Donna F. Vine

Arterial retention of apolipoprotein B48- and B100- containing lipoproteins in atherogenesis

Purpose of review The ‘response to retention’ hypothesis of atherosclerosis suggests that the arterial deposition of cholesterol is directly proportional to the concentration of circulating plasma lipoproteins. However, there is increasing evidence to support the concept that specific lipoproteins may be preferentially retained within the arterial wall, possibly as a result of greater affinity for cell surface and extracellular matrices. Recent findings Recently, key studies have provided insight into mechanisms involved in the interaction of apolipoprotein B (apoB)-containing lipoproteins with extracellular matrices. In addition, novel methods and innovative experimental design has enabled us to differentiate between the delivery, retention and efflux of apoB48- and apoB100-containing lipoproteins. Other studies have demonstrated a relationship between extracellular matrix proteoglycan expression and the development of atherosclerosis in vivo. Discussion in the present review also extends to the mechanisms that are involved in the relative intimal retention of apoB48- and apoB100-containing lipoproteins in order to explain the atherogenicity of these macromolecules. Summary The perspective of this review is to highlight recent advances in the area of arterial lipoprotein retention and the physiological significance these processes may have in the aetiology of cardiovascular disease. Importantly, an understanding of the mechanisms responsible for the retention of apoB48/B100-containing lipoproteins will enable new strategies to be developed for the future management of cardiovascular disease.

Trans-11 Vaccenic Acid Dietary Supplementation Induces Hypolipidemic Effects in JCR:LA-cp Rats

Trans-11 vaccenic acid [VA; 18:1(n-9)] is a positional and geometric isomer of oleic acid and is the precursor to conjugated linoleic acid (CLA) in humans. Despite VA being the predominant trans monoene in ruminant-derived lipids, very little is known about its nutritional bioactivity, particularly in conditions of chronic metabolic disorders, including obesity, insulin resistance, and/or dyslipidemia. The aim of this study was to assess the potential of VA to improve dyslipidemia, insulin sensitivity, or inflammatory status in obese and insulin-resistant JCR:LA-cp rats. The obese rats and age-matched lean littermates were fed a control diet or a control diet supplemented with 1.5% (wt:wt) VA for a period of 3 wk. The incorporation of VA and subsequent conversion to CLA in triglyceride was measured in adipose tissue. Glucose and insulin metabolism were assessed via a conscious adapted meal tolerance test procedure. Plasma lipids as well as serum inflammatory cytokine concentrations were measured by commercially available assays. VA supplementation did not result in any observable adverse health effects in either lean or obese JCR:LA-cp rats. After 3 wk of feeding, body weight, food intake, and glucose/insulin metabolism did not differ between VA-supplemented and control groups. The incorporation of VA and CLA into adipose triglycerides in obese rats fed VA increased by 1.5-fold and 6.5-fold, respectively, compared with obese rats fed the control diet. The most striking effect was a 40% decrease (P < 0.05) in fasting triglyceride concentrations in VA-treated obese rats relative to obese controls. Serum Il-10 concentration was decreased by VA, regardless of genotype (P < 0.05). In conclusion, short-term dietary supplementation of 1.5% VA did not result in any detrimental metabolic effects in JCR:LA-cp rats. In contrast, dietary VA had substantial hypo-triglyceridemic effects, suggesting a new bioactivity of this fatty acid that is typically found in ruminant-derived food products.

Dietary oxysterols are incorporated in plasma triglyceride rich lipoproteins, increase their susceptibility to oxidation and increase aortic cholesterol concentration of rabbits

Early fatty streaks and advanced lesions are characterized by the deposition of cholesterol and cholesterol oxidation products (oxysterols). Oxysterols have been shown to be cytotoxic and pro-atherogenic compared to cholesterol and are found in cholesterol-rich processed foods. The consumption of dietary oxysterols may be significant in the onset and development of vascular disease. In order to study the short term effects of low levels of ingested dietary oxysterols on lipoprotein and aortic cholesterol and oxysterol levels, rabbits were fed either standard chow, chow supplemented with 1.0% oxidized cholesterol (containing 6% oxysterols), or 1.0% purified cholesterol (control). To determine the distribution and uptake of oxysterols after a 2-week dietary period, triglyceride-rich plasma lipoproteins, low density lipoproteins and aorta were analyzed by GC-MS. The concentration of 7beta-hydroxycholesterol was similar in all groups but the oxidized cholesterol-fed animals showed five times the concentration of 5alpha,6alpha-epoxycholesterol and double the level of 7-ketocholesterol in triglyceride-rich lipoproteins compared to the purified cholesterol-fed animals. The presence of 7-ketocholesterol in LDL was exclusive to animals fed the oxidized cholesterol diet. In addition, oxidation of triglyceride-rich lipoproteins was significantly greater in rabbits fed oxidized cholesterol compared to the pure cholesterol-fed animals. The oxidized cholesterol-fed animals also had a 64% increase in total aortic cholesterol, despite lower plasma cholesterol levels compared to the pure cholesterol control animals. Taken together these results suggest that dietary oxysterols may substantially increase the atherogenicity of lipoproteins.

Arterial Permeability and Efflux of Apolipoprotein B–Containing Lipoproteins Assessed by In Situ Perfusion and Three-Dimensional Quantitative Confocal Microscopy

Objectives—There is accumulating evidence that an increased risk of cardiovascular disease (CVD) is not simply caused by the degree of arterial exposure to plasma lipoproteins but, in addition, is determined by the affinity of the vasculature for different lipoprotein phenotypes. In this study we compare the delivery and efflux of 2 atherogenic lipoproteins to further understand the factors that regulate cholesterol accumulation in early atherogenesis. Methods and Results—Lipoproteins containing apolipoprotein (apo) B100 (a low-density lipoprotein [LDL]) and apoB48 (chylomicron remnants) were isolated and differentially conjugated with fluorophores and simultaneously perfused at equivalent concentrations in situ through rabbit carotid vessels. Perfusion systems were established to quantify and differentiate between lipoprotein arterial delivery and efflux. The total average rate of delivery for LDL particles (23 nm) compared with chylomicron remnants (50 nm) was 4427 particles/min−1 per &mgr;m3 and 452 particles/min−1 per &mgr;m3, respectively. In contrast, the average rate of efflux was 3195 particles/min−1 per &mgr;m3 and 163 particles/min−1 per &mgr;m3 for LDL and chylomicron remnants, respectively. Conclusions—Results indicate that although LDL particles have a higher rate of delivery, they efflux more readily from arterial tissue compared with the larger chylomicron remnants. Collectively, our findings highlight that lipoproteins permeate through arterial tissue differently and may be dependent on the phenotype and potential interactions with extracellular matrix components.

Absorption of dietary cholesterol oxidation products and incorporation into rat lymph chylomicrons

Cholesterol oxidation products (oxysterols) induce macrophage lipid loading and accumulate in early arterial fatty streaks. The origin of lesion oxysterols has not been elucidated. The absorption of oxysterols from the diet and transport to the arterial wall by postprandial lipoprotein remnants may be a significant source. This study aimed to investigated the extent of oxysterol absorption and the effect on chylomicron composition. Cholesterol was heat-treated, causing 30% oxidation; the major oxidation products were 7β-hydroxycholesterol, 7-ketocholesterol, 5α,6α-epoxycholesterol, and 5β,6β-epoxycholesterol. Conscious lymph-cannulated rats were given a bolus gastric infusion of 50 mg oxidized cholesterol or 50 mg purified cholesterol in a vehicle of triglyceride. In the rats given the oxidized cholesterol, 6% of the oxysterol load was absorbed and incorporated into lymph chylomicrons. Rats given pure cholesterol had no increase in oxysterols above baseline levels. The incorporation of oxysterols into lymph chylomicrons differed over time with 7β-hydroxycholesterol, having peak absorption at 3 h, followed by 7-ketocholesterol at 4 h and 5α,6α-epoxycholesterol at 5 h. The absorption of oxysterols in animals given the oxidized cholesterol gastric infusate was associated with lymph chylomicron compositional changes at 2–4 h. The oxidized cholesterol-treated group has a twofold increase in the cholesterol (890±84 μg vs. 440±83 μg at 3 h) and triglyceride content (19.76±3.4 μg vs. 8.49±3.8 μg at 3 h). This led to a doubling of chylomicron size over this postprandial period, with particles having a mean diameter of 294 nm in the oxidized cholesterol-treated animals, compared to 179 nm in the purified cholesterol group. In conclusion, dietary oxysterols appear to influence postprandial lipoprotein particle size and composition. These changes may have effects on the clearance of chylomicrons from plasma, arterial delivery of oxysterols, and possible deposition in arterial lesions.

Atopy, eczema and breast milk fatty acids in a high-risk cohort of children followed from birth to 5 yr

Background: The incidence of atopic diseases such as eczema is increasing in westernized societies. The suggestion that there is a ‘protective’ association between the unique fatty acid composition of breast milk, particularly the omega‐3 (n‐3) and omega‐6 (n‐6) essential polyunsaturated fatty acid content, and the development of atopic disease in children was investigated in a cohort study of 263 infants born into families with a history of allergy (one or both parents had asthma, hayfever, eczema). The objectives of this study were to determine the lipid profile [specifically in relation to long‐chain polyunsaturated fatty acid (LC‐PUFA) composition] in maternal breast milk samples collected at 6 wk and at 6 months following birth, and to investigate the potential role of these fatty acids in modulating the phenotype of children at high genetic risk of developing atopic disease. Method: Breast milk samples were available from 91 atopic mothers at their childs ages of 6 wk and 6 months. These samples were analysed for the fatty acid spectrum. Analysis of variance was used to detect differences between groups of outcomes (no atopy or eczema, non‐atopic eczema, atopy, atopic eczema) at ages 6 months and 5 yr, and a multiple comparisons procedure was conducted to isolate the parameters producing the different results (F‐test, LSD test). For the exposure variables, n‐3 and n‐6 fatty acids are expressed as weight percentage and as a ratio (at both time‐points). Results: The fatty acid profiles of maternal breast milk at 6 wk and 6 months were similar. An increased ratio of n‐6: n‐3 fatty acids in both 6 wk and 6 month milk samples was associated with non‐atopic eczema (p < 0.005) but not atopy alone or atopic eczema. Conclusion: We found milk fatty acids were a significant modulator of non‐atopic eczema but not atopy or atopic eczema in infants at 6 months. In mothers with a history of asthma, hayfever or eczema, their 6‐month‐old infants were more likely to develop non‐atopic eczema if their milk had a higher ratio of n‐6: n‐3 LC‐PUFA.

Animal models of polycystic ovary syndrome: a focused review of rodent models in relationship to clinical phenotypes and cardiometabolic risk

OBJECTIVE To review rodent animal models of polycystic ovary syndrome (PCOS), with a focus on those associated with the metabolic syndrome and cardiovascular disease risk factors. DESIGN Review. ANIMAL(S) Rodent models of PCOS. INTERVENTION(S) Description and comparison of animal models. MAIN OUTCOME MEASURE(S) Comparison of animal models to clinical phenotypes of PCOS. RESULT(S) Animals used to study PCOS include rodents, mice, rhesus monkeys, and ewes. Major methods to induce PCOS in these models include subcutaneous injection or implantation of androgens, estrogens, antiprogesterone, letrozole, prenatal exposure to excess androgens, and exposure to constant light. In addition, transgenic mice models and spontaneous PCOS-like rodent models have also been developed. CONCLUSION(S) Rodents are the most economical and widely used animals to study PCOS and ovarian dysfunction. The model chosen to study the development of PCOS and other metabolic parameters remains dependent on the specific etiologic hypotheses being investigated. Rodent models have been shown to demonstrate changes in insulin metabolism, with or without induction of hyperandrogenemia, and limited studies have investigated cardiometabolic risk factors for type 2 diabetes and cardiovascular disease. Given the clinical heterogeneity of PCOS, the utilization of different animal models may be the best approach to further our understanding of the pathophysiologic mechanisms associated with the early etiology of PCOS and cardiometabolic risk.

Trans-11 Vaccenic Acid Reduces Hepatic Lipogenesis and Chylomicron Secretion in JCR:LA-cp Rats

Trans-11 vaccenic acid (VA) is the predominant trans isomer in ruminant fat and a major precursor to the endogenous synthesis of cis9,trans11-conjugated linoleic acid in humans and animals. We have previously shown that 3-wk VA supplementation has a triglyceride (TG)-lowering effect in a rat model of dyslipidemia, obesity, and metabolic syndrome (JCR:LA-cp rats). The objective of this study was to assess the chronic effect (16 wk) of VA on lipid homeostasis in both the liver and intestine in obese JCR:LA-cp rats. Plasma TG (P < 0.001), total cholesterol (P < 0.001), LDL cholesterol (P < 0.01), and nonesterified fatty acid concentrations, as well as the serum haptoglobin concentration, were all lower in obese rats fed the VA diet compared with obese controls (P < 0.05). In addition, there was a decrease in the postprandial plasma apolipoprotein (apo)B48 area under the curve (P < 0.05) for VA-treated obese rats compared with obese controls. The hepatic TG concentration and the relative abundance of fatty acid synthase and acetyl-CoA carboxylase proteins were all lower (P < 0.05) in the VA-treated group compared with obese controls. Following acute gastrointestinal infusion of a VA-triolein emulsion in obese rats that had been fed the control diet for 3 wk, the TG concentration was reduced by 40% (P < 0.05) and the number of chylomicron (CM) particles (apoB48) in nascent mesenteric lymph was reduced by 30% (P < 0.01) relative to rats infused with a triolein emulsion alone. In conclusion, chronic VA supplementation significantly improved dyslipidemia in both the food-deprived and postprandial state in JCR:LA-cp rats. The appreciable hypolipidemic benefits of VA may be attributed to a reduction in both intestinal CM and hepatic de novo lipogenesis pathways.

Dietary supplementation of n-3 PUFA reduces weight gain and improves postprandial lipaemia and the associated inflammatory response in the obese JCR:LA-cp rat

Background: Postprandial dyslipidaemia occurs in obesity and insulin resistance (IR), and is associated with an increased risk of developing cardiovascular disease. We have recently established that the JCR:LA‐cp rodent model develops postprandial dyslipidaemia concomitant with complications of the metabolic syndrome. Dietary n‐3 polyunsaturated fatty acids (n‐3 PUFAs) are proposed to modulate plasma lipids, serum hormone levels, lipoprotein metabolism and the inflammatory state; however, results remain inconsistent during conditions of IR.

Chronic dietary n-3 PUFA intervention improves dyslipidaemia and subsequent cardiovascular complications in the JCR:LA- cp rat model of the metabolic syndrome.

There is increasing interest in the potential chronic beneficial effects of dietary n-3 PUFA on the metabolic syndrome (MetS) and associated cardiovascular complications. We have recently established that increased dietary n-3 PUFA has a profound acute benefit on fasting lipids and the postprandial pro-inflammatory response in the JCR:LA-cp rat, a model of the MetS. However, it is unclear to what extent chronic dietary n-3 PUFA intervention can modulate the progression of end-stage metabolic and vascular complications. The present study aimed to determine the chronic effects of dietary n-3 PUFA supplementation on fasting and non-fasting dyslipidaemia, insulin resistance and vascular complications in the JCR:LA-cp rodent model. JCR:LA-cp rats were fed an isoenergetic lipid-balanced diet supplemented with 5 % n-3 PUFA (w/w) of the total fat (fish oil-derived EPA/DHA) for 16 weeks. Fasting and non-fasting (postprandial) plasma lipid profile was assessed. Hepatic and adipose tissue was probed for the expression of lipogenic proteins (acyl-CoA carboxylase (ACC), fatty acid synthase (FAS) and sterol regulatory element-binding protein-1 (SREBP-1)), while the activity of Jun N-terminal kinase (JNK) was assessed via Western blot to target phosphorylated JNK protein in primary enterocytes. The frequency of myocardial lesions was assessed by haematoxylin and eosin staining. Increased dietary n-3 PUFA improved both the fasting and postprandial lipid profiles (TAG, cholesterol and apoB48) in the JCR:LA-cp rat, potentially via the down-regulation of the hepatic or adipose tissue expression of lipogenic enzymes (ACC, FAS and SREBP-1). Rats fed the 5 % n-3 PUFA diet had lower (58·2 %; P < 0·01) enterocytic phosphorylated JNK protein and secreted less cholesterol (30 %; P < 0·05) into mesenteric lymph compared with the control. The chronic metabolic benefits of dietary n-3 PUFA may underlie the potential to reduce vascular complications during the MetS, including the observed reduction in the frequency (approximately 80 %) of late-stage 3 myocardial lesions.