Peptide inhibitors of renin in cardiovascular studies

Renin is a proteolytic enzyme that may be inhibited in vivo by three classes of compounds: specific antibody, general peptide inhibitors of acid proteases, and substrate analogs. With the availability of highly purified renin, specific polyclonal or monoclonal antibodies have become available. The former have already been used extensively in physiological studies with intact animals. Pepstatin is an inhibitor of many acid proteases. Its in vivo application has been retarded by relative insolubility, but recent chemical modifications, particularly the addition of charged amino acids at the carboxy terminus, have rendered it more useful. The minimal substrate for renin is an octapeptide segment of the protein substrate: His-Pro-Phe-His-Leu-Leu-Val-Tyr. Variants of this sequence have resulted in competitive inhibitors that are useful in vivo. Effectiveness of a given peptide varies among different species of animals, possibly because of different substrate specificity. To support this hypothesis, it has been reported that the amino acid sequences of angiotensinogens around the site where renin cleaves may vary among species. Effectiveness of inhibitors is also dependent on the hydrophobicity of amino acids near the cleavage site. Recently, remarkably active inhibitors have been synthesized by reducing the peptide bond that is cleaved by renin. Studies with monkeys show that a peptide renin inhibitors may cause hypotension after sodium depletion and normalize blood pressure in Goldblatt hypertension to the same degree as a converting-enzyme inhibitor.