Intestinal transport of cystine and cysteine in man: evidence for separate mechanisms

Cystine and Theanine as Stress-Reducing Amino Acids-Perioperative Use for Early Recovery after Surgical Stress

Perioperative nutritional therapy requires the consideration of metabolic changes, and it is desirable to reduce stress aiming at early metabolic normalization. Glutathione (GSH) is a tripeptide composed of glutamic acid, cysteine, and glycine. It is one of the strongest antioxidants in the body and important for adjusting immune function. Cystine and theanine (γ-glutamylethylamide) provide substrates of GSH, cysteine and glutamic acid, promoting the synthesis of GSH. It has been reported that the ingestion of cystine (700 mg) and theanine (280 mg) exhibits inhibitory effects against excess inflammation after strong exercise loads in athletes, based on which its application for invasive surgery has been tried. In patients undergoing gastrectomy, ingestion of cystine (700 mg) and theanine (280 mg) for 10 days from 5 days before surgery inhibited a postoperative increase in resting energy expenditure, promoted recovery from changes in interleukin-6, C-reactive protein, lymphocyte ratio, and granulocyte ratio and inhibited an increase in body temperature. In a mouse small intestine manipulation model, preoperative 5-day administration of cystine/theanine inhibited a postoperative decrease in GSH in the small intestine and promoted recovery from a decrease in behavior quantity. Based on the above, cystine/theanine reduces surgical stress, being useful for perioperative management as stress-reducing amino acids.

Adverse gastrointestinal effects of arginine and related amino acids

Oral supplements of arginine and citrulline increase local nitric oxide (NO) production in the small intestine and this may be harmful under certain circumstances. Gastrointestinal toxicity was therefore reviewed with respect to the intestinal physiology of arginine, citrulline, ornithine, and cystine (which shares the same transporter) and the many clinical trials of supplements of the dibasic amino acids or N-acetylcysteine (NAC). The human intestinal dibasic amino acid transport system has high affinity and low capacity. L-arginine (but not lysine, ornithine, or D-arginine) induces water and electrolyte secretion that is mediated by NO, which acts as an absorbagogue at low levels and as a secretagogue at high levels. The action of many laxatives is NO mediated and there are reports of diarrhea following oral administration of arginine or ornithine. The clinical data cover a wide span of arginine intakes from 3 g/d to>100 g/d, but the standard of reporting adverse effects (e.g. nausea, vomiting, and diarrhea) was variable. Single doses of 3-6 g rarely provoked side effects and healthy athletes appeared to be more susceptible than diabetic patients to gastrointestinal symptoms at individual doses>9 g. This may relate to an effect of disease on gastrointestinal motility and pharmacokinetics. Most side effects of arginine and NAC occurred at single doses of >9 g in adults (>140 mg/kg) often when part of a daily regime of approximately>30 g/d (>174 mmol/d). In the case of arginine, this compares with the laxative threshold of the nonabsorbed disaccharide alcohol, lactitol (74 g or 194 mmol). Adverse effects seemed dependent on the dosage regime and disappeared if divided doses were ingested (unlike lactitol). Large single doses of poorly absorbed amino acids seem to provoke diarrhea. More research is needed to refine dosage strategies that reduce this phenomenon. It is suggested that dipeptide forms of arginine may meet this criterion.

Excess dietary L-cysteine, but not L-cystine, is lethal for chicks but not for rats or pigs

A comparative species investigation of the relative pharmacologic effects of sulfur amino acids was conducted using young chicks, rats, and pigs. Ingestion of excess Met, Cys, or Cys-Cys supplemented at 2.5-, 5.0-, 7.5-, or 10 times the dietary requirement in a corn-soybean meal diet depressed chick growth to varying degrees. Strikingly, ingestion of excess Cys at 30 g/kg Cys (7.5-times the dietary requirement) caused a chick mortality rate of 50% after only 5 d of feeding. Growth was restored and chick mortality was reduced by supplementing diets containing 25 g/kg excess Cys with KHCO3 at 10 g/kg. Additionally, mortality was prevented by supplementing the drinking water of chicks receiving 25 g/kg supplemental Cys with H2O2 (0.05% final concentration). After young rats and pigs consumed excess Cys or Cys-Cys up to 40 g/kg for 14 d, weight gain was severely depressed, but we observed no mortality. An excess of dietary Cys-Cys>or=48 g/kg caused some mortality in rats. Pigs exhibited rapid recovery from growth-depressing excesses of Cys or Cys-Cys. These results lend credence to the acute toxic effects associated with the ingestion of excess sulfur amino acids and highlight the potential for excess dietary cyst(e)ine to be more pernicious than Met in certain species.

Expression of heteromeric amino acid transporters along the murine intestine

Members of the new heterodimeric amino acid transporter family are composed of two subunits, a catalytic multitransmembrane spanning protein (light chain) and a type II glycoprotein (heavy chain). These transporters function as exchangers and thereby extend the transmembrane amino acid transport selectivity to specific amino acids. The heavy chain rBAT associates with the light chain b degrees (,+)AT to form a cystine and cationic amino acid transporter. The other heavy chain, 4F2hc, can interact with seven different light chains to form various transporters corresponding to systems L, y(+)L, asc or x(-)(c). The importance of some of these transporters in intestinal and renal (re)absorption of amino acids is highlighted by the fact that mutations in either the rBAT or b degrees (,+)AT subunit result in cystinuria whereas a defect in the y(+)-LAT1 light chain causes lysinuric protein intolerance. Here we investigated the localization of these transporters in intestine since both diseases are also characterized by altered intestinal amino acid absorption. Real time PCR showed organ-specific expression patterns for all transporter subunit mRNAs along the intestine and Western blotting confirmed these findings on the protein level. Immunohistochemistry demonstrated basolateral coexpression of 4F2hc, LAT2 and y(+)-LAT1 in stomach and small intestine, whereas rBAT and b degrees (,+)AT were found colocalizing on the apical side of small intestine epithelium. In stomach, 4F2hc and LAT2 were localized in H(+)/K(+)-ATPase-expressing parietal cells. The abundant expression of several members of the heterodimeric transporter family along the murine small intestine suggests their involvement in amino acids absorption. Furthermore, strong expression of rBAT, b degrees (,+)AT and y(+)-LAT1 in the small intestine explains the reduced intestinal absorption of some amino acid in patients with cystinuria or lysinuric protein intolerance.

Comparison between SLC3A1 and SLC7A9 cystinuria patients and carriers: a need for a new classification

Recent developments in the genetics and physiology of cystinuria do not support the traditional classification, which is based on the excretion of cystine and dibasic amino acids in obligate heterozygotes. Mutations of only two genes (SLC3A1 and SLC7A9), identified by the International Cystinuria Consortium (ICC), have been found to be responsible for all three types of the disease. The ICC set up a multinational database and collected genetic and clinical data from 224 patients affected by cystinuria, 125 with full genotype definition. Amino acid urinary excretion patterns of 189 heterozygotes with genetic definition and of 83 healthy controls were also included. All SLC3A1 carriers and 14% of SLC7A9 carriers showed a normal amino acid urinary pattern (i.e., type I phenotype). The rest of the SLC7A9 carriers showed phenotype non-I (type III, 80.5%; type II, 5.5%). This makes the traditional classification imprecise. A new classification is needed: type A, due to two mutations of SLC3A1 (rBAT) on chromosome 2 (45.2% in our database); type B, due to two mutations of SLC7A9 on chromosome 19 (53.2% in this series); and a possible third type, AB (1.6%), with one mutation on each of the above-mentioned genes. Clinical data show that cystinuria is more severe in males than in females. The two types of cystinuria (A and B) had a similar outcome in this retrospective study, but the effect of the treatment could not be analyzed. Stone events do not correlate with amino acid urinary excretion. Renal function was clearly impaired in 17% of the patients.

Decreased uptake of L-cystine by duodenal brush border membrane vesicles from patients with cystinuria

BACKGROUND

The pathophysiology of cystinuria remains unclear. Decreased absorption of L-cystine across brush border membranes of small intestinal and renal proximal tubular epithelial cells is likely but has not been directly demonstrated.

AIMS

To compare the rates of L-cystine transport by isolated duodenal brush border membranes of normal individuals and patients with cystinuria.

METHODS

Distal duodenal biopsies were taken from normal individuals and patients with cystinuria. Brush border membrane vesicles (BBMV) were prepared using magnesium aggregation and differential centrifugation and the rates of L-cystine transport into the vesicles measured using a rapid filtration technique.

RESULTS

Rates of L-cystine transport by BBMV from patients with cystinuria were reduced at 5 minute (p = 0.003) and 30 minute (p = 0.053). Time points, indicating that L-cystine absorption across brush border membranes is abnormal in cystinuria.

Profiling of amino acids in body fluids and tissues by means of liquid chromatography

The needs of urgent diagnoses and the needs emerging from acute forms of diseases have directed progress in amino acid profiling to modern, rapid, automated analyses that can be done at reasonable cost. The first step in this direction was the short programmes of classical ion-exchange chromatography. At the beginning of this review we attempted to survey methods of sample preparation and sample treatment, as these are frequently neglected stages where artefacts or erroneous results may arise. There are basically the following approaches in amino acid profiling by liquid chromatographic techniques. For preliminary screening of a large number of samples in clinical routine planar procedures are the methods of choice, as they allow large numbers of samples to be handled with minimum effort and at very reasonable cost. For more precise profiling, particularly where quantitative data are essential, one can choose between some of the modern procedures for separating underivatized amino acids using modern equipment for cation-exchange chromatography, by making use of a stepped series of lithium citrate buffers with ninhydrin, o-phthalaldehyde or 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole detection. Ninhydrin detection is preferred in those situations where the demands on sensitivity are not high. Where, however, only small amounts of samples are available or high sensitivity is required, one of the latter two methods is preferred. The o-phthalaldehyde procedure is not suitable for the detection of secondary amines and, if these are of interest, then diazole derivatization is to be preferred. At present, however, the ninhydrin and o-phthalaldehyde detection procedures are the most popular. The other choice is to use one of the sophisticated HPLC systems equipped with fluorescence detection and to separate amino acids as derivatives. Here o-phthalaldehyde and 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole derivatives offer the most versatile possibilities. Automation and computerization have penetrated both categories of liquid column separation and are applied to automated sample delivery, automated and computerized gradient formation and quantitation of the data obtained. The tables of metabolic disorders of amino acids and the roles of different amino acids in these disorders should provide preliminary information for clinical chemists.

Blood and urinary amino acids in children receiving total parenteral nutrition

Plasma concentrations and urinary outputs of amino acids were estimated in nineteen patients receiving intravenous hyperalimentation to evaluate the adequacy of dosage and composition of the infusates for the maintenance of normal blood concentrations of essential amino acids. The use of high concentrations of branched chain amino acids seems to be appropriate for valine and isoleucine but not for leucine. The high concentration of cysteine in the infusates used induces a very high urinary excretion of cysteine and cystine and are ineffective to bring the decreased plasma cystine levels back to normal.

Cystine uptake by rat jejunal brushborder membrane vesicles

The presence of a sodium-stimulated, saturable uptake process for L-cystine is described in brushborder membrane vesicles isolated from rat jejunal mucosa. Concentration-dependence studies indicate the presence of a single transport system for cystine with Km = 0.053 mM and Vmax = 0.633 nmol/mg/15 s. Lysine completely inhibits the uptake of cystine.

Uptake of L-[35S]cystine by isolated rat brain capillaries

Adult rat brain capillaries were isolated by a simplified procedure and showed an enrichment of the marker enzyme, gamma-glutamyltranspeptidase. The uptake of [35S]cystine at 37 degrees C by this preparation can be divided into two components, a sodium- and energy-dependent transport process for the free amino acid pool, with an apparent Km of 36 microM, and a binding process, with an apparent Km of 1.13 mM. Chemical analysis of the amino acid pool indicates that cystine is the major from of intracapillary 35S. Cystine transport was not inhibited by lysine, but glycine, alpha-methylaminoisobutyric acid and beta-2-aminobicyclo-[2,2,1]-heptane-2-carboxylic acid were inhibitory to a small extent.

High-affinity uptake system for cysteine in crude synaptosomal fractions of rat cerebral cortex

The in vitro uptake of [35S] cysteine was studied in crude synaptosomal preparation of the cerebral cortex of rat. The accumulation of cysteine was found to be temperature- and time-dependent. It was linear at least for four minutes at 37 C with characteristics of saturable kinetics. Uptake of cysteine was Na+- and K+-dependent. Increasing the Na+ ion concentration increased the accumulation of cysteine in synaptosomal preparations; unlike the Na+ ion, an increase was accumulated against concentration gradients by a saturable mechanism. Double reciprocal plot of the cysteine uptake suggests two types of affinity systems, with Km values for the high-affinity uptake of about 12.2 microM and for the low-affinity uptake of about 4 mM. The high-affinity uptake was also significantly inhibited by ouabain, a potent inhibitor of the Na+-K+-dependent ATPase, and other metabolic inhibitors. The results of the effects of cysteine analogues and uptake also suggested that it is a substrate-specific high-affinity uptake system for cysteine.

Transport kinetics of D-glucose in human small intestinal mucosa: rate constants in histologically normal and abnormal mucosal biopsies

Using D-glucose as the probe molecule, we analysed conditions which must be fulfilled in mucosal biopsy studies before the kinetic nature of the transport process can be established. Mucosal biopsies were obtained from the region of the ligament of Treitz from four healthy volunteers and from 47 patients: 29 of the 47 had histologically normal mucosa; seven had mild abnormalities; and 11 had moderate or severe ("flat") abnormalities in villus architecture. The rate of uptake of 40 mM glucose was constant only between 4 and 10 min, extrapolating through zero uptake at zero time with a constant adherent mucosal fluid volume. Incubation for shorter or longer periods was associated with over- or underestimation of the rate of uptake. Failure to use a nonabsorbable marker was also associated with overestimation of the rate of uptake. When biopsies were incubated for 6 min, a curvilinear relationship was observed between uptake rate and concentration. In biopsies with moderate and severe abnormalities, there was a marked reduction in the magnitude of the maximal transport rate and the apparent passive permeability coefficient, with little change in the magnitude of the apparent affinity constant. When human mucosal biopsies are used to study nutrient absorption, certain criteria must be fulfilled to establish valid rate constants and to make comparisons between normal and abnormal mucosa.

Genetics of cystinuria in an inbred population

After the identification of 2 cystinurics in a large eastern Virginia isolate a population study was undertaken to identify carriers of the gene and others who could be affected by it. Of 102 individuals 3 additional homozygous cystinurics and 27 possible carriers were found. The cystinuria gene shows a highly variable expression, although all those affected and carriers could be traced to 1 couple who married about 1890. These studies demonstrate that there is considerable variation in urinary concentrations of cystine even in an affected population. No form of therapy should be based on random or isolated samples.

Prenatal diagnosis of cystinosis

Cystinosis was diagnosed in a small quantity of cultured amniotic cells from a 22-week-old fetus by a modified pulse-labeling technique in which intracellular 35SL-cystine retention was measured. As a result of the above finding, the pregnancy was terminated by administration of prostaglandin. The diagnosis was confirmed when the nonprotein-free cystine content of the kidney, liver, placenta, spleen, thymus, and gut, as well as that of a large amount of cultured amniotic cells, was found to be 100-fold higher than normal levels.

Transport of dibasic amino acids, cystine, and tryptophan by cultured human fibroblasts: absence of a defect in cystinuria and Hartnup disease

Transport of lysine, arginine, cystine, and tryptophan was studied in cultured skin fibroblasts from normal controls and from patients with cystinuria and Hartnup disease. Each of these amino acids was accumulated against concentration gradients by energy-dependent, saturable mechanisms. Lysine and arginine were each transported by two distinct processes which they shared with each other and with ornithine. In contrast, cystine was taken up by a different transport system with no demonstrable affinity for the dibasic amino acids. The time course and Michaelis-Menten kinetics of lysine and cystine uptake by cells from three cystinuric patients differed in no way from those found in control cells. Similarly, the characteristics of tryptophan uptake by cells from a child with Hartnup disease were identical to those noted in control cells. These findings indicate that the specific transport defects observed in gut and kidney in cystinuria and Hartnup disease are not expressed in cultured human fibroblasts, thus providing additional evidence of the important role that cellular differentiation plays in the regulation of expression of the human genome.

Biochemical and genetic studies in cystinuria: observations on double heterozygotes of genotype I-II

10 families with cystinuria were investigated by measuring: (a) quantitative 24 hr urinary excretion of amino acids by column chromatography; (b) endogenous renal clearances of amino acids and creatinine; (c) intestinal uptake of (34)C-labeled L-cystine, L-lysine, and L-arginine using jejunal mucosal biopsies; (d) oral cystine loading tests. All four of these were studied in the probands and the first two in a large number of the family members.49 members of 8 families were found to have a regular genetic pattern as described previously by Harris, Rosenberg, and their coworkers. Clinical or biochemical differences between the homozygotes type I (recessive cystinuria) and homozygotes type II (incompletely recessive cystinuria) have not been found. Both types excreted similarly excessive amounts of cystine, lysine, arginine, and ornithine, and had high endogenous renal clearances for these four amino acids. Some homozygotes of both types had a cystine clearance higher than the glomerular filtration rate. Jejunal mucosa from both types of homozygotes exhibited near complete inability to concentrate cystine and lysine in vitro. This was also documented in vivo with oral cystine loads. The heterozygotes type I were phenotypically normal with respect to the above four measurements. The heterozygotes type II showed moderate but definite abnormalities in their urinary excretion and their renal clearances of dibasic amino acids. Of the four amino acids concerned, cystine was the most reliable marker to differentiate between the heterozygotes type II and the homozygous normals. In this study, type III cystinuria, as described by Rosenberg, was not encountered. In two additional families, double heterozygotes of genotype I/II were found. The disease affecting these is clinically and biochemically less severe than that affecting homozygotes of either type I or type II. With respect to the four parameters used in this study, the double heterozygotes type I/II have results which are intermediate between those of the homozygotes type I and II and those of the heterozygotes type II.

Delineation of cystine and cysteine transport systems in rat kidney cortex by developmental patterns

The impaired ability of neonatal rat kidney cortex slices to take up L-cystine at a time when the ability to accumulate cysteine is similar to that of adult tissues indicates the separate nature of the transport processes for these amino acids. Dissimilarities in dependence on oxygen and temperature are also indicative of different transport systems. The intracellular form of the amino acid was largely cysteine when either cystine or cysteine was the transported substrate although significant amounts of both were incorporated into reduced glutathione. No difference in intracellular forms was found between neonatal and adult tissue.

The reduction of cystine during its transpot into rat jejunal eveted segments and sacs

1. Everted segments and sacs of rat jejunum were incubated in buffer containing [(35)S]cystine. 2. Concentration gradients were achieved by both segments and sacs, and the effects of duration of incubation and of cystine concentration on the isotope distribution ratios were determined. 3. Kinetic constants were determined for the uptake of cystine by both segments and sacs, and the differences between the two systems are discussed. 4. Reduction to cysteine was virtually complete intracellularly and in the sac lumen. Extensive reduction in the medium occurred only when segments were incubated. 5. Anaerobiosis prevented a concentration gradient being obtained between the medium and the tissue, but had little effect on the extent of reduction to cysteine in the tissue and sac lumen. 6. It is concluded that cystine is transported by an active process into rat jejunum, where it is present almost entirely in the reduced form, and that efflux of cysteine occurs through the serosal surface.

Increased cystine in leukocytes from individuals homozygous and heterozygous for cystinosis

In patients with cystinosis, the concentration of free cystine in leukocytes was 80 times greater than normal, and six times the normal content for their parents. This is the first demonstration of an abnormality in heterozygotes for this rare inherited disease of childhood. Three-quarters of the cystine was recovered in the granular fraction of cystinotic leukocytes.