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Biomedical subjects

C Packard

Publications and source records attributed to C Packard.

13 recordsLinked to original sources
PubMed2006

Overproduction of large VLDL particles is driven by increased liver fat content in man.

AIMS/HYPOTHESIS: We determined whether hepatic fat content and plasma adiponectin concentration regulate VLDL(1) production. METHODS: A multicompartment model was used to simultaneously determine the kinetic parameters of triglycerides (TGs) and apolipoprotein B (ApoB) in VLDL(1) and VLDL(2) after a bolus of [(2)H(3)]leucine and [(2)H(5)]glycerol in ten men with type 2 diabetes and in 18 non-diabetic men. Liver fat content was determined by proton spectroscopy and intra-abdominal fat content by MRI. RESULTS: Univariate regression analysis showed that liver fat content, intra-abdominal fat volume, plasma glucose, insulin and HOMA-IR (homeostasis model assessment of insulin resistance) correlated with VLDL(1) TG and ApoB production. However, only liver fat and plasma glucose were significant in multiple regression models, emphasising the critical role of substrate fluxes and lipid availability in the liver as the driving force for overproduction of VLDL(1) in subjects with type 2 diabetes. Despite negative correlations with fasting TG levels, liver fat content, and VLDL(1) TG and ApoB pool sizes, adiponectin was not linked to VLDL(1) TG or ApoB production and thus was not a predictor of VLDL(1) production. However, adiponectin correlated negatively with the removal rates of VLDL(1) TG and ApoB. CONCLUSIONS/INTERPRETATION: We propose that the metabolic effect of insulin resistance, partly mediated by depressed plasma adiponectin levels, increases fatty acid flux from adipose tissue to the liver and induces the accumulation of fat in the liver. Elevated plasma glucose can further increase hepatic fat content through multiple pathways, resulting in overproduction of VLDL(1) particles and leading to the characteristic dyslipidaemia associated with type 2 diabetes.

Adipose Tissue↗
PubMed2002

Management of hypercholesterolaemia in the patient with diabetes.

Coronary heart disease (CHD) is the leading cause of death in patients with type 2 diabetes. The hyperglycaemia that characterises this disease is often accompanied by a cluster of other risk factors, such as dyslipidaemia and hypertension, and effective management of the patient with diabetes requires treatment directed at correcting all of the abnormalities that increase cardiovascular risk. Approximately 90% of patients with diabetes have type 2 disease, and dyslipidaemia in these patients is characterised by elevated plasma triglycerides and very-low-density lipoproteins (VLDL), by reduced high-density lipoprotein cholesterol (HDL-C), and by a shift in LDL distribution towards small, dense particles. All of these lipid abnormalities are important risk factors for CHD. Retrospective subgroup analysis and prospective studies have shown that lipid-lowering therapy can slow the progression of atherosclerosis and reduce the risk for cardiovascular events in patients with diabetes, and both the National Cholesterol Education Program Adult Treatment Panel III and American Diabetes Association have established aggressive treatment goals for lipid-lowering therapy in these patients. All of the major medications used to treat hyperlipidaemia in other populations (niacin, fibrates, bile acid sequestrants and statins) have been used effectively to improve the plasma lipid profile in patients with diabetes. Statins are generally accepted as first-line treatment for these patients, although fibrates also have an important role in patients with pronounced hypertriglyceridaemia. Statins significantly reduce low-density lipoprotein cholesterol (LDL-C) in a broad range of patients. These agents also have substantial effects on plasma triglycerides and, in patients with hypertriglyceridaemia, lower very-low-density lipoprotein cholesterol (VLDL-C) to approximately the same extent as LDL-C. In this regard, the new agent rosuvastatin has been shown, in recent trials, to produce greater decreases in these lipoproteins than currently marketed compounds. Aggressive use of agents that attack the lipid abnormalities characteristic of patients with type 2 diabetes has the potential to significantly reduce CHD risk in these individuals.

Anticholesteremic Agents↗
PubMed2002

High density lipoprotein: guardian of the vascular system?

The role of low-density lipoprotein in the development of coronary heart disease (CHD) is well recognised. There is also growing evidence that high-density lipoprotein cholesterol (HDL-C) is a powerful inverse predictor for premature CHD and that maintaining a high HDL-C level may guard against atherosclerosis. Patients with low HDL-C levels often also have central obesity, insulin resistance and other features of the metabolic syndrome. This syndrome is both increasingly common and strongly implicated in the growing worldwide epidemic of type 2 diabetes. HDL-C may be increased by lifestyle changes, e.g. weight loss, physical activity and smoking cessation. Pharmacological agents such as fibrates, niacin and statins have also been shown significantly to elevate HDL-C. Although current guidelines are beginning to recognise the protective role of HDL-C level in preventing coronary events, HDL-C should be adopted soon as a target for intervention in its own right.

Animals↗
PubMed2000

Effect of pravastatin on coronary disease events in subgroups defined by coronary risk factors: the Prospective Pravastatin Pooling Project.

BACKGROUND: Previous trials have had insufficient numbers of coronary events to address definitively the effect of lipid-modifying therapy on coronary heart disease in subgroups of patients with varying baseline characteristics. METHODS AND RESULTS: The data from 3 large randomized trials with pravastatin 40 mg were pooled and analyzed with the use of a prospectively defined protocol. Included were 19 768 patients, 102 559 person-years of follow-up, 2194 primary end points (coronary death or nonfatal myocardial infarction), and 3717 expanded end points (primary end point, CABG, or PTCA). Pravastatin significantly reduced relative risk in younger (<65 years) and older (>/=65 years) patients, men and women, smokers and nonsmokers, and patients with or without diabetes or hypertension. The relative effect was smaller, but absolute risk reduction was similar in patients with hypertension compared with those without hypertension. Relative risk reduction was significant in predefined categories of baseline lipid concentrations. Tests for interaction were not significant between relative risk reduction and baseline total cholesterol (5% to 95% range 177 to 297 mg/dL, 4.6 to 7.7 mmol/L), HDL cholesterol (27 to 58 mg/dL, 0.7 to 1.5 mmol/L), and triglyceride (74 to 302 mg/dL, 0.8 to 3.4 mmol/L) concentrations, analyzed as continuous variables. However, for LDL cholesterol, the probability values for interaction were 0.068 for the prespecified primary end point and 0.019 for the expanded end point. Relative risk reduction was similar throughout most of the baseline LDL cholesterol range (125 to 212 mg/dL, 3.2 to 5.5 mmol/L) with the possible exception of the lowest quintile of CARE/LIPID (<125 mg/dL) (relative risk reduction 5%, 95% CI 19% to -12%). CONCLUSIONS: Pravastatin treatment is effective in reducing coronary heart disease events in patients with high or low risk factor status and across a wide range of pretreatment lipid concentrations.

Aged↗
PubMed2000

The role of small, dense low density lipoprotein (LDL): a new look.

Plasma low density lipoprotein (LDL) plays a central role in atherogenesis, and elevated levels of LDL are associated with an increased risk of coronary heart disease (CHD). Studies have now revealed that LDL is structurally heterogeneous, based on its size and density. Patients with combined hyperlipidemia exhibit a lipid profile - the so-called atherogenic lipoprotein phenotype - that is associated with elevated triglyceride levels, low levels of high density lipoprotein and a preponderance of atherogenic, small, dense LDL particles. Such individuals are at an increased risk of CHD events, regardless of their total LDL circulating mass. Evidence suggests that when plasma triglycerides exceed a critical threshold of approximately 133 mg/dl (1.5 mmol/l), this favours the formation of small, dense LDL from larger, less dense species. Lipid-lowering agents that are capable of lowering triglyceride levels below this threshold value will cause a shift to a less dense and, therefore, less atherogenic LDL profile. This effect has been demonstrated for the HMG-CoA reductase inhibitor atorvastatin which, in addition to its ability to markedly decrease the total LDL circulating mass, can also shift the LDL profile towards less dense, larger species. This suggests that atorvastatin may also affect the atherogenic lipoprotein phenotype found in patients with combined hyperlipidemia.

Atorvastatin↗
PubMed2000

Blood rheology, cardiovascular risk factors, and cardiovascular disease: the West of Scotland Coronary Prevention Study.

The West of Scotland Coronary Prevention Study (WOSCOPS) showed that pravastatin reduced the risk of coronary heart disease (CHD) events in 6,595 middle-aged hypercholesterolaemic men aged 45-64 years without prior myocardial infarction followed for an average of 4.9 years. We hypothesised prospectively (a) that baseline levels of haemorheological variables were related to baseline and incident CHD and to mortality; and (b) that reduction in lipoproteins by pravastatin would lower plasma and blood viscosity, a potential contributory mechanism to CHD events. We therefore studied plasma and blood viscosity, fibrinogen, haematocrit, and blood cell counts at baseline and 1 year. At baseline, plasma and blood viscosity were related to risk factors, CHD measures, and claudication. On univariate analysis, baseline levels of all rheological variables (except platelet count) were related to incident CHD; CHD mortality; and total mortality. On multivariate analysis including baseline CHD and risk factors, plasma and blood viscosity, haematocrit and white cell count each remained significantly associated with incident CHD; while fibrinogen remained an independent predictor of mortality (all p < 0.03). After one year, lipoprotein reduction by pravastatin was associated with significant reductions (about one quarter of a standard deviation) in plasma viscosity (mean difference 0.02 mPa.s, p <0.001) and in blood viscosity (mean difference 0.06 mPa.s, p<0.001), but was not associated with significant changes in other rheological variables. We therefore suggest that pravastatin therapy, which reduces elevated lipoproteins in hypercholesterolaemic men, may lower risks of CHD and mortality partly by lowering plasma and blood viscosity. Further studies are required to test this hypothesis.

Anticholesteremic Agents↗
PubMed1998

In vivo studies of VLDL metabolism and LDL heterogeneity.

The association between plasma triglyceride levels and coronary heart disease may be explained by the metabolism of triglyceride-apolipoprotein (apo) B100-containing lipoproteins to an atherogenic low density lipoprotein (LDL) fraction. Apo B100 is secreted into the plasma compartment mainly as large triglyceride-rich very low density lipoprotein1 (VLDL1) particles and smaller, comparatively cholesterol ester-rich VLDL2. Both forms of VLDL undergo stepwise delipidation to LDL. A dual tracer VLDL technique has investigated the metabolism of apo B-containing lipoproteins and established that about one-third of the VLDL2 pool is transferred to LDL compared with less than 20% of VLDL1. In addition, LDL derived from VLDL1 has a longer plasma residence time than LDL from VLDL2. A series of experiments using a stable isotope tracer technique showed that the LDL fractional catabolic rate was inversely correlated with plasma triglyceride concentration, which itself is largely determined by VLDL1 concentration. In subjects with triglyceride concentrations between 150-200 mg. dl-1 (1.36 - 2.26 mmol .1(-1)), the prevailing small dense LDL is derived to a larger extent from VLDL precursors, rather than entering the plasma as LDL or IDL, and catabolized more slowly than the large buoyant LDL prevailing in subjects with lower triglyceride levels. These two independent methods show that triglyceride-rich VLDL is the precursor of slowly catabolized LDL particles which constitute an atherogenic lipoprotein subfraction.

Apolipoprotein B-100↗