INHIBITION OF PLASMA MONOAMINE OXIDASE BY CYSTEAMINE

Cysteamine Inhibits Glycine Utilisation and Disrupts Virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a major opportunistic human pathogen which employs a myriad of virulence factors. In people with cystic fibrosis (CF) P. aeruginosa frequently colonises the lungs and becomes a chronic infection that evolves to become less virulent over time, but often adapts to favour persistence in the host with alginate-producing mucoid, slow-growing, and antibiotic resistant phenotypes emerging. Cysteamine is an endogenous aminothiol which has been shown to prevent biofilm formation, reduce phenazine production, and potentiate antibiotic activity against P. aeruginosa, and has been investigated in clinical trials as an adjunct therapy for pulmonary exacerbations of CF. Here we demonstrate (for the first time in a prokaryote) that cysteamine prevents glycine utilisation by P. aeruginosa in common with previously reported activity blocking the glycine cleavage system in human cells. Despite the clear inhibition of glycine metabolism, cysteamine also inhibits hydrogen cyanide (HCN) production by P. aeruginosa, suggesting a direct interference in the regulation of virulence factor synthesis. Cysteamine impaired chemotaxis, lowered pyocyanin, pyoverdine and exopolysaccharide production, and reduced the toxicity of P. aeruginosa secreted factors in a Galleria mellonella infection model. Thus, cysteamine has additional potent anti-virulence properties targeting P. aeruginosa, further supporting its therapeutic potential in CF and other infections.

Evaluation of the assay for serum monoamine oxidase -- an index of hepatic fibrosis

At present, neither the diagnostic efficiency, the analytic reliability nor the practicability of clinical chemical tests for estimation of the degree and/or activity of the fibrotic transformation of the chronically injured liver are satisfactory. Among the various parameters proposed, the determination of the activity of monoamine oxidase (monoamine: O2 oxidoreductase, EC 1.4.3.4) in serum seems to be advantageous. To facilitate its routine use we studied some important practical aspects of the new colorimetric assay for the activity of monoamine oxidase in serum. The reaction proceeds linearly with time for at least two hours and with enzyme concentrations up to kU/l. The buffer composition influences markedly the function of the enzyme; in Tris-HCl buffer (pH 7.2) at 37 degree C the activity is 1.35 time higher than in phosphate buffer (pH 7.3) and the temperature correlation factors are also different for both buffer systems. 0.003 mol/l of the lathyrogenic compound beta-aminopropionitrile inhibits the activity by about 50% whereas Cu2+ up to 130 mu mol/l does not affect enzyme function. Intra- and interassay precision and characterized by a CV of 3.6 and 12%, respectively. Hemolysis and hyperbilirubinemia do not interfere significantly with the determination but in hyperlipemic sera elevated enzyme activities were noticed. During storage of serum at room temperature the catalytic function decrease by about 30%/day. Of the 26 quality control sera tested, only a few contained monoamine oxidase activity that was quantitatively (i.e. similar catalytic activity in tris phosphate buffer) similar to that in human serum, and were therefore suitable for routine precision control analysis.