Influence of native and randomized peanut oil on lipid metabolism and aortic sudanophilia in the vervet monkey

Atherosclerosis,

42 (1982)

Elsevier/North-Holland

53

53-5X

Scientific

Publishers,

Ltd

Influence of Native and Randomized Peanut Oil on Lipid Metabolism and Aortic Sudanophilia in the Vervet Monkey David Kritchevsky ‘, Larry M. Davidson ‘, Michael Weight 2, Nicholas P.J. Kriek 2s* and Jean P. du Plessis 2.** ’ The

Wistur Institute .’Natrowl

oJAncrtom.v ud

Resecrrch Institute

Biology,

for Nutritiortd

36th Street (II Spruce. Phklelph~~. Diswses.

Tvgerherg

PA 19104 (U.S.A.)

7505 (Republic

uttd

of South Afriw)

(Received 13 May. 1981) (Revised, received 17 August, 1981) (Accepted 18August. 198 I)

Summary

Vervet monkeys (Cercopithecus aethiops pygerethrw) were fed cholesterol-free, semipurified diets containing 40% sucrose, 25% casein, 15% cellulose and 14% peanut oil (PNO), randomized peanut oil (RPNO) or corn oil (CO). After 4 months, serum cholesterol and triglyceride levels, serum lecithin-cholesterol acyl transferase (LCAT) activity and plasma lipoprotein lipase (LPL) activity were similar in all groups. Livers of monkeys fed CO converted 156% more acetate and 24% more mevalonate to cholesterol than those of monkeys fed RPNO. Cholesterogenesis in RPNO-fed monkeys was enhanced compared to PNO (68% from acetate; 62% from mevalonate). Incidence of atherosclerosis was 33% in monkeys fed RPNO, 80% in those fed CO and 90% in those fed PNO. Extent of sudanophilia was lowest in aortas of monkeys fed RPNO. Incidence of arteriosclerosis was 40% in monkeys fed CO, 56% in those fed RPNO and 70% in those fed PNO. Extent of aortic surface showing arteriosclerosis was highest in monkeys fed RPNO. Key words: Arteriosclerosis Randomized

- Atherosclerosis - Cholesterogenesis peanut oil - Vervet monkeys

- Peanut

oil -

Supported, in part, by grant HL-05209 and a Research Career Award (HL-00734) from the National Institutes of Health (U.S.A.). *Present address:Faculty of Veterinary Science, Onderstepoort 0110, Republic of South Africa. **Present address: South African Bureau of Standards, Pretoria 0001. Republic of South Africa.

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Q 1982 Elsevier/North-Holland

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Introduction

Peanut oil (PNO) is inordinately atherogenic for rats [l], rabbits [2] and rhesus monkeys [3] when fed as part of a cholesterol-containing diet. It is also more atherogenic than corn oil (CO) when fed to rabbits as part of a semipurified, cholesterol-free diet [4]. Auto-interesterification (randomization) of PNO alters the structure of its component triglycerides but does not affect the fatty acid spectrum or iodine value [5]; it also reduces markedly its atherogenicity [6]. We have studied the effect of native and randomized peanut oil (RPNO) on lipid metabolism and aortic sudanophilia of vervet monkeys fed a semipurified, cholesterol-free diet. When this diet contains saturated fat it is hyperlipidemic and sudanophilic for baboons [7] and vervet monkeys [8]. The results of our study are described below.

Materials and Methods

Vervet monkeys (Cercopithecus aethiops pygerethrus) were maintained in 3 groups of 10 animals each and fed a semipurified diet containing 40% sucrose, 25% casein, 15% cellulose, 14% fat, 5% salt mix * and 1% vitamin mix **. The fats fed were PNO, RPNO and CO. After 4months the monkeys were killed and serum and liver total cholesterol [9] and serum triglyceride were determined [lo]. Serum lecithincholesterol acyl transferase (LCAT) activity was determined using a modification of the method of Lacko et al. [ 111.Plasma lipoprotein lipase (LPL) activity was assayed by the method of Krauss et al. [12] using lipoprotein triglyceride as the substrate. Liver homogenates were prepared in phosphate buffer, pH 7, using a tissue press and Potter-Elvehjem homogenizer [ 131. The homogenates were incubated with either sodium [l- t4C ]acetate [ 141 or [2-‘4C]mevalonic acid [ 151 for 2 h, the suspension saponified with KOH, the free cholesterol isolated as the tomatinide [16] and its specific activity determined. The aorta was removed in toto (the aortic arch was sectioned as close as possible to the heart and distally the aorta included about 2 cm of femoral arteries), slit lengthwise and pinned onto a cork strip. After fixation in formalin for 24 h, the aortas were stained with Oil Red 0 according to the method of Holman et al. [ 171in order to determine the distribution of fatty streaks and plaques. Areas that stained intensely and were demarcated were considered fatty streaks or plaques and classi-

* Salt mix, USP XIV, (percent): AI,(SO,),.(NH,),SO,.24, H,O (0.009); CaHPO,‘2 H,O (I l.2&; CaCO, (6.86), Ca, (C,H,0,)2.4 H,O (30.83); CuSO, (0.008); Fe(NH,) (C,H,O,), (1.526); MgCO, (3.520); MgSO, (3.83); MnSO, (0.02); KC1 (12.47); KI (0.004); KH,PO, (21.88); NaCl (7.71); NaF (0.05). ** Vitamin mix (g/kg diet): p-aminobenzoic acid (0.11); vitamin C (1.017); biotin (O.ooO4); Ca pantothenate (0.066); choline citrate (3.715); folic acid (0.002); inositol(0. II); vitamin K (0.05); nicotinic acid (0.009); pyridoxine-HCl (0.022); riboflavin (0.022); thiamine-HCl (0.002); vitamin A, 500,000 U/g (0.039); vitamin B,, (0.029); vitamin D *, 500,000 U/s (0.004); vitamin E acetate, 250 U/g (0.485).

55

fied as atheromata. Numerous fibrous plaques (white, glistening, raised) which showed little or no lipid staining were classified as arteriosclerotic lesions. The stained aortas were photographed in color and the resulting transparencies projected onto graph paper at a constant magnification. The outline of the entire aorta and of the involved areas was traced onto the graph paper. The surface area of the lesions was determined by counting the points (cross lines) within the area and expressed as a percentage of the total aortic surface. The aortas were also graded visually using a O-4 scale [l&19].

Results and Discussion The analytical data are presented in Table 1. The only significant differences among the parameters measured were in serum cholesterol levels and cholesterol synthesis from acetate. Conversion of acetate to cholesterol by liver homogenates from monkeys fed CO was 332 and 156% higher than by homogenates from groups PNO or RPNO, respectively. Mevalonate conversion to cholesterol by liver preparations from group CO was 101% greater than seen in group PNO and 24% greater than in group RPNO. There is a distinct trend towards more conversion of acetate

TABLE

I

INFLUENCE OF NATIVE (PNO) AND RANDOMIZED (RPNO) PEANUT OIL AND CORN OIL (CO) ON LIPID METABOLISM IN VERVET MONKEYS FED A SEMIPURIFIED DIET FOR 4 MONTHS Values * SEM. Group PNO Number (sex) Final weight (kg) Weight gain (kg) Liver weight (g) Liver (as % body weight) Serum lipids (mg/dl) Cholesterol Triglycerides Liver cholesterol (mg/g)

RPNO

10 (6 M; 4 F) 4.71* 0.46 0.325 0.10 89 -cl 1.97* 0.12 163 *I3 61 *9 4.7 2 0.1

9 (5 M; 4.901 0.39* 97 “8 2.01 *

co 4 F) 0.46 0.08 0.07

147 ?I8 52 *6 4.7 f 0.2

Enzyme studies Serum LCAT (PM/l/h) Plasma LPL (PM/ml/h)

56.1 * 13.9 *

Liver cholesterol biosynthesis (dpm/mg protein) Acetate Mevalonate

3.8 * 0.5 21.2 r 10.2

6.4 2 1.7 34.3 k26.3

(pGO.05)

of variance.

* Difference

among groups

significant

8.1 2.4

by analysis

55.2 * 9.3 *

5.5 1.2

IO (5 M; 4.01 ;f: 0.275 2 83 2.162

5 F) 0.51 0.07 9* 0.38

161 *13* 56 *I2 4.5 * 0.2

61.5 * 10.2 t

8.6 5.4

16.4 * 6.4 * 42.6 * 13.4

56

TABLE 2 ATHEROSCLEROTIC AND ARTERIOSCLEROTIC MONKEYS FED PEANUT OIL (PNO), RANDOMIZED (CO) FOR 4 MONTHS Values * SEM.

LESIONS PEANUT

IN AORTAS OF VERVET OIL (RPNO) OR CORN OIL

Group PNO

RPNO

co

9/10 2.85-c 1.22

3/9 1.57il.29

R/IO 2.681- 1.65

3/10 3/10 9/10

‘/9 ‘/9 3/9

2/10 3/10 8/10

Arteriosclerosis Incidence % of surface

7/10 0.81 kO.27

5/9 1.46kO.75

4/10 0.59*0.30

Site Proximal aorta Distal aorta Arterial branches

O/IO 7/10 o/10

219 5/9 O/IO

o/10 4/10 O/IO

Atherosclerosis Incidence % of surface Site Proximal aorta Distal aorta Arterial branches

and mevalonate to cholesterol in livers from monkeys fed corn oil than from either PNO or RPNO. In the conversion of acetate to cholesterol the difference among the by analysis of variance). Livers of rats fed unsaturated groups is significant (P Q 0.05 fat convert significantly more acetate to cholesterol than livers from rats fed saturated fat [20-241; results obtained using mevalonate are equivocal [22,24]. Our finding that dietary RPNO enhances cholesterogenesis compared to PNO (by 68 and 62% from acetate and mevalonate, respectively) suggests that RPNO may possess more “unsaturated character” and may offer a clue to its reduced atherogenicity. Results of the aorta examination are summarized in Table 2. Average sudanophilia (Table2) was computed by summing the percentage of involvement for each group and dividing by the total number of aortas. If one excludes aortas which exhibited no staining, the averages are: PNO (9/10) 3.16 -C 1.32; RPNO (3/9) 4.72 4 3.59; and CO (8/10) 3.34 * 2.01. The aortas were also graded visually using a O-4 scale [ 18,191 with the following assessment of severity: PNO - 4.7 * 2.1; RPNO - 1.5 i 0.9; and CO - 3.2 * 1.6. Incidence of atherosclerosis in the monkeys fed RPNO was 33% while in those fed PNO or CO it was 90 and 80%. RPNO was 41% less sudanophilic than CO and 45% less than PNO. The principal location of the lesions (at the arterial branches) was the same in all 3 groups. Incidence of arteriosclerosis was 70% in group PNO, 56% in RPNO and 40% in CO. The data obtained in this experiment are consistent with earlier findings [2,3,6] which show that PNO is more atherogenic than CO and that its atherogenicity can

be reduced by randomization. One clue to the metabolic effects of the 3 fats may lie in their effects on hepatic cholesterogenesis. RPNO resembles an unsaturated fat in this regard more than does native PNO. It will be of interest to compare the triglyceride structure of CO with that of RPNO. Acknowledgements

We are indebted to Standard Brands, Inc., Wilton, CT, for generous gifts of the oils used in this study.

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