Ascorbic Acid Infusion Research Articles

Ascorbic Acid Infusion Blunts CD40L Upregulation in Patients Undergoing Coronary Stent

To reduce the increase of oxidative stress and the upregulation of CD40L during stenting procedure using ascorbic acid infusion. CD40L upregulation occurring after coronary percutaneous coronary intervention predicts vascular events but the underlying mechanism is still unclear. Fifty-six patients undergoing elective coronary stenting were randomly allocated to intravenous infusion of the antioxidant ascorbic acid or placebo. Platelet CD40L and plasma levels of soluble CD40L and of 8-hydroxy-2'-deoxyguanosine, a marker of oxidative stress, were measured before and after coronary stenting. In vitro study was also done to measure reactive oxidant species and CD40L expression in platelets exposed to anoxia-reoxygenation. Placebo-treated patients showed a significant increase of platelet CD40L, soluble CD40L and 8-hydroxy-2'-deoxyguanosine compared to baseline values. Patients given ascorbic acid showed no change of soluble CD40L and platelet CD40L but a significant decrease of 8-hydroxy-2'-deoxyguanosine. After 60 and 120 min, soluble CD40L, platelet CD40L and 8-hydroxy-2'-deoxyguanosine were significantly lower in the ascorbic acid-treated group compared to the placebo-treated one. A significant correlation between platelet CD40L and soluble CD40L and between soluble CD40L and 8-hydroxy-2'-deoxyguanosine was observed. Platelets, in vitro exposed to anoxia-reoxygenation, had a burst of ROS and an upregulation of CD40L that were inhibited by ascorbic acid or apocynin, an inhibitor of NADPH oxidase. This study shows that in patients undergoing coronary stenting CD40L is upregulated with a mechanism which is likely mediated by oxidative stress.

The Effects of Ascorbic Acid Supplementation on Muscle Blood Flow in Aged Rats

During exercise aged individuals exhibit endothelial dysfunction and decreased levels of whole-limb blood flow, both of which may be linked mechanistically to age-related increases in reactive oxygen species (ROS). Ascorbic acid (AA) reduces levels of ROS and has been shown to alleviate vascular and hyperemic dysfunction at rest and during small muscle mass exercise in humans (Kirby et al. J Physiol., 2009). However, the effect of AA on vascular function and blood flow (BF) to individual muscles during dynamic whole-body exercise is not known. PURPOSE: To test the hypothesis that a single high-dose infusion of AA would increase BF to the hindlimb musculature of old rats at rest and during treadmill running. METHODS: 18 old (∼28 months) Fischer 344 × Brown Norway rats were randomized into rest (n=9) and exercise (n=9) groups. BF to the hindlimb (28 individual muscles and muscle parts) was evaluated via radiolabeled microspheres before and after intra-arterial AA administration (76 mg/kg in 3 ml heparinized saline, 30 minute infusion) at rest and during submaximal treadmill running (20 m/min, 5% grade). Total antioxidant capacity (TAC) and thiobarbituric acid reactive species (TBARS) were measured before and after AA to determine the ability of this dose of AA to increase levels of plasma antioxidants and decrease levels of ROS, respectively. RESULTS: At rest: AA increased TAC (∼37%, P < 0.05) but did not change TBARS (Pre: 6.8 ± 0.7 vs. Post: 7.0 ± 1.0 μM, P > 0.05). AA decreased total hindlimb BF (Pre: 25 ± 3 vs Post: 16 ± 2 ml/min/100g, P < 0.05) and BF to 8 of the 28 individual muscles that were evaluated. During exercise: TAC was increased (∼35%, P < 0.05) and TBARS were decreased (Pre: 9.8 ± 2.0 vs Post: 6.1 ± 0.5 μM, P < 0.05). However, there was no effect on either total hindlimb BF (Pre: 154 ± 14 vs. Post: 162 ± 13, P > 0.05) or BF to any of the individual muscles that were evaluated. CONCLUSIONS: Increased TAC via AA infusion reduces hindlimb muscle BF at rest but not during whole-body dynamic exercise. Thus, although this specific AA dose decreased TBARS, there was no evidence that AA supplementation increases blood flow to the locomotor muscles during whole-body exercise. Whether other doses of AA or alternative antioxidants provide beneficial outcomes in other models remains unknown. Support: AHA Grant 070090Z

Intravenous Ascorbic Acid Infusion Improves Myocardial Perfusion Grade During Elective Percutaneous Coronary Intervention: Relationship With Oxidative Stress Markers

Our goal was to explore whether antioxidant vitamin C infusion is able to affect the microcirculation perfusion in patients undergoing elective percutaneous coronary intervention for stable angina. Periprocedural myocardial injury in the setting of elective percutaneous coronary intervention is associated with increased risk of death, recurrent infarction, and revascularization at follow-up. Despite excellent epicardial blood flow, impaired microcirculatory reperfusion may persist and increases the risk of vascular recurrences. Post-percutaneous coronary intervention induced-oxidative stress is one of the potential mechanisms accounting for impaired perfusion. Fifty-six patients were enrolled in a prospective, single-center, randomized study comparing 1 g vitamin C infusion (16.6 mg/min, over 1 h before percutaneous coronary intervention) versus placebo. At the baseline, Thrombolysis In Myocardial Infarction (TIMI) myocardial perfusion grade <2 was observed in 89% and in 86% of patients randomized to the placebo or vitamin C infusion group, respectively (p > 0.05). After percutaneous coronary intervention, these percentages decreased in the placebo group (32%) and in greater measure in the vitamin C group (4%, p < 0.01). Complete microcirculatory reperfusion (TIMI myocardial perfusion grade = 3) was achieved in 79% of the vitamin C-treated group compared with 39% of the placebo group (p < 0.01); 8-hydroxy-2-deoxyguanosine (p < 0.002) and 8-iso-prostaglandin F(2alpha) (p < 0.02) plasma levels significantly increased in the placebo group while they were significantly reduced in the vitamin C-treated group (p < 0.0001). TIMI myocardial perfusion grade changes from the baseline showed significant correlation with 8-hydroxy-2-deoxyguanosine (p < 0.006) or 8-iso-prostaglandin F(2alpha) (p < 0.01) plasma levels changes. In patients undergoing elective percutaneous coronary intervention, impaired microcirculatory reperfusion is improved by vitamin C infusion suggesting that oxidative stress is implicated in such a phenomenon.

Potential mechanisms of low-sodium diet-induced cardiac disease: superoxide-NO in the heart.

Patients on a low salt (LS) diet have increased mortality. To determine whether reduction in NO bioactivity may contribute to the LS-induced cardiac dysfunction and mortality. Adult male mongrel dogs were placed on LS (0.05% sodium chloride) for 2 weeks. Body weight (25.4 + or - 0.4 to 23.6 + or - 0.4 kg), left ventricular systolic pressure (137.0 + or - 3.4 to 124.0 + or - 6.7 mm Hg), and mean aortic pressure (111 + or - 3.1 to 98 + or - 4.3 mm Hg) decreased. Plasma angiotensin II concentration increased (4.4 + or - 0.7 to 14.8 + or - 3.7 pg/mL). Veratrine-induced (5 microg/kg) NO-mediated vasodilation was inhibited by 44% in LS; however, the simultaneous intravenous infusion of ascorbic acid or apocynin acutely and completely reversed this inhibition. In LS heart tissues, lucigenin chemiluminescence was increased 2.3-fold to angiotensin II (10(-8) mol/L), and bradykinin (10(-4) mol/L) induced reduction of myocardial oxygen consumption in vitro was decreased (40 + or - 1.3% to 16 + or - 6.3%) and completely restored by coincubation with tiron, tempol or apocynin. Switching of substrate uptake from free fatty acid to glucose by the heart was observed (free fatty acid: 8.97 + or - 1.39 to 4.53 + or - 1.12 micromol/min; glucose: 1.31 + or - 0.52 to 6.86 + or - 1.78 micromol/min). Western blotting indicated an increase in both p47(phox) (121%) and gp91(phox) (44%) as did RNA microarray analysis (433 genes changed) showed an increase in p47(phox) (1.6-fold) and gp91(phox) (2.0 fold) in the LS heart tissue. LS diet induces the activation of the renin-angiotensin system, which increases oxidative stress via the NADPH oxidase and attenuates NO bioavailability in the heart.

Endothelium‐dependent vasodilatation and exercise hyperaemia in ageing humans: impact of acute ascorbic acid administration

Age-related increases in oxidative stress impair endothelium-dependent vasodilatation in humans, leading to the speculation that endothelial dysfunction contributes to impaired muscle blood flow and vascular control during exercise in older adults. We directly tested this hypothesis in 14 young (22 +/- 1 years) and 14 healthy older men and women (65 +/- 2 years). We measured forearm blood flow (FBF; Doppler ultrasound) and calculated vascular conductance (FVC) responses to single muscle contractions at 10, 20 and 40% maximum voluntary contraction (MVC) before and during ascorbic acid (AA) infusion, and we also determined the effects of AA on muscle blood flow during mild (10% MVC) continuous rhythmic handgrip exercise. For single contractions, the peak rapid hyperaemic responses to all contraction intensities were impaired approximately 45% in the older adults (all P < 0.05), and AA infusion did not impact the responses in either age group. For the rhythmic exercise trial, FBF (approximately 28%) and FVC (approximately 31%) were lower (P = 0.06 and 0.05) in older versus young adults after 5 min of steady-state exercise with saline. Subsequently, AA was infused via brachial artery catheter for 10 min during continued exercise. AA administration did not significantly influence FBF or FVC in young adults (1-3%; P = 0.24-0.59), whereas FBF increased 34 +/- 7% in older adults at end-exercise, and this was due to an increase in FVC (32 +/- 7%; both P < 0.05). This increase in FBF and FVC during exercise in older adults was associated with improvements in vasodilator responses to acetylcholine (ACh; endothelium dependent) but not sodium nitroprusside (SNP; endothelium independent). AA had no effect on ACh or SNP responses in the young. We conclude that acute AA administration does not impact the observed age-related impairment in the rapid hyperaemic response to brief muscle contractions in humans; however, it does significantly increase muscle blood flow during continuous dynamic exercise in older adults, and this is probably due (in part) to an improvement in endothelium-dependent vasodilatation.

ATP‐mediated vasodilation is not reduced in aging humans

Endothelium‐dependent vasodilation is reduced with age, as evidenced by blunted vasodilator responsiveness to acetylcholine (ACH) infusions. Circulating adenosine triphosphate (ATP) has been implicated in the control of skeletal muscle vascular tone during mismatches in oxygen delivery and demand (e.g., exercise) via binding to purinergic receptors on the endothelium, and aging is typically associated with reductions in muscle blood flow under such conditions. Therefore, we tested the hypothesis that ATP‐mediated vasodilation is impaired in aging humans and that ascorbic acid (AA) infusion would acutely restore this impairment. We measured forearm blood flow (FBF; venous occlusion plethysmography) responses to local intra‐arterial infusions of ACH, ATP, and sodium nitroprusside (SNP) with and without AA infusion in 13 young and 13 older adults. The peak increase in FBF to ACH was significantly impaired in older compared with younger adults (260±70% vs 620±99%; P&lt;0.05), and this difference was abolished during AA infusion (520±80% vs 560±70%). Peak FBF responses were not different between older and young adults to either ATP (675±105% vs 735±125%) or SNP (1120±110% vs 1140±150%) and AA infusion did not alter these responses (both NS). Thus, in contrast to the observed impairments in ACH responses, the vasodilatory response to exogenous ATP is not reduced with age in healthy humans.

Oxalic acid excretion after intravenous ascorbic acid administration

Ascorbic acid is frequently administered intravenously by alternative health practitioners and, occasionally, by mainstream physicians. Intravenous administration can greatly increase the amount of ascorbic acid that reaches the circulation, potentially increasing the risk of oxalate crystallization in the urinary space. To investigate this possibility, we developed gas chromatography mass spectrometry methodology and sampling and storage procedures for oxalic acid analysis without interference from ascorbic acid and measured urinary oxalic acid excretion in people administered intravenous ascorbic acid in doses ranging from 0.2 to 1.5 g/kg body weight. In vitro oxidation of ascorbic acid to oxalic acid did not occur when urine samples were brought immediately to pH less than 2 and stored at −30°C within 6 hours. Even very high ascorbic acid concentrations did not interfere with the analysis when oxalic acid extraction was carried out at pH 1. As measured during and over the 6 hours after ascorbic acid infusions, urinary oxalic acid excretion increased with increasing doses, reaching approximately 80 mg at a dose of approximately 100 g. We conclude that, when studied using correct procedures for sample handling, storage, and analysis, less than 0.5% of a very large intravenous dose of ascorbic acid is recovered as urinary oxalic acid in people with normal renal function.

High-dose ascorbic acid infusion abolishes chronic vasoconstriction and restores resting leg blood flow in healthy older men

Resting whole leg blood flow and vascular conductance decrease linearly with advancing age in healthy adult men. The potential role of age-related increases in oxidative stress in these changes is unknown. Resting leg blood flow during saline and ascorbic acid infusion was studied in 10 young (25 +/- 1 yr) and 11 older (63 +/- 2 yr) healthy normotensive men. Plasma oxidized LDL, a marker of oxidative stress, was greater in the older men (P < 0.05). Absolute resting femoral artery blood flow at baseline (iv saline control infusion) was 25% lower in the older men (238 +/- 25 vs. 316 +/- 38 ml/min; P < 0.05), and it was inversely related to plasma oxidized LDL (r = -0.56, P < 0.01) in all subjects. Infusion of supraphysiological concentrations of ascorbic acid increased femoral artery blood flow by 37% in the older men (to 327 +/- 52 ml/min; P < 0.05), but not in the young men (352 +/- 41 ml/min; P = 0.28), thus abolishing group differences (P = 0.72). Mean arterial blood pressure was greater in the older men at baseline (86 +/- 4 vs. 78 +/- 2 mmHg; P < 0.05), but it was unaffected by ascorbic acid infusion (P >/= 0.70). As a result, the lower baseline femoral artery blood flow in the older men was mediated solely by a 32% lower femoral artery vascular conductance (P < 0.05). Baseline femoral vascular conductance also was inversely related to plasma oxidized LDL (r = -0.65, P < 0.01). Ascorbic acid increased femoral vascular conductance by 36% in the older men (P < 0.05) but not in the young men (P = 0.31). In conclusion, ascorbic acid infused at concentrations known to scavenge reactive oxygen species restores resting femoral artery blood flow in healthy older adult men by increasing vascular conductance. These results support the hypothesis that oxidative stress plays a major role in the reduced resting whole leg blood flow and increased leg vasoconstriction observed with aging in men.

Carbon Nanotube-Modified Carbon Fiber Microelectrodes for In Vivo Voltammetric Measurement of Ascorbic Acid in Rat Brain

This study demonstrates a new electrochemical method for in vivo measurements of ascorbic acid (AA) in rat brain with multiwalled carbon nanotube (MWNT)-modified carbon fiber microelectrodes (CFMEs) based on the electrochemical property of MWNTs for facilitating AA oxidation. Cyclic voltammetry results indicate that the prepared MWNT-modified CFMEs possess a marked electrocatalytic activity toward AA oxidation and can be used for its selective measurement in the presence of other kinds of electroactive species coexisting in rat brain, such as 3,4-dihydroxyphenylacetic acid, uric acid, and 5-hydroxytryptamine. The selectivity of the MWNT-modified CFMEs toward AA measurement is further studied in vivo by exogenously infusing ascorbate oxidase into the brain, and the results confirm that the prepared electrodes are selective and can thus be used for reliable in vivo measurements of AA in rat brain, combined with their good stability during in vivo measurements. The basal level of striatum AA is determined to be 0.20 +/- 0.05 mM (n = 3). The application of the voltammetric method with the MWNT-modified CFMEs is preliminarily demonstrated for in vivo observation of homeostatic regulation of striatum AA with exogenous infusion of AA into the brain.

Mechanism of Cardiovascular Mortality During Low Sodium Diet: NO Bioavailability And The Renin Angiotensin‐NADPH Oxidase System

Adult male mongrel dogs were placed on low sodium diet (LS) which contains 0.5% sodium chloride for two weeks. Body weight (25±0.4kg to 24±0.4kg), left ventricular systolic pressure (137±3.4 to 124±6.7mmHg) and mean aortic pressure (MAP) (111±3.1 to 98±4.3 mmHg) decreased. Plasma angiotensin II concentration increased (4.4±0.7 to 14.8±3.7pg/ml), and losartan (10mg/kg) decreased MAP (95±4.7 to 52±4.1mmHg) in LS dogs. In LS heart tissues, lucigenin chemiluminescence was increased 2.3 fold to angiotensin II (10−8M) and bradykinin (10−4M) induced reduction of MVO2 was decreased (−40±1.3 to −16±6.3%). These changes were completely restored by coincubation with tiron, tempol (10−3M each), or apocynin (10−4M). Veratrine (5μg/kg) induced NO-dependent coronary vasodilation was inhibited by 44%, but the simultaneous intravenous infusion of ascorbic acid or apocynin completely reversed this inhibition. Switching of cardiac substrate uptake from free fatty acid (FFA) to glucose by the heart was observed (FFA; 8.97±1.39 to 4.53±1.12 μmol/min, Glucose; 1.31±0.52 to 6.86±1.78 μmol/min). Western blotting analysis showed that the protein expression of p47phox was upregulated in the LS heart tissue. In conclusion, LS diet induces the activation of the renin-angiotensin system which increases oxidative stress via the NADPH oxidase, and attenuates the NO bioavailability in the heart.

Hyperhomocysteinemia Alters Cardiac Substrate Metabolism by Impairing Nitric Oxide Bioavailability Through Oxidative Stress

Hyperhomocysteinemia (HHcy) has been considered a vascular disease associated with increased levels of oxidative stress that results in scavenging of NO. However, little is known of the impact of HHcy on cardiac function and especially myocardial metabolism. L-Homocysteine was intravenously infused into conscious dogs, and the dogs were fed methionine to increase plasma homocysteine to 10 micromol/L for acute and 24 micromol/L for chronic HHcy. There was no significant change in hemodynamics with HHcy. Veratrine-induced, NO-dependent, coronary vasodilation (Bezold-Jarisch reflex) was reduced by 32% but was restored by simultaneous intravenous infusion of ascorbic acid or apocynin. Acute and chronic HHcy significantly increased uptake of glucose and lactate and decreased uptake of free fatty acid by the heart. HHcy significantly decreased bradykinin- or carbachol-induced reduction of myocardial oxygen consumption in vitro, and this effect was completely restored by coincubation with ascorbic acid, Tempol, or apocynin. Western blot analysis indicated an increase in Nox2 (82%) and a reduction in endothelial nitric oxide synthase (39%), phospho-endothelial nitric oxide synthase (39%), and superoxide dismutase-1 (45%). Microarray analysis of gene expression in heart tissue from chronic HHcy indicated a switch in cardiac phenotype to enzymes that metabolize glucose. HHcy directly modulates substrate use by the heart independent of changes in hemodynamics or ventricular function by reducing NO bioavailability through the generation of superoxide. The progression of cardiac or coronary heart disease associated with HHcy should be evaluated in light of the impact of alterations in the regulation of cardiac metabolism and substrate use.

Oxidative stress explains differences in large elastic artery compliance between sedentary and habitually exercising postmenopausal women

To determine whether oxidative stress contributes to differences in large elastic artery compliance between sedentary and habitually exercising postmenopausal women. Carotid artery compliance was measured during acute intravenous infusions of saline (control) and supraphysiological doses of the potent antioxidant ascorbic acid (vitamin C) in sedentary (n = 15; 58 +/- 1 years) and endurance exercise-trained (n = 11, 59 +/- 1) healthy postmenopausal women. Carotid artery compliance was 24% higher in the exercising versus sedentary women during control (P < 0.001). During ascorbic acid infusion, carotid artery compliance was increased by 28% in the sedentary women (1.29 +/- 0.12 to 1.60 +/- 0.12 mm/mm Hg x 10, P < 0.001 vs control) but was unchanged in exercising women (1.60 +/- 0.14 vs 1.48 +/- 0.14 mm/mm Hg x 10, P = 0.10), abolishing the habitual exercise-associated baseline difference. The change in compliance with ascorbic acid was most strongly related to maximal aerobic capacity (r = -0.64, P < 0.0001) and body fatness (r = 0.60, P < 0.0001) and was more modestly related to oxidized low-density lipoprotein, waist circumference, interleukin-6, total and low-density lipoprotein cholesterol (all r = 0.40 to 0.49, all P < 0.05), and high-density lipoprotein cholesterol (r = -0.48, P = 0.01). Carotid artery diameter, blood pressure, and heart rate were unaffected by ascorbic acid. These results indicate that the greater large elastic artery compliance in habitually exercising compared with sedentary estrogen-deficient postmenopausal women may be mediated by an absence of oxidative stress, perhaps related in part to more favorable cardiovascular risk factors.

Hyperhomocysteinemia Alters The Cardiac Metabolism by Impairing Nitric Oxide Bioavailability Through Oxidative Stress

Hyperhomocysteinemia (HHcy) has been considered a vascular disease which is associated with increased levels of reactive oxygen species resulting in scavenging of nitric oxide (NO). However, little is known of the impact on cardiac function and myocardial metabolism. L-Homocysteine was intravenously infused into conscious adult male dogs (titrated to give plasma homocysteine up to 10μM over 120 minutes). There was no change in any hemodynamic parameters between baseline and HHcy. Veratrine induced NO dependent coronary vasodilation (Bezold-Jarisch reflex) was reduced by 29% which was restored by simultaneous infusion of ascorbic acid. Myocardial substrate use was calculated as coronary sinus-arterial difference times coronary blood flow. Acute HHcy significantly increased glucose uptake (1.7±1.2 to 6.8±1.2 μmol/min) and decreased FFA uptake (6.0±1.6 to 3.1±1.0 μmol/min). Lactate uptake was also increased (3.9±3.0 to 11.2±6.1 μmol/min). Myocardial oxygen consumption (MVO2) of LV tissue from chronic HHcy dogs (fed with methionine for 2 weeks) was also measured in vitro in response to bradykinin (BK). BK-induced reduction in MVO2 was significantly decreased by HHcy and this effect was completely inhibited with coincubation with ascorbic acid, tempol, or apocynin. In conclusion, HHcy modulates the substrate use of heart by inhibiting NO bioavailability through the generation of superoxide. The progression of the disease associated with HHcy should also be evaluated based on alterations in the regulation of cardiac metabolism and substrate use. Supported by HL-PO1-43023 grant.

Ascorbic Acid Selectively Improves Large Elastic Artery Compliance in Postmenopausal Women

The compliance of large elastic arteries in the cardiothoracic region decreases with advancing age/menopause and plays an important role in the increased prevalence of cardiovascular diseases in postmenopausal women. We determined whether oxidative stress contributes to the reduced large elastic artery compliance of postmenopausal women. Carotid artery compliance was measured during acute intravenous infusions of saline (baseline control) and supraphysiological doses of the potent antioxidant ascorbic acid in premenopausal (n=10; 23+/-1; mean+/-SE) and estrogen-deficient postmenopausal (n=21; 55+/-1 years) healthy sedentary women. Carotid artery compliance was 56% lower in postmenopausal compared with premenopausal women during baseline control (P<0.0001). Ascorbic acid infusion increased carotid artery compliance by 26% in postmenopausal women (1.11+/-0.07 to 1.38+/-0.08 mm2/mm Hgx10(-1); P<0.001) but had no effect in premenopausal women (2.50+/-0.25 versus 2.43+/-0.20 mm2/mm Hgx10(-1)). Carotid artery diameter, blood pressure, and heart rate were unaffected by ascorbic acid. In the pooled population, the change in arterial compliance with ascorbic acid correlated with baseline waist-to-hip ratio (r=0.56; P=0.001), plasma norepinephrine (r=0.58; P=0.001), and LDL cholesterol (r=0.54; P=0.001). These results suggest that oxidative stress may be an important mechanism contributing to the reduced large elastic artery compliance of sedentary, estrogen-deficient postmenopausal women. Increased abdominal fat storage, sympathetic nervous system activity, and LDL cholesterol may be mechanistically involved in oxidative stress-associated suppression of arterial compliance in postmenopausal women.

Effect of acute and chronic ascorbic acid on flow-mediated dilatation with sedentary and physically active human ageing.

Peripheral conduit artery flow-mediated dilatation decreases with ageing in humans. The underlying mechanisms and efficacy of preventive strategies are unknown. Brachial artery flow-mediated dilatation was determined at baseline and after ascorbic acid (vitamin C) intravenous infusion and chronic supplementation (500 mg day(-1) for 30 days) in three groups of healthy men: young sedentary (n= 11; 25 +/- 1 years, mean +/-s.e.m.), older sedentary (n= 9; 64 +/- 2), and older endurance-exercise trained (n= 9; 64 +/- 2). At baseline, flow-mediated dilatation (normalized for the hyperaemic stimulus) was approximately 45% lower in the older (0.015 +/- 0.001) versus young (0.028 +/- 0.004) sedentary men (P < 0.01), but was preserved in older exercising men (0.028 +/- 0.004). Ascorbic acid infusion increased plasma concentrations > 15-fold in all groups and restored flow-mediated dilatation in the sedentary older men (to 0.023 +/- 0.002; P > 0.1 versus other groups), with no effects in the other two groups. Oral ascorbic acid supplementation did not affect flow-mediated dilatation in any group. Brachial artery endothelium-independent dilatation (sublingual nitroglycerin) did not differ among the groups at baseline nor change with ascorbic acid administration. These results provide the first evidence for an important role of oxidative stress in both the impairment in peripheral conduit artery flow-mediated dilatation with sedentary human ageing and the preservation of flow-mediated dilatation with physically active ageing.

Fat content and ascorbic acid infusion influence microbial and physicochemical qualities of electron beam irradiated beef patties

The effects of fat content and post-slaughter ascorbic acid (AA) infusion on microbial and physicochemical qualities of beef patties processed by electron beam irradiation were investigated in a 4 °C storage trial. Beef muscles from AA-infused or control animals were ground and mixed with tallow to achieve a final fat content of 4%, 17% and 30%, respectively. Beef patties were irradiated at 5 and 10 kGy with a linear electron beam accelerator. Non-irradiated and non-infused ground beef patties served as a control. The addition of fat significantly ( p<0.05) increased aerobic, total coliform, E. coli, and psychrotrophic bacteria counts in beef patties during storage. Irradiation at both dosages exerted a pasteurization effect on psychrotrophic bacteria for up to 7 days of storage. No viable aerobic, total coliform, or E. coli bacteria were detected in any irradiated beef patties during storage. Physicochemical changes caused by lipid oxidation and surface discoloration of beef patties were significantly ( p<0.05) increased by both the addition of fat and irradiation processing. Beef patties made from AA-infused animals did not alter bacterial counts. Instead, post-slaughter infusion of AA exerted a pro-oxidant effect in the beef patties that led to a significant ( p<0.0.5) increase in lipid oxidation and surface discoloration of stored patties.

Coronary endothelial dysfunction is not rapidly reversible with ascorbic acid

In humans with cardiovascular risk factors, increased vascular production of superoxide anion may contribute to endothelial dysfunction by its reacting with nitric oxide and reducing its biological activity. High concentrations of ascorbic acid scavenge superoxide anion and restore normal endothelium-dependent vasodilation in humans with cardiovascular risk factors. To investigate the contribution of increased superoxide anion to endothelial dysfunction in atherosclerotic coronary arteries, we examined the effect of sequential infusions of ascorbic acid (final concentration 0.1, 1.0, and 10 mmol/L) or placebo on coronary endothelial function in 26 subjects referred for cardiac catheterization to evaluate coronary artery disease. Coronary vasomotor function was evaluated using intracoronary agonist infusion, quantitative angiography, and intracoronary Doppler measurements. At baseline, endothelium-dependent vasodilation of epicardial arteries and coronary microvessels was impaired to an equivalent extent in the ascorbic acid and placebo groups. Sequential ascorbic acid infusions had no effect on the acetylcholine-induced change in coronary artery diameter (−11±8, −12±10, and −9±9%) compared with the effect of placebo (−14±13, −16±10, and −13±9%) infusions ( p=0.98). Similarly, the changes in coronary blood flow during acetylcholine infusions were equivalent during ascorbic acid (51±44, 67±66, and 62±52%) and placebo (61±104, 55±93, and 50±69%) infusions ( p=0.63). Ascorbic acid also had no effect on the dilator response to intracoronary nitroglycerin ( p=0.19). These data argue against an important role for superoxide-mediated “inactivation” of nitric oxide or another rapidly reversible form of oxidative stress as a mechanism of coronary endothelial dysfunction in patients with coronary atherosclerosis.

Attenuation of ischemic preconditioning in pigs by scavenging of free oxyradicals with ascorbic acid.

Free oxyradicals are involved in the signal transduction of ischemic preconditioning in rats and rabbits. Data from larger mammals in which the infarct development is closer to that in humans are lacking. We have therefore investigated the impact of the radical scavenger ascorbic acid on ischemic preconditioning in pigs. In 33 anesthetized pigs, the left anterior descending coronary artery was perfused from an extracorporeal circuit. Infarct size (measured as percent area at risk) was determined by triphenyltetrazolium chloride staining. In placebo-treated animals undergoing 90 min of severe ischemia and 120 min of reperfusion, infarct size averaged 26.9 +/- 3.9% (mean +/- SE; n = 9). Ischemic preconditioning by 10 min of ischemia and 15 min of reperfusion reduced infarct size to 6.4 +/- 2.4% (P < 0.05 vs. placebo; n = 9). Intravenous infusion of ascorbic acid (30 min before ischemic preconditioning or ischemia; 2-g bolus followed by 25 mg/min until the end of ischemia) had no effect on infarct size per se (22.6 +/- 6.5%; n = 6), but largely abolished the infarct size reduction by ischemic preconditioning (19.1 +/- 5.4%; n = 9). Scavenging of free oxyradicals with ascorbic acid largely attenuates the beneficial effect of ischemic preconditioning in pigs.

Effects of Black Race on Forearm Resistance Vessel Function

Presentation, response to therapy, and clinical outcome in hypertension differ according to race, and these observations could relate to differences in microvascular function. We examined forearm microvascular function in age-matched black (n=56) and white subjects (n=62) using intra-arterial agonist infusion and venous occlusion plethysmography. In normotensive subjects (n=70; 34 black and 36 white normotensives), methacholine-, sodium nitroprusside-, and verapamil-induced vasodilation was equivalent in black and white subjects. In hypertensive subjects (n=48; 22 black and 26 white hypertensives), the vasodilator response to methacholine was markedly lower in black subjects compared with white subjects (P<0.001). The vasodilator responses to sodium nitroprusside and verapamil, however, were equivalent in black and white hypertensive subjects. Acute ascorbic acid infusion improved the methacholine response equally in black and white hypertensive patients, suggesting that a difference in a rapidly reversible form of oxidative stress does not explain these findings. Thus, the present study demonstrates important racial differences in vascular function and a marked impairment in endothelial vasomotor function in black patients with hypertension. Further studies will be required to elucidate the mechanisms and determine whether these insights will lead to more appropriately tailored management of hypertension and its complications.

Beta-amyloid deposition in the brains of rats chronically infused with thiorphan or lipopolysaccharide: the role of ascorbic acid in the vehicle

Beta-amyloid deposition and neuroinflammation are two important features of Alzheimer's disease (AD) that may influence its progression. Chronic infusion of lipopolysaccharide (LPS) into the rodent 4th ventricle reproduces many of the neurobiological changes seen in AD. Chronic infusion of ascorbic acid containing thiorphan, an inhibitor of the enzyme neprilysin that catabolizes beta-amyloid, into the hippocampus induces extracellular deposition of beta-amyloid fibrils. We investigated whether the combined presence of chronic neuroinflammation could exacerbate the deposition of beta-amyloid induced by thiorphan. The infusion of any solution containing ascorbic acid alone or with thiorphan or LPS increased the level of intraneuronal beta-amyloid immunoreactivity. Solutions that did not contain ascorbic acid were not associated with increased intraneuronal beta-amyloid immunoreactivity. The role of neprilysin in the deposition of beta-amyloid in AD brains remains undetermined.