Thymosins are small proteins present in many animal tissues. They are named thymosins because they were originally isolated from the thymus, but most are now known to be present in many other tissues.Thymosins have diverse biological activities, and two in particular, thymosins α1 and β4, have potentially important uses in medicine, some of which have already progressed from the laboratory to the clinic. In relation to diseases, thymosins have been categorized as biological response modifiers.
The discovery of thymosins in the mid 1960s emerged from investigations of the role of the thymus in development of the vertebrate immune system. Begun by Allan L. Goldstein in the Laboratory of Abraham White at the Albert Einstein College of Medicine in New York, the work continued at University of Texas Medical Branch in Galveston and at The George Washington University School of Medicine and Health Sciences in Washington D.C. The supposition that the role of the thymus might involve a hormone-like mechanism led to the isolation from thymus tissue of a biologically active preparation. Known as "Thymosin Fraction 5", this was able to restore some aspects of immune function in animals lacking thymus gland. Fraction 5 was found to contain over 40 small peptides (molecular weights ranging from 1000 to 15,000 Da.),which were named "thymosins" and classified as α, β and γ thymosins on the basis of their behaviour in an electric field. Although found together in Fraction 5, they are now known to be structurally and genetically unrelated. Thymosin β1 was found to be ubiquitin (truncated by two C-terminal glycine residues).
When individual thymosins were isolated from Fraction 5 and characterized, they were found to have extremely varied and important biological properties. However they are not truly thymic hormones in that they are not restricted in occurrence to thymus and several are widely distributed throughout many different tissues.
Thymosin beta-4 was allegedly used by some players in various Australian football codes and is under investigation by the Australian Sports Anti-Doping Authority for anti-doping violations.
The process of hair growth utilizes many cellular and molecular mechanisms common to angiogenesis and wound healing. While studying the influence of thymosin beta-4 (Tβ4) on wound healing, Philp et al. accidentally found that hair grew more rapidly around the edges of wounds. In due course, they showed that Tβ4 induced rapid hair growth on the dorsal skin of healthy mice.
Beta blockers are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack. They are also widely used to treat high blood pressure (hypertension), although they are no longer the first choice for initial treatment of most patients.
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Dihydrotestosterone is an endogenous androgen sex steroid and hormone. The enzyme 5α-reductase catalyzes the formation of DHT from testosterone in certain tissues including the prostate gland, seminal vesicles, epididymides, skin, hair follicles, liver, and brain. This enzyme mediates reduction of the C4-5 double bond of testosterone. Relative to testosterone, DHT is considerably more potent as an agonist of the androgen receptor (AR).
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Thymulin is a nonapeptide produced by two distinct epithelial populations in the thymus first described by Bach in 1977. It requires zinc for biological activity. Its peptide sequence is H-Pyr-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn-OH.
Thymosin beta-4 is a protein that in humans is encoded by the TMSB4X gene. Recommended INN for thymosin beta-4 is 'timbetasin', as published by the World Health Organization (WHO).
Thymosin beta-15A is a protein that in humans is encoded by the TMSB15A gene.
Thymosin beta-15B is a protein that, in humans, is encoded by the TMSB15B gene. The protein is identical in aminoacid sequence to Thymosin beta-15A, product of the TMSB15A gene, although synthesis of the two proteins is independently regulated.
Thymosin α1 is a peptide fragment derived from prothymosin alpha, a protein that in humans is encoded by the PTMA gene.
Beta thymosins are a family of proteins which have in common a sequence of about 40 amino acids similar to the small protein thymosin β4. They are found almost exclusively in multicellular animals. Thymosin β4 was originally obtained from the thymus in company with several other small proteins which although named collectively "thymosins" are now known to be structurally and genetically unrelated and present in many different animal tissues.
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Allan L. Goldstein is Emeritus Professor in the Department of Biochemistry and Molecular Medicine at the George Washington University School of Medicine. He chaired the department from 1978 until March 2009 and was awarded Emeritus status in 2013. He is an authority on the thymus gland and the workings of the immune system, and co-discoverer of the Thymosins, a family of hormone-like peptides isolated from the thymus gland.
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