L’hypertriglycéridémie (hyperTG) est une dyslipidémie fréquente, caractérisée par une augmentation de la concentration plasmatique en triglycérides (TG). L’hyperTG est considérée comme un facteur de risque indépendant de la maladie cardiovasculaire, particulièrement de la maladie coronarienne athérosclérotique. Plusieurs facteurs environnementaux et génétiques ont été associés avec l’hyperTG. Cependant, près de 90% des cas d’hyperTG primaire sont encore incomplètement caractérisés au niveau moléculaire. Dernièrement, la protéine GPIHBP1 (glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1), qui a un rôle clef dans le métabolisme des TG, a été associée à l’expression d’hyperTG sévère et rare chez l’humain. Ce mémoire présente les résultats de nos travaux qui ont été effectués afin d’identifier de nouvelles bases moléculaires associées à l’expression de l’hyperTG dans le locus du gène GPIHBP1. Nous avons observé que le polymorphisme GPIHBP1 g.-469G>A (rs72691625), dont la fréquence de l’allèle mineure a été évaluée à 19,6% dans notre échantillon, serait associé à l’expression d’hyperTG (TG ≥ 2mmol/L) dans une population canadienne-française. Ce polymorphisme est associé à un risque 1,67 fois plus grand d’exprimer une triglycéridémie ≥ 2mmol/L chez les porteurs hétérozygotes et 5,7 fois plus grand chez les porteurs homozygotes, comparativement aux non-porteurs. Ce risque d’hyperTG serait exacerbé par la présence concomitante d’une mutation hypertriglycéridémiante dans le gène codant pour la lipoprotéine lipase. La présence de ce polymorphisme serait particulièrement associée à l’expression de la dysbêtalipoprotéinémie familiale et de l’hypertriglycéridémie familiale endogène. GPIHBP1 g.-469G>A est le premier polymorphisme fréquent identifié dans le promoteur du gène à être associé avec l’expression d’hyperTG. GPIHBP1 émerge de plus en plus comme un gène candidat intéressant pour la recherche de nouvelles bases moléculaires pouvant expliquer certaines formes d’hyperTG primaire fréquente. / Hypertriglyceridemia (hyperTG) is a frequent dyslipidemia referring to an increased fasting plasma triglyceride (TG) level ≥ 2 mmol/L. HyperTG is an independent risk factor for cardiovascular disease, such as coronary artery diseases. Several environmental and genetic factors have been associated with hyperTG. Although several gene factors were associated with hyperTG, nearly 90% of cases of primary hyperTG are still incompletely characterized at the molecular level. Recently, few cases of rare and severe hyperTG have been associated with some rare polymorphisms in the gene coding for GPIHBP1 (glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1). This manuscript resumes our research regarding the identification of new molecular bases associated with the expression of frequent hyperTG subtypes in the gene locus GPIHBP1. Our results show that the GPIHBP1 g.-469G>A polymorphism (rs72691625), whose the minor allele frequency was estimated to 19.6% in our sample, was associated with the expression of hyperTG (TG ≥ 2 mmol/L) in a French-Canadian population. Subjects heterozygous and homozygous for this polymorphism respectively had a 1.67-fold and 5.70-fold increased risk to exhibit plasma TG levels ≥ 2mmol/L as compared to non-carriers. This increased risk of hyperTG observed in g.-469A carriers seems to be exacerbated by the concomitant presence of a frequent loss-of-function lipoprotein lipase gene variant. This polymorphism seems also particularly associated with dysbetalipoproteinemia and familial hypertriglyceridemia. The g.-469G>A polymorphism is the first common polymorphism in the GPIHBP1 gene promoter to be associated with the expression of hyperTG. GPIHBP1 emerges as a significant candidate for the molecular based of primary hyperTG.

Wichtige Marker in der klinischen Routine für die Risikoabschätzung von kardiovaskulären Erkrankungen (CVD) sind Blutcholesterinwerte auf Basis von Lipoproteinklassen wie ''schlechtes'' LDL oder ''gutes'' HDL. Dies vernachlässigt, dass jede Lipoproteinklasse eine nicht-homogene Population von Lipoproteinpartikeln unterschiedlicher Zusammensetzung aus Lipiden und Proteinen bildet. Studien zeigen zudem, dass solche Sub-populationen von Lipoproteinen im Stoffwechsel als auch im Beitrag zu CVD unterschiedlich sind. Mehrwert und routinemäßiger Einsatz einer detaillierteren Auftrennung von Lipoproteinen sind jedoch umstritten, da die experimentelle Fraktionierung und Analyse aufwendig, zeit- und kostenintensiv sind. Die vorliegende Arbeit ''Computational Lipidology'' präsentiert einen neuartigen Modellierungsansatz für die Berechnung von Lipoproteinverteilungen (Lipoproteinprofil) im Blutplasma, wobei erstmals individuelle Lipoproteinpartikel anstelle von Lipoproteinklassen betrachtet werden. Das Modell berücksichtigt elementare Bestandteile (Lipide, Proteine) und Prozesse des Stoffwechsel von Lipoproteinen. Stochastische wie deterministische Simulationen errechnen auf Basis aller Lipoproteinpartikel im System deren Dichteverteilung. Die Modellberechnungen reproduzieren erfolgreich klinisch gemessene Lipoproteinprofile von gesunden Patienten und zeigen Hauptmerkmale von pathologischen Situationen, die durch Störung eines der zugrundeliegenden molekularen Prozesse verursacht werden. Hochaufgelöste Lipoproteinprofile zeigen die Verteilung von sogenannten ''high-resolution density sub-fractions'' (hrDS) innerhalb von Hauptlipoproteinklassen. Die Ergebnisse stimmen mit klinischen Beobachtungen sehr gut überein, was die Arbeit als einen signifikanten Schritt in Richtung Analyse von individuellen Unterschieden, patienten-orientierte Diagnose von Fettstoffwechselstörungen und Identifikation neuer Sub-populationen von potentiell klinischer Relevanz qualifiziert. / Monitoring the major lipoprotein classes, particularly low-density lipoproteins (''bad'' LDL) and high-density lipoproteins (''good'' HDL) for characterizing risk of cardiovascular disease (CVD) is well-accepted and routine in clinical practice. However, it is only one-half of the truth as lipoprotein classes comprise non-homogeneous populations of lipoprotein particles varying significantly in their composition of lipids and apolipoproteins. Various studies have shown differing metabolic behavior and contribution to CVD of individual lipoprotein sub-populations. Nevertheless, the superiority of more detailed lipoprotein fractionation is still a matter of debate because experimental separation and analysis is an elaborate, time-consuming and expensive venture and not yet worthwhile for routine measurements. The present work ''Computational Lipidology'' aims at establishing a novel modeling approach to calculate the distribution of lipoproteins (lipoprotein profile) in blood plasma being the first that settles on individual lipoprotein complexes instead of common lipoprotein classes. Essential lipoprotein constituents and processes involved in the lipoprotein metabolism are taken into account. Stochastic as well as deterministic simulations yield the distribution of lipoproteins over density based on the set of individual lipoprotein complexes in the system. The model calculations successfully reproduce lipoprotein profiles measured in healthy subjects and show main characteristics of pathological situations elicited by disorder in one of the underlying molecular processes. Moreover, the model reveals the distribution of high-resolution lipoprotein sub-fractions (hrDS) within major density classes. The results show satisfactory agreement with clinical observations which qualifies the work as a significant step towards analyzing inter-individual variability, patient-oriented diagnosis of lipid disorders and identifying new sub-fractions of potential clinical relevance.

Motivation: The prevalence of non-communicable diseases such as diabetes mellitus (DM) and cardiovascular disease (CVD) is rapidly increasing in industrialized societies. Experts believe that lifestyle, and in particular its nutritional aspects, plays a decisive role in increasing the burden of these chronic conditions. Dietary habits would, therefore, be modified to exert a positive impact on the prevention and treatment of chronic diseases of lifestyle. It is believed that the state of hyperglycaemia that is observed following food intake under certain dietary regimes contributes to the development of various metabolic conditions. This is not only true for individuals with poor glycaemic control such as some diabetics, but could also be true for healthy individuals. It would, therefore, be helpful to be able to reduce the amplitude and duration of postprandial hyperglycaemia. Selecting the correct type of carbohydrate (CHO) foods may produce less postprandial hyperglycaemia, representing a possible strategy in the prevention and treatment of chronic metabolic diseases. At the same time, a key focus of sport nutrition is the optimal amount of CHO that an athlete should consume and the optimal timing of consumption. The most important nutritional goals of the athlete are to prepare body CHO stores pre-exercise, provide energy during prolonged exercise and restore glycogen stores during the recovery period. The ultimate aim of these strategies is to maintain CHO availability to the muscle and central nervous system during prolonged moderate to high intensity exercise, since these are important factors in exercise capacity and performance. However, the type of CHO has been studied less often and with less attention to practical concerns than the amount of CHO. The glycaemic index (GI) refers to the blood glucose raising potential of CHO foods and, therefore, influences secretion of insulin. In several metabolic disorders, secretion of insulin is inadequate or impossible, leading to poor glycaemic control. It has been suggested that low GI diets could potentially contribute to a significant improvement of the conditions associated with poor glycaemic control. Insulin secretion is also important to athletes since the rate of glycogen synthesis depends on insulin due to it stimulatory effect on the activity of glycogen synthase. Objectives: Three main objectives were identified for this study. The first was to conduct a meta-analysis of the effects of the GI on markers for CHO and lipid metabolism with the emphasis on randomised controlled trials (RCT's). Secondly, a systematic review was performed to determine the strength of the body of scientific evidence from epidemiological studies combined with RCT's to encourage dieticians to incorporate the GI concept in meal planning. Finally, a systematic review of the effect of the GI in sport performance was conducted on all available literature up to date to investigate whether the application of the GI in an athlete's diet can enhance physical performance. Methodology: For the meta-analysis, the search was for randomised controlled trials with a cross-over or parallel design published in English between 1981 and 2003, investigating the effect of low GI vs high GI diets on markers of carbohydrate and lipid metabolism. The main outcomes were serum fructosamine, glycosylated haemoglobin (HbA1c), high-density lipoprotein cholesterol (HDL-c), low-density lipoprotein cholesterol (LDL-c), total cholesterol (TC) and triacylglycerols (TG). For the systematic review, epidemiological studies as well as RCT's investigating the effect of LGI vs HGI diets on markers for carbohydrate and lipid metabolism were used. For the systematic review on the effect of the GI on sport performance, RCT's with either a cross-over or parallel design that were published in English between January 1981 and September 2004 were used. All relevant manuscripts for the systematic reviews as well as meta-analysis were obtained through a literature search on relevant databases such as the Cochrane Central Register of Controlled Trials, MEDLINE (1981 to present), EMBASE, LILACS, SPORTDiscus, ScienceDirect and PubMed. This thesis is presented in the article format. Results and conclusions of the individual manuscripts: For the meta-analysis, literature searches identified 16 studies that met the strict inclusion criteria. Low GI diets significantly reduced fructosamine (p<0.05), HbA1c, (p<0.03), TC(p<0.0001) and tended to reduce LDL-c (p=0.06) compared to high GI diets. No changes were observed in HDL-c and TG concentrations. Results from this meta analysis, therefore, support the use of the GI concept in choosing CHO-containing foods to reduce TC and improve blood glucose control in diabetics. The systematic review combined the results of the preceding meta-analysis and results from epidemiological studies. Prospective epidemiological studies showed improvements in HDL-c concentrations over longer time periods with low GI diets vs. high GI diets, while the RCT's failed to show an improvement in HDL-c over the short-term. This could be attributed to the short intervention period during which the RCT's were conducted. Furthermore, epidemiological studies failed to show positive relationships between LDL-c and TC and low GI diets, while RCT's reported positive results on both these lipids with low GI diets. However, the epidemiological studies, as well as the RCT's showed positive results with low GI diets on markers of CHO metabolism. Taken together, convincing evidence from RCT's as well as epidemiological studies exists to recommend the use of low GI diets to improve markers of CHO as well as of lipid metabolism. 3 From the systematic review regarding the GI and sport performance it does not seem that low GI pre-exercise meals provide any advantages over high GI pre-exercise meals. Although low GI pre-exercise meals may better maintain CHO availability during exercise, low GI pre-exercise meals offer no added advantage over high GI meals regarding performance. Furthermore, the exaggerated metabolic responses from high GI compared to low GI CHO seems not be detrimental to exercise performance. However, athletes who experience hypoglycaemia when consuming CHO-rich feedings in the hour prior to exercise are advised to rather consume low GI pre-exercise meals. No studies have been reported on the GI during exercise. Current evidence suggests a combination of CHO with differing Gl's such as glucose (high GI), sucrose (moderate GI) and fructose (low GI) will deliver the best results in terms of exogenous CHO oxidation due to different transport mechanisms. Although no studies are conducted on the effect of the GI on short-term recovery it is speculated that high GI CHO is most effective when the recovery period is between 0-8 hours, however, evidence suggests that when the recovery period is longer (20-24 hours), the total amount of CHO is more important than the type of CHO. Conclusion: There is an important body of evidence in support of a therapeutic and preventative potential of low GI diets to improve markers for CHO and lipid metabolism. By substituting high GI CHO-rich with low GI CHO-rich foods improved overall metabolic control. In addition, these diets reduced TC, tended to improve LDL-c and might have a positive effect over the long term on HDL-c. This confirms the place for low GI diets in disease prevention and management, particularly in populations characterised by already high incidences of insulin resistance, glucose intolerance and abnormal lipid levels. For athletes it seems that low GI pre-exercise meals do not provide any advantage regarding performance over high GI pre-exercise meals. However, low GI meals can be recommended to athletes who are prone to develop hypoglycaemia after a CHO-rich meal in the hour prior to exercise. No studies have been reported on the effect of the GI during exercise. However, it has been speculated that a combination of CHO with varying Gl's deliver the best results in terms of exogenous CHO oxidation. No studies exist investigating the effect of the GI on short-term recovery, however, it is speculated that high GI CHO-rich foods are suitable when the recovery period is short (0-8 h), while the total amount rather than the type of CHO is important when the recovery period is longer (20-24 h). Therefore, the GI is a scientifically based tool to enable the selection of CHO-containing foods to improve markers for CHO and lipid metabolism as well as to help athletes to prepare optimally for competitions. Recommendations: Although a step nearer has been taken to confirm a place for the GI in human health, additional randomised, controlled, medium and long-term studies as well as more epidemiological studies are needed to investigate further the effect of low GI diets on LDL-c. HDL-c and TG. These studies are essential to investigate the effect of low GI diets on endpoints such as CVD and DM. This will also show whether low GI diets can reduce the risk of diabetic complications such as neuropathy and nephropathy. Furthermore, the public at large must be educated about the usefulness and application of the GI in meal planning. For sport nutrition, randomised controlled trials should be performed to investigate the role of the GI during exercise as well as in sports of longer duration such as cricket and tennis. More studies are needed to elucidate the short-term effect of the GI post-exercise as well as to determine the mechanism of lower glycogen storage with LGI meals post-exercise. / Thesis (Ph.D. (Dietetics))--North-West University, Potchefstroom Campus, 2005.

L’hypertriglycéridémie (hyperTG) est une dyslipidémie fréquente, caractérisée par une augmentation de la concentration plasmatique en triglycérides (TG). L’hyperTG est considérée comme un facteur de risque indépendant de la maladie cardiovasculaire, particulièrement de la maladie coronarienne athérosclérotique. Plusieurs facteurs environnementaux et génétiques ont été associés avec l’hyperTG. Cependant, près de 90% des cas d’hyperTG primaire sont encore incomplètement caractérisés au niveau moléculaire. Dernièrement, la protéine GPIHBP1 (glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1), qui a un rôle clef dans le métabolisme des TG, a été associée à l’expression d’hyperTG sévère et rare chez l’humain. Ce mémoire présente les résultats de nos travaux qui ont été effectués afin d’identifier de nouvelles bases moléculaires associées à l’expression de l’hyperTG dans le locus du gène GPIHBP1. Nous avons observé que le polymorphisme GPIHBP1 g.-469G>A (rs72691625), dont la fréquence de l’allèle mineure a été évaluée à 19,6% dans notre échantillon, serait associé à l’expression d’hyperTG (TG ≥ 2mmol/L) dans une population canadienne-française. Ce polymorphisme est associé à un risque 1,67 fois plus grand d’exprimer une triglycéridémie ≥ 2mmol/L chez les porteurs hétérozygotes et 5,7 fois plus grand chez les porteurs homozygotes, comparativement aux non-porteurs. Ce risque d’hyperTG serait exacerbé par la présence concomitante d’une mutation hypertriglycéridémiante dans le gène codant pour la lipoprotéine lipase. La présence de ce polymorphisme serait particulièrement associée à l’expression de la dysbêtalipoprotéinémie familiale et de l’hypertriglycéridémie familiale endogène. GPIHBP1 g.-469G>A est le premier polymorphisme fréquent identifié dans le promoteur du gène à être associé avec l’expression d’hyperTG. GPIHBP1 émerge de plus en plus comme un gène candidat intéressant pour la recherche de nouvelles bases moléculaires pouvant expliquer certaines formes d’hyperTG primaire fréquente. / Hypertriglyceridemia (hyperTG) is a frequent dyslipidemia referring to an increased fasting plasma triglyceride (TG) level ≥ 2 mmol/L. HyperTG is an independent risk factor for cardiovascular disease, such as coronary artery diseases. Several environmental and genetic factors have been associated with hyperTG. Although several gene factors were associated with hyperTG, nearly 90% of cases of primary hyperTG are still incompletely characterized at the molecular level. Recently, few cases of rare and severe hyperTG have been associated with some rare polymorphisms in the gene coding for GPIHBP1 (glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1). This manuscript resumes our research regarding the identification of new molecular bases associated with the expression of frequent hyperTG subtypes in the gene locus GPIHBP1. Our results show that the GPIHBP1 g.-469G>A polymorphism (rs72691625), whose the minor allele frequency was estimated to 19.6% in our sample, was associated with the expression of hyperTG (TG ≥ 2 mmol/L) in a French-Canadian population. Subjects heterozygous and homozygous for this polymorphism respectively had a 1.67-fold and 5.70-fold increased risk to exhibit plasma TG levels ≥ 2mmol/L as compared to non-carriers. This increased risk of hyperTG observed in g.-469A carriers seems to be exacerbated by the concomitant presence of a frequent loss-of-function lipoprotein lipase gene variant. This polymorphism seems also particularly associated with dysbetalipoproteinemia and familial hypertriglyceridemia. The g.-469G>A polymorphism is the first common polymorphism in the GPIHBP1 gene promoter to be associated with the expression of hyperTG. GPIHBP1 emerges as a significant candidate for the molecular based of primary hyperTG.

Motivation: The prevalence of non-communicable diseases such as diabetes mellitus (DM) and cardiovascular disease (CVD) is rapidly increasing in industrialized societies. Experts believe that lifestyle, and in particular its nutritional aspects, plays a decisive role in increasing the burden of these chronic conditions. Dietary habits would, therefore, be modified to exert a positive impact on the prevention and treatment of chronic diseases of lifestyle. It is believed that the state of hyperglycaemia that is observed following food intake under certain dietary regimes contributes to the development of various metabolic conditions. This is not only true for individuals with poor glycaemic control such as some diabetics, but could also be true for healthy individuals. It would, therefore, be helpful to be able to reduce the amplitude and duration of postprandial hyperglycaemia. Selecting the correct type of carbohydrate (CHO) foods may produce less postprandial hyperglycaemia, representing a possible strategy in the prevention and treatment of chronic metabolic diseases. At the same time, a key focus of sport nutrition is the optimal amount of CHO that an athlete should consume and the optimal timing of consumption. The most important nutritional goals of the athlete are to prepare body CHO stores pre-exercise, provide energy during prolonged exercise and restore glycogen stores during the recovery period. The ultimate aim of these strategies is to maintain CHO availability to the muscle and central nervous system during prolonged moderate to high intensity exercise, since these are important factors in exercise capacity and performance. However, the type of CHO has been studied less often and with less attention to practical concerns than the amount of CHO. The glycaemic index (GI) refers to the blood glucose raising potential of CHO foods and, therefore, influences secretion of insulin. In several metabolic disorders, secretion of insulin is inadequate or impossible, leading to poor glycaemic control. It has been suggested that low GI diets could potentially contribute to a significant improvement of the conditions associated with poor glycaemic control. Insulin secretion is also important to athletes since the rate of glycogen synthesis depends on insulin due to it stimulatory effect on the activity of glycogen synthase. Objectives: Three main objectives were identified for this study. The first was to conduct a meta-analysis of the effects of the GI on markers for CHO and lipid metabolism with the emphasis on randomised controlled trials (RCT's). Secondly, a systematic review was performed to determine the strength of the body of scientific evidence from epidemiological studies combined with RCT's to encourage dieticians to incorporate the GI concept in meal planning. Finally, a systematic review of the effect of the GI in sport performance was conducted on all available literature up to date to investigate whether the application of the GI in an athlete's diet can enhance physical performance. Methodology: For the meta-analysis, the search was for randomised controlled trials with a cross-over or parallel design published in English between 1981 and 2003, investigating the effect of low GI vs high GI diets on markers of carbohydrate and lipid metabolism. The main outcomes were serum fructosamine, glycosylated haemoglobin (HbA1c), high-density lipoprotein cholesterol (HDL-c), low-density lipoprotein cholesterol (LDL-c), total cholesterol (TC) and triacylglycerols (TG). For the systematic review, epidemiological studies as well as RCT's investigating the effect of LGI vs HGI diets on markers for carbohydrate and lipid metabolism were used. For the systematic review on the effect of the GI on sport performance, RCT's with either a cross-over or parallel design that were published in English between January 1981 and September 2004 were used. All relevant manuscripts for the systematic reviews as well as meta-analysis were obtained through a literature search on relevant databases such as the Cochrane Central Register of Controlled Trials, MEDLINE (1981 to present), EMBASE, LILACS, SPORTDiscus, ScienceDirect and PubMed. This thesis is presented in the article format. Results and conclusions of the individual manuscripts: For the meta-analysis, literature searches identified 16 studies that met the strict inclusion criteria. Low GI diets significantly reduced fructosamine (p<0.05), HbA1c, (p<0.03), TC(p<0.0001) and tended to reduce LDL-c (p=0.06) compared to high GI diets. No changes were observed in HDL-c and TG concentrations. Results from this meta analysis, therefore, support the use of the GI concept in choosing CHO-containing foods to reduce TC and improve blood glucose control in diabetics. The systematic review combined the results of the preceding meta-analysis and results from epidemiological studies. Prospective epidemiological studies showed improvements in HDL-c concentrations over longer time periods with low GI diets vs. high GI diets, while the RCT's failed to show an improvement in HDL-c over the short-term. This could be attributed to the short intervention period during which the RCT's were conducted. Furthermore, epidemiological studies failed to show positive relationships between LDL-c and TC and low GI diets, while RCT's reported positive results on both these lipids with low GI diets. However, the epidemiological studies, as well as the RCT's showed positive results with low GI diets on markers of CHO metabolism. Taken together, convincing evidence from RCT's as well as epidemiological studies exists to recommend the use of low GI diets to improve markers of CHO as well as of lipid metabolism. 3 From the systematic review regarding the GI and sport performance it does not seem that low GI pre-exercise meals provide any advantages over high GI pre-exercise meals. Although low GI pre-exercise meals may better maintain CHO availability during exercise, low GI pre-exercise meals offer no added advantage over high GI meals regarding performance. Furthermore, the exaggerated metabolic responses from high GI compared to low GI CHO seems not be detrimental to exercise performance. However, athletes who experience hypoglycaemia when consuming CHO-rich feedings in the hour prior to exercise are advised to rather consume low GI pre-exercise meals. No studies have been reported on the GI during exercise. Current evidence suggests a combination of CHO with differing Gl's such as glucose (high GI), sucrose (moderate GI) and fructose (low GI) will deliver the best results in terms of exogenous CHO oxidation due to different transport mechanisms. Although no studies are conducted on the effect of the GI on short-term recovery it is speculated that high GI CHO is most effective when the recovery period is between 0-8 hours, however, evidence suggests that when the recovery period is longer (20-24 hours), the total amount of CHO is more important than the type of CHO. Conclusion: There is an important body of evidence in support of a therapeutic and preventative potential of low GI diets to improve markers for CHO and lipid metabolism. By substituting high GI CHO-rich with low GI CHO-rich foods improved overall metabolic control. In addition, these diets reduced TC, tended to improve LDL-c and might have a positive effect over the long term on HDL-c. This confirms the place for low GI diets in disease prevention and management, particularly in populations characterised by already high incidences of insulin resistance, glucose intolerance and abnormal lipid levels. For athletes it seems that low GI pre-exercise meals do not provide any advantage regarding performance over high GI pre-exercise meals. However, low GI meals can be recommended to athletes who are prone to develop hypoglycaemia after a CHO-rich meal in the hour prior to exercise. No studies have been reported on the effect of the GI during exercise. However, it has been speculated that a combination of CHO with varying Gl's deliver the best results in terms of exogenous CHO oxidation. No studies exist investigating the effect of the GI on short-term recovery, however, it is speculated that high GI CHO-rich foods are suitable when the recovery period is short (0-8 h), while the total amount rather than the type of CHO is important when the recovery period is longer (20-24 h). Therefore, the GI is a scientifically based tool to enable the selection of CHO-containing foods to improve markers for CHO and lipid metabolism as well as to help athletes to prepare optimally for competitions. Recommendations: Although a step nearer has been taken to confirm a place for the GI in human health, additional randomised, controlled, medium and long-term studies as well as more epidemiological studies are needed to investigate further the effect of low GI diets on LDL-c. HDL-c and TG. These studies are essential to investigate the effect of low GI diets on endpoints such as CVD and DM. This will also show whether low GI diets can reduce the risk of diabetic complications such as neuropathy and nephropathy. Furthermore, the public at large must be educated about the usefulness and application of the GI in meal planning. For sport nutrition, randomised controlled trials should be performed to investigate the role of the GI during exercise as well as in sports of longer duration such as cricket and tennis. More studies are needed to elucidate the short-term effect of the GI post-exercise as well as to determine the mechanism of lower glycogen storage with LGI meals post-exercise. / Thesis (Ph.D. (Dietetics))--North-West University, Potchefstroom Campus, 2005.

Dyslipidemia can be a comorbidity of both insulin-resistance and atherosclerosis. Hypertriglyceridemia is common in hyperglycemia and is associated with hypoalphalipoproteinemia (low HDL) and with altered nucleotide or purinergic signaling. We therefore hypothesized that extracellular nucleotides may affect hepatic lipoprotein metabolism. Our studies confirm this view and show that nucleotides regulate cellular proteolytic pathways in liver cells and thereby control lipoprotein secretion and their metabolism by hepatic lipase (HL). Treatment of liver cells with the nucleotide, adenosine diphosphate (ADP), stimulates VLDL-apoB100 and apoE secretion, but blocks HDL-apoA-I and HL secretion. ADP functions like a proteasomal inhibitor to block proteasomal degradation and stimulate apoB100 secretion. Blocking the proteosome is known to activate autophagic pathways. The nucleotide consequently stimulates autophagic degradation in liver cells and increases cellular levels of the autophagic proteins, LC3 and p62. Confocal studies show that ADP increases cellular LC3 levels and promotes co-localization of LC3 and apoA-I in an autophagosomal degradation compartment. ADP acts through the G-protein coupled receptor, P2Y13, to stimulate autophagy and block both HDL and HL secretion. Overexpression of P2Y13 increases cellular LC3 levels and blocks the induction of both HDL and HL secretion, while P2Y13 siRNA reduce LC3 protein levels and cause up to a ten-fold stimulation in HDL and HL secretion. P2Y13 gene expression regulates autophagy through the insulin receptor (IR-β). A reduction in P2Y13 expression increases the phosphorylation of IR-β and protein kinase B (Akt) >3-fold, while increasing P2Y13 expression inhibits the activation of IR-β and Akt. Experiments with epitope-labeled apoA-I and HL show that activation of purinergic pathways has no effect on the internalization and degradation of extracellular apoA-I and HL, which confirms the view that nucleotides primarily impact intracellular protein transport and degradation. In conclusion, elevated blood glucose levels may promote dyslipidemia by stimulating purinergic signaling through P2Y13 and IR-β and perturbing the intracellular degradation and secretion of both HDL and VLDL.

Dyslipidemia can be a comorbidity of both insulin-resistance and atherosclerosis. Hypertriglyceridemia is common in hyperglycemia and is associated with hypoalphalipoproteinemia (low HDL) and with altered nucleotide or purinergic signaling. We therefore hypothesized that extracellular nucleotides may affect hepatic lipoprotein metabolism. Our studies confirm this view and show that nucleotides regulate cellular proteolytic pathways in liver cells and thereby control lipoprotein secretion and their metabolism by hepatic lipase (HL). Treatment of liver cells with the nucleotide, adenosine diphosphate (ADP), stimulates VLDL-apoB100 and apoE secretion, but blocks HDL-apoA-I and HL secretion. ADP functions like a proteasomal inhibitor to block proteasomal degradation and stimulate apoB100 secretion. Blocking the proteosome is known to activate autophagic pathways. The nucleotide consequently stimulates autophagic degradation in liver cells and increases cellular levels of the autophagic proteins, LC3 and p62. Confocal studies show that ADP increases cellular LC3 levels and promotes co-localization of LC3 and apoA-I in an autophagosomal degradation compartment. ADP acts through the G-protein coupled receptor, P2Y13, to stimulate autophagy and block both HDL and HL secretion. Overexpression of P2Y13 increases cellular LC3 levels and blocks the induction of both HDL and HL secretion, while P2Y13 siRNA reduce LC3 protein levels and cause up to a ten-fold stimulation in HDL and HL secretion. P2Y13 gene expression regulates autophagy through the insulin receptor (IR-β). A reduction in P2Y13 expression increases the phosphorylation of IR-β and protein kinase B (Akt) >3-fold, while increasing P2Y13 expression inhibits the activation of IR-β and Akt. Experiments with epitope-labeled apoA-I and HL show that activation of purinergic pathways has no effect on the internalization and degradation of extracellular apoA-I and HL, which confirms the view that nucleotides primarily impact intracellular protein transport and degradation. In conclusion, elevated blood glucose levels may promote dyslipidemia by stimulating purinergic signaling through P2Y13 and IR-β and perturbing the intracellular degradation and secretion of both HDL and VLDL.

Le récepteur hépatique aux lipoprotéines LSR est impliqué dans la clairance des lipoprotéines riches en triglycérides telles que les résidus de chylomicrons pendant la phase postprandiale. La réduction de l’expression du LSR chez la souris (LSR+/-) est associée à une dyslipidémie et une lipémie postprandiale élevée. Afin de mieux comprendre la régulation de la distribution des lipides alimentaires, nous avons cherché quels étaient les facteurs pouvant affecter le niveau protéique de LSR. La leptine, hormone sécrétée par le tissu adipeux et connue pour son action d’hormone de satiété au niveau du système nerveux central, a été démontrée dans cette thèse comme modulant l’expression de LSR par la régulation de la transcription du gène lsr. La leptine est impliquée dans la régulation de la lipogénèse à travers SREBP-1. Grâce à l’utilisation d’un extrait de Garcinia cambogia contenant un inhibiteur de l’ATP citrate lyase, nous avons démontré une interaction importante entre les enzymes lipogéniques, l’expression de LSR et d’autres récepteurs lipoprotéiques, afin de maintenir un équilibre entre la synthèse de lipides endogènes et l’apport alimentaire de lipides exogènes. Soumises à un régime hyperlipidique, les souris sauvages montrent une diminution de l’expression des enzymes lipogéniques hépatiques, aggravée chez les souris LSR+/-. Ces résultats indiquent qu’il existe un mécanisme de maintien de l’équilibre entre la lipogénèse (synthèse endogène de lipides), la lipolyse (utilisation lipidique comme substrat énergétique) et le stockage de lipides à travers une forte interaction entre les enzymes lipogéniques et LSR. / The hepatic lipoprotein receptor LSR is involved in the clearance of triglyceride-rich lipoproteins including chylomicrons remnants during the post-prandial phase. Reduced LSR protein expression in mice (LSR+/-) is associated with dyslipidemia and increased postprandial lipemia; these mice exhibit increased weight gain with aging or when placed under a high-fat diet. In order to better understand the regulation of the distribution of dietary lipids, we looked for factors that could regulate LSR protein levels. Leptin is a hormone secreted by the adipose tissue that is a centrally-acting satiety factor, and was demonstrated to modulate LSR mRNA and protein expression through the modulation of transcription of the gene lsr. Leptin has been reported be involved in the control of lipogenesis through SREBP-1c. Using Garcinia cambogia extract containing an inhibitor of ATP citrate lyase, we demonstrated that there is an important link between lipogenic enzymes and LSR protein levels and with other lipoprotein receptors that provides the means to maintain a balance between endogenous lipid synthesis and dietary intake of exogenous lipids. When exogenous lipid intake is increased in the form of a high-fat diet, mice exhibited a decrease in hepatic lipogenic enzymes expression, but a deficiency of LSR led to increased lipid content in the peripheral tissues. These results suggest the presence of mechanisms for the maintenance for the balance between lipogenesis (de novo endogenous lipid synthesis), lipolysis (lipids used as energy substrate), and lipid storage through an important link between lipogenic enzymes and LSR.

AIMS: Macrophages (MPs) and vascular smooth muscle cells (VSMCs) closely interact within the growing atherosclerotic plaque. An in vitro co-culture model was established to study how MPs modulate VSMC behaviour. METHODS AND RESULTS: MPs were exposed to fluorescence-labelled-acetylated LDL (FL-acLDL) prior to co-culture with VSMCs. Fluorescence microscopy visualized first transport of FL-acLDL within 6 h after co-culture implementation. When MPs had been fed with FL-acLDL in complex with fluorescence-labelled cholesterol (FL-Chol), these complexes were also transferred during co-culture and resulted in cholesterol positive lipid droplet formation in VSMCs. When infected with a virus coding for a fusion protein of Rab5a and fluorescent protein reporter (FP) to mark early endosomes, no co-localization between Rab5a-FP and the transported FL-acLDL within VSMCs was detected implying a mechanism independent of phagocytosis. Next, expression of lysosome-associated membrane glycoprotein 1 (LAMP1)-FP, marking all lysosomes in VSMCs, revealed that the FL-acLDL was located in non-acidic lysosomes. MPs infected with virus encoding for LAMP1-FP prior to co-culture demonstrated that intact fluorescence-marked lysosomes were transported into the VSMC, instead. Xenogenic cell composition (rat VSMC, human MP) and subsequent quantitative RT-PCR with rat-specific primers rendered induction of genes typical for MPs and down-regulation of the cholesterol sensitive HMG-CoA reductase. CONCLUSION: Our results demonstrate that acLDL/cholesterol-loaded lysosomes are transported from MPs into VSMCs in vitro. Lysosomal transfer results in a phenotypic alteration of the VSMC towards a foam cell-like cell. This way VSMCs may lose their plaque stabilizing properties and rather contribute to plaque destabilization and rupture.

Magister Pharmaceuticae - MPharm / Cardiovascular diseases (CVDs) such as ischaemic heart diseases, heart failure and stroke remain a major cause of death globally. Various deep-rooted factors influence CVD development; these include but are not limited to elevated blood lipids, high blood pressure, obesity and diabetes. A considerable number of proteins are involved directly and indirectly in the transport, maintenance and elimination of plasma lipids, including high and low-density lipoprotein cholesterol (HDL-C and LDL-C). There are several mechanisms involved in the removal of LDL particles from systemic circulation. One such mechanism is associated with the gene that encodes proprotein convertase subtilisin/kexin type 9 (PCSK9), which has become an exciting therapeutic target for the reduction of residual risk of CVDs. Currently, statins are the mainstay treatment to reduce LDL-C, and a need exists to further develop more effective LDL-C-lowering drugs that might supplement statins. This study was aimed at contributing to the generation of knowledge regarding the effect of niacin in reducing LDL levels through PCSK9 interaction. The aims/objectives of this study were achieved by utilizing two approaches, which included animal intervention with niacin followed by genetic screening of five prioritized genes involved in cholesterol synthesis and regulation. For animal intervention, 16 vervet monkeys were divided into two groups of eight animals consisting of a control and an experimental (niacin) group. The control group was given a normal standard diet of pre-cooked maize meal throughout the study, while the experimental group received the same diet supplemented with 100 mg/kg of niacin (SR) for 12 weeks. During the niacin intervention, blood was collected at baseline, every four weeks during the treatment period and the end of the washout period. The collected blood was used for biochemical analysis (total cholesterol, triglycerides, LDL-C, and HDL-C) and downstream genetic applications. The second phase included the screening of PCSK9, LDLR, SREBP-2, CETP and APOB-100 using genotyping and gene expression. Niacin administration produced statistically significant increases in plasma HDL-C at fourtime points (T1, T2, T3 and T4), which resulted in an overall increase in plasma HDL-C. Additionally, niacin administration resulted in a slight reduction in LDL-C and total cholesterol levels. Furthermore, the genotyping analysis revealed 13 sequence variants identified in PCSK9, LDLR, SREBP-2, CETP and APOB-100 genes. Five of these variants were predicted to be disease-causing and correlated with gene expression patterns. Three identified PCSK9 variants (H177N, R148S, G635G) were categorized as LOF mutations, and this was supported by a decline in gene expression in animals harbouring these variants. The LDLR also had LOF variants that were the reason for its decreased mRNA expression. Additionally, SREBP-2 proved to be a key mediator of cholesterol pathways. Therefore, the findings of the study conclusively suggest that niacin does increase HDL-C and decrease LDL-C and total cholesterol. Moreover, an interaction between niacin administration and PCSK9 was observed which resulted in decreased gene expression.