Drugs of the Kallikrein-Kinin System: An Overview

The kallikrein-kinin system consists of the two kininogen substrates, present in blood plasma, and of two serine proteases, the plasma and tissue kallikreins. The action of the latter on kininogens produce small peptides, short lived but endowed by powerful pharmacologic actions on blood vessels and other tissues. Many recent and exciting therapeutic developments in the field are briefly summarized. Notably, various novel strategies are being clinically developed to inhibit the formation of bradykinin or block its receptors in the management of hereditary angioedema. The interventions include orally bioavailable drugs, biotechnological proteins, and gene therapy. Several other medical indications are currently investigated. Harnessing controlled kinin formation is also of potential therapeutic interest as shown by the clinical development of recombinant tissue kallikrein for ischemic stroke and renal disease. Biomarkers of a kinin-mediated disorders, frequently implicating edemas, include the consumption of kininogen(s), plasma kallikrein activity, and the detection of circulating kinin metabolites such as fragments BK1-5 and BK2-9. Based on this, some opportunities to clinically apply the underexploited drugs of the kallikrein-kinin system are briefly reviewed. This personal perspective is offered by an observer of, and a participant in drug characterization during the last 4 decades.