Determination of dimethylarginine dimethylaminohydrolase activity in the kidney

Effect of a Low Dose of Carvedilol on Cyclophosphamide-Induced Urinary Toxicity in Rats—A Comparison with Mesna

One of the major side effects of cyclophosphamide (CPX)—an alkylating anticancer drug that is still clinically used—is urotoxicity with hemorrhagic cystitis. The present study was designed to evaluate the ability of carvedilol to protect rats from cyclophosphamide-induced urotoxicity. Rats were injected intraperitoneally (i.p.) with CPX (200 mg/kg) and administered carvedilol (2 mg/kg) intragastrically a day before, at the day and a day after a single i.p. injection of CPX, with or without mesna (40, 80, and 80 mg/kg i.p. 20 min before, 4 h and 8 h after CPX administration, respectively). Pretreatment with carvedilol partly prevented the CPX-induced increase in urinary bladder and kidney index, and completely protects from CPX-evoked alterations in serum potassium and creatinine level, but did not prevent histological alterations in the urinary bladder and hematuria. However, carvedilol administration resulted in significant restoration of kidney glutathione (GSH) level and a decrease in kidney interleukin 1β (IL-1β) and plasma asymmetric dimethylarginine (ADMA) concentrations. Not only did mesna improve kidney function, but it also completely reversed histological abnormalities in bladders and prevented hematuria. In most cases, no significant interaction of carvedilol with mesna was observed, although the effect of both drugs together was better than mesna given alone regarding plasma ADMA level and kidney IL-1β concentration. In conclusion, carvedilol did not counteract the injury caused in the urinary bladders but restored kidney function, presumably via its antioxidant and anti-inflammatory properties.

Vascular and immunopathological role of Asymmetric Dimethylarginine (ADMA) in Experimental Autoimmune Encephalomyelitis

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase (NOS) inhibitor/uncoupler inducing vascular pathology. Vascular pathology is an important factor for the development and progression of CNS pathology of MS, yet the role of ADMA in MS remains elusive. Patients with multiple sclerosis (MS) are reported to have elevated blood levels of ADMA, and mice with experimental autoimmune encephalomyelitis (EAE, an animal model of MS) generated by auto-immunization of myelin oligodendrocyte glycoprotein (MOG) and blood-brain barrier (BBB) disruption by pertussis toxin also had increased blood ADMA levels in parallel with induction of clinical disease. To explore the role of ADMA in EAE pathogenesis, EAE mice were treated with a daily dose of ADMA. It is of special interest that ADMA treatment enhanced the BBB disruption in EAE mice and exacerbated the clinical and CNS disease of EAE. ADMA treatment also induced the BBB disruption and EAE disease in MOG-immunized mice even without pertussis toxin treatment, suggesting the role of ADMA in BBB dysfunction in EAE. T-cell polarization studies also documented that ADMA treatment promotes T_H 1- and T_H 17-mediated immune responses but without affecting Treg-mediated immune response in EAE mice as well as in in vitro T-cell culture. Taken together, these data, for the first time, document the vascular and immunopathogenic roles of ADMA in EAE, thus pointing to the potential of ADMA-mediated mechanism as a new target of potential therapy for MS.

Specific Lowering of Asymmetric Dimethylarginine by Pharmacological Dimethylarginine Dimethylaminohydrolase Improves Endothelial Function, Reduces Blood Pressure and Ischemia-Reperfusion Injury

Multiple clinical and preclinical studies have demonstrated that plasma levels of asymmetric dimethylarginine (ADMA) are strongly associated with hypertension, diabetes, and cardiovascular and renal disease. Genetic studies in rodents have provided evidence that ADMA metabolizing dimethylarginine dimethylaminohydrolase (DDAH)-1 plays a role in hypertension and cardiovascular disease. However, it remains to be established whether ADMA is a bystander, biomarker, or sufficient contributor to the pathogenesis of hypertension and cardiovascular and renal disease. The goal of the present investigation was to develop a pharmacological molecule to specifically lower ADMA and determine the physiologic consequences of ADMA lowering in animal models. Further, we sought to determine whether ADMA lowering will produce therapeutic benefits in vascular disease in which high ADMA levels are produced. A novel long-acting recombinant DDAH (M-DDAH) was produced by post-translational modification, which effectively lowered ADMA in vitro and in vivo. Treatment with M-DDAH improved endothelial function as measured by increase in cGMP and in vitro angiogenesis. In a rat model of hypertension, M-DDAH significantly reduced blood pressure (vehicle: 187 ± 19 mm Hg vs. M-DDAH: 157 ± 23 mm Hg; P < 0.05). Similarly, in a rat model of ischemia-reperfusion injury, M-DDAH significantly improved renal function as measured by reduction in serum creatinine (vehicle: 3.14 ± 0.74 mg/dl vs. M-DDAH: 1.1 ± 0.75 mg/dl; P < 0.01), inflammation, and injured tubules (vehicle: 73.1 ± 11.1% vs. M-DDAH: 22.1 ± 18.4%; P < 0.001). These pharmacological studies have provided direct evidence for a pathologic role of ADMA and the therapeutic benefits of ADMA lowering in preclinical models of endothelial dysfunction, hypertension, and ischemia-reperfusion injury. SIGNIFICANCE STATEMENT: High levels of ADMA occur in patients with cardiovascular and renal disease. A novel modified dimethylarginine dimethylaminohydrolase by PEGylation effectively lowers ADMA, improves endothelial function, reduces blood pressure and protects from ischemia-reperfusion renal injury.

Positive Effects of Melatonin on Renal Nitric Oxide-Asymmetric Dimethylarginine Metabolism in Fructose-Fed Rats

Background: The incidence of metabolic syndrome is increasing worldwide and this is mainly attributed to high carbohydrate intake, especially of fructose, and sedentary lifestyles. Nitric oxide (NO), which is synthesized by nitric oxide synthase (NOS) enzymes, is a crucial molecule for endothelial and renal health. Asymmetric dimethylarginine (ADMA) is the most potent inhibitor of NOS and it is degraded by dimethylarginine dimethylaminohydrolase (DDAH). The aim of this study was to investigate the effects of melatonin on renal NO-ADMA metabolism using a metabolic syndrome model achieved by fructose administration. Methods: Thirty-two rats were randomly divided into four groups (n = 8): (1) control group, (2) fructose group, (3) melatonin group, and (4) fructose + melatonin group. Fructose (20%) was given in drinking water. Melatonin [20 mg/(kg·day)] was administered in 0.1% ethanol solution. After 8 weeks, kidney tissues were collected to measure tissue levels of nitrite/nitrate (NOx), ADMA, arginine, symmetric dimethylarginine, DDAH activity, and endothelial NOS (eNOS) and inducible NOS (iNOS) protein levels. Results: Fructose led to low arginine/ADMA ratios (AARs) (P < 0.008). Tissue NOx levels of the fructose + melatonin group were significantly higher than those of the fructose group (P < 0.008). ADMA and arginine were significantly higher in the fructose + melatonin group than the control group (P < 0.008). The DDAH activity of the fructose and fructose + melatonin groups was significantly higher than that of the control group (P < 0.008). eNOS protein levels showed no difference and iNOS protein was not detected in any of the groups. Conclusions: A diminished AAR indicates the toxicity of fructose in the kidneys. Melatonin has beneficial effects on the NO-ADMA pathway as it restores NOx levels and increases DDAH activity, possibly as a result of a compensatory mechanism to metabolize increased ADMA.

Enhancing kidney DDAH-1 expression by adenovirus delivery reduces ADMA and ameliorates diabetic nephropathy

Endothelial dysfunction, characterized by reduced bioavailability of nitric oxide and increased oxidative stress, is a hallmark characteristic in diabetes and diabetic nephropathy (DN). High levels of asymmetric dimethylarginine (ADMA) are observed in several diseases including DN and are a strong prognostic marker for cardiovascular events in patients with diabetes and end-stage renal disease. ADMA, an endogenous endothelial nitric oxide synthase (NOS3) inhibitor, is selectively metabolized by dimethylarginine dimethylaminohydrolase (DDAH). Low DDAH levels have been associated with cardiac and renal dysfunction, but its effects on DN are unknown. We hypothesized that enhanced renal DDAH-1 expression would improve DN by reducing ADMA and restoring NOS3 levels. DBA/2J mice injected with multiple low doses of vehicle or streptozotocin were subsequently injected intrarenally with adenovirus expressing DDAH-1 (Ad-h-DDAH-1) or vector control [Ad-green fluorescent protein (GFP)], and mice were followed for 6 wk. Diabetes was associated with increased kidney ADMA and reduced kidney DDAH activity and DDAH-1 expression but had no effect on kidney DDAH-2 expression. Ad-GFP-treated diabetic mice showed significant increases in albuminuria, histological changes, glomerular macrophage recruitment, inflammatory cytokine and fibrotic markers, kidney ADMA levels, and urinary thiobarbituric acid reactive substances excretion as an indicator of oxidative stress, along with a significant reduction in kidney DDAH activity and kidney NOS3 mRNA compared with normal mice. In contrast, Ad-h-DDAH-1 treatment of diabetic mice reversed these effects. These data indicate, for the first time, that DDAH-1 mediates renal tissue protection in DN via the ADMA-NOS3-interaction. Enhanced renal DDAH-1 activity could be a novel therapeutic tool for treating patients with diabetes.

Assessment of the direct effects of DDAH I on tumour angiogenesis in vivo

Nitric oxide (NO) has been strongly implicated in glioma progression and angiogenesis. The endogenous inhibitors of NO synthesis, asymmetric dimethylarginine (ADMA) and N-monomethyl-l-arginine (l-NMMA), are metabolized by dimethylarginine dimethylaminohydrolase (DDAH), and hence, DDAH is an intracellular factor that regulates NO. However, DDAH may also have an NO-independent action. We aimed to investigate whether DDAH I has any direct role in tumour vascular development and growth independent of its NO-mediated effects, in order to establish the future potential of DDAH inhibition as an anti-angiogenic treatment strategy. A clone of rat C6 glioma cells deficient in NO production expressing a pTet Off regulatable element was identified and engineered to overexpress DDAH I in the absence of doxycycline. Xenografts derived from these cells were propagated in the presence or absence of doxycycline and susceptibility magnetic resonance imaging used to assess functional vasculature in vivo. Pathological correlates of tumour vascular density, maturation and function were also sought. In the absence of doxycycline, tumours exhibited high DDAH I expression and activity, which was suppressed in its presence. However, overexpression of DDAH I had no measurable effect on tumour growth, vessel density, function or maturation. These data suggest that in C6 gliomas DDAH has no NO-independent effects on tumour growth and angiogenesis, and that the therapeutic potential of targeting DDAH in gliomas should only be considered in the context of NO regulation.

The farnesoid X receptor agonist obeticholic acid upregulates biliary excretion of asymmetric dimethylarginine via MATE-1 during hepatic ischemia/reperfusion injury

Background

We previously showed that increased asymmetric dimethylarginine (ADMA) biliary excretion occurs during hepatic ischemia/reperfusion (I/R), prompting us to study the effects of the farnesoid X receptor (FXR) agonist obeticholic acid (OCA) on bile, serum and tissue levels of ADMA after I/R.

Material and methods

Male Wistar rats were orally administered 10mg/kg/day of OCA or vehicle for 5 days and were subjected to 60 min partial hepatic ischemia or sham-operated. After a 60 min reperfusion, serum, tissue and bile ADMA levels, liver mRNA and protein expression of ADMA transporters (CAT-1, CAT-2A, CAT-2B, OCT-1, MATE-1), and enzymes involved in ADMA synthesis (protein-arginine-N-methyltransferase-1, PRMT-1) and metabolism (dimethylarginine-dimethylaminohydrolase-1, DDAH-1) were measured.

Results

OCA administration induced a further increase in biliary ADMA levels both in sham and I/R groups, with no significant changes in hepatic ADMA content. A reduction in CAT-1, CAT-2A or CAT-2B transcripts was found in OCA-treated sham-operated rats compared with vehicle. Conversely, OCA administration did not change CAT-1, CAT-2A or CAT-2B expression, already reduced by I/R. However, a marked decrease in OCT-1 and increase in MATE-1 expression was observed. A similar trend occurred with protein expression.

Conclusion

The reduced mRNA expression of hepatic CAT transporters suggests that the increase in serum ADMA levels is probably due to decreased liver uptake of ADMA from the systemic circulation. Conversely, the mechanism involved in further increasing biliary ADMA levels in sham and I/R groups treated with OCA appears to be MATE-1-dependent.

Asymmetric dimethylarginine and symmetric dimethylarginine prospectively relates to carotid wall thickening in black men: the SABPA study

The relationship of both asymmetric (ADMA) and symmetric (SDMA) dimethylarginine with carotid wall thickness is inconclusive especially among black populations. We aimed to compare carotid intima media thickness (cIMT) and dimethylarginine levels in 75 black and 91 white men at baseline and after a 3-year follow-up, and to investigate associations of percentage change in cIMT with percentage change in dimethylarginine levels (ADMA and SDMA). Plasma levels of ADMA and SDMA were determined with a liquid chromatography mass spectrometry method and B-mode ultrasonography was used to determine the cIMT at baseline and follow-up. In black men, mean cIMT (p = 0.79) and ADMA levels (p = 0.67) remained the same, but SDMA levels were lower (p < 0.001) when comparing baseline and follow-up. In white men, cIMT increased (p < 0.001), but both mean ADMA and SDMA levels decreased (p < 0.001) over time. In black men, percentage change in cIMT was positively associated with percentage change in ADMA (R ² = 0.49; β = 0.46; p < 0.001) and percentage change in SDMA (R ² = 0.46; β = 0.41; p < 0.001). These associations were absent in the white men. Despite lower mean SDMA and similar ADMA and cIMT in black men, percentage change in cIMT was independently associated with percentage change in ADMA and percentage change in SDMA. These results suggest an important role for ADMA and SDMA lowering strategies to delay carotid wall thickening, especially in black populations prone to the development of cardiovascular disease.

Effects of betaine supplementation on nitric oxide metabolism, atherosclerotic parameters, and fatty liver in guinea pigs fed a high cholesterol plus methionine diet

OBJECTIVE

The aim of this study was to investigate the effect of high cholesterol (CHOL) and CHOL + methionine (MET) diets on atherogenic and oxidative index parameters and on the factors that influence nitric oxide (NO) bioavailability. Also, attempts were made to determine whether dietary betaine (BET) resulted in any improvement in the changes that occurred after CHOL + MET administration.

METHODS

Guinea pigs were fed chow containing 1.5% CHOL with or without 2% MET for 10 wk. A third group received the CHOL + MET + BET diet. Control groups were given standard chow or standard chow + BET. Arginine, NO, nitrotyrosine (NT), and asymmetric dimethylarginine (ADMA) levels; lipid profile; and dimethylarginine dimethylaminohydrolase (DDAH) activity were measured. The liver and aorta were subjected to histopathologic analysis.

RESULTS

The CHOL + MET diet caused higher serum CHOL and homocysteine levels, but no further increases were seen in aortic CHOL and diene conjugate (DC) levels and histopathologic lesions as compared with the CHOL group. Hepatic lipids and DC levels were also higher, and histopathologic lesions were more severe. CHOL + MET feeding increased ADMA and NT levels as compared with those of the CHOL-fed group. When BET (1 g/kg body weight/d) was added to the CHOL + MET diet, homocysteine and lipid levels decreased and histopathologic changes were reversed. BET diet decreased serum ADMA and hepatic and aortic DC levels and partly restored DDAH activity.

CONCLUSIONS

BET supplementation may be effective in preventing hyperlipidemia, disturbed NO availability, oxidative stress, and the development of fatty liver and atherosclerotic lesions that might result from excess amounts of cholesterol and methionine in the diet.

Vascular function and arginine and dimethylarginines in gentamicin-induced renal failure: a possible effect of heme oxygenase 1 inducer hemin

Increased oxidative stress and disturbance in nitric oxide bioavailability lead to endothelial dysfunction and cardiovascular complication in renal disease. Gentamicin (GM), a commonly used antibiotic, exhibits a toxic effect on renal proximal tubules. Prevention of its nephrotoxicity is important. Therefore, we investigated whether heme oxygenase 1 HO-1) induction influenced kidney and vascular function in GM-administered rats. GM (100 mg·kg^-1·day^-1; i.p.) was given to rats alone or together with hemin (20 mg·kg^-1 on alternate days; i.p.) for 14 days. Plasma and kidney l-arginine, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA) as well as kidney 4-hydroxynonenal (HNE) levels and myeloperoxidase (MPO) activity were measured. Histopathological examinations of kidney and relaxation and contraction responses of aorta were also examined. GM increased serum SDMA, urea nitrogen (BUN), and creatinine levels and caused histopathological alterations in the kidney. GM elevated HO-1 protein and mRNA expressions, 4-HNE level, and MPO activity and decreased antioxidant enzyme activities and l-arginine levels in the kidney. Decreased relaxation and contraction were detected in the aorta. Hemin restored renal oxidative stress and inflammatory changes together with vascular dysfunction, but did not affect SDMA, BUN, or creatinine levels. We conclude that HO-1 induction may be effective in improving renal oxidative stress, inflammation, and vascular dysfunction mediated by GM.

A mini-network balance model for evaluating the progression of cardiovascular complications in Goto-Kakizaki rats

Cardiovascular complications represent a leading cause of mortality in patients with type 2 diabetes mellitus (T2DM). During such complicated progression, subtle variations in the cardiovascular risk (CVR)-related biomarkers have been used to identify cardiovascular disease at the incipient stage. In this study we attempt to integrally characterize the progression of cardiovascular complications and to assess the beneficial effects of metformin combined with salvianolic acid A (Sal A), in Goto-Kakizaki (GK) rats with spontaneous T2DM. The rats were treated with metformin (200 mg·kg^-1·d^-1, ig) alone or in combination with Sal A (1 mg·kg^-1·d^-1, ip) at ages from 8 to 22 weeks. During the treatment, the levels of asymmetric dimethylarginine, L-arginine, superoxide dismutase, malondialdehyde, glucose, high density lipoprotein and low density lipoprotein were assessed. Based on alterations in these biomarkers, a mini-network balance model was established using matrixes and vectors. Radar charts were created to visually depict the disruption of CVR-related modules (endothelial function, oxidative stress, glycation and lipid profiles). The description for the progression of cardiovascular disorder was quantitatively represented by u, the dynamic parameter of the model. The modeling results suggested that untreated GK rats tended to have more severe cardiovascular complications than the treatment groups. Metformin monotherapy retarded disease deterioration, whereas the combination treatment ameliorated the disease progression via restoring the balance. The current study, which focused on the balance of the mini-network and interactions among CVR-related modules, proposes a novel method for evaluating the progression of cardiovascular complications in T2DM as well as a more beneficial intervention strategy.

Effects of asymmetric dimethylarginine on renal arteries in portal hypertension and cirrhosis

AIM

To evaluate the effects of asymmetric dimethylarginine (ADMA) in renal arteries from portal hypertensive and cirrhotic rats.

METHODS

Rat renal arteries from Sham (n = 15), pre-hepatic portal hypertension (PPVL; n = 15) and bile duct ligation and excision-induced cirrhosis (BDL; n = 15) were precontracted with norepinephrine, and additional contractions were induced with ADMA (10^-6-10^-3 mol/L), an endogenous inhibitor of nitric oxide (NO) synthase. Concentration-response curves to acetylcholine (1 × 10^-9-3 × 10^-6 mol/L) were determined in precontracted renal artery segments with norepinephrine in the absence and in the presence of ADMA. Kidneys were collected to determine the protein expression and activity of dimethylarginine dimethylaminohydrolase (DDAH), an enzyme that catabolizes ADMA.

RESULTS

In renal arteries precontracted with norepinephrine, ADMA caused endothelium-dependent contractions. The pD₂ values to ADMA were similar in the Sham and PPVL groups (4.20 ± 0.08 and 4.11 ± 0.09, P > 0.05, respectively), but were lower than those of the BDL group (4.79 ± 0.16, P < 0.05). Acetylcholine-induced endothelium-dependent relaxation that did not differ, in terms of pD₂ and maximal relaxation, among the 3 groups studied. Treatment with ADMA (3 × 10^-4 mol/L) inhibited acetylcholine-induced relaxation in the 3 groups, but the inhibition was higher (P < 0.05) in the BDL group compared with that for the Sham and PPVL groups. The mRNA and protein expression of DDAH-1 were similar in kidneys from the three groups. Conversely, DDAH-2 expression was increased (P < 0.05) in PPVL and further enhanced (P < 0.05) in the BDL group. However, renal DDAH activity was significantly decreased in the BDL group.

CONCLUSION

Cirrhosis increased the inhibitory effect of ADMA on basal- and induced-release of NO in renal arteries, and decreased DDAH activity in the kidney.

The transporter and permeability interactions of asymmetric dimethylarginine (ADMA) and L-arginine with the human blood-brain barrier in vitro

The blood–brain barrier (BBB) is a biological firewall that carefully regulates the cerebral microenvironment by acting as a physical, metabolic and transport barrier. This selectively permeable interface was modelled using the immortalised human cerebral microvascular endothelial cell line (hCMEC/D3) to investigate interactions with the cationic amino acid (CAA) L-arginine, the precursor for nitric oxide (NO), and with asymmetric dimethylarginine (ADMA), an endogenously derived analogue of L-arginine that potently inhibits NO production. The transport mechanisms utilised by L-arginine are known but they are not fully understood for ADMA, particularly at the BBB. This is of clinical significance giving the emerging role of ADMA in many brain and cerebrovascular diseases and its potential as a therapeutic target. We discovered that high concentrations of ADMA could induce endothelial dysfunction in the hCMEC/D3s BBB permeability model, leading to an increase in paracellular permeability to the paracellular marker FITC-dextran (40 kDa). We also investigated interactions of ADMA with a variety of transport mechanisms, comparing the data with L-arginine interactions. Both molecules are able to utilise the CAA transport system y⁺. Furthermore, the expression of CAT-1, the best known protein from this group, was confirmed in the hCMEC/D3s. It is likely that influx systems, such as y⁺L and b^0,+, have an important physiological role in ADMA transport at the BBB. These data are not only important with regards to the brain, but apply to other microvascular endothelia where ADMA is a major area of investigation.

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ADMA interacts with a variety of transporters at the blood-brain barrier.

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These included cationic amino acid transporters, including CAT-1.

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Human blood-brain barrier endothelial cells express CAT-1.

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ADMA at high concentrations can disrupt the blood-brain barrier.

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This disruption is not linked to increased ROS at the blood-brain barrier.

MCD diet-induced steatohepatitis is associated with alterations in asymmetric dimethylarginine (ADMA) and its transporters

Using an experimental model of NASH induced by a methionine-choline-deficient (MCD) diet, we investigated whether changes occur in serum and tissue levels of asymmetric dimethylarginine (ADMA). Male Wistar rats underwent NASH induced by 8-week feeding with an MCD diet. Serum and hepatic biopsies at 2, 4 and 8 weeks were taken, and serum enzymes, ADMA and nitrate/nitrite (NOx), were evaluated. Hepatic biopsies were used for mRNA and protein expression analysis of dimethylarginine dimethylaminohydrolase-1 (DDAH-1) and protein methyltransferases (PRMT-1), enzymes involved in ADMA metabolism and synthesis, respectively, and ADMA transporters (CAT-1, CAT-2A and CAT-2B). Lipid peroxides (TBARS), glutathione, ATP/ADP and DDAH activity were quantified. An increase in serum AST and ALT was detected in MCD animals. A time-dependent decrease in serum and tissue ADMA and increase in mRNA expression of DDAH-1 and PRMT-1 as well as higher rates of mRNA expression of CAT-1 and lower rates of CAT-2A and CAT-2B were found after 8-week MCD diet. An increase in serum NOx and no changes in protein expression in DDAH-1 and CAT-1 and higher content in CAT-2 and PRMT-1 were found at 8 weeks. Hepatic DDAH activity decreased with a concomitant increase in oxidative stress, as demonstrated by high TBARS levels and low glutathione content. In conclusion, a decrease in serum and tissue ADMA levels in the MCD rats was found associated with a reduction in DDAH activity due to the marked oxidative stress observed. Changes in ADMA levels and its transporters are innovative factors in the onset and progression of hepatic alterations correlated with MCD diet-induced NASH.

Changes in Biliary Levels of Arginine and its Methylated Derivatives after Hepatic Ischaemia/Reperfusion

Arginine (Arg) can be methylated to form symmetrical dimethylarginine (SDMA) and asymmetrical dimethylarginine (ADMA), the latter an endogenous inhibitor of nitric oxide synthase (NOS). SDMA is excreted in the urine, while ADMA is mainly subjected to degradation in the liver. Arg competes with ADMA and SDMA for cellular transport across cationic amino-acid transporters (CATs). We evaluated the changes in serum, tissue and biliary levels of Arg, citrulline (Cit), ADMA and SDMA and the modifications in CATs after ischaemia-reperfusion (I/R). Male Wistar rats were subjected to 30-min. partial-hepatic ischaemia or sham-operated. After 60-min. reperfusion, the concentrations of ADMA, SDMA, Arg and Cit in serum, tissue and bile were measured. Serum levels of AST, ALT and alkaline phosphatase (AP) levels were determined. mRNA of cationic transporter 2A (CAT-2A) and 2B (CAT-2B) were also quantified. An increase in ADMA and a decrease in SDMA were observed in bile at the end of reperfusion. On the contrary, lower tissue ADMA levels and higher SDMA levels were quantified. No serum changes in ADMA and SDMA were found. A decrease in Arg and an increase of Cit were detected in serum, bile and tissue after I/R. A marked increase in AST, ALT and AP levels in serum confirmed I/R injury. A decrease in mRNA transporter CAT-2A but not in CAT-2B was detected. This study supported a biliary CAT-2B-dependent transport of ADMA and demonstrated, for the first time, that the liver is also responsible for the biliary excretion of SDMA into the bile.

Effect of rosiglitazone on asymmetric dimethylarginine metabolism in thioacetamide-induced acute liver injury

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, is metabolized in the liver by dimethylarginine dimethylaminohydrolase (DDAH). We aimed to investigate the effect of rosiglitazone, a peroxysome proliferator-activated receptor-gamma (PPAR-γ) agonist, on ADMA metabolism in acute liver injury. Male Sprague Dawley rats were injected thioacetamide (TAA; 500mgkg(-1)) intraperitoneally in order to induce acute liver injury. ADMA, SDMA and arginine levels were determined in plasma by the HPLC. Liver DDAH activity and malondialdehyde (MDA) levels were measured by spectrophotometric procedures. TAA injection caused marked increases in ALT and AST activities. Plasma ADMA levels were increased, while arginine levels and arginine/ADMA ratio were decreased. Liver DDAH activity was significantly diminished and MDA levels were elevated. In another group of animals which were treated with a PPAR-γ agonist (rosiglitazone, 5mgkg(-1)) daily via gastric intubation for a week prior to TAA injection, significant recoveries in DDAH activity and antioxidant status were observed when compared with solely TAA-injected animals. Rosiglitazone pretreatment improved the plasma arginine/ADMA ratio. Our findings indicated that PPAR-γ agonist rosiglitazone beneficially influenced hepatic metabolism of ADMA in TAA-induced acute liver damage.

Metformin reduces asymmetric dimethylarginine and prevents hypertension in spontaneously hypertensive rats

Elevated asymmetric dimethylarginine (ADMA) levels and nitric oxide (NO) deficiency are associated with the development of hypertension. Metformin, an antidiabetic agent, is a structural analog of ADMA. We examined whether metformin can prevent the development of hypertension in spontaneously hypertensive rats (SHRs) by restoration of ADMA-NO balance. SHRs and control normotensive Wistar-Kyoto (WKY) rats were assigned to 4 groups (N = 8 for each group): untreated SHRs and WKY rats, metformin-treated SHRs and WKY rats. Metformin-treated rats received metformin 500 mg/kg per day via oral gavage for 8 weeks. All rats were sacrificed at the age of 12 weeks. We found an increase in the blood pressure of SHRs was prevented by metformin. ADMA levels in the plasma and lung were elevated in SHRs, which metformin prevented. Lung dimethylarginine dimethylaminohydrolase (DDAH, ADMA-metabolizing enzyme) activity was lower in SHRs than WKY rats. Next, metformin had no effect on protein arginine methyltransferase 1 (ADMA-synthesizing enzyme), DDAH-1, DDAH-2, NO synthase enzymes, and DDAH activity in the kidney. Moreover, metformin increased the levels of NO in kidney. Conclusively, the observed antihypertensive effect of metformin in SHRs is because of the restoration of the ADMA-NO pathway. Our findings support the consideration of metformin as an antihypertensive agent for diabetic patients with prehypertension.

Maternal citrulline supplementation prevents prenatal N(G)-nitro-L-arginine-methyl ester (L-NAME)-induced programmed hypertension in rats

Nitric oxide (NO) deficiency induced by the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine-methyl ester (L-NAME) resulted in hypertension. L-citrulline (CIT) can be converted to L-arginine to generate NO. We examined whether maternal CIT supplementation can prevent L-NAME-induced programmed hypertension. Pregnant Sprague-Dawley rats were assigned to four groups: control, L-NAME, control + citrulline (CIT), and L-NAME + citrulline (L-NAME+CIT). Pregnant rats received L-NAME administration at 60 mg/kg/day subcutaneously during pregnancy alone or with additional 0.25% l-citrulline solution in drinking water during the whole period of pregnancy and lactation. Male offspring were sacrificed at 12 wk of age. L-NAME exposure during pregnancy induces hypertension in the 12-wk-old offspring. Maternal CIT therapy prevented L-NAME-induced programmed hypertension, which was associated with a decreased asymmetric dimethylarginine (ADMA) concentration and an increased L-arginine-to-ADMA ratio in the kidney, increased urinary cGMP levels, and decreased renal protein levels of type 3 sodium hydrogen exchanger (NHE3). Together, our data suggest that the beneficial effects of CIT supplementation are attributed to its ability to increase NO level in the kidney and inhibition of NHE3 expression. Our results suggest that supplementing CIT in pregnant women with NO deficiency can improve fetal development and prevent programmed hypertension.

Antidiabetic drug metformin is effective on the metabolism of asymmetric dimethylarginine in experimental liver injury

AIMS

We aimed to investigate the pharmacological efficiency of metformin on asymmetric dimethylarginine (ADMA) metabolism in inflammation caused by the lipopolysaccharide (LPS)/D-galactosamine (D-GalN) treatment.

METHODS

Adult Sprague-Dawley rats were injected LPS/D-GalN intraperitoneally. One half of the animals was injected metformin (250 mg kg(-1) body mass for one week) prior to LPS/D-GalN treatment. Six hours after the LPS/D-GalN injection, livers were removed, and used for the measurements of dimethylarginine dimethylaminohydrolase (DDAH) and myeloperoxidase (MPO) activities, glutathione (GSH), ADMA and arginine levels. Liver tissues were examined histopathologically. The Kruskal-Wallis (posthoc Mann-Whitney U) test was used for the statistics. LPS/D-GalN injections caused liver injury as evidenced by the activities of aminotransferases and arginase. GSH level and DDAH activity were decreased in the liver. Metformin pretreatment alleviated the activity of serum enzymes, and attenuated histopathological lesions caused by LPS/D-GalN injections. LPS/D-GalN-induced inflammation, as confirmed by the increased MPO activity, created an asymmetrical distribution of arginine and ADMA between the tissue and plasma. Metformin decreased tissue ADMA level while it restored the DDAH activity and GSH.

CONCLUSION

Our findings showed that metformin administration for one week has a potency to protect liver through regulating ADMA metabolism in LPS/D-GalN-induced injury.

Serelaxin reduces oxidative stress and asymmetric dimethylarginine in angiotensin II-induced hypertension

Recent findings suggest the therapeutic action of relaxin during hypertension is dependent on nitric oxide synthase (NOS) activation; however, the mechanisms underlying the beneficial effects of relaxin on the NOS system have not been fully elucidated. We hypothesized that the protective effects of relaxin include reducing both oxidative stress and the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA). We examined the effect of Serelaxin [human recombinant relaxin-2 (RLX)] in male Sprague-Dawley rats given high-dose angiotensin (ANG) II (400 ng·kg(-1)·min(-1) sc) for 6 wk or shams. RLX was administered (4 μg/h sc) to half of the rats in each group after 2 wk of ANG II for the remaining 4 wk. ANG II induced hypertension and proteinuria, reduced NO oxidation products (NOx), and increased oxidative stress (NADPH oxidase activity, thiobarbituric acid-reactive substances, and 8-isoprostane excretion) and plasma ADMA. While RLX had no effect on sham rats, RLX attenuated the ANG II-dependent hypertension (165 ± 5 vs. 135 ± 13 mmHg, P < 0.05) and proteinuria at 6 wk (62 ± 6 vs. 41 ± 4 mg·day(-1)·100 g(-1), P < 0.05) and normalized oxidative stress and circulating ADMA, in association with restored NOx excretion and kidney cortex NOx. We found that RLX had no impact on the ADMA-regulatory enzymes protein arginine methyltransferase and dimethylarginine-dimethylaminohydrolase (DDAH). Furthermore, RLX treatment did not increase DDAH activity in kidney cortex or liver. These data suggest that benefits of RLX treatment include reduced ADMA levels and increased NO bioavailability, possibly due to its antioxidant effects.

Changes in ADMA/DDAH pathway after hepatic ischemia/reperfusion injury in rats: the role of bile

We investigated the effects of hepatic ischemia/reperfusion (I/R) injury on asymmetric dimethylarginine (ADMA, a nitric oxide synthase inhibitor), protein methyltransferase (PRMT) and dimethylarginine dimethylaminohydrolase (DDAH) (involved, resp., in ADMA synthesis and degradation), and the cationic transporter (CAT). Male Wistar rats were subjected to 30 or 60 min hepatic ischemia followed by 60 min reperfusion. ADMA levels in serum and bile were determined. Tissue ADMA, DDAH activity, DDAH-1 and CAT-2 protein, DDAH-1 and PRMT-1 mRNA expression, GSH/GSSG, ROS production, and lipid peroxidation were detected. ADMA was found in bile. I/R increased serum and bile ADMA levels while an intracellular decrease was detected after 60 min ischemia. Decreased DDAH activity, mRNA, and protein expression were observed at the end of reperfusion. No significant difference was observed in GSH/GSSG, ROS, lipid peroxidation, and CAT-2; a decrease in PRMT-1 mRNA expression was found after I/R. Liver is responsible for the biliary excretion of ADMA, as documented here for the first time, and I/R injury is associated with an oxidative stress-independent alteration in DDAH activity. These data are a step forward in the understanding of the pathways that regulate serum, tissue, and biliary levels of ADMA in which DDAH enzyme plays a crucial role.

Aging of the nitric oxide system: are we as old as our NO?

Background

Impaired generation and signaling of nitric oxide (NO) contribute substantially to cardiovascular (CV) risk (CVR) associated with hypertension, hyperlipidemia, and diabetes mellitus. In our rapidly aging society, advanced age is, in itself, a consistent and independent CVR factor. Many processes involved in aging are modulated by NO. We therefore postulated that aging might be independently associated with impaired NO signaling.

Methods and Results

In a prospective cohort study of 204 subjects (mean age 63±6 at study entry), we evaluated the effects of 4 years of aging on parameters of NO generation and effect, including platelet aggregability and responsiveness to NO, and plasma concentrations of the NO synthase inhibitor, asymmetric dimethylarginine (ADMA). Clinical history, lipid profile, high‐sensitivity C‐reactive protein, routine biochemistry, and 25‐hydroxyvitamin D levels were obtained at study entry and after 4 years of follow‐up. Aging was associated with marked deterioration of responsiveness of platelets to NO (P<0.0001) and increases in plasma ADMA concentrations (P<0.0001). There was a significant correlation between changes in these parameters over time (r=0.2; P=0.013). On multivariable analyses, the independent correlates of deterioration of responsiveness of platelets to NO were female gender (β=0.17; P=0.034) and low vitamin D concentrations (β=0.16; P=0.04), whereas increases in ADMA were associated with presence of diabetes (β=0.16; P=0.03) and impaired renal function (β=0.2; P=0.004).

Conclusions

Aging is associated with marked impairment of determinants of NO generation and effect, to an extent which is commensurate with adverse impact on CV outcomes. This deterioration represents a potential target for therapeutic interventions.

Restoration of asymmetric dimethylarginine-nitric oxide balance to prevent the development of hypertension

Despite the use of extensive antihypertensive therapy in patients with hypertension, little attention has been paid to early identification and intervention of individuals at risk for developing hypertension. The imbalance between nitric oxide (NO) and reactive oxygen species (ROS) resulting in oxidative stress has been implicated in the pathophysiology of hypertension. NO deficiency can precede the development of hypertension. Asymmetric dimethylarginine (ADMA) can inhibit nitric oxide synthase (NOS) and regulate local NO/ROS balance. Emerging evidence supports the hypothesis that ADMA-induced NO–ROS imbalance is involved in the development and progression of hypertension. Thus, this review summarizes recent experimental approaches to restore ADMA–NO balance in order to prevent the development of hypertension. Since hypertension might originate in early life, we also discuss the putative role of the ADMA–NO pathway in programmed hypertension. Better understanding of manipulations of the ADMA–NO pathway prior to hypertension in favor of NO will pave the way for the development of more effective medicine for the treatment prehypertension and programmed hypertension. However, more studies are needed to confirm the clinical benefit of these interventions.

Lobe-specific heterogeneity in asymmetric dimethylarginine and matrix metalloproteinase levels in a rat model of obstructive cholestasis

We investigated the effects of obstructive cholestasis in different hepatic lobes by evaluating asymmetric dimethylarginine (ADMA) (a nitric oxide synthase inhibitor), protein methyltransferase (PRMT) and dimethylarginine dimethylaminohydrolase (DDAH) (enzymes involved, resp., in its synthesis and degradation), the cationic transporter (CAT), and metalloproteinase (MMP) activity. Sixteen male Wistar rats underwent a 3-day cholestasis by common bile duct ligation (BDL) or sham operation. Blood samples and hepatic biopsies from left lobe (LL), median lobe (ML), and right lobe (RL) were collected. Serum hepatic enzymes, tissue ADMA, DDAH activity, CAT-2 protein, mRNA expression of DDAH and PRMT, and MMP-2 and MMP-9 activity were monitored. Cholestasis was confirmed by altered serum hepatic enzymes. Higher levels of tissue ADMA were detected in RL and ML as compared with LL. PRMT mRNA expression and DDAH activity did not differ among the lobes after BDL. CAT-2 levels are higher in the RL and ML in the sham-operated group. Higher activity in MMP-2 and MMP-9 was found in RL. In conclusion, after cholestasis an increase in hepatic ADMA in RL and ML was detected as well as tissue MMP-2 and MMP-9 activation in RL, supporting the evidence of functional heterogeneity among the liver lobes also occurring in an obstructive cholestasis model.

Renoprotective effects of melatonin in young spontaneously hypertensive rats with L-NAME

BACKGROUND

Nitric oxide (NO) deficiency occurs in humans and animals with hypertension and chronic kidney disease (CKD). An inhibitor of NO synthase, N(G)-nitro-l-arginine methyl ester (L-NAME) exacerbates kidney damage in the adult spontaneously hypertensive rat (SHR). We examined whether L-NAME exacerbated hypertensive nephrosclerosis in young SHRs and whether melatonin protects SHRs against kidney damage by restoration of the asymmetric dimethylarginine (ADMA)-NO pathway.

METHODS

Rats aged 4 weeks were randomly assigned into three groups (n = 10 for each group): Group 1 (control), SHRs without treatment; Group 2 (L-NAME), SHRs received L-NAME (80 mg/L) in drinking water; and Group 3 (L-NAME + melatonin), SHRs received L-NAME (80 mg/L) and 0.01% melatonin in drinking water. All rats were sacrificed at 10 weeks of age.

RESULTS

L-NAME exacerbates the elevation of blood pressure, renal dysfunction, and glomerular sclerosis in young SHRs. L-NAME induced an increase of ADMA and a decrease of arginine-to-ADMA ratio in the SHR kidney. Melatonin therapy prevented L-NAME-exacerbated hypertension and nephrosclerosis in young SHRs. In addition, melatonin restored L-NAME-induced reduction of dimethylarginine dimethylaminohydrolase (DDAH; ADMA-metabolizing enzymes) activity in the SHR kidney. Next, melatonin decreased renal ADMA concentrations, increased renal arginine-to-ADMA ratio, and restored NO production in L-NAME-treated young SHRs. Moreover, melatonin reduced the degree of oxidative damaged DNA product, 8-hydroxydeoxyguanosine immunostaining in L-NAME-treated SHR kidney.

CONCLUSION

Our results indicated that L-NAME/SHR is a useful model for hypertensive nephrosclerosis in young rats. The blood pressure-lowering and renoprotective effects of melatonin is due to increases of DDAH activity, decreases of ADMA, and reduction of oxidative stress in L-NAME-treated SHR kidney. Specific therapy targeting the DDAH-ADMA pathway may be a promising approach to slowing chronic kidney disease progression in children.

Melatonin therapy prevents programmed hypertension and nitric oxide deficiency in offspring exposed to maternal caloric restriction

Nitric oxide (NO) deficiency is involved in the development of hypertension, a condition that can originate early in life. We examined whether NO deficiency contributed to programmed hypertension in offspring from mothers with calorie-restricted diets and whether melatonin therapy prevented this process. We examined 3-month-old male rat offspring from four maternal groups: untreated controls, 50% calorie-restricted (CR) rats, controls treated with melatonin (0.01% in drinking water), and CR rats treated with melatonin (CR + M). The effect of melatonin on nephrogenesis was analyzed using next-generation sequencing. The CR group developed hypertension associated with elevated plasma asymmetric dimethylarginine (ADMA, a nitric oxide synthase inhibitor), decreased L-arginine, decreased L-arginine-to-ADMA ratio (AAR), and decreased renal NO production. Maternal melatonin treatment prevented these effects. Melatonin prevented CR-induced renin and prorenin receptor expression. Renal angiotensin-converting enzyme 2 protein levels in the M and CR + M groups were also significantly increased by melatonin therapy. Maternal melatonin therapy had long-term epigenetic effects on global gene expression in the kidneys of offspring. Conclusively, we attributed these protective effects of melatonin on CR-induced programmed hypertension to the reduction of plasma ADMA, restoration of plasma AAR, increase of renal NO level, alteration of renin-angiotensin system, and epigenetic changes in numerous genes.

N-acetylcysteine prevents hypertension via regulation of the ADMA-DDAH pathway in young spontaneously hypertensive rats

Asymmetric dimethylarginine (ADMA) reduces nitric oxide (NO), thus causing hypertension. ADMA is metabolized by dimethylarginine dimethylaminohydrolase (DDAH), which can be inhibited by oxidative stress. N-Acetylcysteine (NAC), an antioxidant, can facilitate glutathione (GSH) synthesis. We aimed to determine whether NAC can prevent hypertension by regulating the ADMA-DDAH pathway in spontaneously hypertensive rats (SHR). Rats aged 4 weeks were assigned into 3 groups (n = 8/group): control Wistar Kyoto rats (WKY), SHR, and SHR receiving 2% NAC in drinking water. All rats were sacrificed at 12 weeks of age. SHR had higher blood pressure than WKY, whereas NAC-treated animals did not. SHR had elevated plasma ADMA levels, which was prevented by NAC therapy. SHR had lower renal DDAH activity than WKY, whereas NAC-treated animals did not. Renal superoxide production was higher in SHR than in WKY, whereas NAC therapy prevented it. NAC therapy was also associated with higher GSH-to-oxidized GSH ratio in SHR kidneys. Moreover, NAC reduced oxidative stress damage in SHR. The observed antihypertensive effects of NAC in young SHR might be due to restoration of DDAH activity to reduce ADMA, leading to attenuation of oxidative stress. Our findings highlight the impact of NAC on the development of hypertension by regulating ADMA-DDAH pathway.

A novel metabolic balance model for describing the metabolic disruption of and interactions between cardiovascular-related markers during acute myocardial infarction

OBJECTIVE

After acute myocardial infarction (AMI), an integral evaluation of risk using multimarker approach and the understanding of the pathophysiological processes involved have recently received much attention. This study aimed to develop a model to integrally evaluate the metabolic disruption of cardiovascular-related markers and unveil their interactions after AMI.

METHODS

AMI was induced in rats by coronary artery ligation. Several cardiovascular-related markers in plasma and the heart were determined during AMI. A metabolic balance model was developed using matrix equations to assess the metabolic disturbance of, and interactions between, these markers.

RESULTS

Metabolic balance maps intuitively depicted the metabolic disruption of cardiovascular-related markers after AMI. The deviation and magnitude of the disruption were quantitatively and integrally described by φ and k (the dynamic parameter of metabolic balance disruption), respectively. The metabolic balance was disturbed in both the circulatory system and the heart post-AMI. All of the measured markers appeared to be interactional. Among these markers, kidney function and dimethylarginine dimethylaminohydrolase (DDAH) activity in the heart showed a potent effect on the other markers, whereas asymmetric dimethylarginine (ADMA) levels in plasma and adenosine triphosphate (ATP) contents in the heart were susceptible to the effects of the other markers.

CONCLUSION

A metabolic balance model was developed to integrally evaluate the disruption of cardiovascular-related markers after AMI, which proposes a new method for evaluating the disease state post-AMI using a multimarker approach. The unveiled interactions between these cardiovascular-related markers are helpful in understanding the pathophysiological processes.

Modulation of arginine and asymmetric dimethylarginine concentrations in liver and plasma by exogenous hydrogen sulfide in LPS-induced endotoxemia

Plasma levels of asymmetric dimethylarginine (ADMA) are known to be elevated under pathological conditions, but reports on intracellular ADMA levels are scarce. In this study, we investigated whether lipopolysaccharide (LPS)-induced endotoxemia alters the intra- and extra-cellular partition of l-arginine and ADMA. The effect of H2S pretreatment was also researched. Wistar rats were given sodium hydrogen sulfide (NaHS, 1 mg·(kg body mass)(-1)) one hour before the LPS injections (20 mg·kg(-1)). Six hours after the LPS treatment, the animals were sacrificed. Myeloperoxidase (MPO) and dimethylarginine dimethylaminohydrolase (DDAH) activities and levels of hypoxia-inducible factor (HIF)-1α were measured in the liver. ADMA and arginine levels were determined using HPLC. LPS injection caused liver injury, as evidenced by the activities of alanine transaminase, aspartate transaminase, and arginase. LPS increased l-arginine content and decreased DDAH activity in the rat liver. MPO activity and HIF-1α levels indicated inflammation and hypoxia. Despite the accumulation of ADMA in the plasma, the level remained unchanged in the liver. NaHS pretreatment restored both the DDAH activity and intracellular l-arginine levels. It is concluded that increased H2S generation has a potency to restore hepatic l-arginine levels and ADMA handling in endotoxemia. Extra- and intra-cellular partitions of ADMA seem to depend on transport proteins as well as the DDAH activity.

Asymmetric dimethylarginine is associated with developmental programming of adult kidney disease and hypertension in offspring of streptozotocin-treated mothers

Diabetes mellitus complicates pregnancies, leading to diseases in adult life in the offspring. Asymmetric dimethylarginine (ADMA) is increased in diabetes mellitus, kidney disease, and hypertension. We tested whether maternal diabetes causes increased ADMA in rats, resulting in kidney disease and hypertension in the adult offspring, and whether these can be prevented by maternal citrulline supplementation. Newborn female and pregnant Sprague-Dawley rats were injected with streptozotocin (STZ), which made up the nSTZ and STZ models, respectively. For the STZ model, 4 groups of male offspring were killed at age 3 months: the control, STZ, and Cit and STZ+Cit (control and STZ rats treated with 0.25% l-citrulline solution, respectively) groups. The nSTZ rats had lower nephron numbers. The renal level of ADMA was higher in the nSTZ rats than in controls. The STZ group developed kidney injury, renal hypertrophy, and elevated blood pressure at the age of 12 weeks. These conditions were found to be associated with increased ADMA levels, decreased nitric oxide (NO) production, and decreased dimethylarginine dimethylaminohydrolase (DDAH) activity in the kidney. In addition, ADMA caused a nephron deficit in cultured rat metanephroi. Maternal citrulline supplementation prevented hypertension and kidney injury, increased the renal DDAH-2 protein level, and restored the levels of ADMA and NO in the STZ+Cit group. Reduced nephron number and increased ADMA contribute to adult kidney disease and hypertension in offspring of mothers with STZ-induced diabetes. Manipulation of the ADMA-NO pathway by citrulline supplementation may be a potential approach to prevent these conditions.

Effects of losartan and pentoxifylline on renal dimethylarginine dimethylaminohydrolase-1 expression in proteinuric nephropathy

BACKGROUND/AIMS

Circulatory asymmetric dimethylarginine (ADMA) is correlated with proteinuria and endothelial dysfunction in patients with proteinuric renal diseases. However, it is not known whether proteinuria itself affects expression of dimethylarginine dimethylaminohydrolase (DDAH), a degrading enzyme of ADMA, in kidney. The aim of this study is to evaluate the direct effects of losartan and/or pentoxifylline on expression of renal DDAH-1 and its relation to oxidative stress in the setting of albuminuria.

METHODS

Using NRK52E cells, DDAH-1 mRNA and protein were determined after exposure to albumin with losartan and/or pentoxifylline. Reactive oxygen species (ROS), PKC activity, and NOX-4 mRNA were also measured. In addition, the effect of losartan and/or pentoxifylline on renal expression of DDAH-1 and serum ADMA were evaluated in a rat model of proteinuric nephropathy.

RESULTS

Exposure to albumin resulted in increased release of N-acetyl-β-D-glucosaminidase along with an increase of TNF-α, 8-hydroxy-2'-deoxyguanosine, and angiotensin II in NRK52E cells. Losartan and pentoxifylline reversed albumin-induced decrease of DDAH-1 mRNA and protein expression and DDAH-1 activity. The effects of losartan and pentoxifylline on DDAH-1 mRNA were associated with reduction of ROS. In addition, treatment with losartan and pentoxifylline resulted in an attenuated change of renal DDAH-1 protein expression and serum ADMA levels in vivo.

CONCLUSION

DDAH-1 was positively regulated by losartan and pentoxifylline with its antioxidative effect in albumin-exposed renal proximal tubular cells. Combined treatment with losartan and pentoxifylline has a direct beneficial effect on expression of renal DDAH-1, and, thus, at least in part, modulates the circulatory levels of ADMA in proteinuric nephropathy.

Probing AGXT2 enzyme activity in mouse tissue by applying stable isotope-labeled asymmetric dimethyl arginine as substrate

Asymmetric dimethylarginine (ADMA) is a metabolite of the amino acid L-arginine. It competitively inhibits the enzymatic production of the cell-signaling substance nitric oxide. Therefore, increased levels of ADMA are associated with a range of cardiovascular and other diseases. ADMA is biologically eliminated by direct renal excretion and hydrolysis by the enzyme DDAH. Recently, a further elimination pathway via the transamination by the enzyme AGXT2 to α-keto-δ-(N(G),N(G)-dimethylguanidino)valeric acid (DMGV) has come into the focus of biological research. In this work, we describe an assay for the AGXT2 activity in mouse liver and kidney tissue. It is based on the transformation of isotope-labeled ADMA-d(6) to DMGV-d(6). The quantification of the DMGV-d(6) produced by this reaction in tissue homogenate samples was accomplished by chromatographic separation on a porous graphitic carbon column and tandem mass spectrometric detection. DMGV-d(6) with the deuterium labels in different molecular positions was used as internal standard. The overall production rates of DMGV-d(6) in mice were 195.37 pmol/min/mg total protein in liver and 85.21 pmol/min/mg total protein in kidney tissue, with coefficients of variation of 6.31% and 11.25%, respectively. This method can be applied as a tool for the characterization of the ADMA elimination by the AGXT2 pathway.

Dimethylarginine-dimethylaminohydrolase-2 (DDAH-2) does not metabolize methylarginines

Free endogenous methylarginines, N(ω)-monomethyl-L-arginine (L-NMMA) and N(ω),N(ω')-dimethyl-L-arginine (ADMA), inhibit NO synthases (NOSs) and are metabolized by dimethylargininedimethylaminohydrolase (DDAH). A postulated metabolism has been shown several times for DDAH-1, but the involvement of DDAH-2 in the degradation of ADMA and L-NMMA is still a matter of debate. Determination of the isoform-specific DDAH protein expression profiles in various porcine tissue types shows a correlation of DDAH activity only with DDAH-1 levels. DDAH activity (measured as L-citrulline formation from the conversion of methylarginines and alternative DDAH substrates) was detected in DDAH-1-rich porcine tissue types, that is, kidney, liver, and brain, but not in DDAH-2-rich porcine fractions, that is, spleen and thyroid. Furthermore, several ex vivo studies showed DDAH activity to be important for L-citrulline formation in porcine tissue and indicated the absence of an endogenous DDAH inhibitor in porcine tissue. This study provides new insights into tissue distributions as well as substrate selectivity for both DDAH isoforms. Although DDAH-1 is known to metabolize the endogenous NOS inhibitors L-NMMA and ADMA, a physiological function for DDAH-2 has yet to be determined. Hence, determining DDAH activity by methylarginine conversion is not suitable for analyzing isoform selectivity of DDAH-1 inhibitors as postulated.

The protection by heme oxygenase-1 induction against thioacetamide-induced liver toxicity is associated with changes in arginine and asymmetric dimethylarginine

This study was designed to investigate the role of HO-1 induction in prevention of thioacetamide (TAA)-induced oxidative stress, inflammation and liver damage. The changes in hepatic dimethylarginine dimethylaminohydrolase (DDAH) activity as well as plasma arginine and asymmetric dimethylarginine (ADMA) levels were also measured to evaluate nitric oxide (NO) bioavailability. Rats were divided into four groups as control, hemin, TAA and hemin + TAA groups. Hemin (50 mg kg(-1) , i.p.) was injected to rats 18 h before TAA treatment to induce HO-1 enzyme expression. Rats were given TAA (300 mg kg(-1) , i.p.) and killed 24 h after treatment. Although TAA treatment produced severe hepatic injury, upregulation of HO-1 ameliorated TAA-induced liver damage up to some extent as evidence by decreased serum alanine transaminase, aspartate transaminase and arginase activities and histopathological findings. Induction of HO-1 stimulated antioxidant system and decreased lipid peroxidation in TAA-treated rats. Myeloperoxidase activity and inducible NO synthase protein expression were decreased, whereas DDAH activity was increased by hemin injection in TAA-treated rats. Induction of HO-1 was associated with increased arginine levels and decreased ADMA levels, being the main determinants of NO production, in plasma of TAA-treated rats. In conclusion, our results indicate that HO-1 induction alleviated increased oxidative stress and inflammatory reactions together with deterioration in NO production in TAA-induced liver damage in rats.

Endotoxemia exacerbates kidney injury and increases asymmetric dimethylarginine in young bile duct-ligated rats

Cirrhosis increases the risk of kidney injury and sepsis, leading to increased mortality. Elevated levels of plasma asymmetric dimethylarginine (ADMA) occur in patients critically ill with cirrhosis, renal failure, and sepsis. We used a rat model of cirrhosis with superimposed sepsis to assess the relationship of plasma and tissue ADMA profiles with acute kidney injury and survival. Seventeen-day-old male Sprague-Dawley rats (n = 37) were randomly assigned to four groups: (1) sham operation plus diet control (n = 6); (2) bile duct ligation (BDL, n = 8); (3) sham operation plus lipopolysaccharide (LPS, n = 9); and (4) BDL plus LPS (n = 14). Lipopolysaccharide was given by intraperitoneal injection (1 mg/kg in saline) 3 h before sacrifice. All rats were sacrificed 14 days after surgery. Lipopolysaccharide increased the rate of BDL-associated death and dysfunction of the liver and kidneys. These results were supported by increased levels of plasma ADMA and a decreased L-arginine/ADMA ratio (AAR). Plasma and tissue levels of ADMA and AAR were not correlated. Lipopolysaccharide restored BDL-induced ADMA level elevation in the liver but increased ADMA level in the kidneys. Lipopolysaccharide increased hepatic AAR, decreased renal AAR, and paradoxically mediated the expression of neuronal nitric oxide synthase-β in the liver and kidneys. A novel mechanism underlies the LPS-mediated L-arginine-ADMA-nitric oxide pathway activation and exacerbation of kidney injury and mortality in our BDL model. In the presence of cirrhosis with superimposed sepsis, simultaneous lowering of ADMA levels and enhancement of L-arginine levels to restore plasma and renal AARs may be an optimal strategy for the treatment of kidney injury.

Activities of asymmetric dimethylarginine-related enzymes in white adipose tissue are associated with circulating lipid biomarkers

BACKGROUND

Asymmetric NG,NG-dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is regulated by the enzymatic participants of synthetic and metabolic processes, i.e., type I protein N-arginine methyltransferase (PRMT) and dimethylarginine dimethylaminohydrolase (DDAH). Previous reports have demonstrated that circulating ADMA levels can vary in patients with type 1 and type 2 diabetes mellitus (T2DM). White adipose tissue expresses the full enzymatic machinery necessary for ADMA production and metabolism; however, modulation of the activities of adipose ADMA-related enzymes in T2DM remains to be determined.

METHODS

A rodent model of T2DM using 11- and 20-week old Goto-Kakizaki (GK) rats was used. The expression and catalytic activity of PRMT1 and DDAH1 and 2 in the white adipose tissues (periepididymal, visceral and subcutaneous fats) and femur skeletal muscle tissue were determined by immunoblotting, in vitro methyltransferase and in vitro citrulline assays.

RESULTS

Non-obese diabetic GK rats showed low expression and activity of adipose PRMT1 compared to age-matched Wistar controls. Adipose tissues from the periepididymal, visceral and subcutaneous fats of GK rats had high DDAH1 expression and total DDAH activity, whereas the DDAH2 expression was lowered below the control value. This dynamic of ADMA-related enzymes in white adipose tissues was distinct from that of skeletal muscle tissue. GK rats had lower levels of serum non-esterified fatty acids (NEFA) and triglycerides (TG) than the control rats. In all subjects the adipose PRMT1 and DDAH activities were statistically correlated with the levels of serum NEFA and TG.

CONCLUSION

Activities of PRMT1 and DDAH in white adipose tissues were altered in diabetic GK rats in an organ-specific manner, which was reflected in the serum levels of NEFA and TG. Changes in adipose ADMA-related enzymes might play a part in the function of white adipose tissue.

Endogenous nitric oxide synthase inhibitors in the biology of disease: markers, mediators, and regulators?

The asymmetric methylarginines inhibit nitric oxide synthesis in vivo by competing with L-arginine at the active site of nitric oxide synthase. High circulating levels of asymmetric dimethylarginine predict adverse outcomes, specifically vascular events but there is now increasing experimental and epidemiological evidence that these molecules, and the enzymes that regulate this pathway, play a mechanistic role in cardiovascular diseases. Recent data have provided insight into the impact of altered levels of these amino acids in both humans and rodents, however these reports also suggest a simplistic approach based on measuring, and modulating circulating asymmetric dimethylarginine alone is inadequate. This review outlines the basic biochemistry and physiology of endogenous methylarginines, examines both the experimental and observational evidence for a role in disease pathogenesis, and examines the potential for therapeutic regulation of these molecules.

The combined ratios of L-arginine and asymmetric and symmetric dimethylarginine as biomarkers in spontaneously hypertensive rats

Hypertension and hypertensive end-organ damage have been associated with decreased nitric oxide (NO) bioavailability. Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) both can inhibit NO availability by competition with L-arginine (L-Arg). However, whether a combined analysis of these 3 parameters can serve as an ideal biomarker of hypertension remains unclear. We measured the plasma and renal levels of L-Arg, ADMA, and SDMA in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) control rats at 3 stages: 4 weeks old (prehypertensive), 12 weeks old (hypertensive), and 24 weeks old (end-organ damage). The plasma and renal L-Arg/ADMA ratio (AAR) and the ADMA/SDMA ratio (ASR) were computed for all 3 age stages. Our results revealed an ADMA level increase, and an AAR decrease in plasma and kidneys may develop early on, even before the onset of hypertension in 4-week-old SHRs. The renal ADMA level and AAR were restored in SHRs at 24 weeks of age, which might protect SHRs against kidney injury. We found that the plasma AAR is superior to the levels of L-Arg and ADMA in plasma, and it predicted blood pressure and urinary NOx levels. Renal AAR is a strong independent marker of renal dimethylarginine dimethylaminohydrolase (DDAH) activity. The plasma ASR was correlated strongly to blood pressure. However, renal DDAH activity was related to the renal ASR but not the plasma ASR. In conclusion, the AAR and ASR may serve as better markers for disease activity and progression than each individual parameter. Clinical use of these ratios to elucidate the role of ADMA in hypertension awaits further validation.

Arginine and asymmetric dimethylarginine in puromycin aminonucleoside-induced chronic kidney disease in the rat

BACKGROUND/AIMS

Reduced renal L-arginine (L-Arg) synthesis/transport, induction of arginases and increased endogenous NOS inhibitor, asymmetric dimethylarginine (ADMA) will inhibit NO production. This study investigated pathways of L-Arg synthesis/uptake/utilization, ADMA degradation and oxidant/antioxidants in puromycin aminonucleoside (PAN) chronic kidney disease (CKD).

METHODS

Rats were given low- (LD) or high-dose (HD) PAN and followed for 11 weeks for proteinuria. BP was measured and blood and tissues were harvested and analyzed for abundance of argininosuccinate synthase (ASS) and lyase (ASL), arginase, cationic amino acid transporter (CAT1) and dimethylargininedimethylaminohydrolase (DDAH) in kidney, cortex, aorta and liver. Arginase and DDAH activity, plasma L-Arg and ADMA, renal pathology and creatinine clearances were also measured.

RESULTS

PAN caused dose-dependent kidney damage and hypertension and creatinine clearance fell in HD-PAN. Renal ASS fell in HD-PAN, renal cortex and aortic ASL and membrane CAT1 fell in both PAN groups. There was no activation of renal arginase, but aortic arginase increased in LD-PAN. Renal DDAH activity fell moderately in LD-PAN and markedly in HD-PAN where hepatic DDAH activity also fell. Plasma L-Arg was unchanged while ADMA rose moderately and dose-dependently with PAN. There were several indices of oxidative stress which was most prominent in HD-PAN.

CONCLUSION

Reduction in renal ASS/ASL and loss of renal cortex CAT1 compromises renal L-Arg synthesis and release. Loss of aortic CAT1 impairs L-Arg uptake. Increased plasma ADMA was associated with progressive loss of renal DDAH activity. However, loss of renal clearance and falls in hepatic DDAH activity in HD-PAN did not have additive effects on plasma ADMA.

Apocynin attenuates oxidative stress and hypertension in young spontaneously hypertensive rats independent of ADMA/NO pathway

Both NADPH oxidase-derived reactive oxygen species (ROS) and asymmetric dimethylarginine (ADMA) are increased in hypertension. Apocynin, an NADPH oxidase inhibitor, could inhibit ROS, thus we tested whether apocynin can block NADPH oxidase and prevent increases of ADMA and blood pressure (BP) in spontaneously hypertensive rats (SHRs). SHRs and Wistar Kyoto (WKY) rats, aged 4 weeks, were assigned to four groups: untreated SHRs and WKY rats, SHRs and WKY rats that received 2.5 mM apocynin for 8 weeks. BP was significantly higher in SHRs compared to WKY rats, which was attenuated by apocynin. Apocynin prevented p47phox translocation in SHR kidneys, but not the increase of superoxide and H(2)O(2). Additionally, apocynin did not protect SHRs against increased ADMA. Apocynin blocks NADPH oxidase to attenuate hypertension, but has little effect on the ADMA/nitric oxide (NO) pathway in young SHRs. The reduction of ROS and the preservation of NO simultaneously might be a better approach to restoring ROS-NO balance to prevent hypertension.

Aliskiren prevents hypertension and reduces asymmetric dimethylarginine in young spontaneously hypertensive rats

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NOS, decreases NO synthesis. Plasma ADMA concentrations increase markedly in hypertension. We tested whether the development of hypertension and the increases in ADMA in spontaneously hypertensive rats (SHR) are prevented by aliskiren, a renin inhibitor. Male SHRs and normotensive Wistar Kyoto (WKY) control rats, aged 4 weeks (pre-hypertensive stage), were assigned to 4 groups: untreated SHRs and WKY rats, and SHRs that received oral aliskiren 10 and 30 mg/kg/day for 6 weeks. All rats were sacrificed at age 10 weeks. Blood pressure decreased at age 6, 8, and 10 weeks in SHRs that received high-dose aliskiren. Aliskiren mitigated the increases in plasma ADMA in SHRs. Renal ADMA levels were lower in SHRs that received high-dose aliskiren versus SHRs. SHRs experienced decreased plasma and kidney l-Arg-to-ADMA ratios versus control rats, which were reverted by 30 mg/kg aliskiren. Renal cortical neuronal NOS-α and -β levels increased in SHRs fed with high-dose aliskiren. Early aliskiren treatment mitigates increases in ADMA, restores l-Arg-to-ADMA ratios, enhances neuronal NOS-α, prevents decreased nNOS-β levels in the kidney-which might restore NO bioavailability and contribute to the decrease of blood pressure in young SHRs. Our findings suggest that aliskiren is a therapeutic agent for prehypertension that regulates the ADMA/NO pathway.

Melatonin prevents hypertension and increased asymmetric dimethylarginine in young spontaneous hypertensive rats

Nitric oxide (NO) deficiency is associated with development of hypertension. We examined whether melatonin protects against the blood pressure increase is because of the restoration of the NO pathway. Spontaneous hypertensive rats (SHR) and control normotensive Wistar Kyoto (WKY) rats aged 4 weeks were assigned to four groups (N=6 for each group): untreated SHR and WKY, melatonin-treated SHR and WKY. Melatonin-treated rats received 0.01% melatonin in drinking water for 8 wks. All rats were sacrificed at 12 wk of age. SHR had higher blood pressure than WKY, which melatonin prevented. Plasma asymmetric dimethylarginine (ADMA) levels were elevated in SHR, combined with a reduction in plasma L-arginine to ADMA ratio (AAR). In the kidney, L-arginine, ADMA, and AAR were not different between SHR and WKY rats, whereas L-citrulline level was increased in SHR. Melatonin decreased plasma ADMA level and restored plasma AAR. Renal dimethylarginine dimethylaminohydrolase (DDAH, ADMA-metabolizing enzyme) activity was lower in SHR than WKY rats, which melatonin therapy prevented. Also, melatonin elevated both L-arginine and ADMA but reduced L-citrulline level in the kidney in SHR, which was associated with the prevention of reduced renal argininosuccinate lyase (ASL) expression in SHR. Moreover, melatonin reduced the degree of oxidative damaged DNA product, 8- hydroxydeoxyguanosine (8-OHdG) immunostaining in SHR. The observed antihypertensive effects of melatonin in young SHR are because of the restoration of the NO pathway by reduction of plasma ADMA, restoration of plasma AAR, preservation of renal L-Arg availability, and attenuation of oxidative stress.