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Biomedical subjects

H D Lewis

Publications and source records attributed to H D Lewis.

At least 19 recordsLinked to original sources
PubMed2000

L-685,458, an aspartyl protease transition state mimic, is a potent inhibitor of amyloid beta-protein precursor gamma-secretase activity.

Progressive cerebral amyloid beta-protein (A beta) deposition is believed to play a central role in the pathogenesis of Alzheimer's disease (AD). Elevated levels of A beta(42) peptide formation have been linked to early-onset familial AD-causing gene mutations in the amyloid beta-protein precursor (A beta PP) and the presenilins. Sequential cleavage of A beta PP by the beta- and gamma-secretases generates the N- and C-termini of the A beta peptide, making both the beta- and gamma-secretase enzymes potential therapeutic targets for AD. The identity of the A beta PP gamma-secretase and the mechanism by which the C-termini of A beta are formed remain uncertain, although it has been suggested that the presenilins themselves are novel intramembrane-cleaving gamma-secretases of the aspartyl protease class [Wolfe, M. S., Xia, W., Ostaszewski, B. L., Diehl, T. S., Kimberly, W. T., and Selkoe, D. J. (1999) Nature 398, 513-517]. In this study we report the identification of L-685,458 as a structurally novel inhibitor of A beta PP gamma-secretase activity, with a similar potency for inhibition of A beta(42) and A beta(40) peptides. This compound contains an hydroxyethylene dipeptide isostere which suggests that it could function as a transition state analogue mimic of an aspartyl protease. The preferred stereochemistry of the hydroxyethylene dipeptide isostere was found to be the opposite to that required for inhibition of the HIV-1 aspartyl protease, a factor which may contribute to the observed specificity of this compound. Specific and potent inhibitors of A beta PP gamma-secretase activity such as L-685,458 will enable important advances toward the identification and elucidation of the mechanism of action of this enigmatic protease.

Amino Acid Sequence↗
PubMed1995

Amiodarone in patients with congestive heart failure and asymptomatic ventricular arrhythmia. Survival Trial of Antiarrhythmic Therapy in Congestive Heart Failure.

BACKGROUND: Asymptomatic ventricular arrhythmias in patients with congestive heart failure are associated with increased rates of overall mortality and sudden death. Amiodarone is now used widely to prevent ventricular tachycardia and fibrillation. We conducted a trial to determine whether amiodarone can reduce overall mortality in patients with congestive heart failure and asymptomatic ventricular arrhythmias. METHODS: We used a double-blind, placebo-controlled protocol in which 674 patients with symptoms of congestive heart failure, cardiac enlargement, 10 or more premature ventricular contractions per hour, and a left ventricular ejection fraction of 40 percent or less were randomly assigned to receive amiodarone (336 patients) or placebo (338 patients). The primary end point was overall mortality, and the median follow-up was 45 months (range, 0 to 54). RESULTS: There was no significant difference in overall mortality between the two treatment groups (P = 0.6). The two-year actuarial survival rate was 69.4 percent (95 percent confidence interval, 64.2 to 74.6) for the patients in the amiodarone group and 70.8 percent (95 percent confidence interval, 65.7 to 75.9) for those in the placebo group. At two years, the rate of sudden death was 15 percent in the amiodarone group and 19 percent in the placebo group (P = 0.43). There was a trend toward a reduction in overall mortality among the patients with nonischemic cardiomyopathy who received amiodarone (P = 0.07). Amiodarone was significantly more effective in suppressing ventricular arrhythmias and increased the left ventricular ejection fraction by 42 percent at two years. CONCLUSIONS: Although amiodarone was effective in suppressing ventricular arrhythmias and improving ventricular function, it did not reduce the incidence of sudden death or prolong survival among patients with heart failure, except for a trend toward reduced mortality among those with nonischemic cardiomyopathy.

Actuarial Analysis↗
PubMed1994

Prevention of exercise-induced endothelemia by isradipine in men with angina pectoris.

The primary purpose of this study was to determine whether treatment with isradipine would prevent an exercise-induced increase in the concentration of anuclear carcasses of endothelial cells in the blood of men with angina pectoris. Endothelial cells were prepared for microscopic counting by a method involving differential centrifugation of venous blood. The endothelial cell count of 20 men increased from 0.78 +/- (SD) 0.41 per counting chamber approximately 2 h before exercise to 1.28 +/- 0.54 three minutes after moderate angina was induced by treadmill exercise (p = 0.003). After treatment with isradipine, the endothelial cell count decreased with or without treadmill exercise. These results suggest that exercise caused an increase in the endothelial cell count of men with coronary artery disease and that isradipine caused an acute decrease and prevented the exercise-induced increase in the endothelial cell count.

Adult↗
PubMed1993

The effect of sulfinpyrazone on treadmill exercise-induced angina pectoris.

Suspecting that platelet thromboemboli could play a role in the pathogenesis of myocardial ischemia, we have done a random-order, double-blind, crossover study of the effect of the platelet-active drug sulfinpyrazone on treadmill exercise-induced angina pectoris in 30 men with coronary artery disease. The mean duration of exercise before onset of angina was 43 s longer after taking sulfinpyrazone than before and 11 s shorter after taking placebo than before. Analysis of variance for crossover design showed that the mean difference between the values obtained before and after sulfinpyrazone was significantly different (p < 0.01) from the mean difference between the values before and after placebo. Sulfinpyrazone had no effect on the mean heart rate-blood pressure product at onset of angina, change in ST segment during exercise, or preexercise platelet aggregate ratio and bleeding time. Exercise until angina occurred did not affect the platelet aggregate ratio.

Angina Pectoris↗
PubMed1988

Which role for antiplatelet and anticoagulant drugs in unstable angina pectoris?

Two large placebo-controlled, randomized, double-blind clinical trials have demonstrated the benefit of aspirin therapy in preventing myocardial infarction and death in patients with unstable angina. The Veterans Administration Cooperative Study of 1266 men hospitalized with unstable angina showed that 324 mg of aspirin daily for 12 weeks reduced the incidence of myocardial infarction by 51% (p = 0.001), and the data suggested a similar reduction in mortality. The Canadian McMaster University multicenter trial of 555 patients showed that treatment with 1300 mg of aspirin per day for a mean of 18 months reduced the incidence of cardiac death and nonfatal myocardial infarction together by 51% (p = 0.008). The reduction in death alone was 71% (p = 0.004). In the Canadian study there was no observed benefit of sulfinpyrazone. The Canadian trial confirmed the results of the VA Cooperative Study and showed statistical significance for reduction by aspirin of death as well as of myocardial infarction. It showed similar benefits in women as in men with unstable angina. The life-table curves for aspirin-treated and control patients continued to separate throughout the 2-year study period, demonstrating the value of continued treatment. The VA study showed no evidence of gastrointestinal side effects from 324 mg of aspirin daily administered in a buffered solution. Heparin therapy for unstable angina has appeared promising, but no properly conducted randomized trial has been accomplished.(ABSTRACT TRUNCATED AT 250 WORDS)

Angina, Unstable↗
PubMed1988

Babble and random-noise masking of speech in high and low context cue conditions.

"Perceptual" masking of speech by multitalker speech (babble) has been widely reported but poorly quantified. Furthermore, the validity of the construct of perceptual masking is questionable. This report describes an experiment using a newly standardized test of speech perception in noise (SPIN) with both babble and spectrally matched random-noise maskers. Classical psychophysical ogive curves were used to model speech recognition as a function of signal-to-noise ratio (S/N). The two maskers yielded speech recognition functions of the same steepness but different locations on the S/N axis. The high-context items of SPIN yielded speech recognition curves with steeper slope and different locations on the S/N axis than the low-context items. These data are used to argue that perceptual masking was not documented (under certain assumptions) and that the superior masking of babble may be explained in purely acoustical terms. Speculations are offered about the possible acoustical differences that could be responsible for the differences in masking effect.

Acoustics↗
PubMed1986

Role of antithrombotic therapy in unstable angina, myocardial infarction and sudden death.

The role of platelets and the clotting system in the initiation and progression of atherosclerosis has received significant attention. Most importantly, platelets and thrombosis play a pivotal role in the pathogenesis of the acute coronary syndromes of unstable angina, myocardial infarction and sudden death. In each stage of the development of coronary artery disease, from the early symptomatic stage through the growing lesion and finally to the complicated plaque that results in the precipitation of the acute coronary syndromes, platelets and the clotting system serve as a common link among them. Antithrombotic therapy aimed at halting the progression of these syndromes, preventing their occurrence or even reversing them (such as in the early stages of acute myocardial infarction), has provided exciting new modalities to treat these disorders. The use of aspirin in unstable angina in two well designed studies has clearly shown a reduction in fatal as well as nonfatal cardiac events compared with control groups not treated with aspirin. Although demonstration of a benefit of anticoagulant and antiplatelet therapy is difficult owing to a low event rate of thrombotic events (low sensitivity) and other nonthrombotic fatal events (low specificity) after myocardial infarction, pooled results have shown a favorable effect with their use. The usefulness of thrombolytic therapy in the early stages of acute myocardial infarction depends on the timing of initiation of therapy, the severity of the residual stenosis and possible use of agents that protect the ischemic myocardium. Other potential therapies for the acute coronary syndromes are also suggested. Further studies are in progress to establish the clinical benefits of antithrombotic agents in acute coronary syndromes.

Anticoagulants↗
PubMed1985

Cigarette smoking--induced enhancement of platelet function: lack of prevention by aspirin in men with coronary artery disease.

Increased cardiovascular morbidity and mortality among cigarette smokers may be mediated in part by enhanced platelet function. Previous data showed that cigarette smoking--induced lowering of the platelet aggregate ratio of normal individuals was prevented by taking aspirin before smoking. Our study was undertaken to determine whether similar results would occur in men with coronary artery disease and whether platelet factor 4 would be released. A random-order, double-blind crossover study comparing the effects of placebo, 0.15 gm aspirin, and 0.30 gm aspirin was done in 30 male habitual smokers with coronary artery disease. Each man took a tablet containing placebo or aspirin and then abstained from smoking for 12 hours before each of three 20-minute periods of smoking two tobacco cigarettes. Immediately before and after smoking, the platelet aggregate ratio and the concentration of platelet factor 4 in platelet-poor plasma were determined from antecubital venous blood. Twelve hours after placebo, the geometric mean concentration of platelet factor 4 was 13.6 ng/ml before and 19.7 ng/ml after smoking (P = 0.0006). The mean platelet aggregate ratio was 0.77 and 0.72, respectively (P less than 0.00001). Neither dose of aspirin affected the presmoking value of or the smoking-induced change in either variable. The data indicate that smoking stimulated platelet aggregate formation and release of the contents of platelet alpha-granules, which were unaffected by preadministration of aspirin. This contrasts with the previous study of normal habitual smokers whose ingestion of 0.32 gm aspirin prevented a smoking-induced decrease in the platelet aggregate ratio.

Adult↗
PubMed1985

Unstable angina: status of aspirin and other forms of therapy.

A randomized, double-blind clinical trial in 1266 men with unstable angina showed that 324 mg of aspirin daily for 12 weeks reduced the incidence of myocardial infarction by 51% (p = .001), and the data suggested a similar reduction in mortality. The only other therapy for unstable angina that has been studied in randomized trials of adequate size to evaluate mortality and rate of infarction is aortocoronary bypass surgery. Results with heparin therapy have been encouraging, but the studies in which this drug has been tested have been flawed. Nitrates, beta-blockers, calcium blockers, fibrinolytic therapy, and coronary angioplasty have not been adequately evaluated. Randomized trials of aortocoronary bypass surgery have not demonstrated decreased mortality or rates of myocardial infarction in patients with unstable angina. Although surgical techniques have improved since these trials were conducted, medical management has also improved. Mortality and infarct rate in patients with unstable angina are now lower than in the early 1970s. New well-controlled clinical trials are needed.

Angina Pectoris↗
PubMed1983

Protective effects of aspirin against acute myocardial infarction and death in men with unstable angina. Results of a Veterans Administration Cooperative Study.

We conducted a multicenter, double-blind, placebo-controlled randomized trial of aspirin treatment (324 mg in buffered solution daily) for 12 weeks in 1266 men with unstable angina (625 taking aspirin and 641 placebo). The principal end points were death and acute myocardial infarction diagnosed by the presence of creatine kinase MB or pathologic Q-wave changes on electrocardiograms. The incidence of death or acute myocardial infarction was 51 per cent lower in the aspirin group than in the placebo group: 31 patients (5.0 per cent) as compared with 65 (10.1 per cent); P = 0.0005. Nonfatal acute myocardial infarction was 51 per cent lower in the aspirin group: 21 patients (3.4 per cent) as compared with 44 (6.9 per cent); P = 0.005. The reduction in mortality in the aspirin group was also 51 per cent--10 patients (1.6 per cent) as compared with 21 (3.3 per cent)--although it was not statistically significant; P = 0.054. There was no difference in gastrointestinal symptoms or evidence of blood loss between the treatment and control groups. Our data show that aspirin has a protective effect against acute myocardial infarction in men with unstable angina, and they suggest a similar effect on mortality.

Adrenergic beta-Antagonists↗