The role of pro-opiomelanocortin in the ACTH-cortisol dissociation of sepsis

A dopamine D1-like receptor-specific agonist improves the survival of septic mice

In this study, a murine sepsis model was developed using the cecum ligation and puncture (CLP) technique. The expression of the proinflammatory cytokines tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) in the brain increased 6 h after CLP but decreased 24 h later when elevated endogenous dopamine levels in the brain were sustained. Methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride reduced dopamine levels in the striatum and increased mortality in septic mice. Dopamine D1-like receptors were significantly expressed in the brain, but not in the lungs. Intraperitoneally administered SKF-81297 (SKF), a blood-brain barrier-permeable D1-like receptor agonist, prevented CLP-induced death of septic mice with ameliorated acute lung injury and cognitive dysfunction and suppressed TNF-α and IL-1β expression. The D1-like receptor antagonist SCH-23390 abolished the anti-inflammatory effects of SKF. These data suggest that D1-like receptor-mediated signals in the brain prevent CLP-induced inflammation in both the brain and the periphery.

Pro-opiomelanocortin and ACTH-cortisol dissociation during pediatric cardiac surgery

In critically ill adults, high plasma cortisol in face of low ACTH coincides with high pro-opiomelanocortin (POMC) levels. Glucocorticoids further lower ACTH without affecting POMC. We hypothesized that in pediatric cardiac surgery-induced critical illness, plasma POMC is elevated, plasma ACTH transiently rises intraoperatively but becomes suppressed post-operatively, and glucocorticoid administration amplifies this phenotype. From 53 patients (0-36 months), plasma was obtained pre-operatively, intraoperatively and on post-operative day 1 and 2. Plasma was also collected from 24 healthy children. In patients, POMC was supra-normal pre-operatively (p<0.0001) but no longer thereafter (p<0.05). ACTH was never high in patients. While in glucocorticoid-naive patients ACTH became suppressed by post-operative day 1 (p<0.0001), glucocorticoid-treated patients had suppressed ACTH already intraoperatively (p≤0.0001). Pre-operatively high POMC, not accompanied by increased plasma ACTH, suggests a centrally-activated HPA-axis with reduced pituitary processing of POMC into ACTH. Increasing systemic glucocorticoid availability with glucocorticoid treatment accelerated the suppression of plasma ACTH.

The Hypothalamus-pituitary-adrenocortical Response to Critical Illness: A Concept in Need of Revision

Based on insights obtained during the past decade, the classical concept of an activated hypothalamus-pituitary-adrenocortical axis in response to critical illness is in need of revision. After a brief central hypothalamus-pituitary-adrenocortical axis activation, the vital maintenance of increased systemic cortisol availability and action in response to critical illness is predominantly driven by peripheral adaptations rather than by an ongoing centrally activated several-fold increased production and secretion of cortisol. Besides the known reduction of cortisol-binding proteins that increases free cortisol, these peripheral responses comprise suppressed cortisol metabolism in liver and kidney, prolonging cortisol half-life, and local alterations in expression of 11βHSD1, glucocorticoid receptor-α (GRα), and FK506 binding protein 5 (FKBP51) that appear to titrate increased GRα action in vital organs and tissues while reducing GRα action in neutrophils, possibly preventing immune-suppressive off-target effects of increased systemic cortisol availability. Peripherally increased cortisol exerts negative feed-back inhibition at the pituitary level impairing processing of pro-opiomelanocortin into ACTH, thereby reducing ACTH-driven cortisol secretion, whereas ongoing central activation results in increased circulating pro-opiomelanocortin. These alterations seem adaptive and beneficial for the host in the short term. However, as a consequence, patients with prolonged critical illness who require intensive care for weeks or longer may develop a form of central adrenal insufficiency. The new findings supersede earlier concepts such as "relative," as opposed to "absolute," adrenal insufficiency and generalized systemic glucocorticoid resistance in the critically ill. The findings also question the scientific basis for broad implementation of stress dose hydrocortisone treatment of patients suffering from acute septic shock solely based on assumption of cortisol insufficiency.

Sepsis and Adrenal Insufficiency

In sepsis, dysregulation of the hypothalamic-pituitary-adrenal axis, alterations in cortisol metabolism, and tissue resistance to glucocorticoids can all result in relative adrenal insufficiency or critical illness-related corticosteroid insufficiency (CIRCI). The symptoms and signs of CIRCI during sepsis are nonspecific, generally including decreased mental status, unexplained fever, or hypotension refractory to fluids, and the requirement of vasopressor therapy to maintain adequate blood pressure. While we have been aware of this syndrome for over a decade, it remains a poorly understood condition, challenging to diagnose, and associated with significantly diverging practices among clinicians, particularly regarding the optimal dosing and duration of corticosteroid therapy. The existing literature on corticosteroid use in patients with sepsis and septic shock is vast with dozens of randomized controlled trials conducted across the past 4 decades. These studies have universally demonstrated reduced duration of shock, though the effects of corticosteroids on mortality have been inconsistent, and their use has been associated with adverse effects including hyperglycemia, neuromuscular weakness, and an increased risk of infection. In this article, we aim to provide a thorough, evidence-based, and practical review of the current recommendations for the diagnosis and management of patients with sepsis who develop CIRCI, explore the controversies surrounding this topic, and highlight what lies on the horizon as new evidence continues to shape our practice.

Sepsis-Induced Acute Lung Injury Is Alleviated by Small Molecules from Dietary Plants via Pyroptosis Modulation

Sepsis-induced acute respiratory distress syndrome (ARDS) has high morbidity and mortality, and it has three major pathogeneses, namely alveolar-capillary barrier destruction, elevated gut permeability, and reduced neutrophil extracellular traps (NETS), all of which are pyroptosis-involved. Due to limitations of current agents like adverse reaction superposition, inevitable drug resistance, and relatively heavier financial burden, naturally extracted small-molecule compounds have a broad market even though chemically modified drugs have straightforward efficacy. Despite increased understanding of the molecular biology and mechanism underlying sepsis-induced ARDS, there are no specific reviews concerning how small molecules from dietary plants alleviate sepsis-induced acute lung injury (ALI) via regulating pyroptotic cell death. Herein, we traced and reviewed the molecular underpinnings of sepsis-induced ALI with a focus on small-molecule compounds from dietary plants, the top three categories of which are respectively flavonoids and flavone, terpenoids, and polyphenol and phenolic acids, and how they rescued septic ALI by restraining pyroptosis.

Lipid oxidation dysregulation: an emerging player in the pathophysiology of sepsis

Sepsis is a life-threatening organ dysfunction caused by abnormal host response to infection. Millions of people are affected annually worldwide. Derangement of the inflammatory response is crucial in sepsis pathogenesis. However, metabolic, coagulation, and thermoregulatory alterations also occur in patients with sepsis. Fatty acid mobilization and oxidation changes may assume the role of a protagonist in sepsis pathogenesis. Lipid oxidation and free fatty acids (FFAs) are potentially valuable markers for sepsis diagnosis and prognosis. Herein, we discuss inflammatory and metabolic dysfunction during sepsis, focusing on fatty acid oxidation (FAO) alterations in the liver and muscle (skeletal and cardiac) and their implications in sepsis development.

The hypothalamus-pituitary-adrenal axis in sepsis- and hyperinflammation-induced critical illness: Gaps in current knowledge and future translational research directions

The classical model of the vital increase in systemic glucocorticoid availability in response to sepsis- and hyperinflammation-induced critical illness is one of an activated hypothalamus-pituitary-adrenocortical axis. However, research performed in the last decade has challenged this rather simple model and has unveiled a more complex, time-dependent set of responses. ACTH-driven cortisol production is only briefly increased, rapidly followed by orchestrated peripheral adaptations that maintain increased cortisol availability for target tissues without continued need for increased cortisol production and by changes at the target tissues that guide and titrate cortisol action matched to tissue-specific needs. One can speculate that these acute changes are adaptive and that treatment with stress-doses of hydrocortisone may negatively interfere with these adaptive changes. These insights also suggest that prolonged critically ill patients, treated in the ICU for several weeks, may develop central adrenal insufficiency, although it remains unclear how to best diagnose and treat this condition.

Novel insights in endocrine and metabolic pathways in sepsis and gaps for future research

Sepsis is defined as any life-threatening organ dysfunction caused by a dysregulated host response to infection. It remains an important cause of critical illness and has considerable short- and long-term morbidity and mortality. In the last decades, preclinical and clinical research has revealed a biphasic pattern in the (neuro-)endocrine responses to sepsis as to other forms of critical illness, contributing to development of severe metabolic alterations. Immediately after the critical illness-inducing insult, fasting- and stress-induced neuroendocrine and cellular responses evoke a catabolic state in order to provide energy substrates for vital tissues, and to concomitantly activate cellular repair pathways while energy-consuming anabolism is postponed. Large randomized controlled trials have shown that providing early full feeding in this acute phase induced harm and reversed some of the neuro-endocrine alterations, which suggested that the acute fasting- and stress-induced responses to critical illness are likely interlinked and benefical. However, it remains unclear whether, in the context of accepting virtual fasting in the acute phase of illness, metabolic alterations such as hyperglycemia are harmful or beneficial. When patients enter a prolonged phase of critical illness, a central suppression of most neuroendocrine axes follows. Prolonged fasting and central neuroendocrine suppression may no longer be beneficial. Although pilot studies have suggested benefit of fasting-mimicking diets and interventions that reactivate the central neuroendocrine suppression selectively in the prolonged phase of illness, further study is needed to investigate patient-oriented outcomes in larger randomized trials.

Critical Illness-induced Corticosteroid Insufficiency: What It Is Not and What It Could Be

Critical illnesses are hallmarked by increased systemic cortisol availability, a vital part of the stress response. Acute stress may trigger a life-threatening adrenal crisis when a disease of the hypothalamic-pituitary-adrenal (HPA) axis is present and not adequately treated with stress doses of hydrocortisone. Stress doses of hydrocortisone are also used to reduce high vasopressor need in patients suffering from septic shock, in the absence of adrenal insufficiency. Research performed over the last 10 years focusing on the HPA axis during critical illness has led to the insight that neither of these conditions can be labeled "critical illness-induced corticosteroid insufficiency" or CIRCI. Instead, these data suggested using the term CIRCI for a condition that may develop in prolonged critically ill patients. Indeed, when patients remain dependent on vital organ support for weeks, they are at risk of acquiring central adrenal insufficiency. The sustained increase in systemic glucocorticoid availability, mainly brought about by suppressed circulating cortisol-binding proteins and suppressed hepatic/renal cortisol metabolism, exerts negative feedback inhibition at the hypothalamus/pituitary, while high levels of other glucocorticoid receptor ligands, such as bile acids, and drugs, such as opioids, may further suppress adrenocorticotropic hormone (ACTH) secretion. The adrenal cortex, depleted from ACTH-mediated trophic signaling for weeks, may become structurally and functionally impaired, resulting in insufficient cortisol production. Such a central HPA axis suppression may be maladaptive by contributing to lingering vasopressor need and encephalopathy, hence preventing recovery. Here, we review this concept of CIRCI and we advise on how to recognize and treat this poorly understood condition.

Cortisol Levels During Acute Illnesses in Children and Adolescents: A Systematic Review

Importance

Endogenous cortisol levels in children and adolescents during acute illnesses can contribute to the evidence base required to optimize glucocorticoid (GC) stress doses for children and adolescents known to have GC deficiency.

Objective

To identify endogenous cortisol levels during a range of acute illnesses in children and adolescents without GC deficiency from published evidence.

Evidence Review

CINAHL, Cochrane Library, Cochrane Database of Systematic Reviews, Embase, and MEDLINE were searched for studies published between January 1, 2000, and June 30, 2020. Two reviewers independently identified relevant studies. Differences were resolved by joint discussion. Inclusion criteria were common acute illnesses, age from 1 month to 18 years, and basal blood cortisol levels obtained within 48 hours of presentation. Studies with fewer than 5 participants and those that included participants known to have GC deficiency or a history of treatment that could affect cortisol levels were excluded from the review. Data for predefined fields were extracted and independently checked by separate pairs of reviewers. Overall weighted means and pooled SDs for cortisol levels were calculated.

Findings

All 15 studies included were hospital based and included 864 unique participants: 14 studies were prospective observational studies, 1 was part of a trial, and 5 included control individuals. Mean cortisol levels were higher in all participants with an acute illness (n = 689) than in controls (n = 175) (difference in weighted means, 18.95 μg/dL; 95% CI, 16.68-21.22 μg/dL). Cortisol levels were highest in patients with bacterial meningitis (weighted mean [pooled SD], 46.42 [22.24] μg/dL) and were more than 3-fold higher in the group with severe gastroenteritis (weighted mean [pooled SD], 39.64 [21.34] μg/dL) than in the control group. Among the subgroups with sepsis, those with shock had lower cortisol levels than those without shock (weighted mean [pooled SD], 27.83 [36.39] μg/dL vs 37.00 [23.30] μg/dL), but levels in nonsurvivors did not differ from levels in survivors (weighted mean [pooled SD], 24.89 [51.65] μg/dL vs 30.53 [30.60] μg/dL).

Conclusions and Relevance

This systematic review found that, in children and adolescents without GC deficiency, circulating cortisol levels were higher during acute illnesses than those in controls and also varied across a range of acute illnesses. Whether these levels need to be achieved with exogenous GC stress doses tailored according to the nature and severity of the illness in children and adolescents with GC deficiency warrants investigation.

Impact of duration of critical illness and level of systemic glucocorticoid availability on tissue-specific glucocorticoid receptor expression and actions: A prospective, observational, cross-sectional human and two translational mouse studies

Background

Reduced glucocorticoid-receptor (GR) expression in blood suggested that critically ill patients become glucocorticoid-resistant necessitating stress-doses of glucocorticoids. We hypothesised that critical illness evokes a tissue-specific, time-dependent expression of regulators of GR-action which adaptively guides glucocorticoid action to sites of need.

Methods

We performed a prospective, observational, cross-sectional human study and two translational mouse studies. In freshly-isolated neutrophils and monocytes and in skeletal muscle and subcutaneous adipose tissue of 137 critically ill patients and 20 healthy controls and in skeletal muscle and adipose tissue as well as in vital tissues (heart, lung, diaphragm, liver, kidney) of 88 septic and 26 healthy mice, we quantified gene expression of cortisone-reductase 11β-HSD1, glucocorticoid-receptor-isoforms GRα and GRβ, GRα-sensitivity-regulating-co-chaperone FKBP51, and GR-action-marker GILZ. Expression profiles were compared in relation to illness-duration and systemic-glucocorticoid-availability.

Findings

In patients’ neutrophils, GRα and GILZ were substantially suppressed (p≤0·05) throughout intensive care unit (ICU)-stay, while in monocytes low/normal GRα coincided with increased GILZ (p≤0·05). FKBP51 was increased transiently (neutrophils) or always (monocytes,p≤0·05). In patients’ muscle, 11β-HSD1 and GRα were low-normal (p≤0·05) and substantially suppressed in adipose tissue (p≤0·05); FKBP51 and GILZ were increased in skeletal muscle (p≤0·05) but normal in adipose tissue. GRβ was undetectable. Increasing systemic glucocorticoid availability in patients independently associated with further suppressed muscle 11β-HSD1 and GRα, further increased FKBP51 and unaltered GILZ (p≤0·05). In septic mouse heart and lung, 11β-HSD1, FKBP51 and GILZ were always high (p≤0·01). In heart, GRα was suppressed (p≤0·05), while normal or high in lung (all p≤0·05). In diaphragm, 11β-HSD1 was high/normal, GRα low/normal and FKBP51 and GILZ high (p≤0·01). In kidney, 11β-HSD1 transiently increased but decreased thereafter, GRα was normal and FKBP51 and GILZ high (p≤0·01). In liver, 11β-HSD1 was suppressed (p≤0·01), GRα normal and FKBP51 high (p≤0·01) whereas GILZ was transiently decreased but elevated thereafter (p≤0·05). Only in lung and diaphragm, treatment with hydrocortisone further increased GILZ.

Interpretation

Tissue-specific, time-independent adaptations to critical illness guided GR-action predominantly to vital tissues such as lung, while (partially) protecting against collateral harm in other cells and tissues, such as neutrophils. These findings argue against maladaptive generalised glucocorticoid-resistance necessitating glucocorticoid-treatment.

Funding

Research-Foundation-Flanders, Methusalem-Program-Flemish-Government, European-Research-Council, European-Respiratory-Society.

Impact of Hydrocortisone and of CRH Infusion on the Hypothalamus-Pituitary-Adrenocortical Axis of Septic Male Mice

PURPOSE

Sepsis is hallmarked by high plasma cortisol/corticosterone (CORT), low adrenocorticotropic hormone (ACTH), and high pro-opiomelanocortin (POMC). While corticotropin-releasing hormone-(CRH) and arginine-vasopressin (AVP)-driven pituitary POMC expression remains active, POMC processing into ACTH becomes impaired. Low ACTH is accompanied by loss of adrenocortical structure, although steroidogenic enzymes remain expressed. We hypothesized that treatment of sepsis with hydrocortisone (HC) aggravates this phenotype whereas CRH infusion safeguards ACTH-driven adrenocortical structure.

METHODS

In a fluid-resuscitated, antibiotics-treated mouse model of prolonged sepsis, we compared the effects of HC and CRH infusion with placebo on plasma ACTH, POMC, and CORT; on markers of hypothalamic CRH and AVP signaling and pituitary POMC processing; and on the adrenocortical structure and markers of steroidogenesis. In adrenal explants, we studied the steroidogenic capacity of POMC.

RESULTS

During sepsis, HC further suppressed plasma ACTH, but not POMC, predominantly by suppressing sepsis-activated CRH/AVP-signaling pathways. In contrast, in CRH-treated sepsis, plasma ACTH was normalized following restoration of pituitary POMC processing. The sepsis-induced rise in markers of adrenocortical steroidogenesis was unaltered by CRH and suppressed partially by HC, which also increased adrenal markers of inflammation. Ex vivo stimulation of adrenal explants with POMC increased CORT as effectively as an equimolar dose of ACTH.

CONCLUSIONS

Treatment of sepsis with HC impaired integrity and function of the hypothalamic-pituitary-adrenal axis at the level of the pituitary and the adrenal cortex while CRH restored pituitary POMC processing without affecting the adrenal cortex. Sepsis-induced high-circulating POMC may be responsible for ongoing adrenocortical steroidogenesis despite low ACTH.

Solumedrol Treatment for Severe Sepsis in Humans with a Blunted Adrenocorticotropic Hormone-Cortisol Response: A Prospective Randomized Double-Blind Placebo-Controlled Pilot Clinical Trial

PURPOSE

To test the benefits of Solumedrol treatment in sepsis patients with a blunted adrenocorticotropic hormone (ACTH)-cortisol response (delta <13 µg/dL) with regard to the number of days on ventilator, days on intravenous blood pressure support, length of time in an intensive care unit (ICU), 14-day mortality, and 28-day mortality. The trial was prospective, randomized, and double-blind. As part of a larger sepsis trial, 54 patients with sepsis had an intravenous ACTH stimulation test using 250 µg of ACTH, and serum cortisol was measured at times 0, 30, and 60 min. Eleven patients failed to increase their cortisol concentration above 19.9 µg/dL and were excluded from the clinical trial as they were considered to have adrenal insufficiency. The remaining 43 patients had a baseline cortisol of 32 ± 1 µg/dL increased to 38 ± 3 µg/dL at 30 min and 40 ± 3 at 60 min. All cortisol responses were <12.9 µg/dL between time 0 and time 60, which is defined as a blunted cortisol response to intravenous ACTH administration. Twenty-one were randomized to receive 20 mg of intravenous Solumedrol and 22 were randomized to receive a matching placebo every 8 h for 7-days. There was no significant difference between the two randomized groups. Data analysis was carried out bya two-tailed test and P < .05 as significant.

RESULTS

Results: The mean age was 51 ± 2 (mean ± SEM) with 61% female. Groups were well matched with regard to APACHE III score in Solumedrol versus placebo (59 ± 6 vs 59 ± 6), white blood cell count (18.8 ± 2.2 vs 18.6 ± 2.6), and incidence of bacteremia (29 vs 39%). The 28-day mortality rate was reduced in the Solumedrol treated arm (43 ± 11 vs 73 ± 10%; P < .05). There was no change in days in ICU, days on blood pressure agents, or days on ventilator. Seven days of high-dose intravenous Solumedrol treatment (20 mg every 8 h) in patients with a blunted cortisol response to ACTH was associated with an improved 28-day survival. This small study suggests that an inability to increase endogenous cortisol production in patients with sepsis who are then provided steroid treatment could improve survival.

Adrenal function/dysfunction in critically ill patients: a concise narrative review of recent novel insights

The "fight or flight" response to critical illness relies on increased cortisol availability, traditionally attributed to several-fold-increased cortisol production via hypothalamus-pituitary-adrenal-axis activation. Recent studies provided evidence against this concept with clinical implications. First, high cortisol availability during critical illness is driven by suppressed cortisol binding and reduced cortisol breakdown rather than increased cortisol production. This implies reduction of hydrocortisone doses when prescribed in ICU. Second, plasma ACTH is low, explained by feedback inhibition by peripherally driven high free cortisol and/or other central glucocorticoid-receptor ligands. Third, ICU patients have elevated plasma concentrations of the ACTH-precursor hormone, pro-opiomelanocortin, because of impaired pituitary processing into ACTH, and pro-opiomelanocortin could drive some adrenocortical cortisol production in face of low ACTH. Fourth, in prolonged critically ill patients, endogenously suppressed ACTH, aggravated by exogenous corticosteroids, associates with poor outcome. In long-stay ICU patients, central adrenal insufficiency may occur due to lack of trophic ACTH signaling. Finally, the Cosyntropin test is not suitable to assess adrenocortical reserve in ICU patients as the test is confounded by increased cortisol distribution volume. These insights necessitate further research focusing on the need, if any, of treating ICU patients with corticosteroids, and timing thereof, outside indications for pharmacological anti-inflammatory drugs.