Ile-Trp dipeptide prevents diabetic retinopathy via gut Indole/AhR/PXR signaling in type 2 diabetes

Abstract

Purpose : Diabetes-induced dysbiosis leads to gut barrier defects, systemic endotoxemia, and retinal vascular permeability, promoting diabetic retinopathy (DR) in type 1 diabetes, yet unexplored in type 2 diabetes (T2D). Intestinal microbes produce diverse metabolites from tryptophan (Trp), an essential amino acid that regulates intestinal homeostasis and immune function. The absorption of Trp is dependent on intestinal angiotensin converting enzyme 2 (ACE2) and its dimerization with the Trp transporter (B0AT1). However, ACE2 expression is severely reduced in diabetes; thus, we sought to bypass this using a dipeptide Ile-Trp (IW). Dipeptides are absorbed by different transporters (PEPT1; SLC15A1). We examined the impact of IW administration on intestinal and DR endpoints in the db/db mouse, a model of T2D.

Methods : db/db mice were administered IW (5mg/kg body weight, daily) by oral gavage for 6 months, or the control db/db cohort was gavaged with saline. IHC and ELISA for gut barrier integrity, inflammation, dysbiosis, and bacterial metabolites. The DR was assessed using ERG, OKN, and enumeration of acellular capillaries.

Results : After 6 months of diabetes, db/db mice exhibited pronounced gut barrier defects, dysbiosis, impaired vision, and DR. Supplementation with IW significantly preserved gut barrier integrity, evidenced by upregulated expression of ZO1 (p<0.0003), p120-catenin (p<0.0001), VE-cadherin (p<0.001), and decreased PV1 (p<0.0004) in db/db mice. IW-treated cohorts showed reduced plasma levels of gut peptides and endotoxemia. Metatranscriptomic analysis confirmed IW corrected dysbiosis. IW treatment decreased diabetes-induced gut inflammation, with lower levels of IL-1β, IL-2, IL-6, and IFN-γ. IW activated indole/AhR/PXR signaling, evident by increased intestinal indole levels (p<0.03), AhR, and PXR expression. IW enhanced intestinal GLP-1 and GIP secretion, reducing gut inflammation. IW-treated mice exhibited improved retinal responses and visual acuity (ERG: scotopic a and b wave, p<0.02, p<0.03; photopic a wave, p<0.008; OKN, p<0.007). IW-treated db/db mice had significantly fewer acellular capillaries in the retina (p<0.001).

Conclusions : Nutraceuticals such as IW correct diabetes-induced dysbiosis and endotoxemia by generating bacterial metabolites that activate indole/AhR/PXR signaling in the gut, contributing to a healthy gut and preventing diabetic retinopathy in T2D mice.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.