Rosemary L. Walzem

Lipoprotein clearance mechanisms in LDL receptor-deficient "Apo-B48-only" and "Apo-B100-only" mice.

The role of the low density lipoprotein receptor (LDLR) in the clearance of apo-B48-containing lipoproteins and the role of the LDLR-related protein (LRP) in the removal of apo-B100-containing lipoproteins have not been clearly defined. To address these issues, we characterized LDLR-deficient mice homozygous for an apo-B48-only allele, an apo-B100-only allele, or a wild-type apo-B allele (Ldlr-/- Apob48/48, Ldlr-/-Apob100/100, and Ldlr-/-Apob+/+, respectively). The plasma apo-B48 and LDL cholesterol levels were higher in Ldlr-/-Apob48/48 mice than in Apob48/48 mice, indicating that the LDL receptor plays a significant role in the removal of apo-B48-containing lipoproteins. To examine the role of the LRP in the clearance of apo-B100-containing lipoproteins, we blocked hepatic LRP function in Ldlr-/-Apob100/100 mice by adenoviral-mediated expression of the receptor-associated protein (RAP). RAP expression did not change apo-B100 levels in Ldlr-/-Apob100/100 mice. In contrast, RAP expression caused a striking increase in plasma apo-B48 levels in Apob48/48 and Ldlr-/-Apob48/48 mice. These data imply that LRP is important for the clearance of apo-B48-containing lipoproteins but plays no significant role in the clearance of apo-B100-containing lipoproteins.

Incorporation of therapeutically modified bacteria into gut microbiota inhibits obesity

Metabolic disorders, including obesity, diabetes, and cardiovascular disease, are widespread in Westernized nations. Gut microbiota composition is a contributing factor to the susceptibility of an individual to the development of these disorders; therefore, altering a persons microbiota may ameliorate disease. One potential microbiome-altering strategy is the incorporation of modified bacteria that express therapeutic factors into the gut microbiota. For example, N-acylphosphatidylethanolamines (NAPEs) are precursors to the N-acylethanolamide (NAE) family of lipids, which are synthesized in the small intestine in response to feeding and reduce food intake and obesity. Here, we demonstrated that administration of engineered NAPE-expressing E. coli Nissle 1917 bacteria in drinking water for 8 weeks reduced the levels of obesity in mice fed a high-fat diet. Mice that received modified bacteria had dramatically lower food intake, adiposity, insulin resistance, and hepatosteatosis compared with mice receiving standard water or control bacteria. The protective effects conferred by NAPE-expressing bacteria persisted for at least 4 weeks after their removal from the drinking water. Moreover, administration of NAPE-expressing bacteria to TallyHo mice, a polygenic mouse model of obesity, inhibited weight gain. Our results demonstrate that incorporation of appropriately modified bacteria into the gut microbiota has potential as an effective strategy to inhibit the development of metabolic disorders.

Effect of dietary catechin and vitamin E on aortic fatty streak accumulation in hypercholesterolemic hamsters

Male golden Syrian hamsters were fed for 16 weeks on a hypercholesterolemic diet containing, per kg, 150 g of lipids (90 g butterfat, 35 g vitamin E-stripped corn oil and 25 g fish oil), 2 g cholesterol and either 3 IU vitamin E (3 IU E), 3 IU vitamin E and 200 mg catechin hydrate (3 IU E-200 Cat) or 30 IU vitamin E (30 IU E). More fatty streaks, measured by Oil Red O staining, were deposited in aortas of hamsters fed 3 IU E than in those fed either 3 IU E-200 Cat or 30 IU E. Lipid staining increased with plasma low-density lipoprotein cholesterol (LDL-C) in all animals. At the same concentration of LDL-C, animals fed either 3 IU E-200 Cat or 30 IU E developed less fatty streaks than those fed 3 IU E. Plasma LDL-C and total cholesterol were highest in hamsters fed 3 IU E and LDL-C and total cholesterol in animals fed 3 IU-200 Cat were not different from those fed either 3 IU E or 30 IU E. This study showed the importance of circulating plasma LDL-C on atherogenesis and the inhibitory effect on this process of both dietary vitamin E and catechin.

Effect of dietary fats and barley fiber on total cholesterol and lipoprotein cholesterol distribution in plasma of hamsters

Abstract Dietary saturated fatty acids and cholesterol elevate blood lipids, promote hypercholesterolemia and lead to elevation of circulating very low density (VLDL) and low density lipoproteins (LDL). Dietary fiber is suggested to ameliorate hypercholesterolemia. This study was undertaken to determine if dietary fiber would alter the quantity and distribution of cholesterol among plasma lipoproteins in the well-described model of dietary fat-induced hypercholesterolemia, the golden Syrian hamster. Hamsters were fed a basal high fat diet with 2.5% safflower oil and 10% butterfat to which had been added either 2.5% olive oil or 2.5% fish oil. Fiber was provided as cellulose or beta-glucan-enriched barley fiber at 10% of the diet. In hamsters fed 10% butterfat, 2.5% olive oil and cellulose, plasma cholesterol content was 237 mg/100 mL, with 65% of the total plasma cholesterol distributed in high density lipoproteins (HDL) and 35% in LDL plus VLDL. In hamsters fed 10% butterfat and 2.5% fish oil and cellulose, total cholesterol was 297 mg/100 mL, and 32% of the cholesterol was associated with HDL and 68% with LDL plus VLDL. These data indicated a significant redistribution of cholesterol from the HDL to the LDL and VLDL in fish oil fed animals. Substitution of barley fiber for cellulose in diets tended to decrease plasma cholesterol, however, it did not significantly affect the distribution of cholesterol among the lipoprotein classes. Serum triglycerides were higher in plasma of hamsters fed fish oil, and fiber did not alter either total triglycerides or distribution of triglycerides among lipoprotein classes. This study suggested that cholesterol distribution in plasma of hamsters fed cholesterolemic diets is more responsive to dietary fat than fiber and is due to mechanisms additional to hepatic LDL-receptor binding activity.

Cationic Lipid Enhances In Vitro Receptor-Mediated Transfection

The efficiency of cell-specific transfection by receptor-mediated uptake is improved by the use of cationic lipids. Asialoglycoprotein (AP) was conjugated to poly-L-lysine (PL) and complexed with the plasmid pCMVL that contains a luciferase reporter gene. The asialoglycoprotein-poly-L-lysine:pCMVL (AP-PL:pCMVL) complexes then were mixed with the cationic lipid dioctadecylamidoglycylspermine (DOGS). This complex was taken up by the hepatocyte-like cell line, Hep G2, via the asialoglycoprotein receptor. The expression of luciferase in cells transfected with the DOGS/AP-PL: pCMVL complexes were significantly increased compared with AP-PL:pCMVL complexes without DOGS. The ratio of AP-PL to DOGS is an important determinant for both transfection efficiency and for maintaining receptor specificity. Therefore, cationic lipids significantly increased the efficiency of asialoglycoprotein receptor mediated transfection in the hepatoblastoma cell line, Hep G2. The use of cationic lipids with receptor-mediated gene delivery systems could potentially increase transfection efficiency yet maintain cell-target specificity.

Effects of dietary fat restriction on particle size of plasma lipoproteins in postmenopausal women

Hypertriglyceridemia is an independent risk factor for coronary artery disease (CAD) and is also commonly associated with other coronary risk factors, ie, small, dense low-density lipoprotein (LDL) particles and low plasma levels of high-density lipoprotein cholesterol (HDL-C). Dietary fat restriction is recommended for the prevention of nutrition-related cancers. Low-fat, high-carbohydrate intake can increase plasma triglyceride (TG) and decrease HDL-C. In general, plasma TG levels are inversely related to the particle size of LDL. We investigated the effects of dietary fat restriction on the concentration and particle size of plasma lipoproteins in 14 healthy postmenopausal women (aged 61 +/- 11 years). During a 4-month period of eucaloric controlled feeding, dietary fat was reduced stepwise from a habitual intake of 33% +/- 8% to 23% and then to 14% of daily energy. Changes in the plasma lipid level and particle size of very-low-density lipoprotein (VLDL), LDL, and HDL were determined at the end of each dietary phase. Increasing carbohydrate intake without weight loss was associated with an increase in plasma TG (1.86 +/- 0.30 v 2.47 +/- 0.37 mmol/L) and decreases in total cholesterol (5.82 +/- 0.25 v 5.40 +/- 0.21 mmol/L), LDL-C (3.07 +/- 0.18 v 2.61 +/- 0.21 mmol/L), HDL-C (1.42 +/- 0.1 v 1.24 +/- 0.1 mmol/L), and apolipoprotein (apo) A1 (5.14 +/- 0.25 v 4.61 +/- 0.36 mmol/L), whereas plasma apo B did not change. The particle size of VLDL increased (42.7 +/- 1.4 v 47.0 +/- 0.9 nm). However, there was no change in either LDL (25.1 +/- 0.2 v 25.3 +/- 0.2 nm) or HDL particle size. Although at each level of dietary fat intake LDL particle size correlated inversely with plasma TG and apo B, there was no relationship between the increase in plasma TG and LDL particle size. These results show that hypertriglyceridemia caused by a eucaloric high-carbohydrate intake is not associated with a decrease in LDL particle size. Therefore, carbohydrate-induced hypertriglyceridemia may not have the same atherogenic potential as genetic hypertriglyceridemias.

Plasma lipoprotein changes in hens (Gallus domesticus) during an induced molt

Blood plasma lipoproteins were studied during food and light deprivation or prolactin injection-induced involution of ovarian follicles (molt) of laying hens. Egg laying stopped 3 days after initiation of either treatment. Food and light-deprived hens lost 29% of initial body weight during the 10-day experiment (P < 0.05), whereas prolactin-treated hens lost 9% of body weight. Yolk-directed very low density lipoprotein (VLDLy) concentration in plasma decreased in both groups, but declined more rapidly in food and light-deprived hens. Very low density lipoprotein triacylglycerol decreased 40% in food and light-deprived hens by day 2 compared with a 13% decrease in the prolactin-treated hens. By day 5, a lipoprotein particle 21-22 nm in diameter appeared in the d = 1.019-1.046 g/ml density fraction of plasma in both groups. A similar lipoprotein particle, termed HDLR, developed in overfed hens with involuting ovarian follicles. In conclusion, hens undergoing ovarian regression due to food and light deprivation, prolactin treatment or overfeeding display marked decreases in plasma yolk-directed very low density lipoproteins and the appearance of HDLR. Other lipoprotein populations varied depending on whether the hens continued to feed or not.

Dietary vitamin e in an atherogenic hamster model

Regular consumption of fruits, vegetables and cereals moderates development of coronary heart disease and atherosclerosis in humans, possibly as a result of antioxidants present in these foods. The aim of this study was to develop a hamster model sufficiently sensitive to test the effects of nutritional rather than pharmacological amounts of food components on the development of atherosclerosis. The effect of vitamin E on aortic lipid deposition was investigated in hamsters fed a hypercholesterolemic diet containing per kilogram 2 g cholesterol, 90 g butterfat, 35 g vitamin E-stripped corn oil, 25 g fish oil and either the minimum requirement of 3 international units (IU) vitamin E or 30 IU. After 30 weeks, lipoprotein cholesterol fractions did not differ between groups, and the 6:1 LDL-cholesterol : HDL-cholesterol ratio was atherogenic. Early atherosclerosis was measured by lipid staining of aortic arch sections with oil red O and quantified by a photomicroscopy color-scanning technique. The area of lipid deposits in the 30 IU vitamin E group (7.9 ± 1.3%, mean ± SEM) was 58% less than in the 3 IU vitamin E group (18.7 ± 4.4%, p < 0.03). Hamsters fed a mixture of saturated and n-6 and n-3 polyunsaturated fatty acids plus cholesterol became hypercholesterolemic and were sensitive to vitamin E with respect to development of atherosclerosis. This model provides a tool to test atheroprotective effects of individual food components in vivo.

Effects of orchidectomy and hormone replacement on rat hepatic hexose monophosphate pathway enzymes

Abstract This study was designed to determine if the attenuated starvation-refeed (SRF) over shoot response of hepatic G6PDH and 6PGDH observed in adult female rats is due to the presence of high levels of estrogen or lower levels of testosterone in the female. Male rats were castrated as weanlings, then allowed to reach adulthood before initiation of the remainder of the study. Ten days prior to the dietary study, when the rats were 9 weeks old, they began to receive daily injections of one of the following preparations: carrier only, 17- β -estradiol or testosterone propionate. Next, the rats were starved for 2 days and refed either a nonpurified diet or a purified 65% carbohydrate diet (sucrose, fructose, glucose or cornstarch) for 3 days. Castration suppressed the magnitude of the SRF overshoot response by 40% compared to that observed in intact males. Testosterone injections did not restore the SRF response. In fact, the enzyme activities of testosterone- injected, castrated rats were indistinguishable from those of castrated, carrier-injected controls. Estrogen injections doubled basal G6PDH and 6PGDH activities, but decreased the SRF overshoot response by 60% compared to castrated carrier injected rats. These results suggest that estrogen promotes higher basal enzyme activities and suppresses the magnitude of the SRF overshoot response in adult female rats.