Monica Ishola

APOLIPOPROTEINS (a), AI, AND B AND PARENTAL HISTORY IN MEN WITH EARLY ONSET ISCHAEMIC HEART DISEASE

Middle-aged men who had had a myocardial infarction were compared with controls matched for social background, age, cigarette-smoking, blood pressure, and alcohol consumption. Serum cholesterol, triglycerides, very low density lipoprotein, low density lipoprotein, high density lipoprotein (HDL), HDL2 and HDL3 cholesterol, and serum apolipoproteins (apo) (a), AI, and B were measured. Discriminant analysis showed that the combination of these variables that best distinguished patients from controls was provided by apo AI and apo B and a knowledge of parental history of early cardiac death, the most discriminating single factor being apo B. No other variable contributed more than these. Apo (a), however, could be substituted for parental history, which had a major influence on the serum concentration of apo (a). Apo (a) concentration accounted for much of the familial predisposition to cardiac ischaemia. These findings may prove valuable in the clinical assessment of genetic susceptibility to myocardial infarction. They also support the hypothesis that serum apo (a) concentration is a genetic trait that predisposes to arterial thrombosis. Apo B emerged as the main lipoprotein determinant of coronary disease risk.

Influence of proteinuria on vascular disease, blood pressure, and lipoproteins in insulin dependent diabetes mellitus

Patients with insulin dependent diabetes mellitus who develop proteinuria may die prematurely, whereas those who do not develop this complication have a comparatively normal life span. The excess mortality in diabetics with proteinuria is from cardiovascular as well as renal disease, but the reason is unclear. Risk factors for vascular disease were therefore assessed in 22 insulin dependent diabetics with proteinuria, but not renal failure, who were matched for sex, age, duration of diabetes, and glycated haemoglobin (HbA1) values with a similar number who had normal urinary albumin excretion rates. Macrovascular disease (ischaemic heart disease and peripheral vascular disease) was present in 10 patients with proteinuria but in only three with normal albumin excretion rates, and proliferative retinopathy was detected in 11 and four patients in the two groups. There was no significant excess of smokers in the group with proteinuria. Blood pressure was, however, higher in the patients with proteinuria--mean systolic pressure 161 (SD 18) mm Hg compared with 135 (19) mm Hg (95% confidence interval of difference between means 15 to 38 mm Hg); mean diastolic pressure 90 (SD 12) mm Hg compared with 79 (15) mm Hg (confidence interval 3 to 19 mm Hg). The concentration of serum high density lipoprotein (HDL) cholesterol isolated by precipitation was lower in the patients with proteinuria (confidence interval 0.02 to 0.41 mmol/l). Their concentration of HDL2 cholesterol isolated by ultracentrifugation was also decreased (confidence interval 0.02 to 0.40 mmol/l), whereas HDL3 cholesterol tended to be increased (confidence interval -0.01 to 0.23 mmol/l). There was also a trend for serum cholesterol concentrations to be higher in the presence of proteinuria (confidence interval -0.39 to 1.20 mmol/l). The aggregation of risk factors for atherosclerosis in insulin dependent diabetes mellitus complicated by proteinuria helps to explain the increased prevalence of ischaemic heart disease and peripheral vascular disease reported in these patients. Early renal disease in insulin dependent diabetes may have an important role in hypertension and altered lipoprotein metabolism.

Serum lipoprotein(a) in patients heterozygous for familial hypercholesterolemia, their relatives, and unrelated control populations.

Serum lipoprotein(a) (Lp[a]) levels were significantly higher in 89 patients with heterozygous familial hypercholesterolemia (FH) (geometric mean, 22.7 mg/dl) than in 109 normocholesterolemic controls (10.0 mg/dl, p less than 0.05) and 40 controls (9.1 mg/dl, p less than 0.05) with similarly elevated low density lipoprotein cholesterol levels due to other primary hypercholesterolemias. To provide further evidence that the increased serum Lp(a) concentration was due to inheritance of the FH gene, 24 unaffected first-degree relatives were compared with their FH probands. Serum Lp(a) in affected individuals was significantly greater than in unaffected relatives (geometric means, 26.5 versus 13.7 mg/dl, respectively; p less than 0.05). Family membership exerted an effect on serum Lp(a) concentrations, indicating that other genetic influences were also operating, as is known to be the case in general populations. Serum Lp(a) in 30 of the FH patients, who had coronary heart disease, was not significantly different from 30 age- and sex-matched controls with FH but with coronary heart disease (geometric means, 23.6 versus 24.7 mg/dl, respectively). FH is associated with an increase in serum Lp(a). Elevated serum Lp(a) concentrations should probably now be regarded as a component of the clinical syndrome of FH. However, within our FH population Lp(a) did not distinguish those with clinically overt coronary heart disease from those without the disease.

Investigation of lipid transfer in human serum leading to the development of an isotopic method for the determination of endogenous cholesterol esterification and transfer

The rate at which radioactivity appeared in cholesteryl esters (CE) in whole serum and in very low density lipoproteins (VLDL) and low density lipoproteins (LDL) when radioactively labelled free cholesterol (FC) was incubated with serum was investigated. At 4 degrees C equilibration of radioactive FC with native FC occurred, but there was no conversion to CE. At 37 degrees C CE mass increased in parallel with radioactivity in CE both in whole serum and VLDL/LDL. Incubation at 37 degrees C with an inhibitor of lecithin cholesterol acyl transferase (LCAT) abolished the increase in the total CE radioactivity and mass in serum. Transfer of CE from high density lipoprotein (HDL) to VLDL/LDL, however, continued to occur. An assay for LCAT and for cholesteryl ester transfer protein (CETP) was developed, which employed the increases in radioactive CE in whole serum and VLDL/LDL during a single incubation as indices of LCAT and CETP activity, respectively. Determination of the initial serum FC concentration allowed the expression of these activities in nmol/ml per h. References ranges were established in 62 fasting normolipidaemic men and women and increases in both LCAT and CETP were found following a fatty meal. The experiments thus provided further information about the carrier-mediated transfer of CE from its site of esterification on HDL to VLDL/LDL and formed the basis of a relatively simple assay, which has advantages over previously published methods and which may be used in clinical and epidemiological studies to elucidate the role of CETP and LCAT in atherosclerosis.

LIPOPROTEIN ABNORMALITIES IN INSULIN-DEPENDENT DIABETES MELLITUS

Despite the increased risk of atherosclerosis in diabetes mellitus, levels of serum cholesterol, triglycerides, low-density-lipoprotein (LDL) cholesterol, and high-density-lipoprotein (HDL) cholesterol were similar in 57 men with insulin-dependent diabetes mellitus (IDDM) and 81 non-diabetic controls. However, substantially lower serum levels of apolipoprotein B, the principal apolipoprotein of LDL, and a concomitant increase in the cholesterol-loading of apolipoprotein B were found in IDDM. The likely changes in LDL density and particle size resulting from this compositional abnormality might lead to accelerated atherogenesis analogous to that seen in type III hyperlipoproteinaemia. In addition, there was an increase in the concentration of cholesterol in the smaller, denser, HDL3 subfraction of serum HDL in IDDM.

An investigation of the role of lecithin: cholesterol acyltransferase and triglyceride-rich lipoproteins in the metabolism of pre-beta high density lipoproteins

Small high density lipoproteins (HDL) with pre-beta electrophoretic mobility (pre-beta HDL) have recently been shown to be the primary acceptor of cholesterol from cultured cells. We studied the metabolism of these particles by incubating serum at 37 degrees C in the presence and absence of active lecithin: cholesterol acyltransferase (LCAT). We found that the serum pre-beta HDL concentration decreased in the presence of LCAT, but when LCAT was inhibited the concentration remained constant, or increased, depending on the method of inhibition. This suggests that pre-beta HDL are a substrate for LCAT. We also found a significant negative correlation between levels of LCAT activity and pre-beta HDL in 28 fasting healthy subjects, this provides evidence that the activity of LCAT regulates, at least in part the concentration of these particles in vivo. During the early phase of incubation there was a more rapid decrease in pre-beta HDL concentration which was greater in the post-prandial than fasting state. When we infused a triglyceride emulsion into 6 subjects or added this to serum in vitro we observed an immediate fall in pre-beta HDL concentration. These findings suggest that pre-beta HDL interact with triglyceride rich particles. We investigated the origin of pre-beta HDL from blood lipoproteins during their lipolysis, in vivo and in vitro and found that they were produced from both triglyceride-rich and high-density lipoproteins. Formation from triglyceride-rich lipoproteins was evident by the rise in pre-beta HDL concentration during heparin-induced lipolysis when fasting and post-prandially. The rise was greater post-prandially and particularly marked in 4 hypertriglyceridaemic patients following a fat load. Generation from alpha-HDL was evident when we prolonged the action of the heparin-released lipases by incubation of post-heparin sera at 37 degrees C. Continued formation of pre-beta HDL occurred at an equal rate in the fasting and post-prandial samples suggesting release by lipolysis of alpha-HDL. This was supported by the action of lipases on serum and isolated HDL in vitro, where triglyceride lipase rather than phospholipase activity appeared more effective at releasing pre-beta HDL. These findings suggest binding and release of pre-beta HDL by triglyceride-rich lipoproteins depending on the prandial state and production from alpha-HDL through the action of lipases.

Lipoprotein (a) and Microvascular Disease in Type 1 (Insulin-dependent) Diabetes

The influence of albuminuria and proliferative retinopathy on concentrations of serum lipoprotein (a) was examined cross‐sectionally in 90 Type 1 diabetic patients. Concentrations of lipoprotein (a) were less in those with normoalbuminuria (90 (8–882) (median (range)) U l−1) than in those with micro‐ or macro‐albuminuria (137 (19–1722) U l−1, p < 0.05). The prevalence of patients whose lipoprotein (a) concentrations were greater than 200 U l−1 was also greater (45% vs 24%, p = 0.03) among patients with albuminuria, but no difference was found between the microalbuminuric and macroalbuminuric groups (53 and 41%, respectively), or between those with or without proliferative retinopathy. The present finding that lipoprotein (a) concentrations may be increased at an early stage of diabetic renal disease may in part account for the excess ischaemic heart disease associated with diabetic nephropathy.

Placebo‐controlled Trial of the Effects of Guar Gum and Metformin on Fasting Blood Glucose and Serum Lipids in Obese, Type 2 Diabetic Patients

Nineteen obese patients with Type 2 diabetes mellitus were treated for periods of 3 months with placebo, guar gum (5 g three times daily) and metformin (500 mg three times daily) in a randomized double‐blind, double‐placebo, cross‐over study. Both active agents decreased fasting blood glucose from 11.4 ± 3.7 mmol l−1 (mean ± SD) to 8.6 ± 2.8 mmol l−1 on metformin (p<0.001) and to 9.5 ± 3.9 mmol l−1 on guar gum (p<0.01). Metformin significantly reduced the very low density lipoprotein (VLDL) cholesterol concentration from 0.62 (+ 0.73, − 0.34) mmol l−1 (geometric mean (+ SD, ‐ SD)) to 0.43 (+ 0.58, − 0.25) mmol l−1, (p<0.02), but unless hyperlipidaemia was present there were no changes in other serum lipid or lipoprotein levels. In patients with serum cholesterol > 6.5 mmol l−1 decreases in serum triglycerides from 3.29 (+ 3.27, − 1.64) to 2.46 (+ 2.55, − 1.25) mmol l−1 (p<0.02) occurred with metformin. In these patients guar gum produced a reduction in serum cholesterol (from 7.70 ± 0.90 to 6.41 ± 1.11 mmol l−1, p<0.01) due to an effect on low density lipoproteins. These differential effects may be important in planning therapy when hyperlipidaemia accompanies Type 2 diabetes.

Influence of early diabetic nephropathy on very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL) composition.

The procedure of discontinuous gradient ultracentrifugation (DGU) was used to characterize the influence of early diabetic nephropathy on the composition of very low density lipoprotein (VLDL, flotation density 60-400 Svedberg (Sf) units), low density lipoprotein (LDL, flotation density 0-12 Sf) and subfractions of intermediate density lipoprotein (IDL1 and IDL2, 20-60 and 12-20 Sf, respectively). Forty-six subjects with type 1 (insulin-dependent) diabetes and serum creatinine, less than 140 mumol/l were studied, of whom 23 consistently had normal rates of albumin excretion (AER less than 15 micrograms/min), and 23 had persistent albuminuria (AER 20.0-960.6 micrograms/min). The two groups were similar with respect to total serum lipids, glycaemic control, age and body mass. The composition (lipid, protein and phospholipid) and mass of VLDL, LDL and IDL2 was not appreciably altered by early nephropathy, but free and total cholesterol concentration in IDL1 (Sf 20-60) was increased (total cholesterol 0.68 (0.09) (mean (SE)) vs. 0.47 (0.07) mmol/l, and free cholesterol 0.27 (0.04) vs. 0.17 (0.03) mmol/l, both P less than 0.05). The explanation of these findings was probably an accumulation in the circulation of the remnants of chylomicron metabolism and/or intermediates in the conversion from VLDL to IDL1. In addition, there was a decrease in serum high density lipoprotein (HDL) cholesterol in early nephropathy (1.27 (0.06) vs. 1.38 (0.10) mmol/l, P less than 0.05), due to a decrease in the HDL2 cholesterol subfraction (P less than 0.05). These findings may in part explain the increased risk of premature atherosclerosis associated with the development of albuminuria.

Double-blind Placebo-controlled Study of the Effects of Bezafibrate on Blood Lipids, Lipoproteins, and Fibrinogen in Hyperlipidaemic Type 1 Diabetes Mellitus

The effects of bezafibrate 400 mg day−1 or placebo administered for 3 months, were compared in 36 patients with stable Type 1 diabetes and hypercholesterolaemia and/or hypertriglyceridaemia. Baseline characteristics of the 17 bezafibrate‐ and 19 placebo‐treated patients were comparable in most respects with the exception of concentrations of fasting serum triglycerides and blood glucose which were lower (NS) and plasma fibrinogen which were higher (p < 0.05), in those later treated with bezafibrate. Serum cholesterol concentrations decreased after 3 months bezafibrate treatment (from 7.1 (0.2) (SE) to 6.3 (0.3) mmol l−1, p < 0.05), predominantly due to a reduction in low density lipoprotein (LDL) cholesterol (from 4.8(0.3) to 4.2(0.3) mmol l−1, p < 0.05). Over the same period bezafibrate reduced serum triglycerides from 1.78 (95% CI 1.23‐2.57) to 1.26(1.02‐2.09) mmol l−1 (p < 0.05), and plasma fibrinogen from 4.1(0.2) to 2.9(0.2) g l−1, p < 0.001. Serum apolipoprotein B and apolipoprotein (a) showed no statistically significant changes. Overall there was no change in high density lipoprotein (HDL) cholesterol. However, in patients who were initially hypertriglyceridaemic there was significant increase in the cholesterol content of HDL and the HDL2‐cholesterol subfraction (both p < 0.05). After 3 months treatment with bezafibrate, fasting blood glucose levels were reduced from 8.5(1.1) to 6.4(0.7) mmol l−1, p < 0.05, without any change in glycosylated haemoglobin (9.2(0.4) to 9.1(0.5) %). At the end of the 3 months active treatment period, significant differences were recorded between the bezafibrate‐ and placebo‐treated groups for the following variables: fasting blood glucose (p < 0.001), very low density lipoprotein (VLDL) cholesterol, serum triglycerides, apolipoprotein B, HDL2‐and HDL3‐cholesterol and plasma fibrinogen (all p < 0.05). It is concluded that in Type 1 diabetic patients with hyperlipidaemia, bezafibrate is an effective serum lipoprotein modifying agent, and has a potentially important effect in reducing fibrinogen levels.