Down-regulation of liver RNA breakdown by turpentine administration in the starved rat: autophagy and relevant factors

Simultaneous Infusion of Glutamine and Branched-Chain Amino Acids (BCAA) to Septic Rats Does Not Have More Favorable Effect on Protein Synthesis in Muscle, Liver, and Small Intestine Than Separate Infusions

BACKGROUND

Glutamine and branched-chain amino acids (BCAA; valine, leucine, and isoleucine) are used as nutrition supplements in the treatment of proteocatabolic illness. We hypothesized that simultaneous administration of BCAA and glutamine affects protein metabolism more significantly than separate administration. In the present study, we evaluated their effect on protein synthesis in skeletal muscle, liver, and jejunum of septic rats.

METHODS

Twenty-four hours after induction of sepsis by subcutaneous injection of turpentine, the rats were infused for 6 hours with 5 mL of 1.75% glutamine, 1.75% BCAA, 1.75% glutamine+BCAA, or saline solution. The control group consisted of intact rats infused with saline. Protein synthesis was measured at the end of infusion by a "flooding method" with [3,4,5-(3)H]phenylalanine.

RESULTS

In turpentine-treated animals, we observed a decrease in glutamine concentration in blood plasma and skeletal muscle, a decrease in BCAA concentration in liver and jejunum, and a decrease in protein synthesis in all tissues. Glutamine or glutamine+BCAA infusion increased glutamine concentration in plasma and muscle and stimulated protein synthesis in the liver. The BCAA infusion enhanced concentrations of BCAA in plasma and tissues, but the effect of BCAA on protein synthesis was insignificant. Synergistic effect of simultaneous infusion of glutamine and BCAA on protein synthesis was not observed.

CONCLUSIONS

We conclude that glutamine infusion to rats with septic injury may significantly improve impaired protein synthesis in the liver and that there is no synergistic effect of glutamine and BCAA infusion on protein synthesis in skeletal muscle, liver, and jejunum.

Interactions between ω3 polyunsaturated fatty acids and arginine on nutritional and immunological aspects in severe inflammation

BACKGROUND & AIMS

Immune-enhancing diets (IEDs) contain a mixture of nutrients claimed to have immunological properties. Therefore, it seemed relevant to determine the effect of each of their components. The aim of this study was to examine the role of arginine (Arg) and ω3 polyunsaturated fatty acids (ω3 PUFAs) in the effect of an IED (Crucial(®)) in a validated rat model of inflammation induced by turpentine (TI).

METHODS

Forty-two rats were randomized into five groups: AL (ad libitum), TI-EN (TI+standard enteral nutrition (EN): Sondalis(®)HP), TI-EN-Arg (TI+standard EN+Arg in equimolar concentration to Arg in the IED), TI-M-IED (TI+modified IED containing the same ω6/ω3 ratio as in standard EN) and TI-IED (TI+Crucial(®)). Blood was sampled to determine CD25 receptor density on lymphocytes. TNF-α, IL-6 and NO (production and expression) were evaluated on isolated macrophages. Mesenteric lymph nodes, spleen and liver were cultured for analysis of enterobacterial translocation and dissemination.

RESULTS

CD25 density was decreased after TI and was corrected in the TI-EN-Arg, TI-M-IED and TI-IED groups (p<0.05). TI induced an alteration of macrophage mRNA expression of IL-6, TNF-α and iNOS, corrected in the TI-EN-Arg and TI-M-IED groups (p<0.05), but not by the IED. Enterobacterial translocation was observed in all treated groups, nevertheless the amount tended (p=0.054) to be lower in the TI-EN-Arg group.

CONCLUSIONS

Arg and ω3 PUFAs make a major contribution to IED effects, but our study shows interaction between them on macrophage reactivity. This indicates that the individual properties of each pharmaconutrient are not additive in IEDs.

Methods for measuring tissue RNA turnover

Measuring RNA turnover is important because of the significance of rRNA, tRNA and mRNA in tissue protein synthesis. Changes in turnover of each of these species precede important cellular events such as hormone or cytokine action or cell-division itself. Isotopic methods have relied on decay of pulse-labelled RNA or on incorporation of isotopically-labelled precursors. However, recycling of labels may lead to under or overestimation of synthesis rates respectively. The labelling of the intracellular precursor pool must be known if accurate RNA synthesis rates are to be calculated from the degree of incorporation. However, the intracellular nucleotide pools may be anatomically or metabolically compartmented (i.e. via de novo or salvage synthesis routes) and this complicates many study designs. The use of[methyl-14C]- or [methyl-3H]methionine as a means of labelling methylated nucleosides in RNA and protein simultaneously is described in addition to new stable isotopic techniques based on 13C-glycine as a de novo label. Urinary excretion of the numerous modified nucleosides in cellular RNA can be used to calculate whole-body turnover rates of each of the major RNA species. Examples of the effects of critical-illness and glutamine supplementation on RNA turnover are given. We conclude by suggesting that whole-body RNA turnover rates have been significantly underestimated and that this has implications for nutritional therapy, especially with regard to nucleotide supplementation.