Effect of endotoxin treatment on the expression of cyclooxygenase-2 and prostaglandin synthases in spinal cord, dorsal root ganglia, and skin of rats.

Peripheral inflammation causes upregulation of cyclooxygenase in the spinal cord and subsequent increase in prostaglandin biosynthesis. However, prostaglandin synthases, which are downstream of cyclooxygenase control the type of prostaglandin that is formed predominantly. Since there is little known about the regulation of prostaglandin synthases, the present study was conducted in order to determine the effect of endotoxin treatment on the expression of messenger RNA encoding interleukin 1beta, cyclooxygenase-2, and prostaglandin synthases mediating the formation of prostaglandin E(2) (membrane bound prostaglandin E synthase) and prostaglandin D(2) (lipocalin prostaglandin D synthase) in spinal cord, dorsal root ganglia and skin of rats. Endotoxin (2 mg/kg i.p.) induced the expression of interleukin-1beta, cyclooxygenase-2, and membrane bound prostaglandin E synthase messenger RNA in spinal cord, dorsal root ganglia, and skin as determined by reverse transcription polymerase chain reaction. In contrast, basal expression of lipocalin prostaglandin D synthase messenger RNA in spinal cord and dorsal root ganglia was not significantly altered by endotoxin. Dexamethasone (1 mg/kg s.c. at -18 h and -1 h) attenuated the effect endotoxin on the expression of interleukin-1beta, cyclooxygenase-2, and membrane bound prostaglandin E synthase messenger RNA in all tissues investigated, but did not significantly influence expression of lipocalin prostaglandin D synthase mRNA in spinal cord and dorsal root ganglia. In situ hybridisation histochemistry showed endotoxin-induced expression of cyclooxygenase-2 and membrane bound prostaglandin E synthase messenger RNA throughout gray and white matter of spinal cord sections. In dorsal root ganglia, expression of membrane bound prostaglandin E synthase seemed primarily located to non-neuronal cells, while cyclooxygenase-2 messenger RNA was not detectable. The results show that the immune response elicited by endotoxin induced cyclooxygenase-2 and membrane bound prostaglandin E synthase, but not lipocalin prostaglandin D synthase messenger RNA in spinal cord and dorsal root ganglia of rats. The distribution of cyclooxygenase-2 and membrane bound prostaglandin E synthase messenger RNA expressing cells suggests major involvement of non-neuronal cells in spinal prostaglandin biosynthesis. Determination of the regulation of enzymes downstream of cyclooxygenase at the messenger RNA level may represent a valuable tool to investigate effects of analgesic/anti-inflammatory drugs on the regulation of spinal prostaglandin biosynthesis.

Inhibition of prostaglandin biosynthesis in human endotoxin-stimulated peripheral blood monocytes: effects of caffeine.

There is an ongoing debate about possible advantages of the coadministration of caffeine with cyclooxygenase (COX) inhibitors in the treatment of pain. There are results suggesting interference by caffeine with COX expression and activity in rat immune cells. In the present study, we have used, therefore, human endotoxin-stimulated monocytes to investigate a possible influence of caffeine on indometacin-induced inhibition of prostaglandin E(2) (PGE(2)) formation. Endotoxin caused a concentration- and time-dependent increase in immunoreactive PGE(2) that was dependent on CD14-mediated mechanisms. In order to investigate pharmacological inhibition of the COX activity, a submaximal concentration of 1 ng/ml endotoxin (4 h exposure time) was used. Indometacin caused a concentration-dependent inhibition of PGE(2) with an apparent IC(50) of 8.9 +/- 1.4 x 10(-9) mol/l and an I(max) of 1 x 10(-7) mol/l. Caffeine (5 x 10(-6) to 1.5 x 10(-4) mol/l) on its own produced no statistically significant effect on endotoxin-induced PGE(2) formation. In the presence of caffeine (5 x 10(-6) to 1.5 x 10(-4) mol/l), inhibition of PGE(2) biosynthesis by indometacin (1 x 10(-8) mol/l) was not significantly altered. These results show that, in human monocytes, caffeine, up to concentrations severalfold higher than those reached in patients, has no significant effect on endotoxin-induced PGE(2) formation nor on its inhibition by indometacin.