Our tendons support quality movement and thus help prevent pain and an array of health conditions associated with musculoskeletal issues. The health of our tendons is important to study because tendon injuries and repair complications are common and often debilitating. Treatments for tendon injury are necessary to support successful repair and rehabilitation, including maintenance of the normal function of our tendons. N-acetylcysteine for tendon health supports successful repair and rehabilitation, including maintenance of the normal function of our tendons.
What are tendon injuries?
Tendon injuries are widespread and can result in significant pain and disability.3 Injuries to this tissue, like damage to the Achilles tendon and the tendons of the hip and lower back, can happen suddenly (also known as acute injury) or gradually (also known as chronic injury).3
Unfortunately, the repair process is not always smooth and can involve the formation of
- scars,
- fatty deposits,
- or ectopic ossification (bony formation where there shouldn’t be).2,3
The healing process for tendon injuries can be complicated. Any mishaps or ignoring the healing process can impact tendon function but also the function of surrounding joints and muscles. As a result, developing new treatment options is essential to promote the functional recovery of tendon injuries.
What happens during tendon repair?
When a tendon is damaged, promoting local vascularization (nutrient and oxygen flow) required for healing causes oxidative stress (OS) and inflammation.3,4 Following vascularization, cell apoptosis (cell death) and scar formation can occur.3 If repair needs are not matched by the removal of the debris that forms during the healing process, injury-related OS and inflammation can damage the survival and function of tendon stem/progenitor cells (TSPCs).3
TSPCs are necessary for tendon health and spontaneous healing.3 TSPCs have the ability to renew themselves but also to differentiate (change into) in-demand bodily communicators or tissues.3 Because OS can damage their survival and function, tendon repair is impeded.
Oxidative stress can lead to injury-related conditions like
- tendon degeneration,
- easy tendon tearing,
- and movement-related fatigue fractures.3
Therefore, controlling OS and inflammation is critical in promoting tendon repair.
Oxidative stress and ROS
Oxidative stress produces reactive oxygen species (ROS), depleting our body’s own antioxidant supply.3 During tendon repair, the local OS reactions create an imbalance between tenocytes and tenoblasts.3
Tenocytes exist as mature tendon cells found within the body of the tendon and are usually linked to collagen fibers.1 Tenoblasts are young tendon cells that eventually grow into tenocytes.1 Tenoblasts are usually found in groups without anchorage to collagen fibers.1 Both tenocytes and tenoblasts are necessary for tendon health.
A popular antioxidant drug called N-acetylcysteine (NAC) is often used to fight ROS and alleviate OS.3 Essentially, NAC is used to prevent ROS production, helping to maintain the necessary balance between damage, removal of debris, and repair.3
A key component of tendon repair is also the remodeling of collagen fibers in tendon tissues.3 This repair and remodeling is a tightly balanced system. In a recent animal model study, NAC treatment promoted the remodeling of collagen fibers, encouraging tendon repair and diminishing the severity of the tendon injury.3
N-acetylcysteine next steps
Based on these recent findings, it exploring NAC treatment in humans is encouraged to aid the survival of TSPCs and to aid the repair and remodeling of collagen fibers.3 Exploring the best ways to deliver N-acetylcysteine to the injury site is also an area of research worth exploring. Thus, NAC may be a valuable medical agent for treating tendon injury.
References
1. Britannica T. Tendon. Encyclopedia Britannica. Updated May 24 2021. Accessed February 26, 2023. Encyclopedia Britannica. https://www.britannica.com/science/tendon
2. Kewalramani LS. Ectopic ossification. Am J Phys Med. 1977;56(3):99-121. PMID: 405873.https://pubmed.ncbi.nlm.nih.gov/405873/
3. Lu K, Zhou M, Wang L, Wang Y, Tang H, He G, Wang H, Tang C, He J, Wang W, Tang K. N-Acetyl-L-cysteine facilitates tendon repair and promotes the tenogenic differentiation of tendon stem/progenitor cells by enhancing the integrin α5/β1/PI3K/AKT signaling. BMC Molecular and Cell Biology, 2023;24(1):1. DOI:https://doi.org/10.1186/s12860-022-00463-0
4. Science Direct. Vascularization. Science Direct. 2023. Accessed 26 February 2023. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/vascularization.
