Endogenous and exogenous ghrelin enhance the colonic and gastric manifestations of dextran sodium sulphate-induced colitis in mice

Ghrelin in Focus: Dissecting Its Critical Roles in Gastrointestinal Pathologies and Therapies

This review elucidates the critical role of ghrelin, a peptide hormone mainly synthesized in the stomach in various gastrointestinal (GI) diseases. Ghrelin participates in diverse biological functions ranging from appetite regulation to impacting autophagy and apoptosis. In sepsis, it reduces intestinal barrier damage by inhibiting inflammatory responses, enhancing GI blood flow, and modulating cellular processes like autophagy and apoptosis. Notably, in inflammatory bowel disease (IBD), serum ghrelin levels serve as markers for distinguishing between active and remission phases, underscoring its potential in IBD treatment. In gastric cancer, ghrelin acts as an early risk marker, and due to its significant role in increasing the proliferation and migration of gastric cancer cells, the ghrelin-GHS-R axis is poised to become a target for gastric cancer treatment. The role of ghrelin in colorectal cancer (CRC) remains controversial; however, ghrelin analogs have demonstrated substantial benefits in treating cachexia associated with CRC, highlighting the therapeutic potential of ghrelin. Nonetheless, the complex interplay between ghrelin's protective and potential tumorigenic effects necessitates a cautious approach to its therapeutic application. In post-GI surgery scenarios, ghrelin and its analogs could be instrumental in enhancing recovery and reducing complications. This article accentuates ghrelin's multifunctionality, shedding light on its influence on disease mechanisms, including inflammatory responses and cancer progression, and examines its therapeutic potential in GI surgeries and disorders, advocating for continued research in this evolving field.

Oxidative stress, hormones, and effects of natural antioxidants on intestinal inflammation in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing gastrointestinal (GI) disorder characterized by intestinal inflammation. The etiology of IBD is multifactorial and results from a complex interplay between mucosal immunity, environmental factors, and host genetics. Future therapeutics for GI disorders, including IBD, that are driven by oxidative stress require a greater understanding of the cellular and molecular mechanisms mediated by reactive oxygen species (ROS). In the GI tract, oxidative stressors include infections and pro-inflammatory responses, which boost ROS generation by promoting the production of pro-inflammatory cytokines. Nuclear factor kappa B (NF-κB) and nuclear factor erythroid 2-related factor 2 (Nrf2) represent two important signaling pathways in intestinal immune cells that regulate numerous physiological processes, including anti-inflammatory and antioxidant activities. Natural antioxidant compounds exhibit ROS scavenging and increase antioxidant defense capacity to inhibit pro-oxidative enzymes, which may be useful in IBD treatment. In this review, we discuss various polyphenolic substances (such as resveratrol, curcumin, quercetin, green tea flavonoids, caffeic acid phenethyl ester, luteolin, xanthohumol, genistein, alpinetin, proanthocyanidins, anthocyanins, silymarin), phenolic compounds including thymol, alkaloids such as berberine, storage polysaccharides such as tamarind xyloglucan, and other phytochemicals represented by isothiocyanate sulforaphane and food/spices (such as ginger, flaxseed oil), as well as antioxidant hormones like melatonin that target cellular signaling pathways to reduce intestinal inflammation occurring with IBD.

Biodegradable Polymeric Nanoparticles Loaded with Flavonoids: A Promising Therapy for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a group of disorders that cause chronic non-specific inflammation in the gastrointestinal (GI) tract, primarily affecting the ileum and colon. The incidence of IBD has risen sharply in recent years. Despite continuous research efforts over the past decades, the aetiology of IBD is still not fully understood and only a limited number of drugs are available for its treatment. Flavonoids, a ubiquitous class of natural chemicals found in plants, have been widely used in the prevention and treatment of IBD. However, their therapeutic efficacy is unsatisfactory due to poor solubility, instability, rapid metabolism, and rapid systemic elimination. With the development of nanomedicine, nanocarriers can efficiently encapsulate various flavonoids and subsequently form nanoparticles (NPs), which greatly improves the stability and bioavailability of flavonoids. Recently, progress has also been made in the methodology of biodegradable polymers that can be used to fabricate NPs. As a result, NPs can significantly enhance the preventive or therapeutic effects of flavonoids on IBD. In this review, we aim to evaluate the therapeutic effect of flavonoid NPs on IBD. Furthermore, we discuss possible challenges and future perspectives.

Role of the Ghrelin System in Colitis and Hepatitis as Risk Factors for Inflammatory-Related Cancers

It is not known exactly what leads to the development of colorectal cancer (CRC) and hepatocellular carcinoma (HCC), but there are specific risk factors that increase the probability of their occurrence. The unclear pathogenesis, too-late diagnosis, poor prognosis as a result of high recurrence and metastasis rates, and repeatedly ineffective therapy of both cancers continue to challenge both basic science and practical medicine. The ghrelin system, which is comprised of ghrelin and alternative peptides (e.g., obestatin), growth hormone secretagogue receptors (GHS-Rs), and ghrelin-O-acyl-transferase (GOAT), plays an important role in the physiology and pathology of the gastrointestinal (GI) tract. It promotes various physiological effects, including energy metabolism and amelioration of inflammation. The ghrelin system plays a role in the pathogenesis of inflammatory bowel diseases (IBDs), which are well known risk factors for the development of CRC, as well as inflammatory liver diseases which can trigger the development of HCC. Colitis-associated cancer serves as a prototype of inflammation-associated cancers. Little is known about the role of the ghrelin system in the mechanisms of transformation of chronic inflammation to low- and high-grade dysplasia, and, finally, to CRC. HCC is also associated with chronic inflammation and fibrosis arising from different etiologies, including alcoholic and nonalcoholic fatty liver diseases (NAFLD), and/or hepatitis B (HBV) and hepatitis C virus (HCV) infections. However, the exact role of ghrelin in the progression of the chronic inflammatory lesions into HCC is still unknown. The aim of this review is to summarize findings on the role of the ghrelin system in inflammatory bowel and liver diseases in order to better understand the impact of this system on the development of inflammatory-related cancers, namely CRC and HCC.

Potential role of ghrelin in the regulation of inflammation

Several diseases are caused or progress due to inflammation. In the past few years, accumulating evidence suggests that ghrelin, a gastric hormone of 28-amino acid residue length, exerts protective effects against inflammation by modulating the related pathways. This review focuses on ghrelin's anti-inflammatory and potential therapeutic effects in neurological, cardiovascular, respiratory, hepatic, gastrointestinal, and kidney disorders. Ghrelin significantly alleviates excessive inflammation and reduces damage to different target organs mainly by reducing the secretion of inflammatory cytokines, including interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α), and inhibiting the nuclear factor kappa-B (NF-κB) and NLRP3 inflammasome signaling pathways. Ghrelin also regulates inflammation and apoptosis through the p38 MAPK/c-Jun N-terminal kinase (JNK) signaling pathway; restores cerebral microvascular integrity, and attenuates vascular leakage. Ghrelin activates the phosphoInositide-3 kinase (PI3K)/protein kinase B (Akt) pathway and inhibits inflammatory responses in cardiovascular diseases and acute kidney injury. Some studies show that ghrelin exacerbates colonic and intestinal manifestations of colitis. Interestingly, some inflammatory states, such as non-alcoholic steatohepatitis, inflammatory bowel diseases, and chronic kidney disease, are often associated with high ghrelin levels. Thus, ghrelin may be a potential new therapeutic target for inflammation-related diseases.

Diverse and Complementary Effects of Ghrelin and Obestatin

Ghrelin and obestatin are two “sibling proteins” encoded by the same preproghrelin gene but possess an array of diverse and complex functions. While there are ample literature documenting ghrelin’s functions, the roles of obestatin are less clear and controversial. Ghrelin and obestatin have been perceived to be antagonistic initially; however, recent studies challenge this dogma. While they have opposing effects in some systems, they function synergistically in other systems, with many functions remaining debatable. In this review, we discuss their functional relationship under three “C” categories, namely complex, complementary, and contradictory. Their functions in food intake, weight regulation, hydration, gastrointestinal motility, inflammation, and insulin secretion are complex. Their functions in pancreatic beta cells, cardiovascular, muscle, neuroprotection, cancer, and digestive system are complementary. Their functions in white adipose tissue, thermogenesis, and sleep regulation are contradictory. Overall, this review accumulates the multifaceted functions of ghrelin and obestatin under both physiological and pathological conditions, with the intent of contributing to a better understanding of these two important gut hormones.

Novel Role of Ghrelin Receptor in Gut Dysbiosis and Experimental Colitis in Aging

Chronic low-grade inflammation is a hallmark of aging, which is now coined as inflamm-aging. Inflamm-aging contributes to many age-associated diseases such as obesity, type 2 diabetes, cardiovascular disease, and inflammatory bowel disease (IBD). We have shown that gut hormone ghrelin, via its receptor growth hormone secretagogue receptor (GHS-R), regulates energy metabolism and inflammation in aging. Emerging evidence suggests that gut microbiome has a critical role in intestinal immunity of the host. To determine whether microbiome is an integral driving force of GHS-R mediated immune-metabolic homeostasis in aging, we assessed the gut microbiome profiles of young and old GHS-R global knockout (KO) mice. While young GHS-R KO mice showed marginal changes in Bacteroidetes and Firmicutes, aged GHS-R KO mice exhibited reduced Bacteroidetes and increased Firmicutes, featuring a disease-susceptible microbiome profile. To further study the role of GHS-R in intestinal inflammation in aging, we induced acute colitis in young and aged GHS-R KO mice using dextran sulfate sodium (DSS). The GHS-R KO mice showed more severe disease activity scores, higher proinflammatory cytokine expression, and decreased expression of tight junction markers. These results suggest that GHS-R plays an important role in microbiome homeostasis and gut inflammation during aging; GHS-R suppression exacerbates intestinal inflammation in aging and increases vulnerability to colitis. Collectively, our finding reveals for the first time that GHS-R is an important regulator of intestinal health in aging; targeting GHS-R may present a novel therapeutic strategy for prevention/treatment of aging leaky gut and inflammatory bowel disease.

A Novel Pathway of Flavonoids Protecting against Inflammatory Bowel Disease: Modulating Enteroendocrine System

Inflammatory bowel disease (IBD) is a comprehensive term for chronic or relapsing inflammatory diseases occurring in the intestinal tract, generally including Crohn's disease (CD) and ulcerative colitis (UC). Presently, the pathogenesis of IBD is unknown, yet multiple factors have been reported to be related with the development of IBD. Flavonoids are phytochemicals with biological activity, which are ubiquitously distributed in edible plants, such as fruits and vegetables. Recent studies have demonstrated impressively that flavonoids have anti-IBD effects through multiple mechanisms. These include anti-inflammatory and antioxidant actions; the preservation of the epithelial barrier integrity, the intestinal immunomodulatory property, and the shaping microbiota composition and function. In addition, a few studies have shown the impact of flavonoids on enterohormones release; nonetheless, there is hardly any work showing the link between flavonoids, enterohormones release and IBD. So far, the interaction between flavonoids, enterohormones and IBD is elucidated for the first time in this review. Furthermore, the inference can be drawn that flavonoids may protect against IBD through modulating enterohormones, such as glucagon-like peptide 1 (GLP-1), GLP-2, dipeptidyl peptidase-4 inhibitors (DPP-4 inhibitors), ghrelin and cholecystokinin (CCK). In conclusion, this manuscript explores a possible mechanism of flavonoids protecting against IBD.

Protective and Healing Effects of Ghrelin and Risk of Cancer in the Digestive System

Ghrelin is an endogenous ligand for the ghrelin receptor, previously known as the growth hormone secretagogue receptor. This hormone is mainly produced by endocrine cells present in the gastric mucosa. The ghrelin-producing cells are also present in other organs of the body, mainly in the digestive system, but in much smaller amount. Ghrelin exhibits a broad spectrum of physiological effects, such as stimulation of growth hormone secretion, gastric secretion, gastrointestinal motility, and food intake, as well as regulation of glucose homeostasis and bone formation, and inhibition of inflammatory processes. This review summarizes the recent findings concerning animal and human data showing protective and therapeutic effects of ghrelin in the gut, and also presents the role of growth hormone and insulin-like growth factor-1 in these effects. In addition, the current data on the possible influence of ghrelin on the carcinogenesis, its importance in predicting the risk of developing gastrointestinal malignances, as well as the potential usefulness of ghrelin in the treatment of cancer, have been presented.

Regulation of Intestinal Inflammation by Dietary Fats

With the epidemic of human obesity, dietary fats have increasingly become a focal point of biomedical research. Epidemiological studies indicate that high-fat diets (HFDs), especially those rich in long-chain saturated fatty acids (e.g., Western Diet, National Health Examination survey; NHANES 'What We Eat in America' report) have multi-organ pro-inflammatory effects. Experimental studies have confirmed some of these disease associations, and have begun to elaborate mechanisms of disease induction. However, many of the observed effects from epidemiological studies appear to be an over-simplification of the mechanistic complexity that depends on dynamic interactions between the host, the particular fatty acid, and the rather personalized genetics and variability of the gut microbiota. Of interest, experimental studies have shown that certain saturated fats (e.g., lauric and myristic fatty acid-rich coconut oil) could exert the opposite effect; that is, desirable anti-inflammatory and protective mechanisms promoting gut health by unanticipated pathways. Owing to the experimental advantages of laboratory animals for the study of mechanisms under well-controlled dietary settings, we focus this review on the current understanding of how dietary fatty acids impact intestinal biology. We center this discussion on studies from mice and rats, with validation in cell culture systems or human studies. We provide a scoping overview of the most studied diseases mechanisms associated with the induction or prevention of Inflammatory Bowel Disease in rodent models relevant to Crohn's Disease and Ulcerative Colitis after feeding either high-fat diet (HFD) or feed containing specific fatty acid or other target dietary molecule. Finally, we provide a general outlook on areas that have been largely or scarcely studied, and assess the effects of HFDs on acute and chronic forms of intestinal inflammation.

Knockdown of ghrelin-O-acyltransferase attenuates colitis through the modulation of inflammatory factors and tight junction proteins in the intestinal epithelium

Ghrelin-O-acyltransferase (GOAT) is a membrane-bound enzyme that attaches eight-carbon octanoate to a serine residue in ghrelin and thereby acylates inactive ghrelin to produce active ghrelin. In this study, we investigated the function of GOAT in the intestinal mucosal barrier. The intestinal mucosal barrier prevents harmful substances such as bacteria and endotoxin from entering the other tissues, organs, and blood circulation through the intestinal mucosa. Here, we established 5% dextran sodium sulfate (DSS)-induced colitis in mice and found that the body weight and colon weight were significantly decreased in these mice. Furthermore, increased inflammation and apoptosis were observed in the tissues of DSS-induced colitis mice, with increased expression of tumor necrosis factor-α, interleukin-6, phosphorylation of nuclear factor kappa B-p65 (p-NF-κB-p65), and cleaved caspase-3, and decreased expression of tight junction (TJ) proteins such as zonula occluden-1 and occludin. The knockdown of GOAT significantly attenuated colitis-induced inflammation responses and apoptosis, while GOAT overexpression significantly enhanced the induction of colitis. These results suggest that knockdown of GOAT may attenuate colitis-induced inflammation, ulcers, and fecal occult blood by decreasing the intestinal mucosal permeability via the modulation of inflammatory factors and TJ proteins.

Temporospatial effects of acyl-ghrelin on activation of astrocytes after ischaemic brain injury

The protective mechanisms of astrocyte signalling are based on the release of neurotrophic factors and the clearing of toxic substances in the early stages of cerebral ischaemia. However, astrocytes are also responsible for the detrimental effects that occur during the later stages of ischaemia, in which glial scars are formed, thereby impeding neural recovery. Acyl-ghrelin has been found to be neuroprotective after stroke, although the influence of acyl-ghrelin on astrocytes after ischaemic injury is yet to be clarified. In the present study, we used permanent middle cerebral arterial occlusion to establish a brain ischaemia model in vivo, as well as oxygen and glucose deprivation (OGD) to mimic ischaemic insults in vitro. We found that acyl-ghrelin injection significantly increased the number of activated astrocytes in the peri-infarct area at day 3 after brain ischaemia and decreased the number of activated astrocytes after day 9. Moreover, the expression of fibroblast growth factor 2 (FGF2) in the ischaemic hemisphere increased markedly after day 3, and i.c.v. injection of SU5402, an inhibitor of FGF2 signalling, abolished the suppression effects of acyl-ghrelin on astrocyte activation in the peri-infarct region during the later stages of ischaemia. The results from in vitro studies also showed the dual effect of acyl-ghrelin on astrocyte viability. Acyl-ghrelin increased the viability of uninjured astrocytes in an indirect way by stimulating the secretion from OGD-injured astrocytes. It also inhibited the astrocyte viability in the presence of FGF2 in a dose-dependent manner. Furthermore, the expression of acyl-ghrelin receptors on astrocytes was increased after acyl-ghrelin and FGF2 co-treatment. In conclusion, acyl-ghrelin promoted astrocyte activation in the early stages of ischaemia but suppressed the activation in later stages of ischaemic injury. These later effects were likely to be triggered by the increased expression of endogenous FGF2 after brain ischaemia.

Essential Role of Growth Hormone and IGF-1 in Therapeutic Effect of Ghrelin in the Course of Acetic Acid-Induced Colitis

Previous studies have shown that ghrelin exhibits a protective and therapeutic effect in the gut. The aim of the present study was to examine whether administration of ghrelin affects the course of acetic acid-induced colitis and to determine what is the role of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) in this effect. In sham-operated or hypophysectomized male Wistar rats, colitis was induced by enema with 1 mL of 3% solution of acetic acid. Saline or ghrelin (given at the dose of 8 nmol/kg/dose) was administered intraperitoneally twice a day. Seven days after colitis induction, rats were anesthetized and the severity of the colitis was assessed. Treatment with ghrelin reduced the area of colonic mucosa damage in pituitary-intact rat. This effect was associated with increase in serum levels of GH and IGF-1. Moreover, administration of ghrelin improved blood flow in colonic mucosa and mucosal cell proliferation, as well as reduced mucosal concentration of proinflammatory interleukin-1β (IL-1β) and activity of myeloperoxidase. Hypophysectomy reduced serum levels of GH and IGF-1 and increased the area of colonic damage in rats with colitis. These effects were associated with additional reduction in mucosal blood follow and DNA synthesis when compared to pituitary-intact rats. Mucosal concentration of IL-1β and mucosal activity of myeloperoxidase were maximally increased. Moreover, in hypophysectomized rats, administration of ghrelin failed to affect serum levels of GH or IGF-1, as well as the healing rate of colitis, mucosal cell proliferation, and mucosal concentration of IL-1β, or activity of myeloperoxidase. We conclude that administration of ghrelin accelerates the healing of the acetic acid-induced colitis. Therapeutic effect of ghrelin in experimental colitis is mainly mediated by the release of endogenous growth hormone and IGF-1.

Exogenous Ghrelin Accelerates the Healing of Acetic Acid-Induced Colitis in Rats

Previous studies have shown that ghrelin reduces colonic inflammation induced by trinitrobenzene sulfonic acid and dextran sodium sulfate. In the present study we determined the effect of treatment with ghrelin on the course of acetic acid-induced colitis in rats. Rectal administration of 3% acetic acid solution led to induction of colitis in all animals. Damage of the colonic wall was accompanied by an increase in mucosal concentration of pro-inflammatory interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), as well mucosal activity of myeloperoxidase. Moreover, induction of colitis led to a reduction in colonic blood flow and DNA synthesis. Administration of ghrelin after induction of colitis led to faster regeneration of the colonic wall and reduction in colonic levels of IL-1β, TNF-α, and myeloperoxidase. In addition, treatment with ghrelin improved mucosal DNA synthesis and blood flow. Our study disclosed that ghrelin exhibits a strong anti-inflammatory and healing effect in acetic acid-induced colitis. Our current observation in association with previous findings that ghrelin exhibits curative effect in trinitrobenzene sulfonic acid- and dextran sodium sulfate-induced colitis suggest that therapeutic effect of ghrelin in the colon is universal and independent of the primary cause of colitis.

The Influence of Ghrelin on the Development of Dextran Sodium Sulfate-Induced Colitis in Rats

Ghrelin has protective and therapeutic effects in the gut. The aim of present studies was to investigate the effect of treatment with ghrelin on the development of colitis evoked by dextran sodium sulfate (DSS). Methods. Studies have been performed on rats. Colitis was induced by adding 5% DSS to the drinking water for 5 days. During this period animals were treated intraperitoneally twice a day with saline or ghrelin given at the dose of 8 nmol/kg/dose. On the sixth day, animals were anesthetized and the severity of colitis was assessed. Results. Treatment with ghrelin during administration of DSS reduced the development of colitis. Morphological features of colonic mucosa exhibited a reduction in the area and deep of mucosal damage. Ghrelin reversed the colitis-induced decrease in blood flow, DNA synthesis, and superoxide dismutase activity in colonic mucosa. These effects were accompanied by a decrease in the colitis-evoked increase in mucosal concentration of interleukin-1β and malondialdehyde. Treatment with ghrelin reversed the DSS-induced reduction in body weight gain. Conclusions. Administration of ghrelin exhibits the preventive effect against the development of DSS-induced colitis. This effect seems to be related to ghrelin's anti-inflammatory and antioxidative properties.

Ghrelin receptor modulates T helper cells during intestinal inflammation

BACKGROUND

The orexigenic peptide ghrelin has anti-inflammatory properties in colitis, however, the mechanism of action and the immune cells targeted remain still to be elucidated. Here, we assessed the possible effect of ghrelin on T helper (Th) cells in a T cell transfer model of chronic colitis.

METHODS

Disease was induced in the recombination activating gene 1 knockout mice (Rag1(-/-) ) by adoptive transfer of naïve Th cells from ghrelin receptor knockout mice (GRLN-R(-/-) ) or littermate wild-type (WT) mice. The course and severity of colitis was assessed by monitoring body weight, diarrhea score, histological analysis, gene expression, and flow cytometry analysis. The possible effects of ghrelin on Th cell proliferation, polarization, and apoptosis was examined in vitro.

KEY RESULTS

Our data showed that Rag1(-/-) mice injected with GRLN-R(-/-) Th cells displayed increased severity of colitis compared to mice injected with WT Th cells. In addition, Rag1(-/-) mice injected with GRLN-R(-/-) Th cells had significantly higher intestinal inflammation and increased accumulation of Th1 and Th17 cells in the colon. In vitro, ghrelin directly affected proliferation of Th cells and induced apoptosis whereas it did not influence Th cell polarization.

CONCLUSION & INFERENCES

Our observations suggest that ghrelin modulates Th effector cells in the gut controlling proliferation and inducing apoptosis. Our findings further support the use of ghrelin as a novel therapeutic option to treat intestinal inflammatory diseases.

Immunomodulatory effect of ghrelin in the intestinal mucosa

The gastrointestinal tract is the largest endocrine organ in the body and it produces a wide array of hormones and neuropeptides. Ghrelin, a 28-amino acid hormone produced mainly by the X/A-like endocrine cells in the gastric mucosa, has widespread tissue distribution and diverse physiological functions such as hormonal, orexigenic, metabolic, cardiovascular, neurological and immunological activities. Recent research has implicated ghrelin in gastrointestinal pathological conditions and immune system regulation, but its contribution is controversial. Although ghrelin levels are elevated in clinical active inflammatory bowel diseases, confirmation of its exact role using experimental models remains unclear. This review discusses the conflicting effects of ghrelin on intestinal inflammation, through the different possible immune and intracellular mechanisms and highlights new findings.

Therapeutic applications of ghrelin agonists in the treatment of gastroparesis

There remains an unmet need for effective pharmacologic treatments for gastroparesis. Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor and has been shown to regulate energy homeostasis and exert prokinetic effects on gastrointestinal motility. In recent years, several ghrelin receptor agonists have been studied in clinical trials of patients with diabetic gastroparesis. The intravenous macrocyclic peptidomimetic, TZP-101, initially suggested improvement in gastroparesis symptoms with intravenous administration when compared to placebo. However, in subsequent studies of oral preparations, TZP-102 failed to confirm these results. Another ghrelin receptor agonist, RM-131, was recently shown to significantly accelerate gastric emptying (GE) in patients with type 1 and type 2 diabetes and delayed GE. RM-131 reduced total Gastroparesis Cardinal Symptom Index-Daily Diary (GCSI-DD) and composite scores among type 1 diabetics. Continued development of ghrelin agonists should be explored in attempts to expand therapeutic options for the treatment of gastroparesis.

Growth hormone secretagogue receptor is important in the development of experimental colitis

BACKGROUND

Growth hormone secretagogue receptor (GHSR) and its ligand, ghrelin, are important modulators in weight control and energy homeostasis. Recently, ghrelin is also involved in experimental colitis, but the role of GHSR in the development of colitis is unclear. The aim was to examine the underlying mechanism of GHSR in IBD development.

METHODS

The temporal expression of GHSR/ghrelin was determined in dextran sulphate sodium (DSS) induced colitis in Wt mice. The severity of DSS induced colitis from GHSR(-/-) and WT mice was compared at clinical/pathological levels. Furthermore, the function of macrophages was evaluated in vivo and in vitro.

RESULTS

Lack of GHSR attenuated colitis significantly at the clinical and pathological levels with reduced colonic pro-inflammatory cytokines (P < 0.05). This is consistent with the observation of less colonic macrophage infiltration and TLRs expression from DSS-treated GHSR(-/-) mice compared to WT mice (P < 0.05). Furthermore, there was significantly reduced pro-inflammatory cytokines in LPS-stimulated macrophages in vitro from GHSR(-/-) mice than WT mice (P < 0.05). Moreover, D-lys(3)-GHRP6 (a GHSR antagonist) reduced LPS-induced macrophage pro-inflammatory cytokines from WT mice in vitro.

CONCLUSIONS

GHSR contributes to development of acute DSS-induced colitis, likely via elevated pro-inflammatory cytokines and activation of macrophages. These data suggest GHSR as a potential therapeutic target for IBD.

Circulating ghrelin levels and obestatin/ghrelin ratio as a marker of activity in ulcerative colitis

Background/Aims

Ghrelin levels are known to increase in patients with ulcerative colitis (UC), but serum obestatin levels in UC patients are not well elucidated. The aim of this study was to examine the relationship between serum ghrelin and obestatin levels and disease activity in UC patients.

Methods

The serum ghrelin and obestatin levels were measured in 21 UC patients (12 with active disease and 9 in remission) using enzyme-linked immunosorbent assay. The relationship between the circulating levels of these 2 hormones and disease activity was analyzed. The colonic mucosal mRNA expression of ghrelin and obestatin was measured by quantitative reverse transcription polymerase chain reaction.

Results

The mean serum ghrelin values were significantly higher in patients with active disease than in patients with remission (1370.6±404.3 vs. 783.5±235.3 pg/mL, P=0.001). Colonic mucosal mRNA expression of ghrelin was also significantly higher in patients with active disease than in patients in remission (0.805±0.214 vs. 0.481±0.356, P=0.018). However, the mean serum obestatin levels and colonic mucosal mRNA expression of obestatin were not significantly different between both groups. The circulating obestatin/ghrelin ratio was significantly lower in patients with active UC than in patients in remission (0.32±0.08 vs. 0.58±0.20, P=0.001).

Conclusions

The serum ghrelin levels and the obestatin/ghrelin ratio were related to the activity of UC, but serum obestatin was not related to activity of UC. The ghrelin levels and the obestatin/ghrelin ratio could serve as activity markers in patients with UC.

Regulatory neuropeptides (ghrelin, obestatin and nesfatin-1) levels in serum and reproductive tissues of female and male rats with fructose-induced metabolic syndrome

Although, the exact mechanisms underlying the development of the metabolic syndrome (MetS) are not still completely understood, obesity, circulated peptide hormone levels and their interaction with genetic factors are considered largely responsible. The purpose of this study is to explore how the levels of ghrelin, obestatin (OBS) and NUCB2/nesfatin-1 (NES)/NUCB2 change in serum and the reproductive tissues of female and male rats with fructose-induced metabolic syndrome, and whether the levels of each hormone is correlated with the hormones involved with fertility. Experiments were conducted on 5-week-old Sprague-Dawley male and female rats assigned to either a control group or a MetS group. Controls were fed standard rat food and water ad libitum, while the MetS group was fed standard food with 10% (v/v) fructose solution added to their drinking water for 12 weeks with a 12/12h photoperiod circle. Then, all animals were sacrificed after a one night fast. Peptides levels in the serum and reproductive tissues of rats were studied using the ELISA method while the immunoreactivity of reproductive system peptide hormones were shown by immunohistochemical staining method. Furthermore, the other biochemical parameters were measured using Konelab-60 equipment and infertility hormones were measured with Immulite2000. Fasting serum insulin, glucose, triglyceride, alanine aminotransferase (ALT), gamma glutamyl transpeptidase (GGT), low-density lipoprotein cholesterol (LDL-C), and total cholesterol (TC) levels were statistically significantly higher, and the amount of high density lipoprotein cholesterol (HDL-C) was significantly lower, in the MetS groups. Serum and tissue supernatant NES levels were significantly higher in the rats with MetS than the control group. Ghrelin, OBS and NES were expressed in the cytoplasm, concentrated around the apical parts of the epithelial cells in the reproductive tissues of the rats. The amounts of ghrelin were lower in the reproductive tissues of the animals with MetS, while NES levels in the same tissues increased. Obestatin also decreased, though not in the seminal glands.

Ghrelin gene products in acute and chronic inflammation

Ghrelin gene products--the peptides ghrelin, unacylated ghrelin, and obestatin--have several actions on the immune system, opening new perspectives within neuroendocrinology, metabolism and inflammation. The aim of this review is to summarize the available evidence regarding the less known role of these peptides in the machinery of inflammation and autoimmunity, outlining some of their most promising therapeutic applications.

Structure and physiological actions of ghrelin

Ghrelin is a gastric peptide hormone, discovered as being the endogenous ligand of growth hormone secretagogue receptor. Ghrelin is a 28 amino acid peptide presenting a unique n-octanoylation modification on its serine in position 3, catalyzed by ghrelin O-acyl transferase. Ghrelin is mainly produced by a subset of stomach cells and also by the hypothalamus, the pituitary, and other tissues. Transcriptional, translational, and posttranslational processes generate ghrelin and ghrelin-related peptides. Homo- and heterodimers of growth hormone secretagogue receptor, and as yet unidentified receptors, are assumed to mediate the biological effects of acyl ghrelin and desacyl ghrelin, respectively. Ghrelin exerts wide physiological actions throughout the body, including growth hormone secretion, appetite and food intake, gastric secretion and gastrointestinal motility, glucose homeostasis, cardiovascular functions, anti-inflammatory functions, reproductive functions, and bone formation. This review focuses on presenting the current understanding of ghrelin and growth hormone secretagogue receptor biology, as well as the main physiological effects of ghrelin.

Ghrelin signaling in the gut, its physiological properties, and therapeutic potential

BACKGROUND

Ghrelin, an orexigenic hormone secreted from the stomach, was soon after its discovery hypothesized to be a prokinetic agent, due to its homology to motilin. Studies in animals and humans, using ghrelin and ghrelin receptor agonists, confirmed this hypothesis, suggesting a therapeutic potential for the ghrelin receptor in the treatment of gastrointestinal motility disorders. Precilinical studies demonstrated that ghrelin can act directly on ghrelin receptors on the enteric nervous system, but the predominant route of action under physiological circumstances is signaling via the vagus nerve in the upper gastrointestinal tract and the pelvic nerves in the colon. Different pharmaceutical companies have designed stable ghrelin mimetics that revealed promising results in trials for the treatment of diabetic gastroparesis and post-operative ileus. Nevertheless, no drug was able to reach the market so far, facing problems proving superiority over placebo treatment in larger trials.

PURPOSE

This review aims to summarize the road that led to the current knowledge concerning the prokinetic properties of ghrelin with a focus on the therapeutic potential of ghrelin receptor agonists in the treatment of hypomotility disorders. In addition, we outline some of the problems that could be at the basis of the negative outcome of the trials with ghrelin agonists and question whether the right target groups were selected. It is clear that a new approach is needed to develop marketable drugs with this class of gastroprokinetic agents.

Ghrelin is involved in the paracrine communication between neurons and glial cells

BACKGROUND

Ghrelin is the only known peripherally active orexigenic hormone produced by the stomach that activates vagal afferents to stimulate food intake and to accelerate gastric emptying. Vagal sensory neurons within the nodose ganglia are surrounded by glial cells, which are able to receive and transmit chemical signals. We aimed to investigate whether ghrelin activates or influences the interaction between both types of cells. The effect of ghrelin was compared with that of leptin and cholecystokinin (CCK).

METHODS

Cultures of rat nodose ganglia were characterized by immunohistochemistry and the functional effects of peptides, neurotransmitters, and pharmacological blockers were measured by Ca(2+) imaging using Fluo-4-AM as an indicator.

KEY RESULTS

Neurons responded to KCl and were immunoreactive for PGP-9.5 whereas glial cells responded to lysophosphatidic acid and had the typical SOX-10-positive nuclear staining. Neurons were only responsive to CCK (31 ± 5%) whereas glial cells responded equally to the applied stimuli: ghrelin (27 ± 2%), leptin (21 ± 2%), and CCK (30 ± 2%). In contrast, neurons stained more intensively for the ghrelin receptor than glial cells. ATP induced [Ca(2+) ]i rises in 90% of the neurons whereas ACh and the NO donor, SIN-1, mainly induced [Ca(2+) ]i changes in glial cells (41 and 51%, respectively). The percentage of ghrelin-responsive glial cells was not affected by pretreatment with suramin, atropine, hexamethonium or 1400 W, but was reduced by l-NAME and by tetrodotoxin. Neurons were shown to be immunoreactive for neuronal NO-synthase (nNOS).

CONCLUSIONS & INFERENCES

Our data show that ghrelin induces Ca(2+) signaling in glial cells of the nodose ganglion via the release of NO originating from the neurons.

Anti-inflammatory effect of obestatin and ghrelin in dextran sulfate sodium-induced colitis in rats

BACKGROUND AND OBJECTIVES

Obestatin and ghrelin are hormones derived from the same gene but have opposing effects. Ghrelin has anti-inflammatory activities; however, the role of obestatin in the inflammatory processes has not been clearly demonstrated yet. The aim of the study was to analyse and compare the anti-inflammatory effect of exogenous ghrelin and obestatin in a rat model of colitis.

METHODS

Acute and chronic colitis was induced in 96 rats by adding 3% dextran sulfate sodium to the drinking water for 5 and 10 days, respectively. Intraperitoneal pretreatment with ghrelin or obestatin was started before the induction of colitis, and continued for 5 and 10 days. Clinical signs of the disease and histopathological changes were evaluated. By-products of neutrophil activation, lipid peroxidation, and inflammatory and anti-inflammatory cytokines were measured in colonic tissues.

RESULTS

Obestatin and ghrelin significantly ameliorated clinical and histopathological severity of chronic colitis, whereas they were less effective in the acute form. Therapeutic effect of ghrelin and obestatin in acute colitis was associated with reduced lipid peroxidation and TH1-induced inflammatory response, whereas obestatin in chronic colitis was protective via the suppression of polymorphonuclear leukocyte infiltration and enhancement of glutathione synthesis. Moreover, therapeutic effects of ghrelin and obestatin in chronic colitis appear to be associated with inhibition of inflammatory and activation of anti-inflammatory cytokines.

CONCLUSIONS

This study demonstrated the novel anti-inflammatory effect of obestatin and ghrelin in an experimental model of colitis. Although both obestatin and ghrelin exerted anti-inflammatory effects in chronic colitis, they were less effective in acute colitis.

Reg IV is differently expressed in enteroendocrine cells of human small intestine and colon

Reg IV is a 17 kD secreted C-type lectin physiologically found in selected enteroendocrine cells (EEC). It is thought be involved in the regulation of normal and pathological intestinal and/or neuroendocrine differentiation and proliferation but its ultimate functional role(s) is still unclear. We used immunostaining and compared the cellular expression of Reg IV with a panel of neuroendocrine markers in human GI-tract tissue samples. Reg IV showed cellular co-distribution with serotonin and chromogranin A in all parts of GI-tract. Co-localization of Reg IV with somatostatin was seen in colon and with substance P in ileum. Subpopulations of cells expressing Reg IV overlapped with EECs containing GLP-1, GLP-2, secretin, PYY, and ghrelin, depending on the anatomical localization of the samples. The results further underscore the high degree of diversity among EECs and suggest that Reg IV may be involved in the finetuning of functions exerted by the neuroendocrine cells in the GI-tract.

The ghrelin axis--does it have an appetite for cancer progression?

Ghrelin, the endogenous ligand for the GH secretagogue receptor (GHSR), is a peptide hormone with diverse physiological roles. Ghrelin regulates GH release, appetite and feeding, gut motility, and energy balance and also has roles in the cardiovascular, immune, and reproductive systems. Ghrelin and the GHSR are expressed in a wide range of normal and tumor tissues, and a fluorescein-labeled, truncated form of ghrelin is showing promise as a biomarker for prostate cancer. Plasma ghrelin levels are generally inversely related to body mass index and are unlikely to be useful as a biomarker for cancer, but may be useful as a marker for cancer cachexia. Some single nucleotide polymorphisms in the ghrelin and GHSR genes have shown associations with cancer risk; however, larger studies are required. Ghrelin regulates processes associated with cancer, including cell proliferation, apoptosis, cell migration, cell invasion, inflammation, and angiogenesis; however, the role of ghrelin in cancer is currently unclear. Ghrelin has predominantly antiinflammatory effects and may play a role in protecting against cancer-related inflammation. Ghrelin and its analogs show promise as treatments for cancer-related cachexia. Further studies using in vivo models are required to determine whether ghrelin has a role in cancer progression.

Ghrelin and toxicity: recent findings and future challenges

Ghrelin is a novel brain-gut peptide that plays various roles in mammals, including control of food intake and growth hormone release, as well as gastric motility and acid secretion in the gastrointestinal tract. It is mainly secreted by the gastric mucosa, but is also expressed in various other tissues. Different studies confirm the multiple biological roles of and possible protective effects of ghrelin. Multiple in vitro and in vivo studies support the powerful protective action of ghrelin against heart, gastric and liver injury. Moreover, ghrelin has been reported to be beneficial in renal tissue injury and excretory function after ischemia-reperfusion and to exert neuroprotective effects in cerebral ischemic regions. The aim of this review is to summarize and evaluate all the currently available in vivo and in vitro studies regarding the effects of ghrelin on tissue injury induced in different organs and tissues.

Ghrelin prevents levodopa-induced inhibition of gastric emptying and increases circulating levodopa in fasted rats

BACKGROUND

Levodopa (L-dopa) is the most commonly used treatment for alleviating symptoms of Parkinson's disease. However, L-dopa delays gastric emptying, which dampens its absorption. We investigated whether ghrelin prevents L-dopa action on gastric emptying and enhances circulating L-dopa in rats.

METHODS

Gastric emptying of non-nutrient methylcellulose/phenol red viscous solution was determined in fasted rats treated with orogastric or intraperitoneal (i.p.) L-dopa, or intravenous (i.v.) ghrelin 10 min before orogastric L-dopa. Plasma L-dopa and dopamine levels were determined by high pressure liquid chromatography. Plasma acyl ghrelin levels were assessed by radioimmunoassay. Fos expression in the brain was immunostained after i.v. ghrelin (30 μg kg(-1)) 10 min before i.p. L-dopa.

KEY RESULTS

Levodopa (5 and 15 mg kg(-1)) decreased significantly gastric emptying by 32% and 62%, respectively, when administered orally, and by 91% and 83% when injected i.p. Ghrelin (30 or 100 μg kg(-1), i.v.) completely prevented L-dopa's (15 mg kg(-1), orogastrically) inhibitory action on gastric emptying and enhanced plasma L-dopa and dopamine levels compared with vehicle 15 min after orogastric L-dopa. Levodopa (5 mg kg(-1)) did not modify plasma acyl ghrelin levels at 30 min, 1, and 2 h after i.v. injection. Levodopa (15 mg kg(-1), i.p.) induced Fos in brain autonomic centers, which was not modified by i.v. ghrelin.

CONCLUSIONS & INFERENCES

Ghrelin counteracts L-dopa-induced delayed gastric emptying but not Fos induction in the brain and enhances circulating L-dopa levels. Potential therapeutic benefits of ghrelin agonists in Parkinson's disease patients treated with L-dopa remain to be investigated.

Ghrelin as a target for gastrointestinal motility disorders

The therapeutic potential of ghrelin and synthetic ghrelin receptor (GRLN-R) agonists for the treatment of gastrointestinal (GI) motility disorders is based on their ability to stimulate coordinated patterns of propulsive GI motility. This review focuses on the latest findings that support the therapeutic potential of GRLN-R agonists for the treatment of GI motility disorders. The review highlights the preclinical and clinical prokinetic effects of ghrelin and a series of novel ghrelin mimetics to exert prokinetic effects on the GI tract. We build upon a series of excellent reviews to critically discuss the evidence that supports the potential of GRLN-R agonists to normalize GI motility in patients with GI hypomotility disorders such as gastroparesis, post-operative ileus (POI), idiopathic chronic constipation and functional bowel disorders.

Physiological role of ghrelin as revealed by the ghrelin and GOAT knockout mice

Ghrelin is a gastric hormone that has been shown to regulate food intake and energy metabolism. One unique feature of ghrelin is that its activity is regulated post transcriptionally by ghrelin O-acyltransferase (GOAT) through the addition of fatty acid to the serine residue in the N terminal region. Despite much biochemical characterization, to date no other proteins have been shown to be specifically octonylated by GOAT, suggesting a unique matching of the acyl transferase for a single ligand, ghrelin. If this is indeed correct, then genetic deletion of ghrelin or GOAT should produce near identical phenotypes and there should be extensive overlap in expression patterns. This review summarizes the similarities and differences in the phenotypes with the genetic deletion of ghrelin and GOAT in the various knockout mouse lines reported to date. While there is considerable overlap in expression pattern between ghrelin and GOAT, the latter does exhibit some unique tissue expression that could suggest that additional peptides may be acylated and await discovery and characterization.

Use of ghrelin as a treatment for inflammatory bowel disease: mechanistic considerations

Inflammatory bowel diseases (IBD)-and in particular Crohn's disease-are immune-mediated processes that result in denuded intestinal mucosa and can produce decreased appetite, weight loss, and systemic inflammation. Current treatments include anti-inflammatory medications, immunomodulators, and feeding interventions. Ghrelin is an endogenous orexigenic hormone that directly stimulates growth hormone release, increases gut motility, and has cardiovascular and anti-inflammatory properties. Although ghrelin levels are elevated in active IBD, administration of ghrelin in most (but not all) animal models of colitis has produced improvements in disease activity and systemic inflammation. The mechanism for these effects is not known but may relate to decreased inflammation, increased motility, increased appetite, and increased colonic blood flow. Human trials have not been performed, however, and more research is clearly needed.

Ghrelin in gastrointestinal disease

Enteroendocrine cells of the gastric fundus are the predominant source of ghrelin production, although ghrelin gene transcripts and ghrelin-producing cells have been identified throughout the gastrointestinal tract. Various infectious, inflammatory and malignant disorders of the gastrointestinal system have been shown to alter ghrelin production and secretion and consequently to affect endocrine ghrelin levels and activity. Animal studies have demonstrated that ghrelin and synthetic ghrelin mimetics can reduce the severity of gastric and colonic inflammation and human clinical trials are underway to determine the efficacy of ghrelin in improving motility disorders. This review summarises the impact of gastrointestinal disease on ghrelin synthesis and secretion and the potential use of ghrelin and its mimetics for the treatment of these diseases.

The effects of ghrelin on inflammation and the immune system

A number of hormones and metabolic mediators signal the brain of changes in the body's energy status and when an imbalance occurs; the brain coordinates the appropriate changes in energy intake and utilization via the control of appetite and food consumption. Under conditions of chronic inflammation and immune activation, there is often a significant loss of body mass and appetite suggesting the presence of shared ligands and signaling pathways mediating "crosstalk" between the immune and neuroendocrine systems. Ghrelin, the endogenous ligand for growth hormone secretagogue receptor (GHS-R), is produced primarily by cells in the stomach and serves as a potent circulating orexigenic hormone controlling food intake, energy expenditure, adiposity and GH secretion. The functional roles of ghrelin and other growth hormone secretagogues (GHS) within the immune system and under states of inflammatory stress and injury are only now coming to light. A number of reports over the past decade have described ghrelin to be a potent anti-inflammatory mediator both in vitro and in vivo and a promising therapeutic agent in the treatment of inflammatory diseases and injury. Moreover, ghrelin has also been shown to promote lymphocyte development in the primary lymphoid organs (bone marrow and thymus) and to ablate age-associated thymic involution. In the current report, we review the literature supporting a role for ghrelin as an anti-inflammatory agent and immunoregulatory hormone/cytokine and its potential use in the treatment of inflammatory diseases and injury.

Blood chemistry markers for evaluation of inflammatory activity in Crohn's disease during infliximab therapy

OBJECTIVE

There is a discrepancy between clinical activity and biomarkers in inflammatory bowel disease. The Harvey-Bradshaw index (HBi) is steadfast to evaluate disease activity. A set of biological markers (high sensitive C-reactive protein [hs-CRP], calprotectin, total nitrite, soluble urokinase Plasminogen Activator Receptor [suPAR], ghrelin and endothelin) are investigated to study inflammatory activity and correlation with HBi during infliximab therapy.

MATERIAL AND METHODS

Patients with Crohn's disease (n = 22) were assessed and blood samples drawn before and 1 week after infliximab infusion (5 mg/kg) and repeated after 6 months, and compared to healthy volunteers. Hs-CRP, calprotectin, suPAR, ghrelin and endothelin were analyzed with immunoassays, and total nitrite with Griess-reaction. Results were analyzed with Wilcoxon matched-pairs test, Mann-Whitney test and Spearman correlations.

RESULTS

After the first infusion visit, HBi and calprotectin values decreased while nitrite increased (p < 0.05). At the 6-month visit, pre-infusion index and biomarkers had returned to baseline levels. Post-infusion, again the values of HBi, hs-CRP and calprotectin decreased (p < 0.05). The suPAR levels did not change between pre- and post-infusion periods at either visit. Calprotectin, nitrite and suPAR differed from healthy controls throughout the study (p < 0.05). Endothelin decreased with each treatment but was, like ghrelin, not different from controls. We found HBi to correlate with hs-CRP (Spearman r = 0.32, p < 0.05), but calprotectin did not, neither did nitrate nor suPAR.

CONCLUSIONS

Although infliximab ameliorates Crohn's disease symptoms, inflammatory markers are not persistently normalized, indicating a chronic inflammatory condition that may require continued infliximab therapy.

Ghrelin and PYY in the regulation of energy balance and metabolism: lessons from mouse mutants

Effective control of body weight and energy homeostasis requires stringent regulation of caloric intake and energy expenditure. Gut-brain interactions comprise a central axis for the control of energy homeostasis by integrating the intake of nutrients with an effective utilization of ingested calories either by storage or by expenditure as cellular fuel. Ghrelin, a stomach-derived peptide, is the only known circulating orexigenic hormone. It is acylated with a medium-chain fatty acid by the enzyme ghrelin O-acetyltransferase (GOAT) and displays a broad range of activity, from central control of food intake to peripheral functions such as gastric emptying and insulin secretion. PYY, a peptide produced by L cells of the small intestine and rectum, has been shown to inhibit gut motility and is proposed to stimulate a powerful central satiety response. In recent years, pharmacological studies in animals and clinical studies in humans have contributed to our knowledge of principal ghrelin and PYY actions. However, valuable findings from studies using ghrelin-deficient mice, ghrelin receptor [growth hormone secretagogue receptor-1a (GHSR1a)]-deficient mice, double-knockout mice (for ghrelin and GHSR), and GOAT-deficient or -overexpressor mice, as well as mice deficient for PYY or neuropeptide Y receptors have allowed better definition of the actual physiological functions of ghrelin and PYY. This review summarizes findings from mutant mouse studies with emphasis on respective gene knockout and transgenic animals and describes how these studies contribute to the current understanding of how endogenous ghrelin and PYY as two major representatives of endocrine gut-brain communications may regulate energy and glucose homeostasis.

The prokinetic face of ghrelin

This review evaluated published data regarding the effects of ghrelin on GI motility using the PubMed database for English articles from 1999 to September 2009. Our strategy was to combine all available information from previous literature, in order to provide a complete structured review on the prokinetic properties of exogenous ghrelin and its potential use for treatment of various GI dysmotility ailments. We classified the literature into two major groups, depending on whether studies were done in health or in disease. We sub-classified the studies into stomach, small intestinal and colon studies, and broke them down further into studies done in vitro, in vivo (animals) and in humans. Further more, the reviewed studies were presented in a chronological order to guide the readers across the scientific advances in the field. The review shows evidences that ghrelin and its (receptor) agonists possess a strong prokinetic potential to serve in the treatment of diabetic, neurogenic or idiopathic gastroparesis and possibly, chemotherapy-associated dyspepsia, postoperative, septic or post-burn ileus, opiate-induced bowel dysfunction and chronic idiopathic constipation. Further research is necessary to close the gap in knowledge about the effect of ghrelin on the human intestines in health and disease.

Differential adipokine response in genetically predisposed lean and obese rats during inflammation: a role in modulating experimental colitis?

The relationship between a predisposition to obesity and the development of colitis is not well understood. Our aim was to characterize the adipokine response and the extent of colitis in diet-induced obese (DIO) rats. DIO and control, diet-resistant (DR) animals were administered either saline or trinitrobenzene sulfonic acid (TNBS) to induce colitis. Macroscopic damage scores and myeloperoxidase (MPO) activity were measured to determine the extent of inflammation. Trunk blood was collected for the analysis of plasminogen activator inhibitor-1 (PAI-1) as well as leptin, ghrelin, and adiponectin. Colonic epithelial physiology was assessed using Ussing chambers. DIO rats had a modestly increased circulating PAI-1 before TNBS treatment; however, during colitis, DR animals had more than a fourfold increase in circulating PAI-1 compared with DIO rats. Circulating leptin was higher in DIO rats compared with DR animals, in the inflamed and noninflamed states. These changes in TNBS-induced adipokine profile were accompanied by decreased macroscopic tissue damage score in DIO animals compared with DR tissues. Furthermore, TNBS-treated DR animals lost significantly more weight than DIO rats during active inflammation. Colonic epithelial physiology was comparable between groups, as was MPO activity. The factors contributing to the decreased colonic damage are almost certainly multifold, driven by both genetic and environmental factors, of which adipokines are likely to play a part given the increasing body of evidence for their role in modulating intestinal inflammation.

Faces of ghrelin--research for the 21st century

In this issue of Neurogastroenterology and Motility we find three new articles on different aspects of ghrelin, dealing with physiological and pathophysiological actions of the peptide. For the reader this is food for thoughts: Does this peptide do everything? Ghrelin is a gut peptide hormone well established to stimulate motility throughout most parts of the gastrointestinal (GI) tract and appetite. Ghrelin has been linked to various GI regulatory mechanisms, the most evident being hunger, over-eating and obesity. In this setting ghrelin has been studied under physiological conditions converging on obesity as a pathophysiological process where the peptide has been employed as an interesting tool for studying the development of obesity. With a widespread distribution of ghrelin receptors on various immune cells, it has been assumed that ghrelin also possesses immunoregulatory properties, thus also being of interest in intestinal inflammation research. Anti-inflammatory effects of exogenous ghrelin have been claimed in experimental colitis in mice. Further studies on this concept using ghrelin gene knock-out mice, however, show an increased inflammatory activity in experimental colitis in wild-type mice pointing to ghrelin as an enhancer of the inflammatory course of the disease. Taken together, recent studies on ghrelin indicate that the peptide is not only a regulatory agent in pathophysiological processes, but also participates in pathological disease conditions with actions that seem to even involve genetic mechanisms.