Stimulation of liver RNA and protein breakdown in endotoxemic rats: role of glucocorticoids

In systemic or localized acute inflammation, liver ribosomal RNA (rRNA) and protein contents increase. We first determined whether changes in RNA, more specifically rRNA, and protein breakdown rates were involved in the accumulation of both types of macromolecules 24 h after induction of endotoxemia. Liver RNA and protein contents were enhanced by 35 and 19%, respectively, in the endotoxemic rats. RNA and protein degradation rates measured during in situ cyclic perfusions of the livers were significantly higher in the endotoxemic rats than in the controls (42 and 46%, respectively). In order to check that the stimulation of RNA and protein degradation corresponded to an activation of the hepatocyte autophagic pathway, the fractional cytoplasmic volume (FCV) of autophagosomes, digestive autophagic vacuoles and dense bodies was measured by morphometry in electron microscopy. The FCV of the sum of these lysosomal structures was significantly increased in the endotoxemic rats. We next tried to identify the factor(s) responsible for the high breakdown rates. The increase in macromolecular degradation did not result from reduced portal amino acid supply. The effects of dexamethasone, interleukin-6, interleukin-1beta, and tumor necrosis factor alpha on RNA degradation were then investigated in primary cultures of hepatocytes isolated from control rats. Only dexamethasone stimulated RNA breakdown. Finally, pretreatment of endotoxemic rats with RU 38486, a glucocorticoid receptor antagonist, completely abolished the stimulation of RNA degradation observed in the sham-gavaged LPS-treated rats. Our data suggest an important role of glucocorticoids in the high levels of RNA and protein breakdown in endotoxemic rats.

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

OBJECTIVE AND DESIGN

To determine whether the inhibition of RNA breakdown observed in ad libitum fed rats 24 h after turpentine administration still occurs in inflamed rats fasted for 24 h and to examine the mechanism and factors involved.

METHODS

RNA breakdown was measured during cyclic in situ perfusion of livers by the accumulation of [14C] cytidine after in vivo RNA labelling. Autophagic activity was determined by the morphometric analysis of lysosomal structures.

RESULTS

The decrease in RNA breakdown (53%) observed in the inflamed rats was accompanied by a 38% drop in the fractional cytoplasmic volume of initial and digestive autophagic vacuoles. Among amino acids, only the portal levels of glutamate were significantly enhanced by 83%. In vivo suppression of glucocorticoid activity using RU 38486 in inflamed rats did not affect the inhibition of RNA breakdown.

CONCLUSIONS

The results show that turpentine-induced inflammation in fasted rats inhibits RNA degradation as well as autophagy and that glucocorticoids do not seem to be involved.

Inhibition of liver RNA breakdown during acute inflammation in the rat

Liver RNA- and protein-degradation rates were measured after the induction of acute inflammation in the rat. A preliminary study determined changes in hepatic RNA and protein content 12, 18 and 24 h after a turpentine oil injection. The RNA content in turpentine-treated rats compared with pair-fed animals increased significantly and sharply from 12 h (+ 11%) to 18 h (+ 32%) and slightly thereafter (+ 37% at 24 h). The liver protein content was significantly enhanced only at 24 h (+ 11%) in response to inflammation. RNA-degradation rates were determined in livers perfused cyclically in situ for 15 min by measuring the accumulation of radioactive cytidine in the medium 60 h after in vivo labelling of RNA by [5-3H]cytidine instead of [6-14C]orotic acid, the most commonly used radioactive marker. Several validation procedures showed that the method employed was a valid alternative to the use of radioactive orotic acid. RNA-degradation rates, which mainly reflect rRNA breakdown, were significantly lower in the turpentine-treated rats than in respective pair-fed animals at 18 and 24 h (57 and 45% decrease respectively). Proteolysis rates measured at 24 h together with RNA breakdown by valine accumulation in the perfusion medium were not modified after turpentine treatment. The main factors known to regulate RNA degradation (amino acids, insulin/glucagon ratio) were measured in the portal blood 24 h after induction of acute inflammation. Of the known regulatory amino acids, only glutamine and to a lesser extent methionine were increased in the turpentine-treated rats as compared with their pair-fed counterparts. The insulin/glucagon molar ratio was similar in both groups. In conclusion, the reduced breakdown of RNA, especially rRNA, is largely responsible for the accumulation of hepatic RNA during acute inflammation. This inhibition of RNA degradation could possibly be related to the increase in glutamine.

Glucagon administration in vivo stimulates hepatic RNA and protein breakdown in fed and fasted rats

Liver RNA and protein breakdown rates were measured simultaneously in fed and in 24 h-fasted rats during a short-term cyclic perfusion, 1 h after an intraperitoneal injection of glucagon or of saline. RNA was labelled in vivo by an intraperitoneal injection of [6-14C]orotic acid, 60 h before the start of the perfusion. The accumulation of radioactive cytidine and valine in the perfusion medium for 15 min was used to determine RNA breakdown and proteolysis respectively. The portal glucagon/insulin ratio was significantly higher in the fasted glucagon-treated rats than in their fed counterparts. Although glucagon administration significantly increased RNA and protein degradation rates in the fasted and in the fed groups, the effect was greater after 24 h of starvation. The relationship between these biochemical changes and the alterations of the hepatocyte lysosomal system was investigated by determining the fractional cytoplasmic volume of lysosomal structures (autophagic vacuoles and dense bodies) by morphometry in the fasted glucagon-treated rats and in their controls. Hyperlucagonaemia significantly enhanced the relative volume of autophagic vacuoles without affecting that of dense bodies. The results showed that hyperglucagonaemia induced in vivo stimulated both liver RNA and protein breakdown and that this effect was modulated by the nutritional status of the rats.

Plasma zinc and copper in Paris area preschool children with growth impairment

Plasma zinc, copper, and parameters of growth were measured in a group of 116 French preschool children, 2-5 yr-old from low-income households. Participants were selected on the basis of Z-scores of weight for height (WHZ) and height for age (HAZ). Zinc and copper concentrations of children with growth impairment (GI), defined by a WHZ and/or HAZ < -1 Z-score, were compared to those of age, sex, and ethnic origin matched controls (WHZ and HAZ > -1 Z-score). Mean (+/- SD) plasma zinc concentration was 12.58 +/- 1.84 mumol/L in the GI group, and 13.27 +/- 1.98 mumol/L in the controls. The difference of the means of paired samples was 0.69 +/- 2.34, and by paired t-test the significance reached p = 0.028. This effect was primarily a result of the weight retarded group (WHZ < -1 Z-score, p < 0.009) and to the girls (p < 0.05). There were no significant differences in plasma copper concentrations between groups. These results suggest the presence of marginal zinc deficiency in French preschool children with low weight for height Z-scores.

Decreased serum levels of nutritional biochemical indices in healthy children with marginally delayed physical growth

Biochemical markers of nutritional status (albumin, transthyretin, insulin-like growth factor-I and zinc) were measured in slowly growing two- to five-year-old, low-income Parisian children whose weight-for-height or height-for-age z scores (WHZ or HAZ) were between -1 and -2 SD of the NCHS median. The results were compared to controls who were matched for age, sex, and ethnic origin with WHZ and HAZ between -1 and +2 SD. Mean serum levels of transthyretin, albumin and insulin-like growth factor-I and mean plasma zinc concentrations were significantly lower in the growth-impaired children than in the controls (p = 0.002, p = 0.006, p = 0.015, and p = 0.035, respectively). While the height-retarded children had low mean serum insulin-like growth factor-I values, the weight-retarded subjects had decreased levels of albumin, transthyretin and zinc when compared to controls. Lower mean levels of nutritional markers in healthy, slowly growing children suggest that inadequate dietary intakes of zinc, protein and/or energy may result in marginal delays in weight and height gains.

Selenium status of healthy immigrant Parisian preschool children

Plasma selenium (Se) concentration and erythrocyte glutathione peroxidase activity (GPx) were assessed in a population of healthy preschool children two to five years old, residing in the city of Paris. In the 118 subjects, mean (+/- SD) plasma Se concentration was 62.10 +/- 13.96 micrograms/L, and mean GPx activity was 23.58 +/- 8.52 U/g Hb. Mean plasma Se of male children was significantly (p = 0.001) higher (12%) than levels of girls. Plasma selenium levels were not correlated with erythrocyte GPx activity. Children from Mediterranean origin had a slightly lower erythrocyte GPx activity (p < 0.05) than children from other regions. Mean plasma Se concentration of this group corresponded to the lower limit of intervals, which characterizes geographical regions of intermediate selenium concentrations.

Re-expression of thyroxine-binding globulin in post-weaning rats during protein or energy malnutrition

Thyroxine-binding globulin, the highest affinity thyroid hormone binder of rat serum, was studied during 28 days of dietary protein restriction (6% protein vs 18% protein in isocaloric control diet) or energy restriction (60% intake of control diet). Studies were performed on male rats aged four weeks at the beginning of experiments: the animals had reached the ontogenic stage when the thyroxine-binding globulin had declined, after its high postnatal surge, to undetectable levels. Short-term administration (seven days) of one or the other restricted diet similarly induced resynthesis of the protein. Its serum concentrations reached 26-46% of those measured in eight-day pups (peak of the neonatal surge) and its liver mRNAs showed corresponding enhanced signals. Serum T4 binding activities were increased, although concomitantly transthyretin, second specific T4 carrier of the rat serum, decreased markedly (65-75% of controls) in response to the dietary restrictions. Longer-term diet administration (14 or 28 days) resulted in the further increase of the thyroxine-binding globulin in the protein-restricted rats, in contrast to its decline and eventual disappearance in the energy-restricted animals. Protein restriction was associated with increased total and free T3 serum concentrations, in contrast to energy restriction which little affected these parameters. These studies reveal rat thyroxine-binding globulin as a positive (increasing), highly sensitive reactant of malnutrition, able to discriminate between energy deficiency and composition dysequilibrium of diets. They suggest that up-regulation of its synthesis in the two dietary models involves differential mechanisms.

Thymulin activity during very-low-calorie diet

The potential use of thymulin levels as a sensitive and functional marker of energy deficiency was investigated in 13 obese women during a 3-week very-low-calorie diet. Mean weight loss was 8.92 +/- 0.52 kg after 21 days of treatment. The patients were free from infection as assessed by serum orosomucoid and C-reactive protein measurements. Serum albumin levels were not decreased throughout the experiment whereas transthyretin concentrations fell significantly during the first 2 weeks and remained fairly stable thereafter. Orosomucoid levels dropped only after 3 weeks of dieting. Serum zinc concentrations were within the normal range on admission and at the end of the experiment. Thymulin activity was not altered throughout the study, suggesting that this thymic hormone cannot be used as a functional marker of short-term energy restriction.

Regulation of hepatic transthyretin messenger RNA levels during moderate protein and food restriction in rats

This study was designed to determine whether the decrease in serum transthyretin that occurs during food restriction results from gross energy reduction or from depressed protein or lipid intake and to examine the relationship between serum transthyretin and hepatic transthyretin mRNA during moderate protein or food deficiency. Groups of young rats were allowed free access to either a 18% (control) or a 6% protein diet (protein-restricted), or reduced intakes. The food-restricted groups received 60% of control intake from the control diet, a 40% protein-enriched diet, or a 40% lipid-enriched diet, for 28 d. Serum transthyretin concentrations were lower in all experimental groups on d 7 relative to the control group. Control values were reached only in the protein-restricted group by d 14. The low serum transthyretin levels, which were similar in the food-restricted groups, likely resulted from gross energy restriction. Hepatic transthyretin mRNA levels were determined in the control, protein-restricted and food-restricted groups. They were unchanged relative to controls in the protein-restricted group but declined moderately in the food-restricted group on d 7 and 14, before returning to control values by d 28. Thus, the changes in liver transthyretin mRNA levels could partially explain the changes in serum transthyretin in food-restricted rats.

Changes in rat plasma apolipoproteins and lipoproteins during moderate protein deficiency: potential use in the assessment of nutritional status

To test apolipoprotein sensitivity as protein deficiency markers, concomitant evolution of plasma apolipoproteins (apo) and usual nutritional markers (transthyretin, albumin, transferrin) were followed during a 28-d protein restriction in young male Wistar rats. In addition, plasma lipids and chemical composition of lipoproteins were assayed by d 28. The control and the deficient groups were fed 18% and 6% casein diets, respectively. By d 28 the protein-deficient group exhibited hypotriglyceridemia resulting from the decrease in VLDL triacylglycerols; free cholesterol and phospholipids were increased, reflecting the increment in LDL-HLDL1. In plasma total lipoproteins, apo BH, AI and E were not different than controls in the deficient group. Apolipoprotein AIV decreased after d 14 and was significantly less than in controls at d 28. Apolipoprotein BI was considerably reduced by d 14 (43% less) and d 28 (52% less) compared with the control group. Apolipoproteins C + AII were significantly lower in the protein-deficient group by d 14 (43%). By d 28, VLDL apo C were decreased 60% by protein restriction. Transthyretin level was 20% lower in the protein-deficient group by d 7 but returned to control values by d 14. A moderately lower value was observed for albumin by d 7 and d 14 and for transferrin by d 28. These results indicate that, in this model, apo BI and C are more sensitive to protein depletion than usual nutritional markers.

Failure of tryptophan deficiency to reduce specifically serum levels of transthyretin or albumin in rats

Because transthyretin (TTR) is a tryptophan-rich molecule and a sensitive nutritional marker, tryptophan deficiency might markedly influence the circulating level of TTR. The effect of severe tryptophan (Trp) deficiency on serum TTR, as well as on albumin and transferrin levels, was studied in growing rats for 8 d. The animals were then refed a control diet for 12 d. The Trp-deficient and control diets contained 0.008 and 0.34% Trp, respectively. A loss of body weight and a dramatic reduction in food intake were observed in the Trp-deficient rats. Although serum total Trp concentration was significantly less in these rats than in pair-fed controls, serum TTR declined to the same extent in both groups compared to control rats fed ad libitum. Albumin concentrations were not altered, but transferrin levels declined slightly in the Trp-deficient rats compared to both the pair-fed group and the controls fed ad libitum. Refeeding the control diet to Trp-deficient rats restored total and free Trp concentrations, as well as TTR and transferrin levels, but body weight and food intake remained lower than in the control group. To examine the effect of moderate Trp restriction, rats were fed for 2 wk a diet whose Trp content was 50% less than that of the control diet. Although total and free Trp concentrations were significantly lower in the rats fed the Trp-deficient diet than in the control group, body weight, food intake and TTR levels were similar in both groups. The results suggest that acute and severe Trp deficiency per se does not modify TTR and albumin levels.

Value of serum transthyretin measurements in the assessment of marginal protein-energy malnutrition in rats

The influence of a wide range of protein and/or energy intakes on the serum level of rat transthyretin was studied. Young and adult rats were fed ad libitum diets containing 18, 9, 6, 4 and 0.5% protein (wt/wt) or were fed a control diet in restricted amounts. The transthyretin level was lower in young rats and was normal or slightly higher in adult rats fed low protein diets than in those fed the 18% protein diet. It was decreased with decreasing energy intake in all energy-restricted rats. Moderate energy restriction in rats fed equivalent amounts of protein also lowered the transthyretin level. Rats with similar body weights and similar protein intakes showed marked differences in serum transthyretin level, depending on the amount of energy consumed. Serum transthyretin changes were discussed in relation to the level of transthyretin in cerebrospinal fluid and to the serum concentration of albumin, transferrin and thyroid hormones. The results show that serum transthyretin is more closely related to the protein and energy intakes than to the protein and energy content of the diet. Our results indicate that serum transthyretin measurement is a reliable marker in the detection of early moderate and severe protein-energy restriction.

Thymulin (Zn-FTS) activity in protein-energy malnutrition: new evidence for interaction between malnutrition and infection on thymic function

The combined effects of protein-energy malnutrition (PEM) and infection on thymic function evaluated by specific plasma thymulin activity were studied in Senegalese children: 29 hospitalized in Dakar for severe malnutrition and various diseases; 9 infected without sign of severe PEM, living in Dakar; 13 apparently healthy, uninfected, living in Dakar; and 7 apparently healthy, uninfected, living in Paris. Most of the free-living children in Dakar suffered from mild to moderate PEM. The specific thymulin activity (total plasma activity minus the activity recorded after adsorption of the plasma with a monoclonal antithymulin antibody) was almost undetectable in the infected children and was normal only in the children living in Paris. Such activity might be decreased by moderate and severe PEM and severe malnutrition may not be the only underlying cause of depressed level of thymulin in malnourished children from the Third World. Concurrent infections are important factors.

Rat transthyretin: effects of acute short-term food deprivation and refeeding on serum and cerebrospinal fluid concentration and on hepatic mRNA level

To gain some insight into the nutritional factors that affect the blood level of transthyretin (TTR) and its metabolism, we have investigated the response of rat TTR to 1, 2 and 3 d of fasting and to 24 h of fasting followed by refeeding. The observed changes were compared to the level of TTR in cerebrospinal fluid (CSF) and to the amount of circulating thyroid hormones. Dot hybridization of a hepatic mRNA-cDNA probe specific for TTR was used to measure the relative level of TTR mRNA. Serum TTR decreased significantly after fasting and the decrease was proportional to the duration of the treatment. When rats were fasted for 24 h and then refed, serum TTR levels remained low after 2 d of refeeding. The dot hybridization results suggested that reduced liver synthesis was not the only mechanism that could explain this long-lasting effect of fasting. The TTR level in CSF was not influenced by fasting. In addition to the high sensitivity of serum TTR to food deprivation, the study also showed two distinct influences of fasting on the thyroid hormones: a primary effect that probably results in an inhibition of the conversion of thyroxine (T4) to triiodothyronine (T3) and a decreased T4-bound fraction, probably as a result of decreased serum level of TTR.

Variations in plasma thyroxine-binding prealbumin (TBPA) in relation to other circulating proteins in post-operative patients during rapid oral refeeding

Variations in plasma thyroxine-binding prealbumin (TBPA) were investigated in 15 well-nourished patients who underwent minor orthopaedic surgery and resumed normal oral feeding on the first post-operative day. TBPA fluctuations were analysed together with those of other nutritional and inflammatory markers including albumin (ALB), some acute-phase reactant proteins, C-reactive protein (CRP), orosomucoid also named alpha 1-acid-glycoprotein (alpha 1GP), alpha 1-antitrypsin (alpha 1AT) as well as cortisol and haematocrit. Measurements were conducted the day before operation, after the administration of anaesthesia, 2 h after the patient regained consciousness and then daily for a period of one week (days 1 to 7). Assays showed that TBPA and ALB levels began to decline by day 1 reaching minimum values by day 3 (with 35 and 15 per cent total decreases respectively compared to the initial levels). CRP levels began to rise on day 1 reaching maximum levels by day 2, alpha 1 GP and alpha 1 AT started to increase on day 1 and 2 respectively and displayed maximum concentrations by day 3. Cortisol, on the other hand, showed a rapid, yet short-lived increase after the patient regained consciousness on the day of operation. Haematocrit levels decreased from day 1 to day 3 and these low values were maintained until the end of the study. Aside from cortisol and CRP, the initial levels of the other parameters were not yet restored by day 7. These results show that despite an early return to normal oral feeding in post-operative patients, the commonly observed pattern of variation in TBPA levels persisted, indicating that such a pattern seems to be mainly influenced by stress-induced post-operative responses rather than by nutritional supply.