Christoph H. Gleiter

Erythropoietin and erythropoietin receptor in human ischemic/hypoxic brain

Abstract. Using immunohistochemistry, expression of erythropoietin (EPO), a hypoxia-inducible neuroprotective factor, and its receptor (EPOR) were investigated in human brain tissue after ischemia/hypoxia. Autopsy brains of neuropathologically normal subjects were compared to those with ischemic infarcts or hypoxic damage. In normal brain, weak EPO/EPOR immunoreactivity was mainly neuronal. In fresh infarcts, EPO immunoreactivity appeared in vascular endothelium, EPOR in microvessels and neuronal fibers. In older infarcts reactive astrocytes exhibited EPO/EPOR immunoreactivity. Acute hypoxic brain damage was associated with vascular EPO expression, older hypoxic damage with EPO/EPOR immunoreactivity in reactive astrocytes. The pronounced up-regulation of EPO/EPOR in human ischemic/hypoxic brains underlines their role as an endogenous neuroprotective system and suggests a novel therapeutic potential in cerebrovascular disease for EPO, a clinically well-characterized and safe compound.

Measurement of free and bound malondialdehyde in plasma by high-performance liquid chromatography as the 2,4-dinitrophenylhydrazine derivative

We established a method for the detection of free and total (free and bound) malondialdehyde (MDA) in human plasma samples after derivatisation with 2,4-dinitrophenylhydrazine (DNPH). Free MDA was prepared by perchloric acid deproteinisation whereas an alkaline hydrolysation step for 30 min at 60 degrees C was introduced prior to protein precipitation for the determination of total MDA. Derivatisation was accomplished in 10 min at room temperature subsequently chromatographed by HPLC on a reversed-phase 3 microm C(18) column with UV detection (310 nm). The detection limit was 25 pmol/ml for free and 0.3 nmol/ml for total MDA. The recovery of MDA added to different human plasma samples was 93.6% (n=11; RSD 7.1%) for the hydrolysation procedure. In samples from 12 healthy volunteers who underwent a hypoxic treatment (13% O2 for 6 h) we estimated a baseline value of total MDA of 2.16 nmol/ml (SD 0.29) (ambient air) with a significant increase to 2.92 (nmol/ml, SD 0.57; P=0.01) after the end of this physiological oxidative stress challenge. Plasma values of free MDA in these samples were close to our detection limit. The presented technique can easily performed with an isocratic HPLC apparatus and provides highly specific results for MDA as do sophisticated GC-MS methods.

Monoamine Oxidase Inhibitors

Monoamine oxidase inhibitors (MAOIs) are mainly used in psychiatry for the treatment of depressive disorders and in neurology for the treatment of Parkinson’s disease. While the classical, nonselective and nonreversible MAOIs, such as phenelzine and tranylcypromine, are characterised by the risk of inducing a hypertensive crisis when dietary tyramine is ingested, the selective monoamine oxidase-B (MAO-B) inhibitor selegiline (deprenyl) and, even more so, the selective and reversible monoamine oxidase-A (MAO-A) inhibitor moclobemide, are free from this potential interaction.Drug tolerability data for the elderly show that moclobemide is one of the most well tolerated compounds. Selegiline, especially when used in combination with levodopa, can cause anorexia, dry mouth, dyskinesia and, most problematic, orthostatic hypotension. For the traditional MAOIs, phenelzine and tranylcypromine, published data are insufficient to be able to give a conclusive tolerability statement regarding the use of these compounds in elderly people. Although orthostatic hypotension occurs in most patients treated with traditional MAOIs, the incidence in elderly patients with depression does not appear to be greater than that reported with tricyclic antidepressants.

Dexamethasone down‐regulates the expression of L‐selectin on the surface of neutrophils and lymphocytes in humans*

On the basis of previous animal studies, we hypothesized that dexamethasone may reduce the expression of L‐selectin on neutrophils and lymphocytes in healthy men.

Influence of food intake on the bioavailability of thioctic acid enantiomers

Recent controlled clinical trials have demonstrated that long-term administration of 600 mg thioctic acid (TA, R(+)-TA, S([)-TA; a-lipoic acid), once daily, can improve symptoms of peripheral and autonomic neuropathy in patients with diabetes mellitus (Ziegler et al. 1995). In diabetic patients the bioavailability of drugs may be decreased by delayed gastric emptying (due to autonomic neuropathy) and the interaction of drugs with food retained in the stomach. Therefore, the present trial investigated whether a pharmacokinetic interaction between food and TA takes place.

Decreased Neuroendocrine Responses to Meta-Chlorophenylpiperazine (m-CPP) but Normal Responses to Ipsapirone in Marathon Runners

Several clinical studies suggest antidepressive and anxiolytic effects of regular aerobic exercise. To study the effects of exercise on central serotonergic receptor sensitivity, we performed neuroendocrine challenges using oral doses of meta-chlorophenylpiperazine (m-CPP, 0.4 mg/kg), ipsapirone (0.3 mg/kg) and placebo in 12 marathon runners and 12 healthy controls not practicing regular exercise. After administration of the nonselective serotonergic agonist m-CPP, which exerts a number of well-reproducible effects mainly by means of its action on 5-HT2C receptors, marathon runners showed a significantly reduced cortisol response in comparison to the control group. There was also a statistical trend toward a blunted prolactin response after m-CPP in the athlete group. In contrast, the increase of cortisol and the hypothermia observed after administration of the 5-HT1A agonist ipsapirone were of the same magnitude in both groups. The behavioral response to m-CPP or ipsapirone and the mean maximal increases of plasma adrenaline and noradrenaline did not differ between the marathon and the control group. In conclusion, exercise-induced downregulation of 5-HT2C receptors could play an important role in mediating the anxiolytic and antidepressive effects of exercise.

Dose-dependent effect of angiotensin II on human erythropoietin production

Current evidence suggests that angiotensin II may be involved in the regulation of renal erythropoietin (EPO) production. The present study assessed the role of angiotensin II (Axa0II) in different doses in the control of EPO production in humans. In a parallel, randomized, placebo-controlled open design, 60 healthy male volunteers received a 6-h intravenous infusion of: placebo (placebo, electrolyte solution), a pressor dose of Axa0II (1–3xa0µg/min; Axa0II press), a combination of a pressor dose of Axa0II and the selective AT1-receptor blocker losartan, 50xa0mg (Axa0II press + L), a subpressor dose of Axa0II (0.0375–0.15xa0µg/min; Axa0II subpress) and a combination of a subpressor dose of Axa0II and losartan (Axa0II subpress + L). Axa0II press treatment resulted in a significant increase of the maximum EPO concentration (CmaxEPO, 41% higher versus placebo) and the amount of EPO produced in 24xa0h (AUCEPO(0–24xa0h), 61% larger versus placebo), Axa0II subpress treatment increased CmaxEPO (35% higher versus placebo) and AUCEPO(0–24xa0h) (34% larger versus placebo). Axa0II press + L and Axa0II subpress + L treatments did not significantly increase CmaxEPO and AUCEPO(0–24xa0h) compared to placebo. Axa0II affects EPO production in a dose-dependent manner. The signal seems to be mediated via AT1-receptors. Axa0II appears to be one modulator EPO production in humans.

When Are Bioavailability Studies Required? A German Proposal

The Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM), the German drug regulation authority, issued guidelines for determining whether bioavailability/bioequivalence studies are required for certain drugs. This decision tree is based on pharmacodynamic, pharmacokinetic, and physicochemical criteria. Details of this decision tree were worked out by an expert panel, the Bioavailability Commission at the BfArM. The decision tree has been in use by German regulatory authorities for more than 10 years. In the meantime, its essentials were adopted by the European Committee for Proprietary Medicinal Products (CPMP) and by the World Health Organization (WHO) for their “Guidelines on interchangeability of multisource pharmaceutical products.” This article reviews the original decision tree of the BfArM and provides examples of drugs that have been assessed according to its rules. The current procedure of the German regulatory authorities for judging the necessity of bioavailability trials, which reflects the status quo of regulatory practice in Germany, is also discussed.

Bioinequivalence and Drug Toxicity How Great is the Problem and What Can Be Done

Following the expiration of the original manufacturers patent, competition usually provides a wealth of apparently exchangeable generic drug products, socalled interchangeable multisource pharmaceutical products. As these products do not need expensive development programmes they can be priced very competitively. Increasing cost containment of healthcare systems in most industrialised countries forces physicians to exchange original brands for the less expensive generic alternatives. In the past, there have been problems with multisource pharmaceuticals due to a lack of bioequivalence. Therefore, most major drug regulatory agencies have set up guidelines in recent years . These guidelines provide rules for the testing of generic products to assure the bioequivalence of multi source pharmaceuticals. Other indications for the testing of bioequivalence are changes of the manufacturing process, e.g. changes of the formulation of an already marketed drug, or during the development process when a preliminary formulation is replaced by the final product that is intended to be marketed. The use of generics has been advocated for years for economic reasons. For instance, in the US the use of generics has risen from 10% in 1975 to 15% in 1983 and 21 % by 1986.[1] A similar trend can be seen in all major industrialised countries. These numbers highlight the order of magnitude of the problem for drug safety. This article prvides definitions of the terms and demonstrates the need for bioequivalence testing by briefly summarising the history of this issue up to the present. Further, it focuses on what has been achieved for drug safety of interchangeable multisource pharmaceuticals, and on problems that are still to be solved.

Pharmacokinetics of doxepin and desmethyldoxepin: an evaluation with the population approach

HeadingAbstractn Objective. Little information on the population pharmacokinetics of the tricyclic antidepressant doxepine and its pharmacologically active metabolite desmethyldoxepine is available. However, a more individualised drug therapy may be feasible if the influence of various patient characteristics on plasma concentration was known.n Patients and methods. We retrospectively analysed pharmacokinetic therapeutic drug-monitoring data in 114 psychiatric patients (79 females, 35 males) treated with doxepine for a period of 22–306xa0days, mostly due to major depression. The data were analysed using the computer program NONMEM. For both, doxepine and its metabolite desmethyldoxepine, a one-compartment model was chosen. Pharmacokinetic parameters clearance (CL/F) and volume of distribution (V/F) of doxepine and desmethyldoxepine were modelled in terms of both random and fixed effects.n Results. The fit of the model to the concentration–time data was significantly improved when V/F was expressed as a function of weight (P<0.05) and CL/F as a function of age (P<0.05). Co-medication that inhibits P450 isoenzymes lowered CL/F of doxepine by 15%.n Conclusion. The analysis indicates that the factors age and, to some extent, body weight may be a guidance for individual doxepine dose regimens, which however needs confirmation in prospective clinical trials linking pharmacokinetics and therapeutic effect. Co-medication may represent only a minor important covariate.