Evidence for sustained renal hypoxia and transient hypoxia adaptation in experimental rhabdomyolysis-induced acute kidney injury.

Background: Indirect evidence suggests that hypoxia contributes to the pathophysiology of rhabdomyolysis-induced acute kidney injury (AKI). However, the cellular location and kinetics of hypoxia, as well as potential hypoxia adaptation are unclear.
Methods: Rhabdomyolysis was induced in rats by IM glycerol (GLY) injection, which largely recapitulates the full clinical syndrome. Additional rats received IV myoglobin (MYO), in order to assess the contribution of MYO per se. We performed immunohistochemistry for hypoxia markers [pimonidazole (PIM) adducts and hypoxia-inducible factors (HIFs)] and the cell-protective HIF target gene heme oxygenase-1 (HO-1). Furthermore, we sought a potential negative feedback loop to terminate HIF activation, driven by HIF prolyl-hydroxylase-2 (PHD-2).
Results: In GLY, progressive tubular injury, mainly of proximal tubules (PT), developed over time, but its extent was heterogeneous. PIM, HIFalpha and HO-1 were all absent in controls, but strongly positive in GLY, with a specific spatio-temporal pattern. In PT, (a) PIM was detectable throughout the study with a maximum at 6 h, (b) HIF was activated only at 3 h and (c) HO-1 and PHD-2 appeared at 6 h and persisted at a lower level at 24 h. Apart from tubular cast formation, MYO did not cause overt tissue damage, but led to strong activation of HIFs, in a pattern similar to 3 h of GLY.
Conclusions: Our data suggest that renal hypoxia occurs in rhabdomyolysis, and that MYO, at least partly, contributes to hypoxia generation. Since in the most affected tubules transcriptional hypoxia adaptation is transient and inhomogeneous, pharmacologic HIF enhancement holds the potential to improve outcome in rhabdomyolysis-induced AKI.