Kinetensin and Fragments

Definition
Kinetensin is a nanopeptide, originally isolated from pepsin-treated plasma that shares some sequence homology with the C-teminal end of neurotensin. Endogenous neurotensin-like peptide originally isolated from pepsin-treated human plasma. Kinetensin induces histamine release from rat peritoneal mast cells in vitro. Alternative name is Neurotensin-related peptide.

Discovery
Mogard et al., in 1986 isolated a novel nanopeptide with neurotensin-like immunoreactivity from pepsin-treated human plasma by dialysis, ion-exchange chromatography and high performance reversed-phase liquid chromatography. The amino acid sequence was determined by automated gas-phase. Sequence homology with human serum albumin and with the biologically active peptides neurotensin and angiotensin was demonstrated. They proposed the name for this peptide kinetensin 1.

Structural Characteristics
Using a radioimmunoassay toward the COOH-terminal region of neurotensin, an immunoreactive and biologically active neurotensin-related peptide (NRP) was isolated from pepsin-treated fractions of bovine, canine, human, and rat plasma. Bovine NRP was identified as H-Ile-Ala-Arg-Arg-His-Pro-Tyr-Phe- Leu-OH, which is similar in structure to both neurotensin and angiotensin I. Canine and human NRP also had the above amino acid composition, whereas that obtained from rat plasma had valine substituted for isoleucine. The isolated peptides show an amino acid sequence homology to neurotensin and an ability to register in both radioreceptor and bioassays. Using V8 protease, glutamyl residues were shown to lie within 3-4 amino acids of each end of NRP, as also occurs for the related segmenitns albumin. These results suggest that a subset of albumin-related protein(s) could serve as precursor(s) to biologically active neurotensin-related peptide 2.

Mode of Action
Carraway et al., in 1987 isolated human and canine NRP from pepsin-treated plasmas that were shown to increase vascular permeability when injected intra-dermally into rats and to release histamine from rat mast cells in vitro. The pure peptides also cross reacted very effectively at nanomolar concentrations in a radio-receptor assay for neurotensin. The proteins which liberated NRP upon pepsin treatment were purified about 7-fold and shown to behave like albumin during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, isoelectric focusing, and high pressure liquid chromatography. The purified preparations which contain Kinetensin were found to react with anti-albumin antisera during immunodiffusion 2.

Based upon the ability of NRP to release histamine from mast cells and to increase cutaneous vascular permeability, NRP functions as an inflammatory mediator. In this regard, NRP could be formed locally in a manner similar to bradykinin 3, perhaps via the release or activation of acid proteases such as cathepsin D. It is interesting that the second phase of inflammation is thought to be initiated by the release of lysosomal enzymes from phagocytes 4 and that acid protease activity in skin is elevated during an inflammatory response 5.

NRP derived from albumin-related protein is utilized as a modulator of above functions as well. Kinetensin was rapidly metabolized, approximately 200-fold more rapidly than neurotensin. The majority of the metabolism occurred in the circulation demonstrated both in vivo and in vitro. The lung and gut also clear kinetensin. Inhibition of converting enzyme, present in highest concentration in the lung, abolished lung clearance but was without effect on kinetensin metabolism by the gut or in the general circulation 6.Functions

A broad spectrum of biologic effects have been noted for Kinetensin, including effects on the endocrine, cardiovascular, digestive, and reticuloendothelial systems as well as on temperature regulation, nociception, and behavior . NRP is homologous to albumin, particularly to the segment between residues 137 and 149. Six of its 13 residues were identical and 3 were chemically similar to those in albumin, suggesting that albumin and the precursor to neurotensin may have evolved from a common ancestor. Extrapolating from the accepted mutation rate for albumin, one would calculate that this may have taken place before the evolution of vertebrates (about 500 million years ago). During its evolution, albumin has undergone several gene-triplication events, giving rise to at least three major domains in the molecule. Interestingly, the regions within two of these domains, which show partial homologies to neurotensin, are thought to participate in the binding of fatty acids and steroids. These sequence relationships are noteworthy in view of the suggested roles for neurotensin in the regulation of fat digestion, lipid absorption, and blood flow 6.

References
1.Mogard MH, Kobayashi R, Chen CF, Lee TD, Reeve J Jr, Shively JE, Walsh JH (1986). The amino acid sequence of kinetensin, a novel peptide isolated from pepsin-treated human plasma: homology with human serum albumin, neurotensin and angiotensin. Biochem.Biophys.Res.Comm., 136(3):983-988.
2.Carraway RE, Mitra SP, Cochrane DE.(1987). Structure of a biologically active neurotensin-related peptide obtained from pepsin-treated albumin(s). J.Biol.Chem., 262(13):5968-5973.
3.Regoli D, Barabé J.(1980). Pharmacology of bradykinin and related kinins. Pharmacol. Rev., 32(1):1-46.
4.Hoffstein S, Goldstein IM, Weissmann G. (1977). Role of microtubule assembly in lysosomal enzyme secretion from human polymorphonuclear leukocytes. A reevaluation. J Cell Biol., 73(1):242-256. .
5.Lazarus GS (1974). The role of neutral proteinase and cathepsin D in turpentine-induced inflammation. J. Inuest. Derm,. 62(4):367-371.
6.Read D, Shulkes A, Fletcher D, Hardy K (1993). Pharmacokinetics and biological activity of kinetensin in conscious sheep. Journal Inflammation Research., 38(1-2):231-239.

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