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Summary Background & aims Medium-chain triglycerides (TG) (MCT) and fish oil (FO) TG are incorporated as the core TG component into intravenous (IV) lipid emulsions for infusion in parenteral nutrition. Bolus injections of IV emulsions, on the other hand, have emerged as a novel therapeutic approach to treat various acute disorders. However, intravascular metabolism and organ delivery of acute IV injection of emulsions containing both MCT and FO are not fully defined, nor have they been characterized across common experimental animal models. We characterized and compared blood clearance kinetics and organ distribution of bolus injections of MCT/FO emulsions among different animal species. We also examined whether sex differences or feeding status can affect catabolic properties of MCT/FO lipid emulsions. Design Blood clearance rates of lipid emulsions with specific TG composition were compared in rats IV injected with [3H]cholesteryl hexadecyl ether labeled pure n-6 long-chain (LCT) and n-3 FO TG lipid emulsions, or emulsions containing MCT and FO at different ratios (wt/wt), which include 8:2 (80% MCT: 20% FO), 5:4:1 (50% MCT: 40% LCT: 10% FO) and SMOF (30% LCT: 30% MCT: 25% olive oil: 10% FO). Dose-response effects (0.016 mg–1.6 mg TG/g body weight) of the MCT/FO 8:2 emulsions on blood clearance properties and organ delivery were determined in both mice and rats. Blood clearance kinetics and organ uptake of MCT/FO 8:2 emulsions were compared between male and female rats and between fed and fasted rats. Changes in plasma lipid profiles after acute injections of MCT/FO 8:2 lipid emulsion at different doses (0.043, 0.133, and 0.4 mg TG/g body weight) were characterized in non-human primates (Cynomolgus monkeys). Results MCT/FO 8:2 emulsion was cleared faster in rats when compared with other emulsions with different TG contents. Mice had faster blood clearance and higher fractional catabolic rates (FCR) when compared with the rats injected with MCT/FO 8:2 emulsions regardless of the injected doses. Mice and rats had similar plasma TG and free fatty acid (FFA) levels after low- or high-dose injections of the MCT/FO emulsion. Tissue distribution of the MCT/FO 8:2 lipid emulsion are comparable between mice and rats, where liver had the highest uptake per recovered dose among all organs (>60%). Feeding status and sex differences did not alter the blood clearance rate of the MCT/FO 8:2 emulsion in rats. In a nonhuman primate model, dose-response increases in plasma TG and FFA were observed after IV injection of MCT/FO 8:2 emulsions within the 1st 10 min. Conclusion A lipid emulsion containing both MCT and FO TG is cleared rapidly in blood and readily available for organ uptake in rodent and primate animal models. Characterization of the blood clearance properties of the MCT/FO 8:2 emulsion administered in various animal models may provide further insight into the safety and efficacy profiles for future therapeutic use of bolus injections of MCT/FO emulsions in humans.

Objective— Tissue macrophages induce and perpetuate proinflammatory responses, thereby promoting metabolic and cardiovascular disease. Lipoprotein lipase (LpL), the rate-limiting enzyme in blood triglyceride catabolism, is expressed by macrophages in atherosclerotic plaques. We questioned whether LpL, which is also expressed in the bone marrow (BM), affects circulating white blood cells and BM proliferation and modulates macrophage retention within the artery. Approach and Results— We characterized blood and tissue leukocytes and inflammatory molecules in transgenic LpL knockout mice rescued from lethal hypertriglyceridemia within 18 hours of life by muscle-specific LpL expression (MCKL0 mice). LpL-deficient mice had ≈40% reduction in blood white blood cell, neutrophils, and total and inflammatory monocytes (Ly6C/G hi ). LpL deficiency also significantly decreased expression of BM macrophage-associated markers (F4/80 and TNF-α [tumor necrosis factor α]), master transcription factors (PU.1 and C/EBPα), and colony-stimulating factors (CSFs) and their receptors, which are required for monocyte and monocyte precursor proliferation and differentiation. As a result, differentiation of macrophages from BM-derived monocyte progenitors and monocytes was decreased in MCKL0 mice. Furthermore, although LpL deficiency was associated with reduced BM uptake and accumulation of triglyceride-rich particles and macrophage CSF–macrophage CSF receptor binding, triglyceride lipolysis products (eg, linoleic acid) stimulated expression of macrophage CSF and macrophage CSF receptor in BM-derived macrophage precursor cells. Arterial macrophage numbers decreased after heparin-mediated LpL cell dissociation and by genetic knockout of arterial LpL. Reconstitution of LpL-expressing BM replenished aortic macrophage density. Conclusions— LpL regulates peripheral leukocyte levels and affects BM monocyte progenitor differentiation and aortic macrophage accumulation.

Adipose fat storage is thought to require uptake of circulating triglyceride (TG)-derived fatty acids via lipoprotein lipase (LpL). To determine how LpL affects the biology of adipose tissue, we created adipose-specific LpL knock-out (ATLO) mice, and we compared them with whole body LpL knock-out mice rescued with muscle LpL expression (MCK/L0) and wild type (WT) mice. ATLO LpL mRNA and activity were reduced, respectively, 75 and 70% in gonadal adipose tissue (GAT), 90 and 80% in subcutaneous tissue, and 84 and 85% in brown adipose tissue (BAT). ATLO mice had increased plasma TG levels associated with reduced chylomicron TG uptake into BAT and lung. ATLO BAT, but not GAT, had altered TG composition. GAT from MCK/L0 was smaller and contained less polyunsaturated fatty acids in TG, although GAT from ATLO was normal unless LpL was overexpressed in muscle. High fat diet feeding led to less adipose in MCK/L0 mice but TG acyl composition in subcutaneous tissue and BAT reverted to that of WT. Therefore, adipocyte LpL in BAT modulates plasma lipoprotein clearance, and the greater metabolic activity of this depot makes its lipid composition more dependent on LpL-mediated uptake. Loss of adipose LpL reduces fat accumulation only if accompanied by greater LpL activity in muscle. These data support the role of LpL as the "gatekeeper" for tissue lipid distribution.

Objective— Macrophage endothelial lipase (EL) is associated with increased atherosclerosis and inflammation. Because of their anti-inflammatory properties we hypothesized that n-3 fatty acids, in contrast to saturated fatty acids, would lower macrophages and arterial EL and inflammatory markers. Methods and Results— Murine J774 and peritoneal macrophages were incubated with eicosapentaenoic acid or palmitic acid in the presence or absence of lipopolysaccaride (LPS). LPS increased EL mRNA and protein. Palmitic acid alone or with LPS dose-dependently increased EL mRNA and protein. In contrast, eicosapentaenoic acid dose-dependently abrogated effects of LPS or palmitic acid on increasing EL expression. EL expression closely linked to peroxisome proliferator activated receptor (PPAR)γ expression. Eicosapentaenoic acid blocked rosiglitazone (a PPARγ agonist)-mediated EL activation and GW9662 (a PPARγ antagonist)-blocked palmitic acid-mediated EL stimulation. Eicosapentaenoic acid alone or with LPS blunted LPS-mediated stimulation of macrophage proinflammatory interleukin-6, interleukin-12p40, and toll-like receptor-4 mRNA and increased anti-inflammatory interleukin-10 and mannose receptor mRNA. In vivo studies in low density lipoprotein receptor knockout mice showed that high saturated fat rich diets, but not n-3 diets, increased arterial EL, PPARγ, and proinflammatory cytokine mRNA. Conclusion— n-3 fatty acids, in contrast to saturated fatty acids, decrease EL in parallel with modulating pro- and anti-inflammatory markers, and these effects on EL link to PPARγ.

Objective— To determine whether n-3 fatty acids (n-3) influence arterial cholesterol delivery and lipoprotein lipase (LpL) levels in insulin-resistant mice. Methods and Results— Insulin resistance contributes to risk of cardiovascular disease. It was previously reported that saturated fat (SAT) diets increased, but n-3 diets decreased, arterial low-density lipoprotein (LDL) cholesterol deposition from LDL total and selective uptake; this was associated with increased or decreased arterial LpL, respectively. Insulin receptor transgenic knockout mice (L1) were fed a chow, SAT, or n-3 diet for 12 weeks. Double-fluorescent boron dipyrromethene (BODIPY)–cholesteryl ester (CE) and Alexa dye-labeled human LDL were injected to separately trace LDL-CE and LDL–apolipoprotein B whole particle uptake. In contrast to SAT, n-3 diets markedly reduced all plasma lipids, ameliorating progression of insulin resistance. As opposed to SAT, n-3 reduced arterial LDL uptake, CE deposition, and selective uptake. Disparate patterns of CE deposition between diets were comparable with arterial LpL distribution; SAT induced high LpL levels throughout aortic media; LpL was limited only to intima in n-3–fed mice. Conclusion— n-3 diets diminish arterial LDL-cholesterol deposition in mice with insulin resistance, and this is associated with changes in arterial LpL levels and distribution.

Objectives— We previously reported that saturated fat (SAT)-enriched diets increase arterial cholesteryl ester (CE) deposition, especially from LDL-selective uptake (SU), and this was associated with increased arterial lipoprotein lipase (LpL). We now question how n-3 fatty acid rich diets influence arterial cholesterol delivery and arterial LpL levels. Methods and Results— C57BL/6 mice were fed chow or eucaloric high-fat diets enriched in SAT or fish oil (n-3) for 12 weeks, and then injected with double radiolabeled or fluorescent-labeled human LDL to separately trace LDL-CE and LDL-apoB uptake. SAT and n-3 diets increased plasma cholesterol levels similarly; n-3 diets lowered plasma triglyceride concentrations. SAT increased arterial LDL-SU with significantly higher CE infiltration into aortic media. In contrast, n-3 markedly reduced total LDL uptake and CE deposition and abolished SU with LDL localized only in aortic intima. Disparate patterns of CE deposition between diets were consistent with distribution of arterial LpL—SAT diets induced higher LpL levels throughout the aorta; n-3 diets decreased LpL levels and limited LpL expression to the aortic intima. Conclusions— n-3 rich diets decrease arterial total LDL delivery and abrogate LDL-SU in parallel with changing arterial wall LpL expression and distribution.

Objective Effects of progressive substitution of dietary n −3 fatty acids (FA) for saturated FA (SAT) on modulating risk factors for atherosclerosis have not been fully defined. Our previous reports demonstrate that SAT increased, but n −3 FA decreased, arterial lipoprotein lipase (LpL) levels and arterial LDL-cholesterol deposition early in atherogenesis. We now questioned whether incremental increases in dietary n −3 FA can counteract SAT-induced pro-atherogenic effects in atherosclerosis-prone LDL-receptor knockout (LDLR−/−) mice and have identified contributing mechanisms. Methods and results Mice were fed chow or high-fat diets enriched in SAT, n −3, or a combination of both SAT and n −3 in ratios of 3:1 (S: n −3 3:1) or 1:1 (S: n −3 1:1). Each diet resulted in the expected changes in fatty acid composition in blood and aorta for each feeding group. SAT-fed mice became hyperlipidemic. By contrast, n −3 inclusion decreased plasma lipid levels, especially cholesterol. Arterial LpL and macrophage levels were increased over 2-fold in SAT-fed mice but these were decreased with incremental replacement with n −3 FA. n −3 FA partial inclusion markedly decreased expression of pro-inflammatory markers (CD68, IL-6, and VCAM-1) in aorta. SAT diets accelerated advanced atherosclerotic lesion development, whereas all n −3 FA-containing diets markedly slowed atherosclerotic progression. Conclusion Mechanisms whereby dietary n −3 FA may improve adverse cardiovascular effects of high-SAT, high-fat diets include improving plasma lipid profiles, increasing amounts of n −3 FA in plasma and the arterial wall. Even low levels of replacement of SAT by n −3 FA effectively reduce arterial lipid deposition by decreasing aortic LpL, macrophages and pro-inflammatory markers.

Background Lipoprotein lipase (LPL) hydrolyzes triglycerides in plasma lipoproteins and enables uptake of lipolysis products for energy production or storage in tissues. Our aim was to study the localization of LPL and its endothelial anchoring protein glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 (GPIHBP1) in mouse pancreas, and effects of diet and leptin deficiency on their expression patterns. For this, immunofluorescence microscopy was used on pancreatic tissue from C57BL/6 mouse embryos (E18), adult mice on normal or high-fat diet, and adult ob/ob-mice treated or not with leptin. The distribution of LPL and GPIHBP1 was compared to insulin, glucagon and CD31. Heparin injections were used to discriminate between intracellular and extracellular LPL. Results In the exocrine pancreas LPL was found in capillaries, and was mostly co-localized with GPIHBP1. LPL was releasable by heparin, indicating localization on cell surfaces. Within the islets, most of the LPL was associated with beta cells and could not be released by heparin, indicating that the enzyme remained mostly within cells. Staining for LPL was found also in the glucagon-producing alpha cells, both in embryos (E18) and in adult mice. Only small amounts of LPL were found together with GPIHBP1 within the capillaries of islets. Neither a high fat diet nor fasting/re-feeding markedly altered the distribution pattern of LPL or GPIHBP1 in mouse pancreas. Islets from ob/ob mice appeared completely deficient of LPL in the beta cells, while LPL-staining was normal in alpha cells and in the exocrine pancreas. Leptin treatment of ob/ob mice for 12 days reversed this pattern, so that most of the islets expressed LPL in beta cells. Conclusions We conclude that both LPL and GPIHBP1 are present in mouse pancreas, and that LPL expression in beta cells is dependent on leptin.