This application addresses broad Challenge Area (15): """"""""Translational Science"""""""", and specific Challenge Topic, 15-DK-103: """"""""Translate discovery of new molecules and pathways in pathogenesis of NIDDK diseases into potential therapies"""""""". More specifically, this application proposes to validate a therapeutic target and to improve the bioavailability and pharmacokinetic properties of novel small molecule compounds for the prevention and treatment of calcification of the medial layer of arteries, a common and severe condition in patients with chronic kidney disease (CKD), diabetes, obesity and aging that correlates with cardiovascular events and death. To-date there is no effective medical treatment for medial calcification. Research in our laboratories has demonstrated that vascular calcification is normally inhibited by extracellular pyrophosphate (PPi) produced by vascular smooth muscle. Plasma PPi concentrations are reduced in hemodialysis patients and are inversely correlated with vascular calcification. We have shown that levels of PPi are reduced in uremic vascular smooth muscle and that medial calcification in uremic rats and in mouse models of PPi-deficiency is prevented by injections of PPi. The key regulator of extracellular PPi is the ectoenzyme tissue-nonspecific alkaline phosphatase (TNAP) that hydrolyzes PPi, thus destroying its ability to suppress calcification. We have also shown that addition of TNAP to culture medium or overexpression of TNAP by viral transduction causes calcification in cultured aortas and transgenic expression of TNAP in tissues expressing type I collagen is sufficient to cause extraosseous calcification. We have also shown that TNAP is pathophysiologically upregulated at sites of medial calcification in uremic aortas and mouse models of idiopathic infantile arterial calcification, suggesting the putative pathophysiological mechanism that links PPi deficiency to medial calcification in patients with CKD. Using high throughput screening, we have identified potent inhibitors of TNAP that completely prevent calcification of aortas in culture. We hypothesize that medial vascular calcification in renal failure results from increased activity of TNAP in the vasculature and that this ectopic calcification can be prevented by inhibitors of TNAP's pyrophosphatase activity. This RC1 proposal focuses sharply on validating TNAP as a therapeutic target and in improving, via Medicinal Chemistry and structure-activity-relationship studies, the bioavailability and pharmacokinetic properties of novel TNAP inhibitors to enable in vivo testing of the effectiveness of this mechanism-based therapeutic strategy in a uremic rat model of CKD. The clinical management of medial calcification has been limited to minimizing the impact of the associated metabolic bone disease to which it is inextricably linked. This indirect approach has not been very effective in CKD and does not address the calcification that occurs in diabetes or with aging. Thus, there is a need for more specific therapies that directly address the pathogenesis of medial calcification. Pharmacological inhibition of TNAP is a novel approach to this problem that directly addresses the upregulation of TNAP in the vasculature and the ensuing PPi deficiency seen in renal failure. Because TNAP controls extracellular PPi levels under normal conditions this therapy is expected to increase local PPi levels in the vasculature thus inhibiting medial calcification. - Relevance to Public Health Medial calcification of the vasculature is of common occurrence in renal failure, diabetes, obesity and aging, where it contributes to morbidity and mortality through compromised arterial function. Currently there are no treatments for this prevalent condition. Our studies will validate a therapeutic target for medial calcification and will optimize new lead chemicals to prevent/treat arterial calcification in established animal models, thus filling this unmet clinical need.
Medial calcification of the vasculature is of common occurrence in renal failure, diabetes, obesity and aging, where it contributes to morbidity and mortality through compromised arterial function. Currently there are no treatments for this prevalent condition. Our studies will validate a therapeutic target for medial calcification and will optimize new lead chemicals to prevent/treat arterial calcification in established animal models, thus filling this unmet clinical need.
