1H NMR Spectroscopy of pyrrolizidine alkaloids

The ¹H NMR spectra of three pyrrolizidine alkaloids of the macrocyclic diester type, retrorsine, seneciphylline and senecionine, plus their three N-oxides have been assigned. Previous ¹H NMR studies of these pyrrolizidine alkaloids have stressed the difficulties of spectral intrepretation. The results reported here will provide a useful resource for analysis of tertiary structure in these and related compounds.     

Endogenous and Transplanted Small Hepatocytes in Retrorsine-treated/Partially Hepatectomized Rat Liver Show Differences in Growth, Phenotype, and Proximity to Clusters of ��-Glutamyl Transpeptidase-positive Host Hepatocytes

In the present report, we have compared the phenotype and growth of small hepatocyte progenitors (SHPs) induced by retrorsine/partial hepatectomy (R/PH) and small hepatocytes (SHs) isolated from normal adult liver. SHs were isolated by a combination of differential centrifugation and Percoll isodensity fractionation from a liver cell suspension prepared by collagenase perfusion of a dipeptidyl peptidase IV (DPPIV)–positive Fischer F344 rat liver. Following further purification by flow cytometry, the SH-R3 fraction was transplanted via the portal vein into R/PH–treated, DPPIV-negative Fischer F344 rats. Frozen sections from tissue harvested at 5, 7, and 21 days after transplantation were analyzed by indirect immunofluorescence to compare the phenotypic characteristics of colonies formed by exogenous SH-R3s and endogenous SHPs. Colonies of transplanted SHs and endogenous SHPs displayed similar histologies and phenotypes but were distinguished from surrounding hepatocytes by their elevated expression of transferrin receptor. SH-R3 colonies were frequently located within clusters of γ-glutamyl transpeptidase–positive host hepatocytes. Although significantly smaller at 5 and 7 days after PH, by day 21, SH-R3 colonies were similar in size to those formed by SHPs. The present results suggest that endogenous SHPs are derived, at least in part, from SHPs. (J Histochem Cytochem 58:61–72, 2010)     

Pyrrolizidine alkaloid biosynthesis: Derivation of retronecine from l-arginine and l-ornithine

The relative retention of ³H and ¹⁴C on incorporation of d-, l- and dl-isomers of [¹⁴C]arginine and [¹⁴C]ornithine into retrorsine using L-[5-³H]arginine as an internal standard has been measured. The retronecine portion of the pyrrolizidine alkaloid retrorsine, present in Senecio isatideus plants, is shown to be derived from l-arginine and l-ornithine.     

Seasonal variability in pyrrolizidine alkaloids in Senecio inaequidens from the Val Venosta (Northern Italy)

Senecio inaequidens is a neophyte originating from South Africa that has managed to spread to Europe and colonize large areas. This plant has toxic pyrrolizidine alkaloids (PAs) that represent a health risk to humans and animals. The aim of this work was to measure the content of PAs of these plants in continuous intervals over the entire growing season. The plants were separated into their organs, such as sprouts, stems, leaves and inflorescences. PAs were extracted from the dried plants using an acidic methanol solution, purified and measured by GC/MS. The average PA content of plants over the growing season was 0.33% of dry weight. The highest PA levels were about 1% in the dry weight and were found in the young sprouts and flower heads. There were nine PAs present, of which six could be identified. The main alkaloid was retrorsine followed by senecivernine, senecionine, integerrimine, usaramine and seneciphylline. Due to the high PA content of the inflorescences, the long flowering period and the rapid invasion dynamics, this species presents a high health risk for humans and animals.