An alternative approach to the administration of ADO

An alternative approach to the administration of ADO agonists is to amplify the actions of endogenous ADO by inhibiting the ADO-metabolizing enzyme, ADO kinase (AK). Inhibition of AK has the net effect of potentiating the local concentration and the effects of ADO in the extracellular compartment. The enhancement of local ADO concentrations by AK inhibition should be more pronounced in tissues manifesting adverse pathophysiological characteristics thereby limiting systemic side effects (Pawelczyk et al., 2005, Elsherbiny et al., 2013). Indeed, ABT-702, a potent blood different barrier penetrable AK inhibitor, was renoprotective in a rodent model of DN (Pye et al., 2014) through increasing local levels of ADO in diseased kidneys. In the current study, we evaluated a structurally different AK inhibitor A-306989 (Zheng et al., 2003) across different mechanistic models of renal injury in order to further characterize this mechanism in preventing or treating the underlying pathology.
Material and methods
Results
Discussion Growing evidence has suggested that augmenting the endogenous ADO levels at site(s) specific to the pathology of renal injury may avoid the potential safety limitation associated with systemically delivering an exogenous ADO agonist (Gordi et al., 2007, Elsherbiny et al., 2013). AK inhibition was recently reported to be effective in reducing proteinuria, macrophage infiltration, and collagen deposition in a mouse model of type 1 DN (Pye et al., 2014). The current study expands on this data by demonstrating that AK inhibition can protect against or attenuate the consequences of podocyte injury, reduce inflammatory activity following basement membrane disruption, and demonstrate modest efficacy in a model of extreme interstitial fibrosis, indicating that enhancement of endogenous ADO levels is sufficient to modulate renal pathology and mimic some of the beneficial actions of an A2A receptor agonist. PAN-induced renal injury is a widely accepted rat model of nephrotic syndrome, corresponding to minimal change disease in humans (Awad et al., 2008). In the current investigation, prophylactic administration of A-306989 dose-dependently reduced PAN-induced proteinuria and BUN increment. At the highest dose there was complete prevention of proteinuria, which was comparable to mizoribine, an established therapeutic immunosuppressive agent. A-306989 also reduced proteinuria and serum BUN levels following therapeutic treatment initiated two days after PAN injection, albeit with a more limited degree of efficacy, indicating that AK inhibition may be sufficient to attenuate established PAN-induced nephrosis. These data are consistent with the protection and corrective activity of A-306989 on PAN-induced injury in cultured podocytes. Podocytes contribute to the maintenance of the glomerular filtration barrier, and abnormalities of podocyte structure and function lead to a number of glomerular diseases. Preservation of podocyte integrity may attenuate/reverse proteinuria along with the associated recovery of glomerular and renal function (Awad et al., 2006). In the current study, PAN disrupted the highly organized actin cytoskeleton of cultured podocytes, which is known to be critically important to support glomerular ultrafiltration. Application of A-306989 restored this architecture, and maintained the number of the viable podocytes in both mouse and human immortalized cells. Consistent with these actions of an AK inhibitor, application of an A2A receptor agonist reduced albumin permeability and blocked the disruption of the actin cytoskeleton following PAN treatment in cultured podocytes (Awad et al., 2008). The A2A receptor agonist reversed PAN-induced actin cytoskeletal disorganization, restoring normal architecture of the podocyte cytoskeleton. Thus, AK inhibition may protect the integrity of podocytes via preserving the actin cytoskeleton by increasing endogenous ADO levels to activate A2A receptor. Thus, the observed in vivo effects of A-306989 in the PAN model may be linked to an ADO related restoration of normal podocyte structure.