Sepsis is a dysregulated host response to
infection that can cause widespread effects on other organs including cardiovascular depression,
hypotension and organ failure. The receptor for
Nociceptin/Orphanin FQ (N/OFQ), NOP is expressed on immune cells and these cells can release the
peptide. Exogenous N/OFQ can dilate blood vessels and this
peptide is increased in animal and human
sepsis. We hypothesise that NOP receptors are present on vascular endothelial cells and therefore provide the target for released N/OFQ to cause vasodilation and hence
hypotension. Using human umbilical vein endothelial cells (HUVEC) and human vascular smooth muscle cells (HVSMC) freshly prepared from umbilical cords and up to passage 4, we assessed NOP
mRNA expression by Polymerase Chain Reaction (PCR), NOP surface receptor expression using a fluorescent NOP selective probe (N/OFQATTO594) and NOP receptor function with N/OFQ stimulated ERK1/2 phosphorylation. As an in vitro
sepsis mimic we variably incubated cells with 100ng/ml
Lipopolysaccharide and
Peptidoglycan G (LPS/PepG). HUVECs express NOP
mRNA and this was reduced by ~80% (n = 49) after 24-48 hours treatment with LPS/PepG. Untreated cells do not express surface NOP receptors but when treated with LPS/PepG the reduced
mRNA was translated into
protein visualised by N/OFQATTO594 binding (n = 49). These NOP receptors in treated cells produced an N/OFQ (1μM) driven increase in ERK1/2 phosphorylation (n = 20). One (of 50) HUVEC lines expressed NOP
mRNA and receptor
protein in the absence of LPS/PepG treatment. In contrast, HVSMC expressed NOP
mRNA and surface receptor
protein (n = 10) independently of LPS/PepG treatment. These receptors were also coupled to ERK1/2 where N/OFQ (1μM) increased phosphorylation. Collectively these data show that an in vitro
sepsis mimic (LPS/PepG) upregulates functional NOP expression in the vascular endothelium. Activation of these endothelial receptors as suggested from in vivo whole animal work may contribute to the hypotensive response seen in
sepsis. Moreover, blockade of these receptors might be a useful adjunct in the treatment of
sepsis.