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Thomas Hohlfeld

Publications and source records attributed to Thomas Hohlfeld.

At least 19 recordsLinked to original sources
PubMed2006

Human cyclooxygenase-1b is not the elusive target of acetaminophen.

A cyclooxygenase-1 splice variant (cyclooxygenase-1b), cloned from canine brain, was proposed to be an acetaminophen-sensitive enzyme. Unlike in canines, the retention of intron 1 in the human sequence results in a frame shift and predicts a truncation of the protein. We have sought to answer the question whether human cyclooxygenase-1b, if expressed, is a target of acetaminophen. Thus, we studied the pharmacology of complete human cyclooxygenase-1b in which the frame shift was corrected by site-directed mutagenesis (human cyclooxygenase-1bDeltaG). Human cyclooxygenase-1bDeltaG was active but was not inhibited by acetaminophen. In conclusion, full length human cyclooxygenase-1b is clearly not the target of acetaminophen.

Acetaminophen↗
PubMed2006

Aspirin "resistance".

A variable responsiveness to antiplatelet drugs is a clinical phenomenon that does not principally differ from other drug treatments in other therapeutic fields. The pharmacological part is to clarify whether a "true" resistance exists in pharmacological terms, i.e., a reduced potency of the compound to work as suggested and to find out the underlying cellular mechanism(s). Two principally different methods of laboratory control for platelet sensitivity to aspirin (ASA) are available: measurement of platelet function (ex vivo) or measurement of inhibition of thromboxane formation. Both methods have limitations and did not yet result in a generally accepted definition of a pharmacological ASA "resistance". The new typological approach of Weber et al. [A.A. Weber, B. Przytulski, A. Schanz, et al., Towards a definition of aspirin resistance: a typological approach. Platelets 13 (2002) 37.] helps to identify different subtypes of ASA resistance in pharmacological terms by combining in vitro aggregometry with thromboxane measurement. Using this method, a "true" pharmacological resistance, associated with a reduced antiplatelet response to ASA and reduced inhibition of thromboxane formation, was found in patients undergoing coronary artery bypass surgery. Platelets of these patients expressed a hitherto unknown isoform of COX-2-COX-2a which might generate a different gene product. In this context, it is interesting that CABG patients express transiently an immunoreactive COX-2 protein with lower molecular weight. Studies on the significance of this finding for ASA resistance are in progress.

Aspirin↗
PubMed2006

[Selective I(f) channel inhibition: an alternative for treating coronary artery disease?].

Several clinical studies demonstrate the importance of the heart rate for the cardiovascular morbidity and mortality. Over the last 50 years, some thought has been given to those substances that selectively reduce the heart rate. It is now recognized that I(f) ion channels of the sinus node play a major role in the automatism and modulation of the heart rate. Substances that selectively reduce the heart rate should decrease myocardial oxygen consumption and increase oxygen delivery via the prolonged diastolic coronary perfusion. Direct inotropic effects, however, are unlikely. In principle, anti-anginal and anti-ischemic effects of specific bradycardic substances can be expected. The clinical experience with some of the former bradycardic substances has not been sufficiently convincing. The more recent ivabradine (Procoralan presents an exception to this, as it successfully completed a clinical program for the treatment of chronically stable angina pectoris. In this review article, specific bradycardic substances (= I(f) channel inhibitors) are presented together with the corresponding experimental and clinical studies. The studies were selected against the background of the efficacy of I(f) channel inhibitors in the therapy of cardiovascular disease. As only ivabradine has completed a study on 5,000 patients, the discussion on that particular I(f) channel inhibitor is somewhat extensive. In addition, prospective possibilities and limitations of bradycardic substances are presented.

Anti-Arrhythmia Agents↗
PubMed2006

Delayed preconditioning via Angiotensin-converting enzyme inhibition: pros and cons from an experimental study.

1. Bradykinin B(2) receptor activation confers preconditioning from ischaemic injury. In the present study, we tested whether an angiotensin-converting enzyme (ACE) inhibitor (captopril) could mediate delayed preconditioning and, thus, cardioprotection. 2. New Zealand white rabbits received 15 mL infusion of either saline (control group; n = 7) or drugs (0.3 mg/kg captopril (CAP group; n = 7) or 0.3 mg/kg captopril + 0.1 mg/kg HOE 140 (CAPHOE group; n = 7)) via a marginal ear vein over 30 min. After 24 h, hearts were connected to a Langendorff apparatus and buffer perfused. The experimental protocol consisted of 20 min global normothermic hypoxia, followed by 120 min reperfusion. 3. Compared with baseline, the mean (SEM) contractile state (= dP/dt(max)) at 120 min reperfusion was decreased to 42 +/- ;23, 72 +/- ;16 (*P < 0.05 vs control) and 49 +/- ;22% in the control, CAP and CAPHOE groups, respectively. Early relaxation (= dP/dt(min)) was reduced to 55 +/- ;28, 73 +/- ;15 (*P < 0.05 vs control) and 52 +/- ;19% in the control, CAP and CAPHOE groups, respectively. The estimate for myocardial oxygen consumption (MVO(2)= rate-pressure product) was decreased to 52 +/- ;15, 69 +/- ;24 (*P < 0.05 vs control) and 56 +/- ;15% in the control, CAP and CAPHOE groups, respectively. Similarly, coronary flow was decreased in the control, CAP and CAPHOE groups to 49 +/- ;20, 67 +/- ;18 and 46 +/- ;19%, respectively. In contrast, ventricular extrasystoles during reperfusion were significantly elevated in both the CAP and CAPHOE groups (1.3 +/- ;0.2 and 1.1 +/- ;0.3 /min, respectively) compared with control (0.4 +/- ;0.2 /min). 4. Captopril confers delayed preconditioning against stunning via a B(2) receptor-mediated pathway. This pharmacological preconditioning protects against systolic and diastolic stunning, against vascular stunning and preserves cardiac metabolism. In addition to its accepted cardioprotective effects in early preconditioning, captopril should induce delayed preconditioning (e.g. for routine interventional cardiology or in elective cardiac surgery).

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2006

Does a coxib-associated thrombotic risk limit the clinical use of the compounds as analgesic, antiinflammatory drugs? Arguments against.

The issue of the risk-benefit assessment of cyclooxygenase-2 (COX-2) inhibitors, as compared to traditional non-steroidal anti-inflammatory drugs (tNSAIDs), is far from being resolved. These compounds need to be carefully re-evaluated in order to avoid hasty conclusions, as it happened when COX-2 inhibitors were introduced into clinical practice. Several arguments support the concept, that COX-2 inhibitors remain a valuable therapeutic option at least for selected patients.

Analgesics↗
PubMed2005

Cardiospecific overexpression of the prostaglandin EP3 receptor attenuates ischemia-induced myocardial injury.

BACKGROUND: The generation of prostaglandin E2 (PGE2) is significantly increased in acute myocardial ischemia and reperfusion. PGE2, in addition to other prostaglandins, protects the reperfused ischemic myocardium. It has been hypothesized that this cardioprotection is mediated by E-type prostaglandin receptors of the Gi-coupled EP3 subtype. METHODS AND RESULTS: We tested this hypothesis by generating transgenic (tg) mice with cardiospecific overexpression of the EP3 receptor. According to ligand binding, a 40-fold overexpression of the EP3 receptor was achieved in membranes prepared from tg hearts compared with wild-type (wt) littermates. In isolated cardiomyocytes from tg mice, the forskolin-induced rise in cAMP was markedly attenuated, indicating coupling of the overexpressed EP3 receptor to inhibitory G proteins (Gi) with constitutive receptor activity. There was no evidence for EP3 receptor coupling to Gq-mediated protein kinase C signaling. Isolated hearts from tg and wt mice were subjected to 60 minutes of no-flow ischemia and 45 minutes of reperfusion. In tg hearts, ischemic contracture was markedly delayed compared with wt hearts, and the ischemia-induced increase in left ventricular end-diastolic pressure was reduced by 55%. Creatine kinase and lactate dehydrogenase release was significantly decreased by 85% and 73%, respectively, compared with wt hearts. CONCLUSIONS: Constitutive prostaglandin EP3 receptor signaling exerts a protective effect on cardiomyocytes, which is probably Gi mediated and results in a remarkable attenuation of myocardial injury during ischemia and reperfusion. Cardioprotective actions of E-type prostaglandins may be mediated by this receptor subtype.

Adrenergic beta-Antagonists↗
PubMed2005

Is cardiopulmonary bypass a reason for aspirin resistance after coronary artery bypass grafting?

OBJECTIVE: 'Off-pump' coronary artery bypass grafting (OPCAB) is an alternative to conventional coronary artery bypass grafting (CABG) using cardiopulmonary bypass (CPB). While midterm results after OPCAB have become available, systematic studies of changes in platelet function after OPCAB are still missing. Since we have previously shown that oral aspirin treatment (100mg) does not achieve sufficient platelet inhibition in the majority of patients operated on with CPB, we hypothesized that bypass surgery without CPB (off-pump coronary artery bypass, OPCAB) causes less impairment of platelet inhibition by aspirin. The aim of this study was to investigate platelet function and the antiplatelet effect of aspirin after off-pump coronary artery bypass grafting in comparison with conventional on-pump surgery. METHODS: We compared platelet function (in vitro aggregation and thromboxane formation) before and at days 1 and 5 after coronary artery bypass grafting, performed with (n=15) or without (n=14) CPB. Oral aspirin treatment (100mg/d) was started at day 1 after surgery. RESULTS: After a 5 day oral treatment with aspirin, platelet aggregation was inhibited significantly in OPCAB-patients to 55.7+/-16.3% of control before surgery (P<0.05), whereas aggregation remained unchanged after CPB (105.8+/-26.9% of control before surgery; P>0.05). Since aspirin primarily inhibits platelet thromboxane formation, thromoboxane was determined after in vitro aggregation. According to platelet aggregation, thromboxane formation was only inhibited significantly after OPCAB (29.2+/-13.0% of control before surgery, P<0.05), but not after CPB (74.5+/-21.4% of control before surgery, P>0.05). This resistance to aspirin after CPB may be caused by an increased release of new platelets which are competent to form thromboxane, since the number of platelets decreased from 237+/-11x10(3)/microl before CPB to 174+/-13x10(3)/microl at day 1 after surgery and increased significantly the following days reaching 303+/-17x10(3)/microl at day 5. Platelet counts of patients operated on without CPB showed no significant changes (236+/-16x10(3)/microl before OPCAB, 220+/-16x10(3)/microl at day 1 and 266+/-31x10(3)/microl at day 5 after surgery). CONCLUSIONS: The antiplatelet effect of aspirin is largely impaired after CPB, but not after CABG without CPB. Hence, increased platelet turnover after CPB seems to contribute to aspirin resistance, since an increased number of platelets might be competent to form thromboxane within the dosing intervals.

Aged↗
PubMed2004

Cyclooxygenase COX-2a, a novel COX-2 mRNA variant, in platelets from patients after coronary artery bypass grafting.

There are two principal cyclooxygenase isoforms referred to as COX-1 and COX-2. Recently, COX-3 has been identified. We have demonstrated the expression of COX-2 in platelets from patients after coronary artery bypass grafting (CABG). Careful biochemical analysis revealed that, when compared to recombinant COX-2, platelet COX-2 had a slightly higher electrophoretic mobility. Two COX-2 sequences (approximately 1.8 kb, approximately 1.7 kb) were cloned from platelet mRNA. The approximately 1.7 kb sequence, designated COX-2a, differed from the human COX-2 sequence only in a deletion from position +458 to +567. Similar to the human COX-3, there is a frame shift in the COX-2a sequence resulting in a TAA stop codon at position +490. Thus, the expression of a COX-2a protein corresponding to the 67 kDa COX-2 protein is not clear. However, the marked shifting from COX-2 to COX-2a in platelets from some patients after CABG is a striking finding.

Alternative Splicing↗
PubMed2003

Trapidil protects ischemic hearts from reperfusion injury by stimulating PKAII activity.

OBJECTIVE: The cardioprotective effects of trapidil on ischemic reperfused (I/R) rabbit hearts were studied. Recently, we had shown that trapidil might activate protein kinase A (PKA). In this study, we examined the exact mode of PKA stimulating activity of trapidil. Finally, we investigated the effect of trapidil on the phosphorylation state of phospholamban (PLB), a major PKA target in the heart and key regulator of Ca(2+) sequestration via the sarcoplasmic reticulum Ca(2+)-ATPase. METHODS: Langendorff-hearts of New Zealand White rabbits were perfused at constant volume and subjected to global low-flow ischemia for 2 h, followed by 1 h of reperfusion. Subsequently, hearts were used for Western blot analysis of PLB phosphorylation. Furthermore, three different regulatory subunits and one catalytic subunit of PKA were overexpressed in E. coli. These PKA subunits were purified and used in an in vitro assay system to test the impact of trapidil on PKA activities in the absence and presence of cAMP. RESULTS: I/R resulted in a significant increase in left ventricular end-diastolic pressure and creatine kinase efflux in the hearts. Trapidil (10 microM) prevented these alterations. Using recombinant cAMP-free PKA isoforms, it was found that trapidil specifically stimulated PKAII but only did so in the presence of small amounts of added cAMP. Furthermore, the PKA-dependent 16Ser phosphorylation of PLB was markedly reduced in I/R. Trapidil largely normalized the 16Ser phosphorylation of PLB. CONCLUSIONS: The data demonstrate cardioprotective actions of trapidil in I/R and show a PKAII-dependent cAMP sensitizing effect of the compound. They also indicate PKA-dependent PLB phosphorylation as a target, suggesting an improved Ca(2+) uptake by the sarcoplasmic reticulum. This action might be involved in the cardioprotective effects of trapidil.

Animals↗
PubMed2003

Influence of synaptic serotonin level on [18F]altanserin binding to 5HT2 receptors in man.

The feasibility of in vivo serotonin 5HT(2) receptor binding measurement using [18F]altanserin as a radioligand has been well established. In this study, the postsynaptic receptor binding potential of this ligand was examined as a possible indicator of synaptic serotonin content after pharmacological challenge. Studies were performed in 11 subjects with a history of recurrent major depression. Six of them received serotonergic antidepressive treatment at the time of the experiment, the other five patients were untreated. Two PET measurements were carried out in each subject within 2 or 3 days. Before one of the measurements, 25 mg of the serotonin re-uptake inhibitor clomipramine were given intravenously, the other measurement was done without pharmacological challenge. The data were analyzed using non-linear least-square regression and Logan's graphical method. In the whole group of subjects, binding potential and distribution volume of altanserin decreased following clomipramine challenge. The decrease was between 14 (P=0.03) and 23% (P=0.004). This effect was mainly seen in subjects not on antidepressive medication. Clomipramine challenge probably increased the synaptic serotonin level, which competed with altanserin leading to the lowered binding potential. The paradigm might, thus, be useful to estimate serotonin release in vivo. Pretreatment with serotonergic antidepressants reduces the effect of clomipramine.

Adult↗
PubMed2003

A novel activation process of protein kinase C in the remote, non-ischemic area of an infarcted heart is mediated by angiotensin-AT1 receptors.

BACKGROUND: Translocation and activation of protein kinase C (PKC) has been shown to occur in the ischemic heart. It is, however, controversial if this activation process occurs also in the non-ischemic, remote area of an infarcted heart early after infarction. Furthermore, the mechanisms contributing to the translocation process induced by acute myocardial ischemia in both areas are not fully elucidated. METHODS: Regional myocardial infarction was induced by left anterior descending coronary artery (LAD-) ligation in situ for 2.5 min in rats or in pigs. To evaluate the influence of angiotensin and bradykinin signaling, ramiprilat, candesartan, or the bradykinin-receptor antagonist HOE 140 was given. In biopsies from the ischemic and the non-ischemic remote area, PKC activity and intracellular isozyme distribution were determined. RESULTS: Translocation and activation of PKC could be demonstrated for the first time in the myocardium remote from the infarcted area. This activation was conserved both in pigs and in rats. All major cardiac isozymes of PKC were involved. Whereas bradykinin-receptor blockade had no effect, both angiotensin-converting enzyme inhibition (ACEI) and angiotensin receptor could effectively block this activation process of PKC. CONCLUSION: In the area remote from a myocardial infarction, the activation of PKC could be detected for the first time as early as 2.5 min after LAD ligation. This newly characterized activation in the non-infarcted area can be prevented by ACEI via an angiotensin-AT1-receptor-dependent mechanism. It is supposed that this newly characterized activation process of PKC plays an important role in the signal transduction in the remote myocardium in acute myocardial infarction as a trigger for the late development of hypertrophy and heart failure.

Angiotensin I↗
PubMed2003

Norepinephrine-induced delayed cardioprotection against stunning is at the expense of a higher postischemic arrhythmia rate.

OBJECTIVE: alpha(1)-adrenoceptor activation confers myocardial protection from ischemic injury. We tested whether norepinephrine mediates delayed cardioprotection against stunning and whether this alters postischemic arrhythmias. METHODS: New Zealand White rabbits were assigned to three groups: Control-group (n=7): no drugs. Norepinephrine-group (n=7): 75 microg norepinephrine/kg bodyweight (bw). Norepinephrine/prazosin-group (n=7):75 microg norepinephrine and 15 microg prazosin/kg bw. After 24 h, hearts were excised, perfused with buffer and subjected to 20 min of ischemia followed by 120 min of reperfusion. RESULTS: (a) Developed pressures (dP) (P(syst)-P(diast)) at the end of reperfusion: C: 51.2+/-5.0%, NE: 71.7+/-5.1% (p<0.05 vs. C), NEP: 50.7+/-5.0%. (b) Ventricular extra beats (vebs) were detected throughout the experiments. C: 0.41+/-0.15 vebs/min, NE: 1.06+/-0.18 vebs/min (p<0.05 vs. C), NEP: 1.17+/-0.3 vebs/min. CONCLUSION: Norepinephrine confers delayed preconditioning against myocardial stunning via an alpha(1)-adrenoceptor mediated pathway. Norepinephrine-mediated preconditioning involves a beneficial effect towards stunning, but at the expense of a higher rate of postischemic ventricular arrhythmia.

Adrenergic alpha-Agonists↗
PubMed2003

Pharmacokinetics of oral betaine in healthy subjects and patients with homocystinuria.

AIMS: Large oral doses of betaine have proved effective in lowering plasma homocysteine in severe hyperhomocysteinaemia. The pharmacokinetic characteristics and metabolism of betaine in humans have not been assessed and drug monitoring for betaine therapy is not available. We studied the pharmacokinetics of betaine and its metabolite dimethylglycine (DMG) in healthy subjects and in three patients with homocystinuria. METHODS: Twelve male volunteers underwent an open-label study. After one single administration of 50 mg betaine kg-1 body weight and during continuous intake of twice daily 50 mg kg-1 body weight, serial blood samples and 24 h urines were collected to determine betaine and DMG plasma concentrations and urinary excretion, respectively. Patients were evaluated after one single dose of betaine. RESULTS: We found rapid absorption (t(1/2),abs 00.28 h, s.d. 0.17) and distribution (t(1/2), lambda1 00.59 h, s.d. 0.22) of betaine. A Cmax of 0.94 mmol l-1 (s.d. 0.19) was reached after tmax 00.90 h (s.d. 0.33). The elimination half life t(1/2), z was 14.38 h (s.d. 7.17). After repeated dosage, t(1/2), lambda1 (01.77 h, s.d. 0.75) and t(1/2), z (41.17 h, s.d. 13.50) increased significantly (95% CI 0.73, 01.64 h and 19.90, 33.70 h, respectively), whereas absorption remained unchanged. DMG concentrations increased significantly after betaine administration and accumulation occurred to the same extent as with betaine. Renal clearance was low and urinary excretion of betaine was equivalent to 4% of the ingested dose. Distribution and elimination kinetics in homocystinuric patients appeared to be accelerated. CONCLUSIONS: Betaine plasma concentrations change rapidly after ingestion. Elimination half-life increased during continuous dosing over 5 days. Betaine is mainly eliminated by metabolism. More pharmacokinetic and pharmacodynamic studies in hyperhomocysteinaemic patients are needed to refine the current treatment with betaine.

Administration, Oral↗
PubMed2002

Activation of IP and EP(3) receptors alters cAMP-dependent cell migration.

Migration of vascular smooth cells from the media to the intima essentially contributes to neointima formation after percutaneous transluminal angioplasty and stent implantation. The stable prostacyclin mimetic iloprost has been shown to inhibit neointima formation in experimental restenosis, but it is currently unknown whether this may be caused by an antimigratory effect. Hence, the present study analyses (i) the influence of G(s)-coupled prostacyclin (IP) receptors on cell migration and (ii) verifies whether EP(3) receptors with opposite (i.e., G(i)) coupling may conversely stimulate cell migration. In a modified Boyden chamber model, it was shown that iloprost dose-dependently inhibits the migration of primary human arterial smooth muscle cells, which constitutively express the IP receptor. On the other hand, human arterial smooth muscle cell migration was stimulated by the EP(3) receptor agonist M&B 28.767. To independently study the effects of these receptors, IP or EP(3) receptors were stably overexpressed in chinese hamster ovary cells (CHO-IP and CHO-EP(3)). Chemotaxis of CHO cells transfected with G(s)-coupled IP receptors was concentration-dependently inhibited by iloprost (2-100 nM), while there was no effect of iloprost on mock-transfected CHO. By contrast, CHO-cells that overexpressed EP(3) receptors showed a significant, concentration dependent (1-100 nM) increase of cell migration in presence of the selective EP(3) agonist M&B 28.767. It is concluded that the prostacyclin mimetic iloprost inhibits vascular cell migration, which probably depends on a G(s)-mediated increase of intracellular cAMP. EP(3) receptors conversely stimulate CHO migration.

Animals↗
PubMed2002

Flow cytometry analysis of platelet cyclooxygenase-2 expression: induction of platelet cyclooxygenase-2 in patients undergoing coronary artery bypass grafting.

There are conflicting reports about the expression of cyclooxygenase (COX)-2 in human platelets. The present study describes a flow cytometric method for the measurement of platelet COX. Both COX-1 and COX-2 were shown to be expressed in platelets from patients undergoing a coronary artery bypass graft. There was a significant increase in COX-2 expression at day 5 as compared with pre-surgery values (mean fluorescence 12.31 +/- 0.88 versus 9.15 +/- 0.88; means +/- SEM, n = 7, P < 0.05), whereas COX-1 levels did not change (13.45 +/- 1.11 versus 12.38 +/- 1.41; n = 7, P > 0.05).

Aspirin↗