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Host-interaction effector molecules of Lactobacillus plantarum WCFS1
Lee, I.C. - \ 2016
Wageningen University. Promotor(en): Michiel Kleerebezem, co-promotor(en): P.A. Bron. - Wageningen : Wageningen University - ISBN 9789462576858 - 183 p.
lactobacillus plantarum - molecules - probiotics - immunomodulatory properties - lipoproteins - interactions - molecular interactions - host pathogen interactions - moleculen - probiotica - immunomodulerende eigenschappen - lipoproteïnen - interacties - moleculaire interacties - gastheer-pathogeen interacties
Lactobacillus plantarum is found in various environmental habitats, including fermentation products and the mammalian gastrointestinal tract, and specific strains are marketed as probiotics, which are defined as ‘live microorganisms which when administered in adequate amounts confer a health benefit on the host’. Throughout the studies of the mechanisms underlying probiotic activity, it became apparent that the probiotic effects are often species and/or strain specific. This situation has led more researchers to focus on the molecular characteristics of probiotic strains intending to link specific molecular structures to specific probiotic functions, and thereby deduce the mechanisms of molecular communication of probiotics. This thesis focuses on potential cell envelope effector molecules involved in interaction with the mammalian host cells, including lipoteichoic acid (LTA), lipo- and glyco-proteins, and extracellular polysaccharides (EPS), of L. plantarum WCFS1, a model strain for probiotic lactobacilli with a well-annotated genome sequences and sophisticated genetic engineering tools. First, existing research regarding the potential roles in probiotic functionality of Lactobacillus surface molecules in terms of their biosynthesis pathways and structure variations as well as interaction with host Pattern Recognition Receptors (PRRs) and immunomodulatory properties of these molecules are summarized and compared to provide an overview of the state-of-the-art in probiotic effector molecule research. Subsequently, specific molecules that reside in the cell envelope of L. plantarum WCFS1 were study for their role in bacterial physiology, as well as their role as ligands in Toll-like receptor (TLR) 2 signaling and immunomodulatory properties using human-cell co-incubation models. Our results showed that the deficiency of LTA had a drastic impact on cell division, cell morphology and growth in L. plantarum WCFS1, while LTA-deficient cells also elicited more pro-inflammatory responses in PBMCs rather than the expected loss of pro-inflammatory capacity as was observed with similar mutants of Lactobacillus acidophilus NCFM. Further studies on the signaling capacity of the purified LTA from L. plantarum WCFS1 revealed that these molecules are poor TLR2 activators, which is in clear contrast to the highly potent TLR2 stimulatory capacity of LTA obtained from Bacillus subtilis, implying that structural differences of the LTA produced by different bacteria are prominent determinants of their TLR2 signaling capacity and immunomodulatory properties. Lipoproteins of L. plantarum WCFS1 were studied using a derivative strain that is deficient in prolipoprotein diacylglyceryltransferase (Lgt), which transfers acyl chain moieties onto lipoproteins. The lipid moiety was shown to be important for proper anchoring of lipoproteins and TLR1/2 signaling capacity, but did not affect TLR2/6 signaling, suggesting that lipoproteins of L. plantarum WCFS1 are predominantly (if not exclusively) triacylated. The Lgt deficient strain elicited more pro-inflammatory responses in PBMCs as compared to the wild type, indicating that the native lipoproteins could play a role in dampening inflammation upon host-probiotic interaction. In addition, we explored the protein glycosylation machinery in L. plantarum WCFS1, responsible for the glycosylation of the major autolysin (Acm2) of this bacterium, which was previously shown to be O-glycosylated with N-acetylhexosamine conjugates. Using sequence similarity searches in combination with a lectin-based glycan detection and mass spectrometry analysis, two glycosyl-transferases, GtfA and GtfB (formerly annotated as TagE5 and TagE6, respectively), were shown to be required for the glycosylation of Acm2 and other unidentified L. plantarum WCFS1 glycosylated proteins. These results provide the first example of a general protein-glycosylation machinery in a Lactobacillus species. Finally, extracellular polysaccharides (EPS) in L. plantarum were studied in two strains that produce large amounts of EPS: L. plantarum SF2A35B and Lp90, in comparison to the lowly producing model strain WCFS1. Based on genome sequence comparison, both of the high producer strains were found to possess strain-specific and unique polysaccharide gene clusters. These gene clusters were deleted and the mutants were shown to have lost the capacity to produce large amounts of EPS, and were studied in relation to their properties in host-bacteria interaction. The results illustrate strain-specific and variable impacts of the removal of the EPS in the background of individual L. plantarum strains, supporting the importance of EPS in L. plantarum strains as a strain-specific determinant in host interaction. Overall, this thesis showed that surface molecules not only play important roles in bacterial physiology, but also in the interaction with the host mucosa through pattern recognition receptors expressed by the host cells. With the growing amount of evidence of structural variations in surface molecules, which are influenced by genetic background, physiological status, environmental factors, and other biological processes, these molecules form a unique signature associated with each strain that as a consequence elicits a strain-specific response when interacting with host cells.
Regulation and natural functions of lipopeptide biosynthesis in Pseudomonas
Song, C. - \ 2015
Wageningen University. Promotor(en): Francine Govers, co-promotor(en): Jos Raaijmakers. - Wageningen : Wageningen University - ISBN 9789462572690 - 173
pseudomonas fluorescens - lipoproteïnen - biosynthese - genetische kartering - genregulatie - genomica - transcriptomica - verdedigingsmechanismen - protozoa - mutanten - lipoproteins - biosynthesis - genetic mapping - gene regulation - genomics - transcriptomics - defence mechanisms - mutants
Lipopeptides (LPs) are surface-active, antimicrobial compounds composed of a lipid moiety linked to a short linear or cyclic oligopeptide. In bacteria, LPs are synthesized by large nonribosomal peptide synthetases (NRPSs) via a thiotemplate process. Compared to the understanding of LP biosynthesis, little is known about the genetic regulation.
The aims of this PhD thesis were to identify new regulatory genes of LP biosynthesis and to unravel the natural functions of LPs in plant-associated Pseudomonas species. Using a combination of various ‘omics’-based technologies, we identified two small RNAs, designated RsmY and RsmZ, that, together with the repressor proteins RsmA and RsmE, regulate the biosynthesis of the LP massetolide in the rhizosphere bacterium Pseudomonas fluorescens SS101. Four other regulatory genes (phgdh, dnaK, prtR and clpA) of massetolide biosynthesis were identified via random mutagenesis. Mutations in each of these four genes caused a deficiency in massetolide production, swarming motility and biofilm formation, two natural functions associated with the production of LPs in Pseudomonas. Results further indicated that the ClpAP protease complex regulates massetolide biosynthesis via the pathway-specific, LuxR-type regulator MassAR, the heat shock proteins DnaK and DnaJ, and proteins of the TCA cycle.
LPs exhibit broad-spectrum antimicrobial activities and have diverse natural functions for the producing bacteria. LPs of P. fluorescens were shown to play an important role in defense against protozoan predation. Genome-wide transcriptome analysis revealed that 55 and 73 genes were up- and down-regulated respectively in P. fluorescens strain SS101 upon grazing by the protozoan predator Naeglaria americana. The up-regulated genes included the LP biosynthesis genes massABC, but also genes involved in alkane degradation and in putrescine catalysis. Putrescine induced encystment of the protozoa, possibly providing a second line of defense against predation. MALDI imaging mass spectrometry (IMS) and live colony NanoDesi mass spectrometry further revealed, in real time, site-specific LP production at the interface of Pseudomonas-protozoa interactions. When the closely related strain P. fluorescens SBW25 was exposed to N. americana, similar overall transcriptional and metabolic responses were observed as found for strain SS101, but also strain-specific responses were apparent. These results indicate that closely related bacterial strains exhibit common and unique transcriptomic and metabolic responses to protozoan predation. Next to defense against competitors and predators, LPs are well-known for their role in swarming motility, a flagella-driven multicellular behavior of bacteria. Orfamide-deficient mutants of P. protegens Pf-5, either with deletions in the biosynthesis gene ofaA or in the regulatory gene gacA, cannot swarm on their own but ‘hitch-hike’ with parental strain Pf-5. However, distinctly different spatial distributions in co-swarming colonies were observed for these two mutants, with the ofaA mutant moving behind the wild type and the gacA mutant predominating on the edge of the swarming colony. Subsequent experimental evolution assays showed that repeated swarming cycles of strain Pf-5 drives parallel evolution toward fixation of spontaneous gacS/gacA mutants on the edge, ultimately causing colony collapse. Transcriptome analyses revealed that genes associated with resource acquisition, motility, chemotaxis and efflux were significantly upregulated in these regulatory mutants. Moreover, microscopic analysis showed that gacA mutant cells were longer and more flagellated than wild type and ofaA mutant cells, which may explain their predominance on the edge of co-swarming colonies. Collectively, these results indicated that adaptive convergent evolution through point mutations is a common feature of range-expanding microbial populations and that the putative fitness benefits of these spontaneous mutations during dispersal of bacteria into new territories are frequency-dependent.
Genetic Variation in Bile Acid Metabolism: Implications for Lipoprotein Homeostasis
Hofman, M.K. - \ 2005
Wageningen University. Promotor(en): Evert Schouten; Frans Kok. - - 168
cholesterolmetabolisme - galzuren - metabolisme - lipoproteïnen - homeostase - genetische variatie - genetica - atherosclerose - cholesterol metabolism - bile acids - metabolism - lipoproteins - homeostasis - genetic variation - genetics - atherosclerosis
Genetic factors play an important role in the homeostasis of cholesterol in the human body. An important pathway for eliminating cholesterol from the body is to convert it into bile acids in the liver. The rate-limiting enzyme in this catabolism of cholesterol is CYP7A1. In the gene of CYP7A1, a sequence variation was found: the CYP7A1 A-278C polymorphism. We found that this polymorphism affects triglyceride concentrations in healthy individuals and cholesterol concentrations in patients with Hypertriglyceridemia. However, we found that this polymorphism probably plays no role in the response of serum lipid levels to diet. Interestingly, subjects with the genotype CC of the CYP7A1 A-278C polymorphism have an almost twice as high risk of a new clinical event, as compared to subjects with the genotype AA. In addition, subjects with the genotype CC display more progression of atherosclerosis. The results of this thesis contribute to the understanding of the role of variations in genes in cholesterol homeostasis in human.
|Stage-matched nutrition guidance for patients at elevated risk for cardiovascular disease: A randomized intervention study in family practice
Veen, J.E. van der; Bakx, J.C. ; Hoogen, H. van den; Verheijden, M.W. ; Bosch, W. van den; Weel, C. van; Staveren, W.A. van - \ 2002
Journal of Family Practice 51 (2002)9. - ISSN 0094-3509 - p. 751 - 758.
primary-care physicians - coronary heart-disease - general-practice - cholesterol - serum - trial - lipoproteins - promotion - behavior - advice
OBJECTIVE To examine stage-matched nutrition counseling by family physicians and its effect on dietary intake, anthropometry, and serum lipid levels in patients at elevated risk for cardiovascular disease. METHODS In this controlled trial, patients randomized to intervention practices received nutrition information following the Stages-of-Change Model, and patients randomized to control practices received usual care. RESULTS At both 6 and 12 months after baseline, total fat intake and saturated fat intake declined significantly more in the intervention group than in the control group: -5.7% and -2.6% of energy, respectively, at 6 months, and -3.6% and -1.7% of energy, respectively, at 12 months. For energy intake, body weight, and BMI, there were significant differences between groups only at 6 months: -0.8 megajoules (MJ), -0.7 kg, and -0.3 kg/m(2), respectively. None of the serum lipid values changed significantly between groups at 12 months. CONCLUSIONS Nutritional counseling based on stages of change led to reductions in dietary fat intake and Weight loss in the short term. However, we found no corresponding changes in serum lipid concentrations.
Effects of plant sterols and olive oil phenols on serum lipoproteins in humans
Vissers, M.N. - \ 2001
Wageningen University. Promotor(en): M.B. Katan; P.L. Zock. - S.l. : S.n. - ISBN 9789058085023 - 141
voedingsonderzoek bij de mens - planten - sterolen - fenolen - olijfolie - bloedeiwit - lipoproteïnen - mens - human nutrition research - plants - sterols - phenols - olive oil - blood protein - lipoproteins - man
<p>The studies described in this thesis investigated whether minor components from vegetable oils can improve health by decreasing cholesterol concentrations or oxidative modification of low-density-lipoprotein (LDL) particles.</p><p>The plant sterolsβ-sitosterol and sitostanol are known to decrease cholesterol concentrations, but it is not clear whether other chemically related structures have similar effects. We examined the cholesterol-lowering effects of concentrates ofβ-sitosterol and 4,4'-dimethylsterols from rice bran oil and triterpene alcohols from sheanut oil. Plant sterols from rice bran oil lowered serum LDL cholesterol by 9%. This was probably due toβ-sitosterol rather than the 4,4'-dimethylsterols. Triterpene alcohols did not affect serum cholesterol concentration.</p><p>Oxidative modification of LDL is hypothesised to play a role in the development of atherosclerosis. Extra virgin olive oil contains phenols with antioxidant activity that could prevent oxidative modification of LDL. Three weeks of consumption of phenol-rich olive oil or a single dose of olive oil phenols did not decrease LDL oxidisability, neither in fasting plasma nor postprandial plasma samples. We showed that olive oil phenols reduce LDL oxidisability <em>in vitro</em> , but only in amounts that are much higher than can be reached by olive oil consumption <em>in vivo</em> .</p><p>The first requirement for an <em>in vivo</em> action of a dietary antioxidant in humans is that it enters the blood circulation. We therefore studied the absorption and urinary excretion of olive oil phenols in humans. We found that apparent absorption of the ingested olive oil phenols was more than 55-66 mol%. Absorption was confirmed by the urinary excretion of at least 5 mol% tyrosol and hydroxytyrosol. A further requirement for a dietary antioxidant to prevent oxidative modification of LDL is that it becomes present in the circulation or in LDL in a form with antioxidant activity. In the body olive oil phenols are extensively metabolised. The antioxidant activity of these phenol metabolites is unknown. To determine the antioxidant activity of olive oil phenols <em>in vivo</em> future studies should focus on the antioxidant activity of the metabolites actually present in plasma rather than on the <em>in vitro</em> antioxidant activity of the phenols as present in the olive oil.</p><p>In conclusion, although the olive oil phenols are well absorbed, the amount of phenols in olive oil and their consequent attainable plasma concentration in humans is probably too low to reduce LDL oxidisability. Furthermore, our studies provide no evidence that 4,4'-dimethylsterols from rice bran oil or triterpene alcohols from sheanut oil are able to decrease cholesterol concentrations. Thus, there are no indications that the minor components from vegetable oils described in this thesis have important effects on serum lipoproteins.
Dietary fatty acids and risk factors for coronary heart disease : controlled studies in healthy volunteers
Zock, P.L. - \ 1995
Agricultural University. Promotor(en): J.G.A.J. Hautvast; M.B. Katan. - S.l. : Zock - ISBN 9789054853282 - 190
vaatziekten - bloedstoornissen - hart- en vaatziekten - hart- en vaatstoornissen - vetzuren - voedselhygiëne - bloedvetten - lipoproteïnen - plantaardige vetten - plantaardige oliën - voeding - cholesterol - vascular diseases - blood disorders - cardiovascular diseases - cardiovascular disorders - fatty acids - food hygiene - blood lipids - lipoproteins - plant fats - plant oils - nutrition
<p>High levels of LDL cholesterol, blood pressure and Lp(a), and low levels of HDL cholesterol increase the risk for coronary heart disease (CHD). This thesis describes the effects of dietary fatty acids on these risk factors. In each of three trials we fed diets with tailored fatty acid composition to about 60 healthy men and women. Each diet within a trial was supplied to every volunteer for 3 weeks.<p>In the <strong><em>first study</em></strong><em></em> we compared the effects of monounsaturated <em>trans</em> fatty acids with those of linoleic acid, the fatty acid from which <em>trans</em> fatty acids are formed upon partial hydrogenation, and with those of stearic acid, a product of complete hydrogenation of linoleic acid. Relative to linoleic acid, both <em>trans</em> fatty acids and stearic acid raised LDL and lowered HDL cholesterol. Thus, partial as well as complete hydrogenation of linoleic acid produces fatty acids that unfavorably affect serum lipids relative to linoleic acid itself. <em>Trans</em> fatty acids and stearic acid did not influence blood pressure, but <em>trans</em> fatty acids modestly raised Lp(a).<p>The <em><strong>second study</strong></em> addressed the relative cholesterol-raising potentials of two specific saturates, myristic and palmitic acid. Relative to oleic acid, myristic acid was about 1.5 times as cholesterol-raising a's palmitic acid, due to increases in both LDL and HDL cholesterol. The differences between myristic and palmitic acid were statistically significant. However, both saturates caused high LDL cholesterol levels and raise the LDL to HDL cholesterol ratio.<p>In the <em><strong>third study</strong></em> we examined the effect of the positional distribution of fatty acids within dietary triglycerides. Two diets had identical total fatty acid composition, but a major contrast in fatty acid configuration. Total, LDL, and HDL cholesterol levels were the same on both diets. The position of the dietary fatty acids was partly reflected in fasting plasma lipids, but the fatty acid configuration had no important effect on lipoprotein levels.<p>In conclusion, monounsaturated <em>trans</em> fatty acids and the saturates myristic and palmitic acid have adverse effects on the serum lipoprotein risk profile for CHID. People at high risk for CHD should replace the hard fats in their diets by carbohydrates or unsaturated oils.
Effect of monounsaturated fatty acids on high-density and low-density lipoprotein cholesterol levels and blood pressure in healthy men and women
Mensink, R.P. - \ 1990
Agricultural University. Promotor(en): J.G.A.J. Hautvast; M.B. Katan. - S.l. : Mensink - 122
bloedvetten - lipoproteïnen - bloeddruk - bloedsomloop - effecten - oleïnezuur - onverzadigde vetzuren - carbonzuren - acrylzuur - voeding - cholesterol - blood lipids - lipoproteins - blood pressure - blood circulation - effects - oleic acid - unsaturated fatty acids - carboxylic acids - acrylic acid - nutrition
<TT>The purpose of the studies described in this thesis was to examine the effect of monounsaturated fatty acids on the distribution of serum cholesterol over high-density and low-density lipoproteins (HDL and LDL) and on blood pressure in healthy men and women. High levels of LDL cholesterol and blood pressure, and low levels of HDL cholesterol are associated with an increased risk for coronary heart disease.</TT><p><TT>Three controlled dietary studies were carried out. In the first study it was found that that monounsaturated fatty acids (oleic acid) specifically lowered non-HDL cholesterol when they replaced saturated fatty acids in the diet. In contrast, complex carbohydrates lowered both HDL and LDL cholesterol. The results of the second study indicated that it is immaterial whether saturated fatty acids in the diet are replaced by a mixture of monounsaturated and (n- 6)polyunsaturated fatty acids (oleic and linoleic acid) or by (n-6)polyunsaturated fatty acids alone. The two unsaturated-fat-rich diets had the same effect on HDL cholesterol and both lowered the level of LDL cholesterol to the same extent. In the third experiment we found that, when compared with <u>cis</u> monounsaturated fatty acids, <u>trans</u> monounsaturated fatty acids lower HDL cholesterol levels. In addition, <u>trans</u> fatty acids increased the level of LDL cholesterol, although to a lesser extent than did saturated fatty acids.</TT><p><TT>No effects of specific fatty acids on blood pressure were detected in any of the three experiments.</TT><p><TT>It is concluded that replacement of fats rich in saturated or <u>trans</u> fatty acids by oils rich oleic or linoleic acid might be helpful for the prevention of coronary heart disease, as far as lipoprotein levels are concerned. Weight gain, however, might be an unwanted side-effect of such high-oil diets.</TT><p><TT></TT>
Influence of human diets containing casein, soy protein isolate, and soy protein concentrate on serum cholesterol and lipoproteins in humans, rabbits and rats
Raaij, J.M.A. van - \ 1982
Landbouwhogeschool Wageningen. Promotor(en): J.G.A.J. Hautvast, co-promotor(en): M.B. Katan. - Wageningen : van Raaij - 131
bloedvetten - Glycine max - lipoproteïnen - metabolisme - mannen - konijnen - stikstof - voeding - eiwitten - ratten - sojabonen - blood lipids - lipoproteins - metabolism - men - rabbits - nitrogen - nutrition - proteins - rats - soyabeans
It is well known that feeding animals such as rabbits with semipurified diets containing animal proteins, as for example casein, results in hypercholesterolemia and atherosclerosis. On the other hand, diets containing vegetable proteins such as soybean protein maintain low levels of serum cholesterol. Little is known about the effects of the type of protein in the diet in humans.<p/>This thesis deals with the effects of casein and soy protein on serum cholesterol and lipoproteins, as observed in two experiments with human subjects and four experiments using animals. Three principle sources of protein were compared: caseinate; soy protein isolate, which is the purest soy protein preparation available commercially; and soy protein concentrate, a less refined soy protein preparation.<p/>In the first human experiment (Chapter 2), 69 young healthy students aged between 18 and 28 years were given for a period of 38 days diets containing 13% of energy as protein of which 65% consisted of protein from caseinate, or soy protein isolate, or a 2:1 mixture of caseinate and soy protein isolate. After a control period of 10 days during which all the subjects received the casein-soy diet, the subjects were divided into three groups, each group receiving one of the test diets for a test period of 28 days. In the second human experiment (Chapter 3), 57 healthy subjects aged between 29 and 60 years were given for a period of 45 days diets containing 16% of energy as protein of which 60% consisted of protein from caseinate, or soy protein isolate, or soy protein concentrate. After a control period of 17 days during which they received the casein diet, the subjects were divided into three groups, each group receiving one of the test diets for a test period of 28 days. Subjects in both studies were under strict dietary control. Apart from 0.5 MJ (120 kcal) per day in the first study and 1.0 MJ (240 kcal) per day in the second, all of the food eaten was supplied daily to the subjects in amounts appropriate to individual energy requirements. Food records and chemical analysis of the diets indicated that within each study, there were essentially no differences between the experimental diets except for the type of protein and/or the amount of non-protein material derived from the protein preparations. Blood samples were taken at the end of the control and test periods.<p/>During the experiments with human volunteers, two extra portions of each diet were collected. These were later homogenised and fed to animals in two experiments with rabbits and one with rats. A further experiment with rabbits was carried out using semipurified diets, the total protein content of which was test protein. The designs of the animal experiments were similar to those of the human experiments (Chapter 4).<p/>In the two human studies, there was no clear difference in response with respect to total serum cholesterol between the casein and the soy diets. A decrease in low-density-lipoprotein (LDL)- cholesterol and an increase in high-density-lipoprotein (HDL)- cholesterol were observed in those on the soy isolate diet when compared with those on the casein diet. The results on apolipoprotein-B and -A, suggest that the changes in cholesterol concentrations in the lipoprotein fractions resulted mainly from changes in the number of lipoprotein particles. However, these effects were only observed in those on the diets containing soy isolate and not in those on diets containing soy concentrate. With regard to the risk of coronary heart disease, the soy isolate diet can be considered to be beneficial, but the effects are small when compared with the effects of the fat composition and cholesterol content of the diet.<p/>The results of the animal studies using human diets confirm the results reported for semipurified diets. In rabbits, casein was found to be highly hypercholesterolemic when compared with the soy preparations, while in rats the effects were much smaller. The results stress the danger of extrapolating too readily from data from animal experiments on the effect of protein on serum cholesterol directly to man.<p/>Large decreases in level of serum cholesterol have been reported in hypercholesterolemic patients on diets containing soybean protein. Therefore, with regard to prevention of coronary heart disease, it has been suggested that animal protein in the diet should be replaced by vegetable protein. However, the results of the present studies with healthy subjects suggest that the normocholesterolemic human is probably relatively insensitive to the type of protein in his diet. It should be noted, however, that these experiments were of short duration and that the subjects were adults. Effects of a long-term intake of various proteins commencing at an early age have still to be determined.<p/>Although the effects of the type of protein are probably small in normocholesterolemic subjects, the replacement of foods containing animal protein with foods containing vegetable protein in the normal diet may still lead to changes in the concentration of serum lipids, because the main sources of animal protein are often also rich in saturated fat and cholesterol.<p/>In modifying the diet in order to influence certain physiological parameters, it should be realised that other parameters may also be affected (see Chapter 5). Caseinates are practically free of purines, while soy protein preparations like other protein sources such as meat. contain considerable amounts of purines. Uric acid is the end product of human purine metabolism and the subjects on the soy diets showed significantly higher levels of serum urate than the subjects on the casein diets. It is well known that the prevalence of gout is directly related to serum urate concentration.
The effect of semipurified diets containing either casein or soybean protein on the concentration of serum cholesterol and the lipoprotein composition in rabbits
Terpstra, A.H.M. - \ 1981
Landbouwhogeschool Wageningen. Promotor(en): J.G.A.J. Hautvast. - Wageningen : Terpstra - 112
bloedvetten - lipoproteïnen - voedsel - voedingsmiddelen - eiwit - stikstof - voeding - lagomorpha - leporidae - hazen - konijnen - metabolisme - eiwitten - blood lipids - lipoproteins - food - foods - protein - nitrogen - nutrition - hares - rabbits - metabolism - proteins
This thesis deals with the effect of dietary casein and soybean protein on the concentration of serum cholesterol and the lipoprotein composition in rabbits. Special attention has been paid to the time course of the changes produced by the protein in the diet.<p/>After a short introduction, a review of the studies on the effect of dietary protein on serum cholesterol is presented. From these studies, it was concluded that the effect of dietary protein on the concentration of serum cholesterol is only manifested in hypercholesterolaemic subjects and in experimental animals fed a diet high in cholesterol. An exception to this generalisation is the rabbit, an animal highly susceptible to the induction of hypercholesterolaemia and atherosclerosis. In the rabbit, dietary protein is also able to influence serum cholesterol levels when cholesterol-free diets are used.<p/>In the next chapter a method is presented for the separation of serum lipoproteins by density gradient ultracentrifugation. By staining the serum lipoproteins prior to ultracentrifugation the various lipoprotein classes can be easily localized in the gradient after the separation. By means of this technique it was observed that the density profile of the serum lipoproteins of rabbits and other experimental animals differs to that in man.<p/>Subsequently the time course of the changes in serum cholesterol concentration and lipoprotein composition were studied, when rabbits were transferred from a commercial diet to a semipurified diet containing either casein or soybean protein. It was observed that after only one day of feeding a semipurified diet containing casein the serum cholesterol levels had more than doubled. In the rabbits fed soybean protein the serum cholesterol level increased only slightly. The ingestion of semipurified diets resulted in a steep increase in the ratio of cholesterol to protein in all the serum lipoprotein fractions. This suggests that lipoprotein particles relatively rich in cholesterol were formed. Furthermore, marked variations in the density profile of the serum lipoproteins were observed between individual rabbits fed semipurified diets.<p/>In chapter 4 the effect of higher proportions of casein in the diet on the enhancement of the hypercholesterolaemia produced by this protein was examined. A low casein diet (10%) resulted in lower serum cholesterol levels than did a high casein diet (40%), whereas a diet containing 20% casein produced intermediate concentrations of cholesterol in the serum. In the animals with the highest levels of total serum cholesterol (the 40% casein group) most of the cholesterol was transported in the very low density lipoproteins. With moderate hypercholesterolaemia (the 20% casein group), the low density lipoproteins were the main carrier of cholesterol. Elevations in lipoprotein cholesterol were associated with an increased ratio of cholesterol to protein in all of the groups.<p/>In the final experiment, the time course of the regression and progression of hypercholesterolaemia was studied when rabbits were transferred from a semipurified diet containing casein to a semipurified diet with soybean protein and <em>vice versa.</em> In this study high protein diets (40%) were used. When casein in the diet was replaced by soybean protein, a rapid decrease in serum cholesterol occurred. This decrease in serum cholesterol was initially reflected in a decrease in the amount of cholesterol in the very low density lipoproteins followed by a subsequent drop in the cholesterol in the low density lipoproteins. Conversely, the replacement of soybean protein by casein resulted in an steep elevation in the serum cholesterol levels, which was mainly caused by an increase in the cholesterol in the low density lipoproteins.<p/>These studies show that in rabbits very rapid and pronounced changes in serum cholesterol concentrations and lipoprotein composition can be produced by changing the type and amount of dietary protein. These findings underline the suitability of the rabbit as a model for studies of hypercholesterolaemia.
|Lipoproteins in poultry
Anonymous, - \ 1974
Wageningen : [s.n.] (Literatuurlijst / Centrum voor landbouwpublikaties en landbouwdocumentatie no. 3630)
dierlijke producten - bibliografieën - eierproducten - eieren - kippen - lipoproteïnen - pluimvee - eiwitgehalte - zoölogie - animal products - bibliographies - egg products - eggs - fowls - lipoproteins - poultry - protein content - zoology