Letter: Brain-levels of monoamine oxidase in depression

Effects of depression, cigarette smoking, and age on monoamine oxidase B in amygdaloid nuclei

Altered concentrations of dopamine transporter and D2/D3 receptors have been observed in the amygdaloid complex of subjects with major depression. These findings are suggestive of neurochemical abnormalities in the limbic dopamine system in depression. Monoamine oxidase-B (MAO-B) is a key enzyme in the catabolism of biogenic amines, including dopamine, and alterations in this enzyme may underlie dopaminergic abnormalities associated with depression. The specific binding of [(3)H]lazabemide to MAO-B was measured in the right amygdaloid complex of 15 major depressive subjects and 16 psychiatrically normal controls. Subjects of the two study groups were matched as close as possible for age, sex, and postmortem interval. Examination of the regional distribution of MAO-B revealed lower [(3)H]lazabemide binding to MAO-B in the lateral and basal nuclei of the amygdala and higher binding in the medial nucleus. A modest elevation in binding to MAO-B observed in all amygdaloid nuclei in major depressive subjects as compared to control subjects failed to reach statistical significance. A significant decrease in binding to MAO-B was observed when cigarette smokers were compared to nonsmoking subjects. The amount of MAO-B binding positively correlated with the age of subjects in all nuclei investigated. A decreased amount of MAO-B in smokers further validates the pharmacological effect of tobacco smoke on this enzyme.

Ageing and monoamine turnover in the lateral geniculate nucleus and visual cortex of the rat

The effects of ageing on the turnover of dopamine, noradrenaline and serotonin in the lateral geniculate nucleus and the visual cortex were evaluated, using high performance liquid chromatography (HPLC) with electrochemical detection. Compared to adult animals, aged rats showed more changes in the visual cortex than in the lateral geniculate nucleus, with dopamine turnover decreased in both structures and noradrenaline turnover unaltered. Changes in serotonin turnover were witnessed only in the visual cortex. A decrease in the monoamine oxidase-A to -B ratio was also observed with increased age for both the lateral geniculate nucleus and visual cortex.

Monoamine oxidase B in brains from patients with Alzheimer's disease: a biochemical and autoradiographical study

In vitro quantitative autoradiography using [3H]L-deprenyl, an irreversible and preferential inhibitor of monoamine oxidase B, was performed to investigate the localization of the enzyme in brains from senile dementia of Alzheimer type and control cases. Brains from three male patients with the clinical diagnosis of senile dementia of Alzheimer type and from three male control patients, without any known clinical history of neurological disorder, were obtained at autopsy. Cryosections of 100 microns thickness were mounted on gelatinized glass plates and dried over desiccant for one week at -20 degrees C. The sections were incubated with 10 nM [3H]L-deprenyl for 1 h and then exposed to film for four weeks. The autoradiographs were analysed by computer-assisted densitometry. Monoamine oxidase-B activities were also estimated in 1% homogenates from 10 different regions, using 10 microM beta-[ethyl-14C]phenylethylamine, in order to study the consonance between the autoradiographical and biochemical techniques. Both [3H]L-deprenyl binding and monoamine oxidase-B activities in senile dementia of Alzheimer type were higher than in the controls in all brain regions studied. The increase was highest in the white matter (about 70%) and in the order of 20-50% in the various gray matter regions. A high correlation coefficient (r approximately 0.9) was obtained between [3H]L-deprenyl binding and monoamine oxidase-B activity, both in the senile dementia of Alzheimer type and in the control brains.

Biochemical effects of iron deprivation

The consequences of iron deprivation on iron-containing enzymes of different tissues in rat and/or human is reviewed. Iron participates in a wide variety of biochemical processes, including mitochondrial electron transport, catecholamine metabolism and DNA synthesis. Recently, a broad spectrum of biochemical abnormalities resulting from iron deficiency have been described. Effects on skeletal muscle, cardiac muscle, brain tissue, liver tissue gastrointestinal tractus, body temperature regulation, DNA synthesis are successively discussed. The key liabilities of tissue iron deficiency, even at a mild degree relate to decrease in intellectual performance, and in physical capacity during exercise, alteration of temperature regulation, immune function.

Selective decreases in MAO-B activity in post-mortem brains from schizophrenic patients with type II syndrome

The activities of the A and B forms of the enzyme monoamine oxidase (MAO, E.C. 1.4.3.4) have been assessed with the substrates 5-hydroxytryptamine and benzylamine respectively in seven areas of the brains of 39 patients with schizophrenia and 44 control subjects. Whereas previous studies have found the enzyme unchanged in brain in schizophrenia, in this study there was a modest but significant decrease in the activity of MAO-B in frontal and temporal cortices and in amygdala. This decrease could not be accounted for by neuroleptic medication, age, sex or post-mortem variables. In a series of 22 patients who had been assessed in life, the reduction in MAO-B activity was found to be associated specifically with the presence of negative symptoms (flattening of affect and paucity of speech). The findings are therefore consistent with other evidence for structural and neurochemical change in the temporal lobe that have been associated with the type II (defect state) syndrome of schizophrenia. The change in enzyme activity is unlikely to be related to a change in monoamine metabolism but may reflect a disturbance in glial function. The change in MAO-B activity in brain in this study is confined to particular areas of brain and a subgroup of patients; it is thought to be entirely unrelated to earlier reports of reductions of enzyme activity in platelets, which are probably attributable to prolonged neuroleptic medication.

Platelet MAO activity in clinical subtypes of depression and DST suppression

Platelet MAO activity was measured in 75 hospitalized depressed patients and in 31 healthy subjects. Plasmas post dexamethasone cortisol levels were examined in 73 patients. Results indicate that higher platelet MAO activity does not occur in all, but only in male major depressed patients. No relationship between changes of MAO activity and specific clinical subtypes was found. Platelet MAO activity is not different between DST suppressors and DST non suppressors. The authors suggest that platelet MAO activity may be related to non specific factors such as sex, age, but not to diagnosis of depression.

Memory function and brain biochemistry in normal aging and in senile dementia

One might argue that the decrease in the number of brain cells as a function of age could be the source of the functional age deficits in memory performance. However, this possibility seems less likely since the actual loss of neurons up to advanced age is relatively small. There are no good estimates of the loss of synapses. Golgi staining of cortical neurons would indicate that there is a loss with higher age. So far, however, the most convincing data of marked loss with age appear at the biochemical level. Most human data fail to demonstrate a decrease in cholinergic and serotonergic activity as a function of normal aging, although there is a loss of corresponding receptors. In AD/SDAT, however, there is a marked damage to these systems. Conceivably, acetylcholine may be providing informational rather than tone setting or balancing influence on memory function. This may explain the failure of cholinomimetic drugs to improve memory in AD/SDAT due to their inability to supply the informational properties of normal neuronal transmission. The catecholamines, noradrenaline and dopamine are both lost in normal aging and to a much higher degree in AD/SDAT. Animal data show that noradrenaline deficiency results in scattered attention. Such a pattern might also exist in the intact aged and through guidance by means of instructions, contextual cues, and a richer TBR information, the elderly are being forced to attend. This may promote and supersede the normal functions of the noradrenaline system by directions from external rather than internal influences, conceivably by potentiating the remaining noradrenaline neurons. The cortical motor areas are relatively spared from neuro-degenerative changes in normal aging and in AD/SDAT and this might provide a neuroanatomical basis for the elderly's and mildly to moderately demented patients' success in memory performance when motor action is involved. The role of dopamine in motor function and its stability with age in hippocampus may also provide a neurochemical basis for the preservation of memory when the subjects are allowed to act physically during encoding.

The activity of tissue enzymes in iron-deficient rat and man: an overview

The effects of iron deficiency in rat and/or man on iron-containing enzymes of different tissues is reviewed. Iron deficiency results in a decrease of skeletal muscle iron containing proteins e.g. myoglobin, cytochromes c, a + a3, and alpha-glycerophosphate oxidase. Iron deficiency produces a reduction in the activity of several respiratory enzymes in the mitochondrial fraction of cardiac muscle, particularly: NADH cytochrome c reductase, succinic cytochrome c reductase, succinic dehydrogenase and NADH ferricyanide oxidoreductase. The effects of iron deficiency on brain tissue is emphasized with respect to cytochromes, monoaminoxidase and amino acids metabolism. Host defence to infection (controversial data), decrease in body temperature, alteration of DNA synthesis, collagen and lipid metabolism, liver and gastrointestinal mucous cytochromes activity perturbations are discussed.

Titration of human brain monoamine oxidase -A and -B by clorgyline and L-deprenil

The interaction of clorgyline and L-deprenil with the -A and -B forms of human brain monoamine oxidase (MAO) has been studied. Both compounds inhibit cerebrocortical MAO in a manner consistent with a 'suicide' inactivation of the enzyme. The interaction of clorgyline with the -A form of the enzyme appears to take place almost entirely at specific binding sites, and the conditions required for this inhibitor to 'titrate' the concentrations of MAO-A have been elucidated. L-Deprenil has also been used to titrate the concentration of the -B form of MAO in cerebrocortical homogenates, but there is a considerable degree of non-specific binding of this compound. The two inhibitors have been used to titrate the concentrations of the two enzyme forms in frontal cortex homogenates from different age groups. There was a significantly higher MAO-B activity for the age range 73--95 years than for the age range 2--63 years. No significant differences between the two age groups were found for MAO-A. The activity of MAO-A in the samples correlated very well with the concentration of this enzyme form. Titration of the B-form of the enzyme with L-deprenil indicated an increased enzyme concentration with age, although other factors, such as the non-specific binding of this compound, could contribute to this effect.

The effect of age on the activity and molecular properties of human brain monoamine oxidase

The effect of age upon monoamine oxidase -A and -B (MAO-A and -B) in 23 different, regions of human brain was determined. There was a significant positive correlation with age in 19 out of 23 regions for MAO-B, but no positive correlation with age was found for MAO-A. The increased MAO-B activity was found, in 5 out of 5 regions tested, to be due entirely to an increased enzyme concentration, rather than due to an increased molecular turnover number of the enzyme. The responses of the mitochondrial marker enzymes succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) were studied in 5 brain regions, and no consistent change in activity found with age. The lysosomal enzyme acid phosphatase was found to tend towards an increased activity with age. No difference in either the specific activities or molecular characteristics of MAO were found between men and women. Cross-correlation studies of the data, after compensation for the effects of age, indicated that the activities of the two enzyme forms are under some form of organized control across the whole brain. Such a finding is consistent with a genetic regulation of the enzyme forms.

Suicide attempts, platelet monoamine oxidase and the average evoked response

The relationship between suicides and suicide attempts and two biological measures, platelet monoamine oxidase levels (MAO) and average evoked response (AER) augmenting, was examined in 79 off-medication psychiatric patients and in 68 college student volunteers chosen from the upper and lower deciles of MAO activity levels. In the patient sample, male individuals with low MAO and AER augmenting, a pattern previously associated with bipolar affective disorders, showed a significantly increased incidence of suicide attempts in comparison with either non-augmenting low MAO or high MAO patients. Within the normal volunteer group, all male low MAO probands with a family history of suicide or suicide attempts were AER augmenters themselves. Four completed suicides were found among relatives of low MAO probands where as no high MAO proband had a relative who committed suicide. These findings suggest that the combination of low platelet MAO activity and AER augmenting may be associated with a possible genetic vulnerability to psychiatric disorders.

Physiological and pathological changes in tissue monoamine oxidase activity

This article explores the possibility that malfunction of the enzyme monoamine oxidase (E.C. 1.4.3.4., MAO) could lead to aberrations in the catabolism of biogenic amines in the central nervous system and give rise to certain mental abnormalities. No conclusive evidence could be presented to substantiate this. Data on the normal function of the enyzme (for example its existence in multiple forms, the control of MAO activity by hormones or the independent development of MAO activities towards different substrates during maturation) are reviewed.

Intravenous tyramine pressor response in depression

Tyramine-dose/pressor-response curves have been determined in 27 control subjects and 19 patients with primary depressive illness. In the depressive group, significantly lower doses of tyramine were required to elevate the systolic blood-pressure by 30 mm. Hg.

Is there an increase in monoamine-oxidase activity in depressive illness?

In a group of depressed patients who had either been treated with or considered suitable for monoamine oxidase (M.A.O.) inhibitor therapy, a highly significant decrease in conjugated tyramine output was observed after an oral tyramine load compared with normal controls. However, there was no difference in conjugated isoprenaline output between the two groups after isoprenaline ingestion, even though this amine is almost solely metabolised by what is likely to be the same conjugation mechanism. Whilst some explanation in terms of altered gut motility is conceivable, it seems more likely that the apparent deficit in tyramine conjugation in depression represents an increase in functional M.A.O. activity. Consequently, this enzyme would metabolise a greater proportion of available amine, causing a proportionately large decrease in the smaller conjugate pool.