Epac-1 activator 8-O-cAMP augments renoprotective effects of allogeneic murine EPCs in acute ischemic kidney injury

Endothelial progenitor cells (EPCs) protect kidneys from acute ischemic damage. The aim of this study was to identify “treatment parameters” that optimize an EPC-based therapy of acute ischemic renal failure. Male C57BL/6N mice underwent unilateral nephrectomy with simultaneous contralateral renal artery clamping for 30, 35, and 40 min. Tagged murine EPCs were systemically injected at the time of reperfusion. In some experiments, EPCs were pretreated with the Epac (exchange protein directly activated by cAMP-1) activator 8-pCPT-2′- O-Me-cAMP (Epac-1 Ac) and the integrin binding antagonist cyclic Arg-Gly-Asp peptide (cRGD). Injections of 106 EPCs after 30 and 35 min of renal ischemia protected animals from acute renal failure. The same effect occurred with 0.5×106 EPCs after a 35-min period of ischemia. If ischemia lasted for 40 min, 0.5×106 cells mice did not prevent acute renal failure. To analyze whether EPC integrin receptor activation would modify the cells' renoprotective activity, EPCs were pretreated with Epac-1 Ac. Such animals did not develop acute renal failure, even if ischemia lasted for 40 min. This effect was negated if the cells were pretreated with both Epac-1 Ac and cRGD. In kidneys from those animals medullopapillary EPCs were significantly accumulated. In vitro Epac-1 Ac preactivation of EPCs did not increase the overall expression intensity but induced a redistribution of β1-integrins toward the cell membranes. We conclude that EPC pretreatment with the integrin receptor activator 8-pCPT-2′- O-Me-cAMP augments the anti-ischemic potential of the cells.

Heme oxygenase-1 induction improves ischemic renal failure: role of nitric oxide and peroxynitrite

The present study evaluated the effects of heme oxygenase-1 (HO-1) induction on the changes in renal outer medullary nitric oxide (NO) and peroxynitrite levels during 45-min renal ischemia and 30-min reperfusion in anesthetized rats. Glomerular filtration rate (GFR), outer medullary blood flow (OMBF), HO and nitric oxide synthase (NOS) isoform expression, and renal low-molecular-weight thiols (–SH) were also determined. During ischemia significant increases in NO levels and peroxynitrite signal were observed (from 832.1 ± 129.3 to 2,928.6 ± 502.0 nM and from 3.8 ± 0.7 to 9.0 ± 1.6 nA before and during ischemia, respectively) that dropped to preischemic levels during reperfusion. OMBF and –SH significantly decreased after 30 min of reperfusion. Twenty-four hours later, an acute renal failure was observed (GFR 923.0 ± 66.0 and 253.6 ± 55.3 μl·min−1·g kidney wt−1 in sham-operated and ischemic kidneys, respectively; P < 0.05). The induction of HO-1 (CoCl2 60 mg/kg sc, 24 h before ischemia) decreased basal NO concentration (99.7 ± 41.0 nM), although endothelial and neuronal NOS expression were slightly increased. CoCl2 administration also blunted the ischemic increase in NO and peroxynitrite (maximum values of 1,315.6 ± 445.6 nM and 6.3 ± 0.5 nA, respectively; P < 0.05), preserving postischemic OMBF and GFR (686.4 ± 45.2 μl·min−1·g kidney wt−1). These beneficial effects of CoCl2 on ischemic acute renal failure seem to be due to HO-1 induction, because they were abolished by stannous mesoporphyrin, a HO inhibitor. In conclusion, HO-1 induction has a protective effect on ischemic renal failure that seems to be partially mediated by decreasing the excessive production of NO with the subsequent reduction in peroxynitrite formation observed during ischemia.