Increased dietary triacylglycerol markedly enhances the ability of isolated rabbit enterocytes to secrete chylomicrons: an effect related to dietary fatty acid composition

Dietary fats are efficiently absorbed in the small intestine and transported into the blood via the lymph as chylomicrons, despite enormous variations in the amount and composition of the dietary lipid. The aim of the present study was to investigate how enterocytes respond to increased dietary fats of different composition. Rabbits were fed a low fat chow diet, and chow supplemented with sunflower oil (high n–6 polyunsaturated fatty acids), fish oil (high n–3 polyunsaturated fatty acids), or an oil mixture of a composition similar to that of the typical western diet. Feeding fat for 2 weeks markedly stimulated the ability of the isolated enterocytes to synthesize and secrete apolipoprotein B48, triacylglycerol, and cholesteryl ester (up to 18-, 50-, and 80-fold, respectively) in particles of chylomicron density. The magnitude of stimulation was sunflower oil > western diet lipid > fish oil. Single doses of lipid given 18 h prior to isolation of enterocytes stimulated chylomicron secretion by only 10% of that observed after 2 weeks of dietary supplementation. Enterocytes are replaced rapidly (half-life 1–2 days) by cells which move from the crypts to the tips of the villi, where absorption of nutrients takes place. Our observations suggest that dietary lipids modulate the function of enterocytes as they move from the crypts, so that the cells are ‘turned-on’ to lipid absorption. The results also show that diets of different fatty acid composition vary in their effects.—Cartwright, I. J., and J. A. Higgins. Increased dietary triacylglycerol markedly enhances the ability of isolated rabbit enterocytes to secrete chylomicrons: an effect related to dietary fatty acid composition. J. Lipid Res. 1999. 40: 1858–1866. Dietary fats are efficiently absorbed in the small intestine and transported into the blood via the lymph as chylomicrons, despite enormous variations in the amount and composition of the dietary lipid. The aim of the present study was to investigate how enterocytes respond to increased dietary fats of different composition. Rabbits were fed a low fat chow diet, and chow supplemented with sunflower oil (high n–6 polyunsaturated fatty acids), fish oil (high n–3 polyunsaturated fatty acids), or an oil mixture of a composition similar to that of the typical western diet. Feeding fat for 2 weeks markedly stimulated the ability of the isolated enterocytes to synthesize and secrete apolipoprotein B48, triacylglycerol, and cholesteryl ester (up to 18-, 50-, and 80-fold, respectively) in particles of chylomicron density. The magnitude of stimulation was sunflower oil > western diet lipid > fish oil. Single doses of lipid given 18 h prior to isolation of enterocytes stimulated chylomicron secretion by only 10% of that observed after 2 weeks of dietary supplementation. Enterocytes are replaced rapidly (half-life 1–2 days) by cells which move from the crypts to the tips of the villi, where absorption of nutrients takes place. Our observations suggest that dietary lipids modulate the function of enterocytes as they move from the crypts, so that the cells are ‘turned-on’ to lipid absorption. The results also show that diets of different fatty acid composition vary in their effects.—Cartwright, I. J., and J. A. Higgins. Increased dietary triacylglycerol markedly enhances the ability of isolated rabbit enterocytes to secrete chylomicrons: an effect related to dietary fatty acid composition. J. Lipid Res. 1999. 40: 1858–1866. Absorption of dietary lipids involves intralumenal digestion, transfer of the products of digestion across the brush border of the enterocytes, resynthesis of the lipids, and assembly of chylomicrons, which are released into the lamina propria and move via the lymph into the circulation. Chylomicrons are light particles (d < 1.000 g/ml) which are heterogeneous in size (diameters 80–1000 nm) and consist of >90% neutral lipid, predominantly triacylglycerol (TAG) with some cholesteryl ester (CE), stabilized by a shell of amphipathic lipids, phospholipid and cholesterol, and protein (1Hussain M.M. Kancha R.K. Zhou Z Luchoomun J. Zu H. Bakillah A. Chylomicron assembly and catabolism; role of apolipoproteins and receptors.Biochim. Biophys. Acta. 1996; 1300: 151-170Google Scholar). Apolipoprotein B-48 (apoB-48) is the major structural protein component and is essential for the formation and secretion of chylomicrons (1Hussain M.M. Kancha R.K. Zhou Z Luchoomun J. Zu H. Bakillah A. Chylomicron assembly and catabolism; role of apolipoproteins and receptors.Biochim. Biophys. Acta. 1996; 1300: 151-170Google Scholar, 2Glickman R.M. Rogers M. Glickman J.N. Apolipoprotein B synthesis by human liver and intestine in vitro.Proc. Natl. Acad. Sci. USA. 1986; 83: 5296-5300Google Scholar). Electron microscopic studies have shown that the assembly of chylomicrons follows the classic secretary pathway; the lipid and protein components appear in the lumen of the endoplasmic reticulum of the enterocytes, from where they move to the Golgi lumen (3Jones A.L. Ockner R.K. An electron microscopic study of endogenous very low density lipoprotein production in the intestine of rat and man.J. Lipid Res. 1971; 12: 580-589Google Scholar, 4Christensten N.J. Rubin C.E. Cheung M.C. Albers J. Ultrastructural immunolocalisation of apolipoprotein B within human jejunal absorptive cells.J. Lipid Res. 1983; 24: 1229-1242Google Scholar, 5Tso P. Intestinal lipid absorption.in: Johnson L.R. Physiology of the Gastrointestinal Tract. Raven Press, New York1994: 1867-1907Google Scholar, 6Hamilton R.L. Wong J.S. Chan C.M. Neilson L.B. Young S.G. Chylomicron sized particles are formed in the setting of apolipoprotein B deficiency.J. Lipid Res. 1998; 39: 1543-1557Google Scholar). Trans-Golgi vesicles then move to fuse with the lateral borders of the enterocytes releasing the chylomicrons outside the cell. The outline of events in the assembly of chylomicrons resembles that of very low density lipoproteins (VLDL), which transport endogenous lipids into the circulation from the liver. The major differences are that VLDL are considerably smaller than chylomicrons (40–80 nm in diameter), contain proportionally less neutral lipid, and that apoB-100 is the essential structural component of VLDL. ApoB-100 and apoB-48 are products of the same gene. However, in the intestine, the mRNA for apoB-100 is edited by a deaminase (apo-bec-1) which converts cytosine at position 6666 to uracil resulting in codon 2153 being converted to a stop codon. Translation of the edited message produces the truncated form, apoB-48 (7Powell L.M. Wallis S.C. Pease R.J. Edwards Y.H. Knott T.J. Scott J. A novel form of tissue specific RNA processing produces apoB-48 in intestine.Cell. 1987; 50: 831-840Google Scholar, 8Chen S.H. Habib G. Yang C-Y. Gu Z.W. Lee B.R. Weng S-A. Silberman S.R. Cai S.J. Deslypere J.P. Rosseneu M. Gotto A.M. Li W-H. Chan L. ApoB-48 is the product of a messenger RNA with an organ specifc in-frame-stop-codon.Science. 1987; 238: 363-366Google Scholar). The significance of apoB editing is not known; although, as this occurs in the small intestine of all mammals, it appears likely that apoB-48 has a fundamental role in chylomicron assembly. There has been considerable progress in elucidation of the molecular details of VLDL assembly in hepatic cells (9Yao Z. Trans K. McLeod R.S. Intracellular degradation of newly synthesized apolipoprotein B.J. Lipid Res. 1997; 38: 1937-1953Google Scholar, 10Ginsberg H.N. Role of lipid synthesis, chaperone proteins and proteosomes in the assembly of apoprotein B containing lipoproteins from cultured liver cells.Clin. Exp. Pharm. Physiol. 1997; 24: A29-A32Google Scholar, 11Kendrick J.S. Wilkinson J. Cartwright I.J. Lawrence S. Higgins J.A. Regulation of the assembly and secretion of very low density lipoproteins by the liver.Biol. Chem. 1998; 379: 1033-1040Google Scholar), however, very little is known about the intracellular and molecular details of chylomicron assembly and secretion in normal enterocytes. This is in part due to the lack of an appropriate cellular model for such studies (1Hussain M.M. Kancha R.K. Zhou Z Luchoomun J. Zu H. Bakillah A. Chylomicron assembly and catabolism; role of apolipoproteins and receptors.Biochim. Biophys. Acta. 1996; 1300: 151-170Google Scholar). CaCo-2 cells have been used for a number of investigations (12Hughes T.E. Sasak W.V. Ordovas J.M. Forte T.M. Lamon-Fava S. Schaefer E.J. A novel for the study of lipoprotein Chem. 1987; Scholar, I.J. of the human as a model for However, cells are not an as they secrete lipoprotein particles of the density of which contain apoB-100 as as is it to investigate the of diet chylomicron assembly cultured to investigate chylomicron have a for the isolation and of rabbit enterocytes I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar). The of an model to investigate the effect of diet the and function of the enterocytes. have used the rabbit it is a model for studies of lipoprotein and a of enterocytes of chylomicrons with a I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar). The small intestine is to in the amount and composition of dietary which absorbed efficiently and into However, the in which enterocytes respond to a dietary fat and the fat absorption are not the present study have the effect of of the and composition of the diet the ability of the isolated enterocytes to secrete Our observations suggest that increased dietary lipid a of markedly the ability of the isolated enterocytes to secrete This effect is related to the fatty acid composition of the diet. was from and were from were from and were from and were from or as I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar, J. Higgins J.A. P. H. of of apolipoprotein B in rabbit J. Scholar, J. Higgins J.A. P. H. of apolipoprotein B in of rabbit liver with a of Lipid Res. Scholar, I.J. Higgins J.A. of apolipoprotein and in rat liver endoplasmic reticulum and Golgi J. Scholar, I.J. Higgins J.A. and of within the endoplasmic reticulum and Golgi of isolated from normal and acid fed Chem. Scholar, I.J. Higgins J. A Intracellular events in the assembly of very low density lipoprotein lipids with apolipoprotein B in isolated rabbit J. Scholar, I.J. Higgins J.A. Intracellular degradation in the of secretion of apolipoprotein B by rabbit J. 1996; Scholar, J.S. Higgins J.A. Dietary fish events in the assembly of very low density lipoproteins and apoB for degradation within the endoplasmic reticulum of Lipid Res. 40: Scholar). in the of were used for were to and chow fat to of the dietary and were a dietary were low fat and chow supplemented with of sunflower fish or a mixture of similar to that in the typical diet of and The Dietary and of Scholar). The fatty acid of the diets and the of fatty acid to the are shown in and were as J. Higgins J.A. Dietary the assembly of VLDL and of the in rabbit 1998; Scholar), with fish sunflower or the western diet oil The was by and with sunflower oil and to of polyunsaturated fats were at in which were used for and to J. Higgins J.A. Dietary the assembly of VLDL and of the in rabbit 1998; Scholar). The western diet oil mixture was by the to was by in the also and the of the The of fat to in the chow diet was and this increased to in the were for 2 with the h the were some the effect of diet was by a of the appropriate oil or oil mixture 18 h prior to of isolated acid composition of in the of fatty acid to the in a of the fatty acid composition of the western diet with that of a typical as fatty fatty are from the Dietary and of of and The Dietary and of Scholar). The fatty are as a of the in a The in the of fatty acid to the The are from the Dietary and of of and The Dietary and of Scholar). The fatty are as a of the Lipid of a composition similar to in the lumen of the small intestine and were by as I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar). The of the components in the were acid and Enterocytes were isolated from the small intestine of and in at as I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar). The of in the isolation was This results in which contain of the for absorptive with for The was similar from the small of fed the different the synthesis and secretion of apoB-48 the isolated cells in of were with and the synthesis and secretion of and was to the mixture prior to to a of Enterocytes were isolated for different to and by at for 2 Chylomicrons were isolated by from the by at for I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar). of into cellular and apoB-48 and into protein was as I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar, I.J. Higgins J.A. and of within the endoplasmic reticulum and Golgi of isolated from normal and acid fed Chem. Scholar, I.J. Higgins J. A Intracellular events in the assembly of very low density lipoprotein lipids with apolipoprotein B in isolated rabbit J. Scholar, I.J. Higgins J.A. Intracellular degradation in the of secretion of apolipoprotein B by rabbit J. 1996; Scholar, J.S. Higgins J.A. Dietary fish events in the assembly of very low density lipoproteins and apoB for degradation within the endoplasmic reticulum of Lipid Res. 40: Scholar, I.J. Higgins J.A. Wilkinson J. S. J.S. J.M. of the role of lipids in the assembly of very low density lipoproteins in rabbit Lipid Res. 1997; 38: Scholar). and lipids were and by as I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar, I.J. Higgins J. A Intracellular events in the assembly of very low density lipoprotein lipids with apolipoprotein B in isolated rabbit J. Scholar, I.J. Higgins J.A. Wilkinson J. S. J.S. J.M. of the role of lipids in the assembly of very low density lipoproteins in rabbit Lipid Res. 1997; 38: Scholar). of in and was by was by I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar, I.J. Higgins J. A Intracellular events in the assembly of very low density lipoprotein lipids with apolipoprotein B in isolated rabbit J. Scholar, I.J. Higgins J.A. Wilkinson J. S. J.S. J.M. of the role of lipids in the assembly of very low density lipoproteins in rabbit Lipid Res. 1997; 38: Scholar). enterocytes synthesized apoB-48 from at a for the used of apoB-48 was low for the and increased the enterocytes also synthesized and and from of the lipids a in the cells after about and secretion the same as shown I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar), secretion was of to the and >90% of the apoB-48 and lipids was in the chylomicron from the by at for not of the newly synthesized apoB-48 and of the newly synthesized lipid was after that synthesis of chylomicron components is not a in However, the of in the enterocytes was at of secretion The isolated enterocytes synthesize and secrete However, the newly synthesized not with the and a is in the enterocytes at the used in Feeding fat stimulated synthesis and secretion of and by isolated enterocytes, of in the of the enterocytes from fed low fat >90% of the apoB-48 and lipid were in the chylomicron all sunflower oil the effect and fish oil the with the western diet oil mixture of apoB-48 in cells from sunflower was increased by and secretion of newly synthesized apoB was increased by with enterocytes from The of into cellular and protein was similar in from in all dietary not the stimulation of apoB-48 synthesis and secretion is not a of of fat protein synthesis and and synthesis were increased and in cells from sunflower and secretion of and was increased and A of the newly synthesized lipid was by enterocytes from of the into cellular and of enterocytes from sunflower in the chylomicrons after with of the newly synthesized and by cells from the in and it that the specific of the by enterocytes from is that of the cellular the enterocytes from the specific of the cellular increased to with sunflower oil > western diet > fish oil. synthesis of from in the specific of the by enterocytes from was than that by enterocytes from the of the cellular was than that of the of dietary fat for 2 weeks the synthesis and secretion of and cholesteryl ester by isolated enterocytes. enterocytes from fed chow or chow supplemented with different for 2 weeks were with and or with containing as in the of the cells were by and the of into cellular and into and into cellular and and the of cellular and were are the of fish sunflower oil of composition of western diet. with the enterocytes from was a < after in the cellular and and in all from fed The enterocytes of the small intestine are replaced of the of lipids is by enterocytes at the of the villi, the cells are about h M. and 1996; Scholar). The effect of the diets the function of the cells as they move from to or an effect the enterocytes. investigate a of oil was given to 18 h prior to was in the of cellular or in enterocytes from all dietary with the dietary only small were observed in the synthesis and secretion of and by isolated enterocytes with sunflower oil > western diet > fish oil. of and was increased and by sunflower oil with western diet oil and fish oil smaller of apoB and was increased by the sunflower enterocytes and secretion of by were of observed in enterocytes from fed increased fat for 2 weeks and for by in the of part of the the 18 h after the fat of a dietary fat the synthesis and secretion of and cholesteryl ester by isolated enterocytes. enterocytes, from fed a of different 18 h they were were with and or with containing as in the of the cells were by and the of into cellular and into cellular and into cellular and cholesteryl and the of cellular and were are the of fish sunflower oil of composition of western diet. The in the synthesis of cellular and and were not different in enterocytes from with enterocytes from with the of cellular and in enterocytes from sunflower < rabbit enterocytes synthesized and lipoprotein particles of the density of chylomicrons with a of of composition. Feeding an increased fat diet markedly stimulated the of isolated enterocytes to synthesize and secrete and of were used for isolation of cells in all dietary and the and of the cells isolated were have also from the and was in the of the in the with M. production and of transport the jejunal of the Biophys. Acta. have shown that diets in or fat to has effect the production with a low fat diet, the of the and the by for diet. This not to for the of dietary lipids observed in the present observed isolated enterocytes for by such as increased lymph which has been to in to dietary P. Intestinal lipid absorption.in: Johnson L.R. Physiology of the Gastrointestinal Tract. Raven Press, New York1994: 1867-1907Google Scholar, M. and 1996; Scholar). a small stimulation of chylomicron secretion was observed in enterocytes 18 h after a of lipid. the likely for observations is that the of a diet the function of the enterocytes, so that the cells to chylomicron assembly. studies supplemented the chow diet with fat of different The sunflower and fish diets were in n–6 and n–3 However, the fatty acid composition of diets is with the normal human diet, also used a western diet containing fat of a composition similar to that of the diet of the of and The Dietary and of Scholar). in the were given to the by J. Higgins J.A. Dietary the assembly of VLDL and of the in rabbit 1998; Scholar). This was are to However, have the that the amount of fat fed is occurs due to to and the a fat The of fat to the of the diet was for the chow and for the fat This is less that the fat of the western diet which is of and The Dietary and of Scholar). However, as were with to a smaller of which was by the The effect of the diets was sunflower oil > western diet > fish oil for synthesis and secretion of and There was a > the increased secretion of apoB-48 and newly synthesized or that the of chylomicron assembly and secretion was stimulated The of lipid in chylomicrons also that chylomicrons were synthesized as secretion was as by P. Johnson L.R. Intestinal Lipid Absorption in Physiology of the Gastrointestinal Tract. Raven Press, New York1994: 1867-1907Google Scholar). The effect of the diets was not due to an in fat with fatty acid composition. However, was the of fatty acid to dietary and fatty which were present in all diets were an in the amount of fatty and and acid > with increased secretion by enterocytes from fed the western diet and fish not sunflower oil An in acid > with increased secretion by enterocytes from fed the diets not from The effect of the fatty acid diets is a of different of different fatty the present to dietary fatty acid that within the of normal human However, to fatty have specific it to in which the of fatty acid is in of the of different fatty to dietary and the secretion of chylomicron components by isolated enterocytes. The the of different fatty acid components to the of different diets is the secretion of newly synthesized and and the of The are from the shown in The the for diet fish sunflower western have that the specific of the by enterocytes from is considerably than the specific of the cellular I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar). This was in this Feeding fat increased the specific of the cellular by and the specific of the by with enterocytes from observations with that is than intracellular of in enterocytes and that newly synthesized from in is in the cells I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar). However, fat the so that a of the newly synthesized is This effect is related to the composition of the dietary fat with sunflower oil the to observations in which VLDL secretion was by with n–3 or by fish oil J.S. Higgins J.A. Dietary fish events in the assembly of very low density lipoproteins and apoB for degradation within the endoplasmic reticulum of Lipid Res. 40: Scholar, J. Higgins J.A. Dietary the assembly of VLDL and of the in rabbit 1998; Scholar, H. J.A. S. P. size not number of chylomicrons by the small J. Physiol. Scholar, H. fatty intracellular degradation of apolipoprotein B in rat Scholar), chylomicron secretion was stimulated in enterocytes from fed fish oil for 2 weeks and was not by that n–3 not chylomicron assembly in the same as VLDL assembly. the effect of an increased fat diet the effect of fish chylomicron assembly. diets a effect chylomicron assembly than VLDL for apoB-48 secretion by enterocytes was increased by sunflower with an of to in apoB-100 secretion by isolated J.S. Higgins J.A. Dietary fish events in the assembly of very low density lipoproteins and apoB for degradation within the endoplasmic reticulum of Lipid Res. 40: Scholar). The of the small intestine has an cells at the of the crypts and move the crypts to the to the which is into the lumen (1Hussain M.M. Kancha R.K. Zhou Z Luchoomun J. Zu H. Bakillah A. Chylomicron assembly and catabolism; role of apolipoproteins and receptors.Biochim. Biophys. Acta. 1996; 1300: 151-170Google Scholar, M. and 1996; Scholar, M. production and of transport the jejunal of the Biophys. Acta. Scholar). the cells the they and cells at the of the are in absorption of The of absorptive cells is replaced after M. and 1996; Scholar, M. production and of transport the jejunal of the Biophys. Acta. Scholar). the small has a to to dietary a Our observations show that increased dietary fat of the enterocytes so that they have an increased to lipid and secrete The magnitude of stimulation is by the fatty acid composition of the diet. apoB-48 is an essential structural protein of chylomicrons, synthesis is not in chylomicron secretion in fatty acid in rat in to dietary n–3 fatty are with in the intracellular and secretion of apolipoprotein Lipid Res. 1997; 38: Scholar, J. J. P. J. E.J. Ordovas J.M. of fat human apolipoprotein B mRNA and Biophys. Acta. Scholar). ApoB-48 is synthesized in and the protein is I.J. Higgins J.A. rabbit enterocytes as a model for of chylomicron assembly and Lipid Res. 40: Scholar). However, are and cellular at which chylomicron secretion by dietary transport of lipid across the brush of apoB-48 into the synthesis of chylomicron lipids and of into the lumen of the and and assembly of apoB-48 and lipids within the of the endoplasmic The by which dietary fatty the ability of enterocytes to lipid to or to of or of the proteins in A number of studies have that different fatty have M. A.M. Regulation of hepatic transfer protein mRNA by dietary Biophys. Res. Scholar, A.M. J.S. of hepatic apolipoprotein and low density lipoprotein mRNA and lipoprotein by dietary J. Scholar). proteins fatty acid proteins in of fatty across the and the to the endoplasmic reticulum P. Intestinal lipid absorption.in: Johnson L.R. Physiology of the Gastrointestinal Tract. Raven Press, New York1994: 1867-1907Google Scholar, C.M. K. and of transfer Chem. Scholar), of lipid synthesis in the endoplasmic reticulum and (1Hussain M.M. Kancha R.K. Zhou Z Luchoomun J. Zu H. Bakillah A. Chylomicron assembly and catabolism; role of apolipoproteins and receptors.Biochim. Biophys. Acta. 1996; 1300: 151-170Google Scholar, 5Tso P. Intestinal lipid absorption.in: Johnson L.R. Physiology of the Gastrointestinal Tract. Raven Press, New York1994: 1867-1907Google Scholar), proteins in apoB-48 into the transfer protein and (1Hussain M.M. Kancha R.K. Zhou Z Luchoomun J. Zu H. Bakillah A. Chylomicron assembly and catabolism; role of apolipoproteins and receptors.Biochim. Biophys. Acta. 1996; 1300: 151-170Google Scholar, 5Tso P. Intestinal lipid absorption.in: Johnson L.R. Physiology of the Gastrointestinal Tract. Raven Press, New York1994: 1867-1907Google Scholar), and in intracellular of apoB-48 and lipids and molecular of small lipid Johnson L.R. Physiology of the Gastrointestinal Tract. Raven Press, New York1994: Scholar, C.M. P. Intracellular of in the Lipid Res. 1998; 39: Scholar, C.M. of triacylglycerol transport from the endoplasmic reticulum to the Golgi in J. Physiol. 1997; Scholar). enterocytes a model for which of proteins is in to dietary This was by from triacylglycerol ester apolipoprotein B-48 very low density lipoprotein polyunsaturated fatty