Cationic Amino Acid Transporter Research Articles

Possible sources and functions of L-homoarginine in the brain: review of the literature and own findings.

L-Homoarginine is a cationic amino acid derivative, which is structurally related to L-arginine and lysine. Several lines of evidence point to nervous tissue as an important target of homoarginine action. In the mammalian brain homoarginine can be detected in noticeable quantities, but its origin is currently poorly explored. In part I of this review we try to show that both uptake and transport into brain (carried out by cationic amino acid transporters) and local synthesis in the brain (carried out by the homoarginine-synthesizing enzymes L-arginine:glycine amidinotransferase and ornithine transcarbamylse) might contribute to homoarginine brain content. We then give a brief overview about the multiple effects of homoarginine on the healthy brain and show that both homoarginine excess and deficiency are potentially harmful to the central nervous system. In part II, we shortly report about own experiments with regard to the cellular localization of cationic amino acid transporters, as well the enzymes L-arginine:glycine amidinotransferase and ornithine transcarbamylse, in human and rat brains.

Dynamical analysis of mCAT2 gene models with CTN-RNA nuclear retention

As an experimentally well-studied nuclear-retained RNA, CTN-RNA plays a significant role in many aspects of mouse cationic amino acid transporter 2 (mCAT2) gene expression, but relevant dynamical mechanisms have not been completely clarified. Here we first show that CTN-RNA nuclear retention can not only reduce pre-mCAT2 RNA noise but also mediate its coding partner noise. Then, by collecting experimental observations, we conjecture a heterodimer formed by two proteins, p54nrb and PSP1, named p54nrb-PSP1, by which CTN-RNA can positively regulate the expression of nuclear mCAT2 RNA. Therefore, we construct a sequestration model at the molecular level. By analyzing the dynamics of this model system, we demonstrate why most nuclear-retained CTN-RNAs stabilize at the periphery of paraspeckles, how CTN-RNA regulates its protein-coding partner, and how the mCAT2 gene can maintain a stable expression. In particular, we obtain results that can easily explain the experimental phenomena observed in two cases, namely, when cells are stressed and unstressed. Our entire analysis not only reveals that CTN-RNA nuclear retention may play an essential role in indirectly preventing diseases but also lays the foundation for further study of other members of the nuclear-regulatory RNA family with more complicated molecular mechanisms.

Urine Beta2-Microglobulin Is an Early Marker of Renal Involvement in LPI.

Lysinuric protein intolerance (LPI) is a rare autosomal recessive disorder affecting the transport of cationic amino acids. It has previously been shown that approximately one third of the Finnish LPI patients have impaired renal function. The aim of this study was to analyse in detail urine beta2-microglobulin values, renal dysfunction, oral L-citrulline doses and plasma citrulline concentrations in Finnish LPI patients. Of the 41 Finnish LPI patients, 56% had proteinuria and 53% hematuria. Mean plasma creatinine concentration was elevated in 48%, serum cystatin C in 62%, and urine beta2-microglobulin in 90% of the patients. Seventeen per cent of the patients developed ESRD, and five of them received a kidney transplant. L-citrulline doses and fasting plasma citrulline concentrations were similar in adult LPI patients with decreased and normal GFR (mean ± SD 79.5 ± 29.2 vs. 82.4 ± 21.9mg/kg/day, P = 0.619, and 80.3 ± 20.1 vs. 64.8 ± 23.0μmol/l, P = 0.362, respectively). Urine beta2-microglobulin is a sensitive early marker of renal involvement, and it should be monitored regularly in LPI patients. Weight-based oral L-citrulline doses and plasma citrulline concentrations were not associated with renal function. LPI patients with ESRD were successfully treated with dialysis and kidney transplantation.

Renal Involvement in a French Paediatric Cohort of Patients with Lysinuric Protein Intolerance.

Lysinuric protein intolerance (LPI) is a rare autosomal recessive metabolic disorder, caused by defective transport of cationic amino acids at the basolateral membrane of epithelial cells, typically in intestines and kidneys. The SLC7A7 gene, mutated in LPI patients, encodes the light subunit (y+LAT1) of a member of the heterodimeric amino acid transporter family.The diagnosis of LPI is difficult due to unspecific clinical features: protein intolerance, failure to thrive and vomiting after weaning. Later on, patients may present delayed growth osteoporosis, hepatosplenomegaly, muscle hypotonia and life-threatening complications such as alveolar proteinosis, haemophagocytic lymphohistiocytosis and macrophage activation syndrome. Renal involvement is also a serious complication with tubular and more rarely, glomerular lesions that may lead to end-stage kidney disease (ESKD). We report six cases of LPI followed in three different French paediatric centres who presented LPI-related nephropathy during childhood. Four of them developed chronic kidney disease during follow-up, including one with ESKD. Five developed chronic tubulopathies and one a chronic glomerulonephritis. A histological pattern of membranoproliferative glomerulonephritis was first associated with a polyclonal immunoglobulin deposition, treated by immunosuppressive therapy. He then required a second kidney biopsy after a relapse of the nephrotic syndrome; the immunoglobulin deposition was then monoclonal (IgG1 kappa). This is the first observation of an evolution from a polyclonal to a monotypic immune glomerulonephritis. Immune dysfunction potentially attributable to nitric oxide overproduction secondary to arginine intracellular trapping is a debated complication in LPI. Our results suggest all LPI patients should be monitored for renal disease regularly.

Arginine increases development of in vitro-produced porcine embryos and affects the protein arginine methyltransferase-dimethylarginine dimethylaminohydrolase-nitric oxide axis.

Culture systems promote development at rates lower than the in vivo environment. Here, we evaluated the embryo's transcriptome to determine what the embryo needs during development. A previous mRNA sequencing endeavour found upregulation of solute carrier family 7 (cationic amino acid transporter, y+ system), member 1 (SLC7A1), an arginine transporter, in in vitro- compared with in vivo-cultured embryos. In the present study, we added different concentrations of arginine to our culture medium to meet the needs of the porcine embryo. Increasing arginine from 0.12 to 1.69mM improved the number of embryos that developed to the blastocyst stage. These blastocysts also had more total nuclei compared with controls and, specifically, more trophectoderm nuclei. Embryos cultured in 1.69mM arginine had lower SLC7A1 levels and a higher abundance of messages involved with glycolysis (hexokinase 1, hexokinase 2 and glutamic pyruvate transaminase (alanine aminotransferase) 2) and decreased expression of genes involved with blocking the tricarboxylic acid cycle (pyruvate dehydrogenase kinase, isozyme 1) and the pentose phosphate pathway (transaldolase 1). Expression of the protein arginine methyltransferase (PRMT) genes PRMT1, PRMT3 and PRMT5 throughout development was not affected by arginine. However, the dimethylarginine dimethylaminohydrolase 1 (DDAH1) and DDAH2 message was found to be differentially regulated through development, and the DDAH2 protein was localised to the nuclei of blastocysts. Arginine has a positive effect on preimplantation development and may be affecting the nitric oxide-DDAH-PRMT axis.

Involvement of cationic amino acid transporter 1 in L-arginine transport in rat retinal pericytes.

Nitric oxide (NO), a known relaxant, is produced in cells from L-arginine (L-Arg). Because the relaxation of retinal pericytes alters the microcirculatory hemodynamics, it is important to understand the manner of NO production in retinal pericytes. The purpose of this study was to clarify the molecular mechanism(s) of uptake of L-Arg in retinal pericytes using a conditionally immortalized rat retinal pericyte cell line (TR-rPCT1 cells) which expresses the mRNAs of endothelial NO synthase and inducible NO synthase. L-Arg uptake by TR-rPCT1 cells exhibited Na(+)-independence and concentration-dependence with a Km of 28.9 µM. This process was strongly inhibited by substrates of cationic amino acid transporters (CAT), such as L-ornithine and L-lysine. In contrast, L-valine, L-leucine, and L-glutamine, which are substrates of cation/neutral amino acid transport systems, such as system y(+)L, system B(0,+), and system b(0,+), did not strongly inhibit L-Arg uptake by TR-rPCT1 cells. In addition, the expression of mRNA and protein of CAT1 in TR-rPCT1 cells was observed by reverse transcription-polymerase chain reaction and immunoblot analyses. Taking these results into consideration, it appears that CAT1 is involved in L-Arg uptake by retinal pericytes and this is expected to play an important role in the relaxation of retinal pericytes, thereby modulating the microcirculatory hemodynamics in the retina.

1471 delTTCT a Common Mutation of Tunisian Patients with Lysinuric Protein Intolerance.

Lysinuric protein intolerance is an inherited aminoaciduria caused by defective cationic amino acid transport. It is an autosomal recessive disease caused by mutations in the SLC7A 7 gene. The objective of this study was to identify the mutations of Tunisians patients in order to offer the genetic counseling and the prenatal diagnosis to families. Five affected Tunisian children (4 girls and 1 boy) belonging to four consanguineous families were considered. The diagnosis was made based on the plasma for amino acids quantification by Ion Exchange chromatography, the DNA for mutational analysis by DHPLC and sequencing, and the amniotic fluid for prenatal diagnosis. For the 5 patients, clinical features were dominated by failure to thrive, bone marrow abnormalities, hepatosplenomegaly, and mental retardation. The diagnosis for all patients was confirmed by biochemical analysis with hyperammonemia, hyperexcretion of urinary dibasic amino acids, and a high amount of orotic acid in the urine. The 1471 delTTCT mutation was identified in exon 9 in the homozygous state for all Tunisian patients. Genetic counseling was performed for three out of four families, four heterozygous and two homozygous healthy siblings were identified. The result of prenatal diagnosis showed the presence of the 1471 de1TTCT mutation in the homozygous state for the third pregnancy and heterozygous state for the fourth. The 1471 deITTCT mutation seems to be a common mutation of Tunisian population. The identification of this specific mutation provides a tool for confirmatory diagnosis, genetic counseling, and prenatal diagnosis.

Gene expression, serum amino acid levels, and growth performance of pigs fed dietary leucine and lysine at different ratios.

We examined 96 pigs (28.1 ± 0.83 kg) to analyze the effect of Leu:Lys ratios on expression of the cationic amino acid transporters b(0,+) and CAT-1 in the jejunum and liver as well as myosin expression in 2 muscles to estimate the optimum standardized ileal digestible (SID) Leu:Lys ratio for growth rate and efficiency. A wheat-and wheat bran-based diets were formulated to meet the requirements of SID amino acids other than Leu (0.70%) and Lys (0.80%). L-Leu was added to the basal diet in 5 SID Leu:Lys ratios (88, 100, 120, 140, and 160% in diets 1-5). Tissue samples were collected from 8 pigs with ratios of 88, 120, and 160%. Relative expression of b(0,+), CAT-1, and myosin was analyzed. b(0,+) expression in the jejunum was higher but lower in the liver of pigs with the 120% ratio compared to those with the 88 or 160% ratio; myosin expression in longissimus dorsi was also higher in pigs with the 120% ratio (P < 0.05). CAT-1 was lower in the jejunum and longissimus dorsi of pigs with 120 or 160% ratios than in pigs with 88%. Serum concentration of nearly all amino acids decreased with excess dietary Leu (P < 0.05). The SID Leu:Lys of 104 and 109% optimized average daily gain and feed conversion ratio, respectively. Thus, the dietary Leu:Lys ratio affects the expression of genes coding for amino acid transporters and myosin, the availability of Lys, and the growth rate and efficiency in pigs.

Liver plays a central role in asymmetric dimethylarginine-mediated organ injury

Asymmetric-dimethylarginine (ADMA) competes with L-arginine for each of the three isoforms of nitric oxide synthase: endothelial; neuronal; inducible. ADMA is synthesized by protein methyltransferases followed by proteolytic degradation. ADMA is metabolized to citrulline and dimethylamine, by dimethylarginine dimethylaminohydrolase (DDAH) and enters cells through cationic amino-acid transporters extensively expressed in the liver. The liver plays a crucial role in ADMA metabolism by DDAH-1 and, as has been recently demonstrated, it is also responsible for ADMA biliary excretion. A correlation has been demonstrated between plasma ADMA levels and the degree of hepatic dysfunction in patients suffering from liver diseases with varying aetiologies: plasma ADMA levels are increased in patients with liver cirrhosis, alcoholic hepatitis and acute liver failure. The mechanism by which liver dysfunction results in raised ADMA concentrations is probably due to impaired activity of DDAH due to severe inflammation, oxidative stress, and direct damage to DDAH. High plasma ADMA levels are also relevant as they are associated with the onset of multi-organ failure (MOF). Increased plasma concentration of ADMA was identified as an independent risk factor for MOF in critically-ill patients causing enhanced Intensive Care Unit mortality: a significant reduction in nitric oxide synthesis, leading to malperfusion in various organs, eventually culminating in multi organs dysfunction.

Insulin restores l-arginine transport requiring adenosine receptors activation in umbilical vein endothelium from late-onset preeclampsia

IntroductionPreeclampsia is associated with impaired placental vasodilation and reduced endothelial nitric oxide synthase (eNOS) activity in the foetoplacental circulation. Adenosine and insulin stimulate vasodilation in endothelial cells, and this activity is mediated by adenosine receptor activation in uncomplicated pregnancies; however, this activity has yet to be examined in preeclampsia. Early onset preeclampsia is associated with severe placental vasculature alterations that lead to altered foetus growth and development, but whether late-onset preeclampsia (LOPE) alters foetoplacental vascular function is unknown. MethodsVascular reactivity to insulin (0.1–1000 nmol/L, 5 min) and adenosine (1 mmol/L, 5 min) was measured in KCl-preconstricted human umbilical vein rings from normal and LOPE pregnancies using a wire myograph. The protein levels of human cationic amino acid transporter 1 (hCAT-1), adenosine receptor subtypes, total and Ser1177-or Thr495-phosphorylated eNOS were detected via Western blot, and l-arginine transport (0–1000 μmol/L l-arginine, 3 μCi/mL L-[3H]arginine, 20 s, 37 °C) was measured in the presence or absence of insulin and adenosine receptor agonists or antagonists in human umbilical vein endothelial cells (HUVECs) from normal and LOPE pregnancies. ResultsLOPE increased the maximal l-arginine transport capacity and hCAT-1 and eNOS expression and activity compared with normal conditions. The A2A adenosine receptor (A2AAR) antagonist ZM-241385 blocked these effects of LOPE. Insulin-mediated umbilical vein ring relaxation was lower in LOPE pregnancies than in normal pregnancies and was restored using the A2AAR antagonist. Discussion and conclusionsThe reduced foetoplacental vascular response to insulin may result from A2AAR activation in LOPE pregnancies.

Endothelial cationic amino acid transporter-1 overexpression blunts the effects of oxidative stress on pressor responses to behavioural stress in mice.

Observational studies indicate that psychological stress may contribute to the pathogenesis of hypertension and this may be further accentuated by factors such as endothelial dysfunction. On this basis, we aimed to determine whether oxidative stress enhances pressor responses to stressful stimuli and whether augmenting endothelial function by increasing the transport of L-arginine can counter the effects of oxidative stress. Telemetry probes were used to measure mean arterial pressure (MAP) in wild-type (WT; n = 6) and endothelial cationic amino acid transporter-1 (CAT-1)-overexpressing (CAT+) mice (n = 6) before and during an aversive (restraint) and non-aversive (almond feeding) stressor. The superoxide dismutase inhibitor diethyldithiocarbamic acid (DETCA; 30 mg/kg per day; 14 days) was then administered via a minipump to induce oxidative stress. Stress responses to feeding and restraint were repeated during Days 11-12 of DETCA infusion. In WT mice, pressor responses to restraint and feeding were augmented during infusion of DETCA (35 ± 1 and 28 ± 1 mmHg, respectively) compared with respective pretreatment responses (28 ± 2 and 24 ± 1 mmHg, respectively; P ≤ 0.01). In CAT+ mice, pressor responses to feeding were blunted during DETCA (20 ± 1 mmHg) compared with the control response (23 ± 1 mmHg; P = 0.03). In these mice, pressor responses to restraint were similar before (28 ± 1 mmHg) and during (26 ± 1 mmHg) DETCA infusion (P = 0.26). We conclude that endothelial CAT-1 overexpression can counter the ability of oxidative stress to augment pressor responses to behavioural stress.

Effects of Strain and Production-Cycle on Indices of Lysine Catabolism in Turkeys

In typical turkey production diets, lysine is frequently the second limiting amino acid. Understanding its catabolism could provide opportunities to increase the efficiency of lysine use for protein synthesis. We hypothesize that indices of lysine catabolism in turkey liver vary throughout the production cycle. Two commercial strains of turkey, Strain A and B, were analyzed 8 times over a period of 17 weeks (n = 8 birds/sampling time/strain) for lysine alpha-ketoglutarate (LKR) and saccharopine dehydrogenase (SDH) activities and mRNA abundance, in vitro lysine oxidation (LOX), L-amino acid oxidase (LAAO) activity, lysyl oxidase (LO) activity and mRNA expression of cationic amino acid transporters (CAT) 1, 2 and 3. We found differences in hepatic LKR activity (p = 0.007), LKR mRNA (p = 0.0004), SDH activity (p = 0.008), LOX (p<0.0001), lysyl oxidase activity (p<0.01), LAAO (p<0.0001) and CAT1 (p = 0.005) and 2 mRNA abundance (p = 0.0022) throughout the production cycle. We also found an effect of strain on SDH (p = 0.046) and CAT-2 mRNA abundance (p = 0.02); while no age or strain effects were detected for CAT3 mRNA abundance. Interestingly, the average LKR and SDH activities across strains and weeks was 240 and 420 nmol per minute per gram of liver, respectively, as opposed to the average LAAO activity, lysyl oxidase activity and L OX which were 0.70, 0.10 and 13.5 nmol per minute per gram liver, respectively. These data indicate that the saccharopine-dependent pathway is the predominant pathway of lysine degradation in turkey liver and that indices of hepatic lysine catabolism vary throughout the production cycle.

L-arginine stimulates CAT-1-mediated arginine uptake and regulation of inducible nitric oxide synthase for the growth of chick intestinal epithelial cells.

L-arginine (L-Arg) uptake is mediated by members of cationic amino acid transporter (CAT) family and may coincide with the induction of nitric oxide synthases (NOS). The present study was conducted to investigate the extracellular concentrations of L-Arg regulating the CAT-1, CAT-4 and inducible NOS (iNOS) in chick intestinal epithelial cells. The cells were cultured for 4days in Arg-free Dulbecco's modified Eagle's medium containing 10, 100, 200, 400, or 600μM L-Arg. Cell viability, nitric oxide (NO) concentrations, uptake and metabolism of L-[3H]-Arg as well as expression of CAT-1, CAT-4, and iNOS were determined. Our results showed that L-Arg enhances cell growth with a maximal response at 10-400μM. Addition of 100, 200, or 400μM L-Arg increased the L-[3H]-Arg uptake, which was associated with greater conversion of L-[3H]-citrulline and NO production in comparison with 10μM L-Arg group. Increasing extracellular concentrations of L-Arg from 10 to 400μM dose dependently increased the levels of CAT-1 mRNA and protein, while no effect on CAT-4 mRNA abundance was found. Furthermore, supplementation of 100, 200, or 400μM L-Arg upregulated the expression of iNOS mRNA, and the relative protein levels for iNOS in 200 and 400μM L-Arg groups were higher than those in 10 and 100μM L-Arg groups. Collectively, we conclude that the CAT-1 isoform plays a role in L-Arg uptake, and L-Arg-mediated elevation of NO via iNOS promotes the growth of chick intestinal epithelial cells.

The mRNA expression of amino acid transporters, aminopeptidase N, and the di- and tri-peptide transporter PepT1 in the embryo of the domesticated chicken (Gallus gallus) shows developmental regulation

The mRNA expression profile for 10 amino acid transporters, the di-and tri- peptide transporter (PepT1), and aminopeptidase N (APN) during chick embryogenesis was determined. Fertilized eggs were sampled at d 9, 11, 15, 17, 19, and 20 of incubation. Three to 4 embryos were sampled at each time period. At d 9 and 11, the entire intestine was collected due to its undifferentiated appearance. The ceca, duodenum, midgut, and liver were sampled at d 15, 17, 19, and 20. Gene expression was measured using absolute quantitation quantitative reverse-transcription PCR. In the liver, all genes except for PepT1 were expressed at most time points. At d 9, only the expression of Na+-independent cationic amino acid transporter 1, Na+-independent cationic amino acid transporter 2, and excitatory amino acid transporter 3 was detectable in the intestine, but by d 11, all genes associated with transporters of the basolateral surface were expressed, and at higher levels than genes associated with brush border transporters. By d 15, all of the genes tested were expressed in the duodenum, midgut, and ceca at high levels that remained relatively constant until d 20. Statistical analysis shows that at d 15, 17, 19, and 20 there is a significant interaction between the 2 main effects (days of incubation and region of the gut); therefore, it is likely that gene expression in different regions of the gut is dependent on the age of the embryo. At d 9 and 11, the gut may not function in amino acid uptake from the lumen and possibly relies on other structures such as the yolk sac. As the gut matures and protein becomes available in the lumen, amino acid transporters become highly expressed in all parts of the intestine. The data suggest that by d 15 of embryo development the gut may be capable of amino acid absorption.

Olive fly transcriptomics analysis implicates energy metabolism genes in spinosad resistance

BackgroundThe olive fly, Bactrocera oleae, is the most devastating pest of cultivated olives. Its control has been traditionally based on insecticides, mainly organophosphates and pyrethroids. In recent years, the naturalyte spinosad is used against the olive fly. As with other insecticides, spinosad is subject to selection pressures that have led to resistance development. Mutations in the α6 subunit of the nicotinic acetylcholine receptor (nAChR) have been implicated in spinosad resistance in several species (e.g., Drosophila melanogaster) but excluded in others (e.g., Musca domestica). Yet, additional mechanisms involving enhanced metabolism of detoxification enzymes (such as P450 monooxygenases or mixed function oxidases) have also been reported. In order to clarify the spinosad resistance mechanisms in the olive fly, we searched for mutations in the α6-subunit of the nAChR and for up-regulated genes in the entire transcriptome of spinosad resistant olive flies.ResultsThe olive fly α6-subunit of the nAChR was cloned from the laboratory sensitive strain and a spinosad selected resistant line. The differences reflected silent nucleotide substitutions or conserved amino acid changes. Additionally, whole transcriptome analysis was performed in the two strains in order to reveal any underlying resistance mechanisms. Comparison of over 13,000 genes showed that in spinosad resistant flies nine genes were significantly over-expressed, whereas ~40 were under-expressed. Further functional analyses of the nine over-expressed and eleven under-expressed loci were performed. Four of these loci (Yolk protein 2, ATP Synthase FO subunit 6, Low affinity cationic amino acid transporter 2 and Serine protease 6) showed consistently higher expression both in the spinosad resistant strain and in wild flies from a resistant California population. On the other side, two storage protein genes (HexL1 and Lsp1) and two heat-shock protein genes (Hsp70 and Hsp23) were unfailingly under-expressed in resistant flies.ConclusionThe observed nucleotide differences in the nAChR-α6 subunit between the sensitive and spinosad resistant olive fly strains did not advocate for the involvement of receptor mutations in spinosad resistance. Instead, the transcriptome comparison between the two strains indicated that several immune system loci as well as elevated energy requirements of the resistant flies might be necessary to lever the detoxification process.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-714) contains supplementary material, which is available to authorized users.

Augmented endothelial-specific L-arginine transport prevents obesity-induced hypertension.

Hypertension is a major clinical complication of obesity. Our previous studies show that abnormal uptake of the nitric oxide precursor L-arginine, via the cationic amino acid transporter-1 (CAT1), contributes to endothelial dysfunction in cardiovascular disease. In this study, we tested the hypothesis that abnormal L-arginine transport may be a key mediator of obesity-induced hypertension. Mean arterial pressure (MAP) was monitored by telemetry in conscious wild-type (WT; n=13) mice, and transgenic mice with endothelial-specific overexpression of CAT1 (CAT+; n=14) fed a normal or a high fat diet for 20weeks. Renal angiotensin II (Ang II), CAT1 mRNA and plasma nitrate/nitrite levels were then quantified. In conjunction, plasma nitrate/nitrite levels were assessed in obese normotensive (n=15) and obese hypertensive subjects (n=15). Both genotypes of mice developed obesity when fed a high fat diet (P≤0.002). Fat fed WT mice had 13% greater MAP and 78% greater renal Ang II content, 42% lesser renal CAT1 mRNA levels and 42% lesser plasma nitrate/nitrite levels, than WT mice fed a normal fat diet (P≤0.02). In contrast, none of these variables were significantly altered by high fat feeding in CAT+ mice (P≥0.36). Plasma nitrate/nitrite levels were 17% less in obese hypertensives compared with obese normotensives (P=0.02). Collectively, these data indicate that obesity-induced down-regulation of CAT1 expression and subsequent reduced bioavailability of nitric oxide may contribute to the development of obesity-induced hypertension.

The red blood cell: a new key player in cardiovascular homoeostasis? Focus on the nitric oxide pathway.

RBCs (red blood cells) have a fundamental role in the regulation of vascular homoeostasis thanks to the ability of these cells to carry O2 (oxygen) between respiratory surfaces and metabolizing tissues and to release vasodilator compounds, such as ATP and NO (nitric oxide), in response to tissue oxygenation. More recently it has been shown that RBCs are also able to produce NO endogenously as they express a functional NOS (nitric oxide synthase), similar to the endothelial isoform. In addition, RBCs carry important enzymes and molecules involved in L-arginine metabolism, such as arginase, NO synthesis inhibitors and the cationic amino acid transporters. Altogether these findings strongly support the role of these cells as producers, vehicles and scavengers of NO, therefore affecting several physiological processes such as blood rheology and cell adhesion. Consequently, the importance of alterations in the L-arginine/NO metabolic pathway induced by specific conditions, e.g. oxidative stress, in different pathological settings have been investigated. In the present review we discuss the role of RBCs in vascular homoeostasis, focusing our attention on the importance of the NO pathway alterations in cardiovascular diseases and their relationship to major risk factors.

Amino acids in the uterine luminal fluid reflects the temporal changes in transporter expression in the endometrium and conceptus during early pregnancy in cattle.

In cattle, conceptus-maternal interactions are critical for the establishment and maintenance of pregnancy. A major component of this early interaction involves the transport of nutrients and secretion of key molecules by uterine epithelial cells to help support conceptus development during the peri-implantation period of pregnancy. Objectives were to: 1) analyze temporal changes in the amino acid (AA) content of uterine luminal fluid (ULF) during the bovine estrous cycle; 2) understand conceptus-induced alterations in AA content; 3) determine expression of AA transporters in the endometrium and conceptus; and 4) determine how these transporters are modulated by (Progesterone) P4. Concentrations of aspartic acid, arginine, glutamine, histidine, lysine, isoleucine, leucine, phenylalanine and tyrosine decreased on Day 16 of the estrous cycle but increased on Day 19 in pregnant heifers (P<0.05). Glutamic acid only increased in pregnant heifers on Day 19 (P<0.001). Asparagine concentrations were greater in ULF of cyclic compared to pregnant heifers on Day 7 (P<0.05) while valine concentrations were higher in pregnant heifers on Day 16 (P<0.05). Temporal changes in expression of the cationic AA transporters SLC7A1 SLC7A4 and SLC7A6 occurred in the endometrium during the estrous cycle/early pregnancy coordinate with changes in conceptus expression of SLC7A4, SLC7A2 and SLC7A1 (P<0.05). Only one acidic AA transporter (SLC1A5) increased in the endometrium while conceptus expression of SLC1A4 increased (P<0.05). The neutral AA transporters SLC38A2 and SLC7A5 increased in the endometrium in a temporal manner while conceptus expression of SLC38A7, SLC43A2, SLC38A11 and SLC7A8 also increased (P<0.05). P4 modified the expression of SLC1A1, -1A4, -1A5, -38A2, -38A4, -38A7, -43A2, -6A14, -7A1, -7A5 and -7A7 in the endometrium. Results demonstrate that temporal changes in AA in the ULF reflect changes in transporter expression in the endometrium and conceptus during early pregnancy in cattle, some of which are modified by P4.

Regulation of endothelial nitric oxide synthase activity by protein-protein interaction.

Endothelial nitric oxide synthase (eNOS) is expressed in vascular endothelial cells and plays an important role in the regulation of vascular tone, platelet aggregation and angiogenesis. Protein-protein interactions represent an important posttranslational mechanism for eNOS regulation. eNOS has been shown to interact with a variety of regulatory and structural proteins which provide fine tuneup of eNOS activity and eNOS protein trafficking between plasma membrane and intracellular membranes in a number of physiological and pathophysiological processes. eNOS interacts with calmodulin, heat shock protein 90 (Hsp90), dynamin-2, β-actin, tubulin, porin, high-density lipoprotein (HDL) and apolipoprotein AI (ApoAI), resulting in increases in eNOS activity. The negative eNOS interacting proteins include caveolin, G protein-coupled receptors (GPCR), nitric oxide synthase-interacting protein (NOSIP), and nitric oxide synthase trafficking inducer (NOSTRIN). Dynamin-2, NOSIP, NOSTRIN, and cytoskeleton are also involved in eNOS trafficking in endothelial cells. In addition, eNOS associations with cationic amino acid transporter-1 (CAT-1), argininosuccinate synthase (ASS), argininosuccinate lyase (ASL), and soluble guanylate cyclase (sGC) facilitate directed delivery of substrate (L-arginine) to eNOS and optimizing NO production and NO action on its target. Regulation of eNOS by protein-protein interactions would provide potential targets for pharmacological interventions in NO-compromised cardiovascular diseases.

Soy-dairy protein blend and whey protein ingestion after resistance exercise increases amino acid transport and transporter expression in human skeletal muscle

Increasing amino acid availability (via infusion or ingestion) at rest or postexercise enhances amino acid transport into human skeletal muscle. It is unknown whether alterations in amino acid availability, from ingesting different dietary proteins, can enhance amino acid transport rates and amino acid transporter (AAT) mRNA expression. We hypothesized that the prolonged hyperaminoacidemia from ingesting a blend of proteins with different digestion rates postexercise would enhance amino acid transport into muscle and AAT expression compared with the ingestion of a rapidly digested protein. In a double-blind, randomized clinical trial, we studied 16 young adults at rest and after acute resistance exercise coupled with postexercise (1 h) ingestion of either a (soy-dairy) protein blend or whey protein. Phenylalanine net balance and transport rate into skeletal muscle were measured using stable isotopic methods in combination with femoral arteriovenous blood sampling and muscle biopsies obtained at rest and 3 and 5 h postexercise. Phenylalanine transport into muscle and mRNA expression of select AATs [system L amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, system A amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, cationic amino acid transporter 1/SLC7A1] increased to a similar extent in both groups (P < 0.05). However, the ingestion of the protein blend resulted in a prolonged and positive net phenylalanine balance during postexercise recovery compared with whey protein (P < 0.05). Postexercise myofibrillar protein synthesis increased similarly between groups. We conclude that, while both protein sources enhanced postexercise AAT expression, transport into muscle, and myofibrillar protein synthesis, postexercise ingestion of a protein blend results in a slightly prolonged net amino acid balance across the leg compared with whey protein.