Plasma lipoproteins in the golden Syrian hamster (Mesocricetus auratus): heterogeneity of apoB- and apoA-I-containing particles

We present the quantitative and qualitative characteristics of the apolipoprotein (apo) B- and apoA-I-containing lipoprotein subspecies in the plasma of male Golden Syrian hamsters. The spectrum of hamster lipoproteins of d < 1.172 g/ml was subfractionated by isopycnic density gradient ultracentrifugation. ApoB-containing subspecies were distributed up to a density of 1.074 g/ml. Hamster very low density lipoproteins (VLDL, d < 1.018 g/ml; approximately 120 mg/dl plasma) were triglyceride (TG)-rich, deficient in cholesteryl ester (CE), and highly heterogeneous in size, containing chylomicron-like particles. ApoVLDL contained proteins analogous to human apoB-100, apoB-48, and apoE. ApoB-containing subspecies with physicochemical properties typical of low density lipoproteins (LDL) were identified as a single, major size species in the density interval from 1.019 to 1.074 g/ml, particle diameter decreasing progressively with increase in density. Hamster LDL-like subspecies were distinguished from their human counterparts by a relative deficiency in core CE (< 30% by wt) and by enrichment in triglyceride. The high M(r) form of apoB was the major apolipoprotein of all LDL-like subfractions, in which apoE was detected as a minor component. Total plasma levels of LDL (d 1.019-1.074 g/ml) amounted to approximately 140 mg/dl (approximately 25% of d < 1.172 g/ml lipoproteins). The distribution of dense apoB-containing subspecies overlapped that of apoA-I-containing, high density lipoprotein-1 (HDL1)-like particles in the density interval approximately 1.039-1.074 g/ml. ApoA-I-containing subspecies with the physical and chemical characteristics of HDL were exclusively present over the density interval 1.074-1.172 g/ml. Quantitatively, these subspecies predominated in hamster plasma (approximately 270 mg/dl). Light, HDL2-like particles of d 1.065-1.103 g/ml (HDLL) were preponderant, (approximately 66% of total HDL). Marked size heterogeneity was evident, and was associated with distinct particle contents of minor apolipoproteins. Both HDLL and heavy HDL (HDLH, d 1.103-1.172 g/ml) were enriched in CE as evidenced by elevated weight ratios of CE:FC (7-9:1) and of CE:TG (up to approximately 50:1). Considered together, the core lipid contents of apoB- and apoA-I-containing lipoproteins are consistent with the hypothesis that the hamster is partially deficient in neutral lipid (CE, TG) transfer activity.

Ciprofibrate therapy normalises the atherogenic low-density lipoprotein subspecies profile in combined hyperlipidemia

The effect of ciprofibrate treatment on the atherogenic profile of low-density lipoprotein (LDL) subspecies in combined hyperlipidemia (CHL) has been investigated in six patients displaying elevated plasma triglyceride and cholesterol levels (> 200 and > 250 mg/dl, respectively). The E2E2 phenotype was excluded; four patients possessed familial antecedents of premature coronary heart disease (CHD). Analysis of five LDL subclasses separated by isopycnic density gradient ultracentrifugation showed a predominance of dense LDL subspecies (LDL-4 and LDL-5, d 1.039-1.063 g/ml; 51% of total LDL mass) in the asymmetric LDL density profile characteristic of CHL patients at baseline. Ciprofibrate treatment (100 mg/day for 1 month) effected marked reductions in both total plasma LDL and apo B-100 levels (approximately 19% and approximately 23%, respectively). Equally, the plasma profile of LDL subspecies was normalised to a significant degree as a result of preferential reduction in the elevated levels of both dense subspecies (LDL-4 and LDL-5; -43% and -54%, respectively; P < 0.03 and P < 0.006 [corrected], respectively). The circulating concentrations of light LDL (LDL-1, d 1.019-1.023 g/ml) were also diminished significantly by ciprofibrate (-30%; P < 0.006 [corrected]). Furthermore, ciprofibrate not only effected reductions in the elevated triglyceride content of the hydrophobic core of all LDL subspecies but also normalised their common deficiency in free cholesterol. In addition, the abnormally small particle diameters of LDL-4 and -5 were increased to normal. Plasma levels of both apo B-100 and triglycerides were significantly and positively correlated with those of LDL-4 and LDL-5, suggesting not only that the degree of triglyceride elevation is intimately linked to the extent of shift in LDL subclass profile towards denser subspecies, but also that triglyceride reduction upon treatment strongly influences LDL-4 and LDL-5. In conclusion, our findings indicate that ciprofibrate treatment in combined hyperlipidemia results in marked reduction in plasma triglyceride levels (-33%), and that such reduction is intimately linked to normalisation of both the qualitative and quantitative features of the atherogenic LDL subspecies profile typical of this disorder.

Heterogeneity of cellular cholesteryl ester accumulation by human monocyte-derived macrophages

We have studied cholesteryl ester accumulation in human monocyte-derived macrophages, which together with smooth muscle cells, represent the major cell types that accumulate cholesterol in atherosclerotic lesions. Monocyte-derived macrophages were incubated with either acetylated low density lipoprotein (AcLDL) or non-lipoprotein cholesterol and the question as to whether all of the cells, or specific cell subpopulations could accumulate cholesteryl ester was examined. We stained cholesteryl ester in monocyte-macrophages with the fluorescent probe filipin. Cholesteryl ester accumulated as lipid droplets that were widely dispersed in the cell cytoplasm. Interestingly, no more than 65% of monocyte-macrophages accumulated cholesteryl ester during the 1st day of incubation with non-lipoprotein cholesterol. By 2 days of incubation, greater than 90% of cells displayed cholesteryl ester deposition. The cholesteryl ester which accumulated during the 2nd day of incubation was derived from unesterified cholesterol that had accumulated during the 1st day of incubation. This finding was substantiated by the following: (1) chemical measurements showed that the total cholesterol content of monocyte-macrophages did not increase further after the 1st day of incubation, and (2) all monocyte-macrophages had accumulated fluorescent tagged cholesterol during the 1st day of incubation. In contrast to the results obtained with non-lipoprotein cholesterol, more than 90% of monocyte-macrophages incubated with AcLDL for 1 day accumulated cholesteryl ester in two experiments. However, less than 62% of monocyte-macrophages accumulated cholesteryl ester in two other experiments, thereby resembling results obtained with non-lipoprotein cholesterol. Again, the lack of cholesteryl ester accumulation with AcLDL was not due to a lack of uptake of AcLDL, as greater than 90% of monocyte-macrophages accumulated fluorescent tagged AcLDL. The observed heterogeneity in cholesterol esterification among human monocyte-macrophages suggests that functional subpopulations of these cells may exist with respect to cholesterol processing. However, heterogeneity in cholesteryl ester accumulation did not seem to correlate with expression of HLA-DR antigen, a marker of immunological activation of macrophages. Other sources of heterogeneity most likely result from inter-cellular variation at one or more levels of regulation of the cholesterol trafficking and esterification process.

Dense low density lipoprotein subspecies with diminished oxidative resistance predominate in combined hyperlipidemia

Patients presenting combined hyperlipidemia (CHL) display an elevated risk of coronary heart disease. The atherogenic lipoprotein particles implicated in this disorder remain ill defined. We determined the qualitative and quantitative characteristics of the density distribution of low density lipoprotein (LDL) particle subspecies in nine subjects defined phenotypically as presenting CHL, and under strict dietary control. Seven CHL patients possessed familial antecedents of premature coronary heart disease; none were E2E2 homozygotes. Five LDL subspecies were isolated by density gradient ultracentrifugation in the density range 1.019-1.063 g/ml. In all patients, the LDL profile was skewed towards the dense subspecies (LDL-4, d 1.039-1.050 g/ml and LDL-5, d 1.050-1.063 g/ml), representing 47% of total LDL mass; by contrast, these subspecies accounted for only 30% of LDL mass in five normolipidemic subjects (P < 0.01). In addition, plasma LDL mass concentrations were some twofold higher in CHL patients as compared to normolipidemic subjects. The % mass of LDL-4 was positively correlated with plasma triglyceride and apoB levels. LDL-2 and LDL-3 in CHL patients were triglyceride-enriched (11.9 and 7.2%, respectively) as compared to the corresponding subspecies in normolipidemic subjects (6.6 and 3.7%, respectively; P < 0.05 in each case). LDL particle size decreased with increase in density in both groups; however, significant differences were found between corresponding LDL subspecies (LDL-1, -3, -4, and -5) in CHL patients and normolipidemic subjects, a finding suggestive of dissimilar molecular organization, despite correspondence in hydrated density. The copper-induced oxidative modification of LDL subspecies was assessed by determination of conjugated diene formation. In both groups, LDL-5 was distinct in exhibiting a marked diminution in oxidative resistance as indicated by a significant reduction (P < 0.01) in mean lag time. The oxidative susceptibility of LDL subspecies in both groups was independent of vitamin E content when expressed as the ratio vitamin E/LDL mass, although dense LDL in CHL patients tended to be deficient in this antioxidant. The diminished oxidative resistance of dense LDL subspecies could not be accounted for by enrichment in polyunsaturated fatty acids in either group. These studies suggest that in consequence of their elevated circulating concentration and diminished oxidative resistance, dense LDL subspecies represent putative atherogenic subspecies in combined hyperlipidemia.

Management of atrial tachyarrhythmias in the critically ill: a comparison of intravenous procainamide and amiodarone

OBJECTIVE

To compare the efficacy and safety of intravenous (IV) amiodarone and procainamide for the treatment of atrial tachyarrhythmias (AT) in the critically ill.

DESIGN

In this prospective study, patients were allocated to drug treatment on the basis of hospital identification number, even for procainamide and odd for amiodarone.

SETTING

Patients were recruited from a teaching hospital ICU and did not include postoperative cardiac patients.

PATIENTS AND PARTICIPANTS

26 patients with AT sustained for at least 1 h and failure to respond to correction of possible precipitating factors were entered in the study. Exclusion criteria were systolic blood pressure (SBP) < 80 mmHg, and known hypersensitivity to either drug. Two patients with chronic atrial fibrillation (who received amiodarone) were later excluded from the analysis. In the final analysis, 14 patients received procainamide and 10 amiodarone.

INTERVENTIONS

IV amiodarone (3 mg/kg followed by 10 mg/kg/24 h, with repeat dose of 3 mg/kg at 1 h if no response) or i.v. procainamide (10 mg/kg at 1 mg/kg/min followed by infusion of 2-4 mg/min for 24 h, with repeat dose of 5 mg/kg at 1 h if no response).

MEASUREMENTS AND RESULTS

In the procainamide group 10/14 (71%) and in the amiodarone group 7/10 (70%) had converted to sinus rhythm by 12 h. There was no significant difference in response between the groups. SBP was not significantly different from baseline after administration of either drug.

CONCLUSIONS

Procainamide and amiodarone appear to be safe and equally effective in the treatment of AT in the critically ill.

Epinephrine as an inotropic agent in septic shock: a dose-profile analysis

OBJECTIVE

To characterize the acute actions and physiologic dose profile of epinephrine, as a single inotrope, in patients with septic shock.

DESIGN

Prospective clinical study. The relationship between epinephrine dose and cardiovascular variables was analyzed using repeated-measures analysis of variance.

SETTING

ICU in a university teaching hospital.

PATIENTS

Eighteen patients with septic shock, mean age 64 +/- 8 (SD) yrs, and with a mean admission Acute Physiology and Chronic Health Evaluation (APACHE II) score of 23 (range 14 to 35).

INTERVENTIONS

Initial volume loading and the measurement of a baseline hemodynamic profile were followed by the administration of an epinephrine infusion at 3 microgram/min with subsequent increments of 3 micrograms/min and the determination of a hemodynamic profile after each dose increment. Therapy was titrated to clinical goals of perfusion and restoration of premorbid systolic arterial BP.

MEASUREMENTS AND MAIN RESULTS

After volume loading, mean hemodynamic indices were as follows: mean arterial pressure (MAP) 62 +/- 7 mm Hg; cardiac index 3.8 +/- 1.1 L/min/m2; left ventricular stroke work index 25 +/- 11 g.m/m2; oxygen delivery (Do2) index 460 +/- 168 mL/min/m2; and oxygen consumption (VO2) index 165 +/- 64 mL/min/m2. In the dose range of 3 to 18 microgram/min, epinephrine produced linear increases in average heart rate, MAP, cardiac index, left ventricular stroke work index, stroke volume index, VO2, and DO2. No effect was noted on pulmonary artery occlusion pressure (PAOP), mean pulmonary arterial pressure, or systemic vascular resistance index.

CONCLUSIONS

Epinephrine increases DO2 in septic shock by increasing cardiac index without an effect on systemic vascular resistance index or PAOP.

Uptake of exogenous free cholesterol induces upregulation of tissue factor expression in human monocyte-derived macrophages

Lipid-laden macrophages present as foam cells may contribute to the hyperthrombotic state of human atherosclerotic lesions by the production of tissue factor (TF). We investigated the effect of exogenous nonlipoprotein cholesterol on the expression of TF by human monocyte-derived macrophages in culture. Nonlipoprotein cholesterol at 50 micrograms/ml increased TF activity 4-fold; TF induction was dose- and time-dependent. Expression of TF activity was positively correlated with the free cholesterol content of monocyte-derived macrophages, was increased upon inhibition of cholesterol esterification, and reflected de novo synthesis of TF protein. TF expression in cholesterol-loaded macrophages remained sensitive to stimulation (approximately 12-fold) by bacterial lipopolysaccharide, indicating that intracellular free cholesterol and lipopolysaccharide act by distinct mechanisms in inducing TF procoagulant activity. Our results suggest that loading human monocyte-derived macrophages with free cholesterol induces upregulation of TF expression, thereby contributing to thrombus formation at sites of plaque rupture.

Epitope mapping of the human biliary amphipathic, anionic polypeptide: similarity with a calcium-binding protein isolated from gallstones and bile, and immunologic cross-reactivity with apolipoprotein A-I

Biliary amphipathic anionic polypeptide (APF) the major protein of the pigment-lipoprotein complex in bile, and calcium-binding protein (CBP) from gallstones are both small (less than 10 kDa), highly acidic, amphipathic proteins present in bile and closely associated also with pigmented areas in human gallstones. Polyclonal antibodies against APF have shown cross-reactivity with plasma high density lipoproteins (HDL). This study examines the hypothesis that APF and CBP might be closely related or even identical, and might also share common epitopes with the larger apoA-I (23 kDa). To assess this, immunoreactivity of the three delipidated, highly purified proteins was determined against a panel of 12 monoclonal antibodies (MAbs) prepared against APF and a panel of 4 MAbs against apoA-I. APF was isolated from bile by zonal ultracentrifugation. CBP was isolated from proteins precipitated from bile by CaCl2, as well as from the calcium bilirubinate shells of cholesterol gallstones, by extraction successively with methyl-t-butyl ether, methanol, and Na2EDTA, followed by Sephadex G-25 chromatography and two-stage preparative SDS-PAGE. ApoA-I was prepared by two types of chromatography: Sephacryl S200 chromatography and heparin-chromatographic immunoaffinity. Specific polyclonal antibodies to APF and apoA-I were prepared from immunized rabbits. MAbs to APF and apoA-I were prepared by immunization of mice, using standard hybridoma technique. Western blotting of APF and CBP in 15% SDS-PAGE yielded one band with an apparent molecular weight of 6.5 kDa, which, along with apoA-I, was immunostained by polyclonal antibodies to APF and apoA-I. Using 12 MAbs against APF with three types of ELISA (direct antigen binding, competitive antigen displacement, and epitope competition between antibodies), it was shown that APF and delipidated apoA-I shared six epitopes, three of which were detected also on the surface of intact HDL particles. Six other epitopes were present in APF but not apoA-I, four of which were exposed on the surface of HDL. Four MAbs against apoA-I reacted with APF and CBP. Amino acid analyses of APF and CBP were similar with 20-23% acidic and 7-11% basic amino acids and low contents of cysteine, methionine, and tyrosine; both differed from apoA-I in containing isoleucine and cysteine. Using ELISA and one MAb (no. 32) against APF, this polypeptide was detected in human plasma HDL, the pigment-lipoprotein complex in the bile of humans, dogs, and rats, and in both pigment and cholesterol gallstones.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasma lipid transport in the preruminant calf, Bos spp: primary structure of bovine apolipoprotein A-I

The preruminant calf (Bos spp.) is a model of considerable interest with regard to hepatic and intestinal lipoprotein metabolism (Bauchart et al., J. Lipid Res. (1989) 30, 1499-1514 and Laplaud et al., J. Lipid Res. (1990) 31, 1781-1792). As a preliminary step towards future experiments dealing with HDL metabolism in the calf, we have purified apoA-I from this animal and determined its complete amino acid sequence. Thus, approx. 10% of calf apoA-I was shown to contain a propeptide, with the sequence Arg-His-Phe-Trp-Gln-Gln. Enzymatic cleavage of apoA-I resulted in 10 proteolytic peptides. The complete apoA-I sequence was obtained after alignment of peptides on the basis of their homologies with those from rabbit apoA-I. Thus calf apoA-I consists of 241 amino acid residues, and exhibits high sequence homology with all mammalian apoA-I's studied to date. The bovine protein contained 10 hydrophobic amphipathic helical regions, occurring between residues 43-64, 65-86, 87-97, 98-119, 120-141, 142-163, 164-184, 185-206, 207-217 and 218-241. A computer-constructed phylogenetic tree showed that bovine apoA-I was more closely related to its dog counterpart, including the presence of a single methionine, than to the corresponding macaque and human proteins. Comparative predictions of the respective antigenic structures of human and bovine apoA-I's using the Hopp-Woods algorithm indicated similar positions for all 13 detectable antigenic sites, among which 7 were of identical, or closely related, amino acid composition. This finding was confirmed by demonstration of partial immunological identity between the two proteins upon immunodiffusion analysis, a result obtained using a monospecific rabbit antiserum against bovine apoA-I. Finally, comparison of sequence homology between bovine apoA-I and the lecithin:cholesterol acyl transferase (LCAT) activating region of human apoC-I suggests that several LCAT activating domains may be present in calf apoA-I.

Discrete subspecies of human low density lipoproteins are heterogeneous in their interaction with the cellular LDL receptor

The low density lipoproteins (LDL) of human plasma consist of a series of discrete particle subspecies of distinct physicochemical, immunological, and hydrodynamic properties. Such structural differences are intimately linked to the metabolic heterogeneity of circulating LDL in vivo. The current studies were designed to evaluate and compare the interaction of discrete LDL subspecies from normolipidemic subjects with the LDL receptor. Plasma LDL of d 1.019-1.063 g/ml from healthy males were fractionated into 15 subspecies of defined physicochemical characteristics by isopycnic density gradient ultracentrifugation as described earlier (Chapman et al., J. Lipid Res. 1988. 29: 442-458). The major LDL subspecies, LDL-5 to LDL-10, exhibited an overall range in density from 1.0244 to 1.0435 g/ml; individual subspecies increased in density by increments of 0.027 (LDL-5), 0.026 (LDL-6), 0.030 (LDL-7), 0.031 (LDL-8), 0.035 (LDL-9), and 0.042 g/ml (LDL-10), respectively. Taken together, these subspecies accounted for approximately 70% of the total mass of LDL of d 1.019-1.063 g/ml; their cholesterol: protein ratios decreased from 1.70 to 1.12 and particle size from 275 to 260 A with increase in density. ApoB-100 was the unique protein component in subspecies 5-8, with trace amounts (less than 0.2% of apoLDL) of both apoA-I and apoE in subspecies 9 and 10. The interaction of individual LDL subspecies with the LDL receptor on cultured human U-937 monocyte-like cells was compared by determining receptor binding affinities at 4 degrees C. Scatchard analysis of specific binding curves demonstrated a single class of binding site for each subspecies. The lowest dissociation constants were displayed by LDL subspecies 6 (Kd 5.71 nM), 7 (Kd 5.24 nM) and 8 (Kd 4.67 nM), while subspecies 5, 9, and 10 displayed significantly higher Kd values (8.35, 7.20, and 6.87 nM, respectively). Competitive displacement studies at 4 degrees C, in which unlabeled subspecies from the same gradient series competed for binding with 125I-labeled LDL subspecies, confirmed the relative binding affinities of these subspecies. As the hydrophobic lipid core of LDL undergoes a thermotropic transition at approximately 37 degrees C, which may in turn influence the surface structure of the particle, internalization and degradation studies were performed at 37 degrees C. No effect of temperature was detectable; again, LDL subspecies at each extreme of the density distribution (LDL-5 and LDL-10) displayed significantly lower binding affinities for the LDL receptor than that from the peak region (LDL-7).(ABSTRACT TRUNCATED AT 400 WORDS)

Pain control in paediatric burns--the use of patient-controlled analgesia

Eleven children received patient-controlled analgesia (PCA) for the management of severe burn pain, their ages ranged from 4.75 to 14 years. Periods of PCA ranged from 2 to 131 days. Three patients developed evidence of tolerance as shown by high dose requirements, but the patients weaned themselves rapidly when pain levels fell. We conclude that PCA provides good quality analgesia to school-age children requiring debridement and grafting for burns. Its use simplified one major aspect of the management of these children.

Intestinal lymph and plasma lipoproteins in the preruminant calf: partial resolution of particle heterogeneity in the 1.040-1.090 g/ml interval

Our previous studies in the preruminant calf have provided evidence for the heterogeneity of lipoprotein particles in the 1.040-1.090 g/ml density interval in both plasma and postprandial intestinal lymph (Bauchart, D. et al., 1989. J. Lipid Res. 30: 1499-1514; and Laplaud, P. M. et al., 1990. J. Lipid Res. 31: 1781-1792). We therefore attempted to resolve this heterogeneity by use of heparin-Sepharose affinity chromatography. Experiments were performed on three calves; portal vein plasma and intestinal lymph were obtained simultaneously 10 h after a meal, i.e., at peak lipid absorption. In both fluids, the chromatographic profile presented three fractions, I, II, and III. Fraction I was characterized by the presence of cholesteryl ester-rich particles (approximately 35-37% of lipoprotein mass), which migrated electrophoretically as typical high density lipoproteins and exhibited Stokes diameters in the 130-160 A range; apoA-I was the predominant protein. In addition to this polypeptide, fraction II contained small amounts of a supplementary protein (Mr approximately 51,000), exhibiting heparin-binding properties. In the light of results reported in the literature, we suggest that this latter protein could correspond to beta 2 glycoprotein I. The chemical composition of each fraction II closely resembled that of the corresponding fraction I, while their electrophoretic migrations appeared slightly slower and their Stokes diameters slightly larger (155-165 A). Apart from the presence of small amounts of apoA-I, two high Mr proteins (Mr approx. 560,000 and 300,000) were typical of the apolipoprotein moiety of fractions III. The lower Mr form was present as a trace component only in fraction III originating from plasma; its proportion increased in lymph fraction III so as to approximately match that of the higher Mr (i.e., 560,000) protein. In both plasma and lymph, fraction III was electrophoretically heterogeneous, exhibiting a doublet of bands with migration and Stokes diameters (250 A) typical of low density lipoprotein particles. However, no evidence for the presence of a particle resembling lipoprotein[a] in fraction III could be obtained. In lymph only, fraction III contained a supplementary population of lipoproteins with migration intermediary between those of conventional low and high density lipoproteins and with Stokes diameters in the 190-200 A range. Other specific features of lymph fraction III included a sevenfold increase in its triglyceride content (8.5 +/- 3.4% vs. 1.2 +/- 1.1% in the corresponding fraction from plasma), to the detriment of cholesteryl esters, and a higher proportion of protein.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipoprotein(a) and apolipoprotein(a) in a New World monkey, the common marmoset (Callithrix jacchus). Association of variable plasma lipoprotein(a) levels with a single apolipoprotein(a) isoform

In an earlier report (Chapman et al, Biochemistry 1979;18:5096-5108), we suggested that the common marmoset may represent an important model for the study of human plasma lipoprotein metabolism. We now extend the interest of this monkey model to the study of lipoprotein(a) (Lp[a]) and apolipoprotein(a) (apo[a]). Density gradient ultracentrifugal fractionation of marmoset plasma revealed a bimodal distribution of Lp(a), with one peak of concentration occurring in association with very low density lipoproteins (VLDLs) and a second in the density range 1.040-1.080 g/ml. The dense Lp(a) subspecies displayed physicochemical properties (chemical composition, particle size, and electrophoretic mobility) that closely resembled those of its counterpart in humans and baboons but that were distinct from those of low density lipoprotein (LDL). Furthermore, the particle size of marmoset Lp(a) was invariant (31 nm) over the density interval 1.040-1.080 g/ml, whereas that of LDL decreased progressively with an increase in density (approximately 26-25.2 nm). Use of polyclonal and monoclonal antibodies to human apo(a) and of a polyclonal antibody to marmoset Lp(a) allowed immunologic identification of a single apo(a) isoform in the marmoset whose size was similar to that of apo B-100; apo(a) and apo B-100 were associated in Lp(a) particles by a disulfide linkage. The total protein mass of apo-Lp(a) was estimated to be 800,000 or more by electrophoresis in sodium dodecyl sulfate-polyacrylamide-agarose gels. The amino acid compositions of marmoset and human apo(a) resembled each other but were distinct from those of the corresponding forms of apo B-100. Immunologic evidence is provided for a high degree of cross reactivity between apo(a) in marmosets, baboons, and humans, supporting the idea of the existence of a marked degree of structural homology between these proteins. In addition, electroimmunoblotting of marmoset apo(a) and marmoset plasminogen showed that these proteins shared certain epitopes in common, suggesting that marmoset apo(a) may possess kringle-like structural features. Finally, despite possession of a single apo(a) isoform, marmoset Lp(a) levels varied over a 100-fold range (0.5-49 mg/dl plasma). Considered together, our present findings suggest that the common marmoset monkey constitutes a unique model in which to study the regulation of apo(a) gene expression and the posttranslational processing of apo(a), as well as factors that modulate the synthesis, intravascular metabolism, and cellular catabolism of Lp(a).

Native low-density lipoproteins stimulate leukotriene B4 production by human monocyte-derived macrophages

We have evaluated the effect of native low-density lipoproteins (LDL) on the production of leukotriene B4 (LTB4), a potent inflammatory and chemotactic factor, by human monocyte-derived macrophages. The capacity of LDL (d, 1.024-1.050 g/ml) to increase LTB4 secretion was dose-dependent with an optimal response at 100 micrograms LDL protein/ml, representing an approx. 7.5-fold stimulation over basal levels at 10 days of culture; the half-maximal response occurred at 20 micrograms/ml. The effect of LDL on LTB4 production was rapid (within 15 min) and was maintained for at least 21 h. The generation of LTB4 in response to LDL was partially inhibited (approx. 70% inhibition) by EDTA (5 mM) and by a monoclonal antibody (IgG-C7; 160 micrograms/ml) directed against the binding site of the cellular LDL receptor. In addition, the effects of native LDL and acetylated LDL were additive. These findings suggest that the specific interaction of LDL with its high affinity receptor represents a major component in the stimulation of the production of LTB4 by human monocyte-derived macrophages.

Plasma lipoproteins and liver lipids in two breeds of geese with different susceptibility to hepatic steatosis: changes induced by development and force-feeding

Susceptibility to fatty liver in the force-fed goose is partly under genetic control. However, the mechanisms leading to liver steatosis in this avian model are poorly understood, but may involve perturbation in hepatic lipoprotein synthesis. Plasma lipoproteins were fractionated by density gradient ultracentrifugation from plasma of geese differing in their susceptibility to liver steatosis (Landes breed, highly susceptible; Rhine breed, partly resistant). The concentrations and chemical compositions of the major lipoprotein classes (VLDL, IDL, LDL and HDL) were characterized at 8, 22 and 27 wk of age and compared to the lipid composition of the corresponding liver. In non-force-fed geese, the lipoprotein profile was typical of birds, with high-density lipoprotein (HDL) predominating (4-5 g/L). However, at 22 and 27 wk of age, very low-density lipoprotein (VLDL) levels were significantly lower in Landes geese suggesting that this breed may possess a lower ability to export liver lipids, which would explain its susceptibility to liver steatosis when overfed. The livers of force-fed geese were specifically enriched in triglyceride, and to a lesser extent, in cholesteryl esters and non-esterified fatty acids as compared to those of control geese of the same age (27 wk). This accumulation of lipids was more pronounced in the Landes breed and was responsible for the higher liver weight in that breed. In both breeds, liver steatosis was accompanied by an increase in plasma levels of HDL (11 g/L), whereas low-density lipoproteins were essentially absent.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein Lp(a) in homozygous familial hypercholesterolemia: density profile, particle heterogeneity and apolipoprotein(a) phenotype

Homozygous familial hypercholesterolemia (FH) is a genetic disorder featuring a functional defect in cellular LDL receptors, marked elevation in circulating LDL concentrations, and premature atherosclerosis. The potential atherogenic role of apo B-containing lipoproteins other than LDL in this disease is indeterminate. We describe the quantitative and qualitative characteristics of Lp(a) as a function of apo(a) phenotype in a group of eight, unrelated homozygous FH patients. Plasma Lp(a) levels were significantly elevated (2.5-fold; mean 50 +/- 32 mg/dl) as compared to those in healthy subjects. The S2 isoform of apo(a) occurred most frequently (6 of eight patients); the rare B isoform presented in three patients. Plasma Lp(a) levels in homozygous FH did not correspond to those predicted by apo(a) phenotype. Analyses of the density distribution of Lp(a) and of Lp(a) particle size and heterogeneity as a function of density did not reveal any anomalies characteristic of homozygous FH. However, comparison of the hydrated density of Lp(a) particles as a function of apo(a) isoform content revealed a clear influence of isoform on this parameter; thus, in a B/S2 heterozygous patient, the density distribution of Lp(a) fractions containing isoform B alone, B and S2, and S2 alone, demonstrated that the apparent molecular weight of apo(a) plays a determining role in controlling the hydrated density and size of the resulting Lp(a) particle. Indeed, patients expressing the high molecular weight, S2 isoform uniformly displayed a dense form of Lp(a) (hydrated density approximately 1.055 g/ml). In subjects presenting two apo(a) isoforms, each isoform resided on distinct lipoprotein particles; in such cases, the plasma levels of the denser isoform predominated, suggesting differences in rates of formation, or rates of tissular catabolism, or in the plasma stability of the particles, or a combination of these mechanisms. Considered together, our data may be interpreted to suggest that the elevated circulating levels of Lp(a) in homozygous FH patients may reflect either an increased biosynthesis, or diminished catabolism via the cellular LDL receptor pathway, or a combination of both.

Lipoproteins and apolipoproteins in intestinal lymph of the preruminant calf, Bos spp., at peak lipid absorption

We have recently evaluated the in vivo role of the liver in lipoprotein homeostasis in the preruminant calf (Bauchart, D., D. Durand, P. M. Laplaud, P. Forgez, S. Goulinet, and M. J. Chapman, 1989. J. Lipid Res. 30: 1499-1514). We now present the partial characterization of lipoprotein particles in postprandial intestinal lymph at peak lipid absorption (i.e., 10 h after a meal) in the preruminant calf fed a curdled milk replacer. Intestinal lymph from four male preruminant calves was analyzed for its content of lipids and fractionated by sequential and density gradient ultracentrifugation into chylomicrons (Sf greater than 400), very low density lipoproteins (VLDL) (Sf less than 400; d less than 1.006 g/ml), and a series of lipoprotein subfractions with d greater than 1.006 g/ml. Postprandial lymph contained predominantly triglycerides (1099 +/- 611 mg/100 ml), with lesser amounts of phospholipids (197 +/- 107 mg/100 ml) and cholesterol (52 +/- 30 mg/100 ml). The most abundant particles were triglyceride-rich chylomicrons and VLDL which accounted for approximately 76% and approximately 19%, respectively, of total d less than 1.21 g/ml lipoproteins. As judged by negative stain electron microscopy, chylomicron particle diameters ranged from 650 to 2400 A, while VLDL were smaller and distributed over a distinct size range (340-860 A). These two lipoprotein classes each presented protein components with Mr comparable to those of human apoB-48, apoA-I, and C apoproteins, together with an Mr 52,000 protein resembling human beta 2-glycoprotein-I. In addition, VLDL exhibited a polypeptide with Mr approximately 61,000. Lymph lipoproteins with d greater than 1.006 g/ml consisted primarily (approximately 81% of total) of particles distributed over the 1.053-1.119 g/ml density range. Electrophoretic analysis of the latter lipoprotein fraction showed it to be heterogeneous, including particles with the migration characteristics of low and of high density lipoproteins, respectively. Subfractions in the d 1.053-1.076 g/ml range were dominated by particles with Stokes diameters typical of high density lipoproteins (HDL), but also contained three different populations of low density lipoprotein-like particles. The high molecular weight apolipoproteins in these same cholesteryl ester-rich (greater than 30% of lipoprotein mass) subfractions comprised components with Mr resembling those of human apoB-100 and apoB-48, respectively, and with the latter protein predominating to a varying degree. A counterpart to human apoA-I was the major protein component over the entire density range from d 1.053 to 1.119 g/ml.(ABSTRACT TRUNCATED AT 400 WORDS)

Apolipoprotein E expression by human-monocyte-derived macrophages. Modulation by opsonised zymosan and cholesterol

The effects of opsonised zymosan and of acetylated low-density lipoprotein (AcLDL) on the synthesis and secretion of apolipoprotein E (apoE), and of apoE mRNA abundance, have been studied in human-monocyte-derived macrophages (MDM). Stimulation by opsonised zymosan led to a concentration-dependent increase in apoE secretion; non-opsonised zymosan was without effect. Incubation with AcLDL led to a concentration-dependent elevation in apoE synthesis which paralleled the increase in cellular cholesterol content. The opsonised-zymosan-induced stimulation of apoE production was additive to that resulting from cholesterol loading with AcLDL. Opsonised zymosan alone did not affect the cholesterol content of MDM. Cholesterol-loaded MDM remained responsive to opsonised zymosan stimulation, displaying a 3.5-fold elevation in apoE secretion as compared to their non-stimulated counterparts. Cell-associated apoE remained at trace levels under all conditions of cell treatment. Studies involving [35S]methionine incorporation showed de novo synthesis of apoE to be enhanced in both cholesterol-loaded and opsonised-zymosan-stimulated macrophages. Estimation of apoE mRNA in opsonised-zymosan-stimulated and control MDM by dot-blot analysis revealed similar message abundance; by contrast, elevation in cellular cholesterol content following incubation with modified LDL led to a significant increase in apoE mRNA levels. We conclude that the opsonised-zymosan-induced stimulation of apoE synthesis and secretion in human MDM may occur by a mechanism(s) independent of cellular cholesterol content.

Expression of elastase activity by human monocyte-macrophages is modulated by cellular cholesterol content, inflammatory mediators, and phorbol myristate acetate

We investigated the effects of a number of stimulatory agents on the production of both cell-associated and extracellular elastase-type enzymes on human monocyte-macrophages in vitro and of the modulation of such effects by modification of cellular cholesterol content. The stimulatory agents included phorbol myristate acetate (PMA) and the inflammatory mediators, lipopolysaccharide (LPS), opsonized zymosan (OZ), and platelet activating factor (PAF). Using the synthetic substrate, N-succinyl-trialanyl-paranitroanilide (SANA), we detected cell-associated elastase-like activity in monocyte-derived macrophages. Such activity increased markedly with cell maturation over the period from 5 to 15 days of adherence culture. While PAF (10 micrograms/ml) and LPS (10 micrograms/ml) were without effect on cell-associated elastase-like activity in macrophages, PMA (100 ng/ml) and OZ (1 mg/ml) markedly stimulated such activity in cells cultured for 15 days. Furthermore, a fivefold increase in the cell-associated elastase-like activity of macrophages occurred upon cholesterol loading of the cells with acetylated low density lipoprotein (AcLDL). By contrast, this activity was markedly diminished upon depletion of cellular cholesterol content after incubation with high density lipoprotein (HDL3). Latent elastinolytic activity in the culture medium was detected by use of a radioactive substrate, insoluble 3H-elastin, after initial tryptic treatment of the medium. Such latent elastase activity was secreted only by activated macrophages; the relative potency of stimulation was: PMA greater than LPS = PAF greater than OZ. Increase in cellular cholesterol content alone markedly enhanced the secretion of elastase (from undetectable levels to 28 ng of 3H-elastin degraded/hr/micrograms DNA). In all cases, both the cell-associated and secreted latent elastinolytic activities were due to metalloproteases, in view of their 90% inhibition by 2 mM EDTA. Cholesterol-loaded macrophages, which displayed an approximately 40-fold increase in total cholesterol content as compared to control cells, remained sensitive to the action of activators of OZ and PMA, while LPS and PAF exerted only weak effects. Our data indicate that cellular cholesterol content and inflammatory mediators are effective stimulants of the production and secretion of elastase-type enzymes by human monocyte-macrophages. Among these factors, cellular cholesterol content, OZ, PAF, and LPS may represent factors of relevance to the inflammatory role of the macrophage in atherogenesis and more specifically to the alteration of elastin structure in the extracellular matrix of the vessel wall.

Characterization and amino-terminal sequence of apolipoprotein AI from plasma high density lipoproteins in the preruminant calf, Bos spp

The major apolipoprotein of calf plasma high-density lipoproteins, apo-AI, has been isolated and characterized. Apolipoprotein AI (apo-AI) was separated from the protein moiety of high-density lipoproteins (d 1.090-1.180 g/ml) by preparative electrophoresis in SDS-polyacrylamide gels followed by electrophoretic elution. Purified calf apo-AI had an Mr of approx. 27,000-28,000 in SDS-polyacrylamide gels, resembling human apo-AI. The amino acid composition of calf apo-AI displayed an overall similarity to that of its human and other mammalian counterparts (baboon, dog, badger, rabbit, rat and mouse), but differed in having higher proportions of glutamic acid, alanine and isoleucine. Amino-terminal amino acid sequence analysis up to the 47th residue showed close homology between calf apo-AI and those of the mammals with which it was compared. However, residues 2, 7, 20 and 22 in calf AI (i.e. aspartic acid, serine, glutamic acid and isoleucine, respectively) were substituted by glutamic acid, proline or glutamine, aspartic acid, and valine or leucine respectively, in the other mammals.

Plasma lipoproteins and apolipoproteins in the preruminant calf, Bos spp: density distribution, physicochemical properties, and the in vivo evaluation of the contribution of the liver to lipoprotein homeostasis

The in vivo role of the liver in lipoprotein homeostasis in the preruminant calf, a functional monogastric, has been evaluated. To this end, the hydrodynamic and physicochemical properties, density distribution, apolipoprotein content, and flow rates of the various lipoprotein particle species were determined in the hepatic afferent (portal vein and hepatic artery) and efferent (hepatic vein) vessels in fasting, 3-week-old male preruminant calves. Plasma lipoprotein profiles were established by physicochemical analyses of a series of subfractions isolated by isopycnic density gradient ultracentrifugation. Triglyceride-rich very low density lipoproteins (VLDL) (d less than 1.018 g/ml) were minor plasma constituents (approximately 1% or less of total d less than 1.180 g/ml lipoproteins). The major apolipoproteins of VLDL were apoB-like species, while the complement of minor components included bovine apoA-I and apoC-like peptides. Particles with diameters (193-207 A) typical of low density lipoproteins (LDL) were present over the density interval 1.026-1.076 g/ml; however, only LDL of d 1.026-1.046 g/ml were present as a unique and homogeneous size subspecies, containing the two apoB-like species as major protein components in addition to elevated cholesteryl ester contents. LDL represented approximately 10% of total d less than 1.180 g/ml lipoproteins in fasting plasma from all three hepatic vessels. Overlap in the density distribution of particles with the diameters of LDL and of high density lipoproteins (HDL) occurred in the density range from 1.046 to 1.076 g/ml; these HDL particles were 130-150 A in diameter. HDL were the major plasma particles (approximately 90% of total d less than 1.180 g/ml substances) and presented as two distinct populations which we have termed light (HDLL) and heavy (HDLH) HDL. Light HDL (d 1.060-1.091 g/ml) ranged in size from 120 to 140 A, and were distinguished by their high cholesteryl ester (29-33%) and low triglyceride (1-3%) contents; apoA-I was the principal apolipoprotein. Small amounts of apolipoproteins with Mr less than 60,000, including apoC-like peptides, were also present. Heavy HDL (d 1.091-1.180 g/ml) accounted for almost half (47%) of total calf HDL, and like HDLL, were also enriched in cholesteryl ester and apoA-I; they ranged in size from 93 to 120 A. The protein moiety of HDLH was distinct in its possession of an apoA-IV-like protein (Mr 42,000). Blood flow rates were determined by electromagnetic flowmetry, thereby permitting determination of net lipoprotein balance across the liver. VLDL were efficiently removed during passage through the liver (net uptake 1.06 mg/min per kg body weight).(ABSTRACT TRUNCATED AT 400 WORDS)

A methodology for compartmental model indistinguishability

The problem of constructing all minimal compartmental models that are indistinguishable through input-output knowledge alone from some given model is examined. The main tool in this analysis is a set of geometric properties that can be deduced from input-output knowledge and hence must be equally true in any two indistinguishable models. These properties, together with preservation of the form of the model's transfer function(s), provide an effective means for producing a set of candidate models for indistinguishability.

Alterations in plasma lipoproteins and apolipoproteins associated with estrogen-induced hyperlipidemia in the laying hen

The laying hen represents a physiological model in which the mechanisms of action of estrogens on lipid transport can be evaluated. The plasma lipoproteins in the laying hen were subfractionated into discrete particle species by isopycnic density gradient ultracentrifugation and the physicochemical properties and apolipoprotein contents of individual subfractions evaluated. The qualitative and quantitative aspects of this estrogen-specific profile were then compared to those of the immature chicken. As observed earlier, estrogens induced dramatic elevation in very-low-density lipoproteins (VLDL) (up to 900 mg/dl). Indeed, triglyceride-rich lipoproteins with densities up to 1.035 g/ml, i.e. VLDL and their remnants, behaved as a continuum which displayed little variation in size (20.5-21 nm), electrophoretic mobility (beta-like) and apolipoprotein content; apo B-100 (540 kDa) predominated while apo A-I (27 kDa), apo VLDL-II (19 kDa) and an apo-C-like protein (13 kDa) were present as minor components. The typical high-density lipoproteins (HDL) in the immature chicken were replaced by a lipoprotein population whose physicochemical properties were quite distinct. Thus these particles were distributed as a single, asymmetric peak over the density range 1.030-1.158 g/ml, a wide interval which overlapped that of apo-B-rich particles at its lower limit. The rho 1.030-1.158 g/ml lipoproteins were present at concentrations (approximately equal to 200 mg/dl) some twofold to threefold lower than those of HDL in immature birds. Furthermore, they displayed physical and chemical properties in common with both low-density lipoproteins (LDL) and HDL and were LDL-like in exhibiting beta mobility but HDL-like in size (9-15 nm diameter). Their protein moiety was also HDL-like in its predominant content of apo A-I; small amounts of apo VLDL-II and the apo-C-like protein were also detected. Substantial amounts of lipid were found at rho greater than 1.195 g/ml: such substances are absent in the immature chicken and may reflect the presence of vitellogenins. The hyperestrogenic state in the laying hen is therefore associated with major modifications in lipoprotein and apolipoprotein profile. Such modifications may be of relevance to clinical disorders involving estrogen-induced hyperlipidemia.

The problem of model indistinguishability in pharmacokinetics

The problem of model indistinguishability is introduced in the context of linear compartmental models in pharmacokinetics. The two most widely used methods of analyzing model indistinguishability are described. It is shown that as the number of compartments increases, one approach, based on the Laplace transforms of the observations, although conceptually simple, can result in very large numbers of candidate models to be examined for indistinguishability, while the other approach, based on similarity transformations, although systematic, often results in very difficult algebraic expressions. These problems can be eased by the use of some simple geometrical rules, used at the outset of an indistinguishability analysis. The approach is illustrated by application of two 2-compartment drug, 2-compartment metabolite models.

Interrelationship of plasma triglyceride and coagulant factor VII levels in normotriglyceridemic hypercholesterolemia

We have evaluated the potential relationships between plasma levels of certain coagulation factors, i.e. factor VII antigen (F VIIag) and factor VII coagulant activity (F VIIc), and parameters of lipid transport in a group of 90 normotriglyceridemic patients displaying hypercholesterolemia (Fredrickson's type IIa hyperlipoproteinemia). Levels of factor VIIc were significantly elevated (P less than 0.01) in this patient group as compared to a group of healthy normolipidemic subjects. By contrast, levels of factor VIIag were also increased, but such differences were not significant in relation to those of controls. Furthermore, concentrations of F VIIc and F VIIag in hypercholesterolemic males and females resembled each other. Similar observations were made when patients were divided into those either presenting or lacking symptoms of vascular disease. However, plasma levels of both F VIIc and F VIIag were positively correlated with circulating triglyceride concentrations in the hypercholesterolemic group, but not with other parameters of lipid transport such as serum cholesterol, HDL-cholesterol, and apolipoprotein B. When patients were treated with a lipid-lowering agent (cholestyramine), lower levels of both F VIIc and F VIIag were found concomitantly with a decrease of similar order in triglyceride concentrations. We conclude that serum triglyceride levels, even within the normal range, may be associated with elevation in the activity of factor VII in hypercholesterolemic patients, thereby increasing their risk of thrombosis.

Characterization of five mouse monoclonal antibodies to apolipoprotein[a] from human Lp[a]: evidence for weak plasminogen reactivity

We describe the development of five murine monoclonal antibodies (14A12, 39A1, 53A9, 73A7, and 128A6) specific to human apolipoprotein[a] (Mr approximately 570,000), and their characterization by a number of procedures including cotitration, competition and inhibition enzyme-linked immunosorbent assays (ELISA), immunoblotting of native lipoproteins and of SDS-solubilized apolipoproteins electrophoresed in polyacrylamide gels, and dot immunobinding assays. The patterns of immunoreactivity of these antibodies were similar. Each reacted in ELISA assays and upon electroimmunoblotting with purified apo[a], with apo[a] liberated by reduction of Lp[a], and with delipidated Lp[a] solubilized in SDS, but by contrast, they reacted with native Lp[a] to a significant degree only upon electroimmunoblotting. No reactivity was seen with LDL-apoB-100 or with other apolipoproteins. The cross-reactivity of these antibodies with the homologous protein, plasminogen, was examined by comparison of the amount of plasminogen or apo[a] required for 50% inhibition of antibody binding to apo[a], and by an ELISA assay. The inhibition assay showed reactivity with plasminogen to be 37- to 50-fold lower than with apo[a], while dot immunobinding showed the lower limit of detection of plasminogen and of apo[a] to be approximately 320 and 31 micrograms, respectively. In an ELISA sandwich assay based on monoclonal antibodies LHLP-1, 14A12, and 53A9, the lower limit of Lp[a] detection (approximately 1 ng/ml protein) was about 100-fold less than that of plasminogen. Chemical modification of apo[a] revealed a significant contribution of arginine residues to the epitopes of 14A12, 39A1, and 53A9. Modification of cysteine residues with iodoacetamide was without effect, thereby distinguishing these antibodies from LHLP-1. Each antibody reacted with the six major size forms of apo[a] (Mr approximately 450,000-750,000) in immunoblots of human sera electrophoresed in SDS-polyacrylamide gels. Marked heterogeneity in apo[a] phenotype was detected and both single and double band phenotypes were observed in a randomized study. Cotitration and competition binding studies showed varying degrees of interaction between all five epitopes, with the exception of 128A6 which appeared to be independent of 39A1 and 53A9 (and vice versa). These data suggest that our five monoclonal antibodies recognize epitopes on apolipoprotein[a] that are exposed and accessible on the native Lp[a] particle. We conclude that our monoclonal antibodies recognize a specific region of apo[a], and that this region undergoes a conformational change upon adsorption of Lp[a] to plastic thereby diminishing epitope recognition.(ABSTRACT TRUNCATED AT 400 WORDS)

Platelet activating factor is a potent stimulant of the production of active oxygen species by human monocyte-derived macrophages

Platelet activating factor (PAF; C16), 1-O-Hexadecyl-2-acetyl-sn-glycero-3-phosphorylcholine) stimulated the production of active oxygen species by human monocyte-derived macrophages in culture. An optimal response was observed at a concentration of 13 microM PAF with half-maximal stimulation at 5 microM. The generation of superoxide ion (O2-) and hydrogen peroxide (H2O2) in response to PAF was inhibited specifically by a PAF-antagonist (1-O-Hexadecyl-2-acetyl-sn-glycero-3-phospho (N,N,N,-trimethyl) hexanolamine; such generation varied with the degree of maturation of cultured monocytes into macrophages. Production of active oxygen species increased progressively to reach a maximal level between days 4 to 6 of culture and remained maximal to day 12, after which it decreased progressively. Phorbol 12-myristate-13-acetate (PMA) and opsonized zymosan also stimulated generation of O2- and H2O2. PAF was however distinguished by its potent capacity to stimulate O2- and H2O2 production even at late stages of macrophage maturation (18 days), at which time both PMA and zymosan lacked significant effect. These findings suggest that PAF is a factor of potential relevance to the inflammatory role of the macrophage in atherogenesis.

Guinea pig low density lipoproteins: structural and metabolic heterogeneity

The structural and metabolic heterogeneity of low density lipoproteins (LDL, d 1.024-1.100 g/ml) has been investigated in the guinea pig. Two LDL subfractions, of d 1.024-1.050 and 1.050-1.100 g/ml, respectively, were isolated by sequential ultracentrifugation; while both were enriched in cholesteryl ester and apoB-100, the former was heterogeneous displaying three particle size species of diameters 26.9, 25.6, and 24.7 nm, whereas the denser subfraction was relatively homogeneous containing a single, smaller species (diam. 23.6 nm). The fractional catabolic rates (FCR) of the two LDL subfractions were alike (approximately 0.090 pools/hr) in the guinea pig in vivo. After modification of each subfraction by reductive methylation, the FCRs were reduced similarly and indicated that 70-80% of degradation occurred via the cellular LDL receptor pathway. However, the intravascular metabolism of these LDL subfractions, determined from the radioactive content of density gradient fractions as a function of time after injection of radiolabeled native or chemically modified LDL, tended to be distinct. Thus, while radiolabeled apoB-100 in the lighter subfraction maintained the initial density profile up to 48 hr, the radioactive profile of its methylated counterpart changed, the proportion of radioactivity in the lighter gradient fractions (d 1.027-1.032 g/ml) increasing while that in the denser (d 1.037-1.042 g/ml) fractions diminished. A more marked transformation occurred in LDL of d 1.050-1.100 g/ml, in which the radioactive profile shifted towards lighter particles of the d 1.024-1.050 g/ml species; this shift was partially dependent on the LDL receptor, since it was more pronounced in the methylated subfraction. Furthermore, a net increase in the radioactive content of gradient subfractions 7 to 9 (d 1.032-1.042 g/ml) was found 10 hr after injection of methylated LDL of d 1.050-1.100 g/ml, at which time the bulk of LDL radioactivity had been removed from plasma. Several mechanisms, acting alone or in combination, may account for these findings; among them, some degree of transformation of dense to lighter LDL species appears a prerequisite. In conclusion, our data attest to the structural heterogeneity of circulating LDL in the guinea pig, and suggest that the intravascular processing and metabolism of LDL particle subspecies is directly related to their structure and physicochemical properties.

Effects of soy protein and casein in low cholesterol diets on plasma lipoproteins in normolipidemic subjects

Dietary plant proteins may lower plasma cholesterol and LDL concentrations in hypercholesterolemic patients when substituted for animal proteins, particularly in diets with low cholesterol and saturated fat content. Plant protein diets appear, however, to be without effect on plasma lipoprotein levels in normal subjects. In the present study, we have examined whether the origin of the dietary protein, i.e. plant (soy) or animal (casein), affects the plasma lipoproteins in normolipidemic subjects when these proteins are presented as components of diets low in cholesterol and saturated fat. The study followed a crossover design. Five men and 5 women consumed liquid formula diets containing 20% of calories as casein or soy protein, 28% as fat (mainly monounsaturated), and 52% as carbohydrate; the intake of cholesterol was less than 100 mg per day. The two dietary periods, each of 1 month duration, were separated by an interim period of 1 month on self-chosen food. Following an initial 30% reduction of cholesterol and LDL plasma levels on both diets, the concentrations of each of the major lipoprotein classes (VLDL, IDL, LDL, HDL2 and HDL3) were similar during the two experimental dietary periods. Body weights were essentially constant. Dietary soy protein and casein could not be distinguished in their effects on the plasma concentrations and chemical composition of the major lipoprotein classes in normolipidemic subjects.

Density distribution and physicochemical properties of plasma lipoproteins and apolipoproteins in the goose, Anser anser, a potential model of liver steatosis

The fractionation and physicochemical characterization of the complex molecular components composing the plasma lipoprotein spectrum in the goose, a potential model of liver steatosis, are described. Twenty lipoprotein subfractions (d less than 1.222 g/ml) were separated by isopycnic density gradient ultracentrifugation, and characterized according to their chemical composition, particle size and particle heterogeneity, electrophoretic mobility, and apolipoprotein content. Analytical ultracentrifugal analyses showed high density lipoproteins (HDL) to predominate (approximately 450 mg/dl plasma), the peak of its distribution occurring at d approximately 1.090 g/ml (F1.21 approximately 2.5). The HDL class displayed marked density heterogeneity, HDL1-like particles being detected up to a lower density limit of approximately 1.020 g/ml, particle size decreasing progressively from 17-19 nm at d 1.024-1.028 g/ml to 10.5-12 nm (d 1.055-1.065 g/ml), and then remaining constant (approximately 9 nm) at densities greater than 1.065 g/ml. HDL subfractions displayed multiple size species; five subspecies were present over the range d 1.103-1.183 g/ml with diameters of 10.5, 9.9, 9.0, 8.2, and 7.5 nm, four in the range d 1.090-1.103 g/ml (diameters 10.5, 9.9, 9.0, and 8.2 nm) and three over the range d 1.076-1.090 g/ml (diameters 10.5, 9.9, and 9.0 nm). ApoA-I (Mr 25,000-27,000) was the major apolipoprotein in all goose HDL subfractions, while the minor components (apparent Mr 100,000, 91,000, 64,000, 58,000, approximately 42,000, 18,000 and apoC-like proteins) showed marked quantitative and qualitative variation across this density range (i.e., 1.055-1.165 g/ml). The d 1.063 g/ml boundary for separation of goose low density lipoproteins (LDL) from HDL was inappropriate, since HDL-like particles were present in the density interval 1.024-1.063 g/ml, while particles enriched in apoB (Mr approximately 540,000) and resembling LDL in size (approximately 20.5 nm) were detected up to a density of approximately 1.076 g/ml. Goose LDL itself was a major component of the profile (90-172 mg/dl) with a single peak of high flotation rate (Sf approximately 10.5). The physicochemical properties and apolipoprotein content of intermediate density lipoproteins (IDL) and LDL varied but little over the range d 1.013-1.040 g/ml, presenting as two particle species (diameters 20.5 and 21 nm) of essentially constant chemical composition; LDL (d 1.019-1.040 g/ml) were separated from HDL1 by gel filtration chromatography and appeared to contain primarily apoB with lesser amounts of apoA-I.(ABSTRACT TRUNCATED AT 400 WORDS)

Further resolution and comparison of the heterogeneity of plasma low-density lipoproteins in human hyperlipoproteinemias: type III hyperlipoproteinemia, hypertriglyceridemia and familial hypercholesterolemia

The heterogeneity of the plasma low-density lipoproteins (LDL) in subjects with type III hyperlipoproteinemia (3 cases), with hypertriglyceridemia (4 cases) and with the heterozygous form of familial hypercholesterolemia (FH, 4 cases) has been evaluated using a new, high resolution equilibrium density gradient ultracentrifugation procedure. The mass distribution profile, physicochemical properties, particle heterogeneity and apoprotein B content of a series of 13 LDL subfractions was examined in the 3 hyperlipidemic groups and the data were compared with those reported earlier in normolipidemic subjects. In FH, LDL mass was distributed as a narrow peak of d approximately 1.031-1.034 g/ml, whereas the distribution in hypertriglyceridemia was markedly asymmetric with a single peak of elevated density (d approximately 1.037-1.043 g/ml); the distribution in type III subjects was distinguished by its bi- or trimodal nature and broad profile. The chemical composition of LDL gradient subfractions in FH and in hypertriglyceridemia markedly resembled that of the respective parent LDL of d = 1.019-1.063 g/ml, displaying elevated proportions of cholesteryl ester in FH and of protein in hypertriglyceridemia. LDL subfractions in type III disease were enriched in free cholesterol. The Stokes diameters of LDL particles in corresponding subfractions from the 3 hyperlipidemic states were similar; however, whereas a single particle species was characteristic of each LDL subfraction in both FH and in our normolipidemic group, 2 species were frequently present in each subfraction in both type III and type IV diseases; in addition, subfractions from type III subjects occasionally exhibited 3 size species. Apolipoprotein B-100 was the predominant protein component in LDL subfractions from all 3 hyperlipidemic groups. Plasma LDL consist then of multiple particle species which constitute a particularly complex spectrum in type III hyperlipoproteinemia and in hypertriglyceridemia. The origin(s) of such particle subspecies is indeterminate at present; moreover, they may differ in their intravascular metabolism, in their degradation in tissues and in their relative atherogenicities.

Further resolution of the low density lipoprotein spectrum in normal human plasma: physicochemical characteristics of discrete subspecies separated by density gradient ultracentrifugation

The molecular basis of the heterogeneity of plasma low density lipoproteins (LDL, d 1.024-1.050 g/ml) was evaluated in 40 normolipidemic male subjects following fractionation by isopycnic density gradient ultracentrifugation into eight major subspecies. The mass profile of our subjects' LDL uniformly displayed single symmetric or asymmetric peaks as a function of density; the peak occurred most frequently (20 subjects) in subfraction 7 (d 1.0297-1.0327 g/ml). Several physicochemical properties (hydrodynamic behavior, electrophoretic mobility, chemical composition, size and particle heterogeneity, and apolipoprotein heterogeneity) of the LDL subfractions were examined. Hydrodynamic analyses revealed unimodal distributions and distinct peak Sf degree rates in individual subfractions. Such behavior correlated well with particle size and heterogeneity data, in which LDL subspecies were typically resolved as unique narrow bands by gradient gel electrophoresis. Subspecies with average densities of 1.024 to 1.0409 g/ml ranged from 229 to 214 A in particle diameter. LDL protein content increased in parallel with density while the proportion of triglyceride diminished; cholesteryl esters predominated, accounting for approximately 40% or more by weight. Distinct differences in net electric charge were demonstrated by electrophoresis in agarose gel, the subspecies with average density of 1.0314 g/ml displaying the lowest net negative charge. ApoB-100 was the major apoprotein in all subspecies, and constituted the unique protein component over the density interval 1.0271-1.0393 g/ml. ApoE and apo[a] were detected at densities less than 1.0271 and greater than 1.0393 g/ml. While apoE was evenly distributed within these two regions, representing up to 2% of apoLDL, the distribution of apo[a] was skewed towards the denser region, in which it amounted to 3-7% of apoLDL. ApoC-III was detectable as a trace component at densities greater than 1.0358 g/ml. Calculation of the number of molecules of each chemical component per LDL subspecies showed the presence of one copy of apoB-100 per particle, in association with decreasing amounts of cholesteryl ester, free cholesterol, and phospholipid. These data indicate that a similar overall molecular organization and structure is maintained in a unimodal distribution of LDL particle subspecies over the density range approximately 1.02 to 1.05 g/ml. In sum, our data may be interpreted to suggest that microheterogeneity in the physicochemical properties of human LDL subspecies reflects dissimilarities in their origins, intravascular metabolism, tissular fate, and possibly in their atherogenicity.

Pharmacology of fenofibrate

This discussion outlines the major aspects of the human pharmacology of fenofibrate, a hypolipidemic agent. In view of its short half-life, efficient absorption, and elimination, fenofibrate would not appear to accumulate in either plasma or tissues. It is extensively absorbed only in the presence of food and is transported through the bloodstream by albumin. Fenofibrate is taken up by both the liver and kidney. Except for a small percentage (about 5 percent) reduced at the ketone moiety before conjugation, most drug is excreted as a conjugate in the urine. Less than 20 percent is excreted through the bile. In normal persons, at steady state with usual doses of 100 mg three times daily, the plasma half-life approximates 30 hours. Because fenofibrate is not dialyzable, it has a markedly prolonged half life in patients with renal failure and should not be used.

Lipoprotein composition of human suction-blister interstitial fluid

Interstitial fluid (IF) was obtained in 27 apparently healthy subjects (12 males, 15 females) by applying mild suction (200-250 mm Hg) on the skin either on the midvolar forearm or on the paraumbilical region of the abdomen. The IF concentrations of lipids and apolipoproteins (apo) were studied and compared with those of serum (S). The mean ratio between interstitial fluid and serum (IF/S ratio) varied from 0.14 for forearm apoE to 0.29 for apoA-II on the abdomen. This ratio was consistently lower for apoE, C-II, C-III, and B than for apoA-I and A-II, and significantly lower on the arm than on the abdomen for all apolipoproteins studied. The IF/S ratios showed marked variations among individuals. However, interstitial fluid apolipoprotein concentrations at different blister sites were highly correlated within each individual. Studies with agarose gel electrophoresis and density gradient ultracentrifugation revealed that large triglyceride-rich particles were virtually lacking in interstitial fluid and that the relation between the low density lipoproteins (LDL) and high density lipoproteins (HDL) was shifted towards a greater proportion of HDL. The lipoprotein distribution in the HDL range of interstitial fluid differed from that of serum showing one maximum at a density of about 1.070 g/ml (serum HDL2 about 1.090 g/ml) and one at a density of 1.130-1.140 g/ml (serum HDL3, 1.110-1.120 g/ml). The former subfraction contained most of the lipoprotein-bound apoE while the latter contained the major part of apoA-I and apoA-II. Studies of the lipoproteins of interstitial fluid may add to our understanding of the development of atherosclerosis and xanthomatosis and may also provide valuable information on the permeability of the capillary membrane in normo- and pathophysiological states.

Identification of surface-exposed segments of apolipoprotein B-100 in the LDL particle

The isolation and amino acid sequence of eleven peptides liberated by tryptic treatment from surface-exposed regions of apolipoprotein B-100 in the native low-density lipoprotein particle are described. These peptides represent eight segments in the sequence of the B-100 protein, one of which was localised to the amino-terminal thrombolytic fragment T4 (1297 amino acids), four to the T3 fragment (2052 residues) and three to the carboxylterminal fragment T2 (1287 residues). An exposed segment was identified on each side of the T2/T3 cleavage site, in close proximity to two segments enriched in basic amino acids (residues 3147-3157 and 3359-3367 respectively). The surface exposure of this region is consistent with its contribution to the putative apo-B,E receptor binding domain. Four of the eight tryptic segments contribute to regions of proline-rich clusters. Homology between the sequence of the tryptic peptides and those predicted by cDNA cloning was complete.

A study of the structural heterogeneity of low-density lipoproteins in two patients homozygous for familial hypercholesterolaemia, one of phenotype E2/2

The structural heterogeneity of the low-density lipoproteins (d 1.019-1.063 g ml-1) in two female patients homozygous for familial hypercholesterolaemia, one of phenotype E2/2, has been evaluated using a new ultracentrifugal density gradient procedure. The mass distribution, chemical composition, particle size and heterogeneity, hydrated density and apolipoprotein content of 16 LDL subfractions were determined. By gradient gel electrophoresis, the lighter LDL subfractions (d 1.016-1.037 g ml-1) displayed a single particle species which progressively diminished in size from 24.8 to 22.0 nm with increase in density. By contrast, subfractions of higher density (d greater than 1.037 g ml-1) exhibited two LDL particle species of distinct size; one component decreased in size from 21.8 to 20.4 nm with increase in density, while the second maintained an essentially constant diameter (between 22.5 and 23.5 nm) across these LDL subfractions. Immunoblotting with anti-apo-B100 of LDL subspecies separated by gradient gel electrophoresis showed all particles to contain apo-B100. However, dot-blots and immunoblotting with a monoclonal antibody to lipoprotein (a) (Lp(a)) revealed that the LDL particle subspecies of greatest diameter (22.5-23.5 nm) present in the denser subfractions (d greater than 1.037 g ml-1) also contained the Lp(a) antigen. These findings, taken together with the high plasma Lp(a) levels (greater than 60 mg dl-1) in our patients, raise the possibility that Lp(a) may contribute in a significant manner to the atherogenic process in homozygous familial hypercholesterolaemia.