Inhibition of monkey brain semicarbazide-sensitive amine oxidase by various antidepressants

Midbrain FA initiates neuroinflammation and depression onset in both acute and chronic LPS-induced depressive model mice

Both exogenous gaseous and liquid forms of formaldehyde (FA) can induce depressive-like behaviors in both animals and humans. Stress and neuronal excitation can elicit brain FA generation. However, whether endogenous FA participates in depression occurrence remains largely unknown. In this study, we report that midbrain FA derived from lipopolysaccharide (LPS) is a direct trigger of depression. Using an acute depressive model in mice, we found that one-week intraperitoneal injection (i.p.) of LPS activated semicarbazide-sensitive amine oxidase (SSAO) leading to FA production from the midbrain vascular endothelium. In both in vitro and in vivo experiments, FA stimulated the production of cytokines such as IL-1β, IL-6, and TNF-α. Strikingly, one-week microinfusion of FA as well as LPS into the midbrain dorsal raphe nucleus (DRN, a 5-HT-nergic nucleus) induced depressive-like behaviors and concurrent neuroinflammation. Conversely, NaHSO3 (a FA scavenger), improved depressive symptoms associated with a reduction in the levels of midbrain FA and cytokines. Moreover, the chronic depressive model of mice injected with four-week i.p. LPS exhibited a marked elevation in the levels of midbrain LPS accompanied by a substantial increase in the levels of FA and cytokines. Notably, four-week i.p. injection of FA as well as LPS elicited cytokine storm in the midbrain and disrupted the blood-brain barrier (BBB) by activating microglia and reducing the expression of claudin 5 (CLDN5, a protein with tight junctions in the BBB). However, the administration of 30 nm nano-packed coenzyme-Q10 (Q10, an endogenous FA scavenger), phototherapy (PT) utilizing 630-nm red light to degrade FA, and the combination of PT and Q10, reduced FA accumulation and neuroinflammation in the midbrain. Moreover, the combined therapy exhibited superior therapeutic efficacy in attenuating depressive symptoms compared to individual treatments. Thus, LPS-derived FA directly initiates depression onset, thereby suggesting that scavenging FA represents a promising strategy for depression treatment.

Evidence for existence of thyroid hormone inducible semicarbazide-sensitive amine oxidase (SSAO) in rat heart cytosol

BACKGROUND

Semicarbazide-sensitive amine oxidase (SSAO; EC; 1.4.3.6.) has widespread tissue distribution, and the physiological role of SSAO is quite well known through its involvement in several pathological states.

AIMS

The present study examined modulators of SSAO which might be present in the rat heart cytosol and looked for changes in SSAO modulatory activity.

METHODS

An endogenous inhibitor of SSAO was separated by gel filtration from 105,000g supernate of T4-treated rat heart cytosol. SSAO inhibition fraction was referred to as "endogenous SSAO inhibitor".

RESULTS

The inhibition by this inhibitor was concentration-dependent. Inhibition of SSAO was not enhanced by varying the time of preincubation of the enzyme, indicating reversible inhibition of SSAO. The molecular weight of this inhibitor was estimated to be 1000-1100 by gel filtration. The isoelectric point (pI) value was determined to be 4.8 isoelectric focusing. This inhibitor was found to be heat-stable and resistant to protease treatment. SSAO inhibition activity was much lower in the cytosol of thyroidectomized, non-T4-treated rats than T4-treated rats, suggesting that this inhibitor was induced by thyroid hormone T4. SSAO activity in rat heart might be regulated by the level of this inhibitor.

CONCLUSION

These results suggest the presence of SSAO inhibitor in T4-treated rat cytosol and that the level of this inhibitor is regulated by thyroid hormone.

Monoamine oxidase B activity is increased in human gliomas

Glial tumours are the most common type of brain neoplasm in humans. Tumour classification and grading represent key factors for patient management. However, current grading schemes are still limited by subjective histological criteria. In this context, gliosis has been linked to increases in monoamine oxidase B (MAO-B) activity. Thus, in the present study, MAO-B activity in membranes of glial tumours (n=20), meningiomas (n=12) and non-pathological human brains (n=15) was quantified by [14C]PEA oxidation. MAO-B activity was significantly greater in glioblastoma multiformes than in postmortem control brains (p<0.01) or meningiomas (p<0.001). There were no significant differences in MAO-B activity between glioblastoma multiformes (n=11) and low-grade astrocytomas (n=3) or anaplastic astrocytomas (n=6). In conclusion, the present results demonstrate a significant and selective increase in MAO-B activity in human gliomas when compared with meningiomas or non-tumoural tissue. These results suggest that the quantification of MAO-B activity may be a useful diagnostic tool for differentiating glial tumours from other types of brain tumours or surrounding normal brain tissue.

Inhibition of amine oxidases by the histamine-1 receptor antagonist hydroxyzine

The effects of the drug hydroxyzine on the activities of the rat liver monoamine oxidases (EC 1.4.3.6; MAO) and the membrane-bound and soluble forms of bovine semicarbazide-sensitive amine oxidase (EC 1.4.3.6; SSAO) were studied. Hydroxyzine was found to be a competitive inhibitor of MAO-B (Ki - 38 microM), whereas it had a low potency towards MAO-A (IC50 > 630 microM). Although it was a relatively potent competitive inhibitor of bovine plasma SSAO (Ki approximately 1.5 microM), it was a weak inhibitor of the membrane-bound form of the enzyme from bovine lung (IC50 approximately 1 mM). These findings extend our knowledge of the drug binding capabilities of the amine oxidases and suggest that these interactions may contribute to the complex actions of this drug.

Decreased serum semicarbazide sensitive aminooxidase (SSAO) activity in patients with major depression

Semicarbazide sensitive aminooxidase (SSAO) is known to interplay with monoamine oxidases (MAO) and several antidepressants. Taking into account the monoamine hypothesis concerning the pathophysiology of depression, the aim of the present pilot study was to evaluate serum SSAO activity in depressed patients. A total of 21 inpatients with major depression and 41 healthy controls were studied. Serum SSAO activity was determined by HPLC on days 1, 5 and 10 of inpatient treatment. At baseline without medication including antidepressants, highly depressed patients (MADRS score>or=30) had significantly decreased serum SSAO activity (mean 385+/-161 mU/l) when compared to healthy controls (mean 526+/-141 mU/l; p=0.003). This SSAO decrease was less pronounced at day 5 and day 10 under an antidepressive drug regime. Decreased serum SSAO activity was observed in patients with major depression, especially in those with high MADRS scores. The present results support the hypothesis of dysfunctional monoaminergic metabolism in the pathogenesis of depressive disorders. The disputable association between depression and monoamine metabolism requires further investigation, particularly with regard to SSAO activity and medication status.

Endogenous semicarbazide-sensitive amine oxidase (SSAO) inhibitor increases 1-methyl-4-phenylpyridinium ion (MPP+)-induced dopamine efflux by immobilization stress in rat striatum

The present study examined whether or not immobilization stress (IMMO)-inducible semicarbazide-sensitive amine oxidase (SSAO) inhibitor by separated gel filtration from 105,000 g supernate in rat brain cytosol contribute to the dopamine (DA) efflux by 1-methyl-4-phenylpyridinium ion (MPP(+)) in the rat striatum. The isoelectric point (pI) value of this inhibitor was determined by isoelectric focusing (IEF)-gel electrophoresis to about 3.8. The application of IMMO-induced SSAO inhibitor (3 microg) by IEF-gel electrophoresis increased DA efflux by MPP(+) in rat striatum. These results suggest that IMMO-inducible endogenous SSAO inhibitor enhances DA efflux by MPP(+).

Semicarbazide-sensitive amine oxidase (SSAO) in the brain

Semicarbazide-sensitive amine oxidase (SSAO) is widely distributed in almost tissues. However, its presence in brain microvessels is still controversial. The affinity of SSAO towards benzylamine (Bz) is considerably higher than that of monoamine oxidase (MAO). SSAO plays a role in the toxicity of several environmental and endogenous amines. SSAO-mediated production of toxic aldehydes has been proposed to be related to pathophysiological conditions. The most potent of inhibition of SSAO in monkey brain was observed by tricyclic antidepressant drug imipramine, as compared to tetracyclic drug maprotiline or non-cyclic drug nomifensine. An endogenous SSAO modulator in rat brain cytosol after immobilization stress (IMMO) was found and that this inhibitor could be induced by IMMO. SSAO activity in rat brain might be regulated by the level of this inhibitor. Semicarbazide, a SSAO inhibitor, enhances the formation of .OH products of efflux/oxidation due to 1-methyl-4-phenylpyridinium ion (MPP+). The precise physiological functions of SSAO could play an important role in the control of energy balance in adipose tissue. SSAO could play an important role in the regulation of adipocyte homeostasis.

Evidence for existence of immobilization stress-inducible semicarbazide-sensitive amine oxidase inhibitor in rat brain cytosol

An endogenous inhibitor of semicarbazide-sensitive amine oxidase (SSAO) was separated by gel filtration from 105000xg supernate in rat brain cytosol following immobilization stress (IMMO). The molecular weight of this inhibitor was estimated to be 500-700 by gel filtration. This inhibitor was proved to be heat-stable resistant to protease treatment. These results suggest that this inhibitor is induced by IMMO. SSAO activity in rat brain might be regulated by the level of this inhibitor.