Ischemic proximal tubular injury primes mice to endotoxin-induced TNF-α generation and systemic release

Abstract

Endotoxemia (LPS) can exacerbate ischemic tubular injury and acute renal failure (ARF). The present study tested the following hypothesis: that acute ischemic damage sensitizes the kidney to LPS-mediated TNF-alpha generation, a process that can worsen inflammation and cytotoxicity. CD-1 mice underwent 15 min of unilateral renal ischemia. LPS (10 mg/kg iv), or its vehicle, was injected either 45 min before, or 18 h after, the ischemic event. TNF-alpha responses were gauged 2 h post-LPS injection by measuring plasma/renal cortical TNF-alpha and renal cortical TNF-alpha mRNA. Values were contrasted to those obtained in sham-operated mice or in contralateral, nonischemic kidneys. TNF-alpha generation by isolated mouse proximal tubules (PTs), and by cultured proximal tubule (HK-2) cells, in response to hypoxia-reoxygenation (H/R), oxidant stress, antimycin A (AA), or LPS was also assessed. Ischemia-reperfusion (I/R), by itself, did not raise plasma or renal cortical TNF-alpha or its mRNA. However, this same ischemic insult dramatically sensitized mice to LPS-mediated TNF-alpha increases in both plasma and kidney (approximately 2-fold). During late reperfusion, increased TNF-alpha mRNA levels also resulted. PTs generated TNF-alpha in response to injury. Neither AA nor LPS alone induced an HK-2 cell TNF-alpha response. However, when present together, AA+LPS induced approximately two- to fivefold increases in TNF-alpha/TNF-alpha mRNA. We conclude that modest I/R injury, and in vitro HK-2 cell mitochondrial inhibition (AA), can dramatically sensitize the kidney/PTs to LPS-mediated TNF-alpha generation and increases in TNF-alpha mRNA. That ischemia can "prime" tubules to LPS response(s) could have potentially important implications for sepsis syndrome, concomitant renal ischemia, and for the induction of ARF.