Induction of a catabolic state in rats by dexamethasone: dose or time dependency?

The development and use of a drug-induced immunosuppressed rat-model to screen Phela for mechanism of immune stimulation

ETHNOPHARMACOLOGY RELEVANCY

Phela, is code name for a medicinal product made from four South African traditional medicinal plants (Clerodendrum glabrum E. Mey, Polianthes tuberosa (Linn.), Rotheca myricoides (Hochst.) Steane & Mabb. and Senna occidentalis (L.) Link). All these plants have established traditional use in a wide spectrum of diseases. Phela is under development for use as an immune booster in immunocompromised patients, which includes patients with the human immunodeficiency virus (HIV). Already several studies, both pre-clinical and clinical, have shown that Phela is a safe and effective immune booster. Despite some studies on the action of Phela, the mechanism of action by Phela is still not known. Understanding the mechanism of action will enable safer and effective use of the drug for the right indications. Unfortunately, there is no well characterized test-system for screening products for immune stimulant activity. Therefore, the objective of this study was to use Phela as the test article, to develop and validate a rat-model (test system) by which to screen medicines for immune stimulant activity.

MATERIAL AND METHODS

First, the batch of Phela used was authenticated by high performance liquid chromatography (HPLC) techniques; analytical methods for the immunosuppressant drugs, cyclosporine A (CsA), cyclophosphamide (CP) and dexamethasone (Dex) were developed and validated; and a slide-A-Lyzer dialysis was used to test for potential interactions in rat plasma of Phela with CsA, CP and Dex. Thereafter, using Sprague Dawley (SD) rats and in separate experiments, the effective dose of Phela in the study animals was determined in a dose ranging study with levamisole, a known immune stimulant as the positive control; the appropriate doses for immunosuppression by CsA, CP and Dex were determined; the time to reach 'established immunosuppression' with each drug was determined (it was also the time for intervention with Phela); and eventually, the effect of Phela on the immune system was tested separately for each drug induced immunosuppression. The immune system was monitored by observing for changes in plasma profiles of IL-2, IL-10, IgG, IgM, CD4 and CD8 cell counts at appropriate intervals, while in addition to function tests, the kidneys, liver, spleen, thymus, were weighed and examined for any pathology.

RESULTS

The chromatographic fingerprint certified this batch of Phela as similar to the authentic Phela. There was no significant interaction between Phela and CsA, CP and Dex. The effective dose of Phela was determined to be 15.4mg/kg/day. Phela led to a moderate increase in the immune parameters in the normal rats. Co-administration of Phela 15mg/kg/day orally for 21 days with CsA led to stoppage and reversal of the immunosppressive effects of CsA that were exhibited as increased IL-2, IL-10, CD4 and CD8 counts, implying that Phela stimulates the cell mediate immunity (CMI). For CP, Phela led to stoppage and reversal, though moderate, of CP-induced suppression of IL-10, IgM and IgG only, implying that Phela stimulates the humoral immunity (HI) too. Phela had no effect on Dex induced immunosuppression. Stimulation of the CMI means that Phela clinical testing programme should focus on diseases or disorders that compromise the CMI, e.g., HIV and TB. The stimulation of the HI immunity means that Phela may stimulate existing memory cells to produce antibodies.

CONCLUSION

The present study has revealed Phela's mechanism of action as mainly by stimulation of the CMI, implying that the use of Phela as immune booster in HIV patients is appropriate; and that using Phela as the test product, a rat model for screening medicinal products for immune stimulation has been successfully developed and validated, with a hope that it will lead to the testing of other related medicinal products.

Dietary supplementation with shiikuwasha extract attenuates dexamethasone-induced skeletal muscle atrophy in aged rats

Background

Skeletal muscle atrophy is caused by a variety of diseases and conditions. In particular, skeletal muscle atrophy in the elderly contributes to a loss of independence with advanced age and increases the risk of falling. However, the effect of food consumed on a daily basis on skeletal muscle atrophy has been the focus of little research. In this study, the effects of dietary supplementation with shiikuwasha extract or grape extract on dexamethasone-induced skeletal muscle atrophy were evaluated in aged rats.

Methods

Aged male rats (15-month-old) were fed a diet supplemented with either 1 % shiikuwasha extract or 1 % grape extract for 19 days. During the last 5 days of the feeding period, rats were injected with dexamethasone to induce muscle atrophy.

Results

Body weight and hind-limb muscle weight were significantly decreased by dexamethasone treatment. The supplementation of shiikuwasha extract showed no effect on body weight loss, but markedly attenuated tibialis anterior muscle weight loss induced by dexamethasone. On the other hand, grape extract did not affect muscle weight loss. Furthermore, shiikuwasha extract significantly reduced dexamethasone-induced expression of atrogin-1 and MuRF1 mRNA, but did not reduce LC3B-II protein levels.

Conclusion

These results suggest that shiikuwasha extract may partially inhibit the activation of the ubiquitin–proteasome system and may consequently attenuate skeletal muscle atrophy induced by dexamethasone in aged rats.

Effects of exercise and metformin on the prevention of glucose intolerance: a comparative study

We aimed to evaluate the effects of aerobic exercise training (4 days) and metformin exposure on acute glucose intolerance after dexamethasone treatment in rats. Forty-two adult male Wistar rats (8 weeks old) were divided randomly into four groups: sedentary control (SCT), sedentary dexamethasone-treated (SDX), training dexamethasone-treated (DPE), and dexamethasone and metformin treated group (DMT). Glucose tolerance tests and in situ liver perfusion were undertaken on fasting rats to obtain glucose profiles. The DPE group displayed a significant decrease in glucose values compared with the SDX group. Average glucose levels in the DPE group did not differ from those of the DMT group, so we suggest that exercise training corrects dexamethasone-induced glucose intolerance and improves glucose profiles in a similar manner to that observed with metformin. These data suggest that exercise may prevent the development of glucose intolerance induced by dexamethasone in rats to a similar magnitude to that observed after metformin treatment.

The role of skeletal muscle in liver glutathione metabolism during acetaminophen overdose

Marked alterations in systemic glutamate-glutamine metabolism characterize the catabolic state, in which there is an increased breakdown and decreased synthesis of skeletal muscle protein. Among these alterations are a greatly increased net release of glutamine (Gln) from skeletal muscle into blood plasma and a dramatic depletion of intramuscular Gln. Understanding the catabolic state is important because a number of pathological conditions with very different etiologies are characterized by its presence; these include major surgery, sepsis, trauma, and some cancers. Acetaminophen (APAP) overdose is also accompanied by dramatic changes in systemic glutamate-glutamine metabolism including large drops in liver glutathione (for which glutamate is a precursor) and plasma Gln. We have constructed a mathematical model of glutamate and glutamine metabolism in rat which includes liver, blood plasma and skeletal muscle. We show that for the normal rat, the model solutions fit experimental data including the diurnal variation in liver glutathione (GSH). We show that for the rat chronically dosed with dexamethasone (an artificial glucocorticoid which induces a catabolic state) the model can be used to explain empirically observed facts such as the linear decline in intramuscular Gln and the drop in plasma glutamine. We show that for the Wistar rat undergoing APAP overdose the model reproduces the experimentally observed rebound of liver GSH to normal levels by the 24-h mark. We show that this rebound is achieved in part by the action of the cystine-glutamate antiporter, an amino acid transporter not normally expressed in liver but induced under conditions of oxidative stress. Finally, we explain why supplementation with Gln, a Glu precursor, assists in the preservation of liver GSH during APAP overdose despite the fact that under normal conditions only Cys is rate-limiting for GSH formation.

Dissection of glucocorticoid receptor-mediated inhibition of the hypothalamic-pituitary-adrenal axis by gene targeting in mice

Negative feedback regulation of glucocorticoid (GC) synthesis and secretion occurs through the function of glucocorticoid receptor (GR) at sites in the hypothalamic-pituitary-adrenal (HPA) axis, as well as in brain regions such as the hippocampus, prefrontal cortex, and sympathetic nervous system. This function of GRs in negative feedback coordinates basal glucocorticoid secretion and stress-induced increases in secretion that integrate GC production with the magnitude and duration of the stressor. This review describes the effects of GR loss along major sites of negative feedback including the entire brain, the paraventricular nucleus of the hypothalamus (PVN), and the pituitary. In genetic mouse models, we evaluate circadian regulation of the HPA axis, stress-stimulated neuroendocrine response and behavioral activity, as well as the integrated response of organism metabolism. Our analysis provides information on contributions of region-specific GR-mediated negative feedback to provide insight in understanding HPA axis dysregulation and the pathogenesis of psychiatric and metabolic disorders.

Short-term prednisone use antagonizes insulin's anabolic effect on muscle protein and glucose metabolism in young healthy people

Glucocorticoids cause muscle atrophy and weakness, but the mechanisms for these effects are unclear. The purpose of this study was to test a hypothesis that prednisone (Pred) counteracts insulin's anabolic effects on muscle. A randomized, double-blind cross-over design was used to test the effects of 6 days either Pred (0.8 mg x kg(-1) x day(-1)) or placebo use in seven healthy young volunteers. Protein dynamics were measured across the leg using stable isotope tracers of leucine (Leu) and phenylalanine (Phe) after overnight fast and during a hyperinsulinemic (1.5 microU x min(-1) x kg FFM(-1)) euglycemic clamp with amino acid replacement. Fasting glucose, amino acids, insulin, and glucagon were higher (P < 0.01) on Pred vs. placebo, whereas leg blood flow was 18% lower. However, basal whole body and leg kinetics of Leu and Phe were unaltered by Pred. Insulin infusion increased leg glucose uptake in both trials but was 65% lower with Pred than with placebo. Insulin in both trials similarly suppressed whole body flux of Leu and Phe. Importantly, insulin increased net Leu and Phe balance across the leg and the balance between muscle protein synthesis and breakdown, but these changes were 45-140% lower (P < 0.03) in Pred than in placebo. The present study demonstrates that short-term Pred use in healthy people does not alter whole body or leg muscle protein metabolism during the postaborptive state but causes muscle insulin resistance for both glucose and amino acid metabolism, with a blunted protein anabolism. This interactive effect may lead to muscle atrophy with continued use of glucocorticoids.

The effect of high glucocorticoid administration and food restriction on rodent skeletal muscle mitochondrial function and protein metabolism

Background

Glucocorticoids levels are high in catabolic conditions but it is unclear how much of the catabolic effects are due to negative energy balance versus glucocorticoids and whether there are distinct effects on metabolism and functions of specific muscle proteins.

Methodology/Principal Findings

We determined whether 14 days of high dose methylprednisolone (MPred, 4 mg/kg/d) Vs food restriction (FR, food intake matched to MPred) in rats had different effects on muscle mitochondrial function and protein fractional synthesis rates (FSR). Lower weight loss (15%) occurred in FR than in MPred (30%) rats, while a 15% increase occurred saline-treated Controls. The per cent muscle loss was significantly greater for MPred than FR. Mitochondrial protein FSR in MPred rats was lower in soleus (51 and 43%, respectively) and plantaris (25 and 55%) than in FR, while similar decline in protein FSR of the mixed, sarcoplasmic, and myosin heavy chain occurred. Mitochondrial enzymatic activity and ATP production were unchanged in soleus while in plantaris cytochrome c oxidase activity was lower in FR than Control, and ATP production rate with pyruvate + malate in MPred plantaris was 28% lower in MPred. Branched-chain amino acid catabolic enzyme activities were higher in both FR and MPred rats indicating enhanced amino acid oxidation capacity.

Conclusion/Significance

MPred and FR had little impact on mitochondrial function but reduction in muscle protein synthesis occurred in MPred that could be explained on the basis of reduced food intake. A greater decline in proteolysis may explain lesser muscle loss in FR than in MPred rats.

Corticosteroids increase glutamine utilization in human splanchnic bed

Glutamine is the most abundant amino acid in the body and is extensively taken up in gut and liver in healthy humans. To determine whether glucocorticosteroids alter splanchnic glutamine metabolism, the effect of prednisone was assessed in healthy volunteers using isotope tracer methods. Two groups of healthy adults received 5-h intravenous infusions of l-[1-(14)C]leucine and l-[(2)H(5)]glutamine, along with q. 20 min oral sips of tracer doses of l-[1-(13)C]glutamine in the fasting state, either 1) at baseline (control group; n = 6) or 2) after a 6-day course of 0.8 mg.kg(-1).day(-1) prednisone (prednisone group; n = 8). Leucine and glutamine appearance rates (Ra) were determined from plasma [1-(14)C]ketoisocaproate and [(2)H(5)]glutamine, respectively, and leucine and glutamine oxidation from breath (14)CO(2) and (13)CO(2), respectively. Splanchnic glutamine extraction was estimated by the fraction of orally administered [(13)C]glutamine that failed to appear into systemic blood. Prednisone treatment 1) did not affect leucine Ra or leucine oxidation; 2) increased plasma glutamine Ra, mostly owing to enhanced glutamine de novo synthesis (medians +/- interquartiles, 412 +/- 61 vs. 280 +/- 190 mumol.kg(-1).h(-1), P = 0.003); and 3) increased the fraction of orally administered glutamine undergoing extraction in the splanchnic territory (means +/- SE 64 +/- 6 vs. 42 +/- 12%, P < 0.05), without any change in the fraction of glutamine oxidized (means +/- SE, 75 +/- 4 vs. 77 +/- 4%, not significant). We conclude that high-dose glucocorticosteroids increase in splanchnic bed the glutamine requirements. The role of such changes in patients receiving chronic corticoid treatment for inflammatory diseases or suffering from severe illness remains to be determined.

Mitochondrial energy metabolism in a model of undernutrition induced by dexamethasone

The present investigation was undertaken to evaluate whether mitochondrial energy metabolism is altered in a model of malnutrition induced by dexamethasone (DEX) treatment (1·5mg/kg per d for 5d). The gastrocnemius and liver mitochondria were isolated from DEX-treated, pair-fed (PF) and control (CON) rats. Body weight was reduced significantly more in the DEX-treated group (−16%) than in the PF group (−9%). DEX treatment increased liver mass (+59%v.PF, +23%v. CON) and decreased gastrocnemius mass. Moreover, in DEX-treated rats, liver mitochondria had an increased rate of non-phosphorylative O2consumption with all substrates (approximately +42%). There was no difference in enzymatic complex activities in liver mitochondria between rat groups. Collectively, these results suggest an increased proton leak and/or redox slipping in the liver mitochondria of DEX-treated rats. In addition, DEX decreased the thermodynamic coupling and efficiency of oxidative phosphorylation. We therefore suggest that this increase in the proton leak and/or redox slip in the liver is responsible for the decrease in the thermodynamic efficiency of energy conversion. In contrast, none of the variables of energy metabolism determined in gastrocnemius mitochondria was altered by DEX treatment. Therefore, it appears that DEX specifically affects mitochondrial energy metabolism in the liver.

The metabolic changes caused by dexamethasone in the adjuvant-induced arthritic rat

The action of orally administered dexamethasone (0.2 mg kg(-1) day(-1)) on metabolic parameters of adjuvant-induced arthritic rats was investigated. The body weight gain and the progression of the disease were also monitored. Dexamethasone was very effective in suppressing the Freund's adjuvant-induced paw edema and the appearance of secondary lesions. In contrast, the body weight loss of dexamethasone-treated arthritic rats was more accentuated than that of untreated arthritic or normal rats treated with dexamethasone, indicating additive harmful effects. The perfused livers from dexamethasone-treated arthritic rats presented high content of glycogen in both fed and fasted conditions, as indicated by the higher rates of glucose release in the absence of exogenous substrate. The metabolization of exogenous L: -alanine was increased in livers from dexamethasone-treated arthritic rats in comparison with untreated arthritic rats, but there was a diversion of carbon flux from glucose to L: -lactate and pyruvate. Plasmatic levels of insulin and glucose were significantly higher in arthritic rats following dexamethasone administration. Most of these changes were also found in livers from normal rats treated with dexamethasone. The observed changes in L: -alanine metabolism and glycogen synthesis indicate that insulin was the dominant hormone in the regulation of the liver glucose metabolism even in the fasting condition. The prevalence of the metabolic effects of dexamethasone over those ones induced by the arthritis disease suggests that dexamethasone administration was able to suppress the mechanisms implicated in the development of the arthritis-induced hepatic metabolic changes. It seems thus plausible to assume that those factors responsible for the inflammatory responses in the paws and for the secondary lesions may be also implicated in the liver metabolic changes, but not in the body weight loss of arthritic rats.

Synergistic effects of caloric restriction with maintained protein intake on skeletal muscle performance in 21-month-old rats: a mitochondria-mediated pathway

Caloric restriction (CR) delays the onset of age-related mitochondrial abnormalities but does not prevent the decline in ATP production needed to sustain muscle protein fractional synthesis rate (FSR) and contractile activity. We hypothesized that improving mitochondrial activity and FSR using a CR diet with maintained protein intakes could enhance myofibrillar protein FSR and consequently improve muscle strength in aging rats. Wistar rats (21 months old) were fed either an ad libitum (AL), 40% protein-energy restricted (PER) or 40% AL-isonitrogenous energy restricted (ER) diet for 5 months. ATP production, electron transport chain activity, reactive oxygen species (ROS) generation, protein carbonyl content and FSR were determined in both tibialis anterior (TA) and soleus muscle mitochondria. Myosin and actin FSR and grip force were also investigated. The ER diet led to improved mitochondrial activity and ATP production in the TA and soleus muscles in comparison with PER. Furthermore, mitochondrial FSR in the TA was enhanced under the ER diet but diminished under the PER. Mitochondrial protein carbonyl content was decreased by both the ER and PER diets. The ER diet was able to improve myosin and actin FSR and grip force. Therefore, the synergistic effects of CR with maintained protein intake may help to limit the progression of sarcopenia by optimizing the turnover rates and functions of major proteins in skeletal muscle.

The effect of glutamine on prevention of glucocorticoid-induced skeletal muscle atrophy is associated with myostatin suppression

Excess glucocorticoids (GCs) cause muscle atrophy. Glucocorticoid-induced muscle atrophy is associated with increased intramuscular myostatin expression. Myostatin is a negative regulator of skeletal muscle mass. Glutamine prevents GC-induced muscle atrophy. We hypothesized that glutamine effect on reversal of GC-induced muscle atrophy is mediated in part by suppression of myostatin. We administered daily to male Sprague-Dawley rats dexamethasone, dexamethasone plus glutamine, saline or saline plus glutamine, all pair-fed. Animals were killed on day 5. Body weight and weights of gastrocnemius muscles were measured. Myostatin expression was measured by Northern and Western blots, and was compared with glyceraldehyde-3-phosphate dehydrogenase. Myoblast C2C12 cells were exposed to dexamethasone, or dexamethasone and glutamine, and their myostatin messenger RNA and protein expression compared with glyceraldehyde-3-phosphate dehydrogenase. Myostatin promoter activity was measured by luciferase activity of transfected C2C12 cells, grown in medium including dexamethasone, or dexamethasone plus glutamine. Rats that received dexamethasone showed significant body and muscle weight loss accompanied by an increase in intramuscular myostatin expression, compared with their saline-treated controls. Pair-fed rats given dexamethasone plus glutamine had significantly less reduction in body and muscle weights and lower myostatin expression when compared with those treated with dexamethasone alone. In C2C12 myoblast cells, addition of glutamine to dexamethasone prevented the hyperexpression of myostatin induced by dexamethasone. Myostatin promoter activity increased in cells exposed to dexamethasone, but this increase was partially blocked by addition of the glutamine. Administration of glutamine partially prevents GC-induced myostatin expression and muscle atrophy, providing a potential mechanism for the prevention of muscle atrophy induced by glucocorticoids.

The equivocal metabolic response to endotoxaemia in type 2 diabetic and obese ZDF rats

AIMS/HYPOTHESIS

The metabolic and endocrine disturbances associated with obesity and type 2 diabetes may impair the normal metabolic response to injury. Our objective was to investigate amino acid metabolism in endotoxaemic type 2 diabetic obese rats.

MATERIALS AND METHODS

A metabolic study was performed over 4 days using male Zucker diabetic fatty (ZDF) rats (fa/fa) and lean littermates (fa/+) divided into three groups: ad libitum-fed groups which underwent no treatment, lipopolysaccharide (LPS)-treated groups receiving E. coli LPS by i.p. injection, and pair-fed groups to the respective LPS groups. We evaluated the effect of endotoxaemia on body weight, food intake and tissue weights. Nitrogen loss and muscular proteolysis were measured daily by determination of urinary 3-methylhistidine (3-MH) excretion. Plasma, intestine and muscle amino acid levels were measured.

RESULTS

The data showed that ad libitum-fed ZDF rats had lower plasma arginine and glutamine levels than ad libitum-fed control rats. Compared with control rats, the LPS-treated ZDF rats presented lower thymic involution, a lower 3-MH:creatinine ratio and higher cumulative nitrogen balance.

CONCLUSIONS/INTERPRETATION

Against our working hypothesis, ZDF rats did not show an impaired metabolic response, and even appeared to be less sensitive to the stress.

Assessment of branched-chain amino Acid status and potential for biomarkers

BCAAs are not synthesized in the body in humans, but they are crucial in protein and neurotransmitter synthesis. The protein anabolic role of BCAAs seems to be mediated not only by their important role as a promoter of the translation process (and possibly acting at the transcription level) but also by inhibition of protein degradation. Leucine may play a critical role in these signaling pathways. Supplementation with BCAAs spares lean body mass during weight loss, promotes wound healing, may decrease muscle wasting with aging, and may have beneficial effects in renal and liver disease. BCAA supplementation is extensively used in the athletic field with the assumption of improved performance and muscle mass. Measuring serum BCAAs has limited clinical utility beyond the controlled setting because levels are affected by a variety of clinical states, and optimal levels in these scenarios have not been completely elucidated. We discuss the effects diet, hormones, stress, aging, and renal or liver dysfunction have on BCAA levels and how understanding the biological effects of BCAAs may help to develop biomarkers of BCAA status. We also discuss potential biomarkers of BCAA status.

Effect of treatment with dexamethasone on protein intake in adult and old Lou/c/jall rats

A deleterious decrease of protein intake had been evidenced in Lou/c/jall rats during ageing. This result could be induced by an impaired regulation of feeding behaviour. Glucocorticoids inducing specific amino-acid needs for gluconeogenesis and for the synthesis of inflammatory proteins by the liver, we investigated the age-related effect of a 4-days treatment with dexamethasone (DEX) on caloric and protein intake. Males and females aged 7, 19, 25 and 31 months received 573.6 +/- 65.6 microg/(kg day) of dexamethasone via the drinking water. Body weight (BW), caloric and macronutrients intakes were monitored during treatment and during 10 days after the treatment. A strong hypophagia was seen during treatment in all groups, which was mainly due to a decrease in fat intake. In the same time, rats maintained their protein intake so that protein became the main macronutrient of the diet in most of the groups. However, older males showed a lesser efficiency in adjusting their diet. These results are in agreement with previous data obtained in a protein deprivation study. They lead to the conclusion that the loss of appetite for protein in old age probably does not reflect a loss of ability to choose the needed amount of protein. We can hypothesise that the decrease of protein intake in old rats could be due to some inadequacy of casein to the metabolic requirement of aged animals.

Hypoenergetic high-carbohydrate or high-fat parenteral nutrition induces a similar metabolic response with differential effects on hepatic IGF-I mRNA in dexamethasone-treated rats

The optimal level of energy for critically ill patients who require parenteral nutrition (PN) is unclear. Our objective was to determine whether 50% energy (50%E) restriction due to a reduction in carbohydrate or fat, with provision of adequate protein and micronutrients, ameliorates the detrimental effects of dexamethasone (Dex) on body protein catabolism, insulin resistance, and insulin-like growth factor-I (IGF-I) responses in rats administered PN. The experiment included 6 PN groups, adequate energy (AE) +/- Dex, 50% AE with high carbohydrate (50%E CHO) +/- Dex and 50% AE with high fat (50%E FAT) +/- Dex. There was a significant interaction between energy level and Dex such that the increase in body catabolism due to 50%E from CHO or FAT was reduced by approximately 50%, although the amount of body weight and nitrogen lost over 7 d was significantly greater with 50%E than with AE. AE+Dex induced a 60% increase in liver mass, whereas 50%E+Dex reduced the increase to 26%. AE+Dex induced a 5-fold increase in serum insulin level, whereas 50%E+Dex normalized the insulin to glucose ratio. Serum IGF-I levels were reduced 14-18% by Dex and 30% by 50%E. Hepatic immunoreactive IGF-I was significantly correlated with serum IGF-I and nitrogen balance. 50%E CHO and 50%E FAT had differential effects on hepatic IGF-I mRNA with a 40% decrease in IGF-I mRNA due to 50%E FAT+Dex. In summary,CHO or FAT hypoenergetic PN with adequate protein had similar effects in normalizing hyperinsulinemia, attenuating hepatomegaly, and reducing the increment, but not the total amount of body protein catabolism, induced by glucocorticoid excess.

Kinetics and control of oxidative phosphorylation in rat liver mitochondria after dexamethasone treatment

The present investigation was undertaken in order to evaluate the contributions of ATP synthesis and proton leak reactions to the rate of active respiration of liver mitochondria, which is altered following dexamethasone treatment (1.5 mg/kg per day for 5 days). We applied top-down metabolic control analysis and its extension, elasticity analysis, to gain insight into the mechanisms of glucocorticoid regulation of mitochondrial bioenergetics. Liver mitochondria were isolated from dexamethasone-treated, pair-fed and control rats when in a fed or overnight fasted state. Injection of dexamethasone for 5 days resulted in an increase in the fraction of the proton cycle of phosphorylating liver mitochondria, which was associated with a decrease in the efficiency of the mitochondrial oxidative phosphorylation process in liver. This increase in proton leak activity occurred with little change in the mitochondrial membrane potential, despite a significant decrease in the rate of oxidative phosphorylation. Regulation analysis indicates that mitochondrial membrane potential homoeostasis is achieved by equal inhibition of the mitochondrial substrate oxidation and phosphorylation reactions in rats given dexamethasone. Our results also suggest that active liver mitochondria from dexamethasone-treated rats are capable of maintaining phosphorylation flux for cellular purposes, despite an increase in the energetic cost of mitochondrial ATP production due to increased basal proton permeability of the inner membrane. They also provide a complete description of the effects of dexamethasone treatment on liver mitochondrial bioenergetics.

Dexamethasone impairs muscle energetics, studied by (31)P NMR, in rats

AIMS/HYPOTHESIS

Glucocorticoid treatments are associated with increased whole-body oxygen consumption. We hypothesised that an impairment of muscle energy metabolism can participate in this increased energy expenditure.

METHODS

To investigate this possibility, we have studied muscle energetics of dexamethasone-treated rats (1.5 mg kg(-1) day(-1) for 6 days), in vivo by (31)P NMR spectroscopy. Results were compared with control and pair-fed (PF) rats before and after overnight fasting.

RESULTS

Dexamethasone treatment resulted in decreased phosphocreatine (PCr) concentration and PCr:ATP ratio, increased ADP concentration and higher PCr to gamma-ATP flux but no change in beta-ATP to beta-ADP flux in gastrocnemius muscle. Neither 4 days of food restriction (PF rats) nor 24 h fasting affected high-energy phosphate metabolism. In dexamethasone-treated rats, there was an increase in plasma insulin and non-esterified fatty acid concentration.

CONCLUSIONS/INTERPRETATION

We conclude that dexamethasone treatment altered resting in vivo skeletal muscle energy metabolism, by decreasing oxidative phosphorylation, producing ATP at the expense of PCr.

Aortic banding in rat as a model to investigate malnutrition associated with heart failure

Heart failure is a severe pathology, which has displayed a dramatic increase in the occurrence of patients with chronic heart disease in developed countries, as a result of increases in the population's average age and in survival time. This pathology is associated with severe malnutrition, which worsens the prognosis. Although the cachexia associated with chronic heart failure is a well-known complication, there is no reference animal model of malnutrition related to heart failure. This study was designed to evaluate the nutritional status of rats in a model of loss of cardiac function obtained by ascending aortic banding. Cardiac overload led to the development of cardiac hypertrophy, which decompensates to heart failure, with increased brain natriuretic peptide levels. The rats displayed hepatic dysfunction and an associated renal hypotrophy and renal failure, evidenced by the alteration in renal function markers such as citrullinemia, creatininemia, and uremia. Malnutrition has been evidenced by the alteration of protein and amino acid metabolism. A muscular atrophy with decreased protein content and increased amino acid concentrations in both plasma and muscle was observed. These rats with heart failure displayed a multiorgan failure and malnutrition, which reflected the clinical situation of human chronic heart failure.

Effect of short-term prednisone use on blood flow, muscle protein metabolism, and function

Glucocorticoids can cause muscle atrophy, but the effect on muscle protein metabolism in humans has not been adequately studied to know whether protein synthesis, breakdown, or both are altered. We tested the effect of 6 d of oral prednisone (Pred, 0.5 mg/kg.d) on muscle protein metabolism and function. Six healthy subjects (three men/three women, 22-41 yr) completed two trials (randomized, double-blind, cross-over) with Pred and placebo. Fasting glucose, insulin, IGF-I, and glucagon were higher on Pred vs. placebo, whereas IGF-II and IGF binding protein-1 and -2 were lower. Whole-body amino acid fluxes, blood urea nitrogen, and urinary nitrogen loss were not statistically different between trials. Leg blood flow was 25% lower on Pred leading to 15-30% lower amino acid flux among the artery, vein, and muscle. However, amino acid net balance and rates of protein synthesis and breakdown were unchanged, as were synthesis rates of total mixed, mitochondrial, sarcoplasmic, and myosin heavy chain muscle proteins. Muscle mitochondrial function, muscle strength, and resting energy expenditure were also unchanged. These results demonstrate that a short-term moderate dose of prednisone affects glucose metabolism but has no effect on whole-body or leg muscle protein metabolism or muscle function.

Characterization of the alteration of nutritional state in brain injury induced by fluid percussion in rats

OBJECTIVE

Patients suffering from traumatic brain injury (TBI) undergo rapid weight loss with negative nitrogen balance and enhanced whole-body protein breakdown, with protein wasting causing morbidity and increased mortality. Many experimental models of TBI have been used to evaluate strategies to improve the outcome of these patients, but nutritional status has not been considered in experiments published to date, although this may have great importance and influence the results obtained with TBI models. This study characterized the hypercatabolism level and nutritional status of TBI rats.

DESIGN

Twenty-four male Wistar rats were randomized into three groups. Rats from the TBI group were anesthetized and fluid percussion was applied. The pair-fed (PF) group was healthy but was pair-fed to the TBI group. The ad libitum (AL) group was healthy and fed ad libitum. The study was performed over 10 days post-TBI.

MEASUREMENTS AND RESULTS

TBI in rats was characterized by remarkable long-lasting anorexia, renal failure (creatinine clearance: AL 1.8+/-0.2 and PF 1.5+/-0.1 vs. TBI 0.9+/-0.1 l/24 hour), anorexia (appetite depressed throughout the study), increased myofibrillar proteolysis (3-methylhistidine/creatinine ratio (day 2: AL 36+/-1 and PF 38+/-2 vs. TBI 54+/-5 micromol/mmol), and intestinal atrophy (ileum: AL 29.3+/-2.5 and PF 28.7+/-1.1 vs. TBI 22.5+/-1.4 mg/cm). In addition, anorexia led to muscular atrophy and decreased nitrogen balance. The metabolic alterations described above can increase morbidity and mortality.

CONCLUSIONS

TBI by fluid percussion in rats is a model reproducing the metabolic and nutritional alterations observed in clinical practice and is suitable for further studies exploring the efficacy of optimized nutritional support.

Metabolic pathways implicated in the kinetic impairment of muscle glutamine homeostasis in adult and old glucocorticoid-treated rats

An impairment of muscle glutamine metabolism in response to dexamethasone (DEX) occurs with aging. To better characterize this alteration, we have investigated muscle glutamine release with regard to muscle glutamine production (net protein breakdown, de novo glutamine synthesis) in adult and old glucocorticoid-treated rats. Male Sprague-Dawley rats (3 or 24 mo old) were divided into seven groups: three groups received 1.5 mg/kg of DEX once a day by intraperitoneal injection for 3, 5, or 7 days; three groups were pair fed to the three treated groups, respectively; and one control group of healthy rats was fed ad libitum. Muscle glutamine synthetase activity increased earlier in old rats (day 3) than in adult rats (day 7), whereas an increase in muscle glutamine release occurred later in old rats (day 5) than in adult DEX-treated rats (day 3). Consequently, muscle glutamine concentration decreased later in old rats (day 5) than in adults (day 3). Finally, net muscle protein breakdown increased only in old DEX-treated rats (day 7). In conclusion, the impairment of muscle glutamine metabolism is due to a combination of an increase in glutamine production and a delayed increase in glutamine release.

Dexamethasone treatment specifically increases the basal proton conductance of rat liver mitochondria

We investigated the role that mitochondrial proton leak may play in the glucocorticoid-induced hypermetabolic state. Sprague-Dawley rats were injected with dexamethasone over a period of 5 days. Liver mitochondria and gastrocnemius subsarcolemmal and intermyofibrillar mitochondria were isolated from dexamethasone-treated, pair-fed and control rats. Respiration and membrane potential were measured simultaneously using electrodes sensitive to oxygen and to the potential-dependent probe triphenylmethylphosphonium, respectively. Five days of dexamethasone injection resulted in a marked increase in the basal proton conductance of liver mitochondria, but not in the muscle mitochondrial populations. This effect would have a modest impact on energy expenditure in rats.

Evidence that glutamine modulates respiratory burst in stressed rat polymorphonuclear cells through its metabolism into arginine

Glutamine (GLN) and arginine (ARG) are recognized for their ability to modulate immune cell function. However, the metabolic pathways involved in their action remain unclear. It was recently shown that GLN- or ARG-enriched diets increased radical oxygen species (ROS) production by neutrophils from stressed rats. Since these two amino acids have a tied metabolism, we hypothesized that conversion between GLN and ARG (and its active metabolites NO* and polyamines) might be involved. To test this hypothesis male Sprague-Dawley rats (n 117) were randomized into thirteen groups: rats in eleven groups were rendered catabolic by dexamethasone injection (1.5 mg/kg per d for 5 d) and 6.8 mmol either GLN, ARG or non-essential amino acids (NEAA; glycine, alanine and histidine)/kg per d were given by the enteral route; one group was pair-fed to the treated groups. The regimens of all the groups were rendered isonitrogenous by the addition of NEAA. The last group was not treated and was fed ad libitum. For each supplementation three subgroups were formed, each of which received a specific inhibitor: methionine sulfoximine (inhibitor of GLN synthase; 100 mg/kg per d), S-methylthiourea (inhibitor of inducible NO* synthase (iNOS); 50 mg/kg per d) and difluoromethylornithine (inhibitor of ornithine decarboxylase (ODC); 50 mg/kg per d). Oxidative metabolism, intracellular H2O2, and extracellular O2*- production were measured in unstimulated and phorbol myristate acetate-stimulated polymorphonuclear neutrophils. GLN- and ARG-enriched diets increased respiratory burst by neutrophils (oxidative metabolism of 152 (sem 24) and 138 (sem 45) v. 57 (sem 18) mV for GLN-, ARG- and NEAA-enriched diets respectively, P<0.05). In vivo inhibition of iNOS or ODC decreased ROS production induced by GLN and ARG. In vivo inhibition of GLN synthase did not modify the effect of ARG on ROS production. In conclusion, GLN and ARG modulate ROS production in neutrophils from stressed rats by the same pathway involving polyamine and NO* synthesis.

Dexamethasone decreases serum and liver IGF-I and maintains liver IGF-I mRNA in parenterally fed rats

Insulin-like growth factor-I (IGF-I) gene expression is regulated by nutritional and hormonal factors. High-dose glucocorticoids decrease food intake, and this confounds studies addressing glucocorticoid effects on IGF-I gene regulation. We investigated alterations in the hepatic IGF-I endocrine system induced by a catabolic dose of dexamethasone (Dex) in rats given adequate nutrition by continuous infusion of total parenteral nutrition (TPN) solution with or without IGF-I administration. The four TPN groups included control, +Dex, +IGF-I, and +IGF-I + Dex (n = 9-11/group). Dex induced a 12% loss of body weight in association with a 50% decrease in hepatic immunoreactive IGF-I, a 10% decrease in serum IGF-I, and no change in steady-state liver IGF-I mRNA or growth hormone (GH) receptor binding. Exogenous IGF-I increased serum IGF-I, attenuated Dex-induced catabolism, and did not reduce hepatic levels of IGF-I and IGF-I mRNA despite decreased serum GH. These data suggest that Dex-induced catabolism is associated with downregulation of the hepatic IGF-I endocrine system at the translational or posttranslational level when adequate nutrition is provided.