The neuroprotective effects of human bone marrow mesenchymal stem cells are dose-dependent in TNBS colitis

BACKGROUND: The incidence of inflammatory bowel diseases (IBD) is increasing worldwide with patients experiencing severe impacts on their quality of life. It is well accepted that intestinal inflammation associates with extensive damage to the enteric nervous system (ENS), which intrinsically innervates the gastrointestinal tract and regulates all gut functions. Hence, treatments targeting the enteric neurons are plausible for alleviating IBD and associated complications. Mesenchymal stem cells (MSCs) are gaining wide recognition as a potential therapy for many diseases due to their immunomodulatory and neuroprotective qualities. However, there is a large discrepancy regarding appropriate cell doses used in both clinical trials and experimental models of disease. We have previously demonstrated that human bone marrow MSCs exhibit neuroprotective and anti-inflammatory effects in a guinea-pig model of 2,4,6-trinitrobenzene-sulfonate (TNBS)-induced colitis; but an investigation into whether this response is dose-dependent has not been conducted. METHODS: Hartley guinea-pigs were administered TNBS or sham treatment intra-rectally. Animals in the MSC treatment groups received either 1 × 10(5), 1 × 10(6) or 3 × 10(6) MSCs by enema 3 hours after induction of colitis. Colon tissues were collected 72 hours after TNBS administration to assess the effects of MSC treatments on the level of inflammation and damage to the ENS by immunohistochemical and histological analyses. RESULTS: MSCs administered at a low dose, 1 × 10(5) cells, had little or no effect on the level of immune cell infiltrate and damage to the colonic innervation was similar to the TNBS group. Treatment with 1 × 10(6) MSCs decreased the quantity of immune infiltrate and damage to nerve processes in the colonic wall, prevented myenteric neuronal loss and changes in neuronal subpopulations. Treatment with 3 × 10(6) MSCs had similar effects to 1 × 10(6) MSC treatments. CONCLUSIONS: The neuroprotective effect of MSCs in TNBS colitis is dose-dependent. Increasing doses higher than 1 × 10(6) MSCs demonstrates no further therapeutic benefit than 1 × 10(6) MSCs in preventing enteric neuropathy associated with intestinal inflammation. Furthermore, we have established an optimal dose of MSCs for future studies investigating intestinal inflammation, the enteric neurons and stem cell therapy in this model.