CLARIFICATION OF BIOSYNTHESIS OF ANGIOPROTECTIN

Abstract Background and Aims The renin-angiotensin-aldosterone system (RAAS) is involved in the regulation of the blood pressure, water- and electrolyte balance. Pathophysiologically, this system is essential for the development and pathogenesis of both cardiovascular and renal diseases. Recently, the angiotensin peptide ´angioprotectin´ was identified as an antagonist of the contractile effect of angiotensin II. The amino acid sequence of angioprotectin (pro-glu-val-tyr-ile-his-pro-phe) compared to the amino acid sequence of angiotensin II (asp-arg-val-tyr-ile-his-pro-phe) differs in the n-terminal amino acids asp1 and arg2, which are transformed to pro1 and glu2 by endothelial cells (Jankowski et al., 2011). The aim of the study is the identification of the underlying mechanism of the transformation of angiotensin II to angioprotectin. Method To clarify the transformation of angioprotectin diverse angiotensin peptides were incubated with enzymes like glutamic oxaloacetic transaminase (GOT), cofactors like pyridoxal-5’-phosphate (PLP) and other substances like vitamin B6-derivates. Aliquots were collected time-dependently and analyzed by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF). To investigate the impact of angioprotectin on the organism, rats were treated with angiotensin II in the absence and presence of PLP. The blood pressure was used as read-out of the effect of the treatment. Results The incubation of angiotensin II with pyridoxal-5’-phosphate in vitro caused in increased amount of angioprotectin. Since the first two amino acids aspartic acid and arginine of further peptides like angiotensin I, angiotensin (1-6) and cortistatin-17 were also metabolized to proline and glutamic acid, the underlying mechanism is not specific for angiotensin II, but for aspartic acid and arginine. In accordance with this, the blood pressure of spontaneously hypertensive rats (SHR) treated with PLP decreases after three days. The blood pressure of Wistar Kyoto rats (WKY) treated with angiotensin II increases, whereas the blood pressure of WKY rats treated with angiotensin II and PLP decreases to normal level. Conclusion Angiotensin II is obviously metabolized by pyridoxal-5’-phosphate (PLP) to angioprotectin. PLP decreases the blood pressure in spontaneously hypertensive rats and in Wistar Kyoto rats. The first two amino acids aspartic acid and arginine are also metabolized to proline and glutamic acid in other peptides.