Occurrence and nature of O-alkyl and O-alk-1-enyl moieties of glycerol in lipids of morris transplanted hepatomas and normal rat liver

Abstract

1. 1. The lipid class composition and nature of the O-alkyl, O-alk-1-enyl, and acyl chains of major lipid classes were investigated in normal rat liver and 7794A and 7777 Morris hepatomas. Although both hepatomas contained less phospholipid than the normal liver, the relative distribution of the classes within the phospholipid fraction was similar in the three tissues. Almost half the phosphoglycerides consisted of phosphatidyl choline and the remainder was mostly phosphatidyl ethanolamine and phosphatidyl serine-phosphatidyl inositol. The phosphatidyl choline and phosphatidyl ethanolamine fractions of normal rat liver did not contain any significant quantities of ether-containing lipids, but both the 7794A and the 7777 hepatomas contained up to 7% O-alk-1-enyl acyl phosphatidyl ethanolamine. The phosphatidyl choline fraction isolated from the 7777 hepatoma contained more alkyl ethers than the phosphatidyl choline in the 7794A hepatoma or normal rat liver. 2. 2. The neutral lipids in all three tissues were mainly sterol esters, triglycerides, free fatty acids, and cholesterol. The 7777 hepatoma also contained significant quantities of glyceryl ether diesters, and accumulated sterol esters and cholesterol at the expense of triglycerides and phosphoglycerides compared to normal rat liver or the 7794A hepatoma. The 7794A hepatoma did not contain any glyceryl ether diesters, but compared to normal rat liver this tumor also contained increased quantities of sterol esters, free fatty acids, and cholesterol. 3. 3. In the 7777 hepatoma, the O-alkyl moieties in the glyceryl ether diesters and phosphatidyl choline and the O-alk-1-enyl moieties in the phosphatidyl ethanolamine were similar and consisted mainly of 16:0, 18:0, and 18:1 hydrocarbon chains. The proportion of 18:0 to 18:1 side chain was higher in the alk-1-enyl ethers of the phosphatidyl ethanolamines than in those of the alkyl ethers of the phosphatidyl chorines. 4. 4. In all tissues studied, the fatty acid side chains differed completely from the alkyl and alk-1-enyl ether-linked side chains. Both tumors contained about twice as much 18:1 fatty acids in the sterol esters as did normal rat liver, primarily at the expense of 16:0 fatty acids. In contrast, the phosphatidyl ethanolamine and phosphatidyl choline fractions from the hepatomas contained higher quantities of linoleic acid and lower quantities of arachidonic acid than these fractions from normal liver. 5. 5. Our data demonstrate that glyceryl ether diesters and alkyl-acyl cholinecontaining lipids tend to accumulate in hepatoma 7777 which is a relatively fastgrowing tumor. In addition, the relative proportion of 18:2 and 20:4 fatty acids in the phosphoglycerides indicates that essential fatty acids are poorly utilized by hepatomas.