Sarcopenia Experimental Treatments

How To Keep An Old Mouse Swole

What Is Sarcopenia?

Sarcopenia is the clinical term for “not enough muscle,” a problem that shows up in some genetic disorders like muscular dystrophy, as a consequence of total inactivity like bed rest, and in old age. 

It’s something of a success story in nomenclature. In 1989, Irwin Rosenberg coined the term in order to bring more medical attention to the serious health effects of muscle loss in old age. Muscle loss may be part of “normal” aging, but he believed it should be treated as a disease, given that it’s the leading cause of admission to nursing homes and age-related disability.

Sarcopenia is a great age-related disorder to study in lab animals, because mice lose muscle and strength with age just as humans do, and the outcomes that matter for human health are easy to measure in animals.  (Unlike, say, dementia, where it’s much more questionable whether our measurements of cognitive decline in mice correspond to cognitive decline in humans.)

So, what’s the status of pharmacological treatments for sarcopenia?

Treatments in Naturally Aged Mice

There are genetically modified mouse models of sarcopenia, but on general assumptions one should be suspicious that “models” of a disease are not realistic enough to resemble the actual naturally occurring disease.

Particularly when we’re looking at a disease of aging; an aged body is messed up in many ways, while a young mutant is messed up in only one way, so you’d expect treatments that help young mutants to often fail in aged individuals.

I’ve listed these in roughly decreasing order of the magnitude of effects. 

The “bad news” is that mundane interventions (exercise and creatine) are at the top of the list, ahead of any kind of pharmacological intervention. Since lab mice are kept in sedentary conditions by default, this means that we should be skeptical that any intervention with a smaller-magnitude effect would continue to make a difference to animals that exercise.

One happy exception is a study on myostatin inhibition, where the treatment combined with exercise had significant effects relative to an exercise control.

Resistance Exercise

An Australian study found that mice given resistance wheels in their cages starting at middle age (15 months), soleus muscle mass was increased over sedentary controls 47% in males and 27% in females. Myofiber cross-sectional area was increased 22%¹.

Do we believe it?

Yes, of course. Resistance exercise builds muscle and strength. It would be shocking if it didn’t.

Can you try it at home?

Yes. Go lift some weights.

Creatine

In 18-month-old mice, a Korean team found that 5 weeks of creatine treatment increased forelimb grip strength by 50%, treadmill distance by 40%, and muscle cross-sectional area by 40%.²

Do we believe it?

Yes.

Creatine is a component of the body’s “energy currency”, ATP, stored in the muscles and used to generate new ATP. Creatine supplementation reliably improves muscle strength and mass in studies on older adults³, and it's been repeatedly observed to improve athletic performance and muscle growth when combined with exercise.⁴

Can you try it at home?

Yes. Creatine is a popular, legal supplement (you can get it on Amazon) and it’s repeatedly been shown safe in both short-term and long-term human studies, including in the elderly.⁵

Hand2 Overexpression

Hand2 is a transcription factor that governs limb and heart development; it is highest at birth and declines throughout the lifespan.

A team at Wake Forest injected mice with a viral vector to induce Hand2 overexpression, and found that the Hand2 group preserved sympathetic innervation in muscles into old age, attenuating loss in muscle size and strength. The Hand2-overexpressing group had 18% greater gastrocnemius muscle mass, 60% greater muscle fiber cross-sectional area, and 90% longer wire hanging endurance than age-matched controls.⁶

Do we believe it?

Plausibly.

It’s a well-known fact that muscles need nerve activity or they’ll atrophy; if loss of innervation with age precedes loss of muscle mass, preserving peripheral nerves in muscles is a nice upstream strategy for preserving muscle mass and strength.

Can you try it at home?

Nope. Rolling your own gene therapy is kinda out of reach for the average Joe(sephine).

Mesenchymal Stromal Cell Transplant

In a Chinese study, 24-month-old mice subjected to hindlimb immobilization (which causes muscle wasting) had 40% longer hanging endurance, 40% greater gastrocnemius muscle mass, and 30% greater muscle fiber cross-sectional area if they were treated with injections of human umbilical cord mesenchymal stromal cells.  Expression of inflammatory markers and apoptosis markers were also reduced in the treated mice.⁷

Do we believe it?

Maybe?

“Stick some stem cells on it, see if it grows better” is always a priori plausible (stem cells are, y’know, growthy) but they only work in a fraction of applications they’re tried for.

Researchers have claimed to regenerate a lot of things with MSCs — teeth, blood vessels, nerves, livers, etc — but so far there have been no FDA-approved therapies based on MSCs. Around the world, 10 MSC therapies have been approved to regenerate various tissues, including cartilage, heart muscle, spinal cord, and more.⁸

So, why not skeletal muscle?

Can you try it at home?

No. Stem cell transplants are invasive, can cause nasty graft-vs.-host disease, and might give you cancer if they get too growthy. Wait for high-quality human trials on this one.

4E-BP Knockout

4E-BP1 and 4E-BP2 are translation repressor proteins that inhibit protein synthesis. Mice with both genes knocked out have 20% higher total muscle mass by 24 months, as well as 50% higher grip strength, according to a French study.⁹

On the other hand, another more recent hindlimb immobilization study in mice, from Penn State, found that 4E-BP double knockout mice had more muscle protein synthesis than control mice, but it didn’t suffice to prevent atrophy.¹⁰

Do we believe it?

Probably not.

4E-BPs are indeed growth-promoting, but sometimes in a bad way (they worsen obesity and insulin resistance)¹¹¹² and the negative result is rather disappointing.

Can you try it at home?

Not directly; it’s a gene knockout.

Good old rapamycin¹³, interestingly enough, is a 4E-BP1 inhibitor, but not a very specific one.¹⁴

TLR9 Knockout

A Chinese study found that aged mice lacking the TLR9 gene (involved in the innate immune system) had 10% greater gastrocnemius muscle mass, 40% higher grip strength, 15% higher muscle mass overall, and significantly decreased expression of collagen proteins (indicating less muscle fibrosis.)¹⁵

Do we believe it?

Plausibly!

TRL9 knockout mice have altered immune systems; for instance, they don’t get graft-vs-host disease¹⁶. They also get less liver fibrosis¹⁷. And TLR9 is involved in promoting lung fibrosis.¹⁸

Fibrosis is tissue scarring. Fibrosis caused by chronic inflammation is one of the cellular processes behind many of the diseases of aging. Chronic age-related dysfunction of heart, lung, kidney, and other organs is often caused or worsened by fibrosis, sometimes due to senescent “zombie” cells which can no longer function but keep secreting pro-fibrotic signaling molecules.

If you knock out a fibrosis-promoting inflammatory surface protein, should you expect to preserve muscle mass longer? Sure, potentially!

Can you try it at home?

Not directly; once again, it’s a genetic modification.

Now, there are drugs that inhibit the function of the TLR9 protein, including chloroquine (which you may remember as the malaria drug that many mistakenly thought could treat COVID-19).

Other TLR9 inhibitor drug candidates appear to have various beneficial anti-inflammatory effects in animal studies. One TLR9 and TLR7 inhibitor¹⁹, developed by the vaccine company Dynavax, protects a lupus-prone strain of mice from severe autoimmune symptoms. Another compound, developed by Japanese pharma company Eisai, prevents heart failure in a mouse model.²⁰

So inhibiting TLR9 pharmacologically passes the most basic sniff test of "possible and not so obviously stupid that nobody would try."

On the other hand, TLR9 deficiency might not be so great. TLR9-deficient mice actually develop worse lupus²¹, have worse intestinal wound repair²², and more bone loss²³, than controls. A lot of "anti-inflammatory" drugs turn out to be heavy on side effects; even if TLR9 inhibitors do hit the market in a few years, we don't know if they'll be safe enough to make sense for healthy people to take to prevent age-related muscle loss.

Apelin

Apelin is a peptide produced in the muscles by exercise, which increases mitochondrial biogenesis and reduces insulin resistance.

A French team found that (in mice) apelin expression declines with age, and genetically apelin-deficient mice have dramatically accelerated muscle loss, loss of strength, and loss of mitochondria with age. Going the other direction, apelin administered to 24-month-old mice increased muscle mass by 12%, grip strength by 30%, max force by 23%, and max speed by 12%.²⁴

A Japanese team found that mice whose kidneys had been mostly removed, which usually causes muscle atrophy, had 5%-17% more muscle mass if they had been administered apelin.²⁵

Do we believe it?

Yeah.

The observational data support a link between apelin and sarcopenia. Taiwanese medical records²⁶ show a strong inverse association between apelin levels in older adults and sarcopenia.

Apelin administration also has other beneficial effects in human studies, like improving insulin sensitivity in overweight men²⁷ and improving cardiac output in patients with chronic heart failure.²⁸

Can you try it at home?

…Ish.

It’s a research chemical; that means it’s available for purchase, but not at pharma-grade quality.

Sigma-Aldrich is promising 95% purity, which does not sound like a risk I’m personally comfortable with, for instance.

A handful of human studies suggest that it’s safe for short-term administration, but it’s also a “potent” diuretic²⁹ (induces urination) and a vasodilator (increases blood flow)³⁰ and both of those can be Actually Dangerous in excess.

Alternatively, you could just wait for a biotech company to bring apelin or one of its analogues to the clinic.

BioAge is taking an apelin analogue into trials for acute muscle indications; they’re a serious anti-aging company (I know the team) and they have their eye on sarcopenia and frailty in the long term. Their Phase 1b trial results found significant reduction in muscle atrophy compared to placebo after 10 days on the drug — producing a 73% improvement in leg muscle thickness.

APIE Therapeutics is another biotech pursuing the apelin pathway — they’re preclinical and looking at pulmonary fibrosis and kidney disease.

I’m excited about this; it could be the first approved sarcopenia drug!

Pim1 Knockout

The gene Pim1 is a gene involved in cell cycle control, possibly including adipogenesis (the development of fat cells) and is highly expressed in aged muscles. A Chinese team found that aged mice lacking the Pim1 gene had 20% greater grip strength than aged controls, 300% more running endurance, and 50% more lean mass. They also had only 40% the fat mass of aged controls.  In vitro, a Pim1 inhibitor prevented senescent mesenchymal progenitor cells from differentiating into fat cells.³¹

Do we believe it?

Could be. Elevated Pim1 levels are definitely part of the signature of sarcopenia and other aging-related tissue problems like lung fibrosis.

Can you try it at home?

No; it’s a gene therapy.

Pim1-deficient mice, while they have weirdly small blood cells, are “normal, healthy, and fertile”.³² So maybe nothing terrible happens if you lack Pim1.

Drugs that inhibit Pim1 are actively being researched as cancer treatments. Pim1 blocks apoptotic cell death, and thus preserves cancer cells that you want to die; the logic is that Pim1 inhibitors will make cancer easier to kill.³³

One of these Pim1 inhibitors has made it into the clinic as a leukemia drug: SGI-1776, developed by Astex Pharma. The study was withdrawn because the drug caused cardiac toxicity.

A more recent Pim1 inhibitor study, in 8 patients with the bone marrow cancer myelofibrosis, found reasonably low toxicity…but this is cancer, so “>20% of patients had nausea, vomiting, and diarrhea, but none of them actually had to stop taking the drug” is winning on the side effect front.

Can you make a Pim1 inhibitor that’s actually safe enough for a healthy adult to take long-term? It remains to be seen.

Coffee

A Japanese team gave 27-month-old mice coffee for 4 weeks instead of water. Relative to controls, the coffee-treated mice had 11% more hind-limb muscle mass and 20% more grip strength.  The serum from treated mice was lower in the pro-inflammatory markers IL-1a, IL-1b, IL-6, and TNF-alpha, but not the growth factor IGF1.³⁴

Do we believe it?

I have a bad feeling about this one.

I’ve noticed a pattern where specifically Japanese researchers frequently find amazing effects of coffee (or caffeine) that aren’t replicated anywhere else in the world. I suspect that coffee is the kind of thing where a lot of people very much Want to Believe it’s healthy.

On the other hand, a Korean study of 1781 men over age 60 found that men who drank at least 3 cups of coffee a day had half the sarcopenia risk of men who drank none.³⁵ A Japanese study of 6389 middle-aged individuals found a positive association between coffee drinking and muscle mass,³⁶ and another Japanese study of 2085 university faculty and their spouses over age 40 also found an association between coffee drinking and lower risk of sarcopenia.³⁷ And caffeine intake has also been found associated with lower risk of some neurodegenerative diseases. So...maybe it's not crazy.

Can you try it at home?

Yes, obviously. Drink up!

5-aminolevulinic Acid

A Japanese team added 5-aminolevulinic acid (a compound involved in the mitochondrial electron transport chain) to the diet of mice starting at 8 weeks of age. At 25 months (old age), treated mice had 5% greater grip strength, 25% more muscle mass, 80% longer running endurance, and triple the number of mitochondria.³⁸

Do we believe it?

Hard to say.

Genetic deficiency in 5-aminolevulinic acid (in mice) causes insulin resistance and worse mitochondrial function, so it kinda makes sense that you'd want to go the other direction.³⁹

Can you try it at home?

You can, but maybe you shouldn’t.

5-aminolevulinic acid is sold as a topical drug under the name of Levulan, for getting rid of precancerous skin lesions in combination with blue light treatment.

Short-term oral administration of 5-aminolevulinic acid is also used to diagnose bladder cancer; but it can cause dangerous drops in blood pressure.⁴⁰

Myostatin Inhibition

Myostatin is a negative regulator of muscle growth. In a Pfizer study on 24-month-old mice, those treated with the myostatin antibody PF-354 and treadmill exercise had 35% greater running distance on an endurance test than the group that got treadmill exercise alone. There was no effect on grip strength.⁴¹

In a study conducted by a New Zealand team, 24-month mice injected for 6 weeks with a myostatin antagonist protein had a 12% increase in grip strength and a 70% increase in satellite cells in muscle fibers, as well as 22% larger muscle fiber cross-sectional area.⁴²

Do we believe it?

Definitely. Myostatin deficiency mutations is where you get the famous “double-muscled” cattle that look like bodybuilders. The relationship between myostatin and muscle growth is extremely reliable.

Can you try it at home?

It’s complicated.

Myostatin inhibitors keep being developed and failing in the clinic against genetic muscle wasting disorders like muscular dystrophy; Pfizer’s didn’t make the cut.⁴³

But hope springs eternal; for instance, currently SRK-015 is in Phase II trials for spinal muscular atrophy (another genetic muscle wasting disease.)

Would any of these “failed” myostatin inhibitors work on what might be an easier problem — preventing muscle loss in “normal” aging? That’s a question for another post.

Losartan

In a Johns Hopkins study, 21-month-old mice had a hind leg immobilized. Immobilization caused muscle atrophy, with a 40% drop in cross-sectional area and a 33% drop in myofiber count; injections of losartan, in either the immobilized or contralateral leg, prevented the atrophy, i.e. resulted in a 70% increase in cross-sectional area and a 50% increase in myofiber count. Losartan is a blood-pressure-lowering drug that blocks the angiotensin receptor. Losartan increased expression of the growth-related genes mTOR, Akt, and FOXO3A.⁴⁴

Do we believe it?

Not really. I don’t love a study that doesn’t look at functional outcomes like strength as well as muscle size. And a DOD study actually found that losartan impaired muscle healing from injury.⁴⁵

Can you try it at home?

Sure; like other anti-hypertension drugs, it’s approved and intended to be used over long periods by relatively healthy middle-aged adults, so it’s pretty tractable to get an off-label prescription. But I’m not sure it’s worth it, given the weakness of the evidence.

1. White, Zoe, et al. "Voluntary resistance wheel exercise from mid-life prevents sarcopenia and increases markers of mitochondrial function and autophagy in muscles of old male and female C57BL/6J mice." Skeletal Muscle 6.1 (2016): 1-21.

2. Lee, Kippeum, et al. "Lactobacillus plantarum HY7715 ameliorates sarcopenia by improving skeletal muscle mass and function in aged Balb/c mice." International Journal of Molecular Sciences 22.18 (2021): 10023.

3. Candow, Darren G., et al. "Current evidence and possible future applications of creatine supplementation for older adults." Nutrients 13.3 (2021): 745.

4. Cooper, Robert, et al. "Creatine supplementation with specific view to exercise/sports performance: an update." Journal of the International Society of Sports Nutrition 9.1 (2012): 33.

5. Bender, Andreas, et al. "Long-term creatine supplementation is safe in aged patients with Parkinson disease." Nutrition research (New York, NY) 28.3 (2008): 172-178.

6. Rodrigues, Anna Carolina Zaia, et al. "Long‐term, induced expression of Hand2 in peripheral sympathetic neurons ameliorates sarcopenia in geriatric mice." Journal of cachexia, sarcopenia and muscle 12.6 (2021): 1908-1924.

7. Wang, Quan-Quan, et al. "Human umbilical cord Wharton’s jelly derived mesenchymal stromal cells may attenuate sarcopenia in aged mice induced by hindlimb suspension." Medical science monitor: international medical journal of experimental and clinical research 24 (2018): 9272.

8. Wright, Adrienne, Marne L. Arthaud-Day, and Mark L. Weiss. "Therapeutic use of mesenchymal stromal cells: the need for inclusive characterization guidelines to accommodate all tissue sources and species." Frontiers in Cell and Developmental Biology 9 (2021): 632717.

9. Le Bacquer, Olivier, et al. "4E‐BP1 and 4E‐BP2 double knockout mice are protected from aging‐associated sarcopenia." Journal of cachexia, sarcopenia and muscle 10.3 (2019): 696-709.

10. Kincheloe, Gregory N., et al. "Loss of 4E-BPs prevents the hindlimb immobilization-induced decrease in protein synthesis in skeletal muscle." Journal of Applied Physiology 134.1 (2023): 72-83.

11. Le Bacquer, Olivier, et al. "Elevated sensitivity to diet-induced obesity and insulin resistance in mice lacking 4E-BP1 and 4E-BP2." The Journal of clinical investigation 117.2 (2007): 387-396.

12. Tsai, Shihyin, et al. "Muscle-specific 4E-BP1 signaling activation improves metabolic parameters during aging and obesity." The Journal of clinical investigation 125.8 (2015): 2952-2964.

13. Rapamycin is one of the most famous and well-replicated drugs that extends animal lifespans. Mice treated with rapamycin live about 25% longer.

14. Choo, Andrew Y., et al. "Rapamycin differentially inhibits S6Ks and 4E-BP1 to mediate cell-type-specific repression of mRNA translation." Proceedings of the National Academy of Sciences 105.45 (2008): 17414-17419.

15. Lyu, An-kang, et al. "Inhibition of TLR9 attenuates skeletal muscle fibrosis in aged sarcopenic mice via the p53/SIRT1 pathway." Experimental Gerontology 122 (2019): 25-33.

16. Calcaterra, Claudia, et al. "Critical role of TLR9 in acute graft-versus-host disease." The Journal of Immunology 181.9 (2008): 6132-6139.

17. Gäbele, Erwin, et al. "Role of TLR9 in hepatic stellate cells and experimental liver fibrosis." Biochemical and biophysical research communications 376.2 (2008): 271-276.

18. Trujillo, Glenda, et al. "TLR9 differentiates rapidly from slowly progressing forms of idiopathic pulmonary fibrosis." Science translational medicine 2.57 (2010): 57ra82-57ra82.

19. Barrat, Franck J., et al. "Treatment of lupus‐prone mice with a dual inhibitor of TLR7 and TLR9 leads to reduction of autoantibody production and amelioration of disease symptoms." European journal of immunology 37.12 (2007): 3582-3586.

20. Ueda, Hiromichi, et al. "Administration of a TLR9 inhibitor attenuates the development and progression of heart failure in mice." JACC: Basic to Translational Science 4.3 (2019): 348-363.

21. Santiago-Raber, Marie-Laure, et al. "Critical role of TLR7 in the acceleration of systemic lupus erythematosus in TLR9-deficient mice." Journal of autoimmunity 34.4 (2010): 339-348.

22. Ii, William Alfred Rose, Kaori Sakamoto, and Cynthia Anne Leifer. "TLR9 is important for protection against intestinal damage and for intestinal repair." Scientific reports 2.1 (2012): 1-9.

23. Ding, Peng, et al. "Toll-like receptor 9 deficiency induces osteoclastic bone loss via gut microbiota-associated systemic chronic inflammation." Bone Research 10.1 (2022): 42.

24. Vinel, Claire, et al. "The exerkine apelin reverses age-associated sarcopenia." Nature medicine 24.9 (2018): 1360-1371.

25. Enoki, Yuki, et al. "The G protein‐coupled receptor ligand apelin‐13 ameliorates skeletal muscle atrophy induced by chronic kidney disease." Journal of Cachexia, Sarcopenia and Muscle 14.1 (2023): 553-564.

26. Chen, Yuan-Yuei, et al. "Cross-sectional associations among P3NP, HtrA, Hsp70, Apelin and sarcopenia in Taiwanese population." BMC geriatrics 21 (2021): 1-9.

27. Gourdy, Pierre, et al. "Apelin administration improves insulin sensitivity in overweight men during hyperinsulinaemic‐euglycaemic clamp." Diabetes, Obesity and Metabolism 20.1 (2018): 157-164.

28. Japp, A. G., et al. "Acute cardiovascular effects of apelin in humans: potential role in patients with chronic heart failure." Circulation 121.16 (2010): 1818-1827.

29. De Mota, Nadia, et al. "Apelin, a potent diuretic neuropeptide counteracting vasopressin actions through inhibition of vasopressin neuron activity and vasopressin release." Proceedings of the National Academy of Sciences 101.28 (2004): 10464-10469.

30. Japp, Alan G., et al. "Vascular effects of apelin in vivo in man." Journal of the American College of Cardiology 52.11 (2008): 908-913.

31. Shang, Guo‐kai, et al. "Pim1 knockout alleviates sarcopenia in aging mice via reducing adipogenic differentiation of PDGFRα+ mesenchymal progenitors." Journal of cachexia, sarcopenia and muscle 12.6 (2021): 1741-1756.

32. Larid, Peter W., et al. "In vivo analysis of Pim-1 deficiency." Nucleic acids research 21.20 (1993): 4750-4755.

33. Merkel, Anna Lena, Eric Meggers, and Matthias Ocker. "PIM1 kinase as a target for cancer therapy." Expert opinion on investigational drugs 21.4 (2012): 425-436.

34. Guo, Yinting, et al. "Coffee treatment prevents the progression of sarcopenia in aged mice in vivo and in vitro." Experimental gerontology 50 (2014): 1-8.

35. Chung, Hyewon, et al. "Association of coffee consumption with sarcopenia in Korean elderly men: analysis using the Korea National Health and Nutrition Examination Survey, 2008–2011." Korean Journal of Family Medicine 38.3 (2017): 141.

36. Iwasaka, Chiharu, et al. "Association between habitual coffee consumption and skeletal muscle mass in middle‐aged and older Japanese people." Geriatrics & Gerontology International 21.10 (2021): 950-958.

37. Kawakami, Ryoko, et al. "Coffee consumption and skeletal muscle mass: WASEDA’S Health Study." British Journal of Nutrition (2022): 1-10.

38. Fujii, Chikako, et al. "Treatment of sarcopenia and glucose intolerance through mitochondrial activation by 5-aminolevulinic acid." Scientific reports 7.1 (2017): 1-12.

39. Saitoh, Shinichi, et al. "5-aminolevulinic acid (ALA) deficiency causes impaired glucose tolerance and insulin resistance coincident with an attenuation of mitochondrial function in aged mice." PLoS One 13.1 (2018): e0189593.

40. Nohara, Takahiro, et al. "Intraoperative hypotension caused by oral administration of 5‐aminolevulinic acid for photodynamic diagnosis in patients with bladder cancer." International Journal of Urology 26.11 (2019): 1064-1068.

41. LeBrasseur, Nathan K., et al. "Myostatin inhibition enhances the effects of exercise on performance and metabolic outcomes in aged mice." Journals of Gerontology Series A: Biomedical Sciences and Medical Sciences 64.9 (2009): 940-948.

42. Siriett, Victoria, et al. "Antagonism of myostatin enhances muscle regeneration during sarcopenia." Molecular Therapy 15.8 (2007): 1463-1470

43. https://www.fiercebiotech.com/biotech/pfizer-drops-muscle-growth-antibody-after-it-misses-phase-2-endpoint-dmd

44. Burks, Tyesha N., et al. "Losartan restores skeletal muscle remodeling and protects against disuse atrophy in sarcopenia." Science translational medicine 3.82 (2011): 82ra37-82ra37.

45. Motherwell, Jessica M., et al. "Effects of Adjunct Antifibrotic Treatment within a Regenerative Rehabilitation Paradigm for Volumetric Muscle Loss." International journal of molecular sciences 24.4 (2023): 3564.