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Biomedical subjects

J F Keaney

Publications and source records attributed to J F Keaney.

At least 37 records · Page 2Linked to original sources
PubMed2000

Ascorbic acid enhances endothelial nitric-oxide synthase activity by increasing intracellular tetrahydrobiopterin.

Ascorbic acid enhances NO bioactivity in patients with vascular disease through unclear mechanism(s). We investigated the role of intracellular ascorbic acid in endothelium-derived NO bioactivity. Incubation of porcine aortic endothelial cells (PAECs) with ascorbic acid produced time- and dose-dependent intracellular ascorbic acid accumulation that enhanced NO bioactivity by 70% measured as A23187-induced cGMP accumulation. This effect was due to enhanced NO production because ascorbate stimulated both PAEC nitrogen oxide (NO(2)(-) + NO(3)(-)) production and l-arginine to l-citrulline conversion by 59 and 72%, respectively, without altering the cGMP response to authentic NO. Ascorbic acid also stimulated the catalytic activity of eNOS derived from either PAEC membrane fractions or baculovirus-infected Sf9 cells. Ascorbic acid enhanced bovine eNOS V(max) by approximately 50% without altering the K(m) for l-arginine. The effect of ascorbate was tetrahydrobiopterin (BH(4))-dependent, because ascorbate was ineffective with BH(4) concentrations >10 microm or in PAECs treated with sepiapterin to increase intracellular BH(4). The effect of ascorbic acid was also specific because A23187-stimulated cGMP accumulation in PAECs was insensitive to intracellular glutathione manipulation and only ascorbic acid, not glutathione, increased the intracellular concentration of BH(4). These data suggest that ascorbic acid enhances NO bioactivity in a BH(4)-dependent manner by increasing intracellular BH(4) content.

Animals↗
PubMed2000

Nitroglycerin is preferable to diltiazem for prevention of coronary bypass conduit spasm.

BACKGROUND: Diltiazem is widely used to prevent radial artery spasm after coronary bypass grafting (CABG). However, recent in vitro and in vivo studies have shown that nitroglycerin is a superior conduit vasodilator compared to diltiazem. A clinical comparison of these agents in patients undergoing CABG has not been previously performed. METHODS: One hundred sixty-one consecutive patients undergoing isolated CABG with the radial artery were prospectively randomized to 24-hour intravenous infusion of nitroglycerin or diltiazem followed by 6-month treatment with a daily dose of isosorbide mononitrate (n = 84) or diltiazem CD (n = 77). Analyses were performed on "intention-to-treat" basis. RESULTS: Crossovers because of low cardiac output, complete heart block, or sinus bradycardia occurred in 5 patients in the diltiazem group and none in the nitroglycerin group (p = 0.05). Operative mortality (nitroglycerin, 1.2% versus diltiazem, 1.3%), major morbidity (14% versus 16%), perioperative myocardial infarction (1.2% versus 0%), peak serum creatinine phosphokinase MB fraction levels (27 versus 21 U), intensive care unit stay (34+/-19 versus 38+/-30 hours) and total hospital length of stay (4.7+/-1.4 versus 4.7+/-1.3 days) were similar (p = not significant for all). Cardiac pacing was required more often in the diltiazem group (28% versus 13%, p = 0.01). Follow-up longer than 2 months was available in 145 patients (90%). Follow-up mortality (nitroglycerin, 1.2%; diltiazem, 1.3%), myocardial infarction (6%, versus 5%), and reintervention (8% versus 6%) rates and average angina class (1.3+/-0.7 versus 1.1+/-0.4) were similar (p = not significant for all). Thallium stress test obtained in 117 patients showed abnormal perfusion in the radial artery territory in only 4 patients (3%), 2 in each group (p = not significant). Treatment with diltiazem was more costly ($16,340 versus $1,096). CONCLUSIONS: Nitroglycerin is preferable to diltiazem for prevention of conduit spasm. Nitroglycerin is safe, effective, better tolerated, and less costly than diltiazem, and therefore, should be the agent of choice.

Coronary Artery Bypass↗
PubMed2000

Redox control of vascular nitric oxide bioavailability.

NO is an important component of vascular homeostasis and abnormal NO bioactivity has been implicated in number of disease states with important public health implications. One clear mechanism of impaired NO bioactivity and vascular disease is excess vascular oxidative stress. There is now a wealth of developing data that manipulation of vascular antioxidant stress is the considerable influence of the biologic activity of endothelium-derived NO. It remains to be seen if this influence can be exploited in a manner that truly alters the course of human disease.

Animals↗
PubMed2000

Pharmacological concentrations of ascorbic acid are required for the beneficial effect on endothelial vasomotor function in hypertension.

Increased production of superoxide anion may contribute to impaired bioactivity of endothelium-derived nitric oxide in hypertension. Ascorbic acid is capable of scavenging superoxide anion; however, experimental studies have shown that high physiological concentrations (>1 mmol/L) of ascorbic acid are required to prevent superoxide-mediated vascular dysfunction. To seek kinetic evidence that superoxide anion contributes to endothelial vasomotor dysfunction in human hypertension, we examined the effects of 2.4 or 24 mg/min ascorbic acid intra-arterial infusions on forearm blood flow responses to methacholine or sodium nitroprusside in 30 patients with hypertension and 22 age-matched controls. Endothelium-dependent vasodilation to methacholine was significantly impaired in the hypertensive patients, with a response to the highest dose of methacholine (10 microg/min) of 12.3+/-6.7 compared with 16.1+/-5.8 mL. min(-1). dL tissue(-1) in the controls (P<0.001). The response to sodium nitroprusside was equivalent in the 2 groups. Ascorbic acid at 24 mg/min significantly improved the forearm blood flow response to methacholine in hypertensive patients with a peak response of 16.1+/-7.1 mL. min(-1). dL tissue(-1) (P=0.001). This dose produced a cephalic vein ascorbic acid concentration of 3.2+/-1. 4 mmol/L. In contrast, ascorbic acid at 2.4 mg/min had no effect on the methacholine response. Ascorbic acid at both doses had no effect on the vasodilator response to sodium nitroprusside in hypertensive patients or the methacholine response in the controls. These results agree with the predicted kinetics for superoxide anion-mediated impairment of endothelium-derived nitric oxide action. Thus, superoxide anion may contribute to impaired endothelium-dependent vasodilation in patients with hypertension.

Adult↗
PubMed2000

Ascorbic acid and glutathione modulate the biological activity of S-nitrosoglutathione.

Ascorbic acid and glutathione (GSH) are important determinants of the intracellular redox state, and both are known to accelerate the decomposition of S-nitrosoglutathione (GSNO), an endogenous adduct of nitric oxide (NO). The implications of these observations for GSNO bioactivity are not yet clear. We investigated the effect of ascorbic acid and GSH on GSNO bioactivity by using a bioassay with isolated segments of guinea pig aorta suspended in organ chambers. Arterial segments demonstrated relaxation to GSNO (0.1 micromol/L) that was significantly enhanced by 300 micromol/L ascorbic acid (71+/-6% versus 53+/-6%, P<0.05) but not GSH. Both ascorbic acid and GSH significantly shortened the duration of arterial relaxation in response to 0.1 micromol/L GSNO (from >120 minutes to 22.5+/-3.5 and 36.3+/-4.3 minutes, respectively; P<0.05), consistent with accelerated decomposition of GSNO that was confirmed spectrophotometrically. The effect of ascorbic acid was abrogated by either DTPA or the copper(I)-specific agent bathocuproine but not deferoxamine, indicating a dependence on the availability of redox-active copper. Consistent with this notion, the action of ascorbic acid on GSNO bioactivity was also supported by copper-zinc superoxide dismutase, a physiologically relevant source of copper. In contrast, the effect of GSH on GSNO degradation and GSNO-mediated arterial relaxation was independent of transition metal ions, because DTPA had no effect. These data indicate that both ascorbic acid and GSH modulate GSNO bioactivity and suggest a distinction between the mechanism of GSNO degradation by ascorbic acid or GSH. Whereas both ascorbic acid and GSH accelerate the degradation of GSNO, only ascorbic acid is dependent on the presence of transition metal ions.

Animals↗
PubMed1999

Treatment of hypertension with ascorbic acid.

In a randomised, double-blind, placebo-controlled study we showed that treatment of hypertensive patients with ascorbic acid lowers blood pressure. Further studies of ascorbic acid to treat hypertension, with clinical endpoints, are warranted.

Adult↗
PubMed1999

Enhanced nitric oxide-mediated vascular relaxation in radial artery compared with internal mammary artery or saphenous vein.

BACKGROUND: The superior long-term patency of internal mammary artery coronary bypass grafts compared with venous grafts has been attributed in part to increased endothelium-derived nitric oxide (. NO) production. Interest in the radial artery as an alternative bypass conduit has recently been revived; however, its biological characteristics remain incompletely defined. The purpose of this study was to compare the.NO-mediated vasomotor properties of the radial artery to those of the internal mammary artery and saphenous vein. METHODS AND RESULTS: Matched segments of radial artery, internal mammary artery, and saphenous vein (n=24 patients) were examined by use of organ-chamber methodology. Endothelium-dependent and -independent vasomotor responses were assessed by dose-response curves to acetylcholine, N(G)-nitro-L-arginine methyl ester (L-NAME), 8-bromo-cyclic 3',5'-guanosine monophosphate (8-bromo-cGMP), and nitroglycerin. Maximum.NO-mediated radial artery relaxation in response to acetylcholine (86+/-10%) was significantly greater than internal mammary artery (56+/-9%) or saphenous vein (11+/-5%, both P<0.0001). Similarly, acetylcholine-stimulated cGMP accumulation in radial artery (9.1+/-1.7 pmol/mg protein) was also greater than internal mammary artery (6.2+/-0.3 pmol/mg protein) or saphenous vein (1.4+/-0.2 pmol/mg protein, both P<0.05). Estimated basal endothelial.NO production, assayed as the percent maximum contraction in response to L-NAME, was greater in radial artery (39+/-5%) than internal mammary artery (23+/-6%) or saphenous vein (5+/-2%, both P<0.05). Maximum relaxation of all vessels to nitroglycerin was similar, although the sensitivity of radial artery to nitroglycerin was greater (EC(50)=33+/-7 nmol/L) than the internal mammary artery (203+/-32 nmol/L) or saphenous vein (97+/-12 nmol/L, both P<0.05). Vascular cGMP in response to 0.1 micromol/L nitroglycerin was significantly higher in the radial artery (8.3+/-1. 4 pmol/mg protein) compared with the internal mammary artery (3. 5+/-1.3 pmol/mg protein) or saphenous vein (1.4+/-0.3 pmol/mg protein, both P<0.0001). Relaxation to 8-bromo-cGMP was identical for all 3 conduits. CONCLUSIONS: These data indicate that. NO-dependent relaxation of radial artery is greater than that of internal mammary artery or saphenous vein. This difference is related to endothelial production of.NO and/or vessel sensitivity to. NO. Such favorable physiological characteristics of radial artery could conceivably contribute to improved long-term patency of this conduit compared with saphenous vein.

Adult↗
PubMed1999

Long-term ascorbic acid administration reverses endothelial vasomotor dysfunction in patients with coronary artery disease.

BACKGROUND: Loss of endothelium-derived nitric oxide (EDNO) contributes to the clinical expression of coronary artery disease (CAD). Increased oxidative stress has been linked to impaired endothelial vasomotor function in atherosclerosis, and recent studies demonstrated that short-term ascorbic acid treatment improves endothelial function. METHODS AND RESULTS: In a randomized, double-blind, placebo-controlled study, we examined the effects of single-dose (2 g PO) and long-term (500 mg/d) ascorbic acid treatment on EDNO-dependent flow-mediated dilation of the brachial artery in patients with angiographically established CAD. Flow-mediated dilation was examined by high-resolution vascular ultrasound at baseline, 2 hours after the single dose, and 30 days after long-term treatment in 46 patients with CAD. Flow-mediated dilation improved from 6.6+/-3.5% to 10.1+/-5.2% after single-dose treatment, and the effect was sustained after long-term treatment (9. 0+/-3.7%), whereas flow-mediated dilation was 8.6+/-4.7% at baseline and remained unchanged after single-dose (7.8+/-4.4%) and long-term (7.9+/-4.5%) treatment with placebo (P=0.005 by repeated-measures ANOVA). Plasma ascorbic acid concentrations increased from 41.4+/-12. 9 to 115.9+/-34.2 micromol/L after single-dose treatment and to 95. 0+/-36.1 micromol/L after long-term treatment (P<0.001). CONCLUSIONS: In patients with CAD, long-term ascorbic acid treatment has a sustained beneficial effect on EDNO action. Because endothelial dysfunction may contribute to the pathogenesis of cardiovascular events, this study indicates that ascorbic acid treatment may benefit patients with CAD.

Adult↗
PubMed1999

Nitroglycerin is superior to diltiazem as a coronary bypass conduit vasodilator.

BACKGROUND: Recent reports of improved radial artery patency have been attributed, in part, to routine use of diltiazem to prevent vasospasm. However, diltiazem is costly, and its use may be associated with negative inotropic and chronotropic side effects. This study compares the vasodilatory properties of diltiazem to those of nitroglycerin. METHODS: In vitro, with the use of organ chambers, the vasodilatory properties of diltiazem and nitroglycerin were compared in matched segments of radial artery, internal thoracic artery, and saphenous vein that were harvested from the same patients (n = 11). The vasodilatory response of the radial artery to intravenous diltiazem or nitroglycerin was compared in vivo (n = 10) with the use of ultrasonographic measurements of radial artery diameter. RESULTS: The maximum relaxation of radial artery (100% +/- 4%), internal thoracic artery (96% +/- 4%), and saphenous vein (100% +/- 3%) to nitroglycerin were significantly greater than the response to diltiazem (33% +/- 6%, 22% +/- 7%, and 34% +/- 5%, respectively; P <.001). The thromboxane mimetic, U46619, induced radial artery spasm with a median effective concentration of 3.7 +/- 0.8 nmol/L. Physiologic concentrations of nitroglycerin (0.1+/- micromol/L) significantly inhibited the radial artery response to U46619 (median effective concentration, 6.2 +/- 1.1 nmol/L; P =.046), whereas diltiazem (1 micromol/L) did not (median effective concentration, 3.7 +/- 0.8 nmol/L; P =.64). In vivo, nitroglycerin increased radial artery diameter 22% +/- 3%, which was significantly greater than diltiazem (3% +/- 0.5%; P =.001). CONCLUSION: Nitroglycerin is a superior conduit vasodilator and is more effective in preventing graft spasm than diltiazem. Nitroglycerin should be strongly considered as the drug of choice to prevent conduit spasm after coronary bypass grafting.

Adult↗
PubMed1999

Vitamin E and vascular homeostasis: implications for atherosclerosis.

Considerable epidemiologic data suggest that dietary consumption of vitamin E reduces the incidence of cardiovascular disease. The precise mechanisms are not clear, but emerging data indicate that vitamin E has numerous activities that may, in part, explain its effect on vascular disease. In particular, vitamin E enhances the bioactivity of nitric oxide, inhibits smooth muscle proliferation, and limits platelet aggregation. One common mechanism to account for these effects of vitamin E is the inhibition of protein kinase C stimulation. In the setting of atherosclerosis, inhibition of protein kinase C by vitamin E would be expected to maintain normal vascular homeostasis and thus reduce the clinical incidence of cardiovascular disease.

Antioxidants↗
PubMed1998

Ascorbate prevents the interaction of superoxide and nitric oxide only at very high physiological concentrations.

The bioactivity of nitric oxide (.NO) depends, in part, on its interaction with superoxide. Usually, superoxide dismutase (SOD) preserves .NO bioactivity by limiting the availability of superoxide. Ascorbic acid also effectively scavenges superoxide, but the extent to which this interaction is necessary for intact .NO bioactivity is not known. Therefore, the present study examined the effect of ascorbic acid on .NO bioactivity with isolated rabbit arterial segments. A steady flux of superoxide (1.15 to 2.3 micromol . L-1 . min-1) produced either by pyrogallol autoxidation or a hypoxanthine/xanthine oxidase system inhibited endothelium-derived .NO-mediated arterial relaxation elicited by acetylcholine. This effect of superoxide was completely blocked by SOD (300 IU/mL) and the manganese SOD mimic EUK-8 (300 micromol/L) and partially inhibited by ascorbic acid (10 mmol/L). Lower concentrations of ascorbic acid were ineffective despite scavenging >90% of superoxide. We increased the endogenous flux of superoxide (3.2+/-0.3-fold) by inhibiting vascular copper-zinc SOD with diethyldithiocarbamate. This increased endogenous flux of superoxide produced an impairment of .NO-mediated arterial relaxation that was reversed by EUK-8 (300 micromol/L) but not ascorbic acid (10 mmol/L) despite equivalent scavenging of the endogenous superoxide flux. We used 3-nitrotyrosine formation (from peroxynitrite) as an indicator of .NO interaction with superoxide and found that SOD and EUK-8 compete more effectively with .NO for superoxide than does ascorbic acid. These data indicate that preservation of .NO bioactivity by superoxide scavengers depends not only on superoxide scavenging activity, but also on the rate of superoxide scavenging. Normal extracellular concentrations of ascorbic acid (30 to 150 micromol/L) are not likely to prevent the interaction of .NO with superoxide under physiological conditions.

Animals↗