Thymulin
Also known as: Facteur thymique sérique, FTS, Serum thymic factor, Zinc-thymulin, FTS-Zn, Nonathymulin, pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn
Not approved as a medicine anywhere; research peptide
4 notable studies · 9 references
TLDR
Thymulin is a natural nine-amino-acid thymus hormone that works only when bound to zinc. It helps T cells mature, falls with age and with even mild zinc deficiency, and in rodents reduces inflammatory pain and affects pituitary function. Human evidence is limited to observational zinc studies and a tiny 1980s report, and no thymulin therapy is approved.
At a Glance
Classification: Endogenous zinc-dependent thymic nonapeptide hormone; thymic epithelial cell product; immunomodulatory and neuroendocrine-active peptide
Thymulin is a small hormone made by epithelial cells of the thymus, the organ where T cells mature. It was discovered in the 1970s by Jean-François Bach, Mireille Dardenne and colleagues in Paris, who originally named it "facteur thymique sérique" (serum thymic factor, FTS). It is a nine-amino-acid peptide: pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn. Its defining quirk: thymulin is biologically active only when bound to zinc (one zinc ion per molecule). The peptide without zinc circulates but does not work. That makes thymulin activity a sensitive indicator of zinc status, and in humans it falls even with mild zinc deficiency. Thymulin is studied for: • T-cell differentiation and immune regulation • Immune aging, since thymulin levels drop as the thymus shrinks with age • Zinc deficiency • Anti-inflammatory and pain-reducing effects in animal models • Two-way signaling between the thymus and the brain and pituitary (neuroendocrine effects). Watch the spelling: thymulin is not thymalin. Thymalin is a Russian calf-thymus extract drug. They are different products with separate evidence bases. No thymulin product is approved as a medicine. Human administration data are very limited.
What Is Thymulin?
Thymulin is an endogenous peptide hormone, not a synthetic design. Thymic epithelial cells ↓ secrete the nonapeptide ↓ which binds zinc (Zn2+) ↓ active thymulin circulates and acts on T-cell precursors and other targets. Blood thymulin activity is high in childhood and declines with age as the thymus involutes. Researchers have used thymulin levels as a marker of thymic endocrine function and zinc status.
What Are Researchers Studying?
Zinc deficiency and immunity
In a 1988 study, serum thymulin activity fell in mildly zinc-deficient people, including volunteers with diet-induced deficiency and people with sickle cell anemia, even when plasma zinc looked normal. It was corrected by zinc supplementation. T-cell changes tracked these shifts, suggesting thymulin as one link between zinc and T-cell function.
Natural killer cell modulation
Synthetic FTS changed NK cell activity in human blood cells in a dose-dependent way, increasing it at low concentrations and decreasing it at higher ones. In four cancer patients, intravenous FTS raised NK activity in two people with low baseline values and lowered it in two with normal or high values.
Inflammatory pain and neuroinflammation
In rats and mice, high doses of thymulin reduced mechanical and heat hyperalgesia caused by injected bacterial endotoxin. Later work showed it reduced brain pro-inflammatory cytokines after endotoxin was injected into the brain. A thymulin-related analog peptide has also been studied as a possible analgesic.
Thymulin gene therapy and neuroendocrine effects
An Argentine group (Goya, Reggiani and colleagues) built a synthetic gene for a thymulin analog (met-FTS). A single injection of an adenoviral vector restored circulating thymulin for more than 100 days in thymectomized mice and rats. They then studied how thymulin deficiency affects pituitary hormone-producing cells.
Hair follicles
Thymic peptides including thymulin have been tested on cultured human hair follicles. The indexed record is a short research letter without an abstract, so we have not summarized its results.
How Does It Work?
Proposed actions (mainly from animal and cell studies): Zinc-thymulin ↓ promotes expression of T-cell markers and differentiation of immature T cells, inside and outside the thymus ↓ modulates immune cell activity, including natural killer (NK) cells ↓ in the nervous system: reduces pro-inflammatory cytokines (IL-1β, IL-6, TNF-α) and inflammatory pain in rodent models ↓ interacts with the pituitary and hypothalamus (thymus–neuroendocrine axis): thymulin deficiency in mice alters gonadotropin, thyroid and other pituitary-cell populations. A specific thymulin receptor has not been clearly established. Its effects also appear to depend on dose: in one human-cell study, low concentrations increased NK activity while higher concentrations decreased it.
What Does the Research Show?
Human research
LOW Human data are mainly observational (thymulin falls in zinc deficiency) and a tiny, early administration report in four cancer patients. No controlled clinical trials of thymulin treatment were identified.
Animal research
MODERATE Rodent studies show anti-inflammatory and pain-reducing effects, and gene-therapy work restored circulating thymulin in thymectomized animals. Neuroendocrine effects are documented in thymulin-deficient mice.
In-vitro research
MODERATE Immune-cell and zinc-binding biochemistry are well described.
Notable Studies
Effect of a synthetic thymic factor (facteur thymique serique) on natural killer cell activity in humans
humanJournal: International Journal of Immunopharmacology. In blood lymphocytes from healthy donors, low FTS concentrations increased NK activity and higher concentrations decreased it. Given intravenously to four cancer patients, FTS increased NK activity in two with low baseline values and decreased it in two with normal or high values.
Limitations: Four patients, no control group, and an immune-lab endpoint only. Early-1980s methods.
View publication →Serum thymulin in human zinc deficiency
humanJournal: Journal of Clinical Investigation. Serum thymulin activity fell in three groups of mildly zinc-deficient people (two volunteers with diet-induced deficiency, six adults with sickle cell anemia and six other adults) and was restored by zinc supplementation, both in the body and in the test tube. T-cell subset and IL-2 changes during depletion also reversed with zinc.
Limitations: Very small groups. This shows thymulin as a zinc-status marker, not that giving thymulin helps.
View publication →Thymulin reduces hyperalgesia induced by peripheral endotoxin injection in rats and mice
animalJournal: Brain Research. In a localized inflammation model (endotoxin injected into the paw), high doses of thymulin reduced mechanical and thermal hyperalgesia in a dose-dependent way.
Limitations: Rodent pain model. High doses were needed, and human pain effects are untested.
View publication →Gene therapy for long-term restoration of circulating thymulin in thymectomized mice and rats
animalJournal: Gene Therapy. A synthetic gene encoding met-FTS (a biologically active thymulin analog) was placed in an adenoviral vector. A single intramuscular injection restored serum thymulin in thymectomized mice and rats for at least 110 and 130 days, respectively.
Limitations: Shows restored thymulin levels, not clinical benefit. Gene-therapy tool for animal research.
View publication →What We Still Don't Know
• Whether giving thymulin, with zinc, has any clinical benefit in humans; no controlled trials were identified • Its receptor and signaling mechanism • Human pharmacokinetics and how zinc status changes the activity of administered peptide • Whether restoring thymulin in older people meaningfully improves immune function • Whether rodent pain and anti-inflammatory effects translate to humans • Long-term safety • Whether "thymulin" sold outside research settings contains correctly bound zinc and the right sequence. The human literature on thymulin is old and thin.
Related Compounds
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Sources & References
- Dokhelar MC, Tursz T, Dardenne M, Bach JF. Effect of a synthetic thymic factor (facteur thymique serique) on natural killer cell activity in humans. Int J Immunopharmacol. 1983;5(4):277–282.
- Prasad AS, Meftah S, Abdallah J, et al. Serum thymulin in human zinc deficiency. J Clin Invest. 1988;82(4):1202–1210.
- Bach JF, Dardenne M. Thymulin, a zinc-dependent hormone. Med Oncol Tumor Pharmacother. 1989.
- Safieh-Garabedian B, Jalakhian RH, Saadé NE, et al. Thymulin reduces hyperalgesia induced by peripheral endotoxin injection in rats and mice. Brain Res. 1996;717(1-2):179–183.
- Safieh-Garabedian B, Ochoa-Chaar CI, Poole S, et al. Thymulin reverses inflammatory hyperalgesia and modulates the increased concentration of proinflammatory cytokines induced by i.c.v. endotoxin injection. Neuroscience. 2003.
- Reggiani PC, Hereñú CB, Rimoldi OJ, et al. Gene therapy for long-term restoration of circulating thymulin in thymectomized mice and rats. Gene Ther. 2006;13(16):1214–1221.
- Dardenne M, Saade N, Safieh-Garabedian B. Role of thymulin or its analogue as a new analgesic molecule. Ann N Y Acad Sci. 2006.
- Reggiani PC, Schwerdt JI, Console GM, et al. Physiology and therapeutic potential of the thymic peptide thymulin. Curr Pharm Des. 2014.
- Meier N, Langan D, Hilbig H, et al. Thymic peptides differentially modulate human hair follicle growth. J Invest Dermatol. 2012;132(5):1516–1519. (Research letter; no abstract indexed.)
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