Mechanism of reduction of albumin expression induced by lipopolysaccharide in rat hepatocytes / 中华医学杂志(英文版)

ABSTRACT

<p><b>BACKGROUND</b>The severity of hypoalbuminemia has been shown to be related to morbidity and mortality in some critical illnesses, illustrating the need for better understanding of molecular mechanism of hypoalbuminemia. Lipopolysaccharide (LPS) is a key mediator inducing hypoalbuminemia in sepsis and septic shock. The present study was designed to identify if the reduction of albumin expression is directly induced by LPS and modulated by activated extracellular signal-regulated protein kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) in rat hepatocytes.</p><p><b>METHODS</b>Primary rat hepatocytes were divided into five groups. In two of them, hepatocytes were treated with normal saline or 1 microg/ml LPS, then albumin mRNA expression was observed at 0, 2, 8, 12 and 24 hours after treatment. In another group, hepatocytes were pretreated with 100, 40 or 20 micromol/L of cycloheximide (CHX, an inhibitor of protein synthesis) for 30 minutes followed by 1 microg/ml LPS for 24 hours. Then the RNA was extracted from the cells for RT-PCR to detect the expression of albumin. The other two groups were administered 1 micromol/L, 10 micromol/L and 50 micromol/L of SB203580 (p38 MAPK inhibitor) or PD98059 (ERK inhibitor) 30 minutes prior to 1 microg/ml LPS treatment. After 24 hours of LPS treatment, the supernatant was collected and assayed for albumin concentrations. Data were analyzed by one-way analysis of variance, followed by the Newman-Keul test; a P<0.05 was considered significant.</p><p><b>RESULTS</b>There was no marked change in albumin mRNA expression in the control group during 24-hours treatment with normal saline. The reduction did not occur until 24 hours after LPS treatment, and albumin mRNA decreased by 30% approximately compared to the control group at 24 hours (0.587 vs 0.832, P=0.007). CHX could inhibit the decline of albumin mRNA induced by LPS and the effect was correlated with the dose of CHX. The ERK inhibitor PD98059 caused a significant increase in LPS-induced albumin production at the three concentrations (119.7, 111.4 and 80.0 ng/ml vs 44.4 ng/ml, P=0.0013, 0.0025 and 0.009, respectively), whereas SB203580 obviously blocked albumin reduction in LPS-treated cells at the concentrations of 10 and 50 micromol/L (87.5 and 93.6 ng/ml vs 44.4 ng/ml, P=0.0076 and 0.0049, respectively).</p><p><b>CONCLUSIONS</b>LPS can induce the reduction of albumin expression by new synthesized proteins indirectly, and the process may be related to the signal proteins of ERK and p38 kinase. The ERK and p38 kinase are critical signaling pathways in LPS-induced hypoalbuminemia which is worthwhile to understand in studying the molecular mechanism of hypoalbuminemia in sepsis and septic shock.</p>