A Networks Approach to Modeling Enzymatic Reactions.

Modeling enzymatic reactions is a demanding task due to the complexity of the system, the many degrees of freedom involved and the complex, chemical, and conformational transitions associated with the reaction. Consequently, enzymatic reactions are not determined by precisely one reaction pathway. Hence, it is beneficial to obtain a comprehensive picture of possible reaction paths and competing mechanisms. By combining individually generated intermediate states and chemical transition steps a network of such pathways can be constructed. Transition networks are a discretized representation of a potential energy landscape consisting of a multitude of reaction pathways connecting the end states of the reaction. The graph structure of the network allows an easy identification of the energetically most favorable pathways as well as a number of alternative routes.

Warm water vapour in the sooty outflow from a luminous carbon star.

The detection of circumstellar water vapour around the ageing carbon star IRC +10216 challenged the current understanding of chemistry in old stars, because water was predicted to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the star, grain surface reactions, and photochemistry in the outer circumstellar envelope. With a single water line detected so far from this one carbon-rich evolved star, it is difficult to discriminate between the different mechanisms proposed. Here we report the detection of dozens of water vapour lines in the far-infrared and sub-millimetre spectrum of IRC +10216 using the Herschel satellite. This includes some high-excitation lines with energies corresponding to approximately 1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. A plausible explanation for the warm water appears to be the penetration of ultraviolet photons deep into a clumpy circumstellar envelope. This mechanism also triggers the formation of other molecules, such as ammonia, whose observed abundances are much higher than hitherto predicted.

[Weaning of young smokers using a transdermal nicotine patch]. / Entwöhnung junger Raucher mit Hilfe eines transdermalen Nikotinpflasters.

To assess efficacy and tolerance of a transdermal nicotine system (TNS) as adjuvant to tobacco withdrawal, 112 young, nicotine-dependent cigarette smokers were treated for nine weeks with TNS (n = 56) or placebo (n = 56). Initial doses of nicotine (21 or 14 mg/24 h) were based on previous smoking habits and stepwise reduced to 7 mg/24 h if abstinence was achieved during medication. After treatment, 39.3% of the TNS users were abstinent versus 19.6% on placebo (p less than 0.05). The craving for cigarettes diminished steadily, but not more significantly on TNS medication. Tenseness, difficulty in concentration and feelings of hunger were consistently and in part significantly lessened in the TNS group. The other withdrawal symptoms were not influenced by TNS treatment. Nine-month follow-up cotinine-verified abstinence rates were 12.5% in the TNS and 3.6% in the placebo group (n. s.). Transient mild or moderate erythema at the application site appeared in 20% of the TNS and 6.3% of the placebo group, and 7.1% of the TNS users dropped out because of severe localized erythema. Other mild, transient, systemic side effects reported by 33.9% of the TNS and 26.8% of the placebo users (n. s.) did not lead to drop-outs.

Influence of acetylator status on the haemodynamic effects and pharmacokinetics of cadralazine in healthy subjects.

1. Cadralazine is a new antihypertensive agent which causes peripheral vasodilation, probably mediated by a hydrazinopyridazine metabolite. 2. The possible influence of acetylator status on the pharmacokinetics and haemodynamics of the drug was studied in six fast and six slow acetylators over a period of 24 h after administration of a single 10 mg oral dose. 3. There were no differences between the two groups in AUC and Cmax values of cadralazine and apparent metabolite, the latter defined as the sum of the free and conjugated hydrazinopyridazine. Peak plasma concentrations of these compounds were reached after 1 h. Thereafter, the concentration of the metabolite declined more slowly than that of cadralazine. 4. No effects on blood pressure were noted. Changes in heart rate and plasma renin were delayed by 3-5 h with respect to the time-course of drug and metabolite in plasma; maximum responses occurred at 4-6 h after drug administration. The extent of the increase in plasma renin activity was slightly greater in slow than in fast acetylators, but the difference was not significant statistically.

The use of transdermal nicotine in smoking cessation.

The transdermal administration of nicotine by means of a transdermal nicotine system (TNS) affords a novel way of nicotine replacement to alleviate smoking cessation. The plasma levels of nicotine maintained with the TNS are in the range of the footpoint concentrations observed in smokers. The efficacy of the TNS was investigated in two placebo-controlled double-blind smoking cessation programs with minimal contact and minimal psychological support. A total of 311 smokers were treated for 3 months or 9 weeks. The abstinence rates at the end of the treatment and weaning periods were almost doubled in the TNS groups (36% and 39%) as compared to the placebo groups (23% and 20%) with a significant difference for both studies (p less than 0.05). These data suggest that the TNS can also improve the smoking cessation rates under the conditions of general medical advice, making it suitable for use outside of specialized smoking cessation centers.

[Influence of acetylation phenotype on the pharmacokinetics and pharmacodynamics data of cadralazine in normotensive subjects]. / Influence du phénotype d'acétylation sur la pharmacocinétique et les données pharmacodynamiques de la cadralazine chez le sujet normotendu.

Cadralazine is a new antihypertensive drug, acting as a peripheral arteriolar vasodilator through its hydrazinopyridazine metabolite. Since this metabolite actively contributes to the activity of the drug, we administered in a double blind randomized study 10 mg/placebo o.d. to 6 healthy fast and 6 slow normotensive acetylators in order to investigate the influence of the acetylator status on hemodynamics and pharmacokinetics. Blood pressure was measured with a DINAMAP apparatus, forearm hemodynamics with a pulsed doppler and central hemodynamics with impedance-cardiography; active renin (RIA), cadralazine and its metabolite (HPLC) were measured during the 11 measurement points. The results were analysed with repeated analysis of variance (ANOVA). Heart rate significantly increased (p less than 0.001), until the 24th hour (p less than 0.05), meanwhile blood pressure and forearm hemodynamics did not change. Cardiac output was increased as a consequence of the elevation in venous return. The rise in active renin paralleled the increase in heart rate with a significant correlation (r' = 0.580, p less than 0.05). The magnitude of the increase was higher in slow than that in fast acetylators, but did no reached the significance. No differences were found for AUC, Cmax and Tmax between the two groups but the active metabolite was eliminated slower than that of cadralazine. The time course of the effects on heart rate and plasma renin was not parallel to the plasma levels of cadralazine and its metabolite. With respect to the power of the study (1-beta = 80 p. 100), no significant differences were found between the two groups.

Circulatory counter-regulations induced by continuous administration of nitroglycerin.

In a placebo-controlled, double-blind, cross-over study in seven healthy volunteers, continuous transdermal administration of nitroglycerin over 48 h by means of Nitroderm TTS 10 evoked counter-regulations that interfered with the nitrate effects. These counter-regulations comprised an increase in sympathico-adrenal activity, manifested in elevated plasma levels of adrenaline and noradrenaline, and an internal hemodilution, readily perceptible from the decrease in the hematocrit readings. As a result, several of the circulatory effects of nitroglycerin were no longer in evidence, or much weaker on the second day of the study. The effects concerned were the reduction of systolic and diastolic blood pressure, the increase in heart rate, the prolongation of PEPc, and shortening of LVETc, and the change in digital-pulse morphology (increase in the a/b quotient). On the other hand, the increase in venous distensibility and the decrease in hematocrit were unaltered throughout the observation period. The attenuation of the action of nitroglycerin noticeable 24 h after application of the patches is, therefore, not indicative of any loss of effect of the substance per se, but due to the circulatory counter-regulations, which were largely confined to the arterial side of the circulation and scarcely affected the venous system. One or two hours after removal of the patches, counter-regulations had practically ceased.

Pharmacokinetics and bioavailability of nicotine in healthy volunteers following single and repeated administration of different doses of transdermal nicotine systems.

Healthy nicotine-dependent smokers were applied different doses of transdermal nicotine systems (TNS) during single and repeated administrations. Plasma and urine nicotine and cotinine concentrations were determined by high performance liquid chromatography (HPLC). After single application of TNS, the maximal concentration (Cmax) and area under curve (AUC) of nicotine in plasma as well as the amount of nicotine excreted in urine were linearly related to the dose. The stable urinary cotinine excretion was not influenced by the amount of nicotine delivered by the TNS. The relevant 24 h plasma nicotine concentration reached after TNS application compares well with the plasma nicotine footpoints--not the peaks--observed in moderate to heavy cigarette smokers. A comparison between different nicotine doses from different TNS allowed to conclude to the functionality of the systems as regards pharmacokinetics and bioavailability. One or two hours after removal of the systems, there was a very slow decline of the nicotine concentrations. After repeated application of TNS, there was evidence for only a very limited nicotine accumulation in plasma (+14%) or in urine (+9%) over 10 days. The steady-state of nicotine was reached within 4 days. The continuous delivery of nicotine over 24 h resulted in an early morning plasma concentration which probably decreases or prevents the craving for the first cigarette.

Human pharmacological investigations of a transdermal nicotine system.

To define the pharmacological properties of a newly developed transdermal nicotine system (TNS) designed to facilitate abstention from smoking, three human pharmacology studies were performed in healthy, nicotine-dependent smokers. The first study, in which cigarette smoking served as the standard mode of nicotine intake, was carried out to evaluate the most suitable non-invasive methods for detecting the pharmacodynamic effects of nicotine and to provide a baseline for comparisons with the results of the subsequent studies to assess the effects of single and repeated applications of the TNS. The pharmacodynamic changes induced by smoking were generally most pronounced after the first cigarette following 10 hours' abstinence. The most sensitive parameters were heart rate, which increased, stroke volume measured by impedance cardiography, which decreased, cutaneous blood flow measured by Laser Doppler flowmetry and skin temperature, which diminished to a statistically significant extent after each cigarette. Increases in blood pressure were not very pronounced. Plasma catecholamines were consistently elevated after each cigarette, but the changes were not statistically significant. Compared with those induced by cigarette smoking, the cardiovascular effect seen after either a single application of the TNS (10, 20 and 40 mg/24 h) or repeated application of a TNS delivering 14 mg nicotine/24 h were minor. A slight increase in blood pressure was detectable only on the first day of application and had disappeared after 10 days' repetitive application, suggesting the development of partial tolerance. Heart rate was slightly increased by 3-7% and stroke volume decreased by 5-12% on the tenth day of TNS application.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of a transdermal nicotine system in smoking cessation studies.

To investigate the effectiveness and tolerability of a transdermal nicotine system (TNS) as an aid towards easing smoking cessation, two double-blind placebo-controlled randomized field studies were performed. The TNS was available in sizes of 10, 20 and 30 cm2, delivering 7, 14 and 21 mg of nicotine per 24 h. A first study was undertaken in general medical practice by a group of 21 doctors (Practitioner Study). This study involved 199 nicotine-dependent cigarette smokers of whom 100 were allocated to the nicotine group and 99 to the placebo group. The second trial was performed in 112 young people, 56 in each treatment group, at the Universities of Basle and Zurich (University Study). The placebo and the nicotine groups were comparable in both studies. Participants smoking more than 20 cigarettes a day were treated with the 30-cm2 system and the others with the 20-cm2 system. When abstinence, as verified by CO measurements, was achieved, the next smaller system was applied. In the Practitioner Study, the double-blind treatment phase lasted for 12 weeks with consultations every month and in the University Study the consultations during the 9-weeks' treatment period took place every 3 weeks. Abstainers in both studies will be followed up until 12 months after treatment was begun. After 1, 2 and 3 months of treatment 41%, 36% and 36% of the participants in the nicotine group of the Practitioner Study were abstinent. The corresponding figures in the placebo group were 19.4%, 20.4% and 22.5%. The differences were statistically significant for all three months (p = 0.001; p = 0.018 and p = 0.043). Body weight did not increase in the TNS group, but did in the placebo group (+ 4.4 kg). The craving for cigarettes and withdrawal symptoms decreased more under nicotine substitution. Abstinence rates in the University Study were initially higher with 51.8% in the nicotine group and 28.6% in the placebo group after 3 weeks of treatment, but then declined to 42.9% after 6 weeks and 39.3% after 9 weeks in the nicotine group and to 25% and 19.6%, respectively, in the placebo group. The differences between the groups were statistically significant on all 3 occasions, with p = 0.012, p = 0.046 and p = 0.023.(ABSTRACT TRUNCATED AT 250 WORDS)

Controlled trial of transdermal nicotine patch in tobacco withdrawal.

A transdermal nicotine patch, which delivers 0.7 mg/cm2 per 24 h and is available in sizes of 10, 20, and 30 cm2 was tested in subjects from 21 general medical practices in a 3-month, placebo-controlled randomised double-blind study. The nicotine group (n = 100) and the placebo group (n = 99) were similar at entry. Participants who smoked more than 20 cigarettes a day were treated with the 30 cm2 patch and the others with the 20 cm2 patch. When abstinence, defined as smoking 0-3 cigarettes per week and verified by CO measurement, was achieved, the next smallest patch was applied. After 1, 2, and 3 months of treatment 41, 36, and 36%, respectively, in the nicotine group were abstinent. The corresponding figures in the placebo group were 19, 20, and 23%. The differences were significant for all 3 months. Body weight did not increase in the nicotine group, but in the placebo group the mean increase was 4.4 kg. Craving and withdrawal symptoms decreased more with nicotine substitution for cigarettes. The patches were generally well tolerated, although 25% of subjects in the nicotine group and 13% in the placebo group had transient local erythema after application of the patch; 5 members of the nicotine group withdrew because of poor cutaneous tolerance.

Spontaneous motor activity in healthy volunteers after single doses of haloperidol.

Video recordings of the spontaneous motor activity of 6 healthy volunteers after treatment with 0.75 mg haloperidol i.v., or placebo, were transcribed into a time-series protocol of motor behaviour. Characteristic changes seen after the injection of haloperidol consisted in a reduction of the motility of the extremities and prolongation of the phases of both movement and immobility of the head. The tested dose of haloperidol induced a distinct rise in serum prolactin and sedation, but had no effects on the pharmaco-EEG or on the critical flicker-fusion frequency. Analysis of the motor phenomena evoked by neuroleptics in healthy persons and in patients may help, on the other hand, to establish correlations with the motor effects observable in preclinical investigations in animals and might also contribute towards the elucidation of the extrapyramidal side-effects of these drugs.

Pharmacological profiling of cardiovascular agents in healthy volunteers by means of non-invasive methods.

In a placebo-controlled study the hemodynamic effects of single doses of oxprenolol, metoprolol, prenalterol, phentolamine, nifedipine, nitroglycerin, angiotensin II and frusemide have been investigated in 9 healthy volunteers by means of the combined measurement of heart rate, blood pressure, pre-ejection period (systolic time intervals) and stroke volume (impedance cardiography) in the supine and tilted positions (70 degrees). Each cardiovascular agent exhibited its characteristic pharmacodynamic profile, which allowed a clear-cut discrimination. The effects of oxprenolol and metoprolol, however, could not be distinguished by this procedure. The pre-ejection period, although not a very specific parameter, proved to be most sensitive to the pharmacological interventions, whereas stroke volume was less often influenced. It is concluded that the proposed selection of non-invasive parameters is a very suitable and simple means for early cardiovascular drug testing in man.

Laser Doppler flowmetry, a reliable technique for measuring pharmacologically induced changes in cutaneous blood flow?

Laser Doppler flowmetry (LDF) affords a reliable non-invasive method of investigating acute changes in total cutaneous perfusion. However, the reproducibility of measurements of resting blood flow is considered to be poor. Therefore, the potential use of LDF to monitor pharmacological influences on cutaneous perfusion over time may be limited to the investigation of drug-induced changes of the response pattern to standardized provocation procedures. The present study was undertaken to evaluate the reproducibility of cutaneous vasomotor reflexes induced by various test stimuli. Measurements were made in the morning and in the afternoon of the same day at two different skin sites (finger-tip and forearm) in six healthy subjects. Each of the following six interventions induced highly reproducible decreases of total cutaneous flow: Deep inspiration, Vasalva manoeuvre, venous occlusion, arrest of arterial blood flow (followed by reactive hyperaemia), passive head-up tilting and a cold pressor test. The decrease in blood flow was more pronounced at the finger-tip except after venous occlusion. During the cold pressor test, skin perfusion was more persistently reduced at the finger-tip than at the other site. The anatomical and functional differences in the skin between the finger-tip and the forearm may also explain the absence of reactive hyperaemia at the finger-tip. Considering the excellent reproducibility of the resting baseline values and of the changes in total blood flow after standardized provocation tests within the same day, it seems possible that LDF could be a suitable method for the short-term investigation of drug effects on circulation. The long-term day-to-day reproducibility of both baseline blood flow and vasomotor reflexes remains to be further clarified.

Human pharmacokinetics of cadralazine: a new vasodilator.

The pharmacokinetic profiles in plasma and the renal elimination of 2-(3-[6-(2-hydroxypropyl)ethylamino]pyridazinyl)ethylcarbazate+ ++ were investigated in six healthy volunteers following single oral doses of 5, 10 and 20 mg of cadralazine. The study was run in a randomized change-over design experiment. Concentrations of cadralazine in plasma and urine were determined by a high-performance liquid chromatography method. Maximum plasma levels (Cmax) were reached between 0.25 and 1.0 h (tmax) after administration and ranged from 69.8 to 210.0 ng/g after the 5 mg dose, 148.9 to 333.3 ng/g after the 10 mg dose and 292.9 to 474.5 ng/g after the 20 mg dose. The corresponding area under the plasma concentration-time curve (AUC24hO) are 330, 621 and 1168 (ng/g). h. Mean renal elimination of the unchanged-drug ranged from 69 to 73% of the dose. Mean Cmax, AUC24hO and mean total renal elimination were linearly dose-related. An elimination half-life from plasma of about 2.5 h was observed for cadralazine. Estimations for the mean renal and total clearance range from 185 to 216 ml/min and 251 to 295 ml/min, respectively.

Effect of nitroglycerin on blood rheology in healthy subjects.

Transdermal nitroglycerin (Nitroderm TTS 5) and a placebo were applied to 10 healthy male volunteers for 10 days. Before the first application and 6, 24, 48, 96, and 240 h thereafter, the viscosity of plasma and whole blood was measured and the packed-cell volume determined. During nitroglycerin application, the viscosity of plasma and whole blood was significantly diminished, and after 10 days it averaged 5% below the initial value. The greater the initial viscosity, the more marked was the drug-induced reduction: in 5 subjects with plasma and whole-blood viscosities near the lower limit of the normal range, there was only a temporary decrease and the values reverted to their initial levels after 4 days; in the other 5 subjects, whose whole-blood viscosities were near the upper limit of the normal range, a 10% reduction was still demonstrable after 10 days. In those subjects all values measured throughout the 10-day observation period were significantly below the initial values. The haematocrit readings followed the same pattern as the alterations in viscosity. It can be assumed, therefore, that the decrease in viscosity induced by nitroglycerin results from "internal haemodilution". The clinical relevance of the changes observed is discussed. The improvement in the rheological properties of the blood may contribute to the anti-anginal effect of Nitroderm TTS.

The metabolic fate of [14C]oxaprotiline.HCl in man. I. Disposition and preliminary pharmacokinetics.

Absorption, biotransformation and elimination of [14C]oxaprotiline.HCl have been studied after oral administration of 50 mg doses to two human subjects. Absorption was complete, and peak blood concn. of total 14C were 590 and 297 ng equiv./ml after 3-6 h in the two subjects. After 11 days, 84 and 90% dose was excreted in urine, and a total of 98% was excreted. Peak blood concn. of unchanged oxaprotiline were 16 and 19 ng/ml before, and 167 and 207 ng/ml after enzymic hydrolysis. The blood half-life in the two subjects was 23 and 29 h. The blood concn. of the desmethyl metabolite was low (2 ng equiv./ml), but also increased after hydrolysis (11-19 ng equiv./ml). Oxaprotiline was bound (83%) in vitro to serum proteins. Sixty per cent was bound to serum albumin and 20% to alpha 1-acid glycoprotein. In urine only 1% of total 14C was present as unchanged oxaprotiline, and 0.2% as the desmethyl metabolite. After enzymic hydrolysis these increased to 48 and 6%, respectively, and after acid hydrolysis to 85 and 10%.