Glossary of longevity peptide terms

96 concise definitions for terms used across this site — peptide names, mechanistic vocabulary, biology, regulatory framing and research methodology. Each entry links back from peptide pages and protocol pages.

A

AEDGAla-Glu-Asp-GlyPeptide compounds

The single-letter sequence designation for the synthetic tetrapeptide Epitalon (Ala-Glu-Asp-Gly), developed in the Khavinson cytomedine programme as a synthetic equivalent of the active fraction of the pineal polypeptide epithalamin.

Amino acid (natural vs D-)Chemistry

The building blocks of peptides, linked by peptide bonds. Naturally occurring proteins and most endogenous peptides are built from L-amino acids. Some synthetic research peptides substitute a D-amino acid isomer at one or more positions (as in FOX04-DRI, where 'DRI' denotes a D-retro-inverso sequence) to resist enzymatic degradation and extend half-life, at the cost of no longer matching any naturally occurring sequence.

AMPKAMP-activated protein kinaseMechanism

A master regulator of cellular energy homeostasis. Activated when cellular AMP:ATP ratio rises, it switches metabolism toward catabolic ATP-generating pathways (fatty-acid oxidation, glucose uptake) and away from anabolic pathways (lipogenesis, protein synthesis). Central to the mechanism of MOTS-c.

Amyloid-βBiology

A peptide fragment cleaved from amyloid precursor protein (APP) that accumulates in Alzheimer's-disease brain tissue. Aggregation into oligomers and plaques is one of the principal pathological hallmarks of Alzheimer's. Multiple peptide research compounds (Humanin) have been studied for protective effects against amyloid-β cytotoxicity.

Anabolic signallingMechanism

Cellular signalling pathways that drive protein synthesis, growth and tissue building. Includes mTORC1, IGF-1/insulin signalling and androgen-receptor pathways. Declines progressively across the adult lifespan, contributing to sarcopenia and recovery deficits.

ApoptosisBiology

Programmed cell death — the controlled, non-inflammatory form of cell death used to remove damaged, pre-malignant or surplus cells. Mediated by caspase enzyme cascade and pro-apoptotic Bcl-2 family proteins (Bax, Bid). Humanin's mechanism includes direct inhibition of Bax-mediated apoptosis.

AutophagyBiology

The cellular process by which damaged organelles, misfolded proteins and other intracellular debris are enclosed in double-membrane vesicles and delivered to lysosomes for degradation and recycling. Declines with age, contributing to accumulation of cellular damage. Regulated in part by mTOR (autophagy is suppressed under high mTOR activity) and considered one of the hallmarks of ageing.

B

Bacteriostatic waterChemistry

Sterile water containing 0.9% benzyl alcohol as a preservative, used to reconstitute lyophilised peptide vials for research purposes. The preservative inhibits bacterial growth across repeated withdrawals from a multi-use vial, unlike plain sterile water for injection which is intended for single use. Widely referenced in peptide-handling literature; not a therapeutic product in its own right.

BPC-157Body Protection Compound 157Peptide compounds

A 15-amino-acid synthetic peptide derived from a sequence found in gastric juice. Extensively studied in preclinical models for tendon, ligament, gastric mucosal and neural-tissue repair. Has not progressed into completed human RCT. UK regulatory status: unlicensed research compound.

C

CardiolipinBiology

A unique four-acyl phospholipid concentrated almost exclusively in the inner mitochondrial membrane. Essential for cristae structural integrity, respiratory-supercomplex assembly and the function of inner-membrane proteins. Oxidation and disorganisation of cardiolipin is a feature of aged mitochondria and is the binding target of SS-31/elamipretide.

Cellular senescenceBiology

A stable, irreversible cell-cycle arrest that cells enter in response to DNA damage, oncogene activation, telomere attrition or other stressors, distinct from apoptosis in that senescent cells remain metabolically active rather than dying. Senescent cells accumulate with age across most tissues and secrete a pro-inflammatory secretome (see senescence-associated secretory phenotype). One of the central hallmarks of ageing and the rationale behind senolytic research.

Circadian rhythmBiology

Approximately 24-hour cycles in physiology and behaviour coordinated by the suprachiasmatic nucleus (SCN) clock gene cycling (BMAL1, CLOCK, PER, CRY). Disrupts with age, contributing to sleep-architecture decline. Pineal-axis peptides (Epitalon, Pinealon) are studied for circadian restoration in aged neural tissue.

CJC-1295Peptide compounds

A modified GHRH 1-29 analogue with amino-acid substitutions and (in the DAC variant) a drug-affinity-complex modification that binds circulating albumin. Without DAC: ~30-minute half-life producing brief enhanced pulsatile GH release. With DAC: 6–8 day half-life producing sustained GH elevation.

Cochrane reviewResearch methodology

A systematic review produced under the methodology of the Cochrane Collaboration, characterised by pre-registered protocols, exhaustive literature searching and structured risk-of-bias assessment across included trials. Regarded as a high tier of evidence in the research hierarchy, above individual RCTs. No peptide covered on this site is currently the subject of a completed Cochrane review.

Connectivity MapCMapResearch methodology

A computational analysis methodology that compares a query gene-expression signature against a library of reference signatures from drug or perturbation experiments to identify mechanistic similarities. The 2014 Pickart laboratory paper used CMap analysis to classify GHK-Cu's transcriptional signature as a 'reverser' of multiple oncogenic and inflammatory states.

CPNPCosmetic Products Notification PortalRegulatory

The EU notification system (with a UK-specific equivalent, the OPSS Submit portal, since Brexit) through which cosmetic products must be registered before sale. Peptides marketed solely as cosmetic ingredients (for example in topical GHK-Cu formulations) may fall under cosmetic notification rather than medicines regulation, provided no medicinal claims are made. Notification is not equivalent to MHRA licensing and confers no assessment of therapeutic efficacy.

CytomedinesResearch methodology

Term coined in the Khavinson research programme at the St Petersburg Institute of Bioregulation and Gerontology to describe short bioregulatory peptides derived from tissue extracts. The cytomedine framework proposes that short tissue-derived peptides act as gene-regulatory signals selective for the tissue of origin.

D

Dendritic cellBiology

A major antigen-presenting cell type that bridges innate and adaptive immunity. Captures antigens, presents them to T cells in lymphoid tissue, and influences T-cell differentiation through cytokine secretion. Thymosin Alpha-1's principal mechanism involves TLR-mediated activation of dendritic-cell maturation.

DSIPDelta-Sleep-Inducing PeptidePeptide compounds

A nonapeptide identified in 1977 from cerebral venous blood of sleeping rabbits and named for its ability to increase delta-wave (slow-wave) activity in EEG recordings. The endogenous role is contested and the receptor identity is not definitively established.

E

ElamipretidePeptide compounds

The international non-proprietary name (INN) for SS-31, also known as Bendavia or MTP-131. A synthetic aromatic-cationic tetrapeptide that binds inner-mitochondrial-membrane cardiolipin. In clinical development with Stealth BioTherapeutics; not licensed.

EpitalonPeptide compounds

Synthetic tetrapeptide AEDG (Ala-Glu-Asp-Gly), developed in the Khavinson programme as a synthetic equivalent of pineal-polypeptide epithalamin active fraction. Studied for telomerase induction, pineal-axis restoration and lifespan extension in rodent models.

EpithalaminBiology

A polypeptide extract of bovine pineal gland from which Epitalon was derived as a synthetic equivalent. The original 'pineal polypeptide complex' studied by the Khavinson group in the 1970s and 1980s as a candidate ageing intervention.

F

FOX04-DRIPeptide compounds

A D-retro-inverso synthetic peptide designed to interfere with the FOXO4-p53 protein-protein interaction inside senescent cells. Studied in preclinical rodent models as a candidate senolytic that selectively triggers apoptosis in senescent cells while sparing healthy cells. Has not progressed into completed human trials; unlicensed research compound.

FPRL1Formyl peptide receptor-like 1 / FPR2Mechanism

A G-protein-coupled receptor expressed on innate and adaptive immune cells. Part of the heterotrimeric receptor complex (with CNTFR and WSX-1/gp130) through which extracellular Humanin signals to produce its cytoprotective effects.

Free radical theoryBiology

A foundational theory of ageing, proposed by Denham Harman in 1956, holding that accumulated cellular damage from reactive oxygen species (free radicals) generated primarily during mitochondrial respiration is a principal driver of the ageing process. Later refined into the broader mitochondrial free-radical theory of ageing. Largely superseded as a complete explanation by the multi-factorial hallmarks-of-ageing framework, but still influential in framing antioxidant and mitochondrial-support research.

G

GHK-CuGlycyl-L-histidyl-L-lysine copperPeptide compounds

The copper(II)-bound form of the endogenous tripeptide GHK. First isolated from human plasma in 1973 by Loren Pickart. Plasma levels fall ~60% across the adult lifespan. Acts via copper trafficking to lysyl-oxidase, broad gene-expression modulation, and direct fibroblast/keratinocyte signalling.

GHRHGrowth hormone-releasing hormoneBiology

A 44-amino-acid hypothalamic peptide that signals to anterior pituitary somatotrophs to release growth hormone in pulses. The active N-terminal 29 residues constitute the GHRH 1-29 fragment that is the basis of synthetic GHRH analogues (Sermorelin, CJC-1295).

GHRPGrowth hormone-releasing peptidePeptide compounds

A class of synthetic peptide ghrelin-receptor agonists that stimulate pituitary GH release through GHS-R1a binding. Includes early-generation GHRP-2 and GHRP-6 (broader hormonal off-target effects) and selective compounds like Ipamorelin (minimal prolactin/cortisol effects).

GHS-R1aGrowth hormone secretagogue receptor 1aMechanism

The endogenous ghrelin receptor, expressed on anterior pituitary somatotrophs and hypothalamic neurons. Activation triggers phospholipase-C-mediated calcium signalling and complements GHRH-mediated cAMP signalling to drive GH release. Target of Ipamorelin and other GHRPs.

Glymphatic clearanceBiology

The brain's waste-clearance system, in which CSF-ISF exchange flushes metabolic waste (including amyloid-β) from the brain. Active predominantly during slow-wave sleep. Declines with age and is one of the mechanistic links between sleep-architecture preservation and cognitive ageing.

H

Hallmarks of ageingResearch methodology

The conceptual framework introduced by López-Otín et al. (Cell, 2013, expanded 2023) cataloguing the molecular and cellular processes contributing to biological ageing. Includes genomic instability, telomere attrition, mitochondrial dysfunction, cellular senescence, stem-cell exhaustion, altered intercellular communication, and others. Provides the mechanistic vocabulary for most longevity-peptide research.

Hayflick limitBiology

The finite number of divisions (approximately 40–60 for normal human somatic cells, as demonstrated by Leonard Hayflick in 1961) that a cell population can undergo in culture before entering replicative senescence. Driven principally by progressive telomere shortening at each division. A foundational observation in telomere biology and in the framing of telomerase-directed peptide research such as Epitalon.

HormesisBiology

A biphasic dose-response phenomenon in which low-level exposure to a stressor (heat, exercise, caloric restriction, certain phytochemicals) triggers adaptive, protective cellular responses, while higher exposure to the same stressor is harmful. Frequently invoked to explain why moderate physiological stress can upregulate protective pathways such as autophagy and antioxidant defences, relevant to the framing of exercise-mimetic peptides such as MOTS-c.

HumaninHNPeptide compounds

A 24-amino-acid peptide encoded within the mitochondrial 16S ribosomal RNA gene. First mitochondrially-derived peptide (MDP) identified (Hashimoto 2001). Cytoprotective; plasma levels decline with age and are preserved in centenarians.

I

IGF-1Insulin-like growth factor 1Biology

A 70-amino-acid peptide produced predominantly by the liver in response to GH stimulation. Mediates most of the anabolic effects attributed to GH. Lower IGF-1 is associated with longer lifespan in multiple animal models and in some human cohorts — the 'IGF-1 longevity paradox'.

ImmunosenescenceBiology

The age-related decline of adaptive immunity, particularly naive T-cell output. Driven by progressive thymic involution beginning in early adulthood. Clinical consequences include reduced vaccine-response efficiency and increased vulnerability to novel pathogens. Target of Thymosin Alpha-1 research.

ImmunosurveillanceBiology

The process by which the immune system continuously detects and eliminates abnormal cells, including virally infected and pre-malignant cells, before they establish disease. Relies heavily on functional T-cell and natural-killer-cell activity. Declines alongside immunosenescence, and is the theoretical basis for immune-restorative peptide research such as Thymosin Alpha-1.

InflammagingBiology

Chronic low-grade elevation of inflammatory cytokines (IL-6, TNF-α, CRP) characteristic of aged tissues. Contributes to muscle ageing, vascular pathology, neurodegeneration and reduced effective immune-response capacity. GHK-Cu's transcriptional signature includes broad suppression of inflammaging-associated genes.

IpamorelinPeptide compounds

A selective GHS-R1a agonist developed by Novo Nordisk in the late 1990s. Distinguished from earlier-generation GHRPs by minimal off-target effects on prolactin, ACTH and cortisol release. Commonly combined with CJC-1295 in research-context GH-axis protocols.

K

Khavinson programmeResearch methodology

The continuous short-peptide research programme conducted at the St Petersburg Institute of Bioregulation and Gerontology, founded by Vladimir Khavinson. Includes Epitalon, Pinealon, Thymalin and a substantial catalogue of tissue-specific bioregulatory peptides.

L

Longevity geneBiology

A gene whose variants or expression levels are associated with extended lifespan or healthspan in model organisms or human cohorts. Examples studied in the ageing literature include FOXO3, the sirtuin family and components of the IGF-1/insulin signalling pathway. Provides part of the mechanistic backdrop for peptide research targeting these same pathways, such as sirtuin- and mTOR-linked interventions.

LyophilisedChemistry

Describes a substance that has undergone freeze-drying, in which water is removed by sublimation under vacuum after freezing. Most research peptides are supplied as a lyophilised powder in a sealed vial, since this form is substantially more stable in long-term storage than a liquid solution. Lyophilised peptide must be reconstituted, typically with bacteriostatic water, before use.

M

MDPMitochondrially-derived peptideBiology

A class of peptides encoded within mitochondrial genome open reading frames (predominantly within rRNA gene sequences). Includes Humanin (16S rRNA), MOTS-c (12S rRNA) and the SHLP family. Function as endocrine mitokines.

MelatoninBiology

An indolamine produced by the pineal gland from serotonin via AANAT and HIOMT enzymatic steps. Synthesised in darkness; coordinates circadian sleep-wake rhythm. Pineal output declines progressively across the adult lifespan. Not a peptide.

Meta-analysisResearch methodology

A statistical methodology that combines quantitative results from multiple independent studies addressing the same question, producing a pooled effect estimate with greater statistical power than any single included study. Ranked highly in evidence hierarchies when it synthesises well-conducted RCTs, but its conclusions are only as reliable as the studies it pools. No peptide covered on this site currently has a published meta-analysis of human clinical outcomes.

MHRAMedicines and Healthcare products Regulatory AgencyRegulatory

The UK regulator responsible for medicinal product authorisation, pharmacovigilance and clinical-trial oversight. None of the peptides covered on this site holds an MHRA marketing authorisation for any therapeutic indication.

Mitochondrial DNA (mtDNA)mtDNABiology

The small circular genome (roughly 16.6 kb in humans) housed within mitochondria, distinct from nuclear DNA and inherited maternally. Encodes components of the electron-transport chain along with several ribosomal and transfer RNAs. Some of these RNA-coding regions contain additional open reading frames that produce mitochondrially-derived peptides such as Humanin and MOTS-c. mtDNA accumulates mutations with age at a higher rate than nuclear DNA, contributing to mitochondrial dysfunction.

MitokineBiology

A signalling molecule released by mitochondria under stress that produces effects in distant tissues — by analogy with cytokine and adipokine biology. MOTS-c and Humanin are the canonical peptide mitokines.

MOTS-cMitochondrial Open-reading-frame of the Twelve S rRNA-cPeptide compounds

A 16-amino-acid mitochondrially-derived peptide encoded within the mitochondrial 12S rRNA gene. Identified 2015 (Lee et al.). Functions as an endogenous exercise-mimetic through AMPK activation in skeletal muscle.

mTORMechanistic target of rapamycinMechanism

A serine/threonine kinase that sits at the centre of cellular nutrient- and growth-signalling, forming the core of two distinct complexes, mTORC1 and mTORC2. High mTORC1 activity drives anabolic protein synthesis and growth but suppresses autophagy, and chronic overactivation is linked to accelerated ageing phenotypes across model organisms. Inhibition of mTOR (pharmacologically, or through caloric restriction) is one of the most consistently reproduced lifespan-extension interventions in animal studies.

N

NAD⁺Nicotinamide adenine dinucleotideBiology

A central cellular redox cofactor required for sirtuin activity, PARP-mediated DNA damage response and mitochondrial electron transport. Levels decline with age across human tissues. Targeted by small-molecule precursors NMN and NR (which are not peptides).

NF-κBNuclear factor kappa BMechanism

A master transcription-factor family that, upon activation, drives expression of a broad programme of pro-inflammatory cytokine genes. Chronically elevated NF-κB signalling in aged tissue is a principal driver of inflammaging and of the senescence-associated secretory phenotype. A recurring target pathway in the mechanistic literature around GHK-Cu and other anti-inflammatory peptide research.

NMNNicotinamide mononucleotideChemistry

A small-molecule NAD⁺ precursor, not a peptide. Supplied as a nutraceutical in some jurisdictions for NAD⁺-axis support. Outside the primary scope of this peptide-focused site.

NRNicotinamide ribosideChemistry

A small-molecule NAD⁺ precursor and vitamin B3 form, not a peptide. Closely related to NMN. Outside the primary scope of this peptide-focused site.

O

Open-labelResearch methodology

A study design in which participants and investigators are aware of the treatment being administered (no blinding). Lower methodological strength than randomised double-blind designs. Most published human evidence for Epitalon and Pinealon comes from open-label observational cohorts.

Open-label extensionResearch methodology

A follow-on study phase in which participants from a completed randomised trial, and sometimes new participants, continue to receive (or begin receiving) the active treatment with both parties aware of the assignment. Useful for longer-term safety data but carries the same interpretive limitations as any open-label design and cannot support blinded efficacy claims. Relevant to how longer-duration peptide safety data should be read.

P

p53Mechanism

A transcription factor often described as the 'guardian of the genome', activated in response to DNA damage, oncogene activation and other cellular stress. Depending on the severity of the insult, p53 activation can trigger cell-cycle arrest and DNA repair, apoptosis, or entry into cellular senescence. Chronic p53 activity in senescent cells is the mechanistic target of senolytic peptides such as FOX04-DRI, which disrupt an inhibitory interaction between p53 and FOXO4.

Peptide bondChemistry

The covalent amide linkage formed between the carboxyl group of one amino acid and the amino group of the next, releasing a water molecule. The peptide bond is the defining structural link of peptides and proteins alike; the distinction between the two categories is conventionally one of chain length rather than chemistry, with peptides generally referring to chains of roughly 2 to 50 amino acids.

PeptidomeBiology

The complete set of peptides present in a cell, tissue or biological fluid at a given time, studied using mass-spectrometry-based peptidomics. Used to characterise which endogenous short peptides (including mitochondrially-derived peptides such as Humanin and MOTS-c) are present in human plasma and how their abundance shifts with age.

PGC-1αPPAR-gamma coactivator-1 alphaMechanism

A transcriptional coactivator that drives mitochondrial biogenesis programmes. Upregulated by AMPK activation; downstream effector of exercise training and of MOTS-c administration. Reduced expression in aged tissues contributes to mitochondrial-dysfunction phenotypes.

Pineal glandBiology

A small endocrine gland in the brain producing melatonin and other neuroendocrine signals. Output declines progressively across the adult lifespan. Target of Khavinson short-peptide programme interventions (Epitalon, Pinealon).

PinealonPeptide compounds

Khavinson tripeptide Glu-Asp-Arg (EDR). Positioned within the cytomedine framework as a neurotropic short peptide, studied for neuroprotective effects and cognitive-function preservation in aged rodents.

PolysomnographyPSGResearch methodology

The clinical-standard sleep-study methodology, incorporating EEG, EMG, EOG and other physiological signals. Provides objective measurement of sleep architecture. Published peptide research on sleep has relied predominantly on self-report rather than PSG, limiting evidence quality.

R

Randomised controlled trial (RCT)RCTResearch methodology

A study design in which participants are randomly allocated to receive either the intervention under investigation or a comparator (placebo or standard care), minimising selection bias and confounding. Considered the gold-standard methodology for establishing causal treatment effects in humans. Most peptides discussed on this site lack a completed, adequately powered human RCT, a gap flagged throughout the site's research-only framing.

ReconstitutionChemistry

The process of dissolving a lyophilised peptide powder in a liquid diluent, typically bacteriostatic water, to produce a solution suitable for research use. The volume of diluent added determines the resulting concentration. Reconstituted peptide solutions generally have a much shorter stable shelf life than the lyophilised powder and require refrigeration.

Replicative senescenceBiology

The permanent cell-cycle arrest entered by somatic cells after a finite number of divisions (the Hayflick limit), driven by progressive telomere shortening. Foundation of telomere biology and a target of telomerase-activating peptide research (Epitalon).

RLSRisk Limited StatementRegulatory

Editorial framing applied to research-context peptide content where translational efficacy claims would be inappropriate. All peptide pages on this site lead with explicit research-only framing rather than therapeutic claims.

S

SarcopeniaBiology

Age-related loss of skeletal muscle mass and function. Diagnostic criteria include reduced grip strength, slow gait speed and reduced appendicular lean-mass index. UK-recognised clinical diagnosis. Target of GH-axis and mitochondrial-peptide research.

SARMSelective androgen receptor modulatorChemistry

A class of small-molecule (not peptide) androgen-receptor agonists. Often discussed alongside peptide research-protocol literature but mechanistically and structurally distinct. Outside the primary scope of this peptide-focused site.

SelankPeptide compounds

A synthetic heptapeptide analogue of the endogenous immunomodulatory peptide tuftsin, developed at the Institute of Molecular Genetics, Moscow. Studied in Russian-language literature for anxiolytic and nootropic effects. See the Semax entry for the closely related developmental context; UK regulatory status is unlicensed research compound.

SemaxPeptide compounds

A synthetic heptapeptide derived from a fragment of adrenocorticotropic hormone (ACTH 4-10), developed in Russia and studied there for nootropic and neuroprotective effects, including in stroke-recovery research. Structurally and developmentally related to Selank. Not licensed by the MHRA and not the subject of Western regulatory-standard human trials.

Senescence-associated secretory phenotype (SASP)SASPBiology

The pro-inflammatory secretory profile adopted by senescent cells, comprising cytokines (IL-6, IL-8), chemokines, growth factors and matrix-degrading enzymes. SASP factors act on neighbouring cells to spread senescence and drive local tissue inflammation, making the SASP a major contributor to inflammaging. Reducing SASP output, whether by clearing senescent cells with a senolytic or suppressing their secretory programme directly, is a central goal of senescence-targeted research.

SenolyticBiology

A class of compounds that selectively induce apoptosis in senescent cells while sparing healthy cells, thereby reducing the burden of senescent cells and their associated SASP output in ageing tissue. Includes small-molecule combinations (dasatinib plus quercetin) and peptide candidates such as FOX04-DRI. Predominantly preclinical; not an established clinical intervention.

SermorelinPeptide compounds

Synthetic GHRH 1-29 — the active N-terminal 29 residues of human GHRH. Originally licensed (FDA 1997) for paediatric GH-deficiency diagnosis as Geref. Stimulates pulsatile pituitary GH release with intact negative feedback.

SHLP familySmall Humanin-Like Peptide familyPeptide compounds

A group of six mitochondrially-derived peptides (SHLP1–SHLP6) encoded within the mitochondrial 16S rRNA gene alongside Humanin. Identified by the Cohen laboratory (USC). Function less well-characterised than Humanin and MOTS-c.

SIRT1Mechanism

The most extensively studied member of the sirtuin family, an NAD⁺-dependent deacetylase active in the cell nucleus and cytoplasm. Regulates transcription factors involved in metabolism, stress resistance and mitochondrial biogenesis (including PGC-1α and FOXO family members). Activity depends on NAD⁺ availability, which declines with age, linking SIRT1 to the broader NAD⁺-axis literature.

SirtuinBiology

A family of NAD⁺-dependent protein deacetylases (SIRT1–SIRT7) with central roles in metabolism, DNA-damage response and ageing biology. SIRT3, SIRT4 and SIRT5 are mitochondrially-localised. Activity declines with age in parallel with NAD⁺ availability.

Slow-wave sleepN3 / SWSBiology

The deepest stage of non-REM sleep, characterised by delta-wave EEG activity. Critical for memory consolidation and glymphatic clearance. Time spent in SWS declines steeply from middle age. Target of DSIP and pineal-axis peptide research.

SomatopauseBiology

The age-related progressive decline in GH output across the adult lifespan, driven primarily by reduced hypothalamic GHRH signalling rather than pituitary failure. Foundation of GH-axis peptide research (Sermorelin, CJC-1295/Ipamorelin).

SpecialsRegulatory

A UK pharmacy supply route for unlicensed medicines manufactured to order against a specific clinical need. Has historically been used for limited UK access to Thymosin Alpha-1 (licensed elsewhere but without UK MHRA authorisation).

SS-31Peptide compounds

A synthetic aromatic-cationic tetrapeptide developed by Szeto and Schiller at Weill Cornell. Selectively binds inner-mitochondrial-membrane cardiolipin and stabilises cristae structure. Also known as elamipretide, Bendavia, MTP-131. In clinical development.

StackResearch methodology

Informal term for a combination protocol — multiple peptides administered together for synergistic or complementary effects. Used widely in research-peptide literature. Examples include CJC-1295 + Ipamorelin, MOTS-c + SS-31.

STAT3Mechanism

A transcription factor activated by cytokine and growth-factor receptor signalling (notably the IL-6/JAK pathway) that regulates cell proliferation, survival and immune-cell differentiation. Persistent STAT3 activation is implicated in the chronic low-grade inflammation of inflammaging and in tumour biology. Referenced in mechanistic discussions of cytokine-driven ageing pathways alongside NF-κB.

SympathoadrenalBiology

Relating to the sympathetic nervous system and adrenal medulla acting as a combined stress-response axis, releasing catecholamines (adrenaline, noradrenaline). Sympathoadrenal tone changes with age and interacts with the GH and HPA axes; referenced in the broader neuroendocrine-ageing literature relevant to GH-axis and stress-peptide research.

SynergyResearch methodology

An interaction in which the combined effect of two agents exceeds the sum of their individual effects. Demonstrated for combined GHRH-receptor + GHS-R1a stimulation (CJC-1295 + Ipamorelin) on pituitary GH release.

T

T-cellBiology

A major lymphocyte type central to adaptive immunity. Matures in the thymus. Output of naive T cells declines progressively across adult life (immunosenescence), the principal target of Thymosin Alpha-1 research.

TB-500Thymosin Beta-4 fragmentPeptide compounds

A synthetic 17-amino-acid peptide corresponding to the active fragment of Thymosin Beta-4. Studied for actin-dynamics-mediated cell migration and tissue-repair effects. Distinct from Thymosin Alpha-1 covered elsewhere on this site.

TelomeraseBiology

A reverse-transcriptase enzyme complex (hTERT catalytic subunit + hTR RNA template) that extends telomeric repeats. Active in stem cells and germline, low or absent in normal somatic tissue. Reactivation is observed in most cancers. Target of Epitalon research.

TelomereBiology

Repetitive non-coding DNA sequences (TTAGGG in humans) capping the ends of linear chromosomes. Progressive shortening with each cell division underlies replicative senescence. Telomere length is one of the better-characterised molecular biomarkers of biological ageing.

TesamorelinPeptide compounds

A synthetic GHRH analogue licensed by the FDA (as Egrifta) for reduction of excess abdominal visceral fat in HIV-associated lipodystrophy. One of the few GHRH-class peptides with completed Phase III human trial data and an existing marketing authorisation in the US, though it is not currently licensed by the MHRA for use in the UK.

ThymalinPeptide compounds

A polypeptide extract of calf thymus developed within the Khavinson cytomedine programme, distinct from the synthetic single-sequence peptide Thymosin Alpha-1. Studied in Russian-language literature for immune-restorative effects in ageing and after immunosuppressive treatment. Not licensed by the MHRA.

Thymosin Alpha-1Tα1 / thymalfasinPeptide compounds

A synthetic 28-amino-acid N-acetylated peptide originally derived from thymic tissue. Licensed in 30+ countries (Zadaxin, Thymalfasin) for chronic hepatitis B/C and as vaccine adjuvant. Not currently licensed in the UK.

Thymosin Beta-4TB-4Peptide compounds

A 43-amino-acid actin-sequestering peptide. Regulates G-actin/F-actin dynamics and cell migration during wound healing. Distinct from Thymosin Alpha-1; the two share a name but operate through unrelated mechanisms.

TLRToll-like receptorMechanism

A family of innate-immune pattern-recognition receptors (TLR-1 through TLR-10 in humans) that recognise conserved pathogen-associated molecular patterns. Thymosin Alpha-1 signals through TLR-2 and TLR-9 on dendritic cells to produce its immune-restorative effects.

V

VEGFVascular endothelial growth factorMechanism

A signalling protein family that drives angiogenesis, the formation of new blood vessels from existing vasculature. VEGF signalling is central to wound-healing and tissue-repair research, and is one of the pathways referenced in the mechanistic literature around GHK-Cu and other tissue-repair-associated peptides. Reduced angiogenic capacity with age is linked to impaired wound healing and vascular ageing.

Y

Yellow Card schemeUK pharmacovigilanceRegulatory

The MHRA's national pharmacovigilance system through which healthcare professionals and the public can report suspected adverse drug reactions and, since 2023, incidents involving unlicensed products bought online. Reports of adverse effects associated with unlicensed research peptides can be submitted through the Yellow Card scheme even though the products themselves fall outside MHRA-authorised medicines.