Centrally-administered ghrelin blocks LPS-induced colonic hyperpermeability in rats via the vagus nerve
Background
The central nervous system is known to regulate critical gastrointestinal functions, including motility and pain perception. A key component of gut health is the intestinal barrier, which prevents harmful substances from entering the bloodstream. When this barrier becomes excessively leaky, a condition known as intestinal hyperpermeability or "leaky gut," it can contribute to both gastrointestinal diseases like irritable bowel syndrome (IBS) and systemic inflammation. The gut peptide ghrelin is known to act in the brain to modulate gut function, but its specific role in controlling intestinal permeability was poorly understood. This study investigates whether central ghrelin signaling can protect the intestinal barrier from inflammatory insults.
Study Design
The study was conducted on rats to investigate colonic permeability. Intestinal hyperpermeability was induced using lipopolysaccharide (LPS). Colonic permeability was measured in vivo by quantifying the absorption of Evans blue dye in colon tissue. Ghrelin was administered via intracisternal (IC) injection directly into the brain's cerebrospinal fluid. Control groups received intraperitoneal (IP) ghrelin at the same dose, or an IC injection of des-acyl-ghrelin. To probe the mechanism, researchers also used pharmacological blockers, including the ghrelin receptor antagonist (D-Lys3)-GHRP-6, the orexin 1 receptor antagonist SB-334867, and the cholinergic antagonist atropine, as well as surgical bilateral subdiaphragmatic vagotomy.
Results
Intracisternal injection of ghrelin dose-dependently abolished the increased colonic permeability caused by LPS. In contrast, intraperitoneal ghrelin at the same dose or intracisternal des-acyl-ghrelin had no protective effect. The protective action of central ghrelin was prevented by atropine (a cholinergic blocker) and by bilateral subdiaphragmatic vagotomy, confirming the involvement of the vagal cholinergic pathway. The ghrelin receptor antagonist (D-Lys3)-GHRP-6, when administered centrally, significantly blocked the barrier-improving effects of intravenously administered 2-deoxy-d-glucose, a central vagal stimulant, indicating that endogenous ghrelin is required for this vagal effect. Furthermore, the orexin 1 receptor antagonist SB-334867 also blocked the beneficial effects of central ghrelin.
These results suggest that exogenously administered or endogenously released ghrelin acts centrally to improve a disturbed intestinal barrier function through orexinergic signaling and the vagal cholinergic pathway.
Key Findings
- Intracisternal (central) ghrelin dose-dependently reversed LPS-induced colonic hyperpermeability.
- Intraperitoneal (systemic) ghrelin at the same dose failed to block LPS-induced hyperpermeability.
- The protective effect of central ghrelin was blocked by vagotomy and the cholinergic antagonist atropine.
- An orexin 1 receptor antagonist (SB-334867) blocked the beneficial effects of central ghrelin.
- A central ghrelin receptor antagonist, (D-Lys3)-GHRP-6, blocked the gut-protective effects of a central vagal stimulant.
Why It Matters
This research reveals a specific brain-gut axis mechanism where central ghrelin signaling robustly protects the intestinal barrier against inflammatory damage. For individuals exploring peptides, this highlights a potential neurological, rather than just systemic, benefit of compounds that modulate the ghrelin system. The key takeaway is that ghrelin's gut-protective effects are centrally mediated via the vagus nerve, suggesting therapies should target this pathway. This could have implications for conditions associated with intestinal hyperpermeability, such as IBS or even non-gastrointestinal diseases linked to systemic inflammation. While far from a clinical protocol, it points towards novel therapeutic strategies focusing on central ghrelin or orexin signaling to strengthen the gut barrier. It also implies that the route of administration and ability to cross the blood-brain barrier are critical factors for ghrelin-related gut therapies.
