We are developing a novel small molecule cytoprotective drug for the prevention of contrast-induced nephropathy (CIN) following intravenous radiocontrast media (CM) injection. CIN is mediated principally by CM-induced vasoconstriction of the afferent renal arteriololes, resulting in antidiuresis and severely compromised renal blood flow. The consequent renal ischemia induces oxidative and nitrosative stress, in particular within the nucleus of the renal tubules where DNA single strand breakage occurs. When this genomic injury is then recognized by the nuclear DNA repair enzyme poly (ADP-ribose) polymerase ("PARP"), NAD is cleaved to generate the product poly(ADP-ribose). Hyperactivation of PARP after CM injection depletes NAD stores, resulting in the loss of oxidative phosphorylation and interference with ATP synthesis. To address this unmet need, we are developing a cell-permeable thioredoxin mimetic (R-901), a thiol-rich tripeptide that is closely analogous to the native thioredoxin (TRX) motif. R-901 exhibits in vitro potency 450- and 50-fold >than N-acetylcysteine (NAC) and ascorbic acid, respectively, and in vivo potency substantially greater than NAC. Therapeutic administration of R-901 has been shown in a murine model of pulmonary inflammation (induced by ovalbumin sensitization and re-challenge) to reduce histologic injury, diminish leukocytic infiltration, attenuate tissue oxidation, block pr-inflammatory cytokine expression and nuclear translocation of NF-kB, diminish the degradation of the anti-inflammatory cytoplasmic protein IkBalpha, and restore the balance of reduced and oxidized forms of glutathione. In a murine LD100 model of severe redox stress induced by acute Cl2 gas inhalation, post-insult administration of R-901 reduced pulmonary neutrophil infiltration by 50%. Based on its ultrapotent catalysis of redox stress, and the critical relevance of redox stress to the pathophysiology of CIN, we now propose to construct a pharmacodynamic profile of R-901 in a rat model of CIN induced by dehydration, prostaglandin synthetase inhibition, and an IV challenge of CM. A sham injury group will be compared to treatment of CM-challenged rats with NAC or R-901 (over a one log dose range) initiated prior to CM administration under conditions of dehydration or volume loading. At 24 hours plasma will be analyzed for renal function and biochemical, histologic, and immunohistochemical parameters of renal injury. Renal and plasma concentrations of R-901 will be compared to assess tissue R-901 uptake. We expect that level of exposure to R-901 will correlate with the extent of tissue protection, as manifested by renal levels of necrosis (histology), lipid peroxidation, neutrophil infiltration, apoptosis, necrosis, peroxynitrite and poly(ADP- ribose) formation, and serum concentrations of neutrophil gelatinase-associated lipocalin. The proposed studies will provide a rational foundation for advanced commercial development of R-901, with the intent that this product will serve as first-line prophylaxis in high-risk patients undergoing CM injection.
Radiocontrast imaging is an invaluable and frequently used diagnostic modality for but its use is complicated by the subsequent development of kidney injury, often to the extent of requiring dialysis, particularly in populations at greatest risk, suh as the elderly, diabetic, and those with preexisting renal impairment. There are no approved pharmaceutical therapies to prevent this complication. We are developing a novel prophylactic agent that protects the kidney from radiocontrast administration by directly protecting kidney cells from injury. We now propose to test this agent in a clinically-relevant small animal model of radiocontrast-induced kidney failure.