Research-use-only context. This article summarizes published third-party scientific literature and laboratory practice. It is not medical advice, not a therapeutic or performance claim, and not a usage guide. US Prime Peptides products are supplied strictly for in vitro laboratory research and are not for human or veterinary use.
This article covers thymosin alpha-1: its chemistry, where it comes from in the body, what its structure looks like, what cell and mouse immunology studies report, and its unusual regulatory position as a peptide that is an approved drug in many countries but not in the United States. It closes with what a research certificate should show for a 28-residue acetylated peptide.
Thymosin alpha-1 is a 28-residue acidic peptide first sequenced in 1977
Thymosin alpha-1 is a linear peptide of 28 amino acids with an acetylated N-terminal serine, the sequence Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn, and a molecular weight of about 3,108 daltons. Goldstein, Low, McAdoo, and colleagues reported its isolation and complete sequence from calf thymus in a 1977 Proceedings of the National Academy of Sciences paper. They described it as heat-stable and highly acidic (ten of its 28 residues are aspartate or glutamate) and as one of several peptides present in "thymosin fraction 5", a crude thymic extract their laboratory had been studying for a decade. The same paper proposed the naming scheme (alpha, beta, gamma, by isoelectric point) that gave the thymosin family its names.
Because the native peptide carries an N-acetyl group, early recombinant work could not make it exactly. Wetzel and colleagues' 1980 Biochemistry paper assembled a synthetic gene for the peptide, expressed it in Escherichia coli as a fusion with beta-galactosidase, and cleaved it free with cyanogen bromide; the product was identical in sequence but lacked the acetyl group. Chemical synthesis solved that problem. Felix and colleagues described a fragment-condensation synthesis with tert-butyl side-chain protection in 1985, and modern solid-phase methods make the acetylated peptide routinely. The drug substance marketed abroad is the synthetic, acetylated form.
It is a fragment of prothymosin alpha, and whether it is a "hormone" was debated for years
Thymosin alpha-1 corresponds to the first 28 residues of a much larger protein, prothymosin alpha. Haritos, Goodall, and Horecker reported in a 1984 Proceedings of the National Academy of Sciences paper that the major substance in rat thymus reacting with an antibody against thymosin alpha-1 was a polypeptide of about 112 residues carrying the thymosin alpha-1 sequence at its N-terminus; free thymosin alpha-1 was not detected. Their conclusion was that the 28-mer might be an artifact of the acid extraction used to make fraction 5. Szabo and Weksler asked the question directly in a 1992 Clinical Immunology and Immunopathology paper titled "Is thymosin alpha 1 a thymic hormone?"
Later work argued the other way. Franco and colleagues reported in a 1992 Biochimica et Biophysica Acta paper that, using isoelectric focusing on extracts prepared with protease inhibition, thymosin alpha-1 could be found as a native peptide in calf thymus and in several lymphoid and non-lymphoid rat tissues, at concentrations higher than prothymosin alpha itself. Sarandeses, Covelo, Díaz-Jullien, and Freire then identified a mechanism in a 2003 Journal of Biological Chemistry paper: the lysosomal asparaginyl endopeptidase legumain cleaves prothymosin alpha at Asn28-Gly29 and Asn35-Gly36, generating thymosin alpha-1 and thymosin alpha-11 respectively, with thymosin alpha-1 the main product found free in the cytosol. Prothymosin alpha is itself a nuclear protein involved in chromatin remodeling, so the parent and the fragment appear to live in different compartments.
Solution structure: disordered in water, partly helical in membrane-like solvent
Two NMR studies describe the peptide's shape. Grottesi and colleagues' 1998 paper in Peptides combined circular dichroism and two-dimensional NMR and found that thymosin alpha-1 has no preferred conformation in water. In the presence of phospholipid vesicles, sodium dodecyl sulfate micelles, or zinc ions, it became partly structured, and in a water-trifluoroethanol mixture it adopted a beta-turn between residues 5 and 8 and an alpha helix between residues 17 and 24. The authors proposed that this environment-dependent folding might be a step in interaction with lymphocyte membranes.
Elizondo-Riojas, Chamow, Tuthill, and colleagues refined the picture in a 2011 Biochemical and Biophysical Research Communications paper using an 800 MHz spectrometer in 40% trifluoroethanol. They reported an alpha helix spanning residues 14 to 26 and two double beta-turns within the first twelve residues that form a distorted helical segment. For a laboratory, the important point is that thymosin alpha-1 is an intrinsically disordered peptide in aqueous solution, which is consistent with its heat stability and with the absence of a single rigid structure to protect during storage. The storage and stability guide covers the degradation drivers that do apply, chiefly deamidation at the Asn and Gln-free but Asp-rich sequence and hydrolysis of the acetyl cap over long periods in solution.
What cell and mouse immunology studies report
The best-characterized mechanism comes from Romani, Bistoni, and colleagues' 2004 paper in Blood. Working with mouse dendritic cells exposed to Aspergillus fumigatus, they reported that thymosin alpha-1 induced functional maturation and interleukin-12 production through a p38 MAP kinase and NF-kappaB dependent pathway, and that the signal ran through the adaptor protein MyD88 and distinct Toll-like receptors. In mice that had received hematopoietic transplants, the synthetic peptide was associated with Th1-type antifungal responses and faster myeloid recovery. This paper is the origin of the "Toll-like receptor agonist" description that later reviews repeat.
Garaci, Favalli, Pica, and colleagues' 2007 review in the Annals of the New York Academy of Sciences summarizes the preclinical mouse and rat tumor models that preceded human trials, most of them combining the peptide with interferon or interleukin-2, and adds that the peptide increased expression of MHC class I and of tumor and viral antigens in cell systems. King and Tuthill's 2016 chapter in Vitamins and Hormones extends the Toll-like receptor finding to both myeloid and plasmacytoid dendritic cells and describes the mechanism as pleiotropic, acting on several immune cell subsets at once. One narrower but useful paper is Naylor and colleagues' 1996 study in the International Journal of Immunopharmacology, which found that neither exogenous thymosin alpha-1 nor NIH-3T3 cells engineered to overexpress its precursor showed increased proliferation or transformation in soft agar, addressing an early concern that the peptide might act as a growth factor.
| Finding | Model | Paper |
|---|---|---|
| Dendritic-cell maturation, IL-12, via MyD88 and TLR signaling | Mouse dendritic cells; transplanted mice | Romani et al., Blood, 2004 |
| Increased MHC class I and antigen expression | Cell lines; mouse and rat tumor models | Garaci et al., Ann N Y Acad Sci, 2007 |
| Action on myeloid and plasmacytoid dendritic cells | Review of cell and animal data | King and Tuthill, Vitam Horm, 2016 |
| No growth promotion or transformation | NIH-3T3 cells | Naylor et al., Int J Immunopharmacol, 1996 |
| Legumain generates the 28-mer from prothymosin alpha | In vitro enzymology; mammalian tissue | Sarandeses et al., J Biol Chem, 2003 |
Thymalfasin: approved abroad, not an approved drug in the United States
Synthetic thymosin alpha-1 has the international nonproprietary name thymalfasin and is sold under the brand name Zadaxin, originally developed by SciClone Pharmaceuticals. Tuthill, Rios, and McBeath's 2010 overview in the Annals of the New York Academy of Sciences traces the development program from early physician-sponsored studies using impure fraction 5 in children with primary immune deficiency, through phase 3 trials with synthetic peptide in the United States, Italy, and China. Thymalfasin is approved in more than 30 countries, with China and Italy among the first and largest markets, chiefly for chronic hepatitis B and as a vaccine adjuvant in some jurisdictions. Liaw's 2004 review in the Journal of Gastroenterology and Hepatology describes the hepatitis B program from the Asia-Pacific perspective.
The record is mixed in places, and it is worth saying so. Ciancio and Rizzetto's 2010 review notes that a large European phase 3 study in hepatitis C non-responders found thymalfasin did not improve sustained virologic response, though relapse was lower among those who completed the course. In the United States, thymalfasin has held orphan-drug designations but has never received marketing approval, so it is not an approved drug here. Dominari and colleagues' 2020 review in the World Journal of Virology summarizes the 2020 interest in the peptide during the COVID-19 pandemic; that interest did not change its US status. A research-grade vial of thymosin alpha-1 is not Zadaxin, is not thymalfasin, and is not subject to the quality system that governs the approved product abroad. The FDA status reference table lists it with that distinction.
What a research certificate should show for this peptide
Thymosin alpha-1 is a sequence-defined molecule, so its certificate should look like any other single-peptide COA: identity by mass spectrometry against the calculated mass of the acetylated 28-mer (about 3,108 daltons average, with the observed multiply charged ions deconvoluting to that value), purity by reversed-phase HPLC at 214 nm (the peptide has no tryptophan or tyrosine, so 280 nm detection is nearly blind to it), net peptide content by amino acid analysis, and the safety panel of endotoxin, sterility, and heavy metals. Because the N-terminus is acetylated, a des-acetyl impurity differs from product by 42 daltons and is the first thing to look for in the mass spectrum; it is the exact species Wetzel's 1980 recombinant work produced. The LC-MS identity explainer covers how to read that line.
US Prime Peptides posts the lot-matched certificate for Thymosin Alpha-1 5 mg and Thymosin Alpha-1 10 mg on the product page before purchase. For the comparison with the thymic extract fraction that shares its origin but not its chemistry, see thymalin vs thymosin alpha-1.
Frequently Asked Questions
Is thymosin alpha-1 an approved drug?
Outside the United States, yes: synthetic thymosin alpha-1 is approved as thymalfasin (brand name Zadaxin) in more than 30 countries, including China and Italy, mainly for chronic hepatitis B. In the United States it has held orphan designations but is not an approved drug. A research vial is not that product.
What is the sequence of thymosin alpha-1?
Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN: 28 residues, N-terminally acetylated, with a molecular weight near 3,108 daltons. It is the N-terminal segment of the 109-to-112-residue protein prothymosin alpha, from which the enzyme legumain can release it, according to Sarandeses and colleagues (2003).
How does thymosin alpha-1 differ from thymalin?
Thymosin alpha-1 is a single defined peptide that can be synthesized and confirmed by mass spectrometry. Thymalin is an acid extract of calf thymus containing many peptides and has no single sequence. The two share a tissue of origin and nothing else about their documentation.
What receptor does thymosin alpha-1 act on?
No single dedicated receptor has been identified. Romani and colleagues (2004) reported in mouse dendritic cells that the peptide signals through Toll-like receptors and the adaptor MyD88, activating p38 MAP kinase and NF-kappaB. Later reviews describe this as a pleiotropic mechanism rather than a classic ligand-receptor pair.
Citations
- Goldstein AL, Low TL, McAdoo M, et al. Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proc Natl Acad Sci U S A. 1977;74:725-729. PMID 265536
- Wetzel R, Heyneker HL, Goeddel DV, et al. Production of biologically active N alpha-desacetylthymosin alpha 1 in Escherichia coli through expression of a chemically synthesized gene. Biochemistry. 1980;19:6096-6104. PMID 7008828
- Haritos AA, Goodall GJ, Horecker BL. Prothymosin alpha: isolation and properties of the major immunoreactive form of thymosin alpha 1 in rat thymus. Proc Natl Acad Sci U S A. 1984;81:1008-1011. PMID 6583693
- Szabo P, Weksler ME. Is thymosin alpha 1 a thymic hormone? Clin Immunol Immunopathol. 1992;65:195-200. PMID 1451325
- Franco FJ, Diaz C, Barcia M, Freire M. Thymosin alpha 1 is a native peptide in several tissues. Biochim Biophys Acta. 1992;1120:43-48. PMID 1554740
- Sarandeses CS, Covelo G, Díaz-Jullien C, Freire M. Prothymosin alpha is processed to thymosin alpha 1 and thymosin alpha 11 by a lysosomal asparaginyl endopeptidase. J Biol Chem. 2003;278:13286-13293. PMID 12554742
- Grottesi A, Sette M, Palamara T, et al. The conformation of peptide thymosin alpha 1 in solution and in a membrane-like environment by circular dichroism and NMR spectroscopy. Peptides. 1998;19:1731-1738. PMID 9880079
- Elizondo-Riojas MA, Chamow SM, Tuthill CW, et al. NMR structure of human thymosin alpha-1. Biochem Biophys Res Commun. 2011;416:356-361. PMID 22115779
- Romani L, Bistoni F, Gaziano R, et al. Thymosin alpha 1 activates dendritic cells for antifungal Th1 resistance through toll-like receptor signaling. Blood. 2004;103:4232-4239. PMID 14982877
- Garaci E, Favalli C, Pica F, et al. Thymosin alpha 1: from bench to bedside. Ann N Y Acad Sci. 2007;1112:225-234. PMID 17600290
- King R, Tuthill C. Immune modulation with thymosin alpha 1 treatment. Vitam Horm. 2016;102:151-178. PMID 27450734
- Naylor PH, Smith MR, Mutchnick MG, Goldstein AL. Thymosin alpha 1 does not promote growth or oncogenic transformation. Int J Immunopharmacol. 1996;18:321-327. PMID 8933211
- Tuthill C, Rios I, McBeath R. Thymosin alpha 1: past clinical experience and future promise. Ann N Y Acad Sci. 2010;1194:130-135. PMID 20536460
- Liaw YF. Thymalfasin (thymosin-alpha 1) therapy in patients with chronic hepatitis B. J Gastroenterol Hepatol. 2004;19 Suppl 6:S73-S75. PMID 15546254
- Ciancio A, Rizzetto M. Thymalfasin in the treatment of hepatitis B and C. Ann N Y Acad Sci. 2010;1194:141-146. PMID 20536462
- Dominari A, Hathaway D III, Pandav K, et al. Thymosin alpha 1: a comprehensive review of the literature. World J Virol. 2020;9:67-78. PMID 33362999
This article is for laboratory research reference only. US Prime Peptides products are supplied strictly for in vitro research. Not for human consumption.
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