Biological potency of neurotensin metabolites in vivo: importance of alcohol 'fixation' of blood

Adsorption of (Phe-h5)/(Phe-d5)-substituted peptides from neurotensin family on the nanostructured surfaces of Ag and Cu: SERS studies

This work describes an application of Raman (RS) and surface-enhanced Raman scattering (SERS) to characterize the selective adsorption of two peptides belonging to the neurotensin family peptides, such as kinetensin (KN) and xenopsin-related peptide 2 (XP-2) that are known to stimulate the growth of human tumors. To perform a reliable analysis of SERS spectra, the L-Phe residue (at position 8 or 1 in the amino acid sequence of these peptides) was replaced with L-Phe-d₅ (five protons of L-phenylalanine ring substituted by deuterium). Native and (Phe-d₅)-isotopically labeled peptides were deposited on electrochemically nanostructured surfaces of Ag (AgORC) and Cu (CuORC) from an aqueous solution (H₂O). To determine the share of amide bonds in the interaction with the metallic substrate, SERS spectra of peptides adsorbed on AgORC from heavy water (D₂O) were measured. Also, to determine the effect of the C-end on the SERS spectrum, measurements were made for the KN analog in which the C-terminal L-leucine was removed ([desLeu⁹]KN). Based on the analyses of the spectral profiles, in the spectral range of 600-1650 cm^-1, specific conclusions have been drawn regarding specific aromatic ring···metal interactions and changes in the interaction during substrate change.

Pharmacokinetics and biological activity of kinetensin in conscious sheep

Kinetensin is a nonapeptide, originally isolated from pepsin-treated plasma, that shares some sequence homology with the C-terminal end of neurotensin. The present study was designed to determine, by infusing kinetensin to conscious sheep, the pharmacokinetics and a neurotensin-like biological activity (pancreatic polypeptide response) of kinetensin. Kinetensin was rapidly metabolized, approximately 200-fold more rapidly than neurotensin. The majority of the metabolism occurred in the circulation as demonstrated both in vivo and in vitro. The lung and gut cleared kinetensin also. 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. Arterial infusion of kinetensin which achieved high blood kinetensin levels at the pancreas did not increase plasma pancreatic polypeptide. We conclude that the extremely rapid degradation of exogenous kinetensin, together with the lack of biological activity, makes it unlikely that kinetensin plays a role as a circulating regulatory peptide. Nevertheless, since the putative kinetensin substrate circulates at microM concentrations, it is feasible that kinetensin is generated and metabolized at the target organ.

Characterization of neurotensin(6-13) from an hepatic fibrolamellar carcinoma

Neurotensin(6-13) has been isolated and sequenced as the major form of neurotensin-like immunoreactivity (NTLI) in a human hepatic fibrolamellar carcinoma. Circulating NTLI in the patient, especially C-terminal, was very high. In additional studies, NT(6-13) was synthesized and compared with the purified tumor NTLI by HPLC analysis and by testing stability in plasma in vitro. These methods confirmed that the tumor NTLI was identical to NT(6-13). Since the metabolic clearance rate of synthetic NT(6-13) in sheep was 30-fold higher than NT(1-13), it suggests that the elevated plasma levels are the result of impaired clearance and/or markedly elevated production.