Role of apolipoprotein A-I in protecting against endotoxin toxicity.
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.
Ma
Juan
J
Department of Biochemistry, School of Pharmacy, Fudan University, Shanghai 200032, China.
Liao
Xue-Ling
XL
Lou
Bin
B
Wu
Man-Ping
MP
D000818:Animals; D016632:Apolipoprotein A-I / Q000502:physiology*; D002460:Cell Line; D002845:Chromatography; D004591:Electrophoresis, Polyacrylamide Gel; D004731:Endotoxins / Q000378:metabolism* / Q000633:toxicity*; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D008070:Lipopolysaccharides / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D011485:Protein Binding; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D013997:Time Factors; D014461:Ultracentrifugation
D016632:Apolipoprotein A-I; D004731:Endotoxins; D008070:Lipopolysaccharides; D008075:Lipoproteins, HDL; D013778:Tetrazolium Salts; D013844:Thiazoles; C022616:thiazolyl blue