Thrombin stimulates vascular smooth muscle cell polyamine synthesis by inducing cationic amino acid transporter and ornithine decarboxylase gene expression

Targeting Arginine in COVID-19-Induced Immunopathology and Vasculopathy

Coronavirus disease 2019 (COVID-19) represents a major public health crisis that has caused the death of nearly six million people worldwide. Emerging data have identified a deficiency of circulating arginine in patients with COVID-19. Arginine is a semi-essential amino acid that serves as key regulator of immune and vascular cell function. Arginine is metabolized by nitric oxide (NO) synthase to NO which plays a pivotal role in host defense and vascular health, whereas the catabolism of arginine by arginase to ornithine contributes to immune suppression and vascular disease. Notably, arginase activity is upregulated in COVID-19 patients in a disease-dependent fashion, favoring the production of ornithine and its metabolites from arginine over the synthesis of NO. This rewiring of arginine metabolism in COVID-19 promotes immune and endothelial cell dysfunction, vascular smooth muscle cell proliferation and migration, inflammation, vasoconstriction, thrombosis, and arterial thickening, fibrosis, and stiffening, which can lead to vascular occlusion, muti-organ failure, and death. Strategies that restore the plasma concentration of arginine, inhibit arginase activity, and/or enhance the bioavailability and potency of NO represent promising therapeutic approaches that may preserve immune function and prevent the development of severe vascular disease in patients with COVID-19.

Amino Acids in Circulatory Function and Health

Cardiovascular disease is the major cause of global mortality and disability. Abundant evidence indicates that amino acids play a fundamental role in cardiovascular physiology and pathology. Decades of research established the importance of L-arginine in promoting vascular health through the generation of the gas nitric oxide. More recently, L-glutamine, L-tryptophan, and L-cysteine have also been shown to modulate vascular function via the formation of a myriad of metabolites, including a number of gases (ammonia, carbon monoxide, hydrogen sulfide, and sulfur dioxide). These amino acids and their metabolites preserve vascular homeostasis by regulating critical cellular processes including proliferation, migration, differentiation, apoptosis, contractility, and senescence. Furthermore, they exert potent anti-inflammatory and antioxidant effects in the circulation, and block the accumulation of lipids within the arterial wall. They also mitigate known risk factors for cardiovascular disease, including hypertension, hyperlipidemia, obesity, and diabetes. However, in some instances, the metabolism of these amino acids through discrete pathways yields compounds that fosters vascular disease. While supplementation with amino acid monotherapy targeting the deficiency has ameliorated arterial disease in many animal models, this approach has been less successful in the clinic. A more robust approach combining amino acid supplementation with antioxidants, anti-inflammatory agents, and/or specific amino acid enzymatic pathway inhibitors may prove more successful. Alternatively, supplementation with amino acid-derived metabolites rather than the parent molecule may elicit beneficial effects while bypassing potentially harmful pathways of metabolism. Finally, there is an emerging recognition that circulating levels of multiple amino acids are perturbed in vascular disease and that a more holistic approach that targets all these amino acid derangements is required to restore circulatory function in diseased blood vessels.

Dual antiplatelet and anticoagulant APAC prevents experimental ischemia-reperfusion-induced acute kidney injury

BACKGROUND

Renal ischemia-reperfusion predisposes to acute kidney injury (AKI) and mortality. APAC, mast cell heparin proteoglycan mimetic is a potent dual antiplatelet and anticoagulant inhibiting thrombosis in several vascular models.

METHODS

Clinically relevant (0.06 and 0.13 mg/kg) and high (0.32 and 7.3 mg/kg) heparin doses of APAC and unfractionated heparin (UFH) were administered i.v. in pharmacological studies. Antithrombotic action of APAC and UFH was assessed with platelet aggregation to collagen, activated partial thromboplastin (APTT) and prothrombin (PT) times. Pharmacodynamics of [⁶⁴Cu]-APAC or -UFH were monitored by PET/CT. Next, APAC and UFH doses (0.06 and 0.13 mg/kg) were i.v. administered 10 min prior to renal ischemia-reperfusion injury (IRI) in rats.

RESULTS

APAC in contrast to UFH inhibited platelet aggregation. During 0.06 and 0.13 mg/kg dose regimens APTT and PT remained at baseline, but at the high APTT prolonged fourfold to sixfold. Overall bio-distribution and clearance of APAC and UFH were similar. After bilateral 30-min renal artery clamping, creatinine, urea nitrogen and neutrophil gelatinase-associated lipocalin concentrations and histopathology indicated faster renal recovery by APAC (0.13 mg/kg). APAC, unlike UFH, prevented expression of innate immune ligand hyaluronan and tubulointerstitial injury marker Kim-1. Moreover, in severe bilateral 1-h renal artery clamping, APAC (0.13 mg/kg) prevented AKI, as demonstrated both by biomarkers and survival. Compatible with kidney protection APAC reduced the circulating levels of vascular destabilizing and pro-inflammatory angiopoietin-2 and syndecan-1. No tissue bleeding ensued.

CONCLUSION

APAC and UFH were similarly eliminated via kidneys and liver. In contrast to UFH, APAC (0.13 mg/kg) was reno-protective in moderate and even severe IRI by attenuating vascular injury and innate immune activation.

Arginase in retinopathy

Ischemic retinopathies, such as diabetic retinopathy (DR), retinopathy of prematurity and retinal vein occlusion are a major cause of blindness in developed nations worldwide. Each of these conditions is associated with early neurovascular dysfunction. However, conventional therapies target clinically significant macula edema or neovascularization, which occur much later. Intra-ocular injections of anti-VEGF show promise in reducing retinal edema, but the effects are usually transient and the need for repeated injections increases the risk of intraocular infection. Laser photocoagulation can control pathological neovascularization, but may impair vision and in some patients the retinopathy continues to progress. Moreover, neither treatment targets early stage disease or promotes repair. This review examines the potential role of the ureahydrolase enzyme arginase as a therapeutic target for the treatment of ischemic retinopathy. Arginase metabolizes l-arginine to form proline, polyamines and glutamate. Excessive arginase activity reduces the l-arginine supply for nitric oxide synthase (NOS), causing it to become uncoupled and produce superoxide and less NO. Superoxide and NO react and form the toxic oxidant peroxynitrite. The catabolic products of polyamine oxidation and glutamate can induce more oxidative stress and DNA damage, both of which can cause cellular injury. Studies indicate that neurovascular injury during retinopathy is associated with increased arginase expression/activity, decreased NO, polyamine oxidation, formation of superoxide and peroxynitrite and dysfunction and injury of both vascular and neural cells. Furthermore, data indicate that the cytosolic isoform arginase I (AI) is involved in hyperglycemia-induced dysfunction and injury of vascular endothelial cells whereas the mitochondrial isoform arginase II (AII) is involved in neurovascular dysfunction and death following hyperoxia exposure. Thus, we postulate that activation of the arginase pathway causes neurovascular injury by uncoupling NOS and inducing polyamine oxidation and glutamate formation, thereby reducing NO and increasing oxidative stress, all of which contribute to the retinopathic process.

Role of arginase in vessel wall remodeling

Arginase metabolizes the semi-essential amino acid l-arginine to l-ornithine and urea. There are two distinct isoforms of arginase, arginase I and II, which are encoded by separate genes and display differences in tissue distribution, subcellular localization, and molecular regulation. Blood vessels express both arginase I and II but their distribution appears to be cell-, vessel-, and species-specific. Both isoforms of arginase are induced by numerous pathologic stimuli and contribute to vascular cell dysfunction and vessel wall remodeling in several diseases. Clinical and experimental studies have documented increases in the expression and/or activity of arginase I or II in blood vessels following arterial injury and in pulmonary and arterial hypertension, aging, and atherosclerosis. Significantly, pharmacological inhibition or genetic ablation of arginase in animals ameliorates abnormalities in vascular cells and normalizes blood vessel architecture and function in all of these pathological states. The detrimental effect of arginase in vascular remodeling is attributable to its ability to stimulate vascular smooth muscle cell and endothelial cell proliferation, and collagen deposition by promoting the synthesis of polyamines and l-proline, respectively. In addition, arginase adversely impacts arterial remodeling by directing macrophages toward an inflammatory phenotype. Moreover, the proliferative, fibrotic, and inflammatory actions of arginase in the vasculature are further amplified by its capacity to inhibit nitric oxide (NO) synthesis by competing with NO synthase for substrate, l-arginine. Pharmacologic or molecular approaches targeting specific isoforms of arginase represent a promising strategy in treating obstructive fibroproliferative vascular disease.

Local inhibition of ornithine decarboxylase reduces vascular stenosis in a murine model of carotid injury

OBJECTIVES

Polyamines are organic polycations playing an essential role in cell proliferation and differentiation, as well as in cell contractility, migration and apoptosis. These processes are known to contribute to restenosis, a pathophysiological process often occurring in patients submitted to revascularization procedures. We aimed to test the effect of α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, on vascular cell pathophysiology in vitro and in a rat model of carotid arteriotomy-induced (re)stenosis.

METHODS

The effect of DFMO on primary rat smooth muscle cells (SMCs) and mouse microvascular bEnd.3 endothelial cells (ECs) was evaluated through the analysis of DNA synthesis, polyamine concentration, cell viability, cell cycle phase distribution and by RT-PCR targeting cyclins and genes belonging to the polyamine pathway. The effect of DFMO was then evaluated in arteriotomy-injured rat carotids through the analysis of cell proliferation and apoptosis, RT-PCR and immunohistochemical analysis of differential gene expression.

RESULTS

DFMO showed a differential effect on SMCs and on ECs, with a marked, sustained anti-proliferative effect of DFMO at 3 and 8 days of treatment on SMCs and a less pronounced, late effect on bEnd.3 ECs at 8 days of DFMO treatment. DFMO applied perivascularly in pluronic gel at arteriotomy site reduced subsequent cell proliferation and preserved smooth muscle differentiation without affecting the endothelial coverage. Lumen area in DFMO-treated carotids was 49% greater than in control arteries 4 weeks after injury.

CONCLUSIONS

Our data support the key role of polyamines in restenosis and suggest a novel therapeutic approach for this pathophysiological process.

Arginase and arginine dysregulation in asthma

In recent years, evidence has accumulated indicating that the enzyme arginase, which converts L-arginine into L-ornithine and urea, plays a key role in the pathogenesis of pulmonary disorders such as asthma through dysregulation of L-arginine metabolism and modulation of nitric oxide (NO) homeostasis. Allergic asthma is characterized by airway hyperresponsiveness, inflammation, and remodeling. Through substrate competition, arginase decreases bioavailability of L-arginine for nitric oxide synthase (NOS), thereby limiting NO production with subsequent effects on airway tone and inflammation. By decreasing L-arginine bioavailability, arginase may also contribute to the uncoupling of NOS and the formation of the proinflammatory oxidant peroxynitrite in the airways. Finally, arginase may play a role in the development of chronic airway remodeling through formation of L-ornithine with downstream production of polyamines and L-proline, which are involved in processes of cellular proliferation and collagen deposition. Further research on modulation of arginase activity and L-arginine bioavailability may reveal promising novel therapeutic strategies for asthma.

Genome-wide interaction-based association analysis identified multiple new susceptibility Loci for common diseases

Genome-wide interaction-based association (GWIBA) analysis has the potential to identify novel susceptibility loci. These interaction effects could be missed with the prevailing approaches in genome-wide association studies (GWAS). However, no convincing loci have been discovered exclusively from GWIBA methods, and the intensive computation involved is a major barrier for application. Here, we developed a fast, multi-thread/parallel program named "pair-wise interaction-based association mapping" (PIAM) for exhaustive two-locus searches. With this program, we performed a complete GWIBA analysis on seven diseases with stringent control for false positives, and we validated the results for three of these diseases. We identified one pair-wise interaction between a previously identified locus, C1orf106, and one new locus, TEC, that was specific for Crohn's disease, with a Bonferroni corrected P < 0.05 (P = 0.039). This interaction was replicated with a pair of proxy linked loci (P = 0.013) on an independent dataset. Five other interactions had corrected P < 0.5. We identified the allelic effect of a locus close to SLC7A13 for coronary artery disease. This was replicated with a linked locus on an independent dataset (P = 1.09 × 10⁻⁷). Through a local validation analysis that evaluated association signals, rather than locus-based associations, we found that several other regions showed association/interaction signals with nominal P < 0.05. In conclusion, this study demonstrated that the GWIBA approach was successful for identifying novel loci, and the results provide new insights into the genetic architecture of common diseases. In addition, our PIAM program was capable of handling very large GWAS datasets that are likely to be produced in the future.

Arginase: a key enzyme in the pathophysiology of allergic asthma opening novel therapeutic perspectives

Allergic asthma is a chronic inflammatory airways' disease, characterized by allergen-induced early and late bronchial obstructive reactions, airway hyperresponsiveness (AHR), airway inflammation and airway remodelling. Recent ex vivo and in vivo studies in animal models and asthmatic patients have indicated that arginase may play a central role in all these features. Thus, increased arginase activity in the airways induces reduced bioavailability of L-arginine to constitutive (cNOS) and inducible (iNOS) nitric oxide synthases, causing a deficiency of bronchodilating and anti-inflammatory NO, as well as increased formation of peroxynitrite, which may be involved in allergen-induced airways obstruction, AHR and inflammation. In addition, both via reduced NO production and enhanced synthesis of L-ornithine, increased arginase activity may be involved in airway remodelling by promoting cell proliferation and collagen deposition in the airway wall. Therefore, arginase inhibitors may have therapeutic potential in the treatment of acute and chronic asthma. This review focuses on the pathophysiological role of arginase in allergic asthma and the emerging effectiveness of arginase inhibitors in the treatment of this disease.

Nitric oxide and arginine dysregulation: a novel pathway to pulmonary hypertension in hemolytic disorders

Secondary pulmonary hypertension (PH) is emerging as one of the leading causes of mortality and morbidity in patients with hemolytic anemias such as sickle cell disease (SCD) and thalassemia. Impaired nitric oxide (NO) bioavailability represents the central feature of endothelial dysfunction, and is a major factor in the pathophysiology of PH. Inactivation of NO correlates with hemolytic rate and is associated with the erythrocyte release of cell-free hemoglobin, which consumes NO directly, and the simultaneous release of the arginine-metabolizing enzyme arginase, which limits bioavailability of the NO synthase substrate arginine during the process of intravascular hemolysis. Rapid consumption of NO is accelerated by oxygen radicals that exists in both SCD and thalassemia. A dysregulation of arginine metabolism contributes to endothelial dysfunction and PH in SCD, and is strongly associated with prospective patient mortality. The central mechanism responsible for this metabolic disorder is enhanced arginine turnover, occurring secondary to enhanced plasma arginase activity. This is consistent with a growing appreciation of the role of excessive arginase activity in human diseases, including asthma and pulmonary arterial hypertension. New treatments aimed at improving arginine and NO bioavailability through arginase inhibition, suppression of hemolytic rate, oral arginine supplementation, or use of NO donors represent potential therapeutic strategies for this common pulmonary complication of hemolytic disorders.

Arginase promotes neointima formation in rat injured carotid arteries

OBJECTIVE

Arginase stimulates the proliferation of cultured vascular smooth muscle cells (VSMCs); however, the influence of arginase on VSMC growth in vivo is not known. This study investigated the impact of arginase on cell cycle progression and neointima formation after experimental arterial injury.

METHODS AND RESULTS

Balloon injury of rat carotid arteries resulted in a sustained increase in arginase activity in the vessel wall and the induction of arginase I protein in both the media and neointima of injured vessels. Furthermore, local perivascular application of the potent and selective arginase inhibitors S-(2-boronoethyl)-L-cysteine (BEC) or N(G)-hydroxy-nor-L-arginine (L-OHNA) immediately after injury markedly attenuated medial and neointimal DNA synthesis and neointima formation. Substantial arginase I protein and arginase activity was also detected in rat cultured aortic VSMCs. Moreover, treatment of VSMCs with BEC or L-OHNA, or knockdown of arginase I protein, arrested cells in the G(0)/G(1) phase of the cell cycle and induced the expression of the cyclin-dependent protein kinase inhibitor, p21.

CONCLUSIONS

This study demonstrates that arginase is essential for VSMCs to enter the cell cycle and that arginase I contributes to the remodeling response after arterial injury. Arginase I represents a potentially new therapeutic target for the treatment of vasculoproliferative disorders.

IL-4 and IL-13 upregulate ornithine decarboxylase expression by PI3K and MAP kinase pathways in vascular smooth muscle cells

Ornithine decarboxylase (ODC) is the first and rate-controlling enzyme in the synthesis of polyamines, which are essential for normal cell growth. We have previously demonstrated that IL-4 and IL-13 can stimulate rat aortic smooth muscle cell (RASMC) proliferation. The objective of this study was to determine whether IL-4 and IL-13 induce cell proliferation by upregulating ODC expression in RASMC. The results revealed that incubation of RASMC with IL-4 and IL-13 for 24 h caused four- to fivefold induction of ODC catalytic activity. The increased ODC catalytic activity was attributed to the increased expression of ODC mRNA. Moreover, these observations were paralleled by increased production of polyamines. We further investigated the signal transduction pathways responsible for ODC induction by IL-4 and IL-13. The data illustrated that PD-98059, a MEK (MAPK kinase) inhibitor, LY-294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, and H-89, a protein kinase A (PKA) inhibitor, substantially decreased the induction of ODC catalytic activity and ODC mRNA expression induced by IL-4 and IL-13, suggesting positive regulation of the ODC gene by ERK, PI3K, and PKA pathways. Interestingly, dexamethasone, a known inhibitor of cell proliferation, completely abrogated the response of RASMC to IL-4 and IL-13. Furthermore, the inhibition of ODC by these inhibitors led to the reduced production of polyamines and decreased DNA synthesis as monitored by [(3)H]thymidine incorporation. Our data indicate that upregulation of ODC by IL-4 and IL-13 might play an important role in the pathophysiology of vascular disorders characterized by excessive smooth muscle growth.

Arginine homeostasis in allergic asthma

Allergic asthma is a chronic disease characterized by early and late asthmatic reactions, airway hyperresponsiveness, airway inflammation and airway remodelling. Changes in l-arginine homeostasis may contribute to all these features of asthma by decreased nitric oxide (NO) production and increased formation of peroxynitrite, polyamines and l-proline. Intracellular l-arginine levels are regulated by at least three distinct mechanisms: (i) cellular uptake by cationic amino acid (CAT) transporters, (ii) metabolism by NO-synthase (NOS) and arginase, and (iii) recycling from l-citrulline. Ex vivo studies using animal models of allergic asthma have indicated that attenuated l-arginine bioavailability to NOS causes deficiency of bronchodilating NO and increased production of procontractile peroxynitrite, which importantly contribute to allergen-induced airway hyperresponsiveness after the early and late asthmatic reaction, respectively. Decreased cellular uptake of l-arginine, due to (eosinophil-derived) polycations inhibiting CATs, as well as increased consumption by increased arginase activity are major causes of substrate limitation to NOS. Increasing substrate availability to NOS by administration of l-arginine, l-citrulline, the polycation scavenger heparin, or an arginase inhibitor alleviates allergen-induced airway hyperresponsiveness by restoring the production of bronchodilating NO. In addition, reduced l-arginine levels may contribute to the airway inflammation associated with the development of airway hyperresponsiveness, which similarly may involve decreased NO synthesis and increased peroxynitrite formation. Increased arginase activity could also contribute to airway remodelling and persistent airway hyperresponsiveness in chronic asthma via increased synthesis of l-ornithine, the precursor of polyamines and l-proline. Drugs that increase the bioavailability of l-arginine in the airways - particularly arginase inhibitors - may have therapeutic potential in allergic asthma.

Arginase: a critical regulator of nitric oxide synthesis and vascular function

1. Arginase is the focal enzyme of the urea cycle hydrolysing L-arginine to urea and L-ornithine. Emerging studies have identified arginase in the vasculature and have implicated this enzyme in the regulation of nitric oxide (NO) synthesis and the development of vascular disease. 2. Arginase inhibits the production of NO via several potential mechanisms, including competition with NO synthase (NOS) for the substrate L-arginine, uncoupling of NOS resulting in the generation of the NO scavenger, superoxide and peroxynitrite, repression of the translation and stability of inducible NOS protein, inhibition of inducible NOS activity via the generation of urea and by sensitization of NOS to its endogenous inhibitor asymmetric dimethyl-L-arginine. 3. Upregulation of arginase inhibits endothelial NOS-mediated NO synthesis and may contribute to endothelial dysfunction in hypertension, ageing, ischaemia-reperfusion and diabetes. 4. Arginase also redirects the metabolism of L-arginine to L-ornithine and the formation of polyamines and L-proline, which are essential for smooth muscle cell growth and collagen synthesis. Therefore, the induction of arginase may also promote aberrant vessel wall remodelling and neointima formation. 5. Arginase represents a promising novel therapeutic target that may reverse endothelial and smooth muscle cell dysfunction and prevent vascular disease.

Polyamines upregulate the mRNA expression of cationic amino acid transporter-1 in human retinal pigment epithelial cells

We previously showed that ornithine was mainly transported via cationic amino acid transporter (CAT)-1 in human retinal pigment epithelial (RPE) cell line, human telomerase RT (hTERT)-RPE, and that CAT-1 was involved in ornithine cytotoxicity in ornithine-δ-aminotransferase (OAT)-deficient cell produced by a OAT specific inhibitor, 5-fluoromethylornithine (5-FMO). We showed here that CAT-1 mRNA expression was increased by ornithne in OAT-deficient RPE cells, which was reversed by an inhibitor of ornithine decarboxylase (ODC), α-difluoromethylornithine (DFMO). Polyamines, especially spermine, one of the metabolites of ODC, also enhanced the expression of CAT-1 mRNA. ODC mRNA expression was also increased by ornithine and polyamines, and gene silencing of ODC by siRNA decreased ornithine transport activity and its cytotoxicity. In addition, the mRNA of nuclear protein c-myc was also increased in 5-FMO- and ornithine-treated hTERT-RPE cells, and gene silencing of c-myc prevented the induction of CAT-1 and ODC. Increases in expression of CAT-1, ODC, and c-myc, and the inhibition of these stimulated expression by DFMO were also observed in primary porcine RPE cells. These results suggest that spermine plays an important role in stimulation of mRNA expression of CAT-1, which is a crucial role in ornithine cytotoxicity in OAT-deficient hTERT-RPE cells.

Structure and Function of Cationic Amino Acid Transporters (CATs)

The CAT proteins (CAT for cationic amino acid transporter) are amongst the first mammalian amino acid transporters identified on the molecular level and seem to be the major entry path for cationic amino acids in most cells. However, CAT proteins mediate also efflux of their substrates and thus may also deplete cells from cationic amino acids under certain circumstances. The CAT proteins form a subfamily of the solute carrier family 7 (SLC7) that consists of four confirmed transport proteins for cationic amino acids: CAT-1 (SLC7A1), CAT-2A (SLC7A2A), CAT-2B (SLC7A2B), and CAT-3 (SLC7A3). SLC7A4 and SLC7A14 are two related proteins with yet unknown function. One focus of this review lies on structural and functional differences between the different CAT isoforms. The expression of the CAT proteins is highly regulated on the level of transcription, mRNA stability, translation and subcellular localization. Recent advances toward a better understanding of these mechanisms provide a second focus of this review.

Association of arginase 1 gene polymorphisms with the risk of myocardial infarction and common carotid intima media thickness

BACKGROUND

Recently, it was suggested that arginase (ARG)1 plays an important role in atherogenesis. However, because of its complex functions depending on vascular cell type, its impact on atherogenesis remains unclear.

OBJECTIVE

To evaluate the association between ARG1 polymorphisms and phenotypes related to atherosclerosis.

METHODS

Among 10 ARG1 polymorphisms selected from databases, 4 single-nucleotide polymorphisms (rs2781666; rs2781667; rs2781668; rs17599586) were tested for association with myocardial infarction (MI) in a case-control study (350 cases vs 581 controls), and with common carotid artery (CCA) intima-media thickness (CCA-IMT) in an independent sample of 963 subjects (Etude du Vieillissement Artériel (EVA) study).

RESULTS

The genotype distribution of the rs2781666 G/T polymorphism differed significantly between MI cases and controls (p = 0.005), and the risk of MI was consistently increased for both GT heterozygotes (OR (95% CI) 1.5 (1.1 to 2.0)) and TT homozygotes (OR (95% CI) 2.2 (1.1 to 4.4)). In the EVA study, the rs2781666 polymorphism was also associated with an increase in CCA-IMT (p = 0.010), a surrogate marker of MI.

CONCLUSIONS

The ARG1 rs2781666 polymorphism was consistently associated with MI and an increased CCA-IMT. These findings reinforce the hypothesis of a significant role of ARG1 in vascular pathophysiology.

Pathogenic factors in vascular dementia and Alzheimer's disease. Multiple actions of heparin that probably are beneficial

The following areas are discussed in this review: atherogenesis; cerebrovascular factors; hypoperfusion; beta-amyloid production; beta-amyloid fibril formation; beta-sheets; metal cations; reactive oxygen species/free radicals; chronic inflammatory factors; endogenous plasma heparin; lipoprotein lipase; polyamines; protein kinase C; casein kinases; phospholipase A2; serine proteases; myeloperoxidase; cyclooxygenase 2; cysteine proteases; caspases; proprotein convertases; aspartic proteases; cyclin proteinases; thrombin; tau hyperphosphorylation; advanced glycosylation end products; activator protein 1; calcium; apolipoprotein E epsilon4; histamine; blood-brain barrier; glutamate; transglutaminase; insulin-like growth factor 1.

Dietary arginine slightly and variably affects tissue polyamine levels in male swiss albino mice

Many key metabolic and physiologic functions involve arginine and arginine-derived metabolites. Requirements for arginine, a "conditionally essential" amino acid for most mammalian species, are met in variable proportions by dietary intake and endogenous synthesis, the latter being sufficient to fulfill arginine needs in adult humans and mice under nonpathologic conditions. However, dietary arginine restriction causes orotic aciduria and abnormal function of the urea cycle. Furthermore, the importance of dietary arginine in the maintenance of homeostasis of arginine-derived metabolites in the body has not yet been analyzed in detail. We therefore examined whether the deprivation or supplementation of dietary arginine affects tissue and circulating levels of arginine-derived polyamines. We pair-fed male Swiss albino mice (30 g) for 15 or 30 d synthetic diets containing 0, 1.12 or 2.24 g/100 g L-arginine. Tissue and blood levels of the main free polyamines, putrescine, spermidine and spermine, were measured by HPLC. In general, neither the deprivation nor the supplementation of arginine dramatically affected the levels of any of the polyamines analyzed. Variations were organ, time and polyamine specific, and most differences were in the levels of putrescine at 15 d and of spermidine at 30 d. Thus, in contrast to effects on urea cycle function, dietary arginine does not appear to be essential for the maintenance of the homeostasis of free polyamine levels in adult mice, emphasizing the importance of endogenous arginine synthesis in preserving the polyamine body pool.

Amino acid transport regulation and early embryo development

Amino acids are essential components of media utilized to culture fertilized human eggs to the blastocyst stage in vitro. Use of such media has led to a significant increase in the proportion of embryos that implant upon transfer to the uterus and to a decrease in the number that need to be transferred to achieve pregnancy. Little is known about the mechanisms by which amino acids foster development of healthy human blastocysts. Indications are, however, that many of these mechanisms are the same in human and mouse embryos. Both essential and nonessential amino acid transport benefit preimplantation mouse embryo development, albeit at different stages. Nonessential amino acid transport improves development primarily during cleavage, whereas essential amino acid transport supports development of more viable embryos, especially subsequent to the eight-cell stage. This review discusses likely mechanisms for these beneficial effects.

Physiological cyclic stretch directs L-arginine transport and metabolism to collagen synthesis in vascular smooth muscle

Application of cyclic stretch (10% at 1 hertz) to vascular smooth muscle cells (SMC) increased L-arginine uptake and this was associated with a specific increase in cationic amino acid transporter-2 (CAT-2) mRNA. In addition, cyclic stretch stimulated L-arginine metabolism by inducing arginase I mRNA and arginase activity. In contrast, cyclic stretch inhibited the catabolism of L-arginine to nitric oxide (NO) by blocking inducible NO synthase expression. Exposure of SMC to cyclic stretch markedly increased the capacity of SMC to generate L-proline from L-arginine while inhibiting the formation of polyamines. The stretch-mediated increase in L-proline production was reversed by methyl-L-arginine, a competitive inhibitor of L-arginine transport, by hydroxy-L-arginine, an arginase inhibitor, or by the ornithine aminotransferase inhibitor L-canaline. Finally, cyclic stretch stimulated collagen synthesis and the accumulation of type I collagen, which was inhibited by L-canaline. These results demonstrate that cyclic stretch coordinately stimulates L-proline synthesis by regulating the genes that modulate the transport and metabolism of L-arginine. In addition, they show that stretch-stimulated collagen production is dependent on L-proline formation. The ability of hemodynamic forces to up-regulate L-arginine transport and direct its metabolism to L-proline may play an important role in stabilizing vascular lesions by promoting SMC collagen synthesis.

Characterization of L-arginine transporters in rat renal inner medullary collecting duct

Previous work from our laboratory has demonstrated that the inner medullary collecting duct (IMCD) expresses a large amount of nitric oxide synthase (NOS) activity. The present study was designed to characterize the transport of NOS substrate, L-arginine, in a suspension of bulk-isolated IMCD cells from the Sprague-Dawley rat kidney. Biochemical transport studies demonstrated an L-arginine transport system in IMCD cells that was saturable and Na(+) independent (n = 6). L-Arginine uptake by IMCD cells was inhibited by the cationic amino acids L-lysine, L-homoarginine, and L-ornithine (10 mmol/l each) and unaffected by the neutral amino acids L-leucine, L-serine, and L-glutamine. Both L-ornithine (n = 6) and L-lysine (n = 6) inhibited NOS enzymatic activity in a dose-dependent manner in IMCD cells, supporting the important role of L-arginine transport for NO production by this tubular segment. Furthermore, RT-PCR of microdissected IMCD confirmed the presence of cationic amino acid transporter CAT1 mRNA, whereas CAT2A, CAT2B, and CAT3 were not detected. These results indicate that L-arginine uptake by IMCD cells occurs via system y(+), is encoded by CAT1, and may participate in the regulation of NO production in this renal segment.

In vivo assessment of a novel dacron surface with covalently bound recombinant hirudin

Prosthetic arterial graft surfaces are relatively thrombogenic and fail to heal with a cellular neointima. The goal of this study was to characterize the in vivo antithrombin properties of a novel Dacron surface with covalently linked recombinant hirudin (rHir) implanted in a canine thoracic aorta with high flow and shear rates. rHir was bound to a knitted Dacron patch using crosslinker-modified bovine serum albumin (BSA) as a basecoat protein. BSA was first reacted with the heterobifunctional crosslinker, sulfo-SMCC. This BSA-SMCC complex was then bound to the carboxylic acid groups of hydrolyzed Dacron patches using the carbodiimide crosslinker, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. Iodinated, Traut's-modified rHir (125I-rHir-SH) was then reacted with the Dacron-BSA-SMCC surface, thereby covalently binding 125I-rHir. Graft segments were washed and sonicated to remove any nonspecifically bound 125I-rHir. Dacron-BSA-SMCC-S-125I-rHir patches (n = 5) and control Dacron-BSA patches (n = 5) were implanted in series in the thoracic aortas of canines. These patches were exposed to nonheparinized, arterial blood flow for 2 hours. Patches were explanted and assessed for 125I-rHir loss. Antithrombin activity of explanted 1-cm2 patch segments was evaluated using a chromogenic assay with 1, 5, 10, 15 units of added thrombin. Light microscopy was performed to qualitatively examine the pseudointima. Two animals were excluded from the study owing to excessive bleeding through the knitted 125I-rHir patch. Comparison of preoperative and postoperative 125I-rHir gamma counts revealed an overall decrease of 20+/-5.4% over the period studied. Explanted 125I-rHir patch segments were able to inhibit 1, 5, and 7 NIHU of thrombin, demonstrating retained antithrombin activity. Gross and microscopic examination of the control and test Dacron surfaces showed marked differences. Dacron surfaces with covalently bound 125I-rHir had no gross thrombus and a thin pseudointima of platelets and plasma proteins. In contrast, the control patches had a thick pseudointima composed of fibrin-rich thrombus. rHir, covalently bound to Dacron patches, maintains its biologic activity as well as prevents thrombus formation on the graft surface. This novel antithrombin coating, by modifying the blood/ graft interface, may improve both short- and long-term patency in small-diameter prosthetic arterial grafts and has applications with respect to other implantable or indwelling biomaterials.