Inhibition of liver RNA breakdown during acute inflammation in the rat

Influence of an ω3-fatty acid-enriched enteral diet with and without added glutamine on the metabolic response to injury in a rat model of prolonged acute catabolism

OBJECTIVE

In critically ill patients, acute injury alters gut function, causing greater risk for sepsis and malnutrition. Peptide-enriched diets may promote nitrogen absorption, whereas ω3-enriched diets reduce alterations in gut barrier function. The aim of this study was to assess the effectiveness of a peptide- and ω3-enriched diet on the metabolic response to injury and the gut barrier function in a model of prolonged catabolism in the rat. Given the intestinal trophic effect of glutamine, we tested for a synergistic effect of glutamine.

METHODS

We randomized 40 male Sprague-Dawley rats (250 g) into four groups to enterally receive a standard high-protein diet (S), or a peptide- and ω3-enriched diet either alone (IMN) or supplemented with glutamine and alanine supplied as dipeptide (DIP) or as free amino acids (AAs) for 4 d. Metabolic response to injury was induced by turpentine injections on days 1 and 3. At sacrifice, nutritional and inflammatory biomarkers and intestinal and liver function were assessed.

RESULTS

Weight gain (+45-62%) and nitrogen balance (+33-56%) were significantly higher in all groups than in the S group. In jejunal mucosa, total glutathione was significantly higher (+20-30%) and myeloperoxidase activity significantly lower in all groups compared with the S group. Hepatic triacylglycerol content was significantly lower in the AA (0.30 ± 0.04 μM/g) and DIP (0.43 ± 0.08 μM/g) groups than in the S group (0.71 ± 0.08 μM/g).

CONCLUSIONS

In this model of prolonged catabolism, compared with a standard diet, a peptide- and ω3-enriched diet improved metabolic response to injury, with better nitrogen balance and weight recovery, and decreased intestinal myeloperoxidase activity. Only marginal additional effects of glutamine supplementation were observed with decreased hepatic fat content.

Autophagy: A protective mechanism in response to stress and inflammation

Autophagy is one of the intracellular systems that is responsible for protein trafficking (degradation/recycling) in eukaryotic cells. This ubiquitous process contributes to cytosolic homeostasis, but its deregulation is often associated with various pathologies, including neurodegenerative diseases and cancer and pathologies with an altered inflammatory response. This review provides an overview of autophagy and discusses its regulation, function and future therapeutic possibilities, with a focus on the role of autophagy in inflammation.

Efficiency of a cysteine-taurine-threonine-serine supplemented parenteral nutrition in an experimental model of acute inflammation

OBJECTIVE

As is the case with glutamine, requirements for amino acids such as cysteine, taurine, and serine may be increased in stress situations. This study evaluated the potential usefulness of supplementation of total parenteral nutrition with a cysteine, taurine, threonine, and serine mixture (SEAS), with or without glutamine, in an experimental model of turpentine-induced acute inflammation.

DESIGN AND SETTING

Prospective, controlled animal study in male Sprague-Dawley rats.

INTERVENTIONS

Twenty-seven rats received isonitrogenous, isocaloric total parenteral nutrition (260 kcal/kg, 2 gN/kg per day) for 5 days. They were divided into three groups according to the composition of the amino acid admixture: standard amino acids (control, n=9), standard amino acids partly substituted with SEAS (n=10) or with SEAS and glutamine (n=8). All rats received two subcutaneous turpentine injections (0.5 ml/100 g) 24 h (day 2) and 72 h (day 4) after the initiation of parenteral nutrition and were killed on day 5.

MEASUREMENTS AND RESULTS

Nitrogen balance was significantly increased (control 53+/-29, SEAS 153+/-21, SEAS+Gln 187+/-32 mg/24 h) and urinary 3-methylhistidine/creatinine ratio decreased (control 55+/-4, SEAS 43+/-4, SEAS+Gln 38+/-3 micro mol/mmol) on day 5 in the two SEAS-treated groups. Hepatic and extensor digitorum longus muscle protein contents were significantly higher in the SEAS+Gln-treated group than in the other two groups. In addition to slight differences in liver amino acid content, other parameters including liver glutathione did not differ significantly between groups.

CONCLUSIONS

Improved nitrogen balance and reduction in urinary 3-methylhistidine suggest that SEAS supplementation improves nitrogen homeostasis in an experimental model of acute inflammation. Glutamine addition further improves protein status.

Identification of glutathione S-transferase isozymes and gamma-glutamylcysteine synthetase as negative acute-phase proteins in rat liver

Because acute infection and inflammation affect drug metabolism and drug-metabolizing enzymes, the effect of the acute-phase response on the expression of glutathione S-transferase (GST) isoenzymes, glutathione synthesis, and several antioxidant enzymes was investigated. Hepatic expression of GST isozymes, positive and negative acute-phase reactants, and antioxidant enzymes were determined by Northern blotting and hybridization with gene-specific oligonucleotide probes after lipopolysaccharide treatment of rats. Lipopolysaccharide caused the expected acute-phase response as judged by the increased expression of positive and decreased expression of negative acute-phase proteins. The messenger RNA (mRNA) expression of the major hepatic rat GST isozymes A1, A2, A3, M1, and M2 was decreased 50% to 90%. Total hepatic GST activity toward 1-chloro-2,4-dinitrobenzene was also significantly decreased. mRNA expression of gamma-glutamylcysteine synthetase (GCS) large subunit and catalase was reduced by approximately 60%. GCS enzyme activity was also decreased, resulting in a 35% decrease in the hepatic content of reduced glutathione 4 days after lipopolysaccharide challenge. Mn-Superoxide dismutase expression was increased 13-fold, and thioredoxin level was elevated 3-fold after lipopolysaccharide challenge. The expression of all parameters determined returned to near control levels 7 days after treatment. Together, these data show that GSTs and GCS are negative acute-phase proteins and that decreased GCS activity results in a decrease in hepatic glutathione content. Thus, in addition to the phase I drug-metabolizing enzymes known to be decreased during the acute-phase response, some phase II enzymes involved in the elimination of xenobiotics and carcinogens are also decreased.

Regulation of cytochromes P450 during inflammation and infection

Hepatic P450 activities are profoundly affected by various infectious and inflammatory stimuli, and this has clinical and toxicological consequences. Whereas the expression of most P450s in the liver is suppressed, some are induced. Many of the effects observed in vivo can be mimicked by pro-inflammatory cytokines and IFNs, and P450s are differentially regulated by these agents. Therefore, different cytokine profiles and concentrations in the vicinity of the hepatocyte in different models of inflammation may result in qualitatively and quantitatively different effects on populations of P450s. In addition to cytokines, glucocorticoids may have an important role in P450 regulation in stress conditions, including that caused by inflammatory stimuli. Although in many cases the decreases in activity are due primarily to a down-regulation of P450 gene transcription, it is likely that modulation of RNA and protein turnover, as well as enzyme inhibition, contributes to some of the observed effects. The mechanisms whereby these effects are produced may also vary with both the P450 under study and the time course of the effect. The complexity of the P450 response to inflammation and infection means that all of the above factors must be considered when trying to predict the effect of a given infectious or inflammatory condition on the clinical or toxic response of humans or animals to an administered drug or toxin. The question of whether the down-regulation of the hepatic P450 system to inflammation or infection is a homeostatic or pathological response cannot be answered at present. It is difficult to discern the physiological benefit of reducing hepatic P450 activities, unless it is to prevent the generation of reactive oxygen species generated by uncoupled catalytic turnover of the enzymes. On the other hand, as we proposed some years ago [64], the suppression of P450 may be due to the liver's need to utilize its transcriptional machinery and energy for the synthesis of APPs involved in the inflammatory response. In that case, one could ask why the organism has gone to the trouble of employing differential mechanisms for suppression of P450. One answer could be that the response evolved after the divergence of many of the P450 genes, necessitating the evolution of multiple redundant mechanisms for P450 suppression. In contrast to the down-regulation of P450s in the liver, the induction of several forms in this and other tissues suggests a more specific homeostatic role of these effects, e.g., in generation or catabolism of bioactive metabolites.