Catabolism and bioactivity of bradykinin and related peptides

Bradykinin and related peptides (BRPs) are common components of amphibian defensive skin secretions, particularly in ranid and phyllomedusine frogs and in bombinid toads. BRPs are known to be highly vasoactive with some possessing potent effects on blood vessel formation (angiogenesis) - a process known to be initiated by direct effects on endothelial cells. Human microvessel endothelial (HMEC) cells are a stable laboratory cell line often used for preliminary screening in such studies of BRP function. Since these cells are the starting points for fundamental biological studies, we examined their catabolism of bradykinin (BK) and maximakinin (MK). MK represents an N-terminally extended version of the former but with higher potency. Both BK and MK were broken down by proteases present on HMEC cells with half-lives of 5h and 2h, respectively. However, as two major metabolites of MK retained the receptor-active site of BK, the true half-life of non- active metabolite generation was 5h (BK) and 9h (MK). Bradykinin antagonists, kinestatin and QUB919, both from amphibian skin, were not degraded by HMEC cells and their presence did not interfere with the degradation of BK or MK. Using primer sets designed for bradykinin Bland B2 receptors, transcripts of appropriate size were amplified from an HMEC cell cDNA library. Bradykinin-related peptides are thus catabolised in different ways by HMEC cells and the cells were shown to contain polyadenylated mRNAs for both bradykinin receptor sub-types, Bland B2. To examine other functions of BRPs, we screened reverse phase HPLC fractions of venoms and defensive skin secretions to identify, structurally characterise and ultimately chemically-synthesise novel peptides to examine their effects on bradykinin activity using smooth muscle bioassays. Many BRPs exhibited anti- cancer and anti-microbial functions in our experiments giving us a broader perspective for further research in the BRP field. · ';.EThOS - Electronic Theses Online ServiceGBUnited Kingdo