Effects of human Adipose-derived Stem Cell and their secretome on neuropathic pain, neuroinflammation and peripheral cytokines in a preclinical model of diabetes

OBJECTIVE: Painful diabetic neuropathy is a common neurological complication of diabetes mellitus and one of main factors that adversely affect the patients' quality of life. Up to now the pharmacological treatments are not fully satisfactory, therefore it is necessary to explore new therapeutical approaches. In this study we used a preclinical mouse model of diabetes in order to evaluate the effect of adipose-derived mesenchymal stem cells (hASC) and their secretome (conditioned medium, CM) on neuropathic pain, neuroinflammation and peripheral immune activation. MATERIALS AND METHODS: Diabetes was induced in C57BL/6J male mice through low dose of Streptozotocin (STZ) i.p. injections (80mg/Kg for 3 days). When neuropathic pain was established (2 weeks after STZ), mice were treated by i.v. injection with either 106 hASCs or CM obtained from 2x106 serum-free cultured cells. A second group of diabetic mice was treated at a more advanced stage of the disease, 6 weeks after STZ. Mechanical and thermal allodynia were assessed over time through Aesthesiometer and Acetone drop test. The tissue levels of the pro-inflammatory cytokine IL-1 and anti-inflammatory cytokine IL-10 were measured in the main stations involved in nociceptive transmission (nerve, dorsal root ganglia and spinal cord). The release of Th 1 and Th 2 cytokines by splenocytes was also evaluated. Alu sequence detection was employed for hASC localization. RESULTS: Both hASCs and their secretome were able to reverse neuropathic hypersensitivity, although cell efficacy was higher than that of CM. Both effects were very rapid, since a significant relief was present 3 hours after treatments, and long lasting, in fact they were maintained 14 weeks after a single hASC or CM administration. Moreover, both treatments were highly effective when performed at an advanced stage of the disease. In all tissues obtained from neuropathic mice we observed a pro-inflammatory profile, characterized by high IL-1 and low IL-10 levels. hASC and CM treatments were able to restore a correct pro-/anti-inflammatory cytokine balance both 1 week and 12 weeks after treatments. In this model of diabetes, a Th1 polarization is present in the periphery and hASC and CM treatments re-established the correct Th1/Th2 balance. No significant effect on blood glucose levels was evident but diabetic animals regained weight after hASC/CM administration and an improvement of kidney damage was also observed. hASCs were detected inside filter organs in the first 24 hours after injection, but at later time points cells were found also in pancreas and nerves of the diabetic animals. CONCLUSION: The data obtained suggest that hASC treatment may be a favourable approach for diabetic complications such as neuropathic pain, indicate that cell effect is likely to be mediated by their secreted products and suggest that cells may eventually be substituted with their CM.