Studies on the behaviour of semicarbazide-sensitive amine oxidase in Sprague-Dawley rats treated with the monoamine oxidase inhibitor tranylcypromine

Characterization of A7r5 cell line transfected in a stable form by hSSAO/VAP-1 gene (A7r5 hSSAO/VAP-1 cell line)

A smooth muscle cell line (A7r5) was stably transfected with the human SSAO/VAP-1 (hSSAO/VAP-1) gene. The expressed protein was located solely in the membrane fraction of the cell. However it was also shown to be released into the cell-culture medium. Both the membrane-bound and released, soluble, forms had SSAO enzyme activity. Although MAO-A is present in wild-type A7r5 cells, it was undetectable in the transfected cells.

Tranylcypromine: new perspectives on an "old" drug

The irreversible inhibitor of monoamine oxidase, tranylcypromine, is a potent antidepressant, but its use is limited to special indications due to side effects and dietary restrictions. The antidepressant action of tranylcypromine is not completely explainable by its effects on monoamine oxidase. Tranylcypromine also leads to an increase in brain trace amines, which are believed to play a key role in the pathophysiology of depression. It also affects other pathophysiological pathways associated with depression. Tranylcypromine treatment leads to an up-regulation of GABA(B)-receptors and modulates the phospholipid metabolism, which is essential for normal brain function. These findings implicate that the efficacy of tranylcypromine as an antidepressant may be due to its multiple actions within the human brain.

Semicarbazide-sensitive amine oxidase (SSAO): present and future

Although the existence of plasma and tissue-bound semicarbazide-sensitive amine oxidases (SSAOs) has been recognised for a long time, the physiological relevance of these enzymes still remains uncertain. The ability of SSAO to metabolise various aliphatic and aromatic monoamines differs between species, which limits the predictive value of the animal studies for human tissues. SSAO plays a protective role because the oxidative deamination of monoamines reduces their pharmacological activities. However, the products of deamination may be toxic. Several observations indicated that the plasma and tissue SSAO activities differ in certain disease states. It is proposed that selective inhibitors, of low toxicity, might be protective, through inhibiting the formation of the toxic products and the countering the disease-related elevation of SSAO activity. We reported earlier that there was a significant correlation between the serum SSAO activity and severity of atherosclerosis, as well as the intima-media thickness and serum cholesterol levels. Thus SSAO activity might be a clinical marker in the prognostic evaluation of diabetic-vascular complications. Although molecular biological studies are providing more and more reliable knowledge about the enzyme structure, many more studies should be carried out in different disease states are necessary to discover the clinical meaning of the enzyme function.

Inhibition of six copper-containing amine oxidases by the antidepressant drug tranylcypromine

Potential inhibitory effects of the clinically utilized monoamine oxidase inhibitor tranylcypromine (TCP) on mammalian, plant, bacterial, and fungal copper-containing amine oxidases have been examined. The following enzymes have been investigated: human kidney diamine oxidase (HKAO), bovine plasma amine oxidase (BPAO), equine plasma amine oxidase (EPAO), pea seedling amine oxidase (PSAO), Arthrobacter globiformis amine oxidase (AGAO), and Pichia pastoris lysyl oxidase (PPLO). Only BPAO, EPAO, and AGAO were found to lose significant levels of activity when incubated with varying amounts of TCP. Inhibition of BPAO was completely reversible, with dialysis restoring full activity. TCP inhibition of AGAO was also found to be ultimately reversible; however, dialysis did not remove all bound compounds. Chemical displacement with either substrate or a substrate analogue successfully removed all bound TCP, indicating that this compound has a high affinity for the active site of AGAO. The notable lack of TCP inhibition on HKAO argues against the inhibition of diamine oxidase as a potential source for some of the deleterious side effects occurring in patients treated with this antidepressant. The marked differences observed in behavior among these enzymes speaks to the importance of intrinsic structural differences between the active sites of copper amine oxidases (CAO) which affect reactivity with a given inhibitor.