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Biomedical subjects

R J Havel

Publications and source records attributed to R J Havel.

At least 145 records · Page 8Linked to original sources
PubMed1980

Isoprotein specificity in the hepatic uptake of apolipoprotein E and the pathogenesis of familial dysbetalipoproteinemia.

The uptake and catabolism of lamellar complexes of rat 125I-labeled apolipoprotein (apo) E with egg lecithin were increased severalfold in perfused livers of rats given large amounts of 17 alpha-ethynylestradiol for 5 days. Estrogen-stimulated uptake of lamellar complexes of human apo E that contained all of the major normally occurring "isoforms" of the protein (apo E-1, E-2, E-3, and E-4) was comparable to that of rat apo E. By contrast, uptake of complexes containing apo E from individuals with familial dysbetalipoproteinemia (dys beta LP; characterized by a lack of apo E-3 and E-4) was stimualted to a much smaller extent. With complexes containing individual isoforms of human apo E, it was shown that estrogen-stimulated hepatic uptake was largely confined to apo E-3 and E-4; uptake of apo E-2 from normolipoproteinemic or dys beta LP individuals, or of apo E-1 from the latter, was stimulated little or not at all. When considered in the light of available information about the hepatic uptake of lipoproteins and the metabolic defect in familial dys beta LP, these results are consistent with the following hypothesis: (i) apo E comprises an essential component of the site for normal recognition of remnants of triglyceride-rich lipoproteins by a specific hepatic receptor; (ii) accumulation of remnant lipoproteins in familial dys beta LP is caused by lack of apo E-3 and E-4, which are the forms of this protein that are primarily recognized by the receptor; and (iii) the normal conversion of remnants of very low density lipoproteins to low density lipoproteins is mediated by the hepatic remnant receptor.

Abetalipoproteinemia↗
PubMed1980

The effect of a high cholesterol and saturated fat diet on serum high-density lipoprotein-cholesterol, apoprotein A-I, and apoprotein E levels in normolipidemic humans.

The effects of a high cholesterol, high saturated fat diet on serum high density lipoprotein cholesterol, apo A-I, and apo E levels were studied in six normolipidemic subjects. The study was done on an outpatient basis and mixed natural foods normally consumed by humans were used. When compared with a low cholesterol (98 mg/day) high polyunsaturated fat (P/S ratio 1.6) diet, the high cholesterol (1021 mg/day), high saturated fat (P/S ratio 0.4) diet increased serum cholesterol (23%) by raising the cholesterol concentration in very low-density lipoproteins (59%), low-density lipoproteins (15%), and high-density lipoproteins (30%). The low-density lipoprotein-cholesterol/high-density lipoprotein-cholesterol ratio fell significantly from 1.78 to 1.58. The increased high-density lipoprotein-cholesterol was associated with an elevation of serum apo A-I but not apo E. Serum triglycerides did not change significantly.

Adult↗
PubMed1980

Radioimmunoassay of human arginine-rich apolipoprotein, apoprotein E. Concentration in blood plasma and lipoproteins as affected by apoprotein E-3 deficiency.

A radioimmunoassay for apolipoprotein E in human blood serum has been developed that measures equally the major polymorphic species of the protein (apolipoproteins E-1, E-2, E-3, and E-4) and the apo E in the dimer of apolipoproteins E and A-II. The assay is specific and yields values for apolipoprotein E in very low density lipoproteins that agree closely with those obtained by a quantitative electrophoretic method. Apolipoprotein E is also present in at least one species of high density lipoprotein, but the content of apolipoprotein E in the lipoprotein fractions of plasma is uncertain owing to dissociation during ultracentrifugation. The concentration of apolipoprotein E is higher in serum of normolipidemic, premenopausal women than in men of comparable age and is a direct function of the serum triglyceride level. Apolipoprotein E levels are increased out of proportion to triglyceride levels in hyperlipidemic patients with familial dysbetalipoproteinemia (homozygotes for lack of apolipoprotein E-3). Heterozygous relatives of homozygotes have significantly higher apolipoprotein E levels in serum than unaffected relatives. The concentration of partially degraded (remnant) triglyceride-rich lipoproteins also appears to be increased in heterozygotes, who comprise about 15% of the population.

Amino Acids↗
PubMed1980

Partial deficiency of carnitine palmityltransferase: physiologic and biochemical consequences.

Deficiency of muscle carnitine palmityltransferase (CPT), first described in 1973 by DiMauro and associates, is proving to be one of the principal causes of recurrent paroxysmal myoglobinuria. In this disease, oxidation of lipid substrates is impaired, because CPT is necessary for the transport of long-chain fatty acids through the inner mitochondrial membrane. As a result, patients depend excessively on carbohydrate metabolism as a source of energy for muscular work.

Acyltransferases↗
PubMed1980

Interaction of unilamellar liposomes with serum lipoproteins and apolipoproteins.

The effect of rat whole blood plasma, serum, serum lipoproteins, and apolipoproteins on the stability of unilamellar liposomes prepared with French pressure cell was evaluated by measuring the release of entrapped carboxyfluorescein and by electron microscopy. In the absence of serum components, dye escaped very slowly (hours) from egg phosphatidylcholine and phosphatidylcholine-cholesterol (43 mol % cholesterol) vesicles without apparent change in liposomal structure. This slow release was both temperature- and size-dependent. serum and some of its constituents induced a far more rapid (seconds) loss of entrapped dye from phosphatidylcholine liposomes, associated with structural changes. For equal masses of protein the order of potency of this induced activity was: free apolipoproteins (apo A-I, apo E) > isolated lipoproteins (HDL and VLDL) > whole serum or whole plasma. Substantial activity was found in three preparations of bovine serum albumin. This activity could be attributed to small and variable amounts of contaminating lipoprotein-like particles and apolipoprotein A-I. Induced release of dye from liposomes by apolipoproteins was usually associated with rapid formation of discs although other structures were sometimes formed. Purified rat apolipoproteins A-I and E appeared to interact identically with liposomes to induce dye release. This effect was progressively impaired for both apoproteins by increasing amounts of cholesterol and was completely inhibited when liposomes contained 37 mol % cholesterol.

Adult↗
PubMed1980

Unilamellar liposomes made with the French pressure cell: a simple preparative and semiquantitative technique.

A simple, rapid, and almost quantitative technique is described for the preparation of 1-40 ml of homogeneous unilamellar liposomes from dilute or concentrated aqueous suspensions of egg phosphatidylcholine. Aqueous suspensions of lipid are placed with the chamber of a French pressure cell at room temperature and rapidly extruded at 20,000 psi through the small orifice. A single pass transforms more than 70% of the extruded lipid into a homogeneous population of single-wall bilayer vesicles; more than 90% is transformed by recycling the lipid through the French pressure cell. About 95% of these liposomes range between 150-300 A in diameter (mean 200 A). The liposomes are stable for days to months when stored under nitrogen at 0.4 degrees C and can be prepared at 0 degrees, 25 degrees, or 37 degrees C. The liposomes appeared unaltered by repeated passages through the French pressure cell and no degradation of the phospholipid was detected after ten consecutive cycles at 20,000 psi in the absence of a nitrogen atmosphere. The method is especially useful for trapping small molecular weight substances because the concentration of both lipid and solute can be made quite high. Cholesterol up to 45 mole % can be incorporated into larger liposomes of egg phosphatidylcholine (mean diameter 315 A). Other phospholipids and different lipid mixtures can also be transformed into unilamellar vesicles with this method which has the advantage that additional steps of ultracentrifugation, column chromatography, dialysis, and concentrating procedures are usually unnecessary. Multilayered liposomes of small size (980 A mean diameter; > 95% between 500-1,500 A) are produced at lower pressure (3,000 psi). The latter are separated by gel permeation chromatography from a second population of homogeneous vesicles of even smaller size (580 A mean diameter; > 95% between 300-900 A) that contain two bilayer shells.

Biochemistry↗
PubMed1979

Quantification of the hepatic contribution to the catabolism of high density lipoproteins in rats.

Isolated rat livers were perfused for four hours in a recirculating system containing washed rat erythrocytes. Biologically screened radioiodinated rat high density lipoproteins (1.090 < d < 1.21 g/ml) were added to the perfusate with different amounts of whole serum to supply unlabeled rat high density lipoproteins. The protein moiety of the lipoprotein contained more than 95% of the radioiodine. The fraction of apolipoprotein mass degraded during the perfusion was quantified by the linear increment of non-protein-bound radioiodine in the perfusate, corrected for the increment observed during recirculation of the perfusate in the absence of a liver. The small amount of (131)I secreted into bile was added to calculate the fractional catabolic rate. The fractional catabolic rate ranged from 0.22 to 0.63% per hour in 12 experiments and was inversely related to the size of the perfusate pool of high density apolipoprotein. The absolute catabolic rate of high density apolipoprotein (fractional catabolic rate x pool size) in three livers in which the concentration of rat HDL in the perfusate approximated that in intact rats was 69.5 +/- 10.4 micro g hr(-1) (mean +/- SD). The rate of disappearance of cholesteryl esters of rat high density lipoproteins (labeled biologically by injecting donor rats with [5-(3)H]mevalonic acid) from the liver perfusate did not exceed that of the apoprotein component. These rates were compared with catabolic rates for rat high density lipoproteins in intact rats. Fractional catabolic rate in vivo, obtained by multicompartmental analysis of the disappearance curve of (131)I-high density apolipoprotein from blood plasma, was 11.9 +/- 1.3% hr(-1) (mean +/- SD). Total catabolic rate in vivo (fractional catabolic rate x intravascular pool of high density apolipoprotein) was 986 +/- 145 micro g hr(-1) (mean +/- SD). The results suggest that only a small fraction of high density lipoproteins in blood plasma of rats is degraded directly by the liver.-Sigurdsson, G., S-P. Noel, and R. J. Havel. Quantification of the hepatic contribution to the catabolism of high density lipoproteins in rats.

Animals↗
PubMed1978

Secretion of lipoprotein-X by perfused livers of rats with cholestasis.

The major abnormal plasma lipoprotein of cholestasis (LP-X) was isolated from blood plasma and from perfusates of isolated livers of rats with biliary obstruction. In both cases LP-X was composed mainly of about equimolar parts of phospholipids and unesterified cholesterol; the small protein component was primarily the arginine-rich apolipoprotein. By electron microscopy, LP-X appeared as a unilamellar liposome (690 A mean diameter, range 400-1000 A) with the trilaminar staining image typical of phospholipid bilayers. Extensive block staining of cholestatic livers for 48 hr with warmed uranyl acetate (37 degrees) permitted the visualization of vesicles indistinguishable from LP-X within hepatic parenchyma. These trilaminar-staining vesicles occurred predominantly within bile canaliculi. They also were seen in nearby cytoplasmic vacuoles or invaginations between hepatocytes and in the space of Disse. Similar vesicles were not seen in the endoplasmic reticulum or Golgi cisternae. These observations raise the possibility that the vesicles are formed within bile canaliculi and are transported from the canaliculi to the space of Disse within pinocytotic vacuoles.

Animals↗
PubMed1978

Catabolism of the apoprotein of low density lipoproteins by the isolated perfused rat liver.

Isolated rat livers were perfused for 4 hours in a recirculating system containing washed rat erythrocytes. Biologically screened, radioiodinated low density lipoproteins (1.030 < d < 1.055 g/ml) were added to the perfusate with different amounts of whole serum to supply unlabeled rat low density lipoproteins. Apolipoprotein B contained 90% of the bound (131)I, other apolipoproteins contained 4%, and lipids contained the remainder. The fraction of apolipoprotein mass degraded during the perfusion was quantified by the linear increment of non-protein-bound radioiodine in the perfusate, corrected for the increment observed during recirculation of the perfusate in the absence of a liver. The fractional catabolic rate ranged from 0.3 to 1.7%/hr in seven experiments and was inversely related to the size of perfusate pool of low density apolipoprotein. The catabolic rate of low density apolipoprotein (fractional catabolic rate x pool size) in four livers, in which the concentration of rat low density lipoproteins was 50-100% of that present in intact rats, was 5.3 +/- 2.7 micro g hr(-1) (mean +/- SD). Similar results were obtained with human low density lipoproteins. These rates were compared with catabolic rates for the apoprotein of rat low density lipoproteins in intact animals. Fractional catabolic rate in vivo, obtained by multi-compartmental analysis of the disappearance curve of (131)I-labeled low density apolipoprotein from blood plasma, was 15.2 +/- 3.1% hr(-1) (mean +/- SD). Total catabolic rate in vivo (fractional catabolic rate x intravascular pool of low density apolipoprotein) was 76 +/- 14 micro g hr(-1) (mean +/- SD). The results suggest that only a small fraction of low density apolipoprotein mass in rats is degraded by the liver.

Animals↗
PubMed1978

Origin and transport of the A-I and arginine-rich apolipoproteins in mesenteric lymph of rats.

Transport of apolipoprotein A-I and argininerich apolipoprotein in mesenteric lymph was examined in rats given constant intraduodenal infusions of saline, glucose in saline, or emulsified fat. Lymph flow in all groups was constant from 5 to 50 hr after beginning the infusions. Lymphatic transport of triglycerides was about 20-fold greater and transport of apoprotein A-I was about twofold greater in fat-infused rats than in the other two groups. In each group transport of apoprotein A-I bore a significant positive relationship to transport of triglycerides. Lymphatic transport of the arginine-rich apoprotein was only 6-12% of that of apoprotein A-I and was more closely related to lymphatic transport of total protein than to that of triglycerides. In fat-infused rats given [(3)H]lysine intraduodenally, about two-thirds of the (3)H in the chylomicron proteins was in apoprotein A-I and only about 1% was in the arginine-rich apoprotein. Estimated specific activity of chylomicron proteins was highest for apoprotein A-I and apoprotein A-IV, and lowest for the arginine-rich apoprotein and proteins of low molecular weight (mainly C apoproteins). In fat-infused rats given constant intravenous infusions of radioiodinated high density lipoproteins from blood plasma, the specific activity of apoprotein A-I in lymph chylomicrons was only about 5% of that of apoprotein A-I in blood high density lipoproteins, indicating that more than 90% of the apoprotein A-I in chylomicrons was synthesized in the intestine. From these and other data it is concluded that both the intestine and liver are significant sources of apoprotein A-I whereas only the liver synthesizes significant amounts of the arginine-rich apoprotein.

Animals↗
PubMed1978

Composition of proteins of mesenteric lymph chylomicrons in the rat and alterations produced upon exposure of chylomicrons to blood serum and serum proteins.

Protein composition was determined in mesenteric lymph chylomicrons from fat-fed rats. Among the proteins of intermediate molecular weight, apoproteins A-I and the arginine-rich apoprotein accounted for 31% and 4% of the total protein mass, respectively. Apoprotein B and apoprotein A-IV each accounted for about 10% and proteins of low molecular weight (C apoproteins and apoprotein A-II) accounted for most of the remainder. Apoprotein A-I also accounted for more than 30% of the protein mass of mesenteric lymph lipoproteins of density less than 1.006 g/ml ("small chylomicrons") obtained from rats fed glucose. Aproprotein A-I was partially dissociated from chylomicrons during brief ultracentrifugation. Both the arginine-rich apoprotein and the C apoproteins in rat blood serum were transferred to lymph chylomicrons from fat-fed rats during incubation in vitro. Content of arginine-rich apoprotein, determined immunochemically, increased six-fold when chylomicrons were diluted to a final concentration of 500 mg/dl in blood serum. Upon incubation of chylomicrons in equivalent volumes of ultracentrifugal fractions of serum, the increase of the arginine-rich apoprotein was: very low density lipoproteins, 1.5-fold; high density lipoproteins, 1.8-fold; density fraction greater than 1.006 g/ml, 5.0-fold; density fraction greater than 1.21 g/ml, 11-fold. Content of apoprotein A-I, also determined immunochemically, was not altered appreciably by exposure to serum or its ultracentrifugal fractions, whereas content of C apoproteins, estimated from intensity of staining of the low molecular weight protein component in polyacrylamide gel electropherograms, increased in all cases except for the density fraction greater than 1.21 g/ml. The fractional content of apoprotein A-I in the protein of chylomicrons fell after incubation, whereas that of the arginine-rich apoprotein remained constant or rose substantially. The fractional content of apoprotein A-IV in chylomicron-protein tended to follow that of apoprotein A-I, as judged from polyacrylamide gel electropherograms. Transfer of the arginine-rich and C apoproteins to chylomicrons from blood serum was directly related to the volume of serum in which the chylomicrons were diluted and occurred rapidly at room temperature or at 4 degrees C.

Animals↗
PubMed1977

Radioimmunoassay of arginine-rich apolipoprotein of rat serum.

A double-antibody radioimmunoassay was developed for quantification of rat arginine-rich apolipoprotein in sodium decyl sulfate. Arginine-rich protein, labeled with 125I by the chloramine-T method, had the same chromatographic characteristics on Sephadex G-200 as unlabeled arginine-rich protein and up to 70% of 125I-labeled arginine-rich protein was precipitated by antisera to arginine-rich protein in rabbits. The assay is sensitive at the level of 1-10 ng and has intraassay and interassay coefficients of variation of 5.4 and 6.8%, respectively. The specificity of the assay was established by competitive displacement of 125I-labeled arginine-rich protein from its antiserum by arginine-rich protein and lipoproteins containing this protein, but not by rat albumin or other purified apolipoproteins. Immunoreactivity of rat serum and lipoproteins was complete as demonstrated by comparison with their delipidated form. The accuracy of the immunoassay was further substantiated by comparison with the amount of arginine-rich protein in chromatographic fractions of total apoprotein of very low and high density lipoproteins, and by recovery experiments in ultracentrifugally separated fractions of serum. In contrast to an immunoassay reported previously for rat apo A-I, sodium decyl sulfate was not required for complete immunoreactivity of serum and lipoproteins. The inclusion of sodium decyl sulfate (9 mM final concentration) was necessary, however, for stability of labeled and unlabeled preparations of arginine-rich protein. Content (weight %, means values +/- S.D.), of immunoassayable arginine-rich protein in isolated lipoproteins was 15 +/- 1.5% in very density lipoproteins; 6.8% in low density lipoproteins (1.02 less than d less than 1.04 g/m); 7.1 +/- 0.3% in high density lipoproteins; and 4.8 +/- 0.5% in lymph chylomicrons. Concentration in whole serum was 18.1 +/- 1.4 and 20.4 +/- 2.3 mg/dl for male and female rats, respectively. Only about 55% of arginine-rich protein was recovered in the major lipoprotein classes and about 40% was in "lipoprotein-free" serum (d greater than 1.25 g/ml). Among the lipoproteins, the high density lipoprotein fraction contained twice the amount of arginine-rich protein recovered in very low or low density lipoproteins (26.6 vs. 13.5 and 13.4%, respectively). The significance of the large amount of arginine-rich protein in the 1.25 g/ml infranatant fraction is not apparent. Although repetitive centrifugation did not alter the amount recovered in this fraction, the possibility of an artifact induced by centrifugation and high salt concentration cannot be excluded.

Amino Acids↗