cyclic-gmp and Hyperhomocysteinemia

Hyperhomocysteinemia is a risk factor for atherosclerosis and venous thrombosis, probably exerting its effects through endothelial function. Homocysteine levels are lowered by folate supplementation, and such treatment improves endothelial function. However, whether folate supplementation decreases vascular risk and improves survival is unknown. The aim of this study was to evaluate endothelial function and mononuclear leukocyte inflammatory activity during homocysteine lowering in patients with hyperhomocysteinemia and vascular disease.. Endothelial function assessed as plasma (p-)endothelin(ET)-1 and intraplatelet cGMP and cAMP, and mononuclear leukocyte inflammatory activity, assessed as p-neopterin were studied during homocysteine lowering in 50 patients with hyperhomocysteinemia and vascular disease, randomized to folate supplementation or no treatment for 3 months.. P-homocysteine decreased during the 3 months not only in patients on folate supplementation (from 27 [21-52] to 14 [8-41] micromol/l; p<0.001), but also in the untreated group (from 23 [20-35] to 19 [4-31] micromol/l; p<0.001). P-ET-1 decreased during folate supplementation (from 5.7 [2.7-11.6] to 4.1 [1.8-9.0] pg/ml; p<0.01), but was unchanged in the untreated group 4.1 [2.0-9.5] pg/ml and 4.5 [2.7-7.1] pg/ml). P-neopterin was unchanged in patients on folate supplementation (9.7 [5.1-54.4] and 7.6 [5.7-73.0] nmol/l), but increased in the untreated group (from 8.2 [4.7-19.5] to 8.6 [4.6-24.6] nmol/l; p<0.05). Intraplatelet cGMP decreased in patients on folate supplementation (from 0.86 [0.21-2.00] platelets to 0.56 [0.17-1.42] pmol/10(9) platelets; p<0.05), but was unchanged in the untreated group. No significant differences concerning intraplatelet cAMP occurred in either group.. Folate supplementation in hyperhomocysteinemia is associated with decreasing levels of both ET-1 and intraplatelet cGMP, and the absence of an increase in the levels of the inflammatory mediator neopterin.

Topics: Aged; Blood Platelets; Cyclic AMP; Cyclic GMP; Endothelin-1; Female; Folic Acid; Humans; Hyperhomocysteinemia; Male; Neopterin; Vascular Diseases

Although hyperhomocysteinaemia is a risk factor for cardiovascular disease, the mechanisms underlying this association have not been elucidated. It has been demonstrated, however, that copper augments the inhibitory effect of homocysteine on nitric oxide (NO)-mediated relaxation of the rat aorta through increased superoxide formation, which reacts with NO thereby reducing the bioavailability of NO. Since it follows that the administration of a copper chelator may blunt the pathogenic impact of hyperhomocysteinaemia, in vivo, the effect of penicillamine administration on NO-dependent relaxation and superoxide formation in the aortae of hyperhomocysteinaemic rabbits was studied. New Zealand White rabbits were fed a methionine-rich (20 g/kg chow) diet for 1 month+/-penicillamine administered orally (10 mg/kg/day) and aortic relaxation elicited with acetylcholine and superoxide measured. The role of NADPH oxidase was also studied using a range of inhibitors and western analysis of gp47(phox) (a catalytic subunit of NADPH oxidase). The methionine-rich diet markedly increased plasma total homocysteine levels. In hyperhomocysteinaemic rabbits there was a marked reduction of acetylcholine-stimulated relaxation and an increase in superoxide formation that were both inhibited with superoxide dismutase and apocynin, an NADPH oxidase inhibitor. Gp47(phox) expression was also increased in aortae from methionine fed rabbits. Penicillamine administration significantly reduced plasma total copper in methionine-fed rabbits compared to controls. Impaired acetylcholine-stimulated relaxation, increased superoxide formation and increased gp47(phox) expression in aortae from methionine-fed rabbits was reversed by penicillamine administration. These data indicate that hyperhomocysteinaemia augments the formation of arterial superoxide through an increase in NADPH oxidase expression/activity which in turn reduces NO bioavailability. Since these effects were reversed by penicillamine, these data consolidate the hypothesis that copper plays a role in mediating homocysteine-induced vasculopathy.

Topics: Acetophenones; Acetylcholine; Administration, Oral; Animals; Aorta; Blotting, Western; Cyclic GMP; Dietary Supplements; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Inhibitors; Homocysteine; Hyperhomocysteinemia; In Vitro Techniques; Methionine; NADPH Oxidases; Nitric Oxide Donors; Nitroprusside; Onium Compounds; Penicillamine; Rabbits; Superoxides; Time Factors; Vasodilation; Vasodilator Agents

To investigate the effect of sustained hyperhomocysteinaemia (HHCy) on cavernosal smooth muscle function in a rabbit model of HHCy, developed using a methionine-enriched diet in which cavernosal responses were characterized, as elevated plasma levels of homocysteine may be a risk factor for vasculogenic erectile dysfunction.. Six New Zealand White rabbits were fed a diet supplemented with methionine (20 g/kg chow) for 4 weeks, while six control animals were fed a standard diet. Cavernosal strips were mounted in an organ bath and relaxation assessed when stimulated with carbachol, sodium nitroprusside (SNP), or noncholinergic, nonadrenergic (NANC)-mediated relaxation to electrical-field stimulation (EFS). Cavernosal tissue cGMP levels were assessed using an enzyme-linked immunosorbent assay, and superoxide (O(2) (.-)) production assessed using an assay of the superoxide dismutase (SOD)-inhibitable reduction of ferricytochrome c.. The methionine-rich diet led to an early but sustained HHCy; cavernosal strips from animals after 4 weeks of HHCy had a significantly impaired relaxation response to carbachol, an index of endothelium-dependent nitric oxide (NO)-mediated relaxation. This impairment was reversed by incubating with either SOD or catalase. Relaxation with either SNP, an index of endothelium-independent NO-mediated relaxation, or NANC-mediated EFS-induced relaxation, was unaffected by HHCy. There was a corresponding significant reduction in cavernosal cGMP levels (index of NO activity) in the HHCy group, with a more than five-fold increase in cavernosal tissue O(2) (.-) production.. Supplementing the diet of rabbits with methionine for 4 weeks caused an early and sustained HHCy and promoted a marked inhibitory effect on endothelium-dependent relaxation and NO formation in isolated corpus cavernosum, an effect mediated by reactive oxygen species.

Topics: Animals; Cyclic GMP; Hyperhomocysteinemia; Impotence, Vasculogenic; Male; Muscle Relaxation; Muscle, Smooth; Nitric Oxide; Penis; Phenylephrine; Rabbits; Superoxides; Vasoconstrictor Agents

Topics: Animals; Cyclic GMP; Disease Models, Animal; Homocysteine; Hyperhomocysteinemia; Impotence, Vasculogenic; Male; Muscle, Smooth, Vascular; Nitric Oxide; Organ Culture Techniques; Penis; Rabbits; Risk Factors; Superoxides; Veins

Hyperhomocysteinemia is associated with endothelial dysfunction, although the underlying mechanism is unknown. Previous studies have shown that nitric oxide (NO) plays an important role in the regulation of systemic and renal hemodynamics. This study investigated whether hyperhomocysteinemia induces renal oxidative stress and promotes renal dysfunction involving disturbances of the NO-pathway in Wistar rats. During 8 wk, control (C) and hyperhomocysteinemic (HYC) groups had free access to tap water and homocysteine-thiolactone (HTL, 50 mg/kg per d), respectively. At 8 wk, plasma homocysteine concentration, renal superoxide anion (O(2)), nitrotyrosine, and nitrite+nitrate levels, and renal function were measured. To assess NO involvement, the responses to L-Arginine (L-Arg, 300 mg/kg) and N(G)-nitro-L-arginine-methyl-ester (L-NAME, 20 microg/kg per min for 60 min) were analyzed. The HYC group showed higher homocysteine concentration (7.6 +/- 1.7 versus 4.9 +/- 1.0 micromol/L; P < 0.001), (O(2) production (157.92 +/- 74.46 versus 91.17 +/- 29.03 cpm. 10(3)/mg protein), and nitrite+nitrate levels (33.4 +/- 5.1 versus 11.7 +/- 4.3 micro mol/mg protein; P < 0.001) than the control group. Western blot analyses showed a nitrotyrosine mass 46% higher in the HYC group than in the controls. Furthermore, the HYC group showed lower GFR, renal plasma flow (RPF), and higher renal vascular resistance (RVR) than the controls. After L-Arg administration, the responses of GFR, RPF, and RVR were attenuated by 36%, 40%, and 50%, respectively; after L-NAME, the responses of RPF and RVR were exaggerated by 79% and 112%, respectively. This suggests a reduced NO bioavailability to produce vasodilation and an enhanced sensitivity to NO inhibition. In conclusion, hyperhomocysteinemia induces oxidative stress, NO inactivation, and renal dysfunction involving disturbances on the NO-pathway.

Topics: Animals; Cyclic GMP; Homocysteine; Hyperhomocysteinemia; Kidney Diseases; Male; Nitric Oxide; Oxidative Stress; Rats; Rats, Wistar; Renal Circulation; Thiobarbituric Acid Reactive Substances; Tyrosine

Hyperhomocysteinemia (HH) is an independent risk factor for atherosclerosis, including peripheral arterial occlusive disease (PAOD). Because angiogenesis and collateral vessel formation are important self-salvage mechanisms for ischemic PAOD, we examined whether HH modulates angiogenesis in vivo in a rat model of hindlimb ischemia. Rats were divided into 3 groups: the control group was given tap water, the HH group was given water containing L-methionine (1 g x kg(-1) x d(-1)), and the HH+L-arg group was given water containing methionine (1 g x kg(-1) x d(-1)) and l-arginine (2.25 vol%). At day 14 of the dietary modifications, the left femoral artery and vein were excised, and the extent of angiogenesis and collateral vessels in the ischemic limb were examined for 4 weeks. Plasma homocysteine levels significantly increased (P:<0.001), and plasma and tissue contents of nitrite+nitrate as well as tissue cGMP levels significantly decreased in the HH group compared with the control group (P:<0.01). Laser Doppler blood flowmetry (LDBF) revealed a significant decrease in the ischemic/normal limb LDBF ratio in the HH group at days 7, 14, 21, and 28 (P:<0.01 versus control). Angiography revealed a significant decrease in the angiographic score in the HH group at day 14 (P:<0.001 versus control). Immunohistochemistry of ischemic tissue sections showed a significant reduction in the capillary density in the HH group (P:<0. 001 versus control). Oral l-arginine supplementation in rats with HH (HH+L-arg) restored the decreased plasma and tissue nitrite+nitrate and cGMP contents (P:<0.05) as well as angiogenesis, as assessed by LDBF (P:<0.05 versus HH), angiographic score (P:<0.01 versus HH), and capillary density (P:<0.001 versus HH). In summary, HH impaired ischemia-induced angiogenesis and collateral vessel formation in a rat model of hindlimb ischemia in vivo. The mechanism of the HH-induced impairment of angiogenesis might be mediated in part by a reduced bioactivity of endogenous NO in the HH state.

Topics: Angiography; Animals; Arginine; Blood Pressure; Body Weight; Collateral Circulation; Cyclic GMP; Disease Models, Animal; Heart Rate; Hindlimb; Homocysteine; Hyperhomocysteinemia; Immunohistochemistry; Ischemia; Laser-Doppler Flowmetry; Muscle, Skeletal; Neovascularization, Physiologic; Nitrates; Nitrites; Rats; Regional Blood Flow; Time Factors