FOXO4-DRI experiments test senescent-cell clearance; MOTS-c experiments examine metabolic adaptation and physical capacity. Separate mouse results and human endogenous-MOTS-c measurements do not establish a clinical aging or fitness ranking. A pulmonary-vessel harm signal for FOXO4-DRI and major native-MOTS-c safety gaps remain consequential.
Research reviewed October 15, 2026. Educational information only.
A synthetic senescent-cell peptide and a mitochondrial-associated peptide
FOXO4-DRI and MOTS-c enter aging discussions through different experiments. FOXO4-DRI is a synthetic peptide using D-amino acids in reversed order, called D-retro-inverso, derived from a region of FOXO4. MOTS-c is a 16-amino-acid peptide linked to a short sequence in mitochondrial genetic information. Baar et al. (2017) and Lee et al. (2015) describe their different origins.
FOXO4-DRI was tested for its ability to trigger programmed death in certain senescent cells. MOTS-c experiments examined metabolism, responses to insulin and adaptation to physical or metabolic stress. The human MOTS-c exercise studies measured the body’s own peptide; they did not give participants native MOTS-c. A direct treatment comparison between FOXO4-DRI and MOTS-c was not identified.
The main differences
What are the compounds and how do they differ biologically?
These identities describe the original FOXO4-DRI construct and native MOTS-c. Endogenous FOXO4 protein and the modified MOTS-c candidate CB4211 are separate materials.
FOXO4-DRI
FOXO4-DRI is a synthetic D-retro-inverso peptide designed around the FOXO4–p53 interaction. In selected senescent-cell cultures it promoted programmed cell death.
Sources
- Baar MP, Brandt RMC, Putavet DA, et al. Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging. Cell. 2017;169(1):132–147.e16. doi:10.1016/j.cell.2017.02.031.
- Bourgeois B, Spreitzer E, Platero-Rochart D, Paar M, Zhou Q, Usluer S, de Keizer PLJ, Burgering BMT, Sánchez-Murcia PA, Madl T. The disordered p53 transactivation domain is the target of FOXO4 and the senolytic compound FOXO4-DRI. Nature Communications. 2025;16:5672. doi:10.1038/s41467-025-60844-9.
MOTS-c
MOTS-c is a 16-amino-acid peptide linked to mitochondrial genetic information. Its cell and mouse experiments examined metabolic signaling and insulin responses.
Sources
- Lee C, Zeng J, Drew BG, Sallam T, Martin-Montalvo A, Wan J, Kim SJ, Mehta H, Hevener AL, de Cabo R, Cohen P. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Cell Metabolism. 2015;21(3):443–454. doi:10.1016/j.cmet.2015.02.009.
- U.S. Food and Drug Administration, Center for Drug Evaluation and Research. MOTS-c-Related Bulk Drug Substances (MOTS-c Free Base and MOTS-c Acetate). Briefing material for the July 23–24, 2026 Pharmacy Compounding Advisory Committee meeting.
Which physical outcomes changed in the mouse studies?
Baar compared FOXO4-DRI with phosphate-buffered saline in rapid-aging and naturally aged mice. Lee and Reynolds compared MOTS-c with control preparations without the peptide in separate metabolic and running experiments. No shared trial directly compared FOXO4-DRI and MOTS-c.
FOXO4-DRI
Blood urea fell in both aging settings and creatinine also fell in naturally aged mice. These are blood waste products used to assess filtering. Wheel activity in naturally aged mice varied too much for a meaningful activity experiment.
MOTS-c
In Lee’s mouse study, glucose disappeared from blood faster after a glucose challenge, and insulin stimulated more glucose disposal into tissues, indicating greater insulin sensitivity. High-fat-fed mice gained less weight. In Reynolds’s study, 22-month-old treated mice ran longer and farther than old controls without peptide.
Sources
- Lee C, Zeng J, Drew BG, Sallam T, Martin-Montalvo A, Wan J, Kim SJ, Mehta H, Hevener AL, de Cabo R, Cohen P. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Cell Metabolism. 2015;21(3):443–454. doi:10.1016/j.cmet.2015.02.009.
- Reynolds JC, Lai RW, Woodhead JST, Joly JH, Mitchell CJ, Cameron-Smith D, Lu R, Cohen P, Graham NA, Benayoun BA, Merry TL, Lee C. MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis. Nature Communications. 2021;12:470. doi:10.1038/s41467-020-20790-0.
What do the human findings actually test?
Human-origin cells outside the body and measurements in living people represent different settings. A change in the body’s own peptide around exercise does not test administering it.
FOXO4-DRI
Studies include human cells and tissue outside the body, such as cartilage-cell cultures. No completed human treatment trial of FOXO4-DRI was identified in the selected evidence.
Sources
- Baar MP, Brandt RMC, Putavet DA, et al. Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging. Cell. 2017;169(1):132–147.e16. doi:10.1016/j.cell.2017.02.031.
- Huang Y, He Y, Makarczyk MJ, Lin H. Senolytic Peptide FOXO4-DRI Selectively Removes Senescent Cells From in vitro Expanded Human Chondrocytes. Frontiers in Bioengineering and Biotechnology. 2021;9:677576. doi:10.3389/fbioe.2021.677576.
MOTS-c
Reynolds measured endogenous MOTS-c around exercise in ten men. A separate exercise study found an uncertain MOTS-c rise, with a clearer humanin response. Neither administered native MOTS-c.
Sources
- Reynolds JC, Lai RW, Woodhead JST, Joly JH, Mitchell CJ, Cameron-Smith D, Lu R, Cohen P, Graham NA, Benayoun BA, Merry TL, Lee C. MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis. Nature Communications. 2021;12:470. doi:10.1038/s41467-020-20790-0.
- von Walden F, Fernandez-Gonzalo R, Norrbom J, et al. Acute endurance exercise stimulates circulating levels of mitochondrial-derived peptides in humans. Journal of Applied Physiology. 2021;131(3):1035–1042. doi:10.1152/japplphysiol.00706.2019.
- U.S. Food and Drug Administration, Center for Drug Evaluation and Research. MOTS-c-Related Bulk Drug Substances (MOTS-c Free Base and MOTS-c Acetate). Briefing material for the July 23–24, 2026 Pharmacy Compounding Advisory Committee meeting.
What is known about blood exposure after administration?
This question concerns intact peptide concentration over time in a living organism. Cell staining and degradation in a blood sample outside the body cannot establish human absorption or elimination.
FOXO4-DRI
Peptide-associated staining remained detectable inside cultured cells for at least 72 hours. The selected reports do not provide a validated human blood half-life, clearance or absorption profile.
MOTS-c
FDA’s 2026 evaluation found no in-vivo PK studies of native MOTS-c. A laboratory blood-degradation experiment found shorter fragments, without determining a human half-life after administration.
What limits or harms matter beyond a favorable marker?
Different organs and preparations need separate safety evaluation. Neither set of studies establishes the long-term safety of a manufactured human product.
FOXO4-DRI
A mouse pulmonary-vessel model showed loss of cells lining lung vessels and adverse circulation changes after FOXO4-DRI. In a separate human cartilage-cell experiment, clearance did not improve later cartilage formation.
Sources
- Born E, Lipskaia L, Breau M, et al. Eliminating Senescent Cells Can Promote Pulmonary Hypertension Development and Progression. Circulation. 2023;147(8):650–666. doi:10.1161/CIRCULATIONAHA.122.058794.
- Huang Y, He Y, Makarczyk MJ, Lin H. Senolytic Peptide FOXO4-DRI Selectively Removes Senescent Cells From in vitro Expanded Human Chondrocytes. Frontiers in Bioengineering and Biotechnology. 2021;9:677576. doi:10.3389/fbioe.2021.677576.
MOTS-c
FDA identified major clinical and nonclinical safety gaps for native MOTS-c and potential immune-reaction and product-characterization concerns. The human exercise studies cannot estimate harms from administering it.
Sources
- U.S. Food and Drug Administration, Center for Drug Evaluation and Research. MOTS-c-Related Bulk Drug Substances (MOTS-c Free Base and MOTS-c Acetate). Briefing material for the July 23–24, 2026 Pharmacy Compounding Advisory Committee meeting.
- Reynolds JC, Lai RW, Woodhead JST, Joly JH, Mitchell CJ, Cameron-Smith D, Lu R, Cohen P, Graham NA, Benayoun BA, Merry TL, Lee C. MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis. Nature Communications. 2021;12:470. doi:10.1038/s41467-020-20790-0.
- von Walden F, Fernandez-Gonzalo R, Norrbom J, et al. Acute endurance exercise stimulates circulating levels of mitochondrial-derived peptides in humans. Journal of Applied Physiology. 2021;131(3):1035–1042. doi:10.1152/japplphysiol.00706.2019.
Cell elimination and metabolic adaptation require different measurements
In the original FOXO4-DRI cultures, peptide competition disrupted the interaction between FOXO4 and p53, a stress-response protein. Activated p53 left the nucleus, and enzymes that carry out apoptosis became active. Bourgeois et al. (2025) later showed direct binding of the peptide to a flexible p53 region. These measurements help explain how a cell can be made to die.
Lee et al. (2015) instead linked MOTS-c to changes in folate and purine metabolism that activated AMPK, an enzyme that responds to cellular energy conditions. Kim et al. (2018) examined movement into the nucleus and regulation of stress-response genes. A change in metabolic signaling does not by itself measure cell clearance, muscle performance or a clinical benefit.
Kidney filtering markers and treadmill performance came from different mice
Baar et al. (2017) compared FOXO4-DRI with phosphate-buffered saline in rapid-aging and naturally aged mice. Blood urea fell in both settings, and creatinine also fell in naturally aged mice. These waste products help assess kidney filtering. The rapid-aging animals had a DNA-repair disorder, and the naturally aged mice were a separate group. Wheel activity varied too much in the naturally aged animals for a meaningful activity experiment.
Lee et al. (2015) found faster disappearance of glucose from blood after a glucose challenge and greater insulin-stimulated glucose disposal into tissues in MOTS-c-treated mice than in controls without peptide. These measurements indicate improved insulin sensitivity. In a separate high-fat-feeding experiment, treated mice gained less weight. Reynolds et al. (2021) then tested physical capacity in separate groups of young, middle-aged and old mice. In the 22-month-old mouse comparison, 18 treated animals ran longer and farther than 19 old controls without peptide after two weeks. Other treadmill experiments tested younger animals and different diets. A forced treadmill test, spontaneous wheel activity, glucose handling and blood kidney markers describe different functions. Their results do not identify an overall aging-treatment winner.
Human exercise measurements do not test peptide administration
Reynolds et al. (2021) measured MOTS-c in muscle and circulation around exercise in ten sedentary young men. Measurements increased after exercise, with circulating levels returning toward baseline over recovery. That observation asks how the endogenous peptide responds to exertion.
von Walden et al. (2021) separately assigned participants to endurance exercise, resistance exercise or a control condition. The apparent plasma MOTS-c increase after endurance exercise remained uncertain; the clearer circulating change involved humanin, a different peptide. The different MOTS-c findings leave exercise responses dependent on the study and assay. Neither experiment determines whether administering native MOTS-c improves human fitness, and neither compares it with FOXO4-DRI.
Neither side supplies a validated human half-life
For FOXO4-DRI, the original investigators detected peptide-associated staining inside cultured cells for at least 72 hours after exposure. They did not measure a human serial blood concentration profile. The intracellular detection period is therefore different from a circulating elimination half-life. Baar et al. (2017) describe that assay.
The FDA’s 2026 MOTS-c evaluation found no in-vivo PK or toxicokinetic studies for native MOTS-c. The degradation work it identified added MOTS-c to human blood outside the body and detected shorter fragments. That cannot determine absorption, tissue delivery or a human half-life after administration. The modified development candidate CB4211 is a separate preparation and does not supply native-MOTS-c treatment PK.
A tissue-specific harm signal and major treatment-safety gaps
Born et al. (2023) reported loss of pulmonary endothelial cells and adverse lung-circulation changes in serotonin-transporter-overexpressing mice given FOXO4-DRI or ABT263. The abstract does not provide a peptide-specific pressure estimate. Other numerical vascular results concern separate genetic-clearance or ABT263 arms. This directly complicates the idea that removing senescent cells must help every organ.
Huang et al. (2021) supplied another important limit: removing senescent cells from expanded human cartilage-cell cultures did not improve later cartilage formation. The result matters because reducing a cellular marker and restoring a useful tissue function are separate outcomes.
FDA’s 2026 evaluation reported that native MOTS-c free base and acetate were not components of an approved drug and that administered-human safety data were lacking. It raised concerns about immune reactions and product characterization while finding no clinical PK dataset. The existence of endogenous MOTS-c does not establish the safety of an administered manufactured preparation. Neither compound’s selected evidence supports a clinical longevity or fitness recommendation.
Frequently asked questions
Is MOTS-c another senolytic like FOXO4-DRI?
The selected MOTS-c experiments investigated metabolism and stress adaptation. The original FOXO4-DRI experiments deliberately promoted programmed death in certain senescent cells. These mechanisms require different measurements and do not establish equivalent treatment effects.
Did human exercise participants receive MOTS-c?
The cited human studies measured the body’s own MOTS-c before and after exercise. Participants underwent exercise or control conditions rather than treatment with native MOTS-c.
Does a three-day cellular detection period show FOXO4-DRI circulates that long?
The original observation detected peptide-associated material inside cultured cells. Serial intact-peptide blood measurements are needed to estimate circulating elimination after administration; that assay did not provide them.
Can mouse running results establish which compound improves human fitness more?
The experiments tested different mice, tasks and outcomes. Spontaneous wheel activity and treadmill endurance are different behaviors, and neither supplies a direct human comparison between these peptides.
Do CB4211 clinical results establish native MOTS-c effects?
CB4211 is a modified development candidate. Its clinical program concerns that defined preparation; the FDA assessment of native MOTS-c found no clinical exposure dataset that establishes native-peptide safety or effectiveness.
Profiles and related reading
References
- Baar MP, Brandt RMC, Putavet DA, et al. Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging. Cell. 2017;169(1):132–147.e16. doi:10.1016/j.cell.2017.02.031.
Original PMC full text accessed 2026-10-15 after intermittent browser challenges. Identity, Results and figure legends read; no laboratory instructions reproduced. Results Figures 2–7; STAR Methods, FOXO4 D-Retro-Inverso peptide development; Discussion initial safety limits.
- Bourgeois B, Spreitzer E, Platero-Rochart D, Paar M, Zhou Q, Usluer S, de Keizer PLJ, Burgering BMT, Sánchez-Murcia PA, Madl T. The disordered p53 transactivation domain is the target of FOXO4 and the senolytic compound FOXO4-DRI. Nature Communications. 2025;16:5672. doi:10.1038/s41467-025-60844-9.
Original PubMed abstract and original publisher/PMC indexed full-text sections accessed 2026-10-15. Abstract; Results and Discussion concerning p53 TAD2 and the TAT contribution; PMID40593617.
- Huang Y, He Y, Makarczyk MJ, Lin H. Senolytic Peptide FOXO4-DRI Selectively Removes Senescent Cells From in vitro Expanded Human Chondrocytes. Frontiers in Bioengineering and Biotechnology. 2021;9:677576. doi:10.3389/fbioe.2021.677576.
Original PubMed abstract and original Frontiers PDF accessed 2026-10-15. Donor-count discrepancy is recorded in source-check.md. Abstract; original journal PDF Results and conclusion; population doubling levels 3 and 9.
- Born E, Lipskaia L, Breau M, et al. Eliminating Senescent Cells Can Promote Pulmonary Hypertension Development and Progression. Circulation. 2023;147(8):650–666. doi:10.1161/CIRCULATIONAHA.122.058794.
Complete original PubMed abstract accessed 2026-10-15; publisher PDF indexed abstract also checked. Complete peptide-arm methods and numeric results unavailable. Abstract Methods/Results/Conclusions, especially SM22-5-HTT+ arm; separate suicide-gene, ABT263 and rat arms.
- Lee C, Zeng J, Drew BG, Sallam T, Martin-Montalvo A, Wan J, Kim SJ, Mehta H, Hevener AL, de Cabo R, Cohen P. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Cell Metabolism. 2015;21(3):443–454. doi:10.1016/j.cmet.2015.02.009.
Original PubMed abstract and figure legends plus original indexed PMC Results accessed 2026-10-15. Figure 5 glucose-disposal and Figure 6 high-fat-feeding findings freshly checked. Existing baseline pmid-25738459 retained. Abstract; Figures1–5, folate/purine metabolites, AMPK and mouse insulin-resistance experiments.
- Kim KH, Son JM, Benayoun BA, Lee C. The Mitochondrial-Encoded Peptide MOTS-c Translocates to the Nucleus to Regulate Nuclear Gene Expression in Response to Metabolic Stress. Cell Metabolism. 2018;28(3):516–524.e7. doi:10.1016/j.cmet.2018.06.008.
Verified baseline original-source context retained; direct PMC request on2026-10-15 returned a browser challenge. No newly extracted numbers used. Abstract; nuclear translocation under metabolic stress and nuclear gene-expression experiments.
- Reynolds JC, Lai RW, Woodhead JST, Joly JH, Mitchell CJ, Cameron-Smith D, Lu R, Cohen P, Graham NA, Benayoun BA, Merry TL, Lee C. MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis. Nature Communications. 2021;12:470. doi:10.1038/s41467-020-20790-0.
Original PubMed abstract/figure descriptions and original author-hosted journal PDF at https://gero.usc.edu/labs/benayounlab/files/2021/01/Reynolds-2021-Nat_comms_MOTSc_exercise.pdf accessed 2026-10-15. Figure 3 old-mouse n=19 control/n=18 treated and two-week outcome freshly checked. Existing baseline report identity retained. Figure1 human exercise observations; Figures2–5 distinct mouse interventions; PMID33473109.
- von Walden F, Fernandez-Gonzalo R, Norrbom J, et al. Acute endurance exercise stimulates circulating levels of mitochondrial-derived peptides in humans. Journal of Applied Physiology. 2021;131(3):1035–1042. doi:10.1152/japplphysiol.00706.2019.
Original complete PubMed abstract and figure legends accessed 2026-10-15. Baseline pmid-34351816 retained. Abstract;30 participants randomized10 per condition; Figure3B plasma MOTS-c and separate humanin result.
- U.S. Food and Drug Administration, Center for Drug Evaluation and Research. MOTS-c-Related Bulk Drug Substances (MOTS-c Free Base and MOTS-c Acetate). Briefing material for the July 23–24, 2026 Pharmacy Compounding Advisory Committee meeting.
Complete original FDA44-page PDF accessed 2026-10-15. PDF pages6,25–30 and32; section b Pharmacokinetics/Toxicokinetics; Human Safety and effectiveness.
- CohBar, Inc. Annual Report on Form 10-K for the fiscal year ended December 31, 2021. U.S. Securities and Exchange Commission filing. 2022. CB4211 program section.
Original SEC filing freshly accessed2026-10-15; separate candidate identity only, not sponsor efficacy claims. CB4211 research and development discussion.