Crohn's disease and peptides — what the literature actually supports for the transmural, skip-lesion, fistulizing subtype

Why this dossier exists

Crohn's disease is the inflammatory bowel disease subtype defined by transmural inflammation that may involve any segment of the gastrointestinal tract, with discontinuous "skip lesions," a strong predilection for the terminal ileum and right colon, and a natural history dominated by fistulizing and stricturing complications that distinguish it from the mucosa-restricted continuous-inflammation pattern of ulcerative colitis. The broader IBD-and-peptides dossier walks the shared landscape across both subtypes; this dossier is the Crohn's-specific deep dive. The contemporary US epidemiology — Lewis JD et al., Gastroenterology 2023, 165:1197–1205.e2 — estimates approximately 2.39 million adults carry an IBD diagnosis, with Crohn's disease accounting for roughly 40–45% of cases. The Park et al. population-based meta-analysis reports cumulative perianal-fistula risk of 12% by year 1, 21% by year 10, and 26% by year 20.

Standard-of-care advanced therapy for moderate-to-severe Crohn's disease in 2024–2026 is anchored on biologics and small-molecule agents — anti-TNF (infliximab, adalimumab, certolizumab pegol), anti-integrin (vedolizumab), anti-IL-12/23 (ustekinumab), anti-IL-23 (risankizumab on ADVANCE/MOTIVATE plus mirikizumab and guselkumab), and JAK inhibition (upadacitinib) — synthesised in the Lichtenstein et al. 2018 ACG Clinical Guideline and updated in the AGA 2025 living guideline. 5-ASAs have a substantially weaker evidence base in Crohn's than in ulcerative colitis and are no longer first-line. Corticosteroids retain a role for induction but not maintenance; azathioprine and methotrexate retain a place primarily in combination with anti-TNF therapy.

The peptide conversation around Crohn's disease specifically clusters on eight molecules across four mechanistic frames: the BPC-157 / PL 14736 pharmaceutical-development arc; KPV on the PepT1-NF-κB mechanism with a CD45RBhi T-cell-transfer mouse model closer to Crohn's-style chronic inflammation than DSS; the GLP-2 analog class (teduglutide, apraglutide) — the only peptide pharmacology with FDA-approved evidence in a Crohn's-adjacent indication; the GLP-1 receptor agonist class (semaglutide, liraglutide) on a rapidly expanding retrospective-cohort literature with Crohn's-specific subgroups; and three molecules circling the periphery — thymosin α-1, larazotide, and the broader anti-fibrotic / vascular-repair candidates the fistulizing- and stricturing-Crohn's protocols periodically reach for.

The honest read is uncomfortable for the practitioner framing. No published Phase II or III RCT supports BPC-157, KPV, thymosin α-1, or larazotide for induction or maintenance of remission in Crohn's disease specifically. The single Crohn's-disease pivotal-supporting peptide trial in the published literature is Buchman AL et al., Inflamm Bowel Dis 2010, 16:962–973 — a Phase II teduglutide study that reported a directionally favourable but underpowered signal, never advanced to Phase III. The Gorelik et al. 2025 Israeli Epi-IIRN cohort reported a GLP-1-analog protective signal in Crohn's disease (adjusted HR 0.78, 95% CI 0.62–0.99) and the Levine 2025 NYU cohort reported no flare-rate elevation following GLP-1 prescription across a 224-patient mixed-IBD cohort — both retrospective, both hypothesis-generating. Any peptide consideration in Crohn's disease is overlay on top of guideline-supported advanced therapy, not a substitute for it.