This exploratory analysis of glucocorticoid and mineralocorticoid steroids before and after stimulation with a corticotropin analogue yields well-known and novel results on adrenocortical function in sepsis. Both the glucocorticoid and the mineralocorticoid pathway are activated in sepsis, recognizable by the elevated 11-desoxycortisol and 11-desoxycorticosterone concentrations prior to corticotropin stimulation. Compared to healthy individuals, this leads to elevated cortisol but not corticosterone levels. After stimulation with corticotropin, the corticosterone response is more often attenuated in sepsis patients. Patients who died in the hospital show the lowest dynamic corticosterone response to corticotropin stimulation, which is significantly different from in-hospital survivors of sepsis. Excess cortisol over corticosterone is associated with increased shock development and mortality.
A new finding in this exploratory analysis is the impaired mineralocorticoid steroidogenesis in sepsis. Although levels of 11-desoxycorticosterone (precursor of corticosterone) were elevated, this did not result in elevated corticosterone levels. Stimulation with corticotropin clearly unmasked this impediment to corticosterone synthesis despite high precursor levels. In particular, patients with pronounced corticosterone deficiency died more often in hospital.
Corticosterone can be stimulated 4 to 15 times more by corticotropin in healthy humans compared to cortisol (2, 16, 21). Conditions like sepsis appear to significantly impede its stimulability by corticotropin. It is noteworthy that 11ß-hydroxylase (i.e. CYP11B2), which catalyzes the conversion of 11-desoxycorticosterone into corticosterone, is localized on the inner mitochondrial membrane (22, 23). It is conceivable that mitochondrial dysfunction, as can typically occur in sepsis, hinders this enzymatic step (5, 24). For example, the expression of steroidogenic acute regulatory protein (StAR) activity early in sepsis can affect this part of steroidogenesis by reducing the transport of cholesterol from the outer to the inner mitochondrial membrane (25, 26). Unlike cortisol these enzymatic steps appear to be essential for corticosterone.
In many animal species, corticosterone plays the central role in the stress response. In humans, this function falls to cortisol. The exact role of corticosterone in human physiology, other than its role as a precursor of aldosterone, is still unclear. Corticosterone has a higher affinity for the mineralocorticoid receptor (MR) than cortisol and can be detected in higher concentrations in cerebrospinal fluid than in serum (17). Serial measurements of corticosterone and cortisol revealed that the pulsed secretion of both steroids is well synchronized with peaks in the morning (16). Corticosterone metabolism is similar to cortisol with a slightly shorter half-life (21). Corticosterone is released solely through corticotropin and serum levels at rest are very low. In stressful conditions, corticotropin pulses ensure a highly dynamic supply of corticosterone (16, 17).
In a canine model of S. aureus pneumonia-induced septic shock the mineralocorticoid desoxycorticosterone (precursor of corticosterone) decreased sepsis-induced organ dysfunctions, reversed shock and improved survival when given prophylactically (27). This suggests that activation of the mineralocorticoid pathway has a protective effect. However, when deoxycorticosterone was administered after infectious challenge, this protective effect was not observed. It is conceivable that induced mitochondrial dysfunction impede this catalytic step towards corticosterone. The data of this study support the assumption that 11-deoxycorticosterone is no longer adequately converted to corticosterone in sepsis. When administered prophylactically, however, deoxycorticosterone should be converted to corticosterone unhindered. In this context, it is noteworthy that clinical trials that have so far been able to demonstrate an advantage for therapy with steroids in septic shock have always used the combination of hydrocortisone (predominantly a glucocorticoid) and fludrocortisone (a pure mineralocorticoid) (28, 29).
In this exploratory analysis, the cortisol to corticosterone ratio (CCR) after stimulation with corticotropin was identified to be a good predictor of clinical outcome. CCR reflects the balance in activation of both, the glucocorticoid and the mineralocorticoid pathways. If the mineralocorticoid pathway was too compromised compared to activation of the glucocorticoid pathway, and thus, if the CCR was too high, this was associated with a worse clinical outcome.
Like cortisol, corticosterone secretion is suppressed by exogenous steroids like dexamethasone (16). This underlines that corticosterone is dependent on corticotropin and may be compromised by any steroid treatment. For this reason, we separately analyzed the same endpoints in the HYPRESS group randomized to hydrocortisone treatment after corticotropin testing. When using the criterion of cortisol to corticosterone ratio found in patients not treated with hydrocortisone, we saw a different evolution of study endpoints in patients treated with hydrocortisone. Glucocorticoid excess, as determined by the corticotropin stimulated RCC > 32.2, did not predict the development of septic shock when patients were treated with hydrocortisone. A similar pattern was seen when looking at 90-day survival.
This exploratory study has several limitations. First, we measured only a subset of patients enrolled in the HYPRESS trial. Second, we cannot say what results steroid profiling will yield in patients with septic shock. HYPRESS deliberately recruited patients with sepsis without shock testing the hypothesis that with hydrocortisone the development of septic shock might be avoidable. Thirdly, we did not measure aldosterone in short intervals, which would have been necessary due to the significantly shorter half-life of aldosterone (approx. 20 minutes) to provide a better insight into the final pathway of the mineralocorticoid axis. It is quite conceivable that a deficiency of the precursor corticosterone may contribute to aldosterone deficiency in septic shock despite high renin activities (30).
The strengths of this exploratory study are that steroid profiling was performed using tandem mass spectrometry, which has a high analytical sensitivity and selectivity and thus the results are far less prone to be impaired by analytical problems of immunoassays (20, 31). This does not preclude measuring the stimulated cortisol-to-corticosterone ratio with immunoassays in future. The ratio of two key steroids may be less affected by analytical issues in sepsis such as increased volume of distribution. (7, 15). In addition, immunoassays of cortisol and corticosterone show low cross-reactivities (31). In this way, the RCC combined with corticotropin testing may offer an innovative approach to revisit diagnostic challenges in adrenocortical function during sepsis (20).
In conclusion, steroid profiling shows that the mineralocorticoid pathway is more frequently impaired than the glucocorticoid pathway in the stress response to sepsis. After corticotropin stimulation, patients with excess glucocorticoids over mineralocorticoids were more likely to develop septic shock and to die in hospital. The ratio of cortisol to corticosterone after stimulation with corticotropin can predict clinical endpoints such as shock development and mortality in sepsis and can be used to target hydrocortisone therapy. However, these hypotheses have yet to be prospectively validated in large cohorts of patients with sepsis or septic shock.