Monocyte intracellular cytokine production during human endotoxaemia with or without a second in vitro LPS challenge: effect of RWJ‐67657, a p38 MAP‐kinase inhibitor, on LPS‐hyporesponsiveness

In the present study, we investigated the effect of RWJ‐67657, a p38 MAP kinase inhibitor, upon in vivo LPS‐induced monocyte cytokine production and upon monocyte LPS‐hyporesponsiveness. Thirty minutes before a single injection of LPS (4 ng/kg BW), healthy male volunteers received a single oral dose of RWJ‐67657 at increasing dosages (0–1400 mg). Blood samples (pre‐medication, 3, 6 and 24 h after LPS) were immediately incubated with LPS (reflecting LPS‐hyporesponsiveness) or without LPS (reflecting in vivo monocyte stimulation) for 4 h at 37°C. Following red blood cells lysis and white blood cell permeabilization, cells were labelled with α‐CD14‐FITC and α‐IL‐1β, α‐IL‐12 or α‐TNFα (PE‐labelled), fixed, and analysed using flow cytometry. In vivo LPS injection resulted in an increased percentage of circulating monocytes producing IL‐1β, TNFα and IL‐12 only at 3 h after the LPS injection. This was dose‐dependently inhibited by RWJ‐67657 treatment. LPS‐hyporesponsiveness to in vitro LPS treatment was most prominent at 3 and 6 h after the in vivo LPS injection; compared with pre‐medication monocytes, at these intervals a reduced percentage of monocytes produced IL‐1β, TNFα or IL‐12 after the in vitro LPS stimulus. At t = 6 h, this LPS‐hyporesponsiveness could dose‐dependently be inhibited by RWJ‐67657 treatment of the volunteers. We therefore conclude that p38 MAP kinase inhibition with RWJ‐67657 inhibited monocyte production of cytokines following in vivo LPS injection. Treatment with RWJ‐67657 also reversed the LPS‐hyporesponsiveness. Whether this result can be extended to the clinical situation remains to be elucidated. Patients with sepsis or an otherwise high risk for multi‐organ failure are potential study groups.