Potential repurposing of known drugs as potent bacterial ß-glucuronidase inhibitors.

The active metabolite of the chemotherapeutic irinotecan, SN-38, is detoxified through glucuronidation and then excreted into the gastrointestinal tract. Intestinal bacteria convert the glucuronidated metabolite back to the toxic SN-38 using ß-glucuronidase (GUS), resulting in debilitating diarrhea. Inhibiting GUS activity may relieve this side effect of irinotecan. In this study, we sought to determine whether any known drugs have GUS inhibitory activity. We screened a library of Food and Drug Administration-approved drugs with a cell-free biochemical enzyme assay using purified bacterial GUS. After triage, five drugs were confirmed to inhibit purified bacterial GUS. Three of these were the monoamine oxidase inhibitors nialamide, isocarboxazid, and phenelzine with average IC(50) values for inhibiting GUS of 71, 128, and 2300 nM, respectively. The tricyclic antidepressant amoxapine (IC(50) = 388 nM) and the antimalarial mefloquine (IC(50) = 1.2 µM) also had activity. Nialamide, isocarboxazid, and amoxapine had no significant activity against purified mammalian GUS but showed potent activity for inhibiting endogenous GUS activity in a cell-based assay using living intact Escherichia coli with average IC(50) values of 17, 336, and 119 nM, respectively. Thus, nialamide, isocarboxazid, and amoxapine have potential to be repurposed as therapeutics to reduce diarrhea associated with irinotecan chemotherapy and warrant further investigation for this use.

The effects of phenelzine and other monoamine oxidase inhibitor antidepressants on brain and liver I2 imidazoline-preferring receptors.

1. The binding of [3H]-idazoxan in the presence of 10(-6) M (-)-adrenaline was used to quantitate I2 imidazoline-preferring receptors in the rat brain and liver after chronic treatment with various irreversible and reversible monoamine oxidase (MAO) inhibitors. 2. Chronic treatment (7-14 days) with the irreversible MAO inhibitors, phenelzine (1-20 mg kg-1, i.p.), isocarboxazid (10 mg kg-1, i.p.), clorgyline (3 mg kg-1, i.p.) and tranylcypromine (10 mg kg-1, i.p.) markedly decreased (21-71%) the density of I2 imidazoline-preferring receptors in the rat brain and liver. In contrast, chronic treatment (7 days) with the reversible MAO-A inhibitors, moclobemide (1 and 10 mg kg-1, i.p.) or chlordimeform (10 mg kg-1, i.p.) or with the reversible MAO-B inhibitor Ro 16-6491 (1 and 10 mg kg-1, i.p.) did not alter the density of I2 imidazoline-preferring receptors in the rat brain and liver; except for the higher dose of Ro 16-6491 which only decreased the density of these putative receptors in the liver (38%). 3. In vitro, phenelzine, clorgyline, 3-phenylpropargylamine, tranylcypromine and chlordimeform displaced the binding of [3H]-idazoxan to brain and liver I2 imidazoline-preferring receptors from two distinct binding sites. Phenelzine, 3-phenylpropargylamine and tranylcypromine displayed moderate affinity (KiH = 0.3-6 microM) for brain and liver I2 imidazoline-preferring receptors; whereas chlordimeform displayed high affinity (KiH = 6 nM) for these receptors in the two tissues studied, Clorgyline displayed very high affinity for rat brain (KiH = 40 pM) but not for rat liver I2 imidazoline-preferring receptors (KiH = 169 nM). 4. Preincubation of cortical or liver membranes with phenelzine (10-4 M for 30 min) did not alter the total density of I2 imidazoline-preferring receptors, indicating that this irreversible MAO inhibitor does not irreversibly bind to I2 imidazoline-preferring receptors. In contrast, preincubation with 10-6 Mclorgyline reduced by 40% the Bmax of [3H]-idazoxan to brain and liver I2 imidazoline-preferring receptors.5. Chronic treatment (7 days) with the inducers of cytochrome P-450 enzymes phenobarbitone (40 or 80 mg kg-1, i.p.), 3-methylcholanthrene (20 mg kg-1, i.p.) or 2-methylimidazole (40 mg kg-1, i.p.) did not alter the binding parameters of [3H]-idazoxan to brain and liver 12 imidazoline-preferring receptors.The compound SKF 525A, a potent inhibitor of cytochrome P-450 enzymes which forms a tight but reversible complex with the haemoprotein, completely displaced with moderate affinity (KiH = 2-10 microM)the specific binding of [3H]-idazoxan to brain and liver 12 imidazoline-preferring receptors. Preincubation of total liver homogenates with 3 x 10-4 M phenelzine in the presence of 10-3 M NADH, a treatment that irreversibly inactivates the haeme group of cytochrome P-450, did not reduce the density of liver I2 imidazoline-preferring receptors. These results discounted a possible interaction of [3H]-idazoxan with the haeme group of cytochrome P-450 enzymes.6. Together the results indicate that the down-regulation of I2 imidazoline-preferring receptors is associated with an irreversible inactivation of MAO (at least in the brain) that is not related either to the affinity of the MAO inhibitors for I2 imidazoline-preferring receptors or to an irreversible binding to these putative receptors. These findings indicate a novel effect of irreversible MAO inhibitors in the brain and suggest a new target for these compounds that could be of relevance in the treatment of depression, a disease in which an increased density of brain I2 imidazoline-preferring receptors has been reported.

The effect of the monoamine oxidase inhibitor isocarboxazid on the canine metabolism of the cell-differentiating agent hexamethylene bisacetamide.

The acute toxicities of the cellular differentiating agent hexamethylene bisacetamide (HMBA) in humans and animals include CNS toxicity (agitation, somnolence, seizures, hallucinations) and an anion-gap metabolic acidosis. N-Acetyl-1,6-diaminohexane (NADAH), the first metabolite of HMBA, is as active as the parent compound in causing differentiation of leukemic cells in vitro, whereas 6-acetamidohexanoic acid (6AcHA), which is formed by the oxidation of NADAH in the presence of monoamine oxidase (MAO) and aldehyde dehydrogenase, is inactive. To test whether the inhibition of MAO blocks the production of an inactive and possibly toxic HMBA metabolite (6AcHA) or increases the amount of active compounds (HMBA + NADAH) in vivo, we investigated the effect of the MAO inhibitor isocarboxazid on the metabolism and toxicity of HMBA in beagle dogs. Two groups of dogs, composed of one male and one female dog per group, were used in the study. One group received isocarboxazid (3.3 mg/kg p.o. q8h x 9) beginning at 24 h before the initiation of a 48-h i.v. infusion of HMBA (40 mg kg-1 h-1), whereas the other received placebo in an identical fashion prior to the start of an identical HMBA infusion. The mean plasma steady-state concentration (css) of HMBA was 0.91 mM in dogs given HMBA and isocarboxazid as opposed to 0.78 mM in those given HMBA and placebo. As measured spectrophotometrically, plasma MAO activity was inhibited by 86% +/- 3% in dogs receiving isocarboxazid. Gas chromatography/mass spectrometry detected 6AcHA in the plasma of animals that were given placebo but not in the plasma of dogs that received isocarboxazid. Gas chromatographic analysis of urine samples revealed that the total amount of 6AcHA and of NADAH excreted in urine was 8 times less and 3 times greater, respectively, in isocarboxazid-treated dogs than in animals that received HMBA and placebo. One dog was excitable after the initial two doses of isocarboxazid and developed seizures at the end of the HMBA infusion. Another dog was agitated during treatment with HMBA and isocarboxazid. No CNS toxicity occurred in animals that were treated with HMBA and placebo. We conclude that isocarboxazid inhibits the production of 6AcHA in vivo, thus supporting the involvement of MAO in HMBA metabolism. Because the combination of HMBA and isocarboxazid produces CNS toxicity, 6AcHA is probably not the neurotoxic agent in dogs.

Disruption of FR-40 by 5-HT agonists. II. Effects of chronic phenelzine or isocarboxazid.

Effects of chronic treatment with the monoamine oxidase inhibitors phenelzine and isocarboxazid on disruption of FR-40 operant responses by 5-HT agonists have been studied. Three groups of rats that were trained in the FR-40 operant schedule showed marked disruption by 0.1 mg/kg IP lysergic acid diethylamide (LSD), 2 mg/kg IP quipazine (Q), 0.05 mg/kg SC 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT), and 1 mg/kg SC (m-trifluoromethyl-phenyl)piperazine (TFMPP), administered twice weekly in random order. Subsequently, one group received daily IP injection of phenelzine (5 and 10 mg/kg), the second group received 5 mg/kg IP of isocarboxazid, and the third group received vehicle (0.5% methyl cellulose) for 24 days (Period 1 and Period 2). For these periods and 12 days after discontinuing the MAOI treatments (Washout Period), test doses of 5-HT agonists were evaluated for their effects to decrease reinforcements (R) and increase pauses (P). No change in sensitivity to the LSD, Q and TFMPP effects on FR-40 behavior was observed in the vehicle-treated group. However, an attenuated effect of 8-OHDPAT was found in this group. In phenelzine- and isocarboxazid-treated rats the disruption of FR-40 responses by LSD and 8-OHDPAT were significantly reduced during Period 1, Period 2 and Washout Period. A significantly less effect on disruption in FR-40 responses by quipazine and TFMPP during Period 2 and the Washout Period was also seen. Since MAO inhibitors appear to down-regulate both 5-HT1 and 5-HT2 binding sites in brain, the attenuated effects of the 5-HT agonists were anticipated.(ABSTRACT TRUNCATED AT 250 WORDS)

An efficacy study of isocarboxazid and placebo in depression, and its relationship to depressive nosology.

Isocarboxazid and placebo were evaluated in 130 anxious depressives. Drug was superior to placebo on depression, anxiety, interpersonal sensitivity, and global measures, and on symptoms of hostility, anxiety, obsessiveness, and psychological-cognitive components of depression. There were no significant differences between treatment effects on psychomotor and typical vegetative symptoms. Isocarboxazid was more effective than placebo in major, but not in minor, depression. It was significantly more effective in depression classified as endogenous depression or melancholia by various diagnostic criteria. Drug was more effective than placebo in atypical depression with vegetative reversal and in Brief Psychiatric Rating Scale (BPRS)-derived profiles of anxious and hostile depression; there were no drug-placebo differences in atypical depression without vegetative reversal, or in BPRS retarded and agitated/excited depression. Interpersonal sensitivity emerged as an important drug-responsive dimension.

Effects of RS-2232, a potential antidepressant, on the levels of monoamines, precursor amino acids and their related metabolites in mouse brain.

The effects of RS-2232, a new antidepressant, on the levels of monoamines, precursor amino acids and their related metabolites in mouse brain were investigated and compared with some clinically effective antidepressants. RS-2232 (3, 10 and 30 mg/kg, p.o.) increased the levels of norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) dose-dependently, 60 min after administration. Tyrosine (TYR) levels were not changed, but tryptophan (TRP) was significantly increased by 20% at 30 mg/kg of the compound. On the other hand, DA metabolites such as 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were significantly reduced at all doses. 5-Hydroxyindoleacetic acid (5-HIAA), a 5-HT metabolite, was decreased by 32% at 10 mg/kg. These changes caused by RS-2232 administration were similar to those of the classical inhibitor of monoamine oxidase (MAO), isocarboxazid (ISO), but rather different from those of imipramine (IMP) and mianserin (MIA). RS-2232 and ISO antagonized against reserpine (2 mg/kg, s.c.)-induced changes in the contents of monoamines and their metabolites. Furthermore, time-course experiments clearly showed that increase in the levels of monoamines by 10 mg/kg of RS-2232 was restored to the control levels within a few hours. These results suggest that RS-2232 has reversible MAO inhibiting properties in vivo in mouse brain.

The effects of isocarboxazid on blood pressure and pulse.

In a fixed-dose inpatient study, isocarboxazid produced a dose-related lowering of systolic blood pressure at weeks 2 and 4. Systolic blood pressure was also lowered by the drug in a placebo-controlled outpatient study. The magnitude of these reductions was considerable, reaching an average of 14.6 mm in inpatients who received a 50-mg dose, and 18.7 mm in outpatients. There was no evidence for a dose-related orthostatic effect, and greater orthostasis relative to placebo was found only at week 3 in the outpatient study. Significant bradycardia was produced by isocarboxazid in outpatients at weeks 2, 3, and 4 relative to placebo, but no dose-related effect was found among inpatients. Inpatients with a baseline systolic orthostatic drop of greater than or equal to 10 mm showed a significantly better response to isocarboxazid than did those with an orthostasis of less than 10 mm. The theoretical significance of these findings is discussed.

Effects of monoamine oxidase inhibitors on performance during differential reinforcement of low response rate.

The effects of three monoamine oxidase inhibitors (MAOI) on performance under a differential-reinforcement-of-low-rate 72-s schedule (DRL 72-s) for water reinforcement were determined. All three drugs (isocarboxazid, iproniazid, phenelzine) reduced response rate and increased reinforcement rate in rats performing under the DRL schedule. Drugs from other classes (alcohol, chlordiazepoxide, morphine, pentobarbital) did not produce similar effects. The ability of MAOI to increase reinforcement rate under a DRL 72-s schedule is similar to that recently reported for tricyclic antidepressants and the two atypical antidepressants mianserin and iprindole. These findings support the contention that the DRL schedule may be useful as a test for identifying new antidepressants and for elucidating the neurochemical effects of antidepressants that are responsible for their therapeutic actions.

[Central effects of beta-phenylethylamines. (8). Increase in spontaneous motor activities of mice caused by intracerebrally administered metaramino].

Metaraminol (MA) (40, 80 and 160 microng) was injected i.c. into mice and spontaneous motor activity (SMA) measured by photo-cell counters method was found to increase 30 min after the injection. Ninety min after, the SMA was restored to the saline treated control. MA (80 microng i.c.) was also injected into isocarboxazide (Iso) pretreated mice and the SMA markdly increased as compared with the Iso+saline treated group or tween+MA treated group. When MA was injected i.c. into alpha-methyl-p-tyrosine (alpha-MT) pretreated mice, the SMA significantly increased as compared with that of the alpha-MT+saline treated group, but there was a decrease as compared with that of the tween+saline or tween+MA treated group. In alpha-MT treated mice. L-Dopa restored the hyper-motor activity of animals treated with MA. Diethyldithiocarbamate (700mg/kg i.p.) had no influence, whereas haloperidol markedly blocked the hyper-motor activity induced by MA. The hyper-motor activity induced by MA in mice raised the question of a possible role of noradrenaline and dopamine in the mediation of this action.

Effects of amitriptyline and isocarboxazid on 5-hydroxytryptophan induced head twitches in mice.

Effects of amitriptyline and isocarboxazid on brain 5-HT and 5-HIAA were examined in relation to their action on 5-HTP induced head twitches. Amitriptyline reduced 5-HTP induced head twitches but isocarboxazid increased them. Both amitriptyline and isocarboxazid caused a significant increase of brain 5-HT concentration in 5-HTP treated mice. Amitriptyline also caused a significant increase of 5-HIAA concentration, while isocarboxazid reduced 5-HIAA concentration in the brains of 5-HTP treated mice. Probenecid, which significantly increased 5-HIAA concentration without affecting brain 5-HT concentration in 5-HTP treated mice, reduced 5-HTP induced heat twitches. These results suggest that 5-HTP induced head twitches might be induced by an increase of 5-HT concentration, and reduced by an increase of 5-HIAA or a decrease of 5-HT concentration in the brains of mice.

[Effects of beta-phenylethylamine derivatives on the central nervous system. (5) Changes in the volume of spontaneous movement in mice with intracerebral administration of tyramine].

Influence of tyramine (Ty) on behavioural changes in mice was studied and the following results obtained: 1) 30 min after Ty (160 mug, i.c.), brain noradrenaline and serotonin levels decreased while dopamine levels increased. 2) When Ty was injected i.c. into isocarboxazide (Iso) pretreated mice, spontaneous motor activity (SMA) measured by photo-cell counters method increased markedly but SMA by wheel cage method decreased. 3) When Ty was injected i.c. into Iso and p-chlorophenylalanine (p-CPA) (400 mg/kg, i.p., daily X 2) pretended mice, SMA measured by photo-cell counters method increased. While, SMA increased from 30 to 90 min after Ty, SMA measured by wheel cage method decreased till 30 min after Ty. 4) When Ty was injected i.c. into Iso and alpha-methyl-p-tyrosine (alpha-MPT) (125 mg/kg, i.p., daily X 2), SMA measured by photo-cell counters method decreased markedly when compared with Iso+saline treated group. When SMA was measured by wheel cage method, a difference between alpha-MPT+Iso-Ty treated group and Iso-saline group was not obtained. 5) When Ty was injected i.c. into p-CPA+alpha-MPT+Iso pretreated mice, SMA measured by photo-cell counters method did not show any increase compared with control group. 6) SMA produced by Iso-Ty in mice pretreated with haloperidol was significantly inhibited. A 50% dose of inhibition was seen with 0.3 mg/kg. From our results, it appears that an increase of SMA induced by Iso+Ty as revealed by the photo-cell counters method may be related to brain catecholamines and serotonin while a decrease of SMA in wheel cage method may be related to brain serotonin.

[Effects of beta-phenylethylamine derivatives on the central nervous system. (5) The effect of intracerebral administration of tyramine on head twitching in mice pre-treated with isocarboxazid].

Effects of drugs on head-twitches induced by tyramine (Ty) in isocarboxazide (Iso) pretreated mice were studied and the following results obtained: 1) In beta-phenylethylamine derivatives, p-hydroxyamphetamine in non-treated and Iso-pretreated mice and Ty in Iso-pretreated mice produced head-twitches. 2) Injection of 5-HTP (i.c. and i.p.) into mice induced head-twitches. 3) Although head-twitches were not induced by a low dose of 5-HTP (20 mg/kg, i.p.), in Iso pretreated mice, the number of headtwitches increased markedly in the Iso-Ty treated group when Ty was injected i.c. in Iso+5-HTP (20 mg/kg) pretreated mice. 4) When Iso-Ty was injected into alpha-methyl-p-tyrosine pretreated mice, the number of head-twitches increased markedly compared with Iso-Ty treated group. 5) When Iso-Ty was injected into mice sustained with p-chlorophenylalanine, the number of head-twitches decreased markedly compared with the Iso-Ty treated group. 6) The number of head-twitches decreased markedly when Iso-Ty was injected into dimetotiazine pretreated mice, however the administration of Iso-Ty in haloperidol pretreated mice had no influence on head-twitches. 7) It is concluded that serotonin is the acting mediator in the head-twitch response.

[Central action of beta-phenylethylamine derivatives. (4) Effects on spontaneous motor activity and body temperature of beta phenylethyamine derivatives injected into the brain in reserpine pretreated mice].

Effects on spontaneous motor activity and body temperature of beta-phenylethlamine derivatives injected into the cerebral ventricles in reserpine or reserpine and isocarboxazide pretreated mice were investigated with the following results. 1) Each injection of tyramine (40 mug) and dopamine (40 mug) increased the spontaneous motor activity measured by the photo-cell counters method in reserpinized mice. 2) Each injection of tyramine (40 mug), dopamine (40 mug) and beta-phenylethylamine (40 mug) increased the spontaneous motor activity measured by both the wheel cage and photo-cell counters methods in reserpine and isocarboxazide-pretreated mice, but noradrenaline (20 mug) and isoproterenol (80 mug) did not increase the spontaneous motor activity as determined by both methods. 3) The injection of tyramine (40 and 80 mug), dopamine (10 and 40 mug) and p-octopamine (40 mug) increased the body temperature in reserpine and isocarboxazide pretreated mice. 4) Tyramine, dopamine and p-octopamine caused a marked increase in the body temperature as compared with control injection in reserpine and isocarboxazide-pretreated mice, whereas isoproterenol had no influence on body temperature. Our results suggest that beta-phenylethylamine derivatives have different effects in reserpinized and non-pretreated states.

Prediction of psychotropic properties of lisuride hydrogen maleate by quantitative pharmaco-electroencephalogram.

Based on "quantitative pharmaco-EEG" using computer-analyzed EEG (CEEG) measurements, unknown CNS effects of lisuride hydrogen maleate (LHM) were established. CEEG profiles of LHM in low dosages (less than or equal to 10 mcg) are similar to CNS "inhibitory" compounds, while in higher dosages (25 mcg to 100 mcg) they resemble "psychostimulant" compounds. By measuring the brain function using computer period analysis of cerebral biopotentials, dose-efficacy relations were found (in the range of 25-75 mcg) which suggest the bioavailability of LHM at the CNS level. By comparing the CEEG profiles of LHM with the previously studied compounds, five different clinical uses of LHM were predicted. The pilot trials suggest that LHM may have therapeutic potentials in patients with "aging" and/or organic brain syndromes, and in children with behavioral disturbances.

Monoamine oxidase. Its inhibition.

Some 50 years ago the enzyme MAO was discovered by Hare and in the early 1930s Blaschko suggested that MAO may play an important role in the catabolism of monoamines in the central nervous system. With the discovery of iproniazid as an inhibitor of MAO and its introduction as an anti-depressant, many aspects of MAO activity and biogenic amine metabolism in experimental animals and man were examined. Although many other inhibitors of MAO were discovered and used therapeutically as anti-depressants, these drugs fell into disrepute largely because of their side-effects. Furthermore, their anti-depressant properties were questioned. After some years of relative inactivity there is now a revival of interest in the functional role of MAO in the central nervous system and drugs that inhibit or stimulate its activity "specifically". The basic reason for the upsurge of interest is that the enzyme from many tissues, including the brain of animals as well as man, has been purified and characterised. The evidence that neuronal MAO exist with different substrate and inhibitor specificities has led to the suggestion that they have physiological function and that deamination of non-methylated biogenic monoamines can take place in neurons. These findings have led to the advent of new drugs (clorgyline and depranil) with "selective" inhibition of enzyme forms. Their possible usage in the chemotherapy of depressive illness should be considered seriously. Fluctuation in peripheral organs as well as brain MAO is well documented. Recently they have been associated with changes in naturally occurring steroids. Although a decrease in platelet and brain MAO activity has been reported in a number of affect disorders (schizophrenia and bipolar depression) the results of these findings have recently been questioned (20, 141). Obviously further study in this area of research discussed is badly needed.