Direct pathway to the brain.

Whole-body autoradiographic stuidies demonstrated that, when isotopically labeled glucose is placed in the ligated oropharynx, there is a rapid movement of the isotope directly to the intracranial cavity. This passage involves nonspecific diflision, bypassing all recognized rouctes to the brain.

L-Ornithine decarboxylase:an essential role in early mammalian embryogenesis.

The highly selective, enzyme-activated, irreversible inhibitor of L-ornithine decarboxylase, DL-alpha-difluoromethylornithine, suppresses the increase in uterine L-ornithine decarboxylase activity associated with early embryogenesis in the mouse and arrests embryonic development at that stage. Contragestational effects were confirmed in the rat and rabbit. An increase in L-ornithine decarboxylase activity that leads to a rapid increase in putrescine concentration appears to be essential during a critical period after implantation for continued mammalian embryonal growth.

Decarboxylated-S-adenosylmethionine excretion: a biochemical marker of ornithine decarboxylase inhibition by alpha-difluoromethylornithine.

In an attempt to define a biochemical marker of ornithine decarboxylase inhibition in humans, alpha-difluoromethylornithine hydrochloride (DFMO), an irreversible ornithine decarboxylase inhibitor, was infused i.v. in seven cancer patients over 10-day courses at doses of 10-90 g/day and 24-h urinary excretion of polyamines and decarboxylated-S-adenosylmethionine was determined before, during, and after treatment. DFMO produces marked increases in urinary decarboxylated-S-adenosylmethionine excretion, up to 84 times pretreatment values. This response appears to be time dependent, requiring several days to reach a maximum and lasting at least 4-5 days after stopping DFMO. In contrast, urinary excretion of the polyamines putrescine, cadaverine, spermidine, N1-monoacetylspermidine, N8-monoacetylspermidine, and spermine, were not consistently altered by DFMO. We conclude that urinary excretion of decarboxylated-S-adenosylmethionine represents a valid biochemical indicator of ornithine decarboxylase inhibition in humans, whereas urinary polyamines are of no value.

Kinetics of the enantiomers of vigabatrin after an oral dose of the racemate or the active S-enantiomer.

Six healthy men received single oral doses of 1500 mg of vigabatrin [(R,S)-gamma-vinyl-GABA] and 750 mg of S(+)-gamma-vinyl-GABA on two occasions. Concentrations of the individual enantiomers were assayed by a stereoselective procedure based on combined GC/MS. At peak, concentrations of the R(-)-enantiomer exceeded concentrations of the S(+)-enantiomer, with an approximate ratio of 2:1. The mean terminal t1/2 ranged from 6 to 8 hours for both enantiomers. Mean urinary recovery of the S(+)-enantiomer was 49% after both doses and was 65% for the R(-)-enantiomer. Plasma concentration values obtained for the S(+)-enantiomer after a dose of the pure S(+)-enantiomer and an equivalent dose of the racemate showed good agreement for both the concentrations observed at any time point and the elimination characteristics, demonstrating bioequivalence. Renal clearance values for the S(+)-enantiomer are not affected by concomitant dosing with the pharmacologically inactive R(-)-enantiomer. No chiral inversion was detected after dosing with the pure S(+)-enantiomer.

Pharmacokinetics of vigabatrin: implications of creatinine clearance.

The pharmacokinetics of both enantiomers of vigabatrin after a single oral dose in healthy young subjects (mean creatinine clearance 120 ml/min) were compared with kinetics in two groups of elderly subjects, one group aged 60 to 75 years (mean creatinine clearance 86 ml/min) and one group aged 76 to 97 years (mean creatinine clearance 30 ml/min). At a dose of 1500 mg, the group with the eldest subjects and the lowest creatinine clearance values showed mean increases of 3.3-fold in the time to reach the maximum concentration, 2.7-fold in the maximum concentration, and 9.8-fold in the AUC; a twofold prolongation of the t1/2; and reduced urinary excretion of the biologically and pharmacologically active S(+)-enantiomer. Changes in the intermediate group were qualitatively similar but quantitatively less. Parallel observations were made for the inactive R(-)-enantiomer. Most of these changes can be related to decreased renal clearance of vigabatrin. No interference of either enantiomer in the renal clearance of the other was noted. A nonlinear relationship between renal clearance and creatinine clearance for both enantiomers is suggested. Knowledge of the patient's renal function and an appropriate dose adjustment will minimize side effects during vigabatrin therapy, especially in elderly patients.

Kinetics of alpha-difluoromethylornithine: an irreversible inhibitor of ornithine decarboxylase.

We gave alpha-difluoromethylornithine (DFMO), a selective, irreversible inhibitor of ornithine decarboxylase, to six health men in single intravenous doses of 5 and 10 mg/kg body weight and oral doses of 10 and 20 mg/kg. Plasma concentrations were monitored during the 24 hr after each dose. Urine was collected from 0 to 24 hr after drug and amount of unchanged drug excreted was determined. Peak plasma concentrations were reached within 6 hr after oral doses. The decay of the plasma concentrations followed first-order kinetics with a mean half-life (t 1/2) for all four doses studied of 199 +/- 6 min (+/- SD). Mean total body clearance (ClT) for the four doses was 1.20 +/- 0.06 ml . min-1 . kg-1. Mean renal clearance was determined as 0.99 +/- 0.03 ml . min-1 . kg-1, accounting for 83% of drug elimination. Mean apparent volume of distribution (aVD) was 0.337 +/- 0.031 l/kg-1, corresponding to 24 l for 70 kg of body weight. The amount of unchanged drug in 24-hr urine samples was 47 +/- 7% and 40 +/- 11% after 10 and 20 mg/kg orally, and 78% and 81 +/- 8% after 5 and 10 mg/kg intravenously. Bioavailability of the 10 mg/kg dose was estimated as 58% from the urinary recoveries and as 54% from the areas under the plasma concentration curves (AUC 0 leads to infinity). Since doubling of the dose resulted in a doubling of the mean AUC 0 leads to infinity and since other kinetic parameters, such as aVD, t 1/2, ClT, and the urinary recovery of unchanged drug, were essentially the same at all doses, DFMO kinetics follow a dose-linear model.

Kinetics of medroxalol, a beta- and alpha-adrenoceptor antagonist.

Eight healthy men received single oral doses of 400, 800, and 1200 mg medroxalol and a single intravenous dose of 1 mg per kg body weight on four occasions separated by at least 2 wk. Plasma medroxalol concentrations were assayed up to 24 hr after each dose by a specific high-pressure liquid chromatographic assay. Urinary excretion of parent compound was determined as well. Following oral doses medroxalol reached peak plasma concentrations within 2.5 to 3 hr. The t 1/2 of the terminal decay phase was 11.1 hr. Mean apparent volume of distribution (aVD) was between 11.2 and 16.4 l/kg, and mean total body clearance (ClT) was between 0.73 and 0.99 l hr-1 kg-1. Mean urinary recovery of parent drug within 48 hr was 2.3%, 3.9%, and 3.6% after the oral doses compared to 8.2% after the intravenous dose. Bioavailability estimated from AUC was 27.2% after 400 mg, 31.3% after 800 mg, and 37.4% after 1200 mg by mouth. Since aVD, t 1/2, ClT, and urinary excretion did not differ significantly after the three oral doses, medroxalol kinetics appear to follow a dose-linear model.

Kinetics of fenoximone, a new cardiotonic, in healthy subjects.

Fenoximone, a new cardiotonic, was given to six healthy men as a single intravenous dose of 1 mg/kg and a single oral dose of 3 mg/kg as solution in a crossover study. Plasma concentrations were monitored for 8 hr and urine was collected for 24 hr. Peak plasma concentrations (Cmax) were reached 30 min after the oral dose. Decay of plasma concentrations was fitted to a mean (+/- SD) elimination t1/2 (t1/2 beta) of 60 +/- 14 min after intravenous injection and 78 +/- 26 min after oral dosing. Mean total body clearance for intravenous dosing was 2062 +/- 846 ml/min, renal clearance (ClR) was 5.3 +/- 2.4 ml/min, and extrapolated volume of distribution was 0.37 +/- 0.26 l/kg. The sulfoxide derivative was detected as the main metabolite. Cmax of the sulfoxide metabolite occurred 10 min after the end of the intravenous infusion and 20 to 60 min after oral dosing. From the decay of the plasma concentrations of the sulfoxide, the t1/2 beta s were calculated as 132 +/- 15 min after intravenous injection and 140 +/- 27 min after oral dosing of fenoximone. ClR of the sulfoxide was 499 +/- 106 ml/min after intravenous injection; 24-hr urinary recovery of the sulfoxide was 75.7% +/- 5.7% after intravenous injection and 64.3% +/- 10.4% after oral dosing. Mean oral bioavailability of fenoximone was 53% (range 44% to 69%).

Failure of oral L-histidine to influence appetite or affect zinc metabolism in man: a double-blind study.

L-Histidine, 4 g/day in gelatin capsules, was administered orally to eight normal volunteers for 2 weeks in a double-blind, balanced, crossover study with 2 weeks of placebo treatment. Body weight, serum and urinary zinc and histidine concentrations, as well as subjective ratings of appetite, taste and smell perception, and food intake were monitored. L-Histidine therapy had no significant effect on appetite, taste and smell perception, food intake, or body weight. Similarly, no effects were observed on total serum zinc, albumin-bound zinc or alpha 2-macroglobulin-bound zinc concentrations, or on urinary histidine excretion. Serum histidine concentrations increased with therapy. Urinary zinc excretion was increased significantly after 1 week, but not after 2 weeks of L-histidine therapy. It can be concluded that oral L-histidine, at the dose used, has no value as an anorectic agent.

Double-blind study of oral gamma-vinyl GABA in the treatment of dystonia.

Six patients with different forms of dystonia were treated with gamma-vinyl GABA, a specific enzyme-activated inhibitor of GABA-transaminase, in a double-blind, placebo-controlled crossover study. gamma-Vinyl GABA therapy, 2 g daily for 2 weeks, was compared with placebo by weekly assessments. There were no consistent changes in three evaluation scores. Agents that augment CNS GABA are unlikely to benefit patients with generalized dystonia.

Gamma-vinyl GABA treatment of Huntington's disease.

In a double-blind, crossover study gamma-vinyl GABA, 2 g/day, and placebo were administered orally for 2 weeks each to six patients with Huntington's disease. Five patients were treated concomitantly with a neuroleptic maintained at constant dose. No consistent beneficial effects on the hyperkinetic movements, abnormal motor function, or ability to carry out normal activities were evident with gamma-vinyl GABA treatment. Treatment was tolerated without clinically significant alterations in the physiologic or biochemical tests used for monitoring. These results suggest that increasing CNS GABAergic function is unlikely to ameliorate Huntington's disease.

Biochemical and clinical effects of gamma-vinyl GABA in patients with epilepsy.

In a pilot single-blind study, gamma-vinyl GABA, an enzyme-activated irreversible inhibitor of GABA-transaminase (GABA-T), was administered orally to 10 epileptic patients who were refractory to conventional anticonvulsant therapy. Daily doses of 1 g and 2 g for 2 weeks each as add-on therapy were followed by 2 weeks of placebo treatment. CSF obtained from suboccipital and lumbar punctures demonstrated dose-related increases in concentrations of free and total GABA and homocarnosine with treatment, but no changes in 5-hydroxyindoleacetic acid or homovanillic acid levels, indicating effective and selective CNS GABA-T inhibition. These biochemical changes were associated with decreased seizure frequency in seven patients, decreased seizure severity in one, no change in one, and possible worsening in one. gamma-Vinyl GABA may be useful in the therapy of epilepsy.

Treatment of Huntington disease with gamma-acetylenic GABA an irreversible inhibitor of GABA-transaminase: increased CSF GABA and homocarnosine without clinical amelioration.

gamma-Acetylenic GABA (GAG, RMI 71.645), a potent irreversible inhibitor of gamma-aminobutyric acid transaminase, was given orally in various dosage schedules to 14 patients with Huntington disease. The biochemical effects of the drug on cerebrospinal fluid (CSF) concentrations of gamma-aminobutyric acid (GABA) and the GABA-containing dipeptide, homocarnosine, were measured in 10 of 14 patients. Treatment with GAG increased CSF concentrations of GABA and homocarnosine as compared to pretreatment values, suggesting that the drug increased brain GABA concentration. Despite this neurochemical effect, the clinical state was not improved. Except for single seizure episodes in five patients, GAG therapy was well tolerated. These results do not exclude the possibility that agents that augment CNS GABAergic function may prove useful in therapy of Huntington disease.

Difluoromethylornithine, an effective new treatment of Gambian trypanosomiasis. Results in five patients.

Recent studies have shown DL-alpha-difluoromethylornithine (eflornithine), an inhibitor of polyamine biosynthesis, to be curative in various Trypanosoma species infections of laboratory animals. Five patients are described with Gambian trypanosomiasis treated in Belgium with difluoromethylornithine, using various intravenous and oral dosage schedules. Three patients had late-stage and two had early-stage disease. Difluoromethylornithine treatment was associated with clearing of parasites from blood within one to four days, a trend towards normalization of all altered biologic values associated with the disease, and marked amelioration of clinical symptoms. Side effects of difluoromethylornithine, including loose stools in three patients and both anemia, and a decrease in auditory acuity in one patient, were mild, transient, and never required interruption of drug treatment. The presence of difluoromethylornithine in cerebrospinal fluid, determined in three patients, demonstrated that difluoromethylornithine penetrates into the central nervous system. In three patients, follow-up of at least 24 months after treatment demonstrated a continued healthy state without evidence of relapse. These promising, albeit preliminary, results of difluoromethylornithine therapy, even in patients with central nervous system involvement, indicate that extended clinical trials are warranted to determine the optimal dosage regimen in patients with early- and late-stage disease.

Effect of elevated brain GABA concentrations on the actions of bicuculline and picrotoxin in mice.

gamma-Acetylenic GABA and gamma-vinyl GABA, two catalytic irreversible inhibitors of mammalian brain GABA transaminase that produce several-fold increases in brain GABA concentrations were tested for their effects on bicuculline and picrotoxin-induced seizures and mortality in mice. Neither inhibitor influenced the frequency of seizures or death produced by either bicuculline or picrotoxin. Both inhibitors, however, produced a dose-dependent prolongation of the time to onset of seizures and death induced by picrotoxin but by bicuculline. These results suggest differences in the antagonism by bicuculline and picrotoxin of GABA-mediated neural functions.

Treatment of human late stage gambiense trypanosomiasis with alpha-difluoromethylornithine (eflornithine): efficacy and tolerance in 14 cases in Côte d'Ivoire.

alpha-Difluoromethylornithine (DFMO; eflornithine), an inhibitor of polyamine biosynthesis, was used to treat 14 patients with late stage gambiense sleeping sickness, 12 cases having been previously treated with and considered refractory to melarsoprol. alpha-Difluoromethylornithine was administered intravenously at a dose of 400 mg/kg/day for 14 days followed by oral treatment, 300 mg/kg/day, for 21-28 days. In all patients treatment was associated with rapid disappearance of trypanosomes from body fluids (in several cases within 24 hr) and decreased cerebrospinal fluid white blood cell counts. In all but one patient, who died of a pulmonary infection during treatment, alpha-difluoromethylornithine produced a dramatic reversal of clinical signs and symptoms of the disease. Determination of drug concentrations in serum and cerebrospinal fluid of 5 patients demonstrated that alpha-difluoromethylornithine diffuses into the central nervous system with cerebrospinal fluid levels representing up to 51% of corresponding serum concentrations. Diarrhea, abdominal pain, and anemia were the most frequent side effects associated with therapy, but were reversible and did not necessitate discontinuation of treatment. Four patients have been followed for more than 2 years post-treatment without evidence of relapse.

Pharmacokinetics and tolerability of intravenous trecovirsen (GEM 91), an antisense phosphorothioate oligonucleotide, in HIV-positive subjects.

Trecovirsen, a 25-mer antisense phosphorothioate oligonucleotide targeted at the gag site of the HIV gene, was administered to HIV-positive volunteers as an i.v. infusion. Single doses ranged from 0.1 to 2.5 mg/kg in an ascending escalation in cohorts of 6 to 12 subjects. Plasma trecovirsen concentrations and pharmacokinetic parameters could be assessed at doses > or = 0.3 mg/kg. Peak plasma concentrations and AUC values increased disproportionately with increasing dose while elimination half-life increased and plasma clearance decreased, indicating a saturable process over this dose range. The only significant adverse event observed was an isolated, transitory increase in activated partial thromboplastin time at doses > or = 2.0 mg/kg that was related to plasma trecovirsen concentrations and is attributed to the polyanionic character of the molecule. Thus, trecovirsen administration was well tolerated in single i.v. doses up to 2.5 mg/kg.

Treatment of acute myeloid leukemia and blastic phase of chronic myeloid leukemia with combined eflornithine (alpha difluoromethylornithine) and methylglyoxal-bis-guanyl hydrazone (methyl-GAG).

A combined eflornithine-MGBG treatment was studied in patients with acute myeloid leukemia (AML) or blastic transformation of chronic myeloid leukemia (BT CML). The first ten patients (5 AML, 5 BT CML) received i.v. or p.o. eflornithine 6 g m-2 day-1 and i.v. MGBG 500 mg/m2 once a week. The duration of treatment was 5-37 days (median 15) with one to five MGBG infusions (median 2). The results were complete response (CR) in one patient, partial response (PR) in four, minimal response (MR) in one and failure (F) in four. Pronounced side effects, including severe mucositis, gastrointestinal disturbances and skin infiltration, were observed in eight patients. As the four PRs were achieved in patients with BT CML, it was decided also to study ten patients with this indication. In attempts to decrease the incidence and severity of unwanted effects, lower doses of eflornithine-MGBG were used, i.e., eflornithine 4 g m-2 day-1 and MGBG 200 mg m-2 once a week. The duration of treatment was 9-110 days (median 46), with 2-14 MGBG infusions (median 6). Responses observed were CR in two patients (in one of whom it was only transient), transient PR in two, transient MR in four, and F in two. Treatment at lower doses was better tolerated, thus allowing a longer duration of treatment. Five of ten patients had moderate or severe gastrointestinal disturbances and one patient had a severe subjective hearing loss. The eflornithine-MGBG combination may prove to be a useful alternative treatment for AML and BT CML, but comparative trials will ultimately be necessary for a more definitive assessment of the combination.

Audiogenic seizure protection by elevated brain GABA concentration in mice: effects of gamma-acetylenic gaba and gamma-vinyl GABA, two irreversible GABA-T inhibitors.

gamma-Acetylenic GABA and gamma-vinyl GABA, two catalytic irreversible inhibitors of GABA-transaminase, produce marked and sustained elevations in mouse brain GABA concentrations and protect DBA/2 mice against audiogenically induced seizures in a similar dose and time-dependent manner. The acetylenic analog also inhibits GAD activity while the vinyl compound has minimal activity against this enzyme. The increase in brain GABA concentrations induced by these compounds correlates well with attenuation of audiogenic seizure intensity (r = 0.991 and 0.962 for gamma-acetylenic and gamma-vinyl GABA respectively) and with degree of seizure protection (r = 0.974 and 0.834). Seizure intensity is reduced by 50% when brain GABA is increased to 265% and 264% of control values by the two inhibitors and seizure incidence is halved at 322% and 324%. Thus, audiogenic seizure protection in genetically susceptible mice is apparently a function of whole brain GABA concentrations.

The effect of gamma-acetylenic GABA, an enzyme-activated irreversible inhibitor of GABA-transaminase, on dopamine pathways of the extrapyramidal and limbic systems.

gamma-Acetylenic GABA (100 mg/kg i.p.) inhibited GABA-transaminase activity and caused a several-fold increase in the concentration of GABA in rat brain. This increased GABA concentration was associated with a decreased rate of dopamine depletion following alpha-methyl-p-tyrosine treatment and a decrease in homovanillic acid in extrapyramidal and limbic structures suggesting a decrease in dopamine turnover in both pathways. In addition, gamma-acetylenic GABA injected into the ventral mesencephalic tegmentum decreased dopamine turnover in the mesolimbic forebrain. These results are consistent with a modulatory function of GABAergic neurons on extrapyramidal and limbic dopamine pathways. Inhibitory effects on dopaminergic functions of the extrapyramidal and limbic systems were also indicated by the amphetamine and apomorphine-induced ipsilateral turning after unilateral substantia nigral injections of gamma-acetylenic GABA and by the attenuation of dopamine-induced hypermotility after bilateral injections of gamma-acetylenic GABA into the nucleus accumbens.