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Alkaline phosphatase treatment improves renal function in patients with severe sepsis or septic shock

We previously demonstrated that upregulation of renal inducible nitric oxide synthase (iNOS) during systemic inflammation is associated with proximal tubule injury. In several in vitro and animal studies alkaline phosphatase (AP) was found to be effective in attenuating the inflammatory response by dephosphorylating LPS and may prevent organ damage. The objective of this study was to investigate the effect of AP on renal iNOS expression and kidney damage in patients with severe sepsis or septic shock.

Fifteen patients (nine male/six female, age 55 ± 5 years) with Gram-negative bacterial infection, two out of four SIRS criteria (<24 hours) and acute onset of end-organ dysfunction (<12 hours) were included in a randomized, double-blind, placebo-controlled phase IIa study (2:1 ratio). An intravenous bolus injection of 67.5 U/kg bovine intestinal AP was followed by a maintenance dose of 177.5 U/kg for 24 hours. Arterial blood and urine were collected at different time points and analyzed for stable metabolites of NO. iNOS mRNA was determined by quantitative real-time RT-PCR using RNA isolated from renal cells in urine. The urinary excretion of the cytosolic glutathione S-transferase-A1 (GSTA1-1), a marker for proximal tubule damage, was measured using an ELISA. Data are depicted as the median (25–75% range).

NO metabolites in blood were not significantly different between AP-treated (n = 10) and placebo-treated (n = 5) patients. However, the urinary excretion of NO metabolites decreased by 80% (75–85) from 227 (166–531) at baseline to 41 (28–84) μmol/10 mmol creatinine (P < 0.05) after 24 hours of AP administration. After placebo treatment, the amount of urinary NO metabolites increased by 70% (45–570) (from 81 (64–419) to 628 (65–1,479) μmol/10 mmol creatinine, P < 0.05). Baseline expression levels of iNOS in renal cells were 42-fold induced at baseline (vs healthy subjects), and AP administration reduced this induction by 80 ± 5% (Figure 1). Creatinine clearance improved by 45% (30–180) in patients treated with AP and declined by 25% (15–35) in placebo-treated patients. During the first 24 hours the amount of GSTA1-1 in urine of AP-treated patients decreased by 70% (50–80), compared with an increase of 200% (45–525) in placebo-treated patients, which correlated with urinary NO metabolites, indicating NO-induced proximal tubular damage.

In conclusion, in septic patients, infusion of AP results in an attenuated upregulation of iNOS and, subsequent, reduced NO production in the kidney, associated with an improvement in renal function.

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Heemskerk, S., Masereeuw, R., Moesker, O. et al. Alkaline phosphatase treatment improves renal function in patients with severe sepsis or septic shock. Crit Care 11 (Suppl 2), P14 (2007).

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