Endotoxin tolerance of adrenal gland: attenuation of corticosterone production in response to lipopolysaccharide and adrenocorticotropic hormone

The Adrenal Cortex, an Underestimated Site of SARS-CoV-2 Infection

BACKGROUND

The majority of the critically ill patients may have critical illness-related corticosteroid insufficiency (CIRCI). The therapeutic effect of dexamethasone may be related to its ability to improve cortical function. Recent study showed that dexamethasone can reduce COVID-19 deaths by up to one third in critically ill patients. The aim of this article is to investigate whether SARS-CoV-2 can attack the adrenal cortex to aggravate the relative adrenal insufficiency.

METHODS

We summarized the clinical features of COVID-19 reported in currently available observational studies. ACE2 and TMPRSS2 expression was examined in human adrenal glands by immunohistochemical staining. We retrospectively analyzed serum cortisol levels in critically ill patients with or without COVID-19.

RESULTS

High percentage of critically ill patients with SARS-COV-2 infection in the study were treated with vasopressors. ACE2 receptor and TMPRSS2 serine protease were colocalized in adrenocortical cells in zona fasciculata and zona reticularis. We collected plasma cortisol concentrations in nine critically ill patients with COVID-19. The cortisol levels of critically ill patients with COVID-19 were lower than those in non-COVID-19 critically ill group. Six of the nine COVID-19 critically ill patients had random plasma cortisol concentrations below 10 µg/dl, which met the criteria for the diagnosis of CIRCI.

CONCLUSION

We demonstrate that ACE2 and TMPRSS2 are colocalized in adrenocortical cells, and that the cortisol levels are lower in critically ill patients with COVID-19 as compared to those of non-COVID-19 critically ill patients. Based on our findings, we recommend measuring plasma cortisol level to guide hormonal therapy.

Evidence in Favor of an Alternative Glucocorticoid Synthesis Pathway During Acute Experimental Chagas Disease

It is well-established that infectious stress activates the hypothalamus-pituitary-adrenal axis leading to the production of pituitary adrenocorticotropin (ACTH) and adrenal glucocorticoids (GCs). Usually, GC synthesis is mediated by protein kinase A (PKA) signaling pathway triggered by ACTH. We previously demonstrated that acute murine Chagas disease courses with a marked increase of GC, with some data suggesting that GC synthesis may be ACTH-dissociated in the late phase of this parasitic infection. Alternative pathways of GC synthesis have been reported in sepsis or mental diseases, in which interleukin (IL)-1β, prostaglandin E2 (PGE2), and/or cAMP-activated guanine nucleotide exchange factor 2 (EPAC2) are likely to play a role in this regard. Accordingly, we have searched for the existence of an ACTH-independent pathway in an experimental model of a major parasitic disease like Chagas disease, in addition to characterizing potential alternative pathways of GC synthesis. To this end, C57BL/6 male mice were infected with T. cruzi (Tc), and evaluated throughout the acute phase for several parameters, including the kinetic of GC and ACTH release, the adrenal level of MC2R (ACTH receptor) expression, the p-PKA/PKA ratio as ACTH-dependent mechanism of signal transduction, as well as adrenal expression of IL-1β and its receptor, EPAC2 and PGE2 synthase. Our results reveal the existence of two phases involved in GC synthesis during Tc infection in mice, an initial one dealing with the well-known ACTH-dependent pathway, followed by a further ACTH-hyporesponsive phase. Furthermore, inflamed adrenal microenvironment may tune the production of intracellular mediators that also operate upon GC synthesis, like PGE2 synthase and EPAC2, as emerging driving forces for GC production in the advanced course of Tc infection. In essence, GC production seems to be associated with a biphasic action of PGE2, suggesting that the effect of PGE2/cAMP in the ACTH-independent second phase may be mediated by EPAC2.

High Glucose Induces Mouse Mesangial Cell Overproliferation via Inhibition of Hydrogen Sulfide Synthesis in a TLR-4-Dependent Manner

Background/Aims: Overproliferation of mesangial cells was believed to play an important role in the progress of diabetic nephropathy, one of the primary complications of diabetes. Hydrogen sulfide (H2S), a well-known and pungent gas with the distinctive smell of rotten eggs, was discovered to play a protective role in diabetic nephropathy. Methods: MTT assay was used to examine the viability of mesangial cells. Small interfering RNA was used to knock down the expression of TLR4 while specific inhibitor LY294002 to suppress the function of PI3K. H2S generation rate was determined by a H2S micro-respiration sensor. Results: Glucose of 25mM induced significant mesangial cells proliferation, which was accomplished by significantly inhibited endogenous H2S synthesis. And exogenous H2S treatment by NaHS markedly mitigated the overproliferation of mouse mesangial cells. Furthermore, it was found that H2S deficiency could result in TLR4 activation. And H2S supplementation remarkably inhibited TLR4 expression and curbed the mesangial cell overproliferation. Besides, PI3K/Akt pathway inhibition also significantly ameliorated the cell overproliferation. Conclusion: High glucose (HG) induces mouse mesangial cell overproliferation via inhibition of hydrogen sulfide synthesis in a TLR-4-dependent manner. And PI3K/Akt pathway might also play a vital part in the HG-induced mesangial cell overproliferation.

Etomidate Mitigates Lipopolysaccharide-Induced CD14 and TREM-1 Expression, NF-κB Activation, and Pro-inflammatory Cytokine Production in Rat Macrophages

This study was aimed at investigating the effect of etomidate on the viability of rat macrophages and the function of lipopolysaccharide (LPS)-stimulated macrophages as well as the potential mechanisms. Rat macrophages were isolated and treated with different doses of etomidate for 24 h, and their viability was determined by the CCK-8 assay. Furthermore, macrophages were treated with, or without, 1 μg/ml of LPS, and/or 2.5 or 5 μM etomidate in the presence or absence of a TREM-1 inhibitor (LP17, 100 ng/ml), and the levels of TNF-α, IL-6, CD14, and TREM-1 in the different groups of cells were determined by quantitative RT-PCR, ELISA, and Western blot assays. The levels of NF-κB activation in the different groups of cells were analyzed by an electrophoretic mobility shift assay (EMSA). Etomidate at 31.25 μM or a low dose did not affect the viability of rat macrophages, while etomidate at higher doses reduced the viability of macrophages in vitro. Treatment with 2.5 or 5 μM etomidate or with LP17 alone did not affect the levels of TNF-α, IL-6, CD-14, and TREM-1 in macrophages. Treatment with etomidate significantly mitigated LPS-stimulated TNF-α, IL-6, CD-14, and TREM-1 expression (p < 0.05 for all) and inhibited LPS-induced NF-κB activation in macrophages in vitro. However, treatment with both etomidate and LP17 did not enhance the inhibitory effects in macrophages. Hence, etomidate mitigates LPS-up-regulated pro-inflammatory cytokine production and inhibits LPS-enhanced CD14 and TREM-1 expression and NF-κB activation in macrophages.

Resveratrol alleviates endotoxemia-associated adrenal insufficiency by suppressing oxidative/nitrative stress

We have recently demonstrated that endotoxin causes oxidative stress and overproduction of nitric oxide in adrenal glands, thereby leading to adrenocortical insufficiency. The aim of this study is to investigate the effects of resveratrol, a natural plant polyphenol with anti-oxidant and anti-nitrative properties, on endotoxemia-associated adrenocortical insufficiency. Resveratrol was administered immediately before injection of lipopolysaccharide (LPS). Twenty four hours later, the adrenocorticotropic hormone (ACTH) stimulation tests was been performed to measure the plasma corticosterone level and the adrenal gland tissues were collected for histopathologic examination, and determination of malondialdehyde (MDA), total antioxidant capacity (T-AOC), superoxide dismutase (SOD) activity, catalase (CAT) activity, inducible nitric oxide synthase (iNOS) expression, nitric oxide (NO) and peroxynitrite production. Treatment with resveratrol significantly inhibited endotoxemia-induced iNOS expression, NO production, and peroxynitrite formation and also attenuated LPS-induced oxidative stress in the adrenal gland, as evidenced by the decrease of pro-oxidant biomarker (MDA), and the increases of anti-oxidant biomarkers (T-AOC, CAT and SOD activity). H&E staining demonstrated that administration of LPS resulted in increased into the adrenal gland. H&E-stained sections of adrenal glands demonstrated signs of leukocyte infiltration and hemorrhage during endotoxemia, which were significantly improved by resveratrol treatment. In addition, resveratrol reversed the LPS-induced downregulation of ACTH receptor and silent information regulator 1 (SIRT1) in adrenal gland, as well as adrenocortical hyporesponsiveness to ACTH. Resveratrol exerts protective effects against endotoxemia-associated adrenocortical insufficiency by suppressing oxidative/nitrative stress. These findings support the potential for resveratrol as a possible pharmacological agent to improve adrenocortical insufficiency resulting from oxidative/nitrative damage.

Overfeeding during a critical postnatal period exacerbates hypothalamic-pituitary-adrenal axis responses to immune challenge: a role for adrenal melanocortin 2 receptors

Early life diet can critically program hypothalamic-pituitary-adrenal (HPA) axis function. We have previously shown rats that are overfed as neonates have exacerbated pro-inflammatory responses to immune challenge with lipopolysaccharide (LPS), in part by altering HPA axis responses, but how this occurs is unknown. Here we examined neonatal overfeeding-induced changes in gene expression in each step of the HPA axis. We saw no differences in glucocorticoid or mineralocorticoid receptor expression in key regions responsible for glucocorticoid negative feedback to the brain and no differences in expression of key HPA axis regulatory genes in the paraventricular nucleus of the hypothalamus or pituitary. On the other hand, expression of the adrenal melanocortin 2 receptor (MC2R) is elevated after LPS in control rats, but significantly less so in the neonatally overfed. The in vitro adrenal response to ACTH is also dampened in these rats, while the in vivo response to ACTH does not resolve as efficiently as it does in controls. These data suggest neonatal diet affects the efficiency of the adrenally-mediated response to LPS, potentially influencing how neonatally overfed rats combat bacterial infection.

The role of adrenal gland microenvironment in the HPA axis function and dysfunction during sepsis

Sepsis and septic shock in response to bacterial or viral infections remain the major health problem worldwide. Despite decades of intensive research and improvements in medical care, severe sepsis is associated with high mortality. Rapid activation of the adrenal gland glucocorticoid and catecholamine production is a fundamental component of the stress response and is essential for survival of the host. However, in many critically ill patients this homeostatic function of the adrenal gland is often impaired. In these patients, plasma levels of adrenocorticotropic hormone (ACTH) and cortisol are often dissociated. This has been attributed to the stimulatory action of non-ACTH factors within the adrenal gland such as cytokines, and recently with decreased cortisol metabolism and suppressed ACTH synthesis. Regulation of the hypothalamus-pituitary-adrenal (HPA) axis function during sepsis is a complex process which involves various immune and neuroendocrine interactions occurring at the levels of the central nervous system (CNS) and the adrenal gland. A coordinated interaction of numerous cell types and systems within the adrenal gland is involved in the sustained adrenal glucocorticoid production. This review article describes and discusses recent experimental findings regarding the role of adrenal gland microenvironment including the adrenal vasculature and the immune-adrenal crosstalk in the disregulated HPA axis during sepsis conditions. In summary, in addition to the reduced cortisol breakdown and related ACTH suppression, sepsis-mediated chronic activation of the immune-adrenal crosstalk and vascular dysfunction may contribute to the HPA axis dysregulation found in septic patients.

CBS and CSE are critical for maintenance of mitochondrial function and glucocorticoid production in adrenal cortex

AIMS

Mitochondria are known to play a central role in adrenocortical steroidogenesis. Recently, hydrogen sulfide (H2S), a gaseous transmitter endogenously produced by cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE), has been found to improve mitochondrial function. The present study aimed at examining whether CBS and CSE are expressed in adrenal glands, and investigated the role of these enzymes in the maintenance of mitochondrial function and the production of glucocorticoids in adrenocortical cells.

RESULTS

Both CBS and CSE are present in murine adrenocortical cells and account for H2S generation in adrenal glands. Using a combination of both in vivo and in vitro approaches, we demonstrated that either CBS/CSE inhibitors or small interfering RNAs led to mitochondrial oxidative stress and dysfunction, which meanwhile resulted in blunted corticosterone responses to adrenocorticotropic hormone (ACTH). These effects were significantly attenuated by the treatment of H2S donor GYY4137. Lipopolysaccharide (LPS) also caused mitochondrial damage, thereby resulting in adrenal insufficiency. Moreover, LPS inhibited CBS/CSE expression and H2S production in adrenal glands, while H₂S donor GYY4137 protected against LPS-induced mitochondrial damage and hyporesponsiveness to ACTH. Local suppression of CBS or CSE in adrenal glands significantly increased the mortality in endotoxemic mice, which was also improved by GYY4137.

INNOVATION

The identification of endogenous H2S generation as critical regulators of adrenocortical responsiveness might result in the development of new therapeutic approaches for the treatment of relative adrenal insufficiency during sepsis.

CONCLUSIONS

Endogenous H₂S plays a critical role in the maintenance of mitochondrial function in the adrenal cortex, thereby resulting in an adequate adrenocortical response to ACTH.

Divergent neuroendocrine responses to localized and systemic inflammation

The sympathetic nervous system (SNS) is part of an integrative network that functions to restore homeostasis following injury and infection. The SNS can provide negative feedback control over inflammation through the secretion of catecholamines from postganglionic sympathetic neurons and adrenal chromaffin cells (ACCs). Central autonomic structures receive information regarding the inflammatory status of the body and reflexively modulate SNS activity. However, inflammation and infection can also directly regulate SNS function by peripheral actions on postganglionic cells. The present review discusses how inflammation activates autonomic reflex pathways and compares the effect of localized and systemic inflammation on ACCs and postganglionic sympathetic neurons. Systemic inflammation significantly enhanced catecholamine secretion through an increase in Ca(2+) release from the endoplasmic reticulum. In contrast, acute and chronic GI inflammation reduced voltage-gated Ca(2+) current. Thus it appears that the mechanisms underlying the effects of peripheral and systemic inflammation neuroendocrine function converge on the modulation of intracellular Ca(2+) signaling.

Transportation decreases the pulse frequency of growth hormone in the blood of prepubertal male calves

Both the mean concentration and the pulse pattern of growth hormone (GH) in the blood are important for the metabolism and body growth of calves. Transportation is reported to decrease blood GH concentrations in prepubertal male calves. However, the effect of transportation on GH pulsatility remains unknown. Because transportation is important in moving these calves from calf-production farms to markets or fattening farms, we tested whether transportation decreases their GH pulse frequency. Five calves were subjected to transportation by trucking (transport group), while five were left in their shed (non-transport group). Both groups were subsequently subjected to frequent blood sampling at 15-min intervals for 5 h. In the transport group, the cortisol concentrations increased in the first hour (P < 0.05) but significantly decreased thereafter (P < 0.05) to lower than those of the non-transport group. During the 5-hour study period, the transport group displayed a similar mean GH concentration relative to the non-transport group, but displayed a delayed first GH pulse, and a lower number of GH pulses than the non-transport group (P < 0.05). Hence, transportation is suggested to decrease GH pulse frequency under abnormal cortisol states, presumably suppressing metabolism and body growth in prepubertal male calves.

Estrogenic action on arterial smooth muscle: permissive for maintenance of CRHR2 expression

Urocortin (Ucn), a member of CRH family, has been implicated to be one of the endogenous regulators in the cardiovascular system and exerts its effects locally via an autocrine/paracrine fashion. Previous studies have shown the gender difference in CRH-induced vasodilation in human skin, which is related to the concentration of estrogens during the menstrual cycle. The aim of this study was to investigate whether estrogens modulate Ucn/CRH receptor type 2 (CRHR2) expression in vascular smooth muscle, thereby leading to vasodilation. We performed sham operation or bilateral ovariectomy (OVX) on female Sprague Dawley rats. OVX rats were sc administered 17β-estradiol (E₂) at a dose of 30 μg/kg·d or with placebo for 12 wk. Primary smooth muscle cells of aorta were used for the in vitro study. It was found that the Ucn-induced vasodilation and CRHR2 expression were decreased in OVX rats and restored by E₂ replacement treatment for 12 wk. E₂ increased the expression of CRHR2 in cultured smooth muscle cells, which was blocked by estrogen receptor-β antagonist. Ucn significantly suppressed the phenylephrine-induced phospholipase Cβ3 activation, inositol 1,4,5-trisphosphate (IP₃) production, and intracellular Ca²⁺ elevation. Ucn stimulated the expression of active GTP-bound Gαs protein and cAMP production. The suppressive effects of Ucn on phenylephrine-induced IP₃ production and intracellular Ca²⁺ elevation were blocked by the inhibitors of adenylate cyclase and protein kinase A. Our results demonstrate that estrogen maintains the expression of CRHR2 in aorta smooth muscle, thereby enhancing vasodilator actions of Ucn. Ucn exerts its vasorelaxant effects via Gαs-cAMP-protein kinase A signaling, leading to down-regulation of the phospholipase Cβ-IP₃-Ca²⁺ signaling pathway.