TA-65 (Cycloastragenol): Telomerase Activation, Critically Short Telomere Rescue, and Immunosenescence Reversal in Aging Research Models
Abstract & Overview TA65 is the commercial designation for a purified, standardised preparation of cycloastragenol (CA), a lanostanetype triterpenoid (C₃₀H₅₀O₅; MW 490.72 g/mol; CAS 78574944) isolated from the root of Astragalus membranaceus, a plant with a centurieslong history of use in traditional Chinese medicine. Cycloastragenol was originally patented by Geron Corporation and subsequently commercialised by Telomerase Activation Sciences (T.A. Sciences) as a dietary supplement targeting a fundamental mechanism of cellular aging: the progressive shortening of telomeres in somatic tissues. TA65 is currently the most extensively studied smallmolecule telomerase activator in the scientific literature, with a research profile spanning in vitro cell biology, murine aging models, and multiple human clinical investigations including randomised, doubleblind, placebocontrolled trials [1][2][3][4]. Telomeres are the repetitive hexanucleotide sequences (TTAGGG)ₙ that cap the ends of eukaryotic chromosomes, protecting them from degradative processing and endtoend chromosomal fusions. Because conventional DNA polymerases cannot fully replicate the terminal ends of linear chromosomes, telomeres shorten with each cell division — a process compounded by oxidative damage and inflammatory stress. When telomeres reach a critically short length, they trigger the DNA damage response, driving cells into replicative senescence or apoptosis. Telomerase — the ribonucleoprotein enzyme comprising the catalytic reverse transcriptase subunit hTERT and the RNA template component hTERC — can restore telomere length by adding TTAGGG repeats, but is repressed in most adult somatic tissues, leaving cells vulnerable to progressive telomere attrition [5][12]. “Most human cells lack sufficient telomerase to maintain telomeres, hence these genetic elements shorten with time and stress, contributing to aging and disease… Low nanomolar levels of TA65 moderately activated telomerase in human keratinocytes, fibroblasts, and immune cells in culture; similar plasma levels of TA65 were achieved in pilot human pharmacokinetic studies with single 10 to 50mg doses.” — Harley CB et al., Rejuvenation Research (2011) [2]. TA65’s primary mechanism of action is the activation of telomerase in somatic cells, thereby enabling the preferential elongation of critically short telomeres. Preclinical evidence from the Blasco laboratory demonstrated that TA65 increases health span in adult and old mice without augmenting cancer incidence [1]. Human clinical data have demonstrated significant reductions in immunosenescent CD8⁺/CD28⁻ T cells, remodelling of the circulating leukocyte profile toward a more youthful phenotype, and measurable telomere lengthening in randomised controlled trials [2][3][4]. TA65 is classified as a dietary supplement and has not received regulatory approval as a pharmaceutical agent. Molecular Identity and Structural Architecture Cycloastragenol is a tetracyclic triterpenoid of the lanostane subclass, characterised by a C₃₀ carbon skeleton arranged across four fused rings (designated A, B, C, and D). Its IUPAC name — 24α,20Epoxy9,19cyclo9βlanost24ene3β,6α,16β,25tetrol — encodes its most pharmacologically significant structural features. The ‘9,19cyclo’ designation refers to a cyclopropane ring fused across the A/B ring junction, a structural element that is responsible for the ‘cyclo’ prefix in the compound’s name and that is absent in the parent triterpenoid astragenol. This cyclopropane ring introduces conformational rigidity that is believed to be critical for telomeraseactivating activity, as the structurally related but noncyclopropanated compound astragaloside IV shows substantially weaker telomerase activation [11]. Additional key structural features include a 24α,20epoxide bridge (an oxygencontaining threemembered ring spanning carbons 20 and 24), which contributes to the compound’s unique threedimensional conformation and receptorbinding profile, and four hydroxyl groups at positions 3β, 6α, 16β, and 25. The C25 hydroxyl is located on a terminal isopropanol moiety and is thought to contribute to the compound’s interaction with the hTERT catalytic domain. Molecular docking studies using a homologybased 3D model of hTERT have confirmed that cycloastragenol engages the catalytic domain of the enzyme through hydrogen bonding and hydrophobic interactions with key residues, with molecular dynamics simulations confirming stable binding [6]. Cycloastragenol is isolated from the roots of Astragalus membranaceus (Huangqi), a leguminous plant widely used in traditional Chinese medicine as an adaptogenic and immunomodulatory herb. The compound is present in very low concentrations in the raw plant material, necessitating extensive extraction and purification processes to yield the standardised preparations used in research and commercial products. TA65 is formulated at 10 to 50 mg per capsule and is administered orally, with human pharmacoki
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