Amino acid metabolism and the energetics of growth

Poly-pathways metabolomics for high-yielding cordycepin of Cordyceps militaris

Cordycepin is an important quality control marker in Cordyceps militaris. This study aimed to explain the metabolic mechanisms for high-yielding cordycepin of C. militaris. In this study, high-yielding strains of cordycepin were obtained by ultraviolet mutagenesis, and the polysaccharide and protein contents were also changed. In high-yielding strains, the protein content significantly increased, whereas the polysaccharide content decreased. Simultaneously, metabolic differences for high- and low-yielding cordycepin strains were detected by metabolomics. Metabolomics results showed that the relative content of most metabolites decreased in high-yielding cordycepin strains. Various metabolic pathways have been altered in high-yielding cordycepin strains, such as the citric acid cycle, purine metabolism, and pyrimidine metabolism, leading to an increase in cordycepin content. In addition, changes in metabolic poly-pathways related to polysaccharide and protein synthesis, such as galactose metabolism and amino acid metabolism, promoted an increase in cordycepin content. This study analyzes the high yield of cordycepin in C. militaris at the metabolic level and provides a theoretical basis for further increasing cordycepin content.

Metabolic Drivers of Invasion in Glioblastoma

Glioblastoma is a primary malignant brain tumor with a median survival under 2 years. The poor prognosis glioblastoma caries is largely due to cellular invasion, which enables escape from resection, and drives inevitable recurrence. While most studies to date have focused on pathways that enhance the invasiveness of tumor cells in the brain microenvironment as the primary driving forces behind GBM’s ability to invade adjacent tissues, more recent studies have identified a role for adaptations in cellular metabolism in GBM invasion. Metabolic reprogramming allows invasive cells to generate the energy necessary for colonizing surrounding brain tissue and adapt to new microenvironments with unique nutrient and oxygen availability. Historically, enhanced glycolysis, even in the presence of oxygen (the Warburg effect) has dominated glioblastoma research with respect to tumor metabolism. More recent global profiling experiments, however, have identified roles for lipid, amino acid, and nucleotide metabolism in tumor growth and invasion. A thorough understanding of the metabolic traits that define invasive GBM cells may provide novel therapeutic targets for this devastating disease. In this review, we focus on metabolic alterations that have been characterized in glioblastoma, the dynamic nature of tumor metabolism and how it is shaped by interaction with the brain microenvironment, and how metabolic reprogramming generates vulnerabilities that may be ripe for exploitation.

Nutritional regulation of the anabolic fate of amino acids within the liver in mammals: concepts arising from in vivo studies

At the crossroad between nutrient supply and requirements, the liver plays a central role in partitioning nitrogenous nutrients among tissues. The present review examines the utilisation of amino acids (AA) within the liver in various physiopathological states in mammals and how the fates of AA are regulated. AA uptake by the liver is generally driven by the net portal appearance of AA. This coordination is lost when demands by peripheral tissues is important (rapid growth or lactation), or when certain metabolic pathways within the liver become a priority (synthesis of acute-phase proteins). Data obtained in various species have shown that oxidation of AA and export protein synthesis usually responds to nutrient supply. Gluconeogenesis from AA is less dependent on hepatic delivery and the nature of nutrients supplied, and hormones like insulin are involved in the regulatory processes. Gluconeogenesis is regulated by nutritional factors very differently between mammals (glucose absorbed from the diet is important in single-stomached animals, while in carnivores, glucose from endogenous origin is key). The underlying mechanisms explaining how the liver adapts its AA utilisation to the body requirements are complex. The highly adaptable hepatic metabolism must be capable to deal with the various nutritional/physiological challenges that mammals have to face to maintain homeostasis. Whereas the liver responds generally to nutritional parameters in various physiological states occurring throughout life, other complex signalling pathways at systemic and tissue level (hormones, cytokines, nutrients, etc.) are involved additionally in specific physiological/nutritional states to prioritise certain metabolic pathways (pathological states or when nutritional requirements are uncovered).

Metabolic advantages of higher protein diets and benefits of dairy foods on weight management, glycemic regulation, and bone

The Inst. of Medicine and World Health Organization have determined that 0.8 to 0.83 g protein·kg(-1) ·d(-1) is the quantity of protein required to establish nitrogen balance in nearly all healthy individuals. However, consuming higher protein diets may be metabolically advantageous, particularly for overweight and obese adults attempting weight loss, and for physically active individuals such as athletes and military personnel. Studies have demonstrated that higher protein diets may spare lean body mass during weight loss, promote weight management, enhance glycemic regulation, and increase intestinal calcium absorption, which may result in long-term improvements in bone health. The extent to which higher protein diets are beneficial is largely attributed to the digestive and absorptive properties, and also to the essential amino acid (EAA) content of the protein. Proteins that are rapidly digested and absorbed likely contribute to the metabolic advantages conferred by consuming higher protein diets. The EAA profiles, as well as the digestive and absorptive properties of dairy proteins, such as whey protein and casein, are particularly advantageous because they facilitate a rapid, robust, and sustained delivery of EAAs to the periphery. This article reviews the scientific literature assessing metabolic advantages associated with higher protein diets on weight management, glycemic regulation, and bone, with emphasis given to studies evaluating the potential benefits associated with dairy.

Intestinal protein supply alters amino acid, but not glucose, metabolism by the sheep gastrointestinal tract

This study was intended to establish the extent which amino acids (AAs) and glucose are net metabolized by the gastrointestinal tract (GIT) of ruminant sheep when intestinal protein supply is varied. Wether sheep (n = 4, 33 +/- 2.0 kg) were fitted with catheters for measurement of net absorption by the mesenteric (MDV) and portal-drained (PDV) viscera and a catheter inserted into the duodenum for casein infusions. Sheep received a fixed amount of a basal diet that provided adequate metabolizable energy (10.9 MJ/d) but inadequate metabolizable protein (75 g/d) to support 300-g gain per day. Four levels of casein infusion [0 (water), 35, 70, and 105 g/d], each infused for 5.5 d, were assigned to sheep according to a 4 x 4 Latin square design. [methyl-(2)H(3)]leucine was infused (8 h) into the duodenum while [1-(13)C]leucine plus [6-(2)H(2)]glucose were infused (8 h) into a jugular vein. With the exception of glutamate and glutamine, net absorption of AAs increased linearly (P < 0.05, R(2) = 0.46-1.79 for MDV; P < 0.05, R(2) = 0.6-1.58 for PDV) with casein infusion rate. Net absorption by the PDV accounted for <100% of the additional supplies of leucine, valine, and isoleucine (0.6-0.66, P < 0.05) from casein infusion, whereas net absorption by the MDV accounted for 100% of the additional essential AA supply. Glucose absorption (negative) and utilization of arterial glucose supply by the GIT remained unchanged. There was a positive linear (P < 0.05) relation between transfer of plasma urea to the GIT and arterial urea concentration (MDV, P < 0.05, r = 0.90; PDV, P < 0.05, r = 0.93). The ruminant GIT appears to metabolize increasing amounts of the branched-chain AAs and certain nonessential AAs when the intestinal supply of protein is increased.

Weight loss without losing muscle mass in pre-obese and obese subjects induced by a high-soy-protein diet

OBJECTIVE

To determine change of weight, body composition, metabolic and hormonal parameters induced by different intervention protocols.

DESIGN

Randomized, controlled study including participants exhibiting a BMI between 27.5 and 35. Three different interventions containing lifestyle education (LE-G), or a substitutional diet containing a high-soy-protein low-fat diet with (SD/PA-G) or without (SD-G) a guided physical activity program.

SUBJECTS

A total of 90 subjects (mean weight 89.9 kg; mean BMI 31.5), randomly assigned to one of three treatment groups.

MEASUREMENTS

Change in body weight, fat mass and lean body mass measured with the Bod Pod device at baseline, 6 weeks and 6 months; change in metabolic and hormonal parameters.

RESULTS

In all, 83 subjects completed the 6-months study. BMI dropped highly significantly in all groups (LE-G: -2.2+/-1.43 kg/m(2); SD-G: -3.1+/-1.29 kg/m(2); SD/PA-G: -3.0+/-1.29 kg/m(2)). Subjects in the SD-G and in the SD/PA-G lost more weight during the 6-months study (-8.9+/-3.9; -8.9+/-3.9 kg) than did those in the LE-G (-6.2+/-4.2 kg), and had a greater decrease in fat mass (-8.8+/-4.27; -9.4+/-4.54 kg) than those in the LE-G (-6.6+/-4.59 kg). In contrast, no significant intraindividual or between-group changes in the fat-free mass were seen. In all groups, metabolic parameters showed an improvement in glycemic control and lipid profile.

CONCLUSIONS

Our data suggest that a high-soy-protein and low-fat diet can improve the body composition in overweight and obese people, losing fat but preserving muscle mass.

Dose-dependent effects of glutamate in pyridoxine-induced neuropathy

In order to explore the effects of glutamate in a pyridoxine megadose-induced neuropathy, rats were received glutamate either 0.5 or 1 g/kg/day orally with or without pyridoxine 0.8 g/kg/day intraperitoneally for 14 days. The animal's motor coordination, the muscle power and the thermal threshold were observed daily. The nerve conduction velocity was measured at day 0 and day 15 of the treatment. Glutamate either 0.5 or 1 g/kg/day appeared to have no effect on motor coordination, the nerve conduction velocity and the muscle power score compared with control. However, the thermal response latency was significantly decreased (from day 9) in animals treated with 1 g/kg/day glutamate. In pyridoxine-induced neuropathy rats, glutamate 0.5 g/kg/day significantly decreased the effects of pyridoxine on the sciatic nerve conduction velocity, the muscle power score and the motor coordination. Interestingly, glutamate at a dose of 1 g/kg/day worsened the neurotoxic effects cause by pyridoxine.

Enteral glutamine supplementation and morbidity in low birth weight infants

OBJECTIVE

To determine if glutamine-supplemented enteral nutrition decreased the incidence of nosocomial sepsis in neonates.

METHODS

In a multicenter (n = 20) clinical trial, we randomly allocated infants (n = 649) with birth weight between 500 and 1250 g, who were <7 days of age, and had no major anomalies to receive enteral glutamine supplementation (0.3 g/kg/day) or sterile water (placebo) for the first 28 days. The primary outcome variable was the number of infants who had blood culture-proven nosocomial sepsis between 7 days' and 36 weeks' postmenstrual age.

RESULTS

Infants were assigned to placebo (n = 335) or to glutamine supplementation (n = 314). Neonates assigned to glutamine were similar to those assigned placebo for demographic characteristics and nutritional support during the first week. There was no difference in the occurrence of culture-proven nosocomial sepsis (33.7% vs 30.9%) or suspected sepsis (51.6% vs 47.1%) between the placebo and glutamine groups; however, neonates treated with glutamine less often had gastrointestinal dysfunction (7.5% vs 2.5%, P <.01) and severe neurologic sequelae (15.1% vs 10.4%, P =.08).

CONCLUSIONS

At a dose of 0.3 g/kg/day, enteral glutamine does not appear to reduce nosocomial sepsis in premature neonates.

Glutamate in enteral nutrition: can glutamate replace glutamine in supplementation to enteral nutrition in burned rats?

BACKGROUND

Glutamine (GLN) plays many important roles for the enterocytes in health and disease, but no liquid enteral products contain GLN because of its instability. We hypothesized that glutamate (GLU) may replace GLN in supplementation to an enteral diet, and compared the metabolic effect of GLU and GLN on the gut to each other.

METHODS

Rats suffering from a 30% burn received an enteral diet containing 30% GLU (m/w to total amino acids; GLU group), 30% GLN (GLN group), or a standard amino acid formula (CTR group). After a 64-hour feeding period, the small intestine and the portal and arterial blood were harvested to observe portal and arterial amino acid levels, and glutaminase activity and glutathione in the jejunal mucosa. In another study, 3H uptake into the mucosal protein was examined after a massive dose injection of 3H-phenylalanine.

RESULTS

Alanine, a product of GLN or GLU catabolism, significantly increased in the portal blood of the GLU group compared with the GLN group. In the gut mucosa of the GLU group, 3H uptake into protein and total glutathione were higher than those of other two groups. GLN did not elevate the glutaminase activity. Arterial GLU levels increased in the GLU group, however remained within safety limits.

CONCLUSIONS

Enterally delivered GLU may be a preferable fuel for the enterocytes and enhance the mucosal protein synthesis. GLU probably can substitute for GLN in supplementation to an enteral diet regarding many roles GLN plays in the intestinal mucosa under stress situations.