Nitrogen and amino acid metabolism in adults with protein-calorie malnutrition

Undernutrition Disrupts Cecal Microbiota and Epithelium Interactions, Epithelial Metabolism, and Immune Responses in a Pregnant Sheep Model

Undernutrition may change cecal microbiota-epithelium interactions to influence cecal feed fermentation, nutrient absorption and metabolism, and immune function. Sixteen late-gestation Hu-sheep were randomly divided into control (normal feeding) and treatment (feed restriction) groups to establish an undernourished sheep model. Cecal digesta and epithelium were collected to analyze microbiota-host interactions based on 16S rRNA gene and transcriptome sequencing. Results showed that cecal weight and pH were decreased, volatile fatty acids and microbial proteins concentrations were increased, and epithelial morphology was changed upon undernutrition. Undernutrition reduced the diversity, richness, and evenness of cecal microbiota. The relative abundances of cecal genera involved in acetate production (Rikenellaceae dgA-11 gut group, Rikenellaceae RC9 gut group, and Ruminococcus) and negatively correlated with butyrate proportion (Clostridia vadinBB60 group_norank) were decreased, while genera related to butyrate (Oscillospiraceae_uncultured and Peptococcaceae_uncultured) and valerate (Peptococcaceae_uncultured) production were increased in undernourished ewes. These findings were consistent with the decreased molar proportion of acetate and the increased molar proportions of butyrate and valerate. Undernutrition changed the overall transcriptional profile and substance transport and metabolism in cecal epithelium. Undernutrition suppressed extracellular matrix-receptor interaction and intracellular phosphatidyl inositol 3-kinase (PI3K) signaling pathway then disrupted biological processes in cecal epithelium. Moreover, undernutrition repressed phagosome antigen processing and presentation, cytokine-cytokine receptor interaction, and intestinal immune network. In conclusion, undernutrition affected cecal microbial diversity and composition and fermentation parameters, inhibited extracellular matrix-receptor interaction and the PI3K signaling pathway, and then disrupted epithelial proliferation and renewal and intestinal immune functions. Our findings exposed cecal microbiota-host interactions upon undernutrition and contribute to their further exploration. IMPORTANCE Undernutrition is commonly encountered in ruminant production, especially during pregnancy and lactation in females. Undernutrition not only induces metabolic diseases and threatens pregnant mothers' health, but also inhibits fetal growth and development, leading to weakness or even death of fetuses. Cecum works importantly in hindgut fermentation, providing volatile fatty acids and microbial proteins to the organism. Intestinal epithelial tissue plays a role in nutrient absorption and transport, barrier function, and immune function. However, little is known about cecal microbiota and epithelium interactions upon undernutrition. Our findings showed that undernutrition affected bacterial structures and functions, which changed fermentation parameters and energy regimens, and therefore affected the substance transport and metabolism in cecal epithelium. Extracellular matrix-receptor interactions were inhibited, which repressed cecal epithelial morphology and cecal weight via the PI3K signaling pathway and lowered immune response function upon undernutrition. These findings will help in further exploring microbe-host interactions.

The problem of nitrogen disposal in the obese

Amino-N is preserved because of the scarcity and nutritional importance of protein. Excretion requires its conversion to ammonia, later incorporated into urea. Under conditions of excess dietary energy, the body cannot easily dispose of the excess amino-N against the evolutively adapted schemes that prevent its wastage; thus ammonia and glutamine formation (and urea excretion) are decreased. High lipid (and energy) availability limits the utilisation of glucose, and high glucose spares the production of ammonium from amino acids, limiting the synthesis of glutamine and its utilisation by the intestine and kidney. The amino acid composition of the diet affects the production of ammonium depending on its composition and the individual amino acid catabolic pathways. Surplus amino acids enhance protein synthesis and growth, and the synthesis of non-protein-N-containing compounds. But these outlets are not enough; consequently, less-conventional mechanisms are activated, such as increased synthesis of NO∙ followed by higher nitrite (and nitrate) excretion and changes in the microbiota. There is also a significant production of N(2) gas, through unknown mechanisms. Health consequences of amino-N surplus are difficult to fathom because of the sparse data available, but it can be speculated that the effects may be negative, largely because the fundamental N homeostasis is stretched out of normalcy, forcing the N removal through pathways unprepared for that task. The unreliable results of hyperproteic diets, and part of the dysregulation found in the metabolic syndrome may be an unwanted consequence of this N disposal conflict.

Malnutrition and childhood epilepsy in developing countries

A high prevalence of epilepsy in children is frequently found in developing countries. Though high rates of acquired brain injury may contribute, the possibility that malnutrition may lower seizure threshold has rarely been examined. This review suggests potential biochemical mechanisms that could adversely affect seizure threshold, particularly the effect of malnutrition on inhibitory neurotransmitters and electrolytes. Supporting evidence from animal research and epidemiological findings in children are discussed.

The influence of nutrition on IGF-1 in tube-fed profoundly retarded adults

OBJECTIVE

This study was conducted to determine whether IGF-I concentrations are low in nonambulant profoundly retarded adults and to identify associated nutritional factors.

METHODS

Serum IGF-I, albumin, pre-albumin, creatinine, zinc (Zn) and plasma amino acids were measured before and after a four-week 25% increase in formula in 25 individuals, divided into those fed by day (Group A) or by night (Group B).

RESULTS

Circulating IGF-I was low in nine of the 22 subjects (40.9%) included in the analysis. Mean IGF-I increased 10.4% (p=0.004). Despite high intakes of essential amino acids and Zn, initial mean plasma tryptophan and phenylalanine were low, and serum Zn was low in 40.9% of subjects. Plasma tryptophan was low at both samplings and correlated with circulating IGF-I concentrations (p=0.02) at the beginning of the study. Serum IGF-I and Zn also correlated (p=0.02) initially.

CONCLUSIONS

IGF-I is commonly low in this population and is associated with low plasma amino acid and Zn concentrations, despite high intakes of these nutrients. The causes and clinical implications of these abnormalities need further study.

Peripheral plasma amino acid abnormalities in rehabilitation patients with severe brain injury

OBJECTIVE

Acute severe brain injury causes an increased mobilization of amino acids from tissue. The plasma amino acid profile of patients undergoing rehabilitation after brain injury is unknown. This study was aimed at delineating the plasma amino acid profile of rehabilitation patients with brain injury.

DESIGN

Peripheral plasma aminogram, lactate, pyruvate, glycerol, ketone body, and carnitine concentrations were determined in 11 patients with brain injury (34.6+/-15 years old, 60+/-16.8 days after injury) and in 8 controls. Resting energy expenditure and nitrogen balance were also determined.

RESULTS

(1) All essential amino acids and about 50% of nonessential amino acids were significantly lower in brain injury patients than in controls (p < .05). (2) Plasma amino acids were lower irrespective of either energy and protein intake or nitrogen balance. (3) Total carnitine concentration and esterified/free carnitine ratio were higher in brain injury patients than in controls (p < .05).

CONCLUSIONS

Rehabilitation patients with brain injury may have an important reduction of their plasma aminogram. Muscle tissue depletion and the persistence of a hypercatabolic state caused by subclinical infections, pressure sores, and immobility may contribute to this reduction.

Lactation during hibernation in wild black bears: effects on plasma amino acids and nitrogen metabolites

This study examined the seasonal and reproductive influences on individual plasma amino acid concentrations and nitrogen metabolites in a black bear population (Ontario, Canada). During hibernation, 11 of 23 plasma amino acids were significantly higher (13%-108%) in lactating than in nonlactating females, without an alteration in plasma total protein or total essential or nonessential amino acid levels. The greatest changes were observed in glutamine, arginine, and glycine levels. Plasma urea, urea/creatinine, and ammonia levels were significantly lower in hibernating compared with active female bears, but lactation had no effect on these parameters. Taken together these results show that lactation during hibernation is an additional metabolic challenge that results in increased mobilization of individual plasma amino acids and no accumulation of nitrogen end products, underlining the remarkable efficiency of amino acid and urea recycling in denning female black bears.

Plasma concentration of taurine is higher in malnourished than control children: differences between kwashiorkor and marasmus

Plasma free amino acids were determined in the plasma of severely malnourished children under two years of age. A total of thirty-one patients and eleven controls were evaluated: seventeen cases of kwashiorkor, eight cases of marasmus, and six cases of marasmic-kwashiorkor. Fasting plasma samples were taken in the morning on the day of admission. Fasting plasma samples were also taken from nine patients at discharge after two months in the hospital where they received a balanced diet as treatment. A partial reversal of the signs of malnutrition was observed at discharge. In the whole group of patients ad admission, lower concentrations of tyrosine, methionine, tryptophan, and leucine and higher concentrations of aspartate, glutamate, and taurine were observed compared to controls. Taurine continued to be elevated in the malnourished group at the time of discharge. Marasmic children, as compared to controls, had high aspartate and low tryptophan levels, but taurine levels were not significantly different from controls. Kwashiorkor patients had low tyrosine, methionine, tryptophan, and lysine, and significantly higher taurine plasma levels. The elevated concentration of taurine might be the result of a redistribution of this amino acid to provide specific tissues with the required amount for development.

Altered serum amino acid profiles in head and neck cancer

Patients who develop squamous cell carcinoma of the head and neck (SCCHN) are often malnourished because of poor dietary habits, excessive alcohol consumption, local tumor effects, tumor-induced cachexia, and the effects of various therapies. The composition of the diet may be a risk factor for the development of head and neck cancer as well as tumor progression. This study compares the amino acid profiles in the banked serum of patients with and without SCCHN. In comparison to the control group, patients with SCCHN had significantly decreased preoperative serum levels of alanine (p = 0.006), asparagine (p = 0.002), aspartic acid (p = 0.0001), glycine (p = 0.0002), histidine (p = 0.002), 3-methylhistidine (p = 0.001), ornithine (p = 0.001), phenylalanine (p = 0.002), serine (p = 0.002), taurine (p < 0.0001), and threonine (p = 0.001). Levels of cystine were significantly elevated in the group of cancer patients (p < 0.0001). No significant differences were noted on the basis of T stage, N stage, or nutritional status. Serum levels increased postoperatively for the majority of the amino acids tested. Postoperative histidine levels were associated with tumor recurrence (p = 0.04). Serum amino acid levels may prove to be useful markers of disease status and provide prognostic information.

Are leucine turnover measurements valid in the intravenously fed state?

We tested whether the primary or reciprocal pool models for whole-body leucine kinetics accurately depict human adaptation to protein deficiency and repletion in the fed state by comparing model-derived leucine oxidation with urea appearance calculated from urinary urea excretion and changes in the body urea pool. Five normal men consumed a control diet providing maintenance energy and 80 g protein/d for 5 days; this was followed by 7 days of an isoenergetic protein-free diet, and finally by a return to the original control diet for 5 days. At the end of each dietary period, urea appearance and leucine oxidation were measured during a 4-hour intravenous infusion of crystalline amino acids providing a total N to leucine N ratio similar to that in mixed body proteins. Primary pool-derived fed-state leucine oxidation decreased after adaptation to protein deficiency and remained low during refeeding (18.6 +/- 1.2, 13.2 +/- 1.1, and 15.0 +/- 1.8 mumol.kg-1.h-1, respectively, P < .01), in agreement with the physiologic prediction. A similar pattern occurred with the reciprocal pool model (24.4 +/- 2.7, 17.3 +/- 2.0, and 20.3 +/- 2.7 mumol.kg-1.h-1, P < .01) as well as with urea N appearance (3.06 +/- 0.32, 2.34 +/- 0.24, and 2.38 +/- 0.26 mmol N.kg-1.4 h-1, P < .05). Despite these relative agreements, absolute rates of whole-body amino acid oxidation were 25% (reciprocal pool model) to 43% (primary pool model) lower than when estimated from urea N appearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino acid profiles correlate diagnostically with organ site in three kinds of malignant tumors

The hypothesis that tumors arising in a particular organ site impose a characteristic plasma free amino acid (PFAA) pattern was tested by analyzing PFAA in fasting venous blood of preoperative patients with breast cancer, gastrointestinal tract cancer, and head and neck cancer. Healthy volunteers served as control subjects. Levels of 28 PFAA were determined in blood samples using an amino acid analyzer, and the data were compared using discriminant analysis and chi-square testing. Compared with control subjects, the concentrations of seven amino acids (glutamine, threonine, histidine, cysteine, alanine, arginine, and ornithine) in patients with tumors correlated closely with the known diagnoses. By means of discriminant analysis, these seven amino acids had the highest correlation with the specific diagnoses, indicating that PFAA profiles correlate diagnostically with the organ-site origin of three different kinds of malignant tumors.

Protein and energy substrate metabolism in AIDS patients

The objective of this study was to investigate protein and glucose metabolism in ambulatory, asymptomatic acquired immunodeficiency syndrome (AIDS) patients. Nine asymptomatic AIDS patients were compared against 13 controls. We measured whole-body protein synthesis (PSRM), breakdown (PBRM), and the fractional fibrinogen synthesis rate with 15N glycine, glucose cycling from the difference between the glucose appearance rates as measured with 2-d (Ra2-d)- and 6,6-d2 (Ra6,6-d)-labeled glucose. All of these parameters are increased with hypermetabolism and decreased with undernutrition. In addition, we also determined the plasma aminogram. The principal findings were (1) whole-body protein synthesis and breakdown and the fibrinogen fractional synthesis rate were significantly lower in the AIDS patients; (2) glucose cycling was markedly lower in the AIDS patients, and most of this effect was due to a decrease in Ra2-d; there was no difference in the endogenous glucose production rate, Ra6,6d; and (3) the plasma aminogram showed decreased total amino acids and a reduced ratio of essential to nonessential amino acids in the AIDS group. We concluded that the AIDS patients showed a starvation-type response. While the depressed protein synthesis and energy substrate cycling are not likely to be the primary cause of immunodeficiency, they may represent an important facilitating factors contributing to the decreased ability of the patient to respond effectively to opportunistic infections.

Amino acid profiles in tumor-bearing and pair-fed nontumor-bearing malnourished rats

To investigate the metabolic and organ changes accompanying growth of a malignant tumor, ten male Fisher 344 rats weighing 150 to 200 g were inoculated subcutaneously with 10(6) viable MCA sarcoma cells (tumor-bearing). Ten other rats (controls) were similarly inoculated with saline. Both groups were allowed food and water ad libitum. An additional ten rats (pair-fed) were inoculated with saline and fed the same mean daily food intake as the tumor-bearing rats. Thirty-five days after inoculation the rats were killed by exsanguination. Livers, spleens, and tumors were weighed, and amino acid profiles and biochemical parameters were measured. Liver and spleen weights in tumor-bearing rats were significantly greater than control rats (P less than 0.05 and P less than 0.01, respectively). Liver weight in pair-fed rats was significantly less than control rats (P less than 0.01), but spleen weight was greater (P less than 0.01). Amino acid profiles of tumor-bearing rats and pair-fed rats were different from each other and from those of control rats. Branched-chain amino acids were lowest in tumor-bearing rats and significantly different from control and pair-fed rats. Lysine was significantly higher (P less than 0.01) and arginine significantly lower (P less than 0.05) in tumor-bearing rats compared with control rats. These different plasma amino acid profiles and changes in serum biochemistry of cachectic tumor-bearing rats compared with malnourished pair-fed rats suggest specific tumor effects on host metabolism not mediated solely by anorexia.

Transport kinetics of amino acids across the resting human leg

Flux rates of amino acids were measured across the leg after an overnight fast in resting human volunteers. A balanced amino acid solution was, after a primed infusion, continuously infused for 2 h at each of three step-wise and increasing rates corresponding to 8.3, 16.7, 33.2 mg N/kg per h that were equivalent to 0.2, 0.4, 0.8 g N/kg per d. Flux of amino acids across the leg was compared with the flux of glucose, glycerol, lactate, free fatty acids, and oxygen. The size of the muscular tissue pool of amino acids was measured. Whole body amino acid oxidation was estimated by means of the continuous infusion of a 14C-labeled mixture of amino acids. Arterial steady state levels were obtained for most amino acids within 30 to 45 min after the primed constant infusion. Leg flux of amino acids switched from a net efflux after an overnight fast to a balanced flux between infusion rates corresponding to 0.2-0.4 g N/kg per d. At 0.8 g N/kg per d essentially all amino acids showed uptake. The infusion of amino acids stimulated leg uptake of glucose and lactate production and decreased FFA release. Oxygen uptake and leg blood flow increased significantly with increased infusion of amino acids. There was significant variability in transport rate among individual amino acids. Branched chain amino acids showed rapid transport and methionine slow transport rate. Only small changes in the muscle tissue concentration of certain amino acids were registered after 6 h of amino acid infusion despite uptake for several hours. When amino acids were infused at a rate corresponding to 0.8 g N/kg per d, the leg uptake of amino acids was 6% and the simultaneous whole body oxidation of infused amino acids was approximately 10%. Net uptake of leucine across the leg per hour was 62% of the muscle pool of free leucine when amino acids were infused at a rate corresponding to 0.4 g N/kg per d. Multiple regression analysis showed that the arterial concentration of an amino acid was the most important factor for uptake, more so than insulin concentration and blood flow. It is concluded that leg exchange of amino acids is large enough to rapidly change the pool size of the amino acids in skeletal muscle, if not counter-regulated by changes in rates of protein synthesis and degradation. Estimates of the capacity for protein synthesis and transfer RNA acceptor sites in muscles agree in order of magnitude with the net uptake of amino acids at high infusion rates of amino acids. Therefore, measurements of the balance of tyrosine, phenylalanine, and particularly methionine at steady state may reflect net balance of proteins across skeletal muscles even in short-time experiments.

Plasma and erythrocyte amino acid concentrations in anorexia nervosa

Plasma and erythrocyte amino acid concentrations in seven female patients in the acute stage of anorexia nervosa were compared with values in the same subjects after refeeding, and with normal controls. We also compared these values with literature values from patients with protein-calorie malnutrition and prolonged starvation in an attempt to identify a biological indicator of severity and prognosis. Our data indicate: (1) Routine laboratory analyses that reflect protein status do not differentiate normal subjects from patients with anorexia nervosa. (2) The plasma aminogram in the acute stage of anorexia nervosa differs from normal, and differs from values reported for both protein malnutrition and prolonged starvation. (3) The Whitehead ratio clearly separates the acutely ill anorectic state from the treated state and from normal controls. (4) Both erythrocyte and plasma amino acid concentrations differ from normal in anorexia nervosa, but changes in erythrocyte concentrations are more obvious. (5) Erythrocyte glycine concentrations are unique, in that values were persistently elevated at all stages of illness in anorexia nervosa. (6) Erythrocyte-to-plasma amino acid ratios do not provide a biological index of severity and prognosis for patients with anorexia nervosa, in contrast to data reported for individuals with protein malnutrition.

Serum free amino acids of healthy males and pregnant women from Ethiopia

Several clinical, anthropometric and biochemical parameters have been used for the evaluation of the nutritional status and diagnosis of protein-energy malnutrition [1]. Analysis of the complete serum amino-acid spectrum by ion-exchange chromatography provides valuable information on the adequacy of protein intake and on the metabolic response to protein depletion in undernourished subjects. However, the serum aminogram is quite differently affected by acute or chronic starvation or the great variety of starchy but low-protein foods and further toxic factors (e.g. mycotoxins) leading to kwashiorkor. Thus, very complex alterations of the serum amino-acid spectrum had to be expected [5, 9] and stimulated the present investigation for reference purposes. We report the results of amino acid determinations in apparently healthy adult males and pregnant women taking the traditional Ethiopian diet. For want of a better evaluation of the specific nutritional influence, we also collected data on serum amino acids of healthy Ethiopians consuming an average European diet.

Cancer cachexia

Cancer cachexia is a complex syndrome that includes host tissue wasting, anorexia, asthenia, and abnormal host intermediary metabolism. It is present in approximately 50% of cancer patients during treatment and nearly 100% of treated cancer patients at death. Cachexia has a detrimental impact on cancer therapy. The central problem of cancer cachexia is that energy balance is not maintained, and the host has a relative hypophagia which results in host tissue wasting. The tumor by its nature and obligate growth can continue to consume glucose, amino acids, and lipids at the expense of the host. This produces abnormal host intermediary metabolism including elevated glucose production and recycling, decreased muscle protein synthesis, and increased muscle and fat breakdown. The exact mechanisms of cancer cachexia have been only partially elucidated. The identification of signal molecules like cachectin which mediate these changes may be on the horizon. Nutritional support can reverse some of the derangements seen with cachexia, and there is evidence that functional lean body mass or body cell mass can be restored in some (but not all) patients. However, nutritional support has not yet improved response to chemotherapy or radiation therapy, nor has it improved host tolerance of chemotherapy. It has improved operative mortality and morbidity in cachectic cancer patients undergoing major surgical procedures. Optimum host nutritional support appears to be dependent on high insulin concentrations in both humans and rats. Insulin and exercise may be methods to preserve host lean tissue and feed the host rather than the tumor. Future studies depend on better definition of tumor-bearing host metabolism, altering the relationship between neoplasm and host to preferentially feed the host, and making the neoplasm more susceptible to effective treatment.

Plasma arginine in cancer of the gastrointestinal tract: effect of surgical treatment

The concentration of 21 amino acids was measured in the venous plasma of 41 patients with cancer of the gastrointestinal tract who had lost weight, 12 patients who had lost a similar amount of weight from non-malignant, non-septic conditions (benign weight loss), 12 patients with cancer of the gastrointestinal tract who had not lost weight and 21 control patients. Sixteen patients with localised tumours were restudied eight and 12 weeks after successful removal of the primary growth. Six patients with pyloric stenosis (benign weight loss) were similarly studied for comparison after corrective surgery. The concentration of the amino acid arginine was significantly greater in patients with cancer both with weight loss (71.2 +/- 4.1 mumol/l mean +/- SEM) and without weight loss (66.8 +/- 4.1 mumol/l) when compared both with patients with benign weight loss (34.6 +/- 3.2 mumol/l) and with control patients (48.2 +/- 3.5 mumol/l) (p less than 0.05). In patients with cancer subjected to surgery the concentration of arginine (76.4 +/- 7.5 mumol/l) fell to normal levels eight weeks after operation and remained normal 12 weeks after surgery (48.6 +/- 4.4 mumol/l) (p less than 0.05). This was in contrast with the rise in plasma arginine in patients with pyloric stenosis after surgery, suggesting that the raised level of arginine was due to the presence of the primary tumour.

Fasting plasma amino acid levels in cancer patients

The concentration in plasma of 15 fasting amino acids were measured in 14 control volunteers and 55 cancer patients. In addition, 16 patients (7 with, 9 without total parenteral nutrition [TPN] ) with metastatic sarcoma had sequential amino acid profiles measured during 6 weeks of ablative chemotherapy. In four cancer patient groups (lymphoma, sarcoma, osteosarcoma and metastatic sarcoma) with no or minimal weight loss, most plasma amino acid levels were similar to controls. Proline levels were significantly reduced in the lymphoma and sarcoma patients. Esophageal cancer patients with 20% body weight loss had a marked reduction in total and individual amino acid levels (except branched chain amino acids) compared to controls and all others. The metastatic sarcoma patients who received parenteral nutrition had higher levels of plasma lysine and tyrosine during chemotherapy than controls; however, TPN failed to change the majority of amino acid levels. It appears that plasma amino acid levels except proline were well maintained in cancer patients without weight loss. Esophageal cancer patients with weight loss demonstrated marked reduction in all circulating amino acids except branched chain. Parenteral nutrition did not significantly alter the amino acid profile of cancer patients undergoing chemotherapy.

Changes in muscle and plasma amino acid metabolism in severe malnutrition — The influence of total parenteral nutrition

The concentrations of free amino acids in muscle and plasma were determined in nine female patients with severe anorexia nervosa before and after 3 to 5 weeks of total parenteral nutrition (TPN). The patients had lost 25 to 42% of their pre-morbid weight. During TPN their weight gain was around 2.5 kg/week. Initially total non-essential amino acids (NEAA) in muscle were decreased 30% compared to controls. The major part of this depletion was due to a 40% reduction in glutamine. After TPN the level of glutamine normalized. Alanine, being normal before TPN, decreased after TPN. Proline and several other non-essential amino acids in muscle were decreased before and after TPN. Total essential amino acids (EAA) in muscle were initially normal and were not significantly affected by TPN. Total NEAA in plasma were decreased at admission and normalized after TPN. Total EAA in plasma, however, were normal both before and after TPN. This study demonstrates that severely malnourished patients with anorexia nervosa have changes in amino acid patterns in both muscle and plasma. These changes were largely, though not completely, reversed after 3 to 5 weeks of TPN.

Plasma amino acids in rheumatoid arthritis

Plasma amino acid concentrations have been investigated in 12 female patients with rheumatoid arthritis (RA), who were hospitalized for two 14-day periods, one of which included 7 days of total fasting, whereas the other served as control period with normal food intake. All medical treatment was stopped on admission to the hospital. Plasma amino acid levels were repeatedly determined during both periods. Another group, consisting of 8 healthy volunteers, also underwent total fasting, for 6 days. The response to food deprivation with regard to plasma amino acid levels was compared with that in the RA patients. The results obtained from the control period were compared with those derived from age and sex matched healthy controls. RA disease was not characterized by a typical amino acid pattern. Major increases were seen in the concentrations of taurine, aspartate, glutamate, glycine, 1-methyl histidine, isoleucine and arginine. Rather smaller yet significant elevations could be observed in the levels of cystein, threonine, serine, citrulline, methionine and leucine. The only amino acid to show a lowered concentration was alpha-aminobutyrate. Most of the alterations induced by fasting were similar to those in healthy volunteers. An exception was the levels of taurine, which evidenced in RA patients a further increase during starvation, not observed in healthy volunteers, and valine which exhibited, a smaller increment than that apparent in healthy controls. The increase in sulphur-containing amino acids might be interpreted as a sign of an enhanced glutathione (GSH) catabolism, whereas the differing metabolic behaviour of branched chain amino acids (BCAA) suggests a specific reaction of valine in RA disease, similar to that in other catabolic diseases.

Cancer cachexia and protein metabolism

Metabolic abnormalities arising from malnutrition and malignancy are seen in patients with cancer cachexia. To discriminate between the effects of pure malnutrition and tumour-specific metabolic alterations, the kinetics of whole-body metabolism were determined in 7 untreated, malnourished cancer patients and in 11 patients with benign disease, also malnourished, by means of primed constant infusion of 15N-glycine. Patients in both groups received 500 kcal/day as 5% glucose solution without any nitrogen. Whole-body protein turnover was 32% and 35% higher in the cancer patients than in the non-cancer patients and starved normal subjects respectively. Similarly, the rate of protein synthesis was 35% and 54% higher in the cancer patients than in the non-cancer patients and starved normal subjects respectively. Our study supports the view that aberrations of host metabolism in patients with cancer cachexia are different from those in non-cancer patients suffering equivalent weight loss.

Serum amino acids in weight-losing patients with cancer and tuberculosis

A study of arterial and arterio-venous amino acid concentration differences across the forearm was performed in 19 weight-losing cancer (CWL) patients (9 with lung cancer and 10 with other types of cancer), 8 weight-losing patients with active pulmonary tuberculosis (TWL) and 10 normal controls. Arterial concentrations of many of the amino acids measured were found to be lower in CWL than in TWL patients. In addition, the data suggested a venous excess of amino acids in the CWL patients compared with TWL patients and controls. The increased release of alanine from forearm muscles in the CWL group, together with the low arterial glycogenic amino acid levels, supports the concept of enhanced gluconeogenesis in CWL patients. Low arterial amino acid levels and possible increased release of amino acids from forearm muscle in CWL patients implies enhanced proteolysis with increased central clearance or tumour sequestration of these amino acids, though decreased proteogenesis cannot be excluded in accounting for the venous excesses in this group. Hypocitrullinemia in lung cancer patients was marked, and possible mechanisms to account for this are discussed.

Effects of acute and chronic ethanol administration on amino acid metabolism in rabbit brain and blood

Acute administration of ethanol increased the cerebrocortical amino acids derived through the tricarboxylic acid cycle except for GABA and decreased the plasma alanine, valine, isoleucine, leucine, and phenylalanine whereas chronic administration of ethanol caused no significant changes in the cerebrocortical amino acids and increased the plasma glutamic acid, glutamine, glycine, and ornithine, with decreases in taurine and phenylalanine. Result of this experiment suggests that the CNS-depressant effect of ethanol is related to changes in the GABA system and increased uptake by the brain of the branched-chain amino acids while the development of tolerance to ethanol is associated with cellular adaptation in the CNS.

Peripheral amino acid levels in patients with cancer

Peripheral arterial and venous whole blood amino acid concentrations were determined in four groups of subjects after an overnight fast 1) normal people, 2) patients with cancer who had not lost body weight, 3) subjects with cancer who had lost more than 20% of body weight and 4) patients who had lost more than 20% of body weight from diminished intake due to cause other than cancer. Comparison of the arterial blood levels in the four groups showed that patients with cancer and weight loss had amino acid patterns different from patients who were malnourished for other reasons. Branched chain amino acids were normal in patients with malignant disease. Some gluconeogenic amino acids were reduced as in other subjects with weight loss but the characteristic rise in glycine seen with malnutrition was not present. Arterio venous differences in whole blood across the forearm showed no evidence of increase in venous excess in patients with progressive malignant disease, indicating no excessive protein catabolism in muscle tissue. The data are consistent with increased gluconeogenesis in malnourished cancer subjects, probably due to intrinsic change in hepatic metabolism.

Plasma alkaline ribonuclease (EC 3.1.4.22) and nitrogen retention in low-birth-weight infants

1. Nitrogen retention was determined by classical N balance techniques in fourteen rapidly growing low-birth-weight infants receiving 3 g protein/kg body-weight and during their 3rd week of life. This was compared with plasma free alkaline ribonuclease (EC 3.I.4.22; RNase) activity and other biochemical measurements of protein nutrition. 2. Plasma RNase showed a significant positive correlation with N retention and a corresponding negative correlation with urine urea-N. These results were unexpected and suggest a different relationship between RNase and N retention in infants compared with that found by other workers in children and adults. 3. The most likely explanation of this apparent anomaly is that in all instances high activities of plasma RNase are associated with a need to conserve N. In the infants studied this may indicate some measure of 'protein economy' and they could therefore benefit from a higher protein intake.

Hormone-fuel concentrations in anephric subjects. Effect of hemodialysis (with special reference to amino acids)

Arterial blood concentrations of insulin, glucagon, and various substrates were determined in six anephric subjects in the postabsorptive state and immediately after hemodialysis. Plasma glucose and serum insulin concentrations were normal, and declined during dialysis. Plasma glucagon was elevated and remained unchanged. There was moderate hypertriglyceridemia before dialysis, but this decreased significantly after administration of heparin just before the start of dialysis, and at the end of dialysis was lowered further into the normal range. Comparison of postabsorptive whole blood concentrations of amino acids with those in normal, healthy adults revealed striking differences. Glutamine, proline, citrulline, glycine and both 1- and 3-methyl-histidines were increased, while serine, glutamate, tyrosine, lysine, and branched-chain amino acids were decreased. The glycine/serine ratio was elevated to 300% and tyrosine/phenylalanine ratio was lowered to 60% of normal. To investigate the potential role of blood cells in amino acid transport, the distribution of individual amino acids in plasma and blood cell compartments was studied. Despite a markedly diminished blood cell mass (mean hematocrit, 20.6 +/- 1.4%), there was no significant decrease in the fraction of most amino acids present in the cell compartment, and this was explained by increases of several amino acids in cellular water. None were decreased. Furthermore, during dialysis, whole blood and plasma amino acids declined by approximately 30% and 40%, respectively, whereas no significant change was observed in the cell compartment. Alanine was the only amino acid whose concentration declined in the cells as well as in plasma. The results indicate (a) significant alterations in the concentrations of hormones and substrates in patients on chronic, intermittent hemodialysis; (b) removal of amino acids during hemodialysis, predominantly from the plasma compartment, with no significant change in cell content; and (c) a redistribution of amino acids in plasma and blood cell compartments with increased gradients of most of the amino acids per unit cell water, by mechanism(s) as yet undetermined.

Muscle nitrogen metabolism in chronic hepatic insufficiency

Whole blood arterio-venous (A-V) differences for ammonia (NH3) and amino acids were determined across the forearm in 14 patients with decompensated alcoholic cirrhosis and hyperammonemia. NH3 was extracted by the forearm in all patients; however, the fractional extraction of NH3 was significantly less in five individuals with gross muscle wasting (13.3% versus 25.3%). There was neither a significant uptake nor release of NH3 in normal control subjects. The arterial concentrations of 12 out of 20 amino acids were strikingly diminished in the patient group. In contrast to normal subjects, in whom the release of alanine exceeds that of glutamine, the A-V difference for glutamine in the patients was threefold greater than that for alanine. The A-V differences for all other amino acids were not significantly different from zero. The results suggest that (1) muscle plays an important role in disposing of NH3 in patients with hepatic insufficiency and (2) a major fraction of NH3 taken up by muscle is released as glutamine.

Dietary protein intake and dynamic aspects of whole body nitrogen metabolism in adult humans

The constant isotope-infusion method of Picou and Taylor-Roberts was used to study rates of total body protein synthesis and breakdown in adult subjects following acute changes in the level of dietary protein intake. Six healthy adults, four males and two females, were studied after adaptation to dietary protein intakes of 1.5 and 0.38 g of protein/kilogram body weight/day. Dietary periods were from 7 to 15 days duration. 15N-glycine was used as a tracer, and was administered orally for 60 hr at 3-hr intervals, or by continuous intravenous infusion for 48 hr. Results were similar for both routes of isotope administration for the comparison conducted at the higher protein intake. At the 1.5-g protein level the mean N flux was 28.2 mg nitrogen/kg/hr, with total body protein (N x 6.25) synthesis and breakdown rates being 3.0 g/kg/day and 2.7 g/kg/day, respectively. Reducing the protein intake to 0.38 g/kg/day caused an 8% decrease (p less than 0.05) in N flux, a 27% increase (p less than 0.005) in the rate of total body protein breakdown, and a 15% increase (p less than 0.05) in the rate of protein synthesis. Endogenous amino acids were reutilized more efficiently under these conditions. The findings are discussed in relation to the way in which adult subjects adapt to acute changes in dietary protein intake.

Interaction of glucocorticoid hormones with rat skeletal muscle: catabolic effects and hormone binding

The mechanism of action of glucocorticoid hormones on rat skeletal muscle was studied by following their effect on muscle weight, free amino acid content, activity of amino acid-metabolizing enzymes, and binding to cytoplasmic receptor proteins. A significant reduction of gastrocnemius muscle and body weight occurred following administration of cortisol, triamcinolone diacetate, and triamcinolone acetonide to adrenalectomized rats. Treatment with triamcinolone diacetate also reduced the level of several free amino acids and enhanced the activity of a myofibrillar protease in skeletal muscle. The hormone had, however, no effect on the activity of various enzymes involved in amino acid catabolism in muscle. In nephrosis, another condition of muscle wasting, the level of several muscle amino acids were also reduced to a lesser extent. Cortisol and triamcinolone acetonide, both of which induce muscle wasting, were found to bind to two distinct cytoplasmic proteins in muscle. Binding of the labeled hormones was followed at 0 C and could be observed in presence of a 1000-fold excess of the catabolically inactive steroid epicortisol. Binding of 3H-triamcinolone acetonide. In vitro competition experiments further suggest a correlation between steroid binding to the 3H-dexamethasone or 3H-triamcinolone acetonide site and their potency to induce muscle catabolism. It is concluded that skeletal muscle is a direct target organ for glucocorticoids, and that muscle responsiveness involves binding of the active hormones to cytoplasmic receptor sites.

Effects of brief starvation on muscle amino acid metabolism in nonobese man

A reduction in the release of substrate amino acids from skeletal muscle largely explains the decrease in gluconeogenesis characterizing prolonged starvation. Brief starvation is associated with an increase in gluconeogenesis, suggesting increased release of amino acids from muscle. In the present studies, accelerated amino acid release from skeletal muscle induced by brief starvation was sought to account for the accompanying augmentation of gluconeogenesis. To do this amino acid balance across forearm muscles was quantified in 15 postabsorptive (overnight fasted) subjects and in 7 subjects fasted for 60 h. Fasting significantly reduced basal insulin (11.3-7.5 muU/ml) and increased glucagon (116-134 pg/ml). Muscle release of the principal glycogenic amino acids increased. Alanine release increased 59.4%. The increase in release for all amino acids averaged 69.4% and was statistically significant for threonine, serine, glycine, alanine, alpha-aminobutyrate, methionine, tyrosine, and lysine. Thus, with brief starvation, muscle release of glycogenic amino acids increases strikingly. This contrasts with the reduction of amino acid release characterizing prolonged starvation. The adaptation of peripheral tissue metabolism to brief starvation is best explained by the decrease in insulin.

Insulin secretion and glucose tolerance in adults with protein-calorie malnutrition

Glucose tolerance, insulin secretion, and responses to arginine infusion were studied in 17 adults with severe protein-calorie malnutrition (PCM) in Calcutta, India. Patients were selected for the severity of their malnutrition and for absence of other diseases. After 2-4 mo of refeeding there was complete clinical recovery, and control studies were performed. Glucose tolerance, as assessed by intravenous glucose-tolerance test (IVGTT), was reduced in PCM. Insulin response, both to glucose and to arginine infusion, was clearly reduced. The K value of the IVGTT correlated well with the ratio of mean to basal serum insulin during the first 40 min of the test. Basal serum insulin was nearly unchanged in PCM as compared with after recovery, although one patient studied serially showed a temporary drop in basal insulin during the first week of refeeding. In PCM, plasma amino acid levels failed to fall in response to arginine-induced insulin secretion as they did in the control studies. It appears that insulin secretory response is severely reduced in PCM and that a degree of insulin resistance in relation to body weight is present. These changes result in diminished glucose tolerance and probably in a reduced rate of tissue utilization of amino acids. Such alterations may be of adaptive significance in chronic PCM.