Nonselective inhibition of monoamine oxidases A and B by activators of soluble guanylate cyclase.

Several activators of soluble guanylate cyclase were investigated as potential inhibitors of rat liver mitochondrial monoamine oxidases (MAO) A and B. They all fitted into the previously designed "molds" of substrate-inhibitor binding sites of these enzymes. However, only two of them, NO donors (7-nitro-benzotetrazine-1,3-dioxide (7-NBTDO) and benzodifuroxan), caused nonselective inhibition of MAO A and MAO B with IC(50) values of 1.3-1.6 and 6.8-6.3 microM, respectively. The inhibitory effect on both MAO A and MAO B was reduced by mitochondria wash suggesting reversible mode of the enzyme inhibition. There was no correlation between potency of MAO inhibition and activation of human platelet soluble guanylate cyclase. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) had no effect on the manifestation of MAO inhibition by benzodifuroxan and 7-NBTDO; however, at 50 microM concentration carboxy-PTIO caused potent inhibition of MAO A with minor effect on MAO B activity. The data suggest that nonselective inhibition of MAO A and MAO B by benzodifuroxan and 7-NBTDO can be attributed to the properties of the chemical structures of these compounds. The results of the present study demonstrate a real possibility for the development of a new generation of effective reversible nonselective MAO inhibitors exhibiting equal inhibitory activity with respect to both MAO A and MAO B.

Monoamine oxidase inhibition by N-alkyloxycarbonyl derivatives of ethylene diamine.

Urethane type derivatives of ethylene diamine (EDA) were synthesized and tested as inhibitors of rat liver mitochondrial monoamine oxidase (MAO) A and B. The nature of the aromatic ring and the position of substituents in it were crucial for manifestation of the inhibitory activity. 3,4- and 2,4-Chlorobenzyloxycarbonyl-EDA derivatives were the most potent MAO A inhibitors. The inhibition of both MAO A and to a lesser extent MAO B depended on preincubation time with these inhibitors. The activity of both enzymes did not recover completely after repeated sedimentation and resuspension of inhibitor-treated mitochondria. The data suggest that these compounds exhibit properties of tight-binding reversible inhibitors of MAO A and B. The development of a new generation of MAO inhibitors causing simultaneous reversible nonselective inhibition of MAO A and B must meet one important criterion, the same type of inhibition of both the enzymes.

The stimulating effects of ethanol consumption on synthesis of rat brain monoamine oxidases and their sensitivity to the irreversible inhibitor, pargyline.

Administration of a large dose of pargyline (60mg/kg) caused total irreversible inhibition of brain monoamine oxidases (MAOs) in both control and alcoholised rats. During the first 50h the recovery of brain MAO-A (but not MAO-B) activity occurred faster in the alcoholised rats. A low dose of pargyline (10mg/kg) produced significantly higher inhibition of MAO-A in the alcoholised rats, whereas the degree of MAO-B inhibition was the same in both groups. Brain MAOs of control and alcoholised rats exhibited similar sensitivity to pargyline in vitro. Since chronic ethanol feeding reduced the content of reversible endogenous MAO inhibitor, tribulin, higher pargyline-induced inhibition of MAO-A in alcoholised rats may stem from a tribulin deficit. The data obtained suggest that chronic ethanol consumption increases turnover of MAO-A molecules in the brain and reduces the content of endogenous MAO(A) inhibitors.

The effect of ethanol consumption on the sensitivity of rat brain monoamine oxidases to the inhibition by pargyline in vivo and in vitro.

The effect of ethanol consumption on the sensitivity of rat brain mitochondrial monoamine oxidases to the inhibition by pargyline in vivo and in vitro was investigated. Administration of pargyline (10 mg/kg, s.c.) produced significantly higher inhibition of MAO-A in alcoholised rats, whereas MAO-B inhibition did not differ from that observed in control animals. The concentration-response curve for the inhibition of brain mitochondrial MAO-A and MAO-B by pargyline in vitro did not reveal higher sensitivity of MAO from alcoholised rats to pargyline. This probably means that more pronounced inhibition by pargyline of brain MAO-A in alcoholised rats in vivo can be attributed to decreased content of compounds reversibly interacting with the its catalytic site. Taking into consideration some ethanol-induced decrease of brain tribulin content we suggest that the reduced level of endogenous inhibitors (tribulin components?) may have some importance in the development of alcoholism.

Inhibition of monoamine oxidase by pirlindole analogues: 3D-QSAR analysis.

A series of pirlindole analogues were tested as inhibitors of monoamine oxidase A and B. Although we did not find strict dependence between 3D-size of molecules and their inhibitory potency, rigid analogues exhibited potent and selective inhibition of MAO-A. They have 3D size limits of 13 angstroms (length) x 7 angstroms (height) x 4.4 angstroms (widths). Besides MAO-A inhibition flexible analogues also demonstrated potent inhibition of MAO-B. Five compounds were studied as inhibitors of purified human liver MAO-A. Their inhibitory potencies coincided with those obtained using rat liver mitochondrial MAO-A. Each compound induced changes in the spectrum of MAO-A but these did not correlate with the flexibility of the derivative. It is also possible that the oxygen bridge introduced with the flexibility might influence spectral patterns.

Inhibition of monoamine oxidase by pirlindole analogues: 3D-QSAR and CoMFA analysis.

A series of pyrazinocarbazoles, analogues of short acting antidepressant pirlindole (2,3,3a,4,5,6-hexahydro-8-methyl-1H-pyrazino[3,2,1-j,k]carbazole hydrochloride), were tested as inhibitors of monoamine oxidase A (MAO-A) and B (MAO-B). Rigid analogues exhibited potent and selective inhibition of MAO-A and have size limits (X:Y:Z) of 13.0 x 7.0 x 4.4 A. Besides MAO-A inhibition flexible analogues also demonstrated potent inhibition of MAO-B and in contrast to rigid analogues their inhibitory activity did not show the dependence on these sizes. The qualitative information (steric and electrostatic coefficients) from the 3D-QSAR with CoMFA models for MAO-A and -B are different, and this information can be used to determine the structural features influencing inhibitor selectivity.

N-alkyloxycarbonyl derivatives of ethylene diamine as monoamine oxidase inhibitors.

A series of urethane type derivatives of ethylene diamine (EDA) was synthesised and tested as inhibitors of monoamine oxidase (MAO) A and B. Nature of aromatic ring and a position of substituents in it were important for the inhibitory activity. Chlorobenzyloxycarbonyl-EDA derivatives exhibited selective inhibition of MAO-A with 3,4-Cl2-C6H4CH2OCO-EDA being a most potent and selective MAO-A inhibitor (IC50 4 microM). Within the compounds studied, 3,4-dichloro-benzyloxycarbonyl-EDA exhibited most potent inhibition of MAO-A. This compound inhibited the activity of rat liver MAO-A non-competitively with Ki (slope) value of 3.6 microM, whereas the inhibition of rat liver MAO-B was competitive with Ki (slope) value of 56 microM (not shown). 2.4-Dichlorobenzyloxycarbonyl-EDA also inhibited rat liver MAO-A in a non-competitive manner with Ki of 14.6 microM.

Does isatin interact with rat brain monoamine oxidases in vivo?

Isatin is a reversible endogenous monoamine oxidase (MAO) inhibitor found in the brain. The influence of isatin on the degree of irreversible MAO inhibition by phenelzine and pargyline has been studied in vitro and in vivo experiments. In vitro 10 and 100 microM isatin reduced irreversible inhibition of MAO A and MAO B assayed after mitochondria wash. Pretreatment of rats with 'anxiogenic dose' of isatin (10 mg/kg) protected neither MAO A nor MAO B against subsequently administered phenelzine (10 mg/kg). 'Anticonvulsant' dose of isatin (80 mg/kg) reduced phenelzine-dependent inhibition of MAO B but not MAO A. Data obtained suggest that the anticonvulsant effect of isatin does not result from the inhibition of MAO A and the increase of monoamine level in the brain reported in few laboratories is apparently stipulated by a mechanism that does not involve MAO A inhibition.

The influence of some compounds commonly used in biochemical studies of mitochondria on the activity of monoamine oxidases.

It was previously described that low concentrations of sodium azide monoamine oxidase (MAO) B assayed by spectrophotometric measurement of benzaldehyde or by hydrogen peroxide accumulation. We failed to confirm this effect using radiometric determination of MAO activity. Tris or dinitrophenol inhibit MAO. The data suggest that some "regulatory effects" depend on the assay of MAO activity.

Monoamine oxidase inhibition by novel antidepressant tetrindole.

The novel antidepressant tetrindole (2,3,3a,4,5,6-hexahydro-8-cyclohexyl-1H[3,2,1-j,k] carbazole) was found to be a selective inhibitor of monoamine oxidase A (MAO A). In vitro it inhibited rat brain mitochondrial MAO A in a competitive manner with Ki value of 0.4 microM. A 60 min preincubation did not change the competitive mode of interaction between enzyme and tetrindole (Ki value was 0.27 microM). The inhibition of rat brain mitochondrial MAO B was of mixed type with Ki value of 110 microM. Dilution or dialysis of mitochondrial suspension did not restore MAO A activity after inhibition by tetrindole both in vitro and in vivo, whereas inhibition of MAO B in vitro was completely reversible. Oral administration of tetrindole inhibited rat brain and liver mitochondrial MAO A by 80% within 0.5-1 hr and the onset of recovery of enzyme activity became evident after 24 hr. A small inhibition of MAO B (-20-30%) was observed in isolated brain and liver mitochondria within 1-6 hr and enzyme activity had completely recovered after 16 hr. The data obtained indicate that antidepressant activity of tetrindole may be explained by selective inhibition of MAO A, however an apparent discrepancy between competitive manner of MAO A inhibition in vitro and poor recovery of enzyme activity in vivo does not allow us to decide whether tetrindole is a "tight-binding" reversible inhibitor or a selective irreversible inhibitor of MAO A.