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PubMed2004

Liquid chromatographic and tandem mass spectrometric assay for evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors: application of biomarkers in drug discovery.

A simple and selective assay for the evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors was developed through the simultaneous determination of endogenous 5-hydroxy tryptamine, 5-hydroxyindole-3-acetic acid (5-HIAA), tryptophane, and 2-phenethylamine (PEA) in rat brain using liquid chromatography-tandem mass spectrometry (LC/MS/MS). These analytes were separated on a Zorbax SB-C18 column using a gradient elution with acetonitrile and 0.2% formic acid and detected on an electrospray ionization mass spectrometer in positive-ion multiple-reaction-monitoring mode. The susceptibility and variability of these analytes as potential biomarkers in response to MAO inhibition in vivo were evaluated after application to three MAO inhibitors, tranylcypromine, clorgyline, and pargyline. A dramatic increase (about 40-fold) in PEA brain level and a decrease in 5-HIAA by more than 90% were observed after administration of 15 mg/kg of the nonselective MAO inhibitor tranylcypromine. As expected, the brain level of PEA escalated to about 6-fold, while the 5-HIAA level remained unchanged following a dose of the MAO B inhibitor pargyline at 2mg/kg. In contrast, the brain level of 5-HIAA reduced by approximately 53%, but the PEA level was unaffected following the same dose of the MAO A inhibitor clorgyline. The results indicated that 5-HIAA and PEA were susceptible and effective biomarkers in the rat brain in response to MAO A and B inhibition, respectively. The LC/MS/MS method is useful not only for the determination of inhibitory potency but also for the differentiation of the selectivity of a MAO inhibitor against rat brain MAO A and B in vivo.

Animals↗
PubMedDate not supplied

Platelet monoamine oxidase B activity in dementia. A 4-year follow-up.

Platelet monoamine oxidase B (MAO-B) activity has been found to increase significantly in demented patients. For the first time, a 4-year follow-up of platelet MAO-B activity and Mini-Mental State (MMS) was performed in patients with probable dementia of the Alzheimer type (DAT) and age-matched controls. MAO-B activity of DAT patients increased significantly 2 years after the beginning of the study as compared with controls and remained significantly higher for the entire period of the examinations (p < 0.0001). The decrease of the MMS scores did not correlate with the time course of the increase of platelet MAO-B activity (Spearman rank correlation test). The decline of the MMS scores of DAT patients preceded the elevation of MAO-B activity. Since degenerative processes in brain areas which are responsible for cognitive function and are reflected by the MMS scores rather affect cerebral cholinergic than monoaminergic neurotransmitter systems, degeneration of the latter at late stages of DAT might be reflected by increased platelet MAO-B activity.

Aged↗
PubMed1997

Monoamine oxidase B (MAOB)-containing structures in MAOA-deficient transgenic mice.

Monoamine oxidase (MAO)-containing structures were studied for the first time in type A MAO (MAOA)-deficient transgenic mice (Tg8) derived from C3H strain, using MAO enzyme histochemistry. In this mutant line, MAOA activity was not detected in neurons of the locus coeruleus. In contrast, in their dorsal raphe neurons, we noted an intense activity of type B MAO (MAOB). Based on pharmacological MAOA suppression experiments employing a specific inhibitor (clorgyline), we confirmed that the localization of MAOB-positive structures are not different between Tg8 mutant and normal C3H line. Many of MAOB-positive structures which have not been described previously in the rat, cat and primates were described in this study. In the forebrain, MAOB-containing neurons were discriminated in the striatum, septal nuclei, major island of Calleja, diagonal band, medial forebrain bundle, ventral pallidum and amygdaloid nucleus. Stained neurons in the thalamus and hypothalamus were much more extensively distributed in the mouse than the rat. Pontine laterodorsal tegmental neurons showed MAOB activity. The present data suggest that serotonin, a preferential substrate for MAOA, can be oxidized by MAOB in MAOA-deficient Tg8 mice.

Animals↗
PubMed2003

Calcium disodium edetate enhances type A monoamine oxidase activity in monkey brain.

The effects of metal chelators on monoamine oxidase (MAO) isozymes, MAO-A and MAO-B, in monkey brain mitochondria were investigated in vitro. MAO-A activity increased to about 40% with 0.1 microM calcium disodium edetate (CaNa2EDTA) using serotonin as a substrate, and this activation was proportional to the concentration of CaNa2EDTA. On the other hand, MAO-A activities were decreased gradually with an increasing concentration of o-phenanthroline and diethyldithiocarbamic acid, but these metal chelators had no effect on MAO-B activity in monkey brain. The activation of MAO-A activity by CaNa2EDTA was reversible. CaNa2EDTA did not activate both MAO-A and MAO-B activities in rat brain mitochondria. Zn and Fe ions were found in the mitochondria of monkey brain. Zn ions potently inhibited MAO-A activity, but Fe ions did not inhibit either MAO-A or MAO-B activity in monkey brain mitochondria. These results indicate that the activating action of CaNa2EDTA on MAO-A was the result of the chelating of Zn ions contained in mitochondria by CaNa2EDTA. These results also indicate the possibility that Zn ions may regulate physiologically the level of serotonin and norepinephrine content in brain by inhibiting a MAO-A activity.

Animals↗
PubMed1994

Quantitative distribution of rat brain monoamine oxidase A by [14C]clorgyline autoradiography.

The distribution of functionally active monoamine oxidase type A (MAO-A) was investigated by in vivo quantitative autoradiography using [14C]clorgyline in normal, conscious rat brain. [14C]clorgyline was synthesized by the methylation reaction of N-desmethylclorgyline using [14C]methyliodide. Sixty minutes after [14C]clorgyline administration (1.58 MBq/animal i.v.), the brains were removed and prepared for autoradiography by washing the brain sections with 5% trichloroacetic acid solution to remove the nonbinding free tracer. The amount of MAO-A was calculated from the regional acid-insoluble tissue radioactivity and the specific activity of the tracer. The highest amount of MAO-A (5.84 nmol/g tissue) was found in the locus coeruleus. The interpeduncular nucleus, habenular nucleus, fasciculus retroflexus, and solitary tract nucleus possessed over 1.6 nmol/g tissue of MAO-A. Among 23 regions of interest, the lowest amount of MAO-A (0.37 nmol/g tissue) was found in the globus pallidus. The findings of this study suggest that the pattern of MAO-A parallels both in neuroanatomical distribution and in density that of norepinephrine and serotonin innervation. The MAO-A concentration was, however, relatively low in the dopamine-related areas. This corresponded to the previous results obtained by histochemical analysis. In addition, among the white matter structures, a high amount of MAO-A was found specifically in the fasciculus retroflexus.

Animals↗
PubMed2006

Monoamine oxidase A and repressor R1 are involved in apoptotic signaling pathway.

Monoamine oxidase A (MAO A) degrades serotonin, norepinephrine, and dopamine and produces reactive oxygen that may cause neuronal cell death. We have previously reported that a novel transcription factor R1 (RAM2/CDCA7L/JPO2) inhibits the MAO A promoter and enzymatic activities. This study reports the roles of MAO A and R1 in apoptosis and proliferation. We have found that in serum starvation-induced apoptosis, p38 kinase, MAO A, and caspase-3 were increased, whereas Bcl-2 and R1 were reduced. Using a p38 kinase inhibitor, R1 overexpression, and MAO A inhibitor, we have shown that MAO A and R1 are downstream of p38 kinase and Bcl-2, but upstream of caspase-3. Inhibition of MAO A prevents cell apoptosis. This notion was further supported by the finding that serum starvation-induced apoptosis is reduced in cortical brain cells from MAO A-deficient mice compared with WT. In addition, we found that MAO A and R1 are involved in the c-Myc-induced proliferative signaling pathway in the presence of serum. Immunoprecipitation and immunohistochemistry experiments indicate that the oncogene c-Myc colocalizes with R1 and induces R1 gene expression. Using R1 overexpression, R1 small interfering RNA, and a MAO A inhibitor, we found that R1 and MAO A act upstream of cyclin D1 and E2F1. In summary, this study demonstrates the functions of MAO A and its repressor R1 in apoptotic signaling pathways.

Animals↗
PubMed2004

Platelet monoamine oxidase activity in subjects tested for Huntington's disease gene mutation.

Monoamine oxidase activity (MAO) has been related to neuronal damage, since the oxidative deamination of biogenic amines produces free radicals that may enhance oxidative stress. Elevated enzyme activities in brain (MAO-A and MAO-B forms) and in platelets (MAO-B form) have been reported in several degenerative diseases, indicating that MAO activity may be involved in the disease progression. We estimated platelet MAO activity in a group of 59 patients (34 males) with HD, 20 subjects (7 males) at risk, and 29 (14 males) healthy subjects with positive family history for HD, categorized according to clinical features and the number of CAG repeat units (CAG-RN) at the Huntington gene. A group of 64 subjects (36 males) with negative family history for HD served as controls. In contrast to some previous studies, platelet MAO activities in both male and female patients (CAG-RN 40 to 62) with overt symptomatology, were not different compared to same sex control subjects. Subjects at risk (CAG-RN 39 to 52), though, showed significantly lower activities compared to same sex patients or controls. MAO activities seem to increase with disease progression, and tend to be higher in patients with dementia. The increases may be an epiphenomenon of disease pathology, but the possibility that an increase in the expression of the enzyme precedes the onset of the disease and contributes to enhanced oxidative stress should be considered in future longitudinal studies as a possible mechanism that accelerates disease progression.

Antipsychotic Agents↗
PubMed1999

Metabolism of monoamine oxidase inhibitors.

1. The principal routes of metabolism of the following monoamine oxidase inhibitors (MAOIs) are described: phenelzine, tranylcypromine, pargyline, deprenyl, moclobemide, and brofaromine. 2. Acetylation of phenelzine appears to be a minor metabolic pathway. Phenelzine is a substrate as well as an inhibitor of MAO, and major identified metabolites of phenelzine include phenylacetic acid and p-hydroxyphenylacetic acid. Phenelzine also elevates brain GABA levels, and as yet unidentified metabolites of phenelzine may be responsible for this effect. beta-Phenylethylamine is a metabolite of phenelzine, and there is indirect evidence that phenelzine may also be ring-hydroxylated and N-methylated. 3. Tranylcypromine is ring-hydroxylated and N-acetylated. There is considerable debate about whether or not it is metabolized to amphetamine, with most of studies in the literature indicating that this does not occur. 4. Pargyline and R(-)-deprenyl, both propargylamines, are N-demethylated and N-depropargylated to yield arylalkylamines (benzylamine, N-methylbenzylamine, and N-propargylbenzylamine in the case of pargyline and amphetamine, N-methylamphetamine and N-propargylamphetamine in the case of deprenyl). These metabolites may then undergo further metabolism, e.g., hydroxylation. 5. Moclobemide is biotransformed by C- and N-oxidation on the morpholine ring and by aromatic hydroxylation. An active metabolite of brofaromine is formed by O-demethylation. It has been proposed that another as yet unidentified active metabolite may also be formed in vivo. 6. Preliminary results indicate that several of the MAOIs mentioned above are substrates and/or inhibitors of various cytochrome P450 (CYP) enzymes, which may result in pharmacokinetic interactions with some coadministered drugs.

Depression↗
PubMed2002

Analysis of monoamine oxidase A (MAOA) promoter polymorphism in Finnish male alcoholics.

Alterations in monoamine oxidase A (MAOA) expression and enzyme activity may be associated with alcoholism and impulsive behavior. Therefore, functional polymorphisms in the MAOA gene would be good candidates to consider in the interindividual differences that exist in the susceptibility to alcoholism. One variant that has been considered as a candidate in alcoholism is a repeat polymorphism in the MAOA gene promoter. We analyzed a cohort of Finnish males with either type 1 or type 2 alcoholism, as well as controls, for differences in the distribution of MAOA promoter alleles. Based on other studies, we postulated that type 2 alcoholism, which is associated with antisocial behavior, but not type 1 alcoholism, would be correlated with the inheritance of the low promoter activity allele. However, we failed to find a difference in allele distribution in type 1 and type 2 alcoholics. In addition, there was no difference in the allele distribution when each group of alcoholics was compared with controls. However, when both groups of alcoholics were pooled and compared with controls, the difference in allele distribution reached a trend towards significance. Our results suggest a minimal association between the MAOA low activity promoter alleles and alcoholism, regardless of the presence or absence of antisocial behavior. Interestingly, approximately 3% of type 2 alcoholics were found to be heterozygous for the MAOA promoter polymorphism. Since MAOA is X-linked, the heterozygotes are probable cases of Klinefelter's syndrome (47,XXY) suggesting that X-chromosome aneuploidy may increase the risk for developing type 2 alcoholism.

Adult↗
PubMed1999

Variations in the monoamine oxidase B (MAOB) gene are associated with Parkinson's disease.

The monoamine oxidase B gene (MAOB; Xp15.21-4) is a candidate gene for Parkinson's disease (PD) given its role in dopamine metabolism and its possible role in the activation of neurotoxins. The association of MAOB polymorphisms (a [GT] repeat allelic variation in intron 2 and an A-G transition in intron 13) with Parkinson's disease (PD) was studied in an Australian cohort of 204 (male:female ratio 1.60) people with PD and 285 (male:female ratio 1.64) age- and gender-matched control subjects. Genomic DNA was extracted from venous blood and polymerase chain reaction was used to amplify the appropriate regions of the MAOB gene. The length of each (GT) repeat sequence was determined by 5% polyacrylamide denaturing gel electrophoresis and a DNA fragment analyzer, while the G-A genotype was determined using 2% agarose gel electrophoresis. The G-A polymorphism showed no association with PD (odds ratio [OR] = 0.80; p = 0.51; 95% confidence interval [CI] = 0.42-1.53). There was a significant difference in allele frequencies of the (GT) repeat allelic variation between patients and control subjects (chi2 = 20.09; p<0.01). After statistical adjustment for potential confounders using a logistic regression analysis, the (GT) repeat alleles > or =188 base pairs in the intron 2 marker of the MAOB gene were significantly associated with PD (OR = 4.60; p<0.00005; 95% CI = 1.97-10.77). The 186 base pair allele was also significantly associated with PD (OR = 1.85; p = 0.048; 95% CI = 1.01-3.42). The GT repeat in intron 2 of the MAOB gene is a powerful marker for PD in this large Australian cohort.

Aged↗
PubMed1983

Use of a monoclonal antibody for comparative studies of monoamine oxidase B in mitochondrial extracts of human brain and peripheral tissues.

Monoamine oxidase B (MAO B; EC 1.4.3.4) activity in detergent extracts of mitochondria from autopsy brain (gray matter and medulla), liver, lung, and kidney from a single individual and from pooled, human platelets could be immunoprecipitated by a monoclonal anti-human platelet MAO B antibody (MAO-1C2) in combination with appropriate secondary reagents. MAO A activity, which was detected in brain, liver, lung, and kidney, was not immunoprecipitated under the same conditions. All MAO B-containing extracts, regardless of tissue source, inhibited immunoprecipitation of [3H]pargyline-labeled human platelet MAO, and the shapes of the inhibition curves were identical. The concentration of immunologically detectable MAO B protein in the extracts was estimated from immunoprecipitation competition data by reference to a standard curve relating observed inhibition of immunoprecipitation to the concentration of catalytically active platelet MAO added (estimated from [3H]pargyline binding data). MAO B protein concentrations measured by this radioimmunoassay were similar to concentrations of active MAO B as measured by pargyline binding. These results demonstrate that in the brain and peripheral tissues studied, molecules with MAO B activity share a unique antigenic determinant and similar catalytic efficiency. They also extend previous observations that MAO B molecules extracted from mitochondria bear an antigenic determinant which is not present on MAO A molecules. These results demonstrate the validity of a new competitive radioimmunoassay for active plus inactive MAO B concentration in human platelet extracts and extracts of mitochondria from human tissues. This radioimmunoassay should complement [3H]pargyline binding assays and enzyme activity assays in studies designed to clarify the mechanisms of genetic, disease, and treatment factors which lead to differences in MAO B function among individuals.

Adult↗
PubMed1982

Monoamine oxidase inhibition by tranylcypromine: assessment in human volunteers.

The inhibition of monoamine oxidase (MAO) by tranylcypromine was studied in 6 healthy volunteers given increasing doses of 10, 15, 20 and 25 mg/day over a 4-week period. Measurements were made of urinary tryptamine excretion, blood pressure response to tyramine (TY) and norepinephrine (NE), and subjective self-rating. A significant increase in urinary tryptamine, indicating the onset of MAO inhibition, occurred in all 6 subjects once the cumulative dose of 40 mg TC had been administered. Thereafter, urinary tryptamine increased up to 7-fold, dose-dependently with large interindividual variation (78 +/- 27 to 549 +/- 252 microgram/g creatinine). Within 4 days after stopping the drug, control values were reached again. The assessment of TY potentiation by comparison of equieffective doses (S dose) became up to 10 times more sensitive when both the height and the duration of the increase in systolic blood pressure (S AUC) were taken into account. The increases in tyramine sensitivity found with the highest cumulative doses of TC (5.4 +/- 0.8 mg/kg; n =6) were S dose from 8-16 and S AUC from 28-162, respectively. The pharmacodynamic half-life (Pd 1/2) of TC approximated a mean first fast Pd 1/2 of 1.3 d and a slower phase of 14.2 d. During treatment with the highest TC dose, resting blood pressure was significantly elevated from 120 to 128 mm Hg, and the pressor sensitivity to NE (S NE) in 4 of the 6 subjects rose, the mean was 1.7 (n = 6). In 3 volunteers NE sensitivity was normalized within 4 days after stopping TC. There was a significant correlation between increasing vigilance with TC dose in 5 volunteers (r = 0.81, n = 15, p less than 0.01). It is concluded that combination of the results of several tests has provided reliable information about the onset, extent and duration of MAO inhibition in healthy volunteers.

Adult↗
PubMed1989

Pharmacological profile of moclobemide, a short-acting and reversible inhibitor of monoamine oxidase type A.

The novel antidepressant moclobemide is a reversible inhibitor of monoamine oxidase (MAO), preferentially of type A. Moclomide was active in three animal models considered predictive for antidepressant activity: 1) it prevented dose-dependently akinesia and blepharospasm induced in mice and rats by Ro 4-1284, a short-acting amine releasing agent. Prevention of akinesia by moclobemide also depended upon the dose of Ro 4-1284. For comparison also, effects of cimoxatone, harmaline, tranylcypromine and clorgyline are presented: 2) in cats, it selectively and dose-dependently suppressed rapid eye movement sleep without disturbing the sleep-wakefulness cycle; and 3) in the behavioral despair test in mice, it decreased the immobility score to a similar degree as amitriptyline or imipramine. In addition, moclobemide potentiated 5-hydroxytryptophan-induced stereotypies in rats with a potency similar to cimoxatone and with a duration of action of less than 24 hr. Moclobemide had almost no effect on the spontaneous behavior in mice, rats, cats and monkeys. Only in higher doses, marginal sedation and slight impairment in motor performance were seen. Moclobemide did not prevent pilcarpine-induced salivation in mice, demonstrating the absence of anticholinergic activity. Blood pressure and heart rate of freely moving, spontaneously hypertensive rats were only slightly decreased for less than 3 hr. Moclobemide moderately potentiated the pressor effect of p.o. tyramine in rats. In conclusion, the reversible MAO inhibitor moclobemide is active in animal models sensitive to all major drugs used in the treatment of depression. In contrast to imipramine-like antidepressants, it lacks anticholinergic activity and it differs from classic MAO inhibitors by potentiating only weakly the pressor effect of p.o. tyramine.

2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-↗
PubMed1996

The monoamine regulon including syntheses of arylsulfatase and monoamine oxidase in bacteria.

Bacterial cells respond to monoamine compounds, such as tyramine, dopamine, octopamine, or norepinephrine, and induce the syntheses of tyramine oxidase encoded by tynA and monoamine oxidase encoded by maoA. These monoamine compounds also derepress the synthesis of atsA-specified arylsulfatase that is repressed by sulfur compounds. These complex mechanisms of regulons regulated by monoamine and sulfur compounds has been analyzed by cloning and characterization of genes that are involved in the repression and derepression of the synthesis of arylsulfatase. The atsA gene forms an operon with the atsB gene, which encodes an activator of the expression of atsA. The negative regulator gene for arylsulfatase was found to code for dihydrofolate reductase (folA). The maoA gene forms an operon with the maoC gene, which has similarity to a dehydrogenase involved in the tyramine metabolism. The moaF gene encoding a 30-kDa protein, which is induced by tyramine, also forms an operon with the moaE gene. Finally, the moaR gene, which is induced by monoamine, was found to play a central role in the positive regulation of the expression of the monoamine regulon (moa) including the atsBA, maoCA, moaEF, and tyn operons. The moaR expression is subject to autogenous regulation and to cAMP-CRP control. The MoaR protein has a helix-turn-helix motif in its C terminus. Thus, the MoaR protein probably regulates the operons by binding to the regulatory region of the moa regulon.

Arylsulfatases↗
PubMed2004

A high-throughput monoamine oxidase inhibition assay using liquid chromatography with tandem mass spectrometry.

A highly efficient method utilizing liquid chromatography with tandem mass spectrometry (LC/MS/MS) was developed and employed for high-throughput screening of compounds for monoamine oxidase (MAO) inhibition. The method used kynuramine as a common substrate for both MAO-A and MAO-B in incubations, and the 4-hydroxyquinoline (4-HQ) resulting from deamination of kynuramine followed by intramolecular condensation was analyzed using LC/MS/MS; formation of 4-HQ was used as the marker of MAO activity to evaluate the effects of test compounds. Isocratic liquid chromatography was applied to reduce the run time to 2 min. Because of the high specificity and sensitivity of detection of 4-HQ by LC/MS/MS, this method was able to use MAO enzymes at very low concentrations and to perform short incubations; as a result, consumable cost was minimized, and sample preparations were completely avoided. The inhibition data are highly reproducible, and the IC(50) values determined by the method are in good agreement with literature values. The results suggest that this method is very robust and can be used as a generic approach to screen for MAO inhibitors in drug discovery.

Chromatography, High Pressure Liquid↗
PubMed1992

Inhibition of a type B monoamine oxidase inhibitor, (E)-2-(4-fluorophenethyl)-3-fluoroallylamine (MDL-72974A), on semicarbazide-sensitive amine oxidases isolated from vascular tissues and sera of different species.

(E)-2-(4-Fluorophenethyl)-3-fluoroallylamine hydrochloride (MDL-72974A) has been discovered recently to be a very potent and highly selective type B monoamine oxidase inhibitor. We have found that this inhibitor is also capable of inhibiting semicarbazide-sensitive amine oxidases (SSAOs) obtained from vascular tissues and sera of different species. The inhibition of SSAO by MDL-72974A was irreversible and time dependent. It was competitive without preincubation of the enzyme with the inhibitor and demonstrated a mixed-type of inhibition when the enzyme was preincubated with the inhibitor. The IC50 values were estimated to be 2 x 10(-9) M, 5 x 10(-9) M, 8 x 10(-8) M and 2 x 10(-8) M for SSAO from dog aorta, rat aorta, bovine aorta and human umbilical artery, respectively. SSAO obtained from bovine serum was relatively insensitive to MDL-72974A (IC50 = 3 x 10(-7) M. Following intraperitoneal administration of MDL-72974A, rat brain MAO-B was inhibited with the ED50 value being about 0.2 mg/kg. Rat aorta SSAO was also inhibited and to a similar extent by the same dose. MDL-72974A is the most potent SSAO inhibitor that has been described thus far.

Allyl Compounds↗
PubMed2002

Age-dependent increase in hydrogen peroxide production by cardiac monoamine oxidase A in rats.

Oxidative stress is one of the factors involved in age-related impairment of cardiac function. In the present study, we investigated the role of the catecholamine-degrading enzyme monoamine oxidase (MAO) in H(2)O(2) production in the hearts of young, adult, and old rats. MAO-dependent H(2)O(2) production, measured by a chemiluminescence-based assay, increased with age, reaching the maximum in 24-mo-old rats (7.5-fold increase vs. 1-mo-old rats). The following observations indicate that the age-dependent increase in H(2)O(2) generation was fully related to the MAO-A isoform: 1) at all the ages tested, chemiluminescence production was inhibited by the MAO-A inhibitor clorgyline but not by the MAO-B inhibitor RO-19 6327; 2) enzyme assay, Western blot, and semiquantitative RT-PCR analysis showed an age-dependent increase in cardiac MAO-A activity, immunodetection, and mRNA expression, respectively; and 3) the MAO-B isoform was undetectable by enzyme assay and Western blot analysis. These results suggest that MAO-A could be a major source of H(2)O(2) in the aging heart.

Aging↗