Innovative rhein and hydroxy fatty acid ester prodrugs for the treatment of chronic inflammation

Chronic inflammation is related to heart disease, diabetes, cancer, arthritis, and bowel diseases. The rhubarb-derived natural product rhein is highly effective at treating chronic inflammation. However, the gastrointestinal side effects and liver disorders of rhein have limited the long-term clinical application. Herein, we developed a series of rhein-hydroxy fatty acid prodrugs to alleviate the side effects of rhein while enhancing its therapeutic activity.

We developed a novel method to overcome the side effects of rhein and enhance its pharmacological activity. The aim was to synthesize rhein hydroxy fatty acid ester prodrugs that retain anti‑inflammatory activity and alleviate gastrointestinal side effects.

A series of rhein hydroxy fatty acid ester prodrugs were synthesized by linking rhein with hydroxy fatty acid. The chemical structure of these prodrugs was characterized by Fourier transform infrared spectroscopy (FTIR), hydrogen proton nuclear magnetic resonance (¹H NMR), and high-resolution mass spectrum (HRMS). The cytotoxicity of rhein-hydroxy fatty acid ester prodrugs was evaluated using RAW 264.7 and Caco-2 cells. Additionally, in vitro anti-inflammatory, antioxidant, and anti-apoptotic effects were assessed. The targeted rhein-hydroxy fatty acid ester prodrug was verified using the DSS-induced mouse colitis model.

In vitro studies demonstrate that the target compound R-15HA is markedly superior to both the free drug and diacerein in mitigating inflammation, oxidative damage, and apoptosis, while showing almost no cytotoxicity at final concentrations below 160 μmol·L⁻¹. Furthermore, Western blot analysis revealed that R-15HA inhibited the TLR4/NF-κB/MAPK more effectively than free rhein and 15-hydroxypentadecanoic acid. Molecular dynamics simulations demonstrated that the R-15HA compound exhibits a good binding capability with the TLR4 protein. Rhein can partially prevent weight loss, liver and spleen indices colon shortening, expression of proinflammatory cytokines, and epithelial damage, while rhein-hydroxy fatty acid prodrugs R-15HA have a more pronounced effect than rhein in dextran sulfate sodium (DSS)-induced colitis.

Overall, our novel rhein-hydroxy fatty acid ester prodrugs are promising candidates for chronic inflammation in clinical therapy. This study might reveal an avenue to develop rhein hydroxy fatty acid ester prodrugs with satisfactory pharmacological activity to resolve various inflammatory diseases.