Excretion Of Amino Acids Research Articles

Renal Transport of Endogenous Amino Acids

In the late neonatal period of male Wistar rats (10 days old) concentrations in plasma were higher for 5 of 24 amino acids compared to adult animals (2 months old): β-alanine, tyrosine, glycine, histidine, and the dipeptide anserine. The plasma concentrations of tryptophan, valine and leucine were lower in young than in adult rats. The renal clearances of amino acids were lower in young rats, both in relation to 1 g b.w. and related to 1 g kidney weight. In the latter case the differences became more distinct because the relative kidney weight was higher in young than in adult animals (1.17 ± 0.07 vs. 0.82 ± 0.03 g/l00 g b.w.) and significant age differences in renal water content did not exist. The apparently more effective tubular reabsorption capacity in young rats can be explained as follows: Because of the significantly lower GFR in 10-day-old rats compared with adults (0.46 ± 0.03 vs. 1.10 ± 0.09 ml/ min/1 g kidney), the glomerularly filtered load of amino acids is generally lower in young rats (exceptions: tyrosine glycine). Therefore, the amino acid transporting carrier systems are able to reabsorb the absolutely lower amounts of amino acids from the ultrafiltrate in immature animals. This hypothesis is supported if one relates the renal amino acid clearance to the clearance of inulin. In this way it is possible to show that there are absolutely no differences between both age groups indicating mature transport systems for endogenous amino acids as early as in 10-day-old rats. The urinary excretion of amino acids in young and adult animals was less than 1-5% of the filtered load and age differences were not significant.

Renal Transport of Endogenous Amino Acids

Repeated adminisatration of triiodothyronine (T<sub>3</sub>, 20 µg/l00 g b.w., once daily for 3 days) or dexamethasone (60 µg/l00 g b.w., once daily for 3 days) caused significant changes of amino acid plasma concentrations in young (10 days old) and adult rats (2 months old). After treatment with T<sub>3</sub>, in young animals concentrations of β-alanine, aspartic acid, glutamic acid, ornithine, asparagine, leucine, taurine, serine, alanine, and glutamine were enhanced, whereas those of tyrosine, arginine, and threonine were significantly diminished. In adult rats only slight changes occurred after both T<sub>3</sub> and dexamethasone. In the kidney, the reabsorbed fraction of amino acids was enhanced after both T<sub>3</sub> and dexamethasone treatment in young rats, whereas in adult rats the two hormones were without influence on tubular reabsorption of amino acids. Taken together, both different plasma concentrations of amino acids and changes in amounts of amino acids reabsorbed in the tubuli, in adult rats the fractional excretion of amino acids was nearly unchanged following hormone treatment (exception: significant increase in taurine clearance). But in young animals the fractional excretion was reduced in 15 of 22 amino acids after dexamethasone and in 12 of 23 amino acids after T<sub>3</sub> treatment, indicating stimulatory effects of both hormones on tubular amino acid carrier systems in immature animals.

High glycine supplemented casein diets and urinary excretion of amino acids.

High glycine supplemented casein diets and urinary excretion of amino acids.

Differential diagnosis of (inherited) amino acid metabolism or transport disorders

Disorders of amino acid metabolism or transport are most clearly expressed in urine. Nevertheless the interpretation of abnormalities in urinary amino acid excretion remains difficult. An increase or decrease of almost every amino acid in urine can be due to various etiology. To differentiate between primary and secondary aminoacido-pathies systematic laboratory investigation is necessary. Early diagnosis of disorders of amino acid metabolism or transport is very important, because most of them can be treated, leading to the prevention of (further) clinical abnormalities. In those disorders, which cannot be treated, early diagnosis in an index-patient may prevent the birth of other siblings by means of genetic counseling and prenatal diagnosis.Primary aminoacidopathies can be due to genetically determined transport disorders and enzyme deficiencies in amino acid metabolism or degradation. Secondary aminoacidopathies are the result of abnormal or deficient nutrition, intestinal dysfunction, organ pathology or other metabolic diseases like organic acidurias.A survey of amino acid metabolism and transport abnormalities will be given, illustrated with metabolic pathways and characteristic abnormal amino acid chromatograms.

Protein nitrogen, peptide nitrogen and free amino acid nitrogen in endogenous digesta nitrogen at the terminal ileum of the rat

AbstractThe proportions of endogenous protein nitrogen (N), peptide N and free amino acid N in digesta N from the distal ileum of the rat were determined immediately after collection or following storage frozen ( — 20°C and — 196°C). Eighteen growing rats were given a protein‐free diet for 6 days and then euthanased. Samples of digesta were then collected from the terminal 20 cm of ileum. The digesta samples were centrifuged and the supernate was ultrafiltered. Total nitrogen and total amino acids were determined in the precipitate plus retentate (MW> 10 000 Da) and ultrafiltrate (MW < 10 000 Da) fractions, and urea, creatinine, ammonium and free amino acids in the ultrafiltrate. The storage of digesta did not significantly affect the proportions of N‐containing substances in the precipitate plus retentate or ultrafiltrate excepting that ammonium levels in the latter fraction were significantly lower for digesta processed immediately. On average, 67% of the total digesta N was in the precipitate plus retentate fraction and 61% of the total N was protein N. Essential and non‐essential amino acid N comprised 26 and 36%, respectively, of total digesta N in the precipitate plus retentate. On average, the ultrafiltrate fraction contained 33% of the total digesta N, and the total digesta N contained 10.4, 10.6, 1, 1.5, 1.5 and 0.5 g kg−1 free amino acid N, peptide N, urea N, ammonium N and creatinine N, respectively. Nonamino N (urea N + ammonium N + creatinine N) contributed 4% of the total N in the whole digesta. The N from essential and non‐essential amino acids in the ultrafiltrate (free + peptide), expressed as percentages of the total N in the whole digesta, were 8 and 13 %, respectively. On average, 21 % of the total digesta N was present as free amino acid N and peptide N. These findings give support to the application of a proposed method for the determination of total endogenous ileal amino acid excretion under conditions of peptide alimentation.

The ileal digestibility of nitrogen and amino acids in meat and bone meals determined using a rat assay

The proximate and gross amino acid compositions of meat and bone meals from three rendering plants sampled five times throughout the killing season and from one plant sampled on four occasions, were determined. Apparent and true ileal nitrogen and amino acid digestibilities were determined using a rat assay on three of the samples from each plant. There was considerable between- and within-plant variation for most of the chemical components, in particular the amino acids. Mean apparent ileal nitrogen digestibility of the 12 samples was 0.64 with a range of 0.54–0.75. Ileal apparent amino acid digestibilities of the meals, with a few exceptions, showed a similar pattern to nitrogen digestibility. Regression equations derived for the prediction of apparent ileal amino acid digestibilities from apparent ileal nitrogen digestibility had residual standard errors of 0.04–0.10. Endogenous ileal nitrogen and amino acid excretions were determined following protein-free alimentation. The resultant overall mean differences between true and apparent ileal amino acid digestibility ranged from 0.019 (arginine) to 0.094 (threonine) and that for nitrogen digestibility was 0.046. The variable ileal digestible amino acid content of meat and bone meals emphasises the limitation of tabulated analytical values and the need for a routine relatively inexpensive assay if the meals are to be used efficiently as protein supplements in diet formulation.

INTRACELLULAR AND EXTRACELLULAR AMINO ACID POOLS OF THE MARINE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) GROWN ON UNENRICHED SEAWATER IN HIGH‐CELL‐DENSITY DIALYSIS CULTURE1

ABSTRACTThe consumption of inorganic macronutrients (NO3−+ NO2−, NH4+, and PO4−3) and the composition of intra‐ and extracellular dissolved free amino acid pools (IDFAA and EDFAA, respectively) were determined in continuous‐reservoir batch dialysis cultures of the marine diatom Phaeodactylum tricornutum Bohlin maintained on unenriched natural seawater as a growth medium. Nutrient diffusion (Nd), which equals the nutrient uptake of the culture, increased with the cell density and the age of the culture. A concentration of 6.77 × 107 cells · mL−1 was obtained in stationary phase, which coincided with the NO3−+ NO2− diffusion limit (Ndmax) of the dialysis apparatus. The Ndmax for NH4+ occurred much earlier, at the end of exponential growth, whereas Ndmax for PO4−3 was not attained during the growth cycle of the culture, even in early stationary phase. A significant depletion (77%) of the IDFAA pool during exponential phase was followed by a reestablishment–to approximately 60% of the initial level–of internal pools during linear and stationary growth phases. This recovery occurred during the illuminated portion of the photoperiod (12:12 h LD) and involved principally the amino acids GLN, GLU, β‐GLU, and ASN. The recovery of GLN and ASN levels was particularly significant, because the intracellular concentrations of these amino acids were higher at the end of the growth cycle than before. The EDFAA pool was generally dominated by the amino acids SER and GLY+THR; however, during active growth, ORN and LYS often constituted an important fraction. The EDFAA concentration increased until linear growth phase was reached, during which a higher concentration of total free amino acids was attained in darkness than under illumination. The EDFAA component diminished afterward, and in stationary phase this fraction returned to concentrations equivalent to those observed at the beginning of the growth cycle. The variations in EDFAA concentrations were expressed by a pronounced decrease in the cellular excretion of amino acids with increasing cell density. These cellular responses of Phaeodactylum tricornutum in dense culture, specifically the regulation of amino acid excretion and intracellular pool size, may affect the N‐conversion coefficient (YN). Consequently, by prolonging the linear phase of growth and reducing the concentration of autoinhibitory metabolites by diffusion, a markedly enhanced final cell density can be achieved in cultures grown on natural unenriched seawater.

Clinical and Laboratory Findings in the Oculocerebrorenal Syndrome of Lowe, with Special Reference to Growth and Renal Function

The oculocerebrorenal syndrome of Lowe is an X-linked disorder whose clinical manifestations include congenital cataracts, mental retardation, and renal tubular dysfunction. We investigated growth, renal function, and serum chemistry values in patients with the oculocerebrorenal syndrome to determine the natural history of the disorder and its heterogeneity with respect to these characteristics. Twenty-three patients with the oculocerebrorenal syndrome, ranging in age from 4 months to 31 years, were examined. Height was compared with bone age. Renal function was assessed by measurements of proteinuria, urinary volume, and fractional excretions of potassium, phosphate, carnitine, and amino acids. Creatinine clearance was determined as a measure of glomerular function. In the oculocerebrorenal syndrome, linear growth decreases after one year of age; bone age lies between chronologic age and height age. Renal dysfunction occurs in the first year of life, characterized by proteinuria (mean [+/- SD], 1.38 +/- 0.77 g of urinary protein per square meter of body-surface area per day; normal, less than or equal to 0.10), generalized aminoaciduria (mean, 686 +/- 505 mumol of urinary amino acid per kilogram of body weight per day; normal, 94 +/- 45), carnitine wasting (mean fractional excretion, 0.10 +/- 0.05; normal, 0.03 +/- 0.01), and phosphaturia progressing into the third decade. Urinary wasting of individual amino acids is milder than in cystinosis, and branched-chain amino acids are relatively spared. Reciprocal serum creatinine levels fall linearly with age, predicting renal failure in the fourth decade. Concentrations of the muscle enzymes creatine kinase, aspartate aminotransferase, and lactate dehydrogenase, as well as of total serum protein, serum alpha 2-globulin, and high-density lipoprotein cholesterol, are elevated. Renal glomerular deterioration is slowly progressive in the oculocerebrorenal syndrome. Renal tubular dysfunction begins early and persists; most patients require alkalinization therapy, and many benefit from supplemental potassium, phosphate, calcium, or carnitine. Serum enzyme elevations suggest muscle involvement in the oculocerebrorenal syndrome.

Changes in plasma and urinary amino acid levels during diabetic ketoacidosis in children

Plasma and urinary concentrations of different amino acids were investigated during diabetic ketoacidosis (DKA) and 12, 24, 72 hours after initiation of therapy. In DKA, plasma concentration of glutamic acid, aspartic acid, valine, leucine and isoleucine significantly increased while that of asparagine and glutamine decreased compared to levels in well-controlled diabetic patients. The urinary excretion of branchedchain amino acids, histidine, serine and threonine was elevated while those of glutamic acid, glutamine, glycine and taurine were reduced. Among the different amino acids, histidine excretion had the highest variability. A strong correlation was found between the urinary excretion of several amino acids and that of the β-2-microglobulin characterizing tubular dysfunction. Changes in the excretion of different amino acids reflect the altered metabolic state and renal function due to DKA.

Nitrogen, amino acid and starch absorption and endogenous nitrogen and amino acid excretion in chicks fed on diets containing maize as the sole source of protein

The endogenous fraction of nitrogen (N) and amino acid (AA) in the faeces (excreta N  N of uric acid) of maize-fed chicks was calculated to determine true absorption values from the apparent values. The diets contained magnesium ferrite as a marker and various levels of maize as the sole source of protein; an N-free diet of maize starch only was also tested. The true absorption values (N=0.77, AA=0.37–0.85) calculated from the slope of the regression line were higher than the apparent ones (N=0.67, AA=0.26–0.81). The eliminated endogenous fraction, which is represented by the intercept of the regression line, was lower than the values of N and AA determined in the faeces of the N-free diet. As a result, the so-called “true” N absorption values were too high (1.09–1.12). In a second experiment with only one dietary level of maize there was a large difference between the N and AA apparent absorption values if determined in the lower ileum (N=0.81, AA=0.57–0.88) or in the faeces (N=0.57, AA=0.22–0.79), pointing to an endogenous fraction which is greater in the faeces than in the lower ileum. The individual AA absorption values differed distinctly from one another in all cases and were not represented by the apparent and true N absorption values. The high values of starch absorption from maize are 0.997 (excreta) and 0.983 (lower ileum), emphasizing the difference for N and the variability in both apparent and true AA absorption values determined in the lower ileum or faeces.

Effects of Variation in Sodium Intake on Cystinuria

This study was designed to characterize the effect of urinary sodium excretion on amino acid excretion in cystinuria. We studied three homozygous patients with cystinuria at various levels of sodium intake ranging between 50 and 230 mmol/day. A reduction in sodium intake produced a marked decrease in rates of urinary cysteine excretion. The low-sodium diet also reduced the excretion of lysine but had no significant effect on the excretion of ornithine or arginine. We conclude that a dietary restriction of sodium may reduce the urinary excretion of cystine and can provide a simple and safe long-term approach to the treatment of cystinuria.

Endogenous amino acid flow at the terminal ileum of the rat determined under conditions of peptide alimentation

AbstractThe study aimed to determine endogenous ileal amino acid excretion in the growing rat fed an enzymically hydrolysed casein (EHC) based diet with subsequent treatment of the digesta using ultrafiltration technology. Comparison was made with endogenous excretions obtained from rats fed an EHC‐based or a protein‐free diet and without any treatment of the ileal digesta. Preliminary investigations were made to determine the filtration efficiency of the ultrafiltration devices and to examine three alternative prefiltration treatments, trichloroacetic acid (TCA) and perchloric acid (PCA) precipitation, and centrifugation (SPIN). In the preliminary work, 15 purified protein, peptide and amino acid solutions were ultrafiltered using a molecular weight (MW) exclusion limit of 10000 Da, and the recovery of nitrogen indicated an effective filtration (generally >90% separation) on nominal molecular weight. Further, fresh rat ileal digesta samples were treated with either TCA, PCA or SPIN. The resulting supernates were ultrafiltered and the fractions were analysed for nitrogen and amino acids. The precipitates contained 23, 57 and 41% of the total nitrogenous material for the TCA, PCA and SPIN treatments, respectively, indicating that PCA was the most effective precipitant. In the main study, twelve 100‐g male rats were fed either an EHC‐based diet or a protein‐free diet, and samples of ileal digesta were collected after slaughter. The digesta from the six EHC‐fed rats were ultrafiltered after centrifugation, and the high molecular weight fraction was added to the precipitate. Endogenous ileal amino acid flows were determined for the total digesta and for the digesta following the centrifugation plus ultrafiltration treatment. The endogenous amino acid flows were generally higher for the total digesta than for the digesta following centrifugation plus ultrafiltration and significantly so (P<0.05) for lysine, glutamin acid and proline. The protein‐free fed rats had significantly P<0·05) lower amino acid flows than those rats fed the EHC‐based diedt (ultrafiltration treatment), the greatest differences occurring for isoleucine, serine, glutamic acid, valine, leucine, alanine and threonine.

Abnormalities in Essential Amino Acids in Patients with Chronic Fatigue Syndrome

A laboratory study was performed comparing the patterns of urinary amino acid excretion in patients with chronic fatigue syndrome (CFS) with a control group of subjects without fatigue or allergy. Fifteen out of 21 patients in the CFS Group showed abnormal patterns with both reduced and increased excretion of some acids. In contrast, the control subjects showed only increased excretion of some acids, and a finding present in only four out of 20 subjects.

Effects of dietary protein levels on free amino acid and glutathione contents in the tissues of rainbow trout

1. Rainbow trout were fed the high protein and low protein diets for 15 days using casein as the protein source. Levels of free amino acid and glutathione in liver and muscle, and composition of excreted amino acids were determined. 2. The free amino acid level in the tissues was higher in the group of fish fed high protein diet than the group of fish fed low protein diet. 3. There was no significant difference in hepatic glutathione content between the high protein diet group and low protein diet group. However due to the difference in the liver sizes between the two groups, the total hepatic glutathione, when computed based on the total body weight, was appreciably higher in the high protein diet group. 4. The amount of amino acid excreted by the fish on the body weight base and the amino acid composition were very similar between the fish fed the high protein and the low protein diets.

Assessment of Protein Nutritional Status

An evaluation of protein status can be approached by use of anthropometric, clinical, and biochemical data, either singly or in combination, and further aided with dietary data. Each of these approaches has advantages and limitations. Biochemical evaluation has the potential of being the most objective and quantitative. Indicators that have been or might be used include plasma hormone responses to reduced protein intake, plasma levels of specific proteins or specific amino acids, urinary excretion of specific amino acids and other nitrogen-containing compounds, anthropometric and physical measurements of body muscle mass, and functional tests of muscle strength. Several measurements can be combined to produce nutritional indices of broader potential value. The importance of concomitant infection and inflammation, with its many effects on protein metabolism, cannot be ignored in making these assessments. Unfortunately, no single test or group of tests can be recommended at this time as a routine and reliable indicator of protein status. Nonetheless, our increasing knowledge of the metabolism and functions of proteins, together with the recent use of noninvasive stable isotope techniques and of sophisticated physicochemical measurements, provides encouragement that more appropriate indicators are in the offing.

Renal effects of cadmium body burden of the general population

In a cross-sectional population study to assess whether environmental exposure to cadmium is associated with renal dysfunction, 1699 subjects aged 20-80 years were studied as a random sample of four areas of Belgium with varying degrees of cadmium pollution. After standardisation for several possible confounding factors, five variables (urinary excretion of retinolbinding protein, N-acetyl-β-glucosaminidase, β 2-microglobulin, aminoacids, and calcium) were significantly associated with the urinary excretion of cadmium (as a marker of cadmium body burden), suggesting the presence of tubular dysfunction. There was a 10% probability of values of these variables being abnormal when cadmium excretion exceeded 2-4 μg/24 h. Excretion reached this threshold in 10% of non-smokers. There was also evidence that diabetic patients may be more susceptible to the toxic effect of cadmium on the renal proximal tubule.

Protein Supplementation of Human Milk for the Nutrition of VLBW-Infants: Human milk protein vs. meat protein hydrolysate

In 25 very low birth weight infants appropriate for gestational age the influences of different human milk (HM) preparations on weight gain, gross indices of nitrogen metabolism and energy balance were studied during the second month of postnatal life. HM was fortified either by HM-protein (HMP) or by an enzymatic meat protein hydrolysate (PH) to protein concentrations between 1.5 and 1.7 g/100 ml. The caloric densities of both HM preparations were similar between 62 and 68 kcal/100 ml. There were no differences in weight gain (MM + HMP: 18.6 +/- 3.4 g/kg/day; HM + PH: 16.5 +/- 4.1 g/kg/day), nitrogen retention (HM + HMP: 31.5 +/- 3.1 mmol/kg/day; HM + PH: 30.0 +/- 3.2 mmol/kg/day), and the preprandial estimated essential amino acid profiles between the both feeding groups. In contrast the serum concentrations of alpha-amino-nitrogen 60 minutes postprandially were elevated in the infants fed HM + PH in comparison to the infants fed HM + HMP. This high postprandial amino acid concentrations in serum in the group fed HM + PH were accompanied by increased bile acids concentrations in serum, higher renal amino acid excretion and increased fecal fat losses. The results suggest that due to the more rapid intestinal absorption of amino acids from PH than from HMP the concentrations of amino acids increase postprandially which results in a detectable increase of the newborn cholestasis in these infants. Nevertheless, the scale of these metabolic responses to feeding protein hydrolysates is small and without detectable influences on nitrogen retention or weight gain.

Effect of N-benzyl-d-glucamine dithiocarbamate on renal toxicity induced by cadmium-metallothionein in rats

The effect of N-benzyl-D-glucamine dithiocarbamate (BGD) on the renal toxicity induced by acute exposure to cadmium-metallothionein (Cd-MT) in rats was studied. Rats were injected intraperitoneally with BGD (400 mumol/kg) 6, 12, or 24 h after intraperitoneal injection of Cd-MT (1.78 mumol Cd as Cd-MT/kg) and thereafter they received three injections of BGD (400 mumol/kg) daily for 3 days. Urinary protein concentration and aspartate aminotransferase (AST) activity significantly increased 1 day after Cd-MT treatment and decreased to control levels at 9 days after the treatment. Urinary excretion of glucose and amino acids rose gradually reaching maximum levels 5 days after Cd-MT treatment and returned to the control levels at 9 days. BGD injection significantly reduced the increases in the urinary excretion of protein, AST, glucose and amino acid, which were produced by Cd-MT treatment. Significant increases in urine volume were observed after Cd-MT treatment. BGD injection inhibited the increase in urine volume caused by Cd-MT treatment. A long time interval (12 and 24 h) between the administrations of Cd-MT and BGD resulted in a decreased protective effect of BGD against Cd-MT-induced renal damage. Following Cd-MT injection, the major route of excretion of cadmium (Cd) was via the urine and the kidney was the major site of accumulation of Cd. BGD injection remarkably increased the urinary excretion of Cd, resulting in a significant reduction in the kidney Cd concentration. The results of this study indicate that BGD injection is effective in decreasing the Cd concentration in the kidney, resulting in the protective effect on Cd-MT-induced renal damage.

Anabolic steroids in polytrauma patients. Influence on renal nitrogen and amino acid losses: a double‐blind study

Severe trauma leads to considerable losses of nitrogen in the first days after the accident. As nutritional efforts cannot reduce these losses sufficiently, an adjunctive therapy using the anabolic steroid nandrolone decanoate (Nd) was applied. In a double-blind study 10 male multiple-traumatized patients each received 50 mg of Nd on day 3 and 25 mg of Nd on day 6 after the trauma, an additional 10 patients received placebo only. Both groups had identical nutritional support. Nitrogen balance, total nitrogen excretion as well as plasma amino acid concentration, and urine amino acid excretion were measured daily. The anabolic agent improved the nitrogen balance mainly by reducing nitrogen excretion. 3-Methylhistidine excretion and renal amino acid losses were decreased. Nandrolone decanoate increased the concentration of total plasma amino acids. The underlying principle seems to be an amino acid-saving mechanism with a renal site of action. It is shown that in the early posttraumatic period nandrolone decanoate improves nitrogen metabolism. Further studies are required to determine whether this offers a clinical benefit to trauma patients.

Relationship Between Urinary Amino Acids and Diets in Spanish Cardiovascular Diseases and Alimentary Comparison Study

A randomized, cross-sectional study was carried out to examine dietary pattern and urinary amino acids excretion in two Spanish free-living populations. A total of 288 adults (50-54 years old; 50% men and 50% women), randomly selected from the census, took part in the study; of these, 146 were living in an urban district of Madrid and 142 in a rural area. Dietary intakes by 7-day recall questionnaires, smoking habits, and alcohol intake were examined in each participant, and 24-h urine was collected in aliquot cups designed for the Cardiovascular Diseases and Alimentary Comparison (CARDIAC) Study. All amino acid excretions averaged higher in men than in women in both areas, and higher in the urban than in the rural population. Main dietary differences between urban and rural populations were higher consumption of fish in urban than in rural populations and higher consumption of bread in rural than in urban populations. Urinary taurine excretion as well as 3-methylhistidine or histidine were significantly associated with fish and meat consumptions, respectively, estimated by 7-day dietary recall questionnaires.