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

Sex differences in cachexia and branched-chain amino acid metabolism following chemotherapy in mice

Chemotherapy is a major contributor to cachexia, but studies often investigate male animals. Here, we investigated whether sex modifies the effects of chemotherapy on cachexia and BCAA metabolism. Ten-week-old CD2F1 male and female mice were treated with the chemotherapy drug cocktail folfiri (50 mg/kg 5-fluorouracil, 90 mg/kg leucovorin, and 24 mg/kg CPT11) (drug) or vehicle twice a week for 6 weeks. Insulin tolerance tests were conducted and BCAA levels and metabolism were measured in plasma and tissues. Drug treatment reduced body and skeletal muscle weights and anabolic signaling in both sexes, with females showing worsened outcomes (p < 0.05 for all). Drug treatment increased plasma BCAA only in males, but BCAA concentrations in the skeletal muscle of both sexes were decreased; this decrease was more profound in males (p = 0.0097). In addition, muscle expression of the BCAA transporter LAT1 was reduced; this reduction was more severe in females (p = 0.0264). In both sexes, the (inhibitory) phosphorylation of BCKD-E1αser293 was increased along with decreased BCKD activity. In the liver, drug treatment increased BCAA concentrations and LAT1 expression, but BCKD activity was suppressed in both sexes (p < 0.05 for all). Our results demonstrate that altered BCAA metabolism may contribute to chemotherapy-induced cachexia in a sex-dependent manner.

Metabolomics and its Applications in Cancer Cachexia

Cancer cachexia (CC) is a complicated metabolic derangement and muscle wasting syndrome, affecting 50-80% cancer patients. So far, molecular mechanisms underlying CC remain elusive. Metabolomics techniques have been used to study metabolic shifts including changes of metabolite concentrations and disturbed metabolic pathways in the progression of CC, and expand further fundamental understanding of muscle loss. In this article, we aim to review the research progress and applications of metabolomics on CC in the past decade, and provide a theoretical basis for the study of prediction, early diagnosis, and therapy of CC.

Vcp Overexpression and Leucine Supplementation Increase Protein Synthesis and Improve Fear Memory and Social Interaction of Nf1 Mutant Mice

Neurofibromatosis type 1 (NF1) is a dominant genetic disorder manifesting, in part, as cognitive defects. Previous study indicated that neurofibromin (NF1 protein) interacts with valosin-containing protein (VCP)/P97 to control dendritic spine formation, but the mechanism is unknown. Here, using Nf1^+/- mice and transgenic mice overexpressing wild-type Vcp/p97, we demonstrate that neurofibromin acts with VCP to control endoplasmic reticulum (ER) formation and consequent protein synthesis and regulates dendritic spine formation, thereby modulating contextual fear memory and social interaction. To validate the role of protein synthesis, we perform leucine supplementation in vitro and in vivo. Our results suggest that leucine can effectively enter the brain and increase protein synthesis and dendritic spine density of Nf1^+/- neurons. Contextual memory and social behavior of Nf1^+/- mice are also restored by leucine supplementation. Our study suggests that the "ER-protein synthesis" pathway downstream of neurofibromin and VCP is a critical regulator of dendritic spinogenesis and brain function.

Nutritional Interventions in Cancer Cachexia: Evidence and Perspectives From Experimental Models

Cancer cachexia is a complex metabolic syndrome characterized by involuntary skeletal muscle loss and is associated with poor clinical outcome, decreased survival and negatively influences cancer therapy. No curative treatments are available for cancer cachexia, but nutritional intervention is recommended as a cornerstone of multimodal therapy. Optimal nutritional care is pivotal in the treatment of cancer cachexia, and the effects of nutrients may extend beyond provision of adequate energy uptake, targeting different mechanisms or metabolic pathways that are affected or deregulated by cachexia. The evidence to support this notion derived from nutritional intervention studies in experimental models of cancer cachexia is systematically discussed in this review. Moreover, experimental variables and readout parameters to determine skeletal muscle wasting and cachexia are methodologically evaluated to allow critical comparison of similar studies. Single- and multinutrient intervention studies including qualitative modulation of dietary protein, dietary fat, and supplementation with specific nutrients, such as carnitine and creatine, were reviewed for their efficacy to counteract muscle mass loss and its underlying mechanisms in experimental cancer cachexia. Numerous studies showed favorable effects on impaired protein turnover and related metabolic abnormalities of nutritional supplementation in parallel with a beneficial impact on cancer-induced muscle wasting. The combination of high quality nutrients in a multitargeted, multinutrient approach appears specifically promising, preferentially as a multimodal intervention, although more studies investigating the optimal quantity and combination of nutrients are needed. During the review process, a wide variation in timing, duration, dosing, and route of supplementation, as well as a wide variation in animal models were observed. Better standardization in dietary design, and the development of experimental models that better recapitulate the etiology of human cachexia, will further facilitate successful translation of experimentally-based multinutrient, multimodal interventions into clinical practice.

Social behaviors and contextual memory of Vcp mutant mice are sensitive to nutrition and can be ameliorated by amino acid supplementation

Both genetic variations and nutritional deficiency are associated with autism spectrum disorders and other neurological disorders. However, it is less clear whether or how nutritional deficiency and genetic variations influence each other under pathogenic conditions. "Valosin-containing protein" (VCP, also known as p97) is associated with multiple neurological disorders and regulates dendritic spine formation by controlling endoplasmic reticulum formation and protein synthesis efficiency. Increased protein synthesis ameliorates the dendritic spine defects of Vcp-deficient neurons. Therefore, we investigated if Vcp-deficient mice are sensitive to nutritional conditions. Here, we show that social interaction and contextual memory of Vcp-deficient mice are indeed influenced by different dietary protein levels. Moreover, leucine supplementation ameliorates the behavioral deficits and dendritic spine density of Vcp-deficient mice, strengthening evidence for the role of protein synthesis in VCP function. Our study illustrates that genetic variation and nutrient factors cross-talk to influence neuronal and behavioral phenotypes.

The 17β-oestradiol treatment minimizes the adverse effects of protein restriction on bone parameters in ovariectomized Wistar rats: Relevance to osteoporosis and the menopause

Objectives

Insufficient protein ingestion may affect muscle and bone mass, increasing the risk of osteoporotic fractures in the elderly, and especially in postmenopausal women. We evaluated how a low-protein diet affects bone parameters under gonadal hormone deficiency and the improvement led by hormone replacement therapy (HRT) with 17β-oestradiol.

Methods

Female Wistar rats were divided into control (C), ovariectomized (OVX), and 17β-oestradiol-treated ovariectomized (OVX-HRT) groups, which were fed a control or an isocaloric low-protein diet (LP; 6.6% protein; seven animals per group). Morphometric, serum, and body composition parameters were assessed, as well as bone parameters, mechanical resistance, and mineralogy.

Results

The results showed that protein restriction negatively affected body chemical composition and bone metabolism by the sex hormone deficiency condition in the OVX group. The association between undernutrition and hormone deficiency led to bone and muscle mass loss and increased the fragility of the bone (as well as decreasing relative femoral weight, bone mineral density, femoral elasticity, peak stress, and stress at offset yield). Although protein restriction induced more severe adverse effects compared with the controls, the combination with HRT showed an improvement in minimizing these damaging effects, as it was seen that HRT had some efficacy in maintaining muscle and bone mass, preserving the bone resistance and minimizing some deleterious processes during the menopause.

Conclusion

Protein restriction has adverse effects on metabolism, leading to more severe menopausal symptoms, and HRT could minimize these effects. Therefore, special attention should be given to a balanced diet during menopause and HRT.Cite this article: Bone Joint Res 2019;8:573-581.

Leucine-rich diet induces a shift in tumour metabolism from glycolytic towards oxidative phosphorylation, reducing glucose consumption and metastasis in Walker-256 tumour-bearing rats

Leucine can stimulate protein synthesis in skeletal muscle, and recent studies have shown an increase in leucine-related mitochondrial biogenesis and oxidative phosphorylation capacity in muscle cells. However, leucine-related effects in tumour tissues are still poorly understood. Thus, we described the effects of leucine in both in vivo and in vitro models of a Walker-256 tumour. Tumour-bearing Wistar rats were randomly distributed into a control group (W; normoprotein diet) and leucine group (LW; leucine-rich diet [normoprotein + 3% leucine]). After 20 days of tumour evolution, the animals underwent ¹⁸-fludeoxyglucose positron emission computed tomography (¹⁸F-FDG PET-CT) imaging, and after euthanasia, fresh tumour biopsy samples were taken for oxygen consumption rate measurements (Oroboros Oxygraph), electron microscopy analysis and RNA and protein extraction. Our main results from the LW group showed no tumour size change, lower tumour glucose (¹⁸F-FDG) uptake, and reduced metastatic sites. Furthermore, leucine stimulated a shift in tumour metabolism from glycolytic towards oxidative phosphorylation, higher mRNA and protein expression of oxidative phosphorylation components, and enhanced mitochondrial density/area even though the leucine-treated tumour had a higher number of apoptotic nuclei with increased oxidative stress. In summary, a leucine-rich diet directed Walker-256 tumour metabolism to a less glycolytic phenotype profile in which these metabolic alterations were associated with a decrease in tumour aggressiveness and reduction in the number of metastatic sites in rats fed a diet supplemented with this branched-chain amino acid.

Leucine-rich diet alters the 1H-NMR based metabolomic profile without changing the Walker-256 tumour mass in rats

Background

Cachexia is one of the most important causes of cancer-related death. Supplementation with branched-chain amino acids, particularly leucine, has been used to minimise loss of muscle tissue, although few studies have examined the effect of this type of nutritional supplementation on the metabolism of the tumour-bearing host. Therefore, the present study evaluated whether a leucine-rich diet affects metabolomic derangements in serum and tumour tissues in tumour-bearing Walker-256 rats (providing an experimental model of cachexia).

Methods

After 21 days feeding Wistar female rats a leucine-rich diet, distributed in L-leucine and LW-leucine Walker-256 tumour-bearing groups, we examined the metabolomic profile of serum and tumour tissue samples and compared them with samples from tumour-bearing rats fed a normal protein diet (C – control; W – tumour-bearing groups). We utilised ¹H-NMR as a means to study the serum and tumour metabolomic profile, tumour proliferation and tumour protein synthesis pathway.

Results

Among the 58 serum metabolites examined, we found that 12 were altered in the tumour-bearing group, reflecting an increase in activity of some metabolic pathways related to energy production, which diverted many nutrients toward tumour growth. Despite displaying increased tumour cell activity (i.e., higher Ki-67 and mTOR expression), there were no differences in tumour mass associated with changes in 23 metabolites (resulting from valine, leucine and isoleucine synthesis and degradation, and from the synthesis and degradation of ketone bodies) in the leucine-tumour group. This result suggests that the majority of nutrients were used for host maintenance.

Conclusion

A leucine rich-diet, largely used to prevent skeletal muscle loss, did not affect Walker 256 tumour growth and led to metabolomic alterations that may partially explain the positive effects of leucine for the whole tumour-bearing host.

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

BACKGROUND

Cancer-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.

METHODS

Foetuses 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.

RESULTS

Tumour 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.

CONCLUSIONS

These 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 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 supplementation increases serum insulin-like growth factor 1 concentration and liver protein/RNA ratio in rats after a period of nutritional recovery

This study evaluated the effect of leucine on the protein status of rats submitted to 50% food restriction for 1 week, followed by 2 weeks of nutritional recovery. A significant increase of serum insulin-like growth factor 1 and protein/RNA ratio in the liver was observed in leucine-supplemented rats. There was no change in carcass, liver, or gastrocnemius protein content when compared with control animals. The supplementation tested did not favor protein status, although it improved some indicators of an anabolic state.

The administration of food supplemented with cocoa powder during nutritional recovery reduces damage caused by oxidative stress in rat brain

Malnutrition contributes to the development of oxidative damage in the central nervous system. The selective administration of nutrients tends to show positive results in individuals who have suffered from malnutrition. To determine the effect of the administration of cocoa powder on the peroxidation of lipids and glutathione level during the nutritional recovery in brain, rats of 21 days old were subjected to a protocol that resembles malnutrition (MN) by feeding them with 60% of the daily food consumption of the control group (WN) and later to nutritional recovery with regular rodent feed (RFR) or added with cocoa (10 g of cocoa powder/kg of regular rodent feed) (CCR). Animals fed with regular rodent food showed significant reduction in brain glutathione: RFR (84.18 ± 6.38 ng/mg protein) vs. CCR (210.61 ± 50.10 ng/mg protein) and WN (186.55 ± 33.18 ng/mg protein), but with similar level to that of MN (92.12 ± 15.60 ng/mg protein). On the contrary, lipid peroxidation in RFR-fed animals increased RFR (1.32 ± 0.2 μM malondialdehyde/g of tissue), CCR (0.86 ± 0.07 μM malondialdehyde/g of tissue), WN (0.89 ± 0.09 μM malondialdehyde/g of tissue), but their thiobarbituric acid reactive substances concentration is similar to that of MN group (1.50 ± 0.2 μM malondialdehyde/g of tissue). Consumption of cocoa powder as a source of antioxidants favors the restoration of the concentration of glutathione and reduces the damage caused by oxidative stress during nutritional recovery in rat brain.

Essential Amino Acid Supplementation Decreases Liver Damage Induced by Chronic Ethanol Consumption in Rats

The liver sustains the greatest damage from ethanol (EtOH) abuse. EtOH and its metabolites impair hepatocyte metabolism, causing intracellular accumulation of proteins and lipids and increasing radical oxygen species production. These processes are toxic to the mitochondrial respiratory chain and to mitochondrial DNA. We have recently shown that supplementating the diet of rodents with an essential amino acid-enriched mixture (EAAem) significantly increases mitochondrial mass and number in cardiac and skeletal muscles and improves mitochondrial function in aged animals. Thus, in this study we sought to test whether EAAem supplementation could reduce EtOH-induced liver damage. Groups of adult male Wistar rats were fed a standard diet and water ad libitum (the control group), drinking water with 20% EtOH (the EtOH group), or drinking water with 20% EtOH and EAAem supplementation (1.5 g/kg/day) (the EtOH+EAAem group) for 2 months. The blood EtOH concentration was measured, and markers for fat (Oil-Red-O), mitochondria (Grp75, Cyt-c-ox), endoplasmic reticulum (Grp78), and inflammation (Heme Oxigenase 1, iNOS, and peroxisomes) were analyzed in the liver of animals in the various experimental groups. EAAem supplementation in EtOH-drinking rats ameliorated EtOH-induced changes in liver structure by limiting steatosis, recruiting more mitochondria and peroxisomes mainly to perivenous hepatocytes, stimulating or restoring antioxidant markers, limiting the expression of inflammatory processes, and reducing ER stress. Taken together, these results suggest that EAAem supplementation may represent a promising strategy to prevent and treat EtOH-induced liver damage.

Maternal intake of flaxseed-based diet (Linum usitatissimum) on hippocampus fatty acid profile: implications for growth, locomotor activity and spatial memory

OBJECTIVE

To investigate flaxseed as a partial source of protein and an exclusive source of lipids and fibers in the development of the central nervous system by analyzing hippocampal fatty acid composition and cognitive and locomotor functions.

METHODS

Experimental diets were given to dams during preconception, pregnancy, and lactation and to their pups after weaning. Female Wistar rats were separated into three groups according to experimental diet: a control group (CG) and a flaxseed group (FG), fed ad libitum diets, and a modified control group (MCG), pair-fed with the FG. After weaning, the pups received their mothers' diets. After 30 d, eight males from each group were tested in a Morris water maze to assess learning, memory, and motor function.

RESULTS

The offspring of FG dams showed a lower body mass than CG dams, probably due to non-nutritional factors and an imbalance between ω-3 and ω-6 fatty acids of the seed, and displayed a higher concentration of α-linolenic acid, possibly suggesting inhibition of arachidonic acid synthesis. The content of docosahexaenoic acid in the hippocampus was higher in the FG followed by the MCG compared with the CG. Hippocampal docosahexaenoic acid content correlated with better spatial memory performance in the FG, whereas arachidonic acid content correlated with longer time in solving the task.

CONCLUSION

Flaxseed during perinatal and postweaning periods improves spatial memory to the detriment of growth. These findings indicate that there must be caution in encouraging the maternal intake of flaxseed during pregnancy and lactation.

Effects of maternal malnutrition and postnatal nutritional rehabilitation on brain fatty acids, learning, and memory

Undernutrition still affects mothers and children in developing countries and thus remains the major focus of nutritional intervention efforts. Neuronal development, which classically includes neurogenesis, migration, maturation, and synapse refinement, begins in utero and continues into the early postnatal period. These processes are not only genetically regulated but also clearly susceptible to environmental manipulation. Dietary deprivation during early life is known to have adverse effects on brain anatomy, physiology, and biochemistry, and may even lead to permanent brain damage. Although all nutrients are important for the structural development of the central nervous system, lipids such as long-chain polyunsaturated fatty acids, especially docosahexaenoic acid (22:6 n-3) and arachidonic acid (20:4 n-6), are important for normal brain development. The purpose of this literature review is to examine how early undernutrition involving a deficiency in long-chain polyunsaturated fatty acids can affect brain development and function and produce deficits in spatial cognitive learning ability.

Intensive care unit-acquired weakness (ICUAW) and muscle wasting in critically ill patients with severe sepsis and septic shock

Sepsis presents a major health care problem and remains one of the leading causes of death within the intensive care unit (ICU). Therapeutic approaches against severe sepsis and septic shock focus on early identification. Adequate source control, administration of antibiotics, preload optimization by fluid resuscitation and further hemodynamic stabilisation using vasopressors whenever appropriate are considered pivotal within the early-golden-hours of sepsis. However, organ dysfunction develops frequently in and represents a significant comorbidity of sepsis. A considerable amount of patients with sepsis will show signs of severe muscle wasting and/or ICU-acquired weakness (ICUAW), which describes a frequently observed complication in critically ill patients and refers to clinically weak ICU patients in whom there is no plausible aetiology other than critical illness. Some authors consider ICUAW as neuromuscular organ failure, caused by dysfunction of the motor unit, which consists of peripheral nerve, neuromuscular junction and skeletal muscle fibre. Electrophysiologic and/or biopsy studies facilitate further subclassification of ICUAW as critical illness myopathy, critical illness polyneuropathy or critical illness myoneuropathy, their combination. ICUAW may protract weaning from mechanical ventilation and impede rehabilitation measures, resulting in increased morbidity and mortality. This review provides an insight on the available literature on sepsis-mediated muscle wasting, ICUAW and their potential pathomechanisms.

Long-term effects of leucine supplementation on body composition

PURPOSE OF REVIEW

Leucine does not only serve as a substrate for protein synthesis but is also recognized as a potent signal nutrient that regulates protein metabolism. Accordingly, leucine supplementation has been suggested to develop muscle mass or prevent protein loss in several conditions characterized by muscle protein wasting. In the present review, we reported the recent results related to the effect of dietary leucine or leucine-rich amino acid mixture and proteins on whole body composition.

RECENT FINDINGS

Although recent studies corroborate that increasing plasma leucine concentration generally induces an increase in muscle protein synthesis, long-term dietary leucine supplementation has been poorly investigated. Chronic free leucine supplementation alone did not improve lean body or muscle mass during resistance training or in elderly, whereas it was able to limit the weight loss induced by malnutrition. Contradictory data were also reported concerning the effect of leucine supplementation for weight management in obese patients. Leucine-rich amino acid mixture or proteins appeared more efficient than leucine alone to improve muscle mass and performance, suggesting the efficacy of leucine depends nevertheless on the presence of other amino acids.

SUMMARY

Until now, there is no evidence that chronic leucine supplementation is efficient in promoting muscle mass or preventing protein loss during catabolic states. Further studies are required to determine the duration and nutritional conditions of long-term leucine supplementation and to establish whether such nutritional interventions can help to prevent or treat muscle loss in various pathological or physiological conditions.

Influência da desnutrição promovida pela dieta básica regional sobre o perfil de ácidos graxos do leite materno, o crescimento e o desenvolvimento de ratos jovens

OBJETIVO: Avaliar os efeitos do consumo da Dieta Básica Regional e da reabilitação nutricional, durante os períodos críticos de crescimento e desenvolvimento de ratos, sobre a evolução da sua massa corporal e tecidual, bem como o consumo alimentar de mães durante a gestação e lactação e de seus filhotes, machos e fêmeas, até 70 dias de vida. Adicionalmente, verificou-se o percentual dos ácidos graxos nas dietas experimentais e no leite materno. MÉTODOS: Foram utilizados ratos Wistar, de ambos os sexos. Após a constatação da prenhez, as ratas foram divididas em três grupos. 1) Grupo controle, animais alimentados com ração comercial durante o período de gestação e lactação (mães e filhotes) e, após o desmame, os filhotes até 70 dias de vida; 2) Grupo desnutrido, animais alimentados com ração Dieta Básica Regional durante o mesmo período descrito para o grupo controle e 3) Grupo recuperado, animais alimentados com ração Dieta Básica Regional durante o período de gestação e lactação e os filhotes, após o desmame, alimentados com ração comercial até 70 dias de vida. Os animais foram monitorados diariamente, aferindo-se a massa corporal e o consumo alimentar. Os filhotes com 70 dias de vida foram sacrificados por decapitação e o cérebro, o coração, o fígado e os rins foram retirados e pesados. Os animais receberam água e ração ad libitum e foram mantidos em biotério com temperatura e luminosidade controladas. Os testes estatísticos utilizados foram o teste t de Student, a Análise de Variância e o pós-teste de Bonferroni. RESULTADOS: Foram encontradas alterações importantes no percentual de ácidos graxos essenciais na Dieta Básica Regional, assim como no leite materno das mães desnutridas. O ganho de peso das mães desnutridas e de seus respectivos filhotes, tanto machos quanto fêmeas, foi menor que o de animais controle desde a lactação até o final do experimento. As fêmeas recuperadas apresentaram valores de massa corporal estatisticamente semelhantes aos do grupo controle, o que não foi observado nos filhotes machos do grupo recuperado. CONCLUSÃO: O comprometimento da massa corporal materna durante a lactação e o déficit na taxa de crescimento dos filhotes, machos e fêmeas, se deveram à ingestão da Dieta Básica Regional multideficiente. A diminuição dos teores de ácidos graxos específicos do leite materno poderia, ainda que não completamente, justificar o déficit de crescimento observado.

Dieta rica em proteína na redução do peso corporal

A proporção ideal dos macronutrientes em dietas de emagrecimento é atualmente bastante discutida. Existem evidências de que dietas com maior proporção de proteína aumentam a perda de peso e de gordura corporal e diminuem a perda de massa corporal magra durante o emagrecimento. Todavia, os mecanismos responsáveis por estes efeitos não estão totalmente esclarecidos. Além disso, existem poucas conclusões a respeito dos possíveis efeitos colaterais dessas dietas na função renal e no estado nutricional relativo ao cálcio. Assim, este artigo objetiva trazer informações atuais sobre os efeitos de dietas ricas em proteína na perda de peso e na composição corporal e dos mecanismos envolvidos, bem como seus efeitos na função renal e no estado nutricional relativo ao cálcio.

Reduction of hypothalamic protein tyrosine phosphatase improves insulin and leptin resistance in diet-induced obese rats

Protein tyrosine phosphatase (PTP1B) has been implicated in the negative regulation of insulin and leptin signaling. PTP1B knockout mice are hypersensitive to insulin and leptin and resistant to obesity when fed a high-fat diet. We investigated the role of hypothalamic PTP1B in the regulation of food intake, insulin and leptin actions and signaling in rats through selective decreases in PTP1B expression in discrete hypothalamic nuclei. We generated a selective, transient reduction in PTP1B by infusion of an antisense oligonucleotide designed to blunt the expression of PTP1B in rat hypothalamic areas surrounding the third ventricle in control and obese rats. The selective decrease in hypothalamic PTP1B resulted in decreased food intake, reduced body weight, reduced adiposity after high-fat feeding, improved leptin and insulin action and signaling in hypothalamus, and may also have a role in the improvement in glucose metabolism in diabetes-induced obese rats.

Effects of leucine and phenylalanine supplementation during intermittent periods of food restriction and refeeding in adult rats

Although many studies have shown that amino acid ingestion acutely stimulates protein anabolism, only few studies have investigated whether long-term supplementation promotes changes in body composition. We therefore tested the hypothesis that l-leucine (LEU) and l-phenylalanine (PHE) supplementation might have a positive impact on the body composition of rats submitted to intermittent periods of food restriction and refeeding (weight cycling or WC). The WC protocol comprised three cycles, each consisting of 1 week of 50% food restriction followed by 2 weeks of ad libitum ingestion. The groups submitted to WC ingested the control diet (WC-CON) or the diet supplemented with LEU+PHE (WC-AA). A pair-fed group receiving the control diet (PF-CON) was used as a reference for the effects of WC. Although food intake was the same in all groups, higher body weight and energy efficiency were observed in the WC-AA group compared to the PF-CON and WC-CON groups although not significantly in relation to the latter. These results were the consequence of a significant increase of lean body mass and body protein content in the WC-AA group compared to the PF-CON and WC-CON groups. The WC-CON and WC-AA groups presented 36.1% and 18.9% more body fat, respectively, than the PF-CON group but this difference was not significant. Neither fasting insulin nor glucose concentration nor postprandial insulin secretion was significantly affected by the supplemented diet. In conclusion, supplementation with LEU+PHE improved the body composition profile of rats submitted to WC, mainly by increasing lean body mass and body protein content.

Effects of leucine supplementation on the body composition and protein status of rats submitted to food restriction

OBJECTIVE

Acute administration of leucine has been shown to stimulate certain protein synthesis related anabolic processes. However, the effect of chronic leucine administration in a catabolic situation caused by food restriction (FR) has not been established. We therefore evaluated the effect of chronic leucine supplementation on the body composition and some indicators of protein nutritional status of rats submitted to FR.

METHODS

Adult male Wistar rats were submitted to 50% FR for 6 weeks. The control group received the AIN-93M diet and the leucine group received the same diet supplemented with 5.91 g L-leucine/kg ration. We then determined carcass chemical composition, serum leptin, albumin and total protein concentrations, and protein, DNA and RNA concentrations in gastrocnemius muscle and liver.

RESULTS

No difference in final body weight was observed between groups. However, the leucine group presented a lower amount of body fat (P < 0.05). Leptin concentration showed a directly proportional correlation with the amount of body fat (r = 0.88, P < 0.05), but no significant difference in serum leptin concentration was observed between groups (P = 0.08). Regarding protein nutritional status, liver protein concentration was higher in the leucine group (P < 0.05). In the gastrocnemius muscle, a higher RNA concentration (P < 0.05) and a tendency towards higher DNA concentration (P = 0.06) were observed in the leucine group.

CONCLUSION

The results indicate that low-dose leucine supplementation increases body fat loss and improves liver protein status and the capacity of muscle protein synthesis in rats submitted to FR.