Polyamine synthesis inhibition induces S phase cell cycle arrest in vascular smooth muscle cells

The role of polyamine metabolism in cellular function and physiology

Polyamines are molecules with multiple amino groups that are essential for cellular function. The major polyamines are putrescine, spermidine, spermine, and cadaverine. Polyamines are important for posttranscriptional regulation, autophagy, programmed cell death, proliferation, redox homeostasis, and ion channel function. Their levels are tightly controlled. High levels of polyamines are associated with proliferative pathologies such as cancer, whereas low polyamine levels are observed in aging, and elevated polyamine turnover enhances oxidative stress. Polyamine metabolism is implicated in several pathophysiological processes in the nervous, immune, and cardiovascular systems. Currently, manipulating polyamine levels is under investigation as a potential preventive treatment for several pathologies, including aging, ischemia/reperfusion injury, pulmonary hypertension, and cancer. Although polyamines have been implicated in many intracellular mechanisms, our understanding of these processes remains incomplete and is a topic of ongoing investigation. Here, we discuss the regulation and cellular functions of polyamines, their role in physiology and pathology, and emphasize the current gaps in knowledge and potential future research directions.

Macrophage Ontogeny, Phenotype, and Function in Ischemia Reperfusion-Induced Injury and Repair

AKI is characterized by a sudden, and usually reversible, decline in kidney function. In mice, ischemia-reperfusion injury (IRI) is commonly used to model the pathophysiologic features of clinical AKI. Macrophages are a unifying feature of IRI as they regulate both the initial injury response as well as the long-term outcome following resolution of injury. Initially, macrophages in the kidney take on a proinflammatory phenotype characterized by the production of inflammatory cytokines, such as CCL2 (monocyte chemoattractant protein 1), IL-6, IL-1 β , and TNF- α . Release of these proinflammatory cytokines leads to tissue damage. After resolution of the initial injury, macrophages take on a reparative role, aiding in tissue repair and restoration of kidney function. By contrast, failure to resolve the initial injury results in prolonged inflammatory macrophage accumulation and increased kidney damage, fibrosis, and the eventual development of CKD. Despite the extensive amount of literature that has ascribed these functions to M1/M2 macrophages, a recent paradigm shift in the macrophage field now defines macrophages on the basis of their ontological origin, namely monocyte-derived and tissue-resident macrophages. In this review, we focus on macrophage phenotype and function during IRI-induced injury, repair, and transition to CKD using both the classic (M1/M2) and novel (ontological origin) definition of kidney macrophages.

Triclabendazole and clofazimine reduce replication and spermine uptake in vitro in Toxoplasma gondii

Toxoplasmosis is a worldwide zoonosis caused by the protozoan parasite Toxoplasma gondii. Although this infection is generally asymptomatic in immunocompetent individuals, it can cause serious clinical manifestations in newborns with congenital infection or in immunocompromised patients. As current treatments are not always well tolerated, there is an urgent need to find new drugs against human toxoplasmosis. Drug repurposing has gained considerable momentum in the last decade and is a particularly attractive approach for the search of therapeutic alternatives to treat rare and neglected diseases. Thus, in this study, we investigated the antiproliferative effect of several repurposed drugs. Of these, clofazimine and triclabendazole displayed a higher selectivity against T. gondii, affecting its replication. Furthermore, both compounds inhibited spermine incorporation into the parasite, which is necessary for the formation of other polyamines. The data reported here indicate that clofazimine and triclabendazole could be used for the treatment of human toxoplasmosis and confirms that drug repurposing is an excellent strategy to find new therapeutic targets of intervention.

Self-replicating murine ex vivo cultured alveolar macrophages as a model for toxicological studies of particle-induced inflammation

Alveolar macrophages (AM) are integral to maintaining homeostasis within the lungs following exposure to inhaled particles. However, due to the high animal number requirements for in vitro research with primary AM, there remains a need for validated cell models that replicate alveolar macrophages in form and function to better understand the mechanisms that contribute to particle-induced inflammation and disease. A novel, easily adaptable, culture model that facilitates the continued expansion of murine alveolar macrophages for several months, termed murine ex vivo cultured AM (mexAM) has been recently described. Therefore, the present work evaluated the use of mexAMs as a suitable model for primary AM interactions with nano- and micro-sized particles. mexAM displayed a comparable profile of functional phenotype gene expression as primary AM and similar particle uptake capabilities. The NLRP3 inflammasome-driven IL-1β inflammatory response to crystalline silica and various nanoparticles was also assessed, as well as the effects of cationic amphiphilic drugs to block particle-induced inflammation. For all endpoints, mexAM showed a comparable response to primary AM. Altogether, the present work supports the use of mexAM as a validated replacement for primary AM cultures thereby reducing animal numbers and serving as an effective model for mechanistic investigation of inflammatory pathways in particle-induced respiratory disease.

Arginase-1 Is Required for Macrophage-Mediated Renal Tubule Regeneration

BACKGROUND

After kidney injury, macrophages transition from initial proinflammatory activation to a proreparative phenotype characterized by expression of arginase-1 (Arg1), mannose receptor 1 (Mrc1), and macrophage scavenger receptor 1 (Msr1). The mechanism by which these alternatively activated macrophages promote repair is unknown.

METHODS

We characterized the macrophage and renal responses after ischemia-reperfusion injury with contralateral nephrectomy in LysM-Cre;Arg1fl/fl mice and littermate controls and used in vitro coculture of macrophages and tubular cells to determine how macrophage-expressed arginase-1 promotes kidney repair.

RESULTS

After ischemia-reperfusion injury with contralateral nephrectomy, Arg1-expressing macrophages were almost exclusively located in the outer stripe of the medulla adjacent to injured S3 tubule segments containing luminal debris or casts. Macrophage Arg1 expression was reduced by more than 90% in injured LysM-Cre;Arg1fl/fl mice, resulting in decreased mouse survival, decreased renal tubular cell proliferation and decreased renal repair compared with littermate controls. In vitro studies demonstrate that tubular cells exposed apically to dead cell debris secrete high levels of GM-CSF and induce reparative macrophage activation, with those macrophages in turn secreting Arg1-dependent factor(s) that directly stimulate tubular cell proliferation.

CONCLUSIONS

GM-CSF-induced, proreparative macrophages express arginase-1, which is required for the S3 tubular cell proliferative response that promotes renal repair after ischemia-reperfusion injury.

N1-acetylspermidine is a determinant of hair follicle stem cell fate

Stem cell differentiation is accompanied by increased mRNA translation. The rate of protein biosynthesis is influenced by the polyamines putrescine, spermidine and spermine, which are essential for cell growth and stem cell maintenance. However, the role of polyamines as endogenous effectors of stem cell fate and whether they act through translational control remains obscure. Here, we investigate the function of polyamines in stem cell fate decisions using hair follicle stem cell (HFSC) organoids. Compared to progenitor cells, HFSCs showed lower translation rates, correlating with reduced polyamine levels. Surprisingly, overall polyamine depletion decreased translation but did not affect cell fate. In contrast, specific depletion of natural polyamines mediated by spermidine/spermine N1-acetyltransferase (SSAT; also known as SAT1) activation did not reduce translation but enhanced stemness. These results suggest a translation-independent role of polyamines in cell fate regulation. Indeed, we identified N1-acetylspermidine as a determinant of cell fate that acted through increasing self-renewal, and observed elevated N1-acetylspermidine levels upon depilation-mediated HFSC proliferation and differentiation in vivo. Overall, this study delineates the diverse routes of polyamine metabolism-mediated regulation of stem cell fate decisions.

This article has an associated First Person interview with the first author of the paper.

Summary: Reduced protein synthesis is required for stem cell functions. Here, we delineate a complex interplay of polyamines and mRNA translation that determines hair follicle stem cell fate decisions.

Putrescine as indicator of manganese neurotoxicity: Dose-response study in human SH-SY5Y cells

Disrupted polyamine metabolism with elevated putrescine is associated with neuronal dysfunction. Manganese (Mn) is an essential nutrient that causes neurotoxicity in excess, but methods to evaluate biochemical responses to high Mn are limited. No information is available on dose-response effects of Mn on putrescine abundance and related polyamine metabolism. The present research was to test the hypothesis that Mn causes putrescine accumulation over a physiologically adequate to toxic concentration range in a neuronal cell line. We used human SH-SY5Y neuroblastoma cells treated with MnCl2 under conditions that resulted in cell death or no cell death after 48 h. Putrescine and other metabolites were analyzed by liquid chromatography-ultra high-resolution mass spectrometry. Putrescine-related pathway changes were identified with metabolome-wide association study (MWAS). Results show that Mn caused a dose-dependent increase in putrescine over a non-toxic to toxic concentration range. MWAS of putrescine showed positive correlations with the polyamine metabolite N8-acetylspermidine, methionine-related precursors, and arginine-associated urea cycle metabolites, while putrescine was negatively correlated with γ-aminobutyric acid (GABA)-related and succinate-related metabolites (P < 0.001, FDR < 0.01). These data suggest that measurement of putrescine and correlated metabolites may be useful to study effects of Mn intake in the high adequate to UL range.

The Future Challenge of Reactive Oxygen Species (ROS) in Hypertension: From Bench to Bed Side

Reactive oxygen species (ROS) act as signaling molecules that control physiological processes, including cell adaptation to stress. Redox signaling via ROS has quite recently become the focus of much attention in numerous pathological contexts, including neurodegenerative diseases, kidney and cardiovascular disease. Imbalance in ROS formation and degradation has also been implicated in essential hypertension. Essential hypertension is characterized by multiple genetic and environmental factors which do not completely explain its associated risk factors. Thereby, even if advances in therapy have led to a significant reduction in hypertension-associated complications, to interfere with the unbalance of redox signals might represent an additional therapeutic challenge. The decrease of nitric oxide (NO) levels, the antioxidant activity commonly found in preclinical models of hypertension and the ability of antioxidant approaches to reduce ROS levels have spurred clinicians to investigate the contribution of ROS in humans. Indeed, particular effort has recently been devoted to understanding how redox signaling may contribute to vascular pathobiology in human hypertension. However, although biomarkers of oxidative stress have been found to positively correlate with blood pressure in preclinical model of hypertension, human data are less convincing. We herein provide an overview of the most relevant mechanisms via which oxidative stress might contribute to the pathophysiology of essential hypertension. Moreover, alternative approaches, which are directed towards improving antioxidant machinery and/or interfering with ROS production, are also discussed.

Targeting ornithine decarboxylase (ODC) inhibits esophageal squamous cell carcinoma progression

To explore the function of ornithine decarboxylase in esophageal squamous cell carcinoma progression and test the effectiveness of anti-ornithine decarboxylase therapy for esophageal squamous cell carcinoma. In this study, we examined the expression pattern of ornithine decarboxylase in esophageal squamous cell carcinoma cell lines and tissues using immunohistochemistry and Western blot analysis. Then we investigated the function of ornithine decarboxylase in ESCC cells by using shRNA and an irreversible inhibitor of ornithine decarboxylase, difluoromethylornithine. To gather more supporting pre-clinical data, a human esophageal squamous cell carcinoma patient-derived xenograft mouse model (C.B-17 severe combined immunodeficient mice) was used to determine the antitumor effects of difluoromethylornithine in vivo. Our data showed that the expression of the ornithine decarboxylase protein is increased in esophageal squamous cell carcinoma tissues compared with esophagitis or normal adjacent tissues. Polyamine depletion by ODC shRNA not only arrests esophageal squamous cell carcinoma cells in the G2/M phase, but also induces apoptosis, which further suppresses esophageal squamous cell carcinoma cell tumorigenesis. Difluoromethylornithine treatment decreases proliferation and also induces apoptosis of esophageal squamous cell carcinoma cells and implanted tumors, resulting in significant reduction in the size and weight of tumors. The results of this study indicate that ornithine decarboxylase is a promising target for esophageal squamous cell carcinoma therapy and difluoromethylornithine warrants further study in clinical trials to test its effectiveness against esophageal squamous cell carcinoma.

Blocking an enzyme involved in the cellular synthesis of essential compounds called polyamines could help treat esophageal cancer. Zigang Dong from the University of Minnesota’s Hormel Institute, USA, and colleagues showed that this enzyme, called ornithine decarboxylase (ODC), is expressed at elevated levels in tumor tissues taken from patients with esophageal squamous cell carcinoma. The researchers blocked ODC activity in esophageal cancer cells using either RNA interference techniques or a drug called difluoromethylornithine (DFMO). In both cases, the treatment suppressed further growth and induced cell death. DFMO treatment also reduced the size and weight of tumors in mice implanted with human patient-derived esophageal cancer tissue. The findings point DFMO, which is already used as a medication to treat African sleeping sickness and excessive hair growth, as a potential therapy for cancer patients.

Gamma-Glutamylpolyamine Synthetase GlnA3 Is Involved in the First Step of Polyamine Degradation Pathway in Streptomyces coelicolor M145

Streptomyces coelicolor M145 was shown to be able to grow in the presence of high concentrations of polyamines, such as putrescine, cadaverine, spermidine, or spermine, as a sole nitrogen source. However, hardly anything is known about polyamine utilization and its regulation in streptomycetes. In this study, we demonstrated that only one of the three proteins annotated as glutamine synthetase-like protein, GlnA3 (SCO6962), was involved in the catabolism of polyamines. Transcriptional analysis revealed that the expression of glnA3 was strongly induced by exogenous polyamines and repressed in the presence of ammonium. The ΔglnA3 mutant was shown to be unable to grow on defined Evans agar supplemented with putrescine, cadaverine, spermidine, and spermine as sole nitrogen source. HPLC analysis demonstrated that the ΔglnA3 mutant accumulated polyamines intracellularly, but was unable to degrade them. In a rich complex medium supplemented with a mixture of the four different polyamines, the ΔglnA3 mutant grew poorly showing abnormal mycelium morphology and decreased life span in comparison to the parental strain. These observations indicated that the accumulation of polyamines was toxic for the cell. An in silico analysis of the GlnA3 protein model suggested that it might act as a gamma-glutamylpolyamine synthetase catalyzing the first step of polyamine degradation. GlnA3-catalyzed glutamylation of putrescine was confirmed in an enzymatic in vitro assay and the GlnA3 reaction product, gamma-glutamylputrescine, was detected by HPLC/ESI-MS. In this work, the first step of polyamine utilization in S. coelicolor has been elucidated and the putative polyamine utilization pathway has been deduced based on the sequence similarity and transcriptional analysis of homologous genes expressed in the presence of polyamines.

Inhibition of Polyamine Uptake Potentiates the Anti-Proliferative Effect of Polyamine Synthesis Inhibition and Preserves the Contractile Phenotype of Vascular Smooth Muscle Cells

Increased vascular smooth muscle cell (VSMC) proliferation is a factor in atherosclerosis and injury-induced arterial (re) stenosis. Inhibition of polyamine synthesis by α-difluoro-methylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, attenuates VSMC proliferation with high sensitivity and specificity. However, cells can escape polyamine synthesis blockade by importing polyamines from the environment. To address this issue, polyamine transport inhibitors (PTIs) have been developed. We investigated the effects of the novel trimer44NMe (PTI-1) alone and in combination with DFMO on VSMC polyamine uptake, proliferation and phenotype regulation. PTI-1 efficiently inhibited polyamine uptake in primary mouse aortic and human coronary VSMCs in the absence as well as in the presence of DFMO. Interestingly, culture with DFMO for 2 days substantially (>95%) reduced putrescine (Put) and spermidine (Spd) contents without any effect on proliferation. Culture with PTI-1 alone had no effect on either polyamine levels or proliferation rate, but the combination of both treatments reduced Put and Spd levels below the detection limit and inhibited proliferation. Treatment with DFMO for a longer time period (4 days) reduced Put and Spd below their detection limits and reduced proliferation, showing that only a small pool of polyamines is needed to sustain VSMC proliferation. Inhibited proliferation by polyamine depletion was associated with maintained expression of contractile smooth marker genes. In cultured intact mouse aorta, PTI-1 potentiated the DFMO-induced inhibition of cell proliferation. The combination of endogenous polyamine synthesis inhibition with uptake blockade is thus a viable approach for targeting unwanted vascular cell proliferation in vivo, including vascular restenosis.

Inhibition of polyamine formation antagonizes vascular smooth muscle cell proliferation and preserves the contractile phenotype

The polyamines putrescine, spermidine and spermine play essential roles in cell proliferation and migration, two processes involved in the development of vascular disease. Thus, intervention with polyamine formation may represent a way to inhibit unwanted vascular smooth muscle cell (VSMC) proliferation. The aim of the present study was to assess the importance of polyamines for VSMC proliferation and vascular contractility. The rate-limiting step in polyamine biosynthesis is catalysed by ornithine decarboxylase (ODC). Treatment with α-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, reduced DNA synthesis in primary rat VSMCs in a concentration-dependent manner with an IC50 value of 100 μM. Moreover, DFMO reduced VSMC migration assessed in a scratch assay. The DFMO-induced attenuation of VSMC proliferation was associated with lowered cellular amount of polyamines. The antiproliferative effect of DFMO was specific because supplementation with polyamines reversed the effect of DFMO on proliferation and normalized cellular polyamine levels. Isometric force recordings in cultured rat tail artery rings showed that DFMO counteracts the decrease in contractility caused by culture with foetal bovine serum as growth stimulant. We conclude that inhibition of polyamine synthesis by DFMO may limit the first wave of cell proliferation and migration, which occurs in the acute phase after vascular injury. Besides its antiproliferative effect, DFMO may prevent loss of the smooth muscle contractile phenotype in vascular injury.

Arginine supplementation and exposure time affects polyamine and glucose metabolism in primary liver cells isolated from Atlantic salmon

Arginine has been demonstrated to enhance glucose and lipid oxidation in mammals through activation of polyamine turnover. We aimed to investigate how arginine affects energy utilization through polyamine metabolism and whether this effect is time dependent. Primary liver cells were isolated from Atlantic salmon (2.2 kg body weight) fed diets containing 25.5 (low arginine, LA) or 36.1 (high arginine, HA) g arginine/kg dry matter for 12 weeks, to investigate the effect of long-term arginine supplementation. The cells were cultured for 24 h in L-15 medium to which either alpha-difluoromethylornithine (DFMO) or N (1),N (11)-diethylnorspermine (DENSPM) was added. Analysis of the medium by nuclear magnetic resonance revealed significant differences between the two dietary groups as well as between cells exposed to DFMO and DENSPM, with decreased glucose, fumarate and lactate concentrations in media of the HA cells. Liver cells from fish fed the HA diet had higher spermidine/spermine-N1-acetyltransferase protein abundance and lower adenosine triphosphate concentration as compared to the LA-fed fish, while gene expression was not affected by either diet or treatment. Primary liver cells isolated from salmon fed a commercial diet and cultured in L-15 media with or without arginine supplementation (1.82 or 3.63 mM) for 48 h, representing short-term effect of arginine supplementation, showed differential expression of genes for apoptosis and polyamine synthesis due to arginine supplementation or inhibition by DFMO. Overall, arginine concentration and exposure time affected energy metabolism and gene regulation more than inhibition or activation of key enzymes of polyamine metabolism, suggesting a polyamine-independent influence of arginine on cellular energy metabolism and survival.

Activation of GPER Induces Differentiation and Inhibition of Coronary Artery Smooth Muscle Cell Proliferation

Background

Vascular pathology and dysfunction are direct life-threatening outcomes resulting from atherosclerosis or vascular injury, which are primarily attributed to contractile smooth muscle cells (SMCs) dedifferentiation and proliferation by re-entering cell cycle. Increasing evidence suggests potent protective effects of G-protein coupled estrogen receptor 1 (GPER) activation against cardiovascular diseases. However, the mechanism underlying GPER function remains poorly understood, especially if it plays a potential role in modulating coronary artery smooth muscle cells (CASMCs).

Methodology/Principal Findings

The objective of our study was to understand the functional role of GPER in CASMC proliferation and differentiation in coronary arteries using from humans and swine models. We found that the GPER agonist, G-1, inhibited both human and porcine CASMC proliferation in a concentration- (10⁻⁸ to 10⁻⁵ M) and time-dependent manner. Flow cytometry revealed that treatment with G-1 significantly decreased the proportion of S-phase and G2/M cells in the growing cell population, suggesting that G-1 inhibits cell proliferation by slowing progression of the cell cycle. Further, G-1-induced cell cycle retardation was associated with decreased expression of cyclin B, up-regulation of cyclin D1, and concomitant induction of p21, and partially mediated by suppressed ERK1/2 and Akt pathways. In addition, G-1 induces SMC differentiation evidenced by increased α-smooth muscle actin (α-actin) and smooth muscle protein 22α (SM22α) protein expressions and inhibits CASMC migration induced by growth medium.

Conclusion

GPER activation inhibits CASMC proliferation by suppressing cell cycle progression via inhibition of ERK1/2 and Akt phosphorylation. GPER may constitute a novel mechanism to suppress intimal migration and/or synthetic phenotype of VSMC.

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.

Polyamine depletion enhances the roscovitine-induced apoptosis through the activation of mitochondria in HCT116 colon carcinoma cells

Small molecule inhibitors of cyclin-dependent kinases (CDKs) show high therapeutic potential in various cancer types which are characterized by the accumulation of transformed cells due to impaired apoptotic machinery. Roscovitine, a CDK inhibitor showed to be a potent apoptotic inducer in several cancer cells. Polyamines, putrescine, spermidine and spermine, are biogenic amines involved in many cellular processes, including apoptosis. In this study, we explored the potential role of polyamines in roscovitine-induced apoptosis in HCT116 colon cancer cells. Roscovitine induced apoptosis by activating mitochondrial pathway caspases and modulating the expression of Bcl-2 family members. Depletion of polyamines by treatment with difluoromethylornithine (DFMO) increased roscovitine-induced apoptosis. Transient silencing of ornithine decarboxylase, polyamine biosynthesis enzyme and special target of DFMO also increased roscovitine-induced apoptosis in HCT116 cells. Interestingly, additional putrescine treatment was found pro-apoptotic due to the presence of non-functional ornithine decarboxylase (ODC). Finally, roscovitine altered polyamine catabolic pathway and led to decrease in putrescine and spermidine levels. Therefore, the metabolic regulation of polyamines may dictate the power of roscovitine induced apoptotic responses in HCT116 colon cancer cells.

The GPER1 agonist G-1 attenuates endothelial cell proliferation by inhibiting DNA synthesis and accumulating cells in the S and G2 phases of the cell cycle

G protein-coupled receptor 30 (GPR30) or G protein-coupled estrogen receptor 1 (GPER1) is expressed in the vasculature, but the importance of vascular GPER1 remains to be clarified. Here we investigate effects of the GPER1 agonist G-1 on endothelial cell proliferation using mouse microvascular endothelial bEnd.3 cells. The bEnd.3 cells express mRNA for GPER1. The bEnd.3 cells expressed both ERα and ERβ immunoreactivities. Treatment with G-1 reduced DNA synthesis and cell number with IC(50) values of about 2 μM. GPER1 siRNA prevented G-1-induced attenuation of DNA synthesis. G-1 accumulated cells in S and G2 phases of the cell cycle, suggesting that G-1 blocks transition between G2 and M. G-1 had no effect on DNA synthesis in COS-7 cells only weakly expressing GPER1 mRNA. 17β-Estradiol had no effect on DNA synthesis in physiological concentrations (nM). The ER blocker ICI182780 reduced DNA synthesis with similar potency as G-1. Treatment with the ERK/MAP kinase inhibitor PD98059 had no effect on G-1-induced attenuation of DNA synthesis. G-1- induced antiproliferation was observed not only in bEnd.3 cells but also in human umbilical vein endothelial cells and HMEC-1 endothelial cells. We conclude that the GPER1 agonist G-1 attenuates endothelial cell proliferation via inhibition of DNA synthesis and by accumulation of cells in S and G2.

Concentration of arginine and optimal time of hypertonic saline in restoration of T-cell dysfunction

BACKGROUND

Hypertonic saline (HS) restores prostaglandin E(2) (PGE(2))-induced T-cell suppression in the presence of 1100 microM arginine. However, under arginine-free culture conditions, HS dose not restore T-cell proliferation. Therefore, we wanted to determine if HS can restore PGE(2)-induced T-cell suppression in the presence of 80 microM of arginine, the physiologically relevant arginine concentration. We also wanted to determine the concentration of arginine that induces HS restoration of PGE(2)-suppressed T-cell proliferation and whether HS restoration of T-cell dysfunction is dependent on the injection time of HS.

MATERIALS AND METHODS

Jurkat cells were cultured in media containing 0, 40, 80, 400, 800, or 1100 microM arginine. In both the PGE(2)-stimulated and HS-treated group, we measured cell proliferation using MTT assay and arginase activity. We also measured cell proliferation relative to HS injection time.

RESULTS

In 80 microM arginine, HS did not restore Jurkat cell proliferation that had been suppressed by PGE(2). Increased concentrations of arginine in the media increased MTT cell proliferation. In 800 microM arginine media, HS restored PGE(2)-suppressed Jurkat cell proliferation to normal. HS restored PGE(2)-suppressed Jurkat cell proliferation when it was added at 2 h, similar to at same time and 1 h after PGE(2) stimulation.

CONCLUSIONS

In order to restore PGE(2)-suppressed Jurkat cell proliferation, HS requires at least 800 microM arginine. HS restored PGE(2)-suppressed Jurkat cell proliferation even though HS was added at 2 h after PGE(2) stimulation.

Impacts of amino acid nutrition on pregnancy outcome in pigs: mechanisms and implications for swine production

Pigs suffer up to 50% embryonic and fetal loss during gestation and exhibit the most severe naturally occurring intrauterine growth retardation among livestock species. Placental insufficiency is a major factor contributing to suboptimal reproductive performance and reduced birth weights of pigs. Enhancement of placental growth and function through nutritional management offers an effective solution to improving embryonic and fetal survival and growth. We discovered an unusual abundance of the arginine family of AA in porcine allantoic fluid (a reservoir of nutrients) during early gestation, when placental growth is most rapid. Arginine is metabolized to ornithine, proline, and nitric oxide, and these compounds possess a plethora of physiological functions. Nitric oxide is a vasodilator and angiogenic factor, whereas both ornithine and proline are substrates for placental synthesis of polyamines, which are key regulators of protein synthesis and angiogenesis. Additionally, arginine, leucine, glutamine, and proline activate the mammalian target of rapamycin cell-signaling pathway to enhance protein synthesis and cell proliferation in placentae. To translate basic research on AA biochemistry and nutrition into application, dietary supplementation with 0.83% l-arginine to gilts on d 14 to 28 or d 30 to 114 of gestation increased the number and litter birth weight of live-born piglets. In addition, supplementing the gestation diet with 0.4% l-arginine plus 0.6% l-glutamine enhanced the efficiency of nutrient utilization, reduced variation in piglet birth weight, and increased litter birth weight. By regulating syntheses of nitric oxide, polyamines, and proteins, functional AA stimulate placental growth and the transfer of nutrients from mother to embryo or fetus to promote conceptus survival, growth, and development.

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.

Arginine metabolism and nutrition in growth, health and disease

L-Arginine (Arg) is synthesised from glutamine, glutamate, and proline via the intestinal-renal axis in humans and most other mammals (including pigs, sheep and rats). Arg degradation occurs via multiple pathways that are initiated by arginase, nitric-oxide synthase, Arg:glycine amidinotransferase, and Arg decarboxylase. These pathways produce nitric oxide, polyamines, proline, glutamate, creatine, and agmatine with each having enormous biological importance. Arg is also required for the detoxification of ammonia, which is an extremely toxic substance for the central nervous system. There is compelling evidence that Arg regulates interorgan metabolism of energy substrates and the function of multiple organs. The results of both experimental and clinical studies indicate that Arg is a nutritionally essential amino acid (AA) for spermatogenesis, embryonic survival, fetal and neonatal growth, as well as maintenance of vascular tone and hemodynamics. Moreover, a growing body of evidence clearly indicates that dietary supplementation or intravenous administration of Arg is beneficial in improving reproductive, cardiovascular, pulmonary, renal, gastrointestinal, liver and immune functions, as well as facilitating wound healing, enhancing insulin sensitivity, and maintaining tissue integrity. Additionally, Arg or L-citrulline may provide novel and effective therapies for obesity, diabetes, and the metabolic syndrome. The effect of Arg in treating many developmental and health problems is unique among AAs, and offers great promise for improved health and wellbeing of humans and animals.