A

Acetylation

A chemical modification where an acetyl group (CH₃CO–) is added to the N-terminus of a peptide. Acetylation improves metabolic stability and can alter receptor binding. Many synthetic peptides (e.g., TB-500) are N-terminally acetylated (Ac-).

Agonist

A molecule that binds to a receptor and activates it, producing a biological response. Peptide agonists often mimic endogenous ligands — e.g., Ipamorelin acts as an agonist at the GHS-R1a (ghrelin) receptor to stimulate GH release.

Amide (C-terminal amidation)

Replacement of the C-terminal carboxyl group (–COOH) with an amide (–CONH₂). This modification increases resistance to carboxypeptidases and is common in naturally occurring neuropeptides and some synthetic analogues. Denoted as “-NH₂” in sequence notation.

Angiogenesis

The formation of new blood vessels from pre-existing ones. Many healing peptides (BPC-157, TB-500, GHK-Cu) promote angiogenesis as part of their tissue repair mechanism — new vasculature supplies nutrients and oxygen to injured tissue.

B

Bacteriostatic Water (BW)

Sterile water containing 0.9% benzyl alcohol as a preservative. Used to reconstitute lyophilized peptide powders. The benzyl alcohol prevents bacterial growth, allowing multi-dose vials to remain sterile for ~30 days after reconstitution. Not interchangeable with sterile water for injection.

BDNF (Brain-Derived Neurotrophic Factor)

A key neurotrophin involved in neuronal survival, plasticity, and the formation of new synapses. Upregulation of BDNF is one of the proposed mechanisms behind the cognitive-enhancing effects of Semax and other neuropeptides.

Bioavailability

The fraction of a substance that reaches systemic circulation unchanged. Most peptides have poor oral bioavailability due to proteolytic degradation in the gut and liver first-pass metabolism. Routes such as subcutaneous injection, intranasal, or sublingual delivery are used to improve bioavailability.

C

Collagen Synthesis

The production of collagen proteins, essential for structural integrity of tendons, skin, bone, and cartilage. Peptides like GHK-Cu and BPC-157 promote collagen synthesis, accelerating repair of connective tissue injuries.

Cyclic Peptide

A peptide whose N- and C-termini are joined by a peptide bond, forming a ring structure. Cyclic peptides are generally more resistant to enzymatic degradation and can have unique receptor-binding properties. PT-141 (Bremelanotide) is an example of a synthetic cyclic peptide.

D

D-Amino Acid

The mirror-image (enantiomeric) form of a standard L-amino acid. Incorporating D-amino acids into a peptide sequence (e.g., D-Phe, D-Trp) dramatically increases resistance to proteases. Used in GHRP-6, Ipamorelin, and SS-31.

DAC (Drug Affinity Complex)

A lysine-based modification added to CJC-1295 that enables covalent binding to albumin in the bloodstream. This extends the half-life from ~30 minutes to ~7 days, allowing weekly dosing. CJC-1295 with DAC = “Modified GRF with DAC.” Without DAC = “Mod GRF(1-29)” or “CJC-1295 no DAC.”

E

Endogenous

Produced naturally within the body. Contrast with exogenous (administered externally). For example, Thymosin Beta-4 is an endogenous peptide found throughout the body; TB-500 is its exogenous synthetic fragment.

G

GH (Growth Hormone) / GHRPs / GHRHs

Growth Hormone (GH / somatotropin) is secreted by the pituitary. GHRPs (Growth Hormone Releasing Peptides) stimulate GH release via ghrelin receptor agonism. GHRHs (Growth Hormone Releasing Hormones) stimulate GH via GHRH receptor. Combining a GHRP + GHRH produces synergistic GH pulses.

GHS-R1a (Ghrelin Receptor)

The primary receptor through which GHRPs (Ipamorelin, GHRP-6, etc.) stimulate GH release. Also activated by the endogenous hunger hormone ghrelin. GHS-R1a agonism triggers GH secretion from anterior pituitary somatotroph cells.

H

Half-Life (t½)

The time required for plasma concentration of a compound to fall by 50%. Peptide half-lives range from minutes (Semax: ~20 min) to days (TB-500: ~8-10 days, CJC-1295 with DAC: ~7 days). Half-life governs dosing frequency.

I

IGF-1 (Insulin-Like Growth Factor 1)

A hormone primarily secreted by the liver in response to GH stimulation. IGF-1 mediates most of GH’s anabolic effects — muscle growth, fat metabolism, bone density. Monitoring IGF-1 is a key biomarker when using GH-stimulating peptides.

L

Lyophilization (Freeze-Drying)

A preservation process that removes water from a peptide solution under vacuum at low temperatures, producing a stable powder (“lyophilized peptide”). Lyophilized peptides are stable at room temperature and must be reconstituted with bacteriostatic water or sterile water before injection.

M

Melanocortin System

A family of receptors (MC1R–MC5R) and endogenous peptides (α-MSH, ACTH) involved in pigmentation, energy balance, inflammation, and sexual function. PT-141 (Bremelanotide) is a melanocortin receptor agonist used for sexual dysfunction. Semax is an ACTH analogue acting on this system.

N

Nootropic

A compound that enhances cognitive function — memory, focus, learning, or neuroprotection — with low toxicity. Peptides like Semax, Selank, and Dihexa are considered nootropic based on preclinical and (for the Russian peptides) limited clinical data.

P

Peptide

A short chain of amino acids linked by peptide bonds (–CO–NH–). Generally defined as 2–50 amino acids; longer chains are proteins. Peptides are the focus of this knowledge base — they are naturally occurring signaling molecules that can be synthesized and studied for various physiological effects.

Proteolysis / Proteolytic Degradation

The enzymatic breakdown of peptides by proteases (e.g., peptidases, endopeptidases). The main barrier to oral bioavailability of peptides. Chemical modifications (D-amino acids, acetylation, PEGylation, cyclization) are used to improve proteolytic resistance.

R

Reconstitution

The process of dissolving lyophilized peptide powder in liquid (bacteriostatic water, sterile saline, etc.) prior to injection. Standard practice: inject solvent slowly down the side of the vial and gently swirl — never shake. Concentration depends on volume added to the mass of peptide in the vial.

S

Subcutaneous (SubQ) Injection

Injection into the subcutaneous fat layer beneath the skin, using a short (5/16″–1/2″) insulin needle. Common sites: abdomen, thigh, upper arm. Most research peptides are administered subcutaneously. Absorbed more slowly than IV but faster than oral.

Synaptogenesis

The formation of new synapses between neurons. Associated with learning, memory consolidation, and cognitive recovery. Dihexa and BDNF-upregulating peptides (Semax) are studied for their potential to promote synaptogenesis.

T

Telomere

Repetitive DNA sequences (TTAGGG in humans) capping the ends of chromosomes, protecting them from degradation. Telomeres shorten with each cell division and their length is considered a biomarker of cellular aging. Epitalon has been studied for its purported ability to activate telomerase and extend telomeres.

Telomerase

An enzyme that extends telomere length by adding TTAGGG repeats to chromosome ends. Normally suppressed in somatic cells but active in stem cells and cancer cells. Epitalon has been proposed to upregulate telomerase in preclinical models, though human evidence is lacking.