Peptide & Research Glossary

A

Acylation

The attachment of a fatty-acid chain to a peptide. Acylation (e.g. a C20 fatty-acid tail) promotes reversible binding to serum albumin, extending a peptide’s half-life — the basis of once-weekly incretin compounds like Retatrutide and Semaglutide.

Adipose tissue

Body fat tissue. Several research peptides act on adipocytes (fat cells); GIP-receptor activity, for example, is studied for direct effects on adipose-tissue metabolism.

Affinity

How tightly a molecule (ligand) binds to its receptor. Multi-agonists like Retatrutide are engineered with tuned affinity across each of their target receptors to balance the overall effect.

Agonist

A molecule that binds a receptor and activates it, producing a biological response. The opposite of an antagonist. GLP-1, GIP and glucagon receptor agonists are the core of the metabolic-peptide field.

Amino acid

The building blocks of peptides and proteins. Peptides are short chains of amino acids joined by peptide bonds; Retatrutide, for instance, is a 39-amino-acid peptide.

AMPK

AMP-activated protein kinase, a central cellular energy sensor. Activating AMPK is associated with increased glucose uptake and fat oxidation; MOTS-C is studied as an AMPK activator.

Amylin

A hormone co-secreted with insulin that promotes satiety and slows gastric emptying. Amylin analogues such as Cagrilintide act on a different pathway from the incretins and are studied alongside GLP-1 agonists.

Analogue (analog)

A modified version of a natural molecule designed to improve properties such as stability or duration of action. Semaglutide is an analogue of native GLP-1.

Antagonist

A molecule that binds a receptor and blocks it, preventing activation. The opposite of an agonist.

B

Bacteriostatic water

Sterile water containing 0.9% benzyl alcohol, which suppresses bacterial growth. It is the standard diluent for reconstituting multi-use lyophilised research vials.

Bioavailability

The proportion of an administered compound that reaches systemic circulation in active form. Peptides typically have low oral bioavailability, which is why most are formulated for subcutaneous research use.

BMI (Body Mass Index)

A weight-to-height ratio used to classify overweight and obesity; a common inclusion criterion and endpoint modifier in metabolic clinical trials.

C

C-terminal

The end of a peptide chain terminating in a free carboxyl (–COOH) group. Some active peptides (e.g. KPV, an α-MSH fragment) correspond to a C-terminal region of a larger protein.

Certificate of Analysis (COA)

A document tying a specific product batch to its independent test results — typically HPLC purity and mass-spec identity. A per-batch COA is the key quality marker for a research-peptide supplier.

Clearance

The rate at which a compound is removed from the body, via routes such as proteolysis and renal excretion. Albumin binding slows clearance and lengthens half-life.

Clinical trial

A structured human study evaluating a compound’s safety and efficacy, run in sequential phases (1–3). Research-grade compounds sold for in vitro use are not clinical-trial material.

Cmax

The maximum plasma concentration reached after administration. Paired with Tmax (the time at which it occurs) to describe a compound’s absorption profile.

Cohort

A group of trial participants sharing a defined characteristic — for example, a specific dose cohort in a dose-ranging study.

Conjugation

Chemically attaching another chemical group to a peptide (e.g. a fatty acid, or PEG) to alter its half-life, solubility or receptor profile.

Cyclic peptide

A peptide whose chain is closed into a ring, often improving stability and receptor selectivity. PT-141 and Melanotan-II are cyclic peptides.

D

Dalton (Da)

The unit of molecular mass. Retatrutide has a molecular weight of roughly 4,731 Da; one Dalton is approximately the mass of a hydrogen atom.

Dose-response

The relationship between the dose of a compound and the magnitude of its effect. A “clean” dose-response (bigger dose, bigger effect, no plateau) was a notable feature of Retatrutide’s Phase 2 data.

Double-blind

A trial design in which neither participants nor investigators know who receives active compound versus placebo, reducing bias.

Dual agonist

A single molecule that activates two receptors at once. Tirzepatide is a dual GIP/GLP-1 agonist; Mazdutide and Survodutide are dual GLP-1/glucagon agonists.

E

EC50

The concentration of a compound that produces half of its maximal effect — a standard in vitro measure of potency.

Endpoint

A predefined outcome a trial is designed to measure (e.g. percent body-weight change at 48 weeks). Primary endpoints determine the trial’s main conclusion; secondary endpoints are supporting measures.

Excipient

An inactive ingredient in a formulation (e.g. a bulking agent or buffer in a lyophilised vial) that stabilises or preserves the active compound.

F

Fatty-acid conjugation

Attaching a fatty-acid chain to a peptide so it binds albumin and persists longer in circulation — the design principle behind once-weekly incretin compounds.

FDA

The U.S. Food and Drug Administration. Investigational research compounds such as Retatrutide are not FDA-approved; Semaglutide and Tirzepatide are approved medicines but are supplied here strictly as research reagents.

Fibrosis

Scarring of tissue. Liver fibrosis staging (F1–F3) is a key endpoint in MASH trials, such as the Phase 2 study of Survodutide.

Fragment

A portion of a larger protein that retains biological activity. BPC-157 is a 15-amino-acid fragment derived from a protein in gastric juice.

G

Gastric emptying

The rate at which the stomach empties into the intestine. GLP-1 receptor activation slows gastric emptying, contributing to satiety.

GCGR (glucagon receptor)

The receptor for glucagon. Its activation raises hepatic glucose output and lipolysis and increases resting energy expenditure — the “energy-out” arm of triple and GLP-1/glucagon agonists.

Ghrelin

The “hunger hormone.” Its receptor (GHS-R1a) is the target of growth-hormone-releasing peptides such as Ipamorelin and Hexarelin.

GHRH

Growth-hormone-releasing hormone. Analogues such as Sermorelin, Tesamorelin and CJC-1295 stimulate the pituitary to release growth hormone.

GHRP

Growth-hormone-releasing peptide, a class of ghrelin-receptor agonists (e.g. Ipamorelin, GHRP-2, GHRP-6, Hexarelin) studied for GH secretion.

GIP

Glucose-dependent insulinotropic polypeptide, an incretin hormone with insulinotropic activity and effects on adipose tissue. One of the three arms of Retatrutide and one of the two of Tirzepatide.

GIPR

The GIP receptor. A class B G-protein-coupled receptor targeted by dual and triple incretin agonists.

GLP-1

Glucagon-like peptide-1, the principal incretin hormone. It promotes satiety, slows gastric emptying and stimulates glucose-dependent insulin secretion. The most-targeted receptor system in metabolic research.

GLP-1R

The GLP-1 receptor, a class B GPCR expressed on pancreatic β-cells and in appetite-regulating brain regions.

Glucagon

A hormone that raises blood glucose and increases energy expenditure. Adding glucagon-receptor agonism is what distinguishes Retatrutide (triple) and the GLP-1/glucagon duals from GLP-1/GIP compounds.

Glycogenolysis

The breakdown of stored glycogen into glucose in the liver, a process driven by glucagon-receptor activation.

GPCR (G-protein-coupled receptor)

A large family of cell-surface receptors that transmit signals into the cell. GLP-1R, GIPR and GCGR are class B GPCRs — the molecular targets of the incretin peptides.

H

Half-life

The time for a compound’s plasma concentration to fall by half. Retatrutide’s ~6-day half-life supports once-weekly research dosing and steady state after ~4–5 weeks.

HbA1c

Glycated haemoglobin, a marker of average blood glucose over roughly three months. A standard glycaemic endpoint in type 2 diabetes trials.

Hepatic steatosis

Fat accumulation in the liver. Reducing hepatic steatosis (measured by MRI-PDFF) is a key outcome in MASLD/MASH research, where triple and GLP-1/glucagon agonists have shown large effects.

HPLC

High-performance liquid chromatography, the standard analytical method for determining peptide purity. Research-grade peptides are typically verified to ≥99% purity by HPLC on a per-batch COA.

Hydrolysis

The breakdown of chemical bonds by water. In solution, peptides are gradually degraded by hydrolysis — the reason reconstituted vials have a shorter shelf life than lyophilised powder.

I

IGF-1

Insulin-like growth factor 1, a mediator of growth-hormone effects. Long-acting analogues such as IGF-1 LR3 are used as receptor-activation probes in cell-culture research.

In vitro

Latin for “in glass” — research performed outside a living organism, e.g. in cell culture or a test tube. Research peptides sold by RS Bio Labs are for in vitro use only.

In vivo

Research performed within a living organism (animal models). Distinct from in vitro and from human clinical study.

Incretin

A gut hormone released after eating that augments insulin secretion. GLP-1 and GIP are the two principal incretins and the foundation of the metabolic-peptide class.

Insulin sensitivity

How responsive tissues are to insulin. Improvements in insulin sensitivity were reported alongside weight and liver-fat effects in Retatrutide research.

Insulinotropic

Promoting insulin secretion. GLP-1 and GIP are insulinotropic, which lets multi-agonists include a glucagon arm without causing hyperglycaemia.

Investigational compound

A compound under clinical investigation that has not been approved by any regulator. Retatrutide, Cagrilintide and Survodutide are investigational; they are supplied for research use only.

L

Ligand

Any molecule that binds a receptor. Agonists and antagonists are both ligands.

Lipolysis

The breakdown of stored fat into fatty acids. Glucagon-receptor activation drives lipolysis, contributing to the fat-mobilising effect of triple agonists.

Lyophilisation (lyophilised)

Freeze-drying — removing water from a formulation to produce a stable powder. Lyophilised peptides are far more shelf-stable than solutions and are reconstituted before use.

M

MASH

Metabolic dysfunction-associated steatohepatitis (formerly NASH) — a progressive fatty-liver disease with inflammation and fibrosis. A major research target for GLP-1/glucagon and triple agonists.

MASLD

Metabolic dysfunction-associated steatotic liver disease (formerly NAFLD) — fat accumulation in the liver. Retatrutide reduced liver fat by ~82% in a Phase 2a MASLD study.

Mass spectrometry

An analytical technique that confirms a peptide’s identity and molecular mass. Used alongside HPLC in quality control.

MHRA

The UK Medicines and Healthcare products Regulatory Agency. Research compounds sold for in vitro use are not MHRA-approved medicines.

Mitochondrial-derived peptide (MDP)

A peptide encoded within mitochondrial DNA. MOTS-C is an MDP studied for its role in metabolic regulation and AMPK activation.

Molecular weight

The mass of a molecule, expressed in Daltons. A peptide’s molecular weight reflects its amino-acid count plus any conjugated groups.

Mono agonist

A compound that activates a single receptor. Semaglutide is a GLP-1 mono agonist — the baseline against which dual and triple agonists are compared.

MRI-PDFF

Magnetic resonance imaging proton density fat fraction — the imaging measure of liver-fat content used as an endpoint in MASLD/MASH trials.

N

N-terminal

The end of a peptide chain terminating in a free amino (–NH2) group. N-terminal modifications are often used to protect peptides from enzymatic degradation.

NAFLD

Non-alcoholic fatty liver disease, the former name for MASLD.

Nootropic

A compound studied for effects on cognition. Neuropeptides such as Semax and Selank are researched in this area.

O

Oxyntomodulin

A naturally occurring gut hormone that activates both GLP-1 and glucagon receptors. Mazdutide is an oxyntomodulin analogue.

P

PEGylation

Attaching polyethylene glycol (PEG) to a peptide to extend its half-life and reduce clearance. PEG-MGF is a PEGylated peptide.

Peptide

A short chain of amino acids linked by peptide bonds. Peptides are smaller than proteins and are the core product class in metabolic and regenerative research.

Peptide bond

The covalent bond joining one amino acid to the next in a peptide chain.

Pharmacodynamics (PD)

The study of what a compound does to the body — its mechanism and effects. Paired with pharmacokinetics.

Pharmacokinetics (PK)

The study of what the body does to a compound — absorption, distribution, metabolism and excretion, including half-life, Tmax and clearance.

Phase 1 / 2 / 3

The sequential stages of clinical trials: Phase 1 (safety/PK in small groups), Phase 2 (efficacy and dose-finding), Phase 3 (large confirmatory trials). Retatrutide is in Phase 3.

Placebo

An inactive comparator given to a control group so the true effect of the active compound can be isolated.

Potency

The amount of a compound needed to produce a given effect; a more potent compound achieves the effect at a lower dose (see EC50).

Preclinical

Research conducted before human trials — in vitro (cell) and in vivo (animal) studies. Most research-peptide evidence is preclinical unless a clinical phase is specified.

Purity

The proportion of a sample that is the intended compound, verified by HPLC. Research-grade peptides are typically ≥99% pure, documented on the COA.

R

Randomised controlled trial (RCT)

A study in which participants are randomly assigned to active compound or control, the gold-standard design for establishing efficacy.

Receptor

A protein, usually on a cell surface, that a signalling molecule binds to trigger a response. GLP-1R, GIPR and GCGR are the receptors central to metabolic-peptide research.

Reconstitution

Dissolving a lyophilised (freeze-dried) peptide powder into solution, typically with bacteriostatic water, to prepare a research stock. Technique matters — add diluent slowly and swirl, never shake.

Research use only (RUO)

A designation meaning a product is supplied strictly for laboratory research and is not for human consumption, diagnostic or therapeutic use. All RS Bio Labs compounds are RUO.

Resting energy expenditure (REE)

The energy the body uses at rest. Increasing REE via glucagon-receptor activation is the distinguishing mechanism of triple and GLP-1/glucagon agonists.

S

Satiety

The sensation of fullness that reduces food intake. GLP-1 and amylin signalling both promote satiety.

Secretagogue

A substance that causes another substance to be secreted. Growth-hormone secretagogues (e.g. Ipamorelin) prompt the pituitary to release GH.

Sequence

The specific order of amino acids in a peptide, which determines its structure and activity.

Steady state

The point at which a compound’s rate of administration equals its rate of elimination, so plasma levels stabilise — reached after roughly 4–5 half-lives (about 4–5 weeks for Retatrutide).

Sterile

Free from viable microorganisms. Research vials are prepared and handled under sterile technique to prevent contamination.

Subcutaneous

Beneath the skin — the administration route used for most peptides in research protocols (in animal or clinical study), reflecting their low oral bioavailability.

Synergy

A combined effect greater than the sum of the parts. The three receptor arms of a triple agonist are designed to act synergistically on energy balance.

T

Titration

Gradually increasing a dose over time. Titration allows tolerance to gastrointestinal effects to develop as concentrations rise toward steady state.

Tmax

The time after administration at which peak plasma concentration (Cmax) is reached.

Triple agonist

A single molecule that activates three receptors simultaneously. Retatrutide is the first-in-class triple GIP/GLP-1/glucagon agonist.

V

Vial

The sealed glass container in which lyophilised research peptides are supplied, sized by milligram content (e.g. 5–60 mg).

W

Weight management

The research area concerned with body-weight regulation, where the incretin and amylin peptide classes have shown their largest effects.