Asia Pacific J Clin Nutr (1995) 4: 314-318

The relationship between linoleic acid level in serum, adipose tissue and myocardium in humans

Peter T Sexton¹, Andrew J Sinclair², Kerin O'Dea³, Andrew J Sanigorski⁴, Jan Walsh⁵

1.Honorary research fellow, Department of Medicine, University of Tasmania; 2. Professor Department of Food Science, RMIT, Melbourne; 3. Professor, Deakin Institute of Human Nutrition, Deakin University, Geelong; 4. Graduate research assistant, Deakin Institute of Human Nutrition, Deakin University; 5. Nurse research assistant, Department of Medicine, University of Tasmania

---

A cross-sectional study of 80 consecutive cases at necropsy was undertaken to determine the relationship between linoleic acid in the serum, adipose tissue and myocardium of humans. The sample consisted of 55 males and 25 females aged 7 to 92 years who had died from cardiac and non-cardiac causes in the Southern Region of Tasmania, Australia. Fatty acids were extracted from samples of serum, adipose tissue and myocardium and separated using capillary gas liquid chromatography. Means and standard deviations were calculated for each of the main fatty acids in the three tissues studied. In serum and adipose tissue, there were significantly higher levels of linoleic acid (p<0.001 and p<0.001 in serum and adipose tissue, respectively) and total n-6 fatty acids (p< 0.002 and p< 0.001 in serum and adipose tissue, respectively) and significantly lower levels of oleic acid in females than in males (p< 0.001 and p<0.05 in serum and adipose tissue, respectively). In serum and adipose tissue, the ratio of total n-6 to total n-3 fatty acids was significantly higher in females than males (p<0.02 and p<0.001 in serum and adipose tissue, respectively). In myocardium, there were significantly higher levels of oleic acid (p<0.05) and linoleic acid (p<0.001) and significantly lower levels of arachidonic acid (p<0.001) and docosapentaenoic acid (p<0.02) in females than males. Total n-3 fatty acids in myocardium were significantly lower in females (p<0.001) resulting in a significantly higher ratio of total n-6 to total n-3 fatty acids in females (p<0.001). Highly significant Pearson correlations were found between levels of linoleic acid in adipose tissue and myocardium (p<0.0001), between adipose tissue and serum (p<0.001 ) and between serum and myocardium (p<0.001). The proportion of total polyunsaturated fatty acids (PUFA) in the myocardium was inversely related to the proportion of monounsaturated fatty acids (p<0.001) and inversely related to the proportion of saturated fatty acids (p<0.001). There was a significant positive correlation between the ratio of linoleic acid to linolenic acid in all three tissues. This study showed that there was a very strong relationship between the level of linoleic acid in adipose tissue and myocardial tissue, which suggests that dietary linoleic acid influences the level of myocar 1000 dial linoleic acid. These findings support the hypothesis that dietary linoleic acid has a direct influence on myocardial membrane linoleic acid levels.

---

Introduction

Analysis of population trends in dietary consumption suggests an inverse relationship between dietary levels of PUFA and mortality from CHD¹. The finding, that the fatty acid content of subcutaneous fat is a good biological indicator of fat consumption in humans^2,3, has resulted in a number of epidemiological studies using adipose tissue samples to confirm the inverse relationship between dietary levels of PUFA (in particular linoleic acid) and the risk of mortality from CHD^4,5.6. A recent study has shown an inverse relationship between levels of linoleic acid in adipose tissue and the risk of sudden cardiac death⁷. These findings in humans are supported by results of animal studies which suggest a direct effect of dietary fatty acid levels on phospholipid fatty acid composition⁸. Such changes in the fatty acid composition of myocardial phospholipid can influence the susceptibility of the myocardium to develop arrhythmias, and may account for the association between dietary fatty acids and sudden cardiac death⁹.

Given the association between dietary fat, adipose tissue, fatty acid composition and the risk of sudden cardiac death, it is important to establish whether dietary linoleic acid, as reflected in levels of linoleic acid in adipose tissue, correlates significantly with linoleic acid levels in human myocardium. The aim of this study was to examine the correlation between levels of linoleic acid in serum, adipose tissue and myocardium from humans.

Methods

Tissue samples

Where possible, samples of serum (n=62), adipose tissue (n=79) and myocardium (n=79) were taken at necropsy from 80 consecutive cases. The cases included 55 males and 25 females who died from cardiac and non cardiac causes. Ages ranged from 7 years to 92 years. Ethical approval for the collection of tissue samples was granted by the Ethics Committee of the Royal Hobart Hospital.

Serum samples were obtained from blood aspirated from cardiac chambers, usually the left ventricle. Adipose tissue was sampled from the anterior abdominal wall and myocardium was sampled from areas of macroscopically normal myocardium, that is, myocardium free of fibrosis and not involved in a recent myocardial infarction.

Specimens were placed into plastic containers and stored at -70° C until analysis.

Analysis of tissue fatty acids

Lipids were extracted from the thawed samples in chloroform-methanol (2:1) as described previously¹⁰. Aliquots of the total lipids, together with an internal standard of heptadecanoic acid, were treated with KOH in methanol followed by BF3 in methanol.¹⁰ The resulting fatty acid methyl esters were separated by capillary gas liquid chromatography using a 50mm x 0.32mm (ID) CP Sil 88 column (Chrompack, Middelburgh, The Netherlands). The column oven was operated from 110° C to 190° C using helium as the carrier gas at a linear gas velocity of 20 cm/sec. Standard fatty acid methyl esters were routinely chromatographed to establish retention times and to determine response factors for the individual fatty acid methyl esters.

Statistical methods

Means and standard deviations were calculated for each of the main fatty acids in the three tissues studied. Comparisons of mean levels of fatty acids in the tissues studied were calculated using the Students t-test. Correlations were calculat 1000 ed using the Pearson correlation coefficient (r). Correlations did not vary by sex or cause of death and therefore total sample results are given.

Results

The fatty acid composition of the three tissues in males and females is shown in the Table. The main fatty acids in serum were palmitic acid (16:0), palmitoleic acid (16:1), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2n-6), arachidonic acid (20:4n-6) and docosahexaenoic acid (22:6n-3). In serum, there were significantly higher levels of linoleic acid (p<0.001) and total n-6 PUFA (p<0.002) and significantly lower levels of oleic acid in females than in males (p<0.001). The ratio of total n-6 to total n-3 PUFA was significantly higher in females (p<0.02).

Table. Serum, adipose tissue and myocardial fatty acid composition in males and females

		Males			Females
		Serum n=39	Adipose n=54	Myocardium n=54	Serum n=23	Adipose n=25	Myocardium n=25
Fatty Acid		Mean± SDa	Mean± SD	Mean± SD	Mean± SDa	Mean± SD	Mean± SD
Saturated
Myristic	14:0	1.06± 0.41	3.10± 0.99	1.09± 0.50	1.25± 0.77	2.91± 0.88	1.17± 0.66
Palmitic	16:09	21.78± 2.48	22.19± 2.17	16.33± 1.77	22.12± 3.50	22.25± 2.50	16.74± 2.45
Stearic	18:09	7.31± 1.39	5.57± 1.59	11.61± 1.56	7.37± 1.17	5.30± 1.74	11.33± 1.77
Monounsaturated
Palmitoleic	16:1	2.87± 1.17	1000 5.88± 1.89	1.75± 0.86	2.70± 1.57	5.35± 2.30	1.93± 1.31
Oleic	18:1b	25.72± 3.75f	45.84± 5.72c	21.22± 6.42	23.03± 4.15	44.38± 7.43	22.54± 6.78c
Eicosamonoenoic	20:1	0.66± 0.20	1.34± 0.31	0.67± 0.62	0.60± 0.13	1.33± 0.21	0.56± 0.23
Polyunsaturated
Linoleic	18:2n-6	25.40± 6.83	10.18± 4.16	16.76± 3.72	28.14± 7.37f	12.26± 3.67f	18.60± 3.94f
Linolenic	18:3n-3	0.45± 0.19	0.38± 0.08	0.25± 0.14	0.33± 0.10	0.36± 0.10	0.23± 0.11
Eicosadienoic	20:2n-6	0.17± 0.07	0.14± 0.06	0.14± 0.09	0.16± 0.07	0.16± 0.04	0.15± 0.04
Eicosatrienoic	20:3n-6	1.27± 0.56	0.15± 0. 1000 07	0.81± 1.48	1.24± 0.42	0.20± 0.10	0.58± 0.18
Arachidonic	20:4n-6	6.79± 1.67	0.44± 0.33	15.75± 4.58f	6.55± 1.62	0.37± 0.15	13.93± 3.67
Eicosapentaenoic	20:5n-3	0.73± 0.42	0.07± 0.18	0.55± 0.40	0.60± 0.38	0.01± 0.04	0.33± 0.16
Docosatetraenoic	22:4n-6	0.21± 0.08	0.09± 0.07	0.33± 0.16	0.17± 0.08	0.13± 0.11	0.30± 0.09
Docosapentaenoic	22:5n-6	0.12± 0.18	0.02± 0.04	0.25± 0.14	0.09± 0.08	0.00± 0.01	0.16± 0.11
	22:5n-3	0.62± 0.19	0.23± 0.12	1.47± 0.49d	0.51± 0.19	0.27± 0.17	1.08± 0.40
Docosahexaenoic	22:6n-3	1.78± 0.60	0.26± 0.42	3.29± 1.00	1.96± 1.09	0.21± 0.19	2.82± 1.32
	n-6	33.96± 7.06	11.01± 4.22	34.05± 6.04	36.35± 8.61e	13.13± 3.62f	33.79± 7.18
	n-3	3.58± 1.03	0.94± 0.61	5.56± 1.45f	3.41± 1.45	0.85± 0.40	4.46± 1.68
	n-6/n-3	10.58± 4.39	15.55± 10.95	6.50± 1.73	11.96± 4.52d	18.61± 9.07d	9.28± 7.30f

a results shown as mean ± SD of g fatty acid per 100g total fatty acids. b 18:1n-7 and 18:1n-9. c p<0.05 d p<0.02 e p<0.002 f p<0.001 Position of superscripts c, d, e, f indicate gender with significantly higher level of tissue fatty acid. g 16 and 18-carbon aldehydes determined as dimethyl acetal derivatives (DMA) were found in myocardium at levels of 3.25± 1.19 and 3.04± 1.09 for 16:0 DMA for males and females respectively, and 1.48± 0.82 and 1.37± 0.75 for 18:0 DMA for males and females respectively.

The main fatty acids in adipose tissue were myristic acid (14:0), palmitic acid, palmitoleic acid, stearic acid, oleic acid and linoleic acid. In adipose tissue, there were significantly higher levels of linoleic acid (p<0.001) and total n-6 PUFA (p<0.001) and significantly lower levels of oleic acid (p<0.05) in females than males. The ratio of total n-6 to total n-3 PUFA in adipose tissue was significantly higher in females than in males (p<0.001).

The main fatty acids in myocardium were palmitic acid, stearic acid, oleic acid, linoleic acid, arachidonic acid and docosahexaenoic acid. Fatty aldehydes were also detected in this tissue and the levels are reported in the Table. In myocardium, there were significantly higher levels of oleic acid (p<0.05) and linoleic acid (p<0.001) and significantly lower levels of arachidonic acid (p<0.001) and docosapentaenoic acid (22:5n-3) (p<0.002) in females than males. Total n-3 fatty acids were significantly lower in females (p<0.001) resulting in a significantly higher ratio of total n-6 to total n-3 fatty acids in females (p<0.001).

Figures 1 to 3 show that there were highly significant correlations between levels of linoleic acid in adipose tissue and myocardium (p<0.0001), between adipose tissue and serum (p<0.001) and between serum and myocardium (p<0.001).

Figure 1. Correlation between levels of linoleic acid (18:2n-6) in adipose tissue and myocardium (as a percentage of total fatty acids in adipose tissue and myocardium).

Figure 2. Correlation between levels of linoleic acid (18:2n-6) in serum and adipose tissue (as a percentage of total fatty acids in serum and adipose tissue).

Figure 3. Correlation between levels of linoleic acid (18:2n-6) in serum and myocardium (as a percentage of total fatty acids in serum and myocardium).

Discussion

This study showed a very strong relationship between the level of linoleic acid in adipose tissue and myocardial tissue, which suggests that dietary linoleic acid influences the level of myocardial linoleic acid.

Previous studies have shown that adipose linoleic acid levels reflected dietary linoleic acid intake.^2,3 The transport of linoleic acid from the gut via chylomicrons and 1000 subsequent transport in various lipoprotein classes derived from the liver would ensure that all tissues would be likely to incorporate essential PUFA via the action of lipoprotein lipases. Thus, it was not surprising that we showed a strong relationship between the level of linoleic acid in heart and adipose tissue. These findings support the hypothesis that dietary PUFA can have a direct influence on myocardial membrane PUFA. The beneficial effects of linoleic acid might be derived by the displacement of saturated fatty acids in the myocardium as suggested by Riemersma¹¹. In this study, we found that the proportion of PUFA (all n-6 and n-3 PUFA) in the myocardium was inversely related to the proportion of monounsaturated fatty acids (r=0.962, p<0.001). In particular, there was an inverse relationship between oleic acid (the main monounsaturated fatty acid) and arachidonic acid (r=0.872, p<0.001), and between oleic acid and linoleic acid (r=0.530, p<0.001). It was also found that the proportion of PUFA was inversely correlated with the proportion of saturated fatty acids (r=0.491, p<0.001). Thus, increased PUFA levels in the myocardium were mainly associated with a reduced level of monounsaturated fatty acids but also with a reduction in saturated fatty acids.

The presence of linoleic acid itself may be beneficial by acting as a precursor of specific substances in the myocardium such as 13-hydroxyoctadecadienoic acid¹², or as a result of conversion to arachidonic acid, it may stimulate production of myocardial eicosanoids¹³. There was a positive relationship between the level of linoleic acid and arachidonic acid in the myocardium (r=0.253, p<0.05).

The level of saturated fatty acids and polyunsaturated fatty acids in adipose tissue in the present study fell between those reported by Riemersma et al, for three northern European countries and Italy.⁴ That is, the levels of saturated fatty acids were lower and those for linoleic acid were higher than the northern European countries.

There is an increasing interest in dietary n-3 PUFA in relation to processes involved in atherosclerosis, thrombosis and cardiac arrhythmias. It has been suggested that eicosapentaenoic acid (20:5n-3) reduces the production of a variety of eicosanoids derived from arachidonic acid, leading to a reduced production of pro-inflammatory, pro-aggregatory and pro-arrhythmogenic eicosanoids such as thromboxane and the 4-series leukotrienes^13,14. Therefore, we investigated whether there was a relationship between the main n-6 and n-3 PUFA in the three tissues.

Since there is competition between linoleic acid and linolenic acid for metabolism to longer chain PUFA such as arachidonic acid and eicosapentaenoic acid in the liver, diets with high levels of linoleic acid relative to linolenic acid result in tissue with high levels of n-6 PUFA relative to n-3 PUFA¹⁵ and presumably high levels of eicosanoids derived from arachidonic acid¹⁴.

In this study, there was a significant positive correlation between the ratio of linoleic acid to linolenic acid in all three tissues (myocardium v adipose, r=0.23, p<0.05, n=79; myocardium v serum, r=0.19, p<0.05, n=62; adipose v serum, r=0.44, p<0.001, n=62). Since others have shown that the relationship between diet and adipose tissue PUFA is correlated^2,3, these data support the concept of a positive relationship between the ratio of linoleic acid to linolenic acid in the diet and myocardial tissue. The ratio of linoleic acid to linolenic acid in adipose tissue was also significantly correlated with the ratio of total n-6 PUFA to total n-3 PUFA in myocardial tissue (r=0.42, p<0.001, n=79). Since myocardial tissue lipids contain high levels of 20 and 22-carbon PUFA derivatives of linoleic ac 1000 id and linolenic acid, this correlation suggests that the ratio of dietary n-6 PUFA to n-3 PUFA influences the proportion of these two PUFA families in myocardial tissue.

Female subjects had significantly elevated levels of linoleic acid in all three tissues compared with males. This could be due to differences in dietary intake, however data from the 1990 Victorian Nutrition Survey of about 3,000 randomly selected subjects did not reveal any difference in PUFA intake (as percentage of energy) between males and females¹⁶. Another reason for the difference could be genetic and this is supported by several studies which have reported higher levels of linoleic acid in female subjects in plasma phospholipids¹⁷, heart tissue phospholipids¹⁸ and adipose tissue¹⁹.

This study showed that there was a very strong relationship between the level of linoleic acid in adipose tissue and myocardial tissue, which suggests that dietary linoleic acid influences the level of myocardial linoleic acid. These findings support the hypothesis that dietary linoleic acid can have a direct influence on myocardial membrane linoleic acid. These findings might account for the beneficial effects of linoleic acid in reducing sudden cardiac death⁷.

Acknowledgements

We wish to acknowledge the assistance of Dr D Challis in sample collection and Mrs T-L Sexton in data analysis and computing.

---

The relationship between linoleic acid level in serum, adipose tissue and myocardium in humans

Peter T Sexton, Andrew J Sinclair, Kerin O'Dea, Andrew J Sanigorski, Jan Walsh

Asia Pacific Journal of Clinical Nutrition (1995) Volume 4, Number 3: 314-318

---

References

1. Hetzel BS, Charnock JS, Dwyer T, et al. Fall in coronary heart disease mortality in USA and Australia due to sudden death: Evidence for the role of polyunsaturated fat. J Clin Epidemiol 1989; 42: 885-893.
2. van Stavaren WA, Deurenberg P, Katan MB, et al. Validity of the fatty acid composition of subcutaneous tissue micro biopsies as an estimate of the long-term average fatty acid composition of the diet of separate individuals. Am J Epidemiol 1986; 123: 455-463.
3. Hunter DJ, Rimm EB, Sacks FM, et al. Comparison of measures of fatty acid intake by subcutaneous fat aspirate, food frequency questionnaire, and diet records in a free-living population of US men. Am J Epidemiol 1992; 135: 418-427.
4. Riemersma RA, Wood DA, Butler S, et al. Linoleic acid in adipose tissue and coronary heart disease. Br Med J 1986; 292: 1423-1427.
5. Wood DA, Butler S, Riemersma RA, Thomson M, Oliver MF. Adipose tissue and platelet fatty acids and coronary heart disease in Scottish men. Lancet 1984; 2: 117-121.
6. Wood DA, Riemersma RA, Butler S, et al. Linoleic acid and eicosapentaenoic acid in adipose tissue and platelets and risk of coronary heart disease. Lancet 1987; 1: 177-183.
7. Roberts TL, Wood DA, Riemersma RA, et al. Linoleic acid and risk of sudden cardiac death: Br Heart J 1993; 70: 524-529.
8. Charnock JS, McIntosh GH, Abeywardena MY, Russell GR. Changes in fatty acid composition of the 1000 cardiac phospholipids of the cotton-eared marmoset (Callithrix jacchus) after feeding different lipid supplements. Ann Nutr Metab 1985; 29: 83-94.
9. McLennan PL, Abeywardena MY, Charnock JS. Influence of dietary lipids on arrhythmias and infarction after coronary artery ligation in rats. Can J Physiol Pharmacol 1985; 63: 1411-1417.
10. Sinclair AJ, O'Dea K, Dunstan G, Ireland PD and Niall M. Effects on Plasma Lipids and Fatty Acid Composition of Very Low Fat Diets Enriched with Fish or Kangaroo Meat. Lipids 1987; 22: 523-529.
11. Riemersma RA (1993) Polyunsaturated fatty acids and coronary heart disease. in Proceedings of the Third Conference on Essential Fatty Acids and Eicosanoids (Sinclair AJ and Gibson RA, eds.). A.O.C.S. pp. 230-234. Champaign, Illinois.
12. Buchanan MR, Haas TA, Lagarde M, Guichardant M. 13-hydroxyoctadecadienoic acid is the vessel wall chemorepellant factor, LOX. J Biol Chem 1985; 260: 16056-59.
13. Abeywardena MY, McLennan PL, Charnock JS. Differential effects of dietary fish oil on myocardial prostacyclin I2 and thromboxane A2 production. Am J Physiol 1991; 260: H370-H385.
14. Kinsella JE, Lokesh B, Stone RA. Dietary n-3 polyunsaturated fatty acids and amelioration of cardiovascular disease: possible mechanisms. Am J Clin Nutr 1990; 52:128.
15. Lands WEM, Libelt B, Morris WA, et al. Maintenance of lower proportions of n-6 eicosanoid precursors in phospholipids of human plasma in response to added n-3 fatty acids. Biochem Biophys Acta 1992; 1180: 147-162.
16. Baghurst K, Record S, Syrette J, et al. (1993) CSIRO Division of Human Nutrition report on "What are Australians eating", Results from the 1985 and 1990 Victorian Nutrition Surveys, CSIRO Division of Human Nutrition, Adelaide.
17. Sinclair AJ, O'Dea K, Johnson L. Estimation of the n-3 PUFA status in a group of urban Australians by the analysis of plasma phospholipid fatty acids. Aust J Nutr Diet 1994; 51: 53-56.
18. Rocquelin G, Guenot L, Astorg PO, David M. Phospholipid content and fatty acid composition of human heart. Lipids 1989; 21: 775-780.
19. Tavendale R, Lee AJ, Smith WCS, Tunstall-Pedoe H. Adipose tissue fatty acids in Scottish men and women: results from the Scottish Health Heart Study. Atherosclerosis 1992; 94: 161-169.
20. Blackenhorn DH, Johnston RL, Mack WJ, Hafez A, El Zein MD, Vailas LI. The influence of diet on the appearance of new lesions in human coronary arteries. JAMA 1990; 263: 1646-52
21. Hodgeson J, Wahlqvist ML, Boxall JA, Balazs ND. Can linoleic acid contribute to coronary artery disease? Am J Clin Nutr 1993; 58: 228-34.

---

Editors note:

Not all studies support the notion that the levels of tissue linoleic acid currently achieved by some individuals in industrialised, affluent societies are cardio-protective, at least insofar as coronary artery disease is concerned^20,21. The present paper does not, of course, consider health outcome in relation to tissue fatty acid status.

Copyright © 1995 [Asia Pacific Journa 197 l of Clinical Nutrition]. All rights reserved.
Revised: January 19, 1999 .

to the top

0