Leucine-rich Diet Research Articles

Dietary leucine supplementation minimises tumour-induced damage in placental tissues of pregnant, tumour-bearing rats.

BackgroundThe occurrence of cancer during pregnancy merges two complex, poorly understood metabolic and hormonal conditions. This association can exacerbate the conditions of both the mother and the foetus. The branched-chain amino acid leucine enhances cellular activity, particularly by increasing protein synthesis. This study aimed to analyse the modulatory effect of a leucine-rich diet on direct and indirect tumour-induced placental damage. This was accomplished by evaluating the expression of genes involved in protein synthesis and degradation and assessing anti-oxidant enzyme activity in placental tissues collected from pregnant, tumour-bearing rats.ResultsPregnant rats were either implanted with Walker 256 tumour cells or injected with ascitic fluid (to study the indirect effects of tumour growth) and then fed a leucine-rich diet. Animals in a control group underwent the same procedures but were fed a normal diet. On the 20th day of pregnancy, tumour growth was observed. Dams fed a normoprotein diet showed the greatest tumour growth. Injection with ascitic fluid mimicked the effects of tumour growth. Decreased placental protein synthesis and increased protein degradation were observed in both the tumour-bearing and the ascitic fluid-injected groups that were fed a normoprotein diet. These effects resulted in low placental DNA and protein content and high lipid peroxidation (measured by malondialdehyde content). Decreased placental protein synthesis-related gene expression was observed in the tumour group concomitant with increased expression of genes encoding protein degradation-associated proteins and proteolytic subunits.ConclusionsConsumption of a leucine-rich diet counteracted the effects produced by tumour growth and injection with ascitic fluid. The diet enhanced cell signalling, ameliorated deficiencies in DNA and protein content, and balanced protein synthesis and degradation processes in the placenta. The improvements in cell signalling included changes in the mTOR/eIF pathway. In conclusion, consumption of a leucine-rich diet improved placental metabolism and cell signalling in tumour-bearing rats, and these changes reduced the deleterious effects caused by tumour growth.

ID: 47: Nutritional L-leucine supplementation modulates muscle protein wasting and pro-inflammatory cytokines in Walker-256 tumour-bearing rats

Cancer cachexia is characterised by involuntary weight loss; the maintenance of lean body mass in cachectic hosts may contribute to a reduction in the number of deaths and an overall improvement in quality of life. The branched chain amino acid leucine affects cell signalling, thereby leading to an improvement in lean body mass by decreasing muscle protein degradation. We assess the effects of a leucine-rich diet on protein degradation signalling in muscle over the course of tumour growth. Adult Wistar rats were distributed into experimental groups according to whether a tumour or not was inoculated and whether or not a leucine-rich diet was provided. The animals were subsequently sacrificed at three different time points during tumour evolution (7th, 14th and 21st day after tumour implant). Protein degradation signalling, as indicated by ubiquitin–proteasome subunits (11S, 19S and 20S), and pro- and anti-inflammatory cytokines were analysed in each of the experimental groups. Tumour growth promoted a decrease in muscle protein, a sharp increase in pro-inflammatory cytokines (TNF α , IL-6 and IFN γ ) and a progressive increase in proteasome subunits (19S and 20S). Thus, the role of leucine in this specific situation reveals an increased process mainly on the 14th day after tumour implantation and a modulated action on the 21st day of tumour growth. The results indicate that leucine in the diet modulates some important key aspects of the proteasome pathway and inflammatory process in the cancer cachexia state.

A leucine-rich diet modulates the tumor-induced down-regulation of the MAPK/ERK and PI3K/Akt/mTOR signaling pathways and maintains the expression of the ubiquitin-proteasome pathway in the placental tissue of NMRI mice.

Placental tissue injury is concomitant with tumor development. We investigated tumor-driven placental damage by tracing certain steps of the protein synthesis and degradation pathways under leucine-rich diet supplementation in MAC16 tumor-bearing mice. Cell signaling and ubiquitin-proteasome pathways were assessed in the placental tissues of pregnant mice, which were distributed into three groups on a control diet (pregnant control, tumor-bearing pregnant, and pregnant injected with MAC-ascitic fluid) and three other groups on a leucine-rich diet (pregnant, tumor-bearing pregnant, and pregnant injected with MAC-ascitic fluid). MAC tumor growth down-regulated the cell-signaling pathways of the placental tissue and decreased the levels of IRS-1, Akt/PKB, Erk/MAPK, mTOR, p70S6K, STAT3, and STAT6 phosphorylated proteins, as assessed by the multiplex Millipore Luminex assay. Leucine supplementation maintained the levels of these proteins within the established cell-signaling pathways. In the tumor-bearing group (MAC) only, the placental tissue showed increased PC5 mRNA expression, as assessed by quantitative RT-PCR, decreased 19S and 20S protein expression, as assessed by Western blot analysis, and decreased placental tyrosine levels, likely reflecting up-regulation of the ubiquitin-proteasome pathway. Similar effects were found in the pregnant injected with MAC-ascitic fluid group, confirming that the effects of the tumor were mimicked by MAC-ascitic fluid injection. Although tumor progression occurred, the degradation pathway-related protein levels were modulated under leucine-supplementation conditions. In conclusion, tumor evolution reduced the protein expression of the cell-signaling pathway associated with elevated protein degradation, thereby jeopardizing placental activity. Under the leucine-rich diet, the impact of cancer on placental function could be minimized by improving the cell-signaling activity and reducing the proteolytic process.

PM378 Connexin45 Over-Expression Causes Arrhythmia in Rat Hearts

Introduction: Cancer-cachexia state promotes intense involuntary weight loss, wasting skeletal muscle protein due to higher proteolysis and/or decreased protein synthesis. This process can be improved by branched-chain amino acids, as leucine, which provides energy source by skeletal muscle and acts as a cell signaling. Objectives: This work aim to evaluate whether the leucine-rich diet (3%>leu) can modulate theelectrocardiogram (ECG) and cardiac biomarkers in the cachectic tumorbearing rats. Methods: Adult rats were distributed into 4 groups: C–control rats; WWalker-256 tumor tumor-bearing rats; L–leucine supplemented diet (leu-3%) and LW-leucine supplemented diet tumor-bearing rats (5 animals per group). The electrocardiogram was evaluated after anesthesia (ketamine 100mg/Kg. plus xelazine 7mg/Kg intramuscular) during pre-agonic state assayed by LabChart software. Cardiac biomarkers (MPO, TIMP, PAI-total) were evaluated in heart muscle homogenate assayed by multiplex assay (Millipore-Luminex). Difference among groups used one-way ANOVA analyses followed by Bonferroni’s test (P<0.05). Results: ECG parameters: the heart rate reduced in both tumor-bearing groups; QT-c tended to increase in W group, but was recovered in LW rats; T wave amplitude tended to increase in W group and was similar in LW group when compared to control rats. Cardiac biomarkers: MPO, TIMP and PAI increased only in W group, despite having tumor the LW group had similar values as the control rats.

Leucine-rich diet supplementation modulates foetal muscle protein metabolism impaired by Walker-256 tumour

BackgroundCancer-cachexia induces a variety of metabolic disorders of protein turnover and is more pronounced when associated with pregnancy. Tumour-bearing pregnant rats have impaired protein balance, which decreases protein synthesis and increases muscle breakdown. Because branched-chain amino acids, especially leucine, stimulate protein synthesis, we investigated the effect of a leucine-rich diet on protein metabolism in the foetal gastrocnemius muscles of tumour-bearing pregnant rats.MethodsFoetuses of pregnant rats with or without Walker 256 tumours were divided into six groups. During the 20 days of the experiment, the pregnant groups were fed with either a control diet (C, control rats; W, tumour-bearing rats; Cp, rats pair-fed the same normoprotein-diet as the W group) or with a leucine-rich diet (L, leucine rats; LW, leucine tumour-bearing rats; and Lp, rats pair-fed the same leucine-rich diet as the LW group). After the mothers were sacrificed, the foetal gastrocnemius muscle samples were resected, and the protein synthesis and degradation and tissue chymotrypsin-like, cathepsin and calpain enzyme activities were assayed. The muscle oxidative enzymes (catalase, glutathione-S-transferase and superoxide dismutase), alkaline phosphatase enzyme activities and lipid peroxidation (malondialdehyde) were also measured.ResultsTumour growth led to a reduction in foetal weight associated with decreased serum protein, albumin and glucose levels and low haematocrit in the foetuses of the W group, whereas in the LW foetuses, these changes were less pronounced. Muscle protein synthesis (measured by L-[3H]-phenylalanine incorporation) was reduced in the W foetuses but was restored in the LW group. Protein breakdown (as assessed by tyrosine release) was enhanced in the L and W groups, but chymotrypsin-like activity increased only in group W and tended toward an increase in the LW foetuses. The activity of cathepsin H was significantly higher in the W group foetuses, but the proteolytic calcium-dependent pathway showed similar enzyme activity. In parallel, an intense oxidative stress process was observed only in the group W foetuses.ConclusionsThese data suggested that the proteasomal and lysosomal proteolytic pathways and oxidative stress are likely to participate in the process of foetal muscle catabolism of Walker’s tumour-bearing pregnant rats. The present work shows that foetal muscle can be protected by supplementation with a leucine-rich diet.

Leucine-Rich Diet and Light Aerobic Training Modulate GLUT4 Expression And Increase the Glycogen Content in the Gastrocnemius Muscle of Walker-256 Tumour-Bearing Rats

Leucine-Rich Diet and Light Aerobic Training Modulate GLUT4 Expression And Increase the Glycogen Content in the Gastrocnemius Muscle of Walker-256 Tumour-Bearing Rats The intense mobilisation of substrates during cancer induces the loss of body mass, which mainly results from the depletion of muscle protein due to increased proteolysis and/or decreased protein synthesis, leading to cachexia. Leucine is also used as an energy source and as a cell-signalling molecule by skeletal muscle. Additionally, physical activity increases glucose consumption, which reduces the levels of circulating glucose and insulin. This work investigated the effects of leucine supplementation and light aerobic-exercise (swimming) on muscle carbohydrate metabolism in Walker tumour-bearing rats. Trained adult rats were fed a leucine-rich diet and implanted with Walker-256 tumour cells. We assessed the levels of serum glucose, cytokine and hormone and muscle glycolytic gene expression, glycogen content and fibre size.

Leucine improves protein nutritional status and regulates hepatic lipid metabolism in calorie‐restricted rats

Several studies have highlighted the potential of leucine supplementation for the treatment of metabolic diseases including type 2 diabetes and obesity. Caloric restriction is a common approach to improve the health in diabetic and obese subjects. However, very few studies assessed the effects of leucine supplementation in calorie-restricted animals. Rats were subjected to a 30% calorie-restricted diet for 6 weeks to study the effects of leucine supplementation on protein status markers and lipid metabolism. Caloric restriction reduced the body weight. However, increased leucine intake preserved body lean mass and protein mass and improved protein anabolism as indicated by the increased circulating levels of albumin and insulin-like growth factor-1 (IGF-1), and the liver expression of albumin and IGF-1 messenger RNA. Leucine supplementation also increased the circulating levels of interleukin-6 and leptin but did not affect the tumour necrosis factor-α and monocyte chemotactic protein-1 concentrations. Ketone bodies were increased in rats consuming a leucine-rich diet, but we observed no changes in cholesterol or triglycerides concentrations. Caloric restriction reduced the liver expression of peroxisome proliferator activated receptor-α and glucose-6-phosphatase, whereas leucine supplementation increased the liver expression of 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA) reductase and sterol regulatory element-binding transcription factor 1. A leucine-rich diet during caloric restriction preserved whole body protein mass and improved markers of protein anabolism. In addition, leucine modulated the hepatic lipid metabolism. These results indicate that increased leucine intake may be useful in preventing excessive protein waste in conditions of large weight loss.

Leucine-Rich Diet Improves the Serum Amino Acid Profile and Body Composition of Fetuses from Tumor-Bearing Pregnant Mice1

Pregnancy is a complex process that can be jeopardized when associated with cancer, because of the coexistence of two complex metabolic conditions: a fetus and cancer. The aim of this study was to evaluate fetal growth in association with cancer development as well as the indirect effects produced by tumors in pregnant mice subjected to a leucine-rich diet, knowing that leucine supplementation can minimize the tumor effects by acting as a cell signaling agent to improve the protein synthesis process. We evaluated fetuses (n = 6) from NMRI pregnant mice fed either a control or a leucine-rich diet in either the presence or absence of an MAC16 colon adenocarcinoma or ascitic fluid inoculation. The fetal serum amino acids were separated using high-performance liquid chromatography, and fetal cytokine levels were analyzed using a microsphere-based multiplex immunoassay (Luminex xMAP). Fetal body composition was measured as the water, fat, and protein total content and total serum protein, albumin, and glucose content. Tumor growth resulted in a severe reduction in fetal body weight and protein content and increased fetal resorption, associated with placental weight decrease; these effects were minimized by a leucine-rich diet. Serum total protein and glucose content were reduced in fetuses from tumor-bearing dams but were reverted by nutritional supplementation. The serum amino acid profiles differed significantly between the tumor-bearing mice fed with a leucine-rich diet and controls. Certain tumor effects were reproduced in fetuses from ascitic fluid-injected dams, suggesting indirect effects of tumor growth. We conclude that certain effects of tumor growth can be mimicked by ascitic fluid injection and can be modulated by a leucine-rich diet.

P053 Effects of leucine-rich diet and exercise on inflammatory response produced by the tumour growth in rats

Introduction The intense mobilisation of substrates during cancer induces a severe involuntary weight loss, leading to cachexia. Cytokines are important in the alteration of carbohydrate, lipid, and protein metabolism in cancer-cachexia. Methods We examined the effect of leucine-rich diet and exercise on the inflammatory response in Walker 256 tumour-bearing rats. Wistar rats submitted to aerobic exercise, and leucine-rich diet were distributed into 8 groups: C – control rats; TC – trained, W – tumour-bearing; TW – trained tumour-bearing, L – rats fed leucine diet, TL – trained rats fed leucine diet; LW – tumour-bearing fed leucine diet; TLW – trained tumour-bearing fed leucine diet. Results After 21 days, the tumour development induced a significant increase in the proinflammatory cytokines. Tumour necrosis factor (TNF-α) enhanced in tumour groups (W (2.57 ± 0.28), TW (3.2 ± 0.58), LW (2.67 ± 0.29), TLW (2.91 ± 0.75) compared to control groups C (1.60 ± 0.22), TC (1.84 ± 0.11), L (1.65 ± 0.18), TL (1.39 ± 0.15 pg/mL)). Interferon-γ (INF-γ) also increased significantly in tumour groups (W (172.3 ± 28.9), TW (153.0 ± 33.1), LW (238.8 ± 79.4), TLW (226.4 ± 82.1) vs control groups (C (88.3 ± 20.9), TC (68.4 ± 18.9), L (98.9 ± 43.5), TL (107.8 ± 50.6)). The serum concentration of interleukin-6 (IL-6) raised significantly in group W (408.5 ± 275.5) vs groups C (16.23 ± 4.8), TC (16.75 ± 1.35), TW (63.6 ± 10.4), L (27.6 ± 8.0), LW (31.9 ± 9.1) and TWL (43.8 ± 21.9). The trained-rats and leucine-fed group (TL) showed an increase in IL-6 vs control group C, but not as higher as verified in W group. The concentration of interleukin-1α (IL-1α) also increased in group W (40.64 ± 12.5), TL (53.5 ± 4.0), LW (39.9 ± 12.3) and TWL (43.4 ± 23.1) vs groups C (15.8 ± 3.5), TC (14.0 ± 2.3), TW (27.2 ± 11.7), L (20.3 ± 9.9). The interleukin 4 (IL-4), cytokine related to host defence response showed an increase in group TW (13.0 ± 10.4) vs groups C (3.7 ± 0.9), TC (5.3 ± 1.3), W (4.4 ± 0.9), L (5.3 ± 2.1), TL (7.2 ± 3.9), WL (8.5 ± 4.2) and TWL (3.9 ± 1.1). The anti-inflammatory cytokine, IL-10, increased in all groups with tumour, mainly in W group (2481 ± 736,4) compared to other groups (C (124,1 ± 33,06), TC (127,5 ± 40,0), L (75,66 ± 6,12), TL (87,21 ± 9,3)). The IL-10/TNF-apha ratio a marker of the intensity of the inflammatory condition was significant increased in all tumour-bearing groups vs control groups. Despite the accelerated tumour growth, exercise reduced tumour growth, as tumour mass and tumour/body weight ratio were lower than in the other groups. The tumour weight in the TWL group was around 57% less than in the W group. The WL and TW groups had tumour weight reduced in 24% and 28% less compared to W group, respectively. Conclusion Although the tumour development induced chronic inflammation in the production of proinflammatory cytokines in the development of cachexia, the effects produced by the association between exercise and leucine-rich diet showed benefit effects, probably improving the host responses. Supported by: Fapesp #2010/11328-9; #2009/11993-5.

P054 Effects of leucine-rich diet on inflammatory response induced by tumour growth in young, adults and senile rats

Introduction The anorexia–cachexia syndrome is caused by metabolic changes; in particular, induced by cytokines released by tumour cells or in response to the host’s immune system. These cytokines also promote lipolysis and proteolysis. Methods We examined the effect of leucine-rich diet on the inflammatory response in young (21 days old), adults (90 days old) and senile (400 days old) Walker 256 tumour-bearing rats. Wistar rats were submitted to eutrophic diet or leucine-rich diet and distributed into 7 groups: C – control rats; YW – young tumour-bearing; AW – adult tumour-bearing; SW – senile tumour-bearing; YWL – young tumour-bearing fed leucine diet; AWL – adult tumour-bearing fed leucine diet; SWL – senile tumour-bearing fed leucine diet. Results The tumour development induced an increase in proinflammatory cytokines. The serum tumour necrosis factor (TNF-α) content was higher in the young tumour-bearing fed leucine diet (YWL) compared to control group C and to the other groups. Another proinflammatory cytokine, interferon-γ (INF-γ) increased in the young tumour-bearing fed a leucine-rich diet group YWL vs control group C; the other groups showed similar values as the control group. The interleukin 4 (IL-4), cytokine related to defence host response showed an increase in young and senile groups compared to group C. The serum concentration of interleukin-6 (IL-6), a pro-inflammatory cytokine, increased in group YW, YWL, AWL; and SWL in relation to control group. The concentration of interleukin-1α (IL-1α), another pro-inflammatory cytokine, increased in group YW in comparison to control and the other tumour-bearing groups. The anti-inflammatory cytokine, IL-10, increased in all groups with tumour YW (728 + 122 pg/mL); YWL (1684 + 339); AW (1016 + 61); AWL (775 + 140), SW (1414 + 178) and SWL (1445 + 642) vs C (313 + 91). The tumour/body weight ratio was lower in the young tumour-bearing groups versus senile tumour-bearing groups. The serum glucose and protein content reduced in young tumour-bearing groups compared senile tumour-bearing groups. Conclusion Although the tumour growth in young rats induced chronic inflammation increasing the proinflammatory cytokines release, which occur in the development of cachexia; in senile tumour-bearing groups these effects are decreased possibly due to a reduced metabolism. Supported by PIBIC/CNPq and FAPESP #2010/11328-9; # 2010/00260-4.

Light aerobic physical exercise in combination with leucine and/or glutamine-rich diet can improve the body composition and muscle protein metabolism in young tumor-bearing rats

Nutritional supplementation with some amino acids may influence host's responses and also certain mechanism involved in tumor progression. It is known that exercise influences body weight and muscle composition. Previous findings from our group have shown that leucine has beneficial effects on protein composition in cachectic rat model as the Walker 256 tumor. The main purpose of this study was to analyze the effects of light exercise and leucine and/or glutamine-rich diet in body composition and skeletal muscle protein synthesis and degradation in young tumor-bearing rats. Walker tumor-bearing rats were subjected to light aerobic exercise (swimming 30 min/day) and fed a leucine-rich (3%) and/or glutamine-rich (4%) diet for 10 days and compared to healthy young rats. The carcasses were analyzed as total water and fat body content and lean body mass. The gastrocnemious muscles were isolated and used for determination of total protein synthesis and degradation. The chemical body composition changed with tumor growth, increasing body water and reducing body fat content and total body nitrogen. After tumor growth, the muscle protein metabolism was impaired, showing that the muscle protein synthesis was also reduced and the protein degradation process was increased in the gastrocnemius muscle of exercised rats. Although short-term exercise (10 days) alone did not produce beneficial effects that would reduce tumor damage, host protein metabolism was improved when exercise was combined with a leucine-rich diet. Only total carcass nitrogen and protein were recovered by a glutamine-rich diet. Exercise, in combination with an amino acid-rich diet, in particular, leucine, had effects beyond reducing tumoral weight such as improving protein turnover and carcass nitrogen content in the tumor-bearing host.

Leucine-Rich Diet Changes the Cytokine Profile in Maternal and Fetal MAC16 Tumour-Bearing Mice.

Leucine-Rich Diet Changes the Cytokine Profile in Maternal and Fetal MAC16 Tumour-Bearing Mice.

A leucine-rich diet and exercise affect the biomechanical characteristics of the digital flexor tendon in rats after nutritional recovery

An increase in the capacity of athletic performance depends on adequate nutrition, which ensures optimal function of the musculoskeletal system, including tendon stability. However, little is known about the status of tendons and extracellular matrix modifications during malnutrition and nutritional recovery when leucine is used in response to exercise conditioning. The purpose of this study was to evaluate the collagen content and biomechanical aspects of the deep digital flexor tendon (DDFT) in malnourished rats submitted to nutritional recovery (control diet or leucine-rich diet) and aerobic physical activity. After 60days of undernourishment (6% protein diet), the malnourished rats were subsequently nutritionally recovered with a control diet or leucine-rich diet and trained or not (swimming, without overload) for 5weeks. The biomechanical analysis and quantification of hydroxyproline were assessed in the DDFT in all experimental groups. The leucine-rich diet increased hydroxyproline content in the tension region, independently of the training. In the compression region, hydroxyproline content was higher in the malnourished and leucine-trained groups. Biomechanical analysis showed a lower load in the malnourished and all-trained groups. The lowest stress was observed with control-trained animals. The nutritional-recovered groups showed higher strain values corresponding to control group, while the lowest values were observed in malnourished and trained groups. The results suggest that a leucine-rich diet stimulates collagen synthesis of the DDFT, especially when in combination with physical exercise, and seems to determine the increase of resistance and the biomechanical characteristics of tendons.

Physical Exercise and a Leucine-Rich Diet Modulate the Muscle Protein Metabolism in Walker Tumor-Bearing Rats

Leucine-supplemented diet can recover lean body mass and preserve muscle protein mass. Additionally, physical exercise can be an excellent alternative to improve the rehabilitation of cancer patients. Knowing these facts, we examined the effects of a leucine-rich diet with or without physical aerobic exercise on muscle protein metabolism in Walker tumor-bearing rats. Young rats were divided into 4 groups that did or did not perform light aerobic exercise (swim training) and were on a leucine-rich diet or a control diet for 2 mo. After this time, these animals were implanted or not with tumors (subcutaneously) following groups for either control diet or leucine-rich diet fed rats: control, trained, tumor-bearing, and trained tumor-bearing. Twenty-one days after implantation, the tumor growth induced a decrease in the muscle protein synthesis and increased the catabolic process, which was associated with an increase in the expression of the ubiquitin-proteasome subunits (20S, 19S, and 11S). In contrast, the exercise program minimized the muscle degradation process and increased muscle myosin content. Additionally, leucine supplementation also modulated proteasome subunits, especially the 19S and 11S. In summary, the exercise has beneficial effects by reducing tumor growth, leading to an improvement in protein turnover especially when in conjunction with a leucine-rich diet.

PS3-61 Physical exercise and leucine-rich diet improve the inflammatory response produced by the tumour growth in rats

PS3-61 Physical exercise and leucine-rich diet improve the inflammatory response produced by the tumour growth in rats

PS1-60 Leucine-rich diet and ascorbic-acid supplementation change the cytokine profile in tumour-bearing rats

PS1-60 Leucine-rich diet and ascorbic-acid supplementation change the cytokine profile in tumour-bearing rats

94 Leucine-rich diet and ascorbic acid affect the proteolysis-inducing factor level and the muscle antioxidant stress response in tumor-bearing rats

94 Leucine-rich diet and ascorbic acid affect the proteolysis-inducing factor level and the muscle antioxidant stress response in tumor-bearing rats

Leucine-rich diet alters the eukaryotic translation initiation factors expression in skeletal muscle of tumour-bearing rats

BackgroundCancer-cachexia induces a variety of metabolic disorders on protein turnorver, decreasing protein synthesis and increasing protein degradation. Controversly, insulin, other hormones, and branched-chain amino acids, especially leucine, stimulate protein synthesis and modulate the activity of translation initiation factors involved in protein synthesis. Since the tumour effects are more pronounced when associated with pregnancy, ehancing muscle-wasting proteolysis, in this study, the influence of a leucine-rich diet on the protein synthesis caused by cancer were investigated.MethodsPregnant rats with or without Walker 256 tumour were distributed into six groups. During 20 days of experiment, three groups were fed with a control diet: C – pregnant control, W – tumour-bearing, and P – pair-fed, which received the same amount of food as ingested by the W group; three other groups of pregnant rats were fed a leucine-rich diet: L – pregnant leucine, WL – tumour-bearing, and PL – pair-fed, which received the same amount of food as ingested by the WL group.ResultsThe gastrocnemius muscle of WL rats showed increased incorporation of leucine in protein compared to W rats; the leucine-rich diet also prevented the decrease in plasma insulin normally seen in W. The expression of translation initiation factors increased when tumour-bearing rats fed leucine-rich diet, with increase of ~35% for eIF2α and eIF5, ~17% for eIF4E and 20% for eIF4G; the expression of protein kinase S6K1 and protein kinase C was also highly enhanced.ConclusionThe results suggest that a leucine-rich diet increased the protein synthesis in skeletal muscle in tumour-bearing rats possibly through the activation of eIF factors and/or the S6kinase pathway.

Proteasome activity is altered in skeletal muscle tissue of tumour-bearing rats a leucine-rich diet

Leucine can modulate skeletal muscle metabolism by enhancing protein synthesis and decreasing proteolysis. In this study, we investigated the effects of leucine on the ubiquitin-proteasome system in skeletal muscle of pregnant tumour-bearing rats fed a leucine-rich diet. Pregnant Wistar rats were distributed into three groups that were fed a semi-purified control diet (C, control; W, Walker tumour-bearing; P, pair-fed) and three other groups of pregnant rats fed a semi-purified leucine-rich diet (L, leucine; WL, Walker tumour-bearing; PL, pair-fed). The tumour-bearing rats were injected subcutaneously with a suspension of Walker 256 tumour cells. Protein synthesis and degradation were measured in gastrocnemius muscle; the total protein content and tissue chymotrypsin-like and alkaline phosphatase enzyme activities were also determined. Muscle protein extracts were run on SDS-PAGE to assess the expression of the myosin heavy chain (MHC), 20S alpha proteasome subunit, 19S MSSI ATPase regulator subunit and 11S alpha subunit. Although tumour growth decreased the incorporation of [3H]-Phe, the concomitant feeding of a leucine-rich diet increased the rate of protein synthesis. Muscle proteolysis in both tumour-bearing groups was increased more than in the respective control groups. Conversely, the leucine-rich diet caused less protein breakdown in the WL group than in the W group. Only the W group showed a significant reduction (71%) in the myosin content. In WL rats, the 20S proteasome content (32 kDa band) was reduced, while the expression of the 19S subunit was 3-fold less than in the W group and the 11S proteasome subunit reduced, to around 32% less than in the W group. These findings clearly indicate that leucine can stimulate protein synthesis and inhibit protein breakdown in pregnant rats, probably by modulating the activation of the ubiquitin-proteasome system during tumour growth.

Effects of a leucine-rich diet on body composition during nutritional recovery in rats

Objective Protein malnutrition is characterized by a number of morphologic and physiologic alterations, including intestinal mucosal atrophy and impaired nutrient absorption. Impaired absorption accentuates nutritional deficiency and accelerates body weight loss and changes in body chemistry. Because leucine is a ketogenic and oxidative amino acid and stimulates the protein synthesis, we examined the ability of young rats to recover from protein malnutrition by feeding them a control balanced or a leucine-rich diet for 60 d. Methods At the end of the 60-d period, body, liver, and muscle weights; glucose, methionine, and leucine intestinal absorption; and carcass chemical composition were evaluated. Results Body weight gain was higher in the control balanced and leucine-rich groups than in control rats, indicating that adequate refeeding allows body weight to recover in these groups. Methionine and glucose absorptions were impaired in malnourished rats but were restored after nutritional recovery. The leucine-rich diet resulted in an increase in carcass collagen nitrogen but maintained the carcass structural nitrogen. Conclusions These results indicated that leucine supplementation during nutritional recovery from protein malnutrition improves protein carcass restoration. However, the precise mechanism of the leucine effects involved in this response remains to be elucidated.