Abstract
An investigation was made into the effect of different dietary fats (com oil, olive oil and MaxEPA) on membrane phospholipids (phosphatidylinositol, phosphatidylcholine and phosphatidylethanolamine) in the rat mammary gland and red blood cells. It was demonstrated that phosphatidylinositol is the least responsive phospholipid to dietary fatty acid modification in both of the tissues studied. Overall, erythrocytes responded to the different diets more than mammary gland membranes. Phosphatidylethanolamine incorporated more w3 fatty acids from the marine oil diet than either phosphatidylcholine or phosphatidylinositol. The arachidonic acid (20:4w6) content of phosphatidylcholine and phosphatidylethanolamine was highest in animals fed com oil, less in animals fed olive oil and the least in those fed marine oil. The relative proportions of phospholipids in the mammary gland and red blood cell membranes were not affected by feeding rats different diets. It was also demonstrated that the fatty acid profile of phospholipids from rat, N-ethyl-A-nitrosourea (ENU) induced mammary tumours are not very different to those from normal rat mammary tissue. However, in the phosphatidylinositol fraction, in rats on all three diets the stearic acid content was higher in the tumours than in the normal mammary tissue. This was most evident in the olive oil group (12 mol%; p<0.05) and least in the marine oil group (<3 mol%; NS). Rats administered ENU and fed a MaxEPA diet presented with fewer mammary tumours than those fed either a corn oil diet or an olive oil diet (p<0.05). Possible mechanisms for the protective effect of marine oil on mammary tumourigenesis are discussed. The effect of a low fat diet on human female erythrocyte membrane phospholipids was studied. Only a few changes to membrane phospholipids were demonstrated. There was no significant effect on the fatty acid profile of phosphatidylcholine after two months of a low fat diet; and there was only a small change in the phosphatidylinositol fraction (increased arachidonic acid [20:4w6], p<0.05). Serum prolactin and oestradiol were also measured in this study. There was no effect of diet on prolactin levels as measured by radioimmunoassay. However, there was a significant decrease in serum oestradiol (p<0.05) after two months on the low fat diet. This may have significance to the relationship between dietary fat and breast cancer. The effect of marine oil supplementation on erythrocyte and platelet phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine from human volunteers was also investigated. Erythrocyte phosphatidylcholine showed an increased incorporation of eicosapentaenoic acid (20:5w3) and docosahexaenoic acid (22:6w3) after 4 weeks of supplementation. None of the other phospholipids showed a significantly increased incorporation of w3 fatty acids in either erythrocytes or platelets. There was a small change in the w9 content of erythrocyte phosphatidylinositol with decreases in palmitoleic acid (16:1w9) after 3 weeks of supplementation and decreases in oleic acid (18:1w9) after 4 weeks of supplementation. Compliance in this study was considered good as measured by a significant decrease in plasma triglyceride content. This study demonstrated that there are very few changes in the fatty acid profile of erythrocyte and platelet phospholipids after short term dietary marine oil supplementation. Furthermore, the relative proportions of the phospholipids in both tissues studied were found to be resistant to dietary modification under these conditions. The final study was a comparison of the phospholipid fatty acid profiles of human mammary malignant tumours, benign tumours and normal breast tissue. Erythrocytes were also studied to see if these cells reflected any differences detected in the mammary tissue. In breast tissue phosphatidylcholine, differences in oleic acid (18:1w9), eicosatrienoic acid (20:3w6) and arachidonic acid (20:4w6) were seen between the three tissues. Normal tissue differed from both the malignant and benign tumour tissue but the two types of tumours did not differ significantly from each other. In phosphatidylinositol there were fewer differences, however, malignant tissue contained more stearic acid than both benign and normal mammary tissue. These differences were not detected in erythrocyte phospholipids which contained a different fatty acid profile from the mammary tissue.