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Biomedical subjects

M Shechter

Publications and source records attributed to M Shechter.

At least 19 recordsLinked to original sources
PubMed2006

Oral magnesium therapy, exercise heart rate, exercise tolerance, and myocardial function in coronary artery disease patients.

BACKGROUND: Previous studies have demonstrated that in patients with coronary artery disease (CAD) upward deflection of the heart rate (HR) performance curve can be observed and that this upward deflection and the degree of the deflection are correlated with a diminished stress dependent left ventricular function. Magnesium supplementation improves endothelial function, exercise tolerance, and exercise induced chest pain in patients with CAD. PURPOSE: We studied the effects of oral magnesium therapy on exercise dependent HR as related to exercise tolerance and resting myocardial function in patients with CAD. METHODS: In a double blind controlled trial, 53 male patients with stable CAD were randomised to either oral magnesium 15 mmol twice daily (n = 28, age 61+/-9 years, height 171+/-7 cm, body weight 79+/-10 kg, previous myocardial infarction, n = 7) or placebo (n = 25, age 58+/-10 years, height 172+/-6 cm, body weight 79+/-10 kg, previous myocardial infarction, n = 6) for 6 months. Maximal oxygen uptake (VO2max), the degree and direction of the deflection of the HR performance curve described as factor k<0 (upward deflection), and the left ventricular ejection fraction (LVEF) were the outcomes measured. RESULTS: Magnesium therapy for 6 months significantly increased intracellular magnesium levels (32.7+/-2.5 v 35.6+/-2.1 mEq/l, p<0.001) compared to placebo (33.1+/-3.1.9 v 33.8+/-2.0 mEq/l, NS), VO2max (28.3+/-6.2 v 30.6+/-7.1 ml/kg/min, p<0.001; 29.3+/-5.4 v 29.6+/-5.2 ml/kg/min, NS), factor k (-0.298+/-0.242 v -0.208+/-0.260, p<0.05; -0.269+/-0.336 v -0.272+/-0.335, NS), and LVEF (58+/-11 v 67+/-10%, p<0.001; 55+/-11 v 54+/-12%, NS). CONCLUSION: The present study supports the intake of oral magnesium and its favourable effects on exercise tolerance and left ventricular function during rest and exercise in stable CAD patients.

Administration, Oral↗
PubMed2003

Platelet-induced expression of tissue factor procoagulant activity in freshly isolated human mononuclear cells: implications for experimental use.

Monocytes express tissue factor (TF) as a result of cytokine stimulation or endothelial adherence. We evaluated monocyte-platelet interaction in vitro as another trigger for monocyte TF enhancement in human mononuclear cells isolated by density gradient centrifugation from peripheral blood. Cell TF procoagulant activity (TF-PCA) was quantitated by a one-stage recalcification clotting time assay. Platelets were counted and identified by whole blood flow cytometry as CD61 positive particles, activated platelets were characterized by P-Selectin (CD62) expression, and monocytes by surface CD14 expression. A significant correlation between normalized TF-PCA of isolated mononuclear cells and platelet count was shown (r = 0.43, P < 0.001). Percentage of activated platelets in baseline samples was 4.2 +/- 3.5 while adenosine diphosphate (ADP) increased platelet positivity to 34 +/- 17% (P < 0.001). After isolation, 52 +/- 12% of platelets within suspensions were activated (P < 0.0001). Percentage of CD62-positive monocytes (CD14+ particles) increased from baseline 5% to 13 +/- 6% in ADP-stimulated samples to 53 +/- 17% after isolation (P < 0.001). These findings suggest that density gradient centrifugation activates platelets and that an adhesive interaction between monocytes and platelets may promote TF-PCA expression in isolated mononuclear suspensions. Enhanced monocyte TF expression as a result of an activated platelet-monocyte interaction seems to be an important laboratory effect requiring consideration when utilizing this technique in an experimental setup.

Blood Platelets↗
PubMed2001

Solid waste treatment as a high-priority and low-cost alternative for greenhouse gas mitigation.

The increased concern about environmental problems caused by inadequate waste management, as well as the concern about global warming, promotes actions toward a sustainable management of the organic fraction of the waste. Landfills, the most common means to dispose of municipal solid waste (MSW), lead to the conversion of the organic waste to biogas, containing about 50% methane, a very active greenhouse gas (GHG). One unit of methane has a global warming potential of 21 computed for a 100-year horizon or 56 computed for 20 years. The waste sector in Israel contributes 13% of total greenhouse gases (GHG) emissions for a time horizon of 100 years (for a time horizon of 20 years, the waste sector contribution equals to more than 25% of total GHG emissions). The ultimate goal is to minimize the amount of methane (CH4) by converting it to CO2. This can be achieved by physicochemical means (e.g., landfill gas flare, incineration) or by biological processes (e.g., composting, anaerobic digestion). Since the waste in Israel has a high organic material content, it was found that the most cost-effective means to treat the degradable organic components is by aerobic composting (investment of less than US$ 10 to reduce emission of one ton CO2 equivalent per year). Another benefit of this technology is the ability to implement it within a short period. The suggested approach, which should be implemented especially in developing countries, could reduce a significant amount of GHG at relatively low cost and short time. The development of a national policy for proper waste treatment can be a significant means to abate GHG emissions in the short term, enabling a gain in time to develop other means for the long run. In addition, the use of CO2 quotas will credit the waste sector and will promote profitable proper waste management.

Biodegradation, Environmental↗
PubMed2001

Intravenous magnesium in experimental stent thrombosis in swine.

We investigated the effects of magnesium on acute platelet-dependent stent thrombosis in an ex vivo porcine arteriovenous shunt model of high-shear blood flow. Control nitinol stents were expanded to 2 mm in diameter in a tubular perfusion chamber interposed in the shunt and exposed to flowing arterial blood at a shear rate of 2100 s(-1) for 20 minutes (n=156 perfusion runs in 10 swine). Animals were treated with intravenous heparin or MgSO(4) alone (2 g bolus over 20 minutes, followed by 2 g/h infusion) and combined heparin plus MgSO(4) in random fashion. Effects on thrombus weight (TW), platelet aggregation, bleeding time, activated clotting time, mean arterial blood pressure, and heart rate were quantified. Data points in the magnesium-treated animals were examined within 20 minutes after bolus (Mg-early) and >40 minutes after bolus (Mg-late). Stent TW (20+/-3 mg, pretreatment) was reduced by 42+/-21%, 47+/-19%, 48+/-16%, 67+/-12%, and 86+/-8% in the groups treated with Mg-early alone, Mg-late alone, heparin alone, heparin+Mg-early, and heparin+Mg-late, respectively (all P<0.001 versus pretreatment, P<0.001 for heparin+Mg-early and Mg-late versus heparin or magnesium alone, and P<0.05 for heparin+Mg-late versus heparin+Mg-early, ANOVA). Magnesium had no significant effect on platelet aggregation, activated clotting time, or bleeding time. There were no significant effects on heart rate or mean arterial blood pressure. The serum magnesium level was inversely correlated with TW (r=-0.70, P=0.002). In conclusion, treatment with intravenous MgSO(4) produced a time-dependent inhibition of acute stent thrombosis under high-shear flow conditions without any hemostatic or significant hemodynamic complications. Thus, magnesium may be an effective agent for preventing stent thrombosis.

Animals↗
PubMed2000

Improvement in endothelium-dependent brachial artery flow-mediated vasodilation with low-density lipoprotein cholesterol levels <100 mg/dl.

To determine whether the current National Cholesterol Education Program cholesterol recommendations are consistent with beneficial endothelium-dependent vasodilation, we prospectively assessed endothelium-dependent brachial artery vasoreactivity in 50 patients with stable coronary artery disease. Our results showed that endothelial-dependent vasoreactivity was greater when low-density lipoprotein cholesterol was <100 mg/dl, suggesting that it may be beneficial to reach the National Cholesterol Education Program Adult Treatment Panel II target of low-density lipoprotein cholesterol of <100 mg/dl.

Adult↗
PubMed2000

Oral magnesium therapy improves endothelial function in patients with coronary artery disease.

BACKGROUND: Magnesium blocks many of the physiological actions of calcium. Nevertheless, the impact of magnesium supplementation on endothelial function and exercise tolerance in stable coronary artery disease (CAD) patients has not been assessed. METHODS AND RESULTS: In a randomized, double-blind, placebo-controlled trial, 50 stable CAD patients (41 men and 9 women, mean+/-SD age 67+/-11 years, age range 42 to 82 years) were randomized to receive either magnesium (n=25) (30 mmol/d Magnosolv-Granulat; Asta Medica Company, Inc) or placebo (n=25) for 6 months. Before and after 6 months, endothelium-dependent brachial artery flow-mediated vasodilation (FMD) and endothelium-independent NTG-mediated vasodilation were assessed with high-resolution (10-MHz) ultrasound. Exercise stress testing was performed with use of the Bruce protocol. Intracellular magnesium concentrations ([Mg(2+)](i)) were assessed from sublingual cells through x-ray dispersion (EXA) (normal mean+/-SD values 37. 9+/-4.0 mEq/L). The magnesium therapy significantly increased postintervention ([Mg(2+)](i) versus placebo (36.2+/-5.0 versus 32.7+/-2.7 mEq/L, P<0.02). There was a significant correlation in the total population between baseline [Mg(2+)](i) and baseline FMD (r=0. 48, P<0.01). The magnesium intervention resulted in a significant improvement in postintervention FMD (15.5+/-12.0%, P=0.02 compared with baseline), which was not evident with placebo (4.4+/-2.5%, P=0.78 compared with baseline). There was better exercise tolerance (9.3+/-2.0 versus 7.3+/-3.1 minutes, P=0.05) and less ischemic ST-segment changes (4 versus 10 patients, P=0.05) in the magnesium versus placebo groups, respectively. CONCLUSIONS: Oral magnesium therapy in CAD patients is associated with significant improvement in brachial artery endothelial function and exercise tolerance, suggesting a potential mechanism by which magnesium could beneficially alter outcomes in CAD patients.

Administration, Oral↗
PubMed2000

Blood glucose and platelet-dependent thrombosis in patients with coronary artery disease.

OBJECTIVES: To investigate the influence of blood glucose on platelet-dependent thrombosis (PDT). BACKGROUND: Elevated blood glucose is a predictor of adverse cardiovascular risk independent of a diagnosis of diabetes, possibly due to adverse effects promoting thrombosis. The effects of blood glucose on PDT have not been characterized. METHODS: An ex vivo extracorporeal perfusion protocol was used to measure PDT in 42 patients with stable coronary artery disease (CAD). The Badimon chamber was perfused with unanticoagulated venous blood and PDT evaluated using computerized morphometry. Whole blood impedance aggregometry and flow cytometry evaluated platelet aggregation and P-selectin expression, respectively. RESULTS: Using a multivariate stepwise regression model, blood glucose was the best independent predictor of PDT (R2 = 0.19, p < 0.008), followed by apolipoprotein B (R2 = 0.18, p = 0.002) and intracellular magnesium levels (R2 = 0.12, p = 0.02). Platelet-dependent thrombosis was significantly greater in patients with blood glucose >, compared with <, the median value of 4.9 mmol/l (159 +/- 141 vs. 67 +/- 69 microm2/mm, p < 0.01). Neither platelet aggregation nor P-selectin expression was significantly different between the two groups. Insulin levels correlated with blood glucose (r = 0.56, p = 0.0003), but were not independently associated with either PDT, platelet aggregation or P-selectin expression. A two-way analysis of variance demonstrated an interaction between insulin (>126 pmol/l) and blood glucose (>4.9 mmol/l) in modulating PDT (F [1,38] = 8.5, p < 0.006). CONCLUSIONS: Blood glucose is an independent predictor of PDT in stable CAD patients. The relationship is evident even in the range of blood glucose levels considered normal, indicating that the risk associated with blood glucose may be continuous and graded. These findings suggest that the increased CAD risk associated with elevated blood glucose may be, in part, related to enhanced platelet-mediated thrombogenesis.

Aged↗
PubMed2000

Low intracellular magnesium levels promote platelet-dependent thrombosis in patients with coronary artery disease.

BACKGROUND: Although reduced intracellular levels of magnesium have been described in patients with acute myocardial infarction, its significance as a regulator of thrombosis remains unknown. METHODS AND RESULTS: To determine whether reduced intracellular levels of magnesium enhance platelet-dependent thrombosis, we evaluated 42 patients with coronary artery disease (CAD) by exposing porcine aortic media to their flowing unanticoagulated venous blood for 5 minutes by using an ex vivo perfusion (Badimon) chamber. Baseline analysis demonstrated significant associations between intracellular levels of magnesium, platelet-dependent thrombosis (P =.02), and platelet P-selectin (CD62P) expression (P <.05). Patients were divided into 2 groups: below (n = 22) and above (n = 20) the median intracellular levels of magnesium (1.12 microg/mg protein). There were no significant differences in age, body mass index, serum lipids, fibrinogen, platelet count, or serum magnesium levels between the two groups. Platelet-dependent thrombosis was significantly higher in patients with intracellular levels of magnesium below compared with above median (150 +/- 128 vs 45 +/- 28 microm(2)/mm, P <.004). Neither platelet aggregation nor CD62P expression was significantly different between the two groups. CONCLUSIONS: Platelet-dependent thrombosis was significantly increased in patients with stable CAD with low intracellular levels of magnesium, suggesting a potential role for magnesium supplementation in CAD.

Aged↗
PubMed2000

The role of magnesium as antithrombotic therapy.

Meta-analysis of previous relatively small clinical trials, comparing intravenous magnesium with placebo in acute myocardial infarction (AMI) patients, mainly without thrombolytic therapy, demonstrated that magnesium reduced in-hospital mortality by 19%, mainly by reducing the incidence of serious arrhythmias and left ventricular heart failure by one quarter. These findings have led us to hypothesize that magnesium treatment inhibits platelet-dependent thrombosis in patients with coronary artery disease (CAD). In a prospective, double blind, and crossover study, we have recently demonstrated that oral magnesium treatment inhibits thrombus formation measured by platelet-dependent thrombosis in stable CAD patients by 35%. This effect appears to be independent of platelet aggregation and activation, and is additive to that of aspirin. High dose of intravenous magnesium can inhibit thrombus formation and is associated with suppression of platelet aggregation. Magnesium treatment can dose-dependently inhibit a wide variety of agonists of platelet aggregation, such as thromboxane A2 and stimulate prostacyclin synthesis. The molecular basis for these effects is likely modulated via reduction of intracellular calcium mobilization. Hypomagnesemia also selectively impaired the release of nitric oxide from the coronary endothelium. We have recently demonstrated that oral magnesium treatment can improve endothelium-dependent vasodilation in CAD patients with optimal lipid values. Because nitric oxide is a potent endogenous vasodilator and inhibitor of platelet aggregation and adhesion, hypomagnesemia could promote vasoconstriction and coronary thrombosis in hypomagnesemic states. These findings suggest a potential mechanism whereby magnesium may beneficially alter outcomes in CAD patients.

Clinical Trials as Topic↗
PubMed2000

Beneficial antithrombotic effects of the association of pharmacological oral magnesium therapy with aspirin in coronary heart disease patients.

The use of magnesium in the treatment of acute myocardial infarction remains controversial despite preliminary experimental evidence that magnesium plays a beneficial role as a regulator of thrombosis. The aim of our study was to determine whether oral magnesium treatment inhibits platelet-dependent thrombosis (PDT) in stable patients with coronary artery disease (CAD). In a randomized prospective, double-blind, cross-over and placebo controlled study, 42 patients with stable CAD (37 men, 5 women, mean age 68 +/- 9 years) on aspirin received either magnesium oxide tablets (800-1,200 mg/day) or placebo for 3 months (Phase 1) followed by a 4-week washout period, and the cross-over treatment for 3 months (Phase 2). PDT, platelet aggregation, platelet P-selectin flow-cytometry, monocyte tissue factor procoagulant activity (TF-PCA) and adhesion molecules density were assessed before and after each phase. PDT was evaluated by an ex-vivo perfusion model using the Badimon chamber. Median PDT was significantly reduced by 35 percent in patients who received magnesium versus placebo (D change from baseline: -24 vs. 26 microm2/mm; p = 0.02, respectively). There was no significant effect of magnesium treatment on platelet aggregation, P-selectin expression, monocyte TF-PCA or adhesion molecules. Oral magnesium treatment inhibits PDT in patients with stable CAD. This effect appears to be independent of platelet aggregation or P-selectin expression, and is evident despite aspirin therapy. These findings suggest a potential mechanism whereby magnesium may beneficially alter outcomes in patients with CAD.

Administration, Oral↗
PubMed1999

Oral magnesium supplementation inhibits platelet-dependent thrombosis in patients with coronary artery disease.

The use of magnesium in the treatment of acute myocardial infarction remains controversial despite preliminary experimental evidence that magnesium plays a beneficial role as a regulator of thrombosis. This study examines whether oral magnesium treatment inhibits platelet-dependent thrombosis (PDT) in patients with coronary artery disease (CAD). In a randomized prospective, double-blind, crossover, and placebo-controlled study, 42 patients with CAD (37 men, 5 women, mean age 68 +/- 9 years) on aspirin received either magnesium oxide tablets (800 to 1,200 mg/day) or placebo for 3 months (phase 1) followed by a 4-week wash-out period, and the crossover treatment for 3 months (phase 2). PDT, platelet aggregation, platelet P-selectin flow cytometry, monocyte tissue factor procoagulant activity (TF-PCA), and adhesion molecule density were assessed before and after each phase. PDT was evaluated by an ex vivo perfusion model using the Badimon chamber. Median PDT was significantly reduced by 35% in patients who received magnesium versus placebo (delta change from baseline -24 vs 26 mm2/mm; p = 0.02, respectively). There was no significant effect of magnesium treatment on platelet aggregation, P-selectin expression, monocyte TF-PCA, or adhesion molecules. Oral magnesium treatment inhibited PDT in patients with stable CAD. This effect appears to be independent of platelet aggregation or P-selectin expression, and is evident despite aspirin therapy. These findings suggest a potential mechanism whereby magnesium may beneficially alter outcomes in patients with CAD.

Aged↗
PubMed1999

Plasma apolipoprotein B levels predict platelet-dependent thrombosis in patients with coronary artery disease.

Elevated plasma apolipoprotein B is a known risk factor for atherosclerotic coronary artery disease (CAD), however its relationship to arterial thrombosis is unexplored. We prospectively assessed apolipoprotein B and platelet-dependent thrombosis (PDT) in 42 CAD patients (37 men, 5 women, mean age 68 +/- 9 years), by exposing porcine aortic media to their flowing unanticoagulated venous blood for 5 min using an ex vivo perfusion (Badimon) chamber. PDT was significantly correlated with apolipoprotein B (r = 0.41, p = 0.009), intracellular magnesium levels (r = -0.46, p = 0.003) fasting blood glucose (r = 0.47, p = 0.002), and total cholesterol (r = 0.43, p = 0.006). PDT did not correlate with serum total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, apolipoprotein A-I or fibrinogen levels. These findings suggest that the positive relationship of elevated apolipoprotein B to CAD may be, in part, related to its prothrombotic effects.

Aged↗
PubMed1998

Peripheral monocytosis following acute myocardial infarction: incidence and its possible role as a bedside marker of the extent of cardiac injury.

Infiltration by mononuclear cells, mostly monocytes, into necrotic myocardial tissue can be detected beyond the 3rd day after the onset of infarction. These monocytes, mobilized by an unknown mechanism, initiate phagocytosis of necrotic tissue. We observed in patients having sustained an acute myocardial infarction (AMI) a significant increase in monocyte count 2-3 days following presentation, possibly representing peripheral recruitment of monocytes to the injured myocardium. To establish this observation, we prospectively documented monocyte and neutrophil counts throughout hospitalization in 186 consecutive patients (118 patients having sustained an AMI, 34 patients with angina, and 34 patients admitted for nonischemic reasons). Average monocyte count, which rose on the 2nd day and reached a peak on day 3, was significantly elevated in these patients compared with control subjects (p < 0.001). Neutrophil count exhibited a similar phase-shifted response. Peak monocyte count exceeded 800/mm3 (upper limit of normal range) in 69 (58%) of AMI patients but in only 3 of the 68 (4%) non-AMI patients, yielding a sensitivity and specificity of 58 and 95%, respectively, for the diagnosis of AMI by this criterion. A significant correlation between maximal creatine kinase (CK) representing the extent of myocardial necrosis and peak monocyte count was shown (r = 0.51, p < 0.0001). A correlation between CK and monocyte count sum of days 1-3 (r = 0.51, p < 0.001) was found in a substudy of 25 patients with AMI. Similarly, a correlation was shown with cardiac function score as evaluated by 2-dimensional echocardiography (p < 0.001 and p < 0. 008 for difference between CK sum and monocyte count sum of high and low echo score groups, respectively). Hence, the peak monocyte count recorded during the immediate postinfarction period provides a bedside marker of the extent of myocardial damage that is the preponderant prognostic determinant. If validated in future studies this phenomenon may have diagnostic and prognostic implications.

Adult↗
PubMed1998

Intracellular magnesium predicts functional capacity in patients with coronary artery disease.

To determine whether increased intracellular levels of magnesium ([Mg]i) are associated with enhanced functional capacity, we performed symptom-limited exercise treadmill testing on 42 stable coronary artery disease (CAD) patients (37 men, 5 women, mean age 68 +/- 9 years). [Mg]i was found to be an independent and significant predictor of exercise duration (R = 0.31, p = 0.02) in a multivariate stepwise regression model. Patients with > normal [Mg]i of 1.23 microg/mg protein (n = 13) had a significantly greater mean functional capacity, measured in higher achieved metabolic equivalents (10.6 +/- 2.5 vs. 8.9 +/- 2.3, p < 0.05) and exercise duration (9.4 +/- 2.3 vs. 7.9 +/- 2.2 min, p < 0.05) compared to patients with [Mg]i </= the normal (n = 29). Thus, functional capacity is greater in stable CAD patients with higher [Mg]i, suggesting that magnesium may play a role in CAD pathophysiology, possibly via ventricular unloading.

Adult↗
PubMed1997

Acute myocardial infarction without thrombolytic therapy: beneficial effects of magnesium sulfate.

Only one third of hospitalized patients with acute myocardial infarction (AMI) receive thrombolytic therapy despite its proven benefits on outcomes. Elderly patients, have a greater risk of death during myocardial infarction; however, thrombolytic therapy appears to be less used in these patients, as compared to the general AMI-patients. In order to evaluate the impact of magnesium supplementation in AMI-patients without thrombolytic therapy, 194 patients participated in a prospective, randomized and placebo-controlled study: 96 patients received a 48-hour intravenous magnesium sulfate and 98 isotonic glucose as placebo. Magnesium infusion reduced the incidence of arrhythmias, congestive heart failure and in-hospital-mortality compared with placebo (27 vs. 40%, p = 0.04; 18 vs. 23%, p = 0.27; 4 vs. 17%, p < 0.01, respectively); in the subgroup of elderly patients (> 70 years), the benefit was also obvious (42 vs. 50%; 18 vs. 25%; 9 vs. 23%, p = 0.09, respectively). These data suggest that intravenous magnesium supplementation might be justified in order to reduce myocardial damage and mortality rate in subsets of high-risk patients such the elderly and/or patients not suitable for thrombolysis. Additional trials appear to be indicated to evaluate the potential benefit of magnesium in well defined specific subsets of AMT-patients.

Aged↗