Jane McEneny

Novel biomarkers in early diagnosis of acute myocardial infarction compared with cardiac troponin T

AIMS To evaluate the role of novel biomarkers in early detection of acute myocardial infarction (MI) in patients admitted with acute chest pain. METHODS AND RESULTS A prospective study of 664 patients presenting to two coronary care units with chest pain was conducted over 3 years from 2003. Patients were assessed on admission: clinical characteristics, ECG (electrocardiogram), renal function, cardiac troponin T (cTnT), heart fatty acid binding protein (H-FABP), glycogen phosphorylase-BB, NT-pro-brain natriuretic peptide, D-dimer, hsCRP (high sensitivity C-reactive protein), myeloperoxidase, matrix metalloproteinase-9, pregnancy associated plasma protein-A, soluble CD40 ligand. A > or = 12 h cTnT sample was also obtained. MI was defined as cTnT > or = 0.03 microg/L. In patients presenting <4 h of symptom onset, sensitivity of H-FABP for MI was significantly higher than admission cTnT (73 vs. 55%; P = 0.043). Specificity of H-FABP was 71%. None of the other biomarkers challenged cTnT. Combined use of H-FABP and cTnT (either one elevated initially) significantly improved the sensitivities of H-FABP or cTnT (85%; P < or = 0.004). This combined approach also improved the negative predictive value, negative likelihood ratio, and the risk ratio. CONCLUSION Assessment of H-FABP within the first 4 h of symptoms is superior to cTnT for detection of MI, and is a useful additional biomarker for patients with acute chest pain.

Free Radical-Mediated Damage to Barrier Function is not Associated with Altered Brain Morphology in High-Altitude Headache:

The present study combined molecular and neuroimaging techniques to examine if free radical-mediated damage to barrier function in hypoxia would result in extracellular edema, raise intracranial pressure (ICP) and account for the neurological symptoms typical of high-altitude headache (HAH) also known as acute mountain sickness (AMS). Twenty-two subjects were randomly exposed for 18 h to 12% (hypoxia) and 21% oxygen (O2 (normoxia)) for collection of venous blood (0 h, 8 h, 15 h, 18 h) and CSF (18 h) after lumbar puncture (LP). Electron paramagnetic resonance (EPR) spectroscopy identified a clear increase in the blood and CSF concentration of O2 and carbon-centered free radicals (P > 0.05 versus normoxia) subsequently identified as lipid-derived alkoxyl (LO•) and alkyl (LC•) species. Magnetic resonance imaging (MRI) demonstrated a mild increase in brain volume (7.0 ± 4.8mL or 0.6% ± 0.4%, P > 0.05 versus normoxia) that resolved within 6 h of normoxic recovery. However, there was no detectable evidence for gross barrier dysfunction, elevated lumbar pressures, T2 prolongation or associated neuronal and astroglial damage. Clinical AMS was diagnosed in 50% of subjects during the hypoxic trial and corresponding headache scores were markedly elevated (P > 0.05 versus non-AMS). A greater increase in brain volume was observed, though this was slight, independent of oxidative stress, barrier dysfunction, raised lumbar pressure, vascular damage and measurable evidence of cerebral edema and only apparent in the most severe of cases. These findings suggest that free-radical-mediated vasogenic edema is not an important pathophysiological event that contributes to the mild brain swelling observed in HAH.

A rapid method for measurement of the susceptibility to oxidation of low-density lipoprotein.

Oxidation of low-density lipoprotein (LDL) may be important in the pathogenesis of atherosclerosis. We describe a method which measures the oxidation resistance of LDL isolated by a rapid procedure without added antioxidants. LDL was isolated from heparinized plasma by density gradient ultracentrifugation and desalted by gel filtration. The protein concentration was standardized to 50 mg/L and oxidation was promoted by copper (2 μmol/L) at 37°C. The total sample preparation time was 2·5 h. Conjugated diene production was monitored at λ = 234 nm with computation of the lag time. LDL oxidation was inhibited by EDTA but not heparin. Albumin inhibited LDL oxidation but only in concentrations greater than 50 mg/L. LDL was stable in frozen plasma (–70°C) for 10 weeks, but unstable in the isolated and desalted state. The lag time for LDL from patients treated with the antioxidant probucol was markedly prolonged compared to normal subjects.

Altered free radical metabolism in acute mountain sickness: implications for dynamic cerebral autoregulation and blood–brain barrier function

We tested the hypothesis that dynamic cerebral autoregulation (CA) and blood–brain barrier (BBB) function would be compromised in acute mountain sickness (AMS) subsequent to a hypoxia‐mediated alteration in systemic free radical metabolism. Eighteen male lowlanders were examined in normoxia (21% O2) and following 6 h passive exposure to hypoxia (12% O2). Blood flow velocity in the middle cerebral artery (MCAv) and mean arterial blood pressure (MAP) were measured for determination of CA following calculation of transfer function analysis and rate of regulation (RoR). Nine subjects developed clinical AMS (AMS+) and were more hypoxaemic relative to subjects without AMS (AMS–). A more marked increase in the venous concentration of the ascorbate radical (A•−), lipid hydroperoxides (LOOH) and increased susceptibility of low‐density lipoprotein (LDL) to oxidation was observed during hypoxia in AMS+ (P < 0.05 versus AMS–). Despite a general decline in total nitric oxide (NO) in hypoxia (P < 0.05 versus normoxia), the normoxic baseline plasma and red blood cell (RBC) NO metabolite pool was lower in AMS+ with normalization observed during hypoxia (P < 0.05 versus AMS–). CA was selectively impaired in AMS+ as indicated both by an increase in the low‐frequency (0.07–0.20Hz) transfer function gain and decrease in RoR (P < 0.05 versus AMS–). However, there was no evidence for cerebral hyper‐perfusion, BBB disruption or neuronal–parenchymal damage as indicated by a lack of change in MCAv, S100β and neuron‐specific enolase. In conclusion, these findings suggest that AMS is associated with altered redox homeostasis and disordered CA independent of barrier disruption.

Prognostic value of a multimarker approach for patients presenting to hospital with acute chest pain.

To evaluate the prognostic role of novel biomarkers for the risk stratification of patients admitted with ischemic-type chest pain, a prospective study of 664 patients presenting to 2 coronary care units with ischemic-type chest pain was conducted over 3 years beginning in 2003. Patients were assessed on admission for clinical characteristics, electrocardiographic findings, renal function, cardiac troponin T (cTnT), markers of myocyte injury (heart fatty acid-binding protein [H-FABP] and glycogen phosphorylase BB), neurohormonal activation (N-terminal-pro-brain natriuretic peptide [NT-pro-BNP]), hemostatic activity (fibrinogen and D-dimer), and vascular inflammation (high-sensitivity C-reactive protein, myeloperoxidase, matrix metalloproteinase-9, pregnancy-associated plasma protein-A, and soluble CD40 ligand). A >or=12-hour cTnT sample was also obtained. Myocardial infarction (MI) was defined as peak cTnT >or=0.03 microg/L. Patients were followed for 1 year from the time of admission. The primary end point was death or MI. Elevated fibrinogen, D-dimer, H-FABP, NT-pro-BNP, and peak cTnT were predictive of death or MI within 1 year (unadjusted odds ratios 2.5, 3.1, 5.4, 5.4, and 6.9, respectively). On multivariate analysis, H-FABP and NT-pro-BNP were selected, in addition to age, peak cTnT, and left ventricular hypertrophy on initial electrocardiography, as significant independent predictors of death or MI within 1 year. Patients without elevations of H-FABP, NT-pro-BNP, or peak cTnT formed a very low risk group in terms of death or MI within 1 year. A very high risk group had elevations of all 3 biomarkers. In conclusion, the measurement of H-FABP and NT-pro-BNP at the time of hospital admission for patients with ischemic-type chest pain adds useful prognostic information to that provided by the measurement of baseline and 12-hour cTnT.

Electron paramagnetic spectroscopic evidence of exercise-induced free radical accumulation in human skeletal muscle

The present study determined if acute exercise increased free radical formation in human skeletal muscle. Vastus lateralis biopsies were obtained in a randomized balanced order from six males at rest and following single-leg knee extensor exercise performed for 2 min at 50% of maximal work rate (WRMAX) and 3 min at 100% WRMAX. EPR spectroscopy revealed an exercise-induced increase in mitochondrial ubisemiquinone [0.167 ± 0.055 vs. rest: 0.106 ± 0.047 arbitrary units (AU)/g total protein (TP), P < 0.05] and α-phenyl-tert-butylnitrone-adducts (112 ± 41 vs. rest: 29 ± 9 AU/mg tissue mass, P < 0.05). Intramuscular lipid hydroperoxides also increased (0.320 ± 0.263 vs. rest: 0.148 ± 0.071 nmol/mg TP, P < 0.05) despite an uptake of α-tocopherol, α-carotene and β-carotene. There were no relationships between mitochondrial volume density and any biomarkers of oxidative stress. These findings provide the first direct evidence for intramuscular free radical accumulation and lipid peroxidation following acute exercise in humans.

Low-fat versus low-carbohydrate weight reduction diets: effects on weight loss, insulin resistance, and cardiovascular risk: a randomized control trial.

OBJECTIVE Low-fat hypocaloric diets reduce insulin resistance and prevent type 2 diabetes in those at risk. Low-carbohydrate, high-fat diets are advocated as an alternative, but reciprocal increases in dietary fat may have detrimental effects on insulin resistance and offset the benefits of weight reduction. RESEARCH DESIGN AND METHODS We investigated a low-fat (20% fat, 60% carbohydrate) versus a low-carbohydrate (60% fat, 20% carbohydrate) weight reduction diet in 24 overweight/obese subjects ([mean ± SD] BMI 33.6 ± 3.7 kg/m2, aged 39 ± 10 years) in an 8-week randomized controlled trial. All food was weighed and distributed, and intake was calculated to produce a 500 kcal/day energy deficit. Insulin action was assessed by the euglycemic clamp and insulin secretion by meal tolerance test. Body composition, adipokine levels, and vascular compliance by pulse-wave analysis were also measured. RESULTS Significant weight loss occurred in both groups (P < 0.01), with no difference between groups (P = 0.40). Peripheral glucose uptake increased, but there was no difference between groups (P = 0.28), and suppression of endogenous glucose production was also similar between groups. Meal tolerance–related insulin secretion decreased with weight loss with no difference between groups (P = 0.71). The change in overall systemic arterial stiffness was, however, significantly different between diets (P = 0.04); this reflected a significant decrease in augmentation index following the low-fat diet, compared with a nonsignificant increase within the low-carbohydrate group. CONCLUSIONS This study demonstrates comparable effects on insulin resistance of low-fat and low-carbohydrate diets independent of macronutrient content. The difference in augmentation index may imply a negative effect of low-carbohydrate diets on vascular risk.

High-altitude pulmonary hypertension is associated with a free radical-mediated reduction in pulmonary nitric oxide bioavailability

High altitude (HA)‐induced pulmonary hypertension may be due to a free radical‐mediated reduction in pulmonary nitric oxide (NO) bioavailability. We hypothesised that the increase in pulmonary artery systolic pressure (PASP) at HA would be associated with a net transpulmonary output of free radicals and corresponding loss of bioactive NO metabolites. Twenty‐six mountaineers provided central venous and radial arterial samples at low altitude (LA) and following active ascent to 4559 m (HA). PASP was determined by Doppler echocardiography, pulmonary blood flow by inert gas re‐breathing, and vasoactive exchange via the Fick principle. Acute mountain sickness (AMS) and high‐altitude pulmonary oedema (HAPE) were diagnosed using clinical questionnaires and chest radiography. Electron paramagnetic resonance spectroscopy, ozone‐based chemiluminescence and ELISA were employed for plasma detection of the ascorbate free radical (A·−), NO metabolites and 3‐nitrotyrosine (3‐NT). Fourteen subjects were diagnosed with AMS and three of four HAPE‐susceptible subjects developed HAPE. Ascent decreased the arterio‐central venous concentration difference (a‐cvD) resulting in a net transpulmonary loss of ascorbate, α‐tocopherol and bioactive NO metabolites (P < 0.05 vs. LA). This was accompanied by an increased a‐cvD and net output of A·− and lipid hydroperoxides (P < 0.05 vs. sea level, SL) that correlated against the rise in PASP (r= 0.56–0.62, P < 0.05) and arterial 3‐NT (r= 0.48–0.63, P < 0.05) that was more pronounced in HAPE. These findings suggest that increased PASP and vascular resistance observed at HA are associated with a free radical‐mediated reduction in pulmonary NO bioavailability.

The effect of probucol and vitamin E treatment on the oxidation of low-density lipoprotein and forearm vascular responses in humans

Abstract This study investigates the hypothesis that lipid soluble antioxidants may increase the resistance of low‐density lipoprotein (LDL) to oxidation and also enhance vascular endothelial responses in humans. In a double‐blind parallel group study, 24 hypercholesterolaemic patients, already on treatment with simvastatin (20mg day‐1), were randomized to supplementary treatment with probucol (500 mg bd), vitamin E (400 IU daily) or placebo for 8 weeks. Mean serum cholesterol before antioxidant treatment was 7·00 mmol l‐1. Resistance of LDL to oxidation by copper was increased by 830% in the probucol group and by 30% in the vitamin E group. However, thiobarbituric acid reacting substances in whole serum were not altered by either antioxidant. Probucol lowered HDL‐and LDL‐cholesterol levels and increased the QT interval. Forearm vascular responses, as measured by venous occlusion plethysmography, to acetylcholine, glyceryl trinitrate and NG‐monomethyl‐L‐arginine, were not significantly changed by antioxidant treatment. Probucol has a major, and vitamin E a minor, effect on LDL resistance to oxidation but neither compound appears to alter forearm vascular responses in vivo.

Increased cerebral output of free radicals during hypoxia: implications for acute mountain sickness?

This study examined whether hypoxia causes free radical-mediated disruption of the blood-brain barrier (BBB) and impaired cerebral oxidative metabolism and whether this has any bearing on neurological symptoms ascribed to acute mountain sickness (AMS). Ten men provided internal jugular vein and radial artery blood samples during normoxia and 9-h passive exposure to hypoxia (12.9% O(2)). Cerebral blood flow was determined by the Kety-Schmidt technique with net exchange calculated by the Fick principle. AMS and headache were determined with clinically validated questionnaires. Electron paramagnetic resonance spectroscopy and ozone-based chemiluminescence were employed for direct detection of spin-trapped free radicals and nitric oxide metabolites. Neuron-specific enolase (NSE), S100beta, and 3-nitrotyrosine (3-NT) were determined by ELISA. Hypoxia increased the arterio-jugular venous concentration difference (a-v(D)) and net cerebral output of lipid-derived alkoxyl-alkyl free radicals and lipid hydroperoxides (P < 0.05 vs. normoxia) that correlated with the increase in AMS/headache scores (r = -0.50 to -0.90, P < 0.05). This was associated with a reduction in a-v(D) and hence net cerebral uptake of plasma nitrite and increased cerebral output of 3-NT (P < 0.05 vs. normoxia) that also correlated against AMS/headache scores (r = 0.74-0.87, P < 0.05). In contrast, hypoxia did not alter the cerebral exchange of S100beta and both global cerebral oxidative metabolism (cerebral metabolic rate of oxygen) and neuronal integrity (NSE) were preserved (P > 0.05 vs. normoxia). These findings indicate that hypoxia stimulates cerebral oxidative-nitrative stress, which has broader implications for other clinical models of human disease characterized by hypoxemia. This may prove a risk factor for AMS by a mechanism that appears independent of impaired BBB function and cerebral oxidative metabolism.