Katsumi Imaizumi

Low-density lipoprotein receptor-related protein 5 (LRP5) is essential for normal cholesterol metabolism and glucose-induced insulin secretion

A Wnt coreceptor low-density lipoprotein receptor-related protein 5 (LRP5) plays an essential role in bone accrual and eye development. Here, we show that LRP5 is also required for normal cholesterol and glucose metabolism. The production of mice lacking LRP5 revealed that LRP5 deficiency led to increased plasma cholesterol levels in mice fed a high-fat diet, because of the decreased hepatic clearance of chylomicron remnants. In addition, when fed a normal diet, LRP5-deficient mice showed a markedly impaired glucose tolerance. The LRP5-deficient islets had a marked reduction in the levels of intracellular ATP and Ca2+ in response to glucose, and thereby glucose-induced insulin secretion was decreased. The intracellular inositol 1,4,5-trisphosphate (IP3) production in response to glucose was also reduced in LRP5−/− islets. Real-time PCR analysis revealed a marked reduction of various transcripts for genes involved in glucose sensing in LRP5−/− islets. Furthermore, exposure of LRP5+/+ islets to Wnt-3a and Wnt-5a stimulates glucose-induced insulin secretion and this stimulation was blocked by the addition of a soluble form of Wnt receptor, secreted Frizzled-related protein-1. In contrast, LRP5-deficient islets lacked the Wnt-3a-stimulated insulin secretion. These data suggest that Wnt/LRP5 signaling contributes to the glucose-induced insulin secretion in the islets.

New Anti–Monocyte Chemoattractant Protein-1 Gene Therapy Attenuates Atherosclerosis in Apolipoprotein E–Knockout Mice

BackgroundMonocyte recruitment into the arterial wall and its activation may be the central event in atherogenesis. Monocyte chemoattractant protein-1 (MCP-1) is an important chemokine for monocyte recruitment, and its receptor (CCR2) may mediate such in vivo response. Although the importance of the MCP-1/CCR2 pathway in atherogenesis has been clarified, it remains unanswered whether postnatal blockade of the MCP-1 signals could be a unique site-specific gene therapy. Methods and ResultsWe devised a new strategy for anti-MCP-1 gene therapy to treat atherosclerosis by transfecting an N-terminal deletion mutant of the human MCP-1 gene into a remote organ (skeletal muscle) in apolipoprotein E-knockout mice. This strategy effectively blocked MCP-1 activity and inhibited the formation of atherosclerotic lesions but had no effect on serum lipid concentrations. Furthermore, this strategy increased the lesional extracellular matrix content. ConclusionsWe conclude that this anti-MCP-1 gene therapy may serve not only to reduce atherogenesis but also to stabilize vulnerable atheromatous plaques. This strategy may be a useful and feasible form of gene therapy against atherosclerosis in humans.

Serum lipid profiles in Japanese women and men during consumption of walnuts

Objective: To determine the serum cholesterol, apolipoproteins and LDL oxidizability in young Japanese women and men during walnut consumption and to evaluate its active principle.Design: Experimental study with a randomized design.Subjects: Twenty healthy women and 20 healthy men.Interventions: Subjects were randomly assigned to consume each of two mixed natural diets for 4 weeks in a cross-over design. Reference and walnut diets were designed and the walnut diet had 12.5% of the energy derived from walnuts (44–58 g/day).Results: The total cholesterol and serum apolipoprotein B concentrations, and the ratio of LDL cholesterol to HDL cholesterol was significantly lowered in women and men when fed on the walnut diet, than when on the reference diet (P≤0.05). The LDL cholesterol concentration was significantly lowered in women on the walnut diet (0.22 mmol/l, P=0.0008), whereas this decrease was not significant in men (0.18 mmol/l, P=0.078). The most prominent change in the fatty acid composition of the cholesteryl esters from serum after the walnut diet was an elevation of α-linolenic acid in women (76%, P<0.001) and men (107%, P<0.001). This elevation was negatively correlated to the change in LDL cholesterol in women (r=0.496, P=0.019) and men (r=0.326, P=0.138). The LDL oxidizability in women was not influenced by the diets (P=0.19).Conclusions: α-Linolenic acid in the walnut diet appears to be responsible for the lowering of LDL cholesterol in women.Sponsorship: Kyushu University (Fukuoka, Japan) and the California Walnut Commission (California, USA).

Effects of arginine and lysine addition to casein and soya-bean protein on serum lipids, apolipoproteins, insulin and glucagon in rats.

1. The effect of variation in arginine: lysine on the relative cholesterolaemic effects of dietary soya-bean protein and casein was studied. Male rats received semi-purified diets containing soya-bean protein isolate or casein supplemented respectively with varying amounts of lysine or arginine for 40 d and blood samples were taken after a 5 h fast. 2. Neither the addition of arginine to casein nor lysine to soya-bean protein modified the intrinsic effect of these proteins on serum cholesterol. 3. Serum triglyceride levels tended to rise with increasing amounts of lysine supplementation. The opposite trend was obtained with arginine supplementation. 4. Casein caused an increase in the concentration of serum insulin, but not glucagon. The glucagon level was increased proportionately with increasing amounts of arginine, while the addition of lysine showed no effect. The effects of added amino acids on serum insulin were inconclusive. 5. There was a parallel increase in serum apo E and glucagon in response to arginine supplementation, while lysine supplementation increased serum apo E. 6. Thus, arginine: lysine was more effective in regulating serum triglyceride than serum cholesterol. Insulin was associated with different effects of these proteins on serum lipids.

Effects of milk fermented by Lactobacillus gasseri SBT2055 on adipocyte size in rats

Despite adequate scientific evidence of the potential benefits of probiotics to human health or disease prevention, their contribution to the growth of adipose tissue remains to be established. Four-week-old male Sprague-Dawley rats were fed a diet containing skim milk (control diet) or skim milk fermented by Lactobacillus gasseri SBT2055 (LGSP diet) for 4 weeks. Their body weight gain, adipose tissue weight, adipocyte size distribution profile, blood and hepatic lipids, and serum leptin, glucose and adiponectin levels were determined. There was a significant reduction in average adipocyte size in mesenteric white adipose tissue (P = 0.004). Moreover, the rats fed the LGSP diet displayed greater numbers of small adipocytes from mesenteric and retroperitoneal adipose tissues than did those on the control diet. Whereas adiponectin concentrations did not differ between the groups, serum leptin concentrations were decreased to 32 % in the LGSP diet group compared with the control group. Concentrations of serum glucose and lipids, and liver lipids, except for the liver TAG level, were similar in the two groups. These results indicate a possible role for a fermented milk product in the regulation of adipose tissue growth.

Milk fermented by Lactobacillus gasseri SBT2055 influences adipocyte size via inhibition of dietary fat absorption in Zucker rats.

We have demonstrated previously that a diet containing skimmed milk (SM) fermented by Lactobacillus gasseri SBT2055 (LGSP) reduces adipocyte size in Sprague-Dawley rats. Two experiments were conducted to extend these observations in order to elucidate the mechanism involved. In experiment 1, lean and obese Zucker rats were fed a diet containing SM or LGSP for 4 weeks. The LGSP diet, compared with the SM diet, resulted in lowering of the mesenteric adipose tissue weight (23 %; P < 0.05), adipocyte sizes (28 %; P < 0.001) and serum leptin concentration (36 %; P < 0.05) in lean rats. Obese Zucker rats did not display such dietary effects. Only the number of smaller adipocytes was increased (P < 0.05) by the LGSP diet in the subcutaneous adipose tissue of obese rats. The LGSP diet significantly reduced the serum and hepatic cholesterol in rats. In addition, the LGSP diet led to an increased excretion of faecal fatty acids and total neutral faecal sterols in both rat strains. In experiment 2, Sprague-Dawley rats with permanent cannulation of the thoracic duct were fed either the SM or LGSP diets and their lymph was collected. The LGSP diet lowered the maximum transport rate of TAG and phospholipids. These results indicate that fermented milk regulates adipose tissue growth through inhibition at the stage of dietary fat absorption in lean Zucker rats.

Digestion and lymphatic transport of eicosapentaenoic and docosahexaenoic acids given in the form of triacylglycerol, free acid and ethyl ester in rats

Lymphatic transport of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids given as trieicosapentaenoyl glycerol (TriEPA) and tridocosahexaenoyl glycerol (TriDHA) was compared with that of ethyl ester and free acid in rats cannulated with thoracic duct. Trioleoylglycerol (TO) served as a control. EPA and DHA, compared with oleic acid, were slowly transported in lymph irrespective of fat types administered. Total 24-h recovery of DHA in all fat types and ethyl EPA was significantly lower compared to that of oleic acid. Lymphatic recovery of EPA and DHA in rats given TriEPA and TriDHA was significantly higher at the first 3 h after the administration compared to those given as free acid or ethyl ester. The recovery in rats given free acid at a later stage (9-24 h) was higher than that of the other fat types. As a result, the 24-h recovery was comparable between triacylglycerol (TAG) and free acid, while it was significantly lower in ethyl ester. Although TriEPA and TriDHA were slowly hydrolyzed by pancreatic lipase in vitro compared with TO and TAGs rich in EPA or DHA at the second position, the hydrolysis rate at 60 min incubation was comparable among the TAGs examined. The hydrolysis rate of ethyl esters was extremely low even in 6 h incubation with lipase. These observations show that presence of EPA and DHA at the 1- and 3-positions of TAGs does not result in their lower recovery in lymph. Processes after lipolysis may be responsible for their low recovery in lymph. In a separate study, slower lymphatic recovery of DHA given as free acid than TriDHA was improved by the simultaneous administration of TO, but not by free oleic acid. The observations suggest that the slow recovery of free acid is caused by delayed TAG synthesis in mucosal cells and/or low micellar solubility of fatty acids in the intestinal lumen due to a limited supply of 2-monoacylglycerol (MAG). A large portion of EPA and DHA were recovered in lymph chylomicrons and very low density lipoproteins (VLDL, > 95%) and incorporated into TAG (84-92%) fraction in all fat types examined. Lymphatic recovery rate of simultaneously administered cholesterol was influenced by the fat types given.

Dietary gallate esters of tea catechins reduce deposition of visceral fat, hepatic triacylglycerol, and activities of hepatic enzymes related to fatty acid synthesis in rats.

Tea catechins, rich in (−)-epigallocatechin gallate and (−)-epicatechin gallate, or heat-treated tea catechins in which about 50% of the (−)-epigallocatechin gallate and (−)-epicatechin gallate in tea catechins was epimerized to (−)-gallocatechin gallate and (−)-catechin gallate, were fed to rats at 1% level for 23 d. Visceral fat deposition and the concentration of hepatic triacylglycerol were significantly lower in the tea catechin and heat-treated tea catechin groups than in the control group. The activities of fatty acid synthase and the malic enzyme in the liver cytosol were significantly lower in the two catechin groups than in the control group. In contrast, the activities of carnitine palmitoyltransferase and acyl-CoA oxidase in the liver homogenate were not significantly different among the three groups. These results suggest that the reduction in activities of enzymes related to hepatic fatty acid synthesis by the feeding of tea catechins or heat-treated tea catechins can cause reductions of hepatic triacylglycerol and possibly of visceral fat deposition.

Effects of soya-bean protein and casein on serum cholesterol levels in rats.

1. The effect of the soya-bean protein isolate and casein, both given 200 g/kg diet for 3-4 weeks, on serum cholesterol was compared in male rats. 2. Soya-bean protein exerted a hypocholesteramic effect only in a cholesterol-free low-fat (10 g maize oil/kg) diet, when the lowering action appeared independent of the strain of the rat or the feeding pattern. The results obtained with diets containing cholesterol or higher levels of fats or both showed no definite pattern of response. 3. Although the decrease in serum cholesterol appeared greater in alpha-lipoproteins than in beta-lipoproteins, the proportion of the former to total cholesterol remained almost unchanged. The concentration of serum apo A-I was significantly lower in rats given the vegetable protein. 4. Rats given soya-bean protein excreted significantly more neutral sterols. 5. The serum amino acid pattern did not reflect the difference in dietary protein. Addition of cholesterol to the diets modified the serum aminogarm, the decrease in threonine being most marked in both protein groups. 6. This study shows that the hypocholesteraemic action of soya-bean protein is easily modified by the type of diet.

Effects of dietary sphingolipids on levels of serum and liver lipids in rats

Abstract Sphingosine addition to cultured cells has been shown to provoke divergent physiological reactions. The present study was carried out to determine if dietary sphingolipids, which presumably liberate sphingosine during passage through the intestine, influence serum and liver lipids in rats. Rats were given purified diets containing cholesterol (1%) and sphingolipids (0.5 and 2%, composed mainly of ceramide and sphingomyelin) for 2 weeks. Food intake, body weight gain and liver weight were not affected by the supplementation of sphingolipids. The concentration of triglycerides in the serum, but not in the liver, decreased significantly in sphingolipid fed rats, and the accumulation of esterified cholesterol in the liver, but not in the serum increased, depending on the level of dietary sphingolipids. However, no significant changes were observed in the concentration and proportion of the liver phospholipids at 0.5% supplementation, but significant elevation of liver phospholipids when supplemented at 2% level. Thus, it is suggested that sphingosine derived from the dietary sphingolipids can modify serum and liver lipid metabolism.