Isolation, characterization and comparative aspects of the major serum apolipoproteins, B-100 and AI, in the common marmoset, Callithrix jacchus

An evaluation of the marmoset Callithrix jacchus (sagüi) as an experimental model for the dyslipoproteinemia of human Schistosomiasis mansoni

Human infection with the parasite Schistosoma mansoni is a relatively common occurrence in regions of South America and is associated with liver dysfunction and dyslipoproteinemia. Specifically, the activity of plasma lecithin:cholesterol acyltransferase (LCAT) activity is reduced, the concentration of plasma cholesterol esters falls, phospholipid concentrations are elevated and erythrocyte membranes become cholesterol enriched. Previous studies have utilized rodents (rats and mice) as experimental models to study the dyslipoproteinemia induced by S. mansoni infection. However, the plasma lipoprotein profiles in these animals is very different from humans and infection is not accompanied by decreases in LCAT activity or cholesterol enrichment of their erythrocyte membranes. Here we have evaluated the suitability of the marmoset Callithrix jacchus (sagüi) which is small and readily available in Brazil, as a potential animal model for the study of the dyslipoproteinemia of S. mansoni infections. The plasma lipoprotein compositions and distributions in sagüi, unlike rats or mice, approximate those of man with the LDL representing a major lipoprotein species. The molecular species of phospholipids, cholesterol esters and triglycerides present in sagüi plasma are also very similar to man, whereas those of rats and mice favor the longer chain more unsaturated species, Sagüi, like rodents, can be successfully infected with S. mansoni and after 60 days, this results in a 50% reduction in plasma LCAT activity, an 11% reduction in plasma cholesterol esters, an absolute increase of 46% in plasma phospholipids and an 18% increase in the cholesterol content of erythrocyte membranes. These changes are qualitatively and quantitatively very similar to those previously reported following human infections. Based upon these changes, and the observation that the plasma lipoprotein profile of sagüi and human is similar, we conclude that C. jacchus (sagüi) is an appropriate animal model for the study of dyslipoproteinemia associated with S. mansoni infections.

Cholesterol metabolism in New World primates: comparative studies in two tamarin species (Saguinus oedipus and Saguinus fuscicollis) and the squirrel monkey (Saimiri sciureus)

1. Cholesterol metabolism has been characterized in three species of New World primates, the cotton-top tamarin, the saddle-back tamarin, and the squirrel monkey. 2. When fed a diet containing cholesterol, the three species exhibited differing responses of plasma cholesterol levels. 3. Dietary cholesterol absorption was determined and plasma cholesterol die-away kinetics were analyzed in terms of a two-pool model. 4. The results of the analyses of cholesterol turnover are consistent with the observed species-specific differences in plasma cholesterol values and cholesterol absorption. 5. Cholesterol metabolism differs between the two tamarin species, as well as between the tamarins and the squirrel monkey. 6. Implications of species-specific differences between tamarin species are discussed in terms of the use of tamarin species as animal models for comparative studies of cholesterol metabolism and the etiology of cancer and cardiovascular disease.

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).

A class of amphipathic proteins associated with lipid storage bodies in plants. Possible similarities with animal serum apolipoproteins

The lipid-storing tissues of plants contain many small (0.2-1 microns) lipid (normally triacylglycerol) droplets which are surrounded and stabilized by a mixed phospholipid and protein annulus. The proteinaceous components of the lipid storage bodies are termed oleosins and are not associated with any other cellular structures. The major oleosins of rapeseed and radish have been isolated by preparative SDS-PAGE and are respectively classes of 19 kDa and 20 kDa proteins. Both protein classes were N-terminally blocked for direct sequencing, but were partially sequenced following limited proteolytic digestion. The major rapeseed oleosin was made up of at least two 19 kDa polypeptides, termed nap-I and nap-II, which have closely related but different amino acid sequences. A single 20 kDa oleosin, termed rad-I, was found in radish. A near full length cDNA clone for a major rapeseed oleosin was sequenced and found to correspond almost exactly to the sequence of nap-II. The sequences of nap-I and rad-I show very close similarity to one another, as do the sequences of nap-II and the previously determined sequence for the major oleosin from maize. All four oleosins have a large central hydrophobic domain flanked by polar N- and C-terminal domains. Secondary structure predictions for the four oleosins are similar and a novel model is proposed based on a central hydrophobic beta-strand region flanked by an N-terminal polar alpha-helix and a C-terminal amphipathic alpha-helix. The possibility that oleosins exhibit structural and functional similarities with some animal apolipoproteins is discussed.

Isolation and characterization of plasma lipoproteins of common marmoset monkey. Comparison of effects of control and atherogenic diets

This study examines the potential of the common marmoset monkey (Callithrix jacchus) to serve as a model for human lipoprotein metabolism and atherosclerosis. The lipoproteins of animals fed a low-fat, low-cholesterol diet and a high-fat (12% wt/wt lard), high-cholesterol (0.34% wt/wt) diet were characterized by the combination of sequential ultracentrifugation and Pevikon block electrophoresis. Based on chemical and physical properties, equivalents of human very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL), including and HDL-with apolipoprotein E subclass, were demonstrated. In control animals, whose plasma cholesterol concentration was 140.1 +/- 20.2 mg/dl (means +/- SD), approximately 40% of the plasma cholesterol was transported by LDL as compared with approximately 70% in humans. The cholesterol-fed marmosets segregated into two groups: hypo- and hyper-responders. The hyper-responders had plasma cholesterol levels of 450 to 970 mg/ml. The hypercholesterolemia was associated with elevated concentrations of VLDL, intermediate density lipoproteins, and LDL; in addition, these lipoproteins were enriched in cholesteryl esters relative to lipoproteins isolated from control animals. The HDL (d greater than 1.09 g/ml) levels did not change in response to cholesterol feeding, although the HDL-with apolipoprotein E found in the d = 1.02 to 1.09 g/ml fraction increased approximately fivefold. Based on immunological characteristics and sialic acid content, the common marmoset appeared to lack a lipoprotein(a) equivalent. The results of a short-term feeding study (11 months) suggest that this monkey was susceptible to the development of diet-induced atherosclerosis. The hyper-responsive animals developed foam cell lesions and moderately proliferative intimal lesions, predominantly within the thoracic aorta. In summary, the results of our studies indicate that the common marmoset monkey potentially is a useful model for the study of both lipoprotein metabolism and diet-induced atherosclerosis.

Immunological evidence for common antigenic sites in high-density lipoproteins from rainbow trout and man

The plasma high-density lipoproteins (HDL, rho 1.085-1.21 g/ml) of rainbow trout (Salmo gairdneri) have been shown to contain large amounts of apolipoprotein (apo) AI (Mr 28,000) and several other apolipoproteins of Mr less than 14,000 (apo C-like) and of Mr 37,000-38,000, 44,000-45,000 and 53,000-54,000. Comparison of apo AI from trout and human HDL shows them to be similar in Mr and to have some cross-immunoreactivity, whereas apo AII differs in Mr but also possesses common antigenic sites. It is suggested that the major apolipoproteins of fish and human HDL may fulfil similar roles in lipid transport.

A density gradient study of the lipoprotein and apolipoprotein distribution in the chicken, Gallus domesticus

Plasma lipoproteins from 5-week old male chickens were separated over the density range 1.006-1.172 g/ml into 22 subfractions by isopycnic density gradient ultracentrifugation, in order to establish the distribution of these particles and their constituent apolipoproteins as a function of density. Lipoprotein subfractions were characterized by electrophorectic, chemical and morphological analyses, and their protein moieties were defined according to net charge at alkaline pH, molecular weight and isoelectric point. These analyses have permitted us to reevaluate the density limits of the major chicken lipoprotein classes and to determine their main characteristics, which are as follows: (1) very-low-density lipoproteins (VLDL), isolated at d less than 1.016 g/ml, were present at low concentrations (less than 0.1 mg/ml) in fasted birds; their mean diameter determined by gradient gel electrophoresis and by electron microscopy was 20.5 and 31.4 nm respectively; (2) as the the density increased from VLDL to intermediate density lipoproteins (IDL), d 1.016-l.020 g/ml) and low-density lipoproteins (LDL, d 1.020-1.046 g/ml), the lipoprotein particles contained progressively less triacylglycerol and more protein, and their Stokes diameter decreased to 20.0 nm; (3) apolipoprotein B-100 was the major apolipoprotein in lipoproteins of d less than 1.046 g/ml, with an Mr of 350000; small amounts of apolipoprotein B-100 were detectable in HDL subfractions of d less than 1.076 g/ml; urea-soluble apolipoproteins were present in this density range as minor components of Mr 38000-39000, 27000-28000 (corresponding to apolipoprotein A-1) and Mr 11000-12000; (4) high density lipoprotein (HDL, d 1.052-1.130 g/ml) was isolated as a single band, whose protein content increased progressively with increase in density; the chemical composition of HDL resembled that of human HDL2, with apolipoprotein A-1 (M 27000-28000) as the major protein component, and a protein of Mr 11000-12000 as a minor component; (5) heterogeneity was observed in the particle size and apolipoprotein distribution of HDL subfractions: two lipoprotein bands which additional apolipoproteins of Mr 13000 and 15000 were detected. These studies illustrate the inadequacy in the chicken of the density limits applied to fractionate the lipoprotein spectrum, and particularly the inappropriateness of the 1.063 g/ml density limit as the cutoff for LDL and HDL particle populations in the species.

Chimpanzee serum lipoproteins. Isolation, characterisation and comparative aspects of the low density lipoprotein and apolipoprotein-BH

Evaluation of the serum lipoprotein profile in non-fasting, adult chimpanzees by analytical ultracentrifugation revealed a lower mean LDL level (269 mg/dl) than typical of man. The major molecular form(s) of low density lipoprotein (LDL) was then isolated in the density interval 1.024-1.050 g/ml by sequential ultracentrifugation. The physicochemical properties of chimpanzee LDL, including net surface charge as judged by electrophoresis, molecular size (220 A) by electron microscopy, and chemical composition closely resembled those of man. The antigenic structures of chimpanzee and human LDL were essentially indistinguishable, since immunodiffusion against antiserum to either the human or ape lipoprotein produced a precipitin reaction of complete identity between the two antigens. By micro-immunoprecipitation, the immunological cross-reactivity of LDL from the two species was in the range 85-97%, depending on the nature of the assay.