Effect of methionine-deprived total parenteral nutrition on tumor protein turnover in rats

Methionine-dependence and combination chemotherapy on human gastric cancer cells in vitro

AIM: To elucidate whether human primary gastric cancer and gastric mucosa epithelial cells in vitro can grow normally in a methionine (Met) depleted environment, i.e. Met-dependence, and whether Met-depleting status can enhance the killing effect of chemotherapy on gastric cancer cells.

METHODS: Fresh human gastric cancer and mucosal tissues were managed to form monocellular suspensions, which were then cultured in the Met-free but homocysteine-containing (Met^-Hcy⁺) medium, with different chemotherapeutic drugs. The proliferation of the cells was examined by cell counter, flow cytometry (FCM) and microcytotoxicity assay (MTT).

RESULTS: The growth of human primary gastric cancer cells in Met^-Hcy⁺ was suppressed, manifested by the decrease of total cell counts [1.46 ± 0.42 (× 10⁹•L⁻¹) in Met^-Hcy⁺vs 1.64 ± 0.44 (× 10⁹•L⁻¹) in Met⁺Hcy^-, P < 0.01], the decline in the percentage of G₀G₁ phase cells (0.69 ± 0.24 in Met^-Hcy⁺vs 0.80 ± 0.18 in Met⁺Hcy^-, P < 0.01) and the increase of S cells (0.24 ± 0.20 in Met^-Hcy⁺vs 0.17 ± 0.16 in Met⁺Hcy^-, P < 0.01); however, gastric mucosal cells grew normally. If Met^-Hcy⁺medium was used in combination with chemotherapeutic drugs, the number of surviving gastric cancer cells dropped significantly.

CONCLUSION: Human primary gastric cancer cells in vitro are Met-dependent; however, gastric mucosal cells have not shown the same characteristics. Met^-Hcy⁺ environment may strengthen the killing effect of chemotherapy on human primary gastric cancer cells.

Influence of L-methionine-deprived total parenteral nutrition with 5-fluorouracil on gastric cancer and host metabolism

AIM: To investigate the influence of L-methionine-deprived total parenteral nutrition with 5-FU on gastric cancer and host metabolism.

METHODS: N-methyl-N’-nitro-nitrosoguanidine (MNNG) induced gastric cancer rats were randomly divided into four groups: Met-containing TPN group (n = 11), Met-deprived TPN group (n = 12), Met-containing TPN+5-FU group (n = 11) and Met-deprived TPN+5-FU group (n = 12). Five rats in each group were sacrificed after 7 d of treatment and the samples were taken for examination. The remaining rats in each group were then fed separately with normal diet after the treatment until death, the life span was noted.

RESULTS: The tumors were enlarged in Met-containing group and shrank in Met-deprived group markedly after the treatment. The DNA index (DI) of tumor cells and the body weight (BW) of rats had no significant change in the two groups, however, the ratio of tumor cells’ S phase was increased. The ratio of G2M phase went up in Met-containing group, but down in Met-deprived group. In the other two groups that 5-FU was added, the BW of rats, and the diameter of tumors, the DI of tumor cells, the S and G2M phase ratio of tumor cells were all decreased, particularly in Met-deprived plus 5-FU group. Pathological examination revealed that the necrotic foci of the tumor tissue increased after Met-deprived TPN treatment, and the nucleoli of tumor cells enlarged. In -MetTPN+5-FU group, severe nuclear damage was also found by karyopyknosis and karyorrhexis, meanwhile there was slight degeneration in some liver and kidney cells. The serum free Met and Cysteine decreased markedly (P ＜ 0.001), while other amino acids, such as serum free serine and glutamine increased significantly (P ＜ 0.005). All the rats died of multiple organ failure caused by cancer metastasis. The average survival time was 18.6 d in Met-containing TPN group, 31 d in Met-deprived TPN group, 27.5 d in Met-containing TPN+5-FU group, and 43 d in Met-deprived TPN+5-FU group (P ＜ 0.05).

CONCLUSION: Met-deprived TPN causes methionine starvation of tumor cells, and can enhance the anti-tumor effect of 5-FU and prolong the life span of gastric cancer-bearing rats.