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