The suitability of iodinated Angiotensin-(1-7) peptides as pharmacological tools.
BACKGROUND
The heptapeptide Angiotensin-(1-7) [(Ang-(1-7)] is a biologically active component of the Renin-Angiotensin System. Pharmacological studies often involve Ang-(1-7) radioactively labelled with (125)I. Given the small size of the original peptide, we investigated whether introduction of a rather bulky iodine label interferes with the biological activity of Ang-(1-7).


METHODS
Ang-(1-7) was labelled with nonradioactive iodine with the chloramine-T method. The reaction products were separated on HPLC and analysed with mass spectrometry. The products were tested for biological activity in two ways: The ability of labelled Ang-(1-7) to block Ang II-induced contraction in rat aortic rings was tested in an organ bath setup. The affinity of labelled angiotensin for ACE in rat plasma was examined in vitro.


RESULTS
Iodination of Angiotensin-(1-7) resulted in two main products: monoiodinated and diiodinated Ang-(1-7) that could be easily separated on HPLC. In an organ bath experiment, monoiodinated Ang-(1-7) blocked Ang II responses identical to the native compound, whereas diiodinated Ang-(1-7) had lost its ability to block Ang II responses. Likewise, monoiodinated Ang-(1-7) had retained its affinity for ACE, while the affinity of diiodinated Ang-(1-7) was greatly reduced.


CONCLUSIONS
Monoiodinated Ang-(1-7) has a biological activity identical to the native compound, whereas this is lost in diiodinated Ang-(1-7). Therefore, only the monoiodinated radioactive form seems suited for pharmacological studies.
Loot
Annemarieke E
AE
Department of Clinical Pharmacology, Groningen University Institute for Drug Evaluation (GUIDE), University of Groningen, PO Box 196, Groningen 9700 AD, The Netherlands. a.e.loot@med.rug.nl
van Buiten
Azuwerus
A
Roks
Anton J M
AJ
Henning
Robert H
RH
D000110:Acetylcholinesterase / Q000378:metabolism; D000803:Angiotensin I / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001011:Aorta / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D007456:Iodine Isotopes / Q000378:metabolism; D007553:Isotope Labeling; D008297:Male; D013058:Mass Spectrometry; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D000959:Antihypertensive Agents; D007456:Iodine Isotopes; D010446:Peptide Fragments; D000803:Angiotensin I; D000110:Acetylcholinesterase; C118790:angiotensin I (1-7)