The primary objective of this study was to determine the effect of increasing doses of prednisolone on the release of novel biomarkers during human endotoxemia. We show here that prednisolone pharmacologic concentrations peaked at the time of LPS infusion and that the release of MR-proADM, MR-proANP and CT-proAVP was subsequently inhibited in a dose-dependent way. The levels of PCT were not significantly inhibited within the study period of 24 h. However, previously inhibition of PCT was shown by anti-inflammatory agents within a period of 168 h [9
]. The levels of CT-proAVP were, remarkably, increased after prednisolone 3 mg, yet the reason for this remains unclear because the pattern was unique to this biomarker.
The increased levels of MR-proANP, MR-proADM and CT-proAVP reflect activation of their mature counterparts. Difficulties in measurement of the mature hormones made it difficult to determine their roles during sepsis [5
]. The currently investigated biomarkers are produced after proteolytic processing of the same prohormone precursors as the mature hormones; thus, they reflect production levels of mature hormones in stoichiometric concentrations [7
]. In theory, the biomarker assays may measure levels of both cut prohormone fragments and full-length prohormones. However, the meaning of this relationship remains unclear in plasma because no well-defined methods are currently available for measurement of full-length prohormone plasma levels.
The biomarker levels in this study were dose-dependently influenced by corticosteroid intervention, which is important for treatment effect monitoring. The development of new biomarkers is needed for improvement of sepsis stratification methods, which influence trial outcomes. Several sepsis intervention strategies have shown promise [16
]; in this study corticosteroids were selected because they aim primarily at inhibition of the immune response, and for this intervention in particular, effects are dose-dependent and improvement of patient stratification methods is urgently needed [11
]. Prednisolone is among the most frequently applied corticosteroids [18
]; the oral route is convenient and potentially safer than intravenous administration [19
The doses of prednisolone used in our model were chosen according to common dose regimens for prednisolone [18
]. These doses were relatively low (equivalent to 12, 40 and 120 mg hydrocortisone) in comparison to doses used for sepsis intervention (hydrocortisone 200–300 mg per day), yet sufficient to reduce the release of the investigated biomarkers during endotoxemia. Of note, it has been demonstrated that the effects of orally administered doses of prednisolone do not differ from those of comparable doses of intravenously administered hydrocortisone [20
The human endotoxemia model differs from sepsis in many aspects: it uses a single-dose drug intervention and bolus intravenous challenge of LPS, it is self-limiting, and it lacks an infectious source [13
]. The study subjects are healthy young people not using any co-medication. The intervention must be administered before LPS injection in order to reach clinically relevant drug concentrations during endotoxemia because LPS is extremely quickly cleared from the circulation. Due to these differences, data cannot be directly extrapolated to the sepsis field and must always be confirmed in patient studies. Nonetheless, the model is the best available in healthy humans and has proven useful to obtain a proof of principle of the actions of drugs and/or to study mechanisms that contribute to the activation of inflammatory pathways [13
]. With these limitations in mind, we demonstrate here that the levels of the novel biomarkers MR-proADM, MR-proANP, CT-proAVP and PCT are all increased after LPS injection, and that the levels of MR-proADM, MR-proANP and CT-proAVP can be inhibited by prednisolone. These results add to their potential as biomarkers in sepsis.