Macrophages can convert citrulline into arginine.
Ontology highlight
ABSTRACT:
SUBMITTER: Wu GY
PROVIDER: S-EPMC1130638 | biostudies-other | 1992 Jan
REPOSITORIES: biostudies-other
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Project description:The activity of the arginine-citrulline cycle was investigated in macrophages from the spontaneous immunologically mediated diabetic BB rat. Peritoneal macrophages were prepared from male diabetes-prone (BBdp), diabetic (BBd) and age-matched non-diabetes-prone (BBn) rats. Cells were incubated at 37 degrees C for 2 h in Krebs-Henseleit bicarbonate buffer containing 0.5 mM L-arginine, 0.1 mM L-[ureido-14C]citrulline and 5 mM D-glucose to measure the activity of the arginine-citrulline cycle. The uptakes of citrulline and arginine by macrophages were measured during a 5 min incubation period with L-[ureido-14C]citrulline and L-[2,3-3H] arginine respectively. The production of NO3- (the major stable oxidation product of NO) increased (P < 0.01) by 112% and 151% in 75-day-old BBdp and 115-day-old BBd macrophages respectively, compared with age-matched BBn cells. The conversion of [14C]citrulline into [14C]arginine increased (P < 0.01) by 704%, 892% and 904% in 50- and 75-day-old BBdp and 115-day-old BBd macrophages respectively, compared with age-matched BBn cells. The enhanced NO synthesis in BBdp and BBd macrophages was associated with a 25-35% increase in the uptake of L-arginine. However, there were no differences in the uptake of citrulline between BBdp or BBd macrophages and age-matched BBn cells. Our results demonstrate for the first time the activation of the arginine-citrulline cycle in macrophages in an autoimmune condition. The inherent increase in the recycling of L-citrulline to L-arginine in BBdp and BBd macrophages may reflect an innate metabolic disorder in these cells. This increased L-arginine synthesis from L-citrulline may play a role in sustaining a sufficient intracellular L-arginine concentration for prolonged generation of NO in BBdp and BBd macrophages. A role for NO in the autoimmune destruction of pancreatic beta-cells in insulin-dependent diabetes mellitus warrants further investigation.
| S-EPMC1134573 | biostudies-other
Project description:L-citrulline and L-arginine supplementation has been shown to have several beneficial effects on the cardiovascular system. Nitric oxide (NO) protects against the progression of atherosclerosis and is synthesized by nitric oxide synthase (NOS), which converts L-arginine (L-Arg) into L-citrulline (L-Cit). Our previous study revealed that chronic administration of a combination of L-Cit and L- Arg has a better therapeutic effect on high cholesterol-induced atherosclerosis in rabbits. We investigated how L-Arg and L-Cit affect endothelial function, aging and atherosclerosis. Following a 3-day stimulation of human umbilical venous endothelial cells (HUVECs) with high glucose (HG: 22 mM) and L-Arg (300 μM), L-Cit (300 μM) or L-Arg plus L-Cit (LALC: each 150 μM) supplementation, endothelial senescence and function were evaluated. These amino acids were also administered to dyslipidemic type 2 diabetic (ZDFM) rats fed a high cholesterol diet. They were fed L-Arg or L-Cit or LALC for four weeks. Aortic senescence was investigated by measuring senescence-associated ß-galactosidase (SA-ß-gal), telomerase activity, DNA damage and p16INK4a protein expression. Only L-Cit and LALC supplementation retarded the HG-induced endothelial senescence, as evaluated by SA-ß-gal activity, a widely used marker of cellular senescence, p16INK4a expression, a senescence-related protein, and DNA damage. Under HG conditions, L-Cit and LCLA restored telomerase activity to levels observed under normal glucose (NG) conditions. Under HG conditions, L-Cit decreased ROS production, as measured by CM-H2DCFDA and the expression of p67phox, a major component of NADPH oxidase. Under HG conditions, L-Cit and LALC increased NO production, as measured by DAF-2AM. Endothelial NO synthase (eNOS) and phosphorylated eNOS were decreased under HG conditions and L-Cit and LALC significantly increased these levels. Arginase 2 protein expression increased under the HG conditions, and L-Cit and LALC significantly attenuated this effect. In ZDFM rats, SA-ß-gal activity was detected on the aortic endothelial surface; however, L-Cit and LALC reduced these levels. L-Cit and LALC both decreased the proportion of senescent cells. Furthermore, treatment with LALC for 4 weeks increased plasma NO production. Therefore conclusively, L-citrulline supplementation rescued NO levels better than L-arginine supplementation by inhibiting ROS production and arginase 2 protein expression. Consequently, L-Cit and LCLA supplementation retaeded HG-induced endothelial senescence.
| S-EPMC5802914 | biostudies-literature
Project description:Dietary arginine is the main dietary precursor for citrulline synthesis, but it is not known if other precursors can compensate when arginine is absent in the diet. To address this question, the contributions of plasma and dietary precursors were determined by using multitracer protocols in conscious mice infused i.g. either an arginine-sufficient diet [Arg(+)] or an arginine-free diet [Arg(-)]. The plasma entry rate of citrulline and arginine did not differ between the 2 diet groups (156 +/- 6 and 564 +/- 30 micromol kg(-1) h(-1), respectively); however, the entry rate of ornithine was greater in the mice fed the Arg(+) than the Arg(-) diet (332 +/- 33 vs. 180 +/- 16 micromol kg(-1) h(-1)). There was a greater utilization of plasma ornithine for the synthesis of citrulline (49 +/- 4 vs. 36 +/- 3 micromol kg(-1) h(-1), 30 +/- 3% vs. 24 +/- 2% of citrulline entry rate) in the mice fed the Arg(-) diet than the Arg(+) diet. The utilization of plasma arginine did not differ between the 2 diet groups for citrulline synthesis, either through plasma ornithine (approximately 29 +/- 3 micromol kg(-1) h(-1)) or at the site of citrulline synthesis (approximately 12 +/- 3 micromol kg(-1) h(-1)). The contribution of dietary proline to the synthesis of citrulline was mainly at the site of citrulline production (17 +/- 1 micromol kg(-1) h(-1)), rather than through plasma ornithine (5 +/- 0.4 micromol kg(-1) h(-1)). Dietary glutamine was utilized only at the site of citrulline synthesis (4 +/- 0.2 micromol kg(-1) h(-1)). Dietary glutamine and proline made a greater contribution to the synthesis of citrulline in mice fed the Arg(-) diet but remained minor sources for citrulline production. Plasma arginine and ornithine are able to support citrulline synthesis during arginine-free feeding.
| S-EPMC2903302 | biostudies-literature
Project description:Toward the creation of a robust and efficient producer of L-arginine and L-citrulline (arginine/citrulline), we have performed reengineering of a Corynebacterium glutamicum strain by using genetic information of three classical producers. Sequence analysis of their arg operons identified three point mutations (argR123, argG92(up), and argG45) in one producer and one point mutation (argB26 or argB31) in each of the other two producers. Reconstitution of the former three mutations or of each argB mutation on a wild-type genome led to no production. Combined introduction of argB26 or argB31 with argR123 into a wild type gave rise to arginine/citrulline production. When argR123 was replaced by an argR-deleted mutation (Delta argR), the production was further increased. The best mutation set, Delta argR and argB26, was used to screen for the highest productivity in the backgrounds of different wild-type strains of C. glutamicum. This yielded a robust producer, RB, but the production was still one-third of that of the best classical producer. Transcriptome analysis revealed that the arg operon of the classical producer was much more highly upregulated than that of strain RB. Introduction of leuC456, a mutation derived from a classical L-lysine producer and provoking global induction of the amino acid biosynthesis genes, including the arg operon, into strain RB led to increased production but incurred retarded fermentation. On the other hand, replacement of the chromosomal argB by heterologous Escherichia coli argB, natively insensitive to arginine, caused a threefold-increased production without retardation, revealing that the limitation in strain RB was the activity of the argB product. To overcome this, in addition to argB26, the argB31 mutation was introduced into strain RB, which caused higher deregulation of the enzyme and resulted in dramatically increased production, like the strain with E. coli argB. This reconstructed strain displayed an enhanced performance, thus allowing significantly higher productivity of arginine/citrulline even at the suboptimal 38 degrees C.
| S-EPMC2655454 | biostudies-literature
Project description:Recent isotopic tracer studies in mice, piglets, and humans have produced conflicting results as to the main carbon skeleton precursor for citrulline and arginine synthesis. This may be due in part to the different tracers infused and models used to interpret the stable isotope data. Furthermore, previous studies usually investigated a single precursor, which prevented the direct comparison among multiple precursors. To further elucidate the contribution of different precursors to citrulline synthesis, all possible enteral and plasma precursors of citrulline were studied in a mouse model during the postabsorptive and postprandial period using multitracer protocols. In addition, three different models were used to interpret the stable isotope data. The utilization of the classic precursor-product equation, developed for i.v. infused tracers but also used to include i.g. tracers, grossly overestimated the contribution of enteral precursors. Regardless of the model employed, dietary and plasma arginine were the main precursors for citrulline synthesis during feeding and plasma arginine during feed deprivation. The contribution of arginine was directly at the site of citrulline synthesis and through plasma ornithine. The predominant role of arginine and ornithine seen in this study supports the observations in mice, piglets, and humans suggesting that ornithine amino transferase is a pivotal enzyme in this pathway.
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Project description:Mitochondrial diseases represent a growing list of clinically heterogeneous disorders that are associated with dysfunctional mitochondria and multisystemic manifestations. In spite of a better understanding of the underlying pathophysiological basis of mitochondrial disorders, treatment options remain limited. Over the past two decades, there is growing evidence that patients with mitochondrial disorders have nitric oxide (NO) deficiency due to the limited availability of NO substrates, arginine and citrulline; decreased activity of nitric oxide synthase (NOS); and NO sequestration. Studies evaluating the use of arginine in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) presenting with stroke-like episodes showed symptomatic improvement after acute administration as well as a reduction in the frequency and severity of stroke-like episodes following chronic use. Citrulline, another NO precursor, was shown through stable isotope studies to result in a greater increase in NO synthesis. Recent studies showed a positive response of arginine and citrulline in other mitochondrial disorders besides MELAS. Randomized-controlled studies with a larger number of patients are warranted to better understand the role of NO deficiency in mitochondrial disorders and the efficacy of NO precursors as treatment modalities in these disorders.
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Project description:Microbicidal NO production is reliant on inducible NO synthase-mediated L-arginine metabolism in macrophages (MΦs). However, L-arginine supply can be restricted by arginase activity, resulting in inefficient NO output and inhibition of antimicrobial MΦ function. MΦs circumvent this by converting L-citrulline to L-arginine, thereby resupplying substrate for NO production. In this article, we define the metabolic signature of mycobacteria-infected murine MΦs supplied L-arginine, L-citrulline, or both amino acids. Using liquid chromatography-tandem mass spectrometry, we determined that L-arginine synthesized from L-citrulline was less effective as a substrate for arginase-mediated L-ornithine production compared with L-arginine directly imported from the extracellular milieu. Following Mycobacterium bovis bacillus Calmette-Guérin infection and costimulation with IFN-γ, we observed that MΦ arginase activity did not inhibit production of NO derived from L-citrulline, contrary to NO inhibition witnessed when MΦs were cultured in L-arginine. Furthermore, we found that arginase-expressing MΦs preferred L-citrulline over L-arginine for the promotion of antimycobacterial activity. We expect that defining the consequences of L-citrulline metabolism in MΦs will provide novel approaches for enhancing immunity, especially in the context of mycobacterial disease.
| S-EPMC6432794 | biostudies-literature
Project description:A bacterium's ability to acquire nutrients from its host during infection is an essential component of pathogenesis. For the Gram-positive pathogen Streptococcus pyogenes, catabolism of the amino acid arginine via the arginine deiminase (ADI) pathway supplements energy production and provides protection against acid stress in vitro. Its expression is enhanced in murine models of infection, suggesting an important role in vivo. To gain insight into the function of the ADI pathway in pathogenesis, the virulence of mutants defective in each of its enzymes was examined. Mutants unable to use arginine (ΔArcA) or citrulline (ΔArcB) were attenuated for carriage in a murine model of asymptomatic mucosal colonization. However, in a murine model of inflammatory infection of cutaneous tissue, the ΔArcA mutant was attenuated but the ΔArcB mutant was hyperattenuated, revealing an unexpected tissue-specific role for citrulline metabolism in pathogenesis. When mice defective for the arginine-dependent production of nitric oxide (iNOS(-/-)) were infected with the ΔArcA mutant, cutaneous virulence was rescued, demonstrating that the ability of S. pyogenes to utilize arginine was dispensable in the absence of nitric oxide-mediated innate immunity. This work demonstrates the importance of arginine and citrulline catabolism and suggests a novel mechanism of virulence by which S. pyogenes uses its metabolism to modulate innate immunity through depletion of an essential host nutrient.
| S-EPMC3911826 | biostudies-literature
Project description:The kidneys are thought to be a major site of net de novo arginine synthesis, but the quantitative status of arginine metabolism and its substrate precursor relationship to nitric oxide (NO) synthesis in end stage renal disease (ESRD) patients have not been characterized. We have investigated kinetic aspects of whole body arginine metabolism in six patients with ESRD. They received two pre- and two post-hemodialysis intravenous tracer infusion studies with L-[guanidino-(15)N(2)]arginine and L-[(13)C]leucine during the first study, and L-[5-(13)C]arginine and L-[5-(13)C-ureido,5,5, (2)H(2)]citrulline during the second study. Arginine homeostasis in ESRD patients was found to be associated with a lower rate of arginine oxidation, and despite the decrease in renal function, the rate of de novo arginine synthesis appeared to be preserved. Plasma citrulline concentrations and flux were also elevated in these subjects compared with healthy adults. The rate of whole body NO synthesis was increased in the ESRD patients, but apparently not different pre- and post-hemodialysis therapy. The anatomic site(s) responsible for the maintenance of net de novo arginine synthesis and for the elevated NO synthesis and its pathophysiological importance in ESRD remain to be established.
| S-EPMC315437 | biostudies-literature
Project description:In this article, the binding abilities of arginine, citrulline, N-acetyl citrulline and thiocitrulline on the active sites of SARS-COV-2 protease have been investigated using in-silico studies. All the above ligands bind selectively and preferentially to Cys-145 active site and also to other amino acids surrounding to it in the main protease. Of which arginine forms less number of weaker bonds compared to the other ligands, it by itself is a precursor for the formation of citrulline analogues with in the cell. Major advantage of using the above ligands is that in addition to its preferential binding, they have the ability to increase the immunity by assisting NO generation. Our results show that N-acetyl citrulline, citrulline, thiocitrulline and arginine may be used as a supplement during the treatment of SARS-COV-2.
| S-EPMC8021929 | biostudies-literature