Phase I study of ADI-PEG20 plus low-dose cytarabine for the treatment of acute myeloid leukemia.

Most acute myeloid leukemia (AML) cells are argininosuccinate synthetase-deficient. Pegylated arginine deiminase (ADI-PEG20) monotherapy depletes circulating arginine, thereby selectively inducing tumor cell death. ADI-PEG20 was shown to induce complete responses in ~10% of relapsed/refractory or poor-risk AML patients. We conducted a phase I, dose-escalation study combining ADI-PEG20 and low-dose cytarabine (LDC) in AML patients. Patients received 20 mg LDC subcutaneously twice daily for 10 days every 28 days and ADI-PEG20 at 18 or 36 mg/m2 (dose levels 1 and 2) intramuscularly weekly. An expansion cohort for the maximal tolerated dose of ADI-PEG20 was planned to further estimate the toxicity and preliminary response of this regimen. The primary endpoints were safety and tolerability. The secondary endpoints were time on treatment, overall survival (OS), overall response rate (ORR), and biomarkers (pharmacodynamics and immunogenicity detection). Twenty-three patients were included in the study, and seventeen patients were in the expansion cohort (dose level 2). No patients developed dose-limiting toxicities. The most common grade III/IV toxicities were thrombocytopenia (61%), anemia (52%), and neutropenia (30%). One had an allergic reaction to ADI-PEG20. The ORR in 18 evaluable patients was 44.4%, with a median OS of 8.0 (4.5-not reached) months. In seven treatment-naïve patients, the ORR was 71.4% and the complete remission rate was 57.1%. The ADI-PEG20 and LDC combination was well-tolerated and resulted in an encouraging ORR. Further combination studies are warranted. (This trial was registered in ClinicalTrials.gov as a Ph1 Study of ADI-PEG20 Plus Low-Dose Cytarabine in Older Patients With AML, NCT02875093).

Montelukast, a cysteinyl leukotriene receptor antagonist, exerts local antinociception in animal model of pain through the L-arginine/nitric oxide/cyclic GMP/KATP channel pathway and PPARγ receptors.

OBJECTIVE: The leukotrienes are inflammatory mediators. In the present study, the analgesic role of local montelukast, a cysteinyl leukotriene receptor antagonist, and the possible involvement of L-arginine/NO/cGMP/KATP channel pathway and PPARγ receptors was assessed in the formalin test in rats. METHODS AND RESULTS: The local administration of montelukast into the hind paw produced dose-related analgesia during both phases of the formalin test. Furthermore, pre-treatment with L-NAME, methylene blue, and glibenclamide prevented montelukast (10 µg/paw)-induced antinociception in both early and late phases of the test. Moreover, the local L-arginine and diazoxide before the sub-effective dose of montelukast (3 µg/paw) produced an analgesic effect. Also, local GW-9662 blocked antinociception induced by montelukast plus pioglitazone (10 µg/paw). CONCLUSION: In conclusion, montelukast produced peripheral analgesia through PPARγ receptors and activation of the L-arginine/NO/cGMP/KATP channel pathway, with potential for a new topical analgesic drug.

Metabolic therapy with PEG-arginase induces a sustained complete remission in immunotherapy-resistant melanoma.

BACKGROUND: Metastatic melanoma is an aggressive skin cancer with a poor prognosis. Current treatment strategies for high-stage melanoma are based around the use of immunotherapy with immune checkpoint inhibitors such as anti-PDL1 or anti-CTLA4 antibodies to stimulate anti-cancer T cell responses, yet a number of patients will relapse and die of disease. Here, we report the first sustained complete remission in a patient with metastatic melanoma who failed two immunotherapy strategies, by targeting tumour arginine metabolism. CASE PRESENTATION: A 65-year-old patient with metastatic melanoma who progressed through two immunotherapy strategies with immune checkpoint inhibitor antibodies was enrolled in a phase I study (NCT02285101) and treated with 2 mg/kg intravenously, weekly pegylated recombinant arginase (BCT-100). The patient experienced no toxicities > grade 2 and entered a complete remission which is sustained for over 30 months. RNA-sequencing identified a number of transcriptomic pathway alterations compared to control samples. The tumour had absent expression of the recycling enzymes argininosuccinate synthetase (ASS) and ornithine transcarbamylase (OTC) indicating a state of arginine auxotrophy, which was reconfirmed by immunohistochemistry, and validation in a larger cohort of melanoma tumour samples. CONCLUSIONS: Targeting arginine metabolism with therapeutic arginase in arginine auxotrophic melanoma can be an effective salvage for the treatment of patients who fail immunotherapy.

Pyridoxamine: A novel treatment for schizophrenia with enhanced carbonyl stress.

AIM: The aim of this clinical trial was to obtain proof of concept for high-dose pyridoxamine as a novel treatment for schizophrenia with enhanced carbonyl stress. METHODS: Ten Japanese schizophrenia patients with high plasma pentosidine, which is a representative biomarker of enhanced carbonyl stress, were recruited in a 24-week, open trial in which high-dose pyridoxamine (ranging from 1200 to 2400 mg/day) was administered using a conventional antipsychotic regimen. Main outcomes were the total change in Positive and Negative Syndrome Scale score and the Brief Psychiatric Rating Scale score from baseline to end of treatment at week 24 (or at withdrawal). RESULTS: Decreased plasma pentosidine levels were observed in eight patients. Two patients showed marked improvement in their psychological symptoms. A patient who harbors a frameshift mutation in the Glyoxalase 1 gene also showed considerable reduction in psychosis accompanied with a moderate decrease in plasma pentosidine levels. A reduction of greater than 20% in the assessment scale of drug-induced Parkinsonism occurred in four patients. Although there was no severe suicide-related ideation or behavior, Wernicke's encephalopathy-like adverse drug reactions occurred in two patients and were completely suppressed by thiamine supplementation. CONCLUSION: High-dose pyridoxamine add-on treatment was, in part, effective for a subpopulation of schizophrenia patients with enhanced carbonyl stress. Further randomized, placebo-controlled trials with careful monitoring will be required to validate the efficacy of high-dose pyridoxamine for these patients.

[Clinical value of ADMA in patients with pulmonary arterial hypertension combination with congenital heart disease].

OBJECTIVE: To study the concentration of the asymmetrical dimethyl-L-arginine (ADMA) in patients with pulmonary arterial hypertension (PAH) commbination with congenital heart disease (CHD) and its clinical value as a biomaker for diagnosis and prognosis.
 Methods: A total of 100 patients with CHD and 25 healthy adult subjects were recruited. CHD patients were divided into three groups: normal pulmonary arterial pressure group (group A, n=25), mild-to-moderate PAH group (group B, n=25), severe PAH group (group C, n=50). Twenty patients in Group C were treated with sildenafil and followed up for 6 months. The clinical data, including echocardiographic measurements, hemodynamic parameters and ADMA levels, for all subjects were collected.
 Results: The ADMA concentrations in patients with CHD-PAH significantly increased compared with that in the CHD patients without PAH or the health controls, and the ADMA concentrations in CHD patients with severe PAH were significantly higher than that in the CHD patients with mild-to-moderate PAH; serum ADMA concentration was correlated with mean pulmonary arterial pressure (mPAP) (r=0.61, P<0.001) and pulmonary vascular resistance (PVR) (r=0.417, P<0.001) in CHD patients; when using AMDA>0.485 µmol/L as criteria for diagnosis of CHD-PAH, the specificity was 82.7% and the sensitivity was 92.0%; the pulmonary arterial pressure significantly decreased after sildenafil therapy for 6 months, same as the ADMA levels.
 Conclusion: Plasma ADMA could be used as a biomarker to identify PAH in patients with CHD and as a prognosic index to reflect the sildenafil treatment effect.

Effects of Aging and Tocotrienol-Rich Fraction Supplementation on Brain Arginine Metabolism in Rats.

Accumulating evidence suggests that altered arginine metabolism is involved in the aging and neurodegenerative processes. This study sought to determine the effects of age and vitamin E supplementation in the form of tocotrienol-rich fraction (TRF) on brain arginine metabolism. Male Wistar rats at ages of 3 and 21 months were supplemented with TRF orally for 3 months prior to the dissection of tissue from five brain regions. The tissue concentrations of L-arginine and its nine downstream metabolites were quantified using high-performance liquid chromatography and liquid chromatography tandem mass spectrometry. We found age-related alterations in L-arginine metabolites in the chemical- and region-specific manners. Moreover, TRF supplementation reversed age-associated changes in arginine metabolites in the entorhinal cortex and cerebellum. Multiple regression analysis revealed a number of significant neurochemical-behavioral correlations, indicating the beneficial effects of TRF supplementation on memory and motor function.

Epigallocatechin-3-gallate ameliorates erectile function in aged rats via regulation of PRMT1/DDAH/ADMA/NOS metabolism pathway.

Aging-related ED is predominantly attributed to neurovascular dysfunction mediated by NO suppression and increased oxidative stress in penis. The alterations of protein arginine methyltransferases 1 (PRMT1)/dimethylarginine dimethylaminohydrolase (DDAH)/asymmetrical dimethylarginine (ADMA)/NO synthase (NOS) pathway regulate NO production in the vascular endothelium. Epigallocatechin-3-gallate (EGCG) is one of the most abundant and antioxidative ingredients isolated from green tea. In the present study, 40 Sprague-Dawley rats were randomly distributed into four groups: one young rat group and three aged rat groups treated with daily gavage feedings of EGCG at doses of 0, 10 mg kg-1 and 100 mg kg-1 for 12 weeks, respectively. Erectile function was assessed by electrical stimulation of the cavernous nerves with intracavernous pressure (ICP) measurement. After euthanasia, penile tissue was investigated using Western blot and ELISA to assess the PRMT1/DDAH/ADMA/NOS metabolism pathway. Superoxide dismutase (SOD) and malondialdehyde (MDA) levels were detected by colorimetry. We also evaluated smooth muscle contents. The ratio of maximal ICP and mean systemic arterial pressure (MAP) was markedly higher in EGCG-treated aged rats than in untreated aged rats. We found that DDAH1 and DDAH2 were expressed in cavernosal tissue, and they were downregulated in corpora of aged rats. The administration of EGCG upregulated the expression and activity of DDAH. In contrast, EGCG treatment downregulated the expression of PRMT1 and ADMA content. Moreover, EGCG-treated rats showed an improvement in smooth muscle expression, the ratio of smooth muscle cell/collagen fibril, SOD activity, and MDA levels when compared with untreated aged rats.

In vivo microvascular and macrovascular endothelial function is not associated with circulating dimethylarginines in patients with rheumatoid arthritis: a prospective analysis of the DRACCO cohort.

OBJECTIVES: To examine associations between asymmetric (ADMA), symmetric dimethylarginine (SDMA) and ADMA:SDMA ratio with assessments of endothelial function and coronary artery perfusion in RA patients. METHODS: ADMA and SDMA levels were measured in 197 RA individuals [144 (77.4%) females, median age: 66 years (quartiles: 59-73)]. Patients underwent assessments of microvascular endothelium-dependent and endothelium-independent function, macrovascular endothelium-dependent and endothelium-independent function and vascular morphology (pulse wave analysis, carotid intima-media thickness (cIMT), and carotid plaque). Coronary perfusion was assessed by subendocardial viability ratio (SEVR). RESULTS: SEVR correlated with SDMA (r = 0.172, p = 0.026) and ADMA:SDMA (r = -0.160, p = 0.041) in univariable analysis, but not in multivariable analysis accounting for confounding factors. Neither ADMA:SDMA ratio nor SDMA were significantly correlated with microvascular or macrovascular endothelial function, or with arterial stiffness and cIMT. Within subgroup of patients (n = 26) with high inflammatory markers, a post-hoc analysis showed that SDMA and the ADMA:SDMA ratio were significantly associated with endothelium-dependent microvascular function in univariable analysis, with Pearson's r correlation coefficients of -0.440 (p = 0.031) and 0.511 (p = 0.011), respectively. Similar finding were established between ADMA:SDMA ratio and arterial stiffness in univariable analysis, with Pearson's r of 0.493, (p = 0.024). CONCLUSION: Dimethylarginines were not found to be significantly associated with several assessments of vascular function and morphology in patients with RA, however, post-hoc analysis indicates that there may be associations in patients with raised inflammatory markers. Our results suggest that dysregulated NO metabolism may not be the sole mechanism for the development of preclinical atherosclerosis in RA.

Gas6/Axl is the sensor of arginine-auxotrophic response in targeted chemotherapy with arginine-depleting agents.

Many human malignancies lack de novo biosynthesis of arginine (Arg) as the key enzyme argininosuccinate synthetase 1 (ASS1) is silenced. These tumors acquire ectopic Arg for survival, and depleting this source by Arg-depleting recombinant enzyme ADI-PEG20 results in cell death. Mechanisms underlying Arg auxotrophy in these tumors and how they respond to Arg-auxotrophic stress are poorly understood. Here, we report that an immediate-early event of Arg-auxotrophic response involves reactive oxygen species-mediated secretion of Gas6, which interacts with its receptor Axl and activates the downstream Ras/PI3K/Akt growth signal leading to accumulation of c-Myc by protein stabilization. Arg-auxotrophic challenge also transcriptionally upregulates c-Myc expression, which provides a feedback mechanism to enhance Axl expression. c-Myc is a positive regulator of ASS1, but elevated ASS1 provides a feedback mechanism to suppress c-Myc and Axl. Our results revealed multiple inter-regulatory pathways in Arg-auxotrophic response, consisting of Axl, c-Myc and ASS1, which regulate Arg homeostasis and ADI-PEG20 sensitivity. These pathways provide potential targets for improving the efficacy of treating Arg-auxotrophic tumors using Arg-deprivation strategies.

Angiotensin converting enzyme inhibition increases ADMA concentration in patients on maintenance hemodialysis--a randomized cross-over study.

BACKGROUND: Endothelial dysfunction occurs in patients with end-stage renal disease (ESRD) and is associated with increased cardiovascular morbidity and mortality. Asymmetric dimethylarginine (ADMA) contributes to endothelial dysfunction in ESRD. In the general population, angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) decrease ADMA levels, but no study has compared the effect of these drugs in patients with ESRD on maintenance hemodialysis (MHD). METHODS: We evaluated the effect of 1-week treatment with ramipril (5 mg/d), valsartan (160 mg/d), and placebo on ADMA levels in 15 patients on MHD in a double-blind, placebo-controlled, three x three cross-over study. RESULTS: We found that ADMA levels were increased at baseline and throughout the dialysis session during ramipril treatment (p < 0.001 compared to both, placebo and valsartan). Ramipril did not increase ADMA levels in a study of patients without ESRD, suggesting that factors related to ESRD or hemodialysis contribute to the ACE inhibitor-induced increase in ADMA. We have previously shown that ACE inhibition increases bradykinin (BK) levels during hemodialysis. We therefore evaluated the effect of bradykinin on ADMA production in A549 cells; a cell line that expresses BK receptors. Incubation with BK increased intracellular ADMA concentration through BK B2-receptor stimulation. CONCLUSION: These data indicate that short-term ACE inhibition increases ADMA in patients on MHD whereas ARBs do not. In vitro studies further suggest that this may occur through BK-mediated increase in ADMA production during ACE inhibition. TRIAL REGISTRATION: Clinicaltrials.gov NCT00732069 August 6 2008 and NCT00607672 February 4 2008.

Asymmetric dimethylarginine in experimental breast cancer; action of Vitamin C and E.

OBJECTIVE: To investigate the arginase-nitric oxide synthase paradox through asymmetric dimethylarginine, symmetric dimethylarginine and nitric oxide levels, and to see the effect of antioxidant vitamins on this mechanism of cancer action. METHODS: The animal-based study was conducted at Trakya University, Turkey, in 2008, and comprised mice that were divided into five equal groups. Group 1 had healthy controls, while in the other four groups breast cancer was induced. Group 2 received saline solution, group 3 received 200 mg/kg/day vitamin C (tumour +vit C), group 4 received 300 mg/kg/day vitamin E (tumour +vitE) and group 5 received both 200 mg/kg/day vitamin C and 300 mg/kg/day vitamin E (tumour +vit C+vit E) for 15 days intra-peritoneally.Arginine, asymmetric dimethylarginine, symmetric dimethylarginine and nitric oxide levels were determined in each group. RESULTS: The 50 mice in the study were divided into five groups of 10(20%) each. Plasma arginine levels were significantly decreased, asymmetric dimethylarginine and symmetric dimethylarginine levels were increased, while plasma nitric oxide level was significantly decreased in group 2. There was no statistically significant difference in treatment groups for all parameters (p>0.05 each). CONCLUSIONS: Understanding of the mechanism may help to develop new anti-cancer agents.

Association between brachial-ankle pulse wave velocity and the ratio of l-arginine to asymmetric dimethylarginine in patients undergoing coronary angiography.

BACKGROUND: Endothelial dysfunction causes vasomotor dysregulation and vascular stiffening in addition to structural changes. By influencing NO synthesis, deficiency of l-arginine relative to asymmetric dimethylarginine (ADMA), which is an l-arginine derivative that acts as a competitive NO synthase inhibitor, may lead to the promotion of arterial stiffness. This study investigated the relationship between the l-arginine/ADMA ratio and brachial-ankle pulse wave velocity (baPWV), an indicator of arterial stiffness. METHODS AND RESULTS: This cross-sectional study enrolled 74 patients (62 men, 12 women; mean age, 67±10 years) undergoing elective coronary angiography. A total of 54 (73%) patients had coronary artery disease. Serum l-arginine and ADMA were measured by high-performance liquid chromatography with fluorescence detection. The ratio of l-arginine to ADMA and the serum l-arginine level was associated with baPWV in univariate regression analysis (l-arginine/ADMA ratio: ß=-0.323, p=0.005; l-arginine: ß=-0.247, p=0.034). In addition, baPWV was related to blood hemoglobin concentration, hematocrit, brain natriuretic peptide level, symmetric dimethylarginine, renal function, blood pressure, and heart rate. In multivariate analysis, the l-arginine/ADMA ratio was a significant predictor of baPWV (ß=-0.310, p<0.001). In subgroup analyses, the l-arginine/ADMA ratio was associated with baPWV in elderly patients (n=46, ß=-0.359, p=0.004), and in younger patients (n=28, ß=-0.412, p=0.006). CONCLUSION: A low l-arginine/ADMA ratio may be associated with high baPWV in patients undergoing coronary angiography.

Asymmetric dimethylarginine (ADMA) and treatment response relationship in male patients with first-episode schizophrenia: a controlled study.

Nitric oxide (NO) is thought to be involved in the pathogenesis of schizophrenia as well as many neuropsychiatric disease. Asymmetric dimethylarginine (ADMA) reduces the level of NO by inhibiting nitric oxide synthase (NOS) enzyme. In this study it is aimed to be investigated ADMA in patients with first-episode schizophrenia. In this study, according to DSM-IV diagnostic criteria for schizophrenia-like psychotic disorder, 49 male first-episode schizophrenia patients-whose mean age was 23.4±3.5 year-and age and education matched 30 healthy male subjects were included for comparison. ADMA levels of the patients were measured before and after 2 months of therapy. In order to rule out the conditions that may affect the levels of ADMA, people whose physical examination and laboratory findings were within normal range were included in the study. In this study plasma ADMA levels of first-episode schizophrenia patients and control group were 3.6±1.5 µmol/L and 1.02±1.02 respectively. After 2 months of antipsychotic treatment plasma ADMA levels of the schizophrenia patients decreased compared to baseline. There was no relationship between the ADMA levels and the clinical severity of the disease. It is considered to be the role of ADMA in the etiopathogenesis of schizophrenia.

Ambient temperature and dietary supplementation interact to shape mosquito vector competence for malaria.

The extent to which environmental factors influence the ability of Anopheles mosquitoes to transmit malaria parasites remains poorly explored. Environmental variation, such as change in ambient temperature, will not necessarily influence the rates of host and parasite processes equivalently, potentially resulting in complex effects on infection outcomes. As proof of principle, we used Anopheles stephensi and the rodent malaria parasite, Plasmodium yoelii, to examine the effects of a range of constant temperatures on one aspect of host defense (detected as alterations in expression of nitric oxide synthase gene - NOS) to parasite infection. We experimentally boosted mosquito midgut immunity to infection through dietary supplementation with the essential amino acid l-Arginine (l-Arg), which increases midgut nitric oxide (NO) levels by infection-induced NOS catalysis in A. stephensi. At intermediate temperatures, supplementation reduced oocyst prevalence, oocyst intensity, and sporozoite prevalence suggesting that the outcome of parasite infection was potentially dependent upon the rate of NOS-mediated midgut immunity. At low and high temperature extremes, however, infection was severely constrained irrespective of supplementation. The effects of l-Arg appeared to be mediated by NO-dependent negative feedback on NOS expression, as evidenced by depressed NOS expression in l-Arg treated groups at temperatures where supplementation decreased parasite infection. These results suggest the need to consider the direct (e.g. effects of mosquito body temperature on parasite physiology) and indirect effects (e.g. mediated through changes in mosquito physiology/immunity) of environmental factors on mosquito-malaria interactions in order to understand natural variation in vector competence.

Effects of rosuvastatin on ADMA, rhokinase, NADPH oxidase, caveolin-1, hsp 90 and NFkB levels in a rat model of myocardial ischaemia-reperfusion.

AIM: Endothelial dysfunction, oxidative stress and inflammation are among the most important mechanisms of ischaemia-reperfusion (I/R) injury. Besides their cholesterol-lowering effects, statins are known to provide protection against myocardial dysfunction and vascular endothelial injury via nitric oxide-dependent mechanisms. The aim of this study was to investigate the effects of rosuvastatin on certain intermediates involved in the generation of nitric oxide (asymmetrical dimethyl arginin, ADMA, caveolin-1 and hsp 90), oxidative stress (rhokinase, NADPH oxidase) and inflammation (NFkB), using an in vivo model of myocardial infarction in the rat. METHODS: Adult male Sprague Dawley rats were divided into three groups (control, I/R and I/R after 15 days of rosuvastatin administration). Reperfusion was applied for 120 min following left anterior descending coronary artery ischaemia for 30 min. Caveolin-1, hsp 90 and NFkB levels were evaluated with the quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and ADMA, rhokinase and NADPH oxidase levels were evaluated with ELISA. RESULTS: While NFkB and hsp 90 levels were higher in the I/R group, their levels were significantly lower in the rosuvastatin group. While ADMA and NADPH oxidase levels significantly increased with I/R, they were lower in the rosuvastatin-treated group, but not statistically significant. Rhokinase levels were significantly lower in the rosuvastatin group. Caveolin-1 levels were not different between the groups. CONCLUSION: Our results suggest that ADMA, rhokinase, NADPH oxidase, hsp 90 and NFkB could facilitate I/R injury, and rosuvastatin significantly reduced levels of these parameters. These results indicate that rosuvastatin may have a protective role in I/R injury via mechanisms targeting inflammation, endothelial dysfunction and oxidative stress.

Cyclosporine attenuates arginine transport, in human endothelial cells, through modulation of cationic amino acid transporter-1.

BACKGROUND: The spectrum of cardiovascular toxicity by cyclosporine (CsA) includes hypertension, accelerated atherosclerosis, and thrombotic microangiopathy, all of which are the result of endothelial cell dysfunction. Endothelial cell dysfunction is characterized by decreased endothelial nitric oxide synthase (eNOS) activity. Cationic amino acid transporter-1 (CAT-1) is the specific arginine transporter for eNOS. CsA has been shown to attenuate nitric oxide (NO) generation. However, the mechanism remains elusive. We hypothesize that CsA inhibits eNOS activity through modulation of its selective arginine supplier CAT-1. METHODS: We studied the effect of CsA on arginine uptake, NO2/NO3 generation, and CAT-1, protein kinase Cα (PKCα), and phosphorylated PKCα protein expression in human umbilical vein endothelial cell cultures (HUVEC) in the absence and presence of L-arginine. RESULTS: CsA (0.5-2 µg/ml) significantly attenuated arginine transport in a dose- and time-dependent manner, a phenomenon which was prevented by co-incubation with L-arginine (1 mM). The aforementioned findings were accompanied by increased protein nitration, a measure for peroxynitrite accumulation. In contrast, no changes were observed in NO2/NO3 generation. CsA significantly decreased the abundance of CAT-1 protein, an effect that was attenuated by L-arginine. PKCα and phosphorylated PKCα (CAT-1 inhibitors) protein contents were not affected by CsA. CONCLUSION: CsA inhibits arginine transport and induces protein nitration in HUVEC through modulation of CAT-1.

Assessment of the endothelial functions in monocrotaline-induced pulmonary hypertension.

Pulmonary hypertension (PH) is a life-threatening disease that causes endothelial dysfunction in the pulmonary vascular bed. Systemic endothelial dysfunction has also been reported in PH. This study compared the systemic and pulmonary vascular responses and some blood biomarkers of endothelial function in monocrotaline (MCT)-induced PH of rats. It also investigated the effect of sildenafil and iloprost treatment. MCT application induced elevation in the right ventricular pressures of the rat heart that had been reversed by sildenafil and iloprost treatment. Acetylcholine-induced endothelium-dependent relaxations of the isolated pulmonary artery were decreased in the PH group and this failure was reversed by sildenafil and iloprost treatment. Acetylcholine-induced endothelium-dependent relaxations of the isolated thoracic aorta were similar in all groups. Serotonin-induced contractions of the pulmonary artery were augmented by PH. In the isolated aorta, serotonin-stimulated contraction was not different in the control and MCT groups, but sildenafil and iloprost treatment decreased serotonin responses. The nitric oxide (NO) level in systemic circulation was not significantly changed by PH. However, sildenafil and iloprost treatments caused a decrease in the plasma level of NO. Asymmetric dimethylarginine levels in plasma were significantly decreased after MCT application and were not recovered by sildenafil and iloprost treatment. Total antioxidant capacity and H2S level of plasma were similar in all groups. Results of this study showed that MCT-induced PH caused specific toxic effects on pulmonary vasculature without any functional effects on the aorta. In addition, it was also demonstrated that sildenafil and iloprost treatments were effective in the MCT-induced PH.

The therapeutic potential of targeting endogenous inhibitors of nitric oxide synthesis.

Asymmetric dimethylarginine (ADMA)--a naturally occurring amino acid that is a product of protein breakdown--is released into the cytoplasm following the post-translational methylation of arginine residues within proteins and the subsequent proteolysis of these arginine-methylated proteins. ADMA inhibits all three isoforms of nitric oxide synthase and therefore has the potential to produce diverse biological effects, particularly in the cardiovascular system. In addition to its renal clearance, endogenously produced ADMA is metabolized to L-citrulline and dimethylamine by the dimethylarginine dimethylaminohydrolase (DDAH) enzymes. Pharmacological modification of DDAH has therefore been proposed as a mechanism for manipulating endogenous ADMA concentrations and regulating the production of nitric oxide in situations where alterations in nitric oxide signalling have been shown to contribute to pathophysiology. This review describes the biology of ADMA and the potential therapeutic utility of manipulating DDAH activity.

Interaction of new, very potent non-nucleotide antagonists with Arg256 of the human platelet P2Y12 receptor.

The P2Y(12) receptor plays a crucial role in platelet aggregation. In the present study, we analyzed the properties of non-nucleotide antagonists at the recombinant human P2Y(12) receptor and searched for amino acids involved in the molecular interaction. Receptor function was assessed by measuring the cAMP response element (CRE)-directed luciferase expression in Chinese hamster ovary cells. The cellular cAMP production was accelerated by forskolin; 2-methylthio-ADP was used to activate the wild-type P2Y(12) receptor or mutant constructs. 2-Methylthio-ADP inhibited the CRE-dependent luciferase expression with an IC(50) value of approximately 1 nM. The anthraquinone derivative reactive blue 2 used at increasing concentrations shifted the concentration-response curve of 2-methylthio-ADP to the right in a manner compatible with competitive antagonism (pA(2) value, 7.4). Its analog, 1-amino-4-[4-phenylamino-3-sulfophenylamino]-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (PSB-0739), showed a markedly higher antagonistic potency with a pA(2) value of 9.8. In cells expressing the R256A-mutant receptor, the potencies of both reactive blue 2 (apparent pK(B), 5.9) and PSB-0739 (apparent pK(B), 9.1) were decreased. The same was true for the pure reactive blue 2 meta- and para-isomers and for the ortho-isomer cibacron blue 3GA. In contrast, the analog, 1-amino-4-[4-anilino-phenylamino]-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate, lacking a sulfonic acid residue at ring D (PSB-0826), showed similar pK(B) values at wild-type (8.4) and R256A-mutant receptors (8.3). In summary, the results demonstrate that PSB-0739 is the most potent competitive non-nucleotide antagonist at the human P2Y(12) receptor described so far. The results also indicate that the sulfonic acid residue at ring D is involved in the interaction of antagonists derived from reactive blue 2 with the residue Arg256 of the human P2Y(12) receptor.