Ryosuke Matsuoka

Cholesterol esterase accelerates intestinal cholesterol absorption

Mechanisms of acceleration of cholesterol absorption by cholesterol esterase were investigated in various experimental conditions. Lymphatic recovery of cholesterol intubated as a micellar solution containing phosphatidylcholine (PC) into the duodenum was enhanced by the co-administration of cholesterol esterase in rats drained of bile and pancreatic juice. However, no accelerated incorporation was observed when cholesterol was solubilized in PC-depleted micelles. Cholesterol esterase dose-dependently accelerated the incorporation of cholesterol into differentiated Caco-2 cells, only when cholesterol was solubilized in PC-containing micelles. The accelerated incorporation of cholesterol into Caco-2 cells by cholesterol esterase disappeared when the enzyme was preincubated with a suicide inhibitor of cholesterol esterase. Cholesterol esterase has an activity as phospholipase A(2). When 10% of PC in bile salt micelles was replaced by lysophosphatidylcholine (lysoPC), the incorporation of cholesterol into Caco-2 cells was significantly accelerated. Cholesterol esterase enhanced the incorporation of micellar cholesterol into brush border membranes prepared from the rat jejunum. The addition of cholesterol esterase to bile salt micelles accelerated the release of micellar cholesterol in a dose-dependent manner, only when the micelles contained PC. These observations strongly suggest that cholesterol esterase hydrolyzes PC in bile salt micelles and thereby, accelerating the release of cholesterol from bile salt micelles. This may be a major cause of the acceleration of cholesterol absorption by cholesterol esterase.

Mechanism for the cholesterol-lowering action of egg white protein in rats

Eggs are a popular source of dietary cholesterol, but their consumption does not necessarily result in an increased serum cholesterol concentration. We investigated the cholesterol-lowering activity of egg white protein (EWP) and its potential mechanism in rats. The consumption of EWP resulted in a decreased concentration of cholesterol in the serum, liver and intestinal mucosa. The excretion of fecal neutral sterols and bile acids was greater by rats fed with EWP than by those fed with casein. The ratio of cholesterol and bile acids in the micellar phase to those in the solid phase was lower in the intestinal contents from rats fed with EWP than from those fed with casein. These results suggest that the cholesterol-lowering activity of EWP can be attributed to lowering the cholesterol absorption by intervening in the micellar formation in the intestines.

Dietary Egg White Protein Inhibits Lymphatic Lipid Transport in Thoracic Lymph Duct-Cannulated Rats

Dietary egg white protein (EWP) decreases serum cholesterol levels. We previously showed that EWP decreased cholesterol absorption in the intestine. Rats subjected to permanent lymph duct cannulation were used to investigate the effects of dietary EWP on lipid transport. They were fed diets with 20% EWP and casein, and their lymph was collected to quantify lymphatic lipid levels. Dietary EWP decreased lymphatic cholesterol transport compared with casein. It was previously shown that EWP excluded cholesterol from bile acid micelles. Therefore, pepsin-hydrolyzed EWP and casein were prepared. EWP was not completely digested. Ovalbumin, which is the most abundant protein in EWP, showed resistance to digestion by pepsin. This study investigated the effects of EWP pepsin hydrolysate (EWP-ph) on cholesterol micellar solubility, cholesterol transfer from the micellar to the oil phase, water-holding capacity (WHC), settling volume in water (SV), and relative viscosity and compared them with the effects of casein pepsin hydrolysate (C-ph). EWP-ph significantly decreased the micellar solubility and transfer rate and increased the WHC, SV, and relative viscosity compared with C-ph. Moreover, the pepsin hydrolysate of ovalbumin, a major protein in EWP, played a role in decreasing cholesterol micellar solubility, leading to the inhibition of cholesterol absorption. In conclusion, dietary EWP decreased cholesterol intestinal absorption by exerting combined effects of these physicochemical properties in the gut.

Hydrolysis of Micellar Phosphatidylcholine Accelerates Cholesterol Absorption in Rats and Caco-2 Cells

Lymphatic recovery of cholesterol infused into the duodenum as bile salt micelles containing phosphatidylcholine (PC) was accelerated by the co-administration of phospholipase A2 in bile and pancreatic juice diverted rats. Previously we observed that cholesterol esterase, which has the ability to hydrolyze PC, caused the same effect under a similar experimental condition (Ikeda et al., Biochim. Biophys. Acta, 1571, 34–44 (2002)). Accelerated cholesterol absorption was also observed when a part of micellar PC was replaced by lysophosphatidylcholine (LysoPC) and oleic acid. Phospholipase A2 facilitated the incorporation of micellar cholesterol into Caco-2 cells in a dose-dependent manner. There was a highly negative correlation between the incorporation of cholesterol into Caco-2 cells and the content of micellar PC remaining in the culture medium. The release of cholesterol as a monomer from bile salt micelles was enhanced when a part of micellar PC was replaced with LysoPC and oleic acid. These results strongly suggest that the release of monomer cholesterol from bile salt micelles is accelerated by hydrolysis of PC in bile salt micelles and hence that cholesterol absorption is enhanced.

Ingested hyaluronan moisturizes dry skin

Hyaluronan (HA) is present in many tissues of the body and is essential to maintain moistness in the skin tissues, which contain approximately half the body’s HA mass. Due to its viscosity and moisturizing effect, HA is widely distributed as a medicine, cosmetic, food, and, recently marketed in Japan as a popular dietary supplement to promote skin moisture. In a randomized, double-blind, placebo-controlled clinical study it was found that ingested HA increased skin moisture and improved treatment outcomes for patients with dry skin. HA is also reported to be absorbed by the body distributed, in part, to the skin. Ingested HA contributes to the increased synthesis of HA and promotes cell proliferation in fibroblasts. These effects show that ingestion of HA moisturizes the skin and is expected to improve the quality of life for people who suffer from dry skin. This review examines the moisturizing effects of dry skin by ingested HA and summarizes the series of mechanisms from absorption to pharmacological action.

Dietary Hyaluronic Acid Migrates into the Skin of Rats

Hyaluronic acid is a constituent of the skin and helps to maintain hydration. The oral intake of hyaluronic acid increases water in the horny layer as demonstrated by human trials, but in vivo kinetics has not been shown. This study confirmed the absorption, migration, and excretion of 14C-labeled hyaluronic acid (14C-hyaluronic acid). 14C-hyaluronic acid was orally or intravenously administered to male SD rats aged 7 to 8 weeks. Plasma radioactivity after oral administration showed the highest level 8 hours after administration, and orally administered 14C-hyaluronic acid was found in the blood. Approximately 90% of 14C-hyaluronic acid was absorbed from the digestive tract and used as an energy source or a structural constituent of tissues based on tests of the urine, feces, expired air, and cadaver up to 168 hours (one week) after administration. The autoradiographic results suggested that radioactivity was distributed systematically and then reduced over time. The radioactivity was higher in the skin than in the blood at 24 and 96 hours after administration. The results show the possibility that orally administered hyaluronic acid migrated into the skin. No excessive accumulation was observed and more than 90% of the hyaluronic acid was excreted in expired air or urine.

Dietary Guar Gum Reduces Lymph Flow and Diminishes Lipid Transport in Thoracic Duct-Cannulated Rats

Guar gum has a well-recognized hypolipidemic effect. This effect is thought to be due to the physicochemical properties of guar gum, which may cause changes in adsorption of lipids or the viscosity of the intestinal contents. Guar gum is a non-specific absorption inhibitor of any type of lipid-soluble compound. Permanent lymph duct cannulation was performed on rats to investigate the effects of dietary guar gum on lymph flow and lipid transport. Rats fed a 5% guar gum diet were compared with those fed a 5% cellulose diet, and lymph was collected after feeding. The water-holding capacity (WHC), settling volume in water (SV), and viscosity of guar gum were compared with those of cellulose. Rats fed with the guar gum diet had significantly lower lymph flow and lymphatic lipid transport than did rats fed with the cellulose diet. The WHC, SV, and viscosity of guar gum were significantly higher than those of cellulose. We propose that dietary guar gum reduces lymph flow and thereby diminishes lipid transport by means of its physicochemical properties related to water behavior in the intestine.

Heating Has No Effect on the Net Protein Utilisation from Egg Whites in Rats

Egg whites (EW) are a good source of protein; however, they are typically heated prior to consumption. Therefore, we investigated the effects of different heating conditions on the protein utilisation rate of EW. Male Sprague-Dawley rats (n = 36, 198 ± 1 g) were divided into six groups and fed American Institute of Nutrition-76 chow containing unheated EW, soft-boiled EW, boiled EW, milk whey protein, soybean protein, or no protein over a 10-day period using pair-feeding. Urine and faeces were sampled daily beginning on day 5 to measure nitrogen content and the net protein utilisation (NPU) rate. The soybean protein group had a significantly lower level of food intake and was thus excluded from subsequent analyses. The NPU value was similar among the unheated, soft-boiled, and boiled EW groups (97.5 ± 0.4, 96.5 ± 0.1, and 96.5 ± 0.7, resp.). The EW group values were significantly higher than the whey group values (90.5 ± 1.0). These results show that EW serve as a good source of protein, irrespective of heating.

Dietary egg-white protein increases body protein mass and reduces body fat mass through an acceleration of hepatic β-oxidation in rats

Egg-white protein (EWP) is known to reduce lymphatic TAG transport in rats. In this study, we investigated the effects of dietary EWP on body fat mass. Male rats, 4 weeks old, were fed diets containing either 20 % EWP or casein for 28 d. Carcass protein levels and gastrocnemius leg muscle weights in the EWP group were significantly higher than those in the casein group. In addition, carcass TAG levels and abdominal fat weights in the EWP group were significantly lower than those in the casein group; adipocyte size in abdominal fat in the EWP group was smaller than that in the casein group. To identify the involvement of dietary fat levels in the rats, one of two fat levels (5 or 10 %) was added to their diet along with the different protein sources (EWP and casein). Abdominal fat weight and serum and hepatic TAG levels were significantly lower in the EWP group than in the casein group. Moreover, significantly higher values of enzymatic activity related to β-oxidation in the liver were observed in the EWP group compared with the casein group. Finally, abdominal fat weight reduction in the EWP group with the 10 % fat diet was lower than that in the EWP group with the 5 % fat diet. In conclusion, our results indicate that, in addition to the inhibition of dietary TAG absorption reported previously, dietary EWP reduces body fat mass in rats through an increase of body protein mass and the acceleration of β-oxidation in the liver.

Cholesterol Esterase Bound to Intestinal Brush Border Membranes Does Not Accelerate Incorporation of Micellar Cholesterol into Absorptive Cells

We confirmed that cholesterol esterase accelerated the incorporation of unesterified cholesterol solubilized in bile salt micelles into differentiated Caco-2 cells under various experimental conditions. Rat pancreatic juice and bovine cholesterol esterase increased the incorporation of micellar cholesterol into rat intestinal brush border membranes. The incorporation of micellar cholesterol was not changed in the brush border membranes enriched in and depleted of cholesterol esterase. The results suggest that the accelerated incorporation of micellar cholesterol by cholesterol esterase into absorptive cells is not mediated by the enzyme bound to the brush border membranes.