Our results indirectly support the combination of
Our results indirectly support the combination of resveratrol and hesperatin treatment for PDN, as this induces GLO1 activity in patients (Xue et al., 2016), as well as metformin, an FDA-approved anti-diabetic treatment, which acts as an MG scavenger to reduce MG levels in type 2 diabetic patients (Beisswenger et al., 1999; Kender et al., 2014) and attenuates pain-like behavior in streptozotocin rats (Ma et al., 2015). Interestingly, a recent study indicates that metformin ameliorates both the upregulation of DRG membrane TRPA1 and hypersensitivity in db/db (Wang et al., 2018), adding support to targeting TRPA1 inhibition as a pharmacotherapy for PDN in type 2 diabetes. We conclude that MG produces evoked hypersensitivity and affective pain, and sensitization of a spinal TRPA1-AC1-Epac signaling cascade facilitates hyperalgesia in db/db mice, supporting further clinical study of agents targeting this pathway in type 2 diabetic patients with pain.
Declaration of interest
Introduction Whole organ tissue engineering is aiming to build an “off the shelf” Bax inhibitor peptide V5 for transplantation. An intact endothelialized vascular network should provide a metabolically active surface for nutrient transport, while maintaining barrier function in bio-engineered organ. Several investigators have made initial attempts to endothelialize decellularized lung vascular beds [, , , , , ], but these efforts have been limited by the functionality of the resulting endothelium, in terms of barrier and resistance to thrombosis. Numerous chemicals have been identified that enhance endothelial barrier, including angiopoietin (Ang)-1, sphingosine 1-phosphate (S1P), various analogs of cyclic AMP (cAMP), rho-associated proteins, coiled-coil containing protein kinase (ROCK) inhibitors, imatinib, and statins ([, , , , , ] (see Ref.  for review). Cyclic AMP (cAMP), a second messenger downstream of a G-coupled receptor, has been extensively studied as a means of improving endothelial integrity [14,15] primarily through protein kinase A- (PKA-) or exchange protein directly activated by cAMP (Epac) -dependent mechanisms. Transfection with PKA inhibitor attenuated, while mutant PKA inhibitor had no effect on, cAMP-induced endothelial barrier formation . Treatment with 8-(4-chlorophenylthio)-2’-O\'methyladenosine-3′, 5′-cyclic monophosphate, a specific activator for Epac/Rap1, decreased permeability and increased VE-cadherin-mediated adhesion . Similarly, activation of Rap1 resulted in a decrease in permeability, enhancement of VE-cadherin-dependent cell adhesion and cortical actin. In contrast, inactivation of Rap1 had the opposite effect , suggesting a role for cAMP-Epac-Rap1 signalling in regulating barrier protection. Cyclic AMP not only regulates endothelial barrier, but also extracellular matrix remodeling and angiogenesis. Direct activation of PKA by cAMP, or by over-expression of the PKA catalytic subunit, inhibits endothelial cells angiogenesis and matrix remodeling in vivo . Therefore, cAMP analogs may be chemical candidates for improving endothelial function in engineered microvasculature, but these molecules have undergone limited testing heretofore. Induced pluripotent stem cells (iPSCs), provide potential for deriving clinically relevant number of endothelial cells from a small biopsy of patient (recipient) tissue. Recently, an iPSC-derived endothelial cell population, dubbed iPSC-endothelial colony forming cells (iPSC-ECFCs), was described . iPSC-ECFCs displayed some functional properties similar to umbilical cord blood-derived endothelial colony forming cells, with high clonal proliferative potential and robust in vivo vessel-forming ability. iPSC-ECFCs maintained a stable endothelial phenotype and did not undergo replicative senescence for 18 passages in vitro. Furthermore, these cells displayed capacity to repair ischemic mouse retina and limb, with no teratoma formation [17,18]. Thus, the iPSC-ECFCs may provide a clinically relevant source for functional endothelial cells for whole organ tissue engineering. In this study, we evaluated the functionality of iPSC-ECFCs when seeded into acellular lung scaffolds, and studied the effects of multiple small molecules on endothelial barrier function. We demonstrated that the Epac agonist 8CPT-2Me-cAMP has a prolonged effect on barrier enhancement provided by iPSC-ECFCs, both on tissue culture plastic and within repopulated lung matrix scaffolds (see Fig. 1).