Adiponectin affects the mechanical responses in strips from the mouse gastric fundus

Adiponectin affects ileal contractility of mouse preparations

Adiponectin (ADPN) has been reported to induce inhibitory effects on gastric motor activity, which, being a source of peripheral satiety signals, would contribute to the central anorexigenic effects of the hormone in rodents. However, peripheral satiety signals can also originate from the small intestine. Since there are no data on the effects of ADPN in this gut region, the present study aimed to investigate whether ADPN affects murine ileal contractility. Immunofluorescence experiments and Western blot were also performed to reveal the expression of ADPN receptors. Mechanical responses of ileal preparations were recorded in vitro via force-displacement transducers. Preparations showed a tetrodotoxin- and atropine-insensitive spontaneous contractile activity. Electrical field stimulation (EFS) induced tetrodotoxin- and atropine-sensitive contractile responses. ADPN induced a decay of the basal tension and decreased the amplitude of either the spontaneous contractility or the EFS-induced excitatory responses. All ADPN effects were abolished by the nitric oxide (NO) synthesis inhibitor NG-nitro l-arginine. The expression of the ADPN receptor, AdipoR1, but not AdipoR2, was also revealed in enteric glial cells. The present results offer the first evidence that ADPN acts on ileal preparations. The hormone exerts inhibitory effects, likely involving AdipoR1 on enteric glial cells and NO. From a physiological point of view, it could be hypothesized that the depressant action of ADPN on ileal contractility represents an additional peripheral satiety signal which, as also described for the ileal brake, could contribute to the central anorexigenic effects of the hormone.NEW & NOTEWORTHY This study provides the first evidence that adiponectin (ADPN) is able to act on ileal preparations. Functional results demonstrate that the hormone, other than causing a slight decay of the basal tension, depresses the amplitude of both spontaneous contractility and neurally induced excitatory responses of the mouse ileum through the involvement of nitric oxide. The expression of the ADPN receptor AdipoR1 and its localization on glial cells was revealed by Western blot and immunofluorescence analysis.

Adiponectin Modulates Smooth Muscle Cell Morpho-Functional Properties in Murine Gastric Fundus via Sphingosine Kinase 2 Activation

Adipokines are peptide hormones produced by the adipose tissue involved in several biological functions. Among adipokines, adiponectin (ADPN) has antidiabetic and anti-inflammatory properties. It can also modulate food intake at central and peripheral levels, acting on hypothalamus and facilitating gastric relaxation. ADPN exerts its action interacting with two distinct membrane receptors and triggering some well-defined signaling cascades. The ceramidase activity of ADPN receptor has been reported in many tissues: it converts ceramide into sphingosine. In turn, sphingosine kinase (SK) phosphorylates it into sphingosine-1 phosphate (S1P), a crucial mediator of many cellular processes including contractility. Using a multidisciplinary approach that combined biochemical, electrophysiological and morphological investigations, we explored for the first time the possible role of S1P metabolism in mediating ADPN effects on the murine gastric fundus muscle layer. By using a specific pharmacological inhibitor of SK2, we showed that ADPN affects smooth muscle cell membrane properties and contractile machinery via SK2 activation in gastric fundus, adding a piece of knowledge to the action mechanisms of this hormone. These findings help to identify ADPN and its receptors as new therapeutic targets or as possible prognostic markers for diseases with altered energy balance and for pathologies with fat mass content alterations.

Defining the Molecular Mechanisms of the Relaxant Action of Adiponectin on Murine Gastric Fundus Smooth Muscle: Potential Translational Perspectives on Eating Disorder Management

Adiponectin (ADPN), a hormone produced by adipose tissue, facilitates gastric relaxation and can be a satiety signal in the network connecting peripheral organs and the central nervous system for feeding behavior control. Here, we performed preclinical research by morpho-functional analyses on murine gastric fundus smooth muscle to add insights into the molecular mechanisms underpinning ADPN action. Moreover, we conducted a clinical study to evaluate the potential use of ADPN as a biomarker for eating disorders (ED) based on the demonstrated gastric alterations and hormone level fluctuations that are often associated with ED. The clinical study recruited patients with ED and healthy controls who underwent blood draws for ADPN dosage and psychopathology evaluation tests. The findings of this basic research support the ADPN relaxant action, as indicated by the smooth muscle cell membrane pro-relaxant effects, with mild modifications of contractile apparatus and slight inhibitory effects on gap junctions. All of these actions engaged the ADPN/nitric oxide/guanylate cyclase pathway. The clinical data failed to unravel a correlation between ADPN levels and the considered ED, thus negating the potential use of ADPN as a valid biomarker for ED management for the moment. Nevertheless, this adipokine can modulate physiological eating behavior, and its effects deserve further investigation.

Neuronal Nitric Oxide Synthase as a Shared Target for the Effects of Adiponectin and Resistin on the Mechanical Responses of the Mouse Gastric Fundus

It has been reported that adiponectin (ADPN) and resistin are co-secreted by white mouse adipocytes and exert similar inhibitory effects in the mouse gastric fundus, in which resistin was observed to increase neuronal nitric oxide synthase (nNOS) expression. On these grounds, the present work aimed to investigate whether the effects of the two adipokines on the neurally-induced relaxant responses potentiate each other and whether there is a possible correlation with changes in nNOS expression in preparations from the mouse gastric fundus. In carbachol (CCh)-precontracted strips, electrical field stimulation elicited nitrergic relaxant responses, whose amplitude was increased by ADPN or resistin, but no additional enhancements were observed in their concomitant presence. Western blot and immunofluorescence analyses revealed that ADPN, like resistin, was able to up-regulate nNOS expression and to increase the percentage of nNOS-positive neurons in the myenteric plexus: co-treatment with the two adipokines did not induce additional changes. The results indicate that the two adipokines modulate nitrergic neurotransmission, and both do so by up-regulating nNOS expression. Therefore, nNOS appears to be a shared target for the two adipokines' effects, which, rather than mutually reinforcing each other, may represent a dual physiological control mechanism to guarantee gastric fundus relaxation.

Evidence that resistin acts on the mechanical responses of the mouse gastric fundus

Resistin, among its several actions, has been reported to exert central anorexigenic effects in rodents. Some adipokines which centrally modulate food intake have also been reported to affect the activity of gastric smooth muscle, whose motor responses represent a source of peripheral signals implicated in the control of the hunger-satiety cycle through the gut-brain axis. On this basis, in the present experiments, we investigated whether resistin too could affect the mechanical responses in the mouse longitudinal gastric fundal strips. Electrical field stimulation (EFS) elicited tetrodotoxin- and atropine-sensitive contractile responses. Resistin reduced the amplitude of the EFS-induced contractile responses. This effect was no longer detected in the presence of L-NNA, a nitric oxide (NO) synthesis inhibitor. Resistin did not influence the direct muscular response to methacholine. In the presence of carbachol and guanethidine, EFS elicited inhibitory responses whose amplitude was increased by resistin. L-NNA abolished the inhibitory responses evoked by EFS, indicating their nitrergic nature. In the presence of L-NNA, resistin did not have any effect on the EFS-evoked inhibitory responses. Western blot and immunofluorescence analysis revealed a significant increase in neuronal nitric oxide synthase (nNOS) expression in neurons of the myenteric plexus following resistin exposure. In conclusion, the present results offer the first evidence that resistin acts on the gastric fundus, likely through a modulatory action on the nitrergic neurotransmission.

The Controversial Role of Adiponectin in Appetite Regulation of Animals

Eating disorders and obesity are important health problems with a widespread global epidemic. Adiponectin (AdipoQ), the most abundant adipokine in the plasma, plays important roles in the regulation of energy homeostasis, glucose metabolism and lipid metabolism. Plasma adiponectin concentration is negatively associated with obesity and binge eating disorder. There is a growing interest in the appetite regulation function of adiponectin. However, the effect of AdipoQ on feeding behavior is controversial and closely related to nutritional status and food composition. In this review, we summarize the literatures about the discovery, structure, tissue distribution, receptors and regulation of nutritional status, and focus on the biological function of adiponectin in the regulation of food intake in the central and peripheral system.

Nitric Oxide: From Gastric Motility to Gastric Dysmotility

It is known that nitric oxide (NO) plays a key physiological role in the control of gastrointestinal (GI) motor phenomena. In this respect, NO is considered as the main non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter responsible for smooth muscle relaxation. Moreover, many substances (including hormones) have been reported to modulate NO production leading to changes in motor responses, further underlying the importance of this molecule in the control of GI motility. An impaired NO production/release has indeed been reported to be implicated in some GI dysmotility. In this article we wanted to focus on the influence of NO on gastric motility by summarizing knowledge regarding its role in both physiological and pathological conditions. The main role of NO on regulating gastric smooth muscle motor responses, with particular reference to NO synthases expression and signaling pathways, is discussed. A deeper knowledge of nitrergic mechanisms is important for a better understanding of their involvement in gastric pathophysiological conditions of hypo- or hyper-motility states and for future therapeutic approaches. A possible role of substances which, by interfering with NO production, could prove useful in managing such motor disorders has been advanced.

Adiponectin and the regulation of gastric content volume in the newborn rat

BACKGROUND

Oral intake is dependent on the gastric ability to accommodate the food bolus. Comparatively, neonates have a smaller gastric capacity than adults and this may limit the volume of their milk intake. Yet, we previously reported that the newborn rat gastric milk volume is greatest after birth and, when normalized to body weight, decreases with postnatal age. Such age-dependent changes are not the result of intake differences, but greater gastric accommodation and reduced emptying rate.

AIM

Hypothesizing that breastmilk-derived adiponectin is the factor regulating gastric accommodation in neonates, we comparatively evaluated its effects on the rat fundic muscle tone at different postnatal ages.

METHODS

In freshly dispersed smooth muscle cells (SMC), we measured the adiponectin effect on the carbachol-induced length changes.

RESULTS

Adiponectin significantly reduced the carbachol-stimulated SMC shortening independently of age. In the presence of the inhibitor iberiotoxin, the adiponectin effect on SMC shortening was suppressed, suggesting that it is mediated via large-conductance Ca²⁺ sensitive K⁺ channel activation. Lastly, we comparatively measured the newborn rat gastric milk curd adiponectin content in one- and two-week-old rats and found a 50% lower value in the latter.

CONCLUSION

Adiponectin, a major component of breastmilk, downregulates fundic smooth muscle contraction potential, thus facilitating gastric volume accommodation. This rodent’s adaptive response maximizes breastmilk intake volume after birth.

Otilonium Bromide treatment prevents nitrergic functional and morphological changes caused by chronic stress in the distal colon of a rat IBS model

Irritable bowel syndrome (IBS) is a highly prevalent gastrointestinal disorder characterized by periods of remission and exacerbation. Among the risk factors to develop IBS, psychosocial stress is widely acknowledged. The water avoidance stress repeatedly applied (rWAS) is considered effective to study IBS etio-pathogenesis. Otilonium bromide (OB), a drug with multiple mechanisms of action, is largely used to treat IBS patients. Orally administered, it concentrates in the large bowel and significantly ameliorates the IBS symptomatology. Presently, we tested whether rWAS rats developed neuro-muscular abnormalities in the distal colon and whether OB treatment prevented them. The investigation was focussed on the nitrergic neurotransmission by combining functional and morphological methodologies. The results confirm rWAS as reliable animal model to investigate the cellular mechanisms responsible for IBS: exposure to one-hour psychosocial stress for 10 days depressed muscle contractility and increased iNOS expression in myenteric neurons. OB treatment counteracted these effects. We hypothesize that these effects are due to the corticotropin-releasing factor (CRF) release, the main mediator of the psychosocial stress, followed by a CRF1receptor activation. OB, that was shown to prevent CRF1r activation, reasonably interrupted the cascade events that bring to the mechanical and immunohistochemical changes affecting rWAS rat colon.

AdipoRon, an Orally Active, Synthetic Agonist of AdipoR1 and AdipoR2 Receptors Has Gastroprotective Effect in Experimentally Induced Gastric Ulcers in Mice

Introduction: Adiponectin is a hormone secreted by adipocytes, which exhibits insulin-sensitizing and anti-inflammatory properties and acts through adiponectin receptors: AdipoR1 and AdipoR2. The aim of the study was to evaluate whether activation of adiponectin receptors AdipoR1 and AdipoR2 with an orally active agonist AdipoRon has gastroprotective effect and to investigate the possible underlying mechanism. Methods: We used two well-established mouse models of gastric ulcer (GU) induced by oral administration of EtOH (80% solution in water) or diclofenac (30 mg/kg, p.o.). Gastroprotective effect of AdipoRon (dose 5 and 50 mg/kg p.o.) was compared to omeprazole (20 mg/kg p.o.) or 5% DMSO solution (control). Clinical parameters of gastroprotection were assessed using macroscopic (gastric lesion area) and microscopic (evaluation of the gastric mucosa damage) scoring. To establish the molecular mechanism, we measured: myeloperoxidase (MPO), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) activities; glutathione (GSH) level; and IL-1β, adenosine monophosphate-activated protein kinase (AMPK), and phosphorylated AMPK expression in gastric tissue. Results: AdipoRon produced a gastroprotective effect in both GU mouse models as evidenced by significantly lower macroscopic and microscopic damage scores. AdipoRon exhibited anti-inflammatory effect by reduction in MPO activity and IL-1β expression in the gastric tissue. Moreover, AdipoRon induced antioxidative action, as demonstrated with higher GSH levels, and increased SOD and GPX activity. Conclusions: Activation of AdipoR1 and AdipoR2 using AdipoRon reduced gastric lesions and enhanced cell response to oxidative stress. Our data suggest that AdipoR1 and AdipoR2 activation may be an attractive therapeutic strategy to inhibit development of gastric ulcers.

Adiponectin Exerts Peripheral Inhibitory Effects on the Mouse Gastric Smooth Muscle through the AMPK Pathway

Some adipokines, such as adiponectin (ADPN), other than being implicated in the central regulation of feeding behavior, may influence gastric motor responses, which are a source of peripheral signals that also influence food intake. The present study aims to elucidate the signaling pathways through which ADPN exerts its actions in the mouse gastric fundus. To this purpose, we used a multidisciplinary approach. The mechanical results showed that ADPN caused a decay of the strip basal tension, which was abolished by the nitric oxide (NO) synthesis inhibitor, L-N^G-nitro arginine (L-NNA). The electrophysiological experiments confirmed that all ADPN effects were abolished by L-NNA, except for the reduction of Ca²⁺ current, which was instead prevented by the inhibitor of AMP-activated protein kinase (AMPK), dorsomorphin. The activation of the AMPK signaling by ADPN was confirmed by immunofluorescence analysis, which also revealed the ADPN R1 receptor (AdipoR1) expression in glial cells of the myenteric plexus. In conclusion, our results indicate that ADPN exerts an inhibitory action on the gastric smooth muscle by acting on AdipoR1 and involving the AMPK signaling pathway at the peripheral level. These findings provide novel bases for considering AMPK as a possible pharmacologic target for the potential treatment of obesity and eating disorders.

Glucagon-like peptide-2 interferes with the neurally-induced relaxant responses in the mouse gastric strips through VIP release

Glucagon-like peptide-2 (GLP-2) has been reported to indirectly relax gastric smooth muscle. In the present study we investigated, through a combined mechanical and immunohistochemical approach, whether GLP-2 interferes with the electrical field stimulation (EFS)-induced vipergic relaxant responses and the mechanism through which it occurs. For functional experiments, strips from the mouse gastric fundus were mounted in organ baths for isometric recording of the mechanical activity. Vasoactive intestinal peptide (VIP) immunoreactivity in GLP-2 exposed specimens was also evaluated by immunohistochemistry. In carbachol pre-contracted strips, GLP-2 (20 nM) evoked a tetrodotoxin (TTX)-sensitive relaxation, similar in shape to the TTX-insensitive of 100 nM VIP. In the presence of GLP-2, VIP had no longer effects and no more response to GLP-2 was observed following VIP receptor saturation. EFS (4-16 Hz) induced a fast relaxant response followed, at the higher stimulation frequencies (≥ 8 Hz), by a slow one. This latter was abolished either by GLP-2 or VIP receptor saturation as well as by the VIP receptor antagonist, VIP 6-28 (10 μM). A decrease of VIP-immunoreactive nerve structures in the GLP-2 exposed specimens was observed. These results suggest that, in the mouse gastric fundus, GLP-2 influences the EFS-induced slow relaxant response by promoting neuronal VIP release.

Can adiponectin have an additional effect on the regulation of food intake by inducing gastric motor changes?

The regulation of food intake is a complex mechanism, and the hypothalamus is the main central structure implicated. In particular, the arcuate nucleus appears to be the most critical area in the integration of multiple peripheral signals. Among these signals, those originating from the white adipose tissue and the gastrointestinal tract are known to be involved in the regulation of food intake. The present paper focuses on adiponectin, an adipokine secreted by white adipose tissue, which is reported to have a role in the control of feeding by acting centrally. The recent observation that adiponectin is also able to influence gastric motility raises the question of whether this action represents an additional peripheral mechanism that concurs with the central effects of the hormone on food intake. This possibility, which represents an emerging aspect correlating the central and peripheral effects of adiponectin in the hunger-satiety cycle, is discussed in the present paper.

Adiponectin Decreases Gastric Smooth Muscle Cell Excitability in Mice

Some adipokines known to regulate food intake at a central level can also affect gastrointestinal motor responses. These are recognized to be peripheral signals able to influence feeding behavior as well. In this view, it has been recently observed that adiponectin (ADPN), which seems to have a role in sending satiety signals at the central nervous system level, actually affects the mechanical responses in gastric strips from mice. However, at present, there are no data in the literature about the electrophysiological effects of ADPN on gastric smooth muscle. To this aim, we achieved experiments on smooth muscle cells (SMCs) of gastric fundus to find out a possible action on SMC excitability and on membrane phenomena leading to the mechanical response. Experiments were made inserting a microelectrode in a single cell of a muscle strip of the gastric fundus excised from adult female mice. We found that ADPN was able to hyperpolarize the resting membrane potential, to enhance the delayed rectifier K⁺ currents and to reduce the voltage-dependent Ca²⁺ currents. Our overall results suggest an inhibitory action of ADPN on gastric SMC excitation-contraction coupling. In conclusion, the depressant action of ADPN on the gastric SMC excitability, here reported for the first time, together with its well-known involvement in metabolism, might lead us to consider a possible contribution of ADPN also as a peripheral signal in the hunger-satiety cycle and thus in feeding behavior.

Adipocytes-released Peptides Involved in the Control of Gastrointestinal Motility

The present review focuses on adipocytes-released peptides known to be involved in the control of gastrointestinal motility, acting both centrally and peripherally. Thus, four peptides have been taken into account: leptin, adiponectin, nesfatin-1, and apelin. The discussion of the related physiological or pathophysiological roles, based on the most recent findings, is intended to underlie the close interactions among adipose tissue, central nervous system, and gastrointestinal tract. The better understanding of this complex network, as gastrointestinal motor responses represent peripheral signals involved in the regulation of food intake through the gut-brain axis, may also furnish a cue for the development of either novel therapeutic approaches in the treatment of obesity and eating disorders or potential diagnostic tools.