Chronic hyperhomocysteinemia impairs vascular function in ovariectomized rat carotid arteries

Urine metabolic profile in rats with arterial hypertension of different genesis

The diversity of pathogenetic mechanisms underlying arterial hypertension leads to the necessity to devise a personalized approach to the diagnosis and treatment of the disease. Metabolomics is one of the promising methods for personalized medicine, as it provides a comprehensive understanding of the physiological processes occurring in the body. The metabolome is a set of low-molecular substances available for detection in a sample and representing intermediate and final products of cell metabolism. Changes in the content and ratio of metabolites in the sample mark the corresponding pathogenetic mechanisms by highlighting them, which is especially important for such a multifactorial disease as arterial hypertension. To identify metabolomic markers for hypertensive conditions of different origins, three forms of arterial hypertension (AH) were studied: rats with hereditary AH (ISIAH rat strain); rats with AH induced by L-NAME administration (a model of endothelial dysfunction with impaired NO production); rats with AH caused by the administration of deoxycorticosterone in combination with salt loading (hormone-dependent form - DOCA-salt AH). WAG rats were used as normotensive controls. 24-hour urine samples were collected from all animals and analyzed by quantitative NMR spectroscopy for metabolic profiling. Then, potential metabolomic markers for the studied forms of hypertensive conditions were identified using multivariate statistics. Analysis of the data obtained showed that hereditary stress-induced arterial hypertension in ISIAH rats was characterized by a decrease in the following urine metabolites: nicotinamide and 1-methylnicotinamide (markers of inflammatory processes), N- acetylglutamate (nitric oxide cycle), isobutyrate and methyl acetoacetate (gut microbiota). Pharmacologically induced forms of hypertension (the L-NAME and DOCA+NaCl groups) do not share metabolomic markers with hereditary AH. They are differentiated by N,N-dimethylglycine (both groups), choline (the L-NAME group) and 1-methylnicotinamide (the group of rats with DOCA-salt hypertension).

Voluntary Exercise Attenuates Hyperhomocysteinemia, But Does not Protect Against Hyperhomocysteinemia-Induced Testicular and Epididymal Disturbances

The hyperhomocysteinemia (HHcy) is toxic to the cells and associated with several diseases. Clinical studies have shown changes in plasma concentrations of Hcy after physical exercise. This study aimed to assess the effect of HHcy on testis, epididymis and sperm quality and to investigate whether voluntary exercise training protects this system against damage caused by HHcy in Swiss mice. In this study, 48 mice were randomly distributed in the control, HHcy, physical exercise, and HHcy combined with physical exercise groups. HHcy was induced by daily administration of dl-homocysteine thiolactone via gavage throughout the experimental period. Physical exercise was performed through voluntary running on the exercise wheels. The plasma concentrations of homocysteine (Hcy) and testosterone were determined. The testes and epididymis were used to assess the sperm count, histopathology, lipoperoxidation, cytokine levels, testicular cholesterol, myeloperoxidase, and catalase activity. Spermatozoa were analyzed for morphology, acrosome integrity, mitochondrial activity, and motility. In the testes, HHcy increased the number of abnormal seminiferous tubules, reduced the tubular diameter and the height of the germinal epithelium. In the epididymis, there was tissue remodeling in the head region. Ultimately, voluntary physical exercise training reduced plasma Hcy concentration but did not attenuate HHcy-induced testicular and epididymal disturbances.

Homocysteine deteriorates intrahepatic derangement and portal-systemic collaterals in cirrhotic rats

In liver cirrhosis, the altered levels of vasoactive substances, especially endothelin-1 (ET-1) and nitric oxide (NO) lead to elevated intrahepatic resistance, increased portal-systemic collaterals and abnormal intra- and extra-hepatic vascular responsiveness. These derangements aggravate portal hypertension-related complications such as gastro-oesophageal variceal bleeding. Homocysteine, a substance implicated in cardiovascular diseases, has been found with influences on vasoresponsiveness and angiogenesis. However, their relevant effects in liver cirrhosis have not been investigated. In the present study, liver cirrhosis was induced by common bile duct ligation (BDL) in Sprague–Dawley rats. In acute study, the results showed that homocysteine enhanced hepatic vasoconstriction to ET-1 but decreased portal-systemic collateral vasocontractility to arginine vasopressin (AVP). Homocysteine down-regulated hepatic phosphorylated endothelial NO synthase (p-eNOS) and p-Akt protein expressions. Inducible NOS (iNOS) and cyclooxygenase (COX)-2 expressions were up-regulated by homocysteine in splenorenal shunt (SRS), the most prominent intra-abdominal collateral vessel. In chronic study, BDL or thioacetamide (TAA) rats received homocysteine or vehicle for 14 days. The results revealed that homocysteine increased hepatic collagen fibre deposition and fibrotic factors expressions in both BDL- and TAA-induced liver fibrotic rats. Portal-systemic shunting and expressions of mesenteric angiogenetic factors [vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), PDGF receptor β (PDGFRβ) and p-eNOS] were also increased in BDL rats. In conclusion, homocysteine is harmful to vascular derangements and liver fibrosis in cirrhosis.

High Methionine Diet Poses Cardiac Threat: A Molecular Insight

High methionine diet (HMD) for example red meat which includes lamb, beef, pork can pose cardiac threat and vascular dysfunction but the mechanisms are unclear. We hypothesize that a diet rich in methionine can malfunction the cardiovascular system in three ways: (1) by augmenting oxidative stress; (2) by inflammatory manifestations; and (3) by matrix/vascular remodeling. To test this hypothesis we used four groups of mice: (1) WT; (2) WT + methionine; (3) CBS(+/-) ; (4) CBS(+/-) +methionine. We observed high oxidative stress in mice fed with methionine which was even higher in CBS(+/-) and CBS(+/-) +methionine. Higher oxidative stress was indicated by high levels of SOD-1 in methionine fed mouse hearts whereas IL-1β, IL-6, TNFα, and TLR4 showed high inflammatory manifestations. The upregulated levels of eNOS/iNOS and upregulated levels of MMP2/MMP9 along with high collagen deposition indicated vascular and matrix remodeling in methionine fed mouse. We evaluated the cardiac function which was dysregulated in the mice fed with HMD. These mice had decreased ejection fraction and left ventricular dysfunction which subsequently leads to adverse cardiac remodeling. In conclusion, our study clearly shows that HMD poses a cardiac threat by increasing oxidative stress, inflammatory manifestations, matrix/vascular remodeling, and decreased cardiac function.

Consequence of hyperhomocysteinaemia on α1-adrenoceptor-mediated contraction in the rat corpus cavernosum: the role of reactive oxygen species

OBJECTIVES

Our main objective was to investigate the mechanisms underlying the effects of hyperhomocysteinaemia (HHcy) on contractile response mediated by α1-adrenoceptors in the rat corpus cavernosum.

METHODS

Concentration-response curves for phenylephrine (PE) were obtained in strips of corpus cavernosum, in absence or after incubation with tiron, tempol or polyethylene glycol (PEG)-catalase combined or not with tempol. We also measured the superoxide anion (O2(-)) and hydrogen peroxide (H2O2) generation, superoxide dismutase (SOD) and catalase activity and α-actin expression in rat corpus cavernosum from both groups.

KEY FINDINGS

HHcy increased PE-induced contraction in cavernosal strips. Tiron, PEG-catalase or tempol increased PE-induced contraction in strips from control rats, but it was not altered by tiron or PEG-catalase in HHcy rats, whereas tempol reduced this response. The combination of PEG-catalase and tempol did not alter the contractile response to PE in both groups. HHcy increased O2(-) generation and SOD activity, whereas H2O2 concentration was reduced. Finally, HHcy did not alter catalase activity or expression of α-actin.

CONCLUSIONS

The major new finding from this study is that HHcy induced a marked increase in PE-induced contraction in rat corpus cavernosum by a mechanism that involves increased O2(-) generation and it could play a role in the pathogenesis of erectile dysfunction associated with HHcy.

Protective vascular and cardiac effects of inducible nitric oxide synthase in mice with hyperhomocysteinemia

Diet-induced hyperhomocysteinemia produces endothelial and cardiac dysfunction and promotes thrombosis through a mechanism proposed to involve oxidative stress. Inducible nitric oxide synthase (iNOS) is upregulated in hyperhomocysteinemia and can generate superoxide. We therefore tested the hypothesis that iNOS mediates the adverse oxidative, vascular, thrombotic, and cardiac effects of hyperhomocysteinemia. Mice deficient in iNOS (Nos2-/-) and their wild-type (Nos2+/+) littermates were fed a high methionine/low folate (HM/LF) diet to induce mild hyperhomocysteinemia, with a 2-fold increase in plasma total homocysteine (P<0.001 vs. control diet). Hyperhomocysteinemic Nos2+/+ mice exhibited endothelial dysfunction in cerebral arterioles, with impaired dilatation to acetylcholine but not nitroprusside, and enhanced susceptibility to carotid artery thrombosis, with shortened times to occlusion following photochemical injury (P<0.05 vs. control diet). Nos2-/- mice had decreased rather than increased dilatation responses to acetylcholine (P<0.05 vs. Nos2+/+ mice). Nos2-/- mice fed control diet also exhibited shortened times to thrombotic occlusion (P<0.05 vs. Nos2+/+ mice), and iNOS deficiency failed to protect from endothelial dysfunction or accelerated thrombosis in mice with hyperhomocysteinemia. Deficiency of iNOS did not alter myocardial infarct size in mice fed the control diet but significantly increased infarct size and cardiac superoxide production in mice fed the HM/LF diet (P<0.05 vs. Nos2+/+ mice). These findings suggest that endogenous iNOS protects from, rather than exacerbates, endothelial dysfunction, thrombosis, and hyperhomocysteinemia-associated myocardial ischemia-reperfusion injury. In the setting of mild hyperhomocysteinemia, iNOS functions to blunt cardiac oxidative stress rather than functioning as a source of superoxide.

The lignan (-)-cubebin inhibits vascular contraction and induces relaxation via nitric oxide activation in isolated rat aorta

Cubebin, the most abundant lignan in Piper cubeba, has been described as having several effects as trypanocidal, antimycobacterial, antispasmodic, antimicrobial, anti-inflammatory, and analgesic. This study investigated the vasorelaxant effect produced by (-)-cubebin in isolated rat aortic rings pre-contracted with phenylephrine (Phe), and the possible mechanism involved in this event was evaluated. Endothelium-dependent relaxation was evoked by acetylcholine and (-)-cubebin in intact aortic rings, while endothelium-independent vasorelaxation was elicited by sodium nitroprusside and (-)-cubebin in denuded rings. Cumulative concentration-response curves for Phe (10(-10) -10(-5)  M) were determined for endothelium-intact and endothelium-denuded aortic rings in either the presence or absence of (-)-cubebin. Dose-response curves were also constructed for pre-incubation of vascular rings with Nω-nitro-L-arginine methyl ester (L-NAME) (a non-specific nitric oxide synthase inhibitor), indomethacin (an unspecific cyclooxygenase inhibitor), and 1H-[1,2,4] oxadiazolo [4,3-a]quinoxalin-1-one (ODQ) (a guanylyl cyclase inhibitor). (-)-Cubebin was found to exert a vasorelaxant effect irrespective of the presence of endothelium, which was abolished by pretreatment with L-NAME and ODQ, but not with indomethacin. In addition, (-)-cubebin was able to reduce Phe contraction in the case of intact rings. These results suggest that (-)-cubebin promotes vasorelaxation via NO/cGMP pathway in rat aorta, without prostacyclin involvement.

Pharmacological inhibition of inducible nitric oxide synthase (iNOS) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, convalesce behavior and biochemistry of hypertension induced vascular dementia in rats

Cognitive disorders are likely to increase over the coming years (5-10). Vascular dementia (VaD) has heterogeneous pathology and is a challenge for clinicians. Current Alzheimer's disease drugs have had limited clinical efficacy in treating VaD and none have been approved by major regulatory authorities specifically for this disease. Role of iNOS and NADPH-oxidase has been reported in various pathological conditions but there role in hypertension (Hypt) induced VaD is still unclear. This research work investigates the salutiferous effect of aminoguanidine (AG), an iNOS inhibitor and 4'-hydroxy-3'-methoxyacetophenone (HMAP), a NADPH oxidase inhibitor in Hypt induced VaD in rats. Deoxycorticosterone acetate-salt (DOCA-S) hypertension has been used for development of VaD in rats. Morris water-maze was used for testing learning and memory. Vascular system assessment was done by testing endothelial function. Mean arterial blood pressure (MABP), oxidative stress [aortic superoxide anion, serum and brain thiobarbituric acid reactive species (TBARS) and brain glutathione (GSH)], nitric oxide levels (serum nitrite/nitrate) and cholinergic activity (brain acetyl cholinesterase activity-AChE) were also measured. DOCA-S treated rats have shown increased MABP with impairment of endothelial function, learning and memory, reduction in serum nitrite/nitrate & brain GSH levels along with increase in serum & brain TBARS, and brain AChE activity. AG as well as HMAP significantly convalesce Hypt induced impairment of learning, memory, endothelial function, and alterations in various biochemical parameters. It may be concluded that AG, an iNOS inhibitor and HMAP, a NADPH-oxidase inhibitor may be considered as potential agents for the management of Hypt induced VaD.

Cellular hypomethylation is associated with impaired nitric oxide production by cultured human endothelial cells

Hyperhomocysteinemia (HHcy) is a risk factor for vascular disease, but the underlying mechanisms remain incompletely defined. Reduced bioavailability of nitric oxide (NO) is a principal manifestation of underlying endothelial dysfunction, which is an initial event in vascular disease. Inhibition of cellular methylation reactions by S-adenosylhomocysteine (AdoHcy), which accumulates during HHcy, has been suggested to contribute to vascular dysfunction. However, thus far, the effect of intracellular AdoHcy accumulation on NO bioavailability has not yet been fully substantiated by experimental evidence. The present study was carried out to evaluate whether disturbances in cellular methylation status affect NO production by cultured human endothelial cells. Here, we show that a hypomethylating environment, induced by the accumulation of AdoHcy, impairs NO production. Consistent with this finding, we observed decreased eNOS expression and activity, but, by contrast, enhanced NOS3 transcription. Taken together, our data support the existence of regulatory post-transcriptional mechanisms modulated by cellular methylation potential leading to impaired NO production by cultured human endothelial cells. As such, our conclusions may have implications for the HHcy-mediated reductions in NO bioavailability and endothelial dysfunction.

Acidosis induces relaxation mediated by nitric oxide and potassium channels in rat thoracic aorta

We investigated the mechanism by which extracellular acidification promotes relaxation in rat thoracic aorta. The relaxation response to HCl-induced extracellular acidification (7.4 to 6.5) was measured in aortic rings pre-contracted with phenylephrine (Phe, 10(-6) M) or KCl (45mM). The vascular reactivity experiments were performed in endothelium-intact and denuded rings, in the presence or absence of indomethacin (10(-5) M), L-NAME (10(-4) M), apamin (10(-6) M), and glibenclamide (10(-5) M). The effect of extracellular acidosis (pH 7.0 and 6.5) on nitric oxide (NO) production was evaluated in isolated endothelial cells loaded with diaminofluorescein-FM diacetate (DAF-FM DA, 5μM). The extracellular acidosis failed to induce any changes in the vascular tone of aortic rings pre-contracted with KCl, however, it caused endothelium-dependent and independent relaxation in rings pre-contracted with Phe. This acidosis induced-relaxation was inhibited by L-NAME, apamin, and glibenclamide, but not by indomethacin. The acidosis (pH 7.0 and 6.5) also promoted a time-dependent increase in the NO production by the isolated endothelial cells. These results suggest that extracellular acidosis promotes vasodilation mediated by NO, K(ATP) and SK(Ca), and maybe other K(+) channels in isolated rat thoracic aorta.

Extracellular alkalinization induces endothelium-derived nitric oxide dependent relaxation in rat thoracic aorta

AIM

To investigate the mechanism through which the extracellular alkalinization promotes relaxation in rat thoracic aorta.

METHODS

The relaxation response to NaOH-induced extracellular alkalinization (7.4-8.5) was measured in aortic rings pre-contracted with phenylephrine (Phe, 10(-6) M). The vascular reactivity experiments were performed in endothelium-intact and -denuded rings, in the presence or and absence of indomethacin (10(-5) M), NG-nitro-l-arginine methyl ester (L-NAME, 10(-4) M), N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide/HCl (W-7, 10(-7) M), 2,5-dimethylbenzimidazole (DMB, 2×10(-5) M) and methyl-β-cyclodextrin (10(-2) M). In addition, the effects of NaOH-induced extracellular alkalinization (pH 8.0 and 8.5) on the intracellular nitric oxide (NO) concentration was evaluated in isolated endothelial cells loaded with diaminofluorescein-FM diacetate (DAF-FM DA, 5 μM), in the presence and absence of DMB (2×10(-5) M).

RESULTS

The extracellular alkalinization failed to induce any change in vascular tone in aortic rings pre-contracted with KCl. In rings pre-contracted with Phe, the extracellular alkalinization caused relaxation in the endothelium-intact rings only, and this relaxation was maintained after cyclooxygenase inhibition; completely abolished by the inhibition of nitric oxide synthase (NOS), Ca(2+)/calmodulin and Na(+)/Ca(2+) exchanger (NCX), and partially blunted by the caveolae disassembly.

CONCLUSIONS

These results suggest that, in rat thoracic aorta, that extracellular alkalinization with NaOH activates the NCX reverse mode of endothelial cells in rat thoracic aorta, thereby the intracellular Ca(2+) concentration and activating the Ca(2+)/calmodulin-dependent NOS. In turn, NO is released promoting relaxation.