Peptide Research Glossary

A — C

503A

Section 503A of the U.S. Federal Food, Drug, and Cosmetic Act, governing patient-specific compounding by licensed pharmacists. Defines a pathway for individualised compounded preparations under specific conditions; does not, on its own, authorise bulk manufacture. (see FD&C Act §503A (21 U.S.C. 353a))

503B

Section 503B governs registered outsourcing facilities that may compound under cGMP for office use. Distinct from 503A in scope and requirements.

Acetate salt

A peptide salt form in which the counter-ion is acetate, generally produced by lyophilisation from dilute acetic acid. Often preferred over TFA for cell-culture compatibility. See the CoA guide.

Acylation

Covalent attachment of an acyl group (commonly a long-chain fatty acid) to a peptide. Used in semaglutide and liraglutide to promote albumin binding and extend half-life.

ADME

Absorption, distribution, metabolism, and excretion — the four pharmacokinetic processes that determine drug exposure.

Agonist

A ligand that engages a receptor and produces a downstream signalling response. Full agonists produce maximal response; partial agonists a sub-maximal one.

Aib (α-aminoisobutyric acid)

A non-natural amino acid used in peptide engineering. The Aib substitution at position 8 of semaglutide is a key contributor to its DPP-4 resistance and prolonged half-life.

Albumin binding

Reversible association of a drug with serum albumin. For peptide therapeutics, engineered albumin binding extends half-life by reducing renal clearance and proteolytic exposure.

Aliquot

A subdivided portion of a stock solution prepared for single use to avoid repeated freeze–thaw cycles. See the handling guide.

Amylin

A pancreatic peptide co-secreted with insulin that suppresses glucagon, slows gastric emptying, and reduces food intake. Pramlintide and cagrilintide are amylin analogues.

Bacteriostatic water

Sterile water containing 0.9% benzyl alcohol as a preservative. Suppresses microbial growth in multi-use stocks at refrigerator temperature; not appropriate for all assays.

Beta-arrestin

An intracellular adapter protein that binds activated GPCRs and mediates receptor desensitisation, internalisation, and arrestin-biased signalling. Active research area for GLP-1R biology.

Bioavailability

The fraction of an administered dose that reaches systemic circulation in active form. Oral bioavailability of native peptides is typically very low; oral semaglutide is the principal exception.

Boxed warning

The most prominent warning required by U.S. FDA labelling. The GLP-1 RA class boxed warning concerns medullary thyroid C-cell tumour risk. See the side-effects guide.

BPC-157

A pentadecapeptide derived from a sequence in human gastric juice protein, studied predominantly in animal models of tissue repair. Not approved for human therapeutic use in any major jurisdiction. See /docs-bpc-157-10mg/.

Cagrilintide

A long-acting amylin analogue under development as a stand-alone obesity therapy and as part of the CagriSema combination.

CCK (cholecystokinin)

A gut peptide involved in satiety and gallbladder contraction. CCK-receptor agonism is an investigated weight-loss target.

Certificate of Analysis (CoA)

A lot-specific quality record. See the CoA pillar guide.

Clinical-grade

Material manufactured under cGMP and conforming to compendial monographs, suitable for human investigational or therapeutic use. Distinct from research-grade.

Compounding

Preparation of a customised medication by a licensed pharmacist for an individual patient. Governed by 503A; bulk production by registered outsourcing facilities falls under 503B.

D — G

Deamidation

Conversion of asparagine to aspartate (or to isoaspartate) and of glutamine to glutamate. Major peptide degradation pathway, accelerated at neutral-to-alkaline pH and elevated temperature.

DPP-4 (dipeptidyl peptidase-4)

A serine protease that cleaves the N-terminal His-Ala dipeptide of native GLP-1 and GIP, producing inactive metabolites. Pharmacological GLP-1 RAs are engineered to resist DPP-4 cleavage.

Dulaglutide

A once-weekly Fc-fusion GLP-1 RA marketed as Trulicity for type 2 diabetes.

Endotoxin

Lipopolysaccharide from gram-negative bacterial cell walls. Quantified by LAL (USP <85>) and reported in EU/mg. Critical attribute for any peptide intended for cell-culture or animal use.

Exenatide

A GLP-1 RA derived from the exendin-4 sequence of Heloderma suspectum. Available as twice-daily (Byetta) and once-weekly extended-release (Bydureon BCise) formulations.

FDA approval

Marketing authorisation by the U.S. Food and Drug Administration following review of an NDA (small molecules) or BLA (biologics, including some peptides).

Fmoc chemistry

9-fluorenylmethoxycarbonyl protecting-group strategy for solid-phase peptide synthesis. Dominant chemistry in modern commercial peptide production.

Fc fusion

Covalent linkage of a peptide to an antibody Fc fragment. Extends half-life via neonatal Fc receptor recycling. Used in dulaglutide.

Free base

The neutral form of a peptide, exclusive of counter-ion mass. Peptide content on a CoA refers to the free-base fraction of the supplied dry mass.

Freeze–thaw

Cyclic transition between frozen and liquid states. Causes aggregation and oxidative damage in many peptides. Single-use aliquoting is the standard mitigation.

GHK-Cu

Glycyl-L-histidyl-L-lysine copper(II) tripeptide complex. Originally characterised by Pickart in 1973 (PMID 4356974). (Pickart, 1973, BBRC — PMID 4356974)

GIP (glucose-dependent insulinotropic polypeptide)

The second incretin hormone. Engaged by tirzepatide and retatrutide as part of dual and triple agonist mechanisms.

GLP-1 (glucagon-like peptide-1)

An incretin hormone secreted by intestinal L-cells in response to nutrient ingestion. Pharmacological mimics are the GLP-1 receptor agonist class. See the GLP-1 pillar guide.

GLP-1 receptor (GLP-1R)

A class B G-protein-coupled receptor expressed on pancreatic beta cells, gastrointestinal smooth muscle, and central nervous system regions including the area postrema and arcuate nucleus.

GLP-3

Industry shorthand for triple receptor agonists (GLP-1 / GIP / glucagon). Not an endogenous hormone. See the GLP-3 pillar guide.

Glucagon

A pancreatic peptide secreted by alpha cells that raises hepatic glucose output. Sustained glucagon-receptor agonism is a contributor to retatrutide's mechanism.

GMP / cGMP

Good Manufacturing Practice / current GMP — the regulatory framework for pharmaceutical manufacturing. Research-grade material is typically manufactured outside cGMP.

Growth hormone secretagogue

A compound that stimulates endogenous growth hormone release. Includes GHRH analogues (sermorelin, tesamorelin, CJC-1295) and GHRPs (ipamorelin, GHRP-2, GHRP-6).

H — M

HbA1c

Glycated haemoglobin. A 2–3-month integrated measure of glycaemia. Primary endpoint in many type 2 diabetes trials.

HPLC

High-performance liquid chromatography. Principal method for peptide purity quantification; reversed-phase HPLC at 220 nm is the standard.

Ipamorelin

A selective growth-hormone-releasing peptide. See /docs-ipamorelin/.

Karl Fischer titration

Standard method for water-content determination, reported as % by mass. USP <921>.

LAL test

Limulus amebocyte lysate test for endotoxin (USP <85>). Quantitative; results in EU/mg.

LEAN trial

Generic shorthand sometimes used for trials of body-composition outcomes during incretin therapy. Not a single trial; verify the specific protocol referenced.

Liraglutide

A once-daily GLP-1 RA marketed as Victoza (T2DM) and Saxenda (chronic weight management).

Lyophilisation

Freeze-drying. The standard formulation state for shipped research peptides. Lyophilised cake should be reconstituted in an appropriate solvent before laboratory use.

Mass spectrometry (MS)

Mass-based identity confirmation. ESI and MALDI are the two routine techniques for peptides. See the CoA pillar guide.

MCH (melanin-concentrating hormone)

A central neuropeptide involved in feeding and energy balance; an investigated weight-loss target.

MOTS-c

A 16-residue mitochondrial-derived peptide characterised by Lee et al. in 2015 (PMID 25738459). (Lee et al., 2015, Cell Metabolism — PMID 25738459)

N — R

NDA / BLA

New Drug Application / Biologics License Application — the FDA submissions for marketing authorisation of small molecules and biologics, respectively. Most peptide therapeutics fall under one or the other depending on size and complexity.

Off-label use

Clinical use of an FDA-approved drug for an indication, dose, route, or patient population not covered by its approved labelling. Distinct from use of unapproved compounds.

Oral semaglutide

A daily oral formulation of semaglutide co-formulated with the permeation enhancer SNAC. Approved as Rybelsus for type 2 diabetes; higher doses studied for weight management.

Peptide content

The proportion of a supplied lyophilised mass that is the peptide free base, exclusive of counter-ion and water. Critical for accurate dosing calculations.

PEGylation

Covalent conjugation of polyethylene glycol to extend half-life by increasing hydrodynamic radius and reducing renal clearance.

PMID

PubMed identifier — a stable numeric identifier for a citation in NCBI's PubMed database.

Pramlintide

A short-acting amylin analogue approved as Symlin for adjunctive use in insulin-treated diabetes.

Pre-renal AKI

Acute kidney injury due to reduced renal perfusion (e.g., volume depletion). The principal mechanism of GLP-1-RA-associated kidney injury.

PubMed

The NIH-maintained free database of biomedical literature. Primary source of citations for this site.

Recombinant peptide

A peptide produced by expressing the encoding DNA in a microbial or mammalian host. Used for longer or complex sequences less amenable to SPPS.

Research-grade

Material supplied for in vitro and laboratory research, not for human or veterinary use. Contrast pharmaceutical-grade.

Retatrutide

Investigational triple GLP-1/GIP/glucagon receptor agonist (LY3437943). See the GLP-3 pillar guide.

RUO (Research Use Only)

Labelling category indicating material is supplied strictly for laboratory research and not for human or veterinary administration.

S — Z

Semaglutide

A long-acting GLP-1 RA marketed as Ozempic (T2DM, weekly), Wegovy (chronic weight management, weekly), and Rybelsus (T2DM, daily oral).

Sermorelin

A 29-residue GHRH analogue. See /sermorelin/.

Solid-phase peptide synthesis (SPPS)

Stepwise chemical synthesis of peptides on a solid resin support. Pioneered by Bruce Merrifield. Dominant method for synthetic peptides under ~50 residues.

STEP program

The pivotal phase 3 development programme for semaglutide 2.4 mg (Wegovy). STEP 1 is the principal placebo-controlled trial in adults with obesity. (Wilding et al., 2021, NEJM — PMID 33567185)

SURMOUNT program

The pivotal phase 3 development programme for tirzepatide (Zepbound). SURMOUNT-1 is the principal placebo-controlled trial. (Jastreboff et al., 2022, NEJM — PMID 35658024)

Tachyphylaxis

Rapid attenuation of pharmacological response with repeated dosing. Relevant to the gastric-emptying effect of long-acting GLP-1 RAs.

Tesamorelin

A GHRH analogue approved for HIV-associated lipodystrophy. See /docs-tesamorelin-15mg/. The pivotal trial was Falutz et al. 2007 (PMID 17557935). (Falutz et al., 2007, NEJM — PMID 17557935)

TFA salt

Trifluoroacetate salt form. Standard byproduct of Fmoc SPPS purification with TFA-containing mobile phases. Counter-ion content can be 5–15% of dry mass.

Tirzepatide

A once-weekly GLP-1 / GIP dual receptor agonist marketed as Mounjaro (T2DM) and Zepbound (chronic weight management).

TRIUMPH program

Eli Lilly's phase 3 obesity programme for retatrutide. (see ClinicalTrials.gov for TRIUMPH programme entries)

Tritrutide

Common typo for retatrutide; not a separate compound.

USP

United States Pharmacopeia. Compendial source for pharmaceutical-quality standards. Cited general chapters include <85> (endotoxin), <621> (chromatography), <797> (sterile compounding), <921> (water determination).

Wegovy

Trade name for semaglutide 2.4 mg approved by the FDA for chronic weight management.

Zepbound

Trade name for tirzepatide approved by the FDA for chronic weight management.

References

This guide cites primary peer-reviewed and regulatory sources where the underlying claim has been verified. A small number of supporting items remain in active verification and are listed below for transparency.

Verified primary references

1. Pickart L. The Tripeptide GHK and Its Role in Cell Activation. BBRC 1973. PMID 4356974.
2. Lee C et al. MOTS-c Mitochondrial-Derived Peptide. Cell Metabolism 2015. PMID 25738459.
3. Wilding JPH et al. STEP 1. NEJM 2021. PMID 33567185.
4. Jastreboff AM et al. SURMOUNT-1. NEJM 2022. PMID 35658024.
5. Falutz J et al. Tesamorelin in HIV-Associated Lipodystrophy. NEJM 2007. PMID 17557935.

Still seeking primary citation

• TRIUMPH ClinicalTrials.gov NCT identifier
• FD&C Act §503A statutory text (21 U.S.C. 353a)