occurred. Mixing HGF with LASSS at this concentration not only completely prevented nitration-induced functional loss, particularly at position Y198, but also increased the binding affinity of HGF for the c-Met receptor to more than double that of native, untreated protein. This unique structural transformation yielded what researchers term "Super HGF," a hyper-functional protein form that binds c-Met with unprecedented strength while displaying exceptional resistance to oxidative damage. Importantly, this remarkable potentiation was unique to LASSS; glutathione trisulfide failed to produce any enhancement, indicating that LASSS acts via a highly specific structural interaction rather than simple non-specific antioxidant scavenging.

Preclinical In Vivo Findings in Disuse Atrophy

To validate whether the protective and potentiating effects of lipoic acid trisulfide extend beyond isolated molecular assays into living mammalian tissue, the investigators tested LASSS in an established mouse model of disuse muscle atrophy induced by hindlimb tail suspension. Animal models subjected to tail suspension experience rapid skeletal muscle degradation, elevated oxidative stress, and marked accumulation of nitrated HGF, mirroring the acute muscle wasting observed in bedridden geriatric patients or immobilized surgical cases. Mice pretreated with systemic LASSS prior to the tail suspension protocol exhibited significantly lower levels of HGF nitration within their skeletal muscle tissue compared to untreated control animals. In direct alignment with in vitro biochemical observations, treatment with glutathione trisulfide (GSSSG) failed to provide measurable protection against HGF nitration in vivo. These compelling animal results confirm that LASSS effectively protects the endogenous muscle repair apparatus within complex biological systems subjected to mechanical unloading and oxidative stress. By maintaining functional HGF-c-Met signaling, LASSS preserves the capacity of resident satellite cells to respond rapidly to repair cues, thereby attenuating the rate and severity of disuse atrophy. However, the authors emphasize that comprehensive preclinical studies in naturally aged animal models remain essential to fully evaluate long-term safety, pharmacokinetics, and optimal therapeutic dosing before human clinical trials can commence.

Clinical Implications for Sarcopenia Management

The discovery of LASSS-mediated "Super HGF" formation represents a paradigm shift in regenerative medicine and sarcopenia therapeutics. Traditional pharmacological strategies targeting age-related muscle loss have primarily focused on hormonal anabolic agents or broad-spectrum nutritional antioxidants, which often yield limited clinical efficacy or carry undesirable systemic side effects. By targeting the precise post-translational modification that disables endogenous repair signals, LASSS offers a highly targeted mechanism to restore physiological muscle stem cell responsiveness. Because the molecular structure and signaling pathways of hepatocyte growth factor and c-Met receptors are highly conserved across mammalian species, this therapeutic approach holds immense translational promise for human clinical practice as well as veterinary medicine in companion animals. Clinically, restoring HGF functional integrity could revolutionize the clinical management of age-related sarcopenia, prolonged post-surgical bed rest, intensive care unit-acquired weakness, and neurological immobilization. Preserving muscle mass, contractile force, and regenerative capability in elderly populations directly correlates with enhanced mobility, reduced fall risk, preserved functional independence, and overall improved quality of life. As research advances from bench to bedside, trisulfide-mediated protein remodeling may emerge as a foundational strategy in geriatric healthcare and restorative musculoskeletal medicine.

Frequently Asked Questions

Q1: What is the primary biological mechanism by which LASSS enhances ageing muscle repair?

LASSS works by directly interacting with hepatocyte growth factor (HGF), a key protein that activates muscle stem cells (satellite cells). LASSS prevents the age-related chemical addition of nitro groups to critical tyrosine sites (Y198 and Y250) on HGF. At optimal concentrations, LASSS induces a beneficial structural change that creates "Super HGF," doubling its binding affinity to c-Met receptors and protecting it against oxidative damage during muscle recovery.

Q2: How does age-related HGF nitration contribute to muscle loss and sarcopenia?

With advancing age, elevated oxidative stress causes nitration of HGF at specific receptor-binding sites. This structural alteration prevents HGF from docking onto c-Met receptors on satellite cells, akin to a rusted key failing to open a lock. Unable to receive activation signals, muscle stem cells remain dormant, preventing effective tissue repair, promoting fibrosis and fat accumulation, and accelerating the loss of high-power fast-twitch muscle fibers essential for mobility.

Q3: Did other sulfur-based antioxidants achieve similar results to LASSS in preclinical testing?

No, the study compared lipoic acid trisulfide (LASSS) with another potent trisulfide antioxidant, glutathione trisulfide (GSSSG). While both compounds reduced initial protein nitration slightly, only LASSS demonstrated the unique ability to transform HGF into a hyper-active state with more than double the normal receptor-binding affinity. Furthermore, GSSSG failed to protect against HGF nitration or muscle disuse damage in living mouse models, highlighting LASSS's unique structural specificity.

Disclaimer: This content is for informational and educational purposes only. It does not constitute medical advice or replace professional judgment. Refer to the latest local and national guidelines for clinical practice.

References

1. Researchers unveil a compound that can boost ageing muscle repair - ETHealthworld


2. Tatsumi R, et al. Lipoic acid trisulfide (LASSS) protects hepatocyte growth factor from nitration and converts it into Super HGF for muscle regeneration. Sci Rep. 2026;16:10835.


3. Kyushu University Press Release. Scientists find compound that may help muscles stay strong as we age. Published July 24, 2026.