Renalase, a catecholamine-metabolising enzyme?

Recently an intriguing paper described a new flavin-adenine dinucleotide (FAD) containing hormone, named renalase , which is secreted by the kidney and circulates in blood ( Xu et al., 2005 ). Renalase was reported to be an amine oxidase with significant activity towards the catecholamines noradrenaline (NA), adrenaline (ADR) and dopamine (DA), but with little or no activity towards other physiologicallyoccurring amines, such as serotonin, tyramine, benzylamine, methylamine and spermidine. Although the amine oxidase activity of renalase was dependent on its FAD content, it was insensitive to the FAD-containing monoamine oxidase (EC 1.4.3.4) inhibitors pargyline and clorgyline. Thus this reported amine oxidase activity of renalase differs in specificity and inhibitor-sensitivity from the known FAD-containing amine oxidases. Renalase was shown to have significant cardiovascular actions when injected into rats and these were ascribed to its catecholamine-metabolising activity. In patients with end-stage renal disease, renalase was found to be lacking from blood. The authors suggested that the explanation for the increased frequency of hypertension and cardiovascular dysfunction in these patients might be the higher plasma catecholamine concentrations resulting from the absence of renalase. They concluded that renalase might be an important regulatory factor in human (patho)physiology.