Luminal peroxides in intestinal thiol-disulfide balance and cell turnover

The Checkpoints of Intestinal Fat Absorption in Obesity

In this chapter, intestinal lipid transport, which plays a central role in fat homeostasis and the development of obesity in addition to the mechanisms of fatty acids and monoacylglycerol absorption in the intestinal lumen and reassembly of these within the enterocyte was described. A part of the resynthesized triglycerides (triacylglycerols; TAG) is repackaged in the intestine to form the hydrophobic core of chylomicrons (CMs). These are delivered as metabolic fuels, essential fatty acids, and other lipid-soluble nutrients, from enterocytes to the peripheral tissues following detachment from the endoplasmic reticulum membrane. Moreover, the attitudes of multiple receptor functions in dietary lipid uptake, synthesis, and transport are highlighted. Additionally, intestinal fatty acid binding proteins (FABPs), which increase the cytosolic flux of fatty acids via intermembrane transfer in enterocytes, and the functions of checkpoints for receptor-mediated fatty acid signaling are debated. The importance of the balance between storage and secretion of dietary fat by enterocytes in determining the physiological fate of dietary fat, including regulation of blood lipid concentrations and energy balance, is mentioned. Consequently, promising checkpoints regarding how intestinal fat processing affects lipid homeostatic mechanisms and lipid stores in the body and the prevention of obesity-lipotoxicity due to excessive intestinal lipid absorption are evaluated. In this context, dietary TAG digestion, pharmacological inhibition of TAG hydrolysis, the regulation of long-chain fatty acid uptake traffic into adipocytes, intracellular TAG resynthesis, the enlargement of cytoplasmic lipid droplets in enterocytes and constitutional alteration of their proteome, CD36-mediated conversion of diet-derived fatty acid into cellular lipid messengers and their functions are discussed.

Decreased lipid absorption due to reduced pancreatic lipase activity in aging male mice

Malnutrition due to aging is partly caused by decreased absorption of nutrients by the gastrointestinal tract. However, the underlying mechanism is unclear and changes in lipid absorption with aging are poorly understood. In this study, changes in lipid absorption with aging were examined in mice aged 3 and 25 months. After overnight fasting, blood samples were collected from snipped tails and then soybean oil was administered orally. Three hours later, mice were sacrificed by decapitation and the liver, pancreas, small intestine and blood were collected. The increase in serum triacylglycerol after soybean oil administration was significantly lower in the older mice, indicating a decrease in lipid absorption with aging. Measurement of mRNA levels for triacylglycerol absorption-related genes showed that mRNA for pancreatic lipase tended to decrease in 25-month-old mice. There was no significant difference in the protein level of pancreatic lipase, but the enzyme activity showed a significant decrease in the older mice. To examine this mechanism, expression levels of mRNA for protein turnover-related genes in the pancreas were measured. The level of a proteasomal mRNA showed a significant decrease in 25-month-old mice. This suggests that the ability to degrade unfolded protein decreases in the aging pancreas, and that this leads to reduction of pancreatic lipase activity and a decrease in lipid absorption.

Tea catechin auto-oxidation dimers are accumulated and retained by Caco-2 human intestinal cells

Despite the presence of bioactive catechin B-ring auto-oxidation dimers in tea, little is known regarding their absorption in humans. Our hypothesis for this research is that catechin auto-oxidation dimers are present in teas and are absorbable by human intestinal epithelial cells. Dimers (theasinensins [THSNs] and P-2 analogs) were quantified in commercial teas by high-performance liquid chromatography-mass spectrometry. (-)-Epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG) homodimers were present at 10 to 43 and 0 to 62 mumol/g leaf, respectively. The EGC-EGCG heterodimers were present at 0 to 79 mumol/g. The potential intestinal absorption of these dimers was assessed using Caco-2 intestinal cells. Catechin monomers and dimers were detected in cells exposed to media containing monomers and preformed dimers. Accumulation of dimers was significantly greater than monomers from test media. Three-hour accumulation of EGC and EGCG was 0.19% to 0.55% and 1.24% to 1.35%, respectively. Comparatively, 3-hour accumulation of the EGC P-2 analog and THSNs C/E was 0.89% +/- 0.28% and 1.53% +/- 0.36%, respectively. Accumulation of P-2 and THSNs A/D was 6.93% +/- 2.1% and 10.1% +/- 3.6%, respectively. The EGCG-EGC heterodimer P-2 analog and THSN B 3-hour accumulation was 4.87% +/- 2.2% and 4.65% +/- 2.8%, respectively. One-hour retention of P-2 and THSNs A/D was 171% +/- 22% and 29.6% +/- 9.3% of accumulated amount, respectively, suggesting intracellular oxidative conversion of THSNs to P-2. These data suggest that catechin dimers present in the gut lumen may be readily absorbed by intestinal epithelium.

Dietary Fat Feeding Alters Lipid Peroxidation in Surfactant-like Particles Secreted by Rat Small Intestine

Background

Long-term feeding of fish oil (n-3) and corn oil (n-6) markedly enhances levels of lipid peroxidation within isolated rat enterocytes. The effect is 10-fold greater at the villus tip than in the crypt region, correlating with the distribution of deleterious oxidative systems (glutathione reductase) in the tip and beneficial systems (superoxide dismutase) at the base of the villus. Because of this vertical gradient of peroxidation, the process was thought to play a role in apoptosis of enterocytes at the villus tip. Surfactant-like particles (SLPs) are membranes secreted by the enterocyte and a component of these membranes is directed to the intestinal surface overlying villus tips. One suggested role for SLPs has been to protect the mucosal surface from the harsh luminal conditions that might enhance apoptotic loss of enterocytes. The hypothesis to be tested was whether SLP lipids, like those in enterocytes, were also peroxidized, although they were external to the cellular processes that seem to oxidize enterocyte lipids, or whether SLP were immune to these biological processes. Feeding with groundnut oil (n-9) was compared with fish oil (n-3) and corn oil (predominantly n-6) to determine whether oils with various lipid composition would affect peroxidation in both SLP and enterocytes.

Methods

After an overnight fast, Wistar rats were fed 2 mL of dietary oil by gavage. Five hours later SLPs and underlying microvillus membranes (MVM) were isolated and analyzed for generation of thiobarbituric acid reactive substances (TBARS) and for hydrolase activities, at baseline and after addition of an Fe⁺²/ascorbate system to induce peroxidation.

Results

In vitro lipid peroxidation using the Fe²⁺/ascorbate system produced greater peroxidation than in MVM. Intestinal alkaline phosphatase (IAP), sucrase and lactase activities were decreased in SLPs, but were unaltered in MVM except for IAP. The activities of maltase, trehalase, Leucine aminopeptidase and γ–glutamyltranspeptidase, were unaffected both in SLPs and MVM under these conditions.

Conclusions

SLPs are more susceptible to oxidative damage than are the underlying MVMs. This may reflect results of a hostile luminal environment. It is not clear whether SLPs are acting as a lipid ‘sink’ to protect the MVM from greater oxidation, or are providing an initial stimulus for apoptosis of villus tip enterocytes, or both.

Catechin degradation with concurrent formation of homo- and heterocatechin dimers during in vitro digestion

Catechins were subjected to in vitro gastric and small intestinal digestion. EGCG, EGC, and ECG were significantly degraded at all concentrations tested, with losses of 71-91, 72-100, and 60-61%, respectively. EC and C were comparatively stable, with losses of 8-11 and 7-8%, respectively. HLPC-ESI-MS/MS indicated that EGCG degradation under simulated digestion resulted in production of theasinensins (THSNs) A and D (m/z 913) and P-2 (m/z 883), its autoxidation homodimers. EGC dimerization produced the homodimers THSN C and E (m/z 609) and homodimers analogous to P-2 (m/z 579). ECG homodimers were not observed. EGCG and EGC formed heterodimers analogous to the THSNs (m/z 761) and P-2 (m/z 731). EGCG and ECG formed homodimers analogous to the THSNs (m/z 897). This study provides an expanded profile of catechin dimers of digestive origin that may potentially form following consumption of catechins. These data provide a logical basis for initial screening to detect catechin digestive products in vivo.

The scientific basis of immunonutrition

Substrates with immune-modulating actions have been identified among both macro- and micronutrients. Currently, the modes of action of individual immune-modulating substrates, and their effects on clinical outcomes, are being examined. At present, some enteral formulas are available for the clinical setting which are enriched with selected immune-modulating nutrients. The purpose of the present paper is to review the scientific rationale of enteral immunonutrition. The major aspects considered are mucosal barrier structure and function, cellular defence function and local or systemic inflammatory response. It is notable that in critical illness the mucosal barrier and cellular defence are impaired and a reinforcement with enteral immunonutrition is desirable, while local or systemic inflammatory response should be down regulated by nutritional interventions. The results available from clinical trials are conflicting. Meta-analyses of recent trials show improvements such as reduced risk of infection, fewer days on a ventilator, and reduced length of intensive care unit and hospital stay. Thus, a grade A recommendation was proclaimed for the clinical use of enteral immune-modulating diets. Improvement in outcome was only seen when critical amounts of the immune-modulating formula were tolerated in patients classified as being malnourished. However, in other patients with severe sepsis, shock and organ failure, no benefit or even disadvantages from immunonutrition were reported. In such severe conditions we hypothesize that systemic inflammation might be undesirably intensified by arginine and unsaturated fatty acids, directly affecting cellular defence and inflammatory response. We therefore recommend that in patients suffering from systemic inflammatory response syndrome great caution should be exercised when immune-enhancing substrates are involved which may aggravate systemic inflammation.