Involvement of constitutive nitric oxide synthase in ghrelin-induced cytosolic phospholipase A(2) activation in gastric mucosal cell protection against ethanol cytotoxicity

Ghrelin and Cancer: Examining the Roles of the Ghrelin Axis in Tumor Growth and Progression

Ghrelin, a hormone produced and secreted from the stomach, is prim arily known as an appetite stimulant. Recently, it has emerged as a potential regulator/biomarker of cancer progression. Inconsistent results on this subject make this body of literature difficult to interpret. Here, we attempt to identify commonalities in the relationships between ghrelin and various cancers, and summarize important considerations for future research. The main players in the ghrelin family axis are unacylated ghrelin (UAG), acylated ghrelin (AG), the enzyme ghrelin O-acyltransferase (GOAT), and the growth hormone secretagogue receptor (GHSR). GOAT is responsible for the acylation of ghrelin, after which ghrelin can bind to the functional ghrelin receptor GHSR-1a to initiate the activation cascade. Splice variants of ghrelin also exist, with the most prominent being In1-ghrelin. In this review, we focus primarily on the potential of In1-ghrelin as a biomarker for cancer progression, the unique characteristics of UAG and AG, the importance of the two known receptor variants GHSR-1a and 1b, as well as the possible mechanisms through which the ghrelin axis acts. Further understanding of the role of the ghrelin axis in tumor cell proliferation could lead to the development of novel therapeutic approaches for various cancers.

Inhibition of PLA2G4A Reduces the Expression of Lung Cancer-Related Cytokines

Phospholipase A2-IVA (PLA2G4A) is the most abundant subtype of cytoplasmic phospholipase A2 (cPLA2) and is an important enzyme in tumor development. Our study aimed to explore the role of PLA2G4A in the regulation of lung cancer. The contents of cell-related cytokines (microsomal prostaglandin E synthase-1 [mPGES], PGE2, and prostacyclin [PGI2]) in A549 cells were analyzed by ELISA kits. Cell counting kit-8 (CCK8) was used to detect the effects of inhibitor of cPLA2 (arachidonyl trifluoromethyl ketone [AACOCF3]) on the proliferation of A549 cells. The migration and invasion of A549 cells were tested by cell scratch wound healing assay and transwell assay, respectively. Real-time quantitative PCR and Western blotting were used to detect the effect of inhibitor AACOCF3 on the expression of related mRNA and protein in A549 cells. ELISA result showed that the levels of mPGES, PGE2, and PGI2 in control group were significantly higher than those in the AACOCF3 group. Cell inhibition rate in the control group was significantly lower than that in the AACOCF3 group. The percentage of wound healing in the control group was significantly higher than that in the AACOCF3 group. Meanwhile, the relative invasive number of cells in the control group was significantly higher than those in the AACOCF3 group. The expression levels of related mRNA of PLA2G4A and cyclooxygenase-2 (COX-2) and the expression levels of mPGES, COX-1, and COX-2 protein in the control group were significantly higher than those in the AACOCF3 group. Our research showed that PLA2G4A was involved in migration and invasion of lung cancer cells.

Gastrointestinal factors regulating lipid droplet formation in the intestine

Cytoplasmic lipid droplets (CLD) are considered as neutral lipid reservoirs, which protect cells from lipotoxicity. It became clear that these fascinating dynamic organelles play a role not only in energy storage and metabolism, but also in cellular lipid and protein handling, inter-organelle communication, and signaling among diverse functions. Their dysregulation is associated with multiple disorders, including obesity, liver steatosis and cardiovascular diseases. The central aim of this review is to highlight the link between intra-enterocyte CLD dynamics and the formation of chylomicrons, the main intestinal dietary lipid vehicle, after overviewing the morphology, molecular composition, biogenesis and functions of CLD.

Why should neuroscientists worry about iron? The emerging role of ferroptosis in the pathophysiology of neuroprogressive diseases

Ferroptosis is a unique form of programmed death, characterised by cytosolic accumulation of iron, lipid hydroperoxides and their metabolites, and effected by the fatal peroxidation of polyunsaturated fatty acids in the plasma membrane. It is a major driver of cell death in neurodegenerative neurological diseases. Moreover, cascades underpinning ferroptosis could be active drivers of neuropathology in major psychiatric disorders. Oxidative and nitrosative stress can adversely affect mechanisms and proteins governing cellular iron homeostasis, such as the iron regulatory protein/iron response element system, and can ultimately be a source of abnormally high levels of iron and a source of lethal levels of lipid membrane peroxidation. Furthermore, neuroinflammation leads to the upregulation of divalent metal transporter1 on the surface of astrocytes, microglia and neurones, making them highly sensitive to iron overload in the presence of high levels of non-transferrin-bound iron, thereby affording such levels a dominant role in respect of the induction of iron-mediated neuropathology. Mechanisms governing systemic and cellular iron homeostasis, and the related roles of ferritin and mitochondria are detailed, as are mechanisms explaining the negative regulation of ferroptosis by glutathione, glutathione peroxidase 4, the cysteine/glutamate antiporter system, heat shock protein 27 and nuclear factor erythroid 2-related factor 2. The potential role of DJ-1 inactivation in the precipitation of ferroptosis and the assessment of lipid peroxidation are described. Finally, a rational approach to therapy is considered, with a discussion on the roles of coenzyme Q₁₀, iron chelation therapy, in the form of deferiprone, deferoxamine (desferrioxamine) and deferasirox, and N-acetylcysteine.

Impairment of ghrelin synthesis in Helicobacter pylori-colonized stomach: New clues for the pathogenesis of H. pylori-related gastric inflammation

Ghrelin, the ligand of growth hormone secretagogue receptor 1a, takes part in several functions of the digestive system, including regulation of appetite, energy homeostasis, gastric acid secretion and motility. Ghrelin has also immunoregulatory properties and is supposed to inhibit some inflammatory pathways that can mediate gastric damage. Interestingly, ghrelin synthesis is reduced in the gastric mucosa of patients with Helicobacter pylori (H. pylori) infection, a worldwide condition inducing a T helper (Th)1/Th17 cell response-driven gastritis, which may evolve towards gastric atrophy and cancer. In this article, we review the available data on the expression of ghrelin in H. pylori infection and discuss how the defective ghrelin synthesis may contribute to sustain the ongoing inflammatory response in this disease.

Induction in gastric mucosal prostaglandin and nitric oxide by Helicobacter pylori is dependent on MAPK/ERK-mediated activation of IKK-β and cPLA2: modulatory effect of ghrelin

Among the key factors defining the extent of gastric mucosal inflammatory involvement in response to Helicobacter pylori is the excessive generation of prostaglandin (PGE2) and nitric oxide (NO), caused by the overexpression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), and triggered by the activation of mitogen-activated protein kinase (MAPK)/c-Jun N-terminal kinase, p38 and ERK, and nuclear translocation of the cognate transcription factors. In this study, we report on the role of MAPK/ERK in the regulation of H. pylori LPS-induced gastric mucosal expression of COX-2 and iNOS. We show that ERK activation by the LPS leads to phosphorylation of the inhibitory κB kinase-β (IKK-β) and cytosolic phospholipase A2 (cPLA2), and is reflected in the upsurge in NF-κB nuclear translocation, induction in COX-2 and iNOS expression, and up-regulation in cPLA2 activity. The modulatory effect of peptide hormone, ghrelin, on the LPS-induced changes, although associated with further enhancement in ERK, IKK-β, and cPLA2 phosphorylation, was reflected in the suppression of IKK-β and cPLA2 activity through S-nitrosylation. While the effect of ghrelin on S-nitrosylation was susceptible to suppression by the inhibitors of Src/Akt pathway, the inhibition of ERK activation caused the blockage in IKK-β and cPLA2 phosphorylation as well as S-nitrosylation. Taken together, our data show that H. pylori-induced ERK activation plays a critical role in up-regulation of gastric mucosal PGE2 and NO generation at the level of IKK-β and cPLA2 activation, and that ghrelin counters these proinflammatory consequences of the LPS through Src/Akt-dependent S-nitrosylation.

Ghrelin in gastrointestinal diseases

Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor (GHSR). Upon binding to its receptor, Ghrelin can produce a variety of biological effects, such as promoting the release of growth hormone and maintaining energy balance. Besides, it also promotes gastrointestinal motility, increases gastric acid secretion, and is involved in the genesis of tumors. This article reviews the role of Ghrelin in gastrointestinal system disease.

Role of ghrelin-induced cSrc activation in modulation of gastric mucosal inflammatory responses to Helicobacter pylori

A peptide hormone, ghrelin, is recognized as an important modulator of gastric mucosal inflammatory responses to H. pylori through the regulation of nitric oxide synthase (NOS) system. As cSrc kinase plays a major role in transduction of signals that regulate the activity of NOS isozyme system, we investigated the influence of H. pylori LPS on the processes associated with Src activation in gastric mucosal cells. The LPS-induced drop in constitutive (c) cNOS activity and up-regulation in inducible (i) iNOS was associated with the suppression in cSrc kinase activity that was reflected in a decrease in its phosphorylation at Tyr⁴¹⁶. Further, the countering effect of ghrelin on the LPS-induced changes in cSrc activity and the extent of its phosphorylation was accompanied by a marked reduction in the activity of iNOS and an increase in cNOS activation through phosphorylation at Ser¹¹⁷⁹. Moreover, the effect of ghrelin on cSrc activation and its Tyr⁴¹⁶ phosphorylation was associated with the kinase S-nitrosylation that was susceptible to the blockage by cNOS inhibition. Our findings suggest that up-regulation in iNOS with H. pylori infection leads to disturbances in cNOS phosphorylation that exerts the detrimental effect on the processes of cSrc activation through cNOS-mediated S-nitrosylation. We also show that ghrelin attenuation of H. pylori-induced gastric mucosal inflammatory responses involves the enhancement in cSrc activation, elicited by the kinase S-nitrosylation and the increase in its phosphorylation at Tyr⁴¹⁶.

Ghrelin suppression of Helicobacter pylori-induced S-nitrosylation-dependent Akt inactivation exerts modulatory influence on gastric mucin synthesis

Loss of mucus coat integrity and the impairment in its mucin component as well as the disturbance in nitric oxide (NO) generation are well-recognized features of gastric disease associated with H. pylori infection. As ghrelin plays a major role in the regulation of nitric oxide synthase system, we investigated the influence of this hormone on H. pylori LPS-induced interference with gastric mucin synthesis. The results revealed that the LPS-induced impairment in mucin synthesis and accompanied induction in inducible nitric oxide synthase (iNOS) expression, were associated with the suppression in Akt kinase activity and the impairment in constitutive nitric oxide synthase (cNOS) phosphorylation. The LPS effect on Akt inactivation was manifested in the kinase protein S-nitrosylation and a decrease in its phosphorylation at Ser(473). Further, we show that the countering effect of ghrelin, on the LPS-induced impairment in mucin synthesis was reflected in the suppression of iNOS and the increase in Akt activation, associated with the loss in S-nitrosylation and the increase in phosphorylation, as well as cNOS activation through phosphorylation. Our findings demonstrate that up-regulation in iNOS with H. pylori infection and subsequent Akt kinase inactivation through S-nitrosylation exerts the detrimental effect on the processes dependent on Akt activation, including that of cNOS activation and mucin synthesis. We also show that ghrelin protection against H. pylori-induced impairment in mucin synthesis is intimately linked to the events of Akt activation and reflected in a decrease in the kinase S-nitrosylation and the increase in its phosphorylation.

Helicobacter pylori Induces Disturbances in Gastric Mucosal Akt Activation through Inducible Nitric Oxide Synthase-Dependent S-Nitrosylation: Effect of Ghrelin

Gastric mucosal inflammatory response to H. pylori and its key virulence factor, lipopolysaccharide (LPS), are characterized by a massive rise in apoptosis and the disturbances in NO signaling pathways. Here, we report that H. pylori LPS-induced enhancement in the mucosal inducible nitric oxide synthase (iNOS) was associated with the suppression in Akt kinase activity and the impairment in constitutive nitric oxide synthase (cNOS) phosphorylation. Further, we demonstrate that the LPS effect on Akt inactivation, manifested in the kinase protein S-nitrosylation and a decrease in its phosphorylation at Ser⁴⁷³, was susceptible to suppression by iNOS inhibition. Moreover, the countering effect of hormone, ghrelin, on the LPS-induced changes in Akt activity was reflected in the loss in Akt S-nitrosylation and the increase in its phosphorylation at Ser⁴⁷³, as well as cNOS activation through phosphorylation. Our findings demonstrate that up-regulation in iNOS with H. pylori infection leads to Akt inactivation through S-nitrosylation that exerts the detrimental effect on the processes of cNOS activation through phosphorylation. We also report that ghrelin protection against H. pylori-induced disturbances is manifested in a marked increase in Akt activity and evoked by a decrease in the kinase S-nitrosylation and the increase in its phosphorylation at Ser⁴⁷³.

Role of constitutive nitric oxide synthase S-nitrosylation in Helicobacter pylori-induced gastric mucosal cell apoptosis: effect of ghrelin

Infection with H. pylori is a primary factor in the etiology of gastric disease, and the excessive NO generation and a massive rise in apoptosis are well recognized features that characterize the mucosal inflammatory responses to the bacterium and its lipopolysaccharide (LPS). Here, we report that H. pylori LPS-induced enhancement in gastric mucosal cell apoptosis and NO generation was associated with the suppression in constitutive nitric oxide synthase (cNOS) activity and a marked up-regulation in the activity of inducible nitric oxide synthase (iNOS). Further, we demonstrate that the detrimental effect of the LPS on cNOS was manifested in the enzyme protein S-nitrosylation, that was susceptible to suppression by iNOS inhibitor, 1400W. Moreover, we show that the countering effect of peptide hormone, ghrelin, on the LPS-induced changes in apoptosis and cNOS activity was reflected in the loss in cNOS S-nitrosylation and the increase in the enzyme phosphorylation. These findings demonstrate that the disturbances in gastric mucosal NO generation system caused by H. pylori result from the iNOS-derived NO suppression of cNOS activation through S-nitrosylation. We also report that ghrelin protection against H. pylori-induced gastric mucosal proapoptotic events involves cNOS activation manifested by the increase in enzyme protein phosphorylation and a decrease in its S-nitrosylation.

Mechanism of Cytosolic Phospholipase A(2) Activation in Ghrelin Protection of Salivary Gland Acinar Cells against Ethanol Cytotoxicity

Ghrelin, a peptide hormone, newly identified in oral mucosal tissues, has emerged recently as an important mediator of the processes of mucosal defense. Here, we report on the mechanism of ghrelin protection against ethanol cytotoxicity in rat sublingual salivary gland cells. The protective effect of ghrelin was associated with the increase in NO and PGE2, and upregulation in cytosolic phospholipase A₂ (cPLA₂) activity and arachidonic acid (AA) release. The loss in countering effect of ghrelin occurred with cNOS inhibitor, L-NAME, as well as indomethacin and COX-1 inhibitor, SC-560, while COX-2 inhibitor, NS-398, and iNOS inhibitor, 1400W, had no effect. The effect of L-NAME was reflected in the inhibition of ghrelin-induced cell capacity for NO production, cPLA₂ activation and PGE2 generation, whereas indomethacin caused only the inhibition in PGE2. Moreover, the ghrelin-induced up-regulation in AA release was reflected in the cPLA₂ phosphorylation and S-nitrosylation. Inhibition in ghrelin-induced S-nitrosylation was attained with L-NAME, whereas the ERK inhibitor, PD98059, caused the blockage in cPLA₂ protein phosphorylation as well as S-nitrosylation. Thus, ghrelin protection of salivary gland cells against ethanol involves cNOS-derived NO induction of cPLA₂ activation through S-nitrosylation for the increase in AA release at the site of COX-1 action for PGE2 synthesis.

Ghrelin protection against lipopolysaccharide-induced gastric mucosal cell apoptosis involves constitutive nitric oxide synthase-mediated caspase-3 S-nitrosylation

Ghrelin, a peptide hormone produced mainly in the stomach, has emerged as an important modulator of the inflammatory responses that are of significance to the maintenance of gastric mucosal integrity. Here, we report on the role of ghrelin in controlling the apoptotic processes induced in gastric mucosal cells by H. pylori lipopolysaccharide (LPS). The countering effect of ghrelin on the LPS-induced mucosal cell apoptosis was associated with the increase in constitutive nitric oxide synthase (cNOS) activity, and the reduction in caspase-3 and inducible nitric oxide synthase (NOS-2). The loss in countering effect of ghrelin on the LPS-induced changes in apoptosis and caspase-3 activity was attained with Src kinase inhibitor, PP2, as well as Akt inhibitor, SH-5, and cNOS inhibitor, L-NAME. Moreover, the effect of ghrelin on the LPS-induced changes in cNOS activity was reflected in the increased cNOS phosphorylation that was sensitive to SH-5. Furthermore, the ghrelin-induced up-regulation in cNOS activity was associated with the increase in caspase-3 S-nitrosylation that was susceptible to the blockage by L-NAME. Therefore, ghrelin protection of gastric mucosal cells against H. pylori LPS-induced apoptosis involves Src/Akt-mediated up-regulation in cNOS activation that leads to the apoptotic signal inhibition through the NO-induced caspase-3 S-nitrosylation.

Constitutive nitric oxide synthase-mediated caspase-3 S-nitrosylation in ghrelin protection against Porphyromonas gingivalis-induced salivary gland acinar cell apoptosis

Recent advances in identifying the salivary constituents capable of influencing the oral mucosal inflammatory responses have brought to focus the importance of a peptide hormone, ghrelin. Here, we report on the involvement of ghrelin in controlling the apoptotic processes induced in sublingual salivary gland acinar cells by the lipopolysaccharide (LPS) of a periodontopathic bacterium, Porphyromonas gingivalis. We show that the countering effect of ghrelin on the LPS-induced acinar cell apoptosis was associated with the increase in constitutive nitric oxide synthase (cNOS) activity, and the reduction in caspase-3 and inducible nitric oxide synthase (iNOS). The loss in countering effect of ghrelin on the LPS-induced changes in apoptosis and caspase-3 activity was attained with Src kinase inhibitor, PP2, as well as Akt inhibitor, SH-5, and cNOS inhibitor, L-NAME, but not the iNOS inhibitor, 1400W. The effect of ghrelin on the LPS-induced changes in cNOS activity, moreover, was reflected in the increased cNOS phosphorylation that was sensitive to PP2 as well as SH-5. Furthermore, the ghrelin-induced up-regulation in cNOS activity was associated with the increase in caspase-3 S-nitrosylation that was susceptible to the blockage by SH-5 and L-NAME. The findings point to the involvement of ghrelin in Src/Akt kinase-mediated cNOS activation and the apoptogenic signal inhibition through the NO-induced caspase-3 S-nitrosylation.