Effect of dietary fat on the small intestinal mucosa

Intestinal adaptations to energy source of milk replacer in neonatal dairy calves

Most milk replacers (MR) contain more lactose compared with whole milk, which, when fed at a large meal size, could influence gut barrier function in calves. This study evaluated how replacing lactose in MR with fat (on a wt/wt basis) affects intestinal histomorphology and permeability in neonatal dairy calves. Thirty-four Holstein-Friesian bull calves were blocked by dam parity and randomly assigned to 1 of 2 treatments (n = 17): a high-lactose (46.1% lactose, 18.0% crude fat, and 23.9% crude protein of dry matter) or a high-fat MR (HF; 39.9% lactose, 24.6% crude fat, and 24.0% crude protein of dry matter). Calves were individually housed and fed pooled colostrum at 1.5 h and 12 h postnatally, at 18 and 9% of metabolic body weight (BW^0.75), respectively. From 24 h postnatally until the end of the study (d 7), calves were transitioned to be fed MR (prepared at 15% solids) at 18% of BW^0.75 twice daily at 0700 and 1900 h. During postprandial sampling on d 6, intestinal permeability was assessed by mixing lactulose (1.03 g/kg of BW^0.75) and d-mannitol (0.31 g/kg of BW^0.75) into the morning meal without altering total meal volume. Sequential blood samples were collected via jugular catheter, and total urine was collected for 12 h to measure the marker content. Calves were euthanized 3 h after the morning meal on d 7, and gastrointestinal tract tissues and digesta were collected for analysis of histomorphology, digesta osmolality, and gene expression. The empty gastrointestinal tracts of HF calves were heavier, although length did not differ and differences in histomorphology were minor. Digesta osmolality changed along the tract without differences between treatments. Plasma lactulose was greater in HF, although plasma d-mannitol and the recovery of both markers in urine were unaffected. No significant differences were detected in gene expression, although HF calves tended to have lower expression of TJP1 and CLDN2 and higher expression of proinflammatory cytokine IL1B in ileum tissue. In conclusion, partially replacing lactose in MR with fat resulted in a heavier and more permeable gut, with minor histomorphological differences.

Dietary palmitic acid modulates intestinal re-growth after massive small bowel resection in a rat

PURPOSE

Among factors promoting intestinal adaptation after bowel resection, dietary fatty acids have a special role. The purpose of the present study was to evaluate the effects of palmitic acid (PA) on early intestinal adaptation in rats with short bowel syndrome (SBS).

MATERIALS

Male Sprague-Dawley rats underwent either a bowel transection with re-anastomosis (sham rats) or 75% small bowel resection (SBS rats). Animals were randomly assigned to one of four groups: sham rats fed normal chow (sham-NC); SBS rats fed NC (SBS-NC), SBS rats fed high palmitic acid diet (SBS-HPA), and SBS rats fed low palmitic acid diet (SBS-LPA). Rats were sacrificed on day 14. Parameters of intestinal adaptation, overall bowel and mucosal weight, mucosal DNA and protein, villus height and crypt depth, cell proliferation and apoptosis were determined at sacrifice. RT-PCR and Western blotting were used to determine the level of bax and bcl-2 mRNA and protein (parameters of apoptosis), and ERK protein levels (parameter of proliferation). Statistical analysis was performed using Kruskal-Wallis test followed by post hoc test for multiple comparisons with P values of less than 0.05 considered statistically significant.

RESULTS

SBS-HFD rats demonstrated higher bowel and mucosal weight, mucosal DNA and protein in ileum, while deprivation of PA (SBS-LPA) inhibited intestinal re-growth both in jejunum and ileum compared to SBS-NC rats. A significant up-regulation of ERK protein coincided with increased cell proliferation in SBS-HFD rats (vs. SBS-NC). Also, the initial decreased levels of apoptosis corresponded with the early decrease in bax and increase in bcl-2 at both mRNA and protein levels.

CONCLUSION

Early exposure to HPA both augments and accelerates structural bowel adaptation in a rat model of SBS. Increased cell proliferation and decreased cell apoptosis may be responsible for this effect. Deprivation of PA in the diet inhibits intestinal re-growth.

Analysis of the intestinal absorption of essential fatty acids in vivo in the rat

The absorption and competition kinetics of the essential fatty acids (EFAs), linoleic acid (LA), alpha-linolenic acid (alphaLnA) and arachidonic acid (AA) in vivo were studied in the perfused rat jejunum. Uptake of each EFA on its own followed saturable kinetics at low luminal concentrations, suggesting a facilitative transport process, the affinity of which increased with chain length and degree of unsaturation. Absorption of one EFA was enhanced by low, whilst competitively inhibited by high, concentrations of a second EFA. Whereas LA and alphaLnA each interfered with the absorption of one another, both had little effect on AA. There was a strong inverse correlation between the relative unsaturation of an EFA and the change in Km of its absorption observed upon inhibition with another EFA. Overall, the results indicated a specific absorptive mechanism, probably involving a transport protein, the affinity of which increased with the degree of unsaturation of the EFA.

Carboxyl ester lipase activity in milk prevents fat-derived intestinal injury in neonatal mice

Carboxyl ester lipase (bile salt-stimulated lipase) is a pancreatic enzyme capable of hydrolyzing esters of cholesterol and fat-soluble vitamins. It also efficiently digests triglycerides (TG) into free fatty acids and glycerol and is abundant in the milk of humans and several other species. We used the mouse as a model to test the hypothesis that milk-derived carboxyl ester lipase (CEL) digests milk TG and that without its activity milk lipids and their digestion intermediates can disrupt the intestinal epithelium of neonates. CEL protein and enzymatic activity were shown to be abundant in mouse milk. After 24-h administration of the CEL-specific inhibitor, WAY-121,751-5, the small intestines of treated and control neonates were analyzed histologically for signs of fat malabsorption and injury to their villus epithelium. In vehicle-fed controls, TG were digested and absorbed in the duodenum and jejunum, whereas, in inhibitor-fed littermates, large intracellular neutral lipid droplets accumulated in enterocytes of the ileum, resulting in damage to the villus epithelium. Similar results were observed in neonates nursed by CEL knockout females compared with heterozygous controls. The results suggest that lack of CEL activity causes incomplete digestion of milk fat and lipid accumulation by enterocytes in the ileum of neonatal mice.

Prospective evaluation of faecal fatty acid excretion in short bowel syndrome in newborns

Short bowel syndrome (SBS) in the newborn results in limited intestinal absorptive capacity, leading especially to fatty acid (FA) malabsorption. It is unknown whether adaptation occurs in time in FA absorption, and whether this adaptation is chain-length dependent. The aid of the present study was to prospectively evaluate FA absorption and excretion during SBS in the newborn. Twenty-one neonates who underwent small bowel resection (of variable length) for various reasons (necrotizing enterocolitis, intestinal atresia, meconium peritonitis, cloacal extrophy, etc) were studied. Eight neonates had SBS, defined as a small bowel remnant of less than 50% of the original small bowel length related to gestational age. The mean remaining small bowel length in the SBS group was 34% (24% to 42%). The non-SBS control group consisted of 13 neonates who had only minor small bowel resections. The mean remaining bowel length for the non-SBS group was 95% (70% to 100%). The results show that the total fractional excretion of FA (FE-FA) at 2 weeks and 1, 2, 3, and 4 months postsurgery was 51% +/- 37%, 33% +/- 24%, 51% +/- 65%, 53% +/- 27%, and 7% +/- 2% in patients with SBS, versus 12% +/- 8%, 24% +/- 10%, 9% +/- 3%, 8% +/- 3% and 17% +/- 14% in the non-SBS controls, respectively (P < .05 by ANOVA). There appeared to be an amelioration in time in FA absorption, especially in the SBS group, after 3 months. FE-FA was chain-length related, being considerably less for C10 and C12 than for C14 and longer amounts. An amelioration of absorption occurred in the SBS patients, especially with the longer-chain FA. On the basis of the study data, the authors conclude that in the initial adaptation phase shorter chain lengths are better absorbed than longer chain lengths; however, in the latter FA group, substantial adaptation occurs with time.

Phospholipids prevent enteric bacterial translocation in the early stage of experimental acute liver failure in the rat

BACKGROUND

Bacterial infections and bacteremia in acute liver failure may at least partly be attributed to translocation of enteric bacteria. Attempts to prevent or treat such infections by the use of antibiotics may instead result in overgrowth of surviving microbes.

METHODS

In the present study, normal saline (1.5 ml/100 g body weight), phosphatidylcholine (1.5 ml/100 g body weight), and phosphatidylinositol (1.5 ml/100 g body weight) were orally administered by means of a gastric tube both 12 h and 30 min before operation. Effects of enteric administration of phospholipids on the prevention of enteric bacterial translocation, intestinal and mucosal mass, and enterocyte protein contents in acute liver failure induced by subtotal liver resection in the rat were evaluated.

RESULTS

The incidence of bacterial translocation increased significantly 2 and 4 h after 90% hepatectomy as compared with sham-operated animals. Enteric administration of phospholipids, however, significantly reduced the incidence of bacterial translocation after 90% hepatectomy. Phospholipid treatment prevented the postoperative decrease in intestinal mucosal mass and enterocyte protein content.

CONCLUSIONS

Enteral administration of phospholipids thus seems to protect against translocation of enteric bacteria and prevent against a decrease in intestinal mucosal mass and enterocyte protein content after subtotal hepatectomy in the rat.

The effects of energy source and tryptophan on the rate of protein synthesis and on hormones of the entero-insular axis in the piglet

The present experiment was designed to study the influence of dietary energy source (fat or carbohydrate) and tryptophan (TRP) on protein synthesis and plasma insulin concentrations in the piglet. Six dietary regimens, based on either a high-fat (F) or a high-carbohydrate (C) diet with three levels of TRP (deficient, 1; adequate, 2; excess, 3), were used. Fractional protein synthesis rate (ks; % per d) was measured in the liver, Longissimus dorsi (LD), Semitendinosus (ST), skin, femur, brain, pancreas, stomach, mucosa of the duodenum and jejunum, and the whole body, using a 'flooding dose' of 3H-phenylalanine. Mean integrated insulin, gastric inhibitory polypeptide (GIP) and glucose concentrations were higher after the C diets compared with the F diets, TRP supplementation globally augmented ks linearly in the liver, ST, skin and whole body, while it had quadratic effects in the LD (ks highest in the TRP-adequate diet groups) and jejunal mucosa (ks lowest in the TRP-adequate diet groups). Pancreatic ks was increased by TRP addition up to a plateau. Ks was highest after the F diets in the digestive tissues while in the skin and LD ks was highest after the C diets. Fasting concentrations of gluconeogenic amino acids were lower (and urea higher) with the F than the C diets, suggesting their use as precursors for glucose synthesis. In conclusion, we have confirmed the depressive effects of TRP deficiency on ks, RNA activity and growth. We could not establish a relationship between plasma insulin and muscle ks. This may be related to the way in which we manipulated plasma insulin concentrations.

Does the fatty acid profile of dietary fat influence its trophic effect on the small intestinal mucosa?

To compare the enterotrophic effects of different triglycerides, five groups of eight rats were fed mixed diets giving 50% of calories as oils rich in either essential fatty acids (EFA), alpha-linolenic acid, fully saturated fatty acids, oleic acid, or medium chain fatty acids. After 21-24 days there were no significant differences between the groups in overall small intestinal whole gut weight, mucosal weight, or mucosal DNA; overall mucosal protein showed slight variation (p < 0.05) that was compatible with differences in food intake between the groups. However, long chain triglycerides (LCT) and medium chain triglycerides (MCT) differed in their regional effects on cell proliferation; all four LCT rich diets increased mucosal mass and cell proliferation maximally in the mid small intestine, while MCT had their greatest effect proximally. Subsequently, two groups of eight rats were fed diets in which EFA or MCT were given as twice daily boluses (29% of dietary calories) for 20 to 23 days and compared with a third group of eight rats receiving a glucose rich, low fat diet. EFA and MCT boluses increased the overall parameters of small intestinal mucosal mass and for both oils the effects were now maximal in the mid small intestine. Thus different triglycerides have similar effects on overall small intestinal mucosal mass, but MCT differ from LCT in their regional effects on mucosal cell proliferation when they are given in mixed diets, although not when given as boluses.

Trophic effects of different enteral diets in the rat intestine

The trophic effect of 4 commercial diets compared to chow was studied in 50 rats. The 4 commercial diets were: a free amino acid diet, a diet based on soy protein hydrolysate and two diets based on intact protein with and without extra fibre added. Bowel weight, mucosa weight and DNA content were measured after 7 days of treatment. The enteral formula based on a soy protein hydrolysate had a significant growth stimulating effect on the proximal small bowel compared to rat chow. In the ileum and in the colon all diets without fibre supplementation caused significantly lower bowel weights than rat chow.

Effect of dietary fat on the distribution of mucosal mass and cell proliferation along the small intestine

This study investigated how substitution of long chain triglycerides for glucose in a mixed diet affects the overall small intestinal mucosal mass and the distribution of mucosal mass and cell proliferation along the small intestine. Four groups of eight female Wistar rats (180-200 g) were isocalorically fed mixed diets containing the essential fatty acid rich oil Efamol substituted for glucose at concentrations of 1.2%, 10%, 25%, and 50% total calories for 20 to 23 days. The small intestine was divided into three equal length segments and whole gut weights, mucosal weights, protein and DNA determined. Cell proliferation was estimated from the two hour accumulation of vincristine arrested metaphases in microdissected crypts at points 0%, 17%, 33%, 50%, 66%, and 100% small intestinal length. There were no differences between groups in parameters of overall small intestinal or distal segment mucosal mass. With increasing levels of fat, however, there was a significant trend for the mucosal mass of the proximal segment to fall and that of the middle segment to rise. The pattern of two hour metaphase accumulation reflected these changes. These regional changes in mucosal mass and cell proliferation may reflect differences in the sites of absorption of fat and glucose.

Effects of bolus doses of fat on small intestinal structure and on release of gastrin, cholecystokinin, peptide tyrosine-tyrosine, and enteroglucagon

To investigate the enterotrophic effects of bolus doses of long chain triglycerides, two groups of eight female Wistar rats were fed identical diets with 48.2% total calories as the essential fatty acid rich oil Efamol. To one group the oil was given in twice daily bolus doses by gavage, while for the other group the oil was mixed with the remainder of the feed and thus consumed over 24 hours. The animals were killed after 20 to 22 days. Bolus dosing significantly increased parameters of mucosal mass along the length of the small intestine in association with an increase in two hour accumulation of vincristine arrested metaphases in small intestinal crypts. In a second experiment, four replicate studies were carried out, each involving two groups of 12 rats respectively fed as described above. After 21 days one animal from each group was killed every two hours, providing regular plasma samples over 24 hours for measurement of gastrin, cholecystokinin, peptide tyrosine-tyrosine and enteroglucagon. Bolus dosing markedly enhanced release of peptide tyrosine-tyrosine and enteroglucagon, but not of gastrin or cholecystokinin. Thus, the enhanced enterotrophic effects of bolus doses of long chain triglycerides could be mediated by release of a distally located gut peptide, perhaps enteroglucagon.

Nutrition and translocation

It is now clear that atrophy of the intestinal mucosa can occur rapidly after injury and that the degree of atrophy is quantitatively related to the severity of injury. Such atrophy can be associated with translocation of bacteria and endotoxin, which can trigger the hypermetabolic response and induce a septic state, which may ultimately lead to multiple system organ failure. Early enteral feeding following trauma can prevent atrophy of the intestinal mucosa and is associated with a decrease in the hypermetabolic response and the incidence of septic complications and diarrhea. Enteral feeding of complete diets can also improve outcome with other forms of intestinal injury such as gamma irradiation or cytotoxic drugs. In contrast, total parenteral nutrition and elemental enteral diets are associated with atrophy of the intestinal mucosa and increased translocation. The addition of glutamine and/or fiber to elemental diets may decrease translocation in some but not all circumstances. It is now clear that enteral nutrition can influence the incidence and severity of translocation, which in turn can potentially reverse or prevent the adverse effects of injury and inflammation in traumatic injury and serious illness.