> 1. What causes ciprofloxacin (or its class fluoroquinolones) to harm connective tissues?

mTOR Signaling

Fluoroquinolones are known to affect the mTOR (mammalian target of rapamycin) pathway, which is critical for protein synthesis, cell growth, and tissue repair. mTOR integrates signals from nutrients, growth factors, and energy status to regulate cellular anabolic processes like collagen synthesis and fibroblast activity. However, fluoroquinolones can induce oxidative stress and mitochondrial dysfunction, which may disrupt normal mTOR signaling. This interference can impair the normal anabolic functions of mTOR, potentially leading to diminished protein synthesis and weakened connective tissue repair.

Mitochondrial Dysfunction

Fluoroquinolones can damage mitochondrial DNA, which may reduce ATP production and impair cellular energy homeostasis. Since mTOR activity is energy-dependent, reduced ATP availability could downregulate mTOR signaling, inhibiting processes like fibroblast proliferation and collagen synthesis. This could explain the tendinopathy and cartilage damage sometimes associated with fluoroquinolone use.

Collagen Synthesis and Matrix Remodeling

The anabolic processes that support collagen production and extracellular matrix (ECM) remodeling are crucial for connective tissue integrity. Fluoroquinolones have been observed to impair collagen synthesis by disrupting the fibroblast function, and this may be due to their impact on the energy-intensive processes governed by mTOR.

Fluoroquinolones have also been reported to cause central nervous system (CNS) effects, including anxiety, tremors, and other neurological symptoms, suggesting an impact on adrenergic pathways. This dysregulation could interfere with normal stress adaptation mechanisms, including the modulation of inflammatory and regenerative processes in connective tissues.

Connective tissue healing depends on the body’s capacity to manage energy demands and stress responses during recovery. Fluoroquinolones can impair mitochondrial function and create an energy deficit at the cellular level, reducing the ability of fibroblasts to engage in critical processes like collagen synthesis and ECM remodeling. The systemic impact on both dopaminergic and adrenergic systems can further weaken the body’s ability to manage stress and energy during recovery, exacerbating the negative effects on tissue repair.

Fibroblasts and Collagen Production

Fibroblasts are the key cells responsible for producing collagen in connective tissues. Under conditions of oxidative stress and energy depletion, fibroblasts may enter a senescent state, reducing their capacity for collagen synthesis and matrix repair. This can lead to weakened connective tissue and increased susceptibility to injuries like tendon ruptures, which have been reported with fluoroquinolone use.

Collagen and Tendon Health

Fluoroquinolone-induced dysregulation of cell signaling, energy metabolism, and oxidative stress management all converge on a critical issue: the weakening of collagen structure and connective tissue integrity. This has been particularly evident in the association between fluoroquinolones and tendinopathy or tendon rupture, likely linked to the disruption of collagen synthesis, the downregulation of mTOR, and the stress on connective tissue cells such as fibroblasts.

Some Sources:

[ ] https://academic.oup.com/bmb/article/130/1/39/5366272

[ ] https://pubs.rsc.org/en/content/articlelanding/2016/ra/c6ra1...

[ ] https://www.frontiersin.org/journals/physiology/articles/10....

[ ] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10056716/