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Vitamin B₆ Metabolism in Liver and Liver-derived Tumors¹

Department of Biochemistry, University of Vermont College of Medicine, Burlington, Vermont 05405

Vitamin B₆ metabolism has been investigated in several highly and well-differentiated Morris hepatomas. Comparisons have been made with two poorly differentiated Morris hepatomas, with host livers obtained from tumor-bearing animals, and with fetal, neonatal, and adult rat liver. The pyridoxal phosphate content and the activities of pyridoxine kinase and pyridoxine phosphate oxidase of all Morris hepatomas examined were significantly less than those in adult host or control livers and generally fell in the range determined for fetal and neonatal liver. A similar pattern was not evident for the activity of pyridoxine phosphate phosphatase. Relative to control and host livers, the activity in hepatomas of the pyridoxal phosphate (PLP)-dependent enzyme, ornithine decarboxylase, was generally elevated. Dexamethasone, at a dose which caused an elevation in the activity of PLP-dependent tumor tyrosine aminotransferase, had no effect on PLP metabolism. The data indicate that tumor progression in the Morris hepatoma spectrum in relation to vitamin B₆ metabolism falls into an oncodevelopmental pattern characterized by a diminished amount of tissue PLP and a diminished capability to metabolize precursor vitamer forms to PLP.

¹ Supported by NIH Grant AM 25490.

² Cancer Biology Trainee supported by NIH Grant CA T32-09826.

³ To whom requests for reprints should be addressed.

Received 3/15/82. Accepted 6/ 7/82.