Leptin increases small intestinal response to cholecystokinin in leptin-deficient obese mice

Gastrointestinal pathology in a mouse model of mucopolysaccharidosis type IIIA

Mucopolysaccharidosis type IIIA (MPS IIIA) is a lysosomal storage disorder caused by a deficiency in sulphamidase (NS), a lysosomal enzyme required for the degradation of heparan sulphate glycosaminoglycans (gags). The MPS IIIA mouse is a naturally occurring model that accurately reflects the human pathology and disease course. It displays primarily central nervous system pathology accompanied by widespread accumulation of gag in somatic tissues. MPS IIIA mice exhibit greater bodyweight gain than normal littermates and attain a higher mature bodyweight. In this study, gastrointestinal morphology and function was characterised in the IIIA mouse. Stomach and duodenum weight increased in MPS IIIA mice and duodenum length also increased. An increased submucosal thickness was observed in MPS IIIA intestine compared to normal mice and lysosomal storage of gag was observed in this region. Storage was also observed in the lamina propria of the villus tip. All other morphometric measurements including villus height and crypt depth fell within the normal range. The gastric emptying half-life of solid and liquid meals decreased with age in normal mice whereas the T(1/2) of solid meals did not alter with age in MPS IIA mice such that they were elevated above normal by 38 weeks of age. Sucrase activity was higher than normal in MPS IIIA at all ages tested. These abnormalities in GI structure and function observed in MPS IIIA may contribute to weight gain in this disorder.

Effect of macronutrient composition on postprandial peptide YY levels

BACKGROUND

Peptide YY (PYY) is released from the distal small intestine and colon after meals and reduces appetite by increasing satiety. The amount of PYY released is proportional to calories ingested. Fat ingestion has also been reported to stimulate PYY release.

OBJECTIVE

The objective of the study was to determine whether macronutrient composition influences postprandial serum PYY levels by comparing 1 wk of a weight-maintenance low-carbohydrate, high-fat (LCHF) diet with a low-fat, high-carbohydrate (LFHC) diet.

METHODS

In this randomized crossover study, 18 obese subjects (14 females, 4 males, mean body mass index 35.6 +/- 2.9 kg/m(2)) were randomly assigned initially to 1 wk of a weight-maintenance LCHF or LFHC diet, after which a test meal of identical composition was given and serum PYY levels were assessed for 2.5 h postprandially. After a 1-wk washout period, subjects were crossed over and retested.

RESULTS

After 1 wk, mean postprandial area under the curve PYY after the LCHF test meal was 1.5-fold greater than after the LFHC test meal (P < 0.001). The LCHF diet led to 55% higher levels of postprandial serum PYY levels, compared with the LFHC diet (P = 0.005).

CONCLUSIONS

These data show that a LCHF diet stimulates PYY secretion more than a LFHC diet in obese individuals.

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.

Peptide YY levels are decreased by fasting and elevated following caloric intake but are not regulated by leptin

AIMS/HYPOTHESIS

Peptide YY (PYY) is a gut-derived hormone that has been shown to reduce short-term food intake in animals and humans. It has been proposed that deficiency of PYY contributes to obesity in humans. However, the physiology of PYY regulation by factors such as caloric restriction, or by other molecules important in energy homeostasis, e.g. leptin, remains to be fully elucidated.

MATERIALS AND METHODS

We evaluated the effect on PYY levels of: (1) caloric ingestion (a mixed meal) in five healthy normal-weight subjects; (2) fasting for 2 or 3 days in eight lean men and seven lean women respectively; and (3) recombinant human leptin administration at physiological replacement and pharmacological doses.

RESULTS

PYY levels increased 50% after a mixed meal (p=0.01), and short-term complete fasting for 2 or 3 days decreased leptin and PYY levels to 20-30% and 40-60% of baseline, respectively (both p<0.05). However, recombinant human leptin administration at physiological doses to restore the fasting-induced decrease of leptin levels and at pharmacological doses over the short term had no effect on PYY levels.

CONCLUSIONS/INTERPRETATION

PYY increases after meal ingestion and decreases after fasting in a manner consistent with a meal-related signal of energy homeostasis. Importantly, circulating levels of this gut-secreted molecule are independent of regulation by leptin over the short term. These findings contribute towards our understanding of the homeostatic systems that regulate appetite in humans, including the possible redundancy of gastrointestinally secreted and adipocyte-secreted signals. This may be of importance for the future development of medications to treat obesity.