Cycloastragenol

Cycloastragenol (CAG) is a lanostane-type tetracyclic triterpenoid sapogenin obtained by acid or enzymatic hydrolysis of astragaloside IV, the principal bioactive saponin of Astragalus membranaceus (Huangqi), a plant with extensive use in traditional Chinese medicine. The compound gained prominence following a systematic screen of natural product libraries at Geron Corporation in the early 2000s that identified it as a small-molecule activator of human telomerase reverse transcriptase (hTERT), the catalytic subunit of telomerase. This discovery led to the development and commercialization of TA-65, a proprietary cycloastragenol-containing nutraceutical formulation marketed by T.A. Sciences for telomere health and anti-aging applications. The telomerase-activating mechanism involves upregulation of hTERT gene expression, enhanced nuclear localization of the hTERT protein via upregulation of the Hsp90 chaperone complex, and activation of the cAMP response element binding protein (CREB) signaling axis. At the cellular level, cycloastragenol activates telomerase in multiple cell types including peripheral blood mononuclear cells, CD4-positive and CD8-positive T lymphocytes, fibroblasts, and neuronal cells, with functional consequences including telomere elongation, reduced replicative senescence, and enhanced proliferative capacity. A 2016 randomized, double-blind, placebo-controlled clinical trial of TA-65 in 117 cytomegalovirus-positive subjects aged 53 to 87 years demonstrated dose-dependent telomere lengthening in the low-dose group (530 plus or minus 180 base pairs; p equals 0.005) over 12 months, with the placebo group losing telomere length (290 plus or minus 100 base pairs; p equals 0.01). The compound additionally exhibits pharmacological activities independent of the telomerase mechanism. Preclinical studies have characterized anti-inflammatory effects through inhibition of NF-kappaB signaling and pyroptosis pathways; neuroprotective activity through upregulation of SIRT1 expression, activation of the Nrf2/HO-1 pathway, and promotion of BDNF/p-TrkB/CREB signaling; cardioprotective effects through promotion of myocardial autophagy via inhibition of AKT1-RPS6KB1 signaling; anti-fibrotic activity in hepatic and pulmonary models; and antioxidant effects through activation of the Nrf2/ARE transcriptional pathway. Pharmacokinetics in the rat model show oral bioavailability of approximately 25.7 percent following acid hydrolysis-mediated absorption, substantially higher than the parent compound astragaloside IV (2.2 percent), with extensive first-pass hepatic metabolism limiting systemic exposure. In human liver microsomes, only 8.2 percent of cycloastragenol remained after 30 minutes of incubation, indicating rapid phase I metabolism. A 91-day subchronic toxicity study in rats at doses up to 150 mg/kg by oral gavage produced no treatment-related mortalities, no cardiac effects, and no evidence of genotoxicity or carcinogenicity. Clinical safety data from TA-65 studies over 12 months of supplementation report no serious adverse events, with mild gastrointestinal discomfort as the principal dose-dependent adverse effect. The theoretical concern of telomerase activation promoting oncogenesis has not been substantiated in preclinical cancer bioassays or in clinical observation, though the mechanism warrants continued surveillance. This monograph reviews the chemistry and structural classification of cycloastragenol; its discovery as a telomerase activator and subsequent commercial development; the molecular pharmacology across telomerase, anti-inflammatory, neuroprotective, and cardioprotective pathways; the pharmacokinetic profile including metabolism and bioavailability; the preclinical evidence base; the clinical evidence from TA-65 trials and related human studies; sourcing, quality verification, and reconstitution considerations; stack interactions; adverse events and safety signals; and a comparative assessment of five telomerase-modulating or astragalus-derived compounds against cycloastragenol on five competency standards.