L-NAME-treatment alters ectonucleotidase activities in kidney membranes of rats

Antioxidant-rich Terminalia catappa fruit exerts antihypertensive effect via modulation of angiotensin-1-converting enzyme activity and H2S/NO/cGMP signaling pathway in Wistar rats

INTRODUCTION

The present study aimed at investigating the effect of Terminalia catappa fruits on blood pressure, NO/cGMP signalling pathway, angiotensin-1-converting enzyme and arginase activity, and oxidative stress biomarkers in L-NAME-induced hypertensive rats.

MATERIALS AND METHODS

Forty-two Wistar rats were divided into seven groups. Hypertension was induced via oral administration of 40 mg/kg of L-NAME for 21 days. Thereafter, the hypertensive rats were treated with Terminalia catappa fruit-supplemented diet and sildenafil citrate for 21 days. The blood pressure was measured and cardiac homogenate was prepared for biochemical analyses.

RESULTS

The results showed that L-NAME caused a significant (p < 0.05) increase in systolic and diastolic blood pressure, and heart rate as well as ACE, arginase and PDE-5 activity, with a simultaneous decrease in NO and H₂S levels as well as increased oxidative stress biomarkers. However, treatment with Terminalia catappa fruits-supplemented diets and sildenafil citrate lowered blood pressure and modulated ACE, arginase, and PDE-5 activity, improved NO and H₂S levels, as well as antioxidant status.

CONCLUSION

Findings presented in this study provide useful information on the antihypertensive property of Terminalia catappa fruits, alongside some possible mechanisms. Hence, Terminalia catappa fruits could be considered a dietary regimen and functional food in alleviating hypertension.

Endothelial dysfunction due to the inhibition of the synthesis of nitric oxide: Proposal and characterization of an in vitro cellular model

The vascular endothelium plays a pivotal role in the maintenance of vascular homeostasis, mediated by vasoactive molecules produced by endothelial cells. The balance between vasoconstrictor and vasodilator biomolecules is what guarantees this equilibrium. Therefore, an increase in the bioavailability of vasoconstrictors along with a reduction in vasodilators may indicate a condition known as endothelial dysfunction. Endothelial dysfunction is marked by an inflammatory process and reduced activity of vasoprotective enzymes, being characterized by some factors like the reduction of the bioavailability of nitric oxide (NO) and increase in the production of reactive oxygen species (ROS), pro-inflammatory and vasoconstrictor molecules. This condition is a predictive marker of several cardiovascular diseases (e.g., atherosclerosis, hypertension, and diabetes). Research is affected by the scarcity of suitable in vitro models that simulate endothelial dysfunction. The goal of this study was to induce an in vitro condition to mimic endothelial dysfunction by inhibiting NO synthesis in cells. Thymus-derived endothelial cells (tEnd.1) were treated with different concentrations of L-NAME (from 1 to 1,000 μM) for different times (12, 24, 48, 72, 96, and 120 h without and with retreatment every 24 h). Cell viability, nitrite concentration, p22phox, NOX2, NOX4, IL-6, and ACE genes expression and lipid peroxidation were evaluated. The results indicate that the treatment with 100 μM L-NAME for 72 h without retreatment reduced NO concentration and NOX4 gene expression while increasing ACE expression, thus mimicking reduced vascular protection and possibly increased vasoconstriction. On the other hand, treatment with 100 μM L-NAME for 96 h with retreatment reduced the concentration of NO and the expression of the p22phox gene while increasing the expression of the IL-6 and ACE genes, mimicking the increase in inflammation and vasoconstriction parameters. Based on these results, we thus propose that both 100 μM L-NAME for 72 h without retreatment and 100 μM L-NAME for 96 h with retreatment may be used as models for in vitro endothelial dysfunction according to the purpose of the study to be conducted.

Assessment of sexual behavior and neuromodulation of Cyperus esculentus L. and Tetracarpidium conophorum Müll. Arg dietary supplementation regulating the purinergic system in the cerebral cortex of L-NAME-challenged rats

This study examined the behavioral responses, purinergic receptor densities, ectonucleotidases (E-NTPDase), adenosine deaminase (ADA) activity, and nitric oxide (NO) levels along with the parameters of oxidative stress-related to erectile function in the cerebral cortex (CC) of L-NAME-challenged rats pretreated with tigernut (TN) and walnut (WN) dietary supplementation. Wistar rats (male) of 70 total animals (250-300 g) were used in this research and hence separated into seven groups (n = 10): Group I: normal control-fed basal diet; Group II: positive control-fed basal diet/L-NAME/Sildenafil citrate (5 mg kg-1  day-1 ); Group III: ED-induced (placed on a basal diet/L-NAME); Group IV: diet supplemented with processed TN (20%)/L-NAME; Group V: diet supplemented with raw TN (20%)/L-NAME; Group VI: diet supplemented with processed WN (20%)/L-NAME; and Group VII placed on a diet supplemented with raw WN (20%)/L-NAME. The rats were pretreated for 2 weeks before the L-NAME (40 mg kg-1  day-1 ) challenge on their respective diet. L-NAME brought about a decrease in the sexual behaviors evaluated while the effect was significantly reversed by supplemented diets containing TN and WN. L-NAME increased the levels of reactive oxygen species and malondialdehyde, E-NTPDase as well as ADA activities, and caused the level of NO in the CC as well as the purinoreceptor densities to be downregulated. Treatments with enriched diets, however, greatly reverse these effects. The behavioral responses and neuromodulatory capacity of the nuts displayed on the CC can, therefore, further support their aphrodisiac property. PRACTICAL APPLICATIONS: The results revealed the ability of tigernut (TN; Cyperus esculentus L.) and walnut (WN; Tetracarpidium conophorum Müll. Arg.) to enhance behavioral responses; modulate purinergic receptor densities, E-NTPDase, and ADA activities; increase NO levels; and prevent oxidative stress related to erectile function in the CC of L-NAME-challenged Wistar rats. The results show that these nuts are useful feeds for both animal and human nutrition.

Antihypertensive Effects of the Vitex cienkowskii (Verbenaceae) Stem-Bark Extract on L-NAME-Induced Hypertensive Rats

Vitex cienkowskii stem-bark is used in Cameroonian traditional medicine to treat cardiovascular diseases including hypertension. In previous studies, the methanol/methylene chloride stem-bark extract of Vitex cienkowskii (MMVC) showed a preventive activity in L-NAME-induced hypertension and improved blood pressure of spontaneously hypertensive rats. The present study investigated the curative effects in L-NAME-induced hypertensive rats (LNHR). Hypertension was induced in rats by oral administration of L-NAME (40 mg/kg/day) for 28 days. The animals were divided into 2 groups: one group of 5 rats receiving distilled water (10 ml/kg) and another 20 rats receiving L-NAME. At the end of 4 weeks of administration of L-NAME, the animals were divided into 4 groups of 5 rats each: one group of hypertensive rats receiving distilled water, another one receiving captopril (25 mg/kg), and two groups of hypertensive rats receiving MMVC at doses of 200 and 400 mg/kg, respectively. Body weight, food, and water intake were measured weekly. At the end of the treatment, blood pressure and heart rate were recorded by invasive method. Whole heart, left ventricle, kidneys, and liver were weighed. The effects of plant extract on lipid profile and oxidative stress markers, as well as markers of hepatic and renal functions were assessed spectrophotometrically according to well described protocols. Results show that L-NAME significantly increases the mean arterial blood pressure (MABP), atherogenic index, lipid profile, and creatinine and transaminase activities of normotensive rats. MMVC significantly reduced the blood pressure in LNHR. Body weight, food and water intake, left ventricular hypertrophy, antioxidant level, renal and hepatic markers, and lipid profile were improved by the treatment with MMVC. The curative effect of MMVC on L-NAME-induced hypertension is probably related to its antihypertensive, hypolipidemic, and antioxidant properties. These results confirmed the use of Vitex cienkowskii for the treatment of hypertension in traditional medicine.

Lambda-cyhalothrin exposure alters purine nucleotide hydrolysis and nucleotidase gene expression pattern in platelets and liver of rats

Lambda-cyhalothrin (LCT) is a broad-spectrum pesticide widely used in agriculture throughout the world. This pesticide is considered a potential contaminant of surface and underground water as well as food, posing a risk to ecosystems and humans. In this sense, we decided to evaluate the activity of enzymes belonging to the purinergic system, which is linked with regulation of extracellular nucleotides and nucleosides, such as adenosine triphosphate (ATP) and adenosine (Ado) molecules involved in the regulation of inflammatory response. However, there are no data concerning the effects of LCT exposure on the purinergic system, where extracellular nucleotides act as signaling molecules. The aim of this study was to evaluate nucleotide hydrolysis by E-NTPDase (ecto-nucleoside triphosphate diphosphohydrolase), Ecto-NPP (ecto-nucleotide pyrophosphatase/phosphodiesterase), ecto-5'-nucleotidase and ecto-adenosine deaminase (E-ADA) in platelets and liver of adult rats on days 7, 30, 45 and 60 after daily gavage with 6.2 and 31.1 mg/kg bw of LCT. Gene expression patterns of NTPDases1-3 and 5'-nucleotidase were also determined in those tissues. In parallel, lambda-cyhalothrin metabolites [3-(2-chloro-3,3,3- trifluoroprop-1-enyl)-2,2-dimethyl-cyclopropane carboxylic acid (CFMP), 4-hydroxyphenoxybenzoic acid (4-OH-3-PBA), and 3-phenoxybenzoic acid (3-PBA)] were measured in plasma. Results showed that exposure rats to LCT caused a significant increase in the assessed enzymes activities. Gene expression pattern of ectonucleotidases further revealed a significant increase in E-NTPDase1, E-NTPDase2, and E-NTPDase3 mRNA levels after LCT administration at all times. A dose-dependent increase in LCT metabolite levels was also observed but there no significant variations in levels from weeks to week, suggesting steady-steady equilibrium. Correlation analyses revealed that LCT metabolites in the liver and plasma were positively correlated with the adenine nucleotides hydrolyzing enzyme, E-ADA and E-NPP activities in platelets and liver of rats exposed to lambda-cyhalothin. Our results show that LCT and its metabolites may affect purinergic enzymatic cascade and cause alterations in energy metabolism.

Naringenin ameliorates renal and platelet purinergic signalling alterations in high-cholesterol fed rats through the suppression of ROS and NF-κB signaling pathways

Naringenin (NGEN) is a natural flavonoid aglycone of naringin that has been reported to have a wide range of pharmacological properties, such as antioxidant activity and free radical scavenging capacity. The aim of this study was to investigate the protective effect of NGEN on oxidative and inflammatory parameters, as well as to evaluate the hydrolysis of adenine nucleotides in kidney and platelet membranes of rats exposed to a hypercholesterolemic diet (HCD) for 90 days. Kidney oxidative stress and mRNA expression of the ectonucleoside triphosphate diphosphohydrolases (NTPDases), ecto-5'-nucleotidase (CD73), inducible NO synthase (iNOS), tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6) and the nuclear factor kappa B (NF-κB) genes were evaluated by real time RT-PCR. The co-administration of NGEN (50 mg kg(-1)) for 90 days significantly prevented renal failure in HCD rats as indicated by an improvement of renal markers. Histopathological observation findings are also consistent with these effects. Moreover, NGEN (50 mg kg(-1)) significantly decreased the lipid profile and inhibited pro-oxidant and inflammation marker levels in the kidney of HCD rats. Furthermore, the NTPDase activities were significantly decreased in platelets and kidney membranes of HCD-treated rats and these alterations were improved by NGEN. In conclusion, this study suggests that naringenin can potentially improve the renal failure and platelet alterations observed in rats fed a hypercholesterolemic diet probably through its antioxidant effects.

Dietary supplementation of ginger and turmeric improves reproductive function in hypertensive male rats

Ginger [Zingiber officinale Roscoe (Zingiberaceae)] and turmeric [Curcuma longa Linn (Zingiberaceae)] rhizomes have been reportedly used in folk medicine for the treatment of hypertension. However, the prevention of its complication such as male infertility remains unexplored. Hence, the aim of the present study was to investigate the preventive effects of ginger and turmeric rhizomes on some biomarkers of male reproductive function in L-NAME-induced hypertensive rats. Male Wistar rats were divided into seven groups (n = 10): normotensive control rats; induced (L-NAME hypertensive) rats; hypertensive rats treated with atenolol (10 mg/kg/day); normotensive and hypertensive rats treated with 4% supplementation of turmeric or ginger, respectively. After 14 days of pre-treatment, the animals were induced with hypertension by oral administration of L-NAME (40 mg/kg/day). The results revealed significant decrease in serum total testosterone and epididymal sperm progressive motility without affecting sperm viability in hypertensive rats. Moreover, increased oxidative stress in the testes and epididymides of hypertensive rats was evidenced by significant decrease in total and non-protein thiol levels, glutathione S-transferase (GST) activity with concomitant increase in 2′,7′-dichlorofluorescein (DFCH) oxidation and thiobarbituric acid reactive substances (TBARS) production. Similarly, decreased testicular and epididymal NO level with concomitant elevation in arginase activity was observed in hypertensive rats. However, dietary supplementation with turmeric or ginger efficiently prevented these alterations in biomarkers of reproductive function in hypertensive rats. The inhibition of arginase activity and increase in NO and testosterone levels by both rhizomes could suggest possible mechanism of action for the prevention of male infertility in hypertension. Therefore, both rhizomes could be harnessed as functional foods to prevent hypertension-mediated male reproductive dysfunction.

P2 receptors in renal autoregulation

Autoregulation of renal blood flow and glomerular filtration rate is an essential function of the renal microcirculation. While the existence of this phenomenon has been known for many years, the exact mechanisms that underlie this regulatory system remain poorly understood. The work of many investigators has provided insights into many aspects of the autoregulatory mechanism, but many critical components remain elusive. This review is intended to update the reader on the role of P2 purinoceptors as a postulated mechanism responsible for renal autoregulatory resistance adjustments. It will summarize recent advances in normal function and it will touch on more recent ideas regarding autoregulatory insufficiency in hypertension and inflammation. Current thoughts on the nature of the mechanosensor responsible for myogenic behavior will be also be discussed as well as current thoughts on the mechanisms involved in ATP release to the extracellular fluid space.

Purinergic signalling in the kidney in health and disease

The involvement of purinergic signalling in kidney physiology and pathophysiology is rapidly gaining recognition and this is a comprehensive review of early and recent publications in the field. Purinergic signalling involvement is described in several important intrarenal regulatory mechanisms, including tuboglomerular feedback, the autoregulatory response of the glomerular and extraglomerular microcirculation and the control of renin release. Furthermore, purinergic signalling influences water and electrolyte transport in all segments of the renal tubule. Reports about purine- and pyrimidine-mediated actions in diseases of the kidney, including polycystic kidney disease, nephritis, diabetes, hypertension and nephrotoxicant injury are covered and possible purinergic therapeutic strategies discussed.

Purinergic signaling and blood vessels in health and disease

Purinergic signaling plays important roles in control of vascular tone and remodeling. There is dual control of vascular tone by ATP released as a cotransmitter with noradrenaline from perivascular sympathetic nerves to cause vasoconstriction via P2X1 receptors, whereas ATP released from endothelial cells in response to changes in blood flow (producing shear stress) or hypoxia acts on P2X and P2Y receptors on endothelial cells to produce nitric oxide and endothelium-derived hyperpolarizing factor, which dilates vessels. ATP is also released from sensory-motor nerves during antidromic reflex activity to produce relaxation of some blood vessels. In this review, we stress the differences in neural and endothelial factors in purinergic control of different blood vessels. The long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides in promoting migration and proliferation of both vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis and vessel remodeling during restenosis after angioplasty are described. The pathophysiology of blood vessels and therapeutic potential of purinergic agents in diseases, including hypertension, atherosclerosis, ischemia, thrombosis and stroke, diabetes, and migraine, is discussed.

ATP and ADP hydrolysis in cell membranes from rat myometrium

Extracellular nucleotides affect female reproductive functions, fertilization, and pregnancy. The aim of this study was to investigate biochemical characteristics of ATP and ADP hydrolysis and identify E-NTPDases in myometrial cell membranes from Wistar albino rats. The apparent K (m) values were 506.4 ± 62.1 and 638.8 ± 31.3 μM, with a calculated V (max) (app) of 3,973.0 ± 279.5 and 2,853.9 ± 79.8 nmol/min/mg for ATP and ADP, respectively. The enzyme activity described here has common properties characteristic for NTPDases: divalent cation dependence; alkaline pH optimum for both substrates, insensitivity to some of classical ATPase inhibitors (ouabain, oligomycine, theophylline, levamisole) and significant inhibition by suramine and high concentration of sodium azides (5 mM). According to similar apparent K(m) values for both substrates, the ATP/ADP hydrolysis ratio, and Chevillard competition plot, NTPDase1 is dominant ATP/ADP hydrolyzing enzyme in myometrial cell membranes. RT-PCR analysis revealed expression of three members of ectonucleoside triphosphate diphosphohydrolase family (NTPDase 1, 2, and 8) in rat uterus. These findings may further elucidate the role of NTPDases and ATP in reproductive physiology.

Exercise training prevents ecto-nucleotidases alterations in platelets of hypertensive rats

In this study, we investigated the effect of 6 weeks of swimming training on the ecto-nucleotidase activities and platelet aggregation from rats that developed hypertension in response to oral administration of L-NAME. The rats were divided into four groups: control (n = 10), exercise (n = 10), L-NAME (n = 10), and exercise L-NAME (n = 10). The animals were trained five times per week in an adapted swimming system for 60 min with a gradual increase of the workload up to 5 % of animal's body weight. The results showed an increase in ATP, ADP, AMP, and adenosine hydrolysis, indicating an augment in NTPDase (from 35.3 ± 8.1 to 53.0 ± 15.1 nmol Pi/min/mg protein for ATP; and from 21.7 ± 7.0 to 46.4 ± 15.6 nmol Pi/min/mg protein for ADP as substrate), ecto-5'-nucleotidase (from 8.0 ± 5.7 to 28.1 ± 6.9 nmol Pi/min/mg protein), and ADA (from 0.8 ± 0.5 to 3.9 ± 0.8 U/L) activities in platelets from L-NAME-treated rats when compared to other groups (p < 0.05). A significant augment on platelet aggregation in L-NAME group was also observed. Exercise training was efficient in preventing these alterations in the exercise L-NAME group, besides showing a significant hypotensive effect. In conclusion, our results clearly indicated a protector action of moderate intensity exercise on nucleotides and nucleoside hydrolysis and on platelet aggregation, which highlights the exercise training effect to avoid hypertension complications related to ecto-nucleotidase activities.

Thyroid hormones are involved in 5'-nucleotidase modulation in soluble fraction of cardiac tissue

AIMS

To investigate the role of TH (thyroid hormones) in 5'-nucleotidase activity and expression in cardiac soluble fraction (SF).

MAIN METHODS

Male Wistar rats received daily injections of T4 (10, 25 or 50 μg T4/100g body weight) for 14 days to develop a hyperthyroidism condition. Thyroidectomy was performed in other animals to mimic hypothyroidism, and 14 days after surgery they were submitted to TH replacement therapy.

KEY FINDINGS

T4 reduced the 5'-nucleotidase activity (T4-25, P<0.05 and T4-50, P<0.01) in the SF. Conversely, hypothyroidism significantly increased the 5'-nucleotidase activity in this fraction (P<0.001) and TH replacement therapy reversed the latter result (P<0.001 compared to hypothyroid group). The analysis of protein expression in the SF showed that 5'-nucleotidase was more expressed in hypothyroid than in the control group and that the phosphorylated state of PKC observed in this condition may contribute to a possible mechanism of 5'-nucleotidase modulation by thyroid status.

SIGNIFICANCE

Taken together, these data reveal that TH can influence adenosine production by modulating 5'-nucleotidase activity and expression, which may contribute to the cardioprotective effect and the maintenance of cardiac function under TH privation.

Endotoxin-induced effects on nucleotide catabolism in mouse kidney

Extracellular adenosine 5'-triphosphate (ATP) acts as a proinflammatory mediator. Adenosine, the final product of ATP breakdown, is an anti-inflammatory compound, acting mainly on adenosine A(2A) receptors. Considering that the kidney is an organ strongly affected during systemic inflammatory responses and that ectonucleotidases are responsible for the control of extracellular nucleotide and nucleoside levels, we examined the endotoxin-induced effects on ectonucleotidases in kidney membranes of mice, and whether CGS-21680 hydrochloride (3-[4-[2-[[6-amino-9-[(2R,3R,4S,5S)-5-(ethylcarbamoyl)-3,4-dihydroxy-oxolan-2-yl]purin-2-yl]amino]ethyl]phenyl]propanoic acid), a selective adenosine A(2A) receptor agonist, antagonizes the lipopolysaccharide (LPS)-induced effects on nucleotide catabolism in kidney. Animals were injected intraperitoneally with 12 mg/kg LPS and/or 0.5mg/kg CGS-21680 or saline. Nucleotidase activities were determined in kidney membrane preparations and ATP metabolism was measured by high performance liquid chromatography (HPLC) assay. Analysis of ectonucleotidase expression was carried out by semi-quantitative semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Exposure to endotoxemia promoted an increase in ATP and p-Nitrophenyl thymidine 5'-monophosphate (p-Nph-5'-TMP) hydrolysis, and a decrease in adenosine 5'-monophosphate (AMP) hydrolysis. CGS-21680 treatment failed to reverse these changes. HPLC analysis indicated a decrease in extracellular ATP and adenosine levels in groups treated with LPS and LPS plus CGS-21680. The expression pattern of ectonucleotidases revealed an increase in Entpd3, Enpp2, and Enpp3 mRNA levels after LPS injection. These findings indicate that nucleotide and nucleoside availability in mouse kidney is altered at different stages of endotoxemia, in order to protect the integrity of this organ when exposed to systemic inflammation.

Role of adenosine 5'-triphosphate in regulating renal microvascular function and in hypertension

ATP is an essential energy substrate for cellular metabolism, but it can also influence many biological processes when released into the extracellular milieu. Research has established that extracellular ATP acts as an autocrine/paracrine factor that regulates many physiological functions. Alternatively, excessive extracellular ATP levels contribute to pathophysiological processes, such as inflammation, cell proliferation and apoptosis, and atherosclerosis. Renal P2 receptors are widely distributed throughout glomeruli, vasculature, and tubular segments and participate in controlling renal vascular resistance, mediating renal autoregulation, and regulating tubular transport function. This review will focus on the role of ATP-P2 receptor signaling in regulating renal microvascular function and autoregulation, recent advances on the role of ATP-P2 signaling in hypertension-associated renal vascular injury, and emerging new directions.