Pharmacologica/ Research Commun/cations, Vol. 11, No. 4, 1979

311

POSSIBLE ROLE OF GLYCOSAMINOGLYCANS IN REDUCING THE UPTAKE OF HUMAN LIPOPROTEINS BY THE ARTERIAL WALL (+)

A. C a p u r s o , L. Bonomo

L. P a c e ,

F. R e s t a ,

V. R i s o ,

D. Di Monte (o)

and

Istituto di Clinica Medica If, Dept. of Internal Medicine, University of Bari, Bari - Italy Receivedin final form 10 April 1979

SUMMARY The binding of mammalian non aortic glycosaminoglycans to human lipoproteins has been studied by bi-dimensional immunoelectrophoresis and by analytical ultracentrifuge. Complexed lipoprotefns by transmission electron microscopy appear as large agsregates. The physiological significance of these aggregates zs discussed.

INTRODUCTION Binding of glycosaminoglycans (GAG) to plasma lipoproteins, forming soluble and insoluble complexes, has been described by several Authors. In vitro experiments have demonstrated that GAG isolated from atherosclerotic human aortic tissu~complex with rabbit serum lipoproteins (Amenta and Waters, 1960; Anderson, 1963; Dyrbye and Kirk, 1957) as well as with human beta lipoproteins [Bihari-Varga et al., 1964; Bihari-Varga and Vegh, 1967; Bihari-Varga et al., 1968; Gero et al., 1961; Srinivasan et al., 1970). Other in vitro (Day et al., 1975)and in vivo [Sirtori et al., 1976) experiments have indicated that non aortic mammalian GAG may inhibit binding of 1251-LDL to rab bit aorta. It was suggested (Day et al., 1975) that the reduced aortic uptake of labelled LDL may r e s u ~ f r o m saturation by exogenous GAG of specific GAG reactive sites on LDL, thus making LDL unavailable for arterial deposition. Other possible \

[+9 Supported by Consiglio Nazionale delle Ricerche, Rome, Italy. CNR Program of Preventive Hedicine. Subproject: Atherosclerosis RF-I. (o) From: Centro Emotrasfusionale, Policlinico - Bari, Italy.

0031-.-6989/79/040311-121502.00/0

© 1979 The Italian PharmacologicalSociety

Pharmacological Research Communications, Vol. 11, No. 4, 1979

312

mechanisms, information

however, cannot be excluded. To collect further o11 the mechanisms involved in the decreased ar-

terial uptake of lipoprotein-GAG complexes, the physico-chemical characteristics of these complexes have been examined by bi-dimensional immunoelectrophoresis, analytical fuge and trasmission electron microscopy.

ultracentri-

MATEgIALS AND METHODS The lipoprotein-GAG

complexes

were studied using isolated

VLDL and LDL, or whole serum from hyperlipoproteinemic subjects. VLDL (d < 1.O06 g/ml) and LDL (d 1.OO6 to 1.063 g/ml) were isolated by preparative ultracentrifuge (Beckman, model L5-65, rotor 50 Ti) as described by Havel et al. (1955). The purity of the lipoprotein tron microscopy

fractions

was checked by transmission

and by agarose electrophoresis.-The

of, mammalian

non aortic GAG mixture is reported by Casu et al. (1979).

elec-

composition

used in these experiments

Bi-dimensiona ~ immunoelectrophoresis.

Isolated

human LDL and

native sera of type IIA, liB and V were examined by bi-dimensional immunoelectrophoresis according to the method of Clarke and Freeman (1968) as modified by us (Capurso et al., 1976). Usually, agarose,

a first electrophore~:ic run is carried out in normal thereafter the electrophoresed lipoproteins are

transferred onto a second agarose plate (Figure I) and run in crossed immunoelectrophoresis against the antiserum. In our case, we further modified GAG. Two procedures

this method to allow addition

were followed.

In the first,

of

an intermediate

layer of GAG (IOO mg/ml of 0.6% agarose) was placed between lipoproteins and antiserum (anti beta lipoprotein serum Behringwerke

AG, Marburg

Lahn, West Germany)

order to allow passage of lipoproteins GAG containing

(Figure

2),

in

through the intermediate

gel, before reaching the antibody

in the

upper

gel. For controls, the same tripartitioned glass plate was used, not containing GAG in the intermediatelayer. In the second procedure, the crossed immunoelectropho~etic run was performed on a bi-sectioned glass plate, where the GAG

Pharmacological Research Communications, Vok 11, No. 4, 1979

Figure

1 - Scheme

of bi-dimensional

"

313

immunoelectrophoresis.

x

z~/-~-~- ,. . . . i / I

"

. .....

1

"

-

~

0 cAT~H.O I~t-

Figure

2 - Scheme of the tri-part~oned electrophoresis.

bi-dimensional

immuno-

3 -

bi-dimensional

immuno-

0 Figure

Scheme of the electrophoresis

two-sectioned •

Pharmacological Research Communications, VoL 11, No. 4, 1979

314

were added to the antiserum [Figure 3).

in the upper portion of the plate

Analytical ultracentrifugation. Since lipoprotein-GAG complexes are dissociated by solutions of high ionic strength, iml of VLDL and LDL, separated by preparative

Ultracentrifuge ,

were

exhaustively dialyzed against 0.9% NaClrO.Ol% EDTA solution pH 7.4, before adding GAG, in order to reduce salt concentration in the environment. After dialysis, 0.i ml of a 0.2% solution of GAG was added to lipoproteins, followed by stirring on a Vortex mixer, and stored in a refr~geratgr at 4°C for a few hours. Samples were then ultracentrifuged again at 40,000 rpm for 24 hours, in a 1.006 NaCI density gradient, in order to eliminate unbound

GAG from lipoproteins.

After the ultra-

centrifugal washing, lipoproteins were recovered, reconstituted to i ml volume, and examined by analytical ultracentrifugation (Spinco, model E) in a NaCI salt solution d