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ISSN 0582-9879 Acta Biochim et Biophysica Sinica 2004, 36(6):419-424 CN 31-1300/Q

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Role of Apolipoprotein A-I in Protecting against Endotoxin Toxicity

Juan MA, Xue-Ling LIAO, Bin LOU, and Man-Ping WU*

Department of Biochemistry, School of Pharmacy, Fudan University, Shanghai 200032, China

Abstract High density lipoprotein (HDL) binds lipopolysaccharide (LPS or endotoxin) and neutralizes its toxicity. We investigated the function of Apolipoprotein A-I (ApoA-I), a major apolipoprotein in HDL, in this process. Mouse macrophages were incubated with LPS, LPS+ApoA-I, LPS+ApoA-I+LFF (lipoprotein-free plasma fraction d>1.210 g/ml), LPS+HDL, LPS+HDL+LFF, respectively. MTT method was used to detect the mortality of L-929 cells which were attacked by the release-out cytokines in LPS-activated macrophages. It was found that ApoA-I significantly decreased L-929 cells mortality caused by LPS treatment (LPS vs. LPS+ApoA-I, P<0.05) and this effect became even more significant when LFF was utilized (LPS vs. LPS+ApoA-I+LFF, P<0.01; LPS vs. LPS+HDL+LFF, P<0.01). There was no significant difference between LPS+ApoA-I+LFF and LPS+HDL+LFF treatment, indicating that ApoA-I was the main factor. We also investigated in vivo effects of ApoA-I on mouse mortality rate and survival time after LPS administration. We found that the mortality in LPS+ApoA-I group (20%) and in LPS+ApoA-I+LFF group (10%) was significantly lower than that in LPS group (80%) (P<0.05, P<0.01, respectively); the survival time was (43.20 ± 10.13) h in LPS+ApoA-I group and (46.80 ± 3.79) h in LPS+ApoA-I+LFF group, which were significantly longer than that in LPS group (16.25 ± 17.28) h (P<0.01). We also carried out in vitro binding study to investigate the binding capacity of ApoA-I and ApoA-I+LFF to fluorescence labeled LPS (FITC-LPS). It was shown that both ApoA-I and ApoA-I+LFF could bind with FITC-LPS, however, the binding capacity of ApoA-I+LFF to FITC-LPS (64.47 ± 8.06) was significantly higher than that of ApoA-I alone (24.35 ± 3.70) (P<0.01). The results suggest that: (1) ApoA-I has the ability to bind with and protect against LPS; (2) LFF enhances the effect of ApoA-I; (3) ApoA-I is the major contributor for HDL anti-endotoxin function.

Key words Apolipoprotein-I; lipopolysaccharide (LPS); macrophages; FITC-lipopolysaccharide (FITC-LPS); L-929 cells

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Received: January 13, 2004 Accepted: March 11, 2004

This work was supported by a grant from Hongkong Shenzhou Pharmacy R&D Fund

*Corresponding author: Tel, 86-21-64042268; Fax, 86-21-64042268; E-mail, [email protected]