D.Roger Illingworth

COLESTIPOL PLUS NICOTINIC ACID IN TREATMENT OF HETEROZYGOUS FAMILIAL HYPERCHOLESTEROLAEMIA

Thriteen patients with heterozygous familial hypercholesterolaemia (FH) were sequentially treated with: a low-cholesterol, fat-restricted diet; diet and colestipol; and diet and colestipol and nicotinic acid. Concentrations of plasma cholesterol decreased from 415 +/- 69 mg/dl on diet alone to 327 +/- 54 mg/dl on colestipol and fell to 246 +/- 49 mg/dl on the combined drug regimen. Plasma concentrations of LDL cholesterol declined 24% on colestipol; the subsequent addition of nicotinic acid resulted in a further 31% fall so that values on the combined drug regimen were 47% below those seen on diet alone. HDL cholesterol levels were similar on both the diet (40 mg/dl) and colestipol (43 mg/dl) treatment periods but increased to 53 mg/dl on the combined drug regimen. Treatment resulted in significant decreases in the LDL:HDL ratio which fell from 8.4 on diet to 3.3 on the colestipol plus nicotinic acid regimen. In most patients with heterozygous FH, combined use of a bile acid sequestrant and nicotinic acid affords the opportunity to maintain a normal lipid profile. Prolonged use of this regimen may reduce the incidence of premature coronary atherosclerosis which naturally occurs in these patients.

Independence of phospholipid and protein exchange between plasma lipoproteins in vivo and in vitro

Abstract 1. 1. Doubly labeled lipoproteins were isolated by ultracentrifugation from both squirrel monkeys and rabbits 24 h after the injection of l -[4,5- 3 H 2 ]leucine and [Me- 14 C]choline. 2. 2. Phospholipids were found to exchange in vitro between doubly labeled low and very low density lipoproteins and unlabeled high density lipoproteins. The lipoproteins were separated from the incubation media by heparin-Mn 2+ precipitation. 3. 3. The addition of a soluble protein fraction from liver stimulated phospholipid exchange up to 6-fold. The transfer and exchange of protein did not change significantly. 4. 4. The stimulatory protein fraction from liver was inhibited by SH blocking agents. This protein appears to be absent from plasma. 5. 5. After the injection of either doubly labeled low or high density lipoproteins into rabbits, isotopic equilibration of lecithin between lipoproteins was attained in less than 2 h. More than 85% of the 3 H-labeled protein label remained associated with the originally labeled lipoprotein at all times up to 7 h.

Lysolec1thin binding to human and squirrel monkey plasma and tissue components

Abstract The binding of lysolecithin to plasma and tissue components was evaluated using several methods: ultracentrifugation, reverse dialysis, and heparin-Mn 2+ precipitation of low and very low density lipoproteins. The various plasma and tissue fractions differed considerably in their binding capacities and affinities for lysolecithin. Low, very low, and high density lipoproteins bound at least 10 times more lysolecithin than albumin on a protein basis. On a molar basis the binding capacity of low density lipoproteins was 80 times that of albumin; the binding affinity was also several fold greater. The binding capacities of apo-low density and apo-high density lipoproteins were much less than those of native lipoproteins; this suggested a role of lipids in lysolecithin binding. γ-Globulin showed no tendency to bind lysolecithin. The lysolecithin binding capacity of plasma membrane fractions of a number of tissues including liver, white matter of brain, and aortic intima plus inner media was greater than that of any other tissue subtraction (resembling the values for plasma low density lipoproteins) whereas the cytosol fraction had the least attraction for lysolecithin. Studies on the comparative binding of lysolecithin by plasma and tissue proteins in a single system emphasized the high affinity of lysolecithin for lipoproteins and cellular plasma membranes.

The effects of hyperlipidemia on lbpoprotein metabolism in squirrel monkeys and rabbits

We studied the metabolism of different classes of lipoprotein in squirrel monkeys and rabbits. Lipoproteins were labeled in vivo in donor animals with (3H)leucine and (3H)cholesterol. The rate of disappearance from plasma of recipient squirrel monkeys of the protein moiety of the very low density lipoproteins was rapid, that of high density lipoproteins slow, and the rate for low density lipoproteins was intermediate. The fractional turnover of the apoprotein of low density lipoproteins was slightly reduced in hyperlipidemic monkeys, but the absolute rates of synthesis and catabolism were increased. Hyperdipidemia in rabbits resulted in a dramatic reduction in the fractional catabolic rate of low density lipoprotein apoprotein. Hyperlipidemia in the donors of biosynthetic low density lipoproteins also influenced the rates of catabolism in rabbits. We showed the cycloheximide that although there was recycling of (3H)leucine into other proteins, the reutilization of leucine from low density lipoproteins for nascent low density lipoproteins was not significant. In most tissues the ratio of cholesterol:protein radioactivity was much greater than that for plasma 24 h after administration of labeled low density lipoproteins, but the ratios for aortic intima plus inner media and for plasma low density lipoproteins were similar. The presence of atherosclerosis resulted in a large increase in the apparent uptake of low density lipoproteins by the aortas of rabbits and monkeys.

Metabolism of lipoproteins in nonhuman primates. Reduced secretion of very low density lipoproteins in squirrel monkeys with diet-induced hypercholesterolemia.

We have studied the effects of diet-induced hypercholesterolemia on the rates of secretion of triglycerides into the plasma of fasted squirrel monkeys. Two groups of monkeys were studied: control animals which were fed a semipurified diet not associated with hyperlipemia (plasma cholesterol 127 +/- 8 mg/100 ml), and animals made hypercholesterolemic (plasma cholesterol 307 +/- 31 mg/100 ml) by being fed a diet containing 25% butter and 0.5% cholesterol. After intravenous infusion of Triton WR 1339 (300 mg/kg body wt), plasma triglycerides increased almost linearly for 9-12 hours. Analysis of individual lipoproteins separated by ultracentrifugation showed that newly secreted triglycerides were present almost exclusively in the very low density lipoprotein fraction. The rates of triglyceride secretion in the hypercholesterolemic group of monkeys (5.15 +/- 0.86 mg/kg/hr) were less than half those of the control animals (10.96 +/- 2.15 mg/kg/hr). We suggest that in monkeys with diet-induced hypercholesterolemia high concentrations of plasma low density lipoproteins may inhibit the synthesis and/or secretion of their parent very low density lipoprotein molecules into the circulation.

Sterol balance in abetalipoproteinemia: Studies in a patient with homozygous familial hypobetalipoproteinemia

A new case of homozygous familial hypobetalipoproteinemia is reported in a 16-yr-old girl. Apoprotein B was absent from plasma and the patient had acanthocytes and steatorrhea, but minimal neurologic dysfunction. Total body cholesterol synthesis was assessed intermittently over a 30-mo period by sterol balance techniques. The rate of synthesis of cholesterol was higher (15.0 +/- 2.9 mg/kg/day) in the patient (8.3 +/- 0.4 mg/kg/day than in 3 control children, p less than 0.005). Bile acid synthesis was similar (4.6 +/- 1.8 versus 4.0 +/- 1.7 mg/kg/day) in the patient and controls, but total body sterol synthesis was significantly higher (19.6 +/- 3.0 versus 12.2 +/- 2.0, p less than 0.005). The absorption of orally administered [1,2,(3)H] cholesterol in the patient was low and less than 0.5% of the label appeared in the total plasma volume at all times up to 48 hr. Estimates of the extent that malabsorption of biliary cholesterol contributes to the enhanced excretion of neutral sterols in this case indicate that all of the increase can be explained on this basis. Thus, although the mechanisms for the increased sterol synthesis in this case may relate to the absence of chylomicrons and low density lipoproteins in plasma, the magnitude of the increase can be fully explained on the basis of a compensatory mechanism to maintain cholesterol homeostasis in the face of enhanced fecal losses.

Metabolism of lysolecith1n in vivo and in vitro with particular emphasis on the arterial wall

Abstract Lysolecithin labeled with [Me- 3 H]choline and [I- 14 C]palmitate was injected intravenously into squirrel monkeys or was incubated with aortas of squirrel monkeys or rabbits in vitro. Injected lysolecithin rapidly appeared in all tissues where it was acylated or hydrolyzed. In most tissues 3 H : 14 C ratios in lysolecithin and lecithin were the same as those for the injected lysolecithin. Nevertheless some labeled palmitate was found in position 2 of lecithin. In many tissues the ratio of 3 H in water-soluble constituents (glycerophosphorylcholine, phosphorylcholine, choline, and betaine) to 14 C in free fatty acids and glycerides was the same as that for injected lysolecithin. In the aorta wall, plasma, skeletal, and cardiac muscle there were very low ratios due to the absence of water-soluble 3 H. When pieces of squirrel monkey aorta were incubated with labeled lysolecithin, radioactivity was present in lysolecithin, lecithin, and free fatty acids of the tissue and incubation medium, but water-soluble 3 H (mostly glycerophosphorylcholine) was only in the incubation medium. The presence of atherosclerosis had a profound effect on the pre- and postincubation levels and on net uptake of lysolecithin in the intima plus inner media but not in the outer media. Incubation in a mmdium free of lysolecithin resulted in a slight fall in lysolecithin concentrations in the aorta. Lysolecithin was fairly uniformly distributed in subfractions of homogenates of atherosclerotic intima plus inner media but was most prevalent in the plasma membrane and 13 · 10 7 × g . min supernatant fractions.

Metabolic interrelationships between the lipids of very low, low and high density lipoproteins in the squirrel monkey

Abstract We have studied sequential changes in the concentrations of the lipid moieties of plasma lipoproteins after a single infusion of Triton WR 1339 (300 mg/kg) into fasting squirrel monkeys. The constituent lipids of very low density lipoproteins all increased linearly, reached a maximum after 12 h, and then declined. Decreases in the free cholesterol, phospholipid, and, to a lesser extent, cholesterol esters of very low density lipoproteins were followed by sequential increases in the concentrations of these lipids in intermediate ( d 1.006−1.019) and low density lipoproteins and were consistent with a precursor—product relationship. Lecithin: cholesterol acyltransferase activity was inhibited 86–96% in the plasma of Triton-treated monkeys. After infusion of [ 3 H] cholesterol ester-labeled high density lipoprotein into Triton-treated monkeys, the specific activity of this lipid in high density lipoproteins consistently exceeded that of very low density lipoproteins. These observations suggest that most of the esterified cholesterol of very low density lipoproteins which is newly formed after Triton infusion enters plasma as a native constituent of this lipoprotein but that lesser quantities may be derived from transfer from high density lipoproteins.

Changes in brain and sciatic nerve composition with development of the rhesus monkey (macaca mulatta)

Summary We determined the composition of the brain and sciatic nerves of 135 rhesus monkeys (Macaca mulatta) ranging from 58 days gestational age to over 10 years. The period of most rapid increase in size is prior to birth, and at birth the brain is about 70% of adult size. The patterns of change in weight, protein, and DNA of the cerebellum indicate that this area matures later and grows more rapidly than the remainder of the brain. The concentrations (per gram wet weight) of protein increase at all sites in the brain, but those of DNA decrease during the period of most rapid growth. The concentrations of all lipids, particularly those most characteristic of myelin, were much higher in pons, cervical cord, and sciatic nerve than in cortical gray matter. The concentration of those lipids most typical of myelin were essentially absent from the pons at 100 days of gestation, reached more than one-half of adult values at birth, but continued to increase after one year. Cerebrosides and sulfatides most nearly followed that pattern in the pons. The concentrations of sphingomyelin, plasmalogen forms of phosphatidylethanolamine, and cholesterol were the next best indicators of myelination, whilst the concentrations of combined phospholipids, lecithin, phosphatidylserine, and diacyl phosphatidylethanolamine changed less than the first two classes of compounds.

Triacylglycerol and very low density lipoprotein secretion into plasma of squirrel monkeys

We determined the effects of varying the types and level of dietary fat and cholesterol on the increase in plasma total triacylglycerol concentrations after injection of Triton WR-1339, an inhibitor of lipoprotein lipase, into monkeys that had been subjected to an overnight fast. The monkeys that had been treated with Triton WR-1339 were then given a test meal by intragastric intubation. Dietary cholesterol, high levels of fat and saturated fat in the habitual diet reduced the rate of release of triacylglycerol to plasma in the fasted monkey. We also determined the changes in protein and lipid concentrations of the different lipoprotein fractions. The injection of Triton WR-1339 resulted in a linear increase with time in the concentration of protein and triacylglycerol in the very low density (chylomicron-free and d less than 1.006) lipoproteins, but there was an increase in the ratio of traicylglycerol to protein in that fraction. Most of the increase (96%) in very low density protein was in the B protein. Regardless of the habitual diet, a test meal accentuated the rate of triacylglycerol appearance in whole plasma and in the very low density lipoproteins of Triton WR-1339-treated monkeys, and the rate of increase of the protein component after feeding was slightly higher. Thus the administration of a meal to the fasted Triton WR-1339-treated squirrel monkey further increased the proportion of triacylglycerol in very low density lipoproteins. Although dietary cholesterol and saturated fat in the habitual diet depressed the rate of increase in very low density triacylglycerol during fasting, the rate of protein synthesis was not significantly affected. After administration of a test meal the rates of increase in triacylglycerol and protein in the very low density lipoproteins were similar for monkeys from the different diet groups. Triton WR-1339 administration caused a slight and progressive increase in the intermediate density (d 1.006-1.019) lipoproteins and a marked and progressive decrease in the low density (d 1.019-1.063) lipoproteins. There was an immediate (by 5 min) drop of 70% or more in high density (d 1.063-1.21) lipoprotein protein, but the lipids except triacylglycerol remained unchanged. There was a decrease in both the A (the major fraction) and C proteins. The rates of very low density B protein secretion were comparable to the rates of low density lipoprotein catabolism that had been previously demonstrated for this species.