The impact of hydrocortisone treatment on neutrophil gelatinase-associated lipocalin release in porcine endotoxemic shock

Previous studies

The anti-inflammatory effect of glucocorticoids in septic systemic inflammation is well documented, and in a previous experimental study of ours [18], we concluded that steroid treatment prior to endotoxemia had beneficial circulatory effects, which were not mediated by TNF-alpha, IL-6, or NO. Although it is a matter of debate, hydrocortisone is advocated to treat septic shock [19, 20]. Timing of steroid administration could have impact on the survival rate [21]. In this study, we hypothesized that one of the anti-inflammatory mechanisms involved in endotoxin-induced systemic inflammatory response is the attenuation of neutrophil granulocyte activation. NGAL is concentrated within the granules of neutrophil granulocytes. These granules are released into the plasma upon substantial inflammatory stimulation [22] where NGAL exerts bacteriostatic effects [6] and activates neutrophil granulocytes among other functions. Although several other cell types are potential sources of NGAL [23], our data suggest that plasma NGAL is strongly associated to the neutrophil granulocytes. No association between NGAL and renal function was seen. Others have also reported NGAL to be a marker of inflammatory response rather than to that of sepsis [24–26] and specifically pointed out that the origin of NGAL in systemic inflammatory response is neutrophil granulocytes [27]. Endotoxin induces this release of NGAL from these cells via the Toll-like receptor 4 (TLR-4) [28].

To our knowledge, the diminished increase in plasma NGAL with pretreatment with hydrocortisone in the current study has not been reported previously in endotoxemia or sepsis. However, these findings correspond to those in other conditions such as AKI, where reduced oxidative stress [29] and attenuated neutrophil granulocyte response were suggested as possible mechanisms of steroid pretreatment on NGAL levels [30]. Steroids could potentially inhibit the production of NGAL though the IKKB/Nf-KB pathway, which is suppressed by these drugs [31]. We have previously described that hydrocortisone, given to endotoxin-exposed pigs [18], leads to increased circulatory stability in endotoxemic shock and chose NGAL to investigate further the role of neutrophil granulocyte activation. The current experiments show attenuated circulatory and acid-base response to endotoxin in pigs treated with hydrocortisone, but this effect was only partly related to the timing of this treatment. In contrast, the inflammatory response including lower NGAL levels and higher white blood cell counts if hydrocortisone was administered prior to the endotoxin infusion, but not later. This may be contradictory since the release of NGAL occurs early in granulocyte differentiation [7], and given the high turnover and the short half-life of these cells in endotoxemia [32] as well as the short half-life of NGAL [33], one would have expected that the timing of hydrocortisone should not have impacted on neutrophil activation in these experiments. However, released NGAL has not only bacteriostatic functions, but also has an important role in the maturation and activation of neutrophil granulocytes [34, 35], i.e., NGAL-mediated neutrophil activation is a positive feedback loop triggered by e.g., endotoxemia. We therefore postulate that decreased NGAL levels may inhibit the additional recruitment of neutrophils i.e., limiting the inflammatory response. The importance of NGAL in the neutrophil-mediated inflammatory response has been described in NGAL-deficient mice and men [35].

Finally, we did not find a consistent effect of timing on the circulatory effects of hydrocortisone in our study. A possible explanation could be that these effects, apart from the inflammatory response may also be mediated by other mechanisms, e.g., inducible NO synthase [36]. However, there was a strong association between plasma NGAL and circulatory failure induced by endotoxin in this experiment.