Study Shows Metformin Prevents Connective Tissue Aging

Metformin, a common diabetes medication, prevents the degradation of tendons – connective tissue between muscles and bones – by blocking cell aging and inflammation.

Key Points:

Old mice treated with metformin have fewer senescent (aged) and inflammatory cells in their tendons.
Metformin treatment decreases HMGB1 – an inflammatory cell signaling molecule – in the tendons of old mice and increases stem cell growth (proliferation).

Metformin also leads to increased collagen organization, making the collagen within their tendons more similar to young mice.

Metformin has been used for decades to treat diabetes; however, many researchers have recently found that metformin has numerous anti-aging capabilities. A new study shows that metformin can be used to prevent another aging concern, the degradation of tendons – the connective tissue attaching muscles to bones.

The study, from the University of Pittsburgh and published in the Journal of Orthopaedic Research, focused on old mice with tendon degradation due to exercise and overuse. The scientists treated these mice with metformin and found that the metformin decreased senescent cells – aged cells which have stopped growing and dividing – and inflammation within the tendons. Metformin is known to inhibit an inflammatory cell signaling molecule called HMGB1, which was also increased in aged tendons. When HMGB1 was reduced in the tendons by metformin treatment, the number of stem cells increased, and their ability to grow and divide was restored, leading to tendons that may be more easily healed following injury. Furthermore, Zhang and colleagues found that metformin positively affected the cell shape and collagen structure, altering them to be more similar to that of younger mice, suggesting that the tissue was rejuvenated by metformin treatment.

“These findings of this study indicate that Met[formin] exerts anti‐inflammatory and anti‐senescent effects on aging tendon,” the scientists wrote.

Senescence and Inflammation in Old Tendons Improved by Metformin Treatment

The scientists used old mice aged 18 months (approximately 56 in human years) and found that the mice had increased senescent and inflammatory cells in their tendons, which decreased after eight weeks of metformin injections. Both senescent cells and inflammation are common characteristics of aging tissue, and this data further supports metformin’s role as an anti-aging treatment. The scientists found that the effects were dose-dependent, meaning increasing the metformin dose led to fewer and fewer senescent cells and inflammatory cell markers.

(Zhang et al., 2022 | *Journal of Orthopaedic Research*) **Metformin Decreases Senescent Cells**
E) Aged mice have significantly increased senescent cells based on SA-β-gal signaling – a cell marker of senescent cells – as compared to young mice I) Metformin treatments in old mice significantly decreased the number of senescent cells in a dose-dependent manner *as compared to no metformin.

The scientists chose to focus on HMGB1, a known target of metformin which affects cell aging due to its role in initiating inflammatory signaling pathways. HMGB1 can either enhance tissue recovery or lead to increased inflammation and degradation depending on its molecular state. Zhang and colleagues found that within the tendons of aged mice, inflammatory HMGB1, known as dsHMGB1, was moved from the center compartment of the cell (the nucleus) into the surrounding area (the cytoplasm), initiating inflammatory signaling. However, in the tendons of young mice, HMGB1 stayed in the nucleus and mostly remained in a non-inflammatory, pro-proliferative state, known as frHMGB1.

Additionally, the scientists found that in the tendons of young mice, where frHMGB1 is in the nucleus, the stem cells proliferate at a rate 2.6 times faster than aged tendon stem cells. There were also fewer stem cells in the tendons of the old mice, suggesting decreased proliferation. However, when the old mice were given metformin, HMGB1 was reduced in a dose-dependent manner, and the number of stem cells was increased, suggestive of increased proliferation which in turn can help with tissue healing and regeneration.

(Zhang et al., 2022 | *Journal of Orthopaedic Research*) **Metformin Increases Nuclear HMGB1 and Stem Cell Proliferation** I) Metformin treatments increased HMGB1 in the nucleus in a dose-dependent manner in old mice and R) metformin also significantly increased stem cells (as determined by a stem cell marker, CD73), indicative of increased stem cell proliferation.

Furthermore, the scientists found that the tendons of old mice had altered cell shapes and looser collagen fibers – a structural protein – throughout their tendons. Metformin treatments changed the cell shape back to that of the younger mice and made the collagen fibers more organized, indicating that metformin improved the structure of the aged tendon, rejuvenating the tendons back to their youth.

(Zhang et al., 2022 | *Journal of Orthopaedic Research*) **Metformin Leads to More Organized Collagen in Old Mice** Young mice (G,H) have more dense, organized collagen fibers, all stained red, while the untreated, aged mice (I,J) have more disorganized fibers (stained blue). The old mice treated with metformin injections for eight weeks (K,L) have denser, more organized collagen fibers than their untreated counterparts.

Metformin for Antiaging

Zhang and colleagues show here how metformin can be used to reverse tendon aging. Other studies have shown how metformin can rejuvenate aged organs in rats, and this study indicates that tendons are no different. Thymus aging and reproductive aging, both in mice, have also been shown to be positively affected by metformin.

Multiple clinical trials, including the Metformin in Longevity Study (MILES) study and the Targeting Aging with Metformin (TAME) study, are in the works to determine how metformin may affect human aging and the safety of long-term metformin use. As with most medications, metformin is not without its side effects, which can include vitamin B deficiency, loss of appetite, and nausea, among others, and as of now, it is only available as a prescription. Whether metformin becomes an antiaging therapy as the population ages is yet to be seen, but the evidence for its use is compelling.