Increased Amino Acid Catabolism Research Articles

Axenic Culture of Caenorhabditis elegans Alters Lysosomal/Proteasomal Balance and Increases Neuropeptide Expression.

Axenically cultured C. elegans show many characteristic traits of worms subjected to dietary restriction, such as slowed development, reduced fertility, and increased stress resistance. Hence, the term axenic dietary restriction (ADR) is often applied. ADR dramatically extends the worm lifespan compared to other DR regimens such as bacterial dilution. However, the underlying molecular mechanisms still remain unclear. The primary goal of this study is to comprehensively investigate transcriptional alterations that occur when worms are subjected to ADR and to estimate the molecular and physiological changes that may underlie ADR-induced longevity. One of the most enriched clusters of up-regulated genes under ADR conditions is linked to lysosomal activity, while proteasomal genes are significantly down-regulated. The up-regulation of genes specifically involved in amino acid metabolism is likely a response to the high peptide levels found in axenic culture medium. Genes related to the integrity and function of muscles and the extracellular matrix are also up-regulated. Consistent down-regulation of genes involved in DNA replication and repair may reflect the reduced fertility phenotype of ADR worms. Neuropeptide genes are found to be largely up-regulated, suggesting a possible involvement of neuroendocrinal signaling in ADR-induced longevity. In conclusion, axenically cultured worms seem to rely on increased amino acid catabolism, relocate protein breakdown from the cytosol to the lysosomes, and do not invest in DNA maintenance but rather retain muscle integrity and the extracellular matrix. All these changes may be coordinated by peptidergic signaling.

Postprandial Responses of Energy Substrates in Dogs Fed High Fat‐ vs High Protein‐Low Carbohydrate Ketogenic Foods Relative to a High Carbohydrate Food

ObjectiveReduction of dietary carbohydrate (CHO) can increase circulating ketone availability and may aid disease management including inflammatory bowel disease, cancer, diabetes and cognitive decline. Companion animal dogs are prone to all of these maladies. Postprandial to a mixed macronutrient meal, non‐esterified fatty acids (NEFA) and beta‐hydroxybutyrate (BHB) decrease. In contrast, both glucose and blood urea nitrogen (BUN) increase. Triglycerides (TG) comprise circulating fat energy after a fat‐containing meal although medium chain TG (MCT) are preferentially catabolized to ketones. The postprandial responses of dogs to habitual feeding of high fat versus high protein low CHO foods, relative to high CHO foods, is not known. Therefore, we compared fasting (0 hr) and 2‐0 hr delta values for BHB, NEFA, TG, glucose, BUN as markers of available energy for these foods in dogs.MethodsDogs housed in pairs, with daily group exercise in outdoor grassy runs. Dogs returned to the colony healthy after the study; no invasive procedures. Blood collections under approved protocols at 0 hours (immediately before a meal) and at 2 hours postprandial. Macronutrients (P/F/C; % energy) for the 3 foods: HiCHO (25/37/38); LoCHOprot (50/44/6); LoCHOfat (28/68/4). The LoCHOfat food further contained 22% of dietary fat energy as MCT. Prospective randomized crossover trial (2 groups, n = 18). HiCHO was the wash‐in food followed by LoCHOprot or LoCHOfat in randomized order (5 wk feeding each food). Foods analyzed according to AOAC methods. Energy substrates BHB, NEFA, TG, glucose and BUN measured by Cobas or enzymatic reaction. Individual diet differences by dependent samples t‐test, linear mixed modeling for overall diet effect. Significance at α = 0.05.ResultsAnalyzed ketogenic ratios of the foods: HiCHO (0.46), LoCHOprot (1.1), and LoCHOfat (1.7). At fasting, LoCHOprot and LoCHOfat elevated circulating BHB above HiCHO food with LoCHOfat BHB higher than LoCHOprot. Between 0‐2 hours postprandial, BHB decreased for HiCHO (‐23%) and increased more for LoCHOfat (+100%) than LoCHOprot (+33%). Fasting NEFA were higher in LoCHOprot than LoCHOfat, and not different otherwise. From 0‐2 hours postprandial all foods showed decreased NEFA: HiCHO (‐43%), LoCHOprot (‐57%), LoCHOfat (‐12%). Fasting glucose was not different between groups. From 0‐2 hours postprandial LoCHOprot (‐4%) and LoCHOfat (‐8%) showed decreased glucose while HiCHO was unchanged. Fasting TG levels were different between all foods with the LoCHOprot (‐45%) and LoCHOfat (‐37%) lower than HiCHO. From 0‐2 hours postprandial all dogs showed increased TG with all values different between groups: HiCHO (+135%), LoCHOprot (+356%), LoCHOfat (+591%). Fasting BUN was higher with LoCHOprot than either HiCHO (‐27%) or LoCHOfat (‐26%). From 0‐2 hours postprandial all dogs showed increased BUN with all changes different: HiCHO (+17%), LoCHOprot (+42%), LoCHOfat (+23%).ConclusionsThe LoCHOfat food increased postprandial availability of BHB, NEFA and TG energy while decreasing glucose energy. LoCHOprot primarily enhanced available energy from protein as shown by increased amino acid catabolism to BUN, with additional contributions from BHB, NEFA and TG. The HiCHO food presented only glucose and TG as energy postprandial. Together these data show that a moderate protein, high fat, low CHO food with added MCT can selectively apportion postprandial energy toward ketone and fats while decreasing availability of glucose.

Apoptotic and Proteolytic Attributes and Metabolomic Changes in Postmortem Muscles from Pigs Subjected to Post-Weaning Transport at Different Seasons

ObjectivesPost-weaning transport of pigs was commonly practiced in the swine industry, however, adversely impact animal growth and well-being due to concurrent stress from weaning and transport. Further, our recent study found that post-weaning transport may have long-term effects on final pork quality attributes in terms of inferior texture and water-holding capacity. Heat shock proteins (HSPs) are anti-apoptotic chaperone proteins, protecting against apoptosis under a variety of cell death stimuli including postmortem muscle conversion process. While a potential role of apoptosis in meat tenderization has been proposed, how early life stress influences apoptotic/proteolytic process and metabolism of postmortem muscles is largely unknown. Thus, the study objective was to evaluate apoptotic and proteolytic attributes and metabolomic changes in postmortem muscles of market weight pigs exposed to early life transport/weaning stress at two seasons.Materials and MethodsTwo repetitions of newly weaned pigs (N = 480) were transported for 12 h in a trailer truck during July 2016 (SUMMER) and April 2017 (SPRING) in north-central Indiana. Upon reaching market weight, 10 animals were randomly chosen from each season and slaughtered in January 2017 and September 2017, respectively. Pairs of longissimus dorsi and psoas major muscles from each carcass were separated at 1d and 7d postmortem. Proteolytic and apoptotic factors including desmin, troponin T, calpain 1, HSP27, and aβ-crystallin were quantified using Western-blot assays, and mitochondria membrane permeability (MMP) was evaluated. Metabolome profiles of 1d samples were analyzed using the GC-TOF-MS/MS platform. Multivariate analyses PCA and PLS-DA were used to determine changes of metabolites. Data were analyzed using PROC MIXED of SAS to compare the traits across season, muscle, and aging effects.ResultsPreviously, SUMMER pigs were reported showing decreased body weight, muscling, and fat deposition, as well as increased shear force and water loss during aging. In the present study, SPRING muscles exhibited increases in calpain 1 autolysis and structural protein degradation, coincided with accelerated apoptosis shown as higher MMP compared to the SUMMER counterparts (P < 0.05). Moreover, PCA and PLS-DA clustering indicated distinct metabolome profiles affected by season and muscle. Seasonal effect mainly altered lipid, glucose, and nitrogen metabolism. A group of 16C to 18C fatty acids were increased in SPRING, probably due to increased lipid anabolism during warm growing/finishing season. Changes of urea, ornithine, aspartic acid, and 5’methylthioadenosine suggested increased amino acid catabolism in SUMMER, corroborating the decreased lean and fat accretion. Seasonal changes of key metabolites related to stress response, including histidine, GABA, and ascorbic acid, suggested increased stress defense in SUMMER pigs, which implied the suppression of apoptotic and proteolytic activities.ConclusionTaken together, SUMMER pigs showed suppressed onset of apoptosis with compromised growth and meat quality, possibly due to alternations in seasonal metabolic response. This may in turn affect the proteolytic potential of early postmortem muscles. Further studies elucidating the involvement of apoptotic process in proteolytic activities in postmortem muscles should be warranted.

Apoptotic and Proteolytic Attributes and Metabolomic Changes in Postmortem Muscles from Pigs Subjected to Post-Weaning Transport at Different Seasons

ObjectivesPost-weaning transport of pigs was commonly practiced in the swine industry, however, adversely impact animal growth and well-being due to concurrent stress from weaning and transport. Further, our recent study found that post-weaning transport may have long-term effects on final pork quality attributes in terms of inferior texture and water-holding capacity. Heat shock proteins (HSPs) are anti-apoptotic chaperone proteins, protecting against apoptosis under a variety of cell death stimuli including postmortem muscle conversion process. While a potential role of apoptosis in meat tenderization has been proposed, how early life stress influences apoptotic/proteolytic process and metabolism of postmortem muscles is largely unknown. Thus, the study objective was to evaluate apoptotic and proteolytic attributes and metabolomic changes in postmortem muscles of market weight pigs exposed to early life transport/weaning stress at two seasons.Materials and MethodsTwo repetitions of newly weaned pigs (N = 480) were transported for 12 h in a trailer truck during July 2016 (SUMMER) and April 2017 (SPRING) in north-central Indiana. Upon reaching market weight, 10 animals were randomly chosen from each season and slaughtered in January 2017 and September 2017, respectively. Pairs of longissimus dorsi and psoas major muscles from each carcass were separated at 1d and 7d postmortem. Proteolytic and apoptotic factors including desmin, troponin T, calpain 1, HSP27, and aβ-crystallin were quantified using Western-blot assays, and mitochondria membrane permeability (MMP) was evaluated. Metabolome profiles of 1d samples were analyzed using the GC-TOF-MS/MS platform. Multivariate analyses PCA and PLS-DA were used to determine changes of metabolites. Data were analyzed using PROC MIXED of SAS to compare the traits across season, muscle, and aging effects.ResultsPreviously, SUMMER pigs were reported showing decreased body weight, muscling, and fat deposition, as well as increased shear force and water loss during aging. In the present study, SPRING muscles exhibited increases in calpain 1 autolysis and structural protein degradation, coincided with accelerated apoptosis shown as higher MMP compared to the SUMMER counterparts (P < 0.05). Moreover, PCA and PLS-DA clustering indicated distinct metabolome profiles affected by season and muscle. Seasonal effect mainly altered lipid, glucose, and nitrogen metabolism. A group of 16C to 18C fatty acids were increased in SPRING, probably due to increased lipid anabolism during warm growing/finishing season. Changes of urea, ornithine, aspartic acid, and 5’methylthioadenosine suggested increased amino acid catabolism in SUMMER, corroborating the decreased lean and fat accretion. Seasonal changes of key metabolites related to stress response, including histidine, GABA, and ascorbic acid, suggested increased stress defense in SUMMER pigs, which implied the suppression of apoptotic and proteolytic activities.ConclusionTaken together, SUMMER pigs showed suppressed onset of apoptosis with compromised growth and meat quality, possibly due to alternations in seasonal metabolic response. This may in turn affect the proteolytic potential of early postmortem muscles. Further studies elucidating the involvement of apoptotic process in proteolytic activities in postmortem muscles should be warranted.

Untargeted metabolic profiling reveals distinct patterns of thermal sensitivity in two related notothenioids

Antarctic marine ectothermal animals may be affected more than temperate species by rising temperatures due to ongoing climate change. Their specialisation on stable cold temperatures makes them vulnerable to even small degrees of warming. Thus, addressing the impacts of warming on Antarctic organisms and identifying their potentially limited capacities to respond is of interest.The objective of the study was to determine changes in metabolite profiles related to temperature acclimation. In a long-term experiment adult fish of two Antarctic sister species Notothenia rossii and Notothenia coriiceps were acclimated to 0°C and 5°C for three months. Impacts and indicators of acclimation at the cellular level were determined from metabolite profiles quantified in gill tissue extracts using nuclear magnetic resonance (NMR) spectroscopy. Furthermore, the metabolite profiles of the two con-generic species were compared.NMR spectroscopy identified 37 metabolites that were present in each sample, but varied in their absolute concentration between species and between treatments. A decrease in amino acid levels indicated an increased amino acid catabolism after incubation to 5°C. In addition, long term warming initiated shifts in organic osmolyte concentrations and modified membrane structure observed by altered levels of phospholipid compounds. Differences in the metabolite profile between the two notothenioid species can be related to their divergent lifestyles, especially their different rates of motor activity. Increased levels of the Krebs cycle intermediate succinate and a higher reduction of amino acid concentrations in warm-acclimated N. rossii showed that N. rossii is more affected by warming than N. coriiceps.

The dietary protein paradox and threonine 15 N-depletion: Pyridoxal-5'-phosphate enzyme activity as a mechanism for the δ15 N trophic level effect.

Nitrogen stable isotope ratios (δ15 N values) are used to reconstruct dietary patterns, but the biochemical mechanism(s) responsible for the diet to tissue trophic level effect and its variability are not fully understood. Here δ15 N amino acid (AA) values and physiological measurements (nitrogen intake, plasma albumin concentrations, liver-reduced glutathione concentrations and leucine oxidation rates) are used to investigate increased dietary protein consumption and oxidative stress (vitamin E deficiency) in rat total plasma protein. Using gas chromatography/combustion/isotope ratio mass spectrometry, the δ15 N values from N-pivaloyl-i-propyl esters of 15 AAs are reported for rats (n=40) fed casein-based diets with: adequate protein (AP, 13.8%; n=10), medium protein (MP, 25.7%; n=10), high protein (HP, 51.3%; n=10) or HP without vitamin E (HP-E; n=10) for 18weeks. Between the HP and AP groups, the δ15 NAA values of threonine (-4.0‰), serine (+1.4‰) and glycine (+1.2‰) display the largest differences and show significant correlations with: nitrogen intake, plasma albumin concentrations, liver-reduced glutathione concentrations and leucine oxidation rates. This indicates increased AA catabolism by the dietary induction of shared common metabolic pathways involving the enzymes threonine ammonia-lyase (EC 4.3.1.19), serine hydroxymethyltransferase (EC 2.1.2.1) and the glycine cleavage system (EC 2.1.2.10). The δ15 NAA values of the HP-E and HP groups were not found to be significantly different. The 15 N-depleted results of threonine are linked to increased activity of threonine ammonia-lyase, and show potential as a possible biomarker for protein intake and/or gluconeogenesis. We hypothesize that the inverse nitrogen equilibrium isotope effects of Schiff base formation, between AAs and pyridoxal-5'-phosphate cofactor enzymes, play a key role in the bioaccumulation and depletion of 15 N in the biomolecules of living organisms and contributes to the variability in the nitrogen trophic level effect. Copyright © 2017 John Wiley & Sons, Ltd.

Amino Acid Catabolism in Alzheimer's Disease Brain: Friend or Foe?

There is a dire need to discover new targets for Alzheimer's disease (AD) drug development. Decreased neuronal glucose metabolism that occurs in AD brain could play a central role in disease progression. Little is known about the compensatory neuronal changes that occur to attempt to maintain energy homeostasis. In this review using the PubMed literature database, we summarize evidence that amino acid oxidation can temporarily compensate for the decreased glucose metabolism, but eventually altered amino acid and amino acid catabolite levels likely lead to toxicities contributing to AD progression. Because amino acids are involved in so many cellular metabolic and signaling pathways, the effects of altered amino acid metabolism in AD brain are far-reaching. Possible pathological results from changes in the levels of several important amino acids are discussed. Urea cycle function may be induced in endothelial cells of AD patient brains, possibly to remove excess ammonia produced from increased amino acid catabolism. Studying AD from a metabolic perspective provides new insights into AD pathogenesis and may lead to the discovery of dietary metabolite supplements that can partially compensate for alterations of enzymatic function to delay AD or alleviate some of the suffering caused by the disease.

A holistic view of dietary carbohydrate utilization in lobster: digestion, postprandial nutrient flux, and metabolism.

Crustaceans exhibit a remarkable variation in their feeding habits and food type, but most knowledge on carbohydrate digestion and utilization in this group has come from research on few species. The aim of this study was to make an integrative analysis of dietary carbohydrate utilization in the spiny lobster Panulirus argus. We used complementary methodologies such as different assessments of digestibility, activity measurements of digestive and metabolic enzymes, and post-feeding flux of nutrients and metabolites. Several carbohydrates were well digested by the lobster, but maize starch was less digestible than all other starches studied, and its inclusion in diet affected protein digestibility. Most intense hydrolysis of carbohydrates in the gastric chamber of lobster occurred between 2–6 h after ingestion and afterwards free glucose increased in hemolymph. The inclusion of wheat in diet produced a slow clearance of glucose from the gastric fluid and a gradual increase in hemolymph glucose. More intense hydrolysis of protein in the gastric chamber occurred 6–12 h after ingestion and then amino acids tended to increase in hemolymph. Triglyceride concentration in hemolymph rose earlier in wheat-fed lobsters than in lobsters fed other carbohydrates, but it decreased the most 24 h later. Analyses of metabolite levels and activities of different metabolic enzymes revealed that intermolt lobsters had a low capacity to store and use glycogen, although it was slightly higher in wheat-fed lobsters. Lobsters fed maize and rice diets increased amino acid catabolism, while wheat-fed lobsters exhibited higher utilization of fatty acids. Multivariate analysis confirmed that the type of carbohydrate ingested had a profound effect on overall metabolism. Although we found no evidence of a protein-sparing effect of dietary carbohydrate, differences in the kinetics of their digestion and absorption impacted lobster metabolism determining the fate of other nutrients.

Nitrogen Metabolism in Zucker Rats is Affected by Moderate Reduction, but not by Moderate Increase in Dietary Protein

Marked changes in the content of protein in the diet affects the rat's pattern of growth, but there is not any data on the effects to moderate changes. Here we used a genetically obese rat strain (Zucker) to examine the metabolic modifications induced to moderate changes in the content of protein of diets, doubling (high-protein (HP): 30%) or halving (low-protein (LP): 8%) the content of protein of reference diet (RD: 16%). Nitrogen, energy balances, and amino acid levels were determined in lean (L) and obese (O) animals after 30 days on each diet. Lean HP (LHP) animals showed higher energy efficiency and amino acid catabolism but maintained similar amino acid accrual rates to the lean RD (LRD) group. Conversely, the lean LP (LLP) group showed a lower growth rate, which was compensated by a relative increase in fat mass. Furthermore, these animals showed greater efficiency accruing amino acids. Obesity increased amino acid catabolism as a result of massive amino acid intake; however, obese rats maintained protein accretion rates, which, in the OHP group, implied a normalization of energy efficiency. Nonetheless, the obese OLP group showed the same protein accretion pattern as in lean animals (LLP). In the base of our data, concluded that the Zucker rats accommodate their metabolism to support moderates increases in the content of protein in the diet, but do not adjust in the same way to a 50% decrease in content of protein, as shown by an index of growth reduced, both in lean and obese rats.

Effects of Space Flight on the Expression of Liver Proteins in the Mouse

Raw data derived from mass spectroscopic (MS) analyses of formalin-fixed paraffin-embedded (FFPE) tissue sections of the essential metabolic organ, liver, allocated by the provider (Amgen) from mice subjected to 13 days of microgravity on NASA Flight STS-118 were analyzed by two different search engines, using shotgun proteomics. With the eight statistically significant readouts in hand, Ingenuity Pathway Analysis (IPA) was employed to visualize probable biologic pathway relationships among proteins that might be associated with alterations in liver biochemistry due to space flight. Most noteworthy was the finding of up-regulation of the first urea cycle enzyme carbamoylphosphate synthetase, consistent with increased amino acid catabolism resulting from gravitational changes, and/ or other stress associated with missions in space. Down-regulation of fructose-bisphosphate aldolase B, regucalcin, ribonuclease UK114, alpha enolase, glycine N-methyltransferase and S-adenosyl methionine synthetase isoform type-1 was observed. 60 kDa heat shock protein was elevated.

Metabolic profiling of PPARα −/− mice reveals defects in carnitine and amino acid homeostasis that are partially reversed by oral carnitine supplementation

Peroxisome proliferator-activated receptor-alpha (PPARalpha) is a master transcriptional regulator of beta-oxidation and a prominent target of hypolipidemic drugs. To gain deeper insights into the systemic consequences of impaired fat catabolism, we used quantitative, mass spectrometry-based metabolic profiling to investigate the fed-to-fasted transition in PPARalpha(+/+) and PPARalpha(-/-) mice. Compared to PPARalpha(+/+) animals, acylcarnitine profiles of PPARalpha(-/-) mice revealed 2- to 4-fold accumulation of long-chain species in the plasma, whereas short-chain species were reduced by as much as 69% in plasma, liver, and skeletal muscle. These results reflect a metabolic bottleneck downstream of carnitine palmitoyltransferase-1, a mitochondrial enzyme that catalyzes the first step in beta-oxidation. Organic and amino acid profiles of starved PPARalpha(-/-) mice suggested compromised citric acid cycle flux, enhanced urea cycle activity, and increased amino acid catabolism. PPARalpha(-/-) mice had 40-50% lower plasma and tissue levels of free carnitine, corresponding with diminished hepatic expression of genes involved in carnitine biosynthesis and transport. One week of oral carnitine supplementation conferred partial metabolic recovery in the PPARalpha(-/-) mice. In summary, comprehensive metabolic profiling revealed novel biomarkers of defective fat oxidation, while also highlighting the potential value of supplemental carnitine as a therapy and diagnostic tool for metabolic disorders.

Carbohydrate and amino acid metabolism in fasting and aestivating African lungfish ( Protopterus dolloi)

The potential importance of carbohydrates and amino acids as fuels during periods of fasting and aestivation in the African lungfish, Protopterus dolloi, were examined. No significant decreases in tissue glycogen levels were observed following 60 days of fasting or aestivation, suggesting lungfish may undergo ‘glycogen sparing’. Yet glycogenolysis may be important during aestivation based on the differing responses of two flux-generating enzymes of the glycolytic pathway, hexokinase (HK) and pyruvate kinase (PK). PK is required for glycogen breakdown whereas HK is not. HK activity is significantly down-regulated in the heart and gill tissues during aestivation, while PK activity is sustained. The significant negative correlation between the activity of HK and glucose levels in the heart of aestivating lungfish suggests HK may be regulated by glucose concentrations. There was no indication of anaerobic glycolytic flux during aestivation as lactate did not accumulate in any of the tissues examined, and no significant induction of lactate dehydrogenase (LDH) activity was observed. The increase in glutamate dehydrogenase (GDH) and aspartate aminotransferase (Asp-AT) activities in the liver of aestivating P. dolloi suggests some energy may be obtained via increased amino acid catabolism, leading to the generation of tricarboxylic acid (TCA) cycle intermediates. These findings indicate the importance of both carbohydrate and amino acid fuel stores during aestivation in a phylogenetically ancient, air-breathing fish.

Active ammonia transport and excretory nitrogen metabolism in the climbing perch,Anabas testudineus, during 4 days of emersion or 10 minutes of forced exercise on land

The climbing perch, Anabas testudineus, inhabits large rivers, canals, stagnant water bodies, swamps and estuaries, where it can be confronted with aerial exposure during the dry season. This study aimed to examine nitrogen excretion and metabolism in this fish during 4 days of emersion. Contrary to previous reports, A. testudineus does not possess a functional hepatic ornithineurea cycle because no carbamoyl phosphate synthetase I or III activity was detected in its liver. It was ammonotelic in water, and did not detoxify ammonia through increased urea synthesis during the 4 days of emersion. Unlike many air-breathing fishes reported elsewhere, A. testudineus could uniquely excrete ammonia during emersion at a rate similar to or higher than that of the immersed control. In spite of the fact that emersion had no significant effect on the daily ammonia excretion rate, tissue ammonia content increased significantly in the experimental fish. Thus, it can be concluded that 4 days of emersion caused an increase in ammonia production in A. testudineus, and probably because of this, a transient increase in the glutamine content in the brain occurred. Because there was a significant increase in the total essential free amino acid in the experimental fish after 2 days of emersion, it can be deduced that increased ammonia production during emersion was a result of increased amino acid catabolism and protein degradation. Our results provide evidence for the first time that A. testudineus was able to continually excrete ammonia in water containing 12 mmol l(-1) NH4Cl. During emersion, active ammonia excretion apparently occurred across the branchial and cutaneous surfaces, and ammonia concentrations in water samples collected from these surfaces increased to 20 mmol l(-1). It is probable that the capacities of air-breathing and active ammonia excretion facilitated the utilization of amino acids by A. testudineus as an energy source to support locomotor activity during emersion. As a result, it is capable of wandering long distance on land from one water body to another as reported in the literature.

Nitrogen metabolism and excretion in the aquatic chinese soft-shelled turtle,Pelodiscus sinensis, exposed to a progressive increase in ambient salinity

This study aimed to determine effects of 6-day progressive increase in salinity from 1 per thousand to 15 per thousand on nitrogen metabolism and excretion in the soft-shelled turtle, Pelodiscus sinensis. For turtles exposed to 15 per thousand water on day 6, the plasma osmolality and concentrations of Na+, Cl- and urea increased significantly, which presumably decreased the osmotic loss of water. Simultaneously, there were significant increases in contents of urea, certain free amino acids (FAAs) and water-soluble proteins that were involved in cell volume regulation in various tissues. There was an apparent increase in proteolysis, releasing FAAs as osmolytes. In addition, there might be an increase in catabolism of certain amino acids, producing more ammonia. The excess ammonia was retained as indicated by a significant decrease in the rate of ammonia excretion on day 4 in 15 per thousand water, and a major portion of it was converted to urea. The rate of urea synthesis increased 1.4-fold during the 6-day period, although the capacity of the hepatic ornithine urea cycle remained unchanged. Urea was retained for osmoregulation because there was a significant decrease in urea excretion on day 4. Increased protein degradation and urea synthesis implies greater metabolic demands, and indeed turtles exposed to 15 per thousand water had significantly higher O2 consumption rate than the freshwater (FW) control. When turtles were returned from 15 per thousand water to FW on day 7, there were significant increases in ammonia (probably released through increased amino acid catabolism) and urea excretion, confirming that FAAs and urea were retained for osmoregulatory purposes in brackish water.

Histidine-Imbalanced Diets Stimulate Hepatic Histidase Gene Expression in Rats

A high protein concentration in the diet induces the gene expression of several amino acid degrading enzymes such as histidase (Hal) in rats. It is important to understand whether the amino acid pattern of the dietary protein affects the gene expression of these enzymes. The purpose of the present work was to study the effect of a histidine-imbalanced diet on the activity and mRNA concentration of rat hepatic histidase. Seven groups of six rats were fed one of the following diets: 1) 6% casein (basal), 2) 20% casein, 3) 35% casein, 4) an imbalance diet containing 6% casein plus a mixture of indispensable amino acids (IAA) equivalent to a 20% casein diet without histidine (I-20), 5) 6% casein plus a mixture of IAA equivalent to a 35% casein diet without histidine (I-35), 6) a corrected diet containing 6% casein plus IAA including histidine equivalent to a 20% casein diet, 7) a corrected diet containing 6% casein plus IAA including histidine equivalent to a 35% casein diet. Serum histidine concentration was inversely proportional to the protein content of the diet, and it was significantly higher in rats fed the corrected diets compared to their respective imbalanced diet groups. Hal activity increased as the protein content of the diet increased. Greater histidine imbalance resulted in lower food intake and higher Hal activity. Rats fed histidine-corrected diets had lower activity than their respective imbalanced groups. Differences in Hal activity were associated with differences in the concentration of Hal mRNA. These results indicate that rats fed a histidine-imbalanced diet exhibit reduced food intake and weight gain and increased Hal gene expression as a consequence of an increased amino acid catabolism.

Are dietary protein requirements altered in diabetes mellitus?

Authorities in the United States and Canada have recently advised persons with diabetes to limit their protein intake to the level recommended for normal adults, and consider further reductions in the presence of incipient renal disease. This recommendation ignores metabolic data indicating that conventional insulin therapy fails to fully normalize the abnormal protein metabolism characteristic of untreated diabetes. The residual abnormality is an increased or poorly regulated rate of amino acid catabolism. It is proposed in this review that the large amount of protein in the customary diet compensates for this increased amino acid catabolism, and thus protects many diabetic individuals from protein malnutrition. If this is true, protein restriction to a level that still meets the requirement of an individual with normal insulin metabolism could be too little for someone with diabetes. The current assumption that the protein requirement in diabetes is equal to the value set for normal individuals should be reconsidered.

Protein depletion and energy retention in rats with ventromedial hypothalamic lesions.

The catabolic effect of bilateral lesions in the ventromedial are of the hypothalamus (VMH) was studied in nitrogen-balance experiments and compared with the effect of a sham-operation in control animals. A transitory (24 h) increase in urine nitrogen was found in the controls, while in the lesioned animals, a persistent increase was found as long as the animals were fed. Fasting (48 h) eliminated the difference in urea excretion between the groups. Food-dependent effects of the VMH lesion are suggested. The changes in body and organ composition of VMH-lesioned animals, kept for 4 months on a food intake close to normal, were studied. The massive increase of body lipids and marked decrease of body protein and water was primarily due to increased subcutaneous-and abdominal-fat, and reduced skeletal and skin protein. An almost normal composition of the liver and close to normal amounts of protein in the viscera demonstrate that at least some tissues in VMH animals are able to maintain a normal protein content. Hyperphagia as a means to counteract the increased amino acid catabolism and to sustain the lean body mass is discussed.

Plasma amino acid profiles, urea and ammonia —nitrogen in one- and eight-year-old ewes fed two levels of protein

The effect of age and dietary protein level on plasma amino acid, urea and ammonia concentrations were studied using one- and eigth-year-old ewes. A diet containing 10% crude protein was fed at individual maintenance levels to six ewes of each age in trial 1, followed by feeding a similar diet containing 20% crude protein in trial 1, tyrosine, valine, glutamic and aspartic acids were higher in the plasma of young ewes, while citrulline and serine were higher in the old ewes. In trial 2, isoleucine, tyrosine, methionine, alanine, leucine, valine, glutamic acid, phenylalanine, lysine and arginine were higher in young ewes, while citrulline was higher in the old animals, suggesting a differential age-related response to higher dietary protein. Total, essential, nonessential, the ratio of essential to nonessential and branched-chain amino acids did not differ by age in trial 1, while all these values except nonessential amino acids were higher in young ewes in trial 2. Plasma urea nitrogen was higher in old ewes in both trials. No age difference occured in plasma ammonia in trial 1, while old ewes had lower plasma ammonia in trial 2. The decreased plasma amino acid concentrations and elevated urea levels in old ewes at both levels of protein intake suggested increased amino acid catabolism, perhaps reflecting age differences in cellular amino acid metabolism.

Protein metabolism in rats with ventromedial hypothalamic lesions: dietary effects on nitrogen retention.

The protein metabolism of rats bearing bilateral lesions in the ventromedial area of hypothalamus (VMH) was studied in nitrogen balance experiments employing high protein and high fat diets. The catabolic effect of VMH destruction was to a great extent counterbalanced by increased protein intake. This indicates that increased amino acid catabolism, rather than impaired mechanisms for protein synthesis, is responsible for the poor nitrogen retention of VMH-lesioned rat fed normal amounts of protein. A trend of increasing nitrogen excretion with increasing dietary fat was found when the caloric intake of VMH-lesioned animals was elevated by substitution of dietary carbohydrates with fat. Persistent liponeogenesis in spite of the high fat intake, is suggested as a possible explanation for this observation.