Glossary

A molecule that binds a receptor and activates it, producing a response similar to the body’s own signalling molecule.

The building block of peptides and proteins. Twenty standard amino acids are encoded by human genes; each has a common backbone and a distinct side chain.

The growth of new blood vessels from existing ones. It is essential for wound healing, but it also feeds tumour growth, which is why pro-angiogenic claims warrant caution.

A molecule that binds a receptor without activating it, blocking the natural signal from getting through.

aka Also known as: blocker

Brain-derived neurotrophic factor: a protein that supports the survival of neurons and the formation of new connections between them.

aka Also known as: brain-derived neurotrophic factor

The fraction of an administered substance that reaches the bloodstream intact. Most peptides have very low oral bioavailability because they are digested in the gut.

The most abundant structural protein in the body, giving strength to skin, tendon, ligament, bone and cartilage.

Preparation of a customised medication by a licensed pharmacist or physician for an individual patient. In the US, compounded drugs are not FDA-approved and are not reviewed for safety, effectiveness or quality before use.

aka Also known as: compounded drugcompounding pharmacy

A small signalling protein that immune and other cells use to communicate, for example to switch inflammation on or off.

aka Also known as: interleukin

The scaffold of proteins (such as collagen and elastin) and sugars that surrounds cells and holds tissues together.

aka Also known as: ECM

Authorisation by the US Food and Drug Administration to market a drug for a specific use, granted after the FDA judges that evidence from adequate and well-controlled studies shows benefits outweigh risks for that use.

aka Also known as: FDAapproved drugNDABLA

A hormone produced mainly by the stomach that stimulates hunger and triggers growth-hormone release by binding the growth hormone secretagogue receptor.

Growth hormone-releasing hormone: a hypothalamic peptide that signals the pituitary gland to make and release growth hormone. Sermorelin and tesamorelin are GHRH analogues.

aka Also known as: growth hormone-releasing hormoneGRFGHRH analogue

Glucose-dependent insulinotropic polypeptide: an incretin hormone released by the upper small intestine after eating that boosts insulin secretion when blood glucose is high.

aka Also known as: glucose-dependent insulinotropic polypeptidegastric inhibitory polypeptide

Glucagon-like peptide-1: an incretin hormone made in the gut that increases glucose-dependent insulin release, suppresses glucagon, slows stomach emptying and reduces appetite. Natural GLP-1 lasts only minutes in the blood.

aka Also known as: glucagon-like peptide-1GLP-1 receptor agonistGLP-1 RA

A 29-amino-acid hormone from the pancreas that raises blood glucose, mainly by telling the liver to release stored sugar. It acts in opposition to insulin.

Any substance that causes the pituitary to release growth hormone. The term often refers specifically to ghrelin mimetics such as GHRP-2, GHRP-6 and ipamorelin.

aka Also known as: GHSGHRPsecretagogue

The time it takes for the concentration of a substance in the blood to fall by half. Many natural peptides have half-lives of minutes; drug designers extend this with chemical modifications.

aka Also known as: elimination half-life

Insulin-like growth factor 1: a hormone made mainly by the liver in response to growth hormone, which carries out many of growth hormone’s effects on tissue growth.

aka Also known as: insulin-like growth factor 1somatomedin C

Latin for “in glass”: experiments on cells or molecules in a dish or test tube, outside a living organism.

aka Also known as: cell studycell culture

Latin for “in the living”: experiments carried out in a whole living organism, such as a mouse, rat or human.

A gut hormone released after eating that amplifies insulin secretion. GLP-1 and GIP are the two main incretins.

aka Also known as: incretin effect

The body’s protective response to injury or infection, involving immune cells, increased blood flow and swelling. Helpful in the short term; harmful when chronic.

The specific biological process through which a substance produces its effect, such as binding a particular receptor. A plausible mechanism is not evidence that something works in people.

aka Also known as: MoAmechanism

A family of peptide hormones (including α-MSH and ACTH) and their five receptors (MC1R–MC5R), involved in skin pigmentation, appetite, inflammation and sexual function.

aka Also known as: α-MSHalpha-MSHMC4RMC1R

A statistical method that pools results from several studies on the same question to get a more precise overall estimate. Its conclusions are only as good as the studies it combines.

aka Also known as: systematic review

Structures inside cells that produce most of the cell’s usable energy (ATP). They have their own small genome, which encodes a handful of peptides such as humanin and MOTS-c.

aka Also known as: mitochondrionmitochondrial

Preserving nerve cells from injury or degeneration. Many compounds are neuroprotective in animal models; very few have proven so in human trials.

aka Also known as: neuroprotective

A gas made by cells that acts as a short-lived signal, notably relaxing blood vessels to increase blood flow.

aka Also known as: NO

A study in which participants and researchers know who is receiving which treatment. Simpler to run, but more vulnerable to bias than a blinded trial.

aka Also known as: unblinded

An imbalance in which reactive oxygen species (“free radicals”) outpace the body’s antioxidant defences, damaging lipids, proteins and DNA.

aka Also known as: reactive oxygen speciesROSfree radicals

A short chain of amino acids linked by peptide bonds. By a common convention, chains of up to about 50 amino acids are called peptides and longer ones proteins.

aka Also known as: polypeptideoligopeptide

How the body handles a substance over time: absorption, distribution, metabolism and excretion. A pharmacokinetic (PK) study measures blood levels rather than benefits.

aka Also known as: PKADME

Stages of clinical drug development. Phase 1 tests safety and dosing in a small group; phase 2 looks for signs of efficacy and side effects in a few hundred patients; phase 3 confirms efficacy and safety in large trials, typically hundreds to thousands of people.

aka Also known as: phase 1phase 2phase 3phase Iphase IIphase IIIclinical phase

An inactive treatment designed to look identical to the real one. Comparing against placebo separates a substance’s true effect from expectation and natural recovery.

aka Also known as: placebo-controlledsham

Research done before testing in humans, including cell (in vitro) and animal (in vivo) studies. Most compounds that look promising preclinically never succeed in people.

aka Also known as: animal study

A research paper shared publicly before it has been peer-reviewed. Useful for speed, but its findings have not been independently checked.

aka Also known as: bioRxivmedRxiv

A study in which participants are assigned by chance to receive either the treatment or a control (such as placebo). Randomisation makes the groups comparable, so differences in outcome can be attributed to the treatment.

aka Also known as: RCTrandomised controlled trialcontrolled trial

A protein, usually on the surface of a cell, that recognises a specific signalling molecule and relays its message into the cell.

A label stating that a product is not intended for use in humans or for diagnosis or treatment. It confers no approval, quality guarantee or legal permission for human use.

aka Also known as: RUOnot for human consumption

A single amino acid as it sits within a peptide chain, after losing a water molecule to form peptide bonds with its neighbours.

aka Also known as: amino acid residue

The order of amino acids in a peptide, written from the N-terminus to the C-terminus, often using one-letter codes (for example, G for glycine).

aka Also known as: primary structureamino acid sequence

A peptide hormone that inhibits the release of growth hormone and of several other hormones, including insulin and glucagon. It is the natural brake on the growth-hormone axis.

aka Also known as: growth hormone-inhibiting hormoneSST

Vascular endothelial growth factor: a signalling protein that stimulates the formation of new blood vessels (angiogenesis).

aka Also known as: vascular endothelial growth factor

The World Anti-Doping Agency, which publishes the Prohibited List of substances and methods banned in sport. Many research peptides fall under its S0 or S2 sections.

aka Also known as: World Anti-Doping AgencyProhibited Listanti-doping