Chromatographic characterisation of neurotensin-like immunoreactivity in plasma and tissue extracts from hepatoma patients

Expression of the neurotensin gene in fetal human liver and fibrolamellar carcinoma

OBJECTIVE

This study determined whether the neurotensin gene (NT/N) is expressed in the normal adult liver and focal nodular hyperplasia (FNH) and confirmed NT/N expression in fibrolamellar carcinoma; whether NT/N or the neurotensin receptor is expressed in the fetal liver; and whether hepatic resection leads to expression of NT/N.

SUMMARY BACKGROUND DATA

Neurotensin (NT), a gut tridecapeptide localized in the gastrointestinal tract of the adult to the small bowel, is an important hormone-regulating gut motility, secretion, and mucosal growth. Expression of the NT/N gene has been identified in fibrolamellar carcinomas, but NT/N is not known to be expressed in the normal liver.

METHODS

Sensitive ribonuclease (RNase) protection assays were used to determine whether NT/N is expressed in fibrolamellar carcinoma, FNH, or healthy fetal and adult livers. The authors also determined whether the receptor for NT was present in the fetal liver and whether liver resection and subsequent regeneration could lead to re-expression of NT/N in the rat.

RESULTS

Neurotensin is expressed in fibrolamellar carcinoma and in the fetal human liver, but not in the adult liver or the samples of FNH. In addition, the authors were not able to detect expression of the NT receptor in the fetal liver and did not identify NT/N gene activation in the regenerating liver of the rat.

CONCLUSIONS

The NT/N gene will be a useful molecular marker to differentiate fibrolamellar carcinoma from other liver tumors. The finding of NT/N expression in the fetal liver suggests a stem cell descendant that is common to both the liver and gut. The absence of NT/N expression in the regenerating liver suggests that NT does not play a role in this rapid growth process.

Developmental expression of the neurotensin gene in the rat liver

OBJECTIVE

This study determined whether the neurotensin gene is expressed during early development of the liver.

SUMMARY BACKGROUND DATA

Neurotensin (NT), a gut tridecapeptide localized mainly to the distal small bowel and brain of adults, is an important hormone regulating gut motility, secretion and mucosal growth. Expression of NT peptide and the gene is found in fibrolamellar hepatocarcinomas, a variant of hepatocellular carcinoma, but not in the normal adult liver.

METHODS

Northern and in situ hybridization techniques were used to determine expression of the neurotensin gene (NT/N) in the normal developing liver.

RESULTS

NT/N is expressed in the fetal and early postnatal rat liver, but expression is repressed in the liver of the adult. In situ hybridization confirms the authors' Northern data and demonstrates a random distribution of NT/N expression in the fetal and 3-day postnatal liver.

CONCLUSIONS

The authors conclude from this study that NT/N is expressed during early development of the rat liver with subsequent repression in the adult. NT/N may be reexpressed with malignant transformation of the liver.

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.

In vitro degradation of neurotensin in human plasma

To study the degradation of neurotensin in plasma in vitro, fresh human plasma was incubated with neurotensin in the presence and absence of the peptidase inhibitors pepstatin A, EDTA, PMSF and aprotinin. The half-time of disappearance of neurotensin at 37 degrees C was calculated to be 226 min in vitro as opposed to 1.4 min in vivo when measured by radioimmunoassay with a C-terminally directed neurotensin antiserum. Both gel filtration and reversed phase high-pressure liquid chromatography (HPLC) showed that the main degradation product of neurotensin in human plasma in vitro was chromatographically and immunologically identical to neurotensin 1-8 and HPLC also demonstrated the formation of neurotensin 1-11. The loss of neurotensin incubated in human plasma in vitro was greatly reduced by EDTA but not by the other peptidase inhibitors tested. In this respect peptidase(s) responsible for the degradation of neurotensin in plasma differ from those present in brain homogenates. EDTA may be of importance in the preservation of neurotensin in plasma samples.