Agonist potency at P2X7 receptors is modulated by structurally diverse lipids.
OBJECTIVE
The P2X(7) receptor exhibits a high degree of plasticity with agonist potency increasing after prolonged receptor activation. In this study we investigated the ability of lipids to modulate agonist potency at P2X(7) receptors.


METHODS
A variety of lipids, including lysophosphatidylcholine, sphingosylphosphorylcholine and hexadecylphosphorylcholine were studied for their effect on P2X(7) receptor-stimulated ethidium bromide accumulation in cells expressing human recombinant P2X(7) receptors and on P2X(7) receptor-stimulated interleukin-1 beta (IL1 beta) release from THP-1 cells. The effects of the lipids were also assessed in radioligand binding studies on human P2X(7) receptors.


RESULTS
At concentrations (3-30 microM) below the threshold to cause cell lysis, the lipids increased agonist potency and/or maximal effects at P2X(7) receptors in both ethidium accumulation and IL1 beta release studies. There was little structure activity relationship (SAR) for this effect and sub-lytic concentrations of Triton X-100 partially mimicked the effects of the lipids. The lipids caused cell lysis and increased intracellular calcium at higher concentrations (30-100 microM) which complicated interpretation of their effects in functional studies. However, the lipids (3-100 microM) also increased agonist potency 30-100 fold in radioligand binding studies.


CONCLUSIONS
This study demonstrates that a diverse range of lipids increase agonist potency at the P2X(7) receptor in functional and binding studies. The broad SAR, including the effect of Triton X-100, suggests this may reflect changes in membrane properties rather than a direct effect on the P2X(7) receptor. Since many of the lipids studied accumulate in disease states they may enhance P2X(7) receptor function under pathophysiological conditions.
Michel
A D
AD
Neurology & GI Centre of Excellence for Drug Discovery, GlaxoSmithKline Research & Development Limited, New Frontiers Science Park, Harlow, Essex, UK. adm7393@gsk.com
Fonfria
E
E
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004996:Ethidium / Q000378:metabolism; D005470:Fluorometry; D006801:Humans; D053583:Interleukin-1beta / Q000378:metabolism; D008055:Lipids / Q000737:chemistry / Q000494:pharmacology*; D008244:Lysophosphatidylcholines / Q000737:chemistry / Q000494:pharmacology; D051379:Mice; D017830:Octoxynol / Q000494:pharmacology; D010172:Palmitoylcarnitine / Q000737:chemistry / Q000494:pharmacology; D010767:Phosphorylcholine / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D058910:Purinergic P2 Receptor Agonists; D011869:Radioligand Assay; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000378:metabolism*; D058476:Receptors, Purinergic P2X2; D058486:Receptors, Purinergic P2X7; D013110:Sphingosine / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D013501:Surface-Active Agents / Q000737:chemistry / Q000494:pharmacology
D053583:Interleukin-1beta; D008055:Lipids; D008244:Lysophosphatidylcholines; C546401:P2RX2 protein, human; C546468:P2RX7 protein, human; C546402:P2rx2 protein, mouse; C546469:P2rx7 protein, mouse; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D058486:Receptors, Purinergic P2X7; D013501:Surface-Active Agents; C005356:sphingosine phosphorylcholine; D010767:Phosphorylcholine; D010172:Palmitoylcarnitine; D000255:Adenosine Triphosphate; D017830:Octoxynol; D004996:Ethidium; D013110:Sphingosine; D002118:Calcium
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