Larazotide Acetate: Sequence, Zonulin Pathway and Research Record

Larazotide acetate (AT-1001) is an eight-residue synthetic peptide, Gly-Gly-Val-Leu-Val-Gln-Pro-Gly, designed to antagonise zonulin signalling at the intestinal tight junction. Few catalogue peptides share its trial history: it advanced into phase 3 clinical evaluation in celiac disease before the programme was halted. It also differs from most research peptides in two structural respects. Its intended site of action is the luminal side of the gut wall, not the circulation, and it addresses an epithelial junction complex instead of a hormone receptor.

Below we trace where the sequence came from, summarise the junctional biology it was created to probe, review the published record and describe supply format and bench handling.

Origin and structure: from a bacterial toxin to an eight-residue antagonist

The story starts with Vibrio cholerae. Besides cholera toxin, this bacterium secretes zonula occludens toxin (ZOT), a protein that loosens epithelial tight junctions and served researchers in the 1990s as a probe of paracellular transport. Investigation of ZOT pointed to an endogenous human analogue, zonulin, later reported to be pre-haptoglobin-2, which is proposed to control junction opening under normal physiological conditions.

From this line of research came larazotide, a short sequence engineered to counteract junction disassembly instead of provoking it. With a mass of 725.90 g/mol across eight residues, it is compact, net-neutral and mostly aliphatic, containing one glutamine plus a proline that restricts backbone flexibility. There are no aromatic side chains, no cysteine and no ionisable groups apart from the two termini, so synthesis is straightforward and the material is forgiving on the bench, quite unlike a larger, more demanding peptide such as LL-37.

Its intended disposition shapes how it is investigated. The molecule was designed to stay unabsorbed: because the target is located on the apical face of the epithelium, reaching the bloodstream offers no advantage. Most peptide programmes optimise for systemic exposure, whereas this one deliberately avoids it, which is why the catalogue item is an oral capsule and not a lyophilized vial.

How larazotide is thought to work

Tight junctions are assemblies of occludin, the claudin family, junctional adhesion molecules and cytoplasmic ZO scaffold proteins. Together they close the gap between neighbouring epithelial cells and set paracellular permeability. The structure is not static; protein kinase C signalling and remodelling of the actomyosin belt surrounding the junction can open it in a controlled manner.

Published models place zonulin upstream of this opening, with larazotide acting as a pathway antagonist. Reported effects include reduced actin polymerisation and lower myosin light chain phosphorylation within the perijunctional belt, so that tight junction components stay in place instead of being pulled away. The wording is important. Larazotide is not characterised as reinforcing intact junctions; it is characterised as blocking a signal for disassembly. Consistent with that model, published effects tend to appear in systems exposed to a permeability-inducing stimulus and not in untreated monolayers.

The zonulin hypothesis is also contested. Researchers have challenged both the assignment of zonulin as pre-haptoglobin-2 and the reliability of commonly used zonulin assays, so the pathway is best regarded as a working model under investigation, not established physiology.

What research has examined

Intestinal permeability in vitro

Most cell work uses polarised epithelial monolayers, commonly Caco-2, measuring transepithelial electrical resistance and the passage of labelled tracers, frequently following exposure to a gliadin digest or inflammatory cytokines. Immunostaining for occludin, claudins and ZO-1 is used to judge whether junctional proteins stay localised at the membrane.

Animal models

In rodents, investigators have looked at permeability markers and mucosal morphology in gluten-sensitivity models and in models where the barrier is disrupted chemically.

Human clinical investigation

Among the compounds in this catalogue, larazotide stands out for the size of its clinical record. Several phase 2 trials enrolled celiac disease patients already following a gluten-free diet and used symptom scores as endpoints; outcomes differed between trials, with some reporting endpoint differences only at certain exposure levels. A subsequent phase 3 programme was stopped in 2022 following an interim analysis, and no regulator has granted the compound marketing authorisation. For researchers this is informative background: a peptide can accumulate genuine clinical data and still fail to become an approved product.

Barrier research beyond the gut

Since the zonulin pathway is relevant to barrier function generally, larazotide has also been used in early-stage studies of other epithelial and endothelial barriers. Published work in this area remains limited.

Forms and sizes we supply

Consistent with its luminal design, larazotide acetate is offered as oral capsules at 500 micrograms each, in bottles of 30 (€85) or 60 (€150), sealed against tampering and packed with a desiccant. In a capsule format, uniformity of fill weight is more critical than it would be for a vial, since each capsule is the unit of quantity. Other oral research materials include BPC-157 capsules and KPV capsules, all grouped within the gut health peptides range. Our guide to oral peptides, capsules and troches discusses the broader challenge of peptide stability in the digestive tract.

Handling and storage in a laboratory context

No reconstitution step is involved with capsules. For cell-based experiments, the capsule contents may be weighed out and dissolved: one 500 microgram capsule in 1 mL produces 500 mcg/mL (0.5 mg/mL), which corresponds to roughly 689 micromolar given a mass of 725.90 g/mol. Concentrations reported in monolayer studies are generally several orders of magnitude lower, so serial dilution is needed, and capsule excipients must be considered where exact concentrations matter. For such experiments, weighing neat peptide is the better approach than working from capsule contents.

Keep bottles tightly closed in a cool, dry, dark place and leave the desiccant inside; moisture, more than heat, is what degrades a capsule format. The sequence itself is chemically stable, lacking cysteine, methionine and any asparagine-glycine motif. Our peptide storage guide covers the general principles.

Purity, COA and how to read one

Before encapsulation the peptide is purified by reversed-phase HPLC to a minimum of 99%, and each certificate corresponds to the lot number printed on the bottle. Two considerations apply specifically here. The counter-ion is part of the compound identity: "acetate" indicates an acetate salt rather than a TFA salt, and the certificate should state this explicitly. Acetate is usually favoured in cell assays where residual trifluoroacetate might confound results. In addition, the certificate describes the peptide itself, whereas fill weight and content uniformity are distinct manufacturing parameters, and both are relevant when the capsule defines the quantity used. Check the measured mass against 725.90 g/mol for the free peptide and examine the chromatogram, not only the headline purity, as explained in our COA reading guide.

Regulatory status

No marketing authorisation for larazotide exists in the United States, the EU or any other jurisdiction. The celiac disease phase 3 programme was discontinued, and the compound is neither an approved drug, a food supplement ingredient nor a generally available compounded preparation. Clinical publications concern an investigational product tested under controlled trial conditions; their findings cannot be extended to research-grade material, which is for laboratory research use only.

Related peptides and further reading

Among gut-focused research compounds, KPV is studied for its effects on epithelial inflammation via NF-kappa B signalling, and BPC-157 for tissue repair and angiogenesis, so together with larazotide the three address distinct aspects of intestinal physiology. For an overview of the field, consult the peptides for gut health research overview and our gut and enteric system hub.