Lack of circadian rhythm in plasma levels of 3,4-dihydroxyphenylethyleneglycol in healthy human subjects

Steady-state pharmacokinetics and pharmacodynamics of CHF3381, a novel antineuropathic pain agent, in healthy subjects

AIMS

To evaluate the safety, tolerability, pharmacokinetic and pharmacodynamic profiles of CHF3381, a dual NMDA and MAO-A inhibitor, after multiple oral doses in healthy subjects.

METHODS

Forty-eight young males received CHF3381 at doses of 100 mg twice daily, 200 mg twice daily, 400 mg twice daily or placebo for 2 weeks according to a double-blind, randomized, parallel group design. Plasma and urine concentrations of the parent drug and of two major metabolites (CHF3567 and 2-aminoindane) were measured over time. MAO-A activity in plasma was estimated by measuring plasma concentrations of 3,4-dihydroxyphenylglycol. Sustained attention, memory and sedation were assessed throughout the study with standard psychometric tests.

RESULTS

Most of the adverse events were mild in intensity, with dose regimens of 100 mg twice daily and 200 mg twice daily being indistinguishable from placebo. After 400 mg twice daily, the most frequent adverse events were mild dizziness, asthenia and insomnia. At steady-state, 400 mg twice daily slightly increased supine heart rate (+ 9 +/- 2 beats min(-1)) and diastolic blood pressure (+6 +/- 2 mmHg) compared with placebo. There were no dose-dependent or consistent effects of CHF3381 on attention, motor co-ordination or memory, but 400 mg twice daily significantly decreased alertness compared with placebo. Plasma concentrations of CHF3381 peaked at around 3 h and were dose-proportional. The elimination half-life of CHF3381 was estimated to be 4-6 h. At steady-state, significant CHF3381 plasma concentrations were detected at predose with a modest accumulation (1.3-1.5 times), showing that the drug given twice daily is active over the entire 24 h period. Plasma concentrations of CHF3567 and of 2-aminoindane were also proportional to the dose of CHF3381. CHF3381 dose-dependently inhibited MAO-A activity with peak effects at steady-state of 27 +/- 4%, 46 +/- 2% and 65 +/- 5% after 100 mg twice daily, 200 mg twice daily and 400 mg twice daily, respectively. There were no significant effects of CHF3381 on attention (rapid visual information processing), motor co-ordination (body sway) or memory (learning memory task) at any of the doses. At steady-state, there was a significant decrease in alertness (Bond & Lader visual analogue scale) in the 400 mg twice daily group compared with placebo.

CONCLUSIONS

A twice daily regimen of CHF3381 appears to be adequate from a pharmacokinetic and pharmacodynamic perspective. Plasma concentrations reached with 400 mg twice daily exceeded those observed in animals receiving pharmacologically active doses in chronic pain models.

Pharmacodynamics and pharmacokinetics of two dose regimens of befloxatone, a new reversible and selective monoamine oxidase inhibitor, at steady state in healthy volunteers

The pharmacodynamic equipotency of 2 dose regimens (5 mg twice daily versus 10 mg once daily) of befloxatone, a new reversible and selective monoamine oxidase A (MAO-A) inhibitor, after single and multiple doses for 6 days was examined in a randomized, double-blind, three-way crossover, placebo-controlled trial of 12 healthy volunteers. Plasma levels of the deaminated metabolite 3-4 dihydroxyphenylglycol (DHPG), as measured by high-performance liquid chromatography (HPLC) with coulometric electrochemical detection, were used as an index of MAO inhibition. A single dose of befloxatone produced a significant dose-related reduction in plasma DHPG levels, as shown by the decrease in the 24-hour area under the concentration-time curve (AUC0-24) of DHPG, which peaked 2 hours after administration and persisted over 24 hours. Both dose regimens provided equipotent extent and duration of MAO-A inhibition at steady state, suggesting a once daily dosage should be sufficient for most patients. The pharmacokinetic bioavailability at steady state of both dose regimens was also similar. The concentration-time effect curve after a single dose revealed a hysteresis corresponding to the delay necessary to elicit MAO inhibition and/or elimination of DHPG. The relationship between plasma levels of DHPG and/or elimination of plasma concentrations of DHPG and befloxatone after a single dose can be modeled using the Emax model with a mean EC50 of 4.75 ng/mL, and suggests the presence of a maximal response from the single dose. This model permits prediction of steady-state levels of DHPG.

Selectivity of MDL 72,974A for MAO-B inhibition based on substrate and metabolite concentrations in plasma

Plasma concentrations of 3,4-dihydroxyphenylethylglycol (DOPEG), noradrenaline (NA), adrenaline (A), 3,4-dihydroxyphenylalanine (DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), dopamine (DA) and phenylethylamine (PEA) were analyzed in samples taken prior to, during and following the administration of single, daily doses of 12 or 24 mg MDL 72,974A to healthy male volunteers. No effects on the concentrations of DOPA, A, DA or DOPAC were seen during the administration of either dose over 10 days. No treatment-related changes in the concentration of NA were evident at either dose. No changes in DOPEG or PEA concentrations were seen with the 12 mg dose; however, small but significant decreases in plasma DOPEG concentrations and a significant increase in PEA were seen during the administration of the 24 mg dose. This would suggest that at the 24 mg dose some intraneuronal inhibition of MAO-A may be occurring although the lack of increases in NA and A concentrations indicates no accompanying change in sympatho-adrenal activity. Plasma PEA concentrations do not provide a more sensitive or functional indication of MAO-B inhibition. The increase in PEA concentrations at the higher dose may suggest that the inhibition of both forms of the enzyme is necessary to increase its plasma concentration.

Biogenic amines and their metabolites in body fluids of normal, psychiatric and neurological subjects

The biogenic monoamines and their metabolites have been isolated, identified and quantified in human body fluids over the past forty years using a wide variety of chromatographic separation and detection techniques. This review summarizes the results of those studies on normal, psychiatric and neurological subjects. Tables of normal values and the methods used to obtain them should prove to be useful as a reference source for benchmark amine and metabolite concentrations and for successful analytical procedures for their chromatographic separation, detection and quantification. Summaries of the often contradictory results of the application of these methods to psychiatric and neurological problems are presented and may assist in the assessment of the validity of the results of experiments in this field. Finally, the individual, environmental and the methodological factors affecting the concentrations of the amines and their metabolites are discussed.

Assay of catecholamines and dihydroxyphenylethyleneglycol in human plasma and its application in orthostasis and mental stress

A high performance liquid chromatographic method involving electrochemical detection is described which permits the assay of noradrenaline (NA), adrenaline (A), dopamine (DA), and dihydroxyphenylethyleneglycol (DOPEG) in human plasma and brings about analytical recoveries of 70% and more. This method was used to assess the effects of graded orthostasis and mental stress on the plasma levels of these catechols. Orthostasis elicited increases in plasma NA and DOPEG, but did not cause any change in plasma A and DA. The increases in NA and DOPEG were dependent on the degree of orthostasis and correlated closely (rs = 0.724; n = 30, P less than 0.001). Pretreatment with desipramine abolished the DOPEG response to standing, indicating that orthostasis - induced increases in plasma DOPEG are presynaptic in origin. Mental stress evoked pronounced increases in plasma A, less pronounced increases in plasma NA and no changes in plasma DA and DOPEG. Hence, the simultaneous measurement of plasma NA and DOPEG may help to distinguish between various types of activation of the sympathetic nervous system.

Plasma dihydroxyphenylglycol and the intraneuronal disposition of norepinephrine in humans

We examined plasma levels of the sympathetic neurotransmitter norepinephrine (NE) and its deaminated metabolite dihydroxyphenylglycol (DHPG) during supine rest in healthy human subjects and in sympathectomized patients, during physiological (tilt) or pharmacological (yohimbine, clonidine) manipulations known to affect sympathetically mediated NE release, during blockade of neuronal uptake of NE (uptake-1) using desipramine, and during intravenous infusion of NE. Healthy subjects had a mean arteriovenous increment in plasma DHPG in the arm (10%, P less than 0.05), whereas sympathectomized patients had a mean arteriovenous decrement in DHPG in the affected limb (mean decrease 21%, P less than 0.05 compared with healthy subjects). Tilt and yohimbine, which stimulate, and clonidine, which inhibits, release of endogenous NE, produced highly correlated changes in plasma NE and DHPG (r = 0.94). Pretreatment with desipramine abolished DHPG responses to yohimbine while enhancing NE responses. To attain a given increase in plasma DHPG, about a tenfold larger increment in arterial NE was required during NE infusion than during release of endogenous NE. When plasma NE was markedly suppressed after administration of clonidine, plasma DHPG decreased to a plateau level of 700-800 pg/ml. The results indicate that (i) plasma DHPG in humans is derived mainly from sympathetic nerves; (ii) increments in plasma DHPG during stimulation of NE release result from uptake of NE into sympathetic nerve endings and subsequent intraneuronal conversion to DHPG; (iii) plasma DHPG under basal conditions probably is determined mainly by net leakage of NE into the axonal cytoplasm from storage vesicles; and (iv) increments in NE concentrations at neuronal uptake sites can be estimated by simultaneous measurements of DHPG and NE during NE infusion and NE release. Measurement of NE and DHPG provides unique clinical information about sympathetic function.