Rat Liver Monoamine Oxidase Research Articles

Effect of Diethylnitrosamine on Monoamine Oxidase in Rat Liver

The effect of diethylnitrosamine (DEN), a well-known experimental carcinogen, toward MAO-A and MAO-B activity of rat liver was investigated. The oxidations of both β-PEA (MAO-B) and 5-HT (MAO-A) were inhibited by DEN. The K1 values of DEN in the inhibition of rat liver MAO-A and MAO-B activity were determined. The kinetic data show that DEN is a competitive, MAO-B selective inhibitor and its inhibitory effect on MAO-B is about 4-fold more potent than that on MAO-A. DEN might change the proportions of the multiple forms of MAO activity in tumor cells.

Effect of diethylnitrosamine on monoamine oxidase in rat liver.

The effect of diethylnitrosamine (DEN), a well-known experimental carcinogen, toward MAO-A and MAO-B activity of rat liver was investigated. The oxidations of both beta-PEA (MAO-B) and 5-HT (MAO-A) were inhibited by DEN. The K1 values of DEN in the inhibition of rat liver MAO-A and MAO-B activity were determined. The kinetic data show that DEN is a competitive, MAO-B selective inhibitor and its inhibitory effect on MAO-B is about 4-fold more potent than that on MAO-A. DEN might change the proportions of the multiple forms of MAO activity in tumor cells.

P-524 - Effect of diethylnitrosamine on monoamine oxidase in rat liver

P-524 - Effect of diethylnitrosamine on monoamine oxidase in rat liver

Molecular cloning of a cDNA for rat liver monoamine oxidase B

The cDNA for rat monoamine oxidase B mRNA was isolated from liver cDNA library in lambda gt11 using specific antibody and oligonucleotide probes derived from FAD-containing peptide of the enzyme. The primary structure of the protein, deduced from the nucleotide sequence, consisted of 520 amino acid residues and its molecular weight was calculated to be 58.4 kD which is in good agreement with that of the in vitro-synthesized peptide. FAD-binding site is located in the carboxy-terminal region. There is no typical structural feature common to the targeting signals for mitochondria, the periodic distribution of basic amino acids spaced by several uncharged residues, at its amino-terminal region. This region has an uninterrupted stretch of 14 hydrophobic residues.

Aliphatic amines of different chain lengths as substrates for rat liver monoamine oxidase

Aliphatic amines of different chain lengths as substrates for rat liver monoamine oxidase

Effects of nondenaturating zwitterionic detergent chaps, 3-[(3-cholamido propyl) dimethyl ammonio]-1-propanesulfonate, on rat liver mitochondrial and microsomal monoamine oxidase

It has been reported that monoamine oxidase (MAO) activity (EC1.4.3.4) and, in general, enzymes possessing cationic substrates, were activated and inhibited by anionic and cationic detergents, respectively. In order to examine this hypothesis, the effect of the zwitterionic detergent CHAPS 3-[(3-cholamido propyl) dimethyl ammonio]-l-propanesulphonate was studied in comparison with the effects of cationic, anionic, and non-ionic detergents. The non-denaturating zwitterionic detergent CHAPS was used to solubilise rat liver monoamine oxidase MAO (EC1.4.3.4) of mitochondrial and microsomal origin; the solubilisation conditions, purification, inhibition and kinetic studies were then determined. These results are compared with those previously obtained with the non-ionic detergent Triton X-100, which would also be expected to have no net charge, and are interpreted in terms of specific ionic effects.

Short-acting novel MAO inhibitors: in vitro evidence for the reversibility of MAO inhibition by moclobemide and Ro 16-6491.

The inhibition of monoamine oxidase (MAO) in rat liver and brain by the short-acting MAO-A inhibitors moclobemide (Ro 11-1163 = p-chloro-N-[2-morpholinoethyl]benzamide) and brofaremine and by the short-acting MAO-B inhibitors Ro 16-6491 (N-[2-aminoethyl]-p-chloro-benzamide) and almoxatone, administered p.o. at roughly equieffective doses 2 h before decapitation, was investigated for its reversibility under various in vitro conditions. MAO A activity in liver homogenates, inhibited by moclobemide (300 mumol/kg) to approx. 15% of control, time dependently recovered during 0.5 to 2 h of incubation at 37 degrees C, irrespective of whether the homogenates were prepared and incubated in distilled water or Krebs-Ringer buffer (KRB). Dialysis of such homogenates for 4 h in distilled water at 37 degrees C (but not at 13 degrees C) led to a complete return of the MAO activity. In liver homogenates from rats pretreated with brofaremine (30 mumol/kg), dialysis for 4 h at 37 degrees C against distilled water caused only little recovery of the MAO activity. Likewise, MAO-B inhibited by Ro 16-6491 (30 mumol/kg) to approx. 4% of control returned to almost control activity after 4 h of dialysis at 37 degrees C, while inhibition induced by almoxatone (30 mumol/kg) was little or not reversed at all. In brain homogenates prepared in, and dialysed against, distilled water or KRB at 37 degrees C (but not at 13 degrees C), MAO-A inhibited by moclobemide (100-300 mumol/kg) to approx. 15% of control, partially (KRB) or almost completely (dist. water) returned to control activity after 4 h of dialysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of maternal methadone administration on the development of multiple forms of monoamine oxidase in rat brain and liver

The development of total monoamine oxidase (MAO) and MAO-A and MAO-B in the forebrain, brainstem, cerebellum and liver of methadone-treated and normal rats were monitored with tryptamine, serotonin and benzylamine, respectively. Daily administration of methadone (10 mg/kg, s.c.) to pregnant and nursing rats substantially retarded the development of total and the A-form of MAO in the brain regions of pups but had no effect on that of MAO-B. The effect of methadone on the development of total MAO and MAO-A in the liver was only transient and less significant. This finding indicates that the perinatal opiate syndrome associated with maternal exposure to methadone is caused by the inhibition in MAO-A development in monoaminergic neurons in the brain.

Monoclonal antibodies to monoamine oxidase B and another mitochondrial protein from human liver.

A monoclonal antibody has been generated to human liver monoamine oxidase (MAO) B by fusion of mouse myeloma cells with spleen cells from a mouse immunized with a mixture of semi-purified MAO A and MAO B. The antibody, 3F12/G10, an immunoglobulin G1, reacts with its antigen in cryostat sections of human liver, showing an intracellular particulate distribution as demonstrated by immunoperoxidase staining. The antibody indirectly precipitates [3H]pargyline-labelled human MAO B both from liver and platelet extracts but fails to precipitate MAO A from liver extracts. The antibody does not recognise rat liver MAO B, showing that the determinant is not universally expressed on MAO B. The antibody has no effect on the catalytic activity of MAO B. Other monoclonal antibodies were generated but they are directed to a protein with a subunit Mr of 54 000, a contaminant of the MAO preparation. One of these antibodies, A8/C2, an IgG2a, reacts with the same protein in both rat and human liver extracts.

Ontogenesis of multiple forms of monoamine oxidase in rat brain regions and liver.

The postnatal development of total, type-A and type-B monoamine oxidase (MAO) in the brain stem, forebrain and cerebellum, determined with preferred substrates or selective inhibitors, were found to follow different patterns. In the brain regions, MAO-A activity reached adult levels in the brain stem first, followed by the forebrain and cerebellum, while MAO-B reached adult levels in these regions at about the same time and later in postnatal life. On the other hand, both MAO-A and B activities were almost fully developed in the newborn liver. Moreover, total and type-A, but not type-B, showed a caudal-to-rostral sequence of biochemical maturation in the brain. The spatiotemporal pattern of differentiation of type-A and type-B activities in the brain tends to support the classification of brain MAO into two distinct isoenzymic forms.

Serotonin and the Control of Salivation in the Blowfly Calliphora

ABSTRACT The possibility that serotonin acts as a neurohormone stimulating salivation in the blowfly Calliphora vicina was studied by investigation of salivation induced by injections of high-potassium saline. Induced salivation is rapid and appears to be mediated by an active factor released into the haemolymph (High Potassium Salivary Gland Factor: HKSGF) since it is antagonized by cadmium (a calcium channel blocker) and by gramine (a serotonin-receptor blocker). The action of HKSGF on salivary glands in vitro is indistinguishable from that of serotonin: (a) it generates serotonin-like transepithelial potential changes, (b) its effect on salivation is antagonized by gramine, (c) it is as heat stable as serotonin, (d) it has the same solubility in a variety of organic solvents, (e) it is unaffected by incubation with leucine aminopeptidase or trypsin and (d) it is inactivated by rat liver monoamine oxidase type A (a serotonin deaminating enzyme). Radioenzyme assay of haemolymph from high-potassium injected flies shows that the amount of serotonin present could account for all of the retrievable bioactivity. Significant amounts of serotonin were found in the cerebral ganglion, the thoracic ganglion and nerves attached to the thoracic ganglion. Nerve sectioning experiments demonstrated that the abdominal nerves and the anterior nerves supplying the neck muscles are not involved in the normal salivatory response. However the cerebral-thoracic connective must be intact and it is suggested that release of serotonin is effected close to the main body of the thoracic ganglion. Some of the implications of the neurohormonal role of serotonin are discussed.

Comparative aspects of monoamine oxidase.

This short review attempts to summarize a small fraction of the comparative aspects of the flavoprotein enzyme, monoamine oxidase (MAO), which is found mainly in the outer mitochondrial membranes of a wide variety of animal species. It deaminates both aromatic and aliphatic monoamines in the form Open image in new window to their corresponding aldehydes and hydrogen peroxide. Some of the evidence is described which shows that MAO can be divided into two catalytically different forms, called MAO-A and MAO-B. This evidence derives from the fact that the substrate specificity of MAO depends not only on the species but also on the particular tissue studied. Some inhibitors of MAO including the irreversible inhibitors, clorgyline and deprenyl show considerable selectivity towards one or other form of the enzyme. Under appropriate conditions clorgyline is about 1000 times more active against MAO-A while deprenyl is more active against MAO-B. Use of these inhibitors will measure the proportions of the two forms of activity as they deaminate a fixed concentration of a chosen substrate. Such experiments may also reveal the presence of another deaminating enzyme that is not FAD-dependent and is not inhibited by clorgyline. With appropriate radioactive ligands it is possible to measure the number of active centres of each form and thus allow the relative turnover rate constants for MAO-A and MAO-B to be calculated for each substrate. As an example, the determination of MAO-A:B ratio is illustrated for rat and giraffe liver MAO. In addition a summary is given of the type of MAO activity responsible for the deamination of 5-hydroxytryptamine, tyramine, β-phenethylamine and benzylamine in heart, liver and brain of a few animal species.

The nature of the inhibition of rat liver monoamine oxidase types A and B by the acetylenic inhibitors clorgyline, l-deprenyl and pargyline

The kinetics of inhibition of rat liver mitochondrial monoamine oxidase by clorgyline, l-deprenyl and pargyline are consistent with a mechanism whereby a reversible interaction between the inhibitor and the enzyme active site under conditions of thermodynamic equilibrium is followed by a time-dependent formation of the covalently-bound enzyme-inhibitor adduct. The K i value for the reversible interaction between clorgyline and monoamine oxidase A is about 1000 times lower than that towards the B-form of the enzyme, and this difference is sufficient to account for most, but not all, of the selectivity of the inhibition caused by this compound. The K i value of the monoamine oxidase B selective inhibitor l-deprenyl towards that form of the enzyme is only about 40-fold lower than that towards the A-form. However, in this case, the rate of formation of the irreversible adduct is considerably faster for the B-form than for the A-form and this makes a major contribution to the selectivity of this compound. Pargyline shows a K i value towards monoamine oxidase B that is only 8 times lower than that towards the A-form and in this case the rates of formation of the enzyme-inhibitor adducts are similar. The significance of these results are discussed in terms of the selective inhibition of monoamine oxidase.

Glutamate — oxaloacetate transmainase, monoamine oxidase, diamine oxidase and mixed function oxidase activities in rat liver after portacaval shunt

1 month after portacaval shunt, some enzymatic activities of rat liver were tested and a significant increase of diamine oxidase was observed.

Inhibition of rat liver monoamine oxidase by α-methyl- and N-propargyl-amine derivatives

The inhibition of rat liver monoamine oxidase by a number of N-propargyl and α-methyl amine derivatives has been examined. The results indicate that α-methyl-substituted primary and secondary amine derivatives tend to show selectivity as reversible inhibitors towards the A-form of the enzyme. The structural features that result in selectivity in irreversible inhibitors are less easy to define and substitution of an N-propargyl group into a compound that is a selective reversible inhibitor of monoamine oxidase will not necessarily result in retention of that selectivity. Replacement of the acetylenic group in a B-selective irreversible inhibitor by an ethylenic group resulted in a compound that was a reversible inhibitor showing slight selectivity for the A-form of the enzyme.

Purification of rat liver monoamine oxidase by octyl glucoside extraction and reconstitution

Catalytically active isoenzymes of rat liver monoamine oxidase have been copurified from the outer mitochondrial membrane by a novel method involving repetitive solubilization with octyl-β- d-glucopyranoside followed by reconstitution into lipid vesicles. As analyzed using sodium dodecyl sulfate-gel electrophoresis, the purified enzyme migrates as a single band of protein of molecular weight 60,000. The preparation is capable of metabolizing 576 nmol serotonin and 777 nmol β-phenylethylamine/min/mg protein. Apparent K m values and sensitivity to the inhibitor clorgyline are very similar for the purified and outer mitochondrial membrane-bound enzyme when determined with the substrates β-phenylethylamine, serotonin, and tyramine.

Altered imprinting of rat liver monoamine oxidase by o, p'-DDT and methoxychlor

Neonatal administration of o, p'-DDT [1,1,1-trichloro-2-( o-chlorophenyl-2- p-chlorophenyl ethane or methoxychlor resulted in elevated levels of sex-differentiated hepatic monoamine oxidase activities in adult rats, but not in prepubertal animals. Exposure to these hormonally active xenobiotics may have changed the brain hormone environment during the critical period of development, resulting in endocrine alterations that were reflected by latent but permanent increases in hepatic monoamine oxidase activities, i.e. “altered imprinting”. Hepatic glutathione S-transferases and cytochrome P-450 content also underwent sex differentiation, but neonatal treatment with o, p'-DDT or methoxychlor did not alter levels in adult rats. However, glutathione S-transferase activities and cytochrome P-450 content were higher in prepubertal animals treated neonatally with o, p'-DDT. In contrast to monoamine oxidase, effects on glutathione S-transferase activities and cytochrome P-450 content were attributed to induction by these xenobiotics.

Bovine liver mitochondrial monoamine oxidase is not an iron-dependent enzyme.

It has been reported that rat liver monoamine oxidase is an iron-dependent enzyme. Calculations from reported data suggest that rat liver monoamine oxidase contains 2 g atoms of iron/mol of enzyme. However, our data over a 16-year period show that our purified bovine liver monoamine oxidase does not contain sufficient iron to justify being considered an iron protein. In order to ensure the correctness of the iron content, two microchemical analyses and atomic absorption spectroscopy were used to determine the iron content of wet ashed samples. The iron content was also determined during successive steps of enzyme purification and was found to decrease rather than increase. Monoamine oxidase, being a hydrophobic outer membrane enzyme, is very difficult to purify and detailed tests for homogeneity are necessary. Our preparations show a single band when examined by sodium dodecyl sulfate-polyacrylamide disc electrophoresis and behave as a pure protein by end group analysis. Thus, bovine liver monoamine oxidase is not an iron-dependent enzyme.

EFFECTS OF LOCAL ANESTHETICS ON MONOAMINE OXIDASE, AND THEIR MEMBRANE EFFECTS

The effects of various local anesthetics on rat brain and liver monoamine oxidase (MAO) and their antihemolytic and local anesthetic effects were studied. All local anesthetics tested at 1×10-7 M to 1×10-3 M inhibited MAO activity in rat liver mitochondria with 5-hydroxytryptamine (5-HT) as substrate. The order of potency was tetracaine>procaine> dibucaine>Iidocaine>prilocaine. Tetracaine and procaine inhibited 5-HT oxidation much more than β-phenylethylamine (PEA) oxidation. Dibucaine inhibited PEA oxidation as much as 5-HT oxidation. Inhibition of MAO by local anesthetics other than dibucaine was reversible. Tetracaine and procaine inhibited 5-HT oxidation competitively, whereas dibucaine inhibited it non-competitively. Antihemolytic effects were observed with dibucaine and tetracaine at concentrations of 6×10-5 M and 1×10-4 M, respectively. The order of surface anesthetic potencies was dibucaine>tetracaine> prilocaine>iidocaine>procaine. These results suggest that the inhibition of MAO activities by local anesthetics depends on both electrostatic and hydrophobic interactions between these drugs and enzyme-associated phospholipids or the hydrophobic regions of proteins.

Effects of local anesthetics on monoamine oxidase, and their membrane effects.

The effects of various local anesthetics on rat brain and liver monoamine oxidase (MAO) and their antihemolytic and local anesthetic effects were studied. All local anesthetics tested at 1 x 10(-7) M to 1 x 10(-3) M inhibited MAO activity in rat liver mitochondria with 5-hydroxytryptamine (5-HT) as substrate. The order of potency was tetracaine>procaine>dibucaine>lidocaine>prilocaine. Tetracaine and procaine inhibited 5-HT oxidation much more than beta-phenylethylamine (PEA) oxidation. Dibucaine inhibited PEA oxidation as much as 5-HT oxidation. Inhibition of MAO by local anesthetics other than dibucaine was reversible. Tetracaine and procaine inhibited 5-HT oxidation competitively, whereas dibucaine inhibited it non-competitively. Antihemolytic effects were observed with dibucaine and tetracaine at concentrations of 6 x 10(-5) M and 1 x 10(-4), respectively. The order of surface anesthetic potencies was dibucaine>tetracaine>prilocaine>lidocaine>procaine. These results suggest that the inhibition of MAO activities by local anesthetics depends on both electrostatic and hydrophobic interactions between these drugs and enzyme-associated phospholipids or the hydrophobic regions of proteins.