Abstract. Erythropoietin (EPO) is upregulated by hypoxia and causes proliferation and differentiation of erythroid progenitors in the bone marrow through inhibition of apoptosis. EPO receptors are expressed in many tissues, including the kidney. Here it is shown that a single systemic administration of EPO either preischemia or just before reperfusion prevents ischemia-reperfusion injury in the rat kidney. Specifically, EPO (300 U/kg) reduced glomerular dysfunction and tubular injury (biochemical and histologic assessment) and prevented caspase-3, -8, and -9 activation in vivo and reduced apoptotic cell death. In human (HK-2) proximal tubule epithelial cells, EPO attenuated cell death in response to oxidative stress and serum starvation. EPO reduced DNA fragmentation and prevented caspase-3 activation, with upregulation of Bcl-X L and XIAP. The antiapoptotic effects of EPO were dependent on JAK2 signaling and the phosphorylation of Akt by phosphatidylinositol 3-kinase. These findings may have major implications in the treatment of acute renal tubular damage.Erythropoietin (EPO) is the major regulator of proliferation and differentiation of erythroid progenitor cells through its antiapoptotic actions (1). EPO gene expression is under the control of the oxygen-sensitive transcription factor hypoxiainducible factor (HIF-1), which consists of the regulatory subunit HIF-1␣ and the constitutively expressed subunit HIF-1␤. Low oxygen tension adverts enzymatic prolyl-residue hydroxylation by prolyl-4-hydroxylase, which, in normoxia, serves as a signal for polyubiquitination and proteosomal degradation, thereby preventing von-Hippel-Lindau (VHL)-dependent HIF degradation, leading to nuclear accumulation of HIF-1 (2). HIF-1 controls the expression of several cytokines that mediate the adaptive response to ischemia, including vascular endothelial growth factor and glucose metabolism. The prolyl-4-hydroxylase requires iron as a co-factor, and cobalt mimics the effect of hypoxia on HIF-1␣ activation (3). Cobalt administration to rats caused upregulation of HIF-dependent proteins, including EPO, and diminished the degree of renal injury caused by ischemia-reperfusion (I/R), suggesting the HIF/EPO pathway may play an important role in ischemic preconditioning (4). EPO is upregulated in the brain and spinal cord after hypoxic stimuli and protects neurones against ischemic or oxidative injury in vivo and in vitro (5,6). The neuroprotective effects of EPO are dependent on EPO receptormediated JAK2 phosphorylation and NF-B-dependent transcription of antiapoptotic genes, including endogenous inhibitors of apoptosis XIAP and cIAP-2 (7). In the retina, EPO upregulation is essential for hypoxic preconditioning via HIF-1␣ stabilization. The systemic administration of recombinant EPO also reduces the degree of retinal apoptosis induced by high-intensity light insult (8). EPO receptor-mediated intracellular signaling may involve nuclear translocation of the transcription factor NF-B and phosphorylation of Akt (protein kinase B) by phosph...

Erythropoietin (EPO), a member of the type 1 cytokine superfamily, plays a critical hormonal role regulating erythrocyte production as well as a paracrine/autocrine role in which locally produced EPO protects a wide variety of tissues from diverse injuries. Significantly, these functions are mediated by distinct receptors: hematopoiesis via the EPO receptor homodimer and tissue protection via a heterocomplex composed of the EPO receptor and CD131, the ␤ common receptor. In the present work, we have delimited tissueprotective domains within EPO to short peptide sequences. We demonstrate that helix B (amino acid residues 58 -82) of EPO, which faces the aqueous medium when EPO is bound to the receptor homodimer, is both neuroprotective in vitro and tissue protective in vivo in a variety of models, including ischemic stroke, diabetes-induced retinal edema, and peripheral nerve trauma. Remarkably, an 11-aa peptide composed of adjacent amino acids forming the aqueous face of helix B is also tissue protective, as confirmed by its therapeutic benefit in models of ischemic stroke and renal ischemia-reperfusion. Further, this peptide simulating the aqueous surface of helix B also exhibits EPO's trophic effects by accelerating wound healing and augmenting cognitive function in rodents. As anticipated, neither helix B nor the 11-aa peptide is erythropoietic in vitro or in vivo. Thus, the tissue-protective activities of EPO are mimicked by small, nonerythropoietic peptides that simulate a portion of EPO's three-dimensional structure.cognition ͉ cytoprotection ͉ excitotoxicity ͉ ischemia-reperfusion injury ͉ wound healing

These results suggest that L-NIL and AE-ITU reduce the renal dysfunction and injury associated with I/R of the kidney, via inhibition of iNOS activity and subsequent reduction of NO (and peroxynitrite) generation. We propose that selective and specific inhibitors of iNOS activity may be useful against the NO-mediated renal dysfunction and injury associated with I/R of the kidney.

In normal conditions, nitric oxide (NO) is oxidized to the anion nitrite, but in hypoxia, this nitrite may be reduced back to NO by the nitrite reductase action of deoxygenated hemoglobin, acidic disproportionation, or xanthine oxidoreductase (XOR). Herein, is investigated the effects of topical sodium nitrite administration in a rat model of renal ischemia/reperfusion (I/R) injury. Rats were subjected to 60 min of bilateral renal ischemia and 6 h of reperfusion in the absence or presence of sodium nitrite (30 nmol) administered topically 1 min before reperfusion. Serum creatinine, serum aspartate aminotransferase, creatinine clearance, fractional excretion of Na ؉ , and plasma nitrite/nitrate concentrations were measured. The nitrite-derived NO-generating capacity of renal tissue was determined under acidic and hypoxic conditions by ozone chemiluminescence in homogenates of kidneys that were subjected to sham, ischemia-only, and I/R conditions. Nitrite significantly attenuated renal dysfunction and injury, an effect that was abolished by previous treatment of rats with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide (2.5 mol intravenously 5 min before ischemia and 50 nmol topically 6 min before reperfusion). Renal tissue homogenates produced significant amounts of NO from nitrite, an effect that was attenuated significantly by the xanthine oxidoreductase inhibitor allopurinol. Taken together, these findings demonstrate that topically administered sodium nitrite protects the rat kidney against I/R injury and dysfunction in vivo via the generation, in part, of xanthine oxidoreductase-catalyzed NO production. These observations suggest that nitrite therapy might prove beneficial in protecting kidney function and integrity during periods of I/R such as those encountered in renal transplantation. U ntil recently, the nitrite anion was regarded merely as an inactive metabolite of nitric oxide (NO) oxidation produced under normal physiologic conditions, accounting for approximately 70% of the endogenous nitrite pool (1). However, we (2) and others (3) recently demonstrated that, far from being inactive, nitrite has marked protective effects in ischemia/reperfusion (I/R) injury of both the heart and the liver. Moreover, these studies demonstrate that the beneficial effects of nitrite are related to its reduction to NO, under ischemic conditions. J Am Soc NephrolThe generation of NO is attributed conventionally to the enzyme NO synthase (NOS), of which there are three isoforms. Endothelial NOS (eNOS)-derived NO plays an important role in determining and maintaining aspects of normal renal function, for instance proximal tubule sodium reabsorption (4,5), but in elevated concentrations, NO also contributes to renal pathophysiology (6), such as in proximal tubule ischemic injury (4). This dual nature of NO perhaps is an oversimplification, because NO either ameliorates or exacerbates renal injury, depending on the site and the rate of NO production and the chemical fate of NO (7,8). Further...

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