Showing papers by "Joseph Loscalzo published in 1988"

Tissue plasminogen activator.

Abstract: TISSUE plasminogen activator (t-PA) is a naturally occurring protein that catalyzes the conversion of the inactive proenzyme plasminogen into the active serine protease plasmin. It is one of two ma...

Frequency of hypercholesterolemia after cardiac transplantation

Abstract: Cardiac transplant patients are prone to accelerated coronary atherosclerosis. The mechanism by which this process occurs is not yet known, although immunologically mediated arterial injury is thought to play a primary role in its pathogenesis. Despite immunosuppressive potency, patients treated with cyclosporin A remain at significant risk for the development of accelerated atherosclerosis. It is hypothesized that cyclosporin A's hepatotoxic effects might contribute to the atherosclerotic process by impairing low density lipoprotein hepatic clearance in transplant patients, which would be reflected in a more atherogenic lipoprotein profile. To test this hypothesis, serum cholesterol levels were analyzed after transplantation. Significant and progressive increases in total cholesterol and in the total-to-high density lipoprotein cholesterol ratio were found. This atherogenic lipoprotein profile may contribute to accelerated atherosclerosis in cardiac transplant patients treated with cyclosporin A.

Role of platelets in cholesteryl ester formation by U-937 cells.

Abstract: The conversion of tissue macrophages into cholesteryl ester-rich foam cells is a crucial early event in atherogenesis. We studied the platelet as a potential source of cholesterol for esterification by macrophages because (a) platelets are rich in free cholesterol, (b) they adhere to macrophages early in atherogenesis, and (c) vascular injury can induce foam cell formation in the absence of hyperlipoproteinemia. We found that washed, activated human platelets from normocholesterolemic donors stimulated cholesteryl ester formation by the human monocyte-derived cell, U-937. Platelet cholesterol, released from platelets activated with calf skin collagen, was approximately equipotent at donating cholesterol to U-937 cells for esterification as normal human low density lipoprotein cholesterol. The stimulation of cholesteryl ester formation by activated human platelets demonstrated both concentration and time dependence. When hypercholesterolemic donors were studied, it was found that increasing plasma levels of cholesterol correlated directly with the ability of these hypercholesterolemic platelets to support cholesteryl ester synthesis by U-937 cells. Cholesterol-donating activity was also found in a 1,000-g supernatants of activated platelets. These observations point to a new and potentially important role for platelets in atherogenesis and suggest a mechanism for foam cell formation in the absence of marked hypercholesterolemia.

Structural and kinetic comparison of recombinant human single- and two-chain tissue plasminogen activator.

Abstract: We examined the similarities and differences in conformation between recombinant human single-chain tissue plasminogen activator (sct-PA) and two-chain tissue plasminogen activator (tct-PA), and compared these structural data with measurement of enzymatic activity. The intrinsic protein fluorescence of native tct-PA was 54% that of sct-PA. Differences in steady state protein fluorescence were also noted with denaturation of these plasminogen activators, as well as in the quenching of intrinsic fluorescence of the reduced, alkylated species by iodide. Using the chromogenic substrate H-D-isoleucyl-L-prolyl-L-arginine-p-nitroanilide (S-2288), the catalytic efficiency of sct-PA was found to be 26% that of tct-PA, and this was primarily a reflection of the difference in Km. On addition of soluble fibrin monomer prepared with the tetrapeptide glycyl-L-prolyl-L-arginyl-L-proline (GPRP), the catalytic efficiency of both species increased by 13-fold for sct-PA and by 3.5-fold for tct-PA to approximately the same value. Using the fluorophore eosin iodoacetamide covalently coupled to the single free cysteine in the molecule, Cys 83, the microenvironment of the fibrin-binding site located near this residue was studied. On addition of soluble fibrin monomer to eosin-labeled tct-PA, no effect on eosin fluorescence was noted. Eosin-labeled tct-PA had 16% less eosin fluorescence than did sct-PA and on addition of soluble fibrin monomer to eosin-labeled sct-PA, a decrease in eosin fluorescence, approaching that of eosin coupled to tct-PA, was observed. Together, these structural and kinetic data suggest that sct-PA undergoes a conformational change on binding to fibrin monomer that leads to dramatic differences in catalytic efficiency of the single-chain species. In so doing, sct-PA bound to fibrin assumes the kinetic profile of tct-PA bound to fibrin.

Reduced thiols and the effect of intravenous nitroglycerin on platelet aggregation

Abstract: Nitroglycerin inhibits platelet aggregation in vitro and this effect may be important in its overall mechanism of action. In addition, its use has been associated with prolonged bleeding times and hemorrhagic complications. Despite these experimental and clinical observations, no significant antiplatelet effect of nitroglycerin has been observed ex vivo during intravenous nitroglycerin administration to patients. Because the in vitro antiplatelet effects of nitroglycerin have been shown by one of the investigators participating in this study to depend on the presence of sufficient stores of reduced intracellular thiol—which are readily depleted ex vivo by nitroglycerin in the formation of S-nitrosothiols—an attempt was made to unmask nitroglycerin-mediated inhibition of platelet aggregation by exposing platelets taken from patients treated with nitroglycerin to the reduced thiol N-acetylcysteine ex vivo. The obtained data demonstrate that platelets taken from patients treated with intravenous nitroglycerin manifest attenuated aggregation responses ex vivo when thiol stores are repleted. It is therefore proposed that the mechanism of action of nitroglycerin is mediated in part by its antiplatelet effect and that this effect depends on the adequacy of reduced intracellular thiol stores.

S-nitrosocaptopril compounds and the use thereof

Abstract: The invention relates to novel nitroso compounds having the formula: ##STR1## wherein, R is hydroxy, NH 2 , NHR 4 , NR 4 R 5 or C 1 -C 7 alkoxy, wherein R 4 and R 5 are C 1 -C 4 alkyl, aryl, or C 1 -C 4 alkyl substituted by aryl; R 1 is hydrogen, C 1 -C 7 alkyl or C 1 -C 7 alkyl substituted by phenyl, amino, guanidino, NHR 6 or NR 6 R 7 , wherein R 6 and R 7 are methyl, or C 1 -C 4 acyl; R 3 is hydrogen, C 1 -C 7 alkyl or C 1 -C 7 alkyl substituted by phenyl; n is 0 to 2; A is hydrogen, lower C 1 -C 7 alkyl, lower C 2 -C 7 alkylene, lower C 2 -C 7 alkylene substituted by hydroxy, C 1 -C 4 alkyl, aryl, or a C 4 -C 7 ring which may be fused to a benzene ring; B is hyrogen, lower C 1 -C 7 alkyl, phenyl, lower C 1 -C 7 substituted by phenyl, hydroxy, guanidino, amino, imidazoyl, indolyl, mercapto, mercapto substituted by lower C 1 -C 4 alkyl, carbamoyl, or carboxyl, or lower C 2 -C 7 alkylene The invention also relates to compounds having the following formula: ##STR2## wherein R, R 1 , R 3 and n are as defined above; R 2 is hydrogen, hydroxy, C 1 -C 4 alkoxy, aryloxy or C 1 -C 7 alkyl; and m is 1 to 3 The invention also relates to pharmaceutical compositions comprising the nitrosothiol compounds of the invention together with a pharmaceutically acceptable carrier The invention also relates to methods for treating acute myocardial infarction, left ventricular dysfunction without overt heat failure, hypertension, pulmonary hypertension, congestive heart failure, angina pectoris, vascular thrombosis, Raynauds syndrome, Scleroderma, toxemia of pregnancy, acute renal failure, diabetic nephropathy, and renal artery stenosis, and to methods of inhibiting ACE and effecting vasodilation comprising administering the nitrosothiol compounds of the invention to an animal

Tissue plasminogen activator and acute pulmonary embolism.

Abstract: We assessed the efficacy and safety of peripheral intravenous recombinant human tissue-type plasminogen activator (rt-PA) in 47 patients with angiographically documented pulmonary embolism (PE). We administered 50 mg/2 h and, if necessary, an additional 40 mg/4 h. By 6 hours, 94% of the patients had angiographic evidence of clot lysis that was slight in 5, moderate in 12, and marked in 27 patients. Among the 34 patients with pulmonary hypertension prior to treatment, average pulmonary artery pressure decreased from 43/17 (27) to 31/13 (19) mm Hg (P < 0.0001). The average lung scan perfusion defect decreased from 37% before therapy to 16% (P < 0.01) after therapy among the 19 patients who had pre- and post-treatment lung scans. Of 7 patients with pre- and post-treatment imaging and Doppler echocardiograms, hypokinetic right ventricular wall movement (mild in 1, moderate in 2, and severe in 4) normalized in 5 and improved to mild hypokinesis in 2. Right ventricular diameter decreased from 3.9 ± 1.0 to 2.0 ± 0.5 cm (P < 0.005). Fibrinogen decreased 33% from baseline at 2 h and 42% from baseline at 6 h. However, patients with the greatest degree of angiographic clot lysis at 2 h had a preponderance of fibrinogenolysis over fibrinolysis, demonstrated by a lower ratio of cross-linked fibrin degradation products to fibrin(ogen) degradation products (0.14 ± 0.09 vs. 0.54 ± 0.82) (P < 0.04). Among selected patients, peripheral intravenous rt-PA is associated with rapid lysis of PE, improved pulmonary perfusion, and improved right ventricular function.