Deactivation of the LPS antagonist eritoran by HDL-associated apolipoproteins

• Main Author: Fleischer, Jacklyn Gabriella
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/27100

Background: Sepsis is a complex and life-threatening infection by gram-negative bacteria that is caused by the endotoxin lipopolysaccharide or LPS. Lipid A, the active moiety of LPS, exerts its effects through interaction with toll-like receptor 4 (TLR4), triggering a signalling cascade that results in the massive release of pro-inflammatory cytokines such as tumour necrosis-α (TNF-α) and interleukin-1 (IL-1). Eritoran is a synthetic lipid A analogue that is a powerful antagonist of LPS, however it undergoes a time-dependent deactivation after administration as a consequence of binding to high-density lipoproteins (HDL). At present, there remains much uncertainty surrounding the site of eritoran association with HDL. Therefore, the objective of this study was to determine if HDL-associated apolipoproteins inhibit eritoran’s ability to block LPS-induced TNF-α release from whole blood. Methods: Assess eritoran activity after LPS stimulation in human whole blood in the presence of free or reconstituted HDL containing apolipoproteins, including a combination rHDL containing all apolipoproteins found on native HDL/septic HDL. Activity will be measured by TNF-α release. Results: Differences exist in the effects on drug activity when apolipoproteins are free versus lipid-bound. In rHDL, the major apolipoproteins in both the healthy and septic state, A1 and SAA, caused a significant reduction in eritoran antagonistic activity. Additionally, in rHDL, A1 and SAA are superior to minor apolipoproteins A2 and C1 in dampening drug activity, while a native combination rHDL, normal rHDL (NrHDL), deactivated eritoran to a similar degree as rHDL-A1. Conclusions: Apolipoproteins associated with HDL are likely to facilitate eritoran deactivation. Apo A1 and SAA should be of particular focus as they are the major apolipoproteins found on HDL in both the healthy and septic state and were observed to significantly reduce eritoran activity. Further evaluation of the physical association between apolipoproteins and eritoran, particularly binding mechanisms, should be explored. Significance: This study will help to elucidate the components of HDL that facilitate loss of eritoran antagonistic activity, illuminating how associations are formed between lipoproteins and xenobiotics. Clinically, these results can be used to strategize novel ways to thwart drug deactivation in vivo and extend its therapeutic action in septic patients.