THERAPEUTIC EFFECT OF HUMAN ADIPOSE-DERIVED STEM CELLS AND THEIR SECRETOME IN EXPERIMENTAL DIABETES: FOCUS ON NEUROPATHIC PAIN

Diabetes mellitus is one of the most common and serious chronic disease in the world. Although the number of available agents to manage diabetes continues to rapidly expand, treatment of diabetes complications, such as neuropathy that is one of the most frequent complication of diabetes mellitus, remains a substantial challenge [Aring et al., 2005]. Pathophysiology of diabetic neuropathy is complex and not fully elucidated; it has multipathogenic mechanisms that cause a diversity of physical symptoms: allodynia, hyperalgesia, numbness and cutaneous ulceration [Vinik et al., 1995]. Persistent Neuropathic Pain (NP) interferes significantly with quality of life, impairing sleep, and emotional well-being, and is a significant causative factor for anxiety, loss of sleep, and non-compliance with treatment. Recent advances in the mechanisms involved in NP have demonstrated that pro- and anti-inflammatory cytokines produced by immune cells as well as by glia and microglia in nerve, dorsal root ganglia (DRG) and spinal cord are common denominators in neuropathic pain [Sacerdote et al., 2013; Old et al., 2015]. These start a cascade of neuroinflammation-related events that may maintain and worsen the original injury, participating in pain generation and chronicization [Valsecchi et al., 2011; Sommer and Kress, 2004; Austin and Moaelem-Taylor, 2010]. Activation of inflammatory cascade, pro- inflammatory cytokines upregulation, and neuroimmune communication pathways play a vital role in structural and functional damage of the peripheral nerves leading to the diabetic peripheral neuropathy. Unfortunately, most of the available analgesic drugs appear to be relatively ineffective in controlling diabetic neuropathic pain, both for insufficient efficacy and side effects [Galer et al., 2000; Kapur, 2003]. Thus, there is a clear need for new disease-modifying therapeutic approaches. Mesenchymal stem/stromal cells (MSCs) may offer a novel therapeutic option to treat diabetic neuropathy. MSCs modulate the nervous system injured environment and promote repair as they secrete anti-inflammatory, anti-apoptotic molecules, and trophic factors to support axonal growth, immunomodulation, angiogenesis, remyelination, and protection from apoptotic cell death [Ma et al., 2014]. Transplanted MSCs not only directly differentiate into endogenous cells on administration, but also secrete a broad range of biologically active factors, generally referred to as the MSCs secretome; in fact even if initially MSCs were proposed for cell therapy based on their differentiation potential, the lack of correlation between functional improvement and cell engraftment or differentiation at the site of injury has led to the proposal that MSCs exert their effects not through their differentiation potential but through their secreted products [Makridakis, 2016; Blaber et al., 2012]. For these reasons in the present study we analyze in a Streptozotocin mouse model of type 1 diabetes the therapeutic effect of hASC (human adipose stem/stromal cells) and their conditioned media (CM-hASC/ secretome) on allodynia and hyperalgesia, on pro- and anti- inflammatory cytokines expression in the main tissue stations involved in nociception transmission as well as in peripheral immune responses. Type 1 diabetes was induced in mice by intraperitoneal (i.p.) injection of moderate low doses of Streptozotocin (STZ, 80 mg/kg, daily for three consecutive days) while control mice were injected with vehicle (citrate buffer). In all groups, mechanical allodynia was evaluated by Von Frey test before diabetes induction and every week after STZ until the end of protocol (14 weeks after STZ). When allodynia was established (2 weeks after STZ) animals were treated with 106 hASC that have been mechanical