The intestinal absorption of phospholipids in the rat

Supplementation of krill oil with high phospholipid content increases sum of EPA and DHA in erythrocytes compared with low phospholipid krill oil

Background

Bioavailability of krill oil has been suggested to be higher than fish oil as much of the EPA and DHA in krill oil are bound to phospholipids (PL). Hence, PL content in krill oil might play an important role in incorporation of n-3 PUFA into the RBC, conferring properties that render it effective in reducing cardiovascular disease (CVD) risk. The objective of the present trial was to test the effect of different amounts of PL in krill oil on the bioavailability of EPA and DHA, assessed as the rate of increase of n-3 PUFA in plasma and RBC, in healthy volunteers.

Methods and design

In a semi randomized crossover single blind design study, 20 healthy participants consumed various oils consisting of 1.5 g/day of low PL krill oil (LPL), 3 g/day of high PL krill oil (HPL) or 3 g/day of a placebo, corn oil, for 4 weeks each separated by 8 week washout periods. Both LPL and HPL delivered 600 mg of total n-3 PUFA/day along with 600 and 1200 mg/day of PL, respectively.

Results

Changes in plasma EPA, DPA, DHA, total n-3 PUFA, n-6:n-3 ratio and EPA + DHA concentrations between LPL and HPL krill oil supplementations were observed to be similar. Intake of both forms of krill oils increased the RBC level of EPA (p < 0.001) along with reduced n-6 PUFA (LPL: p < 0.001: HPL: p = 0.007) compared to control. HPL consumption increased (p < 0.001) RBC concentrations of EPA, DPA, total and n-3 PUFA compared with LPL. Furthermore, although LPL did not alter RBC n-6:n-3 ratio or the sum of EPA and DHA compared to control, HPL intake decreased (p < 0.001) n-6:n-3 ratio relative to control with elevated (p < 0.001) sum of EPA and DHA compared to control as well as to LPL krill oil consumption. HPL krill oil intake elevated (p < 0.005) plasma total and LDL cholesterol concentrations compared to control, while LPL krill oil did not alter total and LDL cholesterol, relative to control.

Conclusions

The results indicate that krill oil with higher PL levels could lead to enhanced bioavailability of n-3 PUFA compared to krill oil with lower PL levels.

Trial registration

Clinicaltrials.gov# NCT01323036.

Parameterization of a ruminant model of phosphorus digestion and metabolism

The objective of the current work was to parameterize the digestive elements of the model of Hill et al. (2008) using data collected from animals that were ruminally, duodenally, and ileally cannulated, thereby providing a better understanding of the digestion and metabolism of P fractions in growing and lactating cattle. The model of Hill et al. (2008) was fitted and evaluated for adequacy using the data from 6 animal studies. We hypothesized that sufficient data would be available to estimate P digestion and metabolism parameters and that these parameters would be sufficient to derive P bioavailabilities of a range of feed ingredients. Inputs to the model were dry matter intake; total feed P concentration (fPtFd); phytate (Pp), organic (Po), and inorganic (Pi) P as fractions of total P (fPpPt, fPoPt, fPiPt); microbial growth; amount of Pi and Pp infused into the omasum or ileum; milk yield; and BW. The available data were sufficient to derive all model parameters of interest. The final model predicted that given 75 g/d of total P input, the total-tract digestibility of P was 40.8%, Pp digestibility in the rumen was 92.4%, and in the total-tract was 94.7%. Blood P recycling to the rumen was a major source of Pi flow into the small intestine, and the primary route of excretion. A large proportion of Pi flowing to the small intestine was absorbed; however, additional Pi was absorbed from the large intestine (3.15%). Absorption of Pi from the small intestine was regulated, and given the large flux of salivary P recycling, the effective fractional small intestine absorption of available P derived from the diet was 41.6% at requirements. Milk synthesis used 16% of total absorbed P, and less than 1% was excreted in urine. The resulting model could be used to derive P bioavailabilities of commonly used feedstuffs in cattle production.

In vitro and in vivo effects of exogenous lipids on the enzymatic hydrolysis of rat bile phospholipids

The addition of total phospholipids, phosphatidylcholines, triglycerides, cholesterol or glycerol to incubation media containing rat pancreatic juice and bile labeled with [9, 10 3H2] oleic acid (90% of the radioactivity present as phospholipids) had no effect on the hydrolysis of bile endogenous phospholipids. The introduction of 2 or 10 mg of phosphatidylcholines and 0.5 ml of bile (approximately 1.5 mg of phospholipids) into the rat upper duodenum decreased the rate absorption of native bile phospholipids. It was not followed by an increase of free fatty acids released from biliary phospholipids in the intestinal lumen. The introduction of bile (0.5 ml) and small amounts of triolein (1.4--3.5 mg) into the duodenum had little effect on the rate of hydrolysis and absorption of native bile phospholipids, but caused a reduced absorption of the free fatty acids released or those coming from initial nonphosphorus biliary lipids. The introduction of bile (0.5 ml) and large amounts of triolein (30 mg) into the duodenum increased the rates of hydrolysis and absorption of endogenous bile phospholipids. These observations suggest that luminal lipid components can modify the organization of luminal micelles and, consequently, the action of the pancreatic phospholipase A2 and the absorption of bile lipids.

Enhancement of biliary phospholipid radioactivity by intestinal administration of labeled precursors of hepatic lecithin synthesis

An animal model is used to study the effects of different radioactive precursors of lecithin, administered intestinally, upon biliary lecithin synthesis. Choline caused greater biliary lecithin radioactivity than choline-labeled lecithin or palmitic acid. The clinical application of this finding is discussed with relation to patients with gallstones or potentially lithogenic bile. Oral administration of choline may increase biliary lecithin concentration and, thus, cholesterol-holding capacity in this patient group, thereby changing the character of the bile to a non-lithogenic state.

Contrasting effects on plasma lipoproteins of intravenous versus oral administration of a triglyceride-phospholipid emulsion

The effect of fat on plasma lipoproteins was compared when administered by the oral and intravenous routes to healthy control subjects on a low fat diet for 5-6 weeks. During this time each subject underwent two 5 day periods of fat supplementation with a soya bean triglyceride-egg yolk phospholipid emulsion (Intralipid), once via intragastric tube, once intravenously. Changes in plasma lipoproteins were assessed by measurement of their lipid and protein content. Intragastric fat administration significantly decreased the level of very low density lipoprotein (VLDL), whereas intravenous fat administration caused a significant rise in low density lipoprotein (LDL). Morphological evidence of persistence of exogenous phospholipid in plasma following intravenous fat administration was confirmed by alterations in the fatty acid composition of lecithin in the d 1.006-1.063 fraction of plasma. In vitro studies showed that exchange readily occurred between Intralipid and LDL lecithin, causing the latter to assume a more saturated pattern. It is concluded that the occurrence of similar changes in vivo could explain the rise in low density lipoprotein following intravenous fat, possibly by influencing the catabolic rate of the apoprotein. Hydrolysis of ingested phospholipids during absorption presumably explains why none of these changes occurred after oral fat supplementation, and would seem to be an important regulatory function of the small intestine in relation to plasma lipoprotein metabolism.