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Biomedical subjects

C J Packard

Publications and source records attributed to C J Packard.

At least 181 records · Page 10Linked to original sources
PubMed1985

A monoclonal-antibody-based immunoradiometric assay for apoprotein B in low-density lipoprotein.

Five different mouse monoclonal antibodies were raised against apoprotein B, the major protein in human low-density lipoproteins (LDL). Competitive binding studies suggested that these antibodies recognized four different epitopes on the lipoprotein particle. All antibodies bound to very-low-density and intermediate-density lipoproteins, which are the metabolic precursors of LDL and also contain apoprotein B. One antibody (P1C1) displayed a relative specificity for apoprotein B in LDL as compared with that in very-low-density lipoprotein and was used as a radiolabeled first antibody in an immunoradiometric assay for this lipoprotein. Measurements, either on isolated LDL or directly on plasma samples, demonstrated that this assay provides a rapid and precise method of quantification.

Animals↗
PubMed1985

Effects of 1,2-cyclohexanedione modification on the metabolism of very low density lipoprotein apolipoprotein B: potential role of receptors in intermediate density lipoprotein catabolism.

The conversion of very low density (VLDL) to low density lipoproteins (LDL) is a two-step process. The first step is mediated by lipoprotein lipase, but the mechanism responsible for the second is obscure. In this study we examined the possible involvement of receptors at this stage. Apolipoprotein B (apoB)-containing lipoproteins were separated into three fractions, VLDL (Sf 100-400), an intermediate fraction IDL (Sf 12-100), and LDL (Sf 0-12). Autologous 125I-labeled VLDL and 131I-labeled 1,2-cyclohexanedione-modified VLDL were injected into the plasma of four normal subjects and the rate of transfer of apoB radioactivity was followed through IDL to LDL. Modification did not affect VLDL to IDL conversion. Thereafter, however, the catabolism of modified apoB in IDL was retarded and its appearance in LDL was delayed. Hence, functional arginine residues (and by implication, receptors) are required in this process. Confirmation of this was obtained by injecting 125I-labeled IDL and 131I-labeled cyclohexanedione-treated IDL into two additional subjects. Again, IDL metabolism was delayed by approximately 50% as a result of the modification. These data are consistent with the view that receptors are involved in the metabolism of intermediate density lipoprotein.

Adult↗
PubMed1984

Low-density lipoprotein metabolism in mice with soft tissue tumours.

This study examines the potential value of low-density lipoprotein (LDL) as a vehicle for directing cytotoxic drugs to tumour cells in mouse model systems. Control and MAC 13 tumour-bearing NMRI mice were injected with tracer doses of 125I-labelled native and cyclohexanedione-modified 131I-labelled LDL. 18 h later the animals were killed and the radioactivities assimilated by various tissues were measured relative to plasma activity at the time of death. These values were used to calculate specific tissue receptor-mediated LDL uptake. All tissues expressed receptors but the liver and adrenal gland were particularly active. In tumour-inoculated animals, the neoplastic lesions were second only to liver in their net assimilation of LDL. CFLP mice bearing virus-induced parotid adenomata gave results similar to those obtained in NMRI animals. In order to improve the selectivity of LDL assimilation we attempted to downregulate LDL receptors in the liver and adrenal gland by administration of the bile acid sodium taurocholate or by subcutaneous injection of hydrocortisone sodium succinate. These manoeuvres together reduced uptake of the lipoprotein into both organs without affecting tumour activity.

Adenoma↗
PubMed1984

Receptor-independent low-density lipoprotein catabolism. Evaluation of 2-hydroxyacetaldehyde-treated lipoprotein as a probe for its measurement.

This study examines the protein modification procedures available for inhibiting receptor recognition of low-density lipoprotein (LDL). Glycosylation with glucose, idose or ribose blocks the interaction of the lipoprotein with the high-affinity LDL receptor on cultured fibroblast membranes and delays its clearance from the plasma of rabbits. However, the prolonged incubation required in the process also changes the metabolic properties of the lipoprotein. An alternative approach using 2-hydroxyacetaldehyde-treated LDL completely blocks receptor recognition. This modified tracer has the same metabolic properties as the reductively methylated lipoprotein in rabbits and appears to be a suitable probe for the measurement of the receptor-independent LDL catabolic pathway in humans.

Acetaldehyde↗
PubMed1984

Pathophysiology of human lipoprotein receptors: clinical consequences of a cellular defect.

The function of the low density lipoprotein receptor has been reviewed at the cell level and in man. Its key role in cholesterol metabolism is unquestioned and it is central to the actions of a number of important hypocholesterolaemic agents. Clearly it must be involved in atherogenesis since its dysfunction leads to premature and severe atherosclerosis in both animals and man. The tools are now available to address this question and answers should be forthcoming in the near future.

Animals↗
PubMed1984

Apolipoprotein A and B (Sf 100-400) metabolism during bezafibrate therapy in hypertriglyceridemic subjects.

This study describes the effects of bezafibrate, an analogue of clofibrate, on the plasma lipid and lipoprotein profiles of 11 hypertriglyceridemic subjects and on their metabolism of apolipoproteins A-I, A-II, and B. The major action of the drug was to lower plasma triglyceride (by 58%; P less than 0.01). This was accompanied by a reduction in the level of very low density lipoprotein apoprotein B (Svedberg units of flotation [Sf] 60-400), whose mean residence time in the plasma fell threefold (from 3.4 to 1.0 h). Synthesis of the B protein in this fraction was not significantly altered, so the drug acts to accelerate the transit of very low density lipoprotein particles down the delipidation cascade. The metabolism of very low density lipoprotein remnant apoprotein B (Sf 12-100) changed little in response to treatment, although we detected a 30% increment (P less than 0.05) in the plasma concentration of this fraction. The mean residence time of these remnant particles in the plasma did not correlate with that of Sf 100-400 very low density lipoprotein apoprotein B, nor was this parameter altered by the drug. The most consistent and significant perturbation seen in the Sf 0-12 fraction (low density lipoprotein) was a reduction in the fractional catabolism of its apoprotein B moiety (26%; P less than 0.05). In those subjects who were grossly hypertriglyceridemic and who responded well to treatment, the level of this protein rose substantially owing to a combined increase in its synthesis and a reduction in its catabolism. In the group as a whole, high density lipoprotein cholesterol rose 13% (P less than 0.02), and detailed examination showed that this was associated with a small but significant increment in the plasma concentration of the high density lipoprotein subfraction 2. High density lipoprotein subfraction 3 also rose on the average, but this was not a consistent feature in all patients. The plasma concentrations and turnovers of the A proteins (A-I and A-II) were not significantly altered by bezafibrate therapy.

Apolipoproteins A↗
PubMed1984

Metabolism of apolipoprotein B in large triglyceride-rich very low density lipoproteins of normal and hypertriglyceridemic subjects.

The metabolic fate of very low density lipoprotein can be examined by following the transit of its apolipoprotein B moiety through the delipidation cascade, which leads to low density lipoprotein. In this study we have used cumulative flotation ultracentrifugation to follow the metabolism of various lipoprotein subclasses that participate in this process in normal, hypertriglyceridemic (Type IV), and dysbetalipoproteinemic (Type III) subjects. Large triglyceride-rich very low density lipoproteins of Svedberg units of flotation (Sf) 100-400 were converted virtually quantitatively in normal subjects to smaller Sf 12-100 remnant particles. Only a minor fraction appeared thereafter in low density lipoproteins (Sf 0-12), most being removed directly from the plasma. Type IV hyperlipoproteinemic individuals converted the larger Sf 100-400 very low density lipoproteins to intermediate particles at approximately 50% of the control rate but thereafter their metabolism was normal (fractional clearance of Sf 12-100 particles in controls, 1.29 +/- 0.23 pools/d; in Type IV hypertriglyceridemics, 1.38 +/- 0.23 pools/d; n = 4 in each case). Since the apolipoprotein B in large triglyceride-rich particles did not contribute significantly to the mass of the low density lipoprotein apoprotein pool, the latter must come largely from another source. This was examined by following the metabolic fate of small very low density lipoproteins of Sf 20-60 or of the total lipoprotein spectrum of d less than 1.006 kg/liter (approximate Sf 20-400). The small particles were rapidly and substantially converted to low density lipoproteins, suggesting that the major precursor of the latter was to be found in this density range. Whereas only 10% of apolipoprotein B in Sf 100-400 lipoproteins reached the low density lipoprotein flotation range, greater than 40% of Sf 20-100 B protein eventually appeared in Sf 0-12 particles; and when very low density lipoprotein of d less than 1.006 kg/liter is used as a tracer of apolipoprotein B metabolism it is primarily this population of small very low density lipoprotein particles in the Sf 12-100 flotation range that is labeled. A detailed examination was made of apolipoprotein B metabolism in three dysbetalipoproteinemic subjects. The plasma clearance curves of their Sf 100-400 lipoproteins were distinctly biphasic. The quickly decaying component converted rapidly into remnants of Sf 20-60 at a near normal rate (0.56 vs. 0.62 pools/d in normal subjects). Its subsequent processing, however, was retarded. The more slowly catabolized fraction, comprising 30% of the total apolipoprotein B radioactivity, had no counterpart in normal or Type IV hyperlipoproteinemic individuals. These data, taken together, suggest that the very low density lipoprotein consists of a complex mixture of particles with different origins and fates. Within the Sf 20-100 flotation range there are at least two subcomponents. One represents remnants of larger triglyceride-rich particles which are catabolized slowly and feeds little apolipoprotein B into low density lipoprotein. The other is apparently secreted directly into this flotation interval and transfers significant amounts of B protein rapidly into Sf 0-12 lipoproteins.

Apolipoproteins B↗
PubMed1983

Subpopulations of apolipoprotein A-I in human high-density lipoproteins. Their metabolic properties and response to drug therapy.

In this study immunological procedures were used to detect and quantify high-density lipoprotein (HDL) particles of differing apolipoprotein A composition. In the plasma of eight healthy female subjects, 45% of the total apolipoprotein A-I existed in particles (called '(AI)HDL') devoid of apolipoprotein A-II. The remainder circulated in association with apolipoprotein A-II at a molar ratio of approximately 1:1. Nicotinic acid selectively raised the plasma apolipoprotein A-I/A-II ratio by increasing the proportion of (AI)HDL particles. Probucol produced the opposite effect, lowering the plasma concentration of these particles. The kinetic properties of apolipoprotein A-I in total HDL and in the (AI)HDL particle were the same despite the fact that apolipoprotein A-I equilibration between these two species was incomplete. Therefore, there appear to be at least two apolipoprotein A-containing particle populations in HDL which are immunochemically and metabolically distinct.

Adolescent↗
PubMed1983

Cholesterol feeding increases low density lipoprotein synthesis.

This study examines the effects of increased dietary cholesterol (6 eggs/d) on the metabolism of low density lipoproteins in a group of seven healthy volunteers. Egg supplementation raised high density and low density lipoprotein cholesterol levels by 18 and 40%, respectively. The composition of the low density lipoprotein was unaltered and therefore the number of circulating particles must have increased. Kinetic studies indicated that this was due primarily to a 23% rise in the rate of synthesis of the lipoprotein. Catabolism was also affected. The fractional removal rate of native low density lipoprotein fell by 10% (P less than 0.05). However, the clearance of the 1,2 cyclohexanedione-treated lipoprotein remained unchanged (control fractional clearance rate [FCR] = 0.188 pools/d; cholesterol feeding FCR = 0.183 pools/d). Therefore, the reduction in low density lipoprotein catabolism appeared to be due to a fall in receptor activity. Consequently, an increased sterol load (34.2 mumol/kg per d vs. 27.7 mumol/kg per d in the control phase, P less than 0.02) was channelled into the receptor-independent route during egg feeding.

Adult↗
PubMed1983

Plasma lipid abnormalities in retinitis pigmentosa and related conditions.

Plasma samples obtained from 69 fasting retinitis pigmentosa (RP) patients and 110 controls were assayed for cholesterol, triglycerides, lipoproteins, and fatty acids. It was found that many RP patients were hyperlipidaemic compared to their spouses and siblings, as well as compared to unrelated controls. This hyperlipideaemia was particularly severe in men over 35 years of age, and in hemizygotes in X-linked families. In contrast, hypocholesterolaemia was observed in albipunctate retinal dystrophy. Plasma fatty acid titres were, in general, similar in RP patients and controls; however, patients in three families (two X-linked, one autosomal dominant) showed a significant reduction in docosahexaenoic acid (C22:6) compared to their unaffected relatives. These various plasma lipid abnormalities may reflect disorders in lipid metabolism which also may lead to retinal dystrophy.

Adult↗
PubMed1983

The hypolipidemic action of probucol: a study of its effects on high and low density lipoproteins.

This study examines the effects of probucol (1 g/day) on the plasma concentration, composition, and metabolism of low and high density lipoproteins (LDL and HDL) in eleven hyperlipidemic subjects, (seven Type II and four Type IV). The drug lowered plasma cholesterol in the Type II patients by 11% (P < 0.02) without affecting triglyceride. Both LDL and HDL cholesterol levels fell by 6% and 26%, respectively. The small reduction in the former was not associated with a change in the composition of the lipoprotein nor with a measurable alteration in the level of circulating apoLDL. Kinetic studies revealed that probucol had no consistent effect on either the synthesis or catabolism of apoLDL. However, probucol did exert a potent influence on HDL, lowering the level of this lipoprotein in both the Type II and Type IV patients despite the fact that total plasma cholesterol in the latter group was unchanged by treatment. The fall in HDL mass largely affected the HDL(3) subfraction; HDL(2), which was initially low in our subjects, did not show a consistent response to therapy. Not all of the constituents in HDL were equally affected by the drug. Specifically, the fall in total plasma apoA levels (which derived from significant reductions in the rates of synthesis of apoproteins A-I and A-II) was less than that of HDL cholesterol. Direct measurement of the composition of the lipoprotein confirmed that during therapy it carried less cholesterol per unit protein. The significance of these observations in relation to the prophylaxis of ischemic heart disease is not yet clear, but it seems prudent at present to use probucol selectively in subjects who show a substantial hypocholesterolemic response that derives primarily from a reduction in circulating LDL.-Atmeh, R. F., J. M. Stewart, D. E. Boag, C. J. Packard, A. R. Lorimer, and J. Shepherd. The hypolipidemic action of probucol: a study of its effects on high and low density lipoproteins.

Adult↗