Gamma-aminobutyric acid (GABA) formation from putrescine in guinea-pig liver during ontogenesis

An integrated functional genomics and metabolomics approach for defining poor prognosis in human neuroendocrine cancers

Human neuroendocrine (NE) cancers range from relatively indolent to highly aggressive. In this study, we combine functional genomics with metabolomics to identify features of NE cancers associated with a poor outcome. Analysis of GeneChip datasets of primary prostate tumors, as well as lymph node and liver metastases from transgenic mice with a NE cell cancer, plus derived NE cell lines yielded a signature of 446 genes whose expression is enriched in neoplastic mouse prostatic NE cells. This signature was used for in silico metabolic reconstructions of NE cell metabolism, directed liquid chromatography/tandem MS analysis of metabolites in prostatic NE tumors and cell lines, and analysis of GeneChip datasets of human NE tumors with good or poor prognoses. The results indicate that a distinguishing feature of poor-prognosis NE tumors is a glutamic acid decarboxylase-independent pathway for production of GABA and a pathway for production of imidazole-4-acetate that involves dopa decarboxylase and a membrane-associated amine oxidase, amiloride-binding protein 1. Electrophysiological studies disclosed that imidazole-4-acetate can bind and activate GABA(A) receptors expressed by transformed NE cells, thus providing a previously uncharacterized paradigm for NE tumor cell signaling. Transcriptional, metabolic, and electrophysiologic features of transformed mouse NE cells are also evident in neural progenitor cells.

Putrescine, a source of gamma-aminobutyric acid in the adrenal gland of the rat

Putrescine is the major source of gamma-aminobutyric acid (GABA) in the rat adrenal gland. Diamine oxidase, and not monoamine oxidase, is essential for GABA formation from putrescine in the adrenal gland. Aminoguanidine, a diamine oxidase inhibitor, decreases the GABA concentration in the adrenal gland by more than 70% after 4 h, and almost to zero in 24 h. Studies using [14C]putrescine confirm that [14C]GABA is the major metabolite of putrescine in the adrenal gland. Inhibition of GABA transaminase by amino-oxyacetic acid does not change the GABA concentration in the adrenal gland, as compared with the brain, where the GABA concentration rises. With aminoguanidine, the turnover time of GABA originating from putrescine in the adrenal gland is 5.6 h, reflecting a slower rate of GABA metabolism compared with the brain. Since GABA in the adrenal gland is almost exclusively derived from putrescine, the role of GABA may relate to the role of putrescine as a growth factor and regulator of cell metabolism.

Diamine oxidase in the hen

In adult hens diamine oxidase (histaminase) activity was found in gastrointestinal tract (with the highest value in ileum), liver and spleen. Intestinal diamine oxidase is predominantly a particle-bound enzyme. In the intestine oxidation of putrescine leads to delta 1-pyrroline formation, in liver both delta 1-pyrroline and gamma-aminobutyric acid are formed. The inhibitor properties of hen intestinal and rat intestinal diamine oxidases are very similar and differ from pea seedling diamine oxidase. The natural dipeptides carnosine and anserine are relatively potent inhibitors of hen intestinal diamine oxidase.

Diamine oxidase activity and imidazoleacetic acid formation in the foetal and maternal guinea pig liver

Diamine oxidase activity and imidazoleacetic acid formation in the foetal and maternal guinea pig liver during gestation were examined. DAO activity and IMAA formation in the foetal liver increased continuously, while maternal enzyme activity and ImAA formation in the second half of pregnancy simultaneously decreased. The roles of GABA and ImAA are discussed.