Stress and the Stomach: Corticotropin-Releasing Factor May Protect the Gastric Mucosa in Stress Through Involvement of Glucocorticoids

Non-Invasive Remote Ischemic Preconditioning May Protect the Gastric Mucosa Against Ischemia-Reperfusion-Induced Injury Through Involvement of Glucocorticoids

Remote ischemic preconditioning (RIPC) is one of the most effective approaches to attenuate tissue injury caused by severe ischemia-reperfusion (I/R). Experimental studies have demonstrated that RIPC is capable of producing a protective effect not only on heart, but also on brain, lungs, kidneys, liver, intestine, and stomach. We previously demonstrated that glucocorticoids participate in protective effect of local gastric ischemic preconditioning against I/R-induced gastric injury. In the present study we investigated whether RIPC may protect the gastric mucosa against I/R-induced injury through involvement of glucocorticoids. Anesthetized fasted Sprague Dawley male rats were exposed to prolonged gastric I/R (30 min occlusion of celiac artery followed by 3 h of reperfusion) alone or with preliminary brief RIPC (10 min non-invasive occlusion of right hind limb blood flow followed by reperfusion for 30 min). First, we investigated the effect of RIPC on I/R-induced injury by itself. Then to study the role of glucocorticoids similar experiments were carried out: 1) in rats pretreated with the inhibitor of glucocorticoid synthesis, metyrapone (30 mg/kg, i.p), and in control animals; 2) in adrenalectomized rats without or with corticosterone replacement (4 mg/kg, s.c.) and in sham-operated animals; 3) in rats pretreated with glucocorticoid receptor antagonist RU-38486 (20 mg/kg, s.c.) and in control animals. I/R induced corticosterone rise and resulted in the gastric erosion formation. RIPC significantly reduced the erosion area in control animals. Metyrapone injected shortly before RIPC caused a decrease in plasma corticosterone levels and prevented the gastroprotective effect of RIPC and, moreover, further aggravated the deleterious effect of I/R. Adrenalectomy performed 1 week before experiment created long-lasting corticosterone deficiency and had no effect on the gastroprotective effect of RIPC. Nevertheless, corticosterone replacement which mimics the corticosterone rise, similar to RIPS, significantly reduced erosion areas of gastric mucosa in adrenalectomized rats supporting the role of glucocorticoids in gastroprotection. RU-38486, which occupied glucocorticoid receptors, similar to metyrapone prevented the gastroprotective effect of RIPC and, moreover, further aggravated the deleterious effect of I/R. The results of the present study demonstrate for the first time that RIPC may protect the gastric mucosa against I/R-induced injury through involvement of glucocorticoids.

Role of nucleotide binding oligomerization domain-like receptor protein 3 inflammasome in stress-induced gastric injury

BACKGROUND AND AIM

The inflammasomes promote pro-caspase-1 cleavage, leading to processing of pro-interleukin (IL)-1β into its mature form. We investigated the role of the IL-1β and nucleotide binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome in gastric injury in mice receiving water-immersion restraint stress (WIRS), focusing on the cyclooxygenase (COX)-2/prostaglandin (PG) E₂ axis.

METHODS

To induce gastric injury, the mice were placed in a restraint cage and immersed in the water bath to the level of the xiphoid process. Protein levels of mature caspase-1 and IL-1β were assessed by western blotting.

RESULTS

Water-immersion restraint stress induced gastric injury with increase in IL-1β expression by activation of NLRP3 inflammasome. Exogenous IL-1β attenuated the injury, whereas anti-IL-1β neutralizing antibody and IL-1β receptor antibody aggravated it. NLRP3^-/- and caspase-1^-/- mice enhanced the injury with reducing of mature IL-1β, and this aggravation was reduced by exogenous IL-1β supplementation. Toll-like receptor 4^-/- mice were hyporesponsive to WIRS in terms of mature IL-1β production. Rabeprazole attenuated the injury with preventing inflammasome activation. WIRS injured the stomach with promotion of COX-2 mRNA and PGE₂ production, and exogenous IL-1β enhanced these molecules, while IL-1β immunoneutralization exerted opposite effect. PGE₂ supplementation abolished the hypersensitivity in NLRP3^-/- and caspase-1^-/- mice through negative regulation of inflammatory cytokines.

CONCLUSION

These results suggest that NLRP3 inflammasome-derived IL-1β plays a protective role in stress-induced gastric injury via activation of the COX-2/PGE₂ axis. Toll-like receptor 4 signaling and gastric acid may be involved in NLRP3 inflammasome activation.

Toll-like receptor 4 protects against stress-induced ulcers via regulation of glucocorticoid production in mice

Stress-induced gastric ulcer is an important life-threatening condition, while the molecular basis of its development is incompletely understood. Toll-like receptor 4 (TLR4), an innate immune pattern recognition receptor, can induce pro-inflammatory transcription, aggravating a stress ulcer. The present study found that TLR4 played a protective role in a mouse model of water immersion (23 °C) restraint stress. Wild-type (WT) and TLR4^-/- male mice were respectively divided into five groups (5 per group), and exposed to the stressor for 0, 0.5, 1, 2, or 4 hours. Gastric ulcer index, determined post mortem, increased with time in both types of mice but was greater in TLR4^-/- mice. Furthermore, increased serum cortisol and corticosterone concentrations were observed in WT mice only, and such increases were detected only in WT mice 4 h after lipopolysaccharide (LPS) treatment (2 mg/kg, intraperitoneal injection). Moreover, the administration of cortisol alleviated the gastric injury in TLR4^-/- mice. Western blotting showed expression in the adrenal of P450scc (CYP11A1), the first rate-limiting enzyme in the synthesis of steroids, was increased 4 h after water immersion restraint stress or LPS treatment in WT mice, but was conversely decreased in TLR4^-/- mice after either stressor. Furthermore, in adrenal glands of TLR4^-/- mice, structural distortion of mitochondria (which contain CYP11A1) was found with electron microscopy, and lack of lipid-storing droplets was found using light microscopy on adrenal cryosections stained with Oil red O. These data indicate that TLR4 plays a protective role in stress-induced gastric ulcer that is exerted via impacting synthesis of glucocorticoid in the adrenal gland.

The Realization of the Brain-Gut Interactions with Corticotropin-Releasing Factor and Glucocorticoids

BACKGROUND

The brain and the gut interact bi-directionally through the brain-gut axis. The interaction is mediated by the autonomic nervous system and the hypothalamic-pituitary-adrenocortical (HPA) system. The first brilliant demonstration of the brain-gut interactions was the cephalic phase of gastric and pancreatic secretion discovered by Ivan Pavlov, the first physiologist who was awarded the Nobel Prize for Physiology or Medicine in 1904. This review aims to identify the HPA system as a key hormonal branch of the brain-gut axis in stress.

METHODS

We first outlined main components of the brain-gut axis and then focused on the HPA system as a key hormonal branch of the brain-gut axis in stress. We undertook a structured search of bibliographic databases for peer-reviewed research literature using a focused review question.

RESULTS

Seventy-one articles were included in the review, the eleventh of them were articles of Filaretova L. and co-authors. We will discuss in our articles how an endocrinological approach to gastroenterological field can advance our understanding of the HPA axis role in regulation of gastric mucosal integrity and uncover new findings. According to these findings activation of the HPA system is gastroprotective component of the brain-gut axis in stress but not ulcerogenic one as it was generally accepted. Corticotropin-releasing factor (CRF) and glucocorticoids are important natural players provided gastroprotection. The results suggest that an initial action of endogenous glucocorticoids, including stress- and CRF-produced ones, as well as exogenous glucocorticoids, even used at pharmacological doses, is physiological gastroprotective. Prolongation of the hormonal action may lead to the transformation of gastroprotective hormonal effect to proulcerogenic one.

CONCLUSION

The findings of this review demonstrate that corticotropin-releasing factor and glucocorticoids contribute to the realization of the brain-gut interactions and that activation of the HPA system is gastroprotective component of this interaction in stress.