Ganglioside patterns of three morris minimal deviation hepatomas

Changes in plasma gangliosides in relation to tumor growth and their tumor-enhancing effect

Gangliosides in the plasma of Ehrlich ascites tumor-bearing mice showed changes, both quantitative and qualitative, with progress of tumor. Quantitative changes assessed by chemical estimation indicated a gradual increase of gangliosides up to day 6 of tumor growth followed by a decline leading to a level below the normal by day 12. Qualitative changes studied by thin-layer chromatography indicated appearance of new gangliosides in the plasma of tumor-bearing mice, which were absent from normal plasma. One of these gangliosides appears to be of tumor-cell origin. Gangliosides obtained from tumor-bearing mouse plasma enhanced tumor growth when adoptively transferred with tumor cells into normal mice.

Cyclic modulation of enzymes of pyrimidine nucleotide biosynthesis precedes sialoglycoconjugate changes during 2-acetylaminofluorene-induced hepatocarcinogenesis in the rat

Three enzymatic activities associated with pyrimidine nucleotide biosynthesis were monitored at weekly or bi-weekly intervals during 2-acetylaminofluorene- (0.025% in a Farber Basal Carcinogenic diet) induced hepatocarcinogenesis in the rat. Dihydroorotate dehydrogenase, the fourth of six enzymes in de novo pyrimidine biosynthesis, declined in activity while UDP kinase and CTP synthetase showed sequential increases in activity. The alterations in activity appeared to be cyclic, followed by a full or partial return to control values. Three full cycles were monitored. The first cycle preceded nodule formation. The second cycle accompanied nodule formation and preceded sialoglycoconjugate changes reported previously. The third cycle accompanied the early glycoconjugate changes. The cyclic pattern was reproducible in three separate experiments. In each cycle, the order of events was as follows: decrease in dihydroorotate dehydrogenase, sequential increases in UDP kinase, CTP synthetase and CMPsialic acid synthase, and finally increases in the enzyme lactosylceramide: CMPsialic acid sialyltransferase, lipid-soluble sialic acid and total sialic acid. In livers of animals fed 1.87% of the hepatotoxin, 4-acetamidophenol, no biochemical alterations resembling those induced by 2-acetylaminofluorene were obtained, despite acute centrilobular necrosis of the livers. The findings point to a biochemical cascade beginning with administration of carcinogen and continuing through the development of hyperplastic nodules and of frank carcinomas resulting not from hepatotoxicity but as events associated with the hepatocarcinogenic progression.

Sialoglycoconjugate changes during 2-acetylaminofluorene-induced hepatocarcinogenesis in the rat

Previous studies indicated a reproducible pattern of altered glycosphingolipid biosynthesis accompanying late stages of liver tumorigenesis in the rat induced by the carcinogen 2-acetylaminofluorene. The sequence began with a dramatic elevation in CMP-sialic acid:lactosylceramide sialyltransferase and was followed by sequential elevations and eventual depressions in other enzymes catalyzing sugar transfers to glycolipid acceptors. The present study focused on the early events of glycolipid biosynthesis during the first 11 weeks of 2-acetylaminofluorene administration according to the same feeding schedule as used previously. Transient elevations in CMP-sialic acid synthetase and elevations in neutral glycosphingolipid precursors to gangliosides were found to precede the major elevations in CMP-sialic acid:lactosylceramide sialyltransferase (GM3 synthetase) noted earlier. Two cycles of response were observed prior to the initiation of the sustained enhancement of biosynthesis of precursor ganglioside, GM3, and/or a significant increase in total or lipid-soluble sialic acid. In vitro rates of sialyl transfer from CMP-sialic acid to endogenous protein acceptors were not altered. The results suggest that the previous observations of altered ganglioside biosynthesis following 2-acetylaminofluorene administration are not an isolated occurrence but may represent late events in a sequence or 'cascade' of biochemical change involving, as well, biosynthesis of ganglioside precursors, CMP-sialic acid and neutral glycosphingolipids.

Ganglioside patterns of metastatic and non-metastatic transplantable hepatocellular carcinomas of the rat

In previous investigations, we correlated levels of sialic acid, gangliosides, and ganglioside glycosyltransferases with tumorigenesis over a 24-week continuum of growth of hepatocellular neoplasms of the rat induced by the carcinogen N-2-fluorenylacetamide. However, metastatic tumors developed only rarely and were not analyzed. To investigate surface changes associated with metastasis, well-differentiated and poorly differentiated hepatocellular carcinomas were transplanted to syngeneic recipient rats. From those, several metastatic and nonmetastatic isolates were obtained and compared. Both total and ganglioside sialic acid amounts in transplantable hepatomas were elevated above control liver values but were significantly lower for metastatic lines than for nonmetastatic lines. The nonmetastatic lines were characterized by ganglioside patterns depleted in the precursor ganglioside GM3 (sialic acid-galactose-glucose-ceramide) and elevated in the products of the monosialoganglioside pathway. In contrast, metastatic isolates exhibited a restoration of GM3 and nearer normal amounts of other gangliosides. The findings point to differences in sialic acid-containing glycolipids, comparing metastatic and nonmetastatic hepatocellular carcinomas, and further extend the concept that ganglioside alterations do not cause tumorigenesis but are the end result of a cascade of events which apparently continue beyond the onset of metastasis.

Glycolipids as indicators of tumorigenesis

Hyperplastic liver nodules and hepatocellular carcinomas were induced in rats by oral administration of the carcinogen N-2-fluorenylacetamide. Neoplastic tissue was compared with control, fetal, neonatal, and precancerous liver tissues. The development of the tumors was slow, such that temporal changes in the biochemical and morphologic development of carcinogenesis could be identified. Ganglioside sialic acid levels were elevated in all but the most poorly differentiated tumors. Experiments to monitor individual enzymes suggested that the alterations in glycolipid composition were a direct effect of alterations in biosynthetic activities. The pattern during tumorigenesis was the inverse of that during normal development. Also, ganglioside patterns showed a progressive simplification from hyperplastic nodules to well-differentiated hepatomas and through two grades of poorly differentiated hepatomas. An increase in the activity of the branchpoint enzyme of ganglioside biosynthesis preceded both a decrease in the branchpoint enzyme of the disialoganglioside pathway and a marked increase in the galactosyltranferase of GM1 formation. The results indicate that ganglioside deletions are the end result of a cascade of events in the tumorigenic transformation. The onset of ganglioside deletions but not of the cascade per se may correlate with the onset of malignancy. Glycolipid levels are elevated early in certain surrounding tissues especially in the blood. In rats bearing transplantable hepatomas, serum levels of lipid-bound sialic acid were elevated 2.5-fold. Similar results were obtained with sera of mice bearing transplantable mammary carcinomas and of cancer patients. These findings provide new emphasis for gangliosides in both cancer detection and as regulatory signals for growth and multiplication of cells.

Impaired ganglioside synthesis in rat liver after D-galactosamine administration in vivo

D-Galactosamine reduces the hepatic content of uridine phosphates, UDP-galactose, and UDPglucose due to an accumulation of UDP-amino sugars; this deficiency can result in severe hepatocellular damage. Alterations of glycosphingolipid synthesis in the early phase of this pathogenic process were studied by measurements of the incorporation of labeled galactose into glycosphingolipids of rat liver. [1-14C]Galactose was injected 2 h after galactosamine administration and the specific radioactivities of the glycosphingolipid precursors, UCPgalactose and UDPglucose, were determined. The specific radioactivity of UDPgalactose, when integrated over the whole period of radioactive synthesis, was four times higher in the galactosamine-treated animals than in the controls; the corresponding ratio of UDPglucose was 0.85. The pattern of the glycosphingolipids isolated from the livers of normal and galactosamine-treated rats resembled that described by Siddiqui and Hakomori (1970, Cancer Res. 30, 2930-2936); GL1, GM3,GM1, GD1, and a small amount of GT could be characterized. The specific radioactivities of glucose and galactose obtained from individual glycosphingolipids were determined in normal and galactosamine-treated livers. The synthesis of the glycosphingolipids was calculated using the respective data of the UDPhexoses. The labeling of glucosylceramide (GL1) was not altered and only a small change of GM3 could be detected; the synthesis of gangliosides GM1 and GD1, however, was inhibited by 95% or more between 4 and 6 h after galactosamine administration.

Gangliosides of hepatoma 27, normal and regenerating rat liver

The highly malignant rat hepatoma 27 was found to have increased amounts of lipid-bound sialic acid as compared with normal liver whereas in regenerating liver the lipid-bound sialic acid level was reduced. In contrast to the liver the hepatoma contained higher amounts of disialogangliosides and no trisialogangliosides, which are abundant in the liver. The main disialoganglioside of the hepatoma had no analogue among the liver gangliosides and was identified as Gal-GalNAc(AcNeu-AcNeu)-Glc-Cer (GD1b), which in other tissues is known to be a precursor of trisialogangliosides. These findings may be explained by a reduced activity of glycosyltransferases in the hepatoma and apparently do not simply reflect differences in growth rate since the ganglioside pattern of regenerating rat liver was not altered significantly in comparison with the liver. Liver and hepatoma microsomes were found to be enriched in gangliosides as compared with whole cells, liver mitochondria were slightly poorer, while the ganglioside level of hepatoma mitochondria was much higher than that of the hepatoma cells. It thus appears that the existing image of the plasma membranes as the only sites of high ganglioside concentration may not hold true for weakly differentiated hepatomas of high malignancy.

Mammary carcinoma: enzymatic block in disialoganglioside biosynthesis

The sialyl transferase of disialoganglioside formation is depressed in mammary tumors induced in the rat by 7,12-dimethylbenz[a]anthracene. Specific activities of other glycosyltransferases of the pathway ceramide to monosialo-ganglioside are unchanged or elevated so that the ganglioside GM(1) accumulates and higher gangliosides are depressed. These findings with a solid tumor are critical to an involvement of gangliosides in the cell-surface changes of tumorigenesis.

Ganglioside patterns and phenotypic characteristics in a normal variant and a transformed back variant of a simian virus 40-induced hamster tumor cell line

Ganglioside patterns of a cloned Simian virus 40- (SV40) induced hamster tumor cell (Cl(2)TSV(5)-S), its normal variant (Cl(2)TSV(5)-R) which are Cl(2)TSV(5)-S gradually adapted to grow in the presence of 2 microg/ml actinomycin D and exhibit certain normal phenotypic characteristics, and its back variant (Cl(2)TSV(5)-RR), which are Cl(2)TSV(5)-R cells grown in the absence of actinomycin D for more than 60 passages and which exhibit greater phenotypic similarity to Cl(2)TSV(5)-S cells, have been analyzed. All three cell lines contain N(acetylneuraminyl) galactosylglycosyl ceramide (hematoside, GM(3)), N-acetylgalactosaminyl (N-acetylneuraminyl) galactosylglucosyl ceramide (GM(2)), and a higher ganglioside tentatively identified as disialohematoside. However, Cl(2)TSV(5)-R have more GM(2) than Cl(2)TSV(5)-S whereas Cl(2)TSV(5)-RR contain an intermediate amount of GM(2). The amount of GM(2) is correlative with the activity of UDP-N-acetylgalactosamine: hematoside N-acetylgalactosaminyl transferase in the extract of the three cell lines and with their agglutination by wheat germ agglutinin.