Medium-chain triglyceride-induced neutrophil activation is not mediated by the
Pertussis Toxin sensitive G-protein coupled receptor GPR84
M.W. Versleijen1, J. van Esterik1, H. Roelofs1, S.E. van Emst-de Vries2, P.H. Willems2, G. J.
Wanten1
Depts. of Gastroenterology and Hepatology1 and Biochemistry2
Radboud University Nijmegen Medical Centre, The Netherlands.
Immune modulation by lipids might contribute to the high risk for infections that remains
associated with the use of parenteral nutrition. Previously, we have shown that emulsions
containing mixed long- and medium-chain triglycerides (LCT/MCT) or pure MCT, but not
pure LCT, impair crucial neutrophil functions, modulate cell signaling and induce neutrophil
activation in vitro. Others have recently shown that medium-chain fatty acids are ligands for a
pertussis toxin (PTX)-sensitive G-protein-coupled receptor (GPCR), which is known as
GPR84 and is mainly expressed on neutrophils. The present study was conducted to
investigate whether MCT-induced neutrophil activation is mediated by a PTX-sensitive
GPCR.
In the present study, neutrophils were isolated from 7 healthy volunteers. MCT-induced
neutrophil activation was assessed by evaluating stimulus-induced intracellular calcium
signaling of cells loaded with the fluorescent probe Fura-2 and oxygen radical (ROS)
production by luminol-enhanced chemiluminescence as well as by flowcytometric
measurement of the expressions of adhesion (CD11b) and degranulation (CD66b) markers.
Neutrophils were pre-incubated with PTX (500-1000 ng/mL, 1.5 hrs) to assess the
involvement of a PTX-sensitive GPCR in MCT-induced neutrophil activation.
The MCT-dependent modulation of the stimulus-induced biphasic cytosolic calcium increase
was not inhibited by PTX. MCT significantly increased ROS production to 146% of
unstimulated cells (P=0.018). However, pre-incubation with 500 nor 1000 ng/mL PTX
inhibited the MCT-induced ROS production (144% and 150% of unstimulated cells).
Furthermore, the MCT-induced increase in CD11b and CD66b expression (196% and 235%
of unstimulated cells, respectively) was not inhibited by pre-incubation with 500 ng/mL PTX
(222% (CD11b) and 251% (CD66b)) or 1000 ng/mL PTX (199% (CD11b) and 247%
(CD66b)).
Conclusion: MCT-induced neutrophil activation appears not to involve the action of a PTXsensitive GPCR, such as GPR84.