Abstracts / Atherosclerosis Supplements 9 (2008) 83–102
with GLP-2 treatment. PKA inhibition completely abrogated GLP-2-stimulated chylomicron secretion. Closer inspection with pulse-chase experiments on primary enterocytes indicates a fundamental requirement for the PKA pathway in chylomicron secretion. Conclusion: GLP-2 enhanced apoB48-containing lipoprotein secretion possibly through enhanced lipid uptake in a pathway that appears to be CD36-mediated and PKAdependent. We postulate that GLP-2 is a critical regulator of intestinal lipid absorption and the assembly and secretion of TRLs from the intestinal enterocytes. doi:10.1016/j.atherosclerosissup.2008.09.400 Potential cytoprotective effects of chylomicron remnants in vascular cells V. Graham ∗ , C. De Pascale, J. Dalla-Riva, C. Lawson, C.P.D. Wheeler-Jones, K.M. Botham Department of Veterinary Basic Sciences, The Royal Veterinary College, London, UK Background: Previous work has shown that chylomicron remnants (CMR) interact with cells of the vasculature during the transport of lipids from the diet from the gut to the liver. CMR have been found to induce macrophage foam cell formation and to inhibit endothelium-dependent vascular relaxation and potentiate vasoconstriction via interaction with the nitric oxide pathway, suggesting that their effects promote atherogenesis. Little is know, however, about the effects of CMR on inflammatory processes in vascular cells, which are now known to play an important role in the initiation of atherosclerosis. Aims: In this study we have investigated the influence of CMR on inflammatory processes in macrophages and endothelial cells using chylomicron-remnant-like particles (CRLPs) together with macrophages derived from the human monocyte cell line THP-1 and human umbilical vein endothelial cells (HUVEC) as the experimental models. In THP-1 macrophages, effects of CRLPs on the activity of the transcription factor nuclear factor kB (NF-kB), which regulates the expression of inflammatory genes, and the secretion of inflammatory and anti-inflammatory cytokines and chemokines were assessed, and in HUVEC, effects on the production of reactive oxygen species (ROS), activation of the protective Akt pathway and expression of the anti-inflammatory enzyme hemoxygenase-1 (HO-1) were evaluated. Methods: CRLPs containing trilinolein as the sole or predominant triacylglycerol (TG) component were incubated with THP-1 macrophages or HUVEC. Secretion of the anti-inflammatory cytokine tissue growth factor b (TGFb), the pro-inflammatory cytokines interleukin (IL)-1b, IL-6, tumour necrosis factor a (TNFa) and pro-inflammatory chemokines IL-8 and monocyte chemoattractant protein-1 (MCP-1) was measured by ELISA. NF-kB transcriptional
activity was assessed using a TransAM assay. The expression of the active phosphorylated form p65-NF-kB, total NF-kB, HO-1 phosphorylated Akt (pAkt) and total Akt was determined by immunoblotting. ROS production was evaluated by fluorescence microscopy using a commercially available kit. Results: CRLPs strongly decreased the secretion of TNFa (−73 to 80%), IL-6 (−73 to 78%) and MCP-1 (−85%) and caused a small decrease in the secretion of IL-1b (−30%) in THP-1 macrophages after 16–24 h incubation, but had no effect on TGFb or IL-8 secretion. NF-kB transcriptional activity was lower in macrophages exposed to CRLPs for 6 or 24 h (−60 to 70%) and the expression of pNF-kB was also down-regulated after 3 h (−60%) or 6 h (−30%). In HUVEC, the production of ROS was enhanced (+40%) by incubation (3 h) with CRLPs. The expression of HO-1 in these cells was raised by CRLP treatment for 4 h (+20%). In addition, the level of active pAkt was up-regulated after only 5 min (+40%) and this effect was maintained at 10 and 30 min. Conclusions: These results indicate that CRLPs suppress the secretion of pro-inflammatory, but not anti-inflammatory, cytokines and chemokines in macrophages and also downregulate the activity of NF-kB, which is associated with inflammation in the vasculature. In addition, they demonstrate that the particles up-regulate protective mechanisms in endothelial cells by raising the expression of HO-1 and activating the Akt pathway, possibly via induction of ROS production. Thus, CMR induce cytoprotective mechanisms in vascular cells which may counteract some of their proatherogenic effects.
Acknowledgement This work was supported by the British Heart Foundation. doi:10.1016/j.atherosclerosissup.2008.09.401 Differential effects of saturated fatty acid, monounsaturated fatty acid and polyunsaturated fatty acid on chylomicron metabolism in the small intestine S. Galloway 1,∗ , C.C.K. Cheung 2 , R. Takechi 1 , M.M.S.R. Pallebage-Gamarallage 1 , J.C.L. Mamo 1 1 School of Public Health and Australian Technology Network (ATN), Centre for Metabolic Fitness, Curtin University of Technology, Perth, Western Australia, Australia 2 School of Biomedical Sciences, Curtin University of Technology, Perth, Western Australia, Australia
Background: Incorporation and secretion of non-esterified fatty acids (NEFA’s) as chylomicron triglyceride may differ depending on fatty acid chain length and degree of saturation. Approach: In this study, a histological approach was used to explore enterocytic lipid distribution and abundance in mice fed a diet enriched in either monounsaturated fatty acids
Abstracts / Atherosclerosis Supplements 9 (2008) 83–102
(MUFA’s), polyunsaturated fatty acids (PUFA’s) or saturated fatty acids (SFA’s). Methodology: Six-week-old female C57BL/6J mouse were placed on diets containing either 20% (w/w) monounsaturated fatty acid (MUFA), polyunsaturated fatty acids (PUFA) or saturated fatty acids (SFA) for 12 weeks. Mice fed a diet containing 4% PUFA served as low-fat controls. Intracellular lipoprotein metabolism was determined using quantitative immunohistochemistry (IHC) or immunofluorescence microscopy (IFM) for apolipoprotein B and selective staining techniques. Results: Animals fed fat enriched diets showed marked accumulation of enterocytic lipids compared to low-fat fed controls. However, there were substantial differences depending on the type of fatty acid consumed. Animals given the PUFA enriched diet showed substantially less intracellular lipids accompanied by enhanced secretion into lacteals. The SFA’s fed mice had massive cytosolic lipids with little evidence of secretion into lymphatics. A similar response was seen in MUFA fed animals, although the effect was not as pronounced as for SFA fed mice. Conclusion: This study demonstrates that incorporation and secretion of dietary triglycerides as chylomicrons is dependent on the fatty acid composition. Polyunsaturated fatty acids are more rapidly processed within enterocytes than either MUFA’s or SFA’s.
accumulation in a free-living environment. ApoB48 concentrations were determined utilizing an adapted SDS-PAGE and immunoblotting technique. Fasting and postprandial concentrations of plasma glucose, triglycerides (TG), cholesterol, and serum insulin were also measured. Results: Fasting concentrations of plasma apoB48 (type 1 DM group: 22.8 ± 2.5 g/mL vs. control group: 11.6 ± 0.76 g/mL, p = 0.019) and postprandial apoB48 area under the curve (AUC) (222.9 ± 11.3 g/mL vs. control group: 155.4 ± 21.7, p = 0.012) were significantly greater in type 1 DM subjects compared to controls. Subjects with type 1 DM also demonstrated an elevated postprandial glucose AUC, and postprandial TG level at 6 h. There were no differences in fasting glucose, insulin and lipid parameters (low density lipoprotein cholesterol, high density lipoprotein cholesterol, total cholesterol and TG), or postprandial insulin, cholesterol and TG AUC between type 1 DM subjects and controls. Conclusions: An abnormal postprandial chylomicron metabolism is a trait of individuals with type 1 DM even without evidence of traditional fasting dyslipidemia.
Postprandial metabolism of apolipoprotein containing particles in type 1 diabetes mellitus
J. Su ∗ , J. Lambert, E. Ryan, M.T. Clandinin, S.D. Proctor Metabolic and Cardiovascular Disease Laboratory, Alberta Institute for Human Nutrition and the Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada Background: Aberrant metabolism of intestinally derived apolipoprotein B48 (apoB48)-containing chylomicrons and their remnants, a known contributor to the development of atherosclerosis, has been described among individuals with coronary artery disease and type 2 diabetes mellitus (DM). However, little is known regarding postprandial lipoprotein metabolism in type 1 DM. Type 1 DM is associated with a 3-to 4-fold increase in cardiovascular disease (CVD) risk as compared with an age-matched non-diabetic population, despite no abnormalities of the fasting lipid profile. Therefore, the objective of this study was to investigate postprandial chylomicron metabolism in this population. Methods: Nine people (four men and five women) with brittle type 1 DM and four healthy controls (one man and three women) of similar age (type 1 DM group: 53.3 ± 3.3 years; control group: 46.5 ± 6.3) and BMI (type 1 DM group: 24.9 ± 1.2; control group: 23.1 ± 0.47) were enrolled. Blood was drawn at fasting, 2 and 4 h following breakfast, and 6 and 8 h following lunch to follow apoB48 metabolism and
Acknowledgements Support for this work was funded in part by CIHR, Canadian Diabetes Association and NSERC.
Friday—Plenary Seminar Intestinal lipoprotein overproduction in insulin resistant states: Focus on human studies G. Lewis University of Toronto, Toronto, Canada Triglyceride-rich lipoproteins (TRLs) derived from the intestine are increased in insulin resistant states both in the postprandial and fasted state and are associated with increased cardiovascular risk. Impaired clearance has long been invoked to explain this accumulation of intestinal TRLs, but more recent studies have highlighted the fact that the production rate of apolipoprotein (apo) B-48-containing particles is also increased in insulin resistance and type 2 diabetes. This talk will review some of the key recent findings in the field, focusing on recent human studies from our laboratory. doi:10.1016/j.atherosclerosissup.2008.09.404