Leptin: a new growth factor for the small intestine

Hormonal Determinants of Growth and Weight Gain in the Human Fetus and Preterm Infant

The factors controlling linear growth and weight gain in the human fetus and newborn infant are poorly understood. We review here the changes in linear growth, weight gain, lean body mass, and fat mass during mid- and late gestation and the early postnatal period in the context of changes in the secretion and action of maternal, placental, fetal, and neonatal hormones, growth factors, and adipocytokines. We assess the effects of hormonal determinants on placental nutrient delivery and the impact of preterm delivery on hormone expression and postnatal growth and metabolic function. We then discuss the effects of various maternal disorders and nutritional and pharmacologic interventions on fetal and perinatal hormone and growth factor production, growth, and fat deposition and consider important unresolved questions in the field.

Role of Leptin in the Digestive System

Leptin is a pluripotent peptide hormone produced mainly by adipocytes, as well as by other tissues such as the stomach. Leptin primarily acts on the central nervous system, particularly the hypothalamus, where this hormone regulates energy homeostasis and neuroendocrine function. Owing to this, disruption of leptin signaling has been linked with numerous pathological conditions. Recent studies have also highlighted the diverse roles of leptin in the digestive system including immune regulation, cell proliferation, tissue healing, and glucose metabolism. Of note, leptin acts differently under physiological and pathological conditions. Here, we review the current knowledge on the functions of leptin and its downstream signaling in the gastrointestinal tract and accessory digestive organs, with an emphasis on its physiological and pathological implications. We also discuss the current therapeutic uses of recombinant leptin, as well as its limitations.

The Leptin System and Diet: A Mini Review of the Current Evidence

Leptin promotes satiety and modulates energy balance and weight. Diet-induced obesity leads to leptin resistance, exacerbating overeating. We reviewed the literature on the relationship between diet and leptin, which suggests that addressing leptin resistance through dietary interventions can contribute counteracting obesity. Albeit some limitations (e.g., limited rigor, small samples sizes), studies in animals and humans show that diets high in fat, carbohydrates, fructose, and sucrose, and low in protein are drivers of leptin resistance. Despite methodological heterogeneity pertaining to this body of literature, experimental studies show that energy-restricted diets can reduce leptinemia both in the short and long term and potentially reverse leptin resistance in humans. We also discuss limitations of this evidence, future lines of research, and implications for clinical and public health translations. Main limitations include the lack of a single universally-accepted definition of leptin resistance, and of adequate ways to accurately measure it in humans. The use of leptin sensitizers (drugs) and genetically individualized diets are alternatives against leptin resistance that should be further researched in humans. The tested very-low-energy intervention diets are challenging to translate into wide clinical or population recommendations. In conclusion, the link between nutritional components and leptin resistance, as well as research indicating that this condition is reversible, emphasizes the potential of diet to recover sensitivity to this hormone. A harmonized definition of leptin resistance, reliable methods to measure it, and large-scale, translational, clinical, and precision nutrition research involving rigorous methods are needed to benefit populations through these approaches.

Leptin and Its Derivatives: A Potential Target for Autoimmune Diseases

Leptin is an adipocyte-derived hormone product of the obese (ob) gene. Leptin plays an important regulatory role as an immunomodulatory factor in the maintenance and homeostasis of immune functions. Indeed, the role of leptin as an immunomodulator in inflammatory and immune responses has attracted increasing attention in recent years. Leptin mostly affects responses through the immunomodulation of monocytes, dendritic cells, neutrophils, NK cells, and dendritic cells in addition to modulating T and B cell development and functions. Leptin is also an important inflammatory regulator, wherein higher expression influences the secretion rates of IL-6, C-reactive proteins, and TNF-α. Moreover, leptin is highly involved in processes related to human metabolism, inflammatory reactions, cellular development, and diseases, including hematopoiesis. Owing to its diverse immunerelated functions, leptin has been explored as a potential target for therapeutic development in the treatment of autoimmune diseases.

Space radiation exposure persistently increased leptin and IGF1 in serum and activated leptin-IGF1 signaling axis in mouse intestine

Travel into outer space is fraught with risk of exposure to energetic heavy ion radiation such as ⁵⁶Fe ions, which due to its high linear energy transfer (high-LET) characteristics deposits higher energy per unit volume of tissue traversed and thus more damaging to cells relative to low-LET radiation such as γ rays. However, estimates of human health risk from energetic heavy ion exposure are hampered due to lack of tissue specific in vivo molecular data. We investigated long-term effects of ⁵⁶Fe radiation on adipokines and insulin-like growth factor 1 (IGF1) signaling axis in mouse intestine and colon. Six- to eight-week-old C57BL/6J mice were exposed to 1.6 Gy of ⁵⁶Fe ions. Serum and tissues were collected up to twelve months post-irradiation. Serum was analyzed for leptin, adiponectin, IGF1, and IGF binding protein 3. Receptor expressions and downstream signaling pathway alterations were studied in tissues. Irradiation increased leptin and IGF1 levels in serum, and IGF1R and leptin receptor expression in tissues. When considered along with upregulated Jak2/Stat3 pathways and cell proliferation, our data supports the notion that space radiation exposure is a risk to endocrine alterations with implications for chronic pathophysiologic changes in gastrointestinal tract.

Regulation of intestinal SGLT1 by catestatin in hyperleptinemic type 2 diabetic mice

The small intestine is the major site for nutrient absorption that is critical in maintenance of euglycemia. Leptin, a key hormone involved in energy homeostasis, directly affects nutrient transport across the intestinal epithelium. Catestatin (CST), a 21-amino acid peptide derived from proprotein chromogranin A, has been shown to modulate leptin signaling. Therefore, we reasoned that leptin and CST could modulate intestinal Na(+)-glucose transporter 1 (SGLT1) expression in the context of obesity and diabetes. We found that hyperleptinemic db/db mice exhibit increased mucosal mass, associated with an enhanced proliferative response and decreased apoptosis in intestinal crypts, a finding absent in leptin-deficient ob/ob mice. Intestinal SGLT1 abundance was significantly decreased in hyperleptinemic but not leptin-deficient mice, indicating leptin regulation of SGLT1 expression. Phlorizin, a SGLT1/2 inhibitor, was without effect in an oral glucose tolerance test in db/db mice. The alterations in architecture and SGLT1 abundance were not accompanied by changes in the localization of intestinal alkaline phosphatase, indicating intact differentiation. Treatment of db/db mice with CST restored intestinal SGLT1 abundance and intestinal turnover, suggesting a cross-talk between leptin and CST, without affecting plasma leptin levels. Consistent with this hypothesis, we identified structural homology between CST and the AB-loop of leptin and protein-protein docking revealed binding of CST and leptin with the Ig-like binding site-III of the leptin receptor. In summary, downregulation of SGLT1 in an obese type 2 diabetic mouse model with hyperleptinemia is presumably mediated via the short form of the leptin receptor and reduces overt hyperglycemia.

Transcriptome analysis of grass carp (Ctenopharyngodon idella) fed with animal and plant diets

Numerous studies have been focused on the replacement of fish meal by other alternative protein sources. However, little is currently known about the molecular mechanism of utilization of diets with different protein sources in fish. Grass carp is a typical herbivorous fish. To elucidate the relationship between gene expression and utilization of animal and plant diets, transcriptome sequencing was performed in grass carp fed with chironomid larvae and duckweed. Grass carp fed with duckweed had significantly higher relative length of gut than those fed with chironomid larvae. 4435 differentially expressed genes were identified between grass carp fed with chironomid larvae and duckweed in brain, liver and gut, involved in cell proliferation and differentiation, appetite control, circadian rhythm, digestion and metabolism pathways. These pathways might play important roles in utilization of diets with different protein sources in grass carp. And the findings could provide a new insight into the replacement of fish meal in artificial diets.

Transcriptome analysis of food habit transition from carnivory to herbivory in a typical vertebrate herbivore, grass carp Ctenopharyngodon idella

BACKGROUND

Although feeding behavior and food habit are ecologically and economically important properties, little is known about formation and evolution of herbivory. Grass carp (Ctenopharyngodon idella) is an ecologically appealing model of vertebrate herbivore, widely cultivated in the world as edible fish or as biological control agents for aquatic weeds. Grass carp exhibits food habit transition from carnivory to herbivory during development. However, currently little is known about the genes regulating the unique food habit transition and the formation of herbivory, and how they could achieve higher growth rates on plant materials, which have a relatively poor nutritional quality.

RESULTS

We showed that grass carp fed with duckweed (modeling fish after food habit transition) had significantly higher relative length of gut than fish before food habit transition or those fed with chironomid larvae (fish without transition). Using transcriptome sequencing, we identified 10,184 differentially expressed genes between grass carp before and after transition in brain, liver and gut. By eliminating genes potentially involved in development (via comparing fish with or without food habit transition), we identified changes in expression of genes involved in cell proliferation and differentiation, appetite control, circadian rhythm, and digestion and metabolism between fish before and after food habit transition. Up-regulation of GHRb, Egfr, Fgf, Fgfbp1, Insra, Irs2, Jak, STAT, PKC, PI3K expression in fish fed with duckweed, consistent with faster gut growth, could promote the food habit transition. Grass carp after food habit transition had increased appetite signal in brain. Altered expressions of Per, Cry, Clock, Bmal2, Pdp, Dec and Fbxl3 might reset circadian phase of fish after food habit transition. Expression of genes involved in digestion and metabolism were significantly different between fish before and after the transition.

CONCLUSIONS

We suggest that the food habit transition from carnivory to herbivory in grass carp might be due to enhanced gut growth, increased appetite, resetting of circadian phase and enhanced digestion and metabolism. We also found extensive alternative splicing and novel transcript accompanying food habit transition. These differences together might account for the food habit transition and the formation of herbivory in grass carp.

Protracted upregulation of leptin and IGF1 is associated with activation of PI3K/Akt and JAK2 pathway in mouse intestine after ionizing radiation exposure

Ionizing radiation is a known risk factor for gastrointestinal (GI) pathologies including cancer. Hormones and related signaling crosstalk, which could contribute to radiation-induced persistent pathophysiologic changes in the small intestine and colon, remain to be explored. The current study assessed perturbation of GI homeostasis-related hormones and signaling pathways at the systemic as well as at the tissue level in small intestine and colon. Mice (6-8 week old C57BL/6J) were exposed to 2 Gy γ radiation, serum and tissue samples were collected, and insulin like growth factor 1 (IGF-1) and leptin signaling were assessed two or twelve months after radiation exposure. Serum levels of IGF-1, IGF binding protein 3 (IGFBP3), leptin, and adiponectin were altered at these times after irradiation. Radiation was associated with increased IGF1 receptor (IGF1R) and obesity (leptin) receptor (Ob-R), decreased adiponectin receptor 1 (Adipo-R1) and 2 (Adipo-R2), and increased Ki-67 levels in small intestine and colon at both time points. Immunoblot analysis further showed increased IGF1R and Ob-R, and decreased Adipo-R2. Additionally, upregulation of PI3K/Akt and JAK2 signaling, which are downstream of IGF1 and leptin, was also observed in irradiated samples at both time points. These results when considered along with increased cell proliferation in the small intestine and colon demonstrate for the first time that ionizing radiation can persistently increase IGF1 and leptin and activate downstream proliferative pathways, which may contribute to GI functional alterations and carcinogenesis.

Gene alterations and intestinal mucosal changes following growth factor and omega-3 exposure in a rat model of inflammatory bowel disease

BACKGROUND

We have previously shown that there is synergism between Hepatocyte Growth Factor (HGF) and Omega-3 (OM-3) enriched feeds using an immunologic model of inflammatory bowel disease (IBD). This combination decreased inflammation and cytokine levels and increased microvascular density and mucosal mass. This study evaluates the gene alterations that occurred using this same model.

METHODS

Twenty adult female transgenic HLA-B27 rats were divided into four groups: Group 1: (Regular feeds, IV saline); Group 2: (OM-3 feeds, IV saline); Group 3: (Regular feeds, IV HGF 150 μg/kg/day); Group 4: (OM-3 feeds, IV HGF 150 μg/kg/day). Rats were sacrificed 14 days after pump placement. Bowel was harvested and RNA extracted. Microarray gene chips were used. Statistical analysis was done by analysis of variance using Partek Genomics Suite. Results were significant if fold change was more than 2 or less than -2, with P<0.05.

RESULTS

In the ileum, HGF up- or down-regulated 34 genes, while OM-3 affected 60 genes. Together 68 genes were affected. Families with a synergistic effect included Solute Carrier Proteins, ATP Binding Cassette Proteins, and Matrix Metalloproteinases. In the colon, 23 genes were affected by HGF, while 66 genes were affected with OM-3. Combined exposure affected 32 genes, including a synergistic effect on solute carrier proteins, aquaporins, and immunologic factors.

CONCLUSIONS

There is a synergistic gene alteration effect of exposure of two (HGF and Omega-3 enriched feeds) agents on bowel mucosa. Of most interest was the synergistic effect on the solute carrier protein family, a previously identified gene family up-regulated in response to intestinal failure.

Leptin affects intestinal epithelial cell turnover in correlation with leptin receptor expression along the villus-crypt axis after massive small bowel resection in a rat

In this study, we examine the responsiveness of intestinal epithelial cell turnover to leptin (LEP) in correlation with leptin receptor (LEPr) expression along the villus-crypt axis in a rat with short bowel syndrome (SBS). Adult rats underwent either a 75% intestinal resection or a transection. SBS-LEP rats underwent bowel resection and were treated with LEP starting from the fourth postoperative day. Parameters of intestinal adaptation, enterocyte proliferation, and enterocyte apoptosis were determined at sacrifice. RT-PCR technique was used to determine Bax and Bcl-2 gene expression in ileal mucosa. Villus tips, lateral villi, and crypts were separated using laser capture microdissection. LEPr expression for each compartment was assessed by quantitative real-time PCR (Taqman). Treatment with LEP significantly stimulated all parameters of adaptation. LEPr expression in crypts significantly increased in SBS rats (vs Sham rats) and was accompanied by a significant increase in enterocyte proliferation and decreased apoptosis after LEP administration. A significant increase in LEPr expression at the tip of the villus in SBS rats was accompanied by decreased cell apoptosis. In conclusion LEP accelerated enterocyte turnover and stimulated intestinal adaptation. The effect of LEP on enterocyte proliferation and enterocyte apoptosis correlated with receptor expression along the villus-crypt axis.

The relationship between breast milk leptin and neonatal weight gain

AIM

To investigate whether change in leptin content of breast milk during lactation acts on neonatal body weight gain.

METHODS

In total 15 lactating women and their 15 term infants were involved in the study. Breast milk and neonatal serum samples were obtained from the same women and their neonates on the 1st day and any day between the 21st and 30th days after birth. Breast milk and serum leptin concentrations were determined by radioimmunoassay. Anthropometric indexes of the infants were recorded.

RESULTS

The study was completed with 15 multiparious mothers aged 19-37 years and their infants. The mean collection time of the first samples after birth was 6.07 +/- 1.94 h. The leptin level in the mature milk was significantly higher than in the colostrum (p < 0.001). Neonatal weight and height were significantly increased on 21-30 lactation days compared to 1st day of lactation (p < 0.05 and p < 0.001, respectively). The leptin concentration in the mature milk was negatively correlated with delta BMI (r =-0.53; p < 0.05). The delta breast milk leptin concentration was also found to be inversely correlated with delta BMI (r =-0.529; p < 0.05).

CONCLUSION

The results of this study have suggested that change in the leptin content of breast milk during lactation might play a role in the regulation of weight gain in healthy neonates.

Adiponectin blocks multiple signaling cascades associated with leptin-induced cell proliferation in Apc Min/+ colon epithelial cells

We previously demonstrated that leptin, an adipose-derived hormone, induces cell proliferation in a model of preneoplastic (IMCE (Apc(Min/+)), but not normal (YAMC (Apc(+/+)), colon epithelial cells by inducing autocrine IL-6 production and trans-IL-6 signaling. Low serum adiponectin is associated with colon, prostate and breast cancer. Adiponectin is secreted by white adipose tissue; the levels of adiponectin in the blood decrease as body mass index (and leptin) increases. In our study, we tested whether murine recombinant globular adiponectin (gArcp30) could modulate leptin-induced cell proliferation, autocrine IL-6 production, trans-IL-6 signaling and other leptin-induced cell signaling events previously observed in IMCE cells but not YAMC cells. Under serum-free conditions, adiponectin (1 mug/ml) inhibited leptin-induced autocrine IL-6 production, soluble IL-6 receptor shedding, trans-IL-6 signaling and subsequent STAT3 phosphorylation in IMCE cells. Adiponectin inhibited leptin-induced cell proliferation in the IMCE cells and this inhibition was associated with I kappa B-alpha phosphorylation, I kappa B-alpha degradation and decreased NF-kappaB p65 DNA activation and binding. These data indicate that adiponectin acts on preneoplastic colon epithelial cells to regulate cell growth via 2 distinct pathways inhibiting leptin-induced NF-kappaB-dependent autocrine IL-6 production and trans-IL-6 signaling. We hypothesize that adiponectin may be an important regulator of colon epithelial cell homeostasis by linking the observed reduced risk for cancer in populations with high serum adiponectin concentrations to specific mechanisms of cell number homeostasis in a model of preneoplastic colon epithelial cells. These data may have broad implications for diet and lifestyle strategies for the prevention and treatment of obesity-associated cancers.

Insulin-like growth factors (IGFs), IGF binding proteins, and other endocrine factors in milk: role in the newborn

The role of colostrum and milk in the neonate has been chiefly recognized as a comprehensive nutrient foodstuff. In addition, the provision of colostrum-the first milk-for early immune capacity has been well documented for several species. Colostrum is additionally a rich and concentrated source of various factors that demonstrate biological activity in vitro. Three hypotheses have been proposed for the phenotypic function of these secreted bioactive components: (1) only mammary disposal, (2) mammary cell regulation, and (3) neonatal function [gastrointestinal tract (GIT) or systemic]. Traditionally, it was assumed that the development of the GIT is preprogrammed and not influenced by events occurring in the intestinal lumen. However, a large volume of research has demonstrated that colostrum (or milk-borne) bioactive components can basically contribute to the regulation of GIT growth and differentiation, while their role in postnatal development at physiological concentrations has remained elusive. Much of our current understanding is derived from cell culture and laboratory animals, but experimentation with agriculturally important species is taking place. This chapter provides an overview of work conducted primarily in neonatal calves and secondarily in other species on the effects on neonates of selected peptide endocrine factors (hormones, growth factors, in part cytokines) in colostrum. The primary focus will be on insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) and other bioactive peptides, but new interest and concern about steroids (especially estrogens) in milk are considered as well.

The effect of leptin on intestinal recovery following ischemia-reperfusion injury in a rat

Recent evidence suggests that the adipose tissue derived cytokine leptin (LEP) is involved in the modulation of growth and differentiation of normal small intestine. The purpose of the present study was to examine the effect of leptin on enterocyte turnover and intestinal recovery after ischemia-reperfusion (IR) injury in a rat. Male Sprague-Dawley rats were divided into three experimental groups: (1) sham rats underwent laparotomy, (2) IR-rats underwent occlusion of both superior mesenteric artery and portal vein for 30 min followed by 24 h of reperfusion, and (3) IR-LEP rats underwent IR and were treated with leptin given subcutaneously at a dose of 50 microg/kg once a day for 48 h before and 24 h following IR. Intestinal structural changes, enterocyte proliferation and enterocyte apoptosis were determined 24 h following IR. A non-parametric Kruskal-Wallis ANOVA test was used for statistical analysis with P < 0.05 considered statistically significant. Treatment with leptin resulted in a significant increase in bowel weight in ileum, mucosal weight in jejunum and ileum, mucosal DNA content in ileum, mucosal protein content in jejunum and ileum, villus height in jejunum and ileum, and crypt depth in jejunum compared to IR-animals. IR-LEP rats also had a significantly lower intestinal injury score as well as lower apoptotic index and higher cell proliferation index in jejunum and ileum compared to the IR-animals. In conclusion, pre-treatment with leptin prevents gut mucosal damage and improves intestinal rehabilitation following intestinal IR in a rat.

Altered small intestinal absorptive enzyme activities in leptin-deficient obese mice: influence of bowel resection

BACKGROUND

Residual bowel increases absorption after massive small bowel resection. Leptin affects intestinal adaptation, carbohydrate, peptide, and lipid handling. Sucrase, peptidase, and acyl coenzyme A:monoacylglycerol acyltransferase (MGAT) are involved in carbohydrate, protein, and lipid absorption. We hypothesized that leptin-deficient obese mice would have altered absorptive enzymes compared with controls before and after small bowel resection.

METHODS

Sucrase, peptidase (aminopeptidase N [ApN], dipeptidyl peptidase IV [DPPIV]), and MGAT activities were determined from lean control (C57BL/6J, n = 16) and leptin-deficient (Lep(ob), n = 16) mice small bowel before and after 50% resection.

RESULTS

Ileal sucrase activity was greater in obese mice before and after resection. Jejunal ApN and DPPIV activities were lower for obese mice before resection; ileal ApN activity was unaltered after resection for both strains. Resection increased DPPIV activity in both strains. Jejunal MGAT in obese mice decreased postresection. In both strains, ileal MGAT activity decreased after resection, and obese mice had greater activity in remnant ileum.

CONCLUSIONS

After small bowel resection, leptin-deficient mice have increased sucrase activity and diminished ileal ApN, DPPIV, and MGAT activity compared with controls. Therefore, we conclude that leptin deficiency alters intestinal enzyme activity in unresected animals and after small bowel resection. Altered handling of carbohydrate, protein, and lipid may contribute to obesity and diabetes in leptin-deficient mice.

Endocrine and exocrine secretion of leptin by the gastric mucosa

Leptin is a hormone that plays important roles in nutritional status and in obesity. By means of immunocytochemistry, two populations of leptin-secreting cells were found in the lower half of the gastric mucosa. One consists of numerous large cells located around the gastric pits, the Chief epithelial cells, whereas the second refers to much smaller cells, strongly stained, few in number, and scattered between the gastric pits, the endocrine cells. By double immunostaining, leptin and pepsinogen were colocalized in the Chief cells, whereas the endocrine cells were positive only for leptin. Immunoelectron microscopy showed that leptin is present along the rough endoplasmic reticulum-Golgi-granules secretory pathways of the Chief and endocrine cells. On the other hand, leptin-receptor (long and short forms) immunolabelings, although absent in the gastric epithelial cell plasma membranes, were present in enterocytes at the level of their apical and basolateral membranes. Duodenal, jejunal, and ileal enterocytes displayed similar labelings for the leptin receptor. Thus, exocrine and endocrine secretions of leptin together with the presence of leptin receptors on enterocyte plasma membranes constitute a gastroenteric axis that coordinates the role played by leptin in the digestive tract.

Intestinal adaptation after massive intestinal resection

Patients with short bowel syndrome require long term parenteral nutrition support. However, after massive intestinal resection the intestine undergoes adaptation and nutritional autonomy may be obtained. Given that the complications of parenteral nutrition may be life threatening or result in treatment failure and the need for intestinal transplantation, a more attractive option is to wean patients off nutrition support by optimising the adaptive process. The article examines the evidence that after extensive small bowel resection adaptation occurs in humans and focuses on the factors that influence adaptation and the strategies that have been used to optimise this process. The review is based on an English language Medline search with secondary references obtained from key articles. There is evidence that adaptation occurs in humans. Adaptation is a complex process that results in response to nutrient and non-nutrient stimuli. Successful and reproducible strategies to improve adaptation remain elusive despite an abundance of experimental data. Nevertheless given the low patient survival and quality of life associated with other treatments for irreversible intestinal failure it is imperative that clinical research continues into the optimisation of the adaptation.

Intestinal adaptation after massive intestinal resection

Patients with short bowel syndrome require long term parenteral nutrition support. However, after massive intestinal resection the intestine undergoes adaptation and nutritional autonomy may be obtained. Given that the complications of parenteral nutrition may be life threatening or result in treatment failure and the need for intestinal transplantation, a more attractive option is to wean patients off nutrition support by optimising the adaptive process. The article examines the evidence that after extensive small bowel resection adaptation occurs in humans and focuses on the factors that influence adaptation and the strategies that have been used to optimise this process. The review is based on an English language Medline search with secondary references obtained from key articles. There is evidence that adaptation occurs in humans. Adaptation is a complex process that results in response to nutrient and non-nutrient stimuli. Successful and reproducible strategies to improve adaptation remain elusive despite an abundance of experimental data. Nevertheless given the low patient survival and quality of life associated with other treatments for irreversible intestinal failure it is imperative that clinical research continues into the optimisation of the adaptation.

Altered intestinal motility in leptin-deficient obese mice

INTRODUCTION

Leptin is produced by adipocytes and causes satiety by regulating hypothalamic neurotransmission and energy expenditure. Leptin functions through the active long form of its receptor, which is expressed throughout the gastrointestinal tract, including the vagal neurons concerned with small intestinal motility. However, the role of leptin in small intestinal motility is poorly understood. Therefore, we hypothesized that leptin-deficient (Lepob) obese mice would have altered small intestinal response to neurotransmitters and transit time.

MATERIALS AND METHODS

Responses of jejunal and ileal segments from lean control and leptin-deficient obese animals to acetylcholine (ACh) and cholecystokinin (CCK) were determined in an organ bath. In addition, gastric emptying was determined as the amount of gavaged liquid diet remaining in the stomach after 1 h, and intestinal transit time was determined by calculating the geometric center (GC) of passage of a fluorescent-labeled marker.

RESULTS

Leptin deficiency resulted in increased jejunal responses to CCK (P <0.05) and a similar response to ACh compared to lean controls. Also, gastric emptying (97% versus 91%, P <0.001) in obese mice was greater. Overall small intestinal transit (GC) in obese mice was decreased (7.3 versus 8.4, P <0.05) even though proximal transit was increased (5.3 versus 1.5, P <0.06).

CONCLUSIONS

These studies indicate that leptin-deficient (Lepob) obese mice have an increased jejunal response to CCK as well as an increased proximal intestinal transit, but an overall decrease in small intestinal transit.

Does massive proximal small bowel resection influence prostaglandin E2 synthesis in the stomach and ileum during adaptive process in rats?

It is unclear whether massive small bowel resection (SBR) affects prostaglandin E2 synthesis in the gastrointestinal tracts. Thus the aim of this study was to investigate possible changes over tissue levels of prostaglandin E2 in the stomach and ileum after massive proximal SBR. Female Swiss-Albino rats underwent control operation (groups 1, 3, 5) or an 80% SBR (groups 2, 4, 6). The specimens were obtained during relaparotomy at 3 days in groups 1 and 2, at 9 days in groups 3 and 4, at 15 days in groups 5 and 6. Group 2 vs. groups 1 and 6, group 4 vs. groups 3 and 6 had significant increase in the levels of gastric acid (P < 0.01, P < 0.05, respectively). Gastric prostaglandin E2 levels markedly increased in group 2 compared to group 1 (P < 0.01). Ileal prostaglandin E2 levels showed to be significantly higher in group 6 when compared with groups 2, 4, and 5 (P < 0.05). Gastric acidity increased at 3 and 9 days, decreased thereafter at 15 days following massive proximal SBR. While resected rats had increased levels of gastric prostaglandin E2 at 3 days, ileal prostaglandin E2 was markedly elevated at 15 days. Therefore, we conclude that prostaglandin E2 may have a possible role in regulating intestinal adaptation at the end of the adaptive process, and contribute to cytoprotective barrier function in the ileum and stomach at early and late periods of the intestinal adaptation, respectively.

Leptin reduces the development of the initial precancerous lesions induced by azoxymethane in the rat colonic mucosa

BACKGROUND & AIMS

Recent studies suggest that leptin, a hormone involved in food intake regulation, released into the circulation and gastrointestinal juice, may be a growth factor for intestine and may be involved in carcinogenesis; however, data are contradictory. This study investigates in rat colonic mucosa (1) the effects of hyperleptinemia on epithelial cell proliferation and development of aberrant crypts, earliest preneoplastic lesions, and (2) whether luminal leptin affects cell proliferation.

METHODS

Leptin (1 mg/kg/d) or vehicle was administered systemically by miniosmotic pump in Fischer 344 rats either for 7 days (BrdU-labeling indices study) or 23 days (azoxymethane-induced colonic lesions study). The effects of injections or continuous infusion of leptin into the colon were also studied.

RESULTS

In systemic leptin-treated rats, plasma leptin levels were 4- to 5-fold increased (P < 0.008 to P < 0.001); labeling indices were higher in proximal colon than in pair-fed control rats (P = 0.006) but unaffected in distal colon. Unexpectedly, in azoxymethane-treated rats, leptin significantly inhibited aberrant crypt foci formation in the middle and distal colon compared with controls (P = 0.006). Under these conditions, plasma insulin levels were reduced by 41%-58%, but gastrin levels were unchanged. In controls, luminal immunoreactive leptin reached the colon. A 3.6-fold increase in intraluminal leptin had no effect on epithelial cell proliferation.

CONCLUSIONS

This study provides the first evidence that leptin reduces the development of chemically induced precancerous lesions in colon, perhaps through decreased insulinemia, and thus does not support an important role for leptin in carcinogenesis promotion. Moreover, the study indicates that leptin is not a potent growth factor for normal intestine.

Leptin counteracts sodium butyrate-induced apoptosis in human colon cancer HT-29 cells via NF-kappaB signaling

This study shows that leptin induced a rapid phosphorylation of p42/44 mitogen-activated protein kinase, an enhancement of both NF-kappaB DNA binding and transcriptional activities, and a concentration-dependent increase of HT-29 cell proliferation. These effects are consistent with the presence of leptin receptors on cell membranes. The leptin induction of cell growth was associated with an increase of cell population in S and G2/M phase compared with control cells found in G0/G1 phase of the cell cycle. Moreover, cyclin D1 immunoreactivity was enhanced in leptin-treated HT-29 cells and this increase was essentially associated with cell population in G0/G1 phase. On the other hand, we observed that sodium butyrate inhibited cell proliferation by blocking HT-29 cells in G0/G1 phase of the cell cycle. Interestingly, at physiological concentration, leptin prevented sodium butyrate-induced morphological nucleus changes, DNA laddering and suppressed butyrate-induced cell cycle arrest. This anti-apoptotic effect of leptin was associated with HT-29 cell proliferation and activation NF-kappaB pathways. However, the phosphorylation of p42/44 MAP kinase in response to leptin was reduced in butyrate-treated cells. These data demonstrated that leptin is a potent mitogenic factor for intestinal epithelial cells through the MAP kinase and NF-kappaB pathways. They also showed, for the first time, that leptin promotes colon cancer HT-29 cell survival upon butyrate challenge by counteracting the apoptotic programs initiated by this short chain fatty acid probably through the NF-kappaB pathways. Although further studies are required to unravel the precise mechanism, these data may have significance in the pathogenesis of colorectal cancer and ulcerative colitis diseases.