# Dose-dependent effects of capsaicin on intestinal morphology and microbiota composition in mice: Structural, immunohistochemical, and microbial insights

## TL;DR

Low doses of capsaicin improve gut health and microbiota, while high doses cause damage and imbalance in mice.

## Contribution

Reveals dose-dependent effects of capsaicin on gut structure and microbiota, highlighting optimal therapeutic dosing.

## Key findings

- Low-dose capsaicin enhances villus height and tight junction proteins, protecting intestinal mucosa.
- High-dose capsaicin causes epithelial damage, villus atrophy, and dysbiosis with increased Firmicutes.
- All doses stimulate microbial biosynthesis of vitamins and electron carriers, with higher alpha diversity at higher doses.

## Abstract

Capsaicin (CAP), the pungent component of chili peppers, possesses diverse bioactive properties, including antioxidant, anti-inflammatory, and antimicrobial effects. However, its impact on gastrointestinal integrity and microbial ecology remains dose-dependent and incompletely understood. This study aimed to investigate the effects of varying CAP doses on intestinal morphology, tight junction protein expression, goblet cell density, mucosal injury markers, and gut microbiota composition in mice.

Seventy-five male Kunming mice were randomly assigned to five groups (n = 15/group): Normal control, vehicle control (dimethyl sulfoxide), low-dose CAP (5 mg/kg), medium-dose (15 mg/kg), and high-dose (20 mg/kg). Mice received oral gavage every other day for 14 days. Histological assessments (H&E and Alcian Blue-Periodic Acid–Schiff staining), enzyme-linked immunosorbent assays for diamine oxidase, fatty acid-binding protein 2, and plasma endotoxin as well as immunohistochemistry for ZO-1, Claudin-1, and Occludin, and 16S rRNA sequencing were employed to evaluate structural and microbial changes.

Low-dose CAP significantly enhanced villus height, reduced crypt depth, and elevated the villus-to-crypt ratio across all intestinal segments (p < 0.05). Tight junction protein expression and goblet cell counts were highest in the low-dose group, suggesting mucosal protection. In contrast, medium and high-dose CAP induced epithelial damage, villus atrophy, and downregulation of junctional proteins. Microbiota analysis revealed the suppression of Proteobacteria and the expansion of Firmicutes in the medium- and high-dose groups. All CAP doses stimulated microbial biosynthesis of cofactors, vitamins, and electron carriers, with enhanced alpha diversity at higher doses.

CAP exhibits a biphasic effect on intestinal physiology. While low-dose administration supports mucosal integrity and promotes beneficial microbial functions, higher doses disrupt epithelial architecture and induce dysbiosis. These findings underscore the importance of dose consideration in CAP’s dietary and therapeutic applications, providing mechanistic insights into its gut-mediated effects.