The Effects of Glutamine-enriched Total Parenteral Nutrition on Tumor Growth and Host Tissues

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Abstract
The effects of glutamine-enriched total parenteral nutrition (TPN + GLN) were studied in tumor-bearing rats because glutamine can benefit host tissues but also may stimulate tumor growth. Rats were implanted with the methylcholanthrene-induced fibrosarcoma (MCA sarcoma) and were studied when the tumor constituted less than 5% of carcass weight (small tumor) and when the tumor constituted 10% of carcass weight (large tumor). Provision of 20% of TPN protein as glutamine produced‘ a significant increase in the arterial glutamine level and maintained the skeletal muscle intracellular glutamine concentration (2.02 ± 0.1 versus 1.39 ± 0.07 μ mol/g, p < 0.01). Concurrently, hind-quarter GLN fractional release increased nearly threefold (p < 0.05) in the TPN + GLN group. Glutamine-enriched total parenteral nutrition did not affect carcass weight, tumor weight, tumor DNA content, or tumor glutaminase activity. Furthermore, DNA flow cytometric analysis did not demonstrate any difference in percentage of aneuploid tumor cells within the GI, S, or G2M cell cycles. However, the ratio of aneuploid to diploid cells within the tumor mass increased by 20% in animals receiving glutamine. Glutamine-enriched total parenteral nutrition had no effect on tumor glutathione (GSH) levels. No increase in hepatic'GSH levels was observed, but gut mucosal GSH levels were 20% greater in the TPN + GLN group (p < 0.05). The provision of glutamine-enriched TPN may be beneficial to the host by maintaining skeletal muscle glutamine stores and by supporting gut GSH biosynthesis. In this tumor model, TPN + GLN does not appear to increase tumor size, tumor DNA content, or tumor glutamine metabolism, but the ratio of tumor cells to host infiltrating cells within the tumor mass, appears to be increased.