We have exam- ined the fatty acid composition of the retina and brain in guinea ... 22:5n-6 in the retinal lipids were inversely related to the DHA values, being 0.6, 6.6, ..... Postnatal Omega-3 Fatty Acid Deficiency on Retina and Brain in Rhesus ...
Dietary Manipulation of Long-Chain Polyunsaturated Fatty Acids in the Retina and Brain of Guinea Pigs Harrison S. Weisinger a, Algis I. Vingrys a and Andrew I. Sinclair b,* aDepartment of Optometry, University of Melbourne, Parkville, 3052, Victoria, Australia and bDepartrnent of Food Science, Royal Melbourne Institute of Technology, Melbourne, 3000, Victoria, Australia
ABSTRACT: High levels of n-6 docosapentaenoic acid (22:5n-6) have been reported in the retina of guinea pigs fed commercially-prepared grain-based rations (commercial diet). In rats and monkeys, high levels of 22:5n-6 are an indicator of n-3 polyunsaturated fatty acid (PUFA) deficiency. We have examined the fatty acid composition of the retina and brain in guinea pigs fed a commercial diet or one of three semi-purified diets containing three different levels of n-3 PUFA. The diets comprised a diet deficient in n-3 PUFA (semi-purified diet containing safflower oil), two diets containing cc-linolenic acid (standard commercial laboratory diet and semi-purified diet containing canola oil), and a diet containing o~-Iinolenic acid, eicosapentaenoic acid, and docosahexaenoic acid (DHA) (semi-purified diet containing canola oil, safflower oil, and fish oil). Two groups of guinea pigs were given the diets from day 1 to 4 wk or day 1 to 8 wk, when they were sacrificed and the retinal tissues were extracted and analyzed for PUFA content by gas-liquid chromatography. Fatty acid analyses of the retinal phospholipids of the four-week-old animals revealed that the group fed DHA (from the fish oil) had the highest level of DHA (32%), compared with values of 19 and 13% for the groups fed canola oil diet and commercial diet, respectively, and 2% for the group fed the diet deficient in n-3 PUFA. The levels of 22:5n-6 in the retinal lipids were inversely related to the DHA values, being 0.6, 6.6, 11.4, and 20.6 for the fish oil, canola oil, commercial diet, and safflower oil diet groups, respectively. The long-chain PUFA profiles in the brain phospholipids of the fourweek-old group were similar to those from the retina. The retinal PUFA values for the eight-week-old animals were similar to the four-week-old group. The safflower oil diet induced a greater deficit of DHA in retinal lipids than has been reported in rats and monkeys fed similar diets. The guinea pigs fed the commercial diet had retinal and brain PUFA patterns similar to that produced by n-3 PUFA-deficient diets in rats and monkeys. Guinea pigs fed the canola oil diet had significantly greater retinal DHA levels than those fed the commercial diet, but lower *To whomcorrespondenceshould be addressed at the Departmentof Food Science, RoyalMelbourneInStituteof Technology,GPO Box 2476V, Melbourne, 3001, Victoria,Australia. Abbreviations: DHA, docosahexaenoicacid (22:6n-3); PUFA, polyunsaturated fattyacids. Copyright 9 1995 by AOCS Press
than those fed fish oil. The data suggest that the guinea pig has a reduced capacity for DHA synthesis from 0t-linolenic acid as compared with other mammals. Supplementation of guinea pig diets with fish oil produced high retinal and brain DHA levels and prevented the accumulation of 22:5n-6. Lipids 30, 471-473 (1995).
Docosahexaenoic acid (DHA) (22:6n-3) is the major polyunsaturated fatty acid (PUFA) in brain grey matter and retina of most mammalian species (1-3). Animals fed n-3 PUFA-deficient diets develop low levels of DHA in the brain and retina and an increase in n-6 docosapentaenoic acid (22:5n-6) (3-6). High levels of 22:5n-6 and low levels of 22:6n-3 in tissue phospholipids are considered to be a biochemical marker of n-3 PUFA deficiency (3-6). Such fatty acid changes are associated with abnormal electroretinograms in rats and monkeys (3-6), and alterations in enzyme activities in neural tissue (4). In 1986, Leat et al. (7) reported that commercial diet-fed guinea pigs contained a high level of 22:5n-6 and a relatively low level of DHA in the retinal lipids, suggesting that the commercial diet used was deficient in o~-linolenic acid. The guinea pig commercial diet contained linoleic and 0t-linolenic acid as the only dietary PUFA. The finding that the control guinea pigs showed biochemical evidence of reduced DHA levels might explain why Leat et al. (7) were not able to detect electroretinogram differences between the control guinea pigs and those fed a semi-purified diet containing linoleic acid as the only PUFA (n-3-deficient diet). The purpose of this study was to establish whether guinea pigs fed semi-purified diets containing a-linolenic acid and/or DHA could prevent the accumulation of docosapentaenoic acid (22:5n-6) in retinal and brain tissue. MATERIALS A N D M E T H O D S
A n i m a l s a n d diets. Sixteen commereial diet-fed female
guinea pigs (in groups of four) were weaned onto a guinea pig commercial diet (Barrastock Guinea Pig Food; Barrastock, Melbourne, Australia), or one of three semi-purified diets
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based on those described by Leat et al. (7). The diets conmined (g/kg) casein 300, sucrose 100, glucose 70, starch 200, solkafloc 100, oil 100, kaolin 30, L-arginine 3, DL-methionine 2, mineral mix 68, and vitamin pre-mix 27. All diets were supplemented with 10 g fresh carrots daily, and water containing ascorbic acid (400 mg/L) was freely available. Details of the vitamin premix and mineral mix are given in Leat et al. (7). The guinea pig commercial diet contained 14 g/kg linoleic acid, 1.6 g/kg ~t-linolenic acid, and no long-chain PUFA. The semi-purified diets were identical, except for the added oils. The n-3-deficient diet contained safflower oil as the sole source of fat (71 g/kg linoleic acid, 54. The 22:5n-6 comprised less than 1% of the phospholipid fatty acids in the fish oil-fed group by comparison with values of 20% in the safflower group. The data for the brain for the four-week-old animals were similar to the retina, with the DHA/22:5n-6 ratios being 0.1, 0.9, 1.5, and 24 for the safflower, chow, canola, and fish oil diet groups, respectively.
TABLE 1 Fatty Acid Composition of Retinal Phospholipids from Guinea Pigs Fed Diets Containing Different Levels of n-3 PUFA a Age (eight weeks)
Age (four weeks) Fatty acid 16:0 18:0 18:1 18:2n-6 20:4n-6 20:5n-3 22:4n-6 22:5n-6 22:5n-3 22:6n-3 22:6~2:5n-6
Fish oil 19.5• 14.5• I0.0• 2.3• 8.5• 0.8• 1.1• 0.6• 1.8• 32.4• 54.0•
Canola oil b c c b c c c c
18.3• 16.1• 8.3• 2.4• 11,1• d 2.5• 6.6• 1.4• 19.1• 2.9•
Commercial
b c
c c c
20.2• 18,4• 11.2• 2.7• 10.5• __ 2.7• 11.4• 1.0• 13.4• 1.2•
Safflower oil 19.6• 20.5• 9.0• 2.7• 9.1• -4.4• 20.6• 0.3• 2.4• 0,1•
b c c
c c c c
Canola oil
Fish oil 17.5• 21.3• 11.0• 1.3• 7.3• 0.5• 1.1• 0.5• 1.8• 30.8• 61,6•
b c c c c
17.9• 21.0• 11.7• 1.6• 9.2• 2.5• 5.2• 1.3• 21.0• 4.0•
Commercial
b b
c c c c
aMean • standard deviation, n = 6 for four-week-old, n = 12 for eight-week-old animals; PUFA, polyunsaturated fatty acids. bc ' Significantly different from commercial diet fed values: bp < 0.01, cp < 0.001. dLess than 0.1%.
Lipids, Vol. 30, no. 5 (1995)
Safflower oil
17.6• 21.7• 11.2• 1,3• 9.6•
17.6• 21.2• 9.3• 2.6• 9.8•
3.1• 14.1• 0.8• 12.4• 0.9•
4.5• 23.3• 0.2• 2.5• 0.1•
b b
c r c c
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These data show that guinea pigs raised on a diet containing a-linolenic acid (canola oil-based diet or the commercial guinea pig diet) have lower retinal and brain DHA levels relative to those fed fish oil. Furthermore, the group fed the safflower oil diet had very low DHA levels (
