Circulating Levels of Human salusin-β,a Potent Hemodynamic and Atherogenesis Regulator

Using bioinformatics analysis, we previously identified salusin-beta, an endogenous bioactive peptide with diverse physiological activities. Salusin-beta is abundantly expressed in the neuroendocrine system and in systemic endocrine cells/macrophages. Salusin-beta acutely regulates hemodynamics and chronically induces atherosclerosis, but its unique physicochemical characteristics to tightly adhere to all types of plastic and glassware have prevented elucidation of its precise pathophysiological role. To quantitate plasma total salusin-beta concentrations, we produced rabbit and chicken polyclonal antibodies against the C-and N-terminal end sequences, circumvented its sticky nature, and successfully established a sandwich enzyme-linked immunosorbent assay (ELISA). Salusin-beta was abundantly present in the plasma of healthy volunteers, ranging from 1.9 to 6.6 nmol/L. Reverse phase-high performance liquid chromatography analysis showed that a single immunoreactive salusin-beta peak coincided with synthetic authentic salusin-beta. Plasma salusin-beta concentrations were unaffected by postural changes and by potent vasopressin release stimuli, such as hypertonic saline infusion or smoking. However, salusin-beta concentrations showed significant circadian variation; concentrations were high during the daytime and reached the lowest concentrations in the early morning. Plasma salusin-beta levels in subjects with diabetes mellitus, coronary artery disease, and cerebrovascular disease showed distinctly higher levels than healthy controls. Patients with panhypopituitarism combined with complete central diabetes insipidus also showed significantly higher plasma salusin-beta levels. Therefore, the ELISA system developed in this study will be useful for evaluating circulating total salusin-beta levels and for confirming the presence of authentic salusin-beta in human plasma. The obtained results suggest a limited contribution of the neuroendocrine system to peripheral total salusin-beta concentrations and a role for plasma total salusin-beta concentrations as an indicator of systemic vascular diseases.