Endotoxin Contamination of Apolipoprotein A1: Effect on Macrophage Proliferation – A Cautionary Tale

Wednesday, September 24, 2014 — Poster Session IV
10:00 a.m. –12:00 p.m.	FAES Academic Center	NHLBI	CELLBIO-4

Authors

• XT Jin
• Q Xu
• K Champion
• HS Kruth

Abstract

Incubation of human macrophages with human plasma-derived ApoA1 inhibited macrophage proliferation >90%. Recombinant ApoA1 expressed in human cells did not inhibit proliferation, but recombinant ApoA1 expressed in E. coli did. Human plasma-derived ApoA2 did not inhibit proliferation. All apolipoproteins were obtained commercially. We considered the possibility that endotoxin contamination of the apolipoproteins contributed to the differential inhibition of macrophage cell proliferation. Endotoxin alone very potently inhibited macrophage proliferation (>90% at 0.1 ng/ml). Although human cell-derived recombinant ApoA1 and human plasma-derived ApoA1 showed similar levels of total endotoxin contamination (levels sufficient to inhibit macrophage proliferation), the levels of free endotoxin in the human cell-derived recombinant ApoA1 were 1000-fold less than levels in the human plasma-derived ApoA1, explaining why the recombinant ApoA1 did not inhibit macrophage proliferation, but the plasma-derived ApoA1 did. Conclusion: Our findings show that apparent apolipoprotein-mediated cell effects (or effects of any other biological products) can be significantly influenced by endotoxin contamination, especially when these products are tested on highly endotoxin-sensitive cells, such as macrophages. Also, endotoxin potently inhibits macrophage proliferation, which may be a significant pathogenic mechanism by which bacteria escape the immune system.

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