Influence of methionine/valine-depleted enteral nutrition on nucleic acid and protein metabolism in tumor-bearing rats

摘要

AIM: To investigate the effects of methionine/valine-depleted enteral nutrition (EN) on RNA, DNA and protein metabolism in tumor-bearing (TB) rats. METHODS: Sprague-Dawlley (SD) rats underwent jejunostomy for nutritional support. A suspension of Walker-256 carcinosarcoma cells was subcutaneously inoculated. 48 TB rats were randomly divided in 4 groups: A, B, C and D. The TB rats had respectively received jejunal feedings supplemented with balanced amino acids, methionine-depleted, balanced amino acids and valine-depleted for 6 days before injection of 740 KBq ~3H- methionine/valine via jejunum. The ~3H incorporation rate of the radioactivity into RNA, DNA and proteins in tumor tissues at 0.5, 1, 2, 4 h postinjection of tracers was assessed with liquid scintillation counter. RESULTS: Incorporation of ~3H into proteins in groups B and D was (0.500+-0.020) % to (3.670+-0.110) % and (0.708+-0.019) % to (3.813+-0.076) % respectively, lower than in groups A [(0.659+-0.055) % to (4.492+-0.108) %] and C [(0.805+-0.098) % to (4.180+-0.018) %]. Incorporation of ~3H into RNA, DNA in group B was (0.237+-0.075) % and (0.231+-0.052) % respectively, lower than in group A (P<0.01). There was no significant difference in uptake of ~3H by RNA and DNA between group C and D (P>0.05). CONCLUSION: Protein synthesis was inhibited by methionine/valine starvation in TB rats and nucleic acid synthesis was reduced after methionine depletion, thus resulting in suppression of tumor growth.