American Heart Journal
Volume 157, Issue 4 , Page e23, April 2009

Letter to the Editor

Health Products and Food Branch, Health Canada, Ottawa, Ontario, Canada K1A 0K9

published online 09 March 2009.

Article Outline

 

I read with interest the article published in your Journal by Block et al.1 They showed a direct correlation of blood cell levels of trans, trans-linoleic acid with acute coronary syndromes. Strictly, trans, trans isomer of linoleic acid is 9-trans,12-trans octadecadienoic acid (9t,12t-18:2). However, I have my doubts about the presence of this particular fatty acid in blood cells. Several years ago, Ratnayake et al2 showed that 9-cis,13-trans-octadecadienoic acid (9c,13t-18:2) is the major trans isomer of linoleic acid in partially hydrogenated oils2 and in some processed foods.3 The 9t,12t-18:2 isomer is a minor component in partially hydrogenated oils.2, 3 In gas chromatography analysis, the peak for 9t,12t-18:2 overlaps or closely elutes with that for 9c,13t-18:2.2, 4 Because reference standard for 9t,12t-18:2 is readily available but not that of 9c,13t-18:2, many analysts mistakenly identify the 9c,13t-18:2 isomer as 9t,12t-18:2.5 On the 100-m SP-2560 capillary column, 9t,12t-18:2 can be resolved from 9c,13t-18:2, provided the column temperature is operated isothermally at 180°C. However, very often overlaps of these 2 trans isomers occur when the SP-2560 column is operated using a temperature program as used by Block et al.1

Several years ago, we examined the tissue levels of 18:2 trans isomers in rats fed partially hydrogenated canola oil that provided 1.9% and 0.9% of total fat as 9c,13t-18:2 and 9t,12t-18:2, respectively.6 9t,12t-18:2 was not detected in any of the tissue samples, whereas 9c,13t-18:2 was found in all tissues. This would indicate that 9t,12t-18:2 is more rapidly β oxidized than 9c,13t-18:2. Thus, it is reasonable to assume that the 9t,12t-18:2 is also less abundant in human red cells than 9c,13t-18:2.

It is very likely that the fatty acid identified as the trans, trans isomer of linoleic acid by Block et al1 is 9c,13t-18:2. It is important to clarify the correct identification of these 2 isomers because the 9t,12t-18:2 is present to a lesser extent in foods than 9c,13t-18:2.2, 3

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References 

  1. Block RC, Harris WS, Reid KJ, et al. Omega-6 and trans fatty acids in blood cell membranes: A risk factor for acute coronary syndromes?. Am Heart J. 2008;156:1117–1123
  2. Ratnayake WMN, Pelletier G. Positional and geometrical isomers of linoleic acid in partially hydrogenated oils. J Am Oil Chem Soc. 1992;69:95–105
  3. Ratnayake WMN, Zehaluk C. Trans fatty acids in foods and their labelling regulations. In:  Akoh CC,  Oi-Ming L editor. Healthful Lipids. Champaign, IL: AOCS Press; 2005;p. 1–32
  4. Ratnayake WMN. Overview of methods for the determination of trans fatty acids by gas chromatography, silver-ion thin layer chromatography, silver-ion liquid chromatography, and gas chromatography/mass spectrometry. J AOAC Int. 2004;87:523–539
  5. Siguel EN, Ratnayake WMN. Trans fatty acid patterns in patients with documented coronary artery disease. Am J Cardiol. 1995;75:424
  6. Ratnayake WMN, Chen ZY, Pelletier G, et al. Occurrence of 5c,8c,11c,15t-eicosatetraenoic acid and other polyunsaturated fatty acids in rats fed partially hydrogenated canola oil. Lipids. 1994;29:707–714

PII: S0002-8703(09)00066-0

doi:10.1016/j.ahj.2009.01.007

Refers to article:

  • Omega-6 and trans fatty acids in blood cell membranes: A risk factor for acute coronary syndromes? , 15 October 2008

    Robert C. Block, William S. Harris, Kimberly J. Reid, John A. Spertus
    American Heart Journal December 2008 (Vol. 156, Issue 6, Pages 1117-1123)

American Heart Journal
Volume 157, Issue 4 , Page e23, April 2009

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