Effect of low-protein diet and protein supplementation on the expressions of TNF-α, TNFR-I, and TNFR-II in organs and muscle of LPS-injected rats

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Abstract
Previous studies had shown that increasing energy intake in anorexic TNF-α-treated rats increased morbidity due to stabilization of TNF activity by soluble and membrane TNF receptors (TNFR). Although protein supplementation reduces septic morbidity, its effect on TNF and TNFR is unknown. To determine the effect of low protein intake and supplementation on TNF and TNFR, 30 male Wistar rats weighing 250 g were fed a liquid defined-formula diet for 10 days and randomly allocated to 1) controls (C; n = 6), receiving normal energy and protein energy density of 0.047 MJ/60 ml + normal saline (NS); 2) low protein (LP; n = 6), receiving normal energy but a reduced protein-energy density of 0.012 MJ/60 ml + LPS; 3) refeeding (RF; n = 6), initially depleted on low-protein diet (10 days) and then repleted on normal protein (10 days) while receiving LPS; and 4) pair fed (P-F; n = 12), individual P-F rats being paired with individual LP or RF rats receiving NS. Protein and mRNA expression of TNF-α, TNFR-I, and TNFR-II in liver, spleen, and gastrocnemius were measured by Western blot and RT-PCR, respectively. In liver, the changes in TNF-α, TNFR-I, and TNFR-II were translational, whereas in spleen the effects were due to a combination of transcription and translation. In gastrocnemius, the effects were transcriptional/translational for TNFRs. In contrast, TNF-α mRNA was significantly increased, but TNF-α protein expression was reduced in LP rats compared with C and RF groups. In conclusion, protein deficiency in endotoxic rats increases the expression of TNFR-I and TNFR-II in all organs studied and TNF-α in selected ones. This increase is suppressed by refeeding protein. A differential pattern between translation and transcription of TNF-α and its receptors is present. Our data suggest that protein restriction may be deleterious in sepsis.