Nicotinamide Prevents Apolipoprotein B-Containing Lipoprotein Oxidation, Inflammation and Atherosclerosis in Apolipoprotein E-Deficient Mice.

The potential of nicotinamide (NAM) to prevent atherosclerosis has not yet been examined. This study investigated the effect of NAM supplementation on the development of atherosclerosis in a mouse model of the disease. The development of aortic atherosclerosis was significantly reduced (NAM low dose: 45%; NAM high dose: 55%) in NAM-treated, apolipoprotein (Apo)E-deficient mice challenged with a Western diet for 4 weeks. NAM administration significantly increased (1.8-fold) the plasma concentration of proatherogenic ApoB-containing lipoproteins in NAM high-dose (HD)-treated mice compared with untreated mice. However, isolated ApoB-containing lipoproteins from NAM HD mice were less prone to oxidation than those of untreated mice. This result was consistent with the decreased (1.5-fold) concentration of oxidized low-density lipoproteins in this group. Immunohistochemical staining of aortas from NAM-treated mice showed significantly increased levels of IL-10 (NAM low-dose (LD): 1.3-fold; NAM HD: 1.2-fold), concomitant with a significant decrease in the relative expression of TNFα (NAM LD: -44%; NAM HD: -57%). An improved anti-inflammatory pattern was reproduced in macrophages cultured in the presence of NAM. Thus, dietary NAM supplementation in ApoE-deficient mice prevented the development of atherosclerosis and improved protection against ApoB-containing lipoprotein oxidation and aortic inflammation.

Molecular Insights into the Mechanisms Underlying the Cholesterol- Lowering Effects of Phytosterols.

Dietary phytosterols, which comprise plant sterols and stanols, reduce plasma Low-Density Lipoprotein-Cholesterol (LDL-C) levels when given 2 g/day. Since this dose has not been reported to cause health-related side effects in long-term human studies, food products containing these plant compounds are used as potential therapeutic dietary options to reduce LDL-C and cardiovascular disease risk. Several mechanisms have been proposed to explain the cholesterol-lowering action of phytosterols. They may compete with dietary and biliary cholesterol for micellar solubilization in the intestinal lumen, impairing intestinal cholesterol absorption. Recent evidence indicates that phytosterols may also regulate other pathways. Impaired intestinal cholesterol absorption is usually associated with reduced cholesterol transport to the liver, which may reduce the incorporation of cholesterol into Very-Low- Density Lipoprotein (VLDL) particles, thereby lowering the rate of VLDL assembly and secretion. Impaired liver VLDL production may reduce the rate of LDL production. On the other hand, significant evidence supports a role for plant sterols in the Transintestinal Cholesterol Excretion (TICE) pathway, although the exact mechanisms by which they promote the flow of cholesterol from the blood to enterocytes and the intestinal lumen remains unknown. Dietary phytosterols may also alter the conversion of bile acids into secondary bile acids, and may lower the bile acid hydrophobic/hydrophilic ratio, thereby reducing intestinal cholesterol absorption. This article reviews the progress to date in research on the molecular mechanisms underlying the cholesterol-lowering effects of phytosterols.

A Functional Virgin Olive Oil Enriched with Olive Oil and Thyme Phenolic Compounds Improves the Expression of Cholesterol Efflux-Related Genes: A Randomized, Crossover, Controlled Trial.

The consumption of antioxidant-rich foods such as virgin olive oil (VOO) promotes high-density lipoprotein (HDL) anti-atherogenic capacities. Intake of functional VOOs (enriched with olive/thyme phenolic compounds (PCs)) also improves HDL functions, but the gene expression changes behind these benefits are not fully understood. Our aim was to determine whether these functional VOOs could enhance the expression of cholesterol efflux-related genes. In a randomized, double-blind, crossover, controlled trial, 22 hypercholesterolemic subjects ingested for three weeks 25 mL/day of: (1) a functional VOO enriched with olive oil PCs (500 mg/kg); (2) a functional VOO enriched with olive oil (250 mg/kg) and thyme PCs (250 mg/kg; FVOOT), and; (3) a natural VOO (olive oil PCs: 80 mg/kg, control intervention). We assessed whether these interventions improved the expression of cholesterol efflux-related genes in peripheral blood mononuclear cells by quantitative reverse-transcription polymerase chain reactions. The FVOOT intervention upregulated the expression of CYP27A1 (P = 0.041 and P = 0.053, versus baseline and the control intervention, respectively), CAV1 (P = 0.070, versus the control intervention), and LXRß, RXRα, and PPARß/δ (P = 0.005, P = 0.005, and P = 0.038, respectively, relative to the baseline). The consumption of a functional VOO enriched with olive oil and thyme PCs enhanced the expression of key cholesterol efflux regulators, such as CYP27A1 and nuclear receptor-related genes.

Vitamin B3 impairs reverse cholesterol transport in Apolipoprotein E-deficient mice.

INTRODUCTION: High Density Lipoproteins (HDL) are dysfunctional in hypercholesterolemia patients. The hypothesis was tested that nicotinamide (NAM) administration will influence HDL metabolism and reverse cholesterol transport from macrophages to the liver and feces in vivo (m-RCT) in a murine model of hypercholesterolemia. METHODS: Apolipoprotein E-deficient (KOE) mice were challenged with a high-fat diet for 4 weeks. The effect of different doses of NAM on cholesterol metabolism, and the ability of HDL to promote m-RCT was assessed. RESULTS: The administration of NAM to KOE mice produced an increase (∼1.5-fold; P<0.05) in the plasma levels of cholesterol, which was mainly accounted for by the non-HDL fraction. NAM produced a [3H]-cholesterol plasma accumulation (∼1.5-fold) in the m-RCT setting. As revealed by kinetic analysis, the latter was mainly explained by an impaired clearance of circulating non-HDL (∼0.8-fold). The relative content of [3H]-tracer was lowered in the livers (∼0.6-fold) and feces (>0.5-fold) of NAM-treated mice. This finding was accompanied by a significant (or trend close to significance) up-regulation of the relative gene expression of Abcg5 and Abcg8 in the liver (Abcg5: 2.9-fold; P<0.05; Abcg8: 2.4-fold; P=0.06) and small intestine (Abcg5: 2.1-fold; P=0.15; Abcg8: 1.9-fold; P<0.05) of high-dose, NAM-treated mice. CONCLUSION: The data from this study show that the administration of NAM to KOE mice impaired m-RCT in vivo. This finding was partly due to a defective hepatic clearance of plasma non-HDL.

Phytosterols inhibit the tumor growth and lipoprotein oxidizability induced by a high-fat diet in mice with inherited breast cancer.

Dietary phytosterol supplements are readily available to consumers since they effectively reduce plasma low-density lipoprotein cholesterol. Several studies on cell cultures and xenograft mouse models suggest that dietary phytosterols may also exert protective effects against common cancers. We examined the effects of a dietary phytosterol supplement on tumor onset and progression using the well-characterized mouse mammary tumor virus polyoma virus middle T antigen transgenic mouse model of inherited breast cancer. Both the development of mammary hyperplastic lesions (at age 4 weeks) and total tumor burden (at age 13 weeks) were reduced after dietary phytosterol supplementation in female mice fed a high-fat, high-cholesterol diet. A blind, detailed histopathologic examination of the mammary glands (at age 8 weeks) also revealed the presence of less-advanced lesions in phytosterol-fed mice. This protective effect was not observed when the mice were fed a low-fat, low-cholesterol diet. Phytosterol supplementation was effective in preventing lipoprotein oxidation in mice fed the high-fat diet, a property that may explain - at least in part - their anticancer effects since lipoprotein oxidation/inflammation has been shown to be critical for tumor growth. In summary, our study provides preclinical proof of the concept that dietary phytosterols could prevent the tumor growth associated with fat-rich diet consumption.

Dietary phytosterols modulate T-helper immune response but do not induce apparent anti-inflammatory effects in a mouse model of acute, aseptic inflammation.

Although most studies have focused on the cholesterol-lowering activity of phytosterols, other biological actions have been ascribed to these plant sterol compounds, one of which is a potential immune modulatory effect. To gain insight into this issue, we used a mouse model of acute, aseptic inflammation induced by a single subcutaneous turpentine injection. Hypercholesterolemic apolipoprotein E-deficient (apoE(-/-)) mice, fed with or without a 2% phytosterol supplement, were treated with turpentine or saline and euthanized 48 h later. No differences were observed in spleen lymphocyte subsets between phytosterol- and control-fed apoE(-/-) mice. However, cultured spleen lymphocytes of apoE(-/-) mice fed with phytosterols and treated with turpentine showed increased IL-2 and IFN-gamma secretion (T-helper type1, Th1 lymphocyte cytokines) compared with turpentine-treated, control-fed animals. In contrast, there was no change in Th2 cytokines IL-4 and IL-10. Phytosterols also inhibit intestinal cholesterol absorption in wild-type C57BL/6J mice but, in this case, without decreasing plasma cholesterol. Spleen lymphocytes of turpentine-treated C57BL/6J mice fed with phytosterols also showed increased IL-2 production, but IFN-gamma, IL-4 and IL-10 production was unchanged. The Th1/Th2 ratio was significantly increased both in phytosterol-fed apoE(-/-) and C57BL/6J mice. We conclude that phytosterols modulate the T-helper immune response in vivo, in part independently of their hypocholesterolemic effect in a setting of acute, aseptic inflammation. Further study of phytosterol effects on immune-based diseases characterized by an exacerbated Th2 response is thus of interest.

Phytosterol-mediated inhibition of intestinal cholesterol absorption is independent of ATP-binding cassette transporter A1.

An increased activity of ATP-binding cassette transporter (ABC) A1 has been proposed as a mechanism underlying the hypocholesterolaemic effect of phytosterols. In the present study, ABCA1-deficient mice (ABCA1-/- mice) were used to examine the involvement of the ABCA1 in the reduction of intestinal cholesterol absorption in response to a phytosterol-enriched diet. A decrease in intestinal cholesterol absorption of 39 and 35 % was observed after phytosterol treatment in ABCA1+/+ mice and in ABCA1-/- mice, respectively. No statistically significant changes in plasma lipoprotein profile or in intestinal ABCG5, ABCG8 and Niemann-Pick C1-Like 1 gene expression levels were found when phytosterol-treated ABCA1-/- mice and untreated ABCA1-/- mice were compared. We conclude that phytosterol inhibition of cholesterol absorption in mice is independent of ABCA1.