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

The role of hypoleptinemia in the psychological and behavioral adaptation to starvation: implications for anorexia nervosa

This narrative review aims to pinpoint mental and behavioral effects of starvation, which may be triggered by hypoleptinemia and as such may be amenable to treatment with leptin receptor agonists. The reduced leptin secretion results from the continuous loss of fat mass, thus initiating a graded triggering of diverse starvation related adaptive functions. In light of leptin receptors located in several peripheral tissues and many brain regions adaptations may extend beyond those of the hypothalamus-pituitary-end organ-axes. We focus on gastrointestinal tract and reward system as relevant examples of peripheral and central effects of leptin. Despite its association with extreme obesity, congenital leptin deficiency with its many parallels to a state of starvation allows the elucidation of mental symptoms amenable to treatment with exogenous leptin in both ob/ob mice and humans with this autosomal recessive disorder. For starvation induced behavioral changes with an intact leptin signaling we particularly focus on rodent models for which proof of concept has been provided for the causative role of hypoleptinemia. For humans, we highlight the major cognitive, emotional and behavioral findings of the Minnesota Starvation Experiment to contrast them with results obtained upon a lesser degree of caloric restriction. Evidence for hypoleptinemia induced mental changes also stems from findings obtained in lipodystrophies. In light of the recently reported beneficial cognitive, emotional and behavioral effects of metreleptin-administration in anorexia nervosa we discuss potential implications for the treatment of this eating disorder. We postulate that leptin has profound psychopharmacological effects in the state of starvation.

Host-Gut Microbiota Crosstalk in Intestinal Adaptation

Short-bowel syndrome represents the most common cause of intestinal failure and occurs when the remaining intestine cannot support fluid and nutrient needs to sustain adequate physiology and development without the use of supplemental parenteral nutrition. After intestinal loss or damage, the remnant bowel undergoes multifactorial compensatory processes, termed adaptation, which are largely driven by intraluminal nutrient exposure. Previous studies have provided insight into the biological processes and mediators after resection, however, there still remains a gap in the knowledge of more comprehensive mechanisms that drive the adaptive responses in these patients. Recent data support the microbiota as a key mediator of gut homeostasis and a potential driver of metabolism and immunomodulation after intestinal loss. In this review, we summarize the emerging ideas related to host-microbiota interactions in the intestinal adaptation processes.

Intestinal morphology and activity of digestive enzymes in broilers fed crude propolis

Duarte, C. R. A., Eyng, C., Murakami, A. E. and Santos, T. C. 2014. Intestinal morphology and activity of digestive enzymes in broilers fed crude propolis. Can. J. Anim. Sci. 94: 105–114. Propolis is a resin produced by bees that has been investigated for its potential to increase the performance of broiler chickens. Therefore, this study aimed to evaluate the inclusion of crude propolis in the diets of broiler chickens from 1 to 21 d of age. A total of 1020 male chicks were distributed in a completely randomized experimental design into six treatments (0, 100, 200, 300, 400 and 500 ppm of crude propolis), with five replications, and 34 birds per experimental unit. The experimental diets were provided from 1 to 21 d of age and subsequently (from 22 to 42 d of age) the birds were fed a nutritionally complete ration based on corn and soybean meal. All supplemented groups showed similar growth performance in all growth phases (P>0.05); however, there was a linear increase in carcass yield at 42 d of age according to increase in crude propolis inclusion from 1 to 21 d of age (P<0.05). At 7 d of age, relative weight of the gizzard increased linearly (P<0.05) with increasing propolis, and at 21 d of age, relative weight of the large intestine showed a quadratic (P<0.05) response, with the lowest value predicted to occur at 278 ppm of crude propolis. The ileum crypt depth at 21 d of age was affected by propolis, with a quadratic response (P<0.05) and highest value estimated at 323 ppm. At 21 d of age, sucrase activity in the jejunum increased linearly with increasing propolis and maltase activity in the ileum showed a quadratic (P<0.05) response, which predicted highest activity at 292 ppm. Amylase activity was lower in animals supplemented with 100 and 400 ppm of propolis at 21 d of age (P<0.05) compared with the control group. Thus, the crude propolis supplementation is not recommended in broiler diets from 1 to 21 d old given that it does not influence the performance, despite small changes in intestinal morphophysiology at 21 d of age.

Disturbed intestinal nitrogen homeostasis in a mouse model of high-fat diet-induced obesity and glucose intolerance

The oligopeptide transporter peptide cotransporter-1 Slc15a1 (PEPT1) plays a major role in the regulation of nitrogen supply, since it is responsible for 70% of the dietary nitrogen absorption. Previous studies demonstrated that PEPT1 expression and function in jejunum are reduced in diabetes and obesity, suggesting a nitrogen malabsorption from the diet. Surprisingly, we reported here a decrease in gut nitrogen excretion in high-fat diet (HFD)-fed mice and further investigated the mechanisms that could explain this apparent contradiction. Upon HFD, mice exhibited an increased concentration of free amino acids (AAs) in the portal vein (60%) along with a selective increase in the expression of two AA transporters (Slc6a20a, Slc36a1), pointing to a specific and adaptive absorption of some AAs. A delayed transit time (+40%) and an increased intestinal permeability (+80%) also contribute to the increase in nitrogen absorption. Besides, HFD mice exhibited a 2.2-fold decrease in fecal DNA resulting from a reduction in nitrogen catabolism from cell desquamation and/or in the intestinal microbiota. Indeed, major quantitative (2.5-fold reduction) and qualitative alterations of intestinal microbiota were observed in feces of HFD mice. Collectively, our results strongly suggest that both increased AA transporters, intestinal permeability and transit time, and changes in gut microbiota are involved in the increased circulating AA levels. Modifications in nitrogen homeostasis provide a new insight in HFD-induced obesity and glucose intolerance; however, whether these modifications are beneficial or detrimental for the HFD-associated metabolic complications remains an open issue.

Pre-resection gastric bypass reduces post-resection body mass index but not liver disease in short bowel syndrome

BACKGROUND

Obese patients developing short bowel syndrome (SBS) maintain a higher body mass index (BMI) and have increased risk of hepatobiliary complications. Our aim was to determine the effect of pre-resection gastric bypass (GBP) on SBS outcome.

METHODS

We reviewed 136 adults with SBS: 69 patients with initial BMI < 35 were controls; 43 patients with BMI > 35 were the obese group; and 24 patients had undergone GBP before SBS.

RESULTS

BMI at 1, 2, and 5 years was similar in control and GBP groups, whereas obese patients had a persistently increased BMI. Eight (33%) of the GBP patients had a pre-resection BMI > 35, but post-SBS BMI was similar to those <35. Obese patients were more likely to wean off PN (47% vs 20% control and 12% GBP, P < .05). Radiographic fatty liver tended to be higher in the GBP group (54% vs 19% control and 35% obese). End-stage liver disease occurred more frequently in obese and GBP patients (30% and 33% vs 13%, P < .05).

CONCLUSIONS

Pre-resection GBP prevents the nutritional benefits of obesity but does not eliminate the increased risk of hepatobiliary disease in obese SBS patients. This occurs independent of pre-SBS BMI suggesting the importance of GBP itself or history of obesity rather than weight loss.

Maternal protein restriction affects gene expression and enzyme activity of intestinal disaccharidases in adult rat offspring

This study investigated the consequences of intrauterine protein restriction on the gastrointestinal tract and particularly on the gene expression and activity of intestinal disaccharidases in the adult offspring. Wistar rat dams were fed isocaloric diets containing 6% protein (restricted, n = 8) or 17% protein (control, n = 8) throughout gestation. Male offspring (n = 5-8 in each group) were evaluated at 3 or 16 weeks of age. Maternal protein restriction during pregnancy produced offspring with growth restriction from birth (5.7 ± 0.1 vs 6.3 ± 0.1 g; mean ± SE) to weaning (42.4 ± 1.3 vs 49.1 ± 1.6 g), although at 16 weeks of age their body weight was similar to control (421.7 ± 8.9 and 428.5 ± 8.5 g). Maternal protein restriction also increased lactase activity in the proximal (0.23 ± 0.02 vs 0.15 ± 0.02), medial (0.30 ± 0.06 vs 0.14 ± 0.01) and distal (0.43 ± 0.07 vs 0.07 ± 0.02 U·g-1·min-1) small intestine, and mRNA lactase abundance in the proximal intestine (7.96 ± 1.11 vs 2.38 ± 0.47 relative units) of 3-week-old offspring rats. In addition, maternal protein restriction increased sucrase activity (1.20 ± 0.02 vs 0.91 ± 0.02 U·g-1·min-1) and sucrase mRNA abundance (4.48 ± 0.51 vs 1.95 ± 0.17 relative units) in the duodenum of 16-week-old rats. In conclusion, the present study shows for the first time that intrauterine protein restriction affects gene expression of intestinal enzymes in offspring.

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.

Reduced intestinal absorption of dipeptides via PepT1 in mice with diet-induced obesity is associated with leptin receptor down-regulation

Leptin is a major determinant of energy homeostasis, acting both centrally and in the gastrointestinal tract. We previously reported that acute leptin treatment enhances the absorption of di- and tripeptides via the proton-dependent PepT1 transporter. In this study, we investigated the long term effect of leptin on PepT1 levels and activity in Caco2 cell monolayers in vitro. We then assessed the significance of the regulation of PepT1 in vivo in a model of diet-induced obesity. We demonstrated that 1) leptin regulated PepT1 at the transcriptional level, via the MAPK pathway, and at the translational level, via ribosomal protein S6 activation, in Caco2 cells and 2) this activation was systematically followed by a time- and concentration-dependent loss of leptin action reflecting desensitization. Deciphering this desensitization, we demonstrated that leptin induced a down-regulation of its own receptor protein and mRNA expression. More importantly, we showed, in mice with diet-induced obesity, that a 4-week hypercaloric diet resulted in a 46% decrease in PepT1-specific transport, because of a 30% decrease in PepT1 protein and a 50% decrease in PepT1 mRNA levels. As shown in Caco2 cells, these changes in PepT1 were supported by a parallel 2-fold decrease in leptin receptor expression in mice. Taken together, these results indicate that during induction of obesity, leptin resistance may also occur peripherally in the gastrointestinal tract, disrupting the absorption of oligopeptides and peptidomimetic drugs.

Urinary sucrose and fructose as biomarkers of sugar consumption: comparison of normal weight and obese volunteers

Using urinary sugars as a biomarker of consumption, we have previously shown that obese people consume significantly more sugars than individuals of normal weight. However, there is concern that recovery of this biomarker may differ between normal weight and obese individuals. A total of 19 subjects, divided into two groups according to their body mass index (BMI) (normal weight BMI < or = 25 kg/m(2), n=10; obese BMI > or = 30 kg/m(2), n=9), participated in a randomized crossover dietary intervention study of three diets providing 13, 30 and 50% of energy from sugars for 4 days each while living in a volunteer suite. The mean urinary sucrose and fructose excretions in 24-h urine increased with increasing sugar consumption over the three dietary periods in both BMI groups and were significantly different between the diets (P < 0.01). There was no significant interaction effect of BMI class on the mean urinary excretions of these sugars with different sugar intakes, either as absolute values or expressed as a percentage of total sugar intake. In conclusion, BMI does not affect the validity of sucrose and fructose excretions in 24-h urine collections used as biomarkers to estimate total sugar consumption.

The effects of duodenal-jejunal exclusion on hormonal regulation of glucose metabolism in Goto-Kakizaki rats

BACKGROUND

The antidiabetic effect of bariatric surgery has been interpreted as a conceivable result of surgically induced weight loss and decreased caloric intake. However, glycemic control often occurs within days, before significant weight loss has been reached. The aim of our work was to investigate the hormones that control glycemic status in diabetes mellitus after a duodenal-jejunal exclusion in an animal model of nonobese type 2 diabetes.

METHODS

Twelve (12- to 14-week-old) rats (Goto-Kakizaki) randomly underwent one of the following procedures: gastrojejunal bypass (group 1, n = 6) or no intervention (controls) (group 2, n = 6). Both groups were fed with the same type and amount of diet. At basal time (preoperative) and after intervention (1 week and 1 month), weight and fasting glycemia were measured. An oral glucose tolerance test (OGTT) was realized at same times. Hormone levels (insulin, glucagons-like peptide 1 [GLP-1], glucose-dependent insulinotropic peptide [GIP], glucagon, and leptin) were measured after 20 minutes of oral glucose overload. Age-matched Goto-Kakizaki rats were used as controls for all variables.

RESULTS

Rats in group 1 and group 2 remained with the same weight during the protocol. The OGTT showed an improvement in glycemic levels in group 1; glucose levels were better at 1 week and 1 month after the surgery in all times of OGTT (basal, 10 minutes, and 120 minutes). Basal glucose levels at time 0 in basal time, at 1 week, and at 1 month were lower in group 1 than group 2. Postoral glucose overload levels of glucagon, insulin, GLP-1, and GIP remained unchanged during the treatment in both groups. In group 1, leptin levels had a significant decrease at 1 week and 1 month after surgery (basal time (6.1 +/- 1.6 ng/mL) versus 1 week (0.9 +/- 0.9 ng/mL) versus 1 month (0.7 +/- 0.6 ng/mL) (P < .05).

CONCLUSION

Gastrojejunal bypass in a nonobese diabetic model improves glycemic control with a significant decrease in leptin levels, without changes in enteroinsular axis (GLP-1, GIP, glucagons, and insulin levels).