Vitamin E uptake by human intestinal cells during lipolysis in vitro

Comparison of α-Tocopherol, α-Tocopherol Acetate, and α-Tocopheryl Polyethylene Glycol Succinate 1000 Absorption by Caco-2 TC7 Intestinal Cells

(1) Background: vitamin E is often supplemented in the form of tocopherol acetate, but it has poor bioavailability and can fail to correct blood tocopherol concentrations in some patients with severe cholestasis. In this context, α-tocopheryl polyethylene glycol succinate 1000 (TPGS) has been of value, but very little is known about the mechanisms of its absorption. The aim of our work was to evaluate the mechanisms of absorption/secretion of TPGS compared to tocopherol acetate (TAC) and α-tocopherol by human enterocyte-like Caco-2 TC7 cells. (2) Methods: two weeks post-confluence Caco-2 cells were incubated with tocopherol- or TAC- or TPGS-rich mixed micelles up to 24 h and, following lipid extraction, TAC and tocopherol amounts were measured by high performance liquid chromatography (HPLC) in apical, cellular, and basolateral compartments. (3) Results: at equivalent concentrations of tocopherol in the apical side, the amounts of tocopherol secreted at the basolateral pole of Caco-2 cells are (i) significantly greater when the tocopherol is in the free form in the micelles; (ii) intermediate when it is in the TAC form in the micelles (p < 0.001); and (iii) significantly lower with the TPGS form (p < 0.0001). Interestingly, our results show, for the first time, that Caco-2 cells secrete one or more esterified forms of the vitamin contained in TPGS at the basolateral side.

Metabolism and biological activity of α-tocopherol derived from vitamin E-enriched transgenic maize in broilers

BACKGROUND

The aim of this study was to investigate the metabolism of α-tocopherol derived from vitamin E-enriched transgenic maize (VER) and its effects on antioxidant and immune functions in broilers aged 1-42 days. A total of 360 1-day-old male broilers were randomly divided into three groups containing six replicates with 20 broilers per replicate. The negative control (NC) group and the positive control (PC) group were given non-GM maize and non-GM maize plus exogenous vitamin E (VE), respectively, and the VER group was given VER, replacing the non-GM maize given to the NC group. Between days 1 and 21 and days 22 and 42, VE levels were 4.38 and 4.63 mg kg^-1 in the NC group, and 14.11 and 14.91 mg kg^-1 in the PC and VER group, respectively.

RESULTS

The results showed that α-tocopherol from both VER and additives increased α-tocopherol transfer protein and cytochrome P450 concentrations. Serum α-tocopherol and α-tocopherylquinone levels of broilers in the PC and VER groups were also significantly higher than those in the NC group (P < 0.05). Compared with the NC group, broilers in both groups that received α-tocopherol had reduced NF-κB p65 concentrations, significantly decreased serum prostaglandin E₂ , interleukin-6, malondialdehyde, and hydrogen peroxide levels (P < 0.05), and significantly increased glutathione, glutathione peroxidase, and total antioxidant capacity (P < 0.05).

CONCLUSION

In summary, both VER and non-GM maize fortified with exogenous VE showed similar effects on broilers, indicating that the α-tocopherol in VER has sufficient biological activity. © 2020 Society of Chemical Industry.

Nutrients central to maintaining intestinal absorptive efficiency and barrier integrity with fowl

The small intestinal mucosa acts to recover nutrients from the lumen while providing a barrier against potential hazards. Its unstirred water layer (USWL) at the lumen interface involves membrane associated mucin linearly protruding from underlying microvilli that entangles secretory mucin released from local goblet cells. Both mucin sources are dominated by repetitive O-glycosylated areas dependant on threonine, serine, glycine, and proline. Secretory mucin differs from membrane attached mucin by further employing multiple cystines that interconnect these areas into a net-like molecular sieve. All of the glycosylated areas have ionizable acidic groups credited with reducing pH from that in the lumen to create a micro environment favoring enzymes finalizing digestion while optimizing nutrient terms for absorption. Erosion of the USWL and/or abuse of the membrane due to lumen threats require continuous repair. The aforementioned amino acids are necessary in substantial amounts while vitamin B6 collaborates with vitamin A as meaningful cofactors for mucin synthesis. Marginal inadequacies of these nutrients during inordinate demand are expected to impair mucin replacement. In turn, marginal increases in feed conversion likely occur while fostering the probability of necrotic enteritis together with gizzard erosions. Abuse of the absorptive membrane is of particular concern from fatty acid hydroperoxides because of their continual presence in feed and inability of the USWL to provide protection. These hydroperoxides threaten membrane integrity by their inclusion in micelles during digestive events with fat thereby permitting transit through the USWL. Once coalesced with membrane phospholipids, structural aberrations are visualized as interfering with nutrient recovery while enabling leakage of cell contents to potentiate wet excreta. Inclusion of dietary vitamin E along with vitamin A into micelles with fatty acid hydroperoxides provides relief by quenching further peroxidation. Assuring cystine, threonine, glycine, and serine that are directly available as such together with vitamins A, E, and B6 represents one approach toward optimizing maintenance of the intestinal mucosa.

Enhancing vitamin E bioaccessibility: factors impacting solubilization and hydrolysis of α-tocopherol acetate encapsulated in emulsion-based delivery systems

Impact of free fatty acid chain length on vitamin E bioaccessibility: long chain FFAs form mixed micelles that easily accommodate vitamin E, whereas medium chain FFAs do not.

Liver X receptor up-regulates α-tocopherol transfer protein expression and α-tocopherol status

Fat-soluble vitamin E (α-tocopherol) has antioxidant activity. α-Tocopherol transfer protein (α-TTP), a hepatic cytosolic protein, selectively binds α-tocopherol and has an important role regulating circulatory α-tocopherol levels. However, only a few studies have shown the transcriptional regulation of the α-TTP gene. Here, we demonstrate that liver X receptor (LXR) regulates α-TTP expression through direct interaction with the α-TTP gene promoter, and it modulates circulating α-tocopherol levels. LXR belongs to the nuclear receptor superfamily, acts as a ligand-dependent transcription factor for oxysterols and plays an important role in cholesterol metabolism and lipogenesis. We identified an LXR response element (LXRE; DR4, a direct repeat with four-nucleotides spacing) of the human α-TTP gene promoter by using luciferase and electrophoretic mobility shift assays. Mutations in this element abolished activation of this promoter. Moreover, treatment of vitamin E-deficient rats with T0901317, a synthetic LXR ligand, increased α-TTP expression in the liver and cerebrum and increased the plasma α-tocopherol levels. These results indicate that the LXR signaling pathway modulates α-TTP gene expression and plasma α-tocopherol levels. Our observations imply that the LXR signaling pathway might be a useful target for antioxidant properties by controlling the vitamin E status.

Behavior of vitamin E acetate delivery systems under simulated gastrointestinal conditions: lipid digestion and bioaccessibility of low-energy nanoemulsions

Colloidal delivery systems are needed to incorporate oil-soluble vitamins into aqueous-based foods and beverage products. In this study, we encapsulated vitamin E acetate into oil-in-water nanoemulsions produced using either a low-energy method (Emulsion Phase Inversion, EPI) or a high energy method (microfluidization). Oil-in-water nanoemulsions (d<200 nm) could be produced using both low- and high-energy methods from a non-ionic surfactant (Tween 80) and medium chain triglycerides (MCTs). The influence of surfactant-to-oil ratio (SOR) on lipid digestion and vitamin bioaccessibility of EPI nanoemulsions was determined using a gastrointestinal tract (GIT) model that simulated the mouth, stomach, and small intestine. There were increases in the size and negative charge of the oil droplets after passage through the GIT, which was attributed to droplet coalescence and changes in interfacial composition. The rate and extent of lipid digestion decreased with increasing surfactant concentration, but the bioaccessibility of vitamin E acetate was high in all of the samples (>95%). No appreciable influence of the preparation method (low-energy versus high-energy) on lipid digestion and vitamin bioaccessibility was observed. The major advantage of the EPI method for forming nanoemulsions is that no expensive equipment is required, but relatively high surfactant concentrations are needed compared to microfluidization.

Respective contributions of intestinal Niemann-Pick C1-like 1 and scavenger receptor class B type I to cholesterol and tocopherol uptake: in vivo v. in vitro studies

The intestinal absorption of cholesterol and lipid micronutrients such as vitamin E has been shown to share some common pathways. The present study aims to further compare the uptake of cholesterol ([3H]cholesterol v. 22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3-ol (NBD-cholesterol)) and tocopherol in Caco-2 TC-7 cells and in mouse intestine, with special focus on the respective roles of scavenger receptor class B type I (SR-BI) and Niemann-Pick C1-like 1 (NPC1L1). Conversely to NBD-cholesterol, the uptakes of [3H]cholesterol and tocopherol by Caco-2 cells were impaired by both block lipid transport-1 and ezetimibe, which inhibit SR-BI and NPC1L1, respectively. These inhibitions occurred only when cholesterol or tocopherol was delivered to cells included in micelles that contained biliary acid and at least oleic acid as a lipid. In vivo, after 2 h of digestion in mice, the uptake of the two cholesterol analogues and of tocopherol all showed distinct patterns along the duodenum-jejunum axis. [3H]Cholesterol uptake, which correlated closely to NPC1L1 mRNA expression in wild-type (wt) mice, was strongly inhibited by ezetimibe. Intestinal SR-BI overexpression did not change NPC1L1 expression and led to a significant increase in [3H]cholesterol uptake in the distal jejunum. Conversely, neither ezetimibe treatment nor SR-BI overexpression had an effect on NBD-cholesterol uptake. However, in contrast with SR-BI mRNA expression, tocopherol absorption increased strongly up to the distal jejunum in wt mice where it was specifically inhibited by ezetimibe, and was increased in the proximal intestine of intestinal SR-BI-overexpressing mice. Thus, cholesterol and tocopherol uptakes share common pathways in cell culture models, but display different in vivo absorption patterns associated with distinct contributions of SR-BI and NPC1L1.

Tocopherol isomer pattern in serum and stool of human following consumption of black currant seed press residue administered in whole grain bread

BACKGROUND & AIMS

Serum gamma-tocopherol is thought to be associated with human health. The dietary influence of tocopherol and fibre-rich black currant seed press residue on serum and stool tocopherol concentration was investigated in a controlled human intervention study.

METHODS

Thirty-six women consumed bread enriched with black currant press residue (4 weeks). The resultant faecal and serum tocopherol concentrations were compared with those after a period consuming control bread without press residue and a normal baseline diet. Fibre intake and excretion, antioxidant capacity (TEAC), and vitamin C concentrations in serum and urine were also determined. Samples were obtained with a 5-day standardised diet at the end of each period.

RESULTS

The press residue bread lead to significantly increased beta-, gamma-, delta- and total tocopherol intake, serum alpha-, beta-, gamma- and total tocopherol concentration (with and without lipid adjustment), fibre intake and urinary vitamin C concentration compared to control bread (P<0.05). Faecal excretion of total tocopherols and fibre increased compared to baseline (P<0.05).

CONCLUSIONS

Fibre intake and excretion influence total tocopherol concentration in lipid-adjusted serum and in stool. The outstandingly high increase of serum gamma-tocopherol concentration through seed press residue consumption could be due to a presumed interruption of the enzymatic tocopherol degradation mechanism by bread constituents.

ATP-binding cassette transporter A1 is involved in hepatic alpha-tocopherol secretion

Vitamin E (alpha-tocopherol) is an essential fat-soluble nutrient with antioxidant properties. alpha-Tocopherol transfer protein (alpha-TTP), the product of the gene responsible for familial isolated vitamin E deficiency, plays an important role in maintaining the plasma alpha-tocopherol level by mediating the secretion of alpha-tocopherol by the liver. However, the mechanisms underlying hepatic alpha-tocopherol secretion are not fully understood. This study was undertaken to elucidate the mechanism of alpha-tocopherol re-efflux from hepatocytes, the cells that have the most important role in regulating plasma-alpha-tocopherol concentrations. From in vitro experiments using [(3)H]alpha-tocopheryl acetate and McARH7777 cells that stably express alpha-tocopherol transfer protein (alpha-TTP), the following results were obtained. First, addition of apolipoprotein A-I (apoA-I), a direct acceptor of the ATP-binding cassette transporter A1 (ABCA1)-secreted lipids, increased alpha-tocopherol secretion in a dose-dependent manner. Second, probucol, an antiatherogenic compound reported to be an inactivator of ABCA1 reduced hepatic alpha-tocopherol secretion. Third, ABCA1-RNAi suppressed hepatic alpha-tocopherol secretion. In a mouse in vivo experiment, addition of 1% probucol to the diet decreased plasma alpha-tocopherol concentrations. These results strongly suggest that ABCA1 is substantially involved in hepatic alpha-tocopherol secretion.

Nutriomic analysis of fresh and processed fruit products. 2. During in vitro simultaneous molecular passages using Caco-2 cell monolayers

Many studies have used Caco-2 cell monolayers as human intestinal absorption models. However, only a few studied digested foods, instead of pure standard compounds. Moreover, beneficial and nutritional molecules (nutriome) have not been investigated simultaneously. The present study explored nutriome passages from digest solution of fresh, dried, and juiced tomato, mango, and papaya using Caco-2 cell monolayers in apical-->basolateral directions. A validation method using complementary TEER and P(app) values or internal standard caffeine is recommended because physiologically passive diffusion is unlikely to happen. Sugars were transported into basolateral sides, resulting in potential glucose equivalent bioavailability of 2.26-75 mg h(-1)/100 g (WB). Using sugar passage rates (DB) of juices as 100% references, the rate order was tomato (49.8% dried; 89.5% fresh) > mango (56.8% dried; 22.8% fresh) > papaya (18.7% dried; 36.7% fresh). Major indications that phytochemical absorption does not occur in the small intestine were obtained from the bioassay condition selected. Apical organic acid levels decreased, which occasionally were transported into basolateral sides, whereas the disappearances of apical carotenoids and phenolics were not. Pectin substances were predicted to be responsible for the disappearances of bioactive compounds in those pectin-rich fruits. Further investigations on the role of pectin substances in intestinal passages are recommended.

Vitamin E in human health and disease

Vitamin E in nature is comprised of a family of tocopherols and tocotrienols. The most studied of these is alpha-tocopherol (alpha-TOH), because this form is retained within the body, and vitamin E deficiency is corrected with this supplement. alpha-TOH is a lipid-soluble antioxidant required for the preservation of cell membranes, and it potentially acts as a defense against oxidative stress. Many studies have investigated the metabolism, transport, and efficacy alpha-TOH in the prevention of sequelae associated with cardiovascular disease (CVD). Supplementation with vitamin E is considered to provide health benefits against CVD through its antioxidant activity, the prevention of lipoprotein oxidation, and the inhibition of platelet aggregation. However, the results from large prospective, randomized, placebo-controlled clinical trials with alpha-TOH have been largely negative. A recent meta-analysis suggests that alpha-TOH supplements may actually increase all-cause mortality; however, the mechanism for this increased risk is unknown. In vitro studies performed in human cell cultures and animal models suggest that vitamin E might increase the hepatic production of cytochrome P450s and MDR1. Induction of CYP3A4 or MDR1 by vitamin E could potentially lower the efficacy of any drug metabolized by CYP3A4 or MDR1. Other possibilities include an adverse effect of alpha-TOH on blood pressure in high-risk populations. Because of the wide popularity and use of vitamin E supplements, further research into potential adverse effects is clearly warranted.

Comparison of different vehicles to study the effect of tocopherols on gene expression in intestinal cells

Recent studies have focused on the ability of tocopherols to regulate gene expression. For such experiments, the methodology used to deliver molecules to the cells is crucial and could lead to different results depending on the vehicle used. The objective of the present study was to compare commonly used tocopherol vehicles (ethanol, BSA and mixed micelles) in terms of toxicity, stabilization of tocopherols, uptake efficiency of tocopherols by cells and effect on gene expression. Lactate dehydrogenase measurements did not reveal cytotoxicity of any of the tested vehicles. Tocopherol recovery measurements showed that approximately 80% of the tocopherol was lost in ethanolic solutions, while only approximately 30% and 10% were lost in BSA and mixed micelles, respectively. After 24 h incubation, Caco-2 cell monolayers treated with mixed micelles exhibited the highest alpha-tocopherol intracellular concentrations (5-times those measured with the two other vehicles). Similar results were obtained with gamma-tocopherol. Vehicles, except mixed micelles that activate the FXR/bile acids signalling pathway, did not affect expression of nuclear receptors involved in lipid metabolism or their target genes. This study establishes mixed micelles as the best vehicle to deliver tocopherols to intestinal cell monolayers in culture.

Absorption, transport, and tissue delivery of vitamin E

Vitamin E is one of the most abundant lipid-soluble antioxidant agents found in plasma and cells of higher mammals. The uptake, transport and tissue delivery of alpha-tocopherol, a key vitamin E form, involves molecular, biochemical, and cellular processes closely related to overall lipid and lipoprotein homeostasis. This review highlights recent findings that have led to a better understanding of vitamin E transport, including intestinal absorption, hepatic transport, and cellular uptake of alpha-tocopherol in vivo. This new information may be critical for manipulation of vitamin E homeostasis in a variety of oxidative stress-related disease conditions in humans.

Effect of the main dietary antioxidants (carotenoids, gamma-tocopherol, polyphenols, and vitamin C) on alpha-tocopherol absorption

OBJECTIVE

(R,R,R)-alpha-tocopherol is a fat-soluble antioxidant vitamin generally ingested with other dietary antioxidants. The objective of this study was to assess whether the main dietary antioxidant classes, that is carotenoids, polyphenols, vitamin C and gamma-tocopherol, affect the intestinal absorption of alpha-tocopherol. METHODS, DESIGN AND SUBJECTS: We evaluated first the effect of different combinations of antioxidants on (R,R,R)-alpha-tocopherol absorption by a human intestinal cell line (Caco-2 clone TC7). Then we compared the effect of two doses of a dietary antioxidant (lutein) on the postprandial chylomicron alpha-tocopherol responses to an alpha-tocopherol-rich meal. Eight healthy men ate two similar meals in a random order at a 1 month interval. The meals contained 24 mg alpha-tocopherol in sunflower oil plus either 18 or 36 mg lutein. Blood samples were collected during the postprandial periods to compare chylomicron alpha-tocopherol responses.

RESULTS

A mixture of polyphenols (gallic acid, caffeic acid, (+)-catechin and naringenin) and a mixture of carotenoids (lycopene, beta-carotene and lutein) significantly impaired alpha-tocopherol absorption in Caco-2 cells (P<0.001 and P<0.0001, respectively). The inhibitory effect of gamma-tocopherol was close to significance (P=0.055). In contrast, vitamin C had no significant effect (P=0.158). Naringenin was the only polyphenol that significantly impaired alpha-tocopherol absorption. Postprandial alpha-tocopherol response was weakest at the highest dose of lutein (616+/-280 nmol/l h vs 1001+/-287 nmol/l h). The observed extent of reduction (-38%, P=0.069) supported the inhibitory effect of carotenoids observed in the Caco-2 experiments.

CONCLUSION

Naringenin, carotenoids and probably gamma-tocopherol can impair alpha-tocopherol absorption whereas vitamin C and phenolic acids have no effect.

Transport of vitamin E by differentiated Caco-2 cells

In hepatocytes, vitamin E is secreted via the efflux pathway and is believed to associate with apolipoprotein B (apoB)-lipoproteins extracellularly. The molecular mechanisms involved in the uptake, intracellular trafficking, and secretion of dietary vitamin E by the intestinal cells are unknown. We observed that low concentrations of Tween-40 were better for the solubilization and delivery of vitamin E to differentiated Caco-2 cells, whereas high concentrations of Tween-40 and sera inhibited this uptake. Vitamin E uptake was initially rapid and then reached saturation. Subcellular localization revealed that vitamin E primarily accumulated in microsomal membranes. Oleic acid (OA) treatment, which induces chylomicron assembly and secretion, decreased microsomal membrane-bound vitamin E in a time-dependent manner. To study secretion, differentiated Caco-2 cells were pulse-labeled with vitamin E and chased in the presence and absence of OA. In the absence of OA, vitamin E was associated with intestinal high density lipoprotein (I-HDL), whereas OA-treated cells secreted vitamin E with I-HDL and chylomicrons. No extracellular transfer of vitamin E between these lipoproteins was observed. Glyburide, an antagonist of ABCA1, partially inhibited its secretion with I-HDL, whereas plasma HDL increased vitamin E efflux. An antagonist of microsomal triglyceride transfer protein, brefeldin A, and monensin specifically inhibited vitamin E secretion with chylomicrons. These studies indicate that vitamin E taken up by Caco-2 cells is stored in the microsomal membranes and secreted with chylomicrons and I-HDL. Transport via I-HDL might contribute to vitamin E absorption in patients with abetalipoproteinemia receiving large oral doses of the vitamin.

Assessment of carotenoid bioavailability of whole foods using a Caco-2 cell culture model coupled with an in vitro digestion

Epidemiological studies have shown that consumption of carotenoid-rich fruits and vegetables is associated with a reduced risk of developing chronic diseases. beta-Carotene, alpha-carotene, and beta-cryptoxanthin are precursors of vitamin A, a nutrient essential for human health. However, little is known about the bioavailability of carotenoids from whole foods. This study characterized the intestinal uptake performance of carotenoids using monolayers of differentiated Caco-2 human intestinal cells and mimicked human digestion to assess carotenoid absorption from carrots and corn. Results showed that Caco-2 cellular uptake of beta-carotene and zeaxanthin was higher than that of lutein. Uptake performances of pure carotenoids and carotenoids from whole foods by Caco-2 cells were both curvilinear, reaching saturated levels after 4 h of incubation. The time kinetics and dose response of carotenoid uptake presented a similar pattern in Caco-2 cells after plating for 2 and 14 days. Furthermore, the applicability of this new model was verified with whole grain corn, showing that cooked corn grain significantly enhanced carotenoid bioavailability. These results support the feasibility of the in vitro digestion cell model for assessing carotenoid absorption from whole foods as a suitable and cost-effective physiological alternative to current methodologies.

Dietary antibiotic growth promoters enhance the bioavailability of alpha-tocopheryl acetate in broilers by altering lipid absorption

The influence of intestinal microbial bile salt deconjugation on absorption of fatty acids and alpha- and gamma-tocopherol was investigated in a trial with Ross 208 broilers. Birds (n = 1600) were assigned to 4 dietary treatments: no supplementation or supplementation of antibiotics (salinomycin, 40 mg/kg feed and avilamycin, 10 mg/kg feed), and inclusion of either animal fat (10 g/100 g feed) or soybean oil (10 g/100 g feed) in the diet. At d 7, 14, 21, and 35 of age, the intestinal number of the bile salt hydrolase-active bacteria Clostridium perfringens, the concentration of conjugated and unconjugated bile salts, the ileal absorption of fatty acids and tocopherols, and the blood plasma concentrations of tocopherols were measured. All variables were significantly influenced by bird age. C. perfringens counts were lower and bile salt concentrations were greater in birds fed soybean oil. The supplementation of antibiotics reduced the numbers of C. perfringens in the small intestine and reduced the concentration of unconjugated bile salts. The ileal absorption of fatty acids and alpha-tocopherol, as well as the plasma concentration of alpha-tocopherol, was greater in birds fed antibiotics. The absorption and plasma concentration of gamma-tocopherol were not influenced by antibiotics. Unlike gamma-tocopherol, which is present solely as the free alcohol, the major proportion of dietary alpha-tocopherol is present as alpha-tocopheryl acetate, which requires a bile salt-dependent enzymatic hydrolysis before absorption. In conclusion, proper digestion of lipid-soluble compounds is highly dependent on an adequate concentration of bile salts in the small intestine to provide proper lipid emulsification and activation of lipolytic enzymes.

Liver receptor homolog 1 controls the expression of carboxyl ester lipase

The orphan nuclear receptor liver receptor homolog 1 (LRH-1) plays a central role in cholesterol homeostasis by regulating a number of hepatic and intestinal genes critical for reverse cholesterol transport and bile acid homeostasis. Herein, we describe the identification of carboxyl ester lipase (CEL) as a novel target of LRH-1 in pancreas, a tissue in which LRH-1 is abundantly expressed. In situ hybridization and gene expression studies demonstrate that both LRH-1 and CEL are co-expressed and confined to the exocrine pancreas. LRH-1 interacts with a consensus LRH-1 response element in the human CEL promoter, which is perfectly conserved in the rat gene, and induces CEL promoter activity in cotransfection assays. As reported for other LRH-1 target genes, the nuclear receptor short heterodimer partner represses LRH-1-induced CEL promoter activity. Chromatin immunoprecipitation demonstrates that binding of LRH-1 to the CEL promoter increases histone H4 acetylation corresponding with the activation of endogenous CEL gene transcription. Our data, identifying CEL as the first pancreatic LRH-1 target gene, indicate that LRH-1 is an important player in enterohepatic cholesterol homeostasis.

Digestion and absorption of 2 fat emulsions with different droplet sizes in the human digestive tract

BACKGROUND

The extent of fat emulsification affects the activity of digestive lipases in vitro and may govern digestion and absorption of dietary fat.

OBJECTIVE

We investigated the effect of the fat globule size of 2 enteral emulsions on fat digestion and assimilation in humans.

DESIGN

Healthy subjects received intragastrically a coarse (10 microm) and a fine (0.7 microm) lipid emulsion of identical composition in random order. Gastric and duodenal aspirates were collected throughout digestion to measure changes in fat droplet size, gastric and pancreatic lipase activities, and fat digestion. Blood lipids were measured postprandially for fat assimilation.

RESULTS

Despite an increase in droplet size in the stomach (2.75-6.20 microm), the fine emulsion retained droplets of smaller size and its lipolysis was greater than that of the coarse emulsion (36.5% compared with 15.8%; P < 0.05). In the duodenum, lipolysis of the fine emulsion was on the whole higher (73.3% compared with 46.3%). The overall 0-7-h plasma and chylomicron responses given by the areas under the curve were not significantly different between the emulsions, but the triacylglycerol peak was delayed with the fine emulsion (3 h 56 min compared with 2 h 50 min).

CONCLUSIONS

Fat emulsions behave differently in the digestive tract depending on their initial physicochemical properties. A lower initial fat droplet size facilitates fat digestion by gastric lipase in the stomach and duodenal lipolysis. Overall fat assimilation in healthy subjects is not affected by differences in initial droplet size because of efficient fat digestion by pancreatic lipase in the small intestine. Nevertheless, these new observations could be of interest in the enteral nutrition of subjects suffering from pancreatic insufficiency.

Accumulation and retention of micellar β-carotene and lutein by Caco-2 human intestinal cells

Despite the interest in the diverse roles of dietary carotenoids in human health, little is known about the transfer of these plant pigments from foods to micelles during digestion and their subsequent transfer across the intestinal epithelium. We conducted this study to characterize the intestinal uptake of micellarized carotenoids using monolayers of differentiated Caco-2 human intestinal cells. Crystalline beta-carotene (BC) and lutein (LUT), solubilized in mixed micelles for delivery to cells, were stable in a tissue culture environment for 20 hours. Cellular accumulation of micellar BC and LUT was proportional to the media content of carotenoids at </=2 micromol/L and the length of exposure. Cellular accumulation of BC routinely exceeded LUT and was due in part to the enhanced efflux or possible metabolism of LUT. Cellular BC content increased in a curvilinear manner when cultures were incubated in micellar medium containing 2 to 27 micromol/L BC prepared from water miscible beadlets; cellular BC content was maximum when medium BC was >/=18 micromol/L. There was no indication that high levels of BC in medium or within cells adversely affected micellar LUT accumulation. These data support the use of the Caco-2 human cell line as a model for studying the intestinal uptake, absorption, and possible interactions of dietary carotenoids.

Endogenous lipase activity in Caco-2 cells

Dietary triglycerides, the major precursors of long chain fatty acids (FA), require hydrolysis by pancreatic enzymes prior to their absorption by the small intestine. Although Caco-2 cells are frequently employed for the study of enterocyte lipid metabolism, the presence of an endogenous lipase activity has never been previously reported. The major goal of this investigation was to determine the presence of endogenous Caco-2 cell lipase activity, to examine its capacity to hydrolyze triglycerides, and to define its intracellular location. Caco-2 cells were found to have an endogenous lipase activity, capable of hydrolyzing [1-14C]triolein from the apical cell compartment. A time and concentration dependence of lipase activity was observed, with hydrolysis of triolein into free fatty acids and monoglyceride. The majority of the lipase activity was found in the cytosolic cell fraction and, to a lesser extent, in the apical brush border membrane and other organelles. Protamine sulfate markedly reduced the Caco-2 cell lipase activity, yet it remained relatively insensitive to high concentrations of NaCl, taurocholate, calcium, heparin and chloroquine. The addition of exogenous human gastric lipase to the medium of the apical compartment resulted in a significant increased rate of hydrolysis of triolein, followed by enhanced Caco-2 cell fatty acid uptake and basolateral lipid secretion. The major esterified intracellular lipids were triglycerides and phospholipids. We conclude that Caco-2 cells possess an endogenous lipase capable of hydrolyzing cytosolic triglycerides. Furthermore, activity present on the apical membrane and secreted into the apical medium, though quantitatively less important than the cytosolic lipase, may permit an additional route for energy uptake. The addition of gastric lipase to the Caco-2 cell cultures greatly enhanced FA uptake above that seen with the endogenous lipase alone.

Synthesis and secretion of the pancreatic-type carboxyl ester lipase by human endothelial cells

Human aortic extracts contain significant cholesteryl ester hydrolytic activity. The enzymic activity was shown to be activated by trihydroxylated bile salt, but not by dihydroxylated bile salt. Monospecific antibodies prepared against rat pancreatic carboxyl ester lipase (CEL, cholesterol esterase) immunoprecipitated cholesteryl ester hydrolytic activity from human aorta, demonstrating that the neutral CEL in aorta is highly similar to and probably identical with the pancreatic enzyme. Reverse transcriptase PCR amplification of mRNA from human aortic endothelial cells revealed de novo synthesis of the pancreatic-type CEL by these cells. Preincubating human aortic endothelial cells with oxidized or native low-density lipoprotein resulted in an 8- and 3-fold increase in CEL activity secreted into the culture medium respectively. A potential physiological role for the endothelial CEL was demonstrated by studies showing its ability to confer partial protection against the cytotoxic effects of lysophosphatidylcholine. The protective effect of CEL is related to its bile-salt-independent lysophospholipase activity. However, CEL hydrolysis of lysophosphatidylcholine can be inhibited by excess cholesterol. Taken together, these results indicate that pancreatic-type CEL is synthesized by cells lining the vessel wall. Moreover, vascular CEL may interact with cholesterol and oxidized lipoproteins to modulate the progression of atherosclerosis.

Vitamin E incorporated into a very-low-fat meal is absorbed from the intestine of young rats

Vegetable fats and oils are major sources of dietary vitamin E. Consequently the current trend to reduce fat consumption is accompanied by a reduction of the intake of vitamin E. In addition, the absorption of vitamin E is thought to be dependent on the hydrolysis of dietary lipids in the small intestine. It is therefore conceivable that a lower dietary fat intake also diminishes the intestinal absorption of vitamin E. The present 3-week feeding study in young male rats was designed to investigate whether different concentrations of vitamin E added to a very-low-fat product (0, 330 or 1350 mg DL-alpha-tocopheryl acetate/kg product) were absorbed. We therefore incorporated these products into a very-low-fat meal (final fat concentration: 7 g/kg) or a low-fat meal containing 52 g fat/kg. The magnitude of vitamin E absorption from these meals was compared with that from meals containing similar amounts of vitamin E, but a high fat concentration of 190 g/kg. Apparent vitamin E absorption was defined as intake of alpha-tocopherol equivalents (alpha TE) minus faecal alpha TE excretion over 4 d during week 3 of the experimental period. The results of this study showed that apparent absorption of vitamin E from a very-low-fat meal varied, depending on the vitamin E concentration, from 73 to 83%. The magnitude of this vitamin E absorption was not significantly different from that from meals containing a high amount of fat. Liver vitamin E status was equal in rats fed on the very-low-fat meals compared with those fed on the high-fat meals. We conclude that, when very-low-fat or low-fat products are used as a replacement for full-fat products, addition of vitamin E to these products, as DL-alpha-tocopheryl acetate, might be useful in meeting the vitamin E requirements.

Dietary free and esterified cholesterol absorption in cholesterol esterase (bile salt-stimulated lipase) gene-targeted mice

The involvement of pancreatic cholesterol esterase (bile salt-stimulated lipase) in cholesterol absorption through the intestine has been controversial. We have addressed this issue by using homologous recombination in embryonic stem cells to produce mice lacking a functional cholesterol esterase gene. Cholesterol esterase knockout mice and their wild type counterparts were fed a bolus dose of [3H]cholesterol and a trace amount of [beta-14C]sitosterol by gavage. The ratio of the two radiolabels excreted in the feces over a 24-h period was found to be similar in the control and cholesterol esterase-null mice. Similar results were observed when the radiolabeled sterols were supplied in an emulsion with phospholipid and triolein or in lipid vesicles with phosphatidylcholine. Cholesterol absorption results were similar between the control and cholesterol esterase-null mice regardless of whether the animals were fed a low fat diet or a high fat/high cholesterol diet. The rate of [3H]cholesterol appearance in the serum of the gene-targeted mice paralleled that observed in control animals. In contrast to these results, when experiments were performed with [3H]cholesteryl oleate instead of [3H]cholesterol, a higher amount of the 3H radiolabel was found excreted in feces and dramatically less of the radiolabel was detected in the serum of the cholesterol esterase-null mice in comparison with that detected in control animals. Serum cholesterol levels were not significantly different between control and cholesterol esterase-null mice fed either control or an atherogenic diet. These results indicate that cholesterol esterase is responsible for mediating intestinal absorption of cholesteryl esters but does not play a primary role in free cholesterol absorption.

Transport properties are not altered across Caco-2 cells with heightened TEER despite underlying physiological and ultrastructural changes

Selected properties of Caco-2 cells were examined after disparate transepithelial electrical resistance (TEER) measurements were observed in two populations of Caco-2 cells. Comparisons were made between the early passages of Caco-2 cells (Caco-2E, passages 35-47) and the later passages of cells (Caco-2L, passages 87-112). Transmission electron microscopy revealed that regions of Caco-2L cells were composed of multiple cell layers rather than the monolayers observed in Caco-2E cells. Epithelial cell height (or barrier thickness) was not significantly different between the two cell populations. Intercellular and intracellular lumina were observed in the Caco-2L cells, but not in the Caco-2E cells. Results of [3H]thymidine incorporation assays showed significantly higher cell proliferation rates in Caco-2L cells relative to Caco-2E cells. Despite morphological and physiological changes, there were no significant differences in the apparent permeabilities for D-mannitol (paracellular diffusion marker), hydrocortisone (transcellular diffusion marker), or dipeptide, Gly-Sar (carrier-mediated transcellular transport marker) between the two populations of cells. The higher TEER values in Caco-2L cells may be the results of a slight perturbation of tight junctions associated with both the multiple cell layers and the presence of intercellular lumina.

Enhancement of calcium transport in the Caco-2 cell monolayer model

The overall objective of this research was to identify enhancers of calcium transport using an in-vitro Caco-2 cell monolayer model. The enhancers studied were medium-chain triglycerides (MCT) and acylcarnitines (AC). The extent of cell damage associated with the use of these enhancers was determined by monitoring the release of cellular lactate dehydrogenase (LDH). The effect of chain-length and concentration dependence of these agents on enhancement were also determined. The effects of ACs were found to be superior to those of MCTs. However, the ACs elicited a greater release of LDH than the MCTs. The possible mechanisms of enhancer-mediated increase in calcium transport and the potential significance of this study with regard to the prevention of osteoporosis are discussed.

Digestion and absorption of tube-feeding emulsions with different droplet sizes and compositions in the rat

Assimilation of lipid nutrients depends on the efficiency of emulsified fat hydrolysis by digestive lipases. As shown in vitro, the activity of preduodenal and pancreatic lipases is governed by the physicochemical properties of emulsions. Thus the aim of this study was to evaluate in the rat how emulsions are digested and assimilated depending on their droplet size or solute composition. Fasted rats were intragastrically tube fed emulsions with different median droplet sizes (0.6 microns, fine; 22 microns, coarse) or solute composition (0.8 microns, complex fine) containing 14C-triolein and 3H-cholesterol. Two and 5 hours after feeding, fat-droplet size was measured in gastric and duodenal contents, and lipids were radioactively quantified in different compartments. In the stomach, the droplet size of the fine emulsions significantly increased to values (13 microns to 24 microns) comparable with those of the coarse emulsion (35 microns to 36 microns). In the duodenum, the droplet sizes of the three emulsions were in the range of 14 microns to 33 microns. After 2 hours, gastric triglyceride hydrolysis was significantly higher with the fine than with the coarse emulsion and was lower with the complex fine emulsion. Gastric emptying of fat was significantly different, with the following decreasing order: coarse, fine, and complex fine emulsion. In the small intestine, the fine and coarse emulsions were processed comparably, whereas the assimilation of the fine complex emulsion was significantly delayed. Calculations indicate that ingested fatty acids were distributed in the peripheral tissues at different rates with the same decreasing order. The fate of a lipophilic nutrient, cholesterol, was also markedly altered by the type of emulsion. These data support the concept that tube-fed emulsions with different droplet sizes and solute composition are digested differently and thus are metabolized differently.

Epithelial cells in culture as a model for the intestinal transport of antimicrobial agents

The bioavailabilities of orally administered drugs depend to a great extent on their capability of being transported across the intestinal mucosa. In an attempt to develop an in vitro model for studying the intestinal transport of drugs, we used an intestinal epithelial cell line (Caco 2) derived from a human colon adenocarcinoma. A renal epithelial cell line (MDCK) was also used to determine the tissue specificity of drug transport. These cell lines, which were grown on filters, form a monolayer of well-polarized cells coupled by tight junctions and can be used for transcellular transport experiments. We studied the transport of nine antimicrobial agents with different physicochemical and pharmacokinetic characteristics using these epithelial cell monolayers to determine whether this model could be predictive of oral bioavailability. The transepithelial passage was assayed from the apical (AP) to the basolateral (BL) side and in the opposite direction (BL to AP) in both cell lines. Radioactively labeled mannitol was used to monitor the intactness of the cell monolayer during drug passage. The results indicated that all antimicrobial agents tested tended to behave in vitro generally according to their known in vivo absorptive characteristics. In addition, the use of epithelia from different tissues enabled us to divide the drugs into four groups according to their behaviors and suggested the existence of different transport mechanisms. In particular, two antibiotics, gentamicin and teicoplanin, showed no passage in either direction or cell line, in accordance with their very poor in vivo absorbances after oral administration. In contrast, rifapentine, rifampin, and nalidixic acid passed very efficiently at similar rates in both directions and cell lines in a concentration-dependent, nonsaturable manner, which is suggestive of passive diffusion down a concentration gradient. Of the remaining drugs, isoniazid and novobiocin sodium showed some differences in passage between the two cell lines and, given their ionized state at the pH that was used, may use the paracellular route. Finally, trimethoprim and D-cycloserine exhibited differences in passage both with respect to polarity and cell line; in particular, trimethoprim had a faster rate of passage only in Caco 2 cells and in the BL to AP direction, while D-cycloserine was exclusively transported by Caco 2 cells in the AP to BL direction. In both cases it is possible that active transport mechanisms are involved.

Unique features of Helicobacter pylori disease in children

In a six-year period, 41 children had endoscopically documented duodenal ulcer disease or primary H. pylori antral gastritis without duodenal ulcer. Of 37 children with H. pylori gastritis, group 1 comprised 23 patients with duodenal ulcer disease and group 2 had 14 patients without ulcers (primary H. pylori gastritis). Group 3 comprised four children with duodenal ulcer disease and H. pylori-negative antral biopsies. During the study period, all primary chronic ulcer disease was duodenal; no primary chronic gastric ulcer was present. Two distinct types of duodenal ulcer disease were identified; the majority (85%) was always associated with significant active H. pylori antral gastritis (group 1). The minority (15%) had virtually absent gastritis and no H. pylori (group 3). Native Indian children were represented in group 1 quite out of proportion to the referral population and had the most severe disease. While it is established that a higher prevalence of asymptomatic H. pylori infection exists in non-Caucasians, this appears to be the first demonstration of a higher prevalence of symptomatic ulcer disease in non-Caucasian children or adults. Caucasian children tended to have primary H. pylori gastritis (group 2) or duodenal ulcer without H. pylori (group 3). Antral nodularity was found to be an important specific endoscopic sign, unique to those children with H. pylori disease. It has not been described in adult H. pylori disease. Non-Caucasian children, especially Native Indians, in British Columbia have more prevalent and more severe H. pylori disease than Caucasians. Endoscopy with gastric antral biopsies is necessary to distinguish different types of duodenal ulcer disease and to diagnose primary H. pylori gastritis.