The anti-inflammatory effect of leptin on experimental colitis: involvement of endogenous glucocorticoids

Leptin-resistant Zucker rats with trinitrobenzene sulfonic acid colitis present a reduced inflammatory response but enhanced epithelial damage

The role of leptin in the development of intestinal inflammation remains controversial, since proinflammatory and anti-inflammatory effects have been described. This study describes the effect of the absence of leptin signaling in intestinal inflammation. Experimental colitis was induced by intrarectal administration of trinitrobenzene sulfonic acid (TNBS) to lean and obese Zucker rats (n = 10). Effects on inflammation and mucosal barrier were studied. Bacterial translocation and LPS concentration were evaluated together with colonic permeability to 4-kDa FITC-dextran. Obese Zucker rats showed a lower intestinal myeloperoxidase and alkaline phosphatase activity, reduced alkaline phosphatase sensitivity to levamisole, and diminished colonic expression of Nos2, Tnf, and Il6, indicating attenuated intestinal inflammation, associated with attenuated STAT3, AKT, and ERK signaling in the colonic tissue. S100a8 and Cxcl1 mRNA levels were maintained, suggesting that in the absence of leptin signaling neutrophil activation rather than infiltration is hampered. Despite the lower inflammatory response, leptin resistance enhanced intestinal permeability, reflecting an increased epithelial damage. This was shown by augmented LPS presence in the portal vein of colitic obese Zucker rats, associated with induction of tissue nonspecific alkaline phosphatase, LPS-binding protein, and CD14 hepatic expression (involved in LPS handling). This was linked to decreased ZO-1 immunoreactivity in tight junctions and lower occludin expression. Our results indicate that obese Zucker rats present an attenuated inflammatory response to TNBS, but increased intestinal epithelial damage allowing the passage of bacterial antigens.NEW & NOTEWORTHY Obese Zucker rats, which are resistant to leptin, exhibit a diminished inflammatory response in the trinitrobenzenesulfonic acid (TNBS) model of colitis, suggesting leptin role is proinflammatory. At the same time, obese Zucker rats present a debilitated intestinal barrier function, with increased translocation of LPS. Zucker rats present a dual response in the TNBS model of rat colitis.

The role of immune dysfunction in obesity-associated cancer risk, progression, and metastasis

Obesity has been linked to an increased risk of and a worse prognosis for several types of cancer. A number of interrelated mediators contribute to obesity's pro-tumor effects, including chronic adipose inflammation and other perturbations of immune cell development and function. Here, we review studies examining the impact of obesity-induced immune dysfunction on cancer risk and progression. While the role of adipose tissue inflammation in obesity-associated cancer risk has been well characterized, the effects of obesity on immune cell infiltration and activity within the tumor microenvironment are not well studied. In this review, we aim to highlight the impact of both adipose-mediated inflammatory signaling and intratumoral immunosuppressive signaling in obesity-induced cancer risk, progression, and metastasis.

Circulating Leptin Levels as a Potential Biomarker in Inflammatory Bowel Diseases: A Systematic Review and Meta-Analysis

BACKGROUND

The differential diagnosis of inflammatory bowel diseases (IBDs) between Crohn's disease (CD) and ulcerative colitis (UC) is important for designing an effective therapeutic regimen. However, without any adequate gold standard method for differential diagnosis currently, therapeutic design remains a major challenge in clinical practice. In this context, recent studies have showed that circulating leptin stands out as a potential biomarker for the categorization of IBDs. Thus, we aimed to summarize the current understanding of the prognostic and diagnostic value of serum leptin in patients with IBDs.

METHODS

A systematic search was performed in PubMed/MEDLINE, Scopus, Cochrane Library, and Web of Science databases. Articles that aimed to study the relationship between circulating levels of leptin and IBDs were included. Finally, the meta-analysis was performed with the mean serum leptin levels in patients with IBDs and healthy controls using RevMan 5.3 software, with I2 > 50% as a criterion for substantial heterogeneity.

RESULTS

Nineteen studies were included. Serum leptin levels among patients with IBDs and healthy controls did not show a significant difference (95% CI, -2.15 to 0.57; I2, 86%, P ≤ 0.00001). Similarly, there was no association of leptin levels with the activity of IBDs (95% CI, -0.24 to 0.06; I2, 50%; P = 0.13). However, serum leptin levels were significantly higher in patients with CD than those in patients with UC (95% CI, -2.09 to -0.37; I2, 7%; P ≤ 0.36).

CONCLUSION

This review suggested that serum leptin levels might be a promising biomarker to help in the differentiation between CD and UC.

Immunolocalization of leptin and leptin receptor in colorectal mucosa of ulcerative colitis, Crohn's disease and control subjects with no inflammatory bowel disease

The expression of leptin and leptin receptor (Ob-R) has been partially elucidated in colon of patients with inflammatory bowel diseases (IBDs), even though leptin is involved in angiogenesis and inflammation. We previously reported overexpression of GLUT5 fructose transporter, in aberrant clusters of lymphatic vessels in lamina propria of IBD and controls. Here, we examine leptin and Ob-R expression in the same biopsies. Specimens were obtained from patients with ulcerative colitis (UC), Crohn’s disease (CD) and controls who underwent screening for colorectal cancer, follow-up after polypectomy or with a history of lower gastrointestinal symptoms. Immunohistochemistry revealed leptin in apical and basolateral membranes of short epithelial portions, Ob-R on the apical pole of epithelial cells. Leptin and Ob-R were also identified in structures and cells scattered in the lamina propria. In UC, a significant correlation between leptin and Ob-R in the lamina propria was found in all inflamed samples, beyond non-inflamed samples of the proximal tract, while in CD, it was found in inflamed distal samples. Most of the leptin and Ob-R positive areas in the lamina propria were also GLUT5 immunoreactive in inflamed and non-inflamed mucosa. A significant correlation of leptin or Ob-R expression with GLUT5 was observed in the inflamed distal samples from UC. Our findings suggest that there are different sites of leptin and Ob-R expression in large intestine and those in lamina propria do not reflect the status of mucosal inflammation. The co-localization of leptin and/or Ob-R with GLUT5 may indicate concomitance effects in colorectal lamina propria areas.

L-Glutamine and Physical Exercise Prevent Intestinal Inflammation and Oxidative Stress Without Improving Gastric Dysmotility in Rats with Ulcerative Colitis

The aim of this study was to evaluate the effects of glutamine supplementation or exercise on gastric emptying and intestinal inflammation in rats with ulcerative colitis (UC). Strength exercise consisted of jump training 4 × 10 repetitions/5 days a week/8 weeks with progressive overload. Endurance exercise consisted of swimming without overload for a period of 1 h a day/5 days a week/8 weeks. Another group (sedentary) of animals was supplemented with L-glutamine (1 g/kg of body weight) orally for 8 weeks before induction of UC. Colitis was induced by intra-colonic administration of 1 mL of 4% acetic acid. We assessed gastric emptying, macroscopic and microscopic scoring, oxidative stress markers, and IL-1β, IL-6, and (TNF-α) levels. The UC significantly increased (p < 0.05) the gastric emptying compared with the saline control group. We observed a significantly decrease (p < 0.05) in body weight gain in UC rats compared with the control groups. Both exercise interventions and L-glutamine supplementation significantly prevented (p < 0.05) weight loss compared with the UC group. Strength and endurance exercises significantly prevented (p < 0.05) the increase of microscopic scores and oxidative stress (p < 0.05). L-glutamine supplementation in UC rats prevented hemorrhagic damage and improved oxidative stress markers (p < 0.05). Strength and endurance exercises and glutamine decreased the concentrations of inflammatory cytokines IL-1β, IL-6, and TNF-α compared with the UC group (p < 0.05). Strength and endurance exercises and L-glutamine supplementation prevented intestinal inflammation and improved cytokines and oxidative stress levels without altering gastric dysmotility in rats with UC.

Leptin protects brain from ischemia/reperfusion-induced infarction by stabilizing the blood-brain barrier to block brain infiltration by the blood-borne neutrophils

The cellular and molecular mechanisms underlying leptin-mediated brain protection against cerebral ischemia were investigated at the blood-brain barrier (BBB) and neutrophil level. Through the ischemia/reperfusion (I/R) animal model, we found that leptin expression level was significantly decreased in ischemic hemisphere. Brain injection with leptin (15 μg/kg, intracisternally) could block the I/R-increased BBB permeability, activation of matrix metallopeptidase 9 (MMP-9) and brain infiltration of blood-borne neutrophils to reduce the infarct volume of ischemic brain. The brain expression level of tight junction protein ZO-1 as well as number and motility of neutrophils in blood was all increased by the same injection, indicating BBB stability (rather than reduction in neutrophils) played a major role in the leptin-inhibited brain infiltration of neutrophils. Leptin-mediated protection of BBB was further confirmed in vitro, through a BBB cellular model under the in vitro ischemic condition (G/R: glucose-oxygen-serum deprivation followed by GOS restoration). The results showed that leptin again could block the G/R-increased neutrophil adherence to EC layer as well as BBB permeability, likely by stimulating the endothelial expression of ZO-1 and VE-Cadherin. The study has demonstrated that leptin could protect ischemic brain via multiple ways (other than neuronal protection), by inhibiting the BBB permeability, brain infiltration of the blood-borne neutrophils and neutrophil adherence to vascular ECs. The role of leptin in vascular biology of stroke could further support its therapeutic potential in other neurodegenerative diseases, associated with BBB disorder.

Glucocorticoids Promote the Onset of Acute Experimental Colitis and Cancer by Upregulating mTOR Signaling in Intestinal Epithelial Cells

The therapeutic effects of glucocorticoids on colitis and colitis-associated cancer are unclear. In this study, we investigated the therapeutic roles of glucocorticoids in acute experimental ulcerative colitis and colitis-associated cancer in mice and their immunoregulatory mechanisms. Murine acute ulcerative colitis was induced by dextran sulfate sodium (DSS) and treated with dexamethasone (Dex) at different doses. Dex significantly exacerbated the onset and severity of DSS-induced colitis and potentiated mucosal inflammatory macrophage and neutrophil infiltration, as well as cytokine production. Furthermore, under inflammatory conditions, the expression of the glucocorticoid receptor (GR) did not change significantly, while mammalian target of rapamycin (mTOR) signaling was higher in colonic epithelial cells than in colonic immune cells. The deletion of mTOR in intestinal epithelial cells, but not that in myeloid immune cells, in mice significantly ameliorated the severe course of colitis caused by Dex, including weight loss, clinical score, colon length, pathological damage, inflammatory cell infiltration and pro-inflammatory cytokine production. These data suggest that mTOR signaling in intestinal epithelial cells, mainly mTORC1, plays a critical role in the Dex-induced exacerbation of acute colitis and colitis-associated cancer. Thus, these pieces of evidence indicate that glucocorticoid-induced mTOR signaling in epithelial cells is required in the early stages of acute ulcerative colitis by modulating the dynamics of innate immune cell recruitment and activation.

Experimental colitis reduces microglial cell activation in the mouse brain without affecting microglial cell numbers

Inflammatory bowel disease (IBD) patients frequently suffer from anxiety disorders and depression, indicating that altered gut-brain axis signalling during gastrointestinal inflammation is a risk factor for psychiatric disease. Microglia, immune cells of the brain, is thought to be involved in a number of mental disorders, but their role in IBD is largely unknown. In the current work, we investigated whether colitis induced by dextran sulphate sodium (DSS), a murine model of IBD, alters microglial phenotypes in the brain. We found that colitis caused a reduction of Iba-1 and CD68 immunoreactivity, microglial activation markers, in specific brain regions of the limbic system such as the medial prefrontal cortex (mPFC), while other areas remained unaffected. Flow cytometry showed an increase of monocyte-derived macrophages during colitis and gene expression analysis in the mPFC showed pronounced changes of microglial markers including cluster of differentiation 86 (CD86), tumour necrosis factor-α, nitric oxide synthase 2, CD206 and chitinase-like protein 3 consistent with both M1 and M2 activation. Taken together, these findings suggest that experimental colitis-induced inflammation is propagated to the brain altering microglial function.

Elevated expression of the leptin receptor ob‑R may contribute to inflammation in patients with ulcerative colitis

The effect of leptin on ulcerative colitis (UC) has been controversial. The present study aimed to investigate the role of leptin and its receptor ob‑R in UC and the underlying mechanism of this role. The level of serum leptin and the protein expression of the leptin receptor ob‑R in the colonic mucosa were determined in patients with UC. Experimental colitis was induced through intrarectal administration of 2,4,6‑trinitrobenzene sulfonic acid (TNBS) in leptin receptor‑deficient Zucker rats (LR‑D). The body weight, disease activity index, colon length, and macroscopic and histopathological appearance were evaluated. Furthermore, the myeloperoxidase (MPO) enzyme activity and cytokine levels in colon tissues were also determined. The expression of the signal transducer and activator of transcription 3 (STAT3), phosphorylated STAT3 (p‑STAT3), nuclear factor (NF)‑κB‑p65, and Ras homolog gene family member A (RhoA) proteins in colon tissues was assessed. The results revealed that the expression of the leptin receptor ob‑R was increased in the colonic mucosa but the serum leptin level was not altered in patients with UC compared with healthy volunteers. The severity of experimental colitis, represented by body weight loss, disease activity index, colon length, and macroscopic and histological changes, was ameliorated in LR‑D rats compared with the wild‑type (WT) rats. Moreover, the MPO activity; levels of cytokines including interleukin (IL)‑1β, IL‑6, and tumor necrosis factor‑α; and expression of p‑STAT3, NF‑κB, and RhoA proteins were reduced in colon tissues of LR‑D rats compared with WT rats. In conclusion, activation of the leptin receptor ob‑R is an important pathogenic mechanism of UC, and leptin receptor deficiency may provide resistance against TNBS‑induced colitis by inhibiting the NF‑κB and RhoA signaling pathways.

Impact of chronic immobilization stress on parameters of colonic homeostasis in BALB/c mice

The intestinal epithelium is a monolayer of cells arranged side‑by‑side and connected by tight junction (TJ) proteins expressed at the apical extreme of the paracellular membrane. This layer prevents stress‑induced inflammatory responses, thus helping to maintain gut barrier function and gut homeostasis. The aim of the present study was to evaluate the effects of chronic immobilization stress on the colonic expression of various parameters of homeostasis. A total of two groups of female BALB/c mice (n=6) were included: A stressed group (short‑term immobilization for 2 h/day for 4 consecutive days) and an unstressed (control) group. Colon samples were obtained to detect neutrophils and goblet cells by optical microscopy, TJ protein expression (occludin, and claudin ‑2, ‑4, ‑7, ‑12 and ‑15) by western blotting, mRNA levels of TJ genes and proinflammatory cytokines [tumor necrosis factor (TNF)‑α, interleukin (IL)‑1β, ‑6 and ‑8] by reverse transcription‑quantitative PCR, fecal lactoferrin by ELISA and the number of colony‑forming units of aerobic bacteria. Compared with goblet cells in control mice, goblet cells were enlarged and reduced in number in stressed mice, whereas neutrophil cellularity was unaltered. Stressed mice exhibited reduced mRNA expression for all evaluated TJ mRNAs, with the exception of claudin‑7, which was upregulated. Protein levels of occludin and all claudins (with the exception of claudin‑12) were decreased in stressed mice. Fecal lactoferrin, proinflammatory cytokine mRNA levels and aerobic bacterial counts were all increased in the stressed group. These results indicated that immobilization stress induced proinflammatory and potential remodeling effects in the colon by decreasing TJ protein expression. The present study may be a useful reference for therapies aiming to regulate the effects of stress on intestinal inflammatory dysfunction.

Clinical associations of serum leptin and leptin/adiponectin ratio in systemic sclerosis

INTRODUCTION

Leptin and adiponectin have recently received the attention of researchers as attractive biomarkers in systemic sclerosis (SSc) because of their role in the inflammatory process, vascular function and fibrosis. We hypothesized that leptin and adiponectin may be associated with disease activity and severity in patients with SSc.

AIM

To compare serum leptin, adiponectin and leptin/adiponectin levels in patients with SSc and healthy controls and to evaluate their possible relationship with frequently used laboratory markers and clinical findings.

MATERIAL AND METHODS

The study included 48 Caucasian female patients with SSc and 38 healthy controls. Serum concentrations of leptin and adiponectin were measured in patients and controls using commercially available ELISA Kits (Quantikine ELISA Kit R&D Systems, Minneapolis, MN, USA). The results were assessed by the Mann-Whitney U-test and Spearman's correlation test.

RESULTS

Leptin and adiponectin levels correlated with body mas index in SSc patients (r = 0.495, p = 0.000398 and r = -0.306; p = 0.0342) in contrast to healthy controls (p = 0.070 and p = 0.256, respectively), and, in SSc patients only, a strong negative correlation was observed between leptin and adiponectin serum levels (r = -0.314; p = 0.0312). Diffuse form of the disease (dcSSc) was associated with significantly lower serum adiponectin levels (8638.62 ±10382.62). Active disease was associated with significantly lower leptin concentration (13700.49 ±18293.32) and there was a significant negative correlation between leptin serum level and activity index score (r = -0.342; p = 0.0185).

CONCLUSIONS

The results of our study indicate that leptin levels might correlate with disease activity and subtype in SSc patients.

Leptin Prevents Lipopolysaccharide-Induced Depressive-Like Behaviors in Mice: Involvement of Dopamine Receptors

Depression is a chronic and recurrent disorder, associated with high morbidity and risk of suicide. Leptin was firstly described as an anti-obesity hormone, but several actions of leptin in CNS have been reported. In fact, leptin regulates dopaminergic neurotransmission in mesolimbic areas and has antidepressant-like properties in stress-based models. In the present study, we investigated, for the first time, putative antidepressant-like effects of leptin in an animal model of depressive-like behaviors induced by lipopolysaccharide (LPS), and the potential involvement of dopamine receptors as mediators of those behavioral effects. Mice were injected leptin (1.5 mg/kg, IP) or imipramine prior to LPS administration. To evaluate the involvement of dopamine receptors, different experimental groups were pretreated with either the dopaminergic antagonist SCH23390, for D1 receptors or raclopride, for D2/D3 receptors, prior to leptin injection. Twenty-four hours post-LPS, mice were submitted to the forced swimming and sucrose preference tests. In addition, IL-1β levels were determined in the prefrontal cortex (PFC), hippocampus and striatum. BDNF levels were measured in the hippocampus. Our results showed that leptin, similarly to imipramine, prevented the core behavioral alterations induced by LPS (despair-like behavior and anhedonia), without altering locomotion. In neurochemical analysis, leptin restored LPS-induced changes in IL-1β levels in the PFC and striatum, and increased BDNF levels in the hippocampus. The blockade of dopamine D1 and D2/D3 receptors inhibited leptin's antidepressant-like effects, whilst only the blockade of D1-like receptors blunted leptin-induced increments in prefrontal IL-1β levels. Our results indicate that leptin has antidepressant-like effects in an inflammatory model of depression with the contribution, at least partial, of dopamine receptors.

Visceral Inflammation and Immune Activation Stress the Brain

Stress refers to a dynamic process in which the homeostasis of an organism is challenged, the outcome depending on the type, severity, and duration of stressors involved, the stress responses triggered, and the stress resilience of the organism. Importantly, the relationship between stress and the immune system is bidirectional, as not only stressors have an impact on immune function, but alterations in immune function themselves can elicit stress responses. Such bidirectional interactions have been prominently identified to occur in the gastrointestinal tract in which there is a close cross-talk between the gut microbiota and the local immune system, governed by the permeability of the intestinal mucosa. External stressors disturb the homeostasis between microbiota and gut, these disturbances being signaled to the brain via multiple communication pathways constituting the gut-brain axis, ultimately eliciting stress responses and perturbations of brain function. In view of these relationships, the present article sets out to highlight some of the interactions between peripheral immune activation, especially in the visceral system, and brain function, behavior, and stress coping. These issues are exemplified by the way through which the intestinal microbiota as well as microbe-associated molecular patterns including lipopolysaccharide communicate with the immune system and brain, and the mechanisms whereby overt inflammation in the GI tract impacts on emotional-affective behavior, pain sensitivity, and stress coping. The interactions between the peripheral immune system and the brain take place along the gut-brain axis, the major communication pathways of which comprise microbial metabolites, gut hormones, immune mediators, and sensory neurons. Through these signaling systems, several transmitter and neuropeptide systems within the brain are altered under conditions of peripheral immune stress, enabling adaptive processes related to stress coping and resilience to take place. These aspects of the impact of immune stress on molecular and behavioral processes in the brain have a bearing on several disturbances of mental health and highlight novel opportunities of therapeutic intervention.

Dextran sulfate sodium-induced colitis alters stress-associated behaviour and neuropeptide gene expression in the amygdala-hippocampus network of mice

Psychological stress causes disease exacerbation and relapses in inflammatory bowel disease (IBD) patients. Since studies on stress processing during visceral inflammation are lacking, we investigated the effects of experimental colitis as well as psychological stress on neurochemical and neuroendocrine changes as well as behaviour in mice. Dextran sulfate sodium (DSS)-induced colitis and water avoidance stress (WAS) were used as mouse models of colitis and mild psychological stress, respectively. We measured WAS-associated behaviour, gene expression and proinflammatory cytokine levels within the amygdala, hippocampus and hypothalamus as well as plasma levels of cytokines and corticosterone in male C57BL/6N mice. Animals with DSS-induced colitis presented with prolonged immobility during the WAS session, which was associated with brain region-dependent alterations of neuropeptide Y (NPY), NPY receptor Y1, corticotropin-releasing hormone (CRH), CRH receptor 1, brain-derived neurotrophic factor and glucocorticoid receptor gene expression. Furthermore, the combination of DSS and WAS increased interleukin-6 and growth regulated oncogene-α levels in the brain. Altered gut-brain signalling in the course of DSS-induced colitis is thought to cause the observed distinct gene expression changes in the limbic system and the aberrant molecular and behavioural stress responses. These findings provide new insights into the effects of stress during IBD.

Hormonal protection in acute pancreatitis by ghrelin, leptin and melatonin

Acute pancreatitis is a nonbacterial disease of the pancreas. The severe form of this ailment is characterized by high mortality. Whether acute pancreatitis develops as the severe type or resolves depends on the intensity of the inflammatory process which is counteracted by the recruitment of innate defense mechanisms. It has been shown that the hormones ghrelin, leptin and melatonin are able to modulate the immune function of the organism and to protect the pancreas against inflammatory damage. Experimental studies have demonstrated that the application of these substances prior to the induction of acute pancreatitis significantly attenuated the intensity of the inflammation and reduced pancreatic tissue damage. The pancreatic protective mechanisms of the above hormones have been related to the mobilization of non-specific immune defense, to the inhibition of nuclear factor kappa B and modulation of cytokine production, to the stimulation of heat shock proteins and changes of apoptotic processes in the acinar cells, as well as to the activation of antioxidant system of the pancreatic tissue. The protective effect of ghrelin seems to be indirect and perhaps dependent on the release of growth hormone and insulin-like growth factor 1. Leptin and ghrelin, but not melatonin, employ sensory nerves in their beneficial action on acute pancreatitis. It is very likely that ghrelin, leptin and melatonin could be implicated in the natural protection of the pancreatic gland against inflammatory damage because the blood levels of these substances increase in the initial phase of pancreatic inflammation. The above hormones could be a part of the innate resistance system which might remove noxious factors and could suppress or attenuate the inflammatory process in the pancreas.

Physiological concentrations of leptin do not affect human neutrophils

Leptin is an adipokine that is thought to be important in many inflammatory diseases, and is known to influence the function of several leukocyte types. However, no clear consensus is present regarding the responsiveness of neutrophils for this adipokine. In this study a 2D DIGE proteomics approach was used as an unbiased approach to identify leptin-induced effects on neutrophils. Additionally chemotaxis and survival experiments were performed to reproduce results from literature showing putative effects of leptin on these neutrophil responses. Leptin did not induce any significant changes in the proteome provided leptin was added at physiologically relevant concentrations (250 ng). Our leptin batches were biologically active as they induced proliferation in LeptinR expressing Ba/F3 cells. At high concentrations (25000 ng) leptin induced a change in neutrophil proteome. Seventeen differently regulated spots were identified of which twelve could be characterized by mass spectrometry. Two of these identified proteins, SerpinB1 and p40 phox, were chosen for further analysis but leptin-induced expression analyzed by western blot were highly variable. Additionally leptin also induced neutrophil survival at these high concentrations. No leptin-induced chemotaxis of human neutrophils was detected at any concentration. In conclusion, physiological concentrations of leptin do not affect neutrophils. High leptin concentrations induced survival and changes in the neutrophils proteome, but this was most likely mediated by an indirect effect. However, it cannot be ruled out that the effects were mediated by a yet not-identified leptin receptor on human neutrophils.

Leptin: molecular mechanisms, systemic pro-inflammatory effects, and clinical implications

Leptin, the adipokine produced mainly by the white adipose tissue, plays important roles not only in the regulation of food intake, but also in controlling immunity and inflammation. It has been widely demonstrated that the absence of leptin leads to immune defects in animal and human models, ultimately increasing mortality. Leptin also regulates inflammation by means of actions on its receptor, that is widely spread across different immune cell populations. The molecular mechanisms by which leptin determines its biological actions have also been recently elucidated, and three intracellular pathways have been implicated in leptin actions: JAK-STAT, PI3K, and ERK 1/2. These pathways are closely regulated by intracellular proteins that decrease leptin biological activity. In this review, we discuss the molecular mechanisms by which leptin regulates immunity and inflammation, and associate those mechanisms with chronic inflammatory disorders.

Environmental enrichment and gut inflammation modify stress-induced c-Fos expression in the mouse corticolimbic system

Environmental enrichment (EE) has a beneficial effect on rodent behaviour, neuronal plasticity and brain function. Although it may also improve stress coping, it is not known whether EE influences the brain response to an external (psychological) stressor such as water avoidance stress (WAS) or an internal (systemic) stressor such as gastrointestinal inflammation. This study hence explored whether EE modifies WAS-induced activation of the mouse corticolimbic system and whether this stress response is altered by gastritis or colitis. Male C67BL/6N mice were housed under standard or enriched environment for 9 weeks, after which they were subjected to a 1-week treatment with oral iodoacetamide to induce gastritis or oral dextran sulfate sodium to induce colitis. Following exposure to WAS the expression of c-Fos, a marker of neuronal activation, was measured by immunocytochemistry. EE aggravated experimentally induced colitis, but not gastritis, as shown by an increase in the disease activity score and the colonic myeloperoxidase content. In the brain, EE enhanced the WAS-induced activation of the dentate gyrus and unmasked an inhibitory effect of gastritis and colitis on WAS-evoked c-Fos expression within this part of the hippocampus. Conversely, EE inhibited the WAS-evoked activation of the central amygdala and prevented the inhibitory effect of gastritis and colitis on WAS-evoked c-Fos expression in this region. EE, in addition, blunted the WAS-induced activation of the infralimbic cortex and attenuated the inhibitory effect of gastritis and colitis on WAS-evoked c-Fos expression in this area. These data reveal that EE has a region-specific effect on stress-induced c-Fos expression in the corticolimbic system, which is likely to improve stress resilience. The response of the prefrontal cortex – amygdala – hippocampus circuitry to psychological stress is also modified by the systemic stress of gut inflammation, and this interaction between external and internal stressors is modulated by the housing environment.

Leptin and zinc relation: In regulation of food intake and immunity

Leptin is synthesized and released by the adipose tissue. Leptin, which carries the information about energy reserves of the body to the brain, controls food intake by acting on neuropeptide Y (NPY), which exercises a food-intake-increasing effect through relevant receptors in the hypothalamus. Zinc deficiency is claimed to result in anorexia, weight loss, poor food efficiency, and growth impairment. The fact that obese individuals have low zinc and high leptin levels suggests that there is a relation between zinc and nutrition, and consequently also between zinc and leptin. Leptin deficiency increases the predisposition to infections and this increase is associated with the impairments in the production of cytokines. Zinc has a key role in the sustenance of immune resistance against infections. Dietary zinc deficiency negatively affects CD(+) 4 cells, Th functions, and consequently, cell-mediated immunity by causing a decrease in the production of IL-2, IF-γ, and TNF-α, which are Th1 products. The relation between zinc and the concerned cytokines in particular, and the fact that leptin has a part in the immune responses mediated by these cytokines demonstrate that an interaction among cellular immunity, leptin and zinc is inevitable. An overall evaluation of the information presented above suggests that there are complex relations among food intake, leptin and zinc on one hand and among cellular immunity, leptin and zinc on the other. The aim of the present review was to draw attention to the possible relation between zinc and leptin in dietary regulation and cellular immunity.

Stress and animal models of inflammatory bowel disease--an update on the role of the hypothalamo-pituitary-adrenal axis

Chronic psychosocial stress has been repeatedly shown in humans to be a risk factor for the development of several affective and somatic disorders, including inflammatory bowel diseases (IBD). There is also a large body of evidence from rodent studies indicating a link between stress and gastrointestinal dysfunction, resembling IBD in humans. Despite this knowledge, the detailed underlying neuroendocrine mechanisms are not sufficiently understood. This is due, in part, to a lack of appropriate animal models, as most commonly used rodent stress paradigms do not adequately resemble the human situation and/or do not cause the development of spontaneous colitis. Therefore, our knowledge regarding the link between stress and IBD is largely based on rodent models with low face and predictive validity, investigating the effects of unnatural stressors on chemically induced colitis. These studies have consistently reported that hypothalamo-pituitary-adrenal (HPA) axis activation during stressor exposure has an ameliorating effect on the severity of a chemically induced colitis. However, to show the biological importance of this finding, it needs to be replicated in animal models employing more clinically relevant stressors, themselves triggering the development of spontaneous colitis. Important in view of this, recent studies employing chronic/repeated psychosocial stressors were able to demonstrate that such stressors indeed cause the development of spontaneous colitis and, thus, represent promising tools to uncover the mechanisms underlying stress-induced development of IBD. Interestingly, in these models the development of spontaneous colitis was paralleled by decreased anti-inflammatory glucocorticoid (GC) signaling, whereas adrenalectomy (ADX) prior to stressor exposure prevented its development. These findings suggest a more complex role of the HPA axis in the development of spontaneous colitis. In the present review I summarize the available human and rodent data in order to provide a comprehensive understanding of the biphasic role of the HPA axis and/or the GC signaling during stressor exposure in terms of spontaneous colitis development.

Mucosal immunosuppression and epithelial barrier defects are key events in murine psychosocial stress-induced colitis

Chronic psychosocial stress is a risk factor for many affective and somatic disorders, including inflammatory bowel diseases. In support chronic subordinate colony housing (CSC, 19 days), an established mouse model of chronic psychosocial stress, causes the development of spontaneous colitis. However, the mechanisms underlying the development of such stress-induced colitis are poorly understood. Assessing several functional levels of the colon during the initial stress phase, we show a pronounced adrenal hormone-mediated local immune suppression, paralleled by impaired intestinal barrier functions, resulting in enhanced bacterial load in stool and colonic tissue. Moreover, prolonged treatment with broad-spectrum antibiotics revealed the causal role of these early maladaptations in the development of stress-induced colitis. Together, we demonstrate that translocation of commensal bacteria is crucial in the initiation of stress-induced colonic inflammation. However, aggravation by the immune-modulatory effects of fluctuating levels of adrenal hormones is required to develop this into a full-blown colitis.

Toward understanding the role of leptin and leptin receptor antagonism in preclinical models of rheumatoid arthritis

A potential link between obesity, circulating leptin levels and autoimmune disease symptoms suggests that targeting the leptin receptor (ObR) might be a viable novel strategy to combat rheumatoid arthritis (RA). However, studies in animal models and evaluation of clinical cases did not provide clear view on leptin's involvement in RA. To validate ObR as RA target, we used our peptide-based ObR agonists and antagonist in different in vitro and in vivo models of the disease. In human peripheral blood mononuclear cells, leptin and its agonist fragment, desI(2)-E1/Aca, moderately induced constitutive activation of a major proinflammatory transcription factor, NF-κB, while the ObR antagonist peptide Allo-aca inhibited the process. Leptin administration itself did not induce arthritis in rats, but worsened the clinical condition of mice given K/BxN serum transfer arthritis. Simultaneous administration of Allo-aca reduced leptin-dependent increase in disease severity by more than 50%, but the antagonist was ineffective when injected with a 3-day delay. In rats inflicted with mild adjuvant-induced arthritis, both leptin and Allo-aca reduced the extent of joint swelling and the number of arthritic joints. In a more aggressive disease stage, Allo-aca decreased the number of arthritic joints in a dose-dependent manner but did not affect other arthritis markers. In summary, leptin exerts diverse effects on RA depending on the experimental model. This might reflect the heterogeneous character of RA, which is differently impacted by leptin and is unmasked by ObR antagonism. Nevertheless, the results suggest that ObR antagonists might become useful therapeutics in leptin-sensitive early stages of RA.

Diverse roles of leptin in the gastrointestinal tract: modulation of motility, absorption, growth, and inflammation

OBJECTIVE

Leptin was discovered in 1994 as a hormone produced by adipose tissue with a modulatory effect on feeding behavior and weight control. Recently, the stomach has been identified as an important source of leptin and growing evidence has shown diverse functions for leptin in the gastrointestinal tract.

METHODS

Using leptin as a keyword in PubMed, more than 17 000 articles were identified, of which more than 500 articles were related to the role of leptin in the gastrointestinal tract. Available abstracts were reviewed and more than 200 original articles were reviewed in detail.

RESULTS

The available literature demonstrated that leptin can modulate several important functions of the gastrointestinal tract. Leptin interacts with the vagus nerve and cholecystokinin to delay gastric emptying and has a complex effect on motility of the small bowel. Leptin modulates absorption of macronutrients in the gastrointestinal tract differentially in physiologic and pathologic states. In physiologic states, exogenous leptin has been shown to decrease carbohydrate absorption and to increase the absorption of small peptides by the PepT1 di-/tripeptide transporter. In certain pathologic states, leptin has been shown to increase absorption of carbohydrates, proteins, and fat. Leptin has been shown to be upregulated in the colonic mucosa in patients with inflammatory bowel disease. Leptin stimulates gut mucosal cell proliferation and inhibits apoptosis. These functions have led to speculation about the role of leptin in tumorigenesis in the gastrointestinal tract, which is complicated by the multiple immunoregulatory effects of leptin.

CONCLUSION

Leptin is an important modulator of major aspects of gastrointestinal tract functions, independent of its more well-described roles in appetite regulation and obesity.

Anti-inflammatory and analgesic effects displayed by peptides derived from PKI55 protein, an endogenous protein kinase C inhibitor

We recently characterized the PKI55 protein as an endogenous protein kinase C (PKC) inhibitor and investigated, in vitro, the potential anti-inflammatory actions of its N-terminal peptides 1-16 (peptide 5), 1-8 (peptide 8) and 1-5 (peptide 9). We showed their ability to inhibit chemotaxis in human polymorphonuclear leukocytes activated by the N-formyl tripeptide for-Met-Leu-Phe-OMe. In this work, we evaluated the anti-inflammatory and the analgesic effects of the selected peptides by in vivo experiments carried out in the mouse. The peptides 5, 8 and 9 (0.1 and 10 nmol i.c.v.) were effective in both the parameters chosen to test the anti-inflammatory activity, i.e., the xylene-induced ear edema and the acetic acid-induced infiltration of neutrophils in the peritoneal cavity. In addition, they displayed analgesic effect, evaluated by the acetic acid-induced writhing test. All the peptides' effects were shared by the reference compounds, dexamethasone and indomethacin (10 mg kg(-1) i.p.), but not by the 9-scramble peptide (10 nmol i.c.v.). The peptide 9, which represents the shortest active sequence of the PKI55 protein, was tested in the ear edema model even following intraperitoneal (i.p.) administration and proved to be effective in the range doses 3-30 mg kg(-1). Moreover, an increase in plasma corticosterone levels was detected in mice treated with the peptide 9, but not with the 9-scramble peptide (both at 10 nmol i.c.v.). The anti-inflammatory and analgesic effects of the PKI55-derived synthetic peptides, possibly related both to PKC inhibition and hypothalamic-pituitary-adrenal axis activation, deserve further investigation in view of potential therapeutic exploitation.

Cross-talk between adipose and gastric leptins for the control of food intake and energy metabolism

The understanding of the regulation of food intake has become increasingly complex. More than 20 hormones, both orexigenic and anorexigenic, have been identified. After crossing the blood-brain barrier, they reach their main site of action located in several hypothalamic areas and interact to balance satiety and hunger. One of the most significant advances in this matter has been the discovery of leptin. This hormone plays fundamental roles in the control of appetite and in regulating energy expenditure. In accordance with the lipostatic theory stated by Kennedy in 1953, leptin was originally discovered in white adipose tissue. Its expression by other tissues was later established. Among them, the gastric mucosa has been shown to secrete large amounts of leptin. Both the adipose and the gastric tissues share similar characteristics in the synthesis and storage of leptin in granules, in the formation of a complex with the soluble receptor and a secretion modulated by hormones and energy substrates. However while adipose tissue secretes leptin in a slow constitutive endocrine way, the gastric mucosa releases leptin in a rapid regulated exocrine fashion into the gastric juice. Exocrine-secreted leptin survives the extreme hydrolytic conditions of the gastric juice and reach the duodenal lumen in an intact active form. Scrutiny into transport mechanisms revealed that a significant amount of the exocrine leptin crosses the intestinal wall by active transcytosis. Leptin receptors, expressed on the luminal and basal membrane of intestinal epithelial cells, are involved in the control of nutrient absorption by enterocytes, mucus secretion by goblet cells and motility, among other processes, and this control is indeed different depending upon luminal or basal stimulus. Gastric leptin after transcytosis reaches the central nervous system, to control food intake. Studies using the Caco-2, the human intestinal cell line, in vitro allowed analysis of the mechanisms of leptin actions on the intestinal mucosa, identification of the mechanisms of leptin transcytosis and understanding the modulation of leptin receptors by nutrients and hormones. Exocrine-secreted gastric leptin thus participates in a physiological axis independent in terms of time and regulation from that of adipose tissue to rapidly control food intake and nutrient absorption. Adipocytes and gastric epithelial cells are two cell types the metabolism of which is closely linked to food intake and energy storage. The coordinated secretion of adipose and gastric leptins ensures proper management of food processing and energy storage.

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.

Aggravation of DSS-induced colitis after chronic subordinate colony (CSC) housing is partially mediated by adrenal mechanisms

Chronic subordinate colony housing (CSC) is a relevant chronic psycho-social stressor for male mice. Here, we investigated effects of CSC on the severity of dextran sulphate sodium (DSS)-induced colitis and the involvement of adrenal mechanisms. After 19 days of CSC, male C57BL/6 mice were treated with 1% DSS (8 days). After 8 days, inflammatory shortening of the colon and the histological inflammation score were increased in CSC mice. Additionally, the increased secretion of pro-inflammatory cytokines by mesenteric lymph node cells found on day 2 and 4 of DSS treatment was down-regulated in CSC mice on day 8 of DSS treatment, paralleled by an increase in plasma corticosterone. In contrast, in unstressed controls, elevation of cytokine secretion was delayed and only found on day 8 of DSS treatment, associated with a prompt rise in plasma corticosterone. To reveal adrenal mechanisms in CSC-induced effects on colitis, mice were adrenalectomized, exposed to CSC and treated with DSS (8 days). In adrenalectomized CSC mice, the severity of DSS-induced colitis was reduced, as body weight loss, shortening of colon, histological damage score, and cytokine secretion from mesenteric lymph node cells were diminished compared with sham-operated CSC mice. In conclusion, exposure to chronic psycho-social stress increases the severity of acute DSS colitis, an effect which is, at least partly, mediated by adrenal mechanisms.

Mesenteric adipose tissue alterations resulting from experimental reactivated colitis

BACKGROUND

Adipose tissue secretes a large number of hormones that act either locally or at distant sites, modulating immune responses, inflammation, and many endocrine and metabolic functions. Abnormalities of fat in the mesentery have been long recognized in surgical specimens as characteristic features of Crohn's disease; however, the importance of this in chronic inflammatory disease is unknown. Additionally, adipocytes in depots that enclose lymph nodes or other dense masses of lymphoid tissue have many site-specific physiological properties.

METHODS

In this study, the alterations of mesenteric and perinodal mesenteric adipose tissue during experimental colitis, induced by repeated intracolonic trinitrobenzene sulfonic acid instillations, were evaluated, focusing on morphological and activity alterations and the adipocytokine production profile.

RESULTS

After a 35-day protocol, the colitis animals presented greater mesenteric fat masses despite their lower body weights. Another adipose tissue depot, epididymal adipose tissue, was also evaluated and no change in mass was observed. The mesenteric adipocyte from colitis animals had a reduced diameter, normal PPAR-gamma-2 expression, and higher basal lipolysis and TNF-alpha production when compared to normal rats. Perinodal mesenteric adipocytes present normal diameters, downregulated levels of PPAR-gamma-2, higher basal lipolysis and TNF-alpha, and leptin and adiponectin production.

CONCLUSIONS

The findings suggest that mesenteric adipose tissue has a site-specific response during experimental inflammation, where perinodal adipose tissue retains the ability to produce different adipocytokines. These substances may interfere in many lymph node aspects, while mesenteric adipose tissue produces substances that could contribute directly to aggravate the inflammatory process.

Mechanisms underlying reduced expulsion of a murine nematode infection during protein deficiency

Balb/c mice infected with the gastrointestinal nematode Heligmosomoides bakeri were fed protein sufficient (PS, 24%) or deficient (PD, 3%) diets to investigate whether diet, infection or dose of larval challenge (0, 100 or 200 larvae) influenced gut pathophysiology and inflammation. Among the PS mice, worms were more posteriorad in the intestine of mice infected with 200 compared with 100 larvae, suggesting active expulsion in the more heavily infected mice. This was consistent with the positive correlation between worm numbers and fluid leakage in PS mice; similar patterns were not detected in the PD mice. Infection also induced villus atrophy, which was more pronounced in PS than in PD mice. Our cytokine screening array indicated that infection in PD mice elevated a wide range of pro-inflammatory cytokines and chemokines. Whereas serum leptin concentrations were higher in PD mice, monocyte chemotactic protein-5 (MCP-5) in serum increased with increasing larval dose and concentrations were lower in PD than PS mice. We suggest that elevated MCP-5 together with villus atrophy may contribute to the apparent dose-dependent expulsion of H. bakeri from PS mice but that delayed expulsion in PD mice appeared related to a predominant Th1 cytokine profile that may be driven by leptin.

Effect of fish or soybean oil-rich diets on bradykinin, kallikrein, nitric oxide, leptin, corticosterone and macrophages in carrageenan stimulated rats

We have previously demonstrated that both n-3 and n-6 polyunsaturated fatty acids (PUFA)-rich diets decrease the acute inflammatory response partially explained by the high corticosterone basal levels. The present study aimed to determine the effect of hyperlipidic diets (PUFA n-3 or n-6) on phagocytosis, hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) release by macrophages, bradykinin (BK) and NO release in the paw inflammatory perfusate and Kallikrein (KK), corticosterone and leptin blood levels. Hyperlipidic diets decreased H(2)O(2) release from macrophages stimulated by carrageenan or phorbol-miristate-acetate (PMA), NO release from macrophage stimulated by carrageenan, BK and NO release in the edema perfusate, KK plasma levels and the increase of serum leptin after carrageenan stimulus. These data show that both fish and soybean oil-rich diets promote similar alterations on inflammatory mediators of carrageenan edema and a causal association with the anti-inflammatory effect of these diets.

Luminal leptin activates mucin-secreting goblet cells in the large bowel

Leptin has been suggested to be involved in tissue injury and/or mucosal defence mechanisms. Here, we studied the effects of leptin on colonic mucus secretion and rat mucin 2 (rMuc2) expression. Wistar rats and ob/ob mice were used. Secretion of mucus was followed in vivo in the rat perfused colon model. Mucus secretion was quantified by ELISA, and rMuc2 mRNA levels were quantified by real-time RT PCR. The effects of leptin alone or in association with protein kinase C (PKC) and phosphatidylinositol 3-kinase (PI3K) inhibitors on mucin secreted by human mucus-secreting HT29-MTX cells were determined. Leptin was detected in the rat colonic lumen at substantial levels. Luminal perfusion of leptin stimulates mucus-secreting goblet cells in a dose-dependent manner in vivo in the rat. Leptin (10 nmol/l) increased mucus secretion by a factor of 3.5 and doubled rMuc2 mRNA levels in the colonic mucosa. There was no damage to mucosa 24 h after leptin, but the number of stained mucus cells significantly increased. Leptin-deficient ob/ob mice have abnormally dense mucus-filled goblet cells. In human colonic goblet-like HT29-MTX cells expressing leptin receptors, leptin increased mucin secretion by activating PKC- and PI3K-dependent pathways. This is the first demonstration that leptin, acting from the luminal side, controls the function of mucus-secreting goblet cells. Because the gel layer formed by mucus at the surface of the intestinal epithelium has a barrier function, our data may be relevant physiologically in defence mechanisms of the gastrointestinal tract.

Circulating levels of leptin, adiponectin, resistin, and ghrelin in inflammatory bowel disease

BACKGROUND

There is evidence that adipocytokines play an important role in metabolism and in inflammation. Because human metabolism dramatically changes in inflammatory bowel disease (IBD) and chronic inflammation is the hallmark of the disease, we studied serum levels of leptin, adiponectin, resistin, and ghrelin in patients with ulcerative colitis (UC) and Crohn's disease (CD) in comparison with healthy controls (HC).

METHODS

Leptin, adiponectin, resistin, and active ghrelin serum levels were measured in 100 IBD patients (46 UC and 54 CD) and in 60 matched HC using commercially available enzyme-linked immunosorbent assays. Leptin, adiponectin, resistin, and ghrelin levels were correlated with disease activity, type, localization, and treatment.

RESULTS

Mean serum leptin levels were 10.6+/-2.0 ng/mL in UC patients, 12.5+/-2.6 ng/mL in CD patients, and 15.0+/-1.8 ng/mL in HC (P=.01). Mean serum adiponectin levels were 9514.8+/-787.8 ng/mL in UC patients, 7651.1+/-613 ng/mL in CD patients, and 7270.6+/-559.4 ng/mL in HC (P=.05). Mean serum resistin levels were 21.2+/-2.2 ng/mL in UC patients, 18.7+/-1.6 ng/mL in CD patients and 11.8+/-0.6 ng/mL in HC (P=.0002). Mean serum ghrelin levels were 48.2+/-4.2 pg/mL in UC patients, 49.4+/-4.6 pg/mL in CD patients and 14.8+/-3.0 pg/mL in HC (P<.0001). Serum levels of these adipocytokines were not correlated with either C-reactive protein levels or the clinical indices of activity. No association between serum adipocytokines levels and disease localization in both UC and CD patients was found. Only serum ghrelin was significantly higher in ileal compared with colonic CD (P=.04).

CONCLUSIONS

Serum levels of adiponectin, resistin, and active ghrelin are increased whereas serum levels of leptin are decreased in patients with IBD. Further studies are needed to elucidate the role of adipocytokines in IBD.

Effects of intraperitoneal vitamin E, melatonin and aprotinin on leptin expression in the guinea pig eye during experimental uveitis

PURPOSE

To observe ultrastructural changes and leptin expression in the guinea pig eye during experimental uveitis (EU) and the effects of vitamin E, melatonin and aprotinin on leptin expression.

METHODS

Thirty male guinea pigs were randomly classified into five groups. Group 1 was the control group. Groups 2, 3, 4 and 5 received intravitreal injections of bovine serum albumin (BSA) to induce EU. At the same time on the third day, groups 3 (EU + vitamin E), 4 (EU + melatonin) and 5 (EU + aprotinin) received intraperitoneal vitamin E (150 mg/kg), melatonin (10 mg/kg) and aprotinin (20,000 IU/kg), respectively. On the sixth day, histopathological and clinical scoring of inflammation were performed, and leptin expression was investigated in the retina, choroid, sclera, episclera and cornea, and compared.

RESULTS

There was a remarkable increase in leptin expression in the retina, choroid, sclera and episclera in the EU group. Leptin expression in the treatment groups was similar to that in the control group. At light and electron microscopic levels, ganglion cells were oedematous and inner plexiform layer thickness had increased in the EU group retinas. Oedema was decreased in the treatment groups. Comparison of the EU and treatment groups revealed significant differences histopathologically and clinically.

CONCLUSION

Experimental uveitis causes an increase in leptin expression in the retina, choroid, sclera and episclera of guinea pigs. Vitamin E, melatonin and aprotinin inhibit this increase. Leptin seems to be closely related to ocular inflammation.

Intestinal ischemia-reperfusion injury made leptin decreased

To explore the role and the rule of leptin levels in severe traumatism, an ischemia-reperfusion injury model was established to observe change of leptin levels, and platelet activating factor, noradrenaline, lipopolysaccharide, and endothelin-1 were utilized to induce vascular endothelial cells. Leptin concentrations in serum and supernatant were detected by murine and human leptin radioimmunoassay. The results showed that the first serum leptin level significantly decreased after an injury of 60 min ischemia and 30 min reperfusion versus pre-experimental serum values, and leptin level in serum showed a variational trend to increase as reperfusion time extended; the second, supernatant leptin level significantly decreased after PAF and ET-1 treatments of 6 and 24 h versus the control group. It can be concluded that leptin maybe an inflammatory cytokine to play a protection role in acute inflammation and traumatism.

The emerging role of adipocytokines as inflammatory mediators in inflammatory bowel disease

Anorexia, malnutrition, altered body composition and development of mesenteric obesity are well known features of inflammatory bowel disease (IBD). Recent data suggest that dysregulation of protein secretion by white adipose tissue is involved in these manifestations of patients with IBD. Adipocytes are recently recognized as endocrine cells that secrete a variety of bioactive substances known as adipocytokines. There is evidence that adipocytokines are involved in inflammatory and metabolic pathways in human beings. Overexpression of adipocytokines such as leptin, adiponectin and resistin in mesenteric adipose tissue of operated patients with Crohn's disease has recently been reported, suggesting that mesenteric adipocytes in IBD may act as immunoregulating cells. Therefore, it could be suggested that adipocytokines play an important role in the disease pathogenesis. Moreover, modulators of mesenteric adipose function have been suggested as potential therapeutic drugs in IBD. In this review, the importance of white adipose tissue function and adipocytokines, is discussed with respect to IBD.

Leptin ameliorates burn-induced multiple organ damage and modulates postburn immune response in rats

The present study was designed to determine whether exogenous leptin reduces remote organ injury in the rats with thermal burn trauma. Leptin (10 microg/kg) or saline was administered intraperitoneally after burn injury, and the rats were decapitated at either 6 or 24 h. Plasma samples of 24-h burn group were assayed for the determination of monocyte and neutrophil apoptosis. Thermal injury increased tissue-associated myeloperoxidase (MPO) activity and microscopic damage scores in the lung, liver, stomach, colon and kidney of both 6- and 24-h burn groups. In the 6-h burn group, leptin reduced microscopic damage score in the liver and kidney only, while damage scores in the 24-h burn group were reduced in all the tissues except the lung. Also, in both burn groups, leptin reduced elevated MPO activity in all tissues except the lung. The percentage of mononuclear cells was significantly reduced at the 24 h of burn injury, while the granulocyte percentage was increased. Leptin treatment, however, had no significant effect on burn-induced reversal of white blood cell ratios. On the other hand, burn-induced increase in the death of mononuclear cells and granulocytes was significantly reduced in leptin-treated rats. The results of the present study suggest that leptin may provide a therapeutic benefit in diminishing burn-induced inflammation and associated multiple organ failure.