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Biomedical subjects

J Loscalzo

Publications and source records attributed to J Loscalzo.

At least 19 recordsLinked to original sources
PubMed1992

Biochemistry of nitric oxide and its redox-activated forms.

Nitric oxide (NO.), a potentially toxic molecule, has been implicated in a wide range of biological functions. Details of its biochemistry, however, remain poorly understood. The broader chemistry of nitrogen monoxide (NO) involves a redox array of species with distinctive properties and reactivities: NO+ (nitrosonium), NO., and NO- (nitroxyl anion). The integration of this chemistry with current perspectives of NO biology illuminates many aspects of NO biochemistry, including the enzymatic mechanism of synthesis, the mode of transport and targeting in biological systems, the means by which its toxicity is mitigated, and the function-regulating interaction with target proteins.

Amino Acid Oxidoreductases↗
PubMed1992

A noninvasive method of predicting pulmonary-capillary wedge pressure.

BACKGROUND: The noninvasive prediction of pulmonary-capillary wedge pressure (PCWP) is important for the recognition and treatment of a variety of cardiovascular disorders. The response of the arterial pressure to the Valsalva maneuver has been shown to correlate with the PCWP. We therefore devised a noninvasive method to measure this pressure response at the bedside and correlated these measurements with the PCWP measured directly with a pulmonary-artery catheter. METHODS: Simultaneous, blinded, noninvasive measurements of the ratio of the final amplitude to the initial amplitude of the pulse wave form during the stress phase of the Valsalva maneuver (pulse-amplitude ratio) and direct measurements of the PCWP were obtained in 20 clinically stable patients and in 14 clinically unstable patients who were receiving vasoactive agents, 12 of whom also had endotracheal tubes in place. RESULTS: Using linear regression analysis, we found that the pulse-amplitude ratio strongly correlated with the measured PCWP over a range of base-line values from 4 to 32 mm Hg for the 20 clinically stable patients (R2 = 0.80) and the 14 clinically unstable patients (R2 = 0.85). The method also correctly predicted changes in the PCWP after the administration of nitroglycerin or furosemide and after expansion of the intravascular volume (R2 = 0.79). CONCLUSIONS: These preliminary data indicate that a simple noninvasive method can accurately predict the PCWP and changes in the PCWP in response to medical therapy.

Blood Pressure↗
PubMed1992

Effects on platelet aggregation and fibrinolytic activity during upright posture and exercise in healthy men.

The circadian variation of acute myocardial infarction suggests that daily activities such as assuming the upright posture and performing different daily activities may trigger the onset of coronary thrombosis. Such triggering may result from unfavorable alterations in the balance between the prothrombotic and antithrombotic properties of the blood. The present study compares the effects of 2 common daily activities, assuming the upright posture and exercise, on platelet aggregation and fibrinolytic activity. In healthy male subjects, assuming the upright posture in the morning significantly increased platelet aggregation and produced only a moderate increase in fibrinolytic activity within 10 minutes. These changes were still present after 90 minutes in the upright posture. Supine posture for 45 minutes resulted in levels of fibrinolytic activity and platelet aggregation comparable to that observed before initially assuming the upright posture in the morning. Return to the supine posture for 45 minutes resulted in levels of fibrinolytic activity and platelet aggregation comparable to that observed before the initial assumption of upright posture. The changes recurred when upright posture was taken later in the day. Exercise did not increase platelet aggregation to levels beyond that produced by the upright posture, but was associated with a marked increase in fibrinolytic activity. Thus, exercise and upright posture produce distinctive alterations in the thrombogenic potential of the blood that may influence the timing of clinical vascular events.

Adult↗
PubMed1992

Antiplatelet and antithrombotic effects of organic nitrates.

Organic nitrates are believed to provide relief from angina principally by dilating the coronary vasculature. Substantial evidence exists, however, to support a potent antiplatelet effect for these agents as well. Each of these compounds ultimately is metabolized to nitric oxide (or an S-nitrosothiol congener thereof), and this metabolite, in turn, is a potent activator of platelet guanylate cyclase. Activation of guanylate cyclase increases platelet cyclic guanosine monophosphate (cGMP), and is accompanied by inhibition of agonist-mediated calcium flux, and, in turn, reduction of fibrinogen binding to the glycoprotein IIb/IIIa receptor. Since fibrinogen binding is essential for platelet aggregation regardless of the agonist involved, its inhibition appears to be the critical mechanism by which platelet function is impaired by these agents. The recently recognized role that platelet-dependent thrombotic processes play in acute coronary syndromes suggests that the inhibition of platelets by nitrates may offer an additional mechanism by which these compounds improve perfusion to ischemic myocardium.

Animals↗
PubMed1992

S-nitrosylation of tissue-type plasminogen activator confers vasodilatory and antiplatelet properties on the enzyme.

Tissue-type plasminogen activator (t-PA) reacts upon exposure to endothelium-derived relaxing factor (EDRF) by way of the enzyme's single free sulfhydryl (Cys-83) to form a stable S-nitrosothiol protein adduct. S-nitrosylation endows t-PA with potent vasodilatory and antiplatelet properties that are accompanied by elevations in intracellular cyclic GMP analogous to those induced by low molecular weight (e.g., S-nitroso amino acid) S-nitrosothiols. Moreover, this chemical modification does not adversely affect the catalytic efficiency of t-PA, the fibrin stimulation of this activity, the binding of t-PA to fibrinogen, or the interaction of the enzyme with its physiologic serine protease inhibitor, plasminogen-activator inhibitor type I. The coupling of vasodilatory, antiplatelet, and fibrinolytic properties in one molecule makes the S-nitrosylated t-PA a unique molecular species and may provide insight into the mechanisms by which the endothelium maintains vessel patency. These data also suggest a pharmacologic approach to treatment of thromboocclusive disorders.

Animals↗
PubMed1992

Nitric oxide circulates in mammalian plasma primarily as an S-nitroso adduct of serum albumin.

We have recently shown that nitric oxide or authentic endothelium-derived relaxing factor generated in a biologic system reacts in the presence of specific protein thiols to form S-nitrosoprotein derivatives that have endothelium-derived relaxing factor-like properties. The single free cysteine of serum albumin, Cys-34, is particularly reactive toward nitrogen oxides (most likely nitrosonium ion) under physiologic conditions, primarily because of its anomalously low pK; given its abundance in plasma, where it accounts for approximately 0.5 mM thiol, we hypothesized that this plasma protein serves as a reservoir for nitric oxide produced by the endothelial cell. To test this hypothesis, we developed a methodology, which involves UV photolytic cleavage of the S--NO bond before reaction with ozone for chemiluminescence detection, with which to measure free nitric oxide, S-nitrosothiols, and S-nitrosoproteins in biologic systems. We found that human plasma contains approximately 7 microM S-nitrosothiols, of which 96% are S-nitrosoproteins, 82% of which is accounted for by S-nitroso-serum albumin. By contrast, plasma levels of free nitric oxide are only in the 3-nM range. In rabbits, plasma S-nitrosothiols are present at approximately 1 microM; 60 min after administration of NG-monomethyl-L-arginine at 50 mg/ml, a selective and potent inhibitor of nitric oxide synthetases, S-nitrosothiols decreased by approximately 40% (greater than 95% of which were accounted for by S-nitrosoproteins, and approximately 80% of which was S-nitroso-serum albumin); this decrease was accompanied by a concomitant increase in mean arterial blood pressure of 22%. These data suggest that naturally produced nitric oxide circulates in plasma primarily complexed in S-nitrosothiol species, principal among which is S-nitroso-serum albumin. This abundant, relatively long-lived adduct likely serves as a reservoir with which plasma levels of highly reactive, short-lived free nitric oxide can be regulated for the maintenance of vascular tone.

Animals↗
PubMed1992

Molecular approaches to antithrombotic therapy.

Several new approaches to direct and indirect inhibition of thrombin formation or activity promise to extend the benefits of pharmacologic antithrombotic interventions, both prophylactically and in acute therapy. Preliminary studies have found the new agents to be more specific and hemostatically safer than warfarin or heparin.

Amino Acid Chloromethyl Ketones↗
PubMed1992

Capillary zone electrophoretic detection of biological thiols and their S-nitrosated derivatives.

Reduced thiols (RSH) react with certain oxides of nitrogen to yield S-nitroso thiols (RSNO) possessing smooth muscle relaxant and platelet inhibitory properties. Nitrosated derivatives of the biological thiols--glutathione, cysteine, and homocysteine--have therefore been considered as bioactive intermediates in the metabolism of organic nitrates and the endothelium-derived relaxing factor with properties of nitric oxide. As yet, however, there is no established chemical method for identifying the biological S-nitroso thiols and, consequently, little is known of their distinguishing chemical characteristics or biochemistry. In this study, we demonstrate for the first time a simple, rapid, and reproducible method for separating these thiols from their S-nitrosated derivatives using capillary zone electrophoresis. Cysteine, homocysteine, and glutathione were separated from one another and from their corresponding disulfides in 0.01 M phosphate buffer, pH 2.5, by capillary zone electrophoresis and absorbance detection at 200 nm with measured elution times of 5.92-16.15 min; corresponding S-nitroso thiols were selectively detected at 320 nm and eluted at 2.50-18.20 min. These data support the specificity and reproducibility of this technique for separation and identification of thiols, disulfides, and S-nitroso thiol derivatives.

Bradykinin↗
PubMed1992

S-nitrosylation of proteins with nitric oxide: synthesis and characterization of biologically active compounds.

Endothelium-derived relaxing factor (EDRF) activity has been attributed to the highly labile nitric oxide radical (NO). In view of the fact that the plasma and cellular milieux contain reactive species that can rapidly inactivate NO, it has been postulated that NO is stabilized by a carrier molecule that preserves its biological activity. Reduced thiol species are candidates for this role, reacting readily in the presence of NO to yield biologically active S-nitrosothiols that are more stable than NO itself. Because sulfhydryl groups in proteins represent an abundant source of reduced thiol in biologic systems, we examined the reaction of several sulfhydryl-containing proteins of diverse nature and function upon exposure to authentic NO and EDRF. We demonstrate that S-nitroso proteins form readily under physiologic conditions and possess EDRF-like effects of vasodilation and platelet inhibition. These observations suggest that S-nitrosothiol groups in proteins may serve as intermediates in the cellular metabolism of NO and raise the possibility of an additional type of cellular regulatory mechanism.

Animals↗
PubMed1992

Endothelium-derived relaxing factor modulates the atherothrombogenic effects of homocysteine.

Hyperhomocysteinemia is a risk factor for atherosclerosis, and is found in the heterozygous form in approximately one-third of all individuals with coronary artery disease. The sulfhydryl group of homocysteine has been viewed as contributing to the atherogenic effects of this low-molecular-weight thiol, largely as a consequence of facilitating the generation of hydrogen peroxide from oxygen. Hydrogen peroxide, in turn, is presumed to induce dysfunction and damage to the endothelial cell, leading to attenuation of its antithrombotic and vasodilatory properties. As we have shown that endothelium-derived relaxing factor (EDRF) and other oxides of nitrogen can form adducts with thiols, we hypothesized that EDRF released from normal endothelium S-nitrosates homocysteine, rendering it nontoxic to the endothelium. We show that EDRF released from endothelial cells in the presence of homocysteine can lead to the formation of S-nitrosohomocysteine; that, like other S-nitrosothiols, S-nitrosohomocysteine induces vasorelaxation and platelet inhibition; and that, in contrast to homocysteine, S-nitrosohomocysteine does not support hydrogen peroxide generation and does not lead to endothelial dysfunction. These data suggest that normal endothelial cells modulate the adverse effects of homocysteine by facilitating the formation of the EDRF adduct, S-nitrosohomocysteine. The toxic effects of homocysteine may, then, result from an inability of the endothelium to sustain adequate production of EDRF in the face of elevated homocysteine concentration.

Acetylcholine↗
PubMed1992

Effect of thrombin inhibition on the dynamics of thrombolysis and on platelet function during thrombolytic therapy.

To evaluate the effect of thrombin on the dynamics of thrombolysis, we infused rabbits with heparin or hirudin alone or in conjunction with tissue-type plasminogen activator (t-PA) and monitored the kinetics of fibrinolysis and changes in ex vivo platelet aggregation responses over time. Both heparin and hirudin enhanced total fibrinolysis in an ex vivo arteriovenous shunt preparation: 82 +/- 2% and 79 +/- 2%, respectively, compared with 51 +/- 8% for t-PA alone (P less than 0.05) and 50 +/- 4% for t-PA plus aspirin (p less than 0.05). Heparin coadministered with t-PA significantly reduced the half-time for clot lysis compared with t-PA alone (p less than 0.05), whereas hirudin coadministered with t-PA significantly reduced the half-time for clot lysis compared with that for t-PA alone, t-PA plus aspirin, and t-PA plus heparin (5.5 +/- 0.6 versus 12.1 +/- 2.0 versus 12.6 +/- 2.2 versus 10.0 +/- 0.8 minutes, respectively; p less than 0.05). Both heparin and hirudin prevented the increase in ADP-induced platelet aggregation normally seen with t-PA alone (p less than 0.01 by t test; p less than 0.05 by two-way analysis of variance). These data demonstrate that selective, antithrombin III-independent thrombin inhibitors can enhance the efficacy of thrombolysis by modulating the dynamics of the process and preventing platelet activation associated with plasminogen activator therapy.

Animals↗
PubMed1992

The relation between atherosclerosis and thrombosis.

BACKGROUND: The relation between atherosclerosis and thrombosis has been recognized for over a century. Until very recently, however, this pathophysiological association has been largely based on observation with little information available to dissect molecular and cellular mechanism. METHODS AND RESULTS: The known associations between the principal determinants of thrombosis (platelets, fibrin and its proteolytic degradation products, and fibrinolytic enzymes) and atherosclerosis; the regulation of thrombotic determinants by cytokines and growth factors important in atherogenesis; and the modulation of thrombotic determinants by atherogenic lipoproteins, especially lipoprotein(a), are discussed. CONCLUSIONS: Within this conceptual framework, clear molecular and cellular mechanisms emerge, and a better basic understanding of the thrombotic determinants of atherogenesis can be developed.

Arteriosclerosis↗
PubMed1992

The relaxant properties in guinea pig airways of S-nitrosothiols.

Several cellular constituents of the lung have the capacity to synthesize a factor capable of relaxing smooth muscle which has the physicochemical properties of nitric oxide (NO). In other systems, it has been shown that NO may be stabilized in the plasma and cellular milieu by reduced thiol in the form of an S-nitrosothiol (RS-NO). These compounds have half-lives that are significantly greater than that of NO, and also retain the vasorelaxant activity of NO, which is mediated by activating guanylate cyclase and raising cyclic GMP levels. The effects of RS-NO and their potential mechanism of action on airways, however, have not been previously investigated. In this study, we have examined the smooth muscle relaxant properties of several biological and synthetic RS-NO on guinea pig trachea. Our data reveal that RS-NO are generally potent airway smooth muscle relaxants with at least a partial effect through stimulation of cyclic GMP. Relaxations were attenuated significantly by the guanylate cyclase inhibitor methylene blue (P less than .05), and RS-NO-induced increases in cyclic GMP were demonstrated (P less than .0005). The IC50 values for S-nitroso-glutathione, S-nitroso-cysteine, S-nitroso-homocysteine, S-nitroso-N-acetylcysteine, S-nitroso-penicillamine and S-nitroso-captopril were 0.99 +/- 0.09, 3.2 +/- 0.2, 2.1 +/- 0.3, 2.1 +/- 0.8, 1.8 +/- 0.8 and 20 +/- 0.7 microM (mean +/- S.E.M.), respectively. In this system isoproterenol has an IC50 of 0.016 microM and theophylline an IC50 of 74 microM, making the relaxant properties of these NO derivatives of potential pharmacological and physiological relevance.

Animals↗
PubMed1991

Clot-selective coronary thrombolysis with low-dose synergistic combinations of single-chain urokinase-type plasminogen activator and recombinant tissue-type plasminogen activator. The Pro-Urokinase for Myocardial Infarction Study Group.

The effect of simultaneous infusions of low-dose recombinant tissue-type plasminogen activator (t-PA) and single-chain urokinase-type plasminogen activator (scu-PA, pro-urokinase) on coronary arterial thrombolysis was investigated in 23 patients treated within 6 hours (mean 2.6 +/- 1.1, range 1.2 to 5.9) of symptoms of an acute myocardial infarction. Infarct artery patency at 90 minutes was achieved in 16 (70%, 95% confidence limits of 0.47 to 0.87) of 23 patients after a 1-hour intravenous infusion of 20 and 16.3 mg of t-PA and scu-PA, respectively. At 90 minutes, the fibrinogen concentration decreased from 369 +/- 207 to 316 +/- 192 mg/dl (p = not significant), while plasminogen decreased to 69 +/- 24% (p = 0.001) and alpha-2-antiplasmin to 77 +/- 24% (p = 0.001) of pretreatment values. Although no bleeding requiring termination of drug infusion or transfusion occurred, 1 patient with cerebrovascular amyloidosis had a fatal intracerebral hemorrhage. These findings suggest that combination therapy may allow substantial reductions in total thrombolytic doses while still achieving effective fibrin-specific coronary thrombolysis.

Adult↗