Proxofim peptide is an abbreviation for a term called Forkhead box O transcription factor 4-D-Retro-Inverso peptide.(1) Proxofim peptide is similar to FOXO4 protein, but with a modification where L-amino acids are substituted with D-amino acids. This alteration appears to make the Proxofim peptide more resistant to the regular clearance mechanism, leading to its extended presence in the body compared to the FOXO4 protein.
Regarding ‘DRI’ Peptides
Retro Inverso Peptides, also known as DRI peptides, consist of reversed amino acid sequences, leading to a change in the structure’s chirality, with L-amino acids replaced by D-amino acids and vice versa. This structural modification appears to offer an advantage by increasing resistance to peptide degradation, potentially prolonging their half-lives.
D-amino acids are mirror images of the L-amino acids that naturally occur in biological proteins. Replacing L-amino acids with D-amino acids may offer a significant advantage, as the latter are more resistant to degradation, enhancing the protein structure’s durability.
How does the Proxofim Peptide Work?
The Proxofim peptide has been suggested by researchers to hold significant potential as a therapeutic agent, due to its apparent ability to prevent the binding of the FOXO4 protein with the p53 protein. The p53 protein is an endogenous regulator of the cell cycle, including cell death. Specifically, when the FOXO4 protein binds with p53, it prevents p53 from binding with DNA and initiating apoptosis and cell death. However, the presence of the Proxofim peptide appears to inhibit this binding process, allowing p53 to bind with DNA and facilitate the continuation and death of the cell cycle.(2)
Interestingly, the Proxofim peptide may be selective, only targeting senescent cells that have become dysfunctional over time due to aging. By promoting apoptosis in these cells, the peptide may ultimately lead to improved biological functioning of the tissues, promoting cell growth and differentiation. As a result, the Proxofim (or FOXO4-DRI) peptide may potentially mitigate aging effects and improve overall biological functioning.
Research Studies on Proxofim (FOXO4-DRI) Peptide
Proxofim Peptide and Aging and Senescence
The FOXO4 protein functions to protect senescent cells by preventing the binding of the p53 protein with DNA. However, the Proxofim peptide may be capable of blocking this natural protein, thus allowing p53 to bind with DNA and trigger apoptosis in senescent cells. This process is commonly referred to as the “rejuvenation” of biological systems by eliminating aged cells.3
By eliminating senescent cells, the body’s energy production is redirected towards healthy cells, which may lead to improved growth, development, and body function. While the Proxofim peptide does not appear to completely halt the senescence process, studies suggest it may slow it down by preventing FOXO4-mediated senescence.
The process of cell senescence is influenced by various factors, as illustrated in the image below. It can result in various outcomes, such as cell death or the secretion of inflammatory factors contributing to aging and age-related diseases.
In support of this theory, a 2017 study(4) was conducted on aged mice to investigate the effects of the peptide compound. The mice were either administered with the Proxofim peptide or a placebo. The results indicated that the mice receiving the peptide appeared to exhibit improved fitness, better renal functioning, and increased fur density. Although there was no increase in lifespan observed, the findings suggest that the peptide may lead to better cellular and tissue health, reducing age-related ailments and disabilities. As per Marjolein P. Baar et al.:
“It is relevant to note that independent of aging and age-related diseases, FOXO4-DRI may be useful against the progression, stemness, and migration of malignant cancer. Given that SASP factors influence these, it will be particularly interesting to determine whether FOXO4-DRI affects those p53-wt cancer cells that have adopted a more migratory and stem-like state due to reprogramming by chronic SASP exposure. In any case, the here reported beneficial effects of FOXO4-DRI provide a wide range of possibilities for studying the potential of therapeutic removal of senescence against diseases for which few options are available.”(4)
Proxofim Peptide and Insulin Signaling
Studies(5) suggest that the FOXO proteins may play a crucial role in the insulin signaling pathway by regulating inhibitory functions related to cell metabolism, cell cycle, oxidative stress, senescence, and aging. Any deviation in the levels of FOXO proteins can lead to severe disorders such as cancer, metabolic disorders, and altered lifespan. This is particularly concerning in individuals with diabetes, as alterations in FOXO levels can cause hyperlipidemia and hyperglycemia, which may result in stroke, kidney damage, and other complications.
Although further research is necessary to fully understand the mechanism of action, it is believed that Proxofim peptide may enhance the downstream effects of insulin, leading to a reduction in excess blood sugar levels. This could potentially help prevent complications associated with altered FOXO levels and insulin signaling.
Proxofim Peptide and Cardiovascular Ailments
According to research,(6) the likelihood of cardiovascular disorders increases with age. This is attributed to decreased levels of the proteasome enzyme, which plays a vital role in identifying and removing damaged or dysfunctional cells. With age, the number of damaged cells in the body increases due to reduced proteasome levels.
The FOXO4 protein is responsible for regulating proteasome levels in the body. However, its activity alone may not effectively reduce the number of damaged cells in aging organisms. It is believed that the Proxofim peptide could enhance the body’s natural process of eliminating dysfunctional cells, potentially reducing the occurrence of age-related heart diseases.(7) Nevertheless, further clinical trials are required to validate this hypothesis.
Proxofim Peptide and Neurodegenerative Disorders
Age-related cognitive impairment is a common occurrence, and the underlying mechanisms of neurodegenerative disorders, such as Alzheimer’s disease, are still unclear. However, it has been observed that proteasome enzyme activity changes with age, potentially contributing to cognitive decline.
Studies(8) have suggested that proteasome activity is downregulated in neurodegenerative disorders like Parkinson’s, Alzheimer’s, and Prion diseases. However, it is unclear if this downregulation is a primary cause of these diseases.
Further research has revealed that the levels of FOXO proteins are altered in the central nervous system of patients with neurodegenerative disorders.(9) This has led to the hypothesis that exogenous FOXO protein, including the Proxofim peptide, may help regulate optimal levels of FOXO proteins and prevent or alleviate the progression of neurodegenerative disorders associated with this mechanism. Further studies are needed to explore this potential therapeutic option. The study reports state that
“Forkhead box O (FoxO) transcription factors have been implicated in the mechanisms regulating aging and longevity. The functions of FoxOs are regulated by diverse post-translational modifications (e.g., phosphorylation, acetylation, ubiquitination, methylation and glycosylation). FoxOs exert both detrimental and protective effects on NDDs (Neurodegenerative diseases). Therefore, an understanding of the precise function of FoxOs in NDDs will be helpful for developing appropriate treatment strategies.”(9)
Proxofim Peptide and Age-related Male Hypogonadism
Late-onset hypogonadism (LOH) is a common age-related ailment in men characterized by reduced serum testosterone levels, low sexual desire, erectile dysfunction, obesity, and depression. This is primarily due to the impaired functioning of the senescent Leydig cells, which are located adjacent to the tubules in the testicles.
A study(10) was conducted to explore the use of the Proxofim peptide in treating age-related male LOH. An in vitro model composed of senescent Leydig cells, previously isolated from male mice and treated with hydrogen peroxide, was utilized. Upon analysis, researchers suggested that FOXO4 cells appeared to help maintain the viability of these cells and prevent their apoptosis. However, when these isolated senescent cells were treated with Proxofim, results suggested the blockage of the FOXO4 protein, allowing the p53 protein to bind with DNA, leading to the apoptosis of the senescent Leydig cells.
A further study was conducted in naturally aged mice, which suggested that Proxofim peptide improved the functioning and overall health of Leydig cells, resulting in improved testicular functioning and increased testosterone secretion. This indicates that the peptide may be clinically useful in combating male late-onset hypogonadism.
Proxofim, also known as FOXO4-DRI peptide, has an amino acid sequence identical to the endogenous FOXO4 transcription protein, except that the L-amino acids are substituted with D-amino acids. As a result, the peptide is referred to as FOXO4-D-Retro-Inverso peptide.
FOXO4-DRI has a unique mechanism of action in comparison to other similar compounds. It has been researched for its potential to disrupt or reverse the normal function of FOXO4 protein by preventing its binding with p53 protein. Consequently, p53 can bind with DNA instead, leading to the apoptosis of only senescent (damaged) cells. This selective activity would promote the growth of healthier and more functional cells and tissues in the body. Early research suggests that the peptide may potentially treat various age-related conditions and senescence in humans.
It is important to acknowledge that the Proxofim peptide remains unapproved for clinical use. Ongoing trials are necessary to fully explore its effects on human subjects and establish its safety and efficacy profile in the therapeutic domain. It is offered here strictly for research purposes, and is not available for personal use.
- Huang, Yuzhao et al. “Senolytic Peptide FOXO4-DRI Selectively Removes Senescent Cells From in vitro Expanded Human Chondrocytes.” Frontiers in bioengineering and biotechnology vol. 9 677576. 29 Apr. 2021, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8116695/
- Sun, Yan et al. “FOXO4 Inhibits the Migration and Metastasis of Colorectal Cancer by Regulating the APC2/β-Catenin Axis.” Frontiers in cell and developmental biology vol. 9 659731. 23 Sep. 2021. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8495124/
- Krimpenfort P, Berns A. Rejuvenation by Therapeutic Elimination of Senescent Cells. Cell. 2017 Mar 23;169(1):3-5. https://pubmed.ncbi.nlm.nih.gov/28340347/
- Marjolein P. Baar et al, Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging. Vol 169 Issue 1, https://doi.org/10.1016/j.cell.2017.02.031
- Lee, S., & Dong, H. H. (2017). FoxO integration of insulin signaling with glucose and lipid metabolism. The Journal of endocrinology, 233(2), R67–R79. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5480241/
- Anne-Laure Bulteau, Luke I. Szweda, Bertrand Friguet, Age-Dependent Declines in Proteasome Activity in the Heart, Archives of Biochemistry and Biophysics, Volume 397, Issue 2, 2002, Pages 298-304, ISSN 0003-9861, https://doi.org/10.1006/abbi.2001.2663
- Murtaza G, Khan AK, Rashid R, Muneer S, Hasan SMF, Chen J. FOXO Transcriptional Factors and Long-Term Living. Oxid Med Cell Longev. 2017;2017:3494289. doi: 10.1155/2017/3494289. Epub 2017 Aug 15. https://pubmed.ncbi.nlm.nih.gov/28894507
- Ciechanover A, Brundin P. The ubiquitin proteasome system in neurodegenerative diseases: sometimes the chicken, sometimes the egg. Neuron. 2003 Oct 9;40(2):427-46. https://pubmed.ncbi.nlm.nih.gov/14556719
- Wei Hu, Zhi Yang, Wenwen Yang, Mengzhen Han, Baoping Xu, Zihao Yu, Mingzhi Shen, Yang Yang, Roles of forkhead box O (FoxO) transcription factors in neurodegenerative diseases: A panoramic view, Progress in Neurobiology, Volume 181, 2019, 101645, ISSN 0301-0082, https://doi.org/10.1016/j.pneurobio.2019.101645
- Zhang, C., Xie, Y., Chen, H., Lv, L., Yao, J., Zhang, M., Xia, K., Feng, X., Li, Y., Liang, X., Sun, X., Deng, C., & Liu, G. (2020). FOXO4-DRI alleviates age-related testosterone secretion insufficiency by targeting senescent Leydig cells in aged mice. Aging, 12(2), 1272–1284. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7053614/
- Image credit: Senescence and aging: Causes, consequences, and therapeutic avenues. https://doi.org/10.1083/jcb.201708092
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Dr. Marinov (MD, Ph.D.) is a researcher and chief assistant professor in Preventative Medicine & Public Health. Prior to his professorship, Dr. Marinov practiced preventative, evidence-based medicine with an emphasis on Nutrition and Dietetics. He is widely published in international peer-reviewed scientific journals and specializes in peptide therapy research.